SE439653B - Method during paper manufacturing of using a cationic starch composition comprised of cationic starch and carboxymethylcellulose or polyacrylic as well as the liquid for this. - Google Patents

Abstract

The invention refers to a method of increasing retention and binding of pigment during paper manufacturing. The new method is characterized by that one introduces, into pigment slurry with or without fibres, a colloidal solution of an amphoteric starch composition also containing cationic amine groups such as anionic acid groups, whereby the named starch composition is layered onto the pigment surfaces like an amphoteric gel coat with limited strength. Thereafter setting up a non-organic polycationic or polyanionic union for agglomeration and development of a considerably stronger membrane gel outside of the gel coated pigment particles. The thus treated pigment suspension is used in the usual manner for paper manufacturing. For the invention, usual pigments such as kaolin, chalk, talc, titanium dioxide as well as fibre-shaped minerals such as asbestos and wollastonite can be used. Suitable amphoteric starch compounds are products of reactions between cationic starches and compounds such as carboxymethylcellulose or polyacrylic acid. Among the non-organic polyionic compounds, which are suitable for the development of solid gel membrane these include polyaluminum salts and silicic acid preferably in oligomers or polymer form.<IMAGE>

Description

8006600-4 ïâ. market cationic starch normally has a degree of substitution of 0.030 i.e. the number of glucose units is cza 3% substituted with amine groups. The degree of substitution can vary between 0.02 and 0.06, but we have achieved the best results with the lower degrees of substitution around 0.03 and below. The higher degrees of substitution become uneconomical because they make more of the expensive cerboaacymethylcellulose. This means that we prefer a cationic starch with a high viscosity and a degree of substitution of 0.03, which corresponds to an equivalent weight of 5,000-6,000 per breast-up- Of earborymethylcellulose, _CMC, which is present on. market, there is a large spread in viscosity (molecular weight) and degree of substitution. We have found a lower viscosity or molecular weight suitable, more specifically a molecular weight around 100,000 or a viscosity of less than 25 cps in liquid solution. This means a molecular weight, which is lower than that of the starch component. The degree of substitution can vary between 0.5 and 0.9 carboxyl groups per glucose unit. We have mainly used a rel. high degree of substitution of 0.7 and slightly above, which corresponds to an equivalent weight of about 300 per carbozql group.

An equivalent mixture of cationic starch (equivalent weight 5.ooo-6.ooo) and emo (erv. Weight zoo) male theoretically should be about 5.5 parts GMC per 100 parts starch. A mixture of the components within the "equivalence range" 4-8 divides the GMO. 100 parts of starch, when dissolved, gives a fine precipitate, which can be easily filtered off on coarse filter paper, and gives a clear filtrate without viscous. containing less than 1% of the constituent starch.

The filter cake is a gel with 10% dry matter and about 90% water, ie a swollen colloid, whose water content could be 60-707: of the total weight. Such an equivalent reaction product is useful for the process of the invention, especially if the pigment or filler consists of CNIC consumable lime or limestone flour. However, optimal results for retention and paper strength are obtained at about half the equivalence point or 2-3 parts of GMC. per 100 parts of cationic starch, at a ratio of 3/100 there is a limit, above which the reaction product precipitates as a hydrated gel leaving a clear liquid, while below this limit it remains a homogeneous colloidal solution (24%) or suspension, which does not separate into two phases.It is such collo fl al F, | 8006600-4 LP solution with a cation ~ anJon balance just below the separation limit, BUN EGP ° PÜim81t fß fl ulfßfp counter cation / anion ratio of 1-5 / 1.

Such a reaction product can be readily prepared by dry mixing a suitable cationic starch and a suitable OMG in the proportions of 2-3 parts of GMC and 100 parts of starch. When dissolved in water at least 60-70 ° C, the components react immediately with each other.

Such a solution is also easier to handle because it takes less time to prepare than pure GMC solution, i.e. lumps are smaller and give a lower viscosity than starch solution of the same concentration.

In addition to GMC, other polymeric acids can also be used, for example polyacrylic acid, together with cationic starch to give amphoteric reaction products. Here, too, one should avoid an excessively high-molecular and highly viscous product. A molecular weight of 50,000-100,000, corresponding to a viscosity of 5-20 cps in 1% solution at pH 5, has been found to be useful. Since the equivalent weight of acrylic acid is only 72, the equivalence point with the above cationic starch would be only 1.2-1.5 parts of polvacrylic acid per 100 parts of cationic starch. The practical limit for pre-precipitation and phase separation is higher here or at 2.0-2.5 parts of acrylic acid on 100 parts of starch. The optimum ratio for papermaking seems to be 1.5-2.0 per 100 starches. This would indicate that etheric barriers would exist for polyacrylic acid with its closely spaced carboxyl groups, a property for which polyacrylic acid is known.

