JP2007204535A - Light-diffusing styrene-based resin composition and molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a light-diffusing styrene-based resin composition having an excellent light diffusion transmittance, slight warpage by water absorption and excellent heat resistance. <P>SOLUTION: The light-diffusing styrene-based resin composition comprises 100 pts.wt of a styrene-based monomer-(meth)acrylic acid-based monomer-based copolymer (A) composed of 90-99 wt.% of a styrene-based monomer and 1-10 wt.% of a (meth)acrylic acid-based monomer and 0.1-10 pts.wt. of an organic crosslinked particle (B) having an absolute value difference of refractive index between the organic crosslinked particle and the styrene-based monomer-(meth)acrylic acid-based monomer-based copolymer (A) of 0.04-0.12 and 1.0-10μm weight-average particle diameter. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light diffusing composition used in lighting fixtures, electric signboards, and liquid crystal display devices.

  In direct light source devices such as lighting fixtures, electric signboards, and liquid crystal display devices, a milky white resin plate called a diffusion plate is laid to scatter light from the light source. Many of them use acrylic resin plates because of their excellent optical properties, and methods for blending fine particles having different refractive indexes in order to scatter light have been studied. Patent Document 1 includes a technique for blending 1 to 10 μm fine particles, Patent Document 2 includes a technique for blending 10 to 50 μm fine particles, and Patent Document 3 includes 1 to 6 μm silicone resin fine particles and 1 to 7 μm fine particles. Technology that uses inorganic powder together, Patent Document 4 includes a technique that uses a cross-linked resin fine particle of less than 5 μm and a cross-linked resin fine particle of 5 to 10 μm, Patent Document 5 includes a technique that incorporates a light diffusing agent of 1 to 20 μm, etc. In order to improve the diffusion performance of the diffusing plate, many studies have been made on blending various light diffusing agents.

  Further, with the recent increase in size of liquid crystal televisions, there is a problem that the diffusion plate is warped while a direct backlight is used in the liquid crystal television. Acrylic resin used as a diffuser has high water absorption, so when used in a direct type backlight device, due to its structure, one side is close to the light source lamp and exposed to the heat of the light source lamp, so it is dry. On the other hand, since the opposite surface is in an environment that easily absorbs water, a problem has been pointed out that the board warps due to the difference in water absorption between the front and back of the board. In addition to increasing the brightness of the light source, studies have been made to further reduce the distance between the light source lamp and the diffusion plate in order to reduce the thickness and increase the brightness. Due to insufficient heat resistance, the diffusion plate may be deformed depending on the usage conditions. There was a problem. Thus, Patent Document 6 discloses a light guide plate using a copolymer composed of an unsaturated carboxylic acid monomer and an aromatic vinyl monomer, but no technical disclosure regarding the diffusion plate has been made. Neither is it satisfactory in strength.

Japanese Patent Publication No. 60-021662 JP-A-60-139758 Japanese Patent No. 2512544 JP-A-11-060966 JP 2004-050607 A JP 2005-215370 A

  An object of the present invention is to provide a light diffusing styrenic resin composition that has good light diffusivity and water absorption properties and heat resistance.

As a result of sincerity studies to solve the above problems, the present inventors have found that a styrene-based monomer- (meth) acrylic acid-based monomer copolymer having a specific range of monomer composition has a specific range of refractive index. The present inventors have found that the above problems can be solved by dispersing organic crosslinked particles having a weight average particle diameter, and have completed the present invention.
That is, the present invention relates to a styrene monomer- (meth) acrylic acid monomer copolymer comprising 90 to 99% by weight of a styrene monomer and 1 to 10% by weight of a (meth) acrylic acid monomer. The absolute value difference in refractive index with the styrene monomer- (meth) acrylic acid monomer copolymer (A) is 0.04 to 0.12 with respect to 100 parts by weight of the coalescence (A). Further, the present invention relates to a light diffusing styrenic resin composition comprising 0.1 to 10 parts by weight of organic crosslinked particles (B) having a weight average particle diameter of 1.0 to 10 μm. The styrene monomer- (meth) acrylic acid monomer copolymer (A) is composed of 95.5 to 99% by weight of styrene monomer and (meth) acrylic monomer 1-4. It is preferably 5% by weight. Moreover, it is preferable that the polystyrene conversion weight average molecular weight Mw measured by the gel permeation chromatography of the styrene monomer- (meth) acrylic acid monomer copolymer (A) is 16 to 350,000.

