Radiant Energy Curable Acrylic Urethane Prepolymer Resin Compositions and Method

Polyester resins are polycondensation products of a dicarboxylic acid with dihydroxy alcohols. Such polyester resins catalyze to cure or harden, generally at room temperatures, to make a wide variety of products. Unsaturated polyester resins are widely used today to make products for use in the marine, transportation and building industries, and in particular, fiber or particulate reinforced products, such as glass fiber reinforced laminate-type products. Unsaturated polyester resins generally contain ethylenic unsaturation introduced by the employment of unsaturated diacids, thus comprising thermosetting-type resins. As such, unsaturated resins generally employ maleic and fumaric unsaturated acids, although saturated acids, phthalic and adipic acid may also be included to control or reduce the amount of unsaturation in the final unsaturated polyester resin and to control the physical properties. Dihydroxy alcohols most generally used are typically ethylene, propylene, diethylene and dipropylene glycols. Crosslinking agents may be employed with the unsaturated polyester resins. Generally, styrene monomers and di-allyl phthalate are the most common crosslinking agents. The styrene monomers are used to reduce the viscosity of the polyester resin and to act also as a crosslinker in the polyester resins.

It is desirable, particularly in view of the toxicity of the styrene monomer and government regulations, to reduce the concentration levels of the styrene monomer from the usual 40% to 50% by weight of the polyester resin to below 35% or 30% by weight. However, reductions in styrene monomer concentrations present problems in the polyester resins with the increased viscosity of the resin, causing difficulties in applying the resins, such as causing spray problems and glass roll-out when the resin is sprayed or used in conjunction with glass fibers. The reduced styrene monomer polyester resin does not wet the glass in preparing glass fiber laminates, and therefore, the surface of the sprayed glass fiber polyester resin typically must be contacted with a roller to prevent glass fibers from sticking out of the surface. In addition, the physical properties of the styrene monomer-reduced polyester resins are also greatly reduced without the use of additional, supplemental crosslinkers in the polyester resin. The aromatic nature of styrene monomers in the unsaturated polyols improves the hydrolytic stability and increases the chemical resistance to water, detergents and corrosion in the final, cured polyester resin product.

Acrylic monomers, such as methyl methacrylate (MMA) have been added to low or reduced styrene monomer polyester resins for marine grade gel coats and for outdoor applications. However, and unfortunately, MMA has a strong odor, is a skin and eye irritant and results in a slowing of the cure rate of a polyester resin. However, such acrylic monomers usually improve UV, water and chemical resistance. Therefore, it is not desirable to substitute MMA monomer for the styrene monomer or to add it with the styrene monomer, since MMA is also a hazardous material.

It is therefore desirable to provide new and improved, photoinitiated, crosslinkable resin compositions to replace or reduce styrene monomer in unsaturated resins, to provide unsaturated, cured resins with better physical and chemical properties and to provide an unsaturated polyester resin composition having reduced styrene monomer therein.

The invention relates to a modified acrylic urethane prepolymer concentrate for use and admixture with radiation curable, unsaturated polyester resin compositions and to the unsaturated resin compositions containing the concentrate as a diluent and a crosslinking composition and to the photocured unsaturated polyester resin compositions and their uses in and the method of preparing laminates and resin products.

The invention concerns an improved, liquid modified, acrylic urethane prepolymer concentrate adapted for addition to unsaturated resin compositions to provide improved cured resin properties and to provide unsaturated polyester resin compositions of reduced styrene monomer content. The liquid concentration comprises a modified acrylic urethane prepolymer or oligomer prepared by the reaction of a polyisocyanate, such as an aromatic isocyanate, like MDI, or an aliphatic isocyanate, usually in a stoichiometric amount or in a slight excess, with a hydroxyl-containing acrylate monomer with or without the presence of a catalyst and a diluent monomer, like a styrene monomer, generally in an amount of less than 40% by weight of the unsaturated polyester resin composition to which the concentrate is added, and an inhibitor, such as a quinone compound, such as benzoquinone, to retard any prereaction of the prepolymer and the styrene monomer in the concentrate.

