Multi-coating coating and energy-saving drying method applied to high-grade coated paper

Abstract

The invention provides a multi-coating coating and energy-saving drying method applied to high-grade coated paper. The multi-coating coating and energy-saving drying method comprises the following steps: S1, pre-coating; s2, pre-coating and drying; s3, floating coating; s4, floating coat drying; s5, surface coating; s6, drying the top coat; and the like. The invention provides a targeted multi-stage coating process aiming at the characteristic requirements of high-grade coated paper, and targeted drying process control is carried out aiming at the characteristic of each section of coating, so that the integration of a'multi-coating structure 'and a'tail gas recovery type combined drying' process is realized, and the dual targets of high quality, energy conservation and consumption reduction are realized.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a multi-layer coating and energy-saving drying method for high-grade coated paper. Background Technology

[0002] High-grade coated white paperboard is mainly used for surface printing on high-end colored paper boxes and cartons, such as packaging for electronic products and daily necessities. The paper machine coating process consists of three coatings in sequence: pre-coating, intermediate coating, and top coating. Pre-coating is a preliminary coating process to smooth out the unevenness of the paper's fiber layer. Intermediate coating is a transitional filling layer that further improves the smoothness of the paper surface. Top coating focuses on finishing the paper surface, giving it more delicate optical properties and a stable hue to meet the demands of modern high-speed printing presses for high-end, exquisite packaging printing. The functions and rheological properties of the coatings used in different coating processes vary significantly, resulting in different requirements for coating drying.

[0003] The drying process of coatings involves three phases: a liquid phase (67%-80% solids content), a gel phase (80-90% solids content), and a solidified phase (90-100% solids content), consistent with the "filter cake" mechanism. During the coating drying process, it is crucial to delay the rapid formation of a dense "filter cake" on the coating surface as much as possible. This reduces the temperature difference between the inside and outside of the coating while simultaneously raising the temperature to a higher level. This allows the moisture inside and outside the coating to dry synchronously at a relatively uniform temperature, enabling the water vapor interface to gradually extend into the coating. The coating volume shrinks primarily along the cross-section of the paper, forming "capillary channels" within the coating for internal water molecules to evaporate, facilitating the coating's transition to the solidified phase. This is a key aspect of the coating drying process. Especially in today's highly automated coated paper machines, where speeds typically range from 700m / min to 1400m / min, the drying time for each coating pass is generally around 1.0s-2.0s, requiring short drying times and high efficiency.

[0004] Thermal radiation is a high-intensity infrared radiation drying process that does not require a transfer medium and has extremely strong penetrability. In coatings with a thickness of approximately 40-50 μm, it can quickly penetrate into the interior of the coating, rapidly raising the temperature of the coating so that the temperature of the moisture inside the coating is basically the same as the temperature of the coating surface. The moisture inside and outside the coating reaches the evaporation point simultaneously, delaying the surface film formation caused by the evaporation of moisture at the air contact surface. This effectively avoids the premature formation of a dense "filter cake layer" on the coating surface, which would affect the drying of the coating.

[0005] Currently, most paper manufacturers in my country use a drying method consisting of electric infrared drying and a hot air box in the coating section. The main working principle of electric infrared drying is that electrical energy is converted into heat to dry the paper web, while some electrical energy is converted into short-wave radiation to dry the paper surface. This method has relatively weak drying capacity, low energy utilization efficiency in the coating section, and high energy costs. Furthermore, in practical applications, the heating modules (lamp tubes) of the electric infrared dryer have a short lifespan due to being constantly at high temperatures, and some modules may malfunction and shut down, easily leading to uneven heating of the coated paper web and seriously affecting product quality.

[0006] Furthermore, the coating and drying processes significantly impact the quality of high-grade coated white paperboard. If the coating is insufficiently dried in the hot air chamber, it retains a "gel-like" state, which will damage the coating's integrity after being pressed against the drying cylinder, resulting in a rough paper surface. Simultaneously, coating residue will adhere to the drying cylinder, causing coating defects on the paper surface. Conversely, over-drying the coating at high temperatures can easily lead to adhesive aging and bond breakage, resulting in insufficient coating strength and low paper gloss. Therefore, new coating drying technologies need to be strictly controlled to the desired state based on the coating's characteristics. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention proposes a multi-layer coating and energy-saving drying method for high-grade coated paper. It employs a targeted multi-stage coating process tailored to the specific characteristics of high-grade coated paper, and implements targeted drying process control for each layer, thus integrating a "multi-layer structure" with a "tail gas recovery combined drying" process. This achieves the dual goals of high quality and energy saving.

