US3158497A - Paper coating method employing high flexible blade pressures - Google Patents

Description

Nov. 24, 1964 H. 5. FIRD ETAL 3,158,497

PAPER comma METHOD EMPLOYING HIGH FLEXIBLE BLADE PRESSURES Filed Aug. 17, 1961 2 eets-Sheet 1 1-1. G FVIRD ETAL 3,158,497

Nov. 24, 1964 PAPER COATING METHOD EMPLOYING HIGH FLEXIBLE BLADE PRESSURES 2 Sheets-Sheet 2 Filed Aug. 17, 1961 \u 36 In A 3 I! Q is .7, A" .1 I I I I Wil 2 HI" 22 1 I E I? /i agA' United States, Patent ()fitice 3,158,497 Patented Nov. 24, 1964 3,158,497 PAPER QGATING METHOD EMPLGYENG HIGH FLEXIBLE BLADE PRESSURES Harold G. Fird, Kimberly, Wis, and Herman B. Iiustice, Center-ville, Ohio, assignors to Kimberly-Clark Corpo ration, Neenah, Wis., a corporation of Delaware Filed Aug. 17, 1951, Ser. No. 132,036 1 Claim. (1. 111-102) This invention relates to the application of coating materials to traveling paper webs and is particularly directed to the coating of relatively heavy papers of about 60 pounds basic weight and above for the purpose of improving the surface character of such papers.

In the coating of paper webs, compositions which are essentially aqueous fluid suspensions of pigment and adhesives are commonly employed. In certain desirable modes of application of such coatings, usually termed mineral coatings, an excess of the coating material is furnished the web and a flexible blade is used to trowel or smooth the coating onto the paper, the excess being removed by the blade. Occasionally hard particles of such a com position, or particles of foreign material, are carried with the coating composition to the area of contact of the blade and paper. The lodging of such particles between the blade and paper then may result in marking or scratching of the coating on the web; in extreme cases the web may even be torn as it passes beneath the blade.

Such web is, in practice, carried to the flexible blade on a backing roll having a somewhat resilient surface. Pressure is applied to the blade and its holder to maintain the blade in contact with the web and coating composition. Such pressure is generally low and adequate wei hts of coating on the web are attained with coating compositions of a solids content of 50-55%.

We have found that the surface characteristics of such paper may be materially improved, particularly with relation to the tendency of the coating to scratch or streak, by materially increasing the pressure of the blade against the traveling web. In addition, we have found that while the increased pressure tends to decrease the coat weight achieved with a coating formulation of given solids and viscosity, the composition solids may be increased to procure desirable coat weight without occasioning the coating to acquire surface imperfections, and while attaining a smooth surfaced uniform thickness paper sheet.

Accordingly, a primary object of this invention is to provide a novel process for the application of mineral coating materials to traveling paper webs.

The invention may be practiced by the utilization of many different mechanical constructions and, therefore, the arrangement set forth in the accompanying drawings is to be regarded as illustrative only and for the purposes of more clearly setting forth the features of the invention.

Other objects and advantages obtained by our process will become apparent from the drawings wherein:

FIG. 1 is a view showing the cooperation between the blade, paper web and backing roll, and the coating composition supply in a preferred embodiment of the invention.

FIG. 2 is a perspective view of one structural arrangement for the practice of the invention;

FIG. 3 is a side elevational view of the structure of FIG. 2; and

FIG. 4 is a view taken on line 4-4 ofFIG. 3.

In the drawings corresponding parts are designated by similar numerals where such is appropriate.

Referring to the drawings, the numeral 1 designates a longitudinally extending backing roll which suitably has a diameter of about 30 inches and is arranged to be driven or, more specifically, web contact.

ball has a density of 56; suitably, in the practice of the invention this density may lie in the range of 47 to 70.

