High-density EPP (Expanded Polypropylene) foaming forming process

Abstract

The invention belongs to the technical field of EPP forming, and discloses a high-density EPP foaming forming process which comprises the following forming steps: S1, raw material preparation and pretreatment, and polypropylene particle surface treatment: performing surface activation on polypropylene particles by using plasma treatment equipment; and S2, mixing the polypropylene particles with a foaming agent. According to the invention, the foam holes are formed more uniformly in the foaming process, and the size difference between the foam holes is effectively controlled, so that the phenomenon of non-uniform bubbles caused by non-uniform release of a foaming agent in the foaming process of the foam holes is avoided, and the finally formed foaming product has a more uniform structure and a smoother appearance; the polypropylene particles subjected to surface treatment are combined with the foaming agent more tightly, the mechanical property, especially tensile strength and compressive strength, of a foaming body can be improved, the internal structure of the material is more stable under the condition that foam holes are evenly distributed, and the problems of breakage, collapse and the like caused by too large local gaps are avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of EPP molding, and specifically relates to a high-density EPP foaming molding process. Background Art

[0002] High-density EPP (Expanded Polypropylene) foaming molding process is a process commonly used to manufacture high-density, lightweight plastic products with good cushioning performance. EPP foaming materials are widely used in the fields of automobiles, electronics, electrical packaging, sports protection equipment, construction, etc. because of its excellent impact resistance, heat resistance, environmental protection and recyclability.

[0003] The high-density EPP foaming molding process in the prior art is prone to uneven distribution of gas during the foaming process due to the poor compatibility between polypropylene particles and foaming agents, resulting in pores, irregular gaps and surface defects, affecting the density and mechanical properties of the product. In addition, in the traditional foaming process, the foaming agent is unevenly dispersed or released, which will lead to bubble aggregation, uneven foaming or local excessive expansion, thereby generating surface pores, cracks or internal stress problems, affecting the mechanical properties and appearance of the material, and the actual molding quality is poor. Summary of the invention

[0004] The object of the present invention is to provide a high-density EPP foaming molding process to solve the problems raised in the above background technology.

[0005] In order to achieve the above object, the present invention provides the following technical solution: a high-density EPP foaming molding process, comprising the following molding steps:

[0006] S1. Raw material preparation and pretreatment

[0007] Surface treatment of polypropylene particles: Use plasma treatment equipment to activate the surface of polypropylene particles;

[0008] S2. Mixing of polypropylene particles and foaming agent

[0009] High shear mixing technology: The polypropylene particles and the foaming agent are evenly mixed through high shear mixing technology, and a high shear mixer is used for mixing;

[0010] Addition of microcapsule foaming agent: The microcapsule foaming agent is mixed with the surface-treated polypropylene particles. The shell material of the microcapsule has a controllable rupture temperature. The foaming agent ruptures at an appropriate temperature and slowly releases gas.

[0011] S3. Mould design and temperature control system

[0012] Temperature control thermal cycle system design: including the design of temperature control system, heating system and cooling system, and adopting a multi-zone temperature control system to divide the mold into multiple temperature control areas, each area is set at a different temperature to control the uniform expansion of the foam cells;

[0013] Temperature gradient design: including temperature setting and temperature control accuracy. The temperature of the outer area of ​​the mold is maintained at around 150°C, and the inner temperature is set between 180°C and 220°C. The PID control algorithm is used to ensure that the temperature fluctuation is controlled within ±2°C.

[0014] S4, foaming and cooling

[0015] Polypropylene foaming molding: The mixed polypropylene particles and microcapsule foaming agent are loaded into the mold and heated to the set temperature (usually between 150°C and 220°C) under the control of the temperature control system. The foaming agent begins to release gas and the bubbles are gradually formed. The temperature control system continuously adjusts the temperature to make the temperature difference between the inside and outside moderate and complete the uniform expansion of the bubbles. The temperature and pressure are controlled during the foaming process, and the cooling system is used to control the cooling rate inside the mold to complete synchronous cooling.

[0016] S5. Product demoulding and post-processing

[0017] Demolding: After the product cools down to a safe temperature, carefully remove the foamed product and check whether the surface of the product is intact and has no obvious defects during the demoulding process;

[0018] Post-processing and inspection: The surface of the foamed product after demoulding is trimmed to remove possible excess parts, and the product is tested for mechanical properties, including tensile strength, compressive strength, and water absorption, to ensure that it meets quality standards.

