JP3475416B2 - Expandable styrenic resin particles, method for producing the same, and expanded molded article - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expandable styrenic resin particles, a method for producing the same, and a foam-molded product capable of obtaining a foam-molded product having excellent surface smoothness when foam-molded.

[0002]

2. Description of the Related Art In recent years, various types of printing have been frequently performed on the surface of foam molded articles, and foam molded articles having excellent surface smoothness have been demanded. This is because if the surface of the foam-molded product has irregularities, the concave portions remain unprinted and remain white, and the appearance of the printed appearance deteriorates. In particular, in polystyrene foam products using expandable polymer particles, it is more difficult to sufficiently fill the gaps between the foam particles, and therefore it is further required to improve the surface smoothness.

As a technique for improving the surface smoothness, Japanese Unexamined Patent Publication (Kokai) No.
8-222121, JP 62-11740, JP 61-214544, and JP 63-6.
No. 9844, Japanese Unexamined Patent Publication No. 1-29841, Japanese Unexamined Patent Publication No. 1-299843, etc., a surface layer is formed by coating a surface additive that corrodes a skin portion on the surface of expandable polystyrene resin particles impregnated with a foaming agent. It describes a method of providing a layer that does not foam on the part. In addition, JP-A-53-127
Japanese Patent No. 567 discloses that, in addition to the present invention, 0.005 to 5 parts by weight of polyethylene wax and 2 to 10 parts by weight of easily volatile hydrocarbon are added to 100 parts by weight of polystyrene resin particles for the purpose of forming fine and uniform cells. Expandable polystyrene-based resin particles containing the above are described.

[0004]

However, JP-A-58-222121, JP-A-62-11740, JP-A-61-214544, and JP-A-63-
In the methods disclosed in Japanese Patent Application Laid-Open No. 69844, Japanese Patent Application Laid-Open No. 1-29841, Japanese Patent Application Laid-Open No. 1-299843, the foaming agent is likely to dissipate, and the life of the expandable polystyrene resin particles as a product is shortened. There is a drawback that.

On the other hand, the method disclosed in JP-A-53-127567 is similar to the method of the present invention in that polyethylene wax is used. However, this method involves mixing polyethylene wax with polystyrene, and this method has a problem that the expandability of the expandable polystyrene-based resin particles obtained is significantly reduced. The present invention solves all of the above problems, expandable styrenic resin particles excellent in surface smoothness of foamed molded articles, without problems such as escape of foaming agent and deterioration of foamability, and the production thereof. A method and a foamed molded article are provided.

[0006]

Means for Solving the Problems That is, the present invention, in the aqueous medium in which the styrene resin seed particles are suspended, in carrying out the polymerization reaction by continuously or intermittently adding a polymerizable monomer, Polyethylene-styrene mixed paste is mixed with the polymerizable monomer and added to perform polymerization, and a method for producing expandable styrene resin particles, and expandable styrene resin particles obtained by the above production method And a foam-molded article using the same.

First, the polyethylene-styrene mixed paste material used in the present invention will be described. The polyethylene-styrene mixed paste is a mixture of polyethylene and styrene in the form of paste in which polyethylene is finely and uniformly dispersed in styrene. The polyethylene used has a weight average molecular weight of 500 to
2,000 low density polyethylene is preferred. If the weight average molecular weight of polyethylene is less than 500, the effect of improving the surface smoothness tends to be insufficient, while 2,000
If it exceeds, the solubility in hot styrene becomes poor, so that it becomes difficult to obtain a uniform polyethylene-styrene mixed paste, and the effect of improving the surface smoothness tends to be insufficient. A more preferable polyethylene has a weight average molecular weight of 800 to 1,200, and a particularly preferable weight average molecular weight is about 1,000.

