JP2002069113A - Method for producing polystyrene resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a polystyrene resin with high productivity which is not in the former whereby the increase of molecular weight is enough possible, high quality and good moldability are obtained and especially the suitability as a molding material for foamed sheet and foamed molded product is obtained. SOLUTION: The method produces the polystyrene resin of which the weight average molecular weight is 200,000 to 700,000 and the ratio (Mw/Mn) of the weight average molecular weight(Mw) to the number average molecular weight(Mn) is 3.0 or less by using an organic peroxide represented by formula (1) (wherein R1, R2, R3 and R4, which may be the same or different, are each a group of formula (2) (wherein X is an integer of 0 to 3; Y is a tertiary alkyl group or tertiary aralkyl group)) as a polymerization initiator and performing the polymerization of a styrene monomer or a polymerizable composition having the monomer as a principal component.

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 polystyrene resin which is excellent in mechanical strength and moldability and is particularly suitable for a material of a foamed molded product, with high productivity.

[0002]

2. Description of the Related Art Polystyrene resins are generally excellent in transparency, heat resistance, rigidity and the like.
It is used as a material for articles (molded articles) in various fields such as office equipment, industrial parts, and electric appliances. Also, in particular,
Since polystyrene resin foams have characteristics such as surface gloss, lightness, heat insulation and buffering properties, taking advantage of these characteristics, containers such as food trays, lunch boxes, cups, heat insulating materials, and various panels It is widely used after being molded.

By the way, conventionally, high-molecular-weight polystyrene resins have been produced in order to increase the strength of molded articles. However, when trying to increase the molecular weight of the polystyrene resin, the reaction rate must be suppressed, and there has been a problem that productivity is extremely reduced. Therefore, a method using a specific polymerizable unsaturated monomer or a method using a special reactor has been proposed.However, these methods are not enough to increase the reaction rate or have a problem in the quality of the obtained resin. For example, it is not practical to produce a high-molecular-weight polystyrene-based resin without lowering productivity. For example, Japanese Patent Application Laid-Open No. 2-170806 proposes a method for producing a polystyrene resin by adding a polyfunctional vinyl compound. However, a molded article of the resin produced by such a method has a sufficient degree of haze. Not. Japanese Patent Application Laid-Open No. Sho 64-70507 proposes to use a special reactor for producing a high-molecular-weight polystyrene resin, but the method is not versatile because a special reactor is used. Moreover, the reaction speed is not sufficiently improved,
Low productivity. In order to solve these problems, Japanese Patent Application Laid-Open No. 4-272909 proposes a method in which a specific tetrafunctional organic peroxide is used as a polymerization initiator. The improvement is not sufficient, and the reaction time is prolonged to obtain a high molecular weight polymer at a high conversion, and the productivity cannot be sufficiently improved.

[0004] On the other hand, a foamed molded article of a polystyrene-based resin is usually formed by extruding a foaming material containing a polystyrene-based resin and a foaming agent into a foamed sheet, and then further subjected to heat secondary molding. By performing (vacuum forming, pressure forming, press forming, etc.), a foam molded article (molded article) molded into a desired shape is manufactured. For this reason,
From the viewpoint of the quality and productivity of the foamed molded article of the polystyrene resin, it is necessary that the polystyrene resin exhibits good moldability and that the foamed sheet is uniformly heated in the heating secondary molding (that is, the foamed sheet is foamed). If the heating state of the sheet is non-uniform, the sheet is torn by molding, or uneven thickness occurs, resulting in insufficient strength of the molded product and impaired appearance.)

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a high molecular weight (good mechanical strength), high quality, and good moldability. In particular, an object of the present invention is to provide a method for producing a polystyrene resin which can produce a polystyrene resin suitable as a molding material for a foamed sheet and a foamed molded article with an unprecedentedly high productivity.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, when a styrene monomer is polymerized using a specific tetrafunctional organic peroxide as a polymerization initiator, It has a high molecular weight and is excellent in mechanical strength and moldability (especially moldability as a molding material for foam), and has high productivity in producing polystyrene resin with small haze. They found that they could be manufactured and completed the present invention.

That is, the present invention is as follows. (1) An organic peroxide represented by the following general formula (I) is used as a polymerization initiator, and a styrene monomer or a polymerizable composition containing a styrene monomer as a main component is polymerized to obtain a weight average. A method for producing a polystyrene resin having a molecular weight of 200,000 to 700,000 and a ratio (Mw / Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) of 3.0 or less.

