An efficient production method for digital heat transfer paper

Abstract

The present invention discloses an efficient production method for digital thermal transfer paper, belonging to the field of papermaking technology. This method mixes modified starch with water and heats them to form a sizing solution; prepares a surface sizing solution and a coating solution by mixing styrene-acrylic surface sizing agent with rosin size, and light calcium carbonate with sodium carboxymethylcellulose respectively; the pulp is disintegrated, diluted and beaten to form a mixed pulp with appropriate beating degree; the internal sizing solution and PPE wet strength agent are added to the mixed pulp, and after the pulp is screened and purified by a pulp pumping pump, a desander and a pressure screen, it is formed on the wire, and at the same time, additives such as polyethyleneimine, calcium silicate and silica sol are added. After the paper page is pressed for dehydration, surface sized and dried, a digital thermal transfer paper with excellent tensile strength and folding endurance is finally obtained. Compared with the prior art, the method of the present invention not only improves the production efficiency, but also ensures the printing quality and mechanical properties of the digital thermal transfer paper, meeting the market demand for high-performance transfer paper.

Description

Technical Field

[0001] The present invention relates to the technical field of papermaking, and in particular to an efficient production method for digital thermal transfer paper. Background Art

[0002] With the rapid development of digital printing technology, digital thermal transfer paper, as a special printing material, has an increasing market demand. Digital thermal transfer paper can transfer digital images to various substrates through thermal transfer technology, such as clothing, ceramics, metals, etc., and is widely used in personalized customized products. However, there are some limitations in the traditional production methods of digital thermal transfer paper, such as low production efficiency, unstable paper properties, unqualified tensile strength and folding endurance, etc.

[0003] Chinese Patent CN106758536A discloses a production method for lightly coated digital thermal transfer paper, which includes steps such as preparation of internal sizing solution, preparation of surface sizing solution, preparation of surface coating solution, pulping and disintegration, beating - sizing process, forming on the wire, surface sizing, coating, etc. The invention provides a production method for lightly coated digital thermal transfer paper with good ink compatibility, fast drying speed, high transfer rate, and non - curling. This production method organically combines the production of the coating and the production of the base paper and completes the production at one time. However, the tensile strength and folding endurance of the lightly coated digital thermal transfer paper prepared by this invention are poor, which limits its use in some application scenarios. Summary of the Invention

[0004] Aiming at the defects of the prior art, the present invention aims to provide an efficient production method for digital thermal transfer paper. By optimizing the selection of raw materials, improving the preparation processes of sizing solution and coating solution, and precisely controlling the key parameters in the production process, the quality and production efficiency of the paper are improved, and at the same time, it is ensured that the final product has good printing suitability and mechanical properties.

[0005] In order to achieve the above - mentioned invention purpose, the present invention adopts the following technical solutions:

[0006] An efficient production method for digital thermal transfer paper is as follows, by weight:

[0007] Step 1: Preparation of internal sizing solution: Add 3 - 5 parts of modified starch to 100 - 120 parts of water, stir evenly, then heat up to 90 - 100 °C, and keep warm for 10 - 30 minutes to prepare the internal sizing solution;

[0008] Step 2: Preparation of surface sizing solution: Add 0.5 - 2 parts of styrene - acrylic surface sizing agent and 40 - 60 parts of rosin size to 250 - 350 parts of water and mix, heat up to 90 - 100 °C, stir evenly, and keep warm for 10 - 30 minutes to obtain the surface sizing solution;

[0009] Step 3: Preparation of coating sizing solution: Add 0.5 - 2 parts of light calcium carbonate and 3 - 5 parts of sodium carboxymethylcellulose to 10 - 15 parts of water and stir evenly to obtain the coating sizing solution;

[0010] Step 4: Pulp disintegration and beating: Disintegrate the softwood pulp for 10 - 30 minutes, then dilute it with water and beat it into a mixed pulp;

[0011] Step 5: Pulp blending: Pump the beaten mixed pulp into the batching tank, and add 5 - 10 parts of the internal sizing solution prepared in Step 1 per ton of paper and 15 - 18 parts of PPE wet strength agent per ton of pulp into the batching tank and mix evenly;

[0012] Step 6: Sheet forming on the wire: After preparing the pulp in Step 5 to a concentration of 0.7% - 0.9%, screen and purify it through a filling pump, a desander, and a pressure screen, and then form it on the wire; Add 0.1 - 0.3 parts of polyethyleneimine per ton of paper and 35 - 45 parts of calcium silicate per ton of paper at the inlet of the filling pump; Add 2 - 4 parts of silica sol per ton of paper in the low - consistency headbox; Add 5 - 10 parts of GBS - 02 papermaking surface sizing agent per ton of paper in the outlet pipe of the low - consistency headbox; Obtain the paper sheet through sheet forming on the wire, pressing dehydration, and drying;

