NO823317L - DEVICE AND PROCEDURE FOR APPLYING LIQUID IN THE FORM OF IRREGULAR SMALL DRAPS - Google Patents

Description

The present invention relates to non-contact fluidic marking devices which are usually known as "dye application" devices, more specifically the present invention relates to a liquid jet device for printing of the kind stated in the introduction to claim 1, as well as a method for selectively applying a moving substrate small drops of pressurized liquid as stated in the introduction to claim 5.

Paint application devices are generally disclosed in US Patent Nos. 3,373,437, 3,560,988, 3,579,721, 3,596,275. In all of these devices, jets (very closely spaced streams) are formed by forcing a supply of recording fluid or color from a collection line through a series of fine openings or nozzles. The chamber containing the color or the openings by means of which the jets are formed is vibrated or "stimulated" so that the jets are broken up into small drops of uniform size and at regular intervals. Each stream of droplets is formed in the vicinity of an associated selective charging electrode which establishes electrical charges on the droplets as they are formed. The trajectory of the droplets towards a receiving substrate is controlled by the effect of an electrostatic deflection field through which the droplets pass, which selectively deflects them into a path towards the substrate or towards an ink collection and recirculation device (commonly called a "drain") which prevents them from touching the substrate .

While it has been known that a fine liquid jet will break up into discrete droplets in the course of its inherent thermal and acoustic motion even in the absence of external perturbation, it has for this reason generally been assumed that special calibrated separate perturbations at or near the the natural occurrence of droplet formation was a practical necessity to produce small droplets that are regularly spaced, sized and paced across the opening row to effect proper use of the device. Writing with charged droplets requires relatively precise control of the droplet trajectories to the final position on the receiving substrate, and droplet size, spacing, and charge level have generally been considered critical factors. US patent no. 3596275 thus requires pre-perturbation devices to ensure that the small droplets in the flow occur at a distance at regular intervals and have a uniform size.

As noted in this patent, the flow has a natural tendency to break up into successive small droplets not least because of the surface tension of the fluid. While as can be easily seen by a jet of water, which is sprayed through a garden hose nozzle, the droplets are usually not uniform then in terms of size or occurrence. In order to ensure that the drops will be essentially uniform in size and occurrence, the aforementioned patent provides a device for providing what is referred to as "regularly spaced varicosities" in the flow. These varicosities provide waves in the cross-sectional size of the jet stream exiting the nozzle. It is ensured that they occur at or near the natural occurrence of the formation of the droplets. As mentioned in this patent, the frequency can be of the order of 120,000 periods per second.

A large number of varicosity-inducing devices are known in the field. US patent no. 35608988 describes e.g. an ultrasonic vibrator in the pipeline through which color is supplied from the source to the device and in US Patent No. 3579721 color is ejected through openings formed in a perforated plate which is vibrated continuously at a resonant frequency.

Since the invention of US Patent No. 3,596,275, non-contact marking devices utilizing fluid droplet streams have been commercially developed. However, it has been a characteristic feature of color jet devices that all employ some type of varicosity inducing device or "stimulator" to produce regular vibrations in the stream to provide regular and uniform droplets.

As noted in US Patent No. 3,882,508, adequate stimulation has been one of the most difficult problems in the operation of radiation droplet recorders. For high-quality recording, it has been necessary for all the beams to be stimulated at the same frequency and with almost the same power to cause the flow to break up into droplets of uniform size and regular spacing.

It is also necessary that the droplet production is not affected by the production of "satellite droplet" and that break-ups of the current in drops occur at a predetermined location near the charging electrode, both parts being dependent on the output power of each beam. The said patent shows a device for producing a traveling wave along the length of a color supply header, on which an opening plate forms one side. The waveguide thus formed is tapered or progressively reduced in width along its length to counteract and reduce the natural tendency towards damping of droplet stimulating bending waves as they travel down the length of the orifice plate.

U.S. Patent No. 3484793 also describes a liquid jet where the droplets are produced with the help of a uniform or pulsating pressure on liquids, optionally modulated mechanical vibrations, ultrasonic oscillations or the like. The same problems as mentioned above will also be found with the device according to this U.S. patent. It will therefore be necessary to have a properly pulsed pressure and the underlying requirement is also here that there should be a uniform droplet formation.

