JPH10287763A - Heat-resistant expandable resin particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide heat-resistant expandable resin particles which can attain a high expansion ratio of at least 30 by when pre-expanded at a conventional pre-expansion temperature pre-expanded particles which can give a highly heat- resistant foamed molding without aging within a shortened molding cycle. SOLUTION: These particles are made from a composition comprising a base resin comprising 50-90 pts.wt. styrene mixed resin prepared by mixing a high-molecular-weight styrene resin having a weight-average molecular weight of 150,000-500,000 with desirably 1-30 wt.% low-molecular-weight styrene resin having a weight-average molecular weight of 500-100,000 and 50-10 pts.wt. polyphenylene ether resin, 1-15 pts.wt., per 100 pts.wt. base resin, volatile blowing agent and 0.1-10 pts.wt. cycloparaffin (desirably cyclohexane or cyclopentane).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to heat-resistant foamed resin particles, that is, foamed resin particles having high heat resistance, which are made of a blend of a polyphenylene ether resin and a styrene resin. More specifically, the present invention can obtain a sufficiently high expansion ratio in the process of pre-expansion, and can produce a foam molded product having sufficiently high heat resistance in a short molding cycle from the pre-expanded particles. It relates to heat-resistant foamed resin particles where possible.

[0002]

2. Description of the Related Art In general, expandable styrene resin particles are
The resin particles are obtained by impregnating a granular styrene-based polymer with a foaming agent (butane, pentane, or the like), and then are processed into a foam molded article (styrene foam product) through a foaming treatment including preliminary foaming. The foamed product finally produced is used for a wide range of uses such as packing materials for home appliances, building boards and heat insulating blocks, heat insulating containers such as fish boxes, and instant food cups. In recent years, styrene-based foam molded articles have also been used as buried blocks in civil engineering works such as roads. As described above, foamed molded products have a wide variety of uses.However, foamed molded products are used in applications such as heat insulation or heat insulating materials that cover steam pipes or hot water pipes, and heat insulation materials that are installed in attics. It is required to have high heat resistance of 80 to 120 ° C. Also, components for these applications must be able to withstand long-term use even under such high temperature conditions.

[0003] However, conventional styrofoam products may significantly shrink in size during long-term use in the above-mentioned applications, and may not be able to maintain the heat insulating and heat retaining effects as they were at the beginning. It has been required to improve heat resistance. Therefore, several attempts have been made to improve the heat resistance of foam molded articles. Among them, as one promising attempt, JP-B-56-43054 and JP-B-56-43054 have been proposed.
As described in Japanese Patent No. 43055, etc., a blend or copolymer of a polyphenylene ether resin and a styrene resin is used as the base resin for the foamed molded article instead of the styrene resin, and the blend is used. There has been proposed a method for producing a foamed product having high heat resistance using heat-resistant foamed resin particles made of a material or the like as a raw material.

[0004]

The above-mentioned method certainly improves the heat resistance of the foamed molded product as compared with the conventional general styrofoam products. The heat resistance increases as the blending ratio of the polyphenylene ether-based resin increases.
However, this method still has points to be improved, for example, as follows. The pre-expansion of the expandable styrene resin particles is usually performed using steam at about 100 ° C., but in the above-mentioned heat resistant expanded resin particles based on a blend of a polyphenylene ether resin and a styrene resin, However, even if prefoaming is performed under the same conditions as in the case of expandable styrene resin particles, a high expansion ratio of 30 times or more cannot be obtained, and satisfactory prefoamed particles cannot be produced. Further, the heat-resistant foamed resin particles have a tendency that, due to the blending of the polyphenylene ether-based resin, the frequency of the foaming agent escaping over time becomes more intense as compared with conventional general foamable styrene-based resin particles. If the foaming agent impregnated in the heat-resistant foamed resin particles significantly escapes outside the particles, it becomes difficult to achieve a high expansion ratio for the pre-expanded particles obtained therefrom. Therefore, in the storage of the heat-resistant foamed resin particles, particularly in the aging treatment, it is necessary to pay more careful attention to the temperature control. Especially in the hot season (summer season), it will be necessary to store the heat-resistant foamed resin particles in a low-temperature warehouse or the like, but low-temperature storage requires extra refrigeration equipment and operating costs Becomes

