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
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/67—Water-insoluble compounds, e.g. fillers, pigments
  • D21H17/69—Water-insoluble compounds, e.g. fillers, pigments modified, e.g. by association with other compositions prior to incorporation in the pulp or paper
• • 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
  • D21H17/42—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds containing ionic groups anionic
  • D21H17/43—Carboxyl groups or derivatives thereof

Definitions

• the invention relates to a method for separating a binder dissolved in water.
• Aqueous binder solutions or glues play a role in many technical processes in which finely divided substrates such as pigments or fibers are bound to one another or to a solid surface.
• the binding process occurs when a film of the binder solution dries up.
• a separation of the dissolved binder from the water phase and its precipitation on the dispersed substrate are sought.
• the invention therefore also relates to the treatment of a pigment suspended in water for the paper industry with an aqueous binder or the pigment thus treated.
• the invention further relates to a method for producing pigment-containing paper with increased tear strength or with an increased pigment content.
• the coated papers are also used as art paper, art paper or chromo paper and in the highest quality level Designated enamel paper.
• the purpose of the stroke is to form a layer for printing, which consists exclusively of pigments and a binder. This layer is mostly compacted by satin and brought to shine. It enables the reproduction of the finest halftone dots.
• Coating is an expensive process, which is usually carried out in a separate coating system behind the paper machine. Since printing on pigments or pigment layers leads to significantly better printing results than printing on a pure nonwoven fabric, efforts have been made for decades to introduce more pigments into the paper directly on the paper machine without reducing its tear strength. This could avoid the complex coating process.
• Wood-containing, highly filled and highly satinized gravure papers with pigment contents between 17 and 30% by weight are widely used. They are called SC papers (super calendered).
• SC papers super calendered
• the pigments usually kaolin or talc, are bound in the nonwoven fabric by adsorption and filtration.
• binders have also been used, for example modified starch, carboxymethyl cellulose, alginates, mannogalactans (meyproid), gelatin and skin glue. They are used as colloidal solutions in the material input and are adsorptively bound to the pigment and the fiber by electrokinetic forces. This bond is never complete. One finds therefore in the circulation water and in the wastewater Paper mills part of the binder used, which is lost as a result and makes a waste water treatment necessary.
• EP-A 50 316 describes a paper manufacturing process in which, in a first process step, an aqueous suspension of an inorganic pigment is mixed with a classic organic paper binder, such as dextrin, starch, carboxymethyl cellulose, polyvinyl alcohol or plastic dispersions, and the binder precipitates using a cationic flocculant.
• a classic organic paper binder such as dextrin, starch, carboxymethyl cellulose, polyvinyl alcohol or plastic dispersions
• a cationic flocculant are polycationic compounds, such as polyethyleneimine, cationically modified polyacrylamides, polyaluminium chloride and cationic starch.
• the pigment suspension used can optionally contain conventional dispersants, such as polyphosphates or sodium polyacrylate; such dispersants do not act as binders.
• the pigment pretreated in this way is added to an aqueous paper stock and the sheet formation is then carried out. Excellent pigment retention is achieved during sheet formation and paper with improved tear strength is obtained.
• mineral fillers for the paper industry above all calcium carbonate, are provided with a coating made of an organic polymer, which is intended above all to suppress the decomposition of the calcium carbonate in the acidic range.
• the coating can be, for example, from an aqueous solution neutralized acrylic acid polymer can be formed by precipitation using aluminum sulfate.
• the aluminum ions have the effect of imparting a positive charge to the filler or pigment and thereby increasing their affinity for the cellulose fibers.
• dissolved cooking starch is a very good and cheap binder, it is practically not used in the mass sizing of paper. It is known that unmodified cooking starch or nonionically modified starch is only retained as a binder in the paper stock to about 40%, while the majority of the starch remains in the circulating water. For this reason alone, despite their high binding capacity and their low price, the cooking starch has not been able to establish itself in the paper industry. In practice, mainly cationically modified starch is used in connection with retention aids, whereby retention values of up to over 80% can be achieved; see. C.Palm et al. J.-L. Hemmes, Kliblatt für Textilfabrikation 5/1991, pp.149-154.
