Preparation process of matte white cardboard

Abstract

The invention relates to the technical field of a coating process in pulping and papermaking, in particular to a preparation process of a matte white cardboard, which comprises the following steps: grinding and screening raw ore to obtain calcium carbonate with ultrafine particle size distribution, the viscosity of which is 100-150cps, the particle size of which is less than or equal to 2 mu m distribution of 97-99% and the particle size of which is less than or equal to 1 mu m distribution of 79-80%; mixing 100 parts of calcium carbonate with superfine particle size distribution, 0.2 part of a dispersing agent, 0-0.4 part of sodium carboxymethyl cellulose, 10.5-11 parts of styrene-butadiene latex, 0.2 part of a defoaming agent, 0.2 part of a lubricating agent, 0.3 part of a water-resistant agent, 0.15 part of polyvinyl alcohol and 0.1-0.4 part of a rheological agent to prepare a top coating; conveying the prepared topcoat paint to a paper machine, and coating the paper; and drying and coiling the coated paper. By optimizing and improving the particle size distribution of ground calcium carbonate, the consumption of the china clay is reduced, the coating index, the on-machine operation condition and the physical property and printing effect of paper are improved, the matte effect is realized, meanwhile, the dependence on imported china clay is reduced, and the production cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of coating processes in pulping and papermaking, and in particular to a preparation process of matte white cardboard. Background Art

[0002] Gloss is a key performance indicator for coated white cardboard. Low values ​​can result in reduced color saturation and dull colors, affecting the quality of printed materials. However, excessively high gloss can create strong glare when exposed to light and can also easily cause defects such as light spots. Therefore, it is important to ensure gloss is within an appropriate range (according to the national standard GB / T 21301-2007, a 75° gloss of 11% to 54% is considered matte paper). The topcoat is located on the outermost surface of white cardboard, and its pigment composition provides the most direct and effective way to adjust gloss. Currently, the main pigments used for topcoats include ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), china clay, calcined clay, and plastic pigments. GCC is a very important pigment for paper coatings. Its high whiteness, excellent rheological properties, and high solids content require relatively low adhesives. Its abundant supply and low price point perfectly meet the needs of the industry's "business-driven" environment. GCC, after processing such as fine grinding and screening, also exhibits excellent optical hiding properties. PCC is a typical example of a narrow particle size distribution pigment. Because it is a chemically synthesized mineral pigment, its particle size can be very small and uniform. This narrow particle size distribution allows fewer smaller particles to fill the pores created by larger pigment particles within the coating, resulting in more pores within a given thickness. Its ease of calendering also facilitates the formation of thick, bulky coatings with high whiteness and excellent optical hiding properties. However, adding pigments with a wider particle size distribution to PCC results in a relatively closed coating structure, lowering the K&N value and negatively impacting hiding properties. China clay flake pigments, with their large interparticle volume, easily form "bridges" with other pigments. Furthermore, flake pigments can achieve a high gloss and smooth surface at relatively low calendering pressures, resulting in thick, bulky coatings with excellent optical hiding properties. However, these pigments are more expensive than GCC. Calcined clay has a higher whiteness, a high refractive index, and numerous small cavities within its particles. Due to its high price, it is typically used in coatings in limited quantities. Plastic pigments are much less dense than common mineral pigments like kaolin and calcium carbonate. Therefore, for the same coating weight, they produce larger and thicker coatings, imparting excellent optical hiding properties to coated paper. However, plastic pigments are expensive, hindering widespread use. Therefore, kaolin and GCC are currently the primary pigments in most coatings. However, due to the high price of high-quality kaolin, the research and development trend in coating preparation is to increase the GCC dosage and reduce the kaolin mass ratio to reduce costs.

