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
  • D21H19/00—Coated paper; Coating material
  • D21H19/36—Coatings with pigments
  • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
  • D21H19/56—Macromolecular organic compounds or oligomers thereof obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H19/58—Polymers or oligomers of diolefins, aromatic vinyl monomers or unsaturated acids or derivatives thereof
• • 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
  • D21H19/00—Coated paper; Coating material
  • D21H19/36—Coatings with pigments
  • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
  • D21H19/56—Macromolecular organic compounds or oligomers thereof obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H19/60—Polyalkenylalcohols; Polyalkenylethers; Polyalkenylesters

Definitions

• ABSTRACT OF THE DISCLOSURE A method of cast-coating paper using an aqueous paper coating composition wherein the adhesive consists essentially of latices, at least one being alkali-swellable or alkali-soluble and at least one not being alkali-swella'ble or alkali-soluble, the pH of the composition being such that the alkali-swellable or alkali-soluble latex remains in the unswelled or undissolved condition.
• the present invention relates to aqueous paper coating compositions containing latex as the sole adhesive and methods of coating using such compositions, especially the cast coating of paper and paperboard.
• the surface of the finishing drum is higher than 100 C., e.g. from 120 to 150 C., and the pressure in the nip where the coated paper is pressed against the finishing drum is greater than the vapor pressure of water at said temperature.
• a pool of boiling water may be maintained in the casting nip. Steam evolving from this pool precludes air from the nip and prevents the formation of air bubbles in the coating. Moisture provided by the steam and boiling Water also serves to rewet the coating just before contact with the casting drum, thus promoting good bonding of the coating to the drum surface. See US. Pat. 2,950,989 to Freeman assigned to the assignee of the present invention.
• coatings were developed which were gelled or coagulated before reaching the casting nip and thus had greater resistance to the disruptive nip forces.
• coatings were water resistant, and not subject to wash-01f when brought into contact with a pool of boiling water in the casting nip.
• These gelled coatings have been of two basic types: acid-gelled, such as are described in US. Pat. No. 3,078,181; and heat-gelled, of the type taught by US. Pat. No. 3,356,517, both assigned to the assignee of the present invention.
• Such coatings have produced excellent end products when employed in conjunction with the teachings of the Hart and Freeman patents previously cited, and most recent research in cast coating has been done with gelled coatings of one type or the other.
• An adhesive composition for use in coating paper comprising a blend of latices, one of which is capable of being swelled by alkali and the other of which is insoluble and not swellable to any substantial extent in aqueous alkali has heretofore been proposed. See Canadian Pat. 862,188.
• Another patent which discloses the use of an alkali-swellable latex as an adhesive for a paper coating composition is U.S. Pat. 3,409,569. These patents teach, however, that in order to obtain the necessary coating viscosity sufficient alkali must be added to the paper coating composition to swell the latex.
• the binder of the coating composition has shown a tendency to absorb water, swell, and thus coalesce prior to the time the coated web comes into contact with the heated casting drum surface.
• the coating therefore fails to cast when brought into contact with the finishing surface of the casting drum.
• the present invention comprises an aqueous coating composition in which the adhesive component consists essentially of a mixture of a latex which is not capable of being swelled or rendered soluble by alkali and a latex which is capable of being swelled or rendered soluble by alkali.
• the adhesive component of the coating composition of the present invention broadly comprises a mixture of latices of which at least one is insoluble in aqueous alkali solution and at least one is swellable or soluble in aqueous alkali solution.
• the aqueous coating composition is maintained at a pH which is acidic throughout the coating and casting process.
• the alkali-swellable or alkali-soluble latex remains in the unswelled or undissolved condition, and thus uncoalesced until the coated paper surface reaches the casting drum.
• All of the latices of the present invention which the present inventor has studied become water swollen and coalesced at pHs above 7, and many of the most effective systems have shown a tendency to coalesce at a pH of about 6.5 and above. It is theoretically possible that a polymer could be designed which would remain in its free-acid state until a pH substantially above 7 was reached, but none of these has come to the attention of the inventor.
