US 2691606 A
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Description (OCR text may contain errors)
Patented Oct. 12,1954
PROCESS OF FINISHING PAPER Thomas L. Ziliox and William Palmer Taylor, Hamilton, Ohio, assignors to 'The Champion Paper and Fibre Com corporation of Ohio pany, Hamilton, Ohio, at
No Drawing. Application December 7, 1951,- Serial No. 260,564
6 Claims. (01. 117-65) This invention relates to a process of finishing paper and particularly coated paper. By coated paper is meant paper (including post card, cardboard, etc.) which carries a coating of mineral pigment, such as for example, clay, calcium carbonate and the like, and an adhesive. The coatingcomposition is applied as an aqueous suspension either during the manufacture of the paper or as a separate, subsequent operation. Such papers are extensively used for hi h grade pri -1 In order to obtain the smooth surface necessary for high grade printing these papers are subjected to an intensive smoothing or finishing operation by heavy calendering or supercalendering. In this operation the coatingflows to some extent under the heavy pressure exerted. To enhance the plasticity of the coating, or more precisely of the adhesive in the coating, so that it flows morereadily, moisture in som form is often applied to the paper just before or during its passage through the calender or supercalen-,
der. The use of liquid water is particularly effective for this purpose, but in the past it has been necessary to use a coating in which the adhesive is relatively insoluble in water, as otherwise a serious difiiculty commonly called scaling results.
The mechanism of scaling is an imperfectly understood phenomenon, but its results are al-' ways objectionable and in aggravated cases are disastrous. It is clear, however, that the coating composition or some constituent of it becomes detached from the paper and deposits on the metal calender rolls often as discrete flakes. These continuously emboss the coated web at each revolution of the roll thus marring the surface of the sheet. Often these flakes become detached from the roll and become embedded on the surface of the paper. These are difficult to detect in the inspection of the paper and give serious trouble in the subsequent printing of the paper, where the particles pick off the sheet,'
foul the ink and are generally obnoxious.
Starch-containing coatings have long been recognized as being especially prone to scaling. This is thought to be due to the fact that starch coatings are in general relatively Water soluble in the sense that they disintegrate and come off the paper when wet rubbed. Consequently plasti cization of starch coatings by the use of substantial amounts of water has not been found generally practicable. It is believed that one important reason starch, coated papers have been generally inferior tocasein coated papers is that it has notfbeen possible to obtain the desired smooth surface because they cannot be as well plasticized in the calendering operation du to these scaling troubles. Even when the starch has been treated with resins or otherwise to render it more or less insoluble the difiiculty persists to a considerable degree. The trouble exists to some extent even with water soluble casein-containing coatings, but is so much easier to waterproof or insolubilize casein than starch that the scaling problem with casein coatings is notso serious.
Scaling difficulties are particularly likely to occur when relatively large quantities of water. are used to surface plasticize th coatings during a supercalendering operation, such as in themethods described in the Gates Patents Nos. 2,088,893 and 2,293,278, and'in the Montgomery Patent No. 2,251,890. Often coating containing Water soluble adhesive will stick to the rolls, shutting down the supercalender. In fact, heretofore it has been impossible to use thesemethods on starch coatings ona profitable basis.
One object of the present inventionis to provide a method of finishing paper carrying a relatively water-soluble coating by water plasticizing the coating without scaling troubles.
Another object is to provide a fool-proof method of supercalendering coated paper in which the surface-of the coating is plasticized with liquid water during the supercalendering operation.
Another object is to provide an economically practical method of plasticizing starch coated paper with water during a calendering operation.
