Structure, coating system and preparation method of environment-friendly bottom paper-free thermal paper

Abstract

This invention first provides a structure for an environmentally friendly, paperless thermal paper, comprising a substrate, and a thermal coating and a silicone oil layer sequentially laminated on one side of the substrate; the thermal coating comprises a color-developing layer, a pre-coating layer, and a base coating layer sequentially laminated, with the base coating layer laminated on one side of the substrate; secondly, it provides a coating system, the color developer comprising 4,4'-sulfonyl diphenol; and thirdly, it provides a preparation method for preparing thermal paper using the above structure and coating system, including applying the color-developing layer to the surface of the pre-coating layer using a curtain coating method; the novel structure provides a basis for the self-curling release properties of the thermal paper; the use of 4,4'-sulfonyl diphenol in the coating system not only improves the color saturation, lightfastness, and stability of the thermal paper, but also does not react with silicone oil, thus improving release properties; based on the structure and coating system, a curtain coating method is used to effectively improve the coating uniformity and color development properties of the thermal paper, resulting in an environmentally friendly thermal paper with fast printing response, vibrant colors, and high clarity.

Description

Technical Field

[0001] This invention relates to the field of thermal paper preparation technology, specifically to the structure, coating system, and preparation method of environmentally friendly paperless thermal paper. Background Technology

[0002] Compared to traditional self-adhesive labels, backless labels reduce resource consumption and environmental pollution due to their absence of a backing paper, aligning with the principles of energy conservation and environmental protection.

[0003] Thermal paper, a widely used paper material in commerce, logistics and other fields, is favored for its convenience, efficiency and relatively friendly cost. With the increasing environmental awareness and improved production efficiency in various industries, the structure and processing technology of solvent-free silicone oil as the release layer on the surface of thermal paper are receiving more and more attention.

[0004] Traditional self-adhesive thermal paper usually requires the use of solvent-based silicone oil, which makes thermal paper difficult to recycle, has poor environmental performance, and high processing costs. Solvent-free silicone oil has good release properties and high temperature resistance, which can effectively replace traditional solvent-based silicone oil to achieve self-winding and release functions, reduce environmental pollution, and improve the production efficiency of thermal paper.

[0005] Chinese patent document CN111261018A discloses a paperless environmentally friendly thermal label and its preparation method. The patent points out that solvent-free silicone oil has good release properties and high temperature resistance, and can effectively replace traditional solvent-based silicone oil, reduce environmental pollution, and improve production efficiency. The patent also mentions various formulation types of solvent-free silicone oil, which are suitable for different substrates and application scenarios.

[0006] Other patent documents also disclose improved thermal paperless design schemes and preparation technologies, including: a bottom layer, a label support layer, and a thermally sensitive material layer. Applying the material twice can help polish the surface, making it smoother and flatter, which is beneficial for subsequent processing and improving product quality. This type of technology not only improves the appearance and abrasion resistance of thermal paper, but also enhances its sealing and waterproof performance.

[0007] Regarding the formulation of thermal coating systems, most of the publicly available information indicates that thermal coatings are prepared using formulations composed of thermal color developers, sensitizers, and adhesives. There is relatively little research on novel thermal paper coating system formulations.

[0008] Regarding the structure of thermal paper, existing backing-free thermal paper generally consists of a pre-coating layer, a top coating layer, and a top coating layer. The cost of achieving the protective performance of this three-layer structure is high. First, the use of solvent-based silicone oil has the aforementioned shortcomings. Second, based on the formulation and preparation method, the structure of this type of thermal paper has the problem that the components of the thermal coating are prone to react with the solvent-based silicone oil, resulting in a reduction in self-curling release performance. Furthermore, because it is necessary to ensure that the thermal paper has good color development, gloss, and self-curling performance, the thickness of the thermal coating is relatively thin, generally about 6μm to 12μm. In addition, the use of processing methods such as blade coating and roller coating results in poor uniformity and smoothness of the thermal coating, leading to the shortcomings of the interaction between the structure and the preparation method.

[0009] The existing thermosensitive coating system formulations have the following main problems when used in conjunction with solvent-free silicone oils:

[0010] (1) Traditional thermal coating system formulations typically use a combination of 2,4-diphenyl sulfone phenol (DBSP) color developer and colorless dyes, which results in insufficient absorption of solvent-free silicone oil by the thermal coating system formulation. This leads to uneven distribution on the coating surface, resulting in "poisoning" and "not drying" phenomena, reducing the color development effect and service life of thermal paper, and consequently reducing the clarity of text information on thermal paper. Areas with uneven silicone oil layer are difficult to produce release effect, making it impossible to achieve the function of no backing paper.

[0011] (2) The formulation of the thermal coating system reacts with the silicone oil layer, causing the silicone oil layer to lose silicone, resulting in poor dynamic color development performance (saturation color density) and affecting the self-curling ability. In addition, the silicone oil components after losing silicone will contaminate the thermal coating, thereby causing a decrease in the wet heat aging performance and affecting the self-curling ability of the thermal paper.

[0012] (3) The introduction of silicone oil changes the thermodynamic properties of the coating system. Under high temperature conditions, the temperature resistance properties such as dynamic color development performance (saturated color density) are reduced, resulting in poor temperature resistance of the thermal coating. This makes it difficult to dry quickly and effectively after coating with solvent-free silicone oil, affecting the performance after coating with solvent-free silicone oil and limiting the application range of thermal paper in high-temperature application scenarios.

[0013] (4) Because the rheological properties of this type of formulation are relatively poor, the components are highly unstable in the process of processing. Therefore, when it is related to the preparation process, it is generally necessary to rely on the doctor blade coating, roller coating and other methods. However, this type of processing will cause the heat-sensitive coating to have poor uniformity and flatness, and even scratches, thin material and missed coating.

[0014] (5) Regarding the preparation method, for the traditional processing of thermal paper, based on its structural design and thermal coating system formulation design, the thermal coating is generally processed by coating methods such as blade coating and roller coating. Since these processing methods all use external devices to apply external force for processing, they have certain limitations for high-precision processing tools. It is necessary to make up for the shortcomings of the processing method in terms of coating quality control by adjusting equipment parameters and operating steps. For example, multiple coatings or additional drying processes are required. However, this undoubtedly increases energy consumption and equipment wear costs. Moreover, coating quality problems caused by processing will lead to an increase in the defect rate of thermal paper, further increasing production costs and reducing production efficiency. In addition, solvent-free silicone oil is commonly used. Silicone oil is often coated on the surface of the thermal developer layer to provide protection, prevent friction, and facilitate release. However, coating methods such as blade coating and roller coating can easily lead to uneven thickness. Under the influence of factors such as pressure, temperature changes, or the passage of time, silicone oil gradually penetrates into the coating, making thermal paper more susceptible to silicone oil penetration. Once silicone oil penetrates into the thermal coating, it interacts with key components such as the developer and colorless dye, altering their chemical environment and reactivity. This not only causes the silicone oil to lose its release properties and self-curling function but also affects the color development performance of the thermal paper, causing printed or copied text and images to become lighter, blurrier, or even disappear, severely damaging the normal performance of the thermal paper.

