US1737187A - Moistureproof material - Google Patents

Description

Patented Nov. 26, 1929 UNITED STATES;

PArENr o ric E WILLIAM HALE CHARGE AND KARL EDWIN PRINDLE, OF BUFFALO, NEW YORK, ASSIG-NORS, BY MESNE ASSIGNMENTS, 'IO DU PONT CELLOZPHANE COMPANY, INC., OF NEW YORK, N. Y., A CORPORATION OF DELAWARE MOISTUREPROOF MATERIAL 11' 0 Drawing.

It is the object of our invention to provide a materialwhich may be made either in the form of thin sheets or films and which shall be not only waterproof in the ordinary sense but moistureproof.

It is a further object of our invention to provide a material having the above characteristics and which shall also be very thin, transparent, flexible, colorless, odorless and non-tacky. Waxed paper is waterproof in the ordinary sense of the word and also moisturcproof in Varying degrees, but is not transparent and, moreover, is quite thick and stiif, cracking when it becomes crumpled. The products of our invention is some five to ten times thinner than waxed paper and is at least as moistureproof, and because of these qualities and the other qualities noted above, the

uses which may be made thereof are much reater than those for which ordinary waxed paper can be used.

In carrying out our invention we employ a composition comprising a base, a gum or a resin, a wax or wax-like material, and a plasticizer. These materials maybe mixed in different proportions, depending upon the qualities required of the finished composition.

For the base We prefer to use a cellulosic derivative, such as a cellulose ester or ether, and more particularly a nitrocellulose of the pyroxylin type, because of its economy, although cellulose acetate, or ethyl or methyl cellulose may be employed with satisfactory results. The base is preferably one yielding a solution of low viscosity, because this quality permits working with more highly concentrated solutions than could be used with a base yielding a solution of high viscosity.

For the gum we have found that gum dammar is very satisfa-ctory,'either singly or in combination with certain other gums. Some of the other gums that are preferably used either singly or in combination are ester'gum, rosin, gum mastic, or the copal resins. It is to be understood that the gums may be either natural or synthetic, as it is possible-to manufacture certain synthetic gums that are fairly satisfactory substitutes for the natural ones.

' For the wax we prefer to use a high melt- Applicat ion filed January 3, 1927. Serial No. 158,816.

to moisture than the low melting paraffin. The paraffin being colorless and odorless is preferable to other waxes from these standpomts and also from the standpoint of economy. Examples'of other waxes which may be used are ceresin wax, either hard or soft,

and beeswax. The above Waxes may be used either singly or mixed with each other or with other Waxes as may be found desirable.

For the plasticizer we preferably employ one of the compounds or mixtures of compounds having a high boiling point, and which are known as plasticizers or softenors for cellulose esters or others such as nitro cellulose, cellulose acetate, ethyl cellulose, etc. We prefer to use a plasticizer which shall be substantially odorless and have obtained satisfactory results from using tricresyl phosphate, tri-phenyl phosphate, di-

amyl phthalate or di-butyl phthalate, or

a Per cent Base 30 to 70 Gum... 30 to 60 Wax 2 to 6 Plasticizer 5 to 30 The exact proportions of the various ingredients will vary according to the qualities desired in the finished product, and these qualities'will depend upon the use to which the.

product is to be put. For example, if freedom from tackiness is not essential, then the pro portions and kinds of gum and wax may be varied toobtain a mixture which will be easier to make and yet Will have all the desired qualities except freedom from tackiness. By

50 ing paraflin wax as giving greater resistance varying the proportions of the ingredients it is possible to obtain acomposition with wide variations in the various qualities. By vary ing the quality of wax we can obtain a wide range in the degree of resistance to moisture; by varying the quantity of, or even omitting entirely, the plasticizer, all'degrees of flexibility may be obtained; and by regulating the 1 nature. and quantity of the gum, wax and plasticizer, a wide range in the degree of transparency may be obtained.

The amount of base, which is preferably a nitrocellulose of the pyroxylin type, is usually chosen with respect to the particular gum which is employed. The ratio by weight of gum to base may vary between the limits 2: I

and 1: 2. \Vhen the ratio exceeds 2: 1 cracking of the material results. \Ve have found that the best ratios are within the limits of 1:1and1:1%.

