US2273890A - Cellulosic article - Google Patents

Description

Patented Feb. 24, 1942 UNETE ST res a Tarmac tr er.

CELLULO SIC ARTICLE aware N Drawing. Application April 20, 1M0, Serial No. 330,729

5 Claims.

This invention relates to cellulosic articles, especially softened regenerated cellulose film. More particularly it appertains to the prevention of color in softened regenerated structures.

The manufacture of regenerated cellulose film in a continuous manner from viscose is disclosed in U. S. A. Patent No. 1,548,864 (Brandenberger) This procedure (which is particularly well suited to a commercial scale operation) in general involves continuous extrusion of a sheet of cellulose 'xanthate solution (viscose) through a narrow cellulose. After leaving the converting bath, the

web is subjected to a series of treatments such as washing, desulfuring, washing, bleaching (or dyeing, depending upon the use which is to be made of the product), and washing, preferably inzthe order named. These last mentioned treatments (like the coagulating and converting treatments) are conveniently carried out by passing the continuous web through vats containingthe corresponding treatingliquid.

It is customary to provide for softening the cellulose web by passing it through a solution of softener after it leaves the last washing bath and before it is dried. Usually the cellulosic sheet material is dried by passing it over heated rolls. This eliminates most of the water, but not the softener therefrom.

The softener is incorporated in the regenerated cellulose product in order to obtain flexibility, increased durability and other desirable properties. Numerous materials suitable for this purpose are .lmown to the art. The one most commonly used is glycerol, but extensive use has been made of other hygroscopic polyhydroxy compounds, for example, diethylene glycol, sorbitol, etc., and in some cases non-hygroscopic materials exerting a strong flexibilizing influence upon the regenerated cellulose, have been employed. Specific materials of this character are monoethanol amine addition products such as monoethanolamine formate, monoethanolamin hydrochloride and monoethanolamine sulfamate; diethanolamine addition products, triethanolamine addition products, ethanol formamide, urea and the like.

Nearly all of the softening agents commonly used for regenerated cellulose and related films are conducive to discoloration of the softened material after a period of a few weeks or a few months. Films softened with nitrogen containing substances, for example, the formic acid, hydrochloric acid, sulfamic acid addition products of the mono-, di-, and tri-ethanolamines,'are particularly prone to discoloration.

This invention had for an object the prevention or elimination of discoloration in softened regenerated cellulose. Other objects were to produce softened cellulosic materials free from discoloration, and to produce non-fibrous, transparent, regenerated cellulose film which would remain free from discoloration for long periods of time. A still further object was to repress or restrain discoloration of regenerated cellulose film in which has been incorporated nitrogen containing softeher'material, by also incorporating amino-imino-methane sulfoxylic acid and the like. A general advance in the art, and other objects which will appear hereinafter, are also contemplated.

It has now been found that color in regenerated cellulose products (or discoloration) may be avoided (prevented, inhibited, restrained, curbed, repressed, eliminated) by incorporating in the film containing a softener-which causes discoloration of the film with age, material such as amino-imino-methane-sulfoxylic acid of aminoimino-methane-sulfoxylic acid esters and salts. The invention will be further understood from a consideration of-the following examples, in which the parts are given by weight.

Example I A viscose film was extruded into a coagulating and/or regenerating bath, and then passed through the various processing baths described in U. S. A. Patent No. 1,548,864 (Brandenberger).

.At the end of this treatment, the film was clear .upon rolls. The film so prepared was found to be completely free of color and not to develop any appreciable color, even after aging for a period of more than 22 days.

A film prepared similarly, but omitting the sodium salt, was found to exhibit a faint tinge of yellow upon drying, and to be decidedly yellow,

almost approaching a brown color at the end of one day.

Example II Regenerated cellulose film, prepared similarly to that of Example I in the gel state and just prior to drying, was passed through an aqueous bath comprising 7.5% of ethanolamine sulfamate and 0.3% of amino-imino-methane sulfoxylic acid and the superficial water removed. This film, after drying, wasfound to be completely free from color andto remain so for a period of more than 63 days.

Example IV The film like that of Example I was passed through an aqueous bath containing of ethanolamine hydrochloride and 0.6% of the magnesium salt of amino-imino-methane sulfoxylic acid. This produced a film, after removal of excess water, containing 6% water, approximately 20% of ethanolamine hydrochloride and approximately 1.2% of the magnesium salt. This film was free from color and remained so for a period of more than days.

Example V A film similar to that of Example I was passed through an aqueous bath comprising 10% of ethanolamine hydrochloride and 0.6% calcium amino-imino-methane sulfoxylic acid. After drying, the film containing approximately ethanolamine hydrochloride and approximately 1.2% of the calcium salt was completely colorless and remained substantially colorless for a .period of more than 15 days.

Example VI A film prepared according to Example I was passed through an aqueous bath containing 5% glycerol, 0.4% of amino-imino-methane sulfoxylic acid, and after drying was found to contain approximately 10% of glycerol and 0.8% of the acid. This film was completely colorless, and remained substantially colorless for a period of more than days'at around 104 F.

A similar film softened with the same quantity of glycerol, but containing no color inhibitor,

while colorless upon drying, was tinged with yellow in 10 to 20 days when exposed to the same temperature.

