JP2002003531A - Polystyrene resin for injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polystyrene resin for injection molding which excels not only in the balance of fluidity and strength, but also improves a mold- straining when molding. SOLUTION: The polystyrene resin for injection molding in which the ratio (MZ/MW) of a Z average molecular weight (MZ) to a weight average molecular weight (MW) is >=2.0, and the polymer of the molecular weight range of 50,000-300,000 occupies 53 wt.% or more of the whole resin, of which the contents of the dimer and trimer of the styrene monomer and the styrene monomer are below specific concentration, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polystyrene resin composition, and more particularly to a resin composition having a high molecular weight range, controlling the total amount of oligomers and residual monomers to improve the balance between fluidity and strength of the resin, The present invention relates to a polystyrene resin most suitable for injection molding of a thin molded article.

[0002]

2. Description of the Related Art Polystyrene resins have an amorphous molecular structure and have good moldability. Its price is more competitive and practical than other plastic materials, and it is widely applied to various packaging materials, tableware, toys, computer peripheral parts and other products. In general, the higher the weight average molecular weight, the higher the tensile strength of a polystyrene resin, but at the same time, the flowability of the resin deteriorates, and a large amount of paraffin oil is added to increase the flowability, Or use polystyrene having a wide molecular weight distribution containing a low molecular weight polymer of polystyrene. However, these methods greatly reduce the tensile strength of the resin,
When molding at high speed, oil stains easily accumulate on the mold surface, which not only stains the surface of the molded product, but also the surface of the mold, and requires more time and effort for maintenance, resulting in production. This will affect efficiency. Generally, it is difficult to simultaneously improve fluidity and strength of a polystyrene resin. In addition, in pursuit of cost reduction, it is required to make products thinner and shorten the molding cycle. In order to match this trend, it is necessary to increase each of the above-mentioned items, that is, to increase the fluidity and strength in the production of polystyrene resin. Has become an important issue.

[0003]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to overcome the above-mentioned drawbacks in injection molding of a polystyrene resin, and as a result, the molecular weight distribution range of the resin has been adjusted to adjust the styrene monomer content in the resin. Total content of monomers and trimers,
By controlling the amount of the residual styrene monomer, it has been found that the injection moldability of a thin product such as a cover of a compact disk, a storage box of a magnetic tape, etc. is greatly improved.

[0004] That is, the present invention provides a method for preparing a Z-average molecular weight (Mz)
And the ratio of weight average molecular weight (Mw) is Mz / Mw ≧ 2.0
And a polymer having a molecular weight in the range of 50,000 to 300,000 occupies 53% by weight or more of the whole resin, and the total content of the styrene monomer dimer and trimer in the resin is 8,000 ppm. Hereinafter, there is provided a polystyrene resin for injection molding, wherein the content of the styrene monomer in the resin is 1,000 ppm or less.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The polystyrene resin of the present invention comprises
Styrene monomer, inert solvent if necessary, monofunctional vinyl monomer or polyfunctional vinyl monomer as copolymerizable monomer, monofunctional or polyfunctional polymerization initiator, monofunctional or polyfunctional It is obtained by appropriately mixing and mixing a chain transfer agent to cause a radical polymerization reaction. The polymerization system includes a batch system and a continuous system, but a continuous system is preferred.

Specific styrene monomers used in the polystyrene resin of the present invention include, for example, styrene,
α-methylstyrene, paramethylstyrene, ethylstyrene, isopropylstyrene, tert-butylstyrene,
And halogenated styrenes such as dichlorostyrene and brominated styrene. Among them, styrene and α-
Methylstyrene is more preferred. These monomers are 1
Species or two or more species may be used in combination. Styrene-based monomer accounts for 5% of all monomers constituting the polystyrene-based resin.
0-100% by weight, more preferably 60-100% by weight, especially 80
It preferably accounts for 〜100% by weight.

