RETENTION AGENT

Abstract: The use of cationic starch of amylopectin type, obtained from potato that has been modified by genetic engineering to suppress the formation of amylose type of starch, optionally together with an anionic component, as a retention-improving agent added to the stock in paper-making is described.

Description: RETENTION AGENT The present invention relates to the use of amylo- pectin-type cationic starch obtained from potato as a retention-improving agent in papermaking. More precisely, the invention relates to the use of amylopectin-type cationic starch obtained from potato that has been modi¬ fied by genetic engineering to suppress the formation of starch, or derivatives thereof, in order to increase the retention in papermaking. The invention further relates to a complex between the cationic starch of amylopectin type and an anionic component. Background of the Invention Within the papermaking industry an increasingly larger proportion of the fibres is continuously replaced by cheaper components as mineral fillers, such as chalk or clay. A consequence of higher contents of such fillers is that it raises the requirements on the retention system used. By definition, the expression "retention" relates to the proportion of a component present in an original mixture which remains in the mixture at some stage of the process or in the final product. In conventional use of cationic starch within the papermaking industry the starch must be dissolved either by batchwise cooking for approximately 20 min at 95°C while being comparatively vividly stirred, or by continu- ous cooking in a so-called jet digester at 110-130°C. These cooking methods are necessary if the starch is to dissolve. The disadvantage inherent in these cooking methods is, however, that it reduces the molecular weight of the starch, which in turn impairs the effects of retention in the papermaking. If lower temperatures are used an intermediate between a dispersion and a solution is obtained instead, in which case the solution contains residues of swelled starch granules and/or fragments thereof. Starch solutions of this nature lead to consid- erably impaired dewatering and lower strength development for each amount of starch supplied. Consequently, there is a greatly felt need within the paper industry to eliminate these problems. Object of the Invention The object of the present invention is to eliminate the above-mentioned problem by using an agent furthering high retention, satisfactory dewatering, and high strength development. This object is obtained by the use of a retention-improving agent of the kind mentioned in the introduction, which agent exhibits the characteristics defined in the appended claims. Summary of the Invention In accordance with the present invention amylo¬ pectin-type starch or derivatives thereof thus are used as a retention-improving agent in papermaking. The expression "amylopectin-type starch" as used throughout in the present application text relates to starch obtained from potato that has been modified by genetical engineering in order to suppress the formation of amylose-type of starch. The expression "derivatives thereof" relates to chemically, physically and/or enzy¬ matically derivatised amylopectin-type starch. The amy¬ lopectin content of amylopectin-type starch is in excess of 95%, preferably in excess of 98%. The remaining ingre- dient in amylopectin-type starch is amylose. A detailed description of the above amylopectin-type starch and derivatives thereof and the methods of their production is found in the Swedish Patent Specification 9004096-5 (Amylogene HB) . The expression "retention-improving agent" as used throughout in this application concerns an agent which in addition to producing increased retention also produces improved dewatering and strength development in paper¬ making. Prior to its use in accordance with the present in¬ vention the amylopectin-type starch should be substituted by cationic groups by chemical modification. Ammonium compounds are used for this purpose, which compounds preferably are quaternary but could also be primary or tertiary. The chemical composition of the stock system used in the papermaking determines the degree of substi- tution of the amylopectin-type starch required to obtain optimum results. The degree of substitution thus lies between 0.01 and 0.30 (between 0.09 and 2.5%, calculated in the corresponding manner with respect to nitrogen) , preferably between 0.02 and 0.20 (between 0.18 and 1.6%, calculated in the corresponding manner with respect to nitrogen) . The preparation of the cationic starch of amylo¬ pectin type is important, since the solubility curve of amylopectin-type starch deviates