IE43484B1 - A method of and apparatus for brigthening slivers - Google Patents

Description

This invention relates to a method of and an apparatus for quantitatively applying liquid systems in the form of a thin layer to uniformly travelling slivers on the one-way principle.

Slivers are normally produced as follows on so-called silver lines: A plurality of separately produced filaments (filament yarns) deposited in cans are doubled, i.e. loosely combined into a flat sliver consisting οΓ several filaments arranged parallel to one another. This sliver then travels through a drawing arrangement and one or more washing vats where, in the case of polyamides and polyesters, soluble low molecular waight fractions or solvents, for example dimethylformamide (IMF)in the case of polyacrylonitrile, and the spinning preparation are removed.

In many cases, this is followed by vat brightening in order to coat the filaments with a thin layer of a liquid suitable for further processing. The sliver is then dried in order to remove the washing water and excess brightening agent which is generally an oil-in-water emulsion. The substantially dry sliver then enters a crimping stage normally carried out by mechanical means, after which it is fixed and, finally, cut.

In the cutting stage, staple fibres in the form of so-called flocks are cut from the sliver.

The advantage of vat brightening is that the sliver is thoroughly impregnated with the brightening agent and at any time is brightened very uniformly over its cross-section. Unfortunately, this method of brightening is also attended by several disadvantages.

Firstly, the quantity of the brightening agent applied can only be controlled within very narrow limits in baths. - 2 _ In addition, the brightening agent continuously undergoes changes in its composition as a result of impurities entrained into the brightening bath by the sliver, for example water from the washing stage, low molecular weight substances, solvents, spinning preparations after incomplete washing and particles of dirt, and also as a result of evaporation of tbe brightening agent, generally water, due to the sliver entering the brightening bath hot from the washing stage. In addition, the brightening agent can age as a result of chemical changes (e.g. oxidation, bacterial attack). All this culminates in an application which varies as a function of time, in other words the uniformity of brightening over the cross-section of the filament is high at any one time, but subject to fluctuations as a function of time.

On account of the last of the above-mentioned disadvantages, contaminated brightening agents have to be replaced at certain time intervals. Unfortunately, this gives rise to an effluent problem. In general, the sliver is dried after brightening and in this drying stage, a large amount of the brightening agent is removed under suction. This gives rise on the one hand to an emission problem and on the other hand to fluctuations in the quantity of brightening agent applied to the sliver.

In order to obviate both the first and second disadvantages, processes have been proposed and also used where the brightening agent is applied to the sliver on the oneway principle by means of one or more spray nozzles, for example two-component nozzles. This spray brightening is preferably carried out after crimping or after fixing of the crimp. A high degree of atomisation is required, being obtained by using compressed air. Spray systems of this type are described, for example, in Textil-Praxis 23 (1968), No.11, page 725 and in US-PS 5,16(1,941, OE-PS 265,958 and in PT-Gltm 7,055,(Ό.

One major disadvantage of spray brightening is the heavy loss of brightening agent. A large amount of the brightening agent does not reach the sliver, but instead is sprayed past it. In order to protect personnel and machinery, spray brightening has to be carried out in a substantially closed box. The compressed air blown in, and hence a large amount of the aerosol sprayed past the sliver, is removed under suction at the upper end of the box. This gives rise to an emission problem. Another proportion of the aerosol sprayed past is deposited on the walls of the hox and flows off from the lower end of the box in the form of a liquid contaminated with pieces of fibre and dust particles. This gives rise to an effluent problem. Spray brightening involves considerable costs on account of the loss of brightening agent. Xn this process, the quantity of brightening agent applied to the sliver cannot be directly calculated from the apparatus parameters and operational data. Instead it has to he determined hy a calibration process and repeated for each type of sliver.

The object of the present invention is to develop an economic, non-pollutive one-way process with high dosage accuracy in which the brightening agent provided is applied substantially quantitatively to the fibres.

