JPH0423037B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for deinking printed waste paper, and particularly to a method for deinking printed waste paper suitable for deinking waste paper printed on lightweight coated paper. [Conventional technology] Newspapers,
BACKGROUND ART Waste printed paper such as magazines and general printed matter is deinked and used together with virgin pulp. In the old days, deinking of used printed paper was done by adding deinking agents such as alkali and surfactants to the used paper using a difficult-to-disintegrate machine such as a pulper, and disintegrating it at a low concentration of less than 10% of the raw material, diluting it, and washing or flowing it. The deinking process was carried out using a stationary machine, followed by bleaching if necessary. Since then, many improvement proposals have been made; for example, as a method for improving whiteness,
Publication No. 20563 is known. The invention is based on alkali,
A method of adding a deinking agent to disintegrate at a low raw material concentration, dewatering to a concentration of 15% or more, adding the deinking agent, etc. again to perform re-deinking and bleaching, and then diluting, washing or flotation. It is. Furthermore, as a proposal to improve whiteness and paper strength, JP-A-52-1102 proposes that deinking chemicals be added to disintegrate at a low concentration, dehydrated to a concentration of 15% or more, aged for a long time, and then washed. A method is disclosed.
However, in recent years, printing technology has increased the use of offset printing, which produces more beautiful prints than letterpress printing, for used printed paper, making it difficult to sufficiently remove ink using the above-mentioned deinking method. This is because the synthetic resin and vegetable oil of the offset ink undergo oxidative polymerization and adhere to the fibers over time after printing, and the ink is difficult to peel off from the fibers using conventional deinking methods, resulting in unreleased ink. For this reason, a method for deinking offset printed waste paper has been proposed. For example, Japanese Patent Application Laid-Open No. 120705/1987 describes a step A in which a deinking chemical is added to the waste paper with a concentration of 10% or less to disintegrate it, and the concentration of the raw material is reduced to 10%. B dehydrated to more than %
Step C: adding 3% or more alkali to waste paper; D step: soaking in alkali for 3 hours or more at a concentration of 10% or more; E step: stirring for 1 minute or more using a kneader; then dilution. , washing, flotation, bleaching, and other post-treatments in this order. Also, JP-A-55-40850
In the publication, a deinking agent consisting of an alkali and a surfactant and a hydrogen peroxide bleaching agent are added to printed waste paper containing offset waste paper to achieve a concentration of 15% or more and 5.0%.
When the alkali concentration is higher than g/g/(as NaOH), there is a method of mechanical stirring using a refiner, kneader, etc. while applying compressive force under heating. Recently, as an improvement method of JP-A-55-40850, in JP-A-63-28992, after mechanical stirring treatment, aging for 0.5 hours or more, and then mechanical stirring treatment again at a concentration of 15 to 25%. A method is disclosed. On the other hand, as mentioned above, there has been an increase in the use of offset printed waste paper, which is difficult to deink, but in recent years, with the increase in color printing of general magazines, there has been a noticeable reprinting of coated paper in used paper. . Especially when applied with a gate roll coater etc., the coating amount is 10.
For waste paper of medium-quality lightweight coated paper less than g/ ^m2 ,
Compared to coated paper with a weight of 10 g/m ² or more, the ink on the coat layer penetrates into the paper layer. Therefore, although the deinking method for offset ink described above eliminates most of the unpeeled ink, since mechanical agitation treatment is performed before flotation, the peeled ink becomes finer and the ink is removed during the flotation process. It becomes extremely difficult to catch. As a result, the flotation efficiency decreases, and finely divided ink remains on the resulting deinked pulp (DIP), resulting in a dull gray color, and there is a limit to the improvement of whiteness. The current situation is difficult. [Problems to be Solved by the Invention] In view of these current circumstances, the present inventors have considered the following. That is, in the conventional deinking method, in the deinking process of used paper, after immersion in alkali, mechanical agitation treatment is performed using a kneader or the like to perform flotation and post-washing treatment, or mechanical agitation-alkali immersion treatment is performed. - Floatation and washing are performed by mechanical stirring. For this reason, in the case of printed waste paper made of lightweight coated paper, the coating layer that has peeled off from the fibers or has become easily peeled off due to alkali immersion and the offset ink thereon are dispersed by the following mechanical stirring process. At the same time, the unpeeled ink and the peeled ink are dispersed and made finer, and the ink particles even re-adhere to the fibers. Therefore, the finer ink particles reduce the efficiency of flotation in the post-treatment, and even cause the ink particles to re-adhere to the fiber surface, resulting in an increase in the dullness of the color of the fibers. In addition, even if hydrogen peroxide is added at a high rate as a bleaching agent to obtain high whiteness from waste paper raw materials, including offset printed waste paper, it is not limited to medium-weight and lightweight coated paper. There is ineffective consumption of hydrogen.
