A stain-resistant sheet molding compound and a method for preparing the same

Abstract

The application discloses a kind of dirt-resistant sheet molding compound and preparation method thereof, it is related to molding compound technical field.The molding compound mainly includes: 80~120 parts resin matrix, 30~50 parts low shrinkage additive, 1~2 parts initiator, 0.5~1 parts polymerization inhibitor, 5~10 parts crosslinking agent, 5~10 parts release agent, 300~400 parts inorganic filler, 2~5 parts silane coupling agent, 5~10 parts color paste, 2~5 parts thickening agent, 100~450 parts alkali-free glass fiber;Inorganic filler uses different particle sizes of aluminium hydroxide, including: 1-3 μm, 3-5 μm, 6-8 μm in multiple combination grading, improve the density of molding compound product;Mixed resin paste is added to alkali-free glass fiber to be rolled up and compacted, sheet structure is obtained, and sheet molding compound is finally prepared by winding thickening;The sheet molding compound prepared in the application is tested by soy sauce, red wine, ink, salad oil stains, and has good dirt resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molding compound, in particular to a stain-resistant sheet molding compound and a preparation method thereof. BACKGROUND

[0002] Sheet molding compound, abbreviated as SMC, is a sheet-shaped molding material made by impregnating fibers or chopped fiber mats with a resin paste and covering both sides with polyethylene film. Its main components include unsaturated polyester resin matrix material, low shrinkage additives, fillers, curing agents, thickening agents, release agents, and other reinforcing materials. It has numerous excellent physical and chemical properties, such as lightweight and high strength. Compared to metal materials, SMC is lighter and stronger, often used as automotive body panels. Good corrosion resistance makes SMC appear in chemical equipment and marine facility machinery. The formula can be adjusted according to demand to meet the special requirements of different products. The sheet molding compound market has achieved significant growth in the past few years and will continue to grow in the next few years. This trend is not only driven by domestic demand, but also benefits from the increasing demand for high-performance materials in the global market and the progress of related technologies.

[0003] Although sheet molding compound has been widely used in various industries such as automobiles, construction, and electrical appliances with the advancement of technology, research on sheet molding compound has mainly focused on lightweight and recycling. However, there are still some performance deficiencies that need to be improved, such as porosity defects, poor surface properties, and the presence of small voids on the surface, which may limit the further development of SMC in certain fields. SUMMARY

[0004] The purpose of the present application is to provide a stain-resistant sheet molding compound and a preparation method thereof to solve the problems in the prior art.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0006] A preparation method of a stain-resistant sheet molding compound, the specific steps are as follows:

[0007] Prepare raw materials by mass fraction: 80-120 parts of unsaturated polyester, 30-50 parts of low shrinkage additive, 1-2 parts of initiator, 0.5-1 part of polymerization inhibitor, 5-10 parts of crosslinking agent, 5-10 parts of release agent, 300-400 parts of inorganic filler, 2-5 parts of silane coupling agent, 5-10 parts of color paste, 2-5 parts of thickening agent, 100-450 parts of alkali-free glass fiber, and 10-20 parts of modified diatomite.

[0008] S1: Resin paste preparation

[0009] The weighed unsaturated polyester and low shrinkage additive are added to the stirred tank, and stirring is started at 800 r / min for 2 min, then the weighed initiator, polymerization inhibitor, crosslinking agent, release agent, silane coupling agent are added, and stirring is continued at 800 r / min for 5 min, finally the modified diatomite and aluminum hydroxide are added, and then high-speed stirring is carried out at 1000 r / min for 5 min, and the resin paste is uniformly mixed to obtain a resin paste, which is transferred to a storage tank, and the viscosity of the resin paste is controlled to be between 20000-50000CP;

[0010] S2: SMC sheet preparation

[0011] The resin paste prepared in S1, thickening agent, color paste are mixed and stirred in proportion, and at the same time, alkali-free glass fiber is added, and then the material is rolled and compacted by a pressure roller to obtain an SMC sheet.

[0012] S3: Rolling and thickening

[0013] After the material is rolled and packaged, it is placed in an oven at 40℃ for 12h to complete the thickening process, and a sheet molding compound is obtained.

