JPH06257082A - Waste paper reclaiming process - Google Patents

Abstract

PURPOSE:To effectively deink waste paper and remove adhesive material derived from coating paper, especially white pitch, in waste paper reclaiming process by using a flocculant in a floatation process and specifying the amount used of sodium silicate as a deinking chemical. CONSTITUTION:A waste paper reclaiming process comprises of a disintegration process wherein a mixed waste paper of coated waste paper and non-coated waste paper is dispersed in water to make a pulp slurry, a soaking process wherein a deinking agent consisting of a buffer containing an alkaline agent, a surfactant and sodium silicate and/or sodium carbonate is penetrated into pulp and a flotation process wherein ink is separated from pulp. In the present invention, a waste paper reclaiming process is carried out by specifying the amount used of sodium silicate as a buffer in the soaking process, of <=3wt.% based on pulp solid and a flotation process is carried out in the presence of a flocculant.

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 used paper. More specifically, the present invention enables deinking of a mixed waste paper of coated waste paper and non-coated waste paper as well as effective removal of an adhesive substance derived from the coated paper, particularly white pitch. Reproduction processing method

[0002]

2. Description of the Related Art In recent years, the use of recycled paper has been indispensable due to the demand for environmental protection and resource saving on a global scale, and the use of recycled paper is rapidly increasing. On the other hand, technical changes such as diversification of base paper, progress of coating technology and progress of printing method are of course possible, but due to diversification of information transmission means such as diversification of advertisements, multicolored and beautiful printed materials The social demand for quality and quantity is remarkable. for that reason,
Coated paper, in particular coated paper, art printed matter, commercial printed matter, calendar, poster, pamphlet or flyer, etc. are used in large quantities, and printed matter in which coated paper and non-coated paper are mixed, for example, A lot of newspapers (non-coated paper) with leaflets (coated paper) folded in are also running. Therefore, a large amount of waste paper, which is a mixture of coated paper and uncoated paper, is discharged from business establishments and homes. Then, when waste paper, which is a mixture of coated and uncoated paper, is treated by the conventional deinking method such as the flotation method or the washing method, the sticky substance (especially white pitch) derived from the coated paper becomes pulp slurry. When mixed, it enters the papermaking process of recycled paper and adheres to the paper machine and dryer, causing problems such as local peeling and breakage of the paper.

Among the adhesive substances derived from coated paper, the cause of occurrence of troubles is the adhesive substance derived from coated paper, which is the largest amount of coated paper, so-called white pitch. White pitch is a substance with adhesiveness that is a mixture of inorganic substances that give the smoothness of the coating layer to the binder component of coated paper, and where the precipitate is light gray. It has its name. The components of white pitch are said to have a complicated composition, but in an analysis example at a foreign paper mill, for example, inorganic substances (talc, kaolin) 40-60%, latex 15-
35%, resin 8-25% and holocellulose 5-30
% (Public Pulp Technology Association, Vol. 43, No. 4, No. 21)
page). However, the coated paper in Japan is said to have a more complicated white pitch composition, since various base papers and many kinds of binders are used and many kinds of inorganic substances are often used. And, the behavior of white pitch in a pulp slurry is not so clear at all, and therefore basic information for removing it (for example, information about the surface chemistry of white pitch) is obtained. The reality is that they do not. This also applies to adhesive substances derived from coated papers other than coated papers.

It is said that it is difficult to remove the sticky substance (particularly white pitch) in the pulp slurry in the used paper recycling process, and there are very few proposals concerning the removal of white pitch. Some of the proposals are to devise a deinking agent to remove white pitch as an incidental effect in the deinking process, or to add an additive to directly remove white pitch. . For example, U.S. Pat. No. 4,997,
Japanese Patent No. 523 describes a method of adding a diamine compound and a phosphate to a pulper during a waste paper disintegration step to separate and reduce white pitch from coated waste paper.
However, as far as the present inventors know, any of the methods proposed so far has a limited effect of removing white pitch from the pulp slurry, and it cannot be said that it is effective in actual operation. As described above, in the conventional used paper recycling method, an adhesive substance derived from coated paper, particularly white pitch,
No industrially effective means has been adopted to remove the above, and therefore various troubles have occurred in the paper making process of recycled paper due to the adhesion of such an adhesive substance to a dryer or the like.

