Process for improving ash content of finished coated ivory board

Abstract

The invention relates to a process method for improving the finished paper ash content of a coated white cardboard. The process method comprises the following steps: sequentially adding a calcium carbonate filler, polyacrylamide and silica sol into core layer slurry, and then carrying out papermaking. Different from the prior art, loss of fine fibers in a forming net is reduced by flocculating the fine fibers in the white water, so that the retention effect is improved; the calcium carbonate filler and the silica sol are used in the core layer, the flocculation effect of fine fibers in the slurry is improved by utilizing the characteristic of large specific surface area of the filler, and the first-process retention rate is improved by utilizing the silica sol to adsorb the flocculated filler and the fine fibers. The retention of ash components of the paper material is effectively improved, and the concentration and ash content of off-machine water under the net are reduced; the papermaking speed of the paper machine can be increased, the production efficiency is improved, and the cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of papermaking, and in particular to a process for improving the ash content of coated white cardboard. Background Art

[0002] During the papermaking process, the retention process of the ash component (mineral filler) in the paper stock is the process of the filler being adsorbed by cationic polyacrylamide. Due to the bridging effect of the long chain of polyacrylamide, the filler, polyacrylamide, and paper stock fibers are flocculated to form small fiber flocs. The fiber flocs are dehydrated and formed and retained on the wire surface to form a wet paper web, and part of the filler is retained in the paper sheet.

[0003] The existing Chinese patent application CN117802826A, entitled "A high retention process for coating white cardboard", discloses a white cardboard and a production process. The former proposes a method of adding modified bentonite to improve the first-pass retention rate of the core layer, but the core layer retention rate does not exceed 87%; while CN116905278A, entitled "A ternary retention aid and process for reducing the ash content of white water", proposes a method of adding silica sol to the dispersed domestic waste OCC, thereby playing an important role in retaining and filtering the fillers and fine fibers in the paper material, but the ash content of the finished paper does not exceed 15% at most, which affects the cost. Summary of the invention

[0004] In view of the above problems, the present application provides a process for coating white cardboard to improve the ash content of finished paper and the first-pass retention rate of the core layer. The process can effectively improve the retention of the core layer ash components and reduce the white water concentration under the wire and the ash concentration of the white water under the wire.

[0005] The present application provides a process for improving the ash content of coated white cardboard, wherein calcium carbonate filler, polyacrylamide and silica sol are sequentially added to a core layer slurry before papermaking.

[0006] Different from the existing technology, the fine fibers in the white water are flocculated to reduce the loss of fine fibers on the forming net, thereby improving the retention effect; calcium carbonate filler and silica sol are used in the core layer, and the large specific surface area of ​​the filler is used to improve the flocculation effect of the fine fibers in the slurry, and the silica sol is used to adsorb the flocculated filler and fine fibers to improve the first-pass retention rate. It effectively improves the retention of paper stock ash components, reduces the white water concentration and ash content under the net, and enables the papermaking speed of the paper machine to be increased, production efficiency to be improved, and cost to be reduced.

[0007] Furthermore, the calcium carbonate filler and polyacrylamide are added before the first stage pressure screen, and the silica sol is added after the first stage pressure screen.

[0008] Furthermore, the added amount of the calcium carbonate filler is 270kg / t to 320kg / t of absolute dry slurry.

[0009] Furthermore, the amount of polyacrylamide added is 0.35 kg / t of absolute dry slurry, and the concentration is 0.3%.

[0010] Furthermore, the added amount of the silica sol is 3-3.5 kg / t of absolute dry slurry.

[0011] Furthermore, in the calcium carbonate filler, the solid content of calcium carbonate is 30%-40%, wherein the particle size of calcium carbonate below 2 μm accounts for 54%-60%.

[0012] Furthermore, the main active ingredient of the silica sol is anionic silica colloid.

[0013] Furthermore, the solid content of the silica sol is 14-16%; the density is 1060-1200 kg / m 3 ; pH value is 9.5~11.5.

