A method for regulating the moisture resistance of a wrapping paper

Abstract

The application discloses a kind of packaging paper wet resistance performance regulation methods, belong to papermaking field.The present application is used to the composite sizing process and simultaneously applied to the front surface and back surface of raw paper, and the composite sizing process of front and back surface is independently controlled;The composite sizing process includes: using atomization spraying equipment to uniformly spray barrier agent to the surface of raw paper, to form dense continuous moisture barrier layer;And by micro-gravure roller coating sizing agent on the surface of moisture barrier layer, to form the structured hydrophobic grid layer of regular pattern structure.The application is coupled by moisture barrier layer and structured hydrophobic grid layer, so that the water vapor transmission rate of packaging paper is less than 3 g / (m 2 ·24h), water absorption cobb value is 20-35 g / m 2 , with excellent water resistance and moisture resistance and low cost advantage, suitable for cold chain logistics packaging field.

Description

Technical Field

[0001] This invention relates to the field of papermaking, and more specifically to a packaging paper and a method for controlling its moisture resistance. Background Technology

[0002] Packaging paper manufacturing is a key industry supporting social civilization and economic development, closely linked to important sectors such as food, pharmaceuticals, electronics, and chemicals, which are crucial to national welfare and people's livelihoods. Kraft paper is one of the most widely used and consumed packaging papers, boasting advantages such as high strength, good toughness, and low cost. Against the backdrop of the "plastic restriction order" and the ever-increasing demand for cold chain logistics packaging nationwide, high moisture-resistant packaging paper, with its excellent moisture-proof and compression-resistant properties, can effectively solve the problem of leakage in e-commerce fresh food packaging, ensuring the quality and safety of fresh products during distribution. It plays an irreplaceable and crucial role in ensuring the safety of logistics transportation and enhancing the resilience of the supply chain.

[0003] Traditional technologies for improving the moisture resistance of packaging paper mainly focus on in-pulp sizing, interlayer sizing, surface sizing, or a combination of these processes. However, existing technologies suffer from a significant performance-cost contradiction: pursuing better moisture resistance often requires increasing the amount of sizing agent or optimizing the sizing process, directly leading to increased production costs and making it difficult to balance practicality and economy. Further analysis of the failure mechanism of packaging paper in high-humidity environments reveals that its strength reduction and box collapse are mainly due to two types of moisture effects: first, liquid water directly contacts the paper surface and wets the fibers, destroying the inter-fiber bonding force and causing a rapid decline in structural strength; second, water vapor in the environment diffuses into the paper interior, causing the fibers to absorb water and swell, thus leading to deterioration of physical properties. It is important to clarify that "water resistance" and "moisture resistance" are two different performance requirements for paper: water resistance targets the barrier of flowing liquid water, while moisture resistance focuses on inhibiting the penetration of gaseous water vapor. Therefore, how to break through existing technological bottlenecks and achieve long-term stable water resistance and moisture-proof properties of packaging paper while balancing production costs has become a key issue that the industry urgently needs to address. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a composite sizing process that couples a moisture barrier layer and a structured hydrophobic mesh layer, thereby controlling the moisture resistance of packaging paper from both the aspects of water vapor barrier and liquid water repulsion.

[0005] The technical problem to be solved by this invention is achieved through the following technical solution:

[0006] A method for regulating the moisture resistance of packaging paper employs a composite sizing process applied simultaneously to the front and back surfaces of the base paper. The composite sizing process includes the construction of a moisture barrier layer and a structured hydrophobic mesh layer, with the composite sizing processes on the front and back surfaces of the base paper being independently controlled.

[0007] The moisture barrier layer is constructed by uniformly spraying a barrier agent onto the front and back surfaces of the base paper layer (3) using an atomizing spraying device to form a dense and continuous moisture barrier layer (2).

[0008] The structured hydrophobic mesh layer is constructed by coating an adhesive onto the outer surface of the moisture barrier layer (2) with a micro-gravure roller to form a structured hydrophobic mesh layer (1) with a regular pattern.

[0009] Packaging paper is made with a base paper layer (3) as the core layer and a moisture barrier layer (2) and a structured hydrophobic mesh layer (1) sequentially disposed on the front and back surfaces of the base paper layer (3).

[0010] Furthermore, the structured hydrophobic mesh on the back surface and the structured hydrophobic mesh on the front surface are misaligned, with a misalignment angle of 0° to 60°.

[0011] Furthermore, the amount of the barrier agent sprayed is 5~22 g / m². 2 .

[0012] Furthermore, the barrier agent comprises modified starch, nano-silica, and hydroxypropyl cellulose, with a mass ratio of (7:2:1) to (8:1:1); wherein the modified starch is cationic starch or phosphate starch.

