A highly transparent thermal film based on microcapsule technology and its processing technology

Abstract

The present invention relates to the technical field of thermal microcapsules, and discloses a highly transparent thermal film based on microcapsule technology and its processing technology. Specifically, the following technical solutions are proposed: S1: After calcium silicate is modified with an organic nucleating agent, it is melt-blended and extruded with polyethylene glycol and polyethylene terephthalate through a single-screw extruder to obtain a thermal film substrate layer; S2: An imaging layer coating liquid is prepared; S3: A thermal film protective layer coating liquid is prepared; S4: One side of the thermal film substrate layer is plasma-treated, and then the imaging layer coating liquid and the thermal film protective layer coating liquid are sequentially applied to the surface, and a highly transparent thermal film is obtained after drying. While improving the transparency of the thermal film, it is improved in combination with the problems existing in its actual use, and a thermal film with better performance is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of thermosensitive microcapsules, in particular to a highly transparent thermosensitive film based on microcapsule technology and a processing technology thereof. Background Art

[0002] Thermal film is a medical film used for thermal printing. Early thermal films were created by coating a colorant and a colorless dye onto one or adjacent layers of a substrate to create an image. However, due to limitations in image layering, graininess, and resolution, these films have been gradually phased out. In its place, thermal microcapsule film, based on microcapsule technology, is more convenient and faster to process than traditional film, and offers high-quality images with distinct layering. Consequently, it has gained widespread adoption.

[0003] With the continuous upgrading of manufacturing technology for digital medical imaging equipment, traditional thermal microcapsule films have begun to expose some drawbacks, such as poor adhesion between the thermal imaging layer and the substrate layer; poor anti-static performance and easy aging; as well as low transparency, unclear imaging in some subtle areas, and other problems. Therefore, medical personnel have put forward higher requirements for the comprehensive performance of thermal films.

[0004] In order to solve the defects of the existing technology, the present invention is committed to inventing a film with better comprehensive performance. On the basis of the previous technology, it has higher transparency, and the adhesion between its layers is tighter. It has excellent antistatic ability, waterproof ability, mechanical properties and anti-aging ability. Summary of the Invention

[0005] The purpose of the present invention is to provide a highly transparent heat-sensitive film based on microcapsule technology and a processing technology thereof to solve the problems raised in the above background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] S1: Calcium silicate is modified with an organic nucleating agent, and then melt-blended and extruded with polyethylene glycol and polyethylene terephthalate through a single-screw extruder to obtain a heat-sensitive film substrate layer;

[0008] Furthermore, the preparation method of the organic nucleating agent is:

[0009] (1) Bis(2-hydroxyethyl) terephthalate and N,N-dimethylformamide are prepared into a 0.02 mol / mL to 0.04 mol / mL solution, and then 20 mL of 40-50% sodium hydroxide solution is mixed with 50 mL of bis(2-hydroxyethyl) terephthalate solution, a protective gas is introduced, the temperature is raised to 70-120°C, and electromagnetic stirring is performed for 30-50 minutes; while maintaining the temperature, 35 mL of vinyl chloride trimethoxysilane is added dropwise to the solution system, and the reaction is continued by stirring for 16-24 hours; after the solution is cooled to room temperature, the solution is repeatedly washed and separated with deionized water for 3-5 times, and finally dried to obtain a modified silane coupling agent;

[0010] (2) Add the modified silane coupling agent, 2,5-dimercapto-4-dibenzoic acid, and benzoin dimethyl ether (the mass ratio of the three is 21:10:1) into 100 mL of tetrahydrofuran, and completely dissolve the raw materials by ultrasonic dispersion for 15 to 25 minutes. Then, use 365 nm ultraviolet light to react for 40 to 80 minutes at room temperature. After the reaction is completed, the precipitated material is filtered out, washed with deionized water, and dried to obtain an organic nucleating agent.

[0011] Furthermore, the preparation method of the heat-sensitive film substrate layer in S1 is:

[0012] (1) Calcium silicate, an organic nucleating agent, and anhydrous ethanol (the mass ratio of the three is 30:(3-5):2) are placed in a mixer, stirred at a speed of 600-1000 r / min for 20-40 minutes, and then heated to 80-90° C. to dry the mixture until the anhydrous ethanol is completely volatilized to obtain modified calcium silicate;

[0013] (2) The modified calcium silicate, polyethylene glycol and polyethylene terephthalate are melt-blended and extruded with a single-screw extruder to obtain a heat-sensitive film substrate layer.

[0014] Furthermore, the compression ratio of the single-screw extruder is 2.5:1 to 3.5:1, and the extrusion temperature is 250 to 260°C.

[0015] Furthermore, the weight proportions of the components of the heat-sensitive film substrate layer are: 20-30 parts of modified calcium silicate, 5-10 parts of polyethylene glycol, and 80-90 parts of polyethylene terephthalate.

[0016] Furthermore, the thickness of the thermal film substrate layer is 200-260 μm.