strongly from that of traditional potato starch. The dissolution of the cationic starch of amylopectin type should be effected with a minimum of shearing, batchwise or continuously, in the temperature range of 60-130°C, preferably in the tem¬ perature range of 65-95°C. This dissolving method pro- duces a solution of amylopectin-type starch the molecular weight of which is maintained, while at the same time the solution is free of swelled granules or residues thereof. The result is a well digested solution producing high retention and rapid dewatering, despite a lower energy supply than that required in the preparation of tradi¬ tional cationic starch. In papermaking, the cationic starch of amylopectin type is added to the stock while being sufficiently stirred to ensure that it is well admixed therein prior to the paper formation. In one embodiment of the present invention the cationic starch of amylopectin type is com¬ bined with an anionic component, such as colloidal silicic acid, anionic polyacrylamide or bentonite, and in this case the components are added individually while being sufficiently stirred to ensure that they can inter¬ act and act together with the other components of the stock. The amounts of the additives required to reach the desired effect depend on the composition of the stock. Suitable additions of the cationic starch of amylopectin type are 1-50 kg/ton paper, preferably 1-20 kg/ton paper. As mentioned above, the present invention provides highly improved retention levels with respect to the added filling agent as well as to the fine fractions of the fibrous material. In addition, it becomes possible to maintain the strength characteristics of the finished paper despite the larger amounts of filling agent addi¬ tions. Furthermore, the dewatering times in the wet end of the papermaking machine used can be kept brief, de¬ spite the fact that the amylopectin-type starch has been dissolved to provide maximum retention, i.e. its viscos- ity level is maximum. An additional advantage provided by the present invention is that it is applicable to all types and qualities of paper and cardboard products. It is previously known to use cationic starch of amylopectin type within papermaking, such as starch of waxy maize type, but practical tests during which the importance of the preparation method in combination with the solubility curve of the amylopectin in question have been studied, have shown the surprising positive effects of simultaneously providing high retention, satisfactory dewatering and positive strength development. The examples below describe the use of the invention in more detail, viz. on the one hand the use of amylo¬ pectin-type starch separately (Examples 1-3) , and on the other the embodiment according to which this starch is used together with an anionic component (Examples 4-6) . Example 1 In order to evaluate the effects of the cationic starch of amylopectin type on retention, laboratory studies were performed in a so-called DDA apparatus (Dynamic Drainage Analyser) . The pulps of the stock con¬ sisted to 50% of fully bleached chemical hardwood pulp and to 50% fully bleached chemical softwood pulp ground to 25°SR. 40% chalk was added to the stock as a filling agent. The pH value of the stock was adjusted to 8.2 and the conductivity was measured to 600 μS. Prior to the test in the DDA apparatus the stock was diluted to a con- centration of 2g/litre. To measure the retention, deter¬ minations of concentration and ash contents were con¬ ducted on the batch stock as well as on the water that had drained through the wire. Cationic starch of amy¬ lopectin type having a degree of substitution of 0.05 was compared with a traditional cationic potato starch having the same degree of substitution. The cationic amylopectin and the cationic starch were dissolved at a number of various temperature levels in the range of 60-130°C, and the added quantities amounted to 2.5, 5.0, 10.0 and 15.0 kg/ton, respectively. Optimum preparation and addi¬ tions of respectively the cationic starch of amylopectin type and the cationic potato starch gave an improvement of the total retention of approximately 10% and of the filling agent retention of approximately 40% when the cationic starch of amylopectin type was used. Example 2 To evaluate the effects of the cationic starch of amylopectin type on drainage, laboratory studies were carried out in a DDA apparatus. The pulps contained in the stock consisted to 50% of fully bleached chemical hardwood pulp and to 50% fully bleached chemical softwood pulp ground to 25°SR. To the stock was added 40% chalk as a filling agent. The pH value of the stock was adjusted to 8.2 and the conductivity was 600 μS. Prior to the test