Film manufacturing method and film

Abstract

This film manufacturing method comprises: a step for preparing a band-like base material film; and a step for applying a composition for knurling to both width-direction end sections of the surface of the band-like base material film, and then forming a knurling section by drying and curing, wherein the knurling section includes a plurality of protruding sections disposed in the width direction of the base material film, and the volume of protruding sections of the base material film on the width-direction end section side is smaller than the volume of protruding sections on the width-direction central side.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing a film and to a film. [Background technology]

[0002] Resin films, primarily composed of cycloolefin resins and (meth)acrylic resins, possess excellent transparency and dimensional stability, and are therefore used as optical films, such as protective films for polarizing plates. Optical films are typically stored or transported in roll form for ease of handling and manufacturing efficiency.

[0003] When film rolls are stored or transported in a rolled state, significant deformation of the rolls, sticking of films together, or damage can lead to a decrease in film quality. This increases waste in the polarizing plate manufacturing process and the labor costs for quality inspections, ultimately resulting in higher product prices.

[0004] To suppress quality degradation due to deformation of film rolls, a textured surface called embossing is usually applied to both ends of the film in the width direction (see, for example, Patent Document 1). However, the embossed areas formed by embossing are easily crushed, and sometimes the adhesion between films cannot be sufficiently suppressed.

[0005] In contrast, a method is known in which knurled sections are formed on both ends in the width direction of the base film by a coating method (see, for example, Patent Document 2).

[0006] Figure 4A is a plan view of a conventional film, and Figure 4B is a cross-sectional view taken along line 4B-4B in Figure 4A. As shown in Figures 4A and 4B, Patent Document 2 discloses a method for forming knurled portions 2 by applying a knurling solution in a strip to both ends in the width direction of a base film 1 and then drying it. The knurled portions 2 formed by this method have higher strength and are less prone to crushing compared to the uneven structure formed by embossing, and are said to effectively suppress adhesion between films. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2016-89110 [Patent Document 2] Japanese Patent Publication No. 2012-206312 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, in the formation of knurled sections by the coating method shown in Patent Document 2, when the knurling solution applied to the film is dried, the drying shrinkage force makes it easy for the widthwise edges of the film to bend starting from the knurled sections, resulting in curling (see Figure 5). When such curling occurs, not only is it impossible to wind up the film, but even if it can be wound up, the bent edges of the film are prone to breaking during transport.

[0009] The present invention has been made in view of the above circumstances, and aims to provide a method for manufacturing a film and a film that can suppress the occurrence of curl due to shrinkage force when applying and forming the knurled portion, and enable stable winding. [Means for solving the problem]

[0010] The above problem can be solved by the following configuration.

[0011] The present invention provides a method for manufacturing a film, comprising the steps of preparing a strip-shaped base film and applying a knurling composition to both ends of the surface of the strip-shaped base film in the width direction, followed by drying or curing to form knurled portions, wherein the knurled portions include a plurality of protrusions arranged in the width direction of the base film, and the volume of the protrusions on the width direction end side of the base film is smaller than the volume of the protrusions on the width direction center side.

[0012] The film of the present invention is a film including a base film and nailing portions disposed at both end portions in the width direction on the surface of the base film, wherein the nailing portions include a plurality of convex portions disposed in the width direction of the base film, and the volume of the convex portions on the end side in the width direction of the base film is smaller than the volume of the convex portions on the central side in the width direction.

Effect of the Invention

[0013] According to the present invention, it is possible to provide a method for manufacturing a film and a film that can suppress the occurrence of curl due to shrinkage force when forming a nailing portion by coating and enable stable winding.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1A is a plan view of the film according to the present embodiment, and FIG. 1B is a cross-sectional view taken along line 1B-1B of FIG. 1A. [Figure 2] FIG. 2A is a partially enlarged plan view of the dotted line portion of FIG. 1A, and FIG. 2B is a cross-sectional view taken along line 2B-2B of FIG. 2A. [Figure 3] FIGS. 3A and B are partial cross-sectional views showing a modified example of FIG. 2B. [Figure 4] FIG. 4A is a plan view of a conventional film, and FIG. 4B is a cross-sectional view taken along line 4B-4B of FIG. 4A. [Figure 5] FIG. 5 is a partial perspective view showing the occurrence state of curl in a conventional film.

[0015] When applying and forming the nailing composition, the reason for the occurrence of curl at the end of the base film 11 is not clear, but it is presumed as follows.

[0016] In other words, when the knurling composition applied to the surface of the base film 11 is dried or cured, the force of shrinkage caused by the drying or curing of the knurling composition is transmitted to the base film 11, making it easily deformable. In particular, the edges of the base film 11 are more easily deformed than the central part (because they have less weight and a greater degree of freedom), so it is thought that curls occur at the edges of the base film 11, causing them to bend towards the side to which the knurling composition was applied (see Figure 5).

[0017] In contrast, the present invention involves 1) forming a knurling composition in a plurality of island-like (protrusions) in the width direction of the base film, and further, 2) providing a distribution in the volume (preferably height) of these protrusions; specifically, making the volume (preferably height) of the protrusions on the width direction end side of the base film smaller than the volume of the protrusions on the width direction center side. This reduces the contact area between the base film and the protrusions, while making the shrinkage force generated on the width direction end side smaller than the shrinkage force generated on the width direction center side. This suppresses curling at the edges of the base film.

[0018] Furthermore, when transporting a thin base film with a low modulus of elasticity, compressive forces (buckling stress) tend to be generated in the width direction of the base film, which can easily cause wrinkles in the center of the width direction. In contrast, by providing the above-described distribution of the heights of multiple protrusions in the width direction of the base film, an expanding effect (expander effect) can be generated that expands the base film in the width direction. This further suppresses wrinkles caused by buckling stress. The configuration of the present invention will be described below.

