JPH0247496B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention aims to provide a method for producing an inorganic-rich synthetic resin foam that has excellent heat resistance and flame retardancy, a high expansion ratio, and low smoke properties. In general, plastic foams are lightweight and have excellent heat resistance, shock absorption, and sound absorption properties, so they are widely used as construction materials, packaging materials, and flotation materials. In particular, polyolefin foams are highly resistant to chemical and mechanical , has excellent electrical properties. However, a major disadvantage of polyolefin foams is that they are easily flammable, and strict flame retardancy is required from a safety standpoint to prevent disasters caused by fire. The method of making polyolefin flame retardant is to add a large amount of inorganic powder or halogen flame retardant, or if inorganic powder is added, no toxic gas or corrosive gas is generated and no smoke is generated. It is also effective in reducing the amount of carbon dioxide generated, and is also excellent from the perspective of resource conservation. However, since a large amount of inorganic powder is blended, foaming gas escapes during foaming, making it difficult to obtain a foam with a high expansion ratio, and the resulting foam also has large distortions and poor heat resistance. Ta. The present invention has been made as a result of extensive research aimed at improving these drawbacks, and as a result has discovered a method for producing a foam with improved heat resistance and an excellent expansion ratio. That is, the method of the present invention uses a mixture of 1 to 40 parts by weight of styrene-vinyl acetate copolymer and ethylene-vinyl acetate copolymer alone or with another thermoplastic resin.
It is characterized in that a composition prepared by adding 50 to 500 parts by weight of an inorganic powder and desired amounts of a blowing agent and a crosslinking agent to 100 parts by weight of a resin component consisting of 60 parts by weight is heated to cause crosslinking and foaming. In the present invention, the ethylene-vinyl acetate copolymer is intended to have 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 a foam having a particularly high expansion ratio can be obtained. 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 olefins, especially ethylene polymers, are the most preferred in terms of mutuality and processability. These include polyethylene, ethylene-α-olefin copolymer, ethylene-propylene copolymer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate-vinyl chloride copolymer, 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 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 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 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 amount added is not particularly limited, but it is usually blended in the range of 5 to 50 parts by weight; if it is less than 5 parts by weight, it will not be possible to obtain a highly foamed product, and if it is less than 50 parts by weight. This is because if it exceeds the amount, 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 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. In this case, it is necessary to perform foaming by heating to a temperature higher than the decomposition temperature of the foaming agent after radiation crosslinking. Most preferably, peroxides are used in the case of chemical crosslinking. For example, t-butylperbenzoate, 1,1-di-(t-butylperoxy)
-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)diisopropylbenzene, 2,5-dimethyl-2,5-
Di-(t-butylperoxy)hexyne-3 and the like. 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. 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. As the crosslinking accelerator, 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, 1,6 - Diacrylate and dimethacrylate compounds such as hexane glycol diacrylate, 2,2-bis-(4-acryloxydiethoxyphenyl)propane, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, tetramethylolmethane triacrylate triacrylate and trimethacrylate compounds such as, tetraacrylate compounds such as tetramethylolmethanetetraacrylate, polybutadiene compounds such as 1,2-polybutadiene, maleic esters such as divinyl maleate and dipropargyl maleate,
It is an aromatic compound with unsaturated bonds such as divinylbenzene. 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 contain halogen-based flame retardants such as decapromodeiphenyl oxide, flame retardant aids such as antimony trioxide, antioxidants, copper inhibitors, antistatic agents, colorants, pigments, There is no problem in adding lubricants and other processing aids. In the present invention, when it is desired to obtain a blowing agent with particularly excellent flame retardancy, aluminum hydroxide,
In addition to using hydrated metal oxides such as magnesium hydroxide and basic calcium carbonate, so-called halogen flame retardants are also used. In this case, hydrates such as aluminum hydroxide not only improve flame retardancy, but they also play a major role in significantly reducing smoke generation when halogenated flame retardants are added, so flame-retardant foam with low smoke generation is used. will be obtained. Next, a specific example of the manufacturing process of the foam of the present invention will be explained. 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. In addition, in the case of crosslinking with ionizing radiation, the extrusion molded sheet has a
Cross-linking is performed 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 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 by 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. In this way, the method of the present invention improves flammability and processability,
A foam having a high expansion ratio and excellent heat insulation and heat resistance can be obtained. Therefore, the foam produced by the method of the present invention can be used for various purposes by taking advantage of its characteristics. Shaped into a pipe, it can be used as a pipe cover for insulation; as a sheet, it can be used as packaging material, packing material, cushioning material, clothing material, etc.
Of course, it can be used as flotation materials, but due to its low smoke and flame retardant properties, it can also be used as building materials, automobile materials, etc., which have strict legal regulations regarding flame retardancy and smoke emitting properties.
It is used for 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 by weight.) Examples (1) Styrene-vinyl acetate block copolymer with a vinyl acetate content of 50% (MODIPAR manufactured by NOF Corporation)
SV3050B) 20 parts, 60 parts of ethylene-vinyl acetate copolymer with a vinyl acetate content of 61% (EVATHLENE450-P manufactured by Dainippon Ink Chemical Industries, Ltd.), and ethylene-vinyl acetate copolymer with a vinyl acetate content of 25%. Aluminum hydroxide powder (Hygilite H- manufactured by Showa Denko Co., Ltd.) was added to 100 parts of a resin component consisting of 20 parts of a polymer (EVAFLEX360 manufactured by Mitsui Polychemical Co., Ltd.).
42M) 100 parts, azodicarbonamide (hydration chemical
Vinihole AC #1L) 25, dicumyl peroxide (Mitsui Petrochemicals Co., Ltd.) 1.5 parts, trimethylolpropane triacrylate (Shin Nakamura Chemical Co., Ltd.)
A composition consisting of 0.7 parts of A-TMPT) and 1 part of calcium stearate was thoroughly kneaded at 120°C in a Brabender Plastograph, and then hot pressed at 120°C to form a foamable sheet with a thickness of 2 mm. This sheet was left in a silica gel desiccator at 20° C. for 2 days, and then heated for 6 minutes in a hot air constant temperature bath at 220° C. to perform crosslinking and foaming to obtain a foamed product according to the method of the present invention (product of the present invention). Comparative Example (1) For comparison with the product of the present invention, 60 parts of ethylene-vinyl acetate copolymer with a vinyl acetate content of 61% and ethylene-vinyl acetate copolymer with a vinyl acetate content of 25% were used as resin components.
A comparative foam was obtained in the same manner as in Example (1) except that 40 parts of vinyl acetate copolymer was used. Example (2) Styrene-vinyl acetate copolymer with a vinyl acetate content of 70% (MODIPER SV3070B manufactured by NOF Corporation)
Ethylene-vinyl acetate copolymer with 20 parts and 69% vinyl acetate content (manufactured by Dainippon Ink & Chemicals Co., Ltd.)
EVATHLENE350-P) 60 parts, low density polyethylene (Yukalon YF-30 manufactured by Mitsubishi Yuka Co., Ltd.) 20 parts, aluminum hydroxide powder (Hygilite H-32 manufactured by Showa Denko Co., Ltd.) 100 parts, flame retardant Decabromo 20 parts of delphenyl ether (produced by Toyo Soda Co., Ltd.: abbreviated as DBDE), antimony trioxide (manufactured by Nippon Senko Co., Ltd.)
12.5 parts of azodicarbonamide (above), 25 parts of dicumyl peroxide (above), 3 parts of a titanate coupling agent (KEN-REACT TTS manufactured by Kenrich Petrochemical), polyfunctional monomer trimethylolpropane. A composition consisting of 0.7 parts of acrylate (A-TMPT manufactured by Shin-Nakamura Chemical Co., Ltd.) and 1 part of zinc stearate was kneaded and molded to obtain a sheet with a thickness of 2 mm. Thereafter, a foam was obtained in the same manner as in Example 1. Comparative Example (2) 100 parts of low density polyethylene (YF-30 mentioned above), 100 parts of aluminum hydroxide powder (H-32 mentioned above), 25 parts of azodicarbonamide (mentioned above), dicumyl peroxide (mentioned above) ), 3 parts of titanate coupling agent (mentioned above), and 1 part of zinc stearate were kneaded and molded to obtain a sheet with a thickness of 2 mm. A foam was obtained in the same manner as in Example (1). Comparative Example (3) A comparative foam was obtained in the same manner as in Comparative Example (2) except that aluminum hydroxide was removed. Table 2 shows the properties of the obtained foam. Heat resistance was evaluated by the volume change rate of a sample left in a hot air constant temperature bath at 80°C for 22 hours. Flame retardancy is JIS
-K-7201: Judgment was made using the combustion test method for polymeric materials using the oxygen index method. The density was determined using a method of measuring specific gravity by submersion in water. The foaming ratio was determined from the ratio of the densities before and after foaming.

