US2423555A - Coated paper product - Google Patents

Description

y' l July f8,

c. D, 'ENDER l COATEDPAPER PRODUCT Filed Apr1 124, 1944 v CLARENCE DQENDER INVENTORY AGENT Patented Julyy8, 1947 COATED PAPER, PRODUCT Clarence D. Ender, Wilmington, Del., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Application April 24, 1944, serial No. 532,463

2 Claims. A1 This invention relates to coating compositions and more particularly to the application of coating compositions to porous fibrous materials to obtain extremely thin but impervious coatings.

When employed on porous materials, coating solutions tend to impregnate the material. At'

least one sizing treatment has usually been found necessary before the coating solution could be applied. A sizing operation by lling pores of the material acts to retard'impregnation and resultant waste of the more valuable coating solution. -But an uneven surface is nevertheless presented to the first application of coating solution. Consequently, some tiny, porous particlesv usually project through the lm coating, breaking its continuity. The coating solution applied in succeeding coats is then drawn .by capillary action through these particles into the material- Tiny, imperceptible pinholes may persistin this manner even though several coats are applied. The weight of coating required to build up over the projecting particles and seal the pinholes has been found so great as to be uneconomical and makes the coated material unsuited for some purposes. Thus, thin and impervious coatings on porous materials have been diiiicult to prepare.

Now in accordance with this invention, a relatively -thick mass or coat 'of a solution of chlorinated rubber having a nonvolatile content and viscosity Vwithin certain limits, whereby impregnation is avoided, is applied toa web of porous paper. The web then is drawn across a doctor while applying pressure to the web where in contact with the doctor, whereby the doctor by its wiping and spreading action draws out thecoating solution to a thin continuous lm. The volatile solvent is permitted to evaporate. As a result of its high nonvolatile content, the thin film remains continuous and lsubstantially nonilowing during drying. By utilizing a coating composition containing between about 40% and about 80% chlorinated rubber, between about 15% and about 50% plasticizer, for example, dissolved in a volatile solvent toform a solution vious to moisture, oil, grease, nitrated glycerol,

nitrated glycols, and the like.

Having now indicated in a general way the vation view of a knife coater suitable for carrying out the process of the invention.

Referring to the drawing, the paper to be coated l is fed from a reel 2 over tension rolls 3 and 4 and then is picked up by a flexible blanket or belt 5 which provides the motive force for the paper. The blanket or belt is resilient and f may be of rubber. The tension rolls are so adk.iusted' that the paper is held rmly upon the blanket. l

The speed of the blanket is governed by powerdriven rolls 6. In general, the speed of the blanket is held between about` 15 and about 30 ft. per minute.

'lhe coating composition 'l is poured, for example, upon the paper using an adjustable funnel u and allowed to spread roughly over it as the paper approaches a doctorknife 9. The knife may be raised or lowered. It is adjusted so that it exerts pressure upon the paper, which, supported upon the resilient blanket, is held rmly against vthe knife at all times. The knife wipes and spreads the composition and removes excess composition. In its action it draws the coating containing between about 40% and about 80% to a very thin, uniform continuous film. The knife is 'supported' by a strong backing |40 which may contain a heating element. Thus,- the knife may be heated so as to coat solutions too viscous -at room temperature.

The doctor utilized to spread the initially 'coated film and to draw it to a very thin nlm pressed firmly by or against the doctor edge or surface. Asshown by the drawing, a convenient method for applying pressure to the paper against a rigid doctor involves support of the paper by a resilient supporting means, such as a resilient rubber blanket which may be, for example, between about 0.25 and about 2 inches thick. Such a blanket supports the paper web, preventing breakage, and at the same time strongly presses it against the doctor. It also serves by frictional engagement lto pull the paper past the doctor. Accordingly, a preferred embodiment of the present invention involves coating a web, engaging the coated web with a rigid doctor, resiliently nature and purpose of the invention, there follows a more detailed description'of a preferred embodiment thereof with reference to the accompanying drawing.

'Ilie gure represents aA diagrammatic side elesupporting and pressing the web against the doctor, and drawing the web while so pressed across the working surface or edge of the doctorto d raw and thin out the coating. Other means of exerting pressure against the doctor, as by a hard .or resilient roll opposite the doctor, may be employed.

The coated material Il then passes to a dryer or other means for dissipating the solvent.

An alternative procedure involves applying the coating composition to the web by means of a roll-type applicator. The lower part of the applicator dips in a container of the coating solution. The paper or like web is pressed firmly against the applicators upper surface. A scraping knife applied to the applicator roll may act as a regulator of the quantity of coating composition permitted to pass to the paper. The paper, coated with the desired amount of composition, is drawn across a doctor roll or knife which wipes and spreads the composition. Preferably, the doctor is adjusted so that it exerts pressure upon the paper in order to draw the coating to as thin a uniform, continuous lm as possible, but' this is not essential.-

In Table I are given a number of particular formulas as examples of coating compositions used in the process accordingto this invention. Chlorinated rubber andA plasticizer are essential ingredients; resins, waxes, llers, and the like are optional; compositions comprising chlorinated rubber, a plasticizer, a wax, and a resin are preferred.

