A COMPOUND AND METHOD OF REPAIRING SURFACE DEFECTS

Abstract: A compound suitable for patching plastics, metal and the like. The compound comprises a thermosetting unsaturated polyester resin, a thermoplastic resin mixed with said polyester, particulate inorganic filler, as well as additional metallic particulate material, fibrous materials and a catalyst. The material when cured at a relatively elevated temperature provides a low shrink material which can be painted and baked.

Description: ACOMPOUNDANDMETHOD OFREPAIRINGSURFACEDEFECTS In one aspect, this invention relates to resin compositions. In a further aspect, this invention relates to filled resin compositions suitable for use in patching plastics and metal materials. Prior art patching compounds are generally designed to have good adhesion to the materials to which they are applied at normal room temperatures and to some extent at temperatures below room temperature down to and including -30°F. However, such patching compounds have not been formulated which are capable of withstanding temperatures on the order of 375-400 F. without substantial shrinkage. Thus, such compounds when used to repair defects in a plastic or metal part cannot be subjected to the normal painting and baking cycle common with original equipment manufacturing processing. A further problem with prior art compositions is the physical characteristic of sandability. For best results , it is desirable that the cured patching composition have sanding characteristics similar to that of the base material. Thus, upon finishing and sanding, the patched surface, to which an overlying paint or lacquer is to be applied, has a similar texture to the base material. Briefly, the patching compound of this invention has a first thermosetting, unsaturated polyester resin having a ratio of hydroxyl to carboxyl groups of about 5.7 to 0.8; an acid number of at least 14; and an average molecular weight of approximately 800-5,000. A second, thermoplastic resin syrup is mixed with the first unsaturated polyester resin; the thermoplastic resin being dissolved in an unsaturated monomer. To the resinous materials, various fillers are added to achieve the desired physical properties. Exemplary fillers might include 5-20 percent by weight of inert, inorganic particles, about 5-15 percent by weight of metallic particulate filler and about 10-20 percent by weight of milled fibrous material can be added to the polyester resins. A minor amount of a free radical catalyst is added to promote curing. When cured these resins form a solid material which is sandable, and has good adhesion to metal and plastic materials. Further, the material is capable of withstanding normal painting cycles when cured in accordance of the method of this invention. The unsaturated polyester resins employed in the practice of the present invention generally have a ratio of hydroxyl to carboxyl groups between about 5.7 and 0.8, an acid number of at least about 14 and an average molecular weight between about 800-5,000. Resins having these characteristics provide a good thermosetting unsaturated polyester resin which can be cured to form a solid thermoset matrix having good structural integrity when combined with the fillers described hereinafter. The resin preferably has an acid number of at least 14 and a hydroxyl number of at least 14, preferably 1 " 4-120, with the preferred acid- number range being between about 14-70. Such resins will normally have a molecular weight of about 900-3,500. Resins in this preferred range provide a good combination of relatively rapid gel and cure to a matured product, combined with good physical characteristics. The unsaturated polyester resin is normally present in an amount of about 10-30 weight percent dissolved in an aliphatically unsaturated monomer, such as styrene. . The monomer chosen will be compatible with the thermosetting resin and also with the other resinous materials present. Many useful unsaturated polyester resins can be formed for use as starting materials in the practice of this invention. However, three types useful in the practice of this invention will be disclosed in greater detail for the purposes of illustration. A first type of resin in glycol-maleate type resin. This type of unsaturated polyester resin is generally formed from butylene, propylene or ethylene glycol-maleate polyester product and may contain small quantities of other glycols, for example diethylene or dipropylene glycol, neopentyl glycol or the like. Such glycol-maleate products are prepared by cooking together one mole of maleic acid or anhydride, one mole of propylene glycol, 0.1 mcle of ethylene glycol, an esterification catalyst and tertiary butyl catechol or hydroquinone inhibitor. Such glycol-maleate polyesters have the properties of high rigidity, high heat resistance and are highly reactive and readily made into low shrink compositions when incorporated into the resin mixture of this invention. A second type of unsaturated polyester resin useful in the practice of this invention is a glycol-maleate-phthalate type resin prepared from propylene or ethylene glycol, maleate acid or anhydride, and phthalic or isophthalic acid. Also, miscellaneous glycols could be used such as those discussed with respect to the glycol-maleate type. In general, the ratio of maleate to phthalate is about 3:1. Such products are representatively prepared by cooking together 0.75 mole of maleic acid or anhydride, 0.25 mole of isophthalic acid and 1.1 mole of propylene glycol. Such unsaturated polyester resins have the properties of being slightly more resilient, stronger, and slightly lower in heat resistance than the glycol-maleates. These resins are also slightly less reactive than glycol-maleates. It