JPS6140697B2 - - Google Patents

Description

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

More specifically, this invention combines 10 to 35 parts by weight of a styrene-maleic anhydride copolymer resin containing 15 to 30% by weight of a maleic anhydride component and having an average degree of polymerization of 500 or more to 90 to 65 parts by weight of a vinyl aromatic monomer. A thermoplastic resin obtained by dissolving the solution, suspending this solution in an aqueous medium, polymerizing it in the presence of a polymerization catalyst, and adding a blowing agent during or after the polymerization to form foamable thermoplastic resin particles. A method for producing particles is provided.

Polystyrene resins are widely used as resins for molding materials and foaming materials, but their heat distortion temperature is low, making them unsuitable for use in applications requiring heat resistance.

On the other hand, styrene-maleic anhydride copolymer resin has a high heat deformation temperature, but it is currently difficult to obtain pearl-like and small particles due to the manufacturing method. Generally, when particles with a large particle size are used as a molding material, there will be large fluctuations in penetration when feeding into the hopper of a molding machine, and it will take time to melt in the cylinder of the molding machine. In addition, when such large particles are used as expandable particles (beads), they can be used not only for molding large objects, but also for manufacturing small molded objects, thin walled objects, and objects that require fine details. is difficult. From this point of view, various attempts have been made to make the particles of styrene-maleic anhydride copolymer resins smaller, but none have been successful.

For example, even if the above-mentioned copolymer resin is subjected to hot cutting or underwater cutting using an extruder, only pellets with a large particle size can be produced. In an attempt to improve this to some extent, strand cutting, which stretches and cuts the molten resin extruded from the extruder's discharge port, causes orientation of the polymer in the stretching direction and thermal deterioration, making it difficult to use this beret. When molding with beads containing a foaming agent, there were problems such as a narrow molding width (the molding conditions for obtaining a good molded product were narrow).

Furthermore, with styrene-maleic anhydride copolymer resin, it is difficult to polymerize the maleic anhydride component so that it is uniformly distributed within the molecule, requiring complicated control and making it expensive. I have no choice but to do so.

The inventors of this invention arrived at this invention as a result of intensive research to solve the above-mentioned problems. The inventors first dissolved a styrene-maleic anhydride copolymer resin containing a relatively large amount of maleic anhydride in a vinyl aromatic monomer, suspended this solution in water, and polymerized it in a suspended state in the presence of a polymerization catalyst. It has been found that by preparing thermoplastic resin particles by using a thermoplastic resin, the particles obtained can be made small and uniform. When these resin particles are used as a molding material, there is little variation in penetration when feeding into the hopper of a molding machine, and melting in the cylinder of the molding machine takes only a short time. It has been found that it exhibits good foaming properties and can be used to produce small molded products, thin-walled products, and products that require fine details. Moreover, the resin particles can reduce the content of expensive styrene-maleic anhydride copolymer while still
It has the advantage that the inherent heat resistance of the maleic anhydride copolymer is not impaired.

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

If it is less than 15% by weight, no improvement in thermal properties can be expected, and if it exceeds 30% by weight, the styrene-maleic anhydride copolymer becomes difficult to dissolve in the vinyl aromatic monomer, which is not preferred.

As the styrene-maleic anhydride copolymer resin, one having a so-called high degree of polymerization is used. A polymer having an average degree of polymerization of at least about 500 or more is used. If a polymer having an average degree of polymerization of 500 or less is used, the resulting resin particles will have low mechanical strength when molded into a molded product, and the upper limit is preferably about 4000.

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. For example, if a small amount of synthetic rubber such as butadiene rubber is added, the impact resistance will be improved.

The vinyl aromatic monomers used in this invention include styrene, α-methylstyrene, ethylstyrene, chlorostyrene, bromostyrene, vinyltoluene, vinylxylene, isopropylxylene, etc. alone or as a mixture of two or more thereof. If the vinyl aromatic monomer contains 50% by weight or more, it may be a mixture of the vinyl aromatic monomer and a copolymerizable monomer such as acrylonitrile, methyl methacrylate, methyl acrylate, etc. A preferred monomer is styrene alone.

