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
2000-08-09
2003-02-04
Seidleck, James J. (Department: 1711)
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...
C524S320000, C524S321000, C524S317000, C524S318000
Reexamination Certificate
active
06515058
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polyamide resin composition pellets for molding, e.g., injection molding, and to a process for producing the same. More particularly, the invention relates to a polyamide resin composition and pellets thereof having excellent workability, e.g., releasability and plasticity, under a wide range of injection molding conditions and having excellent color tone quality.
DESCRIPTION OF THE RELATED ART
Polyamide resins, especially polyamide 66 resins, are extensively used as injection-molded articles such as connectors and tying bands because of their excellent mechanical properties. In recent years, injection-molded articles having a complicated shape are required and there also is a desire for the fast-cycle production of these articles under various molding conditions.
For example, some molding techniques employ a relatively low cylinder temperature near the melting point of the polymer, while others employ a cylinder temperature as high as 350° C. With respect to mold temperature, some techniques use a mold temperature controller to conduct molding at a mold temperature as low as room temperature or below, while others employ a mold temperature as high as 100° C. or above.
Important means for raising productivity in injection molding are to improve the releasability of molded articles from the molds and to shorten the time required for plasticization. The technique generally used for attaining these properties is to add various additives to pellets. Examples of lubricants for use in polyamide resins include higher fatty acids, metal salts of higher fatty acids, esters of higher fatty acids, and higher fatty acid bisamides.
However, use of any one of these lubricants only improves releasability in a specific narrow mold temperature range and plasticity in a specific narrow cylinder temperature range, and it is difficult in injection molding to simultaneously satisfy releasability in a wide mold temperature range of from a low to a high temperature and plasticity in a wide cylinder temperature range of from a low to a high temperature.
JP-A-7-228770 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a technique in which a combination of a higher fatty acid metal salt and a higher fatty acid ester is attached to the surface of pellets. Use of these lubricants in combination is effective in improving releasability in a wider mold temperature range than in the case of using a single lubricant. However, the technique in which lubricants are merely attached to the pellet surface as in the disclosed technique has an unsolved problem that releasability is apt to fluctuate because of the unevenness of the amount of the lubricants attached to the surface and detachment of the attached lubricants from the surface. Furthermore, especially in molding with a high temperature melting, the technique described above causes a problem that a longer time is required for plasticization upon injection molding, resulting in reduced productivity, etc. The reason for this problem may be that in the case where pellets having a higher fatty acid ester attached to the pellet surface are fed to a high-temperature cylinder, the lubricant present on the pellet surface melts to cause the pellets to fuse to one another and thereby inhibit the pellets from smoothly moving in the cylinder.
U.S. Pat. No. 5,929,200 discloses a technique in which various carboxylic acid salts are incorporated into a polyamide melt during a polymerization process for polyamide production. However, salts of lower aliphatic carboxylic acids are almost ineffective in improving the moldability.of polyamides, while salts of higher aliphatic carboxylic acids, when used alone, are insufficient for attaining a wide range of molding conditions, which attainment is included in the objects of the invention.
JP-B-6-19016 (the term “JP-B” as used herein means an “examined Japanese patent publication”) discloses a technique in which a phosphorous ester, a higher fatty acid metal salt having 10 to 25 carbon atoms, and a higher fatty acid ester are incorporated into a polyamide through kneading with an extruder. Indeed, this composition has improved releasability and further retains impact strength. However, the addition of a nucleating agent such as the phosphorous ester is apt to cause problems that the composition gives a molded article which has a reduced elongation and is brittle and that the viscosity of the polyamide becomes unstable.
JP-A-9-235464 discloses a technique in which an ester of a higher fatty acid with a lower dihydric alcohol is used. However, in the case of using this aliphatic carboxylic acid ester, it is difficult to satisfy releasability under a wide range of mold temperature conditions although releasability in a specific temperature range is improved.
SUMMARY OF THE INVENTION
An object of the invention is to provide polyamide resin pellets which have improved releasability and reduced fluctuations thereof, both in a wide mold temperature range, even without adding a nucleating agent, have improved plasticity characteristics in a wide cylinder temperature range, and further have excellent color tone quality, so as to cope with the recent needs of the market for improved moldability required of polyamide resins.
Other objects and effects of the present invention will become apparent from the following description.
As a result of extensive investigations, the present inventor has found that those problems can be eliminated by using a specific combination of lubricants and incorporating a specific one of these lubricants inside pellets.
Specifically, the above-described objects of the present invention have been achieved by providing the following polyamide pellets.
1. Polyamide resin pellets which comprise:
100 parts by weight of a polyamide resin;
from 0.01 to 1.0 part by weight of lubricant A, which comprises at least one ester of a higher aliphatic carboxylic acid with a higher alcohol; and
from 0.01 to 1.0 part by weight of lubricant B, which comprises at least one higher aliphatic carboxylic acid metal salt,
wherein said lubricant A is present inside the pellets.
2. The polyamide resin pellets of claim 1 , wherein said lubricant B is a metal salt of a higher aliphatic carboxylic acid having 26 to 30 carbon atoms.
3. The polyamide resin pellets of claim 2, wherein lubricant B is attached to the surface of the pellets.
4. The polyamide resin pellets of claim 1, wherein said lubricant B comprises at least two higher aliphatic carboxylic acid metal salts, at least one of which is attached to the surface of the pellets.
5. Polyamide resin pellets which comprise:
100 parts by weight of a polyamide resin;
from 0.01 to 1.0 part by weight of lubricant A, which comprises at least one ester of a higher aliphatic carboxylic acid with a higher alcohol;
from 0.01 to 1.0 part by weight of lubricant B, which comprises at least one higher aliphatic carboxylic acid metal salt; and
from 0.01 to 1.0 part by weight of lubricant C, which comprises a higher aliphatic carboxylic acid amide,
wherein said lubricant A is present inside the pellets.
6. The polyamide resin pellets of claim 5, wherein said lubricant B comprises at least two higher aliphatic carboxylic acid metal salts, at least one of which is attached to the surface of the pellets.
7. The polyamide resin pellets of claim 5, wherein said lubricant A is an ester of an aliphatic carboxylic acid having 15 to 21 carbon atoms.
8. The polyamide resin pellets of claim 6, wherein said lubricant A is an ester of an aliphatic carboxylic acid having 15 to 21 carbon atoms.
9. The polyamide resin pellets of claim 5, wherein said lubricant C is a saturated fatty acid amide.
10. The polyamide resin pellets of claim 6, wherein said lubricant C is a saturated fatty acid amide.
11. The polyamide resin pellets of claim 7, wherein said lubricant C is a saturated fatty acid amide.
12. The polyamide resin pellets of claim 6, wherein said lubricant B that is attached to the pellet surface is a metal sa
Matsumoto Shinya
Tomiyama Hiroshi
Asahi Kasei Kogyo Kabushiki Kaisha
Birch & Stewart Kolasch & Birch, LLP
Rajguru U. K.
Seidleck James J.
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