Sheet molding compound and preparation method thereof

Abstract

The present invention provides a sheet molding compound and a preparation method thereof, the method comprising the following steps: according to the weight parts, 60 to 70 parts of unsaturated polyester resin and 30 to 40 parts of low shrinkage additive are mixed and stirred; then 130 to 180 parts of calcium carbonate powder are added while stirring and continued to stir; then 1 to 3 parts of curing agent are added and stirred to obtain resin paste; 4.5 to 9 parts of thickener are added to the resin paste, and then 50 to 120 parts of glass fiber are soaked in the resin paste to prepare SMC sheet molding compound semi-finished products; the SMC sheet molding compound semi-finished products are placed between two layers of carrier films, the material of the carrier films is PA+PE composite film, and then edge sealing treatment is performed, and then ripening is performed, and the ripening temperature is 50°C to 70°C; the ripened SMC sheet molding compound is cooled and pressed into shape. The present invention compounded the composite thickener with other chemical components in a certain proportion, greatly shortened the ripening time of the sheet molding compound, selected PA+PE carrier film, so that the SMC is quickly heated and ripened and then quickly cooled, and the SMC is realized. High-efficiency continuous production of SMC.

Description

Technical Field

[0001] The invention relates to the technical field of functional composite material preparation, in particular to a sheet molding compound and a preparation method thereof. Background Art

[0002] Sheet molding compound (SMC) is a type of sheet molding material made of resin paste impregnated fiber or short fiber mat covered with polyethylene film on both sides. It has the properties of electrical insulation, heat resistance, flame retardancy, good mechanical strength, light weight, easy and flexible engineering design, etc. Its mechanical properties are comparable to those of some metal materials, so it is widely used in transportation vehicles, construction, electronics, electrical and other industries.

[0003] Traditional SMC sheets are mushy without medium-high temperature aging, and cannot be torn into thin films for compression molding. Therefore, the last step of SMC production is to mature in a drying room at about 50°C for about 24 hours (or 35°C for 3-5 days). The material thickens and hardens before it becomes processable. Then it takes 3-7 days to fully cool to room temperature, and the molded product will have higher quality. However, the time required for the existing SMC to mature and mold is too long, which seriously affects the production efficiency of sheet molding compounds. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a sheet molding compound with excellent performance and short curing time, and a preparation method of the sheet molding compound.

[0005] The present invention proposes a technical solution to solve the above technical problems: a sheet molding compound, comprising an upper and lower carrier film and a resin material located between the two carrier films, wherein the resin material comprises the following components: 60 to 70 parts by weight of unsaturated polyester resin, 30 to 40 parts by weight of low shrinkage agent, 130 to 180 parts by weight of calcium carbonate, 1 to 5 parts by weight of water absorbent, 0.1 to 0.3 parts by weight of polymerization inhibitor, 4.5 to 9 parts by weight of composite thickener, 50 to 120 parts by weight of glass fiber and 1 to 3 parts by weight of curing agent; the composite thickener comprises 3 to 5 parts by weight of magnesium oxide, 1 to 3 parts by weight of isocyanate thickener and 0.5 to 1 part by weight of lithium chloride.

[0006] The edges of the two layers of carrier films are sealed to seal the resin material between the two layers of carrier films. The carrier film is a composite film of nylon and polyethylene.

[0007] The model of the magnesium oxide is RA-40; the isocyanate thickener is toluene diisocyanate.

[0008] The model of the unsaturated polyester resin is PS-H1168; the low shrinkage agent is a polyvinyl acetate solution with a solid content of 35-40%, and the solvent of the polyvinyl acetate solution is styrene; the water absorbent is anhydrous magnesium sulfate; the inhibitor is 2,6-di-tert-butyl-p-cresol; and the curing agent is tert-butyl peroxybenzoate.

[0009] The sheet molding compound further comprises 1 to 3 parts by weight of a release agent, wherein the release agent is zinc stearate.

