Preparation method of high air permeability bamboo pulp lining paper

Abstract

The embodiment of the present application provides a kind of preparation method of high air permeability bamboo pulp lining paper, comprising: S1: fiber raw material is scattered pulp to form first pulp, and the concentration of scattered pulp is 4-6%, and the proportion of bamboo pulp fiber in fiber raw material is greater than or equal to 95%, and the average length of the bamboo pulp fiber is greater than or equal to 1.6mm, and the content of small component in bamboo pulp fiber is less than or equal to 1%, and the proportion of bamboo pulp fiber with length of 1-1.5mm is 6-15%, and then it is ground, formed, dried and wrinkled to form high air permeability bamboo pulp lining paper, so that the high air permeability bamboo pulp lining paper formed by the above method has high strength and high air permeability, and the air permeability is improved by more than 17% compared with the prior art.

Description

Preparation method of high air permeability bamboo pulp liner paper Technical Field

[0001] This invention relates to a method for preparing highly breathable bamboo pulp liner paper. Background Technology

[0002] In disposable absorbent products, liner paper is widely used as a covering layer for the absorbent core. The liner paper can prevent the absorbent core, which is mainly composed of fluff pulp and SAP, from falling off during the manufacturing process of disposable absorbent products, thereby maintaining the shape of the absorbent core.

[0003] For disposable absorbent products, people want them to have good absorbency to quickly absorb bodily fluids, and also good breathability for better comfort. Therefore, they also want the liner paper covering the absorbent core to have good breathability.

[0004] To address this, documents such as CN112575610A have proposed some high-permeability papermaking processes, using softwood pulp and hardwood pulp, and employing wet forming and light dry creping processes to form the paper. However, due to the significant differences between bamboo pulp fibers and wood pulp fibers—more specifically, bamboo pulp fibers have a larger aspect ratio and are finer—the papermaking structure formed using conventional wood pulp preparation processes is more compact, resulting in a significant reduction in its permeability compared to wood pulp.

[0005] In addition, CN106149452A also proposes to use wood pulp but without using a release agent to achieve a higher air permeability (air permeability up to 3 times that of the existing technology). However, for bamboo pulp papermaking, based on the bamboo pulp papermaking process, in practice, because bamboo pulp fibers are more rigid and have more fine fibers, it is necessary to use a release agent in production to improve paper release performance, reduce dust, improve paper surface smoothness, and protect the drying cylinder.

[0006] Therefore, it is necessary to develop a method for preparing high-permeability liner paper based on bamboo pulp to solve the above-mentioned technical problems. Summary of the Invention

[0007] Therefore, the present invention provides a method for preparing high-permeability bamboo pulp liner paper to solve the above-mentioned technical problems.

[0008] A method for preparing high-air-permeability bamboo pulp liner paper, characterized by comprising:

[0009] S1: Provide fiber raw materials and pulp the fiber raw materials to form a first pulp. The pulp concentration is 4-6%. The proportion of bamboo pulp fiber in the fiber raw materials is greater than or equal to 95%, and the average length of the bamboo pulp fiber is greater than or equal to 1.6 mm. The content of fine particles in the bamboo pulp fiber is less than or equal to 1%, and the proportion of bamboo pulp fiber with a length of 1-1.5 mm is 6-15%.

[0010] S2: The first pulp is refined to form the second pulp, with a pulping concentration of 3-6% and a beating degree of 30-35°SR.

[0011] S3: The second pulp is formed, dried, and creased to form a high-permeability bamboo pulp liner paper. The forming process is carried out using a crescent forming machine, the drying process is carried out using a Yankee drying cylinder, and the creasing process is carried out using a creasing doctor blade with a 10° to 20° angle, with a creasing rate of 15 to 25% and a machine speed of 1200 to 1800 meters per minute.

[0012] The fiber raw materials mentioned above are all bamboo pulp fibers.

[0013] The average length of the bamboo pulp fiber is 1.7 to 2.5 mm, and the wall-to-cavity ratio of the bamboo pulp fiber is 1.2 to 6.5.

[0014] The fiber raw material is provided in the form of pulp board, and the bamboo pulp fiber forms bamboo pulp board. The bamboo pulp board has the following technical indicators: tensile strength greater than or equal to 58 N·m / g, bursting index greater than or equal to 4 kPa·㎡ / g, tear index greater than or equal to 8.5 mN·㎡ / g, ash content less than or equal to 1%, and viscosity greater than or equal to 700 ml / g.

