US2044804A - Wrapping material - Google Patents

Description

June 23, 1936- J. a. M NALLY ET AL 2,044,304

WRAPPING MATERIAL Filed June 17, 1932,

I I I, M I i p I g & 0 W I GumWzzcfi Cellulose Sieazale.

r I r I I I I 1 I 1 CelluldbeEslerBaseSIzeeh MmmEBemiM 11106 GM MZIy; gwuentozv,

Patented June 23, 1936 PATENT OFFICE WRAPPING MATERIAL James G. McNally and Norman F. Beach, Rochester, N. Y., assignors to Eastman Kodak Company", Rochester, N. Y., a corporation of New York Application June 17, 1932, Serial No. 617,808

8 Claims.

This invention relates to the manufacture of a thin, flexible, transparent, moisture-proof type of wrapping material, and more particularly to a cellulosic material having an overcoating on one or both sides which renders the sheeting sub-- stantially impermeable to moisture.

It is well known to coat paper,.cloth and various other types of fibrous and non-fibrous materials to render them resistant to the penetration of water and other liquids by applying a composition containing gums, waxes, oils and other ingredients. It has also been proposed to waterproof a sheet of regenerated cellulose by applying thereto a composition containing a cellulose derivative base and various ingredients of a waterproofing character. The present invention is not concerned broadly with waterproofing or moistureproofing, but relates primarily to the treatment of a particular type of base sheet by applying thereto a new and improved moistureproofing composition which, not only cuts down the amount of moisture transmitted by the untreated sheeting, but also renders it substantially impermeable to water and other liquids. The moistureproofing composition of the present invention is of an extremely simple character,

readily formulated and easily applied.

The principal object of our invention is to provide a means of rendering thin sheets of cellulose acetate and similar colloidized organic cellulose ester and/or mixed ester material, such as cellulose propionate, cellulose butyrate, cellulose stearate, cellulose acetate propionate, cellulose acetate butyrate and the like, and even sheets of regenerated cellulose material, waterproof and moistureproof. A further object is to provide a wrapping material which is not only waterproof and moisture-proof, but also highly transparent, flexible, odorless and non-tacky. A further object is to provide a water and moistureproof coating composition suitable for application to thin cellulose acetate sheeting or similar materials which is simple to compound and apply and is distinguishedtfrom other known materials by inclusion of a special component. Other objects will hereinafter appear.

The above objects are accomplished by formulating a moistureprooflng composition in the manner hereinafter described and applying it to a base sheet of cellulose acetate or the like in such manner that an extremely thin moistureprises a mixture of gum, wax, and another ingredient having special properties. We have found that if a mixed cellulose organic ester is employed in connection with gum and wax as the third component, the ability of a sheet material, such as cellulose acetate coated. therewith to transmit moisture will be reduced to a remarkable degree. After conducting many experiments with a large number of compositions of this general nature, we have found that compositions of gum, wax and celluloseacetate stearate are particularly effective and give rise to unexpected moisture-resisting qualities.

As examples of waxes which may be employed in our improved moistureproofing composition may be mentioned paraffin, ceresin, beeswax, pimela, lanolin, spermaceti, Montan,. bayberry, Japan, candelilla and Chinese wax, any of which may be used singly or in combination with one another, or with other waxes of this general na-' ture known to those skilled in the art.

The gums may be either natural or synthetic, typical examples of which are ester gum, damar, rosin, gum mastic, cumar resin, sandarac, certain of the vinyl resins, and other artificial gums or resins. As in the case of the waxes, these may also be used alone or in various combinations.

The mixed cellulose organic ester which we prefer to use with the gums and waxes above referred to is cellulose acetate stearate. While we are not limited to a cellulose acetate stearate of any particular stearyl content, we prefer to use a compound of relatively high stearyl content. We have found, for example, that a cellulose acetate stearate containing 10-40% stearyl is highly satisfactory, and a gum-wax composition containing this particular compound when deposited upon a thin, transparent sheet of cellulose acetate decreases its moisture transmitting propensities to a very marked extent. These mixed esters may be prepared in accordance with the disclosure of the Clark and Malm Patent 1,800,860. Broadly speaking, the higher the stearyl content of the particular mixed ester used, the greater the amount of wax which may be employed in the composition. As stated, 1040% stearyl is satisfactory and 20-30% is probably optimum.