[0010] The water content of the calcium carbonate is 0.1% to 0.15%, and the particle size of the calcium carbonate is 1 to 2 μm.

[0011] A technical solution proposed by the present invention to solve the above technical problems is: a method for preparing a sheet molding compound, comprising the following steps:

[0012] A. Mix 60-70 parts by weight of unsaturated polyester resin and 30-40 parts by weight of low shrinkage agent;

[0013] B. Then add 130-180 parts by weight of calcium carbonate, 1-5 parts by weight of water absorbent, and 0.1-0.3 parts by weight of polymerization inhibitor while stirring;

[0014] C. Add 1 to 3 parts by weight of curing agent and stir to obtain resin paste;

[0015] D. Add 4.5 to 9 parts by weight of a composite thickener into the resin paste, and then soak 50 to 120 parts by weight of glass fiber into the resin paste;

[0016] E. Place the resin paste between two layers of carrier films, which are nylon and polyethylene composite films, and then perform edge sealing to seal the resin paste between the two layers of carrier films, and then perform aging at a temperature of 50°C to 70°C for 1 to 1.5 hours, and then cool to room temperature;

[0017] F. Press the matured sheet molding compound into shape.

[0018] The stirring speed in the above steps A, B and C is 800-1200 r / min, and the stirring time is 3-5 min.

[0019] In the above step D, an SMC molding unit is used to continuously produce sheet molding compound. The vehicle speed is set to 8m / min before the SMC molding unit, the resin paste base liquid flow rate reaches 20.86kg / min, the thickener flow rate reaches 0.42kg / min, and the glass fiber cutting roller speed is 66rpm.

[0020] The upper mold temperature of the press molding in the above step F is 125℃~135℃, the lower mold temperature is 120℃~130℃, and the pressure is 1000T / m2 , holding time 3min.

[0021] The present invention has positive effects:

[0022] (1) The sheet molding compound of the present invention can make the resin thicken more quickly by adjusting the ratio of the resin components, especially by using a composite thickener with specific components. The resin material becomes processable only after thickening and hardening, which can greatly shorten the curing time of the sheet molding compound to only about 1 hour, while the traditional curing time requires 24 hours or even longer. At the same time, the produced sheet molding compound has excellent mechanical properties.

[0023] (2) The sheet molding compound of the present invention uses an isocyanate thickener, lithium chloride and magnesium oxide in combination. The addition of lithium chloride can prevent the isocyanate thickener from undergoing a decarboxylation reaction with the carboxyl group in the unsaturated resin during the thickening process, so that the isocyanate thickener reacts preferentially with the hydroxyl group in the unsaturated resin to thicken, while the magnesium oxide and the carboxyl group in the unsaturated polyester resin are thickened, which greatly accelerates the later thickening of the entire system, thereby greatly shortening the aging time of the sheet molding compound and improving the production efficiency of the sheet molding compound.

[0024] (3) The sheet molding compound of the present invention uses a nylon + polyethylene composite film carrier film, so that the SMC can be quickly heated and matured and then quickly cooled to 25°C, thereby realizing efficient continuous production of SMC. The nylon + polyethylene composite film material can prevent styrene penetration. At the same time, the upper and lower carrier films of the SMC are edge-sealed online with a hot stamping machine to prevent styrene from volatilizing from both sides. Traditional PP film basically does not prevent styrene penetration, so SMC using traditional PP film outer packaging also needs to be sealed with a layer of aluminized film. However, the nylon + polyethylene composite film of the present invention combined with the edge sealing treatment technology does not need to be packaged with aluminized film. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a curve diagram showing the effect of magnesium oxide dosage on early thickening in an embodiment of the present invention;

[0026] Figure 2 is a curve diagram showing the effect of magnesium oxide dosage on late thickening in an embodiment of the present invention;

[0027] Figure 3 This is a comparison chart of thickening performance of different active magnesium oxides in the embodiments of the present invention;

