Thermal stability structure and method for a two-color injection mold

Abstract

A method for stabilizing the heat of a two-color injection mold, which configures a phase change heat storage unit in a rotary two-color injection mold and is embedded in an annular groove opened on the outer wall of the mold cavity on the moving mold side of the two-color injection mold; the phase change heat storage unit encapsulates a phase change heat storage material, and a heat insulation 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; during the first injection molding, the molten first material heated to the first high temperature is injected into the lower mold cavity through the hot runner and solidifies when cooled below the first low temperature; the phase change heat storage unit absorbs the heat of the mold cavity and starts to melt when the temperature rises to the first low temperature, delaying the temperature rise of the mold cavity; during the second injection molding, the molten second material heated to the second high temperature is injected into the upper 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. The present invention can balance the temperature fluctuation of the mold and prevent the softening of the first injection molding material caused by sudden temperature drop.

Description

Technical Field

[0001] The present invention relates to a plastic processing technology, in particular to a heat stabilization structure and method for a two-color injection mold. Background Art

[0002] The application of two-color injection molding technology is becoming more and more widespread. Especially today, with the increasing demand for plastic products that require two colors, the quality requirements for two-color plastic products are getting higher and higher. A two-color injection mold is formed by injecting two different materials or two plastics of the same material but different colors. Such production molds are generally divided into two categories. One is a mixed-color two-color injection mold, and this technology is relatively simple to implement; the other is a double-layer two-color injection mold, that is, a two-color product with an obvious boundary formed by two injection nozzles injecting two materials successively. During the processing, the first injection nozzle injects the material into the first cavity and forms. Then, the mold is opened but not ejected, and the mold rotates 180 degrees and then closes; the second injection nozzle injects another material into the second cavity that already has the first material. In this way, after the two materials are stuck together, the mold is opened and ejected for the second time, and a complete two-color product is injection-molded. For example, the "Two-color Injection Mold with Quick Demolding" with the patent number 202411562944.8 also adopts a rotating structure to achieve two-color injection molding. In such two-color injection molds, a hot runner system (Hot Runner System) is generally used as the temperature control system. Its core goal is to avoid the 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, heating coils) are embedded inside the runner, and the temperature is precisely adjusted through temperature sensors and controllers to ensure that the plastic is always in a molten state. However, even with this temperature control system, there may still be an unstable sudden change in temperature during the second injection in two-color injection molding, resulting in the softening of the first-color material and 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 heat stabilization structure and method for a two-color injection mold, balance the temperature fluctuation of the mold, and prevent the softening of the first injection material caused by a sudden temperature drop.

[0004] The technical solution of the present invention is:

[0005] A heat stabilization method for a two-color injection mold, wherein a phase change heat storage unit is configured in a rotary two-color injection mold. The phase change heat storage unit is an encapsulation unit of a phase change heat storage material, and is embedded in an annular groove formed on the outer wall of the mold cavity on the moving mold side of the two-color injection mold;

[0006] The phase change heat storage unit uses a high-temperature resistant aluminum alloy encapsulation shell to encapsulate the phase change heat storage material inside. It is provided with a heat conduction layer on the outer surface in contact with the mold cavity and an insulating layer 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.

[0007] The two-color injection molding includes a first injection and a second injection after the mold rotates:

[0008] During the first injection, the molten first material heated to the first high temperature is injected into the lower mold cavity through the hot runner and solidifies after cooling below the first low temperature; the phase change heat storage unit absorbs the heat of the mold cavity and starts to melt when the temperature rises to the first low temperature, delaying the temperature rise of the mold cavity.

[0009] During the second injection after the mold rotates, 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.

[0010] For the heat stabilization method of the two-color injection mold as described above, the cooling water channel of the two-color injection mold is arranged outside the phase change heat storage unit on the moving mold side, the mold cavity is located inside the phase change heat storage unit, and an insulating layer is arranged between the phase change heat storage unit and the cooling water channel.

[0011] The two-color injection molding also includes a cooling stage. During the cooling stage, the cooling water circulation of the cooling water channel 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.

