KR20050109318A - Methacrylic resin composition having good heat-resistance - Google Patents

Abstract

The methacrylic resin having excellent heat resistance of the present invention is a monomer mixture consisting of 80 to 98 parts by weight of alkyl methacrylate and 2 to 20 parts by weight of alkyl acrylate, and 0.008 to 0.05 parts by weight of polyfunctional monomer and 0.8 to 2.5 parts by weight of sulfur-containing molecular weight regulator. It is prepared by suspension polymerization by adding a part, and the weight average molecular weight (M _w ) is characterized in that the range of 90,000 to 150,000.

Description

Methacrylic resin having excellent heat resistance {Methacrylic Resin Composition Having Good Heat-resistance}

Field of invention

The present invention relates to a methacrylic resin having excellent heat resistance and melting characteristics. More specifically, the present invention has a specific weight average molecular weight (M _w ) range by introducing an appropriate amount of a multifunctional monomer and a chain transfer agent to the methacrylate monomer mixture, thereby providing excellent heat resistance and melt-stretching properties without deterioration of mechanical properties. It relates to a methacryl-based resin having a.

Background of the Invention

In general, methacrylic resins are well known to have sufficient rigidity, high transmittance and excellent weather resistance. Due to these characteristics, methacryl-based resins have been applied in various fields. For example, injection products of methacryl-based resins are used in taillights, instrument panel covers, and eyeglass lenses of automobiles, and extruded products are used in signboards and various sheet products. .

Therefore, the methacrylic resin is required to have excellent processing characteristics and heat resistance due to the characteristics of such a use. Generally, in order to improve processing characteristics, a method of lowering the molecular weight or a method of preparing a copolymer using an acrylic comonomer is frequently used. However, lowering the molecular weight improves the flow characteristics of the process, while lowering the mechanical properties. In addition, in the case of using an acrylic comonomer, since the heat resistance is affected by the content of the comonomer, there is a limit to the application of the product.

On the other hand, in general, the stretching property of the resin is closely related to the chemical structure of the resin, and for olefinic resins such as polyolefins, the stretching property is more robust and thicker than that of the linear structure when the resin structure is branched. It is known that molded articles having a uniform distribution can be obtained. In the case of resin having a branched structure, the swell ratio has a high characteristic. Swell ratio refers to the diameter of the strand flowing out of the molten state during extrusion divided by the die diameter. The larger the swell ratio, the better the molten stretching characteristic is.

Methacrylic resins generally have poor thermal stability. This is because of the polymerization reaction characteristics of the methacrylic resin. That is, in the case of methacryl-based resin, the heterogeneous stop reaction is predominant, so that even after the reaction is terminated, a large number of unsaturated reactors are included in the chain terminal. As a result, pyrolysis occurs during the machining process, and thus, heat resistance characteristics are deteriorated.

In order to solve this problem, Japanese Patent Nos. 256,551 and 304,045 disclose a method of adding a phosphorus thermal stabilizer or a phenolic thermal stabilizer. However, this method is not preferable because it adversely affects the transmittance or color of the resin.

U. S. Patent No. 3,978, 022 has also proposed a method of suppressing pyrolysis by adding disulfide.

In addition, US Pat. No. 4,661,571 has proposed a method of improving thermal stability by using 2-mercaptoethyl alkanecarboxylate or 3-mercaptopropionate as a chain transfer agent.

US Pat. No. 5,726,268 proposes a method of improving physical properties by introducing a polyfunctional monomer to adjust the molecular weight to about 150,000 to 300,000. However, in the case of methacrylic resins, since the melt viscosity is basically high, processing conditions must be severely maintained in order to process the resin having such a molecular weight. In addition, there is a problem in that the appearance quality is deteriorated due to the relatively high Yellow Index value generated by the cosmetic melt gel.

Therefore, in order to solve the above problems, the present inventors introduce a polyfunctional monomer and a chain transfer agent having an appropriate content in the methacrylic resin polymerization process to have a specific range of molecular weight, thereby improving heat resistance and good flow characteristics without deterioration of mechanical properties. It is early to develop a methacrylic resin showing a.

An object of the present invention is to provide a methacrylic resin having excellent heat resistance.

Another object of the present invention is to provide a methacrylic resin having good stretching properties.

Still another object of the present invention is to provide a methacrylic resin having little unmelted gel formation.

The above and other objects of the present invention can be achieved by the present invention described below. Hereinafter, the content of the present invention will be described in detail.

The methacrylic resin having excellent heat resistance of the present invention is a monomer mixture consisting of 80 to 98 parts by weight of alkyl methacrylate and 2 to 20 parts by weight of alkyl acrylate, and 0.008 to 0.05 parts by weight of polyfunctional monomer and 0.8 to 2.5 parts by weight of sulfur-containing molecular weight regulator. It is prepared by suspension polymerization by adding a part, and the weight average molecular weight (M _w ) is characterized in that the range of 90,000 to 150,000.

The alkyl methacrylates include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, benzyl methacrylate, and the like, of which methyl methacrylate (MMA) is most preferred.