'I'he ingredients are dissolved in a volatile inert solvent to form a solution which, at th'e temperature of coating, has a viscosity between about 600 and about 600,000 cp., preferably between 2,000 and 100,000 cp. It is essential that the viscosity be in this range to avoid impregnation of the material and to permit the film to be drawn out thinly to provide imperviousness in one coat. The nonvolatile content of the solution will be between about 40% and about 80% by weight of the solution, preferably between 50% and 70%. The ranges given are critical. volatile content gives` a coating which may contain pinholes due to shrinkage and owof the drawn lm before drying; too high a nonvolatile content makes a very thin coating too difficult to obtain as it prevents proper drawing-out; i. e., workability, of the composition.

The composition for convenience is preferably applied at temperatures between about 20 C. and about 35 C., that is, at ordinary room tem-y peratures. plied at elevated temperatures, up to about 80 C. Temperatures above about 80 C. must be avoided as too rapid evaporation of solvent occurs during the coating, adversely affecting the uniformity and continuity of the coating and increasing the possibility of pinholes. The viscosity of solutions may sometimes be increased by cooling to below room temperature, if desired, say to about C.

It has been found that to form a coating substantially impervious to moisture and most oils and liquids, a minimum weight of about 4 lbs. ofA

coating per ream of 3600 sq. ft. is required, when coated on one side of the paper, about 2 lbs. per ream of 3600 sq. ft. when applied to both sides of the paper. The minimum weight of coating is preferred. Such a lm has a thickness of about 0.0001 inch. The maximum weight of coating will be governed by economy, by the type of paper used, and'A by other requirements. For example, where the coated paper is to be used for dynamite wrappers, a weight of coating above about 30 lbs. per ream of 3600 sq. ft. coated on one side of the paper is undesirable since on exploding the dynamite in closed places, as in mines, excessive quantities of poisonous or irritating gases are formed. Suchva iilm has a thickness of about 0.0008 inch.

Too low a non-v More viscous Lsolutions may be ap- Y Ingeneral, a weight of coating between about 4 'and about 18 lbs. per ream of 3600 sq. ft. is most satisfactory.

The chlorinated rubber used in this invention must have a chlorine content between about 60% and about '75%, preferably between 60% and 69%.

lIts viscosity characteristic should be between about 20 and about 1,000 cp. The viscosity of the composition solution is directly related t'o the viscosity of the chlorinated rubber; the chlorinated rubber should have a viscosity within the limits given to obtain a nal solution within the critical viscosity range. f

Piasticizers that have been found satisfactory include dibutyl phthalate, diamyl phthalate, butyl acetyl ricinoleate, butyl stearate, tricresyl phosphate, triethyl citrate, triphenyl phosphate, dibutyl 'tartrate, linseed oil, castor oil, soybean oil, tung oil, etc. A plasticizer is essential to retention of imperviousness after coating. It is used in a quantity between about 15% and about 50% by weight` of the nonvolatile ingredients.

Waxes which may be used in the composition include paraflin, beeswax, tallow, japan, carnauba, candelilla, montan, spermaceti, white ceresin, palm, or any waxy substance, such as stearic acid, vaseline, cetyl palmitate, oxidized parain, octadecyl palmitate, oleyl hydroxyoleate, oleyl oleate, cetyl oleate, ceryl cerotate, myricyl palmitate, myricyl cerotate, etc. Waxes impart moisture-vapor-proofness. They may be used in a quantity up to about 5% by weight of the nonvolatile ingredients of the composition,

Resins that have been employed include rosin; rosin maleates; ester gum; hydrogenated rosin; hydrogenated methyl abietate; ethylene glycol ester of rosin or hydrogenated rosin; pentaerythritol ester of rosin; diethylene, tetraethylene, or hexaethylene ester of hydrogenated rosin; polymerized rosin; natural resins; alkyd resins; phenol-formaldehyde resins; urea-formaldehyde resins, coumarone-indene resins; terpene resins; etc. Resins may be incorporated in a quantity up to about 25% of the nonvolatile ingredients.

The composition essentially contains a suitable solvent or solvent mixture which will electively dissolve the chlorinated rubber, plasticizer, and other ingredients where included, and which may-be dissipated following application of the composition to the material being coated. I'he solvent acts merely as a vehicle for the application of the composition. Such a solvent may be a hydrocarbon, such as xylene, toluene, benzene, mesitylene, ethyl benzene, high aromatic content petroleum naphtha, cyclohexane, high-flash naphtha, etc.; an ester, such as hexyl acetate, butyl acetate, methyl acetate, etc.;` a ketone, such as methyl `ethyl ketone, methyl isobutyl ketone, etc.

The proportions of the nonvolatile ingredients in the composition will in general be as follows:

The presence ofwater in the composition solution is undesirable and should be avoided, the adherence and smoothness of the coating being adversely affected. Pinholes tend to form where the water droplets were.

oxygen balance.

l The method according to this invention may be used to coat variousl porous, fibrous materials.

