US2026730A - Manufacture of artificial filaments or threads - Google Patents

Description

Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE MANUFACTURE OF ARTIFICIAL FILAMENTS R THREADS Henry Dreyfus, London, England No Drawing. Application January 4, 1929, Serial 7 N0; 330,408. In Great Britain January 23, 1928 Claims.

:glycols or other polyhydric alcohols, or other organic derivatives of cellulose capable of being formedinto artificial filaments by dry-spinning methods. a i

In U. S. Patents Nos. 1,602,125, 1,541,104 and 1,731,318 processes and apparatus for the production of artificial filaments or fibres are described, in which a solution of cellulose acetate orother cellulose derivative in a volatile solvent liquid is extruded through spinning jets into chambers, through which passes an evaporative medium such as air or other inert gas. These patents include the fundamental advances in the art of dryspinning artificial filaments which have rendered it possible at the present day to manufacture dry-spun cellulose acetate artificial silk of any required denier and of the highest commercial quality, both in regard to strength andlustre and in regard to uniformity, and particularly to uniformity in dyeing properties, the last-mem tioned being of the greatest importance for the production of textile fabrics dyed to an absolutely uniform tint throughout the piece. Briefly stated, the improvements in question comprise the use of spinning chambers or cells coupled with outside winding or spinning of the filaments when associated into threads, the combination therewith of cap-spinning devices, the provision of means for oiling, lubricating or moistening the threads as they pass to the cap-spinning devices, and, most important of all, the provision of means for securing a uniform fiow of air or other evaporative medium through each of the spinning chambers or cells, and subsidiary thereto, means for adjusting the heat supply so as to obtain uniform temperature conditions in each of the spin- The higher the denier and the greater the speed, 7

the larger is the amount of air or other gas used.

; The speed of the evaporative medium is regulated (CI. 18-54) a in accordance with the principles laid down in U. S. Patent No. 1,541,104 so as to give a regular production of filaments or threads in each cell, in the cells of each spinning metier, and also in V the total number of metiers used for the manufacture of threads of thesame denier. Further, it becomes practicable by adjustment of the flow of the air or other gas to spin different deniers in different metiers and even in different cells of the same metier, as desired. The heat supply is 10 controlled to give uniform temperature conditions in each cell, this adjustment being dependent on the regulation of the flow of air or other gas, the latter being of primary importance in securing really uniform temperature conditions.

At the same time the speed of the air or other gas must be adjusted to give such a concentration of the solvent vapours carried away by the air or other gas that the recovery. of the solvent is economical, the amount of air or other gas used being adjusted accordingly in accordance with the amount of solvent evaporated.

The temperatures chosen for spinning are likewise of a definite nature. In order to get the usual lustrous commercial threads,.as'produced according to the previously mentioned patents,

the temperatures employed for a given denier and 50 and 90 when one uses acetone or acetonealcohol mixtures as solvent. When one uses an acetone-alcohol mixture, the spinning temperature is naturally higher, as a liquid of higher boiling point has to be evaporated; the greater the quantity of the latter, the higher the temperature must be.

If, however, lower boiling solvent liquids than acetone or acetone-alcohol mixtures are used, for example, if the acetone is replaced by lower boiling solvents. such as methyl formate or if ethyl alcohol is replaced by methyl alcohol the temperature will be accordingly lower. Again,the

temperature varies according .to the denier spun,

a lower denier requiring a lower temperature. Also, the higher the speed of the air or other gas used for spinning the lower the temperature may be. Further, if a higher or very high temperature is chosen, then the speed of the air or other gas may be less. That is to say, there is an inter-relationship between the different variables. and What it amounts to is that it is the total quantity of heat supplied per unit of time which counts and nothing else. As the rate at which heat is supplied depends on the speed of the air or other evaporative medium, the importance of the improvements comprised in U. S. Patent No. 1,541,104 will be at once apparent, since they enable the air speed to be adjusted according to the denier spun and the temperature adopted and according to the requirements of any particular spinning solution, whether it comprises a single solvent or a combination of solvents.

