JP2604624B2 - Hollow spherical thermoplastic resin foam particles and method for producing expanded molded articles using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Object of the Invention (Industrial Application Field) The present invention relates to a thermoplastic resin foam particle having a substantially hollow spherical structure and a relatively thick particle outer shell, And a method for producing an in-mold foam molded article using the foam particles.

The foam particles of the present invention have a relatively large outer coating thickness and high strength, and can not only be advantageously used as a cushioning material, a landfill material, a heat insulating material, etc., but also can be used as a mold. The molded product obtained by the inner foam molding can be advantageously used as a packaging material, a bumper core material, a cushioning material, a heat insulating material, a toy interior material and the like.

(Prior art) Conventionally, as a packaging cushioning material, a heat insulating material, etc., a pre-expanded polystyrene particle is foamed in a mold by steam heating or the like, and a density of 18 to 30 g / l obtained by fusing the particles together is obtained. In-mold foam molded articles were known.

The particle size used for producing such an in-mold foam molded article is 0.2
The pre-expanded polystyrene particles of up to 20 mm have a multi-bubble structure having a large number of cells such as 60 to 300 cells / mm ^{2 in} number of cells (cells).
It had a relatively thin outer skin having a thickness of 1000 μm (preferably 50 to 300 μm) and an average film thickness of about 0.5 to 3 μm for forming the outer skin of the particles. In addition, the in-mold bead foam molded article obtained by in-mold bead foam molding using such pre-expanded particles has a small bubble particle size of 20 to 1000 μm, a bubble count of about 60 to 300 / mm ² , and is small. The structure had a large number of air bubbles.

As the thermoplastic resin foam particles, polypropylene-based particles (for example, JP-B-59-43491),
Polyethylene (for example, Japanese Patent Publication No. 51-22951,
Japanese Patent Publication Nos. 60-10047 and polymethyl methacrylate copolymers (for example, JP-A-57-182333)
Although the cell structure of these foam particles or pre-expanded particles, and the cell structure of the in-mold foam molded article using those particles, were also substantially similar to those of the above-mentioned polystyrene-based material. .

Conventionally, it has been considered that if the number of cells in such thermoplastic resin foam particles (including pre-expanded particles) is small, the expanded particles shrink or the strength of the expanded particles is weak. Also, it has been said that if the number of cells is small, a molded article obtained by in-mold foam molding also shrinks, and is not practical. Moreover, thermoplastic resin foam particles having a hollow spherical structure have not been known.

Generally, as hollow spherical particles, for example, hollow spherical particles of glass (microballoons) and hollow spherical particles of volcanic ash (silas) have been known. As for thermosetting resin, hollow spherical particles of melamine resin and urea resin produced by casting, injection nozzle method, etc. have been known (Japanese Patent Publication No. 62-20212). However, these known hollow spherical particles can be used as fillers for resins and cement products, but cannot be used for in-mold bead foam molding.

(Problems to be Solved by the Invention) The present invention has a hollow spherical shape and a relatively thick outer coating, and is excellent as a buffer, a landfill, a heat insulating material, a filler and the like as particles. Rather, it provides thermoplastic resin foam particles that can provide excellent in-mold foam molded articles even when used as particles for in-mold foam molding, and further provides in-mold foam molded articles using the foam particles. It is intended to provide a method of manufacturing.

(B) Configuration of the Invention (Means for Solving the Problems) The hollow spherical thermoplastic resin foam particles of the present invention are substantially hollow having one giant cell occupying more than 50% of the total volume of the particles. It is a spherical particle having a particle diameter of 0.5 to 20 mm and an average film thickness of the particle coat of 3 μ or more.

Further, the method for producing a foamed molded article in a thermoplastic resin mold of the present invention comprises filling the above-mentioned hollow spherical thermoplastic resin foamed particles having a secondary foaming ability into a mold and heating and expanding the same to fuse the foamed particles together. It is a method of wearing.

