A digital heat transfer paper with a low reject rate and its preparation method

Abstract

The present invention discloses a digital heat transfer paper with a low rejection rate and a preparation method thereof. The digital heat transfer paper is finally obtained through multiple processes including first preparing a surface coating sizing agent, then pulping, beating, sizing, forming on the wire, surface sizing, and coating. A sizing agent is modified by a grafting agent to obtain a modified sizing agent, and then the modified sizing agent is applied to the digital heat transfer paper. Compared with the prior art, the digital heat transfer paper prepared by the present invention has advantages such as good glossiness and better hydrophobicity.

Description

Technical Field

[0001] The present invention relates to the field of special paper production, and particularly to a digital thermal transfer paper with a low rejection rate and a preparation method thereof. Background Art

[0002] Digital thermal transfer technology is a process of printing images or texts on special transfer papers through digital devices (such as inkjet printers, laser printers, etc.), and then transferring the images to other materials (such as fabrics, ceramics, metals, plastics, etc.) by means of hot pressing or heat sublimation. This technology not only achieves high-precision and high-resolution image transfer, but also can retain the colors and details of the original image, greatly enriching the selection and application scope of printing materials.

[0003] As the core carrier of this technology, digital thermal transfer paper has a series of unique properties and characteristics. Firstly, it has good ink absorbency and color reducibility, which can ensure that the printed images are vivid in color and distinct in levels. Secondly, the surface of the digital thermal transfer paper is specially treated, having excellent adhesion and abrasion resistance, so that the transferred images are not easy to fall off or fade. In addition, it also has good thermal stability and dimensional stability, and can maintain a stable shape and size during the thermal transfer process, ensuring the accuracy and consistency of the transfer effect.

[0004] With the continuous progress of technology and the continuous expansion of the market, the properties and applications of digital thermal transfer paper are also constantly innovating and developing. For example, some new types of digital thermal transfer paper have higher weather resistance and water resistance, and can maintain the vividness and stability of colors in outdoor environments for a long time; some digital thermal transfer papers with special textures and textures also provide users with more choices and space for personalized customization.

[0005] CN106758536A discloses a production method of a lightly coated digital thermal transfer paper, including the preparation of internal sizing liquid, surface sizing liquid, preparation of surface coating liquid, pulping and disintegration, beating - sizing process, forming on the net, surface sizing, and coating steps. The invention provides a production method of a lightly coated digital thermal transfer paper with good ink compatibility, fast drying speed, high transfer rate, and no curling. This production method organically combines the production of the coating with the production of the base paper and completes the production at one time. However, the lightly coated digital thermal transfer paper prepared by this method is prone to problems such as brittle paper quality and high rejection rate.

[0006] CN111636242A discloses a micro-coated sublimation thermal transfer paper and a preparation method thereof, including a base paper and an ink-absorbing coating coated on the base paper. The coating used for preparing the ink-absorbing coating is in parts by weight, and the raw materials include: 0.6 - 2 parts of nano-silica modified by polyepichlorohydrin-dimethylamine, 6 - 16 parts of polyvinyl alcohol modified by acrylamide, 100 - 200 parts of water, and the coating amount of the coating is 3 - 5g / m2 The invention modifies the binder and pigment in the coating, and utilizes the reaction between the binder and the pigment to connect the pigment and the binder by chemical bonds, so as to prevent the pigment from falling off from the binder when the coating is thin and affecting the ink absorption amount; moreover, the modified binder and pigment can not only accelerate the ink absorption, but also fix the ink in the coating to prevent the ink from penetrating into the paper surface. However, the thermal transfer paper prepared by this method is prone to yellowing after being stored for a long time. Summary of the Invention

[0007] In view of the above defects of the prior art, the technical problem to be solved by the present invention is to reduce the rejection rate of digital thermal transfer paper, improve the water resistance of digital thermal transfer paper, make the digital thermal transfer paper more stable after sizing liquid is applied, be able to be placed for a long time, and at the same time improve the glossiness of the paper.

