In-mold coating with improved flowability, part comprising the in-mold coating and method for producing an in-mold coating

Abstract

In-mold coating, comprising: a base material comprising an unsaturated polyester and / or a vinyl ester monomer, and graphs, and further comprising conductive carbon black in an amount of not more than 3% by weight of the in-mold coating.

Description

AREA

[0001] The disclosure relates to an in-mold coating intended to be used within a mold to coat another component. INTRODUCTION

[0002] In-mold coatings are coatings applied to an article, typically while the article is in the mold that creates it. The in-mold coating is a mixture of polymer precursors that crosslink upon catalysis to form a durable, conductive primer layer on the surface of the molded part. In-mold coatings can have several advantages, one of which is sealing the part, as the part may be molded from a more porous material than the in-mold coating material. In the automotive field, exterior parts formed from a polymeric material may have an in-mold coating applied to the base part to provide sealing, scratch resistance, weatherability, adhesion of additional paint layers, and / or other benefits. Such and comparable in-mold coatings are described, for example, in CN 104109450 A, CN 109337534 A and CN 110423496 A.

[0003] Some automobiles may have large exterior parts, such as hoods, tailgates, and door panels, that are difficult to coat evenly within the shape of the part. This is because the in-mold coating begins to cure before flowing over the entire large part. Accordingly, there is a need for an in-mold coating or a process that provides similar benefits to in-mold coatings for use on large exterior parts. SUMMARY

[0004] The present disclosure provides an in-mold coating with improved flowability capable of coating a large part within a mold. The novel in-mold coating comprises graphene within a polymeric base material, which can provide lower shear viscosity, increased flowability (improved shear thinning), improved durability (increased mechanical properties), improved surface appearance (fewer air pockets at the end of flow, increased flow length, and improved weld appearance), and conductivity.

[0005] In one example, which may be combined with or separated from other examples listed herein, an in-mold coating comprises graphene and a base material comprising an unsaturated polyester and / or a vinyl ester monomer.

[0006] In another example, which can be combined with or separated from the other examples listed herein, a part is provided comprising a main body formed from a polymeric resin mat and an in-mold coating disposed on the main body. The in-mold coating comprises graphene and a base material comprising an unsaturated polyester and / or a vinyl ester monomer. The in-mold coating further comprises conductive carbon black, wherein the conductive carbon black is included in an amount of no more than 3% by weight of the in-mold coating.

[0007] In another example, which may be combined with or separated from the other examples listed herein, a method for producing an in-mold coating is provided. The method comprises providing a base material comprising an unsaturated polyester and / or a vinyl ester monomer. The method further comprises adding graphene to the base material. The method further comprises adding conductive carbon black, wherein the conductive carbon black is included in an amount of no more than 3 wt. % of the in-mold coating.

[0008] Optionally, additional features may be provided, including, but not limited to: the graphene is provided in an amount of 0.1 to 10 wt.% of the in-mold coating; the graphene is provided in an amount of 0.2 to 5 wt.% of the in-mold coating; the graphene is provided in an amount of 0.3 to 1 wt.% of the in-mold coating; the graphene is provided as at least one layer of exfoliated graphene; the graphene is provided as a plurality of attached layers of graphene, wherein the plurality of attached layers comprises two to fifteen layers; the graphene is dispersed in the base material; the base material comprises both the unsaturated polyester and the vinyl ester monomer; the base material further comprises a styrene and / or a substituted acrylate monomer; a color coating is disposed on the in-mold coating;Shear mixing the base material and the graphene to disperse the graphene throughout the base material, thereby forming a mixture of the base material and the graphene, exfoliating the graphene into graphene compounds comprising between one and fifteen layers of graphene before adding the graphene to the base material, and adding a catalyst to the mixture of the base material and the graphene.