[0019] 1. Film manufacturing method Figure 1A is a plan view of the strip-shaped film 10 according to this embodiment, and Figure 1B is a cross-sectional view taken along the line 1B-1B in Figure 1A. Figure 2A is a partially enlarged plan view of the dotted line portion 2A in Figure 1A, and Figure 2B is a partially enlarged cross-sectional view of the knurled portion 12 in Figure 1B. Figures 3A and 3B are partial cross-sectional views showing modified examples of Figure 2B. Note that hatching of the cross-sections is omitted in Figures 1B and 2B-3B.

[0020] The present invention provides a method for manufacturing a film, comprising: 1) preparing a strip-shaped base film 11; and 2) applying a knurling composition to both ends of the surface of the strip-shaped base film 11 in the width direction, and then drying or curing it to form knurled portions 12.

[0021] 1) Regarding the process of preparing the base film 11 First, a strip-shaped base film 11 is prepared. The base film 11 is not particularly limited, but is preferably a resin film used for optical films and the like. The base film 11 will be described later.

[0022] The base film 11 can be manufactured by any method, for example, by casting a resin composition containing a thermoplastic resin and then solidifying it. The casting of the resin composition may be carried out by a molten casting method or a solution casting method. In particular, from the viewpoint of being able to use high molecular weight resins, the casting of the resin composition is preferably carried out by a solution casting method.

[0023] In other words, the base film 11 can be obtained through the steps of obtaining a dope (resin composition), casting the obtained dope onto a support, drying and peeling it to obtain a film-like material, and drying and stretching the obtained film-like material.

[0024] (Preparation of dope) A thermoplastic resin is dissolved in a solvent to prepare a resin composition.

[0025] The solvent used includes organic solvents (good solvents) capable of dissolving thermoplastic resins. Examples of good solvents include chlorinated organic solvents such as methylene chloride, and non-chlorinated organic solvents such as methyl acetate, ethyl acetate, acetone, tetrahydrofuran, cyclopentanone, and toluene. Among these, methylene chloride, cyclopentanone, and toluene are preferred from the viewpoint of easily dissolving cycloolefin resins.

[0026] The solvent used may further contain a poor solvent. Examples of poor solvents include linear or branched aliphatic alcohols having 1 to 4 carbon atoms. When the proportion of alcohol in the dope increases, the film-like material is more likely to gel, and peeling from the metal support is easier. Examples of linear or branched aliphatic alcohols having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Among these, methanol and ethanol are preferred from the viewpoint of stability and drying properties.

[0027] (Ryuen) Next, the obtained resin composition is cast onto a support. The resin composition can be cast by extrusion from a casting die. After the solvent in the resin composition cast onto the support is appropriately evaporated (dried), it is peeled off the support to obtain a film-like material.

[0028] (drying / stretching) Then, the resulting film-like material is dried. Drying may be carried out while stretching the material as needed.

[0029] The stretching may be carried out according to the required optical properties, and it is preferable to stretch in at least one direction, but it may also be stretched in two mutually orthogonal directions (for example, biaxial stretching in the width direction of the film (TD direction) and the transport direction (MD direction) perpendicular to it).

[0030] The stretching ratio can be 1.01 to 2 times, for example, when used as a phase difference film. The stretching ratio is defined as (stretched size of the film after stretching) / (stretched size of the film before stretching). When biaxial stretching is performed, it is preferable to use the above stretching ratio for both the TD direction and the MD direction. The in-plane slow axis direction of the film (the direction in which the refractive index is maximum in the plane) is usually the direction in which the stretching ratio is maximum.

[0031] The drying temperature during stretching (stretching temperature) is preferably (Tg-65)°C to (Tg+60)°C, and more preferably (Tg-50)°C to (Tg+50)°C, where Tg is the glass transition temperature of the resin. If the stretching temperature is above a certain level, the solvent is easily evaporated to an appropriate degree, making it easier to adjust the stretching tension to an appropriate range. If the stretching temperature is below a certain level, the solvent does not evaporate excessively, so the stretchability is less likely to be impaired.

[0032] From the viewpoint of further reducing the amount of residual solvent, it is preferable to further dry (post-dry) the film obtained after stretching. For example, it is preferable to further dry the film obtained after stretching while conveying it with rolls or the like (while applying a certain tension).

[0033] The drying temperature is preferably (Tg-30) to (Tg+30)°C, and more preferably (Tg-20) to Tg°C, where Tg is the glass transition temperature of the resin. If the drying temperature is above a certain level, the rate of solvent evaporation from the stretched film is increased, thus improving drying efficiency. If the drying temperature is below a certain level, deformation due to stretching of the film is suppressed.

[0034] The thickness of the base 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.

[0035] The length of the base film 11 is not particularly limited, but is preferably 2,000 to 15,000 m, and more preferably 3,000 to 12,000 m. The width of the base film 11 is not particularly limited, but is preferably 950 to 3,000 mm.

[0036] 2) Regarding the process of forming the knurled section Next, the knurling composition is applied (cast) to both ends in the width direction of the surface of the obtained strip-shaped base film 11, and then dried or cured to form the knurled portion 12.

[0037] (Knurling section 12) The knurling portion 12 includes a plurality of protrusions 13 (13-1, 13-2, and 13-3) arranged on the surface of the base film 11 in the width direction of the base film 11. The number of the plurality of protrusions 13 arranged in the width direction is not particularly limited as long as it is two or more, but for example, it is 2 to 10, preferably 3 to 5.

[0038] Preferably, the vertices of the multiple protrusions 13 arranged in the width direction of the base film 11 are aligned along the width direction of the base film 11 (the straight line connecting the vertices of the multiple protrusions 13 is substantially parallel to the width direction of the base film 11). "Substantially parallel" includes a range of 0 ± 15°.

[0039] In a cross-section of the base film 11 that passes through a plurality of protrusions 13 along the width direction, the shape of the protrusions 13 is not particularly limited and may be rectangular, triangular, or arc-shaped (circular segment). An arc shape is a shape formed by connecting both ends of a circular or elliptical arc with a straight line, and examples include semicircles and semi-ellipses. In this embodiment, the shape of the protrusions 13 in the above cross-section is rectangular (see Figures 1B and 2B).

