US2912347A

US2912347A - Process of producing glossy wax-coated paper

Info

Publication number: US2912347A
Application number: US663269A
Authority: US
Inventors: Yezek Milton; Walter C Utschig
Original assignee: General Foods Corp
Current assignee: General Foods Corp
Priority date: 1957-06-03
Filing date: 1957-06-03
Publication date: 1959-11-10
Anticipated expiration: 1976-11-10
Also published as: GB887932A

Description

Nov. 10, 1959 M. YEZE K ETAL 2,

PROCESS OF PRODUCING cmssy WAX-COATED PAPER Filed June a, 1957 g INVENTORS $3 MILTON YBZEK 3g WALTER'C.UTSCHIG B1 g WW 2 M ATTORNEYS United States Patent 2,912,977 PRoeEss F rnonuemc (mossy WAX-GOATEDPAPER Milton Yezek and Walter C; U'tschig, Battle Creek, Mich assignors to General Foods Corporation, White.Plams, N.Y., a corporation of Delaware Applications June: 33L 1957,: Serial. No. 663,269

8 Claims. (Cl. 117-64) The present invention. relates to. the production of glossy, waX-coatedpapen.

In making wax-coated papers for use as a wrapping material. for commodities itis highly desirable that the wax-coating. offer a high: degree of gloss and yet be free of any imperfections which.- detract fromrthe appearance and utility of. the Waxrcoated paper. Heretofore it has been proposed to provide. glossy wax-coated paper by chilling a paper web, oncethe hot. wax. composition has been applied thereto, by passing. the coated web through a cold water bath or. over chilling rolls-t Buttheseprocedures sufier from a number of disadvantages.v In the caseof cold Water cooling, gloss is attainable.- With some coating formulas but crows. feet are evident on the waxed surface, and at high productionrates the populationof crowsfeet is high. Withconventional coldlroll cooling high glosses are-notattainable. Another possible procedure is fcast-coatingfi in cast-coating, a. molten wax: coatingpreviously applied to the-paper Webis solidi; fied while in contact with the surface of asmooth, polished casting. surface. and, after the coating; has set, the waxcoated paper is'peeled from the casting surface. However, in cast-coating there is alikelihood,.due. to poor synchronization betweenv various rollspeeds andtheweb, that the web of paper will move: relative to. the surface of the cold roll; as the wax composition solidifies and crystallizes therewill be a severe reductioninthesmootm ness or regularity of the surface of the coating andthe gloss will. be considerably reduced, if not destroyed;.this is particularly the case at high production rates. When employing acast coating procedure itisalso required-that the rollv be operated at a slow enough speed/to allow the wax composition to solidify; otherwise picking, virtual peeling of portions of the waxcompositionfrom the coating onto the roll, will occur as the. wax-coated webitself is peeled from the roll; This accumulation of coating composition impairs the efiicacy ofthe casting surface on subsequent revolutions of the casting roll:

. These problems probably stemfrom a number of factors. The bond between the wax composition and the paper web, the releaseproperties of the wax composition or the casting surface or both, and the-tensile strength of the wax compositionitself more or less influence the degree ofglossobtainable at a given rate of web travel t Because ofthe discontinuity of. thecoating resulting from cast-coating athigh production speeds, there is a decrease inthe water vapor transmission resistanceof the I I wax-coated paper. It is desirable, therefore, to provide a waX- coating process where, in addition to improved gloss and over-allappearance of the Wax-coated paper,- there is no accompanying. decrease in its Water vapor transmissionresistance.

. 2" urging the coated paper web with the coating composition ina moltenstate into immovable relation with. the endless casting member, the latter having a smooth mirrorfihished'. surface which contacts the coating composition. Such urging is preferably effected. by means ofthe pres sure of an: impression roll. The coating member is maintained on its smooth surface at temperatures below the point of crystallization of the wax coating composition. The web of'coatedpaper and the smooth surface of the casting member are immediately thereafter further cooled by water also maintained; at temperatures substantially below the point of"crystallization of the coating composition, the water being causedtocontact the Web of paper from the side thereof further removed from thesmooth surface. of the casting member and after contact by the wax coating composition. with the smooth castingsurface. By viitue ofitheshock-cooling. of thecoating which takes place, the web and the coating composition. are maintained in immovable contact with the smooth surface of f the. casting member. until a-temperature substantially be.- low the heat of fusion of' the coating composition is reached and the coating composition is crystallized, whereby a slight bond is created between. the coating. and the contacting surface. ofithe. paper.Web,-. and the coating itself hasdevelopedsufiicient tensile strength to overcome this. bond withoutv any adverse. efi'ects. when. the. Wax:

coated paper islater peeled from the casting. surface. The.

