WO1996000655A1

WO1996000655A1 - Corrosion resistant sheet molding compound

Info

Publication number: WO1996000655A1
Application number: PCT/US1995/006442
Authority: WO
Inventors: Nelson H. Douglass; Sean P. Walsh; Richard J. Pauer
Original assignee: Reichhold Chemicals, Inc.
Priority date: 1994-06-28
Filing date: 1995-05-23
Publication date: 1996-01-11
Also published as: AU2690895A

Abstract

A corrosion resistant sheet molding compound (10) comprising a surface layer (50) overlying a base layer (20). The base layer comprises reinforcing fiber (30) impregnated with a first thermosetting resin (40). The surface layer comprises a corrosion resistant veil (60), not more than 100 mils in thickness, impregnated with a second thermosetting resin (70). A method for making corrosion resistant sheet molding compound is also disclosed. The method comprises the steps of: a) contacting a top face of the base layer with a bottom face of the surface layer; and b) placing the base layer and the surface layer under a compressive molding pressure applied to a bottom face of the base layer and a top face of the surface layer.

Description

CORROSION RESISTANT SHEET MOLDING COMPOUND

Field of the Invention

The present invention relates to sheet molding compounds, and more particularly to corrosion resistant sheet molding compounds.

Background of the Invention

Reinforced thermosetting resins have enjoyed increasing popularity in molding applications requiring high strength, lightweight dimensional stability, and more recently, corrosion resistance. Such reinforced thermosetting resin molded articles have frequently replaced metal components in a wide variety of applications, including bathtubs, water tanks and automobile parts.

Sheet molding compound ("SMC") can be generally defined as a reinforced thermosetting resin composite. Typical SMC compositions include one or more resins, reinforcing fibers, and an inert filler. For example, U.S. Patent No. 4,289,684 to Kallaur proposes a sheet molding compound including an unsaturated polyester resin syrup, particulate fillers, randomly oriented reinforcing fibers, a polyhydroxy poly(meth)acrylate and an organic polyisocyanate. U.S. Patent No. 3,959,209 to Lake proposes a curable solid polyester resin including a filler or fibrous reinforcements impregnated with a solic solution of crystalline polyester and a crosslinking agent.

The reinforcing fiber is typically chopped glass rovings. SMC is typically compression molded to form various molded articles. The presence of chopped glass rovings, however, typically causes microscopic defects in the form of small holes or pores at or near the surface of the molded part . The presence of these small holes coupled with the multitude of filaments which make up each glass roving, provide a wieking action, whereby corrosive agents can be wicked into the SMC and weaken the molded article from within. This is a particularly serious.problem where the SMC is applied as a protective coating to articles, such as rebar. Attempts have been made to substitute pliable fiber fillers for the chopped glass rovings. However, such substitutions have not proven to be practical in light of the expense of the fiber fillers, and the resulting decrease in tensile strength.

Summary of the Invention

It is therefore an object of the present invention to provide a corrosion resistant sheet molding compound. It is a further object to provide a sheet molding compound having high tensile strength. It is a further object of the present invention to provide a corrosion resistant sheet molding compound which can be manufactured using conventional sheet molding compound manufacturing machinery. The phrase "corrosion resistant" as used herein refers to the ability of a particular material to withstand the destructive effects of corrosive agents including but not limited to oxidizing agents and ionic species. These and other objects, features and advantages are provided by the sheet molding compound and methods of the present invention. The sheet molding compound of the present invention comprises a multilayer structure comprising (a) a base layer including reinforcing fiber impregnated with a first thermosetting resin, and (b) a surface layer overlying the base layer, which includes a corrosion resistant veil impregnated with a second thermosetting resin.

The thermosetting resins which may be employed in the practice of the present invention generally include unsaturated polyesters, vinyl esters, vinyl urethanes, and vinyl isocyanurates. The term "thermosetting" as used herein refers to resins which irreversibly solidify or "set" when completely cured. As used herein, the term "veil" refers to a fibrous sheet including elongated randomly oriented, single filament, which is capable of readily absorbing resin. The filament is either one or a few individual filaments which are elongated and wound onto themselves to form the sheet of veil not more than 100 mils in thickness. The single filaments of veil provide new and unique properties to SMC which cannot be achieved using conventional fibrous reinforcing mats, which comprise bundles of a multitude of short fibers. The corrosion resistant veil of the present invention typically comprises a fibrous sheet including elongated randomly oriented single polyester, glass or natural filaments.

