JP2002121345A - Polystyrene resin composition excellent in transparency - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polystyrene resin composition which is excellent in transparency, gives moldings improved in appearance and gives less contamination of a die in molding. SOLUTION: The transparent polystyrene resin composition undergoes a reduction in weight of at most 1 wt.% in the thermal weight reduction test under conditions of 220 deg.C for 20 min, contains at most 10 wt.% of a polystyrene polymer having a molecular weight of 2,000 to 50,000, and has a total content of the trimer of styrene monomer and 8-18C saturated fatty acids of at most 0.7 wt.%.

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 having excellent transparency, which can improve the appearance of a molded product and reduce stains on a mold during molding. The polystyrene resin composition of the present invention is suitable for producing transparent molded articles such as covers for compact discs and storage boxes for magnetic tapes.

[0002]

2. Description of the Related Art A polystyrene resin has an amorphous molecular structure and has good transparency and 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. However, polystyrene resin tends to accumulate oil stains on the mold surface when molded at high temperature and high speed, and not only stains the surface of the molded product, but also rusts easily on the mold surface. In addition, the number of times of maintenance increases, and as a result, production efficiency is affected.

On the other hand, it is required to reduce the thickness of the product to shorten the molding cycle or to increase the mechanical strength. To meet this tendency, a high-flowable, high-molecular-weight polystyrene resin is required. .

In response to demands such as high-speed injection and high-speed flow,
In the prior art, in the polymerization process of a resin, an additive, for example, a chain transfer agent such as a mercaptan is added to enhance the moldability of the resin. In this case, however, the mechanical strength of the resin is increased by the addition of the chain transfer agent. There is a drawback that lowers. In addition, there is a method of improving the moldability by adding a plasticizer such as a mineral oil to the resin. However, a large amount of the mineral oil enhances the stain phenomenon of the mold during high-temperature, high-speed injection molding. In Japanese Patent Publication No. 4-71087, the initial distillation temperature (initi
al boiling point) It has been proposed to improve mold contamination during molding by using mineral oil at 200 ° C or higher. However, the phenomenon of mold contamination during high-speed, high-temperature injection molding is still being solved. There is also a white filth which often becomes opaque on the surface of the molded product.

[0005]

The inventor of the present invention has conducted intensive studies to overcome the above-mentioned disadvantages, and as a result, has found that a polystyrene resin having specific physical properties can improve the above-mentioned disadvantages.

That is, according to the present invention, the weight loss by a thermogravimetric loss test (TGA) at 220 ° C. for 20 minutes is 1% by weight or less, and the molecular weight is 2,000 to 50,000.
0 is 10% by weight or less, and the total content of trimers of styrenic monomers and saturated fatty acids having 8 to 18 carbon atoms is 0.7% by weight or less. And a polystyrene resin composition.

The polystyrene resin composition of the present invention has high transparency, has a good appearance of a molded product, and exhibits an effect of reducing mold contamination.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The polystyrene-based polymer in the polystyrene-based resin composition of the present invention comprises a styrene-based monomer as a main component and, if necessary, a copolymerization reaction using other copolymerizable monomers. Is obtained. Specific styrene monomers include, for example, styrene, α-methylstyrene, paramethylstyrene, ethylstyrene,
Halogenated styrenes such as isopropylstyrene, tert-butylstyrene, and dichlorostyrene and brominated styrene. Among them, styrene and α-methylstyrene are more preferred. These styrene monomers may be used alone or in combination of two or more.
In addition, the copolymerizable monomer used in the present invention refers to other monofunctional or polyfunctional vinyl monomers that can be copolymerized with a styrene monomer, and specific examples include methyl methacrylate, methacrylic acid, and acrylic. Examples include methyl acrylate, butyl acrylate, maleic anhydride, acrylonitrile, and the like. There is no particular limitation on the polyfunctional vinyl monomer used in the present invention, and those capable of radical polymerization are preferred. The molar ratio between the styrene monomer and the copolymerizable monomer is such that the styrene monomer / copolymerizable monomer = 100/0 to 60/40, and 1
00/0 to 70/30, particularly preferably 100/0 to 80/20.

