KR0154913B1 - Process for preparing modified polystyrene bead foam - Google Patents

Abstract

In the present invention, in preparing a modified polystyrene bead foam obtained by impregnating polyaromatic resin particles with polyvinyl aromatic monomar and then foaming, 0.005-0.1 parts by weight of bromine compound which can be dissolved in the styrene monomer is added to 100 parts by weight of styrene monoma. And, to maintain the internal moisture of the polymerized beads 0,1-0.4% by weight to a modified polystyrene bead foam production method characterized in that the pre-foaming after impregnating the blowing agent at 50-90 ℃.

Description

Method for producing modified polystyrene bead foam

Figure 1a is an optical micrograph of the modified polystyrene bead foam prepared according to the method of the present invention (Example 2).

Figure 1b is an optical micrograph of the modified polystyrene bead foam prepared according to the method of the present invention (Example 3).

Figure 2a is an optical micrograph of the modified polystyrene bead foam prepared according to a conventional method (Comparative Example 1).

2b is an optical micrograph of a modified polystyrene bead foam prepared according to a conventional method (Comparative Example 2).

The present invention relates to a method for producing modified polystyrene bead foam. Specifically, in the preparation of the expandable polyethylene-polystyrene composite having a cross-penetrating network structure, the internal moisture of the polymerized beads is kept low, and the pre-foam inner cell is made uniform by pre-foaming by impregnating with a blowing agent at a low temperature. The present invention relates to a method for minimizing the size to prevent shrinkage during preliminary foaming and to increase the foaming gas holding capacity of the preliminary foam.

Modified polystyrene bead foams prepared by copolymerizing polyolefin and polystyrene or by compression kneading in the presence of a compatibilizer are resins that combine the flexibility, toughness and chemical resistance of olefins, and the stiffness and processability of styrene. It is a resin that can be molded into a free shape.

In the production of polystyrene bead foams, beads obtained by impregnating styrene monoma in partially crosslinked polyethylene suspended in an aqueous medium contain excess internal moisture, and thus, when pre-expanding such beads, excess internal moisture The nucleus acts as a nucleus inside the bead, so there is no T to obtain a preliminary foam with a fine, uniform cell, and the cell tends to grow and shrink.

Japanese Patent Laid-Open No. 63-110906 discloses foam characteristics in accordance with a change in the internal moisture content in addition to the blowing agent impregnated in the beads by impregnating the blowing agent at a high temperature. However, when the impregnating agent is impregnated at a high temperature, the cell becomes large, non-uniform, and tends to shrink when pre-foaming due to an increase in internal moisture of the beads.

Therefore, the present inventors have diligently studied to solve the above problems, and as a result of appropriately controlling the internal moisture of the polymerized beads, the pre-foaming agent is pre-foamed by injecting a blowing agent at a low temperature to maintain the internal cells of the pre-foam granules uniformly. Preservation with a cell size of 150-350 microns to keep the size fine, improve the shrinkage of the pre-foamed granules and improve the secondary foaming force of the pre-expanded particles to prevent the deterioration of the fusion of the molded article with the passage of the seal The foam lip was able to be improved.

That is, in the present invention, 30-70 parts by weight of partially cross-linked polyolefin resin is suspended and dispersed in an aqueous medium, 70-30 parts by weight of styrene monomer is added thereto, and then the reaction is completed. The present invention relates to a modified styrene-based foam bead that press-foams and foams, and maintains the internal moisture of the polymerization beads at 0.1-0.4% by weight prior to impregnating the foaming agent, and then press-pre-foams the foaming agent at low temperature.

Hereinafter, the present invention will be described in detail.

As the polyolefin resin component used in the present invention, homopolymers such as linear low density polyethylene, low density polyethylene, ultra low density polyethylene, high density polyethylene and polypropylene, and copolymers such as ethylene vinyl acetate can be used, and preferably low density polyethylene is suitable. . Particularly in the case of low density polyethylene, crosslinking is commonly used to improve processability during foaming. This method is described in detail in US Pat. No. 3,886,100.

In the present invention, a crosslinked polyethylene having a gel content of 0-80% is used, and preferably a gel content of 3-65% is suitable. The crosslinking agent of polyethylene applicable here is dicumyl peroxide 1.1-bis (t-butylperoxy) -3.3, 5-trimethyl cyclohexane, t-butyl cumyl peroxide, 2.5- dimethyl-2.5 (t-butyl peroxy ) Hexane and the like.

The styrene monomer used in the present invention is most preferably styrene monomer, and monomers that are easily copolymerized such as alpha-methylstyrene, acrylonitrile, methyl methacrylate, butyl acrylate, vinyl chloride, and vinyl acetate are used as comonoma. do.