can be used where a slightly longer cure time is desired. A third example of a resin useful in the practice of this invention is an unsaturated polyester resin of the glycol maleate phthalate type having a higher ratio of phthalate to maleate. These unsaturated polyester resins are also formed from ethylene or propylene glycol, maleate acid or anhydride and isophthalic or phthalic acid plus miscellaneous glycols as discussed with respect to the first and second examples. Resins of this type will have a maleate-phthalate ratio generally in the range of about 2:1. Such resins are characterized by extreme toughness, considerably higher elongation, lower heat distoration and a lower reactivity than either of the previously described resin systems . Aside from the characteristics of the unsaturated resins set forth hereinbefore, the exact type of reactants used. to form the unsaturated polyester resin employed is not critical. Polyester resins are known and conventionally made by the condensation of at least one unsaturated dicarboxylic acid or anhydride and at least one glycol wherein water is removed during the condensation-esterification reaction. Examples of suitably unsaturated dicarboxylic acids include alpha, beta ethylenically unsaturated dicarboxylic acids and their anhydrides such as fumaric acid, maleate acid and maleate anhydride. Examples of unsaturated polycarboxylic acids and their anhydrides include the phthalic acids, phthalic anhydride, succinic acid, adipic acid, and itaconic acid. Other polycarboxylic acids usable herein include citric acid, pyro-nellitic acid and trimesic acid. The preferred glycols usable to make the polyester resins used in this invention are the alkylene glycols such as ethylene glycol, propylene c: glycol, neopental glycol, butylene glycol, and bisphenol A, such reactants being well known in the art. Either the dicarboxylic acids or the glycols may be halogenated to reduce the flammability of the molded articles . The acid numbers and the hydroxyl numbers described here and before and in the claims refer to the unsaturated polyester resin itself. It must therefore be understood that these figures are somewhat higher than would be the case where the hydroxyl and carboxyl numbers are given for a resin which has been dissolved in an unsaturated monomer such as styrene. The resin compositions of this invention include, a low-shrink additive consisting essentially of a thermoplastic polymer, ordinarily added to the thermosetting resin dissolved in an unsaturated monomer such as styrene. Such a low shrinkage polymer is generally present in any aount of about 10 to 20 parts by weight of total ingredients. This low-shrink additive, when added to the polyester resin, can be added in the form of a thermoplastic powder which is soluble in part or all of the liquid monomer employed as a solvent with respect to the unsaturated polyester resin. Such low-shrink thermoplastic based additives are described in U.S. Patent No. 3,701,748; the disclosure of said patent with respect to suitable thermoplastic resins and their characteristics is incorporated herein by reference. In particular, the patent is of interest with respect to how thermoplastic polymers or copolymers should be employed to obtain low-shrink characteristics in thermosetting systems; except that for the purposes of this invention, it is not necessary that the thermoplastic polymers be compatible with the thermosetting polymers to form an optically heterogenous cured composition. One example of a suitable thermoplastic material is an acrylic syrup of methylmethacrylate containing about 30-40 percent by weight of solid methylmethacrylate dissolved in styrene monomer. To the combination of resins disclosed hereinbefore, various fillers and reinforcing materials will be added to form the compositions of this invention. For example, generally a reinforcing fiber will be added to the composition, fiber reinforcement being present in the amount of about 5-25 percent by weight of the total composition. Examples of suitable reinforcing fibers are glass fibers , cotton fibers , sisal fibers, Kelvar f bers, asbestos fibers, and other fibers such as metal fibers and whiskers , born fibers and whiskers and graphite fibers and whiskers . In addition, a wide variety of organic or inorganic fibers may be used. Glass fibers are the most desirable for most applications because of their low cost and high strength. In addition to the reinforcing fibers, the compositions of this invention will have one or more particulate fillers added to the resinous material. Many different types of fillers are contemplated within the scope of this invention, such as inorganic fillers, i.e., silicates, asbestor, metal carbonates, mica, barytes , clay, diatomaceous earth, microballoons , microspheres, silica, and fuller's earth. Also contemplated would be organic fillers such as wood flour, cork dust, cotton flock, wool felt, nutshells and the like. A further preferred filler normally present is flake or metal particles such as aluminum flake, steel flake, as well as oxides and sulfides of metals. The amount of metal filler will normally be present in an amount of about 20-60 percent by weight of the final composition. The fillers chosen and their amounts will be adjusted to achieve the desired hardness and sandaility of the patching compound. For example, the filler might consist of talc, a relatively soft inorganic filler, calcium carbonate, also a moderately soft inorganic filler, and aluminum powder. The physical properties of materials can be adjusted by increasing the amount of metal particulate where it is desired to achieve a metal like consistency or by increasing the amounts of inorganic or organic particulate