Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-12-03
2004-11-23
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S100000, C524S102000, C526S351000, C521S060000, C521S094000, C521S907000
Reexamination Certificate
active
06822023
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to flame retardant polyolefin resin pre-expanded particles suitable for the production of thermal insulation materials, cushioning packaging materials, returnable delivery boxes, automobile bumper core, electrical and electronic parts and so on, particularly electrical and electronic parts, and to in-mold foamed articles prepared by in-mold foaming of the pre-expanded particles.
Polypropylene in-mold foaming products are superior in chemical resistance, heat resistance, impact resistance and distortion restoration rate after compression as compared to polystyrene in-mold foaming products. Thus they have been widely used as cushioning packaging materials, returnable delivery boxes, automobile parts such as bumper core, side impact energy absorber and floor material, and others.
In general, however, cellular molded articles of polyolefin resins have the drawback of being flammable, while they have advantages as mentioned above. In particular, cellular molded articles have a higher flammability as compared with non-cellular molded articles and easily burn.
In recent years, automobile parts, building materials, and electrical and electronic parts are strongly demanded to have flame resistance or self-extinguishing property. In order to meet the demand, investigation has been made about production of cellular molded articles imparted with flame resistance.
As a method for imparting a flame resistance to foamed articles (polyolefin foamed articles prepared by an atmospheric pressure foaming method or a pressure foaming method), there is known a method wherein a resin is incorporated with a flame retardant such as an inorganic flame retardant, a halogen-containing flame retardant or a phosphorus-based flame retardant, melt-kneaded at a temperature lower than the decomposition temperature of a thermally decomposable blowing agent and molded into a desired shape such as sheet, and the molded article is expanded by heating at a temperature higher than the melting point (softening point) of the resin and the decomposition temperature of the blowing agent.
For example, JP-A-3-269029 discloses production of flame retardant foamed articles having excellent flexibility, heat resistance, mechanical property, heat insulation property and electric property together with a high flame resistance by molding a flame retardant expandable composition comprising 100 parts by weight of a polyolefin resin, 30 to 200 parts by weight of an inorganic flame retardant such as magnesium hydroxide, 0.1 to 15 parts by weight of a blowing agent and at most 10 parts by weight of a crosslinking agent at a temperature lower than the decomposition temperature of the blowing agent, and heating the resulting molded article under pressure at a temperature higher than the melting point (softening point) of the resin and the decomposition temperature of the blowing agent to expand the molded article at an expansion ratio of 1.1 to 25.
Also, JP-A-5-331310 discloses production of flame retardant foamed articles without problems of generation of harmful gas and discoloration by, after subjecting to molding into sheets and crosslinking by means of electron beam, thermally expanding an expandable polyolefin resin composition comprising 100 parts by weight of a polyolefin resin, 1 to 40 parts by weight of a thermally decomposable blowing agent, 5 to 50 parts by weight of ammonium polyphosphate and 0.5 to 5 parts by weight of zinc stearate.
Further, JP-A-7-238178 discloses production of flame retardant foamed articles having high mechanical strength and good appearance by, after subjecting to molding into sheets and crosslinking by means of electron beam, thermally expanding a flame retardant expandable polyolefin resin composition comprising 100 parts by weight of a polyolefin resin, 5 to 200 parts by weight of a polysiloxane compound, and a blowing agent such as a thermally decomposable blowing agent or a liquefied gas blowing agent.
In JP-A-3-269029, JP-A-5-331310 and JP-A-7-238178, non-halogen flame retardants are used to provide flame retardant polyolefin foamed articles. However, since foamed articles are prepared by heating molded articles under atmospheric pressure or under pressure to decompose a decomposable blowing agent or to volatilize a volatile blowing agent to thereby foam the molded articles, the methods disclosed therein are difficult to apply to in-mold foaming wherein pre-expanded particles are filled in a mold and are fused together by heating with steam. That is to say, it is difficult to achieve good melt adhesion of the pre-expanded particles and good surface appearance by these methods. Further, since a polyolefin is crosslinked, these methods are disadvantageous from the viewpoints of cost and recycling.
It is known that additives incorporated into resins exert an influence on the cell structure of the obtained pre-expanded particles. If inorganic non-halogen flame retardants are incorporated into pre-expanded particles, a problem such as formation of combined cells or fine cells may arise, thus resulting in deterioration of moldability of the pre-expanded particles.
On the other hand, the following methods are known as a method for imparting a flame resistance to pre-expanded particles and in-mold foamed articles prepared therefrom.
For example, JP-A-4-363341 discloses a self-extinguishing foamed article wherein polyolefin expanded particles are fused together and a thermally expandable graphite powder which serves as a flame retardant are present at the adhesion interface between the expanded particles in an amount of 8 to 20% by weight based on the weight of the foamed article. This method requires a step for previously adhering the graphite powder onto the surface of the expanded particles prior to molding the particles in a mold, thereby making the graphite powder intervene at the interface between adjacent particles fused together. Therefore, not only the method is complicated, but also a problem arises that the melt adhesion of expanded particles deteriorates due to the presence of graphite powder in the surface of pre-expanded particles.
Further, JP-A-6-192465 discloses an in-mold foamed article prepared by wetting polyolefin expanded particles with an organic liquid, adding antimony trioxide and a flame retardant such as a brominated aromatic compound together with a film forming agent to the particles, mixing and sintering (fusing together) them in a conventional manner. It is disclosed that the amount of the flame retardant is from 4 to 10% by weight based on the total weight of the mixture. Working examples thereof show production of molded articles meeting a flame resistance of UL94HF-1.
JP-A-7-309967 discloses flame retardant polyolefin expanded particles which contain a bis(alkyl ether)tetrabromobisphenol A flame retardant and/or a bis(alkyl ether)tetrabromobisphenol S flame retardant and a flame retardant synergist such as antimony oxide, and which have excellent melt adhesion of particles in molding, secondary expandability and moldability as well as flame resistance (self-extinguishing property). Working examples thereof show production of molded articles having a flame retardant content of 1.7 to 5% by weight, an expansion ratio of 28 to 32 and an oxygen index of 27 to 32.
JP-A-10-147661 discloses flame retardant polyolefin pre-expanded particles containing ethylenebispentabromodiphenyl or ethylenebistetrabromophthalimide as a flame retardant and antimony oxide as a flame retardant synergist. It is disclosed that the amount of the flame retardant is from 1 to 30 parts by weight per 100 parts by weight of a polyolefin resin. Working examples thereof demonstrate production of molded articles meeting a flame resistance of UL94HF-2.
JP-A-9-227711 discloses flame retardant polyolefin expanded particles containing 1 to 20% by weight of a pentavalent phosphate compound having a brominated aromatic group or a brominated aliphatic group as a flame retardant.
However, halogen-containing flame retardants such as bromine-containing flame
Iwamoto Tomonori
Ogita Tetsuya
Skarke Steven Charles
Stuart John Bready
Yamaguchi Takema
Armstrong Kratz Quintos Hanson & Brooks, LLP
Cheung William
Kaneka Corporation
Wu David W.
LandOfFree
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