WO1995011340A1

WO1995011340A1 - Manufacture and use of a zirconium-protein system

Info

Publication number: WO1995011340A1
Application number: PCT/GB1994/002272
Authority: WO
Inventors: Steven Mann
Original assignee: Mel Chemicals
Priority date: 1993-10-18
Filing date: 1994-10-17
Publication date: 1995-04-27
Also published as: GB9321482D0; AU7942194A

Abstract

A solid zirconium-protein material suitable for use as a one-pot binder in the manufacture of paper and board products may be formed by dry mixing of a zirconium salt and a protein in appropriate amounts; or by absorption of zirconium onto a water insoluble protein from solution, filtering the resulting insoluble product; or by blending a dry protein with a concentrated zirconium containing solution, and drying the resulting damp powder. In each case, the solid material may be dissolved in alkaline solution to give a solution which is generally stable, even when heated. It is believed that significant binding or cross-linking action occurs readily only when the solution, e.g. in the form of a paper coating, is dried.

Description

Manufacture and Use of a Zirconium-Protein System

This invention relates to a zirconium-protein system.

In the manufacture and treatment 'of paper and board products, there is commonly a need to impart strength and/or surface finish to the product. A starch paste can be used to bind paper fibres together, along with powdered fillers which give the paper weight, opacity and good ink receptibility. However, starch itself is water sensitive, and this can produce problems in some areas, such as particular forms of printing.

Similarly solid proteins such as soy protein and casein are used a binders in paper coatings, and as adhesives, but these are also water sensitive.

Thus, modifications to the materials used in the basic process feature in the prior art. The modified materials generally consist of a polymeric component and a cross- linking or insolubilising agent.

For example, the solid proteins are conventionally taken into solution prior to use by treatment with alkali, and, prior to casting the coating film, an insolubiliser such as a zirconium complex, a melamine-formaldehyde resin or glyoxal is added.

European Patent No. 0276894 B relates to an aqueous adhesive comprising starch and a polymer latex prepared in the presence of ammonium hydroxide which can be used to improve the wet strength of corrugated board.

United States Patent No. 3 137 588 relates to the coating of cellulosic webs, particularly fo'r imparting improved wet-rub resistance to a paper pigment coating. It refers to prior art in which modified starches and used, and itself discloses the use of a starch component which assays at least 0.5 weight percent of carboxyl group, together with a water soluble salt of zirconium or titanium. Either the carboxy starch is applied first, followed by treatment with the metal salt, or the two materials are combined as a wet mixture prior to application.

United States Patent No. 4 756 801 describes a papermaking process in which an aqueous suspension of cellulose pulp and a filler is dewatered in the presence of a bonding agent comprising an organic polymer and an inorganic oligomer. Various organic polymers are described, including natural starches and gums. The inorganic oligomer may be a compound of titanium, zirconium, tin and/or boron which hydrolyses to an oligomer in water. The organic and inorganic materials may be added simultaneously or sequentially.

The prior art systems are two-pot, i.e. they involve the provision of two separate components which must be used separately or combined just prior to use. There is a need for a one-pot system in which a single material provides both polymer and cross-linking agent.

From one aspect, the present invention provides a solid zirconium-protein material suitable for use as a one-pot binder in the manufacture of paper and board products. With such a system, there is no need to provide an insolubiliser as a additional component separate from the polymeric component; both components are simultaneously present in one material. This is a considerable advantage in manufacturing processes. The protein may be one which is insoluble in cold water. The solid zirconium-protein material of the invention may comprise a mixture or blend of dry protein and a solid zirconium containing material in proportions such that the resulting mixture will dissolve in aqueous alkali to produce a solution which acts as a binder upon drying. Preferably, in this case, the zirconium material is a salt; more preferably it is potassium zirconium carbonate (KZC) . A preferred protein is a soy protein such as that known as Procote 400 (supplied by Protein Technologies International, Inc.) . Procote is also referred to as PC herein.

Another way of producing a zirconium-protein material is by absorption of zirconium from solution onto a cold water insoluble protein. Thus, from a second aspect, the invention provides a method of making a solid zirconium- protein material, comprising treating a cold water insoluble protein with a solution containing zirconium, such that at least some zirconium .is extracted by, or combines with, the protein, and separating the resulting insoluble fraction.

This fraction contains both the polymeric species (protein) and the insolubilising agent (zirconium) . On dissolution in alkali, it provides a self-crosslinking solution, and is therefore suitable (for example) for use as a "one pot" binder in the manufacture of paper and board products.