[0013] Step 7: Sizing and drying: Perform surface sizing on the dried base paper. The sizing amount of the surface sizing solution prepared in Step 2 is 1 - 3 g / m 2 , and apply it to the front side of the paper sheet; The sizing amount of the coating sizing solution prepared in Step 3 is 1 - 2 g / m 2 , and apply it to the back side of the paper sheet; The coated paper sheet first enters a non - contact hot air drying oven for pre - drying, and then enters the post - drying section for final drying. The moisture content of the finally dried paper sheet is 3 - 5%;

[0014] Step 8: Rewinding and packaging: Rewind, with the rewind end face being neat and the paper surface being flat, and finally package to obtain the finished product.

[0015] In Step 4, the pulp is diluted with water to a weight concentration of 3.5% - 4.5%.

[0016] In Step 4, the mixed pulp is beaten to a beating degree of 25 - 27 0 SR mixed pulp.

[0017] In Step 5, the PPE wet strength agent is obtained by diluting the PPE wet strength agent stock solution 8 - 12 times with water.

[0018] In Step 6, in the pressing dehydration, the pressing section consists of four rolls and three pressing zones. The pressures of the three pressing zones are respectively: 45 - 55 kN / m 2 , 65 - 75 kN / m 2 , 105 - 115 kN / m 2; The dryness of the wet paper sheet after pressing is 40-48%, and the moisture content of the dried paper sheet is 3-5%.

[0019] In step 8, the rewinding speed is controlled at 200-400 m / min, the basis weight is controlled at 70-90 g / m 2 , and the moisture content is controlled at 4-5%.

[0020] The preparation method of the modified starch is as follows, by weight:

[0021] S1. Add 4-6 parts of mixed starch to water, adjust the moisture content to 25-35%, mix evenly in a high-speed mixer at 70-90 °C to obtain gelatinized starch; add 0.5-0.7 parts of sorbitol, 0.3-0.5 parts of N,N-bis(2,3-epoxypropyl)isopropylamine, and 0.005-0.02 parts of sodium persulfate to the gelatinized starch, heat and stir to control the temperature at 60-80 °C, and the stirring time is 1-3 hours; dropwise add 2-5 mol / L dilute hydrochloric acid to adjust the pH value to 7-8 to obtain a mixed material;

[0022] S2. Put the mixed material prepared in step S1 into a twin-screw extruder for extrusion, and set the screw speed at 200-400 rpm; inject 0.04-0.06 parts of methylglyoxal at the fifth barrel of the extruder with a liquid spray gun; put the extruded mixed material into a γ-ray radiation field for radiation irradiation, the irradiation dose is 6-10 kGy, and the irradiation time is 3-5 hours; put the irradiated mixed material into an oven and dry it for 3-8 hours, and set the oven temperature at 60-80 °C; then cool it at room temperature; use a ball mill to grind it through a 200-400 mesh sieve to obtain the modified starch.

[0023] The mixed starch is an equal-mass mixture of cassava starch, corn starch, and potato starch.

[0024] The temperature gradient of the twin-screw extruder is set at 65-75 °C, 85-95 °C, 105-115 °C, 115-125 °C, 125-135 °C, and 135-145 °C.

[0025] In the high-efficiency production method of the digital thermal transfer paper of the present invention, the functions of each substance are as follows:

[0026] The modified starch is used as the main component of the internal sizing solution, enhancing the internal cohesion and sizing effect of the paper, and improving the strength and water resistance of the paper.

[0027] The styrene-acrylic surface sizing agent is mixed with rosin size for surface sizing to improve the surface strength and printing suitability of the paper.

[0028] The rosin size is mixed with the styrene-acrylic surface sizing agent for surface sizing to increase the water resistance and printing adaptability of the paper.

[0029] Light calcium carbonate is used as a filler in the coating sizing solution to improve the smoothness and whiteness of the paper.

[0030] Sodium carboxymethyl cellulose is used as an adhesive in the coating sizing solution to enhance the adhesion of the coating and the coating performance of the paper.

[0031] Softwood pulp is used as the main raw material for papermaking to provide the basic strength and structure of the paper.

[0032] PPE wet strength agent enhances the strength of the paper in the wet state, improving the toughness and usability of the paper.

[0033] Polyethyleneimine is used as a retention aid to help improve the retention rate of fillers and fibers in the paper and enhance the strength of the paper.

[0034] Calcium silicate is used as a filler to improve the smoothness and printability of the paper.

