JPS5914045B2 - Method for producing methacrylic resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a transparent methacrylic resin composition that is weather resistant, impact resistant and moldable.

In particular, the present invention relates to a method for producing a methacrylic resin having improved properties in terms of toughness, transparency, and gloss. Methacrylic resin is widely used due to its excellent transparency, gloss, and weather resistance, but its uses are limited due to unsatisfactory mechanical properties such as toughness and impact strength.

5 Many methods have been proposed to improve this drawback, but the best way to combine good impact strength and good transparency is to inject fine particles with exactly the same refractive index into a hard resin such as methacrylic resin. It is known to disperse elastomer particles10.

Conjugated diengomas are often used as this polymerized elastomer component, and among these, for example,
According to No. 17806, an improvement in 15 impact resistance can be achieved without impairing transparency by selecting a diene rubber composition.

However, when a diene rubber is used as an elastomer component, a decrease in weather resistance cannot be avoided, and this causes not only a decrease in mechanical properties but also a decrease in optical properties.
That is, it means that the original transparency 20 is lost.

In order to impart impact resistance without impairing the weather resistance of polymethyl methacrylate, non-diene rubbers such as acrylic acid alkyl ester polymers, ethylene-vinyl acetate copolymer or ethylene-propylene copolymer rubber are used. 25 and the like, but in this case as well, efforts are being made to closely match the refractive index of the elastomer component to that of the hard resin that is the matrix, in order to ensure the transparency of the hard resin. The present inventors first prepared a hard polymer emulsion by heterogeneously polymerizing methyl methacrylate or a monomer mixture mainly composed of 30 methyl methacrylate in an aqueous medium without using an emulsifier. Then, a monomer (hereinafter abbreviated as rubbery 35 monomer) that provides a rubbery polymer by polymerization is added to this emulsion and polymerized, thereby changing the refractive index of the hard resin phase and the rubber phase. Impact resistance and transparency can be achieved through a simple process without having to consider the match too closely. They discovered that it was possible to produce a methacrylic resin composition with good clarity, and filed a patent application (Japanese Patent Application No. 51-3898, 31805).

Furthermore, it was also confirmed that when an acrylic acid ester is used as a monomer to provide a rubbery polymer, the weather resistance of the methacrylic resin is not impaired. However, in such a manufacturing method, in order to make the final resin composition moldable, the molecular weight of the sheet polymer must be adjusted to such an extent that the intrinsic viscosity [η] (in chloroform, 25°C) is 1.5 or less. It is important to keep the melt viscosity low. However, in this case, when the molecular weight of the sheet polymer was lowered to a point that met the injection molding conditions for ordinary methacrylic resins, there was a drawback that the toughness, especially the tensile elongation, and gloss were considerably low. Furthermore, in some cases, separation of the resin phase and rubber phase was observed by standing for a long time. The purpose of the present invention is to
The purpose of this is to provide a method for producing methacrylic resin that maintains transparency and impact resistance and has high toughness even when the molecular weight of the sheet polymer is lowered to improve fluidity to the point where it can be injection molded. According to the present invention, the molecular weight can be controlled by heterogeneously polymerizing methyl methacrylate or a monomer mixture mainly composed of methyl methacrylate in an aqueous medium in the presence of a molecular weight regulator and without using an emulsifier. An emulsion of a hard polymer is prepared, and then, in this emulsion, (a) a monomer that provides a rubbery polymer by polymerization or a monomer mixture containing the monomer as a living body, and (b) the monomer or 0.01 of the monomer mixture
This can be achieved by carrying out polymerization by adding a radically polymerizable polyfunctional monomer having at least one allyl group or metaallyl group in an amount of 5 mol %. First in the present invention
The key point is to carry out the polymerization of methyl methacrylate-containing monomers in an aqueous medium without the use of so-called emulsifiers to obtain polymer emulsions. As the polymerization catalyst, a redox catalyst such as a potassium persulfate-sodium thiosulfate copper monosulfate system as described in JP-A-50-61484 is preferably used. There is no generation of particles, so-called "Seed"
Polymerization is complete. By adjusting the polymerization conditions such as catalyst amount and monomer concentration, the particle size can be adjusted to 0.1 to 0.3μ.
A stable emulsion of sheet polymer can be obtained. The monomer to be polymerized may be methyl methacrylate alone, and is mainly composed of methyl methacrylate, acrylic acid esters such as methacrylic acid, acrylic acid, methyl acrylate, ethyl acrylate, and butyl acrylate, styrene, and α-methylstyrene. It may also be a mixture with other monomers such as styrene derivatives. These other monomers are used to modify methacrylic resins. In this sheet polymerization,
It is important to control the molecular weight of the sheet polymer by using an appropriate amount of a molecular weight regulator (this is important in order to make the fluidity of the final resin composition appropriate).
Intrinsic viscosity of sheet polymer [η] (in chloroform, 2
5℃) is in the range of 0.3 to 1.0? It is preferred for thermoforming such as injection molding. The second key point of the present invention is to perform polymerization by adding a rubbery monomer to the second stage of sheet polymerization.

