JP3964235B2 - Acrylic resin plate manufacturing method - Google Patents

Description

【００５１】
【表２】

【００５２】
【表３】

【００５３】
【発明の効果】
本発明によれば、アクリル樹脂中の白濁欠陥が低減され、透過損失の少ない光学用に適したアクリル系樹脂板状物の製造方法を提供することができる。このアクリル系樹脂板状物は、特に、薄型の看板や表示装置、液晶表示装置のフロントライト等に用いられる導光板用途に好適である。また特に、樹脂にメタクリル酸メチルとアクリル酸エステルとを含むことによって、さらに透過損失の少ないアクリル樹脂板状物を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an acrylic resin plate-like material in which a white turbidity phenomenon (Tyndall phenomenon) inside a resin due to light incidence is suppressed, and in particular, a front light of a liquid crystal display device, various display surface light source devices, and surface illumination. The present invention relates to a method of manufacturing an optical acrylic resin plate used as a light guide plate such as a device, a light condensing device, or an optical waveguide plate such as a light transmission device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a light source device used for a thin signboard, a display device, a back light source (backlight) and a front light source (front light) of a liquid crystal display device, a surface light emitting device that emits light by being incident on a light guide Are known. In recent years, a surface light-emitting device called a side ride method, in which a light source such as a cold cathode tube or a hot cathode tube is arranged on the side surface of a light guide and emits light in an arbitrary shape or pattern, has become mainstream.
[0003]
This type of light source device is required to have higher brightness and be more compact (light weight and thinner). Further, it is desirable that the light guide used in this light source device has high heat resistance and has as little transmission loss as possible due to light absorption, scattering, and reflection in the light guide. From such a point, an acrylic resin having a high light transmittance is used.
[0004]
However, even when acrylic resin is used, for example, in a front light type display device in which a sidelight type light guide plate is arranged in front of a liquid crystal cell, there is a transmission loss factor such as fogging inside the light guide plate. If present, image characteristics such as color reproducibility and contrast of the liquid crystal display are likely to deteriorate.
[0005]
As an acrylic resin with improved transmission loss used for a light guide, for example, Japanese Patent Application Laid-Open No. 7-33018, Japanese Patent Application Laid-Open No. 9-12822, and Japanese Patent Application Laid-Open No. 9-25386 include a phosphite compound in an acrylic resin. An acrylic resin composition in which the absorption of light due to heating and coloring during injection molding is reduced by containing at a specific concentration is disclosed. Japanese Patent Laid-Open No. 8-334626 discloses an acrylic resin light guide that does not contain an additive that absorbs light, such as an ultraviolet absorber, as an acrylic resin for a light guide plate with little visible light transmission loss. ing.
[0006]
Various methods such as a cast manufacturing method, an extrusion manufacturing method, an injection molding method, and a hot press molding method are known as a molding method of an acrylic resin plate material that is a base material of a light guide plate. In many cases, however, foreign matter of submicron to micron order is mixed. If foreign matter having a refractive index different from that of the acrylic resin is mixed, unevenness of brightness or defective bright spots may occur when light is incident on the light guide plate. Therefore, it is necessary to reduce such foreign matter as much as possible. For example, in JP-A-8-227004, JP-A-10-265530, and JP-A-8-248416, a light guide plate in which the size and amount of foreign matter in the acrylic resin, the type of volatile components, and the residual amount are specified. An acrylic resin composition has been proposed. Japanese Patent Application Laid-Open No. 8-334626 discloses an acrylic light guide that does not contain a substance that has a refractive index greater than the wavelength of light incident on the light guide.
[0007]
However, the acrylic resin composition for a light guide plate disclosed in these publications has reduced transmission loss due to a substance having a refractive index different from that of the light guide plate by the presence or absence of an additive or a physical method. The fundamental problem has not been solved. In particular, in a liquid crystal display device having a diagonal line length of 457 mm or more that uses a light guide plate with a plate thickness exceeding 5 mm, the light guide plate used has a long transmission optical path length, which is more susceptible to transmission loss, and the luminance of the surface light source Unevenness is likely to occur.
[0008]
Currently marketed light guide plates are manufactured by cell casting, extrusion, injection molding, hot press molding, and the like. However, in a light guide plate with a plate thickness exceeding 5 mm, a light guide plate manufactured by an extrusion method, an injection molding method, or a hot press molding method is thermally distorted due to the temperature difference between the inside of the plate and the plate surface portion that occurs during cooling. This may cause optical distortion and cause transmission loss. Such optical distortion causes a problem that an image looks distorted particularly in a light guide plate for a front light. In addition, there is a manufacturing problem that the time required for molding (molding cycle) becomes long.
[0009]
On the other hand, in the conventional cell cast plate making method, as the thickness of the plate to be made increases, a non-uniform composition distribution tends to occur inside the acrylic resin, and unreacted residual unsaturated monomer is started. There are substances having a refractive index different from that of the base material (polymethyl methacrylate), such as a by-product of the agent and an undissolved residue of the additive, and light absorption, scattering, and reflection are caused by them. Therefore, when the obtained acrylic resin light-guide plate injects light from the edge part, white turbidity is confirmed inside resin by light scattering and reflection. In particular, in the case of a light guide plate used in a front light type display device or a large light guide plate having a long optical path length, transmission loss is large.
[0010]
There are many unclear points about the cause of the cloudiness defect that causes such transmission loss, but non-uniform composition distribution occurs inside the acrylic resin, or unreacted residual unsaturated monomer, initiator by-product Substances that have a different refractive index from the base material (polymethyl methacrylate, etc.), such as undissolved residues of materials and additives, which cause light absorption, scattering, and reflection, resulting in white turbidity inside the acrylic resin it is conceivable that.
[0011]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems of the prior art. That is, an object of the present invention is to provide a method for producing an acrylic resin plate-like product in which white turbidity defects in an acrylic resin are reduced and transmission loss is small.
[0012]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventors have been able to reduce the white turbidity generated inside the acrylic resin plate-like material by performing the cell casting plate method in accordance with specific polymerization conditions, and for optical applications. The present inventors have found that an acrylic resin plate that is very suitable for the above can be obtained, and have completed the present invention.
[0013]
That is, the present invention provides a polymerization temperature of 20 ° C. or more and less than 60 ° C. in a method for producing an acrylic resin plate having a thickness of 10 mm or more by polymerizing a polymerizable raw material mainly composed of methyl methacrylate by a cast plate method. in the step of polymerizing further polymer conversion of 30% to 60% by weight or more heating at least one stage, followed by the following polymerization temperature 60 ° C. or higher 130 ° C., and more than the heating at least one stage A step of polymerizing the polymer conversion of the resin to 97% by mass or more, and the time T from the start of the polymerization step under the polymerization temperature condition of 60 ° C. to 130 ° C. until the peak of the exothermic polymerization is expressed by the following formula (1 )
T ≦ 0.4 × t (1)
[Wherein, T is the time from the start of the polymerization step under the polymerization temperature condition of 60 ° C. or higher and 130 ° C. or lower until the peak of the exothermic polymerization (hr), t is the thickness of the acrylic resin plate (mm)]
It is in the range represented by (4), The manufacturing method of the acrylic resin plate-shaped object characterized by the above-mentioned.
The present invention also relates to a method for producing an acrylic resin plate using the polymerizable raw material containing methyl methacrylate as a main component and containing an acrylate ester in the method for producing an acrylic resin plate.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, an acrylic resin plate having a thickness of 10 mm or more is produced by polymerizing a polymerizable raw material mainly composed of methyl methacrylate by a cast plate method. Usually, in the cast plate method having a plate thickness of 10 mm or more, it is necessary to carry out the polymerization while suppressing the polymerization exothermic temperature so as not to foam during the polymerization, and the polymerization is carried out at a low temperature for a long time. However, the acrylic resin plate obtained by the cast plate method under the conventional polymerization conditions has a large internal transmission loss, and the whole plate appears cloudy when observed by edge light incident from the side of the acrylic plate. On the other hand, in the present invention, the initial polymerization temperature is set within a range of 20 ° C. or more and less than 60 ° C., and the polymer conversion of the resin is polymerized to 30% by mass to 60% by mass, and then rapidly at a temperature exceeding 60 ° C. It is a method of polymerizing polymer conversion to 97% by mass or more by performing polymerization. Under such polymerization conditions, it is possible to obtain an acrylic resin plate material in which the internal transmission loss of an acrylic resin plate having a thickness of 10 mm or more is reduced.
[0015]
At a polymerization temperature of less than 20 ° C. or higher 60 ° C., in a step of polymerizing the more polymer conversions or more heating at least one step in 30% to 60% by weight (hereinafter referred to as "initial polymerization step"), the polymerization temperature is 20 If it is less than 0 ° C., it takes a long time for the polymerization, so it is not suitable for industrial production, and if it is 60 ° C. or more, the heat of polymerization exotherm becomes high and foaming defects may occur.
[0016]
In the initial polymerization step, it is preferable to perform polymerization using a warm water bath. Since the polymerization in the hot water bath has a large heat removal effect, it is possible to suppress an increase in the polymerization exotherm temperature, and in particular, it is possible to prevent runaway of the polymerization exotherm temperature in the thick plate polymerization.
[0017]
What is necessary is just to determine suitably the specific value of the superposition | polymerization temperature of an initial stage polymerization process within the above-mentioned temperature range according to the size, board thickness, etc. of the acrylic resin plate-shaped material to be manufactured. Initial In the polymerization step, in a temperature range described above, it is possible to further polymerizing the above heating at least one stage, for example, can also be multi-stepwise raised. When the temperature is raised in multiple stages, the polymerization can be carried out in a short time until a predetermined polymer conversion, so that the polymerization time can be shortened.
[0018]
Polymer conversion at the end of the initial polymerization step is 30% by mass to 60% by mass. If this exceeds 60% by mass, the internal transmission loss of the acrylic resin plate is increased, which is not preferable as an optical material. On the other hand, if it is less than 30% by mass, the polymerization exothermic temperature becomes too high in the polymerization step at a high temperature exceeding 60 ° C. after the initial polymerization step, and foaming defects may occur. Furthermore, the lower limit of polymer conversion is preferably 40% by mass or more, and the upper limit is preferably 50% by mass or less.
[0019]
In the present invention, after the above-mentioned initial polymerization step, a polymerization temperature of 60 ° C. or higher 130 ° C. or less, is polymerized further polymer conversion of the resin to less than 97% by mass or more heating at least one step process (hereinafter "hot The polymerization step). When the polymerization temperature in this high-temperature polymerization step is less than 60 ° C., not only the polymerization time becomes long, but also the internal transmission loss of the acrylic resin plate is increased, which is not preferable as an optical material. On the other hand, if it exceeds 130 ° C., the polymerization exotherm temperature becomes high and foaming defects are likely to occur.
[0020]
In the high temperature polymerization step, it is preferable to perform polymerization using an air bath. Polymerization using an air bath has a small heat removal effect, so that the polymerization exotherm temperature is likely to rise and the polymerization reaction proceeds rapidly, so that the polymer conversion can be rapidly increased.
[0021]
What is necessary is just to determine the specific value of a high temperature polymerization process suitably within the above-mentioned temperature range according to the size, board thickness, etc. of the acrylic resin plate to be manufactured. In the high temperature polymerization process, in a temperature range described above, it is possible to further polymerization in the Atsushi Nobori above at least one stage, for example, can also be multi-stepwise raised. When the temperature is raised in multiple stages, for example, in the polymerization of a thick plate, the polymerization can be carried out while suppressing the heat generated by the polymerization, so that foaming defects can be prevented.
[0022]
The polymer conversion at the end of the high temperature polymerization process is 97% by mass or more. In the produced acrylic resin plate-like product, if the remaining amount of the unreacted monomer is less than 3% by mass, the decrease in heat resistance and light resistance due to the unreacted monomer can be reduced, and A decrease in transmission loss due to light scattering caused by the remaining unreacted monomer can be suppressed.
[0023]
In high temperature polymerization process, in order to increase the polymer conversion of the acrylic resin plate was more than 97% by weight, in particular, next to one step MeNoboru temperature pattern in the high temperature polymerization process, 120 ° C. and the Atsushi Nobori of the second stage The heat treatment is preferably performed at a temperature of 130 ° C. or lower for 1 hour to 20 hours.
[0024]
In the high temperature polymerization step, the time T from the start of the step to the occurrence of the polymerization exothermic peak is expressed by the following formula (1).
T ≦ 0.4 × t (1)
[In the formula, T is the time (hr) from the start of the high-temperature polymerization step to the peak of the exothermic polymerization, and t is the thickness of the acrylic resin plate (mm)].
It is within the range expressed by
[0025]
If the time T from the start of the high-temperature polymerization process to the occurrence of the polymerization exothermic peak exceeds the time represented by the formula (1), the internal transmission loss of the resulting acrylic resin plate is increased, which is not preferable as an optical material. In addition, when the polymerization temperature conditions in the high temperature polymerization step are raised in multiple stages, the time T until the polymerization exothermic peak appears is the time from the start of the first stage high temperature polymerization step to the first polymerization exothermic peak. Represents.
[0026]
Furthermore, this time T is expressed by the following formula (2)
T ≦ 0.25 × t (2)
[T and t agree with formula (1)].
It is preferable to be within the range represented by
[0027]
In the present invention, the polymerizable raw material mainly composed of methyl methacrylate may be a polymerizable raw material containing only methyl methacrylate as a monomer, or other monomer copolymerizable with methyl methacrylate. The polymerizable raw material which consists of a monomer mixture with may be sufficient. Further, it may be a syrup-like polymerizable raw material comprising a methyl methacrylate homopolymer or a monomer mixture polymer and methyl methacrylate or a monomer mixture. The content of methyl methacrylate in the polymerizable raw material (including the content of methyl methacrylate units in the polymer when it includes a methyl methacrylate polymer) is preferably 50 mol% or more.
[0028]
As other monomers copolymerizable with methyl methacrylate, various conventionally known vinyl monomers can be used. For example, methyl acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, Examples include (meth) acrylic acid esters other than methyl methacrylate such as 2-hydroxyethyl (meth) acrylate. Here, “(meth) acrylic acid” is a general term for acrylic acid and methacrylic acid.
[0029]
Among these, a polymerizable raw material composed of methyl methacrylate and an acrylate ester is more preferable. As the acrylate ester, it is most preferable to use at least one selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. When the polymerizable raw material includes an acrylic ester and methyl methacrylate, the content of the acrylic ester is preferably 1 to 10% by mass, and in this range, 3% by mass or more is more preferable, and 7% by mass or less is particularly preferable. . The content of methyl methacrylate is preferably 90 to 99% by mass, and in this range, 93% by mass or more is more preferable, and 97% by mass or less is particularly preferable. When the polymerizable raw material contains an acrylate ester, it becomes easy to obtain an acrylic resin plate having excellent transparency with small transmission loss. However, if the content of the acrylate ester is too large, the heat resistance of the resulting acrylic resin plate is lowered, and in the light guide plate application close to the light source lamp that emits high heat, the resin plate is melted or deformed. There is a fear.
[0030]
Moreover, within the range in which transparency is not impaired and a plate-like product having desired characteristics is obtained, polyfunctionality such as ethylene glycol di (meth) acrylate, diethylene glycol (meth) acrylate, neopentyl glycol di (meth) acrylate ( A (meth) acrylate or the like may be added. Here, “(meth) acrylate” is a general term for acrylate and methacrylate.
[0031]
In the present invention, a polymerization regulator can be used as necessary. The polymerization regulator may be a compound having an action of delaying the polymerization rate, and various conventionally known compounds can be used. For example, mercaptan compounds such as n-butyl mercaptan and n-octyl mercaptan, limonene, myrcene, α-terpinene, β-terpinene, γ-terpinene, terpinolene, β-pinene, α-pinene and other terpenoid compounds, α-methyl Examples include styrene dimer. In particular, terpenoid compounds are preferable. These polymerization regulators may be used alone or in combination of two or more. The addition amount of the polymerization regulator is preferably 0.001 to 0.05 parts by mass with respect to 100 parts by mass of the polymerizable raw material.
[0032]
As the polymerization initiator, for example, an azo compound or a peroxide compound that is soluble in the polymerizable raw material is preferable, and particularly, it dissolves in methyl methacrylate or dissolves in a monomer mixture containing methyl methacrylate. Those are preferred.
[0033]
As the azo compound (azo polymerization initiator), for example, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis ( 2,4-dimethyl-4-methoxyvaleronitrile) and the like.
[0034]
Examples of peroxide compounds (peroxide polymerization initiators) include ketone peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, and cyclohexanone peroxide; isobutyryl peroxide, lauroyl peroxide, and benzoyl peroxide. Diacyl peroxides such as oxide; dialkyl peroxides such as 2,5-dimethyl-2,5-di- (t-butylperoxy) hexane; 1,1-di (t-butylperoxy) -3, Peroxyketals such as 3,5-trimethylcyclohexane; 1,1,3,3-tetramethylbutylperoxyneodecanoate, t-butylperoxyneodecanoate, t-butylperoxyneoheptanoate , T-hexyl peroxypivalate, t-butyl per Alkyl peresters such as xypivalate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate; di-3-methoxybutylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate Peroxycarbonates such as bis (4-t-butylcyclohexyl) peroxydicarbonate, di-isopropylperoxydicarbonate, t-butylperoxyisopropylcarbonate, t-butylperoxy-2-ethylhexylcarbonate; Can be mentioned.
[0035]
These polymerization initiators may be used alone or in admixture of two or more. The amount used is appropriately set according to the polymerization conditions such as the polymerization temperature, but is usually 0.0001 to 1 part by mass with respect to 100 parts by mass of the polymerizable raw material.
[0036]
It is necessary to avoid contamination of foreign matters as much as possible from the viewpoint of preventing the occurrence of defective bright spots during the preparation of the polymerizable raw material, the assembly of the cast cell, and the injection of the raw material into the cell. The polymerizable raw material is preferably polymerized after removing foreign substances with a fine filter medium (membrane filter, sintered metal filter, etc.).
[0037]
In the acrylic resin plate-like material, transparency is not impaired, and within a range where an acrylic resin plate having desired characteristics is obtained, various conventionally known ultraviolet absorbers, stabilizers such as antioxidants, flame retardants, An additive such as an antistatic agent or a release agent that facilitates peeling of the resin plate from the mold may be added.
[0038]
The cast plate making method in the present invention is a method of bulk polymerization of a polymerizable raw material in a mold. As the mold, for example, a mold made of a glass plate, a mirror-polished stainless steel plate, or the like can be used. Moreover, you may use the casting_mold | template which has a micro uneven | corrugated shape on an internal surface. As a batch-type cast plate method, for example, a polymerization initiator is dissolved in a space of a mold composed of two plates (glass plate, mirror-polished stainless steel plate, etc.) and an endless gasket made of vinyl chloride. The polymerizable raw material is injected, the polymerizable raw material is polymerized and cured, and the plate-like polymer is peeled off from the mold and taken out.
[0039]
【Example】
Hereinafter, the present invention will be described specifically by way of examples. Each evaluation was performed according to the following method.
[0040]
(1) Measurement of luminance:
In order to evaluate the degree of white turbidity inside the plate, the luminance was measured as follows. First, the acrylic resin plate was cut into a rectangular shape of 300 mm × 400 mm (optical path length 400 mm), and the four side surfaces around the plate were mirror-polished with an electric plane and a cloth polishing machine. A reflector film (SU119, manufactured by Tsujiden Co., Ltd.) having a reflectance of 96% was disposed on three side surfaces of the four side surfaces excluding one light incident surface. On the back side of the plate-like material, a black plate having a lightness of 2.0 was placed 10 mm away from the plate-like material. Further, a light source of an optical fiber illuminator using a 100 W halogen lamp (light source device manufactured by Mitsubishi Rayon Co., Ltd .: ELI 100J, optical fiber light guide width 1 mm × length 200 mm, illuminance at a location 50 mm away from the light exit surface of the light source: 100000 Lux ) Was installed in parallel to the central portion of the light incident surface in the thickness direction.
