Heat stabilizing structure and method of double-color injection mold

Abstract

According to the heat stabilizing method of the double-color injection mold, a phase change heat storage unit is arranged in the rotary double-color injection mold and embedded in an annular groove formed in the outer wall of a mold cavity on the movable mold side of the double-color injection mold; a phase change heat storage material is packaged in the phase change heat storage unit, and heat insulation layers are arranged on other outer surfaces of the phase change heat storage unit; the melting point of the phase-change heat storage material is lower than the softening point of the plastic material and higher than the demolding temperature of the plastic material; during first injection molding, a molten first material heated to a first high temperature is injected into the lower-layer mold cavity through a hot runner, and is cooled below the first low temperature to be cured; the phase-change heat storage unit absorbs heat of the mold cavity and starts to melt when the temperature rises to a first low temperature, and temperature rise of the mold cavity is delayed; during secondary injection molding, a molten second material heated to a second high temperature is injected into the upper-layer mold cavity; the phase change heat storage unit controls the temperature of the lower-layer mold cavity to be below the third temperature through latent heat absorption, and the first material is prevented from being softened. Temperature fluctuation of the mold can be balanced, and softening of the first injection molding material caused by sudden temperature drop is prevented.

Description

Technical Field

[0001] The invention relates to a plastic processing technology, in particular to a heat stabilizing structure and method of a double-color injection mold. Background Art

[0002] The application of two-color injection molding processing technology is becoming more and more extensive, especially for the increasing demand for two-color plastic products today, the quality requirements of two-color plastic products are getting higher and higher. Two-color injection molds are made by injecting two different materials or two plastics of the same material but different colors. This type of production mold is generally divided into two categories. One is a mixed-color two-color injection mold, which is a relatively simple technology to implement; the other is a double-layer two-color injection mold, that is, two nozzles inject two materials one after another to form a two-color product with a clear boundary. During the processing, the first nozzle injects the material into the first cavity for molding, then opens the mold but does not eject it, and the mold is closed after rotating 180 degrees; the second nozzle injects another material into the second cavity that already has the first material, so that the two materials stick together and then the second mold is opened and ejected to inject a complete two-color product. For example, the "Quick Demolding Two-Color Injection Mold" with patent number 202411562944.8 also uses a rotating structure to achieve two-color injection molding. In this type of two-color injection mold, a hot runner system (Hot Runner System) is generally used as a temperature control system. Its core goal is to avoid material waste and extended production cycle caused by the cooling and solidification of plastics in the runner in the traditional cold runner system. Heating elements (such as heating rods and heating coils) are embedded in the runner, and the temperature is accurately adjusted through temperature sensors and controllers to ensure that the plastic is always in a molten state. However, even with this temperature control system, two-color injection molding may still have unstable and sudden changes in temperature during the second injection, causing the first color material to soften, affecting the quality of the two-color injection molded product. Summary of the invention

[0003] The technical problem solved by the present invention is to provide a thermal stabilization structure and method for a two-color injection mold to balance mold temperature fluctuations and prevent softening of a first injection material caused by a sudden drop in temperature.

[0004] The technical solution of the present invention is: A thermal stabilization method for a two-color injection mold, wherein a phase change heat storage unit is arranged in a rotary two-color injection mold, the phase change heat storage unit is a packaging unit of a phase change heat storage material, and is embedded in an annular groove opened on the outer wall of the mold cavity on the movable mold side of the two-color injection mold; The phase-change heat storage unit uses a high-temperature resistant aluminum alloy packaging shell to encapsulate the phase-change heat storage material inside, and a heat-conducting layer is provided on the outer surface in contact with the mold cavity, and a heat-insulating layer is provided on other outer surfaces; the melting point of the phase-change heat storage material is lower than the softening point of the plastic material and higher than the demoulding temperature of the plastic material; Two-color injection mold injection includes the first injection and the second injection after the mold is rotated: During the first injection molding, the molten first material heated to a first high temperature is injected into the lower mold cavity through the hot runner, and solidified after being cooled to below a first low temperature; the phase change heat storage unit absorbs the heat of the mold cavity, and begins to melt when the temperature rises to the first low temperature, thereby delaying the temperature rise of the mold cavity; During the second injection molding after the mold is rotated, the molten second material heated to the second high temperature is injected into the upper mold cavity, and the heat is transferred to the lower first material area through the mold cavity; the phase change heat storage unit controls the temperature of the lower mold cavity below the third temperature through latent heat absorption to prevent the first material from softening.

