Coated paper and method for producing the same

Abstract

The application provides a copper plate paper and a preparation method thereof. The preparation method comprises the following steps: papermaking a raw paper; a pulp of the raw paper comprises paper pulp, fillers and additives; the paper pulp comprises coniferous chemical pulp and broad-leaved chemical pulp, the coniferous chemical pulp and the broad-leaved chemical pulp both comprise fine grinding pulp and light grinding pulp, the proportion of the fine grinding pulp to the light grinding pulp of the coniferous chemical pulp is 5-35%:65-95%, and the proportion of the fine grinding pulp to the light grinding pulp of the broad-leaved chemical pulp is 5-40%:60-95%; wherein the beating degree of the fine grinding pulp of the coniferous chemical pulp is 90-120 ml, and the beating degree of the light grinding pulp is 380-420 ml; the beating degree of the fine grinding pulp of the broad-leaved chemical pulp is 120-150 ml; a surface sizing layer is formed on the two sides of the raw paper; a base coating layer and a surface coating layer are formed on the surface sizing layer of the front side in sequence; and a back coating layer is formed on the surface sizing layer of the back side. The preparation method realizes the improvement of the surface physical strength of the single-side copper plate paper by optimizing the physical strength, and effectively solves the problems of insufficient paper physical strength and die cutting waste breakage marks in the prior art.

Description

Technical Field

[0001] This application relates to the technical field of papermaking, specifically to a coated paper and its preparation method. Background Technology

[0002] Single-sided coated paper is the most commonly used core substrate for self-adhesive labels and barcode labels. Due to its advantages such as good printability, moderate cost, and smooth surface, it is used extensively in the label printing industry. Currently, commercial single-sided coated paper is mostly produced using large-scale cultural paper machines to improve production efficiency and capacity, and to stabilize product quality.

[0003] With intensifying competition in the self-adhesive label market, manufacturers are increasingly operating on thin profit margins. In pursuit of maximum profit, they are compressing raw material costs, leading to a gradual reduction in the waste removal margin, from the initial 3-5 mm to below 1.5 mm. This significantly increases the risk of label breakage during online automatic waste removal, exacerbating the insufficient strength matching of existing single-sided coated paper. Furthermore, single-sided coated paper itself is stiff, brittle, and has a fragile surface coating. When single-sided coated paper is laminated with the backing paper to form a self-adhesive label, the waste removal edge is prone to breakage under stress during the die-cutting waste removal process. Simultaneously, the coating is prone to peeling and powdering, causing waste removal interruptions, reduced processing yield, and impacting the integrity of the finished label and processing efficiency. Analysis of the single-sided coated paper's base paper processing conditions reveals a single pulping method, making it difficult to simultaneously achieve adequate tear strength and tensile strength, resulting in overall physical strength insufficient for high-speed label processing. These industry pain points, such as label breakage during die-cutting waste removal, hinder the improvement of label paper product quality and application scope. Summary of the Invention

[0004] The first aspect of this application provides a method for preparing coated paper, the method comprising: Papermaking process; the pulp of the papermaking process includes pulp, fillers, and additives; the pulp includes softwood chemical pulp and hardwood chemical pulp, both of which include refined pulp and lightly refined pulp. The ratio of refined pulp to lightly refined pulp in softwood chemical pulp is 5~35%:65~95%, and the ratio of refined pulp to lightly refined pulp in hardwood chemical pulp is 5~40%:60~95%; wherein, the freeness of refined pulp in softwood chemical pulp is 90~120ml, and the freeness of lightly refined pulp is 380~420ml; the freeness of refined pulp in hardwood chemical pulp is 120~150ml, and the freeness of lightly refined pulp is 360~400ml. A surface adhesive layer is formed on both sides of the base paper; A base coat and a top coat are formed sequentially on the surface adhesive layer; A back coating is formed on the surface adhesive layer on the back side.

[0005] In some optional embodiments, the ratio of finely ground softwood chemical pulp to lightly ground softwood chemical pulp is 10-30%: 70-90%, and the ratio of finely ground hardwood chemical pulp to lightly ground hardwood chemical pulp is 10-30%: 70-90%.

[0006] In some optional embodiments, the pulp further includes mechanical pulp and waste pulp; softwood chemical pulp: hardwood chemical pulp: mechanical pulp: waste pulp = 0~40: 45~100: 0~15: 0~30; wherein the pulping freedom of the mechanical pulp is 120~150ml.

[0007] In some optional embodiments, the papermaking process further includes in-pulp sizing, wherein the in-pulp sizing is performed by a combination of alkyl ketene dimer and alkenyl succinate, or by a combination of alkyl ketene dimer and neutral rosin sizing agent.

[0008] In some optional embodiments, in the step of forming a surface sizing layer on each of the two sides of the base paper, the formulation of the surface sizing layer includes corn starch slurry and a surface sizing agent; wherein, the corn starch slurry is prepared by enzymatic conversion of corn starch or oxidized corn starch followed by gelatinization; and the surface sizing agent is a styrene-acrylate copolymer emulsion or an alkyl ketene dimer or a combination of both.