[0009] The above features and advantages, as well as other features and advantages of the present disclosure, are readily apparent from the following detailed description when considered in conjunction with the accompanying drawings and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. The components in the figures are not necessarily to scale, with emphasis instead being placed upon illustrating the principles of this disclosure. Fig. 1 a vehicle according to the principles of the present disclosure in a perspective view, Fig. 2 a section of a part of the vehicle of Fig. 1 according to the principles of the present disclosure in a schematic cross-sectional view, Fig. 3 an in-mold coating of the part of Fig. 1 and Fig. 2 according to the principles of the present disclosure in a schematic cross-sectional view as a close-up, Fig. 4 a single graphene sheet showing a section of the in-mold coating of Fig. 3, according to the principles of the present disclosure in a schematic view, Fig. 5 a multilayer graphene compound forming a section of the in-mold coating of Fig. 3, according to the principles of the present disclosure in a schematic view, Fig. 6 is a block diagram illustrating a method of forming an in-mold coating according to the principles of the present disclosure, Fig. 7 is a block diagram illustrating a method of forming an in-mold coating and a part having the in-mold coating disposed thereon in accordance with the principles of the present disclosure. DETAILED DESCRIPTION

[0011] The following description is merely exemplary and is not intended to limit the present disclosure or its application or uses.

[0012] Referring to the drawings, in which like reference numerals refer to like elements, Fig. 1 shows a vehicle 10 having a number of large exterior parts 12, 14, 16. The vehicle includes, for example, a hood 12, a door 14, and a tailgate 16, each of which may be formed from a polymeric composite resin mat (sheet molding compound, SMC).

[0013] With reference now to Fig. 2 and further reference to Fig.1, the main body 18 of each part 12, 14, 16 is formed from the SMC material. The SMC material may be a fiber-reinforced polymer material. It is desirable to fabricate the hood 12, the door(s) 14, and the tailgate 16, as well as other exterior parts, from polymeric materials because they have a higher strength-to-weight ratio compared to sheet metal, are more resistant to corrosion and weathering, and offer greater design flexibility.

[0014] Sheet molding compound (SMC) refers to a commonly used, ready-to-mold, fiber-reinforced polymer material. The SMC material can be manufactured by applying a quantity of chopped fibers to a thermosetting resin precursor composition supported on a film (usually made of nylon or polyethylene). The fibers then disperse into and through the resin composition, and another film is placed on top of the fiber-resin mixture to bond them together and form a continuous layer (or package) of SMC material. These packages are wound onto a take-up reel and stored for aging and curing until the viscosity of the composite reaches a level sufficient for molding, typically between two and five days.When the SMC material is ready for molding, the mold batches are selected or cut from the aged packages and placed between opposing, complementary, heated steel molds. Heat and pressure are applied to each batch to shape and cure it—to activate the polymerization of the thermosetting resin—resulting in the solidification of the polymer material and the formation of a molded SMC article.

[0015] In some examples, the SMC material may comprise a thermoplastic such as polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl alcohol, polystyrene, acrylonitrile-styrene polymer, acrylonitrile-butadiene-styrene resin, polyacrylate resin, polymethacrylate, methacrylate monomer or polymethyl methacrylate, styrene monomer or polystyrene, polyethylene, including ultra-high molecular weight polyethylene (UHMWPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), polypropylene, thermoplastic olefin resins, caprolactam monomer or polyamide (PA46, PA6, PA66, PA6 / 66, PA11, PA12, PA610), wholly or partially aromatic polyamide resins, polyacetal resin, polybenzimidazole, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyphenylene ether, polyphenylene oxides, polyphenylene sulfide, Polyether sulfones, polyether ether ketones, polyether ketones, polyetherimides, polylactides, polyoxymethylenes,thermoplastic polyurethanes or any combination or copolymer of these resins.

[0016] In some examples, the SMC material may also or alternatively include a thermosetting material such as benzoxazine, bis-maleimide (BMI), cyanate ester polymers, epoxy, phenol (PF), polyacrylate (acrylic), polyimide (PI), unsaturated polyester, polyurethane (PUR), vinyl ester, siloxane, polydicyclopentadiene (PDCPD), copolymers thereof, and combinations thereof.