[0017] In order to obtain a highly transparent thermal film, an organic nucleating agent, bis(2-hydroxyethyl) terephthalate, is used in the preparation of the thermal film substrate layer to promote the nucleation of polyethylene terephthalate, thereby enhancing the transparency of the polyester film. At the same time, the film also needs to have a certain mechanical strength and flexibility, so calcium silicate is added as a filler, which can also synergistically increase the transparency with the organic nucleating agent. Considering calcium silicate is an inorganic particle, to make it more compatible with the polymer, a silane coupling agent is prepared by reacting bis(2-hydroxyethyl) terephthalate with vinyl chloride-based trimethoxysilane. This improves the affinity between calcium silicate and the polymer and promotes compatibility. Simultaneously, the carbon-carbon double bond in the silane coupling agent undergoes a click reaction with mercapto-paraben. Because mercapto-paraben contains benzoic acid groups, this not only promotes compatibility of the silane coupling agent in polyethylene terephthalate, but also further synergizes with calcium silicate and bis(2-hydroxyethyl) terephthalate to promote nucleation, achieving enhanced transparency and achieving higher transparency. Finally, polyethylene glycol, as an excellent compatibilizer and antistatic agent, not only further promotes compatibility and enhances adsorption to the color-developing layer, but also synergizes with calcium silicate to enhance the antistatic ability of thermal films, a crucial performance requirement for thermal films. S2: preparing a dye precursor thermosensitive microcapsule emulsion and a developer emulsion, and mixing the two to obtain an imaging layer coating liquid;

[0018] Furthermore, the preparation method of the dye precursor thermosensitive microcapsule emulsion in S2 is:

[0019] (1) Weighing 2-phenylamino-3-methyl-6-dibutylaminofluoran, 1-methylnaphthalene, and ethyl acetate into a container, heating to 50-70° C., stirring and mixing to completely dissolve 2-phenylamino-3-methyl-6-dibutylaminofluoran in the mixed solvent of 1-methylnaphthalene and ethyl acetate, cooling the mixture to room temperature, adding isophorone diisocyanate, and mixing uniformly to obtain an oil phase;

[0020] (2) preparing a 3-5% aqueous solution of polyvinyl alcohol and deionized water, and adding sodium dodecylbenzene sulfonate to obtain aqueous phase A and aqueous phase B;

[0021] (3) Using a high-speed emulsifying shearing machine, the aqueous phase A is sheared at a speed of 8000-10000 r / min, and the oil phase is added while shearing. After the addition is completed, the shearing and emulsification dispersion is continued for 10-20 minutes to obtain an oil-in-water emulsifier; then an appropriate amount of N-phenylenediamine is added, the temperature is raised to 50-60°C, and the reaction is carried out at 800-1000 r / min for 3-5 hours to obtain a dye precursor microcapsule emulsion.

[0022] Furthermore, the weight proportions of the components in the oil phase are: 8 to 12 parts of 2-phenylamino-3-methyl-6-dibutylaminofluoran, 6 to 8 parts of 1-methylnaphthalene, 30 to 40 parts of ethyl acetate, and 8 to 16 parts of isophorone diisocyanate.

[0023] Furthermore, the volume ratio of polyvinyl alcohol to sodium dodecylbenzene sulfonate in the aqueous phase is 20:1.

[0024] Furthermore, the weight proportions of the components of the dye precursor microcapsule emulsion are as follows: 15 to 25 parts of the aqueous phase A, 10 to 15 parts of the oil phase, and 5 to 10 parts of N-styrene diamine.

[0025] Furthermore, the preparation method of the developer emulsion in S2 is: mixing the aqueous phase B, polyethylene glycol and deionized water into an aqueous solution with a concentration of 3-5%, adding sodium dodecylbenzene alkyl sulfonate, and then adding an appropriate amount of 4-hydroxy-4'-isopropoxydiphenyl sulfone, and grinding with a ball mill at a rate of 200-500 r / min for 5-10 hours to obtain a developer dispersed emulsion.

[0026] Furthermore, the weight proportions of the components of the developer dispersion emulsion are as follows: 15-25 parts of aqueous phase B, 5-10 parts of polyethylene glycol solution, 2-4 parts of sodium dodecylbenzene sulfonate, and 5-10 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone.

[0027] Furthermore, the imaging layer coating liquid is obtained by mixing a dye precursor microcapsule emulsion and a developer dispersed emulsion in a volume ratio of 1:1 to 1.5.

[0028] The above-mentioned solvent uses a mixed solution of 1-methylnaphthalene and ethyl acetate. The two are mixed to obtain greater solubility, allowing the dye precursor to dissolve more in it, and the density of the subsequent imaging will be higher. Secondly, polyethylene glycol is added to the color developer dispersion emulsion to promote better fusion of the dye precursor microcapsule emulsion and the color developer dispersion emulsion. This allows the color developer to better penetrate into the softened capsule when the glass transition temperature is reached, allowing the color development reaction to occur more quickly and making the imaging more uniform and stable. On the other hand, it can also improve the adhesion of the imaging layer coating liquid during coating. At the same time, considering that the film may be subjected to external pressure during use, the wall membrane of the microcapsule should also have a certain strength to avoid damage to the capsule and the inability to use the film normally. Therefore, a benzene-ringed amine is used to react with isophorone diisocyanate to enhance the wall membrane strength.

[0029] S3: Preparation of thermal film protective layer coating liquid;

[0030] Furthermore, the preparation method of the thermal film protective layer coating liquid in S3 is:

[0031] (1) After calcining nano-titanium dioxide at 450-750°C for 1-3 hours, the nano-titanium dioxide and 2,2-dihydroxymethylpropionic acid are added to anhydrous ethanol, subjected to ultrasonic dispersion treatment for 30-60 minutes, introduced into a protective gas in a sealed container, and reacted continuously at 70-90°C for 20-30 hours. The solid particles are centrifuged, washed with deionized water, and dried to obtain modified titanium dioxide;

[0032] (2) Modified titanium dioxide and polyvinyl alcohol are mixed, and after ultrasonic dispersion for 10 to 20 minutes, polymethacrylate is added, and the mixture is stirred at a rate of 100 to 300 r / min for 30 to 40 minutes. Then, cyclotrimethylolpropane methyl acrylate and deionized water are added, and the stirring is continued for 20 to 30 minutes to obtain a thermal film protective layer coating liquid.