[0035] Silica sol is used as an auxiliary agent to improve the coating performance of the paper and enhance the strength of the paper.

[0036] GBS-02 papermaking surface sizing agent further enhances the surface sizing effect of the paper, improving the water resistance and printability of the paper.

[0037] Methylglyoxal is used as a crosslinking agent to enhance the crosslinking density of the modified starch, improving the mechanical strength and folding resistance of the paper.

[0038] Sorbitol is used as a plasticizer to increase the plasticity of the starch, making it easier to process and modify.

[0039] N,N-bis(2,3-epoxypropyl) isopropylamine is used as a cationic etherifying agent to introduce cationic groups onto the starch molecular chain, enhancing its binding force with fibers.

[0040] Sodium persulfate is used as an initiator to promote the etherification reaction of starch.

[0041] Dilute hydrochloric acid is used to adjust the pH value to ensure the smooth progress of the reaction.

[0042] γ-ray radiation field is used for the radiation treatment of modified starch to further improve its performance.

[0043] The combination and interaction of these substances enable the present invention to produce high-quality digital thermal transfer paper with good printability and mechanical properties.

[0044] Compared with the prior art, it has the following several beneficial effects:

[0045] 1) By combining the preparation of modified starch with the production process of digital heat transfer paper, the present invention realizes integrated production, reduces the two processing steps of base paper production and coating processing, and thus improves production efficiency.

[0046] 2) The use of the modified starch in the present invention improves the cohesion and sizing effect of the paper. At the same time, by precisely controlling the preparation and application of the sizing liquid and coating liquid, the surface properties and printing suitability of the paper are improved, making the final product have better tensile strength and folding endurance. Detailed implementation mode

[0047] Main sources of substances:

[0048] Styrene-acrylic surface sizing agent, model: MX-611, Mingxiang Chemical Technology (Shandong) Group Co., Ltd.

[0049] Rosin size: product number: HY-500665, Shandong Haoyao New Materials Co., Ltd.

[0050] Light calcium carbonate: mesh number: 3000 mesh.

[0051] PPE wet strength agent stock solution: product number: JR-1001, Tai'an Jiarun Chemical Co., Ltd.

[0052] Polyethyleneimine: CAS: 9002-98-6, product number: 20240806, Wuhan Jixin Yibang Biotechnology Co., Ltd.

[0053] Calcium silicate: mesh number: 2000 mesh.

[0054] Silica sol: product number: 0450422, Shandong Yousuo Chemical Technology Co., Ltd.

[0055] GBS-02 paper surface sizing agent: product number: GBS-02, Guangzhou Tongda Chemical Engineering Co., Ltd.

[0056] The remaining raw materials in the examples and comparative examples of the present invention are all commercially available products.

[0057] The design concept of the present invention is to optimize the production process of digital heat transfer paper. By precisely controlling the selection and processing steps of raw materials, as well as the preparation of sizing liquid and coating liquid, the quality and production efficiency of the paper are improved. Specifically, by using modified starch to enhance the cohesion and sizing effect of the paper, combining styrene-acrylic surface sizing agent and rosin size to improve the surface properties of the paper, and using sodium carboxymethyl cellulose and light calcium carbonate to improve the uniformity of the coating liquid and the printing suitability of the paper. At the same time, by finely controlling the pulp treatment, forming on the wire, pressing dehydration and drying processes, the paper is ensured to reach the required dryness and moisture content. In addition, the mixture is irradiated with γ-ray radiation field, and glyoxal is injected as a cross-linking agent during the preparation of modified starch in the extrusion process, further improving the cross-linking density of the modified starch and the mechanical strength of the paper. Finally, through the rewinding and packaging steps, the finished product with the basis weight, moisture and surface flatness all meeting the standards is obtained. This design concept aims to improve product performance through technological innovation to meet the needs of high-efficiency production.

[0058] Example 1

[0059] A high-efficiency production method for digital heat transfer paper is as follows:

[0060] Step 1, Preparation of internal sizing liquid: Add 4 kg of modified starch to 110 kg of water, stir evenly and then heat up to 95 °C, keep warm for 20 minutes to prepare the internal sizing liquid;

[0061] Step 2, Preparation of surface sizing liquid: Add 1 kg of styrene-acrylic surface sizing agent and 50 kg of rosin size to 300 kg of water and mix, heat up to 95 °C and stir evenly, keep warm for 20 minutes to obtain the surface sizing liquid;

[0062] Step 3, Preparation of coating liquid: Add 1 kg of light calcium carbonate and 4 kg of sodium carboxymethyl cellulose to 12 kg of water and stir evenly to obtain the coating liquid;