For each particular solvent or solvent mixture used, the limits within Which the filaments are more or less lustrous or even dull, according to requirements, are relatively narrow and can be easily adjusted by an adjustment of the speed of the evaporative medium by the means described in the afore-mentioned patent. Indeed, no method based on any other principle of controlling the operation of dry-spinning plant has yet been suggested, which permits the temperature, the denier spun, and the speed of the air or other gas, which last-mentioned indirectly governs the temperature, to be properly adjusted in their close inter-relationship according to requirements.

The limits between which the flow of the air or other evaporative medium can be varied are also controlled in practice by a number of other considerations. Thus, the adoption of a substantially increased air speed means the dilution of the solvent vapour to such an extent that its recovery may become uneconomical and for this reason it is advisable to keep within certain limits. It is also important, in using solvents which are inflammable, to keep the concentration of solvent vapour Well-below the limit at which explosive mixtures with air are formed.

When filaments produced by the foregoing methods are examined, it is found that they are to some extent cellular or tubular, and that the more voluminous they are in character, the more pronounced is their cellular or tubular structure. 50

This is especially the case when spinning solutions of lower concentrations are employed, e. g.

when the solutions contain 10% to 20% of cellulose acetate instead of concentrations of 25-30% such as are prescribed in U. S. Patent No. 1,688,351. The cellular or tubular structure of the filaments moreover is developed to a larger extent when a high spinning temperature is adopted in order to get .a highly lustrous thread.

In the making of viscose in the past substantial quantities of carbon bisulphide have been used, which still remain in the spinning solution together with all sorts of decomposition products of a gaseous nature, such as sulphide products, especially sulphuretted hydrogen, which are formed in the spinning solution both before and during the coagulation. .The presence of these substances in the spinning solution has enabled already'the production of fibres of a more or less cellular or tubular character. The cellular or tubular fibres produced in this way were only obtained to a limited extent, and did not attract any special notice, untilefforts were made to produce so-called hollow'filaments, when it was suggested tointroduce air or gases into the spinning solutions in order to produce these hol low fibres.

Attempts have also been made to produce hollow filaments by introducing into the spinning solutions small quantities of gases or non-solvent 5 gas-producing liquids, which upon the application of heat should produce industrially valuable hollow fibres. These methods are incapable of application to spinning solutions containing cellulose acetate or other cellulose derivatives, and especially to the production of filaments from such solutions by evaporative processes. On the one hand either the said gases or liquids cannot be introduced into the spinning solution in suflicient quantity or be distributed therein with suiiicient uniformity to give the desired result, or on the other hand, if they are miscible with the spinning solution in sufiicient quantity, they act as precipitants for the cellulose acetate or other cellulose derivative, thus making spinning impossible.

In order to produce fibres of the expected strength and desired denier (and especially of low denier) and anyhow filaments of increased hollowness as compared with the filaments previously produced, it is necessary to incorporate in the spinning solutions used in the dry-spinning process very large quantities of real solvents as the medium for the formation of the cellular or tubular structure, so that they realy constitute the medium for the production of the spinning solution. That is to say, it is necessary to proceed on quite a different basis from the previous attempts, where small quantities of air or gases or insoluble liquids were used for the purpose of producing the desired effect.

In the spinning of nitrocellulose, solvents such as ether are used in substantial quantities and yet one does not get the formation of tubular or cellular threads to such an extent that they are different from the threads produced in normal dry-spinning operations. It might be expected that, if small quantities of air or gases or indifierent volatile liquids give such an effect, a very volatile solvent like the ether employed in nitrocellulose manufacture, especially as it is employed in such large quantities, would be much more likely to produce the efiect of hollowness. However, as will be explained hereafter, quite different conditions are necessary in order to get increased cellular or tubular filament formation.

Hollow filaments can, it is true, be produced from the usual spinning solutions by the use of spinning temperatures substantially higher than the boiling points of the solvent, coupled with a very substantially increased rate of flow of the air used as evaporative medium. Whilst it is a fact that, in using very substantially increased temperatures and a rapid air flow as stated, hollow fibres can be produced, difiiculty has been experienced in drawing out these hollow fibres to lower deniers than about 15 to 10, on account of troubles due to breakage during the spinning operation. The reason for this is easily understood when one considers that the operation of forming the filaments at a very much increased temperature and air speed involves a rapid elimination of the solvent in the filaments, which, naturally, as the solvent tries to escape, weakens or bursts the skin or surface of the filaments so formed. This may affect both the coherence of the filaments and their strength. As a result of the quick elimination of the solvent, which is the characteristic feature in the production of so-called hollowi"filaments, the filaments become dry so quickly that there is no time for drawing them' out to low deniers'before they reacha condition in which the filaments are liable to break.

