Patent Application
20060252868
The present disclosure relates generally to resin formulations for sheet molding compounds. Particularly, but not by way of limitation, the invention relates to low-density thermosetting sheet molding compounds (SMC) comprising an organic-modified, inorganic clay, a thermosetting resin, a low profile agent, a reinforcing agent, a low-density filler, and substantially the absence of calcium carbonate. The present disclosure relates particularly to blends of isophthalate-glycol and maleate-glycol resins that provide thermosetting SMC that yield exterior and structural thermoset articles, e.g. auto parts, panels, etc that have Class A Surface Quality.
The information provided below is not admitted to be prior art to the present invention, but is provided solely to assist the understanding of the reader.
The transportation industry makes extensive use of standard composite parts formed from sheet molding compound (SMC). Sheet molding compound comprising unsaturated polyester fiberglass reinforced plastics (FRP) are extensively used in exterior body panel applications due to their corrosion resistance, strength, and resistance to damage. The automotive industry has very stringent requirements for the surface appearance of these body panels. This desirable smooth surface is generally referred to as a “class A” surface. Surface quality (SQ), as measured by the Laser Optical Reflected Image Analyzer (LORIA), is determined by three measurements—Ashland Index (Al), Distinctness of Image (DOI), and Orange Peel (OP). SMC with Class A SQ is typically defined as having an AI<80, a DOI>70 (scale 0-100), and an OP≧7.0 (scale 0-10).
A molded composite article is a shaped, solid material that results when two or more different materials having their own unique characteristics are combined to create a new material, and the combined properties, for the intended use, are superior to those of the separate starting materials. Typically, the molded composite article is formed by curing a shaped sheet molding compound (SMC), which comprises a fibrous material, e.g. glass fibers, embedded into a polymer matrix. While the mechanical properties of a bundle of fibers are low, the strength of the individual fibers is reinforced by the polymer matrix that acts as an adhesive and binds the fibers together. The bound fibers provide rigidity and impart structural strength to the molded composite article, while the polymeric matrix prevents the fibers from separating when the molded composite article is subjected to environmental stress.
The polymeric matrix of the molded composite article is formed from a thermosetting resin, which is mixed with fibers used to make a SMC. Thermosetting polymers “set” irreversibly by a curing reaction, and do not soften or melt when heated because they chemically cross-link when they are cured. Examples of thermosetting resins include phenolic resins, unsaturated polyester resins, polyurethane-forming resins, and epoxy resins.
Although molded composite article made from SMC based on thermosetting polymers typically have good mechanical properties and surface finish, this is achieved by loading the SMC with high levels of filler. These fillers, however, add weight to the SMC, which is undesirable, particularly when they are used to make automotive or parts of other vehicles that operate on expensive fuels. Therefore, there is an interest in developing SMC that will provide molded composite articles with good mechanical properties that have lower density, in order to improve fuel efficiency.
Additionally, the use of high levels of filler is particularly a problem when highly reactive unsaturated polyesters are used as the thermosetting polymer for making composites. Molded composite articles made from SMC formulations, which employ high reactivity unsaturated polyester resins, often shrink during cure. The shrinkage is controlled with low profile additives (LPA's) and large amounts of fillers, e.g. calcium carbonate, and kaolin clay. Although the resulting molded composite articles have good strength and surface appearance, the density of the composite is high, typically 1.9-2.0 g/cm3. Thus, when used in applications, such as automotive body parts, the added weight lowers fuel efficiency.
Unsaturated polyester resins typically shrink 5-8% on a volume basis when they are cured. In an FRP, this results in a very uneven surface because the glass fibers cause peaks and valleys when the resin shrinks around them. Thermoplastic low profile additives (LPA) have been developed in order to help these materials meet the stringent surface smoothness requirements for a class A surface. LPA are typically thermoplastic polymers which compensate for curing shrinkage by creating extensive microvoids in the cured resin. Unsaturated polyester resins can now be formulated to meet or exceed the smoothness of metal parts which are also widely used in these applications.
In addition to LPA's, formulations contain large amounts of inorganic fillers such as calcium carbonate (CaCO3). These fillers contribute in two critical ways towards the surface smoothness of these compositions. First, the fillers dilute the resin mixture. Typically, there may be twice as much filler as resin on a weight basis in a formulation. This reduces the shrinkage of the overall composition simply because there is less material undergoing shrinkage. The second function of the filler is in aiding the microvoiding that LPA's induce.
