A method for pulping a high-strength low-dust kraft bag paper

Abstract

The application provides a pulping method of high-strength low-dust natural color paper bag paper, and belongs to the technical field of papermaking. The pulping method comprises the following steps: respectively performing cooking treatment on Japanese cedar raw materials, broad-leaved miscellaneous wood raw materials and miscellaneous bamboo raw materials to obtain Japanese cedar pulp, broad-leaved miscellaneous wood pulp and miscellaneous bamboo pulp; wherein the cooking treatment comprises a steam pretreatment stage and an alkali impregnation pretreatment stage; 20% of the Japanese cedar pulp, 15% of the broad-leaved miscellaneous wood pulp and 65% of the miscellaneous bamboo pulp are mixed according to the percentage of absolute dry mass; and the obtained mixed pulp is sequentially subjected to screening treatment, washing treatment, oxygen removal treatment and secondary washing treatment to obtain pulp for papermaking of the high-strength low-dust natural color paper bag paper. By adopting the specific proportioning of the Japanese cedar pulp, the broad-leaved miscellaneous wood pulp and the miscellaneous bamboo pulp and combining the cooking process comprising the steam pretreatment and the alkali impregnation pretreatment, the comprehensive effects of high strength, low dust and stable color phase of the paper are realized while the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, and in particular to a pulping method for high-strength, low-dust, unbleached paper bag paper. Background Technology

[0002] Because unbleached wood pulp does not undergo a bleaching process and does not produce carcinogenic substances such as dioxins, it enjoys a broader market environment. Therefore, the market demand for high-quality unbleached paper bags produced using low-cost, environmentally friendly processes is becoming increasingly urgent.

[0003] Currently, the production of high-strength, unbleached paper bags generally relies on purchasing commercial pulps such as unbleached softwood pulp and hardwood pulp, resulting in high production costs and extremely small profit margins. If the pulp is made in-house, problems such as unstable raw material supply, difficulty in achieving both strength and cleanliness due to a single fiber ratio, difficulty in alkali penetration during the cooking process, high fiber bundle and dust content, and poor fiber bonding are encountered. In particular, when using non-traditional raw materials such as bamboo pulp, the difficulty in fracturing and the rough surface result in insufficient paper uniformity, tensile strength, and bursting strength, making it difficult to simultaneously meet the comprehensive market demands for high strength, low dust, stable color, and low cost. Summary of the Invention

[0004] This invention provides a pulping method for high-strength, low-dust, unbleached paper bags. By using a specific ratio of cedar pulp, hardwood pulp, and mixed bamboo pulp, combined with a cooking process that includes steam pretreatment and alkali impregnation pretreatment, this method aims to solve the technical problems of existing technologies, such as high production costs due to reliance on purchased commercial pulp, difficulty in achieving both strength and cleanliness when making pulp in-house, and insufficient paper performance due to difficulties in alkali penetration, numerous fiber bundles, and poor bonding when processing raw materials such as bamboo pulp. This method achieves a comprehensive effect of high strength, low dust, and stable color in the paper while reducing production costs.

[0005] The technical solution adopted in this invention is:

[0006] A pulping method for high-strength, low-dust, unbleached paper bag paper includes the following steps:

[0007] Step S1 involves steaming the raw materials of Japanese cedar, broadleaf mixed wood, and mixed bamboo to obtain Japanese cedar pulp, broadleaf mixed wood pulp, and mixed bamboo pulp, respectively; wherein the steaming process includes a steam pretreatment stage and an alkali impregnation pretreatment stage.

[0008] Step S2: Mix 20% of the Japanese cedar pulp, 15% of the hardwood pulp, and 65% of the bamboo pulp according to their oven-dry weight percentages; wherein the ratio of the Japanese cedar raw materials, the hardwood raw materials, and the bamboo raw materials is controlled within ±0.5%;

[0009] Step S3 involves sequentially screening, washing, oxygen removal, and secondary washing of the mixed pulp obtained in step S2 to obtain pulp for making the high-strength, low-dust, unbleached paper bag.

[0010] Furthermore, the cooking process employs a sulfate process using a vertical cooking pot with intermittent cooking, which includes sequentially performed stages of loading, steam pretreatment, alkali impregnation pretreatment, mid-term heating and cooking, heat preservation, recovery, and unloading.

[0011] Furthermore, the process conditions for the steam pretreatment stage are as follows: steam is introduced from the bottom of the pot, the steam temperature is 150~160℃, and the pressure is 0.4~0.5 MPa; when the temperature inside the pot reaches 110~115℃, the alkaline impregnation pretreatment stage begins.

[0012] Furthermore, the process conditions for the alkaline impregnation pretreatment stage are as follows: liquid ratio 1:2.5~4, using one or both of freshly prepared alkali solution and recycled white solution at a temperature of 75~80℃, and impregnation time of 20~60 min;

[0013] Specifically, based on Na2O, the amount of alkali used for cooking in one or both of the newly prepared alkali solution and the recovered white liquor is 5 to 10% of the total amount of alkali used for cooking. It should be noted that when the newly prepared alkali solution and the recovered white liquor are used in combination, the amount of alkali used for cooking refers to the total amount of alkali used for cooking after the two are mixed, not the amount of alkali used for cooking a single type. Similar situations in subsequent schemes will also be expressed in this way.