[0008]

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(Wherein R ¹ , R ² , R ³ , and R ⁴ may be the same or different;

[0010]

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Wherein X is an integer of 0 to 3, and Y is a tertiary alkyl group or a tertiary aralkyl group. (2) The method according to the above (1), wherein the organic peroxide represented by the general formula (I) is used in an amount of 10 to 2000 ppm by weight based on the styrene monomer. (3) The method according to the above (1), wherein the polymerization temperature is 60 to 180 ° C.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The styrene monomer used in the present invention means styrene and an aromatic vinyl monomer other than styrene. Examples of the aromatic vinyl monomer other than styrene include, for example, Α-substituted alkylstyrenes such as α-methylstyrene, α-ethylstyrene and α-isopropylstyrene; nuclear-substituted alkylstyrenes such as p-methylstyrene, m-methylstyrene and 2,5-dimethylstyrene; p-chlorostyrene Nucleus-substituted halogenated styrenes such as p-bromostyrene and dibromostyrene. The styrene monomer may be used alone or in combination of two or more.

In the present invention, the target polystyrene resin may be produced by polymerizing only the styrene monomer, but other vinyl compounds (monomer) copolymerizable with the styrene monomer may be used. ) Can also be used in combination. Such vinyl compounds include vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; acrylate compounds such as methyl acrylate and ethyl acrylate; methacrylate esters such as methyl methacrylate, ethyl methacrylate and propyl methacrylate. Compound;
Acrylamide derivatives and the like. These compounds may be used alone or in combination of two or more.

Further, an EPDM rubber,
So-called rubbery polymers such as polybutadiene rubber and styrene-butadiene rubber can be mixed (dissolved) before use. Such rubbery polymers may be used alone or in combination of two or more.

In the present invention, a chain transfer agent may be further mixed (dissolved) with the monomer and used. Examples of the chain transfer agent include an aromatic mercaptan, an aliphatic mercaptan, a polyfunctional mercaptan, and a pentamer. Phenylethane, α-
Methylstyrene dimer and terpinolene are preferred.

As described above, in the present invention, in addition to the styrene monomer, other vinyl compounds (monomers) copolymerizable with the styrene monomer, a rubbery polymer, a chain transfer agent and the like are polymerized. It may be used in combination as a raw material, the "polymerizable composition containing a styrene-based monomer as a main component" in the present invention is mainly composed of a styrene-based monomer, It means a composition in which another copolymerizable vinyl compound (monomer), a rubber-like polymer, a chain transfer agent and the like are mixed (dissolved). Therefore, the polystyrene-based resin in the present invention may be a homopolymer or copolymer (random, block) of a styrene-based monomer, or a copolymer (random, block) of a styrene-based monomer and a vinyl compound other than the styrene-based monomer. ) And further include polymers obtained by further copolymerizing these polymers with a rubbery polymer.

In the organic peroxide represented by the general formula (I) used as a polymerization initiator in the present invention, the compound represented by the formula (I)
In the formula for specifying R ¹ , R ² , R ³ and R ⁴ , the integer of 0 to 3 represented by X is preferably 1 or 2, and the carbon number of the tertiary alkyl group represented by Y Is preferably 4 to 8, particularly preferably a tertiary butyl group, a tertiary amyl group, a tertiary octyl group, and the like, and the tertiary aralkyl group preferably has 9 to 13 carbon atoms.
A-(4-isopropylphenyl) propyl group and the like are particularly preferred. In the formula, R ¹ , R ² , R ³ and R ⁴ are preferably the same. Specific examples of the organic peroxide include polyether tetrakis (tertiary butyl peroxycarbonate), polyether tetrakis (tertiary amyl peroxycarbonate), polyether tetrakis (tertiary hexyl peroxycarbonate), and polyether tetrakis. (Cumyl peroxy carbonate), polyether tetrakis (2- (4-isopropylphenyl) propyl peroxy carbonate)
Among them, polyether tetrakis (tertiary butyl peroxycarbonate), polyether tetrakis (tertiary amyl peroxycarbonate), polyether tetrakis (tertiary hexyl peroxycarbonate) and the like are particularly preferable. These may be used alone or in combination of two or more.