Solvents used for the polymerization of the polystyrene polymer according to the present invention include aromatic compounds such as toluene, ethylbenzene and xylene, ketone compounds such as butanone, ester compounds such as ethyl acetate, cyclohexane, n-hexane and the like. And aliphatic hydrocarbons such as heptane.

The production of the polystyrene polymer according to the present invention includes a thermal polymerization method and a catalytic polymerization method. The polymerization initiator used in the case of catalytic polymerization includes a monofunctional initiator or a polyfunctional initiator.

Examples of the monofunctional initiator include dicumyl peroxide, dibenzoyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, t-butyl peroxybenzoate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxyisopropyl carbonate (abbreviated as BPIC), cyclohexanone peroxide, 2,2′-azo-bis-isobutyronitrile, 1,1′-azo-bis-1-cyclohexanecarbonitrile, 2,2 '-Azo-bis-2-methylbutyronitrile and the like.

Further, as the polyfunctional initiator, 1,1-
Bis- (t-butylperoxy) cyclohexane (abbreviated TX-22), 1,1-bis- (t-butylperoxy) -3,3,5-trimethylcyclohexane (abbreviated TX-29A), 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-butyl peroxyhexahydroterephthalate (abbreviated as BPHTP),
2,2-bis- (4,4-di-t-butylperoxy)
Cyclohexylpropane and the like. One or more of the above-mentioned initiators may be used.

In the present invention, the use of a multifunctional initiator is advantageous for obtaining a suitable molecular weight distribution, among which 1,1-bis- (t-butylperoxy) -3,3,5.
-Trimethylcyclohexane and 1,1-bis-
(T-Butylperoxy) cyclohexane is more preferred.

In the present invention, the initiator is used in an amount of 0.5 part by weight or less based on 100 parts by weight of the styrene monomer.
Preferably it is 0.001-0.2 weight part, More preferably, it is 0.005-0.1 weight part.

In the present invention, among the polystyrene polymers, 2,000 to 50, measured by GPC (Gel Permeation Chromatography) (measurement conditions are described in Examples described later).
Although the ratio of the low molecular weight polystyrene-based polymer of 000 is 10% by weight or less in the composition, when the ratio exceeds 10% by weight, a defect that stains the mold is easily caused. The above control of the molecular weight can be achieved by setting the polymerization temperature, an appropriate conversion distribution, or using an initiator or a chain transfer agent.

The weight average molecular weight of the polystyrene polymer in the resin composition of the present invention is not particularly limited. However, from the viewpoint of the strength of the molded product, it is 240,000 to 350,000.
0, even 250,000-330,000, especially 26
It is preferably from 000 to 320,000. If the weight average molecular weight is 240,000 or more, there is no particular defect in the molding process, and in the case of producing a large thin molded product or a highly fluid molded product, the strength is sufficient and cracks are generated. Etc. can be suppressed. Moreover, the weight average molecular weight is 350,000.
If it is below, the fluidity of the resin becomes good, and it is convenient for molding a high-speed thin material.

The polystyrene resin composition of the present invention comprises 2
Thermogravimetric loss test (TG at 20 ° C for 20 minutes)
The weight loss due to A) is 1% by weight or less. The TGA
In the analysis, the resin composition (sample) was set on a TGA analyzer under a nitrogen atmosphere, and the temperature was first raised to 100 ° C. and left for 10 minutes to remove water. And 5 per minute
The temperature is increased to 220 ° C. at a rate of temperature increase of 0 ° C., and after maintaining this temperature for 20 minutes, the weight% of the resin composition (sample) lost under this condition is measured. When the weight loss due to heat, measured by this method, exceeds 1% by weight, contamination of the mold tends to occur when the resin is molded. In order to control the weight loss of the resin composition of the present invention by the TGA test to 1% by weight or less, a monofunctional or polyfunctional initiator for setting the distribution of the reaction temperature and the conversion in the polymerization reaction is added. And a method of using a monofunctional or polyfunctional chain transfer agent for the polymerization reaction.

Among the chain transfer agents that can be used in the production of the polystyrene polymer according to the present invention, the following are mentioned as monofunctional chain transfer agents. 1) Mercaptans: methyl mercaptan, n-butyl mercaptan, cyclohexyl mercaptan, n-dodecyl mercaptan, stearyl mercaptan, t-dodecyl mercaptan (abbreviation TDM), 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.

