Method for manufacturing a film and film

Abstract

A method for manufacturing a film, comprising: a step of preparing a tape-like base material film; and a step of imparting a knurling composition to both end portions in a width direction of a surface of the tape-like base material film, and then drying or curing the same to form knurling portions, the knurling portions including a plurality of convex portions arranged in the width direction of the base material film, the volume of the convex portions on the width direction end portion side of the base material film being smaller than the volume of the convex portions on the width direction central portion side.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a membrane and to a membrane. Background Technology

[0002] Resin films, primarily composed of cyclic olefin resins and (meth)acrylic resins, are used as optical films, such as polarizing film, due to their excellent transparency and dimensional stability. From the perspective of operability and manufacturing efficiency, optical films are typically stored or transported in rolls.

[0003] If the film roll is significantly deformed, adhered to each other, or damaged when stored or transported in a wound state, the quality of the film will be reduced. This will increase the amount of waste in the polarizer manufacturing process and the time required for quality inspection, leading to an increase in the product price.

[0004] To suppress quality degradation caused by deformation of such film rolls, an embossing process, known as embossing, is typically performed at both ends of the film in the width direction (see, for example, Patent Document 1). On the other hand, the embossed portions formed by the embossing process are prone to flattening, and sometimes cannot adequately suppress the adhesion between the films.

[0005] In contrast, it is also known to form knurled portions at both ends of a substrate film in the width direction by a coating method (see, for example, Patent Document 2).

[0006] Figure 4A This is a top view of a membrane from the past. Figure 4B yes Figure 4A The cross-sectional view of line 4B-4B. (See diagram below.) Figure 4A and Figure 4B As shown in Patent Document 2, a method is disclosed in which a knurling solution is applied in strips to both ends of a substrate film 1 in the width direction, and then dried to form a knurled portion 2. In this way, the knurled portion 2 formed by coating has higher strength and is less prone to flattening compared to the uneven structure formed by embossing, thus effectively suppressing the adhesion between films.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2016-89110

[0010] Patent Document 2: Japanese Patent Application Publication No. 2012-206312 Summary of the Invention

[0011] The technical problem that the invention aims to solve

[0012] However, in the formation of the knurled portion based on the coating method as shown in Patent Document 2, when the knurling solution coated on the film is dried, due to the drying shrinkage force, the ends of the film in the width direction are prone to bending from the knurled portion, which easily leads to curling (see reference). Figure 5 If such curling occurs, not only will it be impossible to wind the film, but even if it is wound, the ends of the film that are bent during transport are prone to breakage.

[0013] The present invention was made in view of the above circumstances, and its object is to provide a method for manufacturing a film and a film capable of suppressing curling caused by shrinkage force during the formation of the knurling portion of the coating.

[0014] means of solving technical problems

[0015] The aforementioned technical problem can be solved by the following configuration.

[0016] The method for manufacturing the membrane of the present invention includes: a step of preparing a strip-shaped substrate membrane; and a step of applying a knurling composition to both ends of the surface of the strip-shaped substrate membrane in the width direction, and then drying or curing it to form a knurled portion, wherein the knurled portion includes a plurality of protrusions arranged along the width direction of the substrate membrane, and the volume of the protrusions at the ends in the width direction of the substrate membrane is smaller than the volume of the protrusions at the center in the width direction.

[0017] The membrane of the present invention includes a substrate membrane and knurled portions disposed at both ends of the surface of the substrate membrane in the width direction. The knurled portions include a plurality of protrusions disposed in the width direction of the substrate membrane. The volume of the protrusions at the ends in the width direction of the substrate membrane is smaller than the volume of the protrusions at the center in the width direction.

[0018] Invention Effects

[0019] According to the present invention, a method for manufacturing a film and a film capable of suppressing curling caused by shrinkage force during the formation of the knurling portion of the coating are provided, and capable of stable winding are also provided. Attached Figure Description

[0020] [Figure 1] Figure 1A This is a top view of the membrane in this embodiment. Figure 1B yes Figure 1A 1B-1B line cross-section diagram.

[0021] [Figure 2] Figure 2A yes Figure 1A Enlarged top view of the dashed line portion. Figure 2B yes Figure 2A 2B-2B line cross-section diagram.

[0022] [Figure 3] Figure 3A and Figure 3B It means Figure 2BPartial cross-sectional view of the deformed example.

[0023] [Figure 4] Figure 4A This is a top view of a membrane from the past. Figure 4B yes Figure 4A 4B-4B line cross-sectional view.

[0024] [ Figure 5 ] Figure 5 This is a partial three-dimensional diagram showing the state of curl formation in a conventional membrane. Detailed Implementation

[0025] The reason for curling at the end of the substrate film 11 during the coating of the knurling composition is not yet clear, but is speculated as follows.

[0026] That is, when the knurling composition applied to the surface of the substrate film 11 dries or cures, the shrinkage force caused by the drying or curing of the knurling composition is transmitted to the substrate film 11, making it prone to deformation. In particular, the ends of the substrate film 11 are more prone to deformation than the central portion (the portion with less weight and higher degree of freedom), therefore it is considered that the ends of the substrate film 11 may curl towards the side to which the knurling composition is applied (see reference). Figure 5 ).

[0027] In this invention, 1) the knurling composition is formed into multiple islands (protrusions) in the width direction of the substrate film, and 2) the volume (preferably height) of these multiple protrusions is distributed; specifically, the volume (preferably height) of the protrusions at the ends in the width direction of the substrate film is smaller than the volume of the protrusions at the center in the width direction. This reduces the contact area between the substrate film and the protrusions, and makes the shrinkage force generated at the ends in the width direction less than the shrinkage force generated at the center in the width direction. This suppresses curling at the ends of the substrate film.

[0028] Furthermore, when transporting a thin substrate film with a low modulus of elasticity, compressive forces (buckling stress) are easily generated in the width direction of the substrate film, which easily leads to wrinkles in the central portion of the width direction. In contrast, by distributing the heights of the multiple protrusions in the width direction of the substrate film as described above, an expansion effect (expansion effect) can be achieved, thereby further suppressing wrinkles caused by buckling stress. The configuration of the present invention will be described below.

[0029] 1. Membrane manufacturing methods

[0030] Figure 1A This is a top view of the strip-shaped membrane 10 of this embodiment. Figure 1B yes Figure 1A 1B-1B line cross-section diagram. Figure 2A yes Figure 1AThe enlarged top view of the dashed section 2A. Figure 2B yes Figure 1B Enlarged cross-sectional view of the knurled part 12. Figure 3A and Figure 3B It means Figure 2B A partial cross-sectional view of a modified example. It should be noted that... Figure 1B In 2B to 3B, the cross-sectional lines of the cross sections are omitted.

