PVC foaming forming method for heat insulation layer of heating equipment

Abstract

This invention discloses a PVC foaming molding method for insulation layers in heating equipment. This invention relates to the field of plastic foaming molding technology, employing a flat molding die with multi-zone independent temperature control and circulating water cooling. Through a step-by-step temperature control and gradient mold-locking integrated process, a three-layer integrated PVC foam insulation layer is formed in situ, with a single mold forming the entire layer in one step. The advantages of this invention are: by using a step-by-step temperature control and step-by-step mold-locking integrated molding process, it breaks away from the conventional process logic of simultaneous foaming of uniform cells throughout the entire area in existing technologies. It constructs a three-layer integrated structure in situ within a single mold, consisting of a dense, bubble-free surface layer, a gradient transition layer in the middle, and a highly foamed insulation core layer, without requiring drastic adjustments to the raw material formula. This breaks the industry's vicious cycle where existing PVC foam materials cannot simultaneously achieve insulation performance, structural strength, and flame retardant safety, and the dense, bubble-free surface structure simultaneously achieves the material's resistance to deformation and structural flame retardancy.

Description

Technical Field

[0001] This invention relates to the field of plastic foaming molding technology, specifically a PVC foaming molding method for use in the insulation layer of heating equipment. Background Technology

[0002] With the continuous advancement of my country's dual-carbon goals and the ongoing upgrading of energy efficiency limits and standards in the home appliance industry, the residential heating equipment industry is rapidly iterating towards high efficiency, energy saving, safety, environmental protection, and long service life. The insulation layer of heating equipment, as a core functional component, is a crucial structure that prevents heat from the core heating element from being conducted to the outer shell, reduces ineffective heat loss, and improves the energy utilization efficiency of the equipment. It also plays a vital role in preventing overheating of the equipment shell and ensuring user safety. The material properties and molding process level of the insulation layer directly determine the energy efficiency level, user experience, and core market competitiveness of the heating equipment.

[0003] Polyvinyl chloride (PVC) foam has become one of the mainstream materials for insulation layers in heating equipment due to its excellent comprehensive performance. This material possesses flexibly adjustable low thermal conductivity insulation properties, stable mechanical support properties, good structural adaptability, and a natural flame-retardant base. Furthermore, its raw materials are widely available, and production costs are controllable. Through adjustments to the molding process, it can flexibly adapt to the installation structures and long-term operating conditions of different types of heating equipment, such as baseboard heaters, convection heaters, fan heaters, and radiant heaters, leading to a continuous expansion in its application scale and scenarios in the field of heating equipment insulation.

[0004] Existing PVC foam materials for heating equipment insulation layers are mainly prepared through a conventional process of one-step mixing and full-area simultaneous molding foaming. This process relies on adding various functional additives to the formula to balance the material's performance, which has certain drawbacks. First, the conventional full-area simultaneous foaming process can only produce homogeneous materials with uniform cell structure, failing to simultaneously achieve low thermal conductivity insulation, structural deformation resistance, and flame retardant safety performance. This creates a common industry problem of unbalanced core performance. Second, to alleviate these performance contradictions, a large amount of flame retardant and rigid toughening filler must be added to the formula, which not only increases raw material costs and material molding difficulty but also leads to odor release problems in the finished product under high-temperature conditions, significantly reducing environmental friendliness and recyclability, failing to meet the safety and environmental standards for household appliances. Therefore, we propose a PVC foaming molding method for heating equipment insulation layers. Summary of the Invention

[0005] The purpose of this invention is to provide a PVC foaming molding method for insulation layers in heating equipment.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a PVC foaming molding method for a heat insulation layer of heating equipment, comprising a flat molding die with independent temperature control modules for upper and lower cavity walls, an independent heating module for the core built into the center of the cavity, and a matching circulating water cooling system; the foaming molding method includes the following steps:

[0007] Step 1: Mix PVC resin, heat stabilizer, foaming agent, lubricant, and processing aids according to the specified ratio and then perform high-speed hot mixing and low-speed cold mixing processes to obtain a uniformly mixed PVC base mixture.

[0008] Step 2: Clean the mold cavity and spray with release agent. After preheating the whole mold, spread the PVC base mixture evenly in the cavity. After closing the mold, apply the initial clamping force to maintain pressure.

[0009] Step 3: Maintain the initial clamping force and core temperature below the PVC foaming start temperature, rapidly heat the upper and lower cavity walls to the PVC gelation temperature and maintain constant temperature and pressure to form a dense, bubble-free cured skin layer on the upper and lower sides of the material in situ.

[0010] Step 4: Keep the temperature of the upper and lower cavity walls and the clamping force stable, and uniformly raise the temperature of the core to the target temperature for PVC foaming. Simultaneously increase the clamping force to the target value and then maintain the temperature and pressure to allow the core to complete foaming in the confined space of the skin layer, forming a three-layer integrated structure in situ.