The invention is also concerned with unsaturated resin compositions subject to curing in the presence of a catalyst, typically a peroxide alone or with a metal promoter, like a metal carboxylate, such as a cobalt or copper salt, alone or in combination with various accelerators, which are amine or amide accelerators. The catalytic amount of the peroxide compound added just prior to use with the resin composition contains a promoting amount of a metal promoter salt at room temperatures in order to provide sufficient exothermic heat to cure the unsaturated polyester resin composition containing the concentrate. An unsaturated polyester resin composition is usually employed either alone or typically in conjunction with filler material, such as particles or fiber materials, like clay, quartz, sand, limestone, mica, pigments or fibers, like glass fibers, and in some cases flame retardants like aluminum trihydrate, viscosity control agents and modifiers like formed silica and flow control agents, or combinations in amounts of about 0% to 30% by weight of the resin in order to prepare cured laminates of the unsaturated polyester resin, such as a spray laminate, containing glass fibers admixed with the polyester resin.

It has been found further that the resin composition of the invention may be cured either alone by photoinitiation or in combination with a peroxide promoter where a dual curing reaction is desired. The employment of radiation compounds by the use of one or more photoinitiators added to the prepolymer used with an unsaturated resin or to the prepolymer (oligomer) concentrate-unsaturated resin composition provides many advantages in the shelf life, storage, handling and processing of the composition and in the resultant radiation cured resin and resin products produced thereby.

The photoinitiators employed may vary, depending on the intensity and type of radiation to be used, and typically are selected to promote or initiate the curing-polymerization reaction of the composition, such as by the generation of free radicals. The radiant energy employed may include high energy radiation beams, but more particularly include visible light (sunlight) or UV light. The selection of the photoinitiator is usually based on the optimum absorption surges, e.g, 250 to 450 nm or to which the curable composition either as centering or molded product is to be exposed. The photoinitiator should be compatible with and admix with the prepolymer-oligomer concentrate and the resin composition.

The photoinitiators are used in a sufficient amount to initiate and promote polymerization, which amount may vary depending on the number and type of photoinitiators and whether the composition also contains chemical curing agents and promotion and the material used in the composition, the thickness of the composition and the radiant energy to be used.

For example, the photoinitiator may be used in amounts of from about 0.01 to 5.0 percent by weight of the unstructured resin composition, such as 1.5 to 3.0 percent by weight.

The photoinitiators may be used alone or in various combinations and generally are organic compounds like, but not limited to benzoins, ketals, ketones, phenones, and thioxanthones, and benzoates. Typical specific photometric compounds are: benzildimethyl ketal, 60% solution of benzildimethyl ketal, mixture of benzoin normal butyl ethers, trimethylbenzophenone blend, alpha hydroxy ketone, blend of trimethylbenzophenone blend and alpha hydroxy ketone, isopropylthioxanthone, blend of isopropylthioxanthone and trimethylbenzophenone blend, ethyl 4-(dimethylamino) benzoate, and benzophenone.

It has been discovered that unsaturated polyester resins and acrylic urethane oligomers made by reacting pentaerythriol triacrylate and either MDI or HDI adducts provide improved physical properties and cycle time. These hybrid resins, as described, are catalyzed using MEKP (methyl ethyl ketone peroxide) and promoted with cobalt octoate (12%) and DMAA (Dimethyl Aceto Acetamide).

It has now been discovered that these peroxide cured resin hybrids can now be cured using photoinitiators (PI) and radiant energy, such as UV or visible light, e.g. 365-450 nanometers. For PI compositions, cycle times can be reduced to 2-3 minutes at 50-120 mils in thickness and up to 50% glass reinforcement. However, glass reinforcement is not necessary when used as a coating.

