US2089524A - Machine for and method of making coated sheet material - Google Patents

Description

Aug. 10, 1937. A. ABRAMS ET AL 2,089,524

MACHINE FOR AND METHOD OF MAKING COATED SHEET MATERIAL Filed Sept. 16, 1935 Patented Aug. 10, 1937 UNITED STATES PATENT OFFICE MACHINE FOR AND METHOD OF MAKING COATED SHEET MATERIAL cousin Application September 16, 1935, Serial No. 40,767

Claims.

This invention relates to a machine for and to a method of making coated sheet material. More particularly the invention relates to the coating of paper and like web material with a 5 thermoplastic composition comprising a body portion, such as a wax, and a binder portion such as rubber.

The copending application of Abrams and Wagner entitled "Coated sheet material, Serial No. 693,741, dated October 16, 1933, Patent No. 2,054,113, September 15, 1936, discloses sheet or web material coated with a rubber-paraffin wax composition of relatively high viscosity. The

present invention constitutes an improvement over the type of apparatus and method disclosed in that application, but not claimed therein. We have found, among other things, that a uniform coating of relatively high transparency and gloss can be more readily obtained and to a higher de- 20 gree if a heated doctor roll is used and if the coated sheet is quickly chilled after the coating has been applied.

It is therefore an important object of this invention to provide an improved machine for and 25 method of coating sheet or web material with a thermoplastic coating composition, whereby a coating of superior quality is obtained.

It is a further important object of this inven-' tion to provide a machine for the coating of web 30 or sheet material with a relatively viscous composition comprising a rubber or a rubber-like substance and a wax or wax-like substance to provide a flexible, thermoplastic and/or adhesive coating film that possesses a relatively high de- 35 gree of moistureproofness, waterproofness and gasproofness.

It is a further important object of this invention to provide a method of coating sheet or web material with a rubber-wax composition to pro- 40 duce flexible, moistureproof, waterproof and gasproof sheet material having heat sealing properties.

Other and further important objects of this invention will become apparent from the fol- 45 lowing specification and the accompanying draw- On the drawing:

Figure 1 represents a partly diagrammatic side elevational view of a coating machine embodying 50 the principles of our invention, with the forward bearing block removed.

As shown on the drawing:

In Fig. 1, the reference numeral Ill indicates a roll having a surface layer or covering H of 55 resilient material, such as a rubber composition or the like. Said roll I0 is provided at its ends with pipes I Z for the circulation therethrough of a heating fluid, such as steam.

A doctor roll I3 is mounted above the roll ill with its axis parallel thereto and with its journals supported in bearing boxes l4 that are adjustably held within guide members l5. Said bearing blocks l4 are provided with internally threaded bosses l6 into which extend the threaded ends of adjusting screws I I for varying the distance between the surfaces of the doctor rolls l3 and the cooperating roll Ill. The screws H are rotatably held in cross members l8 mounted on the guiding members l5. To facilitate the adjustment of the doctor roll [3, the screws I! are provided with manually operable wheels l9. It will be understood, however, that any conventional construction can be used for effecting the adjustability of the doctor roll l3, with respect to the cooperating roll iii.

A chill roll 20 is positioned in close proximity to the roll I 0 for receiving the coated web 2| immediately after leaving the surface of the roll i0. Suitable piping connections 22 permit the circulation of a cooling fluid, such-as brine, through the hollow roll 20.

'In starting up the machine such as shown in Fig. 1, a web of paper 23, for example, is led between the roll Ill and the doctor roll 13 and then the coated web 2| is passed around the chilled roller 20. A mass 24 of the coating composition, in a heated plastic state, is positioned on the traveling web 23 in advance of the doctor roll 13 and the doctor roll [3 is so adjusted as to give the desired thickness of coating to the web as it travels through the nip between the two rolls. The mass 24 of coating composition is of such high viscosity that it does not require the use of a hopper to keep it in position.

