MXPA01002135A - Manufacture of paper - Google Patents

Abstract

A process for making paper on a paper-making machine comprising providing a cellulosic thin stock-suspension, flocculating the suspension by adding an aqueous solution of a polymeric retension aid selected from natural and synthetic polymer and thereby forming a flocculated suspension, shearing the flocculated suspension, reflocculating the sheared suspension by adding an aqueous reflocculating suspension, draining the reflocculated suspension through a wire to form a sheet, and drying the sheet, characterised in that substantially fully cooked starch is added to the suspension after the shearing and before the draining.

Description

PAPER MANUFACTURE This invention relates to the production of paper that is reinforced with starch. Various processes for producing paper, and for producing paper reinforced with starch, are described for example in O95 / 33096, which is incorporated herein by reference. Processes that are currently of particular interest in paper production comprise providing a suspension of thin cellulosic material, flocculating this suspension, shearing the flocculated suspension, reflocculating the sheared suspension, adding an aqueous reflocculation composition, draining the suspension through a wire to form a wet leaf and dry the leaf. Flocculation is generally caused by the use of a natural or synthetic polymeric retention aid and reflocculation is generally caused by the use of an aqueous suspension of bentonite or other anionic microparticle material. It is known to include starch in the final sheet in order to improve the resistance. A conventional treatment comprises applying a starch solution cooked in substantially complete form to the sheet before final drying. It is also known to apply parsial or totally uncooked starch in this position and cook it during drying. It is also known to include starch substantially not cooked in the aqueous suspension before draining, for example as a result of being added with the polymeric retention aid and with the aqueous re-flocculation composition. The substantially uncooked starch may have been lightly stitched in order to facilitate its final cooking, but most or all of the cooking is conducted during the drying step, thereby converting the substantially uncooked starch into substantially fully cooked starch in the final sheet. In the invention, starch cooked in substantially complete form is added to the suspension after the suspension has flocculated, and preferably after the flocculated suspension has sheared. Preferably, the aqueous reflocculation composition comprises the partially cooked starch, the aqueous reflocculation composition preferably comprises an aqueous dispersion of anionic microparticulate material. The starch cooked in substantially complete form and then the stitched starch and the anionic microparticle material can be mixed to form the final dispersion containing both. For example, the starch can be cooked and then mixed with an aqueous dispersion of the microparticulate material. Preferably, however, the reflocculation composition is made by substantially mixing starch not cooked with an aqueous dispersion of the microparticle material and boiling the starch in that dispersion. If necessary or convenient, the resulting dispersion can then be diluted with water. It seems that cooking the starch in the presence of the microparticle material generates a particularly convenient structure with the re-circulation composition. Preferred anionic particulate materials are turpentine clays such as silica, colloidal silicic acid and colloidal silicas, polysilicate and polysilic acid microgels and modified aluminum versions thereof and organic microparticles, for example as described in O95 / 33096. Another reflocculation composition that can be employed is an aqueous solution of a polymer that is generally counter-ionic to the polymeric retention aid that is used to cause the initial flocculation of the slurry of thin cellulosic material, and in particular can be a material as described in WO98 / 29604. The starch can be fully cooked before draining, and preferably before addition to the slurry of the aqueous thin cellulosic material, whereby it is intended that the starch granules must have burst and been gelatinized substantially completely. Naturally it is usual and necessary to keep the starch under some degree of agitation under cooking, as is conventional. Preferably, uncooked starch is substantially included in the suspension that is discharged and thus it is not necessary to resort to boiling the starch during the drying of the sheet. The starches that may be employed may be any of the conventional starches such as cationic, anionic or amphoteric starches and may be derived eg from corn, wheat, potato or tapioca or may be recovered starch. In another embodiment of the invention, the aqueous reflocculation composition may contain, as its essential component, simply cooked starch that is sufficiently counterionic to the sheared cellulose fibers to act as a reflocculation composition. In practice, the cooked starch that best meets this requirement is usually an amphoteric cooked starch. Accordingly, the invention also provides a novel paper production process wherein reflocculation of the sheared suspension is achieved simply by adding a cooked amphoteric or other suitable starch without the usual anionic microparticle material. These processes give satisfactory retention and drainage properties despite the absence of the material in microparticles All the processes of the invention give improved strength, for example as indicated by the burst resistance. The amount of starch to be added will be chosen considering the degree of resistance that is required and considering the other components in the suspension. In general, it is at least 0.5 and usually at least 1% by weight and can be as much as 10 or 15%, based on the dry weight of the thin cellulosic material. The polymeric retention aid that is used may be cationic starch but in general it is a synthetic polymer. The synthetic polymer may comprise a combination of low and high molecular weight polymers, as is known, but in general the final polymeric retention aid which is added is a synthetic polymer having intrinsic viscosity of at least 4 dl / g. The synthetic polymer may be non-ionic, anionic, or cationic, but is usually cationic. Preferably, the retention aid is a synthetic cationic polymer of intrinsic viscosity, of at least 4 dl / g. Typically, the cationic polymers may be copolymers of asrilamide, for example diallyldimethyl ammonium chloride or dialkylamino alkyl (meth) -acrylate or acrylamide polymers (usually as quaternary ammonium salt or acid addition salt). Suitable materials are described, for example, in WO95 / 33096 and in the documents to which it refers. Finally, reference should be made to those documents for a description of process steps and suitable cellulose materials. The process can be used to generate any weight of paper, including cartonboard and in such a way that they can be of low or high weight. The invention is of particular value in materials of relatively low weight, since it is in these materials that it may be difficult to achieve adequate costing of the uncooked starch during the drying step. In this way, for example, the invention is of particular value in the production of sheets of less than 150 grams per square meter, but it can also be applied to sheets or cartons of higher weight. Chelating agent may be incorporated in the reflocculation composition and / or in the aqueous phase in which the starch is to be sewn, if the water is hard. The following examples illustrate the invention: Example 1 110 grams per square meter of test sheet is prepared by flocculating thin cellulosic material with water-soluble cationic polymer of higher molecular weight derived from acrylamide and cationic monomer in conventional manner followed by shearing followed by the addition of an aqueous reflocculation composition.