[0019] Preferably, in S1, the plasma treatment equipment is a low-temperature plasma treatment machine, the treatment voltage is 5-15 kV, the frequency is 20-100 kHz, the treatment time is controlled at 10-30 seconds, the atmosphere is pure oxygen or air, and the gas flow rate is controlled at 100-300 cc / min.

[0020] Preferably, in S2, the high shear mixer is a Silverson high-speed mixer, the rotation speed is set between 3000 rpm and 15000 rpm, and the mixing time is controlled within 2-10 minutes.

[0021] Preferably, in S2, the particle size of the microcapsules is controlled at 10-50 μm, the rupture temperature of the microcapsules is set between 150° C. and 250° C., and the shell material of the microcapsules is a polymer, and the polymer is one or any one of polyurethane (PU) and polyester (PE).

[0022] Preferably, in S2, the order and amount of adding the foaming agent are controlled: the amount of the foaming agent added is 2%-10% of the mass of the polypropylene, and is added gradually.

[0023] Preferably, in S4, the cooling time is 5 to 15 minutes, and the cooling liquid flow rate is controlled between 1-3 L / min.

[0024] Preferably, in said S5, in the quality inspection, the tensile strength is 20-30MPa, the elongation at break is 150-350%, and the impact strength is 5-15kJ / m 2 , and measure the thermal deformation temperature of the material, the standard range is between 80-120℃.

[0025] The beneficial effects of the present invention are as follows:

[0026] 1. After the surface treatment, the polypropylene particles of the present invention can be better dispersed and mixed with the foaming agent, reducing the phenomenon of agglomeration or uneven distribution of the foaming agent during processing. During the foaming process, the foaming agent can release gas evenly, avoiding surface defects and structural instability caused by uneven foaming or excessive bubbles; and the surface treatment enhances the interaction between the polypropylene and the foaming agent, ensuring that the formation of the pores during the foaming process is more uniform, and the size difference between the pores is effectively controlled, avoiding the uneven bubble phenomenon caused by the uneven release of the foaming agent during the foaming process, and the finally formed foamed product has a more uniform structure and a smoother appearance; the surface-treated polypropylene particles are more closely combined with the foaming agent, which is helpful to improve the mechanical properties of the foam, especially the tensile strength and compressive strength. When the pores are evenly distributed, the internal structure of the material is more stable, avoiding the problems of fracture and collapse caused by excessive local voids.

[0027] 2. The present invention combines high shear mixing with a microcapsule foaming agent, so that the uniformity of the foaming agent and the gas release rate are effectively controlled, and the gas expansion during the foaming process is controlled within an ideal range, thereby significantly improving the quality of the foamed product, especially in the structure of fine bubbles and uniform pores, and the appearance and mechanical properties of the finished product are significantly improved.

[0028] 3. The present invention can avoid local overheating or overcooling of the mold by heating and cooling the mold in multiple areas through temperature-controlled thermal cycles, and prevent uneven formation of bubbles in different parts during the foaming process, resulting in rough product surface or irregular internal bubbles. Especially in the early and late stages of foaming, the uniform control of the mold temperature directly affects the uniformity of the bubbles and the density of the foamed body; the temperature gradient design ensures that the foaming agent can gradually release gas during the heating process and expand slowly and evenly, avoiding excessively fast release of gas to cause rapid and uneven expansion of the bubbles, thereby causing bubbles of different sizes. The precise adjustment of the temperature control system ensures that the expansion process of the bubbles is consistent in different areas, avoiding excessively high or low temperature fluctuations that affect the formation of bubbles; and the temperature control system ensures that the temperature fluctuation during the foaming process is minimized, ensuring the flatness of the appearance of the molded product and the uniformity of the bubbles, and can effectively avoid defects such as bubble bursting and surface unevenness caused by uneven temperature, thereby improving the mechanical properties and stability of the finished product. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the system flow of the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] like Figure 1 As shown, the embodiment of the present invention provides a high-density EPP foaming molding process, including the following molding steps:

[0032] S1. Raw material preparation and pretreatment

[0033] Surface treatment of polypropylene particles: Use plasma treatment equipment to activate the surface of polypropylene particles;

[0034] S2. Mixing of polypropylene particles and foaming agent

[0035] High shear mixing technology: The polypropylene particles and the foaming agent are evenly mixed through high shear mixing technology, and a high shear mixer is used for mixing;

[0036] Addition of microcapsule foaming agent: The microcapsule foaming agent is mixed with the surface-treated polypropylene particles. The shell material of the microcapsule has a controllable rupture temperature. The foaming agent ruptures at an appropriate temperature and slowly releases gas.

