JP5597550B2 - Optical molded body, light guide plate and light diffuser using the same - Google Patents

Description

  The present invention relates to an optical molded body, a light guide plate using the same, and a light diffuser.

Acrylic resins are widely used as optical molded articles such as light guide plates, diffusion plates, and lenses because they are excellent in transparency. Recently, various styrenic resins have been proposed and used as optical moldings in place of acrylic resins.
For example, in Patent Document 1, a resin molded body made of a copolymer mainly composed of methyl methacrylate and a styrene monomer is used, and in Patent Document 2, a styrene- (meth) acrylate ester copolymer is used. A light guide plate made of resin has been proposed. Patent Documents 3 and 4 propose resin compositions comprising a copolymer comprising an aromatic vinyl monomer and a methyl methacrylate monomer. Patent Document 5 proposes a multilayer diffusion plate of a styrene polymer or a styrene monomer-methyl methacrylate copolymer.

JP 2001-342263 A Japanese Patent Laid-Open No. 2003-075648 JP 2006-052349 A JP 2006-052350 A JP 2007-264598 A

Acrylic resins are widely used as optical molded articles, but have a problem that warpage and dimensional changes are likely to occur because of their high hygroscopicity. Moreover, since acrylic resin has high thermal decomposability at the time of molding, there is a problem that appearance defects are likely to occur in the molded body when molding at high temperature.
As described above, various styrene resins have been proposed and used for these problems. However, since styrene resins are inferior in transparency and light resistance compared to acrylic resins, their use has been limited.
In particular, a molded article in an optical molded article having a long light transmission distance (hereinafter referred to as “long optical path”), such as a light guide plate of a medium to large display of 20 inches or more, has a low light transmittance styrene resin. There was a problem that could not be used.

  In general, fluorescent tubes (FL tubes), external electrode tubes (EEFL tubes), and cold cathode tubes (CCFL tubes) are used as display light sources. Recently, with the technological innovation of LEDs, A new optical molded body suitable for LED light is desired.

An object of the present invention is to provide an optical molded article having low hygroscopicity, little loss of light transmittance in a long optical path, and excellent light resistance.
Another object of the present invention is to provide a light guide plate for a liquid crystal display, a light guide plate for illumination, or an optical molding useful as various light diffusers, particularly a light guide plate for medium to large liquid crystal displays using LEDs as a light source. It is to provide a light diffusing body useful as a light guide plate that is useful as a light source or a lighting application.

  As a result of intensive studies on the above problems, the inventor molded a styrene resin obtained by polymerizing a styrene monomer having a small amount of a polymerization inhibitor and a low phenylacetylene compound content. The optical molded body is low in hygroscopicity, has little loss of light transmittance in a long optical path, has excellent light resistance, and found that this optical molded body is useful for a light guide plate and a light diffuser, The present invention has been reached.

  The optical molded body according to the present invention is obtained by molding a styrene resin obtained by polymerizing a styrene monomer having a polymerization inhibitor of less than 10 ppm and a phenylacetylene compound of 50 ppm or less. This is an optical molded body.

  The molded article for optics according to the present invention, in particular, the light guide plate and the light diffuser have low hygroscopicity, so there is little warpage and dimensional change, little loss of light transmittance in a long optical path, and good light resistance. The light diffuser also has good total light transmittance and diffusivity.

<Explanation of terms>
In the present specification, the symbol “to” means “above” and “below”. For example, the description “A to B” means A or more and B or less.
In the present specification, the “optical molded body” means, for example, one used for optical applications such as a light guide plate, a diffusion plate, and a lens.
Moreover, in this specification, a (meth) acrylic acid ester monomer is a general term for an acrylic acid ester monomer and a methacrylic acid ester monomer.

  Further, in the present specification, the “light diffuser” means a material that diffuses light and emits light on a flat surface or a curved surface, represented by a diffusion plate or a diffusion cover.

Hereinafter, embodiments of an optical molded body, particularly a light guide plate and a light diffuser according to the present invention will be described in detail.
The molded article for optics according to this embodiment is formed by molding a styrene resin obtained by polymerizing a styrene monomer having a polymerization inhibitor of less than 10 ppm and a phenylacetylene compound of 50 ppm or less. This is an optical molded body.

  Since the optical molded body having the above-described structure has low hygroscopicity, the warpage and dimensional change are small, the light transmittance loss in the long optical path is small, and the light resistance is good. The light diffuser also has good total light transmittance and diffusivity.

[Styrene resin]
The styrene resin is a polymer obtained by polymerizing a styrene monomer.
Examples of the styrene monomer include styrene, α-methyl styrene, p-methyl styrene, o-methyl styrene, m-methyl styrene, ethyl styrene, pt-butyl styrene, and preferably styrene. It is. These styrenic monomers may be used alone or in combination of two or more.

The styrene resin may be a copolymer of a styrene monomer and a monomer copolymerizable with the styrene monomer, and a styrene monomer and a (meth) acrylic acid ester monomer. A styrene- (meth) acrylic acid ester copolymer obtained by copolymerizing a polymer is preferable.
When the styrene resin is a styrene- (meth) acrylic acid ester copolymer, an effect of good light resistance can be obtained.

  As the (meth) acrylic acid ester monomer, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate methacrylate, methyl acrylate, ethyl acrylate, n -Acrylic acid esters such as butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, and decyl acrylate are exemplified, and methyl methacrylate is particularly preferable. These (meth) acrylic acid ester monomers may be used alone or in combination of two or more.

The ratio of styrene monomer units in the styrene resin is 3% by mass or more, preferably 6% by mass to 90% by mass, and more preferably 10% by mass to 60% by mass.
When the ratio of the styrenic monomer units is 3% by mass or more, the hygroscopicity of the optical molded article is lowered, and the thermal stability is improved. If the ratio of the styrene monomer unit is 6% by mass to 90% by mass, not only the hygroscopicity of the optical molded body is lowered and the thermal stability is improved, but also the light transmittance loss of the long optical path is lost. The effect that there is little can be acquired.