In practice, there is often an undesirable interaction between the stimulator and the dye delivery system. This adverse effect can manifest itself as a system-wide tendency to provide non-uniform stimulation across the array of apertures due to reflected and interfering waves (as mentioned in US Patent No. 3,882,508) so that certain apertures do not receive adequate stimulation while others get too much. The system thus has "peaks" or zero points which are reflected as degradation in the quality of the droplet deposition. These variations in effect mean that satellite droplets or very small droplets tend to form between each of the large droplets and cause difficulties in the system in that these fine droplets tend to escape and become dispersed in the surrounding area or below the limits of the acceptable target area . The satellite droplet formation is a sensitivity function of the properties of the dye or treatment liquid that is used so that the stimulation problem is further complicated.

Another and main limiting factor in known color application systems of the perturbation type resulting from the stimulator is that traveling waves produced by means of external or artificial perturbation devices essentially limit the length of these devices. From a practical point of view, such known devices are limited to the opening plate lengths of the transverse machine no greater than 26.67 cm where there are 120 beams per inch and the artificial perturbation device is operated at 48 kilocycles. At higher frequencies, the possible length of the perforated plates is reduced, while at lower frequencies the length can be extended.

There are numerous disadvantages associated with such perforated plate restrictions. The primary disadvantage is encountered in attempting to build a perturbed hole system suitable for processing continuously long, wide objects, e.g. including those in the textile area, corrugated cardboard, paper or other continuous long, wide widths of objects or in the case of continuously or periodically supplied forms of other wide substrates or materials where every other such goods, substrate or material area in width of about 30 cm to about several meters. Experience shows that it is extremely difficult to practically impossible to combine two or more of limited length perturbed orifice plates over the necessary distance in a manner that will effect smooth continuous processing of such goods or material sufficiently to mask the separation between the disturbed perforated plate sections -ones and/or to mask the impact of their shared different operating pattern. It becomes more difficult to provide a satisfactory result as the number of such short lengths of perturbed perforated plates is increased to span the increased width of goods to be processed.

With the present confirmation^_/iltæli^Ba^e,-^ . however, there is no significant limitation on the length of the hole plate or the degree to which such holes may be made available for use across the width of a wide or narrow substrate or receiving medium. Textile paper or other substrates that have widths varying from 61 cm to many meters can thus be processed as they are moved or otherwise guided under a simple machine-wide hole construction. Several such machine-wide openings may of course be operated in pairs or in some predetermined manner or sequence to provide any desired result.

It has been found that although the droplet breakup in an unperturbed, continuous jet system is an irregular process, the distribution of irregular droplet sizes and spacings is nevertheless rather narrow. It has also been found that with smaller opening sizes and greater fluid pressure, the variations among irregularly produced droplets can become sufficiently narrow, so that the resulting irregular droplet flow becomes useful e.g. when applying color patterns or any type of treatment agent or agents to textiles or for applying marks or treatments of various other surfaces using different liquids. - According to the present invention, there is provided a liquid jet device of the type mentioned at the outset, whose characteristic features appear in claim 1, as well as a method for selectively applying small drops of pressurized liquid of the type mentioned at the beginning, whose characteristic features appear in claim 5. Further features of the device and the method appear in the claims.

The "narrow irregular distribution effect" can be used in a device having: a source for treating liquid to be applied at a higher pressure than that normally used for equivalent accuracy of droplet placement, an array of jet orifices of smaller diameter than usual for equivalent accuracy of droplet placement, through which apertures the treatment liquid or dye medium is forced as fine streams that break irregularly into discrete droplets, electrode means for applying an electrostatic charge to the droplets as they are formed, and deflection means for directing the path of selected droplets in the stream toward a receiving substrate or toward a drain or other collecting device. The charging electrode is also more extended than with a stimulated system since the interruption point can vary more in both space and time.

Neither the device nor the method has a perturbation device that will produce a regular cyclic vibration or cause the liquid that is supplied to break into drops more evenly than with a non-perturbed irregular size distribution.

To provide a given accurate placement of the droplets or "droplet misalignment value" an unperturbed system with the same flow rate requires a different orifice size and pressure than a perturbed system. The opening size, i.e. the size must be smaller than it would be used with the same accuracy in a normal perturbed system, generally no more than about 70$ of the opening diameter of the perturbed system that has the same accuracy as the drop placement or drop error detection value. The main liquid pressure is thus alternative, mainly higher, preferably at least about four times that of an enlarged system with similar accuracy. It is also desirable that the charging voltage is higher by a factor of at least 1.5 times.