[0005] The thermal stabilization method of the two-color injection mold as described above, wherein the cooling water channel of the two-color injection mold is arranged on the outside of the phase change heat storage unit on the movable mold side, the mold cavity is located on the inside of the phase change heat storage unit, and an insulation layer is arranged between the phase change heat storage unit and the cooling water channel; The two-color injection mold also includes a cooling stage during injection molding. During the cooling stage, the cooling water circulation of the cooling water circuit is started, the phase change heat storage material in the phase change heat storage unit solidifies, releases the stored heat, slows down the cooling rate of the mold cavity, and reduces the residual stress of the two-color plastic product.

[0006] The thermal stabilization method of the two-color injection mold as described above, wherein the volume of the phase change heat storage unit is calculated, comprises: Calculation of heat storage requirements: The amount of heat to be absorbed is determined by the amount of heat transferred from the melt to the mold cavity: , The heat released by the melt is: , in, is the total heat absorption, Release heat to the melt, is the cooling water heat, is the mass of plastic injection molded in kg, is the specific heat capacity of the plastic (kJ / kg·K); The phase change heat storage capacity is: , is the mass of the phase change unit (kg), L is the latent heat of the phase change heat storage unit (kJ / kg); set up ; Calculation of heat conduction efficiency: Calculate heat flux density using Fourier's law: ; is the cavity surface temperature (°C), is the temperature of the phase change heat storage unit (°C); Volume of phase change heat storage unit: Determine the volume of the phase change heat storage unit according to the heat storage demand: ; is the density of the phase change thermal storage unit (kg / m 3 ).

[0007] The thermal stabilization method of the two-color injection mold as described above, wherein the cooling stage comprises: Initial cooling: When the cooling water circulation starts, the heat of the mold cavity is transferred to the phase change heat storage unit through the heat conduction layer to delay the temperature drop; Mid- and late-stage cooling: The phase change heat storage unit solidifies and releases latent heat. The stored heat is gradually transferred to the cooling water in the cooling water channel through the insulation layer, slowing down the overall cooling rate in the mold cavity.

[0008] In the thermal stabilization method for a two-color injection mold as described above, the cooling stage further includes controlling and reducing the cooling water flow in the cooling water circuit to extend the cooling time.

[0009] The thermal stabilization method of the two-color injection mold as described above, wherein the phase change heat storage unit is in direct contact with the mold cavity through copper foil, 2 to 3 mm away from the mold cavity surface; a 5 mm insulation layer is spaced between the phase change heat storage unit and the cooling water channel, and the insulation layer is thick ceramic fiber.

[0010] The heat stabilization method of the two-color injection mold as described above, wherein the phase change heat storage material is a paraffin-based composite phase change heat storage material with a melting point of 90~100°C and a latent heat of 200kJ / kg; the packaging shell is a high-temperature resistant aluminum alloy with a thermal conductivity of 237W / m·K and a honeycomb structure inside; the thermal conductive layer is copper foil with a thermal conductivity of 401W / m·K, and the thermal insulation layer is a ceramic fiber with a thermal conductivity of 0.1 W / m·K.

[0011] The present invention also discloses a thermal stabilizing structure of a two-color injection mold, which includes a rotary two-color injection mold structure provided with a phase change heat storage unit using the method described above.

[0012] From the above description, it can be seen that the present invention has the following advantages: The invention discloses a heat stabilization structure and method for a two-color injection mold. The phase change heat storage unit is used to balance the mold temperature fluctuation and prevent the softening of the first color material due to a sudden drop in temperature. The temperature stability is enhanced and the dependence on the external cooling system is reduced. The temperature is passively adjusted by utilizing the characteristics of the phase change heat storage material absorbing / releasing latent heat during solid-liquid or solid-solid phase change. The mold itself triggers the phase change without external energy input. The latent heat of the phase change heat storage material buffers the temperature fluctuation, which has the effect of "peak shaving and valley filling".

