DE2715037A1 - METHOD FOR ELECTROSTATIC FLOCKING OF AREAS - Google Patents

Description

Case 2H

PFENNING MAAS
MY IG - LEWKE - Mockery

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40

SOLAR SUEDE CORPORATION Lexington, Kentucky, V.St.A.

Process »in the electrostatic flocking of surfaces

The invention relates to a method for producing coatings by electrostatic means and in particular relates to a method which enables a coating layer of highly conductive flake fibers, ie of particles with a length of over, to be electrostatically applied to a surface coated with an adhesive to apply about 0.25 mm, the electrical resistance being about 5 10 to about 1 χ 10 ohms. These particles are to be distinguished from dry powder particles which are used in the electrostatic application of coatings and which are less than about 0.25 mm in length and in which the electrical resistance is greater than about 1 10 ¹¹ ohms.

There are already various electrostatically operating methods and devices for applying coatings

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Paint, powders or flake fibers are known on wall surfaces or other surfaces. A typical procedure of this kind Measures can include the desired coating material to a hand-held applicator gun containing one or more electrodes charged to a high voltage Has electrodes, by means of which the coating material is electrostatically charged that an electrostatic Field is built up between the pistol and the object to be coated. The object is usually earthed, so that the oppositely charged coating material is attracted to the article and hence the process proceeds to produce a coating quickly and with high efficiency, with little waste of coating material or does not hit the object. The electrostatic field also causes the charged coating material to surrounds grounded object, so that at the same time facing away from the pistol surfaces of the object receive a coating. Of course, if the paint is liquid, it is easy to cause the coating material to adhere to the object. In the case of other covering materials, for example flake fibers, on the other hand, it is necessary to seal the object with an adhesive before the flake material is electrostatically applied to adhere to the article.

In the case of electrostatic application of coatings, it is very Difficult to dry, i.e. non-liquid coating materials for the spray gun with a precisely controlled throughput rate to feed. While liquid paint can easily be pumped through a hose to the gun, with itself can regulate the desired throughput rate, require Powder and flake fibera special measures. With powders It is therefore up to (now common practice to let the dry powder particles be carried away by a stream of air, and for this purpose use is made of a so-called fluidized bed · In such a bed, the particles are shaped a thin layer spread over a flat surface, supported by numerous fine air currents from bottom to top

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is flowed through. This causes the particles to to form a people above the flat surface, and this people is then caught by another air stream for delivery to an applicator gun.

Such fluidized beds have not proven themselves in every respect when flake fibers are to be applied, because such Fibers tend to clump or tangle on a fluidized bed, and they have a higher fill factor than powder. Another Problem, What results from the electrostatic flocking process using a gun is that it has been so far after the flock fibers have been entrained by a stream of air, the fibers are deemed necessary as they exit the gun from the airflow. This is to ensure that the flock fibers in the direction of the to be flocked Object can be moved almost exclusively by the action of the electrostatic field to form a flake coating to create. For the purpose mentioned, the gun is provided with several deflection elements to remove the flock fibers from the to remove airflow carrying them after they have been charged. This prevents the Fibers at high speed onto the object to be coated are thrown and that they ricochet off the object. If one considers the driving effect of the transporting the fibers The air flow is not used, however, the distance over which the fibers are drawn with the aid of the gun is reduced can be thrown off. Furthermore, the direction in which the fibers move towards the object is less straightforward influence. Finally, it does not remove excess fibers that are not held in place by the adhesive layer, with which the object was previously coated. These factors make a slip-on pistol useful the surfaces of the object facing away from it are restricted, inner surfaces and depressions are not flawless Coated and a uniform coating is not obtained on all parts of the object.

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Attempts have been made to improve the supply of flock fibers to a flocking gun. For example is in US-PS 3,551,178 has been proposed to pass the flake fibers through a sieve and then through openings of adjustable Size drop, whereupon they are carried away by a stream of air that transports them. This air flow promotes the entrained fibers to a flocking gun, where they are removed from the carrier flow in a known manner by means of deflection elements be separated. However, there are limitations with regard to the fiber throughput rate, the regulation of the Direction of movement of the charged fibers and the distance over which the fibers can be thrown off.

