JP2010095712A - Optical acrylic film, optical waveguide and backlight unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical acrylic film having both of transparency and strength. <P>SOLUTION: The optical acrylic film comprises a resin composition (C) obtained by mixing an acrylic resin (A) containing a rubber ingredient and a fluorinated resin (B), wherein the content of the rubber ingredient in the acrylic resin (A) is in a range of 1-45 mass% and the mass ratio (A/B) of the acrylic resin (A) to the fluorinated resin (B) is in a range of 50/50-99.9/0.1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical acrylic film suitable for an optical film that requires high transparency, a light guide plate using the same, and a backlight unit, and particularly for use in a light guide plate that requires high transmittance and thinning. The present invention relates to a suitable optical acrylic film.

  Polarizer protective film, diffuser protective film, light guide film, microlens array, various optical members such as antireflection base materials, building materials such as interior materials, automobile members, reflective materials used for road signs, etc. A highly transparent resin film is used in various applications.

  In particular, the amount of resin films used for liquid crystal displays is increasing year by year, and higher transparency is required.

  Among them, since the light guide plate used in the backlight unit of the liquid crystal device is used in a long optical path, the resin film used in such a light guide plate can have transmission loss due to light absorption, scattering, reflection, etc. as much as possible. Less is required. Conventionally, a film (acrylic film) made of an acrylic resin having a high light transmittance, particularly a cast sheet of polymethyl methacrylate has been used for such a resin film.

  On the other hand, in recent years, in order to reduce power consumption, as a primary light source of a liquid crystal display device, a point-like one such as a light emitting diode (LED) is widely used instead of a linear or rod-like one such as a fluorescent lamp. . Since LEDs having small dimensions can be formed, there is a demand for further thinning of liquid crystal display devices using such LEDs. In addition, with the expansion of the field of use of liquid crystal display devices, there is a strong demand for thin backlight units, particularly for small liquid crystal display devices, and thinning of light guide plates used in backlight units is also being promoted. .

  However, as the light guide plate becomes thinner, the number of times the light traveling in the light guide plate is reflected on the surface of the light guide plate increases. Therefore, even if the composition is the same, the light transmission loss increases and the luminance increases. There is a problem that it tends to decrease. In addition, when the light guide plate is made thin, cracks and chips are likely to occur in the manufacturing process of the light guide plate when transferring through each process, slitting to a predetermined size, punching, and imparting uneven shapes to the surface. Thus, the conventional light guide plate made of an acrylic film has a problem of insufficient strength due to such brittleness.

  As an acrylic film, for example, Patent Document 1 discloses, as a technique for improving the impact resistance of an acrylic resin film, an acrylic resin mainly composed of methyl methacrylate, an acrylic elastomer having a multilayer structure, and vinylidene fluoride. An impact resistant film made of a fluororesin as a main component is disclosed.

Patent Document 2 discloses an optical recording medium cover film mainly composed of a mixture of polyvinylidene fluoride and polymethacrylic resin.
JP-A-3-124754 JP 61-78857 A

  Usually, when an acrylic resin, an acrylic elastomer, and a fluororesin are mixed, the difference in refractive index between the matrix and the elastomer becomes large and the transmittance is reduced. It has been difficult to achieve both high transmittance and high transmittance. Patent Document 1 does not describe the transmittance when used in a long optical path.

  As described in Patent Document 2, in the technology of mixing polyvinylidene fluoride and polymethacrylic resin, it is necessary to use a large amount of expensive polyvinylidene fluoride in order to sufficiently increase the strength, which increases the cost. There was a problem. Moreover, the film described in Patent Document 2 is a cover film for optical recording media, and there is no description about the transmittance when used in a long optical path.

  An object of the present invention is to provide an acrylic film having both transparency and strength, and a thin and high-intensity light guide plate and backlight unit.

According to one aspect of the present invention, an acrylic film comprising a resin composition (C) obtained by mixing an acrylic resin (A) containing a rubber component and a fluorine-based resin (B),
The content of the rubber component in the acrylic resin (A) is in the range of 1 to 45% by mass,
The mass ratio (A / B) of the acrylic resin (A) and the fluororesin (B) is in the range of 50/50 to 99.9 / 0.1,
Optical in which light is incident from the end face of the acrylic film, and the brightness of the light emitted from the opposite end face facing the end face is equal to or higher than the brightness of the film made of only the acrylic resin (A) measured under the same conditions. An acrylic film is provided.

  According to another aspect of the invention, the acrylic resin (A) comprises an acrylic polymer (A-1) and a rubber-containing multistage polymer (A-2). And the said acrylic film for optics from which the refractive index difference of a solvent soluble part and a solvent insoluble part becomes 0.005 or less is provided.

  According to the other aspect of this invention, the light-guide plate formed by providing uneven | corrugated shape to both surfaces or one side of said acrylic film is provided.

  According to another aspect of the present invention, a backlight unit incorporating the light guide plate is provided.

  According to the present invention, an acrylic film having both transparency and strength can be obtained. By using this acrylic film, a thin and high-intensity light guide plate and backlight unit can be provided at low cost.

