KR102612870B1 - Method for making polarizer protective film - Google Patents

Abstract

A method for manufacturing a polarizer protective film with excellent bending resistance and adhesion to a polarizer with high productivity is provided.
The method for producing a polarizer protective film of the present invention includes forming a film of a composition containing an acrylic resin and core-shell type particles, and stretching the obtained film, and the stretching temperature is Tg+20°C to Tg+55°C. , the surface magnification is 2.0 to 6.0, and the stretching speed is 3%/sec to 130%/sec.

Description

Method for manufacturing polarizer protective film {METHOD FOR MAKING POLARIZER PROTECTIVE FILM}

The present invention relates to a method of manufacturing a polarizer protective film.

In image display devices (e.g., liquid crystal display devices, organic EL display devices), in many cases, a polarizing plate is disposed on at least one side of the display cell due to the image forming method. Recently, image display devices are becoming thinner and more flexible, and accordingly, there is a strong demand for polarizers and their constituent films (eg, polarizer protective films) to be thinner. When attempts are made to reduce the thickness of the polarizing plate and its constituent films, conveyance of each film in the polarizing plate manufacturing process may become difficult, resulting in a decrease in yield due to conveyance defects and/or breakage. To solve this problem, a technology for adding rubber particles to a polarizer protective film has been proposed (e.g., Japanese Patent Laid-Open No. 2015-210474). However, such a polarizer protective film has a problem in that its adhesion to the polarizer is insufficient and peeling occurs. Additionally, when applying a polarizing plate to a flexible image display device, a polarizing plate having excellent bending resistance is required.

The present invention was made to solve the above-described conventional problems, and its main purpose is to provide a method for manufacturing a polarizer protective film with excellent bending resistance and adhesion to a polarizer with high productivity.

The method for producing a polarizer protective film of the present invention includes forming a film of a composition containing an acrylic resin and core-shell type particles, and stretching the obtained film, wherein the stretching temperature is Tg+20°C to Tg+. The temperature is 55°C, the surface magnification is 2.0 to 6.0, and the stretching speed is 3%/sec to 130%/sec.

In one embodiment, the acrylic resin has at least one selected from the group consisting of glutarimide units, lactone ring units, maleic anhydride units, maleimide units, and glutaric anhydride units.

In one embodiment, the core-shell particles have a core made of a rubbery polymer and a coating layer made of a glassy polymer and covering the core.

In one embodiment, the composition contains 7% to 30% by weight of the core shell particles.

In one embodiment, the stretching is biaxial stretching.

In one embodiment, the ratio of the draw ratio in one direction to the draw ratio in the other direction in the biaxial stretching is 1.0 to 1.5.

In one embodiment, the stretching transforms the core-shell shaped particles into flat particles, and the length/thickness ratio of the flat particles is 4.0 to 7.0.

According to the present invention, polarizer protection with excellent bending resistance and adhesion to a polarizer is achieved by optimizing the combination of stretching temperature, area magnification, and stretching speed in the stretching of a film formed from a composition containing a predetermined acrylic resin and core-shell type particles. Films can be obtained with high productivity.

The method for producing a polarizer protective film according to an embodiment of the present invention includes forming a film of a composition containing an acrylic resin and core-shell particles, and stretching the obtained film.

A. Acrylic resin

A-1. Composition of acrylic resin

As the acrylic resin, any suitable acrylic resin may be employed. Acrylic resins typically contain alkyl (meth)acrylate as a main component as a monomer unit. As used herein, “(meth)acrylic” means acrylic and/or methacrylic. Examples of the alkyl (meth)acrylate constituting the main skeleton of the acrylic resin include linear or branched alkyl groups having 1 to 18 carbon atoms. These can be used alone or in combination. Additionally, any appropriate copolymerization monomer may be introduced into the acrylic resin by copolymerization. The type, number, copolymerization ratio, etc. of such copolymerization monomers can be appropriately set depending on the purpose. The components (monomer units) of the main skeleton of the acrylic resin will be described later with reference to Chemical Formula 2.

The acrylic resin preferably has at least one selected from glutarimide units, lactone ring units, maleic anhydride units, maleimide units and glutaric anhydride units. Acrylic resins having lactone ring units are described, for example, in Japanese Patent Application Laid-Open No. 2008-181078, the disclosure of which is incorporated herein by reference. The glutarimide unit is preferably represented by the formula (1):

[Formula 1]

In Formula 1, R ¹ and R ² each independently represent a hydrogen atom or an alkyl group with 1 to 8 carbon atoms, and R ³ is a hydrogen atom, an alkyl group with 1 to 18 carbon atoms, a cycloalkyl group with 3 to 12 carbon atoms, or 6 carbon atoms. Represents an aryl group of from 10 to 10. In Formula 1, preferably, R ¹ and R ² are each independently a hydrogen atom or a methyl group, and R ³ is a hydrogen atom, a methyl group, a butyl group, or a cyclohexyl group. More preferably, R ¹ is a methyl group, R ² is a hydrogen atom, and R ³ is a methyl group.

The alkyl (meth)acrylate is typically represented by the following formula (2):

[Formula 2]

In Formula 2, R ⁴ represents a hydrogen atom or a methyl group, and R ⁵ represents a hydrogen atom or an aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms, which may be substituted. Examples of the substituent include halogen and hydroxyl group. Specific examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, and n-(meth)acrylate. -hexyl, cyclohexyl (meth)acrylic acid, chloromethyl (meth)acrylic acid, 2-chloroethyl (meth)acrylic acid, 2-hydroxyethyl (meth)acrylic acid, 3-hydroxypropyl (meth)acrylic acid, (meth)acrylic acid Examples include 2,3,4,5,6-pentahydroxyhexyl and 2,3,4,5-tetrahydroxypentyl (meth)acrylate. In formula 2, R ⁵ is preferably a hydrogen atom or a methyl group. Therefore, particularly preferred alkyl (meth)acrylates are methyl acrylate or methyl methacrylate.

