A thermal transfer protective film for heat-sensitive applications and its preparation method

Abstract

This invention belongs to the field of thermal transfer material technology, specifically relating to a thermal transfer protective film for thermal applications and its preparation method. The thermal transfer protective film of this invention includes a back coating layer and a thermal transfer layer coated on both sides of a substrate. The thermal transfer layer sequentially comprises a release layer, an aging-resistant layer, a protective layer, a color-fixing layer, and an adhesive layer. This product has highly efficient heat transfer performance and color enhancement properties. It not only provides excellent aging resistance, solvent corrosion resistance, and scratch resistance to printed thermal labels without affecting the thermal printing effect, but also protects the printhead and extends its service life. Wear tests show that the thermal transfer protective film of this invention can withstand a load of 200g and maintain the thermal label's color after 200 abrasion cycles. It is resistant to the corrosive effects of solvents such as anhydrous ethanol, engine oil, gasoline, solvent oil, and cyclohexane, solving the problem of existing thermal paper's poor solvent resistance.

Description

Technical Field

[0001] This invention belongs to the field of thermal transfer materials technology, specifically relating to a thermal transfer protective film for thermosensitive applications and its preparation method. Background Technology

[0002] In recent years, with the development of thermal technology, the application fields of thermal transfer technology have become increasingly wide, and the demand for thermal printing paper at home and abroad has been increasing.

[0003] In existing technologies, thermal printing technology has advantages such as low printing noise, high printing clarity, fast printing speed, and ease of use, and is loved by consumers in various industries. With economic development, consumers have a growing demand for high-quality, high-performance thermal printing paper. However, existing thermal paper still has disadvantages such as the inability to preserve printed labels for a long time, the text fading during storage, and the significant damage to the print head caused by continuous printing for a long time.

[0004] The subsequent emergence of thermal transfer protective films effectively addresses the shortcoming of thermally printed labels that cannot be preserved for extended periods. Currently, most traditional thermal transfer films on the market consist of a carrier layer, a release layer, and a protective layer. For example, patent CN 204641121U discloses a combined thermal transfer film structure, which requires coating a release layer containing a silicone release agent onto the carrier film surface, leading to complex processes, reduced product yield, and increased costs. Another example is patent application CN101508222 A, which discloses a thermal transfer film for decorating electronic products. However, this film lacks an ink-printed protective layer, making the transferred patterns easily scratched and contaminated during use, and failing to provide lasting protection for the patterns and product appearance. This demonstrates that existing thermal transfer protective films still have various problems.

[0005] Based on this, the present invention adjusts the types and amounts of components in each functional layer of the thermal transfer protective film for thermal applications, in order to ensure that the thermal paper coated with the thermal transfer protective film has properties such as aging resistance, solvent corrosion resistance, and scratch resistance, while also enhancing the service life of the printhead. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a thermal transfer protective film product for thermal applications. This product has high-efficiency heat transfer performance and color enhancement properties. It can not only make the printed thermal labels have excellent aging resistance, solvent corrosion resistance, and scratch resistance without affecting the thermal printing effect, but also has the advantages of protecting the print head and extending its service life.

[0007] The present invention also provides a method for preparing the thermal transfer protective film for thermosensitive applications.

[0008] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0009] A heat transfer protective film for thermal applications includes a back coating layer and a heat transfer layer coated on both sides of a substrate, wherein the heat transfer layer sequentially comprises a release layer, an aging resistant layer, a protective layer, a color-fixing layer, and an adhesive layer.

[0010] The thermal transfer protective film for thermal applications is printed simultaneously with thermal paper using thermal transfer technology. Specifically, the thermal transfer layer is transferred onto the thermal paper using a thermal transfer method, and then divided into several thermal labels. This ensures that a protective layer is precisely attached to the surface of the printed thermal labels. This protective layer has highly efficient heat conduction properties. At the same time, the color-fixing layer undergoes a color-developing reaction during the printing process, compensating for the heat loss caused by the added film during printing, which leads to insufficient heat and light-colored prints on the thermal paper. Meanwhile, the adhesive layer provides sufficient adhesion, ensuring that the protective layer firmly adheres to the surface of the thermal label, giving the thermal label excellent aging resistance, solvent corrosion resistance, and scratch resistance, allowing for long-term storage. Furthermore, the back coating layer effectively protects the print head during the printing process.

[0011] Furthermore, the substrate is, for example, any one of biaxially oriented polyethylene terephthalate (BOPET) film, biaxially oriented polyethylene (BOPE) film, and biaxially oriented polypropylene (BOPP) film.

[0012] Furthermore, the back coating, by weight percentage, comprises: 5-10% curing agent, 3-8% antistatic agent, and the balance being silicone-modified polyurethane resin.

