Coating for Polymeric Labels

Abstract

A coated thermoplastic film is disclosed. The film includes a polymeric substrate and a first coating layer. The polymeric substrate includes a first skin layer. The first coating layer on the first side of the first skin layer includes at least a first filler component. The filler component has a particular particle size relative to the open-cell, closed-cell or uncavitated structure of the first skin layer. Films and labels having improved balance of properties are described.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The application claims priority from U.S. Provisional Application Ser. No. 61/382,656, filed Sep. 14, 2010 and U.S. Provisional Application Ser. No. 61/323,219, filed Apr. 12, 2010, the contents of which are incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

Polymeric labels are applied to a variety of bottles, containers and other surfaces to provide, for example, information about the product being sold or to display a trade name or logo. Polymeric labels can provide various advantageous characteristics not provided by paper labels, such as durability, strength, water resistance, curl resistance, abrasion resistance, gloss, translucence, and others.

The application of cut paper labels to glass and plastic containers using water-based adhesives is still one of the most prevalent labeling techniques. Consequently, there are many existing machines that have been installed for this type of labeling. These cut-label/patch-label labeling techniques using water-based adhesives work well with paper-based labels applied to glass, plastic, or metal substrates, because the wet adhesive wicks into and through the paper label. This release of the adhesive moisture through the labels allows the adhesive to dry fully. This technique does not work, however, on polymeric labels because the polymeric label does not permit wicking of the moisture from the adhesive when used as a decal on a window or a patch-label on a container. This can make the polymeric labels adhered with cold-glue type adhesives prone to “swimming” or moving from the desired label location during downstream processing.

Polymeric label substrates having micro perforations to enhance the rate at which water trapped between the label and the substrate can evaporate have had little success. Initial wet tack with commercially available water-based adhesives remained inadequate. Moreover, the micro perforations tend to permit the passage of wet glue through the pores rendering the printed side of label on the container sticky and marring the graphics.

It is known in the art to construct a multilayer film having a coating layer on the wet-adhesive-receiving surface of the film that includes a filler component. These films can offer fair performance as labels when attached to containers with aqueous-based cold glues. However, these films are known to have manufacturing and processing issues.

US2006/0046005, for example, discloses a polymer film coating for use with cold glue labels, particularly on the adhesive-receiving side of a label film. The coating is resistant to both water and solvent, and includes a filler component and a binder component, at least one of which is hydrophobic. This publication discloses that the fillers having an average particle size ranging from 0.05 μm to 2000 μm may be used. Large particles, e.g., those with a diameter of 10 μm to 200 μm, are described as attenuating surface roughness. Small particles, e.g., those with a particle size of <1.0 μm are described but their function is not discussed. Particles having a diameter of 1 μm to 8 μm are described as useful as anti-abrasives to improve wet-scratch resistance, but such particles are described as serving no purpose in the adhesive side coating, rather they are used only for convenience in a symmetric film structure to facilitate production. US2006/0046005 also describes adhesive side skin layers that may be “open-cell voided,” “closed-cell voided,” or uncavitated layers.

SUMMARY OF THE INVENTION

It has been discovered that where the size of the filler is carefully controlled, in combination with the selection of the adhesive-side skin layer, the films may retain their suitability for cut and stack processes with reduced ink-transfer problems (i.e., ghosting effects) and mitigate print face deformation storing the film in stacking or roll form when the particle size is too large. Thus, contrary to US2006/0046005, the particle size of the filler used in the adhesive face, when coupled with the selection of the proper skin layer structure, serves an important function. Thus, embodiments of the present invention provide improved film and label structures that are suitable for cut and stack as well as roll-fed processes.

Embodiments of the invention provide coated thermoplastic films comprising: (a) a substrate comprising: (i) a first skin layer having an open-cell voided structure, a closed-cell voided structure or an uncavitated structure, comprising a polymer, wherein the first skin layer has a first side and a second side, (ii) an uncavitated core layer comprising a polymer, wherein the core layer has a first side and a second side, and the first side of the core layer is adjacent to the second side of the first skin layer; and (b) a first coating on the first side of the first skin layer, the first coating comprising at least a first filler component, the first filler component comprising particles having an effective diameter of 5.0 μm to 20.0 μm.

Particular embodiments relate to coated films, wherein the first skin layer has an open-cell voided structure, and the first filler component comprises particles having a mean particle diameter satisfying the following equation:

D_mean=N−T_skin

wherein

• D_mean is the mean particle diameter (μm) of the first filler component;
• T_skin is the thickness (μm) of the first skin layer; and
• N is in the range of 10.0 μm to 20.0 μm.

Some embodiments relate to coated films wherein the first skin layer has a closed-cell voided structure or an uncavitated structure, and the first filler component comprises particles having a mean diameter in the range of 5.0 μm to 20.0 μm.

In another yet aspect, embodiments of the invention provide a coated label film for use with a cold glue adhesive, the label film comprising:

• • (a) a substrate comprising:
    • (i) a first skin layer comprising a polymer, wherein the first skin layer has a first side and a second side and is voided with a closed-cell structure;
    • (ii) a core layer comprising a polymer, wherein the core layer has a first side and a second side, and the first side of the second core layer is adjacent to the second side of the first skin layer;
  • (b) a first coating on the first side of the first skin layer comprising at least a first filler component the filler component comprising polyethylene homopolymer or copolymer particles having a mean diameter in the range of 5 μm to 20 μm and <2.0 number % of the filler particles have a diameter >75.0 μm.

In still another aspect, embodiments of the invention provide a coated thermoplastic film comprising:

• • (a) a substrate comprising:
    • (i) a first skin layer having a closed-cell voided or uncavitated structure, comprising a polymer, wherein the first skin layer has a first side and a second side;
    • (ii) a uncavitated core layer comprising a polymer, wherein the core layer has a first side and a second side, and the first side of the core layer is adjacent to the second side of the first skin layer;
    • (iii) second skin layer having a first side and a second side, wherein the first side is adjacent the second side of the core layer;
  • (b) a first coating on the first side of the first skin layer, the first coating comprising a polyethylene filler component, the polyethylene filler component comprising particles having a mean diameter in the range of 5 μm to 20 μm, a second filler component comprising 30 wt % to 60 wt % of a second filler having particle mean diameter of ≦1.0 micron and a self-cross-linking cationic acrylic first binder component; and
  • (c) a second coating on the second side of the second skin layer, the second coating comprising a self-crosslinking cationic acrylic composition.

The term coating can refer to a coating that is resistant to degradation from both water and solvent (e.g., a “resistant coating” or a “water- and solvent-resistant coating”). Particularly useful coatings described herein are both water resistant and solvent resistant.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention provide coated thermoplastic films comprising: (a) a substrate comprising: (i) a first skin layer having an open-cell voided structure, a closed-cell voided structure or an uncavitated structure, comprising a polymer, wherein the first skin layer has a first side and a second side, (ii) an uncavitated core layer comprising a polymer, wherein the core layer has a first side and a second side, and the first side of the core layer is adjacent to the second side of the first skin layer; and (b) a first coating on the first side of the first skin layer, the first coating comprising at least a first filler component, the first filler component comprising particles having an effective diameter of 5.0 μm to 20.0 μm.

The term “mean diameter” is defined broadly to encompass substantially the mean based on the number of particles in a sample of any linear distance across or through a particle having a relatively low aspect ratio, or distance across the long-axis of particles having a high aspect ratio, such as a plate-like particle, or the nominal distance through a nominally spherical particle, as the filler particles may comprise substantially any shape. When applied over the inherently rough first/adhesive-receiving side of the first skin layer, filler materials provide enough effective porosity to allow moisture permeation and mechanical penetration of the water component of the wet glue and/or of the wet glue itself, through the coating layer to the voided sub-layer adjacent to the coating. Insufficient particulate loading or a coating layer that is too thick can diminish retained cold glue adhesion when labeled bottles are immersed in ice water. The mean particle diameter may be determined by any suitable method, particularly by optical microscopic evaluation of the particles of a particular type (i.e., chemically distinguishable species), preferably based on a population size of at least 100 particles or according to ASTM D422. Where all particles in the first skin layer are of the same type (i.e., they are chemically indistinguishable), determination of the mean particle diameter of the first filler component considers only particles having an actual dimension (e.g., diameter) greater than 1.0 μm.

