Method for manufacturing a liquid-repellent film, liquid-repellent film, and packaging material

Abstract

To provide a manufacturing method of a liquid repellent film exhibiting excellent content adhesion prevention property by using a physical amount measurable with an existing method, in stead of directly observing and measuring an air pocket state.SOLUTION: A method of forming a liquid-repellent film 10 includes forming a base coat layer 4 in which hydrophilic silica beads 8 are fixed on a base material 2 with a thermoplastic resin 12 to form a large concave-convex structure, and forming a top coat layer 6 forming a small concave convex structure by fixing hydrophilic silica fine particles 14 on the base coat layer 4 with a resin 16 having a liquid repellent portion. By making such that arithmetic average roughness Ra of a surface is in the range of 0.5 to 2.0 μm, and by defining the surface with a plurality of rectangular mass, a gap area rate of each rectangular mass is measured, and what has a void area rate in the range of 20 to 80% is rendered to be 80% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a liquid-repellent film having excellent liquid repellency, for example, a liquid-repellent film that imparts adhesion prevention of contents to the surface of packaging materials for contents such as foods, pharmaceuticals, cosmetics, and daily necessities, and a method for manufacturing the same.

Background Art

[0002] Conventionally, a liquid-repellent film for preventing adhesion of contents has been formed on the surface of a packaging material. For example, Patent Document 1 discloses a liquid-repellent film that can be manufactured at low cost, allows various materials to be selected for the base material, is thin, and has excellent transparency.

[0003] The liquid-repellent film of Patent Document 1 is obtained by laminating a base coat layer and a top coat layer on a base film. In the base coat layer, large-diameter particles are fixed to the surface of the base film with a thermoplastic resin to form a large uneven structure. In the top coat layer, small-diameter particles are fixed to the surface of the base coat layer with a resin having a liquid-repellent portion to form a small uneven structure. In this way, an uneven structure with a large undulation is formed as a whole.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the contents come into contact with the uneven surface of the liquid-repellent film of Patent Document 1, an air pocket is formed between adjacent convex portions, so that the contact area between the contents and the uneven structure becomes small. In addition, by using a material with high liquid repellency such as a fluororesin for the resin of the top coat layer, the liquid-repellent film exhibits adhesion prevention against the contents.

[0006] Regarding the ability to prevent contents from adhering, large-diameter particles on the order of micrometers form deeper air pockets on their surface the larger their particle size. Furthermore, if the pitch of the large-diameter particles is appropriate, the volume of the air pocket between the contents and the liquid-repellent film can be maintained. However, if the pitch of the large-diameter particles is too small, only small air pockets can be formed, and if the pitch of the large-diameter particles is too large, the contents (such as liquid droplets) will bend and come into contact with the bottom of the air pocket, making it impossible to maintain the volume of the air pocket.

[0007] Furthermore, it is preferable for the wettability of the contact area between the surface of the large-diameter particle-based, uneven structure and the contents to be low. This is because the degree to which the contents flex into the air pocket depends on the wettability of the contact area. If the wettability is high, the contents will flex greatly, and if the wettability is low, they will not flex much, making it easier to create an air pocket.

[0008] However, it is difficult to observe or measure the state of air pockets between the surface irregularities of a liquid-repellent film and the contents in contact with it (such as the depth and size of the air pockets, or the degree to which the contents flex into the air pockets). Therefore, if a liquid-repellent film capable of forming ideal air pockets can be obtained by manufacturing a liquid-repellent film using physical quantities that can be measured by existing methods, so that these physical quantities fall within a predetermined numerical range, it will be possible to stably provide a liquid-repellent film that exhibits excellent content adhesion prevention properties.

[0009] This invention has been made in view of the above problems, and aims to provide a method for producing a liquid-repellent film that exhibits excellent content adhesion prevention properties using physical quantities that can be measured by existing methods, and to provide a liquid-repellent film having such physical quantities, and a packaging material using the same. [Means for solving the problem]

[0010] To solve the aforementioned problems, the inventors conducted extensive research and discovered that by ensuring that the measured values ​​of "arithmetic mean roughness Ra," which can be measured using existing methods, and "void area ratio," which indicates the percentage of areas where protrusions of large-diameter particles are not formed, fall within predetermined numerical ranges, a liquid-repellent film exhibiting excellent content adhesion prevention properties can be manufactured, thus completing the present invention.

[0011] In other words, the method for producing the liquid-repellent film of the present invention is A method for manufacturing a liquid-repellent film having a laminated structure of a base coat layer and a top coat layer, Large-diameter particles of surface-hydrophilic metal oxide are fixed onto a substrate with a thermoplastic resin to form the base coat layer as a large uneven structure. Small-diameter particles of surface-hydrophilic metal oxides are used in the liquid-repellent area. rank The resin having the above is fixed onto the base coat layer to form the top coat layer as a small uneven structure. The arithmetic mean roughness Ra of the surface of the liquid-repellent film is measured to fall within the numerical range of 0.5 to 2.0 μm. The surface of the liquid-repellent film is divided into multiple rectangular squares, the length and width of which are 5 to 20 times the average particle size of the large-diameter particles. The void area ratio, which indicates the percentage of the area in each rectangular square where no protrusions are formed by the large-diameter particles, is measured, and the number of rectangular squares in which the measured value of the void area ratio falls within the numerical range of 20 to 80% is 80% or more of the total number of squares.

