JP2006183210A - Method for producing regenerated pulp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing regenerated pulp, by which a yield for waste paper of raw material can be improved. <P>SOLUTION: This method for producing the regenerated pulp is characterized by spraying a dehydrated filtrate obtained from a concentration process on a screen 10 prepared by superposing at least three screen main bodies 13, 14, 15 in an order that at least three screen main bodies 13, 14, 15 having different opening sizes are sequentially disposed from the screen main body having a small size to the screen main body having a large size from one direction to the other direction, making the sprayed dehydrated filtrate to pass through the screen 10, separating and recovering pulp fibers contained in the dehydrated filtrate, and then adding the recovered pulp fibers and ash to the pulp slurry before a deinking process. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing recycled pulp using waste paper as a raw material.

Conventionally, in order to effectively use resources, recycled pulp is produced from used printing paper such as newspaper, medium-quality paper, high-quality paper, and coated paper, and used as an alternative to virgin pulp. As its manufacturing method, the raw paper raw material is disaggregated by pulper or the like, and then the fiber is disaggregated, and the so-called rough selection step of removing foreign matters from the obtained pulp slurry and the deinking step of removing ink components are performed, and then bleaching is performed. Generally, it is made into a recycled pulp through treatment or the like (see, for example, Patent Document 1). Moreover, between these processes, the concentration process of dehydrating and concentrating with a screw press etc. is performed as needed. The pulp slurry is concentrated by this concentration step, and dehydrated filtrate containing impurities such as ash, carbon and other ink components and fine foreign matters is discharged in addition to the pulp fibers.
This dehydrated filtrate is treated with a white water treatment facility such as a pressurized flotation device, so that pulp fibers, ash, and other impurities are separated and removed and reused as a pulper dilution liquid.

JP-A-5-331789 (page 4)

The dehydrated filtrate in the above-described conventional example, particularly the dehydrated filtrate in the concentration step performed immediately after the coarse selection step, contains a relatively large amount of pulp fiber and ash, and by collecting this, the yield in the production of recycled pulp can be increased. Can be improved.
However, the pulp fibers and ash separated and removed from the filtrate by white water treatment are obtained in a mixed state with other contaminants and at the same time it is difficult to separate and collect only the pulp fibers. No attempt has been made to recover and reuse the pulp fibers contained.
Although it is possible to pass the filtrate through a normal washing machine, in this case, pulp fibers can be recovered, but most of the ash can be recovered because most of the ash passes through the mesh.

  The present invention has been made in view of such circumstances, and provides a method for producing regenerated pulp that can recover pulp fibers and ash contained in a dehydrated filtrate and improve the yield with respect to used paper raw materials. The purpose is to do.

  The inventor has conducted extensive research on methods for improving yield in the production of recycled pulp. In the process, paying attention to the pulp fiber and ash contained in the dehydrated filtrate discharged in the concentration step during the production of recycled pulp, various experimental studies were conducted on methods for recovering the pulp fiber and ash. As a result, it was found that the pulp fibers and ash contained in the dehydrated filtrate can be separated and recovered by spraying the dehydrated filtrate on a predetermined screen, thereby completing the present invention.

That is, the present invention for achieving the above object includes a disaggregation step of disaggregating waste paper raw materials made of waste paper having a whiteness of 60% or more to obtain a pulp slurry, a rough selection step of removing foreign matters from the pulp slurry, and the pulp In a method for producing regenerated pulp, comprising a concentration step of concentrating by dehydrating the slurry, and a deinking step of removing ink from the pulp slurry,
At least three screen bodies each having a mesh with different opening sizes are provided, and the screen bodies are arranged in an overlapping order in which the opening size of these screen bodies increases from one side to the other side. The dehydrated filtrate obtained from the concentration step is sprayed from the one side to the screen, and the pulp fibers and ash mixed in the dehydrated filtrate are separated and recovered, and the recovered pulp fibers and ash are collected. Is added to the pulp slurry before the deinking step.