Other examples include pentaphenylethane,
α-methylstyrene dimer, terpinolene and the like.

Examples of the polyfunctional chain transfer agent include pentaerythritol tetrakis (3-mercaptopropionate), pentaerythritol tetrakis (2-mercaptoacetate), trimethylolpropane tris (2-mercaptoacetate), Methylolpropane tris (3-mercaptopropionate)
(Abbreviated as TMPT), trimethylolpropane tris (6
-Mercaptohexanate) and the like.

Further, better physical properties can be obtained by adding an antioxidant and a lubricant as needed to the polystyrene resin composition of the present invention.

The antioxidant is used for the purpose of preventing the resin from being oxidized and deteriorated. As a typical example, 2,6-di-t is used.
-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, 2,4-bis [(octylthio) phosphite], dilaurylthiodipropionate, 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 include metal soaps such as calcium stearate, magnesium stearate, and zinc stearate, ethylene bisstearyl amide (abbreviated as EBA), methylene bis stearyl amide, palmityl amide, butyl stearate, palmityl stearate, Examples include compounds such as polypropylene glycol monostearate, behenic acid, oleic acid, and hydroxystearic acid, polyethylene wax, montan wax, and the like.

Among the lubricants used in the present invention, zinc stearate and ethylene bisstearyl amide are preferred from the viewpoint of transparency and mold release. The amount of zinc stearate is 5,000 ppm or less in the resin composition, and
00 to 5,000 ppm, especially 200 to 2,000 pp
m is preferred. By using zinc stearate in an appropriate amount, the resin has excellent releasability and good transparency. When the amount is more than 5,000 ppm, the transparency of the resin is reduced. The amount of ethylene bisstearyl amide is 5,000 ppm or less in the resin composition,
5,000 ppm, especially 200-1,500 ppm is preferred. By using ethylene bisstearyl amide in an appropriate amount, the releasability of the resin is improved and the transparency of the resin is improved. If the amount used exceeds 5,000 ppm, the transparency of the resin deteriorates.

The resin composition of the present invention improves the fluidity when molding a resin by adding an appropriate amount of mineral oil as necessary. Particularly, the resin composition is used in high-speed, high-temperature injection molding of large thin products. Mold fouling can be severe and the selection of an appropriate mineral oil becomes more important.

The mineral oil preferably has a weight loss of the mineral oil by TGA of 40% by weight or less, more preferably 2% by weight.
0% by weight or less, more preferably 10% by weight or less.
The measurement conditions are from room temperature to 10 ° C /
This is a method of measuring weight loss after heating to 250 ° C. at a heating rate of 1 minute. In the present invention, the amount of the mineral oil that satisfies such a weight loss rate is 3.5% by weight in the composition.
The following is preferable, and when it is more than 3.5% by weight, the heat resistance and rigidity of the resin may be deteriorated during processing.

In the polystyrene resin composition of the present invention, the total content of trimer of styrene monomer and saturated fatty acid having 8 to 18 carbon atoms contained in the composition is 0.1.
If it is 7% by weight or less, and if it exceeds 0.7% by weight, white opaque contamination occurs on the surface of the resin molded product, which deteriorates the transparency and appearance of the resin. Examples of the saturated fatty acid having 8 to 18 carbon atoms include lauric acid, palmitic acid,
There are stearic acid, isostearic acid and the like, and stearic acid is particularly preferable.

The method for polymerizing a polystyrene copolymer according to the present invention is preferably a bulk and / or solution polymerization method.
The reactor may be a continuous stirring type (CSTR), a plug flow type, a tower type, a static mixing type, or the like. Each of the reactors can be used alone or in combination, and the reactors can be connected in a continuous type, a parallel type, or a combination of these types.

A preferred method for producing the polystyrene resin composition of the present invention is as follows. First, a polymerization reaction solution containing a styrene monomer is continuously charged into a first polymerization tank (the polymerization tank may be a continuous stirring type or a plug flow type), and the reaction temperature is set to 80 to 150 ° C. and the conversion is set to 10 to 36%. keep.
Thereafter, the reaction solution is sent to a plug flow type reaction zone consisting of two or three vertical tower or horizontal drum type reaction tanks, the reaction temperature is set to 100 to 230 ° C., and the final conversion is 50 to 95%. , Preferably 60 to 90%. The temperature in each reactor is carefully controlled to adjust the conversion appropriately. If necessary, an initiator, a chain transfer agent and other additives are added during the polymerization reaction, or the polymer is appropriately devolatilized to obtain a polystyrene resin composition satisfying the requirements of the present invention. be able to.

