Optical film, layered body, and method for producing optical film

Abstract

In an optical film according to the present invention, the temperature-elongation curve of the optical film has a plurality of tension softening points. It is preferable that the optical film includes a plurality of thermoplastic resins, wherein a monomer (A) constituting at least one thermoplastic resin (A) has a functional group with a hydrogen bonding acceptor property, and a monomer (B) constituting another thermoplastic resin (B) has a functional group with a hydrogen bonding donor property.

Description

Optical film, laminate, and method for producing optical film

[0001] The present invention relates to an optical film, a laminate, and a method for manufacturing an optical film. In particular, the present invention relates to an optical film that prevents wrinkles during transport, coating cracks, and the like from occurring in a wide and thin film during processing in a subsequent step following the film manufacturing step.

[0002] In recent years, in addition to the increasing size of TVs, there has been a demand for improving productivity by increasing the length and width of film rolls and for resource conservation by reducing the thickness of the films provided, in order to reduce the environmental impact. Here, before being incorporated into a display device, widened and thinned film rolls are sometimes subjected to a coating process and then bonded in a polarizing plate process to produce polarizing plate components. In this case, when widened and thinned film rolls are used to form functional layers in the coating process and to produce polarizing plates, defects such as wrinkles and coating cracks can occur during transport. Therefore, there has been a demand for improvements to the wrinkles and coating cracks that occur during transport in widened and thinned film rolls.

[0003] Patent Document 1 discloses an acrylic film in which an acrylic resin and a cellulose ester resin are mixed in a specific ratio, which has excellent flexibility and surface properties, and a method for producing the same with high productivity. However, even the film disclosed in Patent Document 1 does not solve the above-mentioned problems such as wrinkles and coating cracks during transportation.

[0004] Patent No. 5333447

[0005] The present invention has been made in view of the above problems and circumstances, and an object of the present invention is to provide an optical film, a laminate, and a method for manufacturing an optical film that prevent wrinkles during transport and coating cracks, etc., from occurring during processing in subsequent steps following the film manufacturing step, particularly in a film that has been made wider and thinner.

[0006] The present inventors have investigated the causes of the above problems in order to solve the above problems. The inventors have determined that the temperature-elongation curve of an optical film has multiple tension-softening points. They have found that this makes it possible to prevent wrinkles during transport, coating cracks, and the like during transport. That is, the above problems according to the present invention are solved by the following means.

[0007] 1. An optical film whose temperature-elongation curve has a plurality of tension softening points.

[0008] 2. The optical film according to item 1, which contains a plurality of thermoplastic resins, wherein the monomer (A) constituting at least one of the thermoplastic resins (A) has a functional group with hydrogen bond acceptor properties, and the monomer (B) constituting the other thermoplastic resin (B) has a functional group with hydrogen bond donor properties.

[0009] 3. The optical film according to item 2, wherein the monomer (B) constituting the thermoplastic resin (B) further has a functional group with hydrogen bond acceptor properties.

[0010] 4. The optical film according to item 2, wherein the thermoplastic resin (A) is an acrylic resin (A), and the thermoplastic resin (B) is a cellulose ester resin (B).

[0011] 5. The optical film according to item 4, wherein the mass ratio of the acrylic resin (A) to the cellulose ester resin (B) is within a range of 95:5 to 30:70, the weight average molecular weight Mw of the acrylic resin (A) is within a range of 80,000 to 1,000,000, the weight average molecular weight Mw of the cellulose ester resin (B) is within a range of 75,000 to 300,000, the total degree of substitution (T) of acyl groups of the cellulose ester resin (B) is within a range of 2.0 to 3.0, and the degree of substitution of acyl groups having 3 to 7 carbon atoms is within a range of 1.2 to 3.0.

[0012] 6. The optical film according to item 1, which is used as a substrate film for coating.

[0013] 7. The optical film according to item 1, which is a multi-stage stretched film.

[0014] 8. The optical film according to item 1, wherein the temperature width of the holding region in the temperature-elongation curve of the optical film is within the range of 10 to 40°C.

[0015] 9. The optical film according to item 1, wherein the optical film has a thickness of 40 μm or less.

[0016] 10. A laminate comprising a curable resin layer and an optical film, wherein the temperature-elongation curve of the optical film has a plurality of tension-softening points.

[0017] 11. A method for producing the optical film according to any one of items 1 to 9, wherein the optical film is produced by multistage stretching.

[0018] 12. The method for producing an optical film according to item 11, wherein the stretching direction of a final stretching step in the multistage stretching is the same as that of any stretching step performed before the final stretching step, and when the stretching step having the same stretching direction as that of the final stretching step is defined as a previous stretching step, the ratio of the stretching magnifications (stretching magnification in the final stretching step / stretching magnification in the previous stretching step) is within the range of 1.15 to 2.00.

[0019] 13. The method for producing an optical film according to item 11, wherein at least one of the multi-stage stretching steps is stretching in the width direction of the optical film.

[0020] 14. The method for producing an optical film according to item 11, wherein at least one of the multi-stage stretching steps is stretching in the transport direction of the optical film and in the width direction of the optical film.

[0021] 15. The method for producing an optical film according to item 12, wherein the ratio of the temperature in the final-stage stretching to the temperature in the previous-stage stretching (temperature in the final-stage stretching / temperature in the previous-stage stretching) is within the range of 1.00 to 1.50.

[0022] The above-described means of the present invention can provide an optical film, laminate, and method for manufacturing an optical film that prevent conveyance wrinkles and coating cracks during processing in subsequent processes following the film manufacturing process, particularly for wide and thin films. The mechanism of action or manifestation of the effects of the present invention is not clear, but the following speculation is made. The inventors believed that heat and / or conveyance tension during processing of wide and thin films caused dimensional fluctuations that had not previously occurred, resulting in conveyance wrinkles. Based on this, the inventors conducted extensive research and concluded that it would be sufficient for the film to maintain its functionality even when energy (load) such as the conveyance tension is applied to the processed film. Specifically, in the temperature-elongation curve of a typical film, the film elongates with increasing temperature, i.e., the film F4 shown in Figure 2 has a right-sloping curve. However, in the present invention, as in the case of film F1 shown in Figure 1, for example, the film elongates once with increasing temperature, then shrinks, stagnates, and then elongates again when the temperature is further increased. That is, it is presumed that the problem described above can be solved by the fact that the film has multiple tension softening points, which allows the film to be processed while maintaining its shape even when energy (load) is applied to the film.

[0023] An example of a temperature elongation curve for explaining the tension softening point. An example of a temperature elongation curve for explaining the tension softening point. A flowchart showing the flow of the manufacturing process of the present invention. A schematic diagram of an apparatus for manufacturing a polarizing plate protective film.

[0024] The optical film of the present invention has a temperature-elongation curve having a plurality of tension-softening points, which is a technical feature common to or corresponding to each of the following embodiments.

[0025] As an embodiment of the present invention, it is preferred that the composition contains a plurality of thermoplastic resins, and that the monomer (A) constituting at least one of the thermoplastic resins (A) has a functional group with hydrogen bond acceptor properties, and the monomer (B) constituting the other thermoplastic resin (B) has a functional group with hydrogen bond donor properties.

[0026] It is preferable that the monomer (B) constituting the thermoplastic resin (B) further has a functional group with hydrogen bond acceptor properties.

[0027] It is preferable that the thermoplastic resin (A) is an acrylic resin (A) and the thermoplastic resin (B) is a cellulose ester resin (B), thereby improving brittleness.

[0028] It is preferable that the mass ratio of the acrylic resin (A) to the cellulose ester resin (B) is within a range of 95:5 to 30:70, and the weight-average molecular weight Mw of the acrylic resin (A) is within a range of 80,000 to 1,000,000. This improves the brittleness of the optical film and improves the transparency when the cellulose ester resin (A) is compatible with the cellulose ester resin (B). Furthermore, it is preferable that the weight-average molecular weight Mw of the cellulose ester resin (B) is within a range of 75,000 to 300,000, the total degree of substitution (T) of the acyl groups of the cellulose ester resin (B) is within a range of 2.0 to 3.0, and the degree of substitution of acyl groups having 3 to 7 carbon atoms is within a range of 1.2 to 3.0. This ensures that the acrylic resin (A) and the cellulose ester resin (B) are sufficiently compatible with each other, and that haze does not become a problem when the film is used as an optical film. Furthermore, there is no decrease in brittleness.

[0029] The optical film of the present invention is preferably used as a substrate film for coating from the viewpoint of exerting the effects of the present invention. Furthermore, the optical film of the present invention is preferably a multi-stage stretched film from the viewpoint of imparting the optical film with the plurality of tension-softening points.

[0030] The temperature retention region in the temperature-elongation curve of the optical film is preferably within a range of 10 to 40°C. This allows the film to be processed while maintaining its shape even when energy (load) is applied to the film. As a result, conveyance wrinkles, coating cracks, and the like can be prevented during conveyance, particularly in wide and thin films.

[0031] Furthermore, it is preferable to set the thickness of the optical film to 40 μm or less in terms of resource conservation.

[0032] The laminate of the present invention is a laminate comprising a curable resin layer and an optical film, wherein the optical film has a temperature-elongation curve with multiple tension-softening points, thereby providing a laminate having an optical film that is prevented from generating wrinkles during transport, coating cracks, etc.

[0033] The optical film manufacturing method of the present invention is a method for manufacturing the optical film, and the optical film is manufactured by multi-stage stretching. This makes it possible to manufacture an optical film having multiple tension softening points. As a result, an optical film is obtained that is free from conveyance wrinkles, coating cracks, and the like that occur during processing in subsequent steps following the film manufacturing step.

[0034] In the optical film manufacturing method of the present invention, it is preferable that, when the stretching direction of the final stretching step in the multistage stretching is the same as that of any stretching step performed before the final stretching step, and the stretching step having the same stretching direction as that of the final stretching step is defined as a previous stretching step, the ratio of the stretching magnifications (stretching magnification of the final stretching step / stretching magnification of the previous stretching step) is within a range of 1.15 to 2.00. This allows the optical film to have the multiple tension-softening points.

[0035] In terms of increasing the width, it is preferable that at least one of the multi-stage stretching steps is stretching in the width direction of the optical film.

[0036] At least one of the multi-stage stretching steps is preferably performed in the transport direction and width direction of the optical film, from the viewpoint of reducing minute film thickness variations in the transport direction and width direction and improving mechanical properties.

[0037] It is preferable that the ratio of the temperature in the final stretching stage to the temperature in the previous stretching stage (temperature in the final stretching stage / temperature in the previous stretching stage) is within the range of 1.00 to 1.50. By setting the ratio within this range, the temperature-elongation curve has multiple tension softening points and an optimal holding temperature region, and the film is processed while maintaining its shape even when energy (load) is applied to the film, preventing wrinkles during transport, coating cracks, and the like.

[0038] The present invention, its components, and embodiments and modes for carrying out the present invention will be described below. In this application, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0039] [Outline of Optical Film of the Present Invention] The optical film of the present invention has a temperature-elongation curve with a plurality of tension-softening points.

[0040] <Tension Softening Point> In the present invention, "having a tension softening point" refers to a point at which the slope of the temperature-elongation curve of an optical film obtained by the method described below changes to more than 0.3% / °C or less than -0.3% / °C. The temperature-elongation curve of an optical film in at least one of the longitudinal direction and the direction perpendicular to the longitudinal direction is obtained by measuring the dynamic viscoelasticity as described below. Here, the longitudinal direction of the optical film refers to the film's conveying direction (MD direction), and the direction perpendicular to the longitudinal direction refers to the film's width direction (TD direction). First, a measurement sample (sample) A was prepared by cutting the optical film to a length of 40 mm and a width of 5 mm so that the longitudinal direction of the optical film was the length direction. Furthermore, a measurement sample (sample) B was prepared by cutting the optical film to a length of 40 mm and a width of 5 mm so that the direction perpendicular to the longitudinal direction of the optical film was the length direction. Then, the dynamic viscoelasticity of each of Samples A and B was measured. The dynamic viscoelasticity measurement device used was an RSA-G2 (manufactured by TA Instruments). A tensile tool was used to attach the sample. The film thickness was measured using a film thickness meter. The dynamic viscoelasticity measurement conditions were a gap length of 20 mm, strain of 0.1%, frequency of 1 Hz, temperature of -70 to 220°C, heating rate of 5°C / min, and initial tension of 40 g. If the slope of the obtained temperature-elongation curve was 0.3% / °C or more or -0.3% / °C or less, it was determined that the sample had a tension softening point, and the number of tension softening points was counted.

[0041] Figures 1 and 2 are temperature-elongation curves of optical films showing examples of tension softening points. Film F1 elongates gradually as the temperature rises, then shrinks, stagnates, and then elongates rapidly again. Film F2 elongates as the temperature rises, then stagnates, and then elongates rapidly again. Film F3 elongates gradually, then shrinks, stagnates, and then elongates rapidly again. Film F4 elongates gradually as the temperature rises, then elongates rapidly again. In Figures 1 and 2, the symbol S indicates the tension softening point. Films F1, F2, and F3 have multiple tension softening points, while film F4 has one tension softening point.

[0042] As a means for providing a plurality of tension softening points, for example, as will be described later, the use of specific thermoplastic resins (A) and (B) and the control of the mass ratio of the thermoplastic resins (A) and (B) can be mentioned. In particular, the use of a specific acrylic resin as the thermoplastic resin (A) and a specific cellulose ester resin as the thermoplastic resin (B) can be mentioned. Furthermore, as a means for providing a plurality of tension softening points, the use of a specific acrylic resin as the thermoplastic resin (A) and a specific cellulose ester resin as the thermoplastic resin (B) can be mentioned. Furthermore, as a means for providing a plurality of tension softening points, the use of a specific acrylic resin as the thermoplastic resin (A) and a specific cellulose ester resin as the thermoplastic resin (B) can be mentioned. Furthermore, as will be described later ... as will be described later, as a means for providing a plurality of tension soft

[0043] The optical film of the present invention preferably has a holding region temperature width in the temperature-elongation curve in the range of 10 to 40°C in at least one of the longitudinal direction and the direction perpendicular to the longitudinal direction of the optical film. This allows the film to be processed while maintaining its shape even when energy (load) is applied to the film. As a result, conveyance wrinkles, coating cracks, and the like can be prevented, particularly in films that are widened and thinned. In the present invention, the "holding region temperature width" refers to a region in the high temperature region above the tension softening point in the temperature-elongation curve, where the slope of the curve is 0.3% / °C or less and -0.3% / °C or more. The means for setting the holding region temperature width within the range are the same as those for providing multiple tension softening points.