[0014] In S1, the low shrinkage additive is one or more combinations of polystyrene type low shrinkage agent, saturated polyester low shrinkage agent, and thermoplastic rubber.

[0015] The initiator is one or more combinations of tert-butyl peroxybenzoate, benzoyl peroxide, tert-butyl peroxyacetate, and tert-amyl peroxybenzoate; and is further set to tert-butyl peroxybenzoate.

[0016] The polymerization inhibitor is one or more combinations of hydroquinone, benzoquinone, trimethylbenzyl ammonium chloride, and bromide; and is further set to benzoquinone.

[0017] The crosslinking agent is styrene.

[0018] The release agent is one or more combinations of zinc stearate, magnesium stearate, and calcium stearate; and is further set to zinc stearate.

[0019] The inorganic filler is a combination of aluminum hydroxide with a particle size of 1-3μm, 3-5μm, and 6-8μm.

[0020] The silane coupling agent is one or more combinations of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, γ-aminopropyltriethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane; and is further set to γ-(methacryloyloxy)propyltrimethoxysilane KH-570.

[0021] The color paste is any one of white, red, yellow, green, blue, gray, and black; and is further set to white color paste.

[0022] The thickening agent is one or a combination of calcium oxide, magnesium oxide, calcium hydroxide and magnesium hydroxide; and the further setting is magnesium oxide.

[0023] The preparation steps of the modified diatomite include: taking diatomite and adding deionized water to stir, heating in a water bath at 90 DEG C, adding dropwise an alcohol solution of coupling agent KH-570 at a rotating speed of 180-200 r / min, adjusting the rotating speed to 1000-1200 r / min after the dropwise adding is completed, and reacting for 1-2 h; then taking out, drying and grinding to obtain silane-modified diatomite; under a nitrogen environment, taking butyl acrylate, methyl methacrylate, acrylic acid and perfluorooctyl methacrylate in toluene, adding benzoyl peroxide to stir and dissolve, heating to 80 DEG C, reacting for 1 h, adding the silane-modified diatomite to mix, and stirring at 80 DEG C for 2 h; after cooling, washing with alcohol and water alternately for 3 times, and drying to obtain the modified diatomite.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] 1. The modified diatomite is added to the sheet molding compound, the modified diatomite is modified by wet coating with a coupling agent, and the polyacrylate is grafted and modified; the polyacrylate has good compatibility with the unsaturated polyester matrix; the diatomite is grafted to improve the compatibility in the matrix; the organic fluorine compound is added in the polymerization of the polyacrylate monomer; and the filler obtained by polymerization of the silane-modified diatomite improves the compatibility and dispersibility of the diatomite particles in the unsaturated polyester matrix while bringing about reinforcing effect; and the modified diatomite has good hydrophobic property, thereby bringing about certain stain resistance to the sheet molding compound.

[0026] 2. The content of the alkali-free glass fiber has certain influence on the mechanical properties and curing shrinkage of the sheet molding compound; different types of low-shrinkage additives have great influence on the curing shrinkage of the molding compound matrix, thereby affecting the mechanical properties of the molding compound; the inorganic filler of aluminum hydroxide with different particle sizes is added to adjust the fluidity of the slurry, reduce or avoid shrinkage and cracking, improve the compactness of the molding compound matrix through grading between different particle sizes, and further improve the stain resistance.

[0027] 3. The complex combination of the unsaturated polyester, low-shrinkage additive, initiator, polymerization inhibitor, crosslinking agent, release agent, inorganic filler, silane coupling agent, color paste, thickening agent and alkali-free glass fiber gives the SMC product good stain resistance and mechanical properties. DETAILED DESCRIPTION

[0028] All other embodiments obtained by a person of ordinary skill in the art without creative labor based on the embodiments in the present application belong to the protection scope of the present application.

[0029] The unsaturated polyester is Huari 1168, the polystyrene is Huari 954, the alkali-free glass fiber is 100 mesh, and the alcohol solution of the coupling agent KH-570 includes 10 ml of anhydrous ethanol and 0.05 g of KH-570.

