DE69534985T2 - papermaking - Google Patents

Abstract

Paper strengthened by starch, typically in amounts of 3 to 15% dry weight, is made by flocculating a cellulosic suspension using a polymeric retention aid which can be dissolved cationic starch but is preferably a synthetic polymer having IV above 4dl/g, shearing the resultant flocculated suspension and reflocculating it by adding bentonite or other microparticulate anionic material, draining the flocculated or reflocculated suspension and drying the resultant wet sheet, wherein insoluble particles of starch are added to the suspension as a slurry of substantially freely dispersed particles in part or all of the aqueous solution of the polymeric retention aid.

Description

These The invention relates to the production of paper by Strength was solidified.

In In practice, paper is produced on a papermaking machine, by a thin one Cellulose fiber raw material suspension is provided, the suspension by adding a solution coagulated from polymeric retention aid and thereby a coagulated suspension is formed, the coagulated suspension is drained by a moving screen to form a wet sheet and the bow through a heated one Drying zone transported to form a dry sheet becomes. The retention aid may be dissolved cationic starch is often a synthetic polymeric material. Although the use of polymer with a rather low molecular weight the retention can improve somewhat, the polymer is preferred in high or very high molecular weight, generally with an intrinsic viscosity above 4 dl / g.

A common alternative to this method involves shearing the coagulated suspension so as to decompose the flocs, and then adding an aqueous suspension of a microparticulate anionic material and thus coagulating the suspension, and then dewatering the re-coagulated suspension through the sieve , Such processes, which utilize cationic starch and colloidal silica, are disclosed in US Pat US 4,388,150 and processes utilizing cationic synthetic polymer and bentonite are described in EP-A-235,893. Methods in which glue is added after coagulation with the cationic polymer are described in EP-A-499,448. Processes utilizing other polymers and suspensions suitable for them are described in WO95 / 02088.

Of the thin cellulose fiber raw material is often formed in part from recycled paper containing soluble starch (cationic or anionic or non-ionic), and thus include the thin one Fiber raw material and the final Bow often soluble Strength. For example, the dry bow can be up to 1% strength, the often comes from recycled paper however, strength to the thin one Fiber raw material added.

Thus, water-soluble cationic starch may be added as part or all of the solution of polymeric retention aid (see, for example, U.S. Pat US 4,388,150 ). The amount required for this purpose is usually not more than about 0.3% (dry weight of starch based on the dry weight of paper).

Strength is often desirable added to solidify the paper. For example, become special prefers significant amounts of starch in corrugating and linerboard introduced. These materials are for usually essentially unfilled and by the increase they can do their strength be used as packaging materials. Desirably, significant Amounts of starch also in bows introduced, because the inclusion is more significant Quantities of filler otherwise it would reduce the strength of the bow.

to increase Strength becomes strength preferably introduced in amounts of up to 5 or 10% or even higher, the Attempting to do so, the process will be with regard to Energy consumption and / or the production rate, however, less efficient or can increase the risk of an unacceptable increase in the chemical Oxygen demand of the effluent from the process due to the increased strength in the wastewater cause.

traditionally, are different varieties of starch commercially available and include varieties that are suitable for usually insoluble in the cellulose suspension are. You can either unmodified or chemically modified. In general, the strength presolubilized at a high temperature to increase the strength in the Cellulose suspension soluble close.

If we say in this description, a strength is insoluble, we mean that it is in the cellulose suspension insoluble and remains undissolved in the cellulosic suspension. If we say a strength is soluble, we think she is soluble in the cellulosic suspension.

Soluble cationic starch is quite important for the cellulosic fibers in amounts up to about 1 to 1.5% by weight of the starch, based on the dry weight of the paper. If the amount of cationic starch in the suspension is significantly increased above this, the amount of starch retained in the paper will increase little or no, instead there is only an increase in the amount of solvent cationic starch, which is in the waste water passing through the sieve. This is undesirable because it must be removed prior to discharge as wastewater because of the high chemical oxygen demand it produces in the wastewater from the mill.

The soluble cationic starch can be prepared by chemical modification of starch or only by cooking raw starch and adding a low molecular weight cationic polymer before, during or after cooking. Suitable low molecular weight cationic polymers have an intrinsic viscosity below 1 dl / g. Examples of such systems are in CA 787,294 and US 3,930,877 described.

In practice, when starch is used as a reinforcing aid, often a polymeric retention aid must also be introduced, and there have been many publications on the addition of combinations of materials. For example, in Tappi, June 1976, 59, 6, pages 120-122, the performance of various dual polymer systems is tested, including the performance of a mixture of soluble canonical starch and hydrolyzed polyacrylamide. In CA 1,232,713 For example, up to 1.5% soluble cationic starch is used in combination with polyethylene oxide or cationic, nonionic or anionic polyacrylamide retention aid of molecular weight over 1 million.

In Tappi Journal, February 1984, pages 104 to 108, the effect is various mixtures of soluble cationic starch and polymers tested, and it is noted that cationic Strengthen at 1 wt .-%, the drainage and improve retention, however at higher Levels dehydration detrimental impairs becomes. It is stated that a ideal polymer for a cardboard paper mill at low shear, apparently a low cationic polymer Molecular weight and high charge density, in particular a polyethyleneimine, is.

In the usual commercial practice has been found that when the amount of cationic starch above about 1 or 1.5% increased will, an elevated Risk exists that the cationic starch interfere with the effectiveness of the polymeric retention aid becomes. As a result, you can Retention and drainage deteriorate, causing the machine to work slower or slower the product quality deteriorated.

