Waste paper dry pulping production process for preparing craft paper

Abstract

The invention discloses a waste paper dry pulping production process for preparing craft paper, which comprises the following steps: firstly, treating a waste paper raw material through a hydraulic pulper, a high-concentration sand remover, a pulp tower, a coarse screen and a grading screen in sequence; the range of the mass ratio of the long fiber pulp to the short fiber pulp obtained by the grading screen treatment is (45: 55)-(40: 60), the long fiber pulp is sent to a long fiber working section, and the short fiber pulp is sent to a short fiber working section. According to the technical scheme provided by the invention, the proportion of the long fibers and the short fibers selected by grading screening is reasonable, so that the strength, the stiffness and other properties of the final finished product kraft linerboard can be well balanced, the waste paper dry grinding pulp can have good strength even if no wood pulp is added into the raw materials, and the quality of the kraft linerboard is improved. The bursting strength of the prepared finished kraft liner paper meets the required requirement, and the production cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of papermaking, and in particular to a waste paper dry pulping production process for preparing kraft paper. Background Art

[0002] When making high-quality kraft paper with high bursting strength, if the strength of the pulp does not meet the requirements, it is difficult to make finished paper with high bursting strength. In the prior art, 20% to 30% of coniferous wood pulp raw materials are usually added during the papermaking process to make the pulp strength meet the requirements. However, compared with recycled waste paper pulp, the price of commercial wood pulp is too high. The large-scale use of wood pulp to improve the strength of finished paper and the large-scale addition of chemical auxiliary products to improve the strength of paper in the flow system of the paper machine can effectively meet the strength requirements of paper quality, but directly increase the papermaking cost. However, if wood pulp is not added, but a large amount of recycled fiber from waste paper is used, the bursting strength of the finished paper is difficult to meet the required requirements. A quality improvement method for dry pulping raw materials of waste paper is now invented, which can improve the quality of pulp, thereby preparing high-strength high-quality kraft paper without adding wood pulp. Summary of the invention

[0003] In view of the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a waste paper dry pulping production process for preparing kraft paper, aiming to solve the technical problem in the prior art that wood pulp must be added to produce highly tear-resistant kraft paper.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A waste paper dry pulping production process for preparing kraft paper comprises the following steps:

[0006] (1) Sending the waste paper raw materials to a hydraulic pulper for pulping;

[0007] (2) The pulp obtained by the hydraulic pulper is sent to the unloading pulp tower after being treated by a high-concentration desander;

[0008] (3) The slurry from the unloading slurry tower is sent to the grading screen after being subjected to coarse screening;

[0009] (4) The mass ratio of long fiber pulp and short fiber pulp obtained by the grading screen treatment is in the range of (45:55) to (40:60), and the long fiber pulp is sent to the long fiber section, and the short fiber pulp is sent to the short fiber section;

[0010] The long fiber section includes:

[0011] (a.1) Long fiber pulp enters the long fiber desander;

[0012] (a.2) The long fiber pulp after being treated by the long fiber desander enters the long fiber fine screen;

[0013] (a.3) After the long fiber fine screening, the long fiber pulp enters the long fiber multi-disc thickener;

[0014] (a.4) The long fiber pulp processed by the long fiber multi-disc concentrator enters the long fiber hot disperser;

[0015] (a.5) The long fiber pulp treated by the long fiber heat disperser enters the long fiber pulp tower and then enters the long fiber disc refiner for pulping;

[0016] (a.6) The long fiber pulp after long fiber disc grinding enters the long fiber pulp pool;

[0017] The staple fiber section includes:

[0018] (b.1) The short fiber pulp enters the short fiber desander;

[0019] (b.2) The short fiber pulp after being treated by the long fiber desander enters the short fiber multi-disc thickener;

[0020] (b.3) The short fiber pulp processed by the short fiber multi-disc concentrator enters the short fiber heat disperser;

[0021] (b.4) The short fiber pulp treated by the short fiber heat disperser enters the short fiber pulp tower and then enters the short fiber grinding disc for beating;

[0022] (b.5) The short fiber pulp after short fiber disc grinding enters the short fiber pulp pool.

[0023] Furthermore, in the waste paper dry pulping production process for preparing kraft paper, the long fiber disc refiner in step (a.5) comprises a first long fiber disc refiner, a second long fiber disc refiner and a third disc refiner which are arranged in series.