[0015] To overcome the above problems, it is necessary to provide a novel structure of environmentally friendly paperless thermal paper, a thermal coating system formulation adapted to this structure and preparation method, and a novel preparation method that can adapt to and enable the system formulation to function well. Summary of the Invention

[0016] This invention addresses the shortcomings of the structure, coating system, and preparation method of paperless thermal paper in the prior art by providing an environmentally friendly paperless thermal paper structure. The structure includes a substrate, and a thermal coating layer and a silicone oil layer sequentially stacked on one side of the substrate. The thermal coating layer includes a color developing layer, a pre-coating layer, and a base coating layer sequentially stacked, with the base coating layer stacked on one side of the substrate.

[0017] Furthermore, the silicone oil is a solvent-free silicone oil.

[0018] Furthermore, a self-adhesive layer is laminated on the other side of the substrate.

[0019] Furthermore, the thermal coating includes at least one of the following features (A) to (C):

[0020] (A) The thickness of the base coating is 3 μm to 10 μm;

[0021] (B) The thickness of the pre-coating layer is 3 μm to 10 μm;

[0022] (C) The thickness of the color development layer is 3 μm to 8 μm.

[0023] The present invention also provides a coating system for an environmentally friendly paperless thermal paper, the coating system comprising the components of the above-mentioned structure, the color developing layer comprising a color developing agent, the color developing agent comprising 4,4'-sulfonyl diphenol.

[0024] Furthermore, the color developer is present in a mass fraction of 20 to 50 parts.

[0025] Furthermore, the color development layer includes an aqueous acrylic resin, wherein the glass transition temperature (Tg) of the aqueous acrylic resin is -20°C to +80°C.

[0026] Furthermore, the color-developing layer comprises calcium stearate and polyethylene wax.

[0027] Furthermore, the calcium stearate is present in parts by weight of 2 to 10, and the polyethylene wax is present in parts by weight of 2 to 6.

[0028] Furthermore, the color developing layer also includes the following components in parts by weight:

[0029] 15 to 30 parts of leuco dye;

[0030] 5 to 20 parts of inorganic nanofiller;

[0031] 1 to 1.5 parts of anionic surfactant;

[0032] 1.5 to 3 parts of anionic functional additives.

[0033] Furthermore, the base coating comprises the following components in parts by weight:

[0034] 50 to 70 parts of calcined kaolin;

[0035] 5 to 30 parts of light calcium carbonate;

[0036] 1 to 5 parts of heavy calcium carbonate;

[0037] 5 to 15 parts of acrylate;

[0038] 10 to 20 parts of styrene-acrylic latex;

[0039] 3 to 8 parts of polylactic acid;

[0040] Thickener 0.5 to 5 parts;

[0041] Boric acid 0.5 to 5 parts.

[0042] Furthermore, the pre-coating comprises the following components in parts by weight:

[0043] 60 to 80 parts of lightweight hollow microspheres;

[0044] 5 to 15 parts of polymer latex;

[0045] 5 to 10 parts of water-based acrylic resin;

[0046] 1 to 5 parts of the second anionic surfactant;

[0047] One to five parts of the second anionic functional additive.

[0048] Furthermore, the thermosensitive coating includes at least one of the following features (D) to (F):

[0049] (D) The content of the base coating in the thermosensitive coating is 30% to 60%;

[0050] (E) The pre-coating layer comprises 10% to 35% of the thermosensitive coating;

[0051] (F) The content of the color-developing layer in the thermosensitive coating is 8% to 25%.

[0052] Furthermore, the moisture content of the thermal paper is 3.0% to 6.0%.

[0053] Furthermore, the thermal coating includes at least one of the following features (H) to (K):

[0054] (H) The surface tension of the pre-coating is 25 mN / m to 30 mN / m;

[0055] (I) The dynamic surface tension of the pre-coating is 35g to 45g;

[0056] (J) The surface tension of the color-developing layer is 25 mN / m to 30 mN / m;

[0057] (K) The dynamic surface tension of the color development layer is 35g to 45g.

[0058] The present invention also provides a method for preparing an environmentally friendly paperless thermal paper, wherein the preparation method comprises preparing the environmentally friendly thermal paper using the above-mentioned coating system: the preparation method includes: applying the color developing layer to the pre-coated surface using a curtain coating.

[0059] Furthermore, the method is characterized in that the preparation method includes applying the base coating to one side of the substrate using a doctor blade.

[0060] Furthermore, the preparation method includes: applying the pre-coating layer to the surface of the base coating layer using a curtain coating method.

[0061] Furthermore, the preparation method includes: applying the silicone oil to the surface of the color development layer using a roller coating or a curtain coating method.

[0062] The beneficial effects of the technical solution of this invention mainly include:

[0063] (1) Thermal paper structure: The smooth side of the substrate is coated with a base layer, a pre-coating layer and a color developing layer in sequence, and a solvent-free silicone oil is coated on the color developing layer to provide good self-curling function and self-release capability for the prepared thermal paper. On the other side of the substrate, a self-adhesive layer is coated. This double-sided coating structure provides good self-curling function for thermal paper. The base layer can improve the smoothness and adhesion of the substrate surface. The pre-coating layer can provide a more uniform and flat base for the color developing layer. The color developing layer can form a good interlayer bonding effect with the base layer and the pre-coating layer, forming a good chemical reaction when continuously heated, so that the thermal paper produces color change. The solvent-free silicone oil forms a protective layer and release properties. The self-adhesive layer gives the paper good adhesion properties, making it easy to stick on various surfaces.

[0064] (2) Regarding the thermal coating system of thermal paper: The use of 4,4'-sulfonyl diphenol as a color developer has a good comprehensive performance improvement effect on the thermal coating system formulation, enabling the thermal paper to achieve rapid, uniform and stable color change. 4,4'-sulfonyl diphenol and solvent-free silicone oil do not react with each other, ensuring good compatibility and stability between the various coatings of the thermal paper; the use of water-soluble acrylic resin enhances the adhesion between the thermal coating and the substrate; the increased use of calcium stearate and polyethylene wax can effectively improve the rheological properties of the color developer layer and enhance the curtain coating. The smoothness and continuity of the fabric enhance the printing adaptability of thermal paper; anionic surfactants effectively reduce the surface tension of liquids, allowing the coating system to spread and flow better during the curtain formation process of curtain coating; surface defoaming and wetting agents help eliminate air bubbles in the coating system and further improve its wetting performance; by rationally combining and optimizing each component, and adjusting the usage ratio and type, the thermal coating system formulation achieves a balance and improvement in multiple aspects of performance while meeting the thermal color development function, thus improving the overall performance of thermal paper.

[0065] (3) Regarding the preparation method of thermal paper: the process of using a doctor blade to coat the base layer, combined with the curtain coating of the pre-coating layer, and combined with the curtain coating of the color developing layer, forms a smooth and continuous processing process. The curtain coating process can accurately control the thickness and uniformity of each coating layer, which is more suitable for the high-precision processing requirements of the base layer, pre-coating layer and color developing layer, and improves the overall processing accuracy, flatness and uniformity of the thermal coating. Preferably, the curtain coating process is used to coat the silicone oil layer, which can avoid the silicone oil being interfered with by air during the coating process and ensure the uniformity and stability of the coating.