[0015] Among them, bamboo pulp fibers with a length of 1 to 1.5 mm account for 7 to 10%.

[0016] Step S1 further includes adjusting the proportion of bamboo pulp fibers of different lengths in the fiber raw material through screening and compounding.

[0017] In this process, after the wet paper sheet is formed, a highly breathable blanket is used to transfer the wet paper sheet, and a vacuum dehydration box is used to dehydrate the wet paper sheet. The air permeability of the highly breathable blanket is 22-24 CFM, and the vacuum degree of the vacuum dehydration box is -28 kPa.

[0018] In this process, after the fiber raw material is pulped to form a first pulp, the first pulp is screened by a first screening device to form a primary pulp. Then, the primary pulp is screened a second time to separate bamboo pulp fibers with a length of 1-1.5 mm and obtain a second pulp. Then, the separated bamboo pulp fibers with a length of 1-1.5 mm are added to the second pulp according to a predetermined ratio to obtain a mixed pulp. In step S2, the mixed pulp is milled. The predetermined ratio refers to the proportion of bamboo pulp fibers with a length of 1-1.5 mm being 6-15%. The proportion refers to the percentage of bamboo pulp fibers with a length of 1-1.5 mm in the mixed pulp.

[0019] The high-permeability bamboo pulp liner paper has a basis weight of 13-16 g / m².

[0020] Beneficial effects: This invention provides a method for preparing high-permeability bamboo pulp liner paper, comprising: S1: pulping fiber raw materials to form a first pulp with a pulp concentration of 4-6%, wherein the proportion of bamboo pulp fiber in the fiber raw materials is greater than or equal to 95%, and the average length of the bamboo pulp fiber is greater than or equal to 1.6 mm, the content of fine components in the bamboo pulp fiber is less than or equal to 1%, and the proportion of bamboo pulp fiber with a length of 1-1.5 mm is 6-15%, and then grinding, forming, drying, and creping are performed to form high-permeability bamboo pulp liner paper. Through the above method, the formed high-permeability bamboo pulp liner paper has high strength and high permeability, and the permeability is improved by more than 17% compared with the prior art. Detailed Implementation

[0021] This invention provides a method for preparing high-permeability bamboo pulp liner paper, which will be further described below.

[0022] S1: Provide fiber raw materials and pulp the fiber raw materials to form a first pulp. The pulp concentration is 4-6%. The proportion of bamboo pulp fiber in the fiber raw materials is greater than or equal to 95%, and the average length of the bamboo pulp fiber is greater than or equal to 1.6 mm. The content of fine particles in the bamboo pulp fiber is less than or equal to 1%, and the proportion of bamboo pulp fiber with a length of 1-1.5 mm is 6-15%.

[0023] In this embodiment, the fiber raw material is provided in the form of pulp board. The pulp board formed from bamboo pulp fiber is called bamboo pulp board. The bamboo pulp board has the following technical indicators: tensile strength greater than or equal to 58 N·m / g, bursting index greater than or equal to 4 kPa·㎡ / g, tear index greater than or equal to 8.5 mN·㎡ / g, ash content less than or equal to 1%, and viscosity greater than or equal to 700 ml / g.

[0024] Furthermore, the fiber raw materials are all bamboo pulp fibers, meaning that the fiber raw materials do not contain wood pulp fibers or other fibers.

[0025] Furthermore, the bamboo pulp fiber has a length of 1.6 mm or more, an aspect ratio of 80 to 160, and a wall-to-cavity ratio of 1 or more. Specifically, the bamboo pulp fiber can be selected from bamboo species such as *Phyllostachys edulis*, *Phyllostachys pubescens*, *Phyllostachys aurea*, *Phyllostachys nigra*, and *Phyllostachys pubescens*, and is produced by sulfate or caustic soda methods. Preferably, the length of the bamboo pulp fiber is 1.7 to 2.5 mm, for example: 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, etc. In addition, preferably, the wall-to-cavity ratio of the bamboo pulp fiber is 1.2 to 6.5, and more preferably, it is 1.6 to 5.0.

[0026] Furthermore, the proportion of bamboo pulp fibers with a length of 1 to 1.5 mm is 7 to 10%, and the fine components refer to components that can be removed by sieving through a sieve with a pore size of 0.4 mm.

[0027] Furthermore, step S1 also includes a step of adjusting the proportion of bamboo pulp fibers of different lengths in the fiber raw material. Specifically, the proportion of bamboo pulp fibers of different lengths can be adjusted by screening and blending. Screening and blending refers to separating fibers of different lengths in the bamboo pulp fiber by screening device, and then mixing the fibers of different lengths to form a blended first pulp.