  The light diffusing styrenic resin composition of the present invention has good light diffusibility and excellent water absorption characteristics and heat resistance, so that warpage due to difference in water absorption is small and has the effect of suppressing deformation due to heat. . And the molded object obtained by shape | molding this composition can be used suitably for a lighting fixture, an electric signboard, and a liquid crystal display device.

The present invention will be described in detail below.
The styrene monomer used in the present invention is an aromatic vinyl monomer, and examples thereof include styrene, α-methyl styrene, p-methyl styrene, pt-butyl styrene, and the like. May be. Of these, styrene is preferred because of its excellent reaction with (meth) acrylic acid. Examples of the (meth) acrylic acid monomer include acrylic acid and methacrylic acid, and methacrylic acid is preferred from the viewpoint of ease of production of the copolymer.
Moreover, you may use the other copolymerizable monomer for these monomers as needed in the range which does not impair the objective of this invention. Examples of other copolymerizable monomers used here include (meth) acrylate monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and maleic anhydride. Acid, anhydride group-containing monomers such as itaconic anhydride, dicarboxylic acid imide group-containing monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide, and N-cyclohexylmaleimide, carboxyls such as maleic acid and itaconic acid And group-containing monomers.

The (meth) acrylic acid unit in the copolymer (A) of the present invention is 1 to 10% by weight. Preferably it is 1 to 4.5 weight%. When the (meth) acrylic acid unit in the copolymer exceeds 10% by weight, the water-absorbing property is inferior, the viscosity of the melt is increased, and the workability is lowered. May be produced in a large amount, which is not preferable. On the other hand, if it is less than 1% by weight, the effect of improving the heat resistance of the copolymer is insufficient, which is not preferable.
The polystyrene-reduced weight average molecular weight Mw measured by gel permeation chromatography of the styrene monomer- (meth) acrylic acid monomer copolymer (A) of the present invention is 16 to 350,000. preferable. More preferably, it is 180,000 to 300,000. When Mw exceeds 350,000, the viscosity of the melt is increased, and workability is extremely lowered, which is not preferable. On the other hand, when it is less than 160,000, the strength of the molded product is undesirably lowered. The range of Mw / Mn is preferably 1.5 to 3.5. When it exceeds 3.5, the distribution becomes too wide in the low molecular region, which is not preferable because the strength of the molded product is lowered. Compositions of less than 1.5 are difficult to supply by bulk polymerization, suspension polymerization, and emulsion polymerization, which are industrially excellent in productivity.

  Examples of the polymerization method of the styrene monomer- (meth) acrylic acid monomer copolymer (A) of the present invention include bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Polymerization or solution polymerization is preferable, and continuous bulk polymerization or continuous solution polymerization is particularly preferable in terms of productivity and economy. That is, styrene monomers, (meth) acrylic monomers and, if necessary, polymerization solvents such as ethylbenzene, toluene and xylene, organic peroxides as chain initiators, chain transfer agents, stabilizers, mineral oils, etc. The raw material solution mixed and dissolved is supplied to a reactor equipped with a stirrer to perform polymerization. When organic peroxide is used as the radical initiator, the polymerization temperature takes into consideration the decomposition temperature of organic peroxide, productivity, the ability to gradually heat the reactor, the fluidity of the intended copolymer, etc. It can be set using a known technique. The polymerization solution exiting the polymerization reactor is guided to a recovery device, and the solvent and unreacted monomers are removed by heating and devolatilization. As the recovery device, a device commonly used in the production of a styrene resin, for example, a flash tank system, a multistage vented extruder, or the like can be used.