[0030] Embodiment 1: The embodiment provides a preparation method of a stain-resistant sheet molding compound, and the specific steps are as follows:

[0031] S1: Resin paste preparation

[0032] 100 parts of unsaturated polyester and 50 parts of polystyrene are added to a stirring kettle, and stirring is started at 800 r / min for 2 min, then 1.5 parts of t-butyl peroxybenzoate, 1 part of benzoquinone, 5 parts of styrene, 8 parts of zinc stearate, and 2 parts of silane coupling agent KH-570 are added, and stirring is continued at 800 r / min for 5 min, finally 250 parts of aluminum hydroxide (6-8 μm) and 100 parts of aluminum hydroxide (1-3 μm) are added, and high-speed stirring is carried out at 1000 r / min for 5 min, and the resin paste is uniformly mixed to obtain a resin paste, which is transferred to a storage tank, and the viscosity of the resin paste is controlled to be between 20,000-50,000 CP;

[0033] S2: SMC sheet preparation

[0034] The resin paste prepared in S1 is sent into an SMC unit, 4 parts of magnesium oxide and 10 parts of white paste are input into an online stirring kettle, and 150 parts of alkali-free glass fiber is added, and the material is pressed and compacted by a pressure roller, the speed of the equipment is controlled to be 10 m / min, and an SMC sheet is prepared.

[0035] S3: Rolling and thickening

[0036] After the material is rolled and packaged, it is placed in an oven at 40°C for 12 h for baking, and the thickening process is completed, and a sheet molding compound is obtained.

[0037] Embodiment 2: The embodiment provides a preparation method of a stain-resistant sheet molding compound, and the specific steps are as follows:

[0038] S1: Resin paste preparation

[0039] Into a stirring kettle, 100 parts of unsaturated polyester and 50 parts of styrene-butadiene-styrene block copolymer were added, and stirring was started at 800 r / min for 2 min, then 1.5 parts of tert-butyl peroxybenzoate, 1 part of benzoquinone, 5 parts of styrene, 8 parts of zinc stearate, and 2 parts of silane coupling agent KH-570 were added, and stirring was continued at 800 r / min for 5 min, finally 250 parts of aluminum hydroxide (6-8 μm) and 100 parts of aluminum hydroxide (1-3 μm) were added, and high-speed stirring was carried out at 1000 r / min for 5 min, and the resin paste was uniformly mixed to obtain a resin paste, which was transferred to a storage tank, and the viscosity of the resin paste was controlled to be between 20000-50000 CP.

[0040] S2: SMC sheet preparation

[0041] The resin paste prepared in S1 was fed into an SMC unit, 4 parts of magnesium oxide and 10 parts of white paste were input into an online stirring kettle, and 150 parts of alkali-free glass fiber was added at the same time, and the equipment speed was controlled to be 10 m / min, and the SMC sheet was prepared by rolling and compacting through a pressure roller;

[0042] S3: winding and thickening

[0043] After the material was wound and packaged, it was placed in an oven at 40℃ for 12h for baking, and the thickening process was completed to obtain a sheet molding compound.

[0044] Example 3: A method for preparing a stain-resistant sheet molding compound is provided, and the specific steps are as follows:

[0045] S1: Resin paste preparation

[0046] Into a stirring kettle, 100 parts of unsaturated polyester and 50 parts of polystyrene were added, and stirring was started at 800 r / min for 2 min, then 1.5 parts of tert-butyl peroxybenzoate, 1 part of benzoquinone, 5 parts of styrene, 8 parts of zinc stearate, and 2 parts of silane coupling agent KH-570 were added, and stirring was continued at 800 r / min for 5 min, finally 10 parts of modified diatomite, 250 parts of aluminum hydroxide (6-8 μm) and 100 parts of aluminum hydroxide (1-3 μm) were added, and high-speed stirring was carried out at 1000 r / min for 5 min, and the resin paste was uniformly mixed to obtain a resin paste, which was transferred to a storage tank, and the viscosity of the resin paste was controlled to be between 20000-50000 CP.