[0005]

In view of the above-mentioned situation of the prior art, the inventors of the present invention, in Japanese Patent Application No. 3-318149, have applied a coagulant in the deinking process by flotation to apply white pitch or the like. We propose a method to effectively remove the sticky substances derived from craft paper. However, according to the subsequent studies by the present inventors, there is a difference in the white pitch removing effect by using the coagulant depending on the conditions during deinking, and particularly in the deinking treatment using a large amount of the buffer, the above effect by the coagulant Was found to be insufficiently expressed. Therefore, the present invention is intended to improve the above method of using a coagulant during deinking of waste paper, and enables the maximum expression of the effect of removing the adhesive substance derived from coated paper by using the coagulant. It is an object to provide a method for recycling used paper.

[0006]

[Means for Solving the Problems]

[Summary of the Invention]
In the method proposed in No. 49, there is a large correlation between the white pitch removing effect of a coagulant and the amount of sodium silicate used as a deinking chemical (buffering agent). It has been found that the amount of soda decreases in inverse proportion to the amount of soda used. The present invention is based on such findings. That is, the used paper recycling method of the present invention is a disaggregation step of dispersing a mixed used paper of coated paper waste and non-coated paper waste in water to form a pulp slurry, an alkali agent, a surfactant and sodium silicate and / or Alternatively, a soaking step of permeating the pulp with a deinking chemical consisting of a buffering agent containing sodium carbonate, a flotation step of separating the ink from the pulp, and a method of recycling the waste paper in a step including a step as a buffering agent in the soaking step. It is characterized in that the amount of sodium silicate used is 3% by weight or less based on the weight of the absolutely dry pulp, and the flotation step is performed in the presence of a flocculant.

[Detailed Description of the Invention] The use of the aggregating agent in the present invention is based on the following findings by the present inventors. (A) Used paper recycling process (especially flotation process)
When an aggregating agent is added to a pulp slurry in which an adhesive substance (particularly white pitch) derived from the above-mentioned coated paper is dispersed as a kind of dispersoid (mostly colloidal), the aggregating agent causes the adhesive substance to exist in the slurry. An unexpected phenomenon, which had never been known so far, was found to act preferentially and specifically on the. In the pulp slurry of the used paper recycling process, especially the pulp slurry of the flotation process, the substances dispersed therein, that is, the pulp, the sticky substance derived from the coated paper and the ink, exist in a state where the electric charges are in harmony with each other. It is a water dispersion liquid. Moreover, by adding the coagulant, the charge of the colloidal particles dispersed in water or waste liquid is neutralized by the charge of the opposite coagulant, and the force acting as a repulsive force between the colloidal particles is weakened. The main function is to strengthen the attractive force between the colloidal particles so that the colloidal particles are bonded to each other and the colloidal particles are formed into a large lump to facilitate sedimentation. Therefore, it is generally recognized that adding a flocculant to a pulp slurry in which colloidal substances and the like have an electric charge dispersed therein causes various phenomena such as flocculation of pulps and re-flocculation of ink into pulp. However, adding a flocculant to the pulp slurry in the used paper recycling process for this purpose has been considered unconventional by those skilled in the art. For example, JP-A-57-78987
The publication describes the effect of adding a cationic polymer to the effluent after separating the pulp in the used paper recycling process. According to this, the addition of the cationic polymer causes the ink and other dispersions to be dispersed. It's supposed to be a big flock.

(B) Addition of a flocculant to a pulp slurry containing a deinking agent (often composed of a surfactant) causes the flocculating agent to act on the deinking agent to reduce the function of the deinking agent. It has been considered inadequate for a person skilled in the art to make the deinking agent and the coagulant coexist in the pulp slurry due to damage. However, according to the finding by the present inventor, contrary to expectation, the action of the coagulant on the deinking agent is slight, and depending on the combination of the coagulant and the deinking agent, the flotation treatment causes It has become clear that the deinking effect may be further improved.

