JPH0649792A - Method for treating waste paper - Google Patents

Abstract

PURPOSE:To obtain deinked pulp having high whiteness, reduced in the number of remaining inks and non-peeled inks, and used for printing, when news paper or high quality waste paper is deinked. CONSTITUTION:In the deinking treatment of news paper or high quality waste paper, a process comprising washing, kneading the washed waste paper in the presence of one or more kinds from among hydrogen peroxide, NaOH, sodium silicate and a deinking agent, bleaching the kneaded product and subsequently subjecting the bleached product to a flotation treatment is repeated twice or three times. In these processes, 30-70wt.% of the bleaching agent to be added in the first stage is added in the first stage, and a micro processor is used as a device for performing the kneading.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a used paper processing method used for recycling used paper. More specifically, when deinking newspaper and high-quality waste paper, high whiteness and residual ink,
The present invention relates to a used paper treatment method for obtaining a deinked pulp for printing with a small number of unpeeled inks.

[0002]

2. Description of the Related Art Conventionally used high-quality waste paper is mainly used for toilet paper, and then used for white paper, magazines and other lower grade paper, and for facial tissue. Recently, the waste treatment of high-quality waste paper discharged from OA equipment has become a problem, and its reuse is demanded rapidly.
However, in order to use deinked pulp for high-quality paper instead of bleached pulp, it is necessary to select deinking treatment equipment and treatment conditions.

For example, in Japanese Unexamined Patent Publication (Kokai) No. 54-120705, an alkali is added together with a deinking agent in the first step, and after aging for 3 hours or more, a kneader is used to peel off the ink floating from the pulp fiber. Has proposed a deinking method for reducing the residual ink by performing the nidding process.
In the publication, the term "aging" means that a deinking agent such as a surfactant is added to a builder such as NaOH or sodium silicate, and the deinking is performed by staying at room temperature or under heating for a certain period of time. It means to promote black ink (including the case where hydrogen peroxide is added and simultaneously bleached). This corresponds to the holding in the reaction tank in the second step of the present invention. Nee
Ding means that various mechanical stresses are applied to the ink adhered to the pulp fibers by printing, the coating liquid, etc. to separate the ink from the fibers and to subdivide the ink. say. This corresponds to the application of shearing force to the stock in the second step of the present invention.

Further, in JP-A-55-40850,
Add deinking agent and H ₂ O ₂ bleach to waste printing paper by offset printing, pulp concentration of about 15% or more and 5.0 g
It proposes a method for deinking used waste paper using a kneader at an alkali concentration of 1 / l (as NaOH) or higher and applying a compressive force under heating. This proposal uses a kneader or the like when simultaneously performing deinking and bleaching, but its purpose is to separate the ink from the pulp fiber, and to aged and float after kneading. -Sequence and deinking process continues. In the publication, "floatation" means removing ink by foaming separation by adding a deinking agent, a builder, etc., and an apparatus therefor is called "floater". This corresponds to the third step of the present invention.

Further, as an improvement thereof, JP-A-63-28
Japanese Patent No. 992 proposes a method for deinking printed waste paper which is matured after kneading and then kneaded again, but this also focuses on peeling or dispersing the ink from pulp fibers. There is. Particularly, in this case, the residual ink of the waste paper pulp can be reduced, but if the processing concentration is increased, the ink is subdivided and kneaded into the pulp fiber, resulting in a decrease in whiteness. -Ding suggests doing less than 25%. In fact, these methods cannot obtain a whiteness of 65% or more when treating waste newspaper, and, as a result, the pulp to be blended with medium-quality paper is extremely limited.

The deinking pulp has the properties that the deinking proceeds to increase the whiteness and the residual ink is noticeable. For this reason, it is important to carry out deinking as much as possible for the high-whiteness deinking pulp mixed in the high-quality paper. From this point of view, in order to obtain the deinked pulp to be blended in the high quality system, the flow equipments 1-2 and 1-2 of the treatment equipment which have been conventionally proposed.
(Sources 1 and 2) include the following.

