US2337013A - Method of making coated paper - Google Patents

Description

- appearance of I bubbles in the coating.

- coating is in 'thick Patented Dec. 14, 1943 UNITED STATES PATENT err-"ice METHOD or $210M PAPER,

Donald B. Bradner, J. Montgomery,

Champion Hamilton,

Mount Healthy, Hamilton, Ohio, Paper and Ohio, a corporation and William assignors to Fibre Company,

of Ohio No Drawing. Application July 6, 1940,

Serial No.

4 Claims. (Cl. Ill-103) This invention relates to coated methods of making same, and more to coated paper having a cast surface such as described in Patent No. 1,719,166, issued July 2, 1929 to Donald B. Bradner, one of the present applicants.

The paper of the present invention is eminently adapted to the production of can and bottle labels, of cigarette and other packages, for fancy paper and particularly candy box wrappings, for carton liners, for book jackets, magazine covers, advertising folders and other uses.

As pointed out in the above mentioned patent,-

' coated pap'ers of especially high gloss and unusual smoothness may be obtained by the casting processes therein described. v

The cast coated papers as described-in the Bradner patent have frequently suifered from microscopic defects which detracted from the appearance and interfered with fine printing. Among the defects or naked eye examination of the mentioned the following: I

Trenches.This is a condition readily observed undena/ power microscope, in which'a coating, instead of being smooth and uniform, presents a surface containing shallow trenches that follow certain of the surface'fibers of the underthese trenches are seen to be more transparent than the surrounding coating.

. When viewed with transmitted" r.

C'rwicea-Mioroscopic irregulan shaped; holes in the coating having the appearance of shrinkage cracks. Holes..l\4icroscopic rounded-holes having the being caused by minute gas StippZe.A'condition of the coating readily seen by the naked eye by transmitted light. The

and thin areas spaced a millimeter or two apar servableby reflected light,

Cockle.A condition of the cast coated paper which has the cockled appearance'of air dried bond paper as contrasted with a fiat calendered paper.

We have discovered that all of these defects, notwithstanding theirdifierent and distinctive nature, are materially r,educed,-in fact'practically eliminated by so controlling the flow or diffusion ofthe aqueousivehicle from theggcoatin g composi--' tions into the .paperfstock, and removal-oi tliei waterthrough the back of theweb, that no considerableproportion ofl the fibers in the paper is Otherwise stated; in the wetted' "at any time.

This condition is often obrate of penetration containing an agent which tion of "water, as for example a paper containing a considerable amount of practice of our improved process we prevent deleterious swelling of the paper by limiting the of the water from the coating into the paperand by water through the back of the sheet.

By a selection of paper stock and coating composition we can retard a rapid penetration of water from the coating into the sheet and by maintaining a high rate of evaporation through the back of the paper we rapidly remove what ever water that does diifuse into the paper. In this way deleterious swelling of the paper, is prevented and defects in the surface of the cast coating are. eliminated or reduced to an extent to permit the manufacture for high grade printing. I

The paper stock should be of a kind :which is not too rapidlywet by the coating composition employed, and it should retard rapid absorption of the coating vehicle into the paper. For this purpose, a dense, wellformed; hard-sized paper is desirable. .By hard-sized paper we mean paper resists rapid absorpof a product suitable rosin sizing which has be precipitated with alum. As an example of W1... we mean by hard-sized paper we may mention the equivalent of a paper of of pounds per ream of 500 sheets 25 x 38 inches and having a sizing value in excess of 15 seconds as measured by the Valley size test. Paper stocks which are well formed and relatively dense are' preferred for the present purpose over widely formed, bulky, porous stocks, as they show a greater resistance to the penetration of water from the coating. r

With regard to the selection ofcoating compositions, those of. high total solids are in general desirable for our purposes. We prefer to use coating compositions considerably higher in solids content than are customarily used in making mineral coated paper. For example, we pregfer to'use coating compositions having a solids content in excess of 45% and advantageously of the order of to By the use of coating" compositions of high solids content, less water is available for penetration into the paper and the higher viscosities usually accompanying high solids coatings also retard rapid flow of the water into the sheet. The ingredients used in the coating compositions may be those commonly employed' in the usual paper coating compositions.

