EPP (Expanded Polypropylene) molding method and device

Abstract

The invention relates to the technical field of molding, in particular to an EPP molding method and device, and the EPP molding method comprises the following steps: S1, spraying a reinforcing solution in a mold cavity; s2, the mold cavity is filled with EPP beads, and the mold is closed; s3, heating is conducted; and S4, cooling and shaping, and opening the mold to obtain an EPP molded product. According to the EPP molding method provided by the invention, the step of spraying the reinforcing solution in advance is set, so that the surface hardness and the bearing capacity of an EPP molded product are improved on the premise of not increasing steam molding energy consumption and not increasing the weight of the product, and therefore, the use strength of the EPP molded product is improved, and the service life of the EPP molded product is prolonged.

Description

Technical Field

[0001] This invention relates to the field of molding technology, and more particularly to an EPP molding method and apparatus. Background Technology

[0002] Polypropylene foam (EPP) is widely used in the automotive and packaging industries due to its lightweight, environmentally friendly, and shock-resistant properties.

[0003] Compared to conventional EPS and EPO products, EPP products have significant advantages in terms of environmental friendliness. However, in terms of product strength, EPP products of the same density have lower rigidity than EPO and EPS, and their overall production cost is also higher than that of EPO and EPS. Although EPP has its own advantages in terms of temperature resistance (above 120℃) and elastic modulus, it still cannot be used to replace EPO / EPS materials on a large scale in structural components, which greatly limits the large-scale promotion of EPP materials in the market.

[0004] Therefore, improving the strength of EPP products is a pressing technical problem that needs to be solved. Summary of the Invention

[0005] To address the issue of low strength in existing EPP products, this invention provides an EPP molding method that can directly reinforce EPP molded parts, thereby improving the surface hardness and load-bearing capacity of the product and solving the problem of low strength in existing EPP products.

[0006] The technical solution adopted by this invention to solve its technical problem is: An EPP molding method includes the following steps: S1: Spray reinforcing solution into the mold cavity; S2: Fill the mold cavity with EPP beads and close the mold; S3: Heating; S4: Cool and solidify, open the mold, and obtain the EPP molded product.

[0007] Optionally, the enhancing solution is a silane coupling agent alcohol solution.

[0008] Optionally, the reinforcing solution may also include reinforcing fibers.

[0009] Optionally, the reinforcing fiber is selected from at least one of glass fiber and carbon fiber.

[0010] Optionally, the amount of alcohol added to the enhanced solution is 100 parts by weight, and the amount of silane coupling agent added is 5-15 parts.

[0011] Optionally, the amount of reinforcing fiber added to the reinforcing solution is 40-60 parts by weight.

[0012] Optionally, the heating process in step S3 includes: introducing steam into the mold cavity through a steam pipe for preliminary heating and sintering; then raising the temperature of the outside of the mold to 170-180°C for plasticizing the molding surface, and then cooling the outside of the mold to 40-50°C for heat preservation.

[0013] Optionally, the steam pressure during the initial heating and sintering process is 0.3-0.8 bar, and the heating time is 8-12 seconds.

[0014] Optionally, the plasticizing heating time of the molding surface is 2-5 seconds; after cooling the outside of the mold to 40-50°C, the holding time is 100-180 seconds.

[0015] Another object of the present invention is to provide an EPP molding apparatus for molding using the EPP molding method described above; the EPP molding apparatus includes a mold, a steam heating unit, and a heat transfer oil heating unit; wherein, The mold includes a mold cavity; The steam heating unit is connected to the mold cavity; The heat transfer oil heating unit is connected to the mold.

[0016] Optionally, the heat transfer oil heating unit includes an oil storage tank, a heat transfer oil heater, and an oil pipeline; the oil storage tank is located on the outside of the mold, and the oil storage tank is connected to the heat transfer oil heater through the oil pipeline.

