Preparation method of direct coating highlight paper

Abstract

A preparation method of direct coating highlight paper belongs to the technical field of papermaking, and comprises the following steps: putting a primer composition into a grinder, grinding until the particle size fineness reaches 5-10 [mu] m, and discharging to obtain a primer; coating the base paper with the primer and the highlight coating in sequence by using a coating machine to obtain coated base paper; and carrying out calendering treatment on the coated raw paper by using a calender to obtain the directly coated high-gloss paper. Wherein the primer composition comprises the following components in percentage by mass: 5%-20% of phenolic resin, 5%-20% of maleic anhydride resin, 10%-30% of titanium dioxide, 10%-30% of kaolin, 10%-40% of water and 2%-4% of other auxiliaries. Compared with a traditional high-gloss paper preparation process (a dry method and a wet method), the high-gloss paper preparation process has the advantages that a direct coating technology is adopted, construction of the primer and the high-gloss coating is completed through single-time coating, production procedures are reduced, meanwhile, use of a PET film and a composite adhesive when the high-gloss paper is prepared through a traditional process is reduced, and the production and manufacturing cost of the high-gloss paper is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of papermaking, and particularly relates to a preparation method of direct-coated high-gloss paper. Background Art

[0002] High-gloss paper is a kind of paper whose surface is treated by a special coating or composite process, with high gloss, flatness and excellent printing suitability. It is widely used in the fields of packaging, advertising, digital photo paper, book covers, etc. Its core structure usually includes a base paper layer and a functional coating layer, and the surface optical properties are improved through coating, embossing or composite processes. High-gloss paper is increasingly widely used in the tobacco industry, especially in cigarette tipping paper, and its consumption is also increasing year by year.

[0003] At present, the production of high-gloss paper is divided into dry method and wet method. In the dry method, the high-gloss coating is first coated on a PET film, then the composite adhesive is coated on a laminator and laminated with the base paper, and then after curing for more than 24 hours, the PET film is peeled off to obtain the high-gloss paper. Its production process is relatively complex, not only consuming a large amount of PET film, but also requiring composite adhesive for lamination, curing and peeling, resulting in a high production cost; in the wet method, the high-gloss paper is directly made on a paper machine with pulp. Before papermaking, a large amount of water needs to be added to make a uniform fiber suspension, and a large amount of water needs to be removed during the papermaking process. The investment in papermaking equipment and funds for producing high-gloss paper by the wet method is relatively large, which is not suitable for the production and promotion of general small and medium-sized enterprises. Summary of the Invention

[0004] In view of the above situation, in order to overcome at least some defects of the above prior art, the present invention provides a preparation method of direct-coated high-gloss paper.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A preparation method of direct-coated high-gloss paper, wherein the base coating composition is put into a grinder and ground until the particle size fineness reaches 5 - 10 μm, and then discharged to obtain the base coating; The base coating and the high-gloss coating are sequentially coated on the base paper by a coater to obtain the coated base paper; The coated base paper is calendered by a calender to obtain the direct-coated high-gloss paper; Among them, the base coating composition includes the following components by mass percentage: phenolic resin 5% - 20%, maleic anhydride resin 5% - 20%, titanium dioxide 10% - 30%, kaolin 10% - 30%, water 10% - 40% and other additives 2% - 4%.

[0006] In some embodiments, the high-gloss coating is an aqueous polyester coating.

[0007] In some embodiments, in the primer coating composition, the other additives include a dispersant and a leveling agent.

[0008] In some embodiments, the dispersant includes sodium polycarboxylate and sodium hexametaphosphate.

[0009] In some embodiments, the leveling agent includes a polyether silicone copolymer.

[0010] In some embodiments, during the coating of the primer coating, the coating speed is 80 - 100 m / min, and the set temperature of the coater is between 60°C and 105°C.

[0011] In some embodiments, during the coating of the high-gloss coating, the coating speed is 80 - 100 m / min, and the set temperature of the coater is between 80°C and 125°C.

[0012] In some embodiments, the calender includes multiple groups of calender rolls, the surface Ra value of the calender rolls is < 0.05 μm, and the hardness is HD96 - 98.

[0013] In some embodiments, during the calendering process, the heating temperature and pressure of the multiple groups of calender rolls increase sequentially.

[0014] In some embodiments, the heating temperature of the multiple groups of calender rolls is between 80 - 150°C, and the pressure is between 50 - 75 kgf / cm 2 .

