Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-05-15
2003-01-28
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S064000, C525S399000, C525S400000, C525S441000, C525S456000, C525S472000
Reexamination Certificate
active
06512047
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel polyoxymethylene resin composition having improved tensile elongation, impact resistance, thermal stability and processibility, which comprises a polyoxymethylene matrix, a polyester elastomer, a polyurethane elastomer, and a maleic anhydride-grafted aliphatic polyolefinic rubbery polymer.
BACKGROUND OF THE INVENTION
Polyoxymethylene resins have been widely used in various applications owing to their good mechanical, chemical, physical and electrical properties. However, the impact resistance of conventional polyoxymethylene resins is not sufficiently high for certain applications. Accordingly, there have been various attempts to develop polyoxymethylene resins having enhanced impact resistance by way of adding another polymer component thereto.
For example, there have been reported a number of polyoxymethylene blends which contain: a rubbery polymer containing nitrile or carboxylic ester groups disclosed in, e.g., Japanese Patent Publication No. 12674/1970; a copolymer of &agr;-olefin and &agr;,&bgr;-unsaturated carboxylic acid disclosed in, e.g., Japanese Patent Publication No. 18023/1970; a copolymer of ethylene and vinylic or acrylic ester disclosed in, e.g., Japanese Patent Publication No. 26231/1970; a rubbery polymer such as a diolefin-nitrile copolymer disclosed in, e.g., U.S. Pat. No. 3,476,832; an aliphatic polyether disclosed in, e.g., Japanese Patent Publication No. 33095/1975; a mixture of a polyolefin polymer and an ethylene-vinyl copolymer disclosed in, e.g., Japanese Patent Laid-open Publication No. 40346/1974; and a polyolefin, polystyrene, polyester or polyamide-based thermoplastic elastomer disclosed in, e.g., Japanese Patent Laid-open Publication No. 164116/1985.
However, the added polymer components in the above-mentioned blends are not readily miscible with polyoxymethylene resins; and despite attempts to homogenize the blends, the resulting improvements in the impact resistance have been limited.
It has also been suggested that segregated discrete particles of a thermoplastic polyurethane elastomer, when dispersed in a polyoxymethylene matrix, can improve the impact resistance thereof. For instance, U.S. Pat. No. 5,286,807 discloses an impact resistant polyoxymethylene composition consisting essentially of 5 to 15 wt % of a thermoplastic polyurethane having a soft segment glass transition temperature of lower than 0 C,, and 85 to 95 wt % of a polyoxymethylene polymer having a number average molecular weight of 20,000 to 100,000, the thermoplastic polyurethane being dispersed in the polyoxymethylene as discrete particles.
Further, U.S. Pat. No. 4,804,716 discloses a polyoxymethylene composition consisting essentially of 60 to 85 wt % of a polyoxymethylene polymer and 15 to 40 wt % of a thermoplastic polyurethane dispersed in the polyoxymethylene polymer as small discrete particles of 0.01 to 0.9 &mgr;m.
However, the above-mentioned polyoxymethylene compositions containing polyurethane elastomer particles suffer from various deficiencies including the handling difficulties in an injection molding process due to their low thermal stability, and in an extrusion process due to their phase separation or die swelling.
U.S. Pat. No. 5,244,946 discloses thermoplastic polymer blends comprising a monovinylidene aromatic copolymer optionally modified with a rubber, a polyoxymethylene polymer and an elastomeric material selected from a thermoplastic polyurethane or an elastomeric copolyester. The monovinylidene aromatic copolymer employed in the polymer blends as a compatibilizer, however, is difficult to synthesize and not commercially available.
Further, U.S. Pat, No. 4,556,690 relates to a polyoxymethylene resin composition comprising a polyoxymethylene base resin and at least one alpha-olefin polymer grafted with an unsaturated carboxylic acid; and U.S. Pat. No. 4,670,508 describes a thermoplastic resin composition comprising at least one thermoplastic resin such as polyoxymethylene resin and an ultra-high molecular weight polyolefin powder such as an ethylene copolymer which may be modified with at least one polar group such as an acid anhydride group. These resin compositions disclosed in these patents have low tensile elongation and impact resistance.
U.S. Pat. No. 4,169,867, on the other hand, discloses a thermoplastic molding composition comprising a mixture of an oxymethylene polymer and a copolyester elastomer in two molecular weight distribution. However, in this composition, the oxymethylene polymer and the copolyester elastomer undergo phase-separation due to low compatability therebetween.
Accordingly, there has existed a need to develop polyoxymethylene resin compositions having improved processibility as well as good tensile elongation, impact resistance and thermal stability.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a novel polyoxymethylene resin composition having improved processibility as well as thermal stability, impact resistance and tensile elongation, by way of adding, to a polyoxymethylene, a thermoplastic polyester elastomer and a thermoplastic polyurethane elastomer together with a maleic anhydride-grafted aliphatic polyolefinic rubbery polymer as a homogenizing agent.
It is another object of the present invention to provide articles formed from the inventive polyoxymethylene resin composition.
In accordance with one aspect of the present invention, there is provided a polyoxymethylene resin composition comprising:
(i) from 45 to less than 97% by weight of a polyoxymethylene resin (Component A);
(ii) from 1 to less than 20% by weight of a thermoplastic polyester elastomer (Component B)
(iii) from 2 to 35% by weight of a thermoplastic polyurethane elastomer (Component C) and
(iv) from 0.1 to less than 10% by weight of a maleic anhydride-grafted aliphatic polyolefinic rubbery polymer (Component D),
based on the total weight of Components A, B, C and D.
In accordance with another aspect of the present invention, there is provided an article shaped from the inventive polyoxymethylene resin composition.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is characterized by the homogenization of a thermoplastic polyester elastomer (Component B) and a thermoplastic polyurethane elastomer (component C) with a polyoxymethylene (Component A) by the action of a maleic anhydride-grafted aliphatic polyolefinic polymer which contains substituted succinic anhydride groups (Component D). Such homogenization of otherwise incompatible Components A, B and C is believed to take place through the chemical reactions of the succinic anhydride groups of Component D with various end groups of the elastomers and the polyoxymethylene base resin, as is further discussed herein.
Each of the constituent components of the inventive composition is described below.
Major Components and Additives
(A) Polyoxymethylene Resin
A polyoxymethylene resin is a polymer having an oxymethylene repeating unit; and the polyoxymethylene resin component (Component A) of the present invention may be a homopolymer having the oxymethylene repeating unit, an oxymethylene-oxyalkylene copolymer, or a mixture thereof.
The homopolymer may be prepared by polymerizing formaldehyde or a cyclic oligomer thereof such as trioxane; and the copolymer may be prepared by polymerizing formaldehyde or a cyclic oligomer thereof with an alkylene oxide or a cyclic formal, e.g., 1,3-dioxolane, diethylene-glycolformal, 1,4-propanediolformal, 1,4-butanediolformal, 1,3-dioxepaneformal, 1,3,6-trioxocane and the like. Representative alkylene oxides include ethylene oxide, propylene oxide, butylene oxide and phenylene oxide.
The homopolymer and the copolymer may be stabilized by capping the terminal groups thereof by esterification or etherification. An oxymethylene-oxyethylene copolymer may be stabilized by removing unstable end-oxymethylene groups to obtain a stabilized copolymer having —CH
2
CH
2
OH end groups according to the method disclosed, e.g., in U.S. Pat. No. 3,219,623, which is incorp
Hong Ki-Chang
Kim Tak-Kyu
Lee Jong-Taek
Anderson Kill & Olick P.C.
Korea Engineering Plastics Co., Ltd.
Short Patricia A.
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