US3791788A

US3791788A - Method for washing a tow

Info

Publication number: US3791788A
Application number: US00315951A
Authority: US
Inventors: E Taylor
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1970-06-30
Filing date: 1972-12-18
Publication date: 1974-02-12
Anticipated expiration: 1991-02-12

Abstract

A method for washing a tow wherein the tow is passed through a confined zone and a stream of water is forced through the tow at a minimum rate at least as great as

Description

United States Patent [191 Taylor, Jr.

[451 Feb. 12,1974

METHOD FOR WASHING A TOW Inventor: Ernest A. Taylor, Jr., Decatur, Ala.

Monsanto Company, St. Louis, Mo.

Filed: Dec. 18, 1972 Appl. No: 315,951

Related US. Application Data Continuation-impart of Ser. No. 198,780, Nov. 15, 1971, abandoned, which is a continuation-in-part of Ser. No, 51,261, June 30, 1970, abandoned.

Assignee:

US. Cl. 8/ 1 37.5, 8 /l3 7 l 34/1 5 Int. Cl. D01f 7/06 Field of Search 8/137, 137.5; 134/15 [5 6] References Cited UNITED STATES PATENTS 2,733,121 1/1956 Griffith, Jr. et al 8/137.5 2,768,057 10/1956 Friederick 8/1375 Primary Examiner-Mayer Weinblatt M95421: i ?l 1 QLEiW:RQb E lfir aqelrst 5 7 ABSTRACT A method for washing a tow wherein the tow is passed through a confined zone and a stream of water is forced through the tow at a minimum rate at least as great as x 1,000T \fWN/h (IL/p) 13 Claims, 3 Drawing Figures m :27 I9 T E I5 L is \J T fi 2340 AT 23 112 1 2/ \M; M

METHOD FOR WASHING A TOW This is a continuation-in-part of application Ser. No. 198,780, filed Nov. 15, 1971, which was a continuation-in-part of application Ser. No. 51,261, filed June 30, 1970 for Method For Washing A Tow in the name of Ernest A. Taylor, .lr. both now abandoned.

BACKGROUND OF THE INVENTION Man-made fibers are formed by extruding a spinning solution through a spinnerette to form a tow made up of a number of individual filaments. 1n the production of certain man-made fibers it is usually necessary that this tow be washed during some state of the manufacture. The washing may be for the purpose of removing a spinning. solvent, applying a dye or finish, removing excess dye after a dyeing operation, neutralizing the fiber or for some other purpose. Conventionally, the tow is washed by passing it through a spray or a bath or by running it through an inclined cascade in a direction counter to the fiow of water in the cascade. These approaches are inefficient, so that the tow must be run through the washing zone at a very low speed or the washing zone must extend a considerable length along the tow processing line. The former lowers the production rate while the latter requires the use of an excessive amount of space which might be better used for some other purpose.

Apparatus other than cascades and sprays has been used to wash tows of filaments. US. Pat. No. 3,267,704, issued to H. G. Mueller, and US. Pat. No. 3,343,383, issued to. E. A. Taylor, Jr., for example, show apparatus used for carrying out the process wherein the washing liquid is continually passed back and forth through the tow until the washing is completed. Unfortunately, the apparatus necessary to carry out this method is usually several feet long and quite expensive to manufacture.

it has been discovered-that confining the tow and the washing liquid to a zone having predetermined dimensional limitations and then forcing the liquid through the tow at a rate based on the dimensions of the confined zone and the number of filaments in the tow a vastly superior washing result is obtained. In carrying out the method of the present invention a very simple and inexpensive apparatus may be used, with the complete washing action being carried out in an apparatus no more than five or six inches long. With this in mind, one of the objects of this invention is to provide a novel and improved method for washing a tow of filaments.

Another object of this invention is to provide a method for washing a tow of filaments in such a manner that excess dye or solvent is rapidly and efficiently removed from the tow.

A further object of this invention is to provide a method for washing a tow of continuous filaments in such a manner that the filaments are completely washed within a very short contact time.

A still further object of this invention is to assure a uniform washing of a tow of filaments.

Some tow washing devices operate much more effectively when the washing fluid is boiling, the stirring effect of the ebullient fluid serving to agitate, vibrate or separate the filaments of a tow during washing. Since in this invention a very effective filament separation is produced by the interaction of the fluid with the tow,

then another object of this invention is to eliminate a high fluid temperature as a prerequisite for effective washing.

