JPH10251430A - Production of plastic foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a plastic foam which scarcely produces cyanide ions when burnt or smoked and therefore is freed from a fear of forming noxious gases on fire by mixing a plastic resin with a mixed blowing agent based on an azodicarbonamide and sodium bicarbonate and a metal phthalocyanine com pound and foaming the resulting mixture by heating. SOLUTION: 100 pts.wt. of low-density polyethylene is mixed with a blowing agent based on 5-10 pts.wt. azodicarbonamide and 2-5 pts.wt. sodium bicarbonate and 1-10 pts.wt. metal phthalocyanine compound (e.g. copper phthalocyanine). The effect is remarkable when the foaming method adopted is pressurized one-stage foaming or two-stage foaming. For example, in the pressurized two- stage foaming, the mixture is packed into a mold and heated at 120-170 deg.C under pressure for a definite time. After the pressure is released, the intermediate primary foam in the state in which the added blowing agent is partially decomposed is withdrawn and is heated to 145-200 deg.C at atmospheric pressure to decompose the undecomposed blowing agent to obtain a foam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a plastic foam capable of reducing cyanide ions during burning or smoking.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a plastic foam, azodicarbonamide is used as a foaming agent.
A method of foaming by heating is generally performed by pressureless one-stage foaming method, two-stage foaming method, endless foaming of chemical crosslinking or electron beam crosslinking. Azodicarbonamide has recently become the most important foaming agent for plastics, and is being mass-produced and sold worldwide. Azodicarbonamide (NH ₂ CONN
CONH ₂ ) has a theoretical gas generation of 193 cc / g
However, by adding various foaming assistants such as zinc white, the decomposition temperature and the amount of generated gas can be adjusted. Further, it is characterized in that the decomposition rate is relatively high, a product with uniform bubbles is obtained, and the calorific value is relatively small.

[0003]

However, since the plastic foam using azodicarbonamide contains a decomposition residue of the blowing agent, the ambient temperature is raised to about 350 ° C. by heating with a heater or the like in a closed chamber. When raised and smoked, a small amount of cyanide ion (CN ⁻ ) is detected in the generated gas. This cyanide ion may be metal cyanide (KCN or the like), hydrogen cyanide (HCN), or cyan ((CN) ₂ ), and it has been strongly desired to reduce the generation amount. Accordingly, an object of the present invention is to solve the problems of the foam using the azodicarbonamide, and to provide a cyanide ion (C
An object of the present invention is to provide a method for producing a plastic foam having an ability to reduce N ⁻ ).

[0004]

The method for producing a plastic foam of the present invention is roughly divided into the following four methods. First, the first method is a method characterized by adding an azodicarbonamide and a metal phthalocyanine compound to a plastic resin and foaming by heating. The second method is to add a foaming agent of a foaming agent containing azodicarbonamide and sodium bicarbonate as a main component and a metal phthalocyanine compound to a plastic resin and heat-foam the resin. The third method is a method in which the above two methods are applied to a method for producing a conductive plastic foam to which conductive carbon black is added.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The metal phthalocyanine compound used in the present invention is not particularly limited as long as it does not inhibit decomposition of a blowing agent and a crosslinking agent and reduces the generation of cyanide ions. It is presumed that the action of accelerating the decomposition of azodicarbonamide reduces the decomposition residue and reduces cyanide ions. Sodium bicarbonate (NaHCO ₃ ) used in the second invention is a blowing agent that generates carbon dioxide gas and does not generate cyanide ions because it does not contain N. However, carbon dioxide gas has a permeability to plastics. It is disadvantageous that the resulting foam is easily shrunk. Therefore, sodium bicarbonate and azodicarbonamide are used in combination, and both foaming agents are used together to produce a high-foamed product and simultaneously reduce the amount of azodicarbonamide added to reduce cyanide ions. Since sodium bicarbonate alone has a low decomposition temperature, a commercially available product obtained by adding a small amount of a foaming inhibitor such as citric acid can be used.

Hereinafter, a method for producing a plastic foam according to the present invention will be specifically described. First, in the first method, azodicarbonamide (preferably 5 to 20 parts) and metal phthalocyanine compound (preferably 1 part) are added to 100 parts by weight (hereinafter, referred to as "parts") of a plastic resin.
-10 parts, and compounding agents such as a foaming aid and a crosslinking agent are appropriately added. The obtained blend is uniformly mixed by a known kneading method such as a mixing roll, a kneader, and an extruder,
It is heated and foamed. The method of foam molding is not particularly limited, such as pressurized one-stage foaming, two-stage foaming, endless foaming of chemical crosslinking or electron beam crosslinking, but when applied to pressure one-stage foaming or two-stage foaming from the viewpoint of imparting functionality, the present invention The effect is particularly remarkable. In the pressure single-stage foaming, the above-mentioned mixture is filled in a mold and heated at 130 to 170 ° C, preferably 145 to 155 ° C under pressure for a certain time to decompose the foaming agent and the cross-linking agent, and then depressurize. To obtain a foam. In the two-stage foaming, the above-mentioned mixture is filled into a mold, and the mixture is pressurized for 12 hours.
Heating at 0-170 ° C, preferably 125-155 ° C,
In a state where the compounded foaming agent is partially decomposed, the intermediate foam is taken out by depressurizing, and then the intermediate foam is heated under normal pressure at 145 to 200 ° C., preferably 150 to 190 ° C., and is not decomposed. To decompose the remaining foaming agent to obtain a foam. As described above, by foaming in two stages, a thick high-foamed body having uniformly fine cells can be obtained. When heating to the decomposition temperature under normal pressure in the second step, for example,
It is heated in a salt bath using one or more molten salts such as a metal bath using a rose alloy, a wood alloy, an oil bath, sodium nitrate, potassium nitrate, and potassium nitrite, or an intermediate foam is formed. Cross-sectional shape, put into an unsealed mold of dimensions, contact or indirect heating method over the metal plate of the mold, for example, heating by contacting a heater to the outer surface of the metal plate, or the flow path of the heat medium to the metal plate The remaining foaming agent is decomposed and foamed by a method of heating through a heating medium such as steam in a jacket system, and a foam having low density and uniform physical properties is obtained.