The average thickness of the outer coating of the hollow spherical thermoplastic resin foam particles of the present invention is 3 μ or more, preferably 5 to 100 μ. In the present invention, the average thickness of the outer skin refers to the average thickness of the outermost outer skin of the foam particles, and has a structure in which the small bubbles 2 ″ in which the outer skin is crushed overlap each other, Alternatively, in the case of a structure in which small bubbles 2 "are formed in close contact with the outer skin inside a giant bubble, the average value of the film thickness including those small bubbles 2" is used. If the outer coating thickness is too thin, the strength such as the compressive strength and the compression recovery rate of the particles themselves and the in-mold foam molded article obtained therefrom are reduced.

The foam particles of the present invention are used in so-called suspension seed polymerization in which two or more unsaturated monomers are polymerized in an aqueous medium in which polymer particles are present as seeds.
By producing a thermoplastic resin foamable particles by absorbing a foaming agent into the polymer particles during or after the polymerization, and by further heating the foamable particles to expand the foamable particles, by adjusting the polymerization conditions Can be manufactured.

That is, in the aqueous suspension system in which the thermoplastic polymer particles having a particle size of 0.1 to 2 mm were suspended as seeds in water, the unsaturated monomer constituting the polymer particles is different from the same monomer. Suspension polymerization is performed while dropping two or more types of monomer mixtures with other unsaturated monomers, and the polymer mixture and the polymer particles being generated absorb the monomer mixture. In the course of or after the suspension polymerization, a foaming agent which does not swell or dissolve or slightly swells the resulting thermoplastic polymer particles is added, and the resulting thermoplastic polymer is added. The same foaming agent is absorbed into the particles to produce expandable resin particles, and the obtained expandable resin particles are separated and then heated to expand the particles so that the apparent density becomes about 10 to 200 g / l. In the method of producing thermoplastic resin foam particles by By adjusting the combination and a monomer mixing ratio, etc. dripping the monomer mixture suitably,
The hollow spherical thermoplastic resin foam particles of the present invention can be produced.

Examples of the thermoplastic polymer particles used as seeds in the suspension seed polymerization include polystyrene, polymethyl methacrylate, ABS, SAN, styrene / α-methylstyrene / acrylonitrile copolymer, and styrene / methyl methacrylate copolymer. Polymer, polyethylene,
Polymer particles such as polypropylene are exemplified. The thermoplastic polymer particles as such seeds may be non-expandable polymer particles containing no foaming agent, or may be foamable polymer particles containing a foaming agent. When non-expandable polymer particles are used as seeds, the obtained foam particles and the in-mold foam molded product obtained therefrom have a good gloss and a translucent shape. When the expandable polymer particles are used as seeds, the obtained foam particles and the in-mold foam molded product obtained therefrom have high opacity. The reason for this is that the foam particles obtained when the former non-expandable particles are used as seeds are, as shown in FIG. In contrast to the structure in which bubbles 2 ″ having a small diameter are formed, the foam particles when the latter expandable particles are used as seeds are the 1-b
As shown in the figure, the structure is such that crushed small bubbles 2 "overlap and an outer skin with a thickness of 10 to 100μ is formed.
Because.

As the unsaturated monomer in the suspension seed polymerization,
For example, styrene, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, alkyl acrylate (having an alkyl group having 1 to 8 carbon atoms), acrylonitrile, acrylamide, α-methylstyrene, p- Examples include methylstyrene, acrylic acid, itaconic acid, maleic acid, N-phenylmaleimide and the like. These unsaturated monomers are, as described above, an unsaturated monomer constituting a polymer particle as a seed and another unsaturated monomer having a different solubility index to water from the monomer. Used in combination with the body.

As a polymerization initiator in the seed polymerization, a decomposition temperature for obtaining a half-life of 10 hours is 60 to 120 ° C., preferably 70 to 110 ° C.
Organic peroxides which are in ° C are suitable. Specific examples of preferred polymerization initiators (the temperature in parentheses added to the specific examples is a decomposition temperature for obtaining a half-life of 10 hours) include t-butylperoxy 2-ethylhexanoate [72 ° C] and benzoyl. Peroxide [74 ° C], 1,1-bis (t-butylperoxy) -3,5,5-trimethylcyclohexane [90
° C], t-butyl peroxylaurate [96 ° C], 2.5
-Dimethyl-2,5-di (benzoylperoxy) hexane [100 ° C], t-butylperoxybenzoate [104
° C), methyl ethyl ketone peroxide (109 ° C),
And dicumyl peroxide (117 ° C.). The polymerization initiator is used at a ratio of 0.05 to 2% by weight based on the monomer mixture.