[0030]

EXAMPLES [Measurement of physical properties] (1) TGA thermogravimetric reduction test Under a nitrogen atmosphere, 10 mg of a polystyrene resin composition was subjected to TGA (thermogravimetry, TA INSTRUUM).
ENTS (USA) THERMAL ANALYST2
Set to 100), raise the temperature to 100 ° C and leave for 10 minutes to remove moisture. Then, the temperature was increased to 220 ° C. at a rate of 50 ° C./min and maintained at this temperature for 20 minutes.
Survey. (2) Measurement of Trimer of Styrene-Based Monomer and Content of Saturated Fatty Acids Having 8 to 18 Carbon atoms The polystyrene resin composition was dissolved in dichloromethane, extracted with methanol, precipitated, and the supernatant was taken. Analyze the resin solution by gas chromatography from Hewlett Packard (with flame ion detector, series number 5890). (3) Measurement of weight average molecular weight and molecular weight distribution GPC of Waters (Series No. 248)
It measures under the following conditions based on 7). -Column: KD-806M-Detector: RI-410, UV-486-Mobile phase: THF (flow rate: 1.0 cc / min)-Measured based on polystyrene having a standard molecular weight.

The ratio of the polystyrene-based polymer having a molecular weight of 2,000 to 50,000 in the resin composition is determined according to a GPC measurement chart, with a molecular weight of 2,000 to 12,000,000.
0 is defined as 100%, and the molecular weight is 2,0
It is measured by the ratio of the integrated area in the range of 00 to 50,000 to the total area. In the resin composition of the present invention, the ratio of the polymer in this range is 10% by weight or less. (4) Flexural strength (FM: kg / cm ² ) Measured by the method of ASTM D-790. (5) Transparency (Haze:%) A disk sample having a diameter of 10 cm and a thickness of 1/8 inch, which was injection-molded at 185 ° C., was measured with a gloss meter (Nippon Denshoku NIPPON).
DENSHOKUUNDH-2000 type) and its Haze
Measure%. The higher the Haze value, the worse the transparency. (6) Mold stain After continuously injecting 50 shots at 280 ° C., the condition of the mold surface is evaluated according to the following criteria. ：: Not contaminated △: Slightly contaminated X: Severely contaminated (7) Appearance of molded article Whether or not white opaque contaminants are generated in the molded article obtained by the above (6) is visually observed. (8) Releasability Molding is performed using a box-shaped mold with a load-cell at a molding temperature of 200 ° C. and a mold temperature of 35 ° C. after the cushion amount is constant. It was measured using a load sensor, and the force acting on the protruding pin when the molded product was taken out was used as a measure of the mold releasability. The acting force on the protruding pin is indicated by kgf, and the smaller the number, the better the releasability. (9) Melting index (MI, melt index: melt i
ndex, 200 ° C., 5 kg) Measured by ASTM D-1238 method. The larger the number, the better the workability.

Example 1 To 94.8% by weight of styrene monomer and 3.0% by weight of ethylbenzene was added 1,1-di-t-butylperoxy-
220 ppm of (3,3,5-trimethylcyclohexane) (initiator TX-29A) and 2.2 parts of mineral oil (7% by weight of TGA thermogravimetric loss after raising from normal temperature to 250 ° C. in the presence of nitrogen). Weight percent and stearic acid at 40
0 ppm was added and mixed, and the mixture was continuously pumped at a flow rate of 55 L / hour to a plug flow reaction tank having three tanks in series and having a capacity of 110 L, and the temperatures at the reaction inlets were 110 ° C., 130 ° C., respectively. The temperature was kept at 150 ° C., the conversion in the last reactor was 80% by weight, and after heating with a heater at 250 ° C., unreacted monomers and inerts were removed in a devolatilization facility in a vacuum of 2.00 kPa (15 torr). Excluding the solvent, the obtained resin composition was pelletized by an extruder. The above measurement was performed using the pellets. Table 1 shows the measurement results.