In order to obtain a polyethylene-styrene mixed paste, a weight ratio of 5 to the polyethylene is used.
The method of adding -50 times the amount of styrene and heat-treating at a temperature of 110 to 140 ° C. for 0.5 to 3 hours and then cooling is a method in which polyethylene is uniformly dispersed and the expandable styrene resin particles have good surface smoothness. It is preferable since a polyethylene-styrene mixed paste to be obtained can be obtained. If the amount of styrene is less than 5 times, it is difficult to obtain a uniform polyethylene-styrene mixed paste, and it is difficult to sufficiently obtain the effect of improving surface smoothness. On the other hand, if the amount exceeds 50 times, it is difficult to form a paste, and polyethylene and styrene tend to be easily separated. More preferable range is 1
The amount is 0 to 30 times. When the temperature is lower than 110 ° C, a uniform polyethylene-styrene mixed paste is difficult to obtain, and the effect of improving the surface smoothness tends to be poor. On the other hand, when the temperature is higher than 140 ° C, thermal polymerization of styrene proceeds. The paste-like product obtained as a result becomes hard and difficult to mix with the polymerizable monomer. The most preferred temperature is about 120 ° C. Further, if the heat treatment time is less than 0.5 hours, it is not sufficient to obtain a uniform paste-like material, while if it exceeds 3 hours, the paste-like material tends to become hard. More preferable time is 0.8 to 2 hours. In addition, when such low density polyethylene powder is directly mixed with a polymerizable monomer to perform polymerization without using such a polyethylene-styrene mixed paste, the polyethylene powder is uniformly converted into a monomer. Without being mixed, the effect of improving the surface smoothness on the resulting expandable styrene resin particles is almost eliminated.

In the present invention, the polyethylene-styrene mixed paste obtained by the above-mentioned method is continuously or intermittently added with a polymerizable monomer in an aqueous medium in which styrene resin particles are suspended. At the time of carrying out the polymerization reaction, the polymerizable monomer is mixed and added to carry out the polymerization. As the timing of mixing and adding to the polymerizable monomer, the total amount of the final addition amount of the polymerizable monomer and the pasty material is 5 to 30% by weight based on the obtained styrene resin particles. It is preferable to mix at the point of time. If the total amount is 30% by weight or less, the expandability of the resulting expandable styrenic resin particles tends to be low, while the total amount is less than 5% by weight. If so, the effect of improving the surface smoothness tends to be insufficient. For the same reason, a more preferable range is between 10 and 25% by weight. The time of mixing and adding is specifically, based on the total amount of the styrene resin seed particles to be suspended in advance, the polymerizable monomer, and the total amount of the paste-like material, the polymerizable mixture of the paste-like material. It can be calculated from the percentage of the total amount of the monomer and the pasty substance.

The amount of polyethylene-styrene mixed pasty matter mixed and added is preferably such that the polyethylene contained in the obtained styrene resin particles is 0.1 to 5% by weight. If this amount is less than 0.1% by weight, the effect of improving the surface smoothness is not sufficient, and if it exceeds 5% by weight, the foamability tends to decrease.

The styrene resin seed particles used in the present invention include styrene homopolymer, styrene, vinyltoluene, isopropylstyrene, α-methylstyrene,
Use copolymers such as styrene derivatives such as chlorostyrene and tert-butylstyrene, acrylonitrile, 1,3-butadiene, acrylic acid ester, methacrylic acid ester, vinyl acetate, maleic acid ester, divinylbenzene and other monomers. However, in the case of a copolymer, it is preferable to use 50% by weight or more of styrene or a styrene derivative. Further, the styrene resin seed particles may contain ethylene vinyl acetate copolymer, ethylene bisstearylamide, methylenebisstearylamide and the like which are known as a cell forming agent. Further, a plasticizer such as dioctyl phthalate and dioctyl adipate may be contained.

