IE49223B1 - Preparation of ink-insensitive starch glues - Google Patents

Abstract

A process for the preparation of ink-insensitive starch glues, primarily for use in the manufacture of corrugated cardboard, employing the washwaters from flexography installations, and eliminating any modification of the gelatinization point and viscosity of the resultant glues by the presence of ink residues comprises incorporating an additive containing one or more salts and/or oxides of Ca, Mg, Ni, Ba, Co, Cr, Al, Fe<3+>, Zn, Sr, Pb, Sn, Ti, V, Cu, Mo, Cd, Sb, W and Bi as well as silicoaluminates, activated charcoal, cements and above all silicates, used under the normal pH conditions of the glues. Starch compositions for use in the process besides starch also contain such an additive, or alternatively the additive may be added to the washwaters referred to.

Description

The invention relates to the preparation of inkinsensitive starch, glues, more especially glues insensitive to the flexography inks used in the corrugated cardboard industry which are introduced into such glues by the use, in their manufacture, of washing-waters from printing machines. Within the scope of this invention there are included not only processes for the preparation of the above mentioned glues, but also a starch composition for use in the manufacture of said glues.

It should first be recalled that starch glues are generally obtained by one of three conventional processes, the first of which, i.e. that known as the Stein-Hall process, consists in mixing a suspension in water of gelatinized (or primary) starch with a starch milk (or secondairy starch), so that the gelatinized starch of the suspension serves as a support for the starch grains of the milk.

A second conventional process involves using a starch milk whose grains undergo a partial gelatinization, thus making the use of the support superfluous - such glues being generally denoted as so-called no-carrier glues.

A third conventional process involves the use of a simple dispersion in water of ready-for-use products, the latter comprising at least one part (consisting for instance of an amylaceous product, carboxymethylcellulose or - 3 polyvinylic alcohol) which is soluble in cold water together with a part of granular starch and a part of an alkaline agent.

Flexography is a printing process used currently for printing corrugated cardboard, and employs inks whose formulation is complex, the principal constituents of these inks being dyes, solvents, surface active agents and the like. Unfortunately the washing-waters evolved when washing down the equipment (tanks and presses) for flexographic printing, and which therefore are charged with flexography inks, cause serious pollution problems which cannot be controlled without further processing.

At best the trouble and expense of setting up a purification installation for such wash-water will very often seem disproportionate in relation to the volume and concentration (usually about 1% to 3%) of the washing waters needed treatment; and even when the plant does have a purification installation, the latter mostly is not very efficient in the treatment of washing-waters originating from machines printing with the aid of flexographic inks, since the latter are very different from one another, and it is thus very difficult to predict the behaviour of the washing-waters in the purification installation.

Against that background, it has already been proposed to dispose of washing-waters containing flexographic inks by incorporating them into glues (adhesives) intended for the manufacture of corrugated cardboard, the latter being liable to be recycled after the flexographic printing - since this expedient causes the ink parameter to disappear.

It so happens however that while many, indeed a relatively high proportion, of the inks are compatible with starch-based adhesives for corrugated cardboard, yet certain among them have a distinctly Incompatible character, and deleteriously affect the gelatinization point and often also the viscosity of the glues. - 4 In order to illustrate these drawbacks, we have prepared glues for corrugated cardboard of the type known as double-face type glues - a name employed for a glue specially appropriate for the gluing of a second covering or paper onto the previously assembled corrugation-covering base. These double-face type glues have been prepared by the Stein-Hall method, which involves preparing a support by gelatinizing a portion of the starch with soda, and then adding water.

In practical detail, 450 litres of water and 50 kg of corn starch were mixed, and the resultant milk was brought to a temperature of 45 C before adding 9 kgs of soda, the quantity needed to enable the starch to be gelatinized.

The mixture was stirred for 15 minutes, and then in sequence there were added: water 700 litres starch 250 kg borax 6 kg The whole of this mixture was stirred for 15 minutes, then 35 kg of flexography ink (corresponding to 5% of the secondary addition of water) were added.