Should a larger amount in strength introduced as 1 to 1.5% be included the conventional one Technique the application of an unmodified starch solution a size press at the end of the papermaking machine, d. h., after the partial or complete Drying of the bow. The application of a solution of strength at this time can lead to a high intake (for example, up to 7 or 10% are common). She can, however cause that the Strength on the surface stronger is concentrated than in the middle of the bow, and she has the special Disadvantage that the Sheet must be dried again, reducing heat energy consumed and / or the process will be slowed down. It would therefore be desirable, these or higher Levels of strength without unacceptable levels of more soluble Strength in the wastewater and without that Bow must be dried again to reach.

One Another known method for providing significant charges in strength in paper covers the Application of a spray or foam, the undissolved starch particles included, on the wet sheet, before being passed through the dryer, followed by cooking the starch while drying. This method also has the disadvantage that it to produce a higher one Concentrate on strength the surface as in the middle of the bow tends. However, it is particularly disadvantageous that it It is very difficult to get a uniform plot of strength through spray or foam application for longer periods due to the tendency of the starch composition, Blockages in the spray or to produce foam applicators.

In the literature are attempts for the inclusion of insoluble in cold water particulate Strength in the suspension before draining but were unsuccessful.

For example, Fowler reviewed the general techniques for adding starch in Paper, 1978, pages 74 and 93. He discussed the above techniques and also stated that when raw uncooked starch is added to the suspension, followed by the addition of retention aid Only a minimal retention of strength can be achieved. He suggested that better retention could be achieved by slurrying the starch with bentonite and adding it to the suspension prior to the retention aid, and also suggesting that retention be achieved by the inclusion of a polymer having an opposite charge to the charge of the catalyst Retention auxiliary to the slurry further increased who that can.

In US 4,347,100 Brucato teaches that mechanical and thermomechanical digestion processes can be improved by the addition of an anionic surfactant or an anionic polymer during the digestion process. He states that the addition of a cationic polymer causes a reaction with the anionic polymer and the formation of a rubbery precipitate which contributes to strength, and he recommends the addition of a cationic polymer in a stoichiometric amount based on the anionic polymer. It describes a titration technique to obtain the desired stoichiometric amount. It also suggests that the optimum strength can be achieved by the inclusion of non-gelatinized starch which is gelatinized during subsequent heat-drying.

He shows that the Reaction of the cationic and anionic polymers for production a rubbery precipitate carries the starch particles and the Strength withholds in the wood fibers. He says, that the paper raw material then the papermaking machine is fed, where it turns into a bow shaped and heat-dried becomes. This leaves it shut down, that the Strength is added to the pulp or to the thick stock fiber. In all examples, the pulp had a consistency of 2.3 %, Brucato points out, however, that higher consistencies are desirable are. The strengths are all measured on test sheets. He gives none Information about it, whether the process is performed on a papermaking machine can, still like this done can still be the extent of Retention of strength, the can be achieved.

Brucato describes in US 4,609,432 another method for obtaining solidified paper, this time using two different cellulosic suspensions. 90 to 98% of the fiber weight is provided by a first cellulosic suspension, usually ground fibers, and 2 to 10% of the fiber weight is added by the addition of a second cellulosic suspension comprising a heat-sensitive binder (such as uncooked starch) to bind the fibers Polymer for attachment of the binder to the fibers of the second suspension contains, provided to this first suspension. For example, the second suspension may contain the second cellulosic fibers together with 20 to 200% uncooked dry starch and 0.01 to 0.1% cationic polymer. The cationic polymer is intended to coat the starch particles and attach them to the fibers of the second suspension. A typical method uses a first suspension containing 95% of the total fibers and a second suspension containing 5% of the fibers, 0.012% polyethyleneimine and 20% starch. From these, a test sheet was formed and this was then dried, and it was found that the starch is activated during drying. Again, there is no indication of how the process is performed on a machine, nor about retention.

Brucato cites the same list of cationic polymers in both patents, namely polyethyleneimines (which are described in US Pat US 4,609,432 preferred), polyamide polyamine resins, urea-formaldehyde resins, melamine-formaldehyde resins, and polyacrylamides. It appears that Brucato wants to use low molecular weight polymers, since all the polymer classes it mentions, except polyacrylamides, necessarily have a very low molecular weight, and the exemplified polyacrylamide is Separan CP7, a trademark of Dow Chemical Co., and we believe that this material also has a relatively low molecular weight of about 1 million.

In there is no indication of any of the two Brucato patents the existence additional Retention aids should be used.

The stoichiometric reaction to form a precipitate in US 4,347,100 will prevent the cationic polymer from acting as an effective retention aid. The total amount of polyethylenimine used in the examples of US 4,609,432 may be sufficient to cause coagulation of the second suspension, but will be far too low to cause coagulation of the combined suspension. For example, the highest dose exemplified is 0.002% based on total fiber weight.

The Brucato processes therefore require a special interaction between the low molecular weight cationic polymer and other materials in the suspension and do not lead to the production of one coagulated or re-coagulated suspension obtained by use synthetic high molecular weight or cationic polymers Strength optionally followed by an anionic microparticulate material available is.

Desirably are essentially not filled sheets of paper (including Cardboard), which are to be used as packaging, solidified, However, there is also a particular need to use starch as a reinforcing aid in bows to be included, which are filled to a high degree since the use a big one Amount of filler weaken the bow becomes. The filler may be pre-coagulated prior to addition to the cellulosic suspension. Although this brings some advantages, a particular weakening of the Bow caused. Therefore, water-soluble starch is known to be pre-coagulated filler introduced, this leads to but to difficulties in handling the coagulated suspension.

