JP2007178514A - Acrylic film for shaping lens shape and lens film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a base film for shaping lens shape less liable to scratching and cracking, and to provide a lens film by using the base film with high yield. <P>SOLUTION: An acrylic film, having a thickness of 50-250 μm formed of a resin composition comprising 20-95 pts.wt. of a methacrylic resin and 5-80 pts.wt. of acrylic rubber particles, is used as the base film for shaping lens shape. The lens film is obtained by shaping the lens shape on the surface of the base film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an acrylic film used as a base film for shaping a lens shape on a surface thereof to obtain a lens film. The present invention also relates to a lens film in which a lens shape is formed on the surface of the acrylic film.

  A resin lens sheet is useful as a member of a screen of a transmissive display device or a backlight of a liquid crystal display device. Generally, (1) a method of shaping a lens shape on the surface of a substrate sheet by press molding, (2) A method in which a raw material resin is formed into a sheet by extrusion molding and a lens shape is imparted to the surface thereof. (3) A lens layer is formed on the surface of the substrate sheet by an ultraviolet curable resin or an electron beam curable resin. It is manufactured by the method etc. Among these, the method (1) has the advantage that it is more adaptable to various lens shapes than the methods (2) and (3), and does not require large or expensive equipment. Yes. And as the base material sheet | seat, sheets, such as a polystyrene resin, polyolefin resin, an acrylic resin, polycarbonate resin, a vinyl chloride resin, are used (for example, refer patent document 1).

JP-A-11-183707 (paragraph 0005)

  The above-mentioned conventional base sheet has a problem that the yield is lowered when the lens shape is formed or when handling before and after the lens shape, because it is easily scratched or cracked. Particularly in recent years, with the increase in image quality of display devices, there is a demand for finer pitch of lenses. To cope with this, if a thin film is used as a base sheet, the above problem is likely to occur. Even fine scratches and cracks can be a problem, and the problem is even greater. Then, the objective of this invention is providing the base film for lens shape shaping which is hard to be damaged and is hard to break. And it is in providing a lens film with a sufficient yield using this base film.

  As a result of intensive studies, the present inventor has found that an acrylic film having a predetermined composition and thickness is suitable as the substrate film, and has completed the present invention. That is, this invention provides the acrylic film for lens shape shaping | molding which consists of a resin composition containing 20-95 weight part of methacryl resins, and 5-80 weight part of acrylic rubber particles, and has a thickness of 50-250 micrometers. Is. Moreover, according to this invention, the lens film by which a lens shape is shape | molded on the surface of this acrylic film is also provided.

  ADVANTAGE OF THE INVENTION According to this invention, the acrylic film for lens shape shaping which is hard to be damaged and cannot be broken can be obtained, and a lens film can be obtained with a sufficient yield.

  Hereinafter, the present invention will be described in detail. The acrylic film of the present invention is an acrylic film used as a base film for obtaining a lens film by shaping a lens shape on the surface thereof, from a resin composition essentially containing a methacrylic resin and acrylic rubber particles. It will be.

  The methacrylic resin, which is one of the essential components of this resin composition, is a polymer mainly composed of methacrylic acid ester, and may be a homopolymer of methacrylic acid ester, or 50% by weight or more of methacrylic acid ester. It may be a copolymer with 50% by weight or less of other monomers. Here, as the methacrylic acid ester, an alkyl ester of methacrylic acid is usually used.

  The preferred monomer composition of the methacrylic resin is 50 to 100% by weight of alkyl methacrylate, 0 to 50% by weight of alkyl acrylate, and 0 to 49% by weight of other monomers based on all monomers. More preferably, the alkyl methacrylate is 50 to 99.9% by weight, the alkyl acrylate is 0.1 to 50% by weight, and other monomers are 0 to 49% by weight.

  Here, examples of the alkyl methacrylate include methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and the like. The alkyl group usually has 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms. It is. Of these, methyl methacrylate is preferably used.