For reasons of standardization all the various inks tested were previously adjusted to a viscosity of 20 seconds, measured by the Ford No. 4 cup method.

In relation to a variety of troublesome inks the various respective preparations were then tested for viscosity and gelatinization point, the measurements being determined as follows: - the Lory viscosity using the flow viscosity equipment of the BRAIVE INSTRUMENTS Company - test machine - 30 rue Bles, 4000 Lieges (Belgium); - 5 - the Brookfield viscosity using the shear viscosity - RVF type viscosimeter - BROOKFIELD Company, 240 Cushing Street, Stoughton, Massachusetts, U.S.A.? and - the gelatinization point using a Brabender vis5 cosigraph (BRABENDER OHG, Duisburg), this latter measurement consisting in heating the whole of the preparation in the bowl of the viscosigraph and measuring the temperature at which the crude starch of the secondary part gelatinizes, as manifested by a sharp increase in the viscosity.

The results recorded with eleven flexography inks are summarized in Table 1 below.

Cn G st* in in CM m to tn sr in cn tn Ό rd >1 Φ P Ή ♦id 1 tn m tn ♦P Φ eM 0 -P tn 0 o G ♦H 0 tn Φ 0 P id 0 cu ra > ** ω •H > >1 P PI φ tn cn Ό >1 •P >1 P PI w Pl ra Eh O co cm O i—ι o st* CM o co r- O o o O cn CM O O CM O in m O O sf σ\ CM O cn CM rd cm Γ* CM O rd Λί G -P G X! -P P -P G o Φ ε in Φ in • +» rd • CO CO in in cn 0 XJ in cn Γ* O m rd rd rd rd cn G G rd St* rd CM rd O rd rd CM cn St* in Ό Γ* co cn rd rdee • • • . • o 0 0 0 0 0 0 0 0 0 0 z z z z z z z s Z z zt . , . • , • • • Md Md Md Md Md tp Md Md Md Md Md Φ Φ Φ φ s Φ s Φ Φ Φ Φ Φ Φ P P P P rd P cn P P P P P P G t—I ra G rd £ o rd rd Φ >1 ε o P XJ u rd rd Φ >1 Φ P XJ u tn 0 ϋ G Φ rd G Π3 G G rd rd Φ P rd Φ ra ra o ra 48223 - Ί It emerges from this table that all the inks have an excessively troublesome effect on the gelatinization point. They sometimes disturb it to a very considerable extent and this always in the sense of increasing it.

Only some inks have an influence on viscosity; but in view of the fact that the washing waters of flexography inks are mixtures, it so happens that there is almost always one ink at least which spoils the viscosity.

Taking these drawbacks into account, the users of flexography inks have practically given up reincorporating washing waters into starch glues.

To overcome the above-mentioned difficulties, it has already been proposed, before using washing waters in glues, to free them from the troublesome constituents of the inks by floculating them and then by removing them, for example by filtration.

Such processes are complex and require a considerable installation of equipment, so that with a few exceptions such operations have not been adopted by users.

It is therefore a particular object of the invention to overcome these drawbacks and to provide means for the manufacture of starch glues, which are ink-insensitivethus enabling the use of washing-waters from the flexography machines in the manufacture of corrugated cardboard glues without the appearance, as in the past, of troublesome changes with respect to the gelatinization point and in the viscosity of the glues produced.

We have been fortunate to discover that this can be achieved by means of an additive agent containing one or more of a salt or oxide of Ca,Mg, Mn, Ni, Ba, Co, Cr, Al, 3+ Fe , Zn, Sr, Pb, Sn, Ti, V, Cu, Mo, Cd, Sb, W, or Bi, silicoaluminates, activated charcoal, cements or silicates, used under the normal pH conditions of the glues.

Within the above-mentioned group we have found it preferable to employ an agent selected from among the - 8 3+ salts and oxides of Ca, Mg, Mn, Hi, Co, Cr, and Fe , the silicoaluminates, activated charcoal and cements, and still more preferahly to employ a silicate.