In GB 2,223,038 For example, filler is introduced into a cellulosic suspension by the addition of a slurry of filler insoluble starch particles and coagulant. Although many of the mentioned coagulants have a very low molecular weight (for example, Magnafloc 1597 is polyamine), some have an average molecular weight. A suspending agent such as gum, a synthetic organic polymer or a swelling clay (e.g., bentonite) may be included, and preferably the suspending agent is selected to reduce the net charge in the composition to near zero. For example, when a cationic coagulant is used, an anionic suspending agent is usually required. The amount of filler in the composition is preferably from 30 to 40%, and the amounts of starch and coagulant (based on filler) are preferably from 1 to 5% and from 0.05 to 0.2%, respectively, with the amount of starch in the final paper is typically 0.05 to 1.5%. The resulting coagulated suspension will contain the starch particles entrapped in the filler flakes and added to the cellulosic suspension, which is then dewatered and heated, with the starch subsequently being boiled. In the examples, the amount of filler is in the range of 7 to 24% and the amount of starch is 4% based on the filler, that is, about 0.3 to 1% based on the paper.

Accordingly supplies none of these in detail any practical solution to the problem of providing a cheap one Technology that readily available Strength uses and does not cause unwanted contamination of the sewage leads and which achieves a very high level of starch in the paper can be and which the problems of the glue press application or the spray or foam application to the wet sheet not involved.

As far as we know, the proposals of Fowler, Brucato and in GB 2,223,038 not led to satisfactory methods for producing sheets containing a large amount of starch as a result of the introduction of the total starch into the suspension prior to dewatering. Accordingly, the problem remains that if large amounts of starch are to be introduced, then they must be added to the wet sheet by spraying or foam or size press, and there is still an urgent need to provide a way to introduce starch into the paper to find thin fiber raw material, so as to enable an efficient and environmentally friendly production of paper with a high starch content.

A confirmation for our Assumption that such a method is not known, arises from the fact that according to the priority this application, in Nordic Pulp and Paper Research Journal, Number 4, 1994, pages 237 to 241, it is stated that when starch is granular, it has a diameter from about 1 to 40 μm, the retention of starch granules very is low when directly to the pulp raw material without dissolving or Sources are added in water. According to the proposals in this Articles can large quantities in strength be introduced in laboratory test sheets, by strength with a particulate Flake form caused by precipitation produced in mineral salts and processing of the precipitate was introduced into the cellulosic suspension. It is commercial not desirable to apply this particular procedure and it would be much cheaper, high levels of strength in paper, on a conventional Papermaking machine, using conventional granular Strengthen and without significant wastewater problems due to excessive drainage of strength to get through the sieve.

Accordingly, that is to be solved by this invention Problem providing a method in which it is possible Strength in the thin ones So to introduce fiber raw material, that relative size Amounts of starch in retained the paper can be without significantly affecting the efficient production of the paper and without creating unacceptable wastewater discharges.

• – die Bereitstellung einer dünnen Cellulosefaserrohstoffsuspension,
• – die Koagulation der Suspension durch Zugabe einer wässerigen Lösung aus polymerem Retentionshilfsmittel, ausgewählt aus gelöster kationischer Stärke und synthetischem Polymer mit einer IV (Grenzviskosität) über 4 dl/g unter Bildung einer koagulierten Suspension,
• – die Scherung der koagulierten Suspension und Wiederkoagulation der gescherten Suspension durch Zugabe einer wässerigen Suspension aus einem mikropartikulären anionischen Material unter Bildung einer wiederkoagulierten Suspension,
• – die Entwässerung der koagulierten oder wiederkoagulierten Suspension durch ein sich bewegendes Sieb zur Bildung eines nassen Bogens, und
• – die Leitung des Bogens durch eine erwärmte Trocknungszone unter Bildung eines trockenen Bogens, wobei unlösliche Stärketeilchen zu der Cellulosesuspension als eine Aufschlämmung aus im wesentlichen frei dispergierten Teilchen als ein Teil oder die gesamte wässerige Lösung aus dem polymeren Retentionshilfsmittel zugegeben werden und die unlöslichen Stärketeilchen während der Trocknung erwärmt werden und lösliche Stärke in den Bogen in Gegenwart von Feuchtigkeit freisetzen.

According to the present invention, we provide paper on a papermaking machine by a method according to claim 1, comprising

• The provision of a thin cellulose fiber raw material suspension,
• Coagulation of the suspension by addition of an aqueous solution of polymeric retention aid selected from dissolved cationic starch and synthetic polymer having an IV (intrinsic viscosity) above 4 dl / g to form a coagulated suspension,
• Shearing the coagulated suspension and re-coagulating the sheared suspension by adding an aqueous suspension of a microparticulate anionic material to form a re-coagulated suspension,
• Dewatering the coagulated or re-coagulated suspension by a moving screen to form a wet sheet, and
• Passing the sheet through a heated drying zone to form a dry sheet wherein insoluble starch particles are added to the cellulosic suspension as a slurry of substantially freely dispersed particles as a part or all of the aqueous solution of the polymeric retention aid and the insoluble starch particles during the drying Drying are heated and release soluble starch in the arc in the presence of moisture.

to advancement good retention, it is necessary that the starch particles with the surfaces of the cellulose fibers and, if present, the anionic microparticulate material can interact. Desirably therefore become the starch particles as a slurry from essentially independent Particles were added so that the Particles with the fibers or the microparticulate anionic material in the essentially independent can interact with each other.

The best results are obtained in the invention when the method includes the shear and recoagulation steps described.