The ratio of the (meth) acrylic acid ester monomer units in the styrene resin is 97% by mass or less, preferably 10% by mass to 94% by mass, and more preferably 40% by mass to 90% by mass. .
When the ratio of the (meth) acrylic acid ester monomer unit is 97% by mass or less, the hygroscopicity of the optical molded article is lowered, and the thermal stability is improved. If the ratio of the (meth) acrylic acid ester monomer unit is 10% by mass to 94% by mass, not only the hygroscopicity of the optical molded body is lowered and the thermal stability is improved, but also the light in the long optical path. The effect that there is little loss of transmittance can be obtained.

  The styrenic resin may be a copolymer of a styrenic monomer and an ethylenically unsaturated monomer copolymerizable with the styrenic monomer, if necessary. Examples of the monomer include acrylonitrile, (meth) acrylic acid, (meth) acrylate, maleic anhydride and the like. When improving the heat resistance of the light guide plate, methacrylic acid or maleic anhydride is preferred. The ethylenically unsaturated monomer may be a mixture of two or more.

Here, the ratio of the ethylenically unsaturated monomer units in the styrene resin is 35% by mass or less, preferably 25% by mass or less, and more preferably 20% by mass or less.
When the ratio of the ethylenically unsaturated monomer units is 35% by mass or less, it is possible to obtain an effect that heat resistance and the like can be improved without losing the low hygroscopicity and molding processability that are characteristic of the styrene resin. it can.

(Molecular weight of styrene resin)
The molecular weight of the styrene resin is preferably a polystyrene-equivalent weight average molecular weight Mw measured by GPC (gel permeation chromatography) of 7 to 450,000, and a molecular weight distribution (weight average molecular weight Mw / number). The average molecular weight Mn) is preferably 1.7 to 2.3.
When the Mw is 70,000 or more, a strong molded product is obtained, and when it is 450,000 or less, the workability during injection molding is good. Moreover, when Mw / Mn is 1.7 or more, workability at the time of extrusion molding is good, and when it is 2.3 or less, a strong molded product can be obtained. In addition, Mw and Mw / Mn can be adjusted with the temperature at the time of superposition | polymerization, the amount of polymerization initiators, etc.

(Photoelastic coefficient of styrene resin)
The photoelastic coefficient of the styrene resin is preferably −6 × 10 ^{−12 to} 6 × 10 ⁻¹² / Pa. More preferably, it is −4 × 10 ⁻¹² to 4 × 10 ⁻¹² / Pa.
A photoelastic coefficient of −6 × 10 ^{−12 to} 6 × 10 ⁻¹² / Pa is preferable because luminance unevenness is reduced when a light guide plate is used. In addition, a photoelastic coefficient can be adjusted with the ratio of the monomer copolymerizable with the styrene-type monomer in the case of superposition | polymerization.

(Styrene resin melt mass flow rate)
The melt mass flow rate of styrene resin (measured at a temperature of 200 ° C. and a load of 49 N based on MFR, JIS K7210) is preferably 0.5 to 30 g / 10 minutes, more preferably 3 to 20 g / 10 minutes. .
When the MFR is 0.5 g / 10 min or more, the injection moldability is good, and when the MFR is 30 g / 10 min or less, the extrusion moldability is good. The MFR can be adjusted by adjusting the molecular weight, the type of monomer copolymerizable with the styrenic monomer, and its ratio during polymerization.

(Shape of styrene resin)
The shape of the styrenic resin is preferably a pellet shape. A known method can be adopted as the pelletizing method. For example, a strand having a diameter of 2 to 5 mm is melt-extruded from a die nozzle, and further cooled by passing through a cooling water tank to a length of 2 to 4 mm. It is obtained by cutting.

Here, it is preferable that the chip contained in a pellet is less than 300 ppm, More preferably, it is 1-200 ppm. The light transmittance in a long optical path becomes it high that a chip is less than 300 ppm. In addition, a chip | tip is often contained in a pellet 1ppm or more on a manufacturing process.
The chip can be calculated by, for example, using a Tyler 20 mesh wire mesh sieve and measuring the amount of the chip that has passed through the wire mesh when 100 g of styrene resin is sieved for 5 minutes. The amount of chips can be adjusted by strand cutting conditions, classification, and the like.

The total amount of the monomer and solvent remaining in the styrene resin is preferably less than 1000 ppm, and more preferably 10 to 800 ppm. In addition, the amount of the monomer and solvent remaining in the styrene resin is often 10 ppm or more in the production process.
When the total amount of the monomer and solvent remaining in the styrene-based resin is less than 1000 ppm, odor during molding and discoloration during long-term use can be reduced. The remaining monomer and residual solvent can be adjusted by temperature, pressure conditions, etc. in devolatilization.

  The amount of oligomer in the styrenic resin is not particularly limited, but it is not preferable to add a large amount of polymerization initiator to reduce the amount of oligomer because the light transmittance in the long optical path is lowered.

  A known antioxidant, light stabilizer, lubricant, plasticizer, and antistatic agent can be added to the styrene resin in an amount of less than 0.5 parts by mass with respect to 100 parts by mass of the styrene resin. When it is a light guide plate, it is preferable not to add. If the said additive is less than 0.5 mass part, there will be little fall of the light transmittance of a long optical path.

[Polymerization inhibitor]
The optical molded body according to the present embodiment is characterized in that the content of the polymerization inhibitor in the styrene monomer is less than 10 ppm. By setting the polymerization inhibitor to less than 10 ppm, the light transmittance in the long optical path is increased and the light resistance is improved.

  Further, the content of the polymerization inhibitor is preferably less than 5 ppm, more preferably less than 1 ppm. When the content of the polymerization inhibitor is less than 5 ppm, it is possible to obtain an effect that the light transmittance in the long optical path is further increased and the light resistance is improved.

Examples of the polymerization inhibitor include hydroquinones and catechols.
Usually, a commercially available styrenic monomer contains about 10 to 30 ppm of a polymerization inhibitor, so it must be removed or reduced. There is no restriction | limiting in particular as a method to remove or reduce, Well-known methods, such as distillation and adsorption | suction, are employable. As this method, vacuum distillation is preferable.
In addition, when copolymerizing the monomer copolymerizable with a styrene-type monomer, it is preferable that the polymerization inhibitor in the monomer copolymerizable with a styrene-type monomer shall also be less than 10 ppm, respectively.

