JP4735117B2 - Paper making method - Google Patents

Description

  The present invention relates to a papermaking method for making a paper by adding a yield drainage improver to a pulp slurry, and more particularly to a papermaking method suitable for using recycled pulp such as waste paper as a papermaking raw material.

  Conventionally, various chemicals such as a paper strength enhancer, a sizing agent, or a yield drainage improver are used in a papermaking process for producing paper. Particularly in recent years, in order to save papermaking raw materials and improve papermaking efficiency, additives that improve drainage or / and yield (hereinafter referred to as “yield drainage improver”) are often used.

  On the other hand, the utilization rate of used paper and waste paper containing fillers such as calcium carbonate as a papermaking raw material, or mechanical pulp containing lignin is improved. Moreover, since the circulation rate of white water for suspending pulp is increased and the papermaking process is being closed, anionic impurities (so-called “anion trash”) are increasing in the water circulating in the papermaking process system. Since anion trash consumes yield drainage improvers, an increase in anion trash reduces the effectiveness of yield drainage improvers, generating pitch and defects, reducing paper product quality, cutting paper and reducing production speed. This leads to a decrease in productivity.

  Measures have been taken to increase the amount of the aluminum compound added to the pulp slurry against the problems resulting from the increase in such anion trash. Examples of the aluminum compound include a case where aluminum chloride is used alone or in combination with hydrochloric acid, or a case where aluminum sulfate is used alone or in combination with sulfuric acid. However, since chloride ions may corrode papermaking equipment and the like, aluminum chloride is rarely used practically.

  On the other hand, aluminum sulfate is easy to handle and is widely used, but when used paper is often used as a papermaking raw material or when calcium carbonate is added as a filler to pulp slurry, Calcium sulfate scales due to reaction with calcium ions, causing a problem of adhering to a papermaking apparatus or the like. For this reason, a method of adding a scale inhibitor to the production of such scale has been proposed.

In addition, since cationic polymers are particularly susceptible to anionic trash, a method for enhancing yield or / and drainage improvement effect (hereinafter referred to as “yield drainage improvement effect”) by using an anionic polymer. Has also been proposed (for example, Patent Document 1).
JP 2001-329484 A

  The countermeasures described above have been proposed for the increase in anion trash, but the concentration of sulfate ion increases as the circulation recovery rate of white water recycled in the papermaking system increases. Even if it is added, an increase in sulfate ion concentration in the system cannot be avoided. For this reason, in the above method of increasing the amount of aluminum sulfate added, in order to prevent the generation of scale by reducing the concentration of sulfate ions in the system, a part of white water that can be circulated originally is discharged, and new city water, etc. In some cases, it is necessary to dilute the sulfate ion concentration by adding.

  In addition, in the paper making process, aluminum sulfate is added for the purpose of accelerating the fixing of paper additives such as sizing agents to the pulp, and the pulp slurry is acidified. The effect may not be exhibited stably. Furthermore, when a cationic polymer and an anionic polymer are used in combination, there is a problem that the amount of the polymer added increases.

  The present invention has been made in view of the problems as described above, and avoids the addition of aluminum sulfate, and can prevent the scale failure such as calcium sulfate even if the white water circulation recovery rate in the papermaking system is increased. It aims to provide a method. Another object of the present invention is to provide a paper manufacturing method that can reduce the amount of yield drainage improver added, and in particular, can prevent obstacles in paper production due to anionic trash even when a cationic polymer is used alone. .

  As a result of intensive studies to overcome the above-mentioned problems, the present inventor added a strong acid prior to the addition of the yield drainage improver to increase the yield rate, and for anionic papermaking such as a sizing agent. The present inventors have found that the effect of the additive is enhanced and completed the present invention. More specifically, the present invention provides the following.

  (1) A papermaking method including a papermaking step of adding paper to a pulp slurry and / or adding a yield drainage improver having an effect of improving drainage, and then papermaking and dewatering, wherein a strong acid is added to the pulp slurry. A papermaking method of adding the yield drainage improver after the addition.