[0008] To achieve the above object, the present invention provides a preparation method of digital thermal transfer paper with a low rejection rate, which includes the following steps:

[0009] Step 1: Preparation of surface sizing liquid: Mix 20 - 30 parts by weight of water, 1 - 5 parts by weight of silicon dioxide and 2 - 7 parts by weight of sodium carboxymethylcellulose to obtain the surface sizing liquid;

[0010] Step 2: Pulp disintegration and beating: Add 20 - 50 parts by weight of softwood pulp to 3 - 7 parts by weight of water, disintegrate for 10 - 20 min, and then add 1 - 5 parts by weight of water to beat into a mixed pulp with a beating degree of 50 - 300 SR;

[0011] Step 3: Pulp blending: Mix 8 - 12 parts by weight of the mixed pulp, 20 - 25 parts by weight of internal sizing liquid and 1 - 5 parts by weight of wet strength agent evenly to obtain a mixed pulp slurry;

[0012] Step 4: Forming on the wire: Dilute 33 - 50 parts by weight of the mixed pulp slurry with 2 - 10 parts of water, form on the wire, and at the same time add 0.3 - 1 part by weight of cationic polyacrylamide and 2 - 6 parts by weight of talc powder; add 4 - 8 parts by weight of silica sol to the low - consistency steady - pulp chest; add 5 - 15 parts by weight of modified sizing agent to the outlet pipe of the low - consistency steady - pulp chest, and then obtain the paper sheet through forming on the wire, pressing dehydration and drying;

[0013] Step 5: Surface sizing and coating: Apply the surface sizing liquid on the front side of the paper sheet through a metering rod in a film - transfer sizing machine, apply the surface coating liquid prepared in Step 1 on the back side of the paper sheet through a metering rod in the film - transfer sizing machine, then dry through a heat converter, an oven and a dryer cylinder, and then obtain the finished product through calendering and winding and slitting.

[0014] Preferably, the coating amount of the coating liquid in Step 1 is 2 - 10 g / m 2; The particle size of silicon dioxide is 2 - 10 mm, and the pore volume is 1.5 - 3.0 cm 3 / g.

[0015] Preferably, the preparation method of the surface sizing solution comprises the following steps: Mix 150 - 200 parts by weight of water and 10 - 20 parts by weight of cationic starch at 300 - 500 rpm for 10 - 20 min, heat up to 85 - 90 °C, and keep warm for 15 - 20 min; Add 1 - 3 parts by weight of a styrene-based copolymer surface sizing agent at 85 - 90 °C and stir and mix at 300 - 500 rpm for 10 - 30 min, control the temperature at 50 - 65 °C and keep warm for 10 - 15 min, then cool to room temperature to obtain the surface sizing solution.

[0016] Preferably, the preparation method of the internal sizing solution is: Mix 100 - 150 parts by weight of water and 8 - 15 parts by weight of cationic starch at 300 - 500 rpm for 20 - 30 min, heat up to 85 - 90 °C, keep warm for 15 - 20 min, and then cool to room temperature with cold air to obtain the internal sizing solution.

[0017] Preferably, the preparation method of the modified sizing agent comprises the following steps, in parts by weight:

[0018] S1: Add 15 - 35 parts of N,N-dimethylformamide, 2 - 5 parts of sizing agent, and 1 - 3 parts of sodium hydroxide, stir and mix at room temperature for 1 - 4 h, then add 0.001 - 1 part of 4-dimethylaminopyridine and 1 - 6 parts of grafting agent, and keep stirring at 30 - 75 °C for 2 - 5 h;

[0019] S2: Filter the substance obtained in S1 to obtain a filter cake, wash it 1 - 3 times with a 70 - 90 wt% ethanol aqueous solution, dry it at 50 - 65 °C for 1 - 4 h, and cool to room temperature to obtain the modified sizing agent.

[0020] Preferably, the sizing agent is any one of hydrogenated rosin glyceride, sodium alginate, and carboxymethyl chitosan.

[0021] Preferably, the grafting agent is any one of methyl malonate, 3-methoxy-2-methyl-3-oxopropionic acid, and 3-[(tert-butoxycarbonyl)thio]propionic acid.

[0022] More preferably, the grafting agent is 3-[(tert-butoxycarbonyl)thio]propionic acid.

[0023] Preferably, in the fifth step, the metering rod is 20 - 50 S, the surface sizing solution is applied on the front side, its viscosity is 10 - 40 mPa·s, and the solid content is 8 - 15%; the sizing solution is coated on the back side, its viscosity is 350 - 500 mPa·s, and the solid content is 30 - 50%.