Flo-1: The raw newspaper waste paper is disintegrated, diluted after completion of disintegration, and floated to separate the ink separated by disaggregation. Next, the residual ink that has been peeled off is further separated by washing, and then dehydrated and concentrated. After concentration to a concentration of about 30%, an alkali is added and nidding is performed to peel off the unpeeled ink. After the kneading is completed, it is aged for a predetermined period of time to be aged. After completion of the aging, the ink is diluted to about 1% and subjected to flotation to separate the ink peeled by the nidding and the aging. Foreign matters are separated from the pulp after the flotation with a screen, a cleaner or the like. Further, the peeling ink which cannot be separated by the flotation is removed by rewashing. 30% of pulp that has been rewashed
Concentrate before and after, and perform kneading again. Also at this time, the bleaching chemical is added prior to the kneading as in the above kneading so that the stirring effect of the chemical is obtained together with the kneading. The pulp that has undergone the re-kneading is again subjected to a bleaching reaction for about 2 hours. The whole process is completed by finally washing the pulp which has been re-bleached.

Flo-2: The raw material waste paper is disintegrated, and then the separated ink is separated by washing, concentrated to 10% concentration, and the pulp is retained in the reaction tower for 2 hours to carry out the aging reaction. After that, dehydration concentration is further performed, concentration is performed to about 30%, deinking agent is added and nidding is performed, and unpeeled ink is peeled off. 1% after finishing the kneading
It is diluted before and after and floated, and the ink separated by aging and kneading is separated. Foreign matters are separated from the pulp after the flotation with a screen, a cleaner or the like. Further, the peeling ink which cannot be separated by the flotation is removed by rewashing. The pulp that has been rewashed is concentrated and dehydrated to 10%, added with a bleaching chemical and then kneaded, and the pulp is retained in the reaction tower for about 2 hours to carry out a bleaching reaction. The whole process is completed by finally washing the bleached pulp. Flow-1 Source: Paper and Paper Cooperative Paper 1990/9, p21-36
(Manufacture of deinked pulp that can substitute hardwood bleached kraft pulp from high-quality waste paper) Flow-2 Source: Alpha 1990/7, p12-18
(Some points to note when using recycled paper for high-quality paper)

[0009]

From the paper quality design,
Even if used paper pulp is white paper and deinking degree that are equivalent to those of ordinary chemical bleached pulp, it is required for used paper pulp to be mixed with high-quality paper. Further, even if recycled waste paper pulp from newspaper waste paper, if it is tried to mix it with high-quality paper of printing grade, the whiteness required by the conventional method,
Deinking degree was not obtained. Even when it was intentionally blended, the blending into paper was limited. That is, the present invention is characterized by deinking all waste paper raw materials such as newspapers, high-quality waste paper, etc., or a mixture thereof, and provides a waste paper processing method that enables high-rate blending into recycled paper. With the goal.

[0010]

Various attempts have been made so far to obtain pulp having higher whiteness than printed waste paper, and a method of using a bleaching agent with a deinking agent in aging, It is also known to rebleach after flotation. Further, it is also known to perform mechanical treatment with a kneader, but this also mechanically peels off difficult-to-deinkable printing ink such as offset printing from pulp fiber or makes the ink conspicuous. It is for the purpose of subdividing into waste size, and with this method alone, it is 65% or more for waste newspaper and 80 or more for color waste paper, but it is 30% for medium and high quality paper. Highly white recycled paper pulp that can be blended as described above cannot be obtained.

The used paper processing method of the present invention will be described below. That is, in the used paper processing method of the present invention,
The waste paper raw material is first disintegrated and washed in an aqueous medium, and then a builder such as hydrogen peroxide, NaOH and sodium silicate, and a deinking agent are added, and then kneaded and then aged, and then floated. -Perform options. It is characterized in that the steps performed in this order are repeated twice or three times. Preferably, 30% to 70% of the bleach to be added is added in the first stage. More preferably, a mica processor is used as the kneading device.