As used herein the term “effective diameter” refers to the mean diameter of the first filler particles described herein minus the portion of the particle diameter that is effectively reduced due to the particle falling, either partially or completely, into pores in the skin layer and/or compressed in the immediate vicinity of the particle by forces caused by winding the coated film into a roll or stacking sheets of the coated film. One skilled in the art can determine the effective diameter from the mean particle diameter, the mean pore size, and the skin layer thickness. Cavitated skin layers with open- or closed-cell voiding would both be susceptible to compression, but generally, compressive effects are relatively small and may be ignored for the purposes of determining the effective diameter unless their consideration changes the effective diameter by >10%.

As used herein, the term “voided” is synonymous with the term “cavitated” as those terms are commonly understood within the art, referring to the creation of cavities, pores, or voids within a polymer film during orientation, whether using a void initiating agent or particle, such as calcium carbonate, or without a void initiating agent, such as orienting the beta-form of polypropylene to create voids.

The term “closed-cell” with respect to film structures means that there is substantially little to no effective inter-pore interconnectivity or communication. The term “closed cell” may be considered to include some degree of near-surface fluid permeation due to surface roughness, including the irregularities, voids, craters, pores, tortuosities, and cavities, formed superficially, that is, on or near the surface of a layer, such as the first side of the first layer, as may be caused by the voiding agents, other particulate additives, and/or orientation. Thereby, in many films, essentially closed cell layers, such as a print side skin layer, may exhibit some small degree of surface absorption due to these features and thus exhibit some degree of openness with respect to the cell type. Such surface features may provide small reservoirs for fluid absorption and adhesive anchoring, even though inter-pore interconnectivity with voids deeper within the first layer may be limited or substantially non-existent. Thereby, those skilled in the art will recognize that film layers having a closed-cell structure may be capable of providing some degree of adhesive moisture absorption or transmission.

The term “hydrophilic,” as used herein, means to be readily wettable by water, having relatively low advancing contact angles with water, (e.g., less than about)45° thereby being capable of binding or absorbing water. “Hydrophobic,” as used herein, is also defined to mean anything other than hydrophilic, including being water resistant or not being readily water wettable.

The term “core layer” as used herein may refer to any inner layer of a film substrate, where that layer is centrally located in a film or not. Core layers described herein may be monolayer or multilayer film structures. Core layers having any number of individual layers are envisioned. A core layer may also comprise regions referred to as tie layers. Tie layers generally form the outer-most layers of the core layer and can function to improve the interaction of the core layer with layers such as skin layers or coatings.

The First Coating

Coating formulations according to this invention comprise at least a first filler component and typically, although not necessarily, a binder component. The coating formulation may also include a second filler component and/or a polymer component. The coating can be applied by any means known in the art including, but not limited to, spraying, dipping, direct gravure, reverse direct gravure, air knife, rod, and offset methods, or combinations thereof.

First Filler

The first filler is selected to have an effective diameter of 5.0 μm to 20.0 μm. As described above, the effective diameter depends on the mean particle diameter, the mean pore size and the thickness of the first skin layer. In some embodiments, particles having an effective diameter in the desired range are provided where the first filler component comprises particles having a mean diameter in the range of 5.0 μm to 20.0 μm. In some embodiments, the first filler particles have a mean diameter in the range of 5.0 μm to 20.0 μm and <2.0 number % of the filler particles have a diameter >75.0 μm. In some embodiments, such first filler components comprise polyethylene homopolymer or copolymer, particularly surface treated polyethylenes. Some embodiments include a second filler component comprising 30 wt % to 60 wt % of a second filler having particle mean diameter of ≦1.0 micron.

Typically, the concept of matching the skin layer thickness to the particle size is achieved using particles having a mean diameter in the range of from 5.0 μm to 20.0 μm. The lower end of the range of mean particle size may be any value within the range of 5.0 μm to 20.0 μm, particularly 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, 10.5 μm, 11.0 μm, 11.5 μm, or 12.0 μm. Similarly, the upper limit of the range of mean particle size may be any value within the range of 5.0 μm to 20.0 μm, particularly 10.0 μm, 10.5 μm, 11.0 μm, 11.5 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm, 15.5 μm 16.0 μm, 16.5 μm, 17.0 μm, 17.5 μm, 18.0 μm, 18.5 μm, 19.0 μm, 19.5 μm, or 20.0 μm. Exemplary ranges of mean particles size are 5.0 μm to 18.0 μm, 8.0 μm to 15.0 μm, or 10.0 μm to 15.0 μm.

Suitable fillers comprise clay materials, natural minerals, surface-treated natural minerals, synthetic minerals, surface-treated synthetic minerals, plastic or thermoplastic pigments or particulates, similar materials, and mixtures thereof.

In particular embodiments, the first filler component has a particular relative amount of particles with in a certain size range. In some embodiments, <2.0 number % of the filler particles have a diameter >75.0 μm, particularly >50.0 μm, more particularly >45.0 μm. In exemplary embodiments, the coating includes a filler having a mean particle dimension in the range of 10 μm to 15 μm wherein <2.0 number % of the filler particles have a diameter >45.0 μm. In other embodiments, the coating includes a filler having a mean particle dimension in the range of 15 μm to 20 μm wherein <2.0 number % of the filler particles have a diameter >65.0 μm. In some embodiments, at least 55.0 to 80.0 number % of the particles have a mean particle diameter in the ranges described in the preceding paragraph. The lower limit on the number % of particles in this range may be 55.0, 60.0, 65.0, 70.0, or 75.0. The upper limit on the range of number % of particles in these ranges may be 78.0, 75.0, 70.0, 65.0, 60.0, or 55.0.

It has been found that such filler components maintain advantage of reduced ghosting (a phenomenon where ink on the print face transfers to the adhesive face when the film is in roll and/or stack form) and remain suitable for cut and stack processes, while also providing reduced print face deformation observed when larger particles are used.

Filler materials may be classified into two functional groups: hydrophilic and hydrophobic. Hydrophilic or hydrophobic particles will each provide sufficient interstitial porosity to the coating to allow penetration that enables good retained adhesion in an ice chest, as taught herein, provided there is sufficient filler particle loading. Hydrophilic fillers may include silicas, hydrophilic clays, barium sulfate, calcium carbonate, titanium dioxide, zinc oxide, tin oxide, aluminum oxide, talc, carbon black, a wide variety of organic and inorganic pigments that could be used to make coated films with a specific color, and mixtures of any two or more of the foregoing, having hydrophilic properties. With hydrophilic fillers, internal particulate pore volume or porosity can influence the ability of given fillers to absorb water. Hydrophilic filler materials may preferably have low porosity or are effectively non-porous. In the context of the present invention, hydrophilic filler particles with low porosity means porosity of less than 3 milliliters/gram (ml/g) of water uptake per gram of filler material, with less than 1.5 ml/g being preferred, and less than 0.5 ml/g being more preferred. Low-porosity and non-porous hydrophilic fillers have been found to provide better properties than their more porous counterparts.

In addition to those listed previously, hydrophobic fillers commonly include, but are not limited to, surface-modified clays, surface-modified silicas, and surface-modified titanium dioxide, which have been rendered water-resistant due to their surface modification with organic moieties. Examples of surface-modified clays include kaolinite clays sold under the trade name Kalophile-2™ by Dry Branch Kaolin Company and Lithosperse® 7015 HS and 7005 CS by Huber Engineered Minerals. An example of surface-modified silica is Aerosil™ RX50 manufactured by Aerosil Nippon, in Japan. In accordance with the present invention, hydrophobic fillers are preferred, because it has been found, as demonstrated herein, that they offer better post-print blocking resistance during die-cutting and, when used on the print surface, these materials offer better wet-scratch resistance.

In particular embodiments, the filler component comprises polyolefin particles. Particular polyolefins include polyethylene which as used herein refers to a polyolefin homopolymer or copolymer containing recurring units derived from ethylene. Such polyethylenes include but are not limited to polyethylene homopolymer and/or copolymer wherein at least 85% (by number) of the recurring units are derived from ethylene. The polyethylene can be a mixture or reactor blend of individual polyethylenes, such as a mixture of two or more polyethylenes. Particular embodiments include a polyethylene wax in the form or particles having a mean diameter of from 5.0 μm to 20 μm, particularly 5.0 μm to 18.0 μm, more particularly 8.0 μm to 15.0 μm. In particular embodiments, such polyethylene waxes have a weight average molecular weight in the range of 2,000 to 15,000 g/mol, particularly in the range of about 5,000 to about 10,000 g/mol. Polyethylene waxes may also have one or more of the following features 1) Mw/Mn of from about 2 to 10, a viscosity number of from 10 to 60 cm³/g, a melting range of from about 129° C. to 131° C. for a homopolymer and about 120° C. to 126° C. for a copolymer, and a density of from 0.930 to 0.970 g/cm³. One suitable polyethylene is an oxidized HDPE, available as Acumist™ A12 or A18 from Honeywell Specialty Additives.