[0028] In one specific embodiment, after the fiber raw material is pulped to form a first pulp, the first pulp is screened by a first screening device to remove fine particles and form a primary sieve pulp. Then, the primary sieve pulp is screened a second time to separate bamboo pulp fibers with a length of 1-1.5 mm and obtain a second sieve pulp. Then, the separated bamboo pulp fibers with a length of 1-1.5 mm are added to the second sieve pulp in a predetermined ratio to obtain a mixed pulp. In step S2, the mixed pulp is milled. It can be understood that the predetermined ratio means that the proportion of bamboo pulp fibers with a length of 1-1.5 mm is 6-15%, and the ratio is the proportion of bamboo pulp fibers with a length of 1-1.5 mm in the mixed pulp.

[0029] In addition, the bamboo pulp fiber is a mixture of at least two kinds of bamboo pulp fibers, and the aspect ratio of the mixed bamboo pulp fibers is 80 to 100, and the wall-to-cavity ratio is 1 to 3.

[0030] It is understood that the lengths mentioned in the description are all average lengths, the aspect ratios are average aspect ratios, the wall-to-cavity ratios are average wall-to-cavity ratios, and the fine components include fine fibers and miscellaneous cells.

[0031] Understandably, fiber raw materials are pulped using pulping equipment. During the pulping process, the fiber raw materials are dispersed in water by mechanical action to form a fiber suspension. The pulping equipment can be a hydraulic pulper.

[0032] In addition, the pulping equipment also includes a pulping tank. Before pulping, carboxymethyl cellulose (CMC) may be added to the pulping tank. Carboxymethyl cellulose is an important cellulose ether, a highly water-soluble polyanionic product obtained by chemically modifying plant fibers. It is easily soluble in cold water and possesses unusual physical and chemical properties such as dispersibility, resistance to spoilage, and biological harmlessness. In this embodiment, CMC is used as a wet strength additive to improve the efficiency of subsequent wet strength agents. Its addition in the initial pulping process of tissue paper preparation increases the interaction time between CMC and bamboo pulp fibers, helping CMC to maximize its effectiveness. The amount of CMC added per ton of bamboo pulp relative to oven-dry pulp can be 1–4 kg, for example: 1 kg, 2 kg, 3 kg, 4 kg, etc.

[0033] S2: The first pulp is refined to form the second pulp, with a pulping concentration of 3-6% and a beating degree of 30-35°SR.

[0034] Pulping is a process that causes fiber raw materials to absorb water, swell, and become finer fibers. This greatly increases the external surface area of ​​the fibers and exposes more hydroxyl groups in the cellulose molecular chains, promoting hydrogen bonding. This increases the uniformity and strength of the paper, reduces the rigidity of the fiber raw materials, weakens their elasticity, increases their plasticity, and makes the fibers soft and malleable.

[0035] In this embodiment, the concentration range of the pulp concentration is controlled to be 3-6%, for example: 3%, 3.5%, 4.5%, 5%, 6%, etc. The pulping equipment for refining bamboo pulp can be a double disc refiner. In the double disc refiner, one disc and one fixed disc act on the bamboo pulp fibers between the two discs, so that the bamboo pulp fibers are subjected to friction, impact, kneading, torsion and shearing forces, thereby completing the pulping in a short time. Moreover, the pulping power of the double disc refiner of the present invention can be set to be greater than 90 kWh / t, more preferably greater than or equal to 100 kWh / t. When the pulp is 100% bamboo pulp, the pulping power is preferably 105-125 kWh / t. Of course, pulping can also be carried out at other power levels. The present invention does not further limit this.

[0036] The beating degree of bamboo pulp after grinding is 30-35°SR, specifically 30°SR, 31°SR, 32°SR, 33°SR, 34°SR, 35°SR, etc.

[0037] Furthermore, a wet strength agent is added to the second slurry, with the amount of wet strength agent added being 5 to 25 kg / t based on oven-dry slurry.

[0038] S3: The second pulp is formed, dried, and creased to form a high-permeability bamboo pulp liner paper. The forming process is carried out using a crescent forming machine, the drying process is carried out using a Yankee drying cylinder, and the creasing process is carried out using a creasing doctor blade with a 10° to 20° angle, with a creasing rate of 15 to 25% and a machine speed of 1200 to 1800 meters per minute.

