JP2006312658A - Acrylic resin composition, acrylic resin molded product composed of the same acrylic resin composition and light diffusing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acrylic resin composition preventing sticking of dust, etc., to a light diffusing plate by use thereof for the surface of the light diffusing plate and resultantly suppressing the deterioration of luminance of the light diffusing plate. <P>SOLUTION: The acrylic resin composition has <1×10<SP>13</SP>Ω value of surface resistivity according to JIS K 6911 when formed into an acrylic resin molded product. The deterioration of the luminance can be suppressed by using the light diffusing plate having the acrylic resin molded product composed of the acrylic resin composition on the surface thereof. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an acrylic resin composition suitable for forming a protective layer on the surface of a light diffusing plate.

As a liquid crystal display device, a backlight type in which a backlight unit is provided on the lower surface side of the liquid crystal layer and the liquid crystal layer is illuminated from the back surface to emit light is widely used. The backlight system is roughly classified into a side type and a direct type according to the arrangement of light sources such as cold cathode tubes. In any liquid crystal display device, it is required to suppress the loss in the light transmission path from the light source to the panel and improve the luminance on the panel. In recent years, however, the liquid crystal has a large screen exceeding 15 inches. The demand for televisions, PC displays, and the like has increased dramatically, and cases where direct type backlight units are used as such large-sized flat light emitting devices are increasing.
The direct type backlight unit is a method of reflecting and diffusing light from the light source by arranging a reflector on the back of the light source and a light diffusing plate on the light emitting surface, so that a lamp can be placed just behind the light emitting surface. Many lamps can be used, and there is an advantage that high brightness can be exhibited.

As a light diffusing plate used in such a direct type backlight unit, one mainly made of polycarbonate resin has been proposed and put into practical use.
For example, Patent Document 1 proposes a light diffusion plate for direct-type backlight made of polycarbonate resin for large liquid crystal displays and liquid crystal television applications. This light diffusing plate is characterized by little warpage, excellent surface light emission, no luminance unevenness, and excellent color tone.
JP 2004-126185 A

  However, such a light diffusing plate has a problem that dust or the like is likely to adhere due to charging, thereby causing a decrease in luminance.

  The present invention has been made in view of the above circumstances, and is used on the surface of a light diffusing plate to prevent dust and the like from adhering to the light diffusing plate. It is an object to provide a resin composition.

As a result of intensive studies, the inventors have conceived that the above problem can be solved by forming the surface of the light diffusing plate with an acrylic resin composition having a specific surface resistance value, thereby completing the present invention. It came to.
The acrylic resin composition of the present invention is an acrylic resin composition that forms the surface of a light diffusing plate, and an acrylic resin molded body made of the acrylic resin composition has a surface resistance value according to JIS K 6911 of 1 ×. It is less than 10 ¹³ Ω.
The acrylic resin molded article of the present invention is characterized by comprising the acrylic resin composition.
The light diffusing plate of the present invention is characterized in that the acrylic resin molded body is provided on the surface.
The backlight unit of the present invention includes the light diffusing plate.
The liquid crystal display device of the present invention includes the backlight unit.

  ADVANTAGE OF THE INVENTION According to this invention, the adhesion of dust etc. to a light diffusing plate is prevented by using on the surface of a light diffusing plate, As a result, the acrylic resin composition which can suppress the brightness fall of a light diffusing plate can be provided.

Hereinafter, the present invention will be described in detail.
[Acrylic resin composition]
The acrylic resin composition of the present invention is suitably used for forming the surface of a light diffusing plate. When an acrylic resin molded body is used, the surface resistance value of the acrylic resin molded body alone is 1 × 10 ¹³ Ω or less. The light diffusing plate is disposed on a light emitting surface of a light source such as a cold cathode tube in a backlight unit of a liquid crystal display device, and diffuses light from the light source.
By forming the surface of the light diffusing plate with such an acrylic resin composition, dust and the like can be prevented from adhering to the light diffusing plate, and as a result, a decrease in luminance of the light diffusing plate can be suppressed. Specifically, a mode in which an acrylic resin film made of an acrylic resin composition is laminated as a protective layer on the surface of the light diffusing plate body to form a light diffusing plate is preferable. In such a method, the dust adhesion preventing effect can be uniformly imparted to the surface of the light diffusion plate.
In the present invention, the surface resistance value is in accordance with JIS K 6911. After the acrylic resin molded body is left in a state of 23 ° C. and 50% RH for 24 hours, the super insulation meter is applied in the same atmosphere under an applied voltage of 500 V. It is the value measured using Toa Denpa Kogyo Co., Ltd. SM-10E type.

The acrylic resin composition is used for forming at least one surface of the light diffusing plate. Preferably, when used on both surfaces, that is, both the light source side surface and the liquid crystal side surface, the luminance of the light diffusing plate is lowered. Can be further suppressed. Moreover, the surface resistance value of the preferable acrylic resin composition is less than 5 × 10 ¹² Ω, more preferably less than 1 × 10 ¹² Ω.

An acrylic resin composition having such a surface resistance value can be obtained, for example, by blending an antistatic agent with an acrylic resin.
As the antistatic agent, surfactants such as alkyl sulfonate and glycerin fatty acid ester, and conductive polymers such as polyether, polyether ester, and polyether ester amide can be used. Among these, glycerin fatty acid mono- or diesters can be uniformly dispersed in an acrylic resin to give sufficient antistatic properties, and from the viewpoints of thermal stability, colorability, transparency, moldability (film forming property), and the like. Or alkylbenzenesulfonate. Specific antistatic agents include “Rikemar S100A” manufactured by Riken Vitamin Co., Ltd. made of glycerol fatty acid ester, “Electrostripper TS-5” manufactured by Kao Co., Ltd. made of glycerol fatty acid ester, and Takemoto made of alkyl sulfonate. An example is “MOA215” manufactured by Yushi Co., Ltd.
The addition amount of the antistatic agent is preferably in the range of 0.2 to 10 parts by mass with respect to 100 parts by mass of the acrylic resin. If it is 0.2 parts by mass or more, antistatic properties are easily developed, and if it is 10 parts by mass or less, for example, a film forming property when forming a film from the acrylic resin composition, transparency of the film, and resistance to warm water whitening are also obtained. It becomes good. A more preferable addition amount is 1 to 5 parts by mass.

  Moreover, when the acrylic resin composition of the present invention is an acrylic resin molded body such as a film, the total light transmittance according to JIS K7361-1 is preferably 80% or more. If the total light transmittance is 80% or more, the light diffusing plate whose surface is formed of the acrylic resin composition efficiently transmits light from the light source, and the liquid crystal display device using the light diffusing plate has good light emission quality. Become. Further preferable total light transmittance is 85% or more, more preferably 90% or more.

Furthermore, when the acrylic resin composition of the present invention is an acrylic resin molded body such as a film, the tensile elastic modulus of the acrylic resin molded body alone (value when testing the tensile properties according to JIS K7161) is 500 to 3000 MPa. It is preferable that
When the tensile elastic modulus is 500 to 3000 MPa, the appearance abnormality due to wrinkles tends to decrease when a film made of an acrylic resin composition is continuously laminated on the light diffusion plate body. Preferably it is 500-2000 MPa, More preferably, it is 700-1500 MPa. Good appearance is the most important factor in a light diffusing plate used in a liquid crystal display device.

The acrylic resin constituting the acrylic resin composition of the present invention is not particularly limited, but the main raw material is at least one selected from the group consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate, and if necessary, the number of carbon atoms Examples thereof include a single polymer or a copolymer obtained by using an acrylic acid ester having 1 to 8 alkyl groups, vinyl acetate, vinyl chloride, styrene, acrylonitrile, methacrylonitrile, or the like as a copolymerization component.
In addition, a multilayer structure polymer as described in JP-B-59-36646, JP-B-62-19309, JP-B-63-20459 and JP-A-63-77963 can be used. .

Preferably, in the acrylic resin composition of the present invention, an acrylic resin containing a rubber-containing polymer whose main component is acrylic (meth) acrylate is used. Examples of the rubber-containing polymer include a multilayer structure polymer (I), a multilayer structure polymer (III), and a rubber-containing graft copolymer (IV) described below. An acrylic resin composition containing at least one of these rubber-containing polymers has good light resistance and transparency, and is therefore suitable for forming the surface of a light diffusion plate.
In addition, when an acrylic resin further containing a thermoplastic polymer (II) described later containing an alkyl methacrylate as a main component together with these rubber-containing polymers is used, the flow when the acrylic resin composition is made into a film, for example, is used. And the stability of the film thickness is good. Furthermore, the obtained film has good transparency and is preferable from the viewpoint of appearance, and is also preferable because it is difficult to cause wrinkles when laminated on the light diffusion plate body.

Hereinafter, the multilayer structure polymer (I), the multilayer structure polymer (III), the rubber-containing graft copolymer (IV), and the thermoplastic polymer (II) will be specifically described.
(Multilayer structure polymer (I))
From the center, the multilayer structure polymer (I) is composed of the innermost layer polymer (IA), the first intermediate layer polymer (IB), the second intermediate layer polymer (IC), and the outermost layer polymer ( It is a multilayer structure polymer arranged in the order of ID).
The innermost layer polymer (IA) includes at least an alkyl methacrylate (I-A1) having an alkyl group having 4 or less carbon atoms, an alkyl acrylate (I-A2) having an alkyl group having 8 or less carbon atoms, and an aromatic vinyl. It is a polymer obtained by polymerizing the monomer (I-A3) and the polyfunctional monomer (I-A4) and having a glass transition temperature of 10 ° C. or higher.
The first intermediate layer polymer (IB) includes at least an alkyl acrylate (I-B1) having an alkyl group having 8 or less carbon atoms, an aromatic vinyl monomer (I-B2), and a polyfunctional monomer. It is a polymer obtained by polymerizing (I-B3) and a graft crossing agent (I-B5) and having a glass transition temperature of 0 ° C. or lower.
The second intermediate layer polymer (IC) is composed of alkyl methacrylate (I-C1) having an alkyl group having 4 or less carbon atoms, alkyl acrylate (I-C2) having an alkyl group having 8 or less carbon atoms, and aromatic vinyl. It is a polymer obtained by polymerizing the monomer (I-C3) and the graft crossing agent (I-C4).
The outermost layer polymer (ID) is composed of an alkyl methacrylate (ID1) having an alkyl group having 4 or less carbon atoms, an alkyl acrylate (ID2) having an alkyl group having 8 or less carbon atoms, and an aromatic vinyl monomer. It is a polymer obtained by polymerizing the body (I-D3) and having a glass transition temperature of 50 ° C. or higher.