[0031] The method for manufacturing the membrane of the present invention includes: 1) a step of preparing a strip-shaped substrate membrane 11; and 2) a step of applying a knurling composition to both ends of the surface of the strip-shaped substrate membrane 11 in the width direction, and then drying or curing it to form a knurled portion 12.

[0032] 1) Regarding the process of preparing substrate film 11

[0033] First, a strip-shaped substrate film 11 is prepared. The substrate film 11 is not particularly limited, but is preferably a resin film used in optical films, etc. The substrate film 11 will be described below.

[0034] The substrate film 11 can be manufactured by any method, for example, by casting a resin composition containing a thermoplastic resin and then curing it. The casting of the resin composition can be carried out by melt casting or solution casting. From the viewpoint of being able to use high molecular weight resins, the casting of the resin composition is preferably carried out by solution casting.

[0035] That is, the substrate film 11 can be obtained by the following steps: obtaining a dopant (resin composition); drying and peeling the obtained dopant onto a support to obtain a film; and drying and stretching the obtained film.

[0036] (Preparation of dopants)

[0037] A resin composition is prepared by dissolving a thermoplastic resin in a solvent.

[0038] The solvent used includes organic solvents (good solvents) capable of dissolving thermoplastic resins. Examples of good solvents include chlorinated organic solvents such as dichloromethane; and non-chlorinated organic solvents such as methyl acetate, ethyl acetate, acetone, tetrahydrofuran, cyclopentanone, and toluene. Among these, dichloromethane, cyclopentanone, and toluene are preferred from the viewpoint of readily dissolving cycloolefin resins.

[0039] The solvent used may further include undesirable solvents. Examples of undesirable solvents include straight-chain or branched aliphatic alcohols with 1 to 4 carbon atoms. When the proportion of alcohol in the dopant increases, the film is prone to gelation and easy to peel off from the metal support. Examples of straight-chain or branched aliphatic alcohols with 1 to 4 carbon atoms include methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, and tert-butanol. Among these, methanol and ethanol are preferred from the viewpoint of stability and drying properties.

[0040] (cast)

[0041] Next, the obtained resin composition is cast onto a support. The casting of the resin composition can be carried out from the casting mold. After the solvent in the resin composition cast onto the support is moderately evaporated (dried), it is peeled off from the support to obtain a film.

[0042] (Drying and stretching)

[0043] Then, the resulting film is dried. Drying can be carried out while stretching as needed.

[0044] Stretching can be performed according to the required optical properties, preferably along at least one direction, but it can also be performed along two mutually orthogonal directions (e.g., biaxial stretching of the film in the width direction (TD direction) and the transport direction (MD direction) orthogonal to it).

[0045] From the viewpoint of using it, for example, as a retardation film, the stretching ratio can be set to 1.01 to 2 times. The stretching ratio is defined as (the magnitude of the stretching direction of the film after stretching) / (the magnitude of the stretching direction of the film before stretching). It should be noted that when performing biaxial stretching, the stretching ratios are preferably set to the aforementioned values ​​for both the TD and MD directions. It should also be noted that the in-plane slow axis direction of the film (the direction with the highest in-plane refractive index) is usually the direction with the highest stretching ratio.

[0046] When the glass transition temperature of the resin is set to Tg, the drying temperature (stretching temperature) during stretching is preferably (Tg-65)℃ to (Tg+60)℃, more preferably (Tg-50)℃ to (Tg+50)℃. Above a certain stretching temperature, the solvent readily evaporates to a moderate degree, thus making it easy to adjust the stretching tension to an appropriate range. Below a certain temperature, the solvent does not evaporate excessively, thus minimizing damage to the stretchability.

[0047] From the viewpoint of further reducing the amount of residual solvent, it is preferable to further dry the film obtained after stretching (post-drying). For example, it is preferable to further dry the film obtained after stretching while conveying it with rollers or the like (under a certain tension).

[0048] When the glass transition temperature of the resin is set to Tg, the drying temperature is preferably (Tg-30) to (Tg+30)℃, more preferably (Tg-20) to Tg℃. When the drying temperature is above a certain value, the evaporation rate of the solvent in the stretched film is easily increased, thus improving the drying efficiency. When the drying temperature is below a certain value, deformation caused by the elongation of the film is easily suppressed.

[0049] The thickness of the substrate film 11 is not particularly limited, but is preferably 5 to 40 μm, more preferably 10 to 40 μm, and even more preferably 15 to 40 μm.

[0050] The length of the substrate film 11 is not particularly limited, but is preferably 2000-15000m, more preferably 3000-12000m. The width of the substrate film 11 is not particularly limited, but is preferably 950-3000mm.

[0051] 2) Regarding the process of forming the knurled part

[0052] Next, after applying (casting) a knurling composition to both ends of the surface of the obtained strip substrate film 11 in the width direction, it is dried or cured to form a knurled portion 12.

[0053] (Knurling section 12)

[0054] The knurled portion 12 includes a plurality of protrusions 13 (13-1, 13-2 and 13-3) arranged along the width direction of the substrate film 11 on the surface of the substrate film 11. There is no particular limitation on the number of the plurality of protrusions 13 arranged along the width direction as long as there are two or more, for example, two to ten, preferably three to five.

[0055] The vertices of the plurality of protrusions 13 disposed in the width direction of the substrate film 11 are preferably arranged along the width direction of the substrate film 11 (the straight line connecting the vertices of the plurality of protrusions 13 to each other is substantially parallel to the width direction of the substrate film 11). The substantially parallel includes a range of 0 ± 15°.

[0056] In the cross-section along the width direction of the substrate film 11 and passing through the plurality of protrusions 13, the shape of the protrusions 13 is not particularly limited; they can be quadrilaterals, triangles, or circular segments. An arc is a shape formed by connecting the two ends of a circular or elliptical arc with a straight line; examples include semicircles and semi-ellipses. In this embodiment, the shape of the protrusions 13 in the cross-section is quadrilateral (see reference). Figure 1B and Figure 2B ).

[0057] Furthermore, among the plurality of protrusions 13 arranged in the width direction of the substrate film 11, the volume of the protrusion 13 at the end side in the width direction (preferably the protrusion 13-3 closest to the end in the width direction) is smaller than the volume of the protrusion 13 at the center side in the width direction (preferably the protrusion 13-1 closest to the center in the width direction). As a result, the shrinkage force generated at the end side in the width direction during drying can be less than the shrinkage force generated at the center side in the width direction, and curling of the ends of the substrate film 11 can be suppressed.