Any suitable reinforcing fiber known to those skilled in the art of SMC manufacture may be employed, with chopped glass roving being preferred. In one embodiment, the reinforcing fiber of the base layer may include multiple reinforcing fibers. For example, in one preferred embodiment, the SMC of the present invention includes a base layer comprising unidirectional fibers and chopped glass roving impregnated with a first thermosetting resin.

As a second aspect, the present invention provides a method of making the corrosion resistant sheet molding compound. The method includes (a) contacting the base layer with the surface layer, and (b) placing the base layer and the surface layer under a compressive molding pressure. The method is disclosed in detail hereinbelow, and is advantageously designed for use in conventional SMC manufacturing machinery.

The foregoing and other objects and aspects of the present invention are explained in detail in the specification set forth below.

Brief Description of the Drawing Figure 1 is an enlarged cross-sectional view of the sheet molding compound of the present invention.

Detailed Description of the Invention Referring to Figure 1, the sheet molding compound 10 of the present invention comprises a multilayer structure comprising (a) a base layer 20 including reinforcing fiber 30 impregnated with a first thermosetting resin 40, and (b) a surface layer 50 overlying the base layer 20 and including a corrosion resistant veil 60 impregnated with a second thermosetting resin 70. In a preferred embodiment, the base layer comprises between about 35 to about 95 percent by weight of a first thermosetting resin and about 5 to about 65 percent by weight of reinforcing fiber, and the surface layer comprises a veil impregnated with about 50 to about 99 percent by weight of a second thermosetting resin.

The first and second thermosetting resins of the present invention each comprise a thermosetting resin, and preferably a corrosion resistant thermosetting resin. A wide variety of corrosion resistant resins are known to those skilled in the art. Exemplary resins include unsaturated polyesters, vinyl ester resins, vinyl isocyanurates, vinyl urethanes, and the like and mixtures and blends thereof.

The first and second thermosetting resins can be the same resin or different resins. In the embodiment wherein the first thermosetting resin differs from the second thermosetting resin, the resins employed must be such that the surface and base layers formed therefrom are capable of being bonded together. Preferably, the surface and base layers formed of different resins will be capable of being bonded without the addition of an adhesive therebetween, although an adhesive may be used, the selection of which will be within the skill of one in the art. In the preferred embodiment, the first and second thermosetting resins comprise the same thermosetting resin.

The first and second thermosetting resins are typically solubilized in a vinyl monomer to provide a resin in liquid or semi-liquid form. Suitable vinyl monomers include styrene, vinyltoluene, methyl methacrylate, p-methylstyrene, divinyl benzene, diallyl phthalate and that like. Styrene is a preferred vinyl monomer.

Unsaturated polyester and vinyl ester resins are preferred. Suitable unsaturated polyester resins include practically any esterification product of a polybasic organic acid and a polyhydric alcohol, wherein either the acid or the alcohol, or both, provide the ethylenic unsaturation. Typical unsaturated polyesters are those thermosetting resins made from the esterification of a polyhydric alcohol with an ethylenically unsaturated polycarboxylic acid. Examples of useful ethylenically unsaturated polycarboxylic acids include maleic acid, fumaric acid, itaconic acid, dihydromuconic acid and halo and alkyl derivatives of such acids and anhydrides, and mixtures thereof. Exemplary polyhydric alcohols include saturated polyhydric alcohols such as ethylene glycol, 1, 3-propanediol, propylene glycol, 1, 3-butanediol, 1,4- butanediol, 2-ethylbutane-l,4-diol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 7-heptanediol, 1, 8-octanediol, 1,4- cyclohexanediol, 1,4-dimethylolcyclohexane, 2,2- diethylpropane-1,3-diol, 2, 2-diethylbutane-l, 3-diol, 3- methylpentane-1,4-diol, 2, 2-dimethylpropane-l, 3-diol, 4, 5-nonanediol, diethylene glycol, triethylene glycol, dipropylene glycol, glycerol, pentaerythritol, erythritol, sorbitol, mannitol, 1,1,1- trimethylolpropane, trimethylolethane, hydrogenated bisphenol-A and the reaction products of bisphenol-A with ethylene or propylene oxide.