[0066] (4) The correlation between structure, coating system and preparation method: The rational structural design of each layer, especially the rational design of each layer of the thermal coating, not only enables the thermal paper to have comprehensive capabilities such as self-curling ability, release ability, and adhesion ability, but also provides the structural conditions for processing using the curtain coating method. Compared with blade coating and roller coating, curtain coating gives the coating better smoothness and uniformity, and reduces processing costs and improves processing efficiency. The preparation method puts forward the requirement for improvement of the coating system formulation. Therefore, the components of calcium stearate and polyethylene wax are used for the color developing layer, and anionic coatings are used for the pre-coating layer and the color developing layer. The components of surfactants and surface defoaming and wetting agents significantly alter the surface properties of the coating system formulation, resulting in a coating material with good surface tension and dynamic tension. This enables the application of curtain coating with stable processing, high coating smoothness and uniformity. The use of 4,4'-sulfonyl diphenol prevents the color development layer from reacting with solvent-free silicone oil, improving the release and self-curling ability of thermal paper. The use of water-soluble acrylic resin enhances the adhesion between the thermal coating and the substrate. The overall technical solution demonstrates a good correlation between the structure, coating system formulation, and preparation method.

[0067] (5) Overall performance of thermal paper:

[0068] Environmental friendliness: Solvent-free silicone oil is used instead of traditional silicone oil and pressure-sensitive adhesive, making the prepared self-adhesive thermal paper labels easy to recycle after being adhered to the carton, which is in line with the concept of environmental protection, and also puts forward the concept of continuous printing of environmentally friendly labels.

[0069] Excellent spreading performance and stable performance: By combining blade coating and curtain coating, a base layer, a pre-coating layer, and a color developing layer are sequentially applied to the smooth side of the substrate. The optimized thermal coating system formula enables the thermal paper to achieve excellent spreading performance. It ensures good release ability and self-curling ability after the solvent-free silicone oil is applied to the thermal coating. The self-adhesive layer has good adhesion to the substrate, which improves the stability and reliability of the thermal paper and fully guarantees the application effect in the labeling field.

[0070] Self-curling property: By coating the other side of the substrate with self-adhesive, a self-curling thermal paper is prepared, which can be used as label paper in logistics, commerce and other fields, improving the practicality and applicability of the label.

[0071] Cost-effectiveness: The use of solvent-free silicone oil and a novel thermal coating system formulation, combined with the preparation method of thermal paper, not only reduces the use of solvents and improves the processability of the formulation, but also reduces the wear and tear on processing equipment and the generation of defective products, thereby significantly reducing production costs and improving production efficiency.

[0072] Application Performance: The environmentally friendly, paperless thermal paper of this invention can be applied to many scenarios such as commerce and logistics, meeting the application requirements of continuous label printing. The optimized thermal paper structure, especially the thermal coating structure and the optimized coating system formula, combined with the novel preparation method, form a thermal paper with advantages such as environmental friendliness, stability, reliability, high yield, and long lifespan. It solves many problems existing when traditional thermal paper is used in conjunction with solvent-free silicone oil, providing high-performance thermal paper products for various application scenarios, effectively enhancing the application value and market prospects of thermal paper. Attached Figure Description

[0073] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0074] Figure 1 This is a schematic diagram of the laminated structure of the thermal paper prepared in Example 1 of the present invention;

[0075] Figure 2 This is a flowchart of the preparation method in Example 1 of the present invention;

[0076] Figure 3 This is a photograph of the thermal paper prepared according to Example 1 of the present invention.

[0077] Figure 4 This is a gloss test image of the thermal paper prepared in Example 1 of the present invention;

[0078] Figure 5 This is a graph showing the test data of the dynamic color development performance (saturation color density) of the thermal paper prepared in Example 1 of the present invention;

[0079] Figure 6 This is a SEM image of the surface of the thermal paper prepared in Example 1 of the present invention.

[0080] Explanation of icon numbers:

[0081] Thermal paper - 10; Substrate - 100; Thermal coating - 200; Primer - 210; Pre-coating - 220; Development layer - 230; Silicone oil layer - 300; Adhesive layer - 400.

[0082] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0083] To facilitate understanding of the present invention, a more comprehensive description is provided below, along with preferred embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. It should be understood that these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0084] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0085] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features; thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0086] The weights of the relevant components mentioned in the embodiments of this invention can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this invention is within the scope disclosed in the embodiments of this invention. Specifically, the units such as μg, mg, g, kg, μm, cm, mm, cm², m², m³, wt%, MPa, L, and mL that may be involved in the specific embodiments of this invention are all well-known units in the field of chemistry.

[0087] Please see Figure 1 , Figure 1 This is a schematic diagram of the laminated structure of the thermal paper prepared in Example 1 of the present invention.

[0088] This embodiment provides a structure for an environmentally friendly paperless thermal paper 10. The thermal paper 10 includes a substrate 100, which is a plant fiber paper substrate 100 or a polymer film substrate 100, and a thermal coating 200 and a silicone oil layer 300 sequentially stacked on one side of the substrate 100; the silicone oil is a solvent-free silicone oil.

[0089] The thermal coating 200 includes a base coating 210, a pre-coating 220, and a color developing layer 230 stacked sequentially, with the base coating 210 stacked on one side of the substrate 100.

[0090] The other side of the substrate 100 is laminated with an adhesive layer 400.

[0091] Thermosensitive coating 200 satisfies at least one of the conditions (A) to (C):

[0092] (A) The thickness of the base coating 210 is 3 μm to 10 μm;

[0093] (B) The thickness of the pre-coating 220 is 3 μm to 10 μm;

[0094] (C) The thickness of the color development layer 230 is 3 μm to 8 μm.

[0095] In the structure provided in this embodiment, a base coating 210, a pre-coating 220, and a color developing layer 230 (i.e., a thermal color developing coating) are sequentially coated on the smooth side of the substrate 100, and a solvent-free silicone oil is coated on the color developing layer 230. The purpose is to prepare the thermal paper 10 with self-curling and self-release capabilities. On the other side of the substrate 100, an adhesive layer 400 is coated, and the resulting double-sided coating structure provides the thermal paper 10 with a self-curling function.

[0096] The main function of the base coating 210 is to improve the smoothness and adhesion of the substrate 100 surface, so that the subsequent heat-sensitive color-developing mixed coating can adhere better. Its formulation usually contains components with high adhesion and filling effect, such as synthetic resins, fillers and additives. This coating is produced using a doctor blade coating method.

[0097] The pre-coating 220 further improves the surface properties of the substrate 100, providing a more uniform and smooth base for the color developing layer 230. Its formulation contains specific chemicals that synergistically interact with the components in the color developing layer 230, enhancing the sensitivity and stability of the thermal reaction. This coating is produced using a curtain coating method to ensure good uniformity and finer coating across the paper width.

[0098] The thermal color-developing coating is the core component of the thermal paper 10. The patented formula includes thermal dyes, color developers, water-based acrylic resins, and anionic surfactants. These components undergo a chemical reaction when continuously heated, producing a color change, thereby achieving the thermal recording function. This coating is also produced using a curtain coating method, which allows for finer coating, more uniform color development, and more precise cost control.

[0099] The application of solvent-free silicone oil forms a smooth protective layer on the surface of the color developer 230, preventing scratches or contamination of the coating. It also provides release properties and reduces friction between papers, improving paper performance. The silicone oil molecules have low surface energy and good lubricity, effectively reducing the coefficient of friction of the coating surface. Solvent-free silicone oil is tailored to different application scenarios and requirements to ensure suitable viscosity and temperature resistance. Solvent-free silicone oil can be applied using both roller and curtain coating methods.