[0012] By the above-mentioned treatment step, high whiteness waste paper pulp can be obtained by deinking all two kinds of waste paper raw materials such as newspapers and high-quality waste paper or a mixture thereof. A feature of the used paper processing method of the present invention is that the steps of washing, kneading and aging are repeated. By repeating this,
It has become possible to obtain a high degree of whiteness and a degree of deinking, which has never been obtained before. Hereinafter, the operation of the present invention will be described in detail.

The present inventor estimated that there are two factors that inhibit the increase in whiteness. That is, one of them is
Originally, the ink contained in waste paper is extremely difficult to bleach, and this effectively bleaches with any of the existing bleaching agents.
It cannot be deinked. Therefore, it is necessary to remove this ink prior to bleaching and deinking, and the removal of this ink was considered first. In high-quality coated paper, a large amount of these inks is easily subdivided and separated from the pulp fibers by the first disaggregation operation.

The inventor of the present invention,
It was found that by removing the coating liquid component by washing, the increase in whiteness in the subsequent steps was remarkably improved. This is because the eluted organic component hinders bleaching, and the separated ink particles are kneaded and are again subjected to mechanical stress to be subdivided into particles, and particles having a high removal rate of 10 microns or more by flotation. Is decreased, and the number of particles of 10 μm or less is increased.

The effect on whitening of the washing operation subsequent to the disaggregation of the used waste paper is the same for the used newspaper.
This is the same in the subsequent steps, and after the step of peeling the ink from the pulp fiber, that is, after performing the operation of dispersing and peeling the ink with a kneader, a high-speed kneader (mica processor), etc. Must necessarily be combined with a washing operation, and the present invention was developed in view of such characteristics of used paper raw materials.

Further, the present inventor has paid attention to the fact that, as a second factor that inhibits the increase in whiteness, sufficient whiteness cannot be obtained by bleaching or deinking and the whiteness is saturated. For example, in a waste newspapers, first in general pulp concentration of about 10% takes place, it has been investigated oxidizing bleaching with H ₂ O _2, H ₂
Even if the O ₂ addition rate is increased, sufficient whiteness cannot be obtained by this step alone. That is, in order to obtain high whiteness,
It is effective to make the pulp concentration during bleaching as high as possible and the bleaching chemical concentration high. However, when examining the relationship between the pulp concentration and whiteness during bleaching, the pulp concentration was 25%.
Although the whiteness increases as the pulp concentration is increased up to the vicinity, the whiteness does not increase even if the pulp concentration is increased to 30 to 40%.

As described above, the cause of saturation of whiteness is
This is because the contact between the pulp fiber and the bleaching agent becomes insufficient.
Focusing on this point, a method in which the bleaching agent is brought into uniform contact with the pulp, that is, washing is performed to remove the ink peeled from the pulp, and then the stock is concentrated and dehydrated to 25% or more, and the temperature is maintained at room temperature or under heating. Then, a method of repeating kneading mixing and bleaching was considered.

Further, the amount of bleaching and deinking chemicals (hydrogen peroxide and NaOH, builder such as sodium silicate) added to the first stage niding step is 30 to 30% of the amount added to all steps.
An excellent effect is exhibited by allocating 70%, and a sufficient effect cannot be obtained when allocating at a ratio other than this.

The effect of bleaching or deinking can be obtained by performing kneading with a bleaching agent added and then performing a bleaching reaction. Therefore, the effect is further improved by repeating this step. In the experiment, the effect of bleaching and deinking was recognized up to 3 times by repeating this step, but the effect of bleaching and deinking was not recognized by repeating this step more than three times. It should be noted that, in the second to fourth repeated steps, even if the third step, that is, the rotation is removed, an effect similar to this can be obtained, and the third step is labor-saving. Good.