In recent years, there has been added pressure on the automotive manufacturers to reduce the weight of cars in order to improve gas mileage. While FRP's have an advantage in this respect compared to competitive materials because of lower specific gravity, the fillers mentioned previously cause the part to be heavier than necessary. Most inorganic fillers have fairly high densities. Calcium carbonate, the most commonly used filler, has a density of about 2.71 g/cc, compared to a density of about 1.2 g/cc for cured unsaturated polyester. A common FRP material used in body panel applications will have a density of about 1.9 g/cc. If this could be reduced by 10 to 20% while maintaining the other excellent properties of unsaturated polyester FRP's, a significant weight savings could be realized.
As the density is reduced, however, maintaining Class A SQ becomes difficult. The industry has expressed a need for low-density SMC having Class A SQ. The industry has expressed a need for SMC formulations that maintain mechanical properties and matrix toughness without increasing the paste viscosity above the range required for SMC sheet preparation.
U.S. Pat. No. 6,287,992 relates to a thermoset polymer composite comprising an epoxy vinyl ester resin or unsaturated polyester matrix having dispersed therein particles derived from a multi-layered inorganic material, which possesses organophilic properties (nanoclay composite). The dispersion of the multi-layered inorganic material with organophilic properties in the polymer matrix is such that an increase in the average interlayer spacing of the layered inorganic material occurs to a significant extent, resulting in the formation of a nanocomposite. Although the patent discloses polymer composites, it does not disclose molded composite articles and their mechanical properties, e.g. tensile strength (psi), modulus (ksi), elongation (%), and heat distortion temperature (° C.), nor does it disclose the manufacture of SMC that contains a reinforcing agent, a LPA, and a filler. Molded articles prepared using the SMC of the '992 patent experience significant shrinkage and are subject to significant internal stress, resulting in the formation of cracks in molded articles. Co-pending Application Number (not yet assigned, Attorney Docket number 20435-00167) discloses low-density SMC and articles molded therefrom comprising nanoclay composites.
SMC's formulated with “high reactivity” UPE resins typically are very brittle with low elongation, and toughness. Addition of “rubber impact modifiers” is well known, but is typically not sufficient to toughen to the desired level. One method, disclosed in U.S. Pat. 6,759,466, teaches the use of “toughened, high elongation UPE resins” modified with oligomeric polyols to reduce cracking and improve “paint-pop” resistance. This modified UPE is very effective at reducing flexural stress cracking and “paint popping” for standard density SMC. SMC formulated with this modified UPE does, however, show a reduced profiling efficiency for thermoplastic LPA's and a significant drop in its flexural modulus, a critical mechanical property for composite automotive body panels. These deficiencies tend to be magnified in the preparation of toughened Class A low density SMC. Low density systems require highly efficient interaction between the UPE resin and the LPA system to ensure good SQ. In addition, maintaining flexural properties without the aid of high CaCO3 levels makes the strength and stiffness of the polymer matrix critical.
Ashland's composite research group has expertise in the development of tough UPE resins. Ashland's product line of toughened resins are typically PG-maleate resins modified with aromatic saturated acids and glycols, such as DEG, DPG, NPG, 2-methyl 1,3-propane diol or other similar low molecular weight glycols. Evaluation of these toughened-UPE's showed poor profiling efficiency with typical LPA systems. Therefore, there is a need for a tough UPE resin that profiles efficiently with LPA systems.
An aspect of the invention provides the desired tough unsaturated polyester (UPE) that profile efficiently with LPA systems. An aspect of the present invention provides UPE resins formed by blending isophthalate modified maleic-glycol polyester resins with maleate-glycol resins to form the basis of tough low-density SMC parts with high mechanicals and Class A surface quality.
An aspect of the invention provides a sheet molding compound (SMC) formulation comprising a blend of isophthalate modified maleic-glycol and maleic-glycol resins, an ethylenically unsaturated monomer that reacts with and forms a thermoset with the resins, a low profiling additive, and a nanoclay filler composition, wherein the SMC paste has a density less than about 1.25 g/cm3. According to a further aspect, the inventive sheet molding compound (SMC) formulation contains a reinforcing roving.
According to an aspect, the isophthalate modified maleic-glycol resin is formed from isophthalic acid, maleic anhydride and a mixture of low molecular weight glycols such that the total moles of glycol range from approximately equivalent to about 10% greater than the total moles of acid equivalent. According to a further aspect, the glycol components may be chosen from ethylene glycol (EG), diethylene glycol (DEG), propylene glycol (PG), dipropylene glycol (DPG), neopentyl glycol (NPG), 1,3-propane glycol, and other similar low molecular weight glycols. According to a preferred aspect, the glycol is a mixture of the various glycols. According to a more preferred aspect the glycol comprises a roughly equimolar mixture of ethylene glycol (EG), diethylene glycol (DEG), and propylene glycol (PG).
