JPH06287879A - Method for recycling colored waste paper and paper using recycled pulp of waste paper - Google Patents

Abstract

PURPOSE:To obtain high-quality recycled paper by stirring or blending a macerated slurry of recovered waste paper colored with direct dye in the presence of ozone to deink the slurry and to give recycled pulp, making paper from the recycled pulp as a main raw material. CONSTITUTION:In recycling recovered waste paper comprising one such as telephone directory colored in yellow with direct dye as a main raw material, a macerated slurry of recovered waste paper having 0.5-3wt.% ulp concentration is fed to a closable container and retained at pH9-11.5. Then thr slurry is stirred or blended in the presence of a gas containing 0.1-3wt.% ozone based on dried pulp in a closed state of the container to give a recycled pulp having high whiteness. The recycled pulp as a main raw material is made into paper to give rcycled paper having excellent strength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recycling waste paper colored with a direct dye, and a paper produced by using waste paper pulp recycled thereby as a main raw material.

[0002]

2. Description of the Related Art Reuse of used paper as a raw material for papermaking has been a social demand in recent years, which not only protects forest resources but also reduces paper waste. Currently, about 50% of the raw materials for paper and board are made up of waste paper. For paper production excluding board, so-called high-grade waste paper such as newspaper waste paper, imitation paper, and top blank paper are used.

[0003] Usually, these recovered waste papers are disintegrated into a slurry and then dedusted, and a deinking agent composed of a phosphate such as sodium polyphosphate, an alkali such as sodium hydroxide and sodium silicate, and a surfactant is used. Received the deinking treatment. The ink separated from the fiber by the deinking treatment in water is removed by a washing method or a flotation method in which ink particles are collected on the surface of bubbles and float-separated.
On the other hand, the waste paper slurry from which the ink has been removed is carefully selected in the screen step, washed, and then sent to the conditioning step as recycled waste paper pulp. In the preparation process, waste paper pulp is mixed with other types of pulp such as mechanical pulp and chemical pulp, retention aids, papermaking additives such as sizing agents, fillers, etc. at a predetermined ratio, and then the purpose in the papermaking process. It is made into paper.

However, when colored waste paper is mixed in a certain ratio or more in the deinking step, the color of the waste paper itself remains, and a color transfer occurs in which the separated dye is redeposited onto the uncolored waste paper. In the recycling process of recovered recycled paper containing colored recycled paper as a main raw material, coloring of recycled pulp is unavoidable as a result, and a bleaching process for decolorizing the colored recycled paper pulp is required.

Hydrogen peroxide and chlorine bleaching agents are used as the main bleaching agents for waste paper pulp, but it is difficult to effectively decolorize dyes with hydrogen peroxide, and chlorine bleaching agents are difficult. Although the dye is decolorized, the pulp itself becomes brown, and the burden of wastewater treatment is also heavy.
Neither is suitable as a bleaching agent for colored waste paper pulp.

In this respect, ozone has excellent properties for the decolorization treatment of colored waste paper pulp, and Japanese Patent Application Laid-Open No. 3-199477 discloses a method for recycling colored waste paper pulp that takes advantage of such properties. Is listed. However, this method is intended to decolorize colored paper used as information paper such as pressure-sensitive / thermosensitive recording paper and de-fluoresce fluorescent brightening paper, and the types of dyes used for coloring colored waste paper. However, there is a drawback that effective decolorization is not always performed under other conditions.

[0007]

DISCLOSURE OF THE INVENTION The present invention is intended to provide a method for more effectively decolorizing and recycling recovered waste paper, which is mainly made of waste paper such as a telephone book colored yellow with a direct dye. It is a thing.

Another object of the present invention is to provide a treatment method in which the pulp strength is less deteriorated when recycling the recovered waste paper.

Still another object of the present invention is to provide a paper using waste paper pulp recycled by the method.