[0044] <Multistage Stretching> The optical film of the present invention is preferably a multistage stretched film. In the present invention, multistage stretching refers to performing stretching multiple times in the production process of the optical film. The method for producing the optical film of the present invention produces the film by multistage stretching. Specifically, in the method for producing the optical film of the present invention, it is preferable that the stretching direction of the final stretching step among the multistage stretching steps is the same as that of any stretching step performed before the final stretching step. Furthermore, when the stretching step having the same stretching direction as that of the final stretching step is defined as the previous stretching step, the ratio of the stretching ratios (stretching ratio of the final stretching step / stretching ratio of the previous stretching step) is preferably within the range of 1.15 to 2.00.

[0045] In addition, in terms of increasing the width, it is preferable that at least one of the multistage stretching processes is stretching in the width direction of the optical film. Furthermore, in terms of reducing minute film thickness variations in the width direction and the conveying direction and improving mechanical properties, it is preferable that at least one of the multistage stretching processes is stretching in the conveying direction and the width direction of the optical film. Therefore, the following process pattern is preferable as the multistage stretching process pattern.

[0046] (a) Film production → MD stretching (first stretching) → TD stretching (second stretching: previous stage stretching) → MD stretching (third stretching) → take-up → pay-out → TD stretching (fourth stretching: final stage stretching) → take-up (b) Film production → TD stretching (first stretching: previous stage stretching) → take-up → pay-out → TD stretching (second stretching: final stage stretching) (c) Film production → TD stretching (first stretching: previous stage stretching) → MD stretching (second stretching) → TD stretching (third stretching: final stage stretching) → take-up (d) Film production → MD stretching (first stretching) → TD stretching (second stretching: previous stage stretching) → TD stretching (third stretching: final stage stretching) → take-up (e) Film formation → Winding → Payout → TD stretching (first stretching: previous stage stretching) → TD stretching (second stretching: final stage stretching)

[0047] In patterns (a) and (b), after film formation, a preliminary stretching is performed, followed by winding and unwinding, followed by final stretching again, and then wound up. In patterns (c) and (d), after film formation, a preliminary stretching is performed, followed by final stretching, and then wound up. In pattern (e), after film formation, a preliminary stretching is performed, followed by winding and unwinding, followed by final stretching, and then wound up. As such, after film formation, a preliminary stretching or final stretching may be performed before winding, or a film may be formed, followed by winding, followed by preliminary stretching or final stretching. Note that the multistage stretching in the present invention is not limited to the above patterns, and winding and unwinding may be performed at any timing.

[0048] In addition, in the (a) pattern, the ratio of the stretching ratio of the TD stretching, which is the final stretching stage, to the stretching ratio of the TD stretching, which is the previous stretching stage (stretching ratio of the TD stretching, which is the final stretching stage / stretching ratio of the TD stretching, which is the previous stretching stage) is within the range of 1.15 to 2.00. Similarly, in the (b) to (e) patterns, the ratio of the stretching ratio of the TD stretching, which is the final stretching stage, to the stretching ratio of the TD stretching, which is the previous stretching stage (stretching ratio of the TD stretching, which is the final stretching stage / stretching ratio of the TD stretching, which is the previous stretching stage) is within the range of 1.15 to 2.00. Among the (a) to (e) patterns, the (a) pattern is preferred in terms of reducing film thickness unevenness and improving mechanical properties.

[0049] In the present invention, MD stretching refers to stretching in the machine direction. The machine direction will also be referred to as the "MD direction" hereinafter. TD stretching refers to stretching in the transverse direction, which is perpendicular to the MD direction within the web plane. The transverse direction will also be referred to as the "TD direction" hereinafter. When stretched in the MD direction, the web shrinks in the TD direction. Hereinafter, the optical film, the method for producing the optical film, and uses of the optical film will be described in detail.

[0050] [Optical Film] The optical film of the present invention has a temperature-elongation curve with multiple tension-softening points. Furthermore, the optical film preferably contains multiple thermoplastic resins. The thermoplastic resin specified in the present invention is not particularly limited as long as it does not impair the effects of the present invention, and examples thereof include polyamide, polyester, polyetherimide, polyether ketone, polyether ether ketone, liquid crystal polymer, polyamideimide, polyimide, polyacetal, polycarbonate, polyarylate, polyphenylene sulfide, polyethersulfone, polysulfone, polyvinyl alcohol, polyethylene-vinyl alcohol copolymer, polyurethane, cellulose resin, acrylic resin, norbornene resin, fluororesin, and cycloolefin resin.

[0051] The thermoplastic resins contained in the optical film preferably have a structure in which at least one of the thermoplastic resins (A) contains a monomer (A) having a hydrogen bond acceptor functional group and the other of the thermoplastic resins (B) contains a monomer (B) having a hydrogen bond donor functional group. Furthermore, the monomer (B) of the thermoplastic resin (B) preferably further contains a hydrogen bond acceptor functional group.

[0052] Examples of the hydrogen bond acceptor functional group and hydrogen bond donor functional group are as described in Table 2 on page 15 of "Introduction to Hydrogen Bonding" by Jeffrey, George A., published by Oxford UP. Specific examples of hydrogen bond acceptor functional groups, hydrogen bond donor functional groups, and functional groups that function as both hydrogen bond acceptors and hydrogen bond donors include the following:

[0053] (Strong Hydrogen Bonds) Functional groups that form strong hydrogen bonds and act as both hydrogen bond donors and hydrogen bond acceptors are shown below.

[0054]

[0055] (Moderate Hydrogen Bonding) Functional groups that form moderate hydrogen bonds and act as both hydrogen bond donors and hydrogen bond acceptors, functional groups that act only as hydrogen bond donors, and functional groups that act only as hydrogen bond acceptors are shown below.

[0056]

[0057] In particular, functional groups with hydrogen bond donor properties are preferably those containing "O-H" or "N." Furthermore, functional groups with hydrogen bond acceptor properties are preferably those containing "C=O," "C-O-C," or "N."

[0058] <Compatibility> From the viewpoint of compatibility, it is preferable that the absolute value of the difference between δH (hydrogen bonding term) in the HSP value of thermoplastic resin (A) and δH (hydrogen bonding term) in the HSP value of thermoplastic resin (B) is 2.5 or less. The HSP value is the "Hansen solubility parameter," an index that represents the solubility of a substance, i.e., the degree to which a substance dissolves in another substance. HSP is a solubility parameter introduced by Hildebrand, divided into three components: dispersion term δD, polar term δP, and hydrogen bonding term δH, and expressed in three-dimensional space. The dispersion term δD represents the effect due to dispersion forces, the polar term δP represents the effect due to dipole-dipole forces, and the hydrogen bonding term δH represents the effect due to hydrogen bonding forces. The dispersion term δD, polar term δP, and hydrogen bonding term δH are expressed as follows (each unit is MPa0.5): δD: Energy derived from intermolecular dispersion forces δP: Energy derived from intermolecular polar forces δH: Energy derived from intermolecular hydrogen bonding forces

[0059] The definition and calculation of HSP are described in the following literature: Charles M. Hansen, Hansen Solubility Parameters: A User's Handbook (CRC Press, 2007). The dispersion term reflects van der Waals forces, the polar term reflects dipole moments, and the hydrogen bond term reflects the effects of water, alcohol, etc. Similar HSP vectors can be determined to have high solubility, and the similarity of the vectors can be determined by the Hansen solubility parameter distance (HSP distance). The Hansen solubility parameter can be used not only to determine solubility, but also as an indicator of how easily a substance can exist in another substance, i.e., how well it disperses.

[0060] In the present invention, HSP [δD, δP, δH] can be easily estimated from the chemical structure by using, for example, computer software Hansen Solubility Parameters in Practice (HSPiP). Specifically, it is determined from the chemical structure by the Y-MB method implemented in HSPiP. If the chemical structure is unknown, it is determined by the Sphere method implemented in HSPiP from the results of dissolution tests using multiple solvents. Specifically, HSPiP version 5.4.01 can be used.

[0061] In the present invention, the thermoplastic resin (A) is preferably an acrylic resin (A), and the thermoplastic resin (B) is preferably a cellulose ester resin (B). That is, the optical film is preferably an optical film containing a resin composition containing the acrylic resin (A) and the cellulose ester resin (B). Furthermore, the mass ratio of the acrylic resin (A) to the cellulose ester resin (B) is preferably within a range of 95:5 to 30:70. Furthermore, the weight-average molecular weight Mw of the acrylic resin (A) is within a range of 80,000 to 1,000,000, and the weight-average molecular weight Mw of the cellulose ester resin (B) is within a range of 75,000 to 300,000. It is preferable that the total degree of substitution (T) of acyl groups in the cellulose ester resin (B) is within a range of 2.0 to 3.0, and the degree of substitution of acyl groups having 3 to 7 carbon atoms is within a range of 1.2 to 3.0.

[0062] The resin composition according to the present invention preferably contains an acrylic resin (A) and a cellulose ester resin (B). The composition of the resin composition will be described below.

[0063] <Acrylic Resin (A)> The acrylic resin used in the present invention also includes a methacrylic resin. Although there are no particular limitations on the resin, it is preferable that the resin is composed of 50 to 99% by mass of methyl methacrylate units and 1 to 50% by mass of other monomer units copolymerizable therewith.

[0064] Examples of other copolymerizable monomers include alkyl methacrylates having an alkyl group with 2 to 18 carbon atoms, alkyl acrylates having an alkyl group with 1 to 18 carbon atoms, α,β-unsaturated acids such as acrylic acid and methacrylic acid, unsaturated group-containing dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α,β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, N-substituted maleimide, glutaric anhydride, and the like, and these can be used alone or in combination of two or more kinds of monomers.

[0065] Among these, preferred are methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, s-butyl acrylate, 2-ethylhexyl acrylate, etc. From the viewpoint of thermal decomposition resistance and fluidity of the copolymer, methyl acrylate and n-butyl acrylate are particularly preferably used as the other copolymerizable monomer.

[0066] The acrylic resin (A) used in the optical film has a weight average molecular weight (Mw) of 80,000 to 1,000,000. By setting the weight average molecular weight within this range, it is preferable in terms of improving the brittleness of the optical film and improving the transparency when it is mixed with the cellulose ester resin (B).

[0067] If the weight average molecular weight (Mw) of the acrylic resin (A) is less than 80,000, sufficient improvement in brittleness cannot be obtained, and compatibility with the cellulose ester resin (B) deteriorates.

[0068] The weight average molecular weight (Mw) of the acrylic resin (A) is particularly preferably in the range of 100,000 to 600,000, and most preferably in the range of 150,000 to 400,000.

[0069] The weight average molecular weight of the acrylic resin according to the present invention can be measured by gel permeation chromatography (GPC) under the following conditions.

[0070] Solvent: methylene chloride Column: Shodex K806, K805, K803G (three columns manufactured by Showa Denko K.K. were connected and used) Column temperature: 25°C Sample concentration: 0.1% by mass Detector: RI Model 504 (manufactured by GL Sciences) Pump: L6000 (manufactured by Hitachi, Ltd.) Flow rate: 1.0 ml / min Calibration curve: A calibration curve was used using 13 samples of standard polystyrene STK standard polystyrene (manufactured by Tosoh Corporation) with Mw = 2,800,000 to 500. It is preferable to use the 13 samples at approximately equal intervals.

[0071] The method for producing the acrylic resin (A) in the present invention is not particularly limited, and the resin can be produced by a known method, such as suspension polymerization, emulsion polymerization, bulk polymerization, or solution polymerization.

[0072] Commercially available acrylic resins can also be used as the acrylic resin of the present invention. Examples of such acrylic resins include Delpet 60N and 80N (manufactured by Asahi Kasei Corporation), Dianale BR52, BR80, BR83, BR85, and BR88 (manufactured by Mitsubishi Chemical Corporation), and KT75 (manufactured by Denka Co., Ltd.). Two or more types of acrylic resins can also be used in combination.

[0073] <Cellulose ester resin (B)> The cellulose ester resin (B) according to the present invention has a total degree of substitution (T) of acyl groups of 2.0 to 3.0, particularly from the viewpoint of improving brittleness and transparency when it is mixed with the acrylic resin (A). Furthermore, the cellulose ester resin (B) has a degree of substitution of acyl groups having 3 to 7 carbon atoms of 1.2 to 3.0, and preferably has a degree of substitution of acyl groups having 3 to 7 carbon atoms of 2.0 to 3.0.

[0074] That is, the cellulose ester resin (B) according to the present invention is a cellulose ester resin substituted with an acyl group having a carbon number of 3 to 7. Specifically, the cellulose ester resin preferably has a propionyl group, a butyryl group, or the like, and the propionyl group is particularly preferably used.

[0075] When the total degree of substitution of acyl groups in the cellulose ester resin (B) is less than 2.0, the residual ratio of hydroxyl groups at the 2-, 3-, and 6-positions of the cellulose ester molecule exceeds 1.0, and in this case, the acrylic resin (A) and the acrylic resin (B) are not sufficiently compatible with each other, causing a problem of haze when the resin is used as an optical film.

[0076] Furthermore, even if the total degree of substitution of acyl groups is 2.0 or more, if the degree of substitution of acyl groups having 3 to 7 carbon atoms is less than 1.2, sufficient compatibility will not be obtained or brittleness will decrease. For example, even if the total degree of substitution of acyl groups is 2.0 or more, if the degree of substitution of acyl groups having 2 carbon atoms, i.e., acetyl groups, is high and the degree of substitution of acyl groups having 3 to 7 carbon atoms is less than 1.2, compatibility will decrease and haze will increase.

[0077] Furthermore, even when the total degree of substitution of acyl groups is 2.0 or more, if the degree of substitution of acyl groups having 8 or more carbon atoms is high and the degree of substitution of acyl groups having 3 to 7 carbon atoms is less than 1.2, brittleness deteriorates and desired properties cannot be obtained.

[0078] The cellulose ester resin (B) according to the present invention has an acyl substitution degree of 2.0 to 3.0 in total, with the degree of substitution of acyl groups having 3 to 7 carbon atoms being 1.2 to 3.0. However, it is preferable that the total degree of substitution of acyl groups having carbon atoms other than 3 to 7, i.e., acetyl groups and acyl groups having 8 or more carbon atoms, is 1.3 or less. It is more preferable that the total degree of substitution of acyl groups in the cellulose ester resin (B) is 2.5 to 3.0.

[0079] In the present invention, the acyl group may be an aliphatic acyl group or an aromatic acyl group. In the case of an aliphatic acyl group, it may be linear or branched and may further have a substituent. The number of carbon atoms of the acyl group in the present invention includes the substituent of the acyl group.