  Examples of alkyl acrylates include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and the like. The alkyl group usually has 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms. is there.

  The monomer other than alkyl methacrylate and alkyl acrylate may be a monofunctional monomer, that is, a compound having one polymerizable carbon-carbon double bond in the molecule, or a polyfunctional monofunctional monomer. Although it may be a monomer, that is, a compound having at least two polymerizable carbon-carbon double bonds in the molecule, a monofunctional monomer is preferably used. Examples of the monofunctional monomer include aromatic alkenyl compounds such as styrene, α-methylstyrene, and vinyl toluene, and alkenyl cyan compounds such as acrylonitrile and methacrylonitrile. Examples of polyfunctional monomers include polyunsaturated carboxylic acid esters of polyhydric alcohols such as ethylene glycol dimethacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, allyl acrylate, allyl methacrylate, and cinnamon. Alkenyl esters of unsaturated carboxylic acids such as allyl acids, polyalkenyl esters of polybasic acids such as diallyl phthalate, diallyl maleate, triallyl cyanurate, triallyl isocyanurate, aromatic polyalkenyl compounds such as divinylbenzene, etc. Can be mentioned.

  In addition, as for said alkyl methacrylate, alkyl acrylate, and monomers other than these, respectively, you may use those 2 or more types as needed.

  The methacrylic resin preferably has a glass transition temperature of 40 ° C. or higher, more preferably 60 ° C. or higher, from the viewpoint of heat resistance of the film. This glass transition temperature can be appropriately set by adjusting the type of monomer and the ratio thereof.

  The methacrylic resin can be prepared by polymerizing the monomer component by a method such as suspension polymerization, emulsion polymerization or bulk polymerization. At that time, in order to obtain a suitable glass transition temperature or to obtain a viscosity showing a formability to a suitable film, it is preferable to use a chain transfer agent during the polymerization. The amount of the chain transfer agent may be appropriately determined according to the type of monomer and the ratio thereof.

  Acrylic rubber particles, which are another essential component of the resin composition constituting the acrylic film, are particles containing an elastic polymer mainly composed of an acrylate ester as a rubber component, and a single layer made of only this elastic polymer. It may be a particle having a structure or a particle having a multilayer structure having a layer of this elastic polymer, but is preferably a particle having a multilayer structure from the viewpoint of the surface hardness of the film. The elastic polymer may be a homopolymer of an acrylate ester or a copolymer of 50% by weight or more of an acrylate ester and 50% by weight or less of other monomers. . Here, as the acrylic ester, an alkyl ester of acrylic acid is usually used.

  The preferable monomer composition of the elastic polymer mainly composed of acrylic acid ester is 50 to 99.9% by weight of alkyl acrylate based on all monomers, and 0 to 49% of other monofunctional monomers. 0.9% by weight and 0.1 to 10% by weight of the polyfunctional monomer.

  Here, the example of alkyl acrylate is the same as the example of alkyl acrylate mentioned above as a monomer component of methacrylic resin, The carbon number of the alkyl group is 1-8 normally, Preferably it is 4-8. is there.

  In addition, the monofunctional monomer other than the alkyl acrylate can be an alkyl methacrylate or other monofunctional monomer, and examples thereof include those of the alkyl methacrylate described above as the monomer component of the methacrylic resin. This is the same as the examples and examples of monofunctional monomers other than alkyl methacrylate and alkyl acrylate.

  Examples of the polyfunctional monomer are the same as the examples of the polyfunctional monomer previously mentioned as the monomer component of the methacrylic resin, and among them, alkenyl esters of unsaturated carboxylic acids and polybasic acids. Polyalkenyl esters are preferably used.

  In addition, as for said alkyl acrylate, the other monofunctional monomer, and a polyfunctional monomer, you may use those 2 or more types as needed, respectively.

