Scratch-resistant shading heat-sensitive paper protective layer as well as preparation method and application thereof

Abstract

The invention relates to a scratch-resistant shading heat-sensitive paper protective layer as well as a preparation method and application thereof, and belongs to the technical field of slurry or paper pulp compositions. The scratch-resistant shading heat-sensitive paper protective layer is mainly composed of gelatin, cellulose nanofibrils and glycerin. The cellulose nanofibrils contain lignin. The scratch-resistant shading heat-sensitive paper protective layer not only has excellent scratch resistance, but also can effectively shield ultraviolet light, so that the service life of the heat-sensitive paper is remarkably prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of pulp or pulp composition, and in particular to a scratch-resistant light-shielding thermal paper protective layer and a preparation method and application thereof. Background Art

[0002] Thermal paper is a special type of printing paper. Its main feature is that it can produce images or text under the action of heat without using ink or ribbon. Its working principle is based on the chemical substances (usually microcapsules and dyes) in the heat-sensitive layer to develop colors under the action of heat energy. When the thermal print head in the print head applies heat energy, the microcapsules in the heat-sensitive layer on the thermal paper will rupture and release the dye; the release of the dye forms text, images or barcodes according to the heating mode of the print head. Because thermal paper has the advantages of simple printing process, fast speed, no noise and space saving (because no ink cartridges or ribbons are required), it is widely used in small printing devices (such as receipt printers, label printers), especially for occasions that require fast printing and do not need to store the print results for a long time. However, it was found in the process of use that the anti-scratch performance of thermal paper is poor, which can easily lead to the unrecognizable printed images or barcode information; it was also found that when thermal paper is exposed to light for a long time, it will also increase the blurring of printed images or fading of colors. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a scratch-resistant light-shielding thermal paper protective layer and a preparation method and application thereof.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] In a first aspect, the present invention provides a scratch-resistant and light-shielding thermal paper protective layer, which is mainly composed of gelatin, cellulose nanofibrils and glycerol; the cellulose nanofibrils contain lignin.

[0006] The present invention combines gelatin, cellulose nanofibrils containing lignin and glycerol, and uses cellulose nanofibrils with a long fiber structure, a high specific surface area and good flexibility as a reinforcing material, so that the cellulose nanofibrils are interlaced with each other to form a skeleton structure, and multiple interactions (electrostatic interactions and hydrogen bonding) occur with gelatin and glycerol uniformly dispersed between the skeleton structures, thereby effectively improving the mechanical strength and toughness of the thermal paper protective layer, thereby significantly improving the scratch resistance of the thermal paper protective layer; at the same time, the carbonyl, phenolic hydroxyl, conjugated double bond structure, methoxy and other chromophore groups provided by the lignin in the cellulose nanofibrils are used to give the thermal paper protective layer a good ultraviolet shielding effect, thereby making the thermal paper protective layer have both good light-shielding performance and excellent scratch resistance, thereby significantly improving the service life of the thermal paper.

[0007] As a preferred embodiment of the scratch-resistant light-shielding thermal paper protective layer of the present invention, the mass ratio of gelatin to cellulose nanofibrils is 10:(0.02-0.2). Optionally, the mass ratio of gelatin to cellulose nanofibrils can be 10:0.05, 10:0.08, 10:0.1, 10:0.12, 10:0.14, 10:0.16, 10:0.18. Studies have found that the mass ratio of gelatin to cellulose nanofibrils mainly affects the strength and light-shielding performance of the thermal paper protective layer. When the mass ratio of the two is within the above range, it can not only better improve the strength of the thermal paper protective layer to improve the scratch resistance, but also have excellent light-shielding performance, thereby significantly improving the long-term stability of the thermal paper.

[0008] As a preferred embodiment of the scratch-resistant light-shielding thermal paper protective layer of the present invention, the mass ratio of gelatin to glycerol is 10:(1-5). Optionally, the mass ratio of gelatin to glycerol can be 10:1.5, 10:2, 10:2.5, 10:3, 10:3.5, 10:4, 10:4.5. Studies have found that although the long fiber structure of cellulose nanofibrils gives it good flexibility, it still has a certain brittleness after combining with gelatin, and the addition of glycerol can work together with cellulose nanofibrils and gelatin to reduce the brittleness of the thermal paper protective layer, improve its flexibility and maintain good strength. When the mass ratio of gelatin to glycerol is within the above range, the flexibility of the thermal paper protective layer can be better improved, so that the thermal paper coating has good deformation properties and deforms synchronously with the deformation of the thermal paper; at the same time, it can also maintain high strength to greatly improve the scratch resistance of the thermal paper coating.

[0009] As a preferred embodiment of the scratch-resistant light-shielding thermal paper protective layer of the present invention, the average diameter of the cellulose nanofibrils is 40 to 80 nm. Optionally, the average diameter of the cellulose nanofibrils can be 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, or 75 nm.

