DIGITAL PRINTING PLASTIC CONTAINERS WITH IMPROVED ADHESION AND RECYCLABILITY

Abstract

A container having an external surface with a digital image printed thereon by droplets of ink is provided. The digital image includes a base coat and a secondary coat that is applied to the base coat. In an embodiment, the digital image adheres to the container with an acceptable or sufficient adhesion score and the image is removable using conventional recycling processes. Methods for digitally printing containers and facilitating recycling are also disclosed.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional patent application Ser. No. 61/106,860, filed Oct. 20, 2008, which is incorporated by reference in its entirety as if fully set forth herein.

TECHNICAL FIELD

The present invention relates generally to plastic containers having digital images printed thereon, particularly containers having improved adhesion and recycling characteristics and methods for digitally printing containers and facilitating recycling.

BACKGROUND

Product manufacturers commonly impose labeling standards on plastic containers that are intended to hold their products. Various tests, including a number of industry standardized tests, have been used to measure and evaluate the quality of label application. Some standard test methods that have been employed include, by way of example and without limitation, ASTM International test designations D 3359-08 (Standard Test Methods for Measuring Adhesion by Tape Test); D 5264-98 (Standard Practice for Abrasion Resistance of Printed Materials by the Sutherland Rubber Tester); and F 1842-02 (Standard Test Method for Determining Ink or Coating Adhesions on Plastic Substrates for Membrane Switch Applications). Product manufacturers often define testing requirements and resultant scores that should be met for a labeled product to be deemed acceptable.

Container manufacturers have recently produced containers with digitally printed labels that are of a sufficient definition and quality to compete with and potentially replace prior conventional labeling techniques. Examples of such printing techniques are described in U.S. patent application Ser. No. 11/562,655, which is incorporated herein by reference. However, for many applications, it is desirable to utilize standards for providing, measuring, and assessing printed images that may serve as labels.

Potential challenges arise introducing containers with digitally printed labels into conventional container recycling processes. There is a clear trend amongst container manufacturers, brand owners, end users, and governmental entities to improve and increase container recycling efforts. Consequently, it would be desirable to provide industry-acceptable containers that are sufficiently compatible with the current recycling infrastructure and processes, or that provide sufficient incentive and/or volumes to effectuate industry-wide changes. At least initially, it would be desirable to provide digitally printed containers that are recyclable using current industry standard processes—i.e., processes that commonly include caustic high-temperature washing and grinding. As such, there is a desire for digitally printed plastic containers that have digital images that adhere to the container without quality issues throughout its useful life, but are readily removable during plastic recycling processes.

SUMMARY

A plastic container is disclosed that has an external surface with a digital image printed thereon by droplets of ink. The digital image includes a base coat and a secondary coat that is applied to the base coat. Embodiments of the invention disclose containers having improved adhesion and/or recycling characteristics. In an embodiment, the digital image adheres to the plastic container and the digital image has an acceptable or “passing” adhesion score (which for some scoring systems is a score of 6.0 or greater). Methods for digitally printing containers and facilitating recycling are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein:

FIG. 1 generally illustrates a side view of a portion of a container with a digital image printed thereon;

FIG. 2 is general representation of a quality review table/matrix that may be used to evaluate the acceptability of a printed image on a container.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the present invention, examples of which are described herein and illustrated in the accompanying drawings. While the invention will be described in conjunction with embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims.

A portion of a surface 10 of a container with a printed digital image 20 is generally illustrated in FIG. 1. The digital image 20 includes a base coat 30 that may be comprised of a plurality of base coat ink droplets 32, and a secondary coat 40 that is comprised of a plurality of secondary coat ink droplets 42.

The base coat 30 may be comprised of a material that serves to improve the application of ink droplets and/or provides a visual characteristic. For embodiments, the base coat 30 may comprise white and/or colorless portions. In embodiments of the invention, at least a first base coat 30 is applied to a surface of a container at a first time t₁ and at a first temperature T₁. The temperature T₁ will be in the range of temperatures that are appropriate for application of the associated base coat. In an embodiment, the base coat 30 may be ultraviolet (UV) curable, and further may be cured prior to an application of a secondary coat.