  The “strong acid” is an acid having an acid dissociation index of 3 or less in an aqueous solution system. In the present invention, either an inorganic or organic strong acid may be used. Examples of strong inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, perchloric acid, and hydrofluoric acid. Examples of strong organic acids include trichloroacetic acid, sulfonic acid, and picric acid.

  The addition amount of the strong acid is preferably 2 to 400 mol / t, particularly 20 to 200 mol / t, with respect to the dry mass of the insoluble suspension (SS) contained in the pulp slurry. Further, the yield drainage improver is preferably added within 5 minutes from the point of addition of the strong acid, particularly preferably within 3 minutes, and more preferably within 60 seconds. If the time from adding the strong acid to adding the retention drainage improver is too long, the added strong acid reacts with substances other than anionic trash, such as calcium carbonate present in the form of particles, and is consumed. In some cases, the charge neutralization effect of anion trash cannot be sufficiently obtained. On the other hand, if the time from the addition of the strong acid to the addition of the yield filtration improver is too short, the reaction between the added strong acid and the anion trash will not proceed sufficiently, and the charge neutralization effect of the anion trash will be sufficient. You may not be able to get into.

  The “yield drainage improver” is added to the pulp slurry in the paper making process to improve the SS yield when making the pulp slurry, or to improve the drainage when dewatering the made pulp. It shall mean a paper additive having at least one or both of the improving effects. Specific examples include cationic, anionic, and amphoteric polymers made of acrylamide, polyethyleneimine, polyvinylamine, and the like, and Hoffman-modified or Mannich-modified products of the above-described polymers can also be used.

  In the present invention, the charge on the anion trash surface can be reduced by adding a strong acid to the pulp slurry before the addition of the yield drainage improver. For this reason, the retention drainage improver used after addition of a strong acid is not particularly limited, and a retention drainage improver made of a cationic polymer that is easily affected by anionic trash can be formulated alone.

  Here, the action mechanism of the yield drainage improvement effect by adding a strong acid will be described. The strong acid added to the pulp slurry in the present invention itself does not neutralize the anionic trash, but since many of the anionic trash have a carboxyl group, the carboxyl group of the anionic trash is added by adding a strong acid to the pulp slurry. According to the following reaction formula, it is considered that it becomes a free type. And it is estimated that this reaction reduces the charge on the surface of the anion trash and prevents the yield drainage improver from being consumed.

（式中、Ｒ−ＣＯＯ⁻はアニオントラッシュを表し、ＨＡは強酸、Ｍは金属を表す）

(Wherein, R-COO ^- represents an anion trash, HA is a strong acid, M represents a metal)

  After adding the strong acid, the pulp slurry to which the yield drainage improver has been added is made into a sheet form from the paper stock outflow part of the paper machine constituting the paper making process, sent to the wire part, and dehydrated at the wire part for paper making. The dehydrated filtrate (hereinafter simply referred to as “filtrate”) produced by dewatering the pulp (hereinafter referred to as “paper pulp”) produced in the form of a sheet in the papermaking process is a raw material adjustment that adjusts the pulp slurry from the papermaking process. It is preferable to recycle to the process and reuse. In this specification, of the water in which the papermaking raw material is suspended, the water that is circulated and recycled is referred to as “white water”, and the water that is newly introduced into the papermaking process, such as city water, is referred to as “fresh water”. .

  (2) The papermaking method according to (1), wherein the pulp slurry includes recycled pulp and / or mechanical pulp.

  The “pulp slurry” is a liquid material obtained by suspending a papermaking raw material in water, and includes SS mainly composed of pulp fibers derived from plant tissue. The pulp slurry is a “concentrated pulp slurry” having an SS concentration of about 2 to 20% by mass, and a “diluted pulp slurry” diluted for papermaking in which the concentrated pulp slurry is diluted to an SS concentration of about 0.1 to 2% by mass. In this specification, the term “pulp slurry” includes both. That is, in the present invention, the strong acid may be added to either the concentrated pulp slurry or the diluted pulp slurry, but it is particularly preferable to add the strong acid to the diluted pulp slurry.