In the method of the present invention becomes a good retention of fibers, starch particles (and filler, if available) through the recoagulation stage. The Application of shear on the coagulated suspension containing the cellulose fibers and the starch particles contains leads to Degradation of flakes in the coagulated suspension and redispersion of the previously coagulated material. As a result, all flakes from starch particles, or fibers without starch particles, break up at the shear.

The The consequence of this is that one very uniform distribution of the individual starch particles in the re-coagulated Suspension, and therefore in the dewatered arc, is achieved. As a result of this uniformity, the gelatinization during the Drying performed more efficiently and the distribution of strength in the arc both before The gelatinization as well as after gelatinization can be more uniform be as if the procedure without shear and coagulation carried out becomes.

The slurry can do some filler or contain some fibers. In general, the slurry consists in all processes of the invention essentially only from the polymeric Retention aids and the insoluble starch particles.

The produced paper can be filled and an advantage of the invention is that papers with good strength can be obtained even if they are big Amounts of filler, For example, more than 20 wt .-% or more than 40 wt .-% and even up to 60% by weight, based on the dry weight of the paper, contain. conventional fillers such as calcium carbonate or sulfate or talc or kaolin or other clays can be used.

One Another very important feature of the invention is that they are the Production of unfilled Paper, that is, Paper that conscious little or no filler is admitted, he allows. This essentially unfilled Paper generally has a filler content of no more as 15% by weight, and for usually not more than 10% by weight of the dry sheet. Usually, any introduced filler is derived recycled paper used to form the cellulosic suspension will, if desired, can however small amounts, for example up to 5% by weight or even 10% Wt .-%, based on the dry weight of the suspension, deliberately to the Suspension are added. The invention is therefore particularly for the production of shaft material or linerboard valuable.

One Unique feature of the invention is that we have a high starch content in the dry arch as a result of the inclusion of the undissolved starch in the Can reach cellulosic suspension, without causing pollution problems. So we can easily get a salary of at least 2 or 3 and typically 5 and even up to 10 or 15% by weight of starch obtained in the dry bow.

Preferably, a high retention of the starch particles (eg over 80% or 90% or more) is achieved, and any starch particles that run into the wastewater can be tolerated since they may be insoluble in the waste water and so on subsequent line recycled through the machine and captured can be. Alternatively, they can be removed by filtration prior to discharge.

at the drainage the coagulated suspension, this suspension can be applied to conventional Way (apart from the addition of starch) are formed. For example It can be made of groundwood, mechanical or thermomechanical wood pulp be, and the thin one Fiber raw material, or the thick fiber raw material from which it is formed may, prior to the addition of the retention aid with bentonite have been treated. In such processes, the retention aid is often essentially non-ionic, for example from 0 to 10 mol% of anionic and / or cationic monomers and 90 to 100 mol% of nonionic monomers. However, the invention is in terms of This aspect does not focus on the use of soiled pulps limited and includes the use of any suitable combination of pulp and retention aids (anionic, nonionic or cationic) high molecular weight or dissolved cationic starch retention aid.

In The method of the invention is the coagulated suspension of Sheared so as to decompose the initial flocs, and is then recoagulated or by the addition of an anionic microparticulate material subjected to supercoagulation. The shear can only be considered one Result of a vortex flow from the time the retention aid is added, until the time when the microparticulate material is added, However, the shear is often caused by the passing through a device such as a Zentrisieb, a fan pump or another deliberate shear mixing stage. The shear leads to reduce the size of the flakes, as described for example in EP-A-235,893.

It is important that the starch as a slurry partially or as the whole aqueous solution Retention aids introduced become. Thus, the retention aid can be absorbed or transferred to another Kind on the surfaces the starch particles be attached before the particles with the cellulosic suspension be mixed. By using a retention aid high molecular weight or less preferably cationic dissolved Strength, promotes the absorbed retention aid bridging the starch particles and the cellulose fibers and promotes so the retention.

The Strength can be in the watery solution be pre-slurried from retention aids, in general However, it is sufficient, the insoluble Strength (usually as an aqueous one slurry) and the watery Retention aids mix when flowing to a point at the retention aid is added to the cellulosic suspension becomes. For example, the strength at a point between the polymer additive feed and the point where the solution is added to the cellulosic suspension, injected into the polymer stream become. Often it is sufficient, the starch particles just before the point, where the solution to the cellulosic suspension is added to the solution Mix.

Frequently becomes the strenght initially as a slurry from 10 to 40% by weight, often around 20% by weight, of starch in water and this slurry is added to the polymer solution Added amounts that are required to the selected dose on polymer and starch to obtain. The dry weight ratio of starch: polymer often ranges from 50: 1 to 500: 1. Often the slurry contains 1 to 50% by weight (preferably 10 to 30% by weight) of starch particles and 0.01 to 2 % By weight of polymer.

Although the slurry, which to the thin one Cellulose fiber raw material suspension is added, other materials may contain, the slurry is generally preferred and conveniently in essential only from the polymer and the starch and water. The amount of Polymer is generally well above the amount that, under relative static conditions, a significant coagulation effect on the starch may have. Therefore, if the selected amount of polymer is stepwise to the watery Medium that the selected Amount of strength contains with moderate mixing is admitted initially with mere Eye to be seen a little coagulation, but the further addition of the polymer, accompanied by additional Mixing, however, will cause that the starch are substantially freely dispersed to the extent that they are not stick together as significant flakes. In practice, the Add the slurry out of strength and polymer normally from shear at the time of addition accompanied, and this will continue the independent nature of the particles promote. With regard to the shear that occurs during the addition can, and with regard to the preferred shear of the coagulated Cellulose suspension, the addition of the polymer and the particles follows, the aggregation of the particles is acceptable. Inclusion of starch particles in flakes of filler or fiber in the slurry is undesirable.