The amount of the organic peroxide used is based on the amount of the monomer (when the monomer is only a styrene-based monomer, on the basis of the styrene-based monomer; And when using other vinyl compounds (monomers) copolymerizable with the styrene monomer, based on the total amount of both)
10-2000 ppm by weight, preferably 20-2000
Ppm by weight. If the amount used is less than 10 ppm by weight, there is no substantial effect, and if it exceeds 2,000 ppm by weight, it becomes difficult to control the molecular weight and the polymerization rate.

In the present invention, if necessary, another polymerization initiator may be used together with the organic peroxide represented by the general formula (I). Such other polymerization initiators include tertiary butyl hydroperoxide, tertiary amyl hydroperoxide, tertiary hexyl hydroperoxide, cumene hydroperoxide, ditertiary butyl peroxide, ditertiary amyl peroxide, ditertiary hexyl Peroxide, benzoyl peroxide, dicumyl peroxide, tertiary butyl peroxybenzoate, tertiary amyl peroxybenzoate,
Tertiary hexyl peroxy benzoate, tertiary butyl peroxy 2-ethylhexanoate, tertiary amyl peroxy 2-ethyl hexanoate, tertiary hexyl peroxy 2-ethyl hexanoate, tertiary butyl peroxy isopropyl carbonate So-called monofunctional organic peroxides such as tertiary amyl peroxyisopropyl carbonate, tertiary hexyl peroxyisopropyl carbonate, 1,1-bis (tertiary butylperoxy) cyclohexane, 1,1-bis (tertiary Bifunctional organic peroxides such as butyl peroxy) -3,3,5-trimethylcyclohexane, and azo-based compounds such as azobisisobutyronitrile and azobis-2,4-dimethylvaleronitrile. The polymerization initiator of the object thereof. These polymerization initiators may be used alone or in combination of two or more.

In the present invention, the polymerization method is not particularly limited, and various methods such as lump, solution, suspension, emulsification or lump / suspension can be applied. In the case of solution polymerization, as the solvent, for example, alkylbenzenes such as toluene, ethylbenzene and xylene, ketones such as methylethylketone, and aliphatic hydrocarbons such as hexane are preferable.

The polymerization temperature varies depending on the polymerization method and the combination of monomers, but is usually from 60 to 180 ° C, preferably from 80 to 160 ° C. If the temperature is lower than 60 ° C., the polymerization time becomes longer and the productivity becomes lower. If the temperature is higher than 180 ° C., the reaction rate becomes remarkably large, and it becomes difficult to control the polymerization reaction. Is difficult to obtain. The polymerization may be carried out at a constant polymerization temperature or continuously or stepwise while increasing the temperature.

In the method of the present invention, the weight average molecular weight (M
w) is 200,000 to 700,000, preferably 300,000 to 700,000, and the ratio (Mw) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) is
/ Mn) is 3.0 or less, preferably 2.0 to 3.0. The polystyrene resin having such molecular weight characteristics has sufficient mechanical strength (the molded article has sufficiently high impact strength), and has good moldability (particularly, a foamed sheet used to obtain a foamed molded article). The load does not increase in extrusion foaming.), And the degree of haze (haze) of the molded product also becomes sufficiently small. That is, when the weight average molecular weight (Mw) is 200,000 or more, the molded article has a sufficiently high impact strength, and the weight average molecular weight (Mw)
When w) is 700,000 or less, the load at the time of extruding the raw resin pellets does not increase, and the haze of the molded product does not deteriorate. Furthermore, it has a weight average molecular weight (Mw) in such a specific range, and has a ratio (Mw / Mw) between the weight average molecular weight (Mw) and the number average molecular weight (Mn).
When Mn) is 3.0 or less, the haze of the molded product is sufficiently small (for example, JIS K 7105).
The haze measured by the prescribed method is approximately 2.0
Below, preferably 1.7 or less. ). In addition, since heat is uniformly transmitted to the sheet during heat molding of the foamed sheet, it is possible to prevent breakage of the sheet due to molding and occurrence of uneven thickness portions, and to obtain a good foamed molded article (molded product) without insufficient strength and a reduced appearance. Obtainable.

The polystyrene-based resin having the above-mentioned specific molecular weight characteristics produced by the present invention exhibits good moldability in various molding methods such as injection molding, extrusion molding, press molding, and vacuum molding. In addition, the polystyrene-based resin produced by the method of the present invention is particularly suitable as a material for a foamed molded article, and by using the polystyrene-based resin, a foamed molded article having high strength and uniform properties can be obtained. .