The acrylic resin may include only a single glutarimide unit, or may include a plurality of glutarimide units in which R ¹ , R ² and R ³ in Formula 1 are different.

The content ratio of the glutarimide unit in the acrylic resin is preferably 2 mol% to 50 mol%, more preferably 2 mol% to 45 mol%, further preferably 2 mol% to 40 mol%, especially preferred. Preferably it is 2 mol% to 35 mol%, most preferably 3 mol% to 30 mol%. If the content ratio is less than 2 mol%, there is a risk that the effects derived from the glutarimide unit (e.g., high optical properties, high mechanical strength, excellent adhesion to a polarizer, thinning) may not be sufficiently exhibited. If the content ratio exceeds 50 mol%, for example, there is a risk that heat resistance and transparency may become insufficient.

The acrylic resin may include only a single alkyl (meth)acrylate unit, or may include a plurality of alkyl (meth)acrylate units where R ⁴ and R ⁵ in Formula 2 are different from each other.

The content ratio of the alkyl (meth)acrylate unit in the acrylic resin is preferably 50 mol% to 98 mol%, more preferably 55 mol% to 98 mol%, and even more preferably 60 mol% to 98 mol%. , particularly preferably 65 mol% to 98 mol%, most preferably 70 mol% to 97 mol%. If the content ratio is less than 50 mol%, there is a risk that the effects derived from the alkyl (meth)acrylate unit (e.g., high heat resistance, high transparency) may not be sufficiently exhibited. If the content is more than 98 mol%, the resin becomes soft and brittle, and there is a risk that the high mechanical strength may not be sufficiently exhibited, leading to a decrease in productivity.

The acrylic resin may include units other than glutarimide units and alkyl (meth)acrylate units.

In one embodiment, the acrylic resin may contain, for example, 0 to 10% by weight of unsaturated carboxylic acid units that do not participate in the intramolecular imidization reaction described later. The content of unsaturated carboxylic acid units is preferably 0 to 5% by weight, more preferably 0 to 1% by weight. If the content is within this range, transparency, retention stability, and moisture resistance can be maintained.

In one embodiment, the acrylic resin may contain copolymerizable vinyl monomer units other than those described above (other vinyl monomer units). Other vinyl monomers include, for example, acrylonitrile, methacrylonitrile, ethacrylonitrile, allyl glycidyl ether, maleic anhydride, itaconic anhydride, N-methylmaleimide, N-ethylmaleimide, N -Cyclohexylmaleimide, aminoethyl acrylate, propylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethylaminopropyl methacrylate, cyclohexylaminoethyl methacrylate, N-vinyldiethylamine, N-acetylvinylamine, Allylamine, methallylamine, N-methylallylamine, 2-isopropenyl-oxazoline, 2-vinyl-oxazoline, 2-acroyl-oxazoline, N-phenylmaleimide, phenylaminoethyl methacrylate, Styrene, α-methylstyrene, p-glycidyl styrene, p-aminostyrene, 2-styryl-oxazoline, etc. can be mentioned. These can be used alone or in combination. Preferably, it is a styrene-based monomer such as styrene and α-methylstyrene. The content ratio of other vinyl monomer units is preferably 0 to 1% by weight, more preferably 0 to 0.1% by weight. Within this range, it is possible to suppress the occurrence of undesired phase difference and the decrease in transparency.

The imidization rate of the acrylic resin is preferably 2.5% to 20.0%. If the imidization rate is within this range, a resin excellent in heat resistance, transparency, and molding processability can be obtained, and the generation of soot and a decrease in mechanical strength during film molding can be prevented. In the above acrylic resin, the imidization rate is expressed by the ratio of glutarimide units and alkyl (meth)acrylate units. This ratio can be obtained, for example, from the NMR spectrum, IR spectrum, etc. of the acrylic resin. In this embodiment, the imidization rate can be obtained by ¹ H-NMR measurement of the resin using ¹ HNMR BRUKER Avance III (400 MHz). More specifically, the peak area derived from the O-CH ₃ proton of alkyl (meth)acrylate around 3.5 to 3.8 ppm is set to A, and the peak area derived from the N-CH ₃ proton of glutarimide around 3.0 to 3.3 ppm is set to A. B can be obtained by the following equation.

Imidation rate Im(%)={B/(A+B)}×100

The acid value of the acrylic resin is preferably 0.10 mmol/g to 0.50 mmol/g. If the acid value is within this range, a resin with an excellent balance of heat resistance, mechanical properties, and molding processability can be obtained. If the acid value is too small, problems such as increased costs due to the use of a denaturant to adjust the acid value to the desired level and generation of a gel-like product due to the remaining denaturant may occur. If the acid value is too large, foaming occurs easily during film molding (for example, during melt extrusion), and the productivity of the molded product tends to decrease. In the acrylic resin, the acid value is the content of carboxylic acid units and carboxylic acid anhydride units in the acrylic resin. In this embodiment, the acid value can be calculated by, for example, the titrimetric method described in WO 2005/054311 or Japanese Patent Application Laid-Open No. 2005-23272.

The weight average molecular weight of the acrylic resin is preferably 1,000 to 2,000,000, more preferably 5,000 to 1,000,000, even more preferably 10,000 to 500,000, particularly preferably 50,000 to 500,000, and most preferably 60,000 to 150,000. The weight average molecular weight can be determined by conversion to polystyrene using, for example, gel permeation chromatography (GPC system, Tosoh Corporation). Additionally, tetrahydrofuran can be used as a solvent.