[0047] S2: SMC sheet preparation

[0048] The resin paste prepared in S1 was fed into an SMC unit, 4 parts of magnesium oxide and 10 parts of white paste were input into an online stirring kettle, and 150 parts of alkali-free glass fiber was added at the same time, and the equipment speed was controlled to be 10 m / min, and the SMC sheet was prepared by rolling and compacting through a pressure roller;

[0049] S3: winding and thickening

[0050] After the material is wound and packaged, it is placed in an oven at 40℃ for 12h to complete the thickening process, and a sheet molding compound is obtained.

[0051] The preparation steps of the modified diatomite include: 2g of diatomite is added to 40ml of deionized water and stirred, heated in a water bath at 90℃, and 10ml of alcohol solution of coupling agent KH-570 is added dropwise at a speed of 200r / min, after the dropwise addition is completed, the speed is adjusted to 1000r / min, and the reaction is carried out for 1h, and then the product is taken out, dried and ground to obtain the modified diatomite; under a nitrogen environment, 20g of butyl acrylate, 30g of methyl methacrylate, 2g of acrylic acid and 2g of perfluorooctyl methacrylate are placed in 50ml of toluene, 0.3g of benzoyl peroxide is added and stirred to dissolve, the temperature is raised to 80℃, and the reaction is carried out for 1h, then the silane-modified diatomite is added and mixed, and the mixture is stirred at 80℃ for 2h, then it is washed with alcohol and water alternately for 3 times, and dried to obtain the modified diatomite.

[0052] Example 4: The present embodiment provides a method for preparing a stain-resistant sheet molding compound, and the specific steps are as follows:

[0053] S1: Preparation of resin paste

[0054] 100 parts of unsaturated polyester and 50 parts of polystyrene are added to a stirring kettle, and stirring is started at a speed of 800r / min for 2min, then 1.5 parts of tert-butyl benzene peroxide, 1 part of benzoquinone, 5 parts of styrene, 8 parts of zinc stearate and 2 parts of silane coupling agent KH-570 are added, and the stirring is continued at a speed of 800r / min for 5min, finally 15 parts of modified diatomite, 250 parts of aluminum hydroxide (6-8μm) and 100 parts of aluminum hydroxide (1-3μm) are added, and then high-speed stirring is carried out at a speed of 1000r / min for 5min to obtain a uniformly mixed resin paste, which is transferred to a storage tank, and the viscosity of the resin paste is controlled to be between 20000-50000CP.

[0055] S2: Preparation of SMC sheet

[0056] The resin paste prepared in S1 is fed into an SMC unit, 4 parts of magnesium oxide and 10 parts of white paste are input into an online stirring kettle, and 150 parts of non-alkali glass fiber is added at the same time, and the material is pressed and compacted by a pressure roller, and the equipment speed is controlled at 10m / min to obtain an SMC sheet.

[0057] S3: Winding and thickening

[0058] After the material is wound and packaged, it is placed in an oven at 40℃ for 12h to complete the thickening process, and a sheet molding compound is obtained.

[0059] The preparation steps of the modified diatomite include: 2 g of diatomite is added into 40 ml of deionized water for stirring, water bath heating is performed at 90°C, 10 ml of alcohol solution of coupling agent KH-570 is added dropwise at a rotation speed of 200 r / min, after the dropwise addition is completed, the rotation speed is adjusted to 1000 r / min, and reaction is performed for 1 h; the modified diatomite is obtained after being taken out, dried and ground; 20 g of butyl acrylate, 30 g of methyl methacrylate, 2 g of acrylic acid and 2 g of perfluorooctyl methacrylate are placed in 50 ml of toluene, 0.3 g of benzoyl peroxide is added for stirring and dissolving, heating is performed to 80°C, reaction is performed for 1 h, the silane-modified diatomite is mixed, and stirring is performed at 80°C for 2 h; after cooling, the modified diatomite is washed with alcohol and water alternately for 3 times, and is dried to obtain the modified diatomite.