According to the method for producing regenerated pulp configured as described above, a considerable proportion of pulp fibers and ash can be recovered by spraying and passing the dehydrated filtrate through the screen. Further, when the dehydrated filtrate is sprayed on the screen, the pulp fibers contained in the dehydrated filtrate collide with the screen. The pulp fiber is subjected to a shearing force by this collision, and the ink is easily peeled off, so that the ink can be easily removed in the subsequent deinking process. Therefore, the pulp fiber is not particularly required to go through the other steps. It can be added to the previous pulp slurry.
Further, since the used paper raw material made of used paper having a whiteness of 60% or more is used, the amount of ash contained in the used paper raw material is relatively small, and the amount of recovered ash is relatively small. Therefore, even if the recovered pulp fibers and ash are added to the pulp slurry before the deinking step, the ash content of the pulp slurry is not increased more than necessary. For this reason, ash can be effectively reused without reducing the whiteness of the recycled paper obtained.

  In the method for producing regenerated pulp, the average value of the mesh opening size of the screen body in the screen is preferably 150 μm or less, and in this case, the pulp fibers in the dehydrated filtrate can be separated and recovered more reliably.

In the method for producing regenerated pulp, the screen is composed of a rotatable cone having the one surface as an inner peripheral surface, and the dehydrated filtrate is rotated from the inside to the outside of the cone while rotating the cone. May be used.
In this case, since the position where the dehydrated filtrate is sprayed always moves, the pulp fibers in the dehydrated filtrate can be separated and recovered continuously and efficiently.

  In the method for producing recycled pulp, the conical surface of the screen is preferably in a range of 45 ° or less with respect to the conical axis of the conical body. In this case, from the dehydrated filtrate remaining on the inner peripheral surface of the screen The separated pulp fibers can be efficiently discharged outside the conical screen.

In the method for producing regenerated pulp, the dehydrated filtrate may be sprayed from one side of the screen and water for cleaning the screen may be sprayed from the other side of the screen.
In this case, clogging of the screen can be prevented by water sprayed from the other surface side of the screen.

  As described above, according to the method for producing regenerated pulp of the present invention, the pulp fiber and ash can be recovered from the dehydrated filtrate discharged from the concentration step, so that the yield with respect to the used paper raw material can be improved.

Next, a preferred embodiment of the present invention will be described in detail. FIG. 1 is a diagram showing a process for producing recycled pulp from waste paper.
As the used paper used as the used paper raw material in the present embodiment, so-called fine used paper having a whiteness of 60% or more can be given. These are first disaggregated in the disaggregation step 1, and the used paper raw material is fiberized to obtain a pulp slurry. Get. For this disaggregation, a known apparatus such as a stirring pulper or a drum pulper can be used. Next, foreign matters are removed from the pulp slurry by a screen device or the like (coarse selection step 2). The pulp slurry at this stage is in the state of a suspension having a solid content of about 4%. Next, the pulp slurry is dehydrated using a screw press and concentrated to a solid content of about 30% (concentration step 3). Thereafter, the concentrated pulp slurry is mechanically stirred using a kneader, a disperser or the like, and the ink contained in the pulp slurry is peeled off by a strong shearing force (stirring step 4).
Next, the pulp slurry after the stirring step 4 is deinked by removing ink by flotation or the like (deinking step 5). The pulp slurry after the deinking step 5 is again subjected to finer foreign matters by a screen device or the like (selection step 6), and is supplied to the papermaking step 7 as recycled pulp. Various known screen devices and cleaner devices can be used for the rough selection step 2 and the fine selection step 6, and those suitable for the rough selection step 2 and the fine selection step 6 are used, respectively.

In the concentration step 3, the dehydrated filtrate is discharged along with dehydration and concentration, and this dehydrated filtrate has a solid content of about 0.8 to 1.0%. Contaminants such as ash and other fine foreign matters are included. The dehydrated filtrate is blown with a predetermined pressure against the inner peripheral surface of the rotating conical screen, and the pulp fibers and ash in the dehydrated filtrate are separated by this screen (pulp fiber recovery step). 8).
FIG. 2 shows an external view of this screen. In the figure, the screen 10 is formed in a conical shape as described above, and is configured to be driven by a motor or the like (not shown) to rotate around a conical axis. A nozzle or the like (not shown) for spraying dehydrated filtrate is arranged on the inner peripheral surface side of the screen 10 and the screen 10 is rotated while the screen 10 is rotated from the inner peripheral surface side toward the outer peripheral surface side. Liquid is sprayed.
Thus, by spraying the dehydrated filtrate while rotating the screen 10, the position of the screen 10 to which the dehydrated filtrate is sprayed always moves, so that the pulp fibers in the dehydrated filtrate are continuously and efficiently removed. Can be separated and recovered.