[0028] Figure 4 is a thickening performance verification curve diagram of resins with different acid values ​​according to an embodiment of the present invention;

[0029] Figure 5 is a curve diagram showing the effects of different shrinkage agents on thickening performance according to an embodiment of the present invention;

[0030] Figure 6 7 is a graph showing a change in water content of calcium carbonate according to an embodiment of the present invention;

[0031] Figure 7 is a comparison chart of thickening performance of calcium carbonate before and after drying according to an embodiment of the present invention;

[0032] Figure 8 This is a graph verifying the effect of the composite thickener according to an embodiment of the present invention;

[0033] Fig. 9 is a graph showing the effect of temperature on the composite thickener according to an embodiment of the present invention;

[0034] Fig.10 It is a curve chart of the temperature and SMC storage stability study of the embodiment of the present invention;

[0035] Fig.11 This is a diagram showing the anti-permeation effect of the carrier film of an embodiment of the present invention on styrene;

[0036] Fig.12 : is a graph showing the effect of the polymerization inhibitor of an embodiment of the present invention on the storage performance stability of SMC;

[0037] Fig.13 : is a graph showing the effect of the curing agent of an embodiment of the present invention on the storage stability of SMC;

[0038] Fig.14 This is a comparison chart of the rapid heating and thickening of the traditional ton packaging and the continuously produced single-layer material in the embodiment of the present invention;

[0039] Fig.15 This is a comparison chart of the rapid cooling and thickening of the traditional ton packaging and the continuously produced single-layer material in the embodiment of the present invention;

[0040] Fig.16 is a comparison chart of the tensile strength of the sheet molding compound of the embodiment of the present invention and the conventional sheet molding compound;

[0041] Fig.17 4 is a comparison chart of the bending strength of the sheet molding compound according to the embodiment of the present invention and the conventional sheet molding compound. DETAILED DESCRIPTION Example 1

[0042] The sheet molding compound of this embodiment includes the following components in parts by weight: 60 parts by weight of unsaturated polyester resin, 30 parts by weight of low shrinkage agent, 130 parts by weight of calcium carbonate, 4.5 parts by weight of composite thickener, 50 parts by weight of glass fiber and 1 part by weight of curing agent; the composite thickener includes 3 parts by weight of magnesium oxide, 1 part by weight of isocyanate thickener and 0.5 part by weight of lithium chloride.

[0043] The preparation method of the sheet molding compound comprises the following steps:

[0044] A. Mix 60 parts by weight of unsaturated polyester resin and 30 parts by weight of low shrinkage agent;

[0045] B. Then add 130 parts by weight of calcium carbonate powder while stirring and continue stirring;

[0046] C. Add 1 part by weight of curing agent and stir to obtain resin paste;

[0047] D. Add 4.5 parts by weight of thickener into the resin paste, and then soak 50 parts by weight of glass fiber into the resin paste to make a semi-finished SMC sheet molding compound;

[0048] In step D, an SMC molding unit is used to continuously produce SMC sheet molding compound. The vehicle speed is set to 8 m / min before the SMC molding unit, the resin paste base liquid flow rate reaches 20.86 kg / min, the thickener flow rate reaches 0.42 kg / min, and the glass fiber cutting roller speed is 66 rpm.

[0049] E. Place the SMC sheet molding compound semi-finished product between two layers of carrier films, the carrier films are made of nylon + polyethylene composite films, then perform edge sealing, and then perform aging at a aging temperature of 50°C;

[0050] F. Cool the matured SMC sheet molding compound and press it into shape. The upper mold temperature is 125℃, the lower mold temperature is 120℃, and the pressure is 1000T / m 2 , holding time 3min.

