GB2288407A

GB2288407A - Ink comprising dye dissolved in vegetable oil

Info

Publication number: GB2288407A
Application number: GB9407183A
Authority: GB
Inventors: Muslim D Lightwala; David M Allen
Original assignee: MIDEARS Ltd
Current assignee: MIDEARS Ltd
Priority date: 1994-04-12
Filing date: 1994-04-12
Publication date: 1995-10-18
Anticipated expiration: 2014-04-12
Also published as: GB2288407B; GB9407183D0

Abstract

An ink comprises a dye dissolved in a vegetable oil. The ink may be used for printing substrates such as paper and may be readily removed from the substrate by treatment with an alkaline solution in which the removed vegetable oil and dye both dissolve.

Description

AN INK The present invention relates to an ink, a method of printing with the ink, and a method of removing the ink from printed material during a recycling process.

Waste paper has become an important source of raw material in today's paper industry. For instance, in the U.K. 55% of the fibre used in the production of paper and board comes from recycled waste paper.

In order to produce a high quality pulp for making paper, waste paper must first be cleaned to remove ink and other impurities. Ink removal, which is a particularly important part of the waste paper recycling process, is known as de-inking.

Most reading material, e.g. newspapers, is printed using letter press or offset lithographic printing processes. The inks used for such processes generally comprise a pigment, e.g. carbon black, dispersed (pigments are insoluble) in a mineral or vegetable oil ink vehicle. The ink vehicle acts as a carrier for the pigment and in some cases as a binder to fix the pigment to the printed surface.

Different ink vehicles are more or less suited to different printing processes and additional components may be added to an ink to, for instance, improve its drying properties.

A conventional de-inking process used in the recycling of such printed paper, comprises a pulping stage in which the ink is removed from the paper by the process of saponification. Alkaline chemicals, typically NaOH, are added to the paper as it is pulped. The oil based ink vehicle is saponified by the alkaline solution and the pigment is released from its bond to the paper. The removal of ink from the paper is aided by the mechanical action of the paper fibres rubbing against each other as the paper is pulped. A surfactant is often added to help stabilise the pigment particles in the solution and reduce re-attachment to the paper.

Once released from the paper the pigment forms a particulate suspension which must be separated from the pulp. This is generally achieved using various floatation and/or washing processes. Such processes can be lengthy and require expensive machinery and the addition of further chemicals for their performance. In addition, the effluent separated from the paper pulp is a sludge which is relatively difficult and costly to dispose of, for instance requiring incineration.

It is an object of the present Invention to obviate or mitigate the abovementioned disadvantages.

According to a first aspect of the present invention there is provided an ink comprising a dye dissolved in a vegetable oil.

According to a second aspect of the present invention there is provided a method of printing on a substrate, comprising applying an ink in accordance with the first aspect of the present invention to a substrate.

According to a third aspect of the present invention there is provided a method of recycling a substrate printed with ink in accordance with the first aspect of the present invention, comprising pulping the substrate in an alkaline solution, whereby the ink is separated from the substrate and dissolved, and separating the pulped substrate from the ink solution by a filtration process.

Preferably the dye at least partially decolorises in an alkaline solution. This has advantages when substrates printed with the ink are recycled, as discussed below.

It is an important feature of inks according to the present invention that they readily separate from substrates, such as newsprint, in an alkaline solution, such as is used in the pulping stage of conventional de-inking processes. The process is one of saponification in which the alkali attacks the vegetable oil and releases the dye from the substrate. However, in contrast to conventional printing inks, which contain pigments, once the ink has been separated from the paper the vegetable oil and dye both dissolve in the alkaline solution as opposed to forming a suspension. The result of this is that the effluent produced by the de-inking process is a solution which is relatively easily separated from the pulped fibres and disposed of, as compared with a sludge effluent produced when material printed with conventional pigment based inks is subjected to known de-inking processes.

Moreover, because dyes bond less strongly to printed material than pigments, the ink comprising a dye and a vegetable oil is easier to separate from the printed material than a conventional pigment based ink. Accordingly, weaker alkaline solutions may be used together with less severe pulping conditions when recycling paper printed with an ink according to the present invention by the above process. This will reduce the amount of damage inflicted on the fibres of the printed material during the de-inking process. Such damage, for instance shortening of the fibres, limits the number of times any particular fibres can be recycled since as they degrade they become incapable of producing pulp of suitable quality for recycling.

Thus reducing the damage to the fibres during the de-inking process effectively increases the recycling life of the substrate fibres.

Furthermore, because the ink is based on vegetable oil, which is biodegradable, the ink is substantially environmentally friendly.

The alkaline solution used in the recycling process may be of a concentration used in conventional de-inking processes, e.g. of the order of 1.5% NaOH by weight of the paper. However, as mentioned above, it is envisaged that the recycling process can beneficially be performed with weaker alkaline solutions.

