Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1992-06-18
1994-01-11
Seidleck, James J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525155, 525165, 525241, 525227, C08L 5902, C08L 2506, C08L 2508, C08L 3310
Patent
active
052782352
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a polyacetal resin composition, and more particularly, to a polyacetal resin composition yielding a favorable surface of resulting molded products, low frictional abrasion and low molding shrinkage percentage, blending thermoplastic polystyrene resin and thermoplastic acrylic resin while having polyacetal resin as its major component.
PRIOR ART
Polyacetal resin demonstrates superior moldability while also possessing balanced mechanical properties, electrical properties, heat resistance, chemical resistance and frictional abrasion characteristics, etc. Moreover, it also possesses outstanding fatigue resistance among plastic materials. Therefore, it is used in an extremely broad range of fields as a representative engineering plastic. However, accompanying expansion of its fields of use, the requirements on the performance of the resin are tending to become increasingly sophisticated. One of these requirements is improvement of shrinkage percentage. In other words, polyacetal resin demonstrates a high molding shrinkage percentage due to its high degree of crystallization. As a result, there are cases when this becomes a problem in applications such as precision parts, thin-walled parts and large parts. As careful mold design is required in consideration of this high molding shrinkage percentage, there are many cases in which improvement of the molding shrinkage percentage is desirable. In addition, although polyacetal resin is classified as having superior frictional abrasion characteristics, there are many cases in which further improvement is desirable.
In general, the blending of other resins has been attempted as a method for improving the various physical properties of polyacetal resin. Blending of polystyrene resin is one example of these attempts as is indicated in Japanese Patent Publication No. 44-946 and Japanese Patent Laid-Open No. 64-38463. The former focuses on a fibrous substance. However, according to studies conducted by the inventors of the present invention, the polymer mixture obtained by that described results in the strong appearance of layer separation and layer peeling phenomena when used for molding, thus giving it no practical value. In addition, although the latter discloses that the use of a specific highly viscous polystyrene resin is effective for overcoming the relevant problems, this still remains inadequate and has problems in terms of molding processing, particularly with respect to increasing the viscosity of the composition.
DISCLOSURE OF THE INVENTION
The present invention is generally directed to solving; the above-mentioned problems for the purpose of providing a polyacetal resin composition demonstrating superior frictional abrasion characteristics and improved shrinkage percentage during molding in which the surface of molded products is uniform and smooth by improving dispersability, while eliminating obstacles such as the appearance of streaked phase separation structures on the surface of injection molded products based on defective dispersion of components and defective adhesion between resin phases, as well as the inhibition of frictional abrasion characteristics, one of the characteristics of polyacetal resins, due to the occurrence of surface layer separation caused by friction, in a polymer blend of polyacetal resin and inexpensive, thermoplastic polystyrene resin. It has therefore been discovered that the above-mentioned defects can be solved and that favorable polyacetal resin molded products can be obtained by blending specific amount of .alpha. specific thermoplastic acrylic resin as third component without using a specific high-viscosity polystyrene like that mentioned above, which led to the present invention.
In other words, the present invention relates to a polyacetal resin composition capable of forming a molding having good surface conditions, characterized by comprising a polyester resin A, a thermoplastic polystyrene resin B and a thermoplastic acrylic resin C in amounts of 55 to 95 pa
REFERENCES:
patent: 3642940 (1972-02-01), Burg et al.
Miyawaki Keiichi
Tajima Yoshihisa
Clark W. R. H.
Polyplastics Co. Ltd.
Seidleck James J.
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