JPH07189154A - Method for producing deinked pulp - Google Patents

Abstract

PURPOSE:To enhance a treating effect in the deinking treatment of printed waste paper, and produce deinked pulp having higher whiteness than those of deinked pulps produced by conventional methods. CONSTITUTION:A method for producing deinked pulp by treating printed waste paper in processes comprising a process for disaggregating the printed waste paper, an alkali soaking process, a flotation process and (or) a washing process and, if necessary, a bleaching process is characterized by treating the pulp with ozone in a neutral to alkaline solution in the alkali soaking process or the bleaching process.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing deinked pulp from printed waste paper. More specifically, the present invention provides
The present invention relates to a method for producing deinked pulp, which enhances the deinking effect by performing ozone treatment under specific conditions when deinking printed waste paper pulp, and makes it possible to further increase the whiteness of the pulp.

[0002]

2. Description of the Related Art Conventionally, used paper has been recycled as an important raw material for papermaking, but against the background of recent strong demands for environmental protection and resource saving on a global scale,
It has become a very important technical problem in the industry to process waste paper at a higher level and to expand the range of recycling. As one direction of this, various deinking and bleaching methods are used in order to remove the printing ink of waste printed paper in the deinking process to obtain deinked pulp with high whiteness and to use it as a raw material for various printing papers. It has been proposed and implemented industrially.

According to the current general method for producing deinked pulp, following the defibrating step of defibrating and defibrating printed waste paper with a pulper, the dehydrated and concentrated defibrated pulp is treated with an alkaline chemical, a surfactant, and hydrogen peroxide. Etc. to swell the pulp fiber and peel the printing ink from the pulp fiber, dilute the soaked pulp, blow the fine air bubbles, and attach the printing ink to the bubbles to float and separate Deinked pulp is produced through a flotation process, a soaking process or a flotation process, and a washing process of diluting and dehydrating pulp fibers with a large amount of water to wash and remove the printing ink.

Alkaline soaking treatment and flotation treatment and / or washing treatment alone can give deinked pulp having a certain degree of whiteness. However, the whiteness of the deinked pulp obtained by these treatment steps is limited, and in order to obtain a deinked pulp having a higher whiteness, a bleaching treatment is required in the subsequent stage. As a bleaching treatment method for deinked pulp, oxidative bleaching treatment with hydrogen peroxide or the like, reduction bleaching treatment with formamidinesulfinic acid or the like is adopted to produce deinked pulp with high whiteness.

Regarding the bleaching of pulp, from the viewpoint of preventing environmental pollution due to organic chlorine compounds, the practical use of ECF or TCF pulp which reduces or eliminates the use of chlorine bleaching agents has been studied and partially put into practical use. . Oxygen-based bleaching agents such as oxygen, hydrogen peroxide and ozone have been used as bleaching agents in place of chlorine-based bleaching agents. Ozone is an oxygen-based bleaching agent that has extremely strong oxidizing power, but since it has too strong oxidizing power,
In addition to the bleaching action of pulp, it also causes the collapse of pulp fibers, and there is a risk of causing a decrease in pulp strength. Also,
Ozone is a gas that hardly dissolves in water at room temperature and atmospheric pressure, has a strong reactivity, undergoes self-ineffective decomposition, and has the property that it is easily decomposed especially in alkaline. Therefore, ozone bleaching of pulp is 30-45% at a relatively low temperature near room temperature.
The gas phase reaction for treating high-concentration pulp is mainly used, and in order to prevent a decrease in pulp strength, it is treated with acidity of about pH 1-3.