[0024] Furthermore, in the waste paper dry pulping production process for preparing kraft paper, the tooth width of the first long fiber disc mill and the second long fiber disc mill are both 3.3-3.6 mm, and the groove width is 4-4.5 mm; the tooth width of the third long fiber disc mill is 2-2.5 mm, and the groove width is 3-3.5 mm.

[0025] Furthermore, in the waste paper dry pulping production process for preparing kraft paper, the short fiber disc refiner in step (b.4) comprises a first short fiber disc refiner and a second short fiber disc refiner arranged in series.

[0026] Furthermore, in the waste paper dry pulping production process for preparing kraft paper, the tooth width of the first short fiber disc is 3.5-4 mm, and the groove width is 3.5-3.8 mm; the tooth width of the second short fiber disc is 1.6-1.8 mm, and the groove width is 3-5 mm.

[0027] Furthermore, in the waste paper dry pulping production process for preparing kraft paper, in step (a.5), the long fiber pulping concentration range is 5% to 6%; in step (b.4), the short fiber pulping concentration range is 5% to 6%.

[0028] Furthermore, in the waste paper dry pulping production process for preparing kraft paper, in step (a.5), the pulping inlet pressure of long fiber pulping is 300-400 kPa, and the pulping outlet pressure is 500-550 kPa; in step (b.4), the pulping inlet pressure of short fiber pulping is 300-400 kPa, and the pulping outlet pressure is 500-550 kPa.

[0029] Beneficial effects: The present invention provides a waste paper dry pulping production process for preparing kraft paper. Compared with the prior art, the present application first pre-treats the waste paper raw material, and then separates the long fibers and the short fibers in a certain proportion and then processes them separately. The reasonable proportion of the separated long fiber pulp and short fiber pulp can make the final finished kraft paper achieve a good balance in properties such as strength and stiffness, and achieves that even if no wood pulp is added to the raw material, the waste paper dry pulp can have good strength, so that the bursting resistance of the prepared finished kraft paper meets the required requirements, thereby reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The flowchart is a waste paper dry pulping production process for preparing kraft paper. DETAILED DESCRIPTION

[0031] The present invention provides a waste paper dry pulping production process for preparing kraft paper. In order to make the purpose, technical scheme and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] See also Figure 1 The present invention provides a waste paper dry pulping production process for preparing kraft paper. The terms "first", "second" and the like described herein are merely different names for similar structures for the convenience of explanation and are not intended to limit the present application.

[0033] A waste paper dry pulping production process for preparing kraft paper, characterized in that it comprises the following steps:

[0034] (1) Sending the waste paper raw materials to a hydraulic pulper for pulping;

[0035] (2) The pulp obtained by the hydraulic pulper is sent to the unloading pulp tower after being treated by a high-concentration desander;

[0036] (3) The slurry from the unloading slurry tower is sent to the grading screen after being subjected to coarse screening;

[0037] (4) The mass ratio of long fiber pulp and short fiber pulp obtained by the grading screen treatment is in the range of (45:55) to (40:60), and the long fiber pulp is sent to the long fiber section, and the short fiber pulp is sent to the short fiber section;

[0038] The long fiber section includes:

[0039] (a.1) Long fiber pulp enters the long fiber desander;

[0040] (a.2) The long fiber pulp after being treated by the long fiber desander enters the long fiber fine screen;

[0041] (a.3) After the long fiber fine screening, the long fiber pulp enters the long fiber multi-disc thickener;

[0042] (a.4) The long fiber pulp processed by the long fiber multi-disc concentrator enters the long fiber hot disperser;

[0043] (a.5) The long fiber pulp treated by the long fiber heat disperser enters the long fiber pulp tower and then enters the long fiber disc refiner for pulping;

[0044] (a.6) The long fiber pulp after long fiber disc grinding enters the long fiber pulp pool;

[0045] The staple fiber section includes:

[0046] (b.1) The short fiber pulp enters the short fiber desander;

[0047] (b.2) The short fiber pulp after being treated by the long fiber desander enters the short fiber multi-disc thickener;

[0048] (b.3) The short fiber pulp processed by the short fiber multi-disc concentrator enters the short fiber heat disperser;

[0049] (b.4) The short fiber pulp treated by the short fiber heat disperser enters the short fiber pulp tower and then enters the short fiber grinding disc for beating;

[0050] (b.5) The short fiber pulp after short fiber disc grinding enters the short fiber pulp pool.

