JPH0432100B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to amorphous expandable vinylidene chloride resin particles having excellent heat resistance, and more specifically, particles based on an amorphous vinylidene chloride resin having a high glass transition point. The present invention relates to novel expandable vinylidene chloride-based resin particles that can be applied to foamed molded products with improved heat resistance and can be used in a wide range of insulation and cushioning applications. (Prior Art) Synthetic resin foams having uniform and fine closed cells have conventionally been excellent in heat insulation and cushioning properties, and have been used for various purposes depending on the characteristics of the base resin. In recent years, research has focused on the functions of foams to improve the added value of synthetic resins.As a result, many synthetic resins can now be foamed, and foaming technology has made great progress. Among these, foams that take advantage of the excellent properties of vinylidene chloride resins, such as high gas barrier properties and flame retardancy, have been expected for many years, but the reality is that they have not yet appeared. The reasons for this are generally that for vinylidene chloride resins, (1) the processing temperature at which the resin is melt-processed and the decomposition temperature at which the decomposition reaction proceeds are too close to each other; therefore, thermal decomposition of the resin tends to occur during the extrusion processing process; (2) The barrier properties of the resin are high, making it difficult to impregnate the resin with a foaming agent. (3) It is difficult to adjust the foaming conditions because the viscoelasticity of the resin is highly dependent on temperature near the foaming temperature. It has been extremely difficult to obtain a highly foamed, well-homogeneous foam without causing thermal decomposition. Under these circumstances, Japanese Patent Application Laid-open No. 127333/1983,
and JP-A-60-125649 propose a foamed molded product in which a large number of expandable particles made of substantially amorphous vinylidene chloride resin and a large number of multicellular foamed particles are fused together. are doing. The technology disclosed in this publication makes it possible to create foams that take advantage of the properties of vinylidene chloride resin (i.e., flame retardancy, oil resistance, chemical resistance, gas barrier properties, mechanical strength, etc.), and allows for low heat resistance. Conductivity (excellent insulation)
This was an epoch-making product that realized a foam that could maintain its properties for a long period of time. (Problems to be Solved by the Invention) However, in the above-mentioned conventional technology, since a vinylidene chloride resin with a low glass transition point (Tg) was used as the base resin, the foam obtained from it was heated to an ambient temperature. In some cases, the gas within the cells expands or contracts, changing the dimensions of the foam, or causing permanent deformation of the cell membranes that make up the foam. In particular, when the temperature is high, secondary expansion occurs due to the ambient temperature, and there is a major problem in that it is extremely susceptible to deformation. As a result, despite the excellent heat insulating performance of the resulting foam, the range of uses for which it can be used is limited. (Means and effects for solving the problems) An object of the present invention is to provide a foam with improved heating dimensional stability of a conventional amorphous vinylidene chloride resin foam molded product. To provide expandable vinylidene chloride resin particles, which are raw material intermediates for foams for heat insulating materials, which can be used as a body in a wide temperature range from high to low temperatures, and whose applicability is expanded. Furthermore, by improving the heat resistance of vinylidene chloride resin, the properties of the resin (such as gas barrier properties, flame retardance, chemical resistance,
Vinylidene chloride resin that enables foams for insulation materials to maintain low thermal conductivity over a long period of time without compromising mechanical strength, etc., and to have excellent properties such as low dimensional change due to ambient temperature. is to provide particles. In addition, by improving heat resistance, stability against thermal decomposition reactions may decrease, impregnability of the blowing agent may decrease, or changes in the viscoelasticity of the resin near the foaming processing temperature may cause it to become unsuitable for foaming. Don't get bored. It is necessary that the properties of the resin for producing the foam achieve the above object without being inferior to the level disclosed in, for example, Japanese Patent Application Laid-open No. 125649/1983. As a result of intensive research under these circumstances, the inventors of the present invention have modified vinylidene chloride by introducing specific heat-resistant monomer units and monomer units copolymerizable with them as base resins. By using a resin, it has been possible to provide expandable vinylidene chloride resin particles that can provide a vinylidene chloride resin foam having excellent heating dimensional stability. That is, the above object of the present invention is to obtain vinylidene chloride,
An organic volatile blowing agent per 100 parts by weight of an amorphous vinylidene chloride copolymer consisting of N-substituted maleimide and one or more vinyl monomers copolymerizable with these and having a glass transition point of 85°C or higher. This can be achieved by employing expandable vinylidene chloride resin particles characterized by containing 1 to 40 parts by weight of. Hereinafter, the content of the present invention will be explained in detail. The key point of the present invention is that an amorphous multi-component copolymer having the above-mentioned composition and a high glass transition point is used as the base resin, and in particular, the glass transition point (Tg) of the base resin is
We adopted an amorphous vinylidene chloride resin that has a tensile elongation of over 200% in the temperature range of Tg + 50°C, and added a volatile organic blowing agent to the resin particles with a relatively uniform particle size distribution. (Tg−10)℃〜(Tg
The reason is that a method of contact impregnation in a temperature range of +20)°C was adopted. The first necessity is to increase the heating dimensional stability of the foam obtained from the expandable resin particles of the present invention.