[0051] The unsaturated polyester resin is PS-H1168, the low shrinkage agent is polyvinyl acetate solution, the magnesium oxide model is RA-40, the isocyanate thickener is toluene diisocyanate, and the curing agent is tert-butyl peroxybenzoate. Example 2

[0052] The sheet molding compound of this embodiment includes the following components by weight: 65 parts by weight of unsaturated polyester resin, 35 parts by weight of low shrinkage agent, 150 parts by weight of calcium carbonate, 6 parts by weight of composite thickener, 100 parts by weight of glass fiber and 2 parts by weight of curing agent;

[0053] The composite thickener comprises 4 parts by weight of magnesium oxide, 2 parts by weight of isocyanate thickener and 0.8 parts by weight of lithium chloride.

[0054] The preparation method of the sheet molding compound comprises the following steps:

[0055] A. Mix 65 parts by weight of unsaturated polyester resin and 35 parts by weight of low shrinkage agent;

[0056] B. Then add 150 parts by weight of calcium carbonate powder while stirring and continue stirring;

[0057] C. Add 2 parts by weight of curing agent and stir to obtain resin paste;

[0058] D. Add 6 parts by weight of thickener into the resin paste, and then soak 100 parts by weight of glass fiber into the resin paste to make a semi-finished SMC sheet molding compound;

[0059] In step D, an SMC molding unit is used to continuously produce SMC sheet molding compound. The vehicle speed is set to 8 m / min before the SMC molding unit, the resin paste base liquid flow rate reaches 20.86 kg / min, the thickener flow rate reaches 0.42 kg / min, and the glass fiber cutting roller speed is 66 rpm.

[0060] E. Place the SMC sheet molding compound semi-finished product between two layers of carrier films, the carrier films are made of nylon + polyethylene composite films, then perform edge sealing, and then perform aging at a aging temperature of 60°C;

[0061] F. Cool the matured SMC sheet molding compound and press it into shape. The upper mold temperature is 130℃, the lower mold temperature is 125℃, and the pressure is 1000T / m 2 , holding time 3min.

[0062] The unsaturated polyester resin is PS-H1168, the low shrinkage agent is polyvinyl acetate solution, the magnesium oxide model is RA-40, the isocyanate thickener is toluene diisocyanate, and the curing agent is tert-butyl peroxybenzoate. Example 3

[0063] The sheet molding compound of this embodiment includes the following components in parts by weight:

[0064] 70 parts by weight of unsaturated polyester resin, 40 parts by weight of low shrinkage agent, 180 parts by weight of calcium carbonate, 9 parts by weight of composite thickener, 120 parts by weight of glass fiber and 3 parts by weight of curing agent;

[0065] The composite thickener comprises 5 parts by weight of magnesium oxide, 3 parts by weight of isocyanate thickener and 1 part by weight of lithium chloride.

[0066] The preparation method of the sheet molding compound comprises the following steps:

[0067] A. Mix 70 parts by weight of unsaturated polyester resin and 40 parts by weight of low shrinkage agent;

[0068] B. Then add 180 parts by weight of calcium carbonate powder while stirring and continue stirring;

[0069] C. Add 3 parts by weight of curing agent and stir to obtain resin paste;

[0070] D. Add 9 parts by weight of thickener into the resin paste, and then soak 120 parts by weight of glass fiber into the resin paste to make a semi-finished SMC sheet molding compound;

[0071] In step D, an SMC molding unit is used to continuously produce SMC sheet molding compound. The vehicle speed is set to 8 m / min before the SMC molding unit, the resin paste base liquid flow rate reaches 20.86 kg / min, the thickener flow rate reaches 0.42 kg / min, and the glass fiber cutting roller speed is 66 rpm.

[0072] E. Place the SMC sheet molding compound semi-finished product between two layers of carrier films, the carrier films are made of nylon + polyethylene composite films, then perform edge sealing, and then perform aging at a aging temperature of 70°C;

[0073] F. Cool the matured SMC sheet molding compound and press it into shape. The upper mold temperature is 135℃, the lower mold temperature is 130℃, and the pressure is 1000T / m 2 , holding time 3min.