[0013] Furthermore, the release layer, by mass percentage, comprises 35-40% waterborne polyurethane resin, 3-10% substrate wetting agent, and the remainder being waterborne polyethylene micron wax.

[0014] Furthermore, the aging-resistant layer, by mass percentage, comprises 20-30% epoxy resin, 10-15% hydrogenated styrene-butadiene block copolymer, and the balance being modified tert-butylphenol resin.

[0015] Furthermore, the protective layer, by weight percentage, comprises 15-25% chlorinated polypropylene resin, 30-40% polyester resin, and the remainder being acrylic resin.

[0016] Furthermore, the color-fixing layer, by mass percentage, comprises 15-25% methylparaben, 15-25% polyvinyl alcohol, 10-15% hydroxymethyl cellulose, 3-8% benzenesulfonamide, 2-5% wetting and dispersing agent, and the balance being fluorane thermosensitive dyes.

[0017] Furthermore, the adhesive layer, by weight percentage, comprises 30-35% waterborne terpene resin, 30-35% waterborne polyester resin, and 30-35% waterborne phenolic resin.

[0018] Furthermore, the total thickness of the thermal transfer protective film for heat-sensitive applications is 5.5~6.6μm, wherein the base layer thickness is 3.5μm, the back coating thickness is 0.1~0.2μm, the release layer thickness is 0.2~0.4μm, the aging resistant layer thickness is 0.4~0.6μm, the protective layer thickness is 0.5~0.7μm, the color fixing layer thickness is 0.6~0.8μm, and the adhesive layer thickness is 0.2~0.4μm.

[0019] Furthermore, the method for preparing the thermal transfer protective film for heat-sensitive applications includes the following steps:

[0020] (1) First, apply a back coating to one side of the substrate surface;

[0021] (2) A release layer is applied to the other side surface of the substrate in step (1);

[0022] (3) Prepare an aging-resistant layer on the surface of the release layer prepared in step (2): Dissolve epoxy resin, modified tert-butylphenol resin and hydrogenated styrene-butadiene block copolymer in a mixed solvent of methyl ethyl ketone and toluene, then coat it evenly on the release layer, and dry it to obtain the aging-resistant layer.

[0023] (4) Prepare a protective layer on the surface of the aging-resistant layer prepared in step (3): Dissolve chlorinated polypropylene resin, polyester resin and acrylic resin in a mixed solvent of butanone and toluene to obtain a clear mixture. Coat the mixture evenly on the surface of the aging-resistant layer and dry it to obtain the protective layer.

[0024] (5) Prepare a color-fixing layer on the surface of the protective layer prepared in step (4): Add methylparaben, polyvinyl alcohol, hydroxymethyl cellulose and benzenesulfonamide to pure water to dissolve, add wetting and dispersing agent, disperse evenly, add fluorane thermosensitive dye, grind, coat the ground mixture evenly on the protective layer, and blow dry to obtain the color-fixing layer.

[0025] (6) Prepare an adhesive layer on the surface of the color-fixing layer prepared in step (5).

[0026] A further preferred embodiment of the method for preparing the thermal transfer protective film for heat-sensitive applications includes the following steps:

[0027] (1) Apply a back coating to the substrate side surface: First, dilute the silicone-modified polyurethane resin with methyl ethyl ketone to form a solution. Then, add the curing agent and antistatic agent to the solution and mix them evenly. Apply the solution evenly to the substrate side surface and dry it at 120-130℃ to form a back coating for later use.

[0028] (2) Apply a release layer to the other side of the substrate in step (1): After mixing the water-based polyurethane resin and the substrate wetting agent evenly with pure water, add the water-based polyethylene micro powder wax to the mixture, disperse and grind it. The particle size after grinding should be <1.5μm. Apply the ground mixture evenly to the side of the substrate without the backing adhesive layer, and dry it at 100-110℃ to obtain the release layer.

[0029] (3) Prepare an aging-resistant layer on the surface of the release layer prepared in step (2): Dissolve epoxy resin, modified tert-butylphenol resin and hydrogenated styrene-butadiene block copolymer in a mixed solvent of methyl ethyl ketone and toluene, then coat it evenly on the release layer, and dry it at 80-90℃ to obtain the aging-resistant layer.

[0030] (4) Prepare a protective layer on the surface of the aging-resistant layer prepared in step (3): Dissolve chlorinated polypropylene resin, polyester resin and acrylic resin in a mixed solvent of butanone and toluene to obtain a clear mixture. Coat the mixture evenly on the surface of the aging-resistant layer and dry it at 80-90℃ to obtain the protective layer.