[0009] In some optional embodiments, the surface sizing agent is used at an oven-dry concentration of 3.0-7.0% of the surface starch, and the application rate is 1.0-1.5 g / m³. 2 / noodle.

[0010] In some optional embodiments, in the step of sequentially forming a base coating and a top coating on the surface adhesive layer, the pigment of the base coating is heavy calcium carbonate, the proportion of heavy calcium carbonate with a particle size of less than or equal to 2 μm is 65-98%, the pigment: styrene-butadiene latex = 100: 8-12; and the solid content is 60.0-65.0%.

[0011] In some optional embodiments, the pigment ratio of the topcoat coating is: light calcium carbonate: heavy calcium carbonate: kaolin = 0~100: 0~100: 0~40, wherein the light calcium carbonate used has a particle size of less than or equal to 2μm accounting for 95%; the heavy calcium carbonate used has a particle size of less than or equal to 2μm accounting for 95~98%; and the kaolin used has a particle size of less than or equal to 2μm accounting for 85~90%. A leveling agent is added to the topcoat coating, with a pigment: leveling agent: 100: 0.8~3.0, and the leveling agent is a polyether modified organosilicon leveling agent or an acrylic leveling agent.

[0012] In some optional embodiments, in the step of forming a back coating on the back surface adhesive layer, the pigment of the back coating is heavy calcium carbonate; wherein the heavy calcium carbonate used has a particle size of less than or equal to 2 μm accounting for 65-98%; the ratio of pigment to styrene-butadiene latex is 100:6-10; a water-resistant agent is also added to the back coating; the ratio of pigment to water-resistant additive is 100:0.5-2.0; the water-resistant additive includes any one of amino resins, metal salts, and polyamide epoxy resins.

[0013] Secondly, embodiments of this application provide coated paper, which is prepared using the preparation method described in the above embodiments.

[0014] The method for preparing coated paper provided in this application improves the physical strength of single-sided coated paper by optimizing its physical strength, effectively solving the problems of insufficient physical strength of paper and waste discharge and broken labels in the prior art. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic flowchart of an embodiment of the method for preparing coated paper according to this application; Figure 2 This is a schematic diagram of the laminated structure after surface adhesive layers are formed on both sides of the base paper during the preparation of coated paper in this embodiment. Figure 3 This is a schematic diagram of the laminated structure of an embodiment of the coated paper of this application. Detailed Implementation

[0017] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the application. Similarly, the following embodiments are only some, not all, embodiments of the present application, and all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present application.

[0018] The terms "first," "second," and "third" used in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationships and movement of components in a specific posture (as shown in the figures). If the specific posture changes, the directional indication will also change accordingly. The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or components inherent to these processes, methods, products, or devices.

[0019] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0020] In view of this, and addressing the technical problems such as insufficient physical strength of existing single-sided coated paper for self-adhesive labels, leading to label breakage and other issues during waste disposal, this invention provides a method for preparing single-sided coated paper. Please refer to [link / reference]. Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of the method for preparing coated paper according to this application. The preparation method includes, but is not limited to, the following steps.

[0021] Step S100: Making the original paper.

[0022] In this step, the pulp of the base paper includes pulp, fillers, and additives; the pulp includes softwood chemical pulp and hardwood chemical pulp, both of which include refined pulp and lightly refined pulp. The ratio of refined pulp to lightly refined pulp in softwood chemical pulp is 5~35%:65~95%, and the ratio of refined pulp to lightly refined pulp in hardwood chemical pulp is 5~40%:60~95%; wherein, the freeness of refined pulp in softwood chemical pulp is 90~120ml, and the freeness of lightly refined pulp is 380~420ml; the freeness of refined pulp in hardwood chemical pulp is 120~150ml, and the freeness of lightly refined pulp is 360~400ml.

[0023] Optionally, the pulp is a base paper made from a mixture of softwood chemical pulp, hardwood chemical pulp, mechanical pulp, waste pulp (or other pulps), fillers, and chemical additives. The pulp portion is refined according to design requirements to achieve the necessary physical strength of the paper. Calculated by weight percentage, the pulp portion of this base paper has the following composition: softwood chemical pulp: hardwood chemical pulp: mechanical pulp: waste pulp = 0~40: 45~100: 0~15: 0~30; filler: pulp = 5~15:100; chemical additives: pulp = 0.02~1.2:100. The filler is heavy calcium carbonate (GCC) or light calcium carbonate (PCC). The chemical additives are several or more of the following: fluorescent whitening agents, dyes, dry strength agents, internal sizing agents, and binary or ternary retention / filtration aids (cationic polyacrylamide + microparticle silica sol / bentonite + anionic polyacrylamide).

[0024] The pulping process involves a blend of softwood chemical pulp and hardwood chemical pulp (fine pulp + light pulp). Fine pulp promotes the full fibrillation of fibers, improving the tensile strength, folding endurance, and cohesive strength of the paper. Light pulp increases the aspect ratio of the fibers, improving the tear strength of the paper. The two processes work together to balance the tensile strength and tear strength of the paper. The composition ratio of refined softwood chemical pulp to lightly refined pulp is 5-35% compared to 65-95%; the composition ratio of refined hardwood chemical pulp to lightly refined pulp is 5-40% compared to 60-95%; the CSF (freeness fraction) of the mechanical pulp is 120-160 ml, and the low freeness fraction helps to reduce the impact of short / hard fibers in the mechanical pulp on the paper surface feel; the base paper sizing system uses a combination of AKD (alkyl ketene dimer) and ASA (alkenyl succinate), or a combination of AKD and a neutral rosin sizing agent; this improves the paper's water resistance, dimensional stability, and wet strength, and reduces paper deformation due to moisture; the base paper weight range is 48-75 g / m². 2 .