[0014] The total amount of alkali used in steaming is 10 to 30% of the oven-dry weight of the corresponding Chinese fir, broadleaf miscellaneous wood, and miscellaneous bamboo raw materials.

[0015] Furthermore, the process conditions for the intermediate heating and cooking stage are as follows: one or more of the following are used: fresh alkali liquor, recycled white liquor and recycled black liquor at 125 ~ 135℃, and cooking aids are added at the same time, while the liquor is heated to the maximum cooking temperature by steam.

[0016] Specifically, based on Na2O, the amount of alkali used for cooking in one or more of the newly prepared alkali solution, the recovered white liquor, and the recovered black liquor accounts for 90-95% of the total alkali used for cooking;

[0017] The amount of the cooking aid is 0.04-0.12%, 0.03-0.12%, and 0.02-0.10% of the oven-dry weight of the raw materials of *Cunninghamia lanceolata*, *Hypericum perforatum*, and *Bambusa textilis*, respectively.

[0018] The maximum cooking temperatures for the raw materials of Japanese cedar, broadleaf mixed wood, and mixed bamboo are 165°C, 160°C, and 155°C, respectively.

[0019] Furthermore, in the first stage: based on Na2O, the amount of alkali used for cooking in one or more of the newly prepared alkali liquor, the recovered white liquor, and the recovered black liquor is 10-12% of the total alkali used for cooking;

[0020] Second stage: Based on Na2O, the amount of alkali used for cooking in one or more of the newly prepared alkali liquor, the recovered white liquor, and the recovered black liquor is 30-35% of the total alkali used for cooking;

[0021] Third stage: Based on Na2O, the amount of alkali used for cooking in one or more of the newly prepared alkali liquor, the recovered white liquor, and the recovered black liquor is 45-55% of the total alkali used for cooking;

[0022] The cooking aid is added in the second stage and the third stage, respectively.

[0023] Furthermore, the cooking aid is anthraquinone, or the cooking aid includes anthraquinone and a nonionic surfactant, and the mass ratio of the two is 1:4 to 6.

[0024] Furthermore, the process conditions for the heat preservation stage are: heat preservation time of 60 to 110 minutes.

[0025] Furthermore, the process conditions for the screening treatment are as follows: a pressure screen is used for screening, the feed slurry concentration is 2.0% to 4.0%, the feed slurry pressure is 0.10 to 0.35 MPa, the inlet and outlet pressure difference is 0.02 to 0.05 MPa, the working temperature is 40 to 80℃, and the screening gap width is 0.10 to 0.45 mm;

[0026] And / or, the process conditions for the washing treatment and secondary washing are: multiple vacuum washing machines are connected in series for countercurrent washing;

[0027] The operating parameters for each vacuum washing machine are as follows: vacuum degree -0.04 ~ -0.06 MPa, initial pulp concentration of 1.2 ~ 2.0% for the first machine, initial pulp concentration of 1.5 ~ 2.5% for subsequent machines, output pulp concentration of 12 ~ 16%, and washing water temperature of 60 ~ 75℃.

[0028] Furthermore, the oxygen removal process conditions are: a single-stage oxygen removal process or a two-stage oxygen removal process;

[0029] The operating parameters for the single-stage oxygen descaling process are as follows: slurry concentration 10-12%, temperature 90-105℃, oxygen pressure 0.9-0.11 MPa, time 60-80 min, sodium hydroxide dosage for oven-dry slurry 2.5-4.0%, and magnesium sulfate protective agent dosage for oven-dry slurry 0.3-0.6%.

[0030] The operating parameters for the two-stage oxygen descaling process are as follows: Stage 1: Slurry concentration 10-12%, temperature 90-105℃, oxygen pressure 0.9-0.11 MPa, time 20-40 min, sodium hydroxide dosage for oven-dry slurry 2.0-3.5%, magnesium sulfate protective agent dosage for oven-dry slurry 0.2-0.4%; Stage 2: Slurry concentration 10-12%, temperature 85-95℃, oxygen pressure 0.9-0.11 MPa, time 50-70 min, sodium hydroxide dosage for oven-dry slurry 1.0-2.0%, magnesium sulfate protective agent dosage for oven-dry slurry 0.2-0.4%.

[0031] The beneficial effects of this invention are:

[0032] 1. Effectively improves the physical strength and overall performance of the finished paper. This invention mixes Japanese cedar pulp, hardwood pulp, and mixed bamboo pulp in a specific oven-dry mass ratio of 20% : 15% : 65%. This ratio fully utilizes the high tensile strength of Japanese cedar long fibers, the high tear strength of mixed bamboo fibers, and the effect of hardwood fibers on improving paper uniformity. This allows the properties of various fibers to complement each other, resulting in a synergistic improvement in key physical strength indicators such as tensile index, bursting index, and tear index of the final paper bag, meeting the strength requirements of high-end packaging paper.

[0033] 2. Significantly improved pulp quality and solved the cooking problem. The cooking process employed in this invention includes a steam pretreatment stage and an alkali impregnation pretreatment stage. First, steam rapidly softens the fibers and establishes pressure, followed by preliminary alkali penetration under relatively mild conditions. The synergistic effect of these two pretreatment stages significantly improves the uniformity and efficiency of alkali penetration into raw materials such as Japanese cedar, broadleaf mixed wood, and mixed bamboo, thereby reducing fiber damage during cooking, minimizing undigested components and fiber bundles, and resulting in three types of natural-colored pulp with lower dust content and better fiber bonding potential.