[0010] As a preferred embodiment of the scratch-resistant light-shielding thermal paper protective layer of the present invention, the gelatin includes at least one of pigskin gelatin, fish skin gelatin, cowhide gelatin, and cow bone gelatin; preferably pigskin gelatin, and the jelly strength of the pigskin gelatin can specifically be 260 to 300 bloom.

[0011] As a preferred embodiment of the scratch-resistant light-shielding thermal paper protective layer of the present invention, the cellulose nanofibrils can be purchased or prepared by the following preparation method: using bleached chemical thermomechanical pulp as raw material, subjecting it to benzene-alcohol extraction according to GB / T2677.6-1994 standard, and subjecting the obtained pulp to filament separation and broom treatment to obtain cellulose nanofibrils.

[0012] The preparation method specifically comprises the following steps: according to GB / T2677.6-1994, the bleached chemical thermomechanical pulp is subjected to benzene-alcohol extraction, and the obtained pulp is immersed in water to obtain a fiber suspension; after pouring it into a grinding device for fibrillation treatment, the ground suspension is homogenized by a high-pressure homogenizer to obtain a cellulose nanofibril suspension, and cellulose nanofibrils are obtained after drying.

[0013] The solid content of the fiber suspension is 1wt% to 3wt%, preferably 1.5wt% to 2.5wt%, and more preferably 2wt%; the grinding disc gap is +20 to -150μm during the ultrafine particle grinding process, the grinding times under each gap is 5 to 20 times, and the rotation speed is 1000 to 2400rpm; preferably 0μm (5 times), -5μm (5 times), the rotation speed is 1500rpm; -80μm (10 times), the rotation speed is 2000rpm; -100μm (20 times), the rotation speed is 2000rpm. The solid content of the suspension after grinding is 0.3wt% to 1wt%.

[0014] In a second aspect, the present invention provides a method for preparing the above-mentioned scratch-resistant and light-shielding thermal paper protective layer, comprising the following steps: uniformly mixing gelatin, cellulose nanofibrils, glycerin and water to obtain a composite solution, and then uniformly coating the composite solution on the surface of a carrier and drying to obtain the scratch-resistant and light-shielding thermal paper protective layer.

[0015] As a preferred embodiment of the scratch-resistant light-shielding thermal paper protective layer of the present invention, the mass fraction of gelatin in the coating slurry is 10% to 40%, specifically 15%, 20%, 25%, 30%, or 35%.

[0016] In a third aspect, the present invention provides application of the scratch-resistant light-shielding thermal paper protective layer in thermal paper.

[0017] In a fourth aspect, the present invention provides a thermal paper, comprising a thermal paper base paper, a thermal color developing coating and a protective layer, wherein the protective layer is the above-mentioned scratch-resistant light-shielding thermal paper protective layer.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention combines gelatin, cellulose nanofibrils containing lignin, and glycerol, and uses cellulose nanofibrils with long fiber structure, high specific surface area, and good flexibility as reinforcing materials, so that they interpenetrate each other to form a skeleton structure, and have multiple interactions (electrostatic interaction and hydrogen bonding) with gelatin and glycerol uniformly dispersed between the skeleton structures, thereby improving the mechanical strength and toughness of the thermal paper protective layer at the same time, thereby significantly improving the scratch resistance of the thermal paper protective layer. In addition, the various chromophores such as carbonyl, phenolic hydroxyl, conjugated double bond structure, and methoxy provided by lignin in the cellulose nanofibrils are used to give the thermal paper protective layer a good ultraviolet shielding effect, thereby making the thermal paper protective layer have both good light-shielding performance and excellent scratch resistance, thereby significantly improving the service life of the thermal paper. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The AFM image of the cellulose nanofibrils of the present invention and its diameter distribution diagram. DETAILED DESCRIPTION

[0021] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0022] Unless otherwise specified, other materials, reagents, etc. used in the examples can be obtained from commercial sources.

[0023] 1) Porcine skin gelatin was purchased from Beijing Jinming Biotechnology Co., Ltd., where the jelly strength of the porcine skin gelatin was 280 bloom;

[0024] 2) The lignocellulose nanofibril suspension is prepared by the following preparation method:

[0025] S1. Using bleached chemical thermomechanical pulp (purchased from Suou Huichuan Paper Co., Ltd.) as raw material, extracting it with benzene-alcohol according to GB / T2677.6-1994 standard, and immersing the obtained pulp in distilled water to obtain a fiber suspension with a solid content of 2wt%;

[0026] S2. Add the fiber suspension with a solid content of 2wt% in S1 into an ultrafine grinding device for filament separation and brooming treatment. The specific grinding process is: 0μm (5 times), -5μm (5 times), the rotation speed is 1500rpm; -8μm (10 times), the rotation speed is 2000rpm; -10μm (20 times), the rotation speed is 2000rpm; the ground suspension (solid content is 1wt%) is homogenized 20 times by a high-pressure homogenizer at a pressure of 100bar to obtain a lignocellulose nanofibril (LCNF) suspension.

