Preparation method of thermally induced dual-response film, film thereof and application

Abstract

The present application relates to the technical field of temperature-sensitive color-changing film, and particularly relates to a preparation method of a temperature-induced double-response film, the film and application thereof. The preparation method comprises the following steps: S1: mixing a color developing agent, a reversible thermochromic dye, a phase change regulator and an encapsulating material, then adding water, preparing an emulsion through high-speed shearing, increasing temperature, self-assembling the emulsion at high temperature, and then sequentially performing suction filtration, washing and drying to obtain temperature-sensitive color-changing microcapsules; S2: dispersing the temperature-sensitive color-changing microcapsules in an organic solvent, then adding a surface activation modifier to obtain modified temperature-sensitive color-changing microcapsules; S3: mixing a base polymer and an epoxy chain extender, then extruding and granulating to obtain a chain-extended base polymer; S4: mixing the chain-extended base polymer and the modified temperature-sensitive color-changing microcapsules, then extruding and granulating, and then casting a film. The temperature-induced double-response film can simultaneously realize high-temperature irreversible response and low-temperature reversible response, and is suitable for preparing food intelligent labels or intelligent packaging.

Description

Technical Field

[0001] This invention relates to the field of thermochromic thin film technology, specifically a method for preparing a thermo-responsive dual-response thin film, the thin film itself, and its applications. Background Technology

[0002] Smart packaging is a packaging technology that uses environmental conditions during food distribution and storage to dynamically provide feedback on product quality. It is primarily used for quality monitoring of perishable goods such as food and pharmaceuticals. Its core functions include monitoring temperature, gas composition, and microbial changes, thereby improving product safety and traceability.

[0003] Thermochromic materials, also known as thermosensitive color-changing materials, refer to materials whose color changes reversibly or irreversibly with temperature. Their visible absorption spectrum changes as the temperature rises or falls, thus exhibiting the characteristic of color variation with temperature. Based on this characteristic, thermochromic materials have been applied in the field of intelligent food packaging. For example, the article "Li Qingyao, Min Tiantian, Cheng Chuanxiang, et al. Thermochromic Materials and Their Application in Intelligent Food Packaging [J]. Packaging Engineering, 2024, 45 (13): 8-17" lists various food packaging products made with thermochromic materials that have already been put into production. Some can determine whether the food has reached an edible temperature based on color changes, while others can display unique patterns at specific temperatures, providing consumers with a visual impact.

[0004] Depending on whether the color-changing material used can repeatedly respond to color changes, thermochromic materials are divided into irreversible thermochromic materials and reversible thermochromic materials. Both types of materials are widely used in the food industry. For example, some foods are sensitive to temperature, and their quality changes at high temperatures. Therefore, if the temperature exceeds the limit during transportation or storage, smart food packaging / labels should irreversibly change color to prevent unscrupulous merchants from selling spoiled food. On the other hand, for some foods, temperature does not affect their quality, or generally does not reach their spoilage temperature. Therefore, smart food packaging / labels are only used to indicate the optimal consumption temperature or simply for aesthetic purposes. In this case, reversible thermochromic materials are suitable.

[0005] The application of thermochromic materials in food packaging typically takes the form of packaging films or smart tags. For example, Chinese patent CN202210501954.5 provides a biodegradable food packaging film with thermochromic and energy storage functions, which uses microencapsulated thermochromic materials added to polylactic acid resin, and then extruded and granulated to form a food packaging film through blown film production; Chinese patent CN202010361827.0 provides a thermosensitive color-changing plastic packaging film, which achieves thermosensitive color-changing function by adding thermosensitive color-changing microcapsules to a layered film structure.

[0006] However, existing thermochromic food packaging materials have the following problems:

[0007] 1) Limited response conditions and output modes: General thermochromic food packaging is either reversible or irreversible, and cannot simultaneously indicate spoilage at high temperatures and suitable consumption temperature.