[0024] A digital heat transfer paper with a low reject rate is prepared by the above method.

[0025] In this formulation, the raw materials and their functions are as follows:

[0026] Cationic starch mainly plays the role of internal sizing. By forming a thin film inside the pulp, it enhances the interfiber bonding force of the paper, improves the water resistance of the paper, and thus reduces the reject rate.

[0027] Silica mainly plays the role of surface coating strengthening agent. By mixing it with sodium carboxymethyl cellulose in a certain proportion to prepare a coating sizing solution and coating it on the reverse side of the paper sheet, silica can significantly improve the surface strength and abrasion resistance of the paper.

[0028] Sodium carboxymethyl cellulose mainly plays the role of bonding and film-forming of the coating sizing solution. It is mixed with silica in a certain proportion to form a coating sizing solution coated on the reverse side of the paper sheet. As a water-soluble polymer, sodium carboxymethyl cellulose has good adhesiveness, film-forming property and water retention property, and can effectively enhance the surface strength and smoothness of the paper.

[0029] Wet strength agent: The wet strength agent mainly plays the role of enhancing the wet strength of the paper. The wet strength agent can form chemical bonds or hydrogen bonds with the paper fibers, thus significantly improving the interfiber bonding force in the wet state of the paper and preventing the paper from cracking or deforming when subjected to external forces.

[0030] Cationic polyacrylamide mainly plays the role of retention and drainage aid. It can adsorb and bridge with particles such as fibers and fillers in the pulp to form larger flocs, thereby accelerating the drainage of water in the pulp, increasing the drainage speed, and contributing to the rapid formation and dehydration of the paper sheet.

[0031] Talc powder, as an inorganic filler, can increase the whiteness and opacity of the paper, making the printed image clearer and more vivid. Secondly, talc powder has good smoothness and dispersibility, can fill the gaps between paper fibers, improve the flatness of the paper surface, and help reduce the penetration and diffusion of ink during printing, thus maintaining the fineness and edge sharpness of the printed image.

[0032] The sizing agent contains hydroxyl functional groups. By undergoing chemical reactions such as esterification and crosslinking with the carboxylic acid functional groups in the grafting agent, the molecular structure and properties of the sizing agent are changed. This modification can make the modified sizing agent better combine with paper fibers, improve the sizing effect and water resistance of the paper, and also contribute to improving other physical properties of the paper, such as strength, smoothness and gloss.

[0033] The grafting agent mainly plays a key role in promoting the chemical modification reaction, thereby enhancing the performance of the sizing agent. Specifically, the grafting agent can undergo an esterification reaction with the active sites on the molecular chain of the sizing agent, introducing new functional groups or chain segments to form a graft copolymer. The grafting agent contains sulfur atoms with a high refractive index, which can improve the gloss of digital thermal transfer paper.

[0034] Advantages of the present invention:

[0035] Compared with the prior art, by using a grafting agent containing sulfur atoms with a high refractive index and a reactive carboxylic anhydride or carboxylic acid, an esterification reaction occurs with the sizing agent containing a hydroxyl functional group under wet conditions, thereby introducing sulfur atoms into the sizing agent to synthesize a modified sizing agent. The modified sizing agent can form an ester bond with the hydroxyl groups of the paper fibers, improving the sizing performance of the paper. At the same time, the high refractive index of the sulfur atoms improves the gloss of digital thermal transfer paper. Detailed implementation methods

[0036] Use the parameters and sources of specific chemical substances.

[0037] Silica, 300 mesh.

[0038] Wet strength agent, model: Kymene TM 557, brand: Solenis.

[0039] Cationic polyacrylamide, viscosity: 5800 - 6200 mPa·s, ionic degree: 30%, sourced from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0040] Silica sol, viscosity (25°C, ≤7.0 mPa·s), diameter 10 - 20 nm, Yantai Hengxin Chemical Technology Co., Ltd.

[0041] Cationic starch, model: CS - YLO3M, white powder, fineness (passing rate through 100 - mesh sieve) ≥95%, viscosity (6%, 95°C, 1 h, NDJ - 8S) ≤2000 mPa·s, degree of substitution 0.015 - 0.130, sourced from Guangdong Hongxin Biotechnology Co., Ltd.

