US2170827A - Cellulosic pellicles and methods for producing same - Google Patents

Description

Patented Aug. .29, 1-939 um'rso STATES PATENT OFFICE 'OEliLULOSIC PELLICLES AND METHODS FOR PRODUCING SAME William Frederick Underwood, Buffalo, N. Y., and

Henry S. Rotliroc Wilmington, Del., assirnors,

by meme assignments,- moors a Company, Wilmington,

notation of Delaware No Drawing. I

zzcnims.

tions.

Cellulosic pellicles which are obtained by coagulation or precipitation from aqueous or alkaline aqueous dispersions of cellulose or cellulose derivatives, as for example pellicles of regenerated cellulose, glycol cellulose, cellulose glycolic acid,

lowly etherlfled or esterifled cellulose such as lowly etherified methy and ethyl cellulose and lowly esterlfled cellulose acetate, are particularly useful as wrapping materials. It is essential, however, that these pellicles be flexible and further that this flexibility be maintained. Cellulosic pellicles of this character seem to depend on the presence of moisture to impart flexibility and the softeners which have been used heretofore have been selected because of their hyg oscopic nature. It has been considered necessary to have the softener assist, by virtue of its hygroscopicity, in the retention of a suitable amount of moisture although the softener has possessed, also, a certain degree of lubricating or plasticizing action so that the pellicle does not become too brittle when practically all of the moisture has been removed. In the absence of a softener other than water, these pellicles become so brittle when dried as to be substantially useless as wrapping tissues. In the presence of the hygroscopic softeners of. the prior art, the loss of moisture is retarded and generally speaking, the flexibility is maintained by the.

moisture present.

Regenerated cellulose pellicles (for convenience the invention will be described in terms of this species), are quite sensitive to changes in moisture content, not only as regards flexibility, but also as regards dimensions. Increase in moisture content causes-a swelling of the cellulosic structure, while decrease in moisture content causes a shrinking apparently due in part to collapse of the cellulose micelles and in part to the loss of water molecules from between the micelles.

Regenerated cellulose wrapping tissues are subject, therefore, to two major defects which develop simultaneously and which are primarily dependent on the softener, namely embrittlement and deformation. Previous attempts to control or prevent embrittlement, however, have not been successful in controlling the deformation for, as mentioned above. the softeners selected have been highly hygroscopic and have reallyresulted in greater sensitivity to moisture conditions, thereby increasing the expansion and contraction of to E. I. du Pont de Ne- DeL. a cor- Application January 4, 1936, Serial No. 57,634

wrapping tissues or similar pelllcular structures,

Thus it is that great care is required in wrapping boxes in regenerated cellulose pellicles to provide. for these conditions. For example, if a cereal box is wrapped in regenerated cellulose sheeting (prepared in accordance with the prior commercial methods and softened with glycerin which is the usual hygroscopic softener) and set aside for storage, it may be subjected to a variety of humidity conditions before it reaches its ultimate consumer. During this time, if the humidity is high, the regenerated cellulose may expand untilthe wrapper becomes loose around the box and in some cases even baggy and wrinkled. On the other hand, if the humidity is low, loss of moisture from the regenerated cellulose will cause the wrapper to contract and this may cause buckling of the box walls, or if the box is sufliciently rigid, the wrapper itself may burst. Thus, under such a variety of humidity conditions, packages wrapped in regenerated cellulose sheeting may have an unsightly and undesirable appearance as the result of the deformation of the regenerated cellulose. Obviously, this defeats the .very important purposes of regenerated cellulose wrappers which are intended to protect and beautify articles wrapped therein.

To overcome the troublesome deformation, wrapping machinery has been designed to allow for a certain slack or looseness in the wrap. This, obviously, will eliminate the effects of contraction, but cannot, help the expansion effects; indeed, it makes them worse. The use of moistureproofed regenerated cellulose pellicles does not eliminate the trouble because the application of a moistureprooflng coatingretards but does not prevent the deformation, which latter is, in'the ultimate, not appreciably affected. These practical means do nothing more than attempt to make the best of the situation and make use of regenerated cellulose sheeting as it is available. No attempt is made to change the inherent properties of the cellulosic material and so provide a. wrapping which will have improved properties and characteristics.

