JPS6216217B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a crosslinked foam that is made of a mixture of vinyl acetate-ethylene copolymer and a large amount of inorganic material and has a high expansion ratio, is flame retardant, and has low smoke properties, and a method for producing the same. In general, plastic foams are used in a wide range of applications such as building materials, packaging materials, and flotation materials because they are lightweight and have excellent properties such as heat insulation, shock absorption, and sound absorption. Among these, polyolefin foams are widely used in a wide range of applications because of their superior chemical, mechanical, and electrical properties compared to other plastics. However, a major drawback of this polyolefin is that it is extremely flammable, and in recent years, from a safety standpoint to prevent disasters caused by fire, strict flame retardant properties have been required for materials using these polyolefins. There is. As a method for making polyolefin flame retardant, a method is known in which a halogen flame retardant or a relatively large amount of inorganic powder is mixed with polyolefin. The former method of mixing halogen-based flame retardants has the advantage that flame-retardant products can be obtained relatively easily, but once this flame-retardant material is combusted in a fire, halogenated hydrogen Because they generate extremely large amounts of smoke containing harmful gases such as, this can actually increase the danger to humans. Moreover, even if direct damage from the heat of the fire was avoided, serious drawbacks such as the corrosion of expensive equipment by the corrosive hydrogen halide generated could not be avoided. On the other hand, the latter method of making polyolefin flame retardant by adding inorganic substances does not have such a dangerous effect and is also an excellent method from the viewpoint of resource saving. However, since a large amount of inorganic powder is blended, foaming gas escapes significantly during foaming, making it difficult to produce a high-magnification foam, and a continuous sheet-like high-magnification foam of particularly good quality has not been realized. For example, examples 2 and 3 of the prior art are as follows. According to Japanese Patent Publication No. 51-37300, a method is proposed in which a foaming agent and a crosslinking agent are added to a composition consisting of a polyethylene resin and aluminum hydroxide, and the composition is heated and foamed. In this method, a composition prepared by adding 0.25 parts by weight of a crosslinking agent and 3.5 parts by weight of a blowing agent to a composition of 40 parts by weight of high-pressure polyethylene and 60 parts by weight of aluminum hydroxide is placed in a closed mold, and after heating. By releasing the mold all at once, a foam with a maximum expansion ratio of 17.5 times (density 0.134g/cm ³ ) is created.
This is what you are getting. For example, a large amount of inorganic powder is added to vinyl chloride resin and kneaded in a closed kneader, then a solvent in which liquefied butane or the like is dissolved is added and mixed, and then poured into a mold under closed pressure. A method of producing a foam having a specific gravity of 0.15 to 0.18 by carrying out two-stage heat foam molding is described in Japanese Patent Application Publication No. 49371/1983. Further, Japanese Patent Application Publication No. 48-85649 discloses that thermoplastic resin 10 containing ethylene-vinyl acetate copolymer
~50% by weight and 50~90% by weight of an inorganic filler containing calcium sulfite as an essential component, a crosslinking agent and a blowing agent are added, mixed uniformly and formed into a plate shape, which is then heated under pressure for 200% by weight. After heating for 10 min at °C.
It is described that a foam with an apparent specific gravity of 0.08 to 0.18 was obtained by rapidly removing the pressure. In this case, as in the above-mentioned known example, the foaming composition is filled into a closed container such as a mold, and in order to suppress free expansion, pressure is applied from the outside, and the crosslinking agent and foaming agent are decomposed in this state. Afterwards, the pressure is rapidly removed to obtain a foam. These methods all involve filling a mold with a foamable material and heating and foaming it under pressure, and it is difficult to obtain a foam with a high ratio of closed cells exceeding 20 times, and it is difficult to produce a long foam sheet. It was something that could not be manufactured. The present inventors investigated filling compositions of various thermoplastic resins, mainly olefin polymers, and inorganic powders, and found that ethylene-vinyl acetate copolymers exhibit poor tensile properties even when filled with a large amount of inorganic powders. It has been found that the polymer exhibits relatively little deterioration in mechanical properties and maintains moldability, making it an excellent polymer for use in highly-filled inorganic materials. It has also been found that when aluminum hydroxide powder is highly loaded, it exhibits significantly higher flame retardancy than polyethylene, polypropylene, etc. due to its synergistic effect with vinyl acetate groups. Therefore, the present inventors developed a flame-retardant foam that is inexpensive, contributes to resource saving, and has low smoke emission, by foaming an ethylene-vinyl acetate copolymer composition containing a high degree of inorganic powder. The present invention was achieved as a result of trying to realize the present invention. (Disclosure of the present invention) The present invention provides a foam having a significantly high expansion ratio made of a composition containing an extremely large amount of inorganic powder and the like, and a method for producing the same. First, the foam of the present invention is as follows. That is, a resin component consisting of an ethylene-vinyl acetate copolymer alone or a mixture with other thermoplastic resins.
It is a crosslinked foam made of a composition containing 50 to 500 parts by weight of inorganic powder per 100 parts by weight, and has an expansion ratio of 25 to 60 times. The foam of the present invention is a high-magnification foam containing a large amount of inorganic material. In many cases, the total amount of other additive components, mainly inorganic substances, is greater than the polymer component, so from the viewpoint of the components, it can be said to be an inorganic form. While it has the flexibility and processability of polymers, it also has the properties of inorganic materials. The portion occupied by the polymer is extremely small, in most cases less than 20g/(specific gravity 1
2vol% or less). The main features of the foam of the present invention are listed below. (1) Despite containing a large amount of inorganic powder, the foaming ratio (composition density/foam density ratio) is 40.
It is an extremely highly cross-linked foam that is more than twice as strong. (2) It is a continuous sheet-like foam with no length limit. (3) It has an extremely high Oxygen Index (usually 30 to 75) and does not exhibit any melt dripping phenomenon that can cause fire spread during forced combustion. (4) Extremely low smoke and heat generation during forced combustion. (5) Extremely high heat resistance as indicated by dimensional shrinkage rate during heating. Crosslinked polyethylene foam deforms to the extent that it does not lose its original shape at temperatures above 130°C, but this foam only exhibits shrinkage deformation of a few percent even at 150 to 180°C. In addition, the periphery of the foam that is hit by the flame during forced combustion does not undergo any abnormal deformation and retains its shape. As a supplement to item (4), it is noteworthy that although this foam is a flammable polymer, it has extremely high flame retardancy and low smoke emission. For this reason, JIS A1321-1975 standards for insulating iron plates made by bonding this foam with a thickness of about 4 mm to galvanized iron plates are required.
When conducting a flame retardancy test according to the surface test in Section 3 of "Flame retardancy test method for building interior materials and construction methods", the number of smoke systems per unit area ( C _A ) and the area (tde) of the portion surrounded by the exhaust temperature curve where the exhaust temperature curve exceeds the standard temperature curve and the standard temperature curve, which is an index of combustion heat, are C _A ≦30 and tde = It is ranked the highest in the same law in terms of smoke generation and heat generation. (That is, it satisfies the conditions that can be defined as class 1 flame retardancy) This is not possible with conventionally known polyolefin foams, and can only be achieved with the foam of the present invention. Regarding the oxygen index in item (3), JIS
According to D1201-1973 "Flammability Test Method for Organic Materials for Automotive Interiors", materials with an oxygen index exceeding 30 are classified as flame retardant class 1, which is the highest ranking category in this test. The foam of the present invention falls under this category. The method for producing the foam of the present invention by chemical crosslinking is as follows. That is, 100 parts by weight of a resin component consisting of an ethylene-vinyl acetate copolymer or a blend of the copolymer and a blendable thermoplastic resin, and an inorganic powder.