The use of ozone in the recycling of waste paper is also being investigated, and according to a report by FA Abadie-Maubert, N. Soteland (Ozone Sci. And Eng. 7 (3) 229 (1985)).
Waste paper is defibrated and dehydrated to fluff it with a pulp concentration of 35%, oxygen gas with an ozone concentration of 2% is supplied, and under acidic conditions (for example, pH 3.0), the ozone addition rate is 1 to 3%.
At room temperature, the pH is adjusted to 8.5 with alkali to decompose residual ozone. According to this report, ozone treatment does not have a deinking effect, but has the potential to improve the mechanical and optical properties of pulp. Also, M.Mu
guet, J. Kogan (Proceeding of the 1992 TAPPI
Pulping Conference, 1992, p.75), after preparing deinked waste paper pulp at 3% concentration to pH 2.5, the pulp concentration was 30%.
Dehydrate to ~ 40%, fluff, ozone concentration 3.
Supplying 5% oxygen, 0.3% to 2% per bone dry pulp
It is processed at 25 ° C. with an ozone consumption rate of the order. In these ozone treatments, ozone is mainly used for bleaching waste paper pulp, and an acid bleaching method is adopted.

In the method of producing deinked pulp from waste printed paper, a method in which pulp fibers are swollen by an alkali soaking treatment, the printing ink is peeled off, and the printing ink is separated from the pulp fibers by a flotation treatment has become mainstream in Japan. ing. It is said that the particle diameter of the printing ink that is easily separated by the flotation treatment is 10 to 100 μm. Therefore, the printing ink that cannot be removed by the flotation process remains in the deinked pulp, causing "dullness" peculiar to the deinked pulp, which is one of the factors that hinder the expansion of applications of the deinked pulp.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, the present invention reduces the printing ink (hereinafter referred to as residual carbon) remaining in the deinking pulp to eliminate the "dullness" peculiar to the deinking pulp. It is an object of the present invention to provide a method for producing a deinked pulp having a reduced whiteness and a higher whiteness.

[0009]

[Means for Solving the Problems]

[Summary of the Invention] The present inventors have found that in the deinking treatment of waste paper pulp, the above object can be achieved by performing ozone treatment under alkaline to neutral conditions in a specific treatment step. That is, the method for producing deinked pulp according to the present invention is a method for producing deinked pulp by treating the printed waste paper with a step including a disintegration step, an alkali soaking step and a flotation step and / or a washing step, and optionally a bleaching step. In the manufacturing method, the pulp is treated with ozone from neutral to alkaline as a pretreatment step of the alkali soaking step or in the alkali soaking step or the bleaching step.

[Detailed Description of the Invention] The ozone treatment according to the present invention is carried out in an alkali soaking step or a bleaching step of the deinking pulp manufacturing step, or as a pretreatment step of the alkali soaking step. Above all, it is preferable to carry out in the alkali soaking step or as a pretreatment thereof, and a greater ozone treatment effect can be obtained. When the ozone treatment is performed in the alkali soaking process or as a pretreatment thereof, the timing of the treatment is before the addition of chemicals in the alkali soaking process or in the intermediate stage of addition of various chemicals, but before the addition of hydrogen peroxide or the latter half of the alkali soaking process. It is also preferably as late as possible, and most preferably when the alkaline soaking treatment is substantially completed. The reason is that in the first half of the alkaline soaking process, especially when ozone is added at the start of the soaking process, that is, immediately after the addition of hydrogen peroxide, the reducing agent is present in the presence of ozone, which is a stronger oxidizing agent than itself. This is because ozone and hydrogen peroxide react directly with each other and the effects on the pulp are offset.

The ozone treatment according to the present invention is carried out by a bleaching step (hydrogen peroxide bleaching, formamidinesulfinic acid (FAS)).
Also in the case of bleaching, etc.), it is preferable to carry out the treatment in the latter half of the step, particularly when the bleaching treatment is substantially completed. When ozone is added at the beginning of the bleaching treatment, as in the case of the ozone treatment in the alkali soaking step described above, hydrogen peroxide used as a bleaching agent, formamidinesulfinic acid, etc. react with ozone to produce respective pulps. The action will be reduced.

