Thermal-sensitive paper coating, preparation method thereof and thermal-sensitive paper

Abstract

The invention discloses a thermo-sensitive paper coating and a preparation method thereof and thermo-sensitive paper, and belongs to the technical field of thermo-sensitive paper.The thermo-sensitive paper coating sequentially comprises a color developing agent layer, a reaction medium layer, a dye precursor layer and a damp-proof layer, the color developing agent layer is close to base paper, the color developing agent layer contains a color developing agent and a sensitizing agent, the dye precursor layer contains a dye precursor, and the damp-proof layer is close to the base paper. The reaction medium layer contains an acidic substance diffusion promoter, and the moisture-proof layer contains a moisture-proof agent and an additive. According to the invention, uniform interaction of the color developing agent and the dye precursor during heating can be improved, meanwhile, good moisture resistance is achieved, and the printing quality of the thermo-sensitive paper is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal paper, and in particular to a thermal paper coating and a preparation method thereof, as well as thermal paper. Background Art

[0002] The printing process for thermal paper primarily relies on thermal printing technology, an inkless printing method that develops color by heating specific areas of the paper to cause a chemical reaction in the heat-sensitive coating. Thermal paper is a common specialty paper widely used in devices such as receipts, labels, and fax machines. The principle behind this phenomenon involves a chemical reaction in the heat-sensitive material and the transfer of heat. The main components of thermal paper include: Base paper: This is the foundation of thermal paper, typically made of regular or synthetic paper; Thermal coating: This is a layer of chemical material applied to the base paper that changes color when heated. The thermal coating primarily contains the following ingredients: Dye precursor: This is a colorless chemical that develops color when reacted with a color developer. Color developer: This substance reacts with the dye precursor, causing it to develop color. Sensitizer: This substance lowers the temperature of the color development reaction, allowing it to occur at a lower temperature.

[0003] The main component of ordinary paper is cellulose, which is highly hygroscopic. In a high-humidity environment, paper will absorb large amounts of water, causing its moisture content to increase. The presence of moisture will change the physical and thermal properties of the paper. Changes in thermal conductivity: Moisture fills the gaps between paper fibers, changing the paper's microstructure. Because water has a higher thermal conductivity than air, the thermal conductivity of paper increases with increasing moisture content. This means that heat will transfer more quickly from the thermal print head to the interior of the paper, rather than being concentrated on the thermal coating, which accelerates heat dissipation. Changes in mechanical properties: When paper absorbs moisture, its strength and flexibility will decrease, and the surface may become rough or wrinkled. This physical change may affect the contact between the thermal print head and the paper, resulting in uneven heat transfer, further affecting print quality.

[0004] The humidity of the thermal paper environment significantly impacts the color development of the thermal paper coating, specifically: Premature color development: The color development of thermal paper typically relies on a chemical reaction between the developer and dye precursor. The presence of moisture may cause the developer to release acid prematurely, initiating the color development reaction. This can cause the thermal paper to exhibit color changes before use. This phenomenon, known as "premature color development" or "background color development," can seriously affect the normal use of the thermal paper. Uneven color development: Uneven distribution of moisture in the coating can cause the color development reaction to occur rapidly in some areas and slowly or not at all in others. This results in uneven color development, affecting the quality of printing or writing. Color fading: Moisture can dilute the concentration of the developer and dye precursor or chemically react with them, causing the color to fade or become lighter, impacting the color sensitivity and durability of the thermal paper. Coating shedding: Moisture penetrating the coating can weaken the adhesion between the coating and the base paper, leading to coating shedding or blistering. This not only affects the appearance of the thermal paper but also its performance. Coating Swelling: Moisture may cause certain components in the coating to swell, changing the coating's microstructure. This can cause cracks or unevenness on the coating surface, affecting the writing or printing quality of the thermal paper. Reduced Abrasion Resistance: Moisture may weaken the coating's abrasion resistance, making the thermal paper more susceptible to damage from friction or scratches, which can affect the durability and lifespan of the thermal paper.