50 to 500 parts by weight, blowing agent 5 to 50 parts by weight, and crosslinking agent
A foamable composition containing 0.1 to 10 parts by weight is mixed with a crosslinking agent and foaming in a state where the water content in the composition is 0.15% by weight or less, more preferably 0.07% by weight or less, and even more preferably 0.05% by weight or less. This is a method for producing a highly inorganic material-filled, high-magnification foam, which is characterized by foaming by heating above the decomposition temperature of the agent. As a result of detailed studies on chemical crosslinking and foaming of ethylene-vinyl acetate copolymer compositions containing inorganic powder, the present inventors found that the foaming performance is greatly affected by the amount of water contained in the foamable composition. As a result, by controlling the water content, it has become possible to easily create foams with extremely high magnification. Therefore, in the present invention, it is most important to maintain the moisture content at a predetermined value. How the foaming performance changes greatly depending on the amount of water contained in the foamable composition will be explained in detail in Examples later, and a typical example thereof is shown in FIG. 1. Figure 1 shows the water content on the horizontal axis and the expansion ratio ρ ₀ /ρ of the foam (ρ: density of the foam, ρ ₀ : density of the foamable composition) on the vertical axis. This figure shows the relationship between the expansion ratio and the water content of a crosslinked foam made of a composition in which a large amount of aluminum hydroxide powder and, if necessary, a halogenated flame retardant, etc. are added. In the figure, curve A is the case of ethylene-vinyl acetate copolymer (EVATHLENE450P: manufactured by Dainippon Ink & Chemicals Co., Ltd.) alone, which has a high vinyl acetate content (61% by weight), and curve F has a low vinyl acetate content. (25%) This is the case of ethylene-vinyl acetate copolymer (EVAFLEX360: manufactured by Mitsui Polychemical Co., Ltd.) alone. In addition, curves B, C, D, and E in FIG. 1 show the above two types of copolymers 450P and EV360 having different vinyl acetate contents at a ratio of 80:20,
Mixing ratios of 60:40, 40:60 and 20:80 (parts by weight)
This is the case when they are combined respectively. As is obvious at first glance, the foaming ratio increases as the water content decreases. Below a certain value (hereinafter referred to as the limit moisture content), the foaming ratio exhibits a behavior that is almost constant regardless of the moisture content. In industrial production where a product of constant quality is required, the objective can be achieved by keeping the water content below the above-mentioned limit value. It is not always clear why the amount of water contained in a foamable composition affects the foaming performance of the foam. However, as a result of the inventors' measurements of the gel fraction and gel swelling degree of the foam, it was found that the presence of a trace amount of water caused a significant change in the gel swelling degree rather than the gel fraction. Judging from this, the water content is ethylene-
Molecular weight between crosslinks of vinyl acetate copolymer
This is thought to increase the weight between crosslinks. Further, the method for producing the foam of the present invention by the ionizing radiation crosslinking method is as follows. That is, a resin component consisting of an ethylene-vinyl acetate copolymer alone or a blend of the copolymer and a thermoplastic resin having a vinyl acetate content of 40 to 90% by weight.
100 parts by weight, 50 to 500 parts by weight of inorganic powder, blowing agent 5
Inorganic-containing ethylene, which is characterized in that the composition is kneaded with ~50 parts by weight and then molded, crosslinked by irradiation with ionizing radiation, and then heated to a temperature higher than the decomposition temperature of the blowing agent to foam the composition. A method for producing a foam made of vinyl acetate copolymer. The ethylene-vinyl acetate copolymer used in the present invention has a vinyl acetate content within a wide range of 5% to 90% by weight. Generally, those containing 5 to 40% by weight of vinyl acetate are crystalline, and those containing 40 to 90% by weight are completely amorphous. In either case, a wide range of molecular weights with a melt index of 0.1 to 300 can be used, but crystalline polymers have molecular weights of 0.5 to 10, and amorphous polymers have molecular weights of 10 to 300.
A range of 100 is preferred. In the present invention, it is preferable to use a polymer with a high vinyl acetate content, specifically a non-crystalline ethylene-vinyl acetate copolymer having 40 to 90% by weight of vinyl acetate groups; Particularly preferred are weight percent polymers. The reason is that when using such polymers,
This is because it is possible to obtain a foam with a particularly high expansion ratio, and because the limit water content is large, industrial production is facilitated. This can be understood by comparing curve A with a polymer with a high vinyl acetate content and curve F with a polymer with a low vinyl acetate content in FIG. In the present invention, not only the above-mentioned ethylene-vinyl acetate copolymer is used as the resin component, but also other blendable thermoplastic resins may be blended. In particular, when the ethylene-vinyl acetate copolymer is a non-crystalline polymer, it is preferable to blend it with a crystalline polymer. There is no particular limit to the blending ratio, but it is usually 20 to 80%. As the thermoplastic resin used at this time, all kinds of commercially available polymers can be used, but olefin-based polymers, especially ethylene-based polymers, are most preferred in terms of compatibility and processability. Polyethylene, ethylene-α-olefin copolymer, ethylene-propylene copolymer, vinyl acetate content 5~
30% ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate-vinyl chloride copolymer, etc. In the present invention, the best foam can be obtained by blending a crystalline ethylene-vinyl acetate copolymer or polyethylene with a vinyl acetate content of 5 to 30% and an amorphous ethylene-vinyl acetate copolymer. In the present invention, the inorganic powder is not particularly limited, but includes, for example, hydrated metal oxides such as aluminum hydroxide, magnesium hydroxide, and basic magnesium carbonate, metal oxides such as alumina and titania, calcium carbonate, and carbonate. Carbonates and bicarbonates such as magnesium, sodium bicarbonate,
Borate such as zinc borate, borax, barium borate,
These include phosphates such as calcium phosphate and potassium metaphosphate, silicates and silicic acids such as talc and clay, sulfates and sulfites such as gypsum, and residues such as blast furnace slag and red mud. Further, when it is desired to obtain a flame-retardant foam, a hydrated metal oxide is used, and the above-mentioned aluminum hydroxide, magnesium hydroxide, and basic magnesium carbonate are preferable. In particular, aluminum hydroxide is preferred because it exhibits a high degree of flame retardancy in a mixture with an ethylene-vinyl acetate copolymer. The particle size of the inorganic powder is usually in the range of 0.01 to 30 microns, preferably 0.05 to 10 microns, particularly 0.1 to 2 microns. If the particle size exceeds this upper limit, the extrusion-molded sheet will have rough skin and the expansion ratio will decrease. Moreover, if it is smaller than this lower limit, it will be difficult to reproduce a uniform dispersion state, and the expansion ratio will decrease. The amount of this inorganic powder added is 50 to 500 parts by weight, preferably 80 to 250 parts by weight, particularly preferably 100 to 200 parts by weight.
Parts by weight. The reason is that if the amount is less than the lower limit, the effect of adding the inorganic substance cannot be exhibited, and if it is more than the upper limit, it becomes difficult to achieve high foaming. In addition, the blowing agents to be blended in the method of the present invention include various organic and inorganic decomposition type blowing agents, and examples of the organic blowing agents include azodicarbonamide,
N,N'-dinitrosopentamethylenetetramine, P,P'-oxybisbenzenesulfonyl hydrazide, and the like. Examples of inorganic blowing agents include sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, and calcium azide. The reason for limiting the amount added to 5 to 50 parts by weight is 5.
If the amount is less than 50 parts by weight, it will not be possible to obtain a highly foamed product, and if it exceeds 50 parts by weight, it will not contribute to improving the expansion ratio and the efficiency will deteriorate significantly. Note that a so-called foaming aid may be added to adjust the decomposition temperature, etc. of the foaming agent. Furthermore, in the present invention, the ethylene-vinyl acetate copolymer must be crosslinked, and unless it has a crosslinked structure, high foaming cannot be achieved. Various chemical methods such as peroxide crosslinking, silane compound crosslinking, and azide compound crosslinking are commonly used as crosslinking methods, but in some cases, irradiation with ionizing radiation such as electron beams is used. It is also possible to use so-called radiation crosslinking. Most preferably, peroxides are used in the case of chemical crosslinking. For example, t-butyl perbenzoate, 1,1-di-(t-butyl peroxy)