[0040] Furthermore, among the multiple protrusions 13 arranged in the width direction of the base film 11, the volume of the protrusion 13 on the width direction end side of the base film 11 (preferably the protrusion 13-3 closest to the width direction end) is smaller than the volume of the protrusion 13 on the width direction center side (preferably the protrusion 13-1 closest to the width direction center). As a result, the shrinkage force that occurs on the width direction end side of the base film 11 during drying can be made smaller than the shrinkage force that occurs on the width direction center side, thereby suppressing curling of the edges of the base film 11.

[0041] The volume of the multiple protrusions 13 can be adjusted by the area or height of the protrusions 13 (when viewed from above), but it is preferable to adjust it by the height of the protrusions 13, from the viewpoint of easily adjusting the support provided by the protrusions 13 after winding. That is, it is preferable that the height of the protrusions 13 on the widthwise end side of the base film 11 (preferably the protrusion 13-3 closest to the widthwise end) is lower than the height of the protrusions 13 on the widthwise center side (preferably the protrusion 13-1 closest to the widthwise center) (see Figures 1B and 2B). The height of the protrusions 13 refers to the height from the surface of the base film 11 to the top of the protrusion 13 (maximum height).

[0042] The height of the multiple protrusions 13 preferably decreases along the width direction of the base film 11 as it approaches the edge of the base film 11 (see Figure 2B). This is because it not only sufficiently suppresses curling of the base film 11 when the knurling portion 12 is applied, but also suppresses wrinkles due to buckling stress. The height of the multiple protrusions 13 may decrease linearly or curvilinearly along the width direction of the base film 11 as it approaches the edge of the base film 11, but from the viewpoint of easily suppressing curling at the edge of the base film 11, it is preferable that it decreases linearly (see Figure 2B).

[0043] In other words, in a cross-section of the base film 11 passing through multiple protrusions 13 along the width direction, the vertices of one or more protrusions 13 (e.g., protrusion 13-2) located between the vertex of the protrusion 13 closest to the center of the base film 11 in the width direction (e.g., protrusion 13-1) and the vertex of the protrusion 13 closest to the end in the width direction (e.g., protrusion 13-3) may lie on the line L (see Figure 2B), or (if the height of the protrusion 13 decreases as it approaches the end of the base film 11 in the width direction) may not lie on the line L (see Figures 3A and 3B). In particular, from the viewpoint of making it easier to suppress curling of the ends of the base film 11, it is preferable that the vertices of one or more protrusions 13 (e.g., protrusion 13-2) located between them lie on the line L (see Figure 2B). If the protrusion 13 has a top surface, the midpoint of the top surface of the protrusion 13 in the X direction is considered the vertex.

[0044] In a cross-section of the base film 11 passing through multiple protrusions 13 along the width direction, the inclination of the straight line L connecting the vertex of the protrusion 13-3 closest to the width direction end of the base film 11 and the vertex of the protrusion 13-1 closest to the width direction center depends on the height of the protrusion 13-1, but for example, 5 × 10 -5 ~3×10 -3 It is preferable that the size be mm / mm, and that it be 8 × 10 -5 ~9×10 -4 mm / mm is also acceptable (see Figure 2B).

[0045] The height distribution of the multiple protrusions 13 can be measured using a laser microscope. For example, a Keyence VK-X1000 laser microscope can be used. Specifically, the measurement can be performed using the following procedure. 1) For a 100 mm lengthwise range of the base film 11, measure the height of the protrusion 13(13-1) closest to the center in the widthwise direction of the base film 11, and the height of the protrusion 13(13-3) closest to the end in the widthwise direction. 2) Based on the average height of the protrusion 13(13-1) closest to the center in the width direction, the average height of the protrusion 13(13-3) closest to the end in the width direction, and the position of the base film 11 in the width direction, the slope of the straight line L is calculated.

[0046] The height (t) of the protrusions 13 is not particularly limited, but is preferably 1 to 30% of the thickness of the base film 11, and 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) may be 1.0 to 15 μm; the height of the protrusion 13 closest to the edge in the width direction (e.g., protrusion 13-3) may be 0.2 to 0.8 μm. The height of the protrusions 13 at each position can be determined as the average value of values ​​measured in the same manner as in 1) above.

[0047] The height of the protrusions 13 can be adjusted by the amount of knurling composition applied (droplet volume), the viscosity of the knurling composition, the resin concentration, the surface treatment of the base film 11, etc. For example, when applying the knurling composition with a dispenser, the height of the protrusions 13 can be increased by increasing the amount applied (droplet volume) or by increasing the viscosity or resin concentration of the knurling composition.

[0048] The average spacing px of the multiple protrusions 13 in the width direction of the base film 11 is not particularly limited, but is preferably, for example, 500 to 5000 μm, and more preferably 100 to 3000 μm (see 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 concentrate locally, and the curling of the base film 11 is further suppressed. If the average spacing px is 5000 μm or less, the gap between adjacent protrusions 13 is not too large, so the support provided by the protrusions 13 is less likely to be impaired, and contact (blocking) between films is less likely to occur. The average spacing py of the multiple protrusions 13 in the length direction of the base film 11 is not particularly limited, but is preferably, for example, 500 to 2000 μm (see Figure 2A).

[0049] The average spacing px (or py) of the multiple protrusions 13 can be determined by measuring the minimum spacing between the multiple protrusions 13 in the width direction (X direction) (or the minimum spacing in the length direction (Y direction)) of the base film 11 over a length of 100 mm of the base film 11, and taking the average value of these measurements.

[0050] (Composition for knurling) The knurling composition may be a solution containing a thermoplastic resin and a solvent, or it may be a curable composition containing a curable compound and a curing agent. In this embodiment, the knurling composition is a solution containing a thermoplastic resin and a solvent.

[0051] The thermoplastic resin included in the knurling composition can be the same as the thermoplastic resin that constitutes the base film 11, and is preferably a cycloolefin resin or a (meth)acrylic resin.

[0052] The thermoplastic resin included in the knurling composition may be the same as or different from the thermoplastic resin constituting the base film. The weight-average molecular weight (Mw) of the thermoplastic resin included in the knurling composition is preferably the same as or lower than the weight-average molecular weight (Mw) of the thermoplastic resin constituting the base film. The Mw of the thermoplastic resin included in the knurling composition is preferably, for example, 100,000 to 1,000,000. When Mw is within this range, the protrusions 13 have appropriate elasticity and are easily crushed by winding pressure.

