US2545918A

US2545918A - Material suitable for decoration by stamping and process of making same

Info

Publication number: US2545918A
Application number: US701042A
Authority: US
Inventors: Austin E Davis; Lloyd M Perry
Original assignee: Nashua Gummed and Coated Paper Co
Current assignee: Nashua Gummed and Coated Paper Co
Priority date: 1946-10-03
Filing date: 1946-10-03
Publication date: 1951-03-20
Anticipated expiration: 1968-03-20

Description

March 20, 1951 A. E. DAvls r-:rAL 2,545,918

MATERIAL SUITABLE FOR DECORATION BY STAMPING AND PRocEss oF MAKING SAME Filed on. s, 194e Patented Mar. 20, 1951 MATERIAL SUITABLE FOR- DEGORATIQN: STAMPING AND PROCESS MAKING.:

SAME

Austin ErDav-isandLloyd M. Eeuw-Nashua; N. H.,.. assignors to NashuaGummed and Coatedrll'apen Company, Naslua, N. Massachusettsa` l This invention" relatesl to* a4v material which', when" operatedv on by what may' be termed* av stamping tool; such as afheated-'die onarilem-u bossing roll or" plate,l will give two-tarief ei'ectswithcleardelnition o-f the-impressed designand? more pronouncedcolr'contrast; than has hitherto been possible.

Many'v uncoatedpapersA and* certain' pigment-f coated papers undergo' such; localized changes" of texture' when treatedbxffembossing' or'Yhot stampe' ing:v as" to provide"A a noticeable degreey of contrast in* tone apart" fronr the* intaglio effect" pro-duced` by" actual" impression of" the' dieyin" the* material-2 with resultant localized offsetting of itssu-rface* throughout they areas of the impressed design. l5 Manufacturers ofphotographal-bums 'and' binders of?" catalogs andadvertising` brochures produceattractivecovendesigns` in this manner; 'Fliedew gree of contrast,y however, ,is slight and insufficient" for. markedeiect Hitherto papercoaters have*increasedthefpossib'ility"of contrastfb'y add'- ing to aqueous. coating" compositions containingl the usual inorganic, infusible'v pigments` oil the coating. art emulsions. o wax,such iorz"example paraffin.. The. wax lquenes under. thee` heat; z5 oitheemhossingnr stampingoperation andifcnatst or partially coats the pigment particles, thus rendering?themasszmoiretra-nsparentand onsequentlyfdarke'r; The opticalfphenomenon tnatli exhibitecl by-fa,v grease; spot ont papen.. Th f eiect4 isffurtherll enhancedf by the; compressi-oni which the coatingundergoes'inithestamped area.- Best results arefr'usualllyf had.. with: pigmentl otflovv:f refractive.: index: Attractive: contrast.; effects are.V obtained in. this manner butthere isconsiderable: demand fonia higher"orderioicontrast thanlhas. hithertobeenachieved.

Such higher orders-'oi contrastare madefip'os-A sible by the present-1 inventionv andf: in'. fact'. its is possible.VA literally to obtain the ultimate; contrast A oiblack and White;

The: ir'nrentionfl will? be explained'. with-z theiaid. off illustrative: examples in:l the:- accornpanlying'` specification; 'Il-oi this; specification' are :annexedi drawings;y which,A asf. will? be Well'. understood;l aref. offai quite.; unrealistic and: diagrammatic naturel and probablyiwill beof'u'se chiefly` a'siasortrof: graphical" .memorandum ofi the: subjectfmatterffor the: convenience" oflthose:whounayfhavezoccasion hereafterto maketuseoff thepatent. Infthese f' drawings-- Y Y Fig. 1'4 isa'pianivieWffefalicoated sheetofpaper;

Fig. 2 Y is a1. section E on?. thefline;Y 2--2 ofz Fig. 1";: and;

' Figs'. Siano; aarzelyiews correspondingto. .1l ami' 2', respectively, atterftfre'.stampingroperation;