It has now been found, according to the present invention that, without relying on the spinning conditions above mentioned of substan-. tially increased spinning temperature and rapid air speed, it is possible, by adopting-the conditions hereinafter described, to produce threads of cellular or tubular character, as required, and also of a cross-sectional area which can be regulated according to requirements by the observance of the special conditions hereinafter described. These conditions give filaments of the desired increased volurninosity which can be drawn out to any filament denier, according to requirements. The said filaments can be pro-' duced on a commercial scale without interruption and have a strength comparable with the strength of the filaments spun under normal conditions, that is to say, when less cellular filaments are formed. For example, if a cellulose acetate of a certain viscosity is chosen which is supposed to give under normalconditions a certain strength, it would according to the present invention give about the same strength. This means in other words that, if a cellulose acetate of very high viscosity is chosen which gives under normal conditions a very much increased strength, voluminous filaments of similar strength can be obtained according to the present invention; also if an acetate of low viscosity is takenwhich gives under normal conditions filaments of lower strength, a corresponding lower strength can be obtained when filaments of cellular or tubular form are produced according to the present invention, and not a relatively reduced strength as when a spinning temperature very substantially higher than the boiling point of the solvent and a very much increased air speed are used. In the above discussion, whether based on the production of defective cellular or tubular filaments in one way or the other according to the prior art, or based on the production of threads according to the methodtwhich is the object of the present invention, it is assumed that the filaments are produced under the best conditions, namely, according to U. S. Patents Nos. 1,602,125 and 1,541,104, as otherwise the filaments would show irregularities from cell to cell or in themselves, unlessthe flow of air or other evaporative medium were controlled in aregular manner as described in U. S. Patent No. 1,541,104, whether the filaments were spun at ordinary temperature or with heat at a temperature appropriate to the speed of the air or other gas.

The present invention consists primarily in a process for the manufacture of voluminous filaments or fibres of a more or less cellular or tubular, or continuously tubular character, consisting in dry spinning solutions of celluloseacetate or other cellulose derivatives dissolved in a solvent mixture containing atv least two volatile constituents in proportions such that the lower boiling constituent varies from a major part of the solvent mixture to a minor according as the boiling point difference of the said constituents is small or great, the boiling points, moreover,,dif-

fering by such an amount that filaments QrLfibres of the desired characteristics as to volurninosity are produced at spinning temperatures below .or at any ratenot substantiallyabove the-[boiling point of the higher boiling of said constituents;

' filaments produced in normal spinning, and cavoluminous filaments of a more or less cellular or tubular or completely tubular character can be produced under these conditions, said filaments having about the'same degree of strength as the pable of being drawn out to low or lower denier as desired. By varying the temperature, it is possible to pass from the normal filaments produced at temperatures slightly above the boiling point of the lower boiling constituent of the solvent 10 mixture through stagesin which the filaments are, first partly cellular, and, then, uniformly cellular or partly tubular, to the stage at which the filaments are completely tubular. At the maximum temperature, the filaments are com- 15 pletely tubular, cellular filaments being obtained at lower temperatures which are at the same time substantially higher than those at which normal filaments are produced.

The spinning temperature varies in accord- 20 ance with the proportion of the lower boiling constituent; the greater the quantity of low boiling constituent, i. e. the lower the quantity of high boiling constituent, the lower may be the spinning temperature. 25

The substances constituting the solvent mixture may each be solvents for the cellulose acetate or other cellulose derivative or one or both of them may be diluents or non-solvents provided that together they form a solvent mixture. Thus, 30 alcohol-benzol mixtures may be employed as solvent, or mixtures containing a solvent, such as acetone, together with small quantities of a nonsolvent, such as water.

The best results are obtained by the use of 36 constituents having a boiling point difference of not less than to'50 C., and preferably between 50 or 60 and 100 C. or higher.