[0012] For the heat stabilization method of the two-color injection mold as described above, calculating the volume of the phase change heat storage unit includes:

[0013] Heat storage demand calculation: The heat to be absorbed is determined by the heat transferred from the melt to the mold cavity: ,

[0014] The heat released by the melt is: ,

[0015] Among them, is the total heat absorption, is the heat released by the melt, is the heat of the cooling water, is the mass of the plastic injected each time (kg), is the specific heat capacity of the plastic (kJ / kg·K);

[0016] The phase change heat storage capacity is: ,

[0017] is the mass of the phase change unit (kg), and L is the latent heat of the phase change heat storage unit (kJ / kg);

[0018] Set ;

[0019] Calculation of heat conduction efficiency: Calculate the heat flux density through Fourier's law: ;

[0020] is the temperature of the cavity surface (°C), is the temperature of the phase change heat storage unit (°C);

[0021] Volume of the phase change heat storage unit:

[0022] Determine the volume of the phase change heat storage unit according to the heat storage demand: ;

[0023] is the density of the phase change heat storage unit (kg / m 3 ).

[0024] The heat stabilization method of the two-color injection mold as described above, wherein the cooling stage includes:

[0025] Initial cooling: When the cooling water circulation starts, the heat of the cavity is transferred to the phase change heat storage unit through the heat conduction layer for absorption, delaying the temperature drop;

[0026] Mid-to-late cooling: The phase change heat storage unit solidifies and releases latent heat, and the stored heat is gradually transferred to the cooling water in the cooling water channel through the heat insulation layer, slowing down the overall cooling rate in the cavity.

[0027] The heat stabilization method of the two-color injection mold as described above, wherein the cooling stage further includes controlling and reducing the flow rate of the cooling water in the cooling water channel and prolonging the cooling time.

[0028] The heat stabilization method of the two-color injection mold as described above, wherein the phase change heat storage unit is in direct contact with the cavity through a copper foil, 2 - 3 mm away from the cavity surface; there is a 5-mm heat insulation layer between the phase change heat storage unit and the cooling water channel, and the heat insulation layer is thick ceramic fiber.

[0029] 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 200 kJ / kg; the encapsulation shell is high-temperature-resistant aluminum alloy, with a thermal conductivity of 237 W / m·K and a honeycomb structure inside; the heat conduction layer is copper foil, with a thermal conductivity of 401 W / m·K, and the heat insulation layer is ceramic fiber with a thermal conductivity of 0.1 W / m·K.

[0030] The present invention also discloses a heat stabilization structure for a two-color injection mold, which includes a rotary two-color injection mold structure provided with a phase change heat storage unit by using the method described above.

[0031] As can be seen from the above description, the present invention indeed has the following advantages:

[0032] The heat stabilization structure and method for a two-color injection mold of the present invention use a phase change heat storage unit to balance the temperature fluctuations of the mold and prevent the softening of the first color material caused by a sudden temperature drop; enhance temperature stability and reduce the dependence on the external cooling system; utilize the characteristics of the phase change heat storage material to absorb / release latent heat during solid-liquid or solid-solid phase changes to passively regulate the temperature; rely on the temperature change of the mold itself to trigger the phase change without external energy input. The latent heat of the phase change heat storage material buffers the temperature fluctuations, having a "peak shaving and valley filling" effect.

[0033] The present invention can effectively balance the temperature fluctuations 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 the characteristics of no energy consumption, reduced operating costs, simplified temperature control system design, and reduced influence 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 obtaining the hot runner system to ensure the fluidity and filling efficiency of the molten plastic; but also the phase change heat storage unit absorbs the excess heat in the key areas of the mold (such as the first color molding position) to prevent the softening of the first color material caused by a sudden temperature drop during the second injection.