An applicator roll 3 is coextensive longitudinally with the backing roll and is in rotatable contact with metering roll 7; the applicator roll 3 is supplied through the metering train rolls 7 with coating composition from pond 5. Pond 5 may itself be supplied with coating composition through nozzle means, one of which is shown at 4. Applicator roll 3 is arranged to be driven in counter rotation to the roll 1 as indicated by the arrow. A nip 6 is formed between the applicator roll and the backing roll.

A web of paper 8 is passed continuously to the nip 6 in the practice of the invention. Coating composition in excess, in the form of a heavy film, is applied to the traveling web at the nip and the coating composition is carried upwardly on the web in the rotation of the backing roll toward the flexible knife blade 1%.

Blade 10 is of tempered steel, has a thickness of about 0.012 inch, and is honed at its tip; the blade in practice is flexed somewhat by applied pressure.

The blade 10 is supported in a blade holder 12 which is itself secured by bolts as at 14 to a mounting i6. Mounting 16, as shown, is triangular in form and composed of three longitudinally extending bars or panels; a plate 18 is welded to each end of the mounting closing the ends. Each plate 18 is also welded to a shaft 29 thereby rigidly fixing the shafts 20 to the mounting. Accordingly, rotation of shafts 20 causes the mounting 16, blade holder 12, and blade 10 to rotate relative to the backing roll 1.

For the purpose of rotating shafts 25), a link 22 is secured to each shaft and is itself secured to a pin as at 24. Pin 24 forms a lower extremity of the flexible joint 26 which at its upper end is secured to the piston rod 28 of an air cylinder 30. Thus air pressure applied to the cylinder 30 depresses the link 22 and rotates the shaft 20 toward the backing roll, applying 10.

The shaft 29 is supported by bearing blocks 32 on each side of the mounting 16. A frame 34 supports each hearing block; each frame is itself supported from the bed plate 36 of the roll-bearing housing 358. Frame 34 is apertured on each side at 39 to provide for the passage of shafts 2d.

Bearing housing 38, one on each side of the machine, carries the roll 1. The blade is thus well supported for pressure application.

Blade pressure as referred to hereinafter and in the ap: pended claims is set forth as the radial load in pounds per lineal inch imposed by the blade on the roll. More specifically, it is the force per lineal inch in the direction of the radius of the backing roll at the line of blade-roll The direction of this force and the radius are designated by the arrow and letter R respectively in FIG. 1.

Commonly, in usual practice, this bladepressure is low-on the order of one or two pounds per lineal inch. With basis weight Webs of 60 pounds and above, such pressures, utilizing a composition having a solids content of approximately 57-59% and a composition viscosity in the range of 50 to poises, yields a coating weight on one side of the web of 89 pounds, with the web speed on the backing roll at about 600-700 feet per minute. For this purpose it is only necessary that the mechanism applying the coating to' the websuch as applicator roll 3furnish the coating composition in excess.

pressure to the blade We have found that marks induced in the finished coatmaterially minimized by increasing the pressure of the blade several fold-to at least 6.5 pounds per lineal inch, without other change in the operation. Such pressure corresponds to very high pressures per square inch since the blade area in contact with the web is low. For example, with a contact length on the roll periphery of 0.020 inch the pressure exceeds 300 pounds per square inch at 6.5 pounds per lineal inch.

In general, it is preferred to maintain the pressure be tween about 6.5 to 9.0 pounds per lineal inch of blade pressure exerted radially of the roll in order to achieve substantial blade mark elimination.

Such pressure does tend to reduce the weight of coating applied. However, we have further found that the coating weight may be maintained if the solids content of the coating is increased also-and that such higher solids content may be employed while retaining the beneficial effect of the higher blade pressures as to the blade marks.

The solids content, in the invention as practiced, is correlated with the blade pressure to achieve the desired coat weight. Thus, a solids content of the coating composition, while maintaining viscosity in the general range indicated, of about 60-64% solids, permits the attainment of coat weights per side in the 8-9 pound range.