[0013] The present invention can effectively balance the temperature fluctuation of the mold, absorb or release heat to stabilize the local temperature, and prevent the softening or defects of the material caused by sudden cooling and heating. It has many characteristics, such as no energy consumption, reduced operating costs, simplified temperature control system design, and reduced impact of temperature fluctuations on material properties. The present invention cooperates with the hot runner system to control the temperature stability of the two-color injection mold, not only to obtain the hot runner system to ensure the fluidity and filling efficiency of the molten plastic; but also the phase change heat storage unit absorbs excess heat in the key area of ​​the mold (such as the first color molding position), to prevent the first color material from softening due to a sudden drop in temperature during the secondary injection molding.

[0014] The phase change heat storage unit of the present invention is independent of the hot runner and only acts on a local area of ​​the mold cavity without affecting the melt flow. The temperature fluctuation of the mold cavity is controlled within ±5°C by absorbing or releasing the latent heat of phase change. The phase change heat storage unit is integrated around the mold cavity by encapsulating the combined structure of the phase change heat storage material, the heat conductive layer and the heat insulating layer, and the temperature is stabilized by absorbing / releasing the latent heat. Finally, efficient and energy-saving two-color injection molding production is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the heat stabilization method of the two-color injection mold of the present invention. DETAILED DESCRIPTION

[0016] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described with reference to the accompanying drawings.

[0017] The present invention provides a thermal stabilization method for a two-color injection mold. In order to achieve a better balance of mold temperature fluctuations and prevent the first color material from softening due to a sudden drop in temperature, please refer to Figure 1 As shown, in a preferred embodiment, the heat stabilization method of the two-color injection mold of the present invention includes: configuring a phase change heat storage unit in a rotary two-color injection mold, the phase change heat storage unit is a packaging unit of a phase change heat storage material, and is embedded in an annular groove provided on the outer wall of the mold cavity on the movable mold side of the two-color injection mold; the phase change heat storage unit uses a high-temperature resistant aluminum alloy packaging shell to encapsulate the phase change heat storage material (PCM) inside, and a heat conductive layer is provided on the outer surface in contact with the mold cavity, and a heat insulating layer is provided on other outer surfaces; the melting point of the phase change heat storage material is lower than the softening point of the plastic material and higher than the demolding temperature of the plastic material; the temperature is passively adjusted by utilizing the characteristics of the phase change heat storage material absorbing / releasing latent heat during solid-liquid or solid-solid phase change; relying on the temperature change of the mold itself to trigger the phase change, without external energy input, to achieve the injection molding effect of balancing the mold temperature fluctuation and preventing the softening of the first color material caused by the sudden drop in temperature.

[0018] The double-color injection mold of the present invention includes a first injection and a second injection after the mold is rotated during injection molding: During the first injection molding, the molten first material heated to a first high temperature (the temperature at which the plastic of the first material melts) is injected into the lower mold cavity through the hot runner, and solidified by cooling to below a first low temperature (the solidification temperature of the first material); the phase change heat storage unit absorbs the heat of the mold cavity, and begins to melt when the temperature rises to the first low temperature, thereby delaying the temperature rise of the mold cavity.

[0019] During the second injection molding after the mold is rotated, the molten second material heated to the second high temperature (the temperature at which the plastic of the second material melts) is injected into the upper mold cavity, and the heat is transferred to the lower first material area through the mold cavity; the phase change heat storage unit controls the temperature of the lower mold cavity below the third temperature (the softening temperature of the second material) by absorbing latent heat to prevent the first material from softening.

[0020] In the preferred embodiment of the heat stabilization method of the two-color injection mold of the present invention as described above, the cooling water channel of the two-color injection mold is arranged outside the phase change heat storage unit on the movable mold side, the mold cavity is located inside the phase change heat storage unit, and a heat insulation layer is arranged between the phase change heat storage unit and the cooling water channel; The two-color injection mold also includes a cooling stage during injection molding. During the cooling stage, the cooling water circulation of the cooling water circuit is started, the phase change heat storage material in the phase change heat storage unit solidifies, releases the stored heat, slows down the cooling rate of the mold cavity, and reduces the residual stress of the two-color plastic product.

