JP7707632B2 - Films and Laminates - Google Patents

Description

The present invention relates to a film and a laminate.

Plastic films are generally lightweight, chemically stable, easy to process, flexible and strong, and can be mass-produced, and are used in a wide variety of applications. Applications are diverse, including packaging materials for food and medicine, IV packs, shopping bags, posters, tapes, optical films for LCD televisions, protective films, decorative films, films to be attached to the body, window films to be attached to windows, vinyl greenhouses, building materials, and more. Specific materials include thermoplastic resins such as polyethylene, polypropylene, polystyrene, acrylic polymethyl methacrylate, polycarbonate, polyamide, polyethylene terephthalate, and polybutylene terephthalate, as well as thermosetting resins such as epoxy resin, polyurethane, and polyimide.

The appropriate plastic material is selected depending on the application, and several types of these are sometimes layered to form a laminate. There are also uses in which several plastic materials are mixed in one layer to make up for the shortcomings of a single material. In many cases, the appropriate film material is selected based on heat resistance, mechanical strength, or transparency. However, it is difficult to say that these materials and layer configurations alone can fully achieve both the required physical properties such as heat resistance and mechanical strength and the flexibility to stretch with a light force.

For example, in preparations such as patches and tapes that are applied to the skin to deliver medicinal ingredients into the body, it is required that the medicinal ingredients are not transmitted or transferred to the support film, but materials that meet this requirement have high strength but lack flexibility, meaning that they do not follow the movements of the skin and do not feel good when applied. In another example, polyethylene terephthalate (PET) film is often used as the base film for various films from the perspectives of heat resistance, durability, chemical resistance, mechanical properties, etc., but PET film is strong and cannot be used in applications where it is expected to stretch with light force.

In addition, plastic films generally have the property that when they are stretched in one direction, they shrink in the direction perpendicular to the stretched direction, meaning that their Poisson's ratio is positive. This poses the problem that stretching them in two directions to increase their area requires a stronger force than stretching them in one direction.

For example, when forming a film into a bag and filling it with contents or inflating it with air or other gas, a much larger force is required than when stretching in one direction. As another example, when trying to protect the surface of a curved object, wrinkling occurs when trying to cover it with a flat film, but if the film can be stretched in two directions and expanded three-dimensionally, it can securely cover the curved surface without wrinkling.

Patent Document 1 discloses a technology for a film that can be stretched with a light force regardless of the plastic material, and can be easily stretched in two directions simultaneously. The film has a shape that is a so-called bellows shape, with repeated mountain folds and valley folds, and by making the bellows shape a specific shape in two dimensions rather than one dimension, the bellows shape folded like origami unfolds, allowing the film to be stretched in any direction, and also in a direction perpendicular to the tensile direction. This touts that even films made of materials that meet the required properties such as heat resistance and mechanical strength have the flexibility to be stretched with a light force, and can easily have their area expanded.

JP 2019-089319 A

According to the technology of Patent Document 1, in order for the film to expand in a direction perpendicular to the tensile direction when pulled, it is necessary to transmit force in the perpendicular direction, and in order to do so, it is necessary to change the bellows shape in accordance with the pulling force. However, it was found that if the material is too soft or the film is too thin, the film will not expand due to a change in the bellows shape, but the material itself will stretch, or a certain surface of the film will be distorted, causing a shape change different from the design and resulting in stretching. When this happens, the film will not expand in the perpendicular direction, but will only stretch in the tensile direction, resulting in the problem of no interlocking stretching in the two directions.

The present invention was developed in consideration of these problems, and aims to provide a film that is flexible enough to stretch with a light force and whose area can be easily expanded, even when the film is made of a material that meets the required characteristics, and a laminate that uses the same.

In order to achieve the above object, a representative film of the present invention is a film having a front surface with a bidirectional uneven shape and a back surface with a bidirectional uneven shape corresponding to the bidirectional uneven shape of the front surface, and the object is achieved by satisfying all of the following formulas 1 to 3, where Ef is the tensile modulus of the film, Em is the tensile modulus of the material constituting the film, H is the height of the uneven shape of the film, and T is the thickness of the film.
Formula 1 T<H
Formula 2 Ef < 0.1 × Em
Formula 3 7000[N/m]<Em×T
The tensile modulus Em of the material constituting the film is 1100 MPa to 3300 MPa, and the tensile modulus Ef of the film indicates the tensile modulus in any direction in the plane of the film.