[0011] Step 5: Keep the target clamping force constant, quickly cool the core to the PVC foaming termination temperature to stop the foaming reaction, and at the same time maintain the temperature of the upper and lower cavity walls to keep the pressure constant to complete the structural stabilization.

[0012] Step 6: Maintain stable clamping force, cool the entire mold uniformly and at a constant speed to the shaping temperature range, and maintain constant temperature and pressure to complete the overall cooling and shaping.

[0013] Step 7: Release pressure at a uniform speed, open the mold, and remove the semi-finished product. After room temperature curing and trimming, the finished PVC foam insulation layer is obtained.

[0014] As a further aspect of the present invention: Step one specifically involves weighing 100-110 parts by weight of PVC resin, 3-5 parts of calcium-zinc heat stabilizer, 2-4 parts of azodicarbonamide foaming agent, 0.5-1.5 parts of stearic acid lubricant, and 1-2 parts of acrylate processing aid. All raw materials are added sequentially to a high-speed mixer. The mixture is first cold-mixed for 3-5 minutes at room temperature and a speed of 800-1000 r / min. Then, the heating module is turned on to raise the temperature of the mixture to 110-120°C, and the speed is simultaneously increased to 1400-1600 r / min for continued hot mixing for 8-12 minutes. After the mixture is evenly mixed without agglomeration or lumps, it is transferred to a low-speed cold mixer and cooled to below 40°C at a speed of 400-600 r / min before being discharged to obtain a premixed, uniformly mixed PVC base mixture.

[0015] As a further aspect of the present invention: In step two, specifically: a flat molding die with independent temperature control modules for the upper and lower cavity walls, an independent heating module for the core built into the cavity center, and a matching circulating water cooling system is used. First, the inner wall of the mold cavity is cleaned, and a layer of fluorine-based release agent is evenly sprayed. All temperature control modules are turned on to preheat the entire mold to 60-80℃ and keep it at that temperature for 5-10 minutes to ensure that the temperature of each area of ​​the mold cavity is uniform and without deviation. Then, the PVC base mixture prepared in step one is evenly spread in the central area of ​​the mold cavity to ensure that the mixture fills the cavity without local accumulation. After the mold is closed, an initial clamping force of 3-5MPa is applied to maintain pressure, and the loading and mold closing operation is completed.

[0016] As a further aspect of the present invention: In step three, specifically: the initial clamping force of step two is kept constant, the temperature of the independent heating module in the core is maintained in the range of 60-80℃, ensuring that the temperature of the central area of ​​the mold cavity is always lower than the foaming initiation temperature of the PVC mixture, and at the same time, the temperature of the upper and lower cavity walls is rapidly raised to 175-185℃ at a heating rate of 10-15℃ / s. After reaching the target temperature, the temperature is held at constant pressure for 20-40s, so that the PVC mixture in direct contact with the inner walls of the upper and lower cavities of the mold completes gelation and pre-curing, forming an integral, uniform, dense, bubble-free cured skin layer on the upper and lower sides of the material in situ. The single-sided thickness of the cured skin layer is... The following calculation formula must be satisfied:

[0017] ;

[0018] in, The thickness of the cured skin layer on one side is in mm. The gelation rate coefficient of PVC mixture is 0.0008-0.0012 mm / (℃·s). The target isothermal temperature for the upper and lower cavity walls, in °C. The gelation initiation temperature of the PVC mixture is fixed at 160℃. The constant temperature and pressure holding time for the upper and lower cavity walls is measured in seconds. The final thickness of the cured skin layer is controlled within the range of 0.2-0.5 mm.

[0019] As a further solution of the present invention: In the fourth step, specifically: keep the temperature of the upper and lower cavity walls stable in the range of 175 - 185 °C, and the clamping force stable in the range of 3 - 5 MPa, maintain the stable curing state of the dense and bubble-free cured skin layer, and at the same time, uniformly raise the temperature of the core independent heating module to the PVC foaming target temperature of 190 - 200 °C at a heating rate of 2 - 5 °C / s. Synchronously, gradually increase the mold clamping force to the target clamping force of 8 - 12 MPa at a constant rate of 0.2 - 0.4 MPa / 10 s. After reaching the target temperature and target clamping force, keep the temperature constant and hold the pressure for 120 - 180 s, so that the uncured PVC mixture in the center of the cavity completes uniform and stable decomposition and foaming in the restricted closed space formed by the upper and lower dense and bubble-free cured skin layers, forming a high-foaming heat-insulating core layer with uniform cell pore diameter and a foaming ratio stable in the range of 15 - 25 times. At the same time, between the dense and bubble-free cured skin layer and the high-foaming heat-insulating core layer, a gradient transition layer with a gradient change of cell pore diameter along the thickness direction is formed in-situ, completing the in-situ construction of the three-layer integrated structure.