[0053] The solvent contained in the knurling composition includes an organic solvent (good solvent) capable of dissolving thermoplastic resins. The good solvent can be the same as the good solvent used in the manufacture of the base film 11.

[0054] In the solution casting method, the concentration of thermoplastic resin in the knurling composition (resin concentration) is preferably lower than the resin concentration of the dope used to obtain the base film 11, and is preferably 50% by mass or less of the resin concentration of the dope. Specifically, the resin concentration of the knurling composition is preferably 1 to 10% by mass, and more preferably 3 to 7% by mass. The height of the protrusions 13 can be adjusted by adjusting the resin concentration of the knurling resin composition.

[0055] (Grant) The knurling composition can be applied by any method, such as a dispenser or an inkjet method.

[0056] The temperature of the knurling composition during application is, for example, 10 to 30°C, preferably room temperature (23°C).

[0057] (Drying) The knurling composition can be dried by any method, such as hot air drying or heating with electromagnetic waves (e.g., heating with an infrared (IR) heater).

[0058] The drying temperature is not particularly limited, but a high temperature is preferred. Specifically, the drying temperature is preferably 40 to (Tg-20)°C, and more preferably 80 to (Tg-10)°C, where Tg is the glass transition temperature of the thermoplastic resin contained in the knurling composition. Specifically, it is preferably 40 to 120°C, and more preferably 80 to 100°C.

[0059] The resulting strip-shaped film 10 may be wound into a roll along its length.

[0060] 3) Regarding the winding process The obtained base film 11 is wound up using a winding machine in the longitudinal direction of the film 10 (a direction perpendicular to the width direction). This makes it possible to obtain a film roll in which the strip-shaped film 10 is wound up in a roll shape around a winding core.

[0061] The winding method is not particularly limited and can be the constant torque method, constant tension method, tapered tension method, etc.

[0062] 2. Film The film 10 according to this embodiment is obtained by the above-described method for manufacturing the film, and includes a base film 11 and knurled portions 12 arranged (coated) at both ends in the width direction on its surface. As described above, the knurled portions 12 include a plurality of protrusions 13 arranged in the width direction on the surface of the base film 11.

[0063] When in use, the knurled portion 12 of such a film 10 is removed, and it is used as an optical film for a display device such as a liquid crystal display device or an organic EL display device. Examples of optical films include polarizing plate protective films (including phase difference films and brightness enhancement films), transparent substrate films, and light diffusion films. Among these, film 10 is preferably used as a polarizing plate protective film.

[0064] The composition of the base film 11 will be described below.

[0065] (Base film 11) As described above, the base film 11 may be a resin film usable as an optical film. The resin film contains a thermoplastic resin.

[0066] The thermoplastic resin contained in the resin film is not particularly limited as long as it is suitable for optical films, but examples include cycloolefin resins, (meth)acrylic resins, polyimides, cellulose esters, polyesters, and polycarbonates. Among these, cycloolefin resins, (meth)acrylic resins, and cellulose esters are preferred from the viewpoint of having good transparency, and cycloolefin resins and (meth)acrylic resins are more preferred from the viewpoint of having low hygroscopicity (high dimensional stability).

[0067] (Cycloolefin resin) Cycloolefin resins are polymers that contain structural units derived from monomers having a norbornene structure (norbornene monomers). Norbornene monomers are represented by the following formula (A). [ka]

[0068] R in equation (A) 1 ~R 4 These represent a hydrogen atom, a halogen atom, a hydrocarbon group, or a polar group, respectively.

[0069] Examples of halogen atoms include fluorine atoms, chlorine atoms, and the like.

[0070] The hydrocarbon group is a hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms, more preferably 1 or 2 carbon atoms. Examples of the hydrocarbon group include alkyl groups such as methyl group, ethyl group, propyl group, and butyl group. The hydrocarbon group may further have a divalent linking group containing an oxygen atom, a nitrogen atom, a sulfur atom, or a silicon atom (for example, a carbonyl group, an imino group, an ether bond, a silyl ether bond, a thioether bond, etc.).

[0071] Examples of the polar group include a carboxy group, a hydroxy group, an alkoxy group, an alkoxycarbonyl group, an allyloxycarbonyl group, an amino group, an amide group, and a group in which these groups are bonded via a linking group such as a methylene group (-(CH2) n -, n is an integer of 1 or more). Among them, an alkoxycarbonyl group and an aryloxycarbonyl group are preferable, and an alkoxycarbonyl group is more preferable.

[0072] Among them, at least one of R 1 ~R 4 is preferably a polar group. A cycloolefin resin containing a structural unit derived from a norbornene monomer having a polar group is easily dissolved in a solvent and easily increases the glass transition temperature of the obtained film when forming a film by, for example, a solution casting method. On the other hand, in the melt film forming method, a cycloolefin resin not containing a structural unit derived from a norbornene monomer having a polar group may be used.

[0073] Also, both of R 1 ~R 4 may be hydrogen atoms, and both of R 1 and R 2 (or both of R 3 and R 4 ) may be hydrogen atoms.

[0074] In formula (A), p represents an integer greater than or equal to 0, preferably 0 or 1. m represents an integer between 0 and 2, preferably 1 or 2 from the viewpoint of improving the heat resistance of the optical film.

[0075] Examples of norbornene monomers represented by formula (A) that have a polar group include the following: [ka]

[0076] Examples of norbornene monomers that do not have polar groups include the following: [ka]

[0077] The content of structural units derived from norbornene monomers can be 50 to 100 mol% relative to the total structural units constituting the cycloolefin resin.

[0078] Cycloolefin resins may further contain structural units derived from norbornene monomers and structural units derived from other copolymerizable monomers. Examples of other copolymerizable monomers include norbornene monomers without polar groups (if the norbornene monomer has polar groups) and cycloolefin monomers without a norbornene skeleton, such as cyclobutene, cyclopentene, cycloheptene, and dicyclopentadiene.