[0014] Furthermore, the ratio of the core layer pulp is: 3-5% bleached softwood kraft pulp, 50-53% chemical mechanical pulp, 18-20% damaged pulp and 22-25% white water multi-disc recovered pulp.

[0015] Furthermore, the operating speed of the paper machine is 795-825 m / min.

[0016] The above-mentioned records related to the invention content are only an overview of the technical solution of the present application. In order to enable ordinary technicians in the field to more clearly understand the technical solution of the present application, and then implement it according to the written contents of the specification, and to make the above-mentioned purpose and other purposes, features and advantages of the present application easier to understand, the specific implementation methods of the present application are explained below. DETAILED DESCRIPTION

[0017] In order to explain the technical content, structural features, achieved objectives and effects of the technical solution in detail, the following is a detailed description in conjunction with specific embodiments.

[0018] In order to explain in detail the possible application scenarios, technical principles, specific schemes that can be implemented, and the purposes and effects that can be achieved, the following is a detailed description in conjunction with the specific embodiments listed. The embodiments described herein are only used to more clearly illustrate the technical solutions of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0019] Reference to "embodiment" herein means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The term "embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or association with other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the various technical features mentioned in the embodiments can be combined in any way to form a corresponding implementable technical solution.

[0020] Unless otherwise defined, the technical terms used in this document have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms in this document is only for describing specific embodiments and is not intended to limit this application.

[0021] In the description of this application, the term "and / or" is an expression used to describe the logical relationship between objects, indicating that three relationships may exist, for example, A and / or B, which means: A exists, B exists, and A and B exist at the same time. In addition, the character " / " in this article generally indicates that the objects before and after are in an "or" logical relationship.

[0022] In the present application, terms such as “first” and “second” are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship of quantity, priority or sequence between these entities or operations.

[0023] Without further limitations, in this application, the words "include", "comprises", "has" or other similar expressions used in the sentences are intended to cover non-exclusive inclusion. These expressions do not exclude the presence of additional elements in the process, method or product including the elements, so that the process, method or product including a series of elements may include not only those limited elements, but also other elements not explicitly listed, or also include elements inherent to such process, method or product.

[0024] Similar to the understanding in the Examination Guidelines, in this application, expressions such as "greater than", "less than", "exceed" and the like are understood to exclude the number itself; expressions such as "above", "below", "within" and the like are understood to include the number itself. In addition, in the description of the embodiments of this application, "multiple" means more than two (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups", "multiple times", etc., unless otherwise clearly and specifically limited.

[0025] In this embodiment, the particle size of 54% to 60% of the calcium carbonate is controlled to be below 2 μm, which is conducive to the adsorption of papermaking fibers, but the retention rate will be reduced, resulting in a waste of raw materials. Therefore, polyacrylamide and silica sol are added in the process to increase the retention rate of calcium carbonate.

[0026] The polyacrylamide described in this embodiment mainly plays the role of adsorbing fine fibers and fillers, and through the bridging effect of polyacrylamide long chains, flocculates the fibers, polyacrylamide long chains, fine fibers and fillers to form fiber flocs.

[0027] The silica sol described in this embodiment is an anionic silica colloidal solution with a high specific surface area and a nanometer-scale structure, which can make the flocculated pulp flocculate again after high-speed shearing of the paper machine, further improve the retention of fine components, and its nanometer-scale particle size can redistribute the paper fiber flocs, improve the agglomeration strength of the re-flocculated fiber flocs, and effectively reduce the damage of high-speed shearing to fiber flocculation, thereby playing an important role in retaining and facilitating the filter of fillers and fine fibers in the paper. After adding silica sol, new micro-flocculates are formed, which improves the retention rate of the wire part, and the wire part will form more water filtration channels, thereby improving the water filtration of the pulp wire part and improving the uniformity of the finished paper.

