A low grammage high strength kraft paper and a preparation method thereof

Abstract

This invention discloses a low-basis-weight, high-strength premium kraft paper and its preparation method, belonging to the field of papermaking technology. The basis weight of the kraft paper is 50-70 g / m³. 2 The raw materials consist of the following components by weight: 0-30 parts hardwood pulp, 20-50 parts softwood pulp, 20-50 parts chemithermomechanical pulp, 0-5 parts waste pulp, and 0-5 parts tumbled pulp. The preparation method includes pulp processing, flow forming, pressing, drying, surface sizing, and winding. This invention, through optimizing the wood pulp blending ratio and combining it with refined control of process parameters, produces pulp with a basis weight of 50-70 g / m³. 2 This product offers a low-grammage premium kraft paper. It addresses the issues of insufficient strength in low-grammage kraft paper and the stability problems such as unevenness, crushing, and paper breakage that easily occur during the production process. The resulting kraft paper combines high strength, environmental friendliness, and production stability, meeting the needs of high-end gift packaging, high-end industrial small packaging, and other application scenarios.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a low-grammage, high-strength kraft paper and its preparation method, which is suitable for the industrial and large-scale production of high-end kraft paper with a basis weight of 50-70 g / m². Background Technology

[0002] Kraft paper is a packaging material made of wood fibers. It is usually yellowish-brown and has a basis weight of 70-120 g / m³. 2 It possesses advantages such as high strength, water resistance, abrasion resistance, and durability, and is widely used in high-end gift packaging, high-end industrial small packaging, and food packaging. With the development of the e-commerce industry, "lightweight and recyclable" packaging has also begun to attract the attention of the paper industry. Lightweight packaging can reduce transportation burden, reduce raw material consumption, and is more environmentally friendly. Therefore, developing low-basis-weight kraft paper with a basis weight of 50~70g / m² is currently a hot research topic in the paper industry. However, the research and development of low grammage kraft paper still faces some difficulties, such as: (1) Insufficient strength: Insufficient grammage will result in a lack of strength in kraft paper. In order to ensure the strength performance of existing low grammage kraft paper, a high amount of chemical reagents need to be added, which not only increases the production cost, but also contradicts the requirements of green and environmentally friendly industry development; (2) Low production qualification rate: Due to its thin paper web and low wet strength, low grammage kraft paper is prone to problems in various stages of production, such as: poor uniformity and screen penetration in the flow forming stage, crushing in the pressing stage, and paper breakage in the winding stage. The production qualification rate is generally lower than 90%; (3) Insufficient sizing uniformity: Low grammage paper web is highly sensitive to surface sizing parameters. Existing processes are prone to uneven sizing, resulting in large differences in paper surface strength and water resistance, which cannot meet the appearance and usage requirements of high-end packaging.

[0003] The existing kraft paper manufacturing process has formed a mature LBKP / NBKP / BCTMP pulp blending system and process parameter specifications, but it is usually only applicable to the production of conventional basis weight products with a basis weight of 70~120g / m². The key to preparing low basis weight kraft paper products with a basis weight of ≤70g / m² is to adjust the existing raw material blending system and production process parameters. Summary of the Invention

[0004] This invention discloses a low-grammage, high-strength kraft paper and its preparation method, which can reduce the grammage of kraft paper while ensuring its high strength, and significantly improve production stability, thus fully meeting the strength requirements of high-end packaging.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] This invention provides a low-basis-weight, high-strength kraft paper, wherein the basis weight of the kraft paper is 50-70 g / m³. 2 The raw materials consist of the following components by weight: 0-30 parts hardwood pulp, 20-50 parts softwood pulp, 20-50 parts chemithermomechanical pulp, 0-5 parts waste pulp, and 0-5 parts tumbled pulp; wherein the beating degree of hardwood pulp is 30-35°SR, the beating degree of softwood pulp is 25-30°SR, and the beating degree of chemithermomechanical pulp is 20-25°SR.

[0007] Among them: softwood pulp: NBKP pulp, fiber length 1.8~2.2mm, provides a strong fiber skeleton for paper and ensures the tensile strength of paper.

[0008] Hardwood pulp: LBKP pulp has short and fine fibers, which can effectively improve the bonding force between fibers and optimize the smoothness of the paper surface.

[0009] Chemithermomechanical pulp: BCTMP pulp can optimize paper bulk and prevent low-grammage paper webs from becoming brittle due to excessive density.

[0010] Furthermore, the low grammage high-strength kraft paper described above is composed of the following components in parts by weight: 10-30 parts hardwood pulp, 40-50 parts softwood pulp, 25-50 parts chemithermomechanical pulp, 2-5 parts waste pulp, and 2-5 parts tumbled pulp.