-3.3.5-trimethylcyclohexane, 2.2-bis-(t-butylperoxy)butane, dicumyl peroxide, 2,5-bis(t-butylperoxy)-2.5-dimethylhexane, 1.4-bis(t-butylperoxy)-2.5-dimethylhexane,
-butylperoxy)diisopropylbenzene,
2.5-dimethyl-2.5-di-(t-butylperoxy)hexyne-3, etc. The amount of these additions is usually 0.1 to 10 phr preferably
It is 0.3~3phr. Further, for crosslinking with a silane compound, for example, vinyltrimethoxysilane, peroxide, and dibutyl tin dilaurylate are added in required amounts, kneaded and molded, and then exposed to a temperature atmosphere such as hot water for a predetermined period of time to effect crosslinking. Note that examples of the silane compound include vinyl-tris-(2-methoxyethoxysilane) and γ-methacryloxypropyltrimethoxysilane. Furthermore, in the present invention, a crosslinking accelerator can be added if necessary. The amount added is usually 0.05
~10 phr, preferably 0.1-2.0 phr. Examples of crosslinking promoters include polyfunctional compounds such as cyanurate compounds such as triaryl isocyanurate and triaryl cyanurate, monoacrylate and monomethacrylate compounds such as methoxydiethyl glycol methacrylate, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, and 1,6-hexane. Diacrylates and dimethacrylate compounds such as glycol diacrylate, 2,2-bis(4-acryloxydiethoxyphenyl)propane, triacrylates such as trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, tetramethylolmethane triacrylate; Trimethacrylate compounds, tetraacrylate compounds such as tetramethylolmethanetetraacrylate, polybutadiene compounds such as 1,2-polybutadiene, maleic acid esters such as divinyl maleate and dipropargyl maleate, aromatic compounds with unsaturated bonds such as divinylbenzene etc. Among these, trifunctional or tetrafunctional acrylates or methacrylates are preferred. Furthermore, since the present invention contains a large amount of inorganic substance, a surface treatment agent such as a silane type surface treatment agent or a titanate type surface treatment agent may be used to improve the compatibility between the inorganic substance and the resin, which is particularly preferred. Those are isopropyl triisostearoyl titanate, isopropyl trioctanoyl titanate,
These are monoalkoxy titanate compounds such as isopropyl distearoyl methacrylic titanate and isopropyl diisostearoyl acrylic titanate. Use of these surface treatment agents facilitates the kneading and molding work of the mixture and improves the foaming rate. In addition, the method of the present invention may optionally include halogen flame retardants such as decabromodiphenyl oxide (the amount added is usually 5 to 3 phr) and flame retardant aids such as antimony trioxide (the amount added is usually 2 to 20 phr). ), antioxidants, copper inhibitors, antistatic agents, colorants, pigments, lubricants, and other processing aids may be added. In the present invention, when it is desired to obtain a foam with particularly excellent flame retardancy, hydrated metal oxides such as aluminum hydroxide, magnesium hydroxide, and basic calcium carbonate are used as inorganic substances, and so-called halogen-based retardants are used. Use with fuel. In this case, hydrates such as aluminum hydroxide not only improve flame retardancy, but also play a major role in reducing smoke generation, which has significantly increased due to the addition of halogen flame retardants.
A flame retardant foam with low smoke emission will be obtained.
As an example, FIG. 2 shows JIB D for a foam with a foaming ratio of about 40 times obtained by the method of the present invention
1201-1973 "Flammability test method for organic materials used in automobile interiors", the flame retardancy expressed by the oxygen index and the smoke emitting property expressed by the maximum extinction coefficient (C _S max) were determined. It is illustrated in relation to the amount of aluminum hydroxide added. The effect of adding aluminum hydroxide is large on both OI and C _S ·max, and in particular C _S ·max, which is an index of smoke generation, shows that it decreases exponentially. Foams that have contradictory properties, such as high flame retardancy and low smoke generation, are desired as thermal insulation materials for buildings and the like. JIS A1321 mentioned above
Tests based on the 1975 ``Flame Retardant Test Methods for Building Interior Materials and Construction Methods'' evaluate exactly this kind of performance. In this case, it is particularly preferable to use the following halogen flame retardants. That is, it has a bromine content of 40 to 80% by weight and has two or more repeating units in its chemical structural formula. For example, bisphenol A tetrabromo, bisphenol A epichlorohydrin glycidyl etherified condensate, tetrabromo bisphenol A diglycidyl ether and brominated bisphenol adduct, poly-4,4-isopropylidene bis(2,6-dibromophenyl) carbonate It is. Specific products of these flame retardants include, for example, Matsunaga Chemical Co., Ltd. product EBR-700 (brome content: approximately 52% by weight), Teijin Chemicals Co., Ltd. product, FIREGUARD 7000 series (brome content: approximately 50% by weight). , Hitachi Chemical Co., Ltd. product HR-128F
(bromine content approximately 50% by weight). In the present invention, the method using chemical crosslinking will be further explained. In this case, the above-mentioned resin component, inorganic powder,
A method of kneading and molding a compound containing a blowing agent, a crosslinking agent, and, if necessary, the various additives mentioned above, to create a foamable composition molded body, and heating this to obtain a crosslinked foam. In this process, it is essential to control the amount of water contained in the foamable composition molded article immediately before being subjected to crosslinking and foaming. As mentioned above, since the water content affects the crosslinking of the polymer, the amount of water at the stage immediately before crosslinking is a problem. That is, if the crosslinking step and the foaming step are separated, it is necessary to control the water content immediately before the crosslinking step, or if the crosslinking and foaming are simultaneous or the same step, the moisture content immediately before the crosslinking step and the foaming step must be controlled. This method may be applied at any stage: at the stage of the raw material containing the ethylene-vinyl acetate copolymer, at the stage of forming the foamable composition into pellets after kneading, or at the stage of forming the foamable composition into a molded article after molding. There are various methods of dehumidification treatment. For example, a method in which a desiccant such as silica gel is placed in a resin or composition container or sealed packaging, a method in which raw materials or composition pellets or molded bodies containing a resin are heated and dried using hot air or (far) infrared radiation, and a method in which a desiccant such as silica gel is placed in a container or sealed package for the resin or the composition, a method in which a resin-containing raw material or a composition pellet or molded product is heated and dried using hot air or (far) infrared radiation, How to process. Methods include using a hopper dryer or vacuum hopper during the extrusion molding process, or dehumidifying while molding with a vented screw. These methods may not be used alone, but two or more methods may be used in combination. By the above means, the water content in the foamable composition molded article immediately before the crosslinking process is adjusted to 0.15% by weight or less, preferably 0.07% by weight or less, and more preferably 0.05% by weight or less based on the composition. Here, the measurement and definition of the water content in the molded article are as follows. After measuring the weight (Wo) of a small piece (30 x 30 mm) of a foamable composition sheet (thickness: 2-3 mm), it was placed in a desiccator (temperature 30 °C) containing a silica gel desiccant.
When measuring the weight (W ₁ ) after being put in for 10 days: Water content = Wo-W ₁ /W ₁ ×100 (% by weight) The water content is defined in this way. An example of the results of tracking changes in the weight of the small pieces over time during this period is shown in FIG. Intermittent slight weight loss is observed, but 7~
We found that it reached a constant weight in 10 days, so
The moisture content was defined as above. Note that the presence of water in polymers containing inorganic fillers and other additives is not unique; water is dissolved in the polymer, adsorbed to the surface of the filler, and attached to the surface. It is a collection of extremely complex states, such as those that exist. On the other hand, in the present invention, since crosslinking mainly involves heat treatment, some water quickly scatters in the initial stage of heating and does not participate in crosslinking at all. Therefore, the water content itself is not the problem;