Example VII A fihn prepared according to Example I was passed through an aqueous bath of 5% glycerol and 0.1% of amino-imino-methane sulfoxylic acid. After drying, this film was found to be substantially colorless, and remained so for a period of 9 days at F.

A similar film softened with the same quantity of glycerol, but containing no inhibitor, exhibited a slight yellowish tinge after two days when exposed to the same temperature.

The invention contemplates as a base any cellulosic structure, particularly those of pellicular nature such as sheet, artificial straw, caps, bands and continuous tubes, such as may be obtained by the coagulation and/or regeneration from an aqueous cellulosic dispersion or aqueous alkaline cellulosic solution.

From a chemical standpoint, the invention contemplates regenerated cellulose (or cellulosic) pellicles such as may be obtained from the viscose process and the cuprammonium process. It also comprehends glycol cellulose, cellulose glycolic acid, alkyl cellulose and other cellulose substitution derivatives, particularly those coagulable from aqueous alkali dispersions thereof. The lowly esterified and etherified cellulose substitution derivatives and other cellulosic structures of similar character may also be improved by the present invention. The expression lowly (or low) substituted (esterified and etherified) cellulose derivatives in ordinary usage covers the more common cellulosic products in which only one ether or ester group is associated with several glucose units of the cellulose molecule.

Various types of paper, especially the glassine type, may be used as the base material.

Sheets of albuminous material including gelatin, casein and the like, are also advantageously processed according to the present invention.

It will be clear, therefore, that the specific description has been made in connection with regenerated cellulose merely as a matter of con-'- venience, and it is to be understood that the scope of the invention is broad enough-to include many other bases with equal applicabi1ity.

Compounds containing the radioal x NH2C -o-s=o such as amino-imino-methane sulfoxylic acid I lfilll NIH-(l3 HOS=O its alkali metal, alkaline earth metal and other soluble salts and esters, constitute the preferred group of color stabilizers.

In general the color inhibiting agent should be present in the softened regenerated cellulose film to the extent of 0.1% to 1.0% (basedon the cellulose). Even more may be used, but usually there is no advantage for the greater amount.

In order to get the aforementioned concentra-' tion in the dried and softened film, it is generally necessary (or convenient) that the matee rial be soluble in an aqueous bath, such as that used for the application of the softener, to the extent of at least 0.03%.

It is desirable that the softening agent and the color inhibiting agent be applied simultaneously to the base. This is conveniently and efficiently done from an aqueous solution or dispersion containing both materials. Such a solution (or aqueou dispersion) may be applied to the gel product during the process of manufacture, for example, before the structure has been dehydrated. A dry article may be rewetted and treated with a solution or dispersion when such a procedure is desirable for some particular reason. The softener and color inhibitor may be applied by spraying as well as by passage of the base through a body of the liquid containing the same.

The greatest advantages in reducing coloration or extending the time after which coloration first appears, is most pronounced in connection with nitrogen containing softening agents, as previously indicated, but the inhibitors are effective and increase the utility of the product with all other softeners, including formamide, carbamide, glycerol, diethylene glycol, and the like.

The cellulosic structures, as prepared according toQthe present invention, have the advantage of improved appearance both when prepared and after aging for long periods of time. The lack of color -in wrapping material, for example, is highly desirable in order that the appearance of the article wrapped remain unchanged. As will be obvious, the development of color in the wrapper (with age) will lead a prospective customer to besuspicious concerning the age and condition of the contents of the. package. This is true even though the discoloration of the wrapper took placein a brief interval of time, which brief interval, for example, is insufficient to adversely affeet the condition of, the wrapped article. From a merchandising standpoint, this last feature is probably more important than the actual appearance of the wrapper. The art has heretofore been restricted in its use of. softening agents, being able to employ only those with which a minor degree of discoloration occurred over.moderate periodsof aging. Stated differently, it has been the practice to avoid a largenumber of materials exhibiting excellent softening characteristics, merely because the softened article would show discoloration in a short period of. time. The present invention therefore not only enables improved results to be obtained with the commonly employed softeners,.but also extends the field of practical softeners. Therefore, by the practice of the present invention manufacturers are enabled to employ softening agents which may exhibit desirable properties, such as a greatr degree of softening action (making possible the use of lower concentrations) flame-proofing action (and hence improved durability of the softened article), and a cost lower than that of the commonly used softening agents, etc. Softeners heretofore impractical are now available for sheet wrapping material, packaging, and the like, in'which discoloration or development of color is indicated as a great 7 disadvantage.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A softened regenerated cellulose article containing an amino-imino-methane sulfoxylic acid color stabilizing agent.

2. The product of claim 1 when the stabilizing agent contains the radical 3. The product of claim 1 when the stabilizing material belongs to the group consisting of the alkali metal salts of amino-imino-methane sulfoxylic acid.

4. The process of repressing color in softened softened regenerated cellulose pellicle which con tains a nitrogenous softening compound, which comprises incorporating in the web an amount,

of a reducing agent containing the radical 0-=o sumcient to retard the discoloration the desired amount.

FRANKLIN TRAVISS PETERS.