US3408435A - Process for extruding elastic poly(epichlorohydrin) filaments - Google Patents

Description

Cd. 29, 1968 LQGAN' JR" ET AL 3,408,435

PROCESS FOR EXTRUDING ELASTIC POLY(EPICHLOROHYDRIN) FILAMENTS Filed Dec. 15, 1966 g ML-6O I ML-45 2 2 l3 X j w .IO 0:

o 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 no no INITIAL DRAW'DOWN RATIO FIG. 2

L. J. LOGAN G. C. OPPENLANDER INVENTORS AGENT United States Patent 3,408,435 PROCESS FOR EXTRUDING ELASTIC POLY(EPI- CHLOROHYDRIDD FILAMENTS Lawrence J. Logan, Jr., Wilmington, DeL, and George C. Oppenlander, Embreeville, Pa., assignors to Hercules Incorporated, Wilmington, Del., a corporation of Delaware Filed Dec. 13, 1966, Ser. No. 601,300 3 Claims. (Cl. 264-210) ABSTRACT OF THE DISCLOSURE Elastic filaments based on epichlorohydrin polymers and copolymers are prevented from breaking when wound upon bobbins by permitting the same to relax at low temperatures prior to winding. Relaxation can be accomplished by operating the take-up rolls (6) at a lower rate than the draw-down rolls.

This invention relates to a process for producing elastic filaments. More particularly, it relates to a method of producing such filaments from predominantly amorphous, elastomeric poly(epichlorohydrin) or epichlorohydrin ethylene oxide copolymers.

Elastomeric polymers and copolymers based upon epichlorohydrin show great promise as elastic filaments for use in applications such as stretch pants, universal size socks and gloves, and other such cases where a form fit or fit over a range of sizes is desirable. In preparing filaments from these elastomers, .the prior art workers have employed the cut filament approach which comprises slitting a sheet of the cured elastomer into narrow, filament-like strips. The cut filament method, however, is not totally satisfactory for several reasons, the most important of which is that it cannot be used for producing very fine filaments.

It would therefore be desirable to produce these elastic filaments by an extrusion and drawdown technique analogous to the drawdown. employed with other synthetic fibers. This procedure can be used to produce much finer filaments than can be prepared by the cut filament approach.

Production of elastic filaments of epichlorohydrin polymers and drawdown has been hampered by the fact that the green filaments exhibit an elastic memory' which causes them to seek to retract in the direction of drawing following the drawdown. In some cases, the green strength of the polymer is not great enough to resist this retractive force and, as a result, the green filaments frequently break if they are restrained from retracting. Thus, if such filaments are extruded, draw down, and immediately collected on a bobbin, the retractive force causes sufiicient breakage to seriously decrease the utility of the filament within a short time. The breakage rate is substantially accelerated if the filaments are heated.

In accordance with this invention, it has been found that the problem of breakage of the drawn-down green filaments can be substantially overcome if, prior to collection of the said filaments they are permitted to relax at low temperatures. Surprisingly, it has been found that for polymers based upon epichlorohydrin and subjected to drawdown under the conditions described hereinafter for green filament formation, the retractive tendency is not great enough to return the filament entirely to its undrawn dimensions. There is always a limiting relaxation ratio for any polymer beyond which it does not seek to relax. The instant invention makes use of this discovery in that a process step is included wherein the green filament is permitted to relax to at least about 80% of this limiting ice relaxation ratio prior to collection on a bobbin or other collection means.

Stated more completely, the invention is a process for preparing elastic filaments from elastomeric, substantially amorphous polymers or copolymers based'on epichlorohydrin which process comprises extruding the polymer through an orifice to form a green filament greater in size than the desired finished filament, drawing down said green filament at about the extrusion temperature by an amount equal to the desired ultimate drawndown multiplied by the intended relaxation ratio, relaxing the filament to at least about of its limiting relaxation ratio, and thereafter collecting the same. The process is particularly applicable to filaments prepared from poly(epichlorohydrin), epichlo'rohydrinethylene oxide copolymer, epichlorohydrinethylene oxideallyl glycidyl ether terpolymer, and mixtures of these materials.

By relaxation ratio in this specification is meant the ratio of the length of the drawn filament to that of the filament which has been relaxed to at least about 80% of its limiting relaxation ratio. The limiting relaxation ratio for any polymer is a function of compounded stock properties, viscosity, temperature of extrusion, and other such variables. However, surprisingly, above a certain drawdown level, which varies with the polymer, it is independent of the initial drawdown.

