JPH1053988A - Deinking - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a deinked pulp having high whiteness and yield and slight in tacky material and ash from various kinds of raw material waste paper by changing pH in the system by >=2 in at least one part of a flotation process. SOLUTION: A surfactant is added to pulp slurry prepared by adding various kinds of chemicals to raw material waste paper and these materials are mechanically stirred to deink the pulp slurry and the pulp slurry containing released ink is introduced into a flotator and pH in the system in a flotation process is changed by at least >=2 (preferably 3-6) and the flotation process is preferably carried out at a range of pH10-4. Ink and filler, etc., removable at each pH are removed even if various kinds of waste papers are mixed therein to improve deinking effect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to newspapers, flyers,
The present invention relates to a deinking method for deinking and recycling used paper such as magazines. More specifically, the present invention relates to a deinking method capable of removing ink and filler more efficiently.

[0002]

2. Description of the Related Art Waste paper is recycled by removing ink from the waste paper by deinking treatment, obtaining recycled pulp, and manufacturing recycled paper from the recycled pulp. The conventional deinking method generally includes a step of removing ink from waste paper and a step of discharging the removed ink. More specifically, the deinking method includes, as its main steps, (1) a pulping (disintegration) step of waste paper, (2) aging, ie, leaving the disintegrated paper as it is, (3) flow Station process,
And (4) including a washing step. That is, in the deinking process,
The ink bound to the waste paper fibers is physically and chemically (or biochemically) peeled to separate the ink from the fibers. The separated ink adheres to the bubbles in the flotation step and is discharged out of the system together with the bubbles. Thereafter, the deinked pulp is washed to obtain a recycled pulp.

[0003] In the conventional deinking treatment as described above, ink removal is generally performed in the presence of an alkaline substance such as caustic soda or sodium silicate in order to enhance the ink removing effect.
H (pH 12 to 9), and subsequently the release ink is removed in the flotation step under the same conditions. Usually, the pH in the system in the flotation treatment is kept at a high pH and hardly changes, and is kept almost constant.

On the other hand, there are very few deinking methods in which a flotation step is carried out at a pH of 9 or less.
There are only disclosures in 3705, 59-53532 and U.S. Pat. No. 4,043,903.
These disclose that the flotation step is performed in a low pH region, but excessive foaming occurs in the flotation step, poor ink release performance, and therefore, pulp with high whiteness cannot be obtained. In addition, the ink cannot be sufficiently removed, and the deinking effect is insufficient.

[0005]

In recent years, properties of waste paper used as a raw material have been diversified due to an increase in demand for beautiful and stable printing and progress of printing technology. In addition, the degree of bonding of the ink to the paper varies widely, from gentle to strong. In such a situation, it is required to improve the quality (whiteness, the number of remaining inks, etc.) and the yield (that is, productivity) of the deinked pulp. In order to achieve this object, various proposals have been made from various aspects such as a deinking process, a deinking agent, and a device used for deinking.

[0006] In the deinking process which is usually performed, a wide variety of raw material waste papers are used, for example, a plurality of brands are mixed as used newspapers, flyers and magazines are mixed therein, and other printed materials are mixed therewith. Generally, printed matter is mixed. In addition, the amount of foreign substances such as adhesive tapes, adhesives, resin strings, etc. has been increasing today,
Its removal is also a problem. Therefore, as a measure to enhance the deinking effect, it is necessary not only to have deinking performance enough to cope with various used waste papers, but also to improve the performance from the viewpoint of removing foreign substances. You. In other words, in the deinking process, the type of used paper (eg, brand name of newspaper used paper, flyer type, magazine type), the degree of deterioration of used paper, the type of ink, filler, pigment, paper surface coating agent, etc., and contamination of foreign matter There are many factors such as these, and for efficient deinking, it is necessary to consider the effects of these factors.However, use a single deinking agent or deinking method to deal with all of them. Is extremely difficult.

[0007]

The inventor of the present invention has studied in detail a method capable of exhibiting a good deinking effect even in a deinking method using various used waste papers. It has been found that the pH range and the chemical addition conditions that are advantageous for the respective removal vary depending on the type of ink, filler, pigment, paper surface coating agent and the like. Furthermore, based on this knowledge, by using a flotation process that changes the pH from a flotation process that has been conventionally performed at almost constant one pH, efficient deinking has been achieved even when using various raw material waste papers. As a result, the present inventors have found that a deinked pulp having high whiteness and a high yield and having little sticky substance and ash can be obtained, and completed the present invention.