[0003] The production of matte paper primarily involves selecting coating pigments and adjusting the pigment particle size and ratio within the coating formula to increase the microscopic roughness of the paper surface. Currently, the most effective method is to adjust the ratio of china clay to calcium carbonate. Reducing the amount of china clay significantly reduces gloss, but also reduces the coating viscosity, making it more susceptible to paper defects such as doctor blade marks. Therefore, the coating formula must be adjusted while taking into account coating performance, machine operation, and final paper quality. Summary of the Invention

[0004] The purpose of the present invention is to address the defects and shortcomings of the existing technology and provide a preparation process for matte white cardboard. By optimizing and improving the particle size distribution of ground calcium carbonate, the amount of porcelain clay used can be reduced, the coating indicators, machine operation conditions, and the physical properties and printing effects of the paper can be improved, and matte can be achieved while reducing dependence on imported porcelain clay and reducing production costs.

[0005] To achieve the above object, the present invention adopts the following technical solution: its operating steps are as follows: Step 1: Grinding of ultra-fine particle size distribution calcium carbonate: The raw ore is ground and sieved to obtain ultra-fine particle size distribution calcium carbonate with a viscosity of 100-150cps, a particle size distribution of 97-99% ≤ 2μm, and a particle size distribution of 79-80% ≤ 1μm; Step 2: Coating configuration: Mix 100 parts of ultrafine particle size distribution calcium carbonate, 0.2 parts of dispersant, 0-0.4 parts of sodium carboxymethyl cellulose (CMC), 10.5-11 parts of styrene-butadiene latex, 0.2 parts of defoamer, 0.2 parts of lubricant, 0.3 parts of water-resistance agent, 0.15 parts of polyvinyl alcohol (PVA), and 0.1-0.4 parts of rheological agent to prepare the topcoat; Step 3: Surface coating: transport the prepared surface coating to the paper machine and coat the paper; Step 4: Dry and roll up the coated paper.

[0006] Furthermore, the mass percentages of the components in the raw ore are as follows: calcium carbonate ≥ 98%, iron oxide ≤ 0.05%, magnesium oxide ≤ 0.8%, and silicon dioxide ≤ 0.1%.

[0007] Furthermore, the raw ore has a calcium hardness of ≤3 and a fineness of ≥325 mesh.

[0008] Furthermore, the grinding medium balls added during the grinding process of the ultrafine particle size distribution calcium carbonate have a Mohs hardness of ≥8 and a specific gravity of 3.2 kg / cm 3 , specifications are 0.8-3.5mm.

[0009] Furthermore, the grinding medium balls are grinding beads.

[0010] Furthermore, the filling rate of the grinding medium balls is 65%-68%. Furthermore, the amount of dispersant added during the grinding process of the ultrafine particle size distribution calcium carbonate is 6.46 kg / bdt in the first stage and 10.86-15.81 kg / bdt in the second stage.

[0011] Furthermore, during the grinding process of the ultrafine particle size distribution calcium carbonate, the rotational speeds of the three wet grinders were 99 r / min, 97 r / min, and 98 r / min, respectively.

[0012] Furthermore, the specific process of the coating preparation is as follows: a dispersant and ultrafine particle size distribution calcium carbonate are added to water at the same time (wherein the ultrafine particle size distribution calcium carbonate accounts for 87%-89% of the total surface coating mass), and a high-speed disperser is used for high-speed dispersion to obtain a white material; a defoamer and a rheological agent are then added to the white material at the same time and stirred evenly; sodium carboxymethyl cellulose, styrene-butadiene latex and polyvinyl alcohol are then added to the stirred white material at the same time, and stirred again to form a semi-finished coating; a water-resistant agent and a lubricant are added to the semi-finished coating, and stirred evenly to finally obtain a surface coating.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a preparation process for matte white cardboard, which reduces the amount of porcelain clay used by optimizing and improving the particle size distribution of ground calcium carbonate, improves coating indicators, machine operation conditions, and physical properties and printing effects of paper, achieves matte while reducing dependence on imported porcelain clay and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a comparison table of the high shear viscosities of the topcoat in the present invention and the topcoat in the prior art (using American porcelain clay instead of the ultrafine particle size distribution calcium carbonate in the present invention).

[0015] Figure 2 The glossiness of the paper produced by the present invention and the paper produced by the prior art is tested. DETAILED DESCRIPTION

[0016] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. The preferred embodiments described are only used as examples. All other embodiments obtained by those skilled in the art without making any creative work are within the scope of protection of the present invention.

