IMPROVED PNEUMATIC TOW BLOOMING PROCESS AND APPARATUS This invention relates to an improved process for "blooming" or "opening" crimped multi- filament tow bands, such as for use in blooming crimped filter tows prior to conversion into tobacco smoke filter rods. "Blooming" refers to the conver¬ sion of a densely packed crimped tow into a rela¬ tively fluffy resilient flat sheet of filaments. In prior art blooming processes, the tow is removed from a bale and is spread by means of a pneumatic banding jet, then bloomed through use of semitension techniques in which alternate sections of the tow band are tensioned and relaxed with grooved metal rolls in order to deregister the fiber crimp and separate the filaments. Although relatively effective, a disadvantage of this method is that the tow must actually be stretched or tensioned to separate the filaments. This is detrimental since stretching the fiber can remove a portion of the crimp and diminish the usefulness of the tow for making filter rods having a range of pressure drop and removal characteristics, i.e. the "capability range" of the tow is diminished. This effect occurs with all semitension processes and becomes more severe as the process speed is increased. Semi¬ tension processes also do not generally separate the filaments in the tow band to an optimum degree. Consequently "tow yield", which is related to the pressure drop per unit weight that can be obtained from the fiber, is lost with a resultant increase in final filter cost.

"Capability range" is the range of pressure drop and weight characteristics which can be obtained from a given tow item, when it is manufactured into a tobacco smoke filter of fixed length and diameter. Additional capability range such as can be obtained

with the process disclosed herein is particularly important for high-speed processing of filter tow since capability range for a given tow item generally decreases as processing speed is increased. Loss in capability range can make it difficult if not impos¬ sible to obtain desired rod weight and pressure drop characteristics.

After the tow is bloomed in the above- described, semitension processes, it is generally sprayed with plasticizer for the purpose of ulti¬ mately bonding the filaments to one another to produce a firm rigid structure that will not soften or collapse during smoking. Failure of the plasti¬ cizer particles to penetrate the band is obviously undesirable and occurs primarily as the result of inadequate separation, that is inadequate blooming, of the filaments at the point of plasticizer applica¬ tion by these processes. The end result is loss of rod firmness and less-than-optimum collapse char- acteristics.

This type of process can also suffer from band width variation through the plasticizer applica¬ tion, which generally causes plasticizer application level to vary. In other processes, blooming is accom¬ plished, after plasticizer application, in a cylin¬ drical air jet. Such a process is described in U.S. Patents 3,258,823 and 3,099,594.

Another process for blooming tow is des- cribed in U.S. Patent 3,079,663. In the process described in this patent, the tow is bloomed prior to plasticiser application. In this blooming process tow is fed to the inlet of a venturi zone where it is subjected to the impingement of air or similar gas. As the gas and tow mixture leaves the venturi throat and enters the diverging portion of the venturi, the filaments diverge from one another, that is, the tow

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is bloomed. However, less than the desired amount of blooming takes place and the patent therefore teaches that it is desirable to repeat the process using a second venturi jet apparatus. Thus, the problem to be solved is to improve the blooming of the tow in this type of venturi jet prior to plasticiser appli¬ cation. This problem is solved by the present process and apparatus.

According to the invention there is provided a process for treatment of a bundle of continuous multifilament crimped tow in which the tow is bloomed prior to plasticizer application, wherein the tow is fed through a venturi first zone where the tow is subjected to the impingement of air or similar gas at the inlet of the venturi zone characterized by the steps of feeding the bundle of filaments into a partially-enclosed second zone from the exit of the venturi zone and in the second zone, momentarily confining and rapidly decelerating the linear speed of the bundle, applying compression against the mass of the bundle and allowing the bundle to be momen¬ tarily stored under conditions of low longitudinal tension, simultaneously allowing the compressed gaseous streams to expand and escape from the second zone prior to the exit for the bundle from the second zone thus. causing the filaments to relax, to bloom and to recover a portion of their crimp and thereby to form a flat wide low density tow.

The second zone will be referred to herein as the "bustle chamber" for convenience.

There is also provided a jet for treating filter tow, the jet having a rectangular nozzle assembly (46) through which tow (16) enters into the jet in banded form and a rectangular throat assembly (48) connected to the nozzle assembly and defining a venturi passage having a width greater than the banded tow and in which the banded form of tow is

caused to spread to a greater width upon being contacted by gases entering through gas passages (50, 52) into the venturi passage and becoming confined in compressed form around the tow, characterized by means connected at the outlet (58) of the venturi passage and defining a rectangular bustle chamber (60) having an inlet (62) and outlet (64) through which tow moves into and out of the bustle chamber from the venturi passage, the bustle chamber having therewithin adjustable tension means (66) for engage¬ ment against the tow to rapidly decelerate and retard its movement through the bustle chamber, the bustle chamber outlet (68) extending through and across the width of the bustle chamber at a location between the inlet and outlet and before the tension means to enable the compressed gas surrounding and accompany¬ ing the tow as it moves into the bustle chamber to expand and escape from the bus.tle chamber and includ¬ ing means (70) for restraining the tow from escaping through the outlet.

