Phase change material shaping and cold packaging method based on high polymer material crosslinking

Abstract

The invention provides a phase change material shaping and cold packaging method based on high polymer material crosslinking, and belongs to the technical field of phase change material shaping and packaging. The method comprises the following steps: uniformly mixing paraffin powder and premixed epoxy resin according to a mass ratio of (7-6): (3-4) in a vacuum environment, curing to obtain a base material of the phase-change composite material, uniformly coating the surface of the base material with a UV photocuring adhesive, then placing the base material under ultraviolet light to form a film, and completing packaging to obtain the phase-change composite material. The low-temperature powdery phase-change material is subjected to efficient cold packaging through a specific polymer matrix material, and the obtained phase-change composite material is low in leakage rate, has excellent thermal management performance and mechanical strength, can be directly prepared into a complex structural part, and has a wide application prospect. The problems that in the prior art, phase-change materials are complex in packaging, high in leakage rate, poor in mechanical performance and difficult to machine into structural parts are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of phase change material forming and encapsulation, and particularly relates to a method for shaping and cold encapsulating phase change materials based on crosslinking of polymer materials. Background Art

[0002] Phase change materials have great application potential, especially in thermal management and energy conservation, because they can achieve effective heat energy storage and release functions through phase change processes. However, existing phase change energy storage materials often have technical problems such as leakage of phase change media, insufficient thermal cycle stability, low mechanical strength, and poor thermal conductivity during use. These problems make it difficult for phase change materials to achieve long-term stable operation in practical applications and severely limit their wide application in industries, buildings, and other fields.

[0003] To suppress the leakage of phase change media, phase change materials are usually encapsulated to prevent the leakage of phase change materials while maintaining their shape and strength. Current phase change material encapsulation and shaping technologies mainly include capsule encapsulation and shaping technology, porous carrier encapsulation and shaping technology, and polymer matrix encapsulation and shaping technology. Among them, capsule encapsulation technology encapsulates phase change materials with an outer shell to produce core-shell capsules. Although this method can achieve the encapsulation of phase change materials to a certain extent, there is a risk of shell rupture under large thermal stress, resulting in the leakage of phase change materials. In addition, capsule encapsulation also increases the overall volume of the material, which has obvious limitations in application scenarios with high-power heat dissipation, limited volume, and strict environmental protection requirements. Porous carrier encapsulation and shaping technology loads materials with microporous structures or large specific surface areas, such as mixtures of hexagonal mesoporous silicate (HMS) and olefin block copolymer (OBC), into phase change materials through porous adsorption or physical blending methods to form multifunctional composite phase change materials. This method has certain feasibility in some thermal comfort fields, such as applications in personal body temperature regulation of textiles and infrared radiation heating fabrics. However, although the matrix material provides certain mechanical flexibility and shape memory recovery functions, such encapsulation methods still have deficiencies in mechanical strength and long-term stability. Polymer matrix encapsulation and shaping technology achieves shape stability by grafting phase change materials onto polymer skeletons. This method can solve the leakage problem of phase change materials to a certain extent, but usually requires sacrificing the effective proportion of phase change materials, resulting in a decrease in energy storage density. In addition, polymer matrix-based encapsulation technologies usually also require complex preparation processes, which increase the manufacturing cost and process complexity.

[0004] The low mechanical strength of phase change materials is also one of the main bottlenecks hindering their application. Phase change materials themselves are usually waxes or salts, and these materials have low mechanical strength in the solid state and are difficult to be directly used as structural components. In addition, the volume of phase change materials changes during the phase change process, and this change will affect the encapsulation of the materials and the stability of the overall structural components. To enhance the mechanical strength of phase change materials, a common practice is to compound them with a certain reinforcing material, but this often introduces additional process complexity and cost burden, and the reinforcement effect is also affected by many factors. In addition, with the development of modern industrial and building systems towards integration and lightweight, more and more application scenarios require multifunctional materials, which not only need to have heat management functions, but also require certain mechanical strength and even be able to be directly used as structural components. However, the current phase change material encapsulation technology is difficult to meet these requirements simultaneously. Traditional encapsulation methods mainly add phase change materials simply into the system, which cannot replace the existing structural components but instead increase the weight and complexity of the entire system. Therefore, how to effectively integrate phase change materials into the structure, without increasing the system complexity and improving the overall heat management ability of the system, has become an important research direction.