[0034] The phase change heat storage unit of the present invention is independent of the hot runner and only acts on the local area of the mold cavity without affecting the melt flow. By absorbing or releasing the latent heat of the phase change, the temperature fluctuations of the mold cavity are controlled within ±5°C. The phase change heat storage unit is integrated around the mold cavity through a combined structure of encapsulating the phase change heat storage material, the heat conducting layer, and the heat insulating layer, and realizes temperature stability by absorbing / releasing the latent heat. Finally, high-efficiency and energy-saving two-color injection molding production is achieved. Description of the Drawings

[0035] Figure 1 It is a schematic diagram of the heat stabilization method for the two-color injection mold of the present invention. Detailed Embodiments

[0036] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the detailed embodiments of the present invention are now described with reference to the drawings.

[0037] For a heat stabilization method of a two-color injection mold of the present invention, in order to achieve a better injection molding effect of balancing the temperature fluctuations of the mold and preventing the softening of the first color material caused by a sudden temperature drop, please refer to Figure 1As shown, in a preferred embodiment of the present invention, the method for stabilizing the temperature of a two-color injection mold 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 for a phase change heat storage material, which is embedded in an annular groove formed on the outer wall of the mold cavity on the moving 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. It is provided with a heat conduction layer on the outer surface in contact with the mold cavity and an insulating layer 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. By utilizing the characteristics of the phase change heat storage material absorbing / releasing latent heat during solid-liquid or solid-solid phase changes, the temperature is passively adjusted. Triggering the phase change depends on the change in the temperature of the mold itself without external energy input, achieving the injection molding effect of balancing the temperature fluctuation of the mold and preventing the softening of the first color material caused by a sudden drop in temperature.

[0038] The injection molding of the two-color injection mold of the present invention includes the first injection molding and the second injection molding after the mold rotates:

[0039] During the first injection molding, the molten first material heated to the 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 solidifies below the first low temperature (the solidification temperature of the first material). The phase change heat storage unit absorbs the heat of the mold cavity and starts to melt when the temperature rises to the first low temperature, delaying the temperature rise of the mold cavity.

[0040] During the second injection molding after the mold rotates, 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) through latent heat absorption, preventing the first material from softening.

[0041] In the method for stabilizing the temperature of the two-color injection mold of the present invention as described above, in a preferred embodiment, the cooling water channel of the two-color injection mold is arranged outside the phase change heat storage unit on the moving mold side, and the mold cavity is located inside the phase change heat storage unit. An insulating layer is arranged between the phase change heat storage unit and the cooling water channel;

[0042] The injection molding of the two-color injection mold also includes a cooling stage. During the cooling stage, the cooling water in the cooling water channel starts to circulate, and the phase change heat storage material in the phase change heat storage unit solidifies, releasing the stored heat, slowing down the cooling rate of the mold cavity, and reducing the residual stress of the two-color plastic product.

[0043] In the method for stabilizing the temperature of the two-color injection mold of the present invention as described above, in a preferred embodiment, 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. Therefore, it is necessary to calculate the volume of the phase change heat storage unit, including:

[0044] Calculation of heat storage demand: The heat to be absorbed is determined by the heat transferred from the melt to the mold cavity: ,

[0045] The heat released by the melt is: ,

[0046] Among them, is the total heat absorption, is the heat released by the melt, is the heat of the cooling water, is the mass of the single-shot injection plastic (kg), is the specific heat capacity of the plastic (kJ / kg·K);

[0047] The phase change heat storage capacity is: ,

[0048] is the mass of the phase change unit (kg), and L is the latent heat of the phase change heat storage unit (kJ / kg);

[0049] Set ;

[0050] Calculation of heat conduction efficiency: Calculate the heat flux density through Fourier's law: ,

[0051] is the surface temperature of the mold cavity (°C), is the temperature of the phase change heat storage unit (°C);

[0052] Volume of the phase change heat storage unit:

[0053] Determine the volume of the phase change heat storage unit according to the heat storage demand: ;

[0054] is the density of the phase change heat storage unit (kg / m 3 ).

[0055] Through the calculation of the above formulas, in accordance with the principle that the heat capacity of the phase change heat storage unit is greater than the total heat of a single injection, based on the relationship of the heat conduction parameters among 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, a ring-shaped groove that can cover the mold cavity is designed around the mold cavity of the moving 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 heat efficiently with the adjacent and separated mold cavities through heat conduction sheets.

