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
  • D21H23/08—Controlling the addition by measuring pulp properties, e.g. zeta potential, pH
  • D21H23/10—Controlling the addition by measuring pulp properties, e.g. zeta potential, pH at least two kinds of compounds being added
• • 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
  • D21H21/14—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 characterised by function or properties in or on the paper
  • D21H21/18—Reinforcing agents
  • D21H21/20—Wet strength agents
• • 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
  • D21H17/37—Polymers of unsaturated acids or derivatives thereof, e.g. polyacrylates
  • D21H17/375—Poly(meth)acrylamide
• • 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
  • D21H17/46—Synthetic macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H17/54—Synthetic macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds obtained by reactions forming in the main chain of the macromolecule a linkage containing nitrogen
  • D21H17/55—Polyamides; Polyaminoamides; Polyester-amides

Definitions

• the present invention refers to a method of producing a particle or group of particles intended for use in paper- and/or nonwovenmaking having a coating of at least two, preferably at least three, outside each other located thin layers of cationic and anionic polymers, at which the particle or group of particles is treated in consecutive steps with solutions of the cationic and anionic polymers. It also refers to a paper or nonwoven product containing such particles or groups of particles. It further refers to paper products containing increased amounts of wet strength agent and to tissue paper having improved wet strength.
• Dual surface treatment of filler particles with anionic and cationic polymers is disclosed in EP-A-0 850 879, WO 95/32335, US-A-4,495,245 and US-A-4,925,530. There is no indication that the treatment takes place under such controlled conditions that a double- or multilayer is created on the pulp fibers with the anionic component in one layer and the cationic component in the other layer.
• the object of the present invention is to provide a method according to above and which offers a way to ensure that each polymer for forming the respective layer on the surface of the particles or group of particles is added only in such an amount in each step that substantially all polymer is adsorbed to the particle surface.
• the Z-potential of the particles or groups of particles may be measured.
• the particles or groups of particles may be of optional type, however fibers, e g cellulosic fibers, regenerated fibers and different types of synthetic fibers, and filler particles are mainly concerned.
• the interacting polymers are preferably alternating cationic and anionic polyelectrolytes, but they may also be so called zwitter ions.
• the particles are cellulose fibers for papermaking and at least one of the polymers is a strength additive such as a wet and/or dry strength agent.
• the invention also refers to a paper- or nonwoven product, which contains fibers and/or filler particles produced by the method described above.
• the term paper used herein refers to all types of paper, such as tissue paper, graphical paper, linerboard, wiping material etc.
• the nonwoven material could be of optional type.
• the invention further refers to paper products containing increased amounts of wet strength agent and to tissue paper having improved wet strength.
• Fig. 1 shows the results of Z-potential measurements of cellulose fibres treated in consecutive steps with cationic and anionic polymers in the form of PAE (polyamino- amide-epichlorhydrine) and CMC (carboxy methyl cellulose).
• PAE polyamino- amide-epichlorhydrine
• CMC carbboxy methyl cellulose
• Fig. 2 shows the result of charge measurements of the colloidal phase before and after washing the fibers in the trial of Fig. 1.
• Fig. 3 shows the wet strength tensile index of 30 gsm paper sheets made from the treated fibers vs. adsorbed amount of PAE.
• Fig. 4 shows Z-potential of the fibres after addition of PAE / CMC / PAE.
• Fig. 5 shows the charge of the colloidal phase from PCD measurements after addition of PAE / CMC /PAE.
• Fig. 6 shows the dry tensile strength index vs. adsorbed amount of PAE.
• Fig. 7 shows the wet tensile strength index vs. adsorbed amount of PAE.
• Fig. 8 shows relative wet strength vs. adsorbed amount of PAE.
• particles or groups of particles are treated with alternating cationic and anionic polymers in order to build up thin multilayers of the interacting polymers on the particle surface.
• the particles are treated in consecutive steps with solutions of the alternating cationic and anionic polymers, at which the treatment time for each step is sufficient for forming a layer of the desired molecular thickness.
• the first layer should be a cationic polymer, and vice versa.
• the addition is controlled in such a way that substantially no excess amount of the respective polymer is added in each step, so that substantially all polymer is adsorbed to the particle surface.