The acrylic resin has a Tg (glass transition temperature) of preferably 110°C or higher, more preferably 115°C or higher, further preferably 120°C or higher, particularly preferably 125°C or higher, and most preferably 130°C or higher. . When Tg is 110°C or higher, a polarizing plate containing a polarizer protective film obtained from such a resin is likely to have excellent durability. The upper limit of Tg is preferably 300°C or lower, more preferably 290°C or lower, further preferably 285°C or lower, particularly preferably 200°C or lower, and most preferably 160°C or lower. If Tg is within this range, moldability may be excellent.

A-2. Polymerization of acrylic resin

The acrylic resin can be produced, for example, by the following method. This method includes (I) copolymerizing an alkyl (meth)acrylate monomer corresponding to the alkyl (meth)acrylate unit represented by Formula 2 and an unsaturated carboxylic acid monomer and/or a precursor monomer thereof to obtain copolymer (a); and (II) treating the copolymer (a) with an imidizing agent to cause an intramolecular imidization reaction between the alkyl (meth)acrylate monomer unit and the unsaturated carboxylic acid monomer and/or its precursor monomer unit in the copolymer (a). It includes introducing the glutarimide unit represented by Formula 1 into the copolymer.

Examples of unsaturated carboxylic acid monomers include acrylic acid, methacrylic acid, crotonic acid, α-substituted acrylic acid, and α-substituted methacrylic acid. Examples of the precursor monomer include acrylamide, methacrylamide, and the like. These can be used alone or in combination. The preferred unsaturated carboxylic acid monomer is acrylic acid or methacrylic acid, and the preferred precursor monomer is acrylamide.

Any suitable method can be used for treating copolymer (a) with an imidizing agent. Specific examples include a method using an extruder and a method using a batch reaction tank (pressure vessel). The method using an extruder includes heating and melting the copolymer (a) using an extruder and treating it with an imidizing agent. In this case, any suitable extruder can be used as the extruder. Specific examples include single-screw extruders, twin-screw extruders, and multi-screw extruders. In the method using a batch reaction tank (pressure vessel), any suitable batch reaction tank (pressure vessel) can be used.

As the imidizing agent, any suitable compound can be used as long as it can produce the glutarimide unit represented by the above formula (1). Specific examples of imidizing agents include amines containing aliphatic hydrocarbon groups such as methylamine, ethylamine, n-propylamine, i-propylamine, n-butylamine, i-butylamine, tert-butylamine, and n-hexylamine; Examples include amines containing aromatic hydrocarbon groups such as aniline, benzylamine, toluidine, and trichloroaniline, and amines containing alicyclic hydrocarbon groups such as cyclohexylamine. In addition, for example, a urea-based compound that generates such an amine by heating can also be used. Examples of urea-based compounds include urea, 1,3-dimethyl urea, 1,3-diethyl urea, and 1,3-dipropyl urea. The imidizing agent is preferably methylamine, ammonia, or cyclohexylamine, and more preferably methylamine.

In imidization, a ring-closure accelerator may be added as needed in addition to the imidizing agent.

The amount of the imidizing agent used in imidization is preferably 0.5 parts by weight to 10 parts by weight, more preferably 0.5 parts by weight to 6 parts by weight, based on 100 parts by weight of copolymer (a). If the amount of imidizing agent used is less than 0.5 parts by weight, the desired imidization rate is often not achieved. As a result, the heat resistance of the resulting resin may be very insufficient, causing appearance defects such as soot after molding. If the amount of the imidizing agent used exceeds 10 parts by weight, the imidizing agent may remain in the resin, and the imidizing agent may cause appearance defects such as soot after molding or foaming.

The production method of this embodiment may include treatment with an esterification agent in addition to the imidization, if necessary.

Esterifying agents include, for example, dimethyl carbonate, 2,2-dimethoxypropane, dimethyl sulfoxide, triethyl orthoformate, trimethyl orthoacetate, trimethyl orthoformate, diphenyl carbonate, dimethyl sulfate, methyltoluenesulfonate, and methyl tri. Fluoromethane sulfonate, methyl acetate, methanol, ethanol, methyl isocyanate, p-chlorophenyl isocyanate, dimethyl carbodiimide, dimethyl-t-butylsilyl chloride, isopropenyl acetate, dimethyl urea, tetramethyl ammonium hydroxide, dimethyl Diethoxysilane, tetra-N-butoxysilane, dimethyl (trimethylsilane) phosphite, trimethyl phosphite, trimethyl phosphate, tricresyl phosphate, diazomethane, ethylene oxide, propylene oxide, cyclohexene oxide, 2-ethylhexyl Glycidyl ether, phenyl glycidyl ether, and benzyl glycidyl ether can be mentioned. Among these, dimethyl carbonate is preferable from the viewpoints of cost, reactivity, etc.

The amount of esterifying agent added can be set so that the acid value of the acrylic resin reaches a desired value.

A-3. Combination use of other resins

In embodiments of the present invention, the acrylic resin and other resins may be used together. That is, the monomer component constituting the acrylic resin and the monomer component constituting the other resin may be copolymerized and the copolymer may be used to form a film described later in section C; A blend of acrylic resin and other resins may be used for film formation. Other resins include, for example, styrene resin, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyether ether ketone, polyester, polysulfone, polyphenylene oxide, polyacetal, polyimide, polyetherimide, etc. Thermosetting resins such as other thermoplastic resins, phenol-based resins, melamine-based resins, polyester-based resins, silicone-based resins, and epoxy-based resins can be mentioned. The type and mixing amount of the resin used together can be appropriately set depending on the purpose and the desired characteristics of the obtained film. For example, a styrene-based resin (preferably an acrylonitrile-styrene copolymer) can be used together as a phase difference control agent.