Usually, since the kneader used in the processing of used paper separates the ink from the pulp fiber, it is desirable to give a compressive force to the pulp, or it is desirable for the pulp fibers to be appropriately rubbed with each other. As the kneader, a kneader which gives a sufficient compressive force or friction to the pulp fiber at a low speed is used, and a high treatment temperature has been selected. Here, the kneader as the meaning of the terms used in the present invention is
This content is meant, and processing by a kneader is referred to as kneading. However, the conventional kneader
Etc., pulp fibers form a lump between the rotating rotor and the stator, and this portion rotates at the same time as the rotation of the rotor, and the ink adhering to the pulp fibers in this lump peels off. There is nothing to do. Further, this lump portion becomes an unbleached portion.

However, in the present invention, a compressive force or a frictional force is not applied to the pulp fiber, but a shearing force is applied to a minute portion of the defibrated pulp fiber as a mechanism.
Moreover, since the purpose is to uniformly mix the bleaching agent with the high-concentration pulp, the equipment used has sufficient space between the rotor or the stator so as not to give friction to the pulp fibers, and A type that can rotate at high speed and uniformly mix in a short time is desirable. Mica Processor- (Ishikawajima Industrial Machinery)
Has a feed blade and a return blade on the rotor, and a stator
There is a sufficient gap between the blade and the blade, and the mechanism is such that the rotor rotates at a high speed of 1000 rpm or more, so that the pulp fiber mass is miniaturized and the pulp fiber with the ink adhered is mixed.
Most preferred because it can be flexed multiple times in the interior and this action can facilitate ink release from the pulp fibers and promote mixing with the bleach. A floater pulper (Kamiya) has a similar mechanism.
In the present invention, such equipment is equipped with a high-speed feeder,
Processing by a high speed kneader is referred to as high speed kneading.

By the above operation, it is possible to obtain a high-whiteness waste paper pulp which cannot be obtained by the conventional bleaching method. On the other hand, in the present invention, if the whiteness of the obtained waste paper pulp is the same, the amount of alkali and the amount of H ₂ O ₂ used can be reduced as compared with the conventional bleaching method.

[0023]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

Examples 1 to 3 (Target, waste newspaper) After disintegrating the raw waste newspaper at a concentration of 15%, and then separating the separated ink by washing on an 80 mesh wire mesh with sufficient running water, After centrifugal dehydration and concentration to 30% concentration, kneading (manufactured by Yamamoto Hyakuma Co .; Lab Kneader)
Use) to peel off the unpeeled ink. A bleaching chemical and a deinking agent are added prior to kneading so that the bleaching chemical and pulp can be stirred. As a bleaching agent, hydrogen peroxide is 0.5% to pulp, 1.5%, and 2.
3 levels of 5% were added. In addition to this, caseisoder and sodium silicate were added in the same amounts as hydrogen peroxide. As the deinking agent, a commercially available deinking agent (DI600, manufactured by Kao Corporation) is used in an amount of 0.3% with respect to pulp.
Was added. After the kneading is completed, the pulp is deaerated and packed in a polyethylene bag, and the pulp is kept as it is in a constant temperature water bath.
The mixture was allowed to stay for a period of time, followed by deinking and bleaching (H ₂ O ₂ was added to obtain a bleaching effect).

After completion of deinking and bleaching, the ink is peeled off in the previous step by diluting to 1% and performing flotation (Labo Floatator manufactured by Kyokuto Shinko Co., Ltd.). Foreign substances are separated from the pulp after the flotation with a lab flat screen or the like. Further, the release ink which could not be separated by the flotation is removed by rewashing on an 80 mesh wire mesh. The whiteness of the sample thus obtained and the residual amount of ink (black dyed fiber) are measured as a sample which has been subjected to the pretreatment. The method for measuring the ink-dyed fiber is as follows. A hand sheet of 60 g / m ² was prepared from the sample pulp, and the number of black dyed fibers (ink-adhered fibers) in this sheet was measured with a 12-fold loupe,
It is expressed as the number of black dyed fibers per 100 g of pulp.
The results of this stage are shown in Table 1 as the previous stage.

