GB2040333A

GB2040333A - Processing waste paper

Info

Publication number: GB2040333A
Application number: GB8000647A
Authority: GB
Original assignee: JM Voith GmbH
Current assignee: JM Voith GmbH
Priority date: 1979-01-19
Filing date: 1980-01-09
Publication date: 1980-08-28
Also published as: JPS5598990A; DE2901942B1; ES487817A1; NL8000316A; FR2446886A1; BR5901789U; IT7969513A0; BE881179A

Abstract

In the processing of waste paper containing a high proportion of dyed and/or wood-containing papers, the usual steps of disintegration, dye particle separation and flotation are followed by a multi-stage bleaching process. The first stage uses a hypochlorite bleach, whilst the second employs sodium hyposulphite or hydrogen peroxide. Preferably, the second stage employs sodium hyposulphite and a third stage hydrogen peroxide.

Description

SPECIFICATION Processing waste paper The invention relates to a process for processing waste paper which contains a high proportion of dyed and/or wood-containing papers, comprising a disintegration of the paper into individual fibres, separation of the printing dye particles, flotation and a bleaching process.

As is known, waste paper consists of a mixture of a wide variety of papers which are often pulpcoloured. For this reason, as well as flotation which, in the main, serves to remove only the printing dye particles, a bleaching process is usually carried out.

This bleaching process is commonly carried out using hydrogen peroxide as a bleaching agent.

However, it is found that not all dyes can be fully bleached in this way.

In the processing of wood-free paper or when large amounts of carbonless copy paper (so-called NCR-papers) are present a bleaching process using sodium hypochlorite has been employed. Sodium hypochlorite is a very good bleaching agent, but has not hitherto been considered suitable for paper which contains wood because it led to a yellowishgrey colouring. Therefore, high-grade paper could not be obtained in this fashion.

Therefore, the aim of the present invention is to provide a process for processing waste paper wherein new paper of good quality can be produced even from dyed and/or wood containing papers.

According to the present invention there is provided a process for processing waste paper containing a high proportion of dyed and/or wood containing papers, comprising a disintegration of the paper into individual fibres, separating the printing dye particles, flotation and bleaching, wherein the bleaching process is a multi-stage bleaching process in the first stage of which a hypochlorite is used as the bleaching agent and in the second stage of which sodium hyposulphite or hydrogen peroxide is used as the bleaching agent.

Paper of various qualities, especially paper which is strongly dyed and contains wood, can be successfully reprocessed by means of this multi-stage bleaching process. Although the hypochlorite bleaching stage stains the suspension yellowishgrey it has been ascertained that this yellowish-grey colouring can be removed together with a residual dye content by means of a subsequent sodium hyposulphite or hydrogen peroxide bleaching process. Thus the good bleaching property of hypochlorite, e.g. sodium- or potassium hypochlorite can be exploited in the case of the papers in question.

In a preferred embodiment of the invention it is provided that sodium hyposulphite is used in the second stage, which is then followed by a third stage using hydrogen peroxide. Alternatively the second stage can be a peroxide bleaching process and the third stage a hyposulphite bleaching process. The first stage of the bleaching process may be carried out using a sodium hypochlorite bleaching process, with an active chlorine content of 1 to 5%, at a temperature of from 30 to 70"C, preferably approximately 40"C.

In a preferred embodiment, the second stage of the bleaching process is carried out using sodium hyposulphite at a temperature of from 40"C to 85"C (preferably 60 - 65"C) in a solution of 1 to 2%.

An exemplary embodiment of the invention will now be described with reference to an example.

The waste paper which is to be processed is disintegrated in conventional fashion in a pulper with a density of 2 to 5% in a temperature range of 40 to 800C. 1 to 4% sodium hydroxide and approximately 1% sodium soap are added in the way of chemicals. Following cleaning, sorting, and possibly despecking, the suspension is floated in a flotation apparatus at a density of approximately 1%.

Next, the first bleaching stage using a sodium hypochlorite (NaOCI) bleach with an active chlorine content of 1 to 5% is effected at approximately 40".

Under the influence of the chlorine the wood containing material turns yellowish-grey. Moreover, a small residual dye content may still be present. The suspension cannot be used in this form. Forthis reason sodium hyposulphite (Na2S204) is added as second bleaching stage at 60 to 650C and 1% Na2S204.

If higher grade material is desired this second bleaching stage can be followed by a third bleaching stage using a hydrogen peroxide bleaching process at a temperature of 40 to 900C. In this case hydrogen peroxide is used in a solution of 1 to 2%.

The pulp density during the multi-stage bleaching process can range between 3 and 15%.

1. A process for processing waste paper containing a high proportion of dyed and/or wood containing papers, comprising disintegration of the paper into individual fibres, separating the printing dye particles, flotation and bleaching, wherein the bleaching process is a multi-stage bleaching process in the first stage of which a hypochlorite is used as the bleaching agent and in the second stage of which sodium hyposulphite or hydrogen peroxide is used as the bleaching agent.

