WATER-SLIDABLE/OIL-SLIDABLE FILM, PRODUCTION METHOD THEREOF, AND ARTICLES HAVING THE SURFACE COATED THEREWITH

Abstract

The problem to be solved by the present invention is to provide a water-slidable/oil-slidable film that is easily producible and has improved durability. A water-slidable/oil-slidable film of the present invention comprises: a porous polymer film having a three-dimensional entangled network structure of a fibrous polymer and a continuous pore structure as the empty space of the network structure, and a slippery liquid infused in the pores of the porous polymer film.

Description

RELATED APPLICATIONS

This application claims the priority of Japanese Patent Application No. 2014-133786 filed on Jun. 30, 2014, which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the provision of a water-slidable/oil-slidable film that can be easily produced and exert an excellent antifouling effect and the improvement of its durability. The invention further relates to the provision of a water-slidable/oil-slidable film having high transparency and sufficient strength as a self-standing film.

BACKGROUND OF THE INVENTION

The development of antifouling surfaces has been desired in numerous fields such as solar cells, automobiles, medical devices, fuel transportation, construction, and food containers. In recent years, slippery liquid-infused porous surfaces (SLIPS) have been reported as the new type of antifouling surface. These are low-energy porous surfaces wherein liquid lubricant is infused (refer to Non-Patent Literature 1). SLIPS exhibit non-wetting properties against most fluids and are stable at a high temperature and a high pressure because the lubricant is inside the pores. For example, non-wetting surfaces based on the lotus leaf effect have been studied over several decades. However, it has been very difficult to obtain an antifouling surface against a low-surface-tension liquid and a surface stable against drop impact, ultra-high temperature, or ultra-high pressure. Thus, SLIPS are a very appealing material.

There are numerous reports concerning the production method of SLIPS; however, they have not been versatile enough because of the following reasons. Won et al. have used a poly(tetrafluoroethylene) mesh and an epoxy resin array as the rough surface for lubricant application (refer to Non-Patent Literature 1). The moldability of a PTFE mesh is very poor; therefore, it cannot be applied to the surface of a complex structure, and it is not transparent in the visible light region. On the other hand, the surface of an epoxy resin array can be formed into a complex structure; however, the two-step soft-lithography process takes a long time. These production processes are not suitable for mass production and they are not versatile.

In addition to these, a photolithography method, deep reactive ion etching method, chemical vapor deposition, etc. can be listed as cumbersome, time-consuming, high-cost processes. On the other hand, Ma et al. reported a production process of SLIPS by alumina sol-gel as a lower-cost simpler method in the formation of a rough surface (refer to Non-Patent Literature 2). This is a simple wet process, and a layer having a high transmittance in the visible light region can be obtained. However, annealing at a high temperature of about 400° C. and the reduction of the surface energy are necessary; thus the selection of substrates is limited. In addition, the additional processes and materials are necessary; thus the cost will increase. The preparation methods such as boehmite treatment of aluminum, alkaline etching of copper, and electrolytic polymerization of polypyrrole also have similar issues.

Among the substrates used as the rough porous surface in the conventional SLIPS, the epoxy resin array by a photolithography method and porous silicon by etching have fine needle-like asperity or non-continuous fine through-holes (lotus root-type through-holes) formed on the surface. An alumina thin film formed by a sol-gel method merely has fine asperity on the surface. Therefore, liquid lubricant infused on these rough porous surfaces, of the SLIPS, relatively easily seeps out or leaks out, and the liquid lubricant must frequently be replenished during use.

A porous PTFE sheet formed by a stretching method has a more complex pore structure; however, it is a uniaxially-stretched window blind-shaped sheet or a biaxially-stretched cobweb-shaped sheet. Thus, liquid lubricant cannot be retained inside the pores over a long period, and in particular, the tolerance to vibration and pressure has not been satisfactory.

Furthermore, the development of a transparent film that can provide an antifouling effect by pasting on the products such as window glass and automobile windshield, which require transparency, is considered to be very useful. However, the surface of the article is directly treated in the case of SLIPS by photolithography, etching, or sol-gel method, and a self-standing film is not formed. On the other hand, a porous PTFE sheet by the stretching method can be a self-standing film; however, the transparency is poor because the film is relatively thick. Thus, there has been no conventional SLIPS having high transparency as well as the sufficient strength as a self-standing film.

CITATION LIST

Non-Patent Literature

• Non-Patent Literature 1: Wong, T.-S.; Kang, S. H.; Tang, S. K. Y.; Smythe, E. J.; Hatton, B. D.; Grinthal, A.; Aizenberg, J. Nature 2011, 477, 443-447.
• Non-Patent Literature 2: Ma, W.; Higaki, Y.; Otsuka, H.; Takahara, A. Chem. Commun. 2013, 49, 597-599.

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

The problem to be solved by the present invention is to provide a water-slidable/oil-slidable film that is easily producible and has improved durability and to provide a production method thereof. In addition, it is to provide a water-slidable/oil-slidable film having high transparency as well as sufficient strength as a self-standing film.

Means to Solve the Problem

The present inventors have diligently studied to solve the above problem. As a result, the present inventors have found that a water-slidable/oil-slidable film that exhibits an excellent antifouling effect can easily be produced by mixing with stirring a polymer and a pore-forming agent, at a specific ratio, in a volatile organic solvent, applying it on the substrate and drying, removing the pore-forming agent with an organic solvent to obtain a porous polymer film, and infusing a slippery liquid to this porous polymer film. The present inventors have also found that the durability of the obtained water-slidable/oil-slidable film is also excellent. Furthermore, the present inventors have found that a water-slidable/oil-slidable film having high transparency and having sufficient strength as a self-standing film can be obtained by this method, thus leading to the completion of the present invention.

That is, the water-slidable/oil-slidable film of the present invention is characterized by comprising: a porous polymer film having a three-dimensional entangled network structure of a fibrous polymer and a continuous pore structure as the empty space of the network structure, and a slippery liquid infused in the pores of the porous polymer film.

In addition, in the water-slidable/oil-slidable film, it is preferable that the average pore diameter of the porous polymer film is 500 to 1000 nm. In addition, it is preferable that the average fiber diameter of the porous polymer film is 100 to 400 nm. In addition, it is preferable that the root-mean-square roughness of the porous polymer film is 0.3 to 0.6 μm.

In addition, it is preferable in the water-slidable/oil-slidable film that the porous polymer film is made of a fluorine-based resin or a silicone resin. Furthermore, it is preferable that the porous polymer film is made of polyvinylidene fluoride or copolymers thereof.

In addition, it is preferable that the slippery liquid has affinity to the porous polymer film in the water-slidable/oil-slidable film. In addition, it is preferable that the slippery liquid is a fluorine-based oil or silicone oil. Furthermore, it is preferable that the slippery liquid is perfluoropolyether.