[0008] To achieve the above technical solution, the present invention provides a multi-layer coating and energy-saving drying method for high-grade coated paper, specifically including the following steps: S1. Pre-coating: The pre-coating material is evenly coated onto the surface of the paper web using a pre-coating coating machine. The pre-coating material has the following composition by weight: 5-15 parts calcined clay, 85-95 parts light calcium carbonate, 8-12 parts latex, and 0.5-1 parts other additives. The solid content is controlled at 68%±0.5; the viscosity is 550±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 12±2 gsm. S2. Pre-coating and drying: The pre-coated paper web is sequentially fed into the pre-coating gas-fired infrared drying chamber, the pre-coating hot air chamber No. 1, and the pre-coating hot air chamber No. 2. The gas infrared power of the pre-coating gas-fired infrared drying chamber is controlled at 12mbar-18mbar, the temperature of the pre-coating hot air chamber No. 1 is controlled at 110-150℃, and the temperature of the pre-coating hot air chamber No. 2 is controlled at 120-160℃. If the exhaust gas temperature of the pre-coating gas-fired infrared drying chamber exceeds 90℃, it is directly recycled to the inlet of the pre-coating hot air chamber No. 1, and after being mixed evenly with the pre-coating hot air chamber No. 1, the paper web is dried. S3. Intermediate Coating: The intermediate coating is evenly applied to the surface of the pre-coated and dried paper web using an intermediate coating coating machine. The intermediate coating has the following composition by weight: 5-15 parts kaolin, 85-95 parts light calcium carbonate, 10-15 parts latex, and 0.5-1 parts other additives. The solid content is controlled at 69%±0.5%; the viscosity is 550±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5℃; and the coating amount is 12±2 gsm. S4. Intermediate Coating Drying: The paper web after intermediate coating is sequentially fed into the intermediate coating gas-fired infrared drying chamber, intermediate coating No. 1 hot air chamber, intermediate coating No. 2 hot air chamber, intermediate coating No. 1 drying cylinder, and intermediate coating No. 2 drying cylinder. The intermediate coating gas-fired infrared power is controlled at 13mbar-20mbar, the temperature of intermediate coating No. 1 hot air chamber is controlled at 120-150℃, the temperature of intermediate coating No. 2 hot air chamber is controlled at 130-160℃, the temperature of intermediate coating No. 1 drying cylinder is controlled at 65-100℃, and the temperature of intermediate coating No. 2 drying cylinder is controlled at 70-100℃. If the exhaust gas temperature of the intermediate coating gas-fired infrared drying chamber exceeds 95℃, it is directly recycled to the inlet of intermediate coating No. 1 hot air chamber, mixed evenly with intermediate coating No. 1 hot air chamber, and then used to dry the paper web. S5. Topcoat: The topcoat coating is evenly applied to the surface of the paper web after the intermediate coating has dried using a topcoat coating machine. The topcoat coating is composed of the following components by weight: 10-20 parts kaolin, 5-15 parts heavy calcium carbonate, 70-80 parts light calcium carbonate, 13-15 parts latex, and 1-2 parts other additives. The solid content is controlled at 68%±0.5; the viscosity is 350±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 14±2 gsm. S6. Top Coating Drying: The top-coated paper web is sequentially fed into the top coating gas-fired infrared drying chamber, top coating hot air chamber No. 1, top coating hot air chamber No. 2, top coating hot air chamber No. 3, top coating drying cylinder No. 1, and top coating drying cylinder No. 2. The power of the top coating gas-fired infrared drying chamber is controlled at 14mbar-22mbar, the temperature of top coating hot air chamber No. 1 is controlled at 110-150℃, the temperature of top coating hot air chamber No. 2 is controlled at 120-160℃, the temperature of top coating hot air chamber No. 3 is controlled at 130-170℃, the temperature of top coating drying cylinder No. 1 is controlled at 40-70℃, and the temperature of top coating drying cylinder No. 2 is controlled at 35-60℃. If the exhaust gas temperature of the top coating gas-fired infrared drying chamber exceeds 90℃, it is directly recycled to the inlet of top coating hot air chamber No. 1, and after being mixed evenly with top coating hot air chamber No. 1, the paper web is dried.

[0009] Preferably, in step S1, the pre-coated paint has the following composition by mass: 10 parts calcined clay, 90 parts light calcium carbonate, 11.5 parts latex, and 0.8 parts other additives, wherein the other additives are: 0.1 parts defoamer, 0.2 parts water-resistant agent, 0.1 parts bactericide, 0.1 parts lubricant, 0.1 parts dispersant, and 0.2 parts carboxymethyl cellulose.

[0010] Preferably, in step S3, the intermediate coating is composed of the following components by weight: 10 parts kaolin, 90 parts light calcium carbonate, 12 parts latex, and 0.6 parts other additives, wherein the other additives are: 0.1 parts defoamer, 0.2 parts water-resistant agent, 0.1 parts bactericide, 0.1 parts lubricant, and 0.1 parts dispersant.

[0011] Preferably, in step S5, the topcoat coating is composed of the following components by weight: 15 parts kaolin, 10 parts heavy calcium carbonate, 75 parts light calcium carbonate, 13.5 parts latex, and 1.3 parts other additives, wherein the other additives are: 0.1 parts defoamer, 0.2 parts water-resistant agent, 0.2 parts bactericide, 0.1 parts lubricant, 0.3 parts dispersant, and 0.4 parts carboxymethyl cellulose.

[0012] Preferably, in step S2, the gas infrared power of the pre-coated gas infrared drying box is controlled at 16 mbar, the temperature of the pre-coated No. 1 hot air box is controlled at 120°C, and the temperature of the pre-coated No. 2 hot air box is controlled at 130°C.

[0013] Preferably, in step S4, the infrared power of the intermediate coating gas is controlled at 18 mbar, the temperature of the intermediate coating No. 1 hot air box is controlled at 130°C, the temperature of the intermediate coating No. 2 hot air box is controlled at 140°C, the temperature of the intermediate coating No. 1 drying cylinder is controlled at 70°C, and the temperature of the intermediate coating No. 2 drying cylinder is controlled at 80°C.

[0014] Preferably, in step S6, the infrared power of the surface coating gas is controlled at 20 mbar, the temperature of the surface coating No. 1 hot air box is controlled at 120°C, the temperature of the surface coating No. 2 hot air box is controlled at 130°C, the temperature of the surface coating No. 3 hot air box is controlled at 150°C, the temperature of the surface coating No. 1 drying cylinder is controlled at 60°C, and the temperature of the surface coating No. 2 drying cylinder is controlled at 40°C.