[0080] When the cellulose ester resin (B) has an aromatic acyl group as a substituent, the number of substituents X substituted on the aromatic ring is 0 to 3. In this case, care must be taken to ensure that the degree of substitution of an acyl group having 3 to 7 carbon atoms, including the substituent, is 1.2 to 3.0. For example, since a benzoyl group has 7 carbon atoms, when it has a substituent containing carbon, the number of carbon atoms as the benzoyl group is 8 or more, and it is not included in the acyl group having 3 to 7 carbon atoms.

[0081] Furthermore, when the number of substituents substituted on an aromatic ring is two or more, they may be the same or different, and may be linked to each other to form a condensed polycyclic compound (e.g., naphthalene, indene, indane, phenanthrene, quinoline, isoquinoline, chromene, chroman, phthalazine, acridine, indole, indoline, etc.).

[0082] In the cellulose ester resin (B) as described above, a structure having at least one aliphatic acyl group having 3 to 7 carbon atoms is used as the structure used in the cellulose resin of the present invention.

[0083] The degree of substitution of the cellulose ester resin (B) according to the present invention is such that the total degree of substitution (T) of acyl groups is 2.0 to 3.0, and the degree of substitution of acyl groups having 3 to 7 carbon atoms is 1.2 to 3.0. In addition, the preferred structure is one in which the sum of the degrees of substitution of acyl groups other than those having 3 to 7 carbon atoms, i.e., acetyl groups and acyl groups having 8 or more carbon atoms, is 1.3 or less.

[0084] The cellulose ester resin (B) according to the present invention is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate. That is, the cellulose ester resin (B) preferably has an acyl group having 3 or 4 carbon atoms as a substituent. Among these, particularly preferred cellulose ester resins are cellulose acetate propionate and cellulose propionate.

[0085] The portion not substituted with an acyl group is usually present as a hydroxy group, and can be synthesized by known methods.

[0086] The degree of substitution of acetyl groups and other acyl groups was determined by the method specified in ASTM-D817-96.

[0087] The weight-average molecular weight (Mw) of the cellulose ester resin according to the present invention is in the range of 75,000 to 300,000, particularly from the viewpoints of compatibility with the acrylic resin (A) and improvement of brittleness. The weight-average molecular weight is more preferably in the range of 100,000 to 240,000, and particularly preferably 160,000 to 240,000. If the weight-average molecular weight (Mw) of the cellulose ester resin is below 75,000, the effects of improving heat resistance and brittleness are insufficient, and the effects of the present invention cannot be obtained. Two or more cellulose resins can also be used in combination in the present invention. The weight-average molecular weight of the cellulose ester resin (B) according to the present invention can be measured in the same manner as the weight-average molecular weight of the acrylic resin (A) described above, i.e., by gel permeation chromatography (GPC). The measurement conditions are also the same as those for the acrylic resin (A) described above.

[0088] In the optical film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are preferably contained in a compatible state in a mass ratio of 95:5 to 30:70. The mass ratio of the acrylic resin (A) to the cellulose ester resin (B) is more preferably 95:5 to 50:50, and even more preferably 90:10 to 60:40. If the mass ratio of the acrylic resin (A) to the cellulose ester resin (B) is greater than 95:5, the effects of the cellulose ester resin (B) cannot be fully obtained. If the mass ratio of the acrylic resin is less than 30:70, the moisture resistance becomes insufficient.

[0089] In the optical film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) must be contained in a compatible state. The physical properties and quality required for an optical film are achieved by mutually compensating for the different resins by making them compatible with each other. Whether the acrylic resin (A) and the cellulose ester resin (B) are compatible with each other is determined by the glass transition temperature Tg.

[0090] When two resins are simply mixed, each resin has its own glass transition temperature, so the mixture has two glass transition temperatures. However, when the two resins become compatible, the glass transition temperatures specific to each resin disappear, and the mixture becomes a single glass transition temperature, which is the glass transition temperature of the compatible resins. The glass transition temperature T ｇ１，２ It is known that can be approximated by the Gordon-Taylor equation. Gordon-Taylor (M. Gordon and J.S. Taylor, 2 J. of Applied Chem. 493-500 (1952)): T ｇ１，２ = (w １ T ｇ１ +Kw ２ T ｇ２ ) / (w １ +Kw ２ ) [Here, w １ and w ２ is the mass fraction of components 1 (acrylic resin (A)) and 2 (cellulose ester resin (B)); T ｇ１ and T ｇ２ are the glass transition temperatures (Kelvin) of components 1 and 2, respectively; T ｇ１，２ is the glass transition temperature of the mixture of components 1 and 2; and K is a constant related to the free volume of the two resins.] The glass transition temperature referred to here is a value measured using a differential scanning calorimeter (DSC-7 model, manufactured by Perkin Elmer). Specifically, a sample that has been previously conditioned for 24 hours in an atmosphere of 23°C and 55% RH is measured in a nitrogen gas flow at a temperature increase rate of 20°C / min, and the midpoint glass transition temperature (Tmg) is determined in accordance with JIS K7121 (1987).

[0091] The acrylic resin (A) and the cellulose ester resin (B) are preferably each an amorphous resin, and either one may be a crystalline polymer or a polymer having partial crystallinity. In particular, in the present invention, it is preferable that the acrylic resin (A) and the cellulose ester resin (B) are compatible with each other to form an amorphous resin.

[0092] In the present invention, "containing the acrylic resin (A) and the cellulose ester resin (B) in a compatible state" means that the respective resins (polymers) are mixed together to form a compatible state. This does not include a state in which a precursor of the acrylic resin, such as a monomer, dimer, or oligomer, is mixed with the cellulose ester resin (B) and then polymerized to form a mixed resin.

[0093] For example, the process of obtaining a mixed resin by mixing an acrylic resin precursor such as a monomer, dimer, or oligomer with a cellulose ester resin (B) and then polymerizing the resulting mixture involves a complex polymerization reaction. Resins prepared by this method are difficult to control, and molecular weight adjustment is also difficult. Furthermore, when resins are synthesized by this method, graft polymerization, crosslinking, or cyclization reactions often occur, resulting in insolubility in solvents or inability to melt when heated. Furthermore, it is difficult to measure the weight-average molecular weight (Mw) of the acrylic resin in the mixed resin. Therefore, it is difficult to control the physical properties, making it unsuitable for stable production of optical films.

[0094] The optical film of the present invention may contain resins and additives other than the acrylic resin (A) and the cellulose ester resin (B) as long as the function as an optical film is not impaired. When the optical film of the present invention contains a resin other than the acrylic resin (A) and the cellulose ester resin (B), the added resins may be in a compatible state or may be mixed without being dissolved.

[0095] The total mass of the acrylic resin (A) and the cellulose ester resin (B) in the optical film of the present invention is preferably 55% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more of the optical film. When resins or additives other than the acrylic resin (A) and the cellulose ester resin (B) are used, it is preferable to adjust the amount added within a range that does not impair the functions of the optical film of the present invention.

[0096] <Acrylic Particles (C)> The optical film of the present invention preferably contains acrylic particles (C). The acrylic particles (C) according to the present invention refer to an acrylic component present in a particulate state (in a non-compatible state) in an optical film containing the acrylic resin (A) and the cellulose ester resin (B) in a compatible state.

[0097] The acrylic particles (C) are prepared, for example, by collecting a predetermined amount of the prepared optical film, dissolving it in a solvent, and stirring the mixture to thoroughly dissolve and disperse it. Once dispersed, the resulting mixture is filtered using a PTFE membrane filter having a pore size smaller than the average particle size of the acrylic particles (C). The weight of the insoluble matter collected by filtration is preferably 90% by mass or more of the acrylic particles (C) added to the optical film.

[0098] The acrylic particles (C) used in the present invention are not particularly limited, but are preferably acrylic particles (C) having a layer structure of two or more layers. The acrylic particles (C) are particularly preferably the following multilayer structure acrylic granular composite.

[0099] The multilayered acrylic granular composite refers to a particulate acrylic polymer having a structure in which, from the center to the periphery, an innermost hard layer polymer, a crosslinked soft layer polymer exhibiting rubber elasticity, and an outermost hard layer polymer are layered together. That is, the multilayered acrylic granular composite is a multilayered acrylic granular composite consisting of, from the center to the periphery, an innermost hard layer, a crosslinked soft layer, and an outermost hard layer. This multilayered acrylic granular composite with a three-layer core-shell structure is preferably used.

[0100] A preferred embodiment of the multilayered acrylic granular composite used in the acrylic resin composition according to the present invention is an acrylic granular composite having a three-layer structure consisting of an innermost hard layer polymer (a), a crosslinked soft layer polymer (b), and an outermost hard layer polymer (c) shown below, wherein the obtained three-layered polymer consists of 5 to 40% by mass of the innermost hard layer polymer (a), 30 to 60% by mass of the soft layer polymer (b), and 20 to 50% by mass of the outermost hard layer polymer (c), and which contains an insoluble portion when fractionated with acetone, and whose methyl ethyl ketone swelling index is 1.5 to 4.0. (a) an innermost hard layer polymer obtained by polymerizing a mixture of monomers consisting of 80 to 98.9% by mass of methyl methacrylate, 1 to 20% by mass of an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, and 0.01 to 0.3% by mass of a polyfunctional grafting agent; (b) a crosslinked soft layer polymer obtained by polymerizing a mixture of monomers consisting of 75 to 98.5% by mass of an alkyl acrylate having 4 to 8 carbon atoms in the alkyl group, 0.01 to 5% by mass of a polyfunctional crosslinking agent, and 0.5 to 5% by mass of a polyfunctional grafting agent in the presence of the innermost hard layer polymer; (c) an outermost hard layer polymer obtained by polymerizing a mixture of monomers consisting of 80 to 99% by mass of methyl methacrylate and 1 to 20% by mass of an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group in the presence of a polymer consisting of the innermost hard layer and crosslinked soft layer.

[0101] In addition to specifying the composition and particle size of each layer of the multilayered acrylic granular composite, it is preferable to set the tensile modulus of the multilayered acrylic granular composite and the methyl ethyl ketone swelling degree of the acetone-insoluble portion within a specific range. This allows for a more satisfactory balance between impact resistance and stress whitening resistance. Specifying the composition and particle size of each layer of the multilayered acrylic granular composite is disclosed in Japanese Patent Publication No. 60-17406 and Japanese Patent Publication No. 3-39095.

[0102] Here, the innermost hard layer polymer (a) constituting the multilayered acrylic granular composite is preferably obtained by polymerizing a mixture of monomers consisting of the following: Mixture: A mixture of monomers consisting of 80 to 98.9 mass % of methyl methacrylate, 1 to 20 mass % of an alkyl acrylate having an alkyl group with 1 to 8 carbon atoms, and 0.01 to 0.3 mass % of a polyfunctional grafting agent.

[0103] Examples of alkyl acrylates having an alkyl group with 1 to 8 carbon atoms include methyl acrylate, ethyl acrylate, and n-propyl acrylate. Examples of the alkyl acrylates include n-butyl acrylate, s-butyl acrylate, and 2-ethylhexyl acrylate, with methyl acrylate and n-butyl acrylate being preferred.

[0104] The proportion of alkyl acrylate units in the innermost hard layer polymer (a) is 1 to 20% by mass. If the proportion is less than 1% by mass, the thermal decomposition of the polymer increases. On the other hand, if the proportion is more than 20% by mass, the glass transition temperature of the innermost hard layer polymer (c) decreases, and the impact resistance-imparting effect of the three-layer structure acrylic granular composite decreases. Therefore, it is not preferable if the proportion of the units is less than 1% by mass or more than 20% by mass.

[0105] The polyfunctional grafting agent may be a polyfunctional monomer having different polymerizable functional groups. Examples of the polyfunctional monomer include allyl esters of acrylic acid, methacrylic acid, maleic acid, and fumaric acid, with allyl methacrylate being preferred. The polyfunctional grafting agent is used to chemically bond the innermost hard layer polymer and the soft layer polymer, and the proportion of the polyfunctional grafting agent used during polymerization of the innermost hard layer is 0.01 to 0.3 mass%.

[0106] The crosslinked soft layer polymer (b) constituting the acrylic granular composite is preferably obtained by polymerizing a mixture of the following monomers in the presence of the innermost hard layer polymer (a): Mixture: A monomer mixture consisting of 75 to 98.5% by mass of an alkyl acrylate having 1 to 8 carbon atoms in the alkyl group, 0.01 to 5% by mass of a polyfunctional crosslinking agent, and 0.5 to 5% by mass of a polyfunctional grafting agent.

[0107] Here, n-butyl acrylate and 2-ethylhexyl acrylate are preferably used as alkyl acrylates having an alkyl group with 4 to 8 carbon atoms. Furthermore, together with these polymerizable monomers, 25% by mass or less of other copolymerizable monofunctional monomers can also be copolymerized.

[0108] Other copolymerizable monofunctional monomers include styrene and substituted styrene derivatives. The higher the ratio of alkyl acrylate having 4 to 8 carbon atoms in the alkyl group to styrene, the lower the glass transition temperature of polymer (b), i.e., the softer the polymer (b) can be.

[0109] On the other hand, from the viewpoint of transparency of the resin composition, it is advantageous to make the refractive index of the soft layer polymer (b) at room temperature close to those of the innermost hard layer polymer (a), the outermost hard layer polymer (c), and the hard thermoplastic acrylic resin, and therefore the ratio of the two is selected taking these into consideration.

[0110] The polyfunctional grafting agent may be any of those listed in the section on the innermost hard layer polymer (a). The polyfunctional grafting agent used here is used to chemically bond the soft layer polymer (b) and the outermost hard layer polymer (c). The proportion of the polyfunctional grafting agent used during polymerization for the innermost hard layer is preferably 0.5 to 5% by mass from the viewpoint of imparting impact resistance.

[0111] As the polyfunctional crosslinking agent, commonly known crosslinking agents such as divinyl compounds, diallyl compounds, diacryl compounds, and dimethacrylic compounds can be used. Polyethylene glycol diacrylate (molecular weight 200 to 600) is preferably used as the polyfunctional crosslinking agent. The polyfunctional crosslinking agent used here generates a crosslinked structure during polymerization of the soft layer (b), and is used to exhibit the effect of imparting impact resistance.

[0112] However, if the polyfunctional grafting agent is used during polymerization of the soft layer, a crosslinked structure of the soft layer (b) is formed to some extent, so the polyfunctional crosslinking agent is not an essential component. However, from the viewpoint of the impact resistance imparting effect, the proportion of the polyfunctional crosslinking agent used during polymerization of the soft layer is preferably 0.01 to 5 mass %.