[0025] To improve the tensile and tear strength of the paper during the papermaking process, the refining process is optimized: softwood chemical pulp and hardwood chemical pulp are blended using a (fine pulp + light pulp) process; the CSF of softwood chemical pulp is 280~350ml during conventional refining, 90~120ml during fine refining, and 380~420ml during light refining when combined with fine pulp; the CSF of hardwood chemical pulp is 300~360ml during conventional refining, 120~150ml during fine refining, and 360~400ml during light refining when combined with fine pulp. The ratio of refined softwood chemical pulp to lightly refined pulp is 10-30% compared to 70-90%; the ratio of refined hardwood chemical pulp to lightly refined pulp is 10-30% compared to 70-90%; the CSF of mechanical pulp is 120-150ml, and the low freeness helps to reduce the impact of short / hard fibers in mechanical pulp on the paper surface feel; the amount of softwood chemical pulp, hardwood chemical pulp, mechanical pulp and filler can be maintained at the same pulp ratio as in conventional refining, without increasing the proportion of softwood pulp or reducing the proportion of mechanical pulp or adding ash.

[0026] To improve the water resistance of paper sizing, the following control conditions were adopted: 1) To reduce the impact of fillers on the sizing effect, heavy calcium carbonate was preferred as the filler, with a particle size of ≤2μm accounting for 60-65%; the filler ratio to oven-dry pulp was 50-75 g / m³. 2 1) Within the base paper range, a moisture content of 10-15% is preferred; 2) The pulp sizing process adopts a composite sizing scheme, using alkyl ketene dimer compounded with alkenyl succinate, with both sizing agents preferably having a high C18 ratio; the addition amount of AKD to pulp fibers is 0.6-0.9%, and the addition amount of ASA to pulp fibers is 0.08-0.14%; 3) Under the condition of ensuring paper uniformity, a ternary retention aid system (cationic polyacrylamide + micro-particle silica sol / bentonite + anionic polyacrylamide) is preferred to improve sizing and retention effects; 4) Under the condition of ensuring that the moisture content of the base paper is within the control requirements, the temperature of the drying cylinders in each section of the paper machine is optimized to improve the curing effect of the sizing agent.

[0027] Step S200: Form a surface adhesive layer on both sides of the base paper.

[0028] Please see Figure 2 , Figure 2 This is a schematic diagram of the laminated structure after the surface adhesive layers are formed on both sides of the base paper during the preparation of coated paper in this embodiment. In the figure, 110 represents the base paper layer, and 121 and 122 represent the front surface adhesive layer and the back surface adhesive layer, respectively.

[0029] The surface sizing layer is directly coated on both sides of the base paper substrate. The surface sizing formula consists of corn starch sizing solution and a surface sizing agent. The corn starch sizing solution is prepared by enzymatic conversion of corn starch or gelatinization of oxidized corn starch. The surface sizing agent is SAE (styrene-acrylate copolymer emulsion), AKD (alkyl ketene dimer), or a combination of both. The surface sizing agent is applied at an oven-dry rate of 3.0–7.0% of the surface starch. The surface starch is sizing using a C2S-structured MSP, with an application rate of 1.0–1.5 g / m³. 2 / side (both sides of the paper are glued).

[0030] In the surface sizing layer (film transfer coating sizing), the surface sizing formulation is (corn starch adhesive + surface sizing agent); the corn starch adhesive is prepared by enzymatic conversion of corn starch followed by gelatinization; the surface sizing agent is an SAE (styrene-acrylate copolymer emulsion) sizing agent. The preferred amount of surface sizing agent relative to the oven-dry weight of the surface sizing starch is 3.5-5.0%.

[0031] Please continue reading. Figure 1 The preparation method in this embodiment also includes step S300, in which a base coating layer and a top coating layer are formed sequentially on the surface adhesive layer on the front side.

[0032] Please see Figure 3 , Figure 3 This is a schematic diagram of the laminated structure of an embodiment of coated paper of this application, wherein 131 is marked as the base coating layer and 132 is marked as the top coating layer.

[0033] In this step, the pigment in the base coat is heavy calcium carbonate, calculated by weight percentage; the heavy calcium carbonate used has a particle size of 2μm or less accounting for 65-98%; the pigment: styrene-butadiene latex ratio is 100:8-12; the coating is mixed with water to prepare a coating with a solid content of 60.0-65.0%; and alkali is added to adjust the pH to 9.0±0.5; coating is applied using methods such as film transfer or doctor blade, with a coating amount of 6.0-8.0 g / m³. 2 / side (coating on the front side of the paper).