According to the present invention, it is possible to provide a film that is flexible enough to stretch with a light force and whose area can be easily expanded, even when the film is made of a material that meets the required characteristics, and a laminate using the same.
Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments.

FIG. 1 is a perspective view showing an example of the film of the present embodiment. FIG. 2 is a top view of an example of the film of the present embodiment. FIG. 3 is a perspective view showing a portion of the film of this embodiment. FIG. 4 is a cross-sectional view showing a portion of the film of this embodiment. FIG. 5 is a top view (c) and cross-sectional views (a) and (b) showing a part of the film of this embodiment. FIG. 6 is a top view showing a portion of the film of this embodiment. FIG. 7 is a top view showing a portion of the film of this embodiment. FIG. 8 is a perspective view showing a model (enlarged from the actual product) of an example of the film of this embodiment. FIG. 9 is a perspective view showing a model (enlarged from the actual product) of another example of the film of this embodiment. FIG. 10 is a perspective view showing a model (enlarged from the actual product) of another example of the film of this embodiment. FIG. 11 is a perspective view showing a model (enlarged from the actual product) of another example of the film of this embodiment. FIG. 12 is a cross-sectional view showing an example of the film of this embodiment. FIG. 13 is a cross-sectional view showing another example of the film of the present embodiment. FIG. 14 is a top view showing an example of the arrangement of the sections when a plurality of sections are present in the film of this embodiment. FIG. 15 is a top view showing another example of the arrangement of the compartments when a plurality of compartments are present in the film of the present embodiment. FIG. 16 is a cross-sectional view showing an example of a film lamination according to this embodiment. FIG. 17 is a cross-sectional view showing another example of lamination of the film of this embodiment. FIG. 18 is a perspective view showing an embodiment of the film.

The following describes an embodiment of the film according to the present invention with reference to the drawings. Each figure is a schematic view, and the size and shape of each part are appropriately exaggerated to facilitate understanding. Also, to simplify the explanation, the same reference numerals are used for corresponding parts in each figure. The terms front and back used in this specification are used for convenience, and either of the pair of surfaces of the film may be the front or back.

The film 1 of the present invention is a film having an uneven shape 4 on both the front surface 2 and back surface 3, and the front surface 2 and back surface 3 face each other in accordance with the uneven shape 4. In other words, the film has a folded shape like origami. Figure 1 shows a perspective view of an example of film 1, and Figure 2 shows a top view of an example of film 1. In addition, in order to clearly show the folded shape, a perspective view and a cross-sectional view of a portion of an example of film 1 are shown in Figures 3 and 4.

In this case, assuming that the tensile modulus of elasticity of the film 1 is Ef, the tensile modulus of elasticity of the material constituting the film 1 is Em, the height of the uneven shape 4 of the film 1 is H, and the thickness of the film 1 is T,
All of the following formulas 1 to 3 are satisfied.
Formula 1: T<H
Formula 2: Ef < 0.1 × Em
Formula 3: 7000[N/m]<Em×T
The tensile modulus Ef of the film 1 indicates the tensile modulus in any direction along a plane (a plane parallel to the x and y directions in FIG. 1) when the film 1 is placed on the plane. In other words, Equation 2 is satisfied in any direction on the plane.

Here, the tensile modulus Ef of film 1 is the tensile modulus defined in JIS K 7161:2014, and the thickness that gives the cross-sectional area of film 1 is given by the sum of the height H of the uneven shape and the film thickness T. In other words, it is the apparent tensile modulus. Furthermore, the tensile modulus Em of the material is the tensile modulus of the film, similarly defined in JIS K 7161:2014 for a flat film without uneven shapes. In this case, the thickness that gives the cross-sectional area of the film is T.