As stated above, the proportion of low boiling constituent to high boiling constituent varies 40 with the diiference in their boiling points. The smaller the boiling point difierence, the larger must be the proportion of the low boiling constituent. If the boiling point difference is under 40 C. the quantity of the lower boiling constituent used should be at least or and preferably 75% or more of the total amount of the solvent mixture used. When the difference in the boiling points of the two constituents is between 40 and 50 C. the quantity of lower boiling con- 50 stituent used is usually higher and preferably substantially higher than the quantity of the higher boiling constituent.

. It will be understood that, subject to the above considerations, it is also possible by adjusting the 5 proportions of the constituents of the solvent mixture to vary to some extent the voluminosity of the filaments so as to produce filaments of a more or less cellular or tubular or completely tubular character. Q

The 'voluminosity or volume oi the filaments is increased and the apparent density is diminished by selecting appropriate conditions, such as more dilute spinning solutions and/ or the employment of plasticizers and/or a spinning temperature 51* which is of such a nature that the higher boiling liquid evaporates at such a rate as to enable the filaments under formation to retain suflicient extensibility until they have achieved the desired highest volume coupled with the thinnest skin C formation. The volume of the filaments can be diminished by using opposite conditions to those employed for getting the greatest volume.

The speed of the air or other evaporative medium usedis adjusted according to the denier 75.,

happens, a liquid, which when used by itself is a the filaments as a plasticizer.

spun (i. e. the higher the denier spun, the more air is used), according to the spinning speed employed (i. e. the greater the spinning speed, the greater the amount of air used), and according to the concentration of the spinning solution (1. e. the higher the concentration of the spinning solution, the less the air speed). The speed of the air or other evaporative medium must also be adjusted together with the temperature used in order to ensure the supply of the requisite heat units, and to enable a uniform grade of filaments to be obtained in each cell of each metier and in all the metiers used.

As a further example of the way in which the spinning factors are related, it may be stated that the lower the denier and the lower the spinning speed, the lower need be the difference in the boiling points of the liquids in the solvent mixture, also the less may be the quantity of lower boiling liquid as compared with the higher boiling liquid.

The said constituents of the solvent mixture, having as previously explained, a certain definite difference between their boiling points, and pref erably a difierence of 50 or 60 to C. or substantially more-though the difference may be less, provided that the proportions of the constituents are suitably adjusted-may each be a mixture of liquids. Thus the lower boiling solvent may be a mixture of solvents just as the higher boiling solvent may be a mixture of solvents. Further, in the lower boiling solvent and/or the higher boiling solvent some diluents may be contained to a certain degree, or, as often so-called diluent, may be combined with another diluent or even with a nonsolvent to form a solvent mixture. For example, alcohol, which is practically not a solvent, may become a positive solvent when used together with acetone; similarly alcohol together with benzol is a solvent, and water can be used with acetone as solvent.

The solvent mixture employed may also contain, in addition to the essential constituent liquids of widely separated boiling points, solvents and/or diluents, having an intermediate boiling point between the boiling points of the said liquids. In such case, it is advisable to adjust the quantity of the higher boiling liquid or solvent, or to use, in addition, a corresponding quantity of a still higher boiling liquid or solvent so as to establish the necessary equilibrium. The spinning should take place at a temperature lower than the boiling point of the higher boiling liquid or solvent, or anyhow not substantially higher, so as to produce voluminous, more or less cellular or tubular filaments as previously explained. V

The higher boiling constituent of the solvent mixture may either function as volatile solvent as explained aboveprovided the spinning temperature chosen is sufficiently high to ensure the elimination of the said higher boiling constituent-or it may function partly as solvent and partly as plasticizer when lower spinning temperatures are used; and especially in the case when the difference between the boiling points of constituent liquids is very great, and a certain amount of the higher boiling solvent remains in In this case it is advisable to adopt a higher spinning temperature, so that the higher boiling solvent remains to an amount substantially under 100%, and preferably to the extent. of only 50-5% orless,

calculated on the weight of the cellulose derivative.

True'plasticizers, as distinguished from high boiling volatile solvents, may also be incorporated in the solvent mixture. If plasticizers of very high boiling point e. g. -200 or over, are employed, such as methyl or ethyl xylene sulphonamides or mixtures thereof, then in order to form the threads with the requisite coherence and strength, it is necessary to use not more than 50%, and preferably 20-5% or less, calculated on the weight of the cellulose derivative. The plasticizer can afterwards remain in the filaments where the qualities imparted to the thread by the plasticizer are useful in the subsequent textile operations, or, if necessary, it may be removed by extracting it with a solvent for the plasticizer, which at the same time is nota solvent for the silk, or it may, as in the case of some of the xylene sulphonamides, for instance, be washed out with chemicals such as dilute soda solution or sodium bicarbonate solution.