[0051] In the above scheme, "waste paper" refers to waste paper, cardboard and other raw materials, preferably American waste (i.e., waste paper raw materials imported from the United States). The paper recycling system of American waste is relatively mature, and the fiber quality of American waste is relatively high.

[0052] In the above scheme, the hydraulic pulper can effectively decompose waste paper into fiber suspension through hydraulic action, avoid excessive mechanical damage, and retain the original length and strength of the fiber to the greatest extent. At the same time, it can process various types of waste paper, has good adaptability, and can provide a relatively stable quality raw material basis for the subsequent pulping process. The pulp after the hydraulic pulper is then treated by a high-concentration desander, which can effectively remove heavy impurities in the pulp, such as sand particles, metal fragments, etc. Further, the pulp of the unloading pulp tower is treated with a coarse screen and then passed through a grading screen. This grading method can effectively separate the long fiber pulp and short fiber pulp in the pulp according to a certain proportion. Accurate screening and grading help to carry out targeted treatment according to the different characteristics of long fibers and short fibers. The reasonable ratio of long fibers and short fibers (45:55-40:60) can make the final kraft paper achieve a good balance in strength and stiffness. Long fibers can provide good strength for paper, and short fibers can improve the surface flatness and uniformity of paper.

[0053] The above-mentioned "the mass ratio of long fiber pulp and short fiber pulp ranges from (45:55) to (40:60)" means that the proportion of long fibers is 40-45%, and the proportion of short fibers is 55-60%. The significance of the relatively small proportion of long fibers and the relatively large proportion of short fibers is: (1) It can better screen the fiber length in the long fiber pulp; if the classification ratio of long fibers is higher than that of short fibers, it is easy to cause more short fiber pulp to be mixed into the long fiber pulp, resulting in a mixture of long and short fibers, which is not conducive to the improvement of the subsequent disc grinding quality and the adjustment of the process parameters of long fiber beating and the selection of disc grinding discs, resulting in a decrease in the quality of long fiber beating; (2) Short fiber pulp fibers are shorter and can better fill the gaps inside the paper during the papermaking process; when the proportion of short fibers is large, these short fibers can be evenly distributed among the long fibers, making the structure of the paper denser and smoother, thereby improving the uniformity of the paper.

[0054] Furthermore, in the above scheme, the long fiber disc refiner in step (a.5) includes a first long fiber disc refiner, a second long fiber disc refiner and a third disc refiner arranged in series. Since the fibers in the long fiber pulp are relatively long, they play a key role in the strength properties of the paper (such as tensile strength, tear strength, etc.). By arranging the first long fiber disc refiner, the second long fiber disc refiner and the third disc refiner in series, the long fiber pulp can be gradually ground. The first long fiber disc refiner first performs preliminary processing on the long fibers, cuts off some overly long fibers, and makes the fiber length distribution more reasonable, thereby achieving the purpose of gradually refining the fibers and improving the strength of the paper.

[0055] Preferably, the tooth width of the first long fiber disc mill and the second long fiber disc mill are both 3.3-3.6 mm, and the groove width is 4-4.5 mm; the tooth width of the third long fiber disc mill is 2-2.5 mm, and the groove width is 3-3.5 mm. This arrangement makes the first long fiber disc mill and the second long fiber disc mill mainly used to cut the fibers, and also to perform fiber separation and brooming to a certain extent. The relatively wide groove width provides enough space for the fibers to enter between the grinding discs. The tooth width of 3.3-3.6 mm means that the grinding disc has enough power to cut the fibers entering the groove during rotation. When the fibers enter the gap between the grinding discs, in addition to being cut, they are also rubbed and squeezed by the tooth patterns on the surface of the grinding disc. Therefore, the first long fiber disc mill and the second long fiber disc mill cut the long fibers and play a certain role in fiber separation and brooming. The third long fiber disc mill adopts a more sophisticated grinding disc structure to separate and broom the long fibers, thereby achieving fine processing of the long fibers.