It has been found in the manufacture of regenerated cellulose pellicles that the degree of deformation is, at least in part, due to the orientation of the cellulosio micelles. Thus, if a sheet of regenerated cellulose is made in such a way as to provide substantially uniform tension in all directions, the degree of deformation will be substantially the same in all directions. Practically, however, regenerated cellulose pellicles are made in a continuous process wherein the pellicle, after This results in an-appreciableJdifferenjce in the degree of deformation if measured in the machine direction, as compared to the degree of deformation if measured at right angles to the machine direction, 1. e., the transverse'direction.

However, in any given process the conditions are such that the degrees of deformation in the machine and transverse directions usually bear a sufficiently constant relationship so that for test purposesit is usually suflicient to determine the degree of deformation in one direction only, usually the machine direction.

For the purposes of this specification the degree of deformation, which may be called simply f deformation, is the per cent change in length of a cellulosic pellicle as measured in the machine di-' rection in accordance with the followingQproce dure: Strips of material areallowed to come to.

equilibrium withan atmosphere of substantially 95% relative humidity at a temperature "of35 C.

and their length accurately measured. The strips are then allowed to reach equilibrium in an atmosphere of substantially 0% relative humidity at the same temperature and their length again accurately measured. The difference in length divided by the length as originally measured multiplied by 100 gives theper cent deformation over the given humidity range at 35 C. and flgures so obtained are conveniently called the deformation. Thus, a sample strip having an original length of 10 inches and a contraction in length of 0.42 inch would be said to have a deformation of 4.2.

It is the object of this invention to provide means for reducing the deformation of cellulosic pellicles. It is also'an object of the invention to effect simultaneous softening and reduction of deformation. It is a further object to provide a method whereby the aforementioned objects may be accomplished in an economically feasible manner and without entailing essential modification of apparatus customarily used in the manufacture of such pellicles.

More specifically, it is the object of the invention to provide means for the production of cellulosic pellicleswhich will show less deformation than the cellulosic pellicles presentlyv commercially available. I

Specifically, it is the object of the invention to produce a pellicle of regenerated cellulose suitable for use as a wrapping tissue which will show a degree of deformation of not in excess of 3.0 when tested in accordance with the method described above. This object also includes the production of a regenerated cellulose pellicle which is combined with a softening material and which shows a deformation not in excess of 3.0.

The above and other objects of the invention may be accomplished by impregnating into the cellulosic pellicle, preferably while the latter is in a wet or gel state, an appreciably water-soluble, highboiling (i. e., relatively non-volatile at ordinary temperatures and j pressures), limitedly hygroscopic material which is stable, essentially colorless and odorless, preferably non-toxic ,and which is preferably also a softening agent for the cellulosic material. The extent of the reduction in deformation which may be obtained depends a temperature of 25 .not necessarily liquids.

on the particular impregnant used and to a certain extent on the amount employed.

The term limitedly hygroscopic is intended to include substances which will absorb 1-80% of their weight of water when exposed alone in a thin layer to an atmosphere of substantially relative humidity at a temperature of '25 C. over a period of hours. The test for hygroscopicity is carried out as follows: A small sample of about 0.5-2.0 grams of thoroughly dried material is spread evenly over the bottom of a weighing bottle (conveniently about 2%" in diameter and 11 5" deep) and the weight of the sample acthen placed in a chamber in which an atmosphere of substantially 95% relative humidity and C. are maintained. The humidatmosphere may be maintained conveniently by means of a sulfuric acid solution (9 parts of water to 1 part sulfuric acid) contained within the chamber. The sample, after 120 hours exposure,- during which time the material is occasionally agitated as by gently tipping the container to cause the material to flow over the bottom of the weighing bottle, is r'eweighed accurately and the percentage increase in weight based on the original weight of the sample represents the hygroscopicity of the material. Thus, if 1 gram of a substance absorbs 0.25 gram of water under the conditions described, it will be said to have a hygroscopicity of 25.