  Here, “papermaking raw material” is a raw material for producing paper (including paperboard), and is roughly divided into so-called virgin pulp such as chemical pulp (also referred to as “kraft pulp”) and mechanical pulp, and recycled pulp. The Recycled pulp includes manufacturing residues (waste paper) and recycled paper used in the papermaking process called “broken pulp”, and “broken pulp” includes both wet broke pulp, dry-broken pulp, and coated broke pulp It is.

  In the present invention, the addition of a strong acid can reduce papermaking troubles due to anion trash, so that the ratio of recycled pulp and mechanical pulp containing a large amount of causative substances of anion trash as a papermaking raw material can be increased. Specifically, in the case of recycled pulp, the blending ratio with respect to the entire papermaking raw material can be 30% by mass or more, and the total amount of the papermaking raw material can also be used as recycled pulp. Moreover, in the case of mechanical pulp, the compounding ratio with respect to the whole papermaking raw material can be 10 mass% or more. Recycled recycled paper may be suspended in water as a papermaking raw material in the raw material adjustment step after pretreatment such as cutting and deinking the collected recovered paper. After suspending in water in the quality adjustment step, deinking treatment or the like may be performed.

  (3) The papermaking method according to (2), wherein the pulp slurry includes an anionic papermaking additive.

  In the present specification, the “paper additive” refers to an internal additive for papermaking contained in a pulp slurry for papermaking. Specifically, it is a yield drainage improver, a paper strength enhancer, a sizing agent, and a dye. Is included. The pulp slurry may contain, as SS, calcium carbonate, clay, talc, silica and the like which are added as fillers in addition to the papermaking additive. Anionic papermaking additives include starch or acrylamide paper strength enhancers, natural rosin sizing agents based on rosin, synthetic sizing agents such as alkenyl succinic anhydride (ASA), and dyes. Can be mentioned.

  According to the present invention, the strong acid reacts with the anionic group on the surface of the anionic paper additive by the same mechanism as the chemical reaction mechanism described above, so that the fixing of these anionic paper additive to the pulp fiber is promoted. Is done.

  (4) The papermaking method according to (3), wherein the anionic papermaking additive is at least one selected from the group consisting of a rosin sizing agent, a synthetic sizing agent, and a dye.

  Specific examples of the synthetic sizing agent include alkyl ketene dimer (AKD), ASA, and alkylamine. In particular, when a rosin-based, AKD-based, or ASA-based sizing agent is used as a sizing agent, a high effect can be obtained as an effect of promoting fixing to pulp fibers by addition of a strong acid.

  The addition amount of the papermaking additive is 0.01 to 0.5% by mass for rosin sizing agent, particularly 0.1 to 0.4% by mass, especially for synthetic sizing agent, as an addition ratio to the dry pulp mass. It is preferable to set it as 0.01-0.5 mass%, especially 0.1-0.4 mass%.

  (5) The papermaking method according to (3) or (4), wherein the strong acid is added after the anionic papermaking additive is added to the pulp slurry.

  Papermaking additives such as sizing agents may be added to the pulp slurry after the addition of the strong acid, but it is preferable to add them before adding the strong acid according to the invention described in (5). The additive for papermaking is present as an SS component together with pulp fibers and the like in the pulp slurry, and by adding a strong acid, the SS fixing rate in the papermaking process can be further improved.

  In addition, when an anionic paper additive is added after the addition of a strong acid, the retention drainage improver may be added either before or after the addition of the anionic paper additive, Although it may be added at the same timing as the anionic papermaking additive, it is preferably added after the addition of the anionic papermaking additive.

  (6) The papermaking method according to any one of (1) to (5), wherein the strong acid is nitric acid.

  The type of strong acid added to the pulp slurry is not particularly limited, but nitric acid is particularly suitable because it has a lower risk of corroding equipment and the like and has a higher effect on yield drainage than sulfuric acid and hydrochloric acid. Can be used. When nitric acid is used, the addition amount is 2 to 400 mol / t, preferably 20 to 200 mol / t.