[0056] Furthermore, the short fiber refiner in step (b.4) comprises a first short fiber refiner and a second short fiber refiner arranged in series, which is conducive to gradually refining the short fiber.

[0057] Furthermore, the tooth width of the first short fiber disc mill is 3.5-4 mm, and the groove width is 3.5-3.8 mm; the tooth width of the second short fiber disc mill is 1.6-1.8 mm, and the groove width is 3-5 mm; the tooth width of the third long fiber disc mill is 2.0 mm, and the groove width is 3.3 mm. The combination of the relatively narrow groove width and slightly wider tooth width of the first short fiber disc mill is conducive to the preliminary cutting of the short fiber pulp. The tooth groove depth is 7 mm, and this depth provides a certain space for the movement of the fiber between the grinding discs. In the deeper tooth grooves, as the grinding disc rotates, the fibers will produce more collisions and friction in the tooth grooves. This helps to better mix the fibers in the short fiber pulp, making the distribution between the fibers more uniform, and also can cause some impurities on the fiber surface to fall off, improving the purity of the fiber. The narrower tooth width and moderate groove width of the second short fiber disc mill are conducive to strengthening the silk separation and brooming process. Since the groove width has a certain range, it can be adjusted according to the different requirements of paper for fibers in actual production.

[0058] Furthermore, in step (a.5), the long fiber beating concentration ranges from 5% to 6%; in step (b.4), the short fiber beating concentration ranges from 5% to 6%. The significance of this setting is that: (1) at this beating concentration, there are sufficient contact opportunities between the fibers, ensuring that the fibers rub and knead each other, which is conducive to the fiber separation and brooming; whether it is long fiber or short fiber, at a concentration of 5% to 6%, the distribution of the fibers in the disc grinding will not be too sparse or too dense; (2) maintaining the consistency of long fiber and short fiber beating concentrations will help produce paper of consistent quality. In the subsequent pulp mixing process, long fibers and short fibers at the same concentration can be better interwoven, making the paper structure more compact and uniform.

[0059] Furthermore, in step (a.5), the pulp inlet pressure of long fiber beating is 300-400 kPa, and the pulp outlet pressure is 500-550 kPa; in step (b.4), the pulp inlet pressure of short fiber beating is 300-400 kPa, and the pulp outlet pressure is 500-550 kPa. The pulp inlet pressure of long fiber and short fiber beating is set at 300-400 kPa. This pressure range can ensure that the pulp flow enters the disc mill stably, and the pulp inlet pressure is not too high, causing the fiber structure of long fibers and short fibers to be damaged. In addition, since the pulp outlet pressure is set to 500-550 kPa, which is higher than the pulp inlet pressure, this pressure difference can effectively promote the fiber pulp after pulping to flow out of the disc mill smoothly.

[0060] The following specific example data are provided to support the present invention.

[0061] The test data related to long fiber beating are as follows:

[0062]

[0063] The test data related to short fiber beating are as follows:

[0064]

[0065]

[0066] Furthermore, the long fiber pulp and short fiber pulp prepared by the above scheme can be used to prepare kraft paper.

[0067] The following examples are given to further illustrate. The kraft paper includes a surface layer, a core layer and a bottom layer. In the pulping of the surface layer, the mass percentage of fluff pulp is 40% to 60%, and the other components of the surface layer can be long-fiber pulp (or other non-wood pulp pulp); in the pulping of the core layer, the mass percentage of fluff pulp is 65% to 75%, and the mass percentage of long-fiber pulp is 25% to 35%; in the pulping of the bottom layer, the mass percentage of fluff pulp is 25% to 35%, and the mass percentage of long-fiber pulp is 65% to 75%. Different from the prior art, the long-fiber pulp and fluff pulp used in the kraft paper are prepared by the waste paper dry pulping production process for preparing kraft paper as described above.

