GB2304741A - Enzyme deinking of paper - Google Patents

Abstract

In a process for deinking paper carrying ink which comprises a resistant binder, the paper is pulped with water in the presence of a deinking enzyme which is added to the water or pulp in the form of a substantially anhydrous, stable, dispersion of enzyme in a non-aqueous liquid. The ink is then separated from the pulp. The non-aqueous liquid may be a surfactant, e.g. a non-ionic surfactant such as a fatty alcohol ethoxylate or it may be surfactant-free. A flotation stage may follow pulping. The process is suitable for laser-printed or xerographic paper.

Description

Allied Colloids Limited Treatment of Cellulosic Material and Compositions for use in this This invention relates to the de-inking of paper. In this specification we use the term "paper" to be generic to a variety of cellulosic sheet materials including filled and unfilled papers and paper board.

It is standard practice to reclaim waste paper so as to allow the reclaimed paper fibres to be used as part or all of the stock of subsequent paper production. The waste paper frequently carries ink particles and so the waste paper needs to be de-inked. It is conventional practice to de-ink paper carrying ink particles by pulping the paper with water in the presence of de-inking additive and then separating the ink from the pulp. The separation may be by, for instance, washing and/or flotation.

During the pulping stage it is intended that the ink particles should be released from the paper fibres allowing for the ink subsequently to be separated from the pulp by flotation and/or washing so as to leave a pulp which is as free as possible of ink.

The ink generally comprises a binder and a pigment.

Traditional de-inking processes involved an alkaline pulping stage and this resulted in sufficient softening or dissolution of many conventional ink binders to result in satisfactory release of the ink from the fibres and satisfactory release of the pigment from the ink.

Appropriate de-inking can the be achieved provided the overall de-inking conditions result in satisfactory bleaching or removal of the pigment or dye from the product. For instance such removal is promoted by appropriate flotation and/or washing processes. It is necessary to prevent re-agglomeration of dispersed particles as otherwise these may create specks in the final product, but known de-inking processes usually result in avoidance of this problem with such inks.

When the pulping is conducted under neutral conditions, an increased number of binders may dissolve or soften insufficiently to release the individual pigment particles and so there can be a tendency for an increased number of particles to be carried through into the final product as specks.

Although most combinations of pulping conditions and ink do result in adequate separation of the ink from the fibres during pulping, in some instances the binder of the ink is so resistant to the pulping conditions that there is increased tendency for the ink to remain bonded to the fibres.

A particular problem arises when the ink is applied by laser printing or by xerographic or by other photocopying techniques. The ink used in these techniques tends to be fused onto the fibres and the binder in the inks tends to be resistant to alkaline and neutral de-inking conditions.

As a result, there is an increased tendency for the ink to remain as particles in the pulp and for the binder to fail to degrade sufficiently to release the pigment or dye into the pulp.

Accordingly, many conventional de-inking processes result in a high speck count when the paper that is being pulped contains laser printed or photocopied paper. Such papers are generally of reasonably high quality with the result that the pulp may have an inherent tendency to have a high brightness, and the main problem with the de-inking of such papers therefore is the need to reduce the speck count.

We describe in W093/21376 and W095/12026 certain deinking processes operated under substantially neutral conditions in the presence of a water soluble carboxylic polymer, such as a moderately low molecular weight polyacrylic acid. In W095/12026 we describe such a process applied to the de-inking of paper carrying ink particles comprising a resistant binder wherein the pulping stage is followed by a flotation stage which is intended to float the ink particle off as a reject fraction, and we show that the flotation is much more effective when flotation is promoted by the addition of a cationic surfactant than when it is promoted by the addition of a conventional soap flotation system or an anionic surfactant.

In recent years, there has been extensive use of enzymes in various processes and products. The enzyme, or microbiological cellular material containing it, is formed initially as an aqueous fermentation broth which is then converted to an aqueous concentrate by conventional techniques. This aqueous concentrate may have only relatively short shelf life and various ways of putting it into different physical forms that have better shelf life and/or which are more convenient to handle are known. For instance we describe in EP-A-356239 a substantially anhydrous, liquid, stable, dispersion of enzyme particles dispersed in a hydrocarbon or other water immiscible liquid, for use in liquid detergent compositions.In W094/25560 we describe stable fluid dispersions of enzyme particles in a non-aqueous liquid of which at least 80% is selected from surfactant and water miscible liquids. The preferred surfactant is ethoxylated fatty alcohol. The compositions are described as being useful in the formulation of liquid detergents.