[0034] 3. Ensures the cleanliness and color stability of the final pulp. This invention systematically purifies and enhances the mixed pulp through a complete post-processing procedure including screening, washing, oxygen desulfurization, and secondary washing. The oxygen desulfurization process selectively removes residual chromophores from the pulp without introducing chlorine bleach, thereby stabilizing the pulp brightness within the target range and obtaining a uniform and stable natural-colored pulp. Combined with thorough washing, the final pulp has low dust content and high purity, providing a fundamental guarantee for producing high-quality natural-colored paper bags with low dust and excellent appearance.

[0035] 4. High-value transformation of specific raw materials is achieved. The method of this invention is specifically adapted to the combination of raw materials such as Japanese cedar, broadleaf miscellaneous wood, and miscellaneous bamboo. Through a complete process chain, these potentially regional and low-cost raw materials are successfully transformed into high-performance paper bag pulp, broadening the source of raw materials for high-quality paper bags. While ensuring the high quality of the product, it has potential cost advantages and environmental friendliness. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart illustrating the pulping method for high-strength, low-dust, unbleached paper bag paper in the embodiments. Detailed Implementation

[0038] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0039] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, these are merely examples and are not intended to limit the present invention.

[0040] The embodiments of the invention will now be described in detail with reference to the accompanying drawings.

[0041] Example 1

[0042] A pulping method for high-strength, low-dust, unbleached paper bag paper, the process of which is as follows: Figure 1 As shown, the steps include:

[0043] [1] Raw material preparation: Prepare Chinese fir wood chips (10-15 years old, moisture content about 45%), broadleaf mixed wood chips (mainly 8-12 year old eucalyptus wood and 8-12 year old money tree mixed in a 1:1 mass ratio, moisture content about 50%), and mixed bamboo chips (mainly 2-3 year old bamboo, moisture content about 55%). The specifications of the raw material chips should meet the requirements for loading into the cooking pot.

[0044] [2] Cooking treatment: Intermittent cooking was carried out in a vertical cooking pot using the sulfate process. The willow cedar wood chips, broadleaf hardwood chips, and mixed bamboo chips were processed in different vertical cooking pots, and the process is as follows:

[0045] (1) For Japanese cedar wood chips

[0046] Loading stage: Load the cedar wood chips into the vertical steamer.

[0047] Steam pretreatment stage: Steam is introduced from the bottom of the pot, and the steam temperature is controlled at 155℃ and the pressure at 0.45 MPa until the temperature inside the pot rises to 112℃, and some air and volatile substances are discharged.

[0048] Alkali impregnation pretreatment stage: Maintain the temperature inside the pot, add fresh alkali solution (containing NaOH + Na2S) at 80℃, with a solution ratio of 1:2.5. The amount of alkali used in the fresh alkali solution, calculated as Na2O, is 8% of the total alkali used in cooking (based on 20% of the oven-dry pulp mass). Impregnate for 60 minutes to allow the alkali solution to initially wet and soften the raw materials.

[0049] It should be noted that the sulfate cooking liquor in this embodiment and the subsequent comparative examples were prepared with a sulfidation degree of 25%.

[0050] Mid-term heating and cooking stage: This is carried out in three stages:

[0051] a) First stage: Add fresh alkali solution at a temperature of 135℃, the amount of alkali used for cooking (calculated as Na2O) is 11% of the total amount of alkali used for cooking.

[0052] b) Second stage: Add fresh alkali solution at a temperature of 135℃. The amount of alkali used for cooking (calculated as Na2O) is 33% of the total amount of alkali used for cooking. At the same time, add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.05% of the oven-dry pulp mass.

[0053] c) Third stage: Add freshly prepared alkali solution at 135℃, with the amount of alkali used for cooking (calculated as Na2O) accounting for 48% of the total alkali used for cooking. Simultaneously add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) at 0.05% of the oven-dry pulp mass. At the same time, heat with steam to the maximum cooking temperature of 165℃.

[0054] Keep warm during the heat preservation stage: keep warm at the highest cooking temperature for 100 minutes.

[0055] Recovery and discharging stage: Hot black liquor is recovered, followed by pulp discharge. Testing showed that the kappa pulp had a kappa number of approximately 28.

[0056] (2) For broadleaf hardwood chips

[0057] Loading stage: Load the cedar wood chips into the vertical steamer.

[0058] Steam pretreatment stage: Steam is introduced from the bottom of the pot, and the steam temperature is controlled at 155℃ and the pressure at 0.45 MPa until the temperature inside the pot rises to 112℃, and some air and volatile substances are discharged.

[0059] Alkali impregnation pretreatment stage: Maintain the temperature inside the pot, add freshly prepared alkali solution (containing NaOH + Na2S) at 80℃, with a solution ratio of 1:2.5. The freshly prepared alkali solution used is calculated as Na2O, and its amount of alkali used for cooking is 8% of the total amount of alkali used for cooking (calculated as 18% of the oven-dry pulp mass). Impregnate for 50 minutes to allow the alkali solution to initially wet and soften the raw materials.

