Sheet molding composition with limited outgassing

Abstract

A low profile additive composition is provided that includes thermoplastic particles and a hydrogen bonding monomer in which the thermoplastic particles are dispersed and which forms hydrogen bonds with the thermoplastic particles. The hydrogen bonding monomer satisfies at least two of the following: a boiling point greater than 210° C., a viscosity less than 140 cps at 25° C., or a vapor pressure less than 5 mm Hg at 20° C. Products made therefrom are also provided. A method of forming the low VOC low profile additive composition is also provided.

Description

[Technical field]

[0001] The present invention relates generally to thermosetting molding compounds and methods of forming same, and more particularly to the partial replacement of curable monomers resulting in reduced outgassing, as manifested by reduced product blistering and reduced volatile organic compound (VOC) emissions.

[0002] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims priority to U.S. Provisional Patent Application No. 63 / 307,650, filed February 8, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0003] Thermosetting molding compositions are generally thermosetting resins that contain inorganic fillers and / or fibers. When heated, the thermosetting monomers initially exhibit a viscosity low enough to allow melt processing and molding of products from the filled monomer composition. Upon further heating, the thermosetting monomers react and cure to form a hard resin. At molding temperatures, the decrease in viscosity often leads to VOC outgassing of the monomers, which can lead to handling complications and product blistering.

[0004] A common industrial application of thermosetting compositions is the molding of automotive parts. These panels have the high dimensional stability and high gloss molded surface finish required for exposed surfaces on a vehicle. Automotive parts must also have high dimensional uniformity and stability to pre-molds to maintain the high degree of fit and finish required in modern automotive manufacturing.

[0005] It is known that thermosetting compositions based on unsaturated polyester or polyurethane resins and styrene can be reduced in shrinkage and have improved surface properties by adding low profile additives (LPAs), which are thermoplastic particles contained in the uncured resin that compensate for shrinkage and improve the surface finish (Non-Patent Documents 1-3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 4,260,538 [Patent Document 2] U.S. Patent No. 4,643,126 [Patent Document 3] U.S. Patent No. 5,100,935 [Patent Document 4] U.S. Patent No. 5,268,400 [Patent Document 5] U.S. Patent No. 5,854,317 [Patent Document 6] U.S. Patent No. 6,001,919 [Patent Document 7] U.S. Patent No. 6,780,923 [Patent Document 8] U.S. Patent No. 7,700,670 [Patent Document 9] U.S. Patent No. 9,868,829 [Non-Patent Document]

[0007] [Non-Patent Document 1] Beheshty, MH et al., Iranian Polymer Journal, 15(2) (2006): 143-153 [Non-Patent Document 2] Dong, J‐P, et al. Journal of Applied Polymer Science, 98(1) (2005): 264-275 [Non-Patent Document 3] Chan-Park M.B. et al. Polymer Composites, 17(4) (1986),537-547 [Non-Patent Document 4] DH Richards, DM Service, and MJ Stewart, Br. Polym.J.16, 117(1984) [Non-Patent Document 5] Shiao-Wei Kuo, J.Polym.Res.15(2008):459-486

[0008] Conventional LPA's include, for example, polyvinyl acetate, polystyrene, polyethylene, polypropylene, polymethacrylate, and copolymers in which any of the foregoing constitutes at least 40 percent of the monomer subunits of the copolymer. Although known low profile additives improve the performance of polyester and polyurethane thermosets, there is a need for compositions that exhibit further improvements, especially in surface properties. A common cause of scrap in molded parts is surface blistering associated with the outgassing of unreacted styrene.

[0009] Styrene is the most common monomer used in SMC formulations and is regulated by the OHSA with short-term exposure limits of approximately 600 ppm and 100 ppm for 8 hours. Other countries have similar regulations. As a result, styrene outgassing affects production costs not only through disposal due to blistering, but also through the need for ventilation associated with the outgassing. Styrene has also been implicated as a component of photochemical smog.

[0010] Thus, there is a need for molding compound compositions that provide reduced VOCs, no blistering, and a high quality paint finish while maintaining dimensional uniformity and stability of the product relative to the preform mold, as well as methods of forming such compositions. Summary of the Invention

[0011] A low profile additive composition is provided that includes thermoplastic particles and a hydrogen bonding monomer in which the thermoplastic particles are dispersed and which forms hydrogen bonds with the thermoplastic particles. The hydrogen bonding monomer satisfies at least two of the following: a boiling point greater than 210° C., a viscosity less than 140 cps at 25° C., or a vapor pressure less than 5 mm Hg at 20° C. Articles made therefrom are also provided. A method of forming the low VOC low shrinkage additive composition is also provided.