  The acrylic film which is one Embodiment of this invention consists of a resin composition (C) containing the acrylic resin (A) containing a rubber component, and a fluorine resin (B). This acrylic film is particularly suitable for light guide plate applications.

  The content of the rubber component in the acrylic resin (A) is preferably in the range of 1 to 45% by mass, and the mass ratio (A / B) of the acrylic resin (A) to the fluororesin (B) is 50 / It is preferably in the range of 50 to 99.9 / 0.1.

  The light is incident from the end face (I) of the acrylic film, and the brightness of the light emitted from the opposite end face (O) opposite to the end face is L1, and consists only of the acrylic resin (A) measured under the same conditions. When the luminance of the film is L2, the luminance ratio (L1 / L2) of these films is preferably 1 or more, more preferably 1.01 or more, and further preferably 1.05 or more. As will be described later, the luminance ratio (L1 / L2) is obtained particularly in a film having a film thickness of 350 μm and a distance of 20 cm from the end face (I) to the end face (O) and having a square planar shape. It is preferred that

  Hereinafter, preferred embodiments of the present invention will be described in detail.

[Acrylic resin (A)]
As the acrylic resin (A) containing a rubber component in the present invention, a resin obtained by mixing an acrylic polymer (A-1) and a rubber-containing multistage polymer (A-2) is used. If the rubber-containing multistage polymer (A-2) itself is an acrylic polymer, it is also possible to use a resin composed only of the rubber-containing polymer (A-2).

The rubber content of the acrylic resin (A) is preferably 1 to 45%. Here, the rubber content indicates the ratio (mass percentage) of the rubber component in 100 parts by mass of the acrylic resin (A). For example, an acrylic resin comprising 30 parts by mass of a rubber-containing multistage polymer (A-2) composed of 60 parts by mass of a rubber component and 40 parts by mass of a graft component and 70 parts by mass of an acrylic polymer (A-1). In the case of (A), if the rubber content is equivalent to the amount of monomer charged and the amount of polymer produced, the following formula:
Rubber content (%) = 30 × 0.6 / (70 + 30) = 18
It can be obtained more.

  If the rubber content in the acrylic resin (A) is too small, the effect of improving the strength is small. Conversely, if the rubber content is too large, the transparency is lowered, which is not preferable. From the viewpoint of strength, the rubber content is preferably 1% or more, more preferably 5% or more, more preferably 10% or more, and from the viewpoint of transparency, the rubber content is preferably 45% or less, more preferably 30% or less, It is more preferably 25% or less, and particularly preferably 20% or less. From the viewpoint of the balance between transparency and strength, it is more preferably in the range of 5 to 25%, and most preferably in the range of 10 to 20%.

  The blending ratio of the acrylic polymer (A-1) and the rubber-containing multistage polymer (A-2) can be set so that the rubber content is obtained, but the acrylic polymer (A-1) 44 The range of 0.5 to 98% by mass and 2 to 45.5% by mass of the rubber-containing multistage polymer (A-2) is preferable.

[Acrylic polymer (A-1)]
The acrylic polymer (A-1) is composed of 50 to 100% by mass of an alkyl methacrylate unit having an alkyl group having 1 to 4 carbon atoms and 0 to 50% by mass of another vinyl monomer unit copolymerizable therewith. Polymers are preferred. The content of the alkyl methacrylate unit is preferably 50% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more from the viewpoint of obtaining desired properties of the acrylic polymer (A-1).

  Examples of the alkyl methacrylate include methyl methacrylate, ethyl methacrylate, butyl methacrylate, propyl methacrylate and the like.

  Here, “polymer” means a homopolymer or a copolymer. When the acrylic polymer is a homopolymer, it is, for example, polymethyl methacrylate, and when it is a copolymer, it is, for example, a copolymer of methyl methacrylate and a vinyl monomer other than methyl methacrylate.

  Examples of other vinyl monomers copolymerizable with the above alkyl methacrylate include alkyl acrylates having 1 to 8 carbon atoms in the alkyl group such as methyl acrylate, ethyl acrylate, butyl acrylate, propyl acrylate, and 2-ethylhexyl acrylate. ; Alkyl methacrylate having 1 to 4 carbon atoms of alkyl group such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate (other than the above alkyl methacrylate); aromatic methacrylate such as phenyl methacrylate, benzyl methacrylate; isobornyl Alicyclic methacrylates such as methacrylates; Aromatic vinyl compounds such as styrene, α-methylstyrene, paramethylstyrene; Bis such as acrylonitrile and methacrylonitrile Lucian compounds and the like, may be used in combination of two or more of these.

  Among these, from the viewpoint of compatibility with the fluororesin (B), transparency of the resulting film, heat resistance, and weather resistance, the co-polymerization of methyl methacrylate and alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. A coalescence is preferable, and a copolymer of methyl methacrylate and methyl acrylate is more preferable. The composition of this copolymer is preferably 80 to 99% by mass of methyl methacrylate units and 1 to 20% by mass of alkyl acrylate units, 90 to 99% by mass of methyl methacrylate units, and 1 to 10% by mass of alkyl acrylate units. % Is more preferable.