According to the invention, this object is achieved by virtue of the fact that the brightening agent is applied to both sides of the sliver in strictly controlled quantities on the one-way principle by means of two or more slot-type nozzles. The sliver is in contact with the slot-type nozzles over its entire width. This brightening treatment is preferably carried out after the drying stage and before the crimping stage.

Accordingly, the present invention provides a method of brightening slivers,of a filament yarn derived from a synthetic polymer wherein the brightening agent is applied to both sides of the said.sliver in controlled quantities on the one-way principle by means of at least two slot-type nozzles, the sliver being in contact with the slot-type nozzles over their entire widths and the brightening treatment preferably being carried out after the drying stage ar.d before the crimping stage of the sliver production line.

It is best to apply substantially half the required quantity oi' brightening agent to each side of the sliver.

The quantity of the brightening agent is best controlled bymeans of gear pumps, in other words one gear pump is used per nozzle. In cases where there are two nozzles, it is also possible to use a double gear pump. The slot-type nozzles are preferably arranged behind on,e another at a distance of at least 10 cm on different sides of the sliver. Although it would also be possible in principle to use nozzles arranged opposite one another, this has the disadvantage that a knot present in the sliver would not be able to pass through the narrow gap between the two nozzles and would therefore give rise to disturbances. Although this difficulty could be obviated by using a displaceable nozzle, this would involve considerable outlay. If the sliver does not travel vertically through the brightening zone, it has been found to be advantageous to arrange a first nozzle above the sliver and a second nozzle below the sliver. The sliver is guided in such a way, or the nozzles are arranged relative to the sliver in such a way, that the sliver is in contact with the slot, from which the brightening agent is pumped, over its entire width. In general, each slot-type nozzle is arranged - 5 43484 perpendicularly of the sliver, the slot extending perpendicularly of the direction of travel of the sliver. Surprisingly, the sliver quantitatively takes up, without dripping, the brightening agent issuing from tlie slot in quantities of up fco about 5$ by weight, based on the sliver mass, and. in a total quantity of almost 10$ by weight in the case of two slot-type nozzles arranged on different sides of the sliver.

A major advantage of the method according to the invention is that, despite strict quantity control and lossfree, i.e. quantitative, application of the brightening agent to the sliver, the method is extremely simple to carry out and. may be incorporated in a relatively narrow space at virtually any desired point of a sliver production line. However, it has been found that, in all sliver production lines, there is one point whieh is particularly favourable for brightening by means of slot-type nozzles, namely the section between the drying stage and the crimping stage. Although brightening could of course also be carried out before the drying stage, this would again give rise to the disadvantage that part of the brightening agent would evaporate in the dryer and give rise to an emission problem. Xn addition, the uniformity of the amount of brightening agent on the sliver would suffer. Tests have shown that, when carried out after the crimping stage, the brightening treatment occasionally produces a streaky pattern of the brightening agent on the sliver. The reason for this is presumably that, due to crimping the surface of the resulting crimped sliver is never strictly flat, there are always points whieh come into contact with the nozzle under pressure and points which have no contact whatever with the slot. However, those points of the sliver which come into contact with the nozzle under Iiressurc are able to draw brightening agent out of the slot, wliieh might not be the case at those points where the sliver does not come into contact with the slot. However, if the brightening treatment is carried out before the crimping stage, it is not possible to detect any streaks left behind by the brightening agent on the sliver. Brightening is very uniform and the same on both sides of the sliver providing the two gear pumps are each adjusted to the same throughput. The brightening treatment is obviously levelled out and the brightening agent uniformly distributed homogeneously throughout the entire volume of the sliver in the crimping stage.

The squeezing roils generally mounted in front of the crimping stage are presumably of assistance in this respect.