The secondary coat 40 may be comprised of a plurality of secondary coat ink droplets 42 that are distributed on at least a portion of the base coat 30. A plurality of secondary coat ink droplets 42 may collectively form a part of an application pattern which, in turn, may form all or a portion of a digital image. Furthermore, as generally illustrated in FIG. 1, portions of one or more adjacent secondary coat ink droplets 42 may overlap or intermix with each other. The secondary coat 40, and the constituent secondary coat ink droplets 42, may comprise various known colors, including without limitation, primary printing colors such as cyan, magenta, and yellow. Further, controlling the overlapping of or combinations of certain colors in certain areas can provide additional “process” colors. Additionally, the secondary coat ink droplets 42 may be curable. For example, UV curable secondary coat ink droplets may comprise all or a portion of the intended digital image. Depending upon the application, the secondary coat ink droplets can vary in diameter, which can range, for instance, from about 10 microns to about 200 microns. The secondary coat 40 may be applied to a surface 10 of a container at a second time t₂ and at a second temperature T₂, wherein the second temperature T₂ at which the secondary coat 40 is applied is typically less than the first temperature T₁ at which the base coat 30 is applied.

In embodiments of the invention, the time between application of a base coat and the application of a secondary coat (e.g., t₂ minus t₁) may be reduced—for example, to as little as ten seconds or less. For some embodiments, the application time differential will be within two to six seconds. Moreover, in embodiments, the application temperature differential between the temperature at which the base coat 30 is applied and the temperature at which a secondary coat 40 is applied to a portion of the base coat 30, i.e., T₁ minus T₂, may be controlled to be equal to or less than about 10° F. For some embodiments, the application temperature differential will be within about 5° F. to about 10° F. Moreover, for some applications, it may be desirable to modify the temperatures associated with the application of the base coat 30 and the secondary coat 40 so that the respective application temperatures are closer together—i.e., so that the temperature differential between the applied coats is reduced or minimized. This can be accomplished, for instance, by (a) lowering/decreasing T₁, (b) raising/increasing T₂, or (c) a combination of (a) and (b). Such aforementioned time and/or temperature control with respect to the base coat and secondary coat can provide for better adhesion of the resulting printed digital image with respect to the container.

It is noted that in addition to time and temperature, irradiance is a factor that can also affect the effective cure rate for a printed image. That is, with certain times (e.g., t₁ and t₂) and temperatures (e.g., T₁ and T₂), there may be an associated irradiance—i.e., ε₁ and ε₂. For example, in embodiments a base coat may be cured at irradiance ε₁, and an associated secondary coat may be cured at irradiance ε₂. Further, in embodiments, the effective cure rate—which may be based on a combination of time, temperature, and irradiance—the irradiance may generally be provided by the following equation:

Irradiance(ε)=(dφ/dA)

• • where, φ=irradiant flux (measured in watts), and
    • A=area (cm²)
      For example, without limitation, the range of irradiance for some embodiments will be between about 0.1 watts/cm² and about 10.0 watts/cm².

The containers (which includes bottles) associated with the present invention are comprised of a plastic material (e.g., PET, HDPE, PP, PE, etc.). The containers may be mono-layer or multi-layer containers, and can be formed using various conventional forming techniques including, without limitation, blow molding, thermoforming, etc. In an embodiment, the outermost layer/surface is comprised of a virgin plastic material. Although, it is noted that containers in accordance with the teachings of the invention may include some percentage of recycled content, including a small percentage (e.g., 20% or less) in the outer layer of the container.

For some applications, such as where a curable ink (e.g., a UV-curable ink) is used, the relevant coat or ink may be cured after each respective print station. For example, without limitation, an embodiment of a process may, at least in part, comprise: application of base coat; cure step; application of secondary coat; and cure step. Alternatively, also by way of example and without limitation, the process may, at least in part, comprise: application of base coat; cure step; application of base coat; cure step; application of secondary coat, and cure step. Moreover, for embodiments of the invention, it can be desirable for the production/subsequent handling rate of containers/bottles to match or substantially match the flow/processing rates of the associated printing machine(s).