• the adhesive components of the paper coating composition of the present invention comprises a major proportion of non-alkali-swellable or soluble latex and a minor proportion of alkali-swellable or soluble latex.
• the alkali-swellable or soluble latex is required primarily for its hydrophilic properties in its acidic state, and not for strength-imparting properties. While these alkali-swellable or alkali-soluble materials are strong adhesives in the alkaline condition in which they were intended to be used, they have relatively little strength at acid pH.
• the binding strength of the adhesive component in the coating composition must therefore be provided by the non-alkali-swellable or nonalkali-soluble latex component of the binder. Too high a percentage of the alkali-swellable or soluble material tends to reduce several strength values of the coated paper, particularly wet pick strength and web rub.
• the alkali-swellable or soluble latex will generally comprise from 2% to 50% of the binder component of the coating composition, and preferably from about 20% to about 40%.
• alkali-swellable or soluble latex of the present invention may be any polymer to which sufiicient carboxyl groups may be attached to produce strong acid.
• acrylic copolymers, styrene-butadiene copolymers or vinyl acetate copolymers have been the commercially available polymers found useful as the alkali-swellable or alkali-soluble latex.
• the nonalkali-swellable or non-alkali-soluble latex of the adhesive component may be copolymers of styrene-butadiene, styrene-isoprene, styrene-vinyl acetate, acrylics, vinyl acetates, vinyl chloride-acrylic, styrene-nitrile, or nitrileacetate.
• the pigment component may be any of the commonly used paper coating pigments, including domestic and foreign clays, hydrated alumina, calcium carbonate, or combinations thereof.
• a coating composition was made by adding the following ingredients under agitation to 200 parts by weight of water: 100 parts by dry weight of a paper-coating quality clay, 0.6 parts by dry weight of sodium acid pyrophosphate and 0.2 parts by dry weight of an anionic, watersoluble polymer (sold commercially by the NOPCO Chemical Division of the Diamond Shamrock Company under the designation Nopcosant L) both as dispersants for the clay, 1 part by dry weight of a defoamer for latex (sold commercially by Colloids, Inc. under the designation Colloid 680), and 0.5 part by dry weight of a nonionic surface active agent as a stabilizer.
• 100 parts by dry weight of a paper-coating quality clay 100 parts by dry weight of a paper-coating quality clay, 0.6 parts by dry weight of sodium acid pyrophosphate and 0.2 parts by dry weight of an anionic, watersoluble polymer (sold commercially by the NOPCO Chemical Division of the Diamond Shamrock Company under the designation Nopcosant L) both as dispers
• binder components consisting of 18 parts by dry weight of an alkali insoluble and unswellable latex (13-15, a soft acrylic copolymer manufactured by Rohm and Haas) and 7 parts by dry weight of an alkali-swellable latex (E-503, an emulsion of an acrylic copolymer manufactured by Rohm and Haas).
• the alkali-insoluble latex was added to the coating composition prior to the addition of the alkali-swellable emulsion.
• the pH of the composition was 5.6. Addition of the 7 parts by dry weight of the unmodified alkali-swellable latex reduced the pH of the entire coating composition to 5.0. This pH increased slightly to 5.15 when 0.13 part by dry weight of polyethylene was added as a release agent for the coating.
• ammonium hydroxide (28% ammonia) were added to the coating composition as an alkaline thickener for the alkali-swellable emulsion.
• the addition of the ammonia caused the coating to thicken markedly, and raised the pH of the coating to 8.5.
• Forty additional parts by weight of water brought the coating solids to 41.6%.
• This coating composition was applied to a conventional base paper and the coated surface was pressed against a casting drum, the surface of which was maintained at a temperature of 240 F. After the coated paper was dry enough to release from the casting drum, it was removed from contact with the drum and subsequently examined for surface quality. The coated paper surface exhibited a mottled, uneven appearance, indicating that it had not cast properly against the finishing drum. The coated surface had a gloss reading of 57 at a 75 angle on a Hunter Glossmeter.
• EXAMPLE II A slurry was prepared from parts by weight of English coating clay, 100 parts by weight of water and 0.7 parts by weight of sodium tetraphosphate as a dispersant for the clay. This mixture was slurried for 20 minutes, following which were added 0.25 part by dry weight of a defoamer, Drew L-50l, manufactured by Drew Chemical Company, and 0.13 part by dry weight of polyethylene as a lubricant.
• the alkali-soluble latex was received from the supplier at a pH of 3.4 and was added directly to the coating composition without modification. When the emulsion was added to the coating composition no appreciable thickening of the coating was observed. After this addition, the entire mixture was maintained under continuous agitation until a homogeneous composition was obtained.