The polymers or elastomers to which the process of this invention is applicable are polymers of epichlorohydrin, or copolymers or terpolymers of this monomer with about 0 to 80 weight percent of other low molecular weight 'alkylene oxides. These materials preferably exhibit less than about 25 to 30% crystallinity and have a reduced specific viscosity of at least about 0.2 measured on a 0.1% solution in a-chloronaphthalene at C. Preparation of epichlorohydrin polymers and its copolymers is described in US. 3,158,580 and 3,158,581, as well as 3,158,591.

The term green filament is used in this specification to refer to the filament in its unvulcanized state. As with most elastomeric materials, the epichlorohydrin polymers do not exhibit useful properties until they have been vulcanized. The strength of the green filaments is usually quite low and with many elastomers it is too low to permit drawing. It must be understood, of course, that the process of this invention is contemplated only as being applicable to materialshaving suflicient green strength to be drawn down.

In the attached drawing, FIG. 1 is a schematic representation of the process of the invention and FIG. 2 is a graph showing the relationship of initial drawdown to relaxation ratio for two polymers having diiferent properties.

In carrying out the process of the invention, as depicted in FIG. 1, heated polymer is extruded int-o green filament 1 through spinneret 2, into water bath 3, where it is quenched, passed around a driven guide roll 4 and on to draw rolls 5. Drawdown is effected by means of draw rolls 5, taking place in the air gap between spinneret 2 and water bath 3. From the draw rolls, the drawn-down green filament passes to take-up rolls 6 and then to wind-up 7, where it is collected onto bobbins or other collecting devices. Relaxation is accomplished in the span between draw rolls 5 and take-up rolls 6 by having the take-up rolls driven at a slower speed than that of the draw rolls, thereby relieving tension in this zone.

The polymer being extruded is usually not in a truly molten state during the extrusion and drawing down thereof. Being elastomeric in nature, these materials normally do not have a clearly defined melting point at which they pass from a solid to a liquid, freely flowable state. Rather, they change from a solid to a visco-elastic state at which they can be made to flow, but only under the influence of strong shearing forces. The desired viscoelastic state is observed at temperatures of about 55 C. and higher. Preferably, extrusion is effected at temperatures in the range of about 100 to 250 C. The lower range of temperatures up to about 150 C. is preferred for el-astomer compositions containing curing or vulcanizing agents. Higher temperatures in such cases lead to scorching or pre-curing of the filaments. When the curing agents are to be added to the elastomer following filament formation, the upper limit of extrusion temperature is determined by the degradation temperature of the polymer usually no greater than about 250 C.

To obtain the highest tensile strength in the finished filaments, it is usually desirable to include a reinforcing filler in the elastomer formulation. A preferred reinforcing filler is silica, but any of the other well-known reinforcing fillers can be used. Examples of other reinforcing fillers include alumina, aluminum silicate, clays, titanium dioxide, and carbon black. Such fillers will usually be used in the amount of about 5 to 50 parts per hundred parts of elastomer, more preferably about to 40 parts per hundred parts of elastomer. Other additives such as antioxidants, dyes, pigments, plasticizers or processing lubricants can likewise be added to the formulations prior to spinning.

Spinning can be carried out by any known method customarily used for melt spinning. Typically, a screw extruder fitted with a suitable spin-head will be used. The choice of spinning method is immaterial since the spinning per se forms no part of the invention.

The degree of initial drawdown to be imparted to the green filament is controlled by the size of the finished filament desired and the relaxation ratio of the polymer being drawn. It can be calculated by multiplying the final drawdown required to produce the desired finished filament size by the relaxation ratio. The amount of final drawdown needed to produce the desired finished filament is determined from the diameter of the desired finished filament and the diameter of the spinning orifice as follows:

Spinning orifice diameter In order to avoid breakage of the filaments, it is necessary to relax the same to at least about 80% of their limiting relaxation ratio. This is accomplished by operating the take-up rolls at a rate less than that of the draw rolls. Relaxation Ratio, which has previously been defined in other terms, can also be defined as the ratio of the speed of the draw rolls to that of the take-up rolls.

To determine the limiting relaxation ratio for any polymer, under any given set of extrusion and drawdown conditions, it is simply necessary to adjust the speed of the take-up rolls to the point where the filament just begins to sag in the gap between the drawn-down and take-up rolls. The appearance of sag indicates that the filament is completely relaxed and the limiting ratio has been reached. As stated, this ratio reaches a maximum at a relatively low level of initial drawdown. Thus, any final drawdown great enough to be commercially practical will usually require an intial drawdown which will exceed that at which the limiting relaxation ratio reaches its maximum. Accordingly, the limiting relaxation ratio observed at any point of practical final drawdown can be used to determine initial drawdown required to yield the desired finished filament size.

The following examples are presented to illustrate the invention. Parts and percentages are by Weight unless otherwise specified.