Further, it has been found that the quality of printed digital images may be, at least in part, controlled and/or improved through one or more of the following techniques:

(a) selection and/or calibration of ink sets;

(b) control of substrate (i.e., container surface) temperature; and/or

(c) timing control.

With respect to the selection and/or calibration of ink sets, this is accomplished, at least in part, by the selection and/or calibration of the inks comprising the base and secondary coats. It has been discovered that the inks used can be selected to provide desired time and/or temperature characteristics, including relative to one another in combination. For example, selection of certain inks having given viscosities can exhibit or provide certain desired temperature related effects.

With regard to the control of the substrate (i.e., container surface) temperature, the temperature of a relevant portion of a sidewall (or other portion of a container) can be treated or controlled to some measure. For example a given portion of the container can be pre-treated. Such pre-treatment can be facilitated using various known techniques that may include, without limitation, flame, corona, and plasma treatment. However, the invention is not limited to those specific pre-treatment techniques.

With respect to timing control, the time associate with the movement of containers, for instance through a production machine, as well as the timing of the applications of the base coat and/or secondary coat, can be controlled. It can be desirable for the production/subsequent handling rate of containers/bottles to match or substantially match the flow/processing rates of the associated printing machine(s).

The present invention also includes a system for assessing or evaluating the “acceptability,” such as the commercial acceptability, of a container having a digitally printed image—such as a digitally printed label. That is, for embodiments of the invention, the system for assessing or evaluating can provide an “adhesion score.” FIG. 2 generally represents a quality review table/matrix that can be used to assess or evaluate the acceptability of a printed image on a container. As generally shown, the Y-axis may involve numbers associated with an overall pass-or-fail score. In the illustrated embodiment, numbers 1 through 5 indicate that the containers are not acceptable, while numbers 6 through 9 indicate that the associated containers are acceptable. It is important to note that while a score of at least a 6 will “pass” as acceptable with respect to the instant table/matrix, the invention is not limited to the specific table/matrix shown and, alternatively, more scores could be provided for and/or the passing score could be raised or lowered as desired or necessary. A plurality of tests—which may include various standard tests, including those previously noted—are represented in the columns provided on the X-axis. For example, without limitation, Test 1 may include a “Sutherland Rub Test,” Test 2 may comprise a “3M #610 Tape Test,” Test 3 may include a “Simulated Ship Test,” and Test 4 may comprise a “3M #810 Tape Test.” As generally shown in the table, various pass-or-fail designations may be represented on the table in connection with each noted Test. With respect to several of the aforementioned “standard” tests, the tests may be modified as appropriate for use in connection with a printed image as opposed to a traditionally applied label. For instance, with various “tape” tests, which may follow the ASTM D 3359-08 standards, the tests associated with the table/matrix may or may not involve the cutting of the digital image portion with a cutting tool prior to applying a pressure sensitive tape. That is, in an embodiment, “Test 2” may involve a “modified” 3M #610 Tape Test in so far as the portion of the digital image portion of a container that is subjected to testing may not be cross-cut or otherwise separated from the container. Moreover, with the table set forth in FIG. 2, an indication of a “pass,” with respect to tape tests directly practicing the modified ASTM standard (i.e., the test does not involve cross-cutting/separation) would generally be represented by any removed portions being no larger than 2.0 mm². With respect to tape tests directly practicing the ASTM standard, an indication of “pass” would generally be a classification “4B” or “5B” (under the ASTM FIG. 1 Classification of Adhesion Test Results), or would involve less than 5% of the printed area removed.

In an embodiment, it is desirable to provide a container with a printed digital image that, at a minimum, passes a modified 3M #610 tape test and is nonetheless “recyclable.” A digital image that is printed on a container is considered to be “recyclable” if it would achieve less then a “4B” classification (i.e., 5% of more of the area is removed) employing an ASTM D 3359 standard #810 tape test. A container with a digital image that passes Test 2 (modified 3M #610 Tape Test) and Test 3 (Simulated Ship Test), yet fails Test 4 (3M #810 Tape Test), would achieve an adhesion score of either 6.0 or 7.0. Such a container with a printed image having an adhesion score of 6.0 or 7.0 is commercially suitable for shipment (i.e., passing a Simulated Ship Test) while providing an adhesion associated with the printed image that is sufficient for normal/intended use but is favorably separable for subsequent recycling. Stated differently, the adhesion associated with the configured digital image is sufficiently strong for intended use but does not impede separation during recycling.