[Phenylacetylene compounds]
The molded article for optics according to this embodiment is characterized in that the content of the phenylacetylene compound in the styrene monomer is 50 ppm or less. By setting the phenylacetylene compound to 50 ppm or less, the light transmittance in the long optical path is increased, and the light resistance is improved.

  The content of the phenylacetylene compound is preferably less than 40 ppm, more preferably less than 20 ppm. When the content of the phenylacetylene compound is less than 40 ppm, it is possible to obtain an effect that the light transmittance in the long optical path is further increased and the light resistance is improved.

  Usually, since phenylacetylene in styrene has a boiling point and is difficult to separate, styrene available on the market contains about 150 ppm of phenylacetylene and needs to be removed or reduced. There is no restriction | limiting in particular as a method to remove or reduce, Well-known methods, such as a hydrogenation process and adsorption | suction, are employable. As this method, a hydrogenation treatment performed in the presence of a hydrogenation catalyst is preferable.

[Polymerization reaction]
The styrene resin used for the optical molded body according to the present embodiment is preferably obtained by solution polymerization, among polymerization reactions.

As the solvent for the solution polymerization, known solvents such as toluene, xylene, ethylbenzene, hexane, cyclohexane, acetone, methyl ethyl ketone, methyl isobutyl ketone and the like can be used.
Preferably the usage-amount of a solvent is 1-70 mass parts with respect to a total of 100 mass parts of the monomer to be used, More preferably, it is 2-30 mass parts.
If the solvent is used in an amount of 1 to 70 parts by mass with respect to 100 parts by mass of the total amount of monomers used, not only can viscosity control during polymerization be easily performed by solution polymerization, The polymerization composition distribution becomes narrow, and the loss of light transmittance in the long optical path is small.

  The polymerization reaction is particularly preferably radical solution polymerization. In radical solution polymerization, compared with anionic polymerization, cationic polymerization, and coordination polymerization, the influence of initiators and auxiliaries remaining in the styrene resin is small, and light transmittance and light resistance of a long optical path are high.

(Polymerization initiator)
At the time of radical polymerization, a known polymerization initiator such as an organic peroxide or an azo compound can be added as a radical generation source.
As the polymerization initiator, those having a one-hour half-life temperature of 95 to 140 ° C., low hydrogen abstraction ability, and no benzene ring are preferable. Those having a low hydrogen abstraction ability are unlikely to generate a micro gel component, so that the loss of light transmittance in the long optical path is small. In addition, those that do not contain a benzene ring are less likely to produce a colored component and have little loss of light transmittance in the long optical path.

  Examples of preferred polymerization initiators include 1,1-di (t-hexylperoxy) -3,3,5-trimethylcyclohexane, 1,1-di (t-hexylperoxy) -cyclohexane, t-hexylper Examples thereof include oxyisopropyl monocarbonate and di-t-hexyl peroxide.

  Moreover, it is preferable that the addition amount of a polymerization initiator is 0.01-0.5 mass part with respect to a total of 100 mass parts of a monomer. More preferably, it is 0.02-0.2 mass part. When the addition amount of the polymerization initiator is 0.01 to 0.5 parts by mass, the light transmittance and light resistance of the long optical path are good.

(Chain transfer agent)
Further, a known chain transfer agent such as n-dodecyl mercaptan, t-dodecyl mercaptan or 2,4-diphenyl-4-methyl-1-pentene may be added during radical polymerization.
The addition amount of the chain transfer agent is preferably 0.001 to 0.5 parts by mass, more preferably 0.005 to 0.2 parts by mass with respect to 100 parts by mass in total of the monomers. When the addition amount of the chain transfer agent is 0.001 to 0.5 parts by mass, the light transmittance in the long optical path is increased and the light resistance is improved.

  The polymerization temperature during the polymerization of the styrene resin is preferably 90 to 180 ° C, more preferably 95 to 170 ° C. When the temperature is 90 to 180 ° C., the light transmittance and light resistance of the long optical path are good.

(Removal of dissolved oxygen)
The styrenic monomer and solvent used in the optical molded body according to this embodiment are preferably subjected to polymerization after removing dissolved oxygen. The method for removing dissolved oxygen is not particularly limited, and a method of bubbling using nitrogen gas or the like can be employed.
When dissolved oxygen is removed, the color of the molded body may be colorless and good for optical applications. In addition, when copolymerizing the monomer copolymerizable with a styrene-type monomer, it is preferable to use for polymerization, after also removing the dissolved oxygen of the monomer copolymerizable with a styrene-type monomer.

(Removal of foreign matter)
In addition, the styrene monomer and solvent used in the optical molded body according to this embodiment are preferably subjected to polymerization after removing foreign substances. There is no restriction | limiting in particular as a method of removing a foreign material, The method etc. which filter with a filter are employable.
When the foreign matter is removed, the light transmittance of the long optical path may increase. In addition, when copolymerizing the monomer copolymerizable with a styrene-type monomer, it is preferable to use for polymerization, after removing the foreign material of the monomer copolymerizable with a styrene-type resin.

In the styrenic resin according to the present embodiment, the styrenic resin can be molded by a known method such as an injection molding method, an extrusion molding method, or a solvent casting method to obtain an optical molded body. In particular, an injection molding method or an extrusion molding method is preferable.
Although there is no restriction | limiting in particular in molding conditions, It is preferable to shape | mold at 200-300 degreeC.

[Light guide plate]
Applications of the optical molded body according to the present embodiment include a light guide plate, a diffusion plate, a lens, and the like. In particular, the molded article for optics according to the present embodiment has little loss of light transmittance in a long optical path, and particularly has good light resistance to light having a wavelength of 400 nm or more. It is useful as a light guide plate, and particularly useful as a light guide plate for medium to large liquid crystal displays using LEDs as light sources.

  The thickness of the light guide plate of this embodiment is preferably 0.3 to 8 mm, more preferably 0.4 to 5 mm. The light guide plate having such a thickness is effective in that it can sufficiently take in light as a light guide plate for medium to large displays of 20 inches or more and has sufficient rigidity for handling.

  In the light guide plate according to the present embodiment, other components such as crosslinked acrylic particles, crosslinked styrene particles, siloxane resin particles, organic light diffusing agents, barium sulfate, carbonate Inorganic light diffusing agents such as calcium and titanium oxide can be blended.