The quantity of gum used depends upon the gum which is chosen, particularly with respect to its complete solubility and its ability to blend with the wax. aud also the amount of base used with it. The preferred ratio of gum to base has been given above. A high ratio of gum to base renders the material brittle when used as a coating and prevents proper adhesion of the coating to the material to which it is applied. A too low per cent-age of gum will result in a poor blending with the wax and thus a decrease of transparency and an increase in greasiness or tackiness.

The wax preferably should be kept below 10% by weight of the total solids, and the best results are obtained when this percent: age is kept between 2% and 6%. When the percentage approaches or exceeds 10%, crystallization of the waxes begins, thus decreasing transparency. However, the moistureproof quality is not materially affected providing the same ratio of plasticizer to wax is retained and, therefore, a relatively large percentage of wax may be used when a relatively low degree of transparency is permissible.

The amount of plasticizer depends chiefly on the amount of wax and also upon the ratio by weight of the amount of gum to the amountof base. lVhen this ratio is relatively large, a greater quantity of plasticizer should be used to overcome the brittleness which is developed by the. relatively large amount of gum. Moreover, the degree of moistureproofness depends partly upon theratio of the wax to the plasticizer and, therefore, this ratio partly determines the percentage of plasticizer employed. The ratio of plasticizer to wax may vary between the limits of 1:1 and 4:1 with good results in the way of achieving a moistureproof material, but for most purposes we have found that the best ratio is between the limits of 2 :1 and 3:1.

lVc have discussed above the proper ratios of gum to base and of plasticizer to wax. It now remains to discuss the preferred ratio of the combined weights of base and gum to the combined weightsof wax and plasticizer. The combined weights of base and :gum are usually several times greater than. the combined weights of wax and plasticizer. The ratio of the weights ofb'ase and gum combined to the weights of wax and plasticizer combined may vary between the limits of about2.3:l and 10:1, but we find that the preferred ratio is between 4:1 and 8:1. If the ratio is less than 2.3:1 the. sheet or coating will either become tacky due to the high percentage of plasticizer or will become opaque and greasy due'to the high percentage of wax. \Vhen the ratio of weights of gum and base .to plasticizer and wax is greater than 10:1 the sheet or coating will usually have a tendency to crack due to the small amount of plasticizer and the relatively large amount of gum, or will possess an undesirably low degree of moisture resistance due to the low amount of wax employed.

It is seen from the above that, in determining the ingredients, the nature and quantity of any one must be chosen with respect to that of all the other ingredients if we are to obtain a product which will exhibit at once all of the desirable properties already enumerated. In this matter the choice is defined by the above approximate limits, but the following examples illustrate several excellent combinations which have been employed with success. We have classed as solids the ingredients of the composition which are dissolved in a solvent for the purpose of manufacturing the finished article. While the plasticizer may appear as a liquid, nevertheless, it is non-volatile and remains in the coating after it is dry, and therefore, for the purpose of this application and for convenience, all of the ingredients are referred to as solids.

Solid constituent luxample 1:

Per cent ha sed on total weight of solids Nitrocellulose 52 Ester gum 35 Di-butyl phthalate 8.7- Paraflin 4.3 Example 2:

Nitrocellulose 50 Gum dammar 34 Tri-cresyl phosphate 12 Paraffin 4 method of application and to the nature andv percentages of the solid ingredients. The solvent mixture must be such as to retain all of the solid ingredients in a homogeneous solution until all solvents are evaporated. The wax and base ordinarily do not mix to form a clear film but by a proper choice of equality and kind of gum it has been found possible to make the combined gum and wax mix with the base and plasticizer. The solvent mixture must then be chosen to retain the gum, wax,

- of the coating which would cause cooling of the surrounding atmosphere and precipitation of water vapor on the material. The

coating or sheet is then dried preferably with warm air not exceeding 90 or 100 C. It

. is preferable to keep the temperature of the air above the melting point of the wax or waxes used, thereby preventing separation or crystallization of the wax during the drying operation. It is also preferable to use air low in moisture content to aid in evaporation of the solvents. By this means it is possible to effect a very great saving in time of drying.