Since both the roll l0 and the doctor roll l3 are heated, preferably to a temperature of around 180 to 200 F. when using our rubber-wax composition, the plastic mass 24 is maintained in a sufficiently plastic condition to be drawn into the nip between the doctor roll I3 and the cooperating roll ID. We have found that it is preferable to revolve the doctor roll l3 at a speed considerably slower than that of the roll Ill and in the same direction as the roll l0. Very satisfactory results are obtained if the surface speed of the doctor roll is equivalent from about 4% up to 15% of the surface speed of the large roll I ll depending upon the degree of viscosity of the composition used. One of the objects of having the doctor roll revolve is that otherwise small specks of dirt may collect between the doctor roll and the cooperating roll. If the doctor roll were not turning, these particles of dirt would remain in situ, thereby causing the film to tear at such 5 point. If, however, the doctor roll turns, the wiping action is sufficient to keep such dirt moving along with the fllm.

As shown, the chilled roll 20 is placed in close proximity to the roll l0 so that the coated web 2| is immediately chilled after it leaves the coating roller ID. We have found that a much more transparent film, higher gloss, greater flexibility, tensile strength and stretch are obtained if the chilling step follows immediately after the coating step.

Since our machine has been developed particularly for the manufacture of sheet or web material coated with thermoplastic compositions, such compositions will be described accordingly.

suitable binders under controlled conditions to certain thermoplastic substances which are brittle and notflexible at ordinary temperatures to render such thermoplastic substances pliable and flexible to a remarkable degree. We have, for example, discovered that substances such as paraflin wax or certain types of asphalt which are brittle and not flexible at ordinary temperatures can be rendered pliable and flexible by adding thereto certain binders such as rubber, gutta percha, "Viskanol" (a straight chain hydrocar hon produced by suitably polymerizing some of the unsaturated hydrocarbon gases produced in cracking petroleum) and other artificial gummy or rubber-like substances, singly or in combination with one another.

We have also found that by properly controlling the proportions and compounding conditions, we can uniformly produce compositions 40 having a desired predetermined viscosity and cohesivenesswhereby they can be employed for coating fabrics.

The major ingredient or body of our composition thus consists essentially of a thermoplastic 45 substance which is not flexible or pliable at ordinary temperatures. Such body substance is furthermore solid at normal temperatures, but liquefies at higher temperatures, is insoluble-in water and acts as a dispersing medium or solvent 50 for the binder which is added thereto. Any sub- By properly compounding these. substances in suitabie proportions and under carefully controlled conditions so as to produce the proper vis-. cosity hereinafter more fully described we have obtained compositions which have distinctly new properties and which, have important commercial A specific embodiment of our composition adapted for coating purposes comprises a composition of rubber, or a rubber-like substance, and a wax, or wax-like substance. Suitable rubber 75 and rubber-like substances include pale crepe We have found that it is possible by adding rubber, smoked sheet rubber, vulcanizable rubbers generally and gutta percha. We have successfully used paraffin-wax, beeswax, spermaceti, and other waxes, in the preparation of our composition, singly or in combination with one another. However, pale crepe rubber and paraflinwax are the ingredients which we prefer to use, for producing a substantially colorless and tasteless product.

Since solutions of rubber and wax have widely varying viscosities, depending upon the proportions of particular ingredients used and upon;

the conditions of preparation, we have found it most satisfactory to determine first the permissible viscosities for coating purposes and then to adjust the proportions and conditions so as to obtain viscosities within the desired range. In

general, rubber-wax compositions having viscosities lower than 8000 sees. (50 c. c. measured on a Scott viscosimeterat 90 C.) are not satisfactory for coating purposes where relatively permeable papers are being coated, since there is a tendency of the coating material to strike through the paper. For example in coating ordinary sulphite pulp stock of about 1'7 lb. weight per ream (24' x 36480), we' have found that a rubber-wax composition containing 12% rubber and having a viscosity of at least 8000 secs. (Scott) will not strike through the paper.

In the case of well hydrated sheets, such as grease-proof, glassine, parchment, and the like, viscosities as low as about 1000 secs. (Scott) can be used. The upper limit of the permissible viscosity range is too high to be measured satisfactorily on 2. Scott viscosimeter, but by using small quantities of the composition, say 5 or 10 c. 0., the viscosities can be computed roughly and have been found to go up as high as several hundred thousand seconds or even a million seconds or more.