By way of specific example: a paper web as at 3, having a basis weight of 70 pounds and absorptive to the fluid coating, is continuously formed on the paper machine and in the customary manner dried and passed to the nip 6; such web normally, on entering the nip, has a low moisture content of about 46%, dependent to some extent upon ambient temperature and humidity conditions.

The composition 5 contains in parts by weight:

Clay 70 Calcium carbonate 30 Starch 19 Sodium hexarnetaphosphate 0.2 Caustic 0.2 Calcium stearate 0.5 Soap 0.5 Watersufiicient to provide 61% solids 77 The viscosity of this formulation is 60 poises; it is to be understood, however, that the viscosity may vary somewhat dependent upon the specific conditions of the materials used, as is known in the art, and the practice of the invention is not adversely afiected by variation of viscosity within the limits indicated-that is, 50 to 80 poises.

This coating composition is carried in the travel of the web to the blade. The blade holder extends at an angle of about 55 to the tangent to the backing roll at the point of blade contact (FIG. 1); the blade itself projects about /1 inch beyond the holder and suitably is of spring steel of a thickness of about 0.012 inch. The blade thickness should not exceed 0.024 inch and, in fact, is somewhat too stiff at this thickness with a inch projection.

Such composition as described when applied to the 70 pound basis weight (25" x 38" x 500 sheets) web 8 (FIG. 1) results in a coating weight of 8-9 pounds per web side when the web speed is about 650 feet per minute and the blade pressure is 6.5 pounds per lineal inch.- The web itself has some effect on the weight pickup and in some instances of web condition 10 pounds per side may be achieved. However, with the same composition, but in creased water content to give lower solids of about 56%, a coat weight of roughly 5-6 pounds per side is attained at the same blade pressure. The lower weight pickup in some instances is not detrimental but generally, in the production of bookpaper, higher coat weights are desired to provide an improved printing surface. In either event blade scratches are minimized and the customarily desired coat weights are achieved and the printing character of the coating determined by correlating the solids content of the composition with the high blade pressures.

At higher blade pressures of about 9.5 pounds per lineal inch the coat weight-tends to drop slightly; accordingly, it is preferable to maintain the composition solids at the high end of the -64% range with this higher blade pressure.

It will be understood that this invention is susceptible to modification in order to adapt to different usages and conditions and, accordingly, it is desired to comprehend such modifications within the invention as may fall within the scope of the appended claim.

What is claimed is:

In a process for the production of coated paper in which a traveling uncoated, absorptive paper web is coated with an aqueous mineral coating composition which is subject to the inclusion therein of scratch producing particles and which web is continuously drawn in the coating process on a resiliently covered rotating backing roll from a first pressure nip formed between the resiliently covered backing roll and a driven applicator roll to a second pressure nip formed between the said backing roll and a flexible blade having a thickness of between about 0.012 and 0.024 inch, the steps of:

(a) driving the said backing roll and said coating applicator roll in counter-rotation and in the direction of web travel;

(12) applying to said web with said applicator roll an excess of the aqueous mineral coating composition having a viscosity of 50 to poises and a solids content of about 60 to 64 percent by weight, said web having a basis weight (25" x 38" x 500 sheets) of at least about 60 pounds;

(c) passing the said web on said backing roll to said second pressure nip formed by said flexible blade and said backing roll at a position spaced 6 round the backing roll from the first pressure nip; and

(d) pressing said blade into contact with said web on said roll surface to trowel excess of coating composition from the web, to smooth the remainder of coating composition on the web and produce a pressure radially of the backing roll on the web of between about 6 /2 to 9 pounds per inch over the length of blade contact with the web, said pressure being at least 300 pounds per square inch andwhich square inch area is based on the area of contact of the blade with the web.

OTHER REFERENCES -Heiser: Paper Coating Trends in the United States, Svensk Pap-pars Tidning (Swedish Paper Journal), pp. 389 et seq., June 30, 1958.

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