(2) Hydrogen peroxide decomposes when using a kneader, etc. (3) There is a limit to the improvement of whiteness by alkali immersion, and there are problems such as poor efficiency of hydrogen peroxide. The present invention was made in order to solve the above-mentioned problems, and the present inventors came up with the idea of performing alkali immersion in two stages. In contrast to the deinking method, the peeled off coating layer and coarse ink particles are removed by flotation before mechanical stirring, and the peeled ink, which was a problem in the past, is made finer by mechanical stirring. After obtaining the knowledge that it is possible to prevent re-adhesion to fibers, the present invention was completed as a result of intensive research. Furthermore, we have also discovered that the deinking method of the present invention is also effective in deinking medium-weight, newspaper offset printed waste paper other than the above-mentioned medium-weight lightweight coated paper, which has recently become an issue as printed paper that is difficult to deink. Obtained. The main purpose of the present invention is to solve the above problems and
Suitable for removing ink from printed waste paper, especially medium-weight, lightweight coated paper, with almost no unpeeled ink.
Another object of the present invention is to provide a method for deinking printed waste paper that yields deinked pulp (DIP) with high brightness. Another object of the present invention is to remove almost no unreleased ink from general recycled printed waste paper, including medium-quality coated, uncoated printed waste paper, high-quality coated printed waste paper, and newspaper waste paper, in addition to the printed waste paper containing the medium-weight lightweight coated paper; Another object of the present invention is to provide a method for deinking printed waste paper that yields deinked pulp with high brightness. [Means for Solving the Problems] The present invention includes a step of adding a deinking agent consisting of an alkaline agent and a surfactant to recovered printed waste paper and performing a preliminary alkaline immersion at a raw material concentration of 10% or more;
Next, a step of diluting the raw material and performing flotation, a further step of dehydrating the raw material, adding a deinking agent consisting of an alkaline agent and a surfactant again, and performing a subsequent alkaline immersion at a raw material concentration of 10% or more; A series of steps of performing mechanical stirring at a raw material concentration of 10% or more before or after the latter alkali immersion, or both before and after the latter alkali immersion, and further washing in the final step of each of the above steps. This is a method for removing ink from printed waste paper, which is characterized by the addition of a step of performing this process. Further, the present invention is a method for deinking printed waste paper as described above, in which a bleaching agent is added in the alkali dipping step and bleaching is carried out simultaneously with the alkali dipping. The deinking method of the present invention is based on the recent deinking method whose basic steps are low-concentration disintegration, high-concentration alkali immersion, high-concentration mechanical stirring, and flotation or washing. It is characterized in that flotation is performed after immersion in alkali, and mechanical stirring treatment is performed before or after the subsequent immersion in alkali. As before,
If mechanical stirring is performed at a high concentration using a kneader or the like after alkali immersion, the ink particles that have been peeled off from the fibers due to alkali immersion will become finer than necessary, and many of them will not be able to be removed by flotation in post-treatment. There was a risk that the ink removal efficiency of the flotation system would be deteriorated and that the ink could not be removed sufficiently. In particular, printed waste paper, such as medium-weight lightweight coated paper that has been coated with paint using a gate roll coater, etc.