According to an aspect, the maleic-glycol resin is formed from maleic anhydride and one or more low molecular weight glycols such that the total moles of glycol range from approximately equivalent to about 10% greater than the total moles of acid equivalent. The term “maleic anhydride” as used herein is understood to encompass maleic acid and maleic anhydride. According to a further aspect, the glycol component may be chosen from ethylene glycol (EG), diethylene glycol (DEG), propylene glycol (PG), dipropylene glycol (DPG), neopentyl glycol (NPG), 1,3-propane glycol, and other similar low molecular weight glycols. According to an aspect, the glycol may be a mixture of the various glycols. According to a preferred aspect the glycol is propylene glycol (PG).
A further aspect of the present invention provides a sheet molding compound (SMC) having an alternative reactive monomer (ARM) present as an aromatic, multiethylenically-unsaturated compound. According to an aspect, the aromatic nucleus of the monomer may be any of benzene, toluene, naphthalene, anthracene, or a higher order aromatic, or any mixture thereof. According to a further aspect, the ethylenic unsaturation may be of di-, tri-, tetra-, and/or higher functionality. According to a preferred aspect, the ethylenically unsaturated aromatic compound is divinylbenzene.
An aspect of the present invention provides a sheet molding compound (SMC) further comprising a low-profiling additive. According to a further aspect, the inventive sheet molding compound includes a low-profiling additive enhancer.
An additional aspect provides a sheet molding compound further comprising one or more additives selected from among mineral fillers, organic fillers, rubber impact modifiers, organic initiators, stabilizers, inhibitor, thickeners, cobalt promoters, nucleating agents, lubricants, plasticizers, chain extenders, colorants, mold release agents, antistatic agents, pigments, fire retardants, and mixtures thereof.
According to an aspect, there is provided an article of manufacture comprising the inventive low-density SMC. According to a further aspect, the article of manufacture has a Class A Surface Quality. Moreover, according to yet a further aspect, the article of manufacture has a surface smoothness quality less than a 80 Ashland LORIA analyzer index.
According to an additional aspect, a method of fabricating an article of manufacture is provided. According to an aspect, the method comprises heating the inventive low-density SMC under pressure in a mold.
Still other aspects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.
An aspect of the invention provides SMC-paste formulations comprising a thermosetting resin, an ethylenically unsaturated monomer, a low profiling additive, a nanoclay filler composition, a rubber impact modifier, and an alternative reactive monomer having the ability to aid in maintaining SQ as the density of the composite is reduced. According to an aspect, the SMC-paste has a density less than about 1.25 g/cm3. According to an aspect, the nanoclay composition is formulated separately and subsequently mixed with the resins, monomers, and the remaining components of the paste. According to a preferred aspect, the various components of the nanoclay composition and the SMC-paste are blended and the nanoclay forms in situ.
The thermosetting sheet molding paste compositions of the present invention comprise: (a) from about 30 to70 parts of thermosetting resin in styrene solution, preferably from about 45 to 65 parts; (b) from about 1 to 10 parts of treated inorganic clay, preferably from about 1 to 6 parts and, more preferred, about 1 to 3 parts; (c) from about 10 to 40 parts of low profile additive, typically as a 50% solution in styrene, and preferably from about 14 to 32 parts; (d) from 1 to 10 parts of rubber impact modifier, preferably from 2 to 6 parts, (e) from 0 to 10 parts styrene, preferably from 0 to5 parts; (f) from 0 to 65 parts of an inorganic filler, preferably from about 30 to 55 parts; and (g), from 1 to 10 parts of ARM, preferably 2 to 6 parts per 100 parts (phr) of ‘formulated resin’, where by definition, ‘formulated resin’ is the sum of (a), (c), (d), (e) and (g). Thus, 100 parts of ‘formulated resin’ becomes the base upon which additional additive and filler additions such as (b) and (f) are made. The SMC sheet comprises from 60 to 85 weight percent SMC paste and from 15 to 40 weight percent, more preferably from about 25 to 35 weight percent, fiber reinforcement.
A first component of sheet molding compounds is a thermosetting resin. Although any thermosetting resin can be used in the SMC-paste, the resin preferably is selected from phenolic resins, unsaturated polyester (UPE) resins, vinyl ester resins, polyurethane-forming resins, and epoxy resins.