[0028] The beating degree mentioned in this application is the beating degree. After the reaction pulp passes through the refiner, the fibers are cut, split, swollen, and hydrated, which are the effects of the refinement. Beating is to use the mechanical action of the grinding disc teeth to treat the fibers in the pulp, so that they are loosened, appropriately cut, and separated; more importantly, the fibers absorb water and swell during beating, so that they have higher elasticity and plasticity, meet the requirements of paper machine production, so that the produced paper can reach the expected quality indicators. The beating degree indicates the water filtration performance of the pulp. Take 2 grams of absolute dry pulp, dilute to 1000 ml, and pass through an 80-mesh screen at 20°C. The amount of water discharged from the side tube of the Shaw beating degree meter is the result of the measurement. The beating degree is an indicator of the properties of paper stock. According to the beating degree of paper stock, it is possible to grasp the water filtration speed of the paper stock on the copper screen of the paper machine in the future, and it is also possible to summarize and predict the mechanical strength, tightness and manageability of the paper produced in the future. Therefore, mastering the beating degree of paper stock is an important technical control method in production.

[0029] Broken paper pulp is a semi-intermediate product produced in papermaking. After being recycled and pulped, it is reused in pulping. Broken paper refers to wet broken paper and dry broken paper produced in the process of pulping on the web. Wet broken paper refers to the trimmed paper of the paper machine web; dry broken paper includes the trimmed paper of the parent roll rewinding, the residual bottom paper of the parent roll, the waste paper generated by paper breaking, and the unqualified returned paper. After the wet broken paper and dry broken paper are re-pulped, the broken paper pulp can be obtained, which is used for pulping the core layer and the bottom layer.

[0030] White water multi-disc recycled pulp refers to the excess white water generated in the papermaking process of the paper machine, which is processed by a white water recovery multi-disc machine. The specific processing process of white water multi-disc recycled pulp includes: adding part of the OCC pulp (usually OCC long fiber pulp to improve water filtration performance) to white water, forming a cushion filter cake on the multi-disc fan blades, and under the vacuum generated by the vacuum water legs of the white water recovery multi-disc machine, water is removed through the filter cake, and most of the fine fibers in the white water are intercepted by the filter cake and recovered. The pulp obtained by peeling the filter cake with pulp spray water is the white water multi-disc recycled pulp.

[0031] The present application provides a process for improving the ash content of coated white cardboard, wherein calcium carbonate filler, polyacrylamide and silica sol are sequentially added to a core layer slurry before papermaking.

[0032] Different from the existing technology, the fine fibers in the white water are flocculated to reduce the loss of fine fibers on the forming net, thereby improving the retention effect; calcium carbonate filler and silica sol are used in the core layer, and the large specific surface area of ​​the filler is used to improve the flocculation effect of the fine fibers in the slurry, and the silica sol is used to adsorb the flocculated filler and fine fibers to improve the first-pass retention rate. It effectively improves the retention of paper stock ash components, reduces the white water concentration and ash content under the net, and enables the papermaking speed of the paper machine to be increased, production efficiency to be improved, and cost to be reduced.

[0033] Furthermore, the calcium carbonate filler and polyacrylamide are added before the first screen, and the silica sol is added after the first screen.

[0034] Furthermore, the added amount of the calcium carbonate filler is 270kg / t to 320kg / t of absolute dry slurry.

[0035] Furthermore, the amount of polyacrylamide added is 0.35 kg / t of absolute dry slurry, and the concentration is 0.3%.

[0036] Furthermore, the added amount of the silica sol is 3-3.5 kg / t of absolute dry slurry.

[0037] Furthermore, in the calcium carbonate filler, the solid content of calcium carbonate is 30%-40%, and the particle size of calcium carbonate below 2 μm accounts for 54%-60%.

[0038] Furthermore, the main active ingredient of the silica sol is anionic silica colloid.

[0039] Furthermore, the solid content of the silica sol is 14-16%; the density is 1060-1200 kg / m 3 ; pH value is 9.5~11.5.

[0040] Furthermore, the ratio of the core layer pulp is: 3-5% bleached softwood kraft pulp, 50-53% chemical mechanical pulp, 18-20% damaged pulp and 22-25% white water multi-disc recovered pulp.