In addition, it is preferable that the refractive index difference between the porous polymer film and the slippery liquid is 0.3 or less in the water-slidable/oil-slidable film. In addition, it is preferable that the average transmittance of the light with the wavelength of 400 to 700 nm is 80% or higher in the water-slidable/oil-slidable film.

The production method of the water-slidable/oil-slidable film of the present invention is characterized by comprising:

a step of mixing and stirring a polymer and a pore-forming agent that does not dissolve the polymer with a volatile organic solvent that can dissolve both the polymer and the pore-forming agent,

a step of forming a coating film by applying the mixture obtained in the preceding step on the surface of an article, and vaporizing the volatile organic solvent,

a step of forming a porous polymer film by contacting the coating film obtained in the preceding step with an organic solvent allowing that can dissolve the pore-forming agent without dissolving the polymer, to remove the pore-forming agent,

a step of infusing a slippery liquid inside the pores of the porous polymer film obtained in the preceding step.

In the production method of the water-slidable/oil-slidable film, it is preferable that the mixing ratio (mass ratio) of the polymer to the pore-forming agent is 1:1.5 to 1:5.

In addition, it is preferable that the polymer is a fluorine-based resin or silicone resin in the production method of the water-slidable/oil-slidable film. Furthermore, it is preferable that the polymer is polyvinylidene fluoride or copolymers thereof. In addition, it is preferable that the polymer is soluble in acetone and insoluble in ethanol in the production method of the water-slidable/oil-slidable film.

In addition, it is preferable that the pore-forming agent is an ethanol-soluble low-molecular-weight solvent in the production method of the water-slidable/oil-slidable film. Furthermore, it is preferable that the pore-forming agent is phthalic acid or derivatives thereof.

In addition, it is preferable that the volatile organic solvent is an organic solvent with a boiling point of 100° C. or lower in the production method of the water-slidable/oil-slidable film. Furthermore, it is preferable that the volatile organic solvent is acetone.

In addition, it is preferable that the organic solvent that can dissolve the pore-forming agent without dissolving the polymer is ethanol in the production method of the water-slidable/oil-slidable film.

In addition, it is preferable that the slippery liquid is a fluorine-based oil or silicone oil in the production method of the water-slidable/oil-slidable film. Furthermore, it is preferable that the slippery liquid is perfluoropolyether.

The article of the present invention is characterized by having the surface coated with the water-slidable/oil-slidable film.

Effect of the Invention

According to the present invention, a water-slidable/oil-slidable film that can be easily produced and has an excellent antifouling effect can be obtained, and its durability is also excellent. In addition, a water-slidable/oil-slidable film having high transparency and sufficient strength as a self-standing film can be obtained by the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of the cross section for the water-slidable/oil-slidable film of the present invention.

FIG. 2 is a schematic illustration of the production method of the water-slidable/oil-slidable film as one example of the present invention.

FIG. 3A is an SEM photograph of a PVD-HFP porous polymer film prepared in the polymer/pore-forming agent (PVDF-HFP/DBP) ratio=1:0.5.

FIG. 3B is an SEM photograph of a PVD-HFP porous polymer film prepared in the polymer/pore-forming agent (PVDF-HFP/DBP) ratio=1:1.

FIG. 3C is an SEM photograph of a PVD-HFP porous polymer film prepared in the polymer/pore-forming agent (PVDF-HFP/DBP) ratio=1:2.

FIG. 3D is an SEM photograph of a PVD-HFP porous polymer film prepared in the polymer/pore-forming agent (PVDF-HFP/DBP) ratio=1:5.

FIG. 4 shows the measurement results of the pore size and fiber diameter for various PVD-HFP porous polymer films.

FIG. 5 shows the measurement results of the surface roughness (root-mean-square roughness) for various PVD-HFP porous polymer films.

FIG. 6 shows the measurement results of the thickness for various PVD-HFP porous polymer films.

FIG. 7 shows the measurement results of the sliding angles for water and oleic acid on various PFPE-infused PVD-HFP porous polymer films.

FIG. 8 shows explanatory illustrations of liquid adhesion on the surface of a PVDF-HFP porous (PFPE-infused) film.

FIG. 9 shows the measurement results of the transmittance, in the visible light region, for various PVDF-HFP films before and after the infusion of PFPE.

FIG. 10 shows the measurement results of the transmittance at the wavelength of 600 nm for various PVDF-HFP films before and after the infusion of PFPE.

FIG. 11 is a photograph of glasses whose lens surface is coated with the PVDF-HFP porous (PFPE-infused) film (left lens: uncoated; right lens: film-coated).

FIG. 12 shows photocurrent density (Jsc)-voltage (Voc) curves for a bare solar cell, a glass-covered solar cell, a solar cell covered with PVDF-HFP film (before PFPE infusion), and a solar cell covered with PVDF-HFP film (after PFPE infusion).

FIG. 13 shows the measurement results of the tensile strength for the PVDF-HFP (PFPE-infused) self-standing film.

FIG. 14 shows measurement results of the extension rate for the PVDF-HFP (PFPE-infused) self-standing film.

FIG. 15 is a photograph of the PVDF-HFP (PFPE-infused) self-standing film.

FIG. 16 shows the measurement results of the water sliding angle for the PVDF-HFP (PFPE-infused) film after spinning at various spin speeds for 1 minute.

FIG. 17 shows the measurement results of the water sliding angle for the PVDF-HFP (PFPE-infused) film after applying abrasion under the loading condition of 80 g/cm² for the stated time.

FIG. 18A is a photograph of the PVDF-HFP (PFPE-infused) film when blood was dropped thereon.

FIG. 18B is a photograph of the PVDF-HFP (PFPE-infused) film when a high-viscosity drink (sweet bean soup) was dropped thereon.

FIG. 18C is a photograph of the PVDF-HFP (PFPE-infused) film when food oil was dropped thereon.

FIG. 18D is a photograph of the PVDF-HFP (PFPE-infused) film when cleaner was dropped thereon.

DESCRIPTION OF REFERENCE NUMBERS

• 10 Water-slidable/oil-slidable film
• 12 Porous polymer film
• 14 Slippery liquid
• 20 External liquid

BEST MODE FOR CARRYING OUT THE INVENTION

Water-Slidable and Oil-Slidable Films

FIG. 1 is a schematic drawing of the cross section for the water-slidable/oil-slidable film of the present invention. As shown in FIG. 1, the water slidable/oil-slidable film 10 of the present invention has a porous polymer film 12, in which a fibrous polymer forms the skeleton of a three-dimensional entangled network structure and the empty space has a continuous pore structure, and a slippery liquid 14 infused in the pores of the porous polymer film. The external liquid 20 on the surface of the water-slidable/oil-slidable film 10 becomes a liquid droplet having a high contact angle and slides down because of its non-affinity to the slippery liquid 14; thus it is removed and does not adhere to the surface.