[0041]
Then, a luminance measuring device (LS-110 manufactured by Minolta Co., Ltd.) equipped with a close-up lens (No. 122 manufactured by Minolta Co., Ltd.) is installed at a position 350 mm away from the front of the plate-shaped object, and the front of the plate-shaped object is installed. The brightness in the vertical direction at the center was measured, and an index of the degree of white turbidity inside the plate was evaluated by brightness. That is, when light is incident on a plate-like object, the light is guided through the acrylic resin by transmission and reflection, and if there is a foreign substance or a non-uniform composition distribution in the resin, light absorption / scattering / reflection occurs. Since white turbidity is confirmed and transmission loss occurs, the degree of white turbidity can be evaluated by measuring the luminance.
[0042]
(2) Measurement of polymer conversion:
The acrylic resin in each step was freeze-pulverized in liquid nitrogen, and 2 g of the obtained resin was dissolved in 100 ml of chloroform, dropped and stirred in 3 L of n-hexane to reprecipitate the acrylic polymer. Thereafter, the solvent was filtered through a glass filter No. 2G3 (pore diameter: 40 μm to 100 μm) to obtain a polymer. Further, the polymer was volatilized and dried overnight in a vacuum dryer at 80 ° C., the weight of the dried polymer was measured, and the ratio of the polymer precipitated from the acrylic resin that was initially dissolved was calculated. Value.
[0043]
(3) Measurement of polymerization exothermic peak time:
When assembling the mold, set the T35 type sheath thermocouple (diameter 1 mm, length 1000 mm) manufactured by Sakaguchi Electric Heat Co., Ltd. so that the tip comes to the center of the plate size and the center of the plate thickness. It was connected to a pen recorder LR4110 manufactured by Co., Ltd., and the polymerization exothermic peak time was measured.
[0044]
<Example 1>
To 100 parts by mass of methyl methacrylate, 0.007 parts by mass of bis (4-t-butylcyclohexyl) -peroxydicarbonate and 0.007 parts by mass of terpinolene were added as a polymerization initiator and stirred for 30 minutes. After deaeration, two glass plates having a length of 400 mm × 500 mm and a thickness of 6 mm were poured into a mold formed through an endless tube made of vinyl chloride, polymerized for 20 hours in a 40 ° C. hot water bath, and subsequently 70 Polymerization was performed for 3 hours in an air bath at a temperature of 3 ° C., followed by completion of polymerization in an air bath at 130 ° C. for 2 hours to obtain an acrylic resin plate having a size of 350 mm × 450 mm and a thickness of 10 mm.
[0045]
Polymer conversion of the resin after polymerization in a 40 ° C. hot water bath was 44% by mass, polymer conversion after polymerization in a 70 ° C. air bath was 85% by mass, and polymer conversion after polymerization in a 130 ° C. air bath was 99% by mass. %Met. The time T from the start of the high-temperature polymerization process in the 70 ° C. air bath to the first peak of the exothermic polymerization was 0.4 hours. The obtained acrylic resin plate was measured for luminance, and the results shown in Table 1 were obtained.
[0046]
<Examples 2 to 8>
As shown in Table 1, an acrylic resin plate was produced in the same manner as in Example 1 except that the thickness of the resin plate, the raw material composition, the amount of the polymerization initiator, the polymerization temperature, and the polymerization time were changed. Here, the methyl methacrylate syrup is a syrup composed of a polymer obtained by polymerizing a part of methyl methacrylate and methyl methacrylate. The polymer conversion in the syrup is 10% by mass, and the viscosity of the syrup is The thing of 500 mPa * s was used. In Examples 6 to 8, the sample size in the luminance measurement was 200 mm × 200 mm. The luminance was measured for the acrylic resin plate obtained in each example, and the results shown in Table 1 were obtained.