Most preferably used as the thermosetting resin are unsaturated polyester resins. Unsaturated polyester resins are the polycondensation reaction product of one or more dihydric alcohols and one or more unsaturated, polycarboxylic acids. The term “unsaturated polycarboxylic acid” is meant to include unsaturated polycarboxylic and dicarboxylic acids; unsaturated polycarboxylic and dicarboxylic anhydrides; unsaturated polycarboxylic and dicarboxylic acid halides; and unsaturated polycarboxylic and dicarboxylic esters. Specific examples of unsaturated polycarboxylic acids include maleic anhydride, maleic acid, and fumaric acid. Mixtures of unsaturated polycarboxylic acids and saturated polycarboxylic acids may also be used. However, when such mixtures are used, the amount of unsaturated polycarboxylic acid typically exceeds fifty percent by weight of the mixture.
Examples of suitable unsaturated polyesters include the polycondensation products of (1) propylene glycol and maleic anhydride and/or fumaric acids; (2) 1,3-butanediol and maleic anhydride and/or fumaric acids; (3) combinations of ethylene and propylene glycols (approximately 50 mole percent or less of ethylene glycol) and maleic anhydride and/or fumaric acid; (4) propylene glycol, maleic anhydride and/or fumaric acid and saturated dibasic acids, such as o-phthalic, isophthalic, terephthalic, succinic, adipic, sebacic, methyl-succinic, and the like. In addition to the above-described polyester one may also use dicyclopentadiene modified unsaturated polyester resins as described in U.S. Pat. No. 3,883,612. These examples are intended to be illustrative of suitable polyesters and are not intended to be all-inclusive. The acid number to which the polymerizable unsaturated polyesters are condensed is not particularly critical with respect to the ability of the low-profile resin to be cured to the desired product. Polyesters, which have been condensed to acid numbers of less than 100 are generally useful, but acid numbers less than 70, are preferred. The molecular weight of the polymerizable unsaturated polyester may vary over a considerable range, generally those polyesters useful in the practice of the present invention having a molecular weight ranging from 300 to 5,000, and more preferably, from about 500-4,000.
According to a preferred aspect of the present invention, the thermosetting resin comprises a mixture of phthalate modified maleic-glycol polyester resins and maleic-glycol polyester resins. According to a more preferred aspect, the modifying acid is isophthalic acid.
The isophthalate modified maleic-glycol modified resins of the present invention are formed from isophthalic acid, maleic acid and low molecular weight glycol. According to an aspect, the glycol component may be chosen from, but is not limited to, ethylene glycol (EG), diethylene glycol (DEG), propylene glycol (PG), dipropylene glycol (DPG), neopentyl glycol (NPG), 1,3-propane glycol, and other similar low molecular weight glycol. According to a preferred aspect, the glycol is a mixture of the various glycols. According to a more preferred aspect the glycol comprises a roughly equimolar mixture of ethylene glycol (EG), diethylene glycol (DEG), and propylene glycol (PG). According to a further aspect, the total moles of the glycol mixture range from approximately equimolar to 10% greater than equimolar with respect to the isophthalic acid and maleic anhydride acid equivalent. In a preferred aspect, the total moles of the glycol mixture range from approximately equimolar to 5% greater than equimolar to the acid equivalent. In a more preferred aspect, the total of the glycol is in slight molar excess over the acid equivalent.
According to an aspect, the maleic resin is formed from maleic acid and low molecular weight glycol. In a preferred aspect, the total moles of glycol range from approximately equimolar to 10% greater than equimolar with respect to the maleic acid equivalent. The term “maleic acid” is understood to encompass maleic anhydride. According to a further aspect, the glycol component may be chosen from, but is not limited to, ethylene glycol (EG), diethylene glycol (DEG), propylene glycol (PG), dipropylene glycol (DPG), neopentyl glycol (NPG), 1,3-propane glycol, and other similar low molecular weight glycol. According to an aspect, the glycol may be a mixture of the various glycols. According to a preferred aspect the glycol is propylene glycol.
In an embodiment, the isophthalate modified, maleic-glycol resin and maleic-glycol resin are present in roughly equal mass ratios. In a preferred embodiment, the maleate-glycol resin is present at from about 60 mass percent to about 95 mass percent. In a more preferred embodiment, the maleate-glycol resin is present at from about 65 mass percent to about 85 mass percent. Correspondingly, the isophthalate modified maleic-glycol resin is present at from about 15 mass percent to about 35 mass percent.
A second component of the SMC formulation is an unsaturated monomer that copolymerizes with the unsaturated polyester. The SMC formulation preferably contains an ethylenically unsaturated (vinyl) monomer. Examples of such monomers include acrylates, methacrylates, styrene, divinyl benzene and substituted styrenes, multi-functional acrylates and methacrylates such as ethylene glycol dimethacrylate or trimethylol propanetriacrylate. The ethylenically unsaturated monomer is usually present in the range of about 20 to 50 parts per 100 parts by weight, based upon the total weight of unsaturated resin, low profile additive, rubber impact modifier and unsaturated monomer. The unsaturated monomer is present at preferably from about 30 to about 45 parts per 100 parts by weight, and more preferably from about 35 to about 45 parts per 100 parts by weight. The vinyl monomer is incorporated into the composition generally as a reactive diluent for the unsaturated polyester. Styrene is the preferred intercalation monomer for forming the nanoclay composite in situ, and is also the preferred ethylenically unsaturated monomer for reaction with the unsaturated polyester resin.