,curately measured. The open weighing bottle is' The test for hygroscopicity as outlined above is satisfactory for determining whether. or not a given substance is suitable for the purposes of the invention. There may be other tests of equal utility for determining hygroscopicity which would give different numerical values. Obviously,

such methods should be calibrated against the method outlined if they are chosen for use. Based on the method described, those substances suitable for use in the practice of the invention will have a hygroscopicity of 1 to 80.

Generally speaking, the test of water-solubility is applied first to determine the suitability of substances for use in the practice of the invention. If the substance is at least 1% and not more than 40% soluble in water at 20 C. its utility is indicated. In the case where the solubility is more than 40%, the hygroscopicity should be determined and in the event that this value should be above 80, the substance will be useless for the purposes of the invention.

' The third physic'al criterion relates to volatility. The substances must be high-boiling, that is, substantially non-volatile at ordinary temperatures and pressures, and should be preferably though Obvously, if substances of appreciable volatility were to be used, they would eventually disappear from the cellulosic pellicles rendering them thereby brittle, fragile and unsuitable for use as wrapping tissues or other applications. It has been found that substances of appropriate water-solubility and hygroscopicity which have a boiling point of C. or higher, at a pressure of 12 mm. of mercury and preferably of C. or higher (at 12 mm.) will be suitable for use.

In the preferred form of the invention substances having limited hydroscopicityand appropriate boiling-point and which are at least 4% soluble in water at 20 C. will be used to impreg'nate the cellulosic pellicles to effect a reduction in deformation. Substances of this character may be introduced into the pellicles by increase the concentration by adding a watermeans of. a simple water solution. In" the case where it is desired to uses. substance which is less than 4% soluble, it may be convenient to miscible organic solvent such as methanol, ethanol, acetone or the like although in no case should more than 25% by volume-of such solvent in the water-solvent mixture be necessary. Substances which require more organic solvent are unsuited for.- the purposes of the invention. In.- asmuch as the use of a portion of organic solvent entails additional expense, it is desirable to use those substances which are at least'4% soluble although the less soluble substances will find many useful applications.

Although the principal objective of the invention relates to the reduction of deformation, it is a part of the invention to provide also a -fiexible .pellicle. This can be done frequently by proper choice of the impregnating agent so that it will be at one and the same time a softener and a deformation reducing agent. For simplicity, such an agent may be termed a nondeforming softener. Obviously, other properties may be combined with these in certain agents, which will have particular advantage.

Generally speaking, compounds of the following types will serve as non-deforming softeners for cellulosic pellicles such as regenerated cellulose: organic compounds containing (a) both ether and ester, groups (called for convenience ether-esters"), (b) both keto and ester drcxyl group for each ester group (conveniently a called "hydroxy-esters"), and (d) compounds of carbamic acid esterified with an alcohol containing an ether group. As a general rule, compounds of these types wherein the hydrocarbon 5 portions are straight chain will be more effective softening agents than those wherein the-hydrocarbon portion is branched chain or cyclic.

Among the substances which may serve as non-deforming agents where softening action is 10 not important, the following types may be men- 1 As illustrative of specificmaterials which are 'useful in the practice of theinvention, a number of compounds are listed in the following table, together with data as to water-solubility and deformation, the latter figures being obtained 30 when regenerated cellulose pellicles were impregnated as will be described in more detail below.

Table I Approximate water solubility at 20 C.

Deformatlon A. Ether-esters:

. 1. Ether-alcohol derivatives (alcohol radical contains an ether group):

a) Bis-ethoxyethyl b Bisyethyl ii (I) Bis-ethoxyethyl m (c) Bis-ct oxyethyl diglyco nis-butox em idl l eouml' (e Glycerol trl-[metho xyacetate]. (D Diethylene glycol dl-[alphe-methoxy B. Ketoaters' (a) Propylene gl col di-[levullnate].-

Diethylene g ycol di-[lcvulinate]; (c) Butoxy-ethoxyethyl levulinate--- Ethylene glycol di-[levulinate] Trimeth lone glycol di-[lcvuhnate].