Further, the angle α formed by the inner and outer peripheral surfaces 11 and 12 as the conical surfaces of the screen 10 and the conical axis is set in a range of 45 ° or less. At this time, the case where the angle α is 0 °, that is, the case where the screen 10 has a cylindrical shape is also included. In this case, the pulp fibers separated from the dehydrated filtrate remaining on the inner peripheral surface 11 of the screen 10 can be dropped downward, and can be efficiently discharged to the outside of the screen 10.
FIG. 3 is a partial sectional view in the axial direction of the screen 10 shown in FIG. As shown in the figure, the screen 10 is constituted by superposing screen bodies 13, 14, and 15 made of three stainless steel wire nets.
Each of the screen bodies 13, 14, and 15 has a mesh with different opening sizes, the opening size of the screen body 13 is the smallest, and the opening size is larger in the order of the screen bodies 14 and 15. That is, the screen 10 has an opening dimension of the screen bodies 13, 14, 15 in order from the smaller to the larger one from the inner peripheral surface 11 that is one surface of the screen 10 toward the outer peripheral surface 12 that is the other surface. The main bodies 13, 14, and 15 are arranged and overlapped.

By using such a screen 10, it is possible to capture almost no fine impurities, and to capture pulp fibers and an appropriate amount of ash (including those contained in pulp fibers) from the dehydrated filtrate. Ash content can be recovered from the inside of the cylindrical screen as a mixture.
Moreover, it is preferable that the average value of the mesh size of the screens 13, 14, 15 is 150 μm or less. In this case, the pulp fibers in the dehydrated filtrate can be separated and recovered more reliably.
Further, the dehydrated filtrate may be sprayed from the inner peripheral surface 11 side of the screen 10 and water for cleaning the screen 10 may be sprayed from the outer peripheral surface 12 side. In this case, the water sprayed from the outer peripheral surface 12 side. Therefore, clogging of the screen 10 can be prevented.
In the pulp fiber recovery step 8 as described above, for example, Conus Trainer (trade name) manufactured by IH Itoit Paper Technology Co., Ltd. can be used.

  Returning to FIG. 1, the dehydrated filtrate after the mixture of pulp fibers and ash is collected is treated with white water using a pressure flotation device or the like (white water treatment step 9). By this white water treatment, impurities in the dehydrated filtrate are separated and recovered as scum and discarded. Moreover, the obtained white water is used for dilution water of the pulper apparatus etc. in the said disaggregation process 1. FIG.

  Next, the pulp fiber and ash mixture obtained in the pulp fiber recovery step 8 is added to the pulp slurry after the stirring step 4, that is, the pulp slurry before the deinking step 5. Here, the pulp fibers in the mixture to be added collide with the screen 10 when the pulp fibers are sprayed on the screen 10 in the pulp fiber recovery step 8, and the pulp fibers receive a shearing force due to the collision, and the ink is discharged. It is easy to peel off. Therefore, the recovered pulp fiber can be easily removed, and can be added to the pulp slurry before the deinking step 5 without going through the stirring step.

  The used paper used as the used paper raw material is so-called used waste paper having a whiteness of 60% or more, and the amount of ash contained in the used paper raw material by such used used paper is relatively small, and the recovered paper contains The content of ash (including those contained in pulp fibers) is relatively small. Therefore, even if this recovered mixture is added to the pulp slurry before the deinking step 5, the ash content of the entire pulp fiber is not increased. For this reason, the recovered ash can be reused without reducing the whiteness of the recycled paper obtained. Furthermore, by collecting and reusing this ash, the amount of scum discharged in the white water treatment step 9 can be reduced, and environmental destruction due to increased waste can be prevented.

  As described above, according to the method for producing regenerated pulp according to the present embodiment, pulp fibers and ash are collected from the dehydrated filtrate discharged from the concentration step 3 and added to the pulp slurry before the deinking step 5. Therefore, the yield with respect to the used paper raw material can be improved.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

(Examples and Comparative Examples)
Waste paper having a whiteness of 60% was used as a waste paper raw material, and this was subjected to disaggregation by a pulper, rough selection by a screen, dehydration concentration by a screw press, stirring by a kneader, fine selection, and deinking.
Next, a predetermined weight of the dehydrated filtrate discharged in the concentration step is collected, and the collected dehydrated filtrate is introduced into Conus Trainer (trade name) manufactured by IHI Paper Technology Co., Ltd. Was sprayed onto a screen having an opening size of 150 μm at a discharge rate of 50 ml / min, and the pulp fibers and ash content in the dehydrated filtrate were separated and recovered as a mixture.