Unsaturated polyester resins can also be derived from the esterification of saturated polycarboxylic acid or anhydride with an unsaturated polyhydric alcohol . Exemplary saturated polycarboxylic acids include oxalic acid, malonic acid, succinic acid, methylsuccinic acid, 2, 2-dimethylsuccinic acid, 2,3- dimethylsuccinic acid, hexylsuccinic acid, glutaric acid, 2-methylglutaric acid, 3-methylglutaric acid, 2, 2-dimethylglutaric acid, 3, 3-dimethylglutaric acid, 3 , 3-diethylglutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebaccic acid, phthalic acid, isophthalic acid, terephthalic acid, tetrachlorophthalic acid, tetrabromophthalic acid, tetrahydrophthalic acid, 1, 2-hexahydrophthalic acid, 1, 3-hexahydrophthalic acid, 1,4-hexahydrophthalic acid, 1, 1-cyclobutanedicarboxylic acid and trans-1,4- cyclohexanedicarboxylic acid. Unsaturated polyhydric alcohols which are suitable for reacting with the saturated polycarboxylic acids include ethylenic unsaturation-containing analogs of the above saturated alcohols (e.g. ,2-butene-l,4-diol) . Unsaturated polyester resins suitable in the present invention are commercially available. For example, ATLAC™ 580-05 is obtainable from Reichhold Chemicals Inc., Research Triangle Park, North Carolina.

Suitable vinyl ester resins include practically any reaction product of an unsaturated polycarboxylic acid or anhydride with an epoxy resin. Exemplary acids and anhydrides include (meth) acrylic acid or anhydride, α-phenylacrylic acid, a- chloroacrylic acid, crotonic acid, mono-methyl and mono-ethyl esters of maleic acid or fumaric acid, vinyl acetic acid, cinnamic acid, and the like. Epoxy resins which are useful in the preparation of the polyvinyl ester are well known and commercially available. Exemplary epoxies include virtually any reaction product of a polyfunctional halohydrin, such as epichlorohydrin, with a phenol or polyhydric phenol. Suitable phenols or polyhydric phenols include for example, resorcinol, tetraphenol ethane, and various bisphenols such as Bisphenol-A, 4,4' -dihydroxydiphenyl- sulfone, 4,4' -dihydroxybiphenyl, 4,4' -dihydroxydi- phenylmethane, 2,2' -dihydroxydiphenyloxide, and the like. Exemplary vinyl ester resins are commercially available, for example, DION™ 31347-00 obtainable from Reichhold Chemicals Inc., Research Triangle Park, North Carolina. The vinyl urethane resins which are useful in the present invention include those proposed in U.S. Patent No. 3,929,929 to Kuehn, the disclosure of which is incorporated herein by reference in its entirety. The vinyl urethanes proposed in Kuehn are prepared by reacting a diol, a polyisocyanate, and a hydroxyl- terminated ester of acrylic or methacrylic acid. Exemplary vinyl urethanes include DION™ 31038-00, available from Reichhold Chemicals Inc., Research Triangle Park, North Carolina. The vinyl isocyanurate resins which are useful in the present invention include those proposed in U.S. Patent No. 4,128,537 to Markiewitz, the disclosure of which is incorporated herein by reference. The ethylenically unsaturated isocyanurates proposed in Markiewitz are prepared by reacting a polyisocyanate with a monohydric alcohol to form a urethane, and then trimerizing the urethane to form an ethylenically unsaturated isocyanurate.

The reinforcing fiber employed in the SMC of the present invention can be any conventional reinforcing fiber. Conventionally known reinforcing fibers include organic fibers such as polyester fibers, polyamide fibers, aromatic polyamide fibers and polyimide fibers, and inorganic fibers such as glass fibers, silicon carbide fibers, alumina fibers, titanium fibers, steel fibers, carbon fibers, and graphite fibers and hybrids thereof. The reinforcing fiber may be supplied in any suitable form, such as scrim, unidirectional fibers, ribbons, tapes, chopped rovings or mats. In one preferred embodiment, the reinforcing fiber is glass in the form of chopped rovings. The reinforcing fibers may also be provided in the form of a combination of two or more forms of reinforcing fiber. In another preferred embodiment, the reinforcing fiber is a combination of unidirectional fibers and chopped rovings. The corrosion resistant veil can be formed of any suitable material which provides randomly oriented, elongated filament which can be wound onto itself to provide a sheet not more than about 100 mils in thickness. The veil is desirably less than about 100 mils so that the resulting sheet molding compound will be capable of conforming to more complex and non-linear mold features than conventional SMC. The thickness of the veil of the present invention is preferably not more than 100 mils, more preferably not more than 60 mils, and most preferably not more than 25 mils. The filaments of the veil are bound together with a binder such as a polyester resin binder, according to means known to those skilled in the art.