C. Hydroxy esters:

' (a) Bisethoxyethylmelate.--

ene glycol di- Glycero trl-[levulinate (as Propionate of bis-methoxyethyl malato Acetate oi bis-methoxyethyl mailma (e) Acetate of bis-ethofi'etgyl malate.

conteinsan th gm (b) Butoxy-ethoxyethy Bis-propoxyethyl malate" (c (d) Ethoxyethyl tertmm lb t l (I) Methcxyethyl Bis'beta-hydroxycthyl beta-hydroxyet'hyl phthalate hthala V D. Cami. eel esters:

(c) Butoxy-ethoxyethyl carbamate ..-l

-ethcxyethyl carbemate.

Iso-buto (b ((3; Butoxyet yl cm a. amides:

- F. Other Agen Ethoxy-ethoxyethyl carbamate (a) N-bcta-hydroxyethy] p-toluene 110mm 187 (b) gipiperldyl dlmethyl urea o (a Monoethyl other olhexamethylene glycol. (b 2-Hydroxy-cyclohcxylether oi dietbylene glycol (c 2-Hydroxy-cyolohexyl other of glycol-01.;

Very 61685;

Mlsclble. Miscible. Mlscible w re w s m s s wrs p s s m s s m 00 cm: u oomawarocaw saom-waq-aua NHHWQH- QOINI- WN -.1

groups with or without ether groups (conveniently called keto-esters), (0) both hydroxyl and ester groups with or without ether groups. but which do not contain more than one ,hy--,

The compounds listed in Table I are representative and it is to be noted that simple organic chemical compounds are elfective for the purposes of the invention. All of the substances 75 manufacture of present-day commercial regenerated cellulose sheeting. 'lhus,- a sheet of gel regenerated cellulose which has been purified and washedis impregnated with an aqueous glycerol solution, the excess of such solution removed by suitable means and the sheet dried. The commercial operation is continuous and the time of immersion in the glycerol bath varies with the speed of the machine although about 20 seconds immersion is probably normal. The concentration of the glycerol in the bath is adjusted to leave a predetermined amount of glycerol in the sheet after the drying operation, which latter removes all but about 68% water, based on the weight of the cellulose; Generally, the amount of glycerol in the final product is of the order of 15% and it has been found that a bath containing about 4-6% glycerol will give the desired results.

Accordingly, in the practice of the present invention the gel pellicle is impregnated with a bath which may contain conveniently about Mitt; of the non-deforming agent. After removal of excess bath, as by squeeze rolls and the removal of excess water by drying, the final product will contain a suitable amount of nondeiorming agent. Obviously, the amount of aaent in the final product will be adjusted to unit desired properties expected in the sheet so that the bath concentration may be more or less than 4% as occasion demands. Kt found however that the effectiveness of most non-deforming agents appears to approach a limiting value so that excessive amounts do not produce sumcient improvement to justify their use. Usually a bath concentration of about l% will be found satisfactory for a realization of good non-deforming properties and at the same time economy oi operation. Where the is to be used at low temperatures and low hnmidities, 21.6% solution may be found adyantaseous.

a specific example, a gel sheet of regenerated cellulose may be impregnated with a 4% aqueous solution of bis-ethoxyethyl malate. The resultant sheet, after dryinil, shows'a deformato'nof about 2.3, whereas a similar sheet impregnoted with glycerol showsa deformation of 4.9M. Both sheets contains approximately.

'es iecially'suitable for use there are a number of hydroxy esters. These may be obtained by the estleriflcation of hydroxy acids such as malic, l ic, glycollic, tartaric, alpha-hydroxy butyric,

haric, gluconic, or the like with alcohols or ether-alcohols which may be monoor polyhydric. If polyhydric alcohols are esterifled with polybasic acids, the proportions of reactants and the method of esteriflcation are chosen so that resinous products are not ob tained. Hydroxy esters may be obtained also by the partial csteriflcation or polyhydric alcohols with carboxylic acids of all kinds, such as acetic, propionic, succinic, adipic, phthalic or the like in which case the alcohol portion of the ester furnishes the hydroxyl group. Similarly, a polybasic acid may be esterifled partially by means of a monohydric alcohol and partially by means of a polyhydric alcohol so as to have at least one tree hydroxyl group in the final molecule. Only those hydroxy'esters, however, which satisfy the required criteria of non-volatility, solubility, and hygroscopicity are useful for the invention.