By satisfying formula 1, in other words, by making the height H of the uneven shape exceed the film thickness T, the film 1 does not have any parts that extend straight along the direction in which the uneven shape is repeated. In other words, when the film 1 is cut along the x and y directions in Figure 1 and at a surface at any position in the z direction, the cut surface is not continuous at any position in the z direction, but is discontinuous. Therefore, rather than the material stretching, like origami, the uneven shape 4 can be deformed to allow it to stretch, creating flexibility that allows it to stretch with a light force.

Furthermore, formula 2 indicates that the tensile test force of film 1 is sufficiently smaller than the tensile test force of a normal film made of the same material and without the uneven shape 4. By satisfying formula 2, film 1 first becomes elongated due to the deformation of the uneven shape 4, without depending on the deformation of the material itself. Depending on the uneven shape 4, the film may exhibit anisotropy in its tensile properties, but in this embodiment, formula 2 is satisfied in any direction of the plane on which film 1 is placed.

Furthermore, Equation 3 expresses the relationship required to transmit the force in the tensile direction to the orthogonal direction. In order to expand in the orthogonal direction as well as the tensile direction, it is necessary to transmit the force in the tensile direction to the orthogonal direction. At this time, it is necessary to develop changes in the tensile direction and the orthogonal direction due to the shape change of the uneven shape 4, but if Equation 3 is not satisfied, when pulled, rather than the shape of the uneven shape 4 changing, the material itself may stretch or one slope of the uneven shape 4 may become distorted. If this happens, the stretching will occur by causing a shape change that differs from the design. In this case, it is not possible to expand in the direction perpendicular to the tensile direction.

As described above, by satisfying formulas 1, 2, and 3, even a film made of a material according to the required characteristics has the flexibility to stretch with a light force due to the change in shape of the uneven shape 4, and can transmit the force in the tensile direction to the perpendicular direction, making it easy to expand the area.

The uneven shape 4 has at least continuous peaks 5 or valleys 6, and the continuous peaks 5 or valleys 6 extend while changing the direction of the ridges.

A portion of the uneven shape 4 is shown in Figure 5. Figures 5(a) and (b) are cross-sectional views, and Figure 5(c) is a top view. In Figure 5(c), the dashed and dotted lines indicate the ridges of the peaks 5 and the dashed lines indicate the ridges of the valleys 6. The dashed and dotted lines are similar in Figures 6 and 7. As shown in Figure 5(c), the ridges of the continuous peaks 5 or valleys 6 that extend in the x direction change direction midway and extend in the y direction. In this way, having a shape that changes direction makes it possible to smoothly change the direction of the force in the tensile direction to a direction perpendicular to the direction.

The change portion that changes the orientation of the ridgeline of the peak portion 5 or the ridgeline of the valley portion 6 may be rounded as shown in FIG. 6(a), may have a mixture of rounded and non-rounded portions as shown in FIG. 6(b), or may be linear as shown in FIG. 6(c). In addition, the change in orientation (the crossing angle between the x and y directions) does not need to be 90°, and can be either an acute angle or an obtuse angle as shown in FIG. 7(a) and (b).

The uneven shape 4 may be formed by arranging the structures shown in Figures 5 to 7. Alternatively, as in Figure 8, the basic shape may be an alternating arrangement of uneven shapes. For example, as in Figure 9, the uneven shapes may be arranged with varying widths, or as in Figure 10, the direction or angle of the ridges may be changed and arranged, or as in Figure 11, the alternating uneven shapes may be arranged inverted. In addition to the above, the above effects can be achieved by arranging the structures shown in Figures 5 to 7, as long as a shape is formed. Note that Figures 8, 9, 10, and 11 are merely schematic diagrams to make the image of the structure easier to understand, and of course do not show the size or detailed structure.

The film thickness T and the uneven shape height H do not need to be uniform within the film 1. For example, as shown in FIG. 12, different values such as T1, T2, and T3 may be used depending on the location of the uneven shape 4. Here, the film thickness Tn at each location indicates the distance between the opposing front surface 2 and back surface 3 as shown in FIG. 12. The film thickness T is expressed as the average value obtained by multiplying the proportion of each location by the thickness at that location. The same is true for the uneven shape height H, which may show different values depending on the location, and the uneven shape height H1 as viewed from the front surface 2 and the uneven shape height H2 as viewed from the back surface 3 may also be different, in which case the uneven shape height H is expressed as the average value.