The objects of this invention are achieved by passing tow to be washed through a confined zone and forcing a stream of water or other treatment fluid through the tow at a rate in excess of a predetermined critical minimum value, the water being maintained at a temperature within a predetermined range. The critical minimum rate at which the water is passed to the tow must be at least as great as x= 1,000T WN/h (pt/p) where x is the water flow rate in gallons per minute, T is the thickness of the stream of water in inches, W is the width of the confined zone in inches, h is the thickness of the confined zone in inches, N is the number of filaments in the tow, p. is the viscosity of the water in pounds per foot-second, and p is the density of the water in pounds per cubic foot. Preferably, the water is forced through the tow at a rate at least three times as great as the critical minimum rate.

Other objects and advantages of the invention will become apparent when the following detailed description is read in conjunction with the appended drawing, in which FIG. 1 is a diagrammatic longitudinal cross-sectional view of one apparatus useful for carrying out the process of the present invention.

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1 showing the cross-sectional area of the confined zone in the washing apparatus through which the tow is passed, and

FIG. 3 is a diagrammatic view of apparatus used with the washing apparatus in carrying out the process of the present invention. I

Referring now in detail to the drawing there is shown, in a more or less diagrammatic manner, a tow washer l0which is useful in carrying out the method of the present invention. The washer 10 is made up of upper and lower units 11 and 12 which are held in a spaced relationship by side plates 13, the side plates 13 being secured to the upper and lower units 11 and 12 by screws 14. The space between the upper and lower units 11 and 12 forms a confined zone through which a tow 15 passes. The lower face 18 of the upper unit 11 and the upper face 19 of the lower unit 12 and the inner faces 20 of the side plates 13 define the limits of the confined zone through which the tow 15 passes. The confined zone thus has a. width W" and a height h" and a cross section area of Wh, as best shown in FIG. 2.

The lower unit 12 is provided with an inlet 21 through which water or some other liquid is applied to the tow 15. The inlet 21 extends across the lower unit 12 from one of the side plates 13 to the other and thus s a width. wilh li sgl .hasa thi knsss t. AL. where A is between 0.05 and 10, with T usually being no greater than about 10h, h being the height or thickness of the confined zone, so as to concentrate the flow of the washing liquid through the tow 15 at one location. The upper unit 11 is provided with a recess or chamber 22 which receives the water passing through the tow 15 from the inlet 21.

The recess 22 directs the water back through the tow at outlets 23 spaced from the inlet 21 in streams having a thickness T (FIG. 1), the value ofT preferably being no greater than about 10h. The preferred value for the dimension T is within the range of 2h to h. The water entering the inlet 21 passes through the tow l5 and is divided into substantially equal parts which pass back through the tow at the outlets 23. The chamber 22 completely fills with water under pressure. This pressure forces the water through the outlets 23, and the tow 15, at a high velocity.

It can readily be seen that the tow is confined, at the outlets 23, to a cross sectional area having the dimensions W and h. The fluid passing through the tow at this point is confined to a cross sectional area having the dimensions W and T, W being width and T being thickness of the fluid stream.

As shown in FIG. 3, the washer l0 is'mounted over a discharge pan 30. Spaced pairs of

rolls

32 and 33 feed the tow 15 through the washer at a uniform speed. A pump 34 connected to the pan 30 and the inlet 21 of the washer 10 pumps the water from the pan 30 through the washer via the inlet 21. The water exiting from the washer -10 falls into the pan 30 and is recirculated by the pump through the washer. Fresh water may be fed to the pan 30 from a supply 38, the pan 30 being provided with an overflow line 39 to maintain a constant water level in the pan 30. The fresh water supply rate is independent of the rate at which water is circulated through the washer 10. Pairs of stripper bars 36 positioned in contact with the tow as shown in FIG. 3 are used to prevent the water from flowing along the tow beyond the edges of the pan 30.

The water makes one pass through the tow at each of the outlets 23, for a total of two passes at the outlets. Since twice as much water passes through-the tow at the inlet 21 as at either of the outlet locations it may be considered that the water makes a double pass, or two passes, through the tow 15 at the inlet 21. Thus, in the apparatus shown it may be said that the water makes four passes through the tow 15. The watercan be deflected back and forth through the tow as many times as desired but the method is so efficient that this is not necessary. At each point where the water passes through the tow the water should be, for maximum efficiency, flowing at a rate in excess of the minimum value given by i i x 1,000T WN/h as set out above. If the water passes through the tow at a lower rate the washing efficiency will be greatly reduced. If a vigorous washing is not required the dimensions of the apparatus 10 may be such that the critical minimum flow rate is exceeded at only one of the out lets 23. In this case the washing will be highly effective only at that outlet. Of course, a portion of the water in a washer such as described above will not pass completely through the tow but will travel along the interstices in the tow (i.e., between the filaments) to the outlets 23. Since it would be very difficult to actually measure the water flow rate inside the tow an easier way of determining whether the minimum flow rate is exceeded is desired. If the outlet dimensions are held within the limits set out above, the flow rate into the inlet 21 can be compared with the minimum critical flow rate.

to determine whether minimum critical flow rate is exacetate ceeded, without regard for actual flow rate in the tow or the fact that some of the water will travel along voids in the tow. Of course, since the one inlet supplies two outlets, the fluid flow into the inlet must be at least twice the critical minimum flow rate as determined by the above equation.

