JPH08120580A - Deinking of printed waste paper - Google Patents

Abstract

PURPOSE: To obtain regenerated pulp of high whiteness at low froth rate, by disaggregating printed waste paper in the presence of a reductive bleaching agent with a pH range from weak alkalinity to acidity without using any alkali chemical. CONSTITUTION: To deink printed waste paper such as newspaper or magazines, the printed waste paper is subjected to disaggregation treatment at a pulp concentration of 1-10 (pref. 3-7)wt.% at 15-40 deg.C for 3-60 (pref. 5-30)min by using a treating liquid of pH4.5-8.5 containing a surfactant such as polyoxyethylene nonyl phenyl ether, enzyme(s) such as cellulase and/or xylanase with its optimal pH value at 4.5-8.5 and a reductive bleaching agent such as sodium hydrosulfite. The system is then concentrated to 10-35wt.% of pulp concentration and incorporated with 1-4wt.%, based on the pulp in terms of genuine solid, of sodium hydroxide and 2.5-20wt.% of sodium silicate (in terms of the JIS #3 sodium silicate) to conduct alkali immersion treatment to separate the ink from the pulp by flotation or washing process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for deinking printed waste paper such as newspapers and magazines, and more particularly to a method for producing deinked pulp having a high degree of whiteness by immersion in an alkali.

[0002]

2. Description of the Related Art Many methods have been proposed for deinking printed waste paper, but in the case of obtaining high-whiteness pulp from those containing offset-printed waste paper that is difficult to deink. The alkali dipping process is indispensable. The method currently adopted in the deinking method including the alkali dipping step is as follows. After disintegrating printed waste paper with a deinking agent consisting of an alkaline chemical and a surfactant with a disintegrator such as a pulper, it is used as waste paper pulp (hereinafter abbreviated as pulp), and the alkaline chemical is added to the pulp.
Hydrogen peroxide and a surface active agent are added and alkali immersion is performed to swell the pulp fiber, peel the printing ink from the pulp fiber, and separate the pulp fiber and the printing ink in a flotation process or a washing process.

[0003]

The addition of alkali in the disaggregation step is mainly added for the purpose of enhancing the deinking effect as a pretreatment of the subsequent alkali dipping step as described above, and swelling of pulp fiber by alkali The effect and the disintegration promoting effect are expected to some extent, but the effect as an alkali is not so large because the disintegration time is short. The pulp disintegration step is usually treated with a relatively low concentration of 3 to 7% pulp concentration, but the alkali dipping step is 10 to 35%.
Since the pulp was treated at a pulp concentration of%, it was dehydrated before the alkali dipping step, and the squeezed liquid having a large ink content was drained. Therefore, although the effect of adding chemicals is low,
Wastewater treatment load was high. In addition, since an alkali is used in the disaggregation process, various restrictions have been placed on the use of enzymes, which are attracting attention because they are effective in promoting disaggregation and deinking.

[0004]

In order to solve the above-mentioned problems, the present invention has any one of the following eight configurations. (1) In a deinking method for waste printing paper including at least a disaggregation step, a concentration step, an alkali dipping step, and an ink-pulp separation step, only a deinking agent comprising a surfactant without using an alkaline chemical in the disaggregation step A method for deinking used waste paper, characterized by adding and disintegrating. (2) The deinking method according to (1), wherein the disintegration step is performed at pH 4.5 to 8.5. (3) The deinking method according to (1) or (2), wherein the pulp concentration in the disaggregation step is 1 to 10% by weight. (4) The deinking method according to any one of (1) to (3), wherein the pulp concentration in the alkali dipping step is 10 to 35% by weight. (5) After the concentration step and before the alkali immersion step, caustic soda of 1 to 4% by weight in terms of pure solid content and pulp, and
2.5 to 20 wt% (JIS No. 3 sodium silicate equivalent conversion)
Characterized by adding sodium silicate (1)
The deinking method according to any one of (5). (6) The deinking according to any one of (1) to (5), characterized in that a cellulase and / or a xylanase enzyme having an optimum pH of pH 4.5 to 8.5 is added in the disaggregation step. Method. (7) The deinking method according to any one of (1) to (6), which is characterized in that a reducing bleaching agent is used together when disaggregating in the disaggregating step. (8) The deinking method according to (7), wherein the reducing bleaching agent is sodium hydrosulfite.