Among the copolymerizable monomers used in the present invention, examples of other monofunctional vinyl monomers copolymerizable with styrene monomers include methyl methacrylate, methacrylic acid, maleic anhydride, acrylonitrile, and the like.

[0008] Among the copolymerizable monomers used in the present invention, polyfunctional vinyl monomers are not particularly limited, and those capable of radical polymerization are preferred. Specific examples of the polyfunctional vinyl monomer include the following. 1) Divinyls such as divinylbenzene, 1,2,4-trivinylbenzene and 1,3,5-trivinylbenzene. 2) ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,3-propylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate,
1,6-hexamethylene glycol dimethacrylate,
Dimethacrylates such as neopentyl glycol dimethacrylate, dipropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, 2,2-bis (4-methacryloxydiethoxyphenylpropane), etc. 3) Trimethylolpropane trimethacrylate, triethylolethane trimethacrylate And other trimethacrylates. 4) ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate,
1,3-dipropylene glycol diacrylate, 1,
4-dibutylene glycol diacrylate, 1,6-hexylene glycol diacrylate, neopentyl glycol diacrylate, dipropylene glycol diacrylate, polypropylene glycol diacrylate,
2,2-bis (4-acryloxypropoxyphenyl)
Diacrylates such as propane and 2,2-bis (4-acryloxydiethoxyphenyl) propane. 5) Triacrylates such as trimethylolpropane triacrylate and triethylolethane triacrylate. 6) Tetraacrylates such as tetramethylolmethanetetraacrylate. 7) As a polyfunctional vinyl monomer not belonging to the above,
For example, tetramethylene bis (ethyl fumarate), hexamethylene bis (acrylamide), triallyl cyanurate, triallyl isocyanurate can be used.

Of these, neopentyl glycol dimethacrylate and neopentyl glycol diacrylate are more preferred. The above-mentioned polyfunctional vinyl monomers may be used alone or in combination of two or more. The amount of the polyfunctional vinyl monomer used is preferably 1.0% by weight or less, more preferably 0.005 to 0.6% by weight, and still more preferably 0.1% by weight, based on all the monomers constituting the polystyrene resin.
0.01 to 0.4% by weight. If the amount of the polyfunctional vinyl monomer exceeds 1.0% by weight, the polymer is apt to gel, and as a result, clogging and contaminants occur in the reaction tank and the devolatilization tank. When a polymerization reaction is performed by adjusting an appropriate ratio of the styrene-based monomer and the polyfunctional vinyl-based monomer, a polystyrene-based polymer having a branched structure is obtained, and the appropriate molecular weight distribution of the present invention is achieved.

The polymerization initiator used in the production of the polystyrene resin of the present invention includes a monofunctional polymerization initiator and a polyfunctional polymerization initiator. Examples of the monofunctional polymerization initiator include benzoyl peroxy oxide, Mill peroxide, dibenzoyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, t-butyl benzoate, di-2-ethylhexyl peroxy dicarbonate, t-butyl peroxyisopropyl carbonate,
Cyclohexanone peroxide, 2,2′-azo-bis-isobutyronitrile, 1,1′-azo-bis-1-cyclohexanecarbonitrile, 2,2′-azo-bis-
2-methylbutyronitrile and the like.

The polyfunctional polymerization initiator used in the present invention includes 1,1-bis- (t-butylperoxy) cyclohexane and 1,1-bis- (t-butylperoxy) -3,3. , 5-Trimethylcyclohexane, 2,5
-Dimethyl-2,5-bis- (2-ethylhexanoxyperoxy) hexane, 4- (t-butylperoxycarbonyl) -3-hexyl-6- [7- (t-butylperoxycarbonyl) heptyl ] Cyclohexane, di-
t-butyl-diperoxyazelate, 2,5-dimethyl-2,5-bis- (benzoylperoxy) hexane, di-t-butylperoxyhexahydro-terephthalate, 2,2-bis- (4 4-di-t-butylperoxy) cyclohexylpropane and the like. One or more of the above-mentioned polymerization initiators may be used.