[0060] Comparative Example 1: Comparative Example 1 adjusts the gradation of aluminum hydroxide according to Example 1, and the specific steps are as follows:

[0061] S1: Resin paste preparation

[0062] 100 parts of unsaturated polyester and 50 parts of polystyrene are added into a stirring kettle, stirring is started, and stirring is performed at 800 r / min for 2 min; then 1.5 parts of tert-butyl benzoyl peroxide, 1 part of benzoquinone, 5 parts of styrene, 8 parts of zinc stearate, 2 parts of silane coupling agent KH-570 and 10 parts of white color paste are added, and stirring is continuously performed at 800 r / min for 5 min; finally, 350 parts of aluminum hydroxide (6-8 μm) is added, and then high-speed stirring is performed at 1000 r / min for 5 min to uniformly mix to obtain a resin paste, which is transferred into a storage tank, and the viscosity of the resin paste is controlled to be between 20000-50000 CP.

[0063] S2: SMC sheet preparation

[0064] The resin paste prepared in S1 is sent into an SMC unit, 4 parts of magnesium oxide and 10 parts of white color paste are input into an online stirring kettle, and 150 parts of alkali-free glass fiber is added at the same time, the material is pressed and compacted through pressure rollers, and the speed of the equipment is controlled to be 10 m / min to prepare an SMC sheet.

[0065] S3: Winding and thickening

[0066] After the material is wound and packaged, it is placed into an oven at 40°C for baking for 12 h to complete the thickening process, and a sheet molding compound is obtained.

[0067] Comparative Example 2: Comparative Example 2 replaces polystyrene with saturated polyester according to Example 1, and the specific steps are as follows:

[0068] S1: Resin paste preparation

[0069] Into a stirring kettle, 100 parts of unsaturated polyester and 50 parts of saturated polyester were added, and stirring was started at 800 r / min for 2 min, then 1.5 parts of t-butyl peroxybenzoate, 1 part of benzoquinone, 5 parts of styrene, 8 parts of zinc stearate, 2 parts of silane coupling agent KH-570, and 10 parts of white paste were added, and stirring was continued at 800 r / min for 5 min, finally 250 parts of aluminum hydroxide (6-8 μm) and 100 parts of aluminum hydroxide (1-3 μm) were added, and high-speed stirring was carried out at 1000 r / min for 5 min, and the resin paste was uniformly mixed to obtain a resin paste, which was transferred to a storage tank, and the viscosity of the resin paste was controlled to be between 20000-50000 CP.

[0070] S2: SMC sheet preparation

[0071] The resin paste prepared in S1 was fed into an SMC unit, 4 parts of magnesium oxide and 10 parts of white paste were input into an online stirring kettle, and 150 parts of alkali-free glass fiber was added at the same time, and the material was pressed and compacted by a pressure roller, and the equipment speed was controlled to be 10 m / min, and an SMC sheet was prepared.

[0072] S3: Rolling and thickening

[0073] After the material was rolled and packaged, it was placed in an oven at 40°C for 12 h for baking, and the thickening process was completed, and a sheet molding compound was obtained.

[0074] Comparative Example 3: In Comparative Example 3, the aluminum hydroxide in Example 1 was replaced with calcium carbonate, and the specific steps were as follows:

[0075] S1: Resin paste preparation

[0076] Into a stirring kettle, 100 parts of unsaturated polyester and 50 parts of polystyrene were added, and stirring was started at 800 r / min for 2 min, then 1.5 parts of t-butyl peroxybenzoate, 1 part of benzoquinone, 5 parts of styrene, 8 parts of zinc stearate, 2 parts of silane coupling agent KH-570, and 10 parts of white paste were added, and stirring was continued at 800 r / min for 5 min, finally 350 parts of calcium carbonate were added, and high-speed stirring was carried out at 1000 r / min for 5 min, and the resin paste was uniformly mixed to obtain a resin paste, which was transferred to a storage tank, and the viscosity of the resin paste was controlled to be between 20000-50000 CP.