  Table 1 shows the separation and recovery conditions and evaluation results of the examples and comparative examples.

The evaluation methods in Table 1 will be described below.
(Yield)
The dehydrated filtrate discharged in the concentration step is collected by a predetermined unit weight, and the mixture of pulp fiber and ash is collected and weighed using filter paper (JIS P3801 type 2 equivalent), and this value is used as the reference mixture. Weight.
Next, a weight of the recovered mixture obtained from the dehydrated filtrate having a predetermined unit weight is calculated from the weight of the mixture separated and recovered from the dehydrated filtrate having a predetermined weight according to the above-described Examples and Comparative Examples, and a standard for the weight of the recovered mixture is calculated. The ratio with respect to the mixture weight was calculated | required and this ratio was made into the yield.
The case where the yield was very high as 80% or more was evaluated as ◎, the case where it was 70% or more and less than 80% as a good value, ○, and the case where the yield was less than 70% was evaluated as x.
(Ash yield)
The dehydrated filtrate discharged in the concentration step is collected by a predetermined unit weight, and a mixture of pulp fiber and ash is collected using filter paper (JIS P3801 type 2 equivalent), and the ash weight in this mixture is determined. It was measured based on the ash test method of JIS P 8128 and used as the standard ash weight.
Similarly, the weight of the ash in the mixture separated and recovered from the dehydrated filtrate of a predetermined weight according to the above examples and comparative examples is measured, the recovered ash weight obtained from the dehydrated filtrate of the predetermined unit weight is calculated, and this recovery is performed. The ratio of the ash weight to the reference ash weight was determined, and this ratio was defined as the ash yield.
A case where the ash yield was 80% or higher, which is a very high value, was evaluated as ◎, a case where it was 70% or higher and less than 80%, which was a good value, and a case where it was less than 70%, which was less than 70%.

From Table 1, it can be seen that in all examples, the yield and the ash yield are good values as compared with the comparative example.
Thus, the mixture of the pulp fiber and ash efficiently recovered from the dehydrated filtrate with a high yield is added to the pulp slurry before deinking (pulp slurry obtained from the clarification step), thereby the recycled pulp. The yield in the manufacturing method can be improved.

It is a figure which shows the process for manufacturing a recycled pulp from used paper. It is an external view of a screen. It is a fragmentary sectional view of the axial direction which shows the structure of a screen.

Explanation of symbols

10 Screen 11 Inner peripheral surface (one side)
12 Outer peripheral surface (the other side)
13, 14, 15 Screen body

Claims (5)

A disaggregation step of disaggregating waste paper raw materials made of waste paper having a whiteness of 60% or more to obtain a pulp slurry, a rough selection step of removing foreign matters from the pulp slurry, a concentration step of concentrating by dehydrating the pulp slurry, A deinking step of removing ink from the pulp slurry,
At least three screen bodies each having a mesh with different opening sizes are provided, and the screen bodies are arranged in an overlapping order in which the opening size of these screen bodies increases from one side to the other side. The dehydrated filtrate obtained from the concentration step is sprayed from the one side to the screen, and the pulp fibers and ash mixed in the dehydrated filtrate are separated and recovered, and the recovered pulp fibers and ash are collected. Is added to the pulp slurry before the deinking step.   The method for producing a regenerated pulp according to claim 1, wherein an average value of a mesh size of the screen body of the screen is 150 μm or less.   The screen comprises a rotatable cone having the one surface as an inner peripheral surface, and the dehydrated filtrate is sprayed from the inside to the outside of the cone while rotating the cone. A method for producing a regenerated pulp according to 1.   The method for producing regenerated pulp according to claim 3, wherein the conical surface of the screen is in a range of 45 ° or less with respect to the conical axis of the conical body.   The method for producing regenerated pulp according to any one of claims 1 to 4, wherein the dehydrated filtrate is sprayed from one side of the screen and water for washing the screen is sprayed from the other side of the screen.

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