The water which diffuses into the paper must be rapidly evaporated {through the back of the web in order tojprevent accumulation of water in rapidly evaporating the a basic weight:

thepaper; which would cause substantial swellweight per thousand square feet of surface, of ing of the fibers. This may be accomplished by coating compos t on c mp s g pi ment and adproviding a blast of hot air on the back of the hesive in aqueous. suspension, contacting the web. Under these conditions it appears that coated surface of said web with a casting surface, the amount of water in the body of the stock 5 bringing a. current of air in contact with the exis maintained at such a low value that the fibers posed surface of the paper web to evaporate the are not wetted sufficiently to produce a swelling V water therefrom, and maintaining the rate of whichis harmful to the coating. It is possible evaporation relatively high with respect to the that the mechanism of the process is that, alrate of absorption of water by the paper web,

though the surface layer of the papernext to whereby the water content of the paper web is the coating may become thoroughly wet, sub insufiicient to cause a significant swelling of stantially all of the water may vaporize through the fibres.

the sheet from this very thin layer, so that there 2. A process of manufacturing cast surfaced is little or no diffusion of liquid water into the coated paper having a coating in excess of two body of the paper. pounds dry weight per thousand square feet of In general it is advisable to apply the coating surface, which comprises applying to one face of to the paper web only a very short time before a paper web having a low rate of water absorpcontact with the finishing surface in order to tion a layer of coating composition comprising reduce the degree of penetration of water into mineral pigment in aqueous suspension, pressing 0 the face of the paper web against a casting surthe paper.

It will be evident that a combination of all face and drying the coating while in contact with three of the above mentioned factors will orthe casting surface until the coating no longer dinarily'give the most beneficial results. For 'ex-. adheres to such surface, said drying being acample, a combination of a water-resistant body complished by bringing a current of air of relastock, high solids coating, and rapid evaporation tively low water content against the exposed suris particularly desirable. Considerable variaface of the web at a rate such as ,to maintain the tion, however, in any of these factors or condiwater content of the paper during the drying options is permissible provided compensation is eration below an amount which will cause a made in the other factors and conditions. For significant swelling ofthe fibres of the paper example, reducing the water impenetrability of web.

the paper stock may be offset by increasing the 3. A process of manufacturing cast surfaced solids or by increasing the viscosity of the coata coated paper having a coating in excess of two ingcomposition, or both. Also, by increasing pounds dry weight per thousand square feet'of the rate of evaporation a higher rate of absorpsurface which comprises applying to one face of a tion. may be permitted. paper web a layer of coating composition com- Although this invention has been described prising mineral pigment and adhesivein aqueprimarily in' connection with the application of a ous suspension having a solids content in excess coating composition directly to the paper andthe of 45%, pressing the face of the paper web subsequent drying of the coating while in con-- against a casting surface and drying the coating tact with a solid finishing surface, the process 40 while in contact with the casting surface until of the invention may also be carried out in acthe coating no longer adheres to such surface, cordance with the method described in our prior said drying being accomplished by bringing a Patent No. 2,029,273. In carrying out this emcurrent of air of relatively low water content bodiment of the present invention, the coating against the exposed surface of the web at a rate composition is applied directly to the finishing such as to maintain the water content of the surface and the web of substantiallydry paper paper during the drying operation below an is contacted with the still wet coating on the amount which will cause a significant swelling finishing surface and the coating is transferred 1 of the fibres of the paper web. I

to the paper during the time the coating is set- 4. A process of manufacturing cast surfaced ting. Dleterious swelling of the fibers in the coated paper having a coating in excess of two paper is prevented in the saine manner as has' pounds dry weight per tholmand square feet of been described in connection with the method surface which comprises, applying to one face of directly applying the coating to the paper, of a paper web having a low rate of water abnamely, by a properselection of the paper stock sorption a layer of coating composition compris and coating composition andby increasing the ing mineral pigment and adhesive in aqueous rate of evaporation, suspension and having a solids content in excess The expression 'cast surface is used in the of 45%, pressing the face of the paper web appended claims to designate coating surfaces, against a casting Surface and drying the coating whatever their composition, which have been.set= while in contact with the casting surface until from a plastic condition in contact with a solid 5 the coating no longer adheres to such surface,

non-adhering casting surface in the manner desaid drying being accomplished by bringing a scribed in the patent to Brander, No. 1,719,166 current of air of relatively low water content and the patent to Bradner and Montgomery, No. against the exposed surface of the web at a rate 2,029,273 so that they have substantially the sam such as to maintain the water content of the finish as the castingsurface itself. p p r during the drying operation below an W claim; amount which will cause a significant swelling 1. A method of making cast surfaced coated of the fibres of tin; paper web.

paper which comprises applying to one face of I DO ALD B. BRADNER,

a paper web a layer, in excess of two pounds dry J. MONTGOMERY.