[0017] The beneficial effects of this invention are: The EPP molding method provided by this invention improves the surface hardness and load-bearing capacity of EPP molded products by setting a step of pre-spraying a reinforcing solution, without increasing the energy consumption of steam molding or the weight of the product. This enhances the strength of EPP molded products and extends their service life. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] Figure 1 This is a schematic diagram of the EPP molding apparatus in this invention. Figure 1 ; Figure 2 This is a schematic diagram of the EPP molding apparatus in this invention. Figure 2 .

[0020] In the diagram: 1-Mold; 11-Mold cavity; 12-Die; 13-Punch; 2-Steam heating unit; 21-Inlet pipe; 22-Exhaust pipe; 3-Heat transfer oil heating unit; 31-Oil reservoir; 311-Die oil reservoir; 312-Punch oil reservoir; 32-Heat transfer oil heater; 321-Die heat transfer oil heater; 322-Punch heat transfer oil heater; 33-Oil circuit; 331-Die oil circuit; 332-Punch oil circuit; 4-Product ejector; 5-Hydraulic ejector rod. Detailed Implementation

[0021] The present invention will now be described in further detail. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0022] To address the problem of low strength in existing EPP products, this invention provides an EPP molding method, which includes the following steps: S1: Spray reinforcing solution into the mold cavity; Specifically, the preferred spray thickness of the enhanced solution is 0.01-0.05 mm; S2: Fill the mold cavity sprayed with the reinforcing solution into the EPP beads, and close the mold; In this preferred step, the mold is closed, leaving a mold gap of no more than 2mm. The pre-pressed EPP beads are then filled into the mold cavity through a material gun, and the mold is closed. S3: Heating; S4: Cool and solidify, open the mold, and obtain the EPP molded product; Preferably, this step involves drying in an oven at 70-80℃, followed by baking and shaping, and then cooling for 2 hours before removing from the oven and packaging. After the product inside the mold has cooled and solidified, the mold is opened to obtain the desired surface-reinforced EPP molded product.

[0023] By repeating the above steps, the desired reinforced EPP products can be obtained continuously.

[0024] Currently, there are two main ways to improve the strength of EPP molded parts. The first is to increase the modulus of the EPP material itself, thereby increasing the overall strength of the product. However, this has a significant drawback: it increases energy consumption in steam molding, thus increasing costs. The second method is to reinforce the EPP parts by adding a composite skeleton inside the molded product. The introduction of the skeleton significantly improves the overall bending resistance of the product, but it also greatly increases the weight and cost of use, which hinders its large-scale promotion.

[0025] Based on this, the present invention strengthens the EPP molded part by uniformly spraying a reinforcing solution into the mold cavity before the molding process begins, without changing the EPP material itself or the internal composite skeleton of the molded product. This directly improves the surface hardness and load-bearing capacity of the product, thereby enhancing its surface strength.

[0026] The EPP molding method provided by this invention improves the surface hardness and load-bearing capacity of EPP molded products by setting a step of pre-spraying a reinforcing solution, without increasing the energy consumption of steam molding or the weight of the product. This enhances the strength of EPP molded products and extends their service life.

[0027] Specifically, the present invention preferably uses a silane coupling agent alcohol solution, that is, the solvent of the enhancement solution is an alcohol, and more preferably glycerol; the solute of the enhancement solution is a silane coupling agent, and more preferably KH-570.

[0028] To further improve the surface strength of the molded product, the present invention preferably includes reinforcing fibers in the reinforcing solution, and more preferably the reinforcing fibers are selected from at least one of glass fiber and carbon fiber, preferably the glass fiber has a length of 5-10 μm, and preferably the carbon fiber has a length of 5-10 μm.

[0029] By spraying this reinforcing solution during the steam molding process, the hydroxyl end of the fiber is adsorbed by hydrogen bonds through the coupling of the silane coupling agent, and the alkyl segment is fixed on the polypropylene chain segment through molecular chain entanglement, thereby making the fiber bond more tightly to the polypropylene.

[0030] In a further preferred embodiment of the present invention, the amount of alcohol added to the reinforcing solution is 100 parts by weight, the amount of silane coupling agent added is 5-15 parts, and the amount of reinforcing fiber added is 40-60 parts.