An optional component of the inventive SMC is second monomer, termed an alternative reactive monomer (ARM), which possesses the ability to aid in maintaining SQ as the density of the composite is reduced. Alternative reactive monomers are disclosed in co-pending application number (not yet assigned; Attorney Docket Number 20435-00168) and the more effective are ethylenically unsaturated aromatic compounds. The preferred alternative reactive monomer (ARM) of this invention is divinylbenzene.
A third component of the inventive SMC is a low profiling additive (LPA) used in the formulation as an aid to reduce the shrinkage of molded articles prepared with the SMC. The LPA's used in the SMC typically are thermoplastic resins. Examples of suitable LPA's include saturated polyesters, polystyrene, urethane linked saturated polyesters, polyvinyl acetate, polyvinyl acetate copolymers, acid functional polyvinyl acetate copolymers, acrylate and methacrylate polymers and copolymers, homopolymers and copolymers include block copolymers having styrene, butadiene and saturated butadienes e.g. polystyrene. U.S. Pat. Nos. 5,116,917 and 5,554,478 assigned to the assignee of the present invention disclose methodology for preparing and using typical saturated polyester thermoplastic low profile additive compositions used with thermosetting resins when preparing SMC.
A fourth component of the inventive SMC is a nanoclay composite filler composition comprising a nanoclay, kaolin clay, and diatomaceous earth. “Nanoclay” is defined as a treated inorganic clay. The term “treated inorganic clay” is meant to include any layered clay having inorganic cations replaced with organic molecules, such as quaternary ammonium salts. See U.S. Pat. No. 5,853,886 for a description of various methods of preparing treated clay. Any treated inorganic clay can be used to practice this invention. Nanoclay composite filler compositions suitable for the present invention are disclosed in co-pending applications number (not yet assigned; Attorney docket numbers 20435-00167 and 20435-00168).
The sheet molding compounds of the present invention may optionally contain a low profile additive enhancer. The LPA enhancing additive aids in maintaining SQ by improving the effectiveness, or “profiling efficiency” of the thermoplastic LPA. This is especially critical as the filler level of the composite is reduced to decrease its density. A methodology for preparing and using such LPA-enhancing additives in SMC is disclosed by Fisher (U.S. Pat. No. 5,504,151) and Smith (U.S. Pat. No. 6,617,394 B2), assigned to the assignee of the present invention, the entire contents of which is specifically incorporated by reference for all purposes. The more preferred methodology is that disclosed by U.S. Pat. No. 5,504,151.
The sheet molding compounds of the present invention may optionally comprise reinforcing mineral fillers such as, but not limited to mica and wollastonite. A suitable composition includes from about I to about 40 phr mineral filler, preferably, from about 5 to about 25 phr and more preferably about 10-15 phr, based on 100 parts of the ‘formulated resin’ as defined above. The SMC preferably contains a low-density filler having a density of 0.5 g/cm3 to 2.0 g/cm3 and preferably from 0.7 g/cm3 to 1.3 g/cm3. Examples of low-density fillers include diatomaceous earth, hollow microspheres, ceramic spheres, and expanded perlite and vermiculite.
The sheet molding compounds of the present invention may optionally comprise organic fillers such as, but not limited to graphite, ground carbon fiber, celluloses, and polymers. A suitable composition includes from about I to about 40 phr organic filler, preferably, from about 5 to about 30 phr and more preferably about 10-25 phr, based on 100 parts of the ‘formulated resin’ as defined above.
The sheet molding compounds of the present invention may optionally comprise rubber impact modifiers to help maintain toughness and mechanical properties, such as tensile and flexural strength and modulus in low density SMC. By “rubber impact modifiers”, impact modifiers that have rubbery physical properties are intended. These include, in particular, those capable of making the thermoset polymer matrix of the invention tougher. Such properties are met, for example, by EP or EPDM rubbers, which are grafted or copolymerized with suitable functional groups. Functional groups such as maleic anhydride, itaconic acid, acrylic acid, glycidyl acrylate and glycidyl methacrylate are suitable for this purpose. Rubber impact modifiers suitable for the present invention are disclosed in U.S. Pat. No. 6,277,905 and in co-pending application number (not yet assigned; Attorney docket number 20435-00168). A suitable composition includes from about I to 10 phr, and preferably, about 3 to 6 phr of rubber impact modifiers for each 100 parts of ‘formulated resin' in the SMC composition. ‘Formulated resin’ for these toughened systems is defined as the sum of the unsaturated polyester resin(s), reactive monomer(s), LPA(s), and rubber impact modifier(s). It is also important that the rubber impact modifiers used have a neutral or positive impact on the overall SQ of the molded SMC.