The term "drop misregistration value or misregistration error" is defined as the offset distance or variation from a straight line, measured in a direction perpendicular to the direction of movement of the substrate, to a mark on the substrate when all the beams are in a row perpendicular to the direction of movement of the substrate and are turned on simultaneously from the is captured by the drainage channel to be delivered to the substrate.

The perturbation that causes droplet disruption in unstimulated jets generally arises from the environment in which the system is placed. This fluctuation is generally produced by normal sound and acoustic motion inherent in the fluid. In somewhat "noisy" environments, however, unwanted external perturbation, such as e.g. factory whistles, vibrations from weasels and other machine movements and also sound vibrations from human voices have an impact and cause a change in the breaking point of the rays in an unstimulated system. The system can be irregularly stimulated as by a noise source that produces irregular vibrations. It is assumed that this can be advantageous when the device is to be used in a noisy area. In such an environment, the use of irregular noise vibration will surprisingly produce a more regular result from beam to beam than the use of regular cyclic vibration.

Other purposes, features and characteristics of the present invention as well as its method and operation and function of related elements and combinations of parts and the economy of manufacture will become more obvious from the following description and the requirements with reference to accompanying drawings, where all parts have the same reference numbers on corresponding parts in the different figures, and where: Fig. 1 shows a diagrammatic cross-section of a binary continuous fluid or liquid radiation device M^^ ms^ e^ iff& é---epp-f^iiffe^ l^s^enf. Fig. 2 shows a diagrammatic perspective of the droplet charging device and the droplet deflection device. Fig. 3 shows a Jio& i~ f" Ts:& ¥^ embodiment of the invention where the device is stimulated by. using an irregular noise generator driving an acoustic horn. Fig. 4 diagrammatically shows another embodiment of an irregular noise perturbed system in accordance with the invention, where a number of piezoelectric crystals add irregular noise perturbation to a fluid wall or the fluid supply manifold or the chamber.

While the invention may be similar to previously known color application recording devices in that similar results can be provided, the main principles of the present invention provide differences from such color application recording systems.

As shown diagrammatically in fig. 1 and 2, the device includes a supply liquid or source of treatment liquid 10 under pressure in a collection line or a chamber which is connected to an orifice plate 12 which has several jet openings 14. Streams or jets of liquid 16 are forced through the opening 14 which pass through the electrostatic droplet charging device 18, 18 which selectively gives the liquid charges which are retained on the droplets when the flow is broken into discrete droplets.

The charging plates 18, 18 must be sufficiently long and have a size wide enough in the direction of the jet flow to charge the droplets without regard to the irregular points at which the breakup occurs. In previously known devices, perturbation devices caused break-up in a narrow zone downstream of the openings. Without the irregular or separate, artificial or external perturbation, the breaking point will vary more. To ensure that all late breakup droplets are charged, rib-like charging plates 18, 18 must supply a field that extends to the region of the breakup of such drops. In practice, the rib-like charging plates should preferably have a size of around 100*d cm in the direction of the jet flow, where d is the opening diameter in centimeters. The width or magnitude of the direction of the drop flow could be from greater than about 30*d to less than about 300*d. The charging voltage for charging the plates 18, 18 is preferably from 50 to about 200 volts.

After charging, the droplets in the escape path pass a deflection rib or device 20 which directs the path of charged droplets towards a suitable drain or collector 22. Uncharged droplets continue towards a receiving substrate 24, which is supported by and can be transported in a predetermined manner by means of device not shown relative to the device in the direction of arrow 26. The deflection rib or device 20 is preferably operated at voltages ranging from about 1000 to about 3000 volts.

Reference should be made to known color jet devices for further details regarding structural elements suitable for use with such devices.

The construction according to the present invention differs from previously known ones in that the currents are broken up into droplets as a result of four different factors including internal factors such as surface tension, internal acoustic movement and thermal movement more than irregular external perturbation. No regular variacous induced device is used contrary to what was previously intended to be significant. The droplet formations take place irregularly.