[0056] Now, take the manufacturing and processing of a specific two-color injection molded product as an example to illustrate the above calculation method:

[0057] Taking the manufacture of a two-color plastic flat plate with a rotary two-color injection mold as an example, the first injection molding is the lower layer of ABS material. The molten ABS (230°C) is injected into the lower mold cavity through the hot runner and solidifies after cooling to below 90°C. The PCM unit, with an initial temperature of 25°C, absorbs the heat of the mold cavity and starts 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. During this process, the volume of the required PCM is calculated through the following parameters.

[0058] The parameters used in this injection molding include:

[0059] Mass of single injection of ABS: 0.1 kg,

[0060] Specific heat capacity of ABS: 1.6 kJ / kg·K,

[0061] Melt temperature: 230°C, target mold cavity temperature: ≤100°C;

[0062] Latent heat of PCM: 200 kJ / kg, density: 900 kg / m³.

[0063] First, calculate the heat released by the melt: ;

[0064] Then, calculate the required mass of PCM: ,

[0065] Finally, calculate the volume of the PCM unit: ,

[0066] Therefore, based on the surface area of the mold cavity being 0.02 m 2 and the thickness of the PCM unit being 10 mm, the required coverage area can be further calculated as: .

[0067] Among them, in actual design, the following points need to be noted:

[0068] 1. Selection of phase change heat storage material: The melting point should be slightly lower than the target temperature control point (e.g., the softening point of ABS is 105°C, select a PCM with a melting point of 90 - 100°C).

[0069] 2. Matching of mold materials: The thermal conductivity of the PCM encapsulation shell should be higher than that of the mold steel (e.g., aluminum > steel) to ensure rapid heat transfer.

[0070] 3. Time synchronization: The injection molding cycle should match the phase change time of the PCM to avoid heat accumulation due to untimely heat release.

[0071] 4. Space limitation: The volume of the PCM unit should be adapted to the space around the mold cavity to avoid interfering with the movement of the mold or the cooling water circuit.

[0072] The phase change heat storage unit is integrated around the mold cavity through a combined structure encapsulating the phase change heat storage material, the heat conducting layer and the heat insulating layer, and realizes temperature stability by utilizing latent heat absorption / release. During the design, the thermal physical properties of the material, geometric parameters and process conditions need to be comprehensively considered, and the heat storage demand and unit size are quantified through the above formula, so as to finally realize efficient and energy-saving two-color injection molding production.

[0073] In the preferred embodiment of the heat stabilization method of the two-color injection mold of the present invention as described above, the cooling stage includes:

[0074] 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 conducting layer for absorption, delaying the temperature drop;

[0075] Mid-late cooling: The phase change heat storage unit solidifies and releases latent heat, and the stored heat is gradually transferred to the cooling water in the cooling water channel through the heat insulating layer, slowing down the overall cooling rate in the mold cavity.

[0076] The positional relationship between the PCM unit and the cooling water channel is that the PCM unit is closely attached to the outer wall of the mold cavity, and the heat insulating layer (5 mm thick ceramic fiber) and the cooling water channel are arranged in sequence on the outside; the cooling water channel is in direct contact with the heat insulating layer and is not directly connected to the PCM unit. This can avoid direct conflict between heat and cold. Otherwise, the low temperature of the cooling water (usually 20 - 50 °C) will quickly absorb heat. If it is directly in contact with the PCM unit, it may prematurely trigger its solidification and heat release, weakening its buffering effect. And the low thermal conductivity of the heat insulating layer (the thermal conductivity of ceramic fiber is 0.1 W / m·K) can reduce the heat transfer rate between the hot and cold regions, making the PCM unit mainly respond to the temperature change of the mold cavity rather than the temperature of the cooling water.

[0077] Furthermore, the PCM unit needs to preferentially absorb the heat of the mold cavity (such as the heat of the high-temperature PC melt during the second injection molding). The heat insulating layer can delay the cooling effect of the cooling water on the PCM unit, ensuring that its heat storage capacity is used in the critical stage. The thermal resistance of the 5 mm thick heat insulating 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.

