JPS6111353B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a deinking method for obtaining pulp with excellent whiteness from printed waste paper containing offset waste paper. Conventionally, waste paper has been recycled from the standpoint of effectively utilizing waste resources. On the other hand, in terms of printing technology, offset printing, which has a cleaner printing surface than letterpress printing, has been increasing in recent years. However, ink for letterpress printing and ink for offset printing have different compositions, an example of which is shown in the following table.

[Table] As shown in the table above, offset ink contains large amounts of phenolic synthetic resins and vegetable oils such as linseed oil, and when printed, these components undergo oxidative polymerization and adhere to the fibers. In the conventional deinking method, which involves adding a deinking agent made of alkali, sodium silicate, surfactant, etc. and a bleaching agent such as hydrogen peroxide to a pulper and disintegrating it, flotation and washing are performed. It was impossible to deink offset waste paper. For this reason, waste paper pulp containing offset waste paper has been used only for lower-grade papers such as paperboard and newspapers, and has not been used for intermediate-grade papers that require high whiteness. The present invention has been made in view of the above-mentioned current situation.
The purpose of the present invention is to provide a method for deinking printed waste paper obtained from printed waste paper containing high whiteness waste paper pulp that can also be used for intermediate grade paper. To achieve the above object, the method for deinking printed waste paper of the present invention includes adding a deinking agent consisting of caustic soda, sodium silicate, and a surfactant, and a hydrogen peroxide bleach to printed waste paper containing offset waste paper, about 15
% or more and an alkali concentration of 5.0 g/(as NaOH) or more, mechanical stirring is performed while applying compressive force under heating using a refiner, kneader, two-wheel mixer, or disperser. It is something. To explain the present invention in detail, the waste paper raw material that can be used in the present invention may be offset waste paper itself or letterpress waste paper mixed therein. The deinking agent added to the waste paper pulp consists of caustic soda, sodium silicate, and a surfactant, and the addition rate of the alkaline agent plays an especially important role, and the alkali concentration in contact with the waste paper pulp is 5.0 g/(as NaOH) or more. is necessary. For example, in the commonly used deinking method, the pulp concentration is 5.0% and the alkali concentration is 3.0%.
The concentration of alkaline in contact with the pulp was as low as 1.6 g/% (based on the pulp), and it was observed that under these conditions, the offset waste paper was not deinked at all.
This high concentration of alkali has the effect of breaking the strongly adhesive film of the offset ink and causing the ink to separate from the fibers.According to experiments, at an alkali concentration lower than 5.0g, the film of the offset ink is broken. The reaction to destroy the ink is slow and the deinking effect is not sufficient. In addition to a high alkali concentration, a high pulp concentration is required for mechanical stirring in the present invention. In other words, a high pulp concentration has the significance of reducing the amount of alkaline agent added, but in addition, in the present invention, a high pulp concentration is necessary in order to perform mechanical stirring while applying compressive force to the pulp. Become. The ink coating on offset waste paper treated with alkali under heating becomes fragile, but by applying compressive force to the pulp and performing mechanical agitation with the fibers in close contact, the ink coating can be peeled off from the fibers. It is further promoted and has a remarkable effect. And the pulp concentration needs to be 15% or more,
If the pulp concentration is lower than this, it becomes difficult to apply sufficient compressive force to the pulp, and the ink cannot be efficiently peeled from the fibers. Desired pulp consistency is 25-35%. Although it is difficult to strictly measure the compressive force exerted on the pulp, it is thought from various test results that a compressive force of 0.5 to 1.0 Kg/cm ² or more is necessary. In the present invention, the above operation is carried out under heating, which is necessary in order to promote the destruction of the ink film by the alkali and to efficiently carry out the bleaching action by H ₂ O ₂ as a bleaching agent. Preferably, the temperature is 50°C or higher; if it is lower than 50°C, ink separation will not be sufficient and the hydrogen peroxide bleach will not proceed effectively, resulting in a poor rate of increase in whiteness.
The concentration of H ₂ O ₂ is generally 0.5 to pulp weight.
A concentration of 5% is preferred. Devices used to promote the ink separation effect by stirring the pulp while applying compressive force include a refiner, which is a beating device, a kneader, a twin-shaft mixer, and a disperser. Although the ink has already been removed from the fibers of the pulp that has been subjected to the above-mentioned treatment of the present invention, this pulp is kept under heating for a certain period of time, further diluted and disintegrated, and subjected to conventional flotation, washing, etc. By carrying out this treatment, it is possible to obtain pulp with high whiteness that could not be obtained by conventional methods. EXAMPLES Next, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited by these in any way. Comparative Example 1 Comparative Example 1 shows the results of deinking offset printed waste newspaper (Hokkaido Asahi Shimbun) using a conventional method. 50g of pre-disintegrated and dehydrated waste paper pulp was placed in a polyethylene bag, diluted with clean water to the prescribed pulp concentration shown in the table below, preheated in a 60°C hot bath, and added with NaOH, Na ₂ SiO ₃ , and interface as deinking agents. A predetermined amount of hydrogen peroxide as shown in the table below was added as an activator and a bleaching agent, and the mixture was maintained for 1 hour. The pulp after retention was diluted to 1.0% and subjected to flotation treatment using a test floatator (manufactured by Kyokuto Shinko Co., Ltd.). The treated pulp was adjusted to pH 5.5 with sulfite water, and a sheet for whiteness measurement was prepared using the Tappi standard method. The results are also listed in the table below. Example 1 Example 1 uses the same offset waste paper as Comparative Example 1.
The results are shown in which the alkali concentration in the deinking agent was changed, the pulp concentration was set to 20%, and a kneader was used in combination to apply compressive force. As in Comparative Example 1, the pulp concentration was adjusted, preheated, and deinking agent and bleaching agent (H ₂ O ₂ ) were added under the conditions shown in the table below, and then the mixture was mixed well so that the chemicals came into uniform contact. After that, test kneader (manufactured by Moriyama Seisakusho)
and kneaded for 20 minutes under heating at 60°C. After kneading, it was kept at this temperature for 1 hour, then diluted 1.0% and subjected to flotation treatment.
A sheet for measuring whiteness was prepared using the Tappi standard method. Kneading was performed at a pulp concentration of 20%.
The measurement results of whiteness are also listed in the table below. Comparative Example 2 The same experiment as in Example 1 was conducted except that the alkali concentrations were 2.0% and 3.0%. The conditions and whiteness are shown in the table below. Example 2 and Comparative Example 3 The same experiment as in Example 1 was conducted with the alkali concentration kept constant at 10.0 g/, and the pulp concentrations shown in the table below, and the whiteness was also measured. Example 3 and Comparative Example 4 Alkali concentration 10.0g/, pulp concentration 20%
The same experiment as in Example 1 was conducted under the temperature conditions shown in the table below, and the whiteness was also measured. Example 4 A reflex eyeliner was used in place of the kneader in Example 1. The experiment was carried out using 500 g of pulp and a test reflex eyeliner (manufactured by Kumagai Riki) under the conditions shown in the table below, and the whiteness was measured. Comparative Example 5 Using Toppan newspaper waste paper as waste paper, experiments were conducted under the conditions shown in the table below, in which mechanical stirring was not performed and in which mechanical stirring was performed using a kneader or refiner. The conditions and measurement results of whiteness in the Examples and Comparative Examples are collectively shown in the following table.