[Light diffuser]
Further, even when the optical molded body according to this embodiment is a light diffuser, the optical properties such as total light transmittance (or light transmittance) and diffusivity are good. Therefore, it is useful as a light diffuser used for various applications such as illumination.

  As a method of diffusing light as a light diffuser, various methods such as a method of kneading a light diffusing agent, a method of shaping on the surface, and application of the light diffusing agent to the surface can be adopted.

  As the light diffusing agent, organic light diffusing agents such as crosslinked acrylic particles, crosslinked styrene particles, and siloxane resin particles, and inorganic light diffusing agents such as barium sulfate, calcium carbonate, and titanium oxide can be used. When cross-linked acrylic particles, cross-linked styrene particles, siloxane resin particles, and calcium carbonate are used as a light diffuser, a good balance of optical properties such as total light transmittance and diffusivity is preferable.

  Although there is no restriction | limiting in particular in content of the light diffusing agent in a light diffusing body, When it contains in the range of 0.1 mass% or more and 10 mass% or less, it is in the total light transmittance, each diffusivity, or the balance of both. An excellent light diffuser can be obtained. By containing the light diffusing agent in an amount of 0.1% by mass or more, high diffusing performance can be obtained, and by making it 10% by mass or less, the decrease in the total light transmittance is small.

  As means for incorporating a light diffusing agent into the light diffuser, a known technique such as extrusion molding can be employed.

  In the light diffuser according to the present embodiment, a known antioxidant, light stabilizer, lubricant, plasticizer, antistatic agent, fluorescent whitening agent, fluorescent material, and phosphorescent material with respect to 100 parts by mass of the styrene resin. In an amount of less than 0.5 parts by mass. If the said additive is less than 0.5 mass part, the fall of optical physical properties, such as a total light transmittance (or light transmittance) and a diffusivity, will be small.

<Function and effect>
Hereinafter, the effect of the optical molded body according to the embodiment, particularly the light guide plate and the light diffuser will be described.

  The molded article for optics according to the embodiment is obtained by molding a styrene resin obtained by polymerizing a styrene monomer having a polymerization inhibitor of less than 10 ppm and a phenylacetylene compound of 50 ppm or less. This is an optical molded body.

  Since the optical molded body according to the above-described embodiment has low hygroscopicity, the warpage and dimensional change are small, the loss of light transmittance in the long optical path is small, and the light resistance is good.

  In particular, when the styrene resin is a styrene- (meth) acrylic acid ester copolymer, the effect of further improving the balance between warpage, dimensional change, light transmittance in a long optical path, and light resistance can be obtained. Can do.

  In addition, since the polymerization reaction is a radical solution polymerization reaction, there is little influence of the initiator and auxiliary agent remaining in the styrene resin, and the light transmittance and light resistance of the long optical path are increased. Can do.

  The optical molded body according to the above embodiment has a small loss of light transmittance in a long optical path, and particularly has good light resistance to light having a wavelength of 400 nm or more. Therefore, a light guide plate for a liquid crystal display or a light guide for illumination. It is useful as a light plate, and particularly useful as a light guide plate for medium to large-sized liquid crystal displays using LEDs as light sources.

  In addition, the optical molded body according to the above embodiment also has good optical properties such as total light transmittance (or light transmittance) and diffusivity. Therefore, it is useful as a light diffuser used for various applications such as illumination.

  As described above, the optical molded body according to the present invention, particularly the light guide plate and the light diffuser, have been described with reference to the embodiments, but the present invention is not limited thereto.

  For example, since the optical molded body according to the present invention has little warpage and dimensional change, it can be preferably used not only for medium to large displays but also for small displays that require precise size adjustment. Furthermore, it can use preferably also for lighting fixtures other than a display, and a display fixture use.

Moreover, the optical molded body according to the present invention may be obtained by a production method including the following steps.
A step of preparing a styrene monomer, a step of reducing the polymerization inhibitor contained in the styrene monomer to less than 10 ppm, and a step of reducing the phenylacetylene compound contained in the styrene monomer to 50 ppm or less. And a method for producing an optical molded body, which includes a polymerization reaction step of polymerizing a styrene monomer to obtain a styrene resin, and a molding step of molding the styrene resin.
The molded article for optics obtained by the above production method has low hygroscopicity, and therefore has little warpage and dimensional change, little loss of light transmittance in a long optical path, and good light resistance.

  Hereinafter, although the detailed content of the molded object for optics which concerns on this invention, especially a light-guide plate and a light diffusing body is demonstrated using an Example, this invention is not limited to a following example.

[Styrene monomer]
First, the styrene monomer used in Examples and Comparative Examples will be described.
(Styrene-1)
When industrial styrene was prepared, it was found that 12 ppm of 4-t-butylcatechol as a polymerization inhibitor and 130 ppm of phenylacetylene as impurities were contained. This industrial styrene is hydrotreated in the presence of a hydrogenation catalyst to selectively hydrogenate the phenylacetylene contained and then distilled under reduced pressure to give 4-t-butylcatechol less than 0.1 ppm, phenyl Styrene-1 containing 10 ppm of acetylene was obtained.
(Styrene-2)
4-t-butylcatechol was added to styrene-1 to obtain styrene-2 containing 7 ppm of 4-t-butylcatechol.
(Styrene-3)
4-t-butylcatechol was added to styrene-1 to obtain styrene-3 containing 12 ppm of 4-t-butylcatechol.
(Styrene-4)
Phenylacetylene was added to styrene-1 to obtain styrene-4 containing 43 ppm of phenylacetylene.
(Styrene-5)
Phenylacetylene was added to styrene-1 to obtain styrene-5 containing 130 ppm of phenylacetylene.

[(Meth) acrylic acid ester monomer]
(MMA-1)
Next, the (meth) acrylic acid ester monomer will be described.
When industrial methyl methacrylate was prepared, it was found that 5 ppm of topanol was contained as a polymerization inhibitor. This is designated as MMA-1.