As a foaming agent to be added during or after the seed polymerization, a liquid or gaseous organic compound is used at normal temperature and normal pressure. Particularly, those having a boiling point lower than the softening temperature of the polymer particles to be impregnated with the foaming agent are used. Is preferred. Specific examples include propane, butane, pentane, hexane,
Examples include aliphatic hydrocarbons such as petroleum ether, cyclic hydrocarbons such as cyclohexane, and halogenated hydrocarbons such as methylene chloride, vinyl chloride, trichlorotrifluoroethane, and dichlorodifluoroethane.

In the suspension seed polymerization, the polymer particles obtained by polymerizing while adjusting the polymerization conditions, and impregnated with a foaming agent are washed, washed and dried, and the foaming agent is 2 to 10% by weight in the polymer particles. %, Preferably 3 to 8% by weight of thermoplastic resin expandable particles, and the expandable particles are 90 to 90% by weight.
Heated with hot water or steam at 110 ℃, apparent density is 10 ~ 2
Foaming to give 00 g / l gives the hollow spherical thermoplastic resin foam particles of the present invention.

The foam particles obtained by such a method may shrink once immediately after foaming, but when left in the air for about 2 to 10 hours (aging), the air pressure in the air bubbles becomes the same as the atmospheric pressure and becomes a hollow spherical shape. Return. And, the hollow spherical foam particles of the present invention usually have secondary foaming ability, and it is confirmed that the secondary foaming ability is not lost even if the particles are left in air for 50 days or more. Was done.

The hollow spherical thermoplastic resin foam particles of the present invention can be obtained by adjusting the polymerization conditions in the above-mentioned suspension seed polymerization, in particular, by adjusting the combination of unsaturated monomers (types) used and the monomer mixing ratio. Although these conditions are obtained, their preferable conditions vary and vary depending on the type of polymer particles as a seed, the type and combination of monomers, and the like.

As an example, the same seed polymer and monomer as in Example 1 described below are used, and other polymerization conditions are also the same, except that the mixing ratio of the monomer mixture to be dropped is shown in Table 1. The polymerization was carried out with various changes as described above. Next, the obtained thermoplastic resin expandable particles were heated and foamed under the same foaming conditions as in Example 1 to produce foam particles. The average film thickness of the monomer content ratio of each of the obtained foam particles, the cell structure, the particle size, and the particle envelope is as follows:
Table 1 shows the results.

The foam particles obtained in Experiment No. 1 (Comparative Example 1 described later) are particles having a multi-bubble structure as shown in FIG. 6, which are conventionally known pre-foam particles (FIG. 10). The number of bubbles is about 200 to 300 / mm ² , that is, a multi-bubble structure in which a number of small bubbles 2 ″ are contained in a particle 1, and the particle outer skin has a thickness of about 0.5 to 1.0. It was as thin as μ and had low compressive strength.

Then, as the number of experiments No. increases (in other words, as the proportion of methyl methacrylate in the dropped monomer mixture increases), the number of bubbles per mm ² decreases, and thus the size of the bubbles decreases. The particles gradually increased in size, and thick particles having a particle skin thickness of 3 to 100 μ were obtained.

More specifically, the foam particles obtained in Experiment No.
As shown in the figure, the number of air bubbles in which relatively large air bubbles 2 ′ and relatively small air bubbles 2 ″ are mixed in one foam particle 1 is about 10 to 30 / mm ² , The foam obtained in Example No. 3 had nine large cells 2 ′ as shown in FIG.
And hollow spherical particles having a large number of small bubbles 2 ″ adhered to the outer coat of the particles, and the average thickness of the outer coat of the particles was relatively thick, about 30 μm.

The foam particles obtained in Experiment No. 4 (Example 1 described later) and Experiment No. 5 are shown in FIGS. 2 and 1-a and 1-b.
As shown in the figures, each of the particles 1 is a hollow spherical particle having substantially only one giant bubble 2 occupying most of the volume of the entire particle 1, and has a structure in which the outer skin contains crushed small bubbles 2 ″. The average film thickness including small bubbles in the outer skin was as thick as about 50 μm, and was one of the representative examples of the foam particles of the present invention.