[0077] S2: SMC sheet preparation

[0078] The resin paste prepared in S1 was fed into an SMC unit, 4 parts of magnesium oxide and 10 parts of white paste were input into an online stirring kettle, and 150 parts of alkali-free glass fiber was added at the same time, and the material was pressed and compacted by a pressure roller, and the equipment speed was controlled to be 10 m / min, and an SMC sheet was prepared.

[0079] S3: Rolling and thickening

[0080] After the material is wound and packaged, it is placed in an oven at 40℃ for 12h to complete the thickening process, and a sheet molding compound is obtained.

[0081] Comparative Example 4: Comparative Example 4 is directed to the increment of diatomite in Example 4, and the specific steps are as follows:

[0082] S1: Resin paste preparation

[0083] 100 parts of unsaturated polyester and 50 parts of polystyrene are added to a stirred tank, stirring is started, and stirring is carried out at 800r / min for 2min, then 1.5 parts of tert-butyl peroxybenzoate, 1 part of benzoquinone, 5 parts of styrene, 8 parts of zinc stearate, 2 parts of silane coupling agent KH-570, 10 parts of white paste are added, and stirring is continued at 800r / min for 5min, and finally 30 parts of modified diatomite, 250 parts of aluminum hydroxide (6-8μm) and 100 parts of aluminum hydroxide (1-3μm) are added, and then high-speed stirring is carried out at 1000r / min for 5min to uniformly mix the resin paste, which is transferred to a storage tank, and the viscosity of the resin paste is controlled to be between 20000-50000CP.

[0084] S2: SMC sheet preparation

[0085] The resin paste prepared in S1 is fed into an SMC unit, 4 parts of magnesium oxide and 10 parts of white paste are input into an online stirred tank, and 150 parts of alkali-free glass fiber is added at the same time, and the material is pressed and compacted by a pressure roller, and the equipment speed is controlled at 10m / min to prepare an SMC sheet.

[0086] S3: Winding and thickening

[0087] After the material is wound and packaged, it is placed in an oven at 40℃ for 12h to complete the thickening process, and a sheet molding compound is obtained.

[0088] The preparation steps of the modified diatomite include: 2g of diatomite is added to 40ml of deionized water and stirred, heated in a water bath at 90℃, and 10ml of alcohol solution of coupling agent KH-570 is added dropwise at a stirring speed of 200r / min, after the dropwise addition is completed, the stirring speed is adjusted to 1000r / min, and the reaction is carried out for 1h, and then the product is taken out, dried, ground, and the modified diatomite is obtained; under a nitrogen environment, 20g of butyl acrylate, 30g of methyl methacrylate, 2g of acrylic acid, and 2g of perfluorooctyl methacrylate are placed in 50ml of toluene, 0.3g of benzoyl peroxide is added and stirred to dissolve, the temperature is raised to 80℃, and the reaction is carried out for 1h, then the silane-modified diatomite is mixed, and stirring is carried out at 80℃ for 2h, after cooling, the product is washed with alcohol and water alternately for 3 times, and then dried to obtain the modified diatomite.

[0089] Detection test:

[0090] 1. Stain resistance test: the above-mentioned sheet material is molded into a 300mm x 300mm x 3mm plate, 5ml of soy sauce, red wine, ink, salad oil, respectively, is dropped on different positions of the plate, and the corresponding position marks are made, after 24h, the stains are wiped with water, and the surface of the stain-resistant coating is checked.

[0091]

[0092] 2. Mechanical property test: the tensile strength and bending strength test is carried out by using a universal testing machine.

[0093]

[0094] According to the above test results, by grading the different particle sizes of aluminum hydroxide, the stain resistance and mechanical strength of the sheet molding compound can be effectively improved, the modified diatomite added in examples 3 and 4 has a certain reinforcing effect on the SMC matrix, slightly improving the mechanical properties of the SMC product; at the same time, the stain resistance of the sheet molding compound prepared by using saturated polyester as a low shrinkage agent is inferior to polystyrene and thermoplastic elastomer, different types of low shrinkage agents affect the curing shrinkage of SMC, and then affect the mechanical strength of the SMC product; in comparative example 3, the particle size graded aluminum hydroxide is replaced by calcium carbonate, which has a slight effect on the stain resistance and mechanical strength of the product; in comparative example 4, the mass fraction of modified diatomite is increased, which is beyond the limited range, and the stain resistance and mechanical strength are lower than those of examples 3 and 4, therefore, the modified diatomite can improve the mechanical properties of the SMC product within a certain range, but excessive amount will reduce the strength.