The burst strength (in KPA) depends on the reflocculation composition. In a series of experiments, the reflocculation composition consists of an aqueous dispersion of bentonite alone or with anionic potato starch. The bursting resistance when bentonite was used alone was 299 KPA. The bursting resistance when cooking the anionic potato starch in the bentonite dispersion was 352 and the burst strength when the anionic starch is cooked and added after being sheared but before the bentonite was 322. Example 2 1 is repeated and the reflocculation composition is varied. When the bentonite alone was added the resistances to trapping were 169. The bursting resistance when pre-cooked anionic starch was included in the bentonite dispersion was 281. The burst strength when the anionic starch was cooked in the bentonite was 350. The Resistance to burst when the anionic starch was pre-cooked and added after shearing but in the absence of bentonite during the process was 308. When amphoteric starch was included and cooked in the bentonite, the bursting resistance was 271. When cooked amphoteric starch and add after the stage of shearing but without the addition of bentonite at that time or subsequently good retention is obtained and the bursting resistance was 379. In this series of experiments, the amount of starch was 7% based on fibers. Example 3 Free drainage test is carried out on paper raw materials with packing grade derived from waste using a copolymer of acrylamide with dimethylamino ethyl acrylate, quaternary ammonium chloride salt of intrinsic viscosity methyl chloride exceeding 12 dl / g as the retention aid and either bentonite or cooked starch as the reflocculation composition. For each dose, the free drainage is measured in seconds for 100 ml, 200 ml and 300 ml of drainage respectively and illustrated in Table 1. Table 1 As can be seen, tests using cooked starch instead of bentonite gave faster free drainage. Example 4 Dynamic retention tests Britt were carried out on raw materials of paper with packing grade that is derived from waste using a copolymer of acrylamide with dimethyl aminoethyl acrylate, quaternary ammonium salt, methyl chloride of intrinsic viscosity exceeding 12 dl / g as the retention aid and either bentonite or cooked starch as the reflocculation composition. The content of solids in the drained water and the retention were measured for each test and illustrated in Table 2. Table 2 As can be seen from the results, the cooked starch test shows improved retention. Example 5 Example 3 is repeated except that periodical paper material is used derived from 70% wasted ink and 30% mechanical pulp. The following results are shown in the Table 3.

Table 3 The test using cooked starch showed improved drainage times. Example 6 Example 4 is repeated except that a newspaper material derived from 70% waste separated from ink and 30% from mechanical pulp is used. The results are illustrated in Table 4. Table 4 Superior retention is achieved using cooked starch instead of bentonite. EXAMPLE 7 The process of Example 1 is repeated using a thousand coffee at 0.7% and using 750 grams per tonne of an acrylamide copolymer with dimethylaminoethyl acrylate, quaternary ammonium methylchloride salt of intrinsic viscosity exceeding 12 dl / g as the retention aid. Five series of experiments were carried out using as the only reflocculating composition an anionic cooked starch, three types of amphoteric cooked starch and an unmodified cooked potato starch at various doses. The trapping resistance of the formed paper sheets was measured and the results are illustrated in Table 5.

Table 5 For comparison, the procedure was repeated using bentonite instead of the cooked starch. The trapping resistance is illustrated in Table 6. Table 6 As can be seen in the trapping resistance of paper, it was greatly improved when cooked starch is used as the reflocculating composition.

Claims (9)

1. CLAIMS 1. A procedure to produce paper in a paper production machine that. comprises providing a suspension of thin cellulosic material, flocculating the suspension by adding an aqueous solution of a polymeric retention aid selected from natural and synthetic polymers and thus forming a flocculated suspension, shearing the flocculated suspension, reflocculating the sheared suspension when adding a suspension of aqueous reflocculation, discharging the reflocculated suspension through a wire to form a sheet and drying the sheet, characterized in that the starch cooked in substantially complete form is added to the suspension after shearing and before discharge.
2. 2. A process according to claim 1, characterized in that the starch cooked in substantially complete form is added in the aqueous reflocculation composition.
3. 3. A process according to any preceding claim, characterized in that the aqueous reflocculation composition comprises an aqueous dispersion of an anionic microparticle material.
4. 4. A method according to claim 3, characterized in that the composition of Aqueous reflocculation comprises an aqueous dispersion of a turgid clay, colloidal silica, polysilicic acid or polysilicate microgel or aluminum-modified silicates.
5. A method according to claim 3 or claim 4, characterized in that it comprises the step of producing the reflocculated composition by mixing substantially uncooked starch with an aqueous dispersion of the microparticulate material and sewing the starch in that dispersion.
6. 6. A process according to claim 2, sarasterized because the starch is amphoteric.
7. 7. A process according to claim 6, characterized in that the aqueous reflocculation composition is substantially free of anionic microparticle material or synthetic polymeric retention aid.
8. 8. A process according to any of claims 1 to 7, characterized in that the retention aid is chosen from cationic starch and synthetic polymer.
9. 9. A method according to any of claims 1 to 8, characterized in that the retention aid is a cationic polymer synthetic with intrinsic viscosity of at least 4 dl / g.