[0008] That is, the present invention provides a deinking method including a flotation step of removing ink peeled from used raw paper, wherein the pH in the system is changed by 2 or more in at least a part of the flotation step. To provide a deinking method.

In general, the ink is peeled from the raw waste paper by appropriately cutting the raw waste paper and then adding a surfactant, which is a deinking agent, to a pulp slurry prepared by adding various agents such as warm water and an alkaline agent. Then, the pulp slurry containing the release ink is introduced into a flotator to perform a flotation step. In the present invention, the pH in the system in the flotation step
Is not constant but varied. here,
The phrase "change in pH" means that a region where at least 2 or more, preferably 3 to 10, and particularly preferably 3 to 6 pH changes is present in the flotation step. Small p in the system derived from
Excludes changes in H. If the change in pH is less than 2, a sufficient deinking effect cannot be obtained. Then, in the deinking method of the present invention, it is sufficient that the pH changes at least once. Further, the “system” in the flotation step refers to a water-pulp slurry at the time of performing the flotation treatment, and in the present invention, the pH of the aqueous solution portion is referred to as “system pH”.

In the present invention, the pH after the change in the system in the flotation step is pH 4 to 10, preferably p.
It is desirable to be in the range of H5 to H9. In particular, pH 4 ~
Preferably, there is a region where the pH changes by 2 or more in the range of 10. The mode of the pH change may be continuous, gradation, or a combination thereof. Specific examples include a method of gradually decreasing the pH from a high pH to a low pH, a method of gradually increasing the pH from a low pH to a high pH, and a method of combining the increase and decrease of the high and low pH. Since a general flotator has a plurality of flotator tanks or a series of several flotator tanks, the pH of the flotation process can be changed by controlling each of the flotator tanks to an arbitrary pH. Can be. When a single flotator tank is used, the pH can be gradually reduced or increased. In the present invention, examples of a method of changing the pH of the system of the flotation step (that is, the treated water) include a method of adding an acid such as hydrochloric acid or sulfuric acid or a base such as sodium hydroxide or potassium hydroxide.

[0011] As described above, the deinking method of the present invention is based on the finding that the removal efficiency of the object to be removed varies depending on the pH in the system in the flotation step. For example, in deinking using newsprint as raw paper, analyzing the ash content of the material removed during flotation, the metal composition of the material removed by flotation, the whiteness of the pulp after flotation, the remaining ink amount, the residual adhesiveness The amount varies depending on the pH. As a result, different newspaper brands such as inks, fillers, pigments, etc.
It was found that there was a subtle deviation. Therefore, it is considered that since various waste papers are mixed in the waste paper collected in the market in the conventional actual operation, even if the flotation treatment is performed at a certain pH, the ink and the filler cannot be sufficiently removed. In the present invention, changing the pH in the system in the flotation step, preferably, changing the pH to 10 to 4
In this range, the ink, filler and the like that are easily removed at each pH are efficiently removed, and as a result, the deinking performance is improved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the ink stripping step, at least one surfactant is usually used for ink stripping. As the surfactant, a surfactant conventionally known as a deinking agent can be used, but a cationic surfactant, an anionic surfactant, and a nonionic surfactant are preferable, and a nonionic surfactant is particularly preferable. Agent. And, as the nonionic surfactant, the following (A) to
One or more selected from (D) is preferred. Particularly preferred are the nonionic surfactants represented by the following (A), (B) and (C), and more preferred are the nonionic surfactants represented by the following (C).

<Nonionic surfactant (A): reaction product obtained by adding an alkylene oxide to a mixture of fats and oils and alcohol> Nonionic surfactant (A) is a mixture of fats and oils, monovalent or polyvalent. It is an alkylene oxide adduct of a mixture with an alcohol. Alkylene oxide is added to the above mixture in an average of 5 to 300 per mole of the mixture.
Moles, preferably 20 to 150 moles.
Examples of the alkylene oxide include ethylene oxide, propylene oxide, and butylene oxide, and they may be used alone or in the form of a mixture of two or more thereof.

The mixing ratio of fats and oils to alcohol is 1
/0.1 to 1/6 is preferred, and 1 / 0.3 to 1/3 is particularly preferred. When the ratio is within the above range, the peeling of the ink is sufficiently performed, so that the regenerated pulp having a good appearance can be obtained.