[Example 1]
52 parts by mass of styrene-1 and 48 parts by mass of MMA-1 and 12 parts by mass of ethylbenzene as a solvent were mixed, and after bubbling with nitrogen for 1 hour to remove dissolved oxygen, the supernatant was filtered through a 1 μm filter. To obtain a raw material solution.
A first fully mixed reactor of about 5 liters with a stirrer, a second fully mixed reactor of about 15 liters, a column type plug flow reactor of about 40 liters, and a preheater are attached. The devolatilization tanks were connected in series.
0.03 part by mass of 1,1-di (t-hexylperoxy) -cyclohexane (Perhexa HC manufactured by NOF Corporation) and 0.015 part by mass of n-dodecyl mercaptan (thiocalcol 20 manufactured by Kao Corporation) were mixed with the raw material solution. And introduced into a first fully mixed reactor controlled at a temperature of 95 ° C. at 6 kg per hour.

In addition, the rotational speed of the stirrer of the first complete mixing type reactor was 300 rpm. The reaction solution was continuously withdrawn from the first complete mixing reactor and introduced into a second complete mixing reactor controlled at a temperature of 125 ° C.
Further, the rotation speed of the stirrer of the second complete mixing type reactor was 180 rpm. The reaction liquid was continuously withdrawn from the second complete mixing type reactor and introduced into a column type plug flow type reactor adjusted so as to have a gradient of 125 ° C. to 160 ° C. in the direction of flow.

While heating this reaction liquid with a preheater, it was introduced into a devolatilization tank controlled at a temperature of 240 ° C. and a pressure of 1.0 kPa to remove volatile components such as a solvent and unreacted monomers.
The resin liquid was extracted with a gear pump, extruded into a strand, and cut while cooling to obtain a pellet-shaped styrene resin. The fine powder contained in the pellets was removed by classification.

The obtained styrenic resin has Mw = 180,000, Mw / Mn = 1.8, and the total amount of the monomer and solvent remaining in the styrenic resin is less than 1000 ppm and the chip is less than 300 ppm. confirmed.
The chips were calculated by measuring the amount of chips that passed through the wire mesh when 100 g of styrene resin was sieved for 5 minutes using a Tyler 20 mesh wire mesh screen.

  The pellets were molded using an electric injection molding machine, J350ELIII, manufactured by Nippon Steel Works, Ltd., and a molded body having a molding temperature of 270 ° C. and a length of 292.5 mm, a width of 220 mm, and a thickness of 2 mm was obtained. The obtained molded article was evaluated for optical properties. The results are shown in Table 1.

[Example 2]
The same procedure as in Example 1 was performed except that 40 parts by mass of styrene-1 and 60 parts by mass of MMA-1 were used. The results are shown in Table 1.

[Example 3]
The same procedure as in Example 1 was performed except that 11 parts by mass of styrene-1 and 89 parts by mass of MMA-1 were used. The results are shown in Table 1.

[Example 4]
The same procedure as in Example 1 was performed except that 100 parts by mass of styrene-1 and 0 parts by mass of MMA-1 were used. The results are shown in Table 1.

[Example 5]
It carried out similarly to Example 1 except having used styrene-2 instead of styrene-1. The results are shown in Table 1.

[Example 6]
It carried out similarly to Example 1 except having used styrene-4 instead of styrene-1. The results are shown in Table 1.

In addition, the characteristic evaluation of the said molded object was performed with the following method.
(1) Polymerization inhibitor (4-t-butylcatechol)
Sodium hydroxide was added to the sample and stirred. The absorbance of the colored liquid was measured with a spectrophotometer (wavelength 486 nm), and the concentration was calculated from a calibration curve prepared in advance.
(2) Residual monomer, residual solvent, phenylacetylene Measured under the GC measurement conditions described below.
Device name: GC12A FID detector column manufactured by Shimadzu Corporation: Glass column φ3mm × 3m
Filler: Polyethylene glycol carrier: Nitrogen temperature: Column 115 ° C, inlet 220 ° C
Sample pellets 0.5 g, cyclopentane 0.001 g, N, N-dimethylformamide were dissolved and measured using cyclopentane as an internal standard.
(3) Hygroscopicity Saturated water absorption (unit:%) was determined by A method based on JIS K7209 using a molded plate. Less than 1.5% was accepted.
(4) Haze
Based on JIS K7105, the haze (unit:%) was measured for the 2 mm thickness part of the shape | molded plate using the haze meter (Nippon Denshoku Industries Co., Ltd. NDH2000). Less than 0.3% was accepted.
(5) Transparency of long optical path (light transmittance)
The end surface of the molded plate was polished using a gate processing machine GCPB manufactured by Megaro Technica Co., Ltd. Using a long optical path measuring device ASA-300A manufactured by Nippon Denshoku Industries Co., Ltd., the transmittance (unit:%) of light that vertically transmitted through the polished surface was measured.
(6) Refractive index The refractive index of the 2 mm thick portion of the molded plate was measured using an Abbe refractometer (Abbe Refractometer 2-T manufactured by Atago Co., Ltd.).
(7) Reflectance Using the following formula, the reflectance (unit:%) was calculated using the refractive index measured in (6).

（８）長光路の透明損失率
下式を用い、（５）で測定した長光路の光透過率と、（７）で算出した反射率を用いて、透明損失率（単位：％）を算出した。なお、反射率を２倍しているのは、入光面と出光面の２面を表す。８％未満を合格とした。

(8) Transparent loss rate of long optical path Using the following formula, the transparent loss rate (unit:%) is calculated using the light transmittance of the long optical path measured in (5) and the reflectance calculated in (7). did. Note that doubling the reflectivity represents two surfaces, a light incident surface and a light output surface. Less than 8% was accepted.