<Waste Paper Recycling Method> The waste paper recycling method of the present invention comprises a disaggregation step, a soaking step and a flotation step. The disaggregation step is usually a step in which the paper is stirred in water by a device called a pulper to disperse the fibers in water. The soaking process is a process in which a chemical having a deinking action is sufficiently penetrated into ink or pulp. It is usually performed at room temperature to about 80 ° C. for about 15 minutes to 1 day. The chemicals used for soaking are alkaline agents,
It is a buffer and a surfactant, and NaO is used as an alkaline agent.
As the buffering agent such as H and KOH, sodium silicate and sodium carbonate are used. The flotation process is to remove the object to be removed from the pulp slurry by causing bubbles generated in the pulp slurry to accompany the object to be removed (such as ink) in the pulp slurry and separating the material that has floated to become floss. Is a process of separating from. The term "floss" is used to mean a foam floating in a pulp slurry. The foam is typically composed of bubbles. The means for generating bubbles in the pulp slurry is arbitrary, and a method of injecting gas into the pulp slurry from the outside (for example, press-fitting) to mix the bubbles into the pulp slurry, or causing turbulent flow in the pulp slurry, in which air is generated Involving
Various means such as a method of mixing bubbles in the pulp slurry can be used. "Following foam" means contained in the water around the foam that adheres to the foam and rises with rising foam.

The sticky substance to be removed by the flotation treatment of the present invention is a sticky substance contained in the pulp slurry in a dispersed (particularly colloidal) state when used paper is pulped. Most of the adhesive substances are derived from coated paper waste paper, and most of the coated paper is actually coated paper. Therefore, most of the adhesive substances are adhesive substances derived from coated paper. , That is, white pitch. In addition, even when used paper other than coated paper is pulped, the adhesive substance dispersed in the pulp slurry has properties close to white pitch (especially properties in terms of surface chemistry). Therefore, it has been confirmed by the present inventor that it can be similarly removed by the method of the present invention.

There are no restrictions on the apparatus used in the flotation process of the present invention (especially the floatator). However, the floatator is preferably made of stainless steel (made of SUS) to which the agglomerated ink and the white pitch are less likely to adhere to the device, in order to prevent the ink and the white pitch from adhering to the device. In the used paper recycling method of the present invention, in addition to the above disaggregation step, soaking step, flotation step, any processing steps conventionally used in used paper recycling processing such as a concentration step and a freeness adjusting step are appropriately added. be able to. In the present invention, the flocculant may be added to the pulp slurry of any step before performing the flotation treatment, may be added at the entrance of the step of performing the flotation treatment, or may be added to the floatator. Good. Further, in the present invention, the sticky substance dispersed in the pulp slurry is removed together with the foam by the flotation treatment, but it does not substantially affect the ink removal effect by the flotation treatment.

FIG. 1 is a flow chart showing an example of a used paper recycling method according to the present invention. The steps were performed under the conditions shown in the figure. In this used paper recycling process, the white water circulation process is omitted for convenience. In FIG. 1, waste paper is treated in the disaggregation step (1) to prepare a pulp slurry with a pulp concentration of about 7%, and the pulp slurry is dewatered in a concentrating step (2) to a pulp slurry with a pulp concentration of about 18%. The deinking agent added thereto is sent to the soaking step (3). Then, a flocculant is added to the pulp slurry whose pulp concentration is adjusted to about 4% in the freeness adjusting step (4), and the flotation step (5) is performed.
to go into. In the flotation step (5), the white pitch in the pulp slurry agglomerates due to the action of the aggregating agent and adheres to the air bubbles, and the air bubbles with both the ink and the white pitch attached rise (float) to become floss. , Floss is collected and taken out of the process. Measuring device (5
In a), in order to confirm the effect of the addition of the flocculant, the pulp slurry at the inlet and the outlet of the flotation step (5) is taken out, and the number of residual colloids in the pulp slurry is measured. Here, the “colloid” of the number of residual colloids is a colloid remaining in the pulp slurry, and mainly refers to colloidal particles such as latex that moves in Brownian motion. The pulp slurry from which both the ink and the white pitch have been removed in the flotation step (5) is concentrated in the concentration step (6) to increase the pulp concentration, and becomes a pulp slurry for recycled paper. This pulp slurry for recycled paper is made into recycled paper in the papermaking step (7), and the whiteness of the recycled paper is measured by the whiteness measuring device (8). In this flow process diagram, the flocculant is added at the inlet of the flotation process (5), but it is better to use low concentration pulp.
This is because there is an advantage that the probability that the pulp and the coagulant are entangled with each other is low.