It follows that the manufacturing process for starch glues for corrugated cardboard employing washing waters of flexography installations is characterized by the fact that there is included, either with the products intended for the manufacture of these glues (among them notably starch) or with the washing waters of the flexo10 graphy installations, or again in the support or in the starch milk destined to be mixed with this support, before the introduction of the washing waters, and at normal pH conditions of the glues to be manufactured, at least one of the agents of the above-defined group and more parti15 cularly of the preferential group and where necessary or appropriate also an alkali; the amount(s) of agent and, when necessary of alkali being adjusted to avoid the appearance of the aforesaid drawbacks.

The additive agent according to the invention which makes possible the manufacture of starch glues for corrugated cardboard from washing waters from machines for flexography printing and which can be introduced under normal conditions of pH of the glues to be manufactured either into the washing waters, or into one of the products intended for the manufacture of the glue, notably the starch and more particularly the support or the starch milk intended to be mixed with this support, is selected from the above-defined group and more particularly from the preferential group.

Finally, the starch in its application for the manufacture of glues according to the invention, for corrugated cardboard by using washing waters of flexographic printing machines, is characterized by the fact that it includes at least one of the agents of the above-defined group and more particularly of the preferential group, in - 9 an amount sufficient, if necessary in the presence of a predetermined amount of alkali, to overcome the adverse effect of the flexography inks upon the viscosity and the gelatinization point of the final glues.

The invention is also directed to other features which are preferably used at the same time, and which will be more explicitly explained below.

It will in any case be well understood by means of the additional description which follows and of the examples, said additional description and examples relating to preferred embodiments.

The amount of agent according to the invention to be used may vary as a function of the nature of the agent and of the ink-content of the washing waters deriving from the flexographic printing machines.

Thus, in the case of an agent other than a silicate, the amount of agent is about 0.01% to 10% by weight, preferably from 0.05 to 5% by weight with respect to the total amount of starch used for the manufacture of the glue plus agent.

In the case of a silicate, the amount of agent is from 0.01% to 49%, preferably from 0.05% to 20% and, more particularly, from 0.1% to 6% by weight with respect to the total amount of starch and silicate used.

In the case where it is necessary to resort to an alkali concomitantly with the agent according to the invention, the amount of alkali is selected to be sufficiently large to correct the deviation of the gelatinization point; it is necessary to correct this deviation when it occurs since otherwise it would be necessary to modify the gluing and speed characteristics of the corrugated cardboard manufacturing machine which uses the glue.

It is stressed that, in the case of the preferred agent constituted by the silicates of sodium, calcium and/ or potassium, it is not necessary to resort to an alkali. - 10 Moreover, the upper limit of the amount of silicates applied is not critical, an excess of silicates being not troublesome.

The agents according to the invention are added to the products for the manufacture of glues, notably the starch (milk or support) or to the recycled wash waters, in liquid form or in solid form according to their presentation.

The silicates of sodium, of calcium and/or of potassium are, for their part, available in powder form and, some of them, in liquid form.

They may hence be added to the starch or again to the support or to the secondary in one of these two forms. It is also possible to conceive the prior incorporation of silicates into the starch either by spraying with liquid silicates or by simple dry admixture where powders are concerned. These powder silicates do not have any free alkalinity liable to disturb the storage of the mixed product.

The silicates corresponding to all the moduli (ratio silica/sodium, calcium and/or potassium oxide) can be used for example, the best advantage can be drawn from the use of the most usual silicates (modulus comprised between 2 and 2.4 for sodium silicates, between 3 and 3.5 for potassium silicates).

The results obtained with the silicates are so good that it is possible to use the washing waters from flexographic printing machines not only in the support or the starch milk of the preparation of glues according to Stein-Hall, but also in the supportless or no-carrier starch glues, in continuous preparations, notably with gelatinization of the primary part at high temperature.

A particularly advantageous industrial product in its application according to the invention is constituted by the mixture of starch intended for the manufacture of corrugated cardboard glues with the amount of silicate 48223 - 11 necessary to enable one to use, in the manufacture of these glues, washing water from flexographic printing machines, this amount being from 0.01% to 49%. preferably from 0.05% to 20% and advantageously from 0.1% to 6% by weight with respect to the amount of quantities of starch and silicate.