The problem is the amount of water that can affect crosslinking. The water content determined by the above measurement method has an extremely good correlation with the foaming performance, as shown in the examples, and is therefore considered to be a water content that directly affects crosslinking. In the present invention, it is preferable to use a method of heat-treating the foamable composition molded article (often in the form of an extrusion-molded sheet) as the dehumidification treatment means. That is, the foaming ratio is improved by heat-treating the molded article at a temperature of 80 to 140° C. for 1 to 30 minutes before the crosslinking and foaming step. In this case, it is of course preferable to use means for dehumidifying the resin-containing raw material or composition (usually composition pellets). The method of the present invention is particularly effective when crosslinking and foaming are carried out under normal pressure. What is normal pressure crosslinking foaming?
Using a hot air heating furnace, infrared heating furnace, or molten salt heating furnace, the foamable composition molded product is heated to a temperature equal to or higher than the decomposition temperature of the blowing agent under conditions approximately equal to atmospheric pressure without adding any special pressurizing conditions. This method is suitable for producing a long continuous foam sheet, which is a method of obtaining a crosslinked foam by heating. When a foamable composition molded article having the composition of the present invention is heated under normal pressure to, for example, 200°C or higher, crosslinking occurs first and foaming and expansion follows due to the difference in decomposition temperature between the crosslinking agent and the blowing agent. However, in reality, the process will proceed in a semi-competitive manner. Therefore, when a polymer filled with a large amount of inorganic powder is used as in the present invention, and the crosslinking is affected by impurities such as trace amounts of water, a slight change in the crosslinking structure has a large effect on the formation of bubbles, and the resulting It is thought that this will affect the properties of the foam. Next, in the method of crosslinking using ionizing radiation according to the present invention, special points to be noted will be explained. In the case of this method, it is essential that the resin component has as its main component a non-crystalline ethylene-vinyl acetate copolymer having a vinyl acetate content of 40 to 90% by weight. When blending thermoplastic resins, polyethylene, crystalline ethylene-vinyl acetate copolymer with a vinyl acetate content of 5 to 30% by weight, ethylene-vinyl acetate-vinyl chloride copolymer, ethylene-ethyl acrylate It is preferable to blend 50% by weight or less of an ethylene polymer such as a copolymer. Furthermore, when using this method, it is preferable to add 1 to 5 parts by weight of carboxylic acid metal salts (salts of carboxylic acids such as stearic acid, capric acid, caproic acid, lauric acid, and acetic acid with zinc, lead, and aluminum). . Usually, these are added as lubricants of about 1phr, but in the case of the present invention, they are not only used as lubricants, but also as necessary to improve the foaming ratio and to obtain highly foamed products, as shown in the examples. This shows the effect of reducing the optimal irradiation dose.
For this purpose, it is preferable to add about 2 to 4 phr, and zinc stearate and lead stearate are particularly suitable. Next, a specific example of the manufacturing process of the foam of the present invention will be described. The polymer, inorganic powder, blowing agent, flame retardant and flame retardant aid if necessary, and other necessary additives are measured and kneaded. Banbury mixer, kneader mixer or two roll mill,
In some cases, a twin screw extruder is used. Usually, after kneading, the pellets are formed into a sheet using an extruder, but in some cases, the pellets are directly extruded into a sheet from a twin-screw extruder or the like to form a molded product. In the case of chemical crosslinking, one or more of the following dehumidification treatments are performed: dehumidification of raw materials containing polymers, dehumidification of kneaded pellets, dehumidification during extrusion molding, and dehumidification of extruded products. . In addition, in the case of crosslinking with ionizing radiation, dehumidification treatment is not necessary, and the extrusion molded sheet has a
Crosslinking can be carried out simply by irradiating with a 5 Mrad electron beam. Next, it is introduced into a heating device for foaming, such as a hot air oven, an infrared heating furnace, or a molten salt bath, to obtain a continuous foam sheet. Although it varies depending on the size of the device, it is usually a sheet-like foam with a thickness of 2 to 20 mm and a width of 1000 to 1500 mm. In addition, when heat treatment is performed as a dehumidification treatment means, it is preferable to place a device for heat treatment immediately before the foaming device. As mentioned above, in the method of the present invention, dehumidification treatment is required when using the chemical crosslinking method, whereas such treatment is not required when using the radiation crosslinking method.
In the radiation crosslinking method, in order to obtain the foam of the present invention, an expensive irradiation device is required, a thick foam cannot be obtained, and the expansion ratio is somewhat low. On the other hand, when the foam of the present invention is obtained using a chemical crosslinking method, a foam with a higher magnification and a thicker wall can be obtained. Therefore,
Which crosslinking method to employ in the method of the present invention may be determined by considering various conditions. The foam of the present invention can be used for various purposes by taking advantage of its characteristics. Formed into a pipe shape and used as a pipe cover for heat insulation, sheet shaped as a packaging material, packing material, etc.
Not only can it be used as cushioning material, clothing material, floating floor material, etc., but also construction material, which has strict legal regulations regarding flame retardancy and smoke emitting properties due to its low smoke and flame retardant characteristics. It is used for automobile materials, railway vehicle materials, ships and aircraft materials, etc. It is also used in a composite state with a metal plate such as an iron plate, a metal foil, or an inorganic material in the form of a fiber, plate, or film. Next, examples of the present invention and comparative examples will be shown. (The following parts and % are all parts by weight and % by weight.) Examples 1 to 6, Comparative Examples 1 to 6 Ethylene-vinyl acetate copolymer with a vinyl acetate content of 25% (Mitsui Polychemical Co., Ltd. Company products:
EVAFLEX360) and an ethylene-vinyl acetate copolymer with a vinyl acetate content of 61% (Dainippon Ink & Chemicals Co., Ltd. product: EVATHLENE450-P) in various ratios shown in Table 1. 100 parts of aluminum hydroxide powder (Showa Denko Co., Ltd. product: Hygilite H-42M), blowing agent azodicarbonamide (Eiwa Kasei Co., Ltd. product:
Viniphor AC#1L) 25 parts, crosslinking agent dicumyl peroxide (Mitsui Petrochemical Co., Ltd. product) and polyfunctional monomer trimethylolpropane triacrylate (Shin Nakamura Chemical Co., Ltd. product: A
-AMPT) in the amounts shown in Table 1, and titanate coupling agent (Ken
Rich Petrochemical product: KEN-REACT
TTS) 3 parts and calcium stearate (reagent)
1 part of the mixture was sufficiently kneaded in a Brabender Plastograph at a temperature of 120°C to obtain a foamable composition, which was then molded in a hot press at a temperature of 120°C to form a foam with a thickness of 2 mm. It was made into a sex sheet. A small piece of 50 x 50 mm was cut out from this and used for subsequent foaming experiments. The foaming experiment was conducted as follows. For the example numbered in Table 1, the foamable sheet pieces were placed in a large desiccator using silica gel as a desiccant for 3 days to dehumidify them, and then heated for 6 minutes in a hot air constant temperature bath heated to 220°C. It foamed. (At this time, sticking can be prevented by placing the fine mesh wire mesh on the bottom.) On the other hand, in the comparative example numbered in Table 1, the foam sheet pieces were left indoors for 3 days and then exposed to the same conditions. It is foamed. The amount of water contained in the foamable sheet was measured by the method described above. Table 1 lists the main components of the composition as well as the water content and density of the foam obtained. Regardless of the blend ratio of ethylene-vinyl acetate copolymers with different vinyl acetate contents, examples in which the water content was reduced by dehumidification treatment resulted in significantly higher foaming, but in comparative examples without dehumidification treatment. Foaming degree is extremely low. In addition, Example 5 is a case where the amount of aluminum hydroxide powder added is 150 phr, and Example 6 is a case where the amount of aluminum hydroxide powder added is 150 phr.
In the case of 70 phr, the foaming was significantly increased in both cases. In all comparative examples that were not subjected to dehumidification treatment, the foaming ratio remained at several times.

