JPH0228225A - Hollow spherical foam particle of thermoplastic resin and production of molded article of foam using the same particle - Google Patents

Abstract

PURPOSE:To obtain the title foam particles suitable as cushioning material, packaging material, heat insulating material, etc., having specific cell volume, average thickness of outer film and excellent strength by using polymer particles as a seed and expanding a suspended polymer containing a blowing agent under heating. CONSTITUTION:(A) Particles of thermoplastic polymer (e.g., polyethylene) having preferably 0.1-2mm particle diameter are suspended as a seed in water, (B) a polymerization initiator is added while dripping an unsaturated monomer such as styrene, the monomer is polymerized at 60-120 deg.C, the polymer is impregnated with (C) preferably 2-10wt.% blowing agent such as propane or butane and the resulting material is washed and dried. The material is heated to preferably 90-110 deg.C, expanded to give foam having 10-200g/apparent density and the aimed foam particles wherein >=50% whole volume of particle is one large cell, particle diameter is 0.5-20mm and average thickness of outer film of particle is >=3mum is obtained.

Description

Detailed Description of the Invention (,) Object of the Invention (Field of Industrial Application) The present invention provides thermoplastic resin foam particles having a substantially hollow spherical structure and having a relatively thick particle outer shell; and a method for producing an in-mold foam molded article using the same foam particles.

The foam particles of the present invention have a relatively thick outer coating and high strength, and can not only be used advantageously as a cushioning material, a landfill material, a heat insulating material, etc., but also can be used to form molds. The molded product obtained by internal foam molding can be used as packaging materials, bumper core materials,
It can be advantageously used as a cushioning material, a heat insulating material, an interior material for toys, etc.

(Prior art) Conventionally, polystyrene particles having a density of 18 to 309% have been used as packaging cushioning materials, heat insulating materials, etc. by foaming pre-expanded polystyrene particles in a mold by steam heating or the like and fusing the particles together.
In-mold foam molded articles of 1 were known.

The particle size used for producing such an in-mold foam molded product is 0.2
Polystyrene pre-expanded particles with ~20 exposures have air bubbles (cells)
It has a multi-cell structure with a large number of bubbles, such as 60 to 300 cells/2, and the particle size of the bubbles is 20 to 1000μ (preferably 50 to 300μ) depending on the expansion ratio, and The average thickness of the bubble film forming the outer skin of
．． It had a relatively thin outer skin of about 5 to 3 microns. In addition, the in-mold bead foam molded product obtained by in-mold bead foam molding using such pre-expanded particles has a particle diameter of 20 to 1000 μm and a number of bubbles of about 60 to 300/2, and is small. It had a structure with many bubbles.

Further, as the thermoplastic resin foam particles, polypropylene-based ones (for example, Japanese Patent Publication No. 59-43491), polyethylene-based ones (for example, Japanese Patent Publication No. 51-22
951, Japanese Patent Publication No. 60-10047) and polymethyl methacrylate copolymer type (for example, Japanese Patent Application Laid-open No. 57-182333), the air bubbles of these foamed particles or pre-expanded particles The structure and the cell structure of the self-foamed molded product using these particles were almost the same as those of the polystyrene-based product described above.

Conventionally, it has been believed that when the number of cells in this type of thermoplastic resin foam particles (including pre-expanded particles) is small, the foam particles shrink or the strength of the foam particles becomes weak. Also,
If the number of cells is small, the molded product obtained by in-mold foam molding will also shrink, making it impractical. Moreover,
Foam particles of thermoplastic resin having a hollow spherical structure have not been known so far.

In addition, in terms of boat fishing, for example, positive hollow spherical particles (microparoons) and hollow spherical particles of volcanic ash (whitebait) have been known as hollow spherical particles. As for thermosetting resins, hollow spherical particles of melamine resins and urea resins manufactured by casting, injection nozzle methods, etc. have been known (Japanese Patent Publication No. 62-20212). However, although these known hollow spherical particles can be used as fillers for resins, cement products, etc., they 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 material, a landfill material, a heat insulating material, a filler material, etc. In addition, the present invention provides thermoplastic resin foam particles that can be used as particles for in-mold foam molding to provide an excellent in-mold foam molded product, and further provides an in-mold foam molded product using the foam particles. The purpose is to provide a manufacturing method.

