JPS6365213B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polyolefin resin foam containing a high concentration of inorganic substances. Filling polyolefin resins with inorganic compounds is carried out for the purpose of making them non-polluting, flame retardant, and conserving resources. For example, hydrates such as Al(OH) ₃ and Mg(OH) ₂ can improve flame retardancy by releasing water of crystallization at a specific temperature, and are more combustible than so-called halogen flame retardants. It is attracting attention because it does not emit toxic gas and is inexpensive. However, when a conventional inorganic-filled polyolefin resin molded product is heated and foamed under normal pressure, it is difficult to obtain a highly foamed product, and even if it is obtained, the bubbles are coarse and the surface is noticeably rough, and it is difficult to obtain a highly foamed product. A large amount of blowing agent was required. In order to obtain a highly foamed inorganic-filled polyolefin resin, there is a method of introducing a crosslinked structure under pressure to decompose the foaming agent, and then heating and expanding it under normal pressure, but continuous production is difficult and it is produced in a batch process. Production efficiency decreases and prices tend to increase,
Furthermore, since it is impossible to produce long foamed products, its applications tend to be limited. The present invention has been made as a result of intensive studies in view of the above situation, and its purpose is to provide a method for producing a high expansion ratio foam made of polyolefin resin filled with a high concentration of inorganic substances, and a method for producing a foam with fine air bubbles and a surface of the foam. The object of the present invention is to provide a method that allows continuous industrial production of smooth and beautiful foams. However, the gist of the present invention is to mix a polyolefin resin with an inorganic compound powder, a thermally decomposable blowing agent, and an organic peroxide, mold it to form an inorganic-filled resin molded product, and then heat it above the decomposition temperature of the blowing agent. A method for producing a polyolefin resin foam filled with an inorganic substance is characterized in that 0.05 to 10 parts by weight of a surfactant are added and mixed to 100 parts by weight of the polyolefin resin. The present invention is an inorganic-filled polyolefin containing 50 to 250 parts by weight of inorganic compound powder, 0.05 to 10 parts by weight of a surfactant, a thermally decomposable blowing agent, and an organic peroxide crosslinking agent per 100 parts by weight of a polyolefin resin. This can be carried out by heating the resin molded product to a temperature higher than the decomposition temperature of the foaming agent and foaming it under normal pressure. The use of surfactants is essential to the practice of this invention. Although the mechanism of action of the surfactant used in the present invention is not clear, it is thought that the addition of the surfactant lowers the surface tension of the resin composition. In other words, the size of the bubbles during foaming is not uniform but varies, and the internal gas pressure of the bubbles increases as the bubble diameter becomes smaller. Therefore, the gas flows between adjacent bubbles across a thin membrane from the smaller diameter to the larger diameter. The bubble diameter becomes larger as the bubbles permeate through the air and finally coalesce into a larger one. Therefore, it becomes a foam with large cells. Since the pressure difference between the cells has a property that it is proportional to the surface tension, by lowering the surface tension, coalescence of the cells can be prevented and a foam with fine cells can be obtained. In addition, since it is difficult to form large bubbles, the bubble film is less likely to be destroyed, and the surface is smooth, and there is less gas escape, so it is thought that the amount of blowing agent added can be reduced. As the surfactant used in the present invention, nonionic surfactants such as alkylphenol type and sorbitan ester type are also effective, but silicone type surfactants and fluorine type surfactants particularly exhibit the above-mentioned effects. . Such a surfactant is available under the trade name NUC Silicone L3550 (Nippon Unicar).
(manufactured by Sumitomo 3M Ltd.) or Florado FC430 (manufactured by Sumitomo 3M Ltd.). The amount of surfactant added is in the range of 0.05 to 10 parts by weight per 100 parts by weight of the polyolefin resin. If it is less than 0.05 parts by weight, no effect can be achieved, and if it exceeds 10 parts by weight, the original properties of the resin will be significantly impaired, which is not preferable. The polyolefin resin in the present invention has a high
Medium and low pressure polyethylene, polypropylene, polybutene-1, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-α-olefin copolymer, ethylene-acrylic acid copolymer, chlorinated polyethylene, chlorsulfone Refers to one type or a mixture of two or more types of polyethylene, polybutadiene, etc. Inorganic compounds in the present invention include aluminum hydroxide, magnesium hydroxide, basic magnesium carbonate, calcium hydroxide, tin oxide hydrate, zirconium oxide, calcium carbonate, magnesium carbonate, talc, clay, bentonite, attapulgite, barium borate, Zinc borate, gypsum, etc., and one or a mixture of two or more thereof. Moreover, the surface of the above-mentioned inorganic compound may be treated with a well-known fatty acid-based, silane-based, or titanium-based coupling agent. These inorganic compounds have an average particle size of 0.01~
It is a 50μ powder. The amount added is 30 to 250 parts by weight, preferably 50 to 200 parts by weight, per 100 parts by weight of the polyolefin resin. The organic peroxide of the present invention is a compound that decomposes when heated to generate radicals, such as di-
t-butyl peroxide, dicumyl peroxide, t-butyl cumyl peroxide, α, α
-bis(t-butylperoxy)P-diisopropylbenzene, 2.5-dimethyl-2.5-di(t-butylperoxy)hexane, 2.5-dimethyl-2.5
Di(t-butylperoxy)hexyne-3, 2.4
-dichlorobenzoyl peroxide, benzoyl peroxide, 1.1-di-t-butylperoxy3.3.5-trimethylcyclohexane, 2.5-dimethyl-2.5-dibenzoylperoxyhexane,
n-butyl-4.4-di-t-butyl peroxyvalerate and the like. Additionally, a crosslinking aid may be used if necessary. The thermally decomposable blowing agent of the present invention is a substance that decomposes upon heating and relatively rapidly generates gas, such as one type of azodicarbonamide, dinitrosopentamethylenetetramine, PP'-oxybisbenzenesulfonyl hydrazide, etc. Or a mixture of two or more. The mixing amount of the blowing agent is appropriately selected depending on the desired expansion ratio of the foam, but in the foam of the present invention, 5 parts by weight per 100 parts by weight of the polyolefin resin.
~50 parts by weight is often added. The foam thus obtained has a specific gravity of 0.2 to 0.02. In the present invention, the above-mentioned inorganic compound, blowing agent, organic peroxide, and surfactant are kneaded with the above-mentioned polyolefin resin using a mixing roll or Banbury mixer at around 100°C, and then pressed or extruded at a temperature that does not decompose the blowing agent. It is made into a plate-shaped product using a machine. Additives such as colorants, anti-aging agents, ultraviolet absorbers, flame retardants, foaming aids, crosslinking aids, and lubricants may be added as necessary. In this step, the molding must be carried out under conditions in which the blowing agent and crosslinking agent do not decompose. The inorganic-filled polyolefin resin molded product obtained in this way is made into a highly foamed body under normal pressure by infrared heating, hot air heating, hot plate heating, submerged or above liquid heating, or a combination of these methods. Ru. A more specific explanation will be given below based on Examples. Examples 1 to 8 The materials shown in Table 1 were kneaded using a mixing roll at 100°C, and press-molded at 100°C into a 1.5 mm thick sheet. This sheet was placed in an oven at 230°C and foamed. The results are shown in Table-2. As shown in Table 2, the foaming density was reduced with the addition of a surfactant, and the bubbles were fine and the surface smoothness was excellent. Comparative Examples 1 to 3 in which no surfactant was added
The bubbles were rough and the surface smoothness was poor.

