Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G59/00—Polycondensates containing more than one epoxy group per molecule; Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups
  • C08G59/18—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/24—Impregnating materials with prepolymers which can be polymerised in situ, e.g. manufacture of prepregs
  • C08J5/248—Impregnating materials with prepolymers which can be polymerised in situ, e.g. manufacture of prepregs using pre-treated fibres
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2363/00—Characterised by the use of epoxy resins; Derivatives of epoxy resins

Definitions

• the present invention relates to thermally curable wet-impregnated rovings which are useful for the production of fiber composites, and especially to wet-impregnated rovings which are packaged and stored with the resin in liquid form, but which can be removed from the package for use without damage.
• Background Art The production of fiber composites using thermally curable impregnated rovings is well known and is taking on increased significance because the fiber composites are light and strong and can be used to form pieces of diverse shape. The production of larger pieces is of particular importance. All sorts of problems have been encountered.
• resins are usually tacky liquids, and the tackiness of the resin causes it to stick to textile machinery so that, for example, the wet-impregnated roving cannot be braided. While impregnation on the way to the fiber composite is not a prime aspect of this invention, it is improved by it.
• the use of preimpregnated rovings has also become significant.
• a prime approach in this direction is the use of a thermoplastic overcoat around the roving which is impregnated with thermosetting resin in semi-solid form.
• Our coworkers at DeSoto, Inc. have made considerable progress in this direction as illustrated in United States Patent No. 4,187,357 issued February 5,
• thermoplastic resin adds to the expense of the product, organic solvents are normally needed and must be removed, and the impregnation and coating process is slow and adds to the cost of the product.
• the opportunity to have an appropriately impregnated roving which can be withdrawn from a supply thereof as needed and handled by textile equipment is advantageous, but there are limitations, some of which have been noted.
• the present invention overcomes the various problems noted hereinbefore by using wet-impregnated rovings which are thermally curable but which possess low tack at relatively high viscosity even though they can be applied at low viscosity to insure proper penetration of the applied liquid resin in the rov ing. To do this without employing organic solvent is an important feature of this invention. Disclosure of Invention
• a viscous liquid polyepoxide has dispersed therein a latent heat- activatable epoxy curing catalyst and the mixture is heated to an elevated temperature insufficient to activate the catalyst in order to lower the viscosity.
• This low viscosity heated mixture is applied to a multifilament roving to impregnate the same and the so-impregnated roving is then utilized, preferably by winding the same into a supply package.
• Contact of the heated mixture with the cool filaments in the roving and with the air causes a rapid reduction in the temperature and increases the viscosity.
• the wet impregnated multifilament roving is wound into a package or applied onto a fiber composite piece, the high viscosity of the cooled polyepoxide mixture prevents it from running.
• a point of importance is the finding that latent catalyst-containing liquid polyepoxide mixtures possess lox>7 tack, quite unlike the ordinary heat-curable resin mixtures. This low tack uniquely enable the wet-impregnated roving to be handled by textile machinery and to be withdrawn from a wet supply package. Another point of importance is that the high viscosity prevents running of the liquid mixture, so that it is no longer necessary to utilize a specially wound supply package.
• dicyandiamide While various latent catalysts can be used, dicyandiamide is particularly applicable since it resists decomposition at a temperature high enough to adequately lower viscosity in the absence of added organic solvent so that the roving can be uniformly impregnated. At the same time, dicyandiamide provides a rapid cure at moderately elevated temperature.
• the preferred polyepoxides are liquid or semi- liquid diglycidyl ethers having an epoxide equivalent weight below about 200.
• Diglycidyl ethers of a bisphenol, such as bisphenol A, are particularly contemplated. These will be illustrated by the Dow product DER-332 which is a viscous liquid having an epoxide equivalent weight of about 175 and an average molecular weight of about 350.
• the Shell product, Epon 828, is also useful.
• a minor proportion of 2% to 20%, based on the total weight of the mixture, of a diglycidyl ether of a polyether of a C 2 -C 4 glycol is added to reduce viscosity.
• the polyoxyalkylene glycol which is utilized may have a molecular weight up to about 500. These products are illustrated by a diglycidyl ether of polyoxypropylene glycol having an epoxide equivalent weight of 190 and an average molecular weight of about 380.
• the Dow product DER-736 is particularly useful. It is a low viscosity liquid and it minimizes the temperature needed to provide the low viscosity which enables uniform impregnation without the use of volatile organic solvent. Moreover, low viscosity is provided at elevated temperature and there is a considerable viscosity increase with decreasing temperature which prevents undesirable running.
• organic solvent is preferably absent, any solvent which is selected must be volatile at low temperature so as to avoid decomposing the latent catalyst.