Typically, coating compositions according to embodiments of the invention include a first filler component in an amount less than 25.0 wt % of the first coating, based on the total weight of the first coating. In some embodiments, the first filler component comprises less than 15.0 wt %, e.g., 5.0 wt % to 10.0 wt %, of the first coating, based on the total weight of the first coating.

Binder

As described in more detail below, solvent resistance is typically imparted by the binder components, such as binders that are crosslinked using a crosslinker or which self-adhere, such as through polar bonding or self-crosslinking Other coating formulations according to embodiments of the invention comprise a hydrophobic binder, as described herein, in combination with a hydrophilic filler, with the binder thereby imparting a predominant portion of the water resistance and solvent resistance, while the filler imparts moisture transmission through the coating. Thus, in many embodiments, the binder component is resistant to both water and solvents. However, in embodiments where the filler is substantially hydrophobic, the binder material need not be as hydrophobic in nature and in some embodiments may permissibly contain some hydrophilic components or may be substantially hydrophilic but comprise a crosslinker to improve solvent resistance.

Optional Second Filler

In some embodiments, the coating also comprises at least 30 wt %, or preferably at least 45 wt %, and more preferably at least 60 wt % of preferably sub-micron size (meaning a particle mean diameter of equal to or less than about 1.0 micron) inorganic or organic filler materials. Suitable fillers comprise clay materials, natural minerals, surface-treated natural minerals, synthetic minerals, surface-treated synthetic minerals, plastic or thermoplastic pigments or particulates, similar materials, and mixtures thereof. In particular embodiments, the first coating includes a first binder component and a second filler component. In some embodiments, a least one of the second filler component and the first binder component is substantially hydrophobic.

Polymer Component

Some coating formulations also preferably comprise at least one polymer. Suitable polymers include, but are not limited to, acrylics, urethanes, hardened epoxies, alkyds, polystyrene copolymers, poly(vinylidene chloride)copolymers, butadiene copolymers, vinyl ester copolymers, nitrocellulose, and olefin copolymers, cross-linked, if necessary, to render them resistant to water and polar ink solvents (alcohols, esters, and ketones).

Optional Coating Additives

Many embodiments of the coating composition comprise a combination of hydrophobic polymer binders, and optionally including minor amounts of other additives, such as another polymer compound, organic or inorganic particles, silica gel, pH modifiers, and buffering agents. The coating formulations for adhesive-receiving layers (and, optionally, the print-face coating) can also contain a wide variety of additives including, but not limited to, wax emulsions, adhesion promoters, emulsifiers, anti-foams, defoamers, anti-static additives, security taggants, co-solvents, surfactants, and other wetting or processing aids known to those skilled in the art.

Substrate

Polymeric substrates referred to herein generally include a first skin layer (having a first and second side) having a closed-cell voided or uncavitated structure and an uncavitated core layer comprising a polymer, wherein the core layer has a first side and a second side, and the first side of the core layer is adjacent to the second side of the first skin layer. The first skin layer generally forms the substrate surface that is adjacent the article when the substrate is used as a label or opposite a side of the substrate that is adjacent a product when the substrate is used as a packaging substrate. This surface of the substrate may typically be referred to as the back-side, e.g., an adhesive-receiving side, of the substrate and is typically the side of the substrate that is adjacent the article, product, or the side of the substrate that receives the labeling adhesive when the substrate is used to form a label. The second surface of the substrate is generally referred to as, e.g., a top-side, front-side, or print-side of the substrate and is the side that is typically opposite the adhesive-receiving side of the substrate. In embodiments including a second skin layer, the second skin layer forms the print-side of the substrate.

The term “polymeric substrate” or “substrate” as used herein may be defined broadly to include any polymer or thermoplastic material comprising one or more monomers as a component thereof, preferably oriented polymeric film structures. The polymeric substrate may be monolayer or multilayer films, including oriented, coextruded, and laminated multilayer films, and may preferably be biaxially oriented films. The polymeric substrate may also comprise other non-thermoplastic or non-polymeric materials, such as paper, cardstock, and/or metallic or nonmetallic substrates, and/or they may be laminated to such non-thermoplastic materials, such as paper, metallic, or non-metallic substrates. The polymeric substrate includes the polymeric portion plus any non-thermoplastic components that make up the structural composition of the substrate. The polymeric substrate may include any clear, matte, cavitated, or opaque film. Many preferred embodiments may comprise an opaque or white film with substantially non-matte surfaces.

In some embodiments, the preferred polymeric substrate is a polyolefin film and more preferably a biaxially oriented, multi-layer or monolayer polyolefin-based film comprising polypropylene, polyethylene, and/or polybutylene homo-, co-, or ter-polymers. Other thermoplastic substrates or layers may also be present within such film embodiments, such as polyesters. However, in other embodiments, the polymeric substrate can include substantially any thermoplastic material that forms a thin film that can be employed for packaging, labeling, or decoration. Other exemplary suitable materials may include nylon, polyethylene terephthalate, polylactic acid, and polycarbonate. The contemplated substrates also include coextrudates of the foregoing materials, laminates of any two or more of these materials or interblends of any of the materials extruded as a single base film. Polyolefin homopolymers and copolymers of propylene and ethylene may be most useful in many labeling applications. One particularly preferred polymeric substrate that is suitable as a facestock for labeling is a polypropylene-based film containing at least 80 wt % of isotactic polypropylene in at least a primary or core layer. Exemplary commercially available materials include Exxon 4252 and FINA 3371.

The polymeric substrate may be coextruded with at least one skin layer or it may be laminated to at least one other film. Typically, when the film is coextruded the thickness of a skin layer may range from about 2% to about 18% of the total film thickness. Multilayer films having three or more layers, e.g., five layers and sometimes even seven layers are contemplated. Five-layer films may include a core layer, two skin layers, and an intermediate layer between the core layer and each skin layer, such as disclosed in U.S. Pat. Nos. 5,209,854 and 5,397,635. The skin layers may include a copolymer (i.e., a polymer comprising two or more different monomers) of propylene and another olefin such as ethylene and/or 1-butene.

Another exemplary preferred substrate is a multilayer polypropylene film comprising at least one of polyethylene, polypropylene, copolymer of propylene and ethylene, copolymer of ethylene and 1-butene, terpolymers of any of the foregoing and maleic anhydride modified polymers. Another useful substrate comprises polypropylene interblended with a minor proportion of at least one of polyethylene, copolymers of ethylene and an alpha olefin, copolymers of propylene and an alpha olefin, terpolymers of olefins and maleic anhydride modified polymers. Multilayer, white opaque, cavitated polypropylene-based films may also be a useful substrate. Such films are described in U.S. Pat. Nos. 4,758,462; 4,965,123; and 5,209,884.

The polymeric substrate may also be treated and/or metallized on at least one side. Many preferred polypropylene polymer-film embodiments may be treated on both sides to improve adherence of the print-side coating and the adhesive to the adhesive-receiving surface. Treatment may typically comprise corona, plasma, or flame treatment. In some embodiments, treatment may also comprise applying a primer to a surface of the polymeric substrate to improve adhesion between the substrate and the back-side coating and/or the polymeric surface layer. Such treatments may facilitate uniform wetting of the coatings and/or increase surface energy to improve coating anchorage to the substrate. The surface treatment typically may be applied after orientation, “in-line” on the coating equipment, though primers may typically be applied using coating equipment. Some embodiments may possess skin layers that do not require surface treatment for acceptable coating, ink, or adhesive adherence, such as layers comprising copolymers of ethylene and/or homopolymers of polyethylene, e.g., medium or high density polyethylene. Metallization may be by vacuum deposition of aluminum or other metals. A print-face coating and printing ink may also be applied to the metallized or treated surface.

The polymeric substrates may be uniaxially oriented, or simultaneously or sequentially biaxially oriented. A typical range of orientation stretches the film 4 to 10 times its original dimension in the machine direction and 7 to 12 times its original dimension in the transverse direction. The thickness of oriented polymeric substrates is not critical and typically ranges from about 10 μm to about 100 μm.