It has been found that the photoinitiating curable prepolymer-resin composition will provide many and significant advantages over the peroxide-curable prepolymer-resin composition. One advantage is the increased shelf or container life of the PI composition, since once in the container and free of radiant energy, a significant increase in shelf and container life is possible over the peroxide-containing prepolymer resin compositions, which are subject to low reaction over time. Thus, the PI compositions may be stored for long periods and are quickly ready for use. Another advantage is that the PI compositions, particularly where used in enclosed areas, have an absence of any peroxide or promoter odor. Also, the PI curable compositions often have improved physical properties over the peroxide curable prepolymer resin compositions and exhibit better processing properties as regards to curing and cycle time. For example, where conventional unsaturated polyester resin compositions often take one to two hours or more to cure and the peroxide-curable prepolymer-resin compositions have reduced cure and cycle times, for example, of as low as five minutes, the PI curable compositions provide cycle times generally of less than about five minutes, such as reduced to 1-3 minutes, and coating thicknesses of about 50 to 120 mils. The PI curable compositions permit complete cures in reduced time, and therefore promote mold efficiencies, since the molded products have been partially cured by radiant energy, and may be rapidly demolded from the mold without waiting for the full cure to take place, as in the peroxide-curing compositions.

The curable prepolymer-resin compositions may be employed with flow modifying agents such as wetting agents, which wet the surface to which the curable composition is to be applied, either in a mold or by spray, and to prevent or reduce the development of "fish eyes" or other deformations in the cured resin surface. It has also been discovered that the PI curable compositions can contain significant amounts of, for example, up to about 15% by weight of particulate flame-retardant materials, such as, but not limited to, aluminum trihydrate, and still be effectively cured by the exposure of the curable composition to radiant energy, thus providing a relatively inexpensive, flame retardant, cured resin product. The PI-curable compositions may also contain minor amounts, as desired, for example, 1-20% or more by weight, of light-reflective materials, such as metal, for example, aluminum particles, glitter and flakes, which provide further disseminating of the radiant energy throughout the curable composition, and increases the efficiency of the time of the radiant cure, and provides a metallic or glitter-looking cured resin surface, for example, for the use on such as boats, or in traffic marking lanes or traffic or other road signs. Where the prepolymer-resin composition is to be employed on a vertical or sloping surface such as in a spraying or coating operation, it is often desirable to add a viscosity-modifying amount of a viscosity-modifying agent to the curable composition to prevent resin flow on the surface prior to cure, especially by the employment of various selected fixative compositions, for example, but not limited to, fumed silica, in the amount of 0.01 to 5% by weight of the curable composition.

It has been discovered that the replacement or reduction in amount of a styrene monomer as a diluent and cross-linking additive to unsaturated polyester resin compositions may be accomplished by employment of modified acrylic urethane prepolymers which result in improved properties to the cured polyester, better handling in preparing laminates as regards to roll-out of the laminate, and permits reduction of the styrene monomer, typically to amounts lower than 40%, for example from 0% to 30% by weight of the polyester resin composition. Particularly, it has been discovered that higher functionality acrylic monomers improve the polyester properties of the cured polyester composition. When a polyisocyanate, like MDI, is added to unsaturated polyester resin compositions by itself, such MDI tends to react with the hydroxyl group unsaturated polyester resin composition leading to increased and high viscosity which greatly reduces the feasibility of employing the unsaturated polyester resin composition as a diluent additive. Employment of a MMA monomer itself provides certain disadvantages. Therefore, the employment of a modified acrylic urethane prepolymer, a liquid concentrate, either alone or together with a styrene monomer and an inhibitor, may be used as a diluent additive to unsaturated polyester resin compositions to improve properties and to prepare compositions of reduced styrene monomer content.

In particular, it has been discovered that the high functionality aliphatic urethane prepolymers provide for a variety of improved cure properties of a polyester resin as set forth, for example, in Table I.

The employment of a special hydroxyl containing high functionality acrylic monomer, that is, an acrylic monomer with hydroxyl groups, being made into a prepolymer by the employment of a polyisocyanate, either aromatic or aliphatic diisocyanate, and which prepolymer so prepared in a preferred embodiment remains in a liquid condition. This liquid concentrate can be added to the low level styrene monomer unsaturated polyester resin compositions and produces a stable polyester resin composition, which does not react unless and until the peroxide catalysts or a catalyst-accelerator promoter combination is added to the unsaturated polyester resin composition. The addition of the catalytic curing composition, such as the use of methyl ethyl ketone peroxide as one example, provides for rapid cure of the polyester without significant loss of unreacted styrene monomer, so that the resulting unsaturated polyester resin with the liquid concentrate wets glass fiber with excellent efficiency and significantly reducing the need to roll-out the glass, where the unsaturated polyester resin composition is sprayed with glass fibers to form a glass fiber reinforced laminate.

