TWI764293B - Optical film and method for producing the same - Google Patents

Abstract

An object of the present invention is to provide an optical film containing a (meth)acrylic resin, excellent in brittle resistance, low retardation characteristics, and excellent in roll stability, and a method for producing the same. The solution for this is that the optical film of the present invention is characterized by containing inorganic particles and (meth)acrylic resin in an amount of 50 to 95 by mass relative to all the structural units constituting the (meth)acrylic resin. % of the structural unit derived from methyl methacrylate, 1 to 25 mass % of the structural unit derived from phenylmaleimide, and 1 to 25 mass % of the copolymer derived from the structural unit of alkyl acrylate, further contains rubber particles, The ratio of the average primary particle diameter of the rubber particles to the secondary particle diameter of the inorganic particles in the film is the ratio of the number of secondary particles of the inorganic particles in the range shown in (Equation 1), which is the ratio of all the inorganic secondary particles. Within the range of 5.0~50% of the number of particles. (Formula 1) 0.9≦(average primary particle diameter of rubber particles)/(secondary particle diameter of inorganic particles)≦1.1

Description

Optical film and method for producing the same

The present invention relates to an optical film and a method for producing the same. More specifically, the present invention relates to an optical film containing a (meth)acrylic resin, excellent in brittleness resistance, low retardation characteristics, and excellent in roll stability, and a method for producing the same.

In recent years, not only optical films such as polarizer protective films or retardation films for display devices, liquid crystal display devices or organic electroluminescence display devices, substrate films such as substrate films for touch panels, and gas barrier substrate films, etc. For thin films, there is a great demand for flexible resin films that achieve high transparency, high functionality, and light weight for substrate films such as substrate films for nanoimprinting and substrate films for flexible electronic circuits.

Among them, acrylic resins are suitably used as optical films because they exhibit excellent transparency or dimensional stability in addition to low hygroscopicity.

Furthermore, in recent years, high water resistance is required for optical films, and acrylic films are used as retardation films for liquid crystal display devices of the IPS (In Plan Switching) method with water resistance. In general, acrylic materials are difficult to handle due to their low brittleness. Especially, acrylic materials with lower retardation display properties, such as those used for IPS retardation films, tend to have particularly low brittleness in their structure. Therefore, as a countermeasure, an optical film whose brittleness is improved by containing rubber particles is known.

On the other hand, with the recent demands for the enlargement and productivity improvement of liquid crystal display devices, it is required to improve the productivity by elongated or widened optical films. After film formation, it is difficult to stably wind the film into a roll shape, and the roll shape of the formed roll laminate is degraded as a problem.

For the above-mentioned problems, in order to prevent sticking and obtain a good roll shape when winding a film, a long or wide optical film in particular, it is known to add inorganic substances to the film for the purpose of transportability during optical film film formation. A method in which the particles are stretched, and irregularities are formed on the surface to impart slidability.

Moreover, the thin film containing the acrylic resin of a low birefringence resin, the acrylic rubber particle, and further the inorganic particle which has birefringence is disclosed (for example, refer patent document 1). By this method, a film with no foreign matter defect, mechanical strength, and high transparency can be obtained. However, by the method disclosed in Patent Document 1, although the low birefringence and brittleness of the thin film are improved, the inorganic fine particles are contained as a material for the purpose of imparting low birefringence in the thin film, and the disclosed thin film is The film was not stretched, and no mention was made of the slipperiness of the stretched film.

The inventors of the present invention investigated the stretched films by adding inorganic particles to low-birefringence acrylic resins and rubber particles, and found that although the brittleness was improved, the retardation increased and the sliding properties were also improved. Insufficient, when a long or wide optical film is produced, a good roll laminate cannot be obtained.

The inventors of the present invention further studied the optical film composed of acrylic resin, rubber particles and inorganic particles, and found that in the optical film thus constituted, the stress during stretching is absorbed by the rubber particles and deformed to exhibit a phase. In addition, it was considered insufficient that the inorganic particles formed surface irregularities. As far as the retardation is exhibited by rubber particles, the use of rubber particles with low birefringence can improve the retardation even if the particles deform . [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 5666751

[The problem to be solved by the invention]

The present invention is made in view of the above-mentioned problems, and an object of the present invention is to provide an optical film containing a (meth)acrylic resin, excellent in brittle resistance, low retardation characteristics, and excellent in roll stability, and a method for producing the same. [means to solve the problem]

The inventors of the present invention, as a result of intensive research in view of the above-mentioned problems, found that by controlling the average primary particle diameter of the rubber particles and the secondary particle diameter of the inorganic particles in the optical film, the stress at the time of film stretching is dispersed/diffused, thereby suppressing the The deformation of the rubber particles and the formation of a surface uneven structure by the inorganic particles, whereby an optical film excellent in brittleness resistance, low retardation characteristics, and excellent roll stability can be obtained, and the present invention has been completed.

That is, the above-mentioned problems of the present invention are solved by the following means.

1. An optical film comprising at least inorganic particles and an optical film of a (meth)acrylic resin, characterized in that The aforementioned (meth)acrylic resin is With respect to all structural units constituting the (meth)acrylic resin, containing Structural units derived from methyl methacrylate within the range of 50 to 95 mass %, Structural units derived from N-phenylmaleimide within the range of 1 to 25% by mass, and Structural units derived from alkyl acrylate in the range of 1 to 25% by mass the copolymer, and further contains rubber particles, The value of the ratio of the average primary particle diameter of the rubber particles to the secondary particle diameter of the aforementioned inorganic particles in the film is the ratio of the number of secondary particles of the inorganic particles in the range shown in the following (Equation 1), relative to In terms of the total number of inorganic secondary particles, it is in the range of 5.0 to 50% by number; (Formula 1) 0.9≦(average primary particle diameter of rubber particles)/(secondary particle diameter of inorganic particles)≦1.1.

2. The optical film according to item 1, wherein the inorganic particles are spherical silica particles, and the secondary particle diameter is in the range of 50 to 500 nm.

3. The optical film according to Item 1 or Item 2, wherein the rubber particles have a structure derived from benzyl (meth)acrylate, a structure derived from dicyclopentyl (meth)acrylate, and a source A monomer of at least one structural unit selected from the structure of phenoxyethyl (meth)acrylate.

4. A method for producing an optical film, which is a method for producing an optical film for producing the optical film according to any one of items 1 to 3, characterized in that It has a step of preparing a dispersion liquid of inorganic particles, and a step of preparing a dispersion liquid of rubber particles, When the treatment time in the step of preparing the dispersion of inorganic particles is At (minutes), and the treatment time in the step of preparing the dispersion of rubber particles is Bt (minutes), Satisfy the conditions specified in the following (formula 2); (Formula 2) At>Bt.

5. As the manufacturing method of the optical film of item 4, the ratio (At/Bt) of the treatment time At (minute) during the dispersion of the aforementioned inorganic particles to the treatment time Bt (minute) during the dispersion of the aforementioned rubber particles The value is in the range of 1.05~15.

6. The method for producing an optical film according to Item 4 or Item 5, wherein the dispersing speed of the inorganic particles in the step of preparing the dispersion liquid of the inorganic particles is As (1/sec), and the prepared rubber particles are When the shear rate of the rubber particles in the dispersion step is Bs (1/sec), Satisfy the conditions specified in the following (formula 3); (Formula 3) As > Bs.

7. The method for producing an optical film according to item 6, wherein the ratio of the shear rate As (1/sec) during the dispersion of the inorganic particles to the shear rate Bs (1/sec) during the dispersion of the rubber particles (As /Bs), which satisfies the relationship of the following (Equation 4);

(Formula 4) As/Bs≧1×10 ² . [Effect of invention]

According to the above-mentioned means of the present invention, an optical film having excellent brittle resistance, low retardation characteristics, and excellent roll stability, and a method for producing the same can be provided.

Although it is not clear about the expression mechanism/action mechanism which can achieve the said objective effect of this invention, it is estimated as follows.

As mentioned above, the optical film composed of acrylic resin, rubber particles, inorganic particles, etc., is deformed due to the absorption of the rubber particles and deformed during stretching, and the formation of the surface irregularities by the inorganic particles is not sufficient. Therefore, The sliding property due to surface unevenness is insufficient, and when a long or wide optical film is formed into a film and laminated into a roll shape, a good roll roll cannot be stably obtained.

As a result of investigations on the above-mentioned problems, the present inventors found that the thin film obtained by adding inorganic particles to low birefringence acrylic resin and rubber particles and extending the film was improved in brittleness, but exhibited retardation and insufficient sliding properties, so that a good film could not be obtained. of rolls.

As a result of in-depth study of the above-mentioned problems, it was found that by controlling the average primary particle diameter of the rubber particles and the secondary particle diameter of the inorganic particles in the optical film, the stress during film stretching can be dispersed/diffused, and the rubber particles can be suppressed. Deformation, and the formation of surface irregularities with inorganic particles.

This is presumed because the inorganic particles exist in the form of aggregates of secondary particle size to a certain extent in the optical film. Therefore, when stress is applied to the film during stretching, the stress can be dispersed to the rubber particles and the inorganic particles, thereby suppressing the rubber particles. Simultaneously with the deformation of the particles, it imparts motion to the inorganic particles, thereby forming concavities and convexities on the surface of the film, and there is no sticking or the like during the winding process of the film forming step, and a stable roll shape can be obtained.

