JP2000265384A - Production of deinked pulp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing deinked waste paper pulp having whiteness equivalent to the case treated with an alkaline chemical by neutralizing pH condition of immersing process in production of deinked pulp, reducing load in water discharge and simultaneousl keeping releasing property of ink. SOLUTION: In this method for producing deinked pulp of printing waste paper, including disintegration process, immersing process and flotation process, the immersing process is carried out in weakly acidic condition to neutral condition in the presence of a dithionite and the flotation process is carried out in the presence of a cationic coagulating agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing deinked pulp, and more particularly to a method for producing deinked pulp from waste printing paper, and more particularly to a method for deinking waste paper pulp having a flotation step.

[0002]

2. Description of the Related Art As a method for producing deinked pulp from used printing paper, generally, a method of separating pulp and ink using a flotator or the like via a disintegration step of printing used paper and an alkali immersion step is generally used. That is, in the general deinking method, the used printing paper is disintegrated with a deinking agent consisting of an alkaline chemical and a surfactant by using a disintegrator such as a pulper, and then is used as a waste paper pulp. An agent is added and alkali immersion (alkali soaking) is performed to swell the pulp fibers and separate the ink. Next, in the flotation step, the ink particles adhere to the air bubbles and float to separate the ink particles from the pulp.

In the alkali immersion step, after the waste paper disintegration step, an alkali chemical, hydrogen peroxide and a surfactant are added, and alkali immersion is performed at a pulp concentration of 10 to 35% to swell the pulp fibers and to form a printing ink. From the pulp fiber. However, by performing the alkali immersion treatment, not only promotes deinking, but also fillers such as clay and talc, titanium dioxide, starch, paper-strengthening agents such as polyvinyl alcohol, latex, starch oxide, calcium carbonate and the like. Not only is the coating composition and fine fibers discharged during washing and dehydration treatments, etc., but also part of the pulp is dissolved by the swelling and dissolving action of the pulp due to alkali, so the COD (chemical oxygen demand) in this wastewater is 1000-4000 ppm, reaching 1-4% per weight of pulp produced. Therefore, it is necessary to dilute or clarify the wastewater in the deinking step in large quantities before discharging the wastewater into a public water area, and there is a problem that a coagulation treatment chemical, equipment costs, and running costs are required. For the purpose of reducing this drainage load, if the alkaline soaking process is to be carried out in a weakly alkaline to weakly acidic neutral region,
Quality problems such as insufficient swelling of the pulp fibers and insufficient peeling of the printing ink, making it difficult for the printing ink to float and separate in the flotation process following this process, and the whiteness of the deinked pulp does not increase. There was a point.

[0004] Further, bleaching of pulp with hydrogen peroxide is usually carried out under alkaline conditions of pH 9 or more, which is considered to be because hydrogen peroxide is activated by alkaline conditions and good bleaching properties can be obtained. The use of alkaline chemicals in the dipping process has become essential.

Examples of using a dithionite as a deinking accelerator are disclosed in JP-B-2-4717, JP-A-7-17-1.
No. 4,558,397, in which the immersion is performed under alkalinity by adding an alkali agent such as caustic soda or sodium carbonate, and is not performed from weakly acidic to neutral. Also, JP-A-3-294589 and JP-A-7-1994.
No. 2,907,074, JP-A-8-35188, JP-A-10-8391, etc., use dithionite as a reducing bleach after deinking or oxidative bleaching of information recording paper or high-quality waste paper. It is. In the prior art, when dithionite is used in the deinking and bleaching steps, multi-stage bleaching is performed.
Sufficient whiteness cannot be obtained.

[0006]

SUMMARY OF THE INVENTION In order to obtain pulp having a reduced drainage load by removing ink from used printing paper,
It is necessary to carry out the alkaline soaking step in a condition of a weakly alkaline to weakly acidic neutral region. However, in a usual treatment, swelling of pulp fibers is not sufficient, and peeling of a printing ink is insufficient, which causes a problem. That is, the present invention neutralizes the pH conditions of the immersion step in the production of deinked pulp to reduce the drainage load and at the same time maintain the releasability of the ink, and has the same whiteness as that of the treatment with an alkaline chemical. The present invention provides a method for producing waste paper pulp.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have intensively studied an ink peeling accelerator which can replace an alkaline chemical. As a result, they have found that the use of dithionite and a cationic flocculant can effectively achieve the object even in a weakly acidic to neutral range. That is, the present invention includes the following inventions.

[0008] 1. In the method for producing a deinked pulp of used printed paper including a defibration step, an immersion step and a flotation step, the immersion step is performed from weakly acidic to neutral in the presence of dithionite, and the flotation step is performed in a cationic manner. A method for producing deinked pulp, which is carried out in the presence of a water-soluble flocculant.

[0009] 2. The method for producing deinked pulp as described above, wherein the pH is slightly to neutral from 4 to 7.