Amides or substituted amides of organic carboxylic or sulfonic acids may be used. This includes amides of all types of organic carboxylic acids which may contain, attached either ,to carbon or nitrogen, any type of an organic group and which preferably contain ether groups in their molecules.

In the above table a large number of compounds has been indicated, each of which is capable of use in the production of a regenerated cellulose pellicle which will show a deformation of not more than 3.0. It is to be understood that the compounds mentioned are illustrative. The list given is by no means exhaustive and this disclosure is intended to embrace all organic compounds or mixtures which have properties as previously set forth. These compounds may be used alone or in combination with each other.

The hygroscopici-ty oi the compound chosen for use will determine, in large measure, the amount of reduction in deformation which will be observed. Thus, compounds having a hygroscopicity of from 60 to 80 will show in most cases a deformation of the order of 2.7 to 3.0, while if the hygrcscopicity is from to 60, a deformation of the order of 2.3 to 3.0 will usuallybe obtained, and if the hygroscopieity is from 1 to 25, a deformation of about 2.3 or less (usually of the order of 2.6 to 2.3) will be achieved in most instances. Thus, it can. be seen that any variation in properties which may be desired in the finished product can be secured by proper selection of a non-deforming agent or non-deforming softener in accordance with the principles set forth herein.

The cellulosie pellicles obtainable by means of the present invention are particularly suited to wrapping purposes since the reduced deformation substantially eliminates warping, swelling, wrin-v kling and breakage. Similarly, the lamination of such pellicles to materials such as paper or fabric is'iacilitated since there is less tendency for the laminated product to curl, buckle or wrinkle. When stacks of sheets are stored, there is a lesser tendency for contiguous sheets to stick-a common experience with glycerol-softened sheets. Generally, the durability, particularly at low temperatures of 0 C. or less is improved- The process described is especially advantageous from an economic viewpoint inasmuch as it offers a meth- 0d of producing this new type of cellulosic pellicle without alteration or present manufacturing equipment.

While it is preferred that the cellulosi'c pellicle be impregnated with a solution of the non-deforming agent while the pellicle is in the gel state, i. e., before it is dried and while' it still contains a large amount or water, it is within the broad scope of the invention to impregnate a film which has been dried and then rewetted.

Although the invention has been described with specific reference to films of regenerated cellulose prepared by the viscose process since it is in this fleld that the invention is of greatest utility, it will be understood that the broad scope of the invention includes the treatment of other types of cellulosic film cast from aqueous or aqueous alkaline solutions. Thus, the non-deforming agents referred to above may be used with advantage in the treatment of films produced from cuprammonium cellulose solutions, from aqueous alkaline solutions of glycol cellulose or cellulose glycollic acid,

from aqueous alkaline solutions of lowly etherified cellulose, e. g., lowly etherified methyl cellulose or lowly etherified ethyl cellulose, or from aqueous alkaline solutions of lowly esterified cellulose, e. g., lowly esterified cellulose acetate.

Since the invention is capable of considerable variation and modification, any change from the above specific details and examples which conforms to the spirit of the invention, is intended to be included within the scope of the claims.

No claim is made herein to the specific use of ether-esters, keto-esters and carbamic acid esters since this specific use is claimed in co-pending patent applications to Henry S. Rothrock, Serial Nos. 57,632 and 57,633 and to Frederick M. Meigs, Serial Nos. 57,635 and 57,636.

We claim:

1. Water-sensitive film suitable for use as a wrapping tissue formed from an aqueous alkaline cellulosic solution containing, as a deformationrestricting agent, a softening agent for said film comprising an organic compound having a hygroscopicity of from 1 to 80, a boiling point of at least 135 C. at a pressure of 12 mm. of mercury, and a solubility of at least 1% in water at 20 0., said, organic compound being present in sufiicient quantity to restrict the deformation of the film to a maximum of 3.0.