<Porous Polymer Film>

The polymer that constitutes a porous polymer film is not especially limited, in the chemical structure etc., so far as the compound has a molecular weight of 10K or higher. However, from the viewpoint of the antifouling effect against the liquids of various properties (water-sliding/oil-sliding effect), it is preferable to use fluorine-based resins or silicone resins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polydimethylsiloxane, polymethylphenylsiloxane, and copolymers thereof. In particular, polyvinylidene fluoride or copolymers thereof can preferably be used.

In the porous polymer film used in the present invention, a fibrous polymer forms the skeleton of a three-dimensional entangled network structure and the empty space has a continuous pore structure. The porous polymer film can be easily produced under mild conditions in a short time by the below-described specific method. In simple terms, a porous polymer film of the above structure can be obtained by mixing with stirring a polymer and a pore-forming agent, at a specific ratio, in a volatile organic solvent, applying the mixture on the substrate and drying, and then by removing the pore-forming agent with an organic solvent. Because of such a specific structure of the porous polymer film, the slippery liquid infused inside of the pores hardly seeps out or leaks out. Thus, a water-slidable/oil-slidable film that has high tolerance especially to vibration and pressure can be obtained. An epoxy resin array by a photolithography method, porous silicon by etching, and an alumina thin film by a sol-gel method, which are used in the conventional SLIPS, have fine asperity on the surface or non-continuous fine through-holes, and an infused slippery liquid easily seeps out or leaks out. In addition, a porous PTFE sheet formed by the stretching method is a uniaxially-stretched window blind-shaped sheet or a biaxially-stretched cobweb-shaped sheet. Thus, the fibrous polymer is not entangled in three-dimensional directions and especially in the sheet thickness direction. Therefore, the pore tortuosity factor is low and the slippery liquid inside the pore seeps out or leaks out by prolonged use or by vibration and pressure; thus the durability is not satisfactory.

The porous polymer film used in the present invention should have the specific structure explained above, but it is desirable that the following structural characteristics are additionally satisfied.

The average pore diameter of the porous polymer film is preferably 500 to 1000 nm and more preferably 500 to 700 nm. If the pore diameter is larger than the above-described range, slippery liquid cannot be retained, the water-sliding/oil-sliding effect cannot satisfactorily be exhibited, and the durability may be poor. On the other hand, if the pore diameter is smaller than the above-described range, the mechanical strength and flexibility of the film itself are not sufficient, and the versatility may be poor. The average pore diameter of the porous polymer film can be directly determined from the photographs taken with a scanning electron microscope (SEM), transmission electron microscope (TEM), or atomic force microscope (AFM), or it is calculated by image processing. Alternatively, it can be determined with the use of commercial measurement instruments based on the gas adsorption method or mercury intrusion technique.

In the porous polymer film, the average fiber diameter of the fibrous polymer, which constitutes the skeleton of a network structure, is preferably 100 to 400 nm and more preferably 300 to 400 nm. If the fiber diameter is larger than the above-described range, the slippery liquid cannot satisfactorily be retained, and the durability may be poor. If the fiber diameter is smaller than the above-described range, the mechanical strength of the film itself may be poor. The average fiber diameter can be calculated, similarly to the above-described average pore diameter, from the photographs taken with SEM, TEM, or AFM.

The root-mean-square roughness of the porous polymer film is preferably 0.3 to 0.6 μm and more preferably 0.3 to 0.45 μm. In the present invention, the root-mean-square roughness is the value [Rq(Rms)] measured according to JIS B0601-2013, and it is defined by the below-described equation. If the root-mean-square roughness is larger than the values in the above-described range, liquid is difficult to slide and the water-sliding/oil-sliding effect may not satisfactorily be exhibited. On the other hand, if the root-mean-square roughness is smaller than the above-described range, the mechanical strength of the film itself may be poor. The root-mean-square roughness can normally be measured with an atomic force microscope (AFM).

$\begin{array}{cc}\mathrm{Rq}=\sqrt{\frac{1}{l}{\int }_0^1Z^2\left(x\right)x}& \left[\mathrm{Equation}1\right]\end{array}$

Rq: root-mean-square roughness, l: reference length, Z(x): height of a contour curve at the position x

The percentage of voids in the porous polymer film is preferably 10 to 99% and more preferably 30 to 90%. If the percentage of voids is larger than the above-described range, slippery liquid cannot be retained, and the durability may be poor. If the percentage of voids is smaller than the above-described range, the amount of infused slippery liquid becomes small, and the water-sliding/oil-sliding effect may not satisfactorily be exhibited. The percentage of voids can be calculated, for example, from the measured bulk density and the true density, which is characteristic of the polymer.

The thickness of the porous polymer film is not limited in particular; however, it is normally about 1 μm to 5 mm and more preferably 2 μm to 2 mm. If the thickness is too small, the amount of infused slippery liquid is small and the durability may be poor. In addition, the strength may not be sufficient as a self-standing film, which is used by patching on an article, and it may not be usable. On the other hand, if the thickness is too large, the flexibility is poor and it is difficult to apply on an article having a complex structure. In addition, the film becomes opaque and may not be usable on an article that needs transparency.

<Slippery Liquid>

The slippery liquid used in the present invention is infused inside the pores of the porous polymer film described above. The slippery liquid needs to be chemically inert to the porous polymer film, for example, it should not dissolve the porous polymer. The slippery liquid can be either hydrophilic or lipophilic; however, it is preferable that the slippery liquid has affinity to the porous polymer film. Here, “has affinity” means that the contact angle of the slippery liquid on the surface of the porous polymer film is less than 90°. If the contact angle of the slippery liquid on the porous polymer film exceeds 90°, it is difficult to infuse the slippery liquid into the pores of the porous polymer film. Even when the slippery liquid could be infused, it may seep out or leak out over time. The contact angle between the slippery liquid and the porous polymer film is more preferably less than 45°.

For example, when an oily liquid is used as the slippery liquid, the antifouling property is mainly exhibited for an aqueous external liquid (water-sliding property). On the other hand, when an aqueous liquid is used as the slippery liquid, the antifouling property is mainly exhibited for an oily external liquid (oil-sliding property). In order to exhibit an antifouling property for every kind of liquid, it is preferable to use fluorine-based oil or silicone oil, namely so-called water/oil repellent liquid, as the slippery liquid. Examples include fluorine-based oils such as perfluoropolyether, perfluoroalkylether, perfluorocycloether, perfluoroalkylamine, perfluoroalkylsulfide, perfluoroalkylsulfoxide, perfluoroalkylphosphine, perfluorocarbon, perfluorocarboxylic acid, fluorinated phosphonic acid, fluorinated sulfonic acid, and fluorinated silane; and silicone oils such as dimethylpolysiloxane, methylphenylpolysiloxane, methylhydrogenpolysiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, amino-modified silicone oil, polyether-modified silicone oil, carboxy-modified silicone oil, alkyl-modified silicone oil, ammonium salt-modified silicone oil, and fluorine-modified silicone oil. Among them, perfluoropolyether can most preferably be used.

