JPS5940165B2 - Method for producing expandable thermoplastic resin particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides foamable thermoplastic resin particles, particularly foamable,
The present invention also relates to a method for producing foamable thermoplastic resin particles for obtaining a foamed body having excellent fusion moldability and good flexibility.

In general, polystyrene foam can be easily obtained with a high expansion ratio, has strong rigidity, and has good shape retention, but is brittle and has poor properties such as chemical resistance, oil resistance, and heat resistance. There were flaws.

On the other hand, foams made of polyolefin resins such as polyethylene or polypropylene are rich in flexibility and elasticity, and are superior in chemical resistance, oil resistance, heat resistance, etc., compared to polystyrene foams. However, the foaming agent impregnated with resin particles such as polyethylene and polypropylene easily escapes, and after producing the foamable resin particles, it is necessary to immediately pre-foam them into foamed particles. It was necessary to store it in a pressurized container. Therefore, it is extremely disadvantageous during storage and transportation, and it has generally been difficult to obtain a foam with a high expansion ratio. In order to obtain a resin that combines the advantages of both polypropylene and polystyrene, even if the two resins are mechanically mixed, the two resins do not mix uniformly and the foam undergoes phase separation, resulting in a beautiful appearance. It cannot be made into a foam.

Much research has already been done to improve this. For example, in the specification of Japanese Patent Publication No. 47-26097, a vinyl aromatic polymer (polystyrene) raw material containing 1 to 15% by weight of polyolefin No. A based on the total amount of resin is thermally melted into strips. A method for obtaining expandable vinyl aromatic polymer resin pellets is shown in which the polyolefin is impregnated with a blowing agent, but this method requires a small amount of polyolefin and the polyolefin and vinyl aromatic polymer are simply physically Since both resins are not mixed uniformly and phase separation occurs, the impregnation of the blowing agent and the expansion ratio become uneven, making it impossible to obtain a uniform foam. Since the amount is small, flexibility and elasticity cannot be improved. In addition, in the specification of Japanese Patent Publication No. 45-32623,
A granular thermoplastic resin mainly composed of an aliphatic olefin resin polymer, a vinyl monomer that can dissolve or swell the polymer, and can be polymerized, a polymerization catalyst, and a crosslinking agent consisting of an organic peroxide. The vinyl monomer is dispersed in an aqueous medium, into which a gas or liquid physical blowing agent is pressurized, and heated to a temperature at which the vinyl monomer has a solvent ability for the aliphatic olefin polymer and at which the crosslinking agent decomposes. , a method for producing a foamable thermoplastic particulate polymer, characterized in that the polymerization of the vinyl monomer, the impregnation with a blowing agent, and the crosslinking reaction are carried out simultaneously under pressure. However, in this method, the polymerization of the vinyl monomer, the impregnation of the blowing agent, and the crosslinking reaction are simultaneously carried out under pressure, and therefore special production equipment is required, which is disadvantageous for production on an industrial scale. In addition, all of the examples using this method had an extremely high content of polyolefin, so that the resulting foamable pellets could not be said to have sufficient scratch retention, and the foams had properties similar to those of foams made of polyolefin alone. As a result of research to obtain a polyolefin resin foam that has good flexibility, excellent chemical resistance, heat resistance, and good cushioning properties, the present inventor discovered polyolefin resin particles having a special composition. is used as a core, and a vinyl aromatic monomer and/or methacrylic acid ester is added to the core in the presence of a polymerization catalyst and a crosslinking agent, and the resulting thermoplastic resin particles are impregnated with a blowing agent to achieve good foaming. The present inventors have discovered that thermoplastic resin particles can be obtained and have completed the present invention.

The present invention includes 20-80% by weight of ethylene/α-olefin/polyene copolymer particles consisting of 20-80% by mol of ethylene, 20-80% by mol of α-olefin and 0.5-20% by mol of a polyene compound, and a vinyl aroma. Group monomers and/or methacrylic esters 20-80% by weight
is suspended in an aqueous medium and polymerized in the presence of a polymerization catalyst and a crosslinking agent to obtain polymerized and crosslinked thermoplastic resin particles. Ethylene α- The olefin/polyene copolymer is a copolymer consisting of ethylene, α-olefin, and polyene.

