Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From aldehyde or derivative thereof as reactant
Reexamination Certificate
2000-12-15
2002-05-07
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From aldehyde or derivative thereof as reactant
C528S239000, C528S489000, C528S491000, C528S499000, C525S088000, C525S095000, C525S098000, C525S154000, C525S155000, C525S232000, C525S237000, C525S402000
Reexamination Certificate
active
06384179
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a polyacetal resin composition with distinguished toughness and creep resistance and also to its moldings.
Polyacetal resin has a good balance between the mechanical properties and the physical properties and a distinguished fatigue resistance and also is distiguished in such properties as heat resistance, chemical resistance, electric characteristics, lubricant characteristics, etc. and also in moldability and processability, and thus is used in a wide range of applications such as mechanical parts, automobile parts, electric and electronic parts, etc. as engineering materials. However, in spite of so many fields of application in which the polyacetal resin can utilize its characteristics, the polyacetal resin has not been fully utilized yet in such fields owing to its poor toughness.
Heretofore, attempts have been made to improve the toughness by adding thereto a thermoplastic elastomer such as urethane-based, ester-based, olefin-based elastomers, etc., but there have been still such problems of deterioration of high rigidity and chemical resistance as advantages of polyacetal resin in exchange of the improved toughness. Polyacetal resin has still now limited uses.
U.S. Pat. No. 5,500,447 proposes a polyacetal molding material comprising linear polyoxymethylene (i.e. polyacetal) copolymer having a melt index of not more than 0.8 g/10 min. and ordinary additives, where the toughness is considerably improved without any addition of thermoplastic elastomer thereto due to higher molecular weight attained by the polyoxymethylene copolymer, but the effect on improvement of the toughness is not yet satisfactory and the flowability is largely lowered in exchange of the improved toughness and also moldings with good appearance and high dimensional precision are hard to obtain by ordinary injection molding.
U.S. Pat. No. 5,458,839 proposes a process for producing hollow moldings or sheet-shaped or rod-shaped moldings by blow molding or extrusion molding polyoxymethylene (i.e. polyacetal) copolymer resin in a substantially linear molecular structure having a melt index of 0.1-2.0 g/10 min. U.S. Pat. No. 4,879,085 proposes film formation of polyacetal resin having a melt index of 0.3-5.0 g/10 min. by inflation molding under specific conditions. Both Patents use polyacetal resins having low melt indices to obtain special moldings not by injection molding, which is the most popular procedure for polyacetal resin, but by blow molding, extrusion molding and inflation molding.
This means that it is well known that the toughness will increase with decreasing melt index of polyacetal resin, i.e. with increasing molecular weight, but the flowability will decrease in exchange of the improved toughness and moldings with good appearance and high dimensional precision will be hard to obtain by ordinary injection molding. In other words, no versatile polyacetal resin applicable to every molding procedure can be obtained only by simply making the molecular weight of polyacetal resin higher, and thus a method for improving the toughness while maintaining distinguished flowability and advantages of polyacetal resin so far attained has been keenly desired.
JP-A-8-325431 proposes hinge part made of polyacetal resin by molding a polyacetal resin composition comprising polyacetal resin having a melt index of 0.1-15 g/10 min., core-shell of polymer consisting of core of rubbery polymer and shell of glassy polymer and oxyalkylene polymer, where the hinge characteristics can be improved but toughness. JP-A-9-40842 proposes a method for improving appearance while maintaining the distinguished creep resistance by using a polyacetal resin composition having a melt index of not less than 5 g/10 min. comprising a mixture of polyacetal copolymer having a melt index of not more than 3 g/10 min. and polyacetal copolymer having a melt index of not less than 25 g/10 min., where the appearance can be improved but toughness, and only the creep resistance of polyacetal resin so far attained can be maintained, but no further improvement of creep resistance can be atained.
JP-B-55-39182 proposes improvement of flowability by using a polyacetal resin composition comprising a mixture of two polyoxymethylene copolymer components having different melt indices, where the component having the high melt index of not more than 300 is in proportion of 20-80% by weight to the entire mixture and a quotient obtained by dividing the melt index of the high melt index component by that of the low melt index component is adjusted to 15 or more, but the process still fails to satisfy the improvement of toughness and creep resistance.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the aforementioned problems and provide a polyacetal resin composition with highly improved toughness and creep resistance without any deterioration of advantages of polyacetal resin so far attained such as high rigidity and distinguished moldability and processability and also provide its moldings.
As a result of extensive studies to solve the aforementioned problems, the present inventors have found that a polyacetal resin composition comprising polyacetal copolymer having a melt index of less than 1.0 g/10 min. and polyacetal copolymer having a melt index of 1.0-100 g/10 min., both copolymers having controlled melting points to a specific range, can largely improve the toughness and creep resistance without any deterioration of advantages of polyacetal resin so far attained.
That is, the present invention provides:
[1] A polyacetal resin composition, which comprises 30-90% by weight of polyacetal copolymer having a melt index of less than 1 g/10 min. as Component (A) and 70-10% by weight of polyacetal copolymer having a melt index of 1-100 g/10 min. as Component (B), melting points of Component (A) and Component (B) each being 155°-162° C. or difference in melting point between Component (A) and Component (B) being not less than 6° C.
[2] A polyacetal resin composition as described in said item [1], wherein the melting points of Component (A) and Component (B) each are 157°-161° C. or the difference in melting point between Component (A) and Component (B) is not less than 7° C.
[3] A polyacetal resin composition as described in said item [1] or [2], wherein the composition comprises 40-80% by weight of Component (A) and 60-20% by weight of Component (B).
[4] A polyacetal resin composition as described in any one of said items [1]-[3], wherein the melt index of Component (A) is 0.1-0.8 g/10 min.
[5] A polyacetal resin composition as described in any one of said items [1]-[4], wherein the melt index Component (B) is 2.0-30 g/10 min.
[6] A polyacetal resin composition as described in any one of said items [1]-[5], wherein the melt index of Component (B) is 2.5-10 g/10 min.
[7] A polyacetal resin composition as described in any one of said items [1]-[6], wherein the polyacetal resin composition has a melt index of 1.0-3 g/10 min.
[8] A polyacetal resin composition as described in any one of said items [1]-[7], wherein Component (A) comprises at least one member selected from the group consisting of the following polyacetal copolymers (D), (E) and (F):
(D) polyacetal copolymer, which is a polyacetal copolymer in such a structure that 0.1-5 moles of oxyalkylene units represented by the following formula is inserted into a polymer of oxymethylene repeat unit (—CH
2
O—) on the basis of 100 moles of the oxymethylene units, where the terminal groups of the polyacetal copolymer are at least one kind of groups selected from the group consisting of an alkoxy group, a hydroxyalkoxy group and a formate group:
wherein R
0
s are selected from hydrogen, an alkyl group a substituted alkyl group, an aryl group and a substituted aryl group, and R
0
s may be the same or different from
Matsushika Tadao
Tanimura Noritaka
Asahi Kasei Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Truong Duc
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