<Waste Paper> The waste paper targeted by the used paper recycling method of the present invention is waste paper in which coated waste paper and non-coated waste paper (mainly newspaper waste paper) are mixed. The ratio of waste coated paper to waste uncoated paper is about 1: 9 to 9: 1. In the present specification, the term "coated paper" means a general coated paper,
For example, the term includes not only art paper, coated paper and light-weight coated paper, but also paper in which a part of the paper surface is treated with a coating agent.

<Deinking Chemicals> Generally, caustic soda is used as the alkaline agent. Sodium silicate as a buffer,
Although sodium carbonate and the like are available, conventionally, sodium silicate is most often used. Especially when a large amount of ink needs to be deinked, such as waste paper mainly made of newspaper waste, caustic soda is used in an amount of 1% (% by weight based on the dry pulp weight).
Represents The same applies hereinafter), and sodium silicate is conventionally used in an amount of 2 to 4 times that of caustic soda. However, in the present invention, since the white pitch removing effect of the coagulant decreases in inverse proportion to the amount of sodium silicate used, the amount of sodium silicate used is 3% or less, preferably 2%, relative to the pulp.
It is necessary to do the following. When a buffering agent is further required, it is preferable to use another buffering agent such as sodium carbonate. Therefore, in the present invention, as a buffering agent, sodium silicate in an amount of 3% or less, preferably 2% or less, relative to pulp is used together with sodium carbonate in an amount of 0 to 6%, preferably 2 to 4%. Is preferred. As the surfactant, any of anionic type, nonionic type and amphoteric type can be used. Examples of the anion type include carboxylic acid type, sulfuric acid ester type, sulfonic acid type, and phosphoric acid ester type. Specific examples include fatty acid soap, fatty acid sulfate,
Examples thereof include sodium alkyl sulfonate and alkyl phosphate. The nonionic type includes ether type and tester type, and specific examples thereof include polyoxyethylene alkyl ether and polyoxyethylene alkyl ester.

<Aggregating agent> According to the used paper recycling method of the present invention, the sticky substance dispersed in the pulp slurry (particularly in the form of colloid), particularly the sticky substance derived from coated paper (that is,
The white pitch) is added to the foam by the action of the coagulant, and the floating froth is removed. As used herein, the term "flocculant" refers to an "agent" that acts on a sticky substance (particularly white pitch) dispersed in a pulp slurry (particularly colloidal) to cause them to flocculate. Means The aggregating agent used in the present invention includes an inorganic aggregating agent and an organic aggregating agent. As an inorganic coagulant,
Inorganic compounds and inorganic macromolecules (including oligomers (including dimers)) are available as coagulants. Organic coagulants include anionic, cationic, or amphoteric polymer coagulants and some in water. Polymeric flocculants that dissociate and carry a charge can be used.

Specific examples of the aggregating agent include (A) aluminum chloride, polyaluminum chloride, sodium aluminate,
Inorganic flocculants such as zirconium salt and polysulfate aluminosilicate, polyacrylamide polymer flocculants such as (B) polyacrylamide, anionic polyacrylamide, cationic polyacrylamide, amphoteric polyacrylamide, and (C) polyethylene oxide. Alkylene oxide polymer flocculant, (D) natural polymer flocculant such as sodium alginate, (E) cationic sodium polyacrylate, polyacrylic ester polymer flocculant such as cationic polyacrylic acid ester, And (F) polyamide polyamine, a polymer flocculant such as a condensation product of dimethylamide and epichlorohydrin. Among the above-mentioned aggregating agents, inorganic aggregating agents and polyacrylamide polymer aggregating agents, particularly inorganic aggregating agents are preferable. Among the inorganic flocculants, aluminum chloride and polyaluminum chloride are preferable, and polyaluminum chloride is particularly preferable. The polyacrylamide polymer flocculant is preferably polyacrylamide. Further, the aggregating agent may be used alone or in combination of two or more kinds,
It has been found by the present inventors that the adhesive substance removing effect may be increased when two or more kinds are used in combination.