[0034] Preferably, the base coat pigment is heavy calcium carbonate; wherein the heavy calcium carbonate used has a particle size of less than or equal to 2μm accounting for 65-70%; the pigment: styrene-butadiene latex ratio is 100:8-10; the coating is mixed with water to prepare a coating with a solid content of 60.0-65.0%, and alkali is added to adjust the pH to the range of 9.0±0.5; the coating is applied by film transfer or doctor blade coating, with a coating amount of 6.0-8.0 g / m³. 2 / side (coating on the front side of the paper).

[0035] The pigment ratio of the topcoat layer in the coating, calculated by weight percentage, is: light calcium carbonate: heavy calcium carbonate: kaolin = 0~100: 0~100: 0~40. Among them, the light calcium carbonate used has a particle size of less than or equal to 2μm accounting for 95%; the heavy calcium carbonate used has a particle size of less than or equal to 2μm accounting for 95~98%; and the kaolin used has a particle size of less than or equal to 2μm accounting for 85~90%. The topcoat coating also contains a leveling agent, with a pigment: leveling agent ratio of 100: 0.8~3.0.

[0036] Optionally, the leveling agent is a polyether-modified silicone leveling agent or an acrylic leveling agent; if applied by a scraper, an acrylic leveling agent is preferred; Pigment: Latex = 100: 9~12; Pigment: Fluorescent whitening agent: Dye: Dispersant: Defoamer: Water-resistant agent: Lubricant: Rheology modifier: Tackifier = 100: 0.06~0.28: 0.003~0.01: 0.05~0.15: 0.05~0.10: 0.2~0.6: 0~0.4: 0.03~0.06: 0.2~0.6; Water is added to prepare a topcoat with a solid content of 66-70%, and alkali is added to adjust the pH to 9.0±0.5; the topcoat is applied by a scraper, with a coating amount of 7.0~13.0 g / m². 2 / side (coating the front of the paper).

[0037] The preparation method in this embodiment further includes step S400, forming a back coating layer on the back surface adhesive layer.

[0038] Please continue reading. Figure 3 , Figure 3 The label 141 indicates the back coating layer. The pigment in the back coating layer, calculated by weight percentage, is heavy calcium carbonate; the proportion of heavy calcium carbonate with a particle size of ≤2μm is 65-98%; the ratio of pigment to styrene-butadiene latex is 100:6-10; the back coating layer also contains a water-resistant agent; the ratio of pigment to water-resistant additive is 100:0.5-2.0; the water-resistant additive includes any one of amino resins, metal salts, or polyamide epoxy resins. Furthermore, the back coating layer is obtained after modifying the original coating; the back coating layer is mixed with water to prepare a coating with a solid content of 20-50%; and the pH is adjusted to 9.0±0.5 by adding alkali; it is applied using film transfer or doctor blade methods, with a coating amount of 3.0-5.0 g / m³. 2 / side (coating on the back of the paper).

[0039] Optionally, the pigment in the back coating is heavy calcium carbonate; wherein the heavy calcium carbonate used has a particle size of less than or equal to 2μm accounting for 65-70%; the ratio of pigment to styrene-butadiene latex is 100:6-8; a water-resistant agent is added to the back coating corresponding to the back side of the single-sided coated paper; the ratio of pigment to water-resistant additive is 100:1.5-2.0; wherein the water-resistant additive is selected from polyamide epoxy resin; the back coating is prepared by adding water to form a coating with a solid content of 20-50%; and alkali is added to adjust the pH to the range of 9.0±0.5; coating is applied by film transfer or blade coating, with a coating amount of 3.0-5.0 g / m². 2 / side (coating on the back of the paper).

[0040] In addition, the top coating in the coating can be specifically formulated according to the physical properties required for printing and post-processing of single-sided coated paper. The detailed characteristics of this part are within the understanding of those skilled in the art and will not be elaborated here.

[0041] In addition to the above, the coatings in this invention can also be combined with other well-known inorganic pigments such as kaolin and calcium carbonate, and organic pigments such as plastic pigments. One or more of the above pigments can be selected as needed. The latex used can also be combined with one or more of styrene-butadiene latex, styrene-acrylic latex, and vinyl acetate latex. The starch used can be selected from one or more of oxidized starch, phosphate starch, hydroxyethyl starch, and dextrin. In addition, as needed, various auxiliary agents commonly used for coated paper, such as dispersants, thickeners, humectants, defoamers, water-resistant agents, and colorants, can be used appropriately.

[0042] The single-sided coated paper prepared using the above method can significantly improve the physical strength of the paper, solving the problem of die-cutting waste and broken labels caused by insufficient physical strength of the paper. The above single-sided coated paper can achieve the following indicators: tear strength ≥34.0gf in the longitudinal direction and ≥48.0gf in the transverse direction; tensile strength ≥12.5kg / 15mm in the longitudinal direction and ≥3.60kg / 15mm in the transverse direction.

[0043] The manufacturing steps of the single-sided coated paper of the present invention are as follows: a base paper is made by mixing softwood chemical pulp, hardwood chemical pulp, mechanical pulp, other pulps, fillers, chemical additives, and internal sizing agents; then, surface sizing is applied to the surface of the base paper in sequence, followed by a base coating, a top coating, and a back coating; and then, after subsequent calendering, single-sided coated paper is produced. In each production stage, the moisture content of the base paper after surface sizing is controlled at 3.0~4.0%; the moisture content after micro-coating is controlled at 4.0~5.0%; the moisture content after top and back coating is controlled at 4.5~6.0%; and the moisture content after supercalendering is controlled at 4.0~4.5%.