[0012] Here, when forming the base coat layer, it is preferable to determine the mixing ratio and coating amount of the large-diameter particles and the thermoplastic resin such that the measured value of the arithmetic mean roughness Ra falls within the numerical range of 0.5 to 2.0 μm, and the number of rectangular squares in which the measured value of the void area ratio falls within the numerical range of 20 to 80% accounts for 80% or more of the total number of squares.

[0013] The arithmetic mean roughness and void area ratio described above can be easily measured using existing methods. By determining the mixing ratio and application amount of the base coat layer so that these measurements fall within their respective numerical ranges, it is possible to manufacture a liquid-repellent film capable of forming ideal air pockets, thereby stably providing a liquid-repellent film that exhibits excellent content adhesion prevention properties.

[0014] The liquid-repellent film of the present invention has a laminated structure of a base coat layer and a top coat layer. The base coat layer comprises large-diameter particles of surface-hydrophilic metal oxide and a thermoplastic resin, wherein the large-diameter particles are fixed on the substrate by the thermoplastic resin to form a large uneven structure. The top coat layer comprises small-diameter particles of surface-hydrophilic metal oxides and liquid-repellent parts. rank The resin contains the small-diameter particles, and the liquid-repellent portion rank A resin having the following properties, fixed onto the base coat layer to form a small uneven structure: The measured arithmetic mean roughness Ra of the surface of the liquid-repellent film falls within the numerical range of 0.5 to 2.0 μm. The aforementioned repelling agent film The surface is divided into multiple rectangular squares, the length and width of which are 5 to 20 times the average particle size of the large-diameter particles. The void area ratio, which indicates the percentage of the area in each rectangular square where no protrusions are formed by the large-diameter particles, is measured, and the number of rectangular squares in which the measured value of the void area ratio falls within the numerical range of 20 to 80% is 80% or more of the total number of squares.

[0015] A liquid-repellent film with this configuration can form ideal air pockets for the contents, exhibiting excellent resistance to content adhesion.

[0016] In this case, it is preferable that the average of the measured values ​​of the void area ratio falls within the numerical range of 10 to 70 mass%. Furthermore, it is preferable that the ratio of the large-diameter particles to the thermoplastic resin content in the base coat layer is 30:70% by mass to 70:30% by mass.

[0017] Also, the ratio of the content of the small-diameter particles in the top coat layer to the resin having the liquid-repellent part is 40:60 to 80:20% by mass, and the coating amount of the top coat layer is 0.5 to 1.2 g / m 2 which is preferable.

[0018] Also, it is preferable that the minimum particle diameter of the large-diameter particles in the base coat layer is larger than the maximum particle diameter of the small-diameter particles in the top coat layer.

[0019] The packaging material of the present invention is characterized in that the liquid-repellent film is provided on the surface.

Brief Description of Drawings

[0020] [Figure 1] It is a diagram schematically showing the structure of a liquid-repellent film according to one embodiment. [Figure 2] It is an explanatory diagram of a method for measuring the arithmetic mean roughness Ra and the void area ratio. [Figure 3] It is a digital microscope image (upper image) of the liquid-repellent films according to Examples and Comparative Examples, and an image obtained by processing these images and showing regions regarded as voids in gray of the same brightness (lower image).

Modes for Carrying Out the Invention

[0021] Hereinafter, referring to the drawings, preferred embodiments of the present invention will be described in detail. FIG. 1 is a schematic cross-sectional view of a liquid-repellent film 10 according to a first embodiment. The liquid-repellent film 10 in FIG. 1(A) includes a base coat layer 4 formed on at least one surface of a substrate 2, and a top coat layer 6 formed by laminating on the surface of the base coat layer 4.

[0022] The substrate 2 is not particularly limited as long as it is a form that serves as a support for the base coat layer 4, and can be formed as appropriate from resin, paper, metal, glass, ceramic, etc. It may be a single layer or a multilayer structure of two or more layers. The surface of the substrate 2 may be subjected to inorganic or metal vapor deposition treatment or printing treatment. There is no particular limit to the thickness of the substrate 2, but films with a thickness of about 1 to 200 μm and sheets with a thickness of about 200 to 10,000 μm are commonly used.

[0023] The base coat layer 4 contains hydrophilic silica particles (referred to here as hydrophilic silica beads 8) and thermoplastic resin 12.

[0024] The hydrophilic silica beads 8 correspond to the large-diameter hydrophilic particles of the present invention, and have an average particle size on the order of micrometers, for example, and can be appropriately selected from crystalline silica, amorphous silica (dry silica, wet silica, silica gel, etc.). The shape of the hydrophilic silica beads 8 is not particularly limited, and various shapes such as polyhedra and uneven shapes can be selected. Porous hydrophilic silica beads 8 may also be used. Furthermore, hydrophilic oxide fine particles such as titanium dioxide, zinc oxide, and aluminum oxide can be used as the large-diameter particles of the present invention.

[0025] The thermoplastic resin 12 is not particularly limited, but examples include polyester, polyolefin, chlorinated polyolefin, polystyrene, nylon, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, acrylonitrile butadiene styrene copolymer, ethylene vinyl acetate copolymer, polyacetal, polymethyl methacrylate, methacrylic styrene copolymer, cellulose acetate, polyurethane, and polycarbonate.

