US2950214A

US2950214A - Cast coated paper and method of making the same

Info

Publication number: US2950214A
Application number: US648227A
Authority: US
Inventors: John W Smith
Original assignee: Mead Corp
Current assignee: Mead Corp
Priority date: 1957-03-25
Filing date: 1957-03-25
Publication date: 1960-08-23
Anticipated expiration: 1977-08-23
Also published as: DE1208173B

Description

Aug 1960 J. w. SMITH 2,950,214

CAST COATED PAPER AND METI-IOD OF MAKING THE SAME Filed March 25, 1957 FINISHING ROLL COATING SYSTEM DIP ROLL COAGULANT BATH INVENTOR. JOl/A/ W. S MITH ATTOQNE Y.

*- t i cc -'2 95a in n at P- r K r s -.:...a l sa Qua a E W v e g Patented Aug. 23, 3960 ing surface. Desirably, this surplus liquid coating washes backwardly against an incoming paper web and allegedly performs the functions of flooding depressions in the sur- 2,950,214

face of the paper web which otherwise would become CAST CGATED PAPER AND METHOD OF air pockets during the casting operation, rejecting foam MAKING THE SAME and air bubbles in the coating, preventing foreign ma- John W. Smith, Chillicothe, oiiio, assigiior to The Mead terial f o niamng the poated p p surface, improving Corporation, Dayton, Ohio, a corporation of Ohio the distribution of coating on the paper Web, reducing difficulties with beads of coating forming on the casting Ffled 19373561" 648327 surface beyond the edges of the paper web, and addi- Claims. (Cl. 117-64) tionally serves, together with the press roll pressure, to govern the final coat weight on the paper. However, a following patent, assigned to the assignee of the aforementioned surplus liquid-coating-material method, and 2;: igg ggi f g j ff ggg gg Eg ggi? 15 relating to a method for continuously cleaningthe edges finiious in 'hod of providing an irri proved mineral or Pi of a g drum i Indicates that cast-coating opera" tion nro ems are st' existent. merited cast-coated pa er havin unusually high brwht- D ness and high gloss, a high degi ee of opacity and god :::-i? f i ?;:;d 2 35g? 11 532233 amniiy for Priming inks And it incorporates the prim ii'ntadt with a caiiin surface siill anothe i roce ss wa" ciple of coagulating certain coatin adhesives to obtain g D n Pd a k Vino im raved fical Dre artias not advanced which allegedly eliminated the liability of en- 52122 3 5 g l a trapping air between a drum and a coated paper surface An early pro osal for producin zi lossy rrinera applied thereio' This process Involves applying a fimd coated a er embodied the a licafiion 0f an a ueou s coatmg to a r-novmg paper- Pressing :[he freshly 0 t PP v b t 1' coated surface into contact With a chrome casting surface, 31 222 32523 323 gg z ig gg g 2 and maintaining a circulating pool of water in the casting ished chromium driin'i surfa e drying the coatin w l ii e mp thereby The Wfate-r paol rewets i sun it remained in such contact and then s ri pin the coated cO-ated Surface dlsplaces an m snauowpocfiets which paper from mp drum surface This .131 P0531 was fi might become non-glossy areas on the finished sheet, and referred to as a cal ndering rather than a coating op raby commuously Washmg the edges of the castmg tion and the mineral coated pa er allegedly produced Pam-y overcom-es the prom??? of edge-beads' i? thereby w s characterized as cast surface paper The if i progss 1S f i 5? sufficlentlg loixgpressme in t e casting mp so at t ere is no re istri ution of term mineral-coated a er relaed to a a r corn risg a filbmus base i f on on: both g a 35 the coating itself, independently of the water pool, the tinuous la er of mineral or i ine nt com osition which required Intimacy OI csmtact bitween the surface of the covers theyfibars of fhe has; g fins the hgnnws batwmln coating and the chromium casting surface cannot be ohthe fibers on the surface of the base 50 that when the pperaqon pr-eSsures high. eiloughto give coated paper is pressed against a heatd chromium drum distributing action, disperse a portion or the coating in surface wh le the coatin isin a lii hl plastic condition 40 the water and certau} of the Suspended olids pressthe coatin is rend red zcmnar tiv lyy on plast c h9g0: ent in the coating composition are inherently transferred \4 L- L4 L1 VJ. 1v I it is remo i/ed rom this surfac The min ral coatin to the Water pool Whlch thereby becomes milky m api c. c g composition was applied to the paper in the form of an ggi gf pfggi g gaggi cl gig z oghiirefidriei iglelalsio aqueous suspension of pigment (usually clay, satin white, d h y 1 a y etc.) and an adhesive or binding a ent (usually casein or E to t 6 paper 15 lost dram and such Starch) loss is an obvious economic liability.

