JP3166760B2 - Manufacturing method of high whiteness waste paper pulp - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high-whiteness pulp obtained by further bleaching deinked pulp (hereinafter abbreviated as DIP) obtained from used printing paper, especially newsprint.

[0002]

2. Description of the Related Art Conventionally, waste paper is a pillar of papermaking raw materials along with wood pulp (called virgin pulp) manufactured from wood.
Magazines were mainly used in newspapers and paperboard, and in fields where whiteness was not so required, such as the back layer. In general, DIP obtained by deinking used printing paper such as newspapers and magazines has low whiteness and yellowish tint, so when used for printing paper or copy paper, it gives an image of lower grade paper. The actual situation was limited. However, the demand for OA paper due to the development of OA equipment in recent years, and the accompanying sharp increase in the generation of waste paper, have developed into social problems,
There is a growing demand for the use of recycled paper in a wide variety of fields, especially paper.

Conventional deinking of used paper mainly focuses on the detachment or dispersion of the printing ink from the fibers. If dispersed finely, the whole will be dull. In this case, bleaching may be added together with the deinking agent, or bleaching may be performed after deinking, but the bleaching effect is not improved. Further, in bleaching after deinking, even if a large amount of a bleaching agent is added to forcibly increase the whiteness, the bleaching effect is poor, so that the COD in the wastewater is increased and practical use has been difficult. In recent years, offset printing has increased, and various attempts have been made to use offset printing ink because the ink is difficult to remove. However, it is extremely difficult to obtain high whiteness waste paper pulp from used newspaper. Was required.

[0004]

According to the tendency of current publications, conventional magazines mainly composed of texts are gradually decreasing, and the world is in the direction of colorization and visualization. This trend has created a vicious cycle in which printed papers are required to have higher and higher whiteness in order to enhance the printing effect, and waste paper pulp having lower whiteness is being increasingly viewed. Therefore, as described above, even if the white paper DIP is bleached to increase its whiteness, the COD of the wastewater increases,
There is a problem that it is not profitable because a large amount of capital investment is required for drainage equipment.

[0005] Another tendency of the current publishing world is that the color of paper tends to be more bluish than yellowish, and in the current bleaching, the yellowish color becomes stronger even with more chemicals. High whiteness recycled pulp could not be obtained.
The present inventors have made intensive studies and completed the present invention as a result of satisfying the conflicting performances of effective use of waste paper, high whiteness of printing paper, and reduction of drainage load.
That is, the present invention solves the above-mentioned problems, and further performs bleaching of DIP obtained from used printing paper, particularly newsprint, so that the drainage load in the bleaching process can be reduced, and a high mixing ratio that can cope with an increase in the use of recycled paper is possible. It is an object of the present invention to provide a method for producing high-whiteness waste paper pulp.

[0006]

According to the present invention, as a method for obtaining high-whiteness pulp from newspapers , the method of simultaneously performing deinking and bleaching has a limit in improving whiteness. And completely separate the deinking and bleaching processes. First, in the deinking process, the ink is removed as much as possible by using the well-known technique so far to obtain a DIP with little black whiskers or the like. Next, when bleaching this DIP, it was found that the following method was excellent as a bleaching condition under which a high whiteness was obtained and the drainage COD was small. That is, in the step of further bleaching the waste paper deinked pulp obtained by deinking newspaper waste paper, the waste paper pulp is dehydrated, and hydrogen peroxide is used as an oxidizing bleach at room temperature or warming at a pulp concentration of 25% or more. Under the mixer
Ri After mixing, soaking, further using formamidine sulfinic acid as a reduction bleaching agent, the pulp concentration 8
A process for producing high-whiteness waste paper pulp , comprising bleaching at 20% and a temperature of 50 to 100 ° C.