The following examples serve to illustrate the various aspects of the invention in respect of at least certain of the aforesaid agents.

Example 1: A double-face type glue intended to be used for the manufacture of double faced corrugated cardboard is manufactured. To do this, a starch milk was prepared with 450 litres of water and 50 kg of starch. This milk is heated to 45°C.

In addition, 9 kg of pure soda are dissolved in 20 litres of water. This solution is added to the starch milk to induce its gelatinization and to manufacture the support or primary part after fairly intense stirring for 15 minutes. 700 litres of water are added, and then 250 kg of starch and then 6 kg of borax, constituting the starch milk or secondary.

After 15 minutes of stirring, a Lory viscosity of 19 seconds, a Brookfield viscosity of 290 centipoises as well as the gelatinization point of 54°C are obtained.

In a second experiment, the water of the secondary is replaced by water containing 4% of flexographic ink constituted by chrome yellow 1. The Lory viscosity is then no longer measurable and the Brookfield viscosity rises to 29 000 centipoises; the gelatinization point is 58°C.

The behaviour of the glue is hence particularly disturbed by the use of water containing a flexographic ink.

In a third experiment, the flexographic ink of the - 12 second experiment is preserved and the starch of the secondary is replaced by a dry mixture of 99.4% starch and 0.6% anhydrous calcium sulphate. The shock of the second experiment no longer occurs. The Lory viscosity is 18 seconds, the Brookfield viscosity is 250 cp. On the other hand, the gelatinization point is 60°C and it is brought back by soda. Consequently, the action of calcium sulphate and of soda cancels the deleterious effect of the flexographic ink.

The amount of soda in the present case is 10.8 kg.

Example 2 The same tests are followed as in Example 1, namely - in a first experiment (1): usual formula in a second experiment (2): the water of the 15 secondary is replaced by water containing 4% of chrome 3 yellow flexographic ink, and - in a third experiment (3): the starch is replaced by a mixture of 99.5% starch and 0.5% of anhydrous calcium sulphate.

The results of the measurements carried out are collected in table II.

TABLE II Lory (viscosity (seconds) Brookfield viscosity (centipoises) Gelatinization point (°C) Experiment (1) 19 280 54 Experiment (2) 39 780 58 Experiment (3) 18 240 58 The conclusions are identical with those of Example 1. It is convenient to add an additional amount of soda (about 1.7 kg). Calcium sulphate enables, under these conditions, counteraction of the deleterious effect of the chrome 3 yellow ink.

Example 3 The tests are identical with Example 1, but in the experiment (3), the mixture of 99.4% of starch and 0.6% of calcium sulphate is replaced by a mixture of 99% of starch and 1% of calcium oxalate.

In this experiment (3) the Lory viscosity was then 20 seconds. The Brookfield viscosity 280 cp and the gelatinization point 59.5°C.

The behaviour of the calcium oxalate is consequently similar to that of the calcium sulphate: it is necessary to add a little soda (about 1.6 kg) to correct fully the effect of the ink.

Example 4 The tests are identical with Example 1 but in experiment (3) the mixture of 99.4% starch and of 0.6% calcium - 14 sulphate is replaced by a mixture of 98.25% of starch and 1.75% of magnesium sulphate.

In the experiment (3), the Lory viscosity is then of 22 seconds on the Lory viscosimeter, 410 cp on the Brook5 field viscosimeter and the gelatinization point is 61°C.

The viscosity conditions are acceptable but it is again necessary to add soda to correct the gelatinization point (about 1.39 kg).