  When the acrylic rubber particles having a multilayer structure are used, a preferable example is one having a polymer layer mainly composed of methacrylic acid ester outside the elastic polymer layer mainly composed of acrylate ester. That is, an at least two-layer structure in which an elastic polymer mainly composed of an acrylate ester is used as an inner layer and a polymer mainly composed of a methacrylic acid ester is used as an outer layer. Here, as the methacrylic acid ester which is a monomer component of the polymer in the outer layer, alkyl methacrylate is usually used. The outer layer polymer is usually formed at a ratio of 10 to 400 parts by weight, preferably 20 to 200 parts by weight with respect to 100 parts by weight of the inner layer elastic polymer. By setting the polymer of the outer layer to 10 parts by weight or more with respect to 100 parts by weight of the elastic polymer of the inner layer, the elastic polymer is less likely to aggregate and the transparency of the film is improved.

  The preferable monomer composition of the polymer of the outer layer is 50 to 100% by weight of alkyl methacrylate, 0 to 50% by weight of alkyl acrylate based on all monomers, and 0 to 50% by weight of other monomers. 49% by weight.

  Here, the example of alkyl methacrylate is the same as the example of alkyl methacrylate previously mentioned as a monomer component of a methacryl resin, The carbon number of the alkyl group is 1-8 normally, Preferably it is 1-4. is there. Of these, methyl methacrylate is preferably used.

  Moreover, the example of alkyl acrylate is the same as that of the alkyl acrylate mentioned above as a monomer component of a methacryl resin previously, The carbon number of the alkyl group is 1-8 normally, Preferably it is 1-4. .

  Monomers other than alkyl methacrylate and alkyl acrylate may be monofunctional monomers or polyfunctional monomers, but monofunctional monomers are preferably used. Examples of this monofunctional monomer are the same as the examples of monofunctional monomers other than the alkyl methacrylate and alkyl acrylate mentioned above as the monomer component of the methacrylic resin, Examples of the monomer are the same as those of the polyfunctional monomer mentioned above as the monomer component of the methacrylic resin.

  In addition, as for said alkyl methacrylate, alkyl acrylate, and monomers other than these, respectively, you may use those 2 or more types as needed.

  Further, as a preferred example of the acrylic rubber particles having a multilayer structure, a polymer layer mainly composed of a methacrylic acid ester is further provided inside the elastic polymer layer mainly composed of an acrylate ester which is the inner layer of the two-layer structure. In other words, the polymer mainly composed of methacrylic acid ester is used as the inner layer, the elastic polymer mainly composed of acrylate ester is used as the intermediate layer, and the polymer mainly composed of the methacrylic acid ester is used as the outer layer. There can also be mentioned at least a three-layer structure. Here, as a methacrylic acid ester which is a monomer component of the polymer of the inner layer, alkyl methacrylate is usually used. The polymer of the inner layer is usually formed at a ratio of 10 to 400 parts by weight, preferably 20 to 200 parts by weight, with respect to 100 parts by weight of the elastic polymer of the intermediate layer.

  The preferable monomer composition of the polymer of the inner layer is 70 to 100% by weight of alkyl methacrylate and 0 to 30% by weight of other monomers based on all monomers.

  Here, the example of alkyl methacrylate is the same as the example of alkyl methacrylate previously mentioned as a monomer component of a methacryl resin, The carbon number of the alkyl group is 1-8 normally, Preferably it is 1-4. is there. Of these, methyl methacrylate is preferably used.

  The monomer other than alkyl methacrylate may be an alkyl acrylate or other monofunctional monomer, or may be a polyfunctional monomer. And examples of this monofunctional monomer are the same as the examples of alkyl acrylates mentioned above as monomer components of methacrylic resins, and examples of monofunctional monomers other than alkyl methacrylates and alkyl acrylates. In addition, examples of the polyfunctional monomer are the same as the examples of the polyfunctional monomer previously mentioned as the monomer component of the methacrylic acid resin.

  In addition, as for said alkyl methacrylate and monomers other than these, respectively, you may use those 2 or more types as needed.

