JP2629078B2 - Method for producing methacrylic resin molding material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a methacrylic resin molding material, and more particularly to a method for producing a methacrylic resin molding material having excellent heat stability and no heat coloring.

[0002]

2. Description of the Related Art Since methacrylic resins have excellent optical properties, excellent weather resistance and high mechanical properties, they are used in automobile parts such as tail lamps and back panels, lighting equipment such as lamp covers and louvers, and the like. It is widely used for indicators such as tuners, audio components such as meter covers, and OA equipment components. All of these parts and the like are required to have transparency, light resistance, and heat resistance. Extrusion molding and injection molding of a methacrylic resin molding material are usually performed in a temperature range of 180 to 280 ° C. However, the thermal decomposition reaction of the methacrylic resin molding material is 2
When the temperature exceeds 50 ° C., the tendency tends to be remarkable, and since the molding conditions and the decomposition temperature are substantially in the same region, the monomers decomposed during the molding process remain in the molded product, and the heat resistance of the molded product is reduced. This causes problems such as causing silver streaks and the like, resulting in deterioration of the appearance of the molded product and reduction in yield. Therefore, in order to maintain the heat resistance of the molded product,
It was necessary to suppress thermal decomposition of the methacrylic resin molding material during heating.

[0003] In the production of a conventional methacrylic resin, initiators used include diacyl peroxide, dialkyl peroxide, peroxydicarbonate, and diazo compounds. However, when these polymerization initiators are used, there are drawbacks such as the generation of a resin having high thermal decomposability and the generation of a resin having high heat coloring, resulting in a decrease in heat resistance and a decrease in yield.

[0004] As a method for suppressing such thermal decomposition, a method of adding a small amount of an antioxidant, for example, a hindered phenol or an amine compound, or a method of adding a sulfur-containing compound (Japanese Patent Publication No. 38-14491). JP, JP-A-51-36258, JP-A-59-15444
And Japanese Patent Publication No. 57-9392).

[0005]

However, the above-mentioned prior arts have drawbacks such as insufficient heat decomposition suppressing effect, an increase in heat coloring, impairing transparency, and smelling the working environment due to odor during processing. Was.

Accordingly, an object of the present invention is to overcome these drawbacks of the conventional methacrylic resin, to have excellent thermal stability, and to be excellent in all of the optical properties such as heat resistance, mechanical strength and heat coloring. To provide a method for producing a methacrylic resin molding material.

[0007]

The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, by using a specific polymerization initiator and a specific amount of mercaptan in combination, heat stability and heat stability are improved. The present inventors have found that a methacrylic resin molding material without coloring can be produced, and have completed the present invention.

That is, the object of the present invention is to polymerize a monomer mixture containing methyl methacrylate alone or a monomer mixture containing methyl methacrylate as a main component, with respect to 100 parts by weight of the monomer, the following general formula ( 1)

[0009]

Embedded image (In the formula, R represents a tertiary alkyl group having 6 to 8 carbon atoms.)
It can be achieved by a method for producing a methacrylic resin molding material in which 5 parts by weight and 0.05 to 1 part by weight of a linear alkyl mercaptan are added and polymerized.

Hereinafter, the present invention will be described in detail.

As the polymerizable monomer of the present invention, methyl methacrylate alone or a mixture of a monomer containing methyl methacrylate as a main component and a monomer copolymerizable therewith is used. .

The monomer copolymerizable with methyl methacrylate used in the present invention is not particularly limited, but preferred examples thereof include acrylates such as methyl acrylate, ethyl acrylate and butyl acrylate, and methacrylic acid. Ethyl acrylate, propyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, cyclodecyl methacrylate, phenyl methacrylate, 2,4, methacrylate
Methacrylic esters such as 6-tribromophenyl, aromatic vinyl compounds such as styrene, monomethylstyrene, α-methylstyrene, and vinyltoluene; nitrile compounds such as acrylonitrile and methacrylonitrile; N-methylmaleimide; N-phenyl Maleimide,
N-substituted maleimide compounds such as No-chlorophenylmaleimide and N-cyclomaleimide are exemplified.

The proportion of methyl methacrylate copolymerized with these esters and the like is at least 50%, preferably at least 60%. 50% methyl methacrylate
If it is less than 1, the optical characteristics and the mechanical strength, which are the characteristics of the methacrylic resin, decrease, which is not preferable.

The polymerization initiator used in the present invention has the following general formula (1)

[0015]

Embedded image (Wherein, R represents a tertiary alkyl group having 6 to 8 carbon atoms), particularly tert-hexylperoxy-2-ethylhexanoate and / or 1,1 2,3,3-Tetramethylbutyl 2-ethylhexanoate is preferably used. One or more of these polymerization initiators can be used in combination. As the amount of the polymerization initiator, 0.02 to 1.5 parts by weight based on 100 parts by weight of the monomer to be subjected to polymerization,
Preferably it is 0.05 to 1 part by weight.