[0060] Mid-term heating and cooking stage: This is carried out in three stages:

[0061] a) First stage: Add fresh alkali solution at a temperature of 135℃, the amount of alkali used for cooking (calculated as Na2O) is 11% of the total amount of alkali used for cooking.

[0062] b) Second stage: Add fresh alkali solution at 135℃, the amount of alkali used for cooking (calculated as Na2O) is 33% of the total amount of alkali used for cooking, and simultaneously add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.05% of the oven-dry pulp mass.

[0063] c) Third stage: Add freshly prepared alkali solution at 135℃, with the amount of alkali used for cooking (calculated as Na2O) accounting for 48% of the total alkali used for cooking. Simultaneously add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) at 0.05% of the oven-dry pulp mass. At the same time, heat with steam to the maximum cooking temperature of 155℃.

[0064] Keep warm during the heat preservation stage: keep warm at the highest cooking temperature for 100 minutes.

[0065] Recovery and discharging stage: Hot black liquor is recovered, followed by pulp discharge. Testing showed that the kappa number of the hardwood pulp was approximately 25.

[0066] (3) For miscellaneous bamboo strips

[0067] Loading stage: Load the mixed bamboo strips into the vertical steamer.

[0068] Steam pretreatment stage: Steam is introduced from the bottom of the pot, and the steam temperature is controlled at 155℃ and the pressure at 0.45 MPa until the temperature inside the pot rises to 112℃, and some air and volatile substances are discharged.

[0069] Alkali impregnation pretreatment stage: Maintain the temperature inside the pot, add fresh alkali solution (containing NaOH + Na2S) at 80℃, with a liquid ratio of 1:2.5. The fresh alkali solution used is calculated as Na2O, and its alkali usage for cooking is 8% of the total alkali usage for cooking (calculated as 17% of the oven-dry pulp mass). Impregnate for 40 minutes to allow the alkali solution to initially wet and soften the raw materials.

[0070] Mid-term heating and cooking stage: This is carried out in three stages:

[0071] a) First stage: Add fresh alkali solution at a temperature of 135℃, the amount of alkali used for cooking (calculated as Na2O) is 11% of the total amount of alkali used for cooking.

[0072] b) Second stage: Add fresh alkali solution at 135℃, the amount of alkali used for cooking (calculated as Na2O) is 33% of the total amount of alkali used for cooking, and simultaneously add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.04% of the oven-dry pulp mass.

[0073] c) Third stage: Add freshly prepared alkali solution at 135℃, with the amount of alkali used for cooking (calculated as Na2O) accounting for 48% of the total alkali used for cooking. Simultaneously add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.04% of the oven-dry pulp mass. At the same time, heat with steam to the maximum cooking temperature of 160℃.

[0074] Keep warm during the heat preservation stage: keep warm at the highest cooking temperature for 60 minutes.

[0075] Recovery and discharging stage: Hot black liquor is recovered, and then the pulp is sprayed out. Testing showed that the kappa number of the mixed bamboo pulp was approximately 23.

[0076] [3] Pulp preparation: Mix 20% of Japanese cedar pulp, 15% of broadleaf mixed hardwood pulp and 65% of mixed bamboo pulp evenly in the pulp tank according to the dry weight percentage.

[0077] [4] Screening: The mixed slurry is pumped to a pressure screen for screening. The slurry concentration is 3.0%, the slurry pressure is 0.25 MPa, the inlet and outlet pressure difference is 0.03 MPa, the working temperature is 60℃, and the screening gap width is 0.25 mm to remove coarse fiber bundles and impurities.

[0078] [5] Washing treatment: The screened pulp is sent to a countercurrent washing system consisting of six vacuum washing machines connected in series. The first machine has a pulp concentration of 1.5%, and the subsequent machines have a pulp concentration of 2.0%. The output pulp concentration is 15%, the washing water temperature is 70℃, and the vacuum degree is -0.05MPa, which removes most of the dissolved organic matter and residual chemicals.

[0079] [6] Oxygen Desulfurization: A single-stage oxygen desulfurization process was adopted. The concentration of the pulp after washing was adjusted to 11%, and 3.0% sodium hydroxide and 0.5% magnesium sulfate protective agent (by weight of oven-dried pulp) were added. The reaction was carried out at 100℃ and 0.6 MPa for 60 min to further remove lignin and reduce the color of the pulp.

[0080] [7] Secondary washing treatment: The pulp after oxygen deoxygenation is washed again by two vacuum washing machines connected in series, with the same process conditions as step [5] washing, and finally a clean pulp is obtained for making high-strength, low-dust, unbleached paper bags.

[0081] Example 2

[0082] This embodiment provides a pulping method for high-strength, low-dust, unbleached paper bag paper. The difference between this embodiment and Embodiment 1 lies in the cooking process in step [2], while the other steps are the same.

[0083] [2] Cooking treatment: Intermittent cooking was carried out in a vertical cooking pot using the sulfate process. The willow cedar wood chips, broadleaf hardwood chips, and mixed bamboo chips were processed in different vertical cooking pots, and the process is as follows:

[0084] (1) For Japanese cedar wood chips

[0085] Loading stage: Load the cedar wood chips into the vertical steamer.

[0086] Steam pretreatment stage: Steam is introduced from the bottom of the pot, and the steam temperature is controlled at 155℃ and the pressure at 0.45 MPa until the temperature inside the pot rises to 112℃, and some air and volatile substances are discharged.