[0021] In the preferred embodiment of the heat stabilization method of the two-color injection mold of the present invention as described above, when specifically configuring the phase change heat storage unit, it is necessary to accurately and effectively determine the size of the heat capacity of the required phase change heat storage unit, so it is necessary to calculate the volume of the phase change heat storage unit, including: Calculation of heat storage requirements: The amount of heat to be absorbed is determined by the amount of heat transferred from the melt to the mold cavity: , The heat released by the melt is: , in, is the total heat absorption, Release heat to the melt, is the cooling water heat, is the mass of plastic injection molded in kg, is the specific heat capacity of the plastic (kJ / kg·K); The phase change heat storage capacity is: , is the mass of the phase change unit (kg), L is the latent heat of the phase change heat storage unit (kJ / kg); set up ; Calculation of heat conduction efficiency: Calculate heat flux density using Fourier's law: , is the cavity surface temperature (°C), is the temperature of the phase change heat storage unit (°C); Volume of phase change heat storage unit: Determine the volume of the phase change heat storage unit according to the heat storage demand: ; is the density of the phase change thermal storage unit (kg / m 3 ).

[0022] Through the calculation of the above formula, according to the principle that the heat capacity of the phase change heat storage unit is greater than the total heat of one injection, and according to the relationship between the heat conduction parameters of the actual plastic material, mold material and phase change heat storage material, the volume of the required phase change heat storage unit can be calculated. According to the calculated volume, an annular groove that can cover the mold cavity is designed around the mold cavity of the movable mold, and a phase change heat storage material unit with a total volume equal to the volume of the required phase change heat storage material is laid, so that it can conduct efficient heat conduction with the adjacent mold cavity through the heat conductive sheet.

[0023] Now let's take a specific two-color injection molding product manufacturing process as an example to illustrate the above calculation method: Take the example of a rotary two-color injection mold making a plastic plate with two colors on the top and bottom. The first injection is the ABS material of the lower layer. The molten ABS (230°C) is injected into the lower mold cavity through the hot runner and solidified when cooled to below 90°C. The PCM unit, with an initial temperature of 25°C, absorbs the heat of the mold cavity and begins to melt when the temperature rises to 90°C. This is a latent heat absorption process that can effectively delay the temperature rise of the mold cavity. In this process, the required volume of PCM is calculated using the following parameters.

[0024] The parameters used in this injection molding include: Single injection ABS mass: 0.1 kg, ABS specific heat capacity: 1.6 kJ / kg·K, Melt temperature: 230°C, target cavity temperature: ≤100°C; PCM latent heat: 200 kJ / kg, density: 900 kg / m³.

[0025] First calculate the heat released by the melt: ; Then calculate the required PCM quality: , Finally, the PCM unit volume is calculated: , Therefore, the area of ​​the cavity surface can be 0.02m 2 and PCM unit thickness 10mm, the required coverage area is further calculated as: .

[0026] Among them, in actual design, we need to pay attention to the following points: 1. Selection of phase change heat storage materials: The melting point needs to be slightly lower than the target temperature control point (e.g. ABS softening point is 105°C, select PCM with a melting point of 90~100°C).

[0027] 2.Mold material matching: The thermal conductivity of the PCM packaging shell must be higher than that of the mold steel (such as aluminum> steel) to ensure rapid heat transfer.

[0028] 3. Time synchronization: The injection molding cycle needs to match the PCM phase change time to avoid heat accumulation due to untimely heat release.

[0029] 4. Space limitation: The volume of the PCM unit needs to fit the space around the mold cavity to avoid interfering with mold movement or cooling water channels.

[0030] The phase change heat storage unit is integrated around the mold cavity by encapsulating the combined structure of phase change heat storage material, heat conductive layer and heat insulation layer, and uses latent heat absorption / release to achieve temperature stability. The design needs to comprehensively consider the thermal properties of the material, geometric parameters and process conditions, and quantify the heat storage requirements and unit size through the above formula, ultimately achieving efficient and energy-saving two-color injection molding production.

[0031] In the above-mentioned heat stabilization method of the two-color injection mold of the present invention, in a preferred embodiment, the cooling stage includes: Initial cooling: When the cooling water circulation starts, the heat of the mold cavity is transferred to the phase change heat storage unit through the heat conduction layer to delay the temperature drop; Mid- and late-stage cooling: The phase change heat storage unit solidifies and releases latent heat. The stored heat is gradually transferred to the cooling water in the cooling water channel through the insulation layer, slowing down the overall cooling rate in the mold cavity.