• This is made by measuring the electric charge of the treatment solution or the liquid in which the treated particles or groups of particles are contained. After having allowed the polymer to adsorb to the particle surface a certain period of time the electric charge of the solution should be close to zero.
• the charge measurements are made with streaming potential measurement, e g with a PCD instrument (Particle Charge Detector).
• the Z-potential is measured according to the method described below.
• the method according to the invention for building the desired multilayers is based on electrostatic attraction between oppositely charged polyelectrolytes. By treating the particles in consecutive steps with a solution containing polyions of opposite charge and permit these spontaneously to adsorb to the particle surface, multilayers of the stated kind are built up. In principle all types of polyelectrolytes may be used.
• the method is used for adsorbing strength additives to cellulosic fibers used for papermaking.
• the first polymer to be adsorbed is a cationic polymer.
• This layer will make the fibre surface cationically charged.
• an anionic polymer e g CMC (carboxy methyl cellulose)
• the fiber surface will then turn anionic again.
• the next layer of cationic polymer can be added and so on.
• ion-exchanging fibers where "membranes" with ion-exchanging properties are provided on the fiber surface, wet strength agents where the added polymers are reactive with the fibers and with each other, in order to provide permanent bonds between the fibers and for the production of highly swelling surface layers, where the added chemicals form swollen gel structures on the fiber surface for use in absorbent hygiene products.
• Another possible application are new types of fibers for printing paper, where the adsorbed polymers change colour when they are exerted to an electric, magnetic or electromagnetic field. Such polymers are available today.
• the fibers that are treated with the method according to the invention can be of optional kind, natural as well as synthetic fibers. Mainly cellulosic fiber are concerned. However it would be possible to treat synthetic fibers, for example for giving them a more hydrophilic surface.
• Anionic polyelectrolytes Anionic starch with different degrees of substitution, anionic guar, polystyrene sulfonate, carboxy methyl cellulose with different degrees of substitution, anionic galactoglucomannan, polyphosphoric acid, polymethacrylic acid, polyvinyl sulphate, alginate, copolymers of acryl amide and acrylic acid or 2-acrylic amide-2-alkylpropane sulphonic acid.
• Cationic poly electrolyte Cationic galactoglucomannan, cationic guar, cationic starch, polyvinyl amine, polyvinyl pyridine and its N-alkyl derivatives, polyvinyl pyrrolidone, chitosan, alginate, modified polyacryl amides, polydiallyl dialkyl, cationic amide amines, condensation products between dicyane diamides, formaldehyde and an ammonium salt, reaction products between epichlorhydrine, polyepichlorhydrine and ammonia, primary and secondary amines, polymers formed by reaction between ditertiary amines or secondary amines or dihaloalkanes, polyethylene imines and polymers formed by polymerisation of -(dialkylam ⁇ noalkyl)acrylic amide monomers.
• the PAE and G-PAM was diluted in deionized water to an active content of 10 g/1 before use.
• the different CMC's were dissolved in deionized water by dispersion using a hand mixer, to a suitable concentration between 5 and 10 g/1 depending on the viscosity.
• the pulp used was a dried fully bleached TCF, Celeste 85, from SCA Ostrand.
• the pulp was beaten to 25°SR and was diluted with tap water to a concentration of 3 g/1.
• the pH during the trials was 7.5 and the conductivity was set to 1200 ⁇ S/cm using NaCl.
• the Z-potential of the fibres was measured with a streaming potential instrument (Magendans SZ2, supplied by Miitek) [Penniman, J.G., Comparison of pulp pad streaming potential measurement and mobility measurement. Tappi Journal, 1992 75 111-115 and Jaycock, M.J.; Assumptions made in the measurement of zeta-potential by streaming current/potential detectors. Paper Technology, 1995 36 35-38.19, 20; Barron, W., et al., The streaming current detector: a comparison with conventional electrokinetic techniques. Colloids and Surfaces, 1994 88 129-139; Sanders, N.D. and J.H. Schaefer, Comparing papermaking wet-end charge-measuring techniques in kraft and groundwood systems.