  According to the present invention, it is possible to prevent deterioration of paper product quality and production efficiency due to anion trash. Moreover, the generation | occurrence | production of the calcium scale in a papermaking process can be suppressed, and the circulation recovery rate of the white water which circulates in the papermaking system can be improved. Furthermore, the effects of anionic papermaking additives such as yield drainage improvers and sizing agents can be enhanced to reduce the amount of these chemicals added.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view schematically showing a papermaking apparatus 1 for carrying out a papermaking method according to the present invention. In the papermaking apparatus 1, paper is manufactured through a quality adjusting process 10 and a papermaking process 20. The raw material adjusting step 10 includes a pulper 14 in which a papermaking raw material and water are introduced to prepare a pulp slurry, a mixing chest 15, a machine chest 16, a seed box 17, and a screen 18. . On the other hand, the paper making process 20 includes a paper machine 40, and the paper machine 40 includes a sheet machine including a head box 21, a wire part 22, a press part 23, and a dryer part 24. Further, a white water tank 11 in which a filtrate to be described later is stored is provided in the system of the paper manufacturing apparatus 1.

  The pulper 14 and the mixing chest 15 are connected by a first passage pipe 31, the mixing chest 15 and the machine chest 16 are connected by a second passage pipe 32, and the machine chest 16 and the seed box 17 are a third passage pipe. 33, the seed box 17 and the screen 18 are connected by a fourth flow path pipe 34. The pulp slurry that has passed through the screen 18 is sent from the fifth flow path pipe 35 to the head box 21 of the paper machine 40.

  A conveyor 12 for supplying waste paper or the like is attached to the pulper 14. The mixing chest 15 includes a DIP pipe 36a for supplying DIP from a deinked waste paper pulp (DIP) storage tank 15a, a CBP pipe 36b for supplying CBP from a coat broke pulp (CBP) storage tank 15b, and kraft pulp (LBKP). An LBKP pipe 36c for supplying LBKP from the storage tank 15c is attached. A first chemical injection device 50 for adding a papermaking additive is connected to the seed box 17 via a first chemical injection pipe 51. A second chemical injection device 60 for adding a strong acid is connected to the seed box 17 side of the fourth flow path pipe 34 via a second chemical injection pipe 61, and a yield drainage improver is added to the screen 18 side. A third chemical injection device 70 to be added is connected via a third chemical injection tube 71.

  A pump P is preferably provided in the middle of the first flow path pipe 31 to the fifth flow path pipe 35. In this embodiment, the pump is provided in the middle of the third flow path pipe 33 and the fourth flow path pipe 34. Each P is provided. In addition, the adjustment stage of the pulp slurry in the raw material adjustment process 10 can be set as appropriate, and the number of chests, pipes, and pumps provided between the pulper 14 and the screen 18 according to the adjustment stage of the pulp slurry is set as appropriate. do it. In the present embodiment, pulp slurry obtained by dissolving waste paper or the like with the pulper 14 is sent to the mixing chest 15, and DIP, CBP, LBKP or the like is blended with the mixing chest 15, and then the seed box 17 via the machine chest 16. The paper making additive such as sizing agent is added.

  Next, a paper manufacturing method using the paper manufacturing apparatus 1 will be described. First, in the raw material adjusting step 10, a papermaking raw material such as recycled pulp is supplied from the conveyor 12 to the pulper 14, mixed with white water supplied from the white water tank 11, and beaten with a refiner or the like to dissolve the pulp. The pulp dissolved in water is supplied to the mixing chest 15 via the first flow path pipe 31, and DIP, CBP, LBKP and the like are appropriately mixed, and white water or the like is added to obtain a pulp slurry. The obtained pulp slurry is sent to the machine chest 16 via the second flow path pipe 32 and then sent from the third flow path pipe 33 to the seed box 17.