[0100] The self-adhesive coating on the other side of the substrate 100 gives the paper excellent adhesion properties, making it easy to stick to various surfaces; self-adhesive is a commonly used self-adhesive product and process on the market.

[0101] This embodiment also provides a coating system for an environmentally friendly paperless thermal paper 10. The coating system consists of the components of the above-described structure. The color developing layer 230 includes a color developing agent, which includes 4,4'-sulfonyl diphenol (CAS No.: 80-09-1). The mass fraction of the color developing agent is 20 to 50 parts.

[0102] This embodiment, through experimental verification, demonstrates that using 4,4'-sulfonyl diphenol instead of commonly used compounds such as 2,4-diphenyl sulfone phenol (DBSP) as a color developer can improve the overall performance of the thermal coating 200 system. The chemical structure of 4,4'-sulfonyl diphenol enables it to react efficiently with colorless dyes to generate stable color products, achieving rapid, uniform, and stable color changes. The saturation, durability, and lightfastness are comparable to traditional formulations. Simultaneously, 4,4'-sulfonyl diphenol does not react with solvent-free silicone oil, ensuring coating compatibility and stability, avoiding silicone oil not drying, and improving the release ability and self-curling ability of thermal paper 10.

[0103] The color development layer 230 of this embodiment comprises an aqueous acrylic resin with a glass transition temperature (Tg) of -20°C to +80°C.

[0104] This embodiment uses water-based acrylic resin as an adhesive. Taking advantage of its glass transition temperature (Tg) of -20°C to +80°C and its water solubility, it has stronger water-soluble penetration into solvent-free silicone oil, enhances the adhesion between the thermal coating 200 and the substrate 100, ensures the stability, gloss and other physical properties of the thermal coating 200 under various environmental conditions, and improves the compatibility between the thermal paper 10 and the solvent-free silicone oil.

[0105] If the glass transition temperature is too high (Tg > 80℃), the film-forming properties are poor, requiring the addition of a large amount of film-forming aids, making it difficult to achieve the effects of "water solubility" and "solvent-free" properties. If the glass transition temperature is too low (Tg < -20℃), it is prone to reverse adhesion problems. If two resins with discontinuous gradients of glass transition temperature > 80℃ and glass transition temperature < -20℃ are blended, a wide particle size distribution will result, making it easy for silicone oil penetration to "get out of control," causing problems such as local drift of release force.

[0106] Experiments have verified that the glass transition temperature range of -20℃ to +80℃ is the only overlapping region that can continuously coexist with both "water-soluble" penetration and "film-forming" rigidity. Waterborne acrylic resin can first act as a "penetration promoter" and then as an "anti-adhesion agent" in the same emulsion.

[0107] The color development layer 230 of this embodiment includes calcium stearate and polyethylene wax; the calcium stearate is in the amount of 2 to 10 parts by mass, and the polyethylene wax is in the amount of 2 to 6 parts by mass.

[0108] Adding calcium stearate and polyethylene wax to the coating system formulation can effectively improve the rheological properties of the color developer layer 230, enhance the smoothness of curtain coating, and improve the continuity of thermal printing. Calcium stearate has good dispersibility, which can form a uniform particle distribution in the coating system, reduce viscosity, and make it easier to flow out of the curtain coating and coat evenly. Polyethylene wax can improve fluidity and smoothness, prevent phenomena such as sticking, unevenness, and breakage during the curtain flow process, and ensure the stability of the coating process. In addition, it can enable the thermal coating 200 to form a uniform dry layer more quickly, avoid problems such as uneven drying and coating peeling, and improve gloss and hardness.

[0109] Calcium stearate can form a fine hydrophobic film on the coating surface, promoting the rapid evaporation of moisture inside the coating, while preventing excessive accumulation of moisture on the coating surface, thus avoiding problems such as uneven drying and coating peeling; polyethylene wax can reduce surface tension during the coating drying process, making the coating smoother and more even, and improving the coating's gloss and hardness.

[0110] The addition of calcium stearate and polyethylene wax can also enhance the adhesion between the heat-sensitive coating 200 and the substrate 100. Calcium stearate can interact weakly with the polar groups on the surface of the substrate 100, such as hydrogen bonding and van der Waals forces, so that the coating can better adhere to the surface of the substrate 100. Polyethylene wax can fill the tiny gaps between the coating and the substrate 100, increase the contact area between the coating and the substrate 100, and further enhance the adhesion.

[0111] Regarding the durability of thermal paper 10, the addition of calcium stearate and polyethylene wax gives thermal coating 200 stronger printing adaptability. During the use of labels, the printer head is prone to scratching the solvent-free silicone oil layer, resulting in the loss of information such as barcodes during continuous printing. The protective film formed by calcium stearate and polyethylene wax can effectively block the erosion of the coating by external environmental factors, reduce the cracking and peeling of the coating, and extend the service life of thermal paper 10.

[0112] The color development layer 230 in this embodiment also includes the following components in parts by weight:

[0113] Leuco dye, or colorless dye, or reversible thermochromic material, 15 to 30 parts (compound name: 4,4'-dihydroxydiphenyl sulfone).

[0114] The inorganic nanofiller is preferably nano-silica, 5 to 20 parts (specifically: silica P954; particle size: 10 nm to 20 nm).

[0115] 1 to 1.5 parts of anionic surfactant;

[0116] Anionic functional additives, or surfactant functional additives, preferably anionic surface defoaming and wetting agents, in 1.5 to 3 parts.

[0117] The base coating 210 of this embodiment comprises the following components in parts by weight:

[0118] 50 to 70 parts of calcined kaolin;

[0119] 5 to 30 parts of light calcium carbonate;

[0120] 1 to 5 parts of heavy calcium carbonate;

[0121] Acrylamide 5 to 15 parts;

[0122] 10 to 20 parts of styrene-acrylic latex;

[0123] 3 to 8 parts of polylactic acid (PLA);

[0124] Thickener 0.5 to 5 parts;

[0125] Boric acid 0.5 to 5 parts.

[0126] The pre-coating layer 220 of this embodiment comprises the following components in parts by weight:

[0127] Lightweight hollow microspheres, or hollow spheres, or functional hollow fillers, 60 to 80 parts;

[0128] Polymer latex, or acrylic water-based adhesive, preferably acrylic latex, 5 to 15 parts;

[0129] Preferably, it is a water-soluble acrylic resin, 5 to 15 parts, which is a water-soluble polymeric film-forming agent or an auxiliary binder;

[0130] The second anionic surfactant, or wetting and dispersing agent, is 1 to 5 parts;

[0131] The second anionic functional additive, or defoaming and wetting agent, is 1 to 5 parts.

[0132] The above-mentioned anionic surfactants and second anionic surfactants can effectively reduce the surface tension of the liquid, allowing the coating system to spread and flow better during the curtain formation process of curtain coating. The addition of anionic functional additives (or anionic surface defoaming and wetting agents) and second anionic functional additives reduces the generation and effective escape of bubbles in the coating system during mixing, stirring, and curtain coating, preventing bubbles from escaping to the surface during processing and forming uncoated bubble points, which would damage the integrity of the coating and affect the thermal color developing layer 230, thus affecting the usability of the thermal paper 10 and causing problems such as missing or broken points during printing or copying. The synergistic effect of these two components reduces the surface tension of the coating system and increases its fluidity, making it easier to maintain a stable curtain shape during curtain coating, avoiding curtain breakage, irregular flow, and other phenomena, and promoting the formation of a uniform and continuous coating.