  Acrylic rubber particles can be prepared by polymerizing the monomer component of the above-mentioned elastic polymer mainly composed of an acrylate ester by at least one stage reaction by an emulsion polymerization method or the like. At this time, as described above, when a polymer layer mainly composed of methacrylic acid ester is formed outside the elastic polymer layer, the monomer component of the outer layer polymer is added to the elastic polymer layer. What is necessary is just to graft to the said elastic polymer by making it superpose | polymerize by reaction of at least 1 step | paragraph by emulsion polymerization method etc. in presence of a polymer. Further, as described above, when a polymer layer mainly composed of methacrylic acid ester is formed inside the elastic polymer layer, first, the monomer component of the polymer in the inner layer is Polymerization is carried out by at least one stage reaction by emulsion polymerization or the like, and then the monomer component of the elastic polymer is polymerized by at least one stage reaction by emulsion polymerization or the like in the presence of the resulting polymer. In the presence of the resulting elastic polymer, the monomer component of the outer layer polymer is polymerized in an at least one-step reaction by an emulsion polymerization method or the like. To be grafted to the elastic polymer. When the polymerization of each layer is performed in two or more stages, it is sufficient that the monomer composition as a whole is within a predetermined range, not the monomer composition of each stage.

  Regarding the particle diameter of the acrylic rubber particles, the average particle diameter of the elastic polymer layer mainly composed of acrylic acid ester in the rubber particles is preferably 0.05 to 0.4 μm, and more preferably 0. The thickness is 1 to 0.3 μm, more preferably 0.14 to 0.25 μm. If the average particle size is too large, the transparency of the film is lowered, which is not preferable. On the other hand, if the average particle size is too small, the surface hardness of the film is lowered and the film is easily scratched, or the flexibility of the film is lowered and the film is easily broken.

  The average particle size is determined by mixing acrylic rubber particles with methacrylic resin to form a film, dyeing the elastic polymer layer with ruthenium oxide in the cross section, and observing with an electron microscope. It can be determined from the diameter. That is, when acrylic rubber particles are mixed with methacrylic resin and the cross section is dyed with ruthenium oxide, the methacrylic resin of the parent phase is not dyed, and the polymer mainly composed of methacrylic ester is outside the elastic polymer layer. If there is a layer, the polymer of this outer layer is not dyed, only the elastic polymer layer is dyed. The diameter can be determined. When a polymer layer mainly composed of methacrylic acid ester is present inside the elastic polymer layer, the polymer of the inner layer is not dyed, and the elastic polymer layer outside the dye is dyed 2 In this case, the outer diameter of the two-layer structure, that is, the outer diameter of the elastic polymer layer may be considered.

  The blending ratio of the methacrylic resin and the acrylic rubber particles is 20 to 95 parts by weight of the methacrylic resin and 5 to 80 parts by weight of the acrylic rubber particles based on the total of 100 parts by weight of both. If the ratio of the methacrylic resin is too small and the ratio of the acrylic rubber particles is too large, the surface hardness of the film is reduced and the film is easily damaged, and the appearance of the product after the shape transfer is deteriorated. On the other hand, if the proportion of the methacrylic resin is too large and the proportion of the acrylic rubber particles is too small, the flexibility of the film is lowered and the film is easily broken.

  The amount of the elastic polymer mainly composed of acrylic ester in the acrylic rubber particles is preferably 5 to 35 parts by weight based on the total of 100 parts by weight of the methacrylic resin and the acrylic rubber particles. More preferred are parts by weight. If the amount of the elastic copolymer is 5 parts by weight or more per 100 parts by weight of the total of methacrylic resin and acrylic rubber particles, the film forming property can be improved without the film itself becoming brittle. On the other hand, if the amount of the elastic copolymer is 35 parts by weight or less per 100 parts by weight of the total of methacrylic resin and acrylic rubber particles, the transparency and surface hardness of the film can be improved.

