Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
  • D21H23/02—Processes or apparatus for adding material to the pulp or to the paper characterised by the manner in which substances are added
  • D21H23/04—Addition to the pulp; After-treatment of added substances in the pulp
  • D21H23/06—Controlling the addition
  • D21H23/14—Controlling the addition by selecting point of addition or time of contact between components
  • D21H23/16—Addition before or during pulp beating or refining
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/33—Synthetic macromolecular compounds
  • D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H17/41—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups
  • D21H17/44—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups cationic
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/33—Synthetic macromolecular compounds
  • D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H17/41—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups
  • D21H17/44—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups cationic
  • D21H17/45—Nitrogen-containing groups
  • D21H17/455—Nitrogen-containing groups comprising tertiary amine or being at least partially quaternised
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/06—Paper forming aids
  • D21H21/10—Retention agents or drainage improvers

Definitions

• Paper and paper board is made by draining an aqueous cellulosic suspension through a screen to form a sheet, and drying the sheet.
• the suspension may be substantially free of filler or may contain substantial amounts of filler.
• Optimum retention occurs when the amount of fibre fines and filler that drains through the screen is minimum.
• Optimum formation occurs when the paper and paper board is of uniform density and thickness both on a macro scale (e.g., across the width of the sheet) and on a micro scale (e.g., at any particular point).
• Optimum drainage occurs when the water of the suspension drains through the screen very quickly.
• Optimum drainage generally occurs when the paper or paper board has a very open structure and so frequently is associated with poor retention and formation.
• water soluble polymeric material In order to modify these properties it is standard practice to include water soluble polymeric material and, depending upon the material that is chosen, an appropriate balance of properties is achieved. For most purposes a relatively high molecular weight polymer is included and this has the effect of causing flocculation of the fibres, and any filler, that is present.
• flocs are very large then although retention and drainage may be good, formation tends to be poor. If the flocs are small then formation is much better, but the other properties may be adversely affected.
• EP-A-O2O278O we describe how reverse phase dispersion polymers that are slightly cross linked can have beneficial effects on floc size and floc strength but this is not directly relevant to the problem we are now confronting, particularly since the use of slightly insolubilised polymers would generally be severely contra indicated.
• a normal standard for polymeric retention aids is that they must be very highly soluble, for fear of leaving insoluble residues on the paper or paper board.
• EP-A-O235893 we describe a particular process in which polymer is added at an early stage in the process, the resultant suspension is then sheared, and bentonite is then added prior to drainage (generally without subsequent shearing). Although this process is very successful it does require the late addition of bentonite. This intermediate shearing of the flocs is an unusual process but the subsequent addition of bentonite then has the effect of converting the sheared flocs into what can be regarded as a very large flocculated structure. Again it is preferred that this final structure should be left substantially undisrupted.
• the cationic retention aids should have an intrinsic viscosity of 12 to 25dl/g. This has not proved to be normal experience and we are unaware of such materials ever having been commercialised.
• a difficulty with cationic polymeric retention aids is that the solubility of the polymer tends to deteriorate as the molecular weight increases and certainly the polymer technology in 1975 could not have produced a solid grade (reverse phase dispersion or powder) retention aid having intrinsic viscosity of 25 and which had adequate solubility.
• the screen of a paper-making machine is travelling as the cellulosic suspension flows, or is forced, on to it. Until recently, the maximum screen speed was up to about 8OO metres per minute. The contact of the suspension with this screen causes substantial acceleration to the suspension and this in turn applies shear to the suspension.
• the cationic retention aids having intrinsic viscosity of up to 7 to 1Odl/g give satisfactory flocs under these conditions.
• paper or paper board is made by drainage through a screen of an aqueous cellulosic suspension containing a water soluble cationic polymeric retention aid formed from water soluble ethylenically unsaturated monomer or monomer blend, and in this process the polymeric retention aid has intrinsic viscosity of at least about 12dl/g, the formation of the paper or paper board is improved without substantial deterioration in retention by subjecting the suspension to shear before or during drainage and the polymer is introduced into the suspension as a solution that has been made by dissolving in water a powdered or reverse phase suspension of the polymer that has a solubility, as defined below, of less than 25 lumps per gram, preferably less than 5 lumps per gram.
• a solubility as defined below
• solubility defined herein is an indication that the polymer is a true solution and will not leave any unwanted polymeric deposits on the paper or paper board.