' After drying the product is preferably subjected to the action of heat and preferably steam for a short time in order to more thoroughly remove the last traces of solvents and thus make the product entirely odorless.

While the particular solvent must be determined separately for the particular composition, we give below the specific solvent combinations Whichwe have found may be used with the respective examples of compositions given above.

Per cent based on total volume of solvent Solvent for Example 1:

Alcohol 25 Ether 43 Toluene 18 Butyl acetate 14 Solvent for Example 2:

Ethyl acetate 62 Toluene 27 Alcohol 9 Butyl acetate 2 The solution may be used in a variety of ways. It may be cast by known methods into thin sheets which are transparent, flexible, have the required tensile strength and at the same time are several times'more moistureproof than anything hitherto known and that havethe other qualities mentioned above. These sheets may be made of any desirable thickness, a thickness of .0003" to .001 being suflicient when the sheets are to be applied to sheets or films of regenerated cellulose.

Again the solution may be applied in the form of a coating to sheets or films of cellulose regenerated from viscose, the coating beingdone by suitable machines. Sheets of regenerated cellulose have been employed as wrappin'gs for various substances which it is desired to protect from dust, handling by the buying public, fly specks, etc. Though they are thin, transparent and flexible they are poorly resistant to the passage of moisture. It has been found that sheets of regenerated cellulose coated on one or both sides with the compositions above-described, the coatings being .00005 to .0005 thick or thicker, when submitted to standard tests give values which clearly indicate that said sheets are at least from one hundred to two hundred times more moistureproof than the uncoated sheet and at least two or three times as lnoistureproof as waxed paper. Moreover, this result is achieved without sacrificing any of the very desirable qual ities of transparency and flexibility which are possessed by the sheets of regenerated cellulose. It is well-known that a waxed paper is stiff and relatively thick as well as opaque, whereas a sheet of material constructed according to our-invention or a sheet of regenerated cellulose coated with our composition isvery thin, flexible and transparent as well as highly moistureproof. In practice it has been found suflieient to apply about .00010 to each side of a sheet of regenerated cellulose which usually has a thickness of .0007" to .002". Coating on one side is sufficient but we prefer to coat both sides. The resulting sheet is still very thin and the necessary transparency and flexibility is retained.

The above is merely given as an illustration of one use to which our invention may be applied. If desired'to make a thicker .sheet of meterial, regenerated cellulose sheets may be built up to form a laminated sheet which may then be coated and which will I still maintain the desired characteristics, the

flexibility obviously decreasing as the thickness increases. Increased thickness of the coating will obviously increase the resistance to moisture and, therefore, the thickness employed will depend largely upon the use to which the finished article is to be put. For instance, regenerated cellulose sheets may be built up into a laminated structure foruse in automobile curtains and when so used the eoating applied for moistureproof purposes will naturally be thicker than that applied to a single sheet that is to be used for wrapping a cake or other articles of food.

A sheet of coated regenerated cellulose used for the purpose of wrapping an article therein will obviously not only keep the moisture in the package but will prevent the entrance of moisture, thereby preserving the contents, such as food, at the proper and desiredmoistness. At the same time if the package is subjected to moisture from without the contents are protected.

One common fault of many waterproof coatings utilizing wax is the fact that their surfaces are or become greasy. This fault is caused by the presence of wax in the coatinguncombined with the other ingredients. \Ve have succeeded in using wax and thereby making the product waterproof and moistureproof, but at the same time have avoided making it greasy? The product made according to our invention is one which has all of the desired propcrties of 1noistm'eproofness, flexibility, tensile strength, transparency, non-tackincss, color and lack of odor.

By the term moistureproof used herein, we mean the ability to resist the diffusion of water vapor to an extent at least as great as or exceeding that displayed by ordinary waxed papers employed as wrappers and functioning to resist the penetration of water vapor therethrough to a substantial degree for a substantial period of time depending on the article being wrapper and/or being approximately 7 times or more as effective as uncoated sheets or films of regenerated cellulose when tested under the same conditions.

