US2146619A - Coating flexible sheets - Google Patents

Description

- Patented Feb, 7, 1939 I COATING FLEXIBLE SHEETS Walter Durgin Bowlby, Jersey City, N. J., assignor to Egyptian Lacquer Manufacturing Company, a. corporation of New Jersey No Drawing. Application November 5, 1935,

Serial No. 48,285

3 Claims. or 91-68) This invention relates to, coating flexible fibrous sheets and is particularly concerned with the production of coating compositions for paper and the like. More specifically, the invention con- 5 templates improvements in lacquers and in lacquered papers.

It has been recognized heretofore that the viscosity characteristic of nitrocellulose decreased with the degree of degeneration of the nitrocellulose, and that if the nitrocellulose were sufficiently degenerated more of it could be dissolved in a given amount of solvent without making the resulting solution too viscous for use. However, as the degree of degeneration of nitrocellulose increases, the material suffers a physical change:

and it has been the general view, heretofore accepted, that nitrocellulose having an exceedingly low viscosity characteristic was an undesirable lacquer ingredient, unless it was used together with other and less degenerated nitrocellulose having a higher viscosity characteristic.

It has also been customary to employ nitrocellulose having a relatively high nitrogen content, say from 11.5% up, in the manufacture of lacquers, and standard works onthe subject state that lacquers must be made with nitrocellulose having a nitrogen content from 11.5 to 12%.

As a result of my investigations I have discovered that lacquers in which the nitrocellulose content has an exceedingly low average viscosity characteristic, i. e. below 50 centipoises, is an admirable coating composition for paper and other flexible fibrous sheets. Such lacquers pos-' sess great adhesiveness and form desirable coat-- ings on paper. Coatings on paper-etc. resulting from the practice of my invention are durable, lustrous, flexible and hard. Moreover, the practice of my invention permits the production of lacquered papers which manifest substantially no tendency to curl,- shrink or wrinkle. This tendency to curl is an undesirable characteristic of lacquered paper made in accordance with prior proposals.

Throughout the application and appended claims I use the term paper to include cardboard, wrapping, sheets, and other flexible fibrous sheet material.

I- have also discovered that nitrocellulose hav- 50 ing a nitrogen content of from 10 to 11% is partlcularly desirable in themanufacture of lacquer intended for coating paper food wrappers or containers, in that nitrocellulose of this character is completelysoluble in alcohols, such as ethyl,

55 methyland butyl alcohols, and when so dissolved will forrriT a substantially odorless and non-toxic film on paper. Nitrocellulose having a nitrogen content substantially belo'w'10% 01: substantially -'above'11% isnotcolnpletdysolubleinthecom- ;monalcchob,andhenc'eslmnlrlnotbeusedin conjunction with alcohol as a single active solvent.

By viscosity characteristic of nitrocellulose, I mean thedegree of viscosity which a given sample of nitrocellulose will impart to a given amount 5 of a standard solvent, as expressed in centipoises. Throughout the specification and the appended claims, the figures for viscosity characteristic are as determined-by the following method:

A solution containing 12% by weight of nitro- 10' cellulose in a solvent consisting of three parts butyl acetate and one part ethyl alcohol is prepared, and the viscosity of the solution in centipoises isdetermined, preferably in a viscosimeter of the capillary tube type, or by other standard 15 methods. The resulting determination in centipoises is taken as the viscosity characteristic of the nitrocellulose in the solution.

In ,accordance with the principles set forth above, my invention contemplates an improved 20 coating composition for paper and the like, comprising nitrocellulose having a viscosity characteristic of from 1 to 50 centipoises, and a solvent therefor. My invention provides a novel curl-resistant sheet comprising paper or other 25 flexible fibrous material having a coating, the nitrocellulose content of which has an average viscosity characteristic ranging from 1 to 50 centipoises. My invention further provides substantially odorless and non-toxic coatings on paper 30 and the like, said coatings containing nitrocellulose having an average nitrogen content ranging from 10 to 11%. When paper wrappings or the like for food products are to be manufactured I prefer to combine the advantages of low vis- 35 cosity characteristic and relatively low nitrogen content of nitrocellulose.

The degree of flexibility and the velvet feel of dried lacquer films made in accordance with my invention may be increased, if desired, by 40 incorporating softening agents into the fluid lac quer. Any of the customary softening agents may be employed, but I have found that raw castor oil, dibutyl phthalate, triethyl citrate, butyl phthalyl butyl glycollate, and mixtures of these compounds are particularly desirable.

The resistance to friction of dried films of lacquer made in accordance with my invention may be decreased by incorporating petroleum jelly, fats or-waxes into the fluid lacquer. When the lacquer is intended for coating wrappers adapted to machine packaging, a low resistance to friction or high slip is desirable, and I have found that a small amount of petroleum jelly,

say 5% or less by weight of the fluid lacquer, is J desirable for imparting this characteristic.

If required, crystallizing agents, (his, solid pigments, bronze powders, or other agents for producing special appearances may be incorporated into the lacquer of my invention. co

My invention will be better understood in the light of the following formulae for lacquers made in accordance therewith.