[0032] The positional relationship between the PCM unit and the cooling water channel is that the PCM unit is close to the outer wall of the mold cavity, and the outer side is the insulation layer (5 mm thick ceramic fiber) and the cooling water channel in turn; the cooling water channel is in direct contact with the insulation layer and is not directly connected to the PCM unit. This can avoid direct conflict between cold and heat. Otherwise, the low temperature of the cooling water (usually 20~50°C) will absorb heat quickly. If it directly contacts the PCM unit, it may trigger its solidification and release heat prematurely, weakening its buffering effect. The low thermal conductivity of the insulation layer (thermal conductivity of ceramic fiber is 0.1 W / m·K) can reduce the heat transfer rate between the cold and hot areas, so that the PCM unit mainly responds to changes in the mold cavity temperature rather than the cooling water temperature.

[0033] Furthermore, the PCM unit needs to absorb the heat of the mold cavity first (such as the heat of the high-temperature PC melt during the second injection molding). The insulation layer can delay the cooling effect of the cooling water on the PCM unit to ensure that its heat storage capacity is used in the critical stage. The thermal resistance of the 5mm thick insulation layer can reduce the heat flow of the cooling water to the PCM unit to less than 10% of the heat flow of the mold cavity, achieving effective isolation.

[0034] In the preferred embodiment of the thermal stabilization method for a two-color injection mold of the present invention as described above, the cooling stage further comprises controlling and reducing the cooling water flow in the cooling water circuit to extend the cooling time.

[0035] The working process of the preferred PCM unit during the cooling phase is as follows, and its heat release mechanism is: Phase change direction: During the cooling stage, the PCM unit changes from liquid (melting state after absorbing heat) to solid (solidified state), releasing latent heat. According to the heat transfer path of mold cavity-PCM unit-cooling water, the heat of the mold cavity is transferred to the PCM unit through the heat conductive layer, and the PCM solidifies to release latent heat, which is then indirectly transferred to the cooling water through the insulation layer. In this process, the core of delaying cooling is that the latent heat release of PCM offsets part of the cooling water's heat dissipation capacity, slowing down the rate of temperature drop in the mold cavity.

[0036] Examples of specific steps: Cooling water starts: the water pump is turned on, and low-temperature cooling water flows into the mold cooling water channel.

[0037] Heat transfer from mold cavity: The high temperature mold cavity (e.g. 100°C) transfers heat to the PCM unit through the heat conductive layer (copper foil); When the temperature of the PCM unit drops to the phase change point (e.g. 90°C), it begins to solidify and releases latent heat (200 kJ / kg).

[0038] This creates a thermal buffer effect: the latent heat released by the PCM partially offsets the heat absorption capacity of the cooling water, and the cavity temperature drops at a slower rate (e.g., it takes 20 seconds to drop from 100°C to 60°C, instead of 15 seconds without PCM).

[0039] Thus, slow cooling reduces the temperature difference between the inner and outer layers of the plastic, resulting in more uniform shrinkage, reduced internal stress concentration, and controlled residual stress.

[0040] Furthermore, a simplified quantitative analysis of the cooling rate is performed through the following examples: The cooling rate in the unit without PCM is: , For example: it takes 15 seconds to cool from 100°C to 60°C, and the rate is ≈ 2.67°C / s; The cooling rate of the unit with PCM is: The latent heat released by PCM is equivalent to an additional heat source, and the cooling time is extended to 20 seconds, with a rate of ≈2.0°C / s, which is 25% slower than when there is no PCM unit.

[0041] Taking the "upper and lower two-color flat plate" as an example, after the second injection molding, it enters the cooling stage: Plastic material: upper layer PC (shrinkage rate 0.6%), lower layer ABS (shrinkage rate 0.5%); Cooling water temperature: 25°C, flow rate 10 L / min; PCM unit parameters: mass 0.1 kg, latent heat 200 kJ / kg; The cooling process is compared as follows: The comparisons between no PCM unit and with PCM unit are: The ratio of cooling time (100℃-60℃) is 15 seconds:20 seconds; The ratio of the temperature difference between the inner and outer layers is 20°C to 10°C; The ratio of residual stress (MPa) is 25 to 15.