[0042] Styrene - based copolymer surface sizing agent, model: JH - 611, viscosity (<50 mPa·s (25°C)), pH value: 2 - 5, solid content (30% ± 1%), Qingzhou Jinhao New Materials Co., Ltd.

[0043] Talc powder, 400 mesh.

[0044] Coniferous wood pulp, using the cultural paper pulp (BPW pulp) from Asia Symbol, belonging to bleached kraft chemical pulp, whiteness ≥89%, dirt content ≤2.0 mm 2 / m 2 .

[0045] 3-Methoxy-2-methyl-3-oxopropanoic acid, CAS No.: 111103-66-3.

[0046] 3-[(tert-Butoxycarbonyl)thio]propanoic acid, CAS No.: 138754-12-8.

[0047]

[0048] Carboxymethyl chitosan, viscosity 10-100 mPa·s, degree of carboxylation ≥80%, sourced from Shanghai Maokang Biotechnology Co., Ltd.

[0049] Hydrogenated rosin glyceride, product number: xyh001, Hubei Xinyuhong Biomedical Technology Co., Ltd.

[0050] The starch is wheat starch, 300 mesh.

[0051] Example 1

[0052] A method for preparing a digital heat transfer paper with a low rejection rate, comprising the following steps:

[0053] Step 1: Preparation of the surface coating sizing solution: Add 1 kg of silica and 4 kg of sodium carboxymethyl cellulose to 20 kg of water, start the disperser and mix at 3000 rpm for 30 min to obtain the surface coating sizing solution, and set aside;

[0054] Step 2: Pulp disintegration and beating: Add 3 kg of water to a hydraulic pulper, then add 4 kg of softwood pulp. After disintegrating for 15 min, add 2 kg of water and beat to obtain a mixed pulp with a beating degree of 200 SR;

[0055] Step 3: Pulp preparation: Pump the mixed pulp prepared in Step 2 into the batching tank, add 20 kg of internal sizing solution and 5 kg of wet strength agent to the batching tank and mix at 1000 rpm for 30 min to obtain the stock;

[0056] Step 4: Sheet forming: Add 10 kg of water to 50 kg of the stock prepared in Step 3, screen and purify it through a filling pump, a desander, and a pressure screen, enter the low-consistency headbox and then form a sheet; at the same time, add 0.3 kg of 0.03 wt% cationic polyacrylamide and 4 kg of talc at the inlet of the filling pump; add 4 kg of silica sol in the low-consistency headbox; add 8 kg of modified sizing agent in the outlet pipe of the low-consistency headbox; after sheet forming, press and dehydrate, and dry to obtain the paper sheet;

[0057] Step 5: Surface sizing and coating: Apply the surface sizing solution onto the front side of the paper sheet through a metering rod in a film transfer sizing machine, and apply the surface coating sizing solution onto the back side of the paper sheet through a 40s metering rod in the film transfer sizing machine. Then, dry it through a heat converter, an oven and a dryer cylinder, and finally make it into a finished product through calendering and winding and slitting.

[0058] Among them, the preparation method of the internal sizing solution is as follows: Stir and mix 100 kg of water and 8 kg of cationic starch at 300 rpm for 20 min, heat up to 90 °C, keep warm for 15 min, and then cool to 25 °C to obtain the internal sizing solution.

[0059] The preparation method of the surface sizing solution is as follows: Stir and mix 200 kg of water and 20 kg of cationic starch at 300 rpm for 20 min, heat up to 90 °C, and keep warm for 15 min; add 1 kg of styrene-based copolymer surface sizing agent at 90 °C and stir and mix at 300 rpm for 30 min, control the temperature at 65 °C and keep warm for 10 min, and then cool to 25 °C to obtain the surface sizing solution.

[0060] Among them, the preparation method of the modified sizing agent includes the following steps:

[0061] S1: Add 20 kg of N,N-dimethylformamide, 5 kg of carboxymethyl chitosan and 2 kg of sodium hydroxide, stir and mix at 25 °C for 2 h, then add 3 kg of 4-dimethylaminopyridine and 5 kg of 3-[(tert-butoxycarbonyl)thio]propionic acid, and keep stirring at 65 °C for 3 h;

[0062] S2: Filter the substance obtained in step one to obtain a filter cake, wash it twice with 75 wt% ethanol aqueous solution; dry it at 65 °C for 2 h, and cool it to room temperature to obtain the modified sizing agent.