Naturally, it is necessary to increase the heat deformation temperature of the base resin, which is the most fundamental aspect of the present invention. As shown in FIG. 1, the volume change rate ( Curve) is published in Japanese Patent Application Publication No. 1983
-Volume change rate (curve) of foam molded product made of vinylidene chloride resin disclosed in Publication No. 125649
It is clear that dimensional stability at higher temperatures is imparted to the material. That is, it can be seen that the N-substituted maleimide as a heat-resistant monomer employed in the present invention greatly contributes to the heating dimensional stability of a foam molded article made of a vinylidene chloride resin that maintains flame retardancy. The following requirements will be explained in relation to the closed cell properties of the foam obtained from the expandable resin particles of the present invention. Generally, the foaming process of thermoplastic resin involves heating the resin containing a foaming agent to soften and fluidize it.
The aim is to generate a large number of independent bubbles by the gas pressure of the blowing agent generated simultaneously. The viscoelastic behavior of the resin is extremely important at this processing temperature; if the elastic modulus is too high, it is difficult to obtain a foam with a high magnification, and if viscous flow is dominant, it is difficult to obtain a foam with individual independent cells. It is well known to those who are familiar with the work that this process leads to continuous cells. As a result of analyzing the tensile stretching behavior of the base resin at high temperatures, the present inventors found that the degree of tensile stretching reached 200% in the temperature range above the glass transition point (Tg) of the base resin and below (Tg + 50) °C. It has been found that resins having a point exceeding For example, Experiment Nos. 8 and 10 in Table 2,
Looking at the 11 resins, the glass transition points (Tg) are 96, 80, and 90℃, respectively, and the tensile elongation at Tg + 25℃ is 380% (120℃), 50% (105℃), and 680℃.
% (115℃). The closed cell ratios of expanded particles obtained by foaming these resins to similar expansion ratios are 60%, 35%, and 72%, respectively. If the tensile elongation is as low as 50%, it is impossible to even obtain an in-mold molded product. In addition, since the value of closed cell ratio also increases as the tensile stretching degree increases,
It can be seen that a closed cell ratio of 60% or more is a preferable requirement for molding a foam. In order to modify the properties of such a resin, it is extremely preferable to introduce a partially crosslinked structure for the purpose of controlling the molecular weight in order to obtain a closed cell foam with a high magnification. The following requirements will be explained in relation to the method for manufacturing expandable resin particles. As in the present invention, the base resin into which the heat-resistant monomer unit is introduced inevitably has a reduced solubility of the blowing agent, and it is necessary to contact and impregnate the blowing agent at as high a temperature as possible. However, vinylidene chloride resins are generally easily decomposed by heat, and the base resin of the present invention cannot escape this property. Therefore, if left in a high-temperature atmosphere for a long time, the dehydrochloride reaction will proceed and the heat of the base resin will deteriorate. lead to degeneration. As a result, there are problems in that the foaming ability of the resin impregnated with the foaming agent is significantly reduced, and furthermore, the physical properties of the foamed molded product are deteriorated. In addition, hydrochloric acid and chlorine generated by thermal decomposition of the resin cause corrosion of equipment such as pressure containers, which poses a major problem in terms of manufacturing safety. As mentioned above, it is necessary to impregnate the base resin with a foaming agent that has sufficient foaming ability while balancing the various problems. The present inventors adjusted the particle size of the base resin particles to a range of 0.1 mm or more to 1.0 mm or less, and set the impregnation temperature (T) of the blowing agent as follows based on the glass transition temperature (Tg) of the base resin. By selecting within the range shown by the formula (Tg-10)°C≦T≦(Tg+20)°C, the above object was achieved. Figure 2 shows the amount of blowing agent contained in vinylidene chloride resin particles of the present invention having various particle sizes when the resin particles are kept in a blowing agent solution at 100°C for 70 hours and impregnated with the resin particles. The graph shows the amount of blowing agent (curve) immediately after impregnation with the particles and the amount (curve) of blowing agent contained in the particles after the particles were left open under atmospheric pressure at 32°C for 8 days. As is clear from these results, the impregnation rate of the blowing agent largely depends on the diameter of the resin particles. The smaller the particle size, the easier it is to impregnate, and there is a linear correlation with the particle size.