[0011] Another aspect of the present invention provides a method for preparing the low-basis-weight, high-strength kraft paper described above, comprising the following steps:

[0012] (1) Slurry treatment: Prepare raw materials according to the weight ratio and mix them, adjust the concentration to 3.3%~3.7%, add chemical additives and stir evenly to obtain the slurry to be fed into the net;

[0013] (2) Flow forming: The pulp to be fed into the wire section of the fourdrinier paper machine is controlled with a wire concentration ≤0.5%, a pulp-to-wire speed ratio of 1.03±0.02, a lip plate opening of 15~21%, a dilution rate of 10%~12%, and a flat roll vacuum of 55~60kPa. After forming, a wet paper web is obtained, and the dryness of the wet paper web exiting the wire section is 20%~25%.

[0014] (3) Pressing: The wet paper web is fed into the press section for pressing, and is pressed in sequence through first press, second press and shoe press. The dryness of the paper web after pressing is 48%~53%;

[0015] (4) Drying: The pressed paper web is fed into the dryer. The moisture content of the pre-dried paper web is 7.0%~9.0%, and the moisture content of the wound paper web after drying is 7.0%~10.0%.

[0016] (5) Surface sizing treatment: The dried paper web is sizing the surface. The sizing solution is starch glue, the starch dosage is 18~20kg / t, the starch concentration is 3wt%~5wt%, the viscosity of the surface sizing feed tank is 12±3cP, and the paper is dried by hot air after sizing.

[0017] (6) Roll it up to form a low-grammage, high-strength kraft paper.

[0018] In step (1), the concentration refers to the slurry concentration after mixing all the above raw materials. Concentration = dry weight of slurry fiber / slurry weight. In the slurry, apart from the dry weight of slurry fiber, the remaining part is water.

[0019] Further, in step (1), the mixing specifically includes: adding hardwood pulp, softwood pulp, chemithermomechanical pulp and waste pulp and tungsten pulp into a mixing tank in the weight ratio, maintaining the temperature in the mixing tank at 35~40℃, the stirring rate at 500~1000r / min, and continuously stirring for 18~30min, so that the pulp components are evenly dispersed without stratification or local aggregation.

[0020] Furthermore, the chemical additives are composed of the following components: based on the total weight of the slurry to be applied, powder retention aid 0.03~0.05kg / t, liquid retention aid 0.10~0.15kg / t, aluminum sulfate in the slurry 10±2kg / t, AKD in the slurry 2.5±0.5kg / t, and dry strength agent 2~4kg / t.

[0021] Furthermore, the dry strength agent is one or both of modified starch-based dry strength agents and polyacrylamide-based synthetic dry strength agents;

[0022] And / or, the powder retention aid is cationic polyacrylamide;

[0023] And / or, the liquid retention aid is anionic polyacrylamide.

[0024] The chemical additives of this invention incorporate a combination of cationic polyacrylamide (powder retention aid) and anionic polyacrylamide (liquid retention aid), which can jointly improve the retention rate of fibers and additives and reduce web loss.

[0025] Aluminum sulfate acts as a retention enhancer, promoting the aggregation of colloidal particles and improving retention efficiency.

[0026] In-pulp AKD, an alkyl ketene dimer, is an in-pulp sizing agent that improves the water resistance of paper.

[0027] The dry strength agent is selected from modified starch-based dry strength agents and / or polyacrylamide-based synthetic dry strength agents, which can enhance the hydrogen bonding force between fibers and effectively compensate for the loss of paper strength under low basis weight.

[0028] Furthermore, in step (2), the lip plate is horizontally controlled at 22±3mm, and there is no tearing or wrinkling when the wet paper web is peeled off.

[0029] In step (2), selecting a suitable pulp-to-wire ratio can ensure uniform fiber spreading, reduce differences in fiber orientation, and improve paper web uniformity; selecting a suitable lip plate opening and lip plate level control can adapt to the basis weight requirements of low basis weight paper webs and avoid paper webs being too thick or too thin; selecting a suitable crease roll vacuum can ensure stable peeling of wet paper webs and avoid tearing and wrinkling defects.

[0030] Furthermore, in step (3), the linear pressure of the first pressure is controlled to be 90~110kN / m, the linear pressure of the second pressure is controlled to be 110~130kN / m, and the linear pressure of the shoe pressure is controlled to be 1290~1310kN / m.

[0031] In step (3), the first press is the initial dewatering stage, and a moderate linear press can avoid crushing defects in the wet paper web; the second press is the deep dewatering stage, and a higher linear press is used to further remove free water between fibers and improve the dryness of the paper web; the shoe press is the high-pressure densification stage, and a suitable high pressure is used to achieve tight fiber bonding and optimize the surface smoothness of the paper web.