[0031] (5) Prepare a color-fixing layer on the surface of the protective layer prepared in step (4): Add methylparaben, polyvinyl alcohol, hydroxymethyl cellulose and benzenesulfonamide to pure water and heat to 50-60℃ to dissolve. After cooling to room temperature, add wetting and dispersing agent. After dispersing evenly, add fluorane thermosensitive dye and grind to a particle size of 0.4-0.6μm. Coat the ground mixture evenly on the protective layer and dry at 25-30℃ to obtain the color-fixing layer.

[0032] (6) Prepare an adhesive layer on the surface of the color-fixing layer prepared in step (5): Add waterborne terpene resin, waterborne polyester resin and waterborne phenolic resin to pure water and mix evenly. Coat the mixture evenly on the surface of the color-fixing layer and dry it at 25-30℃ to obtain the adhesive layer.

[0033] More preferably, in step (1), the back coating has the following composition by mass ratio: methyl ethyl ketone: silicone-modified polyurethane resin: curing agent: antistatic agent = 5: (4-5): 0.3: 0.2.

[0034] In a further preferred embodiment, in step (2), the release layer has the following composition by mass ratio: pure water: waterborne polyurethane resin: waterborne polyethylene micro powder wax: substrate wetting agent = (2-3): 3: 4: 0.5.

[0035] More preferably, in step (3), the components in the aging-resistant layer, by mass ratio, are methyl ethyl ketone: toluene: epoxy resin: modified tert-butylphenol resin: hydrogenated styrene-butadiene block copolymer = 2:4:(1-1.5):1.5:(1-1.5), specifically in the ratio of 2:4:1.4:1.5:1.1, or 2:4:1.2:1.5:1.3.

[0036] More preferably, in step (4), the components in the protective layer, by mass ratio, are methyl ethyl ketone: toluene: chlorinated polypropylene resin: polyester resin: acrylic resin = (3-4): (3-4): 0.6: 0.9: 1.5.

[0037] More preferably, in step (5), the components in the color-fixing layer are, by mass ratio, pure water: methylparaben: polyvinyl alcohol: hydroxymethyl cellulose: benzenesulfonamide: wetting and dispersing agent: fluorane thermosensitive dye = 6: 0.8: 0.8: 0.6: 0.3: 0.2: (1-1.5).

[0038] More preferably, in step (6), the components of the adhesive layer are in the following mass ratio: pure water: waterborne terpene resin: waterborne polyester resin: waterborne phenolic resin = (1-2):1:1:1.

[0039] Specifically, the thermal transfer protective film for thermal sensitivity described in this invention is used in conjunction with thermal paper. During use, the thermal transfer layer is transferred to the surface of the thermal label through thermal transfer, and the adhesive layer makes it firmly adhere to the surface of the thermal label, giving the information on the thermal label excellent aging resistance, solvent corrosion resistance, and scratch resistance.

[0040] The thermal transfer protective film of this invention improves the defect of thermal labels where the text fades and disappears during long-term storage, enabling it to play a greater role in applications such as logistics, warehousing, catering, retail, pharmaceuticals, document management, and chemical labeling, and to achieve automated and digital management.

[0041] Compared with the prior art, the advantages of the present invention are:

[0042] 1. This invention overcomes the shortcomings of existing thermal labels to a certain extent. The thermal transfer protective film provided has a reasonable structural design, is easy to use, and is firmly and reliably adhered to the substrate after being pasted. It also has excellent aging resistance, solvent corrosion resistance, and scratch resistance.

[0043] 2. Wear tests were conducted using a friction tester. The results showed that the thermal transfer protective film for thermal sensitivity of the present invention can withstand a load of 200g and the thermal label can withstand 200 abrasions without discoloration (existing thermal labels discolor after 10 abrasions).

[0044] 3. Abrasion resistance tester test shows that the thermal transfer protective film for thermal sensitivity of the present invention has a thermal transfer layer that is resistant to the corrosion of solvents such as anhydrous ethanol, engine oil, gasoline, solvent oil, and cyclohexane, thus solving the problem of existing thermal paper being not resistant to solvents.

[0045] 4. Regarding the preparation method of the thermal transfer protective film provided by this invention, the preparation can be carried out with reference to existing thermal transfer barcode printing ribbon technology, which has a high degree of technological maturity, is simple in preparation, and is easy to use. Therefore, this invention has good practical value and significance for promotion and application.

[0046] The preparation method of the present invention is simple to operate, low in cost, does not require expensive experimental instruments and equipment, is easy to realize large-scale mass production, and has important application potential. Detailed Implementation

[0047] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0048] The present invention will be further explained below with reference to the embodiments. However, before introducing the specific embodiments, the performance of some materials in the following embodiments will be briefly described as follows.