Particles with particle diameters of less than 0.1 mm or greater than 1 mm deviate greatly from linearity. In addition, it is clear that the foaming agent retainability is more likely to escape as the resin has a smaller particle diameter, but a linear relationship is not necessarily obtained, and it is clear that resin particles with a diameter of less than 0.1 mm cause significant foaming agent escape. Therefore, the particle diameter of the resin particles is preferably 0.1 to 1.0 mm, more preferably
0.2mm to 0.6mm is preferable. Furthermore, if the particle size distribution of the base resin particles is uneven, the expansion ratio distribution of the resulting multicellular foam particles will also be uneven, and if the particles are subjected to in-mold foam molding, local density changes will occur. This means that only foamed molded products with variations can be obtained. Therefore, it is preferable that the particle size distribution of the base resin particles is uniform. Furthermore, Figure 3 shows the expansion ratio when the foaming resin particles adjusted to contain the same amount of the blowing agent are primarily foamed under constant heating conditions by changing the impregnation temperature of the blowing agent. These are the results plotted against temperature. Glass transition point of base resin +20
It is clear that the foaming ratio rapidly decreases when the temperature exceeds ℃. This is considered to be because, as mentioned above, the base resin was thermally denatured by the impregnation treatment, and the viscoelasticity at the heating and foaming temperature changed greatly. To achieve the object of the present invention, the impregnation temperature of the blowing agent must not exceed the Tg of the base resin + 20°C. Furthermore, impregnating the foam material at low temperatures requires a long time to impregnate the required amount of foaming agent. The impregnation temperature of the blowing agent is preferably in the range of (Tg-10)°C to (Tg+20)°C. The modified vinylidene chloride resin used in the present invention is a main component that increases the glass transition point.
-substituted maleimides are selected, such as N-methylmaleimide, N-ethylmaleimide, N-propylmaleimide, N-butylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-2-methylphenylmaleimide, N- -2
-ethylphenylmaleimide, N-2-chlorophenylmaleimide, N-2-methoxyphenylmaleimide, N-2,6-dimethylphenylmaleimide, etc., and one or more of these can be used. N-phenylmaleimide and N-2-chlorophenylmaleimide are preferred because they are easily available industrially, and N-phenylmaleimide is particularly preferred. Vinylidene chloride and one or more vinyl monomers copolymerizable with the above N-substituted maleimide include vinyl chloride, acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, acrylic acid, methacrylic acid, and methyl acrylate. , ethyl acrylate, butyl acrylate, methyl methacrylate, glycidyl methacrylate, 2-ethylexyl acrylate, 2-ethylhexyl methacrylate, hydroxyethyl acrylate, glycidyl methacrylate, etc., and one or more of these can be used. . acrylonitrile, styrene,
Methyl methacrylate is preferred because it can easily raise the glass transition point of the copolymer composition. Further, acrylonitrile is preferable from the viewpoint of imparting flame retardancy, but it is even more preferable to use a mixture of acrylonitrile and styrene because the thermoplasticity and elongation at high temperatures of the copolymer composition will increase. The monomer composition of the amorphous multi-component copolymer includes 30 mol% to 65 mol% of vinylidene chloride, N-
1 mol% to 10 mol% of substituted maleimide and 25 mol% of one or more monomers copolymerizable with these
Preferably, a composition range of ~70 mol% is chosen. If the amount of vinylidene chloride is less than 30 mol%, the resulting foamed molded product will have insufficient flame retardancy, and if it exceeds 65 mol%, impregnation with the blowing agent will be poor. In addition, if the N-substituted maleimide content is less than 1 mol%, the glass transition point of the base resin will be low, resulting in poor dimensional stability when heated, and if it exceeds 10 mol%, the impregnation of the blowing agent will occur. Sexuality becomes poor. In addition, one or more compounds having two double bonds in one molecule represented by the general formula may be used as a crosslinking component.