[0020] As a further solution of the present invention: In the fifth step, specifically: keep the target clamping force of the mold stable at 8 - 12 MPa unchanged, immediately turn off the core independent heating module, and synchronously start the circulating water cooling system supporting the core independent heating module. Rapidly cool the center area of the mold cavity at a cooling rate of 15 - 20 °C / s, and reduce the temperature of the center area of the cavity to the PVC foaming termination temperature range below 160 °C within 8 - 12 s, so that the foaming reaction of the core layer terminates instantly, locking the cell structure and foaming ratio of the core layer. At the same time, keep the temperature of the upper and lower cavity walls stable in the range of 175 - 185 °C, keep the pressure constant for 10 - 20 s, and ensure the structural stability of the dense and bubble-free cured skin layer and the gradient transition layer.

[0021] As a further solution of the present invention: In the sixth step, specifically: keep the mold clamping force stable in the range of 8 - 12 MPa unchanged, synchronously turn off the heating function of the independent temperature control modules of the upper and lower cavity walls, start the circulating water cooling system supporting the whole mold, and uniformly cool the whole mold at a constant cooling rate of 3 - 6 °C / min. After the temperature of the whole mold drops to the range of 40 - 60 °C, keep the temperature constant and hold the pressure for 60 - 90 s, so that the PVC foaming material of the three-layer integrated structure is completely cooled and shaped.

[0022] As a further aspect of the present invention: Step seven specifically involves: releasing the mold clamping force at a constant rate of 0.5-1 MPa / s; opening the mold after the clamping force has been completely released; removing the semi-finished PVC foam insulation layer; placing the semi-finished product in a standard environment with a temperature of 23±2℃ and a relative humidity of 50±5% for 24-48 hours to eliminate residual stress inside the finished product; and after curing, trimming and cutting the edges according to the design dimensions of the insulation layer of the heating equipment to obtain a finished PVC foam insulation layer that can be directly used for the assembly of the heating equipment.

[0023] Compared with the prior art, the beneficial effects of the present invention by adopting the above technical solution are as follows:

[0024] 1. This invention breaks away from the conventional process logic of synchronous foaming with uniform cells throughout the entire area by using an integrated molding process of step-by-step temperature control and step-by-step mold locking within a single mold. It constructs a three-layer integrated structure in situ within a single mold, consisting of a dense, bubble-free surface layer, a gradient transition layer in the middle, and a high-foaming insulation core layer. This does not require any radical adjustments to the raw material formula. It breaks the industry vicious cycle of existing PVC foam materials being unable to simultaneously achieve insulation performance, structural strength, and flame retardancy safety from the root of the molding process. The dense, bubble-free surface structure simultaneously achieves the material's resistance to deformation and structural flame retardancy. The high-foaming core structure ensures stable low thermal conductivity insulation performance. The gradient transition layer avoids the risk of delamination between different structures. Ultimately, it achieves a simultaneous improvement in the three core performance characteristics, fully meeting the long-term and stringent use requirements of insulation layers in heating equipment.

[0025] 2. This invention utilizes a continuous molding process completed entirely within a single mold, eliminating the conventional improvement methods that rely on large amounts of flame retardants and rigid toughening fillers to balance material performance. It eliminates the need for complex new production equipment and additional processing steps, achieving full compliance with core performance standards simply through coordinated control of mold temperature and clamping force. This fundamentally avoids a series of secondary problems caused by high proportions of additives. This process significantly reduces raw material costs and molding difficulty, ensures production process stability and batch consistency, and is suitable for large-scale continuous production of insulation layers for heating equipment. Simultaneously, it avoids odor release issues under high-temperature conditions, ensuring the product's environmental friendliness and recyclability, fully complying with environmental and safety standards for household appliances. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the method steps in an embodiment of the present invention. Detailed Implementation

[0027] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that the description of these embodiments is for the purpose of helping to understand the present invention, but does not constitute a limitation of the present invention.

[0028] Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] Please see the appendix Figure 1 This invention discloses a PVC foaming molding method for use in the insulation layer of heating equipment, comprising a flat molding die with independent temperature control modules for the upper and lower cavity walls, an independent heating module for the core built into the center of the cavity, and a matching circulating water cooling system. The foaming molding method includes the following steps:

[0030] Step 1: Mix PVC resin, heat stabilizer, foaming agent, lubricant, and processing aids according to the specified ratio and then perform high-speed hot mixing and low-speed cold mixing processes to obtain a uniformly mixed PVC base mixture.

[0031] Step 2: Clean the mold cavity and spray with release agent. After preheating the whole mold, spread the PVC base mixture evenly in the cavity. After closing the mold, apply the initial clamping force to maintain pressure.

[0032] Step 3: Maintain the initial clamping force and core temperature below the PVC foaming start temperature, rapidly heat the upper and lower cavity walls to the PVC gelation temperature and maintain constant temperature and pressure to form a dense, bubble-free cured skin layer on the upper and lower sides of the material in situ.

[0033] Step 4: Keep the temperature of the upper and lower cavity walls and the clamping force stable, and uniformly raise the temperature of the core to the target temperature for PVC foaming. Simultaneously increase the clamping force to the target value and then maintain the temperature and pressure to allow the core to complete foaming in the confined space of the skin layer, forming a three-layer integrated structure in situ.