Examples of α-olefins include propylene, butene, benzene, isoprene, hexene, and the like. Particularly preferred are propylene and butene-1. Polyene is a cyclic or almost acyclic polyene containing two or more double bonds, such as hexadiene-1, 4, hexadiene-1, 5, heptadiene-1, 6, 2-methyl-pentadiene-1, etc.・4, octadiene-1, 9, 6-methylheptadiene-1, 5, 9-ethyl undecadiene-1
・Acyclic dienes such as 9,8-ethyldecadiene-1,8, acyclic trienes such as octatriene-1,4,7, ethylidene norbornene, synchropentadiene, cyclooctadiene-1,4, cycloocta Dien-1・
5. Cyclododecadiene 1.6, Cyclododecadiene ~
1,7, cycloheptadiene-1,4, cyclohexadiene-1,4, norbornadiene, methylenenorbornene, 5-ethylidene-2-norbornene, 5-methyltetrahydroindene and other cyclic nonconjugated dienes, cyclododecatriene-1・5・9, and other cyclic non-conjugated trienes can be mentioned. Among these, cyclic non-conjugated dienes are preferred, with synchropentadiene and ethylidene norbornene being particularly preferred. Particularly preferred ethylene/α-olefin/polyene copolymers are ethylene/propylene/synchropentadiene copolymer and ethylene/propylene/ethylidene norbornene copolymer. The ethylene content in the copolymer is from 20 to 80 mol%, preferably from 30 to 80 mol%, and the content of non-conjugated polyene is from 0.5 to 20 mol%, preferably from 0.5 to 15 mol%. Two or more types of the copolymer components of the present invention may be mixed together, or they may be used in combination with other rubbers. A method for producing an olefin copolymer by adding a polyene compound such as a diene or a polyene is described, for example, in Japanese Patent Publication No. 36-194
95, 37-15037, 37-15039, 37-1
5041, 40-22673, 40-22752, 40
-28950, JP-A-49-131237, 50-41
This method is already known from Publication No. 946, 50-41947, etc.

As the ethylene/α-olefin/polyene copolymer in the method of the present invention, a copolymer obtained by the above method can be used. Vinyl aromatic monomers used in the method of the present invention include styrene, α-methylstyrene, ethylstyrene, chlorostyrene, 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, and the like.

In the method of the present invention, a methacrylic acid ester such as methyl methacrylate or ethyl methacrylate can be used in place of or in combination with the vinyl aromatic monomer. When using methacrylic acid ester, it is preferable to use α-methylstyrene in combination. Polymerization catalysts used in the method of the present invention include organic peroxides such as benzoyl peroxide, tert-butyl perbenzoate, lauroyl peroxide, tert-butyl peroxy-12-ethylhexanate, and tert-butyl peroxide; Examples include azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile.

In addition, as a crosslinking agent, dicumyl peroxide, tert-butylcumyl peroxide, 1,1-bis(
tertiarybutyloxy)-3,5,5-trimethylcyclohexane, 2,5-dimethyl(2,5-ditertiarybutylperoxy)hexane, α,α-dimethyl-α-methyl-α-ethylbenzyl peroxide These crosslinking agents are generally used together with crosslinking aids.

Such crosslinking aids include divinylbenzene, polyethylene glycol dimethacrylate, triallyl cyanurate, diallylphthalate, 1,3-butadiene, 1.
Examples include functional vinyl compounds such as 2-polyptadiene and 1,4-polybutadiene, and quinone dioximes and bisamides. To explain the method of the present invention in detail, for example, first, a flask equipped with a stirrer, a thermometer, a gas inlet tube, a gas discharge tube, and a liquid inlet tube is cooled under a nitrogen flow, and methylene chloride is passed through a column of silica gel. Then, panadium tris(acetylacetonate) and diisobutylaluminum monochloride are introduced into the flask.