In the aqueous medium in which the styrene resin seed particles are suspended, tricalcium phosphate, hydroxyapatite, magnesium phosphate, barium phosphate, strontium phosphate, aluminum phosphate, iron phosphate, as a suspension stabilizer,
Sparingly soluble inorganic salts such as cobalt phosphate and calcium pyrophosphate,
Anionic surfactants such as sodium dodecylbenzene sulfonate, sodium styrene sulfonate, sodium dodecyl sulfonate, and sodium dioctyl sulfosuccinate, and water-soluble polymer compounds such as polyvinyl alcohol and hydroxyethyl cellulose can be added and mixed.

Polymerizable monomers that are continuously or intermittently added to an aqueous medium in which styrene resin seed particles are suspended include styrene, vinyltoluene, isopropylstyrene, α-methylstyrene, chlorostyrene, Styrene derivatives such as tertiary butyl styrene, acrylonitrile,
Although monomers such as 1,3-butadiene, acrylic acid ester, methacrylic acid ester, vinyl acetate, maleic acid ester, and divinylbenzene can be used, it is preferable to use styrene or a styrene derivative in an amount of 50% by weight or more. Further, ethylene vinyl acetate copolymer, ethylene bisstearylamide, methylenebisstearylamide, etc., which are known as a bubble forming agent, may be mixed with the polymerizable monomer. Further, a plasticizer such as dioctyl phthalate or dioctyl adipate may be mixed.

A polymerization initiator is used for the polymerization, and examples thereof include benzoyl peroxide, lauroyl peroxide and t.
-Butylperoxy 2-ethylhexanoate, methylbenzoyl peroxide, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, t
Examples include organic peroxide-based polymerization initiators such as -butylperoxybenzoate and t-butylperoxyisopropyl carbonate. Further, these polymerization initiators may be used in combination of several kinds.

The method of continuously or intermittently adding the polymerizable monomer is not particularly limited, but a method of continuously dropping is preferable because blocking of polymer particles does not easily occur. The dropping rate is appropriately selected depending on the polymerization temperature, the type of the polymerization initiator, the amount, etc., but a higher rate than the rate at which the monomers are reduced by the polymerization is preferable in that the initiator efficiency is good, and the rate at which the rate is decreased The closer the value is to, the less blocking of the polymer particles occurs, which is preferable.

In order to make the styrenic resin particles obtained by the above-mentioned polymerization into expandable styrenic resin particles, volatile hydrocarbons such as propane, butane, pentane, hexane, cyclopentane and cyclohexane, methylene chloride and dichlorine are used. A volatile halogenated hydrocarbon such as difluoromethane or trifluoromethane or a foaming agent such as a mixture thereof is impregnated during or after the polymerization. The expandable styrene-based resin particles obtained can be made into a foam-molded product having excellent surface smoothness by, for example, heating and pre-foaming and then filling the molds of various molded products and foam-molding.

[0017]