[0033] Furthermore, the mass ratio of the nano-titanium dioxide to 2,2-dihydroxymethylpropionic acid is 3:5.

[0034] Furthermore, the weight proportions of the components of the heat-sensitive film protective layer coating liquid are: 40-50 parts of polymethacrylate, 10-20 parts of polyvinyl alcohol, 15-20 parts of deionized water, 3-6 parts of cyclotrimethylolpropane formal acrylate, and 5-10 parts of modified titanium dioxide.

[0035] The protective layer of the aforementioned thermal film uses nano-titanium dioxide as a filler, which provides strength and improved transparency. It also resists static electricity and absorbs ultraviolet rays, protecting the film. To improve the compatibility of nano-titanium dioxide in polymers, the carboxyl groups on 2,2-dimethylolpropionic acid form an effective chemical bond with the surface of the nano-titanium dioxide, achieving modification and promoting its compatibility in the polymer. Furthermore, polymethacrylate, the primary material for the protective layer, exhibits excellent water resistance and mechanical properties. However, due to its weak antistatic properties, polyvinyl alcohol is added to synergistically improve these properties with the nano-titanium dioxide. Polyvinyl alcohol also has high transparency and can enhance the adhesion between the protective layer and the imaging layer. Cyclotrimethylolpropane formal acrylate can further enhance the film's strength, antistatic properties, and adhesion, synergizing with nano-titanium dioxide to improve the film, resulting in a thermal film with better overall performance.

[0036] S4: Plasma-treating one side of the thermal film substrate layer, then sequentially coating the imaging layer coating liquid and the thermal film protective layer coating liquid on the surface, and drying to obtain a highly transparent thermal film.

[0037] Furthermore, the coating thickness of the imaging layer coating liquid in S4 is 8 to 12 μm, and the coating density is 80 to 130 g / m 3The coating thickness of the thermal film protective layer coating liquid is 1 to 4 μm, and the coating density is 50 to 80 g / m 3 ; The thickness of the thermal film substrate layer is 200 to 260 μm; The thickness of the substrate layer is 200 to 260 μm.

[0038] Furthermore, the drying temperature of the highly transparent thermal film is 60-80°C.

[0039] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: the present invention can effectively and firmly adhere to the protective layer, the imaging layer, and the substrate layer, making the thermal film clearer and more stable during the imaging process; at the same time, the organic nucleating agent is modified and prepared so that it can promote crystallization and improve transparency, and the inorganic particles can also be modified, greatly improving compatibility; in the preparation of microcapsules, different solvents are used for preparation to enhance the solubility of the dye precursor in the solvent and improve its imaging density; and the density and thickness of the coating of each component are considered to a certain extent, thereby comprehensively obtaining a thermal film with high transparency, waterproofness, antistatic properties, and excellent mechanical properties. DETAILED DESCRIPTION

[0040] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0041] In the following examples, the purity of calcium silicate is 99% and the particle size is 500nm (Hebei Mojin Biotechnology Co., Ltd.), the purity of polyethylene terephthalate is 98%, item number: TF25038599, CAS number: 25038599 (Henan Tianfu Chemical Co., Ltd.), the purity of magnesium ingot is 99.99% (Shanghai Qichen Industrial Co., Ltd.), the purity of toluene is 99% (Jiangyin Ouchen Chemical Co., Ltd.), the purity of bis(2-hydroxyethyl) terephthalate is 99%, item number: JJL95390303030303, CAS number: 959-26-2 (Shanghai Jinjinle Industrial Co., Ltd.), 2, The purity of 5-dimercapto-4-dibenzoic acid is 98%, item number: 25906-66-5, CAS number: 25906-66-5 (Henan Alpha Chemical Co., Ltd.), the purity of benzoin dimethyl ether is 99%, item number: ZT-1903605, CAS number: 24650-42-8 (Hebei Zhentian Food Additive Co., Ltd.), the purity of tetrahydrofuran is 99% (Shandong Yanshuo Chemical Co., Ltd.), the purity of anhydrous ethanol is 99.99% (Shandong Maojun Chemical Technology Co., Ltd.), the purity of vinyl chloride trimethoxysilane is 99% (Wuhan Xinyang Ruihe Chemical Technology Co., Ltd.), the purity of 1-methylnaphthalene is 99 %, CAS number: 90-12-0 (Hebei Crowell Biotechnology Co., Ltd.), 2-phenylamino-3-methyl-6-dibutylaminofluoran purity is 99%, item number: 89331-94-2, CAS number: 89331-94-2 (Chongqing Ruiya Biotechnology Co., Ltd.), ethyl acetate purity is 99% (Henan Yuanlong Biotechnology Co., Ltd.), isophorone diisocyanate purity is 99%, CAS number: 4098-71-9 (Hebei Linwo New Materials Technology Co., Ltd.), polyvinyl alcohol purity is 99.9%, molecular weight is 2000, item number: 9002-89-5 (Shandong Meichang New Materials Technology Co., Ltd.), 2,2-dihydroxymethylpropionic acid with a purity of 98% (Shanghai Yuanye Biotechnology Co., Ltd.), sodium dodecyl alkyl sulfonate with a purity of 90% (Nanjing Chemical Reagent Co., Ltd.), N-styrene diamine with a purity of 98% (Zhengzhou Alpha Chemical Co., Ltd.), 4-hydroxy-4'-isopropoxydiphenyl sulfone with a purity of 99%, item number: D-8, CAS number: 95235-30-6 (Shandong Changyao New Materials Co., Ltd.), polymethacrylate with a purity of 98%, item number: 9003-21-8 (Hubei Rishengchang New Materials Technology Co., Ltd.), and nano-titanium dioxide with a purity of 99.5%, particle size 5-10nm (Hebei Mojin Biotechnology Co., Ltd.), cyclotrimethylolpropane formal acrylate purity 98%, item number: Y0154, CAS number: 66492-51-1 (Hubei Yunmei Technology Co., Ltd.), calcium carbonate purity 99%, particle size 500nm (Hebei Mojin Biotechnology Co., Ltd.), polyethylene glycol purity 99%, molecular weight 6000, item number: 0001, CAS number: 25322-68-3 (Xingtai Xinlanxing Technology Co., Ltd.), sodium hydroxide purity 99% (Henan Tianfu Chemical Co., Ltd.); the following parts are by weight.