As previously pointed out pi ment binders for c t- The use of starch 0 cas e b- W for cast-coated paper leavsi iii uzh io b d cfisii d Inge; mate? p i at gauge the coatmg Surface to suck and not comp etey re ease from the finishing surface thereby example, casein which is preferred to starch in prepar- 50 effecting surface defects in the ultimate cast-coated paper ing cast-coated paper, has the characteristics of slow product or preventin operations entirely. As a proposed water release and low drying rates resistance to ink a remedy, it has been suggested that release a ents such as penetration, deleterious effects on brightness and opacity a film of olea inous material be applied to a chrom um or the finished paper when present in the required quancasting drum before and/or durm the time that the tities, and if heated too greatly durin drying may show D P. 1: a loss of binding ability before or du ring drum finishing g g g i i ggg fii s casunhg lunmon operations. Moreover, there are other disadvantages and g a on a c mmmm Pastmg m glaring defects such as having thfi coatino surfaca Stick nowever, is necessarily dependent on continuously main- 1: a o a v to the drum finishing surface after drying thereon, having :32? 3 g g on i drum and this 18 (16.- air bubbles and occasional particles of foreign matter in fi i: y a S e (-meramr W 0 must (.zarefuuy Watcn the coating to form dull spots the formation of holes e mshefi paper as It leaves the chrommm drum and cracks, and other defects in the cast surface of the pa er j or zi the amount of llqu-1d Oleagimius and the formation of edge beads of coating on portions on t e c onimm drum and/or 111 the coatmg of the drying drum which extend beyond the ed es of co or g g i adequate release of the dated a the paper web, all of which result from attempts to carry gi g? i 3 ,2 1? ig gg i fi g desir d C St out the aforementioned s a minerabcoated Daper Propg al for Producmg a glossy coated paperhas Proven entirely satisfactory. Now in Subsequent pioposals have been directed to methods g fpresent Invention there has been I covere a me 0 or continuousl roducin mn r l for partially overcoming certain of thes dlsadvantar-es y P e 1 s cast-coated paper having outstanding characteristics, and defectsexample, 0116 P has Suggested which method is not subject to the disadvantages of the pooling surplus liquid coating materia at the nip Where the paper web is pressed into contact with a castprior art processes.

Generally, the present invention comprises applying 3 an aqueous, pigmented coating composition containing a pigment binder to' a paper web and thereafter passing the web carrying the coating through a coagulant bath. As a result, the binding or adhesive component of the freshly applied coating without'substantial drying, .is converted by the coagulant into a gel, but in acordance with the invention, the coagulant is applied in such a way as to prevent distortion of the coating film. After substantially complete gelation of the pigment binder, the coating is then passed over a press roll and transferred to a casting surface, as for example, a methyl silicone resin casting surface chemically bonded to a metal substrate. While a Small amount of the coagulant solu- 7 tion may accumulate as a pool in the nip between the It is accordingly an object of'the invention to provide I a cast-surfaced. coated paper having improved optical properties.

Another object is to provide a cast-surfaced coated paper having unusually high brightness and opacity and high gloss.

Another object is to provide a cast-surfaced coated paper having an enhanced aflinity for printing inks.

Still another object is to provide an improved method for continuously producing such a paper having said characteristics, which method facilitates ready release of the coating from the casting surface and decreases normal surface defects on the paper. 7

Another object is to provide a method of the foregoing type adapted to relatively high speed production.

' Another object is to avoid operating defects, such as the occurrence of edge beads, associated with prior processes referred to hereinbefore.