• Methylene chloride will illustrate a suitable solvent which, if used, should be employed in minimal amount so as to minimize the expense involved.
• the latent catalyst-containing liquid polyepoxide mixture should have a tack of less than about 6 on a Thwing-Albert inkometer and a room temperature viscosity of from 2000 to 5000 centipoises, preferably from 3000 to 4000 centipoises.
• dicyandiamide is the preferred latent heat-activatable epoxy curing catalyst
• other catalyses falling within this art recognized group are illustrated by trimellitic anhydride, pyromellitic anhydride and chlorendic anhydride.
• catalyst as used herein embraces agents which release compounds which react directly with the epoxy group, such as the amines released when dicyandiamide is heated.
• the temperature to which the catalyst-containing liquid polyepoxide mixture can be heated in order to reduce its viscosity for effective uniform impregnation without activating the catalyst will depend upon the catalyst which is selected. With dicyandiamide, about 130 °F.
• the impregnation can be carried out in any convenient fashion, as by running the dry roving through a bath of the heated liquid polyepoxide mixture and then squeezing out excess liquid as the wet roving leaves the bath, or by running the dry roving over a roller coated with the mixture.
• the wet roving leaving the bath cools quickly and can be used directly for the formation of fiber composites.
• the wet roving is wound into a package in which the wet roving contacts other wet rovings within the package.
• Dicyandiamide in an amount providing 0.7 equivalents of amine per equivalent of total epoxy functionality is ground into 95 parts of the Dow product DER 332 using a three-roll mill to get a fine dispersion.
• a small portion of this dispersion has added thereto a catalyst for the epoxy-amine cure, namely, the salt of amidazole with adipic acid.
• This salt is available under the trade designation ADX-85, and it is added in an amount of 2%, based on the weight of the dicyandiamide.
• the salt is mixed into the dispersion using a mortar and pestle, and the mixture is then added to the remainder of the dispersion which is then ground to a 3 North Standard grind rating on the Hegman Scale.
• the previously prepared dispersion is thinned by the addition of 5 parts of the Dow product DER 736 to provide a catalyzed thermally curable liquid mixture having a viscosity at room temperature of about 3500 centipoises. On heating to 130°F., the viscosity drops sharply to provide a low viscosity liquid in which the dicyandiamide is stable.
• this liquid mixture has a tendency to crystallize, forming a crumbly solid on standing at room temperature for four days. However, if this crumbly solid is heated to 130°F. , it resumes its low viscosity character and reacquires its about 3500 centipoise viscosity at room temperature.
• This low viscosity liquid at 130°F. is used to impregnate multifilament glass roving (250 yars per pound) and impregnation was uniform with good wetting of the fiber surfaces. Impregnation is obtained by passing the dry roving over a roller immersed in a bath of the hot liquid. It is not necessary to squeeze out the excess from the wet roving which leaves the roller since the amount of resin on the roller is controlled to a measured thickness. The wet impregnated roving is then post-twisted (3/4 twist per linear inch) and wound onto a 6 inch cop. The resin impregnant in the cop is viscous because the liquid on the fibers cools rapidly to room temperature.
• the wet impregnated roving was easily removed from the wound cop at room temperature with the resin in the viscous liquid form which it possesses shortly after exposure to 130°F. , and it was handleable in conventional braiding machines because of its low tack.
• the viscous liquid resin impregnant in the superposed rovings flowed together into a unitary mass, thereby expelling air from between the rovings, but the mass of viscous resin did not run in the uncured composite. In this way air is expelled before the uncured composite is placed in an oven for cure. This is advantageous in the production of large pieces since one can be sure that voids have been eliminated before the piece is cured, it being understood that the discovery of a holiday after cure frequently requires that the cured piece be discarded.
• the wet fiber composite is then cured in conventional fashion by wrapping it in a nonadherent plastic cover which is placed in an oven for cure.
• this invention it is found that while the low viscosity needed for uniform impregnation can be obtained at 130°F. , without activating the dicyandiamide for cure, that the desired cure can be obtained using an oven maintained at 250°F. to 300°F. At 300°F. the cure is rapid and the finished fiber composite was hard and has good flexural strength and good shear strength. These properties are measured by winding a rectangular spar, the cured piece containing 32.6% by weight of resin.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Manufacturing & Machinery (AREA)
• Reinforced Plastic Materials (AREA)
• Laminated Bodies (AREA)
• Epoxy Resins (AREA)
• Nonwoven Fabrics (AREA)

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Applications Claiming Priority (2)

Publications (1)

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Citations (5)

• 1981
  • 1981-04-15 JP JP56501787A patent/JPS6345738B2/ja not_active Expired
  • 1981-04-15 EP EP19810901425 patent/EP0052628A4/en not_active Ceased
  • 1981-04-15 WO PCT/US1981/000487 patent/WO1981003290A1/en not_active Application Discontinuation
  • 1981-04-27 CA CA000376352A patent/CA1158487A/en not_active Expired
  • 1981-05-13 IT IT8148460A patent/IT1209869B/it active
• 1982
  • 1982-01-21 DK DK26082A patent/DK26082A/da not_active Application Discontinuation

Patent Citations (5)

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