[0012] The present invention will now be described in more detail with reference to the following drawings, which are intended to illustrate certain aspects of the invention, but should not be construed as limiting the practice of the invention. [Brief description of the drawings]

[0013] [Figure 1] 1 is a bar graph of total VOC and styrene vapor in ppm for SMC cured with a conventional composition and SMC cured with a composition of the present invention, showing a more than 4-fold reduction in total VOC and a more than 35-fold reduction in styrene vapor for SMC cured with a composition of the present invention. [Diagram 2] 1 is a table showing rate constants for radical monomer reactions. [Diagram 3] The relationship between the reactivity of various monomers and the crosslink density is shown. [Figure 4] 1 is a bar graph showing that approximately 40% substitution of divinylbenzene (DVB) in LPA results in a non-linear reduction of styrene VOCs by 93%, in accordance with an embodiment of the present invention. [Figure 5A] A comparison of the alternative monomers shown in Figures 5B-5E with styrene in Figure 5A is shown. [Figure 5B] A comparison of the alternative monomers shown in Figures 5B-5E with styrene in Figure 5A is shown. [Figure 5C] A comparison of the alternative monomers shown in Figures 5B-5E with styrene in Figure 5A is shown. [Figure 5D] A comparison of the alternative monomers shown in Figures 5B-5E with styrene in Figure 5A is shown. [Figure 5E] A comparison of the alternative monomers shown in Figures 5B-5E with styrene in Figure 5A is shown. [Figure 6] 1 is a bar graph showing the reduction of VOCs in SMC formulations according to an embodiment of the present invention. [Figure 7] 1 shows a free radical reaction in a UPE-styrene SMC. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention is useful as a low profile additive (LPA) that reduces outgassing compared to conventional low profile additives. When the low profile additive of the present invention is included in a molding composition, such as a styrene monomer-based sheet molding composition (SMC), it surprisingly reduces VOC outgassing from cured articles made therefrom while maintaining dimensional control requirements. Reduced scrap and ease of manufacture are obvious improvements of the present invention. Furthermore, the reduced outgassing associated with the present invention allows for increased cure temperatures, thereby enabling shorter molding cycle times and subsequent processes such as E-coating.

[0015] Blistering is essentially the delamination of the cured composite due to outgassing of compounds that volatilize under heating conditions above about 200°C. The viscosity of the molding composition is often reduced by the addition of reactive diluents. Styrene has a boiling point of 145°C, and the related aromatic free radical cured C 8-12 Monomers are lower and also a source of VOC outgassing during molding composition processing.

[0016] Styrene monomer is a typical reactive diluent used to dissolve unsaturated polyesters, vinyl esters, thermoplastic low profile additives, and many other processing aid additives. In some SMC formulations, styrene constitutes a large proportion of the organic portion of the matrix. Unreacted styrene in molded parts can be a significant source of potential volatiles. Typically, gas chromatograph and mass spectrometer (GC-MS) measurements of conventional SMC samples cured at 90°C for 30 minutes, according to the VDA278 standard, indicate that a higher percentage of styrene leads to a higher incidence of blistering when the total VOC concentration in the thermal desorption chamber exceeds 300 parts per million (ppm). This is shown on the left side of Figure 1. As shown in Figure 1, the conventional SMC material (855TCA UltraLite™) has a much higher total VOC (TVOC) compared to the inventive SMC material described here.

[0017] As used herein, a styrenic monomer is one or more of butylstyrene, chlorostyrene, methylstyrene, n-butylstyrene, styrene, or vinylstyrene.

[0018] One way to minimize styrenic monomers in particular is to extend the residence time in the mold or perform a post-cure bake, but these are industrially impractical. These solutions are not viable due to increased energy consumption, reduced throughput, increased costs, and the need for additional capital equipment. Increasing the molding temperature can be counterproductive, as it can cause the styrenic monomers to volatilize faster rather than polymerize, which can lead to blistering during molding.

