JPS5921791A - Regeneration of unbleached 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] The present invention relates to a method for recycling unbleached waste paper.

From the viewpoint of resource and energy conservation, waste paper is widely recycled in various ways. However, its use is limited to applications for which waste paper was used or lower quality applications. For example, waste newspaper is only used for the core and back of newsprint and paperboard, and waste corrugated paper is used for cardboard base paper and paperboard core. However, the present inventors had previously proposed [a method for producing bleached pulp that can be blended into printing paper from unbleached waste paper] as a bleached pulp that can be blended with unbleached waste paper and high-quality paper. -16990). An advanced process that combines delignification of unbleached waste paper with an average lignin content of JIS (P8211-1976) Kappa number of 50 or more, commonly known as Western-style cardboard waste, cardboard waste, and tea imitation waste, and further deinking and bleaching. This is a method of producing high value-added bleached pulp by adding processing. The desired whiteness of the bleached pulp obtained is determined according to JIS (P8123-1961).
) Hunter whiteness is 60% or more. Of course, it is also possible to obtain bleached pulp with a whiteness of 60 inches or less using this production method. However, the lignin content of unbleached waste paper is 50 or more in kappa value. Therefore, in order to prevent deterioration of pulp quality due to an increase in the amount of bleach used, it is necessary to remove the genin by an alkaline cooking method such as the Kraft method or the soda method to lower the kappa number to a predetermined value. In the unbleached waste paper that is the raw material, there are a large amount of foreign substances such as holograms, plastics, and adhesives. When these foreign substances are delignified by cooking, they are subjected to high temperature treatment, and foreign substances having a melting point below the cooking temperature are dissolved and fragmented. In addition, during the operation of rescuing the unbleached pulp from the digester (generally called blowing), the explosion effect caused by the pressure difference between the pressure inside the digester and the atmospheric pressure, and the physics caused when passing through the blow piping at high speed. The above-mentioned foreign matter is also broken into pieces by force. The fragmented foreign matter reduces the dust removal efficiency of the subsequent dust removal equipment.
This causes an increase in impurities in the pulp.

According to research conducted by the present inventors, about 90% of the foreign substances in the obtained pulp are caused by the above-mentioned foreign substances. From this point of view, the present inventors carried out delignification at a cooking temperature of 130 to 150 °C, which is lower than the commonly used 160 to 180 °C,
Furthermore, a method for reducing the above-mentioned foreign substances in the pulp by lowering the temperature in the digester to below -100°C and performing blowing was previously applied for in the ``Method for Producing Bleached Pulp from Unbleached Waste Paper'' (Japanese Patent Application 1983- 49728). This method significantly prevents plasticization during the cooking process and fragmentation of foreign substances due to physical force during blowing, and reduces the amount of foreign substances in the pulp. However, to further reduce impurities, cooking at even lower temperatures is required. However, although the delignification reaction occurs even in the range of 100 to 130° C., the reaction rate is extremely slow and the cooking time is greatly increased, making this reaction industrially worthless.

However, as a result of further research, the present inventors discovered a method for solving the above-mentioned drawbacks and producing bleached pulp with a brightness of 30 to 50%, resulting in the present invention. That is, the purpose of the present invention is to produce unbleached waste paper with a whiteness of 20 to 25% in an untreated state without cooking or bleaching, without delignifying it by cooking, thereby impairing economic efficiency and pulp quality. By simultaneously performing disintegration and bleaching with a peroxide compound in an amount that is not added, bleached pulp with a brightness of 30 to 50 can be obtained, which has a higher yield than the conventional method, has fewer impurities, and has improved pulp strength. To provide a method for recycling excellent high quality and inexpensive bleached pulp from unbleached waste paper.

In the present invention, undisintegrated and unbleached waste paper is placed in a reaction vessel whose contents can be flowed and heated, and a peroxide compound is added to the reaction vessel in an amount of 01 to 10% based on the absolute dry weight of the unbleached waste paper. This is a method for recycling unbleached waste paper, which is characterized by adding an alkaline solution containing an alkaline solution and heating the contents to 40 to 100° C. while flowing the contents in the reaction vessel.

Although all types of peroxide compounds can be used in the present invention, it is preferable to use inorganic peroxide compounds. Among these, hydrogen peroxide is particularly preferred. When hydrogen peroxide is used, an alkaline solution for pH adjustment and a chelating agent such as caustic soda or sodium silicate are used as a stabilizer for the hydrogen peroxide, and if necessary, EDTA.

The amount of peroxide compound added is 0.1 to 0.1 to the absolute dry weight of waste paper.
10 h (as 100 parts H2O2), preferably 2 to 6
Use %.

Figure 1 shows 2.5% caustic soda using cardboard waste paper.
This figure shows the relationship between the amount of hydrogen peroxide added and the degree of whiteness in an alkaline solution containing 5% sodium silicate. As is clear from this figure, if the amount of hydrogen peroxide added is 10% or more, little increase in whiteness can be expected, and it is also disadvantageous from an economic standpoint.

If unbleached waste paper is delignified by cooking, the yield and pulp viscosity (TAPPIT-230) will decrease.