In addition, it is preferable to select a slippery liquid that has a small refractive index difference from the porous polymer film. Thus, a highly transparent water-slidable/oil-slidable film can be obtained because the amount of reflected light at the interface between the porous polymer film and the slippery liquid is small. More specifically, it is preferable that the refractive index difference between the porous polymer film and the slippery liquid is 0.3 or less, and more preferably 0.2 or less. Although it depends upon other conditions such as the porosity (pore diameter, fiber diameter, percentage of voids, etc.) and the thickness of the porous polymer film, a transparent film whose average transmittance of the light with the wavelength of 400 to 700 nm is 80% or higher can normally be obtained by selecting a combination of a porous polymer film and a slippery liquid whose refractive index difference is small. For instance, high transparency is demanded for the surface protective plates for solar cells and automobile windshields. For the antifouling purpose of such transparent products, the highly transparent water-slidable/oil-slidable film can be used.

Production Method

The water-slidable/oil-slidable film of the present invention can be produced, for example, by carrying out the first step to the fourth step described below.

<First Step (Coating Solution Preparation Step)>

The step wherein a polymer and a pore-forming agent that does not dissolve the polymer is mixed with stirring in a volatile organic solvent that can dissolve both the polymer and the pore-forming agent.

<Second Step (Coating Film Formation Step)>

The step wherein a coating film is formed by applying the mixture obtained in the preceding step on the surface of an article and vaporizing the volatile solvent.

<Third Step (Removal of Pore-Forming Agent/Porous Film Formation Step)>

The step wherein a porous polymer film is formed by allowing the coating film, obtained in the preceding step, to contact with an organic solvent that can dissolve the pore-forming agent and removing the pore-forming agent.

<Fourth Step (Slippery Liquid Infusion Step)>

The step wherein a slippery liquid is infused into the pores of the porous polymer film obtained in the preceding step.

FIG. 2 shows the illustrations of the respective steps as one example of the production method of the water-slidable/oil-slidable film of the present invention.

<First Step (Coating Solution Preparation Step)>

In the first step, a polymer and a pore-forming agent are mixed with stirring in a volatile organic solvent.

As described in the section of porous polymer films, the polymer used here is not especially limited, in the chemical structure etc., so far as the compound has a molecular weight of 10K or higher. However, it is preferable to use a fluorine-based resin or a silicone resin such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polydimethylsiloxane, polymethylphenylsiloxane, or a copolymer thereof. In particular, polyvinylidene fluoride or a copolymer thereof can preferably be used. In addition, it is preferable that the polymer is soluble in acetone and insoluble in ethanol.

It is necessary that the pore-forming agent does not dissolve the polymer but is soluble in the below-described volatile organic solvents. That is, the pore-forming agent and the polymer, which are dissolved in the volatile organic solvent in the first step, phase-separates after the vaporization of the volatile organic solvent in the second step. In the third step, when the pore-forming agent is removed, the holes without the pore-forming agent become pores and the porous polymer film is formed. As the pore-forming agent, a low-molecular-weight solvent with the molecular weight of 2000 or less is normally used. For example, ethanol-soluble low-molecular-weight solvents can be used. Among such low-molecular-weight solvents, phthalic acid or derivatives thereof can be preferably used.

The volatile organic solvent preferably has a boiling point of 260° C. or lower and especially preferably 100° C. or lower, and the organic solvent should dissolve both the polymer and the pore-forming agent. Although it depends upon kinds of polymers and pore-forming agents, the examples include hydrocarbon solvents such as toluene, benzene, pentane, hexane, heptane, and cyclohexane; halogenated solvents such as methyl chloride and methyl bromide: ester solvents such as ethyl acetate; ether solvents such as diethyl ether, tetrahydrofuran, and ethyl cellosolve; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; and alcohol solvents such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, and t-butanol.

The mixing ratio of the polymer and the pore-forming agent is preferably in the range of 1:1.5 to 1:5, in the mass ratio, and more preferably in the range of 1:2 to 1:3. The percentage of the pore-forming agent significantly affects the porosity of the obtained polymer porous film, in particular, the percentage of voids, pore diameter, surface roughness, etc. If the percentage of the pore-forming agent is too small, the amount of infused slippery liquid will be limited, and the water-sliding/oil-sliding effect cannot be satisfactorily exhibited. On the other hand, if the percentage of the pore-forming agent is too large, the slippery liquid easily seeps out or leaks out. In addition, the strength and flexibility of the film itself tend to be poor, and it may not be used as a self-standing water-slidable/oil-slidable film. The amount of the volatile solvent is not limited in particular; however, it is preferable to adjust the mass concentration ratio to be 20 to 500 mass % with respect to the polymer. If the amount of the volatile solvent is too large, the formation of a coating film takes time. On the other hand, if the amount of the volatile solvent is too small, the application by casting or spraying is difficult.

The temperature and time for mixing with stirring are not limited in particular; however, it is preferable to carry out the step normally at 20 to 60° C. for about 10 to 240 minutes. If the mixing with stirring is not sufficient, the pore-forming agent is non-uniformly distributed in the mixture; as a result, a porous polymer film having uniform pores may not be obtained.

<Second Step (Coating Film Formation Step)>

In the subsequent second step, a coating film is formed by applying the mixture, obtained in the first step, on the surface of an article and vaporizing the volatile solvent.

An article to be coated can be any object that needs water-sliding oil-sliding properties (antifouling effect). For example, the mixture can be directly applied on the surface of glass, metal, plastics, etc. Alternatively, a self-standing porous polymer film may be formed by applying the mixture on a plate of glass or metal, forming a porous polymer film of a suitable thickness, and peeling it off from the plate.

As the application method of the mixture on the article surface, publicly known coating methods such as a bar-coating method, a spray coating method, a spin coating method, and a dip coating method can be listed. In addition, the mixture may be printed on the article surface by a publicly known printing method. The coating method with the use of a squeegee is shown in FIG. 2; however, the method is not limited to this example.

After the application, a coating film consisting of the polymer and the pore-forming agent is formed on the article surface by vaporizing the volatile solvent. The temperature and time for vaporization depend on the concentration of the polymer and the pore-forming agent (amount of volatile solvent) in the first step; however, the vaporization is normally conducted at 10 to 40° C. for about 1 to 600 seconds, and more specifically at ordinary temperature for about 5 seconds.

<Third Step (Removal of Pore-Forming Agent/Porous Film Formation Step)>

In the third step, a porous polymer film is formed by allowing the coating film obtained in the second step to contact with an organic solvent that does not dissolve the polymer but can dissolve the pore-forming agent and removing the pore-forming agent.

As the organic solvent, for example, hydrophilic solvents such as water, glycerin, methanol, ethanol, and 2-propanol, or mixed solvents thereof having a suitable mixing ratio may be used though it depends upon the kinds of polymers and pore-forming agents. The means for allowing the contact of the coating film and the organic solvent is not limited in particular; for example, the coating film is immersed in the organic solvent for the fixed time as shown in FIG. 2.

