A heat-sensitive coating composition and its use in heat-sensitive colour paper

Abstract

This invention discloses a thermal coating composition and its application in thermal color developing paper, relating to the technical field of thermal color developing compositions. The thermal coating composition comprises the following raw materials in parts by weight: 5-10 parts of a non-phenolic thermal color developer, 2.5-4.5 parts of a colorant, 5-8 parts of a sensitizer, 5-7 parts of a filler, 2.5-7.5 parts of a binder, with the remainder made up to 100 parts with deionized water. By introducing a novel non-phenolic thermal color developer with a specific molecular structure, the activation energy barrier of the color developing reaction is effectively reduced. Its strong electron-withdrawing groups optimize the charge distribution, allowing the color developing process to be triggered rapidly at lower temperatures. The color developing sensitivity and depth are significantly superior to traditional phenolic color developers and other non-phenolic substitutes, thereby improving the clarity and color saturation of printed images.

Description

Technical Field

[0001] This invention relates to the field of thermosensitive colorimetric composition technology, and more specifically to a thermosensitive coating composition and its application in thermosensitive colorimetric paper. Background Technology

[0002] Thermal printing paper has extremely wide applications in modern society, covering multiple fields such as supermarket receipts, logistics labels, medical records, ticketing systems, fax paper, and financial transaction documents. Its core working principle relies on a thermal coating on the paper surface: when the thermal printhead applies localized heat, the chemicals in the coating react to generate visible images or text. Traditional thermal coatings typically consist of multiple components, including non-phenolic thermal developers, colorants, sensitizers, fillers, and binders. Among these, the non-phenolic thermal developer is the key component, responsible for reacting with the colorant under heat to produce a color change. For a long time, phenolic compounds (such as bisphenol A) have been widely used as non-phenolic thermal developers due to their low cost, fast reaction speed, and high color development efficiency. However, phenolic non-phenolic thermal developers have significant drawbacks, including potential health risks and environmental problems.

[0003] Furthermore, traditional phenolic non-phenolic thermosensitive color developers also have many limitations in terms of technical performance. In high-temperature or humid environments, phenolic compounds are prone to degradation, leading to fading, blurring, or poor stability of printed images, affecting the long-term preservation of documents. At the same time, phenolic non-phenolic thermosensitive color developers have high requirements for coating compatibility, often requiring additional additives to maintain reaction efficiency, increasing production costs and process complexity. These problems not only reduce the reliability and lifespan of thermal paper but also limit its expansion in sensitive fields (such as food packaging or medical applications). To address these challenges, the industry has attempted to develop non-phenolic alternatives to non-phenolic thermosensitive color developers, such as certain amide or sulfonamide compounds, but these solutions often introduce new problems: insufficient color sensitivity, insufficient color depth, excessively high activation temperatures, or poor synergistic effects with colorants and sensitizers.

[0004] Therefore, there is an urgent need in the field for an improved heat-sensitive coating composition that can completely avoid the risks of phenols while improving color development efficiency, stability and environmental friendliness. Summary of the Invention

[0005] The purpose of this invention is to provide a safe and environmentally friendly thermosensitive coating composition selected from novel non-phenolic thermosensitive color developers, in order to solve the problems of toxicity and poor image stability of non-phenolic thermosensitive color developers, while ensuring excellent color development performance.

[0006] To achieve the above objectives, the technical solution selected by the present invention is: a thermosensitive coating composition comprising a non-phenolic thermosensitive color developer;

[0007] The non-phenolic thermosensitive colorimetric agent is a compound represented by Formula 1:

[0008] Formula 1: ;

[0009] In Equation 1, R1 is a variable substituent;

[0010] R1 is selected from any one of the following: H, halogen, nitro, alkyl with 1-5 carbon atoms, and alkoxy with 1-5 carbon atoms.

[0011] Furthermore, the halogen is selected from either F or Cl.

[0012] Furthermore, the alkyl group having 1-5 carbon atoms is selected from any one of methyl, ethyl, propyl, and tert-butyl.

[0013] The alkoxy group with 1-5 carbon atoms is selected from either methoxy or ethoxy.

[0014] Furthermore, the non-phenolic thermosensitive colorimetric agent is selected from any one of the following compounds:

[0015] ;

[0016] ;

[0017] ;

[0018] .

[0019] Furthermore, the thermosensitive coating composition comprises the following raw materials in parts by weight: 5-10 parts of non-phenolic thermosensitive color developer, 2.5-4.5 parts of colorant, 5-8 parts of sensitizer, 5-7 parts of filler, 2.5-7.5 parts of binder, and the remainder is made up to 100 parts with deionized water.

[0020] The non-phenolic thermosensitive colorimetric agent is the compound shown in Formula 1.