[0005] In summary, it is urgent to develop a new type of phase change energy storage material encapsulation technology, so that the phase change materials can be effectively encapsulated to prevent leakage, and can also be well combined with the matrix material to form a composite structural component with high mechanical strength, thereby realizing the high integration of heat management and structural functions. This new type of material should have good forming properties and can be processed into structural components with complex shapes through mold forming to adapt to various different application scenarios. At the same time, it should also have a simple preparation process to reduce production costs and environmental impacts. Summary of the Invention

[0006] Aiming at the above deficiencies of the prior art, the present invention provides a shaped cold encapsulation method for phase change materials based on cross-linking of polymer materials. By selecting a suitable polymer matrix material and physically mixing and curing the phase change materials in a specific ratio under specific conditions, a composite phase change material with excellent mechanical properties and heat management properties is prepared. This material can not only effectively solve the leakage problem of phase change materials, but also replace some traditional structural components, realizing material multifunctionalization and system integration, thereby greatly expanding the application scenarios of phase change materials in industrial, building and other heat management related fields.

[0007] To achieve the above object, the specific technical solutions of the present invention are as follows:

[0008] A shaped cold encapsulation method for phase change materials based on cross-linking of polymer materials, comprising the following steps:

[0009] (1) Perform cryogenic solidification treatment on paraffin wax, and grind the solidified paraffin wax in an environment below the phase change temperature of paraffin wax to obtain paraffin wax powder; before grinding the paraffin wax, it is necessary to solidify the paraffin wax below -80 °C to avoid the paraffin wax melting due to heat during the grinding process.

[0010] (2) Premix epoxy resin and curing agent to obtain premixed epoxy resin; mix the paraffin wax powder and the premixed epoxy resin evenly in a vacuum environment according to the mass ratio of (7~6):(3~4), and cure to obtain the substrate of the phase change composite material.

[0011] (3) Flush the surface of the substrate with plasma flow, and then prepare a waterproof coating film on the surface of the substrate to obtain a phase change composite material based on cross-linking of polymer materials.

[0012] Further, the phase change temperature of the paraffin wax is 18~30 °C.

[0013] In order to solve the problems of low proportion of phase change materials and low latent heat and heat capacity per unit mass in the existing phase change composite materials, the present invention directly mixes and cures the paraffin wax powder with the polymer matrix material according to the mass ratio of (7~6):(3~4) under specific conditions, and then coats the UV curable glue on the surface of the formed substrate, and cures it into a film to obtain a phase change composite material based on cross-linking of polymer materials. The method of the present invention has low cost and simple operation, and there is no need to wrap each powder particle separately; while greatly increasing the proportion of the phase change material in the phase change composite material, the obtained phase change composite material also has good mechanical properties and anti-phase change material leakage properties. The present invention selects paraffin wax with a phase change temperature of 18~30 °C as the phase change material, so that the prepared phase change composite material can be widely used in scenarios such as building energy conservation and house heat management; the phase change temperature of 18~30 °C is exactly within the human comfort temperature range, which helps to reduce the energy consumption of air conditioners and heating; moreover, paraffin wax has the advantages of low cost, high phase change latent heat (200 J / g), and good cycle stability, and can still maintain good thermal performance after multiple phase change cycles without obvious thermal performance attenuation.

[0014] Paraffin wax with a phase change temperature of 18 - 30 °C becomes liquid at a slightly higher temperature, so the encapsulation requirements are more stringent. In the preparation process of the phase change composite material of the present invention, first, the paraffin wax is subjected to ultra-low temperature solidification treatment (below -80 °C). The solidified paraffin wax is ground into micron-sized powder particles in an environment below the phase change temperature, and then these micron-sized paraffin wax powders are fully mixed with a pre-mixed epoxy resin with a relatively high viscosity in a vacuum environment, so that the epoxy resin can penetrate into the gaps between the paraffin wax powders; through a chemical cross-linking reaction, a three-dimensional porous network structure containing countless microcavities is formed, and these microcavities effectively limit the volatilization and leakage of the paraffin wax during the encapsulation process; coating the surface of the cured and formed substrate can make the phase change composite material have good waterproof and moisture-proof properties, and further effectively prevent the leakage of the phase change material.