The foamed molded article made of the polystyrene resin is produced by a conventionally known method in the field of polystyrene resin foam molded article. Usually, first, a resin is extruded and foamed to form a foamed sheet, and the obtained foamed sheet is further subjected to heating and secondary molding to obtain a molded article having a desired shape. As an extruder used for extrusion foaming, any known apparatus generally used in the field of foam molding of a polystyrene resin can be used. Further, a foaming agent is added to the polystyrene resin, and such a foaming agent may be a known one generally used in the art,
A decomposable foaming agent, a gaseous or volatile foaming agent (a gaseous or volatile foaming agent at normal temperature) and the like are preferable.

Examples of the decomposable foaming agent include inorganic decomposable foams such as ammonium carbonate, sodium carbonate, calcium carbonate, ammonium bicarbonate, sodium bicarbonate, calcium bicarbonate, ammonium nitrite, calcium azide, sodium azide and sodium borohydride. Compounds, azo compounds such as azodicarbonamide, azobissulfformamide, azobisisobutyronitrile and diazoaminobenzene, N, N'-dinitrosopentamethylenetetramine and N, N'-dimethyl-N, N'-diamine Preferred are nitroso compounds such as nitrosoterephthalamide, benzenesulfonylhydrazide, p-toluenesulfonylsemicarbazide, trihydrazinotriazine, barium azodicarboxylate and the like. These may be used alone or in combination of two or more. Further, in order to adjust the decomposition temperature, the amount of generated gas and the decomposition rate, a foaming aid may be added together with the decomposable foaming agent. Foaming aids include oxalic acid, malonic acid, maleic acid, fumaric acid, succinic acid, itaconic acid, citraconic acid, adipic acid, formic acid, acetic acid, propionic acid, butyric acid, stearic acid, oleic acid, caprylic acid,
Enantonic acid, caproic acid, valeric acid, lactic acid, tartaric acid, citric acid, phthalic acid, benzoic acid, benzenesulfonic acid, organic acids such as toluenesulfonic acid, chloroacetic acid, diglycolic acid, inorganic acids such as boric acid, and acid tartaric acid Acid salts such as potassium are preferred. The amounts of these decomposable foaming agents and foaming assistants are appropriately selected according to the density (porosity) of the target foam molded article.

As the gas foaming agent, nitrogen, carbon dioxide,
Propane, neopentane, methyl ether, difluoromethane dichloride, n-butane, isobutane and the like are preferable,
As the volatile foaming agent, ether, petroleum ether, acetone, n-pentane, isopentane, hexane, isohexane, heptane, isoheptane, benzene, toluene and the like are preferable. One of these foaming agents may be used alone, or two or more thereof may be used in combination. The amount of the foaming agent is appropriately selected according to the density (porosity) of the desired foamed molded article.

In general, in the foam molding of a polystyrene resin, a cell regulator and a filler can be blended together with the foaming agent. In the foam molding of the polystyrene resin produced by the method of the present invention, such a cell regulator and a filler are also used. You may mix | blend an agent. As the foam control agent and the filler, those known in the art can be used.Examples of the foam control agent include talc, inorganic powders such as silica, polycarboxylic acid and sodium carbonate or sodium bicarbonate. Reaction mixtures and the like are preferred. As the filler, inorganic fillers such as talc, calcium carbonate, shirasu, gypsum, carbon black, white carbon, magnesium carbonate, clay, and natural silicic acid, and metal powder are preferable.

Extrusion foaming to obtain a foamed sheet involves melting a resin sufficiently in an extruder, pouring the molten resin into a die while adjusting the temperature to the most suitable temperature for foaming, and then extruding the resin. preferable. Further, the thickness and density of the foam sheet are not particularly limited, and these are appropriately adjusted according to the intended use of the foam molded article.

The forming method of the heating secondary forming of the foam sheet is as follows.
Although there is no particular limitation, vacuum forming, pressure forming, press forming and the like are preferable. Incidentally, in order to improve the releasability of the molded article from the mold during the heating secondary molding, an appropriate amount of silicone oil may be kneaded into the polystyrene resin.
Silicone oil is kneaded into a polystyrene resin with a mixing roll such as a calender roll, then pelletized, and then foamed into a sheet. It can be performed by, for example, a method of press-fitting the resin during extrusion in the extrusion foaming step. As the silicone oil, any of an oil type, a compound type, and a powder type can be used.