[0015] The beneficial effects of the multi-coating and energy-saving drying method for high-grade coated paper provided by this invention are as follows: (1) This invention combines a refined multi-layer structure design with an innovative energy-saving drying process. It has carried out a targeted multi-stage coating process for the characteristics of high-grade coated paper and targeted drying process control for the characteristics of each coating layer. It has achieved the integration of "multi-layer structure" and "tail gas recovery combined drying" process, and achieved the dual goals of high quality and energy saving. While significantly improving the quality of coated paper, it has also achieved the reduction of production energy consumption and the stability and controllability of the process.

[0016] (2) This invention adopts a three-layer coating system of "pre-coating-intermediate coating-top coating", with each layer having a clear function. The pre-coating mainly fills the pores of the plain paper and improves its smoothness; the intermediate coating further enhances its opacity and coating strength; and the top coating directly determines the surface optical properties, printability, and feel of the paper. This design gives the paper superior gloss, smoothness, whiteness, opacity, and printing effect. Precise ranges are set for the pigment combination (calcined clay, porcelain clay, light and heavy calcium carbonate, etc.), latex content, solid content, viscosity, pH value, temperature, and coating amount of each coating layer, achieving precise coating formulation and process control. This ensures the rheological properties, stability, and coating uniformity of the coating, which is the key to obtaining a high-quality, uniform coating surface.

[0017] (3) For each coating layer, the present invention adopts an optimized combination of "gas-fired infrared drying box + multi-stage hot air box" or "gas-fired infrared drying box + multi-stage hot air box + drying cylinder". Gas-fired infrared can provide high heat instantly, quickly solidify the coating surface, and prevent the coating from migrating excessively into the paper; the hot air box provides penetrating drying and removes most of the moisture; the drying cylinder performs final finishing and smoothing. This sequence takes into account both drying efficiency and coating structure integrity. It also creatively recovers the high-temperature exhaust gas of the gas-fired infrared drying box (>90°C or 95°C) directly to the inlet of the corresponding hot air box, directly recovering and utilizing waste heat, reducing the consumption of fresh heating energy (such as steam) in the hot air box, which is in line with the concept of green manufacturing. Moreover, the recovered exhaust gas is mixed with fresh hot air, which makes the airflow temperature at the inlet of the hot air box more uniform and stable, which is conducive to the uniform drying of the paper web and reduces moisture fluctuations. Attached Figure Description

[0018] Figure 1 This is a flowchart of the present invention.

[0019] Figure 2 This is a diagram showing the layout of the process equipment for this invention.

[0020] In the diagram: 1. Pre-coating machine; 2. Pre-coating gas-fired infrared drying oven; 3. Pre-coating hot air box No. 1; 4. Pre-coating hot air box No. 2; 5. Intermediate coat machine; 6. Intermediate coat gas-fired infrared drying oven; 7. Intermediate coat hot air box No. 1; 8. Intermediate coat hot air box No. 2; 9. Intermediate coat drying cylinder No. 1; 10. Intermediate coat drying cylinder No. 2; 11. Topcoat machine; 12. Topcoat gas-fired infrared drying oven; 13. Topcoat hot air box No. 1; 14. Topcoat hot air box No. 2; 15. Topcoat hot air box No. 3; 16. Topcoat drying cylinder No. 1; 17. Topcoat drying cylinder No. 2. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0022] Example 1: A multi-coating and energy-saving drying method for high-grade coated paper.

[0023] Reference Figure 1 and Figure 2 As shown, a system for realizing a multi-layer coating and energy-saving drying method for high-grade coated paper includes: a pre-coating machine 1, a pre-coating gas-fired infrared drying chamber 2, a pre-coating hot air chamber 1 3, a pre-coating hot air chamber 2 4, a mid-coating machine 5, a mid-coating gas-fired infrared drying chamber 6, a mid-coating hot air chamber 1 7, a mid-coating hot air chamber 2 8, a mid-coating drying cylinder 1 9, a mid-coating drying cylinder 2 10, a top-coating machine 11, a top-coating gas-fired infrared drying chamber 12, a top-coating hot air chamber 13, a top-coating hot air chamber 2 14, a top-coating hot air chamber 3 15, a top-coating drying cylinder 16, and a top-coating drying cylinder 2 17. The paper web is first pre-coated by the pre-coating machine 1, and then sequentially enters the pre-coating gas infrared drying chamber 2, the pre-coating hot air chamber 1 3, and the pre-coating hot air chamber 2 4 for pre-coating drying. Then it enters the intermediate coating machine 5 for intermediate coating. After intermediate coating, it sequentially enters the intermediate coating gas infrared drying chamber 6, the intermediate coating hot air chamber 1 7, the intermediate coating hot air chamber 2 8, the intermediate coating drying cylinder 1 9, and the intermediate coating drying cylinder 2 10 for intermediate coating drying. Finally, it enters the top coating machine 11 for top coating. After top coating, it sequentially enters the top coating gas infrared drying chamber 12, the top coating hot air chamber 13, the top coating hot air chamber 2 14, the top coating hot air chamber 3 15, the top coating drying cylinder 16, and the top coating drying cylinder 2 17 for top coating drying.