[0042] Example 1: A process for producing a highly transparent heat-sensitive film based on microcapsule technology, comprising the following steps:

[0043] S1: (1) preparing a 0.03 mol / mL solution of bis(2-hydroxyethyl) terephthalate and N,N-dimethylformamide, then mixing 20 mL of 45% sodium hydroxide solution with 50 mL of bis(2-hydroxyethyl) terephthalate solution, introducing protective gas, heating to 90°C, and electromagnetic stirring for 40 min; maintaining the temperature, adding 35 mL of vinyl chloride trimethoxysilane dropwise to the solution system, and continuously stirring the reaction for 20 h; cooling the solution to room temperature, repeatedly washing and separating the solution with deionized water for 5 times, and finally drying the solution to obtain a modified silane coupling agent;

[0044] (2) 21 parts of a modified silane coupling agent, 10 parts of 2,5-dimercapto-p-dibenzoic acid, and 1 part of benzoin dimethyl ether were added to 100 mL of tetrahydrofuran, and the raw materials were completely dissolved by ultrasonic dispersion for 20 minutes. The reaction was then carried out at room temperature using 365 nm ultraviolet light for 60 minutes. After the reaction was completed, the precipitate was filtered out, washed with deionized water, and dried to obtain an organic nucleating agent.

[0045] (3) 30 parts of calcium silicate, 5 parts of an organic nucleating agent, and 2 parts of anhydrous ethanol are placed in a mixer, stirred at a speed of 900 r / min for 40 minutes, and then the temperature is raised to 80° C. and the mixture is dried until the anhydrous ethanol is completely volatilized to obtain modified calcium silicate; the modified calcium silicate, polyethylene glycol, and polyethylene terephthalate are melt-blended and extruded with a single-screw extruder to obtain a heat-sensitive film substrate layer.

[0046] The compression ratio of the single-screw extruder was 3:1 and the extrusion temperature was 255°C.

[0047] The thickness of the thermal film base material layer is 230 μm.

[0048] The weight proportions of the components of the heat-sensitive film substrate layer are as follows: 25 parts of modified calcium silicate, 8 parts of polyethylene glycol, and 85 parts of polyethylene terephthalate.

[0049] S2: The preparation method of the dye precursor thermosensitive microcapsule emulsion is as follows: (1) weighing 2-phenylamino-3-methyl-6-dibutylaminofluoran, 1-methylnaphthalene, and ethyl acetate into a container, heating to 60°C, stirring and mixing, so that 2-phenylamino-3-methyl-6-dibutylaminofluoran is completely dissolved in the mixed solvent of 1-methylnaphthalene and ethyl acetate, and after cooling to room temperature, adding isophorone diisocyanate, mixing evenly, and obtaining an oil phase; (2) mixing polyvinyl alcohol with deionized water; Prepare a 4% aqueous solution, add sodium dodecylbenzene sulfonate to obtain aqueous phase A and aqueous phase B; (3) use a high-speed emulsifying shearing machine to shear the aqueous phase at a speed of 10,000 r / min, and add the oil phase while shearing. After the addition is completed, continue shearing and emulsification and dispersion for 20 minutes to obtain a water-in-oil emulsifier; then add an appropriate amount of N-phenylenediamine, raise the temperature to 50°C, and react at 1,000 r / min for 4 hours to obtain a dye precursor microcapsule emulsion.

[0050] The weight proportions of the components in the oil phase are: 10 parts of 2-phenylamino-3-methyl-6-dibutylaminofluoran, 7 parts of 1-methylnaphthalene, 36 parts of ethyl acetate, and 12 parts of isophorone diisocyanate.

[0051] The volume ratio of polyvinyl alcohol to sodium dodecylbenzene sulfonate in the aqueous phase is 20:1.

[0052] The weight proportions of the components of the dye precursor microcapsule emulsion are as follows: 25 parts of aqueous phase A, 8 parts of oil phase, and 8 parts of N-styrene diamine.

[0053] The developer emulsion was prepared by mixing aqueous phase B, polyethylene glycol, and deionized water to a 4% aqueous solution, adding sodium dodecylbenzenesulfonate and an appropriate amount of 4-hydroxy-4'-isopropoxydiphenyl sulfone, and grinding the mixture in a ball mill at 400 rpm for 8 h to obtain a developer dispersion emulsion.

[0054] The weight proportions of the components of the developer dispersion emulsion are as follows: 18 parts of polyvinyl alcohol aqueous solution, 3 parts of sodium dodecylbenzene sulfonate, and 8 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone.

[0055] The dye precursor microcapsule emulsion and the developer dispersed emulsion were mixed in a volume ratio of 1:1.5 to obtain an imaging layer coating liquid.