[0005] Therefore, for the purpose of preventing a decrease in the expansion ratio of the pre-expanded particles and the like, several proposals and trials as described below have hitherto been made. As disclosed in Japanese Patent Publication No. 8-19253, heat-resistant foamed resin particles are heated to a temperature higher than the glass transition temperature of the base resin (up to 210 ° C.) using pressurized steam. In which the pre-expanded heat-resistant foamed resin particles are pre-expanded to achieve a high expansion ratio for the obtained pre-expanded particles. As a more specific example, Examples 1 to 3 of the above publication show examples in which pre-foaming of PPE / PS pellets is performed at a temperature of 132 ° C. or 121 ° C. in a steam autoclave. As disclosed in JP-A-2-18428, etc., the base resin of the heat-resistant foamed resin particles is impregnated with a foaming agent such as tetrahydrofuran, diisopropyl ether, methyl ethyl ketone or n-butyl acetate as a plasticizing foaming agent, A method for increasing the plasticity of the base resin, thereby making it easier to expand the heat-resistant expanded resin particles in the pre-expansion process. Another method similar to this is disclosed in JP-A-8-100078.
This is also disclosed in the official gazette. In another method, an organic solvent having a KB value of 20 to 200 and a boiling point of 95 to 400 ° C. is impregnated into a base resin of heat-resistant foamed resin particles together with a foaming agent as a plasticizer.

[0006] The above-mentioned heat-resistant foamed resin particles have another problem in terms of the properties of the final product. That is, when the pre-expanded particles obtained from the heat-resistant foamed resin particles are further heated and foamed to form a foamed molded article, when a large amount of a foaming agent and an organic solvent remain in the foamed molded article, particularly the foamed molded article There is a problem that the dimensional change at a high temperature becomes large and the heat resistance of the foam molded product is significantly reduced. Therefore, the following proposals have conventionally been made for the purpose of improving the heat resistance of a foam molded article. As disclosed in Japanese Patent Publication No. 56-43055, etc., the foamed molded product is aged under special conditions, for example, at a temperature 5 to 40 ° C. lower than the Vicat softening point of the base resin, and The content of the foaming agent is 3% by weight or less.

However, in the above method, it is necessary to introduce a special pressurized prefoaming equipment which is completely different from a foaming machine commonly used for prefoaming expandable styrenic resin particles. It is said. Therefore, this method is not immediately applicable because it causes an increase in production cost. In addition, the method is that, since the boiling point of the organic solvent impregnated in the base resin is generally higher than that of a commonly used foaming agent, even after the final foam molding, the organic solvent is likely to remain in the foam molded article. In addition, there is a disadvantage that the heat resistance of the foam molded article is significantly deteriorated. In addition, the method requires a new equipment such as an aging room for heating and aging the foamed molded product, and thus causes an increase in production cost and a decrease in productivity. It cannot be adopted. As described above, none of the conventional proposals provides a completely satisfactory solution.

The present invention has been made on the basis of such a background, and an object of the present invention is to achieve a sufficiently high foaming ratio of at least 30 times, particularly at least 50 times, for prefoaming. In particular, a desired expansion ratio can be obtained by pre-expansion in the range of the pre-expansion temperature commonly used for conventional expandable styrene-based resin particles. It is another object of the present invention to provide heat-resistant foamed resin particles that can be significantly shortened and that can impart sufficiently high heat resistance to a foamed molded product without special aging treatment.
Other objects, effects and advantages of the present invention will be derived from the following description and the appended claims.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies and found that, first, the molecular weight (generally weight-average molecular weight of 150,000 to 500,000) of a styrene resin commonly used in conventional heat-resistant foamed resin particles. ), Ie a weight average molecular weight of from 500 to 100,0
A styrene resin having a lower molecular weight of 00 functions as a plasticizer, and when a heat-resistant expanded resin particle is finished using a styrene-based mixed resin blended with the styrene resin, a sufficiently high expansion ratio is obtained in the pre-expanded particles obtained therefrom. Have been found, and even in the final foamed molded article, no effect of impairing its heat resistance is shown. Further, the present inventor has suggested that cycloparaffin alone exerts a plasticizing function, and by impregnating it with heat-resistant foamed resin particles, contributes to an improvement in the expansion ratio of the obtained pre-expanded particles, and by itself. In the process of foam molding using the pre-expanded particles, it has been found that they escape very quickly and therefore hardly remain in the foam molded article. Furthermore, the present inventor can achieve a sufficiently high expansion ratio in the process of pre-expansion by combining the blend of the lower molecular weight styrene resin and the impregnation of the cycloparaffin with respect to the heat-resistant foamed resin particles. In the process of foam molding, the foaming agent rapidly escapes, so the molding cycle is greatly shortened, and since there is no residual foaming agent etc., the heat resistance of the foam molded product is also sufficiently high. We have found and completed the present invention here.