As the polymerization apparatus for the styrene monomer- (meth) acrylic acid monomer copolymer (A) of the present invention, any of a complete mixing type, a plug flow type, a plug flow type equipped with a circulation device, and the like are preferable. Can be used. Among these, a complete mixing type polymerization apparatus is preferable from the uniformity of composition distribution.
As the light diffusing particles added for the purpose of imparting light diffusibility to the transparent resin, inorganic fine particles, organic crosslinked particles, and the like are used. However, the inorganic fine particles have a high total light transmittance due to their shape. If the addition amount is decreased for the purpose of achieving the above, there is a problem in light diffusibility such that the haze value is lowered and the transparency tends to occur. There is also a problem that the strength of the product is greatly reduced. Therefore, organic cross-linked particles were used as the light diffusing particles used in the light diffusing styrenic resin composition of the present invention.
Examples of the organic crosslinked particles (B) used in the present invention include acrylic crosslinked particles, styrene crosslinked particles, and methyl methacrylate-styrene copolymer crosslinked particles. Of these, acrylic crosslinked particles having the lowest refractive index and capable of high diffusion are preferred. These organic crosslinked particles can be used alone or in combination.

Further, the absolute value difference between the refractive index of the organic crosslinked particles (B) and the refractive index of the styrene monomer- (meth) acrylic acid monomer copolymer (A) is 0.04 to 0.12. is there. If it is less than 0.04, the light diffusion is lowered, and in order to satisfy the high light diffusibility and the high light transmittance, a large amount of addition is required, so the strength is lowered, which is not preferable. On the other hand, it exceeds 0.12. And the light transmittance is lowered, which is not preferable.
The weight average particle diameter of the organic crosslinked particles (B) is 1.0 to 10 μm. Preferably it is 3-8 micrometers. If the weight average particle diameter is less than 1.0 μm, the concealability is lowered and the transmission wavelength is selected when light is transmitted, which is not preferable. On the other hand, if it exceeds 10 μm, the transparency tends to occur and high light diffusibility and high In order to satisfy the light transmittance, a large amount of addition is required.
The content of the organic crosslinked particles (B) is 0.1 to 10 parts by weight with respect to 100 parts by weight of the styrene monomer- (meth) acrylic acid monomer copolymer (A). Preferably, it is 1 to 5 parts by weight. If it is less than 0.1 parts by weight, it is not preferable from the viewpoint of light diffusibility, whereas if it exceeds 10 parts by weight, it is not preferable from the viewpoint of light transmittance and strength reduction.

In the present invention, at any stage before or after the recovery process at the time of production of the styrene monomer- (meth) acrylic acid monomer copolymer, or at the stage of extruding and molding the light diffusing styrene resin composition If necessary, various additives within the range not impairing the object of the present invention, for example, UV absorbers, light stabilizers, hindered phenols, phosphorus, sulfur-based antioxidants, lubricants, antistatic agents, difficulty A flame retardant, various dyes and pigments, a fluorescent brightener, and a selective wavelength absorber may be added.
Here, an ultraviolet absorber and a light stabilizer can be added to the light-diffusing styrene resin composition of the present invention for the purpose of preventing coloring due to ultraviolet rays generated from the light source lamp. Examples of the ultraviolet absorber include 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- [2-hydroxy-3,5bis (α, α′dimethylbenzyl) phenyl] benzotriazole, 2- ( Benzotriazole ultraviolet absorbers such as 3,5-di-t-amyl-2-hydroxyphenyl) benzotriazole, 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy Benzophenone ultraviolet absorbers such as -4-n-octoxybenzophenone, salicylic acid ultraviolet absorbers such as phenyl salicylate and 4-t-butylphenyl salicylate, 2- (1-arylalkidene) malonic ester ultraviolet absorbers And oxalanilide-based ultraviolet absorbers. Examples of the light stabilizer include hindered amine light stabilizers. Examples of hindered amine light stabilizers include bis (2,2,6,6-tetramethyl-4-piperidyl) separate, N, N′-bis (3-aminopropyl) ethylenediamine, 2,4-bis. And [N-butyl-N- (1,2,2,6,6-pentamethyl-4-piperidyl) amino] -6-chloro-1,3,5-triazine condensate. The ultraviolet absorber and the light stabilizer can be used alone or in combination, and the addition amount is the sum of the ultraviolet absorber and the light stabilizer, which is a styrene monomer- (meth) acrylic acid monomer system. 0.02-2.0 weight part is preferable with respect to 100 weight part of copolymers. More preferably, it is 0.1 to 1.5 parts by weight.