It is important that the added polymer be an effective retention aid for the cellulose In order to ensure that the polymer absorbed on the starch particles has adequate substantivity to the cellulose fibers in the suspension. The selection of a suitable retention aid substantive to the cellulosic suspension can be made in a conventional manner. It may be anionic, nonionic or cationic. The best results are usually obtained when the retention aid is cationic, and thus the suspension is preferably one to which the selected cationic retention aid is substantive.

The Strength is for usually and preferably as a slurry with all the retention aid necessary for the coagulation of the suspension is to be used, if appropriate before shearing and restocking, added, but as needed, the slurry can only with a part, for example at least 5% by weight and often at least 25% by weight, typically up to 50 or 75% by weight of the total amount of retention aid be added. If the retention aid is partially mixed with particulate Strength and partly free of starch admitted, can different retention aids of high molecular weight for the two additions, provided they are compatible, or it can be the same material for every addition can be used.

The Low molecular weight coagulator polymer may, if necessary, in an earlier Stage are added in a known manner, but this will not as a retention aid in the context of the present Considered invention.

Such Coagulator polymers have for usually an intrinsic viscosity below 3 dl / g and often below 1 dl / g. You can get a high cationic Charge density, preferably over 4, and often over 5, m Val / g. The low molecular weight polymer is preferably formed from repeating units, of which at least 70%, and generally at least 90%, are cationic. preferred Polymers are homopolymers of diallyldimethylammonium chloride and Low molecular weight copolymers thereof with a low molecular weight Quantity (for usually below 30% and preferably below 10%) acrylamide, homopolymers with low molecular weight of dialkylaminoalkyl (meth) acrylamide or acrylate quaternary salt or -Säureadditionssalz and copolymers thereof with small amounts (generally below 30 % and preferably less than 10%) acrylamide, polyethyleneimines, polyamines, Epichlorohydrin diamine condensation products, dicyandiamide polymers and other conventional ones low molecular weight cationic coagulator polymers.

The Retention aid with which the particulate starch is mixed prior to addition to the cellulosic suspension can be soluble cationic starch and therefore the system can be made from insoluble starch particles (usually chemical unmodified insoluble Starch) slurried in a solution cationic starch, be. In general, however, the retention aid is preferred a synthetic polymer.

The preferred retention aids for use in the invention are polymers having an intrinsic viscosity above 4 dl / g and usually above 6 dl / g, for example 8-15 dl / g or 8-20 dl / g or higher exhibit.

In In this description, the intrinsic viscosity is buffered at 25 ° C in 1M sodium chloride measured at pH 7 using a suspended particle viscometer.

Nonionic Retention aids that can be used include polyacrylamide or other polymers of water-soluble ethylenically unsaturated Monomer or a monomer mixture and polyethylene oxide.

suitable Anionic retention aids are polymers of anionic ethylenic unsaturated sulfone or carboxylic acid monomer like acrylic acid (usually as a sodium or other water-soluble salt), optionally copolymerized with nonionic ethylenically unsaturated Monomer such as acrylamide. Therefore, the anionic polymer may be, for example from 3 to 50 mol%, often 3 to 20 mol%, of anionic monomer such as sodium acrylate, with the remainder being acrylamide.

amphoteric Polymers containing both anionic and cationic monomer units included, usually with Acrylamide or other non-ionic monomer may be used become.

cationic Polymers are preferred.

The or each high molecular weight cationic polymer is usually a copolymer of an ethylenically unsaturated cationic monomer, the remainder being another water soluble, generally nonionic, ethylenically unsaturated monomer such as acrylamide. The amount of cationic monomer is usually at least 2 or 3 mol%. In general, it is not more than 20 mol%, but may be up to 50 mol% or more. The polymer may be completely water soluble or may be in the form of small particles of a partially soluble, crosslinked polymer as described in EP-A-202,780.

The or any high cationic polymeric retention aid Molecular weight typically has a theoretical cationic Charge density of not more than about 3 mV / g, often not more as about 2 m Val / g. In general, it is at least about 0.1 or for usually at least about 0.5 mVg / g. In this description, the theoretical cal is cationic charge density is the charge density determined by the calculation from the monomeric composition used to form the polymer should be used.

suitable cationic monomers include dialkylaminoalkyl (meth) acrylates and acrylamides as acid addition or quaternary Salts. The alkyl groups can 1-4 carbon atoms and the aminoalkyl group may contain 1-8 carbon atoms. Particularly preferred are dialkylaminoethyl (meth) acrylates or acrylamides and dialkylamino-1,3-propyl (meth) acrylamides.

Although the retention aid for usually preferably has an intrinsic viscosity above 8 dl / g it can, in some cases desirable be a copolymer of diallyldimethylammonium chloride and acrylamide, the an intrinsic viscosity of at least 4 dl / g has to be used as a retention aid, although this is for producing such a polymer having an IV of 8 dl / g and higher Values for other polymers are preferred, will not be practical.

The Total amount of polymeric retention aid is usually 0.01 to 1%, generally 0.02 to 0.1% (200 to 1,000 grams per Ton of dry weight of the suspension). If the procedure is shearing and coagulation with a microparticulate material comprises the amount of retention aid is generally within the range from 0.01 to 0.06% or 0.1%, if the method only with Coagulation, followed by drainage, this means, is performed without shearing and coagulation, the amount is usually in the Range from 0.04 to 0.15%, often 0.06 to 0.1%.