Example 5 The tests are similar to those of Example 1 but, in experiment (2), the chrome 1 yellow ink is replaced by an orange (known under the name orange 802 of the MILLORY brand) which is even more deleterious to the glue than the chrome yellows. In experiment (3), a mixture of 95% starch and 5% ferric sulphate is used. The results are gathered in Table III. TABLE III 20 Lory Viscosity (seconds) Brookfield Viscosity (centipoises) Gelatiniz ation Point (°C) Experiment (1) 19 230 54 Experiment (2) unmeasurable 34 800 58 Experiment (3) 18 470 69 The mixture was a little short but the glue is 25 very suitable. On the contrary, the gelatinization point is greatly raised. It is necessary to correct with soda in large proportions, with the result that, from the practical 48223 - 15 point of view, ferric sulphate is of little interest in the case of this ink.

Example 6 The tests are similar to those of Examples 5, but in the experiment (3), the mixture of starch and ferric sulphate is replaced by a mixture of 99% starch and of 1% sodium silicate (powder of modulus 3.06). The Lory viscosity then becomes 18 seconds. The Brookfield viscosity is 260 cp; the gelatinization point is almost normal at 56°C.

It will be observed that the sodium silicate seems particularly suitable, correcting both viscosity and gelatinization point.

Example 7 The conditions are similar to those of Example 6 but 2% of the sodium silicate is used instead of 1%. The Lory viscosity was then 16 seconds. The Brookfield viscosity was 230 cp. The gelatinization point was 55°C.

The values were very close to those of Example 6.

An excess of sodium silicate is consequently not damaging to the glue.

Example 8 The conditions are similar to those of Example 7, but no orange ink is incorporated.

The Lory viscosity is 19 seconds. The Brookfield viscosity was 250 cp. The gelatinization point was 54°C.

A little soda (about 1.6 kg) to correct fully the effect of the ink.

The formula is consequently absolutely undisturbed by the presence of the sodium silicate. The use of this silicate can then be generalized whether or not washing waters from flexographic printing machines are used. - 16 Example 9 Xn this example, the use of flexographic printing machine washing waters is contemplated both in the preparation of the primary part or support and in the preparat5 ion of the secondary part of a formula of the double face type according to the Stein-Hall method.

Consequently a support or primary is made from a water containing 4% of orange ink and a mixture of 98% starch and 2% sodium silicate, the other conditions remain10 ing the same as those of Example 7.

In other words, this support is obtained from: - 450 1 of the aforesaid washing water, kg of the aforesaid starch-silicate mixture, kg of pure soda, under the conditions of Example 1, the secondary being constituted by: - 700 1 of the aforesaid washing water, - 50 kg of the aforesaid starch-silicate mixture, kg of borax.

The Lory viscosity of the glue obtained is 19 seconds. The Brookfield viscosity is 460 cp. The gelatini zation point is 58°C. The latter hence changes a little.

It could if necessary be corrected with soda (about 1 kg). In practice, this would not often be necessary since the conditions adopted are very severe, and industrially the washing waters are less deleterious and would not necessitate correction of the gelatinization point. 48223 - 17 Example 10 Here a glue formula of the no-carrier or supportless type was used.

To manufacture this glue, a starch milk and a solution of soda are prepared, the two preparations being mixed so that the mixture is at 39°C and the proportion of soda is, in the present case, 3.56% by weight with respect to the commercial starch.

The starch milk is obtained from 225 kg of starch and 705 liters of water.

In a first experiment, the product obtained with water from the tap is subjected to the action of soda for a time X sufficient for the viscosity measured on the Brabender viscosigraph to be 300 Brabender units. This time X is measured.

In a second experiment, the glue is prepared from a milk obtained with starch and water containing 4% of flexography ink of the orange 802 type. The time X is measured.

In a third experiment, the milk necessary for the production of the glue is prepared from a powder mixture of 97% starch and 3% sodium silicate of modules 2.06, and from water containing 4% of flexography ink. This milk is subjected to the action of the soda. The time X is again measured.

In a fourth experiment, procedure is identical with that in the third, except that the water does not contain flexography ink. The time X is measured.

The values of X are summarised in Table IV. - 18 TABLE IV Reaction time X with soda (300 BU) First experiment (control) 22 minutes 5 Second experiment No swelling Third experiment 21 minutes Fourth experiment 26 minutes On examining these results, it is observed that the sensitivities to soda in the first and third experiments are very close. In other words, a good viscosity is obtained after the same time.