It is; believed. an:A unders-tanding; of, the; invention.; bei itacilitatedl by; aizbrie sketch: at?, this: point; 4Whic'lrrsshould notibe understood? either; asiaecornpl'ete;exposition@thereo or as azdefintioni of: its scopethe@tonnerr-heingV provided'. b'yrf the:- specication;V as' ai. Whaler-v and.A ther: latten" by," thei annexedi claims. when:v read; andi understood: L th'glightfof theispecication; Brieflyfit'- mayb said-r" that ai suitable:- base;` material: a which` usually@l will bei: thinesheet;mateni'atsuclr as paper isi-profvid'edfvzitma coatinglordinarily; ofi suciriilmelikel thinness as usual in coat?d'.'papeizr.Whi. :h= coating;-` comprises zaapigment..,eitherfalonef or1 combinedlin significant pitopor-tion,A with: infusilole:pigmentsy ofi the type.- conventional inithe'lartsg. Whichf becausez oid-ts presenceiini tine,V discreter particles; will:4 haveiy markedhidng: powe1r,fhut;. which, asf a:` result ofi' the stampingzoperationpwill'soften Withresuitantt coalescence;V of the: particles te provide: a. rela-,-e tively translucent i'llm at the areas affected.

The charactenisticrf pigment used' may," general:` be.wv mostr advantageously.' selected;Y- from the-- eld of:y resins,l natunal'f on' synthetic..v Certain materials" conmronlyt termed;` waxesf hai/e-V somei what similar physical properties and, .asngdisff tnguished, from. suchsoit waxes as. parafm. are

of adequate hardness to permit their mechanical fracture* into suiciently iine discrete particles to' Ypermit their use *inF accordance 'with the-'prins cipl'es ofl theA invention... eitheralonesvorV` com-2f' bnation' with" resins',y although' whenlusedialone? perhaps not so completely realizing its advantages and potentialities as the resins of4 which examples wiliherein be given: While the improved; degree of colorcontrast isreadil'y appreciatedby'comparisomof the emebo'dim'ents of. the" invention as" those:v here given asexamples with embodimentsofthe art as yalready reierred to, to permit' the improve; ment to.` be apprehended from a merely verbal descriptiomsuch as the present snecification, and for purposes' of deniteness it is desirable to de-'f' ne proceduresr forV deterrriiniig.with,` reasonable; scientiiic'accura'cy'for a'given' coating materiali the properties'of'signicancein attaining therirnfproved: results; andifon'evaluatingzthem .numerically. For: thisrapmposef measurements. may be? effected by: inea-nsf on a knomm' soientiiic; instru# ment for: measuringzthefdiiusive lightsreectan'ceof.. aw given,vv specimen its: dominanti-v huei,l 'Rhei instrumenteutilizedfin olota'iningthenguresrlrerefv inafter given is knownfaszalhotoyoltreectance rneterf? distributedicbyi the: Will-."lCorporatono Roches-terr, New-York, Model'Gl-Of. The:reflectance;- inv lighty screened ini throneh `red;` .green-andi r blue'colonlters islreferreditoethatioimagnesiumj oxide in similarly screened light. The dominant hue of a given specimen is broadly indicated by the color filter which yields the highest value for the specimen. By means of this instrument we may determine values for brightness, opacity and contrast as now to be defined.

Brightness-This term denotes the diffusive light reflectance of a given specimen in its dominant hue. It is expressed as the reflectance value of a specimen in light through that lter (red, green or blue) which yields the highest value, referred to the value of magnesium oxide in similarly filtered light as 100.

Opacity.-This term is expressive of the hiding value of a given composition and is measured by determining the brightness of the given composition when coated on black paper in reference to the brightness of the same composition when coated on White paper. The specific procedure in accordance with which the figures herein given were determined was the following. 85 parts (dry basis) of a given composition are mixed with 15 parts (dry basis) of binder and coated in an amount corresponding approximately to 10 pounds per ream (24" by 36"-500 sheets) (a) on blackpaper having a brightness of approximately 6.0 and (b) on white paper having a brightness of approximately 85.0. Opacity is expressed as the brightness value (a) in relation to the brightness value (b) when a value of'100 is assigned for (b).

` Contrast-This term means the relation of the brightness value of a coated specimen (a) in its areas not subjected to the stamping operation to the brightness value (b) in areas which have been so subjected. Contrast is expressed as the brightness value (a) in relation to the brightness value (b) when a value of 1.0 is assigned for (b). To indicate the significance of some of the values which will be given and as a basis of comparison there is given below data on certain inorganic pigments commonly employed in paper coating:

Bright- Opacness ity English china clay. 58 72 Precipltated Whiting 24. 5 32. 0 Yellow iron oxide 54. 5 100 To provide a further basis of comparison, iigures for brightness and contrast are given as determined from commercially obtained samples of paper designed for stamping and having colored coatings as specified on dark gray stock:

Bright- Conness trast ma 3s. 5 2. 1 Green 12. 5 1. 9 Brown. 14. 5 l. 9

material, as will hereinafter appear, but because, being nominally a wax, it well illustrates the nature of the invention in contrast with the use of emulsions of soft wax in connection with the inorganic pigment coatings of the prior art. The carnauba wax herein referred to in the example was a commercial grade known as No. 3 North Country Carnauba Wax.