• WO 82/01020 (EP-A 60 291) describes a process for the production of papers with high tear strength and high pigment content using cationically modified starch.
• carboxymethyl cellulose and an inorganic polymer are added to the pigment-containing substance, which causes these binders to coacervate.
• polyacrylic acid can also be used. Partially hydrolyzed alum can be used as the inorganic polymer under certain circumstances.
• Cationic starch is now widely used in papermaking to improve strength, tear length, retention and drainage, and to increase filler and waste paper content. Since the cationic state of charge is low, cationic retention aids are mostly used. The effect is based on the electrokinetic fixation of the starch to the cellulose fibers and the fillers.
• Electrokinetic effects which are based on the anionic charges of cellulose fibers, fillers and anionic binders on the one hand and the cationic charges of modified starch, retention aids or cationic surfactants on the other hand, are used in numerous processes in paper production and finishing. Typical examples are the processes according to EP-A 263 519, 279 313 and 234 513. In the latter process, a mixture of cationic starch, an anionic binder polymer and finely dispersed silica is incorporated into a paper stock. As a result of the electrokinetic interactions, precipitation of the previously dissolved binder occurs, there incorrectly referred to as coacervation. The separated binder improves dewatering and filler retention during leaf formation. The strength of the paper is also increased.
• binders precipitated by electrokinetic effects are not bound in a shear-stable manner, so that binders always get into the circulating water during the subsequent sheet formation.
• the aim of the invention is to make native starch usable as a binder in aqueous systems, from which it has so far not been possible to separate it using simple means.
• the aim of the invention is a process for the complete separation of a starch-containing binder dissolved in water in the form of a film on the surface of a solid substrate without flocculation of the binder.
• Another object of the invention is a process for treating a pigment suspended in water for the paper industry with a starch-containing binder and then fixing the binder to form a pigment suspension which is suitable for the production of high-pigment paper by sheet formation from an aqueous paper stock.
• the binder should be bound as firmly as possible to the pigment so that it does not detach from it even after intensive shear treatment.
• the starch can be completely bound. If the treated pigment suspension is sedimented after the coacervation, the supernatant water is completely clear and shows no tyndeal effect. In the aqueous phase of the pigment suspension, practically no portions of the binder are found after the coacervation is complete. As a rule, the aqueous phase contains less than 5% by weight, usually even less than 1% by weight, of the binder originally used.
• the adhesion of the binder to the pigment proves to be shear stable. Even if the pigments treated according to the invention are exposed to high shear forces for a prolonged period, the binder is not detached from the pigment particles again and the aqueous phase remains free of the binder used.
• the content of the binder in the aqueous phase in a shear treatment with an intensive mixer according to Prof. Wilms (“Ultraturrax” (R) , manufactured by Janke & Kunkel) increases to not more than 5 within 3 minutes at 4000 rpm % By weight, based on the total binder content of the suspension.
• the dispersed substrate particles e.g. Pigment particles
• anionic form as they normally exist
• the binder with agglomeration and flocculation of the pigment based on electrokinetic attractive forces would be undesirable in papermaking.
• the electrical charge state of the particles which is also referred to as zeta potential, can be recognized by their migration behavior in the electrical field. Charged particles with negative zeta potential migrate to the anode during electrophoresis.
• a solvation state is sought which lies between the complete solvation of the solution state and the desolvated state of a hard and solid precipitate. This condition is brought about by gradually lowering the zeta potential without reaching or exceeding the isoelectric point of the anionic polymer. Maintaining sufficient solvation, which has a plasticizing and elasticizing effect on the polymer mixture, is important for its binding ability.
• the degree of neutralization and thus also the solvation decrease.
• the polymer containing carboxylate groups is becoming less and less soluble and begins to separate - together with the starch - as a water-containing phase from the surrounding aqueous phase. That is the beginning of coacervation. It is continued until a state of solvation is reached in which the insoluble coacervate, including the starch fraction, has deposited on the surface of the substrate particles, but still contains enough water to develop a high binding force. Only when the sheet formed dries does the binder change to a solid state and develop its binding and strengthening effect.
• the acidifying agent is added with stirring, with as uniform a distribution as possible, at a rate which keeps pace with the reaction with the polymer. In order to avoid uneconomically long coacervation times, stirring as intensely as possible is advantageous.
