US 3244094 A
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Description (OCR text may contain errors)
April 5, 1966 J. T. GRESHAM METAL EMBOSSING ROLLER FOR PAPER 2 Sheets-Sheet 1 Filed July 16, 1962 Patented Apr. 5, 1966 of Delaware Filed July 16, 1962, Ser. No. 210,022 1 Claim. (Cl. 10128) My invention relates to papermaking machines and, more particularly, to apparatus and methods for embossing sheet materials, such as paper.
It has been previously proposed, such as set forth in a patent to F. A. Sunderhau-f et 211., 2,662,002, issued December 8, 1953, to emboss paper by drawing it be tween a pair of metal embossing rolls. Each of the embossing rolls is provided with projections or bosses on its surface separated by depressed surface portions, and one of the embossing rolls is mated with the other, with the bosses of one roll fitting into the depressions of the other so as to provide corresponding bosses and depressions in the paper moving between the rolls.
As described in the Sunderhauf et 211. patent, one of the rolls may be provided with its bosses and depressions by rotating the roll in contact with a relatively short, small diameter, master die roll held in forceful contact with the embossing roll. The embossing roll is in relatively soft condition to thus receive embossing depressions from the die roll. The second embossing roll may be provided as described in this patent by treating its surface to acid resist and rotating it in contact with the first embossing roll so that its acid resisting surface is treated for subsequent etching. Such a master die roll for providing an embossing surface on an embossing roll is also shown, in somewhat greater detail, in the patent to Offenbacher, 681,727, issued September 3, 1901.
I have found that the use of such a master roll die results in bosses on the embossing rolls which have curved blunt edges and which thus do not fold the sheet material being embossed along the edges of the bosses on the surface of the embossing roll so as to provide clearly distinguishable embossed lines on the sheet material. Such master r-oll dies are conventionally hand engraved with the pattern to be transferred to a roll, and this method for providing a pattern on a roll is thus quite expensive.
It is an object of the present invention to provide an improved embossing apparatus comprising an embossing roll which has clearly delineated and undercut bosses such as may be provided by phot-oengraving the embossing roll, the embossing roll cooperating with a resilient surface which forces the material of the product around the sharp edges of the bosses so as to provide sharply delineated embossed lines in the product.
In brief, the invention contemplates that an embossing roll may be easily and economically made by photographically transferring the embossing design desired from a photographic negative onto the surface of a metal roll, and etching the roll after the surface has been so photographically treated, so that the desired bosses are formed on the surface of the roll. It is contemplated that the roll so formed shall be used in conjunction with a mating roll having no particular pattern formed on its periphery but having a soft yieldable peripheral surface to receive the bosses of the metal roll, so that the metal roll is operative to transfer its design onto the paper or other sheet material traveling between the rolls.
The invention consists of the novel constructions, devices and methods to be hereinafter described and claimed for carrying out the above stated objects, and such other objects, as will be apparent from the following descrip tion of a preferred construction for and manner of practicing the invention, illustrated with reference to the accompanying drawings, wherein:
FIG. 1 is a perspective view of a metal embossing roll in blank condition prior to the provision of embossing projections on its outer surface;
FIG. 2 is a plan view of a photographic negative which may be used in treating the surface of the roll;
FIG. 3 is an elevational view showing the roll being dipped in an enamel bath constituting one step of the process of treating the roll surface;
FIG. 4 is a perspective view of the roll showing the photographic negative being applied about the roll;
FIG. 5 is a perspective view of the roll with the photographic negative disposed about it being exposed to the light of an arc; I
FIG. 6 is an elevational view of the roll being dipped in an etching tank;
FIG. 7 is a fragmentary sectional view on an enlarged scale of the roll during the process of formation of bosses on the roll, illustrating the application of an acid resist powder to the roll surface;
FIG. 8 is an end view of the metal embossing roll subsequent to its surface treatment and positioned to have a nip with a rubber covered mating roll;
FIG. 9 is a fragmentary sectional View on an enlarged scale taken on line 99 in FIG. 8;
FIG. 10 is a fragmentary sectional view similar to FIG. 9 but on a still further enlarged scale; and
FIG. 11 is a view similar to FIG. 9 of a prior art metal embossing roll.