[0017] like Figure 1-Figure 2 As shown, this specific embodiment adopts the following technical solution: its operation steps are as follows: Step 1: Grinding of ultra-fine particle size distribution calcium carbonate: The raw ore is ground and sieved to obtain ultrafine particle size distribution calcium carbonate with a viscosity of 100-150 cps, a particle size distribution of 97-99% ≤ 2 μm, and a particle size distribution of 79-80% ≤ 1 μm. The raw ore has a calcium carbonate hardness of ≤ 3 and a fineness of ≥ 325 mesh. The mass percentages of the components in the raw ore are as follows: calcium carbonate ≥ 98%, iron oxide ≤ 0.05%, magnesium oxide ≤ 0.8%, and silicon dioxide ≤ 0.1%. The grinding medium balls added during the grinding of the ultrafine particle size distribution calcium carbonate have a Mohs hardness of ≥ 8 and a specific gravity of 3.2 kg / cm 3 The specifications are 0.8-3.5mm; the grinding medium balls are pickaxe beads with a filling rate of 65%-68%; the amount of dispersant added during the grinding process of ultrafine particle size distribution calcium carbonate is 6.46 kg / bdt in the first stage and 10.86-15.81 kg / bdt in the second stage; the speeds of the three wet mills during the grinding process of ultrafine particle size distribution calcium carbonate are 99r / min, 97r / min, and 98r / min respectively; Step 2: Coating configuration: The raw materials are selected according to the following weight components: 100 parts of ultrafine particle size distribution calcium carbonate, 0.2 parts of dispersant, 0-0.4 parts of sodium carboxymethyl cellulose (CMC), 10.5-11 parts of styrene-butadiene latex, 0.2 parts of defoaming agent, 0.2 parts of lubricant, 0.3 parts of water resistance agent, 0.15 parts of polyvinyl alcohol (PVA), and 0.1-0.4 parts of rheological agent; Then, 0.2 parts of a dispersant and ultrafine particle size distribution calcium carbonate are added to water simultaneously (wherein the ultrafine particle size distribution calcium carbonate accounts for 87%-89% of the total topcoat coating mass), and dispersed at high speed using a high-speed disperser to obtain a white material; then, 0.2 parts of a defoamer and 0.1-0.4 parts of a rheological agent are added to the white material simultaneously, and stirred evenly; then, 0-0.4 parts of sodium carboxymethyl cellulose, 10.5-11 parts of styrene-butadiene latex, and 0.15 parts of polyvinyl alcohol are added to the stirred white material simultaneously, and stirred again to form a semi-finished coating; 0.3 parts of a water-resistant agent and 0.2 parts of a lubricant are added to the semi-finished coating, and stirred evenly to finally obtain a topcoat coating; Step 3: Surface coating: transport the prepared surface coating to the paper machine and coat the paper; Step 4: Dry and roll up the coated paper.

[0018] Experimental comparison: The glossiness of the paper produced by the present invention and the paper produced by the prior art was tracked and tested over a period of time. The topcoat of the prior art described in the present invention comprises: 2 parts of American porcelain clay, 98 parts of ground calcium carbonate, 0.2 parts of dispersant, 0-0.4 parts of sodium carboxymethyl cellulose (CMC), 10.5-11 parts of styrene-butadiene latex, 0.2 parts of defoaming agent, 0.2 parts of lubricant, 0.3 parts of water-resistance agent, 0.15 parts of polyvinyl alcohol (PVA), and 0.1-0.4 parts of rheological agent.