[0017] The SMC material may also comprise a reinforcing filler. In some examples, fibers may be used as the reinforcing filler, such as carbon fibers, glass fibers (e.g., glass fibers, quartz), basalt fibers, aramid fibers (e.g., those sold under the trademark KEVLAR ®sold, polyphenylene benzobisoxazole (PBO) and synthetic para-aramid fibers sold under the trademark TWARON™), polyethylene fibers (e.g., ultra-high molecular weight polyethylene (UHMWPE)), polypropylene fibers (e.g., high-strength polypropylene), boron fibers, ceramic fibers, polyester fibers, natural fibers (e.g., cellulose, cotton, flax, hemp, spider silk, etc.), and combinations thereof. Particulate fillers may also or alternatively be used, including mineral fillers such as calcium carbonate, talc, silica, wollstonite, clay (including kaolin smectite, hectorite, montmorillonite, bentonite, beidellite, saponite, stevensite, sauconite, nontronite, illite, halloysite, and / or mixtures thereof), calcium sulfate, carbon black, mica, glass flakes, hollow glass spheres, aluminum trihydrate, magnesium hydroxide, titanium dioxide, and combinations thereof.

[0018] A representative SMC resin precursor composition consists of approximately (on a fiber-free basis) 16.9 wt.% thermosetting resin, 2.6 wt.% styrene monomer, 13 wt.% low-profile additive, 65 wt.% filler, for example, calcium carbonate, 1.5 wt.% thickener, 0.7 wt.% mold release agent, and 0.3 wt.% polymerization initiator. Reinforcing fibers comprise approximately 27 wt.% of the final SMC composite.

[0019] Another representative SMC material is shown in Table 1. Table 1 Formulation for medium density SMC Material class component Amount (in wt%) resin Unsaturated polyester resin with 37% styrene monomer 12.21 Polyvinyl acetate 9.40 Styrene monomer 1.88 initiator tert-Butyl peroxybenzoate peroxide 0.12 Inhibitor p-Benzoquinone 0.12 Internal lubricant Zinc stearate 0.24 Viscosity reducer fatty acid mixture 0.71 Thickener Magnesium oxide dispersed in polyester 0.82 Mineral filler Calcium carbonate 47.00 Reinforcing filler Fiber optic 27.50

[0020] To seal the part 12, 14, 16 and achieve the above-mentioned advantages, an in-mold coating 20 is disposed on the main body 18 of the part 12, 14, 16. The in-mold coating 20 may, for example, have a thickness in the range of 2 to 5 mils (thousandths of an inch). (In the metric system, this is 50.8 to 127 micrometers). With reference now to Fig. 2-5, the in-mold coating 20 comprises graphene 22 and a base material 24 comprising an unsaturated polyester and / or a vinyl ester monomer. The base material 24 may also comprise other thermoplastics and / or thermosetting materials, such as those described above.

[0021] Graphene 22 is an allotrope of carbon in the form of a layer or layers of atoms 26 arranged in a two-dimensional hexagonal lattice. Graphene 22 can be considered an infinite aromatic molecule. The graphene 22 provided in the in-mold coating 20 can be peeled off into a single layer, as shown in Fig. 4, or the graphene 22 may be provided as multiple layers of graphene 22 attached to one another, as shown in Fig. 5. For example, the multilayer graphene 22 may comprise two to fifteen layers. Grids of graphene 22 of various sizes are distributed throughout the base material 24, as shown in Fig. 3 shown.

[0022] In some examples, the base material 24 of the in-mold coating 20 comprises both an unsaturated polyester and a vinyl ester monomer. The base material 20 may further comprise a styrene and / or a substituted acrylate monomer. Not according to the invention, the in-mold coating 20 may be free of carbon black because the graphene 22 serves to increase the conductivity of the in-mold coating 20. According to the invention, some carbon black is mixed into the in-mold coating 20, but the graphene 22 provides conductivity, so less carbon black is needed than if no graphene 22 were included. According to the invention, conductive carbon black is provided in an amount of 3% or less by weight of the in-mold coating 20.