[0079] The weight-average molecular weight Mw of the cycloolefin resin is not particularly limited, but is preferably between 20,000 and 300,000, more preferably between 30,000 and 250,000, and even more preferably between 40,000 and 200,000. When the Mw of the cycloolefin resin is within the above range, the mechanical properties of the film can be improved without impairing moldability.

[0080] The Mw of cycloolefin resins can be measured in polystyrene equivalent by gel permeation chromatography (GPC). Specifically, it can be measured using a Tosoh HLC8220GPC and columns (Tosoh TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL in series).

[0081] The glass transition temperature (Tg) of cycloolefin resins is usually preferably 110°C or higher, more preferably 110 to 350°C, and even more preferably 120 to 250°C. A Tg of 110°C or higher makes it easier to obtain sufficient heat resistance, while a Tg of 350°C or lower can suppress thermal degradation of the cycloolefin resin during molding.

[0082] Tg can be measured using DSC (Differential Scanning Colorimetry) in accordance with JIS K 7121-2012 or ASTM D 3418-82.

[0083] ((meth)acrylic resin) The (meth)acrylic resin is preferably a polymer containing structural units derived from methyl methacrylate. The polymer may further contain structural units derived from monomers copolymerizable with methyl methacrylate.

[0084] Other monomers copolymerizable with methyl methacrylate include alkyl(meth)acrylates 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; styrenes such as styrene and α-methylstyrene; maleic anhydride; maleimides such as maleimide and N-phenylmaleimide; and glutaric anhydride.

[0085] The content of structural units derived from methyl methacrylate is preferably 50% by mass or more, and more preferably 70% by mass or more, relative to the total structural units constituting the polymer.

[0086] The Mw of the (meth)acrylic resin is preferably between 400,000 and 3,000,000, and more preferably between 500,000 and 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 measured by the same method as described above.

[0087] The Tg of the (meth)acrylic resin is preferably 90°C or higher, and more preferably 100 to 150°C. Having the Tg of the (meth)acrylic resin within this range makes it easier to improve the heat resistance of the optical film. The Tg of the (meth)acrylic resin can be measured by the same method as described above.

[0088] The thermoplastic resin content is preferably 50% by mass or more, and more preferably 70% by mass or more, relative to the base film 11.

[0089] (Other ingredients) The base film 11 may further contain other components as needed. Examples of other components include rubber particles, matting agents, and the like.

[0090] Rubber particles can impart flexibility to the film. The rubber particles are graft copolymers containing rubbery polymers (crosslinked polymers). Examples of rubbery polymers include butadiene-based crosslinked polymers, (meth)acrylic-based crosslinked polymers, and organosiloxane-based crosslinked polymers. Among these, (meth)acrylic-based crosslinked polymers are preferred, and acrylic-based crosslinked polymers (acrylic rubbery polymers) are more preferred, from the viewpoint of having a small refractive index difference with methacrylic resins and not impairing the transparency of the optical film.

[0091] The matting agent can create irregularities on the surface of the base film 11, thereby imparting slipperiness. The matting agent may be inorganic particles or resin particles. Examples of inorganic particles include fine particles of silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, and calcium carbonate, with silicon dioxide particles being preferred.

[0092] (Physical properties) The substrate film 11 may have phase differences Ro and Rt depending on its application. For example, the in-plane phase difference Ro of the substrate film 11, measured at a measurement wavelength of 590 nm and under conditions of 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 difference film to be combined with, for example, a VA-type liquid crystal cell. Furthermore, if the values ​​are 0 nm ≤ Ro ≤ 10 nm and -20 nm ≤ Rt ≤ 20 nm, it is suitable as a phase difference film to be combined with an IPS-type liquid crystal cell.

[0093] Ro and Rt are defined by the following formulas, respectively. Equation (1): Ro = (nx - ny) × d Equation (2): Rt = ((nx + ny) / 2 - nz) × d (In the formula, nx represents the refractive index of the substrate film 11 in the in-plane slow axis direction (the direction in which the refractive index is maximum). ny represents the refractive index in the direction perpendicular to the in-plane slow axis of the base film 11. nz represents the refractive index in the thickness direction of the base film 11. d represents the thickness (nm) of the base film 11.

[0094] The in-plane lagging axis of the substrate film 11 can be confirmed using an automated birefringent AxoScan Mueller Matrix Polarimeter (manufactured by Axometrics).

[0095] Ro and Rt can be measured by the following methods. 1) The base film 11 is conditioned for 24 hours in an environment of 23°C and 55% RH. The average refractive index of this base film 11 is measured using an Abbe refractometer, and the thickness d is measured using a commercially available micrometer. 2) The phase difference Ro and Rt of the substrate film 11 after humidity control are measured at a measurement wavelength of 590 nm using an automated birefringence meter AxoScan (Axo Scan Mueller Matrix Polarimeter: Axometrics Corporation) in an environment of 23°C and 55% RH.

[0096] As described above, the base film 11 is given knurled sections 12 by a coating method, rather than by embossing or laser irradiation. Therefore, the base film 11 does not have thin sections formed by heating and pressing with an embossing roller or by melting with laser irradiation. In other words, the thickness of the base film 11 is constant.

[0097] 3. Variant In the above embodiment, the knurling composition was shown as a solution containing a thermoplastic resin and a solvent, but it is not limited to this, and may be a curable composition containing a curable compound and a curing agent.

[0098] The curable compound is not particularly limited, but may be a compound having an unsaturated double bond, preferably a (meth)acrylate compound. Examples of (meth)acrylate compounds include acrylic prepolymers or oligomers such as polyester (meth)acrylate, urethane (meth)acrylate, epoxy (meth)acrylate, polyether (meth)acrylate, polyol (meth)acrylate, melamine (meth)acrylate, and triazine acrylate; and polyfunctional acrylate monomers such as ethylene glycol (meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol hexa(meth)acrylate, and dipentaerythritol hexa(meth)acrylate. Modified versions of these compounds with PO, EO, etc., can also be used. The content of the curable compound is not particularly limited, but may be, for example, 50 to 95% by mass relative to the knurling composition.