Furthermore, the light diffusing styrenic resin composition of the present invention includes, for example, glycerol fatty acid esters such as glycerol monostearate, higher alcohols such as stearyl alcohol, stearin for the purpose of improving releasability and suppressing gelation during heat retention. A higher fatty acid such as an acid can be added, and in this case, it is used within the range not impairing the object of the present invention, and is usually a styrene monomer- (meth) acrylic acid monomer copolymer 100. It is preferably used at a concentration of 0.5 parts by weight or less with respect to parts by weight.
Furthermore, a masking agent such as a fluorescent brightening agent and a bluing agent can be optionally used in the light diffusion styrene resin composition of the present invention as necessary.
A known method can be selected as a method for producing the light diffusing styrene-based resin composition of the present invention. For example, after mixing the styrene monomer- (meth) acrylic acid monomer copolymer (A) and the organic crosslinked particles (B) and other components as necessary with a Henschel mixer, a tumbler, etc. A composition formed into a pellet shape or a plate shape can be obtained by melt-kneading using a single-screw or twin-screw extruder or various kneaders.
The light diffusing styrene-based resin composition of the present invention can be suitably used as a molding material for lighting fixtures, electric signboards, liquid crystal display devices, and the like, and can be variously molded by methods such as extrusion molding, injection molding, and compression molding. The body can be manufactured. Especially, it is used suitably as a diffusing plate for direct type backlights of liquid crystal display devices.

The present invention will be specifically described below. However, the present invention is not limited to these examples.
In the present invention, the following measurement method and evaluation method were used.
(1) Refractive index It measured at 25 degreeC based on JISK7015 using the appe refractometer.
(2) Determination of (meth) acrylic acid (MMA) unit in the copolymer 0.5 g of the copolymer was dissolved in 30 ml of methyl ethyl ketone, and 1.0% phenolphthalein aqueous solution was added as an indicator, while stirring. Titrate with a 10N potassium hydroxide ethanol solution. From the volume of 1/10 N potassium hydroxide ethanol solution consumed to the end point and the volume of 1/10 N potassium hydroxide ethanol solution consumed to the blank, the moles of carboxylic acid groups of (meth) acrylic acid The number is obtained and the weight of the (meth) acrylic acid unit is obtained by multiplying the molecular weight of (meth) acrylic acid. By calculating the ratio of the weight of the (meth) acrylic acid unit to the weight of the sample used for the measurement, the weight percentage of the (meth) acrylic acid unit in the composition was calculated. The measurement was performed 3 times and the average value was shown.

(3) Weight average molecular weight Mw
The weight average molecular weight Mw of the present invention is the polystyrene equivalent weight average molecular weight of the styrene monomer- (meth) acrylic acid monomer copolymer, and is determined by the RI method using gel permeation chromatography. It is done. The RI method is a differential refractive index detection method, and is measured by gel permeation chromatography using tetrahydrofuran as a solvent. A molecular weight Mw at each elution time may be calculated from an elution curve of a monodispersed polystyrene solution sample having a known molecular weight prepared in the same manner, and a polystyrene equivalent Mw may be calculated.
〔Measurement condition〕
Sample preparation: About 1000 ppm of copolymer resin was dissolved in tetrahydrofuran, and the injection volume was 100 μl.
Measuring equipment: Shodex System 21, manufactured by Showa Denko KK, sample column: two KF-806L, reference column: two KF-800RL, temperature: 40 ° C., carrier: tetrahydrofuran, flow rate: 1 ml / min.

(4) Melt flow rate (MFR)
Measured according to ISO 1133. (200 ℃, load 5kg)
(5) Vicat softening temperature Measured according to ISO 306.
(6) Total light transmittance A 50 × 90 × 2 mm flat plate was formed by injection molding, a 50 mm square test piece was cut out, and the total light transmittance was measured in accordance with JIS K7105.

