JP3292634B2 - Expandable thermoplastic resin particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expandable thermoplastic resin particles. That is, the present invention
Resin particles that have the property of foaming when heated,
The present invention relates to particles used as a material for producing a foamed molded article.

[0002]

2. Description of the Related Art Expandable thermoplastic resin particles are produced by incorporating a foaming agent into a thermoplastic resin. As a resin, any resin can be used in theory, as long as it is a thermoplastic resin. Styrene resins are mainly used because of the properties of the foamed molded articles. In general, foaming agents can be roughly divided into pyrolytic solid compounds, inert gases, hydrocarbons, and halogenated hydrocarbons. Among them, the foaming agents used to make expandable particles are used. Is a hydrocarbon, such as an aliphatic hydrocarbon such as propane, butane or pentane, or a cycloaliphatic hydrocarbon such as cyclopentane or cyclohexane. Therefore, what is practically used as expandable thermoplastic resin particles is made by impregnating aliphatic or cycloaliphatic hydrocarbons into styrene resin particles.

[0003] As described above, expandable thermoplastic resin particles (hereinafter referred to as expandable particles) are used exclusively for heating and foaming to form a foamed molded article. To do so, first heat the expandable particles to form pre-expanded particles, ripen them, put the pre-expanded particles into a mold and heat again, expand the pre-expanded particles in this mold, and fuse them together. An operation of forming the foamed molded article is performed. Therefore, the quality of the expandable particles is determined by the easiness of these operations and the quality of the finally obtained molded foam.

[0004] In order to heat and expand the expandable particles, steam is used as a heating medium, and the steam is brought into direct contact with the expandable particles. At this time, if the temperature of the steam is too low, the expandable particles will not foam satisfactorily, but if the temperature is too high, the expandable particles will not foam satisfactorily, and the contact time with the steam will be insufficient. If it is too short or too long, it does not foam well. For example,
If the contact time with water vapor is too long, the bubbles in the foamed particles tend to be broken, and the foaming ratio tends to decrease. From such a relationship, good expandable particles do not deteriorate foaming performance even when stored for a considerable period of time, and are not affected by slight variations in the temperature of steam. It is said to be foamed uniformly at a high magnification and show satisfactory foaming even if the contact time with water vapor is somewhat longer and shorter, and the foamed particles are fused together in the process of pre-foaming. The prefoamed granules were said to be obtained as being separated without forming blocks.

[0005] In addition, good expandable particles are required to be easily foamed even when the pre-expanded granules produced as described above are foamed and to provide a good-quality foamed molded article after foaming. No. In this case, foaming is performed by heating with arrowhead steam, so that foam is uniformly and well foamed by steam over a wide temperature range as in the case of prefoaming, and the contact time with steam is somewhat longer or shorter. Needed to be well foamed. In addition, a good-quality foamed molded article was required to have a desired shape due to the fused particles being firmly fused together, and that the surface of the molded article should be smooth and glossy. . Here, the surface of the molded body is smooth, because the molded body is formed by mutual fusion of foamed particles, so that the fusion part of the particles should appear as a line on the molded body surface,
This means that this line is inconspicuous. That is, in a molded body having a non-smooth surface, the above-mentioned line may appear as a V-shaped groove in cross section, but the surface smoothness means that the above-mentioned line is completely inconspicuous. ing.

Since the expandable particles are not simply required to be expanded, but are required to be as detailed as described above, great care has been taken to improve the expandable particles. Some of the requirements were inconsistent with each other, and there were difficulties in resolving them. For example, the fact that the foamed particles do not form blocks during prefoaming and the fact that the foamed particles are firmly fused to form a good molded body during foam molding are somewhat inconsistent with each other, and therefore both It has been essentially difficult to provide expandable particles that satisfy the following conditions.

There has been a proposal to add a solvent such as toluene or ethylbenzene to the expandable particles in order to facilitate the expansion of the expandable particles. However, in such a proposal, the particles are blocked in the pre-expansion step. It is easy and the heat resistance of the molded body is impaired. Attempts have been made to add animal oils or vegetable oils instead of the above solvents. However, this method has the disadvantage that the particles are not sufficiently fused in the foam molding step, so that good molded articles cannot be obtained. Was.

