US2157212A - Impervious sheet material - Google Patents

Description

May 9, 1939.

G. A. MOORE IMPERVIOUS SHEET MATERIAL Filed Oct. 26, 1957 INVETNTOR W W f/awco'm M ATTORNE I Patented May 9, 1939 UNITED STATES PATENT OFFICE IMPERVIOUS SHEET MATERIAL Application October 26,

8 Claims.

This invention relates to coated sheet material and to a method of making the same, and more particularly to a method of applying a stratified film to a sheet material such as paper or the like.

An object of the invention is to provide a novel coating for sheet material having pliable, moisture-proof, and adhesive characteristics.

Another object is to provide a novel coating for sheet material comprising a film of a waxy and thermoplastic nature.

Another object is to provide a novel material of the above type which is suitable for use as a blank in the making of containers for tobacco or the like.

Another object is to provide a novel material of the above type having a coating comprising a thermoplastic adhesive possessing properties suitable for effecting a moisture-proof seam.

Another object is to provide a novel material of the above type having a coating which is moisture-proof and, impervious and which presents two primed, thermoplastic, adhesive surfaces.

Another object is to provide a fibrous sheet material coated with a novel stratified film consisting of a layer of waxy material interposed between layers of thermoplastic cellulosic lacquer, said film having a brilliant surface gloss.

Another object is to provide a novel and improved continuous process or method for applying a stratified film of the above type to a web of sheet material.

A still further object is to provide a transparent, stratified film on sheet material, it being understood that the said material may be printed prior to the application of the film to the printed surfacef 'I'heabove and further objects and novel features of the invention will more fully appear from the following detailed description when read in connection with the accompanying drawing.

It is to be expressly understood, however, that the drawing is for the purpose of illustration only and is not intended as a definition of the limits of the invention, reference being had primarily for this latter purpose to the appended claims.

In the drawing wherein like reference characters refer to like partsv throughout the several views,

Fig. l. is a diagrammatic view illustrating one method of coating a sheet material according to the present invention; and

Fig. 2 is an enlarged detail view illustrating 1937, Serial N0. 171,001

(Cl; Ell-68) a seam or joint embodying the present invention.

In the embodiment shown, for purposes of iilustration, the invention has been applied to a strip of sheet material, such as paper, which is 5 suitable for making small containers of the type used for tobacco or the like. It is to be understood, however, that the method may also be ,used for applying a coating to other types of material, such as Cellophane or other cellulosic material, and is adapted, in any event, to produce a moisture-proof, thermoplastic coating thereon.

The invention provides for casting a layer or film of wax between two layers or films of a thermoplastic lacquer such as a nitro-cellulose lacquer, to form a stratified coating having thermo plastic, adhesive properties imparted by the lacquer and having the moisture-proof properties of the wax. The first layer of lacquer serves to size the paper and to prevent the wax from being absorbed thereby. It also supports the wax and is strongly adherent to the paper. The wax can be cast in an extremely thin layer as it is supported on the impervious lacquer base. The outer layer of lacquer protects the layer of wax and facilitates the making of a joint or seam which may be adhesively secured by the use of heat and pressure, as will be more fully described.

In a coating of this type, a careful balance should be maintained between the wax and lacquer because an excess of wax will tend to dissolve the solids from the lacquer and destroy the thermoplastic adhesive properties thereof, whereas a deficiency of wax will decrease the imperviousness of the layers to moisture. It has been found that a thin layer of wax between two thin films of nitro-cellulose lacquer possesses the desired properties and provides a stock that is suitable for making moisture-proof tobacco containers and the like.

Referring to Fig. 1, the invention as shown, by way of example, is carried out by passing the strip material 9, such as paper, Cellophane or the like,

from a reel ll], over an idler roll II. and feed rolls l2, to a first coating station A. In the embodiment shown, this coating station comprises a roll I4 registering with a reverse coating roll IS. The latter engages a transfer roll 16 which, in turn, receives a coating of lacquer of the type to be described from a roll I! rotating in a reservoir l8 which is fed'through an inlet IS with the lacquer or other material to be applied to the strip 9. The rolls I6 and I1 rotate in the bottom of the reservoir It in such a way that a coating of lacquer is picked up from the lit reservoir by the roll I] and is transferred therefrom to the roll I6 and thence to the roll l and to the upper surface of the strip 9. It will be noted that the roll l5 rotates in the reverse direction with respect to the direction of feed of the strip 9 so as to cause the film to be positively removed from the surface of the roll l5 and to be pressed or worked into the surface of the strip. A doctor blade 20 may be mounted in the reservoir I8 to control the film on the roll l6 so as to apply the desired thickness of film.

