A high-efficiency coating process for coating whiteboard paper

Abstract

This invention discloses an efficient coating process for coated whiteboard paper. S1: A coating material is applied to the surface of the coated paper using a coating machine. The pigments in the coating include kaolin and calcium carbonate. Calcium carbonate is generated in situ during coating mixing, forming calcium carbonate particles along the polyvinyl alcohol chain structure and hollow spherical calcium carbonate structures surrounding sodium carboxymethyl cellulose. The calcium carbonate is uniformly dispersed between the kaolin particles. The gaps between the flake-like kaolin and calcium carbonate particles are connected to the hollow spherical structures of calcium carbonate, forming ink absorption channels. S2: The coated paper with the coating layer is dried. S3: The dried coated whiteboard paper is calendered and finished. During calendering, the kaolin relatively shifts and slides above and below the hollow spheres and / or calcium carbonate particles, resulting in the target coated whiteboard paper. This invention effectively improves the coating process efficiency and significantly increases ink absorption rate by improving the coating composition. 。

Description

Technical Field

[0001] This invention relates to the field of coated whiteboard paper technology, and in particular to a highly efficient coating process for coated whiteboard paper. Background Technology

[0002] Coated white cardboard paper consists of a coating layer and a base paper. The coating layer comprises pigments, adhesives, and additives. The coating layer covers the surface of ordinary paper, which has unevenness and large gaps due to fibers, with a layer of fine ions that have good ink absorption, resulting in a smooth paper with good uniformity. Coating can also improve the paper's gloss, stability, and opacity, thus enhancing the product's quality.

[0003] The existing coating layer is a uniform coating obtained by applying the coating. The coating consists of pigments, adhesives and dispersants, etc. The adhesives bind the pigment particles to the base paper, making the pigment particles stick together.

[0004] Kaolin with a hexagonal plate structure is a commonly used pigment for coating whiteboard paper. When coated on the base paper, the hexagonal plate structure of kaolin has a high reflectivity to light, and the resulting coated whiteboard paper has good smoothness and gloss. However, kaolin has a low oil absorption value, which is not conducive to the printability of coated paper. Summary of the Invention

[0005] The purpose of this invention is to provide an efficient coating process for coating whiteboard paper. This invention improves the coating composition, effectively enhances the coating process efficiency, and significantly improves the ink absorption rate.

[0006] To solve this technical problem, the technical solution of the present invention is: a high-efficiency coating process for coating whiteboard paper, comprising the following steps:

[0007] S1. Apply the coating to the surface of the coated paper using a coating machine;

[0008] The pigments in the coating include kaolin and calcium carbonate. Calcium carbonate is generated in situ during the coating mixing process, forming calcium carbonate particles along the polyvinyl alcohol chain structure and hollow spherical calcium carbonate structures around sodium carboxymethyl cellulose. Calcium carbonate is uniformly dispersed between the kaolin particles. The gaps between the flaky kaolin and calcium carbonate particles are connected to the hollow spherical structures of calcium carbonate to form the absorption channels of the ink.

[0009] S2. Dry the coated paper with the coating layer;

[0010] S3. After calendering and finishing, the coated white board paper undergoes relative displacement and sliding between the kaolin and the hollow spheres and / or particles of calcium carbonate during the calendering process, thus obtaining the target coated white board paper.

[0011] The coating used in the preferred coating layer of the white cardboard paper comprises, by weight, the following substances:

[0012]

[0013] The pigment in this invention comprises kaolin and calcium carbonate, with kaolin as the main component. Calcium carbonate, which is generated in situ in the coating slurry, is uniformly generated through a precipitation reaction. Sodium chloride generated at the same time acts as an inorganic thickener to increase the viscosity of the resulting slurry. The amount of calcium carbonate generated is controlled to avoid the salting-out effect caused by excessive sodium chloride, which leads to the aggregation of polyvinyl alcohol molecular chains and ensures that the rheological properties of the coating are suitable for construction.