Accordingly, the present invention clearly provides a blend of a high molecular weight styrene resin having a weight average molecular weight of 150,000 to 500,000 and a lower molecular weight styrene resin having a weight average molecular weight of 500 to 100,000. 50 to 90 parts by weight of the obtained styrene-based mixed resin and 50 to 10 parts of the polyphenylene ether-based resin.
1 to 15 parts by weight of a volatile blowing agent and 0.1 to 10 parts by weight of cycloparaffin, more preferably cyclohexane or cyclopentane, based on 100 parts by weight of the base resin. The present invention relates to a heat-resistant foamed resin particle characterized by containing. In a more preferred aspect of the present invention, the styrene-based mixed resin is obtained by blending 1 to 30% by weight of a lower-molecular-weight styrene resin based on a high-molecular-weight styrene-based resin. The present invention relates to heat-resistant foamed resin particles.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The heat-resistant foamed resin particles of the present invention are:
Resin particles containing a volatile foaming agent and cycloparaffin in the base resin, the main features of which are the composition of the base resin and the blending of cycloparaffin. The base resin is a resin blend of a styrene-based mixed resin and a polyphenylene ether-based resin, and further contains various additives and auxiliaries as necessary. The styrene-based mixed resin may be added to a high-molecular-weight styrene-based resin having a weight-average molecular weight of 150,000 to 500,000, more preferably 200,000 to 300,000, and a weight-average molecular weight of 500 to 100,000. And more preferably a blend of a lower molecular weight styrene resin having a weight average molecular weight of 5,000 to 100,000.

The high molecular weight styrenic resin referred to in the present invention is not limited to a homopolymer of a styrenic monomer, but may be a copolymer with another monomer (a styrenic monomer content of 50% or more). Made using proportions). The high-molecular-weight styrene resin generally corresponds to a styrene resin conventionally used as a part of the base resin of the heat-resistant foamed resin particles. Styrene monomers include α-methylstyrene, ethylstyrene, p
-Substituted styrenes such as chlorostyrene. Also,
Examples of the monomer on the other side of the copolymer include (meth) acrylates such as methyl methacrylate, methyl acrylate, butyl methacrylate, and butyl acrylate, and vinyl monomers such as acrylonitrile, vinyl toluene, and vinyl carbazole. . These may be used alone or in combination of two or more. Accordingly, the high-molecular-weight styrene resin used in the present invention includes, in addition to polystyrene, poly-substituted styrene such as poly-α-methylstyrene and poly-p-chlorostyrene, and styrene and substituted styrene (for example, α-methylstyrene). And a copolymer of styrene and a vinyl-based monomer (eg, acrylonitrile). All of them have a weight average molecular weight of 150,000 to 500,
000. More preferred styrene resins include polystyrene, polystyrene-butadiene copolymer, polystyrene-maleic anhydride copolymer, polystyrene-acrylonitrile copolymer, and styrene graft copolymer. Further, a more preferable styrene resin having a high molecular weight is a resin having a weight average molecular weight of 200,000 to 300,000 from the viewpoint that the final foamed molded article can maintain more desirable physical properties.

