JPH0456057B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a crosslinked foam sheet made of a mixture of vinyl acetate-ethylene copolymer and a large amount of inorganic material, which has a high expansion ratio, is flame retardant, and has low smoke properties. 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,
By opening the mold all at once after heating, a foam with a maximum expansion ratio of 17.5 times (density 0.134 g/cm ² ) was obtained. 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 two-step heat foam molding is described in Japanese Patent Application Laid-open No. 49371/1983. In addition, 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. All of these methods involve filling a mold with foamable material and heating and foaming it under pressure.
It was difficult to obtain a foam with a high magnification of closed cells exceeding twice that of the previous method, and it was also impossible to produce a long foamed sheet. The present inventors investigated filling compositions of various thermoplastic resins and inorganic powders, mainly olefin polymers, 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 have developed a flame-retardant foam that is inexpensive, contributes to resource conservation, and has low smoke emission, by foaming an ethylene-vinyl acetate copolymer composition containing a high degree of inorganic powder. Realized a body sheet. (Disclosure of the Present Invention) The present invention provides a continuous sheet-like foam having an extremely high expansion ratio and made of a composition containing an extremely large amount of inorganic powder and the like. 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 (however,
(The vinyl acetate content in the resin component is more than 10% by weight and less than 90% by weight.) For 100 parts by weight, 50 to 500 parts by weight of inorganic powder, 5 to 40 parts by weight of flame retardant, and 2 to 20 parts by weight of flame retardant aid. It is a sheet-shaped crosslinked foam with 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 long continuous sheet of foam. It has excellent insulation properties and has extremely low water absorption. (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. Cross-linked polyethylene foam deforms to the extent that it does not lose its original shape at temperatures above 130°C, but this foam only shrinks and deforms by a few percent even at 150-180°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. Additionally, regarding item (4), it should be noted that although this foam is a flammable polymer, it has extremely high flame retardancy and low smoke emission. Therefore, JIS A 1321-
1975 "Flame retardancy test method for building interior materials and construction methods" When conducting a flame retardancy test according to the surface test in Section 3, the number of smoke systems per unit area is an indicator of the amount of smoke generated during combustion. (C _A ) and the area (tdθ) of the part 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 tdθ = 0, which ranks the highest in the same law in terms of smoke generation and smoke generation properties. (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. Also,
Regarding the oxygen index in item (3), JIS D 1201−
1973 “Flammability test method for organic materials for automobile interiors”
So, those with an oxygen index of over 30 are classified as flame retardant class 1, which is the highest rank in this test. The foam of the present invention falls under this category. 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, the resin component consists of an ethylene-vinyl acetate copolymer or a blend of the copolymer and a blendable thermoplastic resin, and the total amount of vinyl acetate in the resin component is greater than 10% by weight. less than % by weight. Furthermore, properties close to those of polyethylene resins are often expected, and in that case, a vinyl acetate content of more than 10% by weight and less than 40% by weight is preferred. In particular, 14% by weight
The content is preferably 35% by weight or less. Specifically, the vinyl acetate content is 10-40% by weight
When using an ethylene-vinyl acetate copolymer with a vinyl acetate content of 40 to 90% by weight,
In a resin component made of a blend of a vinyl acetate copolymer and another thermoplastic resin, the total amount of vinyl acetate contained in this resin component may be 10 to 40% by weight. The former is preferred, but in the latter case, i.e. polymers with a high vinyl acetate content, specifically 40~
When using an amorphous ethylene-vinyl acetate copolymer having 90% by weight of vinyl acetate groups, 55
~70% by weight of polymer is particularly preferred. 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 the most preferred in terms of compatibility and processability. polyethylene, ethylene-α-olefin copolymer,
These include ethylene-propylene copolymers, ethylene-vinyl acetate copolymers with a vinyl acetate content of 5 to 30%, ethylene-ethyleacrylate copolymers, ethylene-vinyl acetate-vinyl chloride copolymers, and the like. 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 preferably used. 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 inorganic powder is usually 0.01μ to 30μ, preferably