Since the amount of paint applied is small and the printed ink reaches the paper layer through the coat layer, when mechanical stirring is performed to peel off the unreleased ink, the ink on the coat layer becomes fine particles together with the coat layer. Because
It was even more difficult to remove the ink particles. According to the method of the present invention, the ink particles peeled off from the fibers in the preceding alkali immersion can be removed by flotation in a relatively large state, thereby increasing the efficiency of flotation. In the flotation method, the ink particle size is generally 10~
It is said that ink removal efficiency is good with relatively large particles of about 100 μm, and fine particles of 25 μm or less are effective in cleaning methods. By performing floatation without making the particles finer, the ink removal efficiency of floatation can be maximized. In addition, in the subsequent alkali immersion, unpeeled ink and ink that was not removed by flotation are mechanically agitated using a kneader or the like before or after the alkali immersion, and cleaning efficiency is improved in the post-treatment cleaning step. The ink particles are made as fine as possible for cleaning so that the ink particles become the highest. Furthermore, if the alkali immersion is performed in two stages, bleaching with hydrogen peroxide or the like can be performed in two stages at the same time, so that the efficiency of the bleaching agent is improved. Moreover, when bleaching is carried out in one stage, it is preferable to carry out the bleaching at the same time as the subsequent alkali immersion. In this way, it is possible to efficiently obtain DIP with high whiteness and almost no unreleased ink from used printed paper. The step of adding a deinking agent consisting of an alkaline chemical and a surfactant to the printed waste paper of the present invention and immersing it in alkali at a raw material concentration of 10% or more is usually the first step in waste paper deinking. This is done after disaggregation. As the alkaline agent, a known alkali such as caustic soda or sodium silicate is used, and as the surfactant, a known one conventionally used for deinking is used. Alkali immersion is a process also called aging, and is necessary to fully react the ink that has not been peeled off from the fibers with alkali.The immersion time varies depending on the raw material concentration, amount of alkali added, temperature, etc. In the present invention, for 0.5 hours or more, preferably 1 hour
It takes more than an hour. The amount of alkali added is required as an alkali concentration of 3 g/(as NaOH), preferably 5 g/(as NaOH). The raw material concentration needs to be 10% or more, preferably 15% or more, and in alkali immersion, the alkali concentration can be increased by increasing the concentration, but it is also possible to reduce the amount of alkali added by reducing the alkali concentration. It is. In the alkaline dipping process, in addition to the deinking agent, a bleaching agent such as hydrogen peroxide is also added at the same time to bleach the waste paper raw material. The above-mentioned conditions for alkali immersion and bleaching are the same for the subsequent alkali immersion and bleaching, but depending on the properties of the printed waste paper, the conditions for the latter stage of the first stage may be changed within the range of preferred conditions. , is actually valid. Next, the waste paper raw material is diluted and a floatator is used to remove the peeled ink particles in the raw material as well as the relatively coarse particles of the coated layer consisting of pigments and synthetic resins peeled from the coated waste paper at a known low concentration. Separate and remove. The low-concentration waste paper raw material from which relatively coarse ink particles have been removed is dehydrated, a deinking agent consisting of an alkaline agent and a surfactant is added again, and the paper is subjected to an alkali immersion process at a raw material concentration of 10% or more. In this latter step of alkaline immersion, the unreleased ink on the fibers that could not be removed by the previous step of alkali immersion and flotation is reacted again with the deinking agent and peeled off from the fibers, and the ink is removed by 10% before or after the alkali immersion, or before and after the alkali immersion. By passing through the process of performing mechanical agitation treatment using a kneader or the like at the above raw material concentration, ink particles etc. are made into fine particles so that they can be efficiently washed and removed in the post-treatment washing process. As is known, mechanical agitation treatment using a kneader, etc. is performed by heating the material to a temperature of 50°C or higher, applying compressive force at a high raw material concentration of 10% or more, and using a kneader or mixer in the presence of a deinking agent such as an alkali. , a disperser or the like can be used to destroy the film of unreleased ink such as offset ink that is firmly attached to the fibers, and the ink can be peeled off from the fibers. In the method of the present invention, after this mechanical stirring treatment is preceded by alkaline immersion and flotation treatment to remove relatively coarse ink particles, an alkali immersion is further performed to peel off the unpeeled ink from the fibers or remove the peeled ink. Since mechanical agitation treatment is performed after taking measures to prevent re-adhesion of ink to the fibers, fine ink particles can be effectively removed compared to the effect of mechanical agitation treatment in the conventional deinking method described above. It is excellent in that it can remove Examples of the present invention will be shown below. [Example] Example 1 200 g of printed waste paper made of medium-weight lightly coated paper was pretreated with deinking agents (caustic soda 0.8%, sodium silicate 4.0%,
After adding surfactant (0.25%), disintegrating and dehydrating,
Caustic soda 2 as a deinking agent for waste paper (air-dried)
%, sodium silicate 6% (alkali concentration NaOH: 5.4 g/), surfactant 0.15%, and hydrogen peroxide 1.2% as a bleaching agent, and after mixing well,
Soaking was carried out at 60°C for 2 hours at a raw material concentration of 15%. Next, after diluting the raw material concentration to 4% and disintegrating it for 5 minutes,
The raw material was diluted to a concentration of 1% and subjected to flotation treatment using a test floatator (manufactured by Kyokuto Shinko). Dehydrate the raw material again to a concentration of 20%, and use 2% caustic soda and 9% sodium silicate as deinking agents for the waste paper (air-dried).
