JPS6140701B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to thermoplastic resin particles and a method for producing the same.

More specifically, the present invention provides styrene-maleic anhydride copolymer resin particles containing 15 to 30 weight % of a maleic anhydride component and 13 to 50 weight % of an average degree of polymerization of 500 or more, and a vinyl aromatic monomer substantially contained in the particles. Thermoplastic resin particles consisting of thermoplastic resin particles consisting of 87 to 50% by weight of a vinyl aromatic polymer polymerized in an absorbed state, and a gaseous or liquid blowing agent contained therein; maleic anhydride component 15~30
Styrene with an average degree of polymerization of 500 or more by weight
13 to 50 parts by weight of maleic anhydride copolymer resin particles are suspended in an aqueous medium, 87 to 50 parts by weight of a vinyl aromatic monomer is added to this suspension and substantially absorbed into the particles, and a polymerization catalyst is added. The present invention relates to a method for producing thermoplastic resin particles, which comprises polymerizing in the presence of and adding a blowing agent during or after the polymerization to obtain foamable thermoplastic resin particles.

Polystyrene resins are used as resins for molding materials and foam materials. However, polystyrene resin has a low heat deformation temperature and has various limitations on its use.

Although polystyrene-based resins are widely used as resins for molding materials and foaming materials, their heat distortion temperatures are low and they cannot be used in applications that require heat resistance.

On the other hand, styrene-maleic anhydride copolymer resins generally have a high heat distortion temperature. However, at present, in order to uniformly distribute the maleic acid component in the molecular chain and make it into a polymer, it is extremely difficult to control the reaction and requires complicated methods that are expensive and expensive. Ta. Furthermore, when this copolymer resin is used in an extruder and re-pelletized, the re-pellet obtained tends to shrink when heated.
Also, when this sheet is formed into a sheet,
The sheet was easily stretched during sheet extrusion and was extremely difficult to mold.

Furthermore, when the pellets were foam-molded using foamable particles containing a foaming agent, the range of molding conditions was narrow.

In order to solve this problem, it has been considered to mechanically mix this copolymer resin with polystyrene, which has good flow characteristics, but it has been difficult to mix uniformly because of the temperature characteristics.

In order to solve the above-mentioned problems, the inventors of the present invention made extensive studies and found that they suspended styrene-maleic anhydride copolymer resin particles with a relatively high content of maleic anhydride component in water. A vinyl aromatic monomer is added to the suspension, absorbed into the particles, and polymerized in the presence of a polymerization catalyst to form thermoplastic resin particles, which have excellent heat resistance (for example, when re-pelletized, shrinkage due to heat is reduced). Furthermore, by incorporating a foaming agent into the plastic resin particles, foamability, The present invention was completed based on the discovery that foamable thermoplastic resin particles having excellent moldability and heat resistance can be obtained.

The styrene-maleic anhydride copolymer resin in this invention contains 15 to 30% by weight of maleic anhydride.
The one containing is used. This copolymer resin is
It is obtained by copolymerizing styrene and maleic anhydride using methods known in the art.

If the maleic anhydride content in this copolymer resin is less than 15% by weight, no improvement in thermal properties is expected, and if it exceeds 30% by weight, it becomes difficult for the vinyl aromatic monomer to enter the styrene-maleic anhydride copolymer resin. Undesirable. Moreover, as this copolymer resin, one having a so-called high degree of polymerization is used. And those having an average degree of polymerization of at least about 500 or more are used. If a polymer having an average degree of polymerization of 500 or less is used, the mechanical strength of the resin obtained when molded into a molded article will be low, which is not preferable.

These copolymer resins can be used as raw materials for the present invention even if they contain small amounts of additives to improve or impart desired properties. Impact resistance may be improved if a small amount of synthetic rubber, such as butadiene rubber, is added.

In this invention, the styrene-maleic anhydride copolymer resin used is in the form of pellets, flats, pearls, etc., and has a particle size of about 0.1 to 10 mm.

In the method of this invention, first, the above styrene-
Maleic anhydride copolymer resin particles are dispersed in an aqueous medium. In this case, a dispersant is usually used.

Examples of dispersants include organic compounds such as partially saponified polyvinyl alcohol, polyacrylates, polyvinylpyrrolidone, carboxymethyl cellulose, methyl cellulose, calcium stearate, and ethylene bisstearamide, as well as calcium pyrophosphate, calcium phosphate, calcium carbonate,
Examples include inorganic compounds consisting of fine powder hardly soluble in water, such as magnesium carbonate, magnesium phosphate, magnesium pyrophosphate, and magnesium oxide. In the method of this invention, when an inorganic compound is used as a suspending agent, it is preferable to use a surfactant such as sodium dodecylbenzenesulfonate.