[0019] Additionally, minimization of VOCs is an important factor in preventing blistering. In some embodiments of the present invention, based on a standard calibration curve (toluene equivalent), the total VOC content in the cured articles of the present invention is less than 250 ppm (μg / g), while still retaining the molded article properties and molding resin handling properties of conventional thermosetting SMC resins. The typical thickness of molded articles according to the present invention is 0.8-10 mm. In some embodiments of the present invention, the fiber reinforced thermosetting SMC formulations of the present invention cure at temperatures of 140-160°C and can be compression molded with short cycle times using SMC resins that have the ability to flow and mold complex shapes.

[0020] Where a range of values ​​is provided, it is to be understood that the range is intended to include not only the endpoints of the range, but also any intermediate values ​​expressly included within the range and varied by the last significant digit of the range. By way of example, the range from 1 to 4 is intended to include 1-2, 1-3, 2-4, 3-4, and 1-4.

[0021] A typical length of the chopped fibers according to the present invention is between 10 and 50 mm.

[0022] Some inventive embodiments of the carbon fiber based molding formulations are also amenable to very uniform paint or coating. Low density molding compound formulations are provided having specific gravities of less than 1.65, and in some inventive embodiments as low as 0.89. The formulations include a thermosetting crosslinkable unsaturated polyester, a low profile additive package including a maleic anhydride copolymer, hollow microspheres, and reinforcing fibers in an amount of 0.1 to 55 weight percent. Reinforcing fibers operative herein include glass, carbon, polyaramid, natural fibers, and combinations thereof. The reinforcing fibers are dispersed in at least one of the unsaturated polyester and the low profile additive to produce a cured article.

[0023] The process for producing such molding compound panels includes dispersing a low profile additive (LPA) package in an acrylate solvent to replace styrene and hydrogen bond with the thermoplastic component of the LPA to produce an acrylate modified LPA. The acrylate modified LPA is then dispersed in a molding compound along with reinforcing fibers, and the thermosetting component is cured by contact with mold platens into the shape of the desired product. The volatile styrene content of the cured product has been observed to be reduced by at least an order of magnitude compared to similar products formed with conventional LPAs. In some embodiments of the invention, the complete uncured compound flows with a molding viscosity. A viscosity of 10 to 50 million centipoise is particularly desirable for ease of handling at the manufacturing site.

[0024] Table 1 shows a formulation of the present invention for producing an article of the present invention that can be electronically coated without causing surface blistering.

[0025] Table 1. Typical and preferred ranges of components in the formulations of the present invention. Values ​​are given as total weight percentages including carbon fiber. [Table 1]

[0026] Various base SMC formulations are known, such as those described in U.S. Patents 4,260,538, 4,643,126, 5,100,935, 5,268,400, 5,854,317, 6,001,919, and 6,780,923, and all of these formulations benefit from the inventive process of acrylate modified LPA dispersions, which reduces the VOC content, especially styrene volatility in the cured product. The resulting product is less prone to blistering. Typical amounts of the components of the inventive composition are shown in Table 1.

[0027] The primary component of the mold compound formulation is an unsaturated polyester resin crosslinkable polymer resin. The average molecular weight of the prepolymer polymer resin is typically between 400 and 100,000 Daltons. The polyester prepolymer resin is typically a condensation product resulting from the condensation of an unsaturated diacid and / or anhydride with a polyol. It is understood that saturated diacids or polyacids are also part of the condensation process to form polyester prepolymers with fewer equivalents of reactive ethylenic unsaturation sites. The unsaturated polyester resins disclosed in U.S. Pat. No. 6,780,923 are preferred for use in the present invention.

[0028] As used herein, "unsaturated" refers to the attachment of covalent bonds to the carbon atoms of a carbon-carbon bond being less than the maximum complement of the number of carbon or hydrogen atoms attached, i.e., the carbon-carbon bond is a double bond or a triple bond.

[0029] The polymeric resin prepolymer is suspended, and preferably dissolved, in an ethylenically unsaturated monomer that will copolymerize with the resin during the heat curing process. It is understood that multiple types of monomers can be used in the molding compound. The monomers provide benefits such as reduced prepolymer viscosity, heat curing without producing volatile by-products, etc. Ethylenically unsaturated monomers useful herein include, for example, styrene, alpha-methylstyrene, vinyltoluene, and chlorostyrene. Styrene is the most commonly used monomer in the formation of SMC.