Thus, the process of separating the charged fibers from the air stream carrying them is the same Disadvantages to be calculated as with the known electrostatic flocking process, in which excess amounts of fiber a storage container falling under the effect of gravity in the direction of the earthed object to be covered, while the object is moved between two electrically charged grids. These grids create a Ionization zone through which the fibers fall. Some of the fibers are electrically charged in the ionization zone, whereupon the fibers are attracted to the or any earthed object. However, the greater part of the fibers fall down within the ionization zone so that these fibers do not get onto the objects and / or that they are only loose are held in place by other fibers which are in turn in contact with each other in a physical way as non-glued fibers stand with the adhesive coating.

The invention now provides an electrostatic flocculation process has been created in which the difficulties and disadvantages of the known methods are avoided by that it is possible to feed flock fibers in a controllable manner to an air stream transporting them, and at the same time is possible to cause the airflow to help move the charged flock fibers towards the upper

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fitch · of the sä flocking object ku move and the not old to remove fibers connected to the object by the adhesive.

In one embodiment of the method according to the invention a device is used in which the fibers to be precipitated are kept ready in a storage container, which is closed at its lower end by a sieve. A rotating brush is arranged just above this sieve, which can be rotated in a controllable manner to raise pebbles at a controlled throughput rate falling through the sieve. The fibers fall through into a trough equipped with a vibrator which the fibers are axially aligned and fed to the inlet of a Venturi tube, where they are propelled by one of them Air flow can be detected. This stream of air conveys the flock fibers to and through the flocking gun; this gun has several electrodes charged to a high voltage, which are located in a nozzle at the outlet end are arranged and serve to charge the fibers electrostatically.

The electrostatically charged fibers are discharged from the nozzle of the gun by the said air stream in the direction of the grounded, object coated with adhesive is thrown off. Here, fibers are deposited on the adhesive film on the object deposited, but the fibers that do not bond with the adhesive are blown away by the air flow and either sucked off or whirled back into the ionization slide between the pistol and the object so that they again attracted to the object and brought into contact with the adhesive film then holding them in place.

An embodiment of the invention is explained in more detail below with reference to schematic drawings. It shows:

Fig. 1 is a perspective view of a system for performing the electrostatic flocking process according to the invention;

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FIG. 2 shows, essentially in vertical section, a device for feeding flock fibers to a flocking gun; FIG.

Fig. 3 is a section along the line 3-3 in Fig. 2;

FIG. 4 shows an enlarged axial section of the flocking gun according to FIG. 1; and

FIG. 5 shows an end view of the mouth of the flocking gun according to FIG. 4, drawn on a considerably larger scale.

The electrostatic flocking process according to the invention can be carried out with the aid of the system according to FIG. 1, which includes a storage container 12 for flock fibers which has a device which enables flock fibers to be fed to the flocking gun 14 at a regulated throughput rate. The fibers have a resistance of about 5 10 ⁵ to about 1 χ 10 ¹¹ ohms, and the gun 14 is supplied with an electrical voltage from a DC voltage source 16 in order to electrostatically charge the fibers when they leave the gun. The gun is held in the hand by an operator 22 and is used to fling the flock fibers in the direction of the object 24 to be flocked. The object 24, which has previously been coated with a film of adhesive, is electrically grounded in a manner not shown, and an electrostatic field 25 is established between the gun and the object, so that positively charged flock fibers 20 are attracted to and with the object be firmly attached to him. The electrostatic field has the advantageous effect that the charged fibers are attracted from all sides in the direction of the earthed object 24 in order to produce a coating on it.

The container 12 shown with further details in FIGS. 2 and 3 has a removable cover 27, to allow refilling as needed. The bottom of the container is made up of two inwardly inclined, downwardly converging ones Walls 28 formed, the lower ends of which by a

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Transverse spacing are separated and a fiber dispensing opening 29 delimit. At the opening 29, the two walls 28 are angled inward so that two horizontally arranged folds 30 are present, which carry a removable sieve 31. So that fibers are pressed through the sieve 31 can, there is a rotatable brush 32 which extends above the opening 29 directly over the sieve and, as shown in FIG. 3, is driven by a motor 37 connected to a control panel 33, soft 1 is arranged on the outside of the container. The switchboard is connected to a power source (not shown) connected.