The crimp itself is hardly affected at all by the brightening treatment where such treatment is carried out before the crimping stage. This is presumably associated with (lie fact that the sliver is not fully dried in the dryer, but still has a substantially large moisture content, with the result that the quantity of water entrained by the brightening agent is generally small in relation to the quantity of water still present in the sliver. In addition, the degree of crimp ean be adjusted within certain limits in the crimping stage taking into account the moisture content of the sliver, so that the same crimp can be obtained even where the sliver has different moisture contents. £5 For carrying out the method according to the invention, it is best for the sliver to be guided along a definite path in front of the slot-type nozzles. Experience has shown that a sliver is generally not constant in width over its length and the width of a sliver can also vary as a function of time.

Since the sliver is to be uniformly brightened over its entire width, it is important that the width of the sliver should be equal to the width of the slot of the nozzles. In - 7 34 8 4 order permanently to guarantee this, sliver guides have to he arranged in front of the nozzles. These guides may consist for example of curved rods: a rod with a convex curvature (curvature perpendicular to the direction of travel and to I the width of the sliver) for increasing the width of the sliver, and a rod with a concave curvature for reducing the width of the sliver. In eases where the width of the Sliver is adjusted to a value slightly greater than the width of the slot, the sliver and slot can he made equal in width hy means ) of boundary rods arranged at the sides of the sliver immediately in front of the nozzles.

In order to guarantee uniform application of the brightening agent over the entire width of the slot of the nozzle, which generally amounts to between 10 and JO cm, the pressure in front of the slot i.e. in the briqhtenina agent supply line must be relatively high,the uniformity of application being greater,the higher the pressure, Tests have shown that the pressure should amount to at least 0.1 bar. Pressures suitable for the method according to the invention are in the range from 0.1 to 10 bars. Although in principle there is no upper limit to the pressure, it would appear to be extravagant from the point of view of construction of the nozzle to produce much higher pressures because normally the brightening agents are liquids of relatively low viscosity and because there are limits to the width and length in which slots can be made. Since, in a slot-type nozzle, flow resistance is proportional to the length of the slot in the direction of flow and inversely proportional to the third power of the height of the slot (narrowest slot dimension), the height of the slot should be as small as possible. For economic reasons, the lower limit to the slot height is at about 0.1 mm on account of the inevitable manufacturing tolerances. - 8 Tho slot-type nozzles used in accordance with the invention are plate nozzles each consisting of two flat metal or plasties plates which are screwed together at a spaced interval of, for example from 0.1 to 0.5 mm by means of spacer strips of, for example polytetrafiuorethyl ene. The plates have a length of, for example from 250 to 500 mm (in the direction of flow), a width of for- example 200 mm and a wall thickness of for example 20 mm. The brightening agent enters the gap (slot) between the plates through a distributor whieh may consist, for example, of a prismatic funnel or of a feed channel arranged over the entire width of the slot with openings at several points of the channel. Effective distribution of the brightening agent over the entire width of the slot may readily he obtained by cutting the spacer strips arranged between the metal plates in such a way that the brightening agent enters the slot at the middle of the wide side of the nozzle and the slot then widens steadily until it reaches its full width at the exit point, i.e. the spacer members are in the form of right-angled triangles, the apex of the triangle being cut off on the exit side (ef. Figure 1).

In order more effectively to guide the sliver through the slot, guide plates are arranged in front of and behind the slot perpendicularly of, and attached to, the nozzle plates.

The sliver is drawn over these guide plates. The front edge of the first plate and the rear edge of the second plate (looking in the direction of travel) are rounded off in order to prevent damage to the capillaries. The wear resistance of these plates is best increased by means of protective layers on that side over which the sliver travels. An AlgO^ layer, produced by the plasma spraying process, may be used with advantage as the protective layer. The second plate contributes towards evening out the brightening treatment. <3484 The method and apparatus according to the invention ai-e described in more detail in the following with reference to the accompanying drawings and two Examples.

Figure 1 shows a slot-type nozzle according to the invention. 8 and 9 are metal or plastics plates which are held at a certain spaced interval by means of spaeer plates or films 12. 10 is the inlet opening and 11 the outlet opening for the brightening agent. 13 and 14 are metal or plastics plates which are used for guiding the sliver and ) evening out the brightening treatment.