[0078] In the preferred embodiment of the heat stabilization method of the two-color injection mold of the present invention as described above, the cooling stage further includes controlling and reducing the flow rate of the cooling water in the cooling water channel and prolonging the cooling time.

[0079] The working process of the preferred PCM unit during the cooling stage is as follows, and its heat release mechanism is:

[0080] The phase change direction is as follows: during the cooling stage, the PCM unit changes from the liquid state (the melted state after absorbing heat) to the solid state (the solidified state), releasing latent heat. Following 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 conducting layer. When the PCM solidifies, latent heat is released, and the heat is then indirectly transferred to the cooling water through the heat insulation layer. In this process, the core of delaying cooling is that the release of latent heat by the PCM offsets part of the heat dissipation capacity of the cooling water, slowing down the rate of temperature drop in the mold cavity.

[0081] Examples of specific steps:

[0082] Cooling water starts: The water pump is turned on, and low-temperature cooling water flows into the mold cooling water circuit.

[0083] Heat transfer of the mold cavity: The high-temperature mold cavity (such as 100°C) conducts heat to the PCM unit through the heat conducting layer (copper foil);

[0084] When the temperature of the PCM unit drops to the phase change point (such as 90°C), it begins to solidify and release latent heat (200 kJ / kg).

[0085] The resulting thermal buffering effect: The latent heat released by the PCM partially offsets the heat absorption capacity of the cooling water, and the temperature of the mold cavity drops at a slower rate (for example, it takes 20 seconds to drop from 100°C to 60°C, instead of 15 seconds without PCM).

[0086] Thereby, the slow cooling reduces the temperature difference between the inner and outer layers of the plastic, shrinks more evenly, reduces the concentration of internal stress, and controls the residual stress.

[0087] Furthermore, the quantitative analysis of the cooling rate can be simplified through the following embodiments:

[0088] The cooling rate without the PCM unit is: ,

[0089] For example: it takes 15 seconds to drop from 100°C to 60°C, and the rate is approximately 2.67°C / s;

[0090] The cooling rate with the PCM unit is:

[0091] The latent heat released by the PCM is equivalent to an additional heat source, and the cooling time is extended to 20 seconds, with a rate of approximately 2.0°C / s, which is 25% slower than without the PCM unit.

[0092] Taking the "upper and lower two-color flat plate" as an example, after the second injection molding, it enters the cooling stage:

[0093] Plastic materials: PC (shrinkage rate 0.6%) for the upper layer and ABS (shrinkage rate 0.5%) for the lower layer;

[0094] Cooling water temperature: 25°C, flow rate 10 L / min;

[0095] PCM unit parameters: mass 0.1 kg, latent heat 200 kJ / kg;

[0096] The comparison of the cooling processes is as follows:

[0097] The comparisons for the case without a PCM unit and the case with a PCM unit are respectively:

[0098] The ratio of the cooling time (100°C - 60°C) is 15 s : 20 s;

[0099] The ratio of the temperature difference between the inner and outer layers is 20°C to 10°C;

[0100] The ratio of the residual stress (MPa) is 25 to 15.

[0101] The heat stabilization method of the two-color injection mold of the present invention. In the two-color injection mold, the PCM unit forms a "thermal buffer layer" during the cooling stage by absorbing and releasing the latent heat of phase change, slowing down the cooling rate of the mold cavity. It has obvious core values:

[0102] Avoid residual stress and deformation caused by rapid cooling, balance the cooling efficiency and quality; reduce the high-load operation time of the cooling system, extend the equipment life, save energy and reduce consumption; especially suitable for temperature-sensitive multi-material injection scenarios (such as two-color, combination of hard and soft rubber), with strong process adaptability.

[0103] Therefore, by adopting the heat stabilization method of the two-color injection mold of the present invention, through the reasonable design of the coordinated work of the PCM unit and the cooling system, high-efficiency and low-defect injection production can be achieved.