[0058] The volume of the plurality of protrusions 13 can be adjusted by the area or height of the protrusions 13 (when viewed from above). From the viewpoint of easily adjusting the support of the protrusions 13 after winding, it is preferable to adjust the height of the protrusions 13. That is, the height of the protrusions 13 on the width-direction end side of the substrate film 11 (preferably the protrusions 13-3 closest to the width-direction end) is preferably lower than the height of the protrusions 13 on the width-direction center side (preferably the protrusions 13-1 closest to the width-direction center) (see reference). Figure 1B and Figure 2B The height of the protrusion 13 refers to the height (maximum height) from the surface of the substrate film 11 to the apex of the protrusion 13.

[0059] The height of the plurality of protrusions 13 preferably decreases along the width direction of the substrate film 11 as it approaches the end of the substrate film 11 (see reference). Figure 2B This is because it can not only sufficiently suppress curling of the substrate film 11 during the coating process to form the knurled portion 12, but also suppress wrinkles caused by buckling stress. The height of the plurality of protrusions 13 can decrease linearly or curvilinearly along the width direction of the substrate film 11 as it approaches the end of the substrate film 11. From the viewpoint of easily suppressing curling at the end of the substrate film 11, it is preferable for the height to decrease linearly (see reference). Figure 2B ).

[0060] That is, in a cross section along the width direction of the substrate film 11 and passing through a plurality of protrusions 13, relative to the straight line L connecting the vertex of the protrusion 13 (e.g., protrusion 13-1) closest to the center of the width direction of the substrate film 11 and the vertex of the protrusion 13 (e.g., protrusion 13-3) closest to the end of the width direction, the vertex of one or more protrusions 13 (e.g., protrusion 13-2) located between them can be on the straight line L (refer to...). Figure 2B On the surface, (as long as the height of the protrusion 13 decreases as it approaches the end in the width direction of the substrate film 11) it may not be on a straight line L (refer to...). Figure 3A and Figure 3B From the viewpoint of easily suppressing curling at the ends of the substrate film 11, the apex of one or more protrusions 13 (e.g., protrusion 13-2) located therein is preferably located on a straight line L (see reference). Figure 2BFurthermore, when the convex portion 13 has a top surface, the midpoint of the top surface of the convex portion 13 in the X direction is taken as the vertex.

[0061] In a cross-section along the width direction of the substrate film 11 and passing through the plurality of protrusions 13, the slope of the straight line L formed by connecting the vertex of the protrusion 13-3 closest to the end of the substrate film 11 in the width direction with the vertex of the protrusion 13-1 closest to the center of the width direction also depends on the height of the protrusion 13-1, and is preferably 5×10. -5 ~3×10 -3 mm / mm, or 8×10 -5 ~9×10 -4 mm / mm (refer to Figure 2B ).

[0062] The height distribution of the multiple protrusions 13 can be determined using a laser microscope. For example, a KEYENCE Laser Microscope VK-X1000 can be used. Specifically, the measurement can be performed according to the following steps.

[0063] 1) For a length direction of 100 mm of the substrate film 11, the height of the protrusion 13 (13-1) closest to the center of the width direction of the substrate film 11 and the height of the protrusion 13 (13-3) closest to the end of the width direction are measured respectively.

[0064] 2) Based on the average height of the protrusion 13 (13-1) closest to the center of the width direction obtained in 1), the average height of the protrusion 13 (13-3) closest to the end of the width direction, and the position of the substrate film 11 in the width direction, the slope of the straight line L is calculated.

[0065] The height (t) of the protrusion 13 is not particularly limited, but is preferably 1% to 30% of the thickness of the substrate film 11, more preferably 2% to 10%. Specifically, the height of the protrusion 13 closest to the center in the width direction (e.g., protrusion 13-1) can be set to 1.0 to 15 μm; the height of the protrusion 13 closest to the end in the width direction (e.g., protrusion 13-3) can be set to 0.2 to 0.8 μm. The height of the protrusion 13 at each location can be obtained by averaging the values ​​measured using the same method as described in 1).

[0066] The height of the protrusion 13 can be adjusted by the amount of the knurling composition applied (droplet amount), the viscosity of the knurling composition, the resin concentration, the surface treatment of the substrate film 11, etc. For example, when the knurling composition is applied using a dispenser or the like, if the amount applied (droplet amount) is increased, or the viscosity or resin concentration of the knurling composition is increased, the height of the protrusion 13 can be increased.

[0067] The average spacing (px) of the plurality of protrusions 13 in the width direction of the substrate film 11 is not particularly limited, but is preferably 500 to 5000 μm, and more preferably 100 to 3000 μm (see reference). Figure 2A If the average spacing px is 500 μm or more, the gap between adjacent protrusions 13 is moderately large, so the shrinkage force of the knurling composition is less likely to be concentrated, making it easier to suppress the curling of the substrate film 11. If the average spacing px is less than 5000 μm, the gap between adjacent protrusions 13 is not too large, so the support of the protrusions 13 is less likely to be damaged, and contact (adhesion) between the films is less likely to occur. The average spacing py of the plurality of protrusions 13 in the length direction of the substrate film 11 is not particularly limited, but is preferably 500 to 2000 μm (see reference). Figure 2A ).

[0068] The average spacing px (or py) of the multiple protrusions 13 can be obtained as follows: for a length direction of 100mm of the substrate film 11, the minimum spacing (or the minimum spacing in the length direction (Y direction)) between the multiple protrusions 13 in the width direction (X direction) of the substrate film 11 is measured and used as its average value.

[0069] (Knurling composition)

[0070] The knurling composition can be a solution containing a thermoplastic resin and a solvent, or a curable composition containing a curing compound and a curing agent. In this embodiment, the knurling composition is a solution containing a thermoplastic resin and a solvent.

[0071] The thermoplastic resin included in the knurling composition may be the same thermoplastic resin that constitutes the substrate film 11, preferably a cycloolefin resin or a (meth)acrylic resin.

[0072] The thermoplastic resin included in the knurling composition may be the same as or different from the thermoplastic resin constituting the substrate film. The weight-average molecular weight (Mw) of the thermoplastic resin included in the knurling composition is preferably the same as or lower than that of the thermoplastic resin constituting the substrate film. For example, the Mw of the thermoplastic resin included in the knurling composition is preferably between 100,000 and 1,000,000. If the Mw is within this range, the protrusion 13 has moderate elasticity and is therefore easily and moderately flattened by winding pressure.