[0032] Further, in step (4), the pre-drying steam pressure is controlled at 240~360kPa, the pre-drying temperature is controlled at 80~100℃, the post-drying steam pressure is controlled at 15~55kPa, and the post-drying temperature is controlled at 40~60℃.

[0033] In step (4), the present invention feeds the pressed paper web into the dryer and adopts a composite drying method of high-temperature rapid dehydration in the pre-drying + low-temperature humidification in the post-drying, which not only ensures the dehydration efficiency, but also avoids the paper web from becoming brittle or shrinking unevenly.

[0034] Furthermore, in step (5), the glue flow rate of the glue applicator is controlled to be 800~950L / min and the pressure of the scraper is controlled to be 80~140kPa;

[0035] And / or, in step (5), the solid content of the surface adhesive feeding tank is 3%~5%, the hot air drying temperature is 70~85℃, and the wind speed is 2~3m / s, so that a uniform adhesive film is formed on the surface of the paper web.

[0036] In step (5), the present invention uses starch adhesive in combination with appropriate process parameters to form a uniform sizing film on the paper surface, effectively improving the surface strength, water resistance and bursting strength of the paper.

[0037] Furthermore, in step (6), during winding, the winding tension is controlled to be 550~650N, the winding speed is 700~860m / min, and the winding moisture content is 8±2%.

[0038] In step (6), during the winding process, steam is not introduced into the post-drying section to avoid the paper web from getting too hot and sticking together, or from the paper web being stretched and deformed or breaking due to excessive tension, so as to finally obtain low grammage high strength premium kraft paper.

[0039] The low-grammage, high-strength kraft paper and its preparation method described above have the following significant advantages compared to existing technologies:

[0040] (1) Perfect balance between high strength and low basis weight: Through the precise compounding of LBKP / NBKP / BCTMP paste and the reasonable addition of modified starch dry strength agent, a 50~70g / m 2 High-quality kraft paper has a longitudinal tensile strength ≥2.8kN / m and a bursting index ≥3.3kPa·m. 2 / g, water absorption value ≤50g / m 2 This fully meets the strength requirements of high-end packaging.

[0041] (2) Significantly improved production stability: This invention targets the characteristics of low grammage paper webs and finely controls the process parameters of the entire process, such as flow conveying, pressing, and winding, effectively solving production defects such as poor uniformity, crushing, and paper breakage in the production of low grammage kraft paper, and improving the production qualification rate to over 98%.

[0042] (3) Strong compatibility with process equipment: The preparation process of this invention is developed based on the existing PM5 premium kraft paper process standard, which is highly compatible with the existing production line. It does not require large-scale equipment modification, which reduces the modification cost of industrial production and is suitable for large-scale production.

[0043] (4) Excellent overall performance of the product: The prepared kraft paper has moderate thickness, smooth surface, good water resistance, and no appearance defects such as see-through or crushing. It not only meets the low gram weight and lightweight requirements of the packaging industry, but also meets the appearance and usage requirements of high-end packaging.

[0044] (5) Balancing environmental protection and economy: By optimizing the slurry ratio and combining precise quantitative addition of chemical additives, the raw material cost is reduced by 8-15% while ensuring performance, and the amount of chemical reagents used is reduced, thus improving the environmental protection of the product.

[0045] (6) Industrial applicability: The products prepared by this invention can be widely used in high-end gift packaging, high-end industrial small packaging, food packaging and other scenarios, meeting the market demand for low grammage, high strength and environmentally friendly packaging paper, and have significant industrial application value and broad market prospects. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0047] A low-grammage, high-strength kraft paper, wherein the kraft paper has a basis weight of 50-70 g / m², and the raw materials are composed of the following components in parts by weight: 0-30 parts hardwood pulp, 20-50 parts softwood pulp, 20-50 parts chemithermomechanical pulp, 0-5 parts waste pulp, and 0-5 parts tumbled pulp; wherein the hardwood pulp has a beating degree of 30-35°SR, the softwood pulp has a beating degree of 25-30°SR, and the chemithermomechanical pulp has a beating degree of 20-25°SR.

[0048] The method for preparing low-grammage, high-strength kraft paper described above includes the following steps:

[0049] (1) Slurry treatment: Prepare and mix the raw materials according to the weight ratio, adjust the concentration to 3.3%~3.7% (e.g. 3.3%, 3.4%, 3.5%, 3.6% or 3.7%), add chemical additives and stir evenly to obtain the slurry to be fed into the web;

[0050] (2) Forming: The pulp to be fed into the wire section of the fourdrinier paper machine is fed into the wire section. The wire concentration is controlled to be ≤0.5% (e.g., 0.3%, 0.35%, 0.4%, 0.45% or 0.5%), the pulp-wire speed ratio is 1.03±0.02, the lip plate opening is 15~21% (e.g., 15%, 18%, 19%, 20% or 21%), the dilution rate is 10%~12% (e.g., 10%, 10.2%, 10.5%, 11% or 12%), and the vacuum degree of the flat roll is 55~60kPa (e.g., 55 kPa, 56 kPa, 58 kPa or 60kPa). After forming, a wet paper web is obtained. The dryness of the wet paper web exiting the wire section is 20%~25%.