In the second step, when the amount of the volatile organic solvent is gradually decreased by vaporization, a phase separation takes place gradually because the polymer and the pore-forming agent are immiscible. When the volatile solvent is completely lost, a coating film wherein the polymer and the pore-forming agent are coexistent in the state of phase separation is formed. In the third step, the pore-forming agent is removed by immersing this coating film in an organic solvent, the holes without the pore-forming agent become pores, and a porous polymer film is formed. The contact time of the coating film and the organic solvent is not limited in particular; however, it is normally immersed in an organic solvent for about 10 to 600 seconds and more specifically for about 10 seconds at ordinary temperature.

<Fourth Step (Slippery Liquid Infusion Step)>

In the fourth step, a slippery liquid is infused into the pores of the porous polymer film obtained in the third step.

As described above, the slippery liquid needs to be chemically inert to the porous polymer film, and it is preferable that the slippery liquid has affinity to the porous polymer film. The slippery liquid can be either hydrophilic or lipophilic; however, a fluorine-based oil or a silicone oil having water/oil repellency is preferable, and in particular, perfluoropolyether can preferably be used.

The means for infusing a slippery liquid is not limited in particular; however, dropwise addition with a dropper or spraying with a sprayer can be listed as examples. When the affinity of the slippery liquid and the porous polymer film is high, for example, the contact angle of the slippery liquid on the surface of the porous polymer film is less than 90° or furthermore less than 45°, the slippery liquid can be rapidly infused into the pores of the film only by dropping the slippery liquid on the surface of the porous polymer film.

As explained above, a highly transparent water-slidable/oil-slidable film can be obtained by selecting a suitable kind of slippery liquid so that the refractive index difference is small from the porous polymer film. In this case, the porous polymer film normally displays a pale white color because of the diffuse reflection due to the fine asperity of the surface or that of the interior. However, the porous polymer film instantly turns transparent by infusing a suitable kind (suitable refractive index) of slippery liquid. Thus, such a transparent film can suitably be used for the products requiring transparency.

Thus, the surface of any article can be coated with the water-slidable/oil-slidable film of the present invention, and water-sliding oil-sliding properties, namely the antifouling effect can be provided to the article. Alternatively, a self-standing film can be prepared by forming a water-slidable/oil-slidable film of a suitable thickness, on the surface of a support such as a glass plate, and peeling off the film from the glass plate. This self-standing film may be used as the antifouling film by patching on the surface of any article. In particular, a transparent self-standing film can be suitably used on any product as the antifouling film.

The thickness of a water-slidable/oil-slidable film can be suitably adjusted, for example, by the amount of coating in the second step. The thickness is not limited in particular; however, it is normally about 1 μm to 2 mm. If the thickness is too small, a satisfactory antifouling effect cannot be achieved, and the sufficient strength as the self-standing film may not be obtained. On the other hand, no improved effect is observed even when the thickness is larger than necessary. On the contrary, the transparency is lost, the flexibility is poor in the case of a self-standing film, and the application to the intended article may not be possible.

The water-slidable/oil-slidable film of the present invention can be produced as outlined above. The production does not need a high-temperature heat treatment, and all the steps from the first step to the fourth step can be completed in a very short time. Typically, the first step is about 1 hour, the second step is about 1 minute, the third step is about 1 minute, and the fourth step is about 1 minute; thus a water-slidable/oil-slidable film can be produced in a very short time. In addition, the surface of a heat-sensitive article such as a thermoplastic resin article can be treated because a high-temperature heat treatment, for example, at 100° C. or higher is not involved. The pores of the porous polymer film formed with the pore-forming agent have a skeleton of a three-dimensional entangled network structure of a fibrous polymer and the empty space having a continuous pore structure. Therefore, slippery liquid infused into such pores does not easily seep out or leak out by vibration and pressure, and the water-slidable/oil-slidable film has excellent durability.

Especially suitable articles as the antifouling object for the application of the water-slidable/oil-slidable film of the present invention are, for example, medical devices, containers, optical equipment, etc. In many medical devices, blood adhesion becomes the hindrance of operation. For example, the frequent removal of blood that adheres to an endoscopic instrument is necessary during the operation of the device. In the case of containers, the adhesion of the contents such as food, drinks, and cleaner on the outer surface or the adhesion of the residues of the contents on the inner surface may become problems. In the case of optical equipment, the measurement results may be significantly affected especially by the liquid adhesion on the lens. The water-slidable/oil-slidable film of the present invention slides down various liquids, and their adhesion on the surface can be prevented. The antifouling effect can be exhibited for not only water and oil but also blood, food, drinks, cleaner, etc.; thus it can suitably be used for the above articles.

In addition, the water-slidable/oil-slidable film of the present invention can be prepared to be a highly transparent film. Therefore, transparent glass products such as window glass and automobile windshields, which need transparency, can be coated and an antifouling effect can be provided. In particular, surface-protective glass plates for solar cells are installed outside; therefore, various kinds of matters such as sand and dust due to rain and wind, fallen leaves, and bird droppings adhere on the surface, and the power generation efficiency may be decreased. On the other hand, the adhesion thereof is prevented by coating with the water-slidable/oil-slidable film of the present invention. Even when they temporarily adhere as solid matter, they are washed away with rain water; thus the decrease in the power generation efficiency due to adhered dirt can be prevented.

The water-slidable/oil-slidable film of the present invention may be directly formed on the article surface of an antifouling object. Alternatively, a pre-formed self-standing water-slidable/oil-slidable film may be patched on the object article as described above.

EXAMPLES

Hereinafter, the present invention will be explained in more detail with reference to examples; however, the present invention is not limited by these examples.

<Materials>

Polymer: poly(vinylidene fluoride-hexafluoropropylene) copolymer (manufactured by Sigma Aldrich Co., PVDF-HFP; Mw: ca. 400000, Mn: ca. 130000, HEP/VDF=10 mol %)

Pore-forming agent: di-n-butyl phthalate (manufactured by Kanto Chemical Co., DBP, 99.5%)

Volatile solvent: acetone (manufactured by Kanto Chemical Co., 99.5%)

Pore-clearing organic solvent: ethanol (manufactured by Kanto Chemical Co., 99.5%)

Slippery liquid: perfluoropolyether (manufactured by DuPont, PFPE, Krytox 103)

Substrate: glass plate (manufactured by Matsunami Glass Ind., Microslide glass s 122, RI=1.52)

<Preparation of Polymer/Pore-Forming Agent (PVDF-HFP/DBP) Solution>

PVDF-HFP and DBP were added into acetone so that the concentration is 20 mass % in total. The various solutions with the PVDF-HFP:DVP mass ratio of 1:0.5, 1:1, 1:2, 1:3, 1:4, and 1:5, respectively, were prepared; they were stirred at 50° C. for 1 hour and allowed to stand for 1 day or more.