[0063] Example 2

[0064] The difference between Example 2 and Example 1 of this application is that the carboxymethyl chitosan in Example 1 is replaced by hydrogenated rosin glyceride.

[0065] Example 3

[0066] The difference between Example 3 and Example 1 of this application is that the carboxymethyl chitosan in Example 1 is replaced by sodium alginate.

[0067] Example 4

[0068] The difference between Example 4 and Example 1 of this application is that the 3-[(tert-butoxycarbonyl)thio]propionic acid in Example 1 is replaced by methyl malonate.

[0069] Example 5

[0070] The difference between Example 5 and Example 1 of this application is that 3-[(tert-butoxycarbonyl)thio]propionic acid in Example 1 is replaced by 3-methoxy-2-methyl-3-oxopropionic acid.

[0071] Comparative Example 1

[0072] The difference between Comparative Example 1 and Example 1 of this application is that carboxymethyl chitosan in Example 1 is replaced by starch.

[0073] Comparative Example 2

[0074] A preparation method of digital thermal transfer paper with low rejection rate, comprising the following steps:

[0075] Step 1: Preparation of surface coating sizing solution: Add 1 kg of silica and 4 kg of sodium carboxymethyl cellulose to 20 kg of water, start the disperser and mix at 3000 rpm for 30 min to obtain the surface coating sizing solution, and set aside;

[0076] Step 2: Pulp disintegration and beating: Add 3 kg of water to the hydrapulper, then add 4 kg of softwood pulp, after disintegrating for 15 min, add 2 kg of water, and beat to obtain a mixed pulp with a beating degree of 200 SR;

[0077] Step 3: Pulp blending: Pump the mixed pulp beaten in Step 2 into the batching tank, add 20 kg of internal sizing solution for pulp and 5 kg of PPE wet strength agent into the batching tank, and mix at 1000 rpm for 30 min to obtain the stock;

[0078] Step 4: Sheet forming on the wire: Add 3 kg of water to the stock prepared in Step 3, pass through the pulp pump, desander, pressure screen for screening and purification, enter the low-consistency stuff box and then form on the wire, and add cationic polyacrylamide with a concentration of 0.03% and a dosage of 0.3 kg per ton of paper and 150 kg of talc powder with a concentration of 30% at the inlet of the pulp pump; Add 4 kg of silica sol to the low-consistency stuff box; Add 15 kg of carboxymethyl chitosan to the outlet pipe of the low-consistency stuff box, and then obtain the paper sheet through forming on the wire, pressing dehydration and drying;

[0079] Step 5: Surface sizing and coating: Apply the surface sizing solution on the front side of the paper sheet through a metering rod in the film transfer sizing machine, apply the surface coating sizing solution on the back side of the paper sheet through a 40 s metering rod in the film transfer sizing machine, then dry through a heat converter, oven and drying cylinder, and then make the finished product through calendering and winding and slitting.

[0080] Among them, the preparation method of the surface coating sizing solution is: Add 1 kg of silica and 4 kg of sodium carboxymethyl cellulose to 20 kg of water, start the disperser and mix at 3000 rpm for 30 min to obtain the surface coating sizing solution.

[0081] The preparation method of the surface sizing liquid is as follows: Add 200 kg of water and 20 kg of cationic starch, stir at 300 rpm for 20 min, heat up to 90 °C, keep warm for 15 min, mix 1 kg of styrene-based copolymer surface sizing agent at 300 rpm for 30 min, control the temperature at 65 °C and keep it for standby to obtain the surface sizing liquid.

[0082] Test Example 1

[0083] The coating hydrophobicity (g / ㎡) is detected according to the standard of GB / T 1540-2002 "Determination of water absorbency of paper and board (Köbe method)". The test results are shown in Table 1:

[0084] Table 1: Test of coating hydrophobic effect

[0085]

[0086]

[0087] Test Example 2

[0088] The gloss of the paper is tested according to GB / T8941-2013 "Determination of specular gloss of paper and board". The test results are shown in Table 2:

[0089] Table 2: Test of paper gloss

[0090] Experimental group Glossiness / % Example 1 57.5 Example 2 50.2 Example 3 48.9 Example 4 49.5 Example 5 47.8 Comparative Example 1 38.7 Comparative Example 2 40.6

[0091] From the results of various test data in Examples 1-5 and Comparative Examples 1-2, it can be found that the gloss and hydrophobic effect of the digital thermal transfer paper prepared in Example 1 are the best.