[0042] The thermal stabilization method of the two-color injection mold of the present invention is that in the two-color injection mold, the PCM unit forms a "heat buffer layer" in the cooling stage by absorbing and releasing the latent heat of phase change, thereby slowing down the cooling rate of the mold cavity. It has obvious core value: Avoid residual stress and deformation caused by rapid cooling, balance cooling efficiency and quality; reduce high-load operation time of the cooling system, extend equipment life, save energy and reduce consumption; especially suitable for temperature-sensitive multi-material injection molding scenarios (such as two-color, soft and hard glue combination), with strong process adaptability.

[0043] Therefore, by adopting the thermal stabilization method of the two-color injection mold of the present invention and rationally designing the coordinated work of the PCM unit and the cooling system, high-efficiency and low-defect injection production can be achieved.

[0044] In a preferred embodiment, the thermal stabilization method of the two-color injection mold of the present invention can achieve energy saving and efficiency improvement: reduce the load of the cooling system and shorten the production cycle by about 10-15%.

[0045] Reducing the load on the cooling system involves the role of PCM in the cooling stage. Traditional cooling systems need to run continuously to quickly reduce the mold temperature, but PCM can reduce the burden on the cooling system after absorbing heat, because part of the heat is stored in the PCM instead of relying entirely on cooling water to take it away. The production cycle of two-color injection molding usually includes injection, pressure holding, cooling, mold opening and other stages. The cooling time is reduced, and the entire cycle time can also be shortened accordingly. In addition, the previous statement that PCM slows down the cooling rate does not contradict shortening the cooling time. The reason is: although PCM slows down the cooling rate, due to more uniform temperature or reduced residual stress, it can allow earlier demolding without affecting quality, thereby improving production efficiency and shortening the entire cycle.

[0046] During the cooling phase, PCM absorbs some of the heat, reducing the total amount of heat that the cooling system needs to handle, thereby reducing the load on the cooling system. At the same time, by optimizing temperature control, the time required for cooling can be reduced because PCM helps maintain a more stable temperature, avoiding overcooling or overheating, making cooling more efficient.

[0047] Below, a specific example is used to illustrate that in a two-color injection mold, the integrated phase change thermal storage unit (PCM) can achieve the goal of "reducing the cooling system load and shortening the production cycle by about 10~15%" compared to the traditional cooling system through the following mechanism.

[0048] First, the principle of reducing the cooling system load is: (1) Heat diversion and storage: Traditional cooling system: The heat of molten plastic (such as 280°C PC melt in the second injection) is completely removed by cooling water, and the cooling system needs to run at high load to cool down quickly.

[0049] The cooling system of the integrated PCM unit of the present invention: In the heat absorption stage, the PCM unit absorbs the instantaneous high temperature heat of the mold cavity during the injection molding process (such as the heat of the PC melt during the second injection molding) and stores it as latent heat; Heat release phase: During cooling, PCM slowly releases the stored heat to the cooling water, reducing the “instantaneous heat load peak” that the cooling water needs to handle.

[0050] (2) Reduce cooling water flow demand: Since the PCM shares part of the heat load, the cooling water does not need to run at maximum flow rate continuously. For example: Without PCM: The cooling water flow rate needs to be maintained at 15 L / min to cope with instantaneous high temperature; With PCM: the flow rate can be reduced to 12 L / min, reducing pumping energy consumption by 20%.

[0051] In addition, the present invention can also be illustrated by the following example to shorten the production cycle: (1) Time optimization of the cooling phase compared to traditional cooling systems Bottleneck of traditional cooling system: Cooling time accounts for 60%~70% of the production cycle, and it is necessary to wait for the mold cavity temperature to drop to the demolding threshold (such as ABS demolding temperature needs to be ≤60°C); The PCM unit of the present invention has a buffering effect, comprising: Delaying the temperature rise of the mold cavity: During the second injection, PCM absorbs the heat of the high-temperature melt, preventing the mold cavity temperature from being too high and reducing the time required for subsequent cooling; And uniform cooling: PCM releases latent heat to slow down the cooling rate, but by reducing the temperature gradient, it allows safe demoulding at slightly higher temperatures (such as from 60°C to 70°C), shortening the cooling time.