It may be used in an amount of 0.1 mol% or less. [General formula] R ₁ represents -H or -CH ₃ and R ₂

〔Effect of the invention〕

By heating and foaming the expandable resin particles of the present invention with a heating medium such as steam, hot water, or hot air,
Pre-expanded vinylidene chloride particles with heat deformation resistance and a closed cell ratio of 60% or more can be obtained. The closed cell ratio here is measured with an air comparison type hydrometer, and indicates the ratio of closed cells in the foam to the total cells. The pre-expanded particles thus obtained can be made into an in-mold molded article by a known molding method. That is, pre-expanded particles are filled in a mold that can be closed but cannot be sealed and has many small holes, and foaming and expansion is caused by heating with a fluid such as steam through the small holes from outside the mold wall. After filling the gaps between the particles and fusing them, this is rapidly cooled to form a molded body. By this manufacturing method, a large number of multicellular foamed particles whose base resin is vinylidene chloride resin with excellent heating dimensional stability are made into a single piece by closely contacting the outer surfaces of adjacent particles and fusing them. The structure is a foamed molded body. If the closed cell ratio is less than 60%, the foaming ability of the pre-expanded particles will be extremely poor, resulting in poor in-mold formability, resulting in significant sink marks or the inability to tightly fuse the pre-expanded particles together. Only in-mold foam molded products with many voids can be obtained. The compressive strength required for these foams varies depending on the application, so
It must be handled according to the purpose of use. In the expandable resin particles of the present invention, the expansion ratio can be controlled by the impregnated amount of the blowing agent, the heating temperature during pre-foaming, and the time, and the density of the in-mold foam molded product is 15 to 300 Kg/ ^m3. can be handled. Further, by subjecting the expandable resin particles of the present invention to extrusion foaming, it is possible to obtain a homogeneous and good extruded foam board rich in closed cells with a large cross section, and furthermore, the pre-expanded particles can be used as they are for various lightweight fillers. You can also. The various foams obtained from the expandable resin particles of the present invention have the excellent properties of vinylidene chloride resins, such as flame retardancy, oil and chemical resistance, gas barrier properties, and mechanical strength. In addition, it has excellent dimensional stability in high-temperature or low-temperature atmospheres, which has not been seen before, and can be applied to a wide range of applications. In particular, these foams have not only excellent heat resistance but also excellent heat insulation performance. Generally, those skilled in the art are well aware that the insulation performance of commercially available foams used as insulation materials deteriorates over time, but in the foam obtained from the expandable resin particles of the present invention, Due to its excellent gas barrier properties, it also has the ability to maintain excellent heat insulation performance over a long period of time. As described above, the present invention is a significant invention as it provides a foam material which is extremely useful industrially. [Examples] Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited to these Examples. The evaluation method used in the present invention is as follows. Γ Foam density: Based on JIS K6767. Γ Foaming ratio: Base resin density divided by foam density. Γ Closed cell ratio: Based on ASTM D2856. Γ Thermal conductivity: Based on ASTM C518. Γ5% compressive strength: Based on ASTM D1621, the amount of compressive strain is 5%. Γ Heating dimensional change rate: Cut out a foam sample according to JIS K6767 and measure the volume change rate at each temperature. Γ Glass transition point: Measure the exothermic or endothermic differential curve from the differential calorific value vs. temperature function using a differential scanning calorimeter (DSC) according to ASTM D-3418-75. Γ Tensile stretching degree: Thickness of vinylidene chloride resin 0.2
A sheet of ~0.4 mm and width of 5 mm was cut out, and the distance between the chucks was set to 50 mm, and at each measurement temperature.
Elongation at yield point when pulled at a speed of 200mm/〓,
Or measure elongation at break. Examples/Comparative Example 1 Vinylidene chloride (42
mol%), N-phenylmaleimide (2.4 mol%)
Copolymer resin particles crosslinked with 0.02 parts by weight of divinylbenzene based on 100 parts by weight of resin were subjected to an experiment with a monomer composition ratio of acryloniloryl (44.3 mol%) and styrene (11.3 mol%). The resin had a specific gravity of 1.49 and a glass transition point of 96°C. 100 parts by weight of the resin particles having an average particle diameter of 0.4 mm are placed in an autoclave, and the autoclave is sealed and degassed under vacuum.