[0113] The outermost hard layer polymer (c) constituting the multilayered acrylic granular composite is preferably obtained by polymerizing a mixture of the following monomers in the presence of the innermost hard layer polymer (a) and the soft layer polymer (b): Mixture: A monomer mixture consisting of 80 to 99% by mass of methyl methacrylate and 1 to 20% by mass of an alkyl acrylate having an alkyl group with 1 to 8 carbon atoms.

[0114] The acrylic alkylate may be any of those mentioned above, with methyl acrylate and ethyl acrylate being preferred. The proportion of alkyl acrylate units in the outermost hard layer (c) is preferably 1 to 20% by mass.

[0115] Furthermore, during polymerization of the outermost hard layer (c), alkyl mercaptans or the like can be used as chain transfer agents to adjust the molecular weight in order to improve compatibility with the acrylic resin (A). In particular, providing the outermost hard layer with a gradient in which the molecular weight gradually decreases from the inside to the outside is preferable in terms of improving the balance between elongation and impact resistance. A specific method involves dividing the monomer mixture used to form the outermost hard layer into two or more portions and gradually increasing the amount of chain transfer agent added each time. This method allows the molecular weight of the polymer forming the outermost hard layer to decrease from the inside to the outside of the multilayered acrylic granular composite. The molecular weight formed in this process can also be determined by polymerizing each monomer mixture used in each portion individually under the same conditions and measuring the molecular weight of the resulting polymer.

[0116] The particle size of the acrylic particles (C) preferably used in the present invention is not particularly limited, but is preferably 10 nm or more and 1000 nm or less, more preferably 20 nm or more and 500 nm or less, and most preferably 50 nm or more and 400 nm or less.

[0117] In the acrylic granular composite, which is a multilayer structure polymer preferably used in the present invention, the mass ratio of the core to the shell is not particularly limited. When the entire multilayer structure polymer is taken as 100 parts by mass, the core layer preferably comprises 50 parts by mass or more and 90 parts by mass or less, and more preferably 60 parts by mass or more and 80 parts by mass or less. The core layer here refers to the innermost hard layer.

[0118] A specific example of the acrylic particles (c-1), which are graft copolymers preferably used as the acrylic particles (C) in the present invention, is a graft copolymer obtained by copolymerizing a mixture of the following monomers in the presence of a rubber polymer: Mixture: A mixture of monomers consisting of an unsaturated carboxylic acid ester monomer, an unsaturated carboxylic acid monomer, an aromatic vinyl monomer, and, if necessary, other vinyl monomers copolymerizable therewith.

[0119] The rubbery polymer used in the acrylic particles (c-1) that are graft copolymers is not particularly limited, and examples thereof include diene rubbers, acrylic rubbers, and ethylene rubbers. Specific examples of the rubbery polymer include polybutadiene, styrene-butadiene copolymers, styrene-butadiene block copolymers, acrylonitrile-butadiene copolymers, butyl acrylate-butadiene copolymers, polyisoprene, butadiene-methyl methacrylate copolymers, butyl acrylate-methyl methacrylate copolymers, butadiene-ethyl acrylate copolymers, ethylene-propylene copolymers, ethylene-propylene-diene copolymers, ethylene-isoprene copolymers, and ethylene-methyl acrylate copolymers. These rubbery polymers can be used alone or in a mixture of two or more.

[0120] When acrylic particles (C) are added to the optical film of the present invention, it is preferable that the refractive index of the mixture of the acrylic resin (A) and the cellulose ester resin (B) is close to that of the acrylic particles (C). By adjusting the refractive index in this manner, a film with high transparency can be obtained. Specifically, the difference in refractive index between the acrylic particles (C) and the acrylic resin (A) is preferably 0.05 or less, more preferably 0.02 or less, and particularly preferably 0.01 or less.

[0121] To satisfy the refractive index requirement, methods such as adjusting the composition ratio of each monomer unit in the acrylic resin (A) or adjusting the composition ratio of the rubber polymer or monomer used in the acrylic particles (C) can be used. These methods can reduce the refractive index difference, resulting in an optical film with excellent transparency. The refractive index difference referred to here refers to the difference in refractive index between the soluble portion (acrylic resin (A)) and the insoluble portion (acrylic particles (C)) separated and purified by the following procedure. Specifically, the optical film of the present invention is sufficiently dissolved in a solvent in which the acrylic resin (A) is soluble under appropriate conditions to form a cloudy solution. This cloudy solution is separated into a solvent-soluble portion and an insoluble portion by centrifugation or other procedures. The soluble portion (acrylic resin (A)) and the insoluble portion (acrylic particles (C)) are then purified, and the difference in refractive index (23°C, measurement wavelength: 550 nm) measured thereafter is referred to as the refractive index difference.

[0122] In the present invention, there is no particular limitation on the method for blending the acrylic particles (C) with the acrylic resin (A). In this blending method, the acrylic resin (A) is first blended with other optional components in advance. Then, the resulting mixture is uniformly melt-kneaded using a single-screw or twin-screw extruder, usually at 200 to 350°C, while the acrylic particles (C) are added.

[0123] As a method for blending, a method of adding a solution in which the acrylic particles (C) are previously dispersed to a solution (dope solution) in which the acrylic resin (A) and the cellulose ester resin (B) are dissolved and mixed can be mentioned. Furthermore, as a method for blending, a method of in-line addition of a solution in which the acrylic particles (C) and other optional additives are dissolved and mixed can be used.

[0124] Commercially available products can also be used as the acrylic particles according to the present invention. Examples of such commercially available products include Metablen W-341 (C2) (manufactured by Mitsubishi Chemical Corporation), Chemisnow MR-2G (C3), and MS-300X (C4) (manufactured by Soken Chemical & Engineering Co., Ltd.). Other commercially available products include "Kane Ace" manufactured by Kaneka Corporation and "Paraloid" manufactured by Kureha Corporation. Further commercially available products include "Acryloid" manufactured by Rohm and Haas, "Staphyloid" manufactured by Ganz Chemical Industry Co., Ltd., and "Parapet SA" manufactured by Kuraray Co., Ltd.

[0125] The optical film of the present invention preferably contains acrylic particles (C) in an amount of 0.5 to 30% by mass, more preferably 1.0 to 15% by mass, based on the total mass of the resins constituting the film.

[0126] <Other Additives> In the optical film of the present invention, a plasticizer can be used in combination to improve the fluidity and flexibility of the composition. Examples of plasticizers include phthalate esters, fatty acid esters, trimellitates, phosphate esters, polyesters, and epoxy-based plasticizers. Among these, polyester and phthalate ester plasticizers are preferred. Polyester plasticizers have superior non-migration and extraction resistance compared to phthalate ester plasticizers such as dioctyl phthalate, but are somewhat inferior in plasticizing effect and compatibility. Therefore, by selecting or using these plasticizers in combination depending on the application, the film can be used in a wide range of applications.

[0127] Polyester plasticizers are reaction products of mono- to tetra-carboxylic acids with mono- to hexa-valent alcohols, but those obtained by reacting dicarboxylic acids with glycols are mainly used. Representative dicarboxylic acids include glutaric acid, itaconic acid, adipic acid, phthalic acid, azelaic acid, and sebacic acid. In particular, the use of adipic acid or phthalic acid as the dicarboxylic acid results in products with excellent plasticizing properties. Examples of glycols include ethylene, propylene, 1,3-butylene, 1,4-butylene, 1,6-hexamethylene, neopentylene, diethylene, triethylene, and dipropylene glycols. These dicarboxylic acids and glycols may be used alone or in combination.

[0128] This ester-based plasticizer may be of the ester, oligoester, or polyester type, and its molecular weight should be in the range of 100 to 10,000, with a range of 600 to 3,000 being preferred for its plasticizing effect. The viscosity of a plasticizer is correlated with its molecular structure and molecular weight, and in the case of an adipic acid-based plasticizer, a viscosity in the range of 200 to 5,000 MPa·s (25°C) is preferred due to compatibility and plasticizing efficiency. Furthermore, several polyester-based plasticizers may be used in combination.

[0129] It is also preferable to use a polymer plasticizer in the optical film of the present invention. In particular, the polyesters described in paragraphs 0103 to 0116 of JP-A No. 2007-231157 and the polyester-based plasticizers described above can be preferably used.

[0130] For the optical film of the present invention, it is also preferable to use a sugar ester plasticizer obtained by esterifying the hydroxyl groups of a sugar compound having 1 to 12 bonds of at least one type of structure selected from furanose and pyranose structures. Examples of sugar ester compounds used in the present invention include glucose, galactose, mannose, fructose, xylose, and arabinose. Examples of the sugar ester compound include lactose, sucrose, cellobiose, cellotriose, maltotriose, and raffinose. Particularly preferred are sugar ester compounds having both furanose and pyranose structures, such as sucrose. Commercially available sugar ester compounds include Monopet SB (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[0131] The plasticizer is preferably added in an amount of 0.5 to 30 parts by mass relative to 100 parts by mass of the optical film of the present invention. When the amount of the plasticizer added is 30 parts by mass or less, the surface does not become sticky, which is practically preferable.

[0132] The optical film of the present invention also preferably contains an ultraviolet absorber. Examples of the ultraviolet absorber that can be used include benzotriazole-based, 2-hydroxybenzophenone-based, and salicylic acid phenyl ester-based absorbers. Specific examples of the ultraviolet absorber include triazoles such as 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(3,5-di-t-butyl-2-hydroxyphenyl)benzotriazole, and benzophenones such as 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, and 2,2'-dihydroxy-4-methoxybenzophenone.

[0133] Among ultraviolet absorbers, ultraviolet absorbers with a molecular weight of 400 or more are less likely to volatilize due to their high boiling points and are less likely to scatter during high-temperature molding, and therefore can effectively improve weather resistance with the addition of a relatively small amount.

[0134] Examples of ultraviolet absorbers having a molecular weight of 400 or more include benzotriazole-based compounds such as 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2-benzotriazole and 2,2-methylenebis[4-(1,1,3,3-tetrabutyl)-6-(2H-benzotriazol-2-yl)phenol], hindered amine-based compounds such as bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate and bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, and further 2-(3,5-di-t-butyl-4- Examples of suitable ultraviolet absorbers include hybrids having both hindered phenol and hindered amine structures in the molecule, such as bis(1,2,2,6,6-pentamethyl-4-piperidyl)-2-n-butylmalonate (hydroxybenzyl), and 1-[2-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]ethyl]-4-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]-2,2,6,6-tetramethylpiperidine. These may be used alone or in combination of two or more. In particular, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2-benzotriazole is preferred as the ultraviolet absorber. Furthermore, 2,2-methylenebis[4-(1,1,3,3-tetrabutyl)-6-(2H-benzotriazol-2-yl)phenol] is also particularly preferred as the ultraviolet absorber.

[0135] Furthermore, various antioxidants can be added to the optical film of the present invention in order to improve thermal decomposition and thermal discoloration during molding processing, and an antistatic agent can be added to impart antistatic properties to the optical film.

[0136] The optical film of the present invention may use a flame-retardant acrylic resin composition containing a phosphorus-based flame retardant. Examples of phosphorus-based flame retardants include red phosphorus, triaryl phosphate esters, diaryl phosphate esters, monoaryl phosphate esters, aryl phosphonic acid compounds, aryl phosphine oxide compounds, condensed aryl phosphate esters, halogenated alkyl phosphate esters, halogen-containing condensed phosphate esters, halogen-containing condensed phosphonic acid esters, and halogen-containing phosphites, or mixtures of two or more of these. Specific examples of phosphorus-based flame retardants include triphenyl phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and phenylphosphonic acid. Examples of the phosphorus-based flame retardant include tris(β-chloroethyl)phosphate, tris(dichloropropyl)phosphate, and tris(tribromoneopentyl)phosphate.

[0137] The optical film of the present invention can simultaneously achieve low moisture absorption, transparency, high heat resistance, and improved brittleness, which have not been achieved with conventional resin films.

[0138] [Method of Manufacturing Optical Film] The optical film of the present invention is manufactured by multi-stage stretching. In the following manufacturing method, a film is formed, followed by a first-stage stretching, then winding, unwinding, and then a final-stage stretching is described. However, as mentioned above, the present invention is not limited to this. Furthermore, the following manufacturing method is described using an acrylic resin (A) as the thermoplastic resin (A) and a cellulose ester resin (B) as the thermoplastic resin (B), but the present invention is not limited to this. FIG. 3 is a flowchart illustrating an example of the manufacturing method of the present invention. FIG. 4 is a schematic diagram of an apparatus for manufacturing a polarizing plate protective film. The optical film manufacturing method, which is an example of the manufacturing method of the present invention, includes, for example, a raw film manufacturing process and a processing process. The raw film manufacturing process includes at least the steps of film formation, first-stage stretching (including the first-stage stretching), and winding. The processing process includes at least the steps of unwinding, second-stage stretching (including the final-stage stretching), and winding. Specific examples are as follows.

[0139] 1. Raw Film Manufacturing Process The raw film according to the present invention is a film manufactured by a solution casting film-forming method. The raw film manufacturing process, which is an example of the present invention, includes the following steps: (1.1) A step of casting a dope onto a support to form a web (1.1.1) A step of preparing a dope (by stirring and preparation) (S1) (1.1.2) A step of casting a dope onto a support (S2) (1.1.3) A step of peeling off (S3) (1.2) A step of performing the first stage of stretching of the web (S4) (1.3) A step of drying the web and winding up the formed film (1.3.1) A step of drying (S5) (1.3.2) A first cutting step (S6) (1.3.3) A first winding step (S7) The term "dope" refers to a raw material solution or dispersion obtained by dissolving a film-forming raw material such as a cellulose ester resin in a solvent or dispersing it in a dispersion medium. The term "web" refers to a film formed by casting and containing a certain amount of solvent (solvent).

[0140] (1.1) Step of Casting Dope onto Support to Form Web (1.1.1) Dope Preparation (Stirring Preparation) Step (S1) In the dope preparation (stirring preparation) step (S1), at least a resin and a solvent are stirred in a stirring tank 1a of a stirring device 1 to prepare a dope to be cast onto a support 3 (endless belt). Hereinafter, the dope preparation step will be described using, as an example, a resin composition containing an acrylic resin (A) and a cellulose ester resin (B).

[0141] In the dope preparation step (S1), first, an organic solvent mainly consisting of a good solvent for the acrylic resin (A) and the cellulose ester resin (B) is charged into a dissolution vessel (stirring tank 1a). Next, the acrylic resin (A), the cellulose ester resin (B), optionally the acrylic particles (C), and other additives are dissolved in the dissolution vessel under stirring to prepare a dope. Alternatively, the dope, which is the main solution, is prepared by mixing the acrylic resin (A) and cellulose ester resin (B) solution with the optionally acrylic particle (C) solution and other additive solutions.