[0015] The beneficial effects achieved by the present invention are as follows: By directly coating the primer coating on the surface of the base paper layer, the micropores and pits between the base paper fibers can be effectively filled, the surface roughness of the base paper can be reduced, and better flatness can be obtained when coating the high-gloss coating, which is beneficial to improving the gloss after subsequent calendering.

[0016] Compared with the traditional high-gloss paper preparation processes (dry method and wet method), the present invention adopts a direct coating technology, and the construction of the primer coating and the high-gloss coating is completed through a single coating, reducing the production process. At the same time, the use of PET film and composite glue in the production of high-gloss paper by the traditional process is saved, and the production cost of high-gloss paper is greatly reduced. Detailed embodiments

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0018] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to the described content can be applied to the present invention. The preferred methods and materials described herein are for illustrative purposes only and do not limit the content of this application.

[0019] The endpoints and any values in the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered specifically disclosed herein.

[0020] In view of the deficiencies in the prior art mentioned in the background art, an embodiment of the present invention provides a method for preparing a direct-coated high-gloss paper, including: putting a base coating composition into a grinder, grinding until the particle size fineness reaches 5-10 μm and then discharging to obtain a base coating; using a coater to sequentially coat the base coating and a high-gloss coating on the base paper to obtain the coated base paper; using a calender to perform calendering treatment on the coated base paper to obtain a direct-coated high-gloss paper.

[0021] The base coating on the surface of the base paper layer can effectively fill the micropores and pits between the base paper fibers, reduce the surface roughness of the base paper, and have better flatness when coating the high-gloss coating, which is beneficial to improving the gloss after subsequent calendering. Coating the high-gloss coating on the base coating can enhance the surface gloss of the base coating and give the base paper a high-gloss effect. Moreover, the particle size of grinding directly affects the surface roughness of the coating. If the particle size is too large (>10 μm), microscopic unevenness will form on the coating surface, resulting in light diffuse reflection and reducing the gloss. If the particle size is too fine (<5 μm), it will be difficult to disperse due to the too large specific surface area. By adopting the method of layered coating, sequentially coating the base coating and the high-gloss coating, it can prevent the high-gloss coating from penetrating into the base paper, resulting in surface unevenness and affecting the gloss of the high-gloss paper. The calendering treatment softens the resin in the base coating and the high-gloss coating through high temperature, and then extrudes the coating under high pressure to reduce the surface roughness of the high-gloss paper and form a mirror effect on the surface of the high-gloss paper.

[0022] Among them, the base coating composition includes the following components by mass percentage: phenolic resin 5%-20%, maleic anhydride resin 5%-20%, titanium dioxide 10%-30%, kaolin 10%-30%, water 10%-40% and other additives 2%-4%. The phenolic resin is a thermoplastic polymer material formed by the polycondensation reaction of phenolic compounds and aldehydes. The maleic anhydride resin is a functional resin formed by copolymerization with maleic anhydride as the core monomer. After crosslinking, the phenolic resin forms a dense three-dimensional network structure, which can be embedded in the micropores and pits of paper fibers, so that the base coating has better adhesion fastness on the base paper, thus eliminating the need for subsequent bonding with composite glue, greatly reducing the production cost of high-gloss paper. The introduction of maleic anhydride resin accelerates the curing reaction of the base coating, enabling the base coating to quickly form a continuous film layer at low temperature and reducing pore defects caused by solvent volatilization.

[0023] The high refractive index and particle size uniformity of titanium dioxide can significantly improve the whiteness and optical covering performance of the base coating. Titanium dioxide can effectively reflect and scatter light, reducing the influence of the base color of the base paper fibers on the printing effect. The flat hexagonal crystal structure of kaolin can fill the gaps between the base paper fibers, reduce the porosity of the base coating, and improve the smoothness of the base coating.

[0024] In some embodiments, the high-gloss coating is a waterborne polyester coating. The waterborne polyester coating is an environmentally friendly coating with waterborne polyester resin as the core film-forming substance, having good film-forming properties and high gloss, and can endow the high-gloss paper with high gloss and surface flatness.

[0025] In some embodiments, the other additives include a dispersant and a leveling agent. The dispersant can prevent the agglomeration of particles such as titanium dioxide and kaolin, thereby improving the smoothness of the base coating. The leveling agent promotes its uniform spreading on the base paper by reducing the surface tension of the base coating, eliminating defects such as brush marks and peeling.

[0026] In some embodiments, the dispersant includes sodium polycarboxylate and sodium hexametaphosphate. Sodium polycarboxylate can stabilize the particles in the base coating through the dual mechanisms of steric hindrance and charge repulsion, and shows excellent dispersibility especially for titanium dioxide; the long-chain structure of sodium hexametaphosphate can efficiently chelate metal ions, prevent the precipitation of particles in the base coating, and has a strong dispersing force for inorganic fillers such as kaolin.