The weight ratio of the styrene-maleic anhydride copolymer resin to the vinyl aromatic monomer is 10 to 35 parts by weight of the styrene-maleic anhydride copolymer resin to 90 to 65 parts by weight of the vinyl aromatic monomer. If the amount of copolymer resin used is less than this range, the final thermoplastic resin obtained will have a low degree of thermal deformation, which is undesirable. If the amount of copolymer resin used is more than this range, the copolymer will be It does not dissolve in the liquid, which is unfavorable in terms of the manufacturing process.

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. For example, the impact resistance may be improved if a small amount of synthetic rubber such as butadiene rubber is added.

Dissolving the styrene-maleic anhydride copolymer resin in the vinyl aromatic monomer is usually carried out by adding copolymer resin particles to the monomer and stirring. At this time, it is preferable to heat it.

The solution obtained as described above is dispersed and suspended in water. In this case, a dispersant is usually used.

Examples of dispersants include organic compounds such as partially saponified polyvinyl alcohol, polyacrylates, polyvinylpyrrolidone, carboxymethylcellulose, methylcellulose, calcium stearate, and ethylene bisstearamide, as well as calcium pyrophosphate, calcium phosphate, calcium carbonate, and carbonic acid. Examples include inorganic compounds consisting of fine powder hardly soluble in water, such as magnesium, 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, 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 oxides such as butyl perbenzoate, lauroyl peroxide, tert-butyl peroxy-2-ethylhexanate, tert-butyl peroxide, azo compounds such as azobisisobutyronitrile, azobisdimethylvaleronitrile, etc. are used. can.

The polymerization catalyst is usually used dissolved in a vinyl aromatic monomer.

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

In the polymerization reaction, the type and amount of dispersant, stirring speed,
By adjusting the shape of the stirring blades, the way the cutting board of the reaction vessel is arranged, etc., the size of the droplets dispersed in water can be adjusted, and expandable thermoplastic resin particles of various particle sizes can be produced depending on the purpose. Obtainable.

The blowing agents used in this invention include easily volatile blowing agents, such as propane, n-butane, i-
Aliphatic hydrocarbons such as butane, n-pentane, i-pentane, n-hexane, cycloaliphatic hydrocarbons such as cyclopentane, cyclohexane, methyl chloride, ethyl chloride, dichlorodifluoromethane, chlorodifluoromethane, trichlorofluoromethane Examples include halogenated carbon dioxide such as halogenated carbon dioxide. These blowing agents are generally used in an amount of 3-40% 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.

In this invention, particles of a desired size can be easily obtained in large quantities, and re-pelletization is not necessary. When these resin particles are used as a normal molding material, they can be smoothly fed from the hopper of a molding machine, reducing so-called bite fluctuations, and shortening the melting time in the cylinder of the molding machine, resulting in a shorter molding cycle. It can be shortened, and even small molded items, thin-walled items, and items that require fine details can be molded very well.

Furthermore, there is no need to re-pelletize to obtain small particles, the orientation and thermal deterioration that occur at that time can be prevented, the molding width is wide (good molded products can be obtained under a wide range of molding conditions), and the quality is high. is also stable.

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

Example 1 2000 g of pure water, 4.8 g of metathetical magnesium pyrophosphate, and 10 g of a 2% aqueous solution of sodium dodecylbenzenesulfonate were put into a polymerization vessel with an internal volume of 5.
Furthermore, a styrene-maleic anhydride copolymer with a maleic anhydride content of 21 wt% (average degree of polymerization:
800) 500g, benzoyl peroxide 3.8g, t-butyl perbenzoate 1g styrene monomer 1500g
A mixed solution dissolved in 50 g was added thereto, and the temperature was raised to 90° C. while stirring at 180 rpm. After reacting at 90℃ for 7 hours, the stirring was increased to 250rpm, the temperature was raised to 130℃, and the temperature was increased to 250rpm.
Time was maintained.