In the present invention, the use of a polyfunctional polymerization initiator is advantageous for obtaining a suitable molecular weight distribution, in which di-t-butylperoxyhexahydroterephthalate and 1,1-bis- (t- -Butylperoxy) -3,
3,5-trimethylcyclohexane is more preferred. The amount of the polymerization initiator used in the present invention is 10
0.5 parts by weight or less, preferably 0.0 parts by weight with respect to 0 parts by weight
01 to 0.2 parts by weight, more preferably 0.005 to 0.1 part by weight.
1 part by weight. When the amount of the polymerization initiator exceeds 0.5 parts by weight, it is difficult to control the molecular weight of the polymer, and it is also difficult to control the polymerization rate. The above-mentioned polymerization initiator can be added together with the styrenic monomer at the beginning of the radical reaction, or can be added during the reaction. The addition method may be batch addition or divided addition.

As the chain transfer agent which can be used in producing the polystyrene resin of the present invention, there are monofunctional and polyfunctional chain transfer agents. The monofunctional chain transfer agent includes the following. 1) Mercaptans Methyl mercaptan, n-butyl mercaptan, cyclohexyl mercaptan, n-dodecyl mercaptan, stearyl mercaptan, t-dodecyl mercaptan, n
-Propyl mercaptan, n-octyl mercaptan,
t-octyl mercaptan, t-nonyl mercaptan and the like. 2) Alkylamines Ethylamine, diethylamine, triethylamine, isopropylamine, diisopropylamine, butylamine, di-n-butylamine, tri-n-butylamine.

As another example, pentaphenylethane,
α-methylstyrene dimer, terpinolene and the like.

Examples of the polyfunctional chain transfer agent include pentaerythritol tetrakis (3-mercaptopropionate), pentaerythritol tetrakis (3-mercaptoethanate), and pentaerythritol tetrakis (3
-Mercaptobutanate), pentaerythritol tetrakis (3-mercaptopentanate), pentaerythritol tetrakis (3-mercaptohexanate),
Examples include trimethylolpropane tris (2-mercaptoethanate), trimethylolpropane tris (3-mercaptopropionate), and trimethylolpropane tris (6-mercaptohexanate).

In the production of the polystyrene resin of the present invention, a monofunctional chain transfer agent or a polyfunctional chain transfer agent is used. In order to obtain an appropriate molecular weight distribution, it is preferable to use a polyfunctional chain transfer agent. . The amount of the chain transfer agent to be used is 0.5 part by weight or less, preferably 0.001 to 0.4 part by weight, based on 100 parts by weight of the styrene monomer. If the amount used exceeds 0.5 parts by weight, the molecular weight of the resin decreases, and the mechanical strength of the molded product decreases.

The inert solvent used in the polymerization of the polystyrene resin of the present invention includes aromatic compounds such as toluene, ethylbenzene and xylene, ketone compounds such as butanone, ester compounds such as ethyl acetate, cyclohexane, n-heptane. And the like.

In the production of the polystyrene resin of the present invention, a polyfunctional vinyl monomer, a polyfunctional polymerization initiator or a polyfunctional chain transfer agent may be used as necessary.
Each of the above-mentioned components can be used alone or in combination of two or more.For example, a polyfunctional vinyl monomer is added, or a combination of a polyfunctional vinyl monomer and a polyfunctional polymerization initiator is added. Or the combination of adding a combination of a polyfunctional polymerization initiator and a polyfunctional chain transfer agent.

The polystyrene resin of the present invention is obtained by polymerizing a styrene monomer as a main component.
Types include rubber-containing polystyrene resin and styrene-α
-Methylstyrene resin, styrene-methylmethacrylate resin, polystyrene resin and the like. In terms of transparency, a polystyrene resin containing no rubber component is preferable.