  In the seed box 17, as an anionic papermaking additive from the first chemical injection device 50, for example, a rosin sizing agent is added in an amount of 0.02 to 1% by mass, and an anionic papermaking dye is used as a dye in an amount of 10 to 500 g. Add in the amount of / t added. Furthermore, in order to promote the fixing to pulp, such as a rosin sizing agent, aluminum sulfate is added from the chemical injection apparatus which is not shown in figure with the addition amount of 0.1-5 mass%. In addition, all addition amount is the addition ratio with respect to the mass of dry pulp.

  Next, the pulp slurry to which the papermaking additive is added is supplied to the paper machine 40 through the fourth flow path pipe 34, the screen 18 and the fifth flow path pipe 35. In the present embodiment, a fourth flow path pipe 34, a screen 18, and a fifth flow path pipe 35 each having a pump P such as a spiral pump are provided between the seed box 17 and the paper machine 40. In addition, a cleaner or the like may be provided.

  In the papermaking apparatus 1 of the present embodiment, the second chemical injection pipe 61 connected to the second chemical injection apparatus 60 is connected closer to the seed box 17 than the pump P connected in the middle of the fourth flow path pipe 34, A third medicine instructor 71 connected to the three medicine injection device 70 is connected closer to the screen 18 than the pump P. Therefore, in the present invention, an aqueous solution of nitric acid as a strong acid is added in an amount of 2 to 400 mol / t to the pulp slurry to which the additive for papermaking is added from the second chemical injection device 60 through the second chemical injection tube 61. Add as follows. Next, a yield drainage improver is further added from the third chemical injection device 70 to the pulp slurry to which the strong acid has been added via the third chemical injection tube 71. In addition, the connection position of the 2nd chemical injection pipe 61, the connection position of the 3rd chemical injection pipe 71, and the length of the 4th flow path pipe 34 are after a strong acid is added until a papermaking additive is added. The time is set to be within 5 minutes, preferably within 3 minutes, and more preferably within 60 seconds.

  In this way, in this embodiment, an anionic papermaking additive such as a sizing agent, a strong acid, and a yield drainage improver are sequentially added to the pulp slurry, and are fed from the head box 21 to form a sheet-like papermaking. Pulp 30. The paper pulp 30 is dehydrated by the wire part 22, and the filtrate generated by the dehydration is discharged from the wire part 22. This filtrate is collected by the white water pit 13 and stored in the white water tank 11. The paper pulp 30 dehydrated by the wire part 22 is further sandwiched between the rolls facing each other by the press part 23 and squeezed and dehydrated. The papermaking pulp 30 delivered from the press part 23 is dried by a dry part 24, and a surface treatment agent or the like is added as necessary to produce a paper product.

  In the present invention, by adding a strong acid to the pulp slurry before the addition of the yield drainage improver, the inhibition of the effect of the yield drainage improver by anion trash is prevented, so that the wire part 22 and the press part 23 The generated filtrate is stored in the white water tank 11 through the water collecting pipe 37 and can be recycled to the raw material adjusting step 10 through the reflux pipe 38.

  In addition, what is necessary is just to add a strong acid before a yield drainage improvement agent, and the attachment position of the 2nd chemical injection apparatus 60 which adds a strong acid is not restricted to the said embodiment. For example, you may connect the 2nd chemical injection apparatus 60 to the 3rd flow path pipe 33 as a modification of this embodiment. A pump P is provided in the middle of the third flow path pipe 33, but the second chemical injection pipe 61 connected to the second chemical injection device 60 is on the front side of the pump P, that is, on the side close to the machine chest 16. It may be connected, or it may be connected to the rear side of the pump P, that is, the side close to the seed box 17.