• a streaming potential instrument Magneticendans SZ2, supplied by Miitek
• a PCD 03 Particle Charge Detector supplied by Miitek measures a voltage difference induced by a moving charged medium, e.g. colloidal substances in a white water. High molecular mass polymers and colloidal substances attach to the Teflon surfaces of the equipment. The oscillating piston moves and induces a potential difference that is detected [Jaycock, M.J., Assumptions made in the measurement of zeta-potential by streaming current/potential detectors. Paper Technology, 1995 36 35-38 ; Barron, W., et al., The streaming current detector: a comparison with conventional electrokinetic techniques. Colloids and Surfaces, 1994 88 129-139 and Sanders, N.D. and J.H. Schaefer, Comparing papermaking wet-end charge-measuring techniques in kraft and groundwood systems. Tappi Journal, 1995 78 142-150.20-22].
• PAE and G-PAM adsorption in the sheets was analysed by measuring the total nitrogen content in the sheets.
• the method is based on flash combustion and is called Dumas Total Nitrogen Analysis and the measuring instrument used is Carlo Erba Instrument NA 1500 supplied by CE Termo Quest. A manual is supplied together with the instrument.
• Ion exclusion chromatography is mainly used for analysis of weak inorganic and organic acids.
• the chromatographic column is packed with a stationary phase consisting of a sulfonated polystyrene/divinylbensene based cation exchanger.
• a stationary phase consisting of a sulfonated polystyrene/divinylbensene based cation exchanger.
• different organic acids may diffuse into the stationary phase to a greater or lesser degree.
• This mechanism together with ion exchange is used for chromatographic separation of organic acids in solution. Suppressed conductivity is used for detection.
• the equipment used for the analysis is described below:
• the working range for the method is 0.01- 1.0 % in paper (calculated as dry PAE resin) and the relative standard deviation for a paper sample with 0.3 % PAE (dry resin) is 3.8 %.
• Fig. 1 shows the Z-potential of the fibres during trial 1, before and after washing of the fibres.
• the Z-potential is not largely influenced by washing the fibres.
• a small decrease in the observed Z-potential can be detected when washing the PAE treated fibres and a small increase when washing the CMC treated fibres, which presumedly is due to the additive desorption during the washing step.
• Fig. 2 shows the results of charge measurements of the colloidal phase (PCD measurements) during trial 1, before and after washing of the fibres.
• Fig. 2 shows that when adding PAE / CMC in excess a large amount of the added polymer stays in the colloidal phase instead of adsorbing to the fibres. In the washing step the excess is removed.
• Fig. 3 shows the wet tensile index of the sheets versus the adsorbed amount of PAE.
• Dry tensile strength index show a similar trend as the wet tensile strength index but, as expected, the increase in dry strength is not as high as the increase in wet strength.
• the charge in the colloidal phase is balancing around zero charge, indicating that the adsorption of PAE / CMC on the fibres is almost total, i e not much of the additives end up in the water phase.
• the deviation from zero charge should preferably not exceed ⁇ 5 eq/l, more preferably not exceed ⁇ 2 eq/1.
• Fig. 6 there is shown the dry tensile strength index versus adsorbed amount of PAE, at which e g "7/2/7-10-15" means 7 mg/g PAE, 2 mg/g CMC, then 7, 10, 15 mg/g PAE in the third layer.
• the dry tensile strength index reached its highest level at relatively low adsorbed amounts of PAE. At an adsorbed amount of approximately 5 mg/g the strength is levelling out.
• Fig. 7 there is shown the wet tensile strength index versus adsorbed amount of PAE.
• Fig. 8 shows the relative wet strength versus adsorbed amount of PAE.
• Fig. 7 and 8 show that wet tensile strength index and the relative wet strength level out, but it seems like the highest level is not fully reached.
• the dry tensile index start to level out at 5 mg/g adsorbed amount of PAE.
• the wet tensile strength index levels out but at higher levels of adsorbed amount of PAE. A maximum relative wet strength of 40% is reached.
• the trials show that charge measurements using PCD and Z-potential instruments provide good control of polymer addition.
• the multilayering technique gives an increased amount of additives that are adsorbed to the fibres, which helps to give e g an increased strength up to a certain level.
• the amount of polymer to be added is preferably controlled and determined by Z-potential and PCD measurements after each addition of polymer in each step during the starting up of the process. These amounts are then used in the process.
• the Z-potential and PCD measurements are during the run of the process preferably performed only after the headbox.
• Addition of the first polymer is e g made in the pulper, and the other polymers are then added at different steps in the wet end of the paper machine. In the examples above only the addition of strength additives to cellulose fibers for papermaking are described.