[0027] In some embodiments, the leveling agent includes a polyether silicone copolymer. The polyether silicone copolymer significantly reduces the surface tension of the base coating through the synergistic action of the polysiloxane chain segment (hydrophobic) and the polyether chain segment (hydrophilic) in the molecule, and improves the leveling property of the base coating.

[0028] In some embodiments, during the coating of the base coat, the coating speed is 80 - 100 m / min, and the set temperature of the coater is between 60°C and 105°C. That is to say, after the base coat is coated onto the base paper, it will pass through the temperature zones preset by the coater at a speed of 80 - 100 m / min. In the temperature zones, the initial temperature of 60°C can slowly evaporate the solvent, avoiding the cracking of the base coat caused by rapid drying. The highest temperature of 105°C can reach the optimal curing temperature of the resin, which can promote the curing of the base coat. For example, the set temperatures of the temperature zones of the coater are 60°C - 80°C - 95°C - 105°C - 90°C in sequence.

[0029] In some embodiments, during the coating of the high-gloss coating, the coating speed is 80 - 100 m / min, and the set temperature of the coater is between 80°C and 125°C. That is to say, after the high-gloss coating is coated onto the base coat, it will pass through the temperature zones set by the coater at a speed of 80 - 100 m / min, so as to achieve the drying and curing of the high-gloss coating. Among them, the initial temperature of 80°C can slowly evaporate the solvent, avoiding the cracking of the high-gloss coating caused by rapid drying; the highest temperature of 125°C can promote the full cross-linking of the high-gloss coating, enabling the high-gloss coating to form a continuous film layer. For example, the set temperatures of the temperature zones of the coater are 80°C - 100°C - 110°C - 125°C - 110°C in sequence.

[0030] In some embodiments, the calender includes multiple groups of calender rolls, and the Ra value of the surface of the calender roll is < 0.05 μm, and the hardness is HD96 - 98. The Ra value is the arithmetic mean deviation of the surface roughness. The smaller the value, the smoother the surface. The surface roughness of the calender roll directly affects the glossiness and smoothness of the paper surface. If the Ra value of the surface of the calender roll is too high, the calendered paper may have fine scratches or unevenness, resulting in a decrease in glossiness. Therefore, the Ra value of the surface of the calender roll < 0.05 μm can make the high-gloss paper have extremely high surface smoothness, thereby improving the glossiness of the high-gloss paper. If the hardness of the calender roll is too small, the stability of the calender roll is too poor, and it needs to be frequently replaced due to the deformation of the roll surface. If the hardness of the calender roll is too large, the procurement cost is too high.

[0031] In some embodiments, during the calendering process, the heating temperature and pressure of multiple groups of calender rolls increase in sequence. Among them, in the low-temperature stage, the base paper fibers and the molecular chain segments of the coating can be softened. At this time, low pressure can initially eliminate micropores and avoid fiber breakage. As the temperature rises, the fluidity of the coating also gradually increases. At this time, the increase in pressure can enhance the compactness of the coating and improve the surface flatness after calendering. When the temperature reaches the highest, the high pressure at this time can make the coating form a dense film layer and enhance the glossiness after calendering.

[0032] In some embodiments, the heating temperature of multiple groups of calender rolls is between 80 - 150°C, and the pressure is between 50 - 75 kgf / cm 2If the heating temperature is too high, the coating will adhere to the surface of the calender roller, resulting in peeling defects. If the temperature is too low, the roughness after calendering will be too high and cannot meet the high gloss requirements. If the pressure is too high, it will cause excessive compression, destroy the fiber structure, and defects will appear in local areas. If the pressure is too low, the microscopic unevenness of the coating cannot be eliminated.

[0033] The present invention will be further described below by way of specific embodiments.

[0034] The experimental methods in the following examples are conventional methods unless otherwise specified; the experimental materials used in the following examples are purchased from commercial channels unless otherwise specified.

[0035] The water-based polyester coating of the high-gloss coating in the embodiment is purchased from Guangzhou Huigu Chemical Materials Co., Ltd., model DH002, the dispersant is polycarboxylic acid sodium salt and sodium hexametaphosphate in a mass ratio of 1:1, and the leveling agent is a polyether siloxane copolymer.