[0133] The thermal coating 200 of this embodiment satisfies at least one of the following conditions (D) to (F):

[0134] (D) The content of the primer layer 210 in the thermosensitive coating 200 is 30% to 60%;

[0135] (E) The content of pre-coating 220 in the thermosensitive coating 200 is 10% to 35%;

[0136] (F) The content of the color development layer 230 in the thermosensitive coating 200 is 8% to 25%.

[0137] Furthermore, the moisture content of the thermal paper 10 is 3.0% to 6.0%.

[0138] The function and effect of controlling the solid content of the base coating 210 is to enhance the adhesion between the thermal layer and the base paper, prevent the thermal coating 200 from falling off or peeling during use, and ensure that the base coating 210 has good smoothness and uniformity during the coating process. It can also appropriately increase the overall thickness of the coating and prevent the penetration of silicone coating.

[0139] The purpose of controlling the solid content of the pre-coating layer 220 is to achieve the viscosity and other properties of the coating required for the stability of the curtain formation during curtain coating, improve the heat insulation protection effect, maintain the thickness of the coating, and improve the color rendering and clarity of the heat-sensitive coating 200.

[0140] The purpose of controlling the solid content of the color development layer 230 is to improve the stability of the curtain and to increase the coating thickness required by the formulation combination.

[0141] Controlling the moisture content of the thermal paper 10 is to prevent excessive moisture from reacting with the hydroxyl groups or other active groups in the solvent-free silicone oil, which would slow down the curing speed or cause incomplete curing of the solvent-free silicone oil.

[0142] The thermal coating 200 of this embodiment further includes at least one of the following conditions (H) to (K):

[0143] (H) The surface tension of the pre-coated 220 is 25 mN / m to 30 mN / m;

[0144] (I) The dynamic surface tension of the pre-coating 220 is 35g to 45g;

[0145] (G) The surface tension of the color development layer 230 is 25 mN / m to 30 mN / m;

[0146] (K) The dynamic surface tension of the color layer 230 is 35g to 45g.

[0147] By adjusting the surface tension and dynamic tension of the coating system formulation of pre-coating layer 220 and color development layer 230, the stability of the curtain formation using curtain coating in the preparation method is maintained.

[0148] Please see Figure 2 and Figure 3 ; Figure 2 This is a flowchart of the preparation method in Example 1 of the present invention; Figure 3 This is a photograph of the thermal paper prepared according to Example 1 of the present invention.

[0149] This embodiment also provides a method for preparing environmentally friendly paperless thermal paper 10. The preparation method involves using the above-mentioned coating system to prepare environmentally friendly thermal paper 10, and includes:

[0150] S10: Apply the primer 210 to one side of the substrate 100 using a doctor blade; the doctor blade pressure is 20 bar to 60 bar.

[0151] S20: Apply the pre-coating layer 220 to the surface of the primer layer 210 using a curtain coating method. The flow rate of the curtain coating is 10 kg / min to 25 kg / min, and the vehicle speed is 400 m / min to 800 m / min.

[0152] S30: Apply the color development layer 230 to the surface of the pre-coating layer 220 using a curtain coating method.

[0153] S40: Apply silicone oil to the surface of the color development layer 230 using a roller coating or curtain coating method; the roller coating speed is 6% to 20%, and the amount of silicone oil applied is 0.3 g / m. 2 Up to 1.5g / m 2 The flow rate for curtain coating is 10 kg / min to 25 kg / min.

[0154] S50: After drying and other processing steps, self-adhesive is applied to the other side of the substrate 100 by gravure coating to form a self-adhesive layer 400 with a thickness of 15μm to 20μm. After subsequent processing, thermal paper 10 is formed.

[0155] Using a doctor blade to apply the base coat 210, combined with a curtain coating pre-coating 220, and in conjunction with the curtain coating color development layer 230, the formulation of the thermosensitive coating 200 system is adjusted by increasing calcium stearate, polyethylene wax, anionic surfactants, anionic functional additives, wetting and dispersing agents, and defoaming wetting agents. This results in a coating material with good surface tension and dynamic tension properties, making the curtain coating process smoother and more continuous. This provides a good material formulation foundation for curtain coating to form a curtain, significantly improving the stability of curtain coating processing. Through precise control of the curtain flow rate, continuous... The coating effect ensures the uniformity and integrity of the thermal coating 200. Based on the formulation of the thermal coating 200 system, a coating raw material with good fluidity and stability is formed, reducing problems such as friction between materials and equipment during the curtain coating process. This effectively ensures the continuity and smoothness of the curtain coating. The curtain coating process can precisely control the thickness and uniformity of each coating. Compared with the existing blade coating and roller coating technologies, it is more suitable for the high-precision processing requirements of the base coating 210, pre-coating 220 and color developing layer 230, improving the overall processing accuracy, smoothness and uniformity of the thermal coating 200.

[0156] When coating solvent-free silicone oil on the color development layer 230, a good coating effect can be achieved by using a roller coating or a curtain coating process. Preferably, a curtain coating method is used, which can form a three-layer structure with the pre-coating layer 220 and the color development layer 230 in a one-time multi-layer curtain coating. This improves the processing compatibility and performance compatibility between the layers, and significantly improves the processing uniformity and processing efficiency. Compared with the roller coating method, the coating amount can be controlled by controlling the flow rate of the curtain, effectively avoiding the interference of air on the silicone oil during the coating process, and ensuring the uniformity and stability of the coating.

[0157] It is worth noting that, Figure 1The interlayer structure of the substrate 100, base coating 210, pre-coating 220, color developing layer 230, silicone oil layer 300, and self-adhesive layer 400 is ambiguous, not a clear interlayer structure with defined interfaces. Due to the relatively thin thickness of each layer, a certain degree of penetration and mutual fusion will occur between the layers during processing, forming an interlayer structure with mutual bonding. Furthermore, the coating system formula uses similar components (for example, anionic surfactants and anionic surface defoaming and wetting agents are used in both the color developing layer 230 and the pre-coating 220), which makes the interlayer permeability and compatibility stronger during processing. The overall structure of the thermal paper 10 is more robust and stable, which is beneficial for transportation, storage, and application.

[0158] Please see Figure 4 and Figure 5 ; Figure 4 This is a graph showing the gloss test data of the thermal paper prepared in Example 1 of the present invention; Figure 5 This is a graph showing the test data of the dynamic color development performance (saturation color density) of the thermal paper prepared in Example 1 of the present invention.

[0159] To more fully illustrate that the structure, coating system, and preparation method of this embodiment have better effects than the prior art, thermal paper 10 was prepared using the following examples and comparative examples, and performance tests were conducted for comparison.

[0160] Table 1: Coating system table for Example 1:

[0161]

[0162] The following are the coating systems of Examples 2 to 11 and Comparative Examples 1 to 6, formed by adjusting the corresponding parameters of Example 1 based on Table 1:

[0163] Example 2: The difference from Example 1 is that in the preparation of the color development layer 230, the mass fraction of 4,4'-sulfonyl diphenol is 20 parts and the mass fraction of colorless dye is 15 parts.