• the coacervate from the synthetic and the native binder can be solvated again or even brought into solution. This is important for the processing of waste paper.
• the method according to the invention is not only important for paper manufacture. It can be done with everyone Use methods in which the surface of a solid substrate is coated with a film of a binder previously dissolved in water, without the relative charge state of this surface being important.
• the coated substrate usually only bonds firmly when it is separated from the water phase or deposited on the surface of a larger solid body to form a coating.
• the coacervate film then establishes the connection between the substrate particles and the coated body surface. The full binding power develops when drying.
• Pigment suspensions treated according to the invention are particularly suitable for the production of papers with a high pigment content on the paper machine.
• the highest strength values are achieved when the treated pigment suspension is incorporated into the fiber.
• the procedure can also be such that the pigment, the binder and the fibrous material are mixed in the central unit of the paper machine, made alkaline and the coacervation is effected by adding the acidifying agent to this mixture. You can also work the binder into the alkaline fiber, then add the pigment and then perform the coacervation. Thereafter, the sheet is formed on the screen in accordance with customary methods.
• the paper is then preferably satinized.
• the pigment suspension treated according to the invention can optionally also be used to coat papers.
• the process of the invention can also be carried out without the starch component of the binder using only the anionic polymer.
• this embodiment it forms the subject of the international patent application PCT / DE 91/00376 (currently unpublished). Since native starch is an inexpensive tool widely used in the paper industry, the use of a binder composed of starch and the synthetic anionic polymer is of great economic importance.
• the carboxylate group-containing polymers suitable for the process of the invention can be available as water- or alkali-soluble solid products, as colloidal solutions or aqueous dispersions, such as homopolymers and copolymers based on vinyl acetate and crotonic acid or partially saponified poly (meth) acrylates. Homopolymers and copolymers of acrylic and / or methacrylic acid in the form of their sodium salts are preferred.
• the polymer is not water-soluble in the pure acid form and must be brought into a solvation state suitable for coacervation.
• a sufficient part of the carboxyl groups must be in the form of carboxylate groups. They bring about the solvation of the polymer with water, so that it is in the truly dissolved or at least in the colloidally dissolved state.
• Real solutions are largely clear. Colloidal solutions are characterized by a more or less clear turbidity. If the polymer contains non-neutralized carboxyl groups, a colloidal, slightly cloudy solution can be converted into a real solution by further neutralization.
• the required state of solvation is achieved by a sufficient content of carboxylate groups in the polymer.
• carboxylate groups in the case of polymers with a high carboxyl group, partial neutralization of the carboxyl groups to give carboxylate groups is sometimes sufficient, whereas in the case of copolymers with a low carboxyl group content, complete neutralization is usually necessary.
• the carboxylate content required for sufficient solvation depends on the hydrophilicity of the entire polymer. As a rule, it is in the range from 3 to 10% by weight, calculated as COO ⁇ and based on the weight of the non-neutralized polymer. If the polymer is composed entirely or predominantly of units of an ethylenically unsaturated, free-radically polymerizable carboxylic acid, complete neutralization is admittedly advantageous, but not essential.
• the pH of the binder solution is in the range of about 8 to 11, depending on the degree of neutralization.
• any base which contains monovalent cations is suitable for neutralizing the carboxyl to carboxylate groups.
• Aqueous alkali especially sodium hydroxide solution, is preferred for economic reasons.
• the proportion of the ethylenically unsaturated, free-radically polymerizable carboxylic acid should generally be not less than 6 and not more than 80% by weight, preferably 10 to 80% by weight, in particular 20 to 80% by weight.
• Acrylic and / or methacrylic acid and maleic acid are preferred; Fumaric, itaconic or crotonic acid are also suitable.
• Non-ionic, slightly or poorly water-soluble ethylenically unsaturated, free-radically polymerizable monomers can be involved as comonomers in the structure of the polymer.
• Their proportion is preferably 20 to 90% by weight, particularly preferably 20 to 80% by weight.
• Other comonomers that can be used are e.g. Styrene, acrylonitrile or vinyl acetate.
• More hydrophilic or water-soluble comonomers, such as acrylic and / or methacrylamide or hydroxyalkyl esters of acrylic and / or methacrylic acid, can also be used, for example, in proportions up to a total of about 30% by weight, preferably up to 10% by weight.