It is believed that the rubber monomer swells into the sheet particles and polymerizes inside the particles to form a rubber polymer.
Contrary to the method of the present invention, when the sheet particles are made of a rubbery polymer and methyl methacrylate or a monomer mixture mainly composed of methyl methacrylate is polymerized in the second stage, the desired transparent resin No composition is obtained. In the present invention, the monomers that produce rubber-like polymers when polymerized are monoolefin monomers that produce rubber-like elasticity at room temperature when polymerized, such as methyl acrylate, ethylene, etc. Preferably used are lower alcohol esters such as , propyl and butyl esters, higher alcohol esters of acrylic acid such as octyl ester, and higher alcohol esters of methacrylic acid such as octyl methacrylate. These rubbery monomers can be used alone or mixed with each other or with small proportions of other monomers. The rubber monomer t is preferably used in the polymerization of the methyl methacrylate-containing monomer in the first stage in an amount of 5 to 40% by weight of the hard polymer obtained. The larger the amount used, the higher the impact resistance, but the lower the softening point of the resin. Conversely, if the amount is small, the softening point will approach that of hard resin, but the degree of increase in impact resistance will be small. The second stage of polymerization is carried out by combining these rubbery monomers with a polyfunctional monomer that can moderately crosslink them (this polyfunctional monomer contains at least one allyl The third important point in the present invention is to use a monomer having a group or a meta-allyl group as a functional group.

Examples of such polyfunctional monomers having an allyl or meta-allyl group include allyl acrylate, meta-aryl acrylate, allyl methacrylate, meta-allyl methacrylate, triallyl cyanurate or triallyl isocyanurate, diallyl phthalate, etc. . By crosslinking the rubber phase with one or more monomers selected from these, the mechanical properties, optical properties, especially tensile elongation, and gloss of the final resin obtained can be significantly improved. be. In other words, such polyfunctional monomers are more effective in achieving the intended purpose than when using cross-linked monomers selected from divinylbenzene, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, etc. This has the effect of significantly increasing the toughness and gloss of the resin composition. The amount of such polyfunctional monomer used is 0.01 to 5 mol% of the rubber monomer.
is within the range of If the amount used is too small from this range, impact resistance and transparency will decrease. On the other hand, if the amount used is too large than this range, not only will the impact resistance decrease, but the melt viscosity will become extremely high, resulting in a decrease in fluidity and making it unsuitable for hot molding. The polymerization of the rubber monomer is preferably started after the first stage polymerization of the methyl methacrylate-containing monomer has progressed by 70 to 90%.

It is also desirable to add a small amount of polymerization initiator when adding it to the polymerization system in order to shorten the polymerization time. The dispersed polymer particles obtained in the form of an emulsion according to the present invention have a uniform particle size distribution of about 0.2μ, and can be easily dispersed by mixing the emulsion with a dilute aqueous calcium chloride solution, a dilute aqueous magnesium chloride solution, etc. It can be recovered by salting out or by spray drying.

The resulting particulate resin can be subjected to molding after filtering and drying, and can be extruded or injection molded. Since the methacrylic resin composition obtained in the present invention does not contain emulsifiers or stabilizers, there is no deterioration in product quality such as coloring or water resistance due to these.