First Skin Layer

The first skin layer comprises a polymer. In one embodiment, the thermoplastic polymer of the first skin layer, that is, the layer intended for contact with the coating and/or the adhesive, comprises at least one polyolefin, including homo-, co-polymers (including terpolymers and higher combinations of monomers, as used herein) of polypropylene and/or polyethylene. Examples of suitable polypropylenes include a standard film-grade isotactic polypropylene and/or a highly crystalline polypropylene. An example of a suitable polyethylene is high-density polyethylene. In another embodiment, the first skin layer comprises copolymers of polypropylene including comonomers of C₂ or C₄ to C₁₀ in an amount less than 50 wt % of the copolymer, and blends of said polypropylene homopolymers and polypropylene copolymers. Particularly, the first skin layer comprises one or more polypropylene or polyethylene homopolymers or copolymers and has a density of 0.500 g/cm³ to 0.946 g/cm³.

In embodiments, the first skin layer is uncavitated. In other embodiments, the first skin layer includes a first voiding agent to cavitate the layer during orientation. Examples of suitable cavitating agents for essentially any voided or cavitated layer includes polyamides, polybutylene terephthalate, polyesters, acetals, acrylic resins, nylons, solid preformed glass particles or spheres, hollow preformed glass particles or spheres, metal particles or spheres, ceramic particles, calcium carbonate particles, cyclic olefin polymers or copolymers (collectively, “COC's”), silicon dioxide, aluminum silicate and magnesium silicate and mixtures thereof. COC's are described in U.S. Pat. No. 6,048,608 issued to Peet et al., which is incorporated herein by reference in its entirety. The term “voiding agents” includes cavitating agents, foaming agents or blowing agents, of substantially any shape. Suitable voiding agents (i.e., cavitating agents) and voided skin layers (i.e., cavitated skin layers) are described in U.S. application Ser. No. 09/770,960, which is incorporated herein by reference.

In one embodiment, the first voiding agent makes up from about at least 15.0 wt % to about at least 60.0 wt % of the first skin layer, and more preferably, from about at least 25.0 wt % to about at least 50.0 wt % of the first skin layer and the first voiding agent may have a median particle diameter/size of from about 1.0 μm to about 5.0 μm and more preferably from about 1.0 μm to about 3.0 μm. In another embodiment, the first voiding agent comprises at least about 20.0 wt %, at least about 25.0 wt %, at least about 35.0 wt %, at least about 40.0 wt %, or at least about 50.0 wt % of the first skin layer and the median particle size of the voiding agent is in the range of 1.0 μm to 5.0 μm, preferably 1.0 μm to 3.0 μm. For example, in one embodiment, the median particle size of the voiding agent is at least about 1.4 μm. In another embodiment, the median particle size of the voiding agent is at least about 3.2 μm.

In many embodiments, the voiding agent employed in either the first skin layer or the core layer is calcium carbonate having a particle size range in the range of 1.0 μm to 5.0 μm, preferably 1.0 μm to 2.0 μm and is preferably present in an amount of about 20.0 wt % to about 60.0 wt %, particularly in the skin layer. For example, in various embodiments, the quantity of 1.0- to 2.0-micron calcium carbonate is at least 25.0 wt %, or at least 35.0 wt %, or at least 40.0 wt % of the first skin layer. For some embodiments, the upper quantity limit of the 1.0- to 2.0-micron calcium carbonate is, for example, 60.0 wt % or less, of the respective cavitated layer, while in other embodiments, the upper limit is no more than about 50.0 wt % of the respective cavitated layer. All percentages of calcium carbonate referred to herein are by weight, based on the total weight of the voided layer including the calcium carbonate therein.

This first skin layer may be voided with a suitable first voiding agent to create voids or cells to provide a desired level of porosity and/or permeability to aid absorption and/or dissipation of moisture from aqueous adhesives, among other considerations related to voided films, such as yield, stiffness and opacity.

The first skin layer may have a particular surface roughness. When measured with an M2 Perthometer equipped with a 150 stylus from Mahr Corporation, the average surface roughness (R_a, output as defined in the operating manual of the Perthometer) of the first skin layer is typically greater than 0.5 μm. R_Z (output as defined in the operating manual of the Perthometer), which weighs larger peaks more heavily, is typically greater than 4 μm.

Core Layer

The core layer comprises a polyolefin and has a first side and a second side. The first side of the core layer is adjacent to, though not necessarily directly in contact with, the second side of the first skin layer. Preferably, the core layer has a thickness of approximately 50 to approximately 950 gauge units (13 μm to 240 μm); however, for better economics, the more preferred thickness of the core layer is between about 50 to about 350 gauge units (13 μm to 90 μm).

In one embodiment, the core layer comprises polypropylene. Preferably, the polypropylene of the core layer is either isotactic or high crystalline polypropylene. In another embodiment, the core layer comprises polyethylene. Preferably, the polyethylene is high-density polyethylene. In another embodiment, the copolymer of the core layer is a mini-random copolymer having an ethylene content on the order of 1.0 wt % or less and 99.0 wt % or more of the co-polymer component, such as polypropylene. In many embodiments, the core layer is voided. In such embodiments, the core layer includes a second voiding agent, which may be the same or a different agent as the first voiding agent used in voiding the first skin layer. The core layer may be voided utilizing the voiding agents listed above and in concentrations as listed above, with particle size and concentrations determined by the properties desired to impart to the core layer. In other embodiments, the core may not be voided. In either embodiment, non-void-creating particulate additives or fillers, such as titanium dioxide, can be included in the core layer to enhance opacity.

In some embodiments, the core layer includes a first tie layer that forms the first side of the core layer and is in surface contact with the first skin layer. In some embodiments, the core layer includes a region that may be called a second tie layer. The second tie layer forms the second side/surface of the core layer. Where a second skin layer is present, the second tie layer is in surface contact with the second skin layer. These tie layers may include homo-, co-, or terpolymers comprising polypropylene, polyethylene, polybutylene, or blends thereof and may have a thickness of at least about 0.3 mil (0.75 μm). The first side of the first tie layer is adjacent to the second side of the first skin layer; and the first side of the core layer is adjacent to the second side of the first tie layer. The second side of the second tie layer is adjacent to the first side of the second skin layer; and the second side of the core layer is adjacent to the first side of the second tie layer.

In some embodiments, the core and/or tie layer(s) may also include a conventional non-void-inducing filler or pigment such as titanium dioxide. Generally, from an economic viewpoint at least, it has not been considered to be of any particular advantage to use more than about 10 wt % of titanium dioxide to achieve a white label suitable for printing. Greater amounts could be added for greater opacity so long as there is no undue interference with achieving the desired properties of a thermoplastic label.

Optional Second Skin Layer

Many preferred embodiments also possess a second skin layer on a side of the core layer opposite the first skin layer. The second skin layer comprises a polyolefin and has a first side and a second side. The first side of the second skin layer is adjacent to the second side of the core layer, though not necessarily directly in contact with the core layer. Preferably, the second skin layer is on the order of 10 to 25 gauge units (2.5 μm to 6.4 μm) in thickness. Suitable polyolefins for the second skin layer include polyethylene, polypropylene, polybutylene, polyolefin copolymers, and mixtures thereof. In many label embodiments, the second skin layer is not voided or when voided, is typically only lightly voided and has a substantially closed-cell type void structure. The second/exterior side is suitable for a surface treatment such as flame, corona, and plasma treatment; metallization, coating, printing; and combinations thereof

In one embodiment, the second side of the second skin layer is metallized or is a glossy surface that is capable of dissipating static. In another embodiment, the metallized or glossy surface is coated with a polymeric coating. In still another embodiment, the second side of the second skin layer is coated with a relatively rough, non-glossy material that is also capable of dissipating static. Such coating may be a coating having properties and components according to this invention. For example, the coating on the second side of the second skin layer may be the same coating, as used on the first side of the first skin layer. Still other embodiments will employ a voiding agent in the second skin layer and/or the core layer, wherein such voiding agent has a median particle size of 1.5 μm or less, such that when the second skin layer is metallized, a bright mirrored appearance will result. The second skin layer is preferably treated to improve surface adhesion, such as by corona treatment. In an exemplary embodiment of this invention, the skin layer intended to receive the metallized coating has a thickness of approximately 20 gauge units (5 μm) or less.

Films described in US Patent Application Publication Nos. 2002/0146520 and 2003/0172559, and U.S. Pat. No. 7,288,304, incorporated herein by reference in their entireties, disclose representative compositions suitable as the optional second layer.