[0024] A multi-coating and energy-saving drying method for high-grade coated paper specifically includes the following steps: S1. Pre-coating: The pre-coating material is evenly coated onto the paper web surface using a pre-coating coating machine 1. The pre-coating material consists of 10 parts calcined clay, 90 parts light calcium carbonate, 11.5 parts latex, and 0.8 parts other additives. Among these additives are: 0.1 parts butanol (defoamer), 0.2 parts polyamine polyamide (water-resistant agent), 0.1 parts acrylic emulsion (bactericide), 0.1 parts oleic acid (lubricant), 0.1 parts polyoxyethylene alkylphenol ether (dispersant), and 0.2 parts carboxymethyl cellulose (modifier). The solid content is controlled at 68%±0.5; the viscosity is 550±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 12±2 gsm. S2. Pre-coating and drying: The pre-coated paper web is sequentially fed into the pre-coating gas-fired infrared drying chamber, the pre-coating hot air chamber No. 1, and the pre-coating hot air chamber No. 2. The gas infrared power of the pre-coating gas-fired infrared drying chamber is controlled at 16 mbar, the temperature of the pre-coating hot air chamber No. 1 is controlled at 120℃, and the temperature of the pre-coating hot air chamber No. 2 is controlled at 130℃. If the exhaust gas temperature of the pre-coating gas-fired infrared drying chamber exceeds 90℃, it is directly recycled to the inlet of the pre-coating hot air chamber No. 1, and after being mixed evenly with the pre-coating hot air chamber No. 1, the paper web is dried. S3. Intermediate Coating: The intermediate coating is evenly applied to the surface of the pre-coated and dried paper web using an intermediate coating coating machine. The intermediate coating is composed of the following components by weight: 10 parts kaolin, 90 parts light calcium carbonate, 12 parts latex, and 0.6 parts other additives. Among these, the other additives are: 0.1 parts butanol (defoamer), 0.2 parts polyurethane polyamide (water-resistant agent), 0.1 parts acrylic emulsion (bactericide), 0.1 parts oleic acid (lubricant), and 0.1 parts polyoxyethylene alkylphenol ether (dispersant). The solid content is controlled at 69%±0.5; the viscosity is 550±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 12±2 gsm. S4. Intermediate Coating Drying: The paper web after intermediate coating is sequentially fed into the intermediate coating gas-fired infrared drying chamber, intermediate coating No. 1 hot air chamber, intermediate coating No. 2 hot air chamber, intermediate coating No. 1 drying cylinder, and intermediate coating No. 2 drying cylinder. The intermediate coating gas-fired infrared power is controlled at 18 mbar, the temperature of intermediate coating No. 1 hot air chamber is controlled at 130℃, the temperature of intermediate coating No. 2 hot air chamber is controlled at 140℃, the temperature of intermediate coating No. 1 drying cylinder is controlled at 70℃, and the temperature of intermediate coating No. 2 drying cylinder is controlled at 80℃. If the exhaust gas temperature of the intermediate coating gas-fired infrared drying chamber exceeds 95℃, it is directly recycled to the inlet of intermediate coating No. 1 hot air chamber, mixed evenly with intermediate coating No. 1 hot air chamber, and then used to dry the paper web. S5. Topcoat: The topcoat coating is evenly applied to the surface of the paper web after the intermediate coating has dried using a topcoat coating machine. The topcoat coating is composed of the following components by weight: 15 parts kaolin, 10 parts heavy calcium carbonate, 75 parts light calcium carbonate, 13.5 parts latex, and 1.3 parts other additives. Among these, the other additives are: 0.1 parts butanol (defoamer), 0.2 parts polyurethane polyamide (water-resistant agent), 0.2 parts acrylic emulsion (bactericide), 0.1 parts oleic acid (lubricant), 0.3 parts polyoxyethylene alkylphenol ether (dispersant), and 0.4 parts carboxymethyl cellulose (modifier). The solid content is controlled at 68%±0.5; the viscosity is 350±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 14±2 gsm. S6. Top Coating Drying: The top-coated paper web is sequentially fed into the top coating gas-fired infrared drying chamber, top coating hot air chamber No. 1, top coating hot air chamber No. 2, top coating hot air chamber No. 3, top coating drying cylinder No. 1, and top coating drying cylinder No. 2. The top coating gas-fired infrared power is controlled at 20 mbar, the temperature of top coating hot air chamber No. 1 is controlled at 120℃, the temperature of top coating hot air chamber No. 2 is controlled at 130℃, the temperature of top coating hot air chamber No. 3 is controlled at 150℃, the temperature of top coating drying cylinder No. 1 is controlled at 60℃, and the temperature of top coating drying cylinder No. 2 is controlled at 40℃. If the exhaust gas temperature of the top coating gas-fired infrared drying chamber exceeds 90℃, it is directly recycled to the inlet of top coating hot air chamber No. 1, and mixed evenly with top coating hot air chamber No. 1 to dry the paper web.

[0025] Example 2: A multi-coating and energy-saving drying method for high-grade coated paper.