The alkyl acrylate is selected from acrylic acid derivatives consisting of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate and mixtures thereof.

The monomer mixture of the present invention may further include a single functional unsaturated monomer copolymerizable with methyl methacrylate in addition to the monomer. Examples of copolymerizable monofunctional unsaturated monomers include acid anhydrides such as acrylic acid, unsaturated carboxylic acids such as methacrylic acid, maleic anhydride and the like; Esters containing hydroxy groups such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, monoglycerol acrylate; Acrylamide, methacrylamide, and the like. Nitriles such as acrylonitrile and methacrylonitrile are also possible, including allyl glycidyl ether, glycidyl methacrylate; Styrene-based monomers such as styrene and α-methylstyrene are also possible.

The monomer mixture of the present invention consists of 80 to 98 parts by weight of alkyl methacrylate and 2 to 20 parts by weight of alkyl acrylate. When the alkyl methacrylate is used in an amount of 80 parts by weight or less, there is a problem in that it does not maintain the inherent physical properties of the alkyl methacrylate, and when used in excess of 98 parts by weight, there is a limit in improving physical properties through the comonomer.

In the present invention, a polyfunctional unsaturated monomer is used to form a branched structure. The polyfunctional unsaturated monomers should be 0.05 parts by weight or less of the total monomers, and preferably 0.008-0.05 parts by weight. If the content is 0.05 parts by weight or more, the polymer has a high crosslinking density, and the gel content is rapidly increased. In addition, when used at less than 0.008 parts by weight, it is difficult to obtain a branching structure effect.

There are no particular limitations on the polyfunctional unsaturated monomers that can be used in the present invention, and ethylene glycol dimethacrylate, ethylene glycol acrylate, butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane trimethacrylate, 1, 6-hexanediol diacrylate, pentaerythritol tetraacrylate, divinyl benzene and the like are used.

Sulfur-containing molecular weight modifiers used in the present invention may be those represented by alkyl mercaptans of the form CH ₃ ((CH ₂ ) _n SH. For example, n-butyl mercaptan, n-octyl mercaptan, n-dode N-octyl mercaptan and n-dodecyl mercaptan are particularly suitable, and other tert-alkyl mercaptans and aromatic mercaptans are not preferable in terms of the chain transfer effect and the degree of residual in the resin.

In general, the amount of the chain transfer agent varies depending on the type, but in the present invention, 0.8 to 2.5 parts by weight is used based on 100 parts by weight of the monomer mixture. If it is used at 0.8 parts by weight or less, it is not only difficult to process, but also has a relatively high YI (Yellow Index) value, resulting in poor appearance quality. In addition, when the chain transfer agent is used in excess of 2.5 parts by weight, the molecular weight of the polymer is too low, the mechanical properties are very bad .

In the present invention, a single or copolymer of acrylic acid or methacrylic acid can be applied as a suspension stabilizer. Especially in the case of copolymers, the content of acrylic acid or methacrylic acid should be at least 50 parts by weight of the polymer. They are also preferably in the form of salts of sodium, potassium or ammonium. This is to maintain the proper solubility in the middle of the dispersion monomer and water suspended. The suspension stabilizer of the present invention is suitable for 0.002-0.2 parts by weight of the total monomer, the specific content is somewhat different depending on the components and molecular weight of the suspension stabilizer.

In the present invention, to adjust the solubility characteristics of disodium hydrogen phosphate (sodium dihydrogen phosphate), sodium dihydrogen phosphate (sodium dihydrogen phosphate), a water-soluble polymer or monomer with a phosphoric acid, sulfuric acid, buffer salt for pH adjustment sodium sulfate) may be added.

The polymerization of the methacryl monomer mixture of the present invention is carried out according to a conventional suspension polymerization method. For example, the polymerization is completed by reacting for about 2 to 8 hours at a polymerization temperature of 70 to 120 ° C. in the presence of a chain transfer agent and an initiator.

Examples of the polymerization initiator include octanoyl peroxide, decanyl peroxide, lauroyl peroxide, benzoyl peroxide, monochlorobenzoyl peroxide, dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, tert-butyl perbenzoate, Azobisisobutyronitrile, azobis- (2,4-dimethyl) -valeronitrile, etc. are mentioned.

In the present invention, in addition to the chain transfer agent and the polymerization initiator, a lubricant, an ultraviolet absorber, a heat stabilizer, a dye, a pigment, and the like may be added as necessary. The additive may be added during the polymerization process, or may be added to the pelletization process, and the method is not particularly limited.

After the polymerization is completed, the polymer in the form of particles can be obtained by cooling, washing, dehydration, and drying. The polymer thus obtained was pelletized through an extrusion process to measure physical properties.

It is preferable that the methacrylic resin of the present invention has a weight average molecular weight (M _w ) in the range of 90,000 to 150,000. When the amount exceeds 150,000, the number of unmelted gels is high, and the appearance is deteriorated. When the amount is less than 90,000, mechanical properties decrease.

The invention can be better understood by the following examples, which are intended for the purpose of illustration of the invention and are not intended to limit the scope of protection defined by the appended claims.