[0008] 2) Uneven color change effect: The shell material of the thermosensitive color-changing microcapsule has poor compatibility with the matrix polymer, resulting in uneven dispersion of the microcapsule in the membrane material. When changing color, the color is mottled, affecting the aesthetics and uniformity.

[0009] In summary, there is an urgent need for a thermo-responsive film that can simultaneously achieve both high-temperature irreversible and low-temperature reversible responses, and is safe, non-toxic, has uniform and stable color development, and is aesthetically pleasing. Summary of the Invention

[0010] One of the objectives of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a temperature-induced dual-response thin film, so as to at least achieve the preparation method being industrializable and the prepared temperature-induced dual-response thin film being able to simultaneously achieve both high-temperature irreversible response and low-temperature reversible response.

[0011] A method for preparing a temperature-responsive dual-mode thin film includes the following steps:

[0012] S1: After mixing the color developer, reversible thermochromic dye, phase change modifier and encapsulation material, water is added and an emulsion is prepared by high-speed shearing. The emulsion is heated to allow it to self-assemble at high temperature. Then, it is sequentially filtered, washed and dried to obtain thermosensitive color-changing microcapsules.

[0013] S2: Disperse the thermosensitive color-changing microcapsules in an organic solvent, and then add a surface-activating modifier to obtain modified thermosensitive color-changing microcapsules;

[0014] S3: The matrix polymer and epoxy chain extender are mixed and then extruded and granulated to obtain the chain-extended matrix polymer;

[0015] S4: Mix the extended matrix polymer and the modified thermochromic microcapsules, extrude and granulate, and then cast into a film to obtain the thermochromic dual-response film.

[0016] In some embodiments, in step S1, the color developer includes bisphenol A or boric acid; the reversible thermochromic dye is a reversible color-changing dye.

[0017] In some examples, the reversible color-changing dye includes crystal violet lactone or thermosensitive rose red TF-R1; the color-changing temperature range of crystal violet lactone is 31.2~47.8℃, and the color-changing temperature range of thermosensitive rose red TF-R1 is 47.4~52.7℃.

[0018] In some embodiments, in step S1, the high temperature is 60~80°C, and the polymerization temperature is 6~8h.

[0019] In some embodiments, in step S1, the phase change modifier includes paraffin or fatty acid glycerides.

[0020] In some embodiments, in step S1, the encapsulation material comprises a polymer with shape memory properties; the polymer comprises polycaprolactone, polyurethane, and polylactic acid.

[0021] In some examples, the encapsulation material also includes copolymers obtained by monomer polymerization of the polymer.

[0022] In some embodiments, in step S2, the surface activation modifier includes one of isocyanate coupling agent, epoxy coupling agent and acid anhydride coupling agent, used to graft hydroxyl, carboxyl or aldehyde groups onto the surface of the thermosensitive color-changing microcapsule to improve compatibility with the matrix material, and the amount added is 0.5% to 10% of the mass of the thermosensitive color-changing microcapsule.

[0023] The isocyanate coupling agents include: toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and diphenylmethane diisocyanate;

[0024] The epoxy coupling agent includes: bisphenol A type epoxy resin E-44 or E-51, or ethylene glycol diglycidyl ether or glycerol triglycidyl ether.

[0025] The anhydride coupling agents include: maleic anhydride, phthalic anhydride, and pyromellitic dianhydride.

[0026] In some embodiments, in step S3, the matrix polymer includes one of polylactic acid, polyethylene, or polyethylene terephthalate, wherein the number average molecular weight of the matrix polymer is 100,000 g / mol to 200,000 g / mol, preferably 150,000 g / mol to 180,000 g / mol. The thermal transition temperature of polylactic acid is 60-65°C, the thermal transition temperature of polyethylene is 110-130°C, and the thermal transition temperature of polyethylene terephthalate is 70-80°C.