The material which comprises the veil preferably exhibits corrosion resistant properties . Such corrosion resistant materials can be formed of filament comprising glass, polyester or natural fibers. Preferably, the veil comprises polyester filament. Suitable veil is commercially available, and includes SURMAT™ 100 SF obtainable from Nicofibers, Shawnee Ohio, and REMAY™ 2014 obtainable from Precision Fabrics, Greensboro, North Carolina. The veil preferably has a density sufficient to capture and retain a sufficient amount of liquid resin to provide a resin-rich surface layer. The SMC of the present invention may also include other additives commonly employed in SMC compositions, the selection of which will be within the skill of one in the art. For example, the first and second thermosetting resins may include particulate fillers, thickeners, initiators, mold release agents, catalysts, pigments, flame retardants, and the like, in amounts commonly known to those skilled in the art . The particulate fillers typically include calcium carbonate, hydrated alumina and clay. A variety of suitable thickeners are known to those skilled in the art and include alkali earth metal oxides or hydroxides, crystalline polyesters, polyurethanes, and polyureas. The thickener should increase the viscosity to a sufficient degree that the liquid resin is transformed to a non-dripping, paste form. Polyurethanes are the preferred thickeners. U.S. Patent No. 4,062,826 to Hutchinson et al . , the disclosure of which is incorporated herein by reference in its entirety, proposes a polyurethane thickened polyester resin useful in the practice of the present invention. The initiator may be a high or a low temperature polymerization initiator, or in certain applications, both may be employed. The mold release agents include zinc stearate, calcium stearate and stearic acid. Catalysts are typically required in SMC compositions thickened with polyurethane. The catalyst promotes the polymerization of NCO groups with OH groups. Suitable catalysts include dibutyl tin dilaurate and stannous octoate. The SMC of the present invention has a variety of applications. Typically, the SMC is useful in the manufacture of molded articles such as automobile parts, appliances, sanitary ware, and other compression molded articles. In addition, the SMC of the present invention is useful as a cladding for rebar to provide a corrosion resistant rebar useful in construction.

The method of making the corrosion resistant SMC of the present invention comprises (a) contacting a top face of the base layer with a bottom^' face of the surface layer and (b) placing the base layer and the surface layer under a compressive molding pressure applied to a bottom face of the base layer and a top face of the surface layer. Any suitable means of contacting the top face of the base layer with the bottom face of the surface layer may be employed.

In one embodiment, the top face of the base layer is contacted with the bottom face of the surface layer by (a) impregnating a corrosion resistant veil with a second thermosetting resin to provide the surface layer, (b) positioning a layer of reinforcing fiber on a bottom face of the surface layer, and (c) depositing a layer of the first thermosetting resin on the layer of reinforcing fiber opposite the surface layer such that the first thermosetting resin impregnates the reinforcing fiber to provide a base layer. Thereafter, the base layer and the surface layer are placed under a compressive molding pressure applied to a bottom face of the base layer and a top face of the surface layer.

The surface layer is prepared by impregnating veil with the second thermosetting resin according to any suitable means. For example, the veil may be impregnated with the second thermosetting resin by contacting the veil with the second thermosetting resin. As noted above, the veil of the present invention is preferably not more than 100 mils in thickness and of sufficient density to readily absorb the thermosetting resin.

One method of impregnating the veil with a second thermosetting resin comprises positioning the veil on a layer of the second thermosetting resin. The layer of second thermosetting resin may be provided by depositing a layer of the second thermosetting resin on a carrier film. The resin is typically deposited on the carrier film by passing the carrier film under a supply of resin whereby resin is deposited onto the carrier film. Typically, the carrier film is supplied from a roll such that it can be continuously passed under the resin supply to provide a continuous method of making SMC. Suitable carrier film will be known to those skilled in the art, and typically comprises a film of polyethylene, polypropylene or nylon, although other materials may be employed.

Alternative methods of impregnating the veil with the second thermosetting resin will be readily apparent to those skilled in the art. For example, the step of impregnating the veil may be accomplished by positioning the veil on a carrier film and passing the carrier film having veil thereon, under a resin supply, which deposits the second thermosetting resin onto the veil in a sufficient quantity to impregnate the veil . In yet another example, the step of impregnating the veil may be accomplished by providing a first layer of a second thermosetting resin, positioning a veil on the first layer of second thermosetting resin, and then depositing a second layer of the second thermosetting resin on the veil opposite the first layer of the second thermosetting resin, such that the first and second layers of the second thermosetting resin impregnate the veil.