[0092] The test principle of the Köbe method is based on the amount of water absorbed by the surface of paper and board under a specific pressure within a certain time to measure its water absorbency. Specifically, a circular specimen is placed in the annular clamp of a Köbe absorbency tester, a water absorption pad (usually made of qualitative filter paper or other materials with good water absorbency) is placed above the specimen, and then a certain pressure is applied to make the water be absorbed by the specimen through the water absorption pad within the specified time. Finally, the Köbe water absorbency value is calculated according to the amount of water absorbed by the specimen.

[0093] Comparing the tabular data in Examples 1 - 3 and Comparative Example 2, it is found that the hydrophobic effect of the digital thermal transfer paper prepared in Example 1 is better. The possible reason is the use of different grafting agents. Since the sizing agent has unsatisfactory fluidity and transparency after gelatinization and is prone to becoming turbid and forming gels after cooling, it is generally not directly used as a surface sizing agent. However, the hydroxyl functional groups contained in the sizing agent can undergo an esterification reaction with the carboxylic acid functional groups contained in the grafting agent, so that other functional groups contained in the grafting agent are introduced into the sizing agent, obtaining a modified sizing agent. Applying the modified sizing agent to the digital thermal transfer paper is beneficial to improving the tensile strength and folding endurance of the paper. The hydroxyl groups on the surface of the sizing agent are the reason for its good hydrophilicity. After being modified by the grafting agent, the hydroxyl groups are transformed into hydrophobic ester groups, so the hydrophobicity is better. Comparing the test data in Example 1 and Comparative Example 2, it can be found that no grafting agent was added in Comparative Example 2, and the sizing agent was not modified to introduce hydrophobic groups, thus resulting in a worse hydrophobic effect of the prepared modified sizing agent.

[0094] Comparing the tabular data of Example 1, Example 4, and Example 5, it is found that the digital thermal transfer paper prepared in Example 1 has the best glossiness. This is mainly due to the sulfur element in 3 - [(tert - butoxycarbonyl)thio]propanoic acid. Sulfur atoms have a relatively high refractive index. After grafting, they can significantly enhance the reflection of light on the paper surface, making the glossiness increase significantly. At the same time, the carboxylic anhydride functional group in the grafting agent undergoes an esterification reaction with the hydroxyl group in the sizing agent, forming stable covalent bonds, enhancing the binding force between the sizing agent and the paper fibers, further improving the smoothness of the paper surface, and thus enhancing the gloss. In addition, the hydrophobicity brought by the alkoxy group and sulfur group in the grafting agent reduces the interference of moisture on the surface, making the paper surface smoother and more uniform, indirectly enhancing the gloss performance. In contrast, Example 4 and 5 only contain carboxylic anhydride functional groups and lack sulfur atoms, so the papers prepared therefrom have poorer glossiness.

[0095] In summary, the present invention achieves a low scrap rate through multiple key technical steps. First, a modified sizing agent is used. The sizing agent undergoes a chemical reaction with the carboxylic acid functional groups in the grafting agent to form a modified sizing agent, enhancing the sizing effect of the paper and endowing the paper with better water resistance and strength. Second, the silica in the coating solution is mixed with sodium carboxymethylcellulose, enhancing the strength and abrasion resistance of the paper surface and reducing the damage to the paper during processing. The application of the wet - strength agent further improves the wet strength of the paper, ensuring that the paper is not easily broken or deformed in the wet state and reducing the scrap caused by humidity changes. In addition, by adding talcum powder and cationic polyacrylamide during the forming process, the smoothness and surface hydrophobicity of the paper are enhanced, ensuring the stability of the paper during the printing process and reducing the generation of scraps. Combining these technical means, the present invention greatly improves the quality stability of the digital thermal transfer paper and significantly reduces the scrap rate during the production process.