The sodium silicate enables the very injurious effect of the ink to be corrected which, in the second experiment, prevents all swelling.

On the other hand, in the fourth experiment, it is observed that the sodium silicate, in the absence of ink, leaves the behaviour of the product practically undisturbed.

Measurements are repeated on a complete formulation similar to those used in industry.

This formulation is obtained with the following amounts and conditions: - 225 kg of starch in 705 1 of water, the whole being brought to 36°C, kg of soda in 215 1 of water, the solution being brought to 54°C, - the two preceding solutions are mixed, the tem49223 - 19 perature then reached 39°C.

By means of these basic amounts, four experiments are carried out similar to those described above and the reaction time X is set at 20 minutes with 3.56% soda; it is at the end of this time that 4.5 kg of boric acid is added. The Lory and Brookfield viscosities as well as the gelatinization point are measured on the glues thus obtained.

The results are reported in Table V.

TABLE V Lory Viscosity (seconds) Brookfield Viscosity (centipoises) Gelatinization point (°C) 1st experiment-control 10 780 50 2nd experiment No swelling-unrealizable 3rd experiment 11 1 280 55 4th experiment 11.5 1 000 50.5 On studying the results combined in Table V, it is observed that, if sodium silicate slows down the swelling a little in the presence of soda, the final viscosity, on the contrary, is a little higher when there is no ink (experiment 4).

In the presence of ink (experiment 3,, the Lory viscosity is very suitable. The texture of the glue was a little shorter. The gelatinization point is higher but the swelling time is stabilized, which is remarkable. 223 - 20 Example 11 The same tests follow as in Example 1, that is to say: - a first experiment (1): usual formula, - a second experiment (2): the water of the secondary is replaced by water containing 4% of flexography ink of the RED 824 type (MILLORy brand) and - a third experiment (3): the starch is replaced by a mixture of 98% of starch and 2% of Portland cement.

The results of the measurements carried out collected in Table VI.

TABLE VI Lory Viscosity (seconds) Brookfield Viscosity (centipoises) Gelatinization point (°C) Experiment (1) 19 280 54 Experiment (2) un-measurable 14 200 59 Experiment (3) 43 410 55.5 The cement would appear to be rather inactive but, generally, the mixtures of inks contained in washing waters are less troublesome than the ink considered above and,consequently, in practice its use could suffice to neutralize the effect of the industrial washing waters. - 21 Example 12 The same tests were carried out as in Example 1, that is to say: - a first experiment (1): usual formula, - a second experiment (2): the water of the secondary was replaced by water containing 4% of flexography ink of the RED 824 type (MILLORY brand) and - a third experiment (3): the starch is replaced by a mixture of 99% of starch and 1% of powdered activated charcoal (CECA S.A. Company - 78140 Velizy-Villacoublay).

The results of the measurements carried out are collected in Table VII.

TABLE VII Lory Viscosity (seconds) Brookfield Viscosity (centipoises) Gelatinization point (°C) Experiment (1) 19 280 54 Experiment (2) un-measurable 14 200 59 Experiment (3) 43 550 57 The conclusions are similar to those described for cement. The effect is however less obvious on the gelatinization point and it will perhaps be necessary in a normal industrial market, to correct the gelatinization point by the addition of a small amount of alkali. 3 23 - 22 Ο Ο Ο Consequently and whatever the embodiment adopted, there are thus provided means enabling the use, for preparing glue for the manufacture of corrugated cardboard, of the washing waters of installations for flexography printing, means whose characteristics and advantages result clearly from the foregoing.