[0056] S3: (1) 6 parts of nano-titanium dioxide were weighed and calcined at 550°C for 2 h, and then added together with 10 parts of 2,2-dihydroxymethylpropionic acid in 50 mL of anhydrous ethanol. The mixture was ultrasonically dispersed for 50 min, and then the mixture was reacted at 80°C for 24 h in a sealed container under a protective gas. The solid particles were centrifuged, washed with deionized water, and dried to obtain modified titanium dioxide.

[0057] (2) Modified titanium dioxide and polyvinyl alcohol were mixed, and after ultrasonic dispersion for 20 minutes, polymethacrylate was added and stirred at a rate of 200 r / min for 30 minutes. Cyclotrimethylolpropane methyl acrylate and deionized water were then added and stirred for another 30 minutes to obtain a thermal film protective layer coating liquid.

[0058] The weight proportions of the components of the heat-sensitive film protective layer coating liquid are as follows: 45 parts of polymethacrylate, 10 parts of polyvinyl alcohol, 20 parts of deionized water, 3 parts of cyclotrimethylolpropane formal acrylate, and 7 parts of modified titanium dioxide.

[0059] S4: The coating thickness of the imaging layer coating liquid is 10 μm and the coating density is 120 g / m 3 The coating thickness of the thermal film protective layer coating liquid is 2μm and the coating density is 70g / m 3 , the thickness of the substrate layer is 230 μm.

[0060] The drying temperature of highly transparent thermal film is 70℃.

[0061] Example 2: A process for producing a highly transparent heat-sensitive film based on microcapsule technology, comprising the following steps:

[0062] S1: (1) preparing a 0.02 mol / mL solution of bis(2-hydroxyethyl) terephthalate and N,N-dimethylformamide, then mixing 20 mL of 40% sodium hydroxide solution with 50 mL of bis(2-hydroxyethyl) terephthalate solution, introducing protective gas, heating to 70°C, and electromagnetic stirring for 30 min; maintaining the temperature, adding 35 mL of vinyl chloride trimethoxysilane dropwise to the solution system, and continuously stirring the reaction for 16 h; after the solution was cooled to room temperature, the solution was repeatedly washed and separated with deionized water for 3 times, and finally dried to obtain a modified silane coupling agent;

[0063] (2) 21 parts of a modified silane coupling agent, 10 parts of 2,5-dimercapto-p-dibenzoic acid, and 1 part of benzoin dimethyl ether were added to 100 mL of tetrahydrofuran, and the raw materials were completely dissolved by ultrasonic dispersion for 15 minutes. The reaction was then carried out under 365 nm ultraviolet light at room temperature for 40 minutes. After the reaction was completed, the precipitate was filtered out, washed with deionized water, and dried to obtain an organic nucleating agent;

[0064] (3) 30 parts of calcium silicate, 5 parts of an organic nucleating agent, and 2 parts of anhydrous ethanol are placed in a mixer, stirred at a speed of 600 r / min for 20 minutes, and then heated to 80°C to dry the mixture until the anhydrous ethanol is completely volatilized to obtain modified calcium silicate; the modified calcium silicate, polyethylene glycol, and polyethylene terephthalate are melt-blended and extruded with a single-screw extruder to obtain a heat-sensitive film substrate layer.

[0065] The compression ratio of the single-screw extruder was 2.5:1 and the extrusion temperature was 250°C.

[0066] The thickness of the thermal film base material layer is 230 μm.

[0067] The weight proportions of the components of the heat-sensitive film substrate layer are as follows: 25 parts of modified calcium silicate, 8 parts of polyethylene glycol, and 85 parts of polyethylene terephthalate.

[0068] S2: The preparation method of the dye precursor thermosensitive microcapsule emulsion is as follows: (1) weighing 2-phenylamino-3-methyl-6-dibutylaminofluoran, 1-methylnaphthalene and ethyl acetate into a container, heating to 50°C, stirring and mixing, so that 2-phenylamino-3-methyl-6-dibutylaminofluoran is completely dissolved in the mixed solvent of 1-methylnaphthalene and ethyl acetate, and cooling to room temperature, adding isophorone diisocyanate, and mixing uniformly to obtain an oil phase; (2) polyvinyl alcohol and deionized water are prepared into an aqueous solution with a concentration of 3%, and sodium dodecylbenzene alkyl sulfonate is added to obtain aqueous phase A and aqueous phase B; (3) using a high-speed emulsifying shearing machine to high-speed shear the aqueous phase at a speed of 8000 r / min, while adding the oil phase while shearing, and after the addition is completed, continuing shearing and emulsifying dispersion for 10 minutes to obtain a water-in-water type emulsifier; then adding an appropriate amount of N-phenylenediamine, heating to 50°C, and reacting at 800 r / min for 3 hours to obtain a dye precursor microcapsule emulsion.

[0069] The weight proportions of the components in the oil phase are: 10 parts of 2-phenylamino-3-methyl-6-dibutylaminofluoran, 7 parts of 1-methylnaphthalene, 36 parts of ethyl acetate, and 12 parts of isophorone diisocyanate.

[0070] The volume ratio of polyvinyl alcohol to sodium dodecylbenzene sulfonate in the aqueous phase is 20:1.

[0071] The weight proportions of the components of the dye precursor microcapsule emulsion are as follows: 25 parts of aqueous phase A, 8 parts of oil phase, and 8 parts of N-styrene diamine.

[0072] The developer emulsion was prepared by mixing aqueous phase B, polyethylene glycol, and deionized water into a 3% aqueous solution, adding sodium dodecylbenzenesulfonate and an appropriate amount of 4-hydroxy-4'-isopropoxydiphenyl sulfone, and grinding the mixture in a ball mill at a rate of 200 r / min for 5 h to obtain a developer dispersion emulsion.