However, the film thickness Tn at each location is within the range of 0.5T≦Tn≦2T regardless of the location. Preferably, 0.6T≦Tn≦1.5T. The film thickness T is preferably 1 μm or more and 100 μm or less, and more preferably 5 μm or more and 50 μm or less. The uneven shape height Hn is within the range of 0.6H≦Hn≦1.5H regardless of the location or the front and back surfaces, and preferably 0.8H≦Hn≦1.2H. The uneven shape height H is preferably 5 μm or more and 500 μm or less, and more preferably 10 μm or more and 200 μm or less. As described above, the uneven shape height H needs to exceed the film thickness T, and more preferably, the uneven shape height H is more than twice the film thickness T. By being in such a range, it is possible to have a more flexible stretching characteristic.
Furthermore, the pitch of the uneven shape (the distance between adjacent uneven shapes) is preferably 30 μm or more and 1000 μm or less, more preferably 50 μm or more and 500 μm or less, and more preferably 50 μm or more and 200 μm or less. The inclination angle of the uneven shape is preferably 40° or more and 90° or less, more preferably 45° or more and 85° or less, assuming that the case where there is no uneven shape is 0° and the case where it is perpendicular to the normal direction of the film is 90°. This is because it is possible to obtain more flexible stretching properties.

Although the cross-sectional shape of the film has been illustrated as being triangular in the above, this is not limited to a triangular shape. Other examples are shown in FIG. 13. For example, the top of the uneven cross-section may be rounded as shown in FIG. 13(a), or the shape may be a repeating arrangement of arc-shaped convex shapes as shown in FIG. 13(b), or the uneven cross-section may be trapezoidal as shown in FIG. 13(c), or the convex shapes may be spaced apart as shown in FIGS. 13(d) and (e), or only a portion of the uneven cross-section may be rounded as shown in FIG. 13(f). Furthermore, these shapes may be combined to combine several shapes in one film 1.

The tensile modulus Ef of film 1 should be 1 MPa < Ef < 100 MPa. If it is less than 1 MPa, it will stretch with a light force, making it difficult to handle. If it exceeds 100 MPa, a large force is required to stretch it, and it is difficult to say that it can be stretched to a practical use.

The tensile modulus Em of the material that constitutes film 1 should preferably be 800 MPa < Em < 3000 MPa. If it is within this range, it is possible to produce a film with an appropriate thickness that satisfies formula 3 and has other appropriate physical properties.

The ratio S (surface area ratio) of the surface area of film 1 including the uneven shape 4 to the area of film 1 when viewed from above (in the z direction) is preferably 1.2 or more and 2 or less. The larger the surface area ratio S, the greater the possibility of increasing the amount of elongation due to the change in shape of the uneven shape 4, which is preferable. Therefore, if the surface area ratio S is less than 1.2, a sufficient amount of elongation cannot be ensured. On the other hand, if the surface area ratio S is greater than 2, it becomes difficult to produce the uneven shape 4.

The film 1 may also be constructed by arranging multiple regions (called sections 1A) having the above-mentioned characteristics. That is, as shown in FIG. 14, the film 1 may have multiple sections 1A in the film plane, and each section 1A may have the characteristics of the film 1. In this case, there may not be an uneven shape 4 between adjacent sections 1A. In this way, the film 1 as a whole does not stretch when pulled and can be handled without problems, but by cutting out section 1A or a part of section 1A before use, it is possible to obtain a film that stretches with a light force in any direction.

The sections 1A may be arranged continuously, or may be arranged with gaps between them as shown in FIG. 15. Furthermore, the structure of each section 1A does not need to be the same, and each section may include multiple different structures, for example, as shown in FIGS. 8, 9, 10, and 11.

The film 1 of this embodiment has the effect of stretching even when a force is applied in the film normal direction, and therefore has the effect of high impact resistance. Furthermore, even if the film 1 cannot stretch due to the surrounding environment when a force is applied in the film normal direction, the uneven shape 4 is crushed, and the impact absorption is also high.