In a second method of the present invention, azodicarbonamide is preferably added to 100 parts of a plastic resin in an amount of 5 to 1%.
0 parts, preferably 2 to 5 parts of a blowing agent containing sodium bicarbonate as a main component, and preferably 1 to 10 parts of a metal phthalocyanine compound are added, and a foam is produced in the same manner as in the first method.

[0008] A third method of the present invention is to produce a conductive foam by adding a conductive carbon black in the first or the second method. To 100 parts, 10 to 30 parts of conductive carbon black and an appropriate amount of a foaming agent and a crosslinking agent are added and kneaded, and the obtained crosslinkable foamable composition is filled into, for example, a mold attached in a press. And a temperature at which the blowing agent does not substantially decompose in the mold under pressure.
The composition is crosslinked by heating to ~ 160 ° C, and then the obtained foamable crosslinked composition is taken out of the mold and foamed by heating under normal pressure so as not to rapidly foam or expand. The heating temperature is preferably 150 to 190 ° C., and the heating time is preferably 15 to 190 ° C.
~ 120 minutes. Furnace-based carbon black and acetylene-based carbon black can be suitably used as the conductive carbon black used in the present invention.
A channel-based carbon black for rubber and the like can be used, but a furnace-based carbon black having a surface area (nitrogen adsorption method) of 900 m ² / g or more is particularly preferable.

The plastic resin used in the present invention is:
The resin is not particularly limited as long as it is a resin that can be kneaded with azodicarbonamide and foamed by heating, but the polyolefin foam has excellent physical properties, and the effect is remarkable when the method of the present invention is applied to the polyolefin foam. The polyolefin used in the present invention includes, for example, polyethylene, poly-1,2-butadiene, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-acetic acid which are usually produced by high, medium and low pressure methods commercially available. Vinyl copolymers, copolymers of ethylene with methyl-, ethyl-, propyl-, butyl-acrylates or methacrylates up to a content of 45%, or chlorinated products thereof (chlorine content up to 60% by weight) Or a mixture of two or more of these or a mixture thereof with a polypropylene having an atactic or isotactic structure, and a polyethylene or polypropylene polymerized by a metallocene catalyst. The cross-linking agent referred to in the present invention has a decomposition temperature of at least the flow start temperature of the polyethylene resin in the polyethylene resin, and is decomposed by heating to generate free radicals to generate intermolecular or intramolecular molecules. Organic peroxides which are radical generators that cause cross-linking to occur, such as dicumyl peroxide, 1,1-ditert-butylperoxy-3,
3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-ditert-butylperoxyhexane,
There are 2,5-dimethyl-2,5-di-tert-butylperoxyhexyne, α, α-di-tert-butylperoxyisopropylbenzene, tert-butylperoxyketone, tert-butylperoxybenzoate, etc. The optimal organic peroxide must be selected depending on the resin used. In the present invention, a foaming aid can be added according to the type of the foaming agent. As a foaming aid, a compound containing urea as a main component,
Metal oxides such as zinc oxide and lead oxide; compounds containing salicylic acid, stearic acid and the like as main components, that is, higher fatty acids and metal compounds of higher fatty acids. In the present invention, for the purpose of improving the physical properties of the composition to be used or lowering the price, a compounding agent (filler) that does not significantly affect cross-linking, for example, zinc oxide, titanium oxide, calcium oxide, magnesium oxide, Metal oxides such as silicon oxide,
Carbonates such as magnesium carbonate and calcium carbonate, or fibrous materials such as pulp, or various dyes, pigments, fluorescent materials, and other commonly used rubber compounding agents can be added as necessary.

