JPH0450391A - Production of waste paper pulp having high - Google Patents

Abstract

PURPOSE:To obtain the subject pulp enabling the reduction of waste water load in bleaching process and capable of compounding at a high ratio to cope with the increase in the use of regenerated paper by dewatering deinked waste paper pulp, mixing with an oxidation-type bleaching agent and bleaching the pulp at a prescribed soaking concentration. CONSTITUTION:Deinked waste paper pulp produced by deinking waste printed paper is dewatered, mixed with an oxidation-type bleaching agent with a single-or twin-shaft high-speed highconcentration mixer or processor at a pulp concentration of >=25% at normal temperature or under heating and bleached at a soaking concentration of >=25% to obtain the objective pulp. The bleaching agent is preferably hydrogen peroxide and the mixing is carried out preferably with a single-shaft high-speed mixer or processor.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to the production of high whiteness waste paper pulp obtained by further bleaching deinked pulp (hereinafter abbreviated as DIR) obtained from printed waste paper, especially used newspaper paper. Regarding the method.

[Conventional technology] Waste paper has traditionally been a mainstay of papermaking raw materials along with wood pulp (called virgin pulp), which is made from wood. Waste paper is mainly made from cardboard, and newspapers and magazines are made from newspaper and magazines. It was mainly used in areas where high brightness is not required, such as the inside and surface layers of paperboard. In general, DIR, which is made by deinking old printed paper such as newspapers and magazines, has a low degree of whiteness and has a rather yellowish tinge, so when used for printing paper or copy paper, it gives the impression of being a low-grade paper. The reality is that the field of use is inevitably limited.

However, the increase in demand for OA paper due to the recent development of OA equipment and the resulting dramatic increase in waste paper generation has developed into a social problem, and the demand for the use of recycled paper in a wide range of fields, especially OA paper, has increased. It is coming.

However, conventional deinking of used paper focuses on removing or dispersing the 11I printing ink, and if hard-to-remove ink remains, it will become a black beard, and if the ink is finely dispersed, the overall The actual situation was that the bleaching effect became dull and the bleaching effect was not improved regardless of whether bleach was added together with a deinking agent or bleaching was performed after deinking. Further, in bleaching after deinking, even if a large amount of bleaching agent is added to forcefully increase the whiteness, the bleaching effect is poor and the COD in the waste water increases, making it difficult to put it into practical use. Offset printing has become popular in recent years, and the ink from offset printing waste paper is difficult to remove, so
Although various efforts have been made, it is extremely difficult to obtain waste paper pulp with high whiteness from used newspapers, and a solution to this problem has been sought.

Looking at current trends in publications, traditional text-based magazines are gradually shrinking, and the world is moving toward color and visualization. This trend has created a vicious cycle in which printing paper is required to have increasingly high whiteness in order to improve printing efficiency, and waste paper pulp with low whiteness is increasingly ignored.

Therefore, even if an attempt is made to increase the whiteness by bleaching the DIR of waste paper, as mentioned earlier, there is a problem that the COD of the wastewater increases and a huge capital investment is required for drainage equipment, making it unprofitable. .

In addition, another trend in the current publishing world is that the color of paper tends to be more blue than yellow, and with current bleaching methods, even if a large amount of chemicals are used, the yellowing becomes stronger, so high whiteness It was not possible to obtain waste paper pulp.

[Problems to be Solved by the Invention] As a result of intensive research, the present inventors have developed the present invention in order to satisfy the conflicting performance of effectively utilizing waste paper, increasing the whiteness of printing paper, and reducing wastewater load. This is what I saw when it was completed.

That is, the present invention solves the above-mentioned problems, further bleaches DIR obtained from printed waste paper, especially used newspaper paper, reduces the wastewater load in the bleaching process, and enables high-ratio blending that can accommodate the increased use of recycled paper. The purpose of the present invention is to provide a method for producing high whiteness waste paper pulp.