[0052] Quantitative analysis using actual design examples: A conventional cooling system without PCM takes 30 seconds to cool from 100°C to 60°C; In the cooling system of the integrated PCM unit of the present invention, the PCM absorbs heat to reduce the initial peak temperature of the mold cavity (such as from 100°C to 90°C), and allows the demoulding temperature to be increased to 70°C, and the cooling time is shortened to 25 seconds.

[0053] Cycle shortening ratio: shortening rate = (30-25) / 30×100%=16.7%; In actual applications, the overall cycle is shortened by about 10%~15% because the time of other stages, such as mold opening and ejection, is fixed.

[0054] From the above examples, it can be clearly determined that the thermal stabilization method of the two-color injection mold of the present invention can achieve energy saving and efficiency improvement: reduce the load of the cooling system and shorten the production cycle by about 10-15%.

[0055] As described above, in the preferred embodiment of the heat stabilization method of the two-color injection mold of the present invention, the phase change heat storage unit is in direct contact with the mold cavity through the copper foil, 2 to 3 mm away from the mold cavity surface; a 5 mm insulation layer is spaced between the phase change heat storage unit and the cooling water channel, and the insulation layer is thick ceramic fiber.

[0056] In the heat stabilization method of the two-color injection mold of the present invention as described above, in a preferred embodiment, the phase change heat storage material is a paraffin-based composite phase change heat storage material with a melting point of 90~100°C and a latent heat of 200kJ / kg; the packaging shell is a high-temperature resistant aluminum alloy with a thermal conductivity of 237 W / m·K and a honeycomb structure inside; the thermal conductive layer is a copper foil with a thermal conductivity of 401 W / m·K, and the thermal insulation layer is a ceramic fiber with a thermal conductivity of 0.1 W / m·K.

[0057] The present invention also discloses a thermal stabilizing structure of a two-color injection mold. In a preferred embodiment, the structure comprises a rotary two-color injection mold structure provided with a phase change heat storage unit using the above method.

[0058] The invention discloses a heat stabilization structure and method for a two-color injection mold. The phase change heat storage unit is used to balance the mold temperature fluctuation and prevent the softening of the first color material due to a sudden drop in temperature. The temperature stability is enhanced and the dependence on the external cooling system is reduced. The temperature is passively adjusted by utilizing the characteristics of the phase change heat storage material absorbing / releasing latent heat during solid-liquid or solid-solid phase change. The mold itself triggers the phase change without external energy input. The latent heat of the phase change heat storage material buffers the temperature fluctuation, which has the effect of "peak shaving and valley filling".

[0059] The present invention can effectively balance the temperature fluctuation of the mold, absorb or release heat to stabilize the local temperature, and prevent the softening or defects of the material caused by sudden cooling and heating. It has many characteristics, such as no energy consumption, reduced operating costs, simplified temperature control system design, and reduced impact of temperature fluctuations on material properties. The present invention cooperates with the hot runner system to control the temperature stability of the two-color injection mold, not only to obtain the hot runner system to ensure the fluidity and filling efficiency of the molten plastic; but also the phase change heat storage unit absorbs excess heat in the key area of ​​the mold (such as the first color molding position), to prevent the first color material from softening due to a sudden drop in temperature during the secondary injection molding.

[0060] The phase change heat storage unit of the present invention is independent of the hot runner and only acts on a local area of ​​the mold cavity without affecting the melt flow. The temperature fluctuation of the mold cavity is controlled within ±5°C by absorbing or releasing the latent heat of phase change. The phase change heat storage unit is integrated around the mold cavity by encapsulating the combined structure of the phase change heat storage material, the heat conductive layer and the heat insulating layer, and the temperature is stabilized by absorbing / releasing the latent heat. Finally, efficient and energy-saving two-color injection molding production is achieved.