[Table] Example 7-9, Comparative Example 7-9 This example is an example in which the type of filler was changed. 100 parts of filler per 100 parts of ethylene-vinyl acetate copolymer with 61% vinyl acetate content blowing agent
23 parts of ADCA, 2 parts of crosslinking agent DCP, and trimethylolpropane-triacrylate as a polyfunctional monomer (Shin Nakamura Chemical Co., Ltd. product: A-AMPT)
Compositions comprising a proportion of 0.5 part were tested as in Examples 1 to 6 above. The composition and results are summarized in Table 2. It can be seen that all fillers of aluminum hydroxide, calcium carbonate, and magnesium hydroxide foam to a remarkable degree when subjected to dehumidification treatment.

[Table] Example 10, Comparative Example 10 This example is an illustration showing that the influence of the water content in a foamable sheet on foaming differs depending on the type of ethylene-vinyl acetate copolymer. Ethylene-vinyl acetate copolymer with 61% vinyl acetate content (product of Dainippon Ink & Chemicals Co., Ltd.:
Aluminum hydroxide was added to 100 parts of the resin component with various blend ratios of Evathrene 450-P) and ethylene-vinyl acetate copolymer with a vinyl acetate content of 25% (Mitsui Polychemical Co., Ltd. product: Evaflex 360). 100 parts of powder (product of Showa Denko Co., Ltd.: Hygilite H-42M), titanate coupling agent (product of Kenrich Petrochemi-cal Co., Ltd.:
KEN-REACT TTS) 3 parts, azodicarbonamide (Eiwa Kasei Co., Ltd. product: Vinihole AC
#IL) 25 parts, flame retardant decabromodiphenyl ether (Toyo Soda Co., Ltd. product: EB-
10FP) 25 parts, antimony trioxide (Nippon Seiko Co., Ltd. product) 12.5 parts, crosslinking agent dicumyl peroxide (Mitsui Petrochemical Co., Ltd. product), and polyfunctional monomer trimethylolpropane triacrylate (Shin Nakamura Chemical Co., Ltd.) Product: A-
A foamed sheet having a thickness of 2 mm was obtained by kneading and molding a predetermined amount of TMPT) and 1 part of calcium steering acid in the same manner as in the above example. (In addition
The amounts of DCP and A-TMPT added are the optimum amounts for each polymer composition found in previous experiments, and the amounts (parts by weight) of DCP and A-TMPT are the same as curves A, B, C, D, E
and F polymer compositions are 2.0/0.7 and 1.7/
They were 0.7, 1.5/0.5, 1.3/0.5, 1.0/0.7 and 0.7/0.7. ) This foamable sheet was stabilized for 3 days under constant temperature and humidity conditions of 30°C and 80% relative humidity, then dehumidified and heated for 6 minutes in a 220°C hot air constant temperature bath to form foam. did. The dehumidification treatment was performed by storing the sample at a temperature of 30° C. in a desiccator containing a silica gel desiccant for a predetermined period of time within 10 days. The water content in the foamable sheet was measured by the method described above. These results are plotted as a relationship between the moisture content in the foamable sheet and the expansion ratio, and are shown in FIG. FIG. 4 is an enlarged view of a region with a low water content. From these figures, it can be seen that in order to obtain a foam with a high magnification, it is necessary to reduce the water content in the foamable sheet. Furthermore, it is also shown that when the water content falls below a certain value, the expansion ratio becomes almost constant. For example, in Figure 4, the vinyl acetate content
In the case of curve F in which the resin component is 25% ethylene-vinyl acetate copolymer, the expansion ratio stabilizes at about 30 times when the water content is about 0.03% or less. On the other hand, curve A with vinyl acetate content of 61% has a water content of 0.07.
% or less, the foaming ratio is almost stabilized at 35 times.
In the case of a blend of both polymers, an intermediate value is taken depending on the blend ratio. This example shows the following points. (1) The higher the vinyl acetate content of the ethylene-vinyl acetate copolymer that is the resin component, the higher the expansion ratio will be, even if the water content is high, and the expansion ratio itself will also be higher. (2) When the moisture content falls below a certain limit, the foaming ratio will be constant regardless of the moisture content.
This "limit water content" is larger as the polymer has a higher vinyl acetate content. (3) In the case of a blend of polymers with different vinyl acetate contents, the total amount of vinyl acetate serves as a guideline for determining the limit moisture content. Example 11 This example is an example in which a foamable composition molded sheet was dehumidified by vacuum treatment. 60 parts of ethylene-vinyl acetate copolymer with 61% vinyl acetate content (same as Example 10), 40 parts of ethylene-vinyl acetate copolymer with 25% vinyl acetate content (same as Example 10), hydroxide 90 parts of aluminum powder (same as Example 10), flame retardant decabromodiphenyl ether (Toyo Soda Co., Ltd. product:
(abbreviated as DBDE) 25 parts, antimony trioxide powder (same as Example 10) 12.5 parts, blowing agent azodicarbonamide (above) 25 parts, crosslinking agent DCP (above) 1.5 parts,
A composition consisting of 3 parts of titanate coupling agent (mentioned above), 1 part of polyfunctional monomer A-TMPT (mentioned above) and 1 part of calcium stearate (mentioned above) was mixed in a large kneader with an internal capacity of 120. The mixture was kneaded at a temperature of 0.degree. C. or below, and after stripping with a two-roll mill, pelletization was performed to obtain foamable composition pellets. The pellets are fed into the hopper of a 65mm/mm extruder and extruded from the attached T-die to give a width
A foamable composition sheet having a size of 250 mm and a thickness of 2.3 mm was prepared. Approximately 100 m of this sheet was rolled up, placed in a large vacuum heating furnace, and evacuated at room temperature for one day and night. (At this time, the pressure inside the vacuum furnace was 3 Torr or less.) Next, the vacuum treated sheet was taken out and immediately foamed. That is, the sheets were sequentially fed out onto the conveyor belt of a hot-air heating type foaming device equipped with a built-in wire mesh conveyor, guided into the furnace, and foamed in the furnace.The foam was then continuously taken out from the outlet, cooled, and then rolled up. . At this time, the temperature of the foaming device could be controlled by dividing it into three zones, ranging from 140 to 190 to 250°C from the inlet side, and the conveyor speed was 1.5 m/min. The obtained foam sheet had a width of about 800 mm and a thickness of 8 mm, was composed of uniform fine cells, and had a foaming ratio of 34 times (specific gravity 0.045). The moisture content in the sheet after vacuum treatment was 0.041%. Examples 12 to 13, Comparative Examples 11 to 12 These examples are examples in which a dehumidification process is performed on raw materials in order to control the amount of water contained in a foamable composition molded article. Ethylene-vinyl acetate copolymer with 69% vinyl acetate content (product of Dainippon Ink & Chemicals Co., Ltd.:
Evathren 350-P) 60 parts, low density polyethylene (Mitsubishi Yuka Co., Ltd. product: Yucalon YF-30) 40
parts, aluminum hydroxide powder (Showa Denko K.K. product: Hygilite H-32) 100 parts, flame retardant 20 parts
parts, antimony trioxide (as above) 8 parts, crosslinking agent
2 parts by weight of DCP (mentioned above), crosslinking aid A-TMPT
A composition consisting of 0.5 parts of the foaming agent ADCA (mentioned above), 23 parts of the blowing agent ADCA (mentioned above), and 1 part of zinc stearate was kneaded and molded to obtain a sheet with a thickness of 3 mm. At this time, comparative example 12
In this case, aluminum hydroxide powder was dried in a hot air constant temperature bath at 120°C for 1 hour prior to kneading. In Example 12, only the ethylene-vinyl acetate copolymer dried at 110°C for 1 hour was used. Furthermore, in Example 13, both were dried. On the other hand, in Comparative Example 11, no special dehumidification treatment was performed. Immediately place the above sheet in a hot air constant temperature oven at 220℃ for 5 minutes.
The mixture was heated for a minute to cause foaming. The density etc. of the obtained foam are also listed in Table 3. Both the polymer and the filler that are not dried and the filler that is not dried have a low expansion ratio, whereas the polymer that is dried and the polymer and the filler that are both dried have a high expansion ratio. ing. In other words, it teaches that when dehumidifying raw materials, it is necessary to dehumidify at least the polymer.

