A production process of low grammage corrugated paper

Abstract

The application discloses a production process of low-weight corrugated paper, which comprises the following steps: after waste paper raw materials are disintegrated, the waste paper raw materials are subjected to differential swelling pretreatment by using carboxymethyl cellulose, and then the waste paper raw materials are divided into long fiber fraction, medium-long fiber fraction and short fiber fraction through three-stage fiber classification screening; the three fractions are subjected to low-concentration sand removal purification through differential pressure; the three fractions after beating are proportioned, and then the three fractions are subjected to post-drying, calendering and winding. Through the process, high strength of corrugated paper can be realized under the condition of low weight.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a production process for low-grammage corrugated paper. Background Technology

[0002] Corrugated base paper is the core material of corrugated board. While reducing basis weight can save on raw material and logistics costs, it leads to a decrease in thickness and fiber content, weakening mechanical properties such as ring crush resistance and tensile strength. When corrugated base paper is produced using waste paper as raw material, repeated fiber reuse results in problems such as shortened fiber length, stiffened cell walls, and loss of active groups, making the strength of the finished paper far inferior to that of virgin fiber pulp. Therefore, stabilizing or even improving strength at low basis weights has become a core challenge for the industry.

[0003] Currently, in the corrugated paper production process, the existing two-stage grading process in the fiber grading and sand removal stages is too extensive. It does not separate medium and long fibers separately, resulting in low resource utilization. Short fibers are prone to clogging the screen, and long fibers are prone to entanglement and damage. There is also a lack of differentiated pretreatment before grading. In the sand removal stage, uniform parameters are used for all fibers, but impurities on the surface of long fibers are difficult to remove, and short fibers are easily lost under high pressure. Although nanocellulose reinforcing agents have excellent performance, they are prone to agglomeration and poor dispersion after simple mixing with cationic starch, which limits the reinforcing effect. Surface sizing cannot simultaneously achieve both internal penetration reinforcement and surface film protection, and a single sizing method is difficult to achieve gradient reinforcement.

[0004] More importantly, the aforementioned links are independent of each other and lack coordination, making it impossible to form complementary processes and superimpose advantages, which seriously restricts the quality upgrade of low basis weight high strength corrugated base paper. Summary of the Invention

[0005] The present invention aims to provide a production process for low basis weight corrugated paper, achieving high strength of corrugated base paper under low basis weight conditions.

[0006] To achieve the above objectives, this application provides the following technical solution: A production process for low-basis-weight corrugated paper includes the following steps: S1. Raw material preparation: Mix waste paper raw materials in a certain proportion and send them into the shredding equipment for shredding; S2. Fiber Grading: First, adjust the pH of the broken-down pulp to 6.0-6.5, add carboxymethyl cellulose, and stir at 40-50℃ for 10-15 minutes. Then, pass the pretreated pulp through a three-stage grading sieve to separate the fibers into the following three grades: Long fiber grade: fiber length > 2.0 mm, accounting for 15-25%; Medium-long fiber grade: fiber length 0.8-2.0 mm, accounting for 45-55%; Short fiber grade: fiber length < 0.8 mm, accounting for 25-35%. S3. Graded purification treatment: The fibers of the three grades are purified by independent low-concentration desanding systems. The desanding concentration is 0.8-1.2% for each grade. The desanding pressure for the long fiber grade is 0.30-0.40 MPa, the desanding pressure for the medium and long fiber grade is 0.25-0.30 MPa, and the desanding pressure for the short fiber grade is 0.15-0.22 MPa. S4. Pulping: The purified fractions are pulped separately. S5. Slurry preparation and reinforcement: Mix the three fractions in the following weight percentages for slurry preparation: 20-30% long fiber fraction, 45-55% medium-long fiber fraction, and 20-30% short fiber fraction. Add reinforcement agents, including nanocellulose, cationic starch, and polyacrylamide. The nanocellulose is first mixed with cationic starch at a weight ratio of 1:5-1:8 and stirred at 60-70°C for 15-25 minutes. Then, it is added together with polyacrylamide to the slurry preparation process. S6. Forming and Dewatering: The prepared slurry is formed and dehydrated by a forming device; S7. Press drying: The formed wet paper sheets are dried after being pressed and dehydrated; S8. Sizing: Apply sizing to the dried paper sheets; S9. Post-drying and winding: The sized paper sheets are dried again, calendered, and then wound into paper.