[0037] S3. Mould design and temperature control system

[0038] Temperature control thermal cycle system design: including the design of temperature control system, heating system and cooling system, and adopting a multi-zone temperature control system to divide the mold into multiple temperature control areas, each area is set at a different temperature to control the uniform expansion of the foam cells;

[0039] Temperature gradient design: including temperature setting and temperature control accuracy. The temperature of the outer area of ​​the mold is maintained at around 150°C, and the inner temperature is set between 180°C and 220°C. The PID control algorithm is used to ensure that the temperature fluctuation is controlled within ±2°C.

[0040] S4, foaming and cooling

[0041] Polypropylene foaming molding: The mixed polypropylene particles and microcapsule foaming agent are loaded into the mold and heated to the set temperature (usually between 150°C and 220°C) under the control of the temperature control system. The foaming agent begins to release gas and the bubbles are gradually formed. The temperature control system continuously adjusts the temperature to make the temperature difference between the inside and outside moderate and complete the uniform expansion of the bubbles. The temperature and pressure are controlled during the foaming process, and the cooling system is used to control the cooling rate inside the mold to complete synchronous cooling.

[0042] S5. Product demoulding and post-processing

[0043] Demolding: After the product cools down to a safe temperature, carefully remove the foamed product and check whether the surface of the product is intact and has no obvious defects during the demoulding process;

[0044] Post-processing and inspection: The surface of the foamed product after demoulding is trimmed to remove possible excess parts, and the product is tested for mechanical properties, including tensile strength, compressive strength, and water absorption, to ensure that it meets quality standards.

[0045] Among them, in S1, the plasma treatment equipment is a low-temperature plasma treatment machine, the treatment voltage is 5-15kV, the frequency is 20-100kHz, the treatment time is controlled at 10-30 seconds, the atmosphere is pure oxygen or air, and the gas flow rate is controlled at 100-300cc / min.

[0046] The surface treatment technology of polypropylene particles changes the surface properties of polypropylene particles through plasma or chemical modification, so that more polar groups (such as hydroxyl and carboxyl) are formed on the surface, thereby improving its affinity with the foaming agent.

[0047] After surface treatment, polypropylene particles can be better dispersed and mixed with the foaming agent, reducing the phenomenon of agglomeration or uneven distribution of the foaming agent during processing. During the foaming process, the foaming agent can release gas evenly, avoiding surface defects and structural instability caused by uneven foaming or excessive bubbles; and the surface treatment enhances the interaction between polypropylene and the foaming agent, ensuring that the formation of bubbles during the foaming process is more uniform, and the size difference between the bubbles is effectively controlled, avoiding the uneven bubble phenomenon caused by uneven release of the foaming agent during the foaming process, and the final molded foamed product has a more uniform structure and a smoother appearance; the surface-treated polypropylene particles are more tightly combined with the foaming agent, which helps to improve the mechanical properties of the foam, especially the tensile strength and compressive strength. When the bubbles are evenly distributed, the internal structure of the material is more stable, avoiding problems such as fracture and collapse caused by excessive local voids.

[0048] The working temperature of low-temperature plasma is low (usually below 100°C), which will not cause thermal damage to the substrate itself. Therefore, low-temperature plasma can effectively treat the surface of the material without affecting its internal structure and performance.

[0049] Plasma treatment can introduce a large number of active groups on the surface of materials, such as amino (-NH2), carboxyl (-COOH), hydroxyl (-OH), etc. These groups can significantly improve the hydrophilicity, adhesion and coating adhesion of the material, and improve the subsequent coating, bonding and other properties;

[0050] The processing voltage is controlled within the range of 5-15kV to ensure the formation and stability of plasma, and the frequency is controlled between 20-100kHz to generate stable plasma, which is suitable for fine surface treatment. The processing time of 10-30 seconds can effectively balance the modification effect and the stability of the material to ensure the best surface modification effect. The gas flow rate is controlled between 100-300cc / min to ensure the stability of the plasma and avoid uneven energy distribution or waste due to excessive airflow.