[0008] In addition, in order to prevent blocking during prefoaming, attempts have been made to coat the surface of the foamable particles with metal soap, talc powder or wax. However, in this attempt, since the particles do not fuse together strongly during foam molding, the strength of the molded body is poor, and the fusion line between the particles appears as a deep groove on the surface of the molded body, and the appearance of the molded body is reduced. Was not good. Also, in order to prevent blocking, an attempt was made to add a triglyceride of a higher fatty acid. However, according to this attempt, the obtained molded product was not sufficiently fused, and the fusion line became a groove. Appeared and the appearance was bad.

[0009] Japanese Patent Publication No. 1-40852 proposes that butylbenzyl phthalate be contained in place of the solvent. According to this method, the pre-expansion step and the foam molding step are easily performed and improved, for example, blocking of the pre-expanded particles does not occur, but the obtained foam molded article is not good, and the surface of the arrow-formed article is not good. However, there was a drawback that the particles were not smooth and the fused lines of the particles were conspicuous.

As described above, in the pre-foaming step and the foam molding step, foaming by steam has been variously improved. However, improvement of the appearance of the foam molded article,
In particular, there have been few attempts to make the fusion line inconspicuous on the surface of the compact. The reason is that making the fusion line inconspicuous is closely related to the fact that the foamed particles in the molded body are firmly fused,
This is because the strong fusion of the expanded particles completely contradicts the requirement for preventing the particles from blocking in the pre-expansion step as described above. That is, since making the fusion line inconspicuous is inconsistent with blocking prevention, it was considered that achieving this was essentially difficult.

[0011]

SUMMARY OF THE INVENTION The present invention makes the fusion line in a foam molded article less noticeable without impairing the advantages achieved so far, such as prevention of blocking and easiness of foaming. It is an object to improve the appearance of the body.

[0012]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have studied the improvement of expandable particles. As a result, the present inventor has found that when a specific amount of a specific adipic acid diester is contained in the expandable particles, a good-quality expanded molded article can be obtained without deteriorating the properties of the expandable particles. It has been found that a molded article in which the fusion line on the body surface is inconspicuous can be obtained. The present invention has been completed based on such knowledge.

According to the present invention, an aliphatic hydrocarbon or a cycloaliphatic hydrocarbon having a boiling point lower than the softening point of the resin is contained in the thermoplastic resin particles in an amount of 1 to 15% by weight based on the resin, and diisobutyl adipate. Is contained in the resin in an amount of from 0.2 to 3.0% by weight based on the resin.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The thermoplastic resins usable in the present invention include homopolymers of styrene monomers, copolymers of styrene monomers and other monomers, and other polymers. It contains a graft polymer obtained by graft polymerizing a styrene-based monomer to the coalesced product. The styrene-based monomer contains chlorostyrene, α-methylstyrene and the like in addition to styrene. Further, the above-mentioned copolymer includes a styrene-acrylonitrile copolymer, a styrene-methyl methacrylate copolymer, a styrene-methyl acrylate copolymer, and the like. The above-mentioned graft polymer contains a graft polymer obtained by graft-polymerizing styrene onto an ethylene / vinyl acetate copolymer. These thermoplastic resins are used as particles having a particle size of about 0.1 to 10 mm.

In the present invention, a blowing agent is contained in the thermoplastic resin particles. As the foaming agent, those known in the art can be used. The blowing agent is an aliphatic or cycloaliphatic hydrocarbon having a boiling point lower than the softening point of the resin. As the aliphatic hydrocarbon, propane, butane, pentane, hexane, petroleum ether and the like can be used, and as the cycloaliphatic hydrocarbon, cyclopentane, cyclohexane and the like can be used. These can be used alone or in combination. The content of these foaming agents is in the range of 1 to 15% by weight.

The most important feature of the present invention is that diisobutyl adipate (hereinafter abbreviated as IBA) is included together with the above-mentioned blowing agent. IBA is the molecular formula _{(CH 3) 2 CH-CH} 2 -O-CO- (CH 2) 4 -CO-O-CH 2 - CH (CH 3) a compound represented by _2, melting point - 20 ° C, boiling point 1
It is a liquid at 40 ° C. (4 mmHg) . This compound is generally well compatible with the thermoplastic resin, so that it is easily absorbed into the resin by contact with the resin and heating slightly.
When this compound is absorbed by the resin, it has the property of plasticizing the resin.