[0030] A typical molding compound includes a free radical initiator to initiate crosslinking between the polymeric prepolymer resin and itself or the ethylenically unsaturated monomer, if present. The free radical initiator is usually selected to prevent significant crosslinking at low temperatures. To control heat cure conditions, conventional radical polymerization initiators contain either a peroxide or an azo group. Peroxides useful herein include, for example, benzoyl peroxide, cyclohexanone peroxide, ditertiary butyl peroxide, dicumyl peroxide, tertiary butyl perbenzoate, and 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane. Azo species useful herein include, for example, azobisisobutyronitrile and t-butylazoisobutyronitrile. The amount of radical polymerization initiator present varies depending on factors such as the desired heat cure temperature and decomposition thermodynamics, but the initiator is usually present at 0.1 to 3 percent by total weight. Polymerization inhibitors are often included in the base molding formulation to reduce crosslinking at temperatures below the desired heat cure temperature. Hydroquinone and t-butylcatechol are traditional inhibitors. Inhibitors are typically present at 0-1 percent by weight total. Overall, polymerization initiators and inhibitors are selected to provide less than 100 ppm of decomposition products boiling between 50 and 250°C, in the ranges present.

[0031] The molding compounds of the present invention, in some embodiments of the present invention, include non-conductive particulate fillers. Non-conductive particulate fillers that work in such molding compounds include, for example, hollow glass microspheres, calcium carbonate, calcium silicate, alumina, alumina trihydrate (ATH), silica, talc, dolomite, vermiculite, diatomaceous earth, kaolin clay, and combinations thereof. Factors related to the selection of particulate fillers include, for example, cost of the filler, viscosity of the resulting flow characteristics, resulting shrinkage, surface finish weight, flammability, and chemical resistance of the thermosetting formulation. Typical filler sizes are 0.1 to 50 microns. It is understood that surface derivatization of glass microspheres is preferred for applications requiring high performance. Surface derivatized microspheres are described in detail in U.S. Pat. No. 7,700,670 and U.S. Pat. No. 9,868,829.

[0032] In some invention embodiments, the surface-activating agent molecules covalently bonded to the microspheroid surface have terminal reactive moieties adapted to bond to the surrounding resin matrix during curing. Without wishing to be bound by a particular theory, the covalent bond between the cured resin matrix and the microspheroid enhances the peel strength of the resulting SMC in tests such as ASTM D3359. As used herein, the weight percent of the microspheroids covalently bonded to the surface-activating agent is intended to include the weight of the surface-activating agent.

[0033] Terminal reactive moieties that react with the SMC resin during cure include, for example, tertiary amine moieties, hydroxyl moieties, imine moieties, ethylenically unsaturated moieties such as allyl or acrylic, or cyano moieties, etc. It is understood that matrix curing can occur by mechanisms such as free radical curing, moisture curing, and combinations thereof.

[0034] Tertiary amine-terminated thermoplastics are readily prepared. DH Richards, DM Service, and MJ Stewart, Br. Polym. J. 16, 117 (1984). A representative tertiary amine-terminated thermoplastic is commercially available from Noveon Corporation under the trade designation ATBN1300X21.

[0035] The surface-activating agent molecules that are attached to the microspheres are alkoxysilanes that react with the silica surface of the microspheres. Representative alkoxysilane surface-activating agents for microspheres include, for example: 3-Aminopropyltrimethoxysilane, 3-Aminopropyltriethoxysilane, 3-Glycidoxypropyltrimethoxysilane, 3-Glycidoxypropyltriethoxysilane, (3-Glycidoxypropyl)bis(trimethylsiloxy)methylsilane, (3-Glycidoxypropyl)methyldiethoxysilane, (3-Glycidoxypropyl)dimethylethoxysilane, (3-Glycidoxypropyl)methyldimethoxysilane, Methacryloxymethyltriethoxysilane, Methacryloxymethyltrimethoxysilane, Methacryloxypropyldimethylethoxysilane, Methacryloxypropyl pyrdimethylmethoxysilane, methacryloxypropyltrimethoxysilane, ethacryloxypropylmethyldimethoxysilane, methacryloxypropyltriethoxysilane, methoxymethyltrimethylsilane, 3-methoxypropyltrimethoxysilane, 3-methacryloxypropyldimethylchlorosilane, methacryloxypropylmethyldichlorosilane, methacryloxypropyltrichlorosilane, 3-isocyanatopropyldimethylchlorosilane, 3-isocyanatopropyltriethoxysilane, bis(3-triethoxysilylpropyl)tetrasulfide, and combinations thereof.