The inventors of the present invention have made extensive studies to solve the above-mentioned problems, and as a result, discovered the following items (1) to (3) and completed the present invention. When chemicals are used for the purpose of promoting disintegration and deinking effect by disintegrating waste printed paper in a short time, the effect of using alkali is low. Sufficient disaggregation and deinking effect can be obtained only with the surfactant in the disaggregation step, and deinking effect is poor without the surfactant. In the concentration (dehydration) step before the alkali immersion step, the alkaline chemicals are discharged as waste water, which is a waste of chemicals. The alkali in the wastewater increases the wastewater treatment load. If the disaggregation is performed in the weakly alkaline to neutral to acidic region without using an alkali, an enzyme having a high disaggregating activity or deinking activity in this region can be used. If defibration is carried out in the weakly alkaline to neutral to acidic region, a reducing bleaching agent having a high bleaching activity in this region can be used.

The pulp concentration in the disaggregation step of the present invention is 1 to 10
%, More preferably 3 to 7% by weight. The disaggregation treatment temperature is preferably 15 to 40 ° C. The processing time is
It is 3 to 60 minutes, preferably 5 to 30 minutes. In the present invention, the addition amount of the deinking agent comprising a surfactant in the disaggregation step is not particularly limited and may be a known addition amount, specifically 0.1 to 1% by weight based on the absolutely dried pulp. Added to a degree.

The surfactant used in the deinking agent may be any of anionic type, nonionic type and amphoteric type, and known deinking agents can be used. As the anionic type, a carboxylic acid type, a sulfuric acid ester type, a sulfonic acid type, and a phosphoric acid ester type, and as the nonionic type, an ether type, an ester type, an ether / ester type, a fatty acid alkylol amide type, and an amphoteric type, Amino acid type and betaine type can be used respectively.

When a reducing bleaching agent is added in the disintegration step, the whiteness of the finally obtained deinked pulp is improved, but sodium hydrosulfite, which is often used for bleaching pulp, is highly effective and inexpensive, so Since the effect is higher in the acidic region, it is effective to add it in the disaggregation step in which no alkali is added as in the present invention.

The concentration step is a step of dehydrating and concentrating in order to increase the efficiency of the alkali dipping step, but at the same time, the peeled ink is removed together with the water to be dehydrated. In the concentration step, the pulp solid content concentration is concentrated to 10% by weight or more.

The alkali dipping step is performed by adding an alkaline chemical after the concentration step. As alkaline chemicals, caustic soda, potassium hydroxide, calcium hydroxide,
Although sodium carbonate, sodium silicate, etc. can be used, the most preferable is a combination of caustic soda and sodium silicate. The addition rate of caustic soda in the alkali dipping step may be 1% by weight or more in terms of pure solid content, and preferably 2 to 4% by weight, based on the absolute dry pulp, and the addition rate of sodium silicate is
According to JIS No. 3 sodium silicate, it may be 2.5 to 20% by weight, preferably 5 to 15% by weight. Also,
The pulp concentration in the alkali soaking step is preferably 10 to 35% by weight.

After the alkali soaking step, the ink is separated from the pulp by a flotation method or a washing method. As these methods, known methods can be used. Further, if necessary, a step of mixing chemicals may be performed before the alkali dipping step, and a step of separating the ink from the pulp by a mechanical force such as a kneader may be provided before or after the alkali dipping step. May be.

[0012]

The operation based on the above constitution is as follows: (1) Since the printed waste paper is disintegrated together with the surfactant, the disintegration and deinking effects are enhanced. (2) The alkali chemicals added in the disaggregation step are added to the alkali immersion step, and only the deinking agent consisting of a surfactant is added in the disaggregation step, so the alkali that has been dehydrated and removed before the alkali immersion step is removed. You can use it to the maximum extent. (3) Since the amount of alkali in the wastewater is reduced, the elution of organic substances is reduced and the wastewater treatment load is reduced. (4) Since alkali is not used, the disaggregation process becomes weakly alkaline to neutral to weakly acidic, and has an effect of promoting disaggregation and deinking without pH control, and the optimum pH is weakly acidic to neutral. The use of enzymes is possible. (5) Further, by using a reducing bleaching agent together in the disaggregation treatment, a more excellent deinking effect can be obtained.

[0013]

EXAMPLES Examples of the present invention will be shown below and described in more detail. In the examples,% is% by weight except for whiteness
Displayed in. Evaluation of deinked pulp is JIS P-81
22. Pulp whiteness according to the Hunter whiteness test method for paper and pulp, and the weight ratio of the absolute dry weight of the ink-based separated material (floss) separated and removed by the floater to the dry weight of raw printed paper (floss). Rate).