2. Water-sensitive film as defined in claim 1 characterized in that said organic compound is a hydroxy ester.

3. Water-sensitive film as defined in claim 1 characterized in that said organic compound is bis-ethoxyethyl malate.

4. Water-sensitive film as defined in claim 1 characterized in that said organic compound is an amide. g

5. Water-sensitive film as defined in claim 1 characterized in that said organic compound N-beta-hydroxyethyl p-toluene sulfonamide.

6. Regenerated cellulose film suitable for use as a wrapping tissue containing, as a deformationrestricting agent, a softening agent for said film comprising an organic compound having a hydroscopicity of from 1 to 80, a boiling point of at least 135 C. at a pressure of 12 mm. of mercury, and a solubility of at least 1% in water at 20 C., said organic compound being present in sufiicient quantity to restrict the deformation of the film to a maximum of 3.0.

7. Regenerated cellulose film as defined in claim 6 characterized in that'said organic compound is a hydroxy ester.

8. Regenerated cellulose film as defined in claim 6 characterized in that said organic compound is bis-ethoxyethyl malate.

9. Regenerated cellulose film as defined in claim 6 characterized in that said organic compound is an amide.

10. Regenerated cellulose film as defined in claim 6 characterized in that said organic compound is N-beta-hydroxyethyl p-toluene sulfonamide.

11. A process for reducing the deformation ofwater-sensitive film formed from an aqueous alkaline cellulosic solution, which comprises irnpregnating said film with an aqueous solution containing a sufilcient quantity of a deformationrestricting agent to restrict the deformation of the film to a maximum of 3.0, said deformation-- restricting agent being a softener. for said film and comprising an organic compound having a hygroscopicity of from 1 to 80, a boiling point of at least 135 C. at a pressure of 12 mm. of mercury, and a solubility of at least 1 in water at 20 C.

12. A process for reducing the deformation of water-sensitive film formed from an aqueous alkaline cellulosic solution, which comprises impregnating said film while in the gel state with an aqueous solution containing a suificient quantity of a deformation-restricting agent to restrict the deformation of the film to a maximum of 3.0, said deformation-restricting agent being a softener for said film and comprising an organic compound having a hygroscopicity of from 1 to 80, a boiling point of at least 135 C. at a pressure of 12 mm. of mercury, and a solubility of at least 1% in water at 20 C.

13. A process for reducing the deformation of water-sensitive film as defined in claim 11 characterized in that said organic compound is a ethoxyethyl malate.

15. A process for reducing the deformation of water-sensitive film as defined in claim 11 characterized in that said organic compound is an amide.

16. A process for reducing the deformation of water-sensitive film as defined in claim 11 characterized in that said organic compound is N- beta-hydroxyethyl p-toluene sulfonamide.

17. A process for reducing the deformation of regenerated cellulose film which comprises impregnating said film with an aqueous solution containing a sufficient quantity of a deformationrestricting agent to restrict the deformation of the film to a maximum of 3.0, said deformationrestricting agent being a softener for said film and comprising an organic compound having a hygroscopicity of from 1 to 80, a boiling point of at least 135 C. at a pressure of 12 mm of mercury, and a solubility of at least 1% in water at 20 C.

18. A process for reducing the deformation of gel regenerated cellulose film which comprises impregnating said film with an aqueous solution containing a sufilcient quantity of a deformationrestricting agent to restrict the deformation of the film to a maximum of 3.0, said deformationrestricting agent being a softener for said film and comprising an organic compound having a hygroscopicity of from 1 to 80, a boiling point of at least 135 C. at a pressure of 12 mm. of mercury, and a solubility of at least 1 in water at 20 C.

19. A process for reducing the deformation of regenerated cellulose film as defined in claim 17 characterized in that said organic compound is a hydroxy ester.

20. A process for reducing the deformation of regenerated cellulose film as defined in claim 17 characterized in that said organic compound is bis-ethoxyethyl malate.

21. A process for reducing the deformation of regenerated cellulose film as defined in claim 17 characterized in that said organic compound is an WILLIAM FREDERICK UNDERWOOD. HENRY S. ROTHROCK.