[0039] Preferably, the wrinkling scraper is an alloy scraper, and the replacement time is 2-5 hours.

[0040] Furthermore, after the wet paper sheet is formed, a highly breathable blanket is used to transfer the wet paper sheet, and a vacuum absorbent box is used to dehydrate the wet paper sheet. The air permeability of the highly breathable blanket is 22-24 CFM, and the vacuum absorbent box has a vacuum degree of -28 kPa. Compared with the blankets with 20-21 CFM and vacuum absorbent boxes with a vacuum degree of -34-32 kPa commonly used in the prior art, the air permeability can be further improved by more than 8%. In particular, due to the high aspect ratio of bamboo pulp fiber, it can still achieve good dehydration effect when using a lower vacuum degree for water absorption.

[0041] The felt used in the production of the liner paper has an air permeability of 23 CFM and a vacuum suction box negative pressure of -28 kPa.

[0042] Understandably, before step S3, a bonding agent and a release agent are sprayed onto the Yankee drying cylinder so that the formed paper sheet can easily adhere to the Yankee drying cylinder and then be peeled off by a crease scraper.

[0043] Furthermore, the high-permeability bamboo pulp liner paper has a basis weight of 13-16 g / m². Studies have found that when the basis weight is too low, the strength of the liner paper is insufficient, and when the basis weight of the liner paper is too high, the air permeability of the liner paper decreases.

[0044] The applicant's research found that when using all-bamboo pulp to prepare liner paper, due to the long and thin nature of bamboo pulp fibers and the presence of more fine components (typically, bamboo pulp contains at least 25% fine components), these fine components, after forming the liner paper, firstly, become interspersed between fibers, filling the pores in the three-dimensional structure and thus reducing air permeability; secondly, these fine components also affect the strength and other properties of the liner paper, and simultaneously increase dust content. However, even after removing as many fine components as possible using conventional methods, the small and long fibers of bamboo pulp result in a still dense liner paper structure, leading to insufficient air permeability. In the research... It was found that controlling and adjusting the proportion of bamboo pulp fibers with a length of 1.0–1.5 mm, which is between fine and long fibers, can increase air permeability while ensuring strength performance. This is because bamboo pulp fibers with a length of 1.0–1.5 mm can entangle with other fibers to form a three-dimensional network structure. On the other hand, they are not too long and will not form more twisted shapes. At the same time, their relatively stiff structure is interspersed between the fibers, which makes the three-dimensional network structure form more pores. As a result, the liner paper has good strength and excellent air permeability, which can even exceed that of liner paper made from wood pulp.

[0045] The method for preparing high-permeability bamboo pulp liner paper of this application will be described below with reference to specific embodiments.

[0046] Example 1:

[0047] S11: Provide fiber raw materials and pulp the fiber raw materials to form a first pulp with a pulp concentration of 4.5%. The fiber raw materials contain 100% bamboo pulp fiber, with an average length of 1.75 mm. The content of fine components in the bamboo pulp fiber is less than or equal to 1%, and the proportion of bamboo pulp fiber with a length of 1 to 1.5 mm is 9.7%.

[0048] S12: The first pulp is refined to form the second pulp, with a refining concentration of 4.1% and a beating degree of 32°SR.

[0049] S13: The second pulp is formed into high-permeability bamboo pulp liner paper through papermaking, drying, and creping. The papermaking process uses a crescent forming machine, the drying process uses a Yankee drying cylinder, and the creping process uses a 15° creping doctor blade with a creping rate of 20% and a machine speed of 1500 meters per minute.

[0050] Example 2:

[0051] In step S11, the average length of bamboo pulp fiber is 1.93 mm, and the proportion of bamboo pulp fiber with a length of 1 to 1.5 mm is 8.6%. The remaining steps are the same as in Example 1.

[0052] Comparative Example 1:

[0053] Prepared using the preparation method of Example 1 in CN112575610A.

[0054] Comparative Example 2:

[0055] The preparation method of Example 1 was adopted, wherein in step S11, the fine components were not controlled, and the proportion of bamboo pulp fibers with a length of 1 to 1.5 mm was 12.9%, and the remaining steps were the same as in Example 1.

[0056] The paper sheets prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were tested, and the test results are as follows:

[0057]

[0058] The above items were tested according to the following testing methods.

[0059] Basis weight: Tested according to GB / T 451.2-2002 Determination of basis weight of paper and paperboard.