Further, each of the polymers (IA) to (ID) preferably has the following configuration.
That is, the innermost layer polymer (IA) is an alkyl methacrylate (I-A1) 30 to 99.7% by mass having an alkyl group having 4 or less carbon atoms and an alkyl acrylate (I having an alkyl group having 8 or less carbon atoms). -A2) 0.1 to 69.8% by mass, aromatic vinyl monomer (I-A3) 0.1 to 25% by mass, polyfunctional monomer (I-A4) 0.1 to 10% by mass And a polymer having a glass transition temperature (hereinafter referred to as Tg) of 10 ° C. or higher obtained by polymerizing 0 to 5% by mass of the graft crossing agent (I-A5). In addition, (I-A1) + (I-A2) + (I-A3) + (I-A4) + (I-A5) = 100 mass%.
A Tg of 10 ° C. or higher is preferred because the acrylic resin composition tends to have good transparency. In addition, the amount of the innermost layer polymer (IA) in 100% by mass of the multilayer structure polymer (I) is preferably 2 to 35% by mass in terms of the transparency of the resulting acrylic resin composition.

1st intermediate | middle layer polymer (IB) is alkyl acrylate (I-B1) 60-99.7 mass% which has a C8 or less alkyl group, aromatic vinyl monomer (IB-2) 0. 1 to 39.8% by mass, polyfunctional monomer (I-B3) 0.1 to 10% by mass, monomer having copolymerizable double bond (I-B4) 0 to 20% by mass and A polymer obtained by polymerizing 0.1 to 5% by mass of the graft crossing agent (I-B5) and having a Tg of 0 ° C. or less is preferable. In addition, (I−B1) + (I−B2) + (I−B3) + (I−B4) + (I−B5) = 100 mass%.
When Tg is 0 ° C. or lower, the film forming stability when a film is formed from the acrylic resin composition is excellent. Moreover, the obtained acrylic resin film has sufficient strength, and when it is laminated on the light diffusing plate main body, it does not break and tends to have good workability. Moreover, it is preferable that the quantity of the 1st intermediate | middle layer polymer (IB) which occupies for 100 mass% of multilayer structure polymer (I) is 5-60 mass%.

The second intermediate layer polymer (I-C) is an alkyl methacrylate (I-C1) having an alkyl group having 4 or less carbon atoms of 20 to 89.8% by mass and an alkyl acrylate having an alkyl group having 8 or less carbon atoms (I -C2) 10-79.8% by mass, 0.1-25% by mass of aromatic vinyl monomer (I-C3) and 0.1-5% by mass of graft crossing agent (I-C4) It is preferable to be a polymer obtained. In addition, (I−C1) + (I−C2) + (I−C3) + (I−C4) = 100 mass%.
The amount of the second intermediate layer polymer (IC) in 100% by mass of the multilayer structure polymer (I) is preferably 2 to 20% by mass. Moreover, it is preferable that the latex particle diameter in the 2nd intermediate | middle layer polymer (IC) stage in manufacture of multilayer structure polymer (I) is 0.03-0.2 micrometer.

The outermost layer polymer (ID) is composed of 51 to 99.8% by mass of an alkyl methacrylate (I-D1) having an alkyl group having 4 or less carbon atoms, and an alkyl acrylate (I-D2) having an alkyl group having 8 or less carbon atoms. And a polymer having a Tg of 50 ° C. or higher, obtained by polymerizing 0.1 to 48.9% by mass and 0.1 to 25% by mass of the aromatic vinyl monomer (I-D3). preferable. In addition, (I−D1) + (I−D2) + (I−D3) = 100 mass%.
A Tg of 50 ° C. or higher is preferable because the heat resistance of the acrylic resin composition tends to be good. Moreover, it is preferable that the quantity of outermost layer polymer (ID) which occupies 100 mass% of multilayer structure polymer (I) is 10-80 mass% from the heat resistant point of an acrylic resin composition.

Here, Tg of a polymer is calculated | required by the following Fox formula, for example in the case of the copolymer which consists of monomer a, b, c ....
1 / Tg = ma / Tga + mb / Tgb + mc / Tgc ...
Tg: Tg [K] of the copolymer
ma: Mass fraction of monomer a Tga: Tg [K] of a homopolymer obtained from monomer a
mb: mass fraction of monomer b Tgb: Tg [K] of homopolymer obtained from monomer b
mc: mass fraction of monomer c Tgc: Tg [K] of homopolymer obtained from monomer c

The alkyl methacrylate (I-A1) having an alkyl group having 4 or less carbon atoms constituting the innermost layer polymer (IA) may be either linear or branched, for example, butyl methacrylate, propyl methacrylate, Examples include ethyl methacrylate and methyl methacrylate. These can be used alone or in admixture of two or more. Among these, methyl methacrylate is preferable from the viewpoint of transparency.
Examples of the alkyl acrylate (I-A2) having an alkyl group having 8 or less carbon atoms include methyl acrylate, ethyl acrylate, butyl acrylate, propyl acrylate, 2-ethylhexyl acrylate, and the like. These can be used alone or in admixture of two or more. Of these, butyl acrylate is preferable from the viewpoint of Tg.
Examples of the aromatic vinyl monomer (I-A3) include styrene, α-methylstyrene, paramethylstyrene, and the like. These can be used alone or in admixture of two or more. Of these, styrene is preferable from the viewpoint of economy.
The polyfunctional monomer (I-A4) is a monomer having two or more copolymerizable double bonds in one molecule. Examples of the polyfunctional monomer (I-A4) include alkylene glycol dimethacrylates such as ethylene glycol dimethacrylate, 1,3-butylene dimethacrylate, 1,4-butylene glycol dimethacrylate, and propylene glycol dimethacrylate; Polyvinylbenzene such as divinylbenzene and trivinylbenzene; alkylene glycol diacrylate and the like. These can be used alone or in admixture of two or more. Among these, alkylene glycol dimethacrylate is preferable, and 1,3-butylene glycol dimethacrylate is more preferable.
The graft crossing agent (I-A5) is a monomer having two or more different copolymerizable double bonds in one molecule. Examples of the graft crossing agent (I-A5) include copolymerizable α, β-unsaturated monocarboxylic acid or dicarboxylic acid allyl ester, methallyl ester, crotyl ester, triallyl cyanurate, triallyl isocyanurate, and the like. Is mentioned. These can be used alone or in admixture of two or more. Of these, allyl methacrylate and triallyl cyanurate are particularly preferable.

As the alkyl acrylate (I-B1) having an alkyl group having 8 or less carbon atoms constituting the first intermediate layer polymer (IB), the alkyl acrylate represented by (I-A2) may be used alone or in combination of two or more. Can be mixed and used.
As the aromatic vinyl monomer (I-B2), styrene, α-methylstyrene, paramethylstyrene and the like shown in (I-A3) can be used alone or in admixture of two or more.
Examples of the polyfunctional monomer (I-B3) include ethylene glycol dimethacrylate, 1,3-butylene dimethacrylate, 1,4-butylene glycol dimethacrylate, and propylene glycol dimethacrylate represented by (I-A4). Alkylene glycol dimethacrylate; polyvinyl benzene such as divinylbenzene and trivinylbenzene; alkylene glycol acrylate and the like can be used alone or in admixture of two or more. Among these, alkylene glycol dimethacrylate is preferable, and 1,3-butylene glycol dimethacrylate is more preferable.
As the monomer (I-B4) having a copolymerizable double bond, other than the above-mentioned monomers (I-B1) to (I-B3) and copolymerizable with the above-mentioned monomers Examples of the monomer include acrylic monomers such as lower alkoxy acrylate, cyanoethyl acrylate, acrylamide, acrylic acid, and methacrylic acid, styrene, acrylic substituted styrene, acrylonitrile, and methacrylonitrile. These can be used alone or in admixture of two or more.
As the graft crossing agent (I-B5), allyl ester, methallyl ester, crotyl ester, triallyl cyanurate of the copolymerizable α, β-unsaturated monocarboxylic acid or dicarboxylic acid shown in (I-A5) And triallyl isocyanurate. These can be used alone or in admixture of two or more. Of these, allyl methacrylate and triallyl cyanurate are particularly preferable.

  As the monomer and graft crossing agent constituting the second intermediate layer polymer (IC) and the outermost layer polymer (ID), the innermost layer polymer (IA) and the first intermediate layer polymer The thing similar to (IB) is mentioned. These can be used alone or in admixture of two or more.

  The final latex particle size of the multilayer structure polymer (I) is preferably 0.03 to 0.2 μm, more preferably 0.04 to 0.15 μm, and most preferably 0.05 to 0. .1 μm. When the final latex particle size becomes too large, not only the transparency of the acrylic resin composition is lowered, but also the transparency may change due to a temperature change. As a result, when the surface of the light diffusing plate is formed of an acrylic resin composition, if the transparency changes due to heat from a light source such as a cold cathode tube, the light emission quality may be lowered. On the other hand, if the particle diameter is too small, for example, when the acrylic resin composition is formed into a film, the film is likely to be cut and the workability may be deteriorated. Moreover, when laminating the obtained acrylic resin film on the light diffusing plate main body, the acrylic resin film may be cut due to insufficient strength, and workability may deteriorate. The acrylic resin composition used on the surface of the light diffusing plate preferably has higher transparency in terms of light emission quality when used as a liquid crystal display device, and more preferably has higher impact resistance in terms of workability.

Furthermore, in order to reduce the temperature dependence of the total light transmittance and the haze value, the amount of alkyl methacrylate having 4 or less carbon atoms in each layer in the multilayer polymer (I) is reduced by the first intermediate layer polymer (I- From B), the amount of the alkyl methacrylate monotonously increasing toward the second intermediate layer polymer (IC) and the outermost layer polymer (ID) and occupying the first innermost layer polymer (IA) is the first. The amount is preferably larger than the amount occupied in the intermediate layer polymer (IB).
Moreover, the mass of the aromatic vinyl monomer in each polymer (IA)-(ID) which comprises each layer of multilayer structure polymer (I), and the alkyl acrylate which has a C8 or less alkyl group. The ratio (aromatic vinyl monomer / alkyl acrylate) is preferably 5/95 to 50/50, more preferably 10/90 to 30/70. As the mass ratio goes away from this range, the transparency of the multilayer structure polymer (I) decreases, and when the surface of the light diffusion plate is formed, the light emission quality of a liquid crystal display device using the same tends to decrease.