  The weight average molecular weight of the acrylic polymer (A-1) is preferably in the range of 50,000 to 200,000. If the weight average molecular weight is too small, good mechanical strength cannot be obtained, and if it is too large, melt molding becomes difficult. The weight average molecular weight is more preferably 70,000 to 170,000, and further preferably 80,000 to 120,000.

  The polymerization method for obtaining the acrylic polymer (A-1) is not particularly limited, and various methods such as a usual suspension polymerization method, emulsion polymerization method, bulk polymerization method and the like can be applied. From the viewpoint of excellent transparency, it is preferable to use a suspension polymerization method or a bulk polymerization method.

  As the acrylic polymer (A-1), the Dainar (registered trademark) BR series manufactured by Mitsubishi Rayon Co., Ltd. and the Acrypet (registered trademark) series manufactured by Mitsubishi Rayon Co., Ltd. can be suitably used. Is available.

[Rubber-containing multistage polymer (A-2)]
As the rubber-containing multistage polymer (A-2), a graft polymer formed by multistage polymerization having a laminated structure called a core-shell type having one or more rubber layers inside and a graft layer outside is used. Can do.

  This rubber layer is preferably made of a polymer having a glass transition temperature of 25 ° C. or lower. The glass transition temperature can be measured according to JIS K7121.

  The type of rubber component that forms the rubber layer is not particularly limited, but includes alkyl acrylate monomers, silicone monomers, styrene monomers, nitrile monomers, conjugated diene monomers, and urethane bonds. Examples thereof include rubber formed from a polymerized monomer, ethylene monomer, propylene monomer, isobutene monomer and the like.

  The rubber layer may be cross-linked by a cross-linking agent, and a cross-linking agent may be formed between the rubber layer and a layer adjacent to the rubber layer.

  The rubber-containing multistage polymer (A-2) may have two or more layers, and may have three or more layers or four or more layers. The rubber layer may constitute any inner layer, and may be provided as one layer or two or more layers.

  As for the refractive index of the acrylic film, the difference in refractive index between the solvent-soluble component and the solvent-insoluble component must be 0.005 or less in absolute value. If this difference in refractive index is too large, the film haze becomes too large to be used as an optical film, and is most preferably 0.003 or less.

  For example, if the refractive index of the solvent-soluble component is 1.485, the refractive index of the solvent-insoluble component needs to be 1.480 to 1.490, and is in the range of 1.482 to 1.488. Is most preferred.

  Solvent-soluble and insoluble components refer to components that are dissolved in a common solvent of acrylic resin (A-1) and fluororesin (B), and then centrifuged to separate the precipitated components into solvent-insoluble components. Is a solvent-soluble component.

  What is necessary is just to judge whether a common solvent will be in a state without a precipitate, when an acrylic resin (A-1) and a fluororesin (B) simple substance are dissolved and centrifuged.

As a common solvent for the acrylic resin (A-1) and the fluororesin (B), for example, when the acrylic resin (A-1) is polymethyl methacrylate and the fluororesin (B) is polyvinylidene fluoride, N, N-dimethylacetamide N, N-dimethylformamide and the like.
After separating the soluble component and the insoluble component, each is appropriately formed into a film using a press method or the like, and the refractive index is measured in accordance with JIS K7142.

  The refractive index of each polymer referred to in the present invention is a homopolymer value (polymethyl methacrylate: 1.490, poly n-butyl acrylate: 1.466) at 20 ° C. or 25 ° C. shown in “POLYMER HANDBOOK FOURTH EDITION”. , Polystyrene: 1.59, polymethyl acrylate: 1.472, polyvinylidene fluoride: 1.42), and can be predicted by calculating according to an additive rule according to the composition weight ratio.

  By adjusting the refractive index, the haze of the resulting acrylic film can be reduced, and the decrease in luminance due to haze can be suppressed, so that it can be suitably used as an optical film.

  The rubber-containing multistage polymer (A-2) preferably has an average particle size in the range of 0.01 to 0.5 μm. If the particle size is too large, light scattering tends to occur and the brightness tends to decrease. Therefore, the average particle size is preferably 0.5 μm or less, more preferably 0.3 μm or less, and further preferably 0.15 μm or less. On the other hand, if the particle size is too small, it is difficult to obtain an effect of improving the strength. Therefore, the average particle diameter is preferably 0.01 μm or more, and more preferably 0.05 μm or more. In the present invention, the average particle diameter refers to that obtained by the absorbance method from the latex polymer at the end of the polymerization.

  As a monomer used for forming the rubber layer of the rubber-containing multistage polymer (A-2), an alkyl acrylate having 1 to 8 carbon atoms of an alkyl group is preferable, and butyl acrylate and 2-ethylhexyl acrylate are more preferable. preferable.

  The amount of the alkyl acrylate used is preferably 35% by mass or more, and more preferably 50% by mass or more in the monomer forming the rubber layer. By using such a usage amount, the formed acrylic film has sufficient elongation and can be easily molded and processed.

  For the formation of the rubber layer, another vinyl monomer copolymerizable with the above alkyl acrylate may be used in combination. The amount of the vinyl monomer used is preferably 65% by mass or less, and more preferably 50% by mass or less. Examples of the vinyl monomer include alkyl methacrylates such as methyl methacrylate and butyl methacrylate, cycloalkyl methacrylates such as cyclohexyl methacrylate, styrene, acrylonitrile, and the like, and one or more of these can be used.