In addition, by using a transparent material, it is possible to give the material a certain degree of transparency despite the uneven shape 4. This is because the front surface 2 and back surface 3 are essentially facing each other with the uneven shape 4 in between. However, since the uneven shape 4 exists, it is difficult to make it completely transparent, but conversely, it is possible to give it design value by making it semi-transparent or opaque.

Furthermore, bending rigidity can be improved in both directions. Bending rigidity is determined by the integral of the product of the second moment of area and Young's modulus. Film 1 of this embodiment can increase this second moment of area compared to a normal film with the same amount of resin, and therefore can increase bending rigidity.

Furthermore, the uneven shape 4 also has the effect of increasing the surface area of the film. The surface area of the film affects the speed and amount of release and adsorption of materials kneaded into the film. In addition, increasing the surface area can also improve the efficiency of the exchange of particles, ions, temperature, electricity, etc. through the film.

(Film materials)
The material of the film 1 is preferably a thermoplastic resin. Examples of the material include, but are not limited to, polyethylene, polypropylene, polystyrene, polymethyl methacrylate, ethylene-vinyl acetate copolymer, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyvinylidene chloride, polyacrylonitrile, polylactic acid, cyclic polyolefin, polycarbonate, polyamide, polyethylene terephthalate, polybutylene terephthalate, polyacetal, and derivatives thereof. In addition, there is no problem even if the material is a hardened resin or a metal. These materials may be used alone, or a combination of a plurality of these materials may be used. In addition, a multilayer structure (also called a laminate) in which a plurality of layers are superimposed may be formed.

(Film manufacturing method)
As a manufacturing method, for example, a method using a hot press or a method using an extrusion molding can be used.

In the hot pressing method, the formed film can be produced by passing it between a pair of heated rolls with concave and convex shapes on the surface, or a pair of heated flat presses. In this case, it is important that the concave and convex shapes on the top and bottom are precisely aligned so that the front and back of the pressed film have a structure with continuous peaks and valleys.
In the extrusion molding method, in the cooling step for forming the molten resin extruded from the T-die into a film, a concave-convex structure can be formed by cooling the film while applying nip pressure using a pair of cooling rolls and nip rolls with concave-convex surfaces corresponding to the concave-convex structure. It goes without saying that in this method too, precise alignment of the concave-convex shapes of the cooling roll and nip roll is related to the film performance.

In another method using extrusion molding, a film having a multi-layer structure of two or more layers can be obtained by co-extrusion of a plurality of different resins by a feed block method or a multi-manifold method using a plurality of extruders. In the cooling process for forming the film, a cooling roll having a surface with a concavo-convex shape corresponding to the concavo-convex shape and a nip roll without concavo-convex shapes are used to cool the film while applying nip pressure, so that a concavo-convex structure can be formed on the film surface in contact with the cooling roll. Furthermore, when the height of the concavo-convex shape is large compared to the film thickness of the first resin layer in contact with the cooling roll, a concavo-convex structure is also added to the interface between the first resin layer and the adjacent second resin layer. Therefore, by peeling the second resin layer from the multi-layer film after cooling, a first resin layer having a concavo-convex shape on both sides, i.e., film 1, can be obtained.
Any method for adding a concave-convex structure, such as injection molding, can be selected, and the method is not particularly limited.

(Laminate)
The film 1 may be a single layer, or a laminate may be formed by laminating a plurality of films 1 by increasing the layer structure. For example, the first layer may be a gas barrier layer or a drug non-adsorbing layer, and the second layer may be an inexpensive resin layer (bulk-increasing layer), a high rigidity layer, or a layer that complements the physical properties of the first layer. Of course, the film may be laminated with three or more layers. Also, as shown in FIG. 16, a laminate may be formed by laminating a functional layer 7 such as a vapor deposition layer, a hard coat layer, an anti-reflection layer, or a printed layer by dry coating or wet coating in a post-process on the film 1. At this time, the layer coated on the surface can also be stretched according to the film 1. This is because the layer stretches due to the change in shape of the uneven shape 4. That is, for example, by applying it to a vapor deposition barrier film, it is possible to provide extensibility in two directions while suppressing the destruction of the vapor deposition layer. Examples of vapor deposition films include metal oxides such as alumina and silica, and metals such as aluminum, gold, silver, and copper. Of course, the functions to be expressed are not limited to barrier properties, but also include light-shielding properties, design properties, electrical conductivity, and the like, and are not limited to these functions.