We claim 1. An article of manufacture comprising a sheet or film of regenerated cellulose combined with a moistureproofing composrtlon. 2. An article of manufacture comprising a sheet or -film of regenerated cellulose combined with a moisture-proofing composition, said article being transparent, flexible, and non-tacky.

3. An article of manufacture comprising a sheet or film of regenerated cellulose combined with a moisture-proof, transparent, and non-tacky film.

4. A wrap-ping material comprising a sheet 7 or film of regenerated cellulose combined with a moistureproofing composition.

5. A wrapping material comprising a sheet or film of regenerated cellulose combined with a moistureproofing composition, said article being transparent, flexible and non-tacky. I

6. A wrapping material comprising a sheet or film of regenerated cellulose combined with a. moistureproof, trans-parent, flexible and non-tacky film.

7. An article of manufacture comprising a sheet or film of regenerated cellulose having a coating comprising a cellulose derivative, a wax and a gum, said article being moistureproof, transparent and non-tacky.

8. An article of manufacture comprising a sheet-0r film of regenerated cellulose having a coating comprising a cellulose derivative, a wax, a plasticizer and a gum, said article being moistureproof, transparent, flexible and non-tacky.

9. An article of manufacture comprising a sheet or film of regenerated cellulose having a coating comprising a cellulose derivative, a wax, a plasticizer and a gum, said article 'being moistureproof, transparent, flexible and non-tacky, the ratio of the gum to the cellulose derivative being between the limits of 2: 1 and 1:2 by weight.

10. An article of manufacture comprising a sheet or film of regenerated cellulose having a coating comprising a cellulose derivative, a wax, a plasticizer and a gum, said article being moistureproof, transparent, flexible and non-tacky, the ratio of plasticizer to wax being between the limits of 1 :1 and 4: 1 by weight.

11. An article of manufacture comprising a sheet or film of regenerated cellulose having a coating comprising a cellulose derivative, a wax, a plasticizer and a gum, said article being moistureproof, transparent, flexible and non-tacky, the ratio of thecombined weights of gum and cellulose derivative to the combined weights of wax and plasticizer being between the limits of 2.3 :.1 and 10: 1.

12. An article of manufacture comprising a sheet or film of regenerated cellulose" having. a coating comprising a cellulose derivative, a wax, a plasticizer and a gum, said article being moistureproof, transparent, flexible and non-tacky, the ratio of the gum to the cellulose derivative being between the limits of 2:1 and 1:2 by weight and the ratio of plasticizer to wax being between the limits of 1: 1 and 4: 1 by weight. g

13. An article of manufacture comprising a sheet or film of regenerated cellulose having a coating comprising 30%70% of a cellulose derivative, 30%60% of a gum, less than 10% of a wax and 5%30% of a plasticizer,

said article being moistureproof, transparent,

flexible and non-tacky.

14. An article of manufacture comprising a sheet or film of regenerated cellulose having a coating comprising nitrocellulose, gum dammar, tri-cresyl phosphate and parafiin,

said article being n'ioistureproof, transparent,

flexible and non-tacky. I

15. An article of manufacture comprising a sheet or film of regenerated cellulose having a coating comprising 50% nitrocellulose, 341% gum dammar, 12% tri-cresyl phosphate and 4% .paraflin, said article being moistureproof,-transparent, flexible and non-tacky.

16. A wrapping material comprising a sheet of regenerated cellulose combined with a moistureproof, transparent, flexible, and non-tacky film and being approximatel at least 7 times as eil'ective as the uncoated s eet of regenerated cellulose, said film having a thickness of approximately 1.6 ten-thousandth of an inch.

17. An article of manufacture comprising a sheet or film of regenerated cellulose having CERTIFICATE OF CORRECTION.

Patent No. 1,737,187.

Granted November 26, 1929, to

word "quality" read "quantity"; page 3, line (Seal) WILLIAM HALE CHARCH ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, line 3, for t the 7i, strike out the word "that;

same page, line )5, for the word "or" read "to", and line 118, for the nuisspelled word "meterial" read "material"; page 4, line 36, for the word wrapper" read "wrapped"; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the casein the Patent Office. v

Signed and sealed this 31st day of December, A. D. 1929.

M. J. Moore, Acting Commissioner of Patents.