[0014] The preferred method for preparing the coating includes the following steps:

[0015] S11. Mix calcium chloride, polyvinyl alcohol, carboxymethyl cellulose, cationic fixing agent, and defoamer evenly according to the target mass proportions; the carboxyl groups of sodium carboxymethyl cellulose and polyvinyl alcohol react with the calcium... 2+ Chelation;

[0016] S12. Add kaolin to the slurry obtained in S11 according to the mass fraction and stir evenly.

[0017] S13. Add calcium chloride solution with an equimolar amount of sodium carbonate to the mixture of S12 and stir at a constant speed. CaCl2 and Na2CO3 will precipitate around sodium carboxymethyl cellulose and polyvinyl alcohol between the kaolin particles.

[0018] S14. Add deionized water to adjust the solid content of the resulting coating to obtain the target coating.

[0019] In the preparation of the coating slurry, the present invention first chelates calcium ions of calcium chloride with polyvinyl alcohol and sodium carboxymethyl cellulose respectively, and then adds kaolin. This effectively avoids the agglomeration phenomenon that may occur between kaolin and polyvinyl alcohol during mixing, which would lead to uneven coating.

[0020] The preferred constant-speed stirring conditions in S13 are 800 r / min to 1000 r / min and stirring time is 45 min to 65 min.

[0021] The presence of kaolin particles combined with high-speed stirring inhibits the growth of crystal nuclei formed around sodium carboxymethyl cellulose and polyvinyl alcohol during the precipitation reaction, or their orderly stacking and assembly into large particles. The precipitation of small calcium carbonate particles, along with polyvinyl alcohol and sodium carboxymethyl cellulose, is uniformly dispersed in the slurry, resulting in a slurry with good viscosity.

[0022] The preferred coating layer has a viscosity of 800 mPa*S to 1200 mPa*S and a solid content of 60% to 65%. In this invention, the sodium chloride generated by the precipitation reaction effectively increases the viscosity of the resulting coating slurry.

[0023] The preferred drying conditions for step S2 are as follows: drying at 90°C to 120°C for 20 to 30 seconds.

[0024] The preferred calendering process parameters in step S3 are as follows:

[0025] Temperature ranges from 100℃ to 120℃, and pressure ranges from 20kN / m to 40kN / m.

[0026] Another objective of this invention is to provide a coated whiteboard paper, which significantly improves the whiteness, gloss, and ink absorption rate of the coated whiteboard paper obtained by this invention.

[0027] To solve this technical problem, the technical solution of the present invention is as follows:

[0028] A coated whiteboard paper prepared by the preparation method proposed in this invention is provided.

[0029] Preferably, the coating comprises a coated paper and a coating layer, wherein the coating layer is bonded to the coated paper. The coating layer comprises kaolin, calcium carbonate with a hollow spherical structure, polyvinyl alcohol as an adhesive, and sodium carboxymethyl cellulose as a dispersant along the thickness direction of the coating. The calcium carbonate distributed along the chain structure of polyvinyl alcohol and the surface of sodium carboxymethyl cellulose are distributed along the chain structure of polyvinyl alcohol between the flaky kaolin and the spherical calcium carbonate distributed around the sodium carboxymethyl cellulose, which together form the connecting space between the ink absorption channels to form ink absorption channels.

[0030] By adopting the above technical solution, the beneficial effects of the present invention are:

[0031] This invention discloses a high-efficiency coating process for coating whiteboard paper. The main inventive concept involves using kaolin and calcium carbonate as a composite pigment. During mixing, calcium carbonate particles are distributed around polyvinyl alcohol (a binder) and sodium carboxymethyl cellulose (a dispersant). Calcium ions from calcium chloride, used to generate calcium carbonate, chelate with both polyvinyl alcohol and sodium carboxymethyl cellulose, reducing the concentration of calcium ions in the coating slurry and controlling the dispersion of calcium carbonate. When sodium carbonate solution is added, the low concentration of calcium ions in the solution facilitates the precipitation of nanoparticles formed during the precipitation reaction. Calcium carbonate is inhibited by concentration, making it difficult to stack and grow further, thus ensuring uniform dispersion of calcium carbonate in the slurry. Accompanied by calendering, the flaky kaolin rolls and shifts relative to the calcium carbonate particles or hollow calcium carbonate spheres under pressure, thus ensuring the smoothness of the resulting coating while still retaining the connecting channels for ink absorption. Since small particles or hollow calcium carbonate particles are dispersed around the connecting channels, the small size effect and large specific surface area of ​​the calcium carbonate particles can provide better ink absorption performance, promoting ink absorption and distribution.