GMC and polyacrylic acid are the most common and commercially available polymeric acids. In addition to these, water-soluble copolymers of acrylic acid can be used. Even simple organic polyacids of the citric acid type show a tendency to give amphoteric compositions with high molecular weight cationic starch.

The precipitation point is at about 5-4 åel flr 0ifP0nBYr fl On 100 parts of cationic starch. 2 parts citric acid on 100 parts 8006600-4 4 cationic starch with a degree of substitution 0.03 seems to give optimal effect especially when used on kaolin. The citric acid then prevents the harmful agglomeration of kaolin grains, which occurs when using only cationic starch, and the subsequent surface hardening and flocculation also works satisfactorily.

In the case of citric acid as well as in the use of the truly high molecular weight acids GMC and polyacrylic acid, the starch composition should have a pH between 5 and 9 in order to develop the amphoteric character.

An amphoteric starch composition may be formulated in a concentration of 14%, preferably 2-376. Suitable reaction temperature is 10 DEG-90 DEG C., the higher temperature only necessary when the starch component dissolves. The appropriate pH for the reaction is between 5 and 9.

The reaction between pigment and amphoteric starch composition is relatively rapid, especially if the pigment is in concentrated form corresponding to 10-40% in aqueous suspension. When the starch composition is added in the form of a 2-3% solution, it is rapidly absorbed on the pigment surfaces, and a gel is obtained around the pigment grains, which is unlikely to have a higher dry matter content than 20-3G%, lower at higher dilution.

After the addition of about 5% starch composition, the pigment suspension usually assumes a more grainy character, while a clearer aqueous phase separates from the coated pigment grains. The amount of starch composition added to the pigment or filler can vary widely.

However, in order to achieve a significant retention and strength effect, 2-3% are desirable and levels above 20% are not economically justified. An advantage of amphoteric composition over separate ventures of ex. cationic starch and polyacid are that you can change the dosage without having to adjust the dosage of another component at the same time. The amphoteric composition is usually sufficiently ionically balanced in itself.

Of the common paper pigments, kaolin and titanium dioxide are anionic and therefore rapidly absorb the predominantly cationic starch composition. Without anions in the starch composition, an excessively rapid deposition easily takes place with a too hard agglomeration as a result.

This gives rise to pigment accumulations in the paper, which on transillumination then have a "freckled" appearance, and which have a certain tendency to dust.The amphoteric composition avoids such pigment accumulations ~ 4 accumulations, which is a great advantage from a quality point of view. An amphoteric starch composition thus provides better pigment distribution in the paper web, when treating the pigment in relatively concentrated systems, which is desirable for obtaining optimal strength properties.

Alkaline pigments such as chalk, limestone flour and talc, on the other hand, have a substantially cationic surface character, and therefore deposit the amphoteric starch composition mainly by means of its anions. when using these pigments, it is therefore advantageous to increase the amount of anionic component in the starch composition, although it should not be done at an early stage to the starch composition itself, so that it separates before it has time to adhere to the pigment surfaces. The addition of ex. GMC should therefore be applied separately to the pigment suspension before or after the addition of starch composition.

In order to obtain optimal strength properties of the paper, it is advantageous that the application to the pigment grains takes place from a colloidally soluble (non-phase-separated) starch composition. This is probably partly due to the distribution of starch composition on the pigment surfaces becoming more homogeneous to the precipitated (phase-separated) has an intense tendency to settle on all surfaces, even those, such as non-ionic, e.g. polyethylene walls, cellulose, etc.

But the applied amphoteric starch composition is still colloidally soluble if subjected to larger shear strokes, as is the case with the wire portion of a paper machine. It is admittedly more durable than just cationic starch, which is stored ex. on kaolin, but in order to cope with the shear forces on a paper machine, etc., a form of "surface hardening" and strength increase must be achieved.