[0049] The BOPET film used for the substrate has a thickness of 3.5±0.5μm and a longitudinal tensile strength of not less than 45MPa; the BOPP film has a thickness of 3.5±0.5μm and a longitudinal tensile strength of not less than 30MPa; the BOPE film has a thickness of 3.5±0.5μm and a longitudinal tensile strength of not less than 35MPa.

[0050] The back coating described in the following examples is prepared by mixing silicone-modified polyurethane resin with a curing agent and an antistatic agent.

[0051] The performance requirements for waterborne polyurethane resin are: pH 7.0-8.0, minimum film-forming temperature <30℃;

[0052] Water-based polyethylene micronized wax: spherical structure, softening point: 100-110℃, average particle size ≤7.5μm;

[0053] Epoxy resin: Epoxy equivalent: 550-650, softening point: 80-85℃;

[0054] Modified tert-butylphenolic resin: molecular weight 700-1000, softening point: 85-120℃;

[0055] Hydrogenated styrene-butadiene block copolymer: styrene / rubber weight ratio is 33 / 67, viscosity of 25% toluene solution at 25℃ is >50000 mPa*s;

[0056] Chlorinated polypropylene resin: chlorine content (mass fraction) 28-32%, 20% toluene solution viscosity 800-1200 mPa*s;

[0057] Polyester resin: molecular weight 20,000-30,000, glass transition temperature <25℃, softening point 120℃;

[0058] Acrylic resin: molecular weight 160,000-200,000, glass transition temperature 35℃;

[0059] Aqueous terpene resin: emulsion viscosity <200, pH value 6.0-8.0;

[0060] Waterborne polyester resin: emulsion viscosity 500-1200 mPa*s, pH value 4.0-7.0.

[0061] The organosilicon-modified polyurethane resin is in liquid form, while the waterborne polyurethane resin, waterborne terpene resin, waterborne polyester resin, and waterborne phenolic resin are all in emulsion form.

[0062] Example 1

[0063] Example 1 provides a thermal transfer protective film for thermal applications. In use, it is printed simultaneously with thermal paper using thermal transfer technology. Specifically, a thermal transfer layer is transferred onto the thermal paper, which is then divided into several thermal labels. This ensures that a protective layer is precisely applied to the surface of the printed thermal labels. This protective layer has excellent aging resistance, solvent corrosion resistance, and scratch resistance, enabling the thermal labels to be stored for a long time. Both the thermal transfer technology and the thermal paper are existing technologies and will not be described in detail here.

[0064] The thermal transfer protective film for thermal sensitivity includes a back coating layer and a thermal transfer layer coated on both sides of the substrate, wherein the thermal transfer layer sequentially includes a release layer, an aging resistant layer, a protective layer, a color fixing layer and an adhesive layer.

[0065] The substrate is specifically a biaxially oriented polyethylene terephthalate (BOPET) film;

[0066] The back coating layer, by mass ratio, comprises: silicone-modified polyurethane resin: curing agent: antistatic agent = 4.5:0.3:0.2;

[0067] The release layer, by mass ratio, comprises: waterborne polyurethane resin: waterborne polyethylene micron wax: substrate wetting agent = 3:4:0.5;

[0068] The aging-resistant layer, by mass ratio, comprises epoxy resin: modified tert-butylphenol resin: hydrogenated styrene-butadiene block copolymer = 1.4:1.5:1.1;

[0069] The protective layer, by mass ratio, comprises chlorinated polypropylene resin: polyester resin: acrylic resin = 2:3:5;

[0070] The fixed layer, by mass ratio, comprises the following components: fluorane thermosensitive dye: methylparaben: polyvinyl alcohol: hydroxymethyl cellulose: benzenesulfonamide: wetting and dispersing agent = 1.3:0.8:0.8:0.6:0.3:0.2;

[0071] The adhesive layer, by mass ratio, comprises the following components: waterborne terpene resin: waterborne polyester resin: waterborne phenolic resin = 1:1:1.

[0072] The thermal transfer protective film for thermal sensitivity has a total thickness of 5.5 μm, including a base layer thickness of 3.5 μm, a back coating thickness of 0.1 μm, a release layer thickness of 0.2 μm, an aging resistant layer thickness of 0.4 μm, a protective layer thickness of 0.5 μm, a color-fixing layer thickness of 0.6 μm, and an adhesive layer thickness of 0.2 μm.