Further, by adding an antioxidant and / or a lubricant as needed in the polymerization of the polystyrene resin of the present invention, further excellent physical properties can be obtained. Antioxidants are used to prevent oxidative degradation of the resin,
A typical example is 2,6-di-t-butyl-4-.
Methylphenol, tris (nonylphenyl phosphite), octadecyl-3- (3,5-di-t-butyl-
4-hydroxyphenyl) propionate, thiodiethylenebis (3,5-di-t-4-hydroxyhydroxycinnamate), tetrakis [methylene (3,5-di-t-4-hydroxyhydroxycinnamate)] methane, , 4-bis [(octylthio) phosphite],
Dilauryl thiodipropionate, distearyl thiodipropionate, triethylene glycol bis-3-
(3-t-butyl-4-hydroxy-5-methylphenyl) propionate, 1,1-bis (2-methyl-4
-Hydroxy-5-t-butylphenyl) butane and the like.

Examples of the lubricant used in the present invention include metal soaps such as calcium stearate, magnesium stearate, and zinc stearate, ethylene bisstearyl amide, methylene bis stearyl amide, palmityl amide, butyl stearate, palmityl stearate, and polypropylene. Examples include compounds such as glycol monostearate, behenic acid, and stearic acid, polyethylene wax, and montan wax.

Further, additives such as silicone oil, ultraviolet absorbers, dyes, pigments, fillers, plasticizers, release agents, and antistatic agents can be added to the polystyrene resin of the present invention as needed.

The ratio of the Z average molecular weight (Mz) and the weight average molecular weight (Mw) of the polystyrene resin of the present invention is Mz / M
w ≧ 2.0, preferably Mz / Mw ≧ 2.06. The polystyrene resin of the present invention has a molecular weight of 5
The polymer (including the copolymer) in the range of from 000 to 300,000 accounts for 53% by weight or more, preferably 55% by weight or more, more preferably 57% by weight or more of the whole resin. The Z-average molecular weight (Mz), the weight-average molecular weight (Mw), and the molecular weight of the polymer in the above range are measured by the methods described in Examples described later.

In the polystyrene resin of the present invention, the Z-average molecular weight (Mz) is preferably from 280,000 to 1.8 million, more preferably from 400,000 to 1.2 million. The weight average molecular weight (Mw) is preferably from 140,000 to 600,000, more preferably from 200,000 to 400,000.

The total content of the dimer and trimer of the styrene monomer in the polystyrene resin of the present invention is 8,000 ppm or less, preferably 7,500 ppm or less, and the content of the residual styrene monomer is The amount is 1,00
0 ppm or less, preferably 900 ppm or less.

When the molecular weight, the residual monomer and the like are in the above ranges, the resin is less contaminated during molding, hardly generates bubbles in the molded product, has a good appearance, and has a good balance between fluidity and strength. Is obtained. On the other hand, Mz / M
w <2.0, or molecular weight 50,000-300,000
Is less than 53% by weight of the whole resin, or the total content of dimer and trimer oligomers of styrene-based monomer is more than 8,000 ppm, or the content of residual styrene-based monomer is more than 1,000 ppm. If so, the object of the present invention cannot be achieved.