[0104] In a preferred embodiment, by adopting the heat stabilization method of the two-color injection mold of the present invention, energy conservation and efficiency improvement can be achieved: reducing the load of the cooling system and shortening the production cycle by about 10 - 15%.

[0105] Reducing the load of the cooling system involves the role of the PCM during the cooling stage. The traditional cooling system needs to continuously operate to rapidly reduce the mold temperature, while after the PCM absorbs heat, it can reduce the burden on the cooling system because part of the heat is stored in the PCM instead of being completely dependent on the cooling water to carry away. The production cycle of two-color injection usually includes stages such as injection, holding pressure, cooling, and mold opening. When the cooling time is reduced, the entire cycle time can also be correspondingly shortened. Additionally, the previous mention of the PCM slowing down the cooling rate is not contradictory to shortening the cooling time. The reason is that although the PCM slows down the cooling rate, due to more uniform temperature or reduced residual stress, earlier demolding can be allowed without affecting the quality, thereby improving production efficiency and shortening the entire cycle.

[0106] During the cooling phase, the PCM absorbs some heat, reducing the total amount of heat that the cooling system needs to handle, thus reducing the load on the cooling system. At the same time, by optimizing the temperature control, the cooling time can be reduced because the PCM helps maintain a more stable temperature, avoiding overcooling or overheating, making the cooling more efficient.

[0107] Next, taking a specific embodiment as an example, in a two-color injection mold, the integrated phase change heat storage unit (PCM) can achieve the goal of "reducing the load on the cooling system and shortening the production cycle by about 10 - 15%" compared with the traditional cooling system through the following mechanisms.

[0108] First, the principle of realizing the reduction of the cooling system load is as follows:

[0109] (1) Heat diversion and storage:

[0110] Traditional cooling system: The heat of the molten plastic (such as the PC melt at 280°C in the second injection) completely depends on the cooling water to carry away, and the cooling system needs to operate at a high load to quickly cool down.

[0111] Cooling system with the integrated PCM unit of the present invention:

[0112] During the heat absorption stage, the PCM unit absorbs the instantaneous high-temperature heat in the mold cavity (such as the heat of the PC melt during the second injection) during the injection process and stores it as latent heat;

[0113] During the heat release stage: During cooling, the PCM slowly releases the stored heat to the cooling water, reducing the "instantaneous heat load peak" that the cooling water needs to handle.

[0114] (2) Reducing the demand for cooling water flow:

[0115] Since the PCM shares part of the heat load, the cooling water does not need to run continuously at the maximum flow rate. For example:

[0116] Without PCM: The cooling water flow needs to be maintained at 15 L / min to cope with the instantaneous high temperature;

[0117] With PCM: The flow rate can be reduced to 12 L / min, reducing the pumping energy consumption by 20%.

[0118] In addition, the realization of shortening the production cycle by the present invention can also be illustrated by the following example:

[0119] (1) Optimization of the cooling time in the cooling phase compared with the traditional cooling system

[0120] Bottleneck of the traditional cooling system: The 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 the ABS demolding temperature needs to be ≤60°C);

[0121] The PCM unit of the present invention has a buffering effect, comprising:

[0122] 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;

[0123] 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.

[0124] Quantitative analysis using actual design examples:

[0125] A conventional cooling system without PCM takes 30 seconds to cool from 100°C to 60°C;

[0126] 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.

[0127] Cycle shortening ratio: shortening rate = (30-25) / 30×100%=16.7%;

[0128] 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.

[0129] 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%.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] A heat stabilization structure and method for a two-color injection mold of the present invention uses a phase change heat storage unit to balance the temperature fluctuation of the mold and prevent the softening of the first color material caused by a sudden temperature drop; enhance temperature stability and reduce the dependence on an external cooling system; utilize the characteristic of the phase change heat storage material to absorb / release latent heat during solid-liquid or solid-solid phase change to passively regulate the temperature; rely on the temperature change of the mold itself to trigger the phase change without external energy input. The latent heat of the phase change heat storage material buffers the temperature fluctuation and has a "peak shaving and valley filling" effect.