fillers where it is desired to achieve a softer, more sandable material. The softer materials could be used for patching of imperfect or damaged molded plastic panels, such as those normally used on automobiles while heavily loaded or harder metal filled powders could be used in patching damaged or imperfect metal panels. To the resin composition is added a free radical polymerization catalyst. Such a catalyst is generally present in the amount of about 1-5 parts of catalyst per 100 parts of composition. Such a free radical catalyst is added to the uncured composition, and upon heating to the catalyst activation temperature, the addition-type cross linking polymerization reaction will commence between the polymerizable monomer and the unsaturated polyester resin. Such catalysts are well known in the art. A wide range of free radical generating polymerization catalysts are usable, one group of catalysts being the peroxides. Peroxides usable as free radical polymerization catalysts include benzoyl peroxide, lauroyl peroxide, parachlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, ketone peroxides such as methyl ethyl ketone peroxide, cyclohexanone peroxide, methyl isobutyl ketone peroxide, and other peroxides such as dicumyl peroxide, 2,2' -bis(4,4* -ditertiary butyl peroxy cyclohexyl propane), ditertiary butyl peroxide, cumene hydroperoxide, tertiary butyl cu yl peroxide, and tertiary butyl perbenzoate. In addition, catalyst promoters can be added in amounts of about 1-5 percent by weight of the resin composition. Examples of suitable catalyst promoters are dimethylaniline or diethylaniline added as a 10 percent by weight of active ingredient dissolved in styrene monomer. Such materials can be mixed with the resin composition and will aid the free radical polymerization catalyst in gelling the resin portion of the composition. One example of how a composition can be made according to this invention is: Ingredient Particle Size % by Weight Talc about 1-10 u microns 18 Calcium Carbonate about 1-10 microns 12 Aluminum Flake about 10 to 20 microns 8 Glass Fibers about 0.5 to 6.5 m m 15 Unsaturated Polyester Resins 25 Methylmethacrylate Syrup 17 10% Dimethylaniline in Styrene 3 Benzoyl Peroxide Paste 2 100 The above composition provides a mixture which when applied according to the method set forth hereinafter can be heat cured using a heat gun or baking oven to provide a patch essentially free of shrinkage during further heating and processing. The following procedure outlines one method of using the above composition. For the purposes of illustration it is assumed that a blistered plastic part is being repaired. First, a line is routed around the blister, making an approximately 60° angle from the bottom of the blister to the part's surface and the top of the blister or other imperfection is pried off the molded substrate. Any dry fibrous reinforcing material remaining, such as the fibergalss frequently present in molded plastic articles, is ground off the substrate. The resulting area is then sanded by hand to remove any flaring or imperfections left by cleaning out the blistered area. The prepared area is then cleaned prior to applying the resin composition such as by the use of wiPO dry air to provide a dry, dust free surface. After preparation and cleaning, the composition detailed above comprising fillers and resins was mixed with the free radical catalyst, and the resulting mixture applied to the prepared area. A slight excess of the resin composition is used to allow for any shrinkage of the material during heat curing. The resulting uncured patch extends above the surface of the substrate being repaired. The resulting patch is cured by heating, one method being directing hot air from a hot air heat gun, such as those normally available in laboratory and parts supply houses onto the patch. The gun is held at a distance of about 6-8 inches for approximately two to three minutes. During the heating the patching material will cure and will become tightly bonded to the underlying prepared substrate. After curing, the patch area and the surrounding surface of the part can be sanded using normal sanding and surface finishing techniques . If for some reason a large void should be present in the repaired area, the resulting void can be filled by repeating the above steps. Should there be only minor sanding porosity present, as is the normal case with the composition of this invention, then a standard pitfiller containing small amounts of iron oxide can be smoothed into the resulting porosity to provide an essentially flat porosity-free surface. The resulting repaired part can be placed on normal painting lines for finishing. Generally during processing on these lines, the part will be primed and be given one or more finish coats of colored paint. The paint coats will be baked at temperatures generally exceeding 300°F. (49°C) . A patch made according to this invention is capable of being processed on these standard processing lines at temperatures in excess of 300°F. (49°C) without the patch separating from the underlying substrate due to shrinkage. Such a feature allows repair of parts which would normally be scrapped prior to painting, resulting in substantial cost savings to the user and also considerable less waste of valuable and increasingly expensive resins made from hydrocarbon materials . Various modifications and alterations will become apparent to those skilled in the art without departing from the scope and spirit of this invention and it is understood that this invention is not limited to the illustrative embodiment set forth hereinbefore. As one example, the compound of this invention has good adhesion and could be used as an adhesive or body solder for metal parts.