• the invention may be applied for consecutively adsorption of thin layers of optional types of alternating cationic and anionic polymers on the surface of fibres or other types of particles or groups of particles in order to build up thin multilayers of the interacting polymers on the particle surface.
• wet strength agents such as PAE and G-PAM it is possible by the method according to the invention to produce paper and nonwoven products containing at least 1.5, preferably at least 1.7, more preferably at least 2.0, even more preferably at least 2.2 and most preferably at least 2.5 % by weight or more of a wet-strength agent.
• wet strength agents such as PAE and G-PAM
• these values refer to the amount of wet-strength agent adhering to the fibres and measured according to the total nitrogen method disclosed above. In some of the laboratory trials up to 3.8 % by weight wet-strength agent adhered to the fibres (Fig. 7 and 8).
• tissue paper based on cellulose fibres with no admixture of other types of fibres, such as synthetic reinforcing fibres, having a wet tensile index of at least 6.5, preferably at least 7.0 and more preferably at least 7.5 Nm g.
• tissue paper in this respect does not include materials exerted to hydroentangling.
• No. 1 is a tissue paper used as wiping material sold by SCA Hygiene Products AB under the trademark "M-Tork” and having the following pulp composition: 33% by weight CTMP and 67% by weight softwood kraft pulp (TCF). It contains about 0.7% by weight PAE.
• No. 2 is a paper produced from the same type of pulps as No. 1 and where the cellulose fibres were treated in consecutive steps according to the invention with two layers PAE, one layer G-PAM and two layers CMC. It is from these results seen that tissue paper no. 2 showed improved strength properties. It is further noted that the papers tested contained a mixture of CTMP and softwood kraft pulp. For papers containing higher amounts of or only containing softwood kraft pulp even higher strength values would be expected.
• Table 4 shows the results of measurements for determining the amount of wet strength agent m the form of PAE in some commercially available tissue products and in a tissue paper made with the method according to the invention.
• Sample A is a tissue paper made according to the invention corresponding to the one tested as No. 2 in Table 3
• Sample B is a tissue paper produced by Fort James and sold under the trade name "Lotus Profes”.
• Sample C is a tissue paper produced by Procter & Gamble and sold under the trade name "Bounty”.
• Sample D is a tissue paper produced by Metsa Sarla and sold under the trade name "Katrin Cleany”.
• the amount of PAE in the different tissue papers were measured by the ion exclusion chromatography method described above and gives the amount of PAE adsorbed to the fibres. It is to be noted that normally the amount of PAE or other wet strength agent added to the furnish is given as % of the wet strength agent solution added per weight fibres. Wet strength agents are sold as solutions containing between about 6 and 25 % of the active component. When we talk about the amount of wet strength agent we refer to the amount of the active component adhered to the fibres.

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Citations (6)

• 2000
  • 2000-04-06 SE SE0001268A patent/SE0001268L/sv not_active Application Discontinuation
• 2001
  • 2001-03-22 CN CN01807635.1A patent/CN1422347A/zh active Pending
  • 2001-03-22 PL PL01357809A patent/PL357809A1/xx not_active Application Discontinuation
  • 2001-03-22 SK SK1468-2002A patent/SK14682002A3/sk unknown
  • 2001-03-22 DE DE60102082T patent/DE60102082T2/de not_active Expired - Fee Related
  • 2001-03-22 AT AT01916028T patent/ATE259917T1/de not_active IP Right Cessation
  • 2001-03-22 MX MXPA02009106A patent/MXPA02009106A/es not_active Application Discontinuation
  • 2001-03-22 AU AU2001242971A patent/AU2001242971A1/en not_active Abandoned
  • 2001-03-22 HU HU0300410A patent/HUP0300410A2/hu unknown
  • 2001-03-22 ES ES01916028T patent/ES2215887T3/es not_active Expired - Lifetime
  • 2001-03-22 RU RU2002129503/12A patent/RU2002129503A/ru not_active Application Discontinuation
  • 2001-03-22 BR BR0109841-1A patent/BR0109841A/pt not_active Application Discontinuation
  • 2001-03-22 WO PCT/SE2001/000612 patent/WO2001077437A1/en active IP Right Grant
  • 2001-03-22 EP EP01916028A patent/EP1282741B1/en not_active Expired - Lifetime

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