(b) Structure 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. The particles are characterized by being spherical particles, having a particle size of 0.5 to 20 mm, and an average thickness of the particle outer layer of 3 μm or more.

In addition, the method for producing an in-mold thermoplastic resin foam molded article of the present invention includes filling the above-mentioned hollow spherical thermoplastic resin foam particles having secondary foaming ability into a mold and heating and expanding them to melt the foam particles. This is a way to put it on.

The average thickness of the outer coating of the hollow spherical thermoplastic resin foam particles of the present invention is 3 microns or more, preferably 5 to 100 microns. In the present invention, the average film thickness of the outer skin refers to the average film thickness of the outermost skin of the foam particle, and the outer skin has a structure formed by crushed small cells γ overlapping each other, or In the case of a structure in which small bubbles r are formed inside giant bubbles in close contact with the outer skin, it refers to the average value of the film thickness including those small bubbles r. If the thickness of the outer coating is too thin, the strength such as compressive strength and compression recovery rate of the particles themselves and the resulting in-mold foamed product will decrease.

The foam particles of the present invention can be used during or during the polymerization 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. It can be produced by adjusting the polymerization conditions in a method in which a blowing agent is absorbed into the subsequent polymer particles to produce expandable particles of a thermoplastic resin, and the expandable particles are further heated and foamed. .

That is, in an aqueous suspension system in which thermoplastic polymer particles with a particle size of 0.1 to 2 m are suspended as seeds in water, the unsaturated monomers constituting the polymer particles and the same monomers are added. Suspension polymerization is carried out while dropping a mixture of two or more monomers with different other unsaturated monomers, and the monomer mixture is applied to the polymer particles and the polymer particles that are being formed. Polymerization is carried out with absorption, and during or after the suspension polymerization, a blowing agent that does not swell or dissolve the produced thermoplastic polymer particles, or only slightly swells them, is added to the produced thermoplastic polymer particles. The foaming agent is absorbed into the polymer particles to produce foamable resin particles, and the resulting foamable resin particles are separated and then heated so that the apparent density becomes about 10 to 2001/l. In the method for manufacturing thermoplastic resin foam particles by foaming, the hollow spherical shape of the present invention can be produced by appropriately adjusting the polymerization conditions, especially the combination of monomer mixtures to be added, the monomer mixing ratio, etc. Thermoplastic foam particles can be produced.

Thermoplastic polymer particles used as seeds in the suspension seed polymerization include, for example, polystyrene, polymethyl methacrylate, ABS, SAN, styrene/α-methylstyrene/acrylonitrile copolymer, and styrene/methyl methacrylate copolymer. Examples include polymer particles such as polymers, polyethylene, and polypropylene. The seed thermoplastic polymer particles may be non-expandable polymer particles containing no blowing agent, or may be expandable polymer particles containing a blowing agent. When non-expandable polymer particles are used as seeds, the resulting foam particles and the in-mold foam molded product obtained from them have good gloss and are translucent. Furthermore, when expandable polymer particles are used as seeds, the resulting foam particles and the in-mold foam molded product obtained from them have high opacity. The reason for this is that when the former non-expandable particles are used as seeds, the foam particles have a wall thickness of 10 to 1 mm, as shown in Figure 9.
30 ~ 6 μm in some places on the film-like outer skin
The structure has a structure in which small bubbles γ of 60μ are formed, whereas the foam particles when the latter foamable particles are used as seeds are crushed small bubbles 2' as shown in Figure 1-b.
This is because the structure has a structure in which the two layers are overlapped to form an outer skin with a wall thickness of 10 to 100 μm.

the! @Unsaturated monomers in turbidity P polymerization include:
For example, styrene, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, acrylic acid alkyl ester (alkyl group having 1 to 8 carbon atoms), acrylonitrile, acrylamide, α-methylstyrene, p- Examples include methylstyrene, acrylic acid, itaconic acid, maleic acid, and N-phenylmaleimide. As mentioned above, these unsaturated monomers are composed of the unsaturated monomers constituting the polymer particles as seeds and other unsaturated monomers that have a different water solubility index from the same monomers. Used in combination with the body.