[0142] The acrylic resin (A) and the cellulose ester resin (B) can be dissolved at normal pressure, at or below the boiling point of the main solvent, or under pressure at or above the boiling point of the main solvent. Various dissolution methods, such as a cooling dissolution method or a high-pressure method, can be used for the dissolution, but a method under pressure at or above the boiling point of the main solvent is particularly preferred. The cooling dissolution method is described in JP-A-9-95544, JP-A-9-95557, or JP-A-9-95538. The high-pressure method is described in JP-A-11-21379.

[0143] The total content of the acrylic resin (A) and the cellulose ester resin (B) in the dope is preferably in the range of 15 to 45% by mass. After the additives are added to the dope during or after dissolution and dissolved and dispersed, the dope is filtered with a filter medium, degassed, and sent to the next step by a liquid delivery pump.

[0144] For filtration, it is preferable to use a filter medium with a particle size of 0.5 to 5 μm and a filtering time of 10 to 25 sec / 100 ml.

[0145] In this method, the aggregates remaining during particle dispersion and the aggregates generated during the addition of the main dope can be removed by using a filter with a particle size of 0.5 to 5 μm and a filtration time of 10 to 25 sec / 100 ml. Since the particle concentration in the main dope is sufficiently low compared to the additive solution, the aggregates do not stick together during filtration, causing a sudden increase in filtration pressure.

[0146] If necessary, large aggregates are removed from the acrylic particle feed kettle (not shown) using a filter, and the liquid is sent to a stock kettle, after which the acrylic particle additive liquid is added from the stock kettle to the main dope dissolving kettle.

[0147] The main dope solution is then filtered in a main filter, and an ultraviolet absorber additive solution is added inline to the filtered solution. In many cases, the main dope contains about 10 to 50% by mass of recycled materials. The recycled materials may contain acrylic particles. In such cases, it is preferable to control the amount of the acrylic particle additive solution to match the amount of recycled materials.

[0148] The additive liquid containing acrylic particles preferably contains 0.5 to 20% by mass of acrylic particles. Furthermore, the additive liquid more preferably contains 0.7 to 10% by mass of acrylic particles, and most preferably contains 0.8 to 5% by mass of acrylic particles. Within the above range, the additive liquid has low viscosity, is easy to handle, and can be easily added to the main dope, which is preferable.

[0149] The recycled material is a finely crushed optical film, and is made from the cut-off side portions of the film generated during the production of the optical film, or from a roll of optical film that has fallen out of spec due to scratches, etc. In addition, pellets made by kneading acrylic resin, cellulose ester resin, and, in some cases, acrylic particles in advance can also be preferably used as the sapwood.

[0150] (1.1.2) Casting Step (S2) In the casting step (S2), the web 5 formed from the dope cast on the support 3 is heated on the support 3, and the solvent is evaporated until the web 5 can be peeled from the support 3 with a peel roller 4. The amount of residual solvent immediately before the first-stage stretching can be controlled by the evaporation of the solvent.

[0151] The evaporation is preferably carried out in an atmosphere within a range of 5 to 75°C. Methods for evaporating the solvent include a method of blowing hot air onto the upper surface of the web and / or a method of transferring heat from the back surface of the support 3 using a liquid, and a method of transferring heat from both sides using radiant heat. In the present invention, the method of transferring heat from both sides using radiant heat is preferred because it has good drying efficiency. A combination of these methods is also preferably used.

[0152] From the viewpoint of productivity, the casting width is preferably 1.3 m or more. The casting width is more preferably in the range of 1.3 to 4.0 m. If the casting width does not exceed 4.0 m, stripes will not appear in the production process and the stability in the subsequent transport process will be high. From the viewpoint of transportability and productivity, the width is more preferably in the range of 1.3 to 3.0 m.

[0153] The support 3 in the casting step (S2) preferably has a mirror-finished surface, and is preferably a stainless steel belt or a cast drum with a plated surface.

[0154] The surface temperature of the support 3 in the casting step (S2) is in the range of −50° C. to the boiling point of the solvent, and a higher temperature is preferred because it increases the drying speed of the web. The preferred support temperature is in the range of 0 to 55° C., and more preferably in the range of 22 to 50° C.

[0155] The method for controlling the temperature of the support 3 is not particularly limited, but includes blowing hot or cold air or bringing hot water into contact with the back side of the support. Using hot water is preferable because heat is transferred more efficiently and the time required for the support to reach a constant temperature is shorter. When using hot air, air at a temperature higher than the desired temperature may be used.

[0156] In the casting step (S2), the dope prepared in the dope preparing step (S1) is fed through a conduit to a casting die 2 via a pressure type metering gear pump or the like. Then, the dope is cast from the casting die 2 onto a casting position on a support 3 made of a stainless steel endless belt that is rotated and moves endlessly.

[0157] Here, the part of the casting die slit from which the dope comes out is called the lip. A casting die is preferred because it allows the slit shape of the lip portion to be adjusted and makes it easy to make the film thickness uniform. Casting dies include coat hanger dies and T-dies, and any of these are preferably used. To increase the film production speed of the raw film, two or more of the above-mentioned casting dies may be provided on the support, and the dope amount may be divided and layered. Alternatively, it is also preferred to obtain a raw film with a laminated structure by a co-casting method in which multiple dopes are simultaneously cast.

[0158] The slit can be narrowed by manually turning and pushing the heat bolt, or opened to make the film thickness thinner. A common method is to apply a voltage to the heat bolt to push the film, but these methods are usually used in combination. A push-pull method is also possible. However, the bolt pitch may not be narrow due to the mechanism of the casting die. For high-viscosity dopes (including molten dopes), the pressure load on the lip during discharge from the casting die is large, and the load drops suddenly after discharge, resulting in an increase in film thickness (balance effect), which can cause variations in the film thickness across the width. Therefore, the internal structure of the casting die must be designed to prevent excessive load from being applied to the lip.

[0159] In the casting step (S2), the cast dope is dried on the support 3 to form a web 5. In this case, the inclination of the casting die 2, i.e., the direction of the dope being discharged from the casting die 2 to the support 3, may be appropriately set so that the angle with respect to the normal to the surface of the support 3 (the surface onto which the dope is cast) falls within the range of 0 to 90°.

[0160] The support 3 is made of, for example, a stainless steel belt and is held by a pair of rollers 3a, 3b and multiple rollers positioned between them. In this case, it is preferable that the surface of the support is a mirror finish. One or both of the rollers 3a and 3b are provided with a drive device that applies tension to the support 3, so that the support 3 is used in a tensioned state. The support 3 may also be a drum.

[0161] (1.1.3) Peeling Step (S3) The peeling step (S3) is a step in which the web from which the solvent has evaporated on the support 3 is peeled at the peeling position. At this time, from the viewpoints of surface quality, moisture permeability, and peelability, it is preferable to peel the raw film from the support within a range of 30 to 600 seconds. The position at which the web is peeled from the support is called the peeling point. The roll that assists the peeling is called the peeling roller. In the peeling step (S3), the web is peeled by the peeling roller 4 while maintaining its self-supporting properties. The temperature at the peeling position on the support is preferably within a range of -50 to 40°C, more preferably within a range of 10 to 40°C, and most preferably within a range of 15 to 30°C.

[0162] (Residual Solvent Amount) The residual solvent amount immediately before the first-stage stretching can be adjusted as appropriate depending on the strength of the drying conditions, the length of the support 3, etc. Although it depends on the thickness of the web, if the residual solvent amount at the peeling point is too high, the web may become too soft and difficult to peel, resulting in loss of flatness and the likelihood of horizontal steps, wrinkles, or vertical streaks due to the peeling tension. Conversely, if the residual solvent amount is too low, part of the web may peel off during the process. In order for the web to exhibit good flatness, it is preferable that the residual solvent amount be in the range of 1 to 50% by mass, from the viewpoint of balancing economic speed and quality. Furthermore, from the viewpoint of realizing the effects of the present invention, it is preferable that the residual solvent amount be in the range of 1 to 30% by mass.

[0163] One method for increasing the film formation rate (which allows for peeling while the residual solvent content is as high as possible) is the gel casting method, which allows for peeling even when the residual solvent content is high. One example of this method is to add a poor solvent for the acrylic resin and cellulose ester resin to the dope, and then gel the web after casting the dope. Another example of this method is to cool the support to gel the web, which is then peeled off while it contains a large amount of residual solvent. Another example of this method is to add a metal salt to the dope. As described above, gelling the web on the support and strengthening the film can accelerate peeling and increase the film formation rate.

[0164] The residual solvent amount is defined by the following formula: Residual solvent amount (mass%)={(M-N) / N}×100, where M is the mass of a sample taken at any time during or after the production of the web or polarizing plate protective film, and N is the mass of M after heating at 115°C for 1 hour.

[0165] (Method for measuring the amount of residual solvent) The amount of residual solvent can be measured by headspace gas chromatography. In headspace gas chromatography, a sample is sealed in a container and heated, and the gas in the container is quickly injected into a gas chromatograph while the container is filled with volatile components. Mass spectrometry is then performed to identify the compounds and quantify the volatile components. The headspace method makes it possible to observe all peaks of volatile components using a gas chromatograph, and by using an analytical method utilizing electromagnetic interactions, it is also possible to quantify volatile substances, monomers, etc. with high precision.

[0166] (Peeling Tension) The peeling tension when peeling the support and the web is preferably 300 N / m or less. The peeling tension is more preferably in the range of 196 to 245 N / m, but if wrinkles are likely to occur during peeling, peeling is preferably performed at a tension of 190 N / m or less.

[0167] (1.2) Step (S4) of First-Stage Stretching of Web The step (S4) of first-stage stretching is a step of stretching the web after peeling it from the support. The first-stage stretching includes a previous-stage stretching performed at least once in the same direction as the final-stage stretching described below. Specifically, if the final-stage stretching is, for example, in the TD direction, at least one TD stretching (previous-stage stretching) is performed in the first-stage stretching. If the final-stage stretching is, for example, in the MD direction, at least one MD stretching (previous-stage stretching) is performed in the first-stage stretching. In the present invention, it is preferable that the final-stage stretching (fourth stretching) is in the TD direction, and the first-stage stretching involves stretching in the MD direction (first stretching), followed by stretching in the TD direction (second stretching: previous-stage stretching), and then further stretching in the MD direction (third stretching) (pattern (a) described above).

[0168] In the present invention, the ratio of the stretching ratio in the final stretching stage to the stretching ratio in the previous stretching stage (stretching ratio in the final stretching stage / stretching ratio in the previous stretching stage) is set to a range of 1.15 to 2.00. The final stretching stage refers to the last stretching stage in the second stretching stage described later in (2.2).

[0169] Furthermore, the ratio of the stretching temperature in the final stage to the stretching temperature in the previous stage (stretching temperature in the final stage / stretching temperature in the previous stage) is preferably in the range of 1.00 to 1.50, more preferably in the range of 1.00 to 1.20.

[0170] Furthermore, in the first-stage stretching, the stretching ratios in the MD and TD directions are preferably within the range of 1.03 to 2.0 times for each of the TD and MD directions. The stretching ratio in the MD direction is defined as (the conveying speed of the film after stretching) / (the conveying speed of the film before stretching). The stretching ratio in the TD direction is defined as (the width of the film after stretching) / (the width of the film before stretching).

[0171] (Residual Solvent Amount) In the present invention, the residual solvent amount immediately before the first-stage stretching is the same as the residual solvent amount at the peeling point in the peeling step (S3) described above. In an embodiment of the present invention, the residual solvent amount immediately before the first-stage stretching is preferably in the range of 1 to 15 mass %, and the stretching ratio is preferably in the range of 1.03 to 2.0. By setting the residual solvent amount and the stretching ratio within the above ranges, it is preferable from the viewpoints of improving the adhesiveness of the film and suppressing deterioration of the film strength.

[0172] The first-stage stretching step (S4) promotes entanglement between polymer molecules (matrix molecules) in the web thickness direction. This allows the adhesive to penetrate into the polarizer protective film through the entangled portions (crosslinked portions) between the matrix molecules, even when the polarizer protective film is bonded to the polarizer layer via an adhesive during polarizer production. As a result, the polarizer protective film can be firmly fixed to the polarizer layer via the adhesive, improving the peel strength of the polarizer protective film relative to the polarizer layer. In other words, the adhesion between the polarizer protective film and the polarizer layer is improved, ensuring the ability to suppress deterioration of the film strength. The polarizer layer is also referred to as a "polarizing film," "polarizer film," or "polarizer film."

[0173] Here, when stretching a film in the MD direction, a preferred stretching method is a method in which a difference in peripheral speed between rollers is used to stretch the film in the conveying direction (longitudinal direction of the film; film-forming direction; casting direction; MD direction). When stretching a film in the TD direction, a tenter method is preferred, in which both side edges of the film are fixed with clips or the like and stretched in the width direction (direction perpendicular to the film plane; TD direction). Such a stretching method improves the performance, productivity, flatness, and dimensional stability of the film. Furthermore, in the case of the so-called tenter method, driving the clips with a linear drive system is preferred because smooth stretching can be performed and the risk of breakage, etc. is reduced.

[0174] The width holding or transverse stretching is preferably carried out by a tenter stretching apparatus, which may be a pin tenter or a clip tenter. When a tenter stretching apparatus is used for stretching, it is preferable to use an apparatus that can independently control the gripping length (the distance from the start of gripping to the end of gripping) of the web on the left and right sides by the left and right gripping means of the tenter.

[0175] (1.3) Step of drying the web and winding up the formed film This step comprises a drying step (S5), a first cutting step (S6), and a first winding step (S7).

[0176] (1.3.1) Drying Step (S5) The drying step (S5) is a step in which the web is heated on the support to evaporate the solvent, and the formed film is wound up.

[0177] In the drying device 7 shown in Fig. 4, the web is transported by a plurality of transport rollers arranged in a staggered pattern when viewed from the side, and the web is dried during this transport. The drying method in the drying device 7 is not particularly limited, and the web is generally dried using hot air, infrared rays, heated rollers, microwaves, etc., but from the viewpoint of simplicity, a method of drying the web with hot air is preferred. A combination of these methods is also preferred. The drying step (S5) may be performed as needed.

[0178] Thinner webs dry faster, but drying too quickly can damage the flatness of the finished film. When drying at high temperatures, the amount of residual solvent must be taken into consideration, but ensuring that the amount of residual solvent is not too high can prevent breakdowns due to solvent foaming. Drying is generally carried out at a temperature in the range of 30 to 250°C throughout. Drying within the range of 35 to 200°C is particularly preferred, and it is preferable to increase the drying temperature in stages. The temperature of the support may be the same throughout or may vary depending on the position.