The sheet molding compounds of the present invention may optionally comprise organic initiators. The organic initiators are preferably selected from organic peroxides which are highly reactive and decomposable at the desired temperature and have the desired rate of curing. Preferably, the organic peroxide is selected from those, which are decomposable at temperatures from about 50° C. to about 120° C. The organic peroxides to be used in the practice of the invention are typically selected from tertiary butyl peroxy 2-ethylhexanoate; 2,5-dimethyl-2,5-di(-benzoylperoxy)cyclohexane; tertiary-amyl 2-ethylhexanoate and tertiary-butyl isopropyl carbonate; tertiary-hexylperoxy 2-ethylhexanoate; 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate; tertiary-hexylperoxypivalate; tertiarybutylperoxy pivalate; 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy) cyclohexane; dilauroyl peroxide; dibenzoyl peroxide; diisobutyryl peroxide; dialkyl peroxydicarbonates such as diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, dicyclohhexyl peroxydicarbonate; VAZO52, which is 2,2′-azobis(2,4-dimethyl-valeronitrile); di-4-tertiarybutylcyclohexyl peroxydicarbonate and di-2 ethylhexyl peroxydicarbonate and t-butylperoxy esters, such as t-butylperoxypivalate, t-butyl peroxybenzoate and t-butylperoxypemeodecanoate. More preferably, the initiator is a blend of t-butylperoxy-2-ethylhexanoate and t-butylperoxybenzoate. The initiators are used in a proportion that totals from about 0.1 parts to about 6 phr, preferably from about 0.1 to about 4, and more preferably from about 0.1 to about 2 phr, based on 100 parts of the ‘formulated resin’ as defined above.
The sheet molding compounds of the present invention may optionally comprise stabilizers and/or inhibitors. Stabilizers preferably are those having high polymerization inhibiting effect at or near room temperature. Examples of suitable stabilizers include hydroquinone; toluhydroquinone; di-tertiarybutylhydroxytoluene (BHT); para-tertiarybutylcatechol (TBC); mono-tertiarybutylhydroquinone (MTBHQ); hydroquinone monomethyl ether; butylated hydroxyanisole (BHA); hydroquinone; and parabenzoquinone (PBQ). Stabilizers are used in a total amount ranging from about 0.01 to about 0.4 parts per 100 parts, preferably from about 0.01 to about 0.3 phr and more preferably from about 0.01 to about 0.2 phr, based on 100 parts of the ‘formulated resin’ as defined above.
The sheet molding compounds of the present invention may optionally comprise thickening agent such as oxides, hydroxides, and alcoholates of magnesium, calcium, aluminum, and the like. The thickening agent can be incorporated in a proportion ranging from about 0.05 to about 5 phr, preferably from about 0.1 to about 4 phr and more preferably, from about 1 part to about 3 phr, based on 100 parts of the ‘formulated resin’ as defined above. Additionally or alternatively, the SMC may contain isocyanate compounds and polyols or other isocyanate reactive compounds, which may be used to thicken the SMC.
The sheet molding compounds of the present invention may optionally comprise other additives, e.g. cobalt promoters (Co), nucleating agents, lubricants, plasticizers, chain extenders, colorants, mold release agents, antistatic agents, pigments, fire retardants, and the like. The optional additives and the amounts used depend upon the application and the properties required.
The sheet molding compounds of the present invention further comprises a reinforcing agent, preferably a fibrous reinforcing agent. Fibrous reinforcing agents may be termed “roving”. Fibrous reinforcing agents are added to the SMC to impart strength and other desirable physical properties to the molded articles formed from the SMC. Examples of fibrous reinforcements that can be used in the SMC include glass fibers, carbon fibers, polyester fibers, and natural organic fibers such as cotton and sisal. Particularly useful fibrous reinforcements include glass fibers which are available in a variety of forms including, for example, mats of chopped or continuous strands of glass, glass fabrics, chopped glass and chopped glass strands and blends thereof. Preferred fibrous reinforcing materials include 0.5, 1, and 2-inch fiberglass fibers. The SMC-paste, prior to the addition of roving and prior too cure under pressure has a density of about 1.25 g/cm3.