Any coloration remaining in the pulped fibres once the ink solution has been separated therefrom, may be removed by an additional bleaching process. Such a bleaching process may not be necessary if the ink comprises a dye which decolorises in an alkaline solution.

In addition to the advantages associated with re-pulping as discussed above, ink according to the present invention has the further advantage of being simple in composition and therefore relatively cheap and easy to manufacture.

The ink may be applied to the substrate by any appropriate process, such as a lithographic or offset lithographic process. It has been found that the ink has good printing properties, binding readily to substrates, such as newsprint, and drying very rapidly. Because of these properties the ink is easy to work with. Furthermore, it is not necessary to add additional components to the ink, for instance to aid in drying or binding, which would increase the manufacturing complexity and cost of the ink.

Natural or synthetic dyes may be used in the ink, although synthetic dyes tend to have better colour consistency (from batch to batch) and are more readily available in large quantities. The dye may for instance be an azo dye or an anthraquinone dye. The only criteria the dye must meet is that it must be soluble in the vegetable oil used.

Such dyes may be referred to as solvent dyes.

Inks of the present invention may comprise more than one dye.

For instance, it may be necesary to combine different coloured dyes to obtain a desired ink colour.

Suitable oils are, for example, linseed oil, soyabean oil, cotton seed oil and rape seed oil.

The oil is preferably a relatively quick drying oil such as linseed oil. The drying properties of an oil depend upon the amount of unsaturated bonds it contains. A good measure of the drying properties of an oil is its iodine value, i.e. the amount of iodine which may be absorbed by 100g of the oil (-CH=CH- + I2 = -CHI-CHI-).

Preferably the oil has an iodine value in the range of 100 to 200, or more preferably in the range 140 to 200.

The viscosity of the oil may be varied, for instance to suit applications in different printing processes. For example, for lithographic printing the oil preferably has a viscosity in the range of 15P (poise) to 50P, for instance 15P to 25P. The viscosity of a given oil may be increased if desired by heat treatment (heat polymerisation).

The proportion of dye in the ink may vary depending on, for instance, the solubility of the dye used, the type of oil used, and the required colour density of the ink. The ink may, for example, comprise from 5% to 20% (e.g. 5% to 10%) by weight of dye.

Specific embodiments of the present invention will now be described, by way of example only.

Example 1 An ink was prepared by mixing 10% by weight of a synthetic dye into 25P linseed oil. The dye was Fat Red HRR obtained from Hoechst.

The ink was used to print onto paper using a Rotaprint Delta 35 offset lithographic printing press.

The ink was found to perform well in the printing process and dried very rapidly giving good consistent results.

Paper printed with the ink was subjected to a pulping test under alkaline conditions. It was found that using a solution containing 1.5% by weight (based on the weight of the paper) of NaOH the ink was readily released from the paper into solution. In addition the ink was partially de-colourised. After separating the ink solution from the pulp fibres the fibres retained slight coloration which could readily be removed by additional bleaching.

Examples 2 to 4 The printing and pulping tests described above were performed using three other inks prepared by dissolving three further synthetic dyes in 25 P linseed oil. The dyes used were Fat Brown B, Fat Orange R Ol and Fat Blue B, all of which were obtained from Hoechst.

The results of the printing and pulping tests were substantially the same as detailed under Example 1 above.

Claims

1. An ink comprising a dye dissolved in a vegetable oil.

2. An ink according to claim 1, wherein the oil has an iodine value in the range of 100 to 200.

3. An ink according to claim 2, wherein the vegetable oil has an iodine value in the range of 140 to 200.

4. An ink according to any preceding claim, wherein the oil has a viscosity in the range of 15P to 50P.

5. An ink according to any preceding claim, wherein the dye at least partially decolorises in an alkaline solution.

6. An ink according to claim 5, wherein the dye at least partially decolorises in a solution comprising 1.5% by weight (based on the weight of the substrate) of NaOH.

7. An ink according to any preceding claim, comprising from 5% to 20% by weight of dye.

8. A method of printing on a substrate, comprising applying ink according to any preceding claim to the substrate.

9. A method according to claim 8, wherein the ink is applied to the substrate by a lithographic process.

10. A method according to claim 9, wherein the ink is applied to the substrate by offset lithography.

11. A method according to any one of claims 8 to 10, wherein the substrate is newsprint.

12. A method of recycling a substrate printed with ink according to any one of claims 1 to 7, comprising pulping the substrate in an alkaline solution, whereby the ink is separated from the substrate and dissolved, and separating the pulped substrate from the dye solution by a process of filtration.

13. A method according to claim 12, wherein the alkaline solution contains up to 1.5% by weight (based on the weight of the substrate) of NaOH.

14. A method according to claim 12 or 13, wherein after separation from the ink solution the pulped substrate is bleached to remove any remaining coloration.

15. An ink substantially as hereinbefore described in any one of the foregoing examples.

16. A method of printing on a substrate, substantially as hereinbefore described, with reference to the foregoing examples.

17. A method of recycling a printed substrate, substantially as hereinbefore described.