Enzymes have been proposed for addition to various paper making processes. Thus it is known to add lignases to facilitate the initial pulping process and it is known to add cellulases and hemi-cellulases to facilitate fibre disintegration in the pulp process and to facilitate release of ink from fibres. In particular, it is known to use cellulase or hemi-cellulase enzyme for promoting the separation of fused inks from fibres during a pulping process. It is reasonable to assume that the cellulase or hemi-cellulase attacks the interface between the fused ink and the fibre, so as to release the fused ink into the pulp.

A suitable material is commercially available from (RTM) Novo A/S under the trade name CelluzymeL. It is supplied as an aqueous concentrate and is a mixture of cellulases and hemi-cellulases. Unfortunately, the results obtained with this tend to be inadequate as regards speck count, although brightness may be acceptable, especially since paper which carries laser for xerographic printing is often inherently bright anyway.

One possible reason for the poor speck count is that there is inadequate release of the ink from the fibres.

Another possible reason is that the ink which is released has such a large average particle size that it tends to be physically entrapped within the pulp and may tend to be removed inadequately by conventional washing or flotation processes. Another possible reason may be that ink particles which are initially released as small particles may agglomerate during the process so as to contribute to a significant speck count in the final product.

Whatever the reasons, there remains a need to provide a de-inking process which results in lower speck count and better speck removal, and which preferably allows for the attainment of good brightness values. In particular, it is necessary to achieve this when the paper which is de-inked includes laser printed or photocopy paper in which the ink has been fused onto the fibres.

According to the invention, we de-ink paper carrying ink which comprises a resistant binder by a process comprising pulping the paper with water in the presence of a de-inking enzyme and then separating the ink from the pulp, and we surprisingly find that improved speck removal is achieved if the enzyme is added to the pulp or to the water while it is in the form of a substantially anhydrous, stable, dispersion of enzyme in a non-aqueous liquid.

The improved speck removal is manifested by the fact that it is possible to remove by flotation and/or washing a greater than usual proportion of the specks that are present in a sheet made from the pulp prior to the ink separation stages.

An additional advantage of the invention is that it is possible to obtain satisfactorily low, and indeed very low, speck counts in the final product.

The improvement is found to occur as a direct result of the form in which the enzyme is added to the pulp or the dilution water, and is not due to the ageing conditions to which the enzyme has been subjected. Thus, in the invention, is preferred to put the enzyme into a form of an anhydrous stable dispersion as early as possible after the production of the enzyme, but the improvement is achieved where the user is supplied with an aqueous concentrate and either applies that concentrate to the dilution water or pulp or, substantially immediately before use, converts the concentrate into the prescribed anhydrous dispersion and adds that dispersion to the dilution water or pulp.

Accordingly, it would be expected that the enzymatic activity would be the same irrespective of whether the enzyme was applied as the described dispersion or as aqueous concentrate, and yet we surprisingly find that the inking performance is improved by adding the enzyme as the described dispersion rather than as the concentrate.

The separation of the ink from the pulp can be conducted by any suitable washing and/or flotation process.

Although washing alone is usable, the best results generally involve flotation, and usually a combination of washing and flotation. For instance,the separation may be conducted by washing followed by flotation, flotation followed by washing or washing followed by flotation followed by washing. In each instance, the concentration of the pulp may be adjusted before, during or after a separation stage in conventional manner. For instance, a typical separation process may comprise subjecting the pulp to flotation to form a reject fraction containing the ink and an accept fraction, followed by thickening the accept fraction to provide a thickened product which can then be recycled for use in paper making, optionally after further cleaning procedures.