The linear alkyl mercaptan used in the present invention includes a compound represented by the formula CH ₃ (CH ₂ ) _n SH (where n is 3 to 3).
Which represents an integer of 17) is usually used,
Of these, n-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, n-stearyl mercaptan and the like are mentioned as preferred examples, and n-octyltan captan and n-dodecyl mercaptan are particularly preferably used. Other mercaptans, such as t
ert. When alkyl mercaptans and aromatic mercaptans are used, they often remain in the resin, are colored in yellow, have a strong odor during molding, or have a problem that defects occur during molding, and are preferred. Absent. The amount of the chain transfer agent used is 0.0
It is 5 to 1.0 part by weight, preferably 0.1 to 0.5 part by weight.

When the amounts of the polymerization initiator and the chain transfer agent are small, the effects of the present invention cannot be obtained, a large amount of unreacted monomer remains, and silver streaks and crashes occur during molding. It has drawbacks such as poor appearance, poor moldability, and the like. On the other hand, when the amount of the polymerization initiator and the chain transfer agent is large, the decomposition products of the polymerization initiator, the by-products of the chain transfer agent and the residues of the chain transfer agent are increased, and the thermal decomposition is promoted. It is not preferable because the coloring is large, the molecular weight is further reduced, and it becomes difficult to maintain the mechanical strength. The amounts of these polymerization initiators and chain transfer agents are determined within the above range from the relationship between polymerization conditions such as polymerization temperature and polymerization time and molecular weight.

The polymerization of the present invention is usually carried out at a temperature of 60 to 140 ° C. As the polymerization method, a known polymerization method for methacrylic resin, suspension polymerization method, (continuous) bulk polymerization method, solution polymerization method and the like are applied. .

In the polymerization of the present invention, commonly used additives such as lubricants, ultraviolet absorbers, dyes, pigments, antioxidants and the like can be used. Or a method of mixing with the obtained polymer and then pelletizing.

[0020]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. In the examples, “%” and “parts” are all “% by weight”.
Represents "parts by weight". The evaluation of the physical properties in the examples was performed based on the following methods (1) to (3). (1) Amount of residual monomer Quantification by gas chromatography (2) Thermal stability test Die 2 using injection molding machine N-70A (manufactured by Nippon Steel Works)
A flat mirror mold of 00L × 70W × 3.2t (mm) was attached, and after holding for 3 minutes at a cylinder temperature of 270 ° C. and a mold temperature of 50 ° C., injection molding was performed, and the appearance of the obtained plate was evaluated and the amount of residual monomer was determined. Was carried out. (3) Heating and coloring test 130L × on injection molding machine J75SAV (manufactured by Japan Steel Works)
Attach a mirror flat plate mold of 70W x 5t (mm), cylinder temperature 250 ° C, mold temperature 50 ° C, molding cycle 3
Injection molding is performed in 0 seconds and 600 seconds, and the obtained molded product is J
L, a, b were measured according to the method of IS-Z8722, and 3
The color difference ΔE between 0 seconds and 600 seconds was determined. Example 1 To 100 parts of a monomer mixture of 98% of methyl methacrylate and 2% of methyl acrylate, 0.15 parts of 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate was added.
25.11 kg of a monomer mixture consisting of 0.20 part of n-octyl mercaptan and 0.2 part of stearyl alcohol;
40% 1% aqueous solution of sodium polymethacrylate
0 gr, 11 gr of sodium dihydrogen phosphate and 36 gr of disodium hydrogen phosphate were dissolved in 50 kg of pure water with a stirrer.
After charging into a 00-liter pressure-resistant reaction vessel and performing N ₂ substitution, polymerization was carried out at 70 ° C., and after an exothermic peak, post-polymerization was carried out at 120 ° C. for 1 hour. After completion of the polymerization, a beaded polymer was obtained through cooling, washing, filtration, and drying steps. 40 of these beads
After pelletizing with a mmφ extruder, the residual monomer content was 0.17% in the beads and 0.16% in the pellets as a result of evaluation by the above method. The amount of increase in the monomer was 0.28%, and there was no defect in appearance during 20 shots, which was good. In the heat coloring test, ΔE was 0.12, which was about 以下 or less of the conventional product. Comparative Example 1 0.15 parts of 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate in Example 1 was added to 2,2′-
Except that the azobisisobutyronitrile was changed to 0.1 part,
All were polymerized under the same composition and under the same polymerization conditions as in Example 1, and beads were obtained by the same method. After evaluation, the residual monomer content was 0.22% in the beads and 0 in the pellets. .
According to the thermal stability test result, the amount of monomer increase in the molded article was 0.59%, and the appearance defect was that silver streaks occurred in 6 shots out of 20 shots, and the thermal stability was not good. Was. The results of the heat coloring test show that the color difference ΔE is 0.
20 and the heat coloring was large. Examples 2 to 7 The monomer mixture shown in Table 1 was polymerized in the same manner as in Example 1 using the polymerization temperature, polymerization initiator, and chain transfer agent shown in Table 1, and pelletized. The evaluation was performed according to the evaluation method. The results are shown in Table 2. The heat stability was good, there was no defect in appearance, and the increase in coloring due to heating was small. Comparative Examples 2 to 4 A monomer mixture as shown in Table 1 for comparison was prepared in the same manner as in Example 1 except that the polymerization temperature, the type of the polymerization initiator, and the type and amount of the chain transfer agent were changed. After polymerization and pelletization, evaluation was performed according to the method of Example 1. The results are shown in Table 2. The heat stability was poor, the heat coloring was large, and defects in the appearance of the molded product were likely to occur. Example 8 To 100 parts of a monomer mixture of 95% of methyl methacrylate and 5% of methyl acrylate was added 0.1 part of n-dodecylmercaptan.
A glass cell previously set in a flexible vinyl chloride frame with 4000 gr of a monomer mixture containing 35 parts and 0.06 part of 1,1,3,3, -tetramethylbutylperoxy-2-ethylhexanoate. After polymerization, polymerization was carried out at 60 ° C., and after 1 hour at 130 ° C. after an exothermic peak. The obtained sheet-like polymer was pulverized by a pulverizer (NBCZ type, Torai Tekkosho Co., Ltd.), and then pelletized and evaluated in the same manner as in Example 1. As a result, the amount of residual monomer was determined as pellets. 0.36%, 0.56% at 270 ° C molded product
The amount of increase in the monomer was 0.20%, there was no appearance defect such as silver streaks, and the color difference ΔE was 0.09, which was good. Comparative Example 5 Polymerization and pulverization were carried out in exactly the same manner as in Example 8 except that the amount of n-dodecyl mercaptan was changed to 0.03 parts, and Example 1 was repeated.
Was evaluated in accordance with the method described above. The residual monomer content was 0.38% in the pellet and 0.58% in the 270 ° C molded product, indicating good thermal stability, but poor moldability and transferability, and frequent sink marks and poor filling. It was difficult to obtain a normal molded product.