Claims

1. A method for preparing digital thermal transfer paper with low waste rate, characterized in that: The steps include: Step 1, preparation of surface coating glue: 20-30 parts by weight of water, 1-5 parts by weight of silicon dioxide and 2-7 parts by weight of sodium carboxymethyl cellulose are mixed to obtain a surface coating glue; Step 2, pulp crushing and beating: add 20-50 parts by weight of softwood pulp to 3-7 parts by weight of water, crush for 10-20 minutes, and then add 1-5 parts by weight of water to make a mixed pulp with a beating degree of 50-300SR; Step 3, slurry preparation: 8-12 parts by weight of mixed slurry, 20-25 parts by weight of slurry sizing liquid, and 1-5 parts by weight of wet strength agent are mixed evenly to obtain a mixed slurry; Step 4, forming on the screen: dilute 33-50 parts by weight of the mixed slurry with 2-10 parts of water, form on the screen, and add 0.3-1 parts by weight of cationic polyacrylamide and 2-6 parts by weight of talcum powder; add 4-8 parts by weight of silica sol in the low-concentration stabilizing box; add 5-15 parts by weight of modified sizing agent in the outlet pipe of the low-concentration stabilizing box, and then form on the screen, squeeze and dehydrate, and dry to obtain paper sheets; Step 5, surface sizing and coating: the surface sizing liquid is applied to the front side of the paper sheet through a metering rod in a film transfer sizing machine, and the surface coating glue liquid prepared in step 1 is applied to the back side of the paper sheet through a metering rod in a film transfer sizing machine, and then dried through a heat exchanger, an oven and a drying cylinder, and then calendered, coiled and slit to form a finished product; The preparation method of the modified sizing agent comprises the following steps, measured in parts by weight: S1: Add 15-35 parts of N,N-dimethylformamide, 2-5 parts of sizing agent and 1-3 parts of sodium hydroxide, stir and mix at room temperature for 1-4 hours, then add 0.001-1 parts of 4-dimethylaminopyridine and 1-6 parts of grafting agent, keep stirring at 30-75°C for 2-5 hours; S2: filtering the substance obtained in step S1 to obtain a filter cake, washing it with a 70-90 wt% ethanol aqueous solution for 1-3 times, drying it at 50-65° C. for 1-4 h, and cooling it to room temperature to obtain a modified sizing agent; The sizing agent is any one of sodium alginate and carboxymethyl chitosan; The grafting agent is 3-[(tert-butoxycarbonyl)sulfanyl]propionic acid.

2. The method for preparing digital thermal transfer paper with low waste rate as claimed in claim 1, characterized in that: The coating amount of the adhesive in step 1 is 2-10 g / m 2 ; Silica particle size is 2-10mm, pore volume is 1.5-3.0cm 3 / g.

3. The method for preparing digital thermal transfer paper with low waste rate as claimed in claim 1, characterized in that: The preparation method of the surface sizing solution comprises the following steps: stirring and mixing 150-200 parts by weight of water and 10-20 parts by weight of cationic starch at 300-500 rpm for 10-20 minutes, heating to 85-90° C., and keeping the temperature for 15-20 minutes; adding 1-3 parts by weight of a surface sizing agent containing a styrene ester copolymer at 85-90° C., stirring and mixing at 300-500 rpm for 10-30 minutes, controlling the temperature at 50-65° C. and keeping the temperature for 10-15 minutes, and then cooling to room temperature to obtain the surface sizing solution.

4. The method for preparing digital thermal transfer paper with low waste rate according to claim 1, characterized in that: The preparation method of the slurry sizing solution is: 100-150 parts by weight of water and 8-15 parts by weight of cationic starch are stirred and mixed at 300-500 rpm for 20-30 minutes, heated to 85-90° C., kept warm for 15-20 minutes, and then cooled to room temperature to obtain the slurry sizing solution.

5. The method for preparing digital thermal transfer paper with low waste rate as claimed in claim 1, characterized in that: In the step 5, the metering rod is 20-50S, the surface glue liquid is applied on the front side, the viscosity of which is 10-40mPa.s and the solid content is 8-15%; the back side is coated with a coating glue liquid, the viscosity of which is 350-500mPa.s and the solid content is 30-50%.

6. A digital thermal transfer paper with low waste rate, characterized in that: The method is prepared by any one of claims 1 to 5.

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