Thermal sensitive paper protective coating and preparation method thereof

Abstract

The invention relates to a thermal-sensitive paper protective coating and a preparation method thereof, and the preparation method comprises the following steps: uniformly dispersing TEMPO in ethyl acetate to obtain an additive solution, mixing polyester polyol and MDI, reacting to obtain a polyurethane matrix, adding the additive solution into the polyurethane matrix, and stirring to obtain the thermal-sensitive paper protective coating. The heat-sensitive paper is used for effectively resisting the infringement effect of ultraviolet rays on the heat-sensitive paper.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of paper protective coating, in particular to a thermal paper protective coating and a preparation method thereof. BACKGROUND

[0002] The protective coating of early thermal paper is relatively simple, mainly some materials with basic protection function, such as a thin layer of wax or resin coating on the surface of thermal paper, which plays a certain role in waterproof, oil-proof and slight friction resistance. But the protective performance of such coating is limited, which cannot meet the requirements of long-term preservation and use in harsh environments.

[0003] In order to solve the above problems, the following protective coatings have been produced in the prior art:

[0004] Anti-fouling and wear-resistant protective coating: functionalized polysiloxane is prepared by opening ring polymerization of functionalized cyclotetrasiloxane and trifluoropropylmethylcyclotrisiloxane and end-capping with 1,3-bis(3-aminopropyl)tetramethyldisiloxane, and then the functionalized polysiloxane is mixed with styrene-acrylic emulsion and polyindole-coated nano-silica to prepare a top coating. Polyindole is a conductive polymer that can solve the problem of static accumulation on the surface of thermal paper, and nano-silica as a reinforcing filler can give the coating excellent wear resistance.

[0005] Scratch-resistant and light-shielding thermal paper protective layer: composed of gelatin, cellulose nanofibrils containing lignin and glycerol. The cellulose nanofibrils interpenetrate each other to form a skeleton structure, and have electrostatic interaction and hydrogen bonding with gelatin and glycerol, which improves the mechanical strength and toughness of the protective layer and improves the scratch resistance. At the same time, the lignin in the cellulose nanofibrils has carbonyl, phenolic hydroxyl, conjugated double bond structure and methoxyl groups, which give the protective layer good UV shielding effect.

[0006] Waterproof, plastic-resistant and friction-resistant thermal developing protective coating: water-based acrylic resin is used as the main component to achieve the protective effect, ternary chlorovinyl acetate emulsion can enhance the chemical resistance, water resistance and weather resistance of the coating, and lubricant can improve the printing running property of thermal paper and prevent paper jam. The coating is a water-based system, which can give the thermal paper good waterproof, plastic-resistant and friction-resistant effect after curing, and does not affect the printing and developing of thermal paper.

[0007] Thermal paper heat-insulating coating material: the main raw materials include heat-insulating microspheres, adhesives, water-retaining agents, wetting agents, dispersants, defoamers and fillers, etc. The heat-insulating microspheres are foamed microspheres, which have a higher hollow rate than existing hollow spheres and other barrier materials, and have a better inhibitory effect on heat conduction, which can reduce the migration of heat to the base paper layer, improve the thermal energy of the thermal coating, and increase the sensitivity and developing light density.

[0008] However, the above coating materials have relatively single protection performance, and cannot effectively protect against ultraviolet rays, and are prone to problems of not easy to store, easy to discolor and yellow, and information easy to lose due to poor shielding effect of lignin on ultraviolet rays. SUMMARY

[0009] The present application aims to provide a thermal paper protective coating and a preparation method thereof, which can effectively resist the damage of ultraviolet rays to thermal paper.

[0010] In order to solve the above technical problems, the specific scheme adopted by the present application is as follows: a preparation method of a thermal paper protective coating, TEMPO is uniformly dispersed in ethyl acetate to obtain an additive solution, polyester polyol and MDI are mixed and reacted to obtain a polyurethane matrix, and then the additive solution is added to the polyurethane matrix and stirred to obtain the thermal paper protective coating.

[0011] Preferably, TEMPO and phosphite antioxidant 168 are mixed and then uniformly dispersed in ethyl acetate to obtain an additive solution.

[0012] Preferably, the addition amount of TEMPO is 0.45%-0.53% of the mass of the polyurethane matrix, and the addition amount of phosphite antioxidant 168 is 0.28%-0.33% of the mass of the polyurethane matrix.