[0032] The presence of hollow spherical calcium carbonate particles in the slurry used in this invention not only improves water retention and ink absorption, but also effectively controls the coating process through the squeezing and guiding effects of coating and calendering. This results in a coating on the white cardboard that effectively maintains microporosity. While kaolin and calcium carbonate form a dense coating structure, they retain sufficient channels to facilitate ink absorption. Furthermore, the calcium carbonate in this invention is formed by calcium ions chelated with polyvinyl alcohol and CMC, effectively avoiding surface closure caused by the strong interaction between PVA and pigment ions in the paper, resulting in small void volumes in the coating. Simultaneously, the sheet-like kaolin, calcium carbonate distributed along the polyvinyl alcohol, and hollow calcium carbonate spheres surrounding the CMC form a coating layer with interconnected channels. The pigment particles in the coating layer are regularly stacked, improving the smoothness and uniformity of the resulting white cardboard coating, enhancing the uniform absorption of ink on the paper surface, and improving printing quality and image clarity. Detailed Implementation

[0033] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0034] Example 1

[0035] This embodiment discloses a high-efficiency coating process for coating whiteboard paper, including the following steps:

[0036] S1. Apply the coating to the surface of the coated paper using a coating machine. The coating amount of the coating layer is shown in Table 1.

[0037] The pigments in the coating include kaolin and calcium carbonate. Calcium carbonate is generated in situ during the coating mixing process, forming calcium carbonate particles along the polyvinyl alcohol chain structure and hollow spherical calcium carbonate structures around sodium carboxymethyl cellulose. Calcium carbonate is uniformly dispersed between the kaolin particles. The gaps between the flaky kaolin and calcium carbonate particles are connected to the hollow spherical structures of calcium carbonate to form the absorption channels of the ink.

[0038] S2. Dry the coated paper with the coating layer; the drying process conditions for step S2 are shown in Table 1.

[0039] S3. After calendering and finishing, the coated white board paper undergoes relative displacement and sliding between the kaolin and the hollow spheres and / or particles of calcium carbonate during the calendering process, thus obtaining the target coated white board paper.

[0040] The calendering process parameters in step S3 are shown in Table 1.

[0041] In this embodiment, the composition of the coating used in the coating layer of the whiteboard paper is shown in Table 2 according to the mass parts.

[0042] In this embodiment, the cationic fixing agent is polydimethylamine ethyl acrylate quaternary ammonium chloride.

[0043] The pigment in this invention comprises kaolin and calcium carbonate, with kaolin as the main component. The calcium carbonate, which is generated in situ in the coating slurry, is uniformly generated through a precipitation reaction. The sodium chloride generated at the same time acts as an inorganic thickener to increase the viscosity of the resulting slurry. At the same time, it avoids the aggregation of polyvinyl alcohol molecular chains caused by the salting-out effect due to the generation of sodium chloride, which would affect the rheological and application properties of the coating.

[0044] The preparation method of the coating in this embodiment includes the following steps:

[0045] S11. Mix calcium chloride, polyvinyl alcohol, carboxymethyl cellulose, cationic fixing agent, and defoamer evenly according to the target mass proportions; the carboxyl groups of sodium carboxymethyl cellulose and polyvinyl alcohol react with the calcium... 2+ Chelation;

[0046] S12. Add kaolin to the slurry obtained in S11 according to the mass fraction and stir evenly.