Optional Second Coating Layer

Embodiments of the invention include films having a coating on the print-side of the film. The coating may be applied to the core layer or the optional second skin layer, when present. The coating may be applied by any means known in the art, such as direct gravure, reverse-direct gravure, offset, spraying, or dipping. The optional second coating may also may be applied to a metallized, matte or glossy print-side surface to protect such side and/or to dissipate static charge therefrom. Although anti-static protection may be applied to either side of a film substrate, typically it is not necessary to provide anti-static protection to both sides of the film structure. For example, the surface resistivity of the print surface may be less than 14 log ohms per square (per square geometric region as measured on a circular film sample inserted into a Keithley Model 8008 Resistivity Test Fixture with 500 volts applied using a Keithley Model 487 Picoammeter/Voltage Source, or alternatively using an Autoranging Resistance Indicator Model 880 from Electro-Tech Systems, Inc., Glenside, Pa.), when the relative humidity is greater than 50% and the metallized surface is reflective or the gloss is >30% when measured with a BYK Gardner Micro-gloss 20° meter. Adequate gloss and metallic sheen can be obtained from using a base film which is uniaxially or biaxially oriented and which has a second/print side that contains only substantially closed-cell voids, a relatively low percentage of voids, or no voids at all on the gloss or metallic second/print side. In the metallized embodiments, metal, such as aluminum, is deposited on the smooth, print side.

Formulations described for the first coating may also be used for the optional second coating.

Optional second coatings also include smooth, clear polymeric coatings applied over the core layer, the optional second skin layer, or the metallic layer deposited on thereon Such polymeric coating can be applied by any means known in the art including, but not limited to, application of polymeric material dispersed in water or dispersed in a solvent, and extrusion coating. Such coatings may further enhance gloss or preserve a desired metallic appearance of a metallized film.

The outer print/metallization surface of the film preferably has an average roughness (R_a) of between 0.1 μm and 0.3 μm, preferably less than 0.3 μm, more preferably less than 0.15 μm, before metallization. (R_a can be measured with an M2 Perthometer from Mahr Corporation equipped with a 150 stylus.) In some embodiments, the second skin layer is coated with a relatively rough, non-glossy material that is capable of dissipating static. That is, the surface resistivity is less than 14 log ohms/square when the relative humidity is greater than 50%, gloss is <30% when measured with a BYK Gardner Micro-gloss 20° meter. In some embodiments the surface-applied coating has a roughness R_a that is greater than 0.20 μm and an R_a that is greater than 1.0 micron when measured with a Perthometer S2 from Mahr Corporation, Cincinnati, Ohio, especially such a model equipped with a 150 stylus. For good print quality, the roughness R_a is preferably less than 0.35 and R_Z is preferably less than 3.0 μm. When measured with a Messmer Parker Print-Surf Roughness and Air Permeability Tester Model ME-90, the rough coating for the second side of the second skin layer preferably has an average roughness between 0.75 μm and 3 μm, more preferably between 1 μm and 2 μm. Suitable examples of relatively rough, non-glossy coatings having wet-scratch resistance are described in U.S. Pat. No. 6,025,059 and U.S. Patent Application Publication No. 2003/0207121, which disclosures are incorporated herein by reference in their entireties. Another example is PD900 NT from Process Resources Corporation cross-linked with polyfunctional aziridine, such as CX-100 from Avecia, and NAC-116, an anti-static additive from Process Resources Corporation.

In embodiments wherein the second side of the second skin layer is metallized, preferably, a coating is applied to the metallized surface. Such coatings may provide desirable print qualities including wet-scratch resistance, machinability enhancement, and mar resistance. Suitable examples are described in U.S. Pat. Nos. 6,025,059 and 6,893,722, which disclosures are incorporated herein by reference in their entireties. Additionally, a variety of urethanes, acrylics, polyesters, and blends thereof may also be suitable. Suitable examples are described in U.S. Pat. Nos. 5,380,587 and 5,382,473, which disclosures are incorporated herein by reference in their entireties.

Preferred printable coatings for the optional second coating may provide excellent anchorage for inks, including radiation curable inks, such as ultra-violet (“UV”) radiation cured inks, and many other types of inks such as discussed below. To provide a durable, scratch resistant, or mar resistant print-surface on the film, many preferred embodiments are coated with a cross-linked or cured coating. Preferred coatings may also resist attack by isopropyl alcohol (IPA) and hot water. Examples of such coatings are described by McGee in U.S. Pat. Nos. 6,596,379 and 6,893,722; Touhsaent in U.S. Pat. No. 6,844,034; and Servante in U.S. Pat. No. 7,758,965. These patents and application are incorporated herein, by reference, in their entirety. In many preferred pressure sensitive label embodiments, the coatings described by McGee in U.S. Pat. No. 6,893,722 may be especially preferred, as they may provide a durable, pasteurizable, printable surface. Other suitable front-side coatings may include acrylic-based coatings and other water-or solvent-based printable coatings that are substantially clear when dry.

Preferably, water- and solvent-resistant coatings applied to the metallized surface do not significantly diminish the bright mirrored appearance of the metallized surface. Similar coatings can be used on the second side of the second skin layer without metallizing. However, such structures would lose a significant contribution to the anti-static properties made by the metal and depending upon the formulation of the clear coating, anti-static additives may then be necessary in the coating formulation for the print face.

In some embodiments, the surface resistivity of the second skin layer and the layer coated with the water- and solvent-resistant filled coating is less than about 14 log ohms/square, more preferably less than about 12 log ohms/square, and most preferably less than about 10 log ohms/square. Surface resistivity measurements may be made with an Autoranging Resistance Indicator Model 880 from Electro-Tech Systems, Inc., Glenside, Pa., especially when measuring a surface that is metallized or that has a clear coating over the metal. However, this device cannot measure resistances above 12 log ohms/square. Alternatively, surface resistivity may be measured using a 487 Picoammeter/Voltage Source equipped with an 8008 Resistivity Test Fixture supplied by Keithley Instruments, Cleveland, Ohio, especially when the surface resistivity exceeded 12 log ohms/square. For the measurements made with the Keithley meter, the instrument applies 500 volts to the surface of the sample.

Film Structures

In one embodiment, the label film comprises three layers; that is, a first skin layer on the adhesive-receiving side of the film, a core/interior layer (which may also include tie layers) and a second skin layer on the side of the core layer opposite the first skin layer. The first skin layer has a first side and a second side and includes a thermoplastic polymer. The first skin layer is either voided with a closed-cell structure or uncavitated. In some embodiments, the first side preferably is intended for receiving both a coating according to this invention thereon, and subsequently, a cold-glue type adhesive or a hot-melt type adhesive on the coating. The first skin layer typically has a thickness in the range of 15 to 25 gauge units (0.15 mil to 0.25 mil, or 3.8 μm to 6.4 μm), but this is not critical. Thermoplastic films and labels according to such embodiments typically have an overall thickness, including both skin layers, the core layers and any additional layers, of from about 1 mil to about 10 mils (25 μm to 250 μm), preferably from about 3 mils to about 5 mils (75 μm to 125 μm), with many embodiments comprising a three- to five-layer white opaque film. In some label film embodiments, the adhesive-receiving first skin layer makes up at least about 15 wt % of the film label. In another embodiment, the first skin layer comprises at least about 30 wt % of the film label. Preferably, the thermoplastic films useful according to this invention, including the label films, are biaxially oriented. In another embodiment, the films are uniaxially oriented.

Additional Optional Additives

Other conventional additives, in conventional amounts, may be included in the coatings or films of the invention. Suitable other conventional additives include anti-oxidants, pigments, orientation stress modifiers, flame-retardants, anti-static agents, anti-blocking agents, anti-fog agents, and slip agents. Another class of additives that may be included in the film structures according to this invention is low molecular weight hydrocarbon resins (frequently referred to as “hard resins”). The term “low molecular weight hydrocarbon resins” refers to a group of hydrogenated or unhydrogenated resins derived from olefin monomers, such as the resins derived from terpene monomers, coal tar fractions, and petroleum feedstock. Such suitable resins prepared from terpene monomers (e.g., limonene, alpha and beta pinene) are Piccolyte resins from Hercules Incorporated, Wilmington, Del., and Zonatac resins from Arizona Chemical Company, Panama City, Fla. Other low molecular weight resins are prepared from hydrocarbon monomers, as C₅ monomers (e.g., piperylene, cyclopentene, cyclopentadiene, and isoprene), and mixtures thereof. These are exemplified by the hydrogenated thermally oligomerized cyclopentadiene and dicyclopentadiene resins sold under the trade name Escorez (i.e., Escorez 5300) by ExxonMobil Chemical Company of Baytown, Tex. Others are prepared from C₉ monomers, particularly the monomers derived from C₉ petroleum fractions which are mixtures of aromatics, including styrene, methyl styrene, alpha methyl styrene, vinyl naphthalene, the indenes and methyl indenes and, additionally, pure aromatic monomers, including styrene, α-methyl-styrene, and vinyltoluene. Examples of these resins include hydrogenated a-methyl styrene-vinyl toluene resins sold under the trade name Regalrez by Hercules Incorporated of Wilmington, Del.

