JPS6327477B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing pulp from waste paper, and more specifically, to a method for producing bleached pulp that can be blended into printing grade paper by delignifying unbleached waste paper, then deinking and bleaching it. It is something. From the standpoint 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 used for the core and back of newspapers and paperboards, and waste cardboard is used for corrugated core base paper and paperboard core, etc., and they undergo advanced processing that combines delignification, deinking, and bleaching. , there are no examples of producing bleached pulp that can be incorporated into value-added printing grade paper. The reason for this is that, according to the knowledge so far, there is no suitable method for economical delignification and bleaching, and that the impurities in the resulting pulp cannot be used for printing-grade paper using a normal dust remover. It is thought that some areas cannot be eliminated. Because the ink is primarily derived from waste newspapers and miscellaneous paper, which are used as the source material for unbleached waste paper such as corrugated cardboard and corrugated core base paper, a large amount of bleaching agent is required to mix it into printing-grade paper. This is because it is considered impossible to economically produce high-grade bleached pulp from unbleached waste paper, as it requires The present invention technically overcomes the above-mentioned difficulties and provides a method for producing bleached pulp that can be incorporated into printing grade paper from unbleached waste paper. In the present invention, unbleached waste paper refers to waste paper with an average lignin content of 50 or more in terms of JIS (P8211-1976) Katsupar value, commonly known as Western corrug waste,
Includes things called cardboard scraps, brown imitation paper scraps, etc. Bleached pulp that can be blended into printing paper grade paper has a whiteness of JIS (P8123-1961) Hunter whiteness of 60 or more, and a projected area of 0.05 mm ² or more contained in 100 g of pulp. Defined as bleached pulp that can be blended into printing paper grade paper with a total projected area of impurities of 100 mm2 ^or less. Furthermore, printing paper grade paper refers to printing paper and paper of equivalent quality. Various methods are known for delignifying lignocellulosic materials such as wood chips, but the most common method is the Kraft method, in which a chemical solution containing caustic soda and soda sulfide as main components is applied under high temperature and pressure. It is well known that bleached pulp, which can be incorporated into printing grade paper, can be produced by further bleaching. In kraft cooking, liquid is the total amount of liquid in cubic meters that is present with the raw material at the beginning of cooking, including the amount of water in the raw material, the amount of added chemicals, and other things, per ton of weight of the raw material ligrocellulosic material. It's called ratio. When the amount of alkali in the additive chemical solution is constant, the liquid ratio is an indicator of the degree of dilution of the initial alkali concentration in the cooking system. In the kraft process, when wood chips are used as a raw material, it is considered advantageous to keep the liquid ratio as low as possible in order to increase the delignification rate and reduce energy consumption. For example, when the liquid ratio is 3, the amount of alkali added can be reduced by 20% compared to when the liquid ratio is 6 to achieve the same level of delignification. For this reason, in the craft method using wood chips as raw material, the liquid ratio is 2 to 2.
The conditions between 4.5 and 4.5 are adopted as the optimal conditions. Digesting unbleached waste paper is also possible within this liquid ratio range. However, the present invention is characterized by adopting conditions of a liquid ratio of 5 or more and 10 or less in the process of delignifying unbleached waste paper by kraft cooking. Compared to the conventional method, the delignification rate is improved and the cellulose yield is greatly increased, which is an effect that has not been seen before. Unbleached waste paper is delignified to a lignin content expressed in Katsupar number of 15 to 40, and then subjected to the process of removing or replacing a portion of the liquid phase present with the pulp, that is, generally washing, concentrating, In addition to an operation called dehydration, fine bubbles of air are added to the pulp suspension.
Ink particles on pulp fibers and in a liquid phase containing pulp are selected from the operations called flotation, which floats and separates hydrophobic solids, and are carried out at least once to improve the fiber surface by delignification. It is possible to very effectively remove ink particles which have become liberated or become liberated from the pulp suspension system. Processes such as washing, concentration, dehydration, and flotation to remove ink particles, as well as operations for removing dissolved solids and fine fibers associated with delignification and bleaching processes, are carried out in common steps. , it is economically advantageous because the amount of equipment can be reduced. One of the features of the present invention is that deinking is carried out after delignification, thereby allowing sufficient deinking without adding a special deinking agent such as a surfactant. If deinking is not performed, the pulp will have a grayish hue compared to the pulp that can be blended into printing grade paper unless a large amount of bleach is added in the bleaching process beyond the economically acceptable range. , only get low ratings. However, according to the method of the present invention, it is possible to obtain pulp that can be incorporated into printing grade paper very easily and economically. These effects will be explained using figures. Figure 1 compares the effects of the order of delignification and deinking operations on waste corrugated cardboard and the presence or absence of the use of deinking agents on the deinking effect. 1 in the figure is an example of deinking after delignification; No deinking agent added, 2 is an example of delignification after deinking, no deinking agent was added, 3 is an example of delignification after deinking, 0.5% of deinking agent was added, 1% of caustic soda was added, and reaction was carried out at 80°C for 30 minutes. Shown after deinking. Deinking before delignification requires an alkali and a surfactant, whereas after delignification, no deinking agent is required and simple washing can be sufficient to remove ink. Figure 2 compares the required amount of bleach between pulp that has been deinked according to the present invention and pulp that has not been deinked. 5 represents the case where bleaching was performed after delignification without deinking. By performing the deinking operation, the amount of bleach required is greatly reduced. The amount of lignin remaining after delignification is less than 40 in terms of Katzpar value.