[0007] As a preferred embodiment, in step S1, the waste paper raw material is a mixture of domestic OCC waste paper and imported waste paper, with a mixing weight ratio of domestic OCC waste paper: imported waste paper = 60-80: 20-40.

[0008] As a preferred embodiment, in step S1, the pulping is carried out in a rotary drum pulper, with a pulping concentration of 12-18%, a pulping temperature of 35-45℃, and a pulping time of 15-25 minutes.

[0009] As a preferred embodiment, in step S2, the amount of carboxymethyl cellulose added is 0.3-0.8 kg / ton of paper.

[0010] As a preferred embodiment, in step S5, the amount of cationic starch added is 8-12 kg / ton of paper, the amount of polyacrylamide added is 1-3 kg / ton of paper, and the amount of nanocellulose added is 0.5-1.5 kg / ton of paper.

[0011] As a preferred embodiment, in step S5, the nanocellulose has a diameter of 5-20 nm and a length of 100-500 nm, and the nanocellulose is obtained from pulp fibers by mechanical grinding or acid hydrolysis.

[0012] As a preferred embodiment, in step S9, the post-drying temperature is 80-105℃, and the post-drying degree is controlled to be 92-96%.

[0013] As a preferred embodiment, in step S7, the pressing adopts a four-roller three-pressure zone composite pressing, with the pressing line pressure being 60-80 kN / m, 100-120 kN / m and 120-150 kN / m respectively, and the dryness of the pressing section is controlled at 44-50%; the pre-drying temperature is 90-120 ℃, and the pre-drying degree is controlled at 90-93%.

[0014] As a preferred embodiment, in step S8, the dried paper sheet undergoes differentiated sizing treatment: the sizing amount in the core layer area is 2-4 g / m². 2 The solid content of the rubber compound is 5-8%, and the weight average molecular weight of the high molecular weight component is 800,000-1,200,000; the application rate of the rubber compound in the intermediate transition layer is 1-2 g / m². 2 The solid content of the rubber compound is 8-12%, and the weight average molecular weight of the molecular weight components in the rubber compound is 400,000-600,000; the application rate of the rubber compound in the surface layer is 4-6 g / m². 2 The solid content of the rubber compound is 15-20%, and the weight average molecular weight of the low molecular weight components is 200,000-400,000; the total application rate is 7-12 g / m³. 2 .

[0015] A low-grammage corrugated paper is obtained by the aforementioned production process.

[0016] Working principle and beneficial effects of the present invention: This application utilizes CMC selective swelling treatment in a weakly acidic environment (pH 6.0-6.5) to moderately swell short fibers, resolving sieve clogging while preserving the integrity of long fibers. The fibers are then precisely separated into long, medium, and short grades using a three-stage grading sieve. Long fibers undergo thorough impurity removal under high pressure (0.30-0.40 MPa), while short fibers are treated with low pressure (0.15-0.22 MPa) to reduce loss, significantly improving fiber utilization. Furthermore, by premixing and coating nanocellulose and cationic starch in a 1:5-1:8 ratio at 60-70℃, a core-shell composite structure is formed, completely resolving the agglomeration problem of nano-auxiliaries, improving fiber retention, and upgrading point contact between fibers to surface contact, thus constructing a full-scale cross-linking reinforcement network. A pioneering differential gradient sizing process is employed, involving core layer spraying, transition layer curtain coating, and surface film transfer, with the total sizing amount controlled at 7-12 g / m². 2 By precisely proportioning the molecular weight and solid content of the adhesive in a gradient decreasing and increasing manner from the inside out, cross-linking reinforcement within the paper sheet, smooth interlayer transition, and dense film formation on the surface are achieved, comprehensively improving the structural strength, overall stability, and water resistance of low-grammage corrugated base paper. Attached Figure Description

[0017] Figure 1 This is a production flow diagram for this application; Figure 2 This is a schematic diagram of the adhesive application process. Detailed Implementation

[0018] The following detailed description illustrates the specific implementation method: Example 1: A production process for low basis weight corrugated base paper, comprising the following steps: S1. Raw material preparation: Mix domestic OCC waste paper and imported waste paper at a weight ratio of 70:30 and then feed them into a rotary drum pulper for pulping. The pulping concentration is 15%, the pulping temperature is 40℃, and the pulping time is 20 minutes.