[0034] Step 5: Keep the target clamping force constant, quickly cool the core to the PVC foaming termination temperature to stop the foaming reaction, and at the same time maintain the temperature of the upper and lower cavity walls to keep the pressure constant to complete the structural stabilization.

[0035] Step 6: Maintain stable clamping force, cool the entire mold uniformly and at a constant speed to the shaping temperature range, and maintain constant temperature and pressure to complete the overall cooling and shaping.

[0036] Step 7: Release pressure at a uniform speed, open the mold, and remove the semi-finished product. After room temperature curing and trimming, the finished PVC foam insulation layer is obtained.

[0037] Example 1

[0038] This embodiment discloses a PVC foaming molding method for heat insulation layers in heating equipment, which specifically includes the following steps:

[0039] Step 1: Raw material mixing process: Weigh out 100 parts of PVC resin, 4 parts of calcium-zinc heat stabilizer, 3 parts of azodicarbonamide foaming agent, 1 part of stearic acid lubricant, and 1.5 parts of acrylate processing aid according to the weight ratio. Add all raw materials to the high-speed mixer in sequence. First, cold mix for 4 minutes at room temperature and a speed of 900 r / min. Then, turn on the heating module to raise the temperature of the mixture to 115℃ and simultaneously increase the speed to 1500 r / min to continue hot mixing for 10 minutes. After the mixture is evenly mixed and free of agglomerates, transfer it to a low-speed cold mixer and cool it down to 35℃ at a speed of 500 r / min to discharge the material, thus obtaining a premixed and evenly mixed PVC base mixture.

[0040] Step 2, Mold Pretreatment and Material Loading and Mold Closing Process: A flat molding die with independent temperature control modules for the upper and lower cavity walls, an independent heating module for the core inside the cavity center, and a matching circulating water cooling system is used. First, the inner wall of the mold cavity is cleaned and a layer of fluorine-based release agent is evenly sprayed. All temperature control modules are turned on to preheat the entire mold to 70°C and keep it at that temperature for 8 minutes to ensure that the temperature of each area of ​​the mold cavity is uniform and without deviation. Then, the PVC base mixture prepared in Step 1 is evenly spread in the center area of ​​the mold cavity to ensure that the mixture fills the cavity without local accumulation. After closing the mold, an initial clamping force of 4MPa is applied to maintain pressure and complete the material loading and mold closing operation.

[0041] Step 3, Surface Pre-curing and Shaping Process: Keep the initial clamping force of Step 2 unchanged, maintain the temperature of the core independent heating module at 70℃, ensure that the temperature of the center area of ​​the mold cavity is always lower than the foaming start temperature of the PVC mixture, and at the same time, rapidly raise the temperature of the upper and lower cavity walls to 180℃ at a heating rate of 12℃ / s. After reaching the target temperature, maintain the temperature and pressure for 25s to complete the gelation and pre-curing of the PVC mixture in direct contact with the inner walls of the upper and lower cavities of the mold, and form a dense, bubble-free cured skin layer with a uniform thickness and an integrated structure on the upper and lower sides of the material in situ.

[0042] Among them, the single-sided thickness of the cured skin layer Calculated using the following formula:

[0043] ;

[0044] In the formula, The value is taken as 0.001 mm / (℃·s). It is 180℃. It is 160℃. It is 25s, calculated as follows =0.001×(180−160)×25=0.5mm, which meets the preset requirement of 0.2-0.5mm range;

[0045] Step 4. Core layer gradient limited foaming process: Keep the temperature of the upper and lower cavity walls stable at 180°C and the clamping force stable at 4 MPa. Maintain the stable curing state of the dense and bubble-free cured skin layer. At the same time, uniformly raise the temperature of the core independent heating module to the PVC foaming target temperature of 195°C at a heating rate of 3°C / s. Synchronously, gradually increase the mold clamping force to the target clamping force of 10 MPa at a constant rate of 0.3 MPa / 10 s. After reaching the target temperature and target clamping force, keep the temperature constant and hold the pressure for 150 s, so that the uncured PVC mixture in the center of the cavity completes uniform and stable decomposition and foaming in the restricted closed space formed by the upper and lower dense and bubble-free cured skin layers, forming a high-foaming heat-insulating core layer with uniform cell pore diameter and a foaming ratio stable at 20 times. At the same time, in-situ form a gradient transition layer with a gradient change of cell pore diameter along the thickness direction between the dense and bubble-free cured skin layer and the high-foaming heat-insulating core layer, and complete the in-situ construction of the three-layer integrated structure;