The polymerization initiator in the seed polymerization has a decomposition temperature of 60 to 120°C, preferably 7
Organic peroxides having a temperature of 0 to 110°C are suitable. Specific examples of preferable polymerization initiators include t
-Butylperoxy 2-ethylhexanoate [72℃
], benzoyl l? -Oxide [74℃L 1,1
-bis(t-butylperoxy)-3,5,5-)limethylcyclohexane [90°C], t-butylperoxylaurate [96°C], 2,5-tumethyl-2,5-
cy(-<nsoylperoxy)hexane [100°C],
Examples include t-ff luperoxypenzoate) (104°C), methyl ethyl ketone 7 and -oxide [109°C], and dicumyl peroxide (117°C). It is used in a ratio of .05 to 2 times.

As the blowing agent added during or after the seed polymerization, a liquid or gaseous organic compound is used at room temperature and pressure, but in particular, its boiling point is lower than the softening temperature of the polymer particles to be impregnated with the blowing agent. Preferably. Specific examples include aliphatic hydrocarbons such as propane, butane, pentane, hexane, and petroleum ether, cyclic hydrocarbons such as cyclohexane, and halogenated hydrocarbons such as methylene chloride, vinyl chloride, trichlorotrifluoroethane, and dichlorodifluoroethane. can give.

In such suspension seed polymerization, the polymer particles obtained by polymerization while adjusting the polymerization conditions and impregnated with a blowing agent are filtered, washed, and dried, so that 2 to 10 weight of the blowing agent is contained in the polymer particles. %, preferably 3 to 8 wt. %, the expandable particles are made of thermoplastic resin containing 90
The hollow spherical thermoplastic resin foam particles of the present invention are obtained by heating with hot water or steam at ~110°C and foaming to an apparent density of 10 to 200 l/l.

The foam particles obtained by this method may shrink once immediately after foaming, but if left in the air for about 2 to 10 hours (ripening), the pressure inside the bubbles becomes the same as atmospheric pressure and becomes hollow spherical. return. It was confirmed that the hollow spherical foam particles of the present invention normally have secondary foaming ability, and that this secondary foaming ability is not lost even if the particles are left in the air for 50 days or more. It 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, particularly the combination of unsaturated monomers (types) used, the monomer mixing ratio, etc. However, the preferred conditions vary depending on the type of polymer particles as seeds, the types and combinations of monomers, and are not constant.

As an example, using the same seed polymer and monomer as in Example 1 described later, and using the same other polymerization conditions, only the mixing ratio of the monomer mixture to be added dropwise is shown in Table 1. Polymerization was carried out with various changes.

Next, each of the obtained thermoplastic resin expandable particles was heated and foamed using the same foaming conditions as in Example 1 to produce foam particles. The monomer content ratio, cell structure, particle size, and average film thickness of the particle outer layer of each obtained foam particle are shown in Table 1.
The results were as shown in the following.

1. The foam particles obtained in Experiment A I (Comparative Example 1 described below) have a multicellular structure as shown in Figure WJ6, which is different from the conventional pre-foam particles (see Figure 10). ), the number of bubbles is about 200 to 300/ff111+2, that is, the particle has a multicellular structure containing many small bubbles γ in the particle 1, and the thickness of the particle outer layer is about 0.5 ~1.0μ
It was relatively thin and had low compressive strength.

And, as the number of bubbles increases (in other words, as the proportion of methyl methacrylate in the dropped monomer mixture increases), the number of bubbles per 2 drops becomes smaller, and therefore the size of the bubbles increases. Gradually larger particles were obtained, and the particle outer layer had a thickness of 3 to 100 μm.

Specifically, as shown in FIG. 7, the foam particles obtained in Experiment A2 have a mixture of relatively large bubbles 2' and relatively small bubbles τ' in one foam particle 1. The number of bubbles formed was about 10 to 30/2 bubbles, and the outer coating thickness was also somewhat thick. In addition, the foam obtained at Experimental House 3 had nine large bubbles 2', as shown in Figure 3.
The particles were hollow spherical particles having a large number of small air bubbles 2'' in close contact with the particle outer coating, and the particle outer coating had a relatively thick average thickness of about 30 μm.