The fibers fall under the action of gravity through the sieve 31 into an elongated trough 34, which is equipped with a vibrator 35 is provided; the vibrator is connected to the control panel 33 via the brush drive motor 37 so that the brush

32 is always set in rotation when the vibrator 35 is switched on. The trough 34 is shown in FIG. 2 under one inclined downwards at a small angle so that the fibers picked up by it reach a discharge funnel 36. Since the Fibers are vibrated as they move along the trough 34, a large portion of the fibers become longitudinally oriented until the fibers enter the funnel 36 from the trough.

The funnel 36 leads the fibers continuously to the inlet of a Venturi tube 40 to which a compressed air flow from a Air pump 42 is supplied from which from the control panel

33 is powered off. In the Venturi tube 40, the fibers are entrained by the air flow acting as a blowing agent, and the fibers are conveyed together with the air stream through a hose 54 to the flocking gun 14.

The mesh size of the sieve 31, the speed of rotation of the brush 32 and the flow speed in the venturi 40 all depend on the type, length and denier weight of the used flake fiber material. The fibers can be one length

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from about 0.25 to about 6.4 mm and weigh from about 1.5 to about 30 denier. Are the fiber parameters within of these limits, the mesh size of the screen 31 can correspond to about 8 to about 50 meshes per inch. Furthermore it is If these parameters are observed, it is possible to place the brush 32 at a distance of approximately 6.4 mm above the sieve 31 or in one smaller distance down to a direct contact with the sieve and arrange them with a speed of about 5 to drive about 150 rpm. Furthermore, with fibers whose parameters are within the stated ranges, it is possible To pass compressed air through the venturi 40 at a throughput rate of about 55 to about 285 Itr / min. With this one The air throughput can be about 28 to about 280 g of flock fibers per minute through a tube 54 with an internal width of about 16 mm. Here, the flow speed of the air stream and the fibers carried along by it lies between about 600 and about 1500 m / min. It is possible to work with higher flow velocities, but there is if 1500 m / min is exceeded, there is a risk of too high a percentage of fibers on the surface to be flocked blown past and not deposited and that fibers that have bonded with the adhesive film on the surface, get knocked over and disoriented.

Various types of flocking guns can be used to carry out the method according to the invention; one Embodiment of a pistol 14 is shown in Figures 4 and 5; it has a generally cylindrical barrel 56 a downwardly angled handle 72. A longitudinal channel 58 extends through the barrel in front of the handle 72, which is at the front At the end of the run it merges into an outlet nozzle 62. The compressed air hose 54 for supplying the flock fibers 20 entraining airflow is through a connector 60 at the bottom End of the handle 72 connected to a tube 61 which connects the fitting to the channel 58 of the barrel. Consequently the flock fibers 20 are conveyed by the air flow through the entire gun 14 and at the front end over the nozzle 62 submitted.

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A second connector 64 for attaching an electrical conductor 66 is attached to the lower end of the handle 72, which latter the gun 14 according to FIG. 1 with the high voltage source 16 connects. The conductor 66 protrudes into the pistol 14 and can be actuated with a finger Low voltage trigger switch on the front of the handle 72 connected. The trigger switch 70 can be actuated manually by the operator 22 in order to switch a relay 73 on press, by means of which the conductor 66 is connected to the high voltage source. The high voltage is from the connector 64 from three charging electrodes 76 supplied via a large current limiting resistor 74, which opposite one inclined surface 61 of the gun nozzle 62 protrude outward. According to FIG. 5, the electrodes are at equal angular intervals distributed around the channel 58 of the gun barrel and extend parallel thereto up to the vicinity of the free end of the nozzle 62 within the path of fibers dispensed by the gun. If the electrodes are connected to the high voltage source 16, they are charