JP2010248318A - Optical molded article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical molded article that has good transparency and is less likely to cause the deformation due to heat and to cause the molding failure during the molding process. <P>SOLUTION: The optical molded article is formed from a styrene/methacrylic ester copolymer having (I) a mass ratio of a styrene monomer unit to a methacrylic ester monomer unit of 1:99-25:75, (II) a concentration of a residual methacrylic ester compound of not more than 1,000 ppm and (III) a Vicat softening point of not less than 107°C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to an optical molded body.

A methacrylic resin is known as a resin having excellent transparency. This resin is widely used in optical applications including light guide plates, home appliances, and office automation equipment. However, a commercially available methacrylic resin is copolymerized with an acrylate ester in order to improve thermal stability, and as a result, heat resistance is lowered. Since the heat resistance is low, there is a drawback in that deformation such as warpage is likely to occur due to heat generated from the device. Moreover, since acrylic ester makes a resin composition complicated, it can become a factor of transparency fall. Furthermore, there is a disadvantage that molding defects are likely to occur during molding. As a means for improving the heat resistance, there is a method of imidizing a methacrylic resin with an imidizing agent. However, this method is complicated because the operation is multistage, and there are also problems that transparency increases due to an increase in impurities.

JP 2001-342263 A JP2003-075648 JP 2006-052349 A JP 2006-052350 A Japanese Patent Application No. 2007-252848

The present invention provides a molded article for optics that has good transparency, hardly undergoes deformation due to heat, and hardly causes molding defects during molding.

That is, the present invention provides (1) (I) a mass ratio of styrene monomer units to methacrylate ester monomer units of 1:99 to 25:75, and (II) residual methacrylate ester compounds. An optical molded article comprising a styrene-methacrylic acid ester copolymer having a concentration of 1000 ppm or less and (III) a Vicat softening point of 107 ° C. or more. (2) The optical molded body according to (1), which is a light guide plate.

The molded article for optics of the present invention has good heat resistance, and since the amount of residual methacrylic acid ester compound is low, it has high transparency, so that it can be widely used for optical, household appliances and OA equipment applications. Furthermore, the low amount of residual methacrylic acid ester compound also imparted the effect of making it difficult to cause molding defects during molding of the molded body. Therefore, operability and productivity are improved, which leads to cost reduction.

<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 specification of the present application, the “optical molded body” means a member used for optical purposes, such as a light guide plate, a diffusion plate, and a lens.

Hereinafter, the present invention will be described in detail.
The molded article for optics used in the present invention is composed of a styrene-methacrylic ester copolymer comprising a styrene monomer unit and a methacrylic ester monomer unit.

Examples of the styrene monomer unit include styrene, α-methylstyrene, β-methylstyrene, p-methylstyrene, and the like, and styrene is preferable. These styrenic monomer units may be a single unit or a unit in which two or more types are mixed.

Examples of the methacrylic acid ester monomer units include methyl methacrylate, ethyl methacrylate, cyclohexyl methacrylate, and phenyl methacrylate, with methyl methacrylate being preferred. These methacrylic acid ester monomer units may be used alone or as a mixture of two or more types.

The ratio of the styrene monomer unit to the methacrylic acid ester monomer unit is, as a mass ratio, styrene monomer unit: methacrylic acid ester monomer unit = 1: 99 to 25:75. Preferably, it is 2: 98-15: 85. When the styrene monomer unit is 1% by mass or more, molding defects are hardly caused. When the methacrylic acid ester monomer unit is 75% by mass or more, the transparency is improved and it is difficult to be deformed by heat.

There is no particular limitation on the method for producing a copolymer comprising a styrene monomer unit and a methacrylic acid ester monomer unit, but if suspension polymerization or emulsion polymerization is employed, a dispersant or emulsifier used in the polymerization is used. May remain in the optical molded body and cause a decrease in the transparency of the optical molded body, and thus bulk polymerization and solution polymerization are preferable. From the viewpoints of production cost and filter filtration, continuous bulk polymerization using a small amount of a solvent such as toluene, xylene, ethylbenzene, hexane, cyclohexane, and acetone is more preferable.

As the monomer unit, other copolymerizable monomers can also be used.