The table below shows values of u and p for water at various temperatures.

The following examples are included to show the efficiency of this tow washing process in removing solvent from wet spun acrylonitrile filaments. Four washers (not shown) such as described above were used in series, with the freshly spun tow entering washer A and then passing through washers, B. C and D in that order. Each washer formed a confined zone 5.2 inches long and having the dimensions: T=9/16"; h= 3/16" and W= 3 7 8 Each washer was provided with its own w ex r rm Wh Ehy W t LiQfQ- was circulated through the washer at a' rate in excess of the critical minimum flow rate as determined by the equation given above.

Fresh water was supplied to washer D from its supply 38 and the overflow line 39 of washer D was connected overflow of washer C fed into washer B from which the overflow fed into the pan 30 of washer A. The overflow of washer A was passed to a solvent recovery system (not shown). The fresh water supply rate, which is independent of the circulation rate in each of the washers, was based on the weight of the tow passing through the washers and was varied as shown in the following examples.

The tow was spun from a 93% acrylonitrile, 7% vinyl copolymer into a spin bath of 55% dimethylacetamide/45% water at 38 C. and was led from the spin bath into washer A. The tow entering washer A contained about 50% dimethylacetamide. The tow was made up of 80,000 filaments, 3 denier per filament. The tow was advanced at a speed suchthat a given point on the tow passed through the confined zone in 0.95 seconds. This may be referred to as contact time" or dwell time."

EXAMPLE I Tow was spun at a rate of 600 pounds per hour. The values given under the headings A, B, C and D represent the amount of solvent in the tow exiting from the washers-A, B, C and D, respectively.

tuted for the sodium phosphate in an amount sufficient Fresh Water Solvent in tow by weight to provide a dye concentration of 0.5% based on the pigx fiz weight of the water. The liquid flow rate was in excess A B C D of three times the critical minimum value and the time 125 7,44 L30 045 025 5 Ofthe OW m the treatment zone was approximately 1.5 103 7,75 235 M4 012 seconds. The filaments m the tow were dyed to a deep,

' uniform shade. The amount of dye on the fiber was approximately 2%, based on the weight of the fiber.

1O EXAMPLE V EXAMPLE H A number of runs were made using filaments of dif- I V ferent chemical composition wherein the filaments Tow was spun at a rate of 735 pouhds e hour; Fresh were washed with water containing a finish for the purwater was added to the reservoir or pan 30 of washer is P of aPPlymg the fimsh to the filamentef'ber types D at varying rates and the amount of solvent in the tow Included m these runs were Polyvmyl ehlondey P e after each washer was determined. The results are nylon and e W know to those Sk'lled m Shown in the following table the art. The washing fluid was 98% water and 2% of a conventional finish, at a temperature of 100 C. In addition to being washed, the filaments were 20 stretched. W T T The confined zone had the following dimensions: W Fresh water Solvent in tow by weight {lb-371677; andT-Wlgi with an Overall Supply Rate lb length of 8". The number of filaments in each bundle A B C D 25 of filaments passing through the confined zone was such that the minimum critical flow rate varied up to 12.5 8.86 2.67 0.85 0.34 approximately 0.1 gallon per minute for the different fibers. The actual flow rate through the confined zone was 1.2 gallons per minute. The following table shows 30 the conditions under which these runs were made. Ap-

proximately 1% of the finish, based on the weight of The temperature of the water used for washing may the fiber, was applied to the fiber in each washing run.