[0073] The weight proportions of the components of the developer dispersion emulsion are as follows: 18 parts of polyvinyl alcohol aqueous solution, 3 parts of sodium dodecylbenzene sulfonate, and 8 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone.

[0074] The dye precursor microcapsule emulsion and the developer dispersed emulsion were mixed in a volume ratio of 1:1.5 to obtain an imaging layer coating liquid.

[0075] S3: (1) 6 parts of nano-titanium dioxide were weighed and calcined at 450°C for 1 hour, and then added together with 10 parts of 2,2-dihydroxymethylpropionic acid in 50 mL of anhydrous ethanol. The mixture was ultrasonically dispersed for 60 minutes. Protective gas was introduced into a sealed container and the reaction was continued at 70°C for 20 hours. The solid particles were centrifuged and finally washed with deionized water and dried to obtain modified titanium dioxide.

[0076] (2) Modified titanium dioxide and polyvinyl alcohol were mixed, and after ultrasonic dispersion for 10 minutes, polymethacrylate was added and stirred at a rate of 100 r / min for 30 minutes. Cyclotrimethylolpropane methyl acrylate and deionized water were then added and stirred for 20 minutes to obtain a thermal film protective layer coating liquid.

[0077] The weight proportions of the components of the heat-sensitive film protective layer coating liquid are as follows: 45 parts of polymethacrylate, 10 parts of polyvinyl alcohol, 20 parts of deionized water, 3 parts of cyclotrimethylolpropane formal acrylate, and 7 parts of modified titanium dioxide.

[0078] S4: The coating thickness of the imaging layer coating liquid is 10 μm and the coating density is 120 g / m 3 The coating thickness of the thermal film protective layer coating liquid is 2μm and the coating density is 70g / m 3 , the thickness of the substrate layer is 230 μm.

[0079] The drying temperature of highly transparent thermal film is 60℃.

[0080] Example 3: A process for producing a highly transparent heat-sensitive film based on microcapsule technology, comprising the following steps:

[0081] S1: (1) preparing a 0.04 mol / mL solution of bis(2-hydroxyethyl) terephthalate and N,N-dimethylformamide, then mixing 20 mL of 50% sodium hydroxide solution with 50 mL of bis(2-hydroxyethyl) terephthalate solution, introducing protective gas, heating to 120°C, and electromagnetic stirring for 50 min; maintaining the temperature, adding 35 mL of vinyl chloride trimethoxysilane dropwise to the solution system, and continuously stirring the reaction for 24 h; after the solution was cooled to room temperature, the solution was repeatedly washed and separated with deionized water for 5 times, and finally dried to obtain a modified silane coupling agent;

[0082] (2) 21 parts of a modified silane coupling agent, 10 parts of 2,5-dimercapto-p-dibenzoic acid, and 1 part of benzoin dimethyl ether were added to 100 mL of tetrahydrofuran, and the raw materials were completely dissolved by ultrasonic dispersion for 25 minutes. The reaction was then carried out at room temperature using 365 nm ultraviolet light for 80 minutes. After the reaction was completed, the precipitate was filtered out, washed with deionized water, and dried to obtain an organic nucleating agent.

[0083] (3) 30 parts of calcium silicate, 5 parts of an organic nucleating agent, and 2 parts of anhydrous ethanol are placed in a mixer, stirred at a speed of 1000 r / min for 40 minutes, and then heated to 90°C to dry the mixture until the anhydrous ethanol is completely volatilized to obtain modified calcium silicate; the modified calcium silicate, polyethylene glycol, and polyethylene terephthalate are melt-blended and extruded with a single-screw extruder to obtain a heat-sensitive film substrate layer.

[0084] The compression ratio of the single-screw extruder was 3.5:1 and the extrusion temperature was 260°C.

[0085] The thickness of the thermal film base material layer is 230 μm.

[0086] The weight proportions of the components of the heat-sensitive film substrate layer are as follows: 25 parts of modified calcium silicate, 8 parts of polyethylene glycol, and 85 parts of polyethylene terephthalate.

[0087] S2: The preparation method of the dye precursor thermosensitive microcapsule emulsion is as follows: (1) weighing 2-phenylamino-3-methyl-6-dibutylaminofluoran, 1-methylnaphthalene, and ethyl acetate into a container, heating to 70°C, stirring and mixing, so that 2-phenylamino-3-methyl-6-dibutylaminofluoran is completely dissolved in the mixed solvent of 1-methylnaphthalene and ethyl acetate, and cooling to room temperature, adding isophorone diisocyanate, mixing evenly, and obtaining an oil phase; (2) mixing polyvinyl alcohol with deionized water; Prepare a 5% aqueous solution, add sodium dodecylbenzene sulfonate to obtain aqueous phase A and aqueous phase B; (3) use a high-speed emulsifying shearing machine to shear the aqueous phase at a speed of 9000r / min, and add the oil phase while shearing. After the addition is completed, continue shearing and emulsification and dispersion for 20 minutes to obtain a water-in-oil emulsifier; then add an appropriate amount of N-phenylenediamine, raise the temperature to 60°C, and react at 1000r / min for 5 hours to obtain a dye precursor microcapsule emulsion.

[0088] The weight proportions of the components in the oil phase are: 10 parts of 2-phenylamino-3-methyl-6-dibutylaminofluoran, 7 parts of 1-methylnaphthalene, 36 parts of ethyl acetate, and 12 parts of isophorone diisocyanate.