The resin impregnated veil provides the surface layer of the SMC. The resin-rich surface created by the impregnated veil adds to the corrosion resistance of the SMC.

The base layer is provided by impregnating reinforcing fiber with a first thermosetting resin. The reinforcing fiber may be impregnated with the first thermosetting resin according to any suitable means. Typically, a reinforcing fiber layer is positioned on the surface layer, such that the reinforcing fiber substantially overlies the surface layer. Preferably, the reinforcing fiber is positioned on the surface layer to provide a relatively even and uniform distribution of reinforcing fiber across the surface layer. This step of the method may be carried out using a conventional SMC machine, such as that described in McCluskey et al. , Sheet Molding Compounds Composi tes, Engineer Materials Handbook 1:157 (1987) . Suitable methods of depositing reinforcing fiber onto the surface layer are known to those skilled in the art. According to one preferred method, the prepared surface layer is passed under a chopper which cuts or chops strands of reinforcing fiber and allows the chopped fiber to fall onto the surface layer. In the embodiment of the invention wherein the reinforcing fiber comprises a combination of two or more forms of reinforcing fiber, multiple layers of reinforcing fiber may be deposited on the surface layer.

According to this embodiment, the reinforcing fiber is impregnated by depositing a layer of the first thermosetting resin on the reinforcing fiber. /Any suitable method may be employed for depositing the first thermosetting resin on the reinforcing fiber. Typically, the first thermosetting resin is deposited onto a carrier film and then contacted to the reinforcing fiber on the opposite side from the surface layer, such that the reinforcing fiber is sandwiched between the surface layer and the layer of a first thermosetting resin. Preferably a sufficient amount of resin is applied to thoroughly overlie and permeate the reinforcing fiber. As the layer of first thermosetting resin permeates the reinforcing fiber, the reinforcing fiber becomes impregnated with the first thermosetting resin, to form the base layer. The surface and base layer are then placed under a compressive molding pressure which is applied to the bottom face of the base layer and the top face of the surface layer. Typically, the compressive molding pressure comprises between about 10 to about 100 psi of pressure. Mechanisms for applying sufficient pressure to the surface and base layers to provide the SMC are known to those skilled in the art. In conventional SMC machines, sufficient pressure is typically applied to the surface and base layers by compressing the surface and base layers between one or more pairs of compaction rollers. The use of one or more pairs of compaction rollers is the preferred method of applying pressure to form the SMC, as it permits the continuous manufacture of SMC through the machine.

Alternatively, the top face of the base layer may be contacted with the bottom face of the surface layer by (a) impregnating the reinforcing fiber with the first thermosetting resin to provide the base layer, (b) positioning the veil on the base layer, and (c) depositing a layer of the second thermosetting resin on the veil opposite the base layer, to provide a surface layer. Thereafter, the base layer and the surface layer are placed under a compressive molding pressure, which is applied to a bottom face of the base layer and a top face of the surface layer. The base layer is typically prepared by impregnating the reinforcing fiber according to any suitable means, such as those described above. Preferably, the reinforcing fiber is impregnated with the first thermosetting resin by positioning a layer of reinforcing fiber on a layer of the first thermosetting resin. In the embodiment wherein the reinforcing fiber comprises two or more forms of reinforcing fiber, multiple layer of reinforcing fiber may be positioned on a layer of the first thermosetting resin. The first thermosetting resin layer is provided according to any suitable means. Preferably, the first thermosetting resin layer is provided by depositing a layer of the first thermosetting resin on a carrier film. The resin is typically deposited on the carrier film by passing the carrier film under a resin container which is capable of metering resin onto the carrier film, as described above. Any suitable method may be employed for positioning the reinforcing fiber on the thus provided first thermosetting resin layer. Exemplary methods are described above. The reinforcing fiber is typically impregnated with the first thermosetting resin by, for example, immersing the fibers into the layer of the first thermosetting resin, thus providing the base layer. Alternative methods of impregnating the reinforcing fiber with the first thermosetting resin will be readily apparent to those skilled in the art. For example, the step of impregnating the reinforcing fiber may be accomplished by positioning a layer of reinforcing fiber on a carrier film and passing the carrier film having the reinforcing fiber thereon, under a resin supply, which deposits the first thermosetting resin onto the reinforcing fiber in a sufficient quantity to impregnate the reinforcing fiber. In yet another example, the step of impregnating the reinforcing fiber may be accomplished by providing a first layer of the first thermosetting resin, positioning a layer of reinforcing fiber on the first layer of the first thermosetting resin, and then depositing a second layer of the first thermosetting resin on the layer of reinforcing fiber opposite the first layer of the first thermosetting resin, such that the first and second layers of the first thermosetting resin impregnate the reinforcing fiber. Both of the foregoing methods are similarly useful in embodiments wherein the reinforcing fiber comprises a combination of two or more forms of reinforcing fiber, as will be readily apparent to one skilled in the art .