In addition, the foam particles obtained in Experiment A4 (Example 1 to be described later) and Experimental Point 5 have a total area of 100% of the entire particle 1, as shown in Fig. 2 and Figs. 1-a and 1-b, respectively. It is a hollow spherical particle that has substantially only one giant bubble 2 that occupies most of its volume, and has a structure in which the outer shell contains crushed small bubbles r, including the small bubbles in the outer shell. The average film thickness was as thick as about 50 μm, and it was one of the representative examples of the foam particles of the present invention.

Furthermore, as shown in FIG. 4, the foam particles obtained in Experiment A6 had substantially only one giant bubble 2, similar to those shown in FIGS. 1 and 2. However, one or two small resin (polymer) particles 3 are movably housed within the bubbles 2, and the average thickness of the outer skin is as thick as about 50 μm. Foam particles were also another representative example of foam particles of the present invention. A molded product obtained by in-mold foam molding of a foam in which small resin particles are movably housed within the air bubbles of such particles is a molded product in which small resin particles are movably housed within each individual particle. Since the molded product emits a gentle sound when shaken by hand, it is thought that it can be advantageously used in applications where generation of such a sound is preferred, such as interior materials for toys.

The foam particles of the present invention are thus substantially hollow spherical particles having one giant cell, and have a particle size of 05 to 20 m.
, the average thickness of the particle shell is 3 μ or more, preferably 5 to 10
Since the particle size is about 0 μ, the outer coating thickness is thicker than that of the conventionally known pre-foamed particles with a multi-cell structure, so the particles themselves are also thicker than the conventionally known pre-foamed particles, regardless of their hollow spherical structure. It has excellent strength such as compressive strength, and can be used as a cushioning material,
It can be advantageously used as a landfill material, a heat insulating material, a filler material, etc. In addition, when the foam particles of the present invention are used for the above-mentioned purposes up to f of the particles, the foam particles do not necessarily need to have secondary foaming ability.

However, the foam particles of the present invention produced by the above-mentioned production method (particularly the pre-foaming method) usually have a secondary foaming ability, as described above. The foam particles of the present invention having such 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 secondary foaming ability are filled into a mold according to a conventional method, and heated to a predetermined temperature (for example, 11
5 to 12 minutes using steam or boiling water (0 to 130℃)
When heated to about 0 seconds, they easily foam and fuse together to obtain an in-mold foamed molded product. The in-mold foamed molded product has a thicker outer coating on the particles than a molded product obtained by in-mold foam molding of conventionally known pre-foamed particles, so it has high compressive strength and compression recovery rate. From, packaging materials, bread/
4'-Can be advantageously used as a core material, cushioning material, etc. Furthermore, the molded product obtained by in-mold foam molding of the foam particles of the present invention in which small resin particles are movably housed emits a soft sound when shaken by hand as described above, so it can be used, for example, as a toy. It can be advantageously used as an interior material, etc.

For example, the attached FIG. 5 shows the foam particles (shown in FIG. 2) obtained in Experiment 44 (Example 1 below).
This is an enlarged cross-sectional view of a molded product obtained by in-mold foam molding, which has a structure in which relatively large particles are fused together, and the fused particles are almost hollow spherical. .

(Examples, etc.) The following is a more detailed explanation of Examples and Comparative Examples.

Example 1 Pure water 100011 was added to a polymerization vessel with a stirring device having a capacity of fk31.
10 g of tribasic calcium phosphate, 1 t aqueous solution of sodium dodecylbenzenesulfonate 3.0.9. Expandable styrene polymer particles 212.2/(2oom as pure styrene polymer) sieved to particle size 0.5-0.4 gourd containing 6.1% butane as a blowing agent, and benzoyl peroxide 2
．． 4y was added and stirred at 450 rpm to form a uniform suspension dispersion.

4 while heating this suspended dispersion to 80°C while stirring.
When the temperature reached 0° C., 18II butane was vaporized and supplied to the space of the polymerization vessel in an amount corresponding to a ratio of 10 I/l to the volume of the space. Next, after the temperature of the polymerization system reached 80°C, it was kept at the same temperature for 8 hours, and during this period, from the time when it reached 80°C, 1.2F of tert. added in proportion.