[0013] Furthermore, the hollowed-out area of ​​the micro-gravure roller accounts for 15% to 40%, and the pattern unit is selected from at least one of triangle, hexagon, rhombus, rectangle, and ellipse, with the side length or minor axis length of a single pattern unit being 0.8 to 2.5 mm.

[0014] Furthermore, the sizing agent comprises alkyl ketene dimer (AKD), paraffin emulsion, and reinforcing compound in a mass ratio of (5:3:2) to (6:3:1); wherein the reinforcing compound is selected from at least one of polyamide epichlorohydrin (PAE) and polyurethane prepolymer.

[0015] Furthermore, the coating amount of the sizing agent is 8~16 g / m². 2 .

[0016] Furthermore, during the microgravure roller coating process, the speed ratio of the roller linear velocity to the paper running speed is 1.0~1.2, and the roller pressure is 0.4~0.6 MPa.

[0017] Furthermore, the water vapor transmission rate of the packaging paper is <3 g / (m²). 2 • 24h), water absorption Cobb value is 20~35 g / m³ 2 .

[0018] The technical principle of this invention: The barrier agent used in this invention penetrates into the paper fibers and forms an irreversible hydrophobic film on the surface, which helps to prevent the penetration of gaseous water molecules and ensures good moisture resistance. The structured hydrophobic mesh reduces costs while utilizing the air between the microstructures of the mesh sizing layer to enhance the repulsion of flowing liquids. Simultaneously, the regular and continuous hydrophobic mesh helps to improve the stability of the paper in high-humidity environments. Both structures further improve the waterproof and moisture-proof performance of the packaging paper, effectively solving the problems of box collapse and damage caused by decreased strength in high-humidity environments.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) Significantly improves moisture resistance, achieving dual waterproof and moisture-proof barrier. This invention adopts a composite sizing process, which effectively inhibits water vapor penetration through a dense and continuous moisture barrier layer. At the same time, the regular pattern structure of the structured hydrophobic mesh enhances the repulsion of liquid water, giving the packaging paper both excellent moisture resistance and water resistance. According to the test, the water vapor transmission rate of the obtained packaging paper is <3 g / (m²·24h), and the water absorption Cobb value is controlled at 20~35 g / m². It can still maintain stable physical strength in high humidity environment, effectively solving the problem of box collapse and damage caused by the decrease in strength of traditional packaging paper in high humidity environment.

[0021] (2) Reduce sizing agent usage and control production costs. This invention uses micro-gravure roller coating technology to construct a structured hydrophobic mesh. Through the design of hollow areas (15%~40%), the amount of sizing agent used is significantly reduced while ensuring water repellency. At the same time, the atomized spraying process allows the barrier agent to penetrate evenly and form a film efficiently, further reducing material consumption. Compared with existing full-surface sizing processes, this invention effectively reduces the sizing cost per unit product while achieving the same or better moisture resistance.

[0022] (3) The process is simple and efficient, and is suitable for large-scale industrial production. The method of the present invention is simple and adopts a composite sizing process with independent control on both sides. It can simultaneously complete the sizing of the front and back surfaces on a high-speed paper machine (300~350 m / min), resulting in high production efficiency. The raw materials used are all commercially available conventional papermaking additives. No special equipment or complex post-processing is required. It is easy to operate and can be easily modified on existing production lines. It has good prospects for industrial application and is particularly suitable for fields with strict requirements for packaging moisture resistance, such as cold chain logistics and fresh food e-commerce. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of packaging paper prepared based on the method for regulating the moisture resistance of packaging paper according to the present invention.

[0024] Among them, 1-structured hydrophobic mesh layer, 2-moisture barrier layer, 3-base paper layer. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the invention. Simple modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and substance thereof are all within the scope of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0026] Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0027] like Figure 1 As shown, the packaging paper prepared based on the control method of the present invention has the base paper layer 3 as the central layer, and a moisture barrier layer 2 and a structured hydrophobic mesh layer 1 are sequentially provided on the front and back surfaces of the base paper layer 3.

[0028] Example 1: A method for regulating the moisture resistance of packaging paper according to the present invention

[0029] This implementation case focuses on 250 g / m 2 Kraft paperboard enhances its moisture resistance and moisture-proof performance through a composite sizing process. It is produced using a 350 m / min high-speed paper machine, equipped with a dual-station atomization spraying system and a dual-sided independent micro-gravure coating unit to ensure that the sizing of the front and back surfaces is independently controllable.