[0051] (3) Pressing: The wet paper web is fed into the press section for pressing, and is pressed in sequence through first press, second press and shoe press. The dryness of the paper web after pressing is 48%~53% (e.g. 48%, 49%, 49.5%, 50% or 53%).

[0052] (4) Drying: The pressed paper web is fed into the dryer, and the moisture content of the pre-dried paper web is 7.0%~9.0% (e.g. 7.0%, 7.5%, 8.0%, 8.5% or 9.0%).

[0053] (5) Surface sizing treatment: The dried paper web is sizing the surface. The sizing solution is starch glue, with a starch dosage of 18~20kg / t, a starch concentration of 3wt%~5wt%, and a surface sizing feed tank viscosity of 12±3cP. After sizing, it is dried with hot air.

[0054] (6) Roll it up to form a low-grammage, high-strength kraft paper.

[0055] Further, in step (1), the mixing specifically includes: adding hardwood pulp, softwood pulp, chemithermomechanical pulp, and waste pulp and tumbled pulp in a weight ratio into a mixing tank, maintaining the temperature in the mixing tank at 35~40℃ (e.g., 35℃, 36℃, 37℃, 38℃ or 40℃), and stirring at a speed of 500~1000r / min (e.g., 500 r / min, 600 r / min, 800 r / min, 900 r / min or 1000 r / min), and continuously stirring for 18~22min (e.g., 18min, 20min, 21min or 22min) so that the pulp components are evenly dispersed without stratification or local aggregation.

[0056] Further, the chemical additives are composed of the following components: based on the total weight of the slurry to be applied, powder retention aid 0.03~0.05 kg / t (e.g., 0.03 kg / t, 0.035 kg / t, 0.04 kg / t, or 0.05 kg / t), and liquid retention aid 0.10~0.15 kg / t (e.g., 0.10 kg / t, 0.12 kg / t, 0.14 kg / t, or 0.15 kg / t). 10±2 kg / t of aluminum sulfate in slurry (e.g., 8 kg / t, 9 kg / t, 10 kg / t, 11 kg / t or 12 kg / t), 2.5±0.5 kg / t of AKD in slurry (e.g., 2 kg / t, 2.2 kg / t, 2.5 kg / t, 2.8 kg / t or 3 kg / t), and 2~4 kg / t of dry strength agent (e.g., 2 kg / t, 2.5 kg / t, 3 kg / t, 3.5 kg / t or 4 kg / t).

[0057] Furthermore, the dry strength agent is one or both of modified starch-based dry strength agents and polyacrylamide-based synthetic dry strength agents;

[0058] And / or, the powder retention aid is cationic polyacrylamide;

[0059] And / or, the liquid retention aid is anionic polyacrylamide.

[0060] Furthermore, in step (2), the lip plate is horizontally controlled at 22±3mm, and there is no tearing or wrinkling when the wet paper web is peeled off.

[0061] Further, in step (3), the linear pressure of the first pressure is controlled to be 90~110kN / m (e.g., 90 kN / m, 100kN / m, 105kN / m, 108kN / m or 110kN / m), the linear pressure of the second pressure is controlled to be 110~130kN / m (e.g., 110 kN / m, 115kN / m, 118kN / m, 120kN / m or 130kN / m), and the linear pressure of the shoe pressure is controlled to be 1290~1310kN / m (e.g., 1290 kN / m, 1295kN / m, 1298kN / m, 1300kN / m or 1310kN / m).

[0062] Further, in step (4), the pre-drying steam pressure is controlled to be 240~360 kPa (e.g., 240 kPa, 248 kPa, 300 kPa, 350 kPa or 360 kPa), the pre-drying temperature is 80~100℃ (e.g., 80℃, 85℃, 90℃, 95℃ or 100℃), the post-drying steam pressure is 15~55 kPa (e.g., 15 kPa, 19 kPa, 30 kPa, 50 kPa or 55 kPa), and the post-drying temperature is 40~60℃ (e.g., 40℃, 45℃, 50℃, 55℃ or 60℃).

[0063] Furthermore, in step (5), the glue flow rate of the glue applicator is controlled to be 800~950 L / min (e.g., 800 L / min, 850 L / min, 890 L / min, 920 L / min or 950 L / min), and the scraper pressure is controlled to be 80~140 kPa (e.g., 80 kPa, 98 kPa, 120 kPa, 150 kPa or 160 kPa).