[0021] Furthermore, the colorant is selected from: 2-phenylamino-3-methyl-6-diethylfluorane, 2-phenylamino-6-dibutylamino-3-methylfluorane, or 3-N-isopentyl-N-ethylamino-6-methyl-7-phenylaminofluorane.

[0022] Furthermore, the sensitizer is selected from: benzyl-2-naphthyl ether, 1,2-diphenoxyethane, 1,2-bis(3-methylphenoxy)ethane, or diphenyl sulfone.

[0023] Furthermore, the adhesive is selected from: polyvinyl alcohol, polyethylene glycol, hydroxyethyl cellulose, methyl cellulose or ethyl cellulose.

[0024] Furthermore, the filler is selected from calcium carbonate or silicon dioxide.

[0025] Application of a thermal coating composition in thermal color developing paper.

[0026] The nitrogen atom of the imino group in the non-phenolic thermosensitive chromogenic agent molecule of this invention possesses a lone pair of electrons, which can act as a proton acceptor to form hydrogen bonds or proton transfer complexes with the acidic hydrogen of the chromogenic agent. Upon heating, this interaction is activated, promoting electron transfer and initiating the ring-opening colorimetric reaction of the chromogenic agent. The strong electron-withdrawing property of the carbonyl group polarizes the intramolecular electron distribution through an inductive effect, reducing the electron cloud density of the nitrogen atom of the adjacent imino group and further enhancing its proton acceptor ability. The strong electron-withdrawing property of the sulfone group further optimizes the intramolecular charge distribution, while its tetrahedral configuration provides a rigid framework, enhancing thermal stability and preventing molecular degradation at high temperatures. The sulfone group forms an electron-withdrawing-electron-donating synergistic system with the carbonyl group and imino group, lowering the energy barrier of the colorimetric reaction and enabling rapid triggering of color development at lower temperatures.

[0027] The non-phenolic thermosensitive colorimetric agent described in this invention acts as a proton acceptor, forming a hydrogen bond network with the acidic hydrogen of the colorimetric agent, triggering electron transfer upon heating. The strong electron-withdrawing effect of the carbonyl and sulfone groups in the molecule polarizes the intramolecular charge distribution, lowering the energy barrier of the colorimetric reaction and achieving rapid color development at low temperatures. The acidic hydrogen of the colorimetric agent forms a proton transfer complex with the imino group of the non-phenolic thermosensitive colorimetric agent. The sensitizer, after melting, forms a uniform thermal medium, promoting efficient heat transfer from the printhead to the non-phenolic thermosensitive colorimetric agent-colorimetric agent pair. The aromatic ring structure of the sensitizer forms π-π stacking with the non-phenolic thermosensitive colorimetric agent / colorimetric agent, stabilizing the reaction intermediates and reducing energy loss. The filler regulates the porosity and surface roughness of the coating, ensuring uniform contact of the thermal printhead, while reflecting ultraviolet light to delay fading. The binder forms a flexible network structure, fixing the dispersion of each component and preventing localized failure caused by migration of the non-phenolic thermosensitive colorimetric agent; its hydroxyl groups bond with the non-phenolic thermosensitive colorimetric agent via hydrogen bonds, further enhancing thermal stability.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. Significantly Improved Color Development Efficiency: By introducing a specific molecular structure, the novel non-phenolic thermosensitive color developer effectively lowers the activation energy barrier of the color development reaction. Its strong electron-withdrawing groups optimize the charge distribution, enabling the color development process to be triggered rapidly at lower temperatures. The color development sensitivity and depth are significantly superior to traditional phenolic color developers and other non-phenolic substitutes, thereby improving the clarity and color saturation of printed images.

[0030] 2. Breakthrough in Environmental Stability: The molecular framework of the novel developer (especially the rigid tetrahedral structure of the sulfone group) endows the coating with excellent resistance to degradation. In humid and hot environments, its resistance to hydrolysis and heat aging is significantly enhanced, effectively suppressing image fading and blurring problems caused by the structural instability of traditional phenolic developers. The long-term preservation of printed content is significantly improved, meeting the stringent stability requirements of applications such as medical records and financial documents.