A polyene compound such as synchropentadiene is introduced into this, the flow of nitrogen gas is stopped, and a mixed gas of ethylene and propylene is introduced. When this is stirred, an ethylene-propylene-polyene copolymer such as an ethylene-propylene-synchropentadiene copolymer is obtained as a precipitate. This copolymer is made into pellet-like particles of 1 to 3 mm using, for example, an extruder. Next, the copolymer resin particles are suspended in an aqueous medium to which a dispersant is added. As this dispersant, for example, polyvinyl alcohol, methyl cellulose, calcium phosphate, magnesium pyrophosphate, calcium carbonate, etc. are used, and these dispersants are generally used by adding 0.01 to 5% by weight to water. .
Next, a vinyl aromatic monomer such as a styrene monomer, a methacrylic acid ester, or a mixture thereof (hereinafter simply referred to as a vinyl aromatic monomer), a polymerization catalyst, and a crosslinking agent are added to the suspension in which the copolymer resin particles are dispersed. . This addition method may be to add the whole amount at once, or to gradually drop it in small amounts. The vinyl aromatic monomer, the polymerization catalyst, and the crosslinking agent may be added separately, or the polymerization catalyst and the crosslinking agent may be dissolved or mixed in advance with the vinyl aromatic monomer and added. The aqueous medium may be heated to a temperature at which the vinyl aromatic monomer can be polymerized, and the vinyl aromatic monomer, the polymerization catalyst, and the crosslinking agent may be added thereto, or the vinyl aromatic monomer, the polymerization catalyst, and the crosslinking agent may be added at room temperature, and then , it may be heated to a polymerizable temperature. Furthermore, the vinyl aromatic monomer and/or the polymerization catalyst and crosslinking agent may be used after being dissolved in a solvent that does not interfere with the polymerization reaction. Examples of the solvent include toluene, benzene, 1,2-dichloropropane, and the like. If the vinyl aromatic monomer is used in relatively large amounts, the vinyl aromatic monomer should be gradually added to the suspension in small amounts to prevent the formation of homopolymers of the vinyl aromatic monomer. is desirable.

The vinyl aromatic monomer dropped into the suspension permeates into the interior of the ethylene/α-olefin/polyene copolymer particles and is polymerized and crosslinked within the copolymer particles, resulting in graft polymerization due to this reaction. also occur at the same time.

In this reaction, 20 to 80% by weight of the copolymer resin
and 20 to 80% by weight of vinyl aromatic monomer.

However, if the amount of vinyl aromatic monomer is less than the above-mentioned amount, the expansion ratio of the resulting foam will decrease and a foam with a high expansion ratio cannot be obtained, and conversely, if the amount of vinyl aromatic monomer is too large, Properties such as flexibility, elasticity, heat resistance, and oil resistance of the foam are reduced. Therefore, the mixing ratio of the copolymer resin and the vinyl aromatic monomer is 20 to 8.
0% by weight, 20-80% by weight of vinyl aromatic monomer, preferably 50-30% by weight of copolymer resin, and 50-70% by weight of vinyl aromatic monomer. The vinyl aromatic monomer dropped therein is absorbed into the ethylene/α-olefin/polyene copolymer particles, and a polymerization and crosslinking reaction is carried out in the particles to obtain the thermoplastic resin particles of the present invention.

The thermoplastic resin particles obtained are ethylene. α-olefin. Random polyene copolymers, vinyl aromatic polymers,
The above-mentioned copolymer contains a vinyl aromatic graft polymer, and unlike a case where the vinyl aromatic polymer is simply mixed, phase separation does not occur from each other. This is presumably because the graft polymer has a binder effect and improves the compatibility of the polypolymer and the vinyl aromatic polymer. The graft-polymerized and cross-linked thermoplastic resin particles obtained by the method of the present invention precipitate as insoluble matter (gel fraction) when heated and dissolved in toluene, xylene, etc.

The presence of the gel component improves the retention of the foaming agent and prevents a decrease in the expansion ratio of the foam. The gel content (gel%) varies depending on the ratio of the copolymer and vinyl aromatic monomer used, but is generally 3% to the weight of the copolymer.
Preferably, it is present in an amount of 0% or more. In the present invention, thermoplastic resin particles obtained by polymerizing the copolymer resin particles with a vinyl aromatic monomer are impregnated with a blowing agent under pressure in an aqueous suspension.