[0023] The graphene 22 may be provided in an amount of 0.1 to 10 wt.% of the in-mold coating 20. In particular, the graphene 22 is provided in an amount of 0.2 to 5 wt.% of the in-mold coating 20. More preferably, the graphene 22 is provided in a range of 0.3 to 1 wt.% of the in-mold coating 20.

[0024] An example of an in-mold coating 20 is shown in Table 2. Table 2 Example in-mold coating before adding graphene Material class material Amount (in wt%) resin Styrene 25 Ethoxylated bisphenol A diacrylate 37 Mineral filler Talk 10 Barium sulfate 10 Conductive filler soot 3 solvent Dimethyl adipate 12 Dimethyl succinate 3

[0025] The viscosity of the in-mold coating 20 is adjusted by the addition of non-reactive solvents as listed in Table 2. A desired viscosity may be, for example, 3000-6000 mPas. Prior to use, the in-mold coating 20 may be catalyzed with, for example, 0.8 to 1.5 wt. %, e.g., approximately 1 wt. %, of tert-butyl peroxybenzoate or another alternative free radical-generating initiator, such as dibenzoyl peroxide, azobis(isobutyronitrile), dicumyl peroxide, or di-tert-butyl peroxide.

[0026] One or more lacquer layers 28 and / or gloss layers 30 may be applied over the in-mold coating 20, as in Fig.2. For example, if the in-mold coating 20 covers an exterior vehicle part 12, 14, 16, paint / gloss layers 28, 30 are applied over the in-mold coating 20. Although not shown, more than two paint / gloss layers 28, 30 may be included to achieve a glossy finished part 12, 14, 16. In some examples, the additional layers 28, 30 may include a first primer, a second primer, a base coat, a top coat, and / or any other desired paint, coating, or gloss layers. In other variations, some parts may be sold without coatings 28, 30 applied over the in-mold coating 20.

[0027] In other examples, the in-mold coating 20 may be provided without the automotive part 12, 14, 16. For example, the in-mold coating 20 may be applied over another substrate material, wherein the other substrate material may be made of one of the materials mentioned above.

[0028] With reference now to Fig. 6, a method for producing an in-mold coating 20 is provided, generally designated 100. The method 100 comprises a step 102 of providing a base material 24 comprising an unsaturated polyester and / or a vinyl ester monomer. The method 100 further comprises a step 104 of adding graphene 22 to the base material 24.

[0029] With reference now to Fig.7, a more detailed method for producing an in-mold coating 20 is provided and generally designated 200. The method 200 includes optional steps that are applicable to the method 100 of Fig. 6 are not absolutely necessary, but one or more of which are used in the procedure 100 of Fig. 6 may be included.

[0030] The method 200 includes a step 202 of preparing a base material, which may be an in-mold coating resin mixture as described above with respect to the base material 24. The method 200 then includes a step 204 of adding graphene 22 to the base material 24. The method 200 may include exfoliating the graphene 22 into graphene compounds comprising between one and fifteen layers of graphene 22 before adding the graphene 22 to the base material 24, or the graphene 22 may be purchased with the desired thickness or exfoliation. The graphene 22 may be provided in the amounts described above, such as 0.1 to 10 wt. %, 0.2 to 5 wt. %, or 0.3 to 1 wt. % of the in-mold coating 20, as desired.

[0031] The step 204 of adding the graphene 22 to the base material 24 may include mixing the base material 24 and the graphene 22 under high shear to disperse the graphene 22 throughout the base material 24, thereby forming a mixture of the base material 24 and the graphene 22. In other alternatives, the graphene 22 may be added to the base material 24 using ultrasonics, sand milling, basket milling, three-roll milling, ball milling, or another suitable mixing technique. In some cases, the graphene may be provided as a pre-dispersed material concentrate in one of the other components of the base material. This may provide for easier incorporation and distribution of the graphene into the base materials. The concentration of graphene in such concentrates can be between 10 and 50 wt%, between 15 and 30 wt% or alternatively between 20 and 25 wt% of the base resin component.This graphene concentrate would then be incorporated using the same methods used to incorporate the dry graphene.