[0164] Example 3: The difference from Example 1 is that in the preparation of the color development layer 230, the mass fraction of 4,4'-sulfonyl diphenol is 50 parts and the mass fraction of colorless dye is 30 parts.

[0165] Example 4: The difference from Example 1 is that the calcined kaolin in the base coating 210 is replaced with kaolin.

[0166] Example 5: The difference from Example 1 is that the mass fraction of lightweight hollow microspheres in the pre-coated 220 is 80 parts.

[0167] Example 6: The difference from Example 1 is that the thickness of the base coating 210 is 10 μm, the thickness of the pre-coating layer 220 is 10 μm, and the thickness of the color development layer 230 is 8 μm.

[0168] Example 7: The difference from Example 1 is that the thickness of the base coating 210 is 3μm, the thickness of the pre-coating layer 220 is 3μm, and the thickness of the color development layer 230 is 3μm.

[0169] Example 8: The difference from Example 1 is that the substrate 100 is replaced with 60g / m 2 Polypropylene film.

[0170] Example 9: The difference from Example 1 is that the anionic surfactant in the pre-coating 220 is replaced with a nonionic surfactant.

[0171] Example 10: The difference from Example 1 is that the anionic surfactant in the color development layer 230 is replaced with a nonionic surfactant.

[0172] Example 11: The difference from Example 1 is that the water-soluble polymer in the color development layer 230 is replaced with polyvinyl alcohol.

[0173] Comparative Example 1: The difference from Example 1 is that 4,4'-sulfonyl diphenol in the color development layer 230 is replaced with 3,3'-diallyl-4,4'-sulfonyl phenol.

[0174] Comparative Example 2: The difference from Example 1 is that 4,4'-sulfonyl diphenol in the color development layer 230 is replaced with 2-phenylamino-3-methyl-6-dibutylfluorane.

[0175] Comparative Example 3: The difference from Example 1 is that it does not include the base coating 210.

[0176] Comparative Example 4: The difference from Example 1 is that it does not include the pre-coating 220.

[0177] Comparative Example 5: The difference from Example 1 is that the color development layer 230 does not contain calcium stearate and polyethylene wax.

[0178] Comparative Example 6: The difference from Example 1 is that the color development layer 230 contains zinc stearate.

[0179] According to the coating system of Example 1 in Table 1, thermal paper 10 was prepared using the following preparation method:

[0180] Step 1: Mix and stir each component of the base coating 210, each component of the pre-coating 220, and each component of the color development layer 230 separately, and prepare solvent-free silicone oil.

[0181] Step 2: Apply the base coating 210 to the surface of the substrate 100 using a doctor blade coating method. Apply the pre-coating 220 to the surface of the base coating 210 using a curtain coating method. Apply the color developing layer 230 to the surface of the pre-coating 220 using a curtain coating method. Apply the solvent-free silicone oil (i.e., silicone oil layer 300) to the surface of the color developing layer 230 using a roller coating or a curtain coating method. (It is worth noting that the pre-coating 220, the color developing layer 230, and the solvent-free silicone oil are all applied using a curtain coating method, so multiple layers of curtain coating can be used to complete the coating in one go.)

[0182] Step 3: After drying and other processes, adhesive is applied to the other side of the substrate 100 using a gravure coating method. After subsequent processing, thermal paper 10 is formed.

[0183] The following performance tests were performed on the thermal paper 10 prepared in each embodiment and comparative example:

[0184] Test samples: Thermal paper 10 was prepared using the coating systems of Examples 1 to 11 and Comparative Examples 1 to 6.

[0185] Test method:

[0186] (1) Gloss: The gloss of thermal paper 10 samples was measured using a PN-GM gloss meter.

[0187] (2) Dynamic color development performance (saturation color density): The dynamic color development performance (saturation color density) of each sample was tested according to GB / T28210-2024 Thermal Paper.

[0188] (3) Curing time: the silicone oil layer 300 silicone drop test; according to the curing time conditions of solvent-free silicone oil, perform the corresponding silicone oil curing process. After applying silicone oil and curing, rub the cured silicone oil coating with your hand. If the coating is solid and does not fall off, it is considered that the silicone does not drop; if the coating is liquid or there is oil on your hand and the coating falls off, it is considered that the silicone oil drops.

[0189] (4) Temperature resistance: Each thermal paper 10 sample was placed in an oven at 100℃, 120℃ and 150℃ and baked for 1 hour. The background color of the thermal paper 10 was then tested.

[0190] Table 2: Performance test results of gloss, dynamic color development (saturation color density), curing time, and temperature resistance of thermal paper 10 prepared using Examples 1 to 11 and Comparative Examples 1 to 6.

[0191]

[0192] Results analysis: As shown in Table 2, the test results indicate that:

[0193] (1) Comparing Example 1 and Example 2, it can be seen that when the mass ratio of color developer 4,4'-sulfonyl diphenol to colorless dye is in the range of (1~2):1, the overall performance of the obtained thermal paper and the stability after coating with silicone oil is better.

[0194] (2) Comparing Example 1 and Example 3, it can be seen that when the mass ratio of color developer 4,4'-sulfonyl diphenol to colorless dye is in the range of (1~2):1, the ratio of color developer to colorless dye is not suitable, which results in the thermal paper not being able to perform well.

[0195] (3) Comparing Example 1 and Example 4, it can be seen that: the base coating 210 uses kaolin, and the resulting thermal paper is more suitable for coating with solvent-free silicone oil. Due to the promoting effect of kaolin, the gloss after coating with solvent-free silicone oil is better.

[0196] (4) Comparing Example 1 and Example 5, it can be seen that: the pre-coating 220 uses 80 parts by weight of lightweight hollow microspheres, and the resulting thermal paper is more suitable for coating with solvent-free silicone oil. The high proportion of hollow spheres improves the color clarity of the thermal paper, but reduces the gloss.

[0197] (5) Comparing Example 1 and Example 6, it can be seen that when the overall thickness of the thermal coating 200 is between 12μm and 28μm, the thermal paper has better performance.

[0198] (6) Comparing Example 1 and Example 7, it can be seen that when the overall thickness of the thermal coating 200 is 9μm, the solvent-free silicone oil can easily penetrate into the substrate 100 layer because the thermal coating 200 is too thin, resulting in the solvent-free silicone oil lacking release effect and not suitable for use in the field of paperless thermal paper.

[0199] (7) Comparing Example 1 and Example 8, it can be seen that when the substrate 100 is replaced with polypropylene film material, the thermal paper can also obtain better comprehensive performance, indicating that the coating system of this embodiment has good characteristics that can be matched with different substrates 100.

[0200] (8) Comparing Example 1 with Example 9 and Example 10, it can be seen that when nonionic surfactants are used in the thermal coating 200 system, the surface tension and dynamic tension of nonionic surfactants are not suitable for the operation stability of curtains and are not suitable for matching the drying process of solvent-free silicone oil, resulting in the silicone oil not drying (i.e., appearing as liquid or oil). Therefore, it is not suitable for use in the field of paperless thermal paper.