% (alkaline concentration NaOH: 6.1 g/), surfactant 0.12%, bleach/hydrogen peroxide 2.4%, and after thorough mixing, immersion was performed at 70° C. for 3 hours at a raw material concentration of 15%. After soaking, the waste paper raw material was heated to 70°C and mechanically stirred for 1 minute in a test kneader (manufactured by Yamamoto Hyakuma Seisakusho), diluted to a raw material concentration of 2%, and disintegrated for 2 minutes. DIP was obtained by diluting the raw material to a concentration of 1%, dehydrating it to a raw material concentration of 10%, and washing twice. With the resulting DIP
A handmade sheet with a weight of 100 g/m ² was prepared using the TAPPI standard method, and the amount of unpeeled ink and whiteness of DIP were measured using the following test method. Test method: Amount of unpeeled ink: A handmade sheet was analyzed using an image analysis device (Co., Ltd.)
CCD particle size distribution analyzer)
The area of the lattice portions with a light reflectance of 60% or less observed in an area of 100 mm x 100 mm was totaled and determined as the residual ink area in the handsheet. Whiteness: Measured using a photovolt whiteness tester according to the procedure of JIS P8123 Comparative Example 1 In Example 1, the alkali immersion step was only one stage, and the amount of deinking agent and bleach added was the same as in the first and second stages of Example 1. The sum of That is, 4% caustic soda, 15% sodium silicate (alkali concentration
11.5g/) as NaOH, 0.27% surfactant,
After adding 3.6% hydrogen peroxide and mixing well, immersion was performed at 70° C. for 5 hours at a raw material concentration of 15%. Hereinafter, in the same manner as in Example 1, mechanical stirring was performed using a kneader, and then the raw material concentration was diluted to 2%.
After being disintegrated for a minute, the raw material was diluted to a concentration of 1% and subjected to flotation treatment. After that, the raw material concentration was dehydrated to 10% and diluted to 1% in the same manner as in Example 1.
Washing was repeated twice to obtain DIP. Example 2 In Example 1, general recycled newspaper waste paper consisting of 20% flyers, 30% offset, and 50% convex plates was used as the waste paper, except that mechanical agitation treatment using a kneader was performed before the subsequent alkali immersion process. Example 1
DIP was obtained in exactly the same way. Examples 3 and 4 In Example 2, mechanical stirring treatment using a kneader was performed after the latter alkali immersion step (Example 3)
Alternatively, DIP was obtained in exactly the same manner as in Example 1, except that it was performed twice before and after (Example 4). The conditions for the mechanical stirring treatment were the same before and after the alkali immersion step. Comparative Example 2 Comparative Example 1 was carried out in exactly the same manner as in Comparative Example 1, except that generally recycled newspaper waste paper consisting of 20% leaflet, 30% offset, and 50% convex board was used as waste paper, and no mechanical agitation treatment using a kneader was performed. Got a DIP. Comparative Example 3 DIP was obtained in exactly the same manner as in Comparative Example 2, except that the mechanical stirring treatment using a kneader was changed to be performed after the alkali immersion. Comparative Example 4 DIP was obtained in exactly the same manner as in Comparative Example 2, except that the mechanical stirring treatment using a kneader was performed twice before and after the alkali immersion. Comparative Example 5 In Comparative Example 3, the addition rate of hydrogen peroxide bleach was
DIP was obtained in exactly the same manner as in Comparative Example 3, except that the amount was increased from 3.6% to 6%. Example 5 Completely the same as Example 1, except that offset printed waste newspaper was used instead of printed waste paper with medium weight slightly coated paper, and the first step of the alkali immersion treatment was carried out at 45°C for 16 hours. And got a DIP. Comparative Example 6 Comparative Example 1 was treated in exactly the same manner as in Comparative Example 1, except that offset-printed newspaper waste paper was used instead of printed waste paper with medium-weight slightly coated paper, and the alkali immersion treatment was performed at 60°C for 16 hours. and got DIP. Comparative Example 7 Comparative Example 1 was carried out in exactly the same manner as in Comparative Example 1, except that offset printed old newspaper was used instead of printed waste paper with medium weight slightly coated paper, and an alkali immersion treatment was performed at 70°C for 16 hours. Got a DIP. The DIP test results obtained in the Examples and Comparative Examples described above are shown in the table. According to the results shown in the table, in the deinking of used paper printed on medium-weight lightweight coated paper according to the present invention, alkaline immersion is performed in two stages, front and rear, and bleaching is performed at the same time. Example 1, in which a mechanical agitation treatment is performed after the drying process, has a single step of conventional alkali immersion and bleaching, and then a mechanical stirring treatment, followed by flotation, compared to Comparative Example 1. The area of release ink is reduced to almost nothing, and the whiteness can be significantly increased. In addition, for general recycled newspaper waste paper, Examples 2 to 4 of the present invention are the same as those for medium-weight lightweight coated paper printed waste paper, using the conventional deinking method (Comparative Examples 2 to 4) that includes one stage of alkali immersion and mechanical stirring. High whiteness can be obtained compared to Furthermore, in Comparative Example 5, the amount of hydrogen peroxide bleaching agent was significantly increased, but the high whiteness as in the example could not be obtained. In addition, Example 5 of the present invention, in which offset newspaper waste was subjected to two stages of alkali immersion and bleaching, had a much higher whiteness than Comparative Example 6, which performed one stage of alkali immersion, even when the amount of bleach used was the same for both. can be improved. It should be noted that raising the temperature of alkali immersion as in Comparative Example 7 is not preferable because it causes alkali burn and reduces whiteness. From these results, the deinking method of the present invention does not make the ink particles finer than in the past, reduce the flotation efficiency, and dull the color of the pulp due to the fine ink particles, so it is possible to DIP with high whiteness can be obtained for all types of lightweight coated paper, general recycled newspaper, and offset newspaper.