[0030] First, a moisture barrier layer 2 is constructed. A composite barrier agent (10% solid content) is prepared according to the mass ratio of cationic starch: nano-silica: hydroxypropyl cellulose = 7.5:2:0.5. Then, a 10 g / m² coating is applied to the front and back surfaces of the base paper using high-pressure atomization spraying. 2 and 8 g / m 2 After being dried at a gradient of 80℃→60℃ for 12 s, a dense and continuous moisture barrier layer 2 is formed.

[0031] Subsequently, a structured hydrophobic mesh layer 3 was constructed. A composite sizing agent (15% solid content) was prepared according to the mass ratio of AKD: paraffin emulsion: PAE = 5.5:3:1.5. It was then coated using a double-sided micro-gravure roller: the front roller had a 30% perforated area, and the back roller had a 25% perforated area, both consisting of 1.5 mm side length regular hexagonal patterns, offset by 30°; the coating amount was 15 g / m² on the front side. 2 12 g / m on the back 2 The speed ratio of the roller linear speed to the paper running speed is 1.1, the pressure is 0.4 MPa, and the two-layer structure is fused and cured by segmented drying at 60℃→80℃→70℃ for 18s.

[0032] Final product testing showed that the water vapor transmission rate decreased to 2.8 g / (m²). 2 • 24h), water absorption Cobb value is 30 g / m³ 2 Its moisture resistance fully meets the usage requirements.

[0033] Example 2: A method for regulating the moisture resistance of packaging paper according to the present invention

[0034] This implementation case focuses on 180 g / m 2 Lightweight kraft paperboard enhances moisture resistance through a composite sizing process. It is produced using a 320 m / min high-speed paper machine, equipped with a dual-station atomization spraying system and a dual-sided independent micro-gravure coating unit to ensure independent and controllable sizing on the front and back surfaces.

[0035] First, moisture barrier layer 2 is constructed. A composite barrier agent (8% solid content) is prepared according to the mass ratio of phosphate starch: nano silica: hydroxypropyl cellulose = 8:1:1. Then, a 6 g / m² coating is applied to the front and back surfaces of the base paper via high-pressure atomization spraying. 2 and 5g / m 2 After being dried at a gradient of 75℃→55℃ for 10 s, a dense and continuous moisture barrier layer 2 is formed.

[0036] Subsequently, a structured hydrophobic mesh layer 3 was constructed. A composite sizing agent (12% solid content) was prepared according to the mass ratio of AKD: paraffin emulsion: polyurethane prepolymer = 6:3:1. It was then coated using a double-sided micro-gravure roller: the front roller had a 20% perforated area, and the back roller had a 15% perforated area, both with a 0.8 mm side length rhomboid pattern and a 0° offset; the coating amount was 10 g / m² on the front side. 2 8 g / m on the back 2 The speed ratio of the roller linear speed to the paper running speed is 1.0, the pressure is 0.3 MPa, and the two-layer structure is fused and cured by segmented drying at 55℃→75℃→65℃ for 15 s.

[0037] Final product testing showed that the water vapor transmission rate decreased to 2.5 g / (m²). 2 • 24h), water absorption Cobb value is 35 g / m³ 2 Its moisture resistance meets the requirements for lightweight packaging.

[0038] Example 3: A method for regulating the moisture resistance of packaging paper according to the present invention

[0039] This implementation case focuses on 300 g / m³ 2 High-strength kraft paper is made with a composite sizing process to enhance its moisture resistance and moisture-proof properties. It is produced using a 300 m / min high-speed paper machine, equipped with a dual-station atomization spraying system and a dual-sided independent micro-gravure coating unit to ensure that the sizing of the front and back surfaces is independently controllable.

[0040] First, moisture barrier layer 2 is constructed. A composite barrier agent (solid content 12%) is prepared according to the mass ratio of cationic starch: nano silica: hydroxypropyl cellulose = 7:2:1. 22 g / m² of this agent is then sprayed onto the front and back surfaces of the base paper using high-pressure atomization spraying. 2 and 22 g / m 2 After being dried at a gradient of 85℃→65℃ for 15 s, a dense and continuous moisture barrier layer 2 is formed.

[0041] Subsequently, a structured hydrophobic mesh layer 3 was constructed. A composite sizing agent (18% solid content) was prepared according to the mass ratio of AKD: paraffin emulsion: PAE = 5:3:2. It was then coated using a double-sided micro-gravure roller: the front roller had a 40% perforated area, and the back roller had a 35% perforated area, both forming 2.5 mm side rectangular patterns with a 45° offset; the coating amount on the front side was 16 g / m². 2 14 g / m² on the back 2 The speed ratio of the roller linear speed to the paper running speed is 1.2, the pressure is 0.6 MPa, and the two-layer structure is fused and cured by segmented drying at 65℃→85℃→75℃ for 20s.