When the separation is to involve flotation it is desirable for a flotation surfactant to be added to the pulp after the pulping and before the flotation so as to promote preferential flotation of the ink particles in to the reject fraction. Frequently the flotation surfactant is added to the pulp after it has been diluted, for instance by a factor of 3-30 (eg, 10), after the pulping operation and before the flotation. The flotation surfactant is usually added immediately before the flotation, ie after any preceding pulping, washing or other separation stage.

The non-aqueous liquid in which the enzyme is dispersed may be any of the non-aqueous liquids described in EP-A-356,239 and W094/25560 and may have a water content and be made by methods and from materials as described in those, especially as in W094/25560. In one aspect of the invention the non-aqueous liquid is a liquid which is substantially free of any surfactant, but in the preferred aspect of the invention the non-aqueous liquid is mainly or wholly a surfactant. The concentration of the enzyme in the concentrate or dispersion is typically 5 to 50%, often 20 to 40% in the dispersion. Preferably it is mixed with some of the water that is to be included in the pulper before adding the enzyme to the pulper.

When the non-aqueous liquid is substantially free of any surfactant, the non-aqueous liquid may be a hydrocarbon or other water immiscible liquid or it may be non-aqueous, water miscible, organic solvent. Even though the dispersion is substantially free of surfactant it will usually include a small amount of surfactant, for instance not more than 10 or 15% by weight of the liquid, to facilitate manufacture and use. For instance the nonaqueous may include an oil-in-water emulsifying agent to promote emulsification of the liquid in the dilution water or in the pulper (especially when the remainder of the non aqueous liquid is a water immiscible liquid). The dispersion may include a water-in-oil surfactant and/or an amphipathic polymeric stabiliser to facilitate the production of a stable anhydrous dispersion, eg, as described in EP-A-356239 and WO 94/25560.The amount of each is often in the range of 1 - 10% by weight of the dispersion, typically 0.1 to 5% based on the weight of enzyme.

When the non-aqueous liquid is substantially free of surfactant then best results are obtained in the flotation stage if the flotation surfactant which is added is a cationic surfactant. The cationic surfactant can be cationically charged at the time it is added to the pulp or it can be in free base form which may become cationically charged by interaction with components in the pulp.

Suitable cationic surfactants that can be used include ethoxylated fatty amines and fatty diamines and quaternary fatty ammonium compounds (i.e., quaternary ammonium compounds including at least one fatty group). The fatty groups can be naturally occurring or synthetic fatty groups, generally containing 6 to 24, often 8 to 18, carbon atoms. The fatty group is often alkyl. Ethoxylated fatty amines are preferred.

The cat ionic surfactant can be a surfactant that includes both cationic and anionic groups (i.e., amphoteric) but preferably it is wholly cationic.

The use of non-ionic surfactant as the flotation aid when there is a resistant binder can give reasonable speck removal and dirt count but surprisingly tends to give rather poor brightness.

In the preferred aspect of the invention, the nonaqueous liquid is mainly or wholly surfactant, that is to say at least 50% and usually at least 80% of the nonaqueous liquid is a surfactant or mixture of surfactants.

Preferably it is non-ionic surfactant, most preferably a fatty alcohol ethoxylate. Preferably this has HLB at least 7 and often at least 9. HLB is preferably below 12 but can be higher.

We surprisingly find that despite the preference to use a cationic flotation surfactant when the enzyme is dispersed in a non-surfactant liquid or in the processes described in W095/12026, the use of a cationic flotation surfactant is less satisfactory when the non-aqueous liquid is a non-ionic surfactant. In particular, the dirt count and speck removal obtained using cationic flotation surfactant tends to be much worse when the enzyme is dispersed in non-ionic surfactant than when it is dispersed in a liquid which is substantially free of surfactant. The reason for this is unclear.

In the invention, good de-inking is achieved when the non-aqueous liquid of the enzyme dispersion and the flotation surfactant are both non-ionic surfactants.

The non-ionic flotation surfactants can be, for instance, a fatty acid ethoxylate, a fatty amide ethoxylate or an ethylene oxide and propylene oxide copolymer, but is most preferably a fatty alcohol ethoxylate. The flotation surfactant is generally of the same chemical type as the non-ionic surfactant of the enzyme dispersion, which likewise can be selected from any of these materials. The flotation surfactant generally has an HLB within the same range as the non-ionic surfactant of the enzyme dispersion.

