GB2114178A - A process for producing fibrous material from waste paper - Google Patents

Abstract

A fibrous suspension prepared from waste paper by pulping (at 1), and cleansing by sorting in a screen sorter and/or cyclone (2), is temporarily heated before and/or during its passage through a disintegrating device (7) and prior to the separation of printing ink by flotation (8) or washing (and optically bleeching). The thickened suspension is maintained at temperatures above 85 DEG C during its passage through the disintegrating device (7). This allows types of waste paper, such as xerographic and offset-printed papers, which are difficult to de-ink to be cleaned, and therefore used for the production of fibrous material for paper manufacture. <IMAGE>

Description

SPECIFICATION A process for producing fibrous material from waste paper The invention relates to a process for the production of fibrous material, in particular material which has been freed from printing ink, from waste paper.

A process for the production of fibrous material from waste paper has already been described in German Patent Specification No. 2,311,674, in which the waste paper is puiped, the fibrous suspension formed is cleaned by sorting in a screen sorter and/or cyclone, and printing ink is removed by flotation or washing, and, if necessary, bleaching.

When processing waste paper in a printing ink separating stage, it is necessary to remove the printing ink from the fibres before this separating stage, because the printing ink particles can only be removed from the suspension of fibrous material at this stage by a flotation or washing process.

The separation of the printing ink particles from the fibres is usually carried out in an alkaline medium, in the temperature range of 40-700C.

Frequently, detergent substances are additionally added in order to assist the separation of the ink.

However, when processing offset-printed products, e.g. newspapers, telephone directories, and the like, particularly if they have been stored for a long time, and particular printed products printed with inks having a synthetic resin basis, e.g. xerographic and similar copying papers, this method does not work.

By reacting the fibrous material suspension in the high pulp consistency region, as is described, for example, in German Patent Specification No.

2,339,591 (Lausch) and German Patent Specification No. 2,311 ,674 (Berndt) and in the German Offenlegungsschrift 2,803,804 (Kriebstein), the separation of the printing ink is increased, but there are a number of printed products for which even these processes are not satisfactory, in particular if the de-inked fibrous material is to be used for the production of highquality types of paper.

It is an object of the present invention to provide a process for processing waste paper which enabies a basic fibrous material for the production of high-quality types of paper to be produced from papers which in particular have been printed by the offset process, xerographic printed papers and similar copying papers.

According to the invention, there is provided a process for the production of fibrous material from waste paper, in particular fibrous material cleaned from printing ink, comprising the steps of pulping the waste paper, cleaning the fibrous suspension formed by sorting it in a screen sorting machine and/or a cyclone, and separating printing ink from the suspension by flotation or washing and, if necessary, bleaching, wherein the fibrous suspension between the cleaning step and the printing ink-separating step is subjected at a material consistency of more than 1 5% to a kneading operation in a device with strong fibre disintegrating power where it is subjected to the effect of heat at a temperature of more than 850C, the duration of the application of heat equalling substantially at most the time of passage of the fibrous suspension through the disintegrating device, and is thereafter diluted to a consistency suitable for use in the subsequent flotation or washing step.

The passage of the fibrous material through the disintegrating device is preferably effected under the action, or with admixture of alkali. The application of heat is preferably effected at a temperature below 1 500 C.

The process of the invention surprisingly makes it possible to obtain a fibrous paper material, which has a high brightness and whiteness, using a flotation or washing process, even in the case of such difficult starting materials as previously referred to.

The disintegrating devices which are used in accordance with the invention including known single or double shaft disintegrators and disc disintegrators, widely used technically, have previously been used either to produce a ground fibrous paper pulp having a specific constitution, e.g. having a specific degree of grinding, or in order to finely distribute bitumen, wax materials, or latex materials in the suspension, as a result of the dispersion which takes place when the fibrous suspension passes through the disintegrating device, in order to overcome the disturbing, in particular optical, effect of such materials. These devices have not previously been directly used for removing printing ink from the fibrous suspension.