  As the crosslinking agent used for forming the rubber layer, ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, alkylene glycol dimethacrylate such as propylene glycol dimethacrylate, allyl acrylate, Examples include allyl methacrylate, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, diallyl maleate, trimethylolpropane triacrylate, and allyl cinnamate. These can be used alone or in combination.

  It is preferable to use a crosslinking agent in the range of 0.1-10 mass parts with respect to 100 mass parts of monomers which form a rubber layer. If it is less than 0.1 part by mass, the amount of monomer grafted on the rubber layer is extremely reduced. Although you may use exceeding 10 mass parts, the effect corresponding to addition amount does not express. The range of more preferable usage-amount is 0.3-7 mass parts.

  The graft component to be grafted on the rubber layer is carbon number of cycloalkyl group such as alkyl methacrylate having 1 to 8 carbon atoms such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate and cyclohexyl methacrylate. 3-8 of cycloalkyl methacrylate is mentioned, Among these, 1 type (s) or 2 or more types can be used. Among these, alkyl methacrylate having 1 to 8 carbon atoms in the alkyl group is preferable, and methyl methacrylate is particularly preferable.

  The graft component may be used in combination with the above methacrylate and another vinyl monomer copolymerizable with the methacrylate. Examples of the vinyl monomer include alkyl acrylates having 1 to 8 carbon atoms in alkyl groups such as methyl acrylate and butyl acrylate; cycloalkyl acrylates having 3 to 8 carbon atoms in cycloalkyl groups such as cyclohexyl acrylate; Aromatic vinyl compounds; vinylcyan compounds such as acrylonitrile and the like can be mentioned, and one or more of these can be used. Among these, alkyl acrylates having 1 to 8 carbon atoms in the alkyl group are preferable, and methyl acrylate is particularly preferable.

  The amount of the methacrylate used in the graft component is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 80% by mass or more.

  The mass ratio of the graft component and the component forming the rubber layer (hereinafter referred to as “rubber-forming component”) is 20 to 91 mass of the rubber-forming component with respect to the total of the rubber-forming component (a) and the graft component (b). %, The graft component is preferably in the range of 9 to 80% by mass, more preferably in the range of 33 to 83% by mass of the rubber forming component, and 17 to 67% by mass of the graft component, More preferably, it is in the range of 80% by mass and 20 to 50% by mass of the graft component. That is, the mass ratio (a / b) is preferably within the range of 20/80 to 91/9, more preferably within the range of 33/67 to 83/17, and even more preferably within the range of 50/50 to 80/20. This mass ratio is based on the total amount when there are a plurality of rubber layers, and based on the total amount when there are a plurality of graft layers.

  The rubber-containing multistage polymer (A-2) can be prepared by ordinary emulsion polymerization.

  In this polymerization, a chain transfer agent, other polymerization aids and the like may be used. Known chain transfer agents can be used, and mercaptans are particularly preferred. The amount of the chain transfer agent used is preferably 0.1 to 3.0 parts by mass with respect to 100 parts by mass of the total amount of the monomer mixture from the viewpoint of controlling the gel content and the polymer molecular weight.

  As the surfactant used for preparing the emulsion, anionic, cationic, and nonionic surfactants can be used, and anionic surfactants are particularly preferable. Examples of anionic surfactants include rosin soap, potassium oleate, sodium stearate, sodium myristate, sodium N-lauroyl sarcosinate, dipotassium alkenyl succinate, and sulfate esters such as sodium lauryl sulfate. Sulfonic acid salts such as sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, sodium alkyldiphenyl ether disulfonate; phosphate ester salts such as sodium polyoxyethylene alkylphenyl ether phosphate; phosphorus such as sodium polyoxyethylene alkyl ether phosphate Examples include acid ester salts. Of these, phosphate ester salts such as sodium polyoxyethylene alkyl ether phosphate are preferred.

  Preferred specific examples of the surfactant include NC-718 manufactured by Sanyo Chemical Industries, phosphanol RS-610NA, phosphanol LS-529, phosphanol RS-620NA, and phosphal manufactured by Toho Chemical Industry. Nors RS-630NA, Phosphanol RS-640NA, Phosphanol RS-650NA, Phosphanol RS-660NA, Latemu P-0404, Latemulu P-0405, Latemulu P-0406, Latemulu P-0407 (Kao Corporation) All of the above are trade names).

  As a method for preparing an emulsion, a method in which a surfactant is added after the monomer component is charged in water, a method in which the monomer component is charged after the surfactant is charged in water, And a method of adding water after charging the surfactant. Of these, the method of charging the surfactant after charging the monomer component into water and the method of charging the monomer component after charging the surfactant into water are preferred.

  Examples of the mixing device for preparing the emulsion include a stirrer equipped with a stirring blade; various forced emulsification devices such as a homogenizer and a homomixer; a membrane emulsification device and the like.

  The emulsion to be prepared may have either a W / O type or an O / W type dispersion structure, but an O / W type in which oil droplets of monomer components are dispersed in water is preferable. The diameter of the oil droplets in the dispersed phase is preferably 100 μm or less.

