JP2005089919A - Method for producing waste paper pulp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a waste paper pulp in which the waste paper pulp having high whiteness can be obtained also in the case when waste paper having high ratio of heat-sensitive waste paper is targeted. <P>SOLUTION: A waste paper containing 5-50 mass% heat-sensitive waste paper is disintegrated, oxidized, bleached and deinked to provide waste paper pulp. Oxidative bleaching is carried out by adding an oxidative bleaching agent to waste paper under conditions of 20-30 mass% disintegrated pulp concentration and pH 10.5-11, stirring these components and aging the pulp for 2-5 hr. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing waste paper pulp from waste paper including heat-sensitive waste paper.

  In general, heat-sensitive waste paper has a coating layer made of a basic colorless dye, a color former, a sensitizer, a pigment, a binder, an auxiliary agent, and the like formed on a base paper. In addition, since conventional heat-sensitive waste paper has problems in water resistance, oil resistance, plasticizer resistance, etc., recent heat-sensitive waste paper is further formed on a coating layer from an aqueous emulsion, a water-soluble polymer compound, and the like. A protective layer is formed.

  This type of heat-sensitive waste paper is difficult to recycle (used paper pulp) due to the presence of a coating layer, a protective layer, and the like. According to the standard quality standard (established on January 27, 1986) compiled by the Waste Paper Recycling Promotion Center, it is classified as a contraindicated product B that is not desirable to be mixed and treated as paper that is not suitable for collection and reuse.

  However, from the viewpoint of effective use of resources, it is necessary to recycle the heat-sensitive waste paper, and if heat-sensitive waste paper can be regenerated, there is an advantage that the labor of sorting with other waste paper can be saved.

  Accordingly, various methods of heat-sensitive used paper recycling have been developed. For example, a method of disaggregating using an alkaline liquid containing a surfactant (see, for example, Patent Document 1), followed by neutralization, A method of performing floating selection, washing / concentration, high-speed disaggregation, etc. (for example, refer to Patent Document 2), a method of performing multi-stage bleaching after disaggregation treatment (for example, refer to Patent Document 3), a surfactant, A method of immersing in the presence of hydrogen oxide or the like (see, for example, Patent Document 4) has been proposed.

However, even if these methods are used, it is not possible to obtain high-whiteness wastepaper pulp when targeting wastepaper with a high proportion of heat-sensitive wastepaper. If high-whiteness wastepaper pulp is obtained, the proportion of heat-sensitive wastepaper is The present inventors recognize that it is necessary to make the amount up to about 10% by mass at most. In Patent Document 4, the ratio of heat-sensitive waste paper is limited to 8% or less.
Japanese Patent Laid-Open No. 50-6802 JP-A-63-135585 Japanese Patent Laid-Open No. 5-147873 JP-A-6-299489

  The main problem to be solved by the present invention is to provide a method for producing used paper pulp that can obtain used paper pulp having high whiteness even when used paper with a high proportion of heat-sensitive used paper.

The present invention that has solved the above problems is as follows.
[Invention of Claim 1]
A method for obtaining waste paper pulp by deinking and oxidizing and bleaching waste paper containing 5-50% by weight of heat-sensitive waste paper,
A method for producing waste paper pulp, characterized in that an oxidative bleaching agent is added and stirred under conditions of a disaggregated pulp concentration of 20 to 30% by mass and pH of 10.5 to 11, and then aged for 2 to 5 hours.

[Invention of Claim 2]
The manufacturing method of the used paper pulp of Claim 1 which performs the disaggregation of used paper on the conditions of the temperature of 50-75 degreeC.

[Invention of Claim 3]
The method for producing waste paper pulp according to claim 1 or 2, wherein sodium silicate is added together with caustic soda to adjust the pH to 10.5 to 11.

[Invention of Claim 4]
The method for producing waste paper pulp according to any one of claims 1 to 3, wherein after oxidative bleaching, a reducing bleach is added under conditions of a pulp concentration of 20 to 30% by mass, and then aging is performed for 2 to 5 hours. .

  According to the method for producing waste paper pulp of the present invention, it is possible to obtain waste paper pulp having high whiteness even when used waste paper with a large proportion of heat-sensitive waste paper.

Embodiments of the present invention will be described below.
〔used paper〕
The used paper which is the object of the present invention is used paper containing 5 to 50% by mass of heat-sensitive used paper. Of course, even if the ratio of the heat-sensitive waste paper is less than 5% by mass, a high whiteness waste paper pulp can be obtained. Since the degree of waste paper pulp can be obtained, the method of the present invention cannot be said to be remarkably superior when compared with the conventional method. On the other hand, when the ratio of the heat-sensitive waste paper is more than 50% by mass, the whiteness may be lowered.