Various types of coating material and lacquers have been found suitable, preferably celluloses, such as Du Pont Lacquers Nos. 606, 543, 208, or the like. These materials are thermoplastic in that they become activated when heated and, in addition to forming a coating over the surface of the web material, have sufficient adhesive properties so that the blanks cut from said material may be readily secured in shape by overlapped seams.

Although a particular type of coating mechanism has been described, it is to be understood that any standard type of mechanism may be used for applying a continuous thin film of the lacquer to the strip 9 as it passes the station A.

The strip 9 with the coating 2| (Fig. 2) applied thereto is now passed through a suitable drying tunnel 22 (Fig. 1) for thoroughly drying the lacquer film and is thence passed, at a wax station B, over a wax roll 25 which rotates with a fountain roll 26. The latterroll is located in a bath of wax 21 contained in a reservoir 28 which is heated by suitable means, such as electrical heating elements 29 shown in the base of the reservoir. The roll 25 may also contain an electrical heating unit 30 if desired. It is to be understood that the reservoir 28 is maintained at the temperature required to maintain the wax in a molten condition and to apply the same to the strip 9 as a thin film 32 (Fig. 2) over the surface of the film 2|. Various types of waxes may be used for this purpose, such, for example, as a.

paraflin wax, opal wax, or a resinous series of hot melts, all referred to hereafter as wax. In any event, the wax is adapted to provide a thin, flexible, impervious coating which adheres to and is deposited on the film 2| of thermoplastic lacquer.

After passing the station E, the strip 9 passes around an idler roll 35 (Fig. l) and thence to a station C at which a further coating of thermoplastic lacquer is applied. The web may be cooled by circulating air over the film to harden the wax before it reaches the idler roll 35.

The station C may comprise rolls Ma, l5a, lGa and Na cooperating with a reservoir l8a similar to the elements 14 to [8 described at station A. The reservoir lBa may be supplied with lacquer through an inlet 19a and the roll [6a may be provided with a doctor blade 20. as above described. In this station, a coating 36 (Fig. 2) of lacquer, similar to the coating 2|, is applied over the surface of the wax film 32. This lacquer may be of the same type as that applied at station A.

In certain instances, however, it may be desirable to use one specific lacquer at station A and another specific lacquer at station C, depending upon the desired characteristics of the finished film.

After passing station C, the strip 9 passes through a drying tunnel 38 which may be of considerable length and is preferably maintained at a temperature sufficiently low so as not to soften or destroy the wax film. The tunnel 38 may be sub stantially longer than the tunnel 22 because of the lower temperature maintained therein and the consequent longer time required for drying the film. The strip then passes over an idler roll 39 and a set of feed rolls 40 which are similar to the feed rolls I2 above mentioned and may be geared together therewith so as to cause the strip to move at a uniform rate. The strip then passes over an idler roll 4| and may be rewound onto a reel 42.

It will be noted that the film 2i of lacquer, which is deposited on the strip 9, serves the purpose of priming the paper surface so that the wax is prevented from permeating the same. It also possesses thermoplastic properties and is actuated by heat and pressure for effecting a joint in the manner to be described.

The provision of a thin film of wax between two films of thermoplastic lacquer forms a plastic, pliable coating in which the lacquer protects the wax and imparts thermoplastic adhesive properties to the coating while the wax forms a moisture-proof, impervious layer. The wax film is so thin in relation to the lacquer that the lacquer solids are prevented from being diluted by the presence of the wax and destroying the effectiveness of the lacquer. The use of a lacquer film on each side of the wax film further reduces the tendency of the solids of the lacquer to enter into the wax and thereby reduce the effectiveness thereof.