[0179] In the web drying process, the roller drying method (a method in which the web is dried by passing it alternately through multiple rollers arranged above and below) or the tenter method, in which the web is dried while being transported, is generally used.

[0180] During the drying step, the film may be stretched in the MD direction by adjusting the tenter speed and the take-up speed described below while being transported by a number of rollers.

[0181] (1.3.2) First Cutting Step (S6) In the first cutting step (S6), a cutting unit 8 made of a slitter cuts both widthwise ends of the film F that has been stretched in the first-stage stretching step (S4) and has been through the drying step (S5). The portions of the film F that remain after cutting the both ends constitute product portions that will become the film product. Meanwhile, the portions cut from the film F may be recovered and reused as part of the raw materials for producing a polarizing plate protective film.

[0182] (1.3.3) First Winding Step (S7) In the first winding step (S7), the film F is wound by the winding device 9, completing the raw film manufacturing process. The preferred range of the initial tension when winding the film F in the winding step is within the range of 20 to 300 N / m.

[0183] 2. Processing Step As shown below, the processing step is a step of unwinding the wound film from the roll (S8) and then performing a second-stage stretching. The processing step includes at least a unwinding step (S8), a second-stage stretching step (S9), a second cutting step (S10), and a second winding step (S11). (2.1) Unwinding step (S8) (2.2) Second-stage stretching step (S9) (2.3) Second cutting step (S10) (2.4) Second winding step (S11)

[0184] (Residual Solvent Amount) The residual solvent amount immediately before the second-stage stretching is preferably in the range of 0.1 to 0.5% by mass.

[0185] (2.1) Unwinding Step (S8) In the unwinding step (S8), the film wound in the first winding step is unwound from the roll.

[0186] (2.2) Second-stage stretching step (S9) The second-stage stretching step (S9) is a step including at least a final-stage stretching. The final-stage stretching may be in either the MD direction or the TD direction, but as described above, it is sufficient that at least one stretching in the same direction as the final-stage stretching direction is performed prior to the final-stage stretching. In the present invention, it is preferable that the final-stage stretching is in the TD direction, and that in the first-stage stretching, the film is stretched in the MD direction, then stretched in the TD direction, and then further stretched in the MD direction.

[0187] Furthermore, the ratio of the draw ratios (draw ratio in the final-stage draw / draw ratio in the previous-stage draw) is set to a range of 1.15 to 2.00. That is, the ratio of the draw ratios (draw ratio in the final stage / draw ratio in the previous-stage draw) between the final-stage draw in the second-stage draw process and the previous-stage draw in the first-stage draw process is set to a range of 1.15 to 2.00, more preferably a range of 1.2 to 1.8.

[0188] Furthermore, the ratio of the stretching temperature in the final stage of the second stretching step to the stretching temperature in the previous stage of the first stretching step (stretching temperature in the final stage / stretching temperature in the previous stage) is preferably in the range of 1.00 to 1.50. The ratio is more preferably in the range of 1.00 to 1.20. Such stretching can be performed using stretching apparatus 10.

[0189] In the second-stage stretching step (S9), the film F unwound from the unwinding device 9a is stretched by the stretching device 10. The stretching method when stretching the film in the MD direction and the stretching method when stretching the film in the TD direction are the same as those in the first-stage stretching step described above. In addition to stretching, drying may be performed in the stretching device 10.

[0190] (2.3) Second Cutting Step (S10) In the second cutting step (S10), a cutting unit 11 consisting of a slitter cuts both widthwise ends of the film F stretched in the second stretching step (S9). The portions of the film F remaining after cutting the both ends constitute product portions that will become film products. Meanwhile, the portions cut from the film F may be recovered and reused as part of the raw material for film production.

[0191] (2.4) Second Winding Step (S11) In the second winding step (S11), the film F is wound by the winding device 12. At this time, the film thickness is preferably in the range of 5 to 100 μm, more preferably in the range of 5 to 80 μm. In particular, the film thickness is preferably 40 μm or less, and even more preferably in the range of 5 to 40 μm. The preferred range of the initial tension when winding the film F in the second winding step (S11) is in the range of 20 to 300 N / m.

[0192] (Winding Method) The film F can be wound using a commonly used winder. The winding method can be a method of controlling tension, such as a constant torque method, a constant tension method, a taper tension method, or a program tension control method with constant internal stress, and any of these can be used appropriately. Before winding, the ends can be slit and trimmed to the width of the product, and both ends of the film can be subjected to a surface modification treatment to prevent sticking or scratches during winding.

[0193] [Uses] The optical film of the present invention is preferably used as a substrate film for coating. Specifically, the optical film is preferably used as a film to which a hard coat layer-forming coating liquid is applied in order to form a hard coat layer (described later) on the optical film. The optical film can be used in the following film forms for applications such as liquid crystal display devices. Specifically, the optical film can be used as a polarizing plate protective film, a retardation film, an antireflection film, a brightness enhancement film, a hard coat film, an antiglare film, an antistatic film, an optical compensation film such as a viewing angle widening film, etc. for liquid crystal display devices. Typical uses of the optical film of the present invention include polarizing plate protective films, retardation films, and optical compensation films, among the above.

[0194] <Hard Coat Layer> From the viewpoint of enhancing functionality, such as improving impact resistance and ease of handling, it is preferable to form a hard coat layer on the optical film of the present invention. The strength of the film after the hard coat layer is formed can be confirmed by various known methods. Examples of such known methods include a method of confirming by measuring pencil hardness in accordance with JIS K 5600 5-4 (Pencil Hardness Evaluation Method).

[0195] It is more preferable that the hard coat layer contains an ultraviolet curable resin and silica particles from the viewpoint of improving impact resistance, ease of handling, etc. Furthermore, other additives can be further blended as necessary within a range that does not impair the effects of the present invention.

[0196] (UV-curable resin) As the UV-curable resin, a component containing a monomer having an ethylenically unsaturated double bond is preferably used. By UV irradiation, a hard coat layer excellent in mechanical film strength (scratch resistance, pencil hardness) can be formed. Examples of the UV-curable resin include organic hard coat materials such as organic silicones, melamines, epoxys, acrylates, and polyfunctional (meth)acrylic compounds. Other examples include inorganic hard coat materials such as silicon dioxide.

[0197] Among these, (meth)acrylate-based and polyfunctional (meth)acrylic compounds are preferred as hard coat-forming materials from the viewpoint of good adhesive strength and excellent productivity. Here, (meth)acrylic refers to acrylic and methacrylic. Examples of (meth)acrylates include those having one, two, or three or more polymerizable unsaturated groups in the molecule, and (meth)acrylate oligomers containing three or more polymerizable unsaturated groups in the molecule. For example, examples of polyfunctional acrylates that can be used include pentaerythritol polyfunctional acrylates, dipentaerythritol polyfunctional acrylates, pentaerythritol polyfunctional methacrylates, and dipentaerythritol polyfunctional methacrylates. (Meth)acrylates may be used alone or in combination of two or more types.

[0198] (Silica Particles) When the hard coat layer contains an ultraviolet curable resin and silica particles, the mass ratio of the silica particles to the ultraviolet curable resin (silica particles / ultraviolet curable resin) is preferably within the range of 10 / 90 to 50 / 50. A ratio of 10 / 90 or more is preferred in terms of increasing the hardness of the hard coat layer, and a ratio of 50 / 50 or less is preferred in terms of not deteriorating haze or scratch resistance.

[0199] In order to achieve both haze and surface hardness, it is preferable that the silica particles have an average primary particle size of 200 nm or less. The average primary particle size is preferably within a range of 5 to 100 nm, more preferably within a range of 10 to 50 nm. Although the surface hardness of silica particles increases even when the particle surface is untreated, silica particles having a portion of their surface coated with an organic component and having reactive polymerizable unsaturated groups introduced by the organic component on their surface are preferred. The average primary particle size of the silica particles preferably used in this embodiment is 5 to 200 nm, and examples of silica particles having such a particle size include silica particles having the above-mentioned reactive polymerizable unsaturated groups on their surface.

[0200] Known silica particles that have not been surface-modified can be used, and their shape may be spherical or amorphous. They are not limited to ordinary colloidal silica, and may be hollow particles, porous particles, core / shell type particles, or the like, but colloidal silica is preferred.

[0201] [Dispersion Medium] The dispersion medium for silica particles is preferably water or an organic solvent. Examples of organic solvents include alcohols, ketones, aromatic hydrocarbons, amides, esters, and ethers. Among these, alcohols and ketones are preferred as organic solvents, and these organic solvents can be used alone or in combination. Examples of alcohols include methanol, isopropyl alcohol, ethylene glycol, butanol, and ethylene glycol monopropyl ether. Examples of ketones include methyl ethyl ketone and methyl isobutyl ketone. Examples of aromatic hydrocarbons include toluene and xylene. Examples of amides include dimethylformamide, dimethylacetamide, and N-methylpyrrolidone. Examples of esters include ethyl acetate, butyl acetate, and γ-butyrolactone. Examples of ethers include tetrahydrofuran and 1,4-dioxane.

[0202] [Commercially Available Products] Examples of commercially available colloidal silica include IPA-ST, IPA-ST-L, IPA-ST-ZL, MEK-ST-L, and MEK-ST-MS manufactured by Nissan Chemical Industries, Ltd.

[0203] The reactive silica particles are obtained by surface-treating colloidal silica with an organic compound having a reactive polymerizable unsaturated group. That is, the organic component that coats the surface of the silica particles refers to the organic component derived from the organic compound having a reactive polymerizable unsaturated group used in the surface treatment.

[0204] [Organic Compound Used in Surface Treatment] The organic compound used in the surface treatment to coat the surface of silica particles with an organic component is an organic compound having a polymerizable unsaturated group. The polymerizable unsaturated group is preferably any two or more of a hydroxy group, a carboxy group, an amino group, an epoxy group, an isocyanate group, a (meth)acryloyl group, and a vinyl group. In addition, a combination of a hydroxy group, a carboxy group, an isocyanate group, and a (meth)acryloyl group is particularly preferred. In the present invention, (meth)acrylate means methacrylate or acrylate.

[0205] Specific examples of organic compounds having a polymerizable unsaturated group include coupling agents such as 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane, and vinyltriethoxysilane; acrylic acid esters such as methyl acrylate, 2-ethylhexyl acrylate, methoxyethyl acrylate, butoxyethyl acrylate, butyl acrylate, methoxybutyl acrylate, and phenyl acrylate; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, methoxyethyl methacrylate, ethoxymethyl methacrylate, phenyl methacrylate, and lauryl methacrylate; 2-(N,N-diethylamino)ethyl acrylate, 2-(N,N-dimethyl methacrylate), substituted amino alcohol esters of unsaturated substituted acids such as 2-(N,N-dibenzylamino)ethyl acrylate, 2-(N,N-dibenzylamino)methyl acrylate, and 2-(N,N-diethylamino)propyl acrylate; unsaturated carboxylic acid amides such as acrylamide and methacrylamide; compounds such as ethylene glycol diacrylate, propylene glycol diacrylate, propylene glycol diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, and triethylene glycol diacrylate; polyfunctional compounds such as dipropylene glycol diacrylate, ethylene glycol diacrylate, propylene glycol dimethacrylate, and diethylene glycol dimethacrylate; and / or polythiol compounds having two or more thiol groups in the branch (for example, trimethylolpropane trithioglycolate, trimethylolpropane trithiopropylate, and pentaerythritol tetrathioglycol).

[0206] The use of reactive silica particles having polymerizable unsaturated groups in this way leads to crosslinking between the binder resin and the silica particles, as well as between the silica particles themselves, which improves hardness and prevents particle shedding. In addition, the use of modified silica particles can also improve chemical resistance.

[0207] The organic component preferably covers almost the entire particle surface in order to suppress aggregation of the silica particles and to improve the hardness of the hard coating layer by introducing a large number of reactive functional groups onto the silica particle surface. From this viewpoint, the organic component covering the silica particles is present in an amount of 1.00 × 10 －３ g / m ２ The proportion of the organic component covering the powder can usually be determined as a constant value of the mass loss when the dry powder is completely combusted in air, for example, by thermogravimetric analysis in air from room temperature to typically 800°C.

[0208] The amount of organic compound per unit area can be determined by the following method. First, the value obtained by dividing the mass of the organic component by the mass of the inorganic component (organic component mass / inorganic component mass) is measured by differential thermal gravimetric analysis (DTG). Then, the volume of the entire inorganic component is calculated from the mass of the inorganic component and the specific gravity of the silica used. Assuming that the silica particles before coating are spherical, the volume and surface area per silica particle before coating are calculated from the average particle size of the silica particles before coating. Then, the number of reactive silica particles is determined by dividing the volume of the entire inorganic component by the volume per silica particle before coating. Furthermore, the amount of organic component per reactive silica particle is determined by dividing the mass of the organic component by the number of reactive silica particles. Finally, the amount of organic component per unit area can be determined by dividing the mass of organic component per reactive silica particle by the surface area per silica particle before coating.

[0209] As the method for preparing reactive silica particles, at least a part of the surface is covered with organic component, and the polymerizable unsaturated group introduced by this organic component is on the surface, can appropriately use the conventionally known method according to the kind of polymerizable unsaturated group that wants to be introduced to this silica particle.In addition, as reactive silica particles, powder form that does not contain dispersion medium can be used, but it is preferable to use the one that makes fine particles into solvent dispersion sol, because it can omit dispersion process and has high productivity.

[0210] Commercially available reactive silica particles include MIBK-SD, MIBK-SDMS, MIBK-SDL, IPA-ST, and IPA-SDMS manufactured by Nissan Chemical Industries, Ltd. The average primary particle size of the silica particles can be determined by measuring the dispersed particle size of the silica particles in a dispersion liquid using a zeta potential / particle size measurement system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.).

[0211] (Other Additives) Other additives may be blended into the hard coat layer as needed, provided that the effects of the present invention are not impaired. Examples of the additives that can be used include leveling agents, UV stabilizers, and UV absorbers. Other additives that can be used include various known additives such as antioxidants, surfactants, and antistatic agents.

[0212] [Leveling Agent] A leveling agent is particularly effective in reducing surface irregularities when applying a coating liquid for forming a hard coat layer. As the leveling agent, for example, a silicone-based leveling agent such as a dimethylpolysiloxane-polyoxyalkylene copolymer is suitable.

[0213] [UV Stabilizer] As the UV stabilizer, for example, a hindered amine UV stabilizer, which has high stability against UV rays, is preferably used. When the hard coat layer contains a UV stabilizer, radicals, active oxygen, etc. generated by UV rays are inactivated, thereby improving UV stability, weather resistance, etc.