The proportions of the various ingredients used in the moistureproofing composition in accordance with the present invention may vary within rather wide limits, but, as a general rule, we prefer to maintain the percentage of mixed cellulose organic ester, such as cellulose acetate stearate, at about 20% based on the total solids, the gum and wax components making up the balance of the solids in about equal proportions. The cellulose mixed ester content may run as high as 34% and even higher, as for instance approximately 50%, depending upon the characteristics desired in the finished material.

Our coating composition is particularly characterized in that we are able to incorporate in the composition a much higher percentage of wax than it has heretofore been possible to in' corporate in a moisture-proofing composition with any other celluiosezderivative'. For instance, it is wellknown that moisture-proof, regenerated cellulose sheeting now extensively upon the market, is coated with a moisture-proofing composition containing a cellulose derivative such as cellulose nitrate, together with 15% of wax, based upon the weight of the totals'olids, as the upper limit of the wax content for the coating composition. It is, therefore, most unusual to be able to incorporate in the coating composition, quantities of wax amounting to as much as 40 or 50% of the total weight of the solids contained in the composition or as much as 200% or more of wax based upon the weight of the cellulose derivative itself. Accordingly, our invention stands out as being the first coating composition to contain a cellulose derivative in substantial amounts and a proportion of wax equivalent to one-third or more of the total solids in the composition, or stated otherwise, equivalent to to 200% of the cellulose derivative contained in the composition, together with the desirable properties concomitant with high wax content.

The solid constituents above described are dissolved in a suitable solvent, typical examples of which are toluene, xylene, benzene, ligroin, solvent naphtha, ethylene dichloride, trichlorethylene, and carbon tetrachloride. The solvent is selected primarily upon the basis of its common solvent power for the gum, wax, and the cellulose acetate stearate. It should also be selected on the basis of its lack of solvent power for the material of the base sheet which is to be moistureproofed. As a general rule, the solvent should be of such a character that it will not exert an undesirable softening or weakening action on the base sheet material. This is especially true when applying the herein described coating compositions to thin, cellulose ester material of the order of .001" in thickness. With thicker materials, say of the order of .005 inthickness, the solvent may have a slight softening or swelling action on the base sheet which is not undesirable and in some cases may actually assist in anchoring the moistureproof coating to the sheeting.

As indicated above, the base consists of a thin, flexible, transparent sheet of cellulose ester or material having similar properties. For Wrapping purposes, a sheet having a thickness of .001" is preferred, although material of varying thicknesses may be employed according to the purpose to which the material is eventually to be put. Our invention is not limited to the moistureproofing of cellulose ester material, as the novel moistureproofing compositions herein described may be used for forming a moisture resistant coating over a variety of surfaces, such as those of paper, cloth, wood, and other fibrous or non-fibrous substances.

Our compositions may include, as an optional ingredient, a plasticizer for the mixed cellulose ester, such as triphenyl phosphate, dimethyl phthalate, and others, in' amounts'up to about 10% of the total weight of solids. Likewise, coloring materials, such as dyes, pigments, pearl essence, and the-like may be incorporated in the compositionsto'produce varying eflects."

In the following examples, we" have set forth several of the preferred moistureproofing compositions of our invention, but it is to be understood that they are included merely for purposes of illustration and not as a limitation 5 thereof.

Formula No. I

, Grams Cellulose acetat' eii"s tearat Paramn wax (melting poin Ester gum 40 Dissolved in a mixture of 500 cc. of toluene and 250 cc. of ethyl acetate.

Dissolved in a mixture of 500 cc. of toluene and 20 250 cc. of butyl acetate.

A typical moistureproofing process and product in accordance with the present invention is illustrated in the accompanying drawing in 25 which:

Fig. 1 is a diagrammatic representation of one form of apparatus for carrying out the invention in which the base sheet is coated on both sides simultaneously.