Another object is to provide a method which is adapted to Wide commercial utilization and which produces a,

cast-surfaced paper product that can be used widely.

Numerous other objects of this invention will more fully hereinafter appear.

The accompanying drawing portrays diagrammatically one arrangement of equipment which has been satisfactorily employed for practicing the present invention.

Referring to the drawing, the paper web to be coated is drawn from a roll 10 of suitable paper base stock, and

the web 11, is led over

guide rolls

12 and 13 to pass through the apparatus in the coating color applying zone. ,7

In this modification, the web passes through the nip of the

coating application rolls

14, 15 where a predetermined amount of coating suspension is applied thereto and distributed with sufiicient uniformity over the web surface to give the desired weight of coating material per unit area on the web.

The present invention permits the use of commonly used aqueous, pigmented coatings, containing only such pigments, adhesives and additives as are normally used in preparing, pigmented coatings for printing.

In other I Words, a normally adhesive'coating material such as a suspension or colloidal solution of pigment and adhesive material in asuspending or solvent fluid is applied by such apparatus to the paper web but application thereof is desirably made in such a manner as to provide the coated .of the adhesive coating material appear to remain undisturbed after the coagulant reaction, the coating nevertheless has its characteristics temporarily modified sothat the adhesive tendency which would normally be eifective between thecoating material and a casting surface is so greatly reduced, that the surface coating material does not adhere to the casting surface after drying, but nevertheless acquires the smoothed surface characteristics of the casting surface. In. addition, there is no substantial or practically appreciable disturbance of the smoothed surface coating as it separates completely from the casting surface as a high gloss coated paper.

In practical operations, utilizing the invention and the apparatus illustrated, under commercialoperating conditions, this modification of the coating prior to a finishing operation on a casting surface, is effected by coagulating the mineral surface coating, after the coating has been applied evenly to the paper web, but before the coating is brought into contact with the casting surface. In actual practice, satisfactory results have been obtained by the modifying and/or stabilizing action of this invention by wrapping the freshly coated paper, Without substantial drying, coated side out, tightly around roll 16 which dips into the coagulant solution or bath contained in a tub 17. As illustrated, the coated paper is rolled into and out of the coagulating bath in such a way that the coagulant only contacts the coated surface of the paper web and is reactive with the coating from the time the coating material is first brought into contact with the coagulant, until substantially complete gelation of the coating adhesive has been effected. In this manner, distortion of the coating film is prevented and following gelation, the coated paper 11 is transferred by press roll 18, through nip 19 to a finishing roll 20 having a smoothly bufied methyl silicone casting surface, such as disclosed in co-pending application, Serial No. 635,974, filed I anuary 24, 1957. Roll 20, which is heated, has its smooth silicone surface in contact with the stabilized but moldable coating until the coating spontaneously releases from the silicone surface after it is substantially completely dried and is thereafter removed by tension roll 21. The dried coated paper is thereafter rolled up on winder roll 22.

The accompanying drawing illustrates one form of apparatus for applying the desired quantity of coating smoothly to the web. To accomplish'this result, the

color solids should preferably be adjusted so that the coating is not too viscous for easy application, nor so dilute as to be incapable of forming a tough gel. Relatively high solids content coating suspensions, e.g. of the order of 45%65% solids or more, have been used successfully and, as a general rule, the preferred percentage of solids in the coating is governed by the type and quantity of adhesive selected for-the color. For example, higher adhesive contents require lower solids, and latex may be used at higher solids than protein adhesives. In the apparatus shown, the coating color is fed through a suitable supply line and by suitable means to one or more discharge pipes or nozzles, indicated diagrammatically at 23, and into the nip between rolls 15 and 24- which have the direction of rotation as indicated, the color forming a pool 25. Doctor 26, as shown, functions to maintain the pool in the aforesaid nip between

rolls

15 and 24 and any suitable well known doctoring means may be employed. Color from pool 25 preferably is allowed to overflow at both ends of the nip, and is recirculated. Such overflow of the pool provides a means for removal of grit which otherwise would accumulate in the pool.