[0087] Alkali impregnation pretreatment stage: Maintain the temperature inside the pot, add recycled white liquor at 80℃, with a liquor ratio of 1:2.5. The recycled white liquor used is calculated as Na2O, and its alkali usage for cooking is 8% of the total alkali usage for cooking (calculated as 20% of the oven-dry pulp mass). Impregnate for 50 minutes to allow the alkali solution to initially wet and soften the raw material.

[0088] Mid-term heating and cooking stage: This is carried out in three stages:

[0089] a) First stage: Add the recovered white liquor at a temperature of 135℃, and the amount of alkali used for cooking (calculated as Na2O) is 11% of the total amount of alkali used for cooking.

[0090] b) Second stage: Add the recovered white liquor at a temperature of 135℃. The amount of alkali used for cooking (calculated as Na2O) is 33% of the total amount of alkali used for cooking. At the same time, add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.06% of the oven-dry pulp mass.

[0091] c) Third stage: Add the recovered white liquor at 135℃, with the amount of alkali used for cooking (calculated as Na2O) accounting for 48% of the total alkali used for cooking. Simultaneously add a cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.06% of the oven-dry pulp mass. At the same time, heat with steam to the maximum cooking temperature of 163℃.

[0092] Heat preservation stage: Keep warm at the highest cooking temperature for 110 minutes.

[0093] Recovery and discharging stage: Hot black liquor is recovered (the diluted black liquor at the end of the recovery process can be further processed to obtain recovered white liquor), and then the pulp is discharged. Testing showed that the kappa number of the Japanese cedar pulp was approximately 31.

[0094] (2) For broadleaf hardwood chips

[0095] Loading stage: Load the cedar wood chips into the vertical steamer.

[0096] Steam pretreatment stage: Steam is introduced from the bottom of the pot, and the steam temperature is controlled at 155℃ and the pressure at 0.45 MPa until the temperature inside the pot rises to 112℃, and some air and volatile substances are discharged.

[0097] Alkali impregnation pretreatment stage: Maintain the temperature inside the pot, add recovered white liquor at 80℃, with a liquor ratio of 1:2.5. The recovered white liquor used is calculated as Na2O, and its alkali usage for cooking is 8% of the total alkali usage for cooking (calculated as 18% of the oven-dry pulp mass). Impregnate for 45 minutes to allow the alkali solution to initially wet and soften the raw material.

[0098] Mid-term heating and cooking stage: This is carried out in three stages:

[0099] a) First stage: Add the recovered white liquor at a temperature of 135℃, and the amount of alkali used for cooking (calculated as Na2O) is 11% of the total amount of alkali used for cooking.

[0100] b) Second stage: Add the recovered white liquor at a temperature of 135℃. The amount of alkali used for cooking (calculated as Na2O) is 33% of the total amount of alkali used for cooking. At the same time, add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.06% of the oven-dry pulp mass.

[0101] c) Third stage: Add the recovered white liquor at 135℃, with the amount of alkali used for cooking (calculated as Na2O) accounting for 48% of the total alkali used for cooking. Simultaneously add a cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.06% of the oven-dry pulp mass. At the same time, heat with steam to the maximum cooking temperature of 160℃.

[0102] Heat preservation stage: Keep warm at the highest cooking temperature for 110 minutes.

[0103] Recovery and discharging stage: Hot black liquor is recovered (the diluted black liquor at the end of the recovery process can be further processed to obtain recovered white liquor), and then the pulp is sprayed out. Testing showed that the kappa number of the hardwood pulp was approximately 24.

[0104] (3) For miscellaneous bamboo strips

[0105] Loading stage: Load the mixed bamboo strips into the vertical steamer.

[0106] Steam pretreatment stage: Steam is introduced from the bottom of the pot, and the steam temperature is controlled at 155℃ and the pressure at 0.45 MPa until the temperature inside the pot rises to 112℃, and some air and volatile substances are discharged.

[0107] Alkali impregnation pretreatment stage: Maintain the temperature inside the pot, add recovered white liquor at 80℃, with a liquor ratio of 1:2.5. The recovered white liquor used is calculated as Na2O, and its alkali usage for cooking is 8% of the total alkali usage for cooking (calculated as 17% of the oven-dry pulp mass). Impregnate for 35 minutes to allow the alkali solution to initially wet and soften the raw material.

[0108] Mid-term heating and cooking stage: This is carried out in three stages:

[0109] a) First stage: Add the recovered white liquor at a temperature of 135℃, and the amount of alkali used for cooking (calculated as Na2O) is 11% of the total amount of alkali used for cooking.

[0110] b) Second stage: Add the recovered white liquor at a temperature of 135℃. The amount of alkali used for cooking (calculated as Na2O) is 33% of the total amount of alkali used for cooking. At the same time, add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.05% of the oven-dry pulp mass.

[0111] c) Third stage: Add the recovered white liquor at 135℃, with the amount of alkali used for cooking (calculated as Na2O) accounting for 48% of the total alkali used for cooking. Simultaneously add a cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.05% of the oven-dry pulp mass. At the same time, heat with steam to the maximum cooking temperature of 155℃.

[0112] Heat preservation stage: Keep warm at the highest cooking temperature for 65 minutes.