It is convenient and preferred to use the same material as the surfactant in the non-aqueous liquid in the enzyme dispersion and as the flotation surfactant which is added to the pulp after the pulping, and often after subsequent dilution.

It is particularly surprising that the choice of the non-aqueous liquid (including emulsifiers or stabilisers in it) has such a significant effect on the choice of the flotation surfactant since the amount of non-aqueous liquid is generally relatively low. Thus the amount is generally below 250 g/t (grams non aqueous liquid per tonne dry weight of fibre in the pulp) and is usually lower than this, for instance below 150 or 100 g/t and often below 50 g/t. The amount is usually at least 5 g/t. The amount of flotation surfactant which is added to the pulp is usually larger than the amount of non-ionic surfactant or other non-aqueous liquid added with the enzyme, and is usually at least 2 x and is frequently at least 5 x or at least 10 x the amount of the non-aqueous liquid. The amount of flotation surfactant is usually above lOOg/t and generally above 300g/t.It can be up to, for instance, 3000 or even 5000g/t. Preferred amounts are generally in the range 500 to 1500g/t. All amounts are grams per ton dry weight of fibre in the pulp.

The amount of enzyme that is used influences performance and we find there is a concentration which tends to give peak activity, with less satisfactory deinking occurring at higher or lower concentrations. The optimum amount depends on the particular enzyme which is being used but is generally within the range 1 to 50, often 2 to 10, grams active dry enzyme per tonne fibre in the pulper.

The enzyme which is used can be any de-inking enzyme which will promote de-inking and is preferably a mixture of cellulose and hemi-cellulose. Preferred enzyme products are mixtures which have endoglucanase, cellubiohydrolase, cellubiase, xylanase and hemicellulase activities and the like.

The preferred enzyme which we have used in our experiments is commercially available from Novo A/S in July 1995 under the name Celluzyme. The invention is preferably conducted using this enzyme or using any other enzyme which has de-inking activity substantially the same as or greater than July 1995 Celluzyme.

The pulping can be conducted at any convenient temperature, generally in the range 30 to 60"C, preferably 35 to 500C. We have found temperatures in the range 35 to 400C or 450C, preferably about 370C, to give best results.

The optimum temperature may vary according to the enzyme that is being used.

The pulping can be conducted under alkaline conditions but is preferably conducted under substantially neutral conditions, namely at a pH in the range 6 to 8.5.

Generally the pH is at least 6.5. The pulping may be conducted in the presence of a buffer, generally sodium carbonate and/or sodium bicarbonate, in order to hold the pH at the desired level during the pulping.

Other de-inking additives may be included in the pulper. Preferably a dispersing agent is included. The dispersing agent preferably consists of or includes an anionic polymer formed from water soluble ethylenically unsaturated monomer comprising carboxylic acid monomer, the polymer having molecular weight in the range 2000 to 200000, often 5000 to 100000. Suitable polymers are described in WO95/12026 and other suitable dispersing agents are described in WO93/21376.

Other de-inking additives which may be included, for instance in the pulper, in order to improve the overall deinking include the additives described in detail in our British patent application 9423454.9 filed 21 November 1994.

The pulping stage may be conducted in conventional manner except that the substantially anhydrous dispersion of enzyme is added into the pulper or is added into the water which is supplied to the pulper for pulping. For instance the dispersion can be mixed into water to form an aqueous composition and this aqueous composition can then be added into the pulper. Preferably, however, the dispersion is added direct into the pulper or into the dilution water flowing into the pulper.

After pulping the pulp may be subjected to conventional treatments such as screening to remove grit and one or more flotation stages wherein at least one of the stages preferably uses the defined flotation surfactant, and a thickening stage to thicken the accept fraction as a clean pulp that can either be used as such or may be drained to form a dried pulp. Thickening may be conducted on drums in conventional manner to make a thickened pulp having a fibre content of, for instance, 4 to 15%. The accept fraction from flotation may be subjected to washing with water or with an aqueous surfactant solution before or after any thickening stage.