[0073] The specific steps of the preparation method of the thermal transfer protective film for thermosensitive applications described in this embodiment are as follows:

[0074] (1) Apply a back coating to the substrate side surface: First, dilute the silicone-modified polyurethane resin liquid with methyl ethyl ketone to form a solution with a solid content (weight ratio of solid to solution) of 15-20%. Then, add curing agent and antistatic agent to the solution and mix evenly. Apply the solution evenly to the substrate side surface and dry at 120-130℃ for later use. In the back coating, the components are in the following mass ratio: methyl ethyl ketone: silicone-modified polyurethane resin liquid (manufacturer: Xinwei New Materials, model: 550UR): curing agent (manufacturer: Shanghai Xirun Chemical Technology Co., Ltd., model: crosslinking agent XR-500): antistatic agent (Guangzhou Xiyi Chemical Co., Ltd., model: KD-3) = 5: 4.5: 0.3: 0.2.

[0075] (2) In step (1), the release layer is first coated on the other side of the substrate: after mixing the waterborne polyurethane resin emulsion and the substrate wetting agent with pure water, waterborne polyethylene micro powder wax is added to the mixture, dispersed and ground. The particle size after grinding is required to be <1.5μm. The ground mixture is evenly coated on the side of the substrate without the backing adhesive layer. After drying at 100-110℃, it becomes the release layer. In the release layer, by mass ratio, the components are: pure water: waterborne polyurethane resin emulsion (manufacturer: Oubaodi Resin (Shenzhen) Co., Ltd., model: U8001): waterborne polyethylene micro powder wax (manufacturer: Nanjing Tianshi New Material Technology Co., Ltd., model: PEW-0511): substrate wetting agent (manufacturer: BAK Chemical, model: DISPERBYK-2010) = 2.5:3:4:0.5;

[0076] (3) Prepare an aging-resistant layer on the surface of the release layer prepared in step (2): Dissolve epoxy resin, modified tert-butylphenol resin and hydrogenated styrene-butadiene block copolymer in a mixed solvent of methyl ethyl ketone and toluene, then coat it evenly on the release layer, and dry it at 80-90℃ to obtain the aging-resistant layer; In the aging-resistant layer, by mass ratio, the components are methyl ethyl ketone: toluene: epoxy resin (manufacturer: Tiantai High-tech (Guangzhou) Co., Ltd., model: TT708): modified tert-butylphenol resin (manufacturer: Hebao Plastics, model: phenolic resin 2402): hydrogenated styrene-butadiene block copolymer (manufacturer: KRATON, model: G1651) = 2:4:1.4:1.5:1.1;

[0077] (4) Prepare a protective layer on the surface of the aging-resistant layer prepared in step (3): Dissolve chlorinated polypropylene resin, polyester resin and acrylic resin in a mixed solvent of methyl ethyl ketone and toluene to obtain a clear mixture. Coat the mixture evenly on the surface of the aging-resistant layer and dry it at 80-90℃ to obtain the protective layer. In the protective layer, the components are in the following mass ratio: methyl ethyl ketone: toluene: chlorinated polypropylene resin (manufacturer: Shenzhen Yoshida Chemical, model: chlorinated polypropylene E0101-X): polyester resin (manufacturer: Suzhou Hanhai New Material Co., Ltd., model: HT1150): acrylic resin (manufacturer: Shanghai Bolier Chemical, model: BM218) = 3.5: 3.5: 0.6: 0.9: 1.5;

[0078] (5) Preparation of a color-fixing layer on the surface of the protective layer prepared in step (4): Methylparaben, polyvinyl alcohol, hydroxymethyl cellulose and benzenesulfonamide are added to pure water and heated to 50-60℃ to dissolve. After cooling to room temperature, a wetting and dispersing agent is added. After uniform dispersion, a fluorane thermosensitive dye is added and ground to a particle size of 0.4-0.6μm. The ground mixture is evenly coated on the protective layer and dried at 30℃ to obtain the color-fixing layer. In the color-fixing layer, the components are, by mass ratio, pure water: methylparaben (manufacturer: Zhejiang Shengxiao Chemical Co., Ltd.): polyethylene Alcohol (Changchun Chemical (Jiangsu) Co., Ltd., Model: BP-24): Hydroxymethyl cellulose (Manufacturer: Hebei Xinfeng Chemical Co., Ltd.): Benzenesulfonamide (Manufacturer: Guangdong Fangxin Biotechnology Co., Ltd., Model: N-Butylbenzenesulfonamide): Wetting and dispersing agent (Manufacturer: BAK Chemical, Model: BYKJET-9177): Fluorescein thermosensitive dye (Manufacturer: Hubei Jiufenglong Chemical Co., Ltd., Specific component: 3-N-isopentyl-N-ethylamino-6-methyl-7-phenylaminofluorane) = 6:0.8:0.8:0.6:0.3:0.2:1.3;