[0044] The coated paper in this embodiment consists of a base paper, double-sided sizing layers, a base coating layer, a top coating layer, and a back coating layer. It is formed by surface sizing, base coating, top coating, and back coating. The pulping process, sizing system, and back coating layer are optimized. Sizing agent is added to the sizing layer on the front side of the single-sided coated paper, and the base and top coating layers can be customized according to actual needs. Sizing agent is added to the sizing layer on the back side of the single-sided coated paper, and a water-resistant coating agent is added to the back coating layer to improve the water resistance of the back side of the paper.

[0045] The following describes several specific implementation examples and provides a parameter comparison.

[0046] Blank Example During the papermaking process, the freeness of softwood chemical pulp is 350 ml, and that of hardwood chemical pulp is 360 ml; the freeness of mechanical pulp is 150 ml. A mixed pulp is prepared with a pulp ratio of softwood chemical pulp: hardwood chemical pulp: mechanical pulp = 20%:65%:15%. 12.0% (octane-dry per ton of paper) of heavy calcium carbonate is added as filler, followed by alkyl ketene dimer as an internal sizing agent at 0.80% (dosage per ton of paper). Wet-end starch is added at 0.95% (octane-dry per ton of paper), cationic polyacrylamide-based cationic retention aid at 200 ppm (octane-dry per ton of paper), and silica gel-based anionic retention aid at 3600 ppm (dosage per ton of paper). After dehydration and forming, followed by pressing and drying, a 68.0 g / m³ paper with a moisture content of 3-4% is prepared. 2 The base paper.

[0047] Corn starch sizing solution is applied to the surface of the base paper, with the sizing layer directly coated on both sides of the base paper. The sizing starch is applied using a C2S MSP sizing method at a rate of 1.0 g / m². 2 / side (both sides of the paper are glued). A base coating and a back coating are applied to the surface-sized base paper. The pigment is heavy calcium carbonate; the heavy calcium carbonate used has a particle size of ≤2μm accounting for 65-70%; the ratio of pigment to latex is 100:10; the ratio of pigment to lubricant is 100:0-1; water is added to prepare a coating with a solid content of 60%; and alkali is added to adjust the pH to 9.0±0.5; the base coating application rate is 6.0 g / m². 2 / Front side; Back coating coverage is 3.0 g / m 2 / noodle; After the base paper has been sized, a base coating and a back coating are applied, and then a top coating is applied using a doctor blade. The pigment ratio for the top coating is: heavy calcium carbonate: kaolin = 80:20, where the heavy calcium carbonate has a particle size of ≤2μm and accounts for 95-98%; the kaolin has a particle size of ≤2μm and accounts for 85-90%; pigment: latex = 100:11; pigment: fluorescent whitening agent: dye: dispersant: defoamer: water-resistant agent: lubricant: rheology modifier: tackifier =100:0.06~0.28:0.003~0.01:0.05~0.15:0.05~0.10:0.2~0.6:0~0.4:0.03~0.06:0.2~0.6; Prepare a topcoat with a solid content of 67.0% by adding water, and adjust the pH to 9.0±0.5 by adding alkali; Apply the topcoat using a scraper, with a coating amount of 10.0 g / m². 2 / side (the front of the paper is coated); after the coated paper is dried, it is calendered to control its moisture content at 4.0~4.5%.

[0048] Comparative Example 1 (i.e., Example 1 of this application) During the papermaking process, softwood chemical pulp and hardwood chemical pulp are blended using a (refined pulp + lightly refined pulp) process. The refined softwood chemical pulp has a CSF of 90 ml, and the lightly refined pulp has a CSF of 420 ml. The refined hardwood chemical pulp has a CSF of 120 ml, and the lightly refined pulp has a CSF of 400 ml. The ratio of refined to lightly refined softwood chemical pulp is 10% + 90%; the ratio of refined to lightly refined hardwood chemical pulp is 20% + 80%; the mechanical pulp has a CSF of 150 ml. The ratio of softwood chemical pulp:hardwood chemical pulp:mechanical pulp is 20%:65%:15%. The pulp was prepared by mixing the following proportions: 12.0% (octane-dry per ton of paper) of heavy calcium carbonate was added as filler; a composite sizing agent was added: 0.60% (dosage per ton of paper) of C18 alkyl ketene dimer (AKD); 0.10% (dosage per ton of paper) of high C18 alkenyl succinate (ASA); 0.95% (dosage per ton of paper) of wet-end starch; 200 ppm (octane-dry per ton of paper) of cationic polyacrylamide-based cationic retention aid; and 3600 ppm (dosage per ton of paper) of silica-based anionic retention aid. After dehydration and molding, the pulp was pressed and dried to prepare 68 g / m³ pulp with a moisture content of 3-4%. 2 The base paper.