[0063] Step 4, Pulp disintegration and beating: Disintegrate the softwood pulp for 20 minutes and then dilute it with water to a pulp with a weight concentration of 4%, and beat it into a mixed pulp with a beating degree of 26 0 SR;

[0064] Step 5, Pulp blending: Pump the beaten mixed pulp into the batching tank, add 8 kg of the internal sizing liquid prepared in Step 1 per ton of paper and 16 kg of PPE wet strength agent per ton of pulp into the batching tank and mix evenly. The PPE wet strength agent is obtained by diluting the PPE wet strength agent stock solution with water 10 times;

[0065] Step 6, forming on the wire: After preparing the slurry in Step 5 to a concentration of 0.8%, it is screened and purified through a pulp pump, a desander, and a pressure screen, and then formed on the wire; 0.2 kg of polyethyleneimine per ton of paper and 40 kg of calcium silicate per ton of paper are added to the inlet of the pulp pump; 3 kg of silica sol per ton of paper is added to the low-consistency stuff box; 8 kg of GBS-02 papermaking surface sizing agent per ton of paper is added to the outlet pipe of the low-consistency stuff box; the paper web is obtained through forming on the wire, pressing dehydration, and drying; the pressing section in the pressing dehydration consists of four rolls and three pressing zones, and the pressures of the three pressing zones are: 50 kN / m 2 , 70 kN / m 2 , 110 kN / m 2 ; the dryness of the wet paper web after pressing is 45%, and the moisture content of the dried paper web is 5%;

[0066] Step 7, sizing and drying: Surface sizing is carried out on the dried base paper. The sizing amount of the surface sizing liquid prepared in Step 2 is 2 g / m 2 , which is coated on the front side of the paper web; the sizing amount of the coating sizing liquid prepared in Step 3 is 1.5 g / m 2 , which is coated on the back side of the paper web; the coated paper web first enters a non-contact hot air drying oven for pre-drying, and then enters the post-drying section for final drying. The moisture content of the finally dried paper web is 4%;

[0067] Step 8, rewinding and packaging: The rewinding speed is controlled at 300 m / min, the basis weight is controlled at 80 g / m 2 , the moisture content is controlled at 4.1%, the rewinding end face is neat, the paper surface is flat, and finally it is packaged to obtain the finished product.

[0068] The preparation method of the modified starch is as follows:

[0069] S1. Add 5 kg of mixed starch to water, adjust the moisture content to 30%, and mix evenly in a high-speed mixer at 80 °C to obtain gelatinized starch; add 0.6 kg of sorbitol, 0.4 kg of N,N-bis(2,3-epoxypropyl) isopropylamine, and 0.01 kg of sodium persulfate to the gelatinized starch, heat and stir, control the temperature at 70 °C, and the stirring time is 1.5 hours; dropwise add 4 mol / L dilute hydrochloric acid to adjust the pH value to 7 to obtain a mixture;

[0070] S2. Put the mixture prepared in step S1 into a twin-screw extruder for extrusion, and set the screw speed at 300 rpm; set the temperature gradient of the twin-screw extruder at 70 °C, 90 °C, 110 °C, 120 °C, 130 °C, 140 °C; inject 0.05 kg of methylglyoxal at the fifth barrel of the twin-screw extruder with a liquid spray gun; put the extruded mixture into a γ-ray radiation field for radiation, with an irradiation dose of 8 kGy and an irradiation time of 4 hours; put the irradiated mixture into an oven to dry for 5 hours, and set the oven temperature at 70 °C; then cool it at room temperature; use a ball mill to grind it through a 300-mesh sieve to obtain the modified starch.

[0071] The mixed starch is an equal-mass mixture of cassava starch, corn starch, and potato starch.

[0072] Example 2

[0073] A high-efficiency production method of digital thermal transfer paper is basically the same as that of Example 1, and the only difference is the different preparation method of the modified starch.

[0074] The preparation method of the modified starch is as follows:

[0075] S1. Add 5 kg of mixed starch to water, adjust the moisture content to 30%, mix evenly in a high-speed mixer at 80 °C to obtain gelatinized starch; add 0.6 kg of sorbitol, 0.4 kg of bis(2-methylpropyl)[(oxiran-2-yl)methyl]amine, and 0.01 kg of sodium persulfate to the gelatinized starch, heat and stir, control the temperature at 70 °C, and the stirring time is 1.5 hours; dropwise add 4 mol / L dilute hydrochloric acid to adjust the pH value to 7 to obtain a mixture.