[0047]
<Examples 9 to 14>
As shown in Table 2, an acrylic resin plate was produced in the same manner as in Example 1 except that the thickness of the resin plate, the raw material composition, the amount of the polymerization initiator, the polymerization temperature, and the polymerization time were changed. The methyl methacrylate syrup is a syrup composed of a polymer obtained by polymerizing a part of methyl methacrylate and methyl methacrylate, and the polymer content in the syrup is 10% by mass. A viscosity of 500 mPa · s was used. In Examples 11 to 14, the sample size in the luminance measurement was 200 mm × 200 mm. The acrylic resin plate obtained in each example was measured for luminance, and the results shown in Table 2 were obtained.
[0048]
<Comparative Example 1>
To 100 parts by mass of methyl methacrylate, 0.02 part by mass of bis (4-t-butylcyclohexyl) -peroxydicarbonate was added as a polymerization initiator and stirred for 30 minutes. After deaeration, two glass plates of length 400 mm x width 500 mm and thickness 6 mm are poured into a cell constructed through an endless tube made of vinyl chloride, polymerized in a 40 ° C hot water bath for 17 hours, and subsequently The polymerization was completed in an air bath at 130 ° C. for 2 hours to obtain an acrylic resin plate having a size of 350 mm × 450 mm and a thickness of 10 mm. The polymer conversion of the resin after polymerization in the 40 ° C. hot water bath was 85% by mass, and the polymer conversion after polymerization in the 130 ° C. air bath was 99% by mass. The obtained acrylic resin plate was measured for luminance, and the results shown in Table 3 were obtained.
[0049]
<Comparative Examples 2-5>
As shown in Table 3, an acrylic resin plate was produced in the same manner as in Example 1 except that the thickness of the resin plate, the raw material composition, the type and amount of the polymerization initiator, the polymerization temperature, and the polymerization time were changed. Moreover, the comparative example 4 and the comparative example 5 obtained the resin board in the same size as Examples 6-8. The resulting resin plate was measured for luminance, and the results shown in Table 3 were obtained.
[0050]
[Table 1]

[0051]
[Table 2]

[0052]
[Table 3]

[0053]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the cloudiness defect in an acrylic resin is reduced and the manufacturing method of the acrylic resin plate-shaped material suitable for the optical use with little transmission loss can be provided. This acrylic resin plate is particularly suitable for use as a light guide plate used for thin signboards, display devices, front lights of liquid crystal display devices, and the like. In particular, by including methyl methacrylate and acrylic ester in the resin, an acrylic resin plate-like product with further less transmission loss can be obtained.

Claims (4)

In a method for producing an acrylic resin plate having a thickness of 10 mm or more by polymerizing a polymerizable raw material mainly composed of methyl methacrylate by a cast plate method,
At a polymerization temperature of less than 20 ° C. or higher 60 ° C., a step of polymerizing the more polymer conversions or more heating at least one step in 30% to 60% by weight,
Then, at a polymerization temperature of 60 ° C. or higher 130 ° C. or less, and a step of polymerizing further polymer conversion of the resin to less than 97% by mass or more heating at least one stage,
The time T from the start of the polymerization step under the polymerization temperature condition of 60 ° C. or higher and 130 ° C. or lower until the occurrence of the polymerization exothermic peak is represented by the following formula (1)
T ≦ 0.4 × t (1)
[Wherein, T is the time from the start of the polymerization step under the polymerization temperature condition of 60 ° C. or higher and 130 ° C. or lower until the peak of the exothermic polymerization (hr), t is the thickness of the acrylic resin plate (mm)]
The manufacturing method of the acrylic resin plate-shaped object characterized by being in the range represented by (4). Time T is the following formula (2)
T ≦ 0.25 × t (2)
[T and t agree with formula (1)].
The method for producing an acrylic resin plate according to claim 1, wherein The method according to claim 1, wherein the optical acrylic resin plate is made of a terpenoid chain transfer agent. 2. The method for producing an acrylic resin plate according to claim 1, wherein a polymerizable raw material containing methyl methacrylate as a main component and containing an acrylic ester is used.