The concentrate includes in one example a hydroxyl alkyl, such C.sub.2 -C.sub.6 acrylic monomer, which is reacted with a diisocyanate to provide the modified acrylic urethane prepolymer for use in the concentrate. Low functionality acrylic monomers, while not the preferred embodiment, provide for improved cure, chemical and physical properties of the polyester resin, since such low functionality modified acrylic urethane prepolymers with the low functionality used therein provide for solidified prepolymers or prepolymers which rapidly gel, and a liquid concentrate is the preferred embodiment. Some representative types of the acrylic monomers useful in the invention would include 2-hydroxy ethyl acrylate; hydroxy propyl acrylate; 2-hydroxy ethyl methacrylate; 2-hydroxy ethyl propyl methacrylate; and acrylic urethane prepolymers made from having an 100 index down to a 20 index with solidification occurring in most prepolymers, except for the prepolymers having a 20 or below index.

A preferred acrylic polymer which provides for a liquid concentrate comprises a pentaerythritol acrylate composed of tri-, tetra- and pentacrylate, which acrylic monomer has an hydroxyl group or an active hydrogen for reaction with the diisocyanate. Reaction of this pentaerythritol polyacrylate with diisocyanate, such as MDI, at different levels produces a stable liquid prepolymer, which does not react when added to an unsaturated polyester resin prior to the peroxide agent addition to the promoted unsaturated resin. For example, with a pentaerythritol triacrylate made up of tetra- and pentacrylate, the molecular weight of the acrylic monomer is 298 with a hydroxyl number of 298, which is reacted with MDI with 32% NCO and a 2.3 functionality with the MDI containing both 4--4 and 2-4 isomers.

Other high functionality hydroxyl acrylic monomers suitable for use would include ethoxylated or propoxylated trimethylol propane or glycerol polyacrylate, e.g., tri acrylate monomers. Specific high functionality acrylic monomers suitable for use include ethoxylated trimethylol propane triacrylate; pentaerythritol tri, tetra and pentaacrylate, propoxylated trimethylolpropane triacrylate; propoxylated glycerol triacrylate; di-tri methylol propane tetracrylate; dipentaerythritol pentacrylate; and ethoxylated pentaerythritol tetracrylate and combinations thereof.

The prepolymer is made by reacting with or without a catalyst the hydroxyl-containing acrylic monomer with polyisocyanate, more particularly, an aliphatic or aromatic diisocyanate, such as, but not limited to an aromatic diisocyanate, like MDI, or an aliphatic isocyanate, such as trimerized HDI (hexamethyl diisocyanate) or trimerized IPDI (isophenyl diisocyanate), or other acceptable diisocyantes or prepolymers which will react with the hydroxyl groups in the acrylic monomer. The compound, pentaerythritol triacrylate is a commercial product known as SR 444 of Sartomer Company, Inc. of Exton, Pa.

The prepolymer is added to an unsaturated resin composition, either alone or preferably in the concentrate form, known to contain some styrene monomer for viscosity control purposes, and thereby needing a reduction of the styrene monomer employed in the unsaturated polyester resin. The total amount of styrene monomer in the unsaturated resin composition would be less than 30% by weight. The prepolymer concentrate would also generally contain an inhibiting agent to provide for storage stability of the liquid concentrate, such as to maintain at least two-weeks' stability at 120.degree. F., and which inhibitor generally comprises a quinone compound, such as parabenzonequinone.

The prepolymer concentrate is employed as an additive diluent to unsaturated polyester resin compositions, such as those unsaturated resin compositions, but not limited to polyester resins prepared by reacting dicyclopentadiene (DCPD) with orthophthalic and maleic acid, the reaction of propylene glycol with maleic acid anhydride; and the reaction of isophthalic acid-maleic anhydride with neo pentyl glycol, or other known unsaturated polyester resin compositions.