[0201] (9) Comparing Example 1 and Example 11, it can be seen that after the water-based acrylic resin in the color development layer 230 is replaced with polyvinyl alcohol commonly used in the existing thermal paper formulation, the release effect of the thermal paper is reduced because polyvinyl alcohol has weak oil resistance and silicone oil penetration occurs.

[0202] (10) Comparing Example 1 with Comparative Example 1 and Comparative Example 2, it can be seen that: replacing the color developer or colorless dye in the coating system of color development layer 230 with components of the prior art will not achieve the excellent effect of the thermal paper prepared in this embodiment; 4,4'-sulfonyl diphenol will not react with solvent-free silicone oil, and the gloss value is better.

[0203] (11) Comparing Example 1 with Comparative Example 3 and Comparative Example 4, it can be seen that: removing the base coating 210 or the pre-coating 220 causes the corresponding properties of the thermal coating 200 to disappear, the solvent-free silicone oil to penetrate, and the thickness to decrease, resulting in a significant decrease in gloss, dynamic color development performance (saturated color density), and curing time. The excellent effect of the thermal paper prepared in this embodiment cannot be obtained.

[0204] (12) Comparing Example 1 and Comparative Example 5, it can be seen that: the absence of calcium stearate and polyethylene wax on the surface of the color development layer 230 leads to poor continuous printing of the thermal coating 200, which in turn makes the color development layer 230 unsuitable for use in the preparation method of thermal paper, resulting in a reduction in the performance of the thermal paper. This fully demonstrates the important correlation between the formulation materials of the coating system and the preparation method.

[0205] (13) Comparing Example 1 and Comparative Example 6, it can be seen that adding zinc stearate to the surface of the color development layer 230 will cause the thermal coating 200 to be contaminated when coated with silicone oil, which will lead to the color development of the thermal paper (the thermal paper is prone to contamination and the background color becomes darker). This type of color development layer 230 is not suitable for the preparation of thermal paper, resulting in a reduction in the performance of the prepared thermal paper.

[0206] It is worth noting that, as can be seen from the background color test results in Table 2, the thermal paper prepared using Example 1 has excellent temperature resistance and durability. The optimized temperature resistance allows the thermal paper to maintain stable quality and performance even in dry environments such as solvent-free silicone oil, extending the service life of the thermal paper, reducing the use of release paper, and lowering the cost of use.

[0207] Please refer to it again. Figure 3 It is worth noting that the release properties of the thermal paper prepared into a backless paper according to Table 2 are listed in Table 3 below.

[0208] Table 3: Release performance data of various thermal papers after being prepared into backing paper:

[0209]

[0210] The above release force data were measured according to relevant standards, such as the "Test Method for Peel Strength of Adhesive Tape" (GB / T 2792-2014). Since thermal paper is generally used in rolls after production, in roll or stacked states, a layered structure is formed where the adhesive layer of the upper thermal paper contacts the silicone oil layer of the lower thermal paper. If the release force is too small, it will be difficult to peel (the upper and lower layers will stick together). If the release force is too large, the adhesive layer viscosity will be too low or the silicone oil content will be too large, leading to difficulty in adhesion. The apparent effect of this release force is usually manifested as a "self-curling" phenomenon in this technical field. The reasonable existence of this phenomenon is crucial for the application of backing-less thermal paper. Therefore, the range of release force control is strictly required, generally around 20 N / m.

[0211] As shown in Table 3, when the amount of silicone oil and adhesive applied in each embodiment and comparative example are the same, the thermal paper prepared in Example 1 has a significant advantage in release force.

[0212] Please see Figure 6 ; Figure 6 This is a SEM image of the surface of the thermal paper prepared in Example 1 of the present invention.

[0213] It is worth noting that by using a curtain coating process to develop the color layer, combined with a doctor blade coating process to develop the base layer, combined with a curtain coating process to develop the pre-coating layer, and combined with a roller coating or curtain coating process to develop the silicone oil, a process flow with distinct processing methods for each layer and combined performance is formed. The test results for each thermal paper show that the curtain coating method used in this embodiment has better processability and the resulting thermal paper has better performance.

[0214] The coating thickness formed by traditional blade coating is mainly controlled by the pressure, angle and speed of the blade. This method has the advantages of simple equipment structure, convenient operation and low cost, and is suitable for processing a variety of substrates.

[0215] For example, patent CN117822350A discloses a coated paper, its preparation method and application, and self-adhesive release paper, emphasizing the high efficiency and easy control of blade coating.

[0216] However, for this application, the use of blade coating in solvent-free silicone oil systems has certain limitations. Due to the high viscosity of solvent-free silicone oil, blade coating is prone to defects such as uneven coating, streaks, and bubbles, which affect the appearance and performance of the product. At the same time, blade coating has low precision in controlling the coating thickness, making it difficult to achieve stable production of ultra-thin and uniform coatings.

[0217] In traditional anilox roller coating, the coating amount is determined by the size and depth of the cells on the anilox roller, thus the coating amount is controlled more precisely and the processing is more efficient.

[0218] For example, the invention patent with publication number WO2015003477A1 discloses an ULTRA-THIN SOLVENT-FREE SILICONE OIL RELEASE PAPER AND METHOD FOR MANUFACTURING SAME, which uses an anilox roller coating method to apply solvent-free silicone oil, achieving an ultra-thin coating and having the advantages of being environmentally friendly and energy-saving.

[0219] However, for this application, the uniformity of the processing thickness using anilox roller coating is difficult to meet the application requirements, and problems similar to those of the aforementioned doctor blade coating are likely to occur.

[0220] Therefore, compared with the two methods mentioned above, the curtain coating technology used in this application has significant technical advantages:

[0221] (1) Non-contact coating: makes the coating smoother and more uniform, avoiding defects such as scratches and streaks caused by mechanical contact in doctor blade coating.

[0222] (2) Precise control of coating thickness: By adjusting the flow rate of coating liquid, curtain height and substrate speed, the coating thickness can be controlled at the micron or even submicron level.

[0223] (3) Adaptability to high-speed production: Curtain coating can maintain a stable coating effect under high-speed production conditions, making it suitable for large-scale industrial production.

[0224] (4) High material utilization: The coating process is stable, reducing splashing and edge waste, improving the utilization efficiency of silicone oil, and reducing production costs.

[0225] In summary, the comparison shows that:

[0226] According to the structure of this embodiment, the thermal paper 10 prepared by the preparation method of this embodiment using the coating system of this embodiment has a clear distinction between each layer, resulting in each layer having different characteristic properties, and each property is directly related to the others, resulting in a relatively thick overall thickness that does not affect the application. This provides a good processability basis for the preparation method, and improves the color development performance of the prepared thermal paper 10 by forming a layer structure and layer component properties that effectively resist the penetration of solvent-free silicone oil. Furthermore, the use of solvent-free silicone oil as the surface release layer and the structural optimization of the thermal coating 200 endow the thermal paper 10 with excellent self-curling release properties, forming a structure that matches the preparation method of this embodiment, which allows for automatic curling after coating with solvent-free silicone oil and self-adhesive, facilitating the processing and application of the thermal paper 10.