Eample 1 Parts by weight Carnauba wax Oxidized rosin dispersant 5 Water Oxidized rosin dispersant is prepared from gum rosin which has been oxidized in a manner similar to that described by Schaal in United States Patent 698,741. The oxidized rosin is then dissolved in ammonia and water to yield a solution of approximately 43.8 solids.- and a pH value of approximately 9.0. The dry carnauba wax is first preliminarily ground to a fine powder and then mixed with the other ingredients and ground in a ball mill until of acceptable fineness and opacity. A product acceptable for some purposes may be obtained with about sixteen hours grinding but continued grinding improves the product and a product of excellent fineness and opacity is obtained by grinding for five days, which represents about the optimum period. After grinding is completed, an ammoniacal solution of casein is added for a binder, which may be prepared as follows:

Parts by weight Lactic casein 100 Ammonia (26 B.) 16

Water 550 Brightness 50.2 Opacity 59.7 Contrast l 10.9

Referring now to the drawing, I0 represents a foundation material, such as a sheet of dark paper, and I2l a coating such as that described rendered opaque by the fine'discrete particles of fusible pigment indicated in Fig. 2 by the stippling of the layer I2. Figs. 3 and 4 show a design I4 impressed thereon and the absence of stippling in the area I4 in Fig. 4 indicates the softening of the discrete particles in thaty area and their coalescence into a substantially amorphous film producing a contrast in color with the unchanged body of the light colored coating 4, as indicated by the legend Intermediate on Fig, 3 of the drawing. The change in color in such-case is due partly to the altered light reflectance of the portion I4 of the coating layer itself and in part to the disclosure of the backing layer I because that area is now less opaque than the unaltered portion of the layer I2. The conventional lining of portions of the figures for blue, red and purple may be considered as merely indicating dark, light and intermediate shades and is not intended to represent otherwise the particular example just discussed. Such a color effect, however, is possible in accordance with the invention, as will hereinafter appear.

It will be noted that the value for opacity given in the example is due to the hiding power of the discrete particles of the wax themselves which serve as 'the -on'ly ypigment present. The case is to be distinguished from va paper having a coating formed from inorganic pigments providing a hiding power like that obtained from similar coatings `in ordinary coated paper and to which a minor 'proportion of 'wax was added Vin emulsion form, the additioniof the wax being intended not substantially to diminish such hiding power -until liquefied in the stamping operation and absorbed by the infusible pigment. Moreover, emulsions-prepared inaccordance with the usual processes of the art do not 'provide in the deposited coating discrete particles ofthe emulsied iphase'of the-kind herein discussedand having signcant'hiding power. Paranin is oi such softness vthatlit couldnot be mechanically 'fractured Ato fthe discrete particle form effective -to give opacity. At ordinary temperatures particles tend to lump together and coalesce. Commercial paraflis, moreover, being separated from the petroleumvresiduebyf crystallization, approximate purecrystallinecompounds and exhibit a rather sharpmelting lpoint or 'short range of plastic softness.

EampZeiZ A's another example of hard Wax, figures are given which are similarly determined from a coating prepared in a similar manner from a commercial vsynthetic wax termed Acrawax. This is the commercial'nameof a modified fatty acid ester in the "nature Vo'f'a high'meltin'g hard wax. The particular 'product vused was obtained 'from Glyco Products Company and `was of the grade termed Cfby vthat company. Further description is not Yhere necessary as itis offered merely as a further example of the utilization for the purposes of `the invention of 'material which would lbe'popularly and 'commercially known 'as Wax'but having suilicient hardness Afor the ipurposesv loft-he invention. The figures are:

Brightness 55.5 Opacity 60.3 Contrast A10.4

While useful products may be produced, as the'examples given show, rom'substances commonly and'commercially known as waxes if "sufciently hard, in general even'suchwaxes are less desirable, at least'as the "solepigment ingredient yof the Vcoating film. 'The temperature range wherein they are plastic may be relatively short and they approach the case of pure cry-stalline compounds having adeii-nitemelting point and which pass abruptly from solid 'to liquid phase. Thepurpose here is toprovide a'pigment having goed hiding `power but which under the correlative influences of the heat and pressure of the stamping tool will soften local-ly and rcoalesce into a substantially Yamorphous lm, as manifested by greatly'reduce'd refi'ectance. This may be termeda 'fusible material. 'On'the-other hand, if the material vWeremeltable in the'sense that it -liqueed in the process, unless as in the prior'vartit were utilized merely as a minor ingredient` subsidiary to a major Aproportion of lrifusible pigment, into the mass of which it-Was absorbed on melting, adequate definition of the design'between the heated and unheated areas would not vbe obtained incommerc-ial practice.

Forthis reason it is preferable to utilize either completely or in a signiiicant proportion fusible pigments derived from vrmaterials which are commorily termed resins and which do not become sharply f-u-id-iwhen heated toa point of adequate' softness bu-thave a 'relatively Wide temperature VExamples 3, 4 and `5 *ness Opacity Contrast 3k "Pentalyn 'G 61.0" 74.4 1155 4 .f1.roc1or5460..A 5410 66 10.8 5 Nevindene 63.0 73.* '12.0

Pentalyn G isa `pentaerythritol-abietate resin; Aroclor 5460 is a chlorinated .diphenyl resin, and Nevindene is an .indene resin. The commercial names are given not only because more convenient, but because the gures given are based on the particular commercial products so identied. As resins are not pure crystalline compounds, clearly coatings prepared from substantially similar resins of dilTer-snt commercial origin might yield specifically different figures although of like general magnitude. rThe examples indicate the general range of results to be obtained from a resin judiciously chose in the light of the present specication.

The value of such fusible pigments in securing opacity is dependent on their being suitably ground. For instance, NevindeneRS, ground 24 hours, has an opacity of 59.0. When grinding is continued to 144 hours, as in Example 5, this opacity is increased to 73.2, by grinding for 168 hours to 76.3.. Similarly, Pentalyn G, ground 16 hours, has a opacity of 45.8; with grinding y continued to 144 hours it has an opacity of 74.4

Darker colored 'resinous materials and dark waxes may be usefully employed. For instance, black montan wax may be prepared as in Example 1 and produces in the unheated coated areas a gray tan shade. 'Vinsol resin (a pine wood resin having an acid number of 92, a drop melting point of 119 C., a saponication value of and 6.5% cf unsaponiable matter) yields a light yellow shade. This latter is prepared .by grinding in a dilute aqueous solution of methyl cellulose since the resin is soluble in ammonia. Supplemental amounts of .methyl cellulose may be added as required for adequate .binding of the dried coating. Below are data on brightness, opacity and contrast .for these twomaterials:

Examples 6 and? `Bright ness Opacity Contrast;l

6 Black montan Wax 33.5 64.5 6.1 7 Vlnsol resin 44.5 72.7 8.0

scribed. By that proportion in which opaque fusible pigment replaces infusible pigment will the resultant contrast be improved since, on embossing or stamping, this opaque fusible pigment portion is rendered translucent to diminish, ac cording toits proportion, the opacity of the entire coating in the embossed or stamped area. A significant proportion may be considered twentyfive percent of the total pigment present which would permit tone variation desirable in some applications. In general the proportion of fusible particles is desirably greater and for commercial purposes they preferably constitute the major portion of the pigment present. Full colors as well as tints may be produced in the unheated or uncompressed coated areas with the employment of 90% or more of the pigment which consists of fusible particles as herein described. While a wide range of colored non-fusible pigments may be eectively employed with this high proportion of fusible pigments wh-en tints are desired, organic pigments of the so-called toner strength are most effective in producing full colors. Below are given examples for red, blue and green colors:

Example 8 (Red) Parts by weight 0 Lithol Red toner (color) 5. Pentalyn G resin (resinous fusible pigment) 52.0 Acrawax C (waxy fusible pigment) 20.0 Lactic casein (binder) 23.0

Example .9 (Green) Parts by weight Hansa Yellow toner (color) Monastial Blue tener (color) 2.5

Black iron oxide (non-fusible pigment) 0,5 Pentalyn G resin (resinous fusible pigment) 52 Acrawax C (waxy fusible pigment) 20 Lactic casein (binder) 23 This composition is prepared in a manner similar to that of Example 8.