[0051] Among them, in S2, the high shear mixer is a Silverson high-speed mixer, the speed is set between 3000rpm and 15000rpm, the mixing time is controlled at 2-10 minutes, the particle size of the microcapsules is controlled at 10-50μm, the rupture temperature of the microcapsules is set between 150°C and 250°C, the shell material of the microcapsules is a polymer, the polymer is one or any one of polyurethane (PU) and polyester (PE), and the order and amount of addition of the foaming agent are controlled: the amount of the foaming agent added is 2%-10% of the mass of polypropylene, and is added gradually.

[0052] High shear mixing technology generates strong shear force through a high-speed rotating agitator, which can evenly mix and disperse solid particles (such as polypropylene) with liquid or solid additives (such as foaming agents); microcapsule foaming agents use a shell material to wrap gas to form microcapsules. The rupture temperature of these capsules is precisely controlled, and they can slowly release gas under specific temperature conditions to achieve a more uniform and stable foaming effect.

[0053] In the traditional foaming process, the dispersion of the foaming agent is often uneven due to differences in physical properties or low shear force of the polymer. The high shear mixing technology can refine the foaming agent particles and evenly disperse them in the polypropylene matrix by increasing the shear force, ensuring a more uniform distribution of the foaming agent. The introduction of microcapsule foaming agents makes the release of gas in the foaming process more controllable, avoiding the problem of uneven expansion of the pores or excessive local enlargement caused by the release of gas too early or too quickly by traditional foaming agents. The microcapsule foaming agent can gradually release gas under high temperature conditions, thereby ensuring uniform expansion of the pores and avoiding irregular or cracked pores caused by the instantaneous release of excessive gas by the foaming agent. By combining high shear mixing with microcapsule foaming agents, the uniformity of the foaming agent and the gas release rate are effectively controlled, and the gas expansion during the foaming process is controlled within an ideal range, thereby significantly improving the quality of the foamed products, especially in the structure of fine bubbles and uniform pores, and the appearance and mechanical properties of the finished products are significantly improved.

[0054] Controlling the mixing time within 2-10 minutes can effectively balance the full mixing of materials and the perfect completion of the reaction. The speed range is set between 3000rpm and 15000rpm, which can generate shear forces of different intensities, thereby helping to adjust the shell thickness, particle size and uniformity of the microcapsules. Polyurethane (PU) and polyester (PE) as microcapsule shell materials have good thermal stability, mechanical strength and processability.

[0055] Among them, in S4, the cooling time is 5 to 15 minutes, the coolant flow rate is controlled between 1-3L / min, and in the quality inspection, the tensile strength is 20-30MPa, the elongation at break is 150-350%, and the impact strength is 5-15kJ / m 2 , and measure the thermal deformation temperature of the material, the standard range is between 80-120℃.

[0056] The temperature-controlled thermal cycle and temperature gradient design ensures uniform temperature distribution during the foaming process by precisely controlling the temperature of the mold during the foaming process, avoiding uneven bubbles or product deformation caused by excessive temperature differences. The temperature control system reasonably adjusts the heating and cooling processes according to the foaming requirements at different stages to promote the stability of the foam and the uniformity of the pores.

[0057] The temperature-controlled thermal cycle can avoid local overheating or overcooling of the mold by heating and cooling the mold in multiple areas, and prevent uneven formation of bubbles in different parts during the foaming process, resulting in rough product surface or irregular internal bubbles. Especially in the early and late stages of foaming, the uniform control of the mold temperature directly affects the uniformity of the bubbles and the density of the foam. The temperature gradient design ensures that the foaming agent can gradually release gas during the heating process and expand slowly and evenly, avoiding the rapid and uneven expansion of the bubbles due to excessively fast release of gas, resulting in different sizes of bubbles. The precise adjustment of the temperature control system ensures that the expansion process of the bubbles is consistent in different areas, avoiding excessively high or low temperature fluctuations that affect the formation of bubbles. The temperature control system ensures that the temperature fluctuation during the foaming process is minimized, ensuring the flatness of the appearance of the molded product and the uniformity of the bubbles, and can effectively avoid defects such as bubble bursting and surface unevenness caused by uneven temperature, thereby improving the mechanical properties and stability of the finished product.