(7) Diffusivity Using a goniophotometer manufactured by Optec Co., Ltd., the light that entered the test piece at a right angle with a white light source and transmitted through the opposite side of the test piece was in the range of 0 ° to 70 °. The luminance was measured and calculated by the following formula.
Light diffusivity (%) = (luminance of 20 ° + luminance of 70 °) ÷ (luminance of 5 ° × 2) × 100
(8) Water Absorption Based on JIS K7209, the water absorption rate (%) after 24 hours (that is, (weight after test / weight before test-1) × 100) was measured.
(9) Moisture absorption warpage A compression molded product in which an aluminum foil was bonded to one side of a 250 × 250 × 2 mm flat plate was formed by compression molding, and cut into 250 × 30 × 2 mm strips to create test pieces. The specimen was left for 72 hours in a constant temperature and humidity chamber adjusted to a temperature of 50 ° C. and a relative humidity of 90% with the aluminum foil surface facing down, and the amount of warpage (floating amount) at the center of the specimen was measured. .

[Example]
The light diffusion styrene resin compositions used in Examples and Comparative Examples were produced by the following method.
(Production of styrene-methacrylic acid copolymer A1)
1,1-bis (t-butylperoxy) with respect to 100 parts by weight of a mixture of 82.5% by weight of styrene, 3.0% by weight of methacrylic acid, 12% by weight of ethylbenzene and 2.5% by weight of 2-ethylhexanol. ) 0.023 parts by weight of cyclohexane was added to prepare a raw material solution. The raw material solution was continuously fed at 0.74 liter / hr to a polymerization apparatus having a fully mixed reactor (capacity 4 liters) equipped with a stirring blade. Polymerization was carried out at a polymerization temperature of 130 ° C. in a fully mixed reactor. The resulting polymerization solution was continuously supplied to a devolatilizing extruder with a two-stage vent, and the unreacted monomer and solvent were recovered at an extruder temperature of 225 ° C. and the vacuum of the first and second vents at 15 torr. A styrene-methacrylic acid copolymer was obtained. The monomer polymerization rate was about 70%. The analysis results are shown in Table 1.

(Production of styrene-methacrylic acid copolymer A2)
100 parts by weight of a mixture of 77.7% by weight of styrene, 5.8% by weight of methacrylic acid, 14% by weight of ethylbenzene and 2.5% by weight of 2-ethylhexanol, and the temperature of the complete mixing reactor was set to 133 ° C Were operated in the same manner as styrene-methacrylic acid copolymer A1 to obtain styrene-methacrylic acid copolymer A2. The monomer polymerization rate was about 73%. The analysis results are shown in Table 1.
(Production of styrene-methacrylic acid copolymer A3)
100 parts by weight of a mixture of 76.7% by weight of styrene, 2.8% by weight of methacrylic acid, 18% by weight of ethylbenzene, 2.5% by weight of 2-ethylhexanol, and the temperature of the fully mixed reactor was 140 ° C. Were operated in the same manner as styrene-methacrylic acid copolymer A1 to obtain styrene-methacrylic acid copolymer A3. The monomer polymerization rate was about 75%. The analysis results are shown in Table 1.

(Production of styrene-methacrylic acid copolymer A4)
87.3% by weight of styrene, 3.2% by weight of methacrylic acid, 7% by weight of ethylbenzene, 0.017 part by weight of 1,1-bis (t-butylperoxy) cyclohexane, and the temperature of the complete mixing reactor is 116 ° C. A styrene-methacrylic acid copolymer A4 was obtained in the same manner as in the styrene-methacrylic acid copolymer A1, except that the extruder temperature was 240 ° C. The monomer polymerization rate was about 55%. The analysis results are shown in Table 1.
(Production of styrene-methacrylic acid copolymer A5)
1,1-bis (tert-butylperoxy) with respect to 100 parts by weight of a mixture of 58.1% by weight of styrene, 19.4% by weight of methacrylic acid, 20% by weight of ethylbenzene and 2.5% by weight of 2-ethylhexanol. ) An attempt was made to produce a copolymer under the same conditions as in Example 1 except that a polymerization solution obtained by adding 0.023 parts by weight of cyclohexane was used. However, a significant decrease in fluidity and an acid condensation reaction proceeded excessively. However, gelation occurred and production was impossible.