Without wishing to be bound by any theory, it is beli ^• ed that the zirconium is adsorbed or complexed onto the solid protein and produces cross-linking when the alkaline solution is dried. The result of drying is a proteinaceous polymeric binder or adhesive with low water solubility. From a third aspect of the invention, another way of making a solid zirconium-protein material is by blending a dry protein with a concentrated zirconium containing solution, and drying the resulting damp powder, the ratio of zirconium to protein being such that the resulting dried powder will dissolve in aqueous alkali to produce a solution which acts as a binder upon drying. This process is intermediate the dry blending and the wet process of the second aspect already described above, and the state of the zirconium in the dried powder is not known. The protein is preferably insoluble in cold water.

Preferably, in the solid zirconium-protein material of the invention as set out above, the amount of zirconium, expressed as weight percent equivalent of Zr0₂ relative to the protein is less than 5 weight percent, more preferably from 1.6 to 3.4 weight percent, and even more preferably 2 to 3 weight percent. The protein may be casein, but is preferably a soy protein. The zirconium containing material or solution thereof used to treat the protein may be a zirconium salt, such as the acetate, oxychloride, nitrate, or zirconium ammonium carbonate or zirconium potassium carbonate. The latter two materials are available in stabilised form, the ammonium compound as Bacote.

From a fourth aspect, the invention provides a solution obtained by dissolving the zirconium-protein material of the first, second or third aspects in alkaline solution to provide a binder solution. In general, the binder solution so produced is relatively stable, and it is believed that the protein and zirconium cross-linker are capable of coexisting in solution, even when heated, without readily cross-linking and that cross-linking only readily occurs when the alkaline solution is dried. This feature may well be considered to be surprising and to confer an advantage compared with (two-pot) binders produced, for example, from a zirconium containing material and a starch; such materials need to be combined only shortly before use, in order to avoid premature and excessive cross-linking and gelling in the liquid medium, particularly under warm or hot conditions.

From a fifth aspect, the invention provides a method of manufacturing paper or board products, in which a binder solution according to the fourth aspect is added to a paper or board producing composition, or is coated on an existing paper or board product.

The material of the first aspect, or the fraction provided by the second aspect, or the material provided by the third aspect, or the binder solution of the fourth aspect, have other potential uses, such as a gella-nt for paints, and in the fields of adhesives, inks and textiles where a cross- linked product may be required. Besides the "one-pot" advantage, their use may also avoid the production of ammoniacal smells, which are becoming increasing unacceptable.

The invention will now be described in more detail, with reference to examples, and to the accompanying drawings in which:

Fig 1 illustrates viscosity of two compositions A and B according to the invention, and of two other materials; and

Figure 2 indicates the results of wet rub tests of the same four materials. In an initial assessment of the extraction of zirconium by insoluble protein, a solution of zirconium oxychloride or ammonium zirconium carbonate was added to a 10% slurry of Procote 400 (a cold water insoluble soy protein) , stirred for a predetermined length of time and the solid filtered off. The amount of zirconium in the filtrate indicated that over 95% of the zirconium had been left with the proteinaceous product. This happened even after only 5 minutes of stirring. A typical experiment involved the addition of zirconium solution equivalent to 1.50 gm Zr0₂ to a slurry containing 50 gm of dry protein, and stirring for between 5 and 60 minutes. The amount of Zr0₂ in the filtrate was no greater than 0.01%, compared with 0.33% if no zirconium had been picked up by the protein.

This experiment was repeated with zirconium acetate and Procote 400 with generally similar results. The experiment was also repeated, but applying the zirconium solution directly to the solid protein. However, lumps or balls of material were produced, and after drying the mixture was heterogeneous. The use of Procote slurries stronger than

10 weight percent, and the use of casein BL150 slurries

(casein BL150 is a standard milk derived protein, supplied by American Casein Company) produced problems associated with the filtration step.

Table I illustrates the results obtained when 50 gm of protein was slurried with 150 ml of a solution containing approximately 1 weight percent Zr0₂

After filtration, the amount of zirconium left in the filtrate was measured and used to calculate the amount of zirconium deposited on the protein. The latter figure is given in the table, together with the pH of the slurry. PC400 and PC450 are different grades of cold water insoluble soy protein.

