JPS61194289A - Regeneration of old paper - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for recycling waste paper, and more specifically, the present invention does not use sodium sulfite and generates less pollution due to the cooking method, thus reducing wastewater COD. A method for recycling waste paper that produces high whiteness and high strength recycled pulp with extremely low disintegration, good disintegration of waste paper, and little damage to waste paper fibers [Prior art and its problems] It accounts for approximately 40% of the raw material, making it an important pulp resource along with raw wood, but the recent tightening of the global raw wood situation and rising energy costs have increased the importance of recycled paper. Among these, the de-ining (recycling) of used printing paper is attracting attention as an advanced use of waste paper, and there is a strong demand for the development of efficient de-ining technology.

There are two typical conventional deinking methods for printed waste paper: (1) high-temperature pressure cooking method and (2) pulper method, but the present invention relates to a pressure steaming solution. . The high-temperature pressure cooking method is a method that has been used for a long time. Raw material waste paper and chemicals such as sodium sulfite, an alkaline agent, and a surfactant are placed in a spherical pot and heated under high pressure (approximately 1
Cooking is carried out at a temperature of 20°C to 150°C while rotating the pot. Subsequently, after performing a disaggregation process, dust is removed to remove foreign substances and the product is washed. Furthermore, if necessary, it is bleached with an oxidizing agent such as hydrogen peroxide or sodium hypochlorite to obtain recycled pulp. However, in this method, the waste paper fibers are severely damaged due to the high temperature and high pressure treatment, resulting in a decrease in il1 paper strength. (2) Poor yield. (3) Due to high wastewater COD and high temperature,
(4) Energy costs are high. (5) Since a pressure cooker is required, the equipment cost is high. When high-pressure steam is blown after the ink has been inked, it has various drawbacks, such as the generation of loud noise and bad odor, which often leads to pollution problems.

In particular, wastewater COD regulations are becoming stricter year by year.
In the case of factories that use only coagulation and sedimentation treatment to control heat, wastewater COD
Countermeasures have become the most important theme. Therefore, in order to improve these drawbacks, many places are taking measures such as lowering the cooking temperature. However, since the cooking chemical generally consists of 2 to 596% sodium sulfite and 0.5 to 1.0% soda ash, there is a limit to how low the cooking temperature can be reduced, and temperatures of 100 to 1 are considered defective and cannot be deinked. becomes incapable. Another drawback is that the disintegration properties of waste paper deteriorate and a large amount of undisintegrated fibers are generated. Therefore, low-temperature cooking is not possible as long as sodium sulfite is used.

On the other hand, as a method for reducing wastewater COD,
Japanese Patent No. 192792 discloses a method in which sodium percarbonate is used in place of the conventional sodium sulfite.

However, in the method described in JP-A-59-192792, the cooking temperature is still high at 90 to 180°C.
Damage to waste paper fibers is unavoidable, and the disintegration properties are also poor. Also, drainage C
OD doesn't drop as much as I expected.

Further, Japanese Patent Publication No. 56362/1983 discloses a method of digesting waste paper using sodium sulfite and hydrosulfide. However, since this method is also processed under high temperature and pressure, damage to the waste paper fibers is unavoidable;
The amount of wastewater pollution is large and the wastewater COD is high.

[Problem that the invention seeks to solve]

In view of the disadvantages of the conventional method of deinking and recycling waste paper using the cooking method under high temperature and high pressure, the present invention utilizes the advantages of the cooking method to reduce the amount of pollution generated and reduce the wastewater COD. Another object of the present invention is to obtain a high-whiteness, high-strength recycled pulp that has good disintegration properties for waste paper and is excellent in decolorizing ink from waste paper using an ink that exhibits strong resistance to alkaline chemicals.

In order to obtain recycled waste paper with high whiteness and high strength using the cooking method, which generates less contamination, it is first necessary to lower the cooking humidity and minimize damage to the waste paper fibers.