Suspending agents used in aqueous suspensions are added to prevent the thermoplastic resin particles from binding or coalescing with each other during impregnation with the blowing agent, such as partially saponified polyvinyl alcohol, In addition to organic compounds such as polyacrylate, polyvinylpyrrolidone, carboxymethylcellulose, methylcellulose calcium stearate, and ethylene bisstearamide, calcium pyrophosphate, calcium phosphate, calcium carbonate, magnesium carbonate, magnesium phosphate, magnesium pyrophosphate, and magnesium oxide. Examples include inorganic compounds consisting of fine powders that are sparingly soluble in water. In the method of the present invention, when an inorganic compound is used as a suspending agent, it is desirable to use a surfactant such as sodium dodecylbenzenesulfonate. In addition, the blowing agents used in the method of the present invention include easily volatile blowing agents, such as aliphatic hydrocarbons such as propane, n-butane, 1-butane, n-pentane, i-pentane, and n-hexane; Examples include cycloaliphatic hydrocarbons such as pentane and cyclohexane, and 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. Also, toluene,
A small amount (1 to 5% by weight) of an organic solvent such as xylene may also be used. Impregnation with a blowing agent can be carried out, for example, by suspending thermoplastic resin particles in water containing a suspending agent in an autoclave, heating and pressurizing the blowing agent, thereby obtaining expandable thermoplastic resin particles. It will be done. The expandable thermoplastic resin particles obtained by the method of the present invention have good retention of the blowing agent impregnated therein.

Therefore, unlike the case of polyolefin particles, there is no need to make them into pre-expanded particles immediately after production or to store them in a pressurized container, and it is possible to store or transport them in the form of expandable resin particles. For example, even if expandable resin particles that have been stored for one week under normal pressure are pre-expanded with water vapor, the expanded particles can have a sufficient magnification. This is because the thermoplastic resin is a copolymer of ethylene, α-olefin, and a polyene compound, and the vinyl aromatic monomer is polymerized, resulting in crosslinking and graft polymerization, which improves the retention of the impregnated blowing agent. It is assumed that there is. Further, the expandable thermoplastic resin particles obtained by the method of the present invention can be pre-foamed and then foam-molded in the mold cavity of a mold to form a foam molded product having a desired shape. This foam molded product has excellent properties such as flexibility, chemical resistance such as oil resistance, heat resistance, bending strength, and cushioning properties, and has a small rate of change due to repeated compression, making it suitable for precision instruments, measuring instruments, etc. Not only is it extremely suitable as a packaging cushioning material, etc., but also has good cushioning properties, so it can be used as an underlay material for chairs, carpets, closets, etc., other insulation materials, roof underlay materials, etc.
It can be used for various purposes such as

Furthermore, in the method of the present invention, impregnation with a blowing agent is performed after polymerization and crosslinking of vinyl aromatic monomers, so there is no need to use a high-pressure reaction vessel for polymerization and crosslinking, making particle production extremely easy. It is. Conventionally, if crosslinking is performed before impregnating with a blowing agent, it becomes difficult to impregnate the blowing agent (Japanese Patent Publication No. 4
5-32622), however, in the method of the present invention, sufficient expandable resin particles could be obtained by impregnating a foaming agent after polymerization and crosslinking.
Therefore, according to the method of the present invention, a vinyl aromatic monomer is polymerized in the presence of a polymerization catalyst and a crosslinking agent to resin particles, that is, ethylene/α-olefin/polyene copolymer particles before being impregnated with a blowing agent. Since cross-linked and graft-polymerized thermoplastic resin particles are obtained, these resin particles can be made into foamable thermoplastic resin particles as described above, and can also be fed to an extruder and foamed by press-fitting a foaming agent. It can also be used as a resin for extrusion molding in the form of a sheet, plate-like or rod-like foam. Example 1~
12 Ethylene/propylene obtained by mixing and copolymerizing ethylene, propylene, and synchropentadiene.
A synchropentadiene copolymer (ethylene content: 65 mol%, synchropentadiene content: 1.2 mol%) was suspended in water containing polyvinyl alcohol and sodium dodecylbenzenesulfonate in an autoclave, and then heated at 85°C. The temperature rises to

To this, 0.3 parts by weight of benzoyl peroxide based on the styrene monomer and a styrene monomer in which dicumyl peroxide was dissolved were added dropwise over a period of 7 hours. Thirty minutes after the completion of the dropwise addition, the temperature was raised to 90°C and maintained for 1 hour. Thereafter, the temperature was further heated to 140°C and maintained for 3 hours to complete the reaction. Thereafter, the thermoplastic resin particles are separated by cooling. 100 parts by weight of the thermoplastic resin particles obtained above were filled in a pressure container together with 100 parts by weight of water and 0.02 parts by weight of sodium dodecylbenzenesulfonate, 20 parts by weight of n-butane was press-fitted, and the mixture was heated at 85°C for 8 hours. After cooling and leaving for one night, the expandable thermoplastic resin particles were separated and collected.