[0027] Example 1

[0028] An embodiment of the scratch-resistant light-shielding thermal paper protective layer of the present invention, the scratch-resistant light-shielding thermal paper protective layer in this embodiment is composed of gelatin (pigskin gelatin), wood cellulose nanofibrils and glycerol in a mass ratio of 10:0.2:1, and its average thickness is 15μm.

[0029] The method for preparing the scratch-resistant light-shielding thermal paper protective layer of this embodiment comprises the following steps:

[0030] Gelatin, cellulose nanofibril suspension, glycerol and water were mixed, stirred at 45°C and 400 rpm for 60 min to obtain a composite solution (the mass fraction of gelatin in the composite solution was 30%), and then the composite solution was coated on the surface of a carrier (supermarket shopping receipt), and dried at 60°C for 24 h to obtain a scratch-resistant and light-shielding thermal paper protective layer.

[0031] Example 2

[0032] An embodiment of the scratch-resistant and light-shielding thermal paper protective layer of the present invention is basically the same as that of Embodiment 1, except that the mass ratio of the gelatin, the wood cellulose nanofibrils and the glycerol is 10:0.15:1.

[0033] The preparation method of the scratch-resistant light-shielding thermal paper protective layer in this embodiment is the same as that in Embodiment 1.

[0034] Example 3

[0035] An embodiment of the scratch-resistant and light-shielding thermal paper protective layer of the present invention is basically the same as that of Embodiment 1, except that the mass ratio of the gelatin, the wood cellulose nanofibrils and the glycerol is 10:0.1:1.

[0036] The preparation method of the scratch-resistant light-shielding thermal paper protective layer in this embodiment is the same as that in Embodiment 1.

[0037] Example 4

[0038] An embodiment of the scratch-resistant light-shielding thermal paper protective layer of the present invention is basically the same as that of Embodiment 1, except that the mass ratio of the gelatin, wood cellulose nanofibrils and glycerol is 10:0.05:1.

[0039] The preparation method of the scratch-resistant light-shielding thermal paper protective layer in this embodiment is the same as that in Embodiment 1.

[0040] Example 5

[0041] An embodiment of the scratch-resistant and light-shielding thermal paper protective layer of the present invention is basically the same as that of Embodiment 1, except that the mass ratio of the gelatin (pigskin gelatin), wood cellulose nanofibrils and glycerol is 10:0.2:5.

[0042] The preparation method of the scratch-resistant light-shielding thermal paper protective layer in this embodiment is the same as that in Embodiment 1.

[0043] Comparative Example 1

[0044] A comparative example of the scratch-resistant light-shielding thermal paper protective layer of the present invention, wherein the scratch-resistant light-shielding thermal paper protective layer of the comparative example is composed of gelatin (pigskin gelatin) and glycerin in a mass ratio of 10:1, and has an average thickness of 15 μm.

[0045] The method for preparing the scratch-resistant light-shielding thermal paper protective layer of this comparative example comprises the following steps:

[0046] Gelatin, glycerin and water were mixed, stirred at 45°C and 400 rpm for 60 min to obtain a composite solution (the mass fraction of gelatin in the composite solution was 30%), and then the composite solution was coated on the surface of a carrier (supermarket shopping receipt), and dried at 60°C for 24 h to obtain a scratch-resistant and light-shielding thermal paper protective layer.

[0047] Comparative Example 2

[0048] A comparative example of the scratch-resistant light-shielding thermal paper protective layer of the present invention, the scratch-resistant light-shielding thermal paper protective layer in this comparative example is wood cellulose nanofibrils, and the average thickness thereof is 15 μm.

[0049] The method for preparing the scratch-resistant light-shielding thermal paper protective layer of this comparative example comprises the following steps:

[0050] The lignocellulose nanofibril suspension was coated on the surface of a carrier (supermarket shopping receipt) by a spraying method, and dried at 60° C. for 24 h to obtain a scratch-resistant, light-shielding thermal paper protective layer.

[0051] Comparative Example 3

[0052] A comparative example of the scratch-resistant light-shielding thermal paper protective layer of the present invention, wherein the scratch-resistant light-shielding thermal paper protective layer of the comparative example is composed of gelatin (pigskin gelatin), ethyl cellulose and glycerol in a mass ratio of 10:0.05:1, and has an average thickness of 15 μm.