[0031] 3. Synergistic Optimization of Safety and Compatibility: Completely avoids the ecotoxicity risks of phenolic compounds (such as bisphenol A), while overcoming the poor synergistic effects of some non-phenolic substitutes with colorants and sensitizers. The novel colorant forms a stable composite system with other components in the formulation (such as fluorane colorants and ether sensitizers) through hydrogen bonding networks and π-π stacking interactions, ensuring uniformity of coating reaction and process adaptability while reducing toxicity. Attached Figure Description

[0032] Figure 1 The NMR of the non-phenolic thermosensitive colorimetric reagent 1 described in this invention. Detailed Implementation

[0033] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Preparation Example 1

[0035] Preparation of non-phenolic thermosensitive colorimetric reagent 1:

[0036]

[0037] 10 g of compound A was added to a reaction vessel, followed by 100 mL of dichloromethane and 18.74 g of 2-(7-azabenzotriazole)-N,N,N',N'-tetramethylurea hexafluorophosphate. The mixture was stirred at room temperature for 1 h. 10.81 g of compound C was dissolved in 50 mL of dichloromethane and added dropwise to the reaction vessel at a temperature not exceeding 25°C. After the addition was complete, the system temperature was lowered to 0°C, and then 5.79 g of N,N-diisopropylethylamine was added dropwise to the reaction vessel at a temperature not exceeding 10°C. After the addition was complete, the reaction was allowed to proceed at room temperature for 12 h. After the reaction was complete, the mixture was washed three times with 1 mol hydrochloric acid solution, then three times with saturated sodium bicarbonate solution, followed by washing with saturated brine. The organic phase was then dried with anhydrous sodium sulfate and evaporated to dryness. Finally, column chromatography was performed (silica gel column chromatography, using a mixed solution of n-heptane and ethyl acetate as eluent), and after rotary evaporation, 14.62 g of compound C was obtained. The structure was identified, and the mass spectra (m / z MS+1) of compound C were 405.

[0038]

[0039] 14.62 g of compound C, 10.55 g of compound D, and 180 mL of DMSO were added to a reaction vessel and stirred until uniformly dispersed. Then, 8.08 g of potassium tert-butoxide was added, and the mixture was heated to 50 °C and reacted for 7 h. After the reaction was complete, the mixture was poured into water and extracted four times with 20 mL of ethyl acetate. The organic phase was dried over anhydrous magnesium sulfate and then evaporated to dryness. Finally, column chromatography (silica gel column chromatography, using a mixed solution of n-heptane and ethyl acetate as eluent) was performed, and 28.83 g of non-phenolic thermosensitive chromogenic reagent 1 was obtained after evaporation. The structure was identified, and the mass spectrometry (m / z MS+1) of non-phenolic thermosensitive chromogenic reagent 1 was 570. The NMR spectrum is shown below. Figure 1 .

[0040] Preparation Examples 2-6

[0041] In Preparation Examples 2-6, non-phenolic thermosensitive colorimetric reagents were prepared sequentially, following the preparation method of Preparation Example 1, except that raw material B was replaced, and the rest remained the same as in Preparation Example 1. For details, please refer to Table 1.

[0042] Table 1

[0043]

[0044] Example 1

[0045] A thermal coating composition and preparation of thermal paper:

[0046] 1. Raw material formula:

[0047] Non-phenolic thermosensitive colorimetric reagent: 10 parts, selected from: the non-phenolic thermosensitive colorimetric reagent 1 described in Preparation Example 1;

[0048] Colorant: 3.5 parts, selected from: 2-phenylamino-3-methyl-6-diethylfluorane, purchased from: Hebei Jianxin Chemical Co., Ltd.;

[0049] Sensitizer: 6.5 parts, selected from: benzyl-2-naphthyl ether, purchased from: Beijing Bailingwei Technology Co., Ltd.;

[0050] Filler: 6 parts, selected from: calcium carbonate, purchased from: Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0051] Adhesive: 5 parts, selected from: polyvinyl alcohol, purchased from: Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0052] Deionized water: 69 parts, selected from: complete to a total mass of 100 parts.

[0053] 2. Preparation method

[0054] S1. Add 10 parts of non-phenolic thermosensitive color developer, 3.5 parts of 2-phenylamino-3-methyl-6-diethylfluorane, 6.5 parts of benzyl-2-naphthyl ether, 6 parts of calcium carbonate and 5 parts of polyvinyl alcohol to a mixing container in sequence. Add 69 parts of deionized water to the container and stir continuously for 30 minutes using a high-speed stirrer (speed of 800 rpm). During the stirring process, control the temperature not to exceed 30°C to obtain a slurry.

[0055] S2. The obtained slurry is evenly coated onto the surface of the substrate (thermal paper base paper), dried at 60℃ to constant weight, and then made into thermal recording paper (the dried weight of the coating liquid is approximately 5.5 g / m²). 2 ).

[0056] Examples 2-6

[0057] The preparation of a thermal coating composition and thermal paper is carried out by referring to the preparation method of Example 1, except that the non-phenolic thermal color developer is replaced with the non-phenolic thermal color developer prepared in Preparation Examples 2-6 in turn, and the rest is the same as in Example 1.

[0058] Comparative Example 1

[0059] A thermal coating composition and thermal paper were prepared according to the preparation method of Example 1, except that the non-phenolic thermal color developer was replaced with... The rest remains the same as in Example 1.