Fig. 2 is a cross section through a portion of the coated material illustrating the structure of the finished product, the thickness of the respective portions being greatly exaggerated in the interest of clearness of illustration.

Referring to the drawing in detail, the numeral l' designates a sheet of thin cellulose acetate of about .001 in thickness which is fed from supply roll 2 over guide roll 3 into immersion vat 4 containing liquid moistureproofing composition 5, such as that represented by Formula No. I above. The level of liquid in vat 4 is maintained at such a height that the composition flows into the V- shaped opening between the down-coming and up-going portions of the sheeting and is thereby simultaneously applied to both sides of the sheet. During its passage through the vat 4, the sheet I passes under guide roll 6, up between adjustably mounted scraper bars 1 and 8 which serve to remove excess coating fluid from its surfaces, thence through drying chamber 9 where it is subjected to a drying current of air maintained at a temperature ranging from 50-100 C. As the sheet I emerges from the drying chamber 9 it passes over drum [0 and thence to wind-up roll II.

Fig. 2 illustrates the structure of the finished product. The base sheet A comprises a thin sheet of cellulose ester material, having extremely thin coatings B on both surfaces. These coatings comprise a mixture of gum, wax, and cellulose acetate stearate which substantially prevents the penetration of moisture into or through the sheeting. Optionally, the coating material may be applied to one side of the sheet only by means of a subbing roll or equivalent-means well known to those skilled in the art.

It. is found that the material produced accordingto the present invention resists to a remarkable degree thetransmission of moisture. For 70 example, an untreated sheet of cellulose acetate may under certain conditions transmit as much -as- 1.2 milligrams of moisture per square centimeter per hour. The; improved product ,orthe present invention, underwhe, same conditions, 75

per square centiimportant.

Our invention is not confined to the production of moisture-proof sheeting, since the compositions typified by the formulae given above may be used for a variety of water-proofing or moisture-proofing operations. So far as we are aware, we are the first to have suggested the use of a composition in which an extremely high degree of moistureproofing is obtained by the use of the cellulose mixed. organic esters in connection with gum, wax and other moistureproofing materials.

As is well known, a considerable amount of waste occurs in the ordinary operations of manufacturing coated sheeting and in its use as map ping and packaging material. This would represent a serious economic loss were it not for recovery processes in which the various ingredients of the sheeting can be reclaimed. The material of the present invention is characterized by the fact that it lends itself particularly well to such recovery processes. A simple and convenient method of reclaiming scrap derived from moistureproof sheeting of the type herein described comprises leaching the scrap with an organic solvent which may consist, for example, of toluene or benzene, which removes the moistureproofing coating therefrom. The solvent is then drained off, the material dried, in which condition it may be reused in the production of further sheeting, film or the like.

What we claim is:

1. An article of manufacture comprising a thin,

containing approximately 33% gum, 33% wax, and 34% cellulose acetate stearate.

2. A moistureproofing composition for cellulose acetate sheets or films containing approximately 33% gum, 33% wax, and 34% cellulose acetate stearate dissolved in a solvent comprising about A; by volume ethyl acetate and by volume toluene.

3. A moistureproofing composition for cellulose acetate sheets or films containing cellulose acetate stearate and to 200% wax based upon the weight of cellulose acetate stearate.

4. A moistureproofing composition for cellulose acetate sheets or films containing approximately 20-34% cellulose acetate stearate, 33-40% wax and the remainder gum.

5. A moistureproofing composition for cellulose organic ester sheeting comprising a mixture containing at least 20% wax, at least an equal amount of cellulose acetate stearate, and the remainder gum.

6. An article of manufacture comprising a thin, flexible, transparent sheet of cellulose organic ester material adapted for wrapping purposes coated with a moisture-resistant composition comprising a mixture containing at least 20% wax, at least. an equal amount of cellulose acetate stearate, and the remainder gum.

7. An article of manufacture comprising a thin, flexible, transparent sheet of cellulose acetate adapted for wrapping purposes coated with a moistureresistant composition comprising cel-'

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