[0026] The base coat layer 4 is formed by applying a coating, which is made by dissolving or dispersing hydrophilic silica beads 8 and thermoplastic resin 12 in a solvent, to the substrate 2 and drying it. The solvent is not particularly limited, but examples include hydrocarbons such as n-hexane, cyclohexane, toluene, benzene, and xylene, ketones such as acetone and methyl ethyl ketone, and alcohols.

[0027] The average thickness of the thermoplastic resin 12 is not particularly limited, but is somewhat smaller than the particle size of the hydrophilic silica beads 8 it contains. If all the hydrophilic silica beads 8 are embedded in the thermoplastic resin 12, a textured surface will not be formed by the hydrophilic silica beads 8. Therefore, the amount of thermoplastic resin 12 applied to the hydrophilic silica beads 8 is set so that an appropriate space for air pockets is created between adjacent hydrophilic silica beads 8. For this reason, although the average thickness of the thermoplastic resin 12 is not particularly limited, 0.5 to 1.5 μm is preferred.

[0028] Introduction of arithmetic mean roughness Ra and void area ratio The inventors discovered that by limiting the state of the uneven structure of the base coat layer 4, a liquid-repellent film 10 that can stably exhibit excellent liquid repellency can be produced. In other words, liquid repellency is closely related to the contact area with the contents, and reducing the contact area requires low wettability of the convex parts of the surface uneven shape of the liquid-repellent film 10, the formation of air pockets between the recesses and the contents, and preventing the contents from coming into contact with the recesses. The properties of the top coat layer 6, which will be described later, greatly influence the low wettability of the convex parts.

[0029] If an air pocket is not properly formed between the recess and the contents, for example, if the contents cannot be supported solely by the convex portion and sag into contact with the bottom surface of the recess, the contact area between the contents and the liquid-repellent film 10 increases dramatically, resulting in significantly reduced liquid repellency. In order for an air pocket to be properly formed and for the contents to not come into contact with the recess, it is necessary that there be a step of a certain size between the recess and the convex portion, and that the distance (pitch) between the convex portions does not become too large.

[0030] The conditions for preventing contents from contacting recesses include "step height" and "pitch," but it is virtually impossible to measure these values ​​after forming a liquid-repellent film 10 on the substrate 2. Factors that determine "step height" include the particle size of the hydrophilic silica beads 8 in the base coat layer 4 and the average height (average thickness) of the thermoplastic resin 12 from the substrate 2 after the base coat layer 4 has been formed. The average height of the thermoplastic resin 12 in the base coat layer 4 is determined by the mixing ratio of the thermoplastic resin 12 in the base coat layer 4 and the amount of base coat layer 4 applied. For this reason, the particle size of the hydrophilic silica beads 8, the mixing ratio of the thermoplastic resin 12, and the amount of paint applied to the base coat layer 4 are used as indicators to represent "step height." However, these indicators are unstable as they constantly change depending on the state of application and formation of the base coat layer 4. Therefore, the inventors decided to measure the arithmetic mean roughness Ra and void area ratio after the application and formation of the base coat layer 4 and use them instead of the above indicators to define the state of the base coat layer 4.

[0031] Figure 2 schematically illustrates the measurement methods for arithmetic mean roughness Ra and void area ratio. In measuring surface roughness, a laser microscope (Keyence Corporation's "VK-X1000") is used to measure the surface irregularities of the liquid-repellent film 10 shown in Figure 2(A) as a "roughness curve". Next, the arithmetic mean roughness Ra is calculated based on the roughness curve shown in Figure 2(B). As shown in Figure 2(C), the arithmetic mean roughness Ra is expressed as the average of the absolute values ​​of the height distance from the reference line over the measurement length, with the average value of the surface irregularities serving as the reference line.

[0032] The void area ratio is measured using the automatic area measurement (particle count) mode of a digital microscope (Keyence Corporation "VHX-7000"). A region from which the target object is to be extracted is set on the image of the surface of the liquid-repellent film 10 taken with the digital microscope, and regions with the same brightness level are automatically extracted from that region. The extraction mode is set to brightness (luminance), and the "original image (no processing)" image is selected. For example, if the protrusions made by the hydrophilic silica beads 8 are bright, the dark areas (regions where there are no protrusions made by the hydrophilic silica beads 8, i.e., void regions) below the set brightness level threshold (set to "0" in the range of -255 to 255) are extracted, and the area of ​​the extracted portion is calculated. The void area ratio is expressed as a percentage (%) of the area of ​​the extracted portion per unit area of ​​the extracted region. As schematically shown in Figure 2(D), the void area ratio is calculated by finding the sum of the areas S2 to S5 of regions without protrusions made by the hydrophilic silica beads 8 and representing the ratio to the total area S1.

[0033] The reason for using the arithmetic mean roughness Ra is that it has a strong correlation with "step height" and "pitch," and as mentioned above, this "step height" and "pitch" are determined by the particle size of the hydrophilic silica beads 8, the mixing ratio of the thermoplastic resin 12, and the amount of base coat layer 4 applied. The reason for using the void area ratio is that the void area ratio has a strong correlation with the "pitch" and "particle size" of the hydrophilic silica beads 8, and also depends on the "amount" (number of particles per unit area) and "particle size" (area of ​​one particle) of the hydrophilic silica beads 8. Therefore, the conditions for "step height" and "pitch," which are actually impossible to measure, can be defined by the easily measurable arithmetic mean roughness Ra and void area ratio measurements.