An example of the method for producing the polystyrene resin of the present invention is shown below. The styrene monomer solution is continuously charged into the first polymerization tank. The first polymerization tank is a continuous stirring type reaction tank (CSTR) or a plug flow reaction tank. The reaction temperature is controlled within the range of 80 to 150 ° C, and the conversion is controlled within the range of 10 to 36%. The solution is then sent to the next plug-flow reaction zone (the reaction zone consisting of two or three tower or horizontal drum reactors) and a reaction temperature of 100.
Polymerization is carried out at ~ 230 ° C until the final conversion reaches 50-95%, preferably 60-90%. Appropriate control of the reaction conditions described above can prevent the formation of large amounts of dimers and trimers of styrenic monomers. By carefully controlling the reaction temperature and conversion in each reaction tank, and adding a polyfunctional vinyl monomer or a polyfunctional polymerization initiator or a polyfunctional chain transfer agent to the polymerization reaction as necessary. , Molecular weight 50,000-300,00
Thus, a polystyrene resin having 53% by weight or more of the total polystyrene resin is obtained. This resin has an excellent flow / strength balance. Further, by adjusting the reaction temperature at the beginning or end of the reaction, and by adding a polyfunctional vinyl monomer or a polyfunctional polymerization initiator or a polyfunctional chain transfer agent during the polymerization reaction as necessary, M
z / Mw ≧ 2.0, the moldability and strength of the product are greatly improved, and a resin applicable to injection molding of large thin products can be obtained.

The above-mentioned high conversion reaction solution is sent to a heater, and the polymer is dispersed through the heater,
The mixture is heated to a high temperature of 0 ° C. to reduce its viscosity, and then sent to a devolatilization tank having a degree of vacuum of 5 to 200 torr (0.67 to 26.7 kPa). Evaporates unreacted monomer, inert solvent and dimer and trimer of some styrene monomer and low molecular weight paraffin oil at high temperature and high vacuum, and recovers monomer and inert solvent with a cooler after separation. Allocate to reuse. The molten polymer is continuously extruded by a gear pump at the bottom of the devolatilization tank, passed through a perforated plate to form a strand having a width of 2 to 5 mm, cooled, cut and dried to obtain a final product.

[0029]

The polystyrene resin for injection molding of the present invention has both high strength and high fluidity, and the obtained molded product has good appearance, and is capable of injection molding of a thin product at high temperature and high speed. Suitable for. In addition, the polystyrene-based resin significantly improves the phenomenon of contamination of the mold during injection molding, and enhances the strength of the product.

[0030]

[Example] <Physical property test> Glass transition temperature (Tg: ° C) Differential scanning calorimeter (TA INSRUMENTS DSC
-2910 type).

2. Residual monomer amount The styrenic resin was dissolved in dichloromethane and extracted with methanol. After precipitation, the supernatant was removed and the resin solution was analyzed by Hewlett-Packard gas chromatography with flame ion detector (Series No. 5890A).
Styrene-based monomers and dimers of styrene-based monomers,
The trimer content was measured. In Table 1, dimers and trimers of styrene-based monomers are referred to as “oligomers”.

3. Average molecular weight and molecular weight distribution Measured using a gel permeation chromatography (GPC) (Series No. 2487) manufactured by Waters under the following conditions.

Column: KD-806M Detector: RI-410, UV-486 Mobile phase: THF (flow rate: 1.0 cc / min) Z-average molecular weight (Mz), weight-average molecular weight (M) of the present invention
w) and the proportion of the polymer having a molecular weight in the range of 50,000 to 300,000 in the whole resin is measured by GPC.
In the GPC measurement chart obtained under the above conditions, the ratio is defined as 100% based on the total integrated area of a molecular weight of 2,000 to 12,000,000 and a molecular weight of 50,000.
It is obtained by measuring the ratio occupied by the integrated area in the range of ３００300,000.

4. Mold stains and appearance Using a square sheet mold with a thickness of 1/8 inch and an area of 15 cm x 15 cm, after continuously injecting 50 shots on a flat plate at a molding temperature of 270 ° C, there is oil stain and silver on the surface of the sheet molded product. While observing whether or not, the surface of the mold is wiped off with cotton to determine the accumulation of dirt. ◎: Excellent ○: Good △: Acceptable ×: Poor