Therefore, the inventors used a conventional pressure digester and
As a result of intensive research on a method of simultaneously achieving deinking and fiber disintegration using an alkaline agent and a surfactant at a low temperature below ℃, we found that the fibers can be loosened to some extent by saponifying the ink with the alkali and emulsifying and dispersing the fiber with the surfactant. I learned that it is possible to disintegrate the fibers at the same time as ink is released and dispersed. However, alkali alone was insufficient to remove the ink, which is highly resistant to alkaline chemicals used in multicolor printed waste paper, and recycled waste paper was obtained which was colored due to residual color. Therefore, if a large amount of alkali is used to remove these impurities, no matter how low the temperature is, the waste paper fibers will be damaged, resulting in an increase in wastewater COD, a decrease in yield, and a decrease in whiteness due to alkali coloration of the fibers. Ru.

[Means for solving problems]

Therefore, the inventors deinked and disintegrated with a minimum amount of alkali, and at the same time used a strong reducing agent such as dithionite or thiourea dioxide to create a color that has strong resistance to alkaline chemicals. It was discovered that by simultaneously performing reductive decolorization of the ink and bleaching of waste paper fibers, it was possible to obtain a regenerated valve with high whiteness and high strength, with significantly less contamination than with conventional methods, and the present invention was completed. did.

That is, the present invention is a method of digesting waste paper at low humidity using a chemical consisting of dithionite or thiourea dioxide and an alkaline agent, and further adding a surfactant as desired.

The dithionite used in the present invention is specifically sodium dithionite, which can be obtained by the sodium formate method, or by the borole method, that is, sodium borohydride, caustic soda, and sodium dithionite. There is sodium dithionite obtained by reacting sodium bisulfite, and it also includes formalin adducts of dithionite (rongalite).

In the present invention, thiourea dioxide is used in place of dithionite. These dithionite and thiourea dioxide vary depending on the type of waste paper and the processing temperature, but generally, it is 0.2 to 2.0% (wt) based on the absolute dry weight of waste paper.
used within the range.

In addition, alkaline agents include hydroxides and carbonates of alkali metals such as sodium and potassium, hydroxides and carbonates of alkaline earth metals such as calcium, magnesium, and barium, each of which may be used alone or in mixtures. . Commonly used alkaline agents are caustic soda and soda carbonate.

The amount of alkaline agent used varies depending on the type of H paper, the processing depth, etc., but is generally 0.2 to 2.
The concentration range is 0% (wt).

Furthermore, in the present invention, a surfactant may be used if desired. Using a surfactant improves the permeability of the alkaline agent, improves the disintegration properties of waste paper, and also improves the deinking effect, so depending on the type of waste paper, it may be preferable to use a surfactant. There is.

Examples of surfactants that bring about such effects include nonionic and anionic surfactants that are commonly used for deinking. Examples of nonionic surfactants include polyoxyethylene alkyl phenyl ether, Examples of anionic surfactants include fatty acid soaps, alkylbenzene sulfonates, and higher alcohol sulfate ester salts. The amount of these surfactants used is 0.05 to 0.596 (wt) based on the bone dry weight of the waste paper.

In the present invention, the waste paper treatment concentration is generally 5 to 40%, preferably 10 to 6%, considering the penetration state of the chemical solution.
It is assumed to be 0%.

One feature of the present invention is that the cooking treatment is carried out at a low temperature, and the treatment temperature is generally from room temperature to 100°C, preferably FiA 0 to 80°C. The processing time varies depending on the type of waste paper, the processing temperature, etc., and cannot be determined generally, but for example, when the processing temperature is 60° C. for ordinary printed waste paper, the processing time is 6 to 5 hours.

The present invention provides a method using a conventionally used digester.
It will be applied as is. Here, to briefly explain an embodiment using the agent of the present invention, printed waste paper, fresh water or white water, an alkaline agent, a surfactant as desired, a dithionite salt or thiourea dioxide are added to a pressure digester. After introducing low pressure steam (approximately 0.5 to 9/i), deinking is started without rotating the digester. After heating to a predetermined temperature, the steam is turned off and the kettle is further rotated for a predetermined time to complete deinking. Note that the timing of adding dithionite or thiourea dioxide can be arbitrarily selected, but it is necessary to add it at least 30 minutes before the end of deinking.