[0026] A multi-coating and energy-saving drying method for high-grade coated paper specifically includes the following steps: S1. Pre-coating: The pre-coating material is evenly coated onto the paper web surface using a pre-coating coating machine 1. The pre-coating material consists of 5 parts calcined clay, 95 parts light calcium carbonate, 12 parts latex, and 0.6 parts other additives. Among these additives are: 0.1 parts butanol (defoamer), 0.1 parts polyamine polyamide (water-resistant agent), 0.1 parts acrylic emulsion (bactericide), 0.1 parts oleic acid (lubricant), 0.1 parts polyoxyethylene alkylphenol ether (dispersant), and 0.1 parts carboxymethyl cellulose (modifier). The solid content is controlled at 68%±0.5; the viscosity is 550±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 12±2 gsm. S2. Pre-coating and drying: The pre-coated paper web is sequentially fed into the pre-coating gas-fired infrared drying chamber, the pre-coating hot air chamber No. 1, and the pre-coating hot air chamber No. 2. The gas infrared power of the pre-coating gas-fired infrared drying chamber is controlled at 14 mbar, the temperature of the pre-coating hot air chamber No. 1 is controlled at 110℃, and the temperature of the pre-coating hot air chamber No. 2 is controlled at 120℃. If the exhaust gas temperature of the pre-coating gas-fired infrared drying chamber exceeds 90℃, it is directly recycled to the inlet of the pre-coating hot air chamber No. 1, and after being mixed evenly with the pre-coating hot air chamber No. 1, the paper web is dried. S3. Intermediate Coating: The intermediate coating is evenly applied to the surface of the pre-coated and dried paper web using an intermediate coating coating machine. The intermediate coating is composed of the following components by weight: 12 parts kaolin, 88 parts light calcium carbonate, 12 parts latex, and 0.6 parts other additives. Among these, the other additives are: 0.1 parts butanol (defoamer), 0.2 parts polyurethane polyamide (water-resistant agent), 0.1 parts acrylic emulsion (bactericide), 0.1 parts oleic acid (lubricant), and 0.1 parts polyoxyethylene alkylphenol ether (dispersant). The solid content is controlled at 69%±0.5; the viscosity is 550±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 12±2 gsm. S4. Intermediate Coating Drying: The paper web after intermediate coating is sequentially fed into the intermediate coating gas-fired infrared drying chamber, intermediate coating No. 1 hot air chamber, intermediate coating No. 2 hot air chamber, intermediate coating No. 1 drying cylinder, and intermediate coating No. 2 drying cylinder. The intermediate coating gas-fired infrared power is controlled at 20 mbar, the temperature of intermediate coating No. 1 hot air chamber is controlled at 140℃, the temperature of intermediate coating No. 2 hot air chamber is controlled at 150℃, the temperature of intermediate coating No. 1 drying cylinder is controlled at 75℃, and the temperature of intermediate coating No. 2 drying cylinder is controlled at 85℃. If the exhaust gas temperature of the intermediate coating gas-fired infrared drying chamber exceeds 95℃, it is directly recycled to the inlet of intermediate coating No. 1 hot air chamber, mixed evenly with intermediate coating No. 1 hot air chamber, and then used to dry the paper web. S5. Topcoat: The topcoat coating is evenly applied to the surface of the paper web after the intermediate coating has dried using a topcoat coating machine. The topcoat coating, by weight, consists of: 5 parts kaolin, 15 parts heavy calcium carbonate, 80 parts light calcium carbonate, 13 parts latex, and 1.3 parts other additives. Among these, the other additives are: 0.1 parts butanol (defoamer), 0.2 parts polyamine polyamide (water-resistant agent), 0.2 parts acrylic emulsion (bactericide), 0.1 parts oleic acid (lubricant), 0.3 parts polyoxyethylene alkylphenol ether (dispersant), and 0.4 parts carboxymethyl cellulose (modifier). The solid content is controlled at 68%±0.5; the viscosity is 350±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 14±2 gsm. S6. Top Coating Drying: The top-coated paper web is sequentially fed into the top coating gas-fired infrared drying chamber, top coating hot air chamber No. 1, top coating hot air chamber No. 2, top coating hot air chamber No. 3, top coating drying cylinder No. 1, and top coating drying cylinder No. 2. The top coating gas-fired infrared power is controlled at 22 mbar, the temperature of top coating hot air chamber No. 1 is controlled at 130℃, the temperature of top coating hot air chamber No. 2 is controlled at 140℃, the temperature of top coating hot air chamber No. 3 is controlled at 150℃, the temperature of top coating drying cylinder No. 1 is controlled at 55℃, and the temperature of top coating drying cylinder No. 2 is controlled at 35℃. If the exhaust gas temperature of the top coating gas-fired infrared drying chamber exceeds 90℃, it is directly recycled to the inlet of top coating hot air chamber No. 1, and mixed evenly with top coating hot air chamber No. 1 to dry the paper web.

[0027] Example 3: A multi-coating and energy-saving drying method for high-grade coated paper.