[0013] Preferably, the addition amount of ethyl acetate is 4.8-6 times the total mass of TEMPO and phosphite antioxidant 168.

[0014] Preferably, the polyester polyol is first subjected to high-temperature vacuum dehydration in a reaction kettle, then cooled to 79-85℃, and then MDI is added, and finally stirred for 1.8-2.3h to obtain the polyurethane matrix.

[0015] Preferably, the mass ratio of polyester polyol to MDI is 1:(0.18-0.21).

[0016] Preferably, the additive solution is added to the polyurethane matrix and stirred, then dibutyltin dilaurate is added and stirred to obtain the thermal paper protective coating.

[0017] Preferably, the addition amount of dibutyltin dilaurate is 0.045%-0.055% of the mass of the polyurethane matrix.

[0018] Preferably, the thermal paper protective coating is subjected to defoaming treatment by a vacuum defoaming machine.

[0019] A thermal paper protective coating is prepared by the preparation method of any one of the thermal paper protective coatings described above.

[0020] The protective coating prepared by the organic material (polyurethane) and the free radical material (TEMPO) can keep the scratch-resistant and water-resistant properties of the traditional protective material of the substrate, and improve the ultraviolet absorption and chemical corrosion resistance of the material by introducing the free radical.

[0021] The polyurethane substrate is stable by itself, and the protective film can physically avoid the contact between the heat-sensitive layer and the chemical substance. The special electronic structure (active free radical unpaired single electron) in the free radical makes the unpaired electron in the free radical exist in an unsaturated bond or a lone pair electron orbital, and the energy required for the electron transition (such as π→π* and n→π*) is high. The energy of ultraviolet light (wavelength about 10-400 nm) is just matched with the energy requirement of such transition, so it is easy to be absorbed, thereby the free radical material itself absorbs the ultraviolet band, and the ultraviolet light can be avoided to penetrate the coating and damage the heat-sensitive layer.

[0022] Even if a small amount of chemical substance penetrates the protective layer, the free radical itself is active and easy to be reduced and oxidized, so it can consume the oxidizing and reducing chemical substances, thereby sacrificing itself and reacting with the chemical corrosive substance to avoid damaging the heat-sensitive layer.

[0023] Therefore, the protective coating of the present application can enhance the ultraviolet resistance of the heat-sensitive paper, improve the chemical and physical resistance of the heat-sensitive paper, so that the heat-sensitive paper is not easy to fade, and the text information can be preserved for a long time. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The ESR spectrum of the heat-sensitive paper protective coating prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0025] The present application will be described below by three examples:

[0026] The preparation method of a heat-sensitive paper protective coating in this example involves the following raw materials and equipment. Raw materials: polyester polyol hydroxyl value (hydroxyl value 56 mgKOH / g), MDI (diphenyl methane diisocyanate), TEMPO (2,2,6,6-tetramethylpiperidine oxide), phosphite antioxidant 168 (tris (2,4-di-tert-butylphenyl) phosphite), and dibutyl tin dilaurate. Equipment: high-speed stirrer (maximum speed 2000 rpm), vacuum degassing machine, reaction kettle (with temperature control device), mold and curing equipment, and electronic balance (accuracy 0.001 g).

[0027] The specific preparation method of this example includes the following steps: Step 1) Mix TEMPO and antioxidant 168, then add ethyl acetate and ultrasonically disperse at room temperature for 15 minutes to form a homogeneous additive solution. Antioxidant 168 can inhibit the oxidative degradation of polyester polyols and polyurethanes during processing and use, especially protecting the stability of the material during high-temperature curing and extending its service life. TEMPO resists oxygen in the air and absorbs ultraviolet light, preventing the thermal paper from discoloring.

[0028] Step 2) Add polyester polyol to the reactor and dehydrate under vacuum at 110°C for 2 hours. Then cool down to 80°C, slowly add MDI, and stir at 500 rpm for 2 hours to obtain polyurethane matrix, controlling the -NCO ratio at about 1:1.05.

[0029] Step 3) The dispersed additive solution obtained in Step 1) is slowly added to the polyurethane matrix obtained in Step 2), the stirring speed is increased to 1000 rpm and dispersed for 20 min, then dibutyltin dilaurate is added and stirring is continued for 10 min. Dibutyltin dilaurate acts as a catalyst to accelerate the reaction of -OH and -NCO (carbamate reaction), reduce the activation energy of the reaction, and shorten the curing time.