Table I

Zr solution PC400 PC450

%Zr0₂ %Zr0₂ pH %Zr0₂ pH

Zr acetate 0.99 35.44 4.08 35.44 4.25

Bacote 0.99 73.74 7.28 - 6.91

Zr Oxychloride 0.97 92.78 1.66 50.52 1.50

Zr Orthosulphate 0.96 15.63 1.67 11.46 1.55

Zr Nitrate 0.96 44.79 1.78 15.63 1.41

Potassium zirconium carbonate 1.00 50.00 7.14 - 7.16

Blank - - 5.40 - 4.68

Further experiments, performed using different volumes or different concentrations of zirconium, gave variable amounts of zirconium uptake by the protein. Surprisingly, in general it appeared that absorption was reduced as the amount of zirconium increased, but it is thought that this may be due to the effect of the accompanying pH reduction. This may provide a way of controlling the amount of zirconium uptake.

In a second set of experiments, a zirconium oxychloride solution was added to a 10% slurry of. 80 gm Procote 240 or 400 protein, and the mixture stirred for 15 minutes. The slurry was then filtered and the resulting cake dried at 80°C for analysis: Table II

Protein Wt Zr0₂ % moisture % Zr0₂ of

Sample Type gm of protein solid product

1/2 240 2.16 3.8/3.9 2.9 3/4 240 3.97 7.5/6.2 5.3 5/6 400 3.97 2.1/2.4 5.5

The pairs of sample numbers, and the pairs of figures in the third column relate to different drying levels.

The filtration rate of the product from Procote 400 (which itself is granular) was markedly more favourable than that for the paste-like product from Procote 240 (which itself is a powder) .

Similar experiments were performed using zirconium acetate and ammonium zirconium carbonate with Procote 400, with generally similar results, The slurry from zirconium acetate was much longer in filtering than the product from zirconium oxychloride, however.

Difficulties with the filtration phase indicate that other separation techniques, such as spray drying, or that used by the protein producing companies, may be advantageous. The oven dried product causes the product to agglomerate, and it needs breaking up.

A set of sample products was produced in order to assess the effect of moisture content (LOD = loss on drying) of the product on bacterial growth, which with some binder formulations can begin very quickly, and to produce samples for evaluation of usefulness in paper products. 200 gm of Procote 240 in 1800 gm water and a zirconium oxychloride solution (5.4 gm Zr0₂) were stirred together for 15 minutes, and portions of the solid filtrate were dried at 80°C for different times to produce samples of different moisture content :

Table III

Sample % LOD Drying Time Wt Sample

Hr gm

7 41 1 10

8 29 1.5 12

9 16 2 6

10 5.2 2.5 6

11 2.3 3 7

The results also indicated that about 1.5 weight percent of acid soluble Zr0₂ was being taken up on the protein solids.

The dried cakes showed no sign of bacterial growth after six weeks. 10% solutions were produced by adding 15 gm to 135 gm water, cooking up to 90°C, adding ammonia up to pH 9.5, and holding at temperature for 15 minutes. In each case dissolution occurred.

As a minimum of 20 gm was required for evaluation, samples 7 and 8 were combined, as were samples 9 to 11. T 3 weighted average Zr0₂ content was calculated to be approximately the same in both cases.

Each of the two compositions was used to produce a protein/latex coating mix in the usual manner, except that no crosslinking agent was added, apart from that already taken up by the protein. Two additional coatings were also prepared using the original protein; no crosslinker was added to one of these (the control) and stabilised zirconium ammonium carbonate (Bacote 20) was added to the other to give a level of Zr0₂ equivalent to the "one pot" systems (about half of that normally recommended for a two- pot system, and the requirement for less zirconium in a one-pot system is itself advantageous) . The total formulation of each mix on a dry weight basis was 100 parts clay, 14 parts of latex (Dow 620) , 0.8 parts ammonia, and 5 parts of the protein-zirconium material or the protein itself, made up to give a total solids content of 48%, and with pH adjusted to 9.2 by the addition of sodium hydroxide.

Coating was carried out on a trailing blade coater running at 2.4 metres/minute, and the coating weight was approximately 10 g/m₂.

Viscosity was determined on a Brookfield Digital Viscometer at 10 and 100 rpm, to give the results recorded in Table IV and illustrated in Figure 1. Temperature and pH were also recorded.

Table IV (viscosity data)

Viscosity, cP

Sample pH Temp. °C at 100 rpm blank 9.55 23.2 1280

B20 9.65 23.0 1400

7,8 9.78 23.7 4320

9-11 9.58 24.3 2200 It can be seen that the viscosity of the "one pot" samples is higher than the Bacote 20 formulation, but only by 50% in the case of the lower moisture content material . This possible disadvantage is outweighed by the fact that the wet rub resistance produced by the "one pot" formulations is better than that from the Bacote formulation.