[Means for Solving Problem 1] In the present invention, as a method for obtaining pulp with high whiteness from printed waste paper, there is a limit to the improvement of whiteness with a method of simultaneously performing deinking and bleaching. Completely separate the process and bleaching process. In the deinking step, conventionally known techniques are used to remove as much ink as possible to obtain DIR with fewer black whiskers and the like. Next, when bleaching this DIR, as a bleaching condition that provides high whiteness and low wastewater COD, an oxidizing bleach is added to the DIR that has been dehydrated to a pulp density of 25% or more at room temperature or under heating. Axis or 2-axis high speed
Mix using a high concentration mixer or processor,
A method of bleaching with a soaking concentration of 5% or more, followed by bleaching with an oxidizing bleach, and then using formamidine sulfinic acid (hereinafter abbreviated as FAS) as a reducing bleach, with a pulp concentration of 10 to 20%, 10 at a concentration of 50-100℃
By combining the method of bleaching for ~90 minutes, we have completed a manufacturing method that can obtain waste paper pulp with high whiteness.

Various attempts have been made to obtain pulp with high brightness from printed waste paper, and methods of using a bleaching agent together with a deinking agent and bleaching after pA inking are also known.

It is also known that mechanical processing is performed using a kneader or the like during deinking, but this is also done for the purpose of mechanically peeling off difficult-to-remove printing inks such as offset printing from the fibers. And not for bleaching.

For example, in JP-A-54-120705, an alkali is added together with a deinking agent in the first stage, and after soaking for 3 hours or more, a mixer or kneading machine is used to remove the ink that has risen from the fibers. We have proposed a deinking method that aims to reduce black whiskers by performing a stirring process using a kneader.

Furthermore, in JP-A No. 55-40850, a deinking agent and a hydrogen peroxide bleaching agent are added to printed waste paper containing offset waste paper, and a pulp density of about 15% or more and 5.0 g/jI
At an alkali concentration of (as NaOH) or higher,
We have proposed a method for deinking printed waste paper using a kneader-mixer or a disperser, which performs mechanical agitation while applying compressive force under heating. This proposal uses a kneader, mixer, etc. to perform deinking and bleaching at the same time, but the purpose is to peel the ink from the fibers, and after mechanical treatment, soaking, flotation, and desorption are performed. The ink process continues. In addition, as a further improvement, JP-A-6
No. 3-28992 proposes a deinking method for printed waste paper that involves mechanical stirring, soaking, and then mechanical stirring again, but this also involves a flotation process following the mechanical treatment. All of these methods focus on peeling or dispersing ink from fibers, and do not bleach the deinked pulp to obtain high whiteness pulp.

In the present invention, following the above-mentioned bleaching with the oxidizing bleach, bleaching with the reducing bleach FAS is also carried out.

The proposal to use FAS has been known for a long time, and was published in Japanese Patent Application Laid-Open No. 1986-198.
No. 4289 is a waste paper recycling method that uses a chemical consisting of thiourea dioxide (same as FAS) and an alkaline agent to digest the waste paper at a temperature of 40 to 80°C, and uses a colored ink that has strong resistance to alkaline agents. This method simultaneously performs reductive decolorization and bleaching of waste paper IN, but at a processing temperature of 60℃,
The drawback is that it takes a long time and processing time. Also, JP-A-62-
No. 276094 discloses a method of decolorizing pulp-colored paper and pressure-sensitive copying paper (carbonless paper) using FAS at a pulp concentration of 2 to 20% and a temperature of 20 to 80°C. Normal deinking methods have no effect on colored paper or carbonless paper, so FAS is used to decolorize them, and it is not intended for used printed paper.

The manufacturing method of the present invention will be explained below.

The present inventors first investigated oxidative bleaching of DIR, but when the hydrogen peroxide addition rate was increased, the whiteness increased to some extent, but as the addition rate increased, the wastewater COD increased rapidly, and it is not practical for industrial use. It cannot be used for

In order to reduce wastewater COD, it is effective to make the pulp concentration as high as possible during bleaching and to reduce the components eluted into the wastewater. However, when examining the relationship between pulp concentration during bleaching and whiteness, As the pulp concentration increases, the whiteness improves, but even if the concentration increases to 30 to 40%, the whiteness does not increase.

The present inventors focused on the fact that the reason why these whiteness increases become saturated is that the contact between the pulp fibers and the bleach is insufficient due to the high pulp concentration. In other words, DIR is dehydrated to 25%
We devised a method in which the bleaching agent is added to the above-mentioned high concentration, and then bleached at room temperature or under heating in a high-speed, high-density mixer or processor with one or two screws.