After the addition of the monomer solution was completed, 80 g of pentane, which is an amount equivalent to 10 g of the total amount of the raw material expandable styrene polymer particles and the styrene and methyl methacrylate monomers, was added in liquid form. 1. From 80℃ to 110℃.
The temperature was raised over 5 hours and held at 110° C. for 4 hours to effect polymerization, thereby producing expandable thermoplastic resin particles.

After the completion of polymerization, the aqueous dispersion was cooled, filtered, washed with water, and the resulting thermoplastic resin expandable particles were heated at 98°C for 1.0 k.
The foam particles were pre-foamed by heating with water vapor of g/cm2 to obtain foam particles having a bulk density of 20,971. 3 of these foam particles
The particles were dried (ripened) by being left in the air at 0° C. for 6 hours to obtain particles without shrinkage. This particle has a structure as shown in Fig. 2, and the particle 1 is essentially a huge bubble 2.
The particles had only one particle size, had a particle size of 2 to 3 m+, had an average film thickness of about 50 μm, and had secondary foaming ability.

The foam particles were then left in the air for 24 hours and then
The molded product obtained by filling the cavity of a mold of 00+m x 100m x 200+m and heating with 0.7'g/cm2 of water vapor for 20 seconds to form a foam has a nicum structure as shown in Figure 5. The fused individual foam particles had a substantially hollow sphere structure.

In addition, this molded product has a 5% rating according to JIS A-9511.
The compressive strength was 1.1 kg7cm, and the compression recovery rate after compression of 50 inches was 97%.

Comparative Example 1 Using a monomer mixture of styrene 402I and methyl methacrylate 198y as the monomer to be added dropwise, the polymerization was otherwise performed in the same manner as in Example 1, and the obtained expandable particles were used in Example 1. The number of cells was 200 to 300/II+12, the particle size was 2 to 3 mm, and the thickness of the outer layer of each particle was about 0.5 to 1 μm. This is similar to previously known pre-expanded particles.

In addition, the molded product obtained by in-mold foam molding using the pre-expanded particles in the same manner as in Example IK is
5 inch compressive strength by A-9511 is 1.0 97cm
Compression recovery rate after 250chi compression is f? It was Chi.

Example 2 Instead 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 polymerization was otherwise performed in the same manner as in Example 1 to obtain expandable particles. . Furthermore, this expandable particle was used in Example 1.
When pre-foaming was carried out in the same manner as in , foamed particles having a structure as shown in FIG. 4 and having secondary foaming ability were obtained.

This particle 1 has a particle size of 2 to 3 and an average thickness of the outer skin! .

They were substantially hollow spherical particles that were movably housed.

Further, in-mold foam molding was performed using the foam particles in the same manner as in Example 1. When the obtained molded body is shaken by hand, it can emit a gentle sound based on the small resin particles contained therein, and the same 5 inch compressive strength as in Example 1 is 1.1 ψ'cm and 2.50 inch. The compression recovery rate was 96%.

Example 3 In place of the expandable polystyrene particles 212.21 used in the polymerization of Example 1, 200 g of polystyrene particles containing no blowing agent were used, and the polymerization was otherwise carried out in the same manner as in Example 1. The expandable particles were pre-foamed in the same manner as in Example 1 to obtain foam particles having secondary foaming ability.

These foam particles have a hollow spherical structure with one giant cell similar to the foam particles obtained in Example I, and have a particle size of 2 to 3 cm and an average thickness of the particle outer layer. 1
It was 5μ. In addition, using this foam particle, Example 1
The molded product obtained by in-mold foam molding in the same manner as in Example 1 had a 5-inch compressive strength and a 50% compression recovery rate that were almost the same as those of the molded product obtained in Example 1. The appearance of the molded product of Example 1 was translucent and high gloss, whereas the molded product of Example 1 was opaque and low gloss.

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

That is, 1000 g of pure water, 0.42.1 g of sodium birophosphate, 0.63 g of sodium acetate, and 0.10 g of sodium nitrite were added to a polymerization container with a capacity of 31 mm and equipped with a stirring device.
A homogeneous dispersion was obtained by stirring at rpm.