The surface layer is provided by impregnating the veil with a second thermosetting resin according to any suitable means, such as those described above. Preferably, the veil is impregnated with the second thermosetting resin by positioning the veil on the base layer and depositing a layer of the second thermosetting resin on the veil in a sufficient quantity to impregnate the veil . The veil may be positioned on the base layer according to any suitable means. Typically, the veil is merely placed on top of the base layer. A layer of the second thermosetting resin is then deposited on the veil such that the veil is impregnated with the second thermosetting resin. Typically, the second thermosetting resin is metered onto a carrier film and then contacted to the veil on the opposite side from the base layer, such that the veil is sandwiched between the base layer and the layer of the second thermosetting resin. Preferably a sufficient amount of resin is applied to thoroughly overlie and permeate the veil. As the layer of second thermosetting resin is applied to the base layer having the veil thereon, the second thermosetting resin permeates and impregnates the veil, to form the surface layer.

The surface and base layers are then placed under a compressive molding pressure, which is applied to the bottom face of the base layer and the top face of the surface layer, as described in detail above.

As previously noted, the methods of the present invention are adaptable for use on conventional SMC manufacturing machines. Preferably, the methods of the present invention are practiced using conventional SMC manufacturing machines operating at a rate of about 5 to about 50 ft/min.

As noted above, the SMC of the present invention may be used to prepare molded articles. The method of making molded articles using the SMC of the present invention comprises (a) contacting a top face of the base layer with a bottom face of the surface layer, (b) placing the base layer and the surface layer under a compressive molding pressure applied to a bottom face of the base layer and a top face of the surface layer, to form a corrosion resistant sheet molding compound, and (c) molding the sheet molding compound under heat and pressure to provide a corrosion resistant molded article. The steps (a) and (b) of contacting a top face of the base layer with a bottom face of the surface layer, and placing the base layer and the surface layer under a compressive molding pressure are described above in detail . The further step of molding the SMC under heat and pressure to provide a corrosion resistant molded article may be carried out according to any suitable means. Typically, the SMC is molded according to compression molding techniques known to those skilled in the art. The following examples are provided to illustrate the present invention, and should not be construed as limiting thereof. In these examples, mm means millimeter, min means minute, psi means pounds per square inch, and all parts are given in parts by weight unless otherwise indicated.

EXAMPLE 1 Preparation of the Resin

A urethane modified unsaturated polyester resin is prepared by combining the following ingredients in a 1-gallon container: 90 parts ATLAC™ 580-05, 10 parts 80 percent ATLAC™ G380A in styrene, both available from Reichhold Chemicals, Inc., Research Triangle Park, North Carolina, 1.0 part dibutyl tin dilaurate urethane catalyst, 1.5 parts AKZO™ 29B75 polymerization initiator, and 2.0 parts zinc stearate internal mold release agent. The combination is mixed for about 2 min. Thereafter, 5.5 parts of thickener, RUBINATE™ M1780 is added and mixed for approximately 1 min. The resin mixture is then poured into the resin supply on a conventional SMC machine.

EXAMPLE 2 Preparation of SMC with Veil

In a conventional SMC machine operating at a belt speed of 10 ft/min, a sheet of Nicofibers SURMAT™ 100SF veil having a thickness of 10 mils is placed on a Nylon carrier film, and passed under a resin supply containing the resin preparation of Example 1 above. The excess resin is removed. The resin impregnated veil is then passed under the roving chopper, where 1 inch chopped glass rovings are deposited thereon. Thereafter, a second layer of the resin of Example 1 is placed on a Nylon carrier film. The resin layer is then positioned in abutment with the layer of chopped glass rovings, thereby impregnating the chopped glass rovings with resin. The combined layers of resin impregnated veil, glass rovings and resin are compacted between rollers under about 100 psi of pressure.