As another example, as shown in Figure 17, a laminate can be formed by laminating another layer (or film) 8 to the film 1. In this case, the film 1 and the other layer 8 can be in contact only partially as shown in Figure 17(a), or they can be in contact over the entire uneven shape 4 as shown in Figure 17(c). It may also be somewhere in between as shown in Figure 17(b). In this case, it is preferable that the other layer 8 is made of a soft material so as not to impair the flexibility of the film 1.

(Film usage)
For example, film 1 or a laminate using it can be used as a barrier film, a packaging material, a backing film for patches such as poultices, a backing film for tapes that are attached to the skin or objects, a decorative film, an optical film, a protective film, a substrate for wearables, various film substrates, a design film, and the like, but the uses are not limited to these.

In the case of a patch support film, which is an example of application, resistance to drugs and additives contained in the patch, non-adsorption or barrier properties are required, and stretchability is also desirable. All of these requirements can be met by adding an uneven shape to a material with high chemical resistance, non-adsorption and barrier properties, and making the film 1 stretchable with a light force. Examples of materials with high chemical resistance, non-adsorption and barrier properties include cyclic polyolefin, ethylene-vinyl alcohol copolymer and polyethylene terephthalate. Furthermore, the stress applied to the film 1 at the same elongation is also smaller, making it less likely that the user will feel an uncomfortable pull when stretching.

Although the above describes examples of the present invention, it goes without saying that the present invention is not limited to the above-described embodiments. Furthermore, it is optional to use the above-described embodiments in combination.

The following describes in detail the examples created by the inventors, but the present invention is not limited to the following examples.

Comparative Examples 1, 2, and 3 were flat films without unevenness 4, and the materials constituting the films were a polyethylene terephthalate (PET) resin "Bellpet EFG70" manufactured by Bell Polyester Products Co., Ltd., an ethylene-vinyl alcohol copolymer (EVOH) resin "Soarnol D4403" manufactured by Mitsubishi Chemical Corporation, and a polymethyl methacrylate (PMMA) resin "Acrypet VH000" manufactured by Mitsubishi Chemical Corporation, respectively. The film thickness T was 10 μm in all cases. In the following, PET resin, EVOH resin, and PMMA resin are all intended to refer to the same resin.

Comparative examples 4 and 5 have a shape in which the uneven shape 4 extends in only one direction as shown in Figure 3, and its cross section is a row of triangles with rounded apexes as shown in Figure 13(a), with the peak-valley apex angle being 90°. The uneven shape height H was 60 μm for both, and PET resin was used as the material. The film thickness T was 15 μm and 3 μm, respectively.

In Comparative Examples 6, 7, 8, 9, and 10, the uneven shape 4 extends in two directions as shown in FIG. 1 or 8, the direction of the ridge line changes in a zigzag pattern, and the cross section is a row of triangles with rounded apexes as shown in FIG. 13(a), with the peak-valley apex angle set to 100° in Comparative Example 6, 90° in Comparative Example 7, and 60° in Comparative Examples 8, 9, and 10. The uneven shape height H was 42 μm when the peak-valley apex angle was 100°, 50 μm when the peak-valley apex angle was 90°, and 80 μm when the peak-valley apex angle was 60°. The film material used was PET resin in Comparative Examples 6 and 8, and EVOH resin in Comparative Examples 7, 9, and 10. The film thickness T was 15 μm, 22 μm, 3 μm, 5 μm, and 3 μm for Comparative Examples 6, 7, 8, 9, and 10, respectively.

Table 1 shows the uneven shape 4, film material, uneven shape height H, and film thickness T of the comparative example.