Lord Rayleigh investigated the dynamics of fluid jets around the turn of the 20th century. He found that a fluid stream exiting under pressure from a jet orifice breaks into separate small droplets at droplet-to-droplet intervals that statistically produce the jet. The droplet diameters are on average around 2.ll*d. However, these spaces and sizes are only averages. Real breakups are an irregular process, as the actual droplet sizes and spacings vary. The actual size and spacing normally follow distribution curves around the device defined by Rayleigh's formula and by experiments by the inventor since Lord Rayleigh's work it has been found that the mean spacing is now better represented by the expression 4.51*d with 4.51 being an observed or measured number. In the device which has a paint application pressure of P equal to 0.8436 kg/cm<2> gauge pressure and an opening diameter of about 0.051 cm, the main droplet size is about 0.0102 cm. The normalized standard deviation of the droplet size, (ie the standard deviation of the droplet size divided by the main droplet size) is about 0.1, ie 68% of the drops are within 0.0010 cm of the main droplet size of 0.0102cm. The break-up point also varies from jet to jet with up to 6 droplet gaps. These differences are too great for use in many applications. When it is intended to write a horizontal line across a substrate, all the beams are commanded to write simultaneously by removing the voltage from the charging plate at all beam positions. It should be noted that if all the jets break up into droplets at the same time and the same distance from the opening plate, the system will simultaneously cause all the jets to start and release uncharged droplets and these droplets will continue to the paper in steps.

For the normalized standard deviation of droplet size of about 0.1, which is the case in practice, this corresponds to about a 32% chance that the droplets will be larger or smaller by that amount, and the spot size on the substrate will vary accordingly. This produces variations in the resulting smoothness of a horizontal line. This effect will be smaller, in that for a deviation of 0.1 with a droplet size of 0.0102 in diameter, the variation will however be around 0.0025 cm.

In the path from the breakup point, larger droplets will have more mass than smaller droplets proportional to the third power ratio of their diameter. The fluid dynamic force from the passage through the air which tends to reduce the velocity of the droplets is proportional to the square of the ratio of their diameter so that large droplets tend to maintain their large velocity in their movement towards the substrate. Assuming that all the beams are broken up simultaneously at an aperture diameter of 0.0076 cm, a distance to the substrate of 2.54 cm, a beam speed of 1000 cm/sec. and a deviation of 0.254 cm droplet diameter, however, the misregistration on the substrate will be less than 0.0051 cm.

If a beam is refracted closer to the beam plate than the main breaking point of all the beams at a number n of main droplet spacings (half of total scattering), resulting droplets (which shall be called "late drop") will have a greater distance that they must travel to the substrate than a drop from the main breaking point (which shall be called "main drop"). So far the total dispersion of the _droplet interstices that has been observed is about 6 or +3 and -3 about the main droplet. However, the drop spaces can vary from this, e.g. from about 2 to about 8, but will generally be greater than about 1. If V is the jet speed in cm/sec., d the opening diameter in cm, and V the movement speed of the substrate in cm/sec. the arrival of the late drop at the substrate will be about n (4.51 d/V) seconds after the arrival of the main drop. During this time interval, the moving substrate will have moved a distance of n (4.51 d) V/V cm. Using an example at a substrate speed of 152.4 cm/sec. (corresponding to a substrate moving 91.44 m/min.) a beam velocity of 2032 cm/sec., an aperture diameter of 0.0076 cm, n = 6 the misregistration error will be 0.0155 cm. It should be noted that if d were \I2 larger and V twice smaller, the error would be 2\/2 larger or about 0.0432 cm. The use of a smaller diameter of the opening and higher fluid pressure in the unstimulated system can thus provide less misregistration error than a perturbed system with a normal opening diameter and pressure.

In previously known devices, perturbation devices have been necessary to narrow the droplet size distribution to substantially equal to 0 in order to provide acceptable misregistration errors. However, it has been found that errors due to distribution of the droplet size can be significantly reduced under certain conditions. This is evident from the following analysis. The normalized standard deviation of the droplet size remains constant when the diameter of the orifice is made smaller and also when the pressure P is increased and in the absence of the perturbation device. If the opening diameter is reduced by e.g. a factor of the size of a square root of two (\/2), the opening area will consequently be reduced by a factor equal to two. If the flow rate is simultaneously increased by a factor equal to two, the net flow from the opening remains constant.

For similar charge and deflection fields, the drop paths remain constant, but the natural frequency is now 2\/2 higher and there are now 2\/2 as many drops formed per time unit and the escape time (path time) until the substrate is halved. If the break-up point with a full-sized beam varied by six drops due to the irregularity of the break-up which is often the case, a typo would occur six times the break-up time interval times the speed of the substrate. With the smaller jet of higher pressure, the same error in the cut-off distance will result in an error only l/2\/2 as great, i.e. 2.12 instead of six or only 35$ of the above error. Furthermore, the fluctuation in density will now average over 272 drops, if there is a 32% chance that the droplet radius for the larger opening case varies by 10% with a corresponding volume variation of 33$ there will only be a 9% chance that the smaller opening system will vary thus.