[0015] In the present invention, by performing cold grinding treatment on paraffin wax under fixed pressure and time, the particle size distribution of the paraffin wax powder can be controlled by adjusting the grinding pressure and time, ensuring that the particle sizes of the paraffin wax powders obtained by grinding in different batches remain highly consistent; when the particle size of the paraffin wax powder is too large, the pores of the three-dimensional network porous structure formed by the epoxy resin and the curing agent are relatively large, with a high leakage rate and poor mechanical properties; when the particle size of the paraffin wax powder is too small, the epoxy resin with a relatively high viscosity cannot fully penetrate into the powder gaps, and the agglomeration phenomenon of the paraffin wax powder will increase, which will also lead to problems such as poor mechanical properties. Therefore, keeping the particle size of the paraffin wax powder within a suitable range is very crucial for the performance of the final phase change composite material.

[0016] Furthermore, the grinding method is mortar grinding; the paraffin wax to be ground needs to be pre-cooled to a specific temperature and ground in an environment below the phase change temperature of the paraffin wax to avoid the paraffin wax melting during the grinding process; in addition, the discharging time of mortar grinding is fast (60 s), avoiding the paraffin wax melting caused by long-time grinding in grinding methods such as ball mills. The ground paraffin wax powder is stored in a refrigerator for subsequent use.

[0017] Furthermore, the curing temperature is higher than the curing temperature of the epoxy resin and lower than the phase change temperature of the paraffin wax; the curing of the present invention is carried out at a lower temperature to avoid the paraffin wax melting and leaking caused by slow heat release during the curing process.

[0018] Furthermore, the curing temperature is 5 - 10 °C.

[0019] Furthermore, the mass ratio of the epoxy resin to the curing agent is (1.5 - 3):1.

[0020] Even further, the mass ratio of the epoxy resin to the curing agent is 2.5:1.

[0021] Further, the epoxy resin is a bisphenol F type epoxy resin, and the curing agent is a phenolic amine type curing agent; the epoxy resin can be cured at low temperature, and the mechanical compressive strength of the cured epoxy resin can reach 20 MPa, which can ensure that the phase change composite material has excellent mechanical properties.

[0022] Further, the paraffin powder and the premixed epoxy resin are mixed by vacuum planetary gravity stirring. By using the coupling action of the revolution centrifugal force and the rotation gravity of the mixture, the small particle size paraffin powder and the epoxy resin with higher viscosity are fully mixed, and at the same time, the introduction of air bubbles is avoided.

[0023] Further, the waterproof coating film is a UV curable glue coating film; the operation of preparing the waterproof coating film is as follows: the curable glue is evenly applied on the surface of the formed phase change material through a roller or a spraying tool with a moderate thickness, and the part coated with the glue is placed under an ultraviolet lamp, and it can be quickly cured into a film usually only in a few seconds to dozens of seconds. The UV curable glue includes epoxy-based UV curable glue, and the main component of the epoxy-based UV curable glue includes epoxy acrylate; the epoxy-based UV curable glue undergoes a cationic polymerization reaction under ultraviolet irradiation to form a highly cross-linked three-dimensional network structure. This structure greatly reduces the molecular gap and can effectively hinder the penetration of the phase change material, water molecules and other impurities; in the present invention, the surface of the formed phase change material is treated by a plasma flow, which can not only improve the adhesion, but also introduce oxygen-containing groups (such as C=O, -OH and -COOH). The oxygen-containing groups form chemical bonds with the active monomers in the curable glue, which can strengthen the interfacial bonding and further reduce the waterproof and moisture-proof performance and the leakage rate.