In Example 1, the uneven shape 4 extends in two directions as shown in FIG. 18, the ridges are straight and do not change direction, and the cross section is a trapezoid as shown in FIG. 13(c). The uneven shape height H is 80 μm, the material is PET resin, and the film thickness T is 15 μm.

In Examples 2 to 11, the uneven shape 4 extends in two directions as shown in FIG. 1 or 8, the direction of the ridge line changes in a zigzag pattern, and the cross section is a row of triangles with rounded apexes as shown in FIG. 13(a). The peak-valley apex angle was 120° in Examples 2 and 3, 100° in Example 4, 90° in Examples 5, 6, and 7, and 60° in Examples 8, 9, 10, and 11. The uneven shape height H was 28 μm when the peak-valley apex angle was 110°, 42 μm when the peak-valley apex angle was 100°, 50 μm when the peak-valley apex angle was 90°, and 80 μm when the peak-valley apex angle was 60°. The film material used was PET resin in Examples 2, 3, 4, 5, 6, 8, and 9, EVOH resin in Examples 7 and 10, and PMMA resin in Example 11. The film thickness T was 8 μm for Examples 2, 4, 6, 8, 10, and 11, 5 μm for Examples 3 and 9, and 15 μm for Examples 5 and 7.

Table 2 shows the uneven shape 4, film material, uneven shape height H, and film thickness T of the example.

A tensile test evaluation was performed to calculate the tensile modulus Em and Ef.

The tensile test evaluation was performed in accordance with JIS K 7161:2014 using a Tensilon universal material testing machine (RTC-1250A) manufactured by A&D Co., Ltd. The sample width was 15 mm, the distance between the chucks was 50 mm, and the tensile speed was 100 mm/min. In order to take into account the anisotropy of the sample, evaluation was performed in five directions, with angles changed by 22.5° from the MD (machine direction) to the TD (transverse direction). The average value of the elastic modulus in the five directions of the samples of Comparative Examples 1, 2, and 3 without the uneven shape 4 was taken as the tensile elastic modulus Em of the material, and the maximum value of the elastic modulus in the five directions of the other examples and comparative examples was taken as the tensile elastic modulus Ef-max. The thickness required to calculate the tensile elastic modulus Ef-max was the sum of the uneven shape height H and the film thickness T, that is, the apparent thickness (H+T).

To evaluate the effect of the present invention, that is, "it has flexibility that allows it to stretch with a light force and can easily expand its area," a push-in test evaluation and a tensile test evaluation were carried out.

The indentation test evaluation was carried out using a texture analyzer (EZ-SX) manufactured by Shimadzu Corporation. The sample was fixed to a metal plate with a hole of 50 mm in diameter, and the center of the hole was pressed with an indenter of 30 mm in diameter, and the indentation distance and indentation force were evaluated. The indentation distance was measured from the position where the indenter touched the sample to zero, until it reached a position of 40 mm, or until the sample broke. The indentation speed was 10 mm/min. As for the indentation judgment, when the indentation force exceeded 10 N when the indentation distance was 5 mm, it was marked as ×, when it was 10 N or less, it was marked as ◯, and when it was 5 N or less, it was marked as ◎.
In addition, at this time, the samples were observed, and those in which neck-in, such as obvious partial stretching, was marked with an X as the neck-in evaluation result, and those in which this was not confirmed were marked with an O.

The tensile test evaluation was carried out using a Tensilon universal material testing machine (RTC-1250A) manufactured by A&D Co., Ltd. The sample width was 15 mm, the distance between chucks was 50 mm, and the tensile speed was 100 mm/min. The sample was stopped when it was stretched by 10%, i.e., 5 mm, and the sample width at that point was evaluated to evaluate whether it had spread in the width direction. At this time, evaluation was carried out in three directions, each at an angle of 45° from the MD direction to the TD direction, and the spread in the width direction was evaluated as follows: if the width had shrunk in even one direction, it was marked with an ×; if there was no significant change in any direction, it was marked with an ◯; if it had spread in all directions, it was marked with an ◎.