Film Properties

Thermoplastic films and labels according to the present invention may typically have an overall thickness, including the skin layer(s), the core layers and any additional layers, of from about 1 mil to about 10 mils (25 μm to 250 μm), preferably from about 3 mils to about 5 mils (75 μm to 125 μm), with many embodiments comprising a three- to five-layer white opaque film. In some label film embodiments, the adhesive-receiving first skin layer makes up at least about 15 wt % of the film label. In another embodiment, the first skin layer comprises at least about 30 wt % of the film label. Preferably, the thermoplastic films useful according to this invention, including the label films, are biaxially oriented. In another embodiment, the films are uniaxially oriented.

In film substrate embodiments comprising a cavitated first skin layer and a core layer, and optionally including a first tie layer, the density of the film substrate, excluding any coatings, metallization, and printing inks, etc., is preferably within a range of at least about 0.3 g/cc to about 0.8 g/cc. A lower bulk density may result in a film of unsuitable matrix/structural integrity, unless laminated to a stronger layer, and a higher bulk density may provide insufficient porosity for the effective absorption of moisture from the cold glue adhesive. These bulk density limits may vary somewhat, in films with relatively thick cores or relatively thin skins. For example, a film having a heavily cavitated core and/or tie layer may be cavitated such that the bulk density is slightly lower than 0.3 g/cc, while a film comprising a relatively thin cavitated first skin layer with relatively thick non-cavitated tie and core layers may exhibit a bulk density in excess of 0.8 g/cc. Thus, the term “about” is intended to incorporate such film structures that fall outside of the stated range but which are otherwise utilized according to this invention.

Label Structures

Embodiments of the invention also include containers or substrates labeled with the thermoplastic films described herein. Some such labels provide one or more advantages over currently used paper and polymeric labels. For example, some labels may include coatings on the print side and/or the adhesive-receiving layer of paper labels to make some of the advantages of the coating available to paper label applications. In embodiments related to labels or labeled containers, an adhesive may be applied to the first skin layer. Preferably, the adhesive is a water-based adhesive, e.g., cold glues as commonly used in container or bottle labeling operations. Water-based adhesives are well known in the art for use with traditional paper labels.

As referenced herein, adhesive is applied to the first side of the first skin layer of the films of the present invention. Cold glue adhesives generally comprise solid base materials in combination with water. In one embodiment, the cold glue is an aqueous solution of a natural adhesive (e.g., casein). In another embodiment, the cold glue is an aqueous solution of a resin (e.g., poly(vinyl acetate) (PVA) or ethylene vinyl acetate (EVA)). Cold glues are widely used as an economical alternative to wrap around or pressure sensitive labels. Some cold glues are a colloidal suspension of various proteinaceous materials in water and are derived by boiling animal hides, tendons, or bones that are high in collagen. Alternatively, cold glue can be derived from vegetables (e.g., starch, dextrin). Some cold glues are based on synthetic materials (resins). Examples of cold glues which are suitable for the practice of the present invention include HB Fuller WB 5020, National Starch Cycloflex 14-200A, AABBITT 712-150; Henkel Optal 10-7026; Henkel Optal 10-7300; and Henkel Optal 10-7302. Exemplary suitable hot-melt adhesives include North West Adhesives A48, Henkel 3963, Henkel 377, HB Fuller 4165. The aforementioned list of cold glues contains trademarks of HB Fuller, National Starch, AABBITT, and Henkel, respectively.

The coated film labels comprising the water-based adhesive are attached to containers by means known in the art. The containers have a surface that is adjacent to the glue applied to the coated first/adhesive-receiving side of the first skin layer of the label. Suitable materials for the container include glass, ceramics, thermoplastics, metal and other materials. The present invention provides containers having a thermoplastic film label. These containers include a surface of the container; a water-based adhesive adjacent to the container surface; and a hydrophobic-coated thermoplastic film label. The coated thermoplastic film label is as described above.

Particular Embodiments

• 1. Embodiments of the invention provide a coated thermoplastic film comprising:
  • (a) a substrate comprising:
    • (i) a first skin layer having an open-cell voided structure, a closed-cell voided structure or an uncavitated structure, comprising a polymer, wherein the first skin layer has a first side and a second side;
    • (ii) an uncavitated core layer comprising a polymer, wherein the core layer has a first side and a second side, and the first side of the core layer is adjacent to the second side of the first skin layer; and
  • (b) a first coating on the first side of the first skin layer, the first coating comprising at least a first filler component, the first filler component comprising particles having an effective diameter of 5.0 μm to 20.0 μm. In particular embodiments the first skin layer has an open-cell voided structure, and the first filler component comprises particles having a mean particle diameter satisfying the following equation:

D_mean=N−T_skin

• • wherein
  • D_mean is the mean particle diameter (μm) of the first filler component;
  • T_skin is the thickness (μm) of the first skin layer; and
  • N is in the range of 10.0 μm to 20.0 μm.
• 2. Embodiments of the invention include coated films according to paragraph 1, wherein the first skin layer has a closed-cell voided structure or an uncavitated structure, and the first filler component comprises particles having a mean diameter in the range of 5.0 μm to 20.0 μm.
• 3. Embodiments of the invention include coated films according to any of paragraphs 1 and 2, wherein the first filler component comprises particles having a mean diameter in the range of 8 μm to 18 μm.
• 4. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 3, wherein the first filler component comprises particles having a mean diameter in the range of 5 μm to 15 μm.
• 5. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 4, wherein the first coating further includes a first binder component and a second filler component.
• 6. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 4, wherein the first coating further includes a first binder component and a second filler component, and wherein a least one of the second filler component and the first binder component is substantially hydrophobic.
• 7. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 6, wherein the first skin layer comprises a polypropylene or polyethylene and has a density of 0.500 g/cm³ to 0.946 g/cm³.
• 8. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 7, wherein the substrate (a) further comprises: a second skin layer comprising a polymer, wherein the second skin layer has a first side and a second side, the first side of the second skin layer is adjacent to the second side of the first core layer, and the second side of the second skin layer is suitable for a surface treatment selected from the group consisting of flame, corona, plasma, metallization, prime coating, printing, and combinations thereof
• 9. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 8, wherein the first filler component comprises at least one of: a) a clay material; b) a natural mineral material; c) a surface-treated natural mineral; d) a synthetic mineral; e) a surface-treated synthetic mineral; f) plastic particulates; and g) thermoplastic particulates.
• 10. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 9, wherein the first filler component comprises at least one of: a) a surface-modified clay; b) plastic particulates; and c) thermoplastic particulates.
• 11. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 10, wherein the first filler component comprises a surface-treated polyolefin, e.g., surface-treated polyethylene.
• 12. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 11, wherein the first binder component comprises at least one polymer of the group consisting of acrylics, urethanes, hardened epoxies, alkyds, polystyrene copolymers, poly(vinylidene chloride) copolymers, butadiene copolymers, vinyl ester copolymers, nitrocellulose, and olefin copolymers.
• 13. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 12, wherein the first coating further comprises: at least one of organic particles, inorganic particles, silica gel, anti-static material, wetting agents, surfactants, security taggants, pH modifiers, and buffering agents.
• 14. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 13, wherein the first coating is applied to the film at a weight of from about 0.1 g/m² to about 4.0 g/m², particularly from about 0.2 g/m² to about 2.5 g/m², more particularly from about 0.8 g/m² to about 2.0 g/m².
• 15. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 6 and 8 to 14, wherein the substrate (a) further comprises: a second skin layer comprising a polymer, wherein the second skin layer has a first side and a second side, the first side of the second skin layer is adjacent to the second side of the first core layer, and the second side of the second skin layer is suitable for a surface treatment selected from the group consisting of flame, corona, plasma, metallization, prime coating, printing, and combinations thereof, and a second coating comprising at least a third filler component and a second binder component, the second coating applied to the second side of the second skin layer, wherein at least one of the third filler component and the second binder component is substantially hydrophobic.
• 16. Embodiments of the invention include coated films according to paragraph 15, wherein the second coating is applied to the film at a weight of from about 0.1 g/m² to about 4.0 g/m².
• 17. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 16, wherein the first filler component comprises less than 25.0 wt %, particularly less than 15.0 wt %, more particularly 5.0 wt % to 10.0 wt % of the first coating, based on the total weight of the first coating.
• 18. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 17, wherein the first binder is substantially hydrophobic and the first filler material is substantially hydrophilic, the first filler comprising at least one of: a) silica; b) hydrophilic clays; c) barium sulfate; d) calcium carbonate; e) titanium dioxide; f) zinc oxide; g) tin oxide; h) aluminum oxide; i) talc; j) carbon black; and k) another pigment.
• 19. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 18, wherein the first binder further comprises a crosslinker, particularly where the crosslinker comprises at least one of zirconium salts of mineral acids, polyfunctional aziridine, zinc salts, zirconium salts, glyoxal, melamine-formaldehyde resins, polyfunctional isocyanates, polyfunctional amino compounds, polyfunctional vinyl compounds, and polyfunctional epoxy compounds.
• 20. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 19, wherein the first coating further comprises at least one of wax emulsions, adhesion promoters, emulsifiers, anti-foams, defoamers, anti-statics, security taggants, co-solvents, wetting aids, and processing aids.
• 21. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 20, wherein the first skin layer further comprises a voiding agent selected from the group consisting of polyamides, polybutylene terephthalate, polyesters, acetals, acrylic resins, solid preformed glass particles, hollow preformed glass particles, metal particles, ceramic particles, calcium carbonate, cyclic olefin polymers, cyclic olefin copolymers, silicon dioxide, aluminum silicate, magnesium silicate, and mixtures thereof.
• 22. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 21, wherein the first core layer further comprises a voiding agent selected from the group consisting of polyamides, polybutylene terephthalate, polyesters, acetals, acrylic resins, solid preformed glass particles, hollow preformed glass particles, metal particles, ceramic particles, calcium carbonate, cyclic olefin polymers, cyclic olefin copolymers, silicon dioxide, aluminum silicate, magnesium silicate, and mixtures thereof
• 23. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 22, wherein the polymeric substrate without the first coating has a density of from about 0.30 g/cm³ to about 0.80 g/cm³.
• 24. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 23, wherein the first coating is in the form of a continuous layer on the first side of the first skin layer.
• 25. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 24, wherein the first coating is in the form of a pattern or non-continuous layer on the first side of the first skin layer.
• 26. Embodiments of the invention include coated films according to any combination of paragraphs 1 to 25, wherein the first coating layer further comprises a primer layer in surface contact with the first side of the first skin layer.
• 27. Particular embodiments include coated label films for use with a cold glue adhesive, the label film comprising:
  • (a) a substrate comprising:
    • (i) a first skin layer comprising a polymer, wherein the first skin layer has a first side and a second side and is voided with a closed-cell structure;
    • (ii) a core layer comprising a polymer, wherein the core layer has a first side and a second side, and the first side of the second core layer is adjacent to the second side of the first skin layer; and
  • (b) a first coating on the first side of the first skin layer comprising at least a first filler component the filler component comprising polyethylene homopolymer or copolymer particles having a mean diameter in the range of 5 μm to 20 μm and <2.0 number % of the filler particles have a diameter >75.0 μm.
• 28. Particular embodiments also include coated thermoplastic films comprising:
  • (a) a polymeric substrate comprising:
    • (i) a first skin layer having a closed-cell voided or uncavitated structure, comprising a polymer, wherein the first skin layer has a first side and a second side;
    • (ii) a uncavitated core layer comprising a polymer, wherein the core layer has a first side and a second side, and the first side of the core layer is adjacent to the second side of the first skin layer;
    • iii) second skin layer having a first side and a second side, wherein the first side is adjacent the second side of the core layer;
  • (b) a first coating on the first side of the first skin layer, the first coating comprising a polyethylene filler component, the polyethylene filler component comprising particles having a mean diameter in the range of 5 μm to 20 μm, a second filler component comprising 30 wt % to 60 wt % of a second filler having particle mean diameter of ≦1.0 micron and a self-cross-linking cationic acrylic first binder component; and
  • (c) a second coating on the second side of the second skin layer, the second coating comprising a self-crosslinking cationic acrylic composition.
• 29. Embodiments of the invention include coated films according to paragraph 28, wherein the core layer include a first tie layer region and a second tie layer region, the first tie layer region forming the first side of the core layer and the second tie layer region forming the second side of the core layer.

This disclosure is merely illustrative and descriptive of the invention by way of example and various changes can be made by adding, modifying, or eliminating details without departing from the fair scope of the teaching contained in the disclosure. It will be recognized by those skilled in the art that various changes to the embodiments or methods herein as well as in the details may be made within the scope of the attached claims without departing from the spirit of the invention. However, such modifications and adaptations are within the spirit and scope of the present invention.

EXAMPLES

Comparative Example 1

The underlying film in Comparative Example 1 onto which a coating is applied is a biaxially oriented five-layer opaque film suitable for labeling applications, e.g., 85BF or 160LL302 film available from ExxonMobil Chemical Films. Suitable base films, including 85BF and 160LL302, have a structure shown below, wherein all percentages are by weight based on the total weight of the recited components of individual layers. The relative amounts of the individual layers in the film is also indicated, e.g., in certain embodiments Skin Layer 1 comprises 5.0 wt % to 9.0 wt % of the base film.

Adhesive-Receiving Surface

Skin Layer 1 (5.0-9.0%)   OPP or HCPP + 0.0-60.0% voiding agent +
                          0.0-15.0% Antiblock
Tie Layer 2 (5.0-30.0%)   OPP or HCPP
Core Layer 3 (52.5-88.5%) OPP or HCPP + 0.0-15.0% voiding agent
Tie Layer 4 (0.0-30.0%)   OPP or HCPP + 0.0-10.0% Antistat
Skin Layer 5 (1.0-3.5%)   Propylene-ethylene copolymer + 0.0-15.0%
                          Antiblock

Print-Receiving Surface (with or sans Metal)

The term “OPP” means polypropylene resin, the term “HCPP” means high crystallinity polypropylene resin. An adhesive surface coating is applied to Skin Layer 1 of the 85 BF base film. The coating comprises about 2.3 g/m² of filled coating containing emulsion-based binders and fillers. One component of the filled coating comprises MD145 available from Michelman, Inc., which comprises 175 dry parts (a parts are on a dry basis) of a first filler component (micronized oxidized high-density polyethylene available as ACumist® A-45 from Honeywell) having a mean diameter of 30-40 μm and a largest particle diameter of 125 μm; 250 dry parts of a second filler component (sub-micron clay available as Lithosperse 7005 CS from Huber, which is clay treated with an inorganic material to render the clay hydrophobic) per 100 dry parts of R1117 XL (a cationic acrylic emulsion from Owensboro Specialty Polymer, LLC) as the binder. Prior to coating, MD145 is blended with 68 dry parts epoxy binder described by Steiner et al. (U.S. Pat. No. 4,214,039) per 100 dry parts of R1117 XL. Thus, the completed coating contained about 72 wt % fillers (28% binders), not counting other minor formulation additives. The print face, i.e., Skin Layer 5 is corona treated and metallized before being coated with a coating suitable for printing.

Example 1

Comparative Example 1 is substantially reproduced except that MD145 was replaced with MD118, also from Michelman, Inc. MD118 is similar to MD145 except that the first filler component of Comparative Example 1 is replaced with a filler comprising 36 phr (per 100 phr R1117XL) polyethylene particles (Acumist A18) having a mean particle diameter of 18 μm (individual batches ranged from 16 μm to 19 μm) and a largest particle diameter of 62 μm.

Example 2

Comparative Example 1 is substantially reproduced except that MD145 was replaced with MD112, also from Michelman, Inc. MD112 is similar to MD145 except that the first filler component of Comparative Example 1 is replaced with a filler comprising 36 phr (per 100 phr R1117XL) polyethylene particles (Acumist A12) having a mean particle diameter of 12 μm (individual batches ranged from 10 μm to 13 μm) and a largest particle diameter of 44 μm.

The resulting coated films are evaluated for suitability for both cut and stack and roll-fed processes. Example 1 and Example 2 demonstrate that the smaller first filler outperforms the control/Comparative Example 1 with respect to print face embossing, sheeting performance, ghosting, and moisture absorption.

To evaluate the level of print face embossing, 28″×40″ sheets of film are printed on a 6-color Mitsubishi Off-set printing press at a standard press speed of 7,500 to 8,500 sheets per hour. The printed surface of the film is evaluated based on the density of the embossing defect. Experimental variables were qualitatively rated against the control on a 1-to-5 scale with a score of 3 used for the control film. A score of a 1 or 2 represents an increase in density of the defect seen on the print surface, with 1 representing a higher density than 2. A score of a 4 represents a decrease in the density of the defect. A score of a 5 represents a removal of the embossing defect. Higher numbers are desirable.