[0019] S2. Fiber grading: Adjust the pH of the pulp after disintegration to 6.3, add 0.5 kg / ton of paper carboxymethyl cellulose, and stir at 45°C for 12 minutes; then pass it through a three-stage grading sieve in sequence, with long fiber grade (>2.0mm) accounting for 20%, medium and long fiber grade (0.8-2.0mm) accounting for 50%, and short fiber grade (<0.8mm) accounting for 30%.

[0020] S3. Staged purification treatment: The three stages are purified by independent low-concentration sand removal systems with a sand removal concentration of 1.0%. The sand removal pressure is 0.35MPa for long fiber stage, 0.28MPa for medium and long fiber stage, and 0.18MPa for short fiber stage.

[0021] S4. Pulping: Pulping is performed separately for the three grades, and the degree of freeness is controlled at 35°SR for each grade.

[0022] S5. Pulping and Reinforcement: The three fractions are mixed and pulverized at a ratio of 25% long fiber, 50% medium-long fiber, and 25% short fiber. Nanocellulose (diameter 5-20nm, length 100-500nm) is first mixed with cationic starch at a weight ratio of 1:6 and stirred at 65℃ for 20 minutes, then added together with polyacrylamide. The dosage is: cationic starch 10 kg / ton of paper, polyacrylamide 2 kg / ton of paper, and nanocellulose 1.0 kg / ton of paper.

[0023] S6. Forming: The forming is done by clamping the wire mesh, with a forming concentration of 0.8%, a forming mesh number of 70 mesh, and a dryness of 24% at the exit of the wire mesh.

[0024] S7. Pressing and Drying: Four-roller three-pressure zone compound pressing, with linear pressures of 70 kN / m, 110 kN / m, and 135 kN / m respectively, resulting in a dryness of 47% at the pressing section; the pre-drying temperature is 105 ℃, resulting in a pre-drying degree of 92%.

[0025] S8. Adhesive application: Apply adhesive to the core layer area at a rate of 3 g / m². 2 Solid content 6.5%, weight average molecular weight 1 million; application rate in the transition layer region 1.5 g / m 2Solid content 10%, weight average molecular weight 500,000; surface layer application rate 5 g / m² 2 Solid content 18%, weight average molecular weight 300,000; total sizing amount 9.5 g / m³ 2 .

[0026] S9. Post-drying and winding: Post-drying temperature 95℃, post-drying degree 94%, calendering and winding.

[0027] Example 2: The only difference from Example 1 is: domestic OCC:imported waste paper = 60:40, disintegration concentration 12%, temperature 35℃, time 25 minutes; CMC addition 0.3 kg / ton of paper; sand removal pressure 0.30 MPa for long fibers / 0.25 MPa for medium fibers / 0.15 MPa for short fibers; fiber ratio 20% long fibers, 55% medium-long fibers, 25% short fibers; nanocellulose:cationic starch = 1:5, temperature 60℃, time 25 minutes; 8 kg / ton of paper cationic starch, 1 kg / ton of paper polyacrylamide, 0.5 kg / ton of paper nanocellulose; core layer sizing 2 g / m 2 Solid content 5%, molecular weight 800,000; transition layer 1 g / m 2 Solid content 8%, molecular weight 400,000; surface layer 4 g / m 2 Solid content 15%, molecular weight 200,000, total sizing agent 7 g / m³ 2 The post-drying temperature was 80°C. Everything else was the same as in Example 1.