The flocculating agent preferentially acts on the sticky substance derived from coated paper, particularly white pitch, so that the sticky substance becomes attached to the bubbles generated in the flotation treatment. It is used in an amount within a range that does not cause mutual agglomeration or pulp and deinking agent agglomeration. The amount of the flocculant added varies depending on the pulp slurry conditions at the time of flotation treatment, for example, the pulp concentration, the type and concentration of the deinking agent in the slurry, and the state of electric charge in the slurry, but preferably 0. 0.01 to 3% by weight (based on the weight of dry pulp in the pulp slurry), and particularly preferably 0.05 to 1% by weight. Further, when an appropriate amount of the aggregating agent is used, in addition to the effect of removing the adhesive substance, it may also have the effect of improving the whiteness of the recycled paper.

Further, in order to more effectively bring out the effect of the flocculant, it may be preferable to adjust the pH of the pulp slurry with an acid within an appropriate range. When sulfuric acid is used as the acid, the sulfuric acid itself may act as a flocculant. p
Since the range of application of H varies depending on the aggregating agent used, it is difficult to uniformly determine the range, but in general, the pH may be in the range of 3-12. Further, the target pulp slurry is dispersed at a concentration of 0.1 to 1.5% by weight of pulp (based on the weight of pulp slurry) and 0.01 to 0.1% by weight of ink (based on the weight of pulp slurry). When,
Addition of a flocculant does not cause flocculation of pulps or re-flocculation of ink into pulp, and the flocculating agent is particularly preferential and specific for sticky substances derived from coated paper (especially white pitch). It has been found by the inventor to work. Hereinafter, the present invention will be described more specifically with reference to Examples. The examples are illustrative of the invention and are not intended to limit the invention.

[0019]

[Examples] Examples 1 to 5 and Comparative Example 1 <Recycled Paper Recycling> Disaggregated waste newspaper collected in a plant (80% by weight newspaper, 20 leaflets)
20% of warm water (40 ° C)
Then, the density of waste paper was adjusted to 10%. After being left overnight, it was disintegrated into a pulp slurry with an experimental pulper at a waste paper concentration of 7% for 3 hours.

Soaking treatment Next, the pulp slurry was dewatered by a centrifugal dehydrator to adjust the soaking treatment concentration to 18%.
I chose 0.8% caustic soda, 0.1% nonionic surfactant (3: 1 mixture of polyoxyethylene polyoxypropylene alkyl ether (cloud point 45 ° C.) and stearic acid) in the pulp slurry, and sodium silicate,
Sodium carbonate was added in the amount shown in Table 1 below. Here, the addition amount (%) of each reagent is based on the pulp weight (dry weight). The added pulp slurry was treated with a pulp concentration of 15% at 45 ° C. (using a water bath) for 16 hours.

Adjustment of Freeness The pulp slurry after the soaking treatment was diluted with water cleaned with an ion exchange resin to a pulp concentration of 4%, and made into a freeness of 200 ml CSF with a KRK refiner. The water used in the subsequent experiments was all water that had been cleaned with an ion exchange resin.

Flotation Treatment Flotation treatment was carried out using a laboratory floatator. A flotation amount (amount of pulp slurry equivalent to 42 g of absolute pulp dry amount) of flotation is collected from the pulp slurry (freeness 200 ml CSF) whose freeness has been adjusted, and the flocculating agent is stirred with a disintegrator. As an additive, polyaluminum chloride (PAC) was added in an amount shown in Table 1, and air was blown in from the air bubble blowing port of the laboratory floatator for flotation treatment. During the flotation process,
The operation of scraping out the entire amount of floss was performed every 30 seconds, and the operation was performed 8 times in total. Further, for comparison, the flotation treatment was performed on the pulp slurry to which the flocculant was not added in exactly the same manner.

<Measurement Method> The number of colloidal particles in the pulp slurry (the pulp slurry at the inlet and the outlet of the experimental floatator) before and after the flotation treatment was measured. Further, the pulp slurry after the flotation treatment was hand-made into recycled paper, and its whiteness was measured.