[0010]

Means for Solving the Problems In producing a recycled pulp using waste paper colored with a direct dye as a main material, the present inventors have investigated the dye present on the free or pulp fibers present in the colored waste paper pulp slurry. As a result of research on a method for decolorizing using ozone, the pH was 9 to 11.5.
It was found that by directing the ozone-containing gas into the colored waste paper pulp slurry retained in Table 1, the direct dyes were more efficiently oxidatively decomposed to obtain recycled pulp with high whiteness.

That is, according to the present invention, a colored waste paper pulp slurry having a pulp concentration of 0.5 to 3% by weight is maintained at a pH of 9 to 11.5, and an ozone-containing gas is introduced into the slurry to obtain 0.1 per dry pulp. It is characterized by being treated with -3% by weight, preferably 0.2-1% by weight of ozone. In addition,
Stirring and mixing of ozone and pulp slurry may be carried out while introducing ozone, or may be carried out in a closed reaction vessel after introducing ozone.
Further, the decolorization treatment with ozone of the present invention may be carried out at any step after the disintegration of the recovered waste paper, but ozone may be consumed by reacting with organic substances existing as contaminants in the treatment object. Therefore, it is desirable to treat the pulp from which these contaminants have been removed as a treatment target in order to perform an efficient decolorization treatment, for example, after the deinking step or the screen step.

[0012]

In the present invention, the object to be treated is waste paper colored with a direct dye or waste paper containing this waste paper as a main raw material. The direct dye refers to a dye that is directly dyed on a cellulosic fiber from a neutral or weakly alkaline aqueous solution without using a mordant method, and a typical example thereof is an azo dye. Since these have a -N = N- bond or a benzene ring as a chemical structure, it is considered that the portion is oxidatively decomposed by ozone.

The waste paper is disintegrated to give a pulp concentration of 0.5 to 3
Ozone treatment is performed in a slurry state of weight%. If the pulp concentration is less than 0.5% by weight, the treatment efficiency will be extremely low, and if it exceeds 3% by weight, uniform stirring and mixing may be hindered.

Further, the pH of the pulp slurry is kept at 9 to 11.5 during the ozone treatment. When the pH is less than 9, neither the whiteness nor the coloring degree of the pulp is sufficiently improved, and when the pH is more than 11, both of them are kept together. This is because the ozone deteriorates and ozone becomes unstable and decomposes. Oxygen active species such as OH radicals generated by the decomposition of ozone impair the cellulose that constitutes the pulp fiber, and the properties of the recycled waste paper pulp and the paper made from the pulp, such as a decrease in paper strength. It has an unfavorable effect.

Further, in the present invention, the ozone concentration is 0.1 to 3% by weight based on the dry pulp. Since ozone itself reacts with cellulose as well, in a region where the ozone concentration exceeds 3% by weight, the influence of cellulose damage is more important than the decolorization effect of the decomposition of the dye.
This is because the dye existing in the waste paper cannot be completely decomposed if the content is less than wt%.

Ozone is an allotrope of oxygen represented by the molecular formula O ₃ , and is produced from oxygen and air as raw materials, for example, by silent discharge.

In the present invention, ozone can be used in any form that can achieve the object of the present invention. For example, the ozone-containing gas may be aerated in the reaction vessel, or may be added as a high-concentration ozone solution.

[0018]

EXAMPLES The present invention will be described below based on examples.

Examples 1 and 2 A 1% by weight slurry of recycled waste paper pulp containing 34% by weight virgin pulp was used to prepare 0.1% by weight of yellow direct dye (manufactured by Nippon Kagaku Kogyo Co., Ltd.) per dry pulp. , Direct Paper Yellow 4GL
) Was used to prepare a colored waste paper pulp slurry sample. Next, this slurry was adjusted to pH 10 and 11, and ozone treatment was performed by introducing an ozone-containing gas while stirring under the following conditions. Ozone concentration of supply gas: 20 g / m ₂ Ozone aeration rate per dry pulp: 13.0 g / kg Aeration time: 5.0 min Mixer rotation speed: 1500 / min At this time, ozone consumption is 4. per dry pulp. Three
The g / kg and ozone consumption rate were 0.33.