[0028] Example 3: The only difference from Example 1 is: domestic OCC:imported waste paper = 80:20, disintegration concentration 18%, temperature 45℃, time 15 minutes; CMC addition 0.8 kg / ton of paper; sand removal pressure 0.40 MPa for long fibers / 0.30 MPa for medium fibers / 0.22 MPa for short fibers; fiber ratio 30% long fibers, 45% medium-long fibers, 25% short fibers; nanocellulose:cationic starch = 1:8, temperature 70℃, time 15 minutes; cationic starch 12 kg / ton of paper, polyacrylamide 3 kg / ton of paper, nanocellulose 1.5 kg / ton of paper; core layer sizing 4 g / m 2 Solid content 8%, molecular weight 1.2 million; transition layer 2 g / m 2 Solid content 12%, molecular weight 600,000, surface layer 6 g / m 2 Solid content 20%, molecular weight 400,000, total sizing 12 g / m²; post-drying temperature 105℃. The rest is the same as in Example 1.

[0029] Comparative Example 1: The only difference from Example 1 is that carboxymethyl cellulose is not added for pretreatment in S2; the crushed slurry is directly fed into a three-stage grading sieve for classification. Everything else is exactly the same as Example 1.

[0030] Comparative Example 2: The only difference from Example 1 is that a two-stage grading sieve is used instead of a three-stage grading sieve in S2 to separate the pulp into two grades: long fibers (>0.8mm) and short fibers (≤0.8mm). After grading, the pulp is prepared with a 50% long fiber and 50% short fiber ratio. Everything else is exactly the same as in Example 1.

[0031] Comparative Example 3: The only difference from Example 1 is that the three stages in S3 are purified using the same desanding pressure (0.30 MPa). Everything else is exactly the same as Example 1.

[0032] Comparative Example 4: The only difference from Example 1 is that in S5, nanocellulose, cationic starch, and polyacrylamide are simply mixed and directly added to the slurry preparation process without pre-coating of nanocellulose and cationic starch. Everything else is exactly the same as Example 1.

[0033] Comparative Example 5: The only difference from Example 1 is that a single-film transfer sizing method was used in S8, with a sizing amount of 9.5 g / m³. 2 The rubber compound has a solid content of 15% and a weight-average molecular weight of 500,000. No three-zone differentiated sizing is applied. Everything else is identical to Example 1.

[0034] Blank Group: A production process for low-grammage corrugated base paper, comprising the following steps: S1, Raw material preparation: Mixing domestic OCC waste paper and imported waste paper at a weight ratio of 70:30 and then dissolving them; S2, Pulping: Screening and purifying the pulp after dissolving; S3, Beating: Performing conventional beating of the pulp, with the beating degree controlled at 35°SR; S4, Forming: Forming with a wire mesh; S5, Pressing and drying: Conventional pressing and drying; S6, Winding into paper.

[0035] Ring crush index is tested according to GB / T 2679.8, tensile index according to GB / T 12914, bursting strength index according to GB / T 454, and tear index according to GB / T 455. Water resistance is expressed as Cobb value (g / m²) according to GB / T 13023-2008 "Corrugated Core (Base) Paper" and GB / T 1540 "Determination of Water Absorption of Paper and Paperboard (Cobb Method)" (absorption time 1 min). The lower the value, the better the water resistance. The water absorption requirement for Grade A corrugated base paper is no more than 100 g / m². 2 The data obtained is shown in the table below:

[0036] In summary, this approach comprehensively improves the structural strength, overall stability, and water resistance of low-grammage corrugated base paper.