The low molecular weight styrene resin referred to in the present invention is a styrene having a lower molecular weight than a styrene resin commonly used in conventional heat-resistant foamed resin particles, that is, a styrene having a weight average molecular weight of 500 to 100,000. Refers to a homopolymer of a monomer (polystyrene). The lower molecular weight styrene resin functions as a plasticizer, i.e.,
It has the property of accelerating the plasticization of the base resin of the heat-resistant foamed resin particles, and thus contributing to the improvement of the expansion ratio in the pre-expansion process. In addition, the styrene resin having a lower molecular weight helps the foaming agent and the like escape in the process of foam molding by plasticizing the base resin, and also contributes to the improvement of the heat resistance of the foam molded article. Further, if the molecular weight of the styrene resin having a lower molecular weight is extremely low, the physical properties of the final foamed molded article will be significantly deteriorated. Therefore, a resin having a relatively high molecular weight is more preferable.
From this viewpoint, as a lower molecular weight styrene resin,
Polystyrene having a weight average molecular weight of 5,000 to 100,000 is more preferred.

The above-mentioned high molecular weight styrene resin is generally produced by suspension polymerization of a styrene monomer or the like in an aqueous medium. Also, lower molecular weight styrene resin,
It may be produced by suspension polymerization of a styrene monomer or the like in an aqueous medium. These suspension polymerizations include a radical initiator,
Proceeding in an aqueous suspension system comprising a dispersing agent and a dispersing aid. Examples of the radical initiator include polymerization initiators used in general radical polymerization, for example, organic peroxides such as benzoyl peroxide, butyl perbenzoate, and t-butylperoxybenzoate, or azobisisobutyronitrile. And the like. Examples of the dispersant include poorly water-soluble inorganic salts such as tricalcium phosphate, magnesium phosphate, and hydroxyapatite, and organic polymers such as polyvinyl alcohol, polyvinylpyrrolidone, and methylcellulose. further,
Examples of the dispersing aid used in combination with the dispersing agent include anionic surfactants such as dodecyl phenyl oxide disulfonate, sodium dodecyl benzene sulfonate, sodium α-olefin sulfonate, polyoxyethylene alkyl ether, and polyoxyethylene octyl phenol. Nonionic surfactants such as ethers are included.

In the present invention, a more preferred styrene-based mixed resin is one based on a high-molecular-weight styrene-based resin.
-30% by weight of a lower molecular weight styrene resin. When a low-molecular-weight styrene resin is blended in an amount of less than 1% by weight based on a high-molecular-weight styrene-based resin, its plasticizing action is weak, and the desired effect of improving the expansion ratio in the pre-foaming process is obtained. Cannot be exhibited, and a synergistic effect with cycloparaffin cannot be sufficiently obtained. On the other hand, when the lower molecular weight styrene resin is blended in an amount exceeding 30% by weight, even if the effect of improving the expansion ratio and the synergistic effect with cycloparaffin can be sufficiently obtained, the base resin of the heat-resistant expanded resin particles can be obtained. Becomes extremely brittle, and it becomes extremely difficult to achieve the required physical properties (for example, compressive strength) in the final foam molded article, and it becomes impossible to produce a foam molded article of practical quality. Therefore, in practical use, the styrene-based mixed resin must be a blend of 100 parts by weight of a high-molecular-weight styrene-based resin and 1 to 30 parts by weight of a lower-molecular-weight styrene-based resin.

The polyphenylene ether resin referred to in the present invention is represented by the following formula I:

Embedded image (Wherein R ₁ and R ₂ independently represent an alkyl group having 1 to 4 carbon atoms or a halogen atom,
Represents the degree of polymerization. ) Represents a polyphenylene ether-based resin represented by the following formula:
6-dimethylphenylene-1,4-ether), poly (2,6-diethylphenylene-1,4-ether),
Poly (2,6-dichlorophenylene-1,4-ether), poly (2-methyl-6-ethylphenylene-1,
4-ether), poly (2-chloro-6-methylphenylene-1,4-ether), poly (2-methyl-6-isopropylphenylene-1,4-ether), poly (2,6-di-n) -Propylphenylene-1,4-ether), poly (2-bromo-6-methylphenylene)
1,4-ether), poly (2-chloro-6-bromophenylene-1,4-ether), poly (2-chloro-6)
-Ethylphenylene-1,4-ether) and the like. The polymerization degree n may be 10 to 5000, and is 50
If it exceeds 00, it is difficult to obtain a uniform heat-resistant foam, and 1
If it is less than 0, it is difficult to obtain a foam having the desired heat resistance.