<Preparation of Porous Polymer Film (PVDF-HFP)>

The polymer/pore-forming agent (PVDF-HFP/DBP) solution was applied on the surface of a glass plate by a simple wet squeegee method. On the glass plate, two mending tapes with a thickness of 0.058 mm were wrapped, and the PVDF-HFP/DBP solution was applied to the gap with a squeegee. As a result, the volume of the PVDF-HFP/DBP solution on the surface of the glass plate was 5.8 mm³ per 1.0 cm². The PVDF-HFP/DBP layer was dried at room temperature for 1 minute or more. Meanwhile, phase separation of PVDF-HFP and DBP took place spontaneously, and its structure was fixed by drying. Subsequently, this PVDF-HFP/DBP layer was immersed in ethanol for 1 minute or more to extract DBP: then, a porous polymer film of PVDF-HFP was obtained by blow drying for 10 seconds.

<Production of Water-Slidable/Oil-Slidable Film>

Perfluoropolyether (PFPE) was infused into the PVDF-HFP porous polymer film. Initially, the appearance was translucent; however, it became transparent by the infusion of PFPE. Then, air was blown on the surface of the PVDF-HFP film to remove excess PFPE.

<Measurement of Material Properties>

The surface morphology of the PVDF-HFP porous polymer film was examined with a field emission scanning electron microscope (FE-SEM, S-4700, manufactured by Hitachi Ltd.). The thickness and surface roughness were determined with a laser microscope (VK-9700 Generation II, manufactured by Keyence Corporation). The sliding angle was measured with a contact angle meter (CA-DT, manufactured by Kyowa Interface Science Co., Ltd.). The transmittance was measured with a UV-VIS spectrophotometer (UV-mini 1240, manufactured by Shimadzu Corporation). Photocurrent density-voltage curves of the single-crystal standard solar cell (manufactured by CIC) were measured under the conditions of the coated area of 2.8 cm² and the irradiation with AM1.5 pseudo-sunlight (1000 mWcm⁻²). As the light source, 500 W xenon lamp (UXL-500SX, manufactured by Ushio Inc.) was used. The mechanical strength and flexibility (extension rate) were determined with a tensile strength tester (EZ-LX, manufactured by Shimadzu Corporation). Test samples for the tensile strength was 20×60 mm and the thickness was 2 μm.

Surface Morphology of PVDF-HFP Porous Polymer Films

SEM photographs were taken for the porous polymer films prepared by varying the ratio of polymer/pore-forming agent (PVD-HFP/DBP), and the surface morphology of the respective films were examined. The PVD-HFP/DBP ratios of the used porous polymer film were 1:0.5, 1:1, 1:2, and 1:5. The SEM photographs of the respective porous polymer films are shown in FIGS. 3A to 3D.

As shown in FIGS. 3A to 3D, the surface morphology was different depending upon the PVD-HFP/DBP ratios. In the ratio of 1:0.5, the film surface consisted of flat regions and pores. In the ratios of 1:1, 1:2, and 1:5, a network structure consisting of fibers and pores was formed. If the ratio of 1:0.5 and the ratio of 1:1 are compared, the pore density increases with an increase in the amount of DBP, and the flat regions decrease. Therefore, in the ratio of 1:1, the film surface is fibrous rather than flat. In the ratio of 1:2, the pore density further increases than the ratio of 1:1, and the fiber diameter becomes small. If the ratio of 1:2 and the ratio of 1:5 are compared, the size of individual pores increases though the fiber diameter becomes smaller. This is considered to be due to interconnected pores, which are caused by the increase of pore density.

The measurement results of the pore size and fiber diameter for various porous polymer films with different PVD-HFP/DBP ratios are shown in Table 1 and FIG. 4.

TABLE 1
	PVD-HFP/DBP ratio
	1:0.5	1:1	1:2	1:5
Fiber diameter	650	460	330	250
(nm)
Pore size	660	460	570	850
(nm)

As shown in Table 1 and FIG. 4, the fiber diameter had a decreasing trend with the increase of the proportion of DBP. On the other hand, the pore size was observed to increase with the increase of the amount of DBP except for the ratio of 1:0.5. The pore size for 1:0.5 was larger than that of 1:1 because the pore has an ample-shaped structure in the ratio of 1:1. That is, the pore has a small opening and a larger inner space; therefore, the pore size looks smaller. Such an ample-shaped structure is considered to be formed because DBP with a smaller specific gravity is immobilized during the rise to the surface when acetone is vaporized and the phase separation of PVDF-HFP and DBP takes place in the process of forming a coating film.

Measurement results of the surface roughness (root-mean-square roughness: Rms) for various porous polymer films of different PVD-HFP/DBP ratios are shown in Table 2 and FIG. 5.

	TABLE 2
	PVD-HFP/DBP ratio
	1:0.5	1:1	1:2	1:3	1:4	1:5
Surface Roughness	0.25	0.28	0.4	0.46	0.48	0.49
RMS (μm)

As shown in Table 2 and FIG. 5, the surface roughness was observed to increase with the increase of the proportion of DBP. The difference in the surface roughness was the largest between the ratios of 1:1 and 1:2, and the difference was not so large from the ratio of 1:2 to the ratio of 1:5.

The measurement results of the thickness for various porous polymer films with different PVD-HFP/DBP ratios are shown in Table 3 and FIG. 6.

	TABLE 3
	PVD-HFP/DBP ratio
	1:0.5	1:1	1:2	1:3	1:4	1:5
	Thickness (μm)	2.1	2.1	2.1	1.9	1.7	1.6

As shown in Table 3 and FIG. 6, the thickness of a porous polymer film was almost the same from the ratio of 1:0.5 to 1:3, thinner in the ratio of 1:4, and much thinner in the ratio 1:5. In the range from the ratio of 1:0.5 to 1:3, the increase of the proportion of DBP affects the increase in the porosity (percentage of voids). On the other hand, if the proportion of DBP exceeds 1:4, the thickness is considered to decrease because of excessive DBP. Therefore, a porous polymer film whose PVD-HFP/DBP ratio exceeds 1:4 is considered to be more fragile. The mechanical strength and flexibility of the film will be described later.

Sliding Angle of Water-Slidable/Oil-Slidable Film

The measurement results of the sliding angles of water and oil (oleic acid) on the water-slidable/oil-slidable films prepared from various porous polymer films with different PVD-HFP/DBP ratios are shown in Table 4 and FIG. 7. As the slippery liquid, perfluoropolyether (PFPE) was used.

	TABLE 4
		PVD-HFP/DBP ratio
		1:0.5	1:1	1:2	1:5
	Water-sliding angle	27	25	6	6
	(°)
	Oleic acid-sliding angle	—	—	4	4
	(°)

As shown in Table 4 and FIG. 7, the sliding angles of both water and oleic acid were small on the films of the ratios of 1:2 and 1:5. On the other hand, the sliding angles on the films of the ratios of 1:0.5 and 1:1 were large, and the liquid adhered on the film surface.