The Quantity hangs among other things of the choice of the thin Cellulose fiber raw material from. This one can be cheap Fiber mass or a mixture of fiber masses are formed. Of the thin fiber raw material typically has a cellulose fiber content of 0.2 to 2.0% by weight, usually 0.3 to 1.5% by weight.

The Retention aids with an IV above 4 dl / g (or cationic Strength) and the amount with which it is used in the process must be like that that one good retention of the fiber fine particles and of the filler (if present) is reached. The selection of the retention aid and its Quantity can be on conventional Way done by using the method in the absence of starch with different amounts of different retention aids carried out is an effective combination of retention aids and his amount for to select the particular cellulase suspension being treated. Naturally, should this test with the subsequent Adding a microparticulate anionic material if the whole process is the use of this material includes. includes the starting cellulase suspension anionic waste, the suspension can be initially desirably treated with a cationic coagulator and / or bentonite, so the amount of polymeric retention aid required is to decrease.

The amount of retention aid will always be greater than the amount required to precipitate or interact with the anionic soluble material in the cellulosic suspension. If the retention performance is plotted against the dose of polymer in a typical combination, it will be appreciated that as the dose increases, the retention will be weak and only gradually increase by small values, but will then increase significantly over a relatively small dose range , and then will not continue to rise to a significant extent. The dose at which retention significantly improves is an indication of the need for this suspension for the retention aid and in the invention the total amount of retention aid should be at or above the level at which retention has increased significantly. Accordingly, this amount is above the stoichiometric amount required for reaction with any anionic polymeric material in the cellulosic suspension and any pulp from which it is formed. In general, without the deliberate addition of anionic, poly made of other materials.

If we say that Cellulose suspension is coagulated, we mean that they are in a condition exists for a cellulase suspension containing an effective retention aid treated with high molecular weight in an effective amount, typical.

In preferred method is the retention system (using a high IV or dissolved cationic starch polymer) Retention, drainage and drying properties are selected in a conventional manner and optimized, and the particular Strength is in the polymer solution without significant change of the optimal retention system.

The Strength in the particle must be before Start of drainage remain substantially undissolved in the suspension, otherwise the dissolved Strength expected to run out of suspension. A simple way to determine whether the particles have remained essentially unresolved or not, is the titration of leachate in terms of dissolved starch. is the amount of dissolved Strength in the leachate sufficiently low (after any dissolved starch with Fibers, such as recycled paper, are introduced could), this is an indication that the particles are essentially unsolved remained. The amount of dissolved Strength in the leachate, for example, preferably less than 20%, preferably less than 10%, and most preferably less than 5% of the amount of particulate Strength in the suspension after soluble starch, which comes from elsewhere, was deducted.

One Way, that ensures that the Particles before drainage essentially unresolved stay is the introduction the strength in non-gelatinised, substantially water-insoluble Form and maintaining the conditions in the suspension, so that before Start of drainage no significant gelatinization occurs. In such a procedure must the Strength while the drainage and drying stages are gelatinized.

In usual Procedure is drainage at temperatures above Environment, and drying is done using Heat performed. By the right choice of drainage and drying conditions and the type of non-gelatinised Strength can while the drying step a suitable gelatinization can be achieved while the bow is still wet. Desirably, the conscious warming The wet bow will be applied even before the final drainage is finished to him so before entering the drying stages preheat. For example, the wet sheet can be placed under a fume hood or a heating element such as a Devroniser (brand name), and this can be the complete one Gelatinization and dissolution of strength.

Of the Scherakt the coagulated suspension before re-coagulation is inevitably for breaking up any flakes or aggregates of starch particles to lead, and so this preferred method will lead to starch particles which more evenly the arc are distributed as individual particles. As a result, will a more thorough Gelatinization of these particles take place as if clusters out Particles are present in the arc, and this is an important one Advantage of the preferred methods of the invention, the shear and Coagulation of the coagulated suspension.

The starch have to be gelatinized while there is still moisture in the arch, so that the gelatinization proceeds satisfactorily, and thus the particles so spread in the bow, that in the Unlike just point bonds, a movie is created in the sheet. As a result of starch gelatinization in the presence of moisture, it will migrate between the fibers, so that one more even distribution of Strength on, around and between the paper fibers is obtained. The amount of Moisture that should remain in the bow when the starch is dissolved, can be quite small, and must be sufficient only to the Migration of the gelatinized starch to enable with it an adequate one Distribution of strength obtained by the bow.

to Easier implementation of rapid gelatinization may desirably used a starch which are naturally gelatinized at low temperature or in terms of reducing their gelatinization temperature has been modified, provided it remains before drainage essentially unresolved.

Usually is the strenght an uncooked, raw starch such as raw corn, potato, cereal, wheat or tapioca starch.

swellable or precooked (and therefore soluble) Strength can be considered insoluble Particles introduced become. Therefore, one can count on the insolubility of not gelatinized starch and the subsequent cooking, that while the procedure is instructed, the resolution precooked Strength in the particles of the suspension by the protection of the starch with a water-impermeable Shell or Matrix, which is during the subsequent drainage and drying dissolves, be prevented. Any material that is sufficiently water-insoluble can around the significant resolution the strength before draining to be used, provided the shell or Matrix will dissolve, about the strength during the drainage and / or drying.

The Shell or Matrix did not measure permanently impermeable to water be. For example, a slow dissolving shell or matrix may be used for protection the strength suffice, since even if the cover is partially in the headbox dissolves, the time it takes the trapped starch particles to to dissolve in the headbox, still not enough.