[0037] The above description is merely a preferred embodiment of this application and does not limit the patent scope of this application. Any equivalent structural transformations made based on the inventive concept of this application and the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A production process for low-basis-weight corrugated paper, characterized in that, Includes the following steps: S1. Raw material preparation: Mix waste paper raw materials in a certain proportion and send them into the shredding equipment for shredding; S2. Fiber Grading: First, adjust the pH of the crushed pulp to 6.0-6.5, add carboxymethyl cellulose, and stir at 40-50℃ for 10-15 minutes. Then, pass the pretreated pulp through a three-stage grading sieve to separate the fibers into the following three grades: Long fiber grade: fiber length > 2.0 mm, accounting for 15-25%; Medium-long fiber grade: fiber length 0.8-2.0 mm, accounting for 45-55%; Short fiber grade: fiber length < 0.8 mm, accounting for 25-35%. S3. Graded purification treatment: The fibers of the three grades are purified by independent low-concentration desanding systems. The desanding concentration is 0.8-1.2% for each grade. The desanding pressure for the long fiber grade is 0.30-0.40 MPa, the desanding pressure for the medium and long fiber grade is 0.25-0.30 MPa, and the desanding pressure for the short fiber grade is 0.15-0.22 MPa. S4. Pulping: The purified fractions are pulped separately. S5. Slurry preparation and reinforcement: Mix the three fractions in the following weight percentages for slurry preparation: 20-30% long fiber fraction, 45-55% medium-long fiber fraction, and 20-30% short fiber fraction. Add reinforcement agents, including nanocellulose, cationic starch, and polyacrylamide. The nanocellulose is first mixed with cationic starch at a weight ratio of 1:5-1:8 and stirred at 60-70°C for 15-25 minutes. Then, it is added together with polyacrylamide to the slurry preparation process. S6. Forming and Dewatering: The prepared slurry is formed and dehydrated by a forming device; S7. Press drying: The formed wet paper sheets are dried after being pressed and dehydrated; S8. Sizing: Apply sizing to the dried paper sheets; S9. Post-drying and winding: The sized paper sheets are dried again, calendered, and then wound into paper.

2. The production process according to claim 1, characterized in that, In step S1, the waste paper raw material is a mixture of domestic OCC waste paper and imported waste paper, with a mixing weight ratio of domestic OCC waste paper: imported waste paper = 60-80: 20-40.

3. The production process according to claim 2, characterized in that, In step S1, the pulping is carried out in a rotary drum pulper, with a pulping concentration of 12-18%, a pulping temperature of 35-45℃, and a pulping time of 15-25 minutes.

4. The production process according to claim 3, characterized in that, In step S2, the amount of carboxymethyl cellulose added is 0.3-0.8 kg / ton of paper.

5. The production process according to claim 4, characterized in that, In step S5, the amount of cationic starch added is 8-12 kg / ton of paper, the amount of polyacrylamide added is 1-3 kg / ton of paper, and the amount of nanocellulose added is 0.5-1.5 kg / ton of paper.

6. The production process according to claim 5, characterized in that, In step S5, the nanocellulose has a diameter of 5-20 nm and a length of 100-500 nm, and is obtained from pulp fibers by mechanical grinding or acid hydrolysis.

7. The production process of low basis weight corrugated base paper according to claim 6, characterized in that, In step S9, the post-drying temperature is 80-105℃, and the post-drying degree is controlled at 92-96%.

8. The production process according to claim 7, characterized in that, In step S7, the pressing adopts a four-roller three-pressure zone composite pressing, with pressing line pressures of 60-80 kN / m, 100-120 kN / m and 120-150 kN / m respectively, and the dryness of the pressing section is controlled at 44-50%; the pre-drying temperature is 90-120 ℃, and the pre-drying degree is controlled at 90-93%.

9. The production process according to claim 8, characterized in that, In step S8, the dried paper is subjected to differentiated sizing treatment: the sizing amount in the core layer area is 2-4 g / m². 2 The solid content of the rubber compound is 5-8%, and the weight average molecular weight of the high molecular weight component is 800,000-1,200,000; the application rate of the rubber compound in the intermediate transition layer is 1-2 g / m². 2 The solid content of the rubber compound is 8-12%, and the weight average molecular weight of the molecular weight components in the rubber compound is 400,000-600,000; the application rate of the rubber compound in the surface layer is 4-6 g / m². 2 The solid content of the rubber compound is 15-20%, and the weight average molecular weight of the low molecular weight components is 200,000-400,000; the total application rate is 7-12 g / m³. 2 .

10. A low-grammage corrugated paper, obtained by the production process described in any one of claims 1 to 9.

Images