Other objects will be apparent from the detailed description of the invention which follows. We have discovered that coatings and surface sizings containing starch or other water-soluble adhesive can be water plasticized in a calendering operation without scaling, rubbing off, or sticking of the coating, by employing an aqueous oleaginous emulsion containing a cationic nitrogenous surface active agent. In conventional calendering operations, wheth- '61 with a stack of all metallic rolls or of alterhate rolls of compressed fiber and metal, an increase in gloss and in smoothness is effected by the slippage between the rolls and the heavy pressures applied. As previously mentioned in connection with the Gates patents, and the Montgomery patent, the application of liquid water to the surface of the coating greatly facilitates the calendering, permitting improved finish. However, in commercial operations, paper carrying a surface layer of a water-soluble adhesive such as starch, dextrine, polyvinyl alcohol, watersoluble cellulose derivatives, etc., cannot be so run through a calender on a practical basis. Of the paper so calendered only a relatively small part thereof would be found, upon sorting, to be free of defects and saleable. These adhesives are not necessarily water-soluble in the true sense of the word; they do, however, disperse readily in water and are not water resistant when dry. Perhaps due to rapid absorption of the water by the water-soluble adhesive there is such a lessenin of coherence as not to be able to withstand the physical forces applied in calendering.
The application of an oil film to the metallic rolls of a calender has not been found effective to prevent scaling and disintegration of water plasticized coatings containing water soluble adhesives. Whether this failure is due to wearing off of such a film, or to other causes is not known.
We have found, however, that if a cationic nitrogenous surface active agent is present, starch coatings can be "water plasticized during a calendering operation without the aforementioned disadvantages of scaling, sticking, and the like, and with the advantages of improved finish, freedom from defects, and ease of operation such as are obtained with water-insoluble coatings, for example, casein-formaldehyde coatings. Our invention makes practical and fool-proof the processes of the aforementioned patents, on starch and similar water-soluble coatings, where previously such processes were entirely uneconomical.
. The reason Why emulsions containing a cationic nitrogenous surface active agent will work is not known. It may be that agents of this class form an adherent layer on both the metallic roll and the surface of the coating leaving an easyshearing film of lubricant between the roll and coating. Also, there is some reason to believe that these agents form a protective layer on the pigments, or that they, in a sense, increase the viscosity of the water to the extent of slowing up-its wetting and penetration of the coating. In any event the coating behaves as though it were strengthened enough to withstand the action of a calender stack when water plasticized, yet is softened sufficiently to calender to an improved finish. By improved finish we mean a greater increase in finish (gloss and smoothness) than would be obtained if the coated paper is calenderedwithout plasticizing as in the aforementioned patents.
The following are representative of the various cationic nitrogenous surface active agents:
High molecular weight imidazolinium chlorides .having at least one carbon chain containing .from to 18 carbon atoms (for example Alro Quaternaries, O, C, S, sold by Alrose Chemical Co.)
Myristamidopropyl dimethyl benzyl ammonium chloride (Agent M, sold by American Cyanamid Corp.)
The dialkyl dimethyl ammonium chlorides whose alkyl groups contain from 8 to 18 carbon atoms 4 (for example, Arquad 2C and 2 HT sold by Armour and Co.)
The higher alkyl dimethyl benzylammonium chlorides (for example, Triton K-GO sold by Rohm and Haas Co.)
The fatty acid imidazoline hydroxy acetates (sold as Miranol-OH by the Miranol Chemical Co.)
Long chain substituted oxazolines (such as the oxazoline from oleic acid and 2-amino-2- methyl-1, 3 pentanediol sold as Alkaterge O by Commercial Solvents Corp.)
The long carbon chain primary, secondary, and tertiary amines. Particularly suitable are the amines having one or more alkyl groups containing from 10 to 18 carbon atoms; (for example the primary amines derived from fatty acids and sold as Armeens, or the corresponding acid salts sold as Armacs, by Armour and Co.) The shorter chain amines are not as convenient to handle because of their skin irritating properties.
These cationic agents, which are principally amines or quaternary-ammonium compounds, contain one or more alkyl groups of from 10 to 23 carbon atoms imparting hydrophobic characteristics, and a polargroup imparting hydrophilic properties. The free bases which are not watersoluble are reacted with an acid such as acetic or hydrochloric acid to form a water-soluble salt.