[0010]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the following Examples. Example 1 (First Invention) 9 parts of azodicarbonamide, 4 parts of phthalocyanine copper, 0.5 parts of zinc white in 100 parts of low-density polyethylene (described above)
And 0.4 parts of dicumyl peroxide were kneaded with a mixing roll to give a composition obtained by 30 ^t × 210 × 2
Fill into a 10 mm pressure sealed mold, 100 kg / cm
^After applying an external pressure of ³ and heating at 155 ° C. for 30 minutes, the pressure was released and the primary foam was taken out. The primary foam expanded about 1.6 times in thickness, length and width. The primary foam is immediately placed in a non-hermetic mold (500 × 500 × 110 ^t mm) having a steam jacket and placed in a 160
The mixture was heated with steam at 40 ° C. for 40 minutes, taken out after cooling, and a crosslinked polyethylene foam having uniformly fine cells was obtained. The foam obtained had an apparent density of 0.047 g / cm ³ and 1
Three test pieces cut into a cube having a side of 0.25 inch (0.63 cm) were housed in a closed chamber, and the ambient temperature was heated with a cartridge heater to bring the test pieces into a cube.
The mixture was allowed to stand at 15 ° C. for 15 minutes, smoked, and the concentration of cyanide ion was measured. As a result, the concentration was 0.1 mg / g. Example 2 (First Invention) A crosslinked polyethylene foam was obtained in the same manner as in Example 1 except that copper phthalocyanine was changed to 2 parts under the same composition and under the same conditions. The resulting foam had an apparent density of 0.
As a result of smoking at 047 g / cm ³ in the same manner as in Example 1, the concentration of cyanide ion was 0.12 mg / g.
The effect of reduction by adding copper phthalocyanine was observed. Comparative Example 1 A crosslinked polyethylene foam was produced in the same manner as in Example 1 except that copper phthalocyanine was not added in Example 1, and smoked in the same manner as in Example 1. As a result, the cyanide ion concentration was It was 0.15 mg / g.

Example 3 (Second invention) Example 1 was repeated except that 7.5 parts of azodicarbonamide, 3 parts of a blowing agent containing sodium bicarbonate as a main component, and 3 parts of copper phthalocyanine were added. A crosslinked polyethylene foam was obtained with the same composition and under the same conditions as in Example 1, and was smoked in the same manner as in Example 1. As a result, the cyanide ion concentration was 0.1%.
At a concentration of 04 mg / g, there was a reduction effect due to the addition of copper phthalocyanine and sodium bicarbonate. Example 4 (Third Invention) In 100 parts of low-density polyethylene (described above), a furnace-based carbon black (trade name: Ketjen Black EC,
Surface area (nitrogen adsorption method) 1,000 m ² / g, manufactured by Mitsubishi Chemical Corporation 25 parts, azodicarbonamide 7.5 parts, blowing agent containing sodium bicarbonate as a main component (described above) 3 parts, phthalocyanine copper 3 parts 0.08 parts of active zinc white, urea 0.
A mixture consisting of 03 parts and 0.6 part of α, α'-di-t-butylperoxydiisopropylbenzene (trade name: Percadox, manufactured by Kayaku Nury Co., Ltd.) was kneaded with a mixing roll, and then heated to 145 ° C. After filling in a mold (210 × 210 × 30 ^t mm) in the pressed press and heating for 45 minutes to perform crosslinking, the pressure was released to obtain a foamable crosslinked sheet. The foamed crosslinked sheet is then immediately placed in a non-hermetic mold (500x500x) with a steam jacket.
100 ^t mm) and heated at 160 ° C. for 150 minutes,
The remaining foaming agent was decomposed to obtain a conductive crosslinked polyethylene foam. The obtained foam has an apparent density of 0.04 g / c.
As a result of measuring the cyanide ion concentration at m ³ by the same method as in Example 1, the result was 0.04 mg / g, and a reduction effect by copper phthalocyanine was observed. Example 5 (Third invention) The cyanide ion concentration was measured by the same composition and method as in Example 4 except that copper phthalocyanine was changed to 1 part. As a result, the concentration was 0.08 mg / g, which was reduced by copper phthalocyanine. The effect was seen. Comparative Example 2 In Example 4, the same composition and the same conditions as in Example 4 were used, except that 9 parts of azodicarbonamide, 0 part of a blowing agent containing sodium bicarbonate as a main component (described above), and 0 part of phthalocyanine copper were used. A conductive crosslinked polyethylene foam was obtained. The resulting foam had a cyanide ion concentration of 0.15 mg.
/ G.

[0012]

[Table 1]

[0013]

As described above, the foam obtained by the method for producing a plastic foam according to the present invention has less fear of toxic gas at the time of fire because of reduction of cyanide ions during smoldering. Of course, it is suitable for exports to the United States, building insulation materials, radio wave absorbers, aircraft interior materials, indoor sound absorbing materials, and the like.

Continued on the front page (72) Inventor Mikiya Kuramoto 28, Honcho, Kami-Tobayama, Minami-ku, Kyoto Sanwa Chemical Engineering Co., Ltd.

Claims (3)

[Claims] 1. A method for producing a plastic foam, comprising adding an azodicarbonamide and a metal phthalocyanine compound to a plastic resin and heating and foaming the resin. 2. A method for producing a plastic foam, comprising adding a mixed foaming agent containing azodicarbonamide and sodium bicarbonate as main components and a metal phthalocyanine compound to a plastic resin, followed by heating and foaming. 3. The method according to claim 1, wherein the plastic foam is a conductive crosslinked polyolefin foam.