Further, as shown in FIG. 4, the foam particles obtained in Experiment No. 6 have substantially only one giant gas bubble 2 as shown in FIGS. 1 and 2. However, about one to two small particles of resin (polymer) are movably housed in the bubbles 2, and the average thickness of the outer skin is as large as about 50 μm. This foam particle was another representative example of the foam particle of the present invention. A molded article obtained by in-mold foaming of a foam in which small resin particles are movably accommodated in the air bubbles of such particles has small resin particles movably accommodated in each individual particle. Since the molded article is shaken by hand or the like, the molded article emits a refreshing sound. Therefore, it is considered that the molded article can be advantageously used for applications in which generation of such a sound is preferable, for example, for toy interior materials.

The foam particles of the present invention are substantially hollow spherical particles having one giant cell as described above, and have a particle size of 0.5 to 20 m.
m, the average film thickness of the particle coat is 3 μ or more, preferably 5 to 100
Since it is about μ, the outer coating thickness is thicker than the conventionally known pre-foamed particles having a multi-bubble structure, so that regardless of the hollow spherical structure, the particles themselves are also compared with conventionally known pre-foamed particles. It has excellent strength such as compressive strength, and can be advantageously used as a buffer, a landfill, a heat insulator, a filler, and the like. In the case where the foam particles of the present invention are used in the above-mentioned applications as they are, the foam particles do not necessarily have to have a secondary foaming ability.

However, the manufacturing method as described above (especially the pre-foaming method)
As described above, the foam particles of the present invention produced by the above method usually have secondary foaming ability. The foam particles of the present invention having such a secondary foaming ability can be advantageously used as foam particles for in-mold foam molding. That is,
The foam particles of the present invention having such a secondary foaming ability are filled in a mold according to a conventional method, and a predetermined temperature (for example, 11
When it is heated for about 5 to 120 seconds using steam or hot water at 0 to 130 ° C.), it easily foams and fuses with each other to obtain an in-mold foam molded article. The in-mold foam molded article has a larger outer coating of particles compared to a molded article obtained by in-mold foam molding of conventionally known pre-foamed particles, so that both the compressive strength and the compression recovery rate are high. From, packaging material, bumper core material,
It can be used advantageously as a cushioning material. Also, since the molded product obtained by subjecting the foamed particles of the present invention in which small resin particles are movably stored to in-mold foaming emits a refreshing sound when shaken by hand as described above, for example, a toy interior It can be used advantageously as a material.

For example, the attached FIG. 5 shows that the foam particles (shown in FIG. 2) obtained in the above-mentioned Experiment No. 4 (Example 1 described later) were subjected to in-mold foam molding. FIG. 2 is an enlarged cross-sectional view of the body, which has a structure in which relatively large particles are fused, and the fused individual particles are substantially hollow spheres.

(Examples, etc.) Hereinafter, examples and comparative examples will be described in more detail.

Example 1 1000 g of pure water, 10 g of tribasic calcium phosphate, 3.0 g of a 1% aqueous solution of sodium dodecylbenzenesulfonate, and 3.0 g of a 1% aqueous solution of sodium dodecylbenzenesulfonate were sieved to a polymerization vessel having a capacity of 3 liters having a particle size of 0.5 to 0.4 mm containing 6.1% butane as a blowing agent. Foamable styrene polymer particles
212.2 g (200 g as a pure styrene polymer) and 2.4 g of benzoyl peroxide were added, and stirred at 450 rpm to obtain a uniform suspension and dispersion.

The temperature of this suspension dispersion was raised to 80 ° C. with stirring.
When the temperature of ° C. is reached, in the space of the polymerization vessel,
18 g of butane, an amount corresponding to a ratio of 10 g / l to the volume of the space, was vaporized and supplied. Then, after the temperature of the polymerization system reached 80 ° C., the temperature was maintained at the same temperature for 8 hours. During this time, from the time when the temperature reached 80 ° C., over 6 hours, 1.2 g of tertiary butyl perbenzoate was added to 200 g of styrene and 400 g.
Was dissolved in a monomer mixture with methyl methacrylate in a continuous manner at a rate of 100 g per hour.