Next, 300 parts by weight of a liquid mixed foaming agent containing Freon 11 and Freon 22 in a weight ratio of 90:10 is injected. After being kept under stirring at 100°C for about 70 hours, the mixture is cooled to room temperature, returned to normal pressure, and the particles inside are taken out. The particles were impregnated with about 19 parts by weight of blowing agent. The foamable resin particles were left open in a room for two weeks after being impregnated with a foaming agent, and then heated and foamed with steam at 0.5 kg/cm ² -G for 20 seconds to obtain pre-expanded particles with an expansion ratio of 24 times. The obtained expanded particles had an average particle diameter of about 1.2 mm, an average cell diameter of 0.1 mm, and a closed cell ratio of 95%. Next, the pre-expanded particles with an expansion ratio of 24 times are heated with steam of approximately 1.1 kg/cm ² -G in an in-mold steam molding machine for expandable polystyrene within 30 minutes immediately after foaming, and are in-mold molded. A foamed flat plate molded product having a thickness of 25 mm, a square shape of 300 mm, and a density of 40 Kg/m ³ was obtained. The obtained molded product was cut into a size of 100 ^W x 100 ^L x 25 ^t mm, and heat treated at a predetermined temperature for 24 hours.The dimensional change was read and the volume change rate was measured. The results are shown in Figure 1. Also, the 5% compressive strength is
It was 2.0Kg/ ^cm2 . According to Example 1 of JP-A-60-125649,
Vinylidene chloride and methyl methacrylate 60/40
An in-mold foam molded article made of a copolymer was obtained. The glass transition point of the base resin is 71°C. The obtained molded body was cut into a size of 100×100×25 mm, and the volume change rate after heating was measured in the same manner as in Example 1. The results are shown in FIG. As is clear from FIG. 1, it can be seen that by using the base resin of the present invention, the heating dimensional stability of the conventional vinylidene chloride resin foam is greatly improved. Example/Comparative Example 2 The particle diameter of the base resin was 0.08, 0.1, 0.2, 0.4, 0.6,
Foaming agent-impregnated resin particles were obtained in the same manner as in Example 1 except that the diameters were 0.8, 1.0, and 1.2 mm. The amount of blowing agent contained in the expandable resin particles thus obtained was measured immediately after impregnation (curve) and after being left open for 8 days at 32° C. under normal pressure. The results are shown in FIG. As is clear from the figure, when the particle size of the base resin exceeds 1 mm, the impregnation of the blowing agent is significantly reduced. Furthermore, it can be seen that when the particle size is less than 0.1 mm, the blowing agent escapes significantly due to changes over time. Example/Comparative Example 3 Base resin particles and a blowing agent were placed in an autoclave in the same manner as in Example 1, and a predetermined amount of blowing agent was added by adjusting the impregnation temperature and time of the blowing agent as shown in Table 1. Impregnated expandable resin particles were prepared.
Similarly, the amount of blowing agent contained in each particle was
Shown in the table. These resin particles were left open in a room for two weeks, and then heated and foamed with steam at 1.0 Kg/cm ² -G for 30 seconds to obtain pre-expanded particles. The cell diameter, closed cell ratio, and expansion ratio of the obtained expanded particles are also shown in Table 1. In addition, regarding the expansion ratio, the correlation with impregnation temperature conditions is shown in FIG. As is clear from this figure, when the impregnation temperature was 130°C, the foaming ability was significantly reduced. This is because the base resin exposed to the high temperature conditions of 130°C undergoes a thermal decomposition reaction, which significantly changes the original properties of the resin. Therefore, the impregnation temperature of the blowing agent must be 115°C or lower, that is, Tg of the base resin (=96°C) + 20°C or lower. Further, the pre-expanded particles obtained in this example were aged indoors for one day and then molded using an in-mold molding machine for expandable polystyrene to obtain a molded product with a thickness of 25 mm and a size of 300 mm square. At that time, the steam pressure necessary to fuse the pre-expanded particles in close contact with each other without any voids, and the density of the obtained molded product, plus 5% of that.