[Table] 〓〓〓〓〓

[Table] From the table above, the effect on whiteness is approximately 50%.
In the above case, as shown in Comparative Example 1, it is difficult to deink offset waste paper under the conventional deinking conditions. Example 1 and Comparative Example 2 show the influence of alkali concentration, and if it is 5.0 g/or more, the whiteness is 53 to 54%.
The above is obtained. Example 2 and Comparative Example 3 show the influence of pulp concentration; at a pulp concentration of 5 to 10%, compressive force is not applied to the pulp and the effect of mechanical stirring cannot be obtained, and a pulp concentration of 15% or more is required. Show that. From the results of Example 3 and Comparative Example 4, the whiteness was 50%.
To obtain this, a processing temperature of 50°C or higher is required. Further, Example 4 shows that the refiner treatment has substantially the same effect as the kneader treatment. Comparative Example 5 shows the effect of mechanical agitation on the letterpress waste paper, and an improvement of about 3% is observed for the letterpress waste paper, but compared to No. 3 of Comparative Example 1 and Example 1.
As is clear from the comparison with No. 6, offset waste paper shows a remarkable effect of improving the whiteness by about 13%. As is clear from the above description, the present invention has made it possible to deink and recycle offset waste paper, which was conventionally difficult to recycle as medium-grade paper, and also makes it possible to further alkali the pulp by mechanical agitation that applies compressive force to the pulp. It has the advantage of contributing to saving resources because concentration can be saved. 〓〓〓〓〓

Claims (1)

[Claims] 1. A deinking agent consisting of caustic soda, sodium silicate and a surfactant and a hydrogen peroxide bleach are added to printing waste paper containing offset waste paper to achieve a pulp concentration of about 15% or more and a pulp concentration of about 5.0 g/(as NaOH) or more. A method for deinking printed waste paper at an alkaline concentration, using a refiner, a kneader, a two-wheel mixer, or a disperser, and performing mechanical stirring while applying compressive force under heating.