[0099] As curing agents, for example, photopolymerization initiators such as anthraquinone, benzoin ether, benzophenone, 4,4'-bisdimethylaminobenzophenone, 4,4'-bistrichloromethylbenzophenone, dibutylphenylphosphine, α,α-diethoxyacetophenone, 2-ethylanthraquinone, benzoin bisphenyl, chlorobenzophenone, benzoin, benzoin methyl ether, benzoin butyl ether, anthraquinone thioxanthone, methyl orthobenzoylbenzoic acid, and paradimethylaminoacetophenone can be used. The content of the curing agent may be, for example, 5 to 15% by mass relative to the knurling composition.

[0100] Then, the curable composition can be applied to both ends in the width direction of the surface of the base film 11 and cured to form the knurled portion 12. The curing may be photocured or thermocured. When the curable composition is cured, curing shrinkage force is generated, but by setting the distribution of the volume (preferably height) of the multiple protrusions 13 as described above, curling of the base film 11 caused by curing shrinkage force can be suppressed.

[0101] Furthermore, although the above embodiment shows an example where the base film 11 is a film obtained by solution casting, it is not limited to this, and may be a film obtained by molten casting. [Examples]

[0102] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0103] 1. Film preparation <Preparing Film Roll 1> (Preparation of fine particle dispersion) The following components were mixed and stirred in a dissolver for 50 minutes, and then dispersed in a Manton-Gorin. Furthermore, the mixture was dispersed in an attritor until the secondary particles reached a predetermined size, and then filtered using Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle dispersion. R972V (manufactured by Nippon Aerosil Co., Ltd.): 4% by mass Dichloromethane: 48% by mass Ethanol: 48% by mass

[0104] (Preparation of dope) First, dichloromethane was added to a pressurized dissolution tank at a flow rate of 400 kg / min and ethanol at a flow rate of 20 kg / min. Three minutes after the start of solvent addition, the cyclic polyolefin resin was added to the pressurized dissolution tank while stirring. Next, five minutes after the start of solvent addition, the fine particle additive solution was added and heated to 60°C, and completely dissolved while stirring. The heating temperature was increased from room temperature at a rate of 5°C / min, dissolved for 30 minutes, and then cooled at a rate of 3°C / min. This was filtered using Asaka Filter Paper No. 244 (filtration accuracy 0.005 mm) manufactured by Asaka Filter Paper Co., Ltd. at a flow rate of 300 L / m³. 2 ·h, filtration pressure 1.0×10 6 The mixture was filtered at Pa to prepare a dope with the following composition. Cycloolefin resin G7810 (manufactured by JSR Corporation) (Cycloolefin resin (COP) containing structural units derived from norbornene monomers represented by the following formula, Mw: 140,000, Tg: 170°C): 100% by mass R972V (manufactured by Nippon Aerosil Co., Ltd.): 0.30% by mass Dichloromethane: 380% by mass Ethanol: 20% by mass [ka]

[0105] (Preparation of base film) Next, the obtained dope was uniformly cast onto a stainless steel belt support at a temperature of 31°C and a width of 2300 mm using an endless belt casting apparatus. The temperature of the stainless steel belt was adjusted to 28°C, and the conveying speed of the stainless steel belt was set to 30 m / min. After evaporating the solvent in the cast dope on the stainless steel belt support until the residual solvent content was 30% by mass, the dope was peeled off the stainless steel belt support with a peeling tension of 110 N / m to obtain a film-like material. The obtained film was stretched 1.3 times in the conveying direction (MD direction) while heating to 120°C using a roll method that utilizes the difference in peripheral speed of the conveying rolls, and then stretched 1.65 times in the TD direction while heating to 130°C using a tenter method. The obtained film was conveyed while heating to 70°C until completely dry, and the ends were slit to obtain a base film 1 with a thickness of 20 μm and a width of 2500 mm.

[0106] (Preparation of knurling composition) As a thermoplastic resin, the cycloolefin resin used in the preparation of the base film 1 was prepared and dissolved in a solvent to a concentration of 5% by mass to obtain base material 1. A mixed solvent of dichloromethane and cyclopentanone was used as the solvent, with a mixing ratio of dichloromethane / cyclopentanone = 70 / 30 (by mass).

[0107] Next, using the base material 1 prepared above as a reference, three types of knurling compositions with different resin concentrations were prepared by changing the amount of solvent (amount of dilution with mixed solvent).

[0108] (Formation of knurled sections) Three different knurling compositions with varying resin concentrations were discontinuously dropped onto both ends of the film's surface in the width direction using a dispenser (SUPER HI JET, manufactured by Musashi Engineering Co., Ltd.), forming three rows of multiple protrusions along the length of the film. The rows of protrusions were arranged from the center of the film's width direction towards the ends as rows of protrusion 1, row of protrusion 2, and row of protrusion 3. The knurling compositions with increasing resin concentrations were used in the order of protrusion 1, protrusion 2, and protrusion 3. The base film with the knurled sections formed was then wound onto a core for a length of 8000m to obtain film roll 1.

[0109] <Preparing film rolls 2-6> Film rolls 2 to 6 were obtained in the same manner as film roll 1, except that the resin concentration of the knurling composition was adjusted to change the heights of the protrusions 1, 2, and 3 as shown in Table 1, and knurling was formed on both ends in the width direction of the surface of the base film.

[0110] <Preparation of Film 7> A knurling composition was continuously applied to both ends of the surface of the base film in the width direction using a casting die to form a strip-shaped knurled section along the length direction of the film. When an attempt was made to wind up the resulting film, curling occurred at the ends, making winding impossible.

[0111] <Preparation of Film 8> Except for changing the heights of protrusions 1, 2, and 3 as shown in Table 1, knurled sections were formed on both ends in the width direction of the surface of the base film in the same manner as in film roll 1. When an attempt was made to wind the resulting film, curling occurred at the ends, making winding impossible.