Although in principle a stimulated system can be designed to deliver droplets at high speed, in practice errors occur at intervals of up to two droplets. With an unstimulated system, the break-up point can vary over six to seven drop intervals, but by reducing the orifice size and increasing the pressure, this error can be reduced to that of a stimulated system with a larger orifice size, so that the advantage of an essentially unlimited orifice plate length is still given.

For this purpose, the orifice size may generally be in the range of 0.0008 to 0.05 cm and the fluid or liquid pressure may be in the range of 0.14 to 35 kg/cm<2> gauge pressure. The drop value misregistration error may be less than about 0.254 cm for applications on substrates having a relatively smooth surface, while for applications on the substrate having relatively non-smooth, rough or fibrous surfaces, the drop value misregistration error may be less than about 1.016 cm or also 2.3 cm where such misregistration could be acceptable, such as where writing or the image is only to be viewed from a distance.

More specifically, it has been found that general application of a liquid to treat a substrate requires an aperture diameter of about 0.0102 cm with a center to center spacing of the apertures of about 0.0406 cm. The main fluid pressures behind the openings can vary from about 0.14 to 2.1 kg/cm<2>gauge pressure. However, the preferred pressure range varies from about 0.2 to 0.5 kg/cm<2> gauge pressure. The substrate can be moved at a speed (V) of about 0 to 1300 cm/sec. with a preferred narrower range varying from about 12 to 380 cm/sec. and where the preferred speed is about 152.4 cm/sec. or 91.44 cm/min.

More general ranges for the parameters involved, which include aperture and pressure ranges, are a jet velocity (V) ranging from 500 to 8200 cm/sec. with preferred speed range from about 500 to 1300 cm/sec. for general purpose liquid application and the preferred jet velocity is around 1000 cm/sec. Also in certain cases the substrate can be moved at a speed greater than 1300 cm/sec. so that speeds of 2000 to 2600 cm/sec. and this device could be used to write at such substrate feed rates.

Fine writing, coloring and/or image application on substrates similar to the results that can be provided by a perturbed system can be provided with the present invention by using an opening that has a diameter of about 0.0033 cm with suitable center to center spacing. The pressures will be greater than in the general application circumstance above and will range from about 1 to 5 kg/cm<2>manometer pressure with a preferred pressure of about 2 kg/cm<2>manometer pressure. The jet speed will preferably vary from around 1500 to 2500 cm/sec. with the preferred speed of about 2000 cm/sec.

The color viscosity, color ability or treatment liquid is limited only by the properties of the particular treatment liquid or coloring medium relative to the opening size. From a practical point of view, the liquid or medium will generally have a viscosity of less than about 100 eps and preferably about 1 to about 25 eps.

Since the present invention can provide application devices of almost any opening plate length, as described earlier, the range of application, unlike previously described perturbed systems, is extremely large. This is because the beam openings can not only be constructed in very short lengths, such as a few cm, but they can also extend to any desired distance, e.g. 0.0254 to 460 cm or longer. The present invention is therefore suitable for use with wide weaves or where relatively large surfaces are to be colored or described with marks of one type or another. An example is writing, coloring or otherwise applying images to textiles, but it should be noted that this is not the only application of the invention. Similarly, the properties of the receiving substrate can vary greatly.

In textile applications, all textiles are dyed and dyes and dyes can be used, which are either natural or synthetic as long as they can be combined with the material from which the substrate is constructed, such as stainless steel or other materials resistant to chemicals or combinations of these and which are also compatible with the opening size that it is desirable to use. (Materials with large particles can cause unwanted clumping). Suitable textile dyes include reactive, dyeboiler, spreader, direct, acid, base, alizarin, azoic, naphthol, pigment and sulfur dyes. Included among suitable coloring agents are inks, dyes, vegetable dyes, varnish colors, stains and mineral colors.

Included among the treatment types are any desired writing, coloring or imaging agent or medium, including fixing agents, dispersing agents, salts, reducing agents, oxidizing agents, bleaches, resists, fluorescent brighteners and adhesives as well as other known chemical processing agents such as various resins and reactants and components thereof in addition to further additives and modifiers.r. It is believed that all such materials could be effectively used according to the present invention to provide desired effects on a number of substrates such as e.g. all types of paper and paper-like products, clothing and textile fabrics of various woven, knitted, sewn, knotted, felted, wadding, spun and other non-woven types, metal foils, plastics, glass, plaster and similar composite sheets, various laminates including plywood, chipboard and various fibers and resin composites similar to masonite or other materials as well as a myriad of surfaces including flat, curved, smooth, rough or various other shapes.