The SMC is molded and fully cured using conventional compression molding techniques to give, a molded article having a smooth, glossy surface, which is free of pinholes and other defects.

The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. The invention is defined by the following claims, with equivalents of the claims to be included therein.

Claims

Cl aims :

1. A corrosion resistant sheet molding compound comprising:

(a) a base layer comprising about 35 to about 95 percent by weight of a first thermosetting resin and about 5 to about 65 percent by weight of reinforcing fiber; and

(b) a surface layer overlying the base layer, comprising a corrosion resistant veil impregnated with about 50 to about 99 percent by weight of a second thermosetting resin, wherein the veil is not more than 100 mils in thickness.

2. The sheet molding compound according to Claim 1, wherein the surface and base layers are bonded together.

3. The sheet molding compound according to

Claim 1, wherein the first and second thermosetting resins are corrosion resistant thermosetting resins.

4. The sheet molding compound according to Claim 1, wherein the first and second thermosetting resins are independently selected from the group consisting of unsaturated polyesters, vinyl urethanes, vinyl isocyanurates, and vinyl esters.

5. The sheet molding compound according to Claim 1, wherein the first and second resins are the same.

6. The sheet molding compound according to Claim 1, wherein the first and second thermosetting resins comprise an unsaturated polyester resin.

7. The sheet molding compound according to Claim 1, wherein the reinforcing fiber comprises chopped glass roving.

8. The sheet molding compound according to Claim 1, wherein the reinforcing fiber comprises unidirectional fibers and chopped glass roving.

9. The sheet molding compound according to Claim 1, wherein the veil comprises a sheet of randomly oriented filament selected from the group consisting of glass, polyester, and natural filament.

10. The sheet molding compound according to Claim 1, wherein the veil comprises a sheet of randomly oriented polyester filament.

11. A corrosion resistant molded article comprising the corrosion resistant sheet molding compound of Claim 1.

12. A method of making a corrosion resistant sheet molding compound comprising a multilayer structure having a surface layer overlying a base layer, wherein in the base layer comprises about 35 to about 95 percent by weight of a first thermosetting resin and about 5 to about 65 percent by weight of reinforcing fiber, and the surface layer comprises a corrosion resistant veil impregnated with about 50 to about 99 percent by weight of a second thermosetting resin, said method comprising:

(a) contacting a top face of the base layer with a bottom face of the surface layer; and

(b) placing the base layer and the surface layer under a compressive molding pressure applied to a bottom face of the base layer and a top face of the surface layer.

13. The method according to Claim 12, wherein the surface and base layers are bonded together.

14. The method according to Claim 12, wherein the first and second thermosetting resins are corrosion resistant thermosetting resins.

15. The method according to Claim 12, wherein the first and second thermosetting resins are independently selected from the group consisting of unsaturated polyesters, vinyl urethanes, vinyl isocyanurates, and vinyl esters.

16. The method according to Claim 12, wherein the first and second resins are the same.

17. The method according to Claim 12, wherein the first and second thermosetting resins comprise an unsaturated polyester resin.

18. The method according to Claim 12, wherein the reinforcing fiber comprises chopped glass roving.

19. The method according to Claim 12, wherein the reinforcing fiber comprises unidirectional fibers and chopped glass roving.

20. The method according to Claim 12, wherein the veil comprises a sheet of randomly oriented filament selected from the group consisting of glass, polyester, and natural filament.

21. The method according to Claim 12, wherein the veil comprises a sheet of randomly oriented polyester filament.

22. A method of making a corrosion resistant sheet molding compound comprising a multilayer structure having a surface layer overlying a base layer, wherein the base layer comprises about 35 to about 95 percent by weight of a first thermosetting resin and about 5 to about 65 percent by weight of reinforcing fiber, and the surface layer comprises a corrosion resistant veil impregnated with about 50 to about 99 percent by weight of a second thermosetting resin, said method comprising:

(a) impregnating a corrosion resistant veil with a second thermosetting resin to provide the surface layer,*

(b) positioning a layer of reinforcing fiber on a bottom face of the surface layer;

(c) depositing a layer of the first thermosetting resin on the layer of reinforcing fiber opposite the surface layer, wherein the first thermosetting resin impregnates the reinforcing fiber to provide a base layer,* and

(d) placing the base layer and the surface layer under a compressive molding pressure applied to a bottom face of the base layer and a top face of the surface layer.