[0031] To further improve the performance of the molded products, the heating process in step S3 of this invention preferably includes: introducing steam into the mold cavity through a steam pipe for preliminary heating and sintering; then raising the temperature of the outside of the mold to 170-180°C for plasticizing and heating the molding surface, and then cooling the outside of the mold to 40-50°C for heat preservation.

[0032] In this step, steam is first introduced into the mold cavity through the corresponding steam pipe via the air plug (at this time, the lower exhaust pipe is in a half-open state) for preliminary heating and sintering; the oil storage tank is preheated simultaneously, so that the external temperature of the mold can be rapidly raised to 170-180℃ (preferably in 10 seconds). Then, the upper steam inlet and the lower exhaust outlet are closed, and the plasticizing heating of the molding surface is carried out (plasticizing time 3-8 seconds). The external temperature of the mold is then reduced to 40-50℃ and kept warm.

[0033] This invention heats the exterior of the mold, and in this step, the temperature is rapidly raised to 170-180°C. Through a short period of high-temperature treatment, the outer surface of the EPP molded part is plasticized, thereby forming a fiber / polypropylene plasticized layer and improving the surface hardness of the product.

[0034] Specifically, the steam pressure during the initial heating and sintering process is preferably 0.3-0.8 bar, and the heating time is 8-12 s; the plasticizing heating time of the molding surface is preferably 2-5 s; after cooling the outside of the mold to 40-50°C, the holding time is 100-180 s.

[0035] Compared to traditional EPP production, this molding method can directly reinforce EPP molded parts, improving the surface hardness and load-bearing capacity of the product (for a length of 30cm, width of 10cm, and thickness of 2cm, the deformation under load must not exceed 0.5cm). This molding method can cover all EPP ratios (10-200g / L), especially for low-density products. EPP molded products produced using this process show significant improvements in strength and lifespan. Furthermore, EPP molded products produced using this process exhibit improved performance in terms of stacking indentation and water resistance.

[0036] Another object of the present invention is to provide an EPP molding apparatus for molding by means of the EPP molding method described above; see also Figure 1 , Figure 2As shown, the EPP molding apparatus includes a mold 1, a steam heating unit 2, and a heat transfer oil heating unit 3; wherein, the mold 1 is used for molding and shaping of the molded product, and the mold 1 includes a mold cavity 11; preferably, the mold 1 includes a concave mold 12 and a convex mold 13 adapted to the concave mold 12, and the mold cavity 11 is disposed within the concave mold 12; preferably, both the concave mold 12 and the convex mold 13 are made of aluminum plate, and the thickness of the aluminum plate in both the concave mold 12 and the convex mold 13 is 0.5-1cm; the inner wall of the concave mold 12... The outer surface of the punch 13 is coated with Teflon (0.005-0.01mm thick to prevent the product from adhering to the mold 1 during molding). The outer wall of the punch 13 is also coated with Teflon (0.005-0.01mm thick to prevent the product from adhering to the mold during molding). This coating is used for heat conduction and molding of the product during molding. Specifically, the punch 13 moves towards the cavity 12 within the cavity 12 to achieve mold closing. Conversely, the punch 13 moves away from the cavity 12 within the cavity 12 to achieve mold opening.

[0037] To facilitate the smooth operation of the molding process, the EPP molding apparatus provided by this invention also includes a product feed gun 4 connected to the die 12, which is used for the entry of raw materials during product molding and the sealing of the feed pipe during heating.

[0038] Furthermore, the present invention preferably includes a hydraulic ejector rod 5 connected to the punch 13 for controlling the closing and opening of the mold 1. In order to prevent steam leakage during heating, the contact position of the mold 1 is sealed with a rubber sealing ring.

[0039] To improve structural stability, the EPP molding apparatus also includes a mold frame (not shown in the figure) for fixing the mold.