Examples of oils and fats as raw materials of the nonionic surfactant (A) include vegetable oils such as coconut oil, palm oil, olive oil, soybean oil, rapeseed oil, linseed oil, and animal oils such as lard, beef tallow, bone oil and the like. , Fish oil, their hardened and semi-hardened oils, and the recovered oils obtained in the purification process of these oils and fats. Particularly preferred are coconut oil, palm oil and tallow.

Examples of the monohydric alcohol as a raw material of the nonionic surfactant (A) include those having an alkyl or alkenyl portion having 8 to 24 carbon atoms, and those having an alkyl portion having 6 to 14 carbon atoms. Those having an alkylphenyl moiety are included. Preferably 12 to 18 carbon atoms
Having an alkyl moiety of

Examples of the polyhydric alcohol as a raw material of the nonionic surfactant (A) include ethylene glycol, propylene glycol, glycerin, trimethylolpropane and the like.

<Nonionic surfactant (B): Formula: RCO
Compound represented by O (AO) _m R ′> In the above formula, R represents an alkyl or alkenyl group having 7 to 23 carbon atoms;
Is a hydrogen atom, an alkyl group having 1 to 22 carbon atoms, 2 carbon atoms
Represents an alkenyl group having 2 to 22 carbon atoms or an acyl group having 2 to 22 carbon atoms, preferably hydrogen, AO represents an oxyalkylene group having 2 to 4 carbon atoms, and m is an integer of 1 or more. A
The average number of added moles of O is preferably from 5 to 300 moles. Further, it is preferable to use ethylene oxide and propylene oxide as AO at a molar ratio of ethylene oxide to propylene oxide of 1/5 to 5/1.
Among the nonionic surfactants (B), those having the carbon number of the alkyl or alkenyl group represented by R, particularly those having 11 to 23 carbon atoms, are preferable.

<Nonionic surfactant (C): Formula: RO
Compound represented by (AO) _n H> In the above formula, R represents an alkyl or alkenyl group having 8 to 24 carbon atoms, and AO is
It represents an oxyalkylene group having 2 to 4 carbon atoms, and n is an integer of 1 or more. The average number of moles of AO added is preferably from 5 to 300 moles, more preferably from 7 to 150 moles. Further, it is preferable to use ethylene oxide and propylene oxide as AO at a molar ratio of ethylene oxide to propylene oxide of 1/5 to 5/1.

<Nonionic surfactant (D): a reaction product obtained by adding an alkylene oxide to a polyvalent carboxylic acid or its acid anhydride, or a polyvalent carboxylic acid or its acid anhydride and an alcohol The reaction product obtained by adding an alkylene oxide to a mixture of a nonionic surfactant (D)> is produced using a polycarboxylic acid or its anhydride (I) and an alcohol (II). You. At that time, the compounds (I) and (II) are converted from (I) to (II)
Is preferably used at a molar ratio of 1 / 0.02 to 5, particularly preferably 1 / 0.1 to 3.

As the anionic surfactant, a higher fatty acid or a salt thereof is preferably used. As the cationic surfactant, a quaternary ammonium salt can be used, and a mono-long chain alkyl type quaternary ammonium salt is particularly preferable.

The surfactant may be added to any step of the deinking method. However, it is usually added to the pulping step. The addition amount is not particularly limited. Of course, known deinking agents other than the above nonionic surfactants (A) to (D) can be used in combination therewith.

Further, in the deinking method of the present invention, a cationic compound, an amine, an acid salt of an amine or an amphoteric compound, preferably an amine, an acid salt of an amine, a cationic compound, Preferably, an amine or an acid salt of an amine is present. By using these compounds in combination, the removal efficiency of the object to be removed is further improved. These compounds are particularly effective when the pH in the flotation step is 5 to 9.

Examples of the cationic compound include a quaternary ammonium salt of a mono-long-chain alkyl type, a quaternary ammonium salt of a di-long-chain alkyl type, a pyridinium salt having a substituent on a nitrogen atom, and a cationic polymer. Can be Among the cationic compounds, in particular, the following formulas (a ₁ ) to (c ₁ )
The cationic compound represented by is preferred.