EXAMPLES The present invention will be described below with reference to examples. Example 1 Low-density polyethylene (Pe having a weight average molecular weight of 1,000)
Made by trolite Specialty Polimers Group, product name POLY
Take 5 g of WAX1000) in a 100 ml heat resistant screw cap bottle,
50 g of styrene (manufactured by Denki Kagaku Kogyo Co., Ltd.) was added thereto and the lid was closed. The bottle was placed in a constant temperature bath equipped with a shaker and filled with glycerin as a heat medium, and shaking was started at a speed of 120 times per minute. It takes 90 minutes to raise the temperature to 120 ° C,
After maintaining the temperature at 120 ° C. for a minute, it was cooled to obtain a polyethylene-styrene mixed paste. 10 wt% tricalcium phosphate dispersion liquid (manufactured by Nippon Kagaku Kogyo Co., Ltd., trade name Super Tight 10) in a 4 liter autoclave 60
g, sodium dodecylbenzenesulfonate (manufactured by Wako Pure Chemical Industries, Ltd.) 0.06 g, ion-exchanged water 1200 g,
300 g of polystyrene beads (seed particles, average diameter 0.5 mm, weight average molecular weight 250,000) were added, stirring was started, and the temperature was raised to 90 ° C. As a polymerization initiator, 75 g by weight of benzoyl peroxide wet body (Nippon Yushi Co., Ltd., trade name Nyper BW) 1.2 g and t-butyl peroxyisopropyl carbonate (Nippon Yushi Co., Ltd. trade name, Perbutyl I) 0 0.3 g was added. Ethylene vinyl acetate copolymer (Nippon Gosei Co., Ltd., trade name Soalex CH) 0.2
Styrene (manufactured by Denki Kagaku Kogyo Co., Ltd.) in which 4 g was dissolved 35
Immediately after adding the polymerization initiator, 0 g was added dropwise over 90 minutes. Thirty minutes after the completion of the dropping, the same amount of the polymerization initiator was again added to the autoclave, and 350 g of styrene containing the same amount of the ethylene-vinyl acetate copolymer was dropped for 90 minutes in the same manner. After 30 minutes, 0.6 g of a 75% by weight benzoyl peroxide wet body (manufactured by NOF CORPORATION, trade name: Niper BW) as a polymerization initiator, and t-butylperoxyisopropyl carbonate (manufactured by NOF CORPORATION, 0.15 g of trade name Perbutyl I) was added to the autoclave, and 200 g of styrene in which 3 g of the polyethylene-styrene mixed paste was dissolved was added dropwise over 90 minutes (that is, the final addition amount was about 17% by weight (the obtained styrene-based material was obtained. (Based on the weight of the resin particles) time point). After 30 minutes from the end of the dropping, the autoclave was sealed and the temperature was raised to 115 ° C. for 1 hour to raise the temperature.
It was kept at 115 ° C for 6 hours. Next, the mixture was cooled to 100 ° C. in 1 hour, and while maintaining the temperature at 100 ° C., 24 g of cyclohexane and 70 g of butane were introduced in 1 hour. After that, the temperature was kept at 100 ° C. for 3 hours and then cooled to room temperature to obtain the target expandable styrene resin particles. In order to examine the foamability of the resulting expandable styrenic resin particles, some particles were heated with boiling water for 3 minutes, and foamed to 69 ml / g. The expandable styrenic resin particles were pre-expanded to 55 ml / g. The pre-expanded particles were aged for 24 hours, filled in a mold, and heat-molded at a steam pressure of 0.078 MPa for 5 seconds. The maximum depth of depression of the surface of the obtained foamed molded product is 76.
was μm.

Comparative Example 1 Expandable styrene resin particles were synthesized in the same manner as in Example 1 except that the polyethylene-styrene mixed paste was not used. Some particles in boiling water 3
When heated for a minute, it foamed to 71 ml / g. The maximum depression depth of the surface of the foam-molded article obtained by foam-molding the particles in the same manner as in Example 1 was 98 μm, and the surface smoothness was poor.

Comparative Example 2 In Example 1, 0.3 g of low-density polyethylene powder was used instead of 3 g of the polyethylene-styrene mixed paste material.
The expandable styrene resin particles were synthesized in the same manner as in Example 1 except that was used. When some particles were heated with boiling water for 3 minutes, they foamed to 70 ml / g. The maximum depression depth of the surface of the foam-molded product obtained by foam-molding the particles in the same manner as in Example 1 was 99 μm, and the surface smoothness was poor.