^ hnxuzj& X& rir& f^^ . 1 and- -' 2 -^'r^i^fk^e^p^-t-u^b^r-^^ As previously mentioned, background or other vibrations in the area can in themselves sometimes act as perturbation devices and produce unwanted variable result-E,. /lFig. 3-,ogn, 4 show£?a?=føG&L£2!!§&& implementation fornK of i n n r e t n i rig e nvyrnv o f*— the system is not regularly perturbed, but subject to irregular, or noise perturbation that exceeds or masks such background vibrations.

In fig. 3, the noise source includes an amplifier 30 which supplies noise from a resistive or other electrical source 32 to a transducer such as an acoustic horn 34. The horn emits the noise vibration to the fluid or the collecting line. These irregular perturbations can be added to the fluid using known transducers, but the perturbation they add here is irregular and not regular.

In fig. 4, the noise transducer is a set of piezoelectric crystals 40 which are arranged on the wall 42 of the fluid manifold 12. Other types of transducers can be used which are known in the field. The difference is that they are driven in a narrow range of irregular frequencies, non-regular frequencies.

It has been described that the mldt frequency of the noise approximated the natural frequency of the droplet breakup. This is about V/4.51 d cycles per second where d is the beam diameter in cm and V is the speed of the beam cm/-sec. The bandwidth is preferably less than about 12,000 cycles/sec. so that the irregular vibrations are most effective in providing interruption.

Claims (1)

<\> Liquid jet device for printing, of the type where droplets of pressurized liquid (^ 10), flowing out from a series of openings (14), are selectively directed to strike or not strike a substrate surface (24),/and where the series of openings ( 14) extends in a relief (cross-machine direction) across the direction of movement of the substrate (26), characterized by random perturbation device including a generator (32, 30) for random signals driving an electroacoustic transducer (34, 40) coupled to the liquid (10) to artificially induce random droplet formation processes in the liquid streams (16) from said openings (14)y/ by essentially avoiding traveling waves or other non-uniform stimulation effects over the length of the aperture row associated with regular periodic perturbation which would, if regular periodic perturbation were used, limit the maximum transverse machine size. 2. \ Device according to claim 1, characterized in that it includes: charging electrodes (18) located downstream of the openings (14) and extending across the zone of random droplet formation to selectively impart electrical charge to the droplets as they are randomly formed, and deflection electrode (20) located downstream of the charging electrode (18) to deflect electrically charged droplets away from the surface of the substrate (24). 3. Device According to claim 1 or 2, characterized in that the source of random perturbation includes: one. noise source (32, 30) providing electrical noise signals at an output; \ \ a selective bandpass filter^ (narrowband filter) connected to the noise source output to receive said electrical noise signals from the noise source (32, 30^) and to emit at the filter's output only the part of such signals that occur within a predetermined frequency band; and an electro-acoustic transducer G40) connected to the output of the filter to receive said filtered output signals and to transform them to correspond to mechanical vibrations. Device according to claim 1, 2 or 3, characterized in that the electro-acoustic transducer (40) is one that uses only a predetermined band of signal frequencies within a bandwidth of less than about 12,000 Hz. 5. Method for selectively applying to a moving substrate (.24) small droplets of pressurized liquid (10) radiating from a series of <apertures> ( <14> ) extending in a direction (cross-machine direction) transverse to the direction of movement ( 26) to the substrate (24), / characterized in that a random drop formation process is induced artificially in the liquid flows from said openings (14)\ by means of a generator (30, 34; 40) for random acoustic signals/ by essentially avoiding traveling waves or \ other non-uniform stimulating effects over the length of the opening sequence associated with the regular periodic perturbation which, if regular perturbations were used, would limit the maximum transverse machine size. 6. Method according to claim 5, characterized \ in that the randomly formed droplets are effectively supplied with electric charges and that such charged small droplets are deflected from the surface of the substrate (24). 7. Method according to claim 5 or 6, characterized in that electrical noise signals are generated, that only those noise signals that occur within a predetermined frequency band are passed through to an electrical output terminal, and that the passed-through noise signals are transformed into acoustic vibrations that are coupled to act on the fluid. 8. Method According to claim 5, 6 or 7, characterized in that the acoustic signal used occurs within a bandwidth of less than about 12,000 Hz. 9. Method according to claim 5, 6, 7 or 8, characterized in that a substrate is used which includes a continuous length of textile material which is moved across the transverse direction of the machine.