As a method for producing the multilayer structure polymer (I), a sequential multi-stage polymerization method by an emulsion polymerization method is the most suitable polymerization method. The production of the multilayer structure polymer (I) is not particularly limited, and for example, it may be carried out by an emulsion suspension polymerization method in which, after emulsion polymerization, the polymer is converted into a suspension polymerization system at the time of polymerization of each polymer. Can do.
Although not particularly limited, when the multilayer structure polymer (I) is produced by emulsion polymerization, the monomer component that gives the innermost layer polymer (IA) is preliminarily mixed with water and a surfactant. A method is preferred in which an emulsion is prepared by mixing, this emulsion is supplied to the reactor and polymerized, and then the monomer components constituting the remaining layers are sequentially supplied to the reactor and polymerized.
The monomer component that gives the innermost layer polymer (IA) was mixed with water and a surfactant in advance and supplied to the reactor to be polymerized and dispersed, particularly in acetone. In this case, the multilayer structure polymer (I) in which the number of particles having a diameter of 55 μm or more present in the dispersion is 0 to 50 per 100 g of the multilayer structure polymer (I) can be easily obtained. A film of the acrylic resin composition containing the multilayer structure polymer (I) thus obtained is preferred because it has less fish eyes and a good appearance and optical properties. More preferably, the number of particles having a diameter of 55 μm or more present in the dispersion when dispersed in acetone is 0 to 30, more preferably 0 to 20 per 100 g of the multilayer structure polymer (I). Is a multilayer structure polymer (I).

In addition, when the multilayer structure polymer is dispersed in acetone, the number of particles having a diameter of 55 μm or more present in the dispersion is determined by measuring the weight of the powdered multilayer structure polymer in acetone at a concentration of 5% by mass to It is obtained by dispersing in the range of 10% by mass, preparing a dispersion, and measuring the number of particles having a diameter of 55 μm or more present in the dispersion with a light scattering type particle counter or the like according to JIS B9921.
Further, when preparing the dispersion, in order to sufficiently permeate acetone between the particles of the multilayer structure polymer, the multilayer structure polymer is previously made a good solvent for the multilayer structure polymer on a mesh having an opening smaller than 55 μm. After ultrasonic cleaning, a method in which the residue on the mesh is dispersed again in acetone is preferable. When the dispersion is prepared in this manner, the number of particles having a diameter of 55 μm or more present in the dispersion can be measured more accurately.

  As the surfactant used in preparing the emulsion, anionic, cationic and nonionic surfactants can be used, and anionic surfactants are particularly preferable. Examples of the anionic surfactant include rosin soap; potassium oleate, sodium stearate, sodium myristate, sodium N-lauroyl sarcosinate, dipotassium alkenyl succinate; sulfate ester salts such as sodium lauryl sulfate Sulfonic acid salts such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium alkyldiphenyl ether disulfonate, etc .; phosphate esters such as polyoxyethylene alkylphenyl ether sodium phosphate; polyoxyethylene alkyl ether phosphate Examples thereof include sodium phosphate salts and the like. Of these, phosphate esters such as polyoxyethylene alkyl ether sodium phosphates are preferable from the viewpoint of ecological protection from endocrine disrupting chemicals, which have become a problem in recent years.

  Preferred specific examples of the surfactant include NC-718 manufactured by Sanyo Chemical Industries, phosphanol LS-529, phosphanol RS-610NA, phosphanol RS-620NA, and phospha Nord-RS-630NA, Phosphanol RS-640NA, Phosphanol RS-650NA, Phosphanol RS-660NA, Latemu P-0404, Latemulu P-0405, Latemulu P-0406, Latemulu P-0407 manufactured by Kao Corporation Is mentioned.

In addition, as a method for preparing an emulsion, a method in which a monomer component is charged in water and then a surfactant is added, a method in which a surfactant is charged in water and then a monomer component is charged, For example, a method in which water is added after a surfactant is charged into the monomer component. Among these, the method of charging the surfactant after charging the monomer into water and the method of charging the monomer component after charging the surfactant into water are the methods for obtaining the multilayer structure polymer (I). Is 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.
Further, the emulsion to be prepared may have either a W / O type or an O / W type dispersion structure, and particularly an O / W type in which monomer component oil droplets are dispersed in water, and oil droplets in a dispersed phase. The diameter is preferably 100 μm or less.

  The innermost layer polymer (IA), the first intermediate layer polymer (IB), the second intermediate layer polymer (IC), and the outermost layer polymer (I) constituting the multilayer structure polymer (I) As the polymerization initiator used when forming (ID), known ones can be used. As the addition method, a method of adding to one or both of the aqueous phase and the monomer phase can be adopted. Particularly preferred polymerization initiators include peroxides, azo initiators, or redox initiators in which an oxidizing agent / reducing agent is combined. Among these, a redox initiator is more preferable, and a sulfoxylate initiator combined with ferrous sulfate, ethylenediaminetetraacetic acid disodium salt, longalite, and hydroperoxide is particularly preferable.

The most preferable specific method for producing the multilayer structure polymer (I) is that an aqueous solution containing ferrous sulfate, ethylenediaminetetraacetic acid disodium salt and Rongalite is heated to the polymerization temperature in the reactor, and then the innermost layer weight is increased. An emulsion containing a monomer component that gives the coalescence (IA), an emulsifier and a hydroperoxide is supplied to the reactor for polymerization, and then a first intermediate layer layer containing a polymerization initiator such as peroxide. The monomer component which gives a combination (IB), 2nd intermediate | middle layer polymer (IC), and outermost layer polymer (ID) is supplied to a reactor one by one, and it superposes | polymerizes. The polymerization temperature varies depending on the type and amount of the polymerization initiator used, but is preferably 40 to 120 ° C, more preferably 60 to 95 ° C. Moreover, when obtaining multilayer structure polymer (I) by emulsion polymerization, you may use a chain transfer agent, another polymerization adjuvant, etc. As the chain transfer agent, known ones can be used, and mercaptans are preferred.
The multilayer structure polymer (I) is recovered from the polymer latex produced by the above-described method. Although it does not specifically limit as a collection | recovery method, Methods, such as salting-out or acid precipitation coagulation | solidification, spray-drying, freeze-drying, are mentioned, It collect | recovers with a powder form.

(Multilayer structure polymer (III))
The multilayer structure polymer (III) is a multilayer structure polymer arranged in the order of the innermost layer polymer (III-A), the intermediate layer polymer (III-B), and the outermost layer polymer (III-C) from the center. is there.
The innermost layer polymer (III-A) is a polymer having units derived from an alkyl acrylate (III-A1) having an alkyl group having 1 to 8 carbon atoms and units derived from a graft crossing agent (III-A5). is there.
The intermediate layer polymer (III-B) is a unit derived from an alkyl acrylate (III-B1) having an alkyl group having 1 to 8 carbon atoms, and an alkyl methacrylate (III-B2) having an alkyl group having 1 to 4 carbon atoms. A polymer having a unit different from that of the innermost layer polymer (III-A) and a unit derived from the graft crossing agent (III-B5).
The outermost layer polymer (III-C) is a polymer having units derived from alkyl methacrylate (III-C1) having an alkyl group having 1 to 4 carbon atoms.

Furthermore, each of the polymers (III-A) to (III-C) is from the viewpoint of physical properties such as transparency of the acrylic resin composition containing the multilayer structure polymer (III) and strength of the acrylic resin molded body. The composition is preferably as follows.
That is, the content of each unit in 100% by mass of all monomer units constituting the innermost layer polymer (III-A) is derived from the alkyl acrylate (III-A1) having an alkyl group having 1 to 8 carbon atoms. The unit to be used is preferably 50 to 99.9% by mass, more preferably 55 to 77.9% by mass from the viewpoint of physical properties such as moldability and strength of the acrylic resin composition containing the multilayer structure polymer (III). And most preferably 60 to 69.9% by mass.
The unit derived from the alkyl methacrylate (III-A2) having an alkyl group having 1 to 4 carbon atoms is preferably 0 to 49.9% by mass, more preferably 20% by mass or more, and most preferably 30% by mass. That's it. Most preferably, it is 39.9 mass% or less.
About the unit derived from the other monomer (III-A3) which has a copolymerizable double bond, 0-20 mass% is preferable, More preferably, it is 15 mass% or less.
About the unit derived from a polyfunctional monomer (III-A4), 0-10 mass% is preferable, More preferably, it is 0.1 mass% or more and 6 mass% or less.
The unit derived from the graft crossing agent (III-A5) is preferably 0.1 to 10% by mass. When the content is 0.1% by mass or more, the resulting acrylic resin composition containing the multilayer structure polymer can be molded without degrading optical properties such as transparency. A content of 10% by mass or less is preferable because sufficient flexibility and toughness can be imparted to the multilayer structure polymer. More preferably, it is 0.5 mass% or more and 2 mass% or less.

The content of each unit in 100% by mass of all monomer units constituting the intermediate layer polymer (III-B) is a unit derived from an alkyl acrylate (III-B1) having an alkyl group having 1 to 8 carbon atoms. About 9.9-90 mass% is preferable. From the viewpoint of transparency of the acrylic resin composition containing the multilayer structure polymer (III), it is more preferably 19.9% by mass or more, and most preferably 29.9% by mass or more. Further, it is more preferably 60% by mass or less, and most preferably 50% by mass or less.
About the unit derived from the alkyl methacrylate (III-B2) which has a C1-C4 alkyl group, 9.9-90 mass% is preferable. From the viewpoint of transparency of the acrylic resin composition containing the multilayer structure polymer (III), it is more preferably 39.9% by mass or more, and most preferably 49.9% by mass or more. Further, it is more preferably 80% by mass or less, and most preferably 70% by mass or less.
About the unit derived from the other monomer (III-B3) which has a copolymerizable double bond, it is 0-20 mass%, More preferably, it is 15 mass% or less.
About the unit derived from a polyfunctional monomer (III-B4), it is 0-10 mass%, More preferably, it is 6 mass% or less.
The unit derived from the graft crossing agent (III-B5) is 0.1 to 10% by mass. When the content is 0.1% by mass or more, the acrylic resin composition containing the resulting multilayer structure polymer (III) can be molded without deteriorating optical properties such as transparency. A content of 10% by mass or less is preferable because sufficient flexibility and toughness can be imparted to the multilayer structure polymer (III). More preferably, it is 0.5 mass% or more and 2 mass% or less.