[0112] <Preparing Film Roll 9> Except for making the heights of the protrusions 1, 2, and 3 the same and changing the area of ​​the protrusions 1, 2, and 3 when viewed from above to the values ​​shown in Table 1, knurled sections were formed on both ends in the width direction of the surface of the base film, respectively, in the same manner as film roll 1, to obtain film roll 9.

[0113] <Preparing film roll 10> Except for making the heights and (when viewed from above) areas of the protrusions 1, 2, and 3 the same, knurled sections were formed on both ends in the width direction of the surface of the base film, in the same manner as the film roll 1, to obtain the film roll 10.

[0114] <Rating> The physical properties of the knurled sections (height and spacing of the protrusions), transportability (curl), and winding quality (interlayer contact, deformation over time) of the obtained film rolls 1-6, 9, and 10, as well as films 7 and 8, were evaluated using the following method.

[0115] (1) Height and spacing of the protrusions The height of the protrusions and the spacing between multiple protrusions (in the width and length directions) in the cross-section of the film were measured using a laser microscope. A Keyence VK-X1000 laser microscope was used. For the height of the protrusions, the height of the protrusions was measured for each row over a 100 mm area in the length direction of the film, and the average of these measurements was taken. For the spacing between multiple protrusions, the spacing in the width direction and the spacing in the length direction of the film were measured over a 100 mm area in the length direction of the film, and the average of these measurements was taken.

[0116] (2) Distribution of knurling height The slope of the lines connecting the heights of the protrusions was calculated from the heights of the protrusions (for each row) obtained by the measurement in (1) above, and from the spacing of the protrusions in the width direction.

[0117] (3) Suitable for transport (curl) During the roll transport process, from immediately after forming the knurled section on the base film until it was wound up, the occurrence of curls starting from the knurled section was visually observed, and the results were evaluated according to the following criteria. ○: The base film was transported without curling occurring at the edges during transport. △: The frequency of curling at the edges of the base film during transport is low, and even when it does occur, the curvature is slight and does not pose a practical problem. ×: The edges of the base film curled and broke, making continuous transport impossible.

[0118] (4) Interlayer contact (blocking) The wound film roll was double-wrapped in polyethylene sheets, and with both ends of the core supported by a stand (so that the axis of the winding core was horizontal), it was stored for 5 days under conditions of 40°C and 80% humidity. After that, the film was unwound from the roll, and the blocking (adhesion) state of the overlapping films was visually observed. The film was then evaluated based on the following criteria. ○: No blocking, or very little, so it does not pose a practical problem. △: There is slight blocking, but it does not pose a practical problem. ×: Blocking is clearly visible at a glance.

[0119] (5) Winding deformation The wound film roll was double-wrapped in polyethylene sheets, and both ends of the core were supported by a stand (so that the axis of the winding core was horizontal). It was stored for 5 days under conditions of 40°C and 80% humidity. After that, the polyethylene sheets were removed, and the surface of the film roll was illuminated by reflecting the light from a lit fluorescent lamp, and any distortion or fine irregularities were observed. The film was then evaluated based on the following criteria. ○: There are 0 or 1 or fewer places where the fluorescent light appears slightly bent, so it's not a problem. △: There are two places where the fluorescent light appears slightly bent, but this does not pose a practical problem. ×: There are areas where the fluorescent light is clearly bent and areas where the light is patchy, which is a problem.

[0120] Table 1 shows the evaluation results for film rolls 1-6, 9, and 10, and films 7 and 8.

[0121] [Table 1]

[0122] As shown in Table 1, it can be seen that film rolls 1-6 and 9 all suppress the occurrence of curl. Furthermore, the winding quality of the resulting film rolls is also good.

[0123] In particular, the slope of the line connecting the vertex of convex part 1 and the vertex of convex part 3 is 5 × 10 -5 ~3×10 -4 Within the mm / mm range, it can be seen that curl and blocking can be suppressed in a good balance (comparison of film rolls 1-6).

[0124] In contrast, film roll 7, which has a continuous strip-shaped knurled section, curls significantly and cannot be wound up. As a result, the winding quality could not be evaluated. Furthermore, film roll 8, in which the heights of the protrusions 1, 2, and 3 are reversed compared to film rolls 1-6, also curls and cannot be wound up.

[0125] <Preparing film rolls 11-14> Except for changing the heights of the protrusions 1, 2, and 3, and the spacing between the multiple protrusions as shown in Table 2, knurled sections were formed on both ends in the width direction of the surface of the base film, respectively, in the same manner as film roll 1, to obtain film rolls 11 to 14.

[0126] <Rating> The physical properties of the knurled sections (height and spacing of the protrusions), transportability (curl), and winding quality (interlayer contact, deformation over time) of the obtained film rolls 11-14 were evaluated in the same manner as described above. The results are shown in Table 2.

[0127] [Table 2]

[0128] As shown in Table 2, curling can be further suppressed by setting the spacing of the protrusions in the width direction to 500 μm or more, and the quality of the roll is less likely to be impaired by setting the spacing of the protrusions in the width direction to 5000 μm or less (comparison of film rolls 4 and 11-14).

[0129] <Preparing film rolls 15-19> Except for changing the concentration of the knurling composition as shown in Table 3, knurled sections were formed on both ends in the width direction of the surface of the base film 1, respectively, in the same manner as for film roll 1, thereby obtaining film rolls 15 to 19.

[0130] <Preparation of film roll 20> (Preparation of base film 2) Substrate film 2 was obtained in the same manner as substrate film 1, except that the cycloolefin resin G7810(COP) was changed to a (meth)acrylic resin (Acr) (PMMA, Mw: 800,000).

[0131] (Preparation of knurling composition) As the thermoplastic resin, the acrylic resin used in the production of the base film 2 was prepared and dissolved in a solvent to a concentration of 5% by mass to obtain base material 2. A mixed solvent of dichloromethane and cyclopentanone was used as the solvent, with a mixing ratio of dichloromethane / cyclopentanone = 70 / 30 (by mass).

[0132] Next, using the base material 2 prepared above as a reference, three types of knurling compositions with different resin concentrations were prepared by changing the amount of solvent (amount of dilution with mixed solvent).