• crosslinking comonomers with two or more ethylenically unsaturated, free-radically polymerizable groups in the molecule can be involved in the synthesis of the polymer.
• their proportion must be low enough to permit adequate solvation, for example up to 3, preferably up to 1, in particular up to 0.1% by weight.
• a satisfactory effect as a binder requires a sufficient molecular weight of the polymer. It should generally be at least 20,000, preferably 50,000 to 2 million, each determined as the weight average. Even higher molecular weights lead to high viscosities which make it difficult to use them on the paper machine without being beneficial for the binder effect.
• Preferred binders in the form of an aqueous solution adjusted to pH 9 with sodium hydroxide solution at a concentration of 200 g / l and 20 ° C. have a viscosity of more than 100, in particular more than 1000 mPa s. This viscosity is achieved by very high molecular weight binders at a concentration of around 30 g / l.
• Completely untreated starch such as potato, wheat, corn or tapioca starch, are best suited for the process of the invention. Mixtures of starches of different vegetable origin can also be brought together in solution and used in the method of the invention. Any pretreatment of the native starch increases its price, often many times over, and is therefore unnecessary.
• both binder components In order to ensure the coacervation of the starch with the polymer containing carboxylate groups, both binder components must be in a sufficiently solvated, colloidally dissolved state. A mixture that is as homogeneous as possible is important for the effectiveness of the binder mixture.
• the starch should therefore be gelatinized as intensively as possible. Good starch qualities dissolve sufficiently when cooking. However, it is usually more advantageous to carry out the gelatinization at a temperature above 100 ° C., for example at 105 to 150 ° C., in particular 110 to 130 ° C. These temperatures are reached in pressure cookers or continuous jet cookers at steam pressures of 2 to 7 bar. It is particularly advantageous to digest the native starch in an autoclave at a temperature above 100 ° C. in the presence of the polymer containing carboxylate groups.
• Native starch has the advantage over the cationic starch which is predominantly used today that it contains no constituents which increase the AOX value (absorbable organic halides) of the circulating water.
• AOX value adssorbable organic halides
• the binder is advantageously used in an amount of 1 to 11, preferably 2 to 5,% by weight, calculated as the total weight of the pure, unneutralized polymer and the dry starch. If the binder content is high, there is an increased risk that it will not be completely bound to the pigment.
• the proportion of starch is chosen as high as possible.
• the greater the proportion of the polymer component the better the incorporation of the starch in the co-coacervation. In practice, therefore, a compromise has to be made between the binder costs and the still acceptable loss of starch.
• starch contents below 10% by weight, based on the weight of the binder, the cost advantage is hardly noticeable.
• proportions of 20 to 50% by weight, in particular 25 to 40% by weight the most favorable ratio of low costs and high effectiveness is achieved.
• With a further increase in starch the risk of incomplete binding to the pigment increases.
• the process of the invention can be carried out with all pigments customary in the paper industry.
• the term "pigment” includes all fillers commonly used in the paper industry. Inorganic, especially acid-resistant, pigments are preferred. These include kaolin, talc, calcium carbonate, Calcium sulfate, silica, barium sulfate, titanium dioxide, and mixtures thereof. Kaolin and talc are particularly preferred.
• the particle size of at least 50% by weight of the pigment particles is between 0.1 and 10, preferably between 0.3 and 5 micrometers. Most of the pigments in aqueous slurries have a negative zeta potential, ie they are in the anionic state.
• the acidulant is the acidulant
• they are low molecular weight, in particular inorganic, acidic compounds. These include mineral acids such as Sulfuric acid. It is preferred to use acidic salts, such as alkali hydrogen sulfates or, in particular, aluminum sulfate, which is mostly referred to as alum in the paper industry.
• the amount of acidifying agent is critical in order to achieve the desired coacervation state and to avoid electrical charge reversal of the pigment.
• the pH of the treated suspension depends on the type of polymer. Polymers with a high carboxyl group content achieve the optimal coacervation state at lower pH values, namely about pH 5-6, than polymers with a low carboxyl group content which achieve their best binding ability at about pH 7-8. If a mineral acid is used as an acidifying agent, the acid equivalent amount used below the equivalent amount of the carboxylate groups of the polymer. When using aluminum sulfate, which reacts acidly due to hydrolysis, a stoichiometric calculation of the need for acidifying agents is hardly possible.
