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
1999-08-02
2002-05-21
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...
C524S496000, C524S540000, C525S132000
Reexamination Certificate
active
06391959
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a phenolic resin composition for fiber-reinforced composite materials, of which the prepreg has good releasability and which has good drapability; to a prepreg for fiber-reinforced composite materials, which comprises the composition as the matrix resin; and to a method for producing the prepreg for fiber-reinforced composite materials.
BACKGROUND ART
Owing to high specific strength and high specific rigidity of the reinforcing fibers therein, fiber-reinforced composite materials have heretofore been used for aircraft materials. These days, their applications are being much developed not only for aircraft materials but also for sports and leisure goods and for general-purpose industrial materials including those for vehicles and ships and even for civil engineering and construction, etc. With the development of their applications for such general-purpose industrial materials, fiber-reinforced composite materials are being required to have much improved flame-retardant characteristics of firing retardancy and smoking retardancy.
As the matrix resin for prepregs for fiber-reinforced composite materials, widely used are epoxy resins having good moldability and high mechanical strength. However, one serious defect of epoxy resins is that they are easily combustible. Because of such a defect, it is difficult to use epoxy resins for general-purpose industrial materials such as those mentioned above and for aircraft interior materials. As opposed to them, it is widely known that phenolic resins have excellent flame-retardant characteristics among thermosetting resins. Therefore, even though phenolic resin prepregs are somewhat inferior to epoxy resin prepregs in point of their moldability and mechanical strength, there is increasingly a great demand for phenolic resins.
Two typical methods for producing phenolic resin prepregs. One is a wet method comprising dipping reinforcing fibers in a solution of a matrix resin having a low viscosity; and the other is a hot-melt method in which is used a matrix resin solution having a high viscosity. In the latter hot-melt method, the prepregs formed must specially be releasable from release paper or release film. However, since phenolic resins contain condensed water as generated during their curing, and a solvent for a diluent or a stabilizer, they have a low viscosity and are highly tacky. Therefore, the hot-melt method is hardly applicable to the production of phenolic resin prepregs. For these reasons, at present, the wet method is the mainstream method for producing phenolic resin prepregs. Even in the wet method, however, it is still desired that the phenolic resin prepregs produced have good releasability from rollers, etc.
Various types of composites from prepregs are known. Of those, much used in these days are honeycomb sandwich panels. As being lightweight and highly rigid, honeycomb sandwich panels have many applications for not only aircraft materials but also for sports goods and for construction materials for vehicles, ships, etc. Honeycomb sandwich panels referred to herein are meant to indicate panels which are produced by placing a surface material of a so-called skin panel on both surfaces of a honeycomb core having continuous honeycomb-like pores, followed by heating it under pressure. As the interior material for aircraft, for example, used is a combination of an aramide honeycomb core of so-called Nomex honeycomb and a thermosetting resin prepreg as reinforced with glass fibers, Kevler fibers, carbon fibers or the like.
Even for general-purpose industrial materials and for aircraft interior materials these days, flame-retardant materials of phenolic resin prepregs are being used for honeycomb sandwich panels.
However, where a phenolic resin is used as the matrix resin in those honeycomb sandwich panels, the volatile component peculiar to the phenolic resin will bring about some problems in fabricating the panels. Phenolic resins contain, as a volatile component, condensed water as generated during their fabricating and a solvent for a diluent or a stabilizer. Therefore, where such a phenolic resin is used as the matrix resin in Fabricating honeycomb sandwich panels, he resin prepreg will often peel off from the honeycomb core and the adhesiveness between the prepreg and the core is not often satisfactory. In addition, in that case, the vaporization of the volatile component from the phenolic resin prepreg will lower the surface smoothness of the panels. The wet method of producing phenolic resin prepregs generally comprises a drying step as the most simple and effective means for reducing the amount of the volatile component existing in the phenolic resin, in which reducing the volatile component in the phenolic resin could lower the tackiness of the prepregs formed and improve the releasability thereof. However, merely reducing the amount of the volatile component existing in the phenolic resin in the method will lower the thermal stability of the phenolic resin, whereby the temperature control in the steps constituting the method will be difficult. As a result, it will be difficult to prepare prepregs having stable characteristics and even to produce panels having stable mechanical properties. In addition, since the resin viscosity is increased owing to the reduction in the volatile component, the prepregs produced could not be flexible, or that is, they will no more be drapable. Depending on their applications, honeycomb sandwich panels require complicated shape such as deep drawing or the like. Therefore, one important factor in prepregs for such honeycomb sandwich panels is the drapability to follow the complicated shapes of the panels.
Some techniques for making phenolic resin prepregs have both good releasability and good drapability are known. For example, JP-A-4-306253 and JP-A-5-25363 disclose a method of adding a polyvinyl butyral and a modified silicone oil to phenolic resins; JP-A-3-81340 discloses a method of adding thereto a thermoplastic resin compatible with phenolic resins; and JP-A-4-100851 discloses a method adding thereto a polyacrylamide, an epoxy resin and an inorganic filler. However, the thermoplastic resin used thereon has a relatively low molecular weight, and could hardly satisfy both the releasability and the drapability of prepregs.
On the other hand, for molding honeycomb sandwich panels within a short period of time, it is important that the resins to be used should have good curability. However, resins with high curability are often unstable under heat. The thermal stability of resins is indispensable for good storage of resins and for producing stable resin prepregs, but resins with high curability often have poor thermal stability. Therefore, it is desired to obtain resins having both good curability and good thermal stability, which, however, are contradictory to each other. Specifically, it is desired that resins for prepregs have good thermal stability at temperatures at which they are formed into prepregs, for example, falling between 0 and 70° C., and have good curability at molding temperatures, for example, falling between 130 and 160° C.
For better curability, phenolic resins with high reactivity may be employed, or various curing catalyst may be added to resins. In order to make resins have the contradictory two characteristics noted above, it is considered effective to add curing catalyst with latent potency thereto.
For phenolic resins, it is known that they undergo not only ordinary simple thermal curing reaction but also acid curing reaction for which acid catalysts are generally used. For epoxy resins, acid catalysts with latent potency are available in the market and are used widely. However, many of those acid catalysts for epoxy resins are ionic ones such as onium salts, and, when they are applied to phenolic resins, they will be deactivated by water or polar solvents naturally existing in the resins and will thereby lose their latent potency. In that situation, phenolic resin systems with high latent thermal curability ar
Kishi Hajime
Nagata Hideo
Ninomiya Hiroaki
Terashita Takeshi
Tomioka Nobuyuki
Cain Edward J.
Schnader Harrison Segal & Lewis LLP
Toray Industries Inc.
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