  The resin composition containing the methacrylic resin and the acrylic rubber particles described above may contain other components as necessary, for example, an ultraviolet absorber, an organic dye, an inorganic dye, a pigment, an antioxidant, an antistatic agent, an interface. An activator or the like may be contained.

  By forming the resin composition into a film, the lens shape-molding acrylic film of the present invention is obtained. The method of forming the film is selected as appropriate, but the extrusion method, particularly the method of melt-extruding the resin composition and sandwiching the resin composition between a pair of mirror rolls to form the film has a smooth surface and a uniform thickness. From the point of view, it is advantageously employed.

  The acrylic film for lens shape shaping thus obtained has a thickness of 50 to 250 μm, preferably 60 to 200 μm, and more preferably 75 to 150 μm. Films that are too thick are difficult to adapt to finer pitches of lenses, and when shaping the lens shape, the time required for heating becomes longer, so the production efficiency of the lens film decreases, and the unit price per unit area This is also economically disadvantageous. On the other hand, in the case of a very thin film, film formation by extrusion is difficult due to mechanical restrictions, and shaping of the lens shape is also difficult due to mechanical restrictions. The thickness of the film can be adjusted by adjusting the film forming speed, the thickness of the T-shaped die outlet, the gap between the rolls, and the like. Further, the surface hardness of the film is preferably HB or harder, more preferably F or harder, in terms of pencil hardness, from the viewpoint of suppressing scratches.

  By using the acrylic film as a base film and shaping the lens shape on the surface, a lens film in which the occurrence of scratches and cracks is suppressed can be obtained with high yield. This shaping can be performed by press molding using a shaping plate or shaping roll having a lens mold on the surface, that is, a lens shape opposite to that of the shaping. Specifically, if a single-sided lens film is to be obtained, the substrate film is heated above its glass transition temperature and sandwiched between the shaping plate and the mirror plate, or between the shaping roll and the mirror roll. It is good to insert between and press. If a double-sided lens film is to be obtained, the substrate film is heated above its glass transition temperature and sandwiched between the shaping plate and the shaping plate, or between the shaping roll and the shaping roll. It is good to insert in and press. Instead of heating the base film or in addition to heating the base film, it is also possible to heat the shaping plate or the shaping roll.

  Examples of the shape of the molded lens include a Fresnel lens, a lenticular lens, and a prism lens. The present invention is advantageously applied particularly when the shape of a lenticular lens or a prism lens is molded. . In this case, it is preferable that the pitch of the lens shape is 200 μm or less and the height is 100 μm or less from the viewpoint of the fine pitch of the lens that is required with the recent improvement in image quality of display devices.

  Examples of the present invention will be described below, but the present invention is not limited thereto. In the examples, “%” and “part” representing the content or amount used are based on weight unless otherwise specified.

  As the methacrylic resin, pellets of a thermoplastic polymer (glass transition temperature 104 ° C.) obtained by bulk polymerization of a monomer composed of 97.8% methyl methacrylate and 2.2% methyl acrylate were used.

  As the acrylic rubber particles (A), the innermost layer is a hard polymer obtained by polymerization of a monomer composed of 93.8% methyl methacrylate, 6% methyl acrylate, and 0.2% allyl methacrylate, The intermediate layer is an elastic polymer obtained by polymerization of a monomer composed of 81% butyl acrylate, 17% styrene and 2% allyl methacrylate, and the outermost layer is 94% methyl methacrylate and 6% methyl acrylate. The weight ratio of the innermost layer / intermediate layer / outermost layer is 35/45/20, and the average particle diameter of the elastic polymer layer of the intermediate layer A rubber particle having a spherical three-layer structure by an emulsion polymerization method having a particle size of 0.22 μm was used.

  The acrylic rubber particles (B) have basically the same composition as the acrylic rubber particles (A), but by changing the polymerization conditions, the average particle diameter of the elastic polymer layer of the intermediate layer becomes 0.14 μm. Rubber particles having a spherical three-layer structure were used.