• This coating composition had a pH of 5.2, its solids content was 41.4%, electric water retention (EWR) time was 1.25 seconds and viscosity at 100 r.p.m. was 480 centipoises. In this and the following examples, viscosity was measured with a Brookfield Model RVF-100 viscometer using the #5 spindle. Water retention was determined by measuring the electrical conductivity through a sheet of water leaf paper pressed against the coating. As the water migrates from the coating into the sheet of paper, the conductivity increases. The values given represent the time required for the conductivity to reach 0.5 milliamp.
• the above-described coating was applied by means of an air knife coater to one side of an 8 point Cover Bristol bodystock which had previously been surface sized on the side to be coated.
• the coating was applied in an amount equal to 14 pounds per ream of 3300 square feet. Web speed during the coating and casting operations was feet per minute.
• the Web passed from the coating station past a series of infra-red heaters which served to dry the coated sheet partially prior to reaching the casting drum, but which produced no gelation or coalescence of the coating prior to the entry of the web into the casting nip.
• the web passed through a nip comprised of a backing roll and a chromium-surfaced casting drum with a four foot diameter.
• a vigorously boiling pool of water was maintained at 220 F. This boiling pool produced a large amount of steam which rose above the nip entrance. After passing through the steam, boiling pool and casting nip itself, the coated paper surface cast firmly against the drum surface.
• the paper As the drum revolved, the paper was maintained in intimate adherent contact with the drum surface for the greater portion of a revolution around the drum.
• the drum heated to 260 F. dried the paper to a total moisture content of approximately 4% after the paper had remained in contact with the drum surface for approximately three-quarters of a revolution of the drum. At that point, the coated web released cleanly from the drum and was wound up.
• the cast coated paper thus produced had excellent qualities of gloss and sparkle to the naked eye, and had a gloss reading of 75 when measured at a 75 angle on a Hunter Glossmeter. Microscopic examination of the coated surface showed that the coating was uniform and continuous. The coating was found to be substantially free from pits or other surface defects.
• EXAMPLE III A slurry was prepared by combining 55 parts by weight of water with, by dry weight, 0.3 part tetrasodium pyrophosphate and 100 parts English coating clay. After slurrying for 20 minutes, there were added by dry weight 0.025 part of a defoamer, 15 parts of a non-alkali swellable latex, the soft acrylic copolymer described in Example II, and finally 10 parts of an alkali-soluble latex, ASE 75, an acrylic emulsion copolymer manufactured by Rohm and Haas Company.
• This coating composition had a pH of 5.8. Its electric water retention (EWR) was 4.8 seconds, and its viscosity at 100 rpm. was 302 centipoises. The coating had a solids content of 56%. Under the operating conditions of Example II, it was applied to a casein surface sized bodystock in an amount equal to 13 pounds per 3300 square feet. No gelation of the coating occurred although the coated surface was heated to approximately 200 F. between the coating station and the casting drum, as an aid to drying. The coated paper was pressed against the heated casting drum, which was maintained at a temperature of 264 F. It cast well against the drum, at an operating speed of 200 feet per minute and when removed from the finishing surface of the casting drum the coated paper exhibited at 75 a gloss reading of 88.
• EWR electric water retention
• EXAMPLE IV Employing the same basic formula and operating conditions set forth in Example III, the ASE 75 alkali-swelL able emulsion was replaced by ASE 60, an acid-containing, acrylic emulsion copolymer, manufactured by Rohm and Haas Company.
• This alkali swellable material when used in the same minor proportion (40% of the binder component) to the major proportion of non-alkali swellable latex (B1560% of the binder component) as in Example III, produced a cast sheet with excellent surface characteristics and a 75 gloss reading of 91.
• alkali-swellable or soluble polymers were employed instead of the ASE series of materials used in the examples already described.
• the alkali-swellable emulsion of acrylic copolymer (E503 manufactured by Rohm and Haas) which was unsuccessfully tried in Example I when used according to manufacturers instructions, proved to be a highly desirable binder component in a cast coating composition when employed in an unmodified acidic state.
• Example III the B-15 acrylic copolymer was removed and other latices substituted in the same proportion relative to the ASE-75 alkali-swellable emulsion.