With respect to such a table/matrix, each test may be conducted on a adequate (e.g., statistically significant or representative) sampling of containers. After all tests are completed, results may be tabulated and entered into the table/matrix, to provide an “adhesion” score. The associated score outcomes can then be correlated.

Among other things, the present invention can provide for improved recyclability. For example, without limitation, containers with digitally printed images (which may be formed by cured UV-curable ink) can be conveniently removed in connection with conventional plastic recycling processes. Industry standard recycling process of plastic containers conventionally include grinding containers into granulated plastic flakes, subjecting these flakes to a high-heat caustic wash process, drying the cleaned flakes, sorting, and extruding into resin pellets for resale. With embodiments of the invention, digital image on the container may remain with the resin flakes after the grinding process, the digital image will be substantially separated from the resin flakes during the high-heat caustic wash process, thereby not contaminating the clean resin flakes to be formed into resin pellets.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and various modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to explain the principles of the invention and its practical application, to thereby enable others skilled in the art to utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims

1. A recyclable plastic container comprising:

an external surface with a digital image printed thereon by droplets of ink, the digital image having an adhesion score of at least 6.0.

2. The container of claim 1, wherein the digital image includes:

a base coat including a plurality of cured base coat ink droplets, and

a secondary coat including a plurality of cured secondary coat ink droplets, the secondary coat being applied to at least a portion of the base coat.

3. The container of claim 1, wherein the printed digital image is configured to be substantially separated from the remainder of the container during a recycling process.

4. The container of claim 1, wherein the digital image is configured to, at a minimum, pass a tape test and a simulated shipment test.

5. The container of claim 4, wherein the tape test includes a modified 3M #610 tape test.

6. The container of claim 1, wherein the digital image has an adhesion score of 6.0 or 7.0.

7. The container of claim 2, wherein, at the time the secondary coat is applied to the base coat, the temperature differential between the base coat and the secondary coat is less than about 10° F.

8. The container of claim 1, wherein the container includes a base portion, a sidewall portion, a shoulder portion, and a neck portion, and the neck portion includes a dispensing opening.

9. The container of claim 2, wherein the base coat includes white or colorless portions.

10. The container of claim 2, wherein one or more adjacent secondary coat ink droplets overlap or are intermixed.

11. The container of claim 2, wherein the secondary coat ink droplets are colored.

12. The container of claim 11, wherein the colors include one or more of the following colors: cyan, magenta, and yellow.

13. The container of claim 2, wherein the secondary coat ink droplets vary in diameter.

14. The container of claim 13, wherein the diameters of the secondary coat ink droplets are within the range of about 10 microns to about 200 microns.

15. The container of claim 1, wherein the container is comprised of one or more of the following materials: polyethylene, polyethylene terephthalate, high density polyethylene, and polypropylene.

16. The container of claim 1, wherein the container is a multi-layer container.

17. The container of claim 1, wherein the container includes recycled plastic material.

18. The container of claim 17, wherein the outermost layer of the container has a recycled content, the recycled content being 20% or less.

19. The container of claim 2, wherein the base coat and secondary coat ink droplets are UV cured.

20. A recyclable plastic container comprising:

an external surface with a digital image printed thereon by droplets of ink, the digital image including:

a base coat including a plurality of cured base coat ink droplets, and

a secondary coat including a plurality of cured secondary coat ink droplets, the secondary coat being applied to at least a portion of the base coat;

wherein the digital image is configured to pass a modified 3M #610 tape test and is configured to be substantially separated from the remainder of the container during a recycling process.

21. The container of claim 21, wherein the digital image is configured to fail a standard 3M #810 tape test.