[0060] Tensile index -MD: Tested according to GB / T 24328.3-2020 Toilet paper and its products Part 3: Determination of tensile strength, elongation at maximum force and tensile energy absorption.

[0061] Tensile index - CD: Tested according to GB / T 24328.3-2020 Toilet paper and its products Part 3: Determination of tensile strength, elongation at maximum force and tensile energy absorption.

[0062] Wet-MDT: Tested according to method 7.8 in GB / T 20808-2022 Paper Towels.

[0063] Elongation: Tested according to GB / T 24328.3-2020 Toilet paper and its products Part 3: Determination of tensile strength, elongation at maximum force and tensile energy absorption.

[0064] Air permeability: according to GB / T 22819 The test was conducted according to the "Determination of Air Permeability of Highly Permeable Paper in 2008", with a pressure of 125 Pa during the air permeability test.

[0065] Based on the above test results, the air permeability of the method of this invention is increased by more than 17% compared with the prior art. At the same time, the strength is basically the same as that of the prior art, with only the wet strength being relatively lower. However, better wet strength is not required for the liner paper. Therefore, the reduction in wet strength will not have a significant impact on the product. In addition, compared with untreated bamboo pulp, not only is the strength improved, but the air permeability is also increased by more than 20%.

[0066] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing high-permeability bamboo pulp liner paper, characterized in that, include: S1: Provide fiber raw materials and pulp them to form a first pulp with a pulp concentration of 4-6%. The proportion of bamboo pulp fiber in the fiber raw materials is greater than or equal to 95%, and the average length of the bamboo pulp fiber is greater than or equal to 1.6 mm. The content of fine components in the bamboo pulp fiber is less than or equal to 1%, and the proportion of bamboo pulp fiber with a length of 1-1.5 mm is 6-15%. S2: Refine the first pulp to form a second pulp with a refining concentration of 3-6% and a beating degree of 30-35°SR. S3: Form the second pulp into paper, dry it, and crepe it to form a high-permeability bamboo pulp liner paper. The paper forming is carried out using a crescent forming machine, the drying is carried out using a Yankee drying cylinder, and the creping is carried out using a 10°-20° creping doctor blade with a creping rate of 15-25% and a machine speed of 1200-1800 meters / minute.

2. The preparation method according to claim 1, characterized in that, All of the fiber raw materials mentioned are bamboo pulp fibers.

3. The preparation method according to claim 1, characterized in that, The average length of the bamboo pulp fiber is 1.7 to 2.5 mm, and the wall-to-cavity ratio of the bamboo pulp fiber is 1.2 to 6.

5.

4. The preparation method according to claim 1, characterized in that, The fiber raw material is provided in the form of pulp board, and the bamboo pulp fiber forms bamboo pulp board. The bamboo pulp board has the following technical indicators: tensile strength greater than or equal to 58 N·m / g, bursting index greater than or equal to 4 kPa·㎡ / g, tear index greater than or equal to 8.5 mN·㎡ / g, ash content less than or equal to 1%, and viscosity greater than or equal to 700 ml / g.

5. The preparation method according to claim 1, characterized in that, The proportion of bamboo pulp fibers with a length of 1–1.5 mm is 7–10%.

6. The preparation method according to claim 1, characterized in that, Step S1 also includes a step of adjusting the proportion of bamboo pulp fibers of different lengths in the fiber raw material by screening and compounding.

7. The preparation method according to claim 6, characterized in that, After the fiber raw materials are pulped to form the first pulp, the first pulp is screened by a first screening device to form a primary pulp. Then, the primary pulp is screened a second time to separate bamboo pulp fibers with a length of 1-1.5 mm and obtain a second pulp. Then, the separated bamboo pulp fibers with a length of 1-1.5 mm are added to the second pulp according to a predetermined ratio to obtain a mixed pulp. In step S2, the mixed pulp is milled. The predetermined ratio refers to the proportion of bamboo pulp fibers with a length of 1-1.5 mm being 6-15%. The proportion refers to the percentage of bamboo pulp fibers with a length of 1-1.5 mm in the mixed pulp.

8. The preparation method according to claim 1, characterized in that, The high-permeability bamboo pulp liner paper has a basis weight of 13-16 g / m².

9. The preparation method according to claim 1, characterized in that, After the wet paper sheets are formed, a highly breathable blanket is used to transfer the wet paper sheets, and a vacuum dehydration box is used to dehydrate the wet paper sheets. The air permeability of the highly breathable blanket is 22-24 CFM, and the vacuum degree of the vacuum dehydration box is -28 kPa.

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