[0089] The volume ratio of polyvinyl alcohol to sodium dodecylbenzene sulfonate in the aqueous phase is 20:1.

[0090] The weight proportions of the components of the dye precursor microcapsule emulsion are as follows: 25 parts of aqueous phase A, 8 parts of oil phase, and 8 parts of N-styrene diamine.

[0091] The developer emulsion was prepared by mixing aqueous phase B, polyethylene glycol, and deionized water to a 5% aqueous solution, adding sodium dodecylbenzenesulfonate and an appropriate amount of 4-hydroxy-4'-isopropoxydiphenyl sulfone, and grinding the mixture at a rate of 500 r / min for 10 h using a ball mill to obtain a developer dispersion emulsion.

[0092] The weight proportions of the components of the developer dispersion emulsion are as follows: 18 parts of polyvinyl alcohol aqueous solution, 3 parts of sodium dodecylbenzene sulfonate, and 8 parts of 4-hydroxy-4'-isopropoxydiphenyl sulfone.

[0093] The dye precursor microcapsule emulsion and the developer dispersed emulsion were mixed in a volume ratio of 1:1.5 to obtain an imaging layer coating liquid.

[0094] S3: (1) 6 parts of nano-titanium dioxide were weighed and calcined at 750°C for 3 h, and then added together with 10 parts of 2,2-dihydroxymethylpropionic acid in 50 mL of anhydrous ethanol. The mixture was ultrasonically dispersed for 60 min, and then the reaction was continued at 70°C for 30 h in a sealed container under a protective gas. The solid particles were centrifuged, washed with deionized water, and dried to obtain modified titanium dioxide.

[0095] (2) Modified titanium dioxide and polyvinyl alcohol were mixed, and after ultrasonic dispersion for 20 minutes, polymethacrylate was added and stirred at a rate of 300 r / min for 40 minutes. Cyclotrimethylolpropane methyl acrylate and deionized water were then added and stirred for 30 minutes to obtain a thermal film protective layer coating liquid.

[0096] The weight proportions of the components of the heat-sensitive film protective layer coating liquid are as follows: 45 parts of polymethacrylate, 10 parts of polyvinyl alcohol, 20 parts of deionized water, 3 parts of cyclotrimethylolpropane formal acrylate, and 7 parts of modified titanium dioxide.

[0097] S4: The coating thickness of the imaging layer coating liquid is 10 μm and the coating density is 120 g / m 3 The coating thickness of the thermal film protective layer coating liquid is 2μm and the coating density is 70g / m 3 , the thickness of the substrate layer is 230 μm.

[0098] The drying temperature of high-transparency thermal film is 80℃.

[0099] Comparative Example 1: No organic nucleating agent was prepared. Calcium silicate was modified with a modified silane coupling agent and then melt-blended and extruded with polyethylene glycol and polyethylene terephthalate through a single-screw extruder to obtain a heat-sensitive film substrate layer. Other processes were the same as in Example 1.

[0100] Comparative Example 2: Calcium silicate was directly modified with vinyltrioxysilane to obtain modified calcium silicate, which was then melt-blended and extruded with polyvinyl alcohol and polyethylene terephthalate through a single-screw extruder to obtain a heat-sensitive film substrate layer. Other aspects were the same as in Example 1.

[0101] Comparative Example 3: No modified calcium silicate is added to the substrate layer, that is, the weight proportions of the components of the thermal film substrate layer are: 8 parts of polyethylene glycol, 85 parts of polyethylene terephthalate, and the rest are the same as in Example 1;

[0102] Comparative Example 4: Calcium carbonate was used instead of calcium silicate. The weight proportions of the components of the thermal film substrate layer were: 25 parts modified calcium carbonate, 8 parts polyethylene glycol, and 85 parts polyethylene terephthalate. Other conditions were the same as in Example 1.

[0103] Comparative Example 5: In the preparation of the oil phase, only ethyl acetate was used as the solvent, and the rest was the same as in Example 1;

[0104] Comparative Example 6: The coating thickness of the imaging layer coating liquid is 12 μm and the coating density is 130 g / m 3 The coating thickness of the thermal film protective layer coating liquid is 4μm and the coating density is 80g / m 3 , the thickness of the substrate layer is 260 μm.

[0105] Comparative Example 7: No modified titanium dioxide is added to the protective layer. The weight proportions of the components of the thermal film protective layer coating liquid are: 45 parts of polymethacrylate, 10 parts of polyvinyl alcohol, 20 parts of deionized water, and 3 parts of cyclotrimethylolpropane formal acrylate. Other components are the same as in Example 1.

[0106] Performance Testing: The thermal films prepared in Examples 1-3 and Comparative Examples 1-7 were cut into 8×10-inch pieces, ensuring that the samples were intact. Their light transmittance and haze were measured using a light transmittance tester. Their tensile strength was also measured using a plastic tensile strength testing machine according to GB / T 12914-2008. The resulting data is shown in the table below:

[0107] Example Light transmittance (%) Haze (%) Tensile strength (Mpa) Example 1 95.27 0.87 16.5 Example 2 91.23 1.17 15.2 Example 3 93.17 1.08 15.8 Comparative Example 1 89.87 1.31 15.2 Comparative Example 2 87.38 1.58 14.9 Comparative Example 3 82.88 1.89 13.8 Comparative Example 4 90.37 1.21 15.5 Comparative Example 5 92.68 1.02 16.0 Comparative Example 6 91.38 1.10 17.3 Comparative Example 7 91.34 1.19 16.1

[0108] From the comparison of Examples 1 to 3 and Comparative Examples 1 to 7 in the above table, it can be seen that the addition of an organic nucleating agent has a significant effect on the transparency of the thermal film; a reasonable combination of fillers and organic nucleating agents can maximize the achievement of a thermal film with higher transparency; when coating the thermal film, the coating density and thickness also affect the transparency and tensile strength of the film to a certain extent.