[0058] The flow rate is set between 1-3L / min, which can ensure that the coolant flows evenly on the surface of the material to prevent local overheating or uneven cooling during the cooling process. When the tensile strength is set within the range of 20-30MPa, it has a good load-bearing capacity and can withstand a certain degree of external force to avoid breakage or deformation during use. The elongation at break is set at 150-350%, so that the material has high ductility and can undergo large deformation under tensile stress without being easily broken.

[0059] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-density EPP foaming molding process, characterized in that: The molding process includes the following steps: S1. Raw material preparation and pretreatment Surface treatment of polypropylene particles: Use plasma treatment equipment to activate the surface of polypropylene particles; S2. Mixing of polypropylene particles and foaming agent High shear mixing technology: The polypropylene particles and the foaming agent are evenly mixed through high shear mixing technology, and a high shear mixer is used for mixing; Addition of microcapsule foaming agent: The microcapsule foaming agent is mixed with the surface-treated polypropylene particles. The shell material of the microcapsule has a controllable rupture temperature. The foaming agent ruptures at an appropriate temperature and slowly releases gas. S3. Mould design and temperature control system Temperature control thermal cycle system design: including the design of temperature control system, heating system and cooling system, and adopting a multi-zone temperature control system to divide the mold into multiple temperature control areas, each area is set at a different temperature to control the uniform expansion of the foam cells; Temperature gradient design: including temperature setting and temperature control accuracy. The temperature of the outer area of ​​the mold is maintained at around 150°C, and the inner temperature is set between 180°C and 220°C. The PID control algorithm is used to ensure that the temperature fluctuation is controlled within ±2°C. S4, foaming and cooling Polypropylene foaming molding: The mixed polypropylene particles and microcapsule foaming agent are loaded into the mold and heated to the set temperature (usually between 150°C and 220°C) under the control of the temperature control system. The foaming agent begins to release gas and the bubbles are gradually formed. The temperature control system continuously adjusts the temperature to make the temperature difference between the inside and outside moderate and complete the uniform expansion of the bubbles. The temperature and pressure are controlled during the foaming process, and the cooling system is used to control the cooling rate inside the mold to complete synchronous cooling. S5. Product demoulding and post-processing Demolding: After the product cools down to a safe temperature, carefully remove the foamed product and check whether the surface of the product is intact and has no obvious defects during the demoulding process; Post-processing and inspection: The surface of the foamed product after demoulding is trimmed to remove possible excess parts, and the product is tested for mechanical properties, including tensile strength, compressive strength, and water absorption, to ensure that it meets quality standards.

2. A high-density EPP foaming molding process according to claim 1, characterized in that: In S1, the plasma treatment equipment is a low-temperature plasma treatment machine, the treatment voltage is 5-15 kV, the frequency is 20-100 kHz, the treatment time is controlled at 10-30 seconds, the atmosphere is pure oxygen or air, and the gas flow rate is controlled at 100-300 cc / min.

3. A high-density EPP foaming molding process according to claim 1, characterized in that: In S2, the high shear mixer is a Silverson high-speed mixer, the rotation speed is set between 3000 rpm and 15000 rpm, and the mixing time is controlled within 2-10 minutes.

4. A high-density EPP foaming molding process according to claim 1, characterized in that: In S2, the particle size of the microcapsule is controlled to be 10-50 μm, the rupture temperature of the microcapsule is set between 150° C. and 250° C., and the shell material of the microcapsule is a polymer, and the polymer is one or any one of polyurethane (PU) and polyester (PE).

5. A high-density EPP foaming molding process according to claim 1, characterized in that: In S2, the order and amount of adding the foaming agent are controlled: the amount of the foaming agent added is 2%-10% of the mass of the polypropylene, and is added gradually.

6. A high-density EPP foaming molding process according to claim 1, characterized in that: In S4, the cooling time is 5 to 15 minutes, and the cooling liquid flow rate is controlled between 1-3 L / min.

7. A high-density EPP foaming molding process according to claim 1, characterized in that: In the S5, in the quality inspection, the tensile strength is 20-30MPa, the elongation at break is 150-350%, and the impact strength is 5-15kJ / m 2 , and measure the thermal deformation temperature of the material, the standard range is between 80-120℃.

Images