[0074] The unsaturated polyester resin is PS-H1168, the low shrinkage agent is polyvinyl acetate solution, the magnesium oxide model is RA-40, the isocyanate thickener is toluene diisocyanate, and the curing agent is tert-butyl peroxybenzoate. Example 4

[0075] The sheet molding compound of this embodiment includes the following components in parts by weight: 70 parts by weight of unsaturated polyester resin, 40 parts by weight of low shrinkage agent, 180 parts by weight of calcium carbonate, 9 parts by weight of composite thickener, 120 parts by weight of glass fiber, 3 parts by weight of curing agent, 1 to 3 parts by weight of water absorbent, 0.1 to 0.3 parts by weight of polymerization inhibitor and 1 to 3 parts by weight of release agent;

[0076] The composite thickener comprises 5 parts by weight of magnesium oxide, 3 parts by weight of isocyanate thickener and 1 part by weight of lithium chloride.

[0077] The preparation method of the sheet molding compound comprises the following steps:

[0078] A. Mix 70 parts by weight of unsaturated polyester resin and 40 parts by weight of low shrinkage agent;

[0079] B. Then, add 180 parts by weight of calcium carbonate powder while stirring and continue stirring, wherein the water content of the calcium carbonate is 0.1%, and in other embodiments, the water content may be 0.12%;

[0080] C. Add 3 parts by weight of curing agent and stir to obtain resin paste;

[0081] D. Add 9 parts by weight of thickener, 1-3 parts by weight of water absorbent, 0.1-0.3 parts by weight of polymerization inhibitor and 1-3 parts by weight of release agent to the resin paste. In other embodiments, polymerization inhibitor may also be added. Then, 120 parts by weight of glass fiber is impregnated in the resin paste to prepare a semi-finished SMC sheet molding compound.

[0082] In step D, an SMC molding unit is used to continuously produce SMC sheet molding compound. The vehicle speed is set to 8 m / min before the SMC molding unit, the resin paste base liquid flow rate reaches 20.86 kg / min, the thickener flow rate reaches 0.42 kg / min, and the glass fiber cutting roller speed is 66 rpm.

[0083] E. Place the SMC sheet molding compound semi-finished product between two layers of carrier films, the carrier films are made of nylon + polyethylene composite films, then perform edge sealing, and then perform aging at a aging temperature of 70°C;

[0084] F. Cool the matured SMC sheet molding compound and press it into shape. The upper mold temperature is 135℃, the lower mold temperature is 130℃, and the pressure is 1000T / m 2 , holding time 3min.

[0085] The unsaturated polyester resin is PS-H1168, the low shrinkage agent is polyvinyl acetate solution, the magnesium oxide model is RA-40, the isocyanate thickener is toluene diisocyanate, the curing agent is tert-butyl perbenzoate, the water absorbent is anhydrous magnesium sulfate, and the inhibitor is 2,6-di-tert-butyl-p-cresol.

[0086] The following is the effect verification experiment of the present invention:

[0087] 1. How to effectively shorten the curing time of SMC

[0088] 1.1 Effect of the dosage of thickener magnesium oxide on early thickening and late thickening

[0089] Test method for the effect of early thickening: 60 parts of resin, 40 parts of polyvinyl acetate solution, 150 parts of calcium carbonate, 1%-3% MgO, 800phr, stir for 5 minutes, and then use a Brookfield viscometer to continuously test the viscosity of the resin paste at a constant temperature of 25℃. Read the reading every 10 minutes and plot Figure 1 curve.

[0090] Test method for late thickening effect: 60 parts of resin, 40 parts of polyvinyl acetate solution, 150 parts of calcium carbonate, 1%-3% MgO, 800phr, stir for 5 minutes, then thicken in a 50℃ oven, take out a cup of sample every 5 hours, keep it in a 25℃ water bath for 30 minutes, then test the viscosity with a Brookfield viscometer, and plot Figure 2 curve.