The base resin is a resin blend of the above-mentioned styrene-based mixed resin and polyphenylene ether-based resin, and further, if necessary, various additives (colorant, flame retardant, heat stabilizer, nucleating agent, etc.). Agents, lubricants, etc.) in an appropriate amount. Regarding the mixing ratio of the styrene-based mixed resin and the polyphenylene ether-based resin, in the present invention, the ratio of 50 to 90 parts by weight of the styrene-based mixed resin and 50 to 10 parts by weight of the polyphenylene ether-based resin, more preferably 70% by weight The composition ratio is required to be 90 parts by weight and 30 to 10 parts by weight of the polyphenylene ether resin. When the styrene-based mixed resin exceeds 90 parts by weight (that is, when the polyphenylene ether-based resin is less than 10 parts by weight), the effect of blending the polyphenylene ether-based resin, that is, the effect of improving heat resistance is substantially small, The desired heat resistance (the effect of increasing the melting point) of the base resin of the heat-resistant foamed resin particles cannot be sufficiently obtained. On the other hand, if the amount of the styrene-based mixed resin is less than 50 parts by weight (that is, if the amount of the polyphenylene ether-based resin exceeds 50 parts by weight), the base resin has an effect of confining the volatile foaming agent in the heat-resistant foamed resin particles. It becomes very weak, and the volatile foaming agent escapes rapidly and intensely from the resin particles, making it difficult to achieve the desired foaming ratio in the process of preliminary foaming.

Cycloparaffin is generally C _n
A cyclic saturated hydrocarbon represented by H _2n (where n = 3 to 8) is used. In the present invention, a compound of the cyclic saturated hydrocarbon or a mixture thereof is used. Cyclopentane C ₅ H ₁₀ and cyclohexane C ₆ H ₁₂ where corresponding to the cycloparaffins are present in petroleum.
Other cycloparaffins can be produced by organic synthesis. Cycloparaffin alone exhibits the function of plasticizing the base resin of the heat-resistant foamed resin particles.
Therefore, by impregnating it with heat-resistant foamed resin particles, the obtained pre-expanded particles have an effect of improving the expansion ratio. Moreover, cycloparaffins have a boiling point close to that of volatile blowing agents conventionally used. This is a feature different from the organic solvents proposed in the patent publications and the like. Moreover, the compatibility of the heat-resistant foamed resin particles with the base resin is not so good. Therefore, the cycloparaffin impregnated in the heat-resistant foamed resin particles can quickly and externally escape together with the foaming agent in the process of foaming molding using the pre-foamed particles. Therefore, there is no need to secure a long cooling time after foam molding. That is, the molding cycle in the foam molding process is greatly reduced. In addition, cycloparaffin hardly remains inside the foam molded article after foam molding, so even if the produced foam molded article is placed under high temperature, its dimensional change is small and sufficiently high heat resistance is obtained. It can be applied to foam molded articles.

Cyclopentane C ₅ H ₁₀ has a boiling point of about 49 ° C., close to the boiling point of the volatile blowing agent n-pentane (about 36 ° C.), and cyclohexane C ₆ H ₁₂ has a boiling point of about 81 ° C. The boiling point of the volatile blowing agent n-hexane (about 6
9 ° C). Moreover, these cycloparaffins are practically available. Therefore, in the present invention, the use of cyclopentane or cyclohexane is more preferred. In the present invention, cycloparaffin is blended in an amount of 0.1 to 10 parts by weight, more preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the base resin. Based on 100 parts by weight of the base resin, when cycloparaffin is blended in an amount of less than 0.1 part by weight, the plasticizing action is weak, and the expected effect of improving the expansion ratio in the process of pre-foaming is reduced. In addition, the synergistic effect with a lower molecular weight styrene resin cannot be sufficiently obtained. On the other hand, when cycloparaffin is added in an amount exceeding 10 parts by weight, even if it has sufficiently contributed to the improvement of the expansion ratio, etc., a large amount of cycloparaffin remains in the foam molded article after foam molding, The heat resistance of the finally obtained foam molded article is very low. Therefore, in the present invention, cycloparaffin needs to be blended in an amount of 0.1 to 10% by weight of the base resin.