In order to illustrate the principles of the invention, it will now be described in its application to specific combinations of liquids to form the solvent mixture used for spinning cellulose acetate.

If acetaldehyde (boiling point 21 C.) (preferably in a stabilized form, in which polymerization is prevented in known manner) and acetone (boiling point 58 C.)'are used in a pro: portion, for example of about 50% or 60% to 75% or more of acetaldehyde, and preferably mixed with some methyl or ethyl alcohol, cellular or tubular filaments can be produced at a spinning temperature lower than that of the higher boiling solvent, or anyhow not substantially higher; The lower the proportion of aldehyde, the higher must be the spinning temperature for the production of the same grade of cellular or tubular filament. The foregoing applies when, for example, a spinning solution of 20% to 30% concentration is used. Other concentrations of the spinning solutions will require corresponding conditions.

The difference of boiling points in the above case is about 37 C. If, instead of acetone, methyl or ethyl alcohol is used, the difference in the boiling points is much greater and the production of cellular or tubular filaments is more pronounced, even at a somewhat lower spinning temperature than the boiling point of the higher, boiling constituent. If a mixture of acetaldehyde and alcohol is used containing a certain quantity of acetone to increase its solvent properties, then a spinning temperature intermediate between those previously indicated has to be employed. It is possible to vary the spinning temperature as desired by a suitable addition of a solvent of intermediate boiling point to the acetaldehyde-alcohol mixture.

If instead of acetaldehyde, formaldehyde is used in combination with acetone, then, as formaldehyde is soluble in acetone, and the difference in boiling points is about 79 C., the formation of cellular or tubular filaments takes place more readily at a temperature lower than or not substantially higher than the boiling point of acetone. In fact, when formaldehyde is used, especially if large quantities of it are employed in the spinning solution, the temperature required for forming hollow filaments is relatively low. It will be understood that this is still more pronounced when methyl alcohol or ethyl alcohol are used together with the acetone, or when, I

as is preferred in practice, the formaldehyde is used in the form of a concentrated solution in water. For instance 20 parts of a 40% solution of formaldehyde may be used with 80 parts of acetone to form the solvent mixture.

If instead of acetaldehyde o-r formaldehyde, methyl formate, having a boiling point of about 35 C. is chosen, the boiling point difference be- A tween that and acetone, viz. 23 C., is too small unless the quantity of acetone used is very small,

spinning temperature lower than the boiling point of the higher boiling solvent and, in any 7 event, not substantially higher than the boiling point of the higher boiling solvent. It will be understood that the larger the quantity of lower boiling solvent employed compared with that of the higher boiling solvent, the lower the temperature at which so-called hollow'filaments are produced. i

If however instead of alcohol, water is used with acetone as a solvent for celluloseacetate,

the temperature difference being 42 C., hollow filaments can easily be produced, especially if, for example, based on the employment of 20-25% of water, the temperature chosen is under. the boiling point of water or not-much higher. The greater the proportion of water added, the higher is the spinning temperature employed. The production of tubular filaments is especially favourable when in addition to the water some other higher boiling solvents, such as diacetone alcohol, which easily mix with Water, are addedin proportions of about to 10% or even higher.

In combination with acetone, liquids such as cyclobutanone or monomethylethyleneglycolether or diacetone alcohol may be used, instead of water, in order to produce cellular or tubular filaments, in view of the substantial difference in the boiling points.

Instead of or together with acetone, ethyl formate or methyl acetate or mixtures thereof may be used in any desired proportion, as they have nearly the same boiling point as acetone.

In the foregoing description, the invention has been illustrated in its application to cellulose acetate. Similar considerations apply to the production of voluminous filaments of a more or less cellular or tubular or continuously tubular structure by dry-spinning methods from other cellulose derivatives. For example, it is interesting to note that the same principles exist in the case of solutions of nitrocellulose in mixtures of ether and alcohol; when the ether is present in the solvent mixture in a proportion of more than 50 and preferably in the proportion of about 75%, cellular or tubular filaments are obtainable by dry-spinning at temperatures around, and at any rate not substantially higher than, the boiling point of alcohol.