[0040] The steam heating unit 2 in this invention is connected to the mold cavity 11 and is used to deliver steam to the mold cavity 11 during molding heating to achieve preliminary heating and sintering of the product. Specifically, the steam heating unit 2 includes an air inlet pipe 21 and an exhaust pipe 22. The air inlet pipe 21 is used for the entry of steam during molding heating and the preliminary heating and sintering of the product, and is connected to the upper part of the mold cavity 12. The exhaust pipe 22 is used for the discharge of steam during molding heating and is connected to the lower part of the mold cavity 12. Both the air inlet pipe 21 and the exhaust pipe 22 are connected to the mold cavity 11.

[0041] In this invention, both the air inlet pipe 21 and the air outlet pipe 22 are preferably connected to the mold cavity 11 through pinhole air plugs, and the diameter of the pinhole air plugs is preferably 0.02-0.04 mm, which are used for the introduction and flow of steam during molding to generate thermal circulation during the molding process.

[0042] The heat transfer oil heating unit 3 of the present invention is connected to the mold 1 and is used to heat the mold 1 during the molding process, thereby providing the heat source required for plasticizing the molded surface.

[0043] The EPP molding apparatus provided by this invention has a simple structure. During the EPP molding process, by setting a step of pre-spraying a reinforcing solution, the surface hardness and load-bearing capacity of the EPP molded product are improved without increasing the energy consumption of steam molding or the weight of the product, thereby improving the strength of the EPP molded product and extending its service life.

[0044] The preferred embodiment of this invention, the heat transfer oil heating unit 3, includes an oil storage tank 31, a heat transfer oil heater 32, and an oil passage pipe 33. The oil storage tank 31 provides the heat source required for plasticizing the molding surface, while the heat transfer oil heater 32 regulates the oil temperature and circulates the oil during molding, ensuring the stability of the product heating and cooling process. The heat transfer oil heater 32 works primarily by electrically heating the heat transfer oil in the oil storage tank 31 to a set temperature. During cooling, external cooling water is used to rapidly reduce the temperature of the heat transfer oil in the oil storage tank 31, ensuring the stability of the product molding process and the yield rate. The oil passage pipe 33 connects the oil storage tank 31 and the heat transfer oil heater 32. The heat transfer oil in the oil storage tank 31 flows in from bottom to top, ensuring temperature uniformity in the oil passage. Specifically, the oil storage tank 31 is located on the outside of the mold 1, and the oil storage tank 31 and the heat transfer oil heater 32 are connected via the oil passage pipe 33.

[0045] Preferably, the oil storage tank 31 of this invention includes a die oil storage tank 311 located outside the die 12 and a punch oil storage tank 312 located outside the punch 13; correspondingly, the heat transfer oil heater 32 includes a die heat transfer oil heater 321 and a punch heat transfer oil heater 322; the oil passage 33 includes a die oil passage 331 and a punch oil passage 332; the die oil storage tank 311 is connected to the die heat transfer oil heater 321 through the die oil passage 331 for heating the die 12; the punch oil storage tank 312 is connected to the punch heat transfer oil heater 322 through the punch oil passage 332 for connecting the punch 13.

[0046] The EPP molding apparatus provided by this invention, through the EPP steam molding process described above, can take into account both the EPP molding sintering function and the surface skinning function, thereby effectively improving the surface hardness of the product parts and also improving the product's bending resistance. In addition, due to the surface skinning design, the product has a certain improvement in water vapor permeability compared to EPP products produced by conventional processes, and the product is less prone to water leakage.

[0047] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0048] Unless otherwise specified, the EPP beads in the embodiments and comparative examples of this invention were prepared according to the following method: ① By weight, 100 parts of polypropylene (binary random copolymer polypropylene), 0.5 parts of nucleating agent zinc borate, 1 part of antioxidant 1010, and 1 part of lubricant paraffin are granulated by single-screw extrusion to obtain foamable polypropylene microparticles; the single-screw processing speed is controlled at 800 r / hour and the processing temperature is 170℃. ② The above-mentioned microparticles are foamed by supercritical carbon dioxide in a reactor, with water as the dispersant (water:microparticle mass ratio = 3:1), at a temperature of 145℃ and a back pressure of 2.0MPa, to obtain the required EPP beads after foaming.