[0047] S13. Add calcium chloride solution with an equimolar amount of sodium carbonate to the mixture of S12 and stir at a constant speed. CaCl2 and Na2CO3 will precipitate around sodium carboxymethyl cellulose and polyvinyl alcohol between the kaolin particles.

[0048] The process conditions for constant-speed stirring in S13 are shown in Table 2.

[0049] S14. Add deionized water to adjust the solid content of the resulting coating to obtain the target coating.

[0050] The viscosity of the coating used in this embodiment is 800 mPa*S to 1200 mPa*S, as shown in Table 2, and the solid content is 60% to 65%. The sodium chloride generated by the precipitation reaction in this invention effectively increases the viscosity of the resulting coating slurry.

[0051] The coated whiteboard paper prepared in this embodiment includes coated paper and a coating layer. The coating layer is bonded to the coated paper. The coating layer includes kaolin, calcium carbonate with a hollow spherical structure, polyvinyl alcohol as an adhesive, and sodium carboxymethyl cellulose as a dispersant along the thickness direction of the coating. The calcium carbonate is distributed along the chain structure of polyvinyl alcohol and the surface of sodium carboxymethyl cellulose. The calcium carbonate distributed along the chain structure of polyvinyl alcohol between the sheet-like kaolin and the spherical calcium carbonate distributed around the sodium carboxymethyl cellulose together form the connecting space between the ink absorption channels, forming ink absorption channels.

[0052] Example 2

[0053] The main differences between this embodiment and Embodiment 1 are detailed in Tables 1 and 2.

[0054] Example 3

[0055] The main differences between this embodiment and Embodiment 1 are detailed in Tables 1 and 2.

[0056] Example 4

[0057] The main differences between this embodiment and Embodiment 1 are detailed in Tables 1 and 2.

[0058] Table 1. High-efficiency coating process parameters in Examples 1 to 4

[0059]

[0060] Table 2 shows the composition (parts by mass) and preparation parameters of the coatings in Examples 1 to 4 and the comparative examples.

[0061]

[0062]

[0063] Comparative Example

[0064] This comparative example discloses an efficient coating process for coating whiteboard paper. The main difference between this comparative example and Example 3 is that the coating used in this comparative example comprises the following substances in parts by mass:

[0065]

[0066] The calcium carbonate particles in this comparative example are commercially available calcium carbonate with specific parameters of D50≤12μm and purity≥98%.

[0067] Add the above components to deionized water according to the mass fractions and stir to mix evenly. Add deionized water to adjust the viscosity to 1056 mPa*s.

[0068] The coating process conditions in this comparative example are the same as in Example 3, resulting in coated whiteboard paper.

[0069] The absorption of K&N ink on coated whiteboard paper obtained in Examples 1 to 4 and the comparative examples, as well as the roughness, smoothness, and gloss of the coating surface, were tested respectively. See Table 3 for details.

[0070] Table 3 shows the performance of the coated whiteboard paper obtained in Examples 1 to 4 and the comparative examples.

[0071]

[0072] As shown in Table 3, the K&N value of the coated whiteboard paper obtained by the present invention is significantly improved, while maintaining good gloss and low roughness.