The molecular weight of the styrene-methacrylate copolymer is preferably 70,000 to 150,000 in terms of polystyrene-equivalent weight average molecular weight (Mw) measured by GPC (gel permeation chromatography). The distribution (weight average molecular weight Mw / number average molecular weight Mn) is preferably 1.7 to 2.3.
If the Mw is 70,000 or more, a strong molded product is obtained, and if it is 150,000 or less, the workability during injection molding is good. Further, 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.

The residual methacrylic ester compound refers to a volatile impurity such as a methacrylic ester monomer or a dimer contained in the copolymer.

The concentration of the residual methacrylic ester compound contained in the styrene-methacrylic ester copolymer is preferably 1000 ppm or less, more preferably 800 ppm or less, and even more preferably 500 ppm or less. The lower the residual methacrylate concentration, the better. If the residual methacrylic ester compound concentration is 1000 ppm or less, molding defects are less likely to occur.

As a method of reducing the residual methacrylic acid ester compound of the styrene-methacrylic acid ester copolymer, a two-stage devolatilization using two devolatilization tanks having different vacuum degrees, or a copolymer obtained by polymerization is used. Known methods such as a method of extruding again while devolatilizing can be employed.

The Vicat softening point of the styrene-methacrylic acid ester copolymer is preferably 107 ° C. or higher. When the Vicat softening point is 107 ° C. or higher, deformation due to heat hardly occurs.

As a method of adjusting the Vicat softening point, a method of changing the composition ratio of the methacrylic ester monomer units in the copolymer, a method of reducing the residual methacrylic ester compound concentration in the copolymer, or heat stabilization For example, there may be mentioned a method in which an acrylate ester that may be copolymerized at the same time is not copolymerized.

Examples of the optical molded body include a light guide plate, a diffusion plate, and a screen lens of a projection television. Among them, it is useful as a light guide plate for liquid crystal displays and a light guide plate for illumination, and particularly useful as a light guide plate for medium to large-sized liquid crystal displays using LEDs as light sources.

As the shape of the light guide plate, a shape normally used as a light guide plate such as a plate shape or a wedge shape can be adopted. Moreover, you may give some shaping to the surface.

As a molding method of the optical molded body, a conventionally used molding method such as extrusion molding or injection molding can be employed.

In injection molding, it is preferable to mold at a cylinder temperature of 230 ° C to 300 ° C. When the temperature is higher than 230 ° C., the viscosity is lowered and the moldability is good. On the other hand, when the temperature is lower than 300 ° C., the copolymer is hardly decomposed, and impurities such as residual methacrylic ester compounds in the molded body are reduced.

Impurities contained in the copolymer cause a decrease in the transparency of the optical molded article, so the smaller the better. As a method for reducing these, there is a method of extruding using a fine filter at the time of extrusion. Furthermore, since this method can be used as a means for reducing the residual methacrylic ester compound shown in paragraph 0015, it is efficient as a method for reducing impurities.

For the copolymer used in the present invention, commonly used additives such as plasticizers, lubricants, antioxidants, light proofing agents, antistatic agents, sliding agents, and light diffusing agents can be used.

Hereinafter, although the detailed content of this invention is demonstrated using an Example, this invention is not limited to a following example.

[Test Example 1]
A complete mixing type continuous reaction tank with a capacity of 20 L equipped with a multistage paddle on a stirring blade, a column type plug flow type continuous reaction tank with a capacity of 11 L, and a flash type devolatilization tank with a preheater were connected in series. To a solution composed of 79.2% by weight of methyl methacrylate, 8.8% by weight of styrene, and 12.0% by weight of ethylbenzene, t-butylperoxyisopropyl monocarbonate (1 hour half-life temperature 118 ° C.) 0.009 Mass% and n-dodecyl mercaptan 0.32 mass% were mixed to prepare a raw material solution. The raw material solution was supplied at a rate of 3.9 kg / hour to a fully mixed continuous reaction tank controlled at a temperature of 125 ° C. The conversion rate at the fully mixed continuous reactor outlet was 57% by mass. When this polymerization solution was introduced into a column type plug flow type continuous reaction vessel adjusted so that the temperature gradient from the inlet to the outlet was 120 ° C to 150 ° C, a column type plug flow type continuous reaction vessel was obtained. The conversion rate at the outlet was 77% by mass. While this polymerization solution was heated to 230 ° C with a preheater, it was introduced into a flash-type devolatilization tank depressurized to 1.3 kPa.A, and unreacted monomer and ethylbenzene as a solvent were introduced at a tank temperature of 235 ° C. Removed. The resin was extracted with a gear pump, extruded into a strand, and cut to obtain a pellet-shaped copolymer.
The obtained copolymer was Mw = 78,000 and Mw / Mn = 1.9.