[0028] A multi-coating and energy-saving drying method for high-grade coated paper specifically includes the following steps: S1. Pre-coating: The pre-coating material is evenly coated onto the paper web surface using a pre-coating coating machine 1. The pre-coating material consists of 15 parts calcined clay, 85 parts light calcium carbonate, 12 parts latex, and 1 part other additives. The other additives are: 0.2 parts butanol (defoamer), 0.2 parts polyamine polyamide (water-resistant agent), 0.2 parts acrylic emulsion (bactericide), 0.1 parts oleic acid (lubricant), 0.1 parts polyoxyethylene alkylphenol ether (dispersant), and 0.2 parts carboxymethyl cellulose (modifier). The solid content is controlled at 68%±0.5; the viscosity is 550±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 12±2 gsm. S2. Pre-coating and drying: The pre-coated paper web is sequentially fed into the pre-coating gas-fired infrared drying chamber, the pre-coating hot air chamber No. 1, and the pre-coating hot air chamber No. 2. The gas infrared power of the pre-coating gas-fired infrared drying chamber is controlled at 12 mbar, the temperature of the pre-coating hot air chamber No. 1 is controlled at 110℃, and the temperature of the pre-coating hot air chamber No. 2 is controlled at 120℃. If the exhaust gas temperature of the pre-coating gas-fired infrared drying chamber exceeds 90℃, it is directly recycled to the inlet of the pre-coating hot air chamber No. 1, and after being mixed evenly with the pre-coating hot air chamber No. 1, the paper web is dried. S3. Intermediate Coating: The intermediate coating is evenly applied to the surface of the pre-coated and dried paper web using an intermediate coating coating machine. The intermediate coating consists of the following components by weight: 15 parts kaolin, 85 parts light calcium carbonate, 12 parts latex, and 0.8 parts other additives. Among these, the other additives are: 0.1 parts butanol (defoamer), 0.2 parts polyurethane polyamide (water-resistant agent), 0.2 parts acrylic emulsion (bactericide), 0.1 parts oleic acid (lubricant), and 0.2 parts polyoxyethylene alkylphenol ether (dispersant). The solid content is controlled at 69%±0.5; the viscosity is 550±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 12±2 gsm. S4. Intermediate Coating Drying: The paper web after intermediate coating is sequentially fed into the intermediate coating gas-fired infrared drying chamber, intermediate coating No. 1 hot air chamber, intermediate coating No. 2 hot air chamber, intermediate coating No. 1 drying cylinder, and intermediate coating No. 2 drying cylinder. The intermediate coating gas-fired infrared power is controlled at 13 mbar, the temperature of intermediate coating No. 1 hot air chamber is controlled at 120℃, the temperature of intermediate coating No. 2 hot air chamber is controlled at 130℃, the temperature of intermediate coating No. 1 drying cylinder is controlled at 65℃, and the temperature of intermediate coating No. 2 drying cylinder is controlled at 70℃. If the exhaust gas temperature of the intermediate coating gas-fired infrared drying chamber exceeds 95℃, it is directly recycled to the inlet of intermediate coating No. 1 hot air chamber, mixed evenly with intermediate coating No. 1 hot air chamber, and then used to dry the paper web. S5. Topcoat: The topcoat coating is evenly applied to the surface of the paper web after the intermediate coating has dried using a topcoat coating machine. The topcoat coating is composed of the following components by weight: 15 parts kaolin, 5 parts heavy calcium carbonate, 80 parts light calcium carbonate, 15 parts latex, and 1.5 parts other additives. Among these, the other additives are: 0.2 parts butanol (defoamer), 0.2 parts polyurethane polyamide (water-resistant agent), 0.2 parts acrylic emulsion (bactericide), 0.2 parts oleic acid (lubricant), 0.3 parts polyoxyethylene alkylphenol ether (dispersant), and 0.4 parts carboxymethyl cellulose (modifier). The solid content is controlled at 68%±0.5; the viscosity is 350±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 14±2 gsm. S6. Top Coating Drying: The top-coated paper web is sequentially fed into the top coating gas-fired infrared drying chamber, top coating hot air chamber 1, top coating hot air chamber 2, top coating hot air chamber 3, top coating drying cylinder 1, and top coating drying cylinder 2. The top coating gas-fired infrared power is controlled at 14 mbar, the temperature of top coating hot air chamber 1 is controlled at 110℃, the temperature of top coating hot air chamber 2 is controlled at 120℃, the temperature of top coating hot air chamber 3 is controlled at 130℃, the temperature of top coating drying cylinder 1 is controlled at 40℃, and the temperature of top coating drying cylinder 2 is controlled at 35℃. If the exhaust gas temperature of the top coating gas-fired infrared drying chamber exceeds 90℃, it is directly recycled to the inlet of top coating hot air chamber 1, and after being mixed evenly with top coating hot air chamber 1, the paper web is dried.

[0029] Comparative Example 1 The pre-coated gas infrared drying box 2, the pre-coated gas infrared drying box 6, and the pre-coated gas infrared drying box 12 were replaced with an electric infrared drying box, and the remaining technical features were the same as in Example 1.

[0030] The control standards for the surface strength and optical properties of high-grade coated paper, and the properties of the finished paper from Examples 1-3 and Comparative Example 1 are shown in Table 1: Table 1. Properties of finished paper from Examples 1-3 and Comparative Example 1

[0031] As shown in Table 1, the coated paper produced using the method of this invention (Examples 1-3) exhibits key performance indicators that are superior to the control standards and comprehensively superior to the traditional electro-infrared drying process (Comparative Example 1). The roughness of Examples 1-3 (≤1.0 µm) is far superior to the standard (≤1.3 µm), while Comparative Example 1 (1.5 µm) exceeds the standard. This is attributed to the reasonable coating structure design and precise drying control, which avoids surface roughness caused by over-drying or migration. ISO whiteness (83-88%) and surface gloss (60-65%) both far exceed the standards, ensuring the high-end appearance of the paper and the vibrancy of the printed background color. The printing gloss (88-91%) is significantly higher than the standard (≥80%) and Comparative Example 1 (82%), indicating that a dense and smooth film layer is formed on the coating surface, which is conducive to the uniform spread of ink. The printed surface strength (IGT) (1.8-2.1 m / s) is significantly higher than the standard (≥1.0 m / s), indicating a strong bond between the coating and the paper base, preventing fuzzing and powdering during high-speed printing. The number of printing passes (RI) (5-6 times) far exceeds the standard (≥2 times), demonstrating excellent abrasion resistance and peeling resistance of the coating. Ink absorbance (18-20%) remains stable within the ideal range (18-25%), ensuring rapid ink curing and preventing ink penetration. The ink absorbance of Comparative Example 1 (26%) exceeds the standard, potentially leading to dot gain and decreased gloss.

[0032] This invention employs a gas-fired infrared drying oven as the first drying step after each coating layer is applied. Its high heat flux and rapid heat transfer efficiency allow for instantaneous evaporation of moisture from the coating surface, initially curing the coating and laying the foundation for subsequent hot air drying. Furthermore, the high-temperature exhaust gas (>90℃ / 95℃) from the gas-fired infrared drying oven is recovered and introduced into the corresponding stage's hot air box inlet for mixing and reuse. This design directly recovers high-grade waste heat, significantly reducing the fresh energy consumption of the hot air system and achieving cascaded energy utilization, resulting in a significant reduction in overall drying energy consumption. In contrast to Comparative Example 1, which uses electric infrared drying, although potentially offering precise control, it typically has higher electricity costs and lacks an effective high-grade waste heat recovery design, leading to lower overall energy efficiency compared to this invention.