The optical film of the present invention is an optical film containing at least inorganic particles and a (meth)acrylic resin, and the (meth)acrylic resin is characterized in that the above-mentioned (meth)acrylic resin corresponds to the entire structure of the (meth)acrylic resin. In terms of units, it contains 1) a structural unit derived from methyl methacrylate in the range of 50 to 95 mass %, and 2) a structural unit derived from N-phenylmaleimide in the range of 1 to 25 mass %. 3) The copolymer of the structural unit and the structural unit derived from the alkyl acrylate in the range of 1 to 25% by mass, further contains rubber particles, and the size of the rubber particles is relative to the secondary particle diameter of the inorganic particles in the film. The value of the ratio of the average primary particle diameter is the ratio of the number of secondary particles of the inorganic particles within the range shown in the above (Equation 1), and is in the range of 5.0 to 50% by number relative to the number of total inorganic secondary particles Inside. This feature is a technical feature common to or corresponding to the following embodiments.

As an embodiment of the present invention, the above-mentioned inorganic particles are spherical silica particles, and the average secondary particle diameter is in the range of 50 to 500 nm, which can be more stable It is preferable to form a concavo-convex structure on the surface of the optical film to obtain better roll stability.

In addition, the aforementioned rubber particles include a structure derived from benzyl (meth)acrylate, a structure derived from dicyclopentyl (meth)acrylate, and a structure derived from phenoxyethyl (meth)acrylate The monomer of at least one structural unit selected from among them is preferable from the viewpoint that the above-mentioned effects of the present invention can be further enhanced.

The method for producing an optical film of the present invention is characterized by comprising a step of preparing a dispersion of inorganic particles and a step of preparing a dispersion of rubber particles, and the processing time in the step of preparing the dispersion of inorganic particles is At ( minutes), when the treatment time in the step of preparing the dispersion of the rubber particles is Bt (minutes), the conditions specified in the above (Formula 2) are satisfied. That is, by controlling the primary particle diameter of the rubber particles and the secondary particle diameter of the inorganic particles by the dispersion time, the stress during film stretching can be dispersed and diffused, the deformation of the rubber particles can be suppressed, and the inorganic particles can be used to form surface irregularities. structure.

Further, if the value of the ratio (At/Bt) of the treatment time At (minutes) during the dispersion of the inorganic particles to the treatment time Bt (minutes) during the dispersion of the rubber particles is in the range of 1.05 to 15, elongation is suppressed. It is preferable from the viewpoints of deformation of the rubber particles at the time, and the formation of a surface uneven structure on the inorganic particles, and better roll stability can be obtained.

In addition, the shear rate As (1/sec) at the time of dispersion of the inorganic particles in the step of preparing the dispersion liquid of the inorganic particles and the shearing speed of the rubber particles during the dispersion of the rubber particles in the step of preparing the dispersion liquid of the rubber particles is made. When the speed Bs (1/sec) becomes the condition specified in the above-mentioned (Equation 3), the deformation of the rubber particles during elongation can be suppressed, and the inorganic particles can form a surface uneven structure, and a more excellent roll stability can be obtained. speak better.

Also, similarly, the value of the ratio (As/Bs) of the shear rate As (1/sec) at the time of dispersion of the inorganic particles and the shear rate of the rubber particles at the time of dispersion Bs (1/sec) (As/Bs) satisfies the above-mentioned value. The relationship of (Formula 4) is preferable from the viewpoint of suppressing deformation of the rubber particles during stretching, and from the viewpoints that the inorganic particles can be formed with a surface uneven structure, and that more excellent roll stability can be obtained.

Hereinafter, the present invention and its constituent elements, as well as the forms and aspects for carrying out the present invention, will be described in detail. In addition, "~" shown in the following description is used in the meaning of including the numerical value described before and after it as a lower limit value and an upper limit value.

"Optical Film" The optical film of the present invention is an optical film containing at least inorganic particles and a (meth)acrylic resin, and is characterized by: The aforementioned (meth)acrylic resin is With respect to all structural units constituting the (meth)acrylic resin, containing Structural units derived from methyl methacrylate within the range of 50 to 95 mass %, Structural units derived from N-phenylmaleimide within the range of 1 to 25% by mass, and Structural units derived from alkyl acrylate in the range of 1 to 25% by mass the copolymer, further contains rubber particles, and The value of the ratio of the average primary particle diameter of the rubber particles to the secondary particle diameter of the aforementioned inorganic particles in the film is the ratio of the number of secondary particles of the inorganic particles in the range shown in the following (Equation 1), relative to It is within the range of 5.0 to 50 number % of the total number of inorganic secondary particles. (Formula 1) 0.9≦(average primary particle diameter of rubber particles)/(secondary particle diameter of inorganic particles)≦1.1

[Measurement of secondary particle diameter of inorganic particles and average primary particle diameter of rubber particles] In the present invention, the secondary particle diameter of the inorganic particles and the average primary particle diameter of the rubber particles in the optical film specified above can be obtained by the following methods.

After trimming the cross-section of the optical film of the present invention with a microtome, etc., the ultra-thin section of the cross-section is produced, and then photographed by a transmission electron microscope (TEM), or by a scanning electron microscope. (SEM) A method of directly photographing a cross section, and performing bright-field image observation.

An example of a cross-sectional photograph of the cross-sectional portion of the optical film is shown with a transmission electron microscope. In bright-field images photographed with an electron microscope, the scattering intensity of incident electrons of the observed substances (inorganic particles and rubber particles) is proportional to the atomic number (atomic weight) of the constituent substances. In the present invention, inorganic particles composed of atoms with large atomic numbers, such as Si atoms, show dark contrast, and rubber particles composed of atoms with small atomic numbers, such as C atoms, show bright contrast. Thereby, the secondary particle diameter of the aggregate of the inorganic particles in the optical film and the primary particle of the rubber particle can be confirmed.

Fig. 1 is an electron microscope photograph showing an example of a cross section of an optical film of the present invention in which inorganic particles and rubber particles are present. The black image portion indicated by 1 is inorganic particles (secondary particles), and the majority indicated by G The oval white image that exists is a rubber particle (primary particle).

In the present invention, the secondary particle diameter of the inorganic particles is as described above, and the cross section of the optical film can be observed at a magnification of 500,000 using a transmission electron microscope, and the inorganic particles (secondary particles) that are black are observed as It can be obtained by observing and measuring the particle diameter, and the average secondary particle diameter of the inorganic particles can be obtained from the average value.

Similarly, regarding the average primary particle diameter of the rubber particles, as described above, the cross-section of the optical film was observed with a transmission electron microscope at 500,000 magnifications of the rubber particles (primary particles), as shown in FIG. 1 . The elliptical and white rubber particles G (primary particles) were observed, the major diameter of the ellipse was measured as the primary particle diameter of the rubber particles, and the average value was obtained as the average primary particle diameter of the rubber particles.

The optical film of the present invention is characterized in that the ratio of the number of secondary particles of the inorganic particles with the value of the average primary particle diameter of the rubber particles/the secondary particle diameter of the inorganic particles is 0.9 to 1.1, relative to the total number of inorganic secondary particles , in the range of 5.0 to 50 percent.

In the image shown in (a) of Fig. 1, when an area of 5 μm × 5 μm is used as the observation area, the total number of inorganic secondary particles is 234, and among them, the number of inorganic secondary particles satisfying the condition specified by (Formula 1) 35, and the ratio is 15.0 percent. Furthermore, in the image shown in (b) of FIG. 1 , when an area of 5 μm×5 μm is used as the observation area, the total number of inorganic secondary particles is 206, and among them, the inorganic secondary particles satisfying the conditions specified by (Formula 1) The number is 53, and the ratio is 25.7%.

By having a structure satisfying the above-mentioned conditions, the stress when the optical film is stretched can be dispersed and diffused, the deformation of the rubber particles can be suppressed, and the surface irregularities can be formed by the inorganic particles.

Hereinafter, the main constituent elements of the optical film of the present invention will be described in detail.

[(meth)acrylic resin] The (meth)acrylic resin applied to the optical film of the present invention is characterized by containing, with respect to all structural units constituting the (meth)acrylic resin, a 1) structural units derived from methyl methacrylate within the range of 50 to 95 mass %, 2) structural units derived from N-phenylmaleimide within the range of 1 to 25% by mass, and 3) Structural units derived from alkyl acrylate within the range of 1 to 25 mass % the copolymer.

The ratio of the structural unit derived from methyl methacrylate exists in the range of 50-95 mass %, Preferably it exists in the range of 50-85 mass %.

Moreover, the ratio of the structural unit derived from N-phenylmaleimide is in the range of 1-25 mass %, Preferably it exists in the range of 10-25 mass %.

Moreover, the ratio of the structural unit derived from an alkyl acrylate exists in the range of 1-25 mass %, Preferably it exists in the range of 5-25 mass %.

Specific examples of the alkyl acrylate that can be used in the present invention include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, t-butyl acrylate, hexyl acrylate, and 2-ethylhexyl acrylate. , octyl acrylate, etc.