A range of 0.05 to 10μ, particularly 0.1 to 2μ, is desirable. If the particle size exceeds this upper limit, the extrusion-molded sheet will have a rough surface 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 the present invention, the foam having particularly excellent flame retardancy uses a hydrated metal compound such as aluminum hydroxide, magnesium hydroxide, basic calcium carbonate, etc. as an inorganic substance, and also uses a so-called halogen flame retardant. Commonly used halogen flame retardants include decabromodiphenyl ether (DBDE) and bromobenzene. The amount added is 5
-40 phr, preferably 5-30 phr, more preferably 15-30 phr. In this case, 2 to 20 phr, preferably 10 to 20 phr of a widely used flame retardant aid such as antimony trioxide is added. 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. It becomes a flammable foam. As an example of this, Figure 2 shows the degree of difficulty expressed by the oxygen index after testing the foam of the present invention with an expansion ratio of about 40 in accordance with JIS D 1201-1973 "Testing method for flammability of organic materials for automobile interiors." Flammability as well as maximum extinction coefficient (C _S /
max) is illustrated in relation to the amount of aluminum hydroxide added. The effect of adding aluminum hydroxide is large on both 0I and C _S・max, and in particular, C _S・max, which is an index of smoke generation, shows an exponential decline. The foam of the present invention is characterized by an oxygen index (0I) of 30
and the maximum extinction coefficient ( _CS・
max) is 2.7 or less. 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. It is particularly preferable to use the following halogen flame retardants. That is, it has a prom content of 40 to 80% by weight and has two or more repeating units in its chemical structural formula. For example, bisphenol A tetrabromobisphenol A epichlorohydrin glycidyl etherified condensate, tetrabromobisphenol 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 Kasei Co., Ltd. product,
FIREGUARD 7000 series (brome content approx. 50
weight%), Hitachi Chemical Co., Ltd. product HR-128F (brome content approximately 50% by weight), etc. The foam sheet of the present invention is a crosslinked foam, and is produced by a chemical crosslinking foaming method and a crosslinking foaming method using ionizing radiation. An example of a method for producing the foam of the present invention by a chemical crosslinking method 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.
50-500 parts by weight, foaming agent 5-50 parts by weight, flame retardant 5
~40 parts by weight, 2 to 20 parts by weight of flame retardant aid and crosslinking agent
An extrusion molded sheet of a foamable composition containing 0.1 to 10 parts by weight is prepared in a state where the moisture content in the composition is 0.15% by weight or less, more preferably 0.07% by weight or less, and still more preferably 0.05% by weight or less. It is obtained by foaming by heating above the decomposition temperature of the crosslinking agent and foaming agent. As a result of detailed studies on chemical crosslinking 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. A typical example of how the foaming performance greatly changes depending on the water content in the foamable composition is shown in FIG. Figure 1 shows the water content on the horizontal axis and the foam expansion ratio ρo/ρ (ρ: density of the foam, ρo: 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 containing aluminum hydroxide powder and a large amount of a halogenated flame retardant, if necessary. Curve A in the figure 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. The vinyl acetate content in the resin component is 53.8%, 46.6%, and 39.4%, respectively.
% and 32.2%. 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. Next, particular points to be noted regarding the method of crosslinking using ionizing radiation in the present invention 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, uraric acid, and acetic acid with zinc, lead, and aluminum). . 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. Normally, 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. When using a chemical crosslinking method, 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 or the like. 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 for producing the foam of the present invention,
The chemical crosslinking method requires dehumidification treatment, while the radiation crosslinking method does not require such treatment; however, the radiation crosslinking method requires an expensive irradiation device in the first place to obtain the foam of the present invention. However, a thick foamed product cannot be obtained, and the foaming ratio is slightly 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 is adopted for producing the foam of the present invention may be determined by taking various conditions into account. The foam of the present invention has characteristics such as low smoke and flame retardancy in addition to the various properties (insulating properties, cushioning properties, processability, etc.) of ordinary polyethylene closed cell foams. Therefore, it can be used for various purposes by taking advantage of its characteristics. Of course, it can be formed into a pipe shape to be used as a pipe cover for insulation, and in sheet form to be used as packaging material, packing material, cushion material, costume material, flotation material, etc.; It is used in construction materials, automobile materials, railway vehicle materials, ships and aircraft materials, etc., which have strict legal regulations regarding their smoke-emitting properties. 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 by weight.) Example 1 Ethylene-vinyl acetate copolymer with a vinyl acetate content of 61% (product of Dainippon Ink & Chemicals Co., Ltd.:
Embereth 450-P) 60 parts, vinyl acetate content 25
% ethylene-vinyl acetate copolymer (Mitsui Polychemical Co., Ltd. product: Evflec 360) 40 parts,
90 parts of aluminum hydroxide powder (product of Showa Denko Co., Ltd.: Hygilite H-42M), 25 parts of flame retardant decabromodiphenyl ether (product of Toyo Soda Co., Ltd.: abbreviated as DBDE), 12.5 parts of antimony trioxide powder, foaming 25 parts of agent azodicarbonamide,
Crosslinking agent DCP 1.5 parts, titanate coupling agent (Kenrich Petrochmical product: KEN-
REACT TTS) 3 parts, polyfunctional monomer A-
A composition consisting of 1 part of TMPT (product of Shin Nakamura Chemical Co., Ltd.) and 1 part of calcium stearate was kneaded in a large kneader with a capacity of 75 at a temperature of 120°C or less, and then pelletized after stripping with a two-roll mill. A foamable composition pellet was obtained. The pellets were fed into the hopper of a 65 mm extruder and extruded through the attached T-die to a width of 250 mm.
A sheet of foamable composition with 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 below 3 Torr. ) then
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%. Furthermore, when we measured the thermal conductivity (JIS A 1412), it was 0.04 (Kcal/
m・h・℃) and water absorption rate (JIS K
6767) was 0.001 (g/cm ² ) or less, and these values were almost equivalent to those of closed-cell, high-density foamed crosslinked polyethylene foam. JIS D of this foam
1201-1973 (cited above), the maximum extinction coefficient (C _S max) was 1.086 and the oxygen index (0I) was 35.9. Examples 2 to 7 Vinyl acetate-ethylene copolymer with a vinyl acetate content of 61% (Dainippon Ink Co., Ltd. product Evasuren)
450P) 60 parts, ethylene-vinyl acetate copolymer with 25% vinyl acetate content (Mitsui Polychemical Co., Ltd. product Evaflex 360) 40 parts, aluminum hydroxide fine powder (Showa Denko Co., Ltd. product Hygilite H-42M) 100 parts, foaming agent azodicarbonamide (Eiwa Kasei Co., Ltd. product, Vinihole AC
#1L) 25-30 parts, isopropyl tri(isostearoyl) titanate (U.S.
Kenrich Petrochemical product, KEN−
REACT TTS) 3 parts, dicumyl peroxide (Mitsui Petrochemical Co., Ltd.) 1.5 parts as a crosslinking agent,
0.7 parts of trimethylol pantriacrylate (product of Shin-Nakamura Chemical Co., Ltd.) as a crosslinking aid, bromine-based flame retardant (product of Matsunaga Chemical Co., Ltd., EBR-700)
or 25 copies of DBDE (Nippo Chemical Co., Ltd. product);
A composition consisting of 12 parts of antimony trioxide and 1 part of calcium stearate as flame retardant aids,
The mixture was thoroughly kneaded and pelletized at a temperature of 110°C using a small experimental Banbury mixer. Then 40mm
It was molded into a 2 mm thick sheet using an extruder. This sheet was heat treated in a hot air thermostat at 120°C for 20 minutes, then placed in a 220°C air thermostatic oven for 6 minutes.
When taken out, a highly foamed sheet was obtained. Table 1 summarizes the values of the foam, such as density, magnification, and amount of polymer per unit volume. Examples 2 to 4 are about the flame retardant DBDE.
Examples 5-7 are similar results for the other flame retardant (EBR-700) when ADCA was varied between 25 and 30 parts. All of them are highly foamed products with a foaming rate of 34 to 42 times, and the amount of polymer is 14 to 18 g/
Although it is extremely small, the flame retardants of Examples 5 to 7 have higher foaming than the DBDE-based flame retardants. Examples 8-9 Examples 8 and 9 in Table 1 show similar results when the aluminum hydroxide powder is increased to 120 parts. In this case, the obtained foam was sliced with a slicer to a thickness of about 4 mm 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 pieces were subjected to a surface test according to the method prescribed in JIS A-1321-1975, and the time-temperature area (tdθ), which is an index of the calorific value during combustion, and the smoke generation coefficient (C, which is an index of the amount of smoke produced) were determined. _A ) was measured. The results are shown in the lower part of Table 1. Note that the density and thickness of the foam are also listed in the table. Both Examples 8 and 9 have tdθ=0 and C _A <30, indicating that they are excellent foams with little heat generation and smoke generation. Furthermore, since Example 8 showed similar performance compared to Example 9 even though the sample thickness was considerably thicker, the flame retardant of Example 8 was superior to DBDE. It can be said that In addition, in order to indicate the flame retardancy and smoke generation properties of the foam itself, the oxygen index (0I) and maximum extinction coefficient (C _S
max) values are also listed in Table 1.