[Fluorine resin (B)]
As the fluororesin (B), one having sufficiently high compatibility with the acrylic polymer (A-1) is used. The compatibility between the fluororesin (B) and the acrylic polymer (A-1) is determined by measuring the glass transition point in accordance with JIS K7121 under the blending conditions of the film to be formed and the acrylic polymer (A-1). It is preferable that two glass transition points derived from the fluororesin (B) are not detected and only one glass transition point is detected.

  Further, the fluororesin (B) is derived from the crystal structure of the fluororesin (B) in the measurement of the melting temperature in accordance with JIS K7121 under the blending conditions of the film to be formed with the acrylic polymer (A-1). It is preferable that no melting peak is observed.

  As the fluororesin (B), trifluoroalkyl methacrylate homopolymer, tetrafluoroalkyl methacrylate homopolymer, pentafluoroalkyl methacrylate homopolymer, octafluoroalkyl methacrylate homopolymer, heptadecafluoroalkyl methacrylate homopolymer, Fluorinated alkyl methacrylate polymer such as fluorinated alkyl methacrylate / alkyl methacrylate copolymer; trifluoroalkyl α-fluoroacrylate homopolymer, tetrafluoroalkyl α-fluoroacrylate homopolymer, pentafluoroalkyl α-fluoroacrylate only Polymer, octafluoroalkyl α-fluoroacrylate homopolymer, heptadecafluoroalkyl α-fluoroacrylate homopolymer, etc. Any α-fluoromethacrylate polymer; vinylidene fluoride homopolymer, vinylidene fluoride / tetrafluoroethylene copolymer, vinylidene fluoride polymer such as vinylidene fluoride / hexafluoropropylene copolymer, etc. A mixture of two or more of these may be used.

  Among these, a vinylidene fluoride polymer is preferable and a vinylidene fluoride homopolymer is more preferable from the viewpoint of transparency when blended with the acrylic polymer (A-1).

[Resin composition (C)]
The acrylic film of this invention consists of a resin composition (C), and this resin composition (C) can be formed by blending an acrylic resin (A) and a fluorine resin (B).
As a blending method, a commonly used method can be used. For example, a method of preliminarily mixing with a mixer such as a Henschel mixer and then melt-kneading with a twin-screw extruder can be mentioned, but the method is not limited thereto.

  The mixing ratio of the acrylic resin (A) and the fluororesin (B) is 50 to 99.9 parts by mass for the acrylic resin (A) and 100% by mass for the fluororesin (B) when the total of these is 100 parts by mass. 0.1 to 50 parts by mass, that is, the mixing ratio (A / B) needs to be in the range of 50/50 to 99.9 / 0.1.

  From the viewpoint of obtaining a sufficient transparency improving effect of the fluororesin (B), the mixing ratio of the fluororesin (B) is more preferably 1 part by mass or more, and more preferably 3 parts by mass or more. Further preferred. That is, the mixing ratio (A / B) is more preferably 99/1 or more, and still more preferably 97/3 or more.

  When there are too many fluororesins (B), crystallization of a fluororesin (B) will occur easily, the acrylic film obtained will become cloudy and light transmittance will fall easily. In general, the fluororesin (B) is slightly yellow, and when the amount of the fluororesin (B) added is increased, the yellowishness of the resulting acrylic film tends to increase. Particularly for display applications, it is desired that the yellow color of the film is small. Moreover, the glass transition temperature of a fluorine resin (B) is low compared with an acrylic resin (A), and when the addition amount of a fluorine resin (B) is large, the heat resistance of the acrylic film obtained will fall. Furthermore, in general, the fluororesin (B) is very expensive compared to the acrylic resin (A), and the cost increases when the amount of the fluororesin (B) added is increased. From these viewpoints, the mixing ratio of the fluororesin (B) is more preferably 30 parts by mass or less, further preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less. That is, the mixing ratio (A / B) is more preferably 70/30 or less, further preferably 80/20 or less, and particularly preferably 90/10 or less.

  Considering the above matters, the mixing ratio of the acrylic resin (A) and the fluororesin (B) is 50 to 99 parts by mass of the acrylic resin (A) when the total is 100 parts by mass. The resin (B) is more preferably 1 to 50 parts by mass, the acrylic resin (A) is more preferably 70 to 99 parts by mass, and the fluororesin (B) is more preferably 1 to 30 parts by mass. It is particularly preferable that the resin (A) is 80 to 97 parts by mass and the fluororesin (B) is 3 to 20 parts by mass, the acrylic resin (A) is 90 to 97 parts by mass, and the fluororesin (B) is 3 parts. Most preferably, it is 10 mass parts.

  The resin composition (C) preferably has an extrapolated glass transition start temperature of 70 ° C. or higher, more preferably 80 ° C. or higher, from the viewpoint of the heat resistance of the acrylic film. By using an acrylic film having sufficient heat resistance, a highly reliable display can be provided.