The heat-resistant foamed resin particles of the present invention may contain 1 to 15 parts by weight based on 100 parts by weight of the base resin.
More preferably, 5 to 10 parts by weight of a volatile blowing agent is contained together with the above-mentioned cycloparaffin. As the volatile foaming agent, for example, an aliphatic hydrocarbon such as propane, butane, n-pentane, isopentane, or hexane, or a halogenated hydrocarbon such as methyl chloride or Freon is used. These volatile foaming agents may be used alone or in combination of two or more. However,
As the volatile foaming agent, butane or pentane is more preferred as the volatile foaming agent, and pentane is most preferred, from the viewpoint that the volatile foaming agent loses less heat during the drying treatment of the heat-resistant foamed resin particles. In general, the amount of the volatile foaming agent is an important factor for determining the expansion ratio in the process of pre-expansion. In the case of the present invention, the expansion ratio is different from the amount of the foaming agent. , Depending on the blending ratio of the lower molecular weight styrene resin and the content of cycloparaffin, which are determined in relation to each other.

The heat-resistant foamed resin particles of the present invention may further contain various additives and auxiliaries, such as a flame retardant, a colorant, a heat stabilizer, and the like, in addition to the cycloparaffin and the volatile foaming agent. An appropriate amount of a nucleating agent, a lubricant and the like can be blended with the base resin. For example, as the flame retardant, hexabromocyclododecane, tetrabromobisphenol A, pentabromomonochlorocyclohexane and the like are suitable, and similarly, other additives and the like are appropriately selected from known ones and used. Also, a plasticizer can be added in an amount that does not impair heat resistance. Examples of the plasticizer include DOP, DOA, DBP, coconut oil, palm oil and the like.

The present invention is not particularly limited with respect to the whole process for producing the heat-resistant foamed resin particles. The heat-resistant foamed resin particles of the present invention are prepared by first introducing predetermined amounts of a high-molecular-weight styrene resin, a lower-molecular-weight styrene resin, and a polyphenylene ether-based resin into, for example, an extruder, and melt-kneading them. Molding resin particles (particles, pellets, spheres, etc.)
Next, by impregnating the particles of the base resin with a predetermined amount of the volatile blowing agent and cycloparaffin, more specifically, the particles of the base resin are dispersed in an aqueous suspension system in an autoclave. Subsequently, a volatile foaming agent is prepared by pressing it into the suspension system and heating it appropriately. Further, as a dispersant used in the aqueous suspension system at the time of impregnation of the volatile foaming agent, for example, tricalcium phosphate, magnesium phosphate, poorly water-soluble inorganic salts such as hydroxyapatite, or polyvinyl alcohol, polyvinyl Pyrrolidone,
Organic polymers such as methyl cellulose are exemplified. Also,
Examples of the dispersing aid used in combination with the dispersing agent include anionic surfactants such as dodecyl phenyl oxide disulfonate, sodium dodecyl benzene sulfonate, sodium α-olefin sulfonate, polyoxyethylene alkyl ether, and polyoxyethylene octyl phenol. Nonionic surfactants such as ethers are included.

Thus, the heat-resistant foamed resin particles according to the present invention are pre-foamed to an arbitrary apparent specific gravity if necessary, and then the pre-foamed particles are filled into a mold such as a mold according to a conventional method. , And by heating and foaming with steam,
The pre-expanded particles are fused together to form the desired shape (dimensions)
Can be manufactured.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below, including the best mode.

-Production of heat-resistant foamed resin particles- Table 1 shows a high-molecular-weight polystyrene resin, a lower-molecular-weight polystyrene resin, and a polyphenylene ether-based resin having the weight-average molecular weights shown in Table 1 below. At the desired composition ratio together with the other additives in an extruder, and extrude them in the form of a strand, following melting by heating and kneading with a screw, and then extruding the strand with a rotary pelletizer. And pelletized.
1500 g of the obtained base resin pellets were placed in a 5 L autoclave, and further, 2500 g of ion-exchanged water,
15 g of tricalcium phosphate and 0.15 g of sodium dodecylbenzenesulfonate are introduced into the autoclave as a dispersant, and 150 g of the volatile blowing agent n-pentane (based on the base resin) is then added while stirring the mixture. 1
0% by weight), the cycloparaffins or other organic solvents shown in Table 2 were injected in the amounts shown in the same table. The aqueous suspension in the autoclave was then
The temperature was raised to ° C., and the state was maintained for 6 hours, thereby impregnating the pellets of the base resin with the volatile foaming agent and cyclohexane and / or cyclopentane. After this treatment, the aqueous suspension was cooled to room temperature, and the resulting heat-resistant foamed resin particles were taken out of the autoclave. afterwards,
The obtained heat-resistant foamed resin particles, after washing, are dehydrated by centrifugation using a centrifuge, and then, using a dryer, the dehydrated heat-resistant foamed resin particles are dried with hot air, and then dried. After storage at 5 ° C. for 5 days for aging treatment, heat-resistant foamed resin particles having a particle size of 1.0 to 1.2 mm were obtained.