[0046] Step 5. Foaming termination and structure stabilization process: Keep the target clamping force of the mold at 10 MPa unchanged. Immediately turn off the core independent heating module, and synchronously start the circulating water cooling system supporting the core independent heating module. Rapidly cool the center area of the mold cavity at a cooling rate of 18°C / s, and reduce the temperature of the center area of the cavity to the PVC foaming termination temperature range of 150°C within 10 s, so that the foaming reaction of the core layer is terminated instantly, locking the cell structure and foaming ratio of the core layer. At the same time, keep the temperature of the upper and lower cavity walls stable at 180°C and hold the pressure for 15 s to ensure the structural stability of the dense and bubble-free cured skin layer and the gradient transition layer;

[0047] Step 6. Overall synchronous cooling and shaping process: Keep the mold clamping force stable at 10 MPa unchanged. Synchronously turn off the heating function of the upper and lower cavity wall independent temperature control modules, and start the circulating water cooling system supporting the whole mold. Uniformly cool the whole mold at a constant cooling rate of 4°C / min. After the temperature of the whole mold drops to 50°C, keep the temperature constant and hold the pressure for 75 s to completely cool and shape the PVC foaming material of the three-layer integrated structure;

[0048] Step 7. Mold opening and part taking and post-treatment process: Release the mold clamping force uniformly at a constant rate of 0.8 MPa / s. After the clamping force is completely released, open the mold and take out the semi-finished product of the PVC foaming heat-insulating layer. Place the semi-finished product in a standard environment with a temperature of 23±2°C and a relative humidity of 50±5% for room temperature aging for 36 h to eliminate the residual stress inside the finished product. After the aging is completed, cut and trim according to the designed size of the heat-insulating layer of the heating equipment to obtain the finished product of the PVC foaming heat-insulating layer that can be directly used for the assembly of the heating equipment.

[0049] Example 2

[0050] This embodiment discloses a PVC foaming molding method for insulation layers in heating equipment. The difference between this method and Embodiment 1 lies only in the adjustment of process parameters. Specifically, it includes the following steps:

[0051] Step 1: Raw material mixing process: Weigh out 105 parts of PVC resin, 3.5 parts of calcium-zinc heat stabilizer, 2.5 parts of azodicarbonamide foaming agent, 0.8 parts of stearic acid lubricant, and 1.2 parts of acrylate processing aid according to the weight ratio. Add all raw materials to a high-speed mixer in sequence. First, cold mix for 3.5 minutes at room temperature and a speed of 850 r / min. Then, turn on the heating module to raise the temperature of the mixture to 112℃ and simultaneously increase the speed to 1450 r / min to continue hot mixing for 9 minutes. After the mixture is evenly mixed and free of agglomerates, transfer it to a low-speed cold mixer and cool it down to 38℃ at a speed of 450 r / min before discharging to obtain a premixed and evenly mixed PVC base mixture.

[0052] Step 2, Mold Pretreatment and Material Loading and Mold Closing Process: A flat molding die with independent temperature control modules for the upper and lower cavity walls, an independent heating module for the core inside the cavity center, and a matching circulating water cooling system is used. First, the inner wall of the mold cavity is cleaned and a layer of fluorine-based release agent is evenly sprayed. All temperature control modules are turned on to preheat the entire mold to 65°C and keep it at that temperature for 6 minutes to ensure that the temperature of each area of ​​the mold cavity is uniform and without deviation. Then, the PVC base mixture prepared in Step 1 is evenly spread in the center area of ​​the mold cavity to ensure that the mixture fills the cavity without local accumulation. After closing the mold, an initial clamping force of 3.5MPa is applied to maintain pressure and complete the material loading and mold closing operation.

[0053] Step 3, Surface Pre-curing and Shaping Process: Keep the initial clamping force of Step 2 unchanged, maintain the temperature of the core independent heating module at 65℃, and ensure that the temperature of the center area of ​​the mold cavity is always lower than the foaming start temperature of the PVC mixture. At the same time, raise the temperature of the upper and lower cavity walls to 178℃ at a heating rate of 11℃ / s. After reaching the target temperature, maintain the temperature and pressure for 20s to complete the gelation and pre-curing of the PVC mixture that is in direct contact with the inner walls of the upper and lower cavities of the mold. Form a dense, bubble-free cured skin layer with a uniform thickness and an integrated structure on the upper and lower sides of the material in situ.

[0054] Among them, the single-sided thickness of the cured skin layer Calculated using the following formula:

[0055] ;

[0056] In the formula, The value is 0.0009 mm / (℃·s). It is 178℃. It is 160℃. The value is 20 seconds, calculated as follows: =0.0009×(178 - 160)×20 = 0.324 mm, meeting the requirements of the preset range of 0.2 - 0.5 mm;