The content of the alkyl acrylate, alkyl methacrylate, other monomer having a copolymerizable double bond, polyfunctional monomer, and graft crossing agent forming the outermost layer polymer (III-C) From the viewpoint of moldability and transparency of the acrylic resin composition containing the structural polymer (III), the following ranges are preferred.
About 100-100 mass% of all the monomer units which comprise outermost layer polymer (III-C), about the unit derived from the alkylmethacrylate (III-C1) which has a C1-C4 alkyl group, 80-100 mass %, More preferably 85% by mass or more, and most preferably 90% by mass or more.
About the unit derived from the alkyl acrylate (III-C2) which has a C1-C8 alkyl group, 0-20 mass% is preferable, More preferably, it is 1 mass% or more. Further, it is more preferably 15% by mass or less, and most preferably 10% by mass or less.
About the unit derived from the monomer (III-C3) which has a copolymerizable double bond, 0-20 mass% is preferable, More preferably, it is 15 mass% or less.

The alkyl acrylate (III-A1) having an alkyl group having 1 to 8 carbon atoms constituting the innermost layer polymer (III-A) may be either linear or branched. Specific examples thereof include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate and the like. These can be used alone or in admixture of two or more. Of these, n-butyl acrylate is preferred.
The C1-C4 alkyl methacrylate (III-A2) constituting the innermost layer polymer (III-A) may be either linear or branched. Specific examples thereof include methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate and the like. These can be used alone or in admixture of two or more. Of these, methyl methacrylate is preferred.
Examples of the other monomer (III-A3) having a copolymerizable double bond constituting the innermost layer polymer (III-A) include lower alkoxy acrylate, cyanoethyl acrylate, acrylamide, acrylic acid, and methacrylic acid. An acrylic monomer such as styrene, alkyl-substituted styrene, acrylonitrile, methacrylonitrile and the like can be used.

The polyfunctional monomer (III-A4) constituting the innermost layer polymer (III-A) can be used as necessary. A polyfunctional monomer is defined as a monomer having two or more copolymerizable double bonds in one molecule. Preferable specific examples thereof include alkylene glycol dimethacrylates such as ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, and propylene glycol dimethacrylate. In addition, polyvinylbenzene such as divinylbenzene and trivinylbenzene can be used. Of these, 1,3-butylene glycol dimethacrylate is preferred. Even when the polyfunctional monomer (III-A4) does not act at all, it is possible to form a fairly stable multilayer structure polymer (III) as long as the graft crossing agent (III-A5) is present. Therefore, the polyfunctional monomer (III-A4) may be arbitrarily used depending on the purpose of addition, for example, when the hot strength or the like is strictly required.
The graft crossing agent (III-A5) constituting the innermost layer polymer (III-A) is defined as a monomer having two or more different copolymerizable double bonds in one molecule. Specific examples thereof include allyl, methallyl, or crotyl ester of copolymerizable α, β-unsaturated carboxylic acid or dicarboxylic acid. In particular, acrylic acid, methacrylic acid, maleic acid, or acrylic ester of fumaric acid is preferable. Of these, allyl methacrylate is preferable because of its excellent effect. In addition, triallyl cyanurate, triallyl isocyanurate and the like are also effective. In the graft crossing agent (III-A5), mainly the conjugated unsaturated bond of the ester reacts much faster than the allyl group, methallyl group, or crotyl group and chemically bonds. A substantial portion of the allyl, methallyl, or crotyl group works effectively during the polymerization of the next layer polymer to provide a graft bond between adjacent two layers. In that case, a chain transfer agent may be used.

The Tg of the innermost layer polymer (III-A) alone is an intermediate layer polymer (III) described later from the viewpoint of physical properties such as the strength of a film made of an acrylic resin composition containing the multilayer structure polymer (III). -B) It is preferably less than a single Tg. More preferably, it is less than 5 degreeC, More preferably, it is 0 degreeC or less, Most preferably, it is -5 degreeC or less.
The content of the innermost layer polymer (III-A) in 100% by mass of the multilayer structure polymer (III) is 15 to 15 in terms of transparency of the acrylic resin composition containing the multilayer structure polymer (III). 50 mass% is preferable, More preferably, it is 15-35 mass%. In this case, it is advantageous in terms of optical properties when the surface of the light diffusing plate is formed with an acrylic resin composition containing the multilayer structure polymer (III).

The innermost layer polymer (III-A) may be a single layer, but is preferably composed of two layers. Moreover, the monomer constituent ratios of the two layers in the innermost layer polymer (III-A) may be the same or different.
When the innermost layer polymer (III-A) consists of two layers and the monomer composition ratios of the two layers are different, the Tg of the inner layer (III-A-1) is the outer layer (III-A-2). It may be higher or lower than Tg.
From the viewpoint of transparency, the content of the inner layer (III-A-1) in 100% by mass of the innermost layer polymer (III-A) is preferably 1 to 20% by mass, and the outer layer (III-A- The content of 2) is preferably 80 to 99% by mass. The acrylic resin composition that forms the surface of the light diffusing plate preferably has higher transparency.
As a preferable multilayer structure polymer in the case where the innermost layer polymer (III-A) is composed of two layers, a multilayer structure polymer described in JP-B-62-19309 is exemplified.

The alkyl acrylate (III-B1) having an alkyl group having 1 to 8 carbon atoms constituting the intermediate layer polymer (III-B) may be either linear or branched. Specific examples thereof include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate and the like. These can be used alone or in admixture of two or more. Of these, preferred are methyl acrylate and n-butyl acrylate.
The alkyl methacrylate (III-B2) having an alkyl group having 1 to 4 carbon atoms constituting the intermediate layer polymer (III-B) may be either linear or branched. Specific examples thereof include methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate and the like. These can be used alone or in admixture of two or more. Of these, methyl methacrylate is preferred.
Other monomers (III-B3) having a copolymerizable double bond constituting the intermediate layer polymer (III-B) include lower alkoxy acrylate, cyanoethyl acrylate, acrylamide, acrylic acid, methacrylic acid and the like. Acrylic monomers, styrene, alkyl-substituted styrene, acrylonitrile, methacrylonitrile and the like can be used.

What is necessary is just to use the polyfunctional monomer (III-B4) which comprises an intermediate | middle layer polymer (III-B) as needed. Preferable specific examples thereof include alkylene glycol dimethacrylates such as ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, and propylene glycol dimethacrylate. In addition, polyvinylbenzene such as divinylbenzene and trivinylbenzene can be used. Of these, 1,3-butylene glycol dimethacrylate is preferred. Even when the polyfunctional monomer (III-B4) does not act at all, it is possible to form a fairly stable multilayer structure polymer (III) as long as the graft crossing agent (III-B5) is present. Therefore, the polyfunctional monomer (III-B4) may be used for addition depending on the purpose of addition, for example, when the hot strength or the like is strictly required.
Examples of the graft crossing agent (III-B5) constituting the intermediate layer polymer (III-B) include allyl, methallyl, or crotyl ester of a copolymerizable α, β-unsaturated carboxylic acid or dicarboxylic acid. . In particular, acrylic acid, methacrylic acid, maleic acid, or acrylic ester of fumaric acid is preferable. Of these, allyl methacrylate is preferable because of its excellent effect. In addition, triallyl cyanurate, triallyl isocyanurate and the like are also effective. In the graft crossing agent (III-B5), the conjugated unsaturated bond of the ester mainly reacts and bonds chemically much faster than the allyl group, methallyl group, or crotyl group. A substantial portion of the allyl, methallyl, or crotyl group works effectively during the polymerization of the next layer polymer to provide a graft bond between adjacent two layers. In this case, a chain transfer agent may be used.

The composition of the intermediate layer polymer (III-B) is preferably different from the composition of the innermost layer polymer (III-A). When the compositions of these polymers are different, physical properties such as impact resistance and transparency when the acrylic resin composition containing the multilayered polymer (III) is molded can be satisfied.
Here, “different composition” as used in the present invention means alkyl acrylate, alkyl methacrylate, other monomers having a copolymerizable double bond, a polyfunctional monomer, and a graft. The type and / or amount of crossover agent is different.

The Tg of the intermediate layer polymer (III-B) alone is preferably in the range of 5 to 100 ° C. A Tg of 5 ° C. or higher is preferable because the heat resistance, scratch resistance and transparency of the acrylic resin composition containing the multilayer polymer (III) are improved. More preferably, it is 10 degreeC or more, Most preferably, it is 15 degreeC or more. Moreover, when Tg is 100 degrees C or less, since a multilayer structure polymer with favorable moldability is obtained, it is preferable. More preferably, it is 70 degrees C or less, Most preferably, it is 50 degrees C or less.
Further, although not particularly limited, the content of the intermediate layer polymer (III-B) in 100% by mass of the multilayer structure polymer (III) is preferably 5 to 35% by mass, more preferably 20% by mass. % Or less. If it is in this range, a function required as an intermediate layer, for example, transparency can be expressed.

The alkyl methacrylate (III-C1) having an alkyl group having 1 to 4 carbon atoms constituting the outermost layer polymer (III-C) may be either linear or branched. Specific examples thereof include methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate and the like. These can be used alone or in admixture of two or more. Of these, methyl methacrylate is preferred.
The alkyl acrylate (III-C2) having an alkyl group having 1 to 8 carbon atoms constituting the outermost layer polymer (III-C) may be either linear or branched. Specific examples thereof include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate and the like. These can be used alone or in admixture of two or more. Of these, preferred are methyl acrylate and n-butyl acrylate.
Other monomers (III-C3) having a copolymerizable double bond constituting the outermost layer polymer (III-C) include lower alkoxy acrylate, cyanoethyl acrylate, acrylamide, acrylic acid, methacrylic acid, etc. Acrylic monomers, styrene, alkyl-substituted styrene, acrylonitrile, methacrylonitrile and the like can be used.

  Moreover, although it does not specifically limit, a chain transfer agent can be used at the time of superposition | polymerization of outermost layer polymer (III-C), and the molecular weight of outermost layer polymer (III-C) can be adjusted. This chain transfer agent is preferably selected from those usually used for radical polymerization, and specific examples thereof include alkyl mercaptans having 2 to 20 carbon atoms, mercapto acids, thiophenol, carbon tetrachloride, and the like. These can be used alone or in admixture of two or more. The content of the chain transfer agent is 0.01 to 5 parts by mass with respect to 100 parts by mass of the monomer component ((III-C1) to (III-C3)) that gives the outermost layer polymer (III-C). Is preferred. More preferably, it is 0.2 mass part or more, Most preferably, it is 0.4 mass part or more.

The Tg of the outermost layer polymer (III-C) alone is preferably 60 ° C. or higher. When the Tg is 60 ° C. or higher, an acrylic resin film having good film properties such as excellent scratch resistance when an acrylic resin composition containing the multilayer polymer (III) is formed into a film can be obtained. preferable. More preferably, it is 80 degreeC or more, Most preferably, it is 90 degreeC or more.
Moreover, although it does not specifically limit, 15-80 mass% is preferable at the point of film physical property, and, as for content of outermost layer polymer (III-C) in 100 mass% of multilayer structure polymer (III), More preferably, it is 45. It is -80 mass%, Most preferably, it is 45-70 mass% or less.