  Similarly, the third chemical injection device 70 to which the yield drainage improver is added is not limited to the above embodiment as long as the attachment position of the third chemical injection device 70 is the front stage of the wire part 22. Specifically, a chemical injection device may be provided in the middle of the fifth flow path pipe 35 instead of the third chemical injection device 70. In addition, as shown in FIG. 1, a third medicine injection device 70 may be provided, and a fourth medicine injection device 80 may be provided in the middle of the fifth flow path pipe 35 via a fourth medicine injection tube 81. When the third chemical injection device 70 and the fourth chemical injection device 80 are provided side by side, for example, a cationic retention drainage improver is added from the third chemical injection device 70, and the fourth chemical injection device 80 is anionic. Different kinds of chemicals may be added from the third chemical injection device 70 and the fourth chemical injection device 80, such as adding the yield drainage improver. Or you may add the same kind of, for example, a cationic retention drainage improvement agent from both the 3rd chemical injection apparatus 70 and the 4th chemical injection apparatus 80. Furthermore, the position of an anionic papermaking additive such as a sizing agent is not particularly limited.

Next, examples and comparative examples will be described. The equipment, chemicals and test methods used in the examples and comparative examples are as follows.
[Used equipment]
Yield testing machine: Dynamic filtration system (Mutek)
Sheet machine: Round sheet machine (made by Kumagai Riki Kogyo Co., Ltd.)
[Chemicals used]
Aluminum sulfate: Aluminum nitrate manufactured by Taki Chemical Co., Ltd .: Wako Pure Chemical Industries, Ltd., Wako first grade (aluminum nitrate nonahydrate, purity 99.9%)
Nitric acid: Wako Pure Chemical Industries, Ltd., Wako First Grade Sulfuric Acid: Wako Pure Chemical Industries, Ltd., Wako First Grade Hydrochloric Acid: Wako Pure Chemical Industries, Ltd., Wako First Grade Catalyzed Starch: Nippon NSC Co., Ltd., CATO-3212
Size agent: Arakawa Chemical Industries, Ltd., Size Pine NT-87
Calcium carbonate: TP-121 manufactured by Okutama Kogyo Co., Ltd.
Cationic yield drainage improver: Kurita Kogyo Co., Ltd., High Holder 222

[Example 1]
As raw materials for papermaking, 60% by mass of kraft pulp (LBKP), which is virgin pulp from hardwood collected from a paper mill, 30% by mass of deinked wastepaper pulp (DIP), which is recycled paper, Thermo, which is mechanical pulp After blending at a mechanical pulp (TMP) mass ratio of 10% (both mass ratios relative to dry pulp), tap water was added to prepare a pulp slurry with an SS concentration of 0.8 mass%. This pulp slurry is put into a dynamic filtration system (hereinafter referred to as “DFS”), and sulfuric acid, cationized starch, aluminum sulfate, sizing agent, calcium carbonate, and retention filterability improver are sequentially added to the pulp slurry. Thus, a pulp slurry for papermaking (hereinafter, “papermaking pulp slurry”) was obtained. The addition interval of each chemical was 10 seconds.

  The amounts of chemicals added are all in proportion to the dry pulp weight, sulfuric acid 50 mol / t, cationized starch 0.5% by weight, aluminum sulfate 1% by weight, sizing agent 0.25% by weight, calcium carbonate Was 15% by mass, and the yield drainage improver was 0.01% by mass. Cationized starch was added as a pulp fixing agent and paper strength enhancer, aluminum sulfate was added as a rosin sizing agent fixing agent, and calcium carbonate was added as a filler.

  The filtrate obtained by dehydrating the papermaking pulp slurry obtained by the above-described operation with DFS is collected from the DFS, and the SS concentration of the papermaking pulp slurry and the SS concentration of the filtrate are measured. The rate was determined. Moreover, from the pulp slurry for papermaking and the ash content in SS contained in the filtrate, the yield rate of the ash content was determined.

  Further, the papermaking pulp slurry was put into a round sheet machine, made into a sheet, and dried to produce a paper sheet, and the sizing degree of the paper sheet was measured.

[Example 2]
A pulp slurry for papermaking was prepared in the same manner as in Example 1 except that the chemical addition order was changed to cationized starch, aluminum sulfate, sizing agent, calcium carbonate, sulfuric acid, and yield filtration improver as Example 2. The same test as in Example 1 was performed.