The paper which is to be de-inked in the invention preferably contains a significant amount of waste paper in which the ink has been fused onto the fibres and/or in which the binder of the ink is otherwise a resistant binder such that substantial speck counts are likely to occur in the de-inked product. Thus the paper which is pulped generally includes a significant amount of laser printed or xerographic paper or other office waste or photocopied or other paper in which the ink has been fused onto the paper and which is resistant to the pulping conditions.

Often the pulp is formed wholly or mainly (for instance, more than 75% by weight) from such paper but the invention is of value whenever any such paper is included in the pulp in a proportion such that the speck count in the final product can be significant and thus the inclusion of as little as 30%, or even 10% of such paper in the pulp can justify the use of the invention.

When the pulp is formed of such papers, it often will tend to lead to a product having a satisfactory brightness.

If necessary, brightness can be improved by appropriate selection of the pulping conditions, for instance by a selection of additives such as dispersing agents or bleach to the pulper or to subsequent stages. It also seems to be possible to influence brightness by appropriate selection of the enzyme dispersion. Preferred processes of the invention give products which have good brightness and, in particular, preferred processes can result in a significant lift in brightness between the brightness of a product made from the initial pulp and the brightness of the final product made from the suspension after separation of the ink.

The following are examples of the invention.

Examples In order to test the effectiveness of various deinking systems, 1.5kg of mixed office waste (50% laser 50% xerographic) was pulped at 10% consistency and 450C (unless otherwise stated) for 20 minutes in a Lamort pulper and optionally with added de-inking additives. The pulped stock had a pH of 7.9 and was held at the selected temperature for one hour and was then diluted to 1% consistency and a 125gsm handsheet was formed and labelled sheet 1.

The diluted pulped stock was then subjected to flotation in a Voithllaboratory flotation cell using 18 litres of 1% stock, optionally after adding flotation surfactant. After this flotation another 125gsm handsheet was formed, from the accept fraction, labelled sheet 2.

The accept fraction was then thickened to 10% consistency over a 710Zm sieve and was then rediluted to 18 consistency to allow formation of another 125gsm handsheet, labelled sheet 3.

In each instance, the handsheet was dried at 1100C for 15 minutes on rings and plates and brightness and image analysis measurements were recorded in standard manner.

In those processes using enzyme, the enzyme was added to the pulper at the rate of 4 grams active dry enzyme per ton fibre in the pulper (unless otherwise stated), after dilution of the enzyme concentrate or dispersion 1:100 in water immediately prior to addition to the pulper.

In those processes where a cationic flotation surfactant was used, this was added to the diluted stock entering the Voith cell at a rate of 1250g/ton dry fibre weight. In the processes using non-ionic flotation surfactant, this was added at the rate of 500g/t.

The results are given in the following tables. In these, processes marked 'A' were outside the invention and were conducted by adding to the pulper aqueous Celluzyme concentrate as supplied by Novo AS.

Processes marked 'B' were conducted by forming an anhydrous dispersion of the enzyme in non-ionic surfactants and then adding this dispersion to the pulper. In particular, the aqueous Celluzyme concentrate was subjected to the process described in W094/25560 to provide a dispersion of the enzyme in Softanol 50, trademark for aliphatic ethoxylated alcohol supplied by BP Chemicals having HLB about 10.5.

Processes marked 'C' were conducted by adding to the pulper an anhydrous dispersion of enzyme in a volatile hydrocarbon oil. This dispersion was made by dispersing the aqueous Celluzyme concentrate in oil by the general technique described for the starting materials in W094/25560. The anhydrous dispersions used in processes B and C were each prepared at close to the time of use and so the enzyme in process A, B and C was of substantially the same age.

In all the processes listed in table 1 except for the first three processes, a flotation surfactant was added to the diluted pulped stock before the flotation. 'N' represents the addition to the pulp of 500 g/t Softanol 50 and 'M' represents the addition of 1250 g/t ethoxylated fatty amine surfactant to the pulp.

The results in Table 1 show the effect of varying the form of the enzyme and varying the flotation conditions when conducting the process using 4 g/t enzyme at 450C.