The basic idea of the process in accordance with the invention consists in effecting the increase in temperature and the effect thereof on the fibrous suspension in high concentration for only a very short time.

The supply of steam for heating can expediently take place into the feed screw of the disintegrator used, if such a feed screw is available, as is the case with single-shaft, or disc disi ntegrators (defibrators or despeckers (deflaker). These devices operate at an optimum at very specific concentrations which are well known to the experts in the art and which range between 18 and 35%. It is expedient to feed deinking chemicals either into the disintegrators themselves or into the feed screw; however, in particular cases, it may be advantageous to admix the chemicals required for bleaching or flotation, as well as alkali, before the heating of the material.

The invention will now be further described with reference to the drawing, which is a schematic flow sheet for an exempiary embodiment of the invention.

The waste paper is disintegrated in known manner in a pulper 1 at a concentration of between 4 and 25%. It is then fed by means of a pump 3 into sorting devices which are combined to form a group indicated at 2. These sorting devices can be either sorters provided with sieves, such as vertical sorters, or can be hydrocyclones.

The sorted and thus pre-cleaned material is then fed to a thickening device 4, in which the consistency of the fibrous suspension, is increased to a value in the optimum range of between 1 8 and 35%, the actual concentration depending on the particular disintegrating device to which it is to be fed. From the thickening device 4, it is fed to the feed screw 6 of a disintegrating device 7 which, as illustrated, is a single-shaft defibrator. In addition to steam, chemicals are fed to the feed screw 6 through a line 11, the chemicals being fpr bleaching purposes, e.g.

peroxide, and for flotation, i.e. substances which exhibit frothing and collecting characteristics, such as soap or fatty acids, in an amount of about 2% by weight, together with 1% by weight of alkali, e.g. in the form of NaOH; about 1.5% of water glass may be added, if desired, in addition under certain circumstances, to complex-forming agents. In order to make it possible to maintain the appropriate temperatures in the disintegrating device 7, the feeding screw 6 can either be conical or formed with threads which become ever cioser towards the end of the feeding movement, so that the pressure in the disintegrating device can be maintained by compression of the suspension.

After the disintegrating device, in which the suspension usually stays for at most a time of about 5 minutes (but possibly up to 12 minutes in some cases), the suspension is diluted to a very low consistency with the liquid which has been removed in the thickening device 4 through a line 10 and with additional water to a consistency of 1 to 1.8% and subjected to flotation in a flotation plant 8. The latter consists of primary cells 8' and secondary cells which are indicated by a schematic cell 8" and in which the froth removed is once again floated. The cleaned suspension is then supplied to a thickener 9, e.g. a belt pressure filter where such a high consistency is produced that the suspension can be piled, i.e. requires little space. The further processing, i.e. the preparation of the fibrous material for the paper-making machine can be carried out later.

It may be further pointed out that alkali, i.e.

sodium hydroxide solution, and also peroxide, can be introduced into the pulper 1. The supply of the waste paper into the pulper is carried out in a dry manner, e.g. by means of a conveyor belt 12, as illustrated.

It is pointed out that the time of heating to a high temperature in the chosen process in the feeding screw of the disintegrating device under consideration is quite short. It should basically not exceed 1 minute and preferably not half a minute.

The material thus does not lose its strength. The overall transit time through the screw and the disintegrating device is likewise relatively short and should, in any case, be shorter than 12 minutes. This transit time is generally about 5 minutes. This short transit time is necessary for the same reason.

The levels of whiteness obtained are quite high, over 60%. The initial peripheral whiteness has been exceeded by about 3%-points. For this purpose, the known Elrepho device (filter FMY) was used.

The disintegrating devices used are described in various literature references. A single-disc defibrator is, for example, described in "Das Papier", 1981, pages 67 to 73, in particular page 71, Figures 10 and 11. A single-shaft deflaker is described in "Voith Sonderdruck" No. 2018, W.