The proportion of pale crepe rubber to paraffinwax may, in general, vary between 6% rubber, 94% parafiin-wax and 30% rubber, 70% paraflinwax by weight. Using other rubber-like and wax-like substances the proportions should be so chosen as to give suitable viscosities of at least 8000 secs. (Scott).

The following will illustrate a preferred composition of our invention and a preferred method of preparing the composition:

- 1 Percent by weight Paraflin-wax, melting point between 120 and 180 F 85 to 88 Pale crepe rubber, 0.020 to 0.050 inch in thickness, in sheets 15 to 12 The composition must be prepared under care-.

fully regulated conditions which we have determined by long study and experimentation.

The 'paraflin-wax is first melted by heating in a jacketed vessel, preferably provided with a kneader type of stirrer, to a temperature of about ZOO-210 F. The individual sheets of rubber are then carefully added to the bath so that the surfaces are completely wetted with the molten paraiiin as they are being immersed in the bath so as to avoid sticking and welding of the rubber sheets to each other in the bath.

In the, case of the lower concentrations of rubber, from 0 toabout 15%, there is an adequate volume of wax to facilitate good soaking of the rubber. The main precautions involved in eifecting a solution of this kind is a careful addition of the rubber as described and correct mixing procedure. Concentration offrom 10 to 15% rubber have a final viscosity sufilcient to pull apart soft lumps of rubber which are not properly soaked; concentrations below 10% rubber in wax do not build up such a high viscosity and consequently rigid precaution must be taken to secure proper soaking.

In considering concentrations ranging from 15 to 25% rubber in parailin-wax it is necessary to add the rubber quickly so that the rubber added last will have an adequate chance to soak up its share of the wax. This range of concentrations has a resulting high viscosity which'enables the batch to pull apart lumps which would ordinarily cause trouble in lower concentrations.

It is necessary to use another method for mixing rubber and paraifin-wax in concentrations above 25% rubber. This method resembles somewhat the present commercial method for compounding rubber. The rubber is broken down in the presence of say, an equal weight or less of paraflin-wax. This can be done in several types of mixers like the Banbury or the Werner- Pfieiderer. If a lower concentration is desired, parafiin-wax should be added slowly after the original rubber-wax composition has been thoroughly mixed. This method can also be used for procuring low concentrations of rubber in wax by carefully diluting to the desired composition.

During the addition of the rubber in the specific example of our prepared composition,

the temperature of the bath is permitted to drop to 180 to 190 F. and is maintained at this temperature throughout the compounding operations. After all the rubber has been added the bath is gently stirred with a paddle so as to permit thorough penetration of the parafiin into the rubber and to prevent lumping of the rubber during solution. This stirring operation is continued for about fifteen minutes until the rubber sheets are adequately soaked.

The mixture is now mechanically stirred in a kneader type of mixer until the batch is free of lumps of undissolved rubber. This operation requires 1 to 2 hours. The temperature of the mass is maintained at 180 to 190? F. during the entire period. At the end of this time, any undissolved lumps may be strained out, broken up and returned. However, this is not ordinarily necessary. The composition so prepared is then ready for coating, laminating or direct conversion into thin films.

During the compounding operations, it is necessary to keep the temperature of the rubberparaflin wax mixture at about the temperature indicated in order to avoid overheating, which results in an undesirable darkening of the mass and imparts an odor to it. Howevenif some slight color and odor are permissible, temperatures up to 200 to 220 F. may be employed. Due recognition should be given to the fact that viscosity of the composition drops if the time of heating is prolonged or if higher temperatures are employed.

Various pigments or other coloring matters, fillers, and the like, may be incorporated, either directly or by means of a master batch, into the rubber-wax mixture, depending upon the type 01' pigment, filler, or added ingredients to be incorporated. It is also possible by means of split batches to prepare vulcanizable coating compositions that will become vulcanized after being coated on to the sheet or web material, as described in copending application executed of even date herewith. This method generally consists in preparing two separate batches of our rubberwax composition, one containing a super-accelerator, and the other containing the vulcanizing agent and activator, and then combining the batches prior to the coating operation.