[0041] Furthermore, the operating speed of the paper machine is 795-825 m / min.

[0042] The preparation of the core layer in this embodiment comprises the following steps:

[0043] Step 1, core layer pulp preparation: the raw material ratio is 3-5% bleached softwood kraft pulp, 50-53% chemical mechanical pulp, 18-20% damaged paper pulp and 22-25% white water multi-disc recovered pulp, which are screened and mixed before the core layer flushing pump.

[0044] Step 2: Add calcium carbonate filler in the front of the core layer slurry pump through the pipeline, the added amount is 270kg / t to 320kg / t. The calcium carbonate filler has a solid content of 30% to 40%, and the calcium carbonate particle size below 2μm accounts for 54% to 60%.

[0045] Step 3: Add 3.5kg / t polyacrylamide with a concentration of 0.3% to the pipeline in front of the pressure screen of the core layer.

[0046] Step 4: Add 3-3.5 kg / t silica sol to the pipeline behind the pressure screen of the core layer through the dosing device. The main active ingredient of the silica sol is anionic silica colloid, the solid content of the silica sol is 14-16%; the density is 1060-1200 kg / m 3 ; pH value is 9.5~11.5.

[0047] Step 5: Finally, the slurry is sprayed onto the forming net through the headbox to form a core layer.

[0048] Examples 1 and 2

[0049] High-speed paper machine (running speed 795-825m / min, basis weight 400gsm) core layer pulp on the screen:

[0050] The core layer pulp ratio is: 5% bleached softwood kraft pulp, 50% chemical mechanical pulp, 20% damaged pulp and 25% white water multi-disc recovered pulp.

[0051] Calcium carbonate filler, polyacrylamide and silica sol were added into the papermaking slurry in sequence, and after being fully mixed, the slurry was fed into the paper machine and subjected to a water filtration test. In Example 1-2, the polyacrylamide was maintained at 0.35 kg / t, and the amount of silica sol added was as shown in Table 1.

[0052] With the continuous addition of silica sol, the concentration of white water under the wire decreased, the retention rate of the wire changed, the ash content of the core layer and the ash content of the finished paper increased, and the process parameters and corresponding test results are shown in Table 1.

[0053] Table 1 High-speed paper machine core layer pulp process parameters and test results

[0054]

[0055] It can be seen from Table 1 that when the amount of calcium carbonate filler is 270-320 kg / t, the amount of silica sol is 3-3.5 kg / t pulp, the amount of polyacrylamide is 0.35 kg / t pulp, the core layer pulp concentration on the net is 1.52-1.64%, the white water concentration under the net is 0.152%-0.157%, the first-pass retention rate is 90.40%-90.71%, the water filtration of the net is good, the running speed of the paper machine is 795-825 m / min, the paper uniformity is normal, and the ash content of the finished paper is not less than 30%, which greatly reduces the cost.

[0056] Example 3

[0057] High-speed paper machine (running speed 795-825m / min, basis weight 400gsm) core layer pulp on the screen:

[0058] Step 1: Preparation of core layer pulp: The raw material ratio is 3% bleached softwood kraft pulp, 53% chemical mechanical pulp, 20% damaged paper pulp and 24% white water multi-disc recovered pulp, which are screened and mixed before the core layer flushing pump.

[0059] Step 2: Add 300kg / t of calcium carbonate filler through a pipeline in front of the core layer slurry pump. The solid content of calcium carbonate in the calcium carbonate filler is 30%-40%, and the particle size of calcium carbonate below 2 μm accounts for 54%-60%.

[0060] Step 3: Add 3.5kg / t polyacrylamide with a concentration of 0.3% to the pipeline in front of the pressure screen of the core layer.

[0061] Step 4: Add 3.2kg / t silica sol to the pipeline behind the pressure screen of the core layer through the dosing device. The main active ingredient of the silica sol is anionic silica colloid, the solid content of the silica sol is 14-16%; the density is 1060-1200kg / m 3 ; pH value is 9.5~11.5.