In the present invention, the amount of IBA added is in the range of 0.2 to 3.0% by weight based on the thermoplastic resin particles.
The reason is that if the added amount of IBA is less than 0.2% by weight,
This is because the effect of making the fusion line inconspicuous on the surface of the foamed molded article is poor. Conversely, if the content exceeds 3% by weight, the resin particles are likely to be blocked during the prefoaming.

As described above, since IBA is well compatible with a thermoplastic resin, it can be included in resin particles more easily than a foaming agent. Therefore, various methods can be employed to include IBA in the thermoplastic resin. For example, in the process of producing a styrene-based polymer by suspension-polymerizing a styrene-based monomer, IBA can be included in the polymer particles in addition to the suspension polymerization-based system. More specifically, IBA may be added to the styrene-based monomer, or may be added to the polymer particles obtained after the completion of the polymerization. Further, when a blowing agent is pressed into the polymer particles, IB
A can be included.

As a special impregnation method, an extruder can be used. That is, a mixture obtained by adding IBA to a thermoplastic resin is put into an extruder, the resin is melted and kneaded in the extruder, and then a foaming agent is injected into the kneaded material, and the obtained resin is pressed under pressure. The resin particles are extruded in the form of a string, quenched without giving foam to the resin, and then cut into particles. Thus, polymer particles containing IBA and a foaming agent can be obtained.

In the present invention, a further improvement can be obtained by adding a small amount of cyclohexane, toluene, ethylbenzene or the like as a foaming aid together with IBA. Further, the surface of the foamed particles thus obtained can be coated with a small amount of metal soap, talc powder, wax, or the like to improve the surface of the foam molded article.

[0021]

According to the present invention, an aliphatic hydrocarbon or a cycloaliphatic hydrocarbon having a boiling point lower than the softening point of the resin is contained in the thermoplastic resin particles in an amount of from 1 to 15 parts by weight of the resin.
% By weight, the obtained particles have the same foaming performance as conventional expandable particles, and can be pre-expanded as before. It can be a foam molded article. According to the present invention, 0.2 to 3.0% by weight of the IB is
A included, IBA moderately modified the resin particles,
Blocking does not occur in the prefoaming step, and the particles are well fused to each other in the foam molding step, so that the fusion line is not conspicuous in the molded article, and therefore, a foamed molded article having a smooth surface and gloss is obtained. Can be In this regard, the present invention provides significant benefits.

[0022]

The present invention will now be described in more detail with reference to examples and comparative examples. In the following, simply “parts” means parts by weight.

[0023]

Example 1 A 5-liter autoclave was charged with 100 parts of styrene monomer, 100 parts of water and 0.1 parts of tricalcium phosphate.
25 parts, sodium dodecylbenzenesulfonate 0.005
Parts, benzoyl peroxide 0.25 part, t-butyl peroxybenzoate 0.1 part, and diisobutyl adipate 1.0 part were charged, and polymerized at 90 ° C. for 5 hours. Thereafter, 0.1 part of tricalcium phosphate was added, 0.7 part of cyclohexane and 9.0 parts of butane were press-fitted and kept at 110 ° C. for 5 hours. After cooling, water was separated and dried to obtain expandable polystyrene resin particles.
o. Let it be 1.

For comparison, in the above-mentioned production method, diisobutyl adipate was not used, and cyclohexane 0.1% was added.
7 parts was changed to 1.9 parts, and otherwise expandable polystyrene resin particles were obtained by the same method. 2
And

Sample No. Coatings 1 and 2 were coated with 0.1% by weight of zinc stearate as a blocking inhibitor and 0.08% by weight of triglyceride 12-hydroxystearate as a fusion promoter.

Measurement of expandability In order to examine the expandability of the obtained expandable polystyrene resin particles, the expandable polystyrene resin particles were heated and foamed with steam of 0.7 kgf / cm ² in a foaming tank. The heating time at that time was changed to 2 minutes, 3 minutes, and 5 minutes, and foaming was performed. 10 g of the expanded particles were placed in a measuring cylinder, the volume was measured, and the resulting product was divided by 10 g to obtain an apparent foaming multiple (cc / g). Was. Table 1 shows the results.