[0064] And / or, in step (5), the solid content of the surface adhesive feeding tank is 3%~5% (e.g., 3%, 4%, 4.5% or 5%), the hot air drying temperature is 70~85℃ (e.g., 70℃, 75℃, 80℃, 82℃ or 85℃), and the wind speed is 2~3m / s, so that a uniform adhesive film is formed on the surface of the paper web.

[0065] Furthermore, in step (6), during winding, the winding tension is controlled to be 550~650N (e.g., 550N, 580N, 600N, 620N or 650N), the winding speed is 700~860m / min (e.g., 700m / min, 750m / min, 800m / min, 850m / min or 860m / min), and the winding moisture content is 8±2%.

[0066] The present invention will be further described below by way of examples, but the scope of protection of the present invention is not limited to these embodiments.

[0067] Example 1: Quantitative analysis at 50 g / m 2 Low grammage high strength kraft paper

[0068] Kraft paper is made up of the following components by weight: 10 parts hardwood pulp, 40 parts softwood pulp, 45 parts chemithermomechanical pulp, 3 parts waste pulp, and 2 parts tumbled pulp; wherein the hardwood pulp has a beating degree of 30°SR, the softwood pulp has a beating degree of 25°SR, and the chemithermomechanical pulp has a beating degree of 20°SR.

[0069] The preparation method includes the following steps:

[0070] (1) Slurry treatment: Prepare raw materials according to the weight ratio and mix them. Adjust the slurry concentration to 3.3%. Add 0.03 kg / t of cationic polyacrylamide, 0.10 kg / t of anionic polyacrylamide, 8 kg / t of aluminum sulfate in the slurry, 2.0 kg / t of AKD in the slurry, and 2 kg / t of polyacrylamide synthetic dry strength agent and stir evenly to obtain the slurry to be fed into the grid.

[0071] The mixing process specifically includes: adding hardwood pulp, softwood pulp, chemithermomechanical pulp, and waste pulp and tumbled pulp into a mixing tank in the specified weight proportions. The temperature in the mixing tank is maintained at 35°C, the stirring speed is 500 r / min, and the stirring time is 20 min, so that the pulp components are evenly dispersed without stratification or local aggregation.

[0072] (2) Flow forming: The pulp to be fed into the wire section of the fourdrinier paper machine is controlled with a wire concentration of 0.45%, a pulp-to-wire speed ratio of 1.01, a lip opening of 15%, a dilution rate of 10%, a vacuum degree of 55 kPa on the flat roll, and a lip horizontal control of 19 mm; after forming, a wet paper web is obtained, and the dryness of the wet paper web exiting the wire section is 20%.

[0073] (3) Pressing: The wet paper web is fed into the press section for pressing, and is pressed in sequence through the first press, the second press and the shoe press. The linear pressure of the first press is 90kN / m, the linear pressure of the second press is 110kN / m, and the linear pressure of the shoe press is 1290kN / m; the dryness of the paper web after pressing is 48%.

[0074] (4) Drying: The pressed paper web is fed into the dryer, and the steam pressure of the pre-drying is controlled at 240 kPa and the temperature at 80°C, and the steam pressure of the post-drying is controlled at 15 kPa and the temperature at 40°C; the moisture content of the pre-dried paper web is 7.0%.

[0075] (5) Surface sizing treatment: The dried paper web is sizing. The sizing solution is starch glue, the starch dosage is 18kg / t, the starch concentration is 3%, the surface sizing viscosity is 9CP, the sizing flow rate is 800L / min, and the scraper pressure is 80kPa. The solid content of the surface sizing feed tank is 3%, the hot air drying temperature is 70℃, and the wind speed is 2m / s. After sizing, the paper web is dried by hot air.

[0076] (6) Winding and forming: The winding tension is 550N, the speed is 850m / min, and the moisture content is 8% to obtain low grammage high strength kraft paper.

[0077] Example 2: Quantitative analysis at 60 g / m³ 2 Low grammage high strength kraft paper

[0078] The raw materials for kraft paper consist of the following components in parts by weight: 18 parts hardwood pulp, 42 parts softwood pulp, 35 parts chemithermomechanical pulp, 3 parts waste pulp, and 2 parts tumbled pulp; wherein the hardwood pulp has a beating degree of 32°SR, the softwood pulp has a beating degree of 27°SR, and the chemithermomechanical pulp has a beating degree of 22°SR.

[0079] The preparation method includes the following steps:

[0080] (1) Slurry treatment: Prepare raw materials according to the weight ratio and mix them. Adjust the slurry concentration to 3.5%. Add 0.04 kg / t of cationic polyacrylamide, 0.12 kg / t of anionic polyacrylamide, 10 kg / t of aluminum sulfate in the slurry, 2.5 kg / t of AKD in the slurry, and 3 kg / t of polyacrylamide synthetic dry strength agent and stir evenly to obtain the slurry to be fed into the grid.