Generally, the unsaturated resin compositions contain an inhibitor to prevent prereaction until a promoter or catalyst is added to effect cure in the polyester resin after the addition of the prepolymer concentrate. The unsaturated polyester resin compositions contain a monomer for crosslinking therewith, such as a diluent styrene monomer at reduced levels, where a concentrate prepolymer is employed. A cure is effected by employing an organic peroxide compound, and typically a metal salt, such as a fatty acid salt, like a cobalt octoate or potassium octoate, is employed in combination with an organic ketone, such as methyl ethyl ketone peroxide, to provide for an exothermic curing reaction. The promoter and catalyst composition may also contain amide-type compounds for acceleration purposes, such as the dimethyl acetamide. Generally, the peroxide, metals salts, amines and amides are employed at low levels with the peroxide employed from about 0.1% to 2.5% by weight and the metal salts ranging from about 0.05% to 0.5% by weight and the amine or amide from about 0.05% to about 0.5% by weight. It has been found that after addition of the concentrate prepolymer to the unsaturated polyester resin composition used to prepare laminates, that the roll-out time was reduced, for example, to less than five minutes. The polyester resin composition without the concentrate prepolymer, even though such composition gelled in ten minutes, tended to stay rubbery for five minutes or more until a peak exotherm occurred, while with the use of the concentrate prepolymer, cure of the polyester resins to a rigid physical condition occurred in less than five minutes.

It has been found that the employment of the prepolymer concentrate of the invention helps in reducing roll-out where the unsaturated resin composition is employed with fiberglass, such as in a spray or mold operation, so that in the preparation of cured polyester fiberglass laminates with the use of the liquid concentrate prepolymer, no rolling of the concentrate was required when the concentrate was employed. Further, it has been noted that the polyester resin systems, with the liquid prepolymer concentrate added thereto, had little or no styrene monomer smell within three to four minutes after the spraying of the resin composition, which is believed to occur as a result of the cross linking taking place and tying up the styrene monomer.

The invention will be described for the purposes of illustration only in connection with certain embodiments; however, it is recognized that those persons skilled in the art may make various modifications, changes, additions and improvements to the illustrated embodiments, without departing from the spirit and scope of the invention.

A liquid concentrate prepolymer prepared by admixing together 500 parts per weight of pentaerythritol triacrylate (acrylate SR-444) and 100 parts per weight of MDI (Papi 94, a trademark of Dow Chemical Company) and slowly reacted together without the present of catalyst to provide a liquid pentaerythritol acrylic urethane. Four hundred parts per weight of a styrene monomer were added to the liquid prepolymer and together with 50 ppm of an inhibitor, parabenzoquinone. Employment of straight uretonomini-isocyanate (like Dow L143) and polymeric MDI (like Papi 27) were also employed with the acrylate SR-444. Prepolymer solidification took place while heating the mixture in the oven. Low functionality hydroxyl-containing acrylic acrylates were tried employing diisocyanates of Papi-94 (Dow L143 and Papi 27); however, all these low functionality monomers solidified when the prepolymers were made.

The liquid prepolymer concentrate was added to different types of unsaturated polyester resins, such as a general purpose orthophthalic resin containing 30% styrene monomer and NPG orthoresin containing 30% styrene monomer, an NPG isophthalic resin containing 30% styrene monomer and DCPD ortho resin blends containing 30% styrene monomer. The unsaturated resin composition contained 50 ppm of an hydroquinone inhibitor with the mixing in of the liquid prepolymer concentrate, catalysts and promoters were admixed as follows: 2% catalyst of methyl ethyl ketone peroxide (containing 9% oxygen); 0.2 parts per weight of 12% cobalt octuate as a promoter; 0.2 parts per weight of dimethyl acetyl acetamide (DMAA); and 0.1 parts per weight of potassium octuate (15%). Ten percent of the liquid prepolymer concentrate was added to each resin. Gel time without the concentrate was about 10 minutes, while with the concentrate added, gel time was reduced to 2.5 to 2.8 minutes. All samples prepared without the concentrate, even though they gelled in ten minutes, stayed rubbery for five minutes until a peak exotherm occurred, while the same polyester resin samples with the 10% liquid prepolymer concentrate became rigid in less than five minutes.