[0036] Example 1 Put 40% water, 8% phenolic resin, 7% maleic anhydride resin, 15% titanium dioxide, 27% kaolin, 2% dispersant and 1% leveling agent into the grinder in sequence according to mass percentage, and put the material into the grinder when the particle size is 5-10μm for later use.

[0037] The set temperatures of the coating machine temperature zones are 60-80-95-105-90°C, and the base paper is coated with primer at a speed of 80m / min on the coating machine and rolled up for use.

[0038] The temperature setting zones of the coating machine are 80-100-110-125-110°C, and the base paper coated with the primer is coated with the high-gloss coating at a speed of 80m / min on the coating machine and rolled up for use.

[0039] Set the temperature of the first set of calender rollers of the calender to 80°C and the pressure to 50kgf / cm 2 ; The temperature of the second set of calender rollers is set to 100°C and the pressure is set to 60kgf / cm 2 The temperature of the third set of calender rollers is set to 105°C and the pressure is set to 65kgf / cm 2 ; The temperature of the fourth calender roller group is set to 120℃ and the pressure is set to 70kgf / cm 2 The fifth set of calender rollers is set at 130°C and 75kgf / cm2 respectively. 2 ; The coated paper is calendered and rolled up with a calendering roller at a speed of 80m / min to become direct-coated high-gloss paper.

[0040] Example 2 Put 40% water, 15% phenolic resin, 5% maleic anhydride resin, 13% titanium dioxide, 24% kaolin, 2% dispersant, and 1% leveling agent into the grinder in sequence by mass percentage. After grinding to a particle size fineness of 5 - 10 μm, discharge and set aside.

[0041] Set the temperature of the coater at 60 - 80 - 95 - 105 - 90 °C. Coat the base paper with the base coating at a speed of 100 m / min on the coater and wind it up for later use.

[0042] Set the temperature of the coater at 80 - 100 - 110 - 125 - 110 °C. Coat the base paper coated with the base coating with the high - gloss coating at a speed of 100 m / min on the coater and wind it up for later use.

[0043] Set the temperature of the first set of calender rolls of the calender at 80 °C and the pressure at 50 kgf / cm 2 ; Set the temperature of the second set of calender rolls at 100 °C and the pressure at 60 kgf / cm 2 ; Set the temperature of the third set of calender rolls at 105 °C and the pressure at 65 kgf / cm 2 ; Set the temperature of the fourth set of calender rolls at 120 °C and the pressure at 70 kgf / cm 2 ; Set the temperature of the fifth set of calender rolls at 150 °C and the pressure at 75 kgf / cm 2 ; Pass the coated paper through the calender rolls at a speed of 100 m / min for calendering and winding, and it becomes the direct - coated high - gloss paper.

[0044] Example 3 It is the same as Example 1, except that put 40% water, 15% phenolic resin, 10% maleic anhydride resin, 15% titanium dioxide, 17% kaolin, 2% dispersant, and 1% leveling agent into the grinder in sequence by mass percentage. After grinding to a particle size fineness of 5 - 10 μm, discharge and set aside.

[0045] Example 4 It is the same as Example 1, except that put 40% water, 15% phenolic resin, 15% maleic anhydride resin, 15% titanium dioxide, 12% kaolin, 2% dispersant, and 1% leveling agent into the grinder in sequence by mass percentage. After grinding to a particle size fineness of 5 - 10 μm, discharge and set aside.

[0046] Example 5 It is the same as Example 1, except that put 35% water, 10% phenolic resin, 10% maleic anhydride resin, 25% titanium dioxide, 17% kaolin, 2% dispersant, and 1% leveling agent into the grinder in sequence by mass percentage. After grinding to a particle size fineness of 5 - 10 μm, discharge and set aside.

[0047] Example 6 The same as Example 1, except that 35% of water, 13% of phenolic resin, 15% of maleic anhydride resin, 20% of titanium dioxide, 14% of kaolin, 2% of dispersant and 1% of leveling agent are put into the grinder in sequence according to mass percentage, and the material is discharged when the particle size is 5-10 μm.

[0048] Example 7 The same as Example 1, except that 35% water, 10% phenolic resin, 15% maleic anhydride resin, 15% titanium dioxide, 22% kaolin, 2% dispersant and 1% leveling agent are put into the grinder in sequence according to mass percentage, and the material is discharged when the particle size is 5-10 μm.

[0049] Comparative Example 1 The high-gloss paper is prepared by a dry method. First, the high-gloss coating is applied to the PET film, and then the composite glue is applied on the laminating machine and compounded with the base paper. After aging for more than 24 hours, the PET film is peeled off to obtain the high-gloss paper.