The waste paper that has been deinked in the high-pressure digester as described above is discharged into the pit under the kettle, and the waste paper is immersed in fresh water or white water to a density of 296.
diluted before and after. Subsequently, after being subjected to disintegration treatment, the waste paper and ink are separated by a floatator or washer. Further, after bleaching with sodium hypochlorite or hydrogen peroxide, foreign matter is removed again using a washer and screen, and the deinking and bleaching are completed by sending the paper to the chest.

〔Effect of the invention〕

According to the method of the present invention, since the process can be performed at a significantly lower temperature than conventional methods, there is less damage to the fibers, and therefore (1) paper strength is improved and paper breakage in paper machines, processing machines, etc. is significantly reduced and workability is improved. will improve.

(2) Due to the recent tightening of wastewater regulations, coagulation and sedimentation treatment alone is no longer sufficient to deal with the situation. However, according to the present invention, the number of pollution sources is significantly reduced, so the COD in wastewater is low, and a large amount of investment is required. It is not necessary and production can be increased. (3
) Yield is improved. (41 whiteness is improved.In addition, in the case of the conventional high temperature, high pressure method, deinking can be done by blowing pressurized steam after deinking is completed, which reduces energy costs (improving steam quality and solving pollution problems). can be achieved at the same time,
Moreover, it can be carried out economically.

〔Example〕

Next, examples of the present invention will be described.

In the examples, whiteness was determined according to JIS P 8126, bursting strength was determined according to JIS P 8112, and CO
D! /'1 Measured by the test method of JIS K 0102. In addition, the amounts of the chemicals added in the following examples are expressed as % of heavy weight based on the bone dry weight of waste paper.

Example 1 and Comparative Example 1 After putting colored clay waste paper and imitation waste paper into a high-pressure digester at a ratio of 7=3, fresh water was poured to give a treatment concentration of 3096. Next, NaOH196, NazCOs O, 5%,
Sodium hydrosulfide 0.5% was sequentially added. Close the lid and apply pressure to 0.5Kylcr! The digester was rotated at a rate of 1 revolution/minute after passing low-pressure steam through it. After about 1 to 2 hours, when the paper temperature reached 60 DEG C., the steam was completely turned off, and the paper was left running for 3 to 4 hours to complete the deinking. The total deinking time was 5 hours.

After deinking, the paper was discharged into a chest directly below the digester and diluted with white water to a concentration of 2% waste paper. After passing through a disintegrating machine, screen, and washing machine, the waste paper is dehydrated to a concentration of 10%, and NaC
Bleaching was carried out at 101% (as available chlorine) at room temperature for 3 hours.

Further, foreign matter was removed by washing and a screen to obtain recycled pulp from used paper.

Next, for comparison, deinking was performed using a conventional method (Comparative Example 1)
. After putting waste paper and water into the pressure digester as in Example 1,
2.6% Na2SO3 and 125% NazCOsO were added. The lid was closed and y/cd steam was bubbled to a pressure of 3 for 3 hours. After that, the machine idled for two hours and the deinking was completed. The subsequent operations were performed in the same manner as in Example 1.

The results are shown in Table 1.

Example 2 The same procedure as in Example 1 was carried out except that 0.3% of thiourea dioxide was used instead of sodium hydrosulfide.

The results are shown in Table 1.

Example 3 The same procedure as in Example 1 was carried out except that the hydrosulfide was introduced one hour after the end of deinking.

The results are shown in Table 1.

Example 4 and Comparative Example 2 Polyoxyethylene alkyl phenyl ether (trade name:
Nisnon HUloo (manufactured by Satoda Kako) is 0.29
The same procedure as in Example 1 and Comparative Example 1 was performed except that 6 was added.

The results are shown in Table 2.

Claims (1)

[Claims] 1) A method for recycling waste paper, which comprises digesting waste paper at a low temperature using a chemical consisting of dithionite or thiourea dioxide and an alkaline agent. 2) In addition to the above-mentioned chemicals, The method according to claim 1, characterized in that a surfactant is further added.