【table】

[Table] Examples 10 to 12, Comparative Examples 1 to 3 The various compositions shown in Table 2 were mixed with BRABENDER.
After kneading using PLASTO-GRAPH 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 2 shows the density, magnification, and amount of polymer per unit volume of the obtained foam, as well as JIS D1201
1973 “Flammability test method for organic materials for automobile interiors”
The results of the oxygen index (0I) and maximum extinction coefficient (C _S max), which were conducted according to the above, are also listed. Examples 10 to 12 are included in the foam of the present invention, so
Smoke generation is low, and the amount of polymer in the foam is less than 20g/in each case. Changes in 0I and C _S・max due to filler amount are the second
Illustrated in the figure. In particular, when 50 parts or more is added, smoke generation tends to be significantly reduced. Above this amount added, C _S・max is 2.7 or less.

【table】

[Table] Examples 13 to 15 The compositions shown in Table 3 using ethylene-vinyl acetate copolymers with different vinyl acetate contents as resin components were made into foam sheets in the same manner as Examples 10 to 12,
Flame retardancy and smoke generation were evaluated. The result is the third
Shown in the table. In all compositions, 0I exhibited high flame retardancy of 30 or higher, while C _S max was all 2 or lower, showing extremely low smoke generation. Also, the thermal conductivity is
In all cases, the value was about 0.04 (Kcal/m·h·°C), and the water absorption rate was 0.001 (g/cm ² ) or less.

【table】

【table】 [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 (ρo/ρ) (vertical axis) of the foam obtained therefrom. Figure 2 shows the oxygen index of the foam.
This is a graph plotting the maximum light attenuation coefficient (C _S max), which is an index of smoke generation amount, 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)

[Scope of Claims] 1. A resin component consisting of an ethylene-vinyl acetate copolymer alone or a mixture with other thermoplastic resins (provided that the vinyl acetate content in the resin component is more than 10% by weight and less than 90% by weight) 50 to 500 parts by weight of inorganic powder and 5 to 40 parts by weight of flame retardant per 100 parts by weight of
A high expansion ratio foam sheet with high inorganic substance filling and a high expansion ratio of 25 to 60 times. 2 Thermoplastic resin is polyethylene, ethylene-α
- Characterized by being one or more ethylene polymers from the group consisting of olefin copolymer, ethylene-ethyl acrylate copolymer, ethylene-propylene copolymer, and ethylene-vinyl acetate-vinyl chloride copolymer. A foam sheet according to claim 1. 3. The foam sheet according to claim 3, 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. 4 The inorganic powder is aluminum hydroxide powder and/or
or magnesium hydroxide powder, the foam sheet according to claim 1. 5. The foam sheet according to claim 1, wherein the surface of the inorganic powder is surface-treated with a monoalkoxyorganotitanate compound. 6 The content of the resin component per unit volume of the foam is
The foam sheet according to claim 1, characterized in that the amount is 20 g/or less.