The (meth)acrylic resin of the present invention preferably has a glass transition temperature (Tg) of 110°C or higher. When the glass transition temperature (Tg) of the (meth)acrylic resin is 110° C. or higher, the fluidity is suppressed even at the same elongation temperature, and the rubber particles can be prevented from moving easily. As a result, the rubber particles do not spread too much, so they can be appropriately approached.

Moreover, as for the (meth)acrylic-type resin of this invention, it is preferable that the weight average molecular weight Mw exists in the range of 200,000-2,000,000. When the weight average molecular weight Mw of the (meth)acrylic resin is in the above range, sufficient mechanical strength (toughness) is provided to the film, and the film formability is not easily impaired. The weight average molecular weight Mw of the (meth)acrylic resin is more preferably 300,000 to 2,000,000, and more preferably 500,000 to 2,000,000 from the above viewpoint. The weight average molecular weight Mw can be measured in terms of polystyrene by gel permeation chromatography (GPC).

The (meth)acrylic resin of the present invention can be obtained by synthesizing in accordance with a conventionally known production method. For example, Japanese Patent Laid-Open No. 2006-321871, No. 2012-153743, No. 2012-184364, No. 2017-178975, No. 2018-003005, Japanese Patent No. 5798690, and International Publication No. 2016/052600 obtained by the method described.

[rubber particles] The rubber particles of the present invention can provide flexibility or toughness to the optical film, and at the same time have the function of forming irregularities on the surface of the optical film to provide sliding properties.

The rubber particles of the present invention are preferably graft copolymers comprising a rubber-like polymer (cross-linked polymer), that is, have a core portion comprising a rubber-like polymer (cross-linked polymer), and a shell covering the same The core-shell type of rubber particles.

The glass transition temperature (Tg) of the rubber particles is preferably -10°C or lower. When the glass transition temperature (Tg) of the rubber particles is -10°C or lower, it is easy to impart sufficient toughness to the film. The glass transition temperature (Tg) of the rubber particles is more preferably -15°C or lower, and further preferably -20°C or lower. The glass transition temperature (Tg) of the rubber particles can be measured by the same method as described above.

Rubber-like polymers, including butadiene-based cross-linked polymers, (meth)acrylic-based cross-linked polymers, and organosiloxane-based cross-linked polymers. Among them, an acrylic rubber-like polymer is particularly preferable from the viewpoint of having a small difference in refractive index with the (meth)acrylic resin and hardly impairing the transparency of the optical film.

That is, the rubber particles are preferably an acrylic graft copolymer comprising the acrylic rubber-like polymer (a), that is, have a core portion comprising the acrylic rubber-like polymer (a), and a shell portion covering the acrylic rubber-like polymer (a). core-shell particles. The core-shell type particles are multi-stage polymers (or multi-stage polymers) obtained by polymerizing at least one stage or more of a monomer mixture (b) containing methacrylate as a main component in the presence of an acrylic rubber-like polymer (a). multilayer construction polymers). The polymerization can be carried out by an emulsion polymerization method.

(core part: about acrylic rubber-like polymer (a)) The acrylic rubber-like polymer (a) is a cross-linked polymer mainly composed of acrylate. The acrylic rubber-like polymer (a) is a monomer mixture (a') containing 50 to 100 mass % of acrylate and 50 to 0 mass % of other monomers that can be copolymerized therewith, and each molecule has 2 A cross-linked polymer obtained by polymerizing 0.05 to 10 parts by mass (relative to 100 parts by mass of the monomer mixture (a')) of more than one non-conjugated reactive double bond polyfunctional monomer. The cross-linked polymer can be obtained by mixing and polymerizing all of these monomers, or by changing the monomer composition and polymerizing it twice or more.

The acrylate constituting the acrylic rubber-like polymer (a) is preferably an alkyl acrylate having 1 to 12 carbon atoms, such as an alkyl group such as methyl acrylate and butyl acrylate. Acrylate may be one type or two or more types. From the viewpoint of making the glass transition temperature of the rubber particles -10° C. or lower, the acrylate preferably contains at least an alkyl acrylate having 4 to 10 carbon atoms.

50-100 mass % is preferable with respect to 100 mass % of monomer mixture (a'), as for content of an acrylate, 60-99 mass % is more preferable, 70-99 mass % is more preferable. When the content of the acrylate is 50% by weight or more, it is easy to impart sufficient toughness to the film.

Furthermore, from the viewpoint of making the glass transition temperature of the rubber particles -10°C or lower, the mass ratio of the alkyl acrylate having 4 or more carbon atoms in the alkyl group/monomer mixture (a') is preferably 3 or more, more preferably 4 or more and 10 or less.

Examples of copolymerizable monomers also include methacrylates such as methyl methacrylate; styrenes such as styrene and methylstyrene; unsaturated nitriles such as acrylonitrile and methacrylonitrile, etc. .

Examples of polyfunctional monomers include allyl (meth)acrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, dimaleic acid Allyl ester, divinyl adipate, divinylbenzene, ethylene glycol di(meth)acrylate, diethylene glycol (meth)acrylate, triethylene glycol di(meth)acrylate, Trimethylolpropane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, dipropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate.

The content of the polyfunctional monomer is preferably in the range of 0.05 to 10 mass %, more preferably in the range of 0.1 to 5 mass %, with respect to the total 100 mass % of the monomer mixture (a'). If the content of the polyfunctional monomer is 0.05 mass % or more, the degree of crosslinking of the obtained acrylic rubber-like polymer (a) is easily increased, so the hardness and rigidity of the obtained film will not be impaired, and if it is 10 mass % Below, the toughness of the film is not easily damaged.

(Shell: About the monomer mixture (b)) The monomer mixture (b) is a graft component to the acrylic rubber-like polymer (a), and constitutes a shell portion. The monomer mixture (b) preferably contains methacrylate as a main component.

The methacrylate constituting the monomer mixture (b) is preferably an alkyl methacrylate having 1 to 12 carbon atoms of an alkyl group such as methyl methacrylate. One type of methacrylate may be used, or two or more types may be used.

The content of the methacrylate is preferably 50% by mass or more with respect to 100% by mass of the monomer mixture (b). When the content of the methacrylate is 50% by mass or more, the hardness and rigidity of the obtained film can not be easily reduced. From the viewpoint of reducing the affinity between the (meth)acrylic resin and the rubber particles (making the ΔSP large), the content of the methacrylate is more preferably 70 mass % relative to 100 mass % of the monomer mixture (b). % or more, and more preferably 80% by mass or more.

The monomer mixture (b) may further contain other monomers as needed. Examples of other monomers include acrylates of methyl acrylate, ethyl acrylate, n-butyl acrylate, etc.; benzyl (meth)acrylate, dicyclopentyl (meth)acrylate, phenoxy (meth)acrylate (meth)acrylic monomers (meth)acrylic monomers having an alicyclic structure, a heterocyclic structure, or an aromatic group such as ethyl ethyl ester ((meth)acrylic monomers containing a ring structure).

In the rubber particles of the present invention, those having a structure derived from benzyl (meth)acrylate, a structure derived from dicyclopentyl (meth)acrylate, and a structure derived from phenoxyethyl (meth)acrylate are preferably included. A monomer of at least one structural unit selected from the structure of an ester.

(Core-Shell Type Rubber Particles: For Acrylic Graft Copolymers) An example of an acrylic graft copolymer having a glass transition temperature (Tg) of -15°C or lower, that is, a core-shell type rubber particle, is included in the acrylic rubber as the (meth)acrylic rubber-like polymer (a). In the presence of 5 to 90 parts by mass (preferably 5 to 75 parts by mass) of the polymer, 95 to 25 parts by mass of the monomer mixture (b) containing methacrylate as a main component is subjected to at least one stage of polymerization to obtain obtained polymer.

The acrylic graft copolymer may further contain a hard polymer inside the acrylic rubber-like polymer (a) as required. Such an acrylic graft copolymer can be obtained through the following polymerization steps (I) to (III).

Polymerization step (I) A monomer mixture (c1) containing 40 to 100 mass % of methacrylate, 60 to 0 mass % of other monomers that can be copolymerized therewith, and 0.01 to 10 mass parts of a multifunctional monomer (relative to the monomer) The step of polymerizing and obtaining a hard polymer in the total of 100 parts by mass of the mixture (c1).

Polymerization step (II) A monomer mixture (a1) containing 60 to 100 mass % of acrylate, 0 to 40 mass % of other monomers that can be copolymerized therewith, and 0.1 to 5 mass parts of a multifunctional monomer (relative to the monomer mixture ( a1) in a total of 100 parts by mass) a step of polymerizing to obtain a soft polymer.

Polymerization step (III) A monomer mixture (b1) containing 60 to 100 mass % of methacrylate, 40 to 0 mass % of other monomers that can be copolymerized therewith, and 0 to 10 mass parts of a multifunctional monomer (relative to the monomer) The step of polymerizing and obtaining a hard polymer in total of 100 parts by mass of the mixture (b1).

Between the polymerization steps of (I) to (III), other polymerization steps may be further included.

The acrylic graft copolymer can also be obtained through the polymerization step (IV).

Polymerization step (IV) A monomer mixture (b2) containing 40 to 100 mass % of methacrylates, 0 to 60 mass % of acrylates, 0 to 5 mass % of other copolymerizable monomers, and 0 to 10 multifunctional monomers Parts by mass (with respect to 100 parts by mass of the monomer mixture (b2)) were polymerized to obtain a rigid polymer.