[0060] Comparative Example 2

[0061] A thermal coating composition and thermal paper were prepared according to the preparation method of Example 1, except that the non-phenolic thermal color developer was replaced with... (bis(3-allyl-4-hydroxyphenyl) sulfone (TGSA)), the rest is the same as in Example 1.

[0062] Comparative Example 3

[0063] A thermal coating composition and thermal paper were prepared according to the preparation method of Example 1, except that the non-phenolic thermal color developer was replaced with... The rest remains the same as in Example 1.

[0064] Performance testing:

[0065] 1. Saturation color development test: The test sample was subjected to saturation color development using a thermosensitive color development test device under the conditions of printing voltage 17V and pulse width 1.8ms. The optical concentration after color development was measured using an optical densitometer. The data are shown in Table 2.

[0066] 2. Water resistance test: The test sample was immersed in tap water at room temperature (25℃). After 36 hours, it was removed, dried, and the optical density of the printed area was measured. Residual rate (%) = (optical density of water-treated sample) / (optical density of untreated sample) × 100%, and the data are shown in Table 2.

[0067] 3. Heat resistance test: After placing the test sample at 60℃ for 36 hours, remove it and measure the optical density of the printed area. Residual rate (%) = (optical density of heat-treated product) / (optical density of untreated product) × 100%, and the data are shown in Table 2.

[0068] Table 2

[0069]

[0070] The novel non-phenolic thermosensitive colorimetric agent system used in Examples 1-6 of this invention demonstrates superior performance compared to traditional methods in terms of optical concentration, water resistance, and thermal stability. Its core trends are: 1. Improved colorimetric efficiency: The optical concentrations of all examples remain consistently high, significantly higher than the comparative group, confirming the enhancing effect of the "electron-withdrawing-electron-donating synergistic system" in the novel molecular design on the colorimetric reaction; 2. Excellent environmental stability: The retention rates of water-resistant and heat-resistant optical concentrations consistently approach saturation levels (both > 98%), indicating that the novel colorimetric agent effectively resists the erosion of the colorimetric structure by humid and hot environments, overcoming the easy degradation defects of traditional phenolic colorimetric agents. In contrast, the comparative group (containing traditional phenols and structurally similar compounds) shows a systematic disadvantage in all three indicators, especially a significant decline in environmental stability retention rate, highlighting the breakthrough value of this invention in resolving the contradiction between the toxicity and stability of colorimetric agents.

[0071] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A heat-sensitive coating composition, characterized in that, Including non-phenolic thermosensitive colorimetric agents; The non-phenolic thermosensitive colorimetric agent is a compound represented by Formula 1: Formula 1: ; In Equation 1, R1 is a variable substituent; R1 is selected from any one of the following: H, halogen, nitro, alkyl with 1-5 carbon atoms, and alkoxy with 1-5 carbon atoms.

2. The thermosensitive coating composition according to claim 1, characterized in that, The halogen is selected from either F or Cl.

3. The thermosensitive coating composition according to claim 1, characterized in that, The alkyl group having 1-5 carbon atoms is selected from any one of methyl, ethyl, propyl, and tert-butyl. The alkoxy group with 1-5 carbon atoms is selected from either methoxy or ethoxy.

4. The thermosensitive coating composition according to claim 1, characterized in that, The non-phenolic thermosensitive colorimetric agent is selected from any one of the following compounds: ； ； ； 。 5. The thermosensitive coating composition according to claim 1, characterized in that, The thermosensitive coating composition comprises the following raw materials in parts by weight: 5-10 parts of non-phenolic thermosensitive color developer, 2.5-4.5 parts of colorant, 5-8 parts of sensitizer, 5-7 parts of filler, 2.5-7.5 parts of binder, and the remainder is made up to 100 parts with deionized water. The non-phenolic thermosensitive colorimetric agent is the compound shown in Formula 1.

6. The thermosensitive coating composition according to claim 5, characterized in that, The colorant is selected from: 2-phenylamino-3-methyl-6-diethylfluorane, 2-phenylamino-6-dibutylamino-3-methylfluorane, or 3-N-isopentyl-N-ethylamino-6-methyl-7-phenylaminofluorane.

7. The thermosensitive coating composition according to claim 5, characterized in that, The sensitizer is selected from: benzyl-2-naphthyl ether, 1,2-diphenoxyethane, 1,2-bis(3-methylphenoxy)ethane, or diphenyl sulfone.

8. The thermosensitive coating composition according to claim 5, characterized in that, The adhesive is selected from: polyvinyl alcohol, polyethylene glycol, hydroxyethyl cellulose, methyl cellulose or ethyl cellulose.

9. A thermosensitive coating composition according to claim 5, characterized in that, The filler is selected from calcium carbonate or silicon dioxide.

10. The use of a thermal coating composition according to any one of claims 1-9 in thermal color developing paper.

Images