Roll 24 runs in contact with the application roll 15 and provides for metering thereon a regulated quantity of uniformly distributed coating material which in turn is transferred from roll 15 to the traveling web of paper as it passes through the nip of the

application rolls

14, 15.

The coating apparatus shown is a reverse roll system and has been found to be very satisfactory and effective for transferring from the trough of coating material or so-called coating color, between

rolls

15 and 24, accurately controlled amounts of the coating material. With high solids content coating colors of the order of as high 6 plastorneter reading of the order of 80 to 140 P. & I. when measured with a /s inch ball. And if one or more of these three rolls is hard surfaced, i.e., of metal, Stonite, or the like, then its adjacent roll is preferably resilient surfaced. For example, the following combinations of these coating mechanism rolls have been found commercially suitable and are presented in illustration but not in limitation of the invention.

Roll No.

Type of Roll By Combination l40P&J- 136P&J 8OP&.T 140P&J. Meta -112P&I l30P&J Stonite. 112P&J--- Metal 1l2P&.T 1121 8123.

fluent and flowable so that it may be thus accurately controlled as to quantity and general distribution. The coating material passing in controlled amount through the nip of the

rolls

15, 24 is carried on the surface of roll as it travels up toward the paper web, to transfer the desired quantity of coating material for the predetermined coat weight desired, and in such condition of fiowability that the color will be generally distributed across the surface of the roll 15 as it moves toward the paper and application nip of rolls in such condition of flowability and such distribution when brought in contact with the paper web by roll 15 turning in a direction opposite to the direction of travel of the paper web, there will be transferred to the web a substantially uniformly distributed layer or film of coating material which is of considerable and unexpected smoothness. The coating materials commonly used, contain a substantial amount of adhesive material such as casein. However, by the disclosed reverse roll system, there is sufficient working of the coating color both before it passes into the application nip of the

rolls

14, 15, and also within the nip by reason of the reverse turning of roll 50, so that even high solids content coating colors will be made sufficiently fluid, for securing the desired accurate coat weight, and the uniform distribution -of the film upon the surface of the paper web. Moreover, the apparatus referred to, when using somewhat lower solids content colors with greatly reduced viscosity and corresponding increased fiowability, has been very satisfactory in applying the desired quantity and uniform disleaving a surface which is sufficiently smooth so that it' may be subsequently coagulated and dried on a. finishing surface to give the desired high gloss coated paper. In the latter case, rolls 15, 24- are preferably operated at a low pressure of the order of 10 pounds per lineal inch, or lower and may even be operated at a gap amounting to as much as .005 inch.

Again, referring to the coating apparatus illustrated, very satisfactory results have been attained when

rolls

14 and 15 were rubber covered rolls; roll 14 having a plastorneter reading of about 136 P. & 3. and roll 15 having a plastorneter reading of about 112 P. 5: 3. Rolls 1 and 15 may be operated with a pressure therebetween varying during operation, for example from about 1 to 25 pounds per lineal inch, with satisfactory results having been obtained at a pressure of preferably aoout 10 pounds per lineal inch. Roll 24 in this connection was a hard surfaced Stenite roli.

Rolls

18 and 21 had plastometer readings of and 32 8: 5. respectively, while roll 29 was a metal roll, having a smoothly buffed methyl silicone casting surface, such as disclosed in copending application, supra. Roll 16 was a corrosion resistant roll such as stainless steel. More generally, however, it has been found that rolls 14, 15 and 24 may all be resilient surface type rolls, such as rubber covered rolls having a All plastometer values were measured with a /s inch P. & J. ball.

The pressure in operation between

rolls

18 and 20 may be varied over a substantial range; for example, from about 50 to 150 pounds per lineal inch, with satisfactory results having been obtained at a pressure of about 75 pounds per lineal inch. In thisconnection, it has been found that the upper pressure limit is determined by the strength or toughness of the gelled coating. And the pressure between

rolls

18 and 20 may be varied over wide limits so long as sufficient pressure is used to insure intimate contact between the coating surface and the casting surface.