Figure 2 shows a brightening apparatus according to the invention. A sliver 1 is guided over a last calender roll 2 of a dryer (not shown) into a crimping unit 3. Two plate (slot) nozzles 5 are installed in the section between the first roll of the trio 4 and the last calender roll 2. 6 and are two guide bars.

EXAMPLE 1 According to Figure 2, a polyamide-6 sliver 1 with an overall denier of 1.8 x 10^ dtex (individual denier 1.6 dtex) is washed in a bath and then dried in a calender in the usual way. After it has left the dryer, the sliver has a moisture content of 15% by weight. The sliver is guided upwards from the last calender roll 2 of the dryer into the crimping unit 3 at an angle of approximately 27°. The distance between the last calender roll and the first roll of the trio 4 in front of the crimping unit is 2 metres in the direction of travel of the sliver. A slot nozzle brightening system, consisting of two plate nozzles 5, was installed in this section without any modifications to the other stations of the sliver production line. At this point the sliver has a width fluctuation between l6o and 180 mm. The width ofi the sliver was adjusted to exactly 160 mm at a point 0.5 metre behind - 10 the last calender roll by means of a concave-curved fine steel round bar 6 which is 50 mm in diameter and two lateral guide bars 7.

The sliver travels through slot-type nozzles as illustrated in Figure 1. The two plates 8 and 9 of a slot nozzle each have a material thickness of 18 mm. The slots have the following dimensions: length 250 mm, width 10 mm on the entrance side 10, 160 mm on the exit side 11, height 0.15 mm, 0.15 mm thick polytetrafluorethylene films 12 are used both for sealing purposes and as spacer members. The first nozzle is situated 0.5 metre behind the last calender roll.

It is arranged above the sliver perpendicularly thereof and presses against the sliver. The second nozzle is situated 0.8 metre behind the last calender roll and is also arranged perpendicularly of the sliver, but below it, and presses against the sliver. A guide plate 13 with a length of 40 nun is arranged in front of each slot nozzle in the direction of travel, being coated with AlgO^ hy the plasma spraying process.

A 200 mm long guide plate 14 is arranged behind each nozzle.

The sliver travels at a speed of 200 metres per minute.

The brightening agent, in the form of a 20$ oil-in-water emulsion with a viscosity of 12 mPas at room temperature, is quantity-controlled by means of two gear pumps (each delivering ml per revolution) which are powered by a common drive and run at the same rotational speed. At a rotational speed of the gear pumps of 32 rpm,the brightening agent content of the flocks behind the cutting unit amounted to 0.67$ (petroleum ether extract). The brightening agent was quantitatively taken up by the sliver. The pressure measured immediately in front of the nozzles in the line amounted to 7.0 bars in front of the upper nozzle and 6.9 bars in front of the lower nozzle. No losses of brightening agent, either in liquid or S34 8-1 in vapour form, were detected at any point along the sliver production line after the brightening stage. The slot nozzle brightening system functioned without losses and, hence, without any danger of atmospheric pollution.

EXAMPLE 2 A polyacrylonitrile sliver of dry spun filament yarn with an overall denier of 2 χ 10θ dtex (individual denier 9.7 dtex) is washed in a bath in the usual way and then passes through a vat in which a very weak brightening treatment with an application of concentrate of from 0.06 to 0.07$ is carried out in a bath in order to ensure satisfactory travel of the sliver over the numerous rolls of the following dryer. The silver is then brightened in accordance with the invention between the dryer and erimping stage using two slot-type nozzles of the same type and with the same dimensions as described in Example 1. In this sliver production line, the sliver travels downwards from the dryer into the crimping unit which is situated at a lower level. The sliver travels at a rate of 60 metres per minute. The two slot nozzles were arranged horizontally and perpendicularly of the sliver at a distance of 1 metre therefrom, one on the left and the other on the right of the sliver. A 15$ oil-in-water emulsion with a viscosity of 7 mPas at room temperature was used. The brightening agent was quantity-controlled by means of a 2 x 10 ml double gear pump at 12 rpm. The concentrate content of the flocks (after the cutting unit) amounted to 0.31$ by weight, as determined in the methanol extract.