[0133] (Formation of knurled sections) Film roll 20 was obtained in the same manner as film roll 1, except that three types of knurling compositions with different resin concentrations prepared as described above were used.

[0134] <Creating Film Roll 21> (Preparation of knurling composition) Base material 3 was prepared by mixing the following components. Dipentaerythritol hexaacrylate (DPHA, manufactured by Nippon Kayaku): 100 parts by mass Methyl ethyl ketone: 113 parts by mass Photopolymerization initiator (Irgacure 907, manufactured by Ciba-Gaiky): 3 parts by mass

[0135] Next, using the prepared base material 3 as a reference, three different knurling compositions with varying resin concentrations were prepared by changing the amount of solvent (dilution amount with mixed solvent).

[0136] (Formation of knurled sections) A film roll 21 was obtained in the same manner as the film roll 20, except that it was coated using the three knurling compositions with different resin concentrations prepared above, and then cured by irradiation with ultraviolet light.

[0137] <Rating> The physical properties of the knurled sections (height and spacing of the protrusions), transportability (curl), and winding quality (interlayer contact, deformation over time) of the obtained film rolls 15-21 were evaluated in the same manner as described above. Furthermore, continuous stability was evaluated using the following method.

[0138] (6) Continuous transportability For the knurling formed by coating in the longitudinal direction, the height t of the protrusions was measured every 1000 knurlings using method (1), and the height t of the protrusions for a total of 1000 knurlings was measured. The standard deviation of the variation in the obtained height t of the protrusions was calculated, and the results were evaluated according to the following criteria. ○: σ is 0.1 μm or less △:σ is more than 0.1μm and less than 0.2μm ×: σ is greater than 0.2 μm

[0139] Furthermore, the wrinkles caused by buckling stress in film rolls 3 and 9 were evaluated using the following method.

[0140] (7) Wrinkles due to buckling During the roll transport process, from immediately after forming the knurled section on the base film until it is wound up, the occurrence of wrinkles in the base film as it is supported by the transport roll was visually observed, and the results were evaluated according to the following criteria. ○: No wrinkles occurred, and the transport was successful. △: Wrinkles may occur slightly, but this does not affect practical use. ×: Wrinkles can cause folds near the center of the width, which may lead to tearing.

[0141] The evaluation results for film rolls 15-21 are shown in Table 3, and the evaluation results for film rolls 3 and 9 are shown in Table 4.

[0142] [Table 3]

[0143] [Table 4]

[0144] As shown in Table 3, by setting the resin concentration of the knurling composition within a predetermined range, continuous stability is further enhanced and the roll quality (deformation over time) can be further reduced (comparison of film rolls 15-19). Furthermore, it can be seen that curl can be effectively suppressed not only in the case of COP film but also in the case of acrylic resin film (comparison of films 15 and 20). Moreover, it can be seen that curl due to curing shrinkage can be suppressed even when the knurling composition is replaced with an ultraviolet-curable composition (comparison of film rolls 20 and 21).

[0145] As shown in Table 4, it can be seen that wrinkles caused by buckling stress can be further suppressed by making the height of protrusion 3 lower than the height of protrusion 1 (comparison of film rolls 3 and 9).

[0146] This application claims priority under Japanese Patent Application No. 2021-107944, filed on 29 June 2021. All provisions of the said application are incorporated herein by reference. [Industrial applicability]

[0147] According to the present invention, it is possible to provide a method for manufacturing a film and a film that can suppress the occurrence of curl due to shrinkage force when applying and forming the knurled portion, and that enables stable winding. [Explanation of Symbols]

[0148] 10 Film (film roll) 11. Base film 12 Knurling section 13, 13-1, 13-2, 13-3 Convex part

Claims

1. The process of preparing a strip-shaped base film, The process involves applying a knurling composition to both ends in the width direction of the surface of the strip-shaped base film, and then drying or curing it to form knurled portions. Includes, The knurling portion is The base film includes a plurality of protrusions arranged in the width direction, The volume of the protrusion on the widthwise end side of the base film is smaller than the volume of the protrusion on the widthwise central side, and The height of the protrusion on the widthwise end side of the base film is smaller than the height of the protrusion on the widthwise central side. In a cross-section passing through the plurality of protrusions along the width direction of the base film, The slope of the line connecting the vertex of the protrusion closest to the widthwise end of the base film and the vertex of the protrusion closest to the widthwise center is 5 × 10⁻⁵ to 3 × 10⁻³ mm / mm. A method for manufacturing film.

2. The height of the plurality of protrusions decreases as they approach the widthwise edge of the base film. A method for manufacturing a film according to claim 1.

3. The average spacing between the multiple protrusions in the width direction of the base film is 500 to 5000 μm. A method for manufacturing a film according to claim 1 or 2.

4. The knurling composition comprises a thermoplastic resin and a solvent. A method for manufacturing a film according to any one of claims 1 to 3.

5. The thermoplastic resin is a cycloolefin resin or a (meth)acrylic resin. A method for manufacturing a film according to claim 4.

6. The concentration of the thermoplastic resin is 1 to 10% by mass relative to the knurling composition. A method for manufacturing a film according to claim 4 or 5.

7. The aforementioned base film is a resin film. A method for manufacturing a film according to any one of claims 1 to 6.

8. The thickness of the base film is 10 to 40 μm. A method for manufacturing a film according to any one of claims 1 to 7.

9. A film comprising a base film and knurling portions arranged at both ends in the width direction of the surface of the base film, The knurling portion is The base film includes a plurality of protrusions arranged in the width direction, The volume of the protrusion on the widthwise end side of the base film is smaller than the volume of the protrusion on the widthwise central side, The height of the protrusion on the widthwise end side of the base film is smaller than the height of the protrusion on the widthwise central side. In a cross-section passing through the plurality of protrusions along the width direction of the base film, The slope of the line connecting the vertex of the protrusion closest to the widthwise end of the base film and the vertex of the protrusion closest to the widthwise center is 5 × 10⁻⁵ to 3 × 10⁻³ mm / mm. film.

10. The aforementioned base film is a resin film. The film according to claim 9.

Images