Various coating materials may be employed in practicing the present'invention and as indicated by the formulations hereinafter set forth, the coating material generally comprises a mineral and an adhesive in aqueous medium. Both the adhesive content and the total solids content of the coating materials to be used are predicated on the ultimate high gloss coated paper desired and for highly satisfactory operations, such adhesive and total solids contents may be somewhat critical. For example, it has been found that the preferred range of adhesive contents is of the order of 12%-20%, although more or less adhesive can be used if special end-use requirements of the ultimate high gloss paper product so dictate. Moreover, if starch is used in admixture in the adhesive, more total adhesive is required than if it is not so used. Generally, the higher region of the adhesive content range is useful in preparing papers for offset printing, while the lower range has been found useful for letterpress printing.

A color formula which has been found to function satisfactorily in the practicing of the invention is of the following composition, wherein the parts by weight are taken on a dry basis:

Example I Parts by weight Clay (English coating clay) 42.0 Calcium carbonate 42.0

Casein (Argentina) 12.0

Caustic soda (parts per parts of casein) 6.0 Sodium pyrophosphate 0.75 Calcium stearate 0.5 Dow 512-R latex (butadiene-styrene copolymer Di isobutylphenoxyethoxyethyldimethylbenzylanr moniumchloride, monohydrate (Hyamine 1622, Rohm & Haas C0.) 0.05

' Example 11 a Parts by weight Clay (English coating clay) 42.0 Calcium carbonate 42.0 Soya protein (refined) 12.0 Ammonia, 26 B. (parts per 100 parts of protein) 12.0 Dow 512R latex 4.0 Sodium pyrophosphate 0.75 Calcium stearate 0.5 Hyamine 1622 0.05

Example III Clay (English coating clay) 38.0 Calcium carbonate 41.0 Satin white Alpha protein 12.0

Ammonia, 26 B. (parts per 100 parts of protein) 12.0 Dow 512-R latex 4.0

Sodium pyrophosphate 0.75

Calcium stearate 0.5 Hyamine 1622 0.05

Example VI Clay (domestic coating clay) 81.0 Soya protein (refined) 12.0

Azite (dicyandiamide) (parts per 100 parts of protein) 25.0 Ammonia, 26 B. (parts per 100 parts of protein)- 15.0 Sodium pyrophosphate 0.75 Sulphonatedtallow (Vegetol) 1.0 Calcium stearate 0.5

Dow 512-R latex 7.0 Hyamine 1622 0.1

Particularly satisfactory high gloss coated papers of the invention were produced by applying the coating of Example I, supra, to the web 11 as shown in the drawing. While the layer of coating was still sufliciently mobile or deformable, the web, coated side out, was tightly wrapped around roll 16, as shown, thereby rolling the coated paper into and out of the coagulatingibath and concomitantly initiating gelling of the adhesive componentof the coating. Roll 16 is so spaced from nip 19 as to permit substantially complete gelation during the time the coating on the web is treatedwith coagulant until the web is transferred by press roll 18 tothe heated silicone resin finishing roll 20. In this instance, the coating, after coagulating but prior to casting, was in the form of a nontacky, tough but deformable gel. And the resulting cast coated paper had a Bausch & Lomb gloss of 86.0 and was without megascopic surface defects, such as are frequently found in cast-surfaced coated papers; This paper also had enhanced affinity for printing inks as. compared to cast-surfaced coated paper not produced in accordance with this invention.

Even when using less expensive pigments such as domestic' coating clay in color formulae when practicing this invention,.it has been found that cast-surfaced coated papers have unexpectedly high brightness and opacity. In this connection, reference is made to the following chart which depicts typical brightness and opacity improvement of cast surface coated papers as attained by this inventron, using the coagulating agents designated and the coatmg formula of Example VI, supra:

G.E. Brightness Banach & Lornb TAPPI Coagulating Agent Opacity Usedall solutions 10% by weight solid material Ooagulated Not Goag-ulated Not 7 Coagulated Coagulated Aluminum Sulfate"- 80. 0 78.0 97. 0 96.0 Zinc Sulfate 80. 2 78.3 97. 5 96. 2 Magnesium Chloride. 79. 7 78. 8 97. 0 96. 3 Calcium Chloride.... 79. 7 78. 8 97. 7 96. 3 Zine Chloride 80.0 79.0 97. 3 96.1 Barium Ghl0ride. 80.5 77. 7 97.0 96. 8 Lead Acetate 80.1 77.6 97. 0 96.2 Zinc Acetate 81. 8 78.2 97. 3 96. 2