  Details of the preferred production method of the multilayer structure polymer (III) are the same as those of the multilayer structure polymer (I). According to such a production method, the multilayer structure polymer (III) in which the number of particles having a diameter of 55 μm or more present in the acetone dispersion liquid is 0 to 50 per 100 g of the multilayer structure polymer (III) is easily obtained. be able to. Further, the acrylic resin film using the multilayer structure polymer (III) thus obtained as a raw material has the characteristics that the number of fish eyes in the film is small, the appearance is good, and the optical properties are excellent, which is preferable. . More preferably, the number of particles having a diameter of 55 μm or more present in the dispersion when dispersed in acetone is 0-30, more preferably 0-20, per 100 g of the multilayer structure polymer (III). Is a multilayer structure polymer (III).

As the surfactant used in preparing the emulsion, the same surfactants as those shown for the multilayer structure polymer (I) can be used.
The method for preparing the emulsion is also preferably the same method as for the multilayer structure polymer (I).
In addition, as a mixing device for preparing an emulsion prepared by mixing the monomer component that gives the innermost layer polymer (III-A) constituting the multilayer structure polymer (III) with water and a surfactant. Examples thereof include an apparatus used for preparing an emulsion for producing the multilayer structure polymer (I).
Further, the emulsion to be prepared may have either a W / O type or an O / W type dispersion structure, and particularly an O / W type in which monomer component oil droplets are dispersed in water, and oil droplets in a dispersed phase. The diameter is preferably 100 μm or less.
Further, the type of polymerization initiator, specific polymerization method, polymerization temperature and the like are the same as in the case of the multilayer structure polymer (I). As described above, when the multilayer structure polymer (III) is obtained by emulsion polymerization, a chain transfer agent, other polymerization aids, and the like may be used. As the chain transfer agent, known ones can be used, and mercaptans are preferred.
The multilayer structure polymer (III) is recovered from the polymer latex produced by the above-described method. Although it does not specifically limit as a collection | recovery method, Methods, such as salting-out or acid precipitation coagulation | solidification, spray-drying, freeze-drying, are mentioned, It collect | recovers with a powder form.

(Rubber-containing graft copolymer (IV))
The rubber-containing graft copolymer (IV) is for further improving the moldability of the acrylic resin composition, and in the presence of 100 parts by mass of the elastic copolymer, 50 to 100% by mass of alkyl methacrylate, It is obtained by polymerizing 10 to 400 parts by mass of a graft component composed of 0 to 50% by mass of at least one copolymerizable vinyl monomer in at least one stage, and the latex particle size is 0.15 to 0. .5 μm rubber-containing graft copolymer. Here, the elastic copolymer is 100 parts by mass of a vinyl monomer component consisting of 35 to 100% by mass of alkyl acrylate and 0 to 65% by mass of at least one other vinyl monomer copolymerizable therewith. On the other hand, it has a structure of one or more layers obtained by polymerizing 0.1 to 10 parts by mass of the crosslinkable monomer.

As the alkyl methacrylate used for the vinyl monomer component of the elastic copolymer, known alkyl groups having 1 to 8 carbon atoms are used, of which butyl acrylate, 2-ethylhexyl acrylate and the like are preferable.
Moreover, the usage-amount is used in the range of 35-100 mass% in a vinyl monomer component. If it is 35% by mass or less, the elongation of the acrylic resin composition is insufficient, and it may be difficult to form into a film. A preferable use range is 50 to 90% by mass.
As the vinyl monomer component, another copolymerizable vinyl monomer may be used in an amount of 65% by mass or less. Specifically, alkyl methacrylate such as methyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, Styrene, acrylonitrile and the like are preferable, and one or more of them can be used.

The crosslinkable monomer used in the elastic copolymer is not particularly limited, but preferably ethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, propylene glycol diester. Examples include alkylene glycol dimethacrylate such as methacrylate, allyl acrylate, allyl methacrylate, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, diallyl maleate, trimethylolpropane triacrylate, and allyl cinnamate. One or more can be used.
The crosslinkable monomer is used in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of the vinyl monomer component. If the amount is less than 0.1 parts by mass, the amount of the monomer grafted to the elastic copolymer is extremely small, and the moldability when molding the acrylic resin composition may be insufficient. Although it may be used in excess, the effect commensurate with the added amount is not exhibited. A preferable use range is 0.3 to 7 parts by mass.

  The elastic copolymer can have a structure of one layer or two or more layers. When it is set as the structure of two or more layers, content of the alkyl acrylate as a whole of an elastic copolymer should just be 35 mass% or more. For example, in the case of a hard core structure, the content of the first layer alkyl acrylate may be 35% by mass or less.

As the graft component grafted on the elastic copolymer, 50% by mass or more of alkyl methacrylate is used. Specific examples include methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, and the like, and one or more of these can be used. Furthermore, at least one of the other copolymerizable vinyl monomers can be used in an amount of 50% by mass or less, and specific examples thereof include alkyl acrylates such as methyl acrylate, butyl acrylate, and cyclohexyl acrylate, styrene, acrylonitrile, and the like. 1 or more types can be used.
The graft component is used in an amount of 10 to 400 parts by weight, preferably 20 to 200 parts by weight, based on 100 parts by weight of the elastic copolymer, and can be polymerized in at least one stage.

The rubber-containing graft copolymer (IV) is obtained by ordinary emulsion polymerization. In addition, you may use a chain transfer agent, another polymerization adjuvant, etc. at the time of superposition | polymerization. A known chain transfer agent can be used, but mercaptans are preferred.
The latex particle diameter of the rubber-containing graft copolymer is preferably in the range of 0.15 to 0.5 μm. If it is less than 0.15 μm, the moldability when the acrylic resin composition is molded may be insufficient, and if it is 0.5 μm or more, it is difficult to produce the rubber-containing graft copolymer (IV) itself, and the acrylic resin composition When a film is formed from a product, the transparency of the film also tends to deteriorate.

(Thermoplastic polymer (II))
The thermoplastic polymer (II) includes 50 to 100% by mass of a structural unit derived from an alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms, and a structural unit derived from another vinyl monomer copolymerizable therewith. The polymer has a reduced viscosity (measured at 25 ° C. of 0.1 g of polymer dissolved in 100 ml of chloroform) of 0.1 l / g or less.
As the alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms, methyl methacrylate is most preferable.
Examples of other vinyl monomers copolymerizable with alkyl methacrylate having an alkyl group having 1 to 4 carbon atoms include, for example, alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, propyl acrylate, and 2-ethylhexyl acrylate; butyl Examples include alkyl methacrylates such as methacrylate, propyl methacrylate, ethyl methacrylate, and methyl methacrylate; aromatic vinyl compounds such as styrene, α-methylstyrene, and paramethylstyrene; vinylcyan compounds such as acrylonitrile and methacrylonitrile. More than seeds can be used.

The reduced viscosity of the thermoplastic polymer (II) is 0.1 l / g or less. When the reduced viscosity exceeds 0.1 l / g, the fluidity is deteriorated, which is not preferable in terms of moldability of the acrylic resin composition.
The polymerization method for obtaining such a thermoplastic polymer (II) is not particularly limited, and various methods such as a commonly known suspension polymerization method and emulsion polymerization method are applied.
The thermoplastic polymer (II) is industrially available as Mitsubishi Rayon Co., Ltd.'s Dynal BR series and Mitsubishi Rayon Co., Ltd.'s acripet.

As described above, in the present invention, at least one rubber-containing polymer such as the multilayer structure polymer (I), the multilayer structure polymer (III), or the rubber-containing graft copolymer (IV) is used as the acrylic resin. In addition, the use of those further containing the thermoplastic polymer (II) is suitable for forming the surface of the light diffusion plate from the viewpoint of light resistance, transparency, fluidity, etc. When an acrylic resin in which I) or (III) and the thermoplastic polymer (II) are combined is used, the multilayer structure polymer (I) or (III) is used in an amount of 20 to 90 parts by mass, and the thermoplastic polymer (II) Is preferably 80 to 10 parts by mass ((I) + (II) = 100 parts by mass). If the ratio of the multilayer structure polymer (I) or (III) is 20 parts by mass or more, the strength of the acrylic resin molded product tends to be improved, and if it is 90 parts by mass or less, the acrylic resin composition is molded. Workability tends to be good.
Moreover, when using the acrylic resin which combined rubber-containing graft copolymer (IV) and thermoplastic polymer (II), rubber-containing graft copolymer (IV) is 15-99.9 in 100 mass parts of acrylic resins. The ratio of the crosslinked elastic copolymer used in the range of parts by mass and comprising the elastic copolymer and the graft chain contained in the rubber-containing graft copolymer (IV) in 100 parts by mass of the acrylic resin is 12 parts by mass or more. It is preferable that When the ratio of the crosslinked elastic copolymer contained in the acrylic resin is less than 12 parts by mass, the processability when molding the acrylic resin composition tends to be poor.

(Additive)
Acrylic resin compositions can be added to general compounding agents as required, for example, stabilizers, lubricants, processing aids, plasticizers, impact aids, foaming agents, fillers, antibacterial agents, antifungal agents, mold release agents. Agent, ultraviolet absorber.
Among these, particularly when an ultraviolet absorber is added, light resistance can be imparted when the surface of the light diffusing plate is formed, and yellowing of the light diffusing plate and deterioration resulting therefrom can be effectively suppressed.
The molecular weight of the ultraviolet absorber used is preferably 300 or more, particularly preferably 400 or more. The ultraviolet absorber is not particularly limited, but a benzotriazole type having a molecular weight of 400 or more or a triazine type having a molecular weight of 400 or more can be particularly preferably used. Specific examples of the former include Tinuvin of Ciba Specialty Chemicals Co., Ltd. 234, Adeka Stub LA-31 from Asahi Denka Kogyo Co., Ltd., and specific examples of the latter include Tinuvin 1577 from Ciba Specialty Chemicals.

Moreover, as a processing aid added when shape | molding an acrylic resin composition, the thermoplastic polymer (V) shown below is preferable from the point of shaping | molding stabilization.
The thermoplastic polymer (V) is obtained by polymerizing 50 to 100% by mass of methyl methacrylate and 0 to 50% by mass of another vinyl monomer copolymerizable therewith, and the reduced viscosity ( A polymer obtained by dissolving 0.1 g of a polymer in 100 ml of chloroform and measuring it at 25 ° C.) to be 0.2 to 2 l / g. Workability and chemical resistance when molding an acrylic resin composition It is a component that shows an important role for sex.
The reduced viscosity of the thermoplastic polymer (V) is important, and the particularly preferable reduced viscosity is 0.2 to 0.8 l / g.

