Stock material or miscellaneous articles – Structurally defined web or sheet – Including stitching and discrete fastener – coating or bond
Reexamination Certificate
2001-10-03
2003-07-29
Thomas, Alexander S. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including stitching and discrete fastener, coating or bond
C428S105000, C428S113000, C428S902000
Reexamination Certificate
active
06599610
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a stitched multiaxial reinforcing laminate composed of carbon fiber yarns, in more detail, a stitched multiaxial reinforcing laminate having a thin thickness composed of thick tow-like carbon fiber yarns, a fiber-reinforced plastic using the same, and a production process of the stitched multiaxial reinforcing laminate.
BACKGROUND ART
Carbon fibers have a low specific gravity, high tensile strength and high tensile modulus of elasticity, and carbon fiber reinforced plastics obtained by immobilizing them with a resin (hereinafter called CFRP) are materials having high specific strengths and high specific moduli. The materials are popularly used as component materials of spacecraft, aircraft and sports & leisure articles, and recently, their use for general industrial applications such as motor vehicles is actively studied.
A conventional CFRP is produced, for example, by a method of impregnating a woven fabric with a unit weight of 200 to 300 g/m
2
formed using thin carbon fiber yarns with a fineness of 200 Tex as warp and weft, with a resin, to make a prepreg, laminating plural sheets of the prepreg, and forming the laminate in an autoclave.
Since the conventional CFRP is composed of thin carbon fiber yarns, the carbon fibers are very uniformly dispersed in the CFRP, and the surface of the CFRP is smooth. However, thin carbon fiber yarns are expensive since their productivity is low. The woven fabric composed of them is also low in productivity since it must be produced using numerous carbon fiber yarns. So, the production cost of the woven fabric is high, and the conventional CFRP produced using the woven fabric is a very expensive material disadvantageously.
If the CFRP is isotropic, the strength and other properties can be further improved. For this reason, in the case where at least four sheets of a prepreg are laminated, they are laminated to have carbon fiber yarn intersecting angles of 0°/90°/±45°, and this method is called a pseudo-isotropic lamination method. In this case, as the sheets of the prepreg used for the ±45° layers are obtained by bias-cutting the prepreg used for the 0° and 90° layers. In addition to the necessity of this cutting step, the cutting involves a large loss of the prepreg. So, the pseudo-isotropic CFRP obtained like this has a problem of being expensive.
Even such an expensive material can be used for the aircraft because of the large weight reduction effect obtained. However, the recently examined CFRP expected for general industrial applications such as motor vehicles is requested to be lower in price. That is, the CFRP available for general industrial applications must be able to be produced at a low cost as an essential condition.
As a means for solving the problem, the use of a stitched multiaxial laminate obtained by stitching pseudo-isotropically laminated reinforcing fibers integrally by means of stitching threads attracts attention. Since the laminate is pseudo-isotropic already as one board, neither bias cutting work nor additional lamination work is necessary. In this sense, the laminate is expected as a low cost material.
In the stitched multiaxial laminate, plural sheets, each having numerous thin reinforcing fiber yarns arranged in one direction, are laminated and stitched integrally by means of stitching threads. In the case where the stitched multiaxial laminate is used as a material for CFRP, the unit weight of reinforcing fibers of each sheet must be about 200 g/m
2
. However, in the case where carbon fibers are used as reinforcing fibers of the stitched multiaxial laminate, since the production cost of thin carbon fiber yarns is very high, the stitched multiaxial laminate obtained becomes expensive and cannot be used for general industrial applications disadvantageously.
If it is attempted to use thick carbon fiber yarns low in production cost for obtaining a stitched multiaxial laminate with fibers dispersed uniformly, the laminate has a high unit weight and cannot be used for other than special applications. If it is attempted to obtain a laminate with a practical unit weight, the pitch of the arranged numerous carbon fiber yarns becomes large, and a problem arises that large gaps are formed between the respectively adjacent carbon fiber yarns. If the laminate is used for forming a CFRP, the gaps in the formed CFRP become resin-rich portions, and a problem arises that when a stress acts on the CFRP, the stress is concentrated at the resin-rich portions, to cause rupture at a low external force. Furthermore, the shrinkage caused when the resin is hardened depresses the resin-rich portions corresponding to the gaps between the respectively adjacent carbon fiber yarns, and a problem arises that a CFRP with a smooth surface cannot be obtained. Therefore, in the present situations, such a CFRP cannot be used for applications requiring reliability and accuracy.
The object of the invention is to solve the above-mentioned various problems of the prior art by providing a thin stitched multiaxial reinforcing laminate, in which, even if thick tow-like carbon fiber yarns are used, the carbon fiber yarns are uniformly arranged without forming any gap between the respectively adjacent carbon fiber yarns. The object of the invention also includes providing a process for producing the stitched multiaxial laminate.
DISCLOSURE OF THE INVENTION
The stitched multiaxial reinforcing laminate of the invention for achieving the above object is as follows.
A stitched multiaxial reinforcing laminate, in which plural sheets, each having plural tow-like carbon fiber yarns arranged in parallel to each other, are laminated and stitched integrally by means of stitching threads, to ensure that the directions of the arranged carbon fiber yarn of the respective sheets are kept at different angles against a reference direction, characterized in that the tow-like carbon fiber yarns have a fineness of 1,200 to 17,000 Tex respectively and are arranged at a pitch of 8 to 60 mm, with the yarn width of each of the carbon fiber yarns widened to the pitch of the arranged carbon fiber yarns.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that the pitch of the arranged carbon fiber yarns is in a range of 20 to 60 mm.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that the yarn width of each of the carbon fibers is not less than double the original yarn width. In the stitched multiaxial reinforcing laminate of the invention, it is preferable that the yarn width of each of the carbon fibers is double to five times the original yarn width.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that the hook drop value of the carbon fiber yarns is in a range of 4 to 80 cm.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that a sizing agent is added to the carbon fiber yarns, and that the amount of the deposited sizing agent is in a range of 0.2 to 1.5 wt %.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that the amount of the deposited sizing agent is in a range of 0.2 to 0.6 wt %.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that the unit weight of the carbon fiber yarns in each of the sheets is in a range of 50 to 300 g/m
2
.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that said unit weight is in a range of 100 to 200 g/m
2
.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that at least one sheet of the plural sheets has said carbon fiber yarns arranged substantially at an angle of 0° in reference to the direction in which said stitching threads extend, and that at least one sheet of the plural sheets has said carbon fiber yarns arranged substantially at an angle of 90° C. in reference to the direction in which said stitching threads extend.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that
Homma Kiyoshi
Nishimura Akira
Piper Rudnick LLP
Thomas Alexander S.
Toray Industries Inc.
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