（９）耐光性
ＩＫＧ社製単軸押出機ＰＭＳ４０を用いて、シリンダー温度２３０℃の条件で、三菱レイヨン（株）社製ＰＭＭＡ ＶＨ５、チバ・スペシャルティ・ケミカルズ（株）社製紫外線吸収剤ＴｉｎｕｖｉｎＰ、クラリアントジャパン（株）社製光安定剤ＨｏｓｔａｖｉｎＰＲ−２５を９９：０．５：０．５の質量比で溶融混練し、紫外光フィルター用樹脂を得た。この樹脂を電動射出成形機（株）日本製鋼所社製Ｊ３５０ＥＬIIIにより、成形温度２７０℃で縦２９２．５ｍｍ、横２２０ｍｍ、厚さ２ｍｍの紫外光フィルターを得た。この紫外光フィルターは、波長が４００ｎｍ未満の光はほとんど透過しないことを確認した。
実施例・比較例で得たスチレン系樹脂の成形体と紫外光フィルターを重ね、アトラス社製ウエザオメータＣｉ６５Ａを用いて、温度６３℃、照射強度０．３５Ｗ／ｍ^２（３４０ｎｍにおける強度）の条件で紫外光フィルター側からキセノン光源の光を２００時間照射した。すなわち、スチレン系樹脂の成形体には紫外光フィルターを透過した４００ｎｍ以上の光が当たるようにした。光照射した成形体の２ｍｍ部におけるｂ値（単位：−）を、日本電色工業（株）社製色差計Σ８０を用いて、ＪＩＳ Ｋ７１０５に準拠して測定し、下記の式によりΔｂを算出した。Δｂが１未満を合格とした。
Δｂ＝２００時間照射後のｂ値−照射前のｂ値

(9) Light resistance Using a single screw extruder PMS40 manufactured by IKG, under the condition of a cylinder temperature of 230 ° C., PMMA VH5 manufactured by Mitsubishi Rayon Co., Ltd., UV absorber TinuvinP manufactured by Ciba Specialty Chemicals Co., Ltd. The light stabilizer HostavinPR-25 manufactured by Clariant Japan Co., Ltd. was melt-kneaded at a mass ratio of 99: 0.5: 0.5 to obtain an ultraviolet filter resin. An ultraviolet light filter having a length of 292.5 mm, a width of 220 mm, and a thickness of 2 mm at a molding temperature of 270 ° C. was obtained from this resin using J350ELIII manufactured by Nippon Steel Works, Ltd., an electric injection molding machine. It was confirmed that this ultraviolet filter hardly transmits light having a wavelength of less than 400 nm.
The molded product of the styrene-based resin obtained in Examples and Comparative Examples and an ultraviolet light filter were layered, and using a weatherometer Ci65A manufactured by Atlas Co., at a temperature of 63 ° C. and an irradiation intensity of 0.35 W / m ² (intensity at 340 nm). The xenon light source was irradiated for 200 hours from the ultraviolet filter side. That is, the styrene resin molded product was irradiated with light having a wavelength of 400 nm or more transmitted through an ultraviolet filter. The b value (unit:-) at 2 mm part of the light-irradiated molded product was measured according to JIS K7105 using a color difference meter Σ80 manufactured by Nippon Denshoku Industries Co., Ltd., and Δb was calculated by the following formula. did. The Δb was less than 1 as acceptable.
Δb = b value after irradiation for 200 hours−b value before irradiation

  As can be seen from Table 1, the optical molded articles of Examples according to the present invention had low hygroscopicity, little loss of light transmittance in the long optical path, and good light resistance.

[Comparative Example 1]
The same procedure as in Example 1 was performed except that 0 part by mass of styrene-1 and 100 parts by mass of MMA-1 were used. The results are shown in Table 1.

[Comparative Example 2]
It carried out similarly to Example 1 except having used styrene-3 instead of styrene-1. The results are shown in Table 1.

[Comparative Example 3]
It carried out similarly to Example 1 except having used styrene-5 instead of styrene-1. The results are shown in Table 1.

<Discussion>
Since the optical molded body of the example according to the present invention has low hygroscopicity, the warpage and dimensional change are small, the loss of light transmittance in the long optical path is small, and the light resistance of 400 nm or more is good.

In Comparative Example 1, since only the acrylic resin is used, the hygroscopicity is remarkably high.
In Comparative Example 2, the light transmittance of the long light path is low, and the light transmittance loss of the long light path is large. Further, it can be seen that Δb is large and light resistance is poor. This is thought to be because the content of the polymerization inhibitor is 10 ppm or more.
In Comparative Example 3, it can be seen that the transparent loss of the long optical path is large, in particular, the value of Δb is remarkably large and the light resistance is poor. This is considered to be because the content of the phenylacetylene compound is 50 ppm or more.

As described above, the optical molded body according to the present invention has low hygroscopicity, so that warpage and dimensional change are small, light transmittance in a long optical path is high, and light resistance is good.
Further, when the optical molded body according to the present invention is used as a light guide plate, it is useful as a light guide plate for a liquid crystal display or a light guide plate for illumination, and particularly has good light resistance to light having a wavelength of 400 nm or more. Therefore, it is useful as a light guide plate for medium to large liquid crystal displays using LEDs as light sources.

[Light diffuser]
The detailed contents of the light diffuser according to the present invention will be described using examples, but the present invention is not limited to the following examples.

[Styrene resin]
The styrene resin used in Examples and Comparative Examples will be described.

  The styrene resin obtained by the method of Example 1 is referred to as styrene resin 1. The styrene resin obtained by the method of Example 2 is referred to as styrene resin 2. The styrene resin obtained by the method of Example 3 is referred to as styrene resin 3. The styrene resin obtained by the method of Example 4 is referred to as styrene resin 4.

  A styrene resin obtained by the same method as in Example 1 using styrene 2 is referred to as a styrene resin 5. A styrene resin obtained by the same method as in Example 2 using styrene 2 is referred to as a styrene resin 6. A styrene resin obtained by the same method as in Example 3 using styrene 2 is referred to as a styrene resin 7. A styrene resin obtained by the same method as in Example 4 using styrene 2 is referred to as a styrene resin 8.

  A styrene resin obtained by the same method as in Example 1 using styrene 3 is referred to as a styrene resin 9. A styrene resin obtained by the same method as in Example 2 using styrene 3 is referred to as a styrene resin 10. A styrene resin obtained by the same method as in Example 3 using styrene 3 is referred to as a styrene resin 11. A styrene resin obtained by the same method as in Example 4 using styrene 3 is referred to as a styrene resin 12.

  A styrene resin obtained by the same method as in Example 1 using styrene 4 is referred to as a styrene resin 13. A styrene resin obtained by the same method as in Example 2 using styrene 4 is referred to as a styrene resin 14. A styrene resin obtained by the same method as in Example 3 using styrene 4 is referred to as a styrene resin 15. A styrene resin obtained by the same method as in Example 4 using styrene 4 is referred to as a styrene resin 16.

