Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
  • D21G9/00—Other accessories for paper-making machines
  • D21G9/009—Apparatus for glaze-coating paper webs
• • 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
  • D21H25/00—After-treatment of paper not provided for in groups D21H17/00 - D21H23/00
  • D21H25/08—Rearranging applied substances, e.g. metering, smoothing; Removing excess material
  • D21H25/12—Rearranging applied substances, e.g. metering, smoothing; Removing excess material with an essentially cylindrical body, e.g. roll or rod
  • D21H25/14—Rearranging applied substances, e.g. metering, smoothing; Removing excess material with an essentially cylindrical body, e.g. roll or rod the body being a casting drum, a heated roll or a calender

Definitions

• This invention relates to a new method tor developing finish on mineral coated paper, and to the mineral coated paper produced thereby.
• Mineral coated paper I mean to designate paper having a top coating whose composition on the dry basis comprises at least 70% finely divided mineral filling matter and not more than 30% adhesive. Mineral coated paper as thus defined is commonly used for book and magazine printing purposes.
• mineral coated paper it is customary first to apply to the body stock a coating mixture containing a pigment and a binding agent suspended in water.
• the coat.- ing mixture is applied in a variety of ways, such as for example, by means of brushes, rolls or sprays.
• To obtain mineral coated paper of good quality it is necessary to exercise considerable care in applying the coating mixture in order to secure as even a coating as is ossible.
• the coating n'iixture itself must "e sutiiciently fluid to avoid brush marks. streaki'ngs and other imperfections in the finished paper.
• the mineral coated paper is calen dered by passing it between the rolls of a super calender.
• a super calender which is essentially a stack of alternate steel and either cotton or paper rolls.
• the substantially dry sheets are laid between zinc plates and passed back and forth under a steel roll.
• the degree of gloss or finish produced in the ordinary calendering operation depends on a number of factors, such as for example, the pressure applied to the rolls, the amount of moisture in the paper thephysieal condition of the surface of the rolls, the temperature of the rolls, the speed of operation and the nature of the coating mixture. some of these factors are Very difficult to control in actual practice, with the result that the calendered paper is likely to be non-uniform.
• factors such as for example, the pressure applied to the rolls, the amount of moisture in the paper thephysieal condition of the surface of the rolls, the temperature of the rolls, the speed of operation and the nature of the coating mixture.
• Mineral coated paper having a high tinish is generally more valuable than paper having a low finish.
• Various methods have been employed to secure highly finished paper. Thus satin white has been used in coating mixtures largely for this purpose. Varnisheshavealsobeen applied for the same purpose. tubbing down by hand and polishing with brusheshave also been employed to develop high finished paper. All of these methods are relatively expensive.
• One object of the present invention is to provideamethodot obtaining paperhaving an extremely high finish. Furthermore, the invention provides a method of obtaining paper having practically any degree of fin sh desired. A further object is to provide a simple, less dangerous, less expensive and more easily controlled method of producing mineral coated paper.
• the essential feature of my invention is the pressing of the mineral coated paper against a solid surface while the coating is in ahighly plastic condition and rendering the coating comparativelynon-plastic before it is removed from this surface.
• the coating is plastic when wet it is dried in contact with the solid surface; or if the coating is plastic while hot it is cooled in contact with the solid surface. In this way the coating takes on the finish of the surt'ace with which it is in contact.
• the paper dries with the coating in contact with a very smooth, highly polished surface, the paper will have a very high finish.
• the method of finishing mineral coated paper herein described is also adaptable to producing various markings or designs on the mineral coated paper by contacting the coating while plastic with a solid surface having the desired-markings or designs cut, etched or otherwise inscribed on it.
• paper having a high finish may be obtained in this manner without the use of satin white or other expensive agents.
• a coating containing clay as the only pigment will give a paper by this process having a higher finish than coatings prepared in the usual manner, containing large percentages of satin white.
• the coated side of the paper be contacted with the surface on which it is to harden while the coating is in a plastic condition.
• One convenient method of accomplishing this is to contact the coated side of the paper with the solid surface by means of one or more rolls pressing down on the opposite side of the paper. This operation has the effect of smoothing out irregularities in the distribution of the coating and eliminating brush marks and similar imperfections. It is furthermore advisable that the coated side be kept in contact with the solid surface throughout the greater part of the hardening operation. This may be accomplished in several ways.
• the coating and the solid surface may be of such a nature that the paper will stick to the solid surface of its own accord until set and then break loose spontaneously. Or the paper may be kept more or less tightly in contact with the solid surface by external means such as a belt.