carried out in the DDA apparatus the stock was diluted to a concentration of 2 g/litre. The drainage time was meas¬ ured automatically by the instrument and the results were registered in a computer. Cationic starch of amylopectin type having a degree of substitution of 0.05 was compared with traditional cationic potato starch having the same degree of substitution. The cationic starch of amylopec¬ tin type and the traditional cationic starch were dis- solved at several temperature levels in the range of 60- 130°C and the added quantities amounted to 2.5, 5.0, 10.0 and 15.0 kg/ton, respectively. The tests show that the cationic starch of amylopectin type that had been dis- solved to give maximum retention also maintains rapid dewatering conditions contrary to the case of traditional cationic starch, the latter impairing dewatering under the same conditions. Example 3 To evaluate the adsorption of the cationic starch of amylopectin type to a stock, laboratory studies were car¬ ried out in a DDA apparatus. The pulps contained in the stock consisted to 50% of fully bleached chemical hardwood pulp and to 50% fully bleached chemical softwood pulp, ground to 25°SR. To the stock was added 40% chalk as a filling agent. The pH value of the stock was adjusted to 8.2 and the conductivity was 600 μS. Prior to the tests in the DDA apparatus the stock was diluted to a concentration of 2 g/litre. Cationic starch of amylopectin type having a degree of substitution of 0.05 was compared with tradi¬ tional cationic potato starch having ' the same degree of substitution. The cationic starch of amylopectin type and the traditional cationic starch were dissolved at a number of different temperature levels in the range of 60-130°C and the added quantities amounted to 2.5, 5.0, 10.0 and 5.0 kg/ton, respectively. The amounts of amylopectin and of starch retained in the pulp cake were determined by means of a method according to which the polymer is de¬ graded into glucose by two enzymes. The detection of glucose presence is then effected in a HPLC system. These studies show the significance of high viscosity (molecular weight) to a high degree of adsorption. The cationic starch of amylopectin type possesses, as mentioned in the foregoing, unique properties inasmuch as it may be pre- pared in such a manner that high retention and satisfac¬ tory dewatering are obtained, but it likewise possesses considerable adsorbability of its own. Example 4 To evaluate the interaction between the cationic starch of amylopectin type and anionic components and the effects of retention, laboratory studies were carried out in a DDA apparatus. A colloidal silicic acid was used as the anionic component. The pulps contained in the stock consisted to 50% of fully bleached chemical hardwood pulp and to 50% fully bleached chemical softwood pulp ground to 25°SR. To the stock was added 40% chalk as a filling agent. The pH value of the stock was adjusted to 8.2 and the conductivity was 600 μS. Prior to the tests in the DDA apparatus the stock was diluted to a concentration of 2 g/litre. In order to measure the retention, the concen¬ tration and the ash contents of the supplied stock as well as of the water drained through the wire were deter¬ mined. A cationic starch of amylopectin type having a degree of substitution of 0.05 was compared with a tradi¬ tional cationic potato starch having the same degree of substitution. The cationic starch of amylopectin type and the traditional cationic starch were dissolved at a number of various temperature levels in the range of 60- 130°C and the added quantities amounted to 2.5, 5.0, 10.0 and 15.0 kg/ton, respectively. Sufficient colloidal sil¬ icic acid was added to ensure that the ratio of respec- tively cationic starch of amylopectin type and tradi¬ tional cationic starch to colloidal silicic acid ranged from 1.5:1 to 10:1. Optimum preparation and additions of the cationic starch of amylopectin type and of the tradi¬ tional cationic potato starch, respectively, and of the colloidal silicic acid gave an improvement of the total retention of 25% and of the filling agent retention of approximately 70% when the cationic starch of amyloectin type was used. Example 5 To evaluate the interaction between the cationic starch of amylopectin type and anionic components, and the effects of retention, laboratory studies were carried out in a DDA apparatus. A colloidal silicic acid was used as the anionic component. The pulps contained in the stock consisted to 50% of fully bleached chemical hard¬ wood pulp and to 50% of fully bleached chemical softwood pulp ground to 25°SR. To the stock was added 40% chalk as a filling agent. The pH value of the stock was adjusted to 8.2 and the conductivity