As an overall judgment, if any one of the three judgments of pressing judgment, neck-in evaluation, and widthwise spread evaluation was ×, it was marked as ×, if all were ○ or above, it was marked as ○, and in particular, if both the pressing judgment and widthwise spread evaluation, which were marked as ◎, and the neck-in evaluation was also marked as ○, it was marked as ◎.

The evaluation results for the comparative examples and examples are summarized in Tables 3 and 4, respectively.

From Tables 3 and 4, it can be seen that although the uneven shape 4, film material, uneven shape height H, and film thickness T are important parameters, it is not possible to determine whether an effect will be obtained based on these alone. On the other hand, all of the items that satisfy formulas 1, 2, and 3 have a certain degree of effect.

Comparative Examples 1, 2, and 3, which do not satisfy formula 1 (T<H), did not elongate at all, and all were judged as ×. In addition, Comparative Examples 4, 5, 6, and 7, which do not satisfy formula 2 (Ef-max<0.1×Em), all of the neck-in judgments were ×. Comparative Examples 4 and 6 were very difficult to elongate when pressed, and the pressing force exceeded 10 N. Comparative Examples 5 and 7 had a pressing force of 10 N or less, which suggests that the film was quite thin and had been stretched by plastic deformation. Furthermore, Comparative Examples 5, 8, 9, and 10, which do not satisfy formula 3 (7000 [N/m]<Em×T), were judged as × for widthwise spread, meaning that there was no spread. Comparative Example 10 also had an Ef-max below 1 MPa, making it very difficult to handle as a sample in the first place.

In contrast, all of Examples 1 to 11 satisfied formulas 1, 2, and 3, and the evaluation results were good. However, in Example 1, in which the ridges extending in two directions did not change direction, the "widthwise spread" was insufficient, and the "widthwise spread" judgment did not reach ◎, so the overall judgment was ◯. In addition, in Examples 2 and 5, in which Ef-max exceeded 100 MPa, the pressing force was 10 N or less but exceeded 5 N, so it could not be said to be sufficiently soft, and the "pressing" judgment did not reach ◎, so the overall judgment was ◯. In addition, in Examples 2 and 3, in which the surface area ratio S was below 1.2, the pressing force was 10 N or less but exceeded 5 N, so it could not be said to be sufficiently soft, and the "pressing" judgment did not reach ◎, so the overall judgment was ◯. In addition, since the larger the surface area ratio S, the softer the results, an attempt was made to produce a sample with an uneven shape 4 exceeding 2, but it was difficult to produce a film, and it was ultimately not possible to obtain one.

1 Film 2 Surface 3 Back surface 4 Concave-convex shape 5 Peaks 6 Valleys 7 Functional layer 8 Another layer 1A Section H Height of concave-convex shape 4 T Thickness of film 1

Claims (8)

A film having a surface having a two-way uneven shape and a back surface having a two-way uneven shape corresponding to the two-way uneven shape of the surface,
When the tensile modulus of the film is Ef, the tensile modulus of the material constituting the film is Em, the height of the uneven shape of the film is H, and the thickness of the film is T,
A film characterized by satisfying all of the following formulas 1 to 3.
Formula 1 T<H
Formula 2 Ef < 0.1 × Em
Formula 3 7000[N/m]<Em×T
The tensile modulus Em of the material constituting the film is 1100 MPa to 3300 MPa, and the tensile modulus Ef of the film indicates the tensile modulus in any direction in the plane of the film. The film according to claim 1, characterized in that 1 MPa < Ef < 100 MPa. The uneven shape has at least continuous peaks or valleys,
The continuous peaks or valleys extend while changing the direction of the ridge line.
3. The film according to claim 1 or 2. a ratio S of a surface area of the film including the concave and convex shapes to an area of the film when viewed from above is 1.2 or more and 2 or less;
The film according to any one of claims 1 to 3. forming the uneven shape in the compartment;
A plurality of the sections are arranged, and there is no uneven shape between the adjacent sections.
The film according to any one of claims 1 to 4. A laminate comprising a functional layer laminated on at least one surface of the film described in any one of claims 1 to 5. A laminate comprising multiple films according to any one of claims 1 to 5. A laminate comprising the film described in any one of claims 1 to 5 and another film laminated thereon.