• the test is carried out as follows: 1g polymer is weighed out into a screw top jar. 5ml acetone is added to wet out the polymer. 95ml de-ionised water is added to the jar and the closed jar is shaken on a laboratory shaker for 2 hours to ensure maximum dissolution. A 150 ⁇ m stainless steel sieve is wetted out and the polymer solution is poured onto the sieve. The jar is rinsed once with water which is poured through the sieve. The sieve is gently washed with cold running water to remove excess polymer solution until the back of the sieve is no longer slimy. The back of the sieve is dabbed dry with a paper towel and the number of lumps of polymer retained in the sieve is counted. The total number of lumps gives the solubility as defined above, ie it is the number of lumps per 1g dry polymer or of 100g of a 1% solution of polymer.
• the intrinsic viscosity measurements herein are measured by the following technique.
• the specific viscosity of the test polymer is measured at four different low concentrations (in the range 0.02-0.08% by weight) in 1M buffered sodium chloride solution using a suspended level viscometer at a temperature of 25°C.
• the value of the reduced viscosity which is the specific viscosity divided by the polymer concentration, is plotted against the concentration, which at the low concentrations gives a straight line which intercepts the y-axis to give the reduced viscosity at infinite dilution, which is the intrinsic viscosity, reported in units dl/g.
• the invention is based in part on the surprising discovery that good formation and good retention are easily obtained upon shearing the very large flocs that are inevitably formed when the retention aid is a very high molecular weight water soluble polymer.
• the molecular weight (expressed as intrinsic viscosity) and the degree of shearing that are required for optimum properties are inter-related in that moderately high molecular weight needs to be associated with moderate degrees of shear and very high molecular weight needs to be associated with higher amounts of shear. If the molecular weight is too low having regard to the amount of shear (or if the amount of shear is too high having regard to the molecular weight) retention (and also drainage) will be poor even though formation may be satisfactory. If the molecular weight is too high having regard to the amount of shear (or if the amount of shear is too low having regard to the molecular weight) formation may be satisfactory but retention will be poor. Thus, within these parameters, it is possible to optimise the molecular weight having regard to the amount of shear that is to be applied or, conversely, it is possible to optimise the amount of shear having regard to the molecular weight.
• the invention is of particular value when some or all of the shear is caused by the very fast speed of travel of the drainage screen on to which the suspension is applied.
• an alternative way of defining the invention is to say that the polymeric retention aid has intrinsic viscosity above about 12dl/g and the suspension containing the retention aid is applied on to a drainage screen that is moving very fast.
• the invention provides a solution to the problem of how to achieve good retention and good formation on the very high speed modern paper making machines where the screen travels at above 8OO and usually above 850 metres per minute.
• the speed is generally above 9OO, most usually above 925, metres per minute.
• satisfactory results can be obtained at screen speeds above 95O, above 975 and even at 1,OOO metres per minute or more, for instance up to 1,O5O and 1,1OO metres per minute or more.
• the polymer preferably has an intrinsic viscosity in the range 13 to 17, often 13 to 16, dl/g, with best results often being obtained at about IV 14 or 15 dl/g.
• higher screen speeds are required then higher molecular weights may be used, e.g., up to IV of 2Odl/g or more.
• the polymer can be added in the headbox with gentle agitation, but, because of the high molecular weight of the polymer, it is now possible to incorporate the polymer under the same mixing conditions as are used for the formation of the thin stock and, in particular, it is no longer necessary to take the usual precautions to avoid shearing the suspension in the headbox or prior to the headbox.
• the polymer can be incorporated into the suspension under shear, eg at a centriscreen or fan pump, and the suspension then drained on a relatively slow screen.
• the retention aid should be water soluble. If the retention aid is not water soluble then the retention effect deteriorates and problems may arise due to the appearance of insoluble polymer on or in the paper or paper board.
• the tendency for insolubility increases as the molecular weight of the retention aid increases (which is another reason why conventional thinking dictates the use of medium to low molecular weight retention aids) due to accidental cross linking, for instance due to impurity amounts of cross linking agent.
• ionic regain As defined in EP-A-O2O278O.
• the ionic regain should be below 1O%, preferably below 5% and most preferably in the region O to 2%.
• the polymeric retention aid may be made by reverse phase emulsion or dispersion polymerisation to provide a dispersion of aqueous (or dehydrated) polymer particles having a size generally below 1O ⁇ m dispersed in non-aqueous liquid, in known manner.
• a dispersion may be converted into polymer solution by mixing it into water, generally in the presence of an oil-in-water emulsifier, in known manner.
• oil-in-water emulsifier in known manner.
• the solid may have been made by reverse phase bead polymerisation (followed by azeotroping and separating the beads from the non-aqueous liquid) or by gel polymerisation followed by drying and comminution in conventional manner.
• the polymer is made from cationic monomers alone or from blends thereof with non-ionic monomers or, if an ampholytic polymer is required, with anionic monomers as well.
• the proportion of non-ionic units may be low, e.g., 5 to 5O% by weight but often the polymer is formed from 1O to 5O% by weight cationic units and 9O to 5O% by weight non-ionic units.