[0024] The present invention also provides a phase change composite material based on polymer material cross-linking obtained by using the above-mentioned shaping cold encapsulation method.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. The shaping cold encapsulation method provided by the present invention is simple in operation and low in cost. By directly mixing and curing the paraffin powder in a low-temperature state with the shaping material, there is no need to wrap each paraffin powder separately, which greatly increases the proportion of the phase change material in the phase change composite material. At the same time, the prepared phase change composite material has both heat management function and mechanical strength, and can replace some original structural parts without increasing the system complexity, improving the system integration degree, and having broad industrial application potential.

[0027] 2. The phase change composite material of the present invention can be prepared into structural parts with complex shapes through a mold forming process similar to concrete, thereby greatly expanding the application scenarios of the phase change material in industrial, architectural and other fields.

[0028] 3. The epoxy resin and paraffin involved in the phase change composite material of the present invention are both non-toxic, odorless, environmentally friendly materials with stable chemical properties, and have low costs. They can be directly used for cooling and heating in indoor environments and thermal management of electronic devices.

[0029] 4. The innovative coating strategy in the method of the present invention further reduces the leakage rate of paraffin and significantly improves the service life of the phase change composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flowchart of the method for shaping and cold encapsulating phase change materials based on crosslinking of polymer materials according to the present invention;

[0031] Figure 2 are stress-strain curves of the substrate of the phase change composite material under different paraffin ratios;

[0032] Figure 3 are test results of the leakage rate of the phase change material in the phase change composite material of the present invention;

[0033] Figure 4 are test results of the leakage rate of the phase change composite material prepared with different waterproof coating films;

[0034] Figure 5 are test results of the leakage rate of the phase change composite material prepared with different phase change materials. DETAILED DESCRIPTION OF THE INVENTION

[0035] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0036] The present invention provides a method for shaping and cold encapsulating phase change materials based on crosslinking of polymer materials (see the flowchart in Figure 1 ), including the following steps:

[0037] (1) Perform ultra-low temperature solidification treatment on paraffin, and grind the solidified paraffin in an environment below the phase change temperature of paraffin to obtain paraffin powder;

[0038] (2) Premix epoxy resin and curing agent according to a mass ratio of (1.5 - 3):1 to obtain premixed epoxy resin; mix paraffin powder and premixed epoxy resin evenly in a vacuum environment according to a mass ratio of (7 - 6):(3 - 4), and cure to obtain the substrate of the phase change composite material;

[0039] (3) The surface of the substrate is rinsed with a plasma stream, and then a waterproof coating film is prepared on the surface of the substrate to obtain a phase change composite material based on the crosslinking of polymer materials.

[0040] In some examples, the phase change temperature of the paraffin wax is 18 - 30 °C.

[0041] In some examples, the curing temperature is 5 - 10 °C.

[0042] Example 1

[0043] A phase change composite material based on the crosslinking of polymer materials is prepared as follows:

[0044] The first step is to prepare paraffin powder. Paraffin wax with a phase change temperature of 30 °C is selected as the phase change material. First, the paraffin wax is frozen to below -80 °C, and at the same time, the grinding environment temperature is ensured to be below 25 °C; according to the size of the grinding instrument, the amount of paraffin wax is determined. In this example, the volume of the mortar is about 700 mL, and about 80 g of paraffin wax is put in each time. The maximum pestle pressure is set, and the grinding time is 1 minute. After grinding, the paraffin powder is stored at -80 °C for standby.

[0045] The second step is to prepare a premixed epoxy resin. Bisphenol F type epoxy resin (Nanya 170 bisphenol F type epoxy resin) and phenolic amine curing agent (593 phenolic amine type curing agent) are put into a vacuum planetary gravity mixer for premixing to obtain a premixed epoxy resin. Among them, the rotation speed of the mixer is set to 900 RPM, and the time is 1 minute; then, the paraffin powder and the premixed epoxy resin are put into a vacuum planetary gravity mixer for mixing to obtain a mixture. Before mixing, the premixed epoxy resin and the mixing container need to be frozen to below -20 °C; the mixing is carried out in three stages: the first stage, the rotation speed is 600 PRM, and the time is 1 minute; the second stage, the rotation speed is 900 PRM, and the time is 5 minutes; the third stage, the rotation speed is 600 PRM, and the time is 1 minute.