• any convenient form of equipment may be used to provide the surface in contact with which the coating is to set.
• a moving belt having any desired degree of finish may be used for this purpose.
• the'paper, freshly coated may be run on to the travelling belt, with the freshly coated 3 side of the paper in contact with the belt.
• the coating is allowed to set in contact with the belt. After setting the paper may be detached from the belt and wound on a reel in the usual manner.
• the belt may be made of any suitable material, for example, metal or hard rubber depend- I ing-en the composition of the coating.
• contact or finishifig surface may also take the form of a, revolving drum.
• the drum should be steam heated to hasten the drying.
• the coating is one which is plastic while hot, the drum may be cooled with water.
• the coating may be partially set between the point of application of the coating to the sheet and the point of contact with the finishing surface.
• the means for applying the coating does not have to be at any fixed distance from the finishing surface and neither does the paper have to travel at any particular speed.
• the method does not necessarily require that the hardening be complete in anycase.
• the coating contains an adhesive and should this adhesive prevent the free release of the coated paper after it has set the coating would be imperfect. It is immaterial whether or not the plastic coating adheres at first to the finishing surface, but it is essential that the coated paper when the coating has become substantially non-plastic be practically nonadherent to the finishing surface.
• a suitable material for the finishing surface will as stated above depend upon the composition of the coating. I have found, for example with starch or casein adhesives, that several materials are satisfactory for this purpose, among which may be mentioned chromium, Monel metal, hard rubher and to a lesser extent nickel and brass. Many other substances to which coatings containing starch or casein ordinarily adhere when dried in the manner herein described, may be rendered non-adherent by treatment with a wax. As examples, I mention copper and steel. In case fusible gums or resins are used as adhesives, chromium is quite satisfactory.
• the non-adhering surface may be in the form of a plating or coating on a cheaper base.
• the method of calendering herein described may in general be used with the coating mixtures commonly employed in the manufacture of mineral coated paper.
• These coating mixtures generally consist essentially of an aqueous suspension of pigment (usually clay, satin white. etc.) and an adhesive or binding agent (usually casein, glue or starch).
• Paper havin an extremely high finish may be prepared by the calendering process herein described, using clay and binding a ent alone, but the color and brightness may be improved by the addition of satin white, blanc fixe, etc.
• coating mixtures containing dyes and other minor ingredients often present in the usual coating mixtures may be used with my method of calendering. This process of calendering is adaptable for heavy or light coatings. Also each side of the paper may be coated successively.
• I give the following example of a coating mixture which when applied to a sheet of paper and calendered on a highly polished chromium surface in the manner herein described gives a mineral coated paper of very high quality: 200 pounds clay ((35% solids) and 15 gallons of casein solution (made by dissolving casein in ammonia water and corn t aining about 1.5 pounds casein per gallon) made up with water to a total volume of 30 gallons.
• the method of calendering herein de scribed is of particular advantage with coatings containing starch as an adhesive.
• a coating composition containing parts of clay, 20 parts of uncooked corn starch, 120 parts of water and part gum arabic, the parts being by weight, applied to the paper and gelatinized by contact with steam as described in my application Ser. No. 147,200, filed November 8, 1926, may be employed.
• casein is preferred to starch for several reasons among which may be mentioned: (1) the superior finish obtained with casein. and (2) with starch it is more difficult to apply smooth coatings free from brush marks. On the other hand casein is much more expensive and gives printing results inferior to starch.
• mineral coated paper may be obtained having a higher finish than that obtainable by the use of the more expensive ingredients. casein and satin white, calendered in the usual manner.
• the method of calendering herein described is not limited to use with coating mixtures con aining water.
• the coating mixture may contain a non-aqueous solvent or suspending liquid for the pigment or coating agent, which is evaporated while in contact with the finishing surface.
• the binding agent is plastic when hot, it is not essential that there be any solvent or suspending liquid present.
• the method is applicable for coating very thin paper, medium weight paper, and also very heavy paper or card board.
• Card board cannot be successfully calendered on the ordinary calender or super-calender due to the relatively high curvatures of the rolls, which would'cause the card board to crack. If a large drum is employed to simultaneously dry and calender the web in the manner described herein, the angle of curvature is comparatively low with the result that cracking of the card board does not occur.
• mineral coated paper produced by my new process will have a surface corresponding to the surface in contact with which the coating has been allowed to harden.