When using an acrylic resin and another resin together, the content of the acrylic resin in the blend of the acrylic resin and the other resin is preferably 50% by weight to 100% by weight, more preferably 60% by weight to 100% by weight, even more preferably. Preferably it is 70% by weight to 100% by weight, particularly preferably 80% by weight to 100% by weight. If the content is less than 50% by weight, there is a risk that the high heat resistance and high transparency inherent in acrylic resin may not be sufficiently reflected.

A-4. additive

When polymerizing the acrylic resin, any appropriate additives may be added depending on the purpose. Specific examples of additives include ultraviolet absorbers; Antioxidants such as sterically hindered phenol-based, phosphorus-based, and sulfur-based antioxidants; Stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; Reinforcing materials such as glass fiber and carbon fiber; Near-infrared absorber; Flame retardants such as tris(dibromopropyl)phosphate, triallyl phosphate, and antimony oxide; Antistatic agents such as anionic, cationic, and nonionic surfactants; Colorants such as inorganic pigments, organic pigments, and dyes; Organic or inorganic filler; Resin modifier; Organic or inorganic fillers; plasticizer; Lubricants, etc. can be mentioned. The additive may be added during polymerization of the acrylic resin, or may be added during film formation. The type, number, combination, addition amount, etc. of additives can be appropriately set depending on the purpose. Additionally, additives may be added to the composition during film formation as described later in Section C.

B. Core-shell type particles

Core-shell particles typically have a core made of a rubber-like polymer and a coating layer made of a glass-like polymer and covering the core. The core-shell type particles may have one or more layers composed of a glassy polymer as an innermost layer or an intermediate layer. However, in the embodiment of the present invention, in the process of dispersing the core-shell type particles in the composition, the coating layer is compatible with the resin component in the composition, and there are cases where the coating layer cannot be recognized visually (including through a microscope, etc.). .

The Tg of the rubbery polymer constituting the core is preferably 20°C or lower, more preferably -60°C to 20°C, and even more preferably -60°C to 10°C. If the Tg of the rubbery polymer constituting the core exceeds 20°C, there is a risk that the mechanical strength of the acrylic resin may not be sufficiently improved. The Tg of the glassy polymer (hard polymer) constituting the coating layer is preferably 50°C or higher, more preferably 50°C to 140°C, and even more preferably 60°C to 130°C. If the Tg of the glassy polymer constituting the coating layer is lower than 50°C, there is a risk that the heat resistance of the acrylic resin may decrease.

The content ratio of the core in the core-shell type particles is preferably 30% by weight to 95% by weight, more preferably 50% by weight to 90% by weight. The proportion of the glassy polymer layer in the core is 0 to 60% by weight, preferably 0 to 45% by weight, more preferably 10 to 40% by weight, based on 100% by weight of the total weight of the core. The content of the coating layer in the core-shell type particles is preferably 5% by weight to 70% by weight, more preferably 10% by weight to 50% by weight.

The average particle diameter of the core is preferably 70 nm to 300 nm. With such an average particle diameter, it can be flattened to the desired length and thickness (and thus the ratio of length/thickness) by stretching, which will be described later.

The composition preferably contains 7% to 30% by weight, more preferably 8% to 25% by weight, of core-shell type particles. If the content of core-shell particles is within this range, excellent adhesion to the polarizer and excellent bending resistance can be achieved.

Details of the rubber-like polymer constituting the core of the core-shell particle, the glass-like polymer (hard polymer) constituting the coating layer, their polymerization method, and other configurations are described, for example, in Japanese Patent Application Laid-Open No. 2016-33552. The description in this publication is incorporated herein by reference.

Flattening of core-shell particles (formation of reinforcing particles) is described later in Section D in relation to stretching.

C. Film Formation

Any appropriate method can be employed to form a film from the composition. Specific examples include cast coating method (e.g., casting method), extrusion molding method, injection molding method, compression molding method, transfer molding method, blow molding method, powder molding method, FRP molding method, calendar molding method, and heat pressing method. Preferably, it is an extrusion molding method or a cast coating method. This is because the smoothness of the resulting film can be increased and good optical uniformity can be obtained. Particularly preferred is extrusion molding. This is because there is no need to consider problems caused by residual solvent. Among them, the extrusion molding method using a T die is preferable from the viewpoint of film productivity and ease of subsequent stretching treatment. Molding conditions can be appropriately set depending on the composition or type of the resin used, the desired characteristics of the obtained film, etc.

D. Stretching

As the stretching method, any suitable stretching method and stretching conditions (eg, stretching temperature, stretching ratio, stretching speed, stretching direction) can be employed. Specific examples of stretching methods include free end stretching, fixed end stretching, free end shrinkage, and fixed end shrinkage. These may be used individually, simultaneously, or sequentially.

The stretching direction may be an appropriate direction depending on the purpose. Specifically, the longitudinal direction, width direction, thickness direction, and oblique direction can be mentioned. The stretching direction may be one direction (uniaxial stretching), two directions (biaxial stretching), or three or more directions. In embodiments of the present invention, uniaxial stretching in the longitudinal direction, simultaneous biaxial stretching in the longitudinal and transverse directions, and sequential biaxial stretching in the longitudinal and transverse directions can be typically employed. Preferably biaxial stretching (simultaneous or sequential). This is because the in-plane phase difference is easy to control and optical isotropy is easy to realize.

When biaxial stretching is adopted, the stretching method may be simultaneous biaxial stretching or sequential biaxial stretching. Simultaneous biaxial stretching is less prone to scratches on the film surface because there is no roll stretching process, and has superior film appearance compared to sequential stretching. On the other hand, sequential biaxial stretching is divided into longitudinal stretching and transverse stretching processes, so it is difficult to break the film and has superior productivity. In sequential biaxial stretching, either vertical stretching or transverse stretching may be performed first. Sequential biaxial stretching is preferably carried out in the order of longitudinal stretching and transverse stretching.