Then, to this was added 7 ml of benzoyl peroxide while stirring.
．． 0g, tertiarybutylno-4-benzoate 2.1
．． 9 with 350 g of styrene and 350 g of methyl methacrylate
A solution dissolved in the monomer mixture was added to form a uniform suspension and dispersion.

The temperature of this suspension dispersion was raised to 80°C while stirring, and then the temperature was further raised from 80°C to 115°C over 6 hours.

During this period, 50.9 g of a 10% aqueous solution of polyvinylpyrrolidone was added 1 hour after the temperature reached 80°C, and 10.9 g of a 10% aqueous solution of polyvinylpyrrolidone was added to the monomer mixture of styrene and methyl methacrylate at the same time of 4 hours. The amount is equivalent to 7.
0.9% of the tantan was added in liquid form. After reaching 115°C, the temperature was maintained for 5 hours to complete the polymerization.

The obtained polymerization product was cooled, filtered, and dried, and the obtained particles were cut into 0.7 to 1.0 particles and heated at 98°C.
, 1.0 kg and 7 cm 2 of steam were heated and foamed to obtain pre-expanded particles having a bulk density of 20 E/l.

The cross-sectional structure of the pre-expanded particles is a multi-cell structure as shown in Figure 8, with a particle size of 2 to 3 mm, a particle outer layer thickness of about 0.5 to 1.0 μm, and a number of bubbles. The particles had a secondary foaming ability of approximately 220 particles/2 cups.

Furthermore, a molded article obtained by performing in-mold foam molding using the pre-foamed particles in the same manner as in Example 1 had a 5-inch compressive strength of 0.9 kg/cm, similar to that in Example 1. cm
The 250 inch compression recovery rate was 88 inch.

(c) Effects of the Invention The thermoplastic resin foam particles of the present invention have a substantially hollow spherical shape, have a thick outer coating, and have excellent strength.

In addition, the in-mold foam molded product obtained using this foam particle has a structure in which hollow spherical particles are fused together compared to conventional in-mold foam molded products, so it not only has a better appearance but also has a better compression Both strength and compression recovery rate are extremely high.

[Brief explanation of the drawing]

Figure 1-a, Figure 1-b, Figure 2, Figure 3, Figure 4, Figure 6, and Figure 7 show Experiment A5 and Experiment A4 (Example 1) in Table 1.
), Tie 3 and Tie A6 (Example 2), Tie 1 (Comparative Example 1)
), and enlarged cross-sectional views of foam particles obtained at the same point 2, respectively. Moreover, FIG. 5 is an enlarged cross-sectional view of the in-mold foam molded product of the foam particles obtained in Experiment A 4 (Example 1), and FIG. 8 is an enlarged view of the foam particles obtained in Comparative Example 2. This is a cross-sectional view. Further, 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 the conventionally known pre-foam particles. The multiples appended to each drawing are enlargement magnifications. Each symbol in the figure indicates the following. 1... Foam particles, 2... Huge bubbles of foam particles,
2'... Large bubbles in foam particles, 2''... Small bubbles in foam particles, 3... Small resin particles within giant bubbles in foam particles. Patent applicant: Mitsubishi Yuka Perdice Co., Ltd. Reason
Patent Attorney Mamoru Nakatani Figure 1-a Figure 1-b Figure 3 Figure 4 Figure 6 Figure 8 Figure 10

Claims (1)

[Scope of Claims] 1) Substantially hollow spherical particles having one giant bubble occupying more than 50% of the total volume of the particles, with a particle size of 0.5 to 20 mm, and an average membrane of the particle outer shell. Hollow spherical thermoplastic foam particles having a thickness of 3μ or more. 2) The foam particles according to claim 1, wherein the particle outer skin has an average thickness of 5 to 100 microns. 3) The foam particles according to claim 1 or 2, wherein small resin particles are movably housed in giant cells of the particles. 4) The foam particles according to claim 1, 2, or 3, wherein the particles have secondary foaming ability. 5) At least one kind of thermoplastic resin foam particles selected from the hollow spherical thermoplastic resin foam particles having secondary foaming ability according to claim 4 is filled into a mold and heated and expanded to form a foam. A method for manufacturing thermoplastic resin in-mold foam moldings that fuses particles together. 6) The method of claim 5, wherein the individual fused foam particles have a substantially hollow spherical structure.