【table】

【table】

[Table] ○: Good
×: Surface roughness, unevenness Example 9 The formulation shown in Example 3 was kneaded in a Banbury mixer at 90 to 100°C, then pelletized, and a sheet with a thickness of 3 mm and a width of 200 mm was made using a 40 mm extruder at a temperature of 80 to 100°C. It was molded into. This sheet was placed in a heating foaming furnace to obtain a long foam. This foam has a density
It was a good foam with a smooth surface and a weight of 0.050 g/cm ³ and a number of cells of 18 cells/cm. Examples 10 to 11 The materials shown in Table 3 were kneaded using a mixing roll at 115°C and press-molded at 120°C into a 3 mm thick sheet. This sheet was placed in an oven at 230°C and foamed. The results are shown in Table-4. From Table 4, it was found that the foams to which a surfactant was added had a low foaming density, fine bubbles, and excellent surface smoothness. On the other hand, in Comparative Example 4 in which no surfactant was added, the foam was incomplete and the surface smoothness was poor.

【table】

[Table] As described above, according to the present invention, it has become possible to produce an inorganic-filled foam with fine cells and excellent surface smoothness even when a large amount of inorganic material is added.

Claims (1)

[Scope of Claims] 1 A polyolefin resin is mixed with an inorganic compound powder, a thermally decomposable blowing agent, and an organic peroxide, and molded to form an inorganic-filled resin molded product, which is then heated to a temperature higher than the decomposition temperature of the blowing agent. 1. A method for producing a polyolefin resin foam filled with an inorganic substance, which comprises adding and mixing 0.05 to 10 parts by weight of a surfactant to 100 parts by weight of the polyolefin resin. 2. The manufacturing method according to claim 1, wherein the surfactant is a fluorine-based or silicone-based surfactant.