Claims: The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 1. A patching compound suitable for use in repairing a defect, said patching compound having a thermosetting resin, a filler material and a catalyst suitable for polymerizing the thermosetting resin wherein the improvement comprises: using as said thermosetting resin, a resin having a hydroxyl-carboxyl ratio of about 5.7 to 0.8, an acid number of at least about 14 and an average molecular weight of about 800-5,000 said resin being present in about 10 to 30 percent by weight of said compound; using about 10-20 percent by weight of a thermoplastic material in said compound; using about 5-25 percent by weight of a fiberous reinforcing material in said compound; using about 2Q-60 percent by weight of a particulate material in said compound and using about 1-5 percent by weight of a free radical polymerization catalyst in said compound. 2. The patching compound of claim 1 wherein said thermoset resin has an acid number of at least 14, a hydroxyl number of 14-120 and a molecular weight of about 900-3,500. 3. The patching compound of claim 1 wherein said resin is a glycol-maleate type resin. 4. The patching compound of claim 1 wherein said resin is a glycol-maleate phthalate type resin having a ratio of maleate to phthalate of about 3:1. 5. The patching composition of claim 1 wherein said thermosetting resin is a glycol-maleate phthalate resin having a maleate to phthalate ratio of about 2:1. 6. The patching compound of claim 1 wherein said thermoplastic is a styrene solution of methylmethacrylate. 7. The patching compound of claim 1 wherein said patching compound contains about 1-5 weight percent of a catalyst promoter. 8. The patching compound of claim 1 wherein said fibrous material is glass fiber. 9- The patching compound of claim 1 wherein said compound contains about 10 to 20 percent by weight of particulate talc as a portion of the particulate filler. 10. The patching compound of claim 1 wherein said particulate filler includes about 5 to 15 percent by weight of the total resin composition of metal flake material. 11. The patching compound of claim 10 wherein said metal is aluminum. 12. The patching compound of cl - 1 wherein said catalyst is a peroxide catalyst. 13. In a method of repairing a surface in preparation for further treatment using a patching compound containing a thermosetting resin, a filler, a free radical polymerization catalyst, suitable for curing said resin to a thermoset material, involving the steps of placing said copound on the substrate to be repaired, heating the applied patching compound to a temperature sufficient to cure the thermosetting resin, and finishing the cured compound and surrounding substrate to provide a smooth surface suitable for further treatment wherein the improvement comprises: applying as said patching compound, a material comprising about 10-30 percent by weight of the thermosetting resin, said thermosetting resin having a hydroxyl-carboxyl ratio of about 5.7-0.8, an acid number of at least about 14 and an average molecular weight of about 800-5,000; about 10-20 percent by weight of a thermoplastic material; about 5-25 percent by weight of a fiberous reinforcing material, about 20-60 percent by weight of a particulate material and about 1.5 percent by weight of a free radical polymerization catalyst. 14. The method of claim 13 wherein said heating - - T. m∑ -A QV. VIrO is done by the application of air heated to appi-oximately 300-350° F. for a period of approximately 2 to 3 minutes. 15. The method of claim 14 wherein said particulate material contains about 5-15 percent by weight of the patching compound metal particles. 16. Method of claim 13 wherein said particulate material contains about 10 to 15 percent by weight of calcium carbonate having a particle size of about 1-10 microns . 17. The method of claim 13 wherein said particulate material contains about 10 to 20 percent by weight of talc having a particle size of about 1-10 micro microns. 18. The method of claim 13 wherein said particulate material contains about 5 to 15 percent by weight of metal flake material having a particle size of about 10 to 20 microns. 19. The method of claim 13 wherein said fibrous reinforcing material is glass fiber. 20. The method of claim 19 wherein said glass fibers have a cut length of about 0.5 to 6.5 millimeters .

Inventors: CONNOLLY J, ISELER K, SHAH M
Applicants: BUDD CO
Application year: 1981
Main classification: B29H5
IPC codes: C08F283, C08F299, C08K3, C08K7, C08K13, C08L67, C08L101, C09D5, C09K3