The mixer and kneader normally used in the deinking process strip the ink from the fibers, so it is desirable to apply compressive force to the pulp or to receive moderate friction between the fibers. It is usually preferable to use a kneader or disperser twin-shaft mixer that has a moderate amount of biting in the fibers, applies sufficient compressive force or friction to the fibers at low speed, and also has a high processing temperature because the ink will easily fall off. be.

However, in the present invention, the purpose is not to apply compressive force or friction to the fibers, but to uniformly mix the bleaching agent into high-density pulp, so the mixer or processor used is designed to avoid applying friction to the fibers. It is preferable to use a type that has sufficient space between one or two shafts and can rotate at high speed to uniformly mix in a short time.

Therefore, if it is a single shaft, the rotor has a feed blade and a return blade,
Most preferable is a mica processor that has a sufficient gap between the blades of the stator and rotates at high speed, and may also be a floater pulper that has two shafts with a wide space and can rotate at high speed. Furthermore, since the purpose of the treatment is not to remove the ink, it does not necessarily have to be a high temperature, and the mixing effect can be sufficiently observed even at room temperature.

As already mentioned, in the conventional bleaching method, the increase in whiteness stops when the soaking concentration is 20%, but in the present invention, it has been found that the whiteness increases even at a soaking concentration of 30% or more.

Therefore, in the present invention, if the whiteness of the DIR obtained is the same, the amount of alkali used and the amount of H2O2 used can be reduced compared to the conventional bleaching method, and the wastewater COD can be reduced by half. .

As mentioned above, when bleaching DIR with an oxidizing bleach,
It was found that high-speed mixer treatment at high concentration and high-concentration soaking can yield waste paper pulp with a whiteness of 70 or higher without increasing the wastewater load, but to further increase the whiteness, it is necessary to use a reducing bleach. preferable.

Hydrosulfide is usually used as a reducing bleach, but this agent is easily oxidized, and if the pulp concentration is high, there will be more opportunities for it to come into contact with oxygen in the air, which is undesirable, so it is usually used at a pulp concentration of about 4%. Bleached. With such a low concentration, even if you try to increase the amount of hydrosulfide added to achieve high whiteness, the amount of water will be large, so you cannot increase the amount of hydrosulfide that much relative to the pulp, and there is a limit to the improvement of whiteness. Yes, and the color reversion after bleaching is also great.

Therefore, the present inventors considered the use of formamidine sulfinic acid (FAS) as one of the reducing bleaching agents.

FAS, also known as thiourea dioxide, is a stable white powder with no reducing properties at room temperature, but it decomposes with heat or alkali to generate sulfinic acid and exhibits strong reducing power.

Therefore, unlike hydrosulfide, there is no fear of oxidative decomposition, and by adding an alkali and heating after adding FAS, a high degree of whiteness that cannot be obtained with hydrosulfide can be obtained.

The conditions for further bleaching the DIP oxidation bleached pulp of the present invention with FAS are as follows.

That is, since the pulp concentration is more stable than hydrosulfide, the whiteness is improved at 15% than at 4%, but when the pulp concentration is 30%, the whiteness is improved.
%, it decreases, so 10 to 20% is preferable. The whiteness decreases at higher concentrations due to air oxidation, as with hydrosulfide, and even at a concentration of 30%, there is no decrease in whiteness if the air is replaced with nitrogen.

Further, as a result of testing the reaction temperature at 40'C, θ0C, and 80C, 80C was the best, but in the present invention, a range of 50 to 10C (1C) is sufficient for practical purposes.

The reaction time is preferably 10 to 90 minutes, since the whiteness increases considerably after 15 minutes, sufficiently increases after 60 minutes, and decreases after 24 hours.

The pulp bleached with FAS tends to have a bluish tinge compared to the pulp bleached with H2O2, and it is possible to obtain a pulp with a high brightness that matches the current preference of the plate printing industry.