[0026]

[Table 1]

The pulp which has been rewashed is concentrated to 30% by centrifugal dehydration, and again kneaded. Also at this time, a bleaching chemical is added prior to the kneading as in the above kneading to obtain the stirring effect of the chemical.
As a bleaching agent, hydrogen peroxide is 0.5% to pulp,
Three levels of 1.5% and 2.5% were added. In addition to this, caseisoder and sodium silicate were added in the same amounts as hydrogen peroxide.
The pulp that has undergone the re-kneading is again subjected to a bleaching reaction for about 2 hours. The entire process is completed by finally washing the rebleached pulp on an 80 mesh wire mesh.
The sample thus obtained measures the whiteness and the residual amount of ink (black dyed fiber) as a sample after the post-treatment.
The results of this stage are shown in Table 1 as the latter stage.

As described above, the experimental data are shown in Table 1 as Examples 1 to 1.
3 shows. Example 1 was bleached at a hydrogen peroxide addition rate of 1% in both the first and second stages. Hereinafter, in Example 2, 3%,
In Example 3, the result of 5% is shown in Table 1. As will be described later, the results of Example 19 are also shown in Table 1.

Comparative Examples 1 to 3 (Target: Used Newspaper, Corresponding to Fro-1 of the Prior Art) Raw newspaper waste was disintegrated at a concentration of 15%, and after disintegration, diluted to 1%. Floatation (manufactured by Kyokuto Shinko Co., Ltd .; Labo Floater) is performed to separate the ink that has been peeled off by disaggregation. Next, remove the residual ink that has been peeled off.
After separation by washing with sufficient running water on an 80-mesh wire net, centrifugal dehydration is performed, and after concentration to 30% concentration, kneading (manufactured by Yamamoto Hyakuma Co., Ltd .; Labor kneader) is performed to remove unpeeled material. Peel off the ink. Prior to kneading, a deinking agent, NaOH, and sodium silicate are added in the same manner as in Examples 1 to 3, and aging (H ₂ O ₂ is not added) is performed. The results up to this point are shown in Table 1 as the former stage. After the kneading was completed, the pulp was deaerated and packed in a polyethylene bag, and the pulp was kept for 2 hours in the constant temperature water tank to be aged. Thereafter, in the same manner as in Examples 1 to 3, flotation, washing and concentration, kneading, and bleaching are performed. As a bleaching chemical, hydrogen peroxide was added to pulp of 1.0%, 3.0% and 5.0%.
Level added. In addition to this, caseisoder and sodium silicate were added in the same amounts as hydrogen peroxide. As the deinking agent, a commercially available deinking agent (DI600, manufactured by Kao Corporation) was added to pulp of 0.3%. After that, the same treatment as in Example 1 is performed, and the whiteness and the residual ink amount (black dyed fiber) are measured. The results up to this point are shown as the latter stage in Table 1.

The experimental data are shown in Table 1 as Comparative Examples 1 to 3.
Indicated by. Comparative Example 1 has a hydrogen peroxide addition rate of 1% in the bleaching stage.
Table 1 shows the results of bleaching in No. 3, 3% in Comparative Example 2 and 5% in Comparative Example 3.

Comparative Examples 4 to 6 (target, waste newspaper) The same as Comparative Example 1 except that the order of aging (H ₂ O ₂ is not added) and bleaching is changed as a processing method. The experimental data are shown in Comparative Examples 4 to 6 in Table 1. Comparative Example 4 was bleached at a hydrogen peroxide addition rate of 1%. The results of 3% in Comparative Example 5 and 5% in Comparative Example 6 are shown in Table 1 below.

Comparing the above, the whitening and deinking efficiencies of Examples 1 to 3 are superior to those of Comparative Examples 1 to 6 at each level of chemical addition rate. From these data, the effective range of bleaching chemical distribution is 2 bleaching stages.
First stage: second stage = after being installed on the first stage (H2O2 enters both stages)
50%: 50% as a peak, 1st stage: 2nd stage = 30%: 7
It is in the range of 0% to 70%: 30%.