[0091] like Figure 3 As shown in the figure, it is the effect of magnesium oxide dosage on the later thickening. From the curve, it can be seen that when the magnesium oxide dosage increases to 3%, the later thickening is significantly improved, but the early thickening is Figure 2 As shown in the figure, the viscosity has reached 10000 mNylon·s after 30 minutes, which is the upper limit of glass fiber impregnation. If the dosage is further increased to 2% and 3%, the viscosity will increase significantly and cannot meet the requirement of fully impregnating the glass fiber. Therefore, simply increasing the dosage of thickener cannot achieve the desired effect.

[0092] The thickening performance of different active magnesium oxides was compared and verified. The test method was as follows: 60 parts of resin, 40 parts of polyvinyl acetate solution, 150 parts of calcium carbonate, 1% MgO, 800phr, stirred for 5 minutes, and then thickened in a 50°C oven. One cup of sample was taken out every 5 hours, and the viscosity was tested with a Brookfield viscometer after being kept in a constant temperature water bath at 25°C for 30 minutes.

[0093] like Figure 4 As shown, RA-40 magnesium oxide has the best thickening performance.

[0094] 1.2 Resin selection

[0095] Test method: 60 parts of resin, 40 parts of polyvinyl acetate solution, 150 parts of calcium carbonate, 3% MgO, 800phr, stir for 5 minutes and then thicken in a 50℃ oven. Take out one cup of sample every 5 hours, keep it in a constant temperature water bath at 25℃ for 30 minutes and then test the viscosity with a Brookfield viscometer.

[0096] like Figure 5 As shown, the thickening properties of unsaturated polyester resins with different acid values ​​are compared. Among them, PS-H1168 with the largest acid value has the best later thickening performance. The reason is that the thickening mechanism is the complexation reaction of magnesium oxide and carboxyl, and PS-H1168 has the highest acid value, which makes it have the best thickening performance.

[0097] 1.3 Selection of low shrinkage agent

[0098] Test method: 60 parts of resin, 40 parts of different low shrinkage agents, 150 parts of calcium carbonate, 2% MgO, 800phr, stirred for 5 minutes and then thickened in a 50℃ oven. Take out one cup of sample every 5 hours, keep it in a constant temperature water bath at 25℃ for 30 minutes, and then test the viscosity with a Brookfield viscometer.

[0099] like Figure 6 As shown in the figure, using polyvinyl acetate as a low shrinkage agent, compared with PS and saturated low shrinkage agents, polyvinyl acetate can greatly promote the thickening performance of SMC due to its unique carboxyl group.

[0100] 1.4 Effect of calcium carbonate

[0101] Calcium carbonate is dried at 50℃ for 24h before use. The moisture change curve is as follows Figure 7 As shown, the thickening performance of the calcium carbonate after drying and the calcium carbonate before drying is compared, and the results are as follows Figure 8 As shown in the figure, dried calcium carbonate can greatly promote the thickening performance of SMC. The reason is that moisture will accelerate the early thickening of unsaturated resin and magnesium oxide, which is not conducive to the infiltration of glass fiber. Moisture will reduce the later thickening performance and affect the thickening of SMC.

[0102] 1.5 Effect of composite thickener

[0103] Lithium chloride and toluene diisocyanate (TDI) are used in combination with MgO, with a total dosage of 2% of the entire system, where TDI:MgO:LiCl=2:2:1. Fig. 9 As shown, LiCl is an inorganic salt with extremely strong water absorption, which absorbs water molecules in the resin system to improve the thickening performance. Isocyanate thickener TDI reacts with hydroxyl groups first during the thickening process, but it cannot be excessive, otherwise it will react with the carboxyl groups in the unsaturated resin to undergo decarboxylation, especially in the presence of water. Therefore, in addition to the above effects, the addition of LiCl can also prevent the occurrence of decarboxylation. TDI and the hydroxyl groups in the unsaturated polyester resin thicken, while magnesium oxide and the carboxyl groups in the unsaturated polyester resin thicken, which greatly accelerates the later thickening of the entire system. Therefore, using MgO+LiCl+TDI as a composite thickener can greatly promote the thickening performance of SMC compared to MgO+LiCl, and MgO as a thickener.