The nature of the oleaginous material is not critical; in general any water-immiscible material which exhibits lubricating properties is suitable. Vegetable oils, such as cotton seed oil can be used, and also animal oils, for instance, lard oil. Mineral oils such as light weight petroleum oils, kerosene, and petrolatums are preferred merely because of availability and low cost. Various other oleaginous materials are tributylphosphate, dioctyl phthalate, butyl stearate, ethyl carbonate, and nitroparaffins. Since calender stacks normally operate at elevated temperatures the oleaginous material is not lim ited to oils in the sense of a material which flows at room temperature but may be a semisolid or solid provided it is free flowing at temperatures below F.
The concentration of the emulsion only needs to be such as to insure a very thin film of cationic agent being present. ing from about 1% to 5% total of cationic agent and oleaginous material are suitable for most purposes, but for special purposes may vary from /2% to 8%. The ratio of cationic agent to oleaginous material is normally in the range of 1 part of cationic agent to from 0 to 10 parts of oleaginous material. In this connection it should be noted that some of the cationic agents are in themselves oleaginous. For example, the long carbon chain amines are of an oilor grease-like nature and can in some cases be used without the addition of an oil, but it is usually desirable to use kerosene or a heavier petroleum fraction concomitantly to reduce their viscosity and stickiness. I
One emulsion which we have found particularly satisfactory consists of 20 pounds of white oil, 10 pounds technical grade of high molecular weight aliphatic primary amines prepared from tallow (Armeen T from Armour and Co.) and 3 pounds glacial acetic acid, emulsified in about 1500 pounds of hot steam condensate. This emulsion was used in connection with a web of paper carrying a coating composition consisting of clay Emulsions contain-' 5, and oxidized corn starch .treated with melamine resin. The coated side of the paper was flooded with the emulsion and the excess removed-by passing the paper over a small rodimmediately before contacting a metal roll in a supercalender stack. vOn continued running the paper showed no tendency to scale and the gloss and smoothness of the paper were excellent. The same paper when treated with plain water scaled almost immediately and the product was unsuitable for printing.
If the coating compositionon the paper contains calcium carbonate, it is advisable to incorporate some material like stearic acid or other long chain fatty acid in the emulsion. Possibly these agents react to form a film of calcium soap upon the calcium carbonate particles; at any rate they appear to lubricate these coatings, which normally have a rather high coefiicient of friction, and the result is less tendency to scale.
For example, an aqueous coating composition consisting of 80 parts coating clay, 20 parts finely precipitated calcium carbonate and 18 parts of partially oxidized starch was applied to a web of paper and dried. About 10 pounds of coating (dry weight) per ream of 500 sheets 25" x 38 was applied. The coated web was supercalendered according to the process described in the aforementioned Montgomery patent using an oil emulsion. The oil emulsion consisted of 120 pounds of the acetic acid salts of a mixture of hexadecyl, octadecyl and octadecenyl amines, 80 pounds liquid petrolatum, 10 pounds deodorized kerosene, 20 pounds of stearic acid, and pounds glacial acetic acid, melted together and emulsified in about 7500 pounds hot water. The paper calendereol easily to a high gloss with no trace of scale.
Examples of other emulsions which we have successfully employed are: 15 parts of Miranol- OH (a 45% solution of a fatty acid amide azoline hydroxy acetate), 5 parts of Sohio Technical White Oil No. 62 (a light weight liquid petrolatum), and 1 part of stearic acid, melted together and mixed into 200 parts of hot water.
1 part of Arquad 2C (a dialkyl dimethylammonium chloride in which the alkyl groups consist of a mixture of octyl, decyl, dodecyl, tetradecyl, hexadecyl and octadecyl groups), 4 parts of kerosene, and 100 parts of water.
While the invention has been particularly described in connection with the use of oil-in-water type emulsions, it is within the scope of the present process to use water-in-oil type emulsion. The latter, however, are in general less conveniently used for the present purpose.