[Table] As is clear from the above table, Comparative Example (3) is an example of a conventional polyolefin foam. It can be seen that it foams at a high magnification and has good heat resistance, but is easily flammable. Comparative Example (2) is an example in which the polyolefin foam was highly filled with an inorganic substance in order to impart flame retardancy. Although the oxygen index has increased to 22 and the flame retardance has improved due to the high loading of inorganic substances, it can be seen that there is almost no foaming. Comparative Example (1) has a composition very close to that of the present invention, and has a sufficiently high foaming rate even with a high inorganic content, but because it does not contain the styrene-vinyl acetate copolymer of the present invention, the heat resistance is The result is a significantly inferior foam. As detailed above, the method of the present invention has remarkable effects such as obtaining a product having excellent heat resistance, low smoke properties, and flame retardancy, and also having a high expansion ratio.

Claims (1)

[Claims] 1. To 100 parts by weight of a resin component consisting of 1 to 40 parts by weight of a styrene-vinyl acetate copolymer and 99 to 60 parts by weight of an ethylene-vinyl acetate copolymer alone or a mixture with other thermoplastic resins. A method for producing an inorganic-rich synthetic resin foam, which comprises heating a composition to which 50 to 500 parts by weight of an inorganic powder and desired amounts of a blowing agent and a crosslinking agent are added to crosslink and foam the composition. 2 40-90 as ethylene-vinyl acetate copolymer
2. A method for producing an inorganic highly filled synthetic resin foam according to claim 1, characterized in that an amorphous material having a weight percent of vinyl acetate groups is used. 3 At least one thermoplastic resin selected from polyethylene, ethylene-α-olefin copolymer, ethylene-propylene copolymer, ethylene-ethyl acrylate copolymer, and ethylene-vinyl acetate-vinyl chloride copolymer. The method for producing a highly inorganic-filled synthetic resin foam according to claim 1, characterized in that the foam is made of seeds. 4. The inorganic-rich synthetic resin foam according to claim 1, characterized in that the inorganic powder is at least one selected from aluminum hydroxide, magnesium hydroxide, and basic magnesium carbonate. Production method. 5. The method for producing an inorganic-rich synthetic resin foam according to claim 1, characterized in that the particle size of the inorganic powder is in the range of 0.01 to 30 μm.