In the present invention, the ozone treatment of pulp is carried out under neutral to alkaline conditions. That is, the pulp slurry pH during ozone treatment is generally 7.0 to 13.5, preferably 9.0 to 12.0. This pH range corresponds to the pH range of the pulp slurry at the time of ordinary alkaline soaking treatment and bleaching treatment (hydrogen peroxide bleaching, FAS bleaching, etc.), and therefore, during these treatments (including the end of treatment as described above). It is not necessary to change the pH of the pulp slurry when the ozone treatment is carried out on (1). The amount of ozone used is generally 0.01 to 5% by weight, and preferably 0.05 to 1% by weight, based on dry pulp.

The temperature of the pulp slurry during ozone treatment is
Since the reactivity of ozone is extremely strong and the reaction of ozone is completed in a short time, it is not particularly limited, but generally 5 to 95.
C, preferably 40 to 70C. The treatment time depends on the amount of ozone used, the concentration of ozone, the treatment concentration of pulp, etc., but since the reaction of ozone is completed in a short time, it is generally 0.1 to 60 minutes, preferably 0.5 to 30 minutes. Is. Since ozone is a gas that is difficult to dissolve in water, it is preferable that the concentration of waste paper pulp during ozone treatment is as high as possible in order to improve the contact between ozone and waste paper pulp. It is desirable to be 8 to 45%. In addition, as described above, ozone is a gas that is not easily dissolved in water and is extremely reactive, and therefore it is desirable to stir and mix waste paper pulp during ozone treatment in order to enhance treatment efficiency. The stirring rotational speed during stirring and mixing is 10 to 2000 rpm, particularly 100 to 1500 rpm.
The rpm is preferable from the viewpoint of stirring efficiency and prevention of deterioration of strength of pulp fiber due to high speed rotation.

As the ozone used in the present invention, for example, an ozone-containing gas produced by an ozone generator that silently discharges in a dehumidified oxygen-containing gas stream containing air can be used. The higher the oxygen concentration of the oxygen-containing gas, the higher the ozone concentration produced. When this ozone-containing gas is used, it is desirable that the ozone concentration is high in terms of processing efficiency, and the processing time is shortened. Therefore, as the oxygen-containing gas for ozone production, it is preferable to use a high-concentration oxygen-containing gas by the PSA method of air or a high-purity oxygen-containing gas by the cryogenic separation method, which is also advantageous in terms of cost. The oxygen concentration in these oxygen-containing gases for ozone production is generally 65 to 100% by volume. The ozone concentration in the ozone-containing gas can be varied depending on the oxygen concentration and flow rate of the oxygen-containing gas supplied to the ozone generator and the charging voltage of the silent discharge, but is generally 0.01 to 15% by weight, preferably 5%. ~ 15% by weight. The ozone treatment according to the present invention is usually performed by blowing the ozone-containing gas into the pulp slurry.

Most of the ozone in the ozone-containing gas is decomposed by reaction with waste paper pulp or self-ineffective decomposition during ozone treatment, and the ozone-treated gas contains almost no ozone. However, the exhaust gas, which is the oxygen-containing gas after the ozone treatment, can be reused as the oxygen-containing gas for ozone production. The oxygen-containing gas used in the ozone generator by silent discharge must be dehumidified so as not to short-circuit between the silent discharge electrodes. Therefore, in order to reuse the exhaust gas after the ozone treatment, it is necessary to re-dehumidify the exhaust gas,
It is necessary to dehumidify the dew point under atmospheric pressure to at least −50 ° C. or lower, and more preferably −60 ° C. or lower. This dehumidified oxygen-containing exhaust gas can be recycled to the dehumidified oxygen-containing gas for ozone production, supplied to the ozone generator, and again used as ozone-containing gas in the ozone treatment according to the present invention.