[0057] Step Four: Core layer gradient restricted foaming process: Keep the temperature of the upper and lower cavity walls stable at 178 °C and the clamping force stable at 3.5 MPa. Maintain the stable curing state of the dense and bubble-free cured skin layer. At the same time, uniformly raise the temperature of the core independent heating module to the PVC foaming target temperature of 192 °C at a heating rate of 2.5 °C / s. Synchronously, gradually increase the mold clamping force to the target clamping force of 9 MPa at a constant rate of 0.25 MPa / 10 s. After reaching the target temperature and target clamping force, keep the temperature constant and hold the pressure for 130 s, enabling the uncured PVC mixture in the center of the cavity to complete uniform and stable decomposition and foaming within the restricted closed space formed by the upper and lower dense and bubble-free cured skin layers, forming a high-foaming thermal insulation core layer with uniform cell pore diameter and a stable foaming ratio of 18 times. At the same time, an in-situ gradient transition layer with a gradient change in cell pore diameter along the thickness direction is formed between the dense and bubble-free cured skin layer and the high-foaming thermal insulation core layer, completing the in-situ construction of the three-layer integrated structure;

[0058] Step Five: Foaming termination and structure stabilization process: Keep the target clamping force of the mold at 9 MPa unchanged. Immediately turn off the core independent heating module, and simultaneously activate the circulating water cooling system supporting the core independent heating module. Rapidly cool the center area of the mold cavity at a cooling rate of 16 °C / s, and reduce the temperature of the center area of the cavity to the PVC foaming termination temperature range of 155 °C within 9 s, instantly terminating the foaming reaction of the core layer and locking the cell structure and foaming ratio of the core layer. At the same time, keep the temperature of the upper and lower cavity walls stable at 178 °C and hold the pressure for 12 s to ensure the structural stability of the dense and bubble-free cured skin layer and the gradient transition layer;

[0059] Step Six: Overall synchronous cooling and shaping process: Keep the mold clamping force stable at 9 MPa unchanged. Synchronously turn off the heating function of the independent temperature control modules for the upper and lower cavity walls, and activate the circulating water cooling system supporting the entire mold. Uniformly cool the entire mold at a constant cooling rate of 3.5 °C / min. After the temperature of the entire mold drops to 45 °C, keep the temperature constant and hold the pressure for 70 s to completely cool and shape the PVC foaming material of the three-layer integrated structure;

[0060] Step Seven: Mold opening and part removal and post-treatment process: Release the mold clamping force at a constant rate of 0.6 MPa / s. After the clamping force is completely released, open the mold and take out the semi-finished product of the PVC foaming thermal insulation layer. Place the semi-finished product in a standard environment with a temperature of 23 ± 2 °C and a relative humidity of 50 ± 5% for room temperature aging for 30 h to eliminate the residual stress inside the finished product. After the aging is completed, cut and trim according to the design size of the thermal insulation layer for heating equipment to obtain the finished PVC foaming thermal insulation layer that can be directly used for the assembly of heating equipment.

[0061] Comparative Example

[0062] This comparative example uses a conventional one-step synchronous compression molding process, and the formula is completely identical to that of Example 1, eliminating the interference of formula variables on performance. The specific steps are as follows:

[0063] Step 1: Raw material mixing process: Weigh 100 parts of PVC resin, 4 parts of calcium zinc heat stabilizer, 3 parts of azodicarbonamide foaming agent, 1 part of stearic acid lubricant, and 1.5 parts of acrylate processing aid according to the mass ratio. Use the same mixing process as in Example 1 to prepare PVC basic mixture.

[0064] Step 2, Mold Pretreatment and Material Loading and Mold Closing Process: Using the same flat molding mold as in Example 1, clean the mold cavity and spray a release agent. Preheat the entire mold to 70°C and keep it at that temperature for 8 minutes. Spread the PVC base mixture evenly in the cavity. After closing the mold, apply a clamping force of 4MPa to maintain pressure.

[0065] Step 3, One-step synchronous foaming process: The mold is heated synchronously at a rate of 3℃ / s to raise the overall temperature of the mold to 195℃, and the clamping force is increased to 10MPa. The temperature is kept constant and the pressure is maintained for 150s, so that the mixture can be gelled and foamed synchronously throughout the entire area, forming a uniform cell structure throughout the entire area.

[0066] Step 4, Cooling and Shaping Process: The entire mold is cooled synchronously at a rate of 4℃ / min to 50℃, and then held at a constant temperature and pressure for 75 seconds.

[0067] Step 5: Mold opening and post-processing: Depressurize and open the mold to remove the semi-finished product. Use the same curing and cutting process as in Example 1 to obtain the finished PVC foam insulation layer.

[0068] The finished products prepared in Examples 1, 2, and the comparative example were subjected to various performance tests according to the aforementioned test standards. The test results are shown in Table 1 below:

[0069] Table 1 Performance test results of the finished products of the examples and comparative examples

[0070] Performance indicators unit Example 1 Example 2 Comparative Example thermal conductivity W / (m·K) 0.032 0.035 0.033 Tensile strength MPa 3.8 3.5 1.6 Elongation at break % 120 112 45 Vertical flammability rating - V-0 V-0 V-2 Dimensional change rate at 80℃ for 168 hours % 0.32 0.38 1.85 TVOC emissions mg / m³ 0.21 0.18 0.23

[0071] The test results above show that:

[0072] 1. The finished products prepared in Examples 1 and 2 of the present invention have thermal conductivity comparable to those of the comparative examples, both remaining at a low level, and possess excellent thermal insulation performance, fully meeting the thermal insulation requirements of the insulation layer of heating equipment.