[0025]

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[In the formulas (a ₁ ) to (c ₁ ), R ₁
And R ₂ are the same or different and are each an alkyl, alkenyl or β-hydroxyalkyl group having 10 to 24 carbon atoms, and R ₃ , R ₄ and R ₅ are the same or different and An alkyl or hydroxyalkyl group having 1 to 8 carbon atoms, a benzyl group, or a compound represented by the formula:
-(AO) _n -Z (where AO is an oxyalkylene group having 2 to 4 carbon atoms, Z is a hydrogen atom or an acyl group, and n is an integer of 1 to 50) Group,
R ₆ is alkyl, alkenyl or β having 8 to 36 carbon atoms.
- a hydroxyalkyl group, X ^- is a counterion, Y is alkyl having 8 to 36 carbon atoms, alkenyl or β- hydroxyalkyl group of the formula: R ₆ COOCH ₂ - (wherein, R ₆ is defined Is a group represented by
A group represented by the formula: R ₆ CONHCH ₂ — (where R ₆ is as defined above) or a group represented by the formula: R ₆ OCH ₂ — (where R ₆ is as defined above) It is a group to be performed. ].

Examples of amines and amine acid salts include 1
Secondary amines, secondary amines, tertiary amines, cyclic amines, imidazoles and imidazolines, inorganic acid salts of these amines, organic acid salts of these amines, and polymers containing amino groups. The acid salt of an amine or amine, in particular the following formulas _{(a 2) ~ (c 2} ) salt of an amine or amine represented by are preferred.

[0028]

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[In the formulas (a ₂ ) to (c ₂ ), R ₁ is
An alkyl, alkenyl or β-hydroxyalkyl group having 8 to 36 carbon atoms, wherein R ₂ and R ₃ are the same or different from each other and are each a hydrogen atom, an alkyl group having 1 to 24 carbon atoms or 2 to 2 carbon atoms; 24 alkenyl groups, H
A represents an inorganic or organic acid. ].

Examples of the amphoteric compound include betaine, amine oxide, phospholipid, protein and amphoteric polymer. As the amphoteric compound, in particular, the following formula
(a ₃₎ ~ amphoteric compound represented by (b ₃₎ is preferable.

[0031]

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[In the formulas (a ₃ ) to (b ₃ ), R ₁ , R ₂
And R ₃ are the same or different and are an alkyl group having 1 to 24 carbon atoms or an alkenyl group having 2 to 24 carbon atoms, respectively, and R ₄ is an alkyl group having 8 to 36 carbon atoms, alkenyl or β-. A hydroxyalkyl group, wherein M is
A hydrogen atom, an alkali metal atom, 1/2 mole of an alkaline earth metal atom or an ammonium group. ].

At least one selected from the group consisting of a cationic compound, an amine, an acid salt of an amine and an amphoteric compound is used in the flotation step in an amount of 0.1 to pulp.
005% to 5% by weight, preferably 0.01% by weight
To 1% by weight. These compounds may be added at any time during the flotation step,
The effect is remarkable when the pH in the system is in the range of 5 to 9, and it is preferable to add when the pH in the system is in this range. During the flotation of these compounds,
In other words, the presence in the slurry makes it possible to efficiently remove the ink, the filler, and the foreign matter, and it is possible to achieve both improvement in whiteness and improvement in yield. This is because the cationic compound, amine, amine acid salt and amphoteric compound are selectively adsorbed to the ink, the filler and the foreign matter due to the difference in the properties of the interface between the ink, the filler and the foreign matter, and the pulp interface. It is considered that the air bubbles proceed to be easily removed by the bubbles.

The deinking method of the present invention is characterized in that the pH in the system in the flotation step is changed. Other steps can be performed according to a conventional deinking method. That is, the deinking method may include, as its main steps, a defibration (or pulping) step, an aging step, a kneading step (if necessary), a flotation step, and a washing step. The deinking method may further include other steps if necessary. Each step may be performed two or more times. As a mode of the pH change in the flotation step of the present invention, for example, p
Decrease H, or gradually increase pH in the range of pH 4-12
Is increased. In particular, considering that the ink peeling step is usually performed in an alkaline region, the pH of the flotation step is preferably gradually reduced from the pH while the pH at the start is preferably set to pH 10 to 9, and the pH is gradually reduced. PH at the end of pH 4-6
Is more efficient. Alternatively, the flotation step may be started in an alkaline region, the pH may be gradually reduced to make the mixture acidic once, and the pH may be increased again to bring the pH at the end of the flotation step to the alkaline region. Other methods may be used as long as the pH in the system changes by 2 or more in at least a part of the flotation step.