[0033] This invention employs a stepped synergistic drying method combining infrared radiation, hot air, and a drying cylinder. Drying parameters with progressively varying temperature and power are designed for the different characteristics of the pre-coat, intermediate coat, and topcoat (e.g., solid content, viscosity, coating thickness). This combined drying method balances drying rate and quality: infrared radiation provides rapid setting, hot air penetrates and dries, and the drying cylinder provides final finishing and moisture balancing, avoiding problems such as surface hardening, internal dampness and external dryness, and cracking caused by single drying methods. Examples 1-3 provide different pigment / latex ratios (e.g., the ratio of calcined clay to calcium carbonate, and latex dosage), but the core process parameters such as solid content, viscosity, and pH value remain consistent. This demonstrates that the method system has broad material adaptability, allowing companies to fine-tune it according to raw material costs and performance targets without affecting process stability and the basic quality of the final product.

[0034] This invention systematically and synergistically integrates and optimizes specific coating systems, multi-layer coating processes, composite drying technologies, and energy-saving designs, forming a highly efficient, energy-saving, and high-performance overall solution. This invention does not simply involve three coating layers; instead, it designs specialized coatings with distinct compositions, ratios, and viscosities for the different functional roles of the pre-coat (focusing on coverage and adhesion), intermediate coat (building the main structure and whiteness), and top coat (determining the final printed surface performance). A matching drying intensity and temperature curve is "tailor-made" for each coating layer (e.g., the top coat has the most drying stages and the most precise temperature control), ensuring that each layer dries and cures under optimal conditions, ultimately optimizing the overall coating structure. This represents a refined and scientific improvement over traditional coating and drying processes, achieving synergistic innovation between multi-layer coating systems and stepped drying processes.

[0035] This invention creatively applies fuel-fired infrared drying technology to the multi-layer drying sequence of coated paper, clearly defining its role as the initial high-efficiency drying station. Furthermore, it proposes an innovative method for conditionally (exceeding a set temperature) recovering the high-temperature exhaust gas generated during fuel-fired infrared drying back to the hot air system. This is not merely simple waste heat utilization, but rather a systematic coupling of the heat flow from different drying units, constructing an internal energy cycle and significantly improving the thermal efficiency of the entire drying line.

[0036] Furthermore, as can be seen from the data in Examples 1-3, Comparative Example 1, and Table 1, this invention combines a refined multi-layer structure design with an innovative energy-saving drying process. It employs a targeted multi-stage coating process tailored to the specific requirements of high-grade coated paper, and implements targeted drying process control for each layer. This achieves the integration of a "multi-layer structure" and a "tail gas recovery combined drying" process, realizing the dual goals of high quality and energy saving. While significantly improving the quality of coated paper, it also reduces production energy consumption and ensures stable and controllable processes. Moreover, this invention adopts a three-layer coating system of "pre-coating - intermediate coating - top coating," with each layer having a clearly defined function. The pre-coating mainly fills the pores of the plain paper and improves smoothness; the intermediate coating further enhances opacity and coating strength; and the top coating directly determines the surface optical properties, printability, and feel of the paper. This design gives the paper superior gloss, smoothness, whiteness, opacity, and printing effect. Precise ranges were set for the pigment composition (calcined clay, porcelain clay, light and heavy calcium carbonate, etc.), latex content, solid content, viscosity, pH value, temperature and coating amount of each coating layer, achieving precise coating formulation and process control. This ensures the rheological properties, stability and coating uniformity of the coating, which is the key to obtaining a high-quality and uniform coating surface.

[0037] This invention employs an optimized combination of either a gas-fired infrared drying chamber + multi-stage hot air chamber or a gas-fired infrared drying chamber + multi-stage hot air chamber + drying cylinder for each coating layer. The gas-fired infrared drying chamber provides instantaneous high heat, rapidly curing the coating surface and preventing excessive migration of the coating into the paper. The hot air chamber provides penetrating drying, removing most of the moisture. The drying cylinder performs final finishing and smoothing. This sequence balances drying efficiency with coating structural integrity. Furthermore, it innovatively recovers the high-temperature exhaust gas (>90℃ or 95℃) from the gas-fired infrared drying chamber directly to the inlet of the corresponding hot air chamber, directly recycling waste heat and reducing the consumption of fresh heating energy (such as steam) in the hot air chamber, aligning with green manufacturing principles. Moreover, the mixed recovered exhaust gas and fresh hot air result in a more uniform and stable airflow temperature at the hot air chamber inlet, promoting uniform drying of the paper web and reducing moisture fluctuations.

[0038] The above description is only a preferred embodiment of the present invention, but the present invention should not be limited to the content disclosed in the embodiments and drawings. Therefore, any equivalent or modified embodiments made without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A multi-coating and energy-saving drying method for high-grade coated paper, characterized in that... Specifically, the steps include the following: S1. Pre-coating: The pre-coating material is evenly coated on the surface of the paper web using a pre-coating coating machine. The pre-coating material is composed of the following components by weight: 5-15 parts calcined clay, 85-95 parts light calcium carbonate, 8-12 parts latex, and 0.5-1 parts other additives. The solid content is controlled at 68%±0.5% and the viscosity is 550±50 CPS. The pH value is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 12±2 gsm. S2. Pre-coating and drying: The pre-coated paper web is sequentially fed into the pre-coating gas-fired infrared drying chamber, the pre-coating hot air chamber No. 1, and the pre-coating hot air chamber No.