[Table] Example 14 The foamable composition prepared in Example 11 was press-molded to form a sheet with a thickness of 3 mm. After keeping it under constant temperature and humidity at a relative temperature of 83% and a temperature of 30℃ for 3 days, it was placed in a hot air constant temperature bath heated to 120℃ and heat treated for a predetermined time (0 to 30 minutes). Heating for crosslinking and foaming was applied at 220°C for 5 minutes in a hot air constant temperature bath. The results are summarized in Table 4. It has been shown that by applying the above heat treatment to a molded sheet, the amount of water contained in the sheet is reduced and the expansion ratio is significantly improved.

[Table] Example 15 60 parts of ethylene-vinyl acetate copolymer with 61% vinyl acetate content, 40 parts of crystalline ethylene-vinyl acetate copolymer with 25% vinyl acetate content, 100 parts of aluminum hydroxide powder, titanate 3 parts of coupling agent, 23 parts of blowing agent ADCA, 20 parts of bromine flame retardant (Teijin Kasei Co., Ltd. product: FIRE GUARD7100),
The foamability of a composition prepared by adding polyfunctional monomers of the type shown in Table 5 to 8 parts of antimony trioxide, 2 parts of crosslinking agent DCP, and 1 part of zinc stearate was evaluated for foamability. Note that the foamable composition sheet was placed in a desiccator containing a silica gel desiccant for 3 days, dehumidified, and then foamed. As is clear from Table 5, trifunctional or tetrafunctional acrylic ester compounds provide foams with particularly high expansion ratios.