The samples of coated paper were cured at 140°C for one minute, and strips of both cured and uncured material were cut from the test specimen, at right angles to the coating direction. In a wet rub test, ten revolutions per strip were used to remove a measurable amount of coating, as recorded in Table V and illustrated in Figure 2.

Table V (wet rub tests)

Sample Uncured Cured

Blank 79.0 80.8

B20 85.0 86.2

7,8 88.2 89.4

9-11 86.8 88.4

It will be seen that both "one pot" formulations are superior to the Bacote 20 formulation, and that there is little loss of performance upon going from the "dryer" sample to the "wetter" sample with a greatly advantageous improvement in viscosity.

In a further series of experiments, a set of five precoat formulations were prepared, consisting of 100 parts of clay, 22 parts latex (Dow 620) , 4 parts of protein and 1.5 parts of a zirconium containing material or a control . The zirconium containing material was either Bacote 20, or the combination of protein PC400 with 0 (control), 5, 7.5 or 10 weight percent of 100% active potassium zirconium carbonate (KZC) based on the protein (equivalent to 0, 2, 3 or 4 weight percent of Zr0₂ based on the protein) .

Coating solutions were prepared at 60% total solids, with ammonia added to adjust the pH to 9.0.. Favourable wet rub tests indicated that all tested levels of KZC displayed cross-linking attributes, with the 5 weight percent level being most closely matched to the Bacote based composition in terms of viscosity and water retention. Furthermore, relative to the Bacote based material, the 5 weight percent KZC material had a lower IGT blister, and comparable wet pick and wet trap scores, and accordingly concentrations of zirconium in this region appear to be the most favourable.

In a yet further test, combinations of protein PC400 and KZC were cooked at a pH of 9.0 adjusted with ammonia, and the viscosities measured. There was a decrease in viscosity with decreasing protein content (constant Zr) , and an increase with increasing amounts of KZC constant protein) , and both of these results suggest there is a degree of KZC-protein interaction (I.e. cross-linking) , although the complete mechanism of the reaction is not known. However, as previously stated, such solutions are relatively stable, and generally only appear readily to undergo a degree of cross-linking sufficient to cause insolubilisation upon drying.

Claims

1. A solid zirconium-protein material suitable for use as a one-pot binder in the manufacture of paper and board products.

2. A solid zirconium-protein material according to claim 1 comprising a mixture of a protein and a solid zirconium containing material in proportions such that it will dissolve in aqueous alkali to produce a solution capable of acting as a binder when dried.

3. A material according to claim 1 or claim 2, wherein the protein is a cold water insoluble protein.

4. A material according to any one of claims 1 to 3, wherein the protein is soy protein or casein.

5. A material according to any one of claims 1 to 4, wherein the amount of zirconium expressed as Zr0₂ relative to protein is less than 5 weight percent .

6. A method of making a solid zirconium-protein material, comprising treating a cold water insoluble protein with a solution of zirconium containing material, such that at least some zirconium is extracted by, or combines with, the protein, and separating the insoluble fraction.

7. A method of making a solid zirconium-protein material, comprising treating a protein with a concentrated solution of zirconium containing material to provide a damp powder, and drying the damp powder, the ratio of zirconium to protein being such that the resulting dried powder will dissolve in aqueous alkali to produce a solution which acts as a binder upon drying.

8. A method according to claim 7 wherein the amount of zirconium expressed as Zr0₂ relative to protein is less than 5 weight percent .

9. A method according to any one of claims 6 to 8 wherein the solid zirconium-protein material is suitable for use as a one-pot binder in the manufacture of paper and board products.

10. A method according to any one of claims 6 to 9, wherein the protein is a cold water insoluble protein.

11. A method according to any one of claims 6 to 10, wherein the protein is soy protein or casein.

12. A material according to claim 2 wherein the zirconium containing material is potassium zirconium carbonate and the protein is a soy protein.

13. A material according to any one of claims 1 to 5, or a method according to any one of claims 6 to 11, wherein the zirconium containing material is ^'a zirconium salt.

14. A material or method according to claim 13 wherein the zirconium salt is zirconium acetate, zirconium oxychloride, zirconium nitrate, ammonium zirconium carbonate or potassium zirconium carbonate.

15. A solution obtained by dissolving the solid zirconium- protein material according to any one of claims 1 to 5, or the solid zirconium-protein material obtained by the method according to any one of claims 6 to 11, in alkaline solution.

16. A method of manufacturing paper or board products, in which a solution according to claim 15 is added to a paper or board producing composition, or is coated on an existing paper or board product, either alone, or in conjunction with other coating materials.