2. The gas infrared power of the pre-coating gas-fired infrared drying chamber is controlled at 12mbar-18mbar, the temperature of the pre-coating hot air chamber No. 1 is controlled at 110-150℃, and the temperature of the pre-coating hot air chamber No. 2 is controlled at 120-160℃. If the exhaust gas temperature of the pre-coating gas-fired infrared drying chamber exceeds 90℃, it is directly recycled to the inlet of the pre-coating hot air chamber No. 1, and after being mixed evenly with the pre-coating hot air chamber No. 1, the paper web is dried. S3. Intermediate Coating: The intermediate coating is evenly applied to the surface of the pre-coated and dried paper web using an intermediate coating coating machine. The intermediate coating has the following composition by weight: 5-15 parts kaolin, 85-95 parts light calcium carbonate, 10-15 parts latex, and 0.5-1 parts other additives. The solid content is controlled at 69%±0.5%; the viscosity is 550±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 12±2 gsm. S4. Intermediate Coating Drying: The paper web after intermediate coating is sequentially fed into the intermediate coating gas-fired infrared drying chamber, intermediate coating No. 1 hot air chamber, intermediate coating No. 2 hot air chamber, intermediate coating No. 1 drying cylinder, and intermediate coating No. 2 drying cylinder. The intermediate coating gas-fired infrared power is controlled at 13mbar-20mbar, the temperature of intermediate coating No. 1 hot air chamber is controlled at 120-150℃, the temperature of intermediate coating No. 2 hot air chamber is controlled at 130-160℃, the temperature of intermediate coating No. 1 drying cylinder is controlled at 65-100℃, and the temperature of intermediate coating No. 2 drying cylinder is controlled at 70-100℃. If the exhaust gas temperature of the intermediate coating gas-fired infrared drying chamber exceeds 95℃, it is directly recycled to the inlet of intermediate coating No. 1 hot air chamber, mixed evenly with intermediate coating No. 1 hot air chamber, and then used to dry the paper web. S5. Topcoat: The topcoat coating is evenly applied to the surface of the paper web after the intermediate coating has dried using a topcoat coating machine. The topcoat coating is composed of the following components by weight: 10-20 parts kaolin, 5-15 parts heavy calcium carbonate, 70-80 parts light calcium carbonate, 13-15 parts latex, and 1-2 parts other additives. The solid content is controlled at 68%±0.5; the viscosity is 350±50 CPS; the pH is 9.0±0.2; the coating temperature is 30±5 ℃; and the coating amount is 14±2 gsm. S6. Top Coating Drying: The top-coated paper web is sequentially fed into the top coating gas-fired infrared drying chamber, top coating hot air chamber No. 1, top coating hot air chamber No. 2, top coating hot air chamber No. 3, top coating drying cylinder No. 1, and top coating drying cylinder No.

2. The power of the top coating gas-fired infrared drying chamber is controlled at 14mbar-22mbar, the temperature of top coating hot air chamber No. 1 is controlled at 110-150℃, the temperature of top coating hot air chamber No. 2 is controlled at 120-160℃, the temperature of top coating hot air chamber No. 3 is controlled at 130-170℃, the temperature of top coating drying cylinder No. 1 is controlled at 40-70℃, and the temperature of top coating drying cylinder No. 2 is controlled at 35-60℃. If the exhaust gas temperature of the top coating gas-fired infrared drying chamber exceeds 90℃, it is directly recycled to the inlet of top coating hot air chamber No. 1, and after being mixed evenly with top coating hot air chamber No. 1, the paper web is dried.

2. The multi-coating and energy-saving drying method for high-grade coated paper as described in claim 1, characterized in that: In step S1, the pre-coated paint is composed of the following components by weight: 10 parts calcined clay, 90 parts light calcium carbonate, 11.5 parts latex, and 0.8 parts other additives, wherein the other additives are: 0.1 parts defoamer, 0.2 parts water-resistant agent, 0.1 parts bactericide, 0.1 parts lubricant, 0.1 parts dispersant, and 0.2 parts carboxymethyl cellulose.

3. The multi-coating and energy-saving drying method for high-grade coated paper as described in claim 1, characterized in that: In step S3, the intermediate coating is composed of the following components by weight: 10 parts kaolin, 90 parts light calcium carbonate, 12 parts latex, and 0.6 parts other additives, wherein the other additives are: 0.1 parts defoamer, 0.2 parts water-resistant agent, 0.1 parts bactericide, 0.1 parts lubricant, and 0.1 parts dispersant.

4. The multi-coating and energy-saving drying method for high-grade coated paper as described in claim 1, characterized in that: In step S5, the topcoat is composed of the following components by weight: 15 parts kaolin, 10 parts heavy calcium carbonate, 75 parts light calcium carbonate, 13.5 parts latex, and 1.3 parts other additives, including: 0.1 parts defoamer, 0.2 parts water-resistant agent, 0.2 parts bactericide, 0.1 parts lubricant, 0.3 parts dispersant, and 0.4 parts carboxymethyl cellulose.

5. The multi-coating and energy-saving drying method for high-grade coated paper as described in claim 1, characterized in that: In step S2, the gas infrared power of the pre-coated gas infrared drying box is controlled at 16 mbar, the temperature of the pre-coated No. 1 hot air box is controlled at 120°C, and the temperature of the pre-coated No. 2 hot air box is controlled at 130°C.

6. The multi-coating and energy-saving drying method for high-grade coated paper as described in claim 1, characterized in that: In step S4, the infrared power of the intermediate coating gas is controlled at 18 mbar, the temperature of the intermediate coating No. 1 hot air box is controlled at 130°C, the temperature of the intermediate coating No. 2 hot air box is controlled at 140°C, the temperature of the intermediate coating No. 1 drying cylinder is controlled at 70°C, and the temperature of the intermediate coating No. 2 drying cylinder is controlled at 80°C.

7. The multi-coating and energy-saving drying method for high-grade coated paper as described in claim 1, characterized in that: In step S6, the infrared power of the surface coating gas is controlled at 20 mbar, the temperature of the surface coating No. 1 hot air box is controlled at 120°C, the temperature of the surface coating No. 2 hot air box is controlled at 130°C, the temperature of the surface coating No. 3 hot air box is controlled at 150°C, the temperature of the surface coating No. 1 drying cylinder is controlled at 60°C, and the temperature of the surface coating No. 2 drying cylinder is controlled at 40°C.

Images