[0005] The existing thermal paper coating color developer and dye precursor are mixed together. If the color developer and dye precursor are unevenly distributed in the coating, it will lead to uneven color development effect. Summary of the Invention

[0006] As described in the above-mentioned prior art, one of the objects of the present invention is to provide a thermal paper coating, which can improve the uniform interaction between the developer and the dye precursor when heated, and at the same time has good moisture resistance, thereby improving the printing quality of the thermal paper.

[0007] A second object of the present invention is to provide a method for manufacturing a thermal paper coating, which has simple steps and reliable quality.

[0008] One of the purposes of the present invention is achieved by the following technical solution: A thermal paper coating comprises, in sequence, a developer layer, a reaction medium layer, a dye precursor layer, and a moisture-proof layer. The developer layer is close to the base paper and contains a developer and a sensitizer. The dye precursor layer contains a dye precursor. The reaction medium layer contains an acidic substance diffusion accelerator. The moisture-proof layer contains a moisture-proof agent and an enhancer.

[0009] Furthermore, the moisture-proof agent is Polygonatum sibiricum polysaccharide.

[0010] Furthermore, the reinforcing agent is one of nanocellulose and nanosilica.

[0011] Furthermore, the acidic substance diffusion accelerator is one of silane coupling agent modified nano-silica, nano-alumina or a mixture thereof.

[0012] Furthermore, the thickness of the reaction medium layer is 1-2 microns.

[0013] Furthermore, the dye precursor is 3-dibutylamino-6-methyl-7-anilinofluoran, the color developer is bisphenol A, and the sensitizer is dimethyl terephthalate.

[0014] Furthermore, The second object of the present invention is achieved by adopting the following technical solution: A method for preparing a thermal paper coating comprises the following steps: S1. Making biodegradable high-density paper from environmentally friendly pulp through an environmentally friendly process, and smoothing the surface thereof to obtain base paper; S2. Using a coating device, sequentially apply a solution composed of the components of the developer layer, the reaction medium layer, the dye precursor layer, and the moisture-proof layer on the base paper, and obtain a heat-sensitive coating after drying and curing.

[0015] The third object of the present invention is achieved by adopting the following technical solution: A thermal paper is provided, wherein a thermal paper coating is evenly coated on one surface of the base paper, and carnauba wax is coated on the other side of the base paper.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a thermal paper coating in which a color developer and a dye precursor are distributed in different coatings, thereby improving the problem of uneven distribution of the color developer and dye precursor affecting the color development effect. This improves the uniform interaction between the color developer and dye precursor when heated, and at the same time has good moisture resistance, resulting in a consistent color development reaction, thereby obtaining a clear and uniform printing effect and improving the printing quality of the thermal paper. The moisture-proof layer contains a moisture-proof agent, Polygonatum sibiricum polysaccharide. The polysaccharide component of Polygonatum sibiricum polysaccharide has a certain hydrophilicity and can adjust the hydrophilicity and hydrophobicity of the thermal paper coating. Under high humidity conditions, hydrophilic components can absorb an appropriate amount of moisture to prevent the thermal paper coating from excessive moisture absorption; under dry conditions, hydrophilic components can retain a certain amount of moisture to prevent the thermal paper coating from drying out; polysaccharides usually have good film-forming properties, and Polygonatum sibiricum polysaccharide can enhance the mechanical strength and wear resistance of the thermal paper coating, which helps to improve the durability of the thermal paper during use. Reinforcements such as nano-silica and nano-cellulose mainly improve mechanical properties and adhesion, and further enhance the mechanical strength and wear resistance of Polygonatum sibiricum polysaccharide.

[0017] (2) The present invention provides a thermal paper coating in which, when heated, an acidic substance (such as a proton H⁺) released by a color developer diffuses upward through a reaction medium layer. An acidic substance diffusion accelerator in the reaction medium layer accelerates the diffusion rate of the acidic substance, ensuring that the acidic substance, after reaching the surface layer, contacts the dye precursor and undergoes a color development reaction.