【table】

[Table] Examples 16-21 Vinyl acetate-ethylene copolymer with vinyl acid content 61%, density 1.05 g/cm ³ and melt index 30-50 (Dainippon Ink Co., Ltd. product Evasurene 450)
P) 100 parts, aluminum hydroxide fine powder (Showa Denko Co., Ltd. product, Hygilite H-42M) 100
25 to 30 parts of azodicarbonamide blowing agent (Vinihole AC#IL, product of Eiwa Kasei Co., Ltd.), isopropyl-tri(isostearoyl) titanate (Kenrich, USA) as a surface treatment agent.
Petrochemical product, KEN-REACT TTS) 3
1.5 parts of dicumyl peroxide (Mitsui Petrochemical Co., Ltd.) as a crosslinking agent, 0.7 parts of trimethylolpropane triacrylate (product of Shin-Nakamura Chemical Co., Ltd.) as a crosslinking aid, bromine-based flame retardant (product of Matsunaga Chemical Co., Ltd.) EBR-700) or DBDE
A composition consisting of 25 parts (product of Nippo Chemical Co., Ltd.), 12 parts of antimony trioxide as a flame retardant aid, and 1 part of calcium stearate was thoroughly kneaded at a temperature of 110°C in a small experimental Banbury mixer. It was made into pellets. Next, it was molded into a 2 mm thick sheet using a 40 mm extruder. This sheet was heat-treated in a hot air constant temperature bath at 120°C for 20 minutes, then placed in a constant air bath at 220°C for 6 minutes, and when taken out, a highly foamed sheet was obtained. Table 6 summarizes the values of the foam density, magnification, amount of polymer per unit volume, etc. Examples 16-18 are about flame retardant DBDE
Example when varying ADCA between 25 and 30 parts
19-21 are similar results for another flame retardant (EBR-700). All of them were highly foamed products with a foaming rate of 34 to 42 times, and although the amount of polymer was extremely small at 14 to 18 g/, the flame retardants of Examples 19 to 21 were more foamed than the DBDE type. Examples 22-23 Examples 22 and 23 in Table 6 have similar results when the aluminum hydroxide powder is increased to 120 parts. In this case, the obtained foam was sliced into approximately 4 mm thick pieces using a slicer to obtain a sample having an epidermis on only one side. Next, this foam specimen was
Cut into a size of 22cm x 22cm and the thickness of the same size.
It was heated and bonded to a 0.4 mm galvanized iron plate. The thus obtained sample piece was subjected to a surface test according to the method specified in JISA-1321-1975, and the time-temperature area (tdθ), which is an index of the calorific value during combustion, and the smoke generation coefficient (C _A ), which is an index of the amount of smoke produced, were determined. was measured. The results are shown in the lower part of Table 6. Note that the density and thickness of the foam are also listed in the table. In both Examples 22 and 23, tdθ=0, C _A <30
This shows that it is an excellent foam with low heat generation and smoke generation. Furthermore, since Example 22 shows similar performance even though the sample thickness is considerably thicker than Example 23, the flame retardant of Example 22 is superior to DBDE. It can be said that

[Table] Examples 24 to 28, Comparative Examples 13 to 15 The various compositions shown in Table 7 were applied to BRABENDER PLA.
After kneading using STOGRAPH and forming a sheet using a hot press, the mixture was placed in a desiccator containing a silica gel desiccant for 3 days to dehumidify. A hot air constant temperature bath was used for foaming, and heating was applied at 220°C for 6 minutes to obtain a foam. Table 7 shows the density, magnification, and amount of polymer per unit volume of the obtained foam, as well as the JIS D1201
1973 “Flammability test method for organic materials for automobile interiors”
The results of the oxygen index (OI) and maximum extinction coefficient ( _CS.max ), which were conducted according to the above, are also shown. Examples 24 to 28 are included in the foam of the present invention, and have low smoke generation properties, and the amount of polymer in the foam is 20 g/or less. OI and _CS . The change in max depending on the amount of filler is illustrated in Figure 2. In particular, when 50 parts or more is added, smoke generation tends to be significantly reduced.

[Table] Examples 29 to 34 Comparison of ethylene-vinyl acetate copolymer (described above) with a vinyl acetate content of 61% and crystalline ethylene-vinyl acetate copolymer (described above) with a vinyl acetate content of 25% Aluminum hydroxide powder (Showa Denko K.K. product: Hygilite H-42M) is added to 100 parts of resin components with blend ratios of 100/0, 80/20, and 60/40.
100 parts, foaming agent ADCA (listed above) 23 parts, flame retardant
DBDE (supra) 20 parts Antimony trioxide (supra) 8
and titanate coupling agents (mentioned above:
Add 3 parts of TTS) and knead it uniformly using a Brabender Plastograph, and mold it using a heat press to a thickness of 1.
A sheet of mm was created. Next, after being subjected to electron beam irradiation treatment at 1 to 4 Mrad using an electron beam irradiation device, a foam was obtained by heating at 200° C. for 15 minutes in a hot air constant temperature bath. The results are shown in runs 29-31 of Table 8. Further, Examples 32 to 34 show similar results for the above compositions in which 1 part of zinc steering acid (reagent) was added. A comparison of Examples 29 to 31 shows that the expansion ratio decreases as the blend ratio of crystalline EVA increases. However, as in Examples 32 to 34, it can be seen that when zinc stearate is added, the expansion ratio is significantly improved in all compositions, and the effect is particularly shown when the blend ratio of crystalline EVA is large.
Furthermore, it can be seen that the addition of zinc stearate shifts the irradiation dose that gives the highest expansion ratio to a lower dose.

[Table] Examples 35 to 39 The resin components were 70 parts of ethylene-vinyl acetate copolymer (same as Example 29) and ethylene-vinyl acetate-vinyl chloride terpolymer (Nippon Zeon Co., Ltd. product: Graftomer-GR) -5) The same composition as in Examples 29 to 31 except that the composition consisted of 30 parts was used, and the same composition containing a predetermined amount of various stearates was irradiated and foamed in the same manner. The results are also listed in Table 9 along with the main components of the composition. Example 36, in which 1 to 3 times more stearate was added compared to Example 35, which did not contain stearate metal salt.
~39, the foaming ratio has been significantly improved, and the optimum irradiation dose has fallen to around 2 Mrad, making it extremely efficient. The effects of zinc stearate and lead stearate are particularly pronounced.

【table】

[Table] Example 40 Commercially available vinyl acetate-ethylene copolymer (SOarlex CN manufactured by Nippon Gosei Kagaku Co., Ltd., vinyl acetate content 60%, melt index 50-100, density
1.05g/cm ³ ) 100 parts by weight of finely ground calcium carbonate powder (Nitto Funka Co., Ltd. product NS#1000, density 2.7)
g/cm ³ , average particle size 0.4μ) 150 parts, azodicarbonamide (Eiwa Kasei Co., Ltd. product, VAC#1L) 30
1 part and 3 parts of dicumyl peroxide (Nippon Oil & Fats Co., Ltd. product, Permil-D),
This was heated to 120℃ in a small Banbury mixer for 5 minutes.
Kneaded for a minute. A part of this was heat pressed to a thickness of 3 mm.
It was then molded into a sheet and then held at 160°C for 10 minutes in a hot press to decompose dicumyl peroxide and crosslink it. After taking out this foam sheet and cooling it, it was placed in a hot air constant temperature bath set at 200℃.
When heated for 15 minutes, it foamed significantly and the density decreased.
A foam of 0.045 g/cm ³ was obtained. When this foam was observed using a scanning electron microscope, the cells were extremely fine and had a closed cell structure. A small piece of this foam was pressed into a bubble-free sheet using a hot press, and its density was measured to be 1.64 g/cm ² . Therefore, the foamed material was expanded 36.6 times. 10 in hot toluene at 90°C.
After the time extraction process, the extraction residue was taken out, air-dried and vacuum-dried, weighed, completely burned, the content of inorganic substances was calculated, and the gel fraction was determined by a correction method. It was 76%. Furthermore, when the heating dimensional change rate of this foam was measured using the method according to JIS6767, it was found that at 180℃
% shrinkage and exhibited extremely good heat resistance. Moreover, the amount of polymer in this foam was 16.6g/. Example 41 Aluminum hydroxide (Showa Denko K.K. product, Higilite H-42M, density 2.42) was added to 100 parts of the same vinyl acetate-ethylene copolymer as in Example 1.
g/cm ³ , average particle size 1 μ) was added, and a blowing agent and a crosslinking agent were added in the same manner as in Example 1. When molded and foamed, the density was 0.040 g/cm 3 .
A foam with a foam size of ³⁸ parts and a foaming ratio of 38 parts was obtained. Further, when the heating dimensional change rate of this foam was measured in the same manner as in Example 40, it shrank by 3% at 160°C. Furthermore, slice this foam into 4mm thick pieces.
Cut into 22mm x 22mm size and the same shape with a thickness of 0.4mm
Heat laminated to galvanized iron plate, JIS A1321-1975
When a combustion test was conducted using the method shown below, it met the requirements for flame retardant class 1 (i.e., tdθ=0C _A ≦30). The amount of polymer in this foam was 15.1g/. Examples 42 to 44 The compositions shown in Table 10 using ethylene-vinyl acetate copolymers with different vinyl acetate contents as resin components were made into foams in the same manner as Examples 24 to 28, and the flame-retardant and smoke-emitting properties were was evaluated. The results are shown in Table 10. In all compositions, OI showed high flame retardancy of 28 or more, while C _S max was all 2 or less, showing extremely low smoke generation.