The methacrylates, acrylates, other copolymerizable monomers, and polyfunctional monomers used in each polymerization step can be the same as those described above.

The soft layer can impart shock absorption to the optical film. An example of the soft layer includes a layer containing an acrylic rubber-like polymer (a) containing an acrylate as a main component. The hard layer does not easily impair the toughness of the optical film, and during the production of rubber particles, it can prevent the particles from becoming too large or lumpy. An example of the hard layer includes a layer containing a polymer mainly composed of methacrylate.

The graft ratio of the acrylic graft copolymer (the mass ratio of the graft component (shell part) to the acrylic rubber-like polymer (a)) is preferably 10 to 250%, more preferably 40 to 230%, More preferably, it is 60 to 220%. When the graft ratio is 10% or more, the ratio of the shell portion does not become too small, so that the hardness or rigidity of the film is not easily impaired. When the graft ratio of the acrylic graft copolymer is 250% or less, the ratio of the acrylic rubber-like polymer (a) does not become too small, so the effect of improving the toughness and brittleness of the film is not easily impaired.

In the optical film, it is preferable to adjust the combination of the type of rubber particles (specifically, the monomer composition of the shell portion) and the type of (meth)acrylic resin in order to bring the rubber particles into close proximity.

In the optical film of the present invention, the rubber particles when the cross section is observed are mostly elliptical, and the average aspect ratio of the elliptical rubber particles is preferably 1.2 to 3.0. When the average aspect ratio of the rubber particles is 1.2 or more, the stress (shrinkage force) relative to the extension tension of the rubber particles is easily applied to the optical film immediately after winding, so that the stress remaining in the optical film is easily relieved, and the suppression of Roll failure.

When the average aspect ratio of the rubber particles is 3.0 or less, the contact points between adjacent rubber particles will not be too small, so the effect of dispersing the stress remaining in the optical film is not impaired, and the roll failure can be suppressed. The average aspect ratio of the rubber particles is more preferably in the range of 1.5 to 2.8, and more preferably in the range of 2.0 to 2.5.

The aspect ratio means the ratio of the long diameter to the short diameter of the rubber particles (long diameter/short diameter). In addition, the average aspect ratio means the average value of the aspect ratios of a plurality of rubber particles.

The long diameter of the rubber particle can be measured as the length in the longitudinal direction (length of the long side) of the rectangle circumscribed by the rubber particle in the electron microscope photographed image shown in the aforementioned FIG. 1 . The short diameter of the rubber particle can be measured as the length in the short side direction of the rectangle circumscribed by the rubber particle (the length of the short side) in the TEM image described later.

The average major diameter of the rubber particles is preferably in the range of 200 to 500 nm. When the average major diameter of the rubber particles is 200 nm or more, the stress (shrinkage force) with respect to the stretching tension of the rubber particles is easily applied to the optical film immediately after winding, so that it is easy to sufficiently suppress roll failure. When the average major diameter of the rubber particles is 500 nm or less, the number of contacts between adjacent rubber particles does not become too small, so the effect of dispersing stress is not easily impaired, and it is easy to sufficiently suppress roll failures. The average major diameter of the rubber particles is more preferably in the range of 220 to 400 nm, and more preferably in the range of 250 to 350 nm. The average major diameter of the rubber particles is the average value of the major diameters of the rubber particles.

The content of the rubber particles is preferably in the range of 5 to 20 mass % with respect to the (meth)acrylic resin. When the content of the rubber particles is 5% by mass or more, not only sufficient flexibility and toughness are easily provided to the (meth)acrylic resin film, but also unevenness is formed on the surface to provide sliding properties. When the content of the rubber particles is 20% by mass or less, the haze does not increase excessively. From the viewpoints described above, the content of the rubber particles is more preferably within a range of 5 to 15 mass %, and more preferably within a range of 5 to 10 mass % with respect to the (meth)acrylic resin.

[inorganic particles] Inorganic particles that can be applied to the optical film of the present invention are generally used as a matting agent for the film. In order to improve the poor surface sliding properties, inorganic particles are contained, which increase the roughness of the optical film and perform so-called matting. , in order to reduce adhesion and improve friction resistance.

The average primary particle diameter of the inorganic particles used in the present invention is preferably in the range of 1 to 1000 nm, more preferably in the range of 1 to 500 nm, and particularly preferably in the range of 3 to 100 nm. In addition, the average secondary particle diameter is preferably in the range of 50 to 500 nm.

Inorganic particles include, for example, inorganic fine particles such as barium sulfate, colloidal manganese, titanium dioxide, barium strontium sulfate, and silicon dioxide. Further, examples of the inorganic particles include synthetic silicon dioxide obtained by a wet process or gelation of silicic acid. Silicon dioxide or titanium dioxide (rutile type or anatase type) generated from titanium slag and sulfuric acid.

From the viewpoint of reducing the haze and the haze of the thin film, the inorganic particles used in the present invention are preferably those containing silicon. For example, most of the silica particles are surface-modified with organic matter, which is preferable because the surface haze of the film can be reduced. Preferred organic substances for surface modification include halosilanes, alkoxysilanes, silazanes, siloxanes, and the like.

Among the above-mentioned inorganic particles, silica particles (silicon dioxide particles) are particularly preferred. As the inorganic particles, commercially available products can be preferably used, and the following Aerosil series products of Japan Aerosil Co., Ltd. are suitable.

Commercially available products under the trade names of R972V, R812, R805, R816, NKC130, R711, R7200, R202, RY200, RY200S, RY300, R104, R105, RA200H, RA200HS (above, manufactured by Aerosil Co., Ltd.) can be used.

[Other additives for optical films] In the optical film of the present invention, in addition to the (meth)acrylic resin, rubber particles, and inorganic particles described above, various conventionally known additives can be appropriately selected and used within a range that does not impair the purpose and effect of the present invention.

Applicable additives, for example, may include plasticizers, antioxidants, light stabilizers, antistatic agents, release agents, and the like. Details of the main additives are described below.

(plasticizer) The optical film of the present invention may contain a conventionally known plasticizer. Well-known plasticizers include, for example, phthalate-based, fatty acid-ester-based, trimellitic-ester-based, phosphate-based, polyester-based, sugar-ester-based, and acrylic polymer-based plasticizers. Among them, polyester-based plasticizers and sugar ester-based plasticizers are preferably used.

A polyester-based plasticizer, which can be obtained by polymerizing a dicarboxylic acid and a diol, preferably, 70 mol% or more of the dicarboxylic acid constituent unit (the constituent unit derived from the dicarboxylic acid) is derived from an aromatic dicarboxylic acid. A carboxylic acid, and 70 mol% or more of the diol constituent unit (the constituent unit derived from the diol) is derived from an aliphatic diol.

The sugar ester-based plasticizer is a compound containing at least either a furanose ring or a pyranose ring, and may be a monosaccharide or a polysaccharide having 2 to 12 sugar structures linked thereto.

The sugar ester is a compound in which at least one of the OH groups contained in the sugar structure is esterified, and the average ester substitution degree is preferably within the range of 4.0 to 8.0, more preferably within the range of 5.0 to 7.5.

The amount of plasticizer used varies depending on the type of plasticizer, usage conditions, etc., but is preferably within the range of 0.5 to 10 mass %, more preferably 0.6 to 5, relative to the aforementioned (meth)acrylic resin. within the range of mass %.

(UV absorber) The ultraviolet absorber that can be applied to the optical film of the present invention is not particularly limited, and examples thereof include oxybenzophenone-based compounds, benzotriazole-based compounds, salicylate-based compounds, and benzophenone-based compounds , cyanoacrylate-based compounds, triazine-based compounds, nickel zirconium salt-based compounds, inorganic powders, etc.

The amount of the ultraviolet absorber to be used depends on the type of the ultraviolet absorber, usage conditions, etc., but is preferably within the range of 0.5 to 10% by mass, more preferably 0.6% by mass relative to the aforementioned (meth)acrylic resin. ~4 mass %.

(Antioxidants) In the optical film of the present invention, commonly known compounds can be used as antioxidants. In particular, each of lactone-based, sulfur-based, phenol-based, double-bond-based, hindered amine-based, and phosphorus-based antioxidants can be preferably used.

For example, "Irgafos XP40, Irgafos XP60" which are marketed by BASF Japan Co., Ltd., etc. are mentioned.

Examples of the above sulfur-based antioxidant include "Sumilizer TPL-R" and "Sumilizer TP-D" commercially available from Sumitomo Chemical Co., Ltd.

The above-mentioned phenol-based antioxidant is preferably one having a structure of 2,6-dialkylphenol, for example, "Irganox 1076", "Irganox 1010" available from BASF Japan Co., Ltd., and "Irganox 1010" available from ADEKA "ADK STAB AO-50" sold.

The above-mentioned double bond-based antioxidants are commercially available under the trade names of "Sumilizer GM" and "Sumilizer GS" from Sumitomo Chemical Co., Ltd.

Examples of the hindered amine-based antioxidants include "Tinuvin 144" and "Tinuvin 770" commercially available from BASF Japan Co., Ltd., and "ADK STAB LA-52" commercially available from ADEKA Co., Ltd.