[0081] The mixing process specifically includes: adding hardwood pulp, softwood pulp, chemithermomechanical pulp, and waste pulp and tumbled pulp into a mixing tank in the specified weight proportions. The temperature in the mixing tank is maintained at 38°C, the stirring speed is 600 r / min, and the stirring time is 25 min, so that the pulp components are evenly dispersed without stratification or local aggregation.

[0082] (2) Flow forming: The pulp to be fed into the wire section of the fourdrinier paper machine is controlled with a wire concentration of 0.48%, a pulp-to-wire speed ratio of 1.03, a lip plate opening of 18%, a dilution rate of 11%, a flat roll vacuum of 58 kPa, and a lip plate horizontal control of 20 mm; after forming, a wet paper web is obtained, and the dryness of the wet paper web exiting the wire section is 23%.

[0083] (3) Pressing: The wet paper web is fed into the press section for pressing, and is pressed in sequence through the first press, the second press and the shoe press. The linear pressure of the first press is 100kN / m, the linear pressure of the second press is 120kN / m, and the linear pressure of the shoe press is 1300kN / m; the dryness of the paper web after pressing is 50%.

[0084] (4) Drying: The pressed paper web is fed into the dryer, and the steam pressure of the pre-drying is controlled at 300 kPa and the temperature at 90°C, and the steam pressure of the post-drying is controlled at 35 kPa and the temperature at 50°C; the moisture content of the pre-dried paper web is 8.0%.

[0085] (5) Surface sizing treatment: The dried paper web is sizing the surface. The sizing solution is starch glue, the starch dosage is 19kg / t, the starch concentration is 4wt%, the surface sizing viscosity is 12cP, the sizing flow rate is 880L / min, and the scraper pressure is 110kPa. The solid content of the surface sizing feed tank is 4.5%, the hot air drying temperature is 80℃, and the wind speed is 2.5m / s. After sizing, the paper web is dried by hot air.

[0086] (6) Winding and forming: The winding tension is 600N, the speed is 850m / min, and the winding moisture is 8%, to obtain low grammage high strength kraft paper.

[0087] Example 3: Quantitative analysis at 70 g / m 2 Low grammage high strength kraft paper

[0088] Kraft paper is made up of the following components by weight: 25 parts hardwood pulp, 45 parts softwood pulp, 25 parts chemithermomechanical pulp, 3 parts waste pulp, and 2 parts tumbled pulp; wherein the hardwood pulp has a beating degree of 35°SR, the softwood pulp has a beating degree of 30°SR, and the chemithermomechanical pulp has a beating degree of 25°SR.

[0089] The preparation method includes the following steps:

[0090] (1) Slurry treatment: Prepare raw materials according to the weight ratio and mix them. Adjust the slurry concentration to 3.7%. Add 0.05 kg / t of cationic polyacrylamide, 0.15 kg / t of anionic polyacrylamide, 12 kg / t of aluminum sulfate in the slurry, 3 kg / t of AKD in the slurry, and 4 kg / t of polyacrylamide synthetic dry strength agent and stir evenly to obtain the slurry to be fed into the grid.

[0091] The mixing process specifically includes: adding hardwood pulp, softwood pulp, chemithermomechanical pulp, waste pulp, and tumbled pulp to a mixing tank in the specified weight proportions. The temperature in the mixing tank is maintained at 40°C, the stirring speed is 500 r / min, and the stirring time is 30 min, so that the pulp components are evenly dispersed without stratification or local aggregation.

[0092] (2) Flow forming: The pulp to be fed into the wire section of the long wire paper machine is controlled with a wire concentration of 0.5%, a pulp-wire speed ratio of 1.05, a lip plate opening of 21%, a dilution rate of 12%, a flat roll vacuum of 60 kPa, and a lip plate horizontal control of 19 mm; after forming, a wet paper web is obtained, and the dryness of the wet paper web exiting the wire section is 25%.

[0093] (3) Pressing: The wet paper web is fed into the press section for pressing, and is pressed in sequence through the first press, the second press and the shoe press. The linear pressure of the first press is 110 kN / m, the linear pressure of the second press is 130 kN / m and the linear pressure of the shoe press is 1310 kN / m; the dryness of the paper web after pressing is 53%.

[0094] (4) Drying: The pressed paper web is fed into the dryer, and the steam pressure of the pre-drying is controlled at 360 kPa and the temperature at 100°C, and the steam pressure of the post-drying is controlled at 55 kPa and the temperature at 60°C; the moisture content of the pre-dried paper web is 9.0%.