[0109] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A process for producing a highly transparent thermal film based on microcapsule technology, characterized in that: The following steps are involved: S1: Calcium silicate is modified with an organic nucleating agent, and then melt-blended and extruded with polyethylene glycol and polyethylene terephthalate through a single-screw extruder to obtain a heat-sensitive film substrate layer; S2: preparing a dye precursor thermosensitive microcapsule emulsion and a developer emulsion, and mixing the two to obtain an imaging layer coating liquid; S3: Preparation of thermal film protective layer coating liquid; S4: Plasma-treating one side of the thermal film substrate layer, applying an imaging layer coating liquid and a thermal film protective layer coating liquid to the substrate layer in sequence, and drying the substrate to obtain a highly transparent thermal film. In S1, the weight proportions of the components of the heat-sensitive film substrate layer are: 20-30 parts of modified calcium silicate, 5-10 parts of polyethylene glycol, and 80-90 parts of polyethylene terephthalate; Wherein, the preparation method of the organic nucleating agent is: (1) Bis(2-hydroxyethyl) terephthalate and N,N-dimethylformamide were prepared into a 0.02 mol / mL~0.04 mol / mL solution, and then 40~50% sodium hydroxide solution was mixed with the bis(2-hydroxyethyl) terephthalate solution, and protective gas was introduced. The temperature was raised to 70~120°C and electromagnetic stirring was performed for 30~50 minutes. Vinyl chloride trimethoxysilane was added dropwise to the solution system while maintaining the temperature, and the reaction was continued by stirring for 16~24 hours. After the solution was cooled to room temperature, the solution was repeatedly washed and separated with deionized water for 3~5 times, and finally dried to obtain a modified silane coupling agent. (2) Adding a modified silane coupling agent, 2,5-dimercapto-p-dibenzoic acid, and benzoin dimethyl ether to tetrahydrofuran, the raw materials were completely dissolved by ultrasonic dispersion for 15 to 25 minutes, and then irradiated with 365 nm ultraviolet light at room temperature for 40 to 80 minutes. After the reaction was completed, the precipitate was filtered out, washed with deionized water, and dried to obtain an organic nucleating agent; The mass ratio of modified silane coupling agent, 2,5-dimercapto-4-dibenzoic acid, and benzoin dimethyl ether is 21:10:1; In S3, the weight proportions of the components of the thermal film protective layer coating liquid are: 40-50 parts of polymethacrylate, 10-20 parts of polyvinyl alcohol, 15-20 parts of deionized water, 3-6 parts of cyclotrimethylolpropane formal acrylate, and 5-10 parts of modified titanium dioxide; The preparation method of the thermal film protective layer coating liquid is as follows: (1) After calcining nano-titanium dioxide at 450-750°C for 1-3 hours, the nano-titanium dioxide was added to anhydrous ethanol together with 2,2-dihydroxymethylpropionic acid, and subjected to ultrasonic dispersion treatment for 30-60 minutes. The nano-titanium dioxide was reacted continuously at 70-90°C for 20-30 hours under protective gas. The solid particles were centrifuged, washed, and dried to obtain modified titanium dioxide. (2) Modified titanium dioxide was mixed with polyvinyl alcohol, and after ultrasonic dispersion for 10 to 20 minutes, polymethacrylate was added and stirred at a rate of 100 to 300 r / min for 30 to 40 minutes. Then, cyclotrimethylolpropane methyl acrylate and deionized water were added and stirred for 20 to 30 minutes to obtain a thermal film protective layer coating liquid.

2. The process for producing a highly transparent thermal film based on microcapsule technology according to claim 1, characterized in that: In S1, the preparation method of the heat-sensitive film substrate layer is as follows: calcium silicate, an organic nucleating agent, and anhydrous ethanol are stirred at a speed of 600-1000 r / min for 20-40 minutes to mix uniformly, then the temperature is raised to 80-90°C and the mixture is dried until the anhydrous ethanol is completely volatilized to obtain modified calcium silicate; finally, the mixture is melt-blended and extruded with polyethylene glycol and polyethylene terephthalate through a single-screw extruder to obtain the heat-sensitive film substrate layer.

3. The process for producing a highly transparent thermal film based on microcapsule technology according to claim 2, characterized in that: The compression ratio of the single-screw extruder is 2.5:1~3.5:1, the extrusion temperature is 250~260℃; the thickness of the thermal film substrate layer is 200~260μm.

4. The process for producing a highly transparent thermal film based on microcapsule technology according to claim 1, characterized in that: The imaging layer coating liquid is obtained by mixing a dye precursor microcapsule emulsion and a color developer dispersed emulsion in a volume ratio of 1:1 to 1.

5.

5. The process for producing a highly transparent thermal film based on microcapsule technology according to claim 1, characterized in that: In S4, the coating thickness of the imaging layer coating liquid is 8~12μm, and the coating density is 80~130g / m³; the coating thickness of the thermal film protective layer coating liquid is 1~4μm, and the coating density is 50~80g / m³; the thickness of the thermal film substrate layer is 200~260μm; the drying temperature of the high-transparency thermal film is 60~80℃.

6. A highly transparent thermal film based on microcapsule technology, characterized by: The highly transparent heat-sensitive film is prepared by the processing technology of any one of claims 1 to 5 based on microcapsule technology.