Examples of the phosphorus-based antioxidants include "SumilizerGP" commercially available from Sumitomo Chemical Co., Ltd., "ADK STAB PEP-24G", "ADK STAB PEP-36" and "ADK STAB 3010" commercially available from ADEKA Co., Ltd. ", "Irgafos P-EPQ" from BASF Japan Co., Ltd., and "GSY-P101" from Sakai Chemical Industry Co., Ltd.

[Properties of Optical Films] (Haze) The optical film of the present invention preferably has high transparency. The haze of the optical film is preferably 4.0% or less, more preferably 2.0% or less, and still more preferably 1.0% or less. The haze can be measured according to JIS K-6714 using a haze meter (HGM-2DP, Suga Test Instruments) at 25° C. and 60% RH with a sample of 40 mm×80 nm.

(Phase difference Ro and Rt) In the optical film of the present invention, from the viewpoint of using, for example, a retardation film for IPS, the retardation Ro in the in-plane direction measured in an environment with a measurement wavelength of 550 nm, 23° C., and 55% RH is preferably 0 to 10 nm, More preferably, it is 0 to 5 nm. The retardation Rt in the thickness direction of the optical film of the present invention is preferably -20 to +20 nm, more preferably -10 to +10 nm, and particularly preferably -5 to +5 nm.

Ro and Rt are respectively defined by the following formulae.

Equation (1a) Ro=(n _x -n _y )×d Equation (1b) Rt=((n _x + _ny )/2-n _z )×d In the above formula, n _x represents the in-plane slow axis of the film The refractive index in the direction (the direction of the maximum refractive index), _ny represents the refractive index in the direction perpendicular to the in-plane slow axis of the film, _nz represents the refractive index in the thickness direction of the film, and d represents the thickness (nm) of the film.

The in-plane slow axis of the optical film of the present invention refers to the axis with the largest refractive index on the film surface. The in-plane slow axis of the optical film can be confirmed by an automatic birefringence meter Axo Scan (Axo Scan Mueller Matrix Polarimeter: manufactured by Axometrix Corporation). The in-plane slow axis usually coincides with the direction of the largest elongation ratio.

Ro and Rt can be measured by the following methods.

1) Adjust the humidity of the optical film of the present invention in an environment of 23° C. and 55% RH for 24 hours. The average refractive index of the film was measured with an Abbe refractometer, and the thickness d was measured with a commercially available micrometer.

2) Using an automatic birefringent meter, Axo Scan (Axo Scan Mueller Matrix Polarimeter: manufactured by Axometrix Corporation), the retardation Ro and Rth of the film after humidity conditioning were measured at a measurement wavelength of 550 nm in an environment of 23° C. and 55% RH, respectively.

The retardation Ro and Rt of the optical film of the present invention can be adjusted, for example, by the type of (meth)acrylic resin. In order to reduce the retardation Ro and Rt of the optical film, it is preferable that the content ratio of the retardation can be offset by the structural unit having negative birefringence and the structural unit having positive birefringence.

(membrane thickness) The thickness of the optical film of the present invention can be, for example, in the range of 5 to 100 μm, preferably in the range of 5 to 40 μm.

"Manufacturing method of optical film" [Dispersion step of inorganic particles and rubber particles] As the method for producing the optical film of the present invention, in the optical film of the present invention, the ratio of the average primary particle diameter of the rubber particles to the secondary particle diameter of the inorganic particles is in the range shown in the above-mentioned (Formula 1) The ratio of the number of secondary particles of the inorganic particles inside is in the range of 5.0 to 50% by number of the total number of inorganic secondary particles, and it is characterized by a step of preparing a dispersion liquid of inorganic particles, and preparing rubber particles. In the step of preparing the dispersion liquid, the following ( The conditions specified in formula 2).

(Formula 2) At > Bt

The treatment time At and Bt of each dispersion liquid specified in the above formula 2 depend on the preparation amount of the respective dispersion liquid, so it is a factor determined by the appropriate preparation amount when preparing the same amount of dopant. Since it is difficult to specify an absolute dispersion time, in the present invention, it is preferable to maintain the relationship of At>Bt defined by Equation 2, and to use the treatment time At (minutes) when the inorganic particles are dispersed and the treatment time Bt when the rubber particles are dispersed. In the form of the relative relationship of (minutes), the value of the ratio (At/Bt) is in the range of 1.05 to 15.

The more preferable production conditions are that the shear rate of the inorganic particles during the dispersion of the inorganic particles in the step of preparing the dispersion liquid of the inorganic particles is As (1/sec), and the dispersion of the rubber particles in the step of preparing the dispersion liquid of the rubber particles. When the shear rate is Bs (1/sec), it is preferable to satisfy the conditions specified in the following (Equation 3).

(Formula 3) As > Bs Further, in the present invention, As and Bs also depend on their respective preparation amounts or preparation recipes, so the more preferable production conditions are the shear rate As (1/sec) at the time of dispersion of the inorganic particles, which is the same as the above-mentioned The value of the ratio (As/Bs) of the shear rate Bs (1/sec) at the time of dispersion of the rubber particles satisfies the relationship of the following (Equation 4).

(Formula 4) As/Bs≧1×10 ² More preferably, As/Bs is in the range of 1×10 ² to 1×10 ⁸ . FIG. 2 is a schematic diagram showing an example of the relationship between the shear rate and the dispersion treatment time when the inorganic particle dispersion liquid and the rubber particle dispersion liquid are prepared in the present invention.

In Fig. 2, when the horizontal axis is the treatment time (minutes) in the dispersion step, and the vertical axis is the shear rate during dispersion (1/sec, logarithm), the shear rate As (1/sec) during dispersion by inorganic particles ) and the area surrounded by the processing time At (min) in the step of preparing the dispersion of the inorganic particles is S1; the area surrounded by the shear rate Bs (1/sec) during the dispersion of the rubber particles and the step of preparing the dispersion of the rubber particles is S1 When the area surrounded by the processing time Bt (minutes) is S2, a preferable condition is S1>S2. That is, it is characterized in that the dispersion conditions at the time of preparation of the inorganic particle dispersion liquid are set to be higher than the dispersion conditions at the time of preparation of the rubber particle dispersion liquid.

In the present invention, as a method for controlling the shear rate As (1/sec) of the inorganic particles during dispersion and the shear rate Bs (1/sec) of the rubber particles to be within a desired range of conditions, a rubber particle dispersion liquid is prepared. The shear rate Bs at this time can be appropriately selected and adjusted to adjust the number of revolutions and the type of rotor/stator when using the dispersion conditions of a dispersing device such as a Milder disperser (manufactured by Taiyo Kiko Co., Ltd.). The inorganic particle dispersion liquid is prepared. The shear rate As, when using a Manton-Gaulin disperser as a high-pressure dispersing device, can adjust the valve pressure of the first stage and the second stage of the Manton-Gaulin disperser, and appropriately adjust to A-1 in Table I The relationship of shear rates shown, and the shear rate ratio (As/Bs), to obtain the desired properties.

As a dispersing method, a mixed solution of adding rubber particles or inorganic particles and a solvent (such as dichloromethane, ethanol, etc.) as required is prepared, and a conventionally known dispersing device, for example, a high-pressure dispersing machine can be mentioned, for example, the ultra-high pressure manufactured by Microfluidics Corporation. Homogenizer (trade name Microfluidizer) and NANOMIZER manufactured by NANOMIZER include Manton-Gaulin type high pressure dispersing device, Homogeniser manufactured by IZUMI FOOD MACHINERY, Milder dispersing machine manufactured by Pacific Machinery Co., Ltd., and ultrasonic dispersing machine.

[Film-making method of optical film] The optical film of the present invention is produced by a solution casting method (casting method) in accordance with the following method after preparing the rubber particle dispersion liquid and the inorganic particle dispersion liquid in the above-mentioned dispersion step. That is, the optical film of the present invention is prepared after the rubber particle dispersion liquid and the inorganic particle dispersion liquid are prepared. 1) a step of obtaining a dopant containing at least the (meth)acrylic resin of the present invention, the rubber particle dispersion, the inorganic particle dispersion and the solvent (dopant preparation step); 2) Casting the obtained dopant on the support, drying and peeling off to obtain a film-like film (casting step), 3) the step of stretching the obtained film (stretching step), and 4) A step (winding step) of winding the stretched film into a roll shape is produced.

(1. Dopant preparation step) A dopant is prepared by adding the (meth)acrylic resin of the present invention, the rubber particle dispersion liquid, the inorganic particle dispersion liquid, and if necessary, a solvent and the like.

The solvent used for the preparation of the dopant contains at least an organic solvent (good solvent) capable of dissolving the (meth)acrylic resin. Examples of the good solvent include chlorine-based organic solvents such as dichloromethane, and non-chlorine-based organic solvents such as methyl acetate, ethyl acetate, acetone, and tetrahydrofuran. Among them, dichloromethane is particularly preferred.

The solvent used for the preparation of the dopant may further contain a poor solvent. Examples of poor solvents include linear or branched aliphatic alcohols having 1 to 4 carbon atoms. When the ratio of the alcohol in the dopant is increased, the film-like substance tends to gel, and the peeling from the metal support becomes easy. Examples of linear or branched aliphatic alcohols having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Among them, ethanol is preferred because of the stability of the dopant, the low boiling point, and the good drying properties.