[0113] Recovery and discharging stage: Hot black liquor is recovered (the recovered black liquor can be further processed to obtain recovered white liquor), and then the pulp is sprayed out. Testing showed that the kappa number of the mixed bamboo pulp was approximately 22.

[0114] This embodiment demonstrates the feasibility of using recycled white liquor (from the alkali recovery system). Based on the same process principle, recycled black liquor can also be used partially, provided that process stability is ensured. Specifically, in the first stage of "intermediate heating and cooking", a portion of the recycled white liquor can be replaced with filtered recycled black liquor. Its use must meet the following conditions: (1) Proportion limit: The amount of recycled black liquor replaced shall not exceed 30% of the total volume of liquor in this stage. (2) Concentration guarantee: The effective alkali concentration of the mixed liquor in this stage must be ensured to reach the set value (e.g., 11% of the total alkali used) by online detection and replenishment of white liquor. (3) Stage limit: It is only allowed to be used in the first stage (initial heating, ≤ 85°C). It is prohibited to use it in the subsequent cooking stages at higher temperatures to prevent impurities from interfering with the reaction. This method can maintain the quality of the pulp while realizing resource recycling, and the resulting pulp kappa value is comparable to that of this embodiment.

[0115] Example 3

[0116] This embodiment provides a pulping method for high-strength, low-dust, unbleached paper bag paper. The main difference between this embodiment and Embodiment 1 is the difference in step [3] pulp preparation, while the other steps are the same.

[0117] [3] Pulp preparation: Mix 20.5% of Japanese cedar pulp, 15.5% of broadleaf mixed hardwood pulp and 64% of mixed bamboo pulp evenly in the pulp tank according to the dry weight percentage.

[0118] Example 4

[0119] This embodiment provides a pulping method for high-strength, low-dust, unbleached paper bag paper. The main difference between this embodiment and Embodiment 1 is the difference in step [3] pulp preparation, while the other steps are the same.

[0120] [3] Pulp preparation: Mix 19.5% of Japanese cedar pulp, 14.5% of broadleaf mixed hardwood pulp and 56% of mixed bamboo pulp evenly in the pulp tank according to the dry weight percentage.

[0121] Compare with Example 1

[0122] This comparative example provides a pulping method for unbleached paper bags. The main difference between this method and Example 1 is the difference in step [3] pulp preparation, while the other steps are the same.

[0123] [3] Pulp preparation: Mix 21% of Japanese cedar pulp, 26% of broadleaf mixed hardwood pulp and 63% of mixed bamboo pulp evenly in the pulp tank according to the dry weight percentage.

[0124] Compare with Example 2

[0125] This comparative example provides a pulping method for unbleached paper bags. The main difference between this method and Example 1 is the difference in step [3] pulp preparation, while the other steps are the same.

[0126] [3] Pulp preparation: Mix 19% of Japanese cedar pulp, 14% of broadleaf mixed hardwood pulp and 67% of mixed bamboo pulp evenly in the pulp tank according to the dry weight percentage.

[0127] Compare with Example 3

[0128] This comparative example provides a pulping method for unbleached paper bags. The main difference between this method and Example 1 is the difference in step [2] cooking treatment, while the other steps are the same.

[0129] [2] Cooking treatment: Intermittent cooking was carried out in a vertical cooking pot using the sulfate process. The willow cedar wood chips, broadleaf hardwood chips, and mixed bamboo chips were processed in different vertical cooking pots, and the process is as follows:

[0130] (1) For Japanese cedar wood chips

[0131] Loading stage: Load the cedar wood chips into the vertical steamer.

[0132] Heating and cooking stage: Steam is introduced from the bottom of the pot and carried out in three stages:

[0133] a) First stage: Add fresh alkali solution at a temperature of 135℃, the amount of alkali used for cooking (calculated as Na2O) is 19% of the total amount of alkali used for cooking.

[0134] b) Second stage: Add fresh alkali solution at 135℃, the amount of alkali used for cooking (calculated as Na2O) is 33% of the total amount of alkali used for cooking, and simultaneously add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.05% of the oven-dry pulp mass.

[0135] c) Third stage: Add freshly prepared alkali solution at 135℃, with the amount of alkali used for cooking (calculated as Na2O) accounting for 48% of the total alkali used for cooking. Simultaneously add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) at 0.05% of the oven-dry pulp mass. At the same time, heat with steam to the maximum cooking temperature of 165℃.

[0136] Keep warm during the heat preservation stage: keep warm at the highest cooking temperature for 100 minutes.

[0137] Recovery and discharging stage: Hot black liquor is recovered, followed by pulp discharge. Testing showed that the kappa number of the Japanese cedar pulp was approximately 32.

[0138] (2) For broadleaf hardwood chips

[0139] Loading stage: Load the cedar wood chips into the vertical steamer.

[0140] Heating and cooking stage: Steam is introduced from the bottom of the pot and carried out in three stages:

[0141] a) First stage: Add fresh alkali solution at a temperature of 135℃, the amount of alkali used for cooking (calculated as Na2O) is 19% of the total amount of alkali used for cooking.

[0142] b) Second stage: Add fresh alkali solution at a temperature of 135℃. The amount of alkali used for cooking (calculated as Na2O) is 33% of the total amount of alkali used for cooking. At the same time, add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.05% of the oven-dry pulp mass.