[0073] The solvent included in the knurling composition comprises an organic solvent (good solvent) capable of dissolving thermoplastic resin. The good solvent may be the same good solvent used in the manufacture of the substrate film 11.

[0074] In the solution casting method, the concentration of the thermoplastic resin (resin concentration) in the knurling composition is preferably lower than the resin concentration of the dopant used to obtain the substrate film 11, and preferably less than 50% by mass of the resin concentration of the dopant. Specifically, the resin concentration of the knurling composition is preferably 1 to 10% by mass, more preferably 3 to 7% by mass. By adjusting the resin concentration of the knurling resin composition, the height of the protrusion 13 can be adjusted.

[0075] (Assigned)

[0076] The knurling composition can be applied by any method, such as by a dispenser or inkjet printing.

[0077] The temperature of the knurling composition applied during knurling is, for example, 10°C to 30°C, preferably room temperature (23°C).

[0078] (dry)

[0079] The knurling composition can be dried by any method, such as hot air drying, heating drying using electromagnetic waves (e.g., heating drying using an infrared (IR) heater), etc.

[0080] There are no particular limitations on the drying temperature, but a higher temperature is preferred. Specifically, regarding the drying temperature, when the glass transition temperature of the thermoplastic resin contained in the knurling composition is set as Tg, it is preferably carried out at 40 to (Tg-20) °C, more preferably at 80 to (Tg-10) °C. More specifically, it is preferably 40 °C to 120 °C, more preferably 80 °C to 100 °C.

[0081] The resulting strip-shaped membrane 10 can be wound into a roll along its length.

[0082] 3) Regarding the winding process

[0083] The obtained substrate film 11 is wound along the length direction (orthogonal to the width direction) of the film 10 using a winding machine. Thus, a film roll formed by winding the strip-shaped film 10 around a core can be obtained.

[0084] There are no particular restrictions on the winding method; it can be the constant torque method, the constant tension method, the taper tension method, etc.

[0085] 2. Membrane

[0086] The film 10 of this embodiment is obtained by the film manufacturing method described above, and includes a substrate film 11 and knurled portions 12 disposed (formed by coating) on ​​both ends of its surface in the width direction. As described above, the knurled portions 12 include a plurality of protrusions 13 disposed along the width direction of the substrate film 11 on the surface of the substrate film 11.

[0087] When this film 10 is used, the knurled portion 12 is removed, and it is used as an optical film for display devices such as liquid crystal display devices and organic EL display devices. Examples of optical films include polarizer protective films (including phase retardation films, brightness enhancement films, etc.), transparent substrate films, and light diffusion films. Among these, film 10 is preferably used as a polarizer protective film.

[0088] The structure of the substrate film 11 will be described below.

[0089] (Substrate film 11)

[0090] As described above, the substrate film 11 can be a resin film that can be used as an optical film. The resin film contains a thermoplastic resin.

[0091] The thermoplastic resin contained in the resin film is not particularly limited as long as it is suitable for optical films. Examples include cyclic olefin resins, (meth)acrylic resins, polyimide, cellulose esters, polyester, polycarbonate, etc. Among these, cyclic olefin resins, (meth)acrylic resins, and cellulose esters are preferred from the viewpoint of having good transparency, and cyclic olefin resins and (meth)acrylic resins are more preferred from the viewpoint of having low moisture absorption (high dimensional stability).

[0092] (Cyclic olefin resins)

[0093] Cycloolefin resins are polymers containing structural units derived from monomers having a norbornene structure (norbornene monomers). Norbornene monomers are represented by the following formula (A).

[0094] [Chemical Formula 1]

[0095] Formula (A)

[0096]

[0097] R in equation (A) 1 ~R 4 These represent hydrogen atoms, halogen atoms, hydrocarbon groups, or polar groups, respectively.

[0098] Examples of halogen atoms include fluorine atoms, chlorine atoms, etc.

[0099] The hydrocarbon group is a hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 4, and more preferably 1 or 2. Examples of hydrocarbon groups include alkyl groups such as methyl, ethyl, propyl, and butyl. The hydrocarbon group may further have a divalent linking group containing an oxygen atom, nitrogen atom, sulfur atom, or silicon atom (e.g., carbonyl, imino, ether bond, silyl ether bond, thioether bond, etc.).

[0100] Examples of polar groups include carboxyl, hydroxyl, alkoxy, alkoxycarbonyl, allyloxycarbonyl, amino, amide, and those linked via methylene groups (-(CH2)). n - (n is an integer greater than or equal to 1) and groups to which these groups are bonded. Among them, alkoxycarbonyl and aryloxycarbonyl are preferred, and alkoxycarbonyl is more preferred.

[0101] Among them, R is preferred. 1 ~R 4 At least one of the components is a polar group. Cycloolefin resins containing structural units derived from norbornene monomers having polar groups are readily soluble in solvents, for example, when film is formed by solution casting, and thus readily increase the glass transition temperature of the resulting film. On the other hand, in melt casting, cycloolefin resins that do not contain structural units derived from norbornene monomers having polar groups may be used.

[0102] In addition, R 1 ~R 4 In the middle, R 1 and R 2 These two (or R) 3 and R 4 Both of these can also be hydrogen atoms.

[0103] In formula (A), p represents an integer greater than or equal to 0, preferably 0 or 1. m represents an integer from 0 to 2, and from the viewpoint of improving the heat resistance of the optical film, it is preferably 1 to 2.

[0104] Examples of norbornene monomers with polar groups shown in formula (A) include the following monomers.

[0105] [Chemical Formula 2]

[0106]

[0107] Examples of norbornene monomers that do not have polar groups include the following monomers.

[0108] [Chemical Formula 3]

[0109]

[0110] The content of structural units derived from norbornene monomers can be 50 mol% to 100 mol% relative to all structural units constituting cyclic olefin resins.

[0111] Cycloolefin resins may further comprise structural units derived from other monomers capable of copolymerizing with structural units derived from norbornene monomers. Examples of other copolymerizable monomers include (when the norbornene monomer has a polar group) norbornene monomers without polar groups, cyclobutene, cyclopentene, cycloheptene, dicyclopentadiene, and other cycloolefin monomers that do not have a norbornene skeleton.

[0112] The weight-average molecular weight (Mw) of cyclic olefin resins is not particularly limited, but is preferably 20,000 to 300,000, more preferably 30,000 to 250,000, and even more preferably 40,000 to 200,000. When the Mw of the cyclic olefin resin is within the above range, the mechanical properties of the film can be improved without impairing its processability.

[0113] The molecular weight (Mw) of cyclic olefin resins can be determined by gel permeation chromatography (GPC) using polystyrene as a conversion factor. Specifically, it can be determined using a Tosoh HLC8220 GPC and a column (Tosoh TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL in series).