As described above, when ozone is used as a bleaching agent for bleaching pulp, it is usually acidified to add ozone in order to prevent a decrease in fiber strength of the pulp. On the other hand, in the process of recycling printed waste paper, an alkaline process is extremely often used. Even in the disintegration treatment of waste paper, alkaline chemicals may be added to promote disaggregation.In alkaline soaking, alkaline chemicals such as caustic soda and sodium silicate are added to promote the swelling of pulp fibers in an alkaline manner, and printing ink It is easy to peel off, and bleaching with hydrogen peroxide is also alkaline, and hydrogen peroxide is bleached with HOO anion. Formamidinesulfinic acid (FAS) bleaching also decomposes FAS with alkaline and has a strong reducing property. Bleaching is performed with sulfinate ion (SO ₂ ²⁻ ) indicating Therefore, in the deinking process, which frequently uses an alkaline treatment process, in order to perform ozone treatment in an acidic condition, it is necessary to neutralize with an acid and return to alkaline, and it is necessary to increase the number of processes. According to the present invention, the ozone treatment of the deinked pulp is performed from neutral to alkaline, so that the neutralization step can be omitted.

Ozone treatment of pulp is commonly used for bleaching chemical pulp with low lignin content. This is because if ozone bleaching is adopted for bleaching mechanical pulp containing a large amount of lignin, it is necessary to treat it with a large amount of ozone for a long time in order to oxidize and decompose a large amount of lignin, but the reactivity of ozone is extremely high. This is because it is violent and has no selective reactivity with lignin such as chlorine and chlorine dioxide, so that cellulose is also oxidatively decomposed like lignin, resulting in a decrease in pulp strength. In the present invention, it is possible to treat printed waste paper such as newspaper wastepaper, magazine wastepaper, etc. that contains a large amount of mechanical pulp as the processing target. This is because the ozone treatment of the present invention is not intended to bleach by oxidatively decomposing the mechanical pulp lignin contained in these printed waste papers with ozone, and is neutral to alkaline for a short time,
By treating with a small amount of ozone, the printing ink peeled from the pulp fiber is oxidatively decomposed,
This is because the action of ozone on the cellulose of pulp fibers is extremely small.

The printed waste paper which is the subject of the present invention includes newspaper wastepaper by offset, letterpress, gravure, flexographic printing, screen printing and the like, magazine wastepaper, flyer wastepaper and general commercial wastepaper, and computer output wastepaper and electronic wastepaper. It is printed waste paper including OA waste paper that has been copied or printed by various copying methods such as copying, electrostatic copying, and thermal copying.

[0019]

EXAMPLES Examples of the present invention will be shown below and described in more detail, but these examples do not limit the present invention in any way. In addition, all the addition amounts (%) of chemicals in the examples represent weight% in terms of pure content with respect to the weight of absolutely dry pulp. Examples 1 to 7 and Comparative Example 1 Offset printed newspaper was disaggregated with a test pulper at a density of 5% for 5 minutes. For this disintegrated pulp,
Alkaline soaking treatment was performed under the following conditions. <Treatment conditions> Pulp concentration: 15% Hydrogen peroxide addition: 3.5% Caustic soda addition: 2% Sodium silicate addition: 5% Surfactant ^* addition: 0.2% Treatment temperature: 70 ° C Treatment time : 2 hours * Polyoxyethylene nonyl phenyl ether (n =
8)

Before the addition of the above-mentioned soaking chemicals (Example 1) and immediately after the addition (Example 2), and at the end of the soaking treatment (Examples 3 to 7), ozone treatment was carried out under the following conditions. Here, the ozone treatment was performed by blowing ozone-containing oxygen gas (ozone concentration 5% by weight, oxygen concentration 95% by weight) into the pulp slurry. <Treatment conditions> Pulp concentration: 15% Ozone usage: 0 to 1% Pulp slurry pH: 10 Treatment temperature: 40 ° C Treatment time: 10 minutes Pulp slurry stirring rotation speed: 200 rpm

The pulp slurry after the above ozone treatment was diluted to a pulp concentration of 1% and subjected to a flotation treatment for 15 minutes by a box type test floatator.
The whiteness of the pulp after the flotation treatment is ISO24.
It measured based on 69. The whiteness of the pulp obtained by washing the waste paper pulp after the flotation with deionized water in an amount of 2,500 times as much as the pulp (referred to as completely washed pulp) was similarly measured. Further, the cumulative area ratio (residual carbon%) of the residual carbon ink was obtained by image analysis of the surface of the handmade sheet of this completely washed pulp. Specifically, the area of residual ink was measured using a whiteness measuring sheet using an image analyzer manufactured by Pierce Co., Ltd. and an optical microscope, and the ratio with the measured visual field area was determined. The results are shown in Table 1.