The unsaturated polyester resin samples containing the 10% liquid prepolymer concentrate were put on a Binks B-8 fiberglass spray machine and sprayed with a Binks Century gun with external mix catalyst above and the fiberglass at about 22% by weight was sprayed at 3/4 inch fiber length employing a four by four foot plate mold. With each unsaturated polyester resin system used without the liquid prepolymer concentrate on the surface, the glass required rolling to make an acceptable laminate without air. The liquid prepolymer concentrate added at 10% and sprayed provided for a fiberglass polyester cured laminate requiring no roll out. Further, the resin systems with the liquid concentrate had no styrene monomer smell within three to four minutes of spraying of the polyester resin as a result of cross linking taking place with the styrene monomer.

Physical testing was done on all the polyester resin compositions, with or without the liquid prepolymer concentrate as added at 10%, and the test oligomers are shown on the accompanying Table II.

Compression-molded fiberglass trays were prepared employing an isophthalic polyester resin with a heat-activated catalyst, such as tertiary butyl perbenzoate, and added to a 33% glass fiber mat, with mold temperatures at 280.degree. F., a cycle time of 90 seconds and with 10% of the liquid prepolymer concentrate added to the polyester resin. Upon addition of the liquid prepolymer concentrate, cycle times for curing were reducing to 60 seconds. The glass fiber wet-out was improved, styrene emissions were reduced and the laminate had improved physical properties and chemical resistance.

Further tests were carried out with other polyester resins with and without a styrene monomer added and to which 10% by weight of the liquid concentrate of Example 1 was added. The cycle times of the polyester resin increased to 10 to 12 minutes on all types of polyester resins, and when each polyester resin system was sprayed with the fiberglass, no improvement was seen over the same polyester resin without the presence of the liquid prepolymer concentrate of the invention.

Aliphatic urethane acrylate and 2- (2 Ethoxyethoxy)

Ethyl acrylate ester (Craynor 961-H)

Epoxy acrylate oligomer plus 1, 6 Hexanediol

diacrylate ester (Craynor 120 B)

Aromatic urethane oligomer plus 1, 6 Hexanediol

diacrylate ester (Craynor 970)

In the marine and bathtub industry in the preparation of fiberglass laminate, water absorption is critical to the success of the end product. Extensive boiling tests were run on samples of polyester resins of DCPD, G.P.-Ortho, NPG-Ortho and NPG-Iso polyester resins, both with and without the liquid prepolymer concentrate added. The following Table III shows the percent water absorption at 80.degree. C. for 160 hours.

The above results indicate that all unsaturated polyester resin compositions showed significant improvement in water absorption when the liquid prepolymer concentrate was added at a level of 10% parts by weight.

Thus, the modified prepolymer concentrate prepared by the employment of pentaerythritol triacrylate, MDI and a styrene monomer with an inhibitor when added to unsaturated polyester resin compositions results in improvement in the physical and chemical properties, such as decrease in cure time, reduction in styrene emissions, reduction in styrene odor when sprayed, reduction in roll-out of molded or sprayed laminates, reduction in water absorption, increased chemical resistance, higher heat distortion temperatures and higher impact strength.

The unsaturated polyester resin composition with the modified acrylic-urethane prepolymer or oligomer and with a styrene monomer of less than about 30% by weight may be cured with a methyl ethyl ketone peroxide (1.5%-2.0%) and a cobalt salt (0.1-0.5%). The composition can be sprayed as a glass-fiber barrier coat behind a polyester or polyesteracrylic gel coat with a very fast cure time and with rapid cure. The barrier coat strengthens the gel coat and reduces water absorption and lowers water and vapor transmission. The composition may be sprayed or used with charged glass fibers in an open or closed mold, so that a no-roll surface without air entrapment can be prepared. After the gel coat is applied and a barrier coat is added (prior to resin and glass application), no glass fibers are visible on the gel coat side, eliminating veil mats, to provide a class A finish where a class A mold is used.