[0114] The glass transition temperature (Tg) of cycloolefin resins is generally preferably above 110°C, more preferably 110–350°C, and even more preferably 120–250°C. When the Tg of cycloolefin resins is above 110°C, sufficient heat resistance is easily obtained, and when it is below 350°C, the thermal degradation of cycloolefin resins during molding and processing can be suppressed.

[0115] Tg can be determined using DSC (Differential Scanning Colorimetry) according to the methods in JIS K7121-2012 or ASTM D3418-82.

[0116] ((meth)acrylic resins)

[0117] (Meth)acrylic resins are preferably polymers containing structural units derived from methyl methacrylate. The polymer may further contain structural units derived from monomers capable of copolymerizing with methyl methacrylate.

[0118] Examples of other monomers that can copolymerize with methyl methacrylate include: alkyl methacrylates with 1 to 18 carbon atoms other than methyl methacrylate, such as 2-ethylhexyl methacrylate; α,β-unsaturated acids such as (meth)acrylic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; styrene derivatives such as styrene and α-methylstyrene; maleic anhydride; maleimide derivatives such as maleimide and N-phenylmaleimide; and glutaric anhydride.

[0119] The content of structural units derived from methyl methacrylate is preferably 50% by mass or more, more preferably 70% by mass or more, relative to all structural units constituting the polymer.

[0120] The Mw of the (meth)acrylic resin is preferably 400,000 to 3,000,000, more preferably 500,000 to 2,000,000. When the Mw of the (meth)acrylic resin is within the above range, sufficient mechanical strength can be imparted to the film. The Mw of the (meth)acrylic resin can be determined by the same method as described above.

[0121] The heat resistance (Tg) of (meth)acrylic resins is preferably 90°C or higher, more preferably 100–150°C. When the Tg of (meth)acrylic resins is within this range, the heat resistance of the optical film is easily improved. The Tg of (meth)acrylic resins can be determined by the same method as described above.

[0122] The content of thermoplastic resin relative to the substrate film 11 is preferably 50% by mass or more, and more preferably 70% by mass or more.

[0123] (Other ingredients)

[0124] The substrate film 11 may further contain other components as needed. Examples of other components include rubber particles, matting agents, etc.

[0125] Rubber particles can impart flexibility to the film. The rubber particles are graft copolymers comprising a rubber-like polymer (crosslinked polymer). Examples of rubber-like polymers include butadiene-based crosslinked polymers, (meth)acrylic acid-based crosslinked polymers, and organosiloxane-based crosslinked polymers. Among these, (meth)acrylic acid-based crosslinked polymers are preferred from the viewpoint that they have a small refractive index difference with methacrylic acid resins and are less likely to impair the transparency of the optical film. Acrylic acid-based crosslinked polymers (acrylic rubber-like polymers) are more preferred.

[0126] The matting agent can form unevenness on the surface of the substrate film 11, imparting slipability. The matting agent can be inorganic particles, resin particles, etc. Examples of inorganic particles include microparticles such as silica, titanium dioxide, alumina, zirconium oxide, and calcium carbonate, with silica particles being preferred.

[0127] (physical properties)

[0128] The substrate film 11 can have phase differences Ro and Rt corresponding to its application. For example, the in-plane phase difference Ro of the substrate film 11, measured at a measurement wavelength of 590 nm, 23°C, and 55% RH, preferably satisfies 40 nm ≤ Ro ≤ 60 nm, and the phase difference Rt in the thickness direction preferably satisfies 115 nm ≤ Rt ≤ 145 nm. Such a substrate film 11 is suitable as a phase retardation film, for example, in combination with a VA-type liquid crystal cell. Furthermore, if 0 nm ≤ Ro ≤ 10 nm and -20 nm ≤ Rt ≤ 20 nm, it is suitable as a phase retardation film in combination with an IPS-type liquid crystal cell.

[0129] Ro and Rt are defined by the following formulas respectively.

[0130] Equation (1): Ro=(nx-ny)×d

[0131] Formula (2): Rt=((nx+ny) / 2-nz)×d

[0132] (in the formula,

[0133] nx represents the refractive index of the substrate film 11 in the slow axis direction (the direction with the highest refractive index).

[0134] ny represents the refractive index in the direction orthogonal to the in-plane slow axis of the substrate film 11.

[0135] nz represents the refractive index in the thickness direction of the substrate film 11.

[0136] d represents the thickness (nm) of the substrate film 11.

[0137] The in-plane slow axis of the substrate film 11 can be confirmed by an automatic birefringence meter AXOSCAN (Axo Scan Mueller Matrix Polarimeter: manufactured by AXOMETRICS).

[0138] Ro and Rt can be determined by the following methods.

[0139] 1) The substrate film 11 was conditioned at 23°C and 55%RH for 24 hours. The average refractive index of the substrate film 11 was measured using an Abbe refractometer, and the thickness d was measured using a commercially available micrometer.

[0140] 2) The phase differences Ro and Rt of the conditioned substrate film 11 at a measurement wavelength of 590 nm were measured using an automatic birefringence meter AXOSCAN (Axo Scan Mueller Matrix Polari meter: manufactured by AXOMETRICS) at an environment of 23°C and 55%RH.

[0141] As described above, the substrate film 11 is not formed by embossing or laser irradiation, but by coating to impart the knurled portion 12. Therefore, the substrate film 11 does not have a thin-walled portion formed by heating and pressing with an embossing roller or by melting with laser irradiation. That is, the thickness of the substrate film 11 is constant.

[0142] 3. Variations

[0143] It should be noted that, in the embodiments described, an example is shown where the knurling composition is a solution containing a thermoplastic resin and a solvent, but it is not limited thereto, and may also be a curing composition containing a curing compound and a curing agent.

[0144] The curing compound is not particularly limited and can be a compound with unsaturated double bonds, preferably a (meth)acrylate compound. Examples of (meth)acrylate compounds include: polyester (meth)acrylates, urethane (meth)acrylates, epoxy (meth)acrylates, polyether (meth)acrylates, polyol (meth)acrylates, melamine (meth)acrylates, triazine acrylates, and other acrylic prepolymers or oligomers; ethylene glycol (meth)acrylates, 1,6-hexanediol di(meth)acrylates, trimethylolpropane tri(meth)acrylates, pentaerythritol hexa(meth)acrylates, dipentaerythritol hexa(meth)acrylates, and other polyfunctional acrylate monomers. Furthermore, substances modified with PO, EO, etc., can also be used. The content of the curing compound is not particularly limited and can be, for example, 50-95% by mass relative to the knurling composition.