Fiber Polyvinyl Chloride Polyester Nylon Rayon Polyester Run NO. 1 2 3' 4 5 6 7 s 9 10 11 12 13 14 15 Tow speed entering confined zone (Ft/min) 39.5 20.0 59.0 10 40 50 60 10 40 10 40 -40 10 40 Tow speed leaving confined zone (Ft/mint 156 78.0 235 56.8 180 205 240 52 162.5 45 180 45 52 202.5 Time in coni'ned zone be up to 100 C. The preferred temperature for wash- This process may be used not only to remove solvent ing acrylonitrile filaments to remove solvent is within from a freshly spun tow but also may be used for other the range of C. to 70 C. washing such as application of a dye or finish or removal of excess dye after a dyeing process, etc. The EXAMPLE washing efficiency becomes unsatisfactory if the flow A freshly spun modacrylic tow was washed in a conrate through the washing zone is not maintained above fined zone having the following dimensions: W 3% the critical minimum value as set out above. Preferably, inches; h -"7n2 inehe s and? WT6TiHsTTh 16w the flow rate is at least three times the minimum rate bundle contained 6,000 filaments of 50 denier each. d may be many times as great as the minimum rate, The fibers in the tow had the following composition: The minimum dwell or contact time of the tow in the Acrylonitrile 60.6%, Vinylidene Chloride 23.0%, Vinyl Confined Z0116 e length of time that a given Bromide 11.0%, Styrene 1.4%, Benzene Sulfonate point on the tow requires to pass through the fluid in 2.0% and Antimony Trioxide 2.0%. the confined zone) varies slightly with the washing Water at a temperature of 96 C. and containing 4% operation. For example, if it is desired to wash the tow sodium phosphate was used for washing the fiber. The to apply a finish, a contact time of about 0.1 second or liquid flow rate was in excess of three times the critical o S all that is required. If the washing is done to i i value d h i of h tow i h treatremove solvent from a freshly spun tow a contact time ment zone was approximately 1.5 seconds. The fila- 0 0f 5 econds or more should be used. ments in the tow were neutralized from a pH of 3.9 to at is Claimed is: a pH f g 5 The method of washing a tow of filaments, comprising EXAMPLE Iv a. advancing the tow through a confined zone, and The modacrylic tow of Example 111 was washed in forcing a Stream of liquid through the low in the water at 50 C. in a confined zone having the dimensions of Example lll. A conventional dye, known to be suitable for the dyeing of modacrylic fibers, was substiconfined zone at a rate greater than x 1,000 T WN/h ,1/

"whereifiyifizn mans; mam gallons per minute, T

is the thickness of the stream of liquid in inches, W is the width of the confined zone in inches, h is the height of the confined zone in inches, N is the number of filaments in the tow, p. is the viscosity of the liquid in pounds per foot-second, and p is the density of the liquid in pounds per cubic foot.

2. The method of claim'] wherein the liquid is forced through the tow in the confined zone at a rate at least three times as great as 10. The method of claim 2 wherein the tow is advanced through the confined zone at a speed such that the tow is in contact with the liquid stream for at least 0.1 seconds.

11. The method of washing a tow of filaments, comprising,

a. passing the tow through a washing zone, said zone confining the tow in such a manner that the tow has a cross-sectional area having a width W and a height h, b. forcing a stream of liquid through the tow in said washing zone, said stream of liquid having a width W and a thickness T and also having a flow rate greater than 1,000T VWN/h (lL/P) where N is the number of filaments in the tow, p. is the viscosity of the liquid in pound s per foot-second, and

p is the density of the liquid in pounds per cubic foot.

12. The method of claim 11 wherein the flow rate is at least three times 'acrylic, nylon, polyester, polyvinyl chloride and rayon. =I=

Claims

2. The method of claim 1 wherein the liquid is forced through the tow in the confined zone at a rate at least three times as great as x 1,000T Square Root WN/h ( Mu 1 Rho )
3. The method of claim 2 wherein the liquid makes at least four passes through the tow.
4. The method of claim 2 wherein the temperature of the liquid is in the range of 30* C. to 100* C.
5. The method of claim 2 wherein the filaments are acrylonitrile.
6. The method of claim 2 wherein the filaments are modacrylic.
7. The method of claim 2 wherein the filaments are polyester.
8. The method of claim 2 wherein the filaments are nylon.
9. The method of claim 2 wherein the filaments are rayon.
10. The method of claim 2 wherein the tow is advanced through the confined zone at a speed such that the tow is in contact with the liquid stream for at least 0.1 seconds.
11. The method of washing a tow of filaments, comprising, a. passing the tow through a washing zone, said zone confining the tow in such a manner that the tow has a cross-sectional area having a width W and a height h, b. forcing a stream of liquid through the tow in said washing zone, said stream of liquid having a width W and a thickness T and also having a flow rate greater than 1,000T Square Root WN/h ( Mu / Rho ) where N is the number of filaments in the tow, Mu is the viscosity of the liquid in pounds per foot-second, and Rho is the density of the liquid in pounds per cubic foot.
12. The method of claim 11 wherein the flow rate is at least three times 1,000T Square Root WN/h ( Mu / Rho )
13. The method of claim 12 wherein the filaments are selected from the group consisting of acrylic, modacrylic, nylon, polyester, polyvinyl chloride and rayon.