[0053] The method for preparing the scratch-resistant light-shielding thermal paper protective layer of this embodiment comprises the following steps:

[0054] Gelatin, ethyl cellulose, glycerin and water were mixed, stirred at 45°C and 400 rpm for 60 min to obtain a composite solution (the mass fraction of gelatin in the composite solution was 30%), and then the composite solution was coated on the surface of a carrier (supermarket shopping receipt), and dried at 60°C for 24 h to obtain a scratch-resistant and light-shielding thermal paper protective layer.

[0055] Performance Testing

[0056] 1) Light-shielding performance test

[0057] The composite solutions (i.e., the coatings for the scratch-resistant light-shielding thermal paper protective layer) in each embodiment and comparative example were poured into a polytetrafluoroethylene mold by a cast film method, and after drying at room temperature to form a film (the average thickness of the film was 15 μm), the shielding effect of the ultraviolet light was tested; the transmittance of the film was detected by an ultraviolet spectrophotometer (UV-2600, where the wavelength was 400 nm and the distance between the light source and the sample was a standard optical path of 10 mm). The lower the transmittance, the better the light-shielding performance.

[0058] 2) Scratch resistance test

[0059] Since the scratch-resistant light-shielding thermal paper protective layer in each embodiment and comparative example is prepared with a supermarket shopping receipt as the carrier, it can be directly used as a test sample for testing. After manually rubbing for 20 minutes with a weight of 500g and sandpaper (320 mesh) stuck on the bottom, the L, a, and b values ​​of the rubbed area and the unrubbed area of ​​the scratch-resistant light-shielding thermal paper protective layer are respectively detected by a colorimeter, and then the color difference between the two is calculated. The smaller the ΔE, the closer the color of the rubbed area is to that of the unrubbed area, indicating better scratch resistance.

[0060] Table 1 Performance of the scratch-resistant light-shielding thermal paper protective layer in each embodiment and comparative example

[0061]

[0062]

[0063] According to the data in Table 1, the light transmittance of the scratch-resistant light-shielding thermal paper protective layer in Examples 1 to 5 is less than 7.5%, and ΔE is less than or equal to 5.3, indicating that the thermal paper protective layer of the present invention has good light-shielding performance and excellent scratch-resistant performance. It can be seen from Examples 1 to 4 that with the increase of the content of wood cellulose nanofibrils in the thermal paper protective layer, the light transmittance is found to gradually decrease, indicating that the wood cellulose nanofibrils are beneficial to enhancing the light-shielding performance of the thermal paper protective layer, and the enhancement effect is positively correlated with its content; at the same time, it is found that ΔE shows a trend of first decreasing and then increasing, indicating that the scratch resistance of the thermal paper protective layer is first enhanced and then weakened with the increase of the content of wood cellulose nanofibrils.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A scratch-resistant light-shielding thermal paper protective layer, characterized in that: The scratch-resistant light-shielding thermal paper protective layer is mainly composed of gelatin, cellulose nanofibrils and glycerol; the cellulose nanofibrils contain lignin.

2. The scratch-resistant light-shielding thermal paper protective layer according to claim 1, characterized in that: The mass ratio of the gelatin to the cellulose nanofibrils is 10:(0.02-0.2).

3. The scratch-resistant light-shielding thermal paper protective layer according to claim 1, characterized in that: The mass ratio of the gelatin to glycerol is 10:(1-5).

4. The scratch-resistant light-shielding thermal paper protective layer according to claim 1, characterized in that: The average diameter of the cellulose nanofibrils is 40 to 80 nm.

5. The scratch-resistant light-shielding thermal paper protective layer according to claim 1, characterized in that: The gelatin includes at least one of pig skin gelatin, fish skin gelatin, cow skin gelatin and cow bone gelatin.

6. The scratch-resistant light-shielding thermal paper protective layer according to claim 1, characterized in that: The cellulose nanofibrils are prepared by the following preparation method: using bleached chemical thermomechanical pulp as raw material, extracting it with benzene-alcohol according to GB / T2677.6-1994 standard, and subjecting the obtained pulp to filament separation and broom treatment to obtain cellulose nanofibrils.

7. The method for preparing the scratch-resistant light-shielding thermal paper protective layer according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: uniformly mixing gelatin, cellulose nanofibrils, glycerin and water to obtain a composite solution, and then uniformly coating the composite solution on the surface of a carrier and drying the composite solution to obtain a scratch-resistant light-shielding thermal paper protective layer.

8. The preparation method according to claim 7, characterized in that: The mass fraction of gelatin in the composite solution is 10% to 40%.

9. Use of the scratch-resistant light-shielding thermal paper protective layer according to any one of claims 1 to 6 in thermal paper.

10. A thermal paper, comprising a thermal paper base, a thermal color developing coating and a protective layer, characterized in that: The protective layer is the scratch-resistant light-shielding thermal paper protective layer according to any one of claims 1 to 6.

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