In the deinking method of the present invention, when the pH in the system in the flotation step is changed, the time of the flotation treatment at each pH is arbitrary, and the scale of the flotation step and the change in pH Is different depending on whether it is continuous or gradational, and the processing time may be appropriately selected. In addition, the flotation temperature is not limited, and can be appropriately selected in the range of room temperature to 90 ° C.

[0036]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

REFERENCE EXAMPLE Waste paper (newspaper / flyer = 70/30) collected in the city is cut into 5 × 4 cm, and a certain amount thereof is put into a table disintegrator.
Warm water and sodium hydroxide 1% by weight (based on raw material), sodium silicate 3% by weight (based on raw material), 30% by weight of hydrogen peroxide 1% by weight (based on raw material), and 15 mol of stearyl alcohol EO as a deinking agent (Average number of moles added) / PO
15 mole (average number of moles) block adduct (EO: ethylene oxide, PO: propylene oxide)
2% by weight (based on raw materials) was added to make the pulp concentration 5% by weight,
Disintegrated at 40 ° C. for 10 minutes. After the obtained pulp slurry was aged at 40 ° C. for 60 minutes, warm water was added to dilute the pulp concentration to 1% by weight, and the pH of the pulp slurry was adjusted to a value shown in Table 1 using sulfuric acid. After that, 0.05% by weight of an amine compound (Ia-1) represented by the following formula:
(To the raw material) was added, and a flotation treatment was performed at 40 ° C. for 10 minutes. After the flotation treatment, the amount of effluent and the metal composition of ash in the effluent were measured. Here, the ash content was obtained by accurately weighing the absolute dry amount of a circular pulp sheet having a diameter of 16 cm and incinerating it at 600 ° C. in a crucible, and then obtaining as ash content. The metal composition was determined by atomic absorption analysis of this ash. From the metal composition of the ash, the composition of the filler can be deduced. Table 1 shows the results.

[0038]

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[0039]

[Table 1]

From the results, the pH at which flotation was performed was determined.
Filler components and amounts removed by
It turns out that there is H. That is, it is understood that calcium carbonate and talc are easily removed at a pH of about 7, while other components are easily removed on the alkali side and those easily removed on the acidic side.

Examples 1 to 13 and Comparative Examples 1 to 3 Waste paper collected in the city (newspaper / flyer / tack label =
70 / 29.9 / 0.1) was cut into 5 × 4 cm pieces, and a fixed amount thereof was placed in a tabletop disintegrator, in which warm water and sodium hydroxide 1% by weight (based on raw materials), sodium silicate 3% by weight were added. (Based on raw material), 30% by weight of hydrogen peroxide solution 1% by weight (based on raw material) and 15 mol of EO (average addition mole number) of PO and 15 mol of PO (average addition mole number) of stearyl alcohol as a deinking agent (EO: ethylene) Oxide, PO: propylene oxide) (0.2% by weight (based on raw material)) was added to adjust the pulp concentration to 5% by weight. After the obtained pulp slurry was aged at 40 ° C. for 60 minutes, warm water was added to dilute the pulp concentration to 1% by weight.
When the pH of the pulp slurry is adjusted to the value shown in Tables 2 to 4 using sulfuric acid and sodium hydroxide, and the additives described in Tables 5 to 11 are further added, 0.2% by weight is added here.
(To the raw material) was added, and a flotation treatment was performed at 40 ° C. for 10 minutes. After flotation treatment, pulp sheet (circular sheet with a diameter of 16 cm) using a tappy sheet machine
And after pressurizing 5 kgf / cm ² , air-dry and
The yield, whiteness, number of stickies, and ash content of the pulp after flotation were measured by the following methods. The results are shown in Tables 2 to 4.

The whiteness was adjusted by adding a sulfuric acid band (aluminum sulfate) to the pulp slurry before and after flotation, which had been sampled in advance, to adjust the pH to 5.5. Obtained. The whiteness of the obtained pulp sheet was measured with a colorimeter. It should be noted that an improvement of 1% in the whiteness of the paper-made pulp sheet can be visually recognized as a sufficient effect.