[0027] It is worth noting that the encapsulation material and the matrix polymer are preferably different materials with similar transition temperatures, wherein the encapsulation material has a lower transition temperature and the matrix polymer has a higher transition temperature. If the transition temperatures of the two are significantly different, it will be difficult to achieve synergistic deformation. If the two are made of the same material, the dye in the microcapsules may leak and become inactive during the mixing and granulation process.

[0028] In some examples, in step S3, the extrusion granulation is performed using a twin-screw extruder with an operating temperature of 160~180℃ and a rotation speed of 30~50rpm.

[0029] In some examples, the chain extender is an epoxy chain extender, and the amount added is 0.1% to 2% of the weight of the matrix polymer.

[0030] A second objective of this invention is to provide a thermo-responsive dual-phase film prepared by the above method, wherein the thermosensitive color-changing microcapsules in the thermo-responsive dual-phase film are uniformly dispersed in a chain-extended matrix polymer. The thermosensitive color-changing microcapsules have a core-shell structure, the encapsulation material is a wall material / shell layer, and the color developer, thermochromic dye, and phase change modifier are core materials / core layers.

[0031] In some embodiments, the deformation response temperature of the chain-extended matrix polymer is higher than the response temperature of the color change of the reversible thermochromic dye.

[0032] In some embodiments, the thickness of the film is 50~200μm.

[0033] It is worth noting that this invention uses polymers with shape memory properties as the wall material of the thermosensitive color-changing microcapsules. These polymers have good mechanical properties, which not only fully protect the organic components of the microcapsule core layer, but also have the function of synchronous and synergistic deformation. When the temperature rises, the capsule shell and the matrix can achieve synergistic deformation during the deformation process, which can effectively eliminate interfacial stress concentration, improve the durability of the composite material, and overcome the problem of damage caused by friction and collision between the shell material and the matrix material during deformation when using general rigid shell materials.

[0034] The phase change modifier has a lower melting point than the shell encapsulation material and has the property of absorbing a large amount of heat when melting. When the ambient temperature rises, the phase change modifier located in the core layer will absorb heat and melt, forming a fluid and storing heat, which can uniformly heat the color-changing material of the shell and core layers.

[0035] A third objective of this invention is to provide an application of the aforementioned thermo-responsive dual-film, including: changing the thermo-responsive dual-film from an initial shape to a specific shape by applying external mechanical force.

[0036] In some embodiments, the temperature-responsive dual-response film is used to prepare smart labels or smart packaging.

[0037] In some examples, the thermo-responsive film is cut / folded to form a smart label with a specific shape, which is then placed inside food packaging.

[0038] If the ambient temperature rises from the lower initial storage temperature to the food's suitable consumption temperature, the label color begins to change; if the temperature rises to the food's spoilage temperature, in addition to the color change, the film will also return to its initial shape from a specific shape; if the temperature drops back from the spoilage temperature to the storage temperature, the film's color returns to its initial color while its shape remains unchanged.

[0039] The beneficial effects of this invention are:

[0040] 1. The temperature-responsive dual-response film of the present invention can simultaneously achieve irreversible response at high temperature and reversible response at low temperature, and is suitable for preparing smart food labels or smart packaging. It produces reversible color changes at lower temperatures to indicate the optimal eating temperature, and produces irreversible deformation at higher temperatures to indicate whether the food has spoiled.

[0041] 2. The temperature-responsive dual-effect thin film prepared by this invention has good stability, good mechanical properties, and uniform color development. Attached Figure Description

[0042] Figure 1 This is an experimental example of the present invention, showing the response of the smart tag prepared by the temperature-induced dual-response film in Example 1 to temperature changes.

[0043] Figure 2 This is an experimental example of the present invention, showing the response of the smart tag prepared by the temperature-induced dual-response film of Comparative Example 1 to temperature changes. Detailed Implementation

[0044] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the following description.