EXAMPLES Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

All parts are by weight unless otherwise indicated. Example
1-3 1800 parts of pure water, 282 parts of methyl methacrylate, 18 parts of methyl acrylate, and 1.8 parts of lauryl mercaptan in a 3,000 m1 three-lens flask equipped with a reflux condenser, a thermometer insertion tube, and a mixing device. under a stream of high-purity nitrogen with constant stirring (320
36 parts of potassium persulfate at 1 x 10-1 mol/t (concentration in the system: 1.7 x 10-3 mol/t)
), 36 parts of a 1 x 10-1 mol/t aqueous sodium thiosulfate solution (concentration in the system: 1.7 x 10-3 mol/t), and 5
x 6 parts of a 10-3 mol/t copper sulfate aqueous solution (concentration in the system: 1.
Immediately after adding 4×10 −5 mol/t), the polymerization system became cloudy and polymerization started.

The temperature of the polymerization system was maintained at 70±3°C. After about 3 hours, when the polymerization rate reached almost 80%, butyl acrylate 9
0f! II). 15 parts of styrene, a predetermined amount of allyl acrylate, and 3 parts of an aqueous solution of potassium persulfate at 0-1 mol/t
6 parts were added to continue the polymerization. After about 2 hours, the polymerization was complete. 600 parts of a 1.5% calcium chloride aqueous solution was added to the system and heated to 90°C, the resulting polymer was salted out and coagulated, washed with water to remove the catalyst, filtered, and dried with hot air maintained at 70°C. The mixture was left to dry in the machine overnight to obtain a white powder. The obtained powder was masticated at 180°C for 5 minutes (Plastograph PL-300 manufactured by Brabender Co., Ltd.) and press-formed at 230°C to obtain a sheet, and a sample for physical property measurement was prepared. Physical property measurement results are shown in Table 1.The molded product had good gloss and excellent transparency.It was weather resistant according to JIS-Al41O using a xenon weather tester (Model XW-60V-3 manufactured by Shimadzu Corporation). As a result of conducting a property test, it was found that these physical properties showed almost no deterioration even after 300 hours of irradiation with a weather tester.The results are shown in Table 1.Examples 4 to 6 In Example 1, allyl acrylate Polymerization was carried out in exactly the same manner as in Example 1 except that allyl methacrylate was used instead of , followed by post-treatment and mastication to prepare a sample.

The physical property measurement results are shown in Table 1. The molded product had good gloss and excellent transparency. Comparative Example 1 Polymerization was carried out in exactly the same manner as in Example 1, except that 8 parts of allyl acrylate (8.43 mol % of the total of butyl acrylate and styrene) was used.

The resulting resin composition had a high melt viscosity, making it difficult to masticate using a plastograph, and injection molding at 230 to 250°C (C4B type, manufactured by Arburg) impossible. Comparative Examples 2 to 5 Polymerization was carried out in exactly the same manner as in Example 1, except that a predetermined amount of ethylene glycol dimethacrylate or divinylbenzene was used in place of allyl acrylate.

The physical property measurement results are shown in Table 1. Comparative Example 6 In Example 1, 90 parts of butyl acrylate, 15 parts of styrene, and 0.68 parts of allyl acrylate were used instead of methyl methacrylate, methyl arylate, and lauryl mercaptan in the first stage sheet-forming polymerization, and the second stage Polymerization was carried out in exactly the same manner except that 282 parts of methyl methacrylate, 18 parts of methyl acrylate, and 1.8 parts of lauryl mercaptan were used instead of butyl acrylate, styrene, and allyl acrylate.

A sheet obtained by press-molding the obtained composition was milky white and brittle. Reference Example 1 Polymerization was carried out in exactly the same manner as in Comparative Example 2, except that the molecular weight regulator lauryl mercaptan was not used at all.

Although the resulting composition had an elongation at break of 70%, it had poor fluidity and injection molding at 230 to 250°C (C4BO manufactured by Arburg was impossible.) From the results shown in Table 1, It is clear that the methacrylic acid resin composition according to the present invention has excellent toughness and weather resistance.

Claims (1)

[Claims] 1. By heterogeneously polymerizing methyl methacrylate or a monomer mixture containing methyl methacrylate in an aqueous medium in the presence of a molecular weight regulator and without using an emulsifier, a hard polymer with a controlled molecular weight can be produced. An emulsion is prepared, and then, in this emulsion, (a) a monomer that is polymerized to give a rubbery polymer or a monomer mixture containing the monomer as a living body, and (b) the monomer or the monomer A methacrylic resin composition characterized in that polymerization is carried out by adding a radically polymerizable polyfunctional monomer having at least one allyl group or methalyl group in an amount of 0.01 to 5 mol% of the mixture. Manufacturing method.