The above-described material is particularly suitable for forming blanks from which containers may be made and provides an effective means for making a moisture-proof, strongly adherent seam. The method of making such a seam at the overlapped ends of the blank is illustrated in Fig. 2. It will be noted that the blank has been folded in such a way that the two outer thermoplastic layers 36 are in contact. Suitable heat and pressure is then applied, as, for example, by a heated die 43, to activate the lacquer and at the same time to cause the wax to melt and permeate or mix with the lacquer. The film is also pressed to some extent into the fibrous material, thereby impregnating the seam with moisturerepellent material.

It will be noted that the above-described invention provides an impervious, adhesive and flexible coating for a paper strip or the like which has a wide field of usefulness and is especially suitable for use in making hermetically sealed containers of the type used in packaging tobacco and other similar articles having a definite moisture content which must be maintained therein for a substantial period of time. The film has the combined properties of the wax and thermoplastic adhesive and is so formed that the wax does not prevent a firm adhesion at the overlapped seam. The process may be easily and efficiently carried out and the stratified film provides a dependable means for moisture-proofing the entire container and for effecting an adhesively secured seam. The process is continuous, thus reducing handling time and expense, and avoiding damage to and imperfections in any one layer of the film. The outer surface of the film has a brilliant gloss which greatly enhances the eye appeal and salability of an article embodying the same. If desired, the film may be colored or transparent, and, if transparent, is readily applied over printed matter.

Although a particular embodiment of the invention has been illustrated and described, it is to be expressly understood that the same is not limited thereto, but that various changes may be made therein without departing from the spirit and scope of the invention as will now be understood by those skilled in the art. For a definition of the limits of the invention, reference is had primarily to the appended claims.

What is claimed is: 1. The method of coating 2, fibrous material which comprises applying a film of nitro-cellulose lacquer tothe surface thereof, drying said film, casting a wax film thereon, hardening the latter, casting a second film of nitro-cellulose lacquer on said wax film, and drying said second film.

2. The method of applying thermoplastic, moisture-proof film to a strip of fibrous material which comprises passing said strip continuously past a plurality of coating stations, applying a. film of cellulose lacquer at a first station, passing the strip through a drying zone between the first and second stations, applying at the second station a layer of wax over said first layer, causing the wax to harden, applying at the third station a layer of cellulose lacquer over said wax, and. 5 passing the film through a second drying zone in which the last film is caused to set, said second drying zone being maintained at a temperature suificlently low to prevent undue softening of the wax.

3. A fibrous sheet material having a surface coated with a stratified film comprising a layer .of lacquer in contact with said surface, a layer of wax formed on said first layer and a second layer of lacquer deposited over said layer of wax.

4. A fibrous sheet material having a surface coated with a stratified film comprising a layer of cellulose lacquer in contact with said surface,

a layer of wax formed on said first layer and a second layer of cellulose lacquer deposited over 40 said layer of wax.

5. A fibrous-sheet material having thereon a stratified coating comprising a layer of wax interposed between two layers of cellulose lacquer, said layer of wax being sufiiciently thin with respect to the lacquer layers to prevent the adhesive properties of the lacquer from being materially affected by solution of the solids thereof into the wax.

6. The method of applying a thermoplastic moisture-proof coating to fibrous material which includes applying a thin film of thermoplastic lacquer to the surface. of said material, drying said film, applying a thin layer of wax to the surface of said film, hardening said layer, applying a film of thermoplastic lacquer to the surface of said layer, and immediately drying said last-named film.

7. The method of coating fibrous material which includes applying a thin film of liquid lacquer to the surface of the material, passing the latter through a dryer to dry saidfilm, applying a thin layer of wax to the surface of said dry film, hardening said layer of wax, applying a film of liquid lacquer to the surface of said layer,

and immediately drying said second-named film at a temperature above the melting point of said wax layer.

8. The method of coating fibrous material which comprises applying a film of liquid lacquer to the surface of said material, subjecting said material to heat for drying said lacquer film, applying a thin layer of wax to the surface of said film, passing said material through a cooling zone for hardening said wax layer, applying a thin film of liquid lacquer to the surface of said wax layer, and immediately subjecting the material to heat at a temperature sufilciently low to prevent undue softening of the Wax for drying said second film of lacquer.

GEORGE ARLINGTON MOORE.

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