[0214] [Ultraviolet Absorber] Examples of the ultraviolet absorber include salicylic acid-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, triazine-based ultraviolet absorbers, and benzoxazinone-based ultraviolet absorbers. One or more selected from these groups can be used. Among these, triazine-based ultraviolet absorbers and benzoxazinone-based ultraviolet absorbers are preferred as ultraviolet absorbers from the viewpoint of dispersibility. Polymers having ultraviolet-absorbing groups in the molecular chain are also preferably used as the ultraviolet absorber. The use of such polymers having ultraviolet-absorbing groups in the molecular chain can prevent deterioration of the ultraviolet absorbing function due to bleeding out of the ultraviolet absorber, etc.

[0215] Examples of the ultraviolet absorbing group include a benzotriazole group, a benzophenone group, a cyanoacrylate group, a triazine group, a salicylate group, a benzylidene malonate group, etc. Among these, the benzotriazole group, the benzophenone group, and the triazine group are particularly preferred as the ultraviolet absorbing group.

[0216] (Method for forming a hard coat layer) As a method for forming a hard coat layer on the optical film of the present invention to enhance functionality, for example, the following method can be mentioned. First, a coating liquid for forming an active energy ray-cured material layer, i.e., a coating liquid for forming a hard coat layer, is prepared in advance and applied to the optical film of the present invention. Thereafter, the coating liquid is dried and cured to form a hard coat layer, which is an active energy ray-cured material layer.

[0217] The hard coat layer-forming coating liquid is preferably, for example, a coating liquid containing an ultraviolet curable resin and silica particles, and the coating liquid is prepared using at least two solvents selected from alcohols, esters, ethers, and ketones in order to reduce drying unevenness. Examples of the solvent include chlorine-based solvents such as chloroform and dichloromethane; aromatic solvents such as toluene, xylene, benzene, and mixed solvents thereof; alcohol-based solvents such as methanol, ethanol, isopropanol (IPA), n-butanol, and 2-butanol; methyl cellosolve, ethyl cellosolve, butyl cellosolve, ethylene glycol monomethyl ether, propylene glycol monomethyl ether (PGME), dimethylformamide, dimethyl sulfoxide, dioxane, cyclohexanone, tetrahydrofuran, acetone, methyl ethyl ketone (MEK), ethyl acetate, and diethyl ether.

[0218] When a solution prepared by dissolving at least two solvents selected from alcohols, esters, ethers, and ketones is cast onto a substrate, one of the solvents is preferably a ketone. Among ketones, methyl ethyl ketone (MEK) is preferred from the viewpoint of solubility of the UV-curable resin. The other solvent is preferably an ether. Among ethers, propylene glycol monomethyl ether (PGME) is preferred from the viewpoint of its high boiling point, slow drying time, and suppression of unevenness.

[0219] The coating liquid for forming a hard coat layer can be applied to the optical film of the present invention by any means, such as a dipping method, a die coater method, a wire bar method, or a spray method, and the coating liquid can be dried by a known method after application. The coating film of the coating liquid for forming a hard coat layer can be cured by irradiating it with active energy rays. Examples of light sources for irradiating active energy rays (preferably ultraviolet rays) include low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, carbon arc lamps, metal halide lamps, and xenon lamps.

[0220] The irradiation amount of the light source is 20 to 10,000 mJ / cm ２It is sufficient to have a value of about 50 to 2000 mJ / cm. ２ The irradiation time is preferably within a range of 0.5 seconds to 5 minutes, and from the viewpoint of work efficiency, etc., a range of 3 seconds to 2 minutes is more preferable. The dry layer thickness of the hard coat layer is preferably within a range of 2 to 15 μm, and more preferably within a range of 3 to 8 μm.

[0221] <Antireflection Layer> When a functional layer such as the hard coat layer described above is formed on the optical film of the present invention, an antireflection layer can be coated on the functional layer to use it as an antireflection film having an external light antireflection function. In this case, the antireflection layer is formed by preparing a coating liquid for forming the antireflection layer using a solvent, applying the coating liquid, and drying and curing the coating liquid.

[0222] If necessary, a method may be applied in which irregularities are formed on the surface of a mold without using a solvent, and the irregularities of the mold are transferred onto a film using an ultraviolet-curable resin or a thermoplastic resin to form an anti-glare (AG) layer or the like (a method for forming an embossed AG layer).

[0223] The layer formed on the functional layer is not limited to the anti-reflection layer described above, and any known layer may be formed according to various applications, and other layers such as a conductive layer may also be formed.

[0224] The antireflection layer is preferably laminated taking into consideration the refractive index, layer thickness, number of layers, layer order, etc. so that the reflectance is reduced by optical interference. The antireflection layer is preferably composed of a low refractive index layer having a lower refractive index than the film used as the support, i.e., the optical film of the present invention on which the functional layer is formed, or a combination of a high refractive index layer and a low refractive index layer having a higher refractive index than the optical film of the present invention on which the functional layer is formed.

[0225] (Low Refractive Index Layer) The low refractive index layer preferably contains silica-based fine particles. The refractive index of the low refractive index layer is preferably in the range of 1.30 to 1.45 when measured at 23°C and a wavelength of 550 nm. The thickness of the low refractive index layer is preferably in the range of 5 nm to 0.5 μm, more preferably in the range of 10 nm to 0.3 μm, and most preferably in the range of 30 nm to 0.2 μm.

[0226] The composition for forming a low refractive index layer preferably contains at least one type of silica-based fine particles having an outer shell layer and a porous or hollow interior, and the particles having an outer shell layer and a porous or hollow interior are preferably hollow silica-based fine particles.

[0227] The composition for forming a low refractive index layer may also contain an organosilicon compound represented by the following general formula (OSi-1), or a hydrolyzate thereof, or a polycondensate thereof. General formula (OSi-1): Si(OR) ４ In the above general formula (OSi-1), R represents an alkyl group having 1 to 4 carbon atoms. Specifically, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, etc. are preferably used.

[0228] In addition, a solvent, and, if necessary, a silane coupling agent, a curing agent, a surfactant, etc. may be added. Furthermore, the composition may contain a thermosetting and / or photocurable compound that contains fluorine atoms in the range of 35 to 80% by mass and is primarily composed of a fluorine-containing compound containing a crosslinkable or polymerizable functional group. Specific examples of such compounds include fluorine-containing polymers and fluorine-containing sol-gel compounds. Examples of fluorine-containing polymers include hydrolysates and dehydration condensates of perfluoroalkyl group-containing silane compounds (e.g., (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane). Other examples include fluorine-containing copolymers whose constituent units are fluorine-containing monomer units and crosslinkable reactive units.

[0229] (High Refractive Index Layer) The refractive index of the high refractive index layer is preferably adjusted to be in the range of 1.4 to 2.2 when measured at 23° C. and a wavelength of 550 nm. The thickness of the high refractive index layer is preferably in the range of 5 nm to 1 μm, more preferably in the range of 10 nm to 0.2 μm, and most preferably in the range of 30 nm to 0.1 μm.

[0230] The refractive index can be adjusted by adding metal oxide fine particles, etc. The metal oxide fine particles preferably have a refractive index in the range of 1.80 to 2.60, more preferably 1.85 to 2.50.

[0231] The type of metal oxide microparticles is not particularly limited, and metal oxides containing at least one element selected from Ti, Zr, Sn, Sb, Cu, Fe, Mn, Pb, Cd, As, Cr, Hg, Zn, Al, Mg, Si, P, and S can be used.

[0232] <Conductive Layer> The conductive layer can be formed from a commonly known conductive material, such as indium oxide, tin oxide, indium tin oxide, gold, silver, palladium, or other metal oxide.

[0233] Using these materials, the conductive layer can be formed as a thin film on a film on which a hard coat layer has been formed by vacuum deposition, sputtering, ion plating, solution coating, or the like. Alternatively, the conductive layer can be formed using an organic conductive material that is a π-conjugated conductive polymer. In particular, conductive materials containing as a main component any of indium oxide, tin oxide, or indium tin oxide, which have excellent transparency and conductivity and can be obtained at relatively low cost, are preferably used.

[0234] The thickness of the conductive layer varies depending on the material used and cannot be generalized, but it is preferable that the thickness be such that the surface resistivity is 1000 Ω or less, preferably 500 Ω or less. Considering economic efficiency, the thickness of the conductive layer is preferably 10 nm or more, more preferably in the range of 20 to 80 nm, and even more preferably 70 nm or less. Furthermore, in such a thin film, interference fringes of visible light caused by uneven thickness of the conductive layer are unlikely to occur.

[0235] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. In the following examples, unless otherwise specified, operations were carried out at room temperature (25°C). Furthermore, unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass", respectively.

[0236] [Thermoplastic resin (A)] The following acrylic resins A1 to A3 and cycloolefin resin COP1 were used as the thermoplastic resin (A). The acrylic resin A1 and cycloolefin resin COP1 were commercially available products, while the acrylic resins A2 and A3 were prepared by the following methods. Acrylic resin A1: Dianal BR85 (manufactured by Mitsubishi Chemical Corporation)

[0237] <Preparation of Acrylic Resin A2> Acrylic resin A2 was synthesized in accordance with the method described in paragraphs

[0130] to

[0135] of JP 2006-241263 A, using a mass ratio (MMA:MA) of methyl methacrylate (MMA) to methyl acrylate (MA) of 98:2. As a result, acrylic resin A2 having a weight average molecular weight (Mw) of 80,000 was obtained.

[0238] <Preparation of Acrylic Resin A3> Acrylic resin A3 was synthesized using methyl methacrylate (MMA) and methyl acrylate (MA) in a mass ratio (MMA:MA) of 97:3 according to the method described in paragraphs

[0130] to

[0135] of JP 2006-241263 A. As a result, acrylic resin A3 having a weight average molecular weight (Mw) of 930,000 was obtained.

[0239] <Cycloolefin resin COP1> Cycloolefin resin COP1: ARTON (registered trademark) G7810 (manufactured by JSR Corporation)

[0240] [Thermoplastic Resin (B)] The following cellulose ester resins CE1 to CE4 and acrylic resin A4 were used as the thermoplastic resin (B).

[0241] <Preparation of Cellulose Ester Resin CE1> A mixture of sulfuric acid (7.8 parts by mass per 100 parts by mass of cellulose) as a catalyst and a carboxylic acid anhydride was cooled to -20°C. Then, the mixture was added to cellulose derived from hardwood pulp, and acylation was carried out at 40°C. The type and amount of the carboxylic acid anhydride were adjusted to control the type and substitution ratio of the acyl group. After acylation, the mixture was aged at 40°C to adjust the total degree of substitution. As a result, a cellulose ester resin CE1 was obtained having a total degree of acyl substitution (T) of 2.75, a degree of acetyl group (Ac) substitution of 0.19, a degree of propionyl group (Pr) substitution of 2.56, and a weight-average molecular weight of 200,000.

[0242] <Preparation of cellulose ester resin CE2> In the preparation of the cellulose ester resin CE1, the type and amount of carboxylic acid anhydride are appropriately adjusted to adjust the type and substitution ratio of acyl group.In addition, after acylation, aging is carried out at 40 ° C. to adjust the total substitution degree.As a result, the cellulose ester resin CE2 is obtained, which has a total substitution degree (T) of acyl group of 2.1, a substitution degree of acetyl group (Ac) of 0.8, a substitution degree of propionyl group (Pr) of 1.3, and a weight-average molecular weight of 200,000.

[0243] <Preparation of cellulose ester resin CE3> In the preparation of the cellulose ester resin CE1, the type and amount of carboxylic acid anhydride are appropriately adjusted to adjust the type and substitution ratio of acyl group.In addition, after acylation, aging is carried out at 40 ° C to adjust the total substitution degree.As a result, the cellulose ester resin CE3 is obtained, which has a total substitution degree (T) of acyl group of 2.8, a substitution degree of acetyl group (Ac) of 0.5, a substitution degree of propionyl group (Pr) of 1.15, a substitution degree of butyryl group (Bu) of 1.15, and a weight-average molecular weight of 200,000.

[0244] <Preparation of cellulose ester resin CE4> In the preparation of the cellulose ester resin CE1, the type and amount of carboxylic acid anhydride are appropriately adjusted to adjust the type and substitution ratio of acyl group.In addition, after acylation, aging is carried out at 40 ° C. to adjust the total substitution degree.As a result, the cellulose ester resin CE4 is obtained, which has a total substitution degree (T) of acyl group of 2.75, a substitution degree of acetyl group (Ac) of 0.19, a substitution degree of propionyl group (Pr) of 2.56, and a weight-average molecular weight of 76,000.

[0245] <Preparation of Acrylic Resin A4> A reactor equipped with a stirrer, temperature sensor, cooling tube, and nitrogen inlet tube was charged with 19 parts by mass of 2-hydroxypropyl methacrylate (HPMA), 76 parts by mass of methyl methacrylate (MMA), and 97 parts by mass of toluene as a polymerization solvent. The mixture was heated to 105°C while nitrogen was passed through. Subsequently, solution polymerization was allowed to proceed under reflux at 105-110°C for 1 hour to obtain Acrylic Resin A4. The molecular weight of the obtained Acrylic Resin A4 was determined to be a weight average molecular weight (Mw) of 281,000, a number average molecular weight (Mn) of 133,000, and a molecular weight distribution (Mw / Mn) of 2.1.

[0246] [Preparation of Optical Film] <Preparation of Optical Film 1> (Dope Solution Composition) Thermoplastic resin (A): Acrylic resin A1 160 parts by mass Thermoplastic resin (B): Cellulose ester resin CE1 86 parts by mass Rubber particles: (Kane Ace M210, manufactured by Kaneka Corporation) 2.5 parts by mass Methylene chloride 550 parts by mass Ethanol 100 parts by mass The above compositions were sufficiently dissolved under heating to prepare a dope solution.