[0046] The third step is to cure the substrate of the phase change composite material. The mixture is transferred to a mold. In this example, the mold is a cylindrical silicone mold with a diameter of 60 mm, and it is cured in an environment of 5 °C for one day to obtain the substrates S1 - S6 of the phase change composite material. The details of the raw material mass ratio of S1 - S6 are shown in Table 1. The diameter of the substrate is 60 mm, the thickness is 14 mm, and the weight is 50 g.

[0047] Table 1: Raw material mass ratio of S1 - S6

[0048]

[0049] Figure 2Stress-strain curves of the base materials S3 (α = 70%), S5 (α = 60%), and S6 (α = 80%) of the phase change composite materials. It can be seen from the figure that compared with the material with 0% paraffin content (cured from epoxy resin and curing agent in a mass ratio of 2.5:1), the maximum stress value of the base material incorporated with paraffin decreases significantly, and as the paraffin content increases, the maximum stress value of the base material shows a downward trend. Different phase change composite materials can be selected according to the actual application scenarios and requirements.

[0050] Step 4: Activate the surface of the base material. Rinse the surface of the base material S3 with an oxygen molecule plasma stream in a vacuum environment for 1 minute; use a spraying tool to evenly apply the photocurable adhesive (D-5604 ultraviolet curable adhesive) and the insulating three-proof paint on the surface of the base material S3 with appropriate thickness, and place the part coated with the adhesive under an ultraviolet lamp to form a film, obtaining the phase change composite materials S7 (coating is the photocurable adhesive) and S8 (coating is the insulating three-proof paint) based on the cross-linking of polymer materials.

[0051] Comparative Example 1

[0052] Put epoxy resin and curing agent into a vacuum planetary gravity mixer according to a mass ratio of 2.5:1 for premixing. Set the rotation speed of the mixer to 900 RPM and the time to 1 minute to obtain premixed epoxy resin; put liquid paraffin with a phase change temperature of 30 °C and the premixed epoxy resin into a vacuum planetary gravity mixer according to a mass ratio of 7:3 for mixing. The mixing is carried out in three stages: the first stage, the rotation speed is 600 PRM and the time is 1 minute; the second stage, the rotation speed is 900 PRM and the time is 5 minutes; the third stage, the rotation speed is 600 PRM and the time is 1 minute; transfer the mixture to a mold. In this embodiment, the inside of the mold is a cuboid of 100 mm x 100 mm x 10 mm; cure at 5 °C for one day, but it fails to cure and form.

[0053] Comparative Example 2

[0054] Replace the paraffin in Example 1 with the inorganic phase change material hydrated salt. The preparation steps are as follows: Freeze the hydrated salt (sodium sulfate decahydrate) to below -80 °C, and at the same time ensure that the ambient temperature during grinding is below 25 °C. Determine the dosage of the hydrated salt according to the size of the grinding instrument; in this embodiment, the volume of the mortar is about 700 mL, and 80 g of the hydrated salt is put in each time; set the maximum pestle pressure and the grinding time to 1 minute; freeze the hydrated salt powder at -80 °C for later use.

[0055] Put epoxy resin and curing agent into a vacuum planetary gravity mixer according to a mass ratio of 2.5:1 for premixing. Set the rotation speed of the mixer to 900 RPM and the time to 1 minute to obtain premixed epoxy resin, take it out and store it at -20 °C for later use.

[0056] The hydrated salt powder stored at -80 °C and the premixed epoxy resin are put into a vacuum planetary gravity mixer according to a mass ratio of 7:3 to obtain a mixture. The mixing is carried out in three stages: in the first stage, the rotation speed is 600 PRM and the time is 1 minute; in the second stage, the rotation speed is 900 PRM and the time is 5 minutes; in the third stage, the rotation speed is 600 PRM and the time is 1 minute. The mixture is transferred to a mold. In this embodiment, the inside of the mold is a cuboid with dimensions of 100 mm x 100 mm x 10 mm. It is cured at 5 °C for one day to obtain the substrate S9 of the phase change composite material.