The solid content concentration of the dopant is not particularly limited, and from the viewpoint of the compressive effect caused by drying, the rubber particles or the inorganic particles are easily brought close to each other in the obtained optical film, and the lower one is preferred. Specifically, the solid content concentration of the dopant is preferably 25% by mass or less, more preferably 20% by mass or less, and still more preferably 15% by mass or less. On the other hand, the lower limit of the solid content concentration of the dopant is preferably about 9 mass %, for example, from the viewpoint of easily obtaining a film of a specific thickness.

The preparation of the dopant can be prepared by directly adding the (meth)acrylic resin, the rubber particle dispersion to the aforementioned solvent, and mixing with the inorganic particle dispersion and other additives, or it can be separately prepared and dissolved in the aforementioned solvent. There are resin solutions of (meth)acrylic resins, rubber particle dispersions, inorganic particle dispersions, and other additives, and these are mixed and prepared.

(2. Casting step) The resulting dopant is cast on a support. The casting of the dopant can be carried out by spitting out the casting die.

Next, the solvent in the dopant cast on the support is evaporated and dried. The dried dopant was peeled off from the support to obtain a film-like mesh.

The residual solvent amount of the dopant during peeling from the support (the residual solvent amount of the film during peeling) is preferably 10 to 150 from the viewpoint of easily reducing the retardation of the obtained (meth)acrylic resin film. % by mass, more preferably 20 to 40% by mass. When the residual solvent amount at the time of peeling is 10 mass % or more, the (meth)acrylic resin tends to flow during drying or stretching, and tends to become non-aligned, so that the retardation of the obtained (meth)acrylic resin film can be easily reduced. When the residual solvent amount at the time of peeling is 150 mass % or less, the force required for peeling off the dopant is less likely to be excessively large, so that the breakage of the dopant is easily suppressed.

The residual solvent amount of the dopant at the time of lift-off is defined by the following formula. The following is also the same.

Residual solvent content of dopant (mass %) = (mass of dopant before heat treatment - mass of dopant after heat treatment)/mass of dopant after heat treatment × 100 In addition, the heat treatment at the time of measuring the residual solvent amount means the heat treatment of 140 degreeC and 30 minutes.

The residual solvent amount at the time of peeling can be adjusted by the drying temperature or drying time of the dopant on the support, the temperature of the support, and the like.

(3. Extension step) The peeled web (also referred to as a film) is stretched while being dried.

As long as the stretching is carried out according to the required optical properties, it is preferable to extend in at least one direction (such as the short side direction of the film (TD direction)), and it can also be extended in two directions perpendicular to each other (for example, the short side direction of the film ( TD direction) and the two-axis extension of the conveying direction (MD direction) orthogonal to it).

The stretching ratio is not particularly limited, for example, it is preferably within the range of 20 to 200%, more preferably within the range of 30 to 100%, and more preferably within the range of 50 to 70%. The elongation ratio (%) referred to here is defined as (The amount of change in the length of the film in the extension direction before and after the extension)/(the length in the extension direction of the film before the extension)×100(%). In addition, when biaxial stretching is performed, it is preferable that the above-mentioned stretching magnification is obtained for each of the TD direction and the MD direction.

In addition, the in-plane slow axis direction of the optical film (the direction in which the in-plane refractive index becomes the largest) is usually the direction in which the stretching magnification becomes the largest.

The elongation temperature (drying temperature), when the glass transition temperature of the (meth)acrylic resin is taken as Tg, is preferably in the range of (Tg-65)°C ~ (Tg+60)°C, more preferably (Tg- Within the range of 50)°C ~ (Tg+50)°C, and more preferably within the range of (Tg-30)°C ~ (Tg+50)°C. When the stretching temperature is (Tg-30)°C or higher, it is easy to make the film-like material flexible enough for stretching, and the tension applied to the film-like material during stretching does not become too large, so excess residual stress can be made It is hard to remain|survive in the obtained (meth)acrylic-type resin film. When the stretching temperature is Tg or lower, it is easy to suppress the generation of air bubbles and the like due to the vaporization of the solvent in the film. Specifically, the extension temperature may be in the range of 60 to 220°C.

Stretching temperature, (a) when drying by non-contact heating type such as tenter stretching machine, etc., can be measured as the ambient temperature such as the temperature in the stretching machine or the temperature of hot air; (b) when contact heating with hot rollers, etc. When drying the mold, it can be measured as the temperature of the contact heating part, or (c) can be measured as any temperature of the surface temperature of the film (surface to be dried). Among them, (a) when drying is performed by a non-contact heating type such as a tenter stretching machine, the ambient temperature such as the temperature in the stretching machine or the temperature of the hot air is preferable.

The residual solvent amount in the film at the start of stretching is preferably, for example, 5 to 30% by mass. The amount of residual solvent at the start of elongation can be determined by the same method as described above.

The extension of the film in the TD direction (short-side direction) can be, for example, by fixing both ends of the film with clips or pins, and making the gap between the clips or pins expand in the direction of progress (tenter method) ) to proceed. The stretching of the film in the MD direction can be performed, for example, by a method (roll method) in which a difference in peripheral speed is given to a plurality of rollers and the difference in peripheral speed of the rollers is used therebetween.

(4. Winding step) The film obtained after stretching is further dried as necessary while being wound into a roll shape to obtain a roll laminate of optical films.

The drying temperature can be adjusted to the same range as the stretching temperature in the above (3. stretching step). The drying temperature was measured by the same method as the above (3. extension step). In addition, when drying is performed by the contact heating type such as the hot roller described in the above (b), it is preferable to measure it as the temperature of the contact heating part.

The winding is usually performed while applying tension (winding tension) to the MD direction of the film.

In the roll laminate obtained after winding, the longitudinal direction of the rubber particles is preferably substantially perpendicular to the thickness direction of the optical film. In addition, from the viewpoint of more easily suppressing roll failure of the optical film after winding, the longitudinal direction of the rubber particles is preferably substantially parallel to the extending direction of the optical film (preferably the short-side direction).

In the obtained roller body, the length of the optical film (the length in the MD direction) is preferably within a range of 2000 to 8000 m, more preferably within a range of 5000 to 7000 m. The width of the optical film (the length in the TD direction) is preferably within a range of 1.3 to 3.0 m, more preferably within a range of 2.3 to 2.5 m.

As described above, the force (stress) shrinking in the longitudinal direction acts on the optical film of the roll body immediately after winding by the winding tension, and the force (stress) extending in the transversal direction easily acts. On the other hand, the optical film of the present invention has a structure in which the rubber particles are appropriately close to each other. Thereby, even if the particle diameter of the rubber particles is not large, the above-mentioned stress can be effectively relieved by the optical film of the roll body after winding. Thereby, the transfer of the core due to the force of shrinking in the longitudinal direction and the chain failure due to the force of extending in the short-side direction can be suppressed. Therefore, the winding shape can be improved without increasing the haze of the optical film.

In particular, the longer the optical film (longer in MD direction) and the wider (longer in TD direction), the easier it is to produce roll failures. In the present invention, even in the roll body of such an optical film, roll failure can be suppressed favorably.

The obtained optical film is preferably used as a polarizer protective film or retardation film in various display devices such as liquid crystal displays and organic EL displays. [Example]

The following examples are given to specifically illustrate the present invention, but the present invention is not limited to them. In addition, in the Example, the expression of "part" or "%" is used, unless otherwise specified, it means "mass part" or "mass %".

《Preparation of (meth)acrylic resin》 The (meth)acrylic resins 1 to 5 having the following compositions were synthesized in accordance with a conventionally known synthesis method.

[Synthesis of (meth)acrylic resin 1] Following a conventional method, (methyl methacrylate (85 mol %)/N-phenylmaleimide (10 mol %)/2-ethylhexyl acrylate (5 mol %) was synthesized. base) acrylic resin 1. The weight average molecular weight Mw of the (meth)acrylic resin 1 was 2 million.

[Synthesis of (meth)acrylic resin 2] Following a conventional method, (methyl methacrylate (50 mol %)/N-phenylmaleimide (25 mol %)/2-ethylhexyl acrylate (25 mol %)) was synthesized. base) acrylic resin 2. The weight average molecular weight Mw of the (meth)acrylic resin 1 was 2 million.

[Synthesis of (meth)acrylic resin 3] Following a conventional method, a (meth)acrylic system containing methyl methacrylate (85 mol %)/N-phenylmaleimide (10 mol %)/methyl acrylate (5 mol %) was synthesized Resin 3. The weight average molecular weight Mw of the (meth)acrylic resin 3 was 2 million.

[Synthesis of (meth)acrylic resin 4] Following a conventional method, a (meth)acrylic system containing methyl methacrylate (85 mol %)/N-phenylmaleimide (10 mol %)/butyl acrylate (5 mol %) was synthesized Resin 4. The weight average molecular weight Mw of the (meth)acrylic resin 4 was 2 million.

[Synthesis of (meth)acrylic resin 5] The (meth)acrylic resin 5 obtained by methyl methacrylate (100 mol%) alone was synthesized. The weight average molecular weight Mw of the (meth)acrylic resin 5 was 2 million.