Table 1 Ozone treatment Ozone floate Complete cleaning Complete cleaning Example No. Usage amount Pulp Pulp White Pulp Remaining period (%) Whiteness (%) Chromaticity (%) Carbon (%) Example 1 Before soaking 1.0 57.0 66.5 0.18 〃 2 Soaking 1.0 56.9 64.4 0.25 Immediately after adding chemicals 〃 3 Soaking 0.05 58.1 66.1 0.22 At end 〃 4 〃 0.1 58.5 66.2 0.13 〃 5 〃 0.2 58.7 66.2 − 〃 6 〃 0.5 59.9 66.0 − 〃 7 〃 1.0 61.7 66.5 0.13 Comparative example 1 − 0 56.2 66.0 0.26

As is clear from Table 1, the whiteness of the ozone-treated waste paper pulp after flotation is 2 to 5.5 as compared with the pulp whiteness of ozone-untreated (Comparative Example 1).
While the point is high, the whiteness of the completely washed pulp obtained by washing the waste paper pulp after flotation with 2,500 times the amount of deionized water is 0 to 0.
Only a difference of 0.5 points is not accepted. From this fact,
The action of ozone in alkaline ozone treatment of printed waste paper pulp increases the whiteness of pulp by oxidatively bleaching the pulp by direct ozone action on pulp during acid ozone treatment of ordinary pulp. Instead, it acts on the printing ink particles contained in the printed waste paper pulp and decomposes the printing ink to reduce or eliminate the printing ink particle size, or the printing ink particle size floats due to the reaction with ozone. It is considered that this is because the particle size changed easily, or the surface properties of the printing ink particles changed due to the reaction between the particles of the printing ink and ozone, and the surface properties changed easily to flotation. This estimate is also supported by the fact that the residual carbon% data for completely washed pulp of ozone treated pulp is reduced by as much as 50% compared to unozoned pulp.

[0024]

EFFECTS OF THE INVENTION According to the method of the present invention, by carrying out ozone treatment under alkaline to neutral conditions in the deinking treatment of waste paper pulp, a deinked pulp with a reduced residual carbon and a higher whiteness can be obtained. can get.

Claims (8)

[Claims] 1. A method for producing deinked pulp by treating printed waste paper with a step including a disintegration step, an alkali soaking step, a flotation step and / or a washing step, and optionally a bleaching step, said alkali soaking A method for producing deinked pulp, which comprises treating the pulp with ozone in a neutral to alkaline manner as a pretreatment step of the step or in the alkali soaking step or the bleaching step. 2. The amount of ozone used is 0.01 relative to dry pulp.
The method for producing deinked pulp according to claim 1, wherein the amount is from 10% by weight. 3. The method for producing deinked pulp according to claim 1, wherein the pulp slurry has a pulp concentration of 8 to 45% during ozone treatment. 4. A pulp slurry containing 10 parts during the ozone treatment.
Mixing by stirring at a rotation speed of ~ 2000 rpm.
4. The method for producing deinked pulp according to any one of 3 above. 5. The method for producing deinked pulp according to claim 1, wherein the pH of the pulp slurry during ozone treatment is 9.0 to 12.0. 6. The temperature of the pulp slurry during ozone treatment is 4
The method for producing deinked pulp according to any one of claims 1 to 5, which has a temperature of 0 to 70 ° C. 7. The method for producing deinked pulp according to claim 1, wherein the treatment time of ozone treatment is 0.5 to 30 minutes. 8. The method according to claim 1, wherein the ozone treatment in the alkali soaking step is carried out when the alkali soaking treatment is substantially completed.