[0145] As a curing agent, photopolymerization initiators such as anthraquinone, benzoin ether, benzophenone, 4,4'-bis(dimethylamino)benzophenone, 4,4'-bis(trichloromethyl)benzophenone, dibutylphenylphosphine, α,α-diethoxyacetophenone, 2-ethylanthraquinone, benzoin bisphenyl, chlorobenzophenone, benzoin, benzoin methyl ether, benzoin butyl ether, anthraquinone thioxanone, methyl o-benzoylbenzoic acid, and p-dimethylaminoacetophenone can be used. The content of the curing agent, for example, can be set to 5-15% by mass relative to the knurling composition.

[0146] Then, the curable composition is applied to both ends of the surface of the substrate film 11 in the width direction and cured to form the knurled portion 12. The curing can be photocuring or heat curing. When the curable composition is cured, curing shrinkage force is generated, but by setting the distribution of the volume (preferably the height) of the plurality of protrusions 13 as described, the curling of the substrate film 11 caused by curing shrinkage force can be suppressed.

[0147] Furthermore, in the embodiments described, an example of a film obtained by solution casting is shown, but it is not limited to this and may also be a film obtained by melt casting.

[0148] Example

[0149] The present invention will be specifically described below through embodiments, but the present invention is not limited to these embodiments.

[0150] 1. Membrane preparation

[0151] <Preparation of Membrane Roll 1>

[0152] (Preparation of particulate dispersion)

[0153] The following components were mixed in a dissolver for 50 minutes and then dispersed with Manton-Gaulin. Furthermore, after dispersion using a mill to achieve a given particle size for the secondary particles, the mixture was filtered using a FINEMET NF filter manufactured by Nippon Seiki Co., Ltd., to prepare a particulate dispersion.

[0154] R972V (manufactured by AEROSIL, Japan): 4% by mass

[0155] Dichloromethane: 48% by mass

[0156] Ethanol: 48% by mass

[0157] (Preparation of dopants)

[0158] First, dichloromethane was added to the pressurized dissolving tank at a flow rate of 400 kg / min, and ethanol at a flow rate of 20 kg / min. Three minutes after the solvent addition began, the cyclic polyolefin resin was added to the pressurized dissolving tank while stirring. Next, five minutes after the solvent addition began, the particulate additive solution was added, heated to 60°C, and completely dissolved while stirring. The heating temperature was increased from room temperature at a rate of 5°C / min, and after dissolution for 30 minutes, the temperature was decreased at a rate of 3°C / min. The solution was then filtered using Anji Filter Paper No. 244 (filtration accuracy 0.005 mm) manufactured by Anji Filter Paper Co., Ltd., at a flow rate of 300 L / m³. 2 •h, filtration pressure 1.0×10 6 Pa was filtered to prepare dopants with the following composition.

[0159] Cyclic olefin resin G7810 (manufactured by JSR Corporation) (a cyclic olefin resin (COP) containing structural units derived from norbornene monomers as shown in the following formula, Mw: 140,000, Tg: 170°C): 100% by mass

[0160] R972V (manufactured by AEROSIL, Japan): 0.30% by mass

[0161] Dichloromethane: 380% by mass

[0162] Ethanol: 20% by mass

[0163] [Chemical Formula 4]

[0164]

[0165] (Preparation of substrate film)

[0166] Next, the obtained dopant was uniformly cast onto a stainless steel strip support at a temperature of 31°C and a width of 2300 mm using a ring-shaped tape casting device. The temperature of the stainless steel strip was adjusted to 28°C, and the conveying speed of the stainless steel strip was set to 30 m / min. On the stainless steel strip support, the solvent was allowed to evaporate until the residual solvent content in the cast (cast) dopant reached 30% by mass. Then, it was peeled off from the stainless steel strip support with a peel tension of 110 N / m to obtain a film.

[0167] The obtained film was stretched 1.3 times along the conveying direction (MD direction) while being heated to 120°C using a roller method utilizing the difference in circumferential speed of the conveying rollers. Then, it was stretched 1.65 times along the TD direction while being heated to 130°C using a tenter frame method. The obtained film was then conveyed while being heated to 70°C until completely dry, and the ends were cut to obtain a substrate film 1 with a thickness of 20 μm and a width of 2500 mm.

[0168] (Preparation of Knurling Composition)

[0169] As a thermoplastic resin, a cycloolefin resin used in the preparation of the substrate film 1 is dissolved in a solvent at a concentration of 5% by mass to obtain the substrate 1. The solvent used is a mixture of dichloromethane and cyclopentanone, with a mixing ratio of dichloromethane / cyclopentanone = 70 / 30 (mass ratio).

[0170] Next, using the prepared substrate 1 as a reference, the solvent amount (based on the dilution amount of the mixed solvent) was changed to prepare three knurling compositions with different resin concentrations.

[0171] (Form of the knurled part)

[0172] Three different knurling compositions with varying resin concentrations are discontinuously dripped onto both ends of the membrane surface in the width direction using a dispenser (MUSASHI ENGIN EERING SUPER HI JET). This creates three rows of protrusions arranged along the length of the membrane. These rows of protrusions, extending from the center of the membrane towards the ends in the width direction, are designated as rows of protrusion 1, 2, and 3. A knurling composition with a high resin concentration is used in the order of protrusions 1, 2, and 3. The knurled substrate membrane is then wound onto a core in a roll length of 8000 m to obtain membrane roll 1.

[0173] <Preparation of membrane rolls 2-6>

[0174] By adjusting the resin concentration of the knurling composition, the heights of protrusions 1, 2, and 3 are changed as shown in Table 1. In addition, knurling portions are formed at both ends of the surface of the substrate film in the width direction, similar to film roll 1, to obtain film rolls 2 to 6.

[0175] <Preparation of Membrane 7>

[0176] A knurling composition is continuously coated onto both ends of the surface of a substrate film in the width direction using a casting die to form a strip-shaped knurled portion along the length direction of the film. The resulting film is then wound, but curling occurs at the ends, preventing further winding.

[0177] <Preparation of Membrane 8>

[0178] The heights of protrusions 1, 2, and 3 are modified as shown in Table 1. Otherwise, knurling is formed at both ends of the substrate film surface in the width direction, in the same manner as film roll 1. The resulting film is wound, but curling occurs at the ends, preventing further winding.