One of the features of the present invention is that it has a cut par number of 15 or more.By delignifying to a cut par number of 40 or less, the ink attached to the pulp surface is liberated, and the lignin in the pulp can be easily removed with ordinary bleaching agents. As a result, the projected area of contaminants in 100g of pulp can be reduced to the extent that it can be removed, and the impurities that are alkali-soluble or that become solubilized by alkaline hydrolysis are removed. The total amount can be ^100mm2 or less. In addition, reducing the cut par value to 15 or less will lead to a rapid decrease in yield and quality.
Undesirable. Figure 3 compares the amount of contaminants in pulp produced by bleaching corrugated cardboard after delignification and pulp bleached without delignification, and shows that the dust removal effect is large. In the figure, 6 represents the amount of contaminants before delignification, 7 represents the amount of contaminants after delignification, and 8 represents the amount of contaminants in the pulp subjected to selection treatment after delignification. A indicates black heavy foreign matter, B indicates binding fiber, C indicates brown foreign matter, D indicates printing ink, and E indicates plastics, hot melt, and adhesive. Figure 4 compares the relationship between the delignification time and the Kuppar number, which is an index of lignin content, for waste corrugated paperboards at the same alkali addition rate of 12%. In the figure, 9 represents the relationship between the 170°C holding time and Katsupar number at liquid ratio 3, and 10 represents the relationship between 170°C holding time and Katsupar number at liquid ratio 9. In the delignification of unbleached waste paper, the higher the liquid ratio, the faster the delignification speed, as shown in the figure. FIG. 5 compares the relationship between liquid ratio and yield at the same Kuppar number. In the figure, numeral 11 represents the case where waste cardboard was digested, and numeral 12 represents the case when coniferous wood chips were digested. The yield of kraft cooking using softwood chips as a raw material is higher as the liquid ratio is lower, whereas the yield of kraft cooking of unbleached waste paper is higher as the liquid ratio is higher. The reason for this phenomenon is that unbleached wastepaper is a material that has undergone slight delignification and has a significantly different distribution and amount of lignin from wood chips, making it extremely susceptible to swelling by alkali. . Under these conditions, at a low liquid ratio, there is no free liquid phase and lignin diffuses into the liquid phase, while the high concentration of alkali promotes the separation of carbohydrates such as cellulose. As a result, the lower the liquid ratio, the lower the delignification rate and the lower the yield. A high liquid ratio improves these points, increasing the delignification rate and resulting in a high yield. Hereinafter, the present invention will be explained by way of an example using Western container waste made of unbleached waste paper. Example 1 Waste cardboard was cut into pieces of approximately 5cm square and weighed 800g.
10% in an autoclave, active alkali (based on raw materials) 12%, sulfidity 25%, liquid ratio 1:9, temperature 170℃
Kraft cooking was carried out for 45 minutes, and after release to atmospheric pressure, the resulting pulp was washed, concentrated on a wire mesh, deinked, and then heated using a 0.25 mm wide pore screen and a differential pressure of 2.5 Kg/cm ² . The bleached pulp was carefully selected in a liquid cyclone to remove impurities, and then sequentially bleached with each chemical solution of chlorine, caustic soda, sodium hypochlorite, hydrogen peroxide, and chlorine dioxide. %, flow rate 40/min, temperature 45
The material was beaten several times at ℃, and a 60 g/m ² handmade sheet was prepared and its quality was measured. Table 1 shows the conditions for each treatment. Table 2 shows the results of quality measurements. Comparative Example 1 Waste cardboard was subjected to kraft cooking under the same conditions as in Example 1 except that the liquid ratio was 1:3 and the active alkali (based on the raw material) was 14%. Table 2 shows the measurement results of yield and Katsupar number. Comparative Example 2 Waste corrugated paper was not deinked after cooking, but was otherwise cooked, washed, sorted, bleached, and washed under the same conditions as in Example 1.
A handmade sheet was prepared by beating and the Hunter whiteness was measured. The measurement results are shown in Table 2. Comparative Example 3 800g of softwood chips were packed into 10 autoclaves, active alkali (based on raw materials) 20%, sulfidity 25%,
Kraft cooking was carried out at a liquid ratio of 1:4 and a temperature of 170° C. for 45 minutes, and the other steps were the same as in Example 1 except for the deinking step to produce a handmade sheet. Table 1 shows the bleaching conditions, and Table 2 shows the measurement quality.
Shown in the table.

【table】

【table】 [Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between washed fiber loss rate and whiteness increase, Figure 2 is a diagram showing the relationship between the presence or absence of deinking and the amount of bleach used and the achieved whiteness, and Figure 3 is a diagram showing delignification and contaminants. FIG. 4 is a diagram showing the relationship between delignification rate and liquid ratio. FIG. 5 is a diagram showing the relationship between liquid ratio and yield of corrugated waste paper and softwood chips.

Claims (1)

[Claims] 1 The lignin content expressed in cut par value is 50
In the above method for producing bleached pulp from unbleached wastepaper, unbleached wastepaper is delignified using the Kraft cooking method at a liquid ratio of 5 to 10 until the lignin content expressed by the Katsupar number is in the range of 15 to 40. death,
After that, an operation is performed to remove ink particles on the pulp fibers and in the liquid phase containing the pulp, and the pulp is carefully selected to remove impurities other than the fibers, and then bleached to produce a white color with a Hunter whiteness rating of 60 or higher. A method for producing bleached pulp that can be incorporated into printing paper from unbleached waste paper, characterized by