Stretching temperature can vary depending on the desired optical properties, mechanical properties and thickness of the polarizer protective film, type of resin used, thickness of film used, stretching method (uniaxial stretching or biaxial stretching), stretching ratio, stretching speed, etc. there is. In an embodiment of the present invention, the stretching temperature is Tg+20°C to Tg+55°C as above, preferably Tg+30°C to Tg+50°C, more preferably Tg+35°C to Tg+50°C. It is ℃. When simultaneous biaxial stretching is employed, the stretching temperature is preferably Tg+30°C to Tg+55°C, more preferably Tg+40°C to Tg+55°C, and even more preferably Tg+40°C to Tg. It is +50℃. When sequential biaxial stretching is adopted, the stretching temperature is preferably Tg+20°C to Tg+55°C, more preferably Tg+30°C to Tg+55°C, and even more preferably Tg+35°C to Tg+55°C. Tg+50℃. By stretching at this temperature, a polarizer protective film with appropriate characteristics can be obtained. The specific stretching temperature is, for example, 140°C to 175°C, and is preferably 155°C to 170°C. According to an embodiment of the present invention, a polarizer protective film excellent in both bending resistance and adhesion to a polarizer can be obtained by optimizing the stretching temperature, stretching ratio, and stretching speed in combination. In addition, Tg here is the Tg of the resin component of the composition.

The stretching ratio, like the stretching temperature, also includes the optical properties, mechanical properties and thickness for which the polarizer protective film is intended, the type of resin used, the thickness of the film used, the stretching method (uniaxial stretching or biaxial stretching), stretching temperature, and stretching speed. It may change depending on etc. When biaxial stretching is adopted, the ratio of the draw ratio in one direction to the draw ratio in the other direction is preferably 1.0 to 1.5, more preferably 1.0 to 1.4, and still more preferably 1.0 to 1.3. . In one embodiment, the one direction and the other direction are orthogonal. For example, one of the two directions may be the longitudinal direction (MD), and the other may be the transverse direction (TD). When biaxial stretching is adopted, the surface magnification (the product of the stretching ratio in one direction and the stretching ratio in the other direction) is 2.0 to 6.0, preferably 3.0 to 6.0, and more preferably 4.0. It is 5.9. When simultaneous biaxial stretching is employed, the surface magnification is preferably 2.0 to 5.0, more preferably 2.0 to 4.5, and still more preferably 3.0 to 4.5. When sequential biaxial stretching is adopted, the surface magnification is preferably 2.0 to 6.0, more preferably 3.0 to 5.9, and even more preferably 4.0 to 5.9. According to an embodiment of the present invention, a polarizer protective film excellent in both bending resistance and adhesion to a polarizer can be obtained by optimizing the stretching temperature, stretching ratio, and stretching speed in combination.

Stretching speed, like stretching temperature, also includes the desired optical properties, mechanical properties and thickness of the polarizer protective film, type of resin used, thickness of film used, stretching method (uniaxial stretching or biaxial stretching), stretching temperature, stretching ratio, etc. It may change accordingly. As described above, the stretching speed is 3%/sec to 130%/sec, preferably 4%/sec to 120%/sec, and more preferably 5%/sec to 100%/sec. When coaxial biaxial stretching is adopted, the stretching speed is preferably 3%/sec to 15%/sec, more preferably 4%/sec to 12%/sec, and even more preferably 5%/sec to 10%/sec. %/sec. When sequential biaxial stretching is employed, the stretching speed is preferably 3%/sec to 130%/sec, more preferably 4%/sec to 110%/sec, and even more preferably 5%/sec to 100%/sec. %/sec. When biaxial stretching is adopted, the stretching speed in one direction and the stretching speed in the other direction may be the same or different. When simultaneous biaxial stretching is employed, the ratio of the stretching speed in one direction to the stretching speed in the other direction is preferably 1.0 to 1.3, more preferably 1.0 to 1.2, and still more preferably 1.0 to 1.1. am. For example, when employing sequential biaxial stretching performed in the order of longitudinal stretching and transverse stretching, the ratio (length/transverse) between the stretching speed in the longitudinal direction and the stretching speed in the transverse direction is preferably 7.0 to 17.0, more preferably. is 8.0 to 15.0, more preferably 9.0 to 13.0. According to an embodiment of the present invention, a polarizer protective film excellent in both bending resistance and adhesion to a polarizer can be obtained by optimizing the stretching temperature, stretching ratio, and stretching speed in combination.

By stretching as described above, the core-shell type particles are appropriately flattened (hereinafter, the flattened core-shell type particles are referred to as reinforcing particles).

The length/thickness ratio of the reinforcing particles is preferably 7.0 or less, more preferably 6.5 or less, and even more preferably 6.3 or less. On the other hand, the length/thickness ratio is preferably 4.0 or more, more preferably 4.5 or more, and even more preferably 5.0 or more. If the length/thickness ratio is within this range, the adhesion between the polarizer protective film and the polarizer can be significantly improved while maintaining excellent bending resistance due to containing particles. In this specification, “length/thickness ratio” means the ratio between the representative length and thickness of the plan-view shape of the reinforcing particle. Here, “representative length” refers to the diameter when the plan-view shape is circular, the major axis when it is oval, and the diagonal length when it is spherical or polygonal. The ratio can be obtained, for example, using the following procedure. The obtained film cross-section was photographed with a transmission electron microscope (e.g., acceleration voltage 80 kV, RuO ₄ staining ultra-thin sectioning), and 30 of the reinforcing particles present in the obtained photograph were ordered from the longest (those with a cross-section close to the representative length). The corresponding ratio can be obtained by extracting the number and calculating (average value of length)/(average value of thickness).

The thickness of the core is preferably between 20 nm and 100 nm. A representative length of the core in question is preferably between 200 nm and 600 nm. If the representative length of the core is too short, the improvement in mechanical strength of the resulting film may be insufficient. If the thickness of the core is too thick or the representative length of the core is too long, there is a risk that the adhesion between the resulting film and the polarizer may be impaired.