. In particular, it is useful for coating papers, such as wrapping, bond, ledger, text, and kraft paper, etc., and nbrous sheets, such as jute, cardboard, Bristol board, ber board, Lion Jute tag cardboard, etc.

v 'thin coatings of chlorinated rubber, imperviousI to moisture and most oils, which comprises ap.

Tablel tion is 40-80% by weight and the viscosity of the composition is 600 to 600,000 centipoises by the falling ball method at the temperature of application used, and drawing out the composition by pressure-of a doctor against the moving paper while resiiiently supported, to a continuous coating which,'when dry, will have athickness from about 0.0001 toabout 0.0008 inch and aweight no greaterthan pounds per ream of 3600 square.

feet, and drying the resulting coating. 2. A methodgfor applying to paper extremely plying togal moving continuous web of the paper Example l 2 3 4 5 A. 7 l A 8 9 I chlorinated Rubber 125 cp. Viscosity 750 750 750 750 585 585 585 750 508 Dibutyl Phthalate 250 250 250 250 Diamyl Phth a 235 235A 235 250 Hydmgenated Meth A liefefe 342 Natural Resin-Modified Alkyd Resin (Teglac' Z-52) 145 145 145 White Ceresin BX 35 Parain (M. P. C.) Parailln Wax (M. P. 45"` C.) 35 T I 1,500 666 540 430 820 540 1,000 1,000 Xyiene 6 Per cant Nonvolatile Content... 40 60 65 70 '55 65 50 60 Viscosity 25 C. cp. (Storiner) 2, 374 231,400 22, 160 8,247 26, 900 Viscosity 25 C. cp. (Falling Ball) 63 93,400 370,000 ,230 59,000 2, 6,220 Viscosity 45 C. cp. Falling Ball) 4, 205, 600 Viscosity C. cp. Falling Ball) 529,

Other uses, such as for candy wrappers, bread room wallpapers,.etc., will be apparent.

A highly viscous coating composition is advantageous for several reasons. It is more economical since less solvent and less material are required. To obtain impermeability to moisture and other materials, only one coat is required; a sizing or pore-filling" coat is unnecessary. Impregnation of the material is largely avoided. A coating oi extreme thinness, as low as 0.0001 inch in thicknessis made possible. Materials coated with this composition may be heat-sealed or may be sealed by moistening the surfaces with solvent and then sticking them together.

The viscosity characteristic of the chlorinated rubber was determined by measuring the viscosity in centipoises of a 20% solution in toluol at 25 C. Where the viscosity values of coating composition solutions at the coating temperature are referred to in the speciiication and claims, it will be understood that they are determinedby the falling ball method.V Unless otherwise speciiied, the viscosity valuesof the coating composition solution given in the specification and claims are as determined by the falling ball method at 25 C.

In the speciication and in the claims, the percentages are by weight.

What'I claim and desire to protect by Letters Patent is:

1. yA method for applying to paper extremely thin coatings of chlorinated rubber, impervious to moisture and most oils, which comprises applying to a moving, continuous web of the paper a viscous composition comprising chlorinated rubber in a quantity between ,40% and 80%, Plasticizer between 15% and 50%, 05% wax, 025% resin, the percentages being by weight of total nonvolatile components of the composition, andvolatile solvent for the chlorinated rubber and other ingredients, the solvent being in a quantity such that the nonvolatile content of the composino greater than 30 pounds per ream of 3600 square a viscous composition at 0-80 C. comprising chlorinated rubber having a vviscosity characteristic between 20 and 1,000 centipoises and a chlorine content of 60-70% in a quantity between 40% and 80%, plasticizer between 15% and 50%, 0-5% wax, 0-25% resin, the percentages :being by Weight of total nonvolatile components of the composition, and volatile solvent for the chlorinated rubber and other ingredients, the solvent being in a quantity such that the nonby weight and the viscosity of the composition ,is 600 to 600,000 centipoises by the falling ball method at the temperature of application used, supporting the moving paper web on va resilient belt or blanket, passing the paper against a doctor under pressure against thel paper and its support to spread and draw down the viscous composition to a. continuous surface coating which, when dry, will have a thickness from about 0-.0001 to about 0.0008 inch and a weight ,i feet, and drying the resulting coating.

' CLARENCE D. ENDER.

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

UNrrED STATES PATENTS 471-440 Great Britain Sept, 6, 1937 7` Certificate of Correction I 8 Patent N o. 2,423,555. v July 8, 1947.

CLARENCE D. ENDER i It is hereby certied that errorappears in the printed specification of the above numbered patent requiring correctlon as follows: Column 6,- line 37, claim 2, for GO-70% read 6'0-75%; and that 'the said Letters Patent should be read with this correction therein 'that the same may conform to the record of the case Ain the Patent Office.

Signed andAsealed this 2nd. day of September, A. D. 1947.

[SEAL] LESLIE FRAZER,

First Assistant Uommzssz'onar of Patente.

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