[0042] Final product testing showed that the water vapor transmission rate decreased to 2.5 g / (m²). 2 • 24h), water absorption Cobb value is 20 g / m³ 2 Its moisture-proof and moisture-resistant properties meet the stringent requirements of heavy-duty packaging.

[0043] Example 4: A method for regulating the moisture resistance of packaging paper according to the present invention

[0044] This implementation case focuses on 220 g / m 2 Special kraft paper achieves strong moisture resistance through a composite sizing process. It is produced using a high-speed paper machine of 330 m / min, equipped with a dual-station atomization spraying system and a dual-sided independent micro-gravure coating unit to ensure independent and controllable sizing on the front and back surfaces.

[0045] First, a moisture barrier layer 2 is constructed. A composite barrier agent (9% solid content) is prepared according to the mass ratio of phosphate starch: nano silica: hydroxypropyl cellulose = 7.5:1.5:1. Then, an 8 g / m² coating is applied to the front and back surfaces of the base paper using high-pressure atomization spraying. 2 and 7 g / m 2 After being dried at a gradient of 80℃→60℃ for 12 s, a dense and continuous moisture barrier layer 2 is formed.

[0046] Subsequently, a structured hydrophobic mesh layer 3 was constructed. A composite sizing agent (14% solid content) was prepared according to the mass ratio of AKD: paraffin emulsion: polyurethane prepolymer = 5.5:3:1.5. It was then coated using a double-sided micro-gravure roller: the front roller had a 25% perforated area, and the back roller had a 20% perforated area, both forming elliptical patterns with a minor axis length of 1.2 mm and a 60° offset; the coating amount was 13 g / m² on the front side. 2 11 g / m² on the back 2 The speed ratio of the roller linear speed to the paper running speed is 1.1, the pressure is 0.4 MPa, and the two-layer structure is fused and cured by segmented drying at 60℃→80℃→70℃ for 16 s.

[0047] Final product testing showed that the water vapor transmission rate decreased to 2.9 g / (m²). 2 (24h), water absorption Cobb value is 22 g / m³ 2 Its moisture-resistant properties make it suitable for special usage scenarios such as high humidity and refrigeration.

Claims

1. A method for controlling the moisture resistance of packaging paper, characterized in that: A composite sizing process is adopted and applied simultaneously to the front and back surfaces of the base paper; the composite sizing process includes the construction of a moisture barrier layer and a structured hydrophobic mesh layer, and the composite sizing process of the front and back surfaces of the base paper is controlled independently; The moisture barrier layer is constructed by uniformly spraying a barrier agent onto the front and back surfaces of the base paper layer (3) using an atomizing spraying device to form a dense and continuous moisture barrier layer (2).

2. The structured hydrophobic mesh layer is constructed by coating an adhesive onto the outer surface of the moisture barrier layer (2) with a micro-gravure roller to form a structured hydrophobic mesh layer (1) with a regular pattern. Packaging paper is made with a base paper layer (3) as the core layer and a moisture barrier layer (2) and a structured hydrophobic mesh layer (1) sequentially disposed on the front and back surfaces of the base paper layer (3).

3. The method according to claim 1, characterized in that: The structured hydrophobic mesh on the back surface is misaligned with the structured hydrophobic mesh on the front surface, with a misalignment angle of 0° to 60°.

4. The method according to claim 1, characterized in that: The amount of the barrier agent applied is 5~22 g / m². 2 .

5. The method according to claim 1, characterized in that: The barrier agent comprises modified starch, nano-silica, and hydroxypropyl cellulose in a mass ratio of (7:2:1) to (8:1:1); wherein the modified starch is cationic starch or phosphate starch.

6. The method according to claim 1, characterized in that: The hollowed-out area of ​​the micro-gravure roller accounts for 15% to 40%, and the pattern unit is selected from at least one of triangle, hexagon, rhombus, rectangle and ellipse. The side length or minor axis length of a single pattern unit is 0.8 to 2.5 mm.

7. The method according to claim 1, characterized in that: The sizing agent comprises alkyl ketene dimer, paraffin emulsion and reinforcing compound, with a mass ratio of (5:3:2) to (6:3:1); wherein the reinforcing compound is selected from at least one of polyamide epichlorohydrin and polyurethane prepolymer.

8. The method according to claim 1, characterized in that: The coating amount of the sizing agent is 8~16 g / m². 2 .

9. The method according to claim 1, characterized in that: During the microgravure roller coating process, the speed ratio of the roller linear velocity to the paper running speed is 1.0~1.2, and the roller pressure is 0.4~0.6 MPa.

10. The packaging paper according to claim 1, characterized in that, The water vapor transmission rate of the packaging paper is <3 g / (m²). 2 • 24h), water absorption Cobb value is 20~35 g / m³ 2 .

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