2. A process according to claim 1, in which sodium hyposulphite is used in the second stage of the bleaching process, and including a third bleaching stage using hydrogen peroxide as the bleaching agent.

3. A process according to claim 1 or 2, in which the first stage of the bleaching process is carried out using sodium hypochlorite with an active chlorine content of 1 to 5%, at a temperature in the range 30"C to 70"C.

4. A process according to claim 3, in which the first stage of the bleaching process is carried out at a temperature of approximately 40"C.

5. A process according to any one of the preceding claims, in which the second stage of the bleaching process is carried out using sodium hyposulphite at a temperature in the range 40"C to 85"C in a solution of 1 to 2%.

6. A process according to claim 5, in which the second stage of the bleaching process is carried out

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Processing waste paper The invention relates to a process for processing waste paper which contains a high proportion of dyed and/or wood-containing papers, comprising a disintegration of the paper into individual fibres, separation of the printing dye particles, flotation and a bleaching process. As is known, waste paper consists of a mixture of a wide variety of papers which are often pulpcoloured. For this reason, as well as flotation which, in the main, serves to remove only the printing dye particles, a bleaching process is usually carried out. This bleaching process is commonly carried out using hydrogen peroxide as a bleaching agent. However, it is found that not all dyes can be fully bleached in this way. In the processing of wood-free paper or when large amounts of carbonless copy paper (so-called NCR-papers) are present a bleaching process using sodium hypochlorite has been employed. Sodium hypochlorite is a very good bleaching agent, but has not hitherto been considered suitable for paper which contains wood because it led to a yellowishgrey colouring. Therefore, high-grade paper could not be obtained in this fashion. Therefore, the aim of the present invention is to provide a process for processing waste paper wherein new paper of good quality can be produced even from dyed and/or wood containing papers. According to the present invention there is provided a process for processing waste paper containing a high proportion of dyed and/or wood containing papers, comprising a disintegration of the paper into individual fibres, separating the printing dye particles, flotation and bleaching, wherein the bleaching process is a multi-stage bleaching process in the first stage of which a hypochlorite is used as the bleaching agent and in the second stage of which sodium hyposulphite or hydrogen peroxide is used as the bleaching agent. Paper of various qualities, especially paper which is strongly dyed and contains wood, can be successfully reprocessed by means of this multi-stage bleaching process. Although the hypochlorite bleaching stage stains the suspension yellowishgrey it has been ascertained that this yellowish-grey colouring can be removed together with a residual dye content by means of a subsequent sodium hyposulphite or hydrogen peroxide bleaching process. Thus the good bleaching property of hypochlorite, e.g. sodium- or potassium hypochlorite can be exploited in the case of the papers in question. In a preferred embodiment of the invention it is provided that sodium hyposulphite is used in the second stage, which is then followed by a third stage using hydrogen peroxide. Alternatively the second stage can be a peroxide bleaching process and the third stage a hyposulphite bleaching process. The first stage of the bleaching process may be carried out using a sodium hypochlorite bleaching process, with an active chlorine content of 1 to 5%, at a temperature of from 30 to 70"C, preferably approximately 40"C. In a preferred embodiment, the second stage of the bleaching process is carried out using sodium hyposulphite at a temperature of from 40"C to 85"C (preferably 60 - 65"C) in a solution of 1 to 2%. An exemplary embodiment of the invention will now be described with reference to an example. The waste paper which is to be processed is disintegrated in conventional fashion in a pulper with a density of 2 to 5% in a temperature range of 40 to 800C. 1 to 4% sodium hydroxide and approximately 1% sodium soap are added in the way of chemicals. Following cleaning, sorting, and possibly despecking, the suspension is floated in a flotation apparatus at a density of approximately 1%. Next, the first bleaching stage using a sodium hypochlorite (NaOCI) bleach with an active chlorine content of 1 to 5% is effected at approximately 40". Under the influence of the chlorine the wood containing material turns yellowish-grey. Moreover, a small residual dye content may still be present. The suspension cannot be used in this form. Forthis reason sodium hyposulphite (Na2S204) is added as second bleaching stage at 60 to 650C and 1% Na2S204. If higher grade material is desired this second bleaching stage can be followed by a third bleaching stage using a hydrogen peroxide bleaching process at a temperature of 40 to 900C. In this case hydrogen peroxide is used in a solution of 1 to 2%. The pulp density during the multi-stage bleaching process can range between 3 and 15%. CLAIMS

6. A process according to claim 5, in which the second stage of the bleaching process is carried out at a temperature in the range 60"C to 65"C.

7. A process for processing waste paper substantially as herein described with reference to the example.