Other vinyl monomers that can be copolymerized with methyl methacrylate used for the production of the thermoplastic polymer (V) include alkyl acrylates having an alkyl group having 1 to 8 carbon atoms, and those having 2 to 4 carbon atoms. Examples thereof include alkyl methacrylate having an alkyl group, aromatic vinyl compound, vinyl cyanide compound and the like.
The alkyl acrylate having an alkyl group having 1 to 8 carbon atoms may be linear or branched. Specific examples thereof include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and n-octyl. An acrylate etc. are mentioned.
The alkyl methacrylate having an alkyl group having 2 to 4 carbon atoms may be either linear or branched, and specific examples thereof include ethyl methacrylate, propyl methacrylate, butyl methacrylate and the like.
Examples of the aromatic vinyl compound include styrene, α-substituted styrene, nucleus-substituted styrene and derivatives thereof, for example, α-methylstyrene, chlorostyrene, vinyltoluene and the like.
Examples of the vinylcyan compound include acrylonitrile and methacrylonitrile.

Examples of the polymerization initiator used in the production of the thermoplastic polymer (V) include ordinary inorganic initiators such as persulfates, organic peroxides, azo compounds, and the like. Further, these compounds and sulfites, hydrogen sulfites, thiosulfates, first metal salts, sodium formaldehyde sulfoxylate and the like can be used in combination as redox initiators.
Preferred persulfates as the polymerization initiator include sodium persulfate, potassium persulfate, ammonium persulfate and the like. Examples of the organic peroxide include t-butyl hydroperoxide, cumene hydroperoxide, benzoyl peroxide, lauroyl peroxide, and the like.

The molecular weight and molecular weight distribution of the thermoplastic polymer (V) are important factors for the processability imparting effect. Therefore, when the thermoplastic polymer (V) is produced, an appropriate chain transfer is performed depending on the purpose. Agents can be used.
The polymerization can be carried out under normal emulsion polymerization conditions at a temperature equal to or higher than the decomposition temperature of the polymerization initiator, and can be polymerized in one or more stages depending on the purpose. The polymer can usually be recovered in the form of a powder after salting out or acidifying solidification, followed by filtration and washing with water, or by spray drying and freeze drying.
The thermoplastic polymer (V) is industrially available as Metablene P manufactured by Mitsubishi Rayon Co., Ltd.

  The blending amount of the thermoplastic polymer (V) is, for example, one of a multilayer structure polymer (I), a multilayer structure polymer (III), a rubber-containing polymer (IV), and a thermoplastic polymer (II). 0.1-10 mass parts is preferable with respect to 100 mass parts of acrylic resins using the above. When the blending amount of the thermoplastic polymer (V) is less than 0.1 parts by mass, molding stability such as film-forming stability when the acrylic resin composition is molded into a film tends to be insufficient. Here, the film-forming stability means that a film having a uniform thickness is stably produced. On the other hand, when the compounding quantity of a thermoplastic polymer (V) exceeds 10 mass parts, it exists in the tendency for the melt viscosity at the time of shape | molding an acrylic resin composition to rise, and for a moldability to fall. Furthermore, the compounding quantity of a preferable thermoplastic polymer (V) is 0.5-5 mass parts.

As methods for adding these additives, a method of supplying an acrylic resin composition together with an acrylic resin when molding an acrylic resin composition, and a method of kneading and mixing a mixture obtained by adding an additive to an acrylic resin in advance with various kneaders There is. Examples of the kneader used in the latter method include ordinary single screw extruders, twin screw extruders, Banbury mixers, roll kneaders, and the like.
In addition, when performing melt-kneading here, it is preferable to select an antistatic agent that does not decompose at the melt-kneading temperature with the acrylic resin.

[Acrylic resin molding]
By molding the acrylic resin composition described above into a film or sheet, an acrylic resin molded body can be produced.
In particular, on the surface of the light diffusing plate, it is preferable to provide an acrylic resin film as a protective layer of the acrylic resin molded body, and as a specific method of film molding, a known melt casting method, T-die method, Examples thereof include a melt extrusion method such as an inflation method. Of these, the T-die method is most preferable in terms of economy.
The thickness of the acrylic resin film suitable for the protective layer is 10 to 500 μm in terms of film properties and processability. When the thickness is from 10 to 500 μm, the film has an appropriate rigidity, so that the laminating property, the secondary workability, etc. are facilitated, and the film forming property is stabilized and the production of the film is facilitated. More preferably, it is 15-200 micrometers, More preferably, it is 30-200 micrometers.

[Light diffusing plate, backlight unit, and liquid crystal display]
The light diffusion plate of the present invention is disposed on the light emitting surface of a light source such as a cold cathode tube in a backlight unit of a liquid crystal display device, for example, and diffuses light from the light source. The surface is formed with the composition. As a more preferable form, an acrylic resin film is laminated on the light diffusion plate body as a protective layer. The protective layer is laminated on at least one surface of the light diffusing plate body. Preferably, when the protective layer is laminated on both surfaces, that is, both the light source side surface and the liquid crystal side surface, it is possible to further suppress a decrease in luminance of the light diffusing plate. .
The backlight unit is schematically configured to include a light source composed of a cold cathode tube, a reflection plate that reflects light from the light source, and a light diffusion plate that diffuses light from the light source. Side type and direct type. The backlight unit of the present invention may be either a side type or a direct type. However, when the light diffusion plate of the present invention is employed in a direct type backlight unit capable of exhibiting particularly high brightness, it can be applied to a light diffusion plate such as dust. Adhesion can be prevented, luminance reduction can be suppressed, and higher luminance can be expressed.
In addition, a liquid crystal display device including such a backlight unit and a liquid crystal layer can maintain the color tone and light emission quality in a color liquid crystal display for a long time.

The material of the light diffusing plate body is not particularly limited, and is preferably a sheet-like or plate-like material that is transparent, has a high light transmittance, a low birefringence, and can be easily laminated with an acrylic resin film.
Examples thereof include methacrylic resin, polycarbonate resin, MS resin (methyl methacrylate-styrene resin), polystyrene resin, polyvinyl chloride resin, polyester resin, and cyclic polyolefin resin. Among these, methacrylic resins and polycarbonate resins having particularly high light transmittance are preferable.
In addition, these resins may contain a transparent, light-resistant, heat-resistant, and moisture-resistant material that has high light diffusibility when used as beads, that is, a light diffusing agent, if necessary. Examples of light diffusing agents include acrylic resins, styrene resins, polyester resins, melamine resins, silicone resins, epoxy resins, urethane resins, polyethylene resins, nylon resins, norbornene resins, cyclohexane resins, vinyl chloride resins, and the like. Or organic substances such as crystalline silica, glass, lithium fluoride, calcium carbonate, and barium sulfate.

  As a method for producing a light diffusing plate having a surface formed of an acrylic resin composition, for example, a coextrusion method such as a coextrusion T-die method or a coextrusion lamination method is used for the surface of the light diffusing plate main body. And a method of laminating the acrylic resin composition. In addition, an acrylic resin film is first formed, and this is laminated on the light diffusing plate body appropriately using a known method such as a film lamination method such as dry lamination or thermal lamination, or a coating method such as coating a resin solution. May be. Among these, a coextrusion method and a film lamination method are preferable, and a film lamination method is particularly preferable because a light diffusion plate having a simple apparatus and a stable quality can be obtained easily and continuously.

The light diffusion plate thus obtained has a surface resistance value of 1 × 10 1 after being left for 500 hours in a 60 ° C., 95% RH environment or 80 ° C., DRY environment. and more preferably it is to maintain ¹³ Omega. If such a surface resistance value is maintained, adhesion of dust or the like is suppressed for a long period of time, and the light emission quality of the liquid crystal display device provided with the light diffusion plate can be maintained for a long period of time.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, these are only illustrations and this invention is not limited to these.
In the examples and comparative examples, “part” represents “part by mass”, and “%” represents “% by mass”. Abbreviations in the reference examples are as follows.
Methyl methacrylate MMA
Methyl acrylate MA
Butyl acrylate BA
Styrene St
Allyl methacrylate AMA
1,3-butylene glycol dimethacrylate 1.3BD
t-Butyl hydroperoxide tBH
Cumene hydroperoxide CHP
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.]
Emulsifier (2): sodium hydroxide partial neutralized product of 40% mono (polyoxyethylene nonylphenyl ether) phosphoric acid and 60% di (polyoxyethylene nonylphenyl ether) phosphoric acid [trade name Phosphanol LO529, Toho Chemical Co., Ltd.]

[Production Example 1] Production of light diffusing plate main body Polycarbonate resin having viscosity average molecular weight of 24,300 obtained from bisphenol A and phosgene was added to infusible acrylic polymer fine particles (Paraloid EXL-5136 manufactured by Rohm and Haas Company). , Mass distribution average particle size: 7 μm) is added and mixed, and by a T-die extruder with a vent, the extruder temperature is 250 to 300 ° C., the die temperature is 260 to 300 ° C., and the vacuum degree of the vent portion is 26.6 kPa. Then, a polycarbonate resin light diffusion plate body having a thickness of 2 mm and a width of 1,000 mm was melt extruded.

[Examples 1 to 3, Comparative Examples 1 and 2]
(Manufacture of multilayer structure polymer (H-1))
The multilayer structure polymer (H-1) corresponds to the “multilayer structure polymer (III)” described above, and the following two-layer crosslinked rubber elastic body is the “innermost layer polymer (III-)” described above. A) ".
First, 8.5 parts of ion-exchanged water was charged into a container equipped with a stirrer, and then the monomer component consisting of (I) shown below was added and stirred and mixed. Next, 1.1 parts of the emulsifier (1) was added to the vessel while stirring, and stirring was continued again for 20 minutes to prepare an emulsion (N-1). The average particle size of the dispersed phase in the obtained emulsion was 10 μm.
On the other hand, 186.5 parts of ion-exchanged water is put into a polymerization vessel equipped with a cooler, the temperature is raised to 70 ° C., and a mixture prepared by adding (II) shown below to 5 parts of ion-exchanged water is added all at once. did. Next, the emulsion (N-1) was dropped into the polymerization vessel over 8 minutes while stirring under nitrogen, and then the reaction was continued for 15 minutes to complete the polymerization of the innermost layer polymer (A-1). Here, the Tg of the innermost layer polymer (A-1) alone was -48 ° C.
Then, after adding the monomer component which consists of (III) shown below in 90 minutes, reaction was continued for 60 minutes and the two-layer crosslinked rubber elastic body containing a crosslinked elastic polymer (B-1) was obtained. . Here, the Tg of the crosslinked elastic polymer (B-1) alone was -48 ° C.
Subsequently, a mixture of (IV) shown below was dropped into the polymerization vessel over 45 minutes, and then the reaction was continued for 60 minutes to form an intermediate layer (D-1).
Subsequently, after dropping the monomer component consisting of (V) into the polymerization vessel over 140 minutes, the reaction is continued for 60 minutes to form the outermost layer polymer (C-1), and the multilayer structure polymer (H- The polymer latex of 1) was obtained. Here, the Tg of the outermost layer polymer (C-1) alone was 84 ° C.
The mass average particle diameter measured after polymerization was 0.12 μm.