[0036] In certain embodiments of the present invention, the alkoxysilane surface-activating agent contains ethylenically unsaturated moieties that are reactive under free radical crosslinking conditions to covalently bond the microspheroid surface to the surrounding resin matrix.

[0037] It is understood that the microspheroid surface activator is easily mixed into the pre-cured SMC formulation and the hollow glass microspheroids are added to it to induce activation of the microspheroids before the onset of matrix hardening. Typically, the surface activator is present at a concentration of approximately 0.05-0.5 grams of surface activator per gram of microspheroids.

[0038] Mold release agents are typically provided to facilitate mold release. Mold release agents include fatty acid salts such as oleate, palmitate, and stearate of metal ions such as sodium, zinc, calcium, magnesium, and lithium. Mold release agents are typically present at 0-5 percent by total weight.

[0039] The low-profile additives are provided to improve the surface properties and dimensional stability of the resulting molded article. In particular to reduce the overall VOC and styrene volatiles in the cured article, the low-profile additive package includes a thermoplastic that can hydrogen bond with the acrylate monomer. While it is understood that most conventional low-profile additives are blends or mixtures of multiple thermoplastic polymers dissolved or dispersed in a monomer such as styrene, the low-profile additives that function in the present invention include at least 10 weight percent of the total thermoplastic in the low-profile additive package, including at least one of polyacrylates, phenolic resins, phenoxy resins, poly(vinylphenols), polyamides, polyethylene glycols, polymethyl methacrylates, polyvinyl acetates, polycarbonates, polystyrenes, polyethylene terephthalates, polybutylene terephthalates, saturated polyesters, polyols, or combinations thereof; and copolymers including butadiene, acrylonitrile, and vinyl chloride, specifically styrene butadiene rubber, or combinations thereof. In yet other embodiments, the hydrogen-bonding thermoplastic is present at 5 to 100 weight percent of the total thermoplastic in the low-profile additive package.

[0040] Hydrogen-bonding monomers that work with the present invention have the property of hydrogen-bonding with the thermoplastic component of the low-profile additive. Hydrogen-bonding monomers are selected to meet at least two of the following criteria: boiling point greater than 210° C.; viscosity less than 140 cps at 25° C., ideally less than 10 cps at 25° C.; and vapor pressure less than 5 mmHg at 20° C. Hydrogen-bonding monomers that work with the present invention include, for example: Benzyl acrylate, isobornyl acrylate, 4-tert-butylcyclohexyl acrylate, lauryl acrylate, tridecyl acrylate, tetradecyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate, butyl acrylate, C1-C 16 Alkyl acrylates, C1-C 16 Hydroxyl alkyl acrylates, C1-C 16 Primary Amine Acrylates, C1-C 16 Monoacrylates such as secondary amine acrylates, cyclohexyl acrylate, ethyl acrylate, ethylhexyl acrylate, hexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 3-hydroxypentyl acrylate, 6-hydroxynonyl acrylate, or combinations thereof; diacrylates such as 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate (PEG repeating units 120 to 900), or combinations thereof; Triacrylates such as trimethylolpropane triacrylate; polypropylene glycol monomethacrylate, benzyl methacrylate, phenoxyethyl methacrylate, tetrahydrofurfuryl methacrylate, lauryl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, monomethyl acrylate such as methyl methacrylate or combinations thereof; dimethyl acrylates such as 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, polyethylene glycol dimethacrylate (PEG repeat units 120-900) or combinations thereof; trimethyl acrylates, such as trimethylolpropane trimethacrylate; N-vinyl-2-pyrrolidone, 1-vinyl-2-pyrrolidone, N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, acrylonitrile, fumaric acid esters, maleic acid esters, methacrylonitrile, monomethacryloyloxyethyl phthalate, vinyl acetate, vinylidene chloride, N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, acrylamide, methacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, methacrylic acid, C 1- C 16 Other suitable monomers, including acrylosulfonic acid, itaconic acid; and Any combination of the above.

[0041] Without wishing to be limited to a particular theory, it has been observed that as an alternative to methacrylate / acrylate monomers, methacrylates and acrylates are more reactive than vinyls and act as scavengers for styrene to reduce VOCs. Figure 2 shows a table of rate constants for radical monomer reactions. The rate constants are given by Equation 1: Rp=k[M⋅][M] (Eq. 1) where k is the propagation velocity, M is the monomer, and M is the monomer radical.