"Preparation of Rubber Particles" [Preparation of Rubber Particles G1: Benzyl (Meth)acrylate Rubber Particles] According to the production method of the multilayer structure polymer (B2) described in paragraphs (0379) to (0382) of Japanese Patent No. 5798690, the benzyl (meth)acrylate-based rubber particles G1 with an average primary particle diameter of 121 nm were prepared.

[Preparation of Rubber Particles G2: Dicyclopentyl (meth)acrylate-based Rubber Particles] Dicyclopentyl (meth)acrylate-based rubber particles with an average primary particle diameter of 127 nm were prepared according to the method for producing a multilayer structure polymer (B4) described in paragraphs (0387) to (0390) of Japanese Patent No. 5798690 G2.

[Preparation of rubber particles G3: (meth)acrylate phenoxyethyl ester rubber particles] A phenoxyethyl (meth)acrylate-based rubber with an average primary particle diameter of 133 nm was prepared according to the method for producing a multilayer structure polymer (B3) described in paragraphs (0383) to (0386) of Japanese Patent No. 5798690 Particle G3.

"Optical Film Fabrication" [Production of Optical Film 1] (Preparation of Rubber Particle Dispersion Liquid 1) 25 parts by mass of the rubber particles G1 and 475 parts by mass of dichloromethane were stirred and mixed with a dissolver for 50 minutes, and then dispersed for 40 minutes at 1500 rpm using a Milder disperser (manufactured by Taiyo Kiko Co., Ltd.) to obtain rubber particles Dispersion 1.

(Preparation of Inorganic Particle Dispersion Liquid 1) The following components were stirred and mixed with a dissolver for 50 minutes, and then dispersed for 100 minutes using a Manton-Gaulin disperser. Next, the inorganic particle dispersion liquid 1 was prepared by filtration with Finemet NF manufactured by Nippon Seiko Co., Ltd.

Inorganic particles: Aerosil R812 (manufactured by Aerosil, Japan, primary average particle diameter: 7nm, apparent specific gravity 50g/L) 4 parts by mass Dichloromethane 48 parts by mass 48 parts by mass of ethanol (Dispersion Condition A-1) The dispersion conditions of the above-mentioned rubber particle dispersion liquid 1 and inorganic particle dispersion liquid 1 are as shown in A-1 of Table I.

The shear rate Bs during the preparation of the rubber particle dispersion is appropriately selected to adjust the number of revolutions and the type of rotor/stator, and the shear rate As during the preparation of the inorganic particle dispersion is adjusted in the first stage of the Manton-Gaulin disperser. The valve pressure and the valve pressure of the second stage are appropriately adjusted so that the shear rate ratio (As/Bs) may be obtained from the relationship of the shear rate shown in A-1 of Table 1.

(Film making) <Preparation of dopant> According to the following method, the dopant containing the following composition was prepared. First, dichloromethane and ethanol are added to the pressurized dissolution tank. Next, the (meth)acrylic resin 1 was put into the pressurized dissolution tank while stirring. Next, the rubber particle dispersion liquid 1 prepared above was put in and added while stirring, and then the inorganic particle dispersion liquid 1 was added to prepare a dopant.

The viscosity of the obtained dopant was 16000 mmPa･s, and the water content was 0.50%. This was filtered using SHP150 manufactured by ROKI TECHNO at a filtration flow rate of 300 L/m ² ･h and a filtration pressure of 1.0×10 ⁶ Pa to obtain a dopant.

(Meth)acrylic resin 1         100 parts by mass Dichloromethane 175 parts by mass 90 parts by mass of ethanol Rubber particle dispersion 1       500 parts by mass Inorganic fine particle dispersion 1       20 parts by mass ＜Film making＞ The optical thin film 1 was produced by the following method using a film forming apparatus having a dopant preparation step, a casting step, and a drying step of the solution casting method described in FIG. 1 of JP-A No. 2017-102319.

In the casting step, an endless endless belt casting device was used to uniformly cast the above-prepared dopant on a stainless steel support with a width of 1900 mm at a temperature of 30°C. The temperature of the stainless steel band support was controlled at 28°C. The conveying speed of the stainless steel belt support was set to 20 m/min.

Next, on the stainless steel belt support, the solvent was evaporated until the residual solvent amount in the cast dopant became 30% by mass, and after the mesh was formed, it was supported by the stainless steel belt with a peeling tension of 128 N/m. The body peels off the mesh. While conveying the peeled web sheet with many rollers, the obtained web sheet was stretched by 30% in the short-side direction on the condition of (Tg+15)° C. with a tenter. The residual solvent amount in the mesh at the start of stretching was 10% by mass. After that, it was further dried in a drying step while being conveyed on a roller, and the end held by the tenter clip was cut with a laser cutter and wound to obtain a length of 2.3 m in the short-side direction and a length of 7,000 m in the longitudinal direction. Optical thin film 1 with a thickness of 40 μm.

[Production of Optical Film 2] In the production of the aforementioned optical film 1, the inorganic particle dispersion liquid 2 prepared by changing the dispersion time of the inorganic particle dispersion liquid 1 for production to 80 minutes was used, and the dispersion conditions A-2 described in Table 1 were used, except that The optical film 2 was produced in the same manner.

[Production of Optical Film 3] In the production of the aforementioned optical film 1, the inorganic particle dispersion liquid 3 prepared by changing the dispersion time of the inorganic particle dispersion liquid 1 for production to 60 minutes was used, and the dispersion conditions A-3 described in Table 1 were used, except that The optical film 3 was produced in the same manner.

[Production of Optical Film 4] In the production of the optical film 2 described above, the optical film 4 was produced in the same manner except that the (meth)acrylic resin 1 was changed to the (meth)acrylic resin 2 .

[Production of Optical Film 5] In the production of the aforementioned optical film 2, the dispersion conditions of the inorganic particle dispersion liquid 2 and the rubber particle dispersion liquid 1 were appropriately changed, and the relationship of the shear rate was changed to the dispersion condition B as described in Table 1, except that the optical film was produced in the same manner. Film 5.

[Production of Optical Film 6]

In the production of the aforementioned optical film 2, the dispersion conditions of the inorganic particle dispersion liquid 2 and the rubber particle dispersion liquid 1 were appropriately changed, and the relationship of the shear rate was changed to the dispersion condition C as described in Table 1, except that the optical film was produced in the same manner. Film 6.

[Production of Optical Film 7]

In the production of the aforementioned optical film 2, the dispersion conditions of the inorganic particle dispersion liquid 2 and the rubber particle dispersion liquid 1 were appropriately changed, and the relationship of the shear rate was changed to the dispersion condition D as described in Table 1, except that the optical film was produced in the same manner. Film 7.

[Production of Optical Film 8]

In the preparation of the optical film 2, the optical film 8 was produced in the same manner, except that the rubber particle dispersion 1 was changed to the rubber particle dispersion 2 containing the dicyclopentyl (meth)acrylate-based rubber particles G2.

[Production of Optical Film 9]

In the preparation of the optical film 2, the optical film 9 was prepared in the same manner, except that the rubber particle dispersion 1 was changed to the rubber particle dispersion 3 containing the phenoxyethyl (meth)acrylate-based rubber particles G3.

[Fabrication of Optical Film 10]

In the production of the aforementioned optical film 2, the (meth)acrylic resin 1 is changed into The optical film 10 was produced in the same manner except for the (meth)acrylic resin 3 .

[Fabrication of Optical Film 11]

In the production of the optical film 2 described above, the optical film 11 was produced in the same manner except that the (meth)acrylic resin 1 was changed to the (meth)acrylic resin 4 .

[Fabrication of Optical Film 12]

In the production of the aforementioned optical film 1, the rubber particle dispersion liquid 4 prepared by changing the dispersion time of the rubber particle dispersion liquid 1 for production to 40 minutes was used, and the dispersion conditions E described in Table 1 were used, except that the same was true. The optical film 12 is fabricated in the same manner.

[Production of Optical Film 13]

In the production of the aforementioned optical film 1, the rubber particle dispersion liquid 5 prepared by changing the dispersion time of the rubber particle dispersion liquid 1 for production to 80 minutes was used, and the dispersion time of the inorganic particle dispersion liquid 1 was changed to 40 minutes. The optical film 13 was produced in the same manner except that the prepared inorganic particle dispersion liquid 4 was set to the dispersion conditions F described in Table 1.

[Production of Optical Film 14]

In the production of the aforementioned optical film 2, the (meth)acrylic resin 1 was changed to the (meth)acrylic resin 5, and the optical film was produced in the same manner. Film 14.

[Fabrication of Optical Film 15]

In the production of the optical film 2 described above, the optical film 15 was produced in the same manner except that the rubber particle dispersion liquid 1 was removed.

[Production of Optical Film 16]

In the production of the optical film 2 described above, the optical film 16 was produced in the same manner, except that the organic particle dispersion liquid 5 prepared by the following method was used instead of the inorganic particle dispersion liquid 1 .

(Preparation of Organic Particle Dispersion Liquid 5) <Preparation of Seed Particles>

In a polymerizer equipped with a stirrer and a thermometer, put 1000 g of deionized water, add 50 g of methyl methacrylate and 6 g of t-dodecyl mercaptan to it, and heat it to 70° C. while performing nitrogen substitution under stirring. . The inner temperature was kept at 70°C, and 20 g of deionized water in which 1 g of potassium persulfate was dissolved as a polymerization initiator was added, followed by polymerization for 10 hours. The average particle diameter of the seed particles in the obtained emulsion was 0.05 μm.