cooled wax coated web of paper eventually peeled from. the casting, member, preferably after the Webleaves the zone of application. of thecold watenthe. coated paper being preferably peeled under uniform tension fromlthe casting member under the influence. a. pressure-roll maintainedagaihstthe web. of waxtcoated papen.

Thus, the coatihg}compositior1,-.e.g,,.a wax composition of paraflimblended withadditives such as microcnystalline waxtand/or polymeric compositions such as polyethylene; is. essentially cooled. quite rapidly after contactwith. the

smoothsurface of the. casting member fl'OlTlzbOtl'L sides-of face ofthe casting. member whichispneferably a -cold roll; having a. smooth mirror finished surface thereon. In lieu. of a roll,, anendless belt.also:-having a smooth mirrorfinished. surface may be. employed, The. continuityof theweventual coating. is such that it offers superior re"- sistance to water. vapor transmission despitethe finding It has now been discovered that. a. smooth, extremely glossy wax-coated paper can be produced at highv rates of speed by applying. a hot melt wax coating composition onto a web of paper and shock-cooling? the coating composition while it is; being cast on a portion of an endless coating member. This shock-cooling is achieved by first that theswax-coated paperis capable of beingproducedathigh rates.

. Itv appears-that by shock-cooling the molten waxcoatv ing composition it is caused to go through or; give up, its head of fusion and crystallize rapidly thereby offering unusuallyglossy surfaces. Shock=cooling also serves to? rapidly solidify the coating intermediate. the? paper web and the casting. surface and thereby creates-a bond which reduces any tendency toward relative. mOVEITICIIt IBdUG-r ing or destroying gloss Consequently, high rates-:of web travelin processing can be-employed and at such rates high. gloss results. Advantageously, it hasbeenafound-that, asthe rate ot web: travel isincreased, gloss iscorrespond= ingly increased whentheWaX-coated paper isshock-coole- Furthermore, by reason of the rapid cooling offeredrat high rates of web. travel. the. wax coating quickly develops adequate tensile strength to resist pickingof the compo. sitionfonto the-casting member; and any premature .,dis-

I the coating composition duet'o' improper synr clitonizatibn between the rolls and'the paper was;

The invention will be more clearly understood by reference to the drawing which is a schematic illustration of a preferred coating assembly which can be employed to produce the improved wax-coated paper of the present invention.

The coating assembly comprises a pair of waxing nip rolls 1 which are employed to distribute a molten wax composition on both sides of a Web of paper passing be tween the waxing rolls. The molten wax composition can then be passed under a heated steel polishing roll 2 which further distributes the wax composition over the surface of the web of paper. The web of paper then travels over an impression roll 3 which can be a rubber roll and around a large segment of the surface of a large diameter cold roll 4, the web of paper then being peeled from the surface of the cold roll 4 under the control of a soft rubber wringer roll 5. The cold roll 4 is chilled by a brine circulating within the roll, the temperature to which the roll is cooled being anywhere from between 30 F. to +32 F. and being generally below the fusion point of the wax composition. The cold roll 4 and the web of wax-coated paper trained therearound are submerged in a cold water bath 6 also maintained at a temperature below the fusion point of the wax composition. In this connection, ordinary cold water just above 32 F. is preferably employed, although a cold brine solution may also be employed to advantage in the water bath.