[0049] A corn starch sizing solution is used to sizing the base paper surface, with the sizing layer directly coated on both sides of the base paper. A surface sizing agent (styrene-acrylate copolymer emulsion) is added to the surface starch, with a dry weight ratio of 4.0%. The surface starch is sizing using a C2S structured MSP at a weight of 1.0 g / m³. 2 / side (both sides of the paper are glued).

[0050] A base coating and a back coating are applied to the surface-sized base paper. The base coating pigment is heavy calcium carbonate, with 65-70% of the heavy calcium carbonate having a particle size of 2μm or less. The pigment-to-styrene-butadiene latex ratio is 100:10. The coating is prepared by adding water to achieve a solid content of 60.0-65.0%, and the pH is adjusted to 9.0±0.5 by adding alkali. The coating is applied using methods such as film transfer or doctor blade coating, with a coating weight of 6.0 g / m². 2 / Side coating (front side of the paper); the back coating pigment is heavy calcium carbonate; the heavy calcium carbonate used has a particle size of less than or equal to 2μm, accounting for 65-70%; pigment: styrene-butadiene latex = 100:8; a water-resistant agent is added to the back coating layer corresponding to the back side of single-sided coated paper; pigment: water-resistant additive = 100:1.5; the water-resistant additive is selected from polyamide epoxy resin; the back coating layer is prepared by adding water to form a coating with a solid content of 20-50%; and alkali is added to adjust the pH to 9.0±0.5; coating is applied by film transfer or blade coating, with a coating amount of 3.0g / m 2 / side (coating on the back of the paper).

[0051] After the base paper has been sized, a base coating and a back coating are applied, and then a top coating is applied using a doctor blade. The pigment ratio for the top coating is: heavy calcium carbonate: kaolin = 80:20, where the heavy calcium carbonate has a particle size of ≤2μm and accounts for 95-98%; the kaolin has a particle size of ≤2μm and accounts for 85-90%; pigment: latex = 100:11; pigment: fluorescent whitening agent: dye: dispersant: defoamer: water-resistant agent: lubricant: rheology modifier: tackifier =100:0.06~0.28:0.003~0.01:0.05~0.15:0.05~0.10:0.2~0.6:0~0.4:0.03~0.06:0.2~0.6; Prepare a topcoat with a solid content of 67.0% by adding water, and adjust the pH to 9.0±0.5 by adding alkali; Apply the topcoat using a scraper, with a coating amount of 10.0 g / m². 2 / side (the front of the paper is coated); after the coated paper is dried, it is calendered to control its moisture content at 4.0~4.5%. Comparative Example 2 (i.e., Example 2 of this application) During the papermaking process, softwood chemical pulp and hardwood chemical pulp are blended using a (refined pulp + lightly refined pulp) process. The refined pulp CSF of the softwood chemical pulp is 105 ml, and the lightly refined pulp CSF is 400 ml. The refined pulp CSF of the hardwood chemical pulp is 135 ml, and the lightly refined pulp CSF is 380 ml. The ratio of refined and lightly refined softwood chemical pulp is 10% + 90%; the ratio of refined and lightly refined hardwood chemical pulp is 20% + 80%; the mechanical pulp CSF is 150 ml. A mixed pulp is prepared with a pulp ratio of softwood chemical pulp: hardwood chemical pulp: mechanical pulp = 20%: 65%: 15%, and 12.0% (octane dry to tonne) of heavy calcium carbonate is added as filler. A composite sizing agent is added: an alkyl ketene dimer (AK) in a C18 ratio. D), dosage 0.60% (to ton of paper); add alkenyl succinate (ASA) with a high C18 ratio, dosage 0.10% (to ton of paper); add wet-end starch, dosage 0.95% (to ton of paper, oven-dry); cationic polyacrylamide-based cationic retention aid 200ppm (to ton of paper, oven-dry); silica gel-based anionic retention aid 3600ppm (to ton of paper, solution); after dehydration and molding, and then pressing and drying, prepare 68g / m³ paper with a moisture content of 3-4%. 2 The base paper.

[0052] A corn starch sizing solution is used to sizing the base paper surface, with the sizing layer directly coated on both sides of the base paper. A surface sizing agent (styrene-acrylate copolymer emulsion) is added to the surface starch, with a dry weight ratio of 4.0%. The surface starch is sizing using a C2S structured MSP at a weight of 1.0 g / m³. 2 / side (both sides of the paper are glued).

[0053] A base coating and a back coating are applied to the surface-sized base paper. The base coating pigment is heavy calcium carbonate, with 65-70% of the heavy calcium carbonate having a particle size of 2μm or less. The pigment-to-styrene-butadiene latex ratio is 100:10. The coating is prepared by adding water to achieve a solid content of 60.0-65.0%, and the pH is adjusted to 9.0±0.5 by adding alkali. The coating is applied using methods such as film transfer or doctor blade coating, with a coating weight of 6.0 g / m². 2 / Side coating (front side of the paper); the back coating pigment is heavy calcium carbonate; the heavy calcium carbonate used has a particle size of less than or equal to 2μm, accounting for 65-70%; pigment: styrene-butadiene latex = 100:8; a water-resistant agent is added to the back coating layer corresponding to the back side of single-sided coated paper; pigment: water-resistant additive = 100:1.5; the water-resistant additive is selected from polyamide epoxy resin; the back coating layer is prepared by adding water to form a coating with a solid content of 20-50%; and alkali is added to adjust the pH to 9.0±0.5; coating is applied by film transfer or blade coating, with a coating amount of 3.0g / m 2 / side (coating on the back of the paper).