[0179] <Preparation of Membrane Roll 9>

[0180] The heights of protrusions 1, 2, and 3 are set to be the same, and the areas of protrusions 1, 2, and 3 when viewed from above are changed to the values ​​shown in Table 1. Otherwise, knurling is formed at both ends of the surface of the substrate film in the width direction in the same manner as film roll 1, to obtain film roll 9.

[0181] <Preparation of membrane roll 10>

[0182] The height and (viewed from above) area of ​​protrusions 1, 2 and 3 are made the same. In addition, knurling is formed at both ends of the surface of the substrate film in the width direction in the same manner as film roll 1, to obtain film roll 10.

[0183] <Evaluation>

[0184] The following methods were used to evaluate the physical properties (height and spacing of protrusions), transport adaptability (curling), and roll quality (interlayer contact and deformation over time) of the knurled portions of the obtained membrane rolls 1 to 6, 9 and 10, as well as membranes 7 and 8.

[0185] (1) Height and spacing of the protrusions

[0186] The height of the protrusions and the spacing between multiple protrusions (width and length directions) in the cross-section of the membrane were measured using a laser microscope. A KEYENCE Laser Microscope VK-X1000 was used as the laser microscope. Regarding the height of the protrusions, the heights of the protrusions in a 100mm region along the length direction of the membrane were measured for each column, and their average value was recorded. Regarding the spacing between multiple protrusions, for a 100mm region along the length direction of the membrane, the spacing in both the width and length directions was measured, and their average value was recorded.

[0187] (2) Distribution of knurling height

[0188] The slope obtained by connecting the heights of the protrusions is calculated from the heights of the protrusions (in each column) and the intervals in the width direction of the protrusions obtained by the measurement in (1).

[0189] (3) Transport adaptability (curling)

[0190] In the roller conveying process from the moment the knurling is formed on the substrate film until winding, the curling condition starting from the knurling is visually observed, and the results are evaluated according to the following criteria.

[0191] ○: Enables transport without curling at the ends of the substrate film during transport.

[0192] △: During transport, the frequency of curling at the ends of the substrate film is low, and the curvature is also very small, posing no practical problems.

[0193] ×: The ends of the substrate film are bent and broken due to curling, making continuous delivery impossible.

[0194] (4) Interlayer contact (adhesion)

[0195] The wound film roll was wrapped with two layers of polyethylene sheet and stored for 5 days at 40°C and 80% humidity, with the ends of the roll core supported by a bracket (so that the axis of the roll core is horizontal). Then, the film was pulled out of the roll, and the adhesion (bonding) of the overlapping films was visually observed. Then, the evaluation was carried out based on the following criteria.

[0196] ○: No adhesion, or very little adhesion, no practical problems.

[0197] △: Slightly sticky, but no practical problems.

[0198] ×: The adhesion is so obvious that it is immediately apparent.

[0199] (5) Winding deformation

[0200] The wound film roll was wrapped with two layers of polyethylene sheet and, with the ends of the roll core supported by a bracket (so that the axis of the roll core is horizontal), stored at 40°C and 80% humidity for 5 days. Then, the polyethylene sheet was opened, and a lit fluorescent tube was used to reflect the light onto the surface of the film roll to observe its deformation or minor irregularities. The evaluation was then based on the following criteria.

[0201] ○: The fluorescent light appears slightly bent at 0 or 1 degrees, which is not a problem.

[0202] △: There are only two places where the fluorescent lamp appears slightly bent, so it doesn't pose any practical problems.

[0203] ×: There are areas where the fluorescent light is noticeably bent, creating a mottled effect; this indicates a problem.

[0204] The evaluation results of membrane rolls 1 to 6, 9 and 10, as well as membrane rolls 7 and 8, are shown in Table 1.

[0205] [Table 1]

[0206]

[0207] As shown in Table 1, it can be seen that membrane rolls 1-6 and 9 can all suppress the formation of curl. In addition, it can be seen that the curl quality of the obtained membrane rolls is also good.

[0208] In particular, it can be observed that the slope of the straight line connecting the vertex of convex part 1 and the vertex of convex part 3 is 5 × 10. -5 ~3×10 -4 Within the range of mm / mm, it can effectively suppress curling and adhesion (comparison of film rolls 1-6).

[0209] In contrast, it can be observed that film roll 7, which has continuous knurled sections, exhibits significant curling and cannot be wound. Consequently, the quality of the roll cannot be evaluated. Furthermore, it can be observed that film roll 8, whose heights of protrusions 1, 2, and 3 are set opposite to those of film rolls 1 to 6, also exhibits curling and cannot be wound.

[0210] <Preparation of membrane rolls 11 to 14>

[0211] The heights of protrusions 1, 2 and 3, and the spacing between the protrusions are changed as shown in Table 2. Otherwise, knurling is formed at both ends of the surface of the substrate film in the width direction in the same manner as film roll 1, to obtain film rolls 11 to 14.

[0212] <Evaluation>

[0213] The physical properties (height and spacing of protrusions), transport adaptability (curling), and roll quality (interlayer contact and deformation over time) of the knurled portions of the obtained membrane rolls 11 to 14 were evaluated in the same manner as described above. The results are shown in Table 2.

[0214] [Table 2]

[0215]

[0216] As shown in Table 2, it can be found that by setting the spacing of the protrusions in the width direction to more than 500 μm, curling can be further suppressed, and by setting the spacing of the protrusions in the width direction to less than 5000 μm, the quality of the roll is less likely to be damaged (comparison of film rolls 4 and 11-14).

[0217] <Preparation of membrane rolls 15 to 19>

[0218] As shown in Table 3, the concentration of the knurling composition is changed. Otherwise, knurling portions are formed at both ends of the surface of the substrate film 1 in the width direction, similar to film roll 1, to obtain film rolls 15 to 19.

[0219] <Preparation of membrane roll 20>

[0220] (Preparation of substrate film 2)

[0221] The cyclic olefin resin G7810 (COP) was replaced with (meth)acrylic resin (Acr) (PMMA, Mw: 800,000), and the substrate film 2 was obtained in the same manner as the substrate film 1.

[0222] (Preparation of Knurling Composition)

[0223] As a thermoplastic resin, an acrylic resin used in the preparation of the substrate film 2 is dissolved in a solvent at a concentration of 5% by mass to obtain the substrate 2. The solvent used is a mixture of dichloromethane and cyclopentanone, with a mixing ratio of dichloromethane / cyclopentanone = 70 / 30 (mass ratio).

[0224] Next, using the prepared substrate 2 as a reference, the solvent amount (based on the dilution amount of the mixed solvent) was changed to prepare three knurling compositions with different resin concentrations.

[0225] (The formation of knurled texture)

[0226] In addition to using the three knurling compositions with different resin concentrations prepared above, film roll 20 was obtained in the same manner as film roll 1.