The wax coating composition employed in accordance with the present invention may be molten paraffin wax or parafiin wax having certain additives blended therewith such as microcrystalline wax or synthetic resins such as low molecular weight polyethylene. In general the gloss of all Wax coating compositions is significantly increased when the Web of wax coated paper is shock-cooled by being submerged in the cold water bath 6 while being maintained in intimate contact with the cold roll 4. The cold roll 4, serving as the casting member on which is provided the smooth surface necessary to produce the high gloss of the present invention, preferably has incorporated around its periphery a continuous and extremely smooth sheet of material such as vinyl acetate. This sheet should possess good release properties and offer a degree of smoothness which wil result in a continuous surface on the film of coating which is cast onto the web of paper while it is maintained in immovable relationship to the cold roll 4. Instead of a sheet of vinyl acetate, other compositions capable of offering a smooth, mirror-finished surface and good release properties such as a sheet of copper or aluminum foil may be employed as Well as a lacquer of silicone grease or other resin, or less preferably a polished metal roll or a nickel or chromium plated roll. In general the casting surface of the cold roll 4 should have a mirror-like finish and should have a surface which when cooled to substantially below the fusion point of the coating composition adheres to the coating with only a slight bond such that the waxcoated paper can be readily peeled from the cold roll 4. As a consequence, although the Web of paper with its coating is submerged in a bath of cold water for shock-cooling, sufiicient bond exists between the coating and the roll to prevent the entry of excess moisture therebetween, thereby avoiding any dull spots or areas on the surface of the coating. This bond also acts to avoid any relative movement between the endless casting member and the web of paper due to poor synchronization between the casting member and the paper web.

In order to assure absence of relative movement between the Web of paper, the coating and the cold roll 4, it is preferred that the later be positively driven and that the rubber impression roll 3 and the wringer roll be driven idly by contact with the cold roll 4 through intermediation of the web of paper and the coating. The rubber impression roll 3 is preferably maintained at a temperature generally above the melting point of the wax composition so as to assure that the surface of the coating is complementary to the surface of the cold roll 4. Accordingly, rubber pressure roll 3 is maintained just above the surface of the cold water bath so as to avoid premature solidification of the molten wax composition before it has had an opportunity to conform to the smooth surface of the casting member or cold roll 4. In order to insure an adequate degree of conformity of the coating composition to the surface of the cold roll, positive pressure is applied to the rubber roll 3.

Pressure is also applied to the rubber wringer roll 5 and this roll is also located above the surface of the cold water bath so as to avoid the collection of moisture on the casting surface of the cold roll 4 after the wax-coated paper is peeled therefrom. It is most desirable that steps be taken to avoid accumulation of any moisture on the casting surface of the cold roll 4. Moreover, the axis of wringer roll 5 should be substantially parallel to the axis of the cold roll 4 so that the web of wax-coated paper is peeled without any eccentricity from the cold roll, thereby avoiding any distortion of the surface of the wax coating and tearing of the web.

Although the shock-cooling which takes place while the web of paper and its wax coating is cast on the surface of cold roll 4 is quite considerable, it will still be desirable to employ a series of conventional chilling rolls 7 and doctor blades 8 so as to assure that the coating composition is cooled to the degree that it will not block or retain tackiness after the wax-coated paper is put on a winding roll. Thus, the large diameter chilling roll in combination with the cold water bath crystallizes the wax by taking it rapidly through its heat of fusion and cools the wax substantially therebelow to remove any sensible heat and thereby assures that the heat of fusion is removed. Thereafter the series of chill rolls 7 serve to further cool the coating so that it will not block and the gloss achieved will be preserved by avoiding any tendency of the wax coating to migrate after the wax-coated paper is wound onto a roll.

In the preferred modification of the present invention a molten wax composition comprising about 50 parts by weight of paraffin (M.P. -14S F.) and 50 parts by weight of microcrystalline wax (M.P. -l47 F.) is applied to a web of paper or paperboard which may range from 15 to 300 lbs. per 3000 sq. ft. Preferably a minor proportion of polyethylene ranging in average molecular weight from 2000 to 21,000 is also employed, it being found that the polyethylene serves to promote some degree of resistance to blocking as well as additional gloss to the coating. The eventual wax-coated paper has a thickness ranging anywhere from 0.001 to 0.025 inch. When employing the aforementioned preferred wax composition the rubber impression roll 3 is preferably heated to a temperature between l50-250 F. to assure that the wax composition is sufficiently molten and plastic in nature to assume the smoothness 'of the surface of the cold roll 4. The rubber impression and wringer rolls preferably have a diameter ranging from 4 to 10 inches and the cold roll 4 has a diameter ranging from about 1 /2 to 6 feet, the cold roll being immersed in a bath of cold water and surrounded by the web of paper on the majority of its circumference during its operation. The cold water bath may have added thereto organic materials like ethylene glycol which allow the cold water to be maintained sufficiently cool and yet avoid freezing of the coolant. The cold roll 4 can be chilled with a suitable refrigerant such as a brine which acts to maintain the temperature well below the point of crystallization of the wax composition.