[0076] S2. Put the mixture prepared in step S1 into a twin-screw extruder for extrusion, and set the screw speed at 300 rpm; set the temperature gradient of the twin-screw extruder at 70 °C, 90 °C, 110 °C, 120 °C, 130 °C, 140 °C; inject 0.05 kg of methylglyoxal at the fifth barrel of the twin-screw extruder with a liquid spray gun; put the extruded mixture into a γ-ray radiation field for radiation, with an irradiation dose of 8 kGy and an irradiation time of 4 hours; put the irradiated mixture into an oven to dry for 5 hours, and set the oven temperature at 70 °C; then cool it at room temperature; use a ball mill to grind it through a 300-mesh sieve to obtain the modified starch.

[0077] The mixed starch is the same as that in Example 1.

[0078] Example 3

[0079] A high-efficiency production method of digital thermal transfer paper is basically the same as that of Example 1, and the only difference is the different preparation method of the modified starch.

[0080] The preparation method of the modified starch is as follows:

[0081] S1. Add 5 kg of mixed starch into water, adjust the moisture content to 30%, mix evenly in a high-speed mixer at 80 °C to obtain gelatinized starch; add 0.6 kg of sorbitol, 0.4 kg of [2-(methacryloyloxy)ethyl]dimethylammonium chloride, and 0.01 kg of sodium persulfate into the gelatinized starch, heat and stir to control the temperature at 70 °C, and the stirring time is 1.5 hours; dropwise add 4 mol / L dilute hydrochloric acid to adjust the pH value to 7 to obtain a mixture;

[0082] S2. Extrude the mixture prepared in step S1 in a twin-screw extruder, and set the screw speed at 300 rpm; set the temperature gradient of the twin-screw extruder at 70 °C, 90 °C, 110 °C, 120 °C, 130 °C, 140 °C; inject 0.05 kg of methylglyoxal at the fifth barrel of the twin-screw extruder with a liquid spray gun; put the extruded mixture into a γ-ray radiation field for radiation irradiation, the irradiation dose is 8 kGy, and the irradiation time is 4 hours; put the irradiated mixture into an oven to dry for 5 hours, and set the oven temperature at 70 °C; then cool at room temperature; use a ball mill to grind and pass through a 300-mesh sieve to obtain the modified starch.

[0083] The mixed starch is the same as that in Example 1.

[0084] Example 4

[0085] A high-efficiency production method of digital thermal transfer paper is basically the same as that in Example 1, and the only difference is that the preparation method of the modified starch is different.

[0086] The preparation method of the modified starch is as follows:

[0087] S1. Add 5 kg of mixed starch into water, adjust the moisture content to 30%, mix evenly in a high-speed mixer at 80 °C to obtain gelatinized starch; add 0.6 kg of sorbitol, 0.4 kg of 2,3-epoxypropyltrimethylammonium chloride, and 0.01 kg of sodium persulfate into the gelatinized starch, heat and stir to control the temperature at 70 °C, and the stirring time is 1.5 hours; dropwise add 4 mol / L dilute hydrochloric acid to adjust the pH value to 7 to obtain a mixture;

[0088] S2. Put the mixture prepared in step S1 into a twin-screw extruder for extrusion, and set the screw speed at 300 rpm; set the temperature gradient of the twin-screw extruder at 70 °C, 90 °C, 110 °C, 120 °C, 130 °C, 140 °C; inject 0.05 kg of methylglyoxal at the fifth barrel of the twin-screw extruder with a liquid spray gun; put the extruded mixture into a γ-ray radiation field for radiation exposure, with an irradiation dose of 8 kGy and an irradiation time of 4 hours; put the irradiated mixture into an oven to dry for 5 hours, and set the oven temperature at 70 °C; then cool at room temperature; use a ball mill to grind and pass through a 300-mesh sieve to obtain modified starch.

[0089] The mixed starch is the same as that in Example 1.

[0090] Example 5

[0091] A high-efficiency production method of digital thermal transfer paper is basically the same as that in Example 1, and the only difference is the different preparation method of the modified starch.

[0092] The preparation method of the modified starch is as follows:

[0093] S1. Add 5 kg of mixed starch to water, adjust the moisture content to 30%, mix evenly in a high-speed mixer at 80 °C to obtain gelatinized starch; add 0.6 kg of sorbitol, 0.4 kg of N,N-bis(2,3-epoxypropyl)isopropylamine, and 0.01 kg of sodium persulfate to the gelatinized starch, heat and stir to control the temperature at 70 °C, and the stirring time is 1.5 hours; dropwise add 4 mol / L dilute hydrochloric acid to adjust the pH value to 7 to obtain a mixture.