Musselmann: "Regarding the processing of waste paper in hot pulping plants", in particular at page 9, Figures 11 and 12.

As has already been mentioned, these disintegrating devices have previously been used for completely different purposes, mainly for dispersing printing ink or impurities in the fibrous suspension, i.e. to distribute them so finely that the optical effect of the impurities was no longer disadvantageously apparent. Contrary to the opposite view previously held by experts in the field, a fibrous material of high quality is produced as a starting material for the production of paper by the process of the present invention. Indeed, the experts have hitherto been of the opinion that when using high temperatures, whilst simultaneously carrying out intensive mechanical treatment (as is the case in disintegrating devices of the type described) the printing ink is even more firmly bonded to the fibres, and thus removal of the printing ink is no longer possible in the case of a starting material which itself can only be de-inked with difficulty.

Claims (14)

Claims

1. A process for the production of fibrous material from waste paper, in particular fibrous material cleaned from printing ink, comprising the steps of pulping the waste paper, cleaning the fibrous suspension formed by sorting it in a screen sorting machine and/or a cyclone, and separating printing ink from the suspension by flotation or washing, and, if necessary, bleaching wherein the fibrous suspension between the cleaning step and the printing ink-separating step is subjected at a material consistency of more than 15% to a kneading operation in a device with strong fibre disintegrating power where it is subjected to the effect of heat at a temperature of more than 85at, the duration of the application of heat equalling substantially at most the time of passage of the fibrous suspension through the disintegrating device, and is thereafter diluted to a consistency suitable for use in the subsequent flotation or washing step.

2. A process as claimed in Claim 1, wherein said disintegrating device has a feed screw and wherein the heating effect is exerted on said fibrous suspension by heating during passage through said screw.

3. A process as claimed in Claim 1 or Claim 2, wherein the passage of said fibrous suspension through said disintegrating device is effected under alkaline conditions.

4. A process as claimed in Claim 3, wherein alkali is admixed with the fibrous suspension fed to said disintegrating device.

5. A process as claimed in Claim 4, wherein the addition of bleaching agents, if required and/or detergent substances or the like for the flotation step, is carried out simultaneously with the addition of alkali.

6. A process as claimed in any one of the preceding Claims, wherein the temperature of the heating stage is below 1 SOC C.

7. A process as claimed in any one of the preceding Claims, wherein the material consistency of the fibrous suspension in the disintegrating step is between 1 8 and 35%.

8. A process as claimed in any one of the preceding Claims, wherein the material consistency during the initial pulping of the waste paper is between 4 and 25%.

9. A process as claimed in any one of the preceding Claims, wherein the waste paper used as starting material comprises offset printed paper and/or printed xerographic or like copier paper.

10. A process for the production of fibrous material from waste paper substantially as hereinbefore described with reference to the drawing.

11. Fibrous material produced by a process as claimed in any one of the preceding Claims.

12. Apparatus for the production of fibrous material from waste paper by a process as claimed in Claim 1, comprising means for initially pulping the waste paper, sorting means for cleaning the fibrous suspension leaving said pulper, and means for separating printing ink from the fibrous suspension by flotation or washing, and if necessary, bleaching, wherein a disintegrating device for treating the fibrous suspension and heating means for heating said fibrous suspension before and/or in said disintegrating device, are located between said cleaning means and said printing ink-removing means.

13. Apparatus as claimed in Claim 12, wherein said heating means comprises a steam line for the provision of heating steam before and/or in said disintegrating device.

14. Apparatus as claimed in Claim 12 or Claim 13, wherein said disintegrating device includes a feed screw, said heating means being arranged to heat said fibrous suspension during its passage through said screw.

1 5. Apparatus for the production of fibrous material from waste paper, substantially as hereinbefore described with reference to and as illustrated in the drawing.