[0134] 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 influence of temperature fluctuation 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 can the hot runner system ensure the fluidity and filling efficiency of the molten plastic, but also the phase change heat storage unit absorbs the excess heat in the key areas of the mold (such as the first color molding position) to prevent the softening of the first color material caused by a sudden temperature drop during the second injection.

[0135] The phase change heat storage unit of the present invention is independent of the hot runner and only acts on the local area of the mold cavity without affecting the melt flow. By absorbing or releasing the latent heat of the phase change, the temperature fluctuation of the mold cavity is controlled within ±5°C. The phase change heat storage unit is integrated around the mold cavity through a combined structure of encapsulating the phase change heat storage material, a heat conducting layer, and a heat insulating layer, and realizes temperature stability by absorbing / releasing the latent heat. Finally, an efficient and energy-saving two-color injection molding production is achieved.

[0136] The above is only a schematic specific embodiment of the present invention and is not intended to limit the scope of the present invention. Any equivalent changes and modifications made by those 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 method for stabilizing the heat of a two-color injection mold, characterized in that, A phase change heat storage unit is configured in a rotary two-color injection mold. The phase change heat storage unit is a packaging unit for a phase change heat storage material, and is embedded in an annular groove formed in the outer wall of the cavity on the moving 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. A heat conduction layer is provided on its outer surface in contact with the cavity, and a heat insulation 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 two-color injection mold injection includes a first injection and a second injection after the mold rotates: During the first injection, the molten first material heated to a first high temperature is injected into the lower cavity through the hot runner and solidifies after cooling below the first low temperature. The phase change heat storage unit absorbs the heat of the cavity, starts to melt when the temperature rises to the first low temperature, and delays the temperature rise of the cavity. During the second injection after the mold rotates, the molten second material heated to a second high temperature is injected into the upper cavity, and the heat is transferred to the lower first material area through the cavity. The phase change heat storage unit controls the temperature of the lower cavity below a third temperature through latent heat absorption to prevent the first material from softening.

2. The stable heat method of the two-color injection mold according to claim 1, characterized in that The cooling water path of the two-color injection mold is arranged outside the phase change heat storage unit on the moving mold side, the 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 path. The two-color injection mold injection also includes a cooling stage. During the cooling stage, the cooling water circulation of the cooling water path 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 cavity, and reduces the residual stress of the two-color plastic product.

3. The heat stabilization method of the two-color injection mold according to claim 2, characterized in that, Calculating the volume of the phase change heat storage unit includes: Calculation of heat storage demand: The heat to be absorbed is determined by the heat transferred from the melt to the mold cavity: , The heat released by the melt is: , Among them, is the total heat absorption, is the heat released by the melt, is the heat of the cooling water, is the mass of plastic for single injection molding (kg), is the specific heat capacity of the plastic (kJ / kg·K); The phase change heat storage capacity is: , where \(m\) is the mass of the phase change unit (kg), and \(L\) is the latent heat of the phase change heat storage unit (kJ / kg); Settings ; Calculation of heat conduction efficiency: Calculate the heat flux density through Fourier's law: , is the mold cavity surface temperature (°C), is the phase change heat storage unit temperature (°C); The volume of the 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 heat storage unit (kg / m 3 ).

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

5. The heat stabilization method of the two-color injection mold according to claim 4, characterized in that The cooling stage also includes controlling and reducing the cooling water flow rate in the cooling water path to extend the cooling time.

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

7. The stable heat method of the 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 high-temperature-resistant aluminum alloy, with a thermal conductivity of 237 W / m·K and a honeycomb structure inside. The heat conduction layer is copper foil, with a thermal conductivity of 401 W / m·K, and the heat insulation layer is ceramic fiber, with a thermal conductivity of 0.1 W / m·K.

8. The stable heat structure of a two-color injection mold, characterized in that, Including configuring a rotary two-color injection mold structure containing a phase change heat storage unit by using the method according to any one of claims 1 to 6.

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