• Suitable cationic monomers are dialkylaminoalkyl (meth) acrylates and dialkylaaminoalkyl (meth) acrylamides.
• the cationic monomers are generally used in the form of their acid addition or, preferably, quaternary ammonium salts.
• non-ionic monomers conventionally incorporated into high molecular weight water soluble polymers can be used, but acrylamide is preferred.
• Any anionic monomers may be ethylenically unsaturated carboxylic acids such as methacrylic acid or, preferably, acrylic acid, or ethylenically unsaturated sulphonic acids such as 2-acrylamido methyl propane sulphonic acid.
• Anionic monomers are generally used in the form of ammonium or alkali metal (generally sodium) salts.
• the retention aids are copolymers of acrylamide with cationic monomer, most preferably a copolymer of 1O to 95% (preferably 5O to 9O%) by weight acrylamide with 9O to 5% (preferably 5O to 1O%) cationic monomer, most preferably dialkylaminoethyl acrylate quaternary ammonium salt (or the corresponding methacrylate compound) wherein the alkyl groups are generally methyl or ethyl.
• Particularly preferred copolymers are formed of about 50 to 80%, often 7O to about 8O%, by weight acrylamide and the balance diethylaminoethyl acrylate or methacrylate quaternary ammonium salt.
• Other preferred copolymers include those wherein the quaternary monomer is 50 to 100% of the monomers and acrylamide is 0 to 50% by weight.
• any of the normal quaternising groups may be used, generally methyl sulphate or methyl chloride.
• the intrinsic viscosity of the polymer is preferably around 14 or 15dl/g or more and the polymer is preferably produced as a powder and is dissolved in water to give a solubility as explained above.
• the high molecular weight soluble polymer is the last paper making additive that is added to the suspension and thus normally bentonite or other significant materials are generally not added after it, although bentonite may be added beforehand if desired, for instance as described in EP-A-17353, or subsequently as in EP-A-235893.
• the suspension may either be substantially unfilled, for instance containing not more than about 15%, and generally not more than about 1O%, inorganic filler or it may be filled, for instance containing more than 15% inorganic filler (based on the dry weight of the suspension). If the suspension has a high cationic demand it is particularly preferred to treat it first with bentonite and then to use a substantially non-ionic high molecular weight retention aid, for instance as described in EP-A-17353.
• the amount of retention aid that is incorporated in the suspension is conventional, for instance in the range 1OO to 1,OOO grams dry polymer per tonne dry weight of suspension, often 2OO to 5OO grams, although higher amounts may be used if desired.
• a low or medium molecular weight polymer before the high molecular weight polymer. Suitable amounts are in the range 50 to 1000g/tonne. Generally the low or medium molecular weight polymer is cationic, and the other polymer may be slightly anionic, nonionic or, preferably, cationic.
• Suitable cationic low to medium molecular weight polymers are formed from the cationic monomers quoted above (often as copolymers with acrylamide), diallyldimethylammonium chloride (often copolymerised with acrylamide), or the polymers may be polyethyleneimines or amine-halohydrin or amine-haloalkane polymers.
• the molecular weight is typically in the range 10000 to 1 million, for instance IV 0.1 to 1dl/g or 2dl/g.
• a medium molecular weight cationic retention aid may be made by conventional gel polymerisation of 75% acrylamide with 25% by weight quaternary salt of diethylaminoethyl acrylate to intrinsic viscosity 7. After drying in conventional manner the product typically has a solubility of less than 1O lumps per 1OO grams of 1% aqueous solution (see above). When the same monomer feed is used under polymerisation conditions that are known to favour higher molecular weights it is possible to obtain intrinsic viscosity of, say, 14 but the solubility is liable to be above 30 lumps per 1OO grams. However when the cationic and acrylamide monomers are purified by conventional purification techniques so as to remove substantially all traces of cross linker, a polymer having intrinsic viscosity of about 14 and giving less than 1O lumps per 1OO grams can easily be obtained.
• Two cationic retentionaids were made by conventional gel polymerisation of 75% acrylamide with 25% by weight quaternary salt of diethylaminoethyl acrylate, A to an intrinsic viscosity of 8 dlg ⁇ 1 and B to an intrinsic viscosity of 13 dlg ⁇ 1. Both polymers had a solubility of less than 10 lumps per 1g (polymer). They were then compared for performance on a commercial paper machine using a bleached kraft-pulp finish to produce the paper grades. Each retention aid was run for 30 days on the machine and yielded the following comparative data averaged for each 30 day period.
• POLYMER INTRINSIC VISCOSITY dl/g POLYMER DOSE g/tonne FIRST PASS RETENTION % MACHINE SPEED m/min A 8.0 440 75.6 805 B 13.0 350 75.7 859

Landscapes

• Paper (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Separation Of Suspended Particles By Flocculating Agents (AREA)

Applications Claiming Priority (2)

Publications (2)

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ID=10635686

Family Applications (1)

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• 1988
  • 1988-04-22 GB GB888809588A patent/GB8809588D0/en active Pending
• 1989
  • 1989-04-21 CA CA 597426 patent/CA1329683C/en not_active Expired - Lifetime
  • 1989-04-24 WO PCT/GB1989/000433 patent/WO1989010447A1/en not_active Application Discontinuation
  • 1989-04-24 JP JP50513189A patent/JPH02504049A/ja active Pending
  • 1989-04-24 EP EP19890905452 patent/EP0366764B1/en not_active Revoked
  • 1989-04-24 DE DE1989610639 patent/DE68910639T2/de not_active Revoked
  • 1989-12-13 FI FI895957A patent/FI95827C/fi active IP Right Grant
  • 1989-12-21 NO NO895166A patent/NO175648C/no unknown

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