  The type of used paper other than the heat-sensitive used paper is not limited to profit. For example, used paper such as newspapers and leaflets, and used magazines including various bleach-resistant papers such as coated paper, non-coated paper, color printed paper, and black and white printed paper can be used. .

[Disaggregation processing]
Waste paper including heat-sensitive waste paper is first disaggregated with a disaggregator such as a pulper. This disaggregation is preferably performed under conditions of a temperature of 50 to 75 ° C, and particularly preferably performed under conditions of a temperature of 55 to 60 ° C. Generally, the used paper is disaggregated at a temperature of about 40 ° C. At such a temperature, the coated layer (thermosensitive recording layer), the protective layer, etc. of the heat-sensitive used paper may be in an undissolved state. Therefore, in this embodiment, the disaggregation temperature is set to 50 ° C. or higher. On the other hand, when the disaggregation temperature is around 80 ° C., adhesive foreign matter may be generated and the disaggregation operation may be disturbed, and the colorant in the coating layer dissolves and reacts with the dye to cause a decrease in whiteness. There is a risk of becoming. Therefore, in this embodiment, the disaggregation temperature is set to 75 ° C. or lower.

  The disaggregation of the used paper is preferably performed for 10 to 30 minutes under the condition of 0.05 to 0.3% by mass of a nonionic surfactant.

  The type of the used paper disintegrator is not particularly limited. For example, a separator other than a pulper can be used. As the pulper, for example, a low-concentration pulper such as a hydra pulper, a rotor pulper, or a horizontal pulper, or a high-concentration pulper such as a vertical batch pulper or a drum-type continuous pulper can be used as appropriate.

[Dust removal process]
The disaggregated pulp (fiber suspension) obtained by disaggregation removes comparatively large foreign matters such as hot melt used as laminate paper and magazine back glue contained in it by dust removing means. It is preferable to keep it. Removal of foreign matter such as laminating flaws prevents clogging of the papermaking net in the papermaking process and adhesion of foreign matter to the roll.

  The type of dust removing means is not particularly limited, and for example, dust removing means having a hole such as a hole screen, dust removing means having a slit such as a slit screen, and the like can be used.

  The above dust removal can be performed in two, three, four, or more stages.

[Oxidative bleaching]
The disaggregated pulp obtained by dedusting is adjusted to a pulp concentration of 20 to 30% by mass, more preferably 23 to 25% by mass by dehydration. In the present invention, as will be described later, when chemicals such as caustic soda, sodium silicate, and oxidative bleach are added, if the pulp concentration is less than 20% by mass, the amount of water is large, so it is necessary to increase the amount of chemicals added. This causes problems such as an increase in cost. In addition, increasing the pulp concentration (20% by mass or more) has advantages such as reduction in the size of a processing container such as a tower and suppression of the COD load of the treated wastewater. On the other hand, in the present invention, as described later, when the disaggregated pulp to which the oxidizing bleaching agent is added is stirred, the stirring becomes difficult when the pulp concentration is a high concentration of more than 30% by mass. If it does, there exists a possibility that a fiber may be refined | miniaturized. Moreover, when stirring is insufficient, there exists a problem that contact with a fiber and an oxidizing bleaching agent will become inadequate and a bleaching property will fall rather. In order to solve this, it is conceivable to increase the addition amount of the oxidative bleaching agent. However, the increase in the addition amount may cause an increase in cost, an increase in the COD load of the treated waste water, and the like.

  The disaggregated pulp adjusted to a pulp concentration of 20 to 30% by mass is further adjusted to pH 10.5 to 11, more preferably to pH 11. When the present inventors tested, it was because the bleaching effect by an oxidizing bleaching agent became the most excellent under the conditions of pH 10.5-11. In addition, when the pH is about 12, the reactivity of the oxidative bleaching agent is deteriorated, and a large amount of bubbles is generated in the floating deinking in the subsequent step. From this viewpoint, it can be said that the pH is preferably 11 or less.

  As a method for adjusting the pH, for example, a method of adjusting by adding sodium carbonate, potassium hydroxide or the like can be considered. However, in the present embodiment, adjustment is made by adding sodium silicate together with caustic soda. Caustic soda is used to alkalinize disintegrated pulp, and sodium silicate is used to obtain stability in an alkaline pH by pH buffering action and to obtain an ink re-adhesion preventing effect by chelating action. .

  Once the disaggregated pulp is adjusted to a pulp concentration of 20 to 30% by mass and pH of 10.5 to 11, an oxidizing bleaching agent is added and stirred. As the oxidizing bleaching agent, for example, hydrogen peroxide or ozone can be used, but from the viewpoint of operability and cost (cost), it is preferable to use hydrogen peroxide. Moreover, the method is not specifically limited, for example, can be stirred with a mixing apparatus, a kneading apparatus, etc., for example, for 1 to 10 minutes. Furthermore, in this stirring, it is preferable to heat the disaggregated pulp at 60 to 70 ° C. This is because the reaction efficiency of the oxidizing bleaching agent is improved.