A polarizer protective film can be formed as described above. The polarizer protective film thus obtained contains an acrylic resin and reinforcing particles having a flat shape dispersed in the acrylic resin.

E. Polarizer protective film obtained by the above manufacturing method and its characteristics

The polarizer protective film is preferably substantially optically isotropic. In this specification, “substantially optically isotropic” means that the in-plane retardation Re(550) is 0 nm to 10 nm and the thickness direction retardation Rth(550) is -20 nm to +10 nm. The in-plane retardation Re(550) is more preferably 0 nm to 5 nm, further preferably 0 nm to 3 nm, and particularly preferably 0 nm to 2 nm. The phase difference Rth (550) in the thickness direction is more preferably -5 nm to +5 nm, further preferably -3 nm to +3 nm, and particularly preferably -2 nm to +2 nm. If the Re(550) and Rth(550) of the polarizer protective film are within this range, adverse effects on display characteristics can be prevented when a polarizer including the polarizer protective film is applied to an image display device. Additionally, Re(550) is the in-plane retardation of the film measured with light with a wavelength of 550 nm at 23°C. Re(550) can be obtained by the formula: Re(550)=(nx-ny)×d. Rth (550) is the phase difference in the thickness direction of the film measured with light with a wavelength of 550 nm at 23°C. Rth(550) can be obtained by the formula: Rth(550)=(nx-nz)×d. Here, nx is the refractive index in the direction in which the refractive index within the plane is maximum (i.e., slow axis direction), ny is the refractive index in the direction perpendicular to the slow axis within the plane (i.e., fast axis direction), and nz is the refractive index in the thickness direction. and d is the thickness of the film (nm).

When the thickness of the polarizer protective film is 80 μm, the higher the light transmittance at 380 nm, the more preferable it is. Specifically, the light transmittance is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. If the light transmittance is within this range, the desired transparency can be secured. By optimizing the length/thickness ratio of the reinforcing particles within the above range using the above manufacturing method, not only excellent bending resistance and adhesion to a polarizer but also such light transmittance can be realized. Light transmittance can be measured, for example, by a method based on ASTM-D-1003.

The lower the haze of the polarizer protective film, the more preferable it is. Specifically, the haze is preferably 5% or less, more preferably 3% or less, further preferably 1.5% or less, and particularly preferably 1% or less. If the haze is 5% or less, good transparency can be provided to the film. Moreover, even when used in a polarizing plate on the viewing side of an image display device, the displayed content can be visually recognized well. By optimizing the length/thickness ratio of the reinforcing particles within the above range using the above manufacturing method, not only excellent bending resistance and adhesion to the polarizer but also such haze can be achieved.

YI at a thickness of 80 μm of the polarizer protective film is preferably 1.27 or less, more preferably 1.25 or less, further preferably 1.23 or less, and particularly preferably 1.20 or less. When YI exceeds 1.3, optical transparency may become insufficient. By optimizing the length/thickness ratio of the reinforcing particles within the above range using the above manufacturing method, it is possible to realize such YI as well as excellent bending resistance and adhesion to a polarizer. In addition, YI can be obtained from the color tristimulus values (X, Y, Z) obtained by measurement using, for example, a high-speed integrating sphere type spectral transmittance meter (product name DOT-3C: manufactured by Murakami Color Research Laboratories) using the following equation. .

YI=[(1.28X-1.06Z)/Y]×100

The b value (a color scale based on Hunter's color system) at a thickness of 80 μm of the polarizer protective film is preferably less than 1.5, more preferably 1.0 or less. If the b value is 1.5 or higher, undesirable colors may appear. In addition, the b value is determined by, for example, cutting a sample of a polarizer protective film into 3cm angles, measuring the color using a high-speed integrating sphere type spectral transmittance meter (product name DOT-3C: manufactured by Murakami Color Technology Laboratories), and measuring the color according to Hunter's colorimetric system. This can be achieved through evaluation.

The moisture permeability of the polarizer protective film is preferably 300 g/m ² ·24 hr or less, more preferably 250 g/m ² ·24 hr or less, further preferably 200 g/m ² ·24 hr or less, particularly preferably 150 g/m ² ·24hr or less, most preferably 100g/m ² ·24hr or less. If the moisture permeability of the polarizer protective film is within this range, a polarizing plate excellent in durability and moisture resistance can be obtained.

The tensile strength of the polarizer protective film is preferably 10 MPa or more and less than 100 MPa, and more preferably 30 MPa or more and less than 100 MPa. In the case of less than 10 MPa, sufficient mechanical strength may not be achieved. If it exceeds 100 MPa, there is a risk that processability may become insufficient. Tensile strength can be measured, for example, according to ASTM-D-882-61T.

The tensile elongation of the polarizer protective film is preferably 1.0% or more, more preferably 3.0% or more, and even more preferably 5.0% or more. The upper limit of tensile elongation is, for example, 100%. If the tensile elongation is less than 1%, toughness may be insufficient. Tensile elongation can be measured, for example, according to ASTM-D-882-61T.

The tensile modulus of elasticity of the polarizer protective film is preferably 0.5 GPa or more, more preferably 1 GPa or more, and even more preferably 2 GPa or more. The upper limit of the tensile modulus is, for example, 20 GPa. If the tensile modulus is less than 0.5 GPa, sufficient mechanical strength may not be achieved. Tensile modulus can be measured, for example, according to ASTM-D-882-61T.

An easy adhesive layer may be formed on one side of the polarizer protective film. The easy-adhesion layer includes, for example, water-based polyurethane and an oxazoline-based crosslinking agent.