[0034] Furthermore, since the size of the hydrophilic silica fine particles 14 in the topcoat layer 6, described later, is smaller than the average particle size of the hydrophilic silica beads 8 in the basecoat layer 4, the topcoat layer 6 has almost no effect on the arithmetic mean roughness Ra and void area ratio. For example, the average secondary particle diameter of the hydrophilic silica beads 8 in the basecoat layer 4 is 1 to 12 μm, while the average primary particle diameter of the hydrophilic silica fine particles in the topcoat layer 6 is 7 to 40 nm. Moreover, the uneven structure created by the secondary particles of the hydrophilic silica beads 8 is expected to strengthen the retention force to the surface of the substrate 2 as the thermoplastic resin enters its pores, since the secondary particles themselves are porous. In addition, because the secondary particles themselves are porous, the uneven structure of the basecoat layer 4 becomes more complex, which also has the effect of improving liquid repellency.

[0035] Based on the above findings, the inventors conducted extensive research and discovered that the arithmetic mean roughness Ra of the liquid-repellent film 10 formed on the substrate 2 must fall within the numerical range of 0.5 to 2.0 μm to stably exhibit excellent liquid repellency.

[0036] In addition, the surface of the substrate 2 contains hydrophilic silica beads 8 with an average secondary particle diameter of 5 μm (by volume). However, in reality, beads with smaller or larger diameters (1-12 μm) than the average also exist. Considering the presence of such hydrophilic silica beads 8, we decided to introduce an index that represents the degree of presence of hydrophilic silica beads 8 using the void area ratio mentioned above.

[0037] First, the surface of the liquid-repellent film 10 is divided into multiple rectangular squares, each with a length and width 5 to 20 times the particle size of the hydrophilic silica beads 8, and the void area ratio (%) of each rectangular square is measured. Rectangular squares with a void area ratio of less than 20% have too many hydrophilic silica beads 8, making it difficult to form air pockets of sufficient size. Rectangular squares with a void area ratio exceeding 80% have too few hydrophilic silica beads 8, making it difficult to maintain air pockets as the contents come into contact with the bottom surface of the depressions. As a result of diligent research by the inventors, they measured the void area ratio of each of the multiple rectangular squares and found that having 80% or more of the rectangular squares with a measured void area ratio in the range of 20 to 80% is a requirement for stably exhibiting excellent liquid repellency. This range is preferably 30 to 80%.

[0038] Furthermore, in order to obtain better liquid repellency, it is preferable that the average of the measured values ​​of the void area ratio of multiple rectangular masses falls within the numerical range of 10 to 70% by mass. This numerical range is preferably 20 to 70%, and more preferably 30 to 70%. In addition, it is preferable that the mixing ratio of hydrophilic silica beads 8 and thermoplastic resin 12 in the base coat layer 4 be in the range of 30:70 to 70:30 (by mass%). This is to ensure that the step height and the distance (pitch) between the protrusions of the base coat layer 4 are appropriate. If the mixing ratio of hydrophilic silica beads 8 is 30% by mass or less, the amount of thermoplastic resin 12 is too large, resulting in the step height becoming too low or the distance (pitch) between the protrusions becoming too long, creating an environment where the contents can easily come into contact with the recesses, resulting in poor liquid repellency. Furthermore, if the blending ratio of hydrophilic silica beads 8 is 70% by mass or more, sufficient steps can be secured and the distance (pitch) between the protrusions can be shortened. However, because the amount of thermoplastic resin 12 is small, the bonding between the base material 2 and the hydrophilic silica beads 8 becomes weak, and the hydrophilic silica beads 8 tend to fall off the base material 2. Also, if the distance (pitch) between the protrusions becomes too short, the contact area with the contents increases, making it difficult to secure the size of the air pockets.

[0039] <Top coat layer> The topcoat layer 6 is a liquid-repellent layer and is formed to cover the surface of the basecoat layer 4. The topcoat layer 6 is formed by applying a paint, which is made by dissolving or dispersing hydrophilic silica fine particles 14 and a resin 16 having liquid-repellent parts in a solvent, to the surface of the basecoat layer 4 and drying it.

[0040] As the small-diameter particles of the present invention, hydrophilic oxide fine particles such as titanium dioxide, zinc oxide, and aluminum oxide can also be used, but it is particularly preferable to prepare the coating using hydrophilic silica fine particles 14 having an average primary particle diameter of 7 to 40 nm. When hydrophilic silica fine particles 14 of such particle size are applied, some of them become appropriately aggregated during the coating process, and resin having liquid-repellent parts is held in the porous voids formed in these aggregates, contributing to the low wettability of the surface of the base coat layer 4.

[0041] A fluororesin is preferred as the liquid-repellent portion, and a resin composition containing, for example, a perfluoroalkyl group, a polyfluoroalkyl group, or a perfluoropolyether group as the fluororesin-containing portion is preferred.

[0042] The solvent is not particularly limited, but water, ethanol, isopropyl alcohol (IPA), n-butyl alcohol, etc., can be used.

[0043] The ratio of hydrophilic silica fine particles 14 to the resin 16 having liquid-repellent portions is preferably 40:60% by mass to 80:20% by mass. If the ratio of hydrophilic silica fine particles 14 is less than 40% by mass, the topcoat layer 6 has fewer fine convex shapes, resulting in poor liquid repellency. On the other hand, if the amount exceeds 80% by mass, the resin 16 having liquid-repellent portions of the topcoat layer 6 cannot sufficiently cover the hydrophilic silica fine particles 14, and the hydrophilic silica fine particles 14 are exposed on the outermost surface, resulting in poor liquid repellency. In addition, the function of retaining the hydrophilic silica fine particles 14 on the surface of the basecoat layer 4 is reduced.