[0079] (6) Prepare an adhesive layer on the surface of the color-fixing layer prepared in step (5): Add waterborne terpene resin emulsion, waterborne polyester resin emulsion and waterborne phenolic resin emulsion to pure water and mix evenly. Coat the mixture evenly on the surface of the color-fixing layer and dry it at 30°C to obtain the adhesive layer. In the adhesive layer, the components are in the following mass ratio: pure water: waterborne terpene resin emulsion (manufacturer: Shanghai Shuixing Industrial Co., Ltd., model: TAMANOL E-100): waterborne polyester resin emulsion (manufacturer: Shanghai Cansen Chemical Co., Ltd., model: CS-2189W): waterborne phenolic resin emulsion (manufacturer: Shanghai Xing'an Industrial Co., Ltd., model: M512) = 4:2:2:2.

[0080] Example 2

[0081] The thermal transfer protective film for heat-sensitive applications described in Example 2 differs from that in Example 1 in that:

[0082] The substrate is specifically a biaxially oriented polyethylene terephthalate (PET) film;

[0083] The thermal transfer protective film for thermal sensitivity has a total thickness of 5.7 μm, including a base layer thickness of 3.5 μm, a back coating thickness of 0.1 μm, a release layer thickness of 0.2 μm, an aging resistant layer thickness of 0.4 μm, a protective layer thickness of 0.5 μm, a color-fixing layer thickness of 0.8 μm, and an adhesive layer thickness of 0.2 μm.

[0084] The preparation method of the thermal transfer protective film for thermosensitive materials described in Example 2 is the same as that in Example 1.

[0085] Example 3

[0086] The thermal transfer protective film for heat-sensitive applications described in Example 3 differs from that in Example 1 in that:

[0087] The thermal transfer protective film for thermal sensitivity has a total thickness of 5.9 μm, including a base layer thickness of 3.5 μm, a back coating thickness of 0.1 μm, a release layer thickness of 0.2 μm, an aging resistant layer thickness of 0.4 μm, a protective layer thickness of 0.5 μm, a color-fixing layer thickness of 0.8 μm, and an adhesive layer thickness of 0.4 μm.

[0088] The preparation method of the thermal transfer protective film for thermosensitive materials described in Example 3 is the same as that in Example 1.

[0089] Example 4

[0090] The thermal transfer protective film for heat-sensitive applications described in Example 4 differs from that in Example 1 in that:

[0091] The thermal transfer protective film for thermal sensitivity has a total thickness of 6.6 μm, including a base layer thickness of 3.5 μm, a back coating thickness of 0.2 μm, a release layer thickness of 0.4 μm, an aging resistant layer thickness of 0.6 μm, a protective layer thickness of 0.7 μm, a color-fixing layer thickness of 0.8 μm, and an adhesive layer thickness of 0.4 μm.

[0092] The preparation method of the thermal transfer protective film for thermosensitive materials described in Example 4 is the same as that in Example 1.

[0093] Example 5

[0094] The thermal transfer protective film for heat-sensitive applications described in Example 5 differs from that in Example 1 in that:

[0095] The substrate is, for example, a biaxially oriented polyethylene (BOPE) film;

[0096] The thermal transfer protective film for thermal sensitivity has a total thickness of 6.6 μm, including a base layer thickness of 3.5 μm, a back coating thickness of 0.2 μm, a release layer thickness of 0.4 μm, an aging resistant layer thickness of 0.6 μm, a protective layer thickness of 0.7 μm, a color-fixing layer thickness of 0.8 μm, and an adhesive layer thickness of 0.4 μm.

[0097] The preparation method of the thermal transfer protective film for thermosensitive materials described in Example 5 is the same as that in Example 1.

[0098] Example 6

[0099] The thermal transfer protective film for heat-sensitive applications described in Example 6 differs from that in Example 1 in that:

[0100] The substrate is, for example, a biaxially oriented polypropylene (BOPP) film;

[0101] The thermal transfer protective film for thermal sensitivity has a total thickness of 6.6 μm, including a base layer thickness of 3.5 μm, a back coating thickness of 0.2 μm, a release layer thickness of 0.4 μm, an aging resistant layer thickness of 0.6 μm, a protective layer thickness of 0.7 μm, a color-fixing layer thickness of 0.8 μm, and an adhesive layer thickness of 0.4 μm.

[0102] The preparation method of the thermal transfer protective film for thermosensitive materials described in Example 6 is the same as that in Example 1.

[0103] Example 7

[0104] The thermal transfer protective film for heat-sensitive applications described in Example 7 differs from that in Example 1 in that:

[0105] The aging-resistant layer, by mass ratio, comprises epoxy resin: modified tert-butylphenol resin: hydrogenated styrene-butadiene block copolymer = 1.2:1.5:1.3.