G.E. Brightness Bausch & Lomb TAPPI Opacity Weight Percent Zinc Acetate Ooagulated Not Coagulated Not Coagulated Ooagulated The toughness of the gel preferably is adjusted so that the coatingis plastic enough to deform under the pressure applied at casting nip 19 yet tough enough so that absolutely none of the coating is removed in this nip. It has been found that proper gel toughness may be obtained *by proper selection of an electrolyte within the group of preferred coagulants, by varying the coagulating bath temperature and concentration, and by altering the time .of exposure of the coating to the reaction of the coagulant prior to casting. Selection of the coagulant depends upon the particular adhesive employed in the coating, but it should be a colorless, water-soluble electrolyte, which is neither a strong acid nor a strong alkali. As noted hereinbefore, these factors can be varied over wide limits without critically affecting the operation of the process. When starch is used alone, it is difiicult to obtain a sufliciently tough gel to withstand the casting operation. When casein, soya protein, synthetic rubber latex and similar materials or their mixtures are used as the adhesive, or when mixed with less than an equal amount of starch, the soluble salts of polyvalent metals and weak organic acids perform best. The acetates, or formates of calcium, zinc, barium, lead and aluminum are preferred coagulants, because they function adequately to give the desired effects, yet do not reduce the pH of the finished paper too greatly. Sulfates, chlorides, and other strong 'acid salts of these metals may be used where an acid pH is not objectionable in the paper or when a highly alkaline mineral such as satin white is used in the coating color Q! in an amount sufiicient to neutralize the residual acidity of the coagulant.

In general, it has been found that water soluble compounds within the group of calcium, zinc, barium, lead, magnesium, cadmium or aluminum salts of formic, acetic, citric, tartaric, lactic, hydrochloric and sulfuric acids provide suitable coagulants for this invention. Moreover, under certain conditions free organic acids such as lactic acid may be effective coagulants. And the concentration of the coagulant may, of course, be varied to compensate for its specific activity, the temperature of the coagulant bath and the speed of operation.

Generally, the more active coagulants produce the greatest optical improvement in the finished paper. Coagulant concentrations of from 1 to 20 percent by weight in water are useful, the preferred range being from 3 to 7 percent. And, gelling activity increases with the concentration of the coagulant and in addition, such activity also increases with the coagulant bath temperature. bath temperature from 1 to 90 C. may be employed so long as the coating, after coagulating and just prior to casting, is in the form of a non-tacky, tough but deformable gel. And to attain such a gel condition, the time of exposure of the coating to the coagulant is preferably of the order of 0.5 to 5.0 seconds, or more, i.e., the time interval for transferring the treated coating from coagulant bath 17 to the nip 19.

The surface temperature of the casting drum 29 is preferably from 80 C. to 100 C. during the drying cycle for producing the cast-surfaced coated paper having unusually high brightness and opacity and high gloss of this invention, although temperatures ranging from 65 C. to as high as 105 C. have been used without harmful results. It has been found that temperatures approaching 90-100 C. are advantageous when the more active coagulants are employed.

Ordinarily, after the paper web 11, the coating of which has been gelled by coagulation, has been maintained in contact with the drum 20 until dry, the paper is readily stripped off the drum 20 by roll 21. As pre-' viously set forth, drum 2% preferably has a silicone resin surface but, during some operations in accordance with this invention, it was found that an ordinary metal drum such as a chromium surfaced drum could be utilized and that satisfactory release of the coating was obtained. Presumably, the coating in its gelled condition becomes so stabilized at times that it separates completely from the smoothing, clean surface drum member and is readily separated therefrom by roll 21.