[0042] As you can see, methacrylates are more reactive monomers / monomer radicals than styrene. The HDDMA radical reacts very quickly with styrene monomer (styrene scavenger).

[0043] Additionally, it has been observed that the reduction in VOC levels in embodiments of the present invention may be due to increased crosslink density. Increasing crosslink density is because divinylbenzene has essentially the same polarity (and hydrogen bonding) as styrene, leading to a significant reduction in styrene levels, as shown in Figure 3. Increasing crosslink density may create a more tortuous path for eluting small molecules. As shown in the bar graph in Figure 4, approximately 40% substitution of divinylbenzene (DVB) in LPA resulted in a nonlinear reduction in styrene VOCs by 93%.

[0044] Without wishing to be limited to a particular theory, it is believed that the hydrogen bonding monomer displaces styrene within the voids of the thermoplastic polymer particles in the low profile additive package. Based on hydrogen bonding, styrene is displaced from intimate contact with the particular hydrogen bonding thermoplastic by the hydrogen bonding monomer, thereby reducing the amount of styrene monomer that is unreacted during cure and therefore available for volatilization after cure. Due to the factors used in the selection of the hydrogen bonding monomer, even though the same amount of hydrogen bonding monomer remains uncured compared to styrene in a conventional low profile additive package, the hydrogen bonding monomer does not contribute to the styrene VOC content of the resulting cured product and is less likely to volatilize.

[0045] To make an article according to the present invention, a low profile additive package is created by replacing at least a portion of the styrenic monomer in a conventional low profile additive containing a hydrogen bonding thermoplastic component with a hydrogen bonding monomer, which is accomplished by simply adding the hydrogen bonding monomer to a conventional low profile additive package based on a styrenic monomer and allowing sufficient time for the hydrogen bonding monomer to replace the styrenic monomer.

[0046] In certain invention embodiments, instead of dissolving the thermoplastic beads in styrene, the thermoplastic beads were dissolved in an alternative monomer. Also, styrene and the alternative monomer can be mixed to facilitate dissolution. In some cases, higher heat needs to be applied to dissolve the thermoplastic beads in the alternative monomer. For example, the maximum temperature currently used to dissolve styrene beads is about 45-50°C, and some of the alternative monomers that have been tried required 90-100°C. In some invention embodiments, a conventional low profile additive package is dialyzed against a bath of hydrogen bonding monomer to achieve the monomer exchange.

[0047] An ideal surrogate monomer would have a high boiling point, low vapor pressure, viscosity close to styrene, and high reactivity. Figures 5A-5E show a comparison of styrene in Figure 5A with the surrogate monomers shown in Figures 5B-5E. A selection of unreacted surrogate monomers cannot be detected by GC-MS according to the VDA278 test conditions (VOC 90°C / 30 min, FOG (SVOC) 120°C / 60 min).

[0048] Traditional SMC formulated with styrene as a reactive diluent has a noticeable and unpleasant odor. This is primarily due to the amount, volatility, and odor of styrene. This is well known to anyone who compounds or molds SMC in manufacturing plants. SMC formulated with alternative monomers has been observed to have a much less noticeable odor, and in some cases, no detectable odor at all. This is achieved by reducing styrene and replacing it with a less volatile and lower odor threshold monomer, and by more complete conversion of styrene as previously mentioned.

[0049] In manufacturing, thermoplastic resins are received as raw material beads from a supplier and then dissolved in styrene. Alternatively, the beads are already dissolved in styrene from a resin supplier. In one particular case, saturated polyester LPAs are already dissolved in styrene because saturated polyesters are very viscous liquids and not solids. Therefore, for the LPA work related to this patent, the beads were dissolved directly in the alternative monomer without styrene (blends are also possible) and saturated polyester LPAs were not tried. However, a solvent exchange was performed to see if an alternative monomer should enter the "system" with the LPA. A solvent exchange was simulated with a UPE thermoset (purchased a very viscous liquid already dissolved in styrene from a resin supplier) using a rotary evaporator (and replacing 40wt% of the styrene with the alternative monomer) and the end result was similar to that of the received raw material beads that were then dissolved in styrene, as shown in Figure 6, which seems to indicate that everything is thoroughly mixed by the paste mixer and that the alternative monomer may be introduced into the paste by multiple routes. As mentioned above, replacing styrene by approximately 40% with HDDMA resulted in a nonlinear reduction in styrene and VOCs by over 95%.