We are aware that oils, greases, waxes, and the like have been used to coat or impregnate paper to give it some special property, such as for example, waterproofness. Wax emulsions in water have been proposed for this purpose. The present invention aims in no way to coat or impregnate the paper with an oleaginous material. It is true that a very small amount of such material may exist adventitiously on the surface of paper of this invention after calendering, but it is there only in minute amounts; it forms no visible film and is present in such small amount as not to affect the printability or other properties of the sheet. Ordinarily the finished paper will contain of the order of 0.1 per cent or less and in no case more than about one half per cent by weight of material from the emulsion. Since the cationic agents are effective in minute quantities, and since the more volatile oils such as kerosene tendto be driven off by the heat of the supercalender'the amount of material from the emulsion. left on the paper may be aslittle as 0.01 per cent of its weight.
' In water plasticizing a web byapplying a large amount of liquid water and immediately doctoring off the excess as taught .in the aforementioned patents, the amount of Water, or of emulsion in our case, remaining will be in the range of from ounce to 1 ounces per square feet of web surface.
Although the invention has been described with particular reference to a .supercalendering operation, it can also be employed on mineral-pigment coated paper in the so-called water finishing on all metal-roll calender stacks. Similarly it may be employed to advantage in calendering webs tub sized with starch or other water-soluble adhesive to prevent scaling or sticking.
By the term calendering we mean the process wherein a web of paper is passed through a stack of superimposed rolls, at least some of which are metallic; that is, in a calendering operation the web is passed through either an all metal-roll stack, or a stack containing metalrolls and compressed fiber rolls.
This is a continuation-in-part of our application for patent Serial No. 762,822, filed July 22, 1947, now abandoned.
1. Process of finishing paper carrying a surface layer containing a water-soluble adhesive in a calendering operation which comprises, applying to said surface layer an excess of an aqueous emulsion containing from percent to 8 percent by weight of an oleaginous composition comprising 1 part by weight of a Water-soluble cationic nitrogeneous surface active agent having at least one alkyl group of from 8 to 23 carbon atoms to impart thereto hydrophobic properties and a polar group to impart thereto hydrophilic properties and up to 10 parts by weight of an oleaginous water-immiscible material, which oleaginous composition exhibits lubricating properties and is free flowing at temperatures in the range between room temperature and F'., immediately thereafter wiping off the excess emulsion and pressing the wetted surface of the paper against a metallic calender roll, and completing the calendering to produce a smooth substantially scale-free paper carrying between 0.01 percent and 0.5 percent by weight of said oleaginous composition.
2. Process as defined in claim 1 in which the water-soluble adhesive is starch.
3. Process as defined in claim 1 in which the cationic nitrogenous surface active agent is an acid salt of a long carbon chain amine having at least one alkyl group containing from 10 to 18 carbon atoms.
4. Process as defined in claim 1 in which the cationic nitrogenous surface active agent is a dialkyl dimethyl ammonium chloride, each of said alkyl groups containing from 8 to 18 carbon atoms.
5. Process as defined in claim 1 in which the surface layer of the paper is a coating which contains calcium carbonate and the aqueous emulsion contains a fatty acid.
6. Process of finishing paper carrying a coating containing mineral-pigment and a water-soluble adhesive in a super-calendering operation which comprises, applying to said coating an excess of an aqueous emulsion containing from percent to 8 percent by weight of an oleaginous composition comprising 1 part by weight of a watersoluble cationic nitrogenous surface active agent having at least one alkyl group of from 8 to 23 carbon atoms to impart thereto hydrophobic properties and a polar group to impart thereto hydrophilic properties and up to 10 parts by weight of mineral oil, which oleaginous composition exhibits lubricating properties and is free flowing at temperatures in the range between room temperature and 180 F., immediately thereafter wiping off the excess of said emulsion and pressing the wetted surface of the paper against a metallic calender roll, and completing the supercalendering to produce a smooth, substantially scale-free paper carrying between 0.01 percent and 0.5 percent by weight of said oleaginous composition.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 10 2,069,786 Van der Meulen Feb. 9, 1937 2,293,278 Cates Aug. 18, 1942 2,321,244 Rawling June 8, 1943 2,568,288 Montgomery Sept. 18, 1951