[0095] (5) Surface sizing treatment: The dried paper web is sizing the surface. The sizing solution is starch glue, the starch dosage is 20kg / t, the starch concentration is 5%, the surface sizing viscosity is 15cP, the sizing flow rate is 950L / min, and the scraper pressure is 140kPa. The solid content of the surface sizing feed tank is 5%, the hot air drying temperature is 85℃, and the wind speed is 3m / s. After sizing, the paper web is dried by hot air.

[0096] (6) Winding and forming: with a winding tension of 650N and a speed of 850m / min, and a moisture content of 8%, low grammage and high strength kraft paper is obtained.

[0097] Comparative Example 1: Quantitative amount 50g / m 2 Kraft paper

[0098] Comparative Example 1 is basically the same as Example 1, except that:

[0099] The raw materials for kraft paper consist of the following components in parts by weight: 20 parts hardwood pulp, 55 parts softwood pulp, 20 parts chemithermomechanical pulp, 3 parts waste pulp, and 2 parts tumbled pulp; wherein the hardwood pulp has a beating degree of 35°SR, the softwood pulp has a beating degree of 30°SR, and the chemithermomechanical pulp has a beating degree of 25°SR.

[0100] Comparative Example 2: Quantitative analysis at 60 g / m³ 2 Kraft paper

[0101] Comparative Example 2 is basically the same as Example 2, except that:

[0102] The raw materials for kraft paper consist of the following components in parts by weight: 20 parts hardwood pulp, 55 parts softwood pulp, 20 parts chemithermomechanical pulp, 3 parts waste pulp, and 2 parts tumbled pulp; wherein the hardwood pulp has a beating degree of 35°SR, the softwood pulp has a beating degree of 30°SR, and the chemithermomechanical pulp has a beating degree of 25°SR.

[0103] Comparative Example 3: Quantitative analysis at 70 g / m³ 2 Kraft paper

[0104] Comparative Example 3 is basically the same as Example 3, except that:

[0105] The raw materials for kraft paper consist of the following components in parts by weight: 20 parts hardwood pulp, 55 parts softwood pulp, 20 parts chemithermomechanical pulp, 3 parts waste pulp, and 2 parts tumbled pulp; wherein the hardwood pulp has a beating degree of 35°SR, the softwood pulp has a beating degree of 30°SR, and the chemithermomechanical pulp has a beating degree of 25°SR.

[0106] Comparative Example 4: Quantitative analysis at 70 g / m 2 Kraft paper

[0107] Comparative Example 4 is basically the same as Example 3, except that:

[0108] Kraft paper is made up of the following components by weight: 25 parts hardwood pulp, 55 parts softwood pulp, 15 parts chemithermomechanical pulp, 3 parts waste pulp, and 2 parts tumbled pulp; wherein the hardwood pulp has a beating degree of 35°SR, the softwood pulp has a beating degree of 30°SR, and the chemithermomechanical pulp has a beating degree of 25°SR.

[0109] Comparative Example 5: Quantitative test 70 g / m 2 Kraft paper

[0110] Comparative Example 5 is basically the same as Example 1, except that:

[0111] The raw materials for kraft paper consist of the following components in parts by weight: 45 parts softwood pulp and 55 parts recycled kraft pulp; the beating degree of the softwood pulp is 25°SR; the beating degree of the mixed long and short fibers in the recycled kraft pulp is 40°SR.

[0112] Comparative Example 6: Quantitative test 60 g / m 2 Kraft paper

[0113] Comparative Example 6 is basically the same as Example 2, except that:

[0114] The raw materials for kraft paper consist of the following components in parts by weight: 45 parts softwood pulp and 55 parts recycled kraft pulp; the beating degree of the softwood pulp is 25°SR; the beating degree of the mixed long and short fibers in the recycled kraft pulp is 40°SR.

[0115] The kraft paper prepared in Examples 1-3 and Comparative Examples 1-5 was subjected to full performance testing. The test results are compared with the performance requirements of high-end packaging in Tables 1 and 2.

[0116] Table 1 Performance test results of Examples 1-3

[0117]

[0118] In addition, the production qualification rate of Examples 1-3 can all reach over 98%.

[0119] Table 2 Performance test results of Comparative Examples 1-5

[0120]

[0121] In addition, the production pass rate of comparative examples 1-4 is controlled at approximately 88-92%, and the production pass rate of comparative examples 5-6 is controlled at approximately 93-95%.

[0122] The following conclusions can be drawn from the above performance test results:

[0123] (1) The low-basis-weight high-quality kraft paper prepared by this invention has a basis weight of 50~70 g / m³. 2 All performance indicators meet or exceed the performance requirements of high-end packaging, with excellent burst strength and longitudinal tensile strength, low water absorption and good water resistance.

[0124] (2) No defects such as crushing or paper breakage occurred during the production process of the three embodiments, and the paper web uniformity was good, which proves that the process parameters of the present invention are scientific and reasonable, and effectively solves the technical problem of poor production stability of low grammage fine kraft paper.