• Several styrene-butadienes were each combined individually in a castable coating composition with the alkaliswellable emulsion. These included uncarboxylated styrene butadiene (Dow Chemical Companys 612), slightly carboxylated styrene-butadiene (Dows 620), and a high styrene to butadiene copolymer (Standard Brands Tylac 5071).
• non-alkali swellable component in the same control formula was styrene-isoprene, styrene-acetate, polyacrylics, acrylicstyrene, poly(vinyl acetate) copolymers, poly(-vinyl acetate) terpolymers, vinyl chloride-acrylics, nitrice-acetate, and styrene-nitrile. All of these copolymers were successfully utilized as the major, non-alkali swellable binder component of a cast coating composition containing a minor binder proportion of an alkali swellable latex.
• This coating composition with a high ratio of non-alkali soluble to alkali soluble binder components, had the following characteristics: pH 6.8, EWR 3.8 seconds, and Brookfield viscosity at 100 rpm, centipoises.
• This coating was applied at 57.6% solids, did not gel when heated prior to the casting drum, and cast Well against the heated drum. The coated paper released cleanly from the drum when dry. It exhibited good visual gloss.
• EXAMPLE VI To 100 parts by weight of water were added, by dry weight, 100 parts of domestic, coating-quality clay and 0.5 part of a dispersant for the clay. This mixture was slurried for 20 minutes, at which point 0.25 part of a defoamer, 10 parts by dry Weight of the non-alkali swellable latex of Example II, 025 part of polyethylene as a release agent, and 10 parts by dry weight of the alkaliswellable latex of Example II were added. This composition had a pH of 4.65, a viscosity at 100 rpm. of 480 centipoises and an EWR of 1.5 seconds.
• EXAMPLE VII Due to the basic pH of several components normally present in paper coating compositions, all-latex cast coating compositions to which an unmodified alkali-swellable or alkali soluble latex has not yet been added may have a pH at or above the neutral 7.0. A sudden change in the viscosity and homogeneity of the coating, called shocking, may occur when a strongly acidic, unmodified, alkali-swellable or soluble latex is added. In order to avoid this problem, it is desirable, in some formulations and under some operating conditions, to add a buffering ingredient which will lower the pH of a neutral or alkaline coating somewhat prior to the addition of the unmodified alkali-swellable or soluble latex. This practice is illustrated as follows:
• a slurry of 200 parts by weight of water and 300 parts by dry weight (60% solids) of a domestic, coating-quality clay had a pH of 7.2.
• a defoamer (Drew Chemical Companys L- 501) and 45 parts by dry weight of the non-alkali swellable latex of Example II
• the pH of the composition was 6.1.
• the composition was then buffered against the addition of the alkali-swellable latex by the addition of 1 part by dry weight of succinic anhydride (pH 4.2). This lowered the pH of the entire composition to 4.6.
• a method of cast-coating paper comprising the steps of:
• aqueous coating composition in which the adhesive consists essentially of a mixture of latices comprising 50% to 98% of latex which is not capable of being swelled or rendered soluble by alkali and 2% to 50% of latex which is capable of being swelled or rendered soluble by alkali, the pH of the coating composition being such that the latex capable of being swelled or rendered soluble remains in an unswelled or undissolved condition; and conveying the coated paper web into a casting nip while maintaining the pH of the coating composition on the web at a level such that the latex capable of being swelled or rendered soluble remains in .an unswelled or dissolved condition.
• the casting nip contains a pool of boiling water.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Paper (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Processes Of Treating Macromolecular Substances (AREA)
• Paints Or Removers (AREA)

Priority Applications (10)

Applications Claiming Priority (1)

Related Child Applications (1)

Publications (1)

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Family Applications (1)

Country Status (10)

Cited By (4)

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• 0
  • BE BE793933D patent/BE793933A/xx not_active IP Right Cessation
• 1972
  • 1972-01-14 US US00218012A patent/US3832216A/en not_active Expired - Lifetime
• 1973
  • 1973-01-04 GB GB60373A patent/GB1377717A/en not_active Expired
  • 1973-01-11 NL NL7300445A patent/NL7300445A/xx not_active Application Discontinuation
  • 1973-01-12 FR FR7301079A patent/FR2173940B1/fr not_active Expired
  • 1973-01-12 JP JP605273A patent/JPS5321015B2/ja not_active Expired
  • 1973-01-12 DE DE2302044A patent/DE2302044C2/de not_active Expired
  • 1973-01-12 CA CA161,133A patent/CA999090A/en not_active Expired
  • 1973-01-13 ES ES410582A patent/ES410582A1/es not_active Expired
  • 1973-01-15 IT IT47695/73A patent/IT976892B/it active

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