Such surface curing is accomplished by the additional addition of polyanionic compound such as GMC or polyacrylic acid. If the original composition contains 2.5 parts of GMC per 100 parts of starch, it is advisable to add an additional 0.5-1.5 parts of GMC. You then get a clear agglomeration and contraction (syneresis) of the gel layers around the pigment grains during separation of clear starch-free water. During syneresis, the gel thus changes to a non-soluble coating. To withstand the violent forces of dewatering on wires, harder surface hardening is usually required than what GMC can provide. By far the most effective surface hardening is achieved by means of polymeric silicic acid or 8006600-4 polymeric aluminum salt. Water glass solution or aluminum sulphate solution are also useful, but the polymeric forms are more efficient.

Silicic acid is effective against strongly cationic starch compositions, while aluminum compounds are most effective against compositions to which some GMC or polyacyl-acid acid is subsequently added. The syneresis or gel dewatering becomes very strong with these inorganic compounds as well as the agglomeration. It can therefore cause technical problems with pumpability, etc., to carry out this surface curing in concentrated pigment suspensions. The surface hardening can therefore advantageously be divided into two. step, a first in the pigment suspension and a second in the finished fiber-pigment stock just before dilution with return water.

The amounts of polymeric silicic acid or polymeric aluminum salt e.g. polyaluminum sulphate, which is required for achieving stability in the spring and the recovery rate of well over 90%, is below 10%, often very small, or about 1-424 of the amount of starch used, calculated as SiO Al205. Then an average starch amount is 10% possible pigment. e11er fyiimeaelevilket, becomes need ev cmc o, 25 ~ o, 4% and the need for silicic acid or alum 0.10-0, 4% as S102 resp. 161205 all calculated on pigment weight. This moderate chemical sale effort enables the production of strength- and quality-excellent paper material up to 50-60% filler and a close 10üíš-ig retention at the passage of the stock on a paper machine.

In order to clarify what we mean by polymeric silicic acid and polymeric aluminum sulphate, the following production methods have been stated.

For the production of polymer-silicic acid, water glass (ratio 3.5 een sing-completely 27%) is diluted to Bggr its weight but water 6% S102). at the bottom put-es utsp. sulfuric acid (approx. S-normal) corresponding to half. the need for neutralization (cza 1.3 gq. acid. per g of original water glass).

Spontaneously, the pH is lowered from the pH 13 of the water glass to pH 9. * In connection with the polymerization of the silicic acid, the pH rises again to stay at pH 11 after 30 minutes. This product can be used directly for surface hardening of the starch gel. Should it be stored for more than 12 hours. the solution should be stabilized by acidification to pH 2-3. where it is stable for several days. For the production of polymeric Al-sulphate, ordinary Al-sulphate is dissolved in water to a solution corresponding to 10-305; A12O3 per liter. To this is slowly added utsp. sodium hydroxide-Z normal) whereby the primarily formed precipitate of Al hydrate slowly dissolves again.

At the same time, the pH value rises from the Al sulphate 2.5 to about 4.0. -7L 8006600-4 Neutralization should be continued until 35 to 50% of the sulfuric acid in the aluminum sulphate has been neutralized. You can hardly go further than 50% without permanent felling. It can take up to 48 hours before such a solution clears from primary precipitate. It can be used directly for surface hardening of the starch gel. Both polymeric silicic acid and polymeric aluminum salts are available as standard products on the market. Both polymeric silicic acid and polymeric Al-sulphate can be used fairly independently of the pH of the paper stock, both in acid papermaking, pH 4.5-5.5 and in alkaline 6.5-7.5.

After the starch composition has been applied to the pigment suspension and preferably also partially surface hardened, the suspension can be mixed with the fibrous component consisting of cellulose, wood pulp of any quality and mixing. The storage can also be in stock in the presence of fiber, but this necessarily entails a higher degree of dilution, which is a disadvantage for achieving optimal strength values of the final paper. After: The mixture is generally required for a mild refining or agitation in pump systems, preferably followed by a second surface hardening-agglomeration of the pigments in the stock. Although the pigment suspension at primary primer curing can assume a "doughy" consistency with coarse lumps in clear water, it has a significant ability to distribute in the fiber stock. Despite this, the usual sieving and purification of the stock is justified. This can then be run on a paper machine's wire section after the usual dilution with return water but without extraordinary measures. One should only take into account that the return or backwater is extremely clean with very low levels of fiber and pigment despite pigment levels in the stock of up to 50-60%, ie far above what is common in the paper industry.