Various attempts have been made to obtain pulp having higher whiteness than used waste paper, and it is known that a method using a bleaching agent together with a deinking agent and bleaching after deinking are also known. It is also known that a mechanical treatment is performed with a kneader or the like at the time of deinking, but this is also for the purpose of mechanically peeling off hard-to-removable printing ink such as offset printing from the fiber. Yes, not for bleaching. For example, in Japanese Patent Application Laid-Open No. 54-120705, alkali is added together with a deinking agent in the first stage, and after soaking for 3 hours or more,
There has been proposed a deinking method for reducing black whiskers by performing a stirring treatment with a mixer or a kneader (kneader) in order to peel off the ink floating from the fibers. JP-A-55-40850 discloses that a deinking agent and a hydrogen peroxide bleaching agent are added to printed waste paper containing offset waste paper to obtain a pulp concentration of about 15% or more and a pulp concentration of 5.0 g / l (N
A deinking method of used printing paper is proposed in which a kneader, a mixer or a disperser is used at a higher alkali concentration (as aOH) and mechanical stirring is performed while applying a compressive force while heating. This proposal uses a kneader, mixer, etc. when performing deinking and bleaching at the same time,
The purpose is to peel the ink from the fibers, followed by a mechanical treatment followed by a soaking, flotation and deinking process. Further, as a further improvement,
No. -28992 proposes a deinking method of used printed paper in which mechanical stirring is performed, soaking is performed, and then mechanical stirring is performed again. However, this method also involves a flotation step following mechanical processing. Also, the main purpose is to peel off or disperse the ink from the fiber, and does not bleach the pulp after deinking to obtain a high whiteness pulp.
In the present invention, bleaching is carried out with hydrogen peroxide as an oxidizing bleaching agent, followed by bleaching with formamidine sulfinic acid (hereinafter abbreviated as FAS) as a reducing bleaching agent.

[0008] A proposal for the use of FAS has been conventionally known. Japanese Patent Application Laid-Open No. 61-194289 discloses a method using a chemical consisting of thiourea dioxide (identical to FAS) and an alkaline agent to reduce waste paper to 40 to 40%.
This is a method of recycling used paper that is digested at a temperature of 80 ° C., in which reductive decolorization of colored ink having strong resistance to an alkali agent and bleaching of used paper fibers are performed at the same time.
There is a disadvantage that the processing time is long at 0 ° C. for 3 to 5 hours. Also,
JP-A-62-276094 discloses that a pulp-colored paper and a pressure-sensitive copying paper (carbonless paper) have a pulp concentration of 2 to 2.
It is a method of decolorizing using FAS at 20% and a temperature of 20 to 80 ° C. However, paper colored with pulp with a dye or carbonless paper is not effective with a normal deinking method, so it is decolorized using FAS. It is not intended for used printed paper.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The manufacturing method of the present invention will be described below. The present inventors first examined the oxidative bleaching of DIP. As the hydrogen peroxide addition rate was increased, the whiteness increased to some extent.
The OD increases rapidly, and it cannot be practically used industrially. In order to reduce wastewater COD, it is effective to increase the pulp concentration during bleaching as high as possible and reduce the components eluted in the wastewater.However, when examining the relationship between pulp concentration during bleaching and whiteness, Although the whiteness improves as the pulp concentration increases, the whiteness does not increase even if the concentration is increased to 30 to 40%. The present inventors have noted that the cause of saturation of the increase in whiteness is that the contact between pulp fiber and hydrogen peroxide as a bleaching agent is insufficient due to the high pulp concentration. A method in which hydrogen peroxide is uniformly contacted with pulp, that is, DIP is dehydrated to a high concentration of 25% or more, and after adding hydrogen peroxide,
A method of bleaching at room temperature or under heating with a single-shaft or two-shaft high-speed, high-concentration mixer (hereinafter, in the present invention, a mixing machine generally called a mixer or a processor is generally called a mixer). Thought.