It is effective to use old newspaper as the printed waste paper used as a raw material for DIR used in the method of bleaching DIR to obtain high whiteness waste paper pulp of the present invention. The method of the present invention is characterized in that a high whiteness pulp with a whiteness of 75 or more can be obtained by further bleaching DIR obtained by deinking old newspaper, and such high whiteness pulp can be obtained from old newspaper with a low whiteness. This is something that could not be achieved in the past.

The DIP used in the method of the present invention may be DIR deinked by a conventionally known deinking method, but it is natural that it is preferable to use DIR deinked by a deinking method that yields as high a degree of whiteness as possible. be.

[Example] Examples of the present invention are shown below.

DIR Adjustment Waste newspaper was deinked using the conventional deinking method described below. Add water to offset printed newspaper waste paper and disintegrate it with a test pulper to a concentration of 5%.
After adding 1% H, 51034% Na, and 0.3% surfactant (Toho Chemical Industry - FT301A>0.3%) and stirring, the mixture was dehydrated to a concentration of 20%.Furthermore, 1.- Add 2% NaOH to the mixture.
, Na25i036%, surfactant (above) 0.1%,
Add 2% H2O2 (assuming a concentration of 60%) and raise the temperature to 45℃
Soaked for an hour.

After soaking, the solution was diluted to a concentration of 4%, further diluted to 1%, subjected to flotation treatment for 20 minutes using a test floatator, and dehydrated to obtain DIR.

The whiteness of the obtained DIR was 62%.

Oxidative bleaching and reductive bleaching of the present invention were performed using this DIR.

Example 1 The DIR obtained above was made into an aqueous slurry with a concentration of 30%, and H
4% of 2O2 was added to DIP (Jll dry), passed through a mica processor and thoroughly mixed, and then bleached at a soaking concentration of 30% for 3 hours. The COD of the waste water and the whiteness of the resulting DIR after bleaching are shown in the table.

(The following is a blank space) Comparative Example 1 A bleached DIP was obtained in exactly the same manner as in Example 1 except that a test kneader was used instead of the mica processor.

Comparative Example 2 DIPIE:45P was bleached in exactly the same manner as in Example 1 except that the DIR pulp concentration was 20% and mixing and bleaching were performed.

Example 2 The oxidatively bleached DIR obtained in Example 1 was prepared at a pulp density of 1.
5%, FAS is 0.5 to DIR (air dry weight)
% was added and bleached at a temperature of 80° C. for 60 minutes to obtain reductively bleached DIR.

Example 3 The oxidatively bleached DIR obtained in Example 1 was used to obtain reductively bleached DIP in exactly the same manner as in Example 2, except that 0.2% of FAS was added to DIF). Ta.

Example 4 Oxidatively bleached D[P was obtained in exactly the same manner as in Example 1 except that the pulp concentration was changed to 25%, and this DIP was further processed in Example 2 by changing the amount of FAs added to DIR.
Reduction bleached DIR was obtained in exactly the same manner as in Example 2 except that the pulp concentration was 0.2% and the pulp concentration was 20%.

Example 5 D was oxidatively bleached in exactly the same manner as in Example 1, except that bleaching with H2O2 was carried out at a temperature of 70°C.
fP is obtained, and further this DIR is applied to FAS in Example 2.
DIR was reductively bleached in the same manner as in Example 2 except that the amount added was 0.2% to DIP and the pulp concentration was 8%.
I got it.

Example 6 The oxidatively bleached DIR obtained in Example 1 was treated in Example 2 with an FAS addition amount of 0.2% relative to DIP and a temperature of 40%.
Reduction bleached DIR was obtained in exactly the same manner as in Example 2 except that the temperature was changed to .degree.

Example 7 The oxidatively bleached DIR obtained in Example 1 was treated in exactly the same manner as in Example 2, except that the amount of FAS added was 1.2% relative to DIR and the bleaching time was 15 minutes. Reduction bleached DIP & obtained.

Example 8 The oxidatively bleached DIR obtained in Example 1 was reduced in exactly the same manner as in Example 2, except that the amount of FAS added was 0.2% with respect to DIR and the bleaching time was 180 minutes. A bleached DIR was obtained.

Example 9 The oxidatively bleached DIR obtained in Example 1 was treated in Example 2 with the addition of 1% sodium hydrosulfide (4% at a time) to DIP in place of FAS, at a temperature of 50°C.
A reductive bleached DIP was obtained in the same manner as in Example 2 except that the reductive bleaching was performed for 60 minutes.