The reason why the method according to the present invention can obtain a deinked pulp having a smaller drainage load than the conventional method is as follows.
The present inventors consider as follows. That is, by neutralizing the pH conditions in the immersion step, the amount of alkali elution is reduced, so that deinking can be performed without increasing drainage load. Dithionite has a bleaching effect in the neutral region, and has the effect of preventing the appearance of a new lignin-colored structure generated by alkalinity and preventing the reactivity of the already-developed color-forming group from decreasing. In addition, dithionite bleaching is a relatively rapid reaction compared to the reaction of hydrogen peroxide under alkaline conditions, so the processing time can be reduced, and the oxidative decomposition of pulp such as hydrogen peroxide under alkaline conditions is also reduced. Since it does not occur, an effect of suppressing a decrease in pulp strength can also be expected.

In addition, the effect of peeling and dispersing ink from pulp by a weakly acidic to neutral surfactant and the effect of dispersing and dispersing by mechanical agitation such as dispersion are caused because fine ink particles are generated. Aggregation of the ink particles and the like requires some treatment to increase the efficiency of the flotator treatment, and a chemical suitable for such a purpose, that is, a compound having a surface activity for aggregating the peeled ink particles and the like is required. It is essential to add and process. The present inventors have found that a compound having cationic properties is extremely suitable as such a compound, and have completed the present invention. The reason why the compound having the cationic property is effective is that the cationic flocculant is adsorbed on the fine ink particles peeled and dispersed from the pulp by the mechanical stirring force such as the surfactant and the dispersion. This increases the hydrophobicity of the ink itself, improves the cohesive force between the inks, or improves the adsorptivity of the ink to the foam, and produces aggregates of a size suitable for flotation processing, which is extremely effective in flotation. I guess it is because it will be removed. As a result, without adding the alkali added in the conventional alkaline soaking process, almost the same pulp brightness as the conventional one is obtained, and the amount of alkali in the wastewater is reduced, so that the elution of organic substances is reduced, and the wastewater is discharged. It is estimated that the load will be low.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The used paper to which the present invention is directed includes newspapers, flyers, magazines, books, office papers, and other printing papers produced by copying machines and office automation equipment.

In the production of ordinary deinked pulp,
After the paper disintegration step, an alkaline chemical, hydrogen peroxide and a surfactant are added, and generally 10 to 35% by weight.
The pulp is diluted with alkali in a pulp concentration of the following, and the pulp is diluted in a next step and is applied to a flotator (flotation step) to separate pulp fiber and ink. The method of the present invention is to provide a dithionite immersion step in place of the alkali immersion step, and to add a cationic coagulant before the next step of a flotator. The immersion step and the flotation step are performed in this order, and the existing equipment can be used as it is.

The pH condition of the immersion step of the present invention is that the immersion treatment is carried out from weakly acidic to neutral in the presence of dithionite. Dithionite is alkaline and has a strong reducing ability. However, at pH 7 or more, a new coloring structure of lignin may be revealed, and the reactivity of the already developed coloring group may be reduced. Therefore, there is also a problem that the dissolution of the organic matter due to the water becomes intense and the drainage load increases. In addition, although the reaction rate increases on the acidic side, the rate of ineffective decomposition of dithionite also increases,
The range of the treatment pH is suitably pH 4 to 7, and more preferably pH 5 to 6.

The treatment time of the immersion step of the present invention is 10 to 1
00 minutes, preferably 30 to 60 minutes. Dithionite bleaching is a relatively rapid reaction as compared with the reaction of hydrogen peroxide under alkaline conditions, so that even if the treatment is carried out for 100 minutes or more, further improvement in whiteness is difficult and not practical.

The pulp concentration in the dipping step of the present invention is from 1 to 35.
%, Preferably 3 to 20% by weight, more preferably 3 to 10% by weight. Pulp concentration of 20-35% by weight
When the concentration is from medium to high, the bleaching effect in the pulp slurry increases because the concentration of the bleaching chemicals in the pulp slurry increases, but reducing bleach such as dithionite is oxidized by air and decomposes ineffectively. It is necessary to prevent the ineffective decomposition by replacing the air with nitrogen or the like, and it is necessary to strengthen the stirring process because of the high concentration. When these conditions are not satisfied, it is easier to stir the pulp at a low concentration of 10% by weight or less, and the decomposition of dithionite can be suppressed.

The addition ratio of dithionite in the dipping step is 0.1 to 3% by weight, preferably 0.5 to 2% by weight, more preferably 0.5 to 1% by weight based on the absolutely dried pulp.
% By weight. Even when added in an amount of more than 3% by weight, it is difficult to further improve the whiteness, and on the contrary, the corrosiveness becomes strong, which causes a problem in operation.

In the present invention, a cationic surfactant is used as an aggregating agent. Examples of the cationic surfactant include an amine salt type, a methyl type, a benzyl type, and an imidazoline type, but when cost and operability are considered, the re-adsorption property of the dispersed ink particles to the pulp is relatively low. Weak, primary amines, primary amine acetates, quaternary ammonium salts and the like are preferred.