[Brightness of acrylic film]
The luminance of the acrylic film in the present invention indicates the luminance of light emitted from the end surface (O) facing the end surface (I) when light is incident from the end surface (I) of the acrylic film.
In FIG. 1, sectional drawing along the advancing method of the light for demonstrating the measuring method of the brightness | luminance of an acrylic film is shown. In the figure, reference numeral 1 denotes an acrylic film, reference numeral 2 denotes a reflection sheet, reference numeral 3 denotes a light source, reference numeral 4 denotes an end face (I), and reference numeral 5 denotes an end face (O).

  When measuring the luminance of the acrylic film, the distance from the end surface (I) to the end surface (O) is 5 cm or more when the length of the light guide plate used in a small display such as a mobile phone or a game machine is assumed. It is preferable. Assuming that it is used for a larger screen, it is more preferably 10 cm or more, and further preferably 20 cm or more. When the distance from the end face (I) to the end face (O) is 20 cm or more, a slight difference in transmission loss due to light absorption, scattering, reflection or the like is observed as a large luminance difference. A film capable of obtaining high brightness even when the distance from the end face (I) to the end face (O) is long is particularly suitable for a light guide plate application used in a long optical path.

[Auxiliary]
In the resin composition (C) in the present invention, an auxiliary agent can be added to such an extent that the luminance is not impaired. Specifically, lubricants, plasticizers, antibacterial agents, antifungal agents, light stabilizers, ultraviolet absorbers, bluing agents, antistatic agents, heat stabilizers, and the like may be added.

[Thickness of acrylic film]
The thickness of the acrylic film of the present invention is preferably 500 μm or less. If it is 500 micrometers or less in thickness, the request | requirement of film thickness reduction is especially satisfy | filled and it can use suitably as a thin light-guide plate use. The thickness of the acrylic film is more preferably 50 to 500 μm, further preferably 50 to 400 μm, and particularly preferably 50 to 350 μm.

[Method of forming acrylic film]
The acrylic film of the present invention can be formed using a melt extrusion method using a T die or the like, or a solution casting method. Among these, the melt extrusion method is preferable because it can be produced efficiently and inexpensively.

  The molded acrylic film can be wound on a roll such as a paper tube or a plastic core, or cut or punched into a predetermined size one by one. When producing a light guide plate having a concavo-convex structure using a transfer mold, it is preferable that the light guide plate is wound in a roll shape because it can be produced continuously and efficiently at low cost.

〔Light guide plate〕
The light guide plate of the present invention can take the form of a thin light guide plate in which irregularities are provided on both sides or one side of the acrylic film of the present invention.

  Examples of the method for imparting the concavo-convex shape include a method of hot pressing using a transfer mold member having a concavo-convex shape on the surface, a photocurable resin composition applied to the acrylic film surface, and a photocurable resin composition applied. There is a method of transferring the uneven shape of the transfer surface of the transfer mold member to the layer. Moreover, you may give a dot shape by printing. These concavo-convex shape and the method of imparting the concavo-convex shape may be used alone or in combination.

  Specific examples of the uneven shape of the light guide plate include a mat structure, a dot shape, and a prism array arrangement structure. Since the acrylic film of this invention can give these shapes continuously, a light-guide plate can be manufactured with sufficient productivity.

  The light guide plate of the present invention can be suitably used as a light guide plate for a thin liquid crystal display device in particular because it has excellent light transmission characteristics and satisfies the demand for thinning.

[Backlight unit]
The backlight unit of the present invention is characterized by incorporating the light guide plate of the present invention, and the other configurations can be the same as those of the conventional backlight unit. For example, the light guide plate of the present invention is incorporated by arranging a light source (such as a plurality of LEDs) on the side surface (incident surface) of the light guide plate and laminating a reflection sheet on the lower surface side of the light guide plate as necessary. A backlight unit may be manufactured.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these.

Abbreviations for compound names in the following description are as follows.
Methyl methacrylate: MMA
Methyl acrylate: MA,
Butyl acrylate: BA,
Styrene: St,
Allyl methacrylate: AMA,
t-butyl hydroperoxide: tBH,
n-octyl mercaptan: nOM,
Ethylenediaminetetraacetic acid: EDTA,
Emulsifier (1): sodium mono-n-dodecyloxytetraoxyethylene phosphate (trade name: Phosphanol RS-610NA, manufactured by Toho Chemical Co., Ltd.).
The measurement methods in the examples are shown below.

[Total light transmittance of acrylic film]
The obtained acrylic film having an average thickness of 350 μm was cut into a 5 cm square and measured using NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS K7361-1.

[Acrylic film haze]
The obtained acrylic film having an average thickness of 350 μm was cut into a 5 cm square and measured using NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS K7136.

[Brightness of acrylic film]
As a light source, a reflective sheet made by Reiko Co., Ltd. was placed on a base on which 20 LED lamps (NSC 335 made by Nichia Chemical Co., Ltd.) having a thickness of 450 μm were placed, and an acrylic film was placed thereon. One reflective sheet was installed on top (see FIG. 1). The acrylic film had a square planar shape, a size of 20 cm in length and 5 cm in width, and a film thickness of 350 μm. The distance from the end face (I) to the end face (O) is 20 cm. In addition, the end surface (I) and the end surface (O) used the rotary grinder (AP-120 by Kasai Corporation), and grind | polished the surface using # 1200 abrasive paper.