[0095] Finally, it should be noted that: the above only describes the preferred embodiments of the present application, and is not used to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, for those skilled in the art, the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A stain-resistant sheet molding compound, characterized in that, The stain-resistant sheet molding compound comprises the following raw materials in parts by weight: 80-120 parts unsaturated polyester, 30-50 parts low-shrinkage additive, 1-2 parts initiator, 0.5-1 part polymerization inhibitor, 5-10 parts crosslinking agent, 5-10 parts release agent, 300-400 parts inorganic filler, 2-5 parts silane coupling agent, 5-10 parts color paste, 2-5 parts thickener, and 100-450 parts alkali-free glass fiber; The stain-resistant sheet molding compound also includes 10-20 parts of modified diatomaceous earth. The preparation steps of the modified diatomaceous earth include: adding diatomaceous earth to deionized water and stirring, heating in a water bath at 90°C, adding an alcohol solution of coupling agent KH-570 dropwise at a speed of 180-200 r / min, adjusting the speed to 1000-1200 r / min after the addition is completed, reacting for 1-2 hours, removing, drying and grinding to obtain silane-modified diatomaceous earth; under nitrogen atmosphere, placing butyl acrylate, methyl methacrylate, acrylic acid, and perfluorooctyl methacrylate in toluene, adding benzoyl peroxide and stirring to dissolve, heating to 80°C and reacting for 1 hour, adding silane-modified diatomaceous earth and mixing, keeping at 80°C and stirring for 2 hours, cooling and washing with alcohol and water alternately 3 times, and drying to obtain modified diatomaceous earth; The inorganic filler is aluminum hydroxide, and the particle size of aluminum hydroxide is a combination of 1-3μm and 6-8μm; The low-shrinkage additive is a polystyrene-type low-shrinkage agent.

2. The stain-resistant sheet molding compound according to claim 1, characterized in that, The initiator is one or more combinations of tert-butyl peroxide, benzoyl peroxide, tert-butyl peracetate, and tert-amyl peroxide.

3. The stain-resistant sheet molding compound according to claim 1, characterized in that, The polymerization inhibitor is one or more combinations of hydroquinone, benzoquinone, trimethylbenzylamine chloride and bromide; the crosslinking agent is styrene; and the release agent is one or more combinations of zinc stearate, magnesium stearate and calcium stearate.

4. The stain-resistant sheet molding compound according to claim 1, characterized in that, The silane coupling agent is one or more combinations of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, γ-aminopropyltriethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane; the color paste is any one of white, red, yellow, green, blue, gray, and black; and the thickener is one or more combinations of calcium oxide, magnesium oxide, calcium hydroxide, and magnesium hydroxide.

5. A method for preparing a stain-resistant sheet molding compound as described in any one of claims 1-4, characterized in that, The specific preparation steps are as follows: S1: Resin Paste Preparation Weigh out the unsaturated polyester and low-shrinkage additives and add them to the mixing tank. Start the stirring and stir at 800 r / min for 2 min. Then add the weighed initiator, polymerization inhibitor, crosslinking agent, release agent and silane coupling agent and continue stirring at 800 r / min for 5 min. Finally, add the modified diatomaceous earth and aluminum hydroxide and stir at 1000 r / min for 5 min. Mix evenly to obtain a resin paste and transfer it to a storage tank. Control the viscosity of the resin paste between 20,000 and 50,000 CP. S2: SMC Sheet Preparation Take the resin paste, thickener, and color paste prepared by S1, mix them in proportion, add alkali-free glass fiber, and compact them by pressure roller to obtain SMC sheet. S3: Winding up, thickening After the material is rolled up and packaged, it is placed in a 40℃ oven and baked for 12 hours to complete the thickening process, resulting in sheet molding compound.

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