Gums may be added to our composition with a slight advantage in sealing properties but with a greater tendency to block." By the term "block is meant the property possessed by sheet material to adhere together, as for instance under unusually high climatic temperatures and under high pressures. The use of gum rosin, for example, to replace an equal weight, say up to about 15% of the paraflln can be effected without seriously increasing the blocking tendency of our composition. When the sheets are piled together they do not under ordinary conditions stick to 'each other or block, but to prevent any tendency to block, the surfaces may be dusted with substances, such as mica or starch.

The thickness of the layer of composition applied to the web or sheet material being coated may be varied by adjusting the distance between the doctor i3 and the coating roll Hi. We prefer to adjust our device so that between 10 and 20 pounds of our composition will be coated on to each ream of paper (3000 sq. it.) but any amount between 4 and 60 pounds per ream will produce coatings that are satisfactory for certain purposes.

Paper coated with our rubber-wax composition is water and moistureproof. The coating is nontacky, flexible and adheres to the superficial surface of the web without striking through and with little penetration into the web but remains essentially as a surface layer. The coated paper is tasteless, odorless, gasproof and suitable for wrapping foods or for containers. Our coated paper can be wrinkled or folded without losing its moistureproofness as occurs with ordinary paraflin-wax coated paper. The coated paper is also heat sealing and can be made to adhere to an uncoated sheet by merely superimposing the coated sheets and applying heat and pressure.

Paper coated with our self-vulcanizing rubberwax composition is also waterand moistureproof. At elevated temperatures the coating is tough, non-adhesive and non-tacky.

While our apparatus and method have been specifically described in connection with the coating of paper with a rubber-wax composition, it will be understood that it is particularly adapted to the coating of so-called frangible types of web material, such as paper, cellophane, glassine, parchment, metal foils and the like, with any thermoplastic composition of a highly viscous nature. The invention is particularly applicable to the coating of web material with compositions that are so highly viscous, even in heated condition as to make coating by immersion or by fountain feed rollers impracticable.

We are aware that many changes may be made and numerous details of construction may be varied through a wide range without departing from the principles of this invention, and we, therefore do not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

We claim as our invention:

1. A machine for coating frangible web material with a thermoplastic coating composition, which comprises a driven roll having a resilient surface for supporting the web material to be coated, a heated doctor roll driven at a lesser surface speed than said driven roll, means for adjustably positioning the doctor roll with respect to said first roll to control the thickness of the coating applied to web material passing between I said rolls, said doctor roll being positioned so as not to contact saidcoating after being applied to said web, and a chill roll in close proximity to 5 said first roll to receive and chill the coated paper quickly after being coated. I

2. A machine for coating frangible web material with a thermoplastic coating composition, which comprises a rubber covered roll for sup- 10 porting the web material to be coated, means for heating said roll, means for rotating said roll, a cooperating heated doctor roll, means for ad v 3. A machine for coating frangible web mate'- rial with a thermoplastic coating composition, 25 which comprises a rubber covered roll for supporting the web material to be coated, means for heating said roll, a cooperating heated doctor roll, means for driving said doctor roll at a slower speed than said first roll but with the cooperating 30 surfaces of said rolls moving in the same direction, means for adjustably positioning said doctor roll with respect to said first roll to .control the v 2,080,524 I v thickness of the coating applied to said web ahead of said doctor roll from a mass of said coating composition as said webpasses betweensaid rolls, said doctor roll being positioned so as not to contact said coating after being applied to said web, and a chilled roll around which said coated web is passed after'leaving said first roll. 4. The method of coating frangible web material with 'a thermoplastic composition, which comprises applying the coating composition in a heated plastic condition to the web material while yieldingly supporting said web, further heating .and smoothing said composition to form a thin coating layer, leading said coated web so as not to permit the coating to contact any supporting surface immediately after the coating operation and then chilling said coating layer on the web material.

5. The methodof coating frangible web material with a thermoplastic wax-rubber composition, which comprises applying the coating composition in a heated plastic condition to the web material while yieldingly supporting'said web, further heating and smoothing said composition to form a thin coating layer, leading said coated web so as not to permit the coating to contact any supporting surface immediately after the coating operation and then chilling said coating layer on the web material.

ALLEN ABRAMS. CHARLEY- L. WAGNER,

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