[0073] 2. The tensile strength and elongation at break of the embodiments of the present invention are much higher than those of the comparative example, and the structural strength and resistance to deformation are significantly improved. The dimensional change rate under long-term high temperature conditions of 80°C is only about 1 / 5 of that of the comparative example. It has excellent long-term stability and solves the problem of loose material and easy deformation and damage under high foaming ratio in the prior art.

[0074] 3. The vertical flammability rating of the present invention reaches V-0, which is far superior to the V-2 rating of the comparative example. Without adding any additional flame retardants, the flame retardant performance is greatly improved through the dense, bubble-free surface structure, which solves the core problem of poor flame retardant performance of high-foaming materials in the prior art.

[0075] 4. The TVOC release of the present invention embodiment is basically the same as that of the comparative example, and there is no VOC increase problem caused by the addition of additional additives, which fully meets the environmental protection requirements of home appliances.

[0076] In summary, this invention, through a step-by-step temperature control and step-by-step mold-locking integrated molding process, simultaneously achieves a leapfrog improvement in structural strength and flame retardant performance without reducing thermal insulation performance or adding additional functional additives. It breaks the performance deadlock of existing technologies that cannot simultaneously achieve thermal insulation, strength, and flame retardancy from the root of the molding process, and solves a long-standing technical problem in this field.

[0077] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any variations and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the invention, fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for foaming and molding PVC for use in the insulation layer of heating equipment, characterized in that: The foaming molding method includes a flat molding die with independent temperature control modules for the upper and lower cavity walls, an independent heating module for the core built into the cavity center, and a matching circulating water cooling system. The foaming molding method comprises the following steps: Step 1: Mix PVC resin, heat stabilizer, foaming agent, lubricant, and processing aids according to the specified ratio and then perform high-speed hot mixing and low-speed cold mixing processes to obtain a uniformly mixed PVC base mixture. Step 2: Clean the mold cavity and spray with release agent. After preheating the whole mold, spread the PVC base mixture evenly in the cavity. After closing the mold, apply the initial clamping force to maintain pressure. Step 3: Maintain the initial clamping force and core temperature below the PVC foaming start temperature, rapidly heat the upper and lower cavity walls to the PVC gelation temperature and maintain constant temperature and pressure to form a dense, bubble-free cured skin layer on the upper and lower sides of the material in situ. Step 4: Keep the temperature of the upper and lower cavity walls and the clamping force stable, and uniformly raise the temperature of the core to the target temperature for PVC foaming. Simultaneously increase the clamping force to the target value and then maintain the temperature and pressure to allow the core to complete foaming in the confined space of the skin layer, forming a three-layer integrated structure in situ. Step 5: Keep the target clamping force constant, quickly cool the core to the PVC foaming termination temperature to stop the foaming reaction, and at the same time maintain the temperature of the upper and lower cavity walls to keep the pressure constant to complete the structural stabilization. Step 6: Maintain stable clamping force, cool the entire mold uniformly and at a constant speed to the shaping temperature range, and maintain constant temperature and pressure to complete the overall cooling and shaping. Step 7: Release pressure at a uniform speed, open the mold, and remove the semi-finished product. After room temperature curing and trimming, the finished PVC foam insulation layer is obtained.

2. The PVC foaming molding method for a heat insulation layer of a heating device according to claim 1, characterized in that: In step one, specifically: weigh 100-110 parts of PVC resin, 3-5 parts of calcium-zinc heat stabilizer, 2-4 parts of azodicarbonamide foaming agent, 0.5-1.5 parts of stearic acid lubricant, and 1-2 parts of acrylate processing aid according to the mass ratio. Add all raw materials to a high-speed mixer in sequence. First, cold mix for 3-5 minutes at room temperature and a speed of 800-1000 r / min. Then, turn on the heating module to raise the temperature of the mixture to 110-120℃, and simultaneously increase the speed to 1400-1600 r / min to continue hot mixing for 8-12 minutes. After the mixture is evenly mixed and free of agglomerates, transfer it to a low-speed cold mixer and cool it down to below 40℃ at a speed of 400-600 r / min before discharging to obtain a premixed and evenly mixed PVC base mixture.

3. The PVC foaming molding method for a heat insulation layer in heating equipment according to claim 1, characterized in that: In step two, the specific steps are as follows: a flat molding die with independent temperature control modules for the upper and lower cavity walls, an independent heating module for the core built into the cavity center, and a matching circulating water cooling system is used. First, the inner wall of the mold cavity is cleaned and a layer of fluorine-based release agent is evenly sprayed. All temperature control modules are turned on to preheat the entire mold to 60-80℃ and keep it at that temperature for 5-10 minutes to ensure that the temperature of each area of ​​the mold cavity is uniform and without deviation. Then, the PVC base mixture prepared in step one is evenly spread in the center area of ​​the mold cavity to ensure that the mixture fills the cavity without local accumulation. After the mold is closed, an initial clamping force of 3-5MPa is applied to maintain pressure and complete the loading and mold closing operation.