[0026] Note) MW in Table 1 indicates weight average molecular weight.

[0027] Note) The percentage figures in parentheses in Table 2 represent the weight percentage of cyclopentane, cyclohexane or toluene with respect to the base resin.

-Measurement of expansion ratio of pre-expanded resin particles- The heat-resistant expanded resin particles of each of the above examples were foamed with steam at a temperature of 101 ° C for 4 minutes, and the bulk ratio of the obtained pre-expanded particles was measured. . This bulk ratio is shown in Table 3 below as expansion ratio ¹⁾ .

-Process of foaming molding and measurement of cooling cycle- Preliminarily foamed particles having a bulk ratio of 50 times were prepared from the heat-resistant foamed resin particles of each of the above examples, and were then allowed to stand at room temperature for 12 hours. After that, the mixture was put into a molding die of an automatic molding machine and foamed under the condition of heating at a pressure (gauge pressure) of 1.3 kg / cm ^{2 for} 30 seconds.
A foam molded article having a size of 00 mm was produced. At this time, following cooling with water for 5 seconds, the foaming mold was allowed to cool. The surface pressure of the mold at the time of demolding was set to 0.1 kg / cm ² , and for each of the above examples, the time until the pressure in the foaming mold decreased to this surface pressure, ie, in Table 3, Cooling cycle ²⁾
Was measured respectively.

-Measurement of the amount of the foaming agent remaining in the foam-molded article- After the above-mentioned foam molding, the foam-molded article is allowed to stand at room temperature for 24 hours. Gas chromatography analysis was performed to determine the total amount of the blowing agent, cycloparaffin, and organic solvent remaining in the foam molded article. The total amount is the amount of the blowing agent in Table 3 below ³⁾
As shown.

—Measurement of Heat Resistance of Foam Molded Product— A sample having a size of 100 mm × 100 mm × 25 mm was prepared from the above foam molded product, and this was two days after foam molding.
Placed in a 95 ° C. oven and held for one week. After that, remove the sample from the oven,
The length, width, and thickness were measured, and the average value of the dimensional change in those directions, that is, the dimensional change rate ⁴⁾ in Table 3 was obtained. It is recognized that the smaller the dimensional change ⁴⁾ , the higher the heat resistance of the foam molded article.

The results of the above measurements are summarized in Table 3 below.
I will show you. ^a) Pre-expanded particles having a bulk ratio of 50 times could not be obtained, and thus, foam molding was not performed. Therefore, there is no measurement data on the properties and quality of the foam molded article.

From Table 3, it can be seen that, in the case of the heat-resistant foamed resin particles of Examples 1 to 4, any foaming ratio of 50 times or more can be obtained in the general prefoaming process using the same. In addition, in the subsequent foam molding, the cooling cycle at the time of molding is greatly shortened, productivity can be improved, and further, the dimensional change of the foam molded product is very small, It can be seen that the heat resistance is significantly improved. On the other hand, in the case of the heat-resistant foamed resin particles of Comparative Examples 1 and 2, a desired improvement effect on the expansion ratio cannot be obtained in the pre-expansion process because a styrene resin having a lower molecular weight is not blended. Moreover, the cooling cycle in foam molding is very long, and the productivity of foam molding is poor.
It can be seen that the dimensional change of the foam molded article is large and its heat resistance is also very low. In addition, in the case of the heat-resistant foamed resin particles of Comparative Example 3, although a high expansion ratio can be obtained in the pre-foaming process due to the blending of toluene, the cooling cycle during foam molding is extremely long, and It can be seen that the productivity is extremely poor and, furthermore, since the amount of the foaming agent remaining in the foamed molded article is large, the dimensional change of the foamed molded article is very large and its heat resistance is also extremely low.