[Example 3]
A pulp slurry for papermaking was prepared in the same manner as in Example 1 except that sulfuric acid was changed to hydrochloric acid as Example 3, and the same test as in Example 1 was performed.

[Example 4]
As Example 4, the same test as in Example 2 was performed except that sulfuric acid was changed to hydrochloric acid.

[Example 5]
As Example 5, the same test as in Example 1 was performed except that sulfuric acid was changed to nitric acid.

[Example 6]
As Example 6, the same test as in Example 2 was performed except that sulfuric acid was changed to nitric acid.

[Example 7]
As Example 7, the same test as in Example 6 was performed except that the amount of nitric acid added was 100 mol / t.

[Comparative Example 1]
As Comparative Example 1, the same test as in Example 1 was performed except that no strong acid was added.

[Comparative Example 2]
As Comparative Example 2, the same test as Comparative Example 1 was performed except that the amount of the yield drainage improver was doubled (0.02% by mass).

[Comparative Example 3]
As Comparative Example 3, the same test as Comparative Example 1 was performed except that the amount of aluminum sulfate added was tripled (3% by mass).

  Table 1 shows the types of additive chemicals of Examples 1 to 7 and Comparative Examples 1 to 3, the addition order addition ratio, and the test results. In Table 1, the additive chemicals are arranged from right to left in the order of addition. The cationized starch is abbreviated as “starch”, the aluminum sulfate is abbreviated as “aluminum sulfate”, and the calcium carbonate is abbreviated as “charcoal cal”.

  As shown in Table 1, in Examples 1 to 7 to which a strong acid was added, the degree of size and the yield rate were improved as compared with Comparative Examples 1 to 3 in which no strong acid was added. In particular, Example 2, Example 4 and Example 6 in which a strong acid was added after the addition of a sizing agent were used in Examples 1, 3 and 5 in which a strong acid was added before the sizing agent was added. Compared with this, the sizing degree increased more than twice, and the yield improvement effect also increased. In addition, when nitric acid was used as the strong acid, it was shown that the effect of improving the sizing degree and the yield rate was the highest.

  Since the yield rate in the case of adding a strong acid is equal to or more than that in Comparative Example 2 in which the yield drainage improver twice that of the example is added, according to the present invention, the yield drainage improver of It was shown that the amount added could be greatly reduced. Further, the sizing degree when a strong acid is added and the sizing agent is added is equivalent to Comparative Example 3 in which aluminum sulfate is added in an amount three times that of the Example. However, it was shown that the amount of aluminum sulfate added can be reduced and scale formation can be prevented. Furthermore, in this example, a cationic polymer was used alone as the yield drainage improver, but a good yield and sizing degree were obtained even with a small addition amount.

  The present invention can be used for the manufacture of paper including paperboard.

It is a schematic diagram which shows the paper manufacturing apparatus which implements the paper manufacturing process which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Papermaking apparatus 10 Raw material adjustment process 20 Papermaking process 11 White water tank 14 Pulpa 22 Wire part 23 Press part 24 Dryer part 50 1st chemical injection apparatus 60 2nd chemical injection apparatus 70 3rd chemical injection apparatus

Claims (5)

A papermaking method comprising a papermaking step of making paper and dewatering after adding a yield drainage improver having a yield improvement effect and / or a drainage improvement effect to pulp slurry,
Add an anionic papermaking additive to the pulp slurry;
After the anionic paper additive is added to the pulp slurry, a strong acid is added,
After the addition of the strong acid to the pulp slurry, papermaking method of adding the yield drainage aids. The papermaking method according to claim 1, wherein the pulp slurry includes recycled pulp and / or mechanical pulp. The papermaking method according to claim 1 , wherein the anionic papermaking additive is at least one selected from the group consisting of a rosin sizing agent, a synthetic sizing agent, and a dye. The papermaking method according to any one of claims 1 to 3, wherein the yield drainage improver is added within 5 minutes after the strong acid is added to the pulp slurry. The papermaking method according to any one of claims 1 to 4 , wherein the strong acid is nitric acid.

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