Like characters of reference designate like parts in the several views.
The metal embossing roll 15 of the invention, prior to surface treatment, is illustrated in FIG. 1. The roll 15 has a smooth cylindrical surface 16 and is preferably made of steel. End shafts 17 are provided on the roll for suitably rotatably mounting it.
The invention contemplates that the surface of the roll 15 shall be photographically treated so as to render certain portions of the roll surface resistive to the action of acid and that the surface of the roll shall then be acid treated in order to etch the required depressions into the roll surface and provide the desired bosses on the roll. It will be understood that the various chemicals and method steps may be varied while still practicing the invention; however, for the purpose of illustration, a speclfic example will now be given as to how the bosses may be formed on the roll.
It is desired that the surface of the roll 15 shall be clean, and saturated sodium bichromate and/or chromic acid may be used to wash the roll for this purpose. With out rinsing off these cleaning agents, the roll surface is then scrubbed thoroughly with grit pumice stone, and the surface of the roll 15 is then washed to clean ofi" these agents.
The clean surface of the roll is then coated with a light sensitive enamel. This may, for example, be Photoengravers Hot Top Enamel consisting approximately of percent by volume of saturated aqueous fish glue and 5 percent saturated aqueous sodium bichromate. This is applied to the roll in a workroom of low light level by dipping the surface of the roll into a vessel 18 (see FIG. 3) having the fish glue solution 19 therein and rotating the roll in the solution. Excess solution is then removed from the roll by spinning at a high velocity, and this functions also to distribute a film of the solution on the roll surface. The Water is then dried'frorn the film by heating the roll by spinning it under infrared lights.
The negative 21 that may be used in connection with the roll is illustrated in FIG. 2 and may comprise, for example, a sheet of clear film having a plurality of spaced opaque figures 21 thereon. The film 20 has the pattern on it which it is desired that the embossing roll 15 shall have on its surface and which it is desired shall be em- 3 bossed on the paper or other sheet material. The film 20 may be prepared photographieally to have the figures 21 thereon, and the film may simply be a photograph of such figures drawn on a paper sheet.
The film 20, which has the desired embossing pattern photographed on it, is then wrapped around the photosensitized roll 15, as illustrated in FIG. 4, and is fastened in place in intimate contact with the roll surface 16. The roll 15 is so wrapped with the negative 20 is then exposed to a bright light, such as that from an electric are 212 (see FIG. 5). The are 22 is formed by the conventional carbon rods 23 supplied with current from a generator 24. The roll 15 covered with the film 20 is rotated as it is exposed to the light from the arc 22 so as to uniformly treat the surface of the roll 15. If a 35 ampere are is used, positioned about 36 inches from the roll 15, approximately a -minute exposure on the ro tating roll will be suflicient.
The enamel on the roll surface 16 under the dense figures 21 of the film is then removed from the roll surface by rinsing the roll in running water at about 100 degress Fahrenheit, subsequently to the removal of the film 20 from the roll. The surface of the roll is then dyed in a methyl violet bath, which may be approximately 4 percent methyl violet dissolved in 60 percent ethyl alcohol in water. The excess dye is then rinsed off the roll in water, and the surface of the roll is dried as before by using infrared lights.
The enamel on the surface of the roll that was beneath the clear portions of the film 20 is then burned in or hardened by heating the surface of the roll to about 650 degrees Fahrenheit, and this temperature is maintained until the enamel turns black. The roll surface is then ready for the etching treatment.
