Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
1998-02-17
2001-05-08
Cole, Elizabeth M. (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S299100, C428S299400
Reexamination Certificate
active
06228474
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an epoxy resin composition suitable as a matrix resin for fiber reinforcement, and a yarn prepreg in which reinforcing fibers are impregnated with an epoxy resin. Furthermore, the present invention relates to an intermediate material for a fiber reinforced composite material and a fiber reinforced composite material obtained by using the yarn prepregs, and a concrete member reinforced by the composite material. Moreover, the present invention relates to a method for producing yarn prepregs, a method for winding a yarn prepreg, a method for producing a tube made of a fiber reinforced resin, and an apparatus for producing yarn prepregs.
A prepreg in which reinforcing fibers are impregnated with an epoxy resin composition can be processed into a desired form, for example, by lamination, winding, collection, etc., and the uncured epoxy resin can be heated and cured by press molding, autoclave molding, etc. to obtain a composite material with a desired form such as a plate, tube or beam, etc.
Narrow prepregs called yarn prepregs, tow prepregs or strand prepregs (hereinafter called yarn prepregs) can be made into fiber reinforced composite materials with various forms by methods described below.
Firstly, a yarn prepreg is wound around a core shaft at a predetermined angle according to the tape winding method, then a heat shrinkable tape is wound around it, and then it is heat-cured in an oven, to produce a hollow tubular composite material.
Secondly, yarn prepregs are laminated on a tool by the fiber placement method, covered with a bag film, placed into an autoclave, and heat-cured, to produce a composite material with a curved surface form.
Thirdly an intermediate material obtained by covering a plurality of collected yarn prepregs with fibers, preferably synthetic fibers can be twisted, and heated and cured, to produce a twisted cable of a composite material. Composite materials with such a form can be used as various cables for bridges, braces of buildings, tension members of prestressed concrete, reinforcing bars, rock bolts for ground reinforcement and cable bolts.
Furthermore, concrete members reinforced by twisted cables of a carbon fiber reinforced composite material can be used as marine structures required to be corrosion resistant, concrete piles for a vertical shaft which can be directly excavated by a shield machine, etc.
BACKGROUND ART
Fiber reinforced composite materials with an epoxy resin as the matrix resin are widely used in general industrial fields such as aerospace, sports, civil engineering, architecture, etc., and hitherto prepregs, intermediate materials and composite materials obtained by combining epoxy resins of various compositions and reinforcing fibers with various properties have been proposed.
A prepreg is generally like a sheet, and various reinforcing styles are available for respective purposes, for example, a prepreg with continuous fibers arranged in one direction in the flat face of the sheet, a prepreg provided as a woven fabric of continuous fibers, a prepreg with discontinuous fibers arranged in any desired direction, etc.
In addition to the above prepreg sheets, there are yarn prepregs in which carbon filaments arranged in one direction as a continuous fiber bundle are impregnated with a resin, and they are suitably used as cables for bridges, tension members of prestressed concrete, and members for fiber placement and filament winding. To prepare the yarn prepreg, a continuous fiber bundle is impregnated with a resin and once wound around a bobbin. Then, in the molding of a composite material, the yarn prepreg is unwound from the bobbin and provided for molding according to the method as described before. So, the fiber arrangement, drapability, viscosity characteristic in resin curing, properties of cured resin, etc. greatly affect the properties, grade, etc. of the composite material.
Furthermore in recent years, as a result of pursuing the cost reduction of carbon fibers, carbon fibers of a thick fiber bundle with more than 20,000 filaments have appeared, and a yarn prepreg using such carbon fibers has attracted attention. To impregnate the carbon fibers of a thick fiber bundle homogeneously with a matrix resin, as a general method, usually the fiber bundle is thinly widened by opening, etc., and has the resin deposited on it to allow the resin to migrate easily in the thickness direction of the fiber bundle. However, it is suggested that the yarn prepreg obtained by this method generates various disadvantages unless the width is appropriate. For example, if the width is too large, torsion and folding-in in the transverse direction are likely to occur at the guide portion in the step of arranging yarn prepregs in parallel in the production of a composite material, and as a result, the composite material becomes low in the degree to which tensile strength is translateed, etc. On the contrary, if the width is too small (as a result, if the thickness is too large), the impregnation of the prepreg becomes insufficient, and the composite material obtained generates defects such as voids, to lower the mechanical properties.
To translate excellent mechanical performance in general industrial fields such as aerospace, sports, civil engineering and architecture, it is important to let reinforcing fibers translate a high strength. To realize this, the matrix resin used must be excellent in mechanical properties such as fracture toughness.
As prior art for yarn prepregs, JP-A-55-15870 proposes the use of a matrix resin with a thermoplastic resin added to a thermosetting resin, and JP-A-55-78022 proposes to add a high molecular epoxy resin of 5,000 or more in molecular weight. However, both the methods have a disadvantage that if the yarn prepreg is allowed to stand for a long time, the filaments stick to each other, to lose unwindability. Furthermore, it is proposed to mix a thermoplastic resin having a molecular weight of 10,000 or more, higher alcohol, higher fatty acid, etc. (JP-A-57-21428), and to mix a silicone resin and a silicone oil (JP-A-58-113226). These methods are effective to improve the unwindability and drapability of the yarn prepreg to some extent, but the reinforcing fibers cannot translate a high strength.
In the examples of the above mentioned prior art, a carbon fiber bundle of 12,000 filaments only is referred to, and nothing is suggested as to the method of improving the physical properties of a yarn prepreg using carbon fibers of a thick fiber bundle attracting attention in recent years.
Japanese Patent Publication (Kokoku) No. 3-33485 concerning a method and apparatus for producing a yarn prepreg describes a method comprising the steps of arranging in parallel reinforcing fibers like a sheet through a spacer on a sheet coated with a stage B thermosetting resin, laminating a sheet on the other side, pressurizing and heating to impregnate the reinforcing fibers with a resin, slitting the sheet and the spacer portion by a slitter, and winding, or separating the resin impregnated reinforcing fibers from the sheet, to obtain prepreg tapes. This method is the most reliable method to allow the fibers to be impregnated with a predetermined amount of a resin accurately, but is disadvantageous in view of cost since a sheet is necessary for applying the resin and since raising the line speed is technically difficult.
Japanese Patent Publication (Kokoku) No. 5-80330 describes a method for producing a yarn prepreg, comprising the steps of spreading a continuous fiber bundle, to make a band while carrying it; covering the band with a resin free from any solvent using a heating roller and a doctor blade; kneading the covered band, to impregnate the fibers with the resin; compressing the resin impregnated band; and finally cooling to provide the sectional form.
This method has a feature that the resin coating thickness on the fiber bundle in the covering step is controlled by the die interval or hole between the roller and the doctor blade. So, this method is considered to be more excellen
Kishi Hajime
Kyono Tetsuyuki
Minakuchi Toyokazu
Noma Fumiaki
Tokunoh Masazumi
Cole Elizabeth M.
Morrison & Foerster / LLP
Toray Industries Inc.
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