[0049] Unless otherwise specified, the glass fiber in each embodiment of the present invention has a length of 8 μm and the carbon fiber has a length of 8 μm.

[0050] Example 1 This embodiment provides an EPP molding method, including the following steps: S1: Spray reinforcing solution into mold cavity 11; The enhancement solution comprises the following components by weight: 100 parts of glycerol; KH-570 10 copies; 50 parts of carbon fiber; The thickness of the enhanced solution sprayed is 0.03 mm; S2: Close the mold, leave a mold gap of no more than 2mm, fill the mold cavity with the pre-pressed EPP beads through the material gun, and then close the mold. S3: First, through the upper air inlet pipe 21, steam flows into the mold cavity 11 through the air plug. The steam temperature (preheating temperature) is 110℃, and the preheating time is 12s (at this time, the lower exhaust pipe 22 is in a half-open state). Simultaneously preheat the oil storage tank 31, so that the oil temperature reaches 170℃ (molding temperature) in 10s. Then, close the upper steam inlet and the lower exhaust port, and maintain for 3s (heating time). Then, circulate the oil in the oil storage tank 31 to cool it down to 50℃, and maintain for 180s (cooling time). S4: The product is dried in an oven at 75°C, then cooled and set for 1 hour. The mold is then opened to obtain the EPP molded product.

[0051] The components of the enhanced solution and the molding steps in Examples 2-5 are the same as those in Example 1. The process parameters of Examples 1-5 are shown in Table 1.

[0052] Examples 6-10 follow the same molding steps as Example 1. The composition of the reinforcing solution and process parameters in Examples 6-10 are shown in Table 2.

[0053] Comparative Example 1 This comparative example provides an EPP molding method, including the following steps: S1: Close the mold, leave a mold gap of no more than 2mm, fill the mold cavity with the pre-pressed EPP beads through the material gun, and then close the mold. S2: First, steam is introduced into the mold cavity 11 through the air inlet pipe 21 and the air plug. The steam temperature (preheating temperature) is 110℃ and the preheating time is 12s (at this time, the exhaust pipe 22 below is in a half-open state). Simultaneously, the oil storage tank 31 is preheated. After the oil temperature reaches 170℃ (molding temperature) in 10s, the upper steam inlet and the lower exhaust port are closed. The product pressure is maintained at 2 bar for 3s (heating time). Then, the oil in the oil storage tank 31 is circulated and cooled to 50℃ and maintained for 180s (cooling time). S3: The product is dried in an oven at 75°C, then cooled and set for 8 hours. The mold is then opened to obtain the EPP molded product.

[0054] Comparative Example 2 This comparative example provides an EPP molding method, including the following steps: S1: Spray reinforcing solution into mold cavity 11; The enhancement solution comprises the following components by weight: 100 parts of glycerol; KH-570 10 copies; 50 parts of carbon fiber; The thickness of the enhanced solution sprayed is 0.03 mm; S2: Close the mold, leave a mold gap of no more than 2mm, fill the mold cavity with the pre-pressed EPP beads through the material gun, and then close the mold. S3: First, steam is introduced into the mold cavity 11 through the air plug via the upper air inlet pipe 21. The steam temperature (preheating temperature) is 90℃, and the preheating time is 5s (at this time, the lower exhaust pipe 22 is in a half-open state). After preheating, the lower exhaust pipe 22 is closed, and the mold cavity temperature is raised to 135℃ by steam and maintained for 20s to sinter and shape the product. After heating is completed, the upper air inlet pipe 21 is closed, and the lower drain pipe is opened to cool the mold with cooling water. The cooling water temperature is 50℃, and the cooling time is 170s. S4: The product is dried in an oven at 75°C, then cooled and set for 8 hours. The mold is then opened to obtain the EPP molded product. The performance of the molded products of Examples 1-10 and Comparative Examples 1-2 was tested using the following methods: Surface hardness: Press test was performed using a Shore hardness tester; 10% compressive strength: Tested according to GB / T 8813-2020 "Rigid Foamed Plastics - Determination of Compressive Properties"; Maximum load capacity: determined based on actual usage performance; Whether there is leakage: Determined based on actual usage.