The polymer obtained here is obtained in the form of pearls,
The particle size was distributed at 78wt% between 10 and 20 meshes using a JIS standard sieve. It showed a Vikatsu softening point of 112°C. Further, as a result of differential thermal analysis, two peaks indicating the glass transition points of polystyrene and styrene-maleic anhydride copolymer coexisted.

Example 2 1200 g of the polymer obtained in Example 1 (particle size of 10 to 20 meshes), 2800 g of pure water, 4.8 g of metathesized magnesium pyrophosphate, 10 g of a 2% aqueous solution of sodium dodecylbenzenesulfonate, 48 g of toluene.
was placed in an autoclave with an internal volume of 5. While stirring, 120 g of butane was injected under closed conditions.
The temperature was raised to 100°C, maintained for 20 hours, and then cooled to 30°C to obtain beads containing a foaming agent.

After the beads were dehydrated and dried, they were placed in a sealed container and stored at 15°C for 3 days.

When the foamable beads obtained here were foamed with steam at 100°C, foamed particles having a bulk density of 0.025 kg/ were obtained.

After the foamed particles were left indoors for 24 hours, the mold was slightly overfilled and molded with steam at 1.5 kg/cm ² (gauge pressure). The obtained molded body was left in an air circulation constant temperature oven at 90℃ for one week, and the shape changed from the original size.
It showed a shrinkage rate of 1.5%.

When the foamed particles having a bulk density of 0.025 Kg/ were molded using the same mold with steam at 1.0 Kg/cm ² (gauge pressure), a molded article having similar properties was obtained.

Example 3 In Example 1, instead of 1500 g of styrene monomer in which styrene-maleic anhydride copolymer was dissolved, 1000 g of styrene, 250 g of α-methylstyrene,
Polymerization was carried out under the same conditions except that 250 g of a mixed monomer of nuclear-substituted chlorostyrene was used, and foamable beads were obtained by containing a blowing agent based on Example 2. When these beads were foamed with 95℃ steam,
Expanded particles were obtained with a bulk density of 0.027 Kg/. When a foamed molded article produced using the foamed beads was left at 95° C. for one week, the heat shrinkage was 0.8%.

The results of differential thermal analysis of the resin particles obtained during the polymerization process show that the glass transition point of a ternary copolymer of polystyrene/α-methylstyrene/nucleically substituted chlorostyrene is the same as that of a styrene-maleic anhydride copolymer. It was mixed with Also, the particle size is 10~
The distribution was 70% between 20 meshes.

Example 4 Styrene-maleic anhydride copolymer with a maleic anhydride content of 16 wt% (average degree of polymerization:
800) 500g, benzoyl peroxide 3.8g, t-butyl perbenzoate 0.7g styrene monomer
Expandable beads were obtained by polymerization in the same manner as in Examples 1 and 2, except that 1500 g of the beads were dissolved. The heat shrinkage of this foam molded article (having a density of 0.025 kg/) at 90° C. was 6.5%.

In addition, the resin particles obtained during the polymerization process are 10 to 20
It was distributed 80% among the meshes. In addition, the Vikatsu softening point was 107°C.

Example 5 Styrene-maleic anhydride copolymer with a maleic anhydride content of 21 wt% (average degree of polymerization:
800), 5.0 g of benzoyl peroxide, and 1.2 g of t-butyl perbenzoate were dissolved in 1800 g of styrene. The resulting resin had a 70% distribution between 10 and 20 meshes. The softening temperature of this polymer was 103°C.

In addition, in each of the above examples, wt% is weight%
means.

Claims (1)

[Claims] 1 10 to 35 parts by weight of a styrene-maleic anhydride copolymer resin containing 15 to 30% by weight of maleic anhydride component and having an average degree of polymerization of 500 or more is mixed with a vinyl aromatic monomer.
This solution is suspended in water and polymerized in the presence of a polymerization catalyst. At this time, a blowing agent is added during or after the polymerization to form foamable thermoplastic resin particles. A method for producing thermoplastic resin particles characterized by obtaining.