[0104] 1.6 Effect of aging temperature

[0105] like Fig.10 As shown in the figure, when the aging temperature is increased to 70℃, the thickening time can be shortened to 1h, and the late thickening viscosity can reach 44*10 6 mpa·s, which meets the use requirements of SMC. If the aging temperature continues to increase to 80℃, the thickening performance will be further accelerated, but 80℃ will cause the curing time of SMC to decay, affecting the use performance and life. Fig.10 As shown in the figure, there is an obvious attenuation process after 5 hours, so it is more appropriate to control the thickening temperature within 70℃.

[0106] 1.7 Choice of carrier film

[0107] Test method: Take about 100g of SMC of PP carrier film and nylon / polyethylene carrier film respectively, put them in a 50℃ oven, take out the remaining SMC weight every 12h, and record the curve as follows: Fig.11 .

[0108] from Fig.11 It can be seen that the nylon / polyethylene carrier film is used to prevent styrene penetration. At the same time, the upper and lower carrier films of SMC are sealed online with a hot stamping machine to prevent styrene from volatilizing from both sides. The effects of traditional PP film and nylon / polyethylene film on styrene penetration at 50°C are as follows. Traditional PP film basically does not prevent styrene penetration, so SMC using traditional PP film outer packaging needs to be sealed with a layer of aluminized film, while nylon / polyethylene film combined with edge sealing technology does not need to be packaged with aluminized film.

[0109] 2. How to ensure the stability of materials during high temperature aging

[0110] 2.1 Inhibitors can improve product stability

[0111] like Fig.12 As shown, adding 2,6-di-tert-butyl-p-cresol inhibitor prevents the inhibitor from decaying during the high-temperature aging process, which leads to a decrease in product stability. The effect of adding 0.1% and 0.3% is the same, so adding 0.1% is sufficient.

[0112] 2.2 Curing agent can improve product stability

[0113] like Fig.13 As shown in the figure, the attenuation of TBPB and TG-05 curing agents is more obvious, while TG-01 has almost no attenuation within 20 hours, so TG-01 curing agent is more stable.

[0114] 3. How to achieve rapid heating of SMC

[0115] In traditional ton packaging, SMC is stacked together, and the outer packaging is insulated by aluminized film and carton, so the heat transfer efficiency is very slow. Fig.14 As shown in the figure, the temperature of the materials in the traditional ton packaging box slowly rises to about 42°C after being placed in a 50°C drying room for 10 hours, while the temperature of a single SMC piece can be quickly raised to 45°C within 1 hour in a 50°C drying room.

[0116] 4. How to achieve rapid cooling of SMC

[0117] like Fig.15 As shown in the figure, like the heating curve, the traditional ton packaging cools down very slowly. Under the constant temperature condition of 25℃, the temperature of the material just out of the drying room drops from 45℃ to 39℃ after cooling for 5 hours, while the temperature of the single-piece material can drop to 30℃ within 10 minutes and can be fully cooled to 25℃ in 25 minutes.

[0118] 5. Mechanical properties verification

[0119] Test method: The rapid thickening material prepared by the method of the present invention is tested for tensile strength, bending strength and impact strength against conventional materials currently on the market that use magnesium oxide as a thickener.

[0120] 5.1 Tensile strength test

[0121] Table 1 Tensile strength test data

[0122]

[0123] from Fig.16 It can be seen from the curve that the rapid thickening material prepared by the method of the present invention has a tensile strength comparable to that of conventional materials on the market.

[0124] 5.2 Bending strength test

[0125] Table 2 Bending strength test data

[0126]

[0127] from Fig.17 It can be seen from the curve that the flexural strength of the rapid thickening material prepared by the method of the present invention is comparable to that of conventional materials on the market.