[0054] After the base paper has been sized, a base coating and a back coating are applied, and then a top coating is applied using a doctor blade. The pigment ratio for the top coating is: heavy calcium carbonate: kaolin = 80:20, where the heavy calcium carbonate has a particle size of ≤2μm and accounts for 95-98%; the kaolin has a particle size of ≤2μm and accounts for 85-90%; pigment: latex = 100:11; pigment: fluorescent whitening agent: dye: dispersant: defoamer: water-resistant agent: lubricant: rheology modifier: tackifier =100:0.06~0.28:0.003~0.01:0.05~0.15:0.05~0.10:0.2~0.6:0~0.4:0.03~0.06:0.2~0.6; Prepare a topcoat with a solid content of 67.0% by adding water, and adjust the pH to 9.0±0.5 by adding alkali; Apply the topcoat using a scraper, with a coating amount of 10.0 g / m². 2 / side (the front of the paper is coated); after the coated paper is dried, it is calendered to control its moisture content at 4.0~4.5%.

[0055] Comparative Example 3 (i.e., Example 3 of this application) During the papermaking process, softwood chemical pulp and hardwood chemical pulp are blended using a (refined pulp + lightly refined pulp) process. The refined pulp CSF of the softwood chemical pulp is 120 ml, and the lightly refined pulp CSF is 380 ml. The refined pulp CSF of the hardwood chemical pulp is 150 ml, and the lightly refined pulp CSF is 360 ml. The ratio of refined and lightly refined softwood chemical pulp is 10% + 90%; the ratio of refined and lightly refined hardwood chemical pulp is 20% + 80%; the mechanical pulp CSF is 150 ml. A mixed pulp is prepared with a pulp ratio of softwood chemical pulp: hardwood chemical pulp: mechanical pulp = 20%: 65%: 15%, and 12.0% (octane dry to tonne) of heavy calcium carbonate is added as filler. A composite sizing agent is added: an alkyl ketene dimer (AK) in a C18 ratio. D), dosage 0.60% (to ton of paper); add alkenyl succinate (ASA) with a high C18 ratio, dosage 0.10% (to ton of paper); add wet-end starch, dosage 0.95% (to ton of paper, oven-dry); cationic polyacrylamide-based cationic retention aid 200ppm (to ton of paper, oven-dry); silica gel-based anionic retention aid 3600ppm (to ton of paper, solution); after dehydration and molding, and then pressing and drying, prepare 68g / m³ paper with a moisture content of 3-4%. 2 The base paper.

[0056] A corn starch sizing solution is used to sizing the base paper surface, with the sizing layer directly coated on both sides of the base paper. A surface sizing agent (styrene-acrylate copolymer emulsion) is added to the surface starch, with a dry weight ratio of 4.0%. The surface starch is sizing using a C2S structured MSP at a weight of 1.0 g / m³. 2 / side (both sides of the paper are glued).

[0057] A base coating and a back coating are applied to the surface-sized base paper. The base coating pigment is heavy calcium carbonate, with 65-70% of the heavy calcium carbonate having a particle size of 2μm or less. The pigment-to-styrene-butadiene latex ratio is 100:10. The coating is prepared by adding water to achieve a solid content of 60.0-65.0%, and the pH is adjusted to 9.0±0.5 by adding alkali. The coating is applied using methods such as film transfer or doctor blade coating, with a coating weight of 6.0 g / m². 2 / Side coating (front side of the paper); the back coating pigment is heavy calcium carbonate; the heavy calcium carbonate used has a particle size of less than or equal to 2μm, accounting for 65-70%; pigment: styrene-butadiene latex = 100:8; a water-resistant agent is added to the back coating layer corresponding to the back side of single-sided coated paper; pigment: water-resistant additive = 100:1.5; the water-resistant additive is selected from polyamide epoxy resin; the back coating layer is prepared by adding water to form a coating with a solid content of 20-50%; and alkali is added to adjust the pH to 9.0±0.5; coating is applied by film transfer or blade coating, with a coating amount of 3.0g / m 2 / side (coating on the back of the paper).

[0058] After the base paper has been sized, a base coating and a back coating are applied, and then a top coating is applied using a doctor blade. The pigment ratio for the top coating is: heavy calcium carbonate: kaolin = 80:20, where the heavy calcium carbonate has a particle size of ≤2μm and accounts for 95-98%; the kaolin has a particle size of ≤2μm and accounts for 85-90%; pigment: latex = 100:11; pigment: fluorescent whitening agent: dye: dispersant: defoamer: water-resistant agent: lubricant: rheology modifier: tackifier =100:0.06~0.28:0.003~0.01:0.05~0.15:0.05~0.10:0.2~0.6:0~0.4:0.03~0.06:0.2~0.6; Prepare a topcoat with a solid content of 67.0% by adding water, and adjust the pH to 9.0±0.5 by adding alkali; Apply the topcoat using a scraper, with a coating amount of 10.0 g / m². 2 / side (the front of the paper is coated); after the coated paper is dried, it is calendered to control its moisture content at 4.0~4.5%.