5. Melt index (MI, melt inde)
x, 200 ° C, 5 kg) Measured by ASTM D-1238 method. The unit is g / 10
Minutes.

6. Tensile strength (TSb, Tensile
(Strength) Measured by ASTM D-638 method. The unit is kg / cm
² .

Example 1 100 parts by weight of styrene monomer and ethylbenzene
Di-t-butylperoxy-hexahydro-terephthalate (abbreviated as BPHT) was used as a polymerization initiator in 7 parts by weight.
P) and 0.05 parts by weight of ethylenebisstearylamide (abbreviation: EBA) as a lubricant were added and mixed, and the mixture was flowed at a flow rate of 55 liters / hour in a three-tank series with a capacity of 100 liters. The temperature of the reaction inlet is kept at 110 ° C., 130 ° C., and 150 ° C., respectively, and the conversion rate of the first reaction vessel is 30% and the final conversion rate is 76%. Becomes 250 ° C
After heating with a heater at 15 torr (2.0 kP
The unreacted monomer and the inert solvent were removed in the vacuum devolatilization apparatus of a), and the obtained resin was pelletized by an extruder. Table 1 shows the measurement results.

Example 2 In Example 1, styrene monomer 1 was used as a raw material composition.
00 parts by weight, 3.7 parts by weight of ethylbenzene, 0.016
Parts by weight of neopentyl glycol dimethacrylate (abbreviated as PGDMA) and 0.016 parts by weight of 1,1
-Di-t-butylperoxy- (3,3,5-trimethylcyclohexane) (abbreviated as TX-29A) and 0.01
Parts by weight of t-dodecyl mercaptan (TDM for short) were added as a polymerization initiator and a chain transfer agent, respectively. The temperature of the third reaction tank was raised from 150 ° C. to 180 ° C., the conversion in the first reaction tank was 32%, and the final conversion was 82%. Table 1 also shows the measurement results.

Example 3 In Example 2, neopentyl glycol dimethacrylate in the raw material composition was changed to 0.03 parts by weight of neopentyl glycol diacrylate (abbreviated as PGDA), and t-
The amount of dodecyl mercaptan (abbreviated as TDM) is reduced to 0.0
Changed to 2 parts by weight. Table 1 shows the measurement results.

Example 4 In Example 2, the chain transfer agent was changed to 0.01 parts by weight of trimethylolpropane tris- (3-mercaptopropionate) (abbreviated as TMPT). Table 1 shows the physical properties and the like of the obtained resin.

Example 5 In Example 2, 0.025 parts by weight of t was used as the polymerization initiator.
-Butyl peroxyisopropyl carbonate (abbreviation B)
PIC). Table 1 shows various physical properties and the like.

EXAMPLE 6 3.7 parts by weight of ethylbenzene, 0.03 parts by weight into a mixture of 95 parts by weight of styrene monomer, 2.5 parts by weight of α-methylstyrene monomer and 2.5 parts by weight of methyl methacrylate (MMA) A part by weight of di-t-butylperoxyhexahydroterephthalate (abbreviated as BPHTP) and 0.05 part by weight of ethylenebisstearylamide are added, and the obtained raw material composition is fed into the reaction vessel at a flow rate of 55 liter / hour. send. Other operating conditions are the same as in the first embodiment. Table 1 shows the measurement results.

Comparative Example 1 100 parts by weight of styrene monomer, 2.0 parts of ethylbenzene
Parts by weight and 0.05 parts by weight of ethylenebisstearylamide as the raw material composition, and continuously pumped up to a plug-flow reaction tank in a series of three tanks (capacity is 100 liters each) at a flow rate of 55 liters / hour, The temperatures at the reaction inlets were maintained at 120 ° C., 135 ° C., and 175 ° C., respectively, and the conversion of the first reaction tank was 38%, and the final conversion was 80%.
After heating with a heater at 45 ° C., 15 torr (2.0 k
The unreacted monomer and solvent were removed in a vacuum devolatilization apparatus of Pa), and the resin was pelletized by an extruder. Table 1 shows the measured properties and the like.