HP 1161 unsaturated polyester resin was used as a base material. This base material is a NPG orthophthalic resin with 30% styrene monomer, and a 10% by weight acrylic oligomer made by reacting pentaerythritol triacrylate and a low functionally MDI adduct and blended with 2% by weight of photoinitiator KB-1 (Benzil dimethyl ketal). No peroxide or promoters were used. The PI containing composition material was applied to a piece of wood at 50 mil thickness. The wood sample was taken outside in sunlight. Cure time was two minutes with a tack free surface. Total cure and hardness occurred in five minutes.

The same composition was promoted using cobalt octoate 12% and DMAA at levels of 0.1 and 0.3% respectively.

The PI promoted composition was coated on a wood sample at 50 mils thickness and placed outside. No difference in cure was seen. The promoted resin systems and photoinitiator was cured using 2% MEKP (925 Norac 9% O.sub.2).

A 3" disc 120 mils thick was cast of the PI-promoted composition and cured in five minutes. This resin system was taken outside after being applied at 50 mils to a wood sample. The sample was cut in half and half was placed in direct sunlight and half in indirect light. Results showed the direct sunlight sample cured in 2-3 minutes and the indirect light sample cured in 10 minutes, but remained tacky at the surface. It is well known that unsaturated polyester resins in their films usually have paraffin wax added to prevent air inhibition. It is also known that acrylic oligomers and monomers will not cure when exposed to air in their films.

The hybrid resin composition with its acrylic oligomers and the photoinitiator was added to 50% glass cloth. Two glass plates were used to contain the resin and glass to form a sandwich. The plates were taken outside and exposed to direct sunlight, and after five minutes the plates were removed. A stiff tackfree resin-covered glass laminate resulted. It should be noted that no smell of styrene monomer was present.

The same resin composition with promoters and catalyzed with MEKP at 2% was added to 50% glass cloth. The sample was allowed to cure for five minutes and removed. The sample was rubbery and had a styrene monomer and peroxide smell. Ten minutes after the sample was removed, the sample was cured and stiff.

The unsaturated polyester resin HP 1161 was tried without the acrylic oligomer. The photoinitiator was added at the same level, 50 mils was added on a wood sample. The sample was taken outside and exposed to direct sunlight. The sample cured in 12 minutes and remained sticky for 20 minutes. The hardness was never reached when compared to the same material with the acrylic oligomer added.

A standard acrylic oligomer produced by Sartomer Company, Inc. of Exton, Pa., called CN 975 was tried. The material was cut in 1,6 hexane diacrylate to reduce the viscosity at a 60/40 ratio. Ten percent of the oligomer was added to 1164 resin with the photoinitiator. The sample was placed outside on the wood sample. Cure was quick but the surface remained wet for 30 minutes. Stickiness never disappeared.

The same standard oligomer from Sartomer, CN 975, was tried by itself. Two percent KP-1 PI was added at 50 mils to a wood sample. This sample was exposed to direct sunlight. The sample did not cure on the surface, but did cure under the surface. The wetness did not go away.

It should be noted that the PI prepolymer-resin composition also cures well when using 0.5 to 1 mil thickness and high intensity light on a commercial UV curable machine.

The new hybrid PI compositions, using HP 1161 resin and the special oligomers (prepolymers), are a superior coating or laminating resin.

The PI composition was spray applied at 50 mils thickness to concrete and asphalt surfaces. The hybrid PI composition cured in 2-3 minutes with a beautiful high gloss coating. For vertical surfaces a 1-2% fumed silica was added as a viscosity control agent. No differences in cure were seen.

CaCO.sub.3 and aluminum trihydrate were tried at levels up to 50% in the PI hybrid composition in direct sunlight. The PI composition still cured rapidly without tackiness.

The hybrid resin was sprayed as a gel coat 20 mils on a waxed fiberglass mold. The mold was exposed to direct sunlight for three minutes. The PI hybrid composition was put through a standard fiberglass machine where 30% of 1" chopped glass was added to the spray pattern. The PI resin composition was sprayed 125 mils over the 20 mil coating. No rolling was necessary, because of the low surface tension of the resin composition. The mold was again taken outside and exposed to direct sunlight. The sample was left for five minutes in the mold and removed. A cured fiberglass laminate was made without MEKP or styrene odor.