[0045] Example 1

[0046] This embodiment provides a method for preparing a temperature-responsive dual-mode thin film, the specific method of which is as follows:

[0047] 1) Crystal violet lactone, bisphenol A (BPA), paraffin and polylactic acid (model 4043D, number average molecular weight 165,000 g / mol) were mixed to obtain an oil phase. Then deionized water was added to form an emulsion. The emulsion was sheared for 3 minutes at 2000 r / min using a high-speed shearing machine to form a uniform fine emulsion. The emulsion was then heated to 80℃ and held for 8 hours to allow the components to self-assemble into microcapsule emulsions. The emulsions were then filtered, washed and dried to obtain thermosensitive color-changing microcapsules.

[0048] 2) The thermosensitive color-changing microcapsules were dispersed in anhydrous ethanol / toluene mixed solvent (volume ratio 1:1) at an amount of 10 wt%, and then toluene diisocyanate was added for surface grafting reaction at a reaction temperature of 90℃ for 10 h to obtain surface-functionalized modified thermosensitive color-changing microcapsules.

[0049] 3) The matrix polymer polylactic acid 4043D and the chain extender ADR-4468 were added to a twin-screw extruder to be blended and prepared into granules. The working temperature of the extruder was 160℃ and the speed was 50rpm to obtain the chain extended matrix polymer.

[0050] 4) The extended matrix polymer and modified thermosensitive color-changing microcapsules are added to a twin-screw extruder to be blended and prepared into granules. The working temperature of the extruder is 160℃ and the speed is 50rpm. Then the obtained granules are added to a casting machine to cast a film. The equipment temperature is 160℃ to obtain a thermosensitive dual-response film. The film changes color at 60℃, and the matrix transition temperature is 59~60℃.

[0051] In this embodiment, the substrate transition temperature is slightly lower than the color change temperature, and the color change and deformation of the film occur simultaneously.

[0052] Example 2

[0053] This embodiment provides a method for preparing a temperature-responsive dual-mode thin film, the specific method of which is as follows:

[0054] 1) Mix thermosensitive rose red TF-R1, bisphenol AF (BPAF), fatty acid ester and polyurethane (model E580, Meirui New Materials) to obtain an oil phase, then add deionized water to form an emulsion, and shear at 2000 r / min for 3 min using a high-speed shearing machine to form a uniform fine emulsion. Then heat to 80℃ and hold for 8 h to allow the components to self-assemble into microcapsule emulsion. Then filter, wash and dry to obtain thermosensitive color-changing microcapsules.

[0055] 2) The thermosensitive color-changing microcapsules were dispersed in anhydrous ethanol / toluene mixed solvent (volume ratio 1:1) at an amount of 10 wt%, and then ethylene glycol diglycidyl ether was added for surface grafting reaction at a reaction temperature of 90℃ for 10 h to obtain surface-functionalized modified thermosensitive color-changing microcapsules.

[0056] 3) The matrix polymer polylactic acid 4043D and the chain extender ADR-4468 were added to a twin-screw extruder to be blended and prepared into granules. The working temperature of the extruder was 160℃ and the speed was 50rpm to obtain the chain extended matrix polymer.

[0057] 4) The extended matrix polymer and modified thermosensitive color-changing microcapsules were added to a twin-screw extruder to be blended and prepared into granules. The working temperature of the extruder was 160℃ and the speed was 50rpm. The obtained granules were then added to a casting machine to be cast into a film. The equipment temperature was 160℃ to obtain a thermosensitive dual-response film. The film changed color at 31℃ and the matrix transition temperature was 59~60℃.

[0058] In this embodiment, the substrate transition temperature is higher than the color change temperature. The film undergoes reversible color change at low temperature and irreversible deformation at high temperature.

[0059] Comparative Example 1

[0060] This embodiment provides a method for preparing a temperature-responsive dual-response film, which is the same as in Embodiment 1, except that the encapsulation material is replaced with urea-formaldehyde resin (prepared by polymerization of urea and formaldehyde, freshly prepared).