F. Uses of polarizer protective film

The polarizer protective film obtained by the manufacturing method of the present invention can be applied to a polarizing plate. A polarizing plate typically has a polarizer and a polarizer protective film disposed on at least one side of the polarizer. Since the polarizer may have a configuration known in the industry, a detailed description is omitted. Polarizers can be applied to image display devices. Representative examples of image display devices include liquid crystal displays and organic electroluminescence (EL) displays. Since the image display device adopts a configuration well known in the industry, detailed description is omitted.

[Example]

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. The measurement method for each characteristic is as follows. Additionally, unless otherwise specified, “part” and “%” in the examples are based on weight.

<Example 1>

(Production of polarizer protective film)

MS resin (MS-200; copolymer of methyl methacrylate/styrene (molar ratio) = 80/20, manufactured by Nippon Chemical Co., Ltd.) was imidized with monomethylamine (imidation rate: 5%). The obtained imidized MS resin is a glutarimide unit represented by Formula 1 (R ¹ and R ³ are methyl groups, R ² is a hydrogen atom), and a (meth)acrylic acid ester unit represented by Formula 2 (R ⁴ and R ⁵ is a methyl group) and has a styrene unit. In addition, for the imidization, an intermeshing type co-rotating twin-screw extruder with a diameter of 15 mm was used. The set temperature of each temperature control zone of the extruder was 230°C, the screw rotation speed was 150 rpm, MS resin was supplied at 2.0 kg/hr, and the supply amount of monomethylamine was 2 parts by weight based on 100 parts by weight of MS resin. MS resin was introduced from the hopper, the resin was melted and filled using a kneading block, and then monomethylamine was injected from the nozzle. A seal was placed at the end of the reaction zone to fill the resin. The by-products and excess methylamine after the reaction were devolatilized by reducing the pressure at the exhaust port to -0.08 MPa. The resin that came out as a strand from the die installed at the extruder outlet was cooled in a water bath and then pelletized with a pelletizer. The imidization rate of the obtained imidized MS resin was 5.0%, the acid value was 0.5 mmol/g, and the Tg was 120°C.

90 parts by weight of the imidized MS resin obtained above and 10 parts by weight of core-shell type particles (manufactured by Kaneka, brand name "Kane Ace M-210") were placed in a single screw extruder and melt-extruded at 260°C to obtain a film with a thickness of 120 ㎛. . The obtained extruded film was simultaneously biaxially stretched twice (plane magnification 4.0) in the longitudinal direction and the width direction at a stretching temperature of 160°C (Tg+40°C). The stretching speed was 10%/sec in both the longitudinal and width directions. By this stretching, the core-shell particles were flattened and reinforced particles were formed. The length/thickness ratio of the reinforcing particles was 6.3. In this way, a polarizer protective film was produced. The thickness of the obtained polarizer protective film was 40 μm, the in-plane retardation Re(550) was 2 nm, and the thickness direction retardation Rth(550) was 2 nm. The obtained polarizer protective film was subjected to the evaluation (2) above. The results are shown in Table 1.

(Production of polarizer)

1. Fabrication of polarizer

A long roll of 30 ㎛ thick polyvinyl alcohol (PVA)-based resin film (manufactured by Kuraray, product name "PE3000") is uniaxially stretched in the longitudinal direction by a roll stretching machine to a length of 5.9 times, while simultaneously swelling, dyeing, and crosslinking. , washing treatment, and finally drying treatment to produce a polarizer with a thickness of 12 μm.

Specifically, the swelling treatment was performed with pure water at 20°C and stretched 2.2 times. Next, the dyeing treatment was carried out in an aqueous solution at 30°C with a weight ratio of iodine and potassium iodide of 1:7, where the iodine concentration was adjusted so that the resulting polarizer had a single transmittance of 45.0%, and was stretched 1.4 times. In addition, the crosslinking treatment adopted a two-stage crosslinking treatment, and the first stage crosslinking treatment was stretched 1.2 times while being treated in an aqueous solution of boric acid and potassium iodide at 40°C. The boric acid content of the aqueous solution in the first stage crosslinking treatment was 5.0% by weight, and the potassium iodide content was 3.0% by weight. In the second stage of crosslinking treatment, the material was stretched 1.6 times while being treated in an aqueous solution of boric acid and potassium iodide at 65°C. The boric acid content of the aqueous solution in the second stage crosslinking treatment was 4.3% by weight, and the potassium iodide content was 5.0% by weight. Additionally, the washing treatment was performed with an aqueous potassium iodide solution at 20°C. The potassium iodide content of the aqueous solution for washing treatment was set to 2.6% by weight. Finally, the drying treatment was performed at 70°C for 5 minutes to obtain a polarizer.

2. Production of polarizer

A polarizing plate was obtained by attaching the polarizer protective film obtained above to one side of the polarizer through a polyvinyl alcohol-based adhesive. The obtained polarizing plate was subjected to evaluation of adhesion. The results are shown in Table 1. In addition, evaluation of adhesion was performed as follows. A peeling test was performed on the obtained polarizing plate to evaluate the adhesion between the polarizer protective film and the polarizer. Specifically, it is as follows. The polarizing plate was cut to a size of 200 mm in the direction of the absorption axis of the polarizer and 15 mm in the direction perpendicular to the absorption axis. A cut was made between the protective film and the polarizer with a cutter knife, and this was attached to a glass plate. The protective film and polarizer were peeled off in a 90-degree direction by Tensilon at a peeling speed of 300 mm/min, and the initial peel strength (N/15 mm) was measured. It was evaluated based on the following criteria.