[0125] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-grammage, high-strength kraft paper, characterized in that: The kraft paper has a basis weight of 50~70g / m³. 2 The raw materials consist of the following components by weight: 0-30 parts hardwood pulp, 20-50 parts softwood pulp, 20-50 parts chemithermomechanical pulp, 0-5 parts waste pulp, and 0-5 parts tumbled pulp; wherein the beating degree of hardwood pulp is 30-35°SR, the beating degree of softwood pulp is 25-30°SR, and the beating degree of chemithermomechanical pulp is 20-25°SR.

2. The low-basis-weight, high-strength kraft paper according to claim 1, characterized in that... ； The raw materials consist of the following components by weight: 10-30 parts hardwood pulp, 40-50 parts softwood pulp, 25-50 parts chemithermomechanical pulp, 2-5 parts waste pulp, and 2-5 parts tumbled pulp.

3. The method for preparing low-basis-weight, high-strength kraft paper according to claim 1 or 2, characterized in that... Includes the following steps: (1) Slurry treatment: Prepare raw materials according to the weight ratio and mix them, adjust the concentration to 3.3%~3.7%, add chemical additives and stir evenly to obtain the slurry to be fed into the net; (2) Flow forming: The pulp to be fed into the wire section of the fourdrinier paper machine is controlled with a wire concentration ≤0.5%, a pulp-to-wire speed ratio of 1.03±0.02, a lip plate opening of 15~21%, a dilution rate of 10%~12%, and a flat roll vacuum of 55~60kPa. After forming, a wet paper web is obtained, and the dryness of the wet paper web exiting the wire section is 20%~25%. (3) Pressing: The wet paper web is fed into the press section for pressing, and is pressed in sequence through first press, second press and shoe press. The dryness of the paper web after pressing is 48%~53%; (4) Drying: The pressed paper web is fed into the dryer. The moisture content of the pre-dried paper web is 7.0%~9.0%, and the moisture content of the wound paper web after drying is 7.0%~10.0%. (5) Surface sizing treatment: The dried paper web is sizing the surface. The sizing solution is starch glue, the starch dosage is 18~20kg / t, the starch concentration is 3wt%~5wt%, the viscosity of the surface sizing feed tank is 12±3cP, and the paper is dried by hot air after sizing. (6) Roll it up to form a low-grammage, high-strength kraft paper.

4. The preparation method according to claim 3, characterized in that: In step (1), the mixing specifically includes: adding hardwood pulp, softwood pulp, chemithermomechanical pulp and waste pulp and tungsten pulp into the mixing tank in the weight ratio, maintaining the temperature in the mixing tank at 35~40℃, the stirring rate at 500~1000r / min, and stirring continuously for 18~30min, so that the pulp components are evenly dispersed without stratification or local aggregation.

5. The preparation method according to claim 3, characterized in that: The chemical additives consist of the following components: based on the total weight of the slurry to be bonded, powder retention aid 0.03~0.05kg / t, liquid retention aid 0.10~0.15kg / t, aluminum sulfate in the slurry 10±2kg / t, AKD in the slurry 2.5±0.5kg / t, and dry strength agent 2~4kg / t.

6. The preparation method according to claim 5, characterized in that: The dry strength agent is one or both of modified starch-based dry strength agents and polyacrylamide-based synthetic dry strength agents; And / or, the powder retention aid is cationic polyacrylamide; And / or, the liquid retention aid is anionic polyacrylamide.

7. The preparation method according to claim 3, characterized in that: In step (2), the lip plate is horizontally controlled at 22±3mm, and there is no tearing or wrinkling when the wet paper web is peeled off.

8. The preparation method according to claim 3, characterized in that: In step (3), the linear pressure of the first pressure is controlled to be 90~110kN / m, the linear pressure of the second pressure is 110~130kN / m, and the linear pressure of the shoe pressure is 1290~1310kN / m; And / or, in step (4), the pre-drying steam pressure is controlled at 240~360kPa, the pre-drying temperature is controlled at 80~100℃, the post-drying steam pressure is controlled at 15~55kPa, and the post-drying temperature is controlled at 40~60℃.

9. The preparation method according to claim 3, characterized in that: In step (5), the glue flow rate of the glue applicator is controlled to be 800~950L / min and the pressure of the scraper is controlled to be 80~140kPa; And / or, in step (5), the solid content of the surface adhesive feeding tank is 3%~5%, the hot air drying temperature is 70~85℃, and the wind speed is 2~3m / s, so that a uniform adhesive film is formed on the surface of the paper web.

10. The preparation method according to claim 3, characterized in that: In step (6), during winding, the winding tension is controlled at 550~650N, the winding speed is 700~860m / min, and the winding moisture content is 8±2%.

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