JPH0120642B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a methacrylic resin for information recording media. Methacrylic resin, whose main component is methyl methacrylate, not only has extremely high transparency and weather resistance, but also has well-balanced properties such as mechanical properties, thermal properties, and moldability. By taking advantage of these characteristics, it can be used as a sheet material or molding material for signboards, lighting equipment parts,
It is used in a wide variety of applications, including electrical equipment parts, automobile parts, and miscellaneous goods. Recently, methacrylic resin has begun to be used as a material for information recording media such as video discs, audio discs, and computer information file discs, taking advantage of its excellent properties including transparency. In particular, vinyl chloride resin, polystyrene, and
The use of sheets and films made of methacrylic resin has been proposed, but methacrylic resin has excellent light transmittance, is less prone to scratches than vinyl chloride resin, has a low birefringence, and has good surface precision and a beautiful finish. Because of these features, it is most suitable for information recording media that is optically reproduced using laser light. However, methacrylic resin has a relatively high hygroscopicity compared to polyolefin resins and polystyrene resins, resulting in dimensional changes due to moisture absorption, warping of molded products, etc.
Alternatively, cracks may occur due to long repeated cycles of moisture absorption and drying, and there are some fields where the use of ordinary methacrylic resins is restricted. In particular, materials for information recording media such as video disks, audio disks, large-capacity image files, and large-capacity computer disk memories are required to have a high degree of dimensional stability, such as the absence of warpage in molded products, and are highly hygroscopic. Improvements are requested. The problem of hygroscopicity of methacrylic resin is, to some extent, an inherent property caused by the chemical structure of the polymer, and so far there have been few proposals for modification methods, and of course, no commercialization has been carried out. It is. In view of the current situation, the inventors of the present invention have conducted intensive studies to improve the hygroscopicity of methacrylic resin and to develop a methacrylic resin with excellent optical properties. By copolymerizing a specific amount of methyl methacrylate, we discovered a completely new effect in that the hygroscopicity of methyl methacrylate polymer, which is completely different from the previously known optical properties, was significantly reduced. We discovered that copolymers within the range of ingredients possess the excellent properties inherent to methacrylic resins, such as transparency, weather resistance, mechanical properties, thermal properties, and moldability as sheet materials or molding materials. This invention has been achieved. That is, the present invention is based on the formula () 50 to 90% by weight of methyl methacrylate (A) units represented by the formula () Cyclohexyl methacrylate (B) unit 5 represented by
~30% by weight, formula () 5 to 30% by weight of benzyl methacrylate (C) units represented by and formula () (R in the formula is a linear or branched alkyl group having 1 to 8 carbon atoms) or an alkyl acrylate represented by the formula () This is a methacrylic resin for information recording media comprising 0 to 10% by weight of at least one vinyl compound (D) unit selected from the styrenes shown below. The homopolymer of cyclohexyl methacrylate used as a copolymerization component of the methacrylic resin of the present invention has a higher refractive index than other methacrylate polymers and also has excellent light dispersion properties, so it has excellent basic performance as a plastic lens material. Although it has been known for some time that the polymer possesses a . Furthermore, although the homopolymer of benzyl methacrylate has a high refractive index, it has a low heat deformation temperature and poor thermal properties, which poses extremely serious problems for practical use. The present invention provides that a methacrylic resin with excellent optical properties and improved hygroscopicity can be obtained by copolymerizing cyclohexyl methacrylate and benzyl methacrylate as components giving a high refractive index with methyl methacrylate. This is what we discovered. In the present invention, 50 to 90% by weight of methyl methacrylate (A) is used in order to impart optical properties, weather resistance, mechanical properties, thermal properties, or moldability inherent to methacrylic resin to the resulting copolymer. composition range, more preferably 55 to 75% by weight
It is. If the content is less than 50% by weight, the above-mentioned properties will be impaired, and if it exceeds 90% by weight, the effect of improving hygroscopicity will be reduced. In the present invention, cyclohexyl methacrylate (B)
The usage ratio of 5 to 30% by weight is the amount of component necessary to modify the hygroscopicity of the resulting copolymer, and more preferably 15 to 25% by weight. This is because if it is less than 5% by weight, the effect of improving hygroscopicity is not sufficient, and if it exceeds 30% by weight, the mechanical properties of the copolymer will be greatly reduced. In the present invention, the proportion of benzyl methacrylate (C) used in the range of 5 to 30% by weight is an amount for improving the hygroscopicity of the resulting copolymer without deteriorating its mechanical properties, and more preferably, 15-25% by weight