Comparative Examples 7 to 9 (target: waste newspaper, corresponding to Fro-2 of the prior art) Raw newspaper waste was disaggregated at a concentration of 15%, and then the peeled ink was placed on an 80 mesh wire mesh. After separating by washing with sufficient running water, centrifuge dehydration is performed, and after concentration to 10% concentration, the pulp is degassed and packed in a polyethylene bag,
As it was, it was allowed to stay in the constant temperature water tank for 2 hours for aging reaction. After that, centrifugal dewatering is further performed, the solution is concentrated to 30%, and kneading (manufactured by Yamamoto Hyakuma Co., Ltd .; Labor kneader) is performed to remove unpeeled ink. Prior to kneading, a deinking agent is added to prepare for the next flotation operation. Nee
After finishing the dyeing, it is diluted to 1% and subjected to flotation (manufactured by Kyokuto Shinko Co., Ltd .; Labo Floater) to separate the ink peeled by aging and kneading.

Foreign matter is separated from the pulp after the flotation by a lab screen or the like. Further, the release ink which could not be separated by the flotation is removed by rewashing on an 80 mesh wire mesh. The whiteness and the residual amount of ink (black dyed fiber) of the sample thus obtained are measured as the samples that have been subjected to the pretreatment. The pulp that has been rewashed is concentrated to 10% by centrifugal dehydration, added with a bleaching agent and stirred, and the pulp is degassed and packed in a polyethylene bag. I do. The entire process is completed by final washing the bleached pulp on an 80 mesh wire mesh. The whiteness and the residual amount of ink (black dyed fiber) of the sample thus obtained are measured as a sample after the second-stage treatment.

The experimental data are shown in Table 2 as Comparative Examples 7-9.
Indicated by. Comparative Example 7 was bleached at a hydrogen peroxide addition rate of 1%. The results of 3% in Comparative Example 8 and 5% in Comparative Example 9 are shown in Table 2 below.

[0036]

[Table 2]

Examples 4 to 6 (target, high-quality waste paper) Evaluation is carried out by the same procedure as in Example 1 except that high-quality waste paper is used as the waste paper to be treated and the residual ink amount (black dyed fiber) is not measured. . Experimental data are shown in Table 3 as Example 4 to
It is shown by 6. Example 4 was bleached at a hydrogen peroxide addition rate of 1% in both the first and second stages. Hereinafter, in Example 5, 3%,
In Example 6, the result of 5% is shown in Table 3.

Comparative Examples 10 to 12 (target, high-quality waste paper) Evaluation is performed in the same procedure as in Comparative Example 1 except that high-quality waste paper is used as the waste paper to be treated and the residual ink amount (black dyed fiber) is not measured. . The experimental data are shown in Table 3 as Comparative Example 10.
-12. Comparative Example 10 was bleached at a hydrogen peroxide addition rate of 1% in the bleaching stage. Hereinafter, in Comparative Example 11, 3%,
In Comparative Example 12, the result of 5% is shown in Table 3.

[0039]

[Table 3]

Comparative Examples 13 to 15 (target, high-quality waste paper) Evaluation is performed in the same procedure as in Comparative Example 4 except that high-quality waste paper is used as the waste paper to be treated and the residual ink amount (black dyed fiber) is not measured. . The data of the experiment is shown in Table 3 as Example 13
It is shown by ~ 15. Comparative Example 13 has a hydrogen peroxide addition rate of 1%.
Bleached in. Hereinafter, in Comparative Example 14, 3%, Comparative Example 1
In Table 5, the results of 5% are shown in Table 3.

Comparing the above, the whitening efficiency is excellent in Examples 4 to 6, which is the same as in the case of waste newspaper. The effective range of distribution of bleaching chemicals from these data is that the bleaching stage is divided into two stages, and the front stage: the rear stage = 50%: 50% is the apex, and the front stage: the rear stage = 30.
%: 70% to 70%: 30%.