Formula 1 Parts by weight Nitrocotton (viscosity characteristic 1-50 \centipoises) 25 Raw castor oil 15 Dibutyl phthalate Ethyl alcohol Total 10o Formula 2 Parts by weight Parts byweight Nitrocotton (viscosity characteristic 1-50 centipoises) 45 Butyl phthalyl butyl glycollateu 20 Alcohol 15 Methyl ethyl ketone l0 Petroleum spirits 10 Total The preparation of the lacquers of my invention (as illustrated in the foregoing formulae) requires no special procedure or apparatus andv may be conducted in any of the customary ways. As shown by the foregoing examples, the solid content of lacquers prepared in accordance with my invention may be unusually high, thus permitting a great economy in the use of solvents, and enabling lacquers to replace spirit varnishes and similar materials in the coating of paper and the like. As compared with varnishes, lacquers prepared in accordance with my invention offer the following advantages in coating paper: (1) Freedomfrom residual odor,

(2) Greater adhesion to the paper, (3) Increased resistance to marring, scufflng and cracking, Greater fluidity and ease of application, Increased speed of drying, Thicker coatings, if desired, Less discoloration of the paper, Higher-gloss, and Better feel.

(4) (5) (6) ('7) (8) (9) 1 Lacquers prepared in accordance with the foregoing formulae do not cause paper to shrink, wrinkle or curl when they are applied thereto. A lacquer which is particularly desirable for coating paper intended for wrappers or containers of food has-the following formulae:

Formula 4 Parts by weight Nitrocotton (nitrogen content 10.5%, viscosi-- This lacquer dries quickly into a lustrous uniform film having great adhesiveness and resistance to scumng. It has a high slip and may be used to coat papers intended for use in automatic packaging machines. when dry it is practically odorless and non-toxic. It does not cause the paper to which it is-applied to shrink, curl, or wrinkle. I

When residual odor or slight toxicity are unobjectionable in the product, many other solvents may be employed. Thus, acetone or amyl acetate may be employed as active solvents, and toluol, butyl aldehyde etc. may be used as diluents.

The lacquers of my invention may be applied to paper in the same manner that varnish etc. are customarily applied. Reverse roll machines, knife coaters and various kinds of rolls may be used.

My lacquers may be used to coat printed papers, transparent papers, colored papers, etc. when used in thick films on printed paper a coating is formed which is comparable in appearance and utility with a regenerated cellulose wrapping. Moreover, the cost of such films is less than half the cost of equivalent cellulose wrapping sheets,

and there is a further saving in that the separate wrapping operation with the transparent sheet is eliminated.

In general, I have foundthat the gloss of lacquer films on paper increases as the average viscosity characteristic of the nitrocellulose in the lacquer decreases. There is no decrease in the apparent strength, flexibility, or adhesiveness of the film as the viscosity characteristic of its nitrocellulose content is decreased below 50 centipoises, and films in which the total nitrocellulose content has a viscosity characteristic of only one centipoise are useful. I attribute the apparent strength, toughness, flexibility and durability of these lacquer films on paper to the remarkable adhesion between the fibrous paper backing and the lacquer film, whereby the film and the paper are enabled to cooperate and the tensile strength of the paper is imparted to the whole mass.

Nitrocellulose which has been degenerated in any of the customary methods'may be employed in the practice of my invention, provided that its viscosity characteristic is sufficiently low. Thus, nitrocotton degenerated by heat and pressure or by alkaline or acid reagents may be used, provided such nitrocellulose has a viscosity characteristic ranging from 1 to 50 centipoises, a range which was heretofore considered substantially useless.

It will be understood that the practice of my invention is not limited to the use of the specific solvents, diluents. softening agents, and crystallizing agents, nor to particular proportions of the various ingredients set forth in the formulae.

I claim:

1. A flexible composite sheet comprising a flexible paper base and a covering film containing essentially nitro-celluiose of such degree of degeneration that in solution the average viscosity characteristic of all of the nitro-cellulose ranges from 1 to 50 centipoises and is inherently brittle in film form, said film adhering to the paper base with a tenacity suillclent to overcome its inherent tendency to crack andscparate from the paper when the latter is flexed.

2. A composite flexible sheet comprising a flexible paper base and a covering film containing essentially alcohol-soluble nitro-cellulose contaming not substantially less than 10% o stantially more than 11% nitrogen and of such degree of degeneration that in solution the average viscosity. characterlsticof all of the nitrocellulose ranges'from 1 to 50 centipoises'and is inherently brittle in film form, said film adhering to the paper base 'with a tenacity suflicient to overcome its inherent tendency to crack and separate from the paper when the latter is flexed.

3. A flexible composite sheet comprising a paper base and a covering film containing the nonvolatile constituents from a coating composition which is substantially free from resin, comprising to 45% of nitro-cellulose containing not substantially less than 10% nor substantially more than 11% nitrogen and or such degree of degeneration that in solution it has an average viscosity characteristic of from 1 to 50 centipoises is'inherently brittle in mm form, from 20% to 01 a softener, and from to of.

WALTZR DURGIN BOWLBY. 10v