[0018] (3) The present invention provides a thermal paper, wherein the thermal paper coating is uniformly coated on one surface of the base paper, and the other surface of the base paper is coated with carnauba wax, which has waterproof properties and prevents the influence of moisture on the substrate properties. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with specific embodiments. It should be noted that, under the premise of no conflict, the embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0020] Example 1 This embodiment provides a thermal paper coating, which includes a color developer layer, a reaction medium layer, a dye precursor layer, and a moisture-proof layer in sequence. The color developer layer is close to the base paper, the color developer layer contains a color developer and a sensitizer, the dye precursor layer contains a dye precursor, the reaction medium layer contains nano-silica, which is an acidic substance diffusion promoter, and the moisture-proof layer contains a moisture-proof agent, Polygonatum sibiricum polysaccharide, and an additive, nano-cellulose.

[0021] In this embodiment, the dye precursor is 3-dibutylamino-6-methyl-7-anilinofluoran, the color developer is bisphenol A, and the sensitizer is dimethyl terephthalate. 3-dibutylamino-6-methyl-7-anilinofluoran undergoes structural changes when heated, releasing active groups; the dye precursor reacts with these active groups to generate a colored product; and dimethyl terephthalate, as a sensitizer, can promote this process, allowing color development to be achieved at a lower temperature.

[0022] In this embodiment, the reinforcing agents such as nano-silica and nano-cellulose are mainly used to improve the mechanical properties and processability, and can also improve the wear resistance and adhesion of the thermal paper coating.

[0023] Nano-silicon dioxide: has good chemical stability and moisture resistance, and can reduce the penetration of moisture into the thermal paper coating.

[0024] In this embodiment, the nano-silica has a large specific surface area and high porosity, providing a site for the adsorption and diffusion of acidic substances. Surface modification of the nano-silica with a silane coupling agent can reduce its surface hydrophilicity. The silane coupling agent can form a hydrophobic organic layer on the surface of the nano-silica, reducing the interaction between the acidic substance and the silica surface, thereby reducing the adsorption of the acidic substance and making the acidic substance more easily diffused.

[0025] Nano-alumina (Al2O3): Porous properties: It has a porous structure, which provides a diffusion channel for acidic substances and has good chemical stability. It helps to maintain the structure and performance stability of the reaction medium layer and ensure the persistence of the diffusion path of acidic substances. Adsorption capacity: It has a certain adsorption effect on acidic substances and can control their release rate, but its adsorption capacity is relatively weaker than that of nano-silica.

[0026] In this embodiment, the effects of Polygonatum sibiricum polysaccharide are as follows: Flexibility: Polygonatum sibiricum polysaccharides are composed of caramel, glucose, and fructose, which form a network structure with a certain degree of elasticity in the coating. This structure improves the flexibility of the coating, making it less likely to break when folded or bent.

[0027] Mechanical properties: Polysaccharides generally have good film-forming properties. Polygonatum sibiricum polysaccharide can enhance the mechanical strength and wear resistance of the coating, which helps to improve the durability of thermal paper during use.

[0028] Hydrophilicity: The polysaccharide components of Polygonatum sibiricum polysaccharide have a certain degree of hydrophilicity, which can adjust the hydrophilicity and hydrophobicity of the coating. In high humidity conditions, the hydrophilic components can absorb a moderate amount of water, preventing the coating from excessive moisture absorption; in dry conditions, the hydrophilic components can retain a certain amount of moisture, preventing the coating from drying out.

[0029] This embodiment also provides a method for preparing a thermal paper coating, comprising the following steps: S1. Making biodegradable high-density paper from environmentally friendly pulp through an environmentally friendly process, and smoothing the surface thereof to obtain base paper; S2. Use a slot coater to sequentially coat the solution containing the components of the developer layer, the reaction medium layer, the dye precursor layer, and the moisture-proof layer on the base paper, and then dry and cure them to obtain a heat-sensitive coating.

[0030] Example 2 This embodiment provides a thermal paper coating, which includes a color developer layer, a reaction medium layer, a dye precursor layer, and a moisture-proof layer in sequence. The color developer layer is close to the base paper, the color developer layer contains a color developer and a sensitizer, the dye precursor layer contains a dye precursor, the reaction medium layer contains nano-alumina, which is a diffusion promoter of acidic substances, and the moisture-proof layer contains polygonatum polysaccharide, which is a moisture-proof agent, and nano-silica, which is an additive.