  A luminance meter CS-100A manufactured by Konica Minolta was installed at a position 1 m from the end face (O), light was transmitted from the end face (I), and the brightness of the light emitted from the end face (O) was measured.

[Elongation at break of acrylic film]
The obtained acrylic film having an average thickness of 350 μm was punched into a dumbbell No. 1 type using a dumbbell super dumbbell cutter (trade name: SDK-100D), and a tensile test was conducted at a room temperature of 50 mm / min at room temperature. It was. At that time, the average elongation at the time when the sheet broke was defined as the breaking elongation.

[Separation of refractive index and insoluble component of solvent-soluble component and measurement of refractive index]
The obtained acrylic film having an average thickness of 350 μm was dissolved in N, N-dimethylacetamide and extracted for 6 hours under reflux. Subsequently, the extraction processing liquid was separated into a solvent-insoluble part and a solvent-soluble part by centrifuging for 30 minutes at an atmospheric temperature of 4 ° C. and 14000 rpm.

  The separated solvent-soluble component was recovered by a reprecipitation method using a hexane solvent. The soluble component was collected by filtration as it was. The soluble part and the insoluble part were each pressed at 220 ° C. and rapidly cooled to room temperature to prepare a sheet having a thickness of 0.2 mm, which was a sample piece having a length of 20 mm and a width of 10 mm, respectively.

Based on JIS K7142, the refractive index of the obtained sample piece was measured using Abbe refractometer (NAR-2: manufactured by Atago Co., Ltd.) and 1-bromonaphthalene as the contact liquid.

Below, the raw material preparation method of an acrylic film and the Example and comparative example of an acrylic film are demonstrated.

[Synthesis Example 1] Synthesis of rubber-containing multistage polymer (A-2-i) In a reaction vessel equipped with a cooler, 142.5 parts by mass of ion-exchanged water, 0.02 parts by mass of sodium carbonate, emulsifier (1) 0. 1 part by mass was added and the temperature was raised to 80 ° C.

  Subsequently, 5 parts by mass of ion exchange water, 0.0001 part by mass of ferrous sulfate, 0.0002 part by mass of EDTA, and 0.3 part by mass of sodium formaldehyde sulfoxylate were added and held for 5 minutes.

  Next, ST11.5 parts by mass, 51 parts by mass of BA, 0.56 parts by mass of AMA, 0.19 parts by mass of tBH, 0.79 parts by mass of emulsifier (1) were added dropwise over 120 minutes, and then the reaction was continued for 60 minutes. An inner polymer was obtained.

  Next, 2.5 parts by mass of ion-exchanged water and 0.075 parts by mass of sodium formaldehyde sulfoxylate were added and held for 20 minutes, then MMA 35.6 parts by mass, MA 1.9 parts by mass, tBH 0.06 parts by mass, 0.17 parts by mass of nOM and 0.25 part by mass of emulsifier (1) were added dropwise over 90 minutes, and the reaction was continued for 60 minutes to form an outermost layer polymer. A rubber-containing multistage polymer having a multilayer structure (A- 2-I) latex was obtained.

  The rubber-containing multistage polymer (A-2-I) latex is put into an aqueous solution containing 3 parts by mass of calcium acetate to salt out the rubber-containing multistage polymer (A-2-I), washed with water, and separated. After recovering, it was dried to obtain a powdery rubber-containing multistage polymer (A-2-i).

  The polymer particle size of the obtained rubber-containing multistage polymer (A-2-i) latex was measured by an absorbance method using an ultraviolet-visible spectrophotometer (Shimadzu UVmini-1240), and was found to be 0.12 μm. It was. The rubber content of the rubber-containing multistage polymer (A-2-i) is 62.5% by mass.

[Synthesis Example 2] Synthesis of rubber-containing multistage polymer (A-2-ro) A rubber-containing multistage polymer (A-2-ro) was prepared in the same manner as in Synthesis Example 1 except that ST 5 parts by mass and BA 57.5 parts by mass were used. )

[Synthesis Example 3] Synthesis of rubber-containing multistage polymer (A-2-ha) A rubber-containing multistage polymer (A-2) was prepared in the same manner as in Synthesis Example 1, except that ST 1.2 parts by mass and BA 61.3 parts by mass were used. -C) was obtained.

[Acrylic polymer (A-1)]
As the acrylic polymer (A-1), an acrylic resin (trade name: Dianar BR80) manufactured by Mitsubishi Rayon Co., Ltd. was used.

[Fluorine resin (B)]
As the fluororesin (B-1-I), a vinylidene fluoride homopolymer (trade name: Kureha KF Polymer T # 1000) manufactured by Kureha Corporation was used.
As the fluororesin (B-1-ro), a vinylidene fluoride homopolymer (trade name: Kynar 720) manufactured by Arkema Co., Ltd. was used.

[Example 1]
95 parts by mass of acrylic resin (A) (rubber content is 18.8%) consisting of 30 parts by mass of rubber-containing multistage polymer (A-2-i) and 70 parts by mass of acrylic polymer (A-1); Vent type twin screw extruder (TEM-35B manufactured by Toshiba Machine Co., Ltd.) in which 5 parts by mass of fluororesin (B-1-i) was mixed with a Henschel mixer and the resulting mixture was heated to 200 to 240 ° C. And kneaded to obtain pellets.