The SMC is useful for preparing molded articles, particularly sheets and panels. The sheets and panels can be used to cover other materials, for example, wood, glass, ceramic, metal, or plastics. They can also be laminated with other plastic films or other protective films. They are particularly useful for preparing parts for recreational vehicles, automobiles, trucks, boats, and construction panels. SMC sheet may be shaped by conventional processes such as vacuum or compression (pressure) and is cured by heating, contact with ultraviolet radiation, and/or catalyst, or other appropriate means. Using the preferred industry-standard conditions of heat and pressure, the inventive SMC yields a Class A surface.
The invention also has inherent advantages over standard density SMC during the typical industrial molding process. The increase in resin content and reduced filler level allows the sheet to flow smoothly and fill the mold at conditions of heat and pressure significantly lower than industry-standard. In addition to reducing the cost of molding parts, the reduction of mold pressure and temperature yields substantial improvement in the SQ of the part, especially the short-term DOI and OP values as shown by the data in TABLES 3 and 4.
Surface quality (SQ), as measured by the Laser Optical Reflected Image Analyzer, or LORIA, is determined by three measurements—Ashland Index (Al), Distinctness of Image (DOI), and Orange Peel (OP). SMC with Class A SQ is typically defined as having an AI<80, a DOI≧70 (scale 0-100), and an OP≧7.0 (scale 0-10). A preferred methodology for the determination of surface quality is disclosed by Hupp (U.S. Pat. No. 4,853,777), the entire contents of which is specifically incorporated by reference for all purposes.
In addition to Surface Quality, the mechanical properties of the inventive SMC were determined. The tensile strength is measured by pulling a sample in an Instron instrument as is conventional in the art. The tensile modulus is determined as the slope of the stress-strain curve generated by measurement of the tensile strength. Flexural strength is determined conventionally using an Instron instrument. The flexural modulus is the slope of the stress-strain curve. Toughness is conventionally the area under the stress-strain curve.
A conventional SMC formulation has the following approximate composition (based on 100 g of formulated resin, which in our formulations would include the UPE resin(s), LPA(s), reactive momoner(s), and rubber modifier(s). The remaining additives, fillers, etc. are charged on a phr, or ‘parts per hundred resin’ basis): 65.0 g of a high reactivity unsaturated polyester (UPE); 7 g of a styrene monomer; and 28 g of low profile additives (LPA) as a 50% solution in styrene. For each ‘100 g of resin”190 g of calcium carbonate filler; 9 g of magnesium oxide containing thickener; 4.5 g mold release; 1.5 g tertiary butyl perbenzoate catalyst; and 0.05 g of a co-activator (cobalt, 12% in solution ) are charged to generate the ‘SMC paste.’ Conventional SMC formulations typically have densities of>1.9 g/cc for molded parts. The present invention provides molded parts having a density of from 1.45 to 1.6 g/cc while maintaining the mechanicals, Class A SQ, and toughness. As the density is reduced, however, maintaining these properties becomes increasingly difficult. The present invention provides a tough, low-density SMC having industry-required mechanicals and Class A SQ modifying the ‘formulated resin’ with a ‘toughened UPE resin’ and a ‘rubber impact modifier’ and by replacing high density calcium carbonate with an inventive (low-density, low profiling) filler additive composition.
The invention is illustrated with one example. SMC paste formulations were evaluated for shrinkage and molded into cured reinforced panels. To evaluate shrinkage, SMC paste without fiber glass was molded and cured in a Carver Laboratory Press at 300° F. and evaluated for shrinkage. For further testing, SMC paste was combined, on a SMC machine, with fiber glass roving, chopped to 1-inch lengths, allowed to thicken for 2 to 3 days, and then molded at 300° F. to form 0.1 inch thick plates. The plates were tested for density, surface appearance, and mechanical strength. The surface appearance was analyzed using a LORIA surface analyzer to measure the Ashland Index for ‘long term waviness’ and the Distinctness of Image(DOI) and Orange Peel(OP) for ‘short term’ surface distortion.
The present invention reduces the SMC density to 1.45 to 1.6 g/cm3 while maintaining the mechanicals, SQ and toughness. Our strategy has been to strengthen the UPE and to replace the 190g of high density calcium carbonate with a package of additives. Nanoclays, exfoliated in unsaturated polyester, act as very efficient fillers and aid efficient profiling by the LPA. Strengthening the UPE thermoset resin matrix by addition of a ‘toughened’ UPE resin and replacing CaCO3 with fillers such as diatomaceous earth, mica, wollastonite, kaolin clays, carbon, or cellulose-based materials enable one to maintain mechanical strength as the density is reduced. It is critical that the addition of the ‘toughened’ UPE resin does not reduce the effectiveness of the formulation's low profile additive package, and thus reduce SQ.