[0106] The thermal transfer protective film for thermal sensitivity has a total thickness of 6.6 μm, including a base layer thickness of 3.5 μm, a back coating thickness of 0.2 μm, a release layer thickness of 0.4 μm, an aging resistant layer thickness of 0.6 μm, a protective layer thickness of 0.7 μm, a color-fixing layer thickness of 0.8 μm, and an adhesive layer thickness of 0.4 μm.

[0107] The preparation method of the thermal transfer protective film for thermosensitive materials described in Example 7 is the same as that in Example 1.

[0108] Example 8

[0109] The thermal transfer protective film for heat-sensitive applications described in Example 8 differs from that in Example 1 in that:

[0110] The thermal transfer protective film for thermal sensitivity has a total thickness of 6.6 μm, including a base layer thickness of 3.5 μm, a back coating thickness of 0.2 μm, a release layer thickness of 0.4 μm, an aging resistant layer thickness of 0.6 μm, a protective layer thickness of 0.7 μm, a color-fixing layer thickness of 0.8 μm, and an adhesive layer thickness of 0.4 μm.

[0111] The preparation method of the thermal transfer protective film for thermosensitive materials described in Example 8 is the same as that in Example 1.

[0112] Performance testing

[0113] The performance of the thermal transfer protective films for heat-sensitive applications prepared in Examples 1-8 was tested.

[0114] 1. Wear test was conducted using a conventional abrasion resistance tester. Specifically, a thermal transfer protective film was attached to the surface of the thermal label. The test method was to use a ball bearing of a friction tester to perform the abrasion resistance test with a load of 200g, and record the number of friction cycles when the friction mark on the thermal paper turned black. The results showed that the number of friction cycles could reach 250. In contrast, the thermal paper without the protective film turned black after 50 friction cycles.

[0115] 2. Solvent resistance tests were conducted using an abrasion resistance tester. Specifically, the heat transfer layer of the protective film was transferred onto the surface of uncoated thermal paper, with a load of 500g. Friction tests were performed using friction cloths soaked in anhydrous ethanol, engine oil, cyclohexanone, gasoline, solvent oil, and cyclohexane, respectively, until the thermal paper became wet. The number of friction cycles was recorded. The results showed that the number of friction cycles for all three types of thermal labels reached 40. In contrast, when thermal labels without a protective film were subjected to friction tests with cyclohexanone, gasoline, and cyclohexane, the markings turned black after the labels were soaked in the test reagents.

[0116] 3. The 3M tape peel tester was used for testing. Specifically, a 19mm wide tape with an adhesive strength of 2.91N / 19mm~3.33N / 19mm, a PE substrate, a synthetic acrylic adhesive, and an aromatic solvent was applied to the hot stamping surface of a flat sample by rolling it back and forth three times with a rubber-metal roller with a load of 20N±0.5N and a width of 45mm. After leaving the sample for 5min~10min, the tape was peeled off at a speed of 0.6m / s~1.0m / s. The results showed that there was no peeling or curling of the imprint.

[0117] 4. The test was conducted using an artificial accelerated aging chamber. Specifically, the blackboard temperature was 50±3℃, no water was sprayed, and the relative humidity was 65%±5%. The front of the sample was exposed to radiation with a wavelength of 290~800nm, and the radiation intensity was 550W / m2±50W / m2. The test time was 1200h. The test results showed that the imprint had no obvious traces of fading, discoloration, wrinkles, blistering, cracking, delamination, or curling. In contrast, ordinary thermal labels showed fading after the artificial accelerated aging test.

[0118] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A heat transfer protective film for thermal applications, characterized in that, It includes a back coating layer and a heat transfer layer applied to both sides of the substrate, wherein the heat transfer layer sequentially comprises a release layer, an aging resistant layer, a protective layer, a color fixing layer and an adhesive layer; The back coating layer, by mass percentage, comprises: 5-10% curing agent, 3-8% antistatic agent, and the remainder being silicone-modified polyurethane resin. The release layer, by mass percentage, comprises: 35-40% waterborne polyurethane resin, 3-10% substrate wetting agent, and the remainder is waterborne polyethylene micron wax. The aging-resistant layer, by mass percentage, comprises: 20-30% epoxy resin, 10-15% hydrogenated styrene-butadiene block copolymer, and the remainder is modified tert-butylphenol resin. The protective layer, by mass percentage, comprises 15-25% chlorinated polypropylene resin, 30-40% polyester resin, and the remainder is acrylic resin. The color-fixing layer, by mass percentage, comprises methylparaben 15-25%, polyvinyl alcohol 15-25%, hydroxymethyl cellulose 10-15%, benzenesulfonamide 3-8%, wetting and dispersing agent 2-5%, and the balance being fluorane thermosensitive dyes. The adhesive layer, by weight percentage, comprises 30-35% waterborne terpene resin, 30-35% waterborne polyester resin, and 30-35% waterborne phenolic resin.