The addition ratio of these cationic surfactants is 0.005 to 1% by weight based on the absolutely dried pulp.
Preferably it is 0.005 to 0.7% by weight, more preferably 0.01 to 0.5% by weight. The whiteness of the cationic surfactant is improved by increasing the addition rate, but the yield of the pulp in the flotator is reduced and the cost of chemicals is increased. Therefore, the content of the cationic surfactant is preferably 0.5% by weight or less.

[0020]

Next, the present invention will be described in detail with reference to examples, but the examples do not limit the present invention. In this example, the percentage (%) means weight% except for whiteness, and the chemical addition rate is shown by weight% based on absolute dry pulp. The quality of deinked pulp is J
Pulp whiteness according to Hunter whiteness test method for paper and pulp according to ISP-8123, tear length by pulp sheet beaten to the same freeness according to strength test method for paper pulp according to JIS P-8113, and after flotation Was evaluated by COD in the dehydrated filtrate. The pH before the immersion step is additionally shown.

<Embodiment 1> Offset-printed used newspaper 70
%, 30% flyer waste paper was added to 30 ° C. hot water, defibrated with a test pulper under the following conditions, and dehydrated to a concentration of 17%. Pulp concentration 4% Caustic soda addition rate 0.5% Surfactant addition rate 0.4% (Non-ionic surfactant DI-767 manufactured by Kao Corporation) Next, after diluting the pulp concentration to 5% with warm water of 30 ° C,
The pH was adjusted to 6 with sulfuric acid, and the pulp was treated under the following conditions as a dipping step. Pulp concentration 5% Processing time 1 hour Processing temperature ··· 60 ° C sodium dithionite addition rate ··· 1% After completion of the immersion step, dilute the pulp concentration to 4% with warm water at 30 ° C and use a disintegrator for 2 minutes. The mixture was stirred.
Next, after diluting the pulp concentration to 1%, tetradecylamine acetate as a coagulant was added in an amount of 0.1% in terms of pure content per absolutely dry pulp, and the mixture was placed in a laboratory flotator and added to a lab flotator.
Flotate at an air flow rate of 20 L / hr for 10 minutes. After dewatering the floated pulp slurry to a pulp concentration of 10%, the pulp concentration was diluted to 0.5%, a hand-made sheet was prepared by a TAPPI standard method, and air-dried. The hand-made sheet was measured for pulp brightness and breaking length, and the results are shown in Table 1 as Example 1.

<Comparative Example 1> In Example 1, after the used paper was disintegrated and dewatered to 17%, pulp was treated under the following conditions as a conventional alkaline soaking step instead of the immersion step with sodium dithionite. A treatment was performed in the same manner as in Example 1 except that a flotation treatment was performed without adding a cationic coagulant. The results are shown in Table 1 as Comparative Example 1. Pulp concentration 15% Processing time 2 hours Processing temperature ··· 60 ° C Caustic soda addition rate ······ 1% Sodium silicate addition rate ······ 2% (converted to pure content) Hydrogen peroxide addition rate 0.5% (converted to pure content) <Comparative Example 2> Except that no cationic coagulant was added before flotation in Example 1. Treated as in Example 1. The results are shown in Table 1 as Comparative Example 2.

<Example 2> All treatments were performed in the same manner as in Example 1 except that the pH was set to 5 in the immersion step with sodium dithionite. The results are shown in Table 1 as Example 2. <Example 3> All treatments were performed in the same manner as in Example 1 except that the pH was set to 4 in the immersion step with sodium dithionite.
The results are shown in Table 1 as Example 3.

Example 4 In the immersion step, the same treatment as in Example 1 was carried out except that Zn dithionite was used instead of Na dithionite. Table 1 shows the results as Example 4.
It was shown to.

<Comparative Example 3> All treatments were performed in the same manner as in Example 1 except that the pH was set to 3 in the immersion step with sodium dithionite. The results are shown in Table 1 as Comparative Example 3. <Comparative Example 4> Except that the pH was adjusted to 8 by adding caustic soda in the immersion step with sodium dithionite,
The same treatment was performed. The results are shown in Table 1 as Comparative Example 4. <Comparative Example 5> In the immersion step, the same treatment as in Example 1 was carried out except that sodium hydrogen sulfite was used instead of sodium dithionite. The results are shown in Table 1 as Comparative Example 5.

[0026]

[Table 1]

[0027]

As described above, the present invention has been described in detail. According to the method of the present invention for deinking a used printing paper without adding an alkali added in a conventional alkali immersion step, almost the same pulp whiteness as the conventional one is obtained. The pulp with a small amount of organic substances eluted in the wastewater and a reduced drainage load could be produced. Further, in the present invention, the treatment time is short, and there is no decrease in pulp strength because there is no influence of alkali chemicals.

Claims (2)

[Claims] 1. A method for producing a deinked pulp of used printed paper, comprising a defibration step, a dipping step and a flotation step, wherein the dipping step is carried out in the presence of dithionite from weakly acidic to neutral. A method for producing a deinked pulp, wherein the flotation step is performed in the presence of a cationic flocculant. 2. The process for producing deinked pulp according to claim 1, wherein the pH of the pulp is weakly acidic to neutral.