23. The method according to Claim 22, wherein the step of impregnating the corrosion resistant veil with the second thermosetting resin comprises positioning the veil on a layer of the second thermosetting resin.

24. The method according to Claim 22, wherein the step of impregnating a corrosion resistant veil with a second thermosetting resin comprises depositing a layer of the second thermosetting resin on the veil .

25. The method according to Claim 22, wherein the first and second thermosetting resins comprise unsaturated polyester and wherein said step (a) of impregnating a corrosion resistant veil with a second thermosetting resin comprises positioning the veil on a layer of unsaturated polyester.

26. The method according to Claim 22, wherein the first and second thermosetting resins comprise vinyl ester and wherein said step (a) of impregnating a corrosion resistant veil with a second thermosetting resin comprises positioning the veil on a layer of vinyl ester.

27. The method according to Claim 22, wherein the first and second thermosetting resins comprise unsaturated polyester and wherein said step (a) of impregnating a corrosion resistant veil with a second thermosetting resin comprises depositing a layer of unsaturated polyester on the veil.

28. The method according to Claim 22, wherein the first and second thermosetting resins comprise vinyl ester and wherein said step (a) of impregnating a corrosion resistant veil with a second thermosetting resin comprises depositing a layer of vinyl ester on the veil.

29. A method of making a corrosion resistant sheet molding compound comprising a multilayer structure having a surface layer overlying a base layer, wherein in the base layer comprises about 35 to about 95 percent by weight of a first thermosetting resin and about 5 to about 65 percent by weight of reinforcing fiber, and the surface layer comprises a corrosion resistant veil impregnated with about 50 to about 99 percent by weight of a second thermosetting resin, the veil being not more than 100 mils in thickness,* said method comprising

(a) impregnating the reinforcing fiber with the first thermosetting resin to provide the base layer,*

(b) positioning the veil on the base layer;

(c) depositing a layer of the second thermosetting resin on the veil opposite the base layer, to provide a base layer; and (d) placing the base layer and the surface layer under a compressive molding pressure applied to the bottom face of the base layer and the top face of the surface layer.

30. The method according to Claim 29, wherein the step (a) of impregnating the reinforcing fiber with the second thermosetting resin comprises providing a layer of the second thermosetting resin and depositing a layer of reinforcing fiber thereon such that the second thermosetting resin impregnates the reinforcing fiber.

31. The method according to Claim 29, wherein the step (a) of impregnating the reinforcing fiber with the second thermosetting resin comprises providing a layer of reinforcing fiber and depositing a layer of the second thermosetting resin thereon such that the second thermosetting resin impregnates the reinforcing fiber.

32. The method according to Claim 29, wherein the first and second thermosetting resins comprise unsaturated polyester and wherein said step (a) of impregnating reinforcing fiber with a second thermosetting resin comprises providing a layer of unsaturated polyester and depositing a layer of reinforcing fiber thereon.

33. The method according to Claim 29, wherein the first and second thermosetting resins comprise vinyl ester and wherein said step (a) of impregnating reinforcing fiber with a second thermosetting resin comprises providing a layer of vinyl ester and depositing a layer of reinforcing fiber thereon.

34. The method according to Claim 29, wherein the first and second thermosetting resins comprise unsaturated polyester and wherein said step (a) of impregnating reinforcing fiber with a second thermosetting resin comprises providing a layer of reinforcing fiber and depositing a layer of unsaturated polyester thereon.

35. The method according to Claim 29, wherein the first and second thermosetting resins comprise vinyl ester and wherein said step (a) of impregnating a reinforcing fiber with a second thermosetting resin comprises positioning the veil on a layer of vinyl ester.

36. A method of making a corrosion resistant molded article comprising a multilayer structure having a surface layer overlying a base layer, wherein in the base layer comprises about 35 to about 95 percent by weight of a first thermosetting resin and about 5 to about 65 percent by weight of reinforcing fiber, and the surface layer comprises a corrosion resistant veil impregnated with about 50 to about 99 percent by weight of a second thermosetting resin, the veil being not more than 100 mils in thickness; said method comprising:

(a) contacting a top face of the base layer with a bottom face of the surface layer;

(b) placing the base layer and the surface layer under a compressive molding pressure applied to a bottom face of the base layer and a top face of the surface layer, to form a corrosion resistant sheet molding compound; and

(c) molding the sheet molding compound under heat and pressure to provide a corrosion resistant molded article.