• the coacervation takes place in such a way that the binder solution, which has a pH in the alkaline range, is acidified, preferably with aluminum sulfate, whereby the colloidal system is destroyed at a certain pH and the binder fails.
• the inorganic pigment is suspended in water in a concentration of 2 to 30% by weight, preferably 2 to 20% by weight.
• Common dispersants such as polyphosphates, can be used as long as they do not interfere with coacervation.
• the pH of the suspension is adjusted to the pH of the binder solution. With stirring, the binder is stirred into the suspension in the form of an aqueous solution and distributed evenly. Then an aqueous solution of the acidifying agent is gradually stirred in, avoiding local acidification, which triggers the coacervation.
• the suspension is added to the fiber before or after coacervation.
• All of the fibrous materials commonly used in papermaking can be used, such as ground wood pulp, cellulose, semi-cellulose, high-yield materials, waste paper.
• the fibrous material has the added Pigment suspension preferably has a solids content of 3 to 4% by weight and is diluted to 0.1 to 1% by weight with circulating water before sheet formation.
• the mixture is expediently prepared directly in the central unit of a paper machine.
• Common additives such as defoamers, dispersants, thickeners, retention aids, optical brighteners, dyes, fungicides, bactericides, lubricants, can also be used in customary amounts. All of the process steps mentioned can be carried out at the temperatures customary in paper production.
• the mass is then formed into a sheet in the usual way and can then be satinized.
• Papers with a basis weight of 32 to 170 g / m 2 are preferably produced. They have the quality of known SC papers or even surpass them. They are particularly suitable as printing papers.
• a 5% suspension of kaolin in water is adjusted to pH 11 with sodium hydroxide solution. Then an alkaline solution of the binder is added with stirring. A pH of 5.5 is set by gradually adding aluminum sulfate. Measuring the zeta potential ensures that the pigment has a negative surface charge.
• This mixture is mixed in the central unit of a paper machine with the fibrous material, consisting of spruce pulp and ground wood in a ratio of 1: 1, so that a solids content of 0.5% by weight results. The mass is then shaped into a sheet in the usual way. The tear length is measured on the finished paper.
• Rohagit S mV (trade name of Röhm GmbH, Darmstadt): Powdery alkali-soluble acrylic resin with an acid number of 405 - 440 mg KOH / g.
• a 3% aqueous solution adjusted to pH 9 with NaOH has a viscosity of about 4000 mPa s.
• Starch Oxidized, hot water-soluble potato starch with about 16 to 20 mg carboxyl groups per 100 g (commercial product "Perfectamyl R PH 255 SH, AVEBE GmbH, Düsseldorf)
• Experiments V1 to V13 were carried out as blank tests without the addition of a binder or using starch or the synthetic polymer alone, in order to have a basis for comparison for the tear length with the same pigment content, but without the binder according to the invention.

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• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Paper (AREA)
• Water Treatment By Sorption (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)
• External Artificial Organs (AREA)
• Processes Of Treating Macromolecular Substances (AREA)
• Heterocyclic Carbon Compounds Containing A Hetero Ring Having Nitrogen And Oxygen As The Only Ring Hetero Atoms (AREA)
• Heterocyclic Carbon Compounds Containing A Hetero Ring Having Oxygen Or Sulfur (AREA)

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Cited By (1)

Citations (2)

• 1991
  • 1991-11-09 DE DE4136909A patent/DE4136909A1/de not_active Withdrawn
• 1992
  • 1992-11-02 NO NO92924216A patent/NO924216L/no unknown
  • 1992-11-05 AT AT92118929T patent/ATE123092T1/de active
  • 1992-11-05 DE DE59202335T patent/DE59202335D1/de not_active Expired - Lifetime
  • 1992-11-05 EP EP92118929A patent/EP0542125B1/fr not_active Expired - Lifetime
  • 1992-11-05 FI FI924995A patent/FI924995L/fi not_active Application Discontinuation

Patent Citations (2)

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