[0059] The specific experimental parameters are compared in the table below.

[0060]

[0061] The method for preparing coated paper in this embodiment improves fiber bonding strength by combining softwood chemical pulp and hardwood chemical pulp (fine pulp + light pulp). This allows the amounts of softwood chemical pulp, hardwood chemical pulp, mechanical pulp, and fillers to be maintained at the same pulp ratio as in conventional refining, without increasing the proportion of softwood pulp, reducing the proportion of mechanical pulp, or adding ash. This improves the physical strength of both the base paper and the finished paper. Through this method, the tear strength of the paper increases by 21.0~24.2%, and the tensile strength increases by 21.4~28.2%. This effectively improves and prevents paper breakage due to waste discharge.

[0062] The above description is only a part of the embodiments of this application and does not limit the scope of protection of this application. Any equivalent device or equivalent process transformation made based on the content of this application specification and drawings, or direct or indirect application in other related technical fields, are similarly included in the patent protection scope of this application.

Claims

1. A method for preparing coated paper, characterized in that, The preparation method includes: Papermaking process; the pulp of the papermaking process includes pulp, fillers, and additives; the pulp includes softwood chemical pulp and hardwood chemical pulp, both of which include refined pulp and lightly refined pulp. The ratio of refined pulp to lightly refined pulp in softwood chemical pulp is 5~35%:65~95%, and the ratio of refined pulp to lightly refined pulp in hardwood chemical pulp is 5~40%:60~95%; wherein, the freeness of refined pulp in softwood chemical pulp is 90~120ml, and the freeness of lightly refined pulp is 380~420ml; the freeness of refined pulp in hardwood chemical pulp is 120~150ml, and the freeness of lightly refined pulp is 360~400ml. A surface adhesive layer is formed on both sides of the base paper; A base coat and a top coat are formed sequentially on the surface adhesive layer; A back coating is formed on the surface adhesive layer on the back side.

2. The preparation method according to claim 1, characterized in that, The ratio of refined pulp to lightly refined pulp in softwood chemical pulp is 10~30%:70~90%, and the ratio of refined pulp to lightly refined pulp in hardwood chemical pulp is 10~30%:70~90%.

3. The preparation method according to claim 2, characterized in that, The pulp also includes mechanical pulp and waste pulp; softwood chemical pulp: hardwood chemical pulp: mechanical pulp: waste pulp = 0~40: 45~100: 0~15: 0~30; wherein, the pulping freeness of the mechanical pulp is 120~150ml.

4. The preparation method according to claim 1, characterized in that, The papermaking process also includes in-pulp sizing, which is performed by combining alkyl ketene dimer with alkenyl succinate, or by combining alkyl ketene dimer with neutral rosin sizing agent.

5. The preparation method according to claim 1, characterized in that, In the step of forming a surface sizing layer on both sides of the base paper, the formulation of the surface sizing layer includes corn starch slurry and a surface sizing agent; wherein, the corn starch slurry is prepared by enzymatic conversion of corn starch or oxidized corn starch followed by gelatinization; and the surface sizing agent is a styrene-acrylate copolymer emulsion or an alkyl ketene dimer or a combination of both.

6. The preparation method according to claim 5, characterized in that, The surface sizing agent has an oven-dry dosage of 3.0-7.0% for the surface starch, and an application rate of 1.0-1.5 g / m³. 2 / noodle.

7. The preparation method according to claim 1, characterized in that, In the step of sequentially forming a base coating and a top coating on the surface adhesive layer, the pigment of the base coating is heavy calcium carbonate, the proportion of heavy calcium carbonate particles with a particle size of less than or equal to 2μm is 65~98%, the pigment: styrene-butadiene latex = 100: 8~12; the solid content is 60.0~65.0%.

8. The preparation method according to claim 7, characterized in that, The pigment ratio of the topcoat is: light calcium carbonate: heavy calcium carbonate: kaolin = 0~100: 0~100: 0~40, wherein the light calcium carbonate used has a particle size of less than or equal to 2μm accounting for 95%; the heavy calcium carbonate used has a particle size of less than or equal to 2μm accounting for 95~98%; and the kaolin used has a particle size of less than or equal to 2μm accounting for 85~90%. A leveling agent is added to the topcoat, with a pigment: leveling agent: 100: 0.8~3.

0. The leveling agent is a polyether modified organosilicon leveling agent or an acrylic leveling agent.

9. The preparation method according to claim 1, characterized in that, In the step of forming a back coating layer on the back side, the pigment of the back coating coating is heavy calcium carbonate; wherein the heavy calcium carbonate used has a particle size of less than or equal to 2μm accounting for 65-98%; Pigment: Styrene-butadiene latex = 100: 6~10; Water-resistant agent is also added to the back coating; Pigment: Water-resistant additive = 100: 0.5~2.0; Water-resistant additives include any one of amino resins, metal salts, and polyamide epoxy resins.

10. A type of coated paper, characterized in that, The coated paper is prepared using the preparation method described in any one of claims 1-9.

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