However, it has been found that any required As previously pointed out, a small amount of the coagulant solution may accumulate as a pool in the nip 19 between the press roll 18 and the casting surface 20. While it has been found that such a pool merely consists of clear, excess coagulant that is squeezed from the surface of the coating at the casting nip, it may, nevertheless, be desired in some operations to provide a rotating brush or a felt covered roll 27 between the nip 19 and tension roll 21 for maintaining a clean casting surface, substantially free of coagulant solution. In addition, it is preferable that the coagulant in the bath =17 be recirculated by any well known means during operations to maintain uniformity of the coagulant in the bath.

While the methods, apparatus and products herein described are for the purpose of illustration only, it is to be understood that the present invention includes all modifications and equivalents which fall within the scope of the invention which is defined by the appended claims.

What is claimed is:

1. In the coating of paper to provide a cast-surfaced mineral coated paper having unusually high brightness and opacity and high gloss with enhanced aflinity for receiving printing and the like, the process which comprises the steps of applying and distributing a predetermined i0 7 and metered quantity of fluent mineral coating consisting essentially of an aqueous suspension of pigment and adhesive material to form a substantially smooth surface coating on the paper, bringing the coated surface of said paper into contact with an adhesive coagulating electrolyte while said coating is still fluent on said paper to progressively convert said adhseive into a substantially tough deformable gel while maintaining a substantially uniform and smooth surfaced layer of coating, bringing said coated surface of said paper into contact with a. substantially smooth casting surface after said adhesive has been converted to said tough deformable gel, and drying said coating while said coating is in contact with said substantially smooth casting surface, and removing said coated paper from said casting surface.

2. In the manufacture of cast-surfaced mineral coated paper having improved optical properties and enhanced aflinity for printing inks, the steps comprising progressively coagulating the coating while still mobile and fluent and deformable on the paper by direct contact with a coagulating electrolyte to stabilize the coating against adhesion to the surface of a casting surface, thereafter bringing said coating while so stabilized in intimate contact with said casting surface and drying said coating on said casting surface, separating said coating from said casting surface.

3. The process of making cast-surfaced mineral coated paper having unusually high brightness and opacity and high gloss which comprises applying to a web of paper a coating color consisting essentially of an aqueous suspension of pigment and adhesive material, said coating color having from about 45% to about 65 total solids and having said adhesive present in an amount between about 12% and about 20% of said solids, progressively coagulating said coating to form a substantially nontacky tough deformable gel by contacting said coating color with a water solution of an adhesive coagulating electrolyte, and thereafter bringing said coating in contact with a casting surface.

4. In the coating of paper to provide a cast-surfaced mineral coated paper having unusually high brightness and opacity and high gloss with enhanced afiinity for receiving printing and the like, the process which comprises the steps of applying an aqueous suspension of pigment and adhesive material of approximately 45 to 65% solids content to the paper in an initially fluent and deformable condition to form a coating thereon, stabilizing said coating against adhesion to the surface of a heated casting surface by progressively coagulating said coating with a coagulating electrolyte sufliciently to form a non-tacky'tough deformable gel, thereafter bringing said coating in intimate contact with said casting surface, drying said coating against said casting surface, and withdrawing said paper from said casting surface with separation of the coating therefrom.

5. The process of producing cast-surfaced mineral coated paper of the character described comprising applying to the surface of a web of paper a coating color consisting essentially of an aqueous suspension of pigment and adhesive material, said coating color having from about 45% to about 65% total solids and having said adhesive present in an amount between about 12% and about 20% based on the weight of said total solids, said adhesive being selected from the group consisting of casein and soya protein and mixtures thereof with latex, and after application of said coating color progressively coagulating said adhesive to a tough deformable gel by contacting said coating color with a water solution of a coagulating agent selected from the group consisting of soluble calcium, zinc, barium, lead and aluminum salts of formic, acetic, citric, tartaric, lactic, hydrochloric and sulfuric acids, squeezing off the excess solution, thereafter bringing said coating in intimate contact with a heated smoothly finished casting surface, drying said coating against said casting surface, and withdrawing said paper 1 1 from said casting surface with substantially complete separation of the coating therefrom.