Comparative Example 2 In Example 1, the raw material composition was changed to styrene monomer 100
Parts by weight, 3.2 parts by weight of ethylbenzene, 1,1-di-t
-Butylperoxy (3,3,5-trimethylcyclohexane) 0.02 parts by weight, ethylenebisstearylamide 0.025 parts by weight, and the temperature of the third reaction vessel was 15
0 ° C. was raised to 185 ° C. and the conversion of the first reactor was 30
% And the final conversion is 88%. Table 1 shows the measurement results.

Comparative Example 3 In Example 1, the raw material composition was changed to styrene monomer 100.
Parts by weight, 6.5 parts by weight of ethylbenzene, 1.0 part by weight of paraffin oil, 1,1-di-t-butylperoxy-
The content was 0.02 parts by weight of cyclohexane (abbreviated as TX-22) and 0.05 parts by weight of ethylenebisstearylamide.
The temperature of the third reactor is 180 ° C., the conversion of the first reactor is 30%, and the final conversion is 88%. Table 1 shows the physical properties and the like of the obtained resin.

Comparative Example 4 In Example 3, the amount of t-dodecyl mercaptan as a chain transfer agent was changed from 0.02 parts by weight to 0.01 part by weight, and the vacuum conditions of the devolatilization equipment were changed to 25 torr (3.3 kP).
The procedure was carried out under the same conditions except for a). Table 1 shows the physical properties and the like of the obtained resin.

[0047]

[Table 1]

Note) 1) MMA: methyl methacrylate 2) PGDMA (polyfunctional vinyl group monomer): neopentyl glycol dimethacrylate 3) PGDA (polyfunctional vinyl group monomer): neopentyl glycol diacrylate 4) BPHTP (poly) 5) TX-29A (polyfunctional polymerization initiator): 1,1-di-t-butylperoxy (functionalized polymerization initiator): di-t-butylperoxyhexahydroterephthalate, manufactured by Nippon Kayaku Novell 3,3,5-trimethylcyclohexane) 6) TX-22 (polyfunctional polymerization initiator): 1,1-di-
t-butyl peroxycyclohexane 7) BPIC (monofunctional polymerization initiator): t-butyl peroxyisopropyl carbonate 8) TDM (monofunctional chain transfer agent): t-dodecyl mercaptan 9) TMPT (polyfunctional chain) Transfer agent): trimethylolpropane tris- (3-mercaptopropionate) 10) EBA (lubricant): ethylenebisstearylamide 11) Molecular weight distribution (% by weight): molecular weight 50,000-30
000 refers to the weight% of the total resin (G
(Measured by PC)

Claims (7)

[Claims] The ratio between the Z average molecular weight (Mz) and the weight average molecular weight (Mw) is Mz / Mw ≧ 2.0, and the molecular weight is 5
The polymer in the range of from 000 to 300,000 occupies 53% by weight or more of the whole resin, and the total content of the styrene monomer dimer and trimer in the resin is 8,000 ppm.
Hereinafter, when the content of the styrene monomer in the resin is 1,000,
A polystyrene resin for injection molding having 0 ppm or less. 2. The polystyrene resin for injection molding according to claim 1, which does not contain a rubber component. 3. The polystyrene resin for injection molding according to claim 1, wherein a polyfunctional vinyl monomer is contained as a copolymerization component. 4. The polystyrene resin for injection molding according to claim 3, wherein the polyfunctional vinyl monomer is neopentyl glycol dimethacrylate or neopentyl glycol diacrylate. 5. The polyfunctional vinyl monomer has a ratio of 0.005 to 0.005 of all monomers constituting the polystyrene resin.
5. The polystyrene resin for injection molding according to claim 3, wherein the content is 0.6% by weight. 6. The polystyrene resin for injection molding according to claim 1, which is obtained by polymerization using a polyfunctional polymerization initiator. 7. The polystyrene resin for injection molding according to claim 1, which is obtained by polymerization using a polyfunctional chain transfer agent.