Claims (10)

1. A process for the preparation of ink-insensitive starch glues at normal pH conditions of the glues to be manufactured, the glues being suitable for the manufacture of corrugated cardboard, said process employing the washing waters from flexography installations, in which at least one of the Ingredients destined for the manufacture of such ink-insensitive starch glues incorporates at least one of the following agents, namely a salt or oxide of Ca, Mg,Mn, Ni, Ba, Co, Cr, Al, Fe 3+ , Zn, Sr, Pb, Sn, Ti, V, Mo, Cd, Sb, W or Bi, silica, a silicoaluminate, activated charcoal, a cement or a silicate, together if necessary with an alkali, the amounts of said agent (s) and {if present) of alkali being such as substantially to eliminate any troublesome modification of the gelatinization point and of the viscosity of the glue obtained due to the presence of the flexography inks contained in the washing waters from the flexography installations.

2. A process as claimed in claim 1, in which the ingredient destined for the manufacture of the ink-insensitive starch glue that incorporates the said agent is or includes starch.

3. A process as claimed in claim 1 or claim 2, in which the ingredient destined for the manufacture of the ink-insensitive starch glue that incorporates the said agent is or includes washing waters from a flexography installation.

4. A process as claimed in any of the preceding claims, in which the ingredient destined for the manufacture of the ink-insensitive starch glue that incorporates the said agent is or includes a support with which starch milk is mixed prior to the introduction of the washing waters, 223 - 24 5. A process as claimed in any of the preceding claims, in which the ingredient destined for the manufacture of the ink-insensitive starch glue that incorporates the said agent is or includes starch milk with which a support is mixed prior to the introduction of the washing waters.

5. 21. A starch composition as claimed in claim 20, in which the silicate is present in an amount of from 0.1% to 6% by weight with reference to the amount of both starch material and of silicate. 22. A starch composition as claimed in any of

6. A process as claimed in any of the preceding claims, in which the said agent is at least one of the following agents, namely a salt or oxide of Ca, Mg, Mn, Ni, 3+ Co, Cr or Fe , silicoaluminate, activated charcoal or a cement.

7. A process as claimed in any of the preceding claims, in which the said agent (other than silicate) is present in an amount of from 0.01% to 10% by weight with reference to the amount of starch material present.

8. A process as claimed in claim 7, in which the said agent is present in an amount of from 0.05% to 5% by weight with reference to the amount of starch material present.

9. A process as claimed in any of claims 1 to 5, in which the said agent is or includes a silicate. 10. A process as claimed in claim 9, in which the silicate is present in an amount of from 0.01% to 49% by weight with reference to the amount of starch material and silicate present. 11. A process as claimed in claim 10, in which the silicate is present in an amount of from 0.05% to 20% by weight with reference to the amount of both starch material and silicate present. 12. A process as claimed in claim 11, in which the silicate is present in an amount of from 0.1% to 6% by - 25 weight with reference to the amount of both starch material and silicate present. 13. A process for the preparation of ink-insensitive starch glues, as claimed in any of the preceding claims and substantially as herein described. 14. For use in a process for the preparation of ink-insensitive starch glues, a starch composition which besides starch also contains an effective amount of one or a mixture of more than one of the following agents, namely 3+ a salt or oxide of Ca, Mg, Mn, Ni, Ba, Co, Cr, Al, Fe , Zn, Sr, Pb, Sn, Ti, V, Cu, Mo, Cd, Sb, W or Bi, a silicoaluminate, activated charcoal, a cement or a silicate. 15. A starch composition as claimed in claim 14, in which the agent is selected from salts and oxides of Ca, Mg, Mn, Ni, Co, Cr and Fe 3+ , the silicoaluminates, activated charcoal and cements. 16. A starch composition as claimed in claim 15, in which the agent is present in an amount of from 0.01% to 10% by weight with reference to the amount of both starch material and agent. 17. A starch composition as claimed in claim 16, in which the agent is present in an amount of from 0.05% to 5% by weight with reference to the amount of both starch material and agent. 18. A starch composition as claimed in claim 14, in which the agent is or includes a silicate. 19. A starch composition as claimed in claim 18, in which the silicate is present in an amount of from 0.01% to 49% by weight with reference to the amount of both starch material and of silicate. - 26 20. A starch composition as claimed in claim 19, in which the silicate is present in an amount of from 0.05 to 20% by weight with reference to the amount of both starch material and of silicate.

10. Claims 14 to 21 and substantially as herein described.