[0068] The long fiber pulp and short fiber pulp prepared in Examples 1-6 were made into kraft paper according to the above method, and the bursting resistance index of the finished paper was tested. The bursting resistance index ranged from 3.79 to 3.87 (kPa.㎡ / g). When packaging general items (such as daily necessities, etc.), such a bursting resistance index can ensure that the paper will not break easily during normal transportation and storage. The above kraft paper has good performance because: (1) the mass percentage of short fiber pulp in the surface layer is 40% to 60%; the short fibers can form a fine fiber layer on the surface of the paper, making the surface layer of the kraft paper smoother, so that the surface layer has good surface smoothness and printability; (2) the mass percentage of short fiber pulp in the core layer is 65% to 75%, and the long fiber pulp is 25% to 35%. The long fibers provide the basic strength skeleton of the paper, and a large amount of short fibers can enhance the structural tightness of the core layer, improve the overall strength and stiffness of the paper, thereby enhancing the strength and stiffness of the paper; (3) the long fiber pulp with more bottom layer can provide strong strength and toughness for the bottom layer of the kraft paper.

[0069] From the above analysis, it can be seen that after adopting the new process, even if no wood pulp is added to the pulp, the finished Newcard paper has good burst resistance, thus achieving the purpose of cost saving.

[0070] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the protection scope of the present invention.

Claims

1. A waste paper dry pulping production process for preparing kraft paper, characterized in that: The following steps are involved: (1) Sending the waste paper raw materials to a hydraulic pulper for pulping; (2) The pulp obtained by the hydraulic pulper is sent to the unloading pulp tower after being treated by a high-concentration desander; (3) The slurry from the unloading slurry tower is sent to the grading screen after being subjected to coarse screening; (4) The mass ratio of long fiber pulp and short fiber pulp obtained by the grading screen treatment is in the range of (45:55) to (40:60), and the long fiber pulp is sent to the long fiber section, and the short fiber pulp is sent to the short fiber section; The long fiber section includes: (a.1) Long fiber pulp enters the long fiber desander; (a.2) The long fiber pulp after being treated by the long fiber desander enters the long fiber fine screen; (a.3) After the long fiber fine screening, the long fiber pulp enters the long fiber multi-disc thickener; (a.4) The long fiber pulp processed by the long fiber multi-disc concentrator enters the long fiber hot disperser; (a.5) The long fiber pulp treated by the long fiber heat disperser enters the long fiber pulp tower and then enters the long fiber disc refiner for pulping; (a.6) The long fiber pulp after long fiber disc grinding enters the long fiber pulp pool; The staple fiber section includes: (b.1) The short fiber pulp enters the short fiber desander; (b.2) The short fiber pulp after being treated by the long fiber desander enters the short fiber multi-disc thickener; (b.3) The short fiber pulp processed by the short fiber multi-disc concentrator enters the short fiber heat disperser; (b.4) The short fiber pulp treated by the short fiber heat disperser enters the short fiber pulp tower and then enters the short fiber grinding disc for beating; (b.5) The short fiber pulp after short fiber disc grinding enters the short fiber pulp pool.

2. The waste paper dry pulping production process for preparing kraft paper according to claim 1, characterized in that: The long fiber disc refiner in step (a.5) comprises a first long fiber disc refiner, a second long fiber disc refiner and a third disc refiner which are arranged in series.

3. The waste paper dry pulping production process for preparing kraft paper according to claim 2, characterized in that: The tooth width of the first and second long fiber disc mills is 3.3-3.6 mm, and the groove width is 4-4.5 mm; the tooth width of the third long fiber disc mill is 2-2.5 mm, and the groove width is 3-3.5 mm.

4. The waste paper dry pulping production process for preparing kraft paper according to claim 1, characterized in that: The short fiber refiner in step (b.4) comprises a first short fiber refiner and a second short fiber refiner arranged in series.

5. The waste paper dry pulping production process for preparing kraft paper according to claim 4, characterized in that: The first staple disc mill has a tooth width of 3.5-4 mm and a groove width of 3.5-3.8 mm; the second staple disc mill has a tooth width of 1.6-1.8 mm and a groove width of 3-5 mm.

6. The waste paper dry pulping production process for preparing kraft paper according to claim 1, characterized in that: In step (a.5), the long fiber pulping concentration range is 5% to 6%; in step (b.4), the short fiber pulping concentration range is 5% to 6%.

7. The waste paper dry pulping production process for preparing kraft paper according to claim 1, characterized in that: In step (a.5), the inlet pressure of long fiber pulping is 300-400 kPa, and the outlet pressure is 500-550 kPa; in step (b.4), the inlet pressure of short fiber pulping is 300-400 kPa, and the outlet pressure is 500-550 kPa.

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