[0044] Furthermore, to obtain even better liquid repellency, the amount of paint applied to form the topcoat layer 6 is 0.5 to 1.2 g / m². 2Preferably, it is 0.5 g / m 2 If the amount is less than 1.2 g / m², the number of liquid-repellent sites in the liquid-repellent film 10 will be too small, and sufficient liquid repellency will not be obtained. 2 If the thickness exceeds this, the steps in the uneven structure of the hydrophilic silica beads 8 in the base coat layer 4 become shallower, resulting in poor liquid repellency. The thickness of the top coat layer 6 is not particularly limited, but may be 0.1 to 1.5 μm. For the liquid repellency of the top coat layer 6, it is preferable that the contact angle when in contact with oleic acid is 130 degrees or more.

[0045] Regarding the particle sizes of the hydrophilic silica beads 8 in the base coat layer 4 and the hydrophilic silica fine particles 14 in the top coat layer 6, it is preferable that the minimum particle size of the hydrophilic silica beads 8 is larger than the maximum particle size of the hydrophilic silica fine particles 14. The minimum particle size of the hydrophilic silica beads 8 is, for example, 25 times or more, preferably 50 times or more, and more preferably 150 times or more, the maximum particle size of the hydrophilic silica fine particles 14. Alternatively, the minimum particle size of the hydrophilic silica beads 8 is, for example, 2000 times or less, preferably 1500 times or less, the maximum particle size of the hydrophilic silica fine particles 14.

[0046] According to the liquid-repellent film 10 of this embodiment, the hydrophilic silica fine particles 14 contained in the topcoat layer 6 are smaller than the hydrophilic silica beads 8 of the basecoat layer 4. As a result, the hydrophilic silica fine particles form an uneven structure on the surface of the uneven structure created by the hydrophilic silica beads 8, resulting in an overall uneven structure with significant undulations, which enhances liquid repellency. Figure 1(B) schematically shows an example of a state in which a fine uneven structure is formed on the surface of the hydrophilic silica beads 8 by the hydrophilic silica fine particles 14. The surface of the fine uneven structure created by the hydrophilic silica fine particles 14 is further covered by a resin 16 having liquid-repellent parts, which further enhances liquid repellency. By making the topcoat layer 6 a material and structure that can obtain excellent liquid repellency, the protrusions of the basecoat layer 4 exhibit low wettability, reducing the contact area with the contents and resulting in excellent liquid repellency.

[0047] The resin 16 having a liquid-repellent portion in the topcoat layer 6 can be a copolymer of a liquid-repellent portion and a hydrophilic portion. In particular, by using a fluorine-based copolymer resin, a liquid-repellent film suitable for preventing the adhesion of oil-in-water (O / W) emulsions such as coffee creamer can be suitably obtained. Such copolymers include, for example, a block copolymer structure of a polymer containing a liquid-repellent portion and a polymer containing a hydrophilic portion. As the liquid-repellent portion, a liquid-repellent portion made of fluororesin (perfluoroalkyl group, polyfluoroalkyl group, perfluoropolyether group, etc.) is preferred, but liquid-repellent portions other than fluorine may also be used. As the hydrophilic portion, hydroxyl groups, carboxyl groups, amino groups, oxyethylene groups, etc. can be used. When such a block copolymer covers hydrophilic silica fine particles, under an air atmosphere, the copolymer containing the liquid-repellent portion will surface-oriented due to the relationship of their surface free energies. Furthermore, the copolymer containing the hydrophilic portion has a high affinity for hydrophilic silica fine particles 14 that have surface hydrophilicity such as silanol groups, and is useful for bonding the block copolymer and the hydrophilic silica fine particles 14.

[0048] Herein, formula (1) shows an example of a fluororesin-containing

[0049] [ka]

[0050] Furthermore, an example of the hydrophilic portion constituting the copolymer resin of the liquid-repellent portion and the hydrophilic portion that can be used in the liquid-repellent film 10 of this embodiment is given in formula (2).

[0051] [ka] Here, R in the formula represents hydrogen or preferably no more than six alkyl groups. n is an integer.

[0052] O / W type emulsions are in a state where fine oily micelles are dispersed in an aqueous liquid. In this embodiment, when the resin 16 having liquid-repellent parts is made of a block copolymer of a polymer containing liquid-repellent parts such as fluorine and a polymer containing hydrophilic parts, it exhibits an effect of preventing adhesion of O / W type emulsions for the following reasons.

[0053] First, when the hydrophilic silica fine particles 14 of the top coat layer 6 are covered with a block polymer resin, the hydrophilic portion of the block polymer resin is oriented toward the hydrophilic silica fine particles 14, and consequently, the liquid-repellent portion is oriented toward the outside.

[0054] When the O / W type emulsion comes into contact with the topcoat layer 6, its hydrophilic portion attracts water, which is the continuous phase of the emulsion. This makes it difficult for the micelles, which are the oil component of the O / W type emulsion, to come into contact with the topcoat layer 6, thus preventing damage to the micelles.