[0030]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In addition, all ppm in an Example and a comparative example is a weight basis.

Example 1 A glass ampoule having a capacity of 20 ml was charged with 200 g of 4 g of styrene and 200 pp of polyethertetrakis (tert-butyl peroxycarbonate).
m (active oxygen amount: 13.3 ppm). Then, after replacing the ampoule tube with nitrogen, the tube was sealed and polymerized in a thermostat at 130 ° C. for 4 hours.

Example 2 400 p of polyether tetrakis (tertiary butyl peroxycarbonate)
A polymerization reaction was carried out in the same manner as in Example 1 except that pm (active oxygen amount: 26.5 ppm) was added.

Example 3 800 p of polyether tetrakis (tertiary butyl peroxycarbonate)
A polymerization reaction was carried out in the same manner as in Example 1 except that pm (active oxygen amount: 53.0 ppm) was added.

Example 4 400 p of polyether tetrakis (tertiary butyl peroxycarbonate)
pm (active oxygen amount: 26.5 ppm), and the polymerization reaction was carried out in the same manner as in Example 1 except that polymerization was carried out in a thermostat at 120 ° C. for 2 hours and in a thermostat at 145 ° C. for 2 hours.

Comparative Example 1 A polymerization reaction was carried out in the same manner as in Example 1 except that 116 ppm (active oxygen content: 13.3 ppm) of 2,2-bis (4,4-ditert-butylperoxycyclohexyl) propane was added. went.

Comparative Example 2 A polymerization reaction was carried out in the same manner as in Example 1 except that 232 ppm (26.5 ppm of active oxygen) of 2,2-bis (4,4-ditert-butylperoxycyclohexyl) propane was added. went.

Comparative Example 3 A polymerization reaction was carried out in the same manner as in Example 1, except that 464 ppm (active oxygen amount: 53.0 ppm) of 2,2-bis (4,4-ditert-butylperoxycyclohexyl) propane was added. went.

Comparative Example 4 A polymerization reaction was carried out in the same manner as in Example 4 except that 216 ppm (active oxygen amount: 26.5 ppm) of 1,1-di (tert-butylperoxy) cyclohexane was added.

The polymerization conversion in the polymerization reaction in the above Examples and Comparative Examples, the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the produced polymer (after removing the remaining monomer) are shown below. (Evaluation).

[Polymerization conversion rate] The produced polymer was diluted and dissolved in THF, and the remaining monomers were quantified by gas chromatography (GC), and the polymerization conversion rate was calculated based thereon. For gas chromatography (GC), GC-353B manufactured by GL Sciences Corporation was used, and a column manufactured by GL Sciences Corporation (10% PEG-20M 2) was used.
m) using a column temperature of 110 ° C. and a sample concentration of 0.25
It was measured as% by weight.

[Molecular weight of polymer] The molecular weight was measured by gel permeation chromatography (GPC). The GPC apparatus uses LC600 / GPC manufactured by GL Sciences Co., Ltd., and a column (Showex GPC) manufactured by Showa Denko KK
KF-805L was used), the column temperature was 40 ° C., the solvent was THF, and the sample concentration was 0.5% by weight, and the measurement was performed using a differential refractometer.

The results are shown in Table 1 below.

[0043]

[Table 1]

[0044]

As is apparent from the above description, according to the method of the present invention, a polystyrene resin having excellent mechanical strength and moldability, and particularly having a molecular weight characteristic suitable for a molding material of a foamed molded article is produced. It can be manufactured with good quality.

Claims (3)

[Claims] An organic peroxide represented by the following general formula (I) is used as a polymerization initiator to polymerize a styrene monomer or a polymerizable composition containing a styrene monomer as a main component. The weight average molecular weight is 200,000 to 700,000, and the weight average molecular weight (M
w) and the number average molecular weight (Mn) ratio (Mw / Mn) is 3.
A method for producing a polystyrene resin of 0 or less. Embedded image (Wherein R ¹ , R ² , R ³ , and R ⁴ may be the same or different, and each has the formula: (In the formula, X represents an integer of 0 to 3, and Y represents a tertiary alkyl group or a tertiary aralkyl group.) ) 2. The method according to claim 1, wherein the amount of the organic peroxide represented by the general formula (I) is 10 to 2000 ppm by weight based on the styrene monomer. 3. The method according to claim 1, wherein the polymerization temperature is 60 to 180 ° C.