Comparative Examples 16 to 18 (target, high-quality waste paper) Evaluation is performed in the same procedure as in Comparative Example 7 except that high-quality waste paper is used as the waste paper to be treated and the residual ink amount (black dyed fiber) is not measured. . The experimental data are shown in Table 4 as Comparative Example 16.
Shown at -18. Comparative Example 16 has a hydrogen peroxide addition rate of 1%.
Bleached in. Hereinafter, in Comparative Example 17, 3%, Comparative Example 1
In Table 8, the result of 5% is shown in Table 4.

[0043]

[Table 4]

Examples 7 to 12 and Comparative Examples 19 to 24 (target, waste newspaper) In Example 1 (two-stage bleaching before and after), one more time and two times of repetitions were added and combined up to four steps. Was processed. The experimental data are shown in Examples 7 to 12 in Table 5,
The results are shown in Comparative Examples 19 to 24. Examples 7 and 8 and Comparative Example 1
Nos. 9 and 20 were bleached together in 1 to 4 stages with a hydrogen peroxide addition rate of 1%. The distribution of chemicals in each stage was divided into equal parts.
Hereinafter, in Examples 9 and 10 and Comparative Examples 21 and 22, 3%,
The results of 5% in Examples 11 and 12 and Comparative Examples 23 and 24 are shown in Table 5. Table 5 also shows the chemical distribution rate to the first stage. As is clear from Table 5, at various chemical addition rates, the maximum bleaching level is obtained when the number of bleaching stages is around 3, and then the level is turned off.

[0045]

[Table 5]

Examples 13 to 18 and Comparative Examples 25 to 30 (target, waste newspaper) Repeated 2 to 4 times, except for the flotation operation, Examples 7 to 12 and Comparative Examples 19 to 24 It processed similarly. Also in these experiments, a bleaching effect similar to that of Examples 7 to 12 was obtained. The results are shown in Table 6.

[0047]

[Table 6]

Example 19 (Target, newspaper waste paper) In Example 3, the kneading machine was changed from the conventional type in which the number of rotations of the rotor was around 200 times per minute to 100 per minute.
Table 1 shows the results when the processing was performed with 0 or more rotations (made by Ishikawajima Sangyo Kikai Co., Ltd .; mica processor). As is apparent from this embodiment, the deinking effect is further enhanced by adopting a kneader having a rotor that rotates at 1000 rpm or more.

[0049]

As described above, according to the present invention, it is possible to obtain deinked pulp having a high whiteness and a small number of residual ink and unpeeled ink when deinking newspapers and high-quality waste paper.

Claims (4)

[Claims] 1. A method for treating waste paper, comprising disintegrating waste paper,
The first step of washing the disintegrated stock to remove fine solids containing the separated ink from the pulp component,
%, Dehydrated to a concentration of more than 100%, added with at least one chemical selected from deinking agents containing NaOH, sodium silicate, hydrogen peroxide and a surfactant, and stirring the paper stock at high speed. After passing through a device that violently collides with each other to give a shearing force and mixes with a chemical, the second step of holding in a reaction tank and then diluting it into a fluid state together with pulp components, air to the paper stock And the third step of separating the hydrophobic component containing the ink separated from the pulp component through the device for separating bubbles from the pulp component, washing the paper material, and removing the fine solid content containing the dissolved component and the ink particles into the pulp. A used paper processing method, characterized in that used paper is processed by four steps including a fourth step of removing the components. 2. The used paper processing method according to claim 1, wherein after the first step, the second to fourth steps are repeated twice or three times. 3. An arbitrary position in each of the first to fourth steps,
The used paper processing method according to claim 1 or 2, further comprising a dust removing step. 4. The used paper treatment method according to claim 1, 2 or 3, wherein the amount of hydrogen peroxide added to the first stage is 30 to 70% of the amount added during the entire treatment step.