Example

Example 1

Completely uniform by mixing 0.3 parts by weight of lauroyl peroxide, 0.85 parts by weight of n-dodecylmercaptan and 0.01 parts by weight of ethylene glycol dimethacrylate in a monomer mixture consisting of 95 parts by weight of methyl methacrylate and 5 parts by weight of methyl acrylate. Made it. 0.1 parts by weight of sodium polyacrylate was dissolved in 150 parts by weight of ion-exchanged water in a stainless high pressure reactor equipped with a stirrer, and a small amount of disodium hydrogen phosphate and sodium sulfate were added. The monomer mixture was poured into an aqueous solution in which sodium polyacrylate was dissolved, and vigorously stirred. The inside of the reactor was filled with an inert gas such as nitrogen and argon, followed by heating. The reaction was terminated by polymerization at 80 ° C. for 2 hours and at 110 ° C. for 1 hour. After the reaction was completed, the particles were obtained by washing, dehydration and drying, and the molecular weight thereof was measured. In addition, the specimens were obtained through extrusion and injection processing, and their physical properties were measured. The results are shown in Table 1.

Example 2

The same procedure as in Example 1 was carried out except that 0.02 parts by weight of ethylene glycol dimethacrylate was added.

Example 3

The same procedure as in Example 1 was conducted except that 0.03 parts by weight of ethylene glycol dimethacrylate was added.

Comparative Example 1

0.4 parts by weight of n-dodecyl mercaptan was added, and the same procedure as in Example 1 was performed except that no ethylene glycol dimethacrylate was added.

Comparative Example 2

0.4 parts by weight of n-dodecyl mercaptan was added, and 0.02 parts by weight of ethylene glycol dimethacrylate was added in the same manner as in Example 1.

Comparative Example 3

0.85 parts by weight of n-dodecyl mercaptan was added, and the same procedure as in Example 1 was carried out except that ethylene glycol dimethacrylate was not added.

The dosage and physical properties of n-dodecyl mercaptan and ethylene glycol dimethacrylate used in each Example and Comparative Example for 100 parts by weight of the monomer mixed with methyl methacrylate and methyl acrylate are shown in Table 1 below. It was.

Example Comparative example One 2 3 One 2 3 Monomer MMA 95 95 95 95 95 95 Methyl acrylate 5 5 5 5 5 5 n-DDM 0.85 0.85 0.85 0.4 0.4 0.85 EGDMA 0.01 0.02 0.03 - 0.02 - Molecular Weight (M _w ) 97,000 110,000 150,000 102,000 260,000 43,000 YI 0.87 0.82 0.83 1.21 1.15 0.86 VST (℃) 109.4 109.1 111.4 110.8 112.5 104.6 Swellby 1.1 1.5 1.8 1.0 2.2 1.0 Number of undissolved gels a a b b c a

n-DDM: n-dodecyl mercaptan

* EGDMA: ethylene glycol dimethacrylate

Property evaluation method

(1) Molecular weight: Measured using GPC (Gel Permeation Chromatography).

(2) YI (Yellow Index): A 100 × 100 × 3 mm specimen was produced by injection molding, and measured by a Minolta spectrophotometer CM-3700d.

(3) VST (Vicat softening temperature): It measured based on ASTMD-1525, 1 kg conditions.

(4) Swell ratio: When the strand is made at the melt index measuring device at 230 ° C and 3.8 kg, the strand diameter is divided by the orifice diameter. However, the orifice was 2.09 mm in diameter and 8 mm in length was used.

(5) Number of unmelted gels: The number of unmelted gels found in the strand having a length of 100 mm when extruded at 230 ° C. was measured: a = 0-5, b = 6-10, c = 11- Indicates 20.

The present invention has a specific range of molecular weight by introducing a polyfunctional monomer and a chain transfer agent of an appropriate content in the methacryl-based resin polymerization process, thereby having excellent heat resistance and melt-stretching properties without deterioration of mechanical properties, and the formation of unmelted gel It has the effect of providing little methacrylic resin.

Simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

Claims (2)

To the monomer mixture consisting of 80 to 98 parts by weight of alkyl methacrylate and 2 to 20 parts by weight of alkyl acrylate, 0.008 to 0.05 parts by weight of polyfunctional monomer and 0.8 to 2.5 parts by weight of sulfur-containing molecular weight modifier are added to prepare a suspension polymerization. Methacrylic resin, characterized in that the molecular weight (M _w ) is in the range of 90,000 to 150,000. The method of claim 1, wherein the alkyl methacrylate is selected from methacrylic acid esters consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate and benzyl methacrylate, wherein the alkyl acrylate Is selected from acrylic acid derivatives consisting of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and mixtures thereof, wherein the multifunctional monomer is ethylene glycol dimethacrylate, ethylene glycol acrylic Butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane trimethacrylate, 1,6-hexanediol diacrylate, pentaerythritol tetraacrylate and divinyl benzene, the sulfur Molecular weight modifier containing Methacrylic resin, characterized in that selected from the group consisting of n-butyl mercaptan, n-octyl mercaptan, and n-dodecyl mercaptan.