The described blooming method and apparatus operates with low pressure 21 kilopascals blower- produced air instead of the high pressure 69 kilo¬ pascals air which is normally required for conven- tional pneumatic blooming jets such as those des¬ cribed in U.S. Patent 3,079,663. Use of low pressure is possible because of the large air-to-fiber inter¬ face area provided by the flat jet and the provision of the bustle chamber. The capability of using low pressure air allows the entire process to be self- contained with regard to air supply requirements because the air may be supplied by an internal blower. This eliminates the need for the large capital investment in expensive air compressing and piping facilities.

To illustrate, for example, the degree of filament separation at the time of plasticizer

application that is possible with the process of the present invention, an average center-to-center distance between filaments on a plane perpendicular to the longitudinal axis of the tow band can be determined. When processing 3.4 D/F 45,000 total denier Y cross-section tow on this process (using only one venturi blooming jet), this distance was found to be 0.58 mm. The average distance between filaments of the same tow item as it passed through the plasticizer applicator of a conventional semi¬ tension process was found to be only about 0.20 mm. The details of the invention will be des¬ cribed in connection with the accompanying drawings, in which Fig. 1 is an elevational view in cross section of the rectangular jet and rectangular bustle tow blooming chamber;

Fig. 2 is a partial plan view of the rec¬ tangular tow blooming chamber shown in Fig. 1 and partly broken away;

Referring to Figures.1 and 2, there is shown the. combination of the flat pneumatic jet and bustle tow blooming chamber shown generally by 28, which converts the banded ribbon-like tow 16 into a wide, flat, low density bundle of fiber. This jet uses a rectangular nozzle assembly 46 and a rectangular throat assembly 48 which is connected to the nozzle assembly and defines a venturi passage having a width greater than the entering banded tow. The banded tow, which for example may have a width of about 16.51 centimeters, passes through the rectangular nozzle assembly 46 and into the rectangular throat assembly 48. The jet operates by directing or impelling two flat streams of pressurized air or gas against the tow band from passages 50,52 connected, respectively, to upper air or gas chamber 54 and lower air or gas chamber 56. This causes the tow

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band to be spread to a greater width or to a width equal to the interior width of the rectangular throat assembly, which for example may be about 25.4 centi¬ meters . The two streams of air or gas impinge on the tow band from opposite sides at an angle of less than 90°, preferably about 30°, to the longitudinal axis of the tow band.

The pressurized gases penetrate the tow band, encompass the filaments of the tow band with the gaseous streams in compressed form and propel the tow band through the jet and bustle tow blooming chamber.

The bustle tow blooming chamber is connected to the outlet 58 of the venturi passage and includes a rectangular bustle chamber 60 having an inlet end 62 and an outlet end 64. As the tow band passes from the outlet 58 of the venturi passage into the inlet end 62 of the bustle chamber, the tow band becomes confined by a tension plate 66 and is thereby forced to rapidly decelerate, its movement through the bustle chamber being retarded. The tension plate may be adjusted against or away from the tow by the adjustment screw 67, which threadingly extends through lever 69 and abuts against abutment 71. The lever is connected to pivotal rod 73, which is connected to one end of the tension plate. Simul¬ taneously the compressed gases surrounding the filaments of the tow band are allowed to expand and escape from the bustle chamber, causing the indi- vidual filaments in the band to be pulled apart and become separated or "bloomed". The compressed gases for the most part escape from the bustle chamber through vented outlets 68, which extend through and across the width of the bustle chamber at a location between the inlet end 62 and the outlet end 64 and before the tension plate 66. The vented outlets are preferably rectangular and are provided with screens

70 (upper screen not shown in Figure 2) to prevent the filaments of the tow band from escaping there¬ through along with the gases.

The bustle chamber is very significant to the tow blooming process. Without the bustle chamber the tow can be aspirated and spread to some extent, but will not be sufficiently bloomed, particularly when low pressure air is used. It also provides a location where the bloomed tow can be temporarily stored under conditions of low tension. Under the latter conditions, the fiber is free to "relax" and recover a portion of the crimp that has been extended during earlier processing steps where tension was involved. The crimp recovery in turn provides added capability range to the tow.

The remainder of the tow processing method including removal of tow from the tow bale (see U.S. Patent 2,908,045), plasticiser application and subsequent filter making are conventional. It should be noted however that it is preferred to include at least one additional banding jet (the apparatus of U.S. 2,908,045 already includes one) just prior to the venturi blooming jet. This banding jet improves the uniformity of the final filter material.