FIG. 8 shows explanatory illustrations of liquid adhesion on the surface of the PVDF-HFP porous (PFPE-infused) film. As shown in FIGS. 3A and 3B, flat regions were present on the film surface in the cases of 1:0.5 and 1:1. In addition, the surface roughness was also smaller compared with that of the film of the ratio of 1:2 or 1:5. Therefore, the films of the ratios of 1:0.5 and 1:1 do not have a structure suitable for the retention of slippery liquid. That is, the slippery liquid cannot be retained on the flat region. As shown in the top section of FIG. 8, liquid droplets are trapped on the exposed flat region and adhere thereto. On the other hand, the films of the ratios of 1:2 and 1:5 have hardly any flat regions as shown in the bottom section of FIG. 8; thus both water and oleic acid display very small sliding angles. The films of the ratios of 1:2 and 1:5 also display small sliding angles 3.4° and 3.6°, respectively, to hexane having a smaller surface energy. Thus, these water-slidable/oil-slidable films slide down and remove various kinds of liquids; as a result, the dirt due to adhesion thereof may be prevented.

Transparency of Water-Slidable/Oil-Slidable Films

The measurement results of the transmittance in the visible light region, for various PVDF-HFP films before and after the infusion of the slippery liquid (PFPE), are shown in FIG. 9. In FIG. 9, solid line A is after the infusion of PFPE, and dotted line B is before the infusion of PFPE. In addition, the measurement results for the transmittance of light with the wavelength of 600 nm are shown in Table 5 and FIG. 10.

	TABLE 5
	PVD-HFP/DBP ratio
	1:0.5	1:1	1:2	1:5	Glass
Transmittance	Before PFPE	72.7	62.1	33.9	35.9	92.0
of 600 nm light	Infusion
(%)	After PFPE	88.8	87.0	87.4	88.1	92.0
	Infusion

As shown in FIG. 9, the transmittance in the visible light region was less than 80%, for all the PVDF-HFP films, before the infusion of PFPE. However, the transmittance after the infusion of PFPE was roughly about 80%. As shown in Table 5 and FIG. 10, the transmittance of light with the wavelength of 600 nm was about 88% after the infusion of PFPE. The refractive index (RI) of PVDF-HFP film is 1.40, and PVDF-HPF (RI=1.40) and air (RI=1.00) are present, before the infusion of PFPE, in the light path inside the film. On the other hand, PVDF-HPF (RI=1.40) and PFPE (RI=1.29) are present inside the film after the infusion of PFPE and the refractive index difference is small; therefore, the reflection at the interface is also very small. The light reflectance between the two materials were calculated to be 2.8% for PVDF-HFP/air and 0.17% for PVDF-HFP/PFPE. Accordingly scattered reflection is generated at the interface between the PVDF-HPF fibers and air, before the infusion of PFPE, and resulting in low transparency. On the other hand, light reflection at the interface between PVDF-HFP and PFPE becomes small after the infusion of PFPE, resulting in high transparency. The light transmittance of the PVDF-HPF film after the infusion of PFPE is only about 5% different from that of the uncoated glass plate, and the transparency was confirmed to be very high.

FIG. 11 shows a photograph of glasses in which a PVDF-HFP porous (PFPE-infused) film was formed on the surface of a rounded lens by a cast method. The left lens is uncoated, and the right lens is coated with the PVDF-HFP porous (PFPE-infused) film. As shown in FIG. 11, the transparency of the right lens coated with the PVDF-HFP porous (PFPE-infused) film is comparable to that of the uncoated left lens, and it is satisfactorily usable as glasses. In FIG. 11, water droplets on the surface of the right lens are sliding; the arrows in the figure indicate the sliding directions of water droplets.

A bare solar cell, a solar cell covered a glass plate, solar cells covered with the respective glass plates coated with a PVDF-HFP film (before PFPE-infusion) and a PVDF-HFP film (after PFPE infusion) were prepared, and the photocurrent density (Jsc)-voltage (Voc) curves for the respective solar cells were measured; and the results are shown in FIG. 12. The film of the PVD-HFP/DBP ratio of 1:2 was used. In addition, the fill factor (FF) and the photoelectric conversion efficiency η were measured for the respective solar cells. The results are shown in Table 6.

TABLE 6
	Voc	Jsc		η
	[V]	[mA/cm2]	FF	[%]
Bare solar cell	1.073	13.722	0.701	10.323
Glass covered cell	1.073	13.093	0.705	9.898
PVDF-HFP Film	1.058	9.337	0.684	6.751
(Before PFPE Infusion)
PVDF-HFP Film	1.066	12.934	0.677	9.333
(After PFPE Infusion)

The results shown in FIG. 12 and Table 6 are approximately in agreement with the results of transmittance measurements shown in FIGS. 9 and 10. As shown in Table 6, the cell characteristics, in particular the photoelectric conversion efficiency η decreased significantly in the solar cell prepared with the use of a PVDF-HFP film before the infusion of PFPE compared with that for the bare solar cell or the glass-covered solar cell. However, in the solar cell prepared with the use of a PVDF-HFP film after the infusion of PFPE, the decreases in various cell characteristics were suppressed. The tests were performed with the use of PVDF-HFP films coated on the glass plates; therefore, a decrease in the photoelectric conversion efficiency η due to the coating of the PVDF-HFP film after the infusion of PFPE is virtually 0.565% (difference from the glass-covered solar cell). From these results, the PVDF-HFP film after the infusion of PFPE is considered to be useful as the antifouling film for solar cells.

Mechanical Strength and Flexibility of Water-Slidable/Oil-Slidable Films

An adhesive tape was pasted at the edge of the PVDF-HFP film that was prepared on a glass plate. The tape was peeled off and the PVDF-HFP film was simultaneously separated from the glass plate. The tensile strength of the obtained self-standing film of PVDF-HFP (PFPE-infused) was measured and the results are shown in Table 7 and FIG. 13, and the extension rate was also measured and the results are shown in Table 8 and FIG. 14.

TABLE 7
	PVD-HFP/DBP ratio
	1:0.5	1:1	1:2	1:5
Tensile strength	0.80	0.37	0.22	—
(N)

	TABLE 8
		PVD-HFP/DBP ratio
		1:0.5	1:1	1:2	1:5
	Extension rate	334.0	344.3	168.8	—
	(%)

As shown in Table 7 and FIG. 13, the tensile strength decreased with the increase of the proportion of DBP; a self-standing film could not be obtained in the ratio of 1:5. This is because the density of the PVDF-HFP skeleton decreases inversely with the increase of the proportion of DBP, as is clear from FIGS. 3A to 3D. The tensile strength of the film with the proportion of DBP of 1:2 was the smallest and it was 0.22 N. As shown in Table 8 and FIG. 14, the extension rate of the self-standing film of PVDF-HFP (PFPE-infused) was 168.8% or higher and excellent flexibility was displayed.