These dispersants are generally added in an amount of 0.01 to 5% by weight based on water.

Next, a vinyl aromatic monomer is added to the above suspension.

Vinyl aromatic monomers used in this invention include styrene, α-methylstyrene, ethylstyrene, nuclear-substituted chlorostyrene, nuclear-substituted bromostyrene, vinyltoluene, vinylxylene, isopropylxylene, etc. alone or in a mixture of two or more. It may also be a mixture of a vinyl aromatic monomer containing 50% by weight or more of these vinyl aromatic monomers and a copolymerizable monomer such as acrylonitrile, methyl methacrylate, methyl acrylate, etc.

The weight ratio of the styrene-maleic anhydride copolymer resin and the vinyl aromatic monomer is 10 to 35 parts by weight of the styrene-maleic anhydride copolymer resin per 100 parts by weight of the vinyl aromatic monomer.

Next, this dispersion is polymerized in a suspended state in the presence of a polymerization catalyst. Examples of the polymerization catalyst used in this invention include benzoyl peroxide, tert-
Organic peroxides such as butyl perbenzoate, lauroyl peroxide, tert-butyl peroxy-2-ethylhexanate, tert-butyl peroxide, azo compounds such as azobisisobutyronitrile, azobisdimethylvaleronitrile, etc. Can be used.

The polymerization catalyst can be used by being dissolved in the above-mentioned vinyl aromatic monomer, or it can be used by being dissolved in a solvent such as benzene, toluene, xylene, etc. that does not inhibit polymerization.

Polymerization is carried out by heating and stirring at a temperature of 65 to 95°C, preferably about 80 to 90°C, and a very small amount of remaining monomer is reacted at 120 to 140°C to complete the polymerization.

The blowing agents used in this invention include easily volatile blowing agents, such as aliphatic hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, and n-hexane, cyclopentane, Examples include cycloaliphatic hydrocarbons such as cyclohexane, halogenated hydrocarbons such as methyl chloride, ethyl chloride, dichlorodifluoromethane, chlorodifluoromethane, and trichlorofluoromethane. These blowing agents are generally used in an amount of 3 to 40% by weight based on the thermoplastic resin particles. Further, a small amount of an organic solvent such as toluene or xylene may be used in combination.

The blowing agent may be added at any time during the polymerization or after the polymerization is complete. Preferably, the product particles are impregnated after the polymerization is completed. To impregnate thermoplastic resin particles with a blowing agent after polymerization is completed, for example, the thermoplastic resin particles are suspended in a suspension containing a suspending agent in an autoclave, and the blowing agent is forced into the suspension by heating. This is done by

The suspending agent used in the aqueous suspension is added to prevent the thermoplastic resin particles from bonding or coalescing with each other during impregnation with the blowing agent, and includes the above-mentioned compound as a dispersing agent. Or simply surfactants are used.

The expandable thermoplastic resin particles obtained as described above are separated from water, washed and dried as appropriate, and then used.

The obtained thermoplastic resin has excellent heat resistance (for example, when re-pelletized, shrinkage due to heat is small), and even when it is made into a sheet using this resin, it has good moldability. In particular, when molded, it has excellent foamability and heat resistance, and can be used under a wide range of molding conditions.

According to the method of the present invention, the vinyl aromatic monomer that enters the intermolecular gaps of the styrene-maleic anhydride copolymer polymerizes while remaining in the small gaps, so that the vinyl aromatic monomer produced by the polymerization of this monomer is It is thought that the molecules of the group polymer and the molecules of the styrene-maleic anhydride copolymer are attracted to each other through some kind of physical or chemical interaction. This is also understood from the fact that the obtained expandable thermoplastic resin particles exhibit the excellent properties described above.

Next, the present invention will be explained with reference to Examples.

Example 1 In a polymerization vessel with an internal capacity of 5, 2000 g of water, 4.8 g of metathetical magnesium pyrophosphate, 10 g of a 2% by weight aqueous solution of sodium dodecylbenzenesulfonate, and a styrene-maleic anhydride copolymer with a maleic anhydride content of 21% by weight were added. Add 600g of polymer particles,
The temperature was raised to 85°C. 1400 g of styrene monomer in which 4.2 g of benzoyl peroxide and 1.0 g of tert-butyl perbenzoate were dissolved while maintaining the temperature at 85°C.
was added dropwise over a period of 4 hours, maintained at 85°C for an additional 2 hours, then raised to 130°C, held for 3 hours, and cooled with water. The resin obtained here has a softening temperature of 110℃,
Also, as a result of differential thermal analysis, polystyrene and styrene
Peaks indicating the glass transition points of each maleic anhydride copolymer were mixed together.