[0019] The following conclusions were drawn from the experimental data: By increasing the number of pick beads, increasing the amount of dispersant, and subsequently increasing the wet mill speed (from 93 / 96 / 98 to 99 / 97 / 98), the stable preparation of ultrafine particle size distribution of calcium carbonate was finally achieved; Ultrafine particle size distribution calcium carbonate is used to replace American china clay in the preparation of topcoat. The storage and reflux high shear viscosity of the resulting coating are lower than those of the coating containing imported china clay. This means that the probability of coated paper defects such as scratching after being put on the machine is smaller, that is, the ultrafine particle size distribution calcium carbonate coating paper machine operation effect is better; After applying the topcoat prepared with 100% ultra-fine particle size distribution calcium carbonate, all key indicators are comparable to those of the topcoat containing imported porcelain clay. In addition, it not only stably meets the matte conditions, but is also more cost-effective.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a preparation process for matte white cardboard, which reduces the amount of porcelain clay used by optimizing and improving the particle size distribution of ground calcium carbonate, improves coating indicators, machine operation conditions, and physical properties and printing effects of paper, achieves matte while reducing dependence on imported porcelain clay and reducing production costs.

[0021] For those skilled in the art, they can modify the technical solutions described in the aforementioned embodiments and make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A process for preparing matte white cardboard, characterized by: Its operation steps are as follows: Step (1): Grinding of ultrafine particle size distribution calcium carbonate: The raw ore is ground and sieved to obtain ultra-fine particle size distribution calcium carbonate with a viscosity of 100-150cps, a particle size distribution of 97-99% ≤ 2μm, and a particle size distribution of 79-80% ≤ 1μm; Step (2), coating configuration: Mix 100 parts of ultrafine particle size distribution calcium carbonate, 0.2 parts of dispersant, 0-0.4 parts of sodium carboxymethyl cellulose, 10.5-11 parts of styrene-butadiene latex, 0.2 parts of defoamer, 0.2 parts of lubricant, 0.3 parts of water-resistance agent, 0.15 parts of polyvinyl alcohol, and 0.1-0.4 parts of rheological agent to prepare a topcoat; Step (3), surface coating: transporting the prepared top coating to the paper machine and coating the paper; Step (4): Dry and roll up the coated paper.

2. The process for preparing matte white cardboard according to claim 1, characterized in that: The mass percentages of the components in the raw ore are as follows: calcium carbonate ≥ 98%, iron oxide ≤ 0.05%, magnesium oxide ≤ 0.8%, and silicon dioxide ≤ 0.1%.

3. The process for preparing matte white cardboard according to claim 1, characterized in that: The raw ore has a calcium hardness of ≤3 and a fineness of ≥325 mesh.

4. The process for preparing matte white cardboard according to claim 1, characterized in that: The grinding medium balls added during the grinding process of the ultra-fine particle size distribution calcium carbonate have a Mohs hardness of ≥8 and a specific gravity of 3.2 kg / cm 3 , specifications are 0.8-3.5mm.

5. The process for preparing matte white cardboard according to claim 4, characterized in that: The grinding medium balls are grinding beads.

6. The process for preparing matte white cardboard according to claim 5, characterized in that: The filling rate of the grinding medium balls is 65%-68%.

7. The process for preparing matte white cardboard according to claim 1, characterized in that: The amount of dispersant added during the grinding process of the ultrafine particle size distribution calcium carbonate is 6.46 kg / bdt in the first stage and 10.86-15.81 kg / bdt in the second stage.

8. The process for preparing matte white cardboard according to claim 1, characterized in that: During the grinding process of the ultrafine particle size distribution calcium carbonate, the rotation speeds of the three wet grinders were 99 r / min, 97 r / min, and 98 r / min respectively.

9. The process for preparing matte white cardboard according to claim 1, characterized in that: The specific process of the coating preparation is as follows: a dispersant and ultrafine particle size distribution calcium carbonate are added to water at the same time, wherein the ultrafine particle size distribution calcium carbonate accounts for 87%-89% of the total topcoat coating mass, and a high-speed disperser is used for high-speed dispersion to obtain a white material; a defoamer and a rheological agent are then added to the white material at the same time and stirred evenly; sodium carboxymethyl cellulose, styrene-butadiene latex and polyvinyl alcohol are then added to the stirred white material at the same time and stirred again to form a semi-finished coating; a water-resistant agent and a lubricant are added to the semi-finished coating, stirred evenly, and finally a topcoat coating is obtained.

Images