Example 10 The pulp obtained by oxidative bleaching in exactly the same manner as in Example 1 was subjected to oxidative bleaching again in exactly the same manner as in Example 1 at a pulp concentration of 30%, and was subjected to two-stage oxidative bleaching. D.I.R.
I got it.

The results obtained in Comparative Examples 1 and 2 and Examples 2 to 10 are shown in the table.

Test Method Wastewater COD JIS KO101&:Pulp Whiteness Measured by Photovolt Meter Color Tone According to the results shown on the clothes measured by Murakami Color Difference Meter, D
As a result of applying IR to bleaching (Example 1), a high whiteness pulp with a whiteness of 76 could be obtained, and the whiteness was 2 points higher than that of pulp mixed and bleached using a conventional kneader (Comparative Example 1). Moreover, the wastewater COD was reduced by almost half.

In addition, when bleaching is performed at a pulp concentration of 20% (Comparative Example 2)
Whiteness is slightly reduced.

When DIR bleached by the oxidative bleaching method of the present invention is further subjected to reductive bleaching using FAS (Example 2), the pulp brightness is 81.
A whiteness of 80 can be obtained even when the amount of FAS added is 0.2% (Example 3), and a whiteness of 79 is obtained even when oxidative bleaching is performed at a pulp concentration of 25% (Example 4).

When reductive bleaching is performed at a pulp concentration of 8% (Example 5), the whiteness decreases by 1 point, and when the reductive bleaching temperature is 40°C (Example 6), the whiteness decreases by nearly 3 points.
It is more preferable that the pulp concentration in reduction bleaching is 10% or more and the humidity is 50° C. or more.

Further, the reductive bleaching time was 15 minutes (Example 7), and the whiteness was 79.
Therefore, it is preferable that the time is 10 minutes or more, but if it is too long, such as 180 minutes (Example 8), the whiteness will actually decrease, so it is preferable to keep it at about 90 minutes.

When the DIP subjected to the oxidative bleaching of the present invention is bleached with conventional hydrosulfide (Example 9), the whiteness increases by only about 1 point.

In addition, when the oxidative bleaching of the present invention is repeated in two stages (Example 10), Example 2 where reductive bleaching with FAS is performed in the latter stage.
The whiteness is lower, the color is yellowish, and the amount of wastewater COD increases.

[Effects of the Invention] The manufacturing method of the present invention performs oxidative bleaching or oxidative bleaching and reductive bleaching using FAS on DIR obtained from printed waste paper, particularly used newspaper paper, thereby reducing the wastewater load in the bleaching process and increasing the use of recycled paper. It is possible to obtain a high whiteness pulp that can be blended at a high rate and is compatible with the following.

Claims (1)

[Scope of Claims] 1. In the step of further bleaching the deinked pulp of used paper obtained by deinking the printed waste paper, dewatering the deinked pulp of the used paper;
A high-density bleaching agent characterized by mixing an oxidizing bleach with a pulp concentration of 25% or more in a single- or twin-shaft high-speed, high-density mixer or processor at room temperature or heating, and then bleaching with a soaking concentration of 25% or more. Method for producing whiteness waste paper pulp. 2. The production of high brightness waste paper pulp according to claim 1, characterized in that hydrogen peroxide is used as the oxidative bleaching agent and a single-shaft high-speed mixer or processor is used as the high-speed, high-concentration mixer or processor. Method. 3. The high whiteness waste paper pulp according to claim 1 or 2, characterized in that the waste paper deinked pulp is mixed with an oxidizing bleach and then bleached, and then bleached using formamidine sulfinic acid as a reducing bleach. manufacturing method. 4. After bleaching the deinked waste paper pulp with an oxidizing bleach, use formamidine sulfinic acid as a reducing bleach, pulp concentration 10-20%, temperature 50-100°C
3. The method for producing high whiteness waste paper pulp according to claim 1 or 2, wherein bleaching is carried out for 10 to 90 minutes. 5. Claim 1, 2, 3 or 4, wherein the printed waste paper is used newspaper paper.
The method for producing the high whiteness waste paper pulp described above.