[0073] The main inventive concept of this invention is to use kaolin and calcium carbonate as a pigment, and during the mixing process, calcium carbonate particles are dispersed around polyvinyl alcohol (as a binder) and sodium carboxymethyl cellulose (as a dispersant). Calcium ions from calcium chloride, used to generate calcium carbonate, chelate with both polyvinyl alcohol and sodium carboxymethyl cellulose, thereby reducing the concentration of calcium ions in the paint slurry and controlling the dispersion of calcium carbonate in the slurry. When sodium carbonate solution is added, the low concentration of calcium ions in the solution inhibits the accumulation and further growth of the calcium carbonate nanoparticles formed by the precipitation reaction, thus ensuring uniform dispersion of calcium carbonate in the slurry. During calendering, the flaky kaolin, under pressure, rolls and shifts relative to the calcium carbonate particles or hollow calcium carbonate spheres. This ensures the smoothness of the resulting coating while retaining the interconnected channels for ink absorption. Because small or hollow calcium carbonate particles are dispersed around these channels, their small size and large specific surface area provide better ink absorption, promoting ink absorption and distribution. This invention utilizes the combination of calcium carbonate of suitable particle size and flaky kaolin generated during mixing to improve the smoothness and uniformity of the coating, enhance the uniform absorption of ink on the paper surface, and improve print quality and image clarity. In Example 4, the in-situ generated calcium carbonate precipitate has a higher mass fraction than in Examples 1, 2, and 3. However, the excessive sodium chloride generated is detrimental to the coating's gloss and roughness. The micron-sized particles used in the comparative example have a small specific surface area, making it difficult to improve the ink absorption performance of the resulting coating. Furthermore, ordinary nano-calcium carbonate, due to its high surface energy, is difficult to disperse when directly added to the mixture, making the high specific surface area characteristic of nanomaterials difficult to apply.

Claims

1. A high-efficiency coating process for coating whiteboard paper, characterized in that: Includes the following steps: S1. Apply the coating to the surface of the coated paper using a coating machine; The pigments in the coating include kaolin and calcium carbonate. The calcium carbonate consists of calcium carbonate particles generated in situ along the polyvinyl alcohol chain structure during the coating mixing process, as well as hollow spherical calcium carbonate structures generated in situ around sodium carboxymethyl cellulose. The calcium carbonate is uniformly dispersed between the kaolin particles. The gaps between the flaky kaolin and calcium carbonate particles are connected to the hollow spherical structures of calcium carbonate to form the absorption channels of the ink. S2. Dry the coated paper with the coating layer; S3. After calendering and finishing, the coated white board paper undergoes relative displacement and sliding between the kaolin and the hollow spheres and / or particles of calcium carbonate during the calendering process to obtain the target coated white board paper. The coating used in the coating layer of coated whiteboard paper comprises the following substances in parts by weight: 40 to 60 parts of kaolin; 15 to 20 parts calcium carbonate; 10 to 20 parts of polyvinyl alcohol; 3 to 5 parts sodium carboxymethyl cellulose; 2 to 5 parts of cationic fixing agent; 0.1 to 0.5 parts of defoamer; The preparation method of the coating includes the following steps: S11. Mix calcium chloride, polyvinyl alcohol, sodium carboxymethyl cellulose, cationic fixing agent, and defoamer evenly according to the target mass proportions; the carboxyl groups of sodium carboxymethyl cellulose and polyvinyl alcohol react with the calcium chloride and polyvinyl alcohol respectively. 2+ Chelation; S12. Add kaolin to the slurry obtained in S11 according to the mass fraction and stir evenly. S13. Add sodium carbonate solution with an equimolar amount of calcium chloride to the mixture of S12 and stir at a constant speed. CaCl2 and Na2CO3 will precipitate around sodium carboxymethyl cellulose and polyvinyl alcohol between the kaolin particles. S14. Add deionized water to adjust the solid content of the resulting coating to obtain the target coating.

2. The high-efficiency coating process for coating whiteboard paper as described in claim 1, characterized in that: The constant-speed stirring process in S13 is 800 r / min to 1000 r / min, and the stirring time is 45 min to 65 min.

3. The high-efficiency coating process for coating whiteboard paper as described in claim 1, characterized in that: The viscosity of the coating used in the coating layer is 800 mPa·S to 1200 mPa·S, and the solid content is 60% to 65%.

4. The high-efficiency coating process for coating whiteboard paper as described in claim 1, characterized in that: The drying process conditions in step S2 are as follows: drying at 90℃ to 120℃ for 20 to 30 seconds.

5. The high-efficiency coating process for coating whiteboard paper as described in claim 1, characterized in that: The calendering process parameters in step S3 are as follows: Temperature ranges from 100℃ to 120℃, and pressure ranges from 20kN / m to 40kN / m.

6. A coated whiteboard paper produced by the efficient coating process according to any one of claims 1 to 5.

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