On the other hand, as the reaction initiator that can be used for the polymerization of styrene, benzoyl peroxide, lauryl peroxide, t-butyl per pivalate, t-butyl per benzoate, dicumyl peroxide, etc. may be used alone and more preferably. Is the use of two or more of these initiators in combination.

Butadiene, isoprene, divinylbenzene, butane diol polyacrylate, hexane diol diacrylate, etc. are mentioned as a crosslinkable monomer which has an olefinic double bond used as a crosslinking agent of styrene, The use of divinyl benzene is preferable.

In the present invention, bromine compounds added to styrene monomas to obtain prefoams having uniformly fine cells include tetrabromer bisphenol A-bis (2,3-dibromopropyl ether) and tetra soluble in styrene monomas. Bromo bisphenol A-bis (arylether), octa bromo diphenyl oxide, hexa bromo cyclo dodecane, 2, 4,6-tribromo phenol, pentabromo diphenyl oxide, 2,3-dibromo One or two or more of conventional brominated flame retardants such as propanol, tetra bromo fortylate ester and tetra bromo pralade diol may be mixed and used, and 0.055-0.1 parts by weight per 100 parts by weight of styrene monomer is preferably used.

In the present invention, after properly controlling the internal moisture of the polymerized beads in order to obtain a pre-foamed granule having a fine and uniform cell, the blowing agent was indented, pre-exposure experiment was carried out. When the internal moisture content in the polymerization beads is more than 0.4% by weight, the inner cell of the foam becomes non-uniform even when using a bronze-based compound, and when the internal moisture is 1.5% by weight or more, the cell becomes large and the prefoam tends to shrink. However, when the foaming agent is fed and pre-foamed by adjusting the water content in the polymerization beads to 0.4 wt% or less, a pre-foam having a fine and uniform cell having excellent fusion and molding processability can be obtained even after 4 weeks of pre-expanding.

The blowing agent present in the foamable polymer is 5 to 30% by weight of C3 to C6 hydrocarbon, such as propane, butane, isobutane, n-pentane, isopentane, neopentane or hexane, based on the polymer after the impregnation polymerization, and also dichlorodiol. Freon-based blowing agents that are fluoro compounds such as chloromethane are applicable.

Dispersants for aqueous suspensions used in the present invention include inorganic dispersants such as tricalcium phosphate or pyromagnesium phosphate, aluminum oxide, aluminum hydroxide and anionic surfactants such as alkyl benzene sulfonate salts, as disclosed in US Pat. No. 2,673,194. May be used alone or in combination.

In the present invention, when the crosslinked polyethylene particles suspended in the aqueous medium are impregnated with styrene-based monomas, the styrene monomers in which the initiator, the crosslinkable monomer and the bromine-based compound are dissolved are continuously added at one time or several hours. Was maintained at 70-100 ℃ to uniformly impregnated styrene monoma and then the temperature was raised step by step between 85-150 ℃ to complete the reaction. At this time, the stirring speed was maintained at 200-500 rpm, and the inside of the pressure resistant reaction was maintained in a nitrogen atmosphere.

The polymerized beads were dehydrated and dried to adjust the internal moisture in the polymerized beads to 0.4% by weight or less, followed by a blowing agent impregnation process. After adjusting the internal temperature of the reactor to 50-90 ° C, pressurize the foaming gas for 3 hours or more, cool it at room temperature, dehydrate it, and pre-bubble it with water vapor of 0.1-0.6KG so that the cell size is uniform and fine. A foamed granule having excellent chemical resistance was obtained.

On the other hand, the crosslinking degree of the initially partially crosslinked polyethylene was determined by measuring the gel content, which was calculated by the weight change after extraction for 24 hours in xylene boiling by the method of ASTM D2765-68. Bead internal moisture content was measured using a Karl Fischer moisture content meter. The fusion rate of the molded body was expressed as the ratio of the number of broken beads to the total number of beads shown at the fracture surface after breaking with a knife to a depth of about 5 mm from the surface of the molded body and breaking by applying a force in the crack direction. .

Next, the present invention will be described in detail by Examples and Comparative Examples, and the properties of the compositions prepared in Examples and Comparative Examples were measured, and the results are shown in Table 1.

[Production Example 1]

2000 g of low-density polyethylene resin (MI = 3.0), 4000 g of pure water, and 10 g of tricalcium phosphate as a dispersant were added to a 10 L pressurized reactor, and 6 g of dicumyl peroxide was added while stirring, followed by stirring at 400 rpm. At this time, the temperature was maintained for 2 hours to uniformly disperse the dicumyl peroxide into the PE beads, and then heated to 140 ℃ to obtain a partially cross-linked polyethylene beads after the reaction for 4 hours. Its gel content was 15-25% as measured after extraction with boiling xylene.