[0128] 5.3 Impact strength

[0129] Table 3 Impact strength test data

[0130]

[0131] The above mechanical properties test results show that the performance of the rapid thickening material is comparable to that of conventional SMC.

Claims

1. A sheet molding compound, comprising two upper and lower carrier films and a resin material located between the two carrier films, characterized in that: The resin material comprises the following components: 60-70 parts by weight of unsaturated polyester resin, 30-40 parts by weight of low shrinkage agent, 130-180 parts by weight of calcium carbonate, 1-5 parts by weight of water absorbent, 0.1-0.3 parts by weight of polymerization inhibitor, 4.5-9 parts by weight of composite thickener, 50-120 parts by weight of glass fiber and 1-3 parts by weight of curing agent; the composite thickener comprises 3-5 parts by weight of magnesium oxide, 1-3 parts by weight of isocyanate thickener and 0.5-1 parts by weight of lithium chloride.

2. The sheet molding compound according to claim 1, characterized in that The edges of the two layers of carrier films are sealed to seal the resin material between the two layers of carrier films. The carrier film is a composite film of nylon and polyethylene.

3. The sheet molding compound according to claim 1, characterized in that The model of the magnesium oxide is RA-40; the isocyanate thickener is toluene diisocyanate.

4. The sheet molding compound according to claim 1, characterized in that The model of the unsaturated polyester resin is PS-H1168; the low shrinkage agent is a polyvinyl acetate solution with a solid content of 35-40%, and the solvent of the polyvinyl acetate solution is styrene; the water absorbent is anhydrous magnesium sulfate; the inhibitor is 2,6-di-tert-butyl-p-cresol; and the curing agent is tert-butyl peroxybenzoate.

5. The sheet molding compound according to any one of claims 1 to 4, characterized in that: The invention also comprises 1 to 3 parts by weight of a release agent, wherein the release agent is zinc stearate.

6. The sheet molding compound according to any one of claims 1 to 4, characterized in that: The water content of the calcium carbonate is 0.1% to 0.15%, and the particle size of the calcium carbonate is 1 to 2 μm.

7. A method for preparing a sheet molding compound, characterized in that: The following steps are involved: A. Mix 60-70 parts by weight of unsaturated polyester resin and 30-40 parts by weight of low shrinkage agent; B. Then add 130-180 parts by weight of calcium carbonate, 1-5 parts by weight of water absorbent, and 0.1-0.3 parts by weight of polymerization inhibitor while stirring; C. Add 1 to 3 parts by weight of curing agent and stir to obtain resin paste; D. Add 4.5 to 9 parts by weight of a composite thickener to the resin paste, and then soak 50 to 120 parts by weight of glass fiber in the resin paste, wherein the composite thickener includes 3 to 5 parts by weight of magnesium oxide, 1 to 3 parts by weight of an isocyanate thickener, and 0.5 to 1 part by weight of lithium chloride; E. Place the resin paste between two layers of carrier films, which are nylon and polyethylene composite films, and then perform edge sealing to seal the resin paste between the two layers of carrier films, and then perform aging at a temperature of 50°C to 70°C for 1 to 1.5 hours, and then cool to room temperature; F. Press the matured sheet molding compound into shape.

8. The method for preparing a sheet molding compound according to claim 7, characterized in that: The stirring speed in steps A, B and C is 800-1200 r / min, and the stirring time is 3-5 min.

9. The method for preparing a sheet molding compound according to claim 7, characterized in that: In the step D, an SMC molding unit is used to continuously produce sheet molding compound. The vehicle speed is set to 8 m / min before the SMC molding unit, the resin paste base liquid flow rate reaches 20.86 kg / min, the thickener flow rate reaches 0.42 kg / min, and the glass fiber cutting roller speed is 66 rpm.

10. The method for preparing a sheet molding compound according to claim 7, characterized in that: The upper mold temperature of the compression molding in step F is 125°C to 135°C, the lower mold temperature is 120°C to 130°C, and the pressure is 1000T / m 2 , holding time 3min.

Images