Example 10 (Brown) Parts by weight .4

Lithol Red toner (color) l Hansa Yellow toner (color) 2.8

Black iron oxide (color) 2.1 Pentalyn G resin (resinous fusible pigment) 5-2 Acrawax C (waxy fusible pigment) 19.5

Lactic casein (binder) 23.0

This composition is prepared in a manner similar to that of Example 8.

Brightness, opacity and contrast data, with coated specimens prepared in a manner similar to those of Example 1, except for the higher -prp-gportion of binder employed, are here given:

These figures may be compared with those above given for commercial red, green and brown coatings of the prior art.

In Examples 8, 9 and 10 the pigment, apart from the small amount of color-giving material, consists of two fusible components each of which initially exists in independent, nely divided form, the two being in intimate mechanical mixture andeach component being significant in its contribution to hiding power. In the stamping operation they merge and coalesce into a substantially amorphous lm of low reflectance. Whether the individual particles are supercially softened and weld together or whether a merger occurs or both phenomena are present, it is unnecessary to speculate. The individuality of the particles is to such an extent lost that their hiding power is substantially eliminated and a film of low re-l flectance takes their place. The heterogeneous mixture acts for the purposes of theinvention aS a material exhibiting a wide range of plastic softening without objectionable liquefaction which would interfere with proper definition of the design or development of objectionable stickiness either during the stamping operation or in the finished work. f

Reference has been made to opacity as due to fineness of the discrete pigment particles to b secured by adequate grinding. In a, sense the opacity of the coating measures the nenessof the particles. In general the opacity should be as good as that of a coating of similar weight of precipitated Whiting which may be considered as a standard of substantial opacity as referred to in the claims. As the examples show, greater opacity, of the order of that provided by English china clay, may be obtained and is to -be recommended. An opacity of less than 50 as deter#- mined by the procedures herein described should, except for special applications, be considered an unnecessarily inefficient application of the prin-l cples of the invention. n

An important feature of the invention `istle uniformity with which coatings of a desired character may be prepared. It therefore findsY a desirable application even when the contrasts de-f sired are not so great as here described. A formula being established, material may be prepared therefrom at any time from the same materials under easily controlled identical conditions to produce uniformly like results in use.

In referring to the particles of fusible pigment as hard, reference is made to the fact that they retain their form and individuality without any substantial tendency to re-coalesce during their preparation or at ordinary temperatures to which the product is subjected during shipment or storage, while reference to a resin or wax as hard implies the possibility of reducing it to such hard discrete particles by mechanical fracture.

The reference to the material as hard indicates also that it is not plastically responsive at room temperatures in the absence of substantial pressure and that its melting point is ade-s quately high. On; the `other. hand, it should have a plastic` response permitting coalescence of the Particlesunder practical values for theA correlative temperature and pressure of the stamping tool. Obviously if the coating is on paper a red hot iron which would burn the paper would not. be. used.

, Thefpaper` or similar base may itself bev dyed or; lled or a first colored coating with infusible pigments may be applied thereto.y Such materials as textile fabrics, metal foil, organic foils, gla'ssin'e paper and the like are equivalent to paper and such thin base materials may be mounted on press board or the like, the mounted material being stamped as a unit as in the production of book covers.

Reference has been made to the stamped design as a decoration which will be understood to include designs such as printed letters or other characters having primarily an intellectual rather than a purely aesthetic appeal.

We claim:

l. As a new article of manufacture a material for decoration by stamping to produce two tone effects comprising a base material having adherent thereover a pigmented lm of substantial opacity, at least a quarter of the pigment therein consisting of hard discrete particles of commi nuted material which is fusible in the sense that it will plastically respond to the heat and pressure of the stamping tool with resultant localized coalescence of the softened particles to provide diminished reflectance in the treated area. r2. As a new article of manufacture a material for decoration by stamping to produce two tone effects comprising a base material having adherent thereover a pigmented film of substantial opacity, the major portion of the pigment therein consisting of hard discrete particles of comminuted material which is fusible in the sense that it will plastically respond to the heat and pressure of the stamping tool with resultant localized coalescence of the softened particles to provide diminished reflectance in the treated area.