[0027]

[Table 1]

Measurement of blocking occurrence rate during prefoaming The foamable polystyrene resin particles 1 and 2 were prefoamed 50 times in apparent volume. At this time, the so-called blocking particles in which the resin particles are agglomerated are opened with an opening of 10%.
Separation was performed using a sieve having a thickness of mm, the weight was measured, and the weight was divided by the weight of all the charged particles to obtain a blocking occurrence rate. Table 2 shows the results.

[0029]

[Table 2]

Test of Formability Each of the foamable polystyrene resin particles 1 and 2 was prefoamed 50 times in apparent volume, left at room temperature for 24 hours, and then subjected to a molding test. Molding is ACE-3
300mm cavity size with SP molding machine (Sekisui Koki)
Using a mold of × 400mm × 100mm, heating time is 3
0.6 kg / cm ² the molding pressure was fixed at 0 seconds, 0.8K
g / cm ² and 1.0 kg / cm ² . Table 3
The results are shown in FIG. In the table, △, △, Δ, × indicate the surface state of the molded body, ◎ indicates no particle gap, 粒子 indicates a slight gap, Δ indicates a gap, and × indicates a large gap.

[0031]

[Table 3]

[0032]

Example 2 The same procedure as in Example 1 was carried out except that the amounts of diisobutyl adipate and cyclohexane were changed.
Produced in exactly the same manner except that diisobutyl adipate was 0.2 part and cyclohexane was 1.5 parts. 3 and the same evaluation was performed. The results are shown in Table 4.

[0033]

[Table 4]

[0034]

Example 3 The same operation as in Example 1 was carried out except that the amounts of diisobutyl adipate and cyclohexane were changed.
Produced in exactly the same manner except that 3.0 parts of diisobutyl adipate and 0 of cyclohexane were used. 4 and the same evaluation was performed. Table 5 shows the results.

[0035]

[Table 5]

[0036]

Comparative Example 1 The same procedure as in Example 1 was carried out except that the amounts of diisobutyl adipate and cyclohexane were changed, and 3.5 parts of diisobutyl adipate and 0 parts of cyclohexane were used.
The same procedure was followed to produce a foamable polystyrene resin sample no. 5 and the same evaluation was performed, but the blocking occurrence rate was high. The results are shown in Table 6.

[0037]

[Table 6]

[0038]

Comparative Example 2 This comparative example was carried out in accordance with the teaching of Japanese Patent Publication No. 1-40852.

In Example 1, butylbenzyl phthalate 1.0 part was used instead of diisobutyl adipate 1.0 part.
Except that we decided to use the part, it was manufactured in exactly the same way,
Expandable polystyrene resin sample No. 6 was obtained, and the same evaluation was performed. The results are shown in Table 7.

[0040]

[Table 7]

[0041]

Comparative Example 3 The same procedure was followed as in Example 1 except that 1.0 part of diisobutyl adipate was used instead of 1.0 part of diisobutyl adipate. 7 and the same evaluation was performed. The results are shown in Table 8.

[0042]

[Table 8]

According to these Examples and Comparative Examples, it is found that the expandable particles according to the present invention are superior to those described in JP-B-1-40852.

[0044]

Comparative Example 4 This comparative example is a case where an adipate other than IBA is used.

Preparation was carried out in the same manner as in Example 1, except that 1.0 part of di-2-ethylhexyl adipate was used instead of diisobutyl adipate. Polystyrene resin sample No. 8 was obtained and the same evaluation was performed. Table 9 shows the results.
It was shown to.

[0046]

[Table 9]

Claims (1)

(57) [Claims] 1. A copolymer of polystyrene and styrene or
In a resin particle made of a graft polymer of styrene, an aliphatic hydrocarbon or a cycloaliphatic hydrocarbon having a boiling point lower than the softening point of the resin is added in an amount of 1 to 15% by weight based on the resin.
And expandable thermoplastic resin particles containing 0.2 to 3.0% by weight of diisobutyl adipate.