  The pellets produced by the above method were dried at 80 ° C. for a whole day and night. The dried pellets were supplied to a 30 mmφ non-vent screw type extruder equipped with a 15-cm wide T die, and the extruder temperature was 200 to 240 ° C., T Film formation was performed at a die temperature of 240 ° C. and a cooling roll temperature of 95 ° C. to produce an acrylic film having a thickness of 350 μm. Table 1 shows the luminance, total light transmittance, haze, and elongation at break of this acrylic film. The refractive index difference between the solvent-soluble and solvent-insoluble components of the acrylic film was 0.003.

[Comparative Example 1]
An acrylic resin (A) was prepared from 30 parts by mass of a rubber-containing multistage polymer (A-2-i) and 70 parts by mass of an acrylic polymer (A-1), and no fluororesin (B) was added. Except for this, an acrylic film having a thickness of 350 μm was produced in the same manner as in Example 1. Table 1 shows the luminance, total light transmittance, haze, and elongation at break of this acrylic film.

[Comparative Example 2]
The thickness was the same as in Example 1 except that the acrylic resin (A) was prepared from only 20 parts by mass of the rubber-containing multistage polymer (A-2-i) and 80 parts by mass of the acrylic polymer (A-1). A 350 μm thick acrylic film was produced.

[Example 2]
84 parts by mass of an acrylic resin (A) (rubber content is 14.9%) comprising 20 parts by mass of a rubber-containing multistage polymer (A-2-ro) and 64 parts by mass of an acrylic polymer (A-1). An acrylic film having a thickness of 350 μm was prepared in the same manner as in Example 1 except that the fluorine-based resin (B-1-ro) was changed to 16 parts by mass. In addition, the refractive index difference of the solvent soluble part and the solvent insoluble part of this acrylic film was zero.

Example 3
76 parts by mass of an acrylic resin (A) (rubber content is 15.6%) consisting of 20 parts by mass of a rubber-containing multistage polymer (A-2-C) and 56 parts by mass of an acrylic polymer (A-1) An acrylic film having a thickness of 350 μm was produced in the same manner as in Example 1 except that 24 parts by mass of the fluororesin (B-1-ro) was changed. In addition, the refractive index difference of the solvent soluble part and the solvent insoluble part of this acrylic film was zero.

[Comparative Example 3]
An acrylic film having a thickness of 350 μm was produced in the same manner as in Example 2, except that the type of rubber-containing multistage copolymer was changed to (A-2-i). In addition, the refractive index difference of the solvent soluble part and the solvent insoluble part of this acrylic film was 0.012. When the luminance of this acrylic film was measured, scattering occurred remarkably and the luminance of the end face was zero.

From these results, by blending the specific acrylic resin (A) and the fluorine-based resin (B) with a specific composition, the light transmission loss is suppressed when compared with an acrylic film consisting only of the acrylic resin (A), It can be seen that a film with improved luminance at the end face (b) is obtained.

From Comparative Example 3, it can be seen that when the refractive index difference between the solvent-soluble component and the insoluble component is large, light scattering increases and the luminance of the end face (B) decreases.

  The acrylic film provided by the present invention can be applied to a light guide plate used for thin liquid crystal displays, flat panel displays, plasma displays, mobile phone displays, mobile phone keypad lighting, personal computer keyboard lighting, and other signs.

  In addition to light guide plate applications, various types of housings that require transparency, such as electrical and electronic parts, optical filters, automobile parts, mechanical mechanism parts, housings for OA equipment and home appliances, and their parts, general goods, etc. Applicable to the field. Specifically, Fresnel lens, polarizing film, polarizer protective film, retardation film, light diffusion film, viewing angle widening film, reflective film, antireflection film, antiglare film, brightness enhancement film, prism sheet, microlens array It can be applied to conductive materials for touch panels, reflective materials used for road signs and the like.

It is a figure explaining the measuring method of the brightness | luminance of an acrylic film.

1 Acrylic film 2 Reflective sheet 3 Light source 4 End face (I)
5 End face (O)

Claims (4)

An acrylic film comprising a resin composition (C) obtained by mixing an acrylic resin (A) containing a rubber component and a fluororesin (B),
The content of the rubber component in the acrylic resin (A) is in the range of 1 to 45% by mass,
The mass ratio (A / B) of the acrylic resin (A) and the fluororesin (B) is in the range of 50/50 to 99.9 / 0.1,
Optical in which light is incident from the end face of the acrylic film, and the brightness of the light emitted from the opposite end face facing the end face is equal to or higher than the brightness of the film made of only the acrylic resin (A) measured under the same conditions. Acrylic film.   The optical acrylic film according to claim 1, wherein the acrylic resin (A) comprises an acrylic polymer (A-1) and a rubber-containing multistage polymer (A-2), wherein the solvent-soluble component and the solvent An acrylic film having a refractive index difference of insolubles of 0.005 or less.   The light-guide plate formed by providing uneven | corrugated shape to both surfaces or one side of the acrylic film as described in any one of Claim 1 or 2.   A backlight unit in which the light guide plate according to claim 3 is incorporated.

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