Finally, we would like to highlight in particular some of the technical differences that exist between this invention and previous applications submitted in the last two years. In previous applications, silicic acid was used in combination with cationic starch partly as a yeast agent against the pigment surfaces, and partly as a precipitating agent for cationic starch. According to this invention, silicic acid or aluminum compounds constitute a "surfactant" for the gel of starch composition already applied to the pigments. Furthermore, according to this invention, we have developed a balanced and non-precipitated colloidal composition of amphoteric character, which works better as a binder than direct precipitation of cationic starch with silicic acid. 8006600-4 Example 1. zog nam (meaeiperfikelstoriex 4u) eiemmsaes 1 water e now a 257m aim-ry. m meta: - mfrxeieelaenmg uereaaee me .. containing 2% cationic starch of high viscosity and with a degree of substitution 0.03 and 0,31 nitrogen. Furthermore, the solution contained 2.51 GMC calculated on the amount of starch or 0.05% of the amount of the solution. The GMC product was manufactured by Hercules Corp. with the trade name TL? - Ö According to catalogs, this should mean a degree of substitution of 0.7 and a further low viscosity corresponding to a molecular weight of 89,000 and high purity (food grade). cmc possibly significantly lower purity can be used, but we have in these examples chosen the horse defined product, which we ktmnat find.

The amiotic starch solution was charged to the slurry while stirring in an amount corresponding to 10% starch and 0.25% GMC by weight of bite. The mixture then assumed a fine-grained character. After 10 minutes, a 2% solution of "semi-neutralized and then acidified water glass" was charged according to the description described above. A total amount of silicic acid corresponding to 0.33% S10 coarse 1-5mm lumps were formed in a completely clear aqueous phase 20g cellulose bleached sulphate, 60% birch and 40% pine, ground to 30 ° SR eloge up in lichen-mix een: another-uu with 0.5% lquepelR, The combined stock then had the h-ice slurry as above. , of which sheets of paper were made with a basis weight of oza 100g / n2.

After mixing, the stock was given only a short stirring in the tour mixer at the lowest speed. The balcvatmet after the wire was completely clear and the total sheet weight was 42.20; against theoretical 42.12g thus a retention of 100%.

The paper showed an excellent formation without Uumpar and had: the following date: lnragmaez 33 nm / g yield 2.9% d Ia: p-u. 16 (Dennison) 6, Opaoitet 96% e L fi usn, 77% 8006600-4 Example 2. Same: experiments were done as according to Example 1), only with the difference that 1.5% polyacrylic acid: had to replace the 2.5% GMC , which was used according to ex. 1). The molecular weight of polyacrylic acid was estimated at 50-70,000. Also in this case, the measured retention value became about 100%. The paper tensile index was 30 Nm / g and Wax pick up acc. Dennison 14. (The percentages refer to the amount of starch) Example 3. The same experiment was performed as in Example 1), except that the silicic acid additive was replaced by an additional GMC additive of 1.0% based on the starch and that the final lcrit: the fiber mixture was added with polymeric Al-suliat corresponding to 2.0% Al 2 O; the amount of starch. The formex in this case was extremely fine, while the measured retention was 9%. The paper's tensile index was 32 Nm / g and Wax pick up between 14- oeh 16.

Example 4. 20g kaolin (dry) English qual. E with a particle size of 2-5 μl was slurried in water to a 25% slurry. For this the same amphoteric starch composition with GMC was used as in ex. 1). The amphoteric starch solution was charged to the kaolin solvent while stirring in an amount corresponding to 10% cation starch and 0.25% CMG calculated on. weight kaolin. Then the grainy. the mixture was nomogenized, an additional 0.10% cMc (dropped on kaoi amount) was added.

The same cellulose xnponent was prepared sozï in ex 1) with end. the difference that no Aquapel was added. After mixing the kaolin and cellulose components in a turmeric apparatus, a polymeric aluminum sulphate solution (neutralized to 35%) was added in an amount corresponding to 0.295 Algöš (calculated on the amount of kaolin). The retention, calculated on average on the 10 sheets, was 98%.

Pull index 28 Nm / g allowance 2.2% Wax pm. 11 (Dennison) Opacity 98 ïë Iijushet 75 35 8006600-4 10 Example 5. Kaolin enl. ex. 4) was slurried in water. To the Zßíåiga slurry was added a 2¶šig amphoteric starch composition consisting of the same lcation starch as in ex. 1), but with 2% citric acid instead of GMC. After homogenizing the first granular mixture, 4% polymeric silicic acid (stabilized on the acidic side as described above) was added. A strong syneresis effect occurred during the separation of clear water from the kaolin grains with amphoteric starch composition. The amount of cation starch was 10% calculated on. kaolin.