[0143] c) Third stage: Add freshly prepared alkali solution at 135℃, with the amount of alkali used for cooking (calculated as Na2O) accounting for 48% of the total alkali used for cooking. Simultaneously add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) at 0.05% of the oven-dry pulp mass. At the same time, heat with steam to the maximum cooking temperature of 160℃.

[0144] Keep warm during the heat preservation stage: keep warm at the highest cooking temperature for 100 minutes.

[0145] Recovery and discharging stage: Hot black liquor is recovered, followed by pulp discharge. Testing showed that the kappa number of the hardwood pulp was approximately 22.

[0146] (3) For miscellaneous bamboo strips

[0147] Loading stage: Load the mixed bamboo strips into the vertical steamer.

[0148] Heating and steaming: Steam is introduced from the bottom of the pot and carried out in three stages:

[0149] a) First stage: Add fresh alkali solution at a temperature of 135℃, the amount of alkali used for cooking (calculated as Na2O) is 19% of the total amount of alkali used for cooking.

[0150] b) Second stage: Add fresh alkali solution at 135℃, the amount of alkali used for cooking (calculated as Na2O) is 33% of the total amount of alkali used for cooking, and simultaneously add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.04% of the oven-dry pulp mass.

[0151] c) Third stage: Add freshly prepared alkali solution at 135℃, with the amount of alkali used for cooking (calculated as Na2O) accounting for 48% of the total alkali used for cooking. Simultaneously add cooking aid (composed of anthraquinone and emulsifier OP-10 in a mass ratio of 1:5) accounting for 0.04% of the oven-dry pulp mass. At the same time, heat with steam to the maximum cooking temperature of 155℃.

[0152] Keep warm during the heat preservation stage: keep warm at the highest cooking temperature for 60 minutes.

[0153] Recovery and discharging stage: Hot black liquor is recovered, and then the pulp is sprayed out. Testing showed that the kappa number of the mixed bamboo pulp was approximately 19.

[0154] Referring to the requirements of ISO 2470-1:2016 "Measurement of blue diffuse reflectance of paper, paperboard and pulp under indoor daylight conditions (ISO luminance)", the ISO luminance of the pulp in the above examples and comparative examples was determined.

[0155] The pulp from both the examples and the control examples was fed to a paper machine and subjected to the same process: flow feeding, wire winding, pressing, drying, calendering, and winding, to obtain paper samples with a basis weight of 80 g / m². Fifty paper samples were randomly selected, and their relevant properties were measured according to GB / T 7968-2015 Paper Bag Paper and GB / T 1541-2013 Determination of Dust Content in Paper and Paperboard. The distribution of statistical data was analyzed. The test results are shown in the table below.

[0156] Table of test results

[0157]

[0158] The test data in the table shows that, in a specific oven-dry weight ratio of 20% : 15% : 65%, the present invention fully utilizes the high tensile strength of the long fibers of cedar, the high tear strength of the fibers of bamboo, and the improving effect of the fibers of broadleaf trees on paper uniformity. This allows the properties of various fibers to complement each other, resulting in a synergistic improvement in key physical strength indicators such as tensile index, bursting index, and tear index of the final paper bag, which can meet the strength requirements of high-end packaging paper. Simultaneously, the present invention employs a cooking process that includes a steam pretreatment stage and an alkali impregnation pretreatment stage. First, steam is used to rapidly soften the fibers and establish pressure, followed by preliminary alkali penetration under relatively mild conditions. The synergistic effect of these two pretreatment processes significantly improves the uniformity and efficiency of alkali penetration into raw materials such as Japanese cedar, broadleaf mixed wood, and mixed bamboo, thereby reducing fiber damage during the cooking process, reducing the generation of undigested fractions and fiber bundles, and resulting in three types of natural-colored pulps with lower dust content and better fiber bonding potential.

Claims

1. A pulping process for high-strength, low-dust, unbleached sack paper, characterized in that Includes the following steps: Step S1 involves steaming the raw materials of Japanese cedar, broadleaf mixed wood, and mixed bamboo to obtain Japanese cedar pulp, broadleaf mixed wood pulp, and mixed bamboo pulp, respectively; wherein the steaming process includes a steam pretreatment stage and an alkali impregnation pretreatment stage. Step S2: Mix 20% of the Japanese cedar pulp, 15% of the hardwood pulp, and 65% of the bamboo pulp according to their oven-dry weight percentages; wherein the ratio of the Japanese cedar raw materials, the hardwood raw materials, and the bamboo raw materials is controlled within ±0.5%; Step S3 involves sequentially screening, washing, oxygen removal, and secondary washing of the mixed pulp obtained in step S2 to obtain pulp for making the high-strength, low-dust, unbleached paper bag.

2. The pulping method of high strength low dust kraft sack paper according to claim 1, characterized in that, The cooking process employs a sulfate process using a vertical cooking pot with intermittent cooking, which includes the following stages in sequence: loading stage, steam pretreatment stage, alkali impregnation pretreatment stage, mid-term heating and cooking stage, heat preservation stage, recovery stage, and unloading stage.