[Comparative Examples 1 to 3] Ozone treatment was carried out in the same manner except that the pH of the colored waste paper pulp slurry used in Example 1 was changed to three conditions of 6, 8 and 12.

The whiteness and yellowness of the pulps treated in Examples 1 and 2 and Comparative Examples 1 to 3 are shown in Table 1 together with the measured values of the untreated pulp.

[Table 1] When the pH of the pulp slurry is 11, the decolorization of the pulp proceeds most effectively, and the whiteness of the treated pulp is 46.4%,
The yellowness was 22.8%, which was a value very close to that of undyed pulp.

Table 2 shows the measurement results of the physical properties of the pulp obtained in Example 2 and the paper made from this pulp.

[Table 2] Before and after the ozone treatment, the physical properties of the pulp and the paper made from the pulp were hardly changed, and the burst strength and tensile strength were rather improved.

[Example 3] A colored waste paper pulp slurry sample was prepared in the same manner as in Example 2, except that a yellow direct dye (Kayafect Yellow YT Liquid) manufactured by Nippon Kayaku Co., Ltd. was used as the dye. This pulp slurry was subjected to ozone treatment in the same manner as in Example 2.

Comparative Examples 4 and 5 Instead of the colored waste paper pulp slurry sample of Example 3, two kinds of commercially available yellow telephone directory paper (using basic dye) were disaggregated to obtain a slurry having a pulp concentration of 1% by weight. The object was subjected to ozone treatment in the same manner as in Example 3.

Table 3 shows the yellowness reduction rate of the pulp after the treatment. The yellowness reduction rate of 100% means that the yellowness of the treated pulp is reduced to the same level as that of the undyed pulp.

[Table 3] Decolorization with ozone showed a high effect on pulp dyed with direct dyes, and the yellowness reduction rate of these pulps by ozone treatment reached 90% or more.

Example 4 The colored waste paper pulp slurry used in Example 1 was placed in a closed reaction vessel, and an ozone-containing gas was introduced into the reaction vessel. After stopping the introduction of the ozone-containing gas, stirring of the slurry was started. The detailed ozone treatment conditions are as follows. Pulp concentration (wt%): 1.0% pH value: 11 Ozone concentration of feed gas: 20 g / m ₂ Ozone aeration amount per dry pulp: 2.6 g / kg Aeration time: 1.0 min Mixing time: 4.0 min Mixer Rotation speed: 1500 / min

Table 4 shows the measurement results of the whiteness, yellowness, and physical properties of the treated pulp.

[Table 4] The ozone consumption at this time is 2.0 per dry pulp.
The g / kg and ozone consumption rate were 0.77.

The ozone consumption rate was improved by mixing after aeration of ozone, and a reduction rate of yellowness of 99% was achieved at an ozone aeration rate of 0.26% by weight.

[0029]

As described above, by carrying out the ozone treatment of the present invention, the waste paper pulp colored with the direct dye is more effectively decolorized to the same degree as the uncolored pulp, and the recycled pulp with high whiteness is obtained. Can be obtained.

Moreover, since the pulp strength is not impaired before and after the decoloring treatment, by using the waste paper pulp recycled according to the present invention, recycled paper having higher strength can be obtained.

Claims (5)

[Claims] 1. A method for recycling waste paper colored with a direct dye, wherein the pulp density of the disintegrated waste paper is 0.5 to
The slurry is agitated or mixed for decolorization in the presence of 0.1 to 3% by weight of ozone with respect to the dry pulp while the 3% by weight slurry is maintained at pH 9 to 11.5. How to recycle colored waste paper. 2. The method for recycling colored waste paper according to claim 1, wherein after the introduction of ozone, the slurry is stirred or mixed in a closed reaction vessel to decolorize the waste paper. 3. The method for recycling colored waste paper according to claim 1, wherein the ozone is introduced as an ozone-containing gas. 4. The method for recycling colored waste paper according to claim 1, wherein the direct dye is a yellow direct dye. 5. A paper obtained by a conventional method using waste paper pulp recycled by the method according to any one of claims 1 to 4 as a main raw material.