The pressure roll 3 is urged with the pressure of 50 to 200 lbs. per linear inch against the cold roll 4 and preferably has a hardness in the order of 60 to 100 (Shore A durometer hardness) in order to assure that the wax coating composition is applied uniformly and in a continuous film against the smooth surface of the cooling 01 are being exercised to avoid crystallization of the wax composition before it assumes a smoothness like that of the cold roll on which it is to be cast. Thereafter the wax composition is rapidly chilled by the cooling bath and the cold roll absorbing its heat so that the wax quickly goes through a plastic condition to assume a crystalline state having very small crystals. By virtue of the dual cooling mediums, the heat absorbed on the casting surface of the cold roll 4 is quickly transferred to the coolant circulated within the roll and to the cold bath. During the shock-cooling process the wax-coating composition sets at such a high rate that opportunity for any relative movement between the web of paper, the coating or the casting surface of the cold roll is nil, such that during crystallization of the wax composition little, if any, displacement thereof occurs. The coating sets with a slight bond against the smooth casting surface and can be readily peeled therefrom by training the waxcoated paper around the wringer roll 5 from the cold roll. When the aforementioned preferred wax composition is used it is possible to operate the cold roll at extremely high rates of speed and produce very glossy waxcoated paper at a rate in the order of 1000 linear feet per minute and above.

Thereafter, the web of glossy wax-coated paper is cooled, when the preferred wax composition is used, to a temperature in the order of 115 F. and below, the doctor blade 8 being employed to remove any moisture condensing or otherwise collected on the surface of the wax-coated paper.

Although various formulations for wax coating compositions can be employed in the present invention to produce improved results with respect to the degree of gloss obtained, and although these compositions usually contain parafiin as a principal constituent, it is preferred to employ microcrystalline wax in the formulation in combination with the paraflin. The preferred microcrystalline wax is one which has been de-oiled since this type of wax results in a coating of relatively high tensile strength. in general blends of parafiin and microcrystalline wax result in higher gloss and allow higher production rates in the present process than in instances where paraffin wax is employed solely.

It will be understood that the term paper web, or web of paper, as used herein, includes both continuous and discontinuous webs, as the advantages of the invention are obtainable with either.

While the present invention has been described with particular reference to specific examples, it is not to be limited thereby, but reference is to be had to the appended claims for a definition of its scope.

What is claimed is:

1. The method of producing a glossy wax-coated paper which comprises applying a hot melt wax-coating composition onto a web of paper, bringing the resulting coated surface of the paper web with positive pressure and with said composition in a molten state into intimate contact with a rapidly moving endless casting member having a smooth mirror-finished surface, the molten wax composition being thereby uniformly distributed between the web and the surface of the casting member and being solidified rapidly by cooling said casting member on its smooth surface to a temperature below the point of crystallization of the wax-coating composition at least after contact therewith and by simultaneouly cooling the uncoated surface of said web during said contact by the application thereto of water maintained at a temperature substantially below the temperature of crystallization of said coating composition, moving said web and said casting member at the same linear speeds with said composition solidifying between them in contact with said smooth surface whereby said web and said coatlng composition are maintained in intimate immovable relation with said smooth surface and entry of cooling water between them is prevented until the heat of fusion of said coating composition is removed and it is crystallized, and thereafter peeling the cooled coated web of paper from said casting member.

2. The method of claim 1 wherein the wax-coating composition comprises paraflin.

3. The method of claim 1 wherein the wax-coating composition comprises a blend of paraffin and microcrystalline wax.

4. The method of claim 1 wherein said positive pressure is provided and said coating composition is distributed by an impression roll urging said coated web into initial contact with said casting member.

