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...
Reexamination Certificate
2001-03-29
2004-08-17
Cain, Edward J. (Department: 1714)
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...
C524S305000, C524S315000, C524S394000, C525S09200D, C525S398000, C525S399000, C525S400000, C525S401000, C528S230000
Reexamination Certificate
active
06777487
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polyacetal ABA type block copolymer having a shorter crystallization time, a higher roundness and distinguished long-term dimensional characteristics and durability, when molded. In addition, such block copolymer has superior compatibility with other polymer compounds and superior adhesibility to inorganic fillers. Furthermore, the present invention relates to a composition comprising such a polyacetal ABA type block copolymer, and moldings obtained from the polyacetal ABA type block copolymer or a composition comprising the polyacetal ABA type block copolmer.
BACKGROUND ART
A polyacetal resin is a material with a distinguished slidability and is used preferably as gear material. However, in reality, the conventional polyacetal resins obtained by homopolymerization of formaldehyde or copolymerization of formaldehyde, trioxane and cyclic ether often fail to produce gears of large diameters, e.g. pitch circle diameters of 60 mm or larger, which are satisfactory from the viewpoint of performances, by injection molding. That is, (1) The larger the gear diameter, the thicker the gear itself, and the cooling time is prolonged in the injection molding step. As a result, such a problem has been encountered that the injection molding cycle will be prolonged in case of other resin materials than those having a higher crystallization rate and thus the productivity will be lowered. (2) In case of the conventional polyacetal resin, the roundness of large-diameter gears produced by injection molding is not satisfactory and as a result such a problem has been encountered that in copiers or printers using such gears, power transmission accuracy will be lowered, resulting in uneven dot distances and failure of clear print/image. (3) When large-diameter gears are injection molded from the conventional polyacetal resin, the dimensions of injection molded large-diameter gears are unstable when left standing for a long time, and application of such gears to copier or printers will give rise to failure in meshing between gears at pitch points, when used for a long time (in worst cases the meshing between gears will be brought into complete failure), causing generation of uneven vibration during the revolutionary transmission and generation of dislocated print/image. (4) Furthermore, the larger the gear diameter, the more unsatisfactory the gear durability, one of resin material properties, and thus application of such gears to copiers or printers gives rise to breakage of a gear tooth (gear teeth) due to wear, rupture or fatigue of gear when used for a long time, and thus the long-term functioning of copiers or printer cannot be so far guaranteed.
Attempts have been made with polyacetal block polymers to improve the problem of the conventional polyacetal resins, as proposed, for example, in JP-A-3-21657 and JP-A-5-9363, which disclose polyacetal polymers, which are AB type block copolymers, blocked at one end by alkylene oxide as an adduct to alcohol or carboxylic acid.
JP-A-4-306215 discloses AB type and ABA type polyacetal block copolymers comprising a polyoxymethylene segment (A) and a polymethylene segment (B), obtained by polymerizing one end or both ends of the polymethylene segment with formaldehyde, trioxane or the like in the presence of a compound containing one functional group selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, an ester group and an alkoxy group. It is further disclosed that hydrogenated polybutadiene can be used as a polymethylene segment.
Furthermore, JP-A-11-51154 discloses gears made from polyacetal copolymer having a specific monomer formulation, or the polyacetal copolymer admixed with &agr;-olefin oligomer, an inorganic filler or the like as resin materials.
However, the polyacetal copolymers disclosed in the foregoing references fail to obtain the above-mentioned characteristics necessary for the large-diameter gears.
DISCLOSURE OF THE INVENTION
An object of the present invention is to solve the foregoing problems and provide a polyacetal ABA type block copolymer and a resin composition comprising the block copolymer, which have a high crystallization rate and are capable of molding large-diameter gears with a high roundness and distinguished dimensional stability and durability.
As a result of extensive studies to solve the foregoing problems, the present inventors have found that a polyacetal ABA type block copolymer comprising a polyacetal copolymer and a specific polymer or a polyacetal resin composition comprising the ABA type block copolymer and a specific polymer compound are distinguished in the necessary characteristics required for large-diameter gears, that is, crystallization rate, roundness, dimensional stability and durability, and have established the present invention.
That is, the present invention provides:
[1] An ABA type block copolymer, which comprises polyacetal segments (A) and a hydrogenated polybutadiene segment (B) hydroxyalkylated at both ends, represented by the following formula (1):
[where A comprises 95-99.9 mol % of oxymethylene units and 0.1-5 mol % of oxyalkylene units represented by the following formula (2):
(where R
2
is independently selected from the group consisting of hydrogen, an alkyl group, a substituted alkyl group, an aryl group and a substituted aryl group, and j is an integer selected from 2 to 6), and the terminal groups are polyacetal copolymer residues having a structure represented by the following formula (3):
(where R
2
and j have the same meanings as defined above), B′ is a hydrogenated polybutadiene having an iodine value of 20 g-I
2
/100 g or less and containing 70-98 mol % of 1,2-bonds and 2-30 mol % of 1,4-bonds, R
1
is independently selected from the group consisting of hydrogen, an alkyl group, a substituted alkyl group, an aryl group and a substituted aryl group, and k is an integer selected from 2 to 6 where two ks may be the same or different from each other], the hydrogenated polybutadiene segment (B) hydroxyalkylated at both ends having a number average molecular weight of 500-10,000 and the ABA type block copolymer having a number average molecular weight of 10,000-500,000;
[2] An ABA block copolymer as described in the foregoing [1], wherein B′ is a hydrogenated polybutadiene containing 80-95 mol % of 1,2-bonds and 5-20 mol % of 1,4-bonds;
[3] A polyacetal resin composition, which comprises 100 parts by weight of a polymer compound (I) comprising 20-100% by weight of the ABA type block copolymer as described in [1] or [2] and 0-80% by weight of a polyacetal copolymer having a number average molecular weight of 10,000-500,000, represented by the following formula (4):
(where R
3
and R
4
are independently selected from the group consisting of hydrogen, an alkyl group, a substituted alkyl group, an aryl group and a substituted aryl group, p=95-99.9 mol %, q=0.1-5 mol %, p+q=100 mol %, and z is an integer selected from 2 to 6), and 0.1 to 200 parts by weight of at least one of polymer compounds (II) having a number average molecular weight of 500 or more, selected from the group consisting of a polyolefin-based polymer compound, a polyurethane-based polymer compound, a polyester-based polymer compound, a polystyrene-based polymer compound, a polyacryl-based polymer compound and a polyamide-based polymer compound;
[4] A polyacetal resin composition as described in the foregoing [3], wherein the polymer compound (II) is a polyolefin-based polymer compound comprising &agr;-olefin-based polymer compound;
[5] A polyacetal resin composition, as described in the foregoing [4], wherein the &agr;-olefin-based polymer compound comprises 0.1 to 6 parts by weight of an ethylene-&agr;-olefin random copolymer having a number average molecular weight of 500-10,000, comprising 10-70 mol % of ethylene unit and 30-90 mol % of &agr;-olefin unit;
[6] A polyacetal res
Komatsu Sumio
Nakamura Hideki
Niino Masahiko
Asahi Kasei Kabushiki Kaisha
Cain Edward J.
Dickstein Shapiro Morin & Oshinsky LLP.
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