Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1994-03-09
1995-08-29
Morgan, Kriellion S.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524196, 524291, 524495, C08L 6128
Patent
active
054460867
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND ART
1. Technical Field
The present invention relates to a polyoxymethylene composition which is improved in heat stability, particularly little generating formaldehydic stench in molding, and in the occurrence of mold deposits.
More particularly, the present invention relates to a polyoxymethylene composition which exhibits excellent antistatic properties and is improved in the occurrence of mold deposits, one which is excellent in the resistances to weather and heat and is improved in the occurrence of mold deposits, one which exhibits excellent impact resistance and is improved in the occurrence of mold deposits, and an electrically conductive polyoxymethylene composition which is improved in the occurrence of mold deposits.
2. Description of the Related Art
A polyoxymethylene resin is excellent in mechanical properties, resistances to fatigue, wear, abrasion, chemicals and heat, and moldability, and has therefore been utilized in various fields including automobile, precision machines such as electrical and electronic appliances, building materials, piping and so forth. With enlargement and diversification in the application field, however, there has arisen a tendency to require the resin to have higher-level quality.
As one of properties to be demanded, there is cited that the reduction of the mechanical strengths thereof in its extrusion or molding step, the occurrence of deposits formed on the mold (i.e., mold deposits) or the like should be kept under controll in a lowered level. One of the chief factors causing such unfavorable phenomena is the decomposition of the polymer by heating.
Polyoxymethylene has an essential property of being easily decomposed in a hot oxidizing atmosphere or under an acidic or alkaline condition owing to its chemical structure. With respect to a polyoxymethylene homopolymer, a method wherein the chemically active ends thereof is esterified (e.g., acetylation), or a method wherein trioxane is copolymerized with a monomer having an adjacent carbon-carbon bond (such as a cyclic ether or a cyclic formal) and then the unstable ends of the obtained copolymer are decomposed, for example, are known for the stabilization of the chemically active ends of the polyoxymethylene homopolymer. However, a polyoxymethylene resin also suffers from the cleavage of the backbone chain in heating, and this phenomenon cannot be inhibited by the above means alone, thus necessitating the addition of an antioxidant and other stabilizer in practice.
The antioxidant to be added to a polyoxymethylene resin includes sterically hindered phenol compounds and sterically hindered amine compounds, while the stabilizer other than antioxidants includes polyamides, urea derivatives, amidine compounds, hydroxides of alkali or alkaline earth metals and salts of these metals with organic or inorganic acids. Various combinations of these antioxidants with these stabilizers are used.
However, even a polyoxymethylene composition containing these stabilizers is not sufficiently prevented from suffering decomposition of the polymer. Actually, when such a composition is exposed to heat and oxygen in a molding cylinder during molding, the composition generates formaldehyde by the cleavage of the backbone chain or from insufficiently stabilized ends to worsen the working atmosphere in extrusion molding. Further, when the molding work is prolonged, powdery or tarry deposits (mold deposits) adheres on the mold surface, which is one of the chief factors causing lowering in the working efficiency and the deterioration of the surface appearance of a molded article. Further, the decomposition of the polymer brings about lowering in the mechanical strengths thereof. Although various attempts have been made under these circumstances to find a more effective stabilizer formula, no satisfactory result has been obtained as yet. For example, a proposal to add a melamine-formaldehyde polycondensate together with an antioxidant and other heat stabilizer to polyoxymethylene is disclosed in Japanese Patent Publication-A No.
REFERENCES:
patent: 5086095 (1992-02-01), Katsumata
patent: 5149723 (1992-09-01), Hayes
patent: 5171770 (1992-12-01), Nakagawa
patent: 5208279 (1993-05-01), Katsumata
Patent Abstracts of Japan, vol. 9, No. 233 (C-304) Sep. 1985 & JP-A-60 090 250 (Mitsubishi Gas) 21 May 1985.
Chisoku Arisa
Kamiya Makoto
Miyaji Hiroyuki
Sugiyama Noriyuki
Yamamoto Kaoru
Morgan Kriellion S.
Polyplastics Co. Ltd.
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