EXAMPLE 1 polymer Mooney viscosity of 69 (ML+4 at 212 F.).

The above composition was transferred to a two-roll mill and 24 parts epoxy silane, 24 parts zinc oxide and 24 parts calcium stearate were added and blended thoroughly to yield a compounded material having a Mooney viscosity of 60 (ML+4 at 212 F., ASTM D-1643-63).

The compounded material was extruded at 121 C. through a spinneret having eight 20 mil orifices at a rate of 2.95 g./minute/orifice into a water bath 7 from the spinneret and maintained at 18 C. The resulting filaments were drawn down using an equipment arrangement of the type shown in FIG. 1. Five wraps of the filament were taken on each of the drawing and take-up rolls.

At the start of the operation in each case, the draw rolls and the take-up rolls were driven at the same speed. Then the speed of the take-up rolls was gradually decreased until slack appeared in the span between the rolls. This indicated that there was no tension upon the filament. The speed of the take-up rolls was carefully adjusted so that the amount of the slack between these rolls remained constant, whereupon the filament was collected on a bobbin.

This operation was conducted at a series of drawdown ratios and the relaxation ratio was determined for each drawdown. The relationship between these values is shown graphically in FIG. 2, identified as ML-60. The constancy of the relaxation ratio above about 4.0 X drawdown ratio is apparent.

Samples of filament were drawn at varying initial drawdown ratios, allowed to relax fully and collected. The ratios used and the final drawdown ratio in each instance are shown in the following table.

Initial Drawdown (A) Relaxation Final Drawdown Rat1o* (B) (A/ *Determined from FIG. 2.

Simultaneously, control filaments were drawn directly to the same final drawdown ratios without relaxation and were collected on bobbins.

In each case, the unrelaxed samples contained a large number of breaks after sitting for about 30 minutes at room temperature on the bobbin. When the unrelaxed samples were placed in an oven at 340 F., they fractured immediately. The samples which had been relaxed prior to collection exhibited no breaks after sitting at room temperature for 7 days or after 1 hour in the oven at 340 F. The oven test was conducted at 340 F. for one hour to simulate the customary curing conditions employed with this polymer.

EXAMPLE 2 A second composition was prepared which was identical to that of Example 1 except that it was subjected to an additional 10 minutes mastication in the Banbury mixer at 340 F. to reduce its viscosity. The Mooney viscosity of this composition was 45 (ML+4 at 212 F.).

Specimens of this composition were drawn and relaxed in the same manner as is described in Example 1. The relationship of draw ratio to relaxation ratio for this composition is also shown in FIG. 2, identified as ML-45. Here again, the limiting relaxation ratio attained by the composition is clearly evident although its value is different from that reached by the composition of Example 1.

As was the case in Example 1, the relaxed samples did not break when stored on bobbins either at room temperature or at 340 F., whereas unrelaxed samples drawn to the same denier contained a large number of breaks. The following drawndown ratios were employed:

Drawdown Ratio Relaxation Ratio Final Drawdown The green filaments which have been prepared according to the invention will usually be vulcanized or cured in order to impart strength and other desirable properties thereto. Curing is usually accomplished by contacting the filaments with a curing agent and heating on the bobbin at about 50 to 200 C. Effective curing agents include ammonia, hydrogen sulfide and polyamines, preferably those containing more than one primary amino group. Vulcanization can be effected by heating the filaments in a hot gaseous atmosphere containing the curing agent or by wetting the fiber with a solution of the curing agent and heating. In some instances, the curing agent can 'be incorporated in the elastomer prior to extrusion, where-by curing can be effected by simply heating the formed filament to a temperature within the effective temperature range. In such cases, it is necessary to carry out the extrusion at temperatures sufliciently low to preclude scorching or pre-curing. An example of a curing agent which can be employed in this manner is Z-mercaptoimidazoline which v-ulcanizes the elastomer at about 171 C.

What we claim and desire to eat is:

1. A process for preparing elastic filaments from predominantly amorphous, elastomeric polymers and copolymers based on epichlorohydrin which comprises extruding said polymer through an orifice to form a green filament greater in size than the desired finished filament, drawing down said green filament at about the extrusion temperature by an amountequal to the desired drawdown multiplied by the intended relaxation ratio, relaxing the filament at low temperature to at least about of its limiting relaxation ratio, and thereafter collecting the same.

2. the process of claim 1 wherein the elastic filament is prepared from poly(epichlorohydrin).

3. The process of claim 1 wherein the filament is prepared from a copolymer of epichlorohydrin and 0 to 80% ethylene oxide.

protect by Letters Pat- JULIUS FROME, Primary Examiner.

I. H. WOO, Assistant Examiner.

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