4. The PVC foaming molding method for a heat insulation layer of a heating device according to claim 1, characterized in that: In step three, specifically: Maintaining the initial clamping force from step two unchanged, keeping the temperature of the independent heating module in the core within the range of 60-80℃, ensuring the temperature in the center area of ​​the mold cavity remains below the foaming initiation temperature of the PVC mixture, and simultaneously rapidly raising the temperature of the upper and lower cavity walls to 175-185℃ at a heating rate of 10-15℃ / s. After reaching the target temperature, maintain the temperature and pressure for 20-40 seconds, allowing the PVC mixture in direct contact with the inner walls of the upper and lower cavities of the mold to complete gelation and pre-curing. This forms an integral, uniformly thick, dense, bubble-free cured skin layer on both the upper and lower sides of the material. The single-sided thickness of the cured skin layer is... The following calculation formula must be satisfied: ； in, The thickness of the cured skin layer on one side is in mm. The gelation rate coefficient of PVC mixture is 0.0008-0.0012 mm / (℃·s). The target isothermal temperature for the upper and lower cavity walls, in °C. The gelation initiation temperature of the PVC mixture is fixed at 160℃. The constant temperature and pressure holding time for the upper and lower cavity walls is measured in seconds. The final thickness of the cured skin layer is controlled within the range of 0.2-0.5 mm.

5. The PVC foaming molding method for a heat insulation layer of a heating device according to claim 1, characterized in that: In the fourth step, specifically: keep the temperature of the upper and lower cavity walls stable within the range of 175 - 185°C and the clamping force stable within the range of 3 - 5 MPa, maintain the stable curing state of the dense and bubble-free cured skin layer, and at the same time, uniformly raise the temperature of the core independent heating module to the PVC foaming target temperature of 190 - 200°C at a heating rate of 2 - 5°C / s. Synchronously, gradually increase the mold clamping force to the target clamping force of 8 - 12 MPa at a constant rate of 0.2 - 0.4 MPa / 10s. After reaching the target temperature and target clamping force, keep the temperature constant and hold the pressure for 120 - 180 s, so that the uncured PVC mixture in the center of the cavity completes uniform and stable decomposition and foaming within the restricted closed space formed by the upper and lower dense and bubble-free cured skin layers, forming a highly foamed heat-insulating core layer with uniform cell pore diameter and a foaming ratio stable within the range of 15 - 25 times. At the same time, an in-situ gradient transition layer with a gradient change in cell pore diameter along the thickness direction is formed between the dense and bubble-free cured skin layer and the highly foamed heat-insulating core layer, completing the in-situ construction of the three-layer integrated structure.

6. The PVC foaming molding method for a heat insulation layer of a heating device according to claim 1, characterized in that: In the fifth step, specifically: keep the target clamping force of the mold at 8 - 12 MPa unchanged, immediately turn off the core independent heating module, and synchronously start the circulating water cooling system supporting the core independent heating module. Rapidly cool the central area of the mold cavity at a cooling rate of 15 - 20°C / s, and reduce the temperature of the central area of the cavity to the PVC foaming termination temperature range below 160°C within 8 - 12 s, so that the foaming reaction of the core layer terminates instantly, locking the cell pore structure and foaming ratio of the core layer. At the same time, keep the temperature of the upper and lower cavity walls stable within the range of 175 - 185°C and hold the pressure for 10 - 20 s to ensure the structural stability of the dense and bubble-free cured skin layer and the gradient transition layer.

7. The PVC foaming molding method for a heat insulation layer of a heating device according to claim 1, characterized in that: In the sixth step, specifically: keep the mold clamping force stable within the range of 8 - 12 MPa unchanged, synchronously turn off the heating function of the independent temperature control modules for the upper and lower cavity walls, start the circulating water cooling system supporting the whole mold, and uniformly cool the whole mold at a constant cooling rate of 3 - 6°C / min. After the temperature of the whole mold drops to the range of 40 - 60°C, keep the temperature constant and hold the pressure for 60 - 90 s to completely cool and shape the PVC foaming material of the three-layer integrated structure.

8. The PVC foaming molding method for a heat insulation layer of a heating device according to claim 1, characterized in that: In the seventh step, specifically: release the mold clamping force at a constant rate of 0.5 - 1 MPa / s uniformly. After the clamping force is completely released, open the mold, take out the semi-finished product of the PVC foaming heat-insulating layer, place the semi-finished product in a standard environment with a temperature of 23 ± 2°C and a relative humidity of 50 ± 5% for room temperature aging for 24 - 48 h to eliminate the residual stress inside the finished product. After the aging is completed, cut and trim according to the designed size of the heat-insulating layer of the heating equipment to obtain the finished PVC foaming heat-insulating layer that can be directly used for the assembly of the heating equipment.

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