It saw. the obtained kaolin suspension was mixed with cellulose according to ex 1) but without Aquapel. The mixing ratio was thus. in this example as in the others: filler / cellulose = 1/1. When the combined stock of cellulose and kaolin showed a completely clear aqueous phase, no additional polymeric silicic acid or aluminum compound was added for a secondary surface hardening, but sheet forming took place directly. During sheet formation, a slight turbidity in the backwater was observed, and the obtained sheet weights indicated a retention of "only" 9575. Draginaex became 30.5 Nm / g and the Wax pick-up value 13-14.

Example 6. Particle size 1-4-talc was slurried to a 10% slurry using 0.12% GMC (Hercules 7I: F). To the slurry was added an amphoteric starch composition of 10% cation starch and 0.25% GMC all calculated. the amount of talc. After homogenization, a primary surface purification was performed with 0.3% S102 in the form of acidic stabilizing polymeric silicic acid, whereby clear water was separated by syneresis of the amziotic starch coating. Then mix the stable component with cellulose according to ex. 1) and in the proportions 1/1.

To the mixed stock was added for secondary surface hardening and agglomeration an additional 0.275 SiO 2 as polymeric silicic acid solution.

During sheet formation, the backwater became clear, and the total sheet weights showed a retention of 98%. The resulting paper showed a tensile index of 23 Nm / g and a wax pick-up value of only 7.

Example 7. When comparative examples without amphoteric starch composition cannot be fermented, since paper with filler / cellulose ratio of 1/1 cannot be made, examples with cellulose alone and with cellulose plus amphoteric starch composition are shown here. n 8006600-4 4g cellulose according to ex. 1) was slurried and filed. The sheet weight indicated a retention of * 97%. The tensile index was 57 Nm / g and the wax-pick-up value was 13. To an example also of 4 g of cellulose was added an amphoteric starch composition, consisting of 100 parts of lacation starch and 2.5 parts of cmc, according to: ex. 1). The amount was chosen to be 5% cation starch. the cellulose mixture (which thus corresponds to le 10% of the filler weight or half the furnish weight, as used in the previous one). For surface hardening and agglomeration, 0.15% Al 2 O was added; as polymeric aluminum sulphate, calculated on the cellulose weight.

The obtained paper sheet showed a retention of 100%, a tensile index of 62 Nm / g and a wax pick-up value of 23.

It can be seen from this that paper so-called Z-strength (surface strength) is affected extremely strongly and to a greater degree than the tensile strength by using amzphoteric starch composition as a binder.

Claims (5)

8006600-4 11 Patent claims: A method of improving retention and bonding in papermaking, characterized in that a colloidal amphoteric starch composition is added to a pigment and / or fiber slurry, consisting of a reaction product between cationic starches, preferably with a degree of substitution of 0.02-0. , 04 amine groups per glucose unit, and carboxymethylcellulose or polyacrylic acid, allowing said starch composition to be deposited on pigment and / or fibrous surfaces as a hydrated gel layer, and finally subjecting this gel layer to a strength-increasing curing reaction by adding a polymeric aluminum salt and / or polysilicic acid, preferably in the form of polycondensed water glass. 2. A method according to claim 1) characterized in that the amphoteric starch composition consists of the reaction product between cationic starch with a degree of substitution of 0.02-0.04 amino groups per glucose unit and carboxymethyloellulose, preferably with a degree of substitution of 0.5-0, 9 carboxyl groups per glucose unit, and that these components are included in such an amount ratio that the ratio of amine groups / carboxyl groups is between 1/1 and 3/1, preferably between 1.5 / 1 and 3, o / 1. 3. A method according to claim 1) characterized in that the amphoteric starch composition consists of the reaction product between cationic starch with a degree of substitution of 0.02-0.04 amine groups per glucose unit and polyacrylic acid, preferably in an amount ratio corresponding to 1.5-2, 0 parts polyacrylic acid per 100 parts by weight of cationic starch. 4. A method according to claims 1-3) characterized in that the gel-curing polyaluminum or polysilicic acid compound is added in an amount corresponding to 1-10% by weight of the amphoteric starch composition, preferably 1-4% by weight, calculated as Al 2 O 5 or S10 2. Means for carrying out the method according to claim 1), characterized in that it consists of cationic starch mixed with carboxymethylcellulose in dry form and in such a proportions ratio that the ratio of amine groups / carboxyl groups is between 1/1 and 3/1. nl