However, in the present invention, this point is improved since cooking is not performed. Figure 2 shows the yield of pulp with a brightness of 40 by the method of the present invention and the method of delignifying by cooking and bleaching (chlorine-alkali-hypochlorite treatment), and the pulp Shows the change in viscosity. As is clear from this figure, pulp with a higher yield and higher viscosity can be obtained in the present invention. Therefore, the present invention provides a method for producing pulp that is inexpensive and of high quality (it is known that pulp strength such as specific tear strength improves when pulp is made with a high viscosity).

A further great advantage of the present invention is that the amount of contaminants in the resulting pulp is greatly reduced. In the present invention, delignification by cooking is not performed, so high-temperature treatment as described above is not required. The bleaching temperature used in the present invention is 40 to 1o.
It is 0°C.

Therefore, the fragmentation of foreign substances due to plasticization can be minimized, and fragmentation during blowing can also be prevented, and the amount of foreign substances in the pulp is significantly reduced. This effect will be explained using figures. Figure 3 shows 1. The unbleached pulp obtained by blowing at 70°C, and the unbleached pulp obtained by cooking at 140°C and blowing at 100°C were screened, cleaned, and bleached, and the unbleached pulp obtained by the method of the present invention was bleached, screened, and cleaned. This is a comparison of impurities in each pulp (resulting from bot melt, glass sticks, and adhesive-based foreign substances). As shown in the figure, it can be seen that the present invention reduces the amount of impurities in the pulp.

The present invention is to carry out bleaching in a reaction vessel while flowing the contents. By doing so, it becomes possible to disintegrate the raw material at the same time as bleaching in the bleaching process without going through the process of disintegrating the raw material. Bleaching usually requires disintegrating the raw material. However, disintegration requires devices such as a plurality of disintegrators, a screen for removing undisintegrated materials, and a dehydrator, and requires a large amount of power energy. However, the present invention does not require such a device, and the power energy is also about 10% or less. Methods of imparting fluidity to the contents include methods such as vibrating or rotating the reaction container, and methods of rotating are particularly preferred. Using such a reaction vessel, uniformly bleached and fully disintegrated pulp can be obtained under the bleaching conditions described above, with a content concentration of about 5 to 15%, and a processing time of about 1 to 3 hours. can get.

According to the present invention, bleached pulp with less impurities and excellent pulp strength can be recycled at low cost from unbleached waste paper with less equipment and energy.

The present invention will be explained below using an example using cardboard waste made of unbleached waste paper.

Example 1 500 kg of press corrugated waste paper was put in an air-dried state into a rotatable reaction vessel, and 5% hydrogen peroxide (as 100 parts lI202) and 2.5% of caustic soda were added to the absolute dry weight of the waste paper.
5% and 5% sodium silicate were added, water was added so that the liquid ratio was 9, and the reaction vessel was heated by blowing steam while rotating the reaction vessel. Rotate at 40 revolutions per hour for 120 minutes and heat at 6
I went to j at 0℃. Next, the rotation and heating were stopped, the pulp in the reaction vessel was taken out, washed, and further 0.15 mm thick.
wide pore screen, and differential pressure 2.5 Kg/cr
A hydrocyclone for removing heavy foreign matter giving a pressure difference of 6.0 Kg/cnl and a hydrocyclone for removing foreign matter by displacement giving a differential pressure of 6.0 Kg/cnl were selected.

Table 1 shows the processing conditions, and Table 2 shows the results of quality measurement of the obtained pulp.

Comparative Example 1 20 K9 waste paper was air-dried and 300 K9 was packed in a chemical circulation digester, and activated alkali (absolute dry weight of raw material) was added.
20%, liquid ratio 1゛9, temperature maintained at 170°C for 15 minutes to perform kraft cooking, release to atmospheric pressure at 170°C and blow the pulp, and the obtained pulp was processed in the same manner as in Example 1. They were washed and selected, and then bleached with a chlorine-caustic nodah hypochlorous acid nodah can solution.

Table 1 shows the processing conditions, and Table 2 shows the results of quality measurement of the obtained pulp.

Baboon Comparative Example 2 Kraft cooking was carried out under the same conditions as in Comparative Example 1 except that cardboard waste paper was kept at a temperature of 140°C for 180 minutes, and after the temperature inside the pot was lowered to 100°C by degassing, the pulp was blown. Washing, selection, and bleaching were performed under the same conditions as in Comparative Example 1.

Table 1 shows the processing conditions, and Table 2 shows the results of quality measurement of the obtained pulp.

Example Table 2 Quality Comparison l) Contaminants caused by hot melt, plastics, and adhesive foreign substances *2) Total contaminants

[Brief explanation of drawings]

Figure 1 shows the relationship between the amount of hydrogen peroxide added and whiteness, Figure 2 shows the change in yield and viscosity in each process, and Figure 3 shows the relationship between processing conditions and the amount of contaminants in the pulp. figure. A...Yield without cooking/'-

Claims (1)

[Claims] Undisintegrated unbleached waste paper is placed in a reaction vessel that allows the contents to flow and be heated, and an alkaline solution containing 0.1 to 10% peroxide compound based on the absolute dry weight of the unbleached waste paper is placed in the reaction vessel. 40 minutes while adding the solution and flowing the contents within the reaction vessel.
A method for recycling unbleached waste paper, characterized by heating it to ~100°C.