Prior to the actual etching, the roll 15 is given a quick wash in 5 percent of concentrated (approximately 0.6 molar) hydrochloric acid to remove all foreign matter from the bare metal surfaces which were beneath the figures 21. The roll is then etched in photoengravers iron etchant 25 contained in a tank 26 by dipping the surface of the roll in the etchant and rotating the roll as illustrated in FIG. 6. The etchant may be aqueous ferric chloride, approximately 28 to percent by weight, with a very small amount of free HCl and a wetting agent. The etching process is allowed to continue until etched depressions 27, bounded by sides 28 of .002 to .005 inch and forming bosses 29, develop in the portions of the roll surface which are not covered by the enamel and which have been beneath the figures 21 of the film 20. This initial etching step results in undercutting by the etchant of the external surface 16 of the roll 15, producing the undercut surfaces 27a which form the sides 28 at this stage. The undercut surfaces 27a extend beneath the external surface 16 of the roll and form, with the adjoining external roll surface 16, acute angled knife edges 27]) at which the surfaces 27a meet with the external roll surface 16 (see FIGS. 9 and 10). The enameled portions of the roll surface form the bosses 29 as will be understood. The roll is then washed with tap water and dried.
Photoengravers powder 30 is then brushed on the surface of the roll in such a way that the sides 28 of the depressions 27 are covered with powder as illustrated in FIG. 7. The powder may be a specially prepared dyed form of polyvinyl chloride resin in very fine powder form. The roll is then heated over a flame to melt the powder so as to protect the sides 28 from subsequent attack by etchnat. The etching. process as described above, in which the roll 15 is dipped and rotated in the bath 25, is then repeated to increase the depth of the depressed areas 27; and the powderin-g, powder melting and etching steps are repeated a number of times in succession until the depressions reach the desired depth which may be .020 to .030 inch. The powdering and powder mel ing steps covering the sides 28 assure that the etchin process is controlled so that the enamel areas are not greatly undercut and so that the pattern on the periphery of the roll is not damaged. When the etching process has continued to the desired depth, the enamel and melted powder are removed from the surface of the roll by dipping the roll in a benzol bath and Washing the roll in trisodium-phosphate metal cleaning solution. The surface of the roll is now ready for flame hardening and/or chromium plating, as desired.
The roll 15 is preferably run in connection with another roll 31 which has a covering 32 of rubberlike material. The rolls 15 and 31 are on parallel axes to have a pressure nip between them, and the paper 33 or other sheet material to be embossed moves between the rolls as the rolls are rotated. The rubberlike surface 32 of the roll 31 deforms and presses the paper 33 into the depressions 27 in the roll surface so as to emboss figures of the size and shape of the figures 21 into the paper or sheet material.
Referring to FIGS. 9 and 10 which illustrate a finished depression 27 bounded by surrounding bosses 29 in the surface of the roll 15, it will be seen that the sides 28 of the depressions 27, are in general relatively straight and normal to the surfaces of the bosses 29, and the acute angled knife edges 27b bound the bosses 29, particularly due to the above described mode of etching out the depressions. It will be observed from these figures that the rubber covering of the roll 31 in effect folds the paper sheet 33 around the knife edges 27b and forces it into the depressions 27 with some stretching of the paper. The knife edges 2% of the bosses 29 thus provide sharp folds and sharply delineated lines at the edges of the embossed figures in the paper. It may be mentioned at this point that the sheet material 33 should be preferably of a type that is yiel-dable to allow stretching without rupture of the sheet material under the action of the rubber roll cover 32 forcing the paper about the sharp knife edges 27]) and into the depressions 27, and the sheet maerial 33, for example, may be creped tissue paper. Such paper may be made by creping paper off of the Yankee drier drum of a papermaking machine by a doctor blade so that the paper is quite stretchable.
The difference between the knife edges 27b at the edges of the depressions 27 in the roll and the relatively rounded corners produced by prior roll making methods may be noted by comparing FIGS. 9, 10 and 11. FIG. 11 shows a prior art metal roll having bosses 35 defined by depressions 36 which have edges 37. The corners 38 between the outer surfaces of the bosses 35 and the edges 37 are relatively rounded due to the prior art modes of making such embossing rolls. Obviously, such round corners cannot produce sharply delinated lines in the embossed material comparable to the lines produced by the knife edges 27b.