[Test Example 2]
T-Butylperoxyisopropyl monocarbonate (1 hour half-life temperature 118 ° C.) 0.006 with respect to a solution composed of 79.8% by weight of methyl methacrylate, 2.2% by weight of styrene and 18.0% by weight of ethylbenzene Mass% and n-dodecyl mercaptan 0.32 mass% were mixed to prepare a raw material solution. Otherwise, the same procedure as shown in Test Example 1 was performed.
The obtained copolymer was Mw = 84,000 and Mw / Mn = 2.0.

[Test Example 3]
0.02% by mass of t-butylperoxyisopropyl monocarbonate (1 hour half-life temperature 118 ° C.) with respect to a solution composed of 65.5% by mass of methyl methacrylate, 19.5% by mass of styrene and 15% of ethylbenzene, and n-dodecyl mercaptan 0.32% by mass was mixed to prepare a raw material solution. Otherwise, the same procedure as shown in Test Example 1 was performed.
The obtained copolymer was Mw = 76,000 and Mw / Mn = 2.1.

[Test Example 4]
To a solution composed of 76.6% by mass of methyl methacrylate, 8.8% by mass of styrene, 2.6% by mass of methyl acrylate, and 12.0% by mass of ethylbenzene, t-butylperoxyisopropyl monocarbonate (1 hour half-life) (Temperature 118 ° C.) 0.009% by mass and n-dodecyl mercaptan 0.32% by mass were mixed to obtain a raw material solution. Otherwise, the same procedure as shown in Test Example 1 was performed.
The obtained copolymer was Mw = 80,000 and Mw / Mn = 2.0.

[Test Example 5]
0.006% by mass of t-butylperoxyisopropyl monocarbonate (1 hour half-life temperature 118 ° C.) and 0.32% by mass of n-dodecyl mercaptan with respect to a solution composed of 80% by mass of methyl methacrylate and 20% of ethylbenzene Were mixed to obtain a raw material solution. Otherwise, the same procedure as shown in Test Example 1 was performed.
The obtained copolymer was Mw = 83,000 and Mw / Mn = 2.0.

[Test Example 6]
0.05% by mass of t-butylperoxyisopropyl monocarbonate (1 hour half-life temperature 118 ° C.) and n-dodecyl mercaptan with respect to a solution composed of 51% by mass of methyl methacrylate, 34% by mass of styrene and 15% of ethylbenzene 0.32 mass% was mixed to make a raw material solution. Otherwise, the same procedure as shown in Test Example 1 was performed.
The obtained copolymer was Mw = 77,000 and Mw / Mn = 1.9.

[Example 1]
The pellet-shaped copolymer shown in Test Example 1 was extruded again through a mesh having a mesh size of 5 μm while vacuum devolatilization to obtain a pellet-shaped resin product. This was dried at 80 ° C for 3 hours or longer, and using an injection molding machine (IS130) manufactured by Toshiba Machine Co., Ltd., at a cylinder temperature of 250 ° C and a mold temperature of 70 ° C, 126 mm long × 126 mm wide × 3 mm thick A flat plate was formed.
Using this flat plate, the following measurements (1) to (6) were performed and evaluated. The obtained results are shown in Table 1.

[Comparative Example 1]
The pellet-shaped copolymer shown in Test Example 1 was dried at 80 ° C. for 3 hours or more, and using a Toshiba Machine Co., Ltd. injection molding machine (IS130), the cylinder temperature was 250 ° C. and the mold temperature was 70 ° C. A flat plate having a length of 126 mm, a width of 126 mm, and a thickness of 3 mm was formed under the conditions. Using this flat plate, the following measurements (1) to (6) were performed and evaluated. The obtained results are shown in Table 1.

[Example 2]
A molded body was obtained under the conditions shown in Example 1 except that the pellet-shaped copolymer shown in Test Example 2 was used. The obtained results are shown in Table 1.