[0062] Step 5: Finally, the slurry is sprayed onto the forming net through the headbox to form a core layer.

[0063] Example 4

[0064] High-speed paper machine (running speed 795-825m / min, basis weight 400gsm) core layer pulp on the screen:

[0065] Step 1: Preparation of core layer pulp: The raw material ratio of 4% bleached softwood kraft pulp, 52% chemical mechanical pulp, 19% damaged paper pulp and 25% white water multi-disc recovered pulp is screened and mixed before the core layer flushing pump.

[0066] Step 2: Add 300kg / t of calcium carbonate filler through a pipeline in front of the core layer slurry pump. The solid content of calcium carbonate in the calcium carbonate filler is 30%-40%, and the particle size of calcium carbonate below 2 μm accounts for 54%-60%.

[0067] Step 3: Add 3.5kg / t polyacrylamide with a concentration of 0.3% to the pipeline in front of the pressure screen of the core layer.

[0068] Step 4: Add 3.0kg / t silica sol to the pipeline behind the pressure screen of the core layer through the dosing device. The main active ingredient of the silica sol is anionic silica colloid, the solid content of the silica sol is 14-16%; the density is 1060-1200kg / m 3 ; pH value is 9.5~11.5.

[0069] Step 5: Finally, the slurry is sprayed onto the forming net through the headbox to form a core layer.

[0070] In this technical solution, the fine fibers in the white water are flocculated to reduce the loss of fine fibers on the forming net, thereby improving the retention effect; calcium carbonate filler and silica sol are used in the core layer, and the large specific surface area of ​​the filler is used to improve the flocculation effect of the fine fibers in the slurry, and the silica sol is used to adsorb the flocculated filler and fine fibers to improve the first-pass retention rate. It effectively improves the retention of paper stock ash components, reduces the white water concentration and ash content under the net, and enables the papermaking speed of the paper machine to be increased, the production efficiency to be improved, and the cost to be reduced.

[0071] Finally, it should be noted that although the above embodiments have been described in the text of the specification of this application, this does not limit the scope of patent protection of this application. All technical solutions generated by replacing or modifying equivalent structures or equivalent processes based on the essential concept of this application using the contents recorded in the text of the specification of this application, as well as directly or indirectly implementing the technical solutions of the above embodiments in other related technical fields, are included in the scope of patent protection of this application.

Claims

1. A process for increasing the ash content of coated white cardboard, characterized in that: Calcium carbonate filler, polyacrylamide and silica sol are added to the core layer slurry in sequence before papermaking.

2. The process according to claim 1, characterized in that The calcium carbonate filler and polyacrylamide are added before the first stage pressure screen, and the silica sol is added after the first stage pressure screen.

3. The process according to claim 1, characterized in that The added amount of the calcium carbonate filler is 270kg / t to 320kg / t of absolute dry slurry.

4. The process according to claim 1, characterized in that The added amount of the polyacrylamide is 0.35 kg / t of absolute dry slurry, and the concentration is 0.3%.

5. The process according to claim 1, characterized in that The added amount of the silica sol is 3-3.5 kg / t of absolute dry slurry.

6. The process according to claim 1, characterized in that The calcium carbonate filler has a solid content of 30%-40%, of which the calcium carbonate particles with a diameter below 2 μm account for 54%-60%.

7. The process according to claim 1, characterized in that The main effective component of the silica sol is anionic silica colloid.

8. The process according to claim 1, characterized in that The solid content of the silica sol is 14-16%; the density is 1060-1200 kg / m 3 ; pH value is 9.5~11.

5.

9. The process according to claim 1, characterized in that The proportion of the core layer pulp is: 3-5% bleached softwood kraft pulp, 50-53% chemical mechanical pulp, 18-20% damaged pulp and 22-25% white water multi-disc recovered pulp.

10. The process according to claim 1, characterized in that The operating speed of the paper machine is 795-825m / min.

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