It is also understood that a plasticizer having a very high boiling point and therefore practically non-volatile may be incorporated in the spinning solution and remain permanently inthe filaments unless it is afterwards extracted by solvents or chemicals, as explainedbefore.

It shouldbe noted that, in using spinning solutions comprising a solvent mixture containing 5 high and low boiling constituents as herein described, if the spinning temperature be lower than those at which cellular or tubular filaments are formed, the spinning operation will then produce normal filaments in a manner substantially simi- 10.

lar to those described in U. S. Patents Nos. 1,- 566,384 and 1,669,158.

The following examples are given as an indication of how the invention may be carried into effect, but they are not to. be construed as in any way limitative.

Example I A solvent mixture of acetone and acetaldehyde in equal proportions (boiling point diiference 37C.) is used to make a spinning solution containing 26.1% cellulose acetate and the solution is spun into air at a temperature of 72 C., filaments of a cellular character being produced.

Example II I i Spinning is. carried out under the same conditions as in Example I, but into air at a temperature of 78? C, Almost completely tubular fila ments are produced) Example III A 20.7% solution of cellulose acetate in a solvent mixture containing acetone and acetaldehyde in the proportions of 25/75 is spun into air at a temperature of 65 C. Again, almost completely tubular filaments are produced.

Example IV Alcohol and methyl formate in the proportions of 30/70 are used to form a solvent mixture with a boiling point difierence of 43 C., and a spinning solution containing 20.6% cellulose acetate in the solvent mixture is spun into air at a temperature of 63 C. Cellular filaments are produced.

Example VI Example VII 60 The spinning solution used in the two previous examples is spun into air at a temperature of 95 C. to produce almost completely tubular filaments. 7 r

The foregoing examples and illustrations are 55 only explanatory and are not limitative, and any solvents or combinations of solvents may be employed which give the above-mentioned effects.

The spinning operation is preferably effected in relatively narrow cells and/or when collectors are used in conjunction with the spinning jets, as described in the specification accompanying U. S. patent application S. No. 236,448 filed 29th November, 1927, and especially when the collectors are associated or formed with heating devices.

What I claim and desire to secure by Letters Patent.is:-V-'

1. Process for the production of voluminous filaments of a cellular or tubular character, said process comprising dry-spinning a solution of cellulose acetate dissolved in a solvent mixture containing alcohol and 70% methyl formate at temperatures from 63 C. to 95 C.

2; Process for the production of voluminous filaments of a cellular or tubular character, said process comprising dry-spinning a solution containing 20.6% cellulose acetate dissolved in a solvent mixture comprising 30% alcohol and 70% methyl formate at temperatures from 63 C. to 95 C.

3. Process for the production of voluminous filaments of a cellular or tubular character, which comprises dissolving an organic derivative of cellulose in a solvent medium containing at least two volatile constituents whose boiling points difier by at least C., at least one of which is itself a --solvent for the cellulose derivative, the quantity of the lower boiling constituents being from about to of the total solvent medium employed, and dry spinning the solution at temperatures near to, but, at the most, not substantially exceeding the boiling points of the higher boiling constituents.

4. Process for the production oi voluminous filaments of a cellular or tubular character, which comprises dissolving an organic deriva-- tive of cellulose in a solvent medium containing at least two volatile constituents whose boiling points difier by at least 40 C., at least one lower boiling constituent being itself a solvent for the cellulose derivative, the proportion of such lower boiling constituent being from about 50% to 75% of the total solvent medium employed, and dry spinning the solution at temperatures near to, but, at the most, not substantially exceeding the boiling points of the higher boiling constituents.

5. Process for the production of voluminous filaments of a cellular or' tubular character, which comprises dissolving cellulose acetate in a solvent medium containing at least two volatile constituents whose boiling points difier by at least 40 C., at least one higher boiling constituent and one lower boiling constituent being 20 themselves solvents for the cellulose acetate, the quantity of the lower boiling constituents being from about 50% to 75% of the total solvent medium employed, and dry spinning the solution at temperatures near to, but, at the most, not sub- 25 stantially exceeding the boiling points of the higher boiling constituents. Y

HENRY DREYFUS;