-Production of other heat-resistant foamed resin particles and measurement of mechanical strength of the foamed molded product-The blending amount of the lower molecular weight polystyrene resin with respect to the high molecular weight polystyrene resin is in the range of 0.5 to 40% by weight. Except for various changes, several examples of the heat-resistant foamed resin particles having the same composition as that of Example 1 were produced according to the production procedure and conditions of the above-mentioned Example. Then, from the obtained heat-resistant foamed resin particles, a foamed molded product having a density of 20 kg / m ³ is produced in the same manner as in the above-described example, and then the bending strength and 5% compressive strength of the foamed molded product are measured according to JIS A951.
1 was measured. The results are shown in Table 4 below.

[0035]

According to this table, in Comparative Example 5 in which a lower molecular weight styrene resin was blended in an amount exceeding 30% by weight, required physical properties (flexural strength) could not be achieved in the foam molded article. It can be seen that a foam of a practical quality cannot be obtained. On the other hand, the lower molecular weight styrene resin
In Comparative Example 4 blended in an amount less than% by weight, it was confirmed by a test not mentioned that the desired effect of improving the expansion ratio was not obtained in the process of preliminary expansion.

[0037]

As described above, according to the present invention,
Regarding the preliminary foaming using the heat-resistant foamed resin particles, a sufficiently high foaming ratio of at least 30 times, especially at least 50 times, can be achieved. Pre-foaming temperature (about 100
Pre-expansion at (° C.) has an effect that a desired expansion ratio can be obtained. According to the present invention,
With respect to the foam molding, the molding cycle can be significantly shortened as compared with the related art, and the effect that a sufficiently high heat resistance can be imparted to the foam molded article without special aging treatment can be obtained.

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[Procedure amendment]

[Submission date] April 15, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies and found that, first, the molecular weight (generally weight-average molecular weight of 150,000 to 500,000) of a styrene resin commonly used in conventional heat-resistant foamed resin particles. ), Ie a weight average molecular weight of from 500 to 100,0
A styrene resin having a lower molecular weight of 00 functions as a plasticizer, and when a heat-resistant expanded resin particle is finished using a styrene-based mixed resin blended with the styrene resin, a sufficiently high expansion ratio is obtained in the pre-expanded particles obtained therefrom. Have been found, and even in the final foamed molded article, no effect of impairing its heat resistance is shown. Further, the present inventor has suggested that cycloparaffin alone exerts a plasticizing function, and by impregnating it with heat-resistant foamed resin particles, contributes to an improvement in the expansion ratio of the obtained pre-expanded particles, and by itself. In the process of foam molding using the pre-expanded particles, it has been found that they escape very quickly and therefore hardly remain in the foam molded article. Furthermore, the present inventor can achieve a sufficiently high expansion ratio in the process of pre-expansion by combining the blend of the lower molecular weight styrene resin and the impregnation of the cycloparaffin with respect to the heat-resistant foamed resin particles. In the process of foam molding, it has been found that the foaming agent is rapidly dissipated, so that the molding cycle is greatly shortened, and the heat resistance of the foam molded product is sufficiently high, and the present invention is completed here. Reached.

Claims (3)

[Claims] 1. A weight average molecular weight of 150,000 to 5
50 to 90 parts by weight of a styrene-based mixed resin obtained by blending a high-molecular-weight styrene-based resin having a weight-average molecular weight of 500 to 100,000 with a high-molecular-weight styrene-based resin having a weight-average molecular weight of 500 to 100,000; Base resin consisting of parts by weight, and based on 100 parts by weight of the base resin, 1 to 15 parts by weight of a volatile foaming agent and 0.1 to 10 parts by weight of cycloparaffin. Heat-resistant foamed resin particles. 2. The styrene-based mixed resin according to claim 1, wherein 1 to 30% by weight of a lower-molecular-weight styrene resin is blended based on the high-molecular-weight styrene-based resin. Heat resistant foamed resin particles. 3. The heat-resistant foamed resin particles according to claim 1, wherein the cycloparaffin is cyclohexane or cyclopentane.