2. The thermal transfer protective film for thermosensitive applications as described in claim 1, characterized in that, The total thickness of the thermal transfer protective film for thermal sensitivity is 5.5~6.6μm, of which the base layer thickness is 3.5μm, the back coating thickness is 0.1~0.2μm, the release layer thickness is 0.2~0.4μm, the aging resistant layer thickness is 0.4~0.6μm, the protective layer thickness is 0.5~0.7μm, the color fixing layer thickness is 0.6~0.8μm, and the adhesive layer thickness is 0.2~0.4μm.

3. The method for preparing the thermal transfer protective film for heat-sensitive applications according to claim 1 or 2, characterized in that, Includes the following steps: (1) Apply a back coating to one side of the substrate surface; (2) A release layer is applied to the other side surface of the substrate in step (1); (3) Prepare an aging resistant layer on the surface of the release layer prepared in step (2): Dissolve epoxy resin, modified tert-butylphenol resin and hydrogenated styrene-butadiene block copolymer in a mixed solvent of methyl ethyl ketone and toluene, then coat it evenly on the release layer, and dry it to obtain the aging resistant layer. (4) Prepare a protective layer on the surface of the aging-resistant layer prepared in step (3): Dissolve chlorinated polypropylene resin, polyester resin and acrylic resin in a mixed solvent of butanone and toluene to obtain a clear mixture. Coat the mixture evenly on the surface of the aging-resistant layer and dry it to obtain the protective layer. (5) Prepare a color-fixing layer on the surface of the protective layer prepared in step (4): Add methylparaben, polyvinyl alcohol, hydroxymethyl cellulose and benzenesulfonamide to pure water to dissolve, add wetting and dispersing agent, disperse evenly, add fluorane thermosensitive dye, grind, coat the ground mixture evenly on the protective layer, and blow dry to obtain the color-fixing layer. (6) Prepare an adhesive layer on the surface of the color-fixing layer prepared in step (5).

4. The method for preparing the thermal transfer protective film for heat-sensitive applications according to claim 1 or 2, characterized in that, Includes the following steps: (1) Apply a back coating to one side of the substrate: First, dilute the silicone-modified polyurethane resin with methyl ethyl ketone to form a solution. Then, add the curing agent and antistatic agent to the solution and mix them evenly. Apply the solution evenly to one side of the substrate and dry it at 120-130℃ to form a back coating for later use. (2) Apply a release layer to the other side of the substrate in step (1): Mix the water-based polyurethane resin and the substrate wetting agent evenly with pure water to obtain a mixture. Add water-based polyethylene micro powder wax to the mixture, disperse and grind it. The particle size after grinding should be <1.5μm. Apply the ground mixture evenly to the side of the substrate without the back coating. Dry it at 100-110℃ to obtain the release layer. (3) Prepare an aging resistant layer on the surface of the release layer prepared in step (2): Dissolve epoxy resin, modified tert-butylphenol resin and hydrogenated styrene-butadiene block copolymer in a mixed solvent of methyl ethyl ketone and toluene, then coat it evenly on the release layer, and dry it at 80-90℃ to obtain the aging resistant layer. (4) Prepare a protective layer on the surface of the aging-resistant layer prepared in step (3): Dissolve chlorinated polypropylene resin, polyester resin and acrylic resin in a mixed solvent of butanone and toluene to obtain a clear mixture. Coat the mixture evenly on the surface of the aging-resistant layer and dry it at 80-90℃ to obtain the protective layer. (5) Prepare a color-fixing layer on the surface of the protective layer prepared in step (4): Add methylparaben, polyvinyl alcohol, hydroxymethyl cellulose and benzenesulfonamide to pure water and heat to 50-60℃ to dissolve. After cooling to room temperature, add wetting and dispersing agent. After dispersing evenly, add fluorane thermosensitive dye and grind to a particle size of 0.4-0.6μm. Coat the ground mixture evenly on the protective layer and dry at 25-30℃ to obtain the color-fixing layer. (6) Prepare an adhesive layer on the surface of the color-fixing layer prepared in step (5): Add waterborne terpene resin, waterborne polyester resin and waterborne phenolic resin to pure water and mix evenly to obtain a mixture. Coat the mixture evenly on the surface of the color-fixing layer and dry it at 25-30℃ to obtain the adhesive layer.