Example 2 Pellets were obtained in the same manner as in Example 1 except that the amount of stearic acid was changed to 800 ppm. The above measurement was performed using the pellets. Table 1 shows the measurement results.
Shown in

Example 3 In Example 1, the amount of styrene was increased to 94.5% by weight.
The amount of initiator TX-29A is changed to 250 ppm, and 800 ppm of zinc stearate is added instead of 400 ppm of stearic acid. Other operating conditions are unchanged.
The above measurement was performed using the obtained pellets. Table 1 shows the measurement results.

Example 4 In Example 3, zinc stearate was changed to 640 ppm, and 400 ppm of ethylenebisstearyl amide was further added. Other conditions are unchanged. Table 1 shows the measurement results of the physical properties.

Example 5 In Example 4, the initiator was changed to t-butyl peroxyisopropyl carbonate (BPIC), and the reaction temperatures in the reactor were 115 ° C., 135 ° C., and 150 ° C., respectively.
And Other conditions are unchanged. The conversion in the last reactor is 75% by weight. The above measurement was performed using the obtained pellets. Table 1 shows the measurement results.

COMPARATIVE EXAMPLE 1 In Example 4, the amount of the initiator TX-29A was changed to 150 p
pm, the amount of zinc stearate is 680 ppm, the amount of ethylenebisstearyl amide is 425 ppm, and the reaction temperatures in the reaction vessel are 112 ° C., 135 ° C., 1
70 ° C. Other conditions are unchanged. The conversion in the last reactor is 88% by weight. The above measurement was performed using the obtained pellets. Table 1 shows the measurement results.

Comparative Example 2 In Example 4, the amount of styrene was 95% by weight, the amount of ethylbenzene was 2.5% by weight, and no initiator was used.
The reaction temperature of the reactor in the reactor is 120 ° C.,
140 ° C and 170 ° C. Other conditions are unchanged. The conversion in the last reactor is 85% by weight. The above measurement was performed using the obtained pellets. Table 1 shows the measurement results.

Comparative Example 3 In Example 4, the amount of styrene was changed to 97.5% by weight, and ethylbenzene was not used.
A thermogravimetric loss of 80% by weight is used. Other conditions are unchanged. The above measurement was performed using the obtained pellets. Table 1 shows the measurement results.

Example 6 In Example 4, 600 zinc stearate was used instead of zinc stearate.
ppm calcium stearate is used. Other conditions are unchanged. The above measurement was performed using the obtained pellets. Table 1 shows the measurement results.

Example 7 In Example 4, 600 zinc stearate was used instead of zinc stearate.
ppm magnesium stearate is used. Other conditions are unchanged. The above measurement was performed using the obtained pellets. Table 1 shows the measurement results.

Comparative Example 4 In Example 4, 300 g of zinc stearate was used instead of zinc stearate.
0 ppm (0.3% by weight) of stearic acid is used.
Other conditions are unchanged. The above measurement was performed using the obtained pellets. Table 1 shows the measurement results.

Comparative Example 5 In Example 4, 250 ppm of t-
Dodecyl mercaptan (chain transfer agent) was added, and the reaction temperature of the reactor in the reaction vessel was 110 ° C., 135 ° C., respectively.
C and 155C. Other conditions are unchanged. The above measurement was performed using the obtained pellets. Table 1 shows the measurement results.

[0044]

[Table 1]

Claims (5)

[Claims] 1. A weight loss by a thermogravimetric loss test (TGA) at 220 ° C. for 20 minutes is 1% by weight or less, and a ratio of a polystyrene polymer having a molecular weight of 2,000 to 50,000 is 10%. A highly transparent polystyrene resin composition having a total content of trimer of styrene monomer and saturated fatty acid having 8 to 18 carbon atoms of 0.7% by weight or less. 2. The polystyrene resin composition according to claim 1, wherein the weight average molecular weight of the polystyrene polymer in the composition is from 240,000 to 350,000. 3. The polystyrene resin composition according to claim 1, comprising 100 to 5,000 ppm of zinc stearate. 4. The polystyrene resin composition according to claim 1, which contains 100 to 5,000 ppm of ethylene bisstearyl amide. 5. The polystyrene resin composition according to claim 1, wherein the saturated fatty acid is stearic acid.