(I) MMA 0.3 part
BA 4.5 parts
1.3BD 0.2 parts
AMA 0.05 parts
CHP 0.025 part (II) Sodium formaldehyde sulfoxylate 0.2 part
Ferrous sulfate 0.0001 parts
EDTA 0.0003 part (III) MMA 1.5 part
22.5 parts of BA
1.3BD 1.0 part
AMA 0.25 part
CHP 0.016 parts (IV) MMA 6 parts
BA 4 parts
AMA 0.075 parts
CHP 0.0125 part (V) MMA 55.2 parts
4.8 parts of BA
nOM 0.204 parts
0.08 parts tBH

The polymer latex of the obtained multilayer structure polymer (H-1) is filtered using a vibration type filtration device in which a SUS mesh (average opening 62 μm) is attached to the filter medium, and then an aqueous solution containing 3 parts of calcium acetate. The solution was poured into the solution, salted out, washed with water, separated and recovered, and then dried to obtain a powdery multilayer structure polymer (H-1).
The gel content of the multilayer structure polymer (H-1) was 60%. Further, when the multilayer structure polymer (H-1) was dispersed in acetone, the number of particles having a diameter of 55 μm or more present in the dispersion was 18.

(Manufacture of acrylic resin composition)
Next, 100 parts of multilayer structure polymer (H-1), 2.1 parts of “ADK STAB LA-31RG” manufactured by Asahi Denka Co., Ltd. as an ultraviolet absorber, “ADK STAB AO— manufactured by Asahi Denka Co., Ltd. as an antioxidant. 0.1 part of 50 ", 0.3 part of" Adekastab LA-57 "manufactured by Asahi Denka Co., Ltd. as a hindered amine light stabilizer," Riquemar S100A "manufactured by Riken Vitamin Co., Ltd. as an antistatic agent, manufactured by Kao Corporation "Electro stripper TS-5" and "MOA215" manufactured by Takemoto Yushi Co., Ltd. were added in the blending amounts shown in Table 1 and then mixed using a Henschel mixer, and the resulting mixture was heated to 230 ° C and deaerated. Was supplied to a machine (TEM-35B manufactured by Toshiba Machine Co., Ltd.) and kneaded to obtain pellets.

(Manufacture of light diffusion plate)
The pellets produced by the above method were dried at 80 ° C. all day and night, and the dried pellets were supplied to a 40 mmφ non-vent screw type extruder (L / D = 26) equipped with a 300 mm wide T-die. An acrylic resin film was produced. The conditions at that time were a cylinder temperature of 200 ° C. to 240 ° C., a T die temperature of 250 ° C., and a cooling roll temperature of 70 ° C. And the obtained acrylic resin film was heat laminated at 140 degreeC on the single side | surface of the light-diffusion board main body, and the light-diffusion board was obtained.
Table 1 shows the surface resistance value, total light transmittance, tensile elastic modulus measurement results of the obtained acrylic resin film, antistatic performance durability, dust adhesion, and light resistance (degree of discoloration after exposure test) of the light diffusion plate. Shown in
Various evaluation methods and measurement methods are shown below.

1) Mass average particle diameter of multilayer structure polymer and rubber-containing polymer For polymer latex obtained by emulsion polymerization, a light scattering photometer DLS-700 manufactured by Otsuka Electronics Co., Ltd. was used. Measured and determined.
2) Gel content rate of multilayer structure polymer and rubber-containing polymer Each weighed polymer was subjected to extraction treatment under reflux in an acetone solvent, and this extraction treatment liquid was fractionated by centrifugation. Subsequently, after drying the obtained solid content, mass measurement (mass after extraction) was carried out and it calculated | required with the following formula | equation.
Gel content rate (%) = (mass before extraction (g) −mass after extraction (g)) / mass before extraction (g)
3) Total light transmittance of acrylic resin film It evaluated based on JISK7361-1.
4) Tensile elastic modulus of acrylic resin film It evaluated based on JISK7127.
5) Surface resistance value of acrylic resin film In accordance with JIS K 6911, the obtained acrylic resin film was left in a state of 23 ° C. and 50% RH for 24 hours and then super-insulated in the same atmosphere under an applied voltage of 500V. The surface resistance value was measured and calculated using a meter (SM-10E type manufactured by Toa Denpa Kogyo Co., Ltd.).
6) Antistatic performance durability of light diffusion plate (endurance test)
The obtained light diffusing plate was allowed to stand for 500 hours in an environment of 60 ° C., 95% RH and 80 ° C., DRY, and then the surface resistance value of the light diffusing plate was measured and calculated, and evaluated according to the following criteria.
○: Less than 1 × 10 ¹³ Ω △: 1 × 10 ¹³ Ω or more and less than 1 × 10 ¹⁵ ×: 1 × 10 ¹⁵ Ω or more 7) Dust adhesion of light diffusion plate The obtained light diffusion plate is kept indoors for two months. It was hung and the degree of dust adhesion was visually evaluated according to the following criteria.
○: Dust adhesion is hardly seen ×: Dust adheres and the light diffusing plate appears cloudy 8) Light resistance of the light diffusing plate The conditions of the surface of the light diffusing plate formed of the acrylic resin composition are as follows: Then, the cold-cathode tube was actually exposed and the degree of discoloration of the light diffusion plate was evaluated. A mark with no discoloration is indicated with a circle, and a mark with no mark is indicated with a cross.
Cold cathode tube actual exposure conditions Cold cathode tube: φ2.6 lamp Lamp current: 8 mA, 3 in parallel.
Atmospheric temperature: 23 ° C, 50RH%
Lamp-sample surface distance: 1.4mm (design value)
Sample surface temperature: about 50 ° C Exposure period: 6 months

[Example 4]
(Production of multilayer structure polymer (L-1))
The multilayer structure polymer (L-1) corresponds to the “multilayer structure polymer (I)” described above.
195 parts of ion exchange water was charged into a reaction vessel equipped with a cooler, the temperature was raised to 70 ° C., and a mixture prepared by adding (LL1) shown below to 5 parts of ion exchange water was added all at once. Next, while stirring under nitrogen, a first monomer component consisting of (LL2) shown below was dropped into the reaction vessel over 8 minutes, and then the reaction was continued for 15 minutes, whereby the innermost polymer (L- 1-A) was obtained. Here, Tg of the innermost layer polymer (L-1-A) was 13 ° C.
Subsequently, the second monomer component consisting of (LL3) shown below is added to the polymerization vessel over 90 minutes, and then the reaction is continued for 60 minutes to contain the first intermediate layer layer containing the cross-linked elastic polymer. The union (L-1-B) was obtained. Here, Tg of the first intermediate layer polymer (L-1-B) was −40 ° C.
Subsequently, the third monomer component (LL4) shown below was dropped into the polymerization vessel over 30 minutes, and then the reaction was continued for 60 minutes to obtain the second intermediate layer polymer (L-1-C). ) Was formed.
Next, after dropping the fourth monomer component (LL5) shown below into the polymerization vessel over 130 minutes, the reaction is continued for 60 minutes to obtain the outermost layer polymer (L-1-D). An acrylic resin latex containing the multilayer structure polymer (L-1) was obtained. Here, Tg of the outermost layer polymer (L-1-D) was 94 ° C. The mass average particle diameter measured after polymerization was 0.09 μm.
The polymer latex of the obtained multilayer structure polymer (L-1) was filtered in the same manner as in Example 1, and then salted out in an aqueous solution containing 3 parts of calcium acetate, washed and recovered, dried. A powdery multilayer structure polymer (L-1) was obtained.
The gel content of the obtained multilayer structure polymer (L-1) was 70%. Further, when the multilayer structure polymer (L-1) was dispersed in acetone, the number of particles having a diameter of 55 μm or more present in the dispersion was 8.

(LL1) Sodium formaldehyde sulfoxylate 0.10 parts
Ferrous sulfate 0.0002 parts
EDTA 0.0006 parts (LL2) MMA 2.3 parts
2.13 parts of BA
St 0.37 parts
1.3BD 0.2 parts
CHP 0.01 parts
Emulsifier (1) 1.3 parts (LL3) BA 24.54 parts
St 4.26 parts
1.3BD 1.2 parts
AMA 0.225 parts
CHP 0.03 part (LL4) MMA 6 parts
3.28 parts of BA
St 0.72 parts
AMA 0.15 parts
CHP 0.02 part (LL5) MMA 52.25 parts
BA 2.26 parts
St 0.49 parts
nOM 0.193 parts
tBH 0.055 parts

(Manufacture of acrylic resin composition)
Next, 50 parts of the multilayer structure polymer (L-1), 50 parts of Dianal BR-75 (manufactured by Mitsubishi Rayon Co., Ltd., reduced viscosity 0.057 l / g) as the thermoplastic polymer, Asahi Denka as the UV absorber "Adekastab LA-31RG" manufactured by Co., Ltd. 1.5 parts, Ciba Specialty Chemicals Co., Ltd. "Irganox 1076" 0.1 parts as an antioxidant, Asahi Denka Co., Ltd. as a hindered amine light stabilizer 0.2 part of “ADK STAB LA-57”, 1 part of “Rikemar S100A” manufactured by Riken Vitamin Co., Ltd. as an antistatic agent, 1 part of “Electro Stripper TS-5” manufactured by Kao Co., Ltd. “ After adding 1 part of MOA215 ", the mixture was mixed using a Henschel mixer, and the resulting mixture was supplied to a degassing extruder (TEM-35B manufactured by Toshiba Machine Co., Ltd.) heated to 230 ° C. And kneaded to obtain pellets.

(Manufacture of light diffusion plate)
The pellet produced by the above method was processed in the same manner as in Example 1 to produce an acrylic resin film having a thickness of 75 μm. Moreover, the obtained acrylic resin film was laminated | stacked on the light diffusing plate main body like Example 1. FIG.
Table 1 shows various evaluations and measurement results of the obtained acrylic resin film and light diffusion plate.