It is important to remember that the weak brightening treatment carried out before the drying stage produces a slight increase in the brightener content of the flocks in relation to slot-nozzle brightening alone. The brightening agent introduced through the slot nozzles is quantitatively - 12 43-18 taken up by the polyacryloni t ri i e silver. The uut 1'oJ‘Wtt.v of brightening alter the crimping stage is excellent. A piece ol' sliver 1 metre long was cut into H parallel equally wide strips (2 cm) and each strip cut in turn into 10 equally long (10 cm) pieces. Each of the 80 pieces of sliver were analysed.

All the concentrate values were in the range (0.32 + 0.02)5½.

Where It is intended to obtain a concentrate content in the flocks of approximately 0.35½ by vat brightening on the same sliver production line using the same brightening agent, the consumption of brightening agent in the vat is substantially double that in slot nozzle brightening, quite apart from the change which the brightening agent undergoes in the vat and its resulting replacement by fresh brightening agent. A substantially doubled consumption of brightening agent means that approximately the same quantity of brightening agent subsequently to be found on the flocks evaporated beforehand in the dryer.

Claims (14)

CLAIMS:

1. A method of brightening slivers of a filament yarn derived from a synthetic polymer, wherein a brightening agent is applied to both sides of a sliver of a filament yarn derived from a synthetic polymer in controlled quantities of the 5 one-way principle by means of at least two slot-type-nozzles arranged on different sides of the sliver, the sliver contacting the slot type nozzles over their entire widths.

2. A method as claimed in Claim 1, wherein the brightening agent is applied after drying of the sliver and prior to crimping in a sliver production line.

3. A method as claimed in Claim 1 or 2, wherein two slottype nozzles are used and half the required quantity of brightening agent is applied through each nozzle.

4.. A method as claimed in any of Claims 1 to 3, wherein the pressure in the brightening agent supply line in front of the slot-type nozzle is at least 0.1 bar.

5. A method as claimed in Claim 4, wherein the pressure is between 0.1 and 10 bars.

6. A method as claimed in any of Claims 1 to 5, wherein, before it reaches the slot-type nozzles,the width of the sliver is made equal to the slot width of the slot nozzles by means of guides.

7. An apparatus for brightening slivers comprising at least two slot-type nozzles each consisting of two metal or plastics plates which are held at a spaced interval by means of spacer plates or films thereby defining a slot, the nozzles being arranged to be situated on different sides of a sliver to be brightened and guide means for maintaining a width of the sliver which is equal to the width of the slot.

8. An apparatus for brightening slivers as claimed in Claim 7, wherein the slot-type nozzles are arranged at a distance of at least 10 cm behind one another in the direction of travel of the sliver.

9. An apparatus for brightening slivers as claimed in Claim 7 or 8, wherein the distance between the plastics plates or metal plates is from 0.1 to 0.5 mm.

10. An apparatus for brightening slivers as claimed in any of Claims 7 to 9 wherein metal or plastics plates are fixed to the metal or plastics plates in front of and behind the slot-type nozzle parallel to the direction of travel of the sliver and perpendicularly of an exit slot for the brightening agent.

11. An apparatus for brightening slivers as claimed in any of Claims 7 to 9 wherein spacer plates or films positioned between the metal or plastics plates of the slot-type nozzle(s) form a slot which uniformly increases in width, beginning at the middle of an entrance for the brightening agent, to an exit for the brightening agent.

12. An apparatus for brightening slivers substantially as herein described with reference to the accompanying drawings.

13. A method of brightening slivers substantially as herein described with reference to the accompanying drawings and/or either of the specific Examples.

14. A sliver of a filament yarn derived from a synthetic polymer brightened by a method as claimed in any of Claims 1 to 6 and 13.