A mixer or kneader usually used in the deinking process desirably applies a compressive force to the pulp or applies moderate friction to the fibers in order to peel off the ink from the fibers. It is preferable to use a kneader or disperser, a twin-screw mixer, etc., which have a moderate bite between the blades and give sufficient compressive force or friction to the fiber at a low speed, and that the processing temperature is high because the ink tends to fall off. Is common. However, in the present invention, rather than imparting a compressive force or friction to the fiber,
The purpose of the mixer is to uniformly mix the bleaching agent with the high-concentration pulp. A type that can be uniformly mixed in a short time is preferable.
Therefore, if one axis, the rotor has a feed blade and a return blade,
The most preferable is a my car processor (manufactured by Ishikawajima Sangyo Kikai Co., Ltd.), which is a one-axis mixer that can rotate at a high speed and has a sufficient clearance between the stator blades. It may be a pulper. Furthermore, since the processing temperature is not the purpose of removing the ink,
It is not always necessary to be at a high temperature, and a sufficient mixing effect can be recognized even at room temperature.

As described above, in the conventional bleaching method, the increase in whiteness stops at a soaking concentration (pulp concentration at the time of soaking) of 20%, but in the present invention, the soaking concentration is 25% to 30% or more. Whiteness was found to increase. Therefore, in the present invention, the obtained D
If the whiteness of IP is the same, the amount of alkali used and the amount of H ₂ O ₂ used can be reduced as compared with the conventional bleaching method, and the COD of waste water can be reduced by half.

As described above, when bleaching DIP with hydrogen peroxide, high-speed mixer processing at high concentration and high-concentration soaking can provide wastepaper pulp having a whiteness of 70 or more without increasing drainage load. It is a feature of the present invention to use a reducing bleach to further increase the whiteness of this, and formamidine sulfinic acid (FAS) is used as the reducing bleach. Hydrosulfite is usually used as a reducing bleaching agent. However, this agent is easily oxidized, and if the pulp concentration is high, the chance of contact with oxygen in the air increases, which is not preferable. Bleached. At such a low concentration, the amount of water is large even if the amount of hydrosulfite added is increased in order to increase the whiteness, so that the amount of pulp cannot be so large, and the improvement in whiteness is limited. There is also a large color return after bleaching.

Therefore, the present inventors considered the use of formamidine sulfinic acid (FAS) as one of the reducing bleaching agents. FAS, also called thiourea dioxide, is a white powder that is stable at room temperature and has no reducibility, but decomposes with heat or alkali to generate sulfinic acid and exerts a strong reducing power. Therefore, unlike a hydrosulfite, there is no fear of oxidative decomposition, and a high whiteness that cannot be obtained with a hydrosulfite can be obtained by adding an alkali after adding FAS and heating.

In the present invention, pulp obtained by oxidatively bleaching DIP with hydrogen peroxide and further subjected to reduction bleaching by FAS are as follows. That is, since FAS is more stable than hydrosulfite, whiteness is more improved when the pulp concentration is 15% than when the concentration is as low as about 4%, but is reduced when the concentration is 30%. % Is preferred. As with hydrosulfite, the decrease is caused by air oxidation. Even when the concentration is 30%, there is no decrease in whiteness when air is replaced with nitrogen. As a result of testing at 40 ° C., 60 ° C., and 80 ° C., the reaction temperature is most preferably 80 ° C., but in the present invention, it may be practically in the range of 50 to 100 ° C. The reaction time significantly increases in whiteness in 15 minutes, increases sufficiently in 60 minutes, and decreases in whiteness when treated for 24 hours. Therefore, a preferable range is 10 to 90 minutes. The pulp bleached with FAS has a tendency to have a bluish tint compared to the pulp bleached with H ₂ O _{2, and} a pulp having a high whiteness that matches the current tendency of the publishing industry can be obtained. It is effective that the used printing paper used as the raw material of the DIP used in the method for obtaining high whiteness used paper pulp of the present invention is used newspaper paper. The method of the present invention is characterized in that DIP obtained by deinking newspaper waste paper is further bleached to obtain a high whiteness pulp having a whiteness of 75 or more. Is something that could not be done before. The DIP used in the method of the present invention may be a DIP that has been deinked by a conventionally known deinking method. is there.