It is. This is because if it is less than 5% by weight, the effect of modifying hygroscopicity is insufficient, and if it exceeds 30% by weight, the heat deformation resistance of the copolymer will be poor. The vinyl compound (D) copolymerizable with (A), (B), and (C), which can be used as necessary in the copolymer of the present invention, is a linear or branched alkyl acrylate having 1 to 8 carbon atoms or It is at least one kind of vinyl compound selected from styrene, and its usage ratio is preferably 10% by weight or less. In particular, when the copolymer of the present invention is put to practical use as a molding material, in order to improve the thermal decomposition resistance of the copolymer in consideration of molding in a relatively high temperature range,
Preferably, 0.5 to 10% by weight of vinyl compound (D) is used. If the proportion of (D) used is less than 0.5% by weight, the heat decomposition resistance will not be sufficient, and if it exceeds 10% by weight, the transparency may decrease, the hygroscopicity may decrease, and the heat distortion temperature may decrease. There is a problem that it may deteriorate. Particularly preferable components for the vinyl compound (D) include ethyl acrylate and butyl acrylate from the viewpoints of heat decomposition resistance, hygroscopicity, and heat deformation resistance. The polymerization method for obtaining the methacrylic resin of the present invention may be any polymerization method such as bulk polymerization, solution polymerization, suspension polymerization, or emulsion polymerization, but when obtaining the methacrylic resin as a sheet material, a bulk polymerization method using a cast method is used.
When the purpose is a molding material, suspension polymerization or emulsion polymerization is preferred from the viewpoint of productivity and workability. For specific implementation, it is sufficient to use a very commonly used formulation. For example, in the case of bulk polymerization using the cast method, partial polymerization is first performed from a monomer mixture blended in a predetermined ratio. The material may be prepared, poured into a glass or stainless steel cell equipped with a vinyl chloride resin frame, and polymerized at a temperature of 30 to 130°C for several hours. When using suspension polymerization or emulsion polymerization, a monomer mixture containing a radical polymerization initiator and a chain transfer agent for controlling molecular weight is dispersed in water in which a suspension dispersant or emulsifier is dissolved. , the polymerization may be carried out at a temperature range of 30 to 130°C for several hours. The methacrylic resin of the present invention may be used by mixing other polymers as necessary, and may also be used by adding additives such as oxidation stabilizers, weathering stabilizers, colorants, and mold release agents. It's okay. The methacrylic resin of the present invention has greatly improved hygroscopicity without sacrificing the original properties of methacrylic resin, and is particularly useful as an information recording medium because of small dimensional changes due to environmental changes. EXAMPLES The specific content of the present invention will be explained below with reference to Examples, but the content of the present invention is not limited thereby. Example 1 3 equipped with a condenser, stirrer, and thermocouple
1500 g of pure water was placed in a separable flask, and 15 g of polyvinyl alcohol was added as a dispersant and dissolved in the pure water. On the other hand, a chain transfer agent n-octyl mercaptan was added to a monomer mixture of 600 g of methyl methacrylate, 250 g of cyclohexyl methacrylate, 130 g of benzyl methacrylate, and 20 g of butyl acrylate.
Add 1.5g of azobisisobutyronitrile as an initiator and dissolve with stirring.The mixture was poured into a separable flask containing pure water in which the dispersant prepared earlier was dissolved, and rotated at a temperature of 80℃. Polymerization was carried out while stirring at several 350 rpm, and after the peak time, polymerization was carried out at 98°C for 3 hours. The obtained polymer was dried at 75°C for 24 hours and shaped into pellets at a cylinder temperature of 240°C. This pellet was injection molded at a cylinder temperature of 235°C and a mold temperature of 60°C to form a 2m/m x 110mm x 110mm pellet.
An injection molded plate of mm was fabricated. This injection molded plate
The water absorption rate was measured by heating in boiling water at 100°C for 4 hours in accordance with ASTMD-570 and found to be 1.1%.
In addition, bending strength, total light transmittance haze value, heat distortion temperature [HDT], and FR were measured, and the results shown in Table 2 were obtained. Furthermore, one side of this molded plate is vapor-deposited with aluminum,
When this was immersed in water at 23℃ for 72 hours, we measured the warpage (hygroscopic strain) at the center and found that the hygroscopic strain was
It was less than 0.1mm. In contrast, the conventional methacrylic resin (shown in Comparative Example 5) had a water absorption rate of 2.1% and a hygroscopic strain of 1.5 mm, indicating that the copolymer of this example had significantly improved hygroscopicity. Comparative Examples 1 to 4 Polymerization was carried out in the same manner as in Example 1 except that the monomer composition in Example 1 was changed as shown in Table 1, and the obtained polymer was injection molded to form an injection molded plate. The physical properties were measured and the results are shown in Table 2 together with those of Example 1. As is clear from the results in Table 2, it can be seen that the examples of the present invention have well-balanced physical properties such as optical properties, mechanical properties, thermal properties, and hygroscopicity.