【table】

[Table] Sium

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the water content in a foamable composition molded article (horizontal axis) and the expansion ratio (ρ ₀ /ρ) (vertical axis) of a foam obtained therefrom. Figure 2 shows the oxygen index of the foam.
This is a graph in which the maximum light attenuation coefficient ( _CS.max ), which is an index of the amount of smoke generated, is plotted against the amount of aluminum hydroxide added (horizontal axis). FIG. 3 is a graph showing the relationship between the number of days elapsed and the amount of moisture removed when a foamable composition sheet is dehumidified in a desiccator using a silica gel desiccant. FIG. 4 is a graph showing an enlarged view of the region of FIG. 1 with a low water content.

Claims (1)

[Claims] 1. A resin component consisting of an ethylene-vinyl acetate copolymer alone or in a mixture with other thermoplastic resins.
A foam with a high expansion ratio and high inorganic filling of 25 to 60 times, which is made of a composition containing 100 parts by weight of an inorganic powder and 50 to 500 parts by weight of an inorganic powder. 2. The foam according to claim 1, wherein the ethylene-vinyl acetate copolymer has a vinyl acetate content of 40 to 90% by weight. 3 Thermoplastic resin is polyethylene, ethylene-α
-Olefin copolymer, vinyl acetate content 5-30
% by weight of one or more ethylene-based polymers from the group consisting of ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-propylene copolymer, and ethylene-vinyl acetate-vinyl chloride copolymer. A foam according to claim 1, characterized in that: 4. The foam according to claim 1, wherein the composition further contains 5 to 30 phr of a flame retardant and 2 to 20 phr of a flame retardant aid. 5. The foam according to claim 4, wherein the flame retardant has a bromine content of 40 to 80% by weight and has two or more repeating units in its chemical structural formula. 6 The inorganic powder is aluminum hydroxide powder and/or
or magnesium hydroxide powder, the foam according to claim 1. 7 The content of the resin component per unit volume of the foam is
The foam according to claim 1, characterized in that the amount is 20 g/or less. 8. The foam according to claim 1, wherein the surface of the inorganic powder is surface-treated with a monoalkoxyorganotitanate compound. 9. Resin component 100 consisting of an ethylene-vinyl acetate copolymer or a blend of the copolymer and one or more thermoplastic resins that can be blended with the copolymer.
parts by weight, inorganic powder 50-500 parts by weight, blowing agent 5-500 parts by weight
A foamable composition containing 50 parts by weight and 0.1 to 10 parts by weight of a crosslinking agent is crosslinked and foamed by heating in a state where the water content contained in the foamable composition is 0.15% by weight or less. A method for producing a high expansion ratio foam with high inorganic substance filling. 10. The method for producing a foam according to claim 9, wherein the water content is 0.07% by weight or less. 11. The method for producing a foam according to claim 9, wherein the foamable composition contains 0.1 to 10 parts by weight of a polyfunctional monomer as a crosslinking aid. 12. The method for producing a foam according to claim 9, wherein the ethylene-vinyl acetate copolymer is an ethylene-vinyl acetate copolymer having a vinyl acetate content in the range of 40 to 90% by weight. . 13 The thermoplastic resin is polyethylene, ethylene-α-olefin copolymer, vinyl acetate content 5
~30% by weight of ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-propylene copolymer, ethylene-vinyl acetate-
One or two of the group consisting of vinyl chloride copolymers
10. The method for producing a foam according to claim 9, wherein the foam is made of at least one type of polymer. 14. The method for producing a foam according to claim 9, wherein the foamable composition molded product is cross-linked and foamed by heating under normal pressure. 15. The method for producing a foam according to claim 9, wherein the foamable composition further contains 5 to 30 phr of a flame retardant and 2 to 20 phr of a flame retardant aid. 16. The method for producing a foam according to claim 9, wherein the flame retardant has a bromine content of 40 to 80% and has two or more repeating units in its chemical structural formula. 17. The method for producing a foam according to claim 9, wherein the foamable composition is heat-treated at a temperature of 80 to 140°C to reduce the moisture content to 0.15% by weight or less. 18. The method for producing a foam according to claim 11, wherein the polyfunctional monomer is a trifunctional or tetrafunctional acrylate or methacrylate. 19 100 parts by weight of a resin consisting of an ethylene-vinyl acetate copolymer alone or a blend of the copolymer and a thermoplastic resin having a vinyl acetate content of 40 to 90% by weight, 50 to 500 parts by weight of an inorganic powder, and 5 to 5 parts by weight of a blowing agent. 50
An inorganic-containing ethylene-vinyl acetate copolymer foam, which is formed by molding a composition containing parts by weight, crosslinking it by irradiating it with ionizing radiation, and then foaming it by heating it to a temperature higher than the decomposition temperature of the blowing agent. manufacturing method. 20 Thermoplastic resin is polyethylene, ethylene-α-olefin copolymer, vinyl acetate content 5
~30% by weight of one or more of the group consisting of crystalline ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-vinyl chloride copolymer, ethylene-ethyl acrylate copolymer, and ethylene-propylene copolymer 20. The method for producing a foam according to claim 19, wherein the foam is an ethylene polymer. 21. The method for producing a foam according to claim 19, wherein the composition further contains 5 to 30 phr of a flame retardant and 2 to 20 phr of a flame retardant aid. 22. The method for producing a foam according to claim 21, wherein the flame retardant has a bromine content of 40 to 80% by weight and has two or more repeating units in its chemical structural formula. 23. The method for producing a foam according to claim 19, wherein the composition further contains a metal salt of stearic acid as an additive for improving crosslinking and foaming properties.