[0094] S2. Put the mixture prepared in step S1 into a twin-screw extruder for extrusion, and set the screw speed at 300 rpm; set the temperature gradient of the twin-screw extruder at 70 °C, 90 °C, 110 °C, 120 °C, 130 °C, 140 °C; inject 0.05 kg of sodium hexametaphosphate at the fifth barrel of the twin-screw extruder with a liquid spray gun; put the extruded mixture into a γ-ray radiation field for radiation exposure, with an irradiation dose of 8 kGy and an irradiation time of 4 hours; put the irradiated mixture into an oven to dry for 5 hours, and set the oven temperature at 70 °C; then cool at room temperature; use a ball mill to grind and pass through a 300-mesh sieve to obtain modified starch.

[0095] The mixed starch is the same as that in Example 1.

[0096] Example 6

[0097] A high-efficiency production method of digital thermal transfer paper is basically the same as that in Example 1, and the only difference is the different preparation method of the modified starch.

[0098] The preparation method of the modified starch is as follows:

[0099] S1. Add 5 kg of mixed starch into water, adjust the moisture content to 30%, and mix evenly in a high-speed mixer at 80 °C to obtain gelatinized starch; add 0.6 kg of sorbitol, 0.4 kg of N,N-bis(2,3-epoxypropyl)isopropylamine, and 0.01 kg of sodium persulfate into the gelatinized starch, heat and stir, control the temperature at 70 °C, and the stirring time is 1.5 hours; dropwise add 4 mol / L dilute hydrochloric acid to adjust the pH value to 7 to obtain a mixture;

[0100] S2. Put the mixture prepared in step S1 into a twin-screw extruder for extrusion, and set the screw speed at 300 rpm; set the temperature gradient of the twin-screw extruder at 70 °C, 90 °C, 110 °C, 120 °C, 130 °C, 140 °C; inject 0.05 kg of glyoxal into the fifth barrel of the twin-screw extruder with a liquid spray gun; put the extruded mixture into a γ-ray radiation field for radiation, the irradiation dose is 8 kGy, and the irradiation time is 4 hours; put the irradiated mixture into an oven for drying for 5 hours, and set the oven temperature at 70 °C; then cool at room temperature; use a ball mill to grind and pass through a 300-mesh sieve to obtain the modified starch.

[0101] The mixed starch is the same as that in Example 1.

[0102] Comparative Example 1

[0103] A high-efficiency production method of digital thermal transfer paper is as follows:

[0104] Step 1. Preparation of internal sizing solution: Add 4 kg of mixed starch into 110 kg of water, stir evenly and then heat up to 95 °C, keep warm for 20 minutes to prepare the internal sizing solution;

[0105] Step 2. Preparation of surface sizing solution: Mix 1 kg of styrene-acrylic surface sizing agent and 50 kg of rosin size into 300 kg of water, heat up to 95 °C, stir evenly, and keep warm for 20 minutes to obtain the surface sizing solution;

[0106] Step 3. Preparation of coating solution: Add 1 kg of light calcium carbonate and 4 kg of sodium carboxymethylcellulose into 12 kg of water and stir evenly to obtain the coating solution;

[0107] Step 4. Pulp disintegration and beating: Disintegrate the softwood pulp for 20 minutes, then add water to dilute it to a pulp with a weight concentration of 4%, and beat it into a mixed pulp with a beating degree of 26 0 SR;

[0108] Step 5, pulp preparation: Pump the well-beaten mixed pulp into the batching tank, add 8 kg of the internal sizing agent prepared in Step 1 per ton of paper and 16 kg of PPE wet strength agent per ton of pulp into the batching tank and mix evenly. The PPE wet strength agent is obtained by diluting the PPE wet strength agent stock solution with 10 times of water;

[0109] Step 6, forming on the wire: After preparing the pulp in Step 5 to a concentration of 0.8%, screen and purify it through a filling pump, a desander, and a pressure screen, and then form it on the wire; Add 0.2 kg of polyethyleneimine per ton of paper and 40 kg of calcium silicate per ton of paper at the inlet of the filling pump; Add 3 kg of silica sol per ton of paper in the low-consistency headbox; Add 8 kg of GBS-02 paper surface sizing agent per ton of paper in the outlet pipe of the low-consistency headbox; Obtain the paper sheet through forming on the wire, pressing dehydration, and drying; The pressing section in the pressing dehydration consists of four rolls and three pressing zones, and the pressures of the three pressing zones are: 50 kN / m 2 、70 kN / m 2 、110 kN / m 2 ; The dryness of the wet paper sheet after pressing is 45%, and the moisture content of the dried paper sheet is 5%;

[0110] Step 7, sizing and drying: Perform surface sizing on the dried base paper. The sizing amount of the surface sizing agent prepared in Step 2 is 2 g / m 2 , and it is coated on the front side of the paper sheet; The sizing amount of the coating sizing agent prepared in Step 3 is 1.5 g / m 2 , and it is coated on the back side of the paper sheet; The coated paper sheet first enters a non-contact hot air drying oven for pre-drying, and then enters the post-drying section for final drying. The moisture content of the finally dried paper sheet is 4%;

[0111] Step 8, rewinding and packaging: The rewinding speed is controlled at 300 m / min, the basis weight is controlled at 80 g / m 2 , the moisture content is controlled at 4.1%, the rewinding end face is neat, the paper surface is flat, and finally it is packaged to obtain the finished product.