[0057] The surface of the substrate S9 is rinsed in a vacuum environment with an oxygen molecular plasma flow for 1 minute. The photocurable adhesive is evenly applied to the surface of the substrate S9 through a spraying tool with a proper thickness. The coated part is placed under an ultraviolet lamp to form a film, obtaining the phase change composite material S10 based on the cross-linking of polymer materials.

[0058] The substrates S1 - S6, S9 of the phase change composite materials and the phase change composite materials S7, S8, S10 based on the cross-linking of polymer materials are respectively placed in an oven with an ambient temperature of 50 °C and continuously heated. Then, their masses are measured again. The ratio of the mass reduction to the original mass is the leakage rate. The test results are as Figures 3 to 5 shown. It can be seen from Figure 3 that after continuous heating for 450 h, when the mass ratio of epoxy resin to curing agent is 2.5:1, the leakage rate is the lowest; when the mass ratio of paraffin powder to premixed epoxy resin is 7:3, the leakage rate is the lowest; after preparing a waterproof coating film on the substrate surface, the leak-proof performance of the material is further enhanced (after continuous heating for 450 h, the leakage rate of S7 remains within 5%); it can be seen from Figure 4 that in this invention, VU photocurable adhesive is used as the waterproof coating film, and its leak-proof effect is more excellent than that of the insulating three-proof paint coating film; it can be seen from Figure 5 that when paraffin is used as the phase change material, its leak-proof effect is more excellent than that of hydrated salt. The above results show that the phase change composite material obtained by the shaping and encapsulation method of this invention has good leak-proof performance.

[0059] The above specific embodiments have described the implementation of the present invention in detail. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solutions of the present invention, and these simple variations all belong to the protection scope of the present invention.

Claims

1. A phase change material shaped cold packaging method based on polymer material cross-linking, characterized in that: The following steps are involved: (1) subjecting paraffin wax to ultra-low temperature solidification treatment, and grinding the solidified paraffin wax in an environment below the phase transition temperature of the paraffin wax to obtain paraffin wax powder; (2) premixing the epoxy resin and the curing agent to obtain a premixed epoxy resin; uniformly mixing the paraffin powder and the premixed epoxy resin in a mass ratio of (7-6): (3-4) under a vacuum environment, and curing to obtain a substrate of a phase change composite material; (3) The surface of the substrate is washed with a plasma jet, and then a waterproof coating film is prepared on the surface of the substrate to obtain a phase change composite material based on cross-linking of polymer materials.

2. The method for cold packaging of phase change materials based on cross-linking of polymer materials according to claim 1, characterized in that: The phase transition temperature of the paraffin wax is 18-30°C.

3. The method for cold packaging of phase change materials based on cross-linking of polymer materials according to claim 1, characterized in that: The curing temperature is higher than the curing temperature of epoxy resin and lower than the phase transition temperature of paraffin wax.

4. The method for cold packaging of phase change materials based on cross-linking of polymer materials according to claim 3, characterized in that: The curing temperature is 5-10°C.

5. The method for cold packaging of phase change materials based on cross-linking of polymer materials according to claim 1, characterized in that: The mass ratio of the epoxy resin to the curing agent is (1.5~3):

1.

6. The method for cold packaging of phase change materials based on cross-linking of polymer materials according to claim 1, characterized in that: The epoxy resin is bisphenol F epoxy resin; the curing agent is a phenolic amine curing agent.

7. The method for cold packaging of a phase change material based on cross-linking of a polymer material according to claim 1, characterized in that: The grinding method is mortar grinding.

8. The method for cold packaging of phase change materials based on cross-linking of polymer materials according to claim 1, characterized in that: The paraffin wax powder and the premixed epoxy resin are mixed by vacuum planetary gravity stirring.

9. The method for cold packaging of phase change materials based on cross-linking of polymer materials according to claim 1, characterized in that: The waterproof coating film is a UV light curing adhesive coating film.

10. A phase change composite material based on cross-linking of polymer materials obtained by the phase change material shaping cold packaging method as claimed in any one of claims 1 to 9.

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