Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1999-03-25
2000-11-14
Sanders, Kriellion
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
524109, 524223, 524310, 524400, C08K 534, C08K 515, C08K 520, C08K 510, C08K 504
Patent
active
061471461
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an oxymethylene polymer resin composition and an extrusion molded article thereof. More particularly, the present invention is concerned with an oxymethylene polymer resin composition comprising an oxymethylene polymer, a sterically hindered phenol compound, a low-density polyethylene, a calcium salt of a fatty acid having 10 to 36 carbon atoms, wherein the calcium salt has very low contents of calcium ions and chlorine ions which are derived from impurities, and a substance containing a formaldehyde-reactive nitrogen atom. The invention is also concerned with an extrusion molded article produced from the resin composition. The resin composition of the present invention is advantageous not only in that it has excellent extrusion moldability and exhibits excellent anti-slip properties when contacting the screw of an extruder during extrusion molding, but also in that an extrusion molded article produced therefrom has a remarkably reduced occurrence of whitened portions and void portions comprising microvoids and hence has excellent mechanical properties and an excellent appearance.
2. Prior Art
Oxymethylene polymers have been known as engineering plastics which have a good balance of mechanical properties and excellent moldability, and have been used in the production of a wide variety of articles, such as automobile parts, parts for electric and electronic equipment, industrial sundry goods, toys and the like. Among these articles, small-size and mass-produced articles are mainly made by an injection molding method. On the other hand, large-size articles and non-mass-produced articles are usually made by a method in which an oxymethylene polymer is subjected to extrusion molding, and the resultant extrusion molded article is subjected to secondary processing, such as cutting. Representative examples of articles produced by extrusion molding include a cylindrical bar having a diameter of from about 10 to 200 mm (hereinafter referred to as a "rod"), a sheet having a thickness of from about 10 to 100 mm (hereinafter referred to as a "large-thickness sheet"), and the like.
The inherent moldability of oxymethylene polymers is unsatisfactory for producing molded articles, such as a rod and a large-thickness sheet, by extrusion molding. Specifically, the obtained extrusion molded articles are disadvantageous in that they have an interior portion which exhibits a color tone different from that of the surrounding portions (such interior portion is hereinafter referred to as a "whitened portion") or they have an interior void portion comprising microvoids and the like. The occurrence of these whitened and void portions unfavorably leads to a lowering of not only mechanical properties but also the appearance of the molded articles. For example, when a screw is produced by cutting a rod (disadvantageously containing a void portion) which is produced from an oxymethylene polymer by extrusion molding, the mechanical strengths (such as flexural strength, tensile strength and impact strength) of the screw are reduced at the void portion therein, so that the screw is more likely to break under stress. Thus, it has been desired to reduce the occurrence of a whitened portion and a void portion in extrusion molded articles produced from oxymethylene polymers.
In order to improve the moldability of oxymethylene polymers, various attempts have been made. However, many of these attempts are intended to solve problems which accompany the injection molding of an oxymethylene polymer. Examples of these attempts include methods for improving mold release properties [see Unexamined Japanese Patent Application Laid-Open Specification No. 59-4641, Unexamined Japanese Patent Application Laid-Open Specification No. 60-104151, Unexamined Japanese Patent Application Laid-Open Specification No. 63-295661 (corresponding to U.S. Pat. No. 4,900,769) and Unexamined Japanese Patent Application Laid-Open Specification No. 4-100847 (corresponding to U.S. Pat. N
REFERENCES:
patent: 5191006 (1993-03-01), Matsumoto et al.
patent: 5519075 (1996-05-01), Matsumoto et al.
Horio Mitsuhiro
Seyama Toshiharu
Asahi Kasei Kogyo Kabushiki Kaisha
Sanders Kriellion
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