[0227] <Preparation of membrane roll 21>

[0228] (Preparation of Knurling Composition)

[0229] Mix the following components to prepare substrate 3.

[0230] Dipentaerythritol hexaacrylate (DPHA, manufactured by Nippon Kayaku): 100 parts by weight

[0231] Methyl ethyl ketone: 113 parts by weight

[0232] Photopolymerization initiator (IRGACURE 907, manufactured by Ciba-Geigy): 3 parts by weight

[0233] Next, using the prepared substrate 3 as a reference, the solvent amount (based on the dilution amount of the mixed solvent) was changed to prepare three knurling compositions with different resin concentrations.

[0234] (The formation of knurled texture)

[0235] After coating with three knurling compositions of different resin concentrations prepared therefrom, the mixture was cured by irradiation with ultraviolet light. Otherwise, film roll 21 was obtained in the same manner as film roll 20.

[0236] <Evaluation>

[0237] The physical properties (height and spacing of protrusions), transport adaptability (curling), and roll quality (interlayer contact and deformation over time) of the knurled portions of membrane rolls 15 to 21 were evaluated in the same manner as described above. Furthermore, continuous stability was evaluated using the following methods.

[0238] (6) Continuous conveying

[0239] Regarding the knurling formed by coating along the length direction, the height t of the protrusion is measured every 1000 pieces using method (1), for a total of 1000 measurements of the height t of the protrusion. The standard deviation of the obtained height t of the protrusion is calculated, and the result is evaluated according to the following criteria.

[0240] ○: σ is below 0.1μm

[0241] △: σ exceeds 0.1μm and is less than 0.2μm

[0242] ×: σ exceeds 0.2μm

[0243] Furthermore, for membrane rolls 3 and 9, the wrinkles caused by buckling stress were further evaluated using the following method.

[0244] (7) Wrinkles caused by bending

[0245] In the roller conveying process from the moment the knurling is formed on the substrate film until it is wound, the formation of wrinkles in the substrate film as it is supported by the conveying rollers is visually observed, and the results are evaluated according to the following criteria.

[0246] ○: No wrinkles were produced, and it is capable of conveying.

[0247] △: Slight wrinkles may occur, but it is not a problem in practical use.

[0248] ×: Due to wrinkles, bending occurs near the center of the width, sometimes resulting in breakage.

[0249] The evaluation results of membrane rolls 15 to 21 are shown in Table 3, and the evaluation results of membrane rolls 3 and 9 are shown in Table 4.

[0250] [Table 3]

[0251]

[0252] [Table 4]

[0253]

[0254] As shown in Table 3, it can be seen that by keeping the resin concentration of the knurling composition within a given range, continuous stability is further improved, and roll quality (deformation over time) can also be further reduced (comparison of film rolls 15 to 19). Furthermore, it can be seen that curling can be well suppressed not only in the case of COP films but also in the case of acrylic resin films (comparison of films 15 and 20). Moreover, it can be seen that even when the knurling composition is replaced with a UV-curable composition, curling caused by curing shrinkage can be suppressed (comparison of film rolls 20 and 21).

[0255] As shown in Table 4, it can be found that by making the height of protrusion 3 lower than the height of protrusion 1, wrinkles caused by buckling stress can be further suppressed (comparison of membrane rolls 3 and 9).

[0256] This application claims priority based on Japanese Patent Application No. 2021-107944, filed on June 29, 2021. All contents set forth in that application are incorporated herein by reference.

[0257] Industrial applicability

[0258] According to the present invention, a method for manufacturing a film and a film capable of suppressing curling caused by shrinkage force during the formation of the knurled portion of the coating are provided, and a film capable of stable winding is provided.

[0259] Symbol Explanation

[0260] 10 Film (film roll)

[0261] 11 Base film

[0262] 12 Knurled portion

[0263] 13, 13-1, 13-2, 13-3 Protrusion

Claims

1. A method for manufacturing a membrane, comprising: The process of preparing strip-shaped substrate films; and The process of forming a knurled portion by applying a knurling composition to both ends of the surface of the strip substrate film in the width direction and then drying or curing it. The knurled portion includes a plurality of protrusions arranged along the width direction of the substrate film. The volume of the protrusion at the end of the substrate film in the width direction is smaller than the volume of the protrusion at the center in the width direction. The height of the protrusion closest to the center of the width direction of the substrate film is 1.0~15μm, and the height of the protrusion closest to the end of the width direction is 0.2~0.8μm. The average spacing between the plurality of protrusions in the width direction of the substrate film is 500~5000μm. The height of the plurality of protrusions decreases as they approach the width-direction end of the substrate film. In a cross-section along the width direction of the substrate film and passing through the plurality of protrusions, the slope of the straight line connecting the vertex of the protrusion closest to the end side in the width direction to the vertex of the protrusion closest to the center side in the width direction is 5 × 10⁻⁶. -5 ~3×10 -3 mm / mm.

2. The method for manufacturing a membrane according to claim 1, wherein, The knurling composition comprises a thermoplastic resin and a solvent.

3. The method for manufacturing a membrane according to claim 2, wherein, The thermoplastic resin is a cyclic olefin resin or a (meth)acrylic resin.

4. The method for manufacturing a membrane according to claim 2, wherein, The concentration of the thermoplastic resin is 1 to 10% by mass relative to the knurling composition.

5. The method for manufacturing a membrane according to claim 1, wherein, The substrate film is a resin film.

6. The method for manufacturing a membrane according to claim 1, wherein, The thickness of the substrate film is 10~40μm.

7. A film comprising a substrate film and knurled portions disposed at both ends in the width direction of the surface of the substrate film, wherein, The knurled portion includes a plurality of protrusions arranged along the width direction of the substrate film. The volume of the protrusion at the end of the substrate film in the width direction is smaller than the volume of the protrusion at the center in the width direction. The height of the protrusion closest to the center of the substrate film in the width direction is 1.0~15μm, and the height of the protrusion closest to the end in the width direction is 0.2~0.8μm. The average spacing between the plurality of protrusions in the width direction of the substrate film is 500~5000μm. The height of the plurality of protrusions decreases as they approach the width-direction end of the substrate film. In a cross-section along the width direction of the substrate film and passing through the plurality of protrusions, the slope of the straight line connecting the vertex of the protrusion closest to the end side in the width direction to the vertex of the protrusion closest to the center side in the width direction is 5 × 10⁻⁶. -5 ~3×10 -3 mm / mm.

8. The membrane according to claim 7, wherein, The substrate film is a resin film.

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