○: Initial peel strength is 1.0 (N/15mm) or more

×: Initial peel strength is less than 1.0 (N/15mm)

<Example 2>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 1, except that the stretching temperature was 165°C (Tg+45°C). The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 3>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 1, except that the stretching temperature was 170°C (Tg+50°C). The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 4>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 1, except that the stretching temperature was 175°C (Tg+55°C). The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 5>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 1, except that the stretching temperature was 155°C (Tg+35°C). The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Comparative Example 1>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 1, except that the stretching temperature was 180°C (Tg+60°C). The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 6>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 1, except that the stretching ratio in the width direction was 1.5 times and the surface magnification was 3.0. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 7>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 1, except that the stretching ratio in the width direction was 2.6 times and the surface magnification was 5.2. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 8>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 1, except that the stretching speed was set to 3%/sec in both the longitudinal and width directions. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 9>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 1, except that the stretching speed was set to 5%/sec in both the longitudinal and width directions. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 10>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 1, except that the stretching speed was set to 15%/sec in both the longitudinal and width directions. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Comparative Example 2>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 1, except that the stretching speed was set to 1%/sec in both the longitudinal and width directions. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 11>

Except that the stretching temperature was set to 170°C (Tg+50°C), the stretch ratio in the width direction was set to 1.5 times, the surface magnification was set to 3.0, and the draw speed was set to 3%/sec in both the longitudinal and width directions. A polarizer protective film and a polarizing plate were produced in the same manner as in Example 1. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 12>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 11, except that the stretching speed was set to 5%/sec in both the longitudinal and width directions. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 13>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 11, except that the stretching speed was set to 10%/sec in both the longitudinal and width directions. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 14>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 11, except that the stretching speed was set to 15%/sec in both the longitudinal and width directions. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 15>

Except that the stretching temperature was set to 175°C (Tg+55°C), the stretch ratio in the width direction was set to 1.5 times, the surface magnification was set to 3.0, and the draw speed was set to 3%/sec in both the longitudinal and width directions. A polarizer protective film and a polarizing plate were produced in the same manner as in Example 1. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 16>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 15, except that the stretching speed was set to 5%/sec in both the longitudinal and width directions. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 17>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 15, except that the stretching speed was set to 10%/sec in both the longitudinal and width directions. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 18>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 15, except that the stretching speed was set to 15%/sec in both the longitudinal and width directions. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Comparative Example 3>

After stretching in the longitudinal direction at a stretching temperature of 160°C and a stretching rate of 100%/sec, a surface magnification of 5.8 times was stretched in the width direction at a stretching temperature of 136°C and a stretching rate of 12%/sec to produce a polarizer protective film and a polarizing plate. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 19>

A polarizer protective film and a polarizing plate were produced in the same manner as in Comparative Example 3, except that the stretching temperature in the width direction was set to 140°C. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 20>

A polarizer protective film and a polarizing plate were produced in the same manner as in Comparative Example 3, except that the stretching temperature in the width direction was set to 160°C. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 21>

A polarizer protective film and a polarizing plate were produced in the same manner as in Comparative Example 3, except that the stretching temperature in the width direction was set to 170°C. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Comparative Example 4>

A polarizer protective film and a polarizing plate were produced in the same manner as Example 20, except that the stretching speed in the longitudinal direction was 40%/sec and the stretching speed in the width direction was 2%/sec. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Example 22>

A polarizer protective film and a polarizing plate were produced in the same manner as Example 20, except that the stretching speed in the longitudinal direction was 60%/sec and the stretching speed in the width direction was 4%/sec. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

<Comparative Example 5>

A polarizer protective film and a polarizing plate were produced in the same manner as in Example 20, except that the surface magnification was set to 7.0. The obtained polarizing plate was subjected to the same evaluation as Example 1. The results are shown in Table 1.

[Table 1]

＊"Simultaneous" is simultaneous biaxial stretching, and "sequential" is sequential biaxial stretching in which longitudinal stretching and transverse stretching are performed in this order.

＊The “/” in “sequential” indicates “conditions for vertical stretching/conditions for horizontal stretching.”

<Evaluation>

As can be seen in Table 1, the method for manufacturing a polarizer protective film according to an embodiment of the present invention can obtain a polarizer protective film (and consequently a polarizer) with excellent balance of adhesion to the polarizer with excellent productivity.

The polarizer protective film obtained by the manufacturing method of the present invention is preferably used for a polarizing plate. Polarizing plates are preferably used in image display devices. Image display devices include portable devices such as personal digital assistants (PDAs), smartphones, mobile phones, watches, digital cameras, and portable game consoles; OA devices such as computer monitors, laptops, and copiers; Home appliances such as video cameras, televisions, and microwave ovens; Automotive devices such as back monitors, monitors for car navigation systems, and car audio; Display devices such as electronic signs and information monitors for commercial stores; Equipment such as surveillance monitors; It can be used for various purposes such as nursing and medical devices such as nursing monitors and medical monitors.

Claims (7)

It includes forming a film of a composition containing an acrylic resin and core-shell type particles, and stretching the obtained film,
In the stretching, the stretching temperature is Tg+35°C to Tg+55°C, the area magnification is 2.0 to 6.0, and the stretching speed is 3%/sec to 130%/sec. According to paragraph 1,
A production method wherein the acrylic resin has at least one selected from the group consisting of glutarimide units, lactone ring units, maleic anhydride units, maleimide units, and glutaric anhydride units. According to paragraph 1,
A production method wherein the core-shell particles have a core made of a rubber-like polymer and a coating layer made of a glass-like polymer and covering the core. According to paragraph 1,
A production method wherein the composition contains 7% to 30% by weight of the core-shell type particles. According to paragraph 1,
A manufacturing method wherein the stretching is biaxial stretching. According to clause 5,
A manufacturing method wherein in the biaxial stretching, the ratio of the draw ratio in one direction to the draw ratio in the other direction is 1.0 to 1.5. According to paragraph 1,
A manufacturing method wherein the core-shell particles are deformed into a flat shape by the stretching, and the length/thickness ratio of the flat particles is 4.0 to 7.0.