<Example 1> Water was added to printed waste paper consisting of offset printed newspaper, letterpress printed newspaper, and flyer waste paper, and disintegrated with a test pulper under the following conditions to dehydrate to a concentration of 20%. Pulp concentration ----- 4.2% by weight Surfactant addition rate --- 0.2% by weight (vs. pulp, the same applies hereinafter) The surfactant is polyoxyethylene nonyl phenyl ether (the number of moles of ethylene oxide n = 9) Further, an alkali dipping step (same meaning as the soaking step) was performed under the following treatment conditions. Pulp concentration -------- 15% by weight Treatment time -------------- 4 hours Treatment temperature----80.degree. C. Addition rate of caustic soda --- 2.8% by weight ( Soluble silicate addition rate --- 10% by weight (against pulp, JI
S3 No. 3 silicic acid equivalent weight percent, the same below) Surfactant addition rate --- 0.07 weight percent (the types of surfactants are the same as above) Hydrogen peroxide addition rate --- 2.5 weight % (Pure weight conversion, based on pulp weight%, the same applies below) This pulp treatment liquid is diluted to 4%, and further diluted to 1%,
A deinked pulp obtained by performing flotation treatment for 5 minutes using a test floatator, separating and removing the floated ink, and dehydrating it was set as Example 1.

Example 2 A deinked pulp obtained by treating in exactly the same manner as in Example 1 except that the surfactant was added in the alkali dipping step of Example 1 was used as Example 2. Surfactant addition rate ------ 0.14% by weight

<Comparative Example 1> Example 1 is the same as Example 1 except for the chemicals added in the disaggregation step and the alkali dipping step and their addition rates.
The deinked pulp obtained by treating in exactly the same manner as in Comparative Example 1. Disaggregation process (testing pulper) Caustic soda addition rate --- 0.8% Sodium silicate addition rate --4% Surfactant addition rate --- 0.2% Alkaline immersion step Caustic soda addition rate --2% Silicic acid Soda addition rate --6% Surfactant addition rate --0.14% Hydrogen peroxide addition rate --2.5%

<Comparative Example 2> Example 1 is the same as Example 1 except for the chemicals added in the disaggregation step and the alkali dipping step and their addition rates.
The deinked pulp obtained by treating in exactly the same manner as in Example 2 was used as Comparative Example 2. Disaggregation process (test pulper) Chemical-free alkali soaking process Caustic soda addition rate --- 2.8% Sodium silicate addition rate --10% Surfactant addition rate --- 0.34% Hydrogen peroxide addition rate- --2.5%

<Example 3> The additive chemicals were all the same as in Example 2, and further, Example 3 was prepared by adding 1.5% by weight of sodium hydrosulfite in the disaggregation step. The above results are shown in Table 1.

[0019]

[Table 1]

[0020]

INDUSTRIAL APPLICABILITY The present invention has been described in detail above. By the deinking method for waste printed paper of the present invention, a pulp having a high whiteness which cannot be achieved by the conventional deinking method can be obtained with a low froth rate.

Claims (8)

[Claims] 1. A method of deinking used waste paper, which comprises at least a disintegration step, a concentration step, an alkali dipping step, and an ink-pulp separation step, which comprises a surfactant without using an alkaline chemical in the disaggregation step. A method for deinking used waste paper, characterized by adding only a chemical to disintegrate. 2. The deinking method according to claim 1, wherein the disintegration step is carried out at a pH of 4.5 to 8.5. 3. The deinking method according to claim 1 or 2, wherein the pulp concentration in the disaggregation step is 1 to 10% by weight. 4. The pulp concentration in the alkali soaking step is 10 to 3
The deinking method according to claim 1, wherein the deinking method is 5% by weight. 5. After the concentration step and before the alkali immersion step,
A caustic soda content of 1 to 4% by weight and a 2.5 to 20% by weight (JIS No. 3 sodium silicate equivalent conversion) sodium silicate are added in terms of pure solids.
~ The deinking method according to claim 4. 6. An optimum pH of 4.5 to 8.5 is set in the disaggregation step.
The deinking method according to any one of claims 1 to 5, wherein the cellulase and / or the xylanase-based enzyme is added. 7. The deinking method according to any one of claims 1 to 6, wherein a reducing bleaching agent is used together when disaggregating in the disaggregating step. 8. The deinking method according to claim 7, wherein the reducing bleaching agent is sodium hydrosulfite.