[Table] [Effects of the Invention] The present invention is a method for removing ink from used printed paper, which cannot be effectively deinked to the extent that it can be efficiently blended into high-grade, intermediate-grade paper using conventional deinking methods for used printed paper. This makes it possible to remove ink. The DIP obtained by the present invention has almost no unreleased ink, and by simultaneously performing bleaching in the two alkali immersion steps before and after the method of the present invention, the use of bleaching agents such as hydrogen peroxide is more efficient than in the conventional method. DIP with high whiteness can be obtained using the deinking method, and it can be incorporated at a high rate into high-grade intermediate paper. Furthermore, unlike conventional deinking methods, the present invention
The alkali immersion process is carried out in two stages, one before and one after the other, and in the first stage where the amount of ink is large, the ink particles are removed by flotation while remaining large, and in the second stage where the amount of ink is small before and after the alkali immersion process, a kneader etc. is used. This is a unique deinking method in which the ink particles are broken down by a mechanical agitation process and then removed in a subsequent washing process. It is effective for removing ink from commonly collected used newspapers, including the problematic offset-printed used newspapers, as well as medium-quality coated, uncoated, and high-quality coated used newspapers. Furthermore, in recent years, general printed matter such as newspapers, magazines, advertisements, etc. have become colored, and paper has become lighter.As a result, the amount of ink relative to waste paper fibers has increased, making it difficult to remove ink, which can reduce the efficiency of flotation. This is an excellent deinking method that can be used and is effective.

Claims (1)

[Scope of Claims] 1. A step of adding a deinking agent consisting of an alkaline chemical and a surfactant to printed waste paper and performing alkali immersion in the first stage at a raw material concentration of 10% or more, then diluting the raw material and performing floatation. Further, the step of dehydrating the raw material, adding a deinking agent consisting of an alkali agent and a surfactant again, and carrying out a subsequent alkali immersion at a raw material concentration of 10% or more, and a step of 10% or more before the latter alkali immersion. A method for deinking printed waste paper, characterized by including a step of performing mechanical stirring at the above raw material concentration, and further comprising a subsequent step of washing with an alkaline immersion step. 2 A step in which a deinking agent consisting of an alkali agent and a surfactant is added to the printed waste paper, and the first stage is immersed in alkali at a raw material concentration of 10% or more, then a step in which the raw material is diluted and floatation is performed, and the raw material is further diluted. After dehydration, a deinking agent consisting of an alkali agent and a surfactant is added again, and a subsequent alkaline immersion is performed at a raw material concentration of 10% or more, and a machine is applied at a raw material concentration of 10% or more after the latter alkaline immersion. A method for deinking printed waste paper, which includes a step of washing after passing through a step of agitating the paper. 3 A step in which a deinking agent consisting of an alkali agent and a surfactant is added to the printed waste paper, and the first stage is immersed in an alkali at a raw material concentration of 10% or more, followed by a step in which the raw material is diluted and floatation is carried out, and then the raw material is further diluted. The process of dehydrating and adding a deinking agent consisting of an alkali agent and a surfactant again, and performing a subsequent alkali immersion at a raw material concentration of 10% or more, and before and after the latter alkali immersion, the raw material has a concentration of 10% or more. A method for deinking printed waste paper, comprising a series of steps of performing mechanical stirring at a concentration, and a step of washing after passing through the latter step of mechanical stirring. 4. The method for deinking printed waste paper according to any one of claims 1 to 3, wherein a bleaching agent is added in the alkali immersion step and bleaching is carried out simultaneously with the alkali immersion.