[0050] Figure 7 shows the free radical reactions in a UPE-styrene SMC. As shown in Figure 7, the possible reactions that can occur during the cure of UPE resin are as follows: (a) Intermolecular reaction with styrene bonds and (b) Intermolecular reaction without styrene bonds (c) Intramolecular reaction with styrene bonds and (d) Intramolecular reaction without styrene bonds (e) Styrene branch (f) Styrene-styrene homopolymerization (g) Unreacted free styrene detected as a VOC

[0051] To minimize the VOCs due to unreacted free styrene (g), the other reactions (a)-(f) must be maximized.

[0052] In some embodiments of the invention, a thixotrope, or thickener, is added to adjust the change in viscosity associated with the inclusion of hydrogen-bonding monomer. It is understood that novel low-profile additives are also readily formed that include a hydrogen-bonding thermoplastic component that is first dissolved or dispersed in the hydrogen-bonding monomer. Regardless of preparation technique, once the low-profile additive package of the present invention is formed, it is used in SMC formulations in a manner similar to conventional low-profile additive packages.

[0053] Hydrogen bonding between the hydrogen bonding monomers and the thermoplastic polymer components of the low profile additive package is readily detected by IR spectroscopy based on techniques detailed in Shiao-Wei Kuo, J. Polym. Res. 15 (2008): 459-486.

[0054] It is understood that the present invention also incorporates additional additives, if desired, including flame retardants, plasticizers, colorants, and other processing additives conventionally used in the art.

[0055] The molding compounds of the present invention are suitable for the rapid production of molded composite articles having a high gloss finish as measured by ASTM D523 and low potential for surface blistering.

[0056] The present invention is particularly suited for the manufacture of a variety of vehicle panel products including bumper beams, fenders, vehicle door panel components, automotive floor components, spoilers, hoods, engine cradles; and housings for a variety of industrial and consumer products.

[0057] The present invention will be described in further detail with reference to the following non-limiting examples, which are not intended to limit the scope of the appended claims. EXAMPLES

[0058] Comparative Example A Formulations containing a low profile additive package based on a combination of unsaturated polyester crosslinked with styrene; saturated polyester, polymethyl methacrylate, polyvinyl acetate, and styrene butadiene rubber; suspended in styrene; and thickened with metal oxides. The final SMC sheet may contain 5-35 wt% monomer. In certain inventive embodiments, low density Class A formulations are based on unsaturated polyester and do not have an interpenetrating polymer network for thickening. Traditional thickening is by metal oxides. Class A is associated with high quality surface finishes, such as in the automotive industry, characterized by high surface gloss, and is typically only obtainable with highly tailored resin formulations. Class A surfaces are generally required for vehicle surface panels (doors, hoods, quarter panels, trunks, roof structures, bumpers, etc.). Formulations have a combination of LPAs. Monomers range from 10-20 wt% of the total SMC sheet. SMC plaques with dimensions 30 x 30 mm are cured from the formulations under conventional compression molding conditions, such as at 140-155°C for 1-3 minutes.

[0059] Example 1 The formulation of Comparative Example A is modified to include a low profile additive containing the same thermoplastic resin suspended in 1,6-hexanediol dimethacrylate instead of styrene. The LPA used in Example A is in the form of thermoplastic beads, pellets, flakes, powders, chips, etc., and is dissolved in the alternative monomer by low or high shear mixing with or without heating up to 100°C at concentrations similar to conventional styrene-based LPAs. As a result, the amount of styrene in the formulation is reduced by 40 weight percent compared to Comparative Example A. SMC plaques form under conditions similar to those of Comparative Example A.

[0060] Example 2 For the VOC analysis, the plaques of Comparative Example A and Example 1 are heated according to the standardized VDA278 test method, where thermal desorption from molded SMC plaques occurs at 90° C. for 30 minutes. Volatiles are captured, thermally desorbed, and injected into a GC / MS for analysis. Concentrations are given in ppm (μg / g) based on a standard calibration curve (toluene equivalent). The results are summarized in a figure, showing that the plaque of Comparative Example A has a total VOC (TVOC) of 373 ppm and styrene desorption of 175 ppm, while the corresponding values ​​for the inventive plaque of Example 1 are 93 ppm and 5 ppm, respectively. Thus, a more than 30-fold reduction in styrene volatiles is observed by reducing the amount of styrene present in the formulation by only 40 weight percent.