[0247] (Optical Film Formation and First-Stage Stretching) The dope solution was uniformly cast onto a 2-m wide stainless steel band support (e.g., support 3 in Figure 4) at 22°C using a belt casting apparatus. The solvent was evaporated on the stainless steel band support until the residual solvent amount was 40% by mass, and the web was peeled off from the stainless steel band support at a peel tension of 150 N / m. The solvent was evaporated from the peeled acrylic resin web at 35°C, and the web was slit to a width of 1.6 m. The rotation speed of the stainless steel band support and the speed of a stretching device (tenter) (stretching device 6 in Figure 4) were then adjusted, and the web was stretched in the MD direction (first stretching). The first stretching ratio was calculated to be 1.2 times the rotation speed of the stainless steel band support and the stretching device (tenter) speed. The first stretching ratio in the MD direction was defined as (the conveying speed of the film after stretching) / (the conveying speed of the film before stretching). The stretching temperature in the first stretching was 50°C. The film was then heated to 135°C in a tenter and stretched 1.1 times in the width direction (TD direction) (second stretching). The second stretching ratio in the TD direction was defined as (film width after stretching) / (film width before stretching). The residual solvent content at the start of stretching in the tenter was 10% by mass. After stretching in the tenter, the film was transported through a drying zone (drying device 7 in Figure 4) at 110°C using multiple rollers, and the drying was completed. The tenter speed and take-up speed were then adjusted to stretch the film in the MD direction (third stretching). The third stretching ratio was calculated from the tenter speed and take-up speed to be 1.2 times. The third stretching ratio in the MD direction was defined as (film transport speed after stretching) / (film transport speed before stretching). Furthermore, both ends were cut to a width of 1.5 m, and both ends of the film were subjected to knurling with a width of 10 mm and a height of 5 μm. The film was wound around a core having an inner diameter of 15.24 cm under an initial tension of 220 N / m and a final tension of 110 N / m to obtain an acrylic resin film, Optical Film 1-1. The residual solvent amount of Optical Film 1-1 was 0.3 mass %, the film thickness was 47 μm, and the wound length was 4000 m.

[0248] (Second-Stage Stretching) The wound-up film 1-1 was then unwound from the roll and then heated to 140°C in a stretching apparatus (stretching apparatus 10 in FIG. 4 ) where it underwent a second-stage stretching in the width direction (TD) to a stretching ratio of 1.35 (fourth stretching). Similar to the first cutting step, both ends of the stretched film were cut to a width of 1.5 m. The film was wound around a core with an inner diameter of 15.24 cm under an initial tension of 60 N / m and a final tension of 25 N / m, yielding Optical Film 1, an acrylic resin film. The thickness of Optical Film 1 was 35 μm (47 μm / 1.35=35 μm). The stretching directions, stretching temperatures, and stretching ratios in the first to fourth stretching steps are as shown in Table I below.

[0249] <Preparation of Optical Films 2 to 15> Optical films 2 to 14 were prepared in the same manner as optical film 1, except that the types and amounts of thermoplastic resin (A), thermoplastic resin (B), rubber particles, and UV absorber, as well as the stretching conditions for each stretching step, were changed as shown in the table below. Optical film 15 was also prepared in the same manner as optical film 1, except that cycloolefin resin COP1 was used instead of acrylic resin A1, and acrylic resin A4 was used instead of cellulose ester resin CE1, with the changes shown in the table below. Here, in optical film 15, the thermoplastic resin (A) was cycloolefin resin COP1, and the thermoplastic resin (B) was acrylic resin A4. Cycloolefin resin COP1 has a functional group with hydrogen bond acceptor properties, and acrylic resin A4 has functional groups with both hydrogen bond donor and hydrogen bond acceptor properties. Films 2 to 15 were subjected to only the first and second stretching, and all were stretched in the TD direction. The first stretching performed on Films 2 to 15 corresponds to the second stretching (first-stage stretching process) for Film 1. The second stretching performed on Films 2 to 15 corresponds to the fourth stretching (second-stage stretching process after winding and unwinding) for Film 1. Tinuvin 928 was used as the UV absorber. The amount of the UV absorber was 3% by mass relative to the total mass of the film. Tinuvin 928 is (2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol). The amount of "rubber particles (M210)" added shown in the table below represents the mass % of the rubber particles relative to the total mass of the acrylic resin, cellulose ester resin, and rubber particles.

[0250]

[0251]

[0252] In Tables I and II, the total degree of substitution of acyl groups and the degree of substitution of acyl groups having 3 to 7 carbon atoms were determined by the method specified in ASTM-D817-96. The weight-average molecular weights of the acrylic resin (A) and the cellulose ester resin (B) were measured by gel permeation chromatography (GPC) as described above. The measurement conditions were also as described above.

[0253] <Tension Softening Point and Temperature Range of Maintained Tensile Strength> The temperature-elongation curve of the obtained optical film was obtained by measuring the dynamic viscoelasticity in the longitudinal direction and in a direction perpendicular to the longitudinal direction as described below. Here, the longitudinal direction refers to the film's conveying direction (MD direction), and the direction perpendicular to the longitudinal direction refers to the film's width direction (TD direction). First, a measurement specimen (sample) A was prepared by cutting the optical film to a length of 40 mm and a width of 5 mm so that the longitudinal direction of the optical film was the length direction. Furthermore, a measurement specimen (sample) B was prepared by cutting the optical film to a length of 40 mm and a width of 5 mm so that the direction perpendicular to the longitudinal direction of the optical film was the length direction. Then, the dynamic viscoelasticity of each of Samples A and B was measured. An RSA-G2 (manufactured by TA Instruments) was used as the dynamic viscoelasticity measuring device. A tensile tool was used to mount the sample. The film thickness was measured using a film thickness meter. The dynamic viscoelasticity was measured under the following conditions: gap length 20 mm, strain 0.1%, frequency 1 Hz, temperature -70 to 220°C, heating rate 5°C / min, and initial tension 40 g. When the slope of the obtained temperature-elongation curve was 0.3% / °C or more or -0.3% / °C or less, it was deemed to have a tension softening point, and the number of tension softening points was counted. In the high temperature region above the tension softening point in the temperature-elongation curve, the region where the slope was 0.3% / °C or less and -0.3% / °C or more was defined as the temperature width of the holding region, and this temperature width of the holding region was calculated. The calculated number of tension softening points and temperature width of the holding region are shown in the table below.

[0254] [Evaluation] A hard coat layer was formed on each of the optical films 1 to 15 prepared above by the following method to form a hard coat film.

[0255] <Formation of Hard Coat Layer> (Preparation of Silica Particles A) First, silica particles A used to form a hard coat layer were prepared as follows. (1) Removal of Surface-Adsorbed Ions Water-dispersed colloidal silica (Nissan Chemical Industries, Ltd., Snowtec N, average particle size 12 nm, pH 9.0 to 10.0) was subjected to ion exchange for 3 hours using 500 g of cation exchange resin (Mitsubishi Chemical Corporation, Diaion SK1B). Next, ion exchange was performed for 3 hours using 300 g of anion exchange resin (Mitsubishi Chemical Corporation, SA20A). Thereafter, the resultant was washed with ion-exchanged water to obtain an aqueous dispersion of silica fine particles with a solid content of 20% by mass. Na ２ The O content was 5 ppm by mass.

[0256] (2) Surface Treatment (Introduction of Monomer) 300 ml of isopropanol, 4.0 g of 3,6,9-trioxadecanoic acid, and 4.0 g of methacrylic acid were added to 20 g of the aqueous dispersion of silica microparticles treated in (1) above, and the mixture was stirred for 1 hour. The resulting mixture was stirred while heating at 60°C for 6 hours, yielding a silica microparticle dispersion in which methacryloyl groups had been introduced into the silica microparticles. Distilled water, isopropanol, and methacrylic acid were removed from the resulting silica microparticle dispersion using a rotary evaporator. Methyl ethyl ketone was added without drying, and the same amount (100%) of methacrylic acid as used in the surface treatment was added to obtain a silica dispersion in methyl ethyl ketone with a solids content of 50% by mass. The remaining water and isopropanol were adjusted to 0.1% by mass or less. The resulting silica particles A were measured using a particle size analyzer (Microtrac, manufactured by Nikkiso Co., Ltd.) to determine the average primary particle size, d ５５ = 13 nm.

[0257] (Preparation of Coating Liquid for Forming Hard Coat Layer) A mixed liquid was prepared by mixing the following ultraviolet-curable resin, surfactant, silica particles A, and propylene glycol monomethyl ether, and then the mixed liquid was stirred for 30 minutes to prepare a coating liquid for forming a hard coat layer. UV-curable resin "A-DPH" (manufactured by Shin-Nakamura Chemical Co., Ltd.) 60 parts by mass Surfactant "Surflon S-651" (manufactured by AGC Seimi Chemical Co., Ltd.) 0.1 parts by mass Silica particles A (40% dispersion in methyl ethyl ketone) 100 parts by mass Propylene glycol monomethyl ether (PGME) 40 parts by mass

[0258] (Application, drying, and curing of coating liquid for forming hard coat layer) The coating liquid for forming hard coat layer was applied to one surface of each of the optical films 1 to 15 using a microgravure machine so as to have a dry film thickness of 5 μm, and then dried to form a coating film. Next, a high-pressure mercury lamp was used to apply a light amount of 270 mJ / cm to the coating film in the atmosphere. ２ The coating was cured by irradiating with ultraviolet light at a temperature of 100° C. to form a hard coat layer on each of the optical films 1 to 15.

[0259] <Coating Unevenness> A heat-resistant double-sided tape (manufactured by Horikoh Co., Ltd.) without a substrate was attached to a black acrylic plate (Kurarex, manufactured by Nitto Jushi Kogyo Co., Ltd.). The optical film having the hard coat layer formed thereon was attached to the black acrylic plate with the coated surface (hard coat layer) facing outward, and the sample was placed on a desk 80 cm above the floor. Two 40W daylight-colored straight fluorescent lamps (FLR40S-D / M-X, manufactured by Matsushita Electric Industrial Co., Ltd.) were installed in a set 3 m above the floor on the ceiling. Under these fluorescent lamps, an evaluator was positioned directly in front of the sample, with the fluorescent lamps facing behind the evaluator's head. The sample was tilted 25° from the perpendicular to the desk so that the fluorescent lamps were reflected. The coating unevenness of the sample was evaluated according to the following criteria. In the following criteria, "A" and "B" were deemed acceptable for practical use. (Criteria) A: No coating unevenness was observed on the sample, and it was comfortable to use. B: Very slight color unevenness due to application is observed on the sample, but it can be used comfortably. C: Color unevenness due to application is observed on the sample, and it is difficult to say that it can be used comfortably.

[0260] <Coating cracks> The sample consisting of "an optical film with a hard coat layer attached to a black acrylic plate with double-sided tape" used in the evaluation of coating unevenness was 15 cm x 5 cm (75 cm ２ ) was visually observed, the number of cracks was counted, and the average value of 10 samples was used to evaluate the quality according to the following criteria. In the criteria below, "A", "B" and "C" were determined to be acceptable for practical use. (Criteria) A: 0 cracks B: 1 to 5 cracks C: 6 to 10 cracks D: 11 or more cracks

[0261]

[0262] As shown by the above results, it is recognized that the optical film of the present invention can prevent coating unevenness and coating cracks compared to the optical film of the comparative example.

[0263] The δH (hydrogen bond parameter) in the HSP values ​​of the acrylic resin A1 and the cellulose resin CE1 used in the preparation of optical film 1 was calculated using the method described above. As a result, the δH of the acrylic resin A1 was 3.6, and the δH of the cellulose resin CE1 was 3.8, with a difference of 0.2, indicating that a highly transmittant film was obtained. Similarly, the δH of the cycloolefin resin COP1 and the acrylic resin A4 used in the preparation of optical film 15 was calculated. As a result, the δH of the cycloolefin resin COP1 was 2.5, and the δH of the acrylic resin A4 was 4.6, with a difference of 2.1, indicating that a highly transmittant film was also obtained.

[0264] INDUSTRIAL APPLICABILITY The present invention can be used in an optical film, a laminate, and a method for manufacturing an optical film that prevent conveyance wrinkles, coating cracks, and the like from occurring in a widened and thinned film during processing in subsequent steps following the film manufacturing step.

[0265] REFERENCE SIGNS LIST 1, 1a Stirring device (stirring tank) 2 Casting die 3 Support (endless belt, drum) 3a, 3b Roller 4 Peeling roller 5 Web 6 Stretching device 7 Drying device 8 Cutting section 9 Winding device 9a Paying device 10 Stretching device 11 Cutting section 12 Winding device F Film F1 to F4 Film S Tension softening point

Claims

1. An optical film whose temperature-elongation curve has multiple tensile softening points.

2. The optical film according to claim 1, which contains a plurality of thermoplastic resins, wherein the monomer (A) constituting at least one of the thermoplastic resins (A) has a functional group with hydrogen bond acceptor properties, and the monomer (B) constituting the other thermoplastic resin (B) has a functional group with hydrogen bond donor properties.

3. The optical film according to claim 2, wherein the monomer (B) constituting the thermoplastic resin (B) further has a functional group with hydrogen bond acceptor properties.

4. The optical film according to claim 2, wherein the thermoplastic resin (A) is an acrylic resin (A), and the thermoplastic resin (B) is a cellulose ester resin (B).

5. The optical film according to claim 4, wherein the mass ratio of the acrylic resin (A) to the cellulose ester resin (B) is within the range of 95:5 to 30:70, the weight average molecular weight Mw of the acrylic resin (A) is within the range of 80,000 to 1,000,000, the weight average molecular weight Mw of the cellulose ester resin (B) is within the range of 75,000 to 300,000, the total degree of substitution (T) of acyl groups of the cellulose ester resin (B) is within the range of 2.0 to 3.0, and the degree of substitution of acyl groups having 3 to 7 carbon atoms is within the range of 1.2 to 3.

0.

6. The optical film according to claim 1, which is used as a substrate film for coating.

7. The optical film according to claim 1, which is a multi-stage stretched film.

8. The optical film according to claim 1, wherein the temperature range of the temperature-elongation curve of said optical film is in the range of 10 to 40°C.

9. The optical film according to claim 1, wherein the thickness of the optical film is 40 μm or less.

10. A laminate comprising a curable resin layer and an optical film, wherein the temperature-elongation curve of the optical film has a plurality of tension softening points.

11. A method for producing an optical film according to any one of claims 1 to 9, wherein the optical film is produced by multi-stage stretching.

12. The method for producing an optical film according to claim 11, wherein the stretching direction of the final stretching step in the multi-stage stretching is the same as that of any stretching step performed before the final stretching step, and when the stretching step having the same stretching direction as that of the final stretching step is defined as the previous stretching step, the ratio of the stretching ratios (stretching ratio of the final stretching step / stretching ratio of the previous stretching step) is within the range of 1.15 to 2.

00.

13. The method for producing an optical film according to claim 11, wherein at least one of the multi-stage stretching steps is stretching in the width direction of the optical film.

14. The method for producing an optical film according to claim 11, wherein at least one of the multi-stage stretching steps is stretching in the machine direction of the optical film and in the width direction of the acrylic film.

15. The method for producing an optical film according to claim 12, wherein the ratio of the temperature in the final stretching stage to the temperature in the previous stretching stage (temperature in the final stretching stage / temperature in the previous stretching stage) is within the range of 1.00 to 1.50.

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