Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
1999-06-03
2001-08-28
Weisberger, Richard (Department: 1774)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C428S902000, C528S170000, C528S183000, C528S337000, C528S348000, C528S481000, C528S499000, C442S060000, C442S179000, C442S334000, C442S394000, C264S184000, C264S203000, C264S336000
Reexamination Certificate
active
06280843
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to wholly aromatic polyamide fibers, a sheet comprising same and a method of producing the sheet. More particularly, the present invention relates to wholly aromatic polyamide fibers having a high heat resistance and an excellent electric insulating property under high temperature and high humidity conditions, and a sheet comprising the heat resistant and electrically insulating wholly aromatic polyamide fibers and at least one member selected from binder resins and heat resistant organic polymer fibrids, and usable as an electric insulating material, and a method of producing the wholly aromatic polyamide fibers.
2. Description of the Related Art
It is well-known that wholly aromatic polyamide fibers have excellent heat resistance and mechanical strength and thus are useful for various uses.
In the case where the wholly aromatic polyamide fibers are used as a resin-reinforcing material, for example, FRP material or parts of OA machines and devices which have to exhibit a very accurate dimensional stability, however, the dimensions of the aromatic polyimide fibers in the longitudinal direction thereof and in the transverse directions at right angles from the longitudinal direction change to a great extent in an atmosphere in which an increase and a decrease of the temperature are repeated, and the change in the dimensions due to absorption and desorption of moisture in the fibers is significant. Therefore, in a fiber-reinforced resin composite laminate plate, a strain is created in the interfaces between the reinforcing fibers and the resin, and the strain causes the laminate plate to exhibit a reduced durability to repeated load, and an interfacial separation occurs. Particularly, when used as an electric insulation material while an electric current is flowed therethrough for a long period, water is accumulated in a small amount in the interfaces between the resin and the reinforcing fibers, to promote movement of impurity ions contained in the resin or fibers, or to cause an interfacial separation due to a temperature-increase and water-evaporation. As an attempt for solving the above-mentioned problems, for example, Japanese Unexamined Patent Publication No. 5-83,096, No. 62-218,425 and No. 62-225,539 discloses a method of improving interfacial adhesion of aromatic polyamide fibers to a resin by heat treatment. However, this method is disadvantageous in that the fiber-reinforced resin material has a high content of impurity ions and a high moisture content, and thus is unsuitable for electrically insulating uses. These problems have not yet been fully solved.
The wholly aromatic polyamide fibers have a very high resistance to cutting and thus are used in various protective materials as disclosed in, for example, Japanese Unexamined Patent Publications No. 4-14,277, No. 6-280,140. However, this very high cutting resistance causes such a problem in that when a resin composite laminate plate reinforced by the wholly aromatic polyamide fibers is subjected to a piercing work with a drill, the reinforcing fibers are not sharply cut, the reinforcing fibers are divided into fine fibrils or not completely cut, and thus the resultant hole has a rough inner face. Particularly, in recent piercing work, a very small size of hole is required to be formed with a high accuracy, and thus a new piercing method using a carbon dioxide gas laser has been attempted. Therefore, a solution of the above-mentioned problem is strongly demanded in industry.
Also, when the fiber-reinforced composite resin laminate material is subjected to cutting work, the reinforcing fibers are not sharply cut and the resultant fine fibrils from the reinforcing fibers project from the cut face. This problem must be solved.
SUMMARY OF THE INVENTION
An object of the present invention is to provide holly aromatic polyamide fibers having a very high dimensional stability even when employed in an atmosphere in which the temperature repeatedly changes and in which the moisture is absorbed by or desorbed from the fibers, a sheet comprising the fibers and a method of producing the fibers.
Another object of the present invention is to provide wholly aromatic polyamide fibers which, when used as reinforcing fibers for a fiber-reinforced resin composite laminate plate, and subjected to a piercing, cutting or laser treatment work, can be sharply cut, exhibit a high resistance to fibril-formation from the fibers, and thus cause the laminate plate to exhibit smooth and sharp cut faces, a sheet comprising the fibers, and a method of producing the sheet.
The above-mentioned objects can be attained by the wholly aromatic polyamide fibers, the sheet comprising the fibers and the method of producing the sheet, of the present invention.
The wholly aromatic polyamide fibers of the present invention are characterized by comprising wholly aromatic polyamide crystals having apparent crystal sizes determined from a wide angle X-ray diffraction intensity curve in accordance with the Scherrer's equation and satisfying the requirements (1), (2) and (3);
(1) the crystal size (A) in a (110) plane is 7.5 nm (75 angstroms) or more,
(2) the crystal size (B) in a (200) plane is 8.2 nm (82 angstroms) or more, and
(3) the product (A×B) of the crystal size (A) and the crystal size (B) is 61.50 to 630.00, and having a thermal linear expansion coefficient within the range of from −1.0×10
−6
/° C. to −7.5×10
−6
/° C.
In the wholly aromatic polyamide fibers of the present invention, when the wholly aromatic polyamide fibers in an amount of 2 g are cut into a short length of 1 mm or less and immersed in 50 ml of a distilled water, and are heat-treated in an autoclave at a temperature of 121° C. under a pressure of 2 kg/cm
2
G, to extract impurity ions from the fibers, and the extracted impurity ion-containing water is subjected to a ICP analysis and to a chromatographic analysis to determine the amount of the extracted impurity ions, namely sodium, potassium and chlorine ions, per liter of the extracted impurity ion-containing water, the extracted impurity ions preferably satisfy the requirements (a), (b) and (c):
(a) the amount of the extracted sodium ions is not more than 40 mg/liter.
(b) the amount of the extracted potassium ions is not more than 3.0 mg/liter, and
(c) the amount of the extracted chlorine ions is not more than 7.5 mg/liter.
The wholly aromatic polyamide fiber sheet of the present invention comprises, as principal components, 60 to 96% by weight of wholly aromatic polyamide staple fibers, and 4 to 40% by weight of at least one member selected from the group consisting of organic resin binders and heat-resistant organic polymer fibrids,
said wholly aromatic polyamide staple fibers containing the specific wholly aromatic polyamide fibers of the present invention in the form of staple fibers.
The wholly aromatic polyamide fiber sheet of the present invention preferably has a maximum change in the longitudinal dimension of 50 &mgr;m or less per length of 20 mm, determined by such a test method for dimensional change of a sheet due to moisture-absorption and desorption of the sheet, that a sample of the sheet having a length of 20 mm and a width of 5 mm is left standing in the ambient atmosphere at room temperature at a relative humidity of 85% RH or more for 120 hours or more to allow the sheet to fully absorb moisture; the moisture-absorbed sheet sample is subjected to heating to a temperature of 280° C. at a heating rate of 10° C./minute, then to cooling to room temperature at a cooling rate of 10° C./minute to dry the sheet sample, the above-mentioned heating and cooling procedures being repeated three times in total under the same conditions as mentioned above; and a maximum change in the longitudinal dimension of the sheet sample generated during the repeated heating and cooling procedures is measured per 20 mm in the longitudinal dimension.
The method of the present invention for producing a wholly aromatic p
Matsui Michikage
Murayama Sadamitsu
Wada Masanori
Sughrue Mion Zinn Macpeak & Seas, PLLC
Teijin Limited
Weisberger Richard
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