• the surface thus produced may be aptly characterized as a cast surface and the term cast surface as used in the following claims is intended to define the character of surface obtained by contacting a mineral coated paper while the coating is in a plastic condition with a solid non-adhering surface having a finish substantially the same as that desired on the mineral coated paper and rendering the coating substantially non-plastic before removing it from the solid surface.
• Mineral coated paper made according to the process described herein, in which the coating hardcus in contact with a highly polished surface is characterized by an extremely smooth surface. lfhe surface of this paper is much smoother than even the best grades of mineral coated paper made in the past.
• this new paper has an entirely different appearance from the customary mineral coated paper. @rdinary mine 'al coated paper. even the highest grade of twice-coated, high finished paper, when viewed at approximately the angle of the incident light, has a more or less mottled appearance due to the fact that the surface of the coating tends to conform to the irregular surface of the paper base.
• the new product on the other hand, whether of the high finish type or of the dull or matt-tinish type, is substantially free from this lack of uniformity.
• the high-finish product has the smooth, homogeneous appearance of a fine porcelain.
• the glaze or finish may be extremely high, resembling or surpassing a high grade varnished, coated paper in this respect.
• it is the coating itself which provides this surface and finish, and not a film of varnish or other costly, more or less colored, diliicultly printable material.
• non-adits herin'g surface means a surface from which the mineral coated aper can be easily removed aftcr the coating has set, without. destroyin the finish imparted to the coating by condition with a solid non-adhering surface having a-ifinish substantially the same as that desired on the mineral coated paper, rendering the coating substantially non-plastic, and
• Process of finishing mineral coated paper which comprises, contacting the coated side thereof while the coating is in a plastic condition with a revolving drum having a non-adhering surface, rendering the coating substantially non-plastic, and thereafter removing the mineral coated paper from the drum.
• Process offinishing mineral coated paper which comprises contacting the coated side thereof while the coating is in a plastic condition with a chromium surface, render: in g the coating substantially non-plastic, and thereafter removing the mineral coated paper from the chromium surface.
• Process of finishing mineral coated paper which comprises drying the coating in contact with a solid non-adhering surface having a finish substantially the same as that desired 0n the mineral coated paper.
• Process of finishing mineral coated paper which comprises drying the coating in contact with a highly polished non-adhering surface.
• Process .of finishing mineral coated paper which comprises drying the coating in contact with a heated revolving drum having a non-adhering surface.
• Process of finishing mineral coated paper which comprises drying a coating containing water in contact with a solid non-adhering surface having a finish substantially the same as thatdesired on the mineral coated paper.
• Process of finishing mineral coated paper which comprises drying a coating containing water in contact with a highly polished neg-adhering surface.
• Process of finishing mineral coated paper which comprises drying a coating containing water in contact with a heated revolving drum having a non-adhering surface.
• Process of finishing mineral coated paper which comprises drying a coating containing water in contact with a chromium surface.
• Process of finishing mineral coated paper which comprises drying a coating containing starch as a binding agent in contact with a solid non-adhering surface having a finish. substantially the same as that desired on the mineral coated paper.
• Process of finishing mineral coated paper which comprises drying a coating containing starch as a binding agent in contact with a highly polished non-adhering surface.
• Process of finishing mineral coated paper which comprises drying a coating containing starch as a binding agent in contact with a heated revolving drum having a non adhering surface.
• Process of finishing mineral coated paper which comprises drying a coating containing starch as a binding agent in contact With a chromium'surface.
• Process of making mineral coated paper which comprises applying a fluid to plastic adhesive mineral coating composition to the paper web or sheet and drying the coating to a substantially non-plastic condition in contact with a non-adhering solid surface.
• Mineral ,coated paper having a coating con'iprising at least of a mineral filling material and not more than 30% of an adhesive, and having a cast surface.
• Mineral coated paper having a coating comprising clay and an adhesive, and having a cast surface.
• Mineral coated paper having a coating comprising at least 70% of clay and not more than 30% of starch, and having a cast surface.

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Priority Applications (4)

Applications Claiming Priority (1)

Publications (1)

Family

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Family Applications (1)

Country Status (4)

Cited By (17)

Families Citing this family (3)

• 0
  • NL NL205374D patent/NL205374A/xx unknown
• 1927
  • 1927-01-03 US US158837A patent/US1719166A/en not_active Expired - Lifetime
• 1929
  • 1929-04-10 DE DEC42896D patent/DE561688C/de not_active Expired
  • 1929-04-12 FR FR673032D patent/FR673032A/fr not_active Expired

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