The Shell or Matrix may be a thermoplastic material with such Melting point be that one premature dissolution the shell or matrix is prevented. For example, the normal temperature is the suspension, which is led to the headbox, typically in Range from 40 to 50 ° C and the ambient temperature around the dewatering screen is typically in the same area. Are the particles with a coating or Matrix provided, which has a melting temperature at or above the Headbox temperature is substantially up to the headbox no melting occurs, and most of the melting and essentially the entire resolution the strength will not occur until the drainage is largely completed. Suitable thermoplastic materials that may be used include Hydrocarbon waxes.

Instead of the use of a thermoplastic shell or matrix may be a pH sensitive shell or Matrix can be used. For example, the cooked starch of a polymer that is insoluble in water and at the pH of the starch dispersion, the mill supplied is not swellable, enclosed or otherwise protected, and this dispersion is added to the headbox which has a pH the polymer swells or dissolves added. For example the protective polymer may be a copolymer of water-soluble and water-insoluble, ethylenically unsaturated Monomers such as methacrylic acid or another water-soluble Monomer and ethyl acrylate or another water-insoluble Be monomer. The preparation of pH-sensitive polymers of this general Art by oil-in-water emulsion polymerization is well known.

method for the introduction of an active agent in particles of a protective matrix or in a shell generally known and can used in the invention. For example, the mixture out of strength and the protective material spray-dried or a coacervate coating can be added to the starch particles be formed.

The Amount of strength, which introduced into the bow will normally be at least 0.05% and usually at least 0.2% dry weight be. The biggest advantages of the process are achieved when the amount is over 2 or 3 wt%, for example 5 wt .-%, 10 wt .-% or even up to 12 or 15 wt .-% is. One Advantage of the method of the invention, however, is that the method either at high starch loadings or small starch loadings can work only by changing the amount of strength without significant change in the rest of the procedure.

The Size of the particles is generally at least 90 wt .-% below 100 microns, preferably less than 50 μm, often 5 to 50 microns. 90% by weight of the starch particles can a size of at least up to 10 μm, generally 5-10 microns have. The strenght is preferably granular, so that everyone three dimensions are largely similar are.

The anionic microparticulate or colloidal material (if used) is preferably bentonite, that is, an inorganic swelling clay, as described, for example, in EP-A-235,893. However, colloidal silica (as in US 4,643,801 polysilicate microgel (as described in EP-A-359,552), polysilicic acid microgel as described in EP-A-348,366, or aluminum modified versions of each of these. Instead of an inorganic anionic colloid material, an organic material may be used. Thus, an anionic organic polymeric emulsion can be used. The emulsified polymer particles may be insoluble because they are formed from a copolymer of, for example, a water-soluble anionic polymer and one or more insoluble monomers such as ethyl acrylate, but preferably the polymeric emulsion is a crosslinked microemulsion of a water-soluble mo nomeren material. The particle size of the colloidal material is generally less than 2 microns, preferably less than 1 micron, and most preferably less than 0.1 microns.

The Amount of colloidal material (dry weight, based on dry weight the cellulosic suspension) generally at least 0.03% and usually at least 0.1%. she may for example be up to 2%, but is generally below 1%. The choice and amount of anionic colloidal material should be like that, what often referred to as "super coagulation", brought becomes.

The anionic microparticulate or colloidal material is preferred to the suspension after the last one Point high shear, for example, the headbox, added, and the suspension may then be dewatered in a conventional manner.

The initial Selection of suitable materials may be based on experiments with conventional lab equipment like a Britt vessel and the Prüfbogentechnik However, commercial operation of the process will occur a papermaking machine in which the thin cellulosic fiber raw material in conventional Way, in general by dilution of a thick fiber raw material with sewage, and provided to a headbox by a suitable device like a fan pump and a Zentrisieb transferred and is discharged from the headbox onto a moving screen.

This Sieve can be conventional Screen speeds run normally over 100 meters per minute and typically in the range of 700 to 1500 meters per minute.

The Machine will include a drying zone in a conventional manner Advantage of the invention, however, is that the machine is not with a Size press or with any other device for applying the Strength be equipped on the wet sheet or the dried bow got to.

ever however, additional may be required Strength on the wet sheet or the dried bow on conventional Way to be applied.

following are examples.

example 1

One Milling trial was underway on a Fourdrinier machine a shaft material at 600 m / min of 100% waste paper raw material carried out. A cationic polymer of acrylamide with 10 mol% cationic Acrylate, IV 12 dl / g, became the thin one Fiber raw material in front of the centrifuge at a dosage level of 800 g / ton added. A 20% raw starch slurry was added just before the addition of the polymer to the thin fiber stock in sufficient Quantities, so 5% starch, based on the dry weight of paper, supplied to the polymer line. Bentonite became the thin one Fibrous raw material after the centric sieve and just before the headbox added at a dosage level of 0.5%.

The Analysis of strength, which remained in the sheet showed that over 95% of the added starch in the Retained bow were. The warming while The drying stages of the machine caused the starch to gel during drying has been.

Example 2

linerboard weighing in at about 140 grams per square foot was up a Fourdrinier machine produced in a process that has a aqueous solution of a polymer of acrylamide with 10 mol% dimethylaminoethyl acrylate quaternary salt [DMAEAq], with an IV of 12 dl / g, at a dosage of 850 g / tonne in the top layer and 790 g / ton in the bottom layer, before the Centrifuge added and bentonite at a dosage of 5 kg / t in both the upper and lower layers, added after Zentrisieb, uses. The suspension contained recycled paper and the starch content in the bow, without conscious Adding starch, fluctuated between about 0.9 and 1.2%.

Partly raw potato starch was then used as a slurry into the polymer feed line at a dosage of 1.42%, based on the dry weight of the suspension, injected. When operational conditions were produced, the amount was in strength in the arc 2.49%, which is the substantially complete retention the particular Strength displays.