5. The method of producing a glossy wax-coated paper which comprises applying a hot melt wax-coating composition onto a web of paper, bringing the resulting coated side of the paper web, with said composition in a molten state, into intimate immovable relation with a segment of the surface of a rapidly rotating mirror-finished smooth roll so that said coated side makes contact with the roll surface, said coated paper web being urged into contact with said roll under positive pressure from an impression roll acting to uniformly distribute the wax-coating composition between the web and the surface of the mirrofinished roll, said mirror-finished roll being maintained on its smooth surface at a temperature substantially below the point of crystallization of the wax coating composition, thereby to cool said coated paper web, said web of coated paper and said smooth surface then being simultaneously and further cooled by moving the same through a body of cold water maintained at a temperature substantially below the temperature of crystallization of said coating composition, said body of cold water making contact with said web of paper on the side thereof further removed from said smooth surface, said web and said coating composition thereon being maintained in immovable contact with, and relatively to, said smooth surface and being submerged in said body of cold water until the heat of fusion of said coating composition is removed and it is crystallized, and thereafter peeling the cooled coated web of paper from said mirror-finished roll after said web leaves the zone of application of said water.

6. The method of claim 5 wherein the crystallized waxcoated paper web is peeled under tension from the mirrorfinished roll by causing said web to travel over an idling pressure roll whose axis is parallel to the axis of the mirror-finished roll and which is resiliently maintained thereagainst.

7. The method of claim 6 wherein the composition comprises paraflin.

8. The method of claim 6 wherein the wax-coating composition comprises paraflin and microcrystalline wax.

wax-coating References Cited in the file of this patent UNITED STATES PATENTS 2,642,366 Rumberger June 16, 1953 2,753,275 Wiles et a1. July 3, 1956 2,829,980 Redd Apr. 8, 1958 UNITED STATES PATENT OFFICE CETIFICATE 0F QQRRECTION Patent Noo 2,912,347 November 10, 1959 Milton Yezze-k et ale It is hereby certified that error appears in the printed specificatior of the above numbered patent re uiri correction and t at the said Letters Patent should read as corrected below.

Column 1., line '72, and column 2, line 6, for "coating", each occurrence, reed. casting F column 2', line 57, for "head" read My heat column 3, line 43, for "Wil" read w ll .Llne' o9 ior Hater" read. letter column 6, lines 36 and 51, tor "mrro umshed read. mirror-finished o Signed and sealed this 3rd day of May 1966.,

E Attsst:

KARL 1-10 ILINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

Claims

1. THE METHOD OF PRODUCING A GLOSSY WAX-COATED PAPER WHICH COMPRISES APPLYING A HOT MELT WAX-COATING COMPOSITION ONTO A WEB OF PAPER, BRINGING THE RESULTING COATED SURFACE OF THE PAPER WEB WITH POSITIVE PRESSURE AND WITH SAID COMPOSITION IN A MOLTEN SATE INTO INTIMATE CONTACT WITH A RAPIDLY MOVING ENDLESS CASTING MEMBER HAVING A SMOOTH MIRROR-FINISHED SURFACE, THE MOLTEN WAX COMPOSITION BEING THEREBY UNIFORMLY DISTRIBUTED BETWEEN THE WEB AND THE SURFACE OF THE CASTING MEMBER AND BEING SOLIDIFIED RAPIDLY BY COOL/NG SAID CASTING MEMBER ON ITS SMOOTH SURFACE TO A TEMPERATURE BELOW THE POINT OF CRYSTALLIZATION OF THE WAX-COATING COMPOSITION AT LEAST AFTER CONTACT THEREWITH AND BY SIMULTANEOULY COOLING THE UNCOATED SURFACE OF SAID WEB DURING SAID CONTACT BY THE APPLICATION THERETO WATER MAINTAINED AT A TEMPERATURE SUBSTANTIALLY BELOW THE TEMPERATURE OF CRYSTALLIZATION OF SAID COATING COMPOSITION, MOVING SAID WEB AND SAID CASTING MEMBER AT THE SAME LINEAR SPEEDS WITH SAID COMPOSITION SOLIDIFYING BETWEEN THEM IN CONTACT WITH SAID SMOOTH SURFACE WHEREBY SAID WEB AND SAID COATING COMPOSITION ARE MAINTAINED IN INTIMATE IMMOVABLE RELATION WITH SAID SMOOTH SURFACE AND ENTRY OF COOLING WATER BETWEEN THEM IS PREVENTED UNTIL THE HEAT OF FUSION OF SAID COATING COMPOSITION IS REMOVED AND IT IS CRYSTALLIZED, AND THEREAFTER PEELING THE COOLED COATED WEB OF PAPER FROM SAID CASTING MEMBER.