FIG. 15 shows a photograph of the self-standing film of PVDF-HFP (PFPE-infused) prepared with the proportion of DBP of 1:2 in the above-described test. As shown in FIG. 15, the self-standing film obtained by peeling off from the glass plate has high transparency, and it is also usable as a self-standing film. Therefore, the film can be used, for example, by pasting on any article as a disposable antifouling film.

Durability of Water-Slidable/Oil-Slidable Films

PFPE was infused into a PVDF-HFP film formed on the surface of a glass plate, the film was rotated for 1 minute at various spin speeds, and then the water sliding angle was measured. The results are shown in Table 9 and FIG. 16.

	TABLE 9
		Spin speed (rpm)
		0	1000	2000	4000	6000
	Water-sliding angle	5.5	5.5	5.5	5.6	5.8
	(°)

As shown in Table 9 and FIG. 16, the water-sliding effect (water sliding angle) was hardly affected by the rotation of the PVDF-HFP (PFPE-infused) film. From the results, it was clarified that PFPE does not seep out or leak out, from the PVDF-HFP porous film, by rotation and that the water-slidable/oil-slidable film has excellent durability.

Similarly to the above-described test, abrasion was applied to the PVDF-HFP (PFPE-infused) film under a loading condition of 80 g/cm² for the defined time, and the water sliding angle was measured; the results are shown in Table 10 and FIG. 17.

	TABLE 10
		Abrasion time (sec)
		0	100	500	1000
	Water-sliding angle	5.5	5.5	5.8	5.7
	(°)

As shown in Table 10 and FIG. 17, the measurement results of the water sliding angle hardly changed after the application of abrasion to the PVDF-HFP (PFPE-infused) film. Thus, it was confirmed that PFPE does not seep out or leak out from the PVDF-HFP porous film. Similarly to the above rotation test, the excellent durability is considered to be due to the internal structure of the PVDF-HFP porous film. That is, fibrous polymer forms a skeleton, which has a three-dimensional entangled network structure, inside the PVDF-HFP porous film, and PFPE is infused inside the continuous pores of the empty space. Therefore, PFPE inside the pores does not easily seep out or leak out by rotation or abrasion. As a result, a water-slidable/oil-slidable film with excellent durability can be obtained.

Antifouling Property Against Various Liquids

To the PVDF-HFP (PFPE-infused) film, of PVDF-HFP/DBP ratio of 1:2, prepared on the surface of a glass plate, various liquids with different properties were dropped, and the antifouling property against the liquids were evaluated. FIGS. 18A to 18D show their photographs. The used liquids are as follows, A: blood, B: high-viscosity drink (sweet bean soup), C: food oil, D: cleaner.

As shown in FIGS. 18A to 18D, the PVDF-HFP (PFPE-infused) film displays high contact angles for all the liquids, and liquid droplets immediately slid down when the glass plate is slanted (FIGS. 18A to 18D show photographs in which liquid droplets are sliding). Thus, an excellent antifouling effect can be provided, against various liquids having different properties, by the PVDF-HFP (PFPE-infused) film.

Claims

1. A water-slidable/oil-slidable film comprising:

a porous polymer film having a three-dimensional entangled network structure of a fibrous polymer and a continuous pore structure as the empty space of the network structure, and

a slippery liquid infused in the pores of the porous polymer film.

2. The water-slidable/oil-slidable film of the claim 1, wherein an average pore diameter of the porous polymer film is 500 to 1000 nm.

3. The water-slidable/oil-slidable film of the claim 1, wherein an average fiber diameter of the porous polymer film is 100 to 400 nm.

4. The water-slidable/oil-slidable film of the claim 1, wherein root-mean-square roughness of the porous polymer film is 0.3 to 0.6 μm.

5. The water-slidable/oil-slidable film of the claim 1, wherein the porous polymer film is made of a fluorine-based resin or silicone resin.

6. The water-slidable/oil-slidable film of the claim 5, wherein the porous polymer film is made of polyvinylidene fluoride or copolymer thereof.

7. The water-slidable/oil-slidable film of the claim 1, wherein the slippery liquid has affinity to the porous polymer film.

8. The water-slidable/oil-slidable film of the claim 1, wherein the slippery liquid is a fluorine-based oil or silicone oil.

9. The water-slidable/oil-slidable film of the claim 8, wherein the slippery liquid is perfluoropolyether.

10. The water-slidable/oil-slidable film of the claim 1, wherein the refractive index difference between the porous polymer film and the slippery liquid is 0.3 or less.

11. The water-slidable/oil-slidable film of the claim 1, wherein an average transmittance of the light with the wavelength of 400 to 700 nm is 80% or higher.

12. A production method of water-slidable/oil-slidable film comprising:

a step of mixing with stirring a polymer and a pore-forming agent that does not dissolve the polymer and a volatile organic solvent that can dissolve both the polymer and the pore-forming agent,

a step of forming a coating film by applying the mixture obtained in the preceding step on the surface of an article, and vaporizing the volatile organic solvent,

a step of forming a porous polymer film by contacting the coating film obtained in the preceding step with an organic solvent allowing that can dissolve the pore-forming agent without dissolving the polymer, to remove the pore-forming agent from the coating film,

a step of infusing a slippery liquid inside the pores of the porous polymer film obtained in the preceding step.

13. The production method of water-slidable/oil-slidable film of the claim 12, wherein a mixing ratio (mass ratio) of the polymer to the pore-forming agent is 1:1.5 to 1:5.

14. The production method of water-slidable/oil-slidable film of the claim 12, wherein the polymer is a fluorine-based resin or silicone resin.

15. The production method of water-slidable/oil-slidable film of the claim 12, wherein the polymer is polyvinylidene fluoride or copolymers thereof.

16. The production method of water-slidable/oil-slidable film of the claim 12, wherein the polymer is soluble in acetone and insoluble in ethanol.

17. The production method of water-slidable/oil-slidable film of the claim 12, wherein the pore-forming agent is an ethanol-soluble low-molecular-weight solvent.

18. The production method of water-slidable/oil-slidable film of the claim 12, wherein the pore-forming agent is phthalic acid or derivatives thereof.

19. The production method of water-slidable/oil-slidable film of the claim 12, wherein the volatile organic solvent is an organic solvent with a boiling point of 100° C. or lower.

20. The production method of water-slidable/oil-slidable film of the claim 12, wherein the volatile organic solvent is acetone.

21. The production method of water-slidable/oil-slidable film of the claim 12, wherein the organic solvent that can dissolve the pore-forming agent without dissolving the polymer is ethanol.

22. The production method of water-slidable/oil-slidable film of the claim 12, wherein the slippery liquid is a fluorine-based oil or silicone oil.

23. The production method of water-slidable/oil-slidable film of the claim 22, wherein the slippery liquid is perfluoropolyether.

24. An article having the surface coated with the water-slidable/oil-slidable film of the claim 1.