[0055] The test results of Examples 1-5 and Comparative Examples 1-2 are shown in Table 1, and the test results of Examples 6-10 are shown in Table 2.

[0056] Table 1 Table 2 As can be seen from the data in Tables 1 and 2 above, the EPP steam molding process provided by the present invention, through the design and modification of the original equipment, has created a new EPP steam molding process that combines the EPP molding sintering function with the surface skinning function. This effectively improves the surface hardness of the product parts and also improves the product's bending resistance. In addition, due to the surface skinning design, the product has a certain improvement in water vapor permeability compared to EPP products produced by conventional processes, making the product less prone to leakage.

[0057] In Comparative Example 1, compared to Example 1, no reinforcing solution was sprayed inside the mold cavity 11. Although the mold 1 was heated by the heat-conducting oil heating unit 3, the product surface did not have fiber-induced skinning and curing, resulting in no significant difference in performance compared to conventional EPP molding. In addition, since no reinforcing solution was sprayed in Comparative Example 1, the reinforcing coating's contribution to drying was reduced compared to Example 1. Therefore, the drying time of Comparative Example 1 was longer than that of Example 1 in order to achieve sufficient drying.

[0058] Compared with Example 1, although the reinforcing solution was sprayed in the mold cavity 11 in Comparative Example 2, the mold 1 was not heated by the heat transfer oil heating unit 3. Due to the temperature limitations of conventional heating methods, the product surface could not form a skin, and its performance could not be demonstrated. There was no significant difference from conventional EPP molding.

[0059] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. An EPP molding method, characterized in that, Includes the following steps: S1: Spray reinforcing solution into the mold cavity; S2: Fill the mold cavity with EPP beads and close the mold; S3: Heating; S4: Cool and solidify, open the mold, and obtain the EPP molded product.

2. The EPP molding method as described in claim 1, characterized in that, The enhancing solution is a silane coupling agent alcohol solution.

3. The EPP molding method as described in claim 2, characterized in that, The reinforcing solution also includes reinforcing fibers.

4. The EPP molding method as described in claim 3, characterized in that, The reinforcing fiber is selected from at least one of glass fiber and carbon fiber.

5. The EPP molding method as described in claim 4, characterized in that, The amount of alcohol added to the enhanced solution is 100 parts by weight, and the amount of silane coupling agent added is 5-15 parts.

6. The EPP molding method as described in claim 5, characterized in that, The amount of reinforcing fiber added to the reinforcing solution is 40-60 parts by weight.

7. The EPP molding method according to any one of claims 1-6, characterized in that, The heating process in step S3 includes: introducing steam into the mold cavity through a steam pipe for preliminary heating and sintering; then raising the temperature of the outside of the mold to 170-180°C for plasticizing the molding surface, and then cooling the outside of the mold to 40-50°C for heat preservation.

8. The EPP molding method as described in claim 7, characterized in that, The steam pressure during the initial heating and sintering process is 0.3-0.8 bar, and the heating time is 8-12 seconds.

9. The EPP molding method as described in claim 7, characterized in that, The plasticizing and heating time of the molding surface is 2-5 seconds; after the outside of the mold is cooled to 40-50℃, the holding time is 100-180 seconds.

10. An EPP molding apparatus, characterized in that, The EPP molding process is performed using the EPP molding method as described in any one of claims 1-9; the EPP molding apparatus includes a mold (1), a steam heating unit (2), and a heat transfer oil heating unit (3); wherein, The mold (1) includes a mold cavity (11); The steam heating unit (2) is connected to the mold cavity (11); The heat transfer oil heating unit (3) is connected to the mold (1).

11. The EPP molding apparatus as described in claim 10, characterized in that, The heat transfer oil heating unit (3) includes an oil storage tank (31), a heat transfer oil heater (32), and an oil pipeline (33); the oil storage tank (31) is located on the outside of the mold (1), and the oil storage tank (31) and the heat transfer oil heater (32) are connected through the oil pipeline (33).

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