[0031] In this embodiment, the dye precursor is 3-dibutylamino-6-methyl-7-anilinofluoran, the color developer is bisphenol A, and the sensitizer is dimethyl terephthalate. 3-dibutylamino-6-methyl-7-anilinofluoran undergoes structural changes when heated, releasing active groups; the dye precursor reacts with these active groups to generate a colored product; and dimethyl terephthalate, as a sensitizer, can promote this process, allowing color development to be achieved at a lower temperature.

[0032] This embodiment also provides a method for preparing a thermal paper coating, comprising the following steps: S1. Making biodegradable high-density paper from environmentally friendly pulp through an environmentally friendly process, and smoothing the surface thereof to obtain base paper; S2. Use a spraying device to sequentially coat the solution composed of the components of the developer layer, the reaction medium layer, the dye precursor layer, and the moisture-proof layer on the base paper, and obtain a heat-sensitive coating after drying and curing.

[0033] Example 3 This embodiment provides a thermal paper coating, which includes a color developer layer, a reaction medium layer, a dye precursor layer, and a moisture-proof layer in sequence. The color developer layer is close to the base paper, the color developer layer contains a color developer and a sensitizer, the dye precursor layer contains a dye precursor, the reaction medium layer contains nano-silica, which is an acidic substance diffusion promoter, and the moisture-proof layer contains a moisture-proof agent, Polygonatum sibiricum polysaccharide, and an additive, nano-silica.

[0034] In this embodiment, the dye precursor is 3-dibutylamino-6-methyl-7-anilinofluoran, the color developer is bisphenol A, and the sensitizer is dimethyl terephthalate. 3-dibutylamino-6-methyl-7-anilinofluoran undergoes structural changes when heated, releasing active groups; the dye precursor reacts with these active groups to generate a colored product; and dimethyl terephthalate, as a sensitizer, can promote this process, allowing color development to be achieved at a lower temperature.

[0035] This embodiment also provides a method for preparing a thermal paper coating, comprising the following steps: S1. Making biodegradable high-density paper from environmentally friendly pulp through an environmentally friendly process, and smoothing the surface thereof to obtain base paper; S2. Use a slot coater to sequentially coat the solution containing the components of the developer layer, the reaction medium layer, the dye precursor layer, and the moisture-proof layer on the base paper, and then dry and cure them to obtain a heat-sensitive coating.

[0036] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A thermal paper coating, characterized in that: The invention comprises a developer layer, a reaction medium layer, a dye precursor layer and a moisture-proof layer in sequence. The developer layer is close to the base paper, the developer layer comprises a developer and a sensitizer, the dye precursor layer comprises a dye precursor, the reaction medium layer comprises an acidic substance diffusion accelerator, and the moisture-proof layer comprises a moisture-proof agent and an enhancer.

2. A thermal paper coating according to claim 1, characterized in that: The moisture-proof agent is polygonatum flower polysaccharide.

3. The thermal paper coating according to claim 1, wherein: The reinforcing agent is one of nano cellulose and nano silicon dioxide.

4. The thermal paper coating according to claim 1, wherein: The acidic substance diffusion accelerator is one of silane coupling agent modified nano silicon dioxide and nano aluminum oxide or a mixture thereof.

5. The thermal paper coating according to claim 1, wherein: The thickness of the reaction medium layer is 1-2 microns.

6. A thermal paper coating according to claim 5, characterized in that: The dye precursor is 3-dibutylamino-6-methyl-7-anilinofluoran, the color developer is bisphenol A, and the sensitizer is dimethyl terephthalate.

7. The method for preparing a thermal paper coating according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Making biodegradable high-density paper from environmentally friendly pulp through an environmentally friendly process, and smoothing the surface thereof to obtain base paper; S2. Use a coating device to sequentially coat the solution composed of the components of the developer layer, the reaction medium layer, the dye precursor layer, and the moisture-proof layer on the base paper, and obtain a heat-sensitive coating after drying and curing.

8. Drying and curing: Place the coated thermal paper at an appropriate temperature to ensure that the sensitizer is evenly distributed.

9. The thermal paper coating according to claim 7, wherein: The coating equipment is a slit coater or a spray coating equipment.

10. A thermal paper, characterized in that: The thermal paper coating according to any one of claims 1 to 6 is uniformly coated on one surface of the base paper, and carnauba wax is coated on the other side of the base paper.