The compressive strengths are also summarized in Table 1. As is clear from the above, the blowing agent impregnation condition of 130° C. requires a steam pressure exceeding the equipment pressure resistance (approximately 1.5 kg/cm ² ) of an in-mold molding machine for expandable polystyrene, which is not preferable. On the other hand, if the impregnation temperature of the blowing agent is too low, an extremely long time is required to impregnate the desired blowing agent, which is not preferable. as an acceptable temperature
The temperature is preferably 85°C, that is, Tg of the base resin - 10°C or higher. Example/Comparative Example 4 The molar ratio of vinylidene chloride (VDC), N-phenylmaleimide (N-PMI), acrylonitrile (AN) and styrene (st) is as shown in Table 2, and as a crosslinking agent Divinylbenzene (DVB) is mixed with Freon 11 and ethylene chloride in a weight ratio of 90:10 with base resin particles having a particle size of 0.5 mm, which are also adjusted as shown in Table 2 for 100 parts by weight of resin. A blowing agent was impregnated in the same manner as in Example 1. The amount of blowing agent impregnated was adjusted by changing the impregnation time as shown in Table 2. After leaving the foamable resin particles indoors for 2 weeks, 0.5Kg/cm ² -G
The mixture was heated and foamed with steam for 30 seconds to obtain pre-expanded particles. The expansion ratio, closed cell ratio, and
The particle sizes are shown in Table 2. Further, these expanded particles were aged indoors for one day to obtain in-mold molded products, whose density and volume change rate after heating at 70° C. for 24 hours are shown in Table 2. Next, as a comparison, a copolymer of vinylidene chloride (VDC) and acrylonitrile (AN), and a copolymer of vinylidene chloride (VDC) and acrylonitrile (AN)
Also for the copolymer with methacrylonitrile (MAN), the particle size of the composition shown in Table 2 is 0.5 mm.
The resin particles were impregnated with a foaming agent mixture containing Freon-11 and ethylene chloride in a weight ratio of 90:10 in the same manner as in Example 4 to obtain expandable resin particles. Pre-expanded particles and in-mold foam molded articles were similarly obtained for these, and the results of evaluation for each are shown in Table 2. For Experiment Nos. 9, 10, and 11 in Table 2, the tensile elongation degree of the base resin at (Tg+25)°C is also shown. Resin No. 10 had an extremely low tensile elongation of 50% during heating, and the closed cell ratio of the pre-expanded particles was 35%. On the other hand, No.9,
The tensile elongation of the 11 resins is 380% and 680%, respectively, and the closed cell ratio of the expanded particles is 60% and 72%. The higher the degree of tensile stretching of the resin, the higher the closed cell ratio of the resulting foam tends to be. but,
Although the cause of the pre-expanded particles obtained from resin No. 11 is unknown, the cell size is large compared to the particle size, making it difficult to obtain porous particles.

【table】

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between volume change rate and heating temperature of a molded product obtained by foaming the particles of the present invention and a foamed molded product of the particles described in JP-A-60-125649. The figure is a graph showing the relationship between the amount of blowing agent and resin particle diameter immediately after impregnating the particles of the present invention with a blowing agent and after leaving them at 32°C and atmospheric pressure for 8 days. 1 is a graph showing the relationship between the expansion ratio of pre-expanded particles of the present invention and the blowing agent impregnation temperature.

Claims (1)

[Scope of Claims] 1. An amorphous vinylidene chloride copolymer comprising vinylidene chloride, N-substituted maleimide, and one or more vinyl monomers copolymerizable with these, and having a glass transition point of 85°C or higher. 1. Expandable vinylidene chloride resin particles containing 1 to 40 parts by weight of an organic volatile blowing agent per 100 parts by weight. 2. Claim No. 2, characterized in that an amorphous vinylidene chloride resin has a point where the degree of tensile elongation exceeds 200% in a temperature range from the glass transition point (Tg) of the resin to Tg + 50°C or less. Expandable vinylidene chloride resin particles according to item 1. 3. The expandable vinylidene chloride resin particles according to claim 1, wherein the particle size of the amorphous vinylidene chloride resin particles is in the range of 0.1 mm to 1 mm. 4 The amorphous vinylidene chloride resin contains 30 mol% to 65 mol% vinylidene chloride, 1 mol% to 10 mol% N-substituted maleimide, and 25 mol% to 25 mol% of one or more vinyl monomers copolymerizable with these. 70 mol% of the expandable vinylidene chloride resin particles according to claim 1. 5. The expandable vinylidene chloride resin particles according to claim 1, wherein the organic volatile blowing agent has a boiling point lower than the glass transition point of the amorphous vinylidene chloride resin. 6. The expandable vinylidene chloride resin particles according to claim 1, wherein the organic volatile blowing agent has a molar average solubility coefficient in the range of 5.7 to 7.0.