【table】

[Table] Example 2 A monomer mixture of 580 g of methyl methacrylate, 200 g of cyclohexyl methacrylate, 200 g of benzyl methacrylate, and 20 g of styrene was polymerized in exactly the same manner as in Example 1, and the resulting polymer was injection molded. The physical properties of the injection molded plates were measured and the results are shown in Table 3.

[Table] Example 3 A monomer mixture of 600 g of methyl methacrylate, 250 g of cyclohexyl methacrylate, and 150 g of benzyl methacrylate was placed in a 3-separable flask equipped with a stirrer and a condenser, and 0.6 g of azobisvaleronitrile was added as an initiator. The mixture was charged, dissolved, and polymerized at 115°C for 5 minutes to obtain a partially polymerized product. To 500 g of this partially polymerized product, 0.05 g of ultraviolet absorber Titabin P (manufactured by Ciba Geigy) and 0.35 g of azobisvaleronitrile as an initiator were added and mixed and dissolved, then poured into a glass cell and polymerized at 65°C for 4 hours.
Polymerization was carried out at 120°C for 2 hours to obtain a sheet-like polymer.
The water absorption, total light transmittance, haze value, bending strength, and HDT of this polymer were measured, and the results shown in Table 4 were obtained.

[Table] Example 4 Put 3000 g of pure water into a 5-separable flask equipped with a stirrer and condenser, add 30 g of emulsifier Sarcosinate LN (manufactured by Nikko Chemicals),
0.015 g of ferric sulfate and 0.06 g of ethylenediaminetetraacetate disodium salt were added and dissolved, and then 6 g of the reducing agent Rongalit was dissolved.
Meanwhile, 870g of methyl methacrylate, 360g of cyclohexyl methacrylate, 225g of benzyl methacrylate
g, t- to a monomer mixture of 45 g of butyl acrylate.
After mixing and dissolving 4.5 g of butyl hydroperoxide and 3 g of n-octyl mercaptan, the mixture was placed in a separable flask and polymerized at 65° C. and 300 rpm for 6 hours. The obtained latex was coagulated using sulfuric acid as a coagulant, and then washed, dehydrated, and dried to obtain a powdery polymer. This polymer is shaped and molded to improve water absorption, total light transmittance,
The haze value, bending strength, HDT, and FR were measured and the results shown in Table 5 were obtained.

【table】

Claims (1)

[Claims] 1 Formula () 50 to 90% by weight of methyl methacrylate (A) units represented by the formula () Cyclohexyl methacrylate (B) unit 5 represented by
~30% by weight, formula () 5 to 30% by weight of benzyl methacrylate (C) units represented by and formula () (R in the formula is a linear or branched alkyl group having 1 to 8 carbon atoms) or an alkyl acrylate represented by the formula () A methacrylic resin for information recording media, comprising 0 to 10% by weight of at least one vinyl compound (D) unit selected from the styrenes shown below.