[0032] According to the invention, the method 200 comprises a step 206 of adding conductive carbon black to the mixture of graphene 22 and base material 24 to adjust the conductivity and flowability of the mixture of the in-mold coating 20 as desired. In step 208, the in-mold coating 20 is then fed to a former.

[0033] In a step 210, the method 200 includes adding a catalyst to the mixture of the in-mold coating 20. High shear mixing may be used to add the catalyst. In some variations, the method 200 may include continuing to mix the in-mold coating 20 until it is ready to be placed into a mold. Alternatively, continuous mixing is not required, and the in-mold coating 20 may be stored until needed.

[0034] In step 212, the method 200 includes injecting the in-mold coating 20 into a mold having an unfinished part 12, 14, 16 and closing the mold to provide additional shear flow and allow the coating 20 to crosslink. The method 200 may then include a step 214 of ejecting the coated part 12, 14, 16. Paint and / or gloss layers 28, 30 may then be applied to the part 12, 14, 16 having the in-mold coating 20, or such layers 28, 30 may be applied after the parts 12, 14, 16 have been assembled with the rest of the vehicle 10.

[0035] Accordingly, the in-mold coating 20 provides a seal for the porous SMC parts 12, 14, 16 as well as a conductive surface that ensures good application of the paint and gloss layers 28, 30. The graphene 22 interspersed into the base material 24 of the in-mold coating 20 can provide improved flowability, durability, surface appearance, and conductivity. By adding graphene 22 to the base material 24 of the in-mold coating, the resulting in-mold coating 20 becomes thixotropic (shear-thinning). Due to the increased flowability under shear influence, the in-mold coating 20 containing graphene 22 is able to flow and cover the entire part 12, 14, 16 during the coating process, so that the entire part 12, 14, 16 is covered before the coating 20 cures.

[0036] Accordingly, even large parts such as the hood 12, the door(s) 14 and the tailgate 16 can be coated with the in-mold coating 20 before the in-mold coating 20 cures or solidifies in the mold.

Claims

[1] In-mold coating, comprising: a base material comprising an unsaturated polyester and / or a vinyl ester monomer, and graphs, and further comprising conductive carbon black in an amount of not more than 3% by weight of the in-mold coating. [2] The in-mold coating according to claim 1, wherein the graphene is provided in an amount of 0.1 to 10 wt% of the in-mold coating, preferably in an amount of 0.2 to 5 wt% of the in-mold coating, and more preferably in an amount of 0.3 to 1 wt% of the in-mold coating. [3] In-mold coating according to any one of the preceding claims, wherein the graphene is provided as at least one layer of exfoliated graphene, the graphene being dispersed in the base material. [4] The in-mold coating of any preceding claim, wherein the base material comprises both the unsaturated polyester and the vinyl ester monomer, and the base material further comprises a styrene and a substituted acrylate monomer. [5] Part, comprising: a main body formed of a polymer composite resin mat, and an in-mold coating according to any one of the preceding claims 1 to 4, wherein the in-mold coating is arranged on the main body. [6] The part of claim 5, further comprising a lacquer layer disposed on the in-mold coating. [7] A method for producing an in-mold coating, the method comprising: Providing a base material comprising an unsaturated polyester and / or a vinyl ester monomer, Adding graphene to the base material, and wherein the method further comprises a step of adding conductive carbon black, wherein the conductive carbon black is contained in an amount of not more than 3 wt% of the in-mold coating. [8] The method of claim 7, further comprising: Shear mixing the base material and the graphene to disperse the graphene in the base material, thereby forming a mixture of the base material and the graphene, Peeling the graphene into graphene compounds comprising between one and fifteen graphene layers before adding the graphene to the base material, Providing the graphene in an amount of 0.2 and 5 wt.% of the in-mold coating and Adding a catalyst to the mixture of the base material and the graphene.

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