[0112] The mixed starch is an equal-mass mixture of tapioca starch, corn starch, and potato starch.

[0113] Test Example 1

[0114] The tensile strength (kN / m) is detected according to the standard of GB / T 12914-2018 "Paper and Board - Determination of Tensile Strength - Constant Rate Elongation Method (20 mm / min)".

[0115] The test results are shown in Table 1.

[0116] Table 1

[0117]

[0118] Test Example 2

[0119] Folding endurance: The folding endurance of the paper was tested using a paper folding endurance tester (Sanquan Zhongshi Experimental Instrument Co., Ltd., Jinan, China). Test parameters: At room temperature, the paper cut into 5 cm × 1 cm was folded back and forth until it broke.

[0120] The test results are shown in Table 2.

[0121] Table 2

[0122]

[0123]

[0124] From the data in Table 1 and Table 2, it can be seen that the digital thermal transfer paper prepared in Example 1 has better tensile strength and folding endurance.

[0125] N,N-bis(2,3-epoxypropyl) isopropylamine, as a cationic etherifying agent, plays a key role in the preparation of modified starch. This compound's molecular structure contains two epoxy groups, which can react with the hydroxyl groups in starch molecules to form stable ether bonds. This reaction not only improves the cationic properties of starch but also enhances its adhesiveness and dispersibility during paper sizing. The mechanism of action of N,N-bis(2,3-epoxypropyl) isopropylamine is mainly through the ring-opening reaction of its epoxy groups with the hydroxyl groups of starch molecules to introduce cationic groups, thereby obtaining modified starch. The presence of the isopropylamine group in its molecular structure makes this compound have good hydrophilicity and reactivity, and can form a strong cross-linking network between starch molecules, improving the mechanical stability and water resistance of starch. In contrast, the cross-linking agents used in other examples may not provide the same degree of cross-linking effect due to different molecular structures, resulting in differences in the performance of the final products.

[0126] In Example 1, methylglyoxal, with the chemical formula C3H4O2, contains a methyl group, a carbonyl group, and an aldehyde group, where the carbonyl group is connected to the methyl group. During the paper modification process, the reactive aldehyde group of methylglyoxal can undergo a nucleophilic addition reaction with the hydroxyl groups in cellulose molecules to form Schiff bases, and then enhance the intermolecular crosslinking through polymerization reactions, improving the tensile strength and folding endurance of the paper. The presence of the methyl group in methylglyoxal provides hydrophobicity, which helps to form a stable crosslinking network on cellulose fibers, thereby enhancing the mechanical properties of the paper. In contrast, sodium hexametaphosphate is commonly used as a chelating agent and pH regulator. Although it can also act as a crosslinking agent, its crosslinking ability and reactivity may not be as active and effective as those of organic crosslinking agents. Glyoxal also has two aldehyde groups, but its molecule is smaller and it does not contain hydrophobic groups, so it may not be able to provide the multi-point crosslinking and stability like methylglyoxal. Therefore, in paper modification, methylglyoxal exhibits more excellent properties due to its unique molecular structure and reaction characteristics.