[0030] Step 4) Transfer the mixture obtained in Step 3 to a vacuum degassing machine and degas at -0.09 MPa for 15 minutes to obtain the thermal paper protective coating. The degassing treatment ensures the product is free of pores, has uniform density, and improves material transparency.

[0031] In this embodiment, the amount of TEMPO added is 0.45% of the mass of the polyurethane matrix, and the amount of phosphite antioxidant 168 added is 0.28% of the mass of the polyurethane matrix. The amount of ethyl acetate added is 4.8 times the total mass of TEMPO and phosphite antioxidant 168. The mass ratio of polyester polyol to MDI is 1:0.18. The amount of dibutyltin dilaurate added is 0.045% of the mass of the polyurethane matrix.

[0032] like Figure 1 As shown, the thermal paper protective coating prepared in this embodiment produced a significant ESR signal, indicating that free radicals were generated in the material and the structure was consistent with expectations.

[0033] Example 2

[0034] The raw materials, equipment and preparation method steps used in this example are the same as in Example 1, except that the amount of TEMPO added is 0.5% by mass of the polyurethane base, the amount of phosphite antioxidant 168 added is 0.3% by mass of the polyurethane base, the amount of ethyl acetate added is 5 times the total mass of TEMPO and phosphite antioxidant 168, the mass ratio of polyester polyol to MDI is 1:0.2, and the amount of dibutyl tin dilaurate added is 0.05% by mass of the polyurethane base.

[0035] Example 3

[0036] The raw materials, equipment and preparation method steps used in this example are the same as in Example 1, except that the amount of TEMPO added is 0.53% by mass of the polyurethane base, the amount of phosphite antioxidant 168 added is 0.33% by mass of the polyurethane base, the amount of ethyl acetate added is 6 times the total mass of TEMPO and phosphite antioxidant 168, the mass ratio of polyester polyol to MDI is 1:0.21, and the amount of dibutyl tin dilaurate added is 0.055% by mass of the polyurethane base.

Claims

1. A method for preparing a thermal paper protective coating, characterized in that: TEMPO was uniformly dispersed in ethyl acetate to obtain an additive solution. Polyester polyol and MDI were mixed and reacted to obtain a polyurethane matrix. The additive solution was then added to the polyurethane matrix and stirred to obtain a thermal paper protective coating.

2. The method for preparing a thermal paper protective coating as described in claim 1, characterized in that: First, TEMPO and phosphite antioxidant 168 are mixed and then evenly dispersed in ethyl acetate to obtain an additive solution.

3. The method for preparing a thermal paper protective coating as described in claim 2, characterized in that: The amount of TEMPO added is 0.45%-0.53% of the mass of the polyurethane matrix, and the amount of phosphite antioxidant 168 added is 0.28%-0.33% of the mass of the polyurethane matrix.

4. The method for preparing a thermal paper protective coating as described in claim 2, characterized in that: The amount of ethyl acetate added is 4.8-6 times the total mass of TEMPO and phosphite antioxidant 168.

5. The method for preparing a thermal paper protective coating as described in claim 1, characterized in that: First, the polyester polyol is dehydrated under high temperature and vacuum in a reactor. Then, after cooling to 79-85℃, MDI is added. Finally, the reaction is stirred for 1.8-2.3 hours to obtain the polyurethane matrix.

6. The method for preparing a thermal paper protective coating as described in claim 1, characterized in that: The mass ratio of polyester polyol to MDI is 1:(0.18-0.21).

7. The method for preparing a thermal paper protective coating as described in claim 1, characterized in that: Thermosensitive paper protective coating is prepared by adding the additive solution to the polyurethane matrix and stirring, then adding dibutyltin dilaurate and stirring.

8. The method for preparing a thermal paper protective coating as described in claim 7, characterized in that: The amount of dibutyltin dilaurate added is 0.045%-0.055% of the mass of the polyurethane matrix.

9. The method for preparing a thermal paper protective coating as described in claim 1, characterized in that: The thermal paper protective coating was degassed using a vacuum degassing machine.

10. A thermal paper protective coating, prepared by any of the preparation methods of thermal paper protective coatings according to claims 1-9.

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