Example 2 Low density polyethylene (Pe having a weight average molecular weight of 1,000)
Made by trolite Specialty Polimers Group, product name POLY
2.5 g of WAX1000) was placed in a 100 ml heat-resistant screw cap bottle, to which 50 g of styrene (manufactured by Denki Kagaku Kogyo Co., Ltd.) was added and the lid was closed. The bottle was placed in a constant temperature bath equipped with a shaker and filled with glycerin as a heat medium, and shaking was started at a speed of 120 times per minute. It takes 90 minutes to heat up to 120 ° C,
After maintaining the temperature at 120 ° C. for 90 minutes, it was cooled to obtain a polyethylene-styrene mixed paste. 10 wt% tricalcium phosphate dispersion in a 4 liter autoclave (Nippon Kagaku Kogyo KK, trade name Super Tight 10)
60 g, sodium dodecylbenzenesulfonate (manufactured by Wako Pure Chemical Industries, Ltd.) 0.06 g, ion-exchanged water 1200
g, polystyrene beads (average diameter 0.8 mm, weight average molecular weight 260,000, ethylenebisstearylamide (Nippon Kasei Co., Ltd., trade name Three Packs E) 800
Add 1,000 g (containing ppm) to start stirring, and
The temperature was raised to ° C. 75% by weight benzoyl peroxide wet body as a polymerization initiator (Nippon Yushi Co., Ltd., trade name Niper BW)
0.5 g and t-butyl peroxyisopropyl carbonate (manufactured by NOF CORPORATION, trade name Perbutyl I).
2 g was added. 200 g of styrene in which 4 g of polyethylene-styrene mixed paste was dissolved was added dropwise over 90 minutes (that is, the final addition amount of the polymerizable monomer was about 17% by weight (based on the weight of the obtained styrene resin particles). ). After 30 minutes from the end of the dropping, the autoclave was sealed, the temperature was raised to 115 ° C. for 1 hour, and the temperature was raised to 115 ° C. for 6 hours. Next, it takes 1 hour to cool to 100 ° C,
While maintaining the temperature at 00 ° C., 24 g of cyclohexane and 70 g of butane were introduced for 1 hour. After that, the temperature was kept at 100 ° C. for 3 hours and then cooled to room temperature to obtain the target expandable styrene resin particles. In order to examine the foamability of the resulting expandable styrenic resin particles, some particles were heated with boiling water for 3 minutes, and foamed to 70 ml / g.
The expandable polystyrene resin particles were pre-expanded to 55 ml / g. Aging of pre-expanded particles for 24 hours, 0.078MPa
Heat molding was performed for 5 seconds with the steam pressure of. The maximum depth of depression on the surface of the obtained foamed molded product was 77 μm.

[0021]

The expandable styrenic resin particles obtained by the production method of the present invention have no problems such as deterioration of foamability.
It is possible to obtain a foam-molded article having excellent surface smoothness when foam-molded.

Claims (7)

(57) [Claims] 1. When a polymerizable monomer is continuously or intermittently added to an aqueous medium in which styrene resin seed particles are suspended to carry out a polymerization reaction, a polyethylene-styrene mixed paste is prepared as described above. Polymerization is carried out by mixing with a polymerizable monomer, and a foaming agent is included during or after the polymerization.
A method for producing expandable styrenic resin particles, which comprises dipping. 2. The polyethylene used in the polyethylene-styrene mixed paste material has a weight average molecular weight of 500 to 2
2. The method for producing expandable styrenic resin particles according to claim 1, which is 000 low-density polyethylene. 3. A polyethylene-styrene mixed paste is prepared by adding 5 to 50 times the weight ratio of styrene to polyethylene, heat treating at a temperature of 110 to 140 ° C. for 0.5 to 3 hours, and then cooling. Claim 1 obtained
Or the method for producing expandable styrenic resin particles according to 2. 4. A polyethylene-styrene mixed paste material, wherein the total amount of the final addition amount of the polymerizable monomer and the paste material is 5 with respect to the obtained styrene resin particles.
3. Mixing at the time of .about.30% by weight.
Or the method for producing expandable styrenic resin particles according to item 3. 5. The polyethylene-styrene mixed pasty material is mixed in such an amount that polyethylene contained in the resulting styrene resin particles is 0.1 to 5% by weight. The method for producing expandable styrenic resin particles. 6. Expandable styrenic resin particles obtained by the method according to any one of claims 1 to 5. 7. A foam-molded article obtained by foam-molding the expandable styrenic resin particles according to claim 6.