In the above reaction, the gel percentage and blowing agent contained in the thermoplastic resin particles obtained by changing the blending ratio of the ethylene-propylene-synchropentadiene copolymer and styrene monomer and the amount of dicumyl peroxide are injected. Table 1 shows the expansion ratio of the expandable thermoplastic resin particles obtained.

All percentages in the table are by weight. In the table above, dicumyl peroxide and gel are weight percent relative to the copolymer. In Example 9, ethylene/propylene/5-ethylidene-2-norbornene copolymer (ethylene content 73 mol%, 5-ethylidene-2-norbornene copolymer) was used instead of the ethylene/propylene/synchropentadiene copolymer. This is an example in which the same procedure was carried out using 3 mol %). As is clear from the above example, in terms of expansion ratio, ethylene-propylene-synchropentadiene copolymer is 30%, and styrene monomer is 7%.
A thermoplastic resin having a ratio of 0% is most preferable. Generally, the higher the styrene content, the better the expansion ratio, and the higher the gel percentage, the higher the expansion ratio tends to be. However, if the copolymer is extremely small and the styrene content is high, for example, if the copolymer is 15% and the styrene is 85%, it will take an extremely long time to add the styrene monomer, and if it is added too quickly, the copolymer will The aggregates coalesce to form blocks, making it difficult to obtain expandable particles industrially. Also, gel%
If the foaming ratio is less than 30%, the foaming ratio is insufficient, so it is generally
It is preferable that the content is 0% or more. However, if the styrene content is high, the gel% may be relatively low. The results of measuring the cyclic compression set according to JIS K-6401 of the foam obtained by the method of the present invention are shown together with comparative examples.

In this test, a test piece of soil with a side of 50 mm or more and a thickness of 20 mm was repeatedly compressed to 50% of its original thickness (60 mm per minute).
After compressing continuously 80,000 times, the sample was left to stand for 30 minutes, and the rate of decrease in thickness is shown as a percentage. Comparative Example 1 is a foamed resin obtained by adding styrene monomer to polyethylene particles, Comparative Example 2 is a crosslinked polyethylene foam, and Comparative Example 3 is a non-crosslinked extruded polyethylene foam.

Note that all of the sample foams were foams that were expanded 25 to 30 times.

Claims (1)

[Claims] 1 20-80 mol% ethylene, 20-80 mol% α-olefin
20-80% by weight of ethylene/α-olefin/polyene copolymer particles consisting of 80% by mole and 0.5-20% by mole of a polyene compound, and 20-80% by weight of a vinyl aromatic monomer and/or methacrylic acid ester in an aqueous medium. This is suspended in aqueous suspension and polymerized in the presence of a polymerization catalyst and a crosslinking agent to obtain polymerized and crosslinked thermoplastic resin particles, which are composed of easily volatile hydrocarbons or halogenated hydrocarbons in an aqueous suspension. 1. A method for producing expandable thermoplastic resin particles, which comprises pressurizing a foaming agent to obtain expandable thermoplastic resin particles. 2 α-olefin is propylene, butene, pentene,
A method for producing expandable thermoplastic resin particles according to claim 1, wherein the particles are isoprene, hexene or a mixture thereof. 3 The vinyl aromatic monomer is a monomer of styrene, α-methylstyrene, ethylstyrene, chlorostyrene, bromostyrene, vinyltoluene, vinylxylene, isopropylxylene, a mixture thereof, or a mixture of these vinylaromatic monomers. 2. The method for producing expandable thermoplastic resin particles according to claim 1, which is a mixture of a vinyl aromatic monomer and a copolymerizable monomer containing at least % by weight.