Claims

1. A method for efficiently producing digital thermal transfer paper, characterized in that: The method is as follows, in parts by weight: Step 1, preparation of slurry sizing solution: add 3-5 parts of modified starch to 100-120 parts of water, stir evenly, heat to 90-100°C, keep warm for 10-30 minutes, and prepare slurry sizing solution; Step 2, preparation of surface sizing solution: adding 0.5-2 parts of styrene acrylic surface sizing agent and 40-60 parts of rosin glue to 250-350 parts of water, mixing, heating to 90-100° C., stirring evenly, and keeping warm for 10-30 minutes to obtain surface sizing solution; Step 3, preparation of coating glue: adding 0.5-2 parts of light calcium carbonate and 3-5 parts of sodium carboxymethyl cellulose to 10-15 parts of water and stirring evenly to obtain coating glue; Step 4, pulp crushing and beating: crush the softwood pulp for 10 to 30 minutes, then dilute with water to form a mixed pulp; Step 5, slurry preparation: pump the mixed slurry into a batching tank, add 5-10 parts of the sizing solution prepared in step 1 per ton of paper and 15-18 parts of the PPE wet strength agent per ton of pulp into the batching tank and mix them evenly; Step 6, forming on the screen: after the slurry in step 5 is prepared to a concentration of 0.7% to 0.9%, it is screened and purified by a slurry pump, a sand remover, and a pressure screen, and then formed on the screen; 0.1 to 0.3 parts of polyethyleneimine per ton of paper and 35 to 45 parts of calcium silicate per ton of paper are added to the inlet of the slurry pump; 2 to 4 parts of silica sol per ton of paper are added to the low-concentration stabilizing box; 5 to 10 parts of GBS-02 papermaking surface sizing agent per ton of paper are added to the outlet pipe of the low-concentration stabilizing box; the paper sheets are obtained by forming on the screen, squeezing and dehydrating, and drying; Step 7, sizing and drying: Surface sizing is performed on the dried base paper, and the sizing amount of the surface sizing solution prepared in step 2 is 1-3 g / m 2 , applied to the front of the paper sheet; the amount of the coating glue prepared in step 3 is 1~2g / m 2 , applied on the reverse side of the paper; the coated paper first enters the non-contact hot air drying oven for pre-drying, and then enters the post-drying section for final drying. The moisture content of the paper after final drying is 3-5%; Step 8, rewinding and packaging: rewinding, the end surface of the rewinding is neat, the paper surface is flat, and finally packaging is performed to obtain the finished product; The preparation method of the modified starch is as follows, in parts by weight: S1. Add 4-6 parts of mixed starch into water, adjust the water content to 25-35%, and mix them evenly in a high-speed mixer at 70-90° C. to obtain gelatinized starch; add 0.5-0.7 parts of sorbitol, 0.3-0.5 parts of N,N-di(2,3-epoxypropyl)isopropylamine, and 0.005-0.02 parts of sodium persulfate into the gelatinized starch, heat and stir to control the temperature at 60-80° C. for 1-3 hours; add 2-5 mol / L dilute hydrochloric acid dropwise to adjust the pH value to 7-8 to obtain a mixture; S2, putting the mixed material prepared in step S1 into a twin-screw extruder for extrusion, and setting the screw speed to 200-400rpm; injecting 0.04-0.06 parts of acetone aldehyde into the fifth barrel of the extruder with a liquid spray gun; putting the extruded mixed material into a γ-ray radiation field for radiation irradiation, and the irradiation dose is 6-10 kGy, and the irradiation time is 3-5 hours; putting the irradiated mixed material into an oven for drying for 3-8 hours, and the oven temperature is set to 60-80°C; then cooling at room temperature; grinding with a ball mill to pass through a 200-400 mesh sieve to obtain modified starch.

2. The high-efficiency production method of digital thermal transfer paper according to claim 1, characterized in that: In step 4, water is added to dilute the slurry to a weight concentration of 3.5-4.5%.

3. The high-efficiency production method of digital thermal transfer paper according to claim 1, characterized in that: In step 4, the mixed slurry is beaten to a beating degree of 25 to 27 0 Mixed slurry of SR.

4. The high-efficiency production method of digital thermal transfer paper according to claim 1, characterized in that: In step 5, the PPE wet strength agent is obtained by diluting the PPE wet strength agent stock solution by 8 to 12 times with water.

5. The high-efficiency production method of digital thermal transfer paper according to claim 1, characterized in that: The pressing section of the squeezing and dehydration in step 6 is composed of four rollers and three pressing zones, and the pressures of the three pressing zones are: 45~55kN / m 2 , 65~75kN / m 2 , 105~115kN / m 2 The dryness of the wet paper after pressing is 40~48%, and the moisture content of the dried paper is 3~5%.

6. The high-efficiency production method of digital thermal transfer paper according to claim 1, characterized in that: In step 8, the rewinding speed is controlled at 200-400 m / min, and the basis weight is controlled at 70-90 g / m 2 , the moisture content is controlled at 4~5%.

7. The high-efficiency production method of digital thermal transfer paper according to claim 1, characterized in that: The mixed starch is a mixture of cassava starch, corn starch and potato starch in equal quantities.

8. The high-efficiency production method of digital thermal transfer paper according to claim 1, characterized in that: The temperature gradient of the twin-screw extruder is set to 65-75°C, 85-95°C, 105-115°C, 115-125°C, 125-135°C, and 135-145°C.

9. A digital thermal transfer paper, characterized in that: Prepared by the production method according to any one of claims 1 to 8.

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