The results in Tables 2 and 3 show the effect of varying the conditions in processes where a non-aqueous dispersion of the enzyme in non-ionic surfactants is used and is followed by non-ionic flotation surfactants, Table 2 showing the effect of using 4 g/t enzyme at different temperatures and Table 3 showing the effect of using different amounts of enzyme at 370C.

Table 4 shows the results obtained on a similar paper stock by different de-inking processes.

D is a conventional alkaline soap de-inking composition which is added to the pulper and also causes flotation and contains 0.7% soap, 7% sodium hydroxide, 2.5% silicate and 1% hydrogen peroxide (all based on the dry fibre weight) together with calcium chloride to make 250ppm hardness.

E is a process in which pulping is conducted in the presence of low molecular weight sodium polyacrylate followed by ethoxylated fatty amine as a flotation surfactant as in W095/12026.

F is a process in which Softanol 50 is the only additive, and is added to the pulper.

G is a process in which no additions are made to the pulper or the flotation stage.

Table 1

Do inking Sheet Brightness Tappi % Speck Conditions number Lift Dirt I Removal count A 1 ~ 163671 2 2.50 59758 64.7 3 57729 B 1 202560 2 4.28 25120 85.9 3 28502 C 1 234781 2 6.17 71546 73.2 3 62921 A + N 1 146540 2 2.75 52273 75.3 3 36195 B + N 1 176521 2 4.89 8743 95 3 8888 C + N 1 93768 2 1.88 18647 84.8 3 14258 A + M 1 174281 2 1.75 30025 80.1 3 34681 B + M 1 162463 2 3.37 40821 75.5 3 39786 C + M 1 185217 2 4.49 4927 93.9 3 11256 Table 2

Deinking Pulper Sheet Brightness Tappi % Speck Conditions Temperature Number Lift Dirt Removal Count 179830 B + N 35 C 2 5.21 16429 93.2 3 12228 1 175265 B + N 370C 2 7.71 2077 99,5 3 870 1 173861 B + N 40 C 2 6.06 8652 97.3 3 4694 1 185002 B + N 43.50c 2 5.66 9236 94.1 3 10915 1 176521 B + N 450C 2 4.89 8743 95 3 8888 Table 3

Drinking Enzyme Sheet Brightness Tappi % Speck Conditions Amount g/t Number Lift Dirt Removal count 1 159227 B + N 0 2 1.56 34637 69.3 3 48937 1 185433 B + N 2 2 3.13 34981 82.7 3 32084 1 175265 B + N 4 2 7.71 5265 99.5 3 2077 870 1 179600 B + N 6 2 4.54 11570 87.4 3 22621 1 161259 B + N 8 2 2.85 39998 83.6 3 26441 Table 4

Do inking Sheet Brightness Lift Sappy Dirt % speck conditions count Removal 1 165024 D 2 4.68 19468 84.7 3 25169 1 159277 E 2 5.71 34637 69.3 3 48937 1 159227 F 2 1.56 34637 69.3 3 48937 1 85169 G 2 3.93 137487 -41.7 3 120724 Although the brightness lift values are all quoted, and some do demonstrate very significant improvements in brightness, the paper did inherently give a relatively bright sheet.For instance the blank (G) gave brightness values for sheets 1, 2 and 3 of 76.7 and 76.8 and 80.7 respectively. Nevertheless, the brightness obtainable in some of the processes of the invention are particularly useful. Thus, for instance in Table 2, the brightness values for sheets 1, 2 and 3 in the process conducted at 370C were 77.2, 82.8 and 84.9 respectively and the values for the process conducted at 450C were 77.5, 81.4 and 82.4 respectively.

The speck count values in Table 1, and in particularly the percentage speck removal, shows that formulating the enzyme as a dispersion in oil gives better results than the aqueous enzyme concentrate (compare A with C) but that the use of the enzyme as a dispersion in surfactant gives better results (compare B with A and with C). When the flotation surfactant is cationic then the dispersion in oil gives best results (C + M) but better results are achieved using a dispersion in non-ionic surfactant followed by nonionic surfactant flotation aid (B + N).