[0015]

Examples of the present invention will be described below. Adjustment of DIP Waste newspaper was deinked by the following conventional deinking method. Add water to offset-printed newspaper waste paper and disintegrate it with a test pulper to a concentration of 5%.
_Hl%, agitated with the addition of Na 2 _SiO 3 4%, and surfactant (manufactured by Toho Chemical Industry (Ltd.) FT301A) 0.3%, and dewatered to 20%. In addition, NaOH 2%
Na ₂ SiO ₃ 6% and a surfactant (the FT301
A) 0.1% and 2% of hydrogen peroxide (with a concentration of 60%) were added, and soaking was performed at a temperature of 45 ° C. for 1 hour. After soaking, the resultant was diluted to a concentration of 4%, further diluted to 1%, subjected to a flotation treatment using a test flotator for 20 minutes, and dehydrated to obtain DIP. The whiteness of the obtained DIP was 62%. Using this DIP, oxidation bleaching and reduction bleaching of the present invention were performed.

REFERENCE EXAMPLE 1 Reference Example 1 corresponds to the pretreatment of each of the following examples. The DIP obtained above was converted into a 30% aqueous slurry, and H ₂ O ₂ was converted into DIP (air-dried). ) Was passed through a My Car Processor (manufactured by Ishikawajima Sangyo Kikai Co., Ltd.) and mixed well, and then bleached at a soaking concentration of 30% for 3 hours. Wastewater CO
Table D shows the whiteness of D and the resulting bleached DIP.

Comparative Example 1 A bleached DIP was obtained in the same manner as in Reference Example 1 except that a test kneader was used in place of the my car processor. Comparative Example 2 A bleached DIP was obtained in exactly the same manner as in Reference Example 1, except that mixing and bleaching were performed with the pulp concentration of DIP being 20%.

Example 1 DIP oxidized and bleached with hydrogen peroxide obtained in Reference Example 1 was adjusted to a pulp concentration of 15%, and
AS was added in an amount of 0.5% based on DIP (air-dry weight), and bleached at a temperature of 80 ° C. for 60 minutes to obtain reduced bleached DIP.

Example 2 The DIP oxidized and bleached with hydrogen peroxide obtained in Reference Example 1 was replaced with FAS in Example 1.
Was reduced and bleached in exactly the same manner as in Example 1 except that 0.2% was added to DIP.

Example 3 A DIP oxidized and bleached with hydrogen peroxide was obtained in the same manner as in Example 1 except that the pulp concentration was changed to 25%. The amount of FAS added is 0.2
% And a pulp concentration of 20%, and a reduction-bleached DIP was obtained in exactly the same manner as in Example 1.

[Embodiment 4] In Reference Example 1, the temperature was set to 70
Except that bleaching with H ₂ O ₂ was carried out at 0 ° C., an oxidatively bleached DIP was obtained in exactly the same manner as in Reference Example 1, and this DIP was further obtained.
In Example 1, the amount of FAS added was 0.2
% And a pulp concentration of 8%, and a reduction bleached DIP was obtained in the same manner as in Example 1.

Example 5 The DIP oxidized and bleached with hydrogen peroxide obtained in Reference Example 1 was prepared in the same manner as in Example 1 except that the amount of FAS was 0.2% of DIP and the temperature was 40 ° C. DIP reduced and bleached was obtained in exactly the same manner as in Example 1.

Example 6 DIP oxidized and bleached with hydrogen peroxide obtained in Reference Example 1 was used except that the amount of FAS added was 0.2% of DIP and the bleaching time was 15 minutes in Example 1. DIP reduced and bleached exactly as in Example 1.
I got

Example 7 DIP oxidized and bleached with hydrogen peroxide obtained in Reference Example 1 was used except that the amount of FAS added was 0.2% of DIP and the bleaching time was 180 minutes in Example 1. DI reduced and bleached exactly as in Example 1.
P was obtained.

Comparative Example 3 The DIP oxidized and bleached with hydrogen peroxide obtained in Reference Example 1 was replaced with sodium hydrosulfite (concentration: 4%) in place of FAS used in Example 1 by 1% with respect to DIP. Add, temperature 50 ° C, time 6
A reduction bleached DIP was obtained in exactly the same manner as in Example 1 except that the reduction bleaching was performed in 0 minutes.