After the completion of the addition of the monomer solution, 80 g of pentane, which is equivalent to 10% of the total amount of the raw material expandable styrene polymer particles and styrene and methyl methacrylate monomer, is added in a liquid state. After that, the temperature was raised from 80 ° C. to 110 ° C. over 1.5 hours, and kept at 110 ° C. for 4 hours to perform polymerization.
Thermoplastic foam particles were produced.

After cooling, the aqueous dispersion after completion of the polymerization was cooled, filtered, washed with water, and dried to obtain a thermoplastic resin expandable particle at 98 ° C. and 1.0 kg / cm ²
And prefoamed by heating with water vapor to obtain foam particles having a bulk density of 20 g / l. The foam particles were left in the air at 30 ° C. for 6 hours and dried (aged) to obtain particles without shrinkage. The particle has a structure as shown in FIG. 2, and the particle 1 has substantially only one huge bubble 2 with a particle size of 2 to 3 mm and an average film thickness of about 50 μm. Yes,
The particles had secondary foaming ability.

Then, after leaving the foam particles in the air for 24 hours, 10
0.7 kg filled in a mold cavity of 0 mm x 100 mm x 200 mm
The molded body obtained by foaming by heating with steam of 20 cm / cm ² for 20 seconds has a honeycomb structure as shown in FIG. 5, and the individual fused foam particles substantially have It had a hollow sphere structure. Also, this molded product is JIS A-951
The 5% compression strength according to 1 was 1.1 kg / cm ² and the compression recovery after 50% compression was 97%.

Comparative Example 1 A monomer mixture of styrene (402 g) and methyl methacrylate (198 g) was used as a monomer to be dropped.
Was polymerized using the same method as in Example 1, and the obtained expandable particles were pre-expanded by the same method as in Example 1.
The obtained expandable particles 1 have a multi-bubble structure having many small bubbles 2 ″ as shown in FIG.
200-300 pcs / mm ² , particle size 2-3mm, particle skin thickness
0.5-1 μm. This is similar to previously known pre-expanded particles.

A molded article obtained by in-mold foam molding using the pre-expanded particles in the same manner as in Example 1 is JIS
The 5% compression strength according to A-9511 was 1.0 kg / cm ² , and the compression recovery after 50% compression was 88%.

Example 2 In place of the monomer mixture used in Example 1, a monomer mixture of 120 g of styrene and 480 g of methyl methacrylate was used, and the others were polymerized in the same manner as in Example 1 to obtain expandable particles. . Further, when the expandable particles were prefoamed in the same manner as in Example 1, foam particles having a secondary expandability having a structure as shown in FIG. 4 were obtained. This particle 1 has a particle size of 2-3 mm and an average thickness of the outer skin of 5 mm.
It was a substantially hollow spherical particle having 0 μm and having substantially only one huge bubble 2 and one small resin particle 3 movably contained in the bubble 2.

In-mold foam molding was performed using the foam particles in the same manner as in Example 1. The obtained molded body can emit a refreshing sound based on the stored small resin particles when shaken by hand, and has the same 5% compressive strength as in Example 1, 1.1 kg / cm ² , 50% compressive strength. The recovery rate was 96%.

Example 3 In place of 212.2 g of the expandable polystyrene particles of the seed used in the polymerization of Example 1, 200 g of polystyrene particles containing no foaming agent were used, and the other processes were carried out in the same manner as in Example 1 to obtain a foam. The foamed particles were prefoamed in the same manner as in Example 1 to obtain foamed particles having secondary foaming ability.

The foam particles have a hollow sphere structure having one huge bubble similar to the foam particles obtained in Example 1, and have a particle diameter of 2 to 3 mm and an average film thickness of the particle outer skin of 1.
5μ. Example 1 was prepared using the foam particles.
In the molded article obtained by in-mold foam molding in the same manner as in the above, both the 5% compressive strength and the 50% compressive recovery were almost the same as those of the molded article obtained in Example 1. ,
Its appearance was translucent and high gloss, while the molded article of Example 1 was opaque and low gloss.

Comparative Example 2 This is an example of the conventional method.