To test sheeting performance, film is run on a Valmet TSK Twin Synchronous Knife machine. Two parameters are used to evaluate the performance of the film: 1) the speed of the machine; and 2) the amount of operator attention required to complete the sheeting operation is recorded for each variable: Comparative Example 1 (control film, 45μ particle size variable film), and (Example 1 and Example 2) the experimental variables, 18μ and 12μ particle size film. The control film, 45μ particle size film, runs at 200 feet per minute and requires constant operator attention. The 18μ particle runs at 200-210 feet per minute without any operator attention. The 18μ particle film runs up to 250 feet per minute with intermittent operator attention. The 12μ particle runs up to 250 feet per minute without any operator attention. The film is rated against the control on a 1-to-5 scale with a score of 3 used for the control film. A score of 4 represents an improvement in one of the two parameters evaluated: machine speed or amount operator attention required. A score of 5 represents an improvement in two of the two parameters evaluated.

Ghosting is the term used in the trade when, as the ink dries, any amount of ink on the printed surface transfers to the backside of the film. Ghosting occurs after the film is printed with ink and the film is then rewound or stacked on top of itself. No ghosting is desirable. The film was evaluated for ghosting after printing on a 6-color Mitsubishi Off-set printing press. Comparative Example 1 exhibited ink transfer. Example 1 and Example 2 exhibited no ink transfer.

Wettability/Surface Energy is measured via a contact angle meter (from Tantec AS). Contact angle is defined as the angle between the tangent line at the contact point and the horizontal line of the surface. The change in the contact angle (in degrees) of a droplet of DI H₂O onto the adhesive receiving surface of the coated film is measured over a 5 minute test. This test is completed twice and the result reported is the average change in angle. The average range is from 0 to 22.5 degrees. Higher numbers are desirable. The following table shows the results:

TABLE 1
Summary of Testing Results
	Comparative
	Example 1	Example 1	Example 2
	45μ particle	18μ particle	12μ particle
Print Face Embossing	3	5	5
Sheeting Performance	3	4	5
Ghosting	Yes	No	No
Wettability/Surface	11.5	18.5	16.3
Energy (degrees)

Examination of the data in Table 1 reveals that Example 1 and Example 2 preformed better than Comparative Example 1 in the areas of Print Face Embossing, Sheeting Performance, Ghosting, and/or Wettability (i.e., Surface Energy).

Claims

1. A coated thermoplastic film comprising:

(a) a substrate comprising: (i) a first skin layer having an open-cell voided structure, a closed-cell voided structure or an uncavitated structure, comprising a polymer, wherein the first skin layer has a first side and a second side; (ii) an uncavitated core layer comprising a polymer, wherein the core layer has a first side and a second side, and the first side of the core layer is adjacent to the second side of the first skin layer; and

(b) a first coating on the first side of the first skin layer, the first coating comprising at least a first filler component, the first filler component comprising particles having an effective diameter of 5.0 μm to 20.0 μm.

2. The coated film according to claim 1, wherein the first skin layer has an open-cell voided structure, and the first filler component comprises particles having a mean particle diameter satisfying the following equation:

Dmean=N−Tskin

wherein

Dmean is the mean particle diameter (μm) of the first filler component;

Tskin is the thickness (μm) of the first skin layer; and

N is in the range of 10.0 μm to 20.0 μm.

3. The coated thermoplastic film according to claim 1, wherein the first skin layer has a closed-cell voided structure or an uncavitated structure, and the first filler component comprises particles having a mean diameter in the range of 5.0 μm to 20.0 μm.

4. The coated film according to claim 1, wherein the first filler component comprises particles having a mean diameter in the range of 5.0 μm to 18.0 μm.

5. The coated film according to claim 4, wherein the first filler component comprises particles having a mean diameter in the range of 8.0 μm to 15.0 μm.

6. The coated film according to claim 1, wherein the first coating further includes a first binder component and a second filler component.

7. The coated film according to claim 6, wherein a least one of the second filler component and the first binder component is substantially hydrophobic.

8. The film according to claim 1, wherein the first skin layer comprises a polypropylene or polyethylene and has a density of 0.500 g/cm3 to 0.946 g/cm3.

9. The coated film according to claim 1, wherein the substrate further comprises: a second skin layer comprising a polymer, wherein the second skin layer has a first side and a second side, the first side of the second skin layer is adjacent to the second side of the first core layer, and the second side of the second skin layer is suitable for a surface treatment selected from the group consisting of flame, corona, plasma, metallization, prime coating, printing, and combinations thereof.

10. The coated film according to claim 9, further comprising: a second coating comprising at least a third filler component and a second binder component, the second coating applied to the second side of the second skin layer, wherein at least one of the third filler component and the second binder component is substantially hydrophobic.

11. The coated film according to claim 1, wherein the first filler component comprises at least one of: a) a clay material; b) a natural mineral material; c) a surface-treated natural mineral; d) a synthetic mineral; e) a surface-treated synthetic mineral; f) plastic particulates; g) thermoplastic particulates, h) silica; i) hydrophilic clays; j) barium sulfate; k) calcium carbonate; 1) titanium dioxide; m) zinc oxide; n) tin oxide; o) aluminum oxide; p) talc; and q) carbon black.

12. The coated film according to claim 1, wherein the first filler component comprises at least one of: a) a surface-modified clay; b) plastic particulates; and c) thermoplastic particulates.

13. The coated film according to claim 1, wherein the first filler component comprises a surface-treated polyolefin.

14. The coated film according to claim 13, wherein the first filler component comprises surface-treated polyethylene.

15. The coated film according to claim 1, wherein the first coating and/or the second coating is applied to the first skin layer at a weight of from about 0.1 g/m2 to about 4.0 g/m2.

16. The coated film according to claim 1, wherein the first filler component comprises less than 25.0 wt % of the first coating, based on the total weight of the first coating.

17. The coated film according to claim 1, wherein the first binder further comprises a crosslinker.

18. The coated film according to claim 1, wherein the first coating further comprises at least one of wax emulsions, adhesion promoters, emulsifiers, anti-foams, defoamers, anti-statics, security taggants, co-solvents, wetting aids, and processing aids.

19. The coated film according to claim 1, wherein the first skin layer comprises a voiding agent.

20. The coated film according to claim 1, wherein the substrate without the first coating has a density of from about 0.30 g/cm3 to about 0.80 g/cm3.

21. The coated film according to claim 1, wherein the first coating is in the form of a continuous layer on the first side of the first skin layer.

22. The coated film according to claim 1, wherein the first coating is in the form of a pattern or non-continuous layer on the first side of the first skin layer.

23. The coated film according to claim 1, wherein the first coating layer further comprises a primer layer in surface contact with the first side of the first skin layer.

24. A coated label film for use with a cold glue adhesive, the label film comprising:

(a) a substrate comprising: (i) a first skin layer comprising a polymer, wherein the first skin layer has a first side and a second side and is voided with a closed-cell structure; (ii) a core layer comprising a polymer, wherein the core layer has a first side and a second side, and the first side of the core layer is adjacent to the second side of the first skin layer; and

(b) a first coating on the first side of the first skin layer, the first coating comprising at least a first filler component, the filler component comprising polyethylene homopolymer or copolymer particles having a mean diameter in the range of 5 μm to 20 μm and <2.0 number % of the filler particles have a diameter >75.0 μm.

25. A coated thermoplastic film comprising:

(a) a polymeric substrate comprising: (i) a first skin layer having a closed-cell voided or uncavitated structure, comprising a polymer, wherein the first skin layer has a first side and a second side; (ii) a uncavitated core layer comprising a polymer, wherein the core layer has a first side and a second side, and the first side of the core layer is adjacent to the second side of the first skin layer; iii) a second skin layer having a first side and a second side, wherein the first side is adjacent the second side of the core layer;

(b) a first coating on the first side of the first skin layer, the first coating comprising a polyethylene filler component, the polyethylene filler component comprising particles having a mean diameter in the range of 5 μm to 20 μm, a second filler component comprising 30 wt % to 60 wt % of a second filler having particle mean diameter of ≦1.0 micron and a self-cross-linking cationic acrylic first binder component; and

(c) a second coating on the second side of the second skin layer, the second coating comprising a self-crosslinking cationic acrylic composition.