Comparative Example 4 A pulp obtained by oxidative bleaching with hydrogen peroxide in exactly the same manner as in Reference Example 1 was subjected to oxidative bleaching again in exactly the same procedure as in Reference Example 1 with a pulp concentration of 30%. Then, a two-stage oxidation bleached DIP was obtained. Table 1 shows the results obtained in Comparative Examples 1 and 2, Examples 1 to 7 and Comparative Examples 3 and 4.

[0027]

[Table 1]

[Test Method] Wastewater COD Pulp whiteness measured by JIS K0101 Measured by photovolta meter Color tone Measured by Murakami colorimeter According to the results shown in Table 1, the oxidative bleaching method using hydrogen peroxide of the present invention was carried out. As a result of applying to the bleaching of DIP obtained by a normal deinking method (Reference Example 1), a pulp having a relatively high whiteness of 76 was obtained, which was mixed and bleached with a conventional kneader (Comparative Example) Compared with 1), the whiteness was improved by 2 points, and the COD of waste water was reduced by almost half. Further, when bleaching is performed at a pulp concentration of 20% (Comparative Example 2), the whiteness is slightly lowered. According to the method of the present invention, DIP bleached by the oxidative bleaching method using hydrogen peroxide is further subjected to reduction bleaching by FAS (Example 1), and the pulp brightness is 81 points and exceeds 80, and the amount of FAS added is 0.2. % (Example 2)
However, a whiteness of 80 was obtained, and a whiteness of 79 was obtained by oxidative bleaching with hydrogen peroxide at a pulp concentration of 25% (Example 3).

Pulp temperature of reduction bleaching is 8% (Example 4)
When the bleaching is performed, the whiteness is reduced by one point from Examples 1 and 2, and when the temperature of the reduction bleaching is set to 40 ° C. (Example 5), the whiteness is reduced by nearly 3 points. Is more preferably 10% or more, and the temperature is more preferably 50 ° C. or more. Further, reduction bleaching time is 15 minutes (Example 6).
The whiteness is 79 and is preferably 10 minutes or more, but if it is too long as 180 minutes (Example 7), the whiteness is rather lowered. Therefore, it is preferable to keep the whiteness at about 90 minutes. The whiteness of the DIP which was oxidized and bleached with hydrogen peroxide of the reference example and bleached with a conventional hydrosulfite (Comparative Example 3) was increased by only about 1 point. Further, the oxidative bleaching of Reference Example 1 is repeated in two stages (Comparative Example 4).
Then, the whiteness is lower than in Example 1 in which reductive bleaching by FAS is performed in the subsequent stage, the tint is yellow, and the wastewater COD increases.

[0030]

As described above, according to the production method of the present invention, the DIP obtained from used printing paper, particularly newsprint, is oxidized and bleached with hydrogen peroxide and reduced and bleached with FAS to reduce the drainage load in the bleaching process. It is possible to obtain a high whiteness pulp that can be reduced and that can be blended at a high rate that can cope with an increase in the use of recycled paper.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-276094 (JP, A) JP-A-2-2344991 (JP, A) JP-B-53-1362 (JP, B1) “PULP & PAPER CAN ADA 90:10 "(1989) 95-101 (58) Fields investigated (Int. Cl. ⁷ , DB name) D21C 5/02 D21C 9/10-9/16

Claims (1)

(57) [Claims] In the step of further bleaching the deinked pulp obtained by deinking newspaper waste paper, the waste paper pulp is dewatered, and hydrogen peroxide is used as an oxidative bleach at a pulp concentration of 25% or more. After mixing with a mixer at room temperature or under heating,
Soaking, and further using formamidine sulfinic acid as a reducing bleach, pulp concentration of 8 to 20%, hot
A method for producing high whiteness waste paper pulp , comprising bleaching at a temperature of 50 to 100 ° C.