Measurement of the number of colloidal particles EKDS hemocytometer [Kayagaki Medical Science Co., Ltd. (THO
(MA type)] and the cover glass were washed with alcohol and then completely adhered so that Newton's rings could be formed on the convex portions at both ends of the hemocytometer. In that state, the volume of one section in the hemocytometer is 50 μm × 50 μm × 0.1 mm (depth). The microscope is 15 (eyepiece) x 40 (objective) =
It was measured at the maximum light intensity by using a 600 times magnification. The number of colloidal particles was counted at a pulp concentration of 0.1% (weight basis) and converted into a pulp slurry having a pulp concentration of 1%. As for the colloidal particles, only particles that were completely spherical (about 1 μm in diameter) and were in Brownian motion were counted (N =
8). To calculate the number of colloidal particles, multiply the number of colloidal particles in one section (A) by the hemocytometer depth correction coefficient (C),
It was divided by the volume (V) of one section and further divided by the concentration (Pc) to obtain the number of colloidal particles converted into a 1% concentration pulp slurry. The calculation formula is shown below.

Measurement of whiteness The whiteness is based on ISO 2470-1977, and ELREPHO 20 manufactured by DATACOLOR is used as a measuring instrument.
00 was used. The whiteness is represented by the average value of the measured whiteness values of the front and back surfaces of the recycled paper.

<Measurement results> Effect of reducing the number of residual colloidal particles (removal of colloidal particles
%) The number of residual colloidal particles at the outlet of the floatator of the pulp slurry to which the coagulant was added was measured by the above method, and the number of residual colloidal particles of the pulp slurry at the outlet of the flowter without addition of the coagulant was calculated as 100. The reduction rate (%) of the number of residual latex particles (removal rate of colloidal particles) was used to evaluate the effect of reducing residual colloidal particles. The obtained results are shown in Table 1 below together with the whiteness measurement results. In Table 1, the addition amount (%) of the reagent represents% by weight based on the weight of the absolutely dry pulp. Table 1 PAC Sodium silicate Sodium carbonate Colloidal whiteness Addition amount (%) Addition amount (%) Addition amount (%) Particle removal rate (%) Example 1 0.1 2 2 41.6 58.6 Example 2 0.5 2 2 87.2 59.7 Implementation Example 3 0.1 0 4 75.2 51.7 Example 4 0.1 0 0 75.1 48.3 Example 5 0.1 3 0 26.0 59.5 Comparative Example 1 0.1 4 0 14.5 59.7

[0027]

EFFECTS OF THE INVENTION According to the present invention, with respect to a mixed waste paper of a coated waste paper and a non-coated waste paper, the adhesiveness derived from the coated paper which cannot be removed by the conventional waste paper recycling method by the flotation method or the washing method It becomes possible to remove substances, particularly white pitch, industrially effectively, thereby eliminating troubles caused by the sticky substance in the papermaking process of recycled paper, such as local peeling and breaking of paper.

[Brief description of drawings]

FIG. 1 is a flow process chart showing an example of a used paper recycling method of the present invention.

[Explanation of symbols]

 1 Disaggregation process 2 Concentration process 3 Soaking process 4 Freeness adjusting process 5 Flotation process 5a Measuring device 6 Concentrating process 7 Paper making process 8 Measuring device

Claims (3)

[Claims] 1. A disintegration step of dispersing a mixed waste paper of a coated waste paper and a non-coated waste paper in water to form a pulp slurry, a disintegration step, an alkali agent, a surfactant and a buffer containing sodium silicate and / or sodium carbonate. In a method of recycling waste paper by a step including a soaking step of infiltrating a pulp with a deinking chemical consisting of an agent, a flotation step of separating ink from the pulp, the amount of sodium silicate used as a buffer in the soaking step Is 3% by weight or less based on the weight of the absolutely dried pulp, and the flotation step is performed in the presence of a flocculant. 2. As the aggregating agent, aluminum chloride, polyaluminum chloride, polysulfate aluminosilicate, sodium aluminate, zirconium salt, polyacrylamide, anionic polyacrylamide, cationic polyacrylamide, amphoteric polyacrylamide, polyethylene oxide, alginic acid. The method according to claim 1, wherein at least one of soda, cationic sodium polyacrylate, cationic polyacrylic ester, polyamide polyamine, modified epichlorohydrin, and condensation product of dimethylamide and epichlorohydrin is used. . 3. As a buffer in the soaking step, 0 to 2% of sodium silicate and 2 to 4% of sodium carbonate are used.
3. The method according to claim 1 or 2, characterized in that (both in% by weight with respect to the dry pulp weight) is used.