<Preparation of Organic Particles>

In a polymerizer equipped with a stirrer and a thermometer, 800 g of deionized water in which 2.4 g of sodium lauryl sulfate was dissolved as a gelation inhibitor was placed, and 66 g of methyl methacrylate and styrene as a monomer mixture were added to it. 20g and A mixed solution of 64 g of ethylene glycol dimethacrylate and 1 g of azobisisobutyronitrile as a polymerization initiator. Next, the mixed liquid was stirred with T.K. HomoMixer (manufactured by Tokki Chemical Industry Co., Ltd.) to obtain a dispersion liquid.

To the obtained dispersion liquid, 60 g of the emulsion containing the above-mentioned seed particles was added, and the mixture was stirred at 30° C. for 1 hour to absorb the monomer mixture into the seed particles. Next, the absorbed monomer mixture was heated at 50° C. for 5 hours under nitrogen flow to polymerize, and then cooled to room temperature (about 25° C.) to obtain a slurry of polymer fine particles (organic particles 4 ). The obtained organic particles 5 had an average particle diameter of 0.14 μm and a Tg of 280°C.

(Production of aggregates of organic particles)

This emulsion was spray-dried under the following conditions with a spray dryer (type: Atomizer Take-up system, type: TRS-3WK) manufactured by Sakamoto Giken Co., Ltd. as a spray dryer to obtain an aggregate of organic particles. The average secondary particle diameter of the organic particles was 200 nm.

Supply speed: 25mL/min

Atomizer rotation number: 11000rpm

Air volume: 2m ³ /min

Slurry inlet temperature of spray dryer: 100℃

Polymer particle aggregate outlet temperature: 50°C

The average secondary particle size of the organic particles was measured with a Zeta potential/particle size measurement system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.).

Table I below shows a list of dispersion conditions.

The following Table II shows the constitution of each optical film produced above.

"Determination of Particle Characteristic Values" [Measurement of Average Secondary Particle Diameter of Inorganic Particles] For the cross-section of the optical thin film trimmed with a microtome, use a transmission electron microscope to observe the inorganic particles at 500,000 times, observe the inorganic particles of the secondary particles, and measure the particle diameter, which is the second of the inorganic particles. Secondary particle diameter. In addition, the average value thereof was obtained and used as the average secondary particle diameter.

[Measurement of the ratio of the average primary particle diameter of rubber particles to the secondary particle diameter of inorganic particles in optical films] In the same manner as above, for the cross-section of the optical film trimmed with a microtome, use a transmission electron microscope to observe rubber particles and inorganic particles at 500,000 times, and observe the average primary particle diameter of the rubber particles. , and the secondary particle diameter obtained by observing the inorganic particles, the value of the ratio of (average primary particle diameter of rubber particles)/(secondary particle diameter of inorganic particles) was obtained according to formula (1).

[Evaluation of Optical Films] (Evaluation of Brittleness Resistance: Determination of Elongation at Break) The elongation at break was measured according to the method according to JIS K 7127 (1999), and the evaluation of brittleness resistance was carried out according to the following criteria.

◎: The elongation at break in one direction is 20% or more 〇: The elongation at break in one direction is 15% or more and less than 20% △: Elongation at break in one direction is 10% or more and less than 15% ×: Elongation at break in one direction is less than 10% If it is more than △, it is judged that it is a practical characteristic.

(Retardation Characteristics: Measurement of Rt) Each optical film produced above was measured at a wavelength of 590 nm in an environment of 23°C and 55% RH using an automatic birefringent meter KOBRA-21ADH (manufactured by Oji Scientific Instruments Co., Ltd.). Three-dimensional refractive index measurement, obtain the refractive index n _x of the slow axis direction, the refractive index _ny of the fast axis direction, and the refractive index _nz of the thickness direction, and take the thickness (nm) of the optical film as d, according to the following (formula 5) The retardation Rt in the thickness direction was obtained, and the retardation was evaluated according to the following criteria.

(Equation 5) Rt=[(n _x + _ny )/2-n _z ]×g(nm) The hysteresis Rt in the thickness direction measured as described above is classified into the following grades, and the (low) retardation characteristic is performed evaluation.

◎: Rt is -5nm or more and less than +5nm ○: Rt is -10nm or more and less than -5nm, or +5nm or more and less than +10nm △: Rt is -20nm or more and less than -10nm, or +10nm or more and less than +20nm ×: Rt is less than -20nm, or +20nm or more

(Evaluation of sliding property) ＜Evaluation of sticking resistance＞ For the 7000 m long roll-shaped laminated optical film produced above, the optical film was rolled out to its full length in an environment of 23°C and 55% RH, and it was visually observed whether the films adhered to each other, and adhered according to the following criteria An assessment of patience.

◎: No sticking occurred up to the entire length ○: Good quality although very little sticking is observed △: Although the occurrence of partial sticking was observed, it was easily peeled off ×: There is a lot of sticking throughout the entire length, and it is not easy to peel off

<Observation of the roll shape of the roll laminate> The 7000-m-long roll-shaped laminate produced above was stored in an environment of 40°C and 80% RH for 10 days, then unwound, and the length (m) of the optical film resulting from the transfer from the core was measured according to the following The following benchmarks are used for roll evaluation.

◎: The transfer generation position from the core is less than 10m 〇: The transfer generation position from the core is 10m or more and less than 50m △: The transfer generation position from the core is 50m or more and less than 100m ×: The transfer generation position from the core is 100m or more In the above-mentioned evaluation, it was judged that it was good if it was △ or more.

The results obtained above are shown in Table III.

From the results described in Table III, it can be seen that the optical film having the characteristics of the present invention is excellent in brittle resistance (elongation at break), maintains low retardation characteristics, and slidability (adhesion resistance or lamination) compared to the comparative example. It is excellent in roll form when in roll form.

1: Secondary particles of inorganic particles G: Primary particle of rubber particle S1: Dispersion area of inorganic particles S2: Dispersion area of rubber particles

Fig. 1 is an electron microscope photograph showing an example of a cross section of the optical film of the present invention in which inorganic particles and rubber particles are present [ Fig. 2 ] A schematic diagram showing an example of the relationship between the shear rate of the inorganic particles and the rubber particles and the dispersion treatment time in the present invention

S1: Dispersion area of inorganic particles

S2: Dispersion area of rubber particles

Claims (7)

An optical film comprising at least inorganic particles and (meth)acrylic resin, characterized in that The aforementioned (meth)acrylic resin is With respect to all structural units constituting the (meth)acrylic resin, containing Structural units derived from methyl methacrylate within the range of 50 to 95 mass %, Structural units derived from phenylmaleimide within the range of 1 to 25% by mass, and Structural units derived from alkyl acrylate in the range of 1 to 25% by mass the copolymer, further contains rubber particles, The value of the ratio of the average primary particle diameter of the rubber particles to the secondary particle diameter of the aforementioned inorganic particles in the film is the ratio of the number of secondary particles of the inorganic particles in the range shown in the following (Equation 1), relative to In terms of the total number of inorganic secondary particles, it is in the range of 5.0 to 50% by number; (Formula 1) 0.9≦(average primary particle diameter of rubber particles)/(secondary particle diameter of inorganic particles)≦1.1. The optical film of claim 1, wherein the inorganic particles are spherical silica particles, and the average secondary particle diameter is in the range of 50-500 nm. The optical film according to claim 1 or claim 2, wherein the rubber particles include a structure derived from benzyl (meth)acrylate, a structure derived from dicyclopentyl (meth)acrylate, and a structure derived from ( A monomer of at least one structural unit selected from the structure of phenoxyethyl meth)acrylate. A method for producing an optical film, which is a method for producing an optical film such as the optical film according to any one of claim 1 to claim 3, characterized in that It has a step of preparing a dispersion liquid of inorganic particles, and a step of preparing a dispersion liquid of rubber particles, When the treatment time in the step of preparing the dispersion of inorganic particles is At (minutes), and the treatment time in the step of preparing the dispersion of rubber particles is Bt (minutes), Satisfy the conditions specified in the following (formula 2); (Formula 2) At>Bt. The method for producing an optical film according to claim 4, wherein the value of the ratio (At/Bt) of the treatment time At (minutes) during the dispersion of the inorganic particles to the treatment time Bt (minutes) during the dispersion of the rubber particles (At/Bt) is Within the range of 1.05~15. The method for producing an optical film according to claim 4 or claim 5, wherein in the step of preparing a dispersion liquid of inorganic particles, the shear rate during dispersion of the inorganic particles is As (1/sec), and the dispersion of the prepared rubber particles is When the shear rate of the rubber particles in the liquid step is Bs (1/sec), Satisfy the conditions specified in the following (formula 3); (Formula 3) As > Bs. The method for producing an optical film according to claim 6, wherein the ratio (As/Bs) of the shear rate As (1/sec) during dispersion of the inorganic particles to the shear rate Bs (1/sec) of the rubber particles during dispersion ), satisfies the relationship of the following (Formula 4): (Formula 4) As/Bs≧1×10 ² .

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