Table 1 sets forth the compositions of resins which compare a formulation with no toughened UPE (TLM-1), two with ‘toughened’ UPE's that significantly reduce SQ (TLM-3 and TLM-4), and a UPE wherein the various molecular components of the toughened and ‘high-reactivity’ UPE's are present as a single ‘toughened unit-cook’ UPE (TLM-5), against an embodiment of the present invention consisting of a blend of a ‘toughened’ UPE and ‘high-reactivity’ UPE (TLM-2). Additionally, the formulations in Table 1 contain nanoclay and the lowered filler levels, required to yield a low density SMC (about 1.5-1.6 g/cc).
Table 2 compares SQ and mechanical properties for the various formulations. It shows that Formulation TLM-2, in which 25 weight % of AropolTM Q6585 was substituted with the inventive toughened UPE results in the maintenance of the mechanical properties and class A surface quality seen for the TLM-1 formulation. TLM-2 also shows its ‘toughness’ in the dramatic decrease in the number of ‘paint pops’. Formulations for TLM-3, TLM-4 and TLM-5, however, show an unacceptable drop in SQ to well below class A standards. This performance drop further demonstrates the uniqueness of the Q6585/Toughened UPE blend in terms of maintaining mechanical properties, surface quality, and improving ‘paint-pop’ resistance. (Aropol™ Q6585, Aropol™ A7324, Aropol™ A7221H, and Aropol™ M Q8000 are trade names for Ashland's polyester resins).
Further aspects of the present invention relate to methods and processes for fabricating molded composite vehicle and construction parts having a density less than 1.6 grams per cm3. In an aspect the methods comprises admixing unsaturated polyester thermosetting resin, an olefinically unsaturated monomer capable of copolymerizing with the unsaturated polyester resin, a thermoplastic low profile additive, free radical initiator, alkaline earth oxide or hydroxide thickening agent, and a nanoclay composite filler composition. According to an aspect, the nanoclay composite is provided as a pre-formed composition. According to another aspect, the nanoclay composite is formed in situ from precursor materials.
According to an aspect of the method, the various starting materials are mixed to form a paste which is dispensed on a carrier film above and below a bed of chopped roving, forming a molding sheet. According to an aspect, the molding sheet is enveloped in a carrier film and consolidated. According to further aspects of the method, the sheet is matured until a molding viscosity of 3 million to 70 million centipoise is attained and the sheet is non-tacky. Following consolidation, the sheet is released from the carrier film.
According to various aspects of the inventive method, the consolidated sheet is molded into composite parts to be assembled into vehicles. The sheets may be molded into composite construction materials. According to an aspect of the method, the sheets are placed in a heated mold and compressed under pressure whereby a uniform flow of resin, filler and glass occurs outward to the edges of said part. Table 3 demonstrates the performance of the inventive SMC at various molding temperatures. According to an aspect, the sheet is heated in the mold to a temperature from 250° F. to 305° F. In a preferred aspect the sheet is heated to a temperature of from 270° F. to 290° F. In a most preferred aspect the sheet is heated to a temperature of from 275° F. to 285° F. Table 4 demonstrates the performance of the inventive SMC at various molding pressures. In an aspect, the sheets are molded at a pressure of from 200 psi to 1400 psi; preferably from 400 psi to 800 psi.
According to preferred aspects, the paste is composed of auxiliary components that may include mineral fillers, organic fillers, auxiliary monomers, rubber impact modifiers, resin tougheners, organic initiators, stabilizers, inhibitor, thickeners, cobalt promoters, nucleating agents, lubricants, plasticizers, chain extenders, colorants, mold release agents, antistatic agents, pigments, fire retardants, and mixtures thereof.
The foregoing description of the invention illustrates and describes the present invention. Additionally, the disclosure shows and describes only the preferred embodiments of the invention but, as mentioned above, it is to be understood that the invention is capable of use in various other combinations, modifications, and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein, commensurate with the above teachings and/or the skill or knowledge of the relevant art. The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with the various modifications required by the particular applications or uses of the invention. Accordingly, the description is not intended to limit the invention to the form disclosed herein. Also, it is intended that the appended claims be construed to include alternative embodiments.
All publications, patents, and pre-grant patent application publications cited in this specification are herein incorporated by reference, and for any and all purposes, as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. In particular co-pending applications (Serial Numbers not yet assigned, Attorney Docket Numbers 20435-00167 and 20435-00168) are specifically incorporated by reference. In the case of inconsistencies the present disclosure will prevail.