Example 2 The resin obtained in Example 1 was extruded in the form of a strand from a mold having three 1.2 mmφ slits.
After cooling with water, use a pelletizer with a diameter of 1.5 mmφ and a length of 2.5 mm.
A pellet of mm size was obtained. In addition, this pellet
Stored in a constant temperature bath at 150℃ for 24 hours, the length direction is 1.8
It was shortened to mm. 1,200 g of this pellet was placed in an autoclave with an internal volume of 5, 2,800 g of water, 4.8 g of metathetical magnesium pyrophosphate, 10 g of a 2% aqueous solution of sodium dodecylbenzenesulfonate, and 48 g of toluene.
120 g of butane was added under pressure while stirring. After raising the temperature to 85℃ and maintaining it for 24 hours, the temperature is increased to 30℃
The beads containing the foaming agent were obtained by cooling to a temperature of 100%. After washing, dehydrating and drying the beads, they were stored at 15℃ for 3 days and foamed with steam at 100℃, resulting in 0.030kg/
Expanded particles were obtained having a bulk density of . After leaving the foamed particles indoors for 24 hours, ^the mold was slightly overfilled and molded ^.
A good molded product with a specific gravity of 0.027 Kg/cm ² was obtained using steam at (gauge pressure).

Comparative Example 1 A styrene-maleic anhydride copolymer containing 6.2% by weight of maleic anhydride was obtained in the same manner as in Example 2 to obtain pellets with a diameter of 1.5 mm and a length of 2.5 mm, and a blowing agent was added under the same conditions. When beads were foamed and molded, a good molded product was obtained only with steam in the range of 1.0Kg/cm ² to 1.2Kg/cm ² , and above 1.2Kg/cm ² the surface layer melted or dimensional shrinkage occurred and the metal The molded product did not match the mold dimensions. In addition, 150℃
When the pellets were left in a constant temperature bath for 24 hours, they shrank to 1.4 mm in the length direction.

Example 3 In a polymerization vessel with an internal volume of 5, 2000 g of water, 4.8 g of metathetical magnesium pyrophosphate, 10 g of a 2% by weight aqueous solution of sodium dodecylbenzenesulfonate, and styrene-maleic anhydride with a maleic anhydride content of 21% by weight Add 300g of copolymer particles
The temperature was raised to 85°C. While maintaining the temperature at 85°C, a solution prepared by dissolving 6.0 g of benzoyl peroxide and 1.7 g of tert-butyl perbenzoate in 1,700 g of styrene monomer was added dropwise over 8 hours, and then the temperature was further increased to 85°C.
After maintaining the temperature for 2 hours, the temperature was raised to 130℃,
This was maintained for 3 hours. The resulting resin was then cooled with water and taken out. The softening temperature of the obtained resin was 105°C. Further, as a result of differential thermal analysis, peaks indicating the glass transition points of polystyrene and styrene-maleic anhydride copolymer were present together.

Example 4 The reaction was carried out under the same conditions as in Example 1 except that styrene-maleic anhydride copolymer particles containing 16% by weight of maleic anhydride (average degree of polymerization 1100) were used. The softening temperature of the resin obtained here is
It was 108℃.

Claims (1)

[Scope of Claims] 1. Styrene-maleic anhydride copolymer resin particles containing 15 to 30% by weight of a maleic anhydride component and having an average degree of polymerization of 500 or more, and 13 to 50% by weight of a vinyl aromatic monomer in the particles. Thermoplastic resin particles comprising a gaseous or liquid blowing agent contained in resin particles consisting of 87 to 50% by weight of a vinyl aromatic polymer polymerized in an absorbed state. 2. 13 to 50 parts by weight of styrene-maleic anhydride copolymer resin particles containing 15 to 30% by weight of a maleic anhydride component and having an average degree of polymerization of 500 or more are suspended in an aqueous medium, and a vinyl aroma is added to this suspension. Group monomers 87~
adding 50 parts by weight to substantially absorb into the particles;
A method for producing expandable thermoplastic resin particles, which comprises polymerizing in the presence of a polymerization catalyst and adding a blowing agent during or after the completion of the polymerization to obtain expandable thermoplastic resin particles.