In other words, pure water was placed in a polymerization vessel with a stirrer having a capacity of
1000 g, 0.42 g of sodium pyrophosphate, 0.63 g of sodium acetate, and 0.10 g of sodium nitrite were added, and stirred at 350 rpm to obtain a uniform dispersion. Then, with stirring, 7.0 g of benzoyl peroxide, tert-butyl perbenzoate 2.
A solution in which 1 g was dissolved in a monomer mixture of 350 g of styrene and 350 g of methyl methacrylate was added to obtain a uniform suspension dispersion.

The temperature of the suspension dispersion was increased to 80 ° C. while stirring, and further increased from 80 ° C. to 115 ° C. over 6 hours. During this period, one hour after reaching 80 ° C., 50 g of a 10% aqueous solution of polyvinylpyrrolidone was added. At the same time, four hours later, 10% by weight based on the monomer mixture of styrene and methyl methacrylate was added. A quantity of 70 g of pentane, corresponding to, was added in liquid form. After reaching 115 ° C., the temperature was maintained at the same temperature for 5 hours to complete the polymerization.

The obtained polymerization product was cooled, passed, dried, and the obtained particles were cut into 0.7 to 1.0 mm.
The foam was heated and foamed with steam of g / cm ² to obtain pre-foamed particles having a bulk density of 20 g / l.

The cross-sectional structure of the pre-expanded particles is a multi-bubble structure as shown in FIG. 8, having a particle size of 2 to 3 mm, a particle outer film thickness of about 0.5 to 1.0 μm, and a bubble count of about 220 / a particle having a secondary foaming capacity of mm ^2.

A molded product obtained by subjecting the pre-foamed particles to in-mold foam molding in the same manner as in Example 1 has a 5% compressive strength of 0.9 kg / cm ² as in Example 1. , 50%
The compression recovery was 88%.

(C) Effects of the Invention The thermoplastic resin foam particles of the present invention have a substantially hollow sphere, a thick outer particle coating, and high strength of the particles themselves. In addition, the in-mold foam molded article obtained by using the foam particles has a structure in which hollow spherical particles are fused to each other as compared with a conventional in-mold foam molded article, and has not only a good appearance but also a compression property. Both strength and compression recovery are significantly higher.

[Brief description of the drawings]

FIGS. 1-a and 1-b, FIGS. 2, 3, 4, 6, and 7 show Experiment Nos. 5 and 4 in Table 1 (Example 1). , No. 3 and No. 6 (Example 2), No. 1 (Comparative Example 1), and an enlarged cross-sectional view of the foam particles obtained in No. 2 respectively. FIG. 5 is an enlarged sectional view of an in-mold foam molded article of the foam particles obtained in Experiment No. 4 (Example 1), and FIG. 8 is a view of the foam particles obtained in Comparative Example 2. It is an expanded sectional view. FIG. 9 is an enlarged cross-sectional view of the foam particles obtained in Example 3, and FIG. 10 is an enlarged cross-sectional view of conventionally known pre-foam particles. The magnification shown in each drawing is the magnification. Each symbol in the figure indicates the following. 1 ... foam particles, 2 ... huge bubbles of foam particles, 2 '
... large bubbles of foam particles, 2 "... small bubbles of foam particles, 3 ... small resin particles in giant cells of foam particles.

Claims (6)

(57) [Claims] 1. A substantially hollow spherical particle having one giant cell occupying more than 50% of the total volume of the particle,
Hollow spherical thermoplastic resin foam particles having a particle size of 0.5 to 20 mm and an average film thickness of the particle skin of 3 μ or more. 2. The foam particles according to claim 1, wherein the average particle thickness of the particle skin is 5 to 100 μm. 3. The foam particles according to claim 1 or 2, wherein the small resin particles are movably accommodated in the giant cells of the particles. 4. The foam particles according to claim 1, wherein the particles have secondary foaming ability. 5. A mold is filled with at least one kind of thermoplastic resin foam particles selected from the hollow spherical thermoplastic resin foam particles having the secondary foaming ability according to claim 4, and heated and expanded. For producing a foamed article in a thermoplastic resin mold in which foam particles are fused together. 6. The method of claim 5, wherein the individual fused foam particles have a substantially hollow spherical structure.