[0050] The performance tests were conducted on the high-gloss papers prepared in Examples 1-7 and Comparative Example 1. The specific test contents are as follows: Gloss test: The glossiness of the high-gloss paper prepared in Examples 1-7 and Comparative Example 1 was tested using a gloss meter model SC-380 produced by Caipu Technology (Zhejiang) Co., Ltd. The test angle was 60°, and the samples to be tested were cut into flat samples of 50×50 mm. Before the test, the samples were placed in an environment of 23±2°C and 50±5% humidity for 24 hours to eliminate the influence of temperature and humidity on the reflectivity of the coating. The samples were spread flat on the test bench, and 3 measuring points were taken along the longitudinal and transverse directions of the paper (avoiding 10 mm from the edge), for a total of 6 measurements. Outliers (such as a value deviating from the mean by ±5%) were eliminated, and the average value of the remaining data was taken as the final result.

[0051] Smoothness test: The test was carried out using a smoothness tester of model PN-BSTF from Hangzhou Pinxiang Technology Co., Ltd. On the extracted high-gloss paper, specimens sufficient for 10 tests on both the front and back were evenly cut at a distance of 15 mm from the edge along the cross direction. The specimen area was at least 60 mm × 60 mm, and it was ensured that there were no folds, wrinkles, visible cracks or other paper defects on the specimens. If there were watermarks, they should be avoided as much as possible during the test. The specimens should be conditioned according to GB / T 10739 and tested under the same atmospheric conditions. During the test, the measuring surface of the specimen was placed against the glass plate, then the rubber pad and the upper pressure plate were placed on the specimen, a pressure of (100 ± 2) kPa was applied, and a vacuum of 50.66 kPa was generated in a large vacuum container. Measure and record the time required for the vacuum to drop from 50.66 kPa to 48.00 kPa, expressed in seconds. If the time exceeds 300 s, a smaller volume should be used and another specimen should be retested. If the time is less than 15 s, another specimen should be used to test the time required for the vacuum to drop from 50.66 kPa to 29.33 kPa. The time from when the load was applied to the start of timing for the specimen should be approximately 60 s.

[0052] The test results are shown in Table 1.

[0053] Table 1

[0054] As can be seen from Table 1, the glossiness and smoothness of Examples 1-7 are both higher than those of Comparative Example 1. It can be seen that the high-gloss paper prepared by the method of directly coating the primer and high-gloss coating of the present invention not only has simple steps and low cost, but also has better glossiness and smoothness of the prepared high-gloss paper.

[0055] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0056] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the protection scope of the present invention.

Claims

1. A preparation method of direct coating high-gloss paper, characterized in that, Comprising: Put the primer coating composition into a grinding machine, grind it until the particle size fineness reaches 5 - 10 μm, and then discharge the material to obtain the primer coating; Use a coater to coat the primer coating and the high-gloss coating on the base paper in sequence to obtain the coated base paper; Use a calender to calender the coated base paper to obtain the direct-coated high-gloss paper; Among them, the primer coating composition comprises the following components by mass percentage: phenolic resin 5% - 20%, maleic anhydride resin 5% - 20%, titanium dioxide 10% - 30%, kaolin 10% - 30%, water 10% - 40% and other additives 2% - 4%.

2. The preparation method according to claim 1, characterized in that, The high-gloss coating is a water-based polyester coating.

3. The preparation method according to claim 1, characterized in that, In the primer coating composition, the other additives include a dispersant and a leveling agent.

4. The preparation method according to claim 3, wherein The dispersant includes sodium polycarboxylate and sodium hexametaphosphate.

5. The preparation method according to claim 3, characterized in that, The leveling agent includes a polyether silicone copolymer.

6. The preparation method according to claim 1, characterized in that, In the coating of the primer coating, the coating speed is 80 - 100 m / min, and the set temperature of the coater is between 60°C and 105°C.

7. The preparation method according to claim 1, characterized in that, In the coating of the high-gloss coating, the coating speed is 80 - 100 m / min, and the set temperature of the coater is between 80°C and 125°C.

8. The preparation method according to claim 1, wherein The calender includes multiple groups of calender rolls, the surface Ra value of the calender rolls < 0.05 μm, and the hardness is HD96 - 98.

9. The preparation method according to claim 8, characterized in that, In the calendering process, the heating temperature and pressure of the multiple groups of calender rolls increase sequentially.

10. The preparation method according to claim 9, wherein The heating temperature of the multiple groups of calender rollers ranges from 80 to 150 °C, and the pressure ranges from 50 to 75 kgf / cm 2 .

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