  A styrene resin obtained by the same method as in Example 1 using styrene 5 is referred to as a styrene resin 17. A styrene resin obtained by the same method as in Example 2 using styrene 5 is referred to as a styrene resin 18. A styrene resin obtained by the same method as in Example 3 using styrene 5 is referred to as a styrene resin 19. A styrene resin obtained by the same method as in Example 4 using styrene 5 is referred to as a styrene resin 20.

[Example 7]
Using a twin-screw extruder TEM-35B manufactured by Toshiba Machine Co., Ltd., 96 mass% of styrene resin 1 under the condition of a tip temperature of 230 ° C., calcium carbonate manufactured by Nemoto Special Chemical Co., Ltd. (product name) : Lumipearl DSN-7) was kneaded and mixed at a mixing ratio of 4% by mass to obtain a pellet-shaped resin composition. This pellet-shaped resin composition was molded under the conditions of a cylinder temperature of 230 ° C. and a mold temperature of 60 ° C. using an injection molding machine J140AD-180H manufactured by Nippon Steel Works, and was 90 mm long, 90 mm wide, 90 mm wide and 2 mm thick. A molded body was obtained.

[Example 8]
The same procedure as in Example 7 was performed except that styrene resin 1 was used as the styrene resin, and cross-linked acrylic particles (product name: Techpolymer MBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Example 9]
The same procedure as in Example 7 was performed except that 98% by mass of styrene resin 1 was used as the styrene resin, 2% by mass of siloxane resin particles (product name: Tospearl 120) manufactured by Momentive Performance Materials were used as the light diffusing agent. It was.

[Example 10]
The same procedure as in Example 7 was performed except that styrene resin 2 was used as the styrene resin, and cross-linked styrene particles (product name: Techpolymer SBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Example 11]
The same procedure as in Example 7 was performed except that styrene resin 2 was used as the styrene resin, and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Example 12]
The same procedure as in Example 7 was performed except that 98% by mass of styrene resin 2 was used as the styrene resin and 2% by mass of siloxane resin particles (product name: Tospearl 120) manufactured by Momentive Performance Materials were used as the light diffusing agent. It was.

[Example 13]
The same procedure as in Example 7 was conducted except that styrene resin 3 was used as the styrene resin, and cross-linked styrene particles (product name: Techpolymer SBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Example 14]
The same procedure as in Example 7 was performed except that styrene resin 3 was used as the styrene resin, and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Example 15]
The same procedure as in Example 7 was performed except that styrene resin 4 was used as the styrene resin, and cross-linked acrylic particles (product name: Techpolymer MBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Example 16]
The same procedure as in Example 7 was performed except that styrene resin 5 was used as the styrene resin, and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Example 17]
The same procedure as in Example 7 was performed except that styrene resin 5 was used as the styrene resin, and cross-linked acrylic particles (product name: Techpolymer MBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Example 18]
The same procedure as in Example 7 was conducted except that 98% by mass of styrene resin 5 was used as the styrene resin, 2% by mass of siloxane resin particles (product name: Tospearl 120) manufactured by Momentive Performance Materials were used as the light diffusing agent. It was.

[Example 19]
The same procedure as in Example 7 was performed except that styrene resin 6 was used as the styrene resin, and cross-linked styrene particles (product name: Techpolymer SBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Example 20]
The same procedure as in Example 7 was performed except that styrene resin 6 was used as the styrene resin, and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Example 21]
The same procedure as in Example 7 was performed except that 98% by mass of styrene resin 6 was used as the styrene resin, and 2% by mass of siloxane resin particles (product name: Tospearl 120) manufactured by Momentive Performance Materials was used as the light diffusing agent. It was.

[Example 22]
The same procedure as in Example 7 was performed except that styrene resin 7 was used as the styrene resin, and cross-linked styrene particles (product name: Techpolymer SBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Example 23]
The same procedure as in Example 7 was performed except that styrene resin 7 was used as the styrene resin, and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Example 24]
The same procedure as in Example 7 was performed except that styrene resin 8 was used as the styrene resin, and cross-linked acrylic particles (product name: Techpolymer MBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Example 25]
The same procedure as in Example 7 was performed except that styrene resin 13 was used as the styrene resin, and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Example 26]
The same procedure as in Example 7 was performed except that styrene resin 13 was used as the styrene resin, and cross-linked acrylic particles (product name: Techpolymer MBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Example 27]
The same procedure as in Example 7 was performed except that 98% by mass of styrene resin 13 was used as the styrene resin, 2% by mass of siloxane resin particles (product name: Tospearl 120) manufactured by Momentive Performance Materials were used as the light diffusing agent. It was.

[Example 28]
The same procedure as in Example 7 was carried out except that styrene resin 14 was used as the styrene resin, and cross-linked styrene particles (product name: Techpolymer SBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Example 29]
The same procedure as in Example 7 was carried out except that styrene resin 14 was used as the styrene resin, and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Example 30]
The same procedure as in Example 7 was performed except that 98% by mass of styrene resin 14 was used as the styrene resin, and 2% by mass of siloxane resin particles (product name: Tospearl 120) manufactured by Momentive Performance Materials were used as the light diffusing agent. It was.

[Example 31]
The same procedure as in Example 7 was carried out except that styrene resin 15 was used as the styrene resin, and cross-linked styrene particles (product name: Techpolymer SBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Example 32]
The same procedure as in Example 7 was performed except that styrene resin 15 was used as the styrene resin, and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Example 33]
The same procedure as in Example 7 was performed except that styrene resin 16 was used as the styrene resin, and cross-linked acrylic particles (product name: Techpolymer MBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Comparative Example 4]
The same procedure as in Example 7 was performed except that styrene resin 9 was used as the styrene resin, and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Comparative Example 5]
The same procedure as in Example 7 was performed except that styrene resin 9 was used as the styrene resin, and cross-linked acrylic particles (product name: Techpolymer MBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Comparative Example 6]
The same procedure as in Example 7 was performed except that 98% by mass of styrene resin 9 was used as the styrene resin, 2% by mass of siloxane resin particles (product name: Tospearl 120) manufactured by Momentive Performance Materials were used as the light diffusing agent. It was.