[0021]

[Table 1] In Table 1 above, the abbreviations for the polymerization initiator are as follows. THX: t-hexylperoxy-2-ethylhexanoate TMB: 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate LPO: lauroyl peroxide AIBN: 2,2'-azobis Isobutyronitrile

[0022]

[Table 2] In Table 2 above, 1) is the amount of residual monomer in the molded article after staying at 270 ° C. for 180 seconds. 2) is the difference between the residual monomer amount of the pellet and the residual monomer amount of the molded article after staying at 270 ° C. for 180 seconds.

Comparative Example 6 In Example 1, 1,1,3,3-tetramethylbuty
Instead of 0.15 parts of luperoxy 2-ethylhexanoate
Tert-butyl peroxy 2-ethylhexanoe
The same composition as in Example 1 except that 0.15 parts of
The polymerization was carried out to obtain a beaded polymer. This bead
Was pelletized with a 40 mmφ extruder and evaluated by the above method
As a result, the residual monomer content was 0.23% in the beads,
It is 0.2% in the molded product.
Of monomer is 0.35%, and the defect of appearance is 20 shot
Silver streaks occur in 3 shots and thermal stability is poor
It was good. In the heat coloring test, ΔE was 0.30.
And coloring by heating was large.

As described above, the production method of the present invention makes it possible to easily supply a methacrylic resin molding material which has excellent heat and stability and is less likely to generate silver streaks and to be less colored by heating due to heating for a long time. Can be useful. Further, the molding material obtained by the method of the present invention has a poor thermal stability and is not easily molded. Lighting fixtures, louvers, large molded articles such as rear panels for automobiles, and optical components such as lenses that require long-term heating retention. This is advantageous because it can contribute to solving problems in molding such as

Continuation of the front page (56) References JP-A-55-16015 (JP, A) JP-A-55-5950 (JP, A) JP-A-62-280269 (JP, A) RESARCH DISCLOSUR E, ~ 314! , (1990, JUNE), "INTERNARY COLORED POLYMACRYLIC CAST INGS", p. 594

Claims (3)

(57) [Claims] When a methyl methacrylate alone or a monomer mixture containing methyl methacrylate as a main component is polymerized, the following general formula (1) is used with respect to 100 parts by weight of the monomer. (In the formula, R represents a tertiary alkyl group having 6 to 8 carbon atoms.)
A method for producing a methacrylic resin molding material, wherein 5 parts by weight and 0.05 to 1 part by weight of a linear alkyl mercaptan are added and polymerized. 2. The method of claim 1, wherein the peroxyester is tert-hexylperoxy-2-ethylhexanoate and / or 1,1,3,3-tetramethylbutylperoxy-
2. The production method according to claim 1, wherein the production method is 2-ethylhexanoate. 3. A monomer mixture containing methyl methacrylate as a main component comprises methyl methacrylate, an acrylate ester, a methacrylate ester (excluding methyl methacrylate), an aromatic vinyl compound, (meth) acrylonitrile, The method according to claim 1 or 2, comprising at least one selected from N-substituted maleimide compounds and containing 50% by weight or more of methyl methacrylate.