3. The pulping method for high-strength, low-dust, unbleached paper bag paper according to claim 2, characterized in that, The process conditions for the steam pretreatment stage are as follows: steam is introduced from the bottom of the pot, the steam temperature is 150~160℃, and the pressure is 0.4~0.5 MPa; when the temperature inside the pot reaches 110~115℃, the alkaline impregnation pretreatment stage begins.

4. The pulping method for high-strength, low-dust, unbleached paper bag paper according to claim 2, characterized in that, The process conditions for the alkaline impregnation pretreatment stage are as follows: liquid ratio 1:2.5~4, using one or both of freshly prepared alkali solution and recycled white solution at a temperature of 75~80℃, and impregnation time of 20~60 min; Specifically, based on Na2O, the amount of alkali used for cooking in one or both of the newly prepared alkali solution and the recovered white liquor is 5-10% of the total amount of alkali used for cooking; The total amount of alkali used in steaming is 10 to 30% of the oven-dry weight of the corresponding Chinese fir, broadleaf miscellaneous wood, and miscellaneous bamboo raw materials.

5. The pulping method for high-strength, low-dust, unbleached paper bag paper according to claim 2, characterized in that, The process conditions for the intermediate heating and cooking stage are as follows: one or more of the following are used: fresh alkali liquor, recovered white liquor and recovered black liquor at 125 ~ 135℃, cooking aids are added at the same time, and the liquor is heated to the maximum cooking temperature by steam. Specifically, based on Na2O, the amount of alkali used for cooking in one or more of the newly prepared alkali solution, the recovered white liquor, and the recovered black liquor accounts for 90-95% of the total alkali used for cooking; The amount of the cooking aid is 0.04-0.12%, 0.03-0.12%, and 0.02-0.10% of the oven-dry weight of the raw materials of *Cunninghamia lanceolata*, *Hypericum perforatum*, and *Bambusa textilis*, respectively. The maximum cooking temperatures for the raw materials of Japanese cedar, broadleaf mixed wood, and mixed bamboo are 165°C, 160°C, and 155°C, respectively.

6. The pulping method for high-strength, low-dust, unbleached paper bag paper according to claim 5, characterized in that, First stage: Based on Na2O, the amount of alkali used for cooking in one or more of the newly prepared alkali liquor, the recovered white liquor, and the recovered black liquor is 10-12% of the total alkali used for cooking; Second stage: Based on Na2O, the amount of alkali used for cooking in one or more of the newly prepared alkali liquor, the recovered white liquor, and the recovered black liquor is 30-35% of the total alkali used for cooking; Third stage: Based on Na2O, the amount of alkali used for cooking in one or more of the newly prepared alkali liquor, the recovered white liquor, and the recovered black liquor is 45-55% of the total alkali used for cooking; The cooking aid is added in the second stage and the third stage, respectively.

7. The pulping method for high-strength, low-dust, unbleached paper bag paper according to claim 5 or 6, characterized in that, The cooking aid is anthraquinone, or the cooking aid includes anthraquinone and a nonionic surfactant, and the mass ratio of the two is 1:4 to 6.

8. The pulping method for high-strength, low-dust, unbleached paper bag paper according to claim 2, characterized in that, The process conditions for the heat preservation stage are: heat preservation time of 60 to 110 minutes.

9. The pulping method for high-strength, low-dust, unbleached paper bag paper according to any one of claims 1 to 6 and 8, characterized in that, The screening process conditions are as follows: a pressure screen is used for screening, the feed slurry concentration is 2.0% to 4.0%, the feed slurry pressure is 0.10 to 0.35 MPa, the inlet and outlet pressure difference is 0.02 to 0.05 MPa, the working temperature is 40 to 80℃, and the screening gap width is 0.10 to 0.45 mm; And / or, the process conditions for the washing treatment and secondary washing are: multiple vacuum washing machines are connected in series for countercurrent washing; The operating parameters for each vacuum washing machine are as follows: vacuum degree -0.04 ~ -0.06 MPa, initial pulp concentration of 1.2 ~ 2.0% for the first machine, initial pulp concentration of 1.5 ~ 2.5% for subsequent machines, output pulp concentration of 12 ~ 16%, and washing water temperature of 60 ~ 75℃.

10. The pulping method for high-strength, low-dust, unbleached paper bag paper according to any one of claims 1 to 6 and 8, characterized in that, The oxygen removal process conditions are: a single-stage oxygen removal process or a two-stage oxygen removal process. The operating parameters for the single-stage oxygen descaling process are as follows: slurry concentration 10-12%, temperature 90-105℃, oxygen pressure 0.9-0.11MPa, time 60-80 min, sodium hydroxide dosage for oven-dry slurry 2.5-4.0%, and magnesium sulfate protective agent dosage for oven-dry slurry 0.3-0.6%. The operating parameters for the two-stage oxygen descaling process are as follows: Stage 1: Slurry concentration 10-12%, temperature 90-105℃, oxygen pressure 0.9-0.11MPa, time 20-40 min, sodium hydroxide dosage for oven-dry slurry 2.0-3.5%, magnesium sulfate protective agent dosage for oven-dry slurry 0.2-0.4%; Stage 2: Slurry concentration 10-12%, temperature 85-95℃, oxygen pressure 0.9-0.11MPa, time 50-70 min, sodium hydroxide dosage for oven-dry slurry 1.0-2.0%, magnesium sulfate protective agent dosage for oven-dry slurry 0.2-0.4%.

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