(Production of GP polystyrene G1)
Styrene 8% by weight, ethylbenzene 14% by weight, 2-ethylhexanol 100% by weight, except that the temperature of the fully mixed reactor was 133 ° C. The same operation as in the case of the methacrylic acid copolymer A1 was performed to obtain GP polystyrene G1. The monomer polymerization rate was about 73%. The analysis results are shown in Table 1.
(Polymethyl methacrylate resin M1)
Asahi Kasei Chemicals Corporation trade name Delpet 70NHX (refractive index: 1.49) was used.
(Organic crosslinked particles (B))
Table 2 shows the properties of the organic crosslinked particles used in Examples and Comparative Examples.

[Examples 1 to 7, Comparative Examples 2 and 4]
Styrene-methacrylic acid copolymer (A) and organic crosslinked particles (B) are mixed in the composition shown in Table 3, melt-kneaded in a 30 mm twin screw extruder, pelletized, and light diffusing styrene type. A resin composition was obtained. MFR was measured with the obtained light diffusing styrene resin pellets. In addition, test pieces were prepared by injection molding and compression molding, and the Vicat softening temperature and moisture absorption warpage were measured. Moreover, the sheet molded object was produced with the sheet extruder of 30 mmphi and L / D = 38. The sheet molding was adjusted by the lip opening and the polishing roll clearance so that the thickness of the sheet compact was 2 mm, and the extruder and die temperatures were 220 to 230 ° C. A test piece was cut out from the obtained sheet compact, and the total light transmittance, diffusivity, and water absorption were measured. The results are shown in Table 3.

[Comparative Example 1]
It replaced with a styrene-methacrylic acid copolymer (A), and it was the same as that of Examples 1-7 and Comparative Examples 2, 4, and 5 except having set it as the mixing | blending composition which shows GP polystyrene G1 and organic crosslinked particle B2 in Table 3. Various measurements were performed. The results are shown in Table 3.
[Comparative Example 3]
Various measurements were carried out in the same manner as in Examples 1 to 7 and Comparative Examples 2, 4, and 5, except that the organic crosslinked particles were not blended and the styrene-methacrylic acid copolymer A1 was used. The results are shown in Table 3.
[Comparative Example 5]
In place of the styrene-methacrylic acid copolymer (A), the polymethyl methacrylate resin M1 and the organic crosslinked particles B6 have the blending composition shown in Table 3, and the sheet extruder and die temperature are 240 to 250 ° C. Were operated in the same manner as in Examples 1 to 7 and Comparative Examples 2, 4, and 5, and various measurements were performed. The results are shown in Table 3.

  The light diffusing styrene-based resin composition of the present invention can be suitably used as a molding material for lighting fixtures, electric signboards, liquid crystal display devices, and the like, and can be variously molded by methods such as extrusion molding, injection molding, and compression molding. The body can be manufactured. Especially, it is used suitably as a diffusing plate for direct type backlights of liquid crystal display devices.

Claims (4)

100% by weight of styrene monomer- (meth) acrylic acid monomer copolymer (A) comprising 90 to 99% by weight of styrene monomer and 1 to 10% by weight of (meth) acrylic acid monomer Part, the absolute value difference in refractive index with the styrene monomer- (meth) acrylic acid monomer copolymer (A) is 0.04 to 0.12, and the weight average particle diameter is A light diffusing styrenic resin composition comprising 0.1 to 10 parts by weight of organic crosslinked particles (B) having a size of 1.0 to 10 μm. Styrene monomer- (meth) acrylic acid monomer copolymer (A) is composed of 95.5 to 99% by weight of styrene monomer and (meth) acrylic acid monomer 1 to 4.5. The light-diffusing styrenic resin composition according to claim 1, which is a styrene-based monomer- (meth) acrylic acid-based monomer copolymer consisting of% by weight. The polystyrene equivalent weight average molecular weight Mw measured by gel permeation chromatography of the styrene monomer- (meth) acrylic acid monomer copolymer (A) is 16 to 350,000. A light diffusing styrene resin composition. The diffusion plate which shape | molds the light diffusable styrene-type resin composition in any one of Claims 1-3, and is 1-3 mm in thickness.