[0061] Example 3 Common odor tests such as the VDA270 use a numerical scale to classify the odor of materials in a vehicle interior. Such a rating system uses the following scale:

[0062] [Table 2]

[0063] Some SMC formulations were formulated with alternative monomers for odor evaluation. All formulations using alternative monomers were observed by volunteers to have less unpleasant odor (grades 1-3) than conventional SMC formulated with only styrene as a reactive diluent (grades 4-6). When alternative monomers were used, the odor was judged to be undetectable by volunteers (grade 1).

[0064] The patent documents and publications mentioned in this specification are indicative of the level of skill of those in the art to which this invention pertains, and are herein incorporated by reference to the same extent as if each individual document or publication was specifically and individually indicated to be incorporated by reference herein.

Claims

1. A plurality of thermoplastic particles; the plurality of thermoplastic particles are dispersed therein and include a hydrogen bonding monomer that forms hydrogen bonds with the plurality of thermoplastic particles; The hydrogen bonding monomer is The boiling point is greater than 210°C. A viscosity of less than 140 cps at 25° C.; or The vapor pressure is less than 5 mmHg at 20°C. At least two of the following conditions must be met: A low profile additive composition.

2. further comprising a styrenic monomer substituted with said hydrogen bonding monomer; The low profile additive composition of claim 1.

3. The composition has an odor test rating of 1 to 3 as measured by the standardized VDA 270 odor test method. The low profile additive composition of claim 1.

4. The plurality of thermoplastic particles include polyacrylates, phenolic resins, phenoxy resins, poly(vinylphenols), polyamides, polyethylene glycols, polymethyl methacrylates, polyvinyl acetates, polycarbonates, or combinations thereof; and Copolymers containing butadiene, acrylonitrile, and vinyl chloride, specifically styrene butadiene rubber, or combinations thereof At least one hydrogen-bonding thermoplastic resin of The low profile additive composition of claim 1.

5. the hydrogen bonded thermoplastic resin is at least 10 percent by weight of the plurality of thermoplastic resin particles; The low profile additive composition of claim 4.

6. A cured matrix formed by a polyurethane or polyurea polymerized with a styrenic monomer; and The low profile additive composition according to any one of claims 1 to 4. Including, The cured product has a styrenic monomer volatility of less than 40 parts per million (ppm) as measured by the standardized VDA 278 test method.

7. 7. The cured product of claim 6, wherein the styrenic monomer is less than 10 ppm styrene.

8. Further comprising a thickener, The thickening agent is an alkaline earth metal oxide, an alkaline earth metal hydroxide, or a combination thereof; The cured product according to claim 6.

9. Further comprising a coating applied to the surface of the cured product; said coating is free of blisters visible to the naked eye of the normal human eye; The cured product according to claim 6.

10. Further comprising fiber reinforcement, The cured product according to any one of claims 6 to 9.

11. Having the shape of a bumper beam, a fender, a vehicle door panel part, an automobile floor part, a spoiler, a hood, or an engine cradle; The cured product according to any one of claims 6 to 9.

12. having an odor test grade of 1-3 as measured by the standardized VDA 270 odor test method; The cured product according to any one of claims 6 to 9.

13. 1. A method of forming a low VOC, low profile additive composition comprising: exposing a low profile additive composition comprising a plurality of thermoplastic particles dispersed in a styrenic monomer to a hydrogen bonding monomer in which the plurality of thermoplastic particles are dispersed to form hydrogen bonds with the plurality of thermoplastic particles; allowing sufficient time for said hydrogen bonding monomer to displace said styrenic monomer from contact with said plurality of thermoplastic particles to form a low VOC, low profile additive composition; Including, The hydrogen bonding monomer is The boiling point is greater than 210°C. A viscosity of less than 140 cps at 25° C.; or The vapor pressure is less than 5 mmHg at 20°C. A method that satisfies at least two of the following requirements.

14. further comprising dialysing the styrenic monomer from the low VOC low profile additive composition. The method of claim 13.

15. 15. The method of claim 13 or 14, wherein the styrenic monomer is styrene.

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