The pulp yield at the time of flotation was determined from the ratio of the absolutely dry pulp weight in the pulp slurry before the flotation and the absolutely dry pulp weight in the flotation reject. A 1% increase in yield can be recognized as a significant difference.

Paper making was carried out at a rate of 100 g per square meter for the number of stickies, and the number of stickies in a pulp sheet of 25 cm × 25 cm was visually counted. If the number of sticky substances is two or less, in the case of an actual machine, it can be removed in screening after flotation, etc., and sufficiently endures practical use, but if it is three or more, it is considered that equipment measures are required.

The ash content of the pulp is an index of the residual filler. The absolute dryness of a circular pulp sheet having a diameter of 16 cm is precisely weighed, and after burning in a crucible at 600 ° C., the residual ash content is measured. I asked. In general, the smaller the amount of the residual filler, the easier the subsequent steps can be adjusted, and a 0.5% decrease in the ash content can be sufficiently recognized as a significant difference.

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4]

(Note) In the table, "F / T" stands for flotation. In Examples 1 to 13, the pH at the time of flotation was changed from the upper value in the table to the lower value. In addition, the example which added the additive shows that the additive initially added continued to exist in the system (that is, p
H is not added with the change of H). The additives are compounds shown in Tables 5 to 11 below.

[0050]

[Table 5]

[0051]

[Table 6]

[0052]

[Table 7]

[0053]

[Table 8]

[0054]

[Table 9]

[0055]

[Table 10]

[0056]

[Table 11]

Examples 14 to 21 and Comparative Examples 4 to 6 Pulp sheets were prepared in the same manner as in Example 1 except that the deinking agents and additives shown in Tables 12 and 13 were used, and the same evaluation was performed. . The results are shown in Tables 12 and 13.

[0058]

[Table 12]

[0059]

[Table 13]

(Note) In the table, the symbol of the deinking agent has a meaning. Deinking agent A: EO stearic acid 15 mol (average addition mole number) PO 10 mol (average addition mole number) random adduct Deinking agent B: EO7 of tallow / glycerin (1: 1) mixture
0 mol (average addition mol number) PO 10 mol (average addition mol number) block adduct Deinking agent C: dimer acid EO 30 mol (average addition mol number)
PO 30 mol (average addition mole number) block adduct The additives are compounds shown in Tables 14 to 16 below.

[0061]

[Table 14]

[0062]

[Table 15]

[0063]

[Table 16]

As shown in the above examples, the method of the present invention not only has high whiteness after flotation, but also has a small amount of sticky substances considered to be derived from foreign matters and a small amount of ash in pulp as a residual filler. Quality pulp was obtained. Furthermore, since the difference in whiteness before and after the flotation is large and the yield is high, it can be seen that the deinking efficiency is high.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor ▲ Taka ▼ Hirotsu 1334 Minato, Wakayama-shi, Wakayama Pref.

Claims (8)

[Claims] 1. A deinking method including a flotation step of removing ink peeled from raw material waste paper, wherein the pH in the system is changed by 2 or more in at least a part of the flotation step. . 2. The deinking method according to claim 1, wherein the pH after the change in the system in the flotation step is in the range of pH 4 to 10. 3. The pH in the system in the flotation step
3. The deinking method according to claim 1, wherein the change is a decrease from a high pH to a low pH. 4. The pH in the system in the flotation step
3. The deinking method according to claim 1, wherein the change is a rise from a low pH to a high pH. 5. The pH in the system at the start of the flotation step
Is in the range of pH 12 to 9, and the pH in the system at the end of the flotation step is in the range of pH 6 to 4.
The deinking method according to any one of the above items. 6. The method according to claim 1, wherein at least a part of the flotation step is performed in the presence of at least one selected from the group consisting of an amine compound, an acid salt of an amine, a cationic compound and an amphoteric compound. The deinking method according to claim 1. 7. The method according to claim 6, wherein at least one compound selected from the group consisting of the amine compound, amine acid salt, cationic compound and amphoteric compound is added in an amount of 0.005% by weight to 5% by weight per pulp. The deinking method described. 8. The method of claim 1, wherein the pH in the system is in the range of pH 5 to 9 in at least a part of the flotation step.
8. The deinking method according to claim 6, wherein at least one compound selected from the group consisting of the amine compound, amine acid salt, cationic compound and amphoteric compound is added to the system in the H range.