If the amount of particulate Strength increased in the suspension to 3.11% was, the amount in the arc rose to 4.34%, and when the amount in the suspension rose to 3.50%, the amount increased in the arc to 4.55%, which in turn gives essentially complete retention indicated.

The Burst strength was increased by about 35% and the CMT value increased by about 20%.

Example 3

to execution a preliminary screening of suitable combinations of materials was a waste paper raw material from 60% newsprint, 30% cardboard and 10% magazines made and in a laboratory disintegrator Digested for 20 minutes and then diluted to a 0.5% thin fiber stock suspension at 25 ° C to build. It was allowed to stand for conditioning for 24 hours. It had a pH of 7.5 to 7.7.

500 ml thinner Fibrous raw materials were placed in a Britt Dynamic Drainage vessel, that with a paper machine screen with a stirrer setting of 1500 rev / min Is provided. The required amount of a 20% starch slurry became mixed with the required amount of a 0.5% solution of polymer and placed in the drainage vessel. After stirring for 60 Seconds at 1500 rpm, the stirrer was slowed to 800 rpm and the required amount of the bentonite slurry was added. To Mixing for 10 seconds, the white water was collected for 30 seconds.

The collected white water was boiled at 100 ° C for 30 minutes, the volume to the original one Volume reset and centrifuging the sample to remove the fibers. An acidified potassium iodide / iodine reagent was added and the blue starch / iodine complex was optically evaluated and compared to a calibration graph, an ad for the starch content of the water. Due to the special analysis techniques, which were used, the values show relative values rather than absolute values Values on, but an increase in value indicates increased retention at.

In a first series of tests was polymer (acrylamide with 10 mol% Dimethylaminoethylacrylatquartärsalz, IV 12 dl / g) at 750 grams per tonne fiber, bentonite at 2,000 grams per ton of fiber and starch with 80 kg per ton of fiber (8%) added. It became the following Results obtained.

These Results indicate that the best results are obtained when the starch is mixed with the polymer is (followed by bentonite). A useful retention will also obtained when the polymer is added separately, and the starch with Bentonite is added. The addition of starch alone, before or after Polymer, leads to bad results.

Example 4

It a procedure was repeated as far as possible in Example 3, in which the retention (measured as in Example 3) at 4%, 6% and 8% strength when no polymer and bentonite (control) were present is, or if the strength with 750 g / t polymer, followed by 2,000 g / t bentonite is added.

The Amount of added starch, based on the volume of the suspension at the levels of 4%, 6% and 8%, based on the weight of fiber, was 200, 300 or 400 ppm.

Example 5

It a procedure was described as much as in example 3, used, except that in the three carried out Tests, the polymer without anionic microparticulate material use, the strength with the polymer solution the drainage vessel with a stirrer setting of 800 rpm and after mixing for 10 seconds the white water for 30 seconds was collected. The starch retention was as in Example 3 measured.

The results were as follows:

These Results clearly show the enormously improved retention, the obtainable using a cationic polymer of high IV, compared to low molecular weight cationic polymers. They also show that good Results using polysilicic acid as the anionic microparticulate material can be obtained but the direct comparison between the two tests with the cationic Polyacrylamide is due to different conditions, the for this Tests have been used, not entirely reliable.

Claims (12)

A process for making paper on a papermaking machine comprising - providing a thin cellulosic fiber stock suspension, - coagulating the suspension by adding an aqueous solution of polymeric retention aid selected from dissolved cationic starch and IV synthetic polymer over 4 dl / g to form a coagulated suspension; shearing of the coagulated suspension and re-coagulation of the sheared suspension by adding an aqueous suspension of a microparticulate anionic material to form a recoagulated suspension; dewatering the coagulated or coagulated suspension by a moving screen to form a wet sheet; Passing the sheet through a heated drying zone to form a dry sheet, insoluble starch particles becoming substantially free of the cellulosic suspension as a slurry dispersed particles as a part or all of the aqueous solution of the polymeric retention aid are added and the insoluble starch particles are heated during drying and release soluble starch into the sheet in the presence of moisture. The method of claim 1, wherein the anionic microparticulate material inorganic swelling clays, colloidal silica, polysilicate microgels, Polykieselsäuremikrogelen and aluminum-modified colloidal silica, aluminum-modified Polysilicate microgel and aluminum-modified polysilicic acid microgel selected is. A method according to claim 1 or claim 2, wherein the paper filled Paper is. A method according to claim 1 or claim 2, wherein the paper is essentially unfilled paper. A method according to any one of the preceding claims, wherein the strenght in the particles is not gelatinized, so that before draining essentially no resolution the strength in the suspension occurs, and the strength during drainage or drying is gelatinized. A method according to any one of the preceding claims, wherein the retention aid comprises a synthetic polymeric material an intrinsic viscosity of at least 4 dl / g. A method according to any one of the preceding claims, wherein the retention aid comprises a synthetic polymeric material an intrinsic viscosity of at least 8 dl / g. A method according to any one of the preceding claims, wherein the polymeric retention aid is cationic. A method according to any one of the preceding claims, wherein the insoluble Particles of strength as a slurry in a solution from essentially the entire polymeric retention aid are given. Method according to one of claims 1 to 3 or one of claims 5 to 9, wherein the sheet contains 20 to 60 wt .-% filler. A method according to claim 1 or claim 2, or one of the claims 4 to 9, wherein the sheet is a substantially unfilled bow which is a shaft material or linerboard. A method according to any one of the preceding claims, wherein the amount of strength in the bow is 2 to 15%.