[0227] In the coating system, compared with the existing technology that uses color developers such as 2,4-diphenylsulfone phenol (abbreviated as: DBSP), bisphenol A (compound name: 2,2-bis(p-hydroxyphenyl)propane), 3,3'-diallyl-4,4'-sulfonylphenol or 2-phenylamino-3-methyl-6-dibutylfluorane), this embodiment uses 4,4'-sulfonyl diphenol as a color developer, and forms the above-mentioned optimal ratio range with the colorless dye. This allows the thermosensitive coating 200 to achieve rapid, uniform and stable color change in the thermosensitive color reaction (i.e.: saturation color density test of dynamic color performance). It not only has good recognizability, but also has comparable color saturation, durability and lightfastness to the formulation of the existing technology. The unique chemical structure of the 4,4'-sulfonyl diphenol color developer enables it to undergo an efficient chemical reaction with the colorless dye during heating, generating a stable color product.

[0228] Furthermore, it was verified that the 4,4'-sulfonyl diphenol color developer and the solvent-free silicone oil do not react with each other, thereby avoiding the phenomenon of the solvent-free silicone oil layer not drying. This not only ensures good matching with the structure of this embodiment, forming good compatibility and stability between the layers of the thermal paper 10, but also matches the preparation method of this embodiment, providing a more reliable guarantee for the production and application of the thermal paper 10.

[0229] Furthermore, the use of water-based acrylic resin in the coating system forms a good adhesive, which enhances the adhesion between the thermal coating 200 and the substrate 100, ensuring the stability of the physical properties such as gloss of the thermal coating 200 under various environmental conditions. At the same time, it improves the compatibility between the thermal coating 200 and the solvent-free silicone oil, preventing the solvent-free silicone oil from easily penetrating into the substrate 100, which would reduce the release effect of the thermal paper 10.

[0230] Furthermore, the coating system uses calcium stearate and polyethylene wax components as lubricants and anti-sticking agents to improve the lubricity and anti-sticking properties of the thermal coating 200. This prevents the coefficient of friction of the thermal coating 200 from increasing and the lubricity from decreasing, which would make the prepared thermal paper 10 prone to sticking during curling and use, making it difficult to unfold and use normally. This would affect the continuous printing of the thermal paper 10 in the field of transit labels such as logistics labels, affecting practicality and convenience. In addition, matching the preparation method of this embodiment, the addition of calcium stearate and polyethylene wax components can effectively reduce the coefficient of friction of the thermal coating 200, thereby improving the feasibility and processing effect of curtain coating. It can also reduce equipment wear, maintenance costs and repair frequency, and improve production efficiency and economic benefits.

[0231] The use of other components in the coating system further optimizes the stability of the thermal coating 200 during the curtain coating process.

[0232] In the preparation method, a curtain coating method is used for the pre-coating layer 220 and the color developing layer 230. On the one hand, based on the above structure and formula, a good, smooth and feasible processing process that is conducive to curtain coating can be formed, resulting in thermal paper 10 with good overall performance such as uniform gloss and overall dynamic color development performance (saturation color density). On the other hand, for the thermal coating 200, the curtain coating method, compared with blade coating, roller coating and other processing methods, can better ensure the continuity and uniformity of the coating, reduce the need for production control methods such as equipment adjustment and improvement of operation steps, improve the continuity and uniformity of the thermal coating 200, reduce the multiple coating and drying processes of the thermal coating 200, and reduce energy consumption, equipment wear and other costs.

[0233] The thermal paper 10 provided in this embodiment has excellent color development performance and stability for continuous printing. The color development performance can reach 1.20 or higher, exceeding the national standard requirement of ≥1.10. When printing, the thermal paper 10 can develop colors quickly and evenly, with bright colors and high clarity, effectively improving the readability and recognizability of labels, and effectively using environmentally friendly components, thus improving environmental performance.

[0234] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0235] The above embodiments are merely examples of several implementations of the present invention, intended to facilitate a detailed understanding of the technical solutions of the present invention. However, they should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided by the present invention through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of the present invention patent should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. An environmentally friendly, no base paper type thermal paper, characterized by: The paper substrate comprises a thermal coating and a solvent-free silicone oil layer sequentially laminated on one side of the paper substrate; the thermal coating comprises a color developing layer, a pre-coating layer, and a base coating layer sequentially laminated, the base coating layer being laminated on one side of the paper substrate; the color developing layer comprises a color developer, the color developer comprising 4,4'-sulfonyl diphenol; the color developer is present in a mass fraction of 20 to 50 parts; an adhesive layer is also laminated on the other side of the paper substrate to provide the thermal paper with a self-curling function through the double-sided coating structure. The thermal coating includes all of the following features (A) through (C): (A) The thickness of the base coating is 5 μm to 10 μm; (B) The thickness of the pre-coating is 6 μm to 10 μm; (C) The thickness of the color-developing layer is 4 μm to 8 μm; The color development layer includes an aqueous acrylic resin with a glass transition temperature of -20°C to +80°C, and also includes 2 to 10 parts by weight of calcium stearate and 2 to 6 parts by weight of polyethylene wax. The colorimetric layer also includes the following components in parts by weight: 15 to 30 parts of leuco dye; 5 to 20 parts of inorganic nanofiller; 1 to 1.5 parts of anionic surfactant; 1.5 to 3 parts of anionic functional additives; The base coating comprises the following components in parts by weight: 50 to 70 parts of calcined kaolin; Light calcium carbonate, 5 to 30 parts; 1 to 5 parts of heavy calcium carbonate; Acrylamide 5 to 15 parts; 10 to 20 parts of styrene-acrylic latex; 3 to 8 parts of polylactic acid; Thickener 0.5 to 5 parts; Boric acid 0.1 to 0.5 parts; 30 to 45 parts water; The pre-coating comprises the following components in parts by weight: 60 to 80 parts of lightweight hollow microspheres; 5 to 15 parts of polymer latex; 5 to 10 parts of water-based acrylic resin; 1 to 5 parts of the second anionic surfactant; 1 to 5 parts of the second anionic functional additive; 25 to 35 parts water.

2. The environment-friendly, no-base-paper type thermal paper according to claim 1, characterized by: The thermal coating includes at least one of the following features (D) to (F): (D) The content of the base coating in the thermosensitive coating is 30% to 60%; (E) The pre-coating layer comprises 10% to 35% of the thermosensitive coating; (F) The content of the color-developing layer in the thermosensitive coating is 8% to 25%.

3. The environment-friendly, no-base-paper type thermal paper according to claim 1, characterized by: The moisture content of the thermal paper is 3.0% to 6.0%.

4. The environment-friendly, no-base-paper type thermal paper according to claim 1, characterized by: The thermal coating includes at least one of the following features (G) to (J): (G) The surface tension of the pre-coating is 25 mN / m to 30 mN / m; (H) The dynamic surface tension of the pre-coating is 35g to 45g; (I) The surface tension of the color-developing layer is 25 mN / m to 30 mN / m; (J) The dynamic surface tension of the color development layer is 35g to 45g.

5. A method for preparing an environmentally friendly, non-bottom paper type thermal paper, characterized by: The preparation method is used to prepare the environmentally friendly paperless thermal paper according to any one of claims 1 to 4. The preparation method includes: applying the base coating layer to one side of the paper substrate using a doctor blade coating; applying the pre-coating layer to the surface of the base coating layer using a curtain coating; and applying the color developing layer to the surface of the pre-coating layer using a curtain coating.

6. The method of claim 5, wherein: The production method includes: using a method of roll coating or curtain coating to coat the silicone oil to the surface of the color developing layer.

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