Table 2 shows this process is influenced by the temperature and that best results with this enzyme are achieved at 370C and Table 3 shows that the process is optimised by varying the amount of enzyme and that best results with this enzyme are achieved at 4g/t enzyme.

It is surprising that improved results are obtained if the enzyme is first formulated as a substantially anhydrous dispersion in oil or, preferably, surfactant, especially since the enzyme in these experiments is diluted in water before it is added to the pulp. It seems that a beneficial effect is being provided by a combination of the enzyme with the water-in-oil emulsifier and/or the amphipathic stabiliser which is used in the process of converting the enzyme into the anhydrous and substantially non-aqueous dispersion, and/or with the oil-in-water emulsifier which can be included to facilitate distribution of the dispersion into the dilution water or pulp.

Thus an important feature of the invention may reside in applying the enzyme to the pulp in the presence of a high HLB surfactant and/or water-in-oil emulsifier and/or an amphipathic polymeric stabiliser as described in W094/25560 and/or an oil-in-water emulsifier. The invention includes also all processes of de-inking wherein enzyme is introduced into the pulper in combination with such materials and the ink is then separated from the pulper by the general methods as described above. The preferred processes of the invention ara those wherein the pulping is conducted in the presence of the enzyme (introduced in dispersion, aqueous concentrate or other suitable form) and water-in-oil emulsifier typically in an amount of 0.1% to 5% by weight of the enzyme and/or in the presence of non-ionic surfactant having HLB above 7 typically in an amount greater than the amount of enzyme.

Claims (14)

1. A process for de-inking paper carrying ink which comprises a resistant binder, the process comprising pulping the paper with water in the presence of a de-inking enzyme and then separating the ink from the pulp, characterised in that the enzyme is added to the pulp or to the water while in the form of a substantially anhydrous, stable, dispersion of enzyme in a non-aqueous liquid.

2. A process according to claim 1 in which the nonaqueous liquid is a liquid which is substantially free of surfactant.

3. A process according to claim 1 in which the nonaqueous liquid is mainly or wholly surfactant.

4. A process according to claim 1 in which the ink is separated from the pulp by subjecting the pulp to flotation to form a reject fraction containing the ink and an accept fraction followed by thickening the accept fraction, and in which flotation surfactant is added to the pulp after pulping and before flotation to promote preferential flotation of the ink particles into the reject fraction.

5. A process according to claim 4 in which the nonaqueous liquid is a liquid which is substantially free of surfactant and the flotation surfactant is a cat ionic surfactant.

6. A process according to claim 4 in which the nonaqueous liquid is mainly or wholly non-ionic surfactant and the flotation surfactant is a non-ionic surfactant.

7. A process according to claim 6 in which both non-ionic surfactants are fatty alcohol ethoxylates having HLB above 7.

8. A process according to claim 6 or claim 7 in which the same surfactant is used as the non-aqueous liquid and as the flotation surfactant which is subsequently added.

9. A process according to any of claims 4 to 8 in which the amount of non-aqueous liquid is 5 to 250g/ton and the amount of flotation surfactant is at least 5 times the amount of the non aqueous liquid and is 300 to 5000g/t.

10. A process according to any preceding claim in which the substantially anhydrous dispersion of enzyme in nonaqueous liquid is mixed with water to form an aqueous composition and this aqueous composition of enzyme is added to the pulp.

11. A process according to any preceding claim in which the pulping is conducted at a pH of 6 to 8.5.

12. A process according to any preceding claim in which the pulp is conducted in the presence of a water soluble polymer formed from water soluble ethylenically unsaturated monomer comprising carboxylic monomer and which has molecular weight 2000 to 200000.

13. A process according to any preceding claim in which the paper comprises laser printed or xerographic paper.

14. A process for de-inking paper carrying ink particles which comprise a resistant binder, the process comprising pulping the paper with water in the presence of a de-inking enzyme and then separating the ink from the pulp, characterised in that the enzyme is incorporated into the pulp in combination with water-in-oil emulsifier and/or amphicpathic polymeric stabiliser and/or oil-in-water emulsifier and/or surfactant having HLB above 7.