[Comparative Example 7]
The same procedure as in Example 7 was performed except that styrene resin 10 was used as the styrene resin, and cross-linked styrene particles (product name: Techpolymer SBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Comparative Example 8]
The same procedure as in Example 7 was performed except that styrene resin 10 was used as the styrene resin, and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Comparative Example 9]
The same procedure as in Example 7 was performed except that 98% by mass of styrene resin 10 was used as the styrene resin, 2% by mass of siloxane resin particles (product name: Tospearl 120) manufactured by Momentive Performance Materials were used as the light diffusing agent. It was.

[Comparative Example 10]
The same procedure as in Example 7 was conducted except that styrene resin 11 was used as the styrene resin, and cross-linked styrene particles (product name: Techpolymer SBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Comparative Example 11]
The same procedure as in Example 7 was performed except that styrene resin 11 was used as the styrene resin, and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Comparative Example 12]
The same procedure as in Example 7 was performed except that styrene resin 12 was used as the styrene resin, and cross-linked acrylic particles (product name: Techpolymer MBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Comparative Example 13]
The same procedure as in Example 7 was performed except that styrene resin 17 was used as the styrene resin, and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Comparative Example 14]
The same procedure as in Example 7 was carried out except that styrene resin 17 was used as the styrene resin, and cross-linked acrylic particles (product name: Techpolymer MBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Comparative Example 15]
The same procedure as in Example 7 was performed except that 98% by mass of styrene resin 17 was used as the styrene resin, and 2% by mass of siloxane resin particles (product name: Tospearl 120) manufactured by Momentive Performance Materials were used as the light diffusing agent. It was.

[Comparative Example 16]
The same procedure as in Example 7 was performed except that styrene resin 18 was used as the styrene resin, and cross-linked styrene particles (product name: Techpolymer SBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Comparative Example 17]
The same procedure as in Example 7 was performed except that styrene resin 18 was used as the styrene resin and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Comparative Example 18]
The same procedure as in Example 7 was performed except that 98% by mass of styrene resin 18 was used as the styrene resin, 2% by mass of siloxane resin particles (product name: Tospearl 120) manufactured by Momentive Performance Materials were used as the light diffusing agent. It was.

[Comparative Example 19]
The same procedure as in Example 7 was performed except that styrene resin 19 was used as the styrene resin, and cross-linked styrene particles (product name: Techpolymer SBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

[Comparative Example 20]
The same procedure as in Example 7 was performed except that styrene resin 19 was used as the styrene resin and calcium carbonate (product name: Lumipearl DSN-7) manufactured by Nemoto Special Chemical Co., Ltd. was used as the light diffusing agent.

[Comparative Example 21]
The same procedure as in Example 7 was performed except that styrene resin 20 was used as the styrene resin, and cross-linked acrylic particles (product name: Techpolymer MBX-8) manufactured by Sekisui Plastics Co., Ltd. were used as the light diffusing agent.

The following evaluations were performed on the molded bodies of Example 7 to Example 33 and Comparative Examples 4 to 21.
(10) Total light transmittance, Haze
Based on JIS K7105, the total light transmittance and Haze (unit:%) of the molded body were measured using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.).
(11) Diffusivity Using a variable angle photometer (Nippon Denshoku Industries Co., Ltd., GC5000L), the light transmittance at each angle of the molded product was measured. Using the numerical value of the light transmittance at a specific angle, the diffusion rate (%) defined by the following formula was calculated (diffusion rate: JIS Z8113 number 04100).

(12) Dispersion of illuminance Illuminance was measured by the method shown below based on JIS C7612 using an illuminometer (manufactured by TOKYO OPTICAL, IM-3). In the illuminance distribution on the horizontal plane where the vertical distance from the molded body attached to the illumination is 1 m, the half-value width (unit: cm) is the illuminance dispersion.
[Illuminance measurement method]
The cover attached to the LED lighting (manufactured by Toshiba Lighting & Technology, Midget Reflex type, LEL-SL5N-F 40W) was removed, and each molded body was attached (the distance between the LED chip and the molded body was 8 mm). This was turned on in a dark place, allowed to stand for 30 minutes or more to stabilize the light source, and then the illuminance at a predetermined place was measured.
(13) Light resistance The test was carried out in the same manner as the “(9) Light resistance” test except that the molded products of Examples 7 to 33 and Comparative Examples 4 to 21 were used as test products.

  The results of the above examples and comparative examples are shown in Tables 2 to 6.

<Discussion>
As shown in Tables 2 to 4, the optical molded bodies of the examples according to the present invention had good total light transmittance and diffusivity, and good light resistance of 400 nm or more.

  The reason why the diffusivity is lowered in the comparative example is considered to be that the amount of the inhibitor is 10 ppm or more, or the amount of the phenylacetylene compound is 50 ppm or more. The reason why the Δb value indicating light resistance is large in the comparative example is considered to be that the amount of the polymerization inhibitor is 10 ppm or more and the content of the phenylacetylene compound is 50 ppm or more.

As described above, the light diffuser according to the present invention has good total light transmittance and diffusivity, and good light resistance. Therefore, it is useful as a light diffuser used for various applications such as lighting.
Moreover, since the light resistance with respect to light having a wavelength of 400 nm or more is good, it is also useful as a light diffuser (such as a diffusion plate or a diffusion cover) using an LED as a light source.

Claims (6)

An optical molded body obtained by molding a styrene resin obtained by polymerizing a styrene monomer having a polymerization inhibitor of less than 10 ppm and a phenylacetylene compound of 50 ppm or less. The optical molded body according to claim 1, wherein the styrene resin is a styrene- (meth) acrylic acid ester copolymer. The optical molded body according to claim 1, wherein the polymerization reaction is a radical solution polymerization reaction. A light guide plate using the optical molded body according to claim 1. A light diffuser using the optical molded body according to claim 1. 6. The light diffuser according to claim 5, comprising at least one mass diffusing agent selected from the group consisting of crosslinked acrylic particles, crosslinked styrene particles, siloxane resin particles, and calcium carbonate.