  The disaggregated pulp after stirring is aged for 2 to 5 hours, more preferably 4 to 5 hours. Since the reaction (dynamic reaction) of the oxidizing bleaching agent by stirring proceeds only to about 70%, the remaining 30% of the reaction (static reaction) is realized by aging. Aging for 2 hours or more is the minimum time required for such a static reaction. On the other hand, aging for more than 5 hours is not preferable because the color may change due to so-called alkali burning or water burning.

[Reduction bleaching]
The deoxidized pulp that has been oxidatively bleached is added with a reducing bleaching agent in a state where the pulp concentration remains at 20 to 30% by mass, more preferably at a pulp concentration of 23 to 25% by mass, and is appropriately stirred. The reason why the pulp concentration is 20 to 30% by mass is the same as in the case of oxidative bleaching.

  As the reducing bleach, for example, formamidine sulfinic acid (FAS), hydrosulfite, and the like can be used. From the viewpoint of decolorization power (bleaching power) and safety, FAS is used. preferable. Moreover, the method is not specifically limited, for example, can be stirred with a mixing apparatus, a kneading apparatus, etc., for example, for 1 to 10 minutes. Furthermore, at the time of this stirring, it is preferable to heat the disaggregated pulp to 60 to 80 ° C. This is because the reaction efficiency of the reducing bleaching agent is improved.

  The disaggregated pulp after stirring is aged for 2 to 5 hours, more preferably 4 to 5 hours. Since the reaction (dynamic reaction) of the reducing bleach by stirring proceeds only to about 70%, the remaining 30% of the reaction (static reaction) is realized by aging. Aging for 2 hours or more is the minimum time required for such a static reaction. On the other hand, aging for more than 5 hours is not preferable because it may reduce the effect of the oxidizing bleaching agent when using white water infiltrated with the reducing agent.

[Floating deinking]
As described above, the disaggregated pulp that has undergone the two-step bleaching process of oxidative bleaching and reductive bleaching is subjected to floating deinking means such as a floatator to obtain basic colorless dyes, colorants, sensitizers, pigments, binders, auxiliaries, etc. Floating and removing foreign matters such as finely divided coating layer components, finely divided protective layer components such as aqueous emulsions and water-soluble polymer compounds, and ink.

[Others]
(1) In this invention, a well-known process can be suitably provided besides the above process.

(2) In this embodiment, the floating deinking step is provided after the bleaching step. However, the floating deinking step can be provided before the bleaching step to remove relatively large impurities.

Examples of the present invention will be described below.
Waste paper 4600 kg including heat-sensitive waste paper was disaggregated, oxidatively bleached using an oxidative bleach, and then deinked to obtain waste paper pulp. The whiteness of the wastepaper pulp obtained (measured with a Hunter whiteness meter) by changing the blending amount (mass%) of heat-sensitive wastepaper, pulp concentration [mass%], pH and aging time [hr] during oxidative bleaching. , JIS P 8123). The results are shown in Table 1.

  About Test Example 3 of Example 1, the temperature [° C.] at the time of disaggregation was changed, and the whiteness (measured with a Hunter whiteness meter, JIS P 8123) of the obtained waste paper pulp was examined. The results are shown in Table 2.

  In Test Example 3 of Example 1, reductive bleaching was further performed using formamidinesulfinic acid (FAS) after oxidative bleaching and before deinking. The whiteness (measured with a hunter whiteness meter, JIS P 8123) of the obtained waste paper pulp was examined by changing the pulp concentration and the aging time during reductive bleaching. The results are shown in Table 3.

Claims (4)

A method for obtaining waste paper pulp by deinking and oxidizing and bleaching waste paper containing 5-50% by weight of heat-sensitive waste paper,
A method for producing waste paper pulp, characterized in that an oxidative bleaching agent is added and stirred under conditions of a disaggregated pulp concentration of 20 to 30% by mass and pH of 10.5 to 11, and then aged for 2 to 5 hours. The manufacturing method of the used paper pulp of Claim 1 which performs the disaggregation of used paper on the conditions of the temperature of 50-75 degreeC. The method for producing waste paper pulp according to claim 1 or 2, wherein sodium silicate is added together with caustic soda to adjust the pH to 10.5 to 11. The method for producing waste paper pulp according to any one of claims 1 to 3, wherein after the oxidative bleaching, the reduced bleaching agent is added under the condition of a pulp concentration of 20 to 30% by mass, followed by aging for 2 to 5 hours. .