[0061] Experimental Example

[0062] This embodiment provides an application of a temperature-responsive dual-response film in smart food labels, as detailed below:

[0063] The temperature-induced dual-response films prepared in Example 1 and Comparative Example 1 were cut into petal shapes (initial shapes), and then folded into smart tags with temporary shapes, such as... Figure 1 and Figure 2 As shown.

[0064] Deionized water was poured into a beaker and heated with a heating rod to a temperature of 68°C. The label from Example 1 was then placed in the hot water. Within 12 seconds, the label quickly changed from red to light yellow and returned to its original shape.

[0065] The labels are then removed from the water and allowed to cool naturally. Within 60 seconds, the label color gradually changes from pale yellow to red, but the label shape no longer changes.

[0066] This experimental example demonstrates that the thermo-responsive dual-temperature film of the present invention can simultaneously achieve both high-temperature irreversible response and low-temperature reversible response. In practical applications, the color change temperature and deformation temperature can be controlled by adjusting the selection of dyes, color developers, and matrix polymers in the thermo-responsive dual-temperature film to adapt to specific food application scenarios.

[0067] When the label of Comparative Example 1 was placed in 68℃ hot water, deformation and discoloration occurred simultaneously, but the discoloration was uneven. After removing the label from the hot water and allowing it to cool naturally, the overall discoloration was slower. The label color gradually changed from yellow to red within 60 seconds, but some areas changed color slowly, especially the previously deformed and bent areas, where mottled yellow areas remained even after 120 seconds. Figure 2 As shown, this is because the microcapsules at the bend are squeezed and damaged during the deformation of the matrix, causing the color developer, reversible thermochromic dye and phase change modifier to escape, thereby losing or weakening the reversible color change ability.

[0068] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for preparing a temperature-responsive dual-mode thin film, characterized in that, Includes the following steps: S1: After mixing the color developer, reversible thermochromic dye, phase change modifier and encapsulation material, water is added and an emulsion is prepared by high-speed shearing. The emulsion is heated to allow it to self-assemble at high temperature. Then, it is sequentially filtered, washed and dried to obtain thermosensitive color-changing microcapsules. S2: Disperse the thermosensitive color-changing microcapsules in an organic solvent, and then add a surface-activating modifier to obtain modified thermosensitive color-changing microcapsules; S3: The matrix polymer and epoxy chain extender are mixed and then extruded and granulated to obtain the chain-extended matrix polymer; S4: Mix the extended matrix polymer and the modified thermosensitive color-changing microcapsules, extrude and granulate, and then cast into a film to obtain the thermosensitive dual-response film; In step S1, the encapsulation material includes polyurethane and polylactic acid; In step S2, the surface-activating modifier includes one of toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, E-44, E-51, ethylene glycol diglycidyl ether, glycerol triglycidyl ether, maleic anhydride, phthalic anhydride, and pyromellitic dianhydride. In step S3, the matrix polymer is polylactic acid.

2. The preparation method according to claim 1, characterized in that: In step S1, the color developer includes bisphenol A or boric acid; the reversible thermochromic dye includes crystal violet lactone or thermosensitive rose red TF-R1.

3. The preparation method according to claim 1, characterized in that: In step S1, the phase change modifier includes paraffin or fatty acid glycerides.

4. The preparation method according to claim 1, characterized in that: In step S3, the number average molecular weight of the matrix polymer is 100,000 g / mol to 200,000 g / mol.

5. The thermo-responsive dual-response thin film prepared by the preparation method according to any one of claims 1-4.

6. The temperature-induced dual-response thin film according to claim 5, characterized in that: The deformation response temperature of the extended matrix polymer is higher than the response temperature of the color change of the reversible thermochromic dye.

7. The application of the thermo-responsive dual-response thin film as described in any one of claims 5-6, characterized in that, include: The temperature-induced dual-response film is changed from its initial shape to a specific shape by applying external mechanical force.

8. The application according to claim 7, characterized in that: The temperature-responsive film is used to prepare smart labels or smart packaging.

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