Example 1

In a 10 L pressurized reactor, 800 g of partially crosslinked polyethylene resin (MI = 3.0, gel content = 15-25) obtained in Preparation Example 1, 3200 g of pure water, 16 g of tricalcium phosphate as a dispersant, and 6 g of sodium dodecyl benzene sulfonate were added. The mixture was kept at 85 ° C. while stirring at 400 rpm. Subsequently, after impregnating 1200 g of styrene monomer mixed with 8 g of benzoyl peroxide, 0.6 g of t-butyl perbenzoate, 0.8 g of divinylbenzene, and 0.6 g of bromine compound, hexa bromocyclo dodecane, the temperature was 130 ° C. The reaction mixture was heated for 5 hours, cooled, and dehydrated to obtain beads having a very fine structure of polystyrene dispersion.

In a 10 L pressurized reactor, 2000 g of polymerized beads, 3200 g of pure water, and 6 g of sodium dodecyl benzene sulfonide, each of which had adjusted the internal moisture of the polymerized beads to 0.3% by weight, were stirred at 400 rpm and r-pentane was used as a blowing agent. After pre-inflated for 5 hours at ℃ 0.5KG-0.6KG using a steam of pre-foaming was obtained a pre-foamed granule 52 times the foam size of about 200-300 microns. After 4 weeks, the molded product with excellent fusion was obtained as a result of molding with 1.0KG steam in EPS type molding machine.

Example 2

Under the same conditions as in Example 1, but after adjusting the internal moisture of the polymerized beads to 0.1% by weight 1% and impregnated and pre-expanded foaming agent under the same conditions as in Example 1 as a fine and uniform cell size 150-250 microns Prefoamed granules without shrinkage of 55 times the foaming ratio were obtained. As a result of molding after 4 weeks, a molded article having excellent fusion was obtained.

Example 3

Under the same conditions as in Example 1, but using the bromine compound octabromo diphenyl oxide 0.6g to adjust the internal moisture of the polymerized beads to 0.4% by weight, impregnated with foaming agent and pre-foaming under the same conditions as in Example 1 As a result, a prefoamed granule having a foaming ratio of 50 times that of a uniform cell size of 200-350 microns was obtained.

This was molded after 4 weeks under the same conditions as in Example 1 to obtain a molded article having excellent fusion.

Comparative Example 1

It was carried out under the same conditions as in Example 1, but the internal moisture of the polymerized beads was maintained at 1.5% by weight or more, impregnated and pre-foamed with the blowing agent under the same conditions as in Example 1, the cell size was uneven to 400-1200 microns and pre-expanded Lip shrinkage was observed, and the expansion ratio was about 25 times.

This was molded after 4 weeks under the same conditions as in Example 1, but the fusion property was good but the shrinkage of the molded product was severe.

Comparative Example 2

Under the same conditions as in Example 1, but the internal moisture of the polymerized beads was maintained at 0.8% by weight, impregnated and pre-foamed with a blowing agent under the same conditions as in Example 1, the cell size was about 300-700 microns, surface shrinkage phenomenon Did not appear, and the presentation magnification was about 38 times.

As a result of molding after 4 weeks under the same conditions as in Example 1, the adhesion was good.

Claims (4)

In preparing a modified polystyrene bead foam obtained by impregnating polyolefin resin particles with polyvinyl aromatic monomar and then foaming, 0.055-0.1 parts by weight of bromine compound which can be dissolved in the styrene monomer is added to 100 parts by weight of styrene monoma, and the polymerization is performed. Method of producing a modified polystyrene bead foam characterized in that the internal moisture of the finished bead is maintained at 0.1-0.4 weight 5 and pre-foamed after impregnating the blowing agent at 50-90 ℃. The method according to claim 1, wherein after controlling the internal moisture of the polymerized beads obtained by impregnating the foaming agent by impregnating the foaming agent to maintain a cell size of 150-350 microns. The method of claim 1, wherein the polyolefin resin is polyethylene, an ethylene-vinyl acetate copolymer, and has a crosslinking degree of 5% by weight to 80% by weight based on the gel content. The bromine-based compound which can be dissolved in the styrene monomer is tetrabromo bisphenol A-bis (2,3-dibromo propyl ether), tetra bromo bisphenol A-bis (aryl ether), octa. Bromo diphenyl oxide, hexa bromo cyclododecane, 2, 4, 6-tribromo phenol, pentabromo diphenyl oxide, 2,3-dibromo-propanol, tetrabromo phthalate ester, tetra bromo A method for producing a modified polystyrene bead foam, characterized by using one or two or more of phthalate diols.