  The average particle diameter of the elastic polymer layer of the intermediate layer in the acrylic rubber particles (A) and (B) was measured by the following method.

(Measurement of average particle diameter of elastic polymer layer)
Acrylic rubber particles are mixed with a methacrylic resin to form a film, and the resulting film is cut into an appropriate size, and the slice is immersed in a 0.5% aqueous ruthenium tetroxide solution at room temperature for 15 hours. The polymer layer was dyed. Further, the sample was cut to a thickness of about 80 nm using a microtome, and then photographed with a transmission electron microscope. After randomly selecting 100 dyed elastic copolymer layers from this photograph and calculating the particle diameter of each, the number average value was taken as the average particle diameter.

Examples 1-4, Comparative Example 1
The above methacrylic resin pellets and acrylic rubber particles (A) or (B) were mixed at a ratio shown in Table 1 with a super mixer, and melt-kneaded with a twin-screw extruder to obtain resin composition pellets. . Next, this pellet is melted with a 65 mmφ single screw extruder manufactured by Toshiba Machine Co., Ltd., and extruded through a T-type die having a set temperature of 275 ° C., and the resulting film-like product is a metal roll having a pair of smooth surfaces. And sandwiched in between. Thus, an acrylic film having the thickness shown in Table 1 was produced, the following evaluation was performed, and the results are shown in Table 1.

[Flexibility test]
According to JIS K 5600-5-1: 1999, the bending resistance of an acrylic film is evaluated, and the test piece is not broken and has good flexibility, and the test piece is broken and has poor flexibility. X.

〔surface hardness〕
The pencil hardness of the acrylic film was measured according to JIS K 5600-5-4: 1999.

(Shape transfer)
Using a plate-shaped press mold having a prism lens mold with a pitch of 50 μm and a height of 25 μm on the surface, an acrylic film was pressed at a mold temperature of 220 ° C. and a press pressure of 100 kg / cm ² , and obtained after cooling. The lens film was observed. The case where the lens shape was almost completely transferred was indicated by ◯, and the case where the lens shape was not sufficiently transferred was indicated by ×.

Comparative Example 2
The above evaluation was performed using a polycarbonate resin film manufactured by Teijin Chemicals Ltd. The results are shown in Table 1.

Claims (7)

  An acrylic film for lens shape shaping, comprising a resin composition containing 20 to 95 parts by weight of a methacrylic resin and 5 to 80 parts by weight of acrylic rubber particles, and having a thickness of 50 to 250 μm.   The methacrylic resin is a polymer obtained by polymerizing 50 to 100% by weight of alkyl methacrylate, 0 to 50% by weight of alkyl acrylate, and 0 to 49% by weight of other monomers. 1. The acrylic film according to 1.   Acrylic rubber particles in a proportion of 50 to 99.9% by weight of alkyl acrylate, 0 to 49.9% by weight of other monofunctional monomers, and 0.1 to 10% by weight of polyfunctional monomers The acrylic film according to claim 1, wherein the acrylic film is a particle containing an elastic polymer obtained by polymerization.   Acrylic rubber particles have a ratio of 50 to 100% by weight of alkyl methacrylate, 0 to 50% by weight of alkyl acrylate, and 0 to 49% by weight of other monomers on the outside of the elastic polymer layer. The acrylic film according to claim 3, wherein the acrylic film is a particle having a multilayer structure having a polymer layer obtained by polymerization.   A polymer layer in which acrylic rubber particles are polymerized at a ratio of 70 to 100% by weight of alkyl methacrylate and 0 to 30% by weight of other monomers inside the elastic polymer layer. The acrylic film according to claim 4, which is a particle having a multilayer structure.   A lens film obtained by forming a lens shape on the surface of the acrylic film according to claim 1. The lens film according to claim 6, wherein the lens shape is a lenticular lens, a prism lens, or a Fresnel lens.