3. As a new article of manufacture a material for decoration by stamping to produce two tone eifects comprising a base material having adherent thereover a iilm containing ne discrete particles providing substantial opacity and including a significant proportion of hard comminuted resin which is fusible in the ksense that it will plastically respond to the heat and pressure of the stamping tool with resultant localized coalescence of the resin particles to provide diminished reflectance in the treated area.

4. As a new article of manufacture a material for decoration by stamping to produce two tone effects comprising a base material having adherent thereover a lm containing line discrete particles providing substantial opacity and including a significant proportion of hard comminuted wax which is fusible in the sense that it will plastically respond to the heatl and pressure of the stamping tool withv resultant localized coalescence of the wax particles to provide diminished reflectance in the treated area.

` 5. As a new article of manufacture a material for decoration by stamping to produce two tone effects comprising a base material having adherent thereover a film containing fine discrete particles providing substantial opacity and comprising in major proportion an intimate mixture of two .fusible components, one of which is a hard comminuted resin, the heterogeneous mixture softening without apparent liquef action through.

out a wide temperature range under the correlative heat and pressure of the stamping tool sub.- stantially to merge the individuality of the particles into a coherent lm of markedlyI reduced reiiectance corresponding to the treated area.

6. As a new artcleof manufacture a material for decoration by Stamping to produce two tone effects comprising a base material'having` adherent thereover a film containing fine discrete particles providing substantial opacity and comprising in major proportion an intimate mixture of two fusible components, one ofwhich is a hard comminuted resin and the other a hard comminuted wax, the mixture softeningunder the cor.-- relative heat and pressure of the stamping tool substantially to merge the particles with loss of individuality into a coherent lm of markedly reduced reectance corresponding to the treated area.

7. As a new article of manufacture a material for decoration by stamping to produce two tone effects comprising a base material having adherent thereover a film containing ne discrete particles providing substantial opacity and comprising infusible pigment particles zero to 25%, the balance of the discrete particles comprising comminuted hard resin 10% to 100% of said balance and any remainder comminuted hard wax, the wax and resin being of a fusible character as manifested by their plastic response to the correlative heat and pressure of the stamping tool with resultant localized coalescence of the.

fusible particles to provide diminished reflectance in the treated area without apparent liquefaction or development of stickiness.

8. A's a new article of manufacture a material for decoration by stamping to produce two tone eifects comprising a base material having adherent thereover a lm containing fine discrete particles providing substantial opacity and comprising infusible pigment particles zero to 25%, the balance of the discrete particles comprising a significant proportionof comminuted hard resin and the rest hard fusible material which together with the resin softens withoutl apparent liquefaction throughout a wide temperature range under the correlative heat and pressure of the stamping tool substantially to merge the individuality of the particles into a coherent film of markedly reduced reectance corresponding to the treated area. Y

9. The process of manufacturing a material for decoration by stamping to produce two tone effects which comprises mechanically grinding into discrete particles of a predetermined order of neness effective to lend substantial opacity to the film hereinafter referred to as hard pigment which is fusible in the sense that it will respond plastically to the heat and pressure of a stamping with resultant localized coalescence of adjacent particles, incorporating such pigment particles in a pigmented coating composition in which they represent at least a quarter of the pigment present and coating the mixture as a thin film on a base material.

10. The process of manufacturing a material for decoration by stamping to produce two tone effects which comprises mechanically grinding into discrete particles of a predetermined order of neness effective to lend substantial opacity to the film hereinafter referred to at least two hard pigments, one of which is a hard resin, and which have the characterizing property of softening without apparent liquefaction throughout a wide temperature range under the correlative heat and pressure of the stamping tool substantially to merge the individuality of the particles into a coherent film of markedly reduced reflectance, incorporating such pigment particles in intimate mixture in a pigmented coating composition in which they represent at least 25% of the pigment present and coating the mixture as a thin lm on a base material.

AUSTIN E. DAVIS.

LLOYD M. PERRY.

REFERENCES CITED The following references are of record in the file of this patent:

Number 1`2 UNITED STATES PATENTS Namel Date A Birnbaum NOV. 4, 1879 Kress et al Nov. 3, 1936 Overton et al. Dec. 29, 1936 Rafton May 10, 1938 Bezzenberger May 16, 1939 Mitter Feb. 20, 1940 Ford May 5. 1942 Helfrich Aug. 11, 1942