[0061] The above description is only an illustrative embodiment of the present invention and is not intended to limit the scope of the present invention. Any equivalent changes and modifications made by any person skilled in the art without departing from the concept and principle of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A thermal stabilization method for a two-color injection mold, characterized in that: A phase-change heat storage unit is arranged in the rotary two-color injection mold, wherein the phase-change heat storage unit is a packaging unit of a phase-change heat storage material and is embedded in an annular groove provided on the outer wall of the mold cavity on the movable mold side of the two-color injection mold; The phase-change heat storage unit uses a high-temperature resistant aluminum alloy packaging shell to encapsulate the phase-change heat storage material inside, and a heat-conducting layer is provided on the outer surface in contact with the mold cavity, and a heat-insulating layer is provided on other outer surfaces; the melting point of the phase-change heat storage material is lower than the softening point of the plastic material and higher than the demoulding temperature of the plastic material; Two-color injection mold injection includes the first injection and the second injection after the mold is rotated: During the first injection molding, the molten first material heated to a first high temperature is injected into the lower mold cavity through the hot runner, and solidified after being cooled to below a first low temperature; the phase change heat storage unit absorbs the heat of the mold cavity, and begins to melt when the temperature rises to the first low temperature, thereby delaying the temperature rise of the mold cavity; During the second injection molding after the mold is rotated, the molten second material heated to the second high temperature is injected into the upper mold cavity, and the heat is transferred to the lower first material area through the mold cavity; the phase change heat storage unit controls the temperature of the lower mold cavity below the third temperature through latent heat absorption to prevent the first material from softening.

2. The heat stabilization method for a two-color injection mold according to claim 1, characterized in that: The cooling water channel of the two-color injection mold is arranged on the outer side of the phase change heat storage unit on the movable mold side, the mold cavity is located on the inner side of the phase change heat storage unit, and an insulation layer is arranged between the phase change heat storage unit and the cooling water channel; The two-color injection mold also includes a cooling stage during injection molding. During the cooling stage, the cooling water circulation of the cooling water circuit is started, the phase change heat storage material in the phase change heat storage unit solidifies, releases the stored heat, slows down the cooling rate of the mold cavity, and reduces the residual stress of the two-color plastic product.

3. The heat stabilization method for a two-color injection mold according to claim 2, characterized in that: Calculate the volume of the phase change thermal storage unit, including: Calculation of heat storage requirements: The amount of heat to be absorbed is determined by the amount of heat transferred from the melt to the mold cavity: , The heat released by the melt is: , in, is the total heat absorption, Release heat to the melt, is the cooling water heat, is the mass of plastic injection molded in kg, is the specific heat capacity of the plastic (kJ / kg·K); The phase change heat storage capacity is: , is the mass of the phase change unit (kg), L is the latent heat of the phase change heat storage unit (kJ / kg); set up ; Calculation of heat conduction efficiency: Calculate heat flux density using Fourier's law: , is the cavity surface temperature (°C), is the temperature of the phase change heat storage unit (°C); Volume of phase change heat storage unit: Determine the volume of the phase change heat storage unit according to the heat storage demand: ; is the density of the phase change thermal storage unit (kg / m 3 ).

4. The heat stabilization method for a two-color injection mold according to claim 2, characterized in that: The cooling stage includes: Initial cooling: When the cooling water circulation starts, the heat of the mold cavity is transferred to the phase change heat storage unit through the heat conduction layer to be absorbed, delaying the temperature drop; Mid- and late-stage cooling: The phase change heat storage unit solidifies and releases latent heat. The stored heat is gradually transferred to the cooling water in the cooling water channel through the insulation layer, slowing down the overall cooling rate in the mold cavity.

5. The heat stabilization method for a two-color injection mold according to claim 4, characterized in that: The cooling stage also includes controlling to reduce the cooling water flow in the cooling water circuit to extend the cooling time.

6. The thermal stabilization method for a two-color injection mold according to claim 5, characterized in that: The phase change heat storage unit is in direct contact with the mold cavity through the copper foil, and is 2-3 mm away from the mold cavity surface; a 5 mm insulation layer is provided between the phase change heat storage unit and the cooling water channel, and the insulation layer is thick ceramic fiber.

7. The thermal stabilization method for a two-color injection mold according to claim 6, characterized in that: The phase change heat storage material is a paraffin-based composite phase change heat storage material with a melting point of 90-100°C and a latent heat of 200 kJ / kg; the packaging shell is a high-temperature resistant aluminum alloy with a thermal conductivity of 237 W / m·K and a honeycomb structure inside; the thermal conductive layer is copper foil with a thermal conductivity of 401 W / m·K, and the thermal insulation layer is a ceramic fiber with a thermal conductivity of 0.1 W / m·K.

8. A thermal stabilization structure for a two-color injection mold, characterized in that: The invention comprises adopting the method described in any one of claims 1 to 6, and providing a rotary two-color injection mold structure with a phase change heat storage unit.

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