6. Process as defined in claim 5, in which the. coagulation agent is calcium formate.

7. Process as defined in claim 5, in which the coagulation agent is aluminum sulfate.

8. Process as defined in claim 5, in which the coagulation agent is calcium lactate.

9. Cast surfaced coated paper produced in accordance with the process of claim 5.

10. The process of producing cast-surfaced mineral coated paper of the character described comprising applying to the .surface of a Web of paper a coating color con sisting essentially of an aqueous suspension of pigment and adhesivetmaterial, said coating color having from about 45% to about 65% total solids and having said adhesive present in an amount between about 12% and about 20% based on the weight of said total solids, and after application of said coating color progressively coagulating said adhesiveto a tough deformable gel by contacting said coating color with a water solution of a coagulating agent selected from the group consisting of soluble polyvalent metal salts of formic, acetic, citric, tartaric, lactic, hydrochloric and sulfuric acids, squeezing ofi the excess solution, thereafter bringing said coating in intimate contact with a heated smoothly finished casting surface, drying said coating against said casting surface, and thereafter withdrawing said paper from said casting surface with substantially complete separation of the coating therefrom.

11. Process as defined in claim 10, in which the coagulation agent is cadmium sulfate.

12. Process as defined in claim 10, in which the coagulation agent is zinc acetate.

13. Process as defined in claim 10, in which the coagu lating agent is a mixture of calcium formate and zinc acetate.

14. In the cast-surfaced coating of paper of the character described to produce surface characteristics adapted for receiving printing and the like, the method of forming a smooth surface on a layerof coating composition applied to paper which comprises the steps of stabilizing said coating prior to drying thereof against adhesion to the surface of a heated casting surface by progressively coagulating said coating with a coagulating electrolyte sufficiently to form a non-tacky tough deformable: gel, thereafter bringing said coating in intimate contact With said casting surface, drying said coating against said casting surface, and withdrawing said paper from said casting surface with substantially complete separation of the coating therefrom.

15. The process of making cast-surfaced mineral coated 1 paper having unusually high brightness and opacity and high gloss which comprises applying to a web of'paper a fluent mineral coating color consisting essentially of an aqueous suspension of pigment and adhesive material, said coating color having from about 45% to about 65% total solids and having said adhesive present in anamount between about 12% and about 20% of said solids, said adhesive selected from the group consisting of casein and soya protein and mixtures thereof with latex, progressively coagulating said coating to form a substantially nontacky tough deformable gel by contacting said coating color with a water solution of an adhesive coagulating electrolyte, and thereafter bringing and drying said coating in intimate contact with a casting surface.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. IN THE COATING OF PAPER TO PROVIDE A COAST-SURFACED MINERAL COATED PAPER HAVING UNUSUALLY HIGH BRIGHTNESS AND OPACITY AND HAVING GLOSS WITH ENHANCED AFFINITY FOR RECEIVING PRINTING AND LIKE, THE PROCESS WHICH COMPRISES THE STEPS OF APPLYING AND DISTRIBUTING A PREDETERMINED AND METERED QUANTITY OF FLUENT MINERAL COATING CONSISTING ESSENTIALLY OF AN AQUEOUS SUSPENSION OF PIGMENT AND ADHESSIVE MATERIAL TO FORM A SUBATANTIALLY SMOOTH SURFACE COATING ON THE PAPER, BRINGING THE COATED SURFACE OF SAID PAPER INTO CONTACT WITH AN ADHESIVE COAGULATING ELECTROLYTE WHILE SAID COATING IS STILL FLUENT ON SAID PAPER TO PROGRESSIVELY CONVERT SAID ADHSEIVE INTO A SUBSTANTIALLY TOUGH DEFORMABLE GEL WHILE MAINTAINING A SUBSTANTIALLY UNIFORM AND SMOOTH SURFACE LAYER OF COATING, BRINGING SAID COATED SURFACE OF SAID PAPER INTO CONTACT WITH A SUBSTANTIALLY SMOOTH CASTING SURFACE AFTER SAID ADHESIVE HAS BEEN CONVERTED TO SAID TOUGH DEFORMABLE GEL, AND DRYING COATING WHILE SAID COATING IS IN CONTACT WITH SAID SUBSTANTIALLY SMOOTH CASTING SURFACE, AND REMOVING SAID COATED PAPER FROM SAID CASTING SURFACE.