was 600 μS. Prior to the tests in the DDA apparatus the stock was diluted to a concentration of 2 g/litre. The drainage times were meas- ured automatically by the instrument and the results were registered by a computer. A cationic starch of amylopec¬ tin type having a degree of substitution of 0.05 was com¬ pared with traditional cationic potato starch having the same degree of substitution. The cationic starch of amy- lopectin type and the traditional cationic starch were dissolved at a number of various temperature levels in the range of 60-130°C and the added quantities amounted to 2.5, 5.0, 10.0 and 15.0 kg/ton, respectively. The addition of colloidal silicic acid was sufficient to ensure that the ratio of respectively cationic starch of amylopectin type and traditional cationic starch to col¬ loidal silicic acid ranged from 1.5:1 to 10:1. These studies show that cationic starch of amylopectin type, having been dissolved to provide maximum retention, main- tains rapid dewatering qualities, also in combination with colloidal silicic acid. Example 6 In order to evaluate the adsorption of cationic starch of amylopectin type to a stock when affected by an anionic component, laboratory studies were carried out in a DDA apparatus. A colloidal silicic acid was used as the anionic component. In order to evaluate the adsorption of cationic starch of amylopectin type to a stock, labora¬ tory studies were carried out in a DDA apparatus. The pulps contained in the stock consisted to 50% of fully bleached chemical hardwood pulp and to 50% of fully bleached chemical softwood pulp ground to 25°SR. To the stock was added 40% chalk as a filling agent. The pH value of the stock was adjusted to 8.2 and the conductiv¬ ity was 600 μS. Prior to the tests in the DDA apparatus the stock was diluted to a concentration of 2 g/litre. Cationic starch of amylopectin type having a degree of substitution of 0.05 was compared with traditional cati¬ onic potato starch having the same degree of substitu¬ tion. The cationic starch of amylopectin type and the traditional cationic starch were dissolved at a number of various temperature levels ranging from 60 to 130°C and the added amounts were 2.5, 5.0, 10.0 and 15.0 kg/ton, respectively. The addition of colloidal silicic acid was sufficient to ensure that the ratio of cationic starch of amylopectin type and traditional cationic starch, respec- tively, to colloidal silicic acid ranged from 1.5:1 to 10:1. The amounts of respectively amylopectin and of starch retained in the stock cake were determined by a method according to which the polymers were degraded into glucose by two enzymes. Detection of glucose presence is then carried out in a HPLC system. These studies show the importance of high viscosity (molecular weight) in order to obtain a high degree of adsorption. The anionic compo¬ nent contributes to increased adsorption of the cationic starch of amylopectin type to a higher extent than in combination with traditional cationic starches.

Claims: CLAIMS 1. The use of cationic starch of amylopectin type, obtained from potato which has been modified by genetic engineering in order to suppress the formation of amy¬ lose-type starch, optionally together with an anionic component, as a retention-improving agent added to the stock in papermaking. 2. The use in accordance with claim 1, wherein the amylopectin-type starch contains more than 95% amylo¬ pectin, preferably more than 98% amylopectin. 3. The use according to claim 1, wherein one or several derivatives of amylopectin-type starch that has/have been subjected to chemical, physical and/or enzymatic derivatisation is/are used as a retention- improving agent. 4. The use according to any one of the preceding claims, wherein amylopectin-type starch or derivatives thereof is/are added to the stock in amounts of 1-50, preferably 1-20, kg/ton manufactured paper. 5. The use as claimed in any one of the preceding claims, wherein the anionic component is colloidal silicic acid, an anionic polyacrylamide and/or bentonite. 6. The use according to any one of the preceding claims, wherein prior to its addition to the stock the amylopectin-type starch is substituted with cationic groups through chemical modification with an ammonium compound, preferably a quaternary ammonium compound. 7. The use as claimed in any one of the preceding claims, wherein the degree of substitution of the cati¬ onic amylopectin in the stock is 0.01-0.30, preferably 0.02-0.20.

Inventors: WIKSTROEM OLLE, WIKSTROEM, OLLE
Applicants: SVERIGES STAERKELSEPRODUCENTER, WIKSTROEM OLLE, SVERIGES STAERKELSEPRODUCENTER, FOERENING UPA, WIKSTROEM, OLLE
Application year: 1996
Main classification: D21H17
IPC codes: C08B35, D21H17, D21H21