The rubberlike cover 32 may be more or less resilient with good results, however, I have found that excellent results are obtained if the cover 32 has a Durometer A value of resiliency of 40 to 50. The Durometer mode of measuring resilence is standard, and a description of it is set forth on pages 37 to 43 and 298 to 301 (particularly the latter) of 1959 supplement to Book ASTM Standards Including Tentatives, par. 9, Plastics, Electrical Insulation, Rubber, Carbon Black, published by the American Society for Testing Materials, 1916 Race Street, Philadelphia, Pennsylvania. In order that the rubberlike surface 32 of the roll 31 does not enter the depressions 27 on the same parts of the rubber covered roll 31, the roll 31 shall preferably have a different diameter than the roll 15.
In the event that it is desired that a second matching metal roll be used instead of the rubber covered roll 31, such a second metal matching roll may be made by the method described in the Sunderhauf patent, 2,662,002 mentioned above.
An embossing roll made in accordance with my invention and having acute angled knife edges defining the figures on the roll surface advantageously provides an embossed sheet which has the figures on it very clearly defined. The use of the rubber covered roll 31 in connection with the metal embossing rol-l advantageously provides a paper sheet that has more bulk and more absorbency than would be provided if two metal rolls are used in accordance with prior art teachings. These attributes of greater bulk and absorbency are desirable in connection with paper tissue if the tissue is intended for toweling use, for example, and these attributes are provided by the use of the rubber covered roll, since such a roll provides a less unit pressure on the paper sheet as it passes between the rolls than do a pair of matching steel rolls due to the fact that the rubber covering is deformed by the steel roll and produces a relatively long roll nip. A metal embossing roll made according to the invention is advantageously less costly and may be made in much less time than with prior methods utilizing a master roll die which is generally engraved by hand. Since the herein described method of making embossing rolls is relatively fast and cheap, obviously a relatively larger number of embossed patterns for marketing studies may be examined from actual embossed product than if the prior expensive and time consuming methods of making embossing rolls are relied on.
I wish it to be understood that my invention is not to be limited to the specific constructions and methods shown and described, except only insofar as the claim may be so limited, as it will be understood to those skilled in the art that changes may be made without departing from the principles of the invention.
What is claimed is:
In embossing apparatus for yieldable sheet material,
a pair of rolls mounted on parallel axes for passing the sheet material therebetween and applying pressure to the material to emboss it as the rolls are rotated, one of said rolls being made of steel and having a cylindrical external embossing surface, said surface being provided with a plurality of bosses spaced by depressions which have a depth of at least .020 inch, said bosses being defined by acute angled edges which are provided by said cylindrical surface and adjoining edge surfaces undercutting thebosses, the other of said rolls being covered with a resilient material for pressing portions of the yieldable sheet material into said depressions and around said acute angled edges so as to provide the formation of a clear embossed pattern in the yieldable sheet material passed between said rolls.
References Cited by the Examiner UNITED STATES PATENTS 1,152,393 9/1915 Brown 101-23 1,325,529 12/1919 Oberly 101-23 1,459,669 6/1923 Berold 156-14 1,709,327 4/1929 Spalding et al. 15614 X 2,043,351 6/1936 Fourness et a1 161-129 2,429,107 10/1947 Petren et a1. 15614 X 2,662,002 12/1953 Sunderhauf et al 15614 2,684,291 7/1954 Wilson et a1 15610 2,704,512 3/1955 Alexander 156-14 X 2,887,042 5/1959 Broderick et a1. 156-11 2,925,332 2/1960 Standley 15614 ALEXANDER WYMAN, Primary Examiner. JACOB STEINBERG, EARL M. BERGERT, Examiners.