[0055] Furthermore, the presence of polymers in the liquid-repellent portion of the topcoat layer 6 prevents the topcoat layer 6 from becoming wet with attracted water. This anti-adhesion function is maintained even after the O / W type emulsion has been in contact with the topcoat layer 6 for an extended period of time.

[0056] The liquid-repellent film 10 of this embodiment is suitable for packaging films or sheets, and is also suitable for lamination to existing packaging films or sheets. For example, the liquid-repellent film 10 of this embodiment can be used as packaging material for pouches containing food, cosmetics, detergents, shampoos, conditioners, etc., or as packaging material for lids of food containers such as yogurt, pudding, and jelly. Furthermore, the liquid-repellent film 10 of this embodiment can be used as packaging material for cakes using cream, or as packaging material for foods with viscous sauces, such as mochi dumplings. [Examples]

[0057] The present invention will be described in more detail below based on the examples, but the present invention is not limited to the contents of these examples.

[0058] <Examples 1-5 and Comparative Examples 1-5> A sample of the liquid-repellent film was prepared as follows. (1) Base material A 20 μm thick biaxially oriented polypropylene film was used as the substrate. The coated surface of the substrate was treated with corona to enhance wettability. (2) Base coat layer As large-diameter particles with surface hydrophilicity, commercially available hydrophilic silica beads with an average particle size of 3 μm or 5 μm were used, and as the thermoplastic resin, a chlorinated polyolefin resin was used. These were dissolved and dispersed in a solvent in the mixing ratio (mass %) of hydrophilic silica beads:thermoplastic resin:solvent shown in Table 1 to prepare a base coat coating. The prepared coating was then applied to a substrate in the amount shown in Table 1 and dried to create a base coat layer. The application amount is the value of the solids content excluding the solvent. (3) Top coat layer As small-diameter particles with surface hydrophilicity, commercially available hydrophilic fumed silica fine particles with an average primary particle diameter of 20 nm were used, and a fluorine-based copolymer resin was used as the resin containing liquid-repellent parts. These were dissolved and dispersed in a solvent in a mixing ratio (mass %) of hydrophilic fumed silica fine particles: resin containing liquid-repellent parts: solvent = 4.4:3.0:92.6 to prepare a topcoat coating. The mixing ratio of the components of the topcoat layer was the same in Examples 1-5 and Comparative Examples 1-5, and the mixing ratio of solids only (hydrophilic fumed silica fine particles: resin containing liquid-repellent parts) was 59.5:40.5 (mass %). The prepared coating was then applied to the surface of the basecoat layer in the amounts shown in Table 1 and dried to create a topcoat layer.

[0059] The coating conditions for Examples 1-5 and Comparative Examples 1-5 are summarized in Table 1.

[0060] [Table 1]

[0061] (4) Method for determining application conditions The mixing ratio of hydrophilic silica beads and thermoplastic resin, and the set values ​​for the application amount of the base coat layer were determined as follows. Base coat layers were prepared in advance using several different set values, and a top coat layer was prepared on the surface of the base coat layer. The "arithmetic mean roughness Ra" and "void area ratio" of each surface were measured. A liquid-repellent film whose measured values ​​fall within a predetermined numerical range was selected, and the set values ​​used in the preparation of its base coat layer were adopted. The numerical range for the arithmetic mean roughness Ra of the liquid-repellent film is 0.5 to 2.0 μm.

[0062] To determine the void area ratio, first, the surface image of the liquid-repellent film (110 μm vertically and 147 μm horizontally) is divided into nine rectangular cells. Each rectangular cell will contain an area of ​​36.8 μm vertically and 49.1 μm horizontally. The number of divisions should be adjusted according to the particle size of the hydrophilic silica beads. For example, the number of divisions should be set so that the vertical and horizontal lengths of each cell after division are 5 to 20 times the particle size of the hydrophilic silica beads. Next, the void area ratio (%) of each of the nine rectangular cells is measured. Then, the number of rectangular cells whose measured void area ratio falls within the range of 20 to 80% is counted, and those where this count is 80% or more of the total number of cells are selected.

[0063] In Examples 1-5, hydrophilic silica beads with an average particle size of 5 μm were used. However, the same method can be used to determine the set values ​​when using materials other than these hydrophilic silica beads (for example, other surface-hydrophilic metal oxide particles) or when using large-diameter particles with different average particle sizes (for example, in the range of 1 to 12 μm).

[0064] <Evaluation Method> The liquid-repellent properties of the liquid-repellent film were evaluated as follows. First, a cylindrical plastic container with a diameter of 30 mm was placed over a 5 ml oleic acid solution, with the liquid-repellent film sample facing downwards. With the sample in place, the container was inverted 180 degrees, and left to stand for 1 minute with the oleic acid inside the container in contact with the liquid-repellent film. After 1 minute, the container was inverted 180 degrees back to its original position, the sample was immediately removed from the container, and its weight was measured. The change in sample weight before and after contact with the oleic acid was calculated as the amount of oleic acid adhering to the liquid-repellent film. If the amount of oleic acid adhering was less than 30 mg, it was evaluated as "exhibiting excellent liquid repellency," and this was indicated with a "○". If the amount of oleic acid adhering was 30 mg or more, it was evaluated as "insufficient liquid repellency," and this was indicated with a "×".

[0065] The evaluation results for liquid repellency are shown in Table 2, along with the arithmetic mean roughness, the average void area ratio, and the percentage of rectangular cells with a void area ratio of 20-80%. Note that the void area ratio for Comparative Example 5 was measured using the original size image before partitioning, and is shown as a reference value.