[Example 5]
(Production of rubber-containing graft copolymer (I-2))
The rubber-containing graft copolymer (I-2) corresponds to the “rubber-containing graft copolymer (IV)” described above.
Under a nitrogen atmosphere, 244 parts of deionized water was placed in a reaction vessel equipped with a reflux condenser, and the temperature was raised to 80 ° C. Then, (15) shown below was added, and while stirring, 1/15 of the raw material (b) for the innermost polymer inner layer (I-2-A ₁ ) shown below was charged and held for 15 minutes. . Next, the remaining raw material (b) was continuously added at an increase rate of 8% / hour of the monomer component [raw material (b)] with respect to water, and then held for 60 minutes, and the innermost polymer inner layer ( A latex of I-2-A ₁ ) was obtained. The Tg of the innermost polymer inner layer (I-2-A ₁ ) alone was 24 ° C.
Subsequently, 0.6 parts of sodium formaldehyde sulfoxylate was added to the latex and held for 15 minutes. Then, while stirring at 80 ° C. under a nitrogen atmosphere, the raw material (c) for the innermost layer polymer outer layer (I-2-A ₂ ) shown below is used as a monomer component [raw material (c)] for water. After the continuous addition at an increase rate of 4% / hour, the innermost layer polymer outer layer (I-2-A ₂ ) was polymerized by holding for 120 minutes to polymerize the innermost layer polymer (I-2- A latex of A) was obtained. The Tg of the innermost polymer outer layer (I-2-A ₂ ) alone was −38 ° C.
Subsequently, 0.4 parts of sodium formaldehyde sulfoxylate was added to the latex and held for 15 minutes. Then, while stirring at 80 ° C. in a nitrogen atmosphere, the raw material (d) for the outermost layer polymer (I-2-C) shown below is increased by the monomer component [raw material (d)] with respect to water. After continuously adding at 10% / hour, holding for 60 minutes, the outermost layer polymer (I-2-C) is polymerized to obtain a polymer latex of the rubber-containing polymer (I-2). It was. The Tg of the outermost layer polymer (I-2-C) alone was 99 ° C. The mass average particle diameter of the rubber-containing polymer (I-2) measured after the polymerization was 0.28 μm.
The polymer latex of the rubber-containing polymer (I-2) obtained was filtered using a vibration type filtration device in which a SUS mesh (average opening 150 μm) was attached to the filter medium, and then an aqueous solution containing 3 parts of calcium acetate. Salting out was carried out, recovered by washing with water, and then dried to obtain a powdery rubber-containing polymer (I-2). The resulting rubber-containing graft copolymer (I-2) had a gel content of 90%.

(B) Sodium formaldehyde sulfoxylate 0.6 part Ferrous sulfate 0.00012 part EDTA 0.0003 part (b) MMA 22.0 parts nBA 15.0 parts St 3.0 parts AMA 0.4 parts 1 .3BD 0.14 part tBH 0.18 part Emulsifier (2) 1.0 part (c) nBA 50.0 part St 10.0 part AMA 0.4 part 1.3BD 0.14 part tBH 0.2 part Emulsifier (2) 1.0 part (d) MMA 57.0 parts MA 3.0 parts nOM 0.3 parts tBH 0.06 parts

(Manufacture of acrylic resin composition)
Next, 16 parts of rubber-containing polymer (I-2), 84 parts of Acripet MD (manufactured by Mitsubishi Rayon Co., Ltd., reduced viscosity 0.057 l / g) as the thermoplastic polymer, Asahi Denka Co., Ltd. as the ultraviolet absorber ) “Adeka Stub LA-31RG” 1.0 part manufactured by Asahi Denka Co., Ltd. “Adeka Stub AO-60” 0.1 part as an antioxidant, Asahi Denka Co., Ltd. “Adeka Stub LA-31” 67 "0.15 part, 2 parts" Metbrene P-551A "manufactured by Mitsubishi Rayon Co., Ltd. as a film-forming improver, 0.8 part" Metbrene L-1000 "manufactured by Mitsubishi Rayon Co., Ltd. as an antistatic agent, Antistatic agent After adding 1 part of “Rikemar S100A” manufactured by Riken Vitamin Co., Ltd., 1 part of “Electro Stripper TS-5” manufactured by Kao Co., Ltd., and 1 part of “MOA215” manufactured by Takemoto Yushi Co., Ltd. The resultant mixture was supplied to a degassing extruder (TEM-35B manufactured by Toshiba Machine Co., Ltd.) heated to 230 ° C. and kneaded to obtain pellets.

(Manufacture of light diffusion plate)
The pellet produced by the above method was processed in the same manner as in Example 1 to produce an acrylic resin film having a thickness of 125 μm. Moreover, the obtained acrylic resin film was laminated | stacked on the light-diffusion board main body like Example 1, and the light-diffusion board was obtained.
Table 1 shows various evaluations and measurement results of the obtained acrylic resin film and light diffusion plate.

[Example 6]
(Production of multilayer structure polymer (Y-1))
The multilayer structure polymer (Y-1) corresponds to the “multilayer structure polymer (III)” described above, and the crosslinked rubber elastic body described below is the “innermost layer polymer (III-A)” described above. Is equivalent to.
First, after charging 10.8 parts of deionized water in a container equipped with a stirrer, a monomer component consisting of (YY1) shown below was added and stirred and mixed at room temperature. Next, 1.3 parts of emulsifier (1) was added to the vessel while stirring, and stirring was continued again for 20 minutes to prepare an emulsion.
Next, 139.2 parts of deionized water is charged into a polymerization vessel equipped with a condenser, the temperature is raised to 75 ° C., and a mixture prepared by adding (YY2) shown below to 5 parts of ion-exchanged water is added to the mixture. A batch was charged into the polymerization vessel. Next, the emulsion was dropped into the polymerization vessel over 8 minutes while stirring under nitrogen, and then the reaction was continued for 15 minutes to complete the polymerization to obtain the innermost layer polymer (Y-1-A1).
Subsequently, a monomer component consisting of (YY3) shown below was dropped into the polymerization vessel over 90 minutes, and then the reaction was continued for 60 minutes to obtain a crosslinked rubber elasticity containing a crosslinked elastic polymer (Y-1-A2). Got the body. Here, the Tg of the innermost layer polymer (Y-1-A1) alone was −48 ° C., and the Tg of the crosslinked elastic polymer (Y-1-A2) alone was −10 ° C.
Subsequently, a monomer component consisting of (YY4) shown below was dropped into the polymerization vessel over 45 minutes, and then the reaction was continued for 60 minutes to form an intermediate layer polymer (Y-1-B). Here, the Tg of the intermediate layer polymer (Y-1-B) alone was 60 ° C.
Next, after dropping the monomer component consisting of (YY5) shown below into the polymerization vessel over 140 minutes, the reaction is continued for 60 minutes to form the outermost layer polymer (Y-1-C). A polymer latex of the polymer (Y-1) was obtained. Here, the Tg of the outermost layer polymer (Y-1-C) alone was 99 ° C. The mass average particle diameter measured after polymerization was 0.11 μm.
The polymer latex of the obtained multilayer structure polymer (Y-1) is filtered by the same method as in Example 1, and then salted out in an aqueous solution containing 3.5 parts of calcium acetate, washed with water, recovered and dried. As a result, a powdery multilayer structure polymer (Y-1) was obtained. The resulting multilayer structure polymer (Y-1) had a gel content of 70%. Further, when the multilayer structure polymer (Y-1) was dispersed in acetone, the number of particles having a diameter of 55 μm or more present in the dispersion was 20.

(YY1) MMA 0.3 part
4.45 parts of BA
1.3BD 0.2 parts
AMA 0.05 parts
CHP 0.025 part (YY2) sodium formaldehyde sulfoxylate 0.20 part
Ferrous sulfate 0.0001 parts
EDTA 0.0003 parts (YY3) MMA 9.5 parts
14.25 parts of BA
1.3BD 1.0 part
AMA 0.25 part
CHP 0.016 parts (YY4) MMA 5.96 parts
MA 3.97 parts
AMA 0.07 parts
CHP 0.0125 part (YY5) MMA 57 parts
MA 3 parts
nOM 0.264 parts
0.075 parts tBH

(Manufacture of acrylic resin composition)
Next, 75 parts of multilayer structure polymer (Y-1), Acrypet VH (manufactured by Mitsubishi Rayon Co., Ltd., reduced viscosity 0.059 l / g) as a thermoplastic polymer, and Ciba Specialty as an antioxidant. 0.1 part of “Irganox 1076” manufactured by Chemicals Co., Ltd., 1.4 parts of “Cinuvin 234” manufactured by Ciba Specialty Chemicals Co., Ltd. as an ultraviolet absorber, “Asahi Denka Co., Ltd.” manufactured by Asahi Denka Co., Ltd. 0.3 parts of ADK STAB LA-67, 1 part of “Rikemar S100A” manufactured by Riken Vitamin Co., Ltd. as an antistatic agent, 1 part of “Electro Stripper TS-5” manufactured by Kao Co., Ltd. “MOA215” manufactured by Takemoto Yushi Co., Ltd. After adding 1 part, the mixture was mixed using a Henschel mixer, and the resulting mixture was heated to 230 ° C. (Toshiba Machine Co., Ltd. TEM-35) Supplied to), it was kneaded to obtain pellets.

(Manufacture of light diffusion plate)
The pellets produced by the above method were dried at 80 ° C. for a whole day and night and processed by the same method as in Example 1 to produce an acrylic resin film having a thickness of 50 μm. Moreover, the obtained acrylic resin film was laminated | stacked on the light-diffusion board main body like Example 1, and the light-diffusion board was obtained.
Table 1 shows various evaluations and measurement results of the obtained acrylic resin film and light diffusion plate.

From the examples and comparative examples, the following became clear.
It was suggested that the light diffusing plate of each example hardly adheres to dust and suppresses a decrease in luminance. It was also suggested that the antistatic performance was excellent and that dust adhesion was prevented for a long time. Therefore, it was clarified that the acrylic resin composition and the light diffusion plate of the examples have high industrial utility value.

Claims (5)

An acrylic resin composition that forms the surface of the light diffusing plate,
An acrylic resin composition characterized in that a surface resistance value in accordance with JIS K 6911 of an acrylic resin molded body made of the acrylic resin composition is less than 1 × 10 ¹³ Ω.   An acrylic resin molded body comprising the acrylic resin composition according to claim 1.   A light diffusing plate comprising the acrylic resin molded body according to claim 2 on a surface thereof.   A backlight unit comprising the light diffusing plate according to claim 3. A liquid crystal display device comprising the backlight unit according to claim 4.