[Example 3]
A molded body was obtained under the conditions shown in Example 1 except that the pellet-shaped copolymer shown in Test Example 3 was used. The obtained results are shown in Table 1.

[Comparative Example 2]
A molded body was obtained under the conditions shown in Example 1 except that the pellet-shaped copolymer shown in Test Example 4 was used. The obtained results are shown in Table 1.

[Comparative Example 3]
A molded body was obtained under the conditions shown in Comparative Example 1 except that the pellet-shaped copolymer shown in Test Example 5 was used. The obtained results are shown in Table 1.

[Comparative Example 4]
A molded body was obtained under the conditions shown in Example 1 except that the pellet-shaped copolymer shown in Test Example 6 was used. The obtained results are shown in Table 1.

In addition, the characteristic evaluation of the said molded object was performed with the following method.
(1) Residual methacrylic ester compound amount The residual methacrylic ester compound amount in the copolymer was measured under the following GC measurement conditions.
Apparatus: GC12A FID detector column manufactured by Shimadzu Corporation: Glass column 3 mmφ × 3 m
Filler: Polyethylene glycol Carrier: Nitrogen temperature: Column 115 ° C, inlet 220 ° C
Sample pellets 0.5 g and cyclopentane 0.001 g were dissolved in N, N-dimethylformamide and measured using cyclopentane as an internal standard.

(2) Vicat softening point Using an injection molding machine (IS-80CNV) manufactured by Toshiba Machine Co., Ltd., a test piece having a length of 12.7 mm, a width of 64 mm, and a thickness of 6.4 mm was molded at a cylinder temperature of 220 ° C. Using this test piece, measurement was performed under the condition of a load of 49.0 N in accordance with JIS-K7206.

(3) Light loss rate The end faces of the molded bodies of the examples and comparative examples were polished and smoothed.
Next, the parallel light transmittance Y (%) was measured by the following measuring method.
Apparatus: Measuring instrument (ASA-300A) manufactured by Nippon Denshoku Industries Co., Ltd.
Optical path: The part that passes vertically through the polished surface

The light loss rate (%) was calculated by the following formula, where the parallel light transmittance was Y (%), the refractive index was n, and the reflectance was R (%).
Light loss rate (%) = 100− (Y + 2R)
However, R (%) = (n -1) 2 / (n + 1) 2 × 100

(4) The number average molecular weight (Mn) and the weight average molecular weight (Mw) of the average molecular weight copolymer were measured under the following GPC measurement conditions.
Equipment: SYSTEM-21 Shodex manufactured by Showa Denko
Column: 3 PLGel MIXED-B in series Temperature: 40 ° C
Detector: Differential refractive index Solvent: Tetrahydrofuran concentration: 2% by mass
Calibration curve: Prepared using standard polystyrene manufactured by PL, and the average molecular weight was expressed in terms of polystyrene.

(5) In the measurement of the heat deformation Vicat softening point, the one having a Vicat softening point of 107 ° C. or higher was rated as “◯”, and the one having 104 ° C. or lower was evaluated as “X”.

(6) Molding failure Under the molding conditions shown in the examples and comparative examples, five molded products from a certain point in time are sampled continuously, and this is defined as one cycle. When no molding defect occurs in the molded product in one cycle, the cycle is determined as “permitted”, and when one or more defects occur, the cycle is determined as “impossible”. This was repeated for 5 cycles, and “0” was assigned to “no” in 5 cycles, and “1” was assigned to 1 or more.

The resin molded body of the present invention has good heat resistance and high transparency due to the low amount of residual methacrylic acid ester compound. Therefore, it can be widely used in optical, household appliances and OA equipment applications. Because of its high transparency, it is suitable for optical molded articles, particularly light guide plates. Furthermore, there is an advantage that molding defects are hardly caused when the molded body is molded. Therefore, it is also effective in terms of operability and productivity.

Claims (2)

(I) The mass ratio of the styrene monomer unit to the methacrylic acid ester monomer unit is 1:99 to 25:75, (II) the residual methacrylic acid ester compound concentration is 1000 ppm or less, and (III ) An optical molded article made of a styrene-methacrylate copolymer having a Vicat softening point of 107 ° C or higher. The optical molded body according to claim 1, which is a light guide plate.