[0066] [Table 2]

[0067] Table 3 shows the measured values ​​of the void area ratio (%) for the nine rectangular cells after partitioning. The position of each rectangular cell is indicated from "top left" to "bottom right".

[0068] [Table 3]

[0069] Furthermore, Figure 3 shows 2000x digital microscope images (upper image) of the liquid-repellent film samples from Examples 1-5 and Comparative Examples 1-4, along with images used for calculating the void area ratio (lower image).

[0070] The digital microscope image shows the surface of the liquid-repellent film magnified 2000 times, displaying an area measuring 110 μm vertically and 147 μm horizontally. The raised areas due to the hydrophilic silica beads are bright, while the areas without these raised areas are dark.

[0071] The procedure for calculating the void area ratio will be explained again using Figure 3. The digital microscope image is divided into nine rectangular cells, and the void area is measured for each of the nine rectangular cells. The division lines are displayed in the upper image of each embodiment. Then, the ratio of the void area to the area of ​​each rectangular cell is calculated as the void area ratio (%) for each rectangular cell. Note that in the lower image of each embodiment in Figure 3, the areas where protrusions due to hydrophilic silica beads are considered to be absent (void areas) are shown in gray of the same brightness to make them easier to see.

[0072] As shown in Table 2, in Examples 1-5, the application conditions (Table 1) for the base coat and top coat layers were set so that the arithmetic mean roughness Ra of the liquid-repellent film surface fell within the range of 0.5 to 2.0 μm, and the number of rectangular squares with a void area ratio of 20 to 80% accounted for 80% or more of the total number of squares. As a result, in all cases, the amount of oleic acid adhering was less than 30 mg, indicating excellent liquid repellency.

[0073] In contrast, in Comparative Examples 1-5, although the application conditions for the base coat and top coat layers (Table 1) were not significantly different from those in Examples 1-5, the amount of oleic acid adhering to each was 30 mg or more, resulting in insufficient liquid repellency.

[0074] Looking at the measured values ​​of the arithmetic mean roughness Ra and the percentage of rectangular cells with a void area ratio of 20-80% in Table 2, which were introduced in this invention, in Comparative Examples 1-3, the arithmetic mean roughness Ra falls outside the standard range (0.5-2.0 μm), and the percentage of rectangular cells with a void area ratio of 20-80% is also below the standard (80%). In other words, in Comparative Examples 1 and 2, it can be said that there is a correlation between the arithmetic mean roughness Ra of the liquid-repellent film surface being smaller than the standard range, the percentage of rectangular cells with a void area ratio of 20-80% being lower than the standard, and the large amount of oleic acid deposited. In the case of Comparative Example 3, it can be said that there is a correlation between the arithmetic mean roughness Ra being larger than the standard range at 2.06 μm, the percentage of rectangular cells with a void area ratio of 20-80% being lower than the standard at 67%, and the large amount of oleic acid deposited at 79.4 g. Furthermore, in Comparative Example 4, although the arithmetic mean roughness Ra (1.65 μm) was within the standard range, the proportion of rectangular cells with a void area ratio of 20-80% (78%) was lower than the standard. In this case as well, the amount of oleic acid deposited was high at 97.6 g. This indicates a correlation between a low proportion of rectangular cells with a void area ratio of 20-80% and a high amount of oleic acid deposited.

[0075] While the coating conditions shown in Table 1 do not reveal any clear difference between Examples 1-5 and Comparative Examples 1-5, if the uneven structure of the actually formed liquid-repellent film could be directly observed and measured, it would be possible to see differences in the pitch of the protrusions and the depth of the depressions caused by the hydrophilic silica beads. It is expected that these differences in the shape of the uneven structure manifest as differences in the amount of oleic acid deposited. Furthermore, in this invention, even without directly observing and measuring the pitch of the protrusions and the depth of the depressions, the liquid repellency of the liquid-repellent film can be correctly evaluated using the measured values ​​of the introduced arithmetic mean roughness Ra and void area ratio. The measured values ​​and evaluation results in Table 2 support the finding that there is a correlation between the ratio of rectangular squares with an arithmetic mean roughness Ra and void area ratio of 20-80% and the liquid repellency of the liquid-repellent film.

[0076] Furthermore, as shown in Comparative Examples 1-3 in Table 2, the fact that the average void area ratio falls outside the numerical range of 10-70% (only in Comparative Example 3) can be said to affect the evaluation of the liquid repellency of the liquid-repellent film. If the numerical range of the average void area ratio is 20-70% (comparative examples 2 and 3 are outside this range), or even 30-70% (comparative examples 1-3 are outside this range), the correlation with the evaluation of the liquid repellency of the liquid-repellent film becomes larger.

[0077] Although the coating conditions for Comparative Example 4 are almost the same as those for Example 2, as shown in Table 1, the ratio of hydrophilic silica beads to thermoplastic resin (29:71 mass%) falls outside the range of the ratios for Examples 1-5 (30:70 mass% to 70:30 mass%). For Comparative Example 4, it is expected that a more superior liquid-repellent film can be obtained by revising the ratio of hydrophilic silica beads to thermoplastic resin so that the proportion of rectangular cells with a void area ratio of 20-80% is 80% or more, particularly by bringing it within the range of 30:70 mass% to 70:30 mass%.

[0078] Furthermore, the coating conditions for Comparative Example 5 were almost the same as those for Example 2, but the amount of topcoat layer applied (1.24 g / m²) was different. 2 ) is the coating amount (0.5~1.2g / m²) of Examples 1-5. 2 ) falls outside the range. In particular, for Comparative Example 5, this application amount is 0.5~1.2g / m 2 By positioning it within this range, it is expected that a more superior liquid-repellent film can be obtained.

[0079] <Evaluation of Uniform Dispersion of Hydrophilic Silica Beads> In the liquid-repellent film according to the present invention, it is assumed that the large-diameter particles (hydrophilic silica beads) constituting the base coat layer are uniformly dispersed on the substrate. For example, it is possible to determine whether the hydrophilic silica beads are uniformly dispersed based on the degree of variation (standard deviation) of the void area ratio of the nine rectangular squares shown in Table 3. As a guideline, if the standard deviation is 25% (preferably 20%) or less, it can be evaluated that the hydrophilic silica beads are dispersed almost uniformly. The standard deviations of Examples 1-5 and Comparative Examples 1-4 are all 25% or less, and it is judged that the uniform dispersion of the hydrophilic silica beads in all of them meets the criteria.

[0080] In Comparative Examples 1-4, based on the standard deviation mentioned above, the hydrophilic silica beads can be evaluated as being dispersed almost uniformly. However, the reason for the low evaluation of liquid repellency is that the proportion of rectangular cells with a void area ratio of 20-80% does not meet the standard (80% or more). [Explanation of symbols]

[0081] 2 Base material 4. Base coat layer 6. Top coat layer 8. Hydrophilic silica beads (large-diameter particles of metal oxide with surface hydrophilicity) 10 Liquid repellent film 12 Thermoplastic resin 14. Hydrophilic silica nanoparticles (small-diameter particles of metal oxides with surface hydrophilicity) 16 Resins having liquid-repellent properties

Claims

1. A method for manufacturing a liquid-repellent film having a laminated structure of a base coat layer and a top coat layer, Large-diameter particles of surface-hydrophilic metal oxide are fixed onto a substrate with a thermoplastic resin to form the base coat layer as a large uneven structure. Small-diameter particles of surface-hydrophilic metal oxides are fixed onto the base coat layer with a resin having liquid-repellent portions, thereby forming the top coat layer as a small uneven structure. The arithmetic mean roughness (Ra) of the surface of the liquid-repellent film is measured to fall within the numerical range of 0.5 to 2.0 μm. The surface of the liquid-repellent film is divided into multiple rectangular squares, each with a length and width that is 5 to 20 times the average particle size of the large-diameter particles. The void area ratio, which indicates the percentage of the area in each rectangular square where no protrusions are formed by the large-diameter particles, is measured. The number of rectangular squares in which the measured value of the void area ratio falls within the range of 20 to 80% is 80% or more of the total number of squares. A method for producing a liquid-repellent film, characterized by the above.

2. When forming the base coat layer, the measured value of the arithmetic mean roughness (Ra) falls within the numerical range of 0.5 to 2.0 μm, and The number of rectangular squares in which the measured value of the void area ratio falls within the numerical range of 20 to 80% shall be 80% or more of the total number of squares. A method for producing a liquid-repellent film according to claim 1, characterized by determining the blending ratio of the large-diameter particles and the thermoplastic resin and the amount to be applied.

3. A liquid-repellent film having a laminated structure of a base coat layer and a top coat layer, The base coat layer comprises large-diameter particles of surface-hydrophilic metal oxide and a thermoplastic resin, wherein the large-diameter particles are fixed on the substrate by the thermoplastic resin to form a large uneven structure. The top coat layer comprises small-diameter particles of surface-hydrophilic metal oxide and a resin having liquid-repellent portions, wherein the small-diameter particles are fixed on the base coat layer by the resin having liquid-repellent portions, forming a small uneven structure. The measured arithmetic mean roughness (Ra) of the surface of the liquid-repellent film falls within the numerical range of 0.5 to 2.0 μm. The surface of the liquid-repellent film is divided into multiple rectangular squares, each with a length and width 5 to 20 times the average particle size of the large-diameter particles. The void area ratio, which indicates the percentage of the area in each rectangular square where no protrusions are formed by the large-diameter particles, is measured. The number of rectangular squares in which the measured value of the void area ratio falls within the range of 20 to 80% is 80% or more of the total number of squares. A liquid-repellent film characterized by the following features.

4. The liquid-repellent film according to claim 3, characterized in that the average of the measured values ​​of the void area ratio falls within the numerical range of 10 to 70% by mass.

5. The liquid-repellent film according to claim 3 or 4, characterized in that the ratio of the content of the large-diameter particles to the thermoplastic resin in the base coat layer is 30:70% by mass to 70:30% by mass.

6. The ratio of the content of the small-diameter particles to the resin having the liquid-repellent portion in the top coat layer is 40:60% by mass to 80:20% by mass. The amount of the topcoat layer applied is 0.5 to 1.2 g / m². ２ A liquid-repellent film according to any one of claims 3 to 5, characterized in that it is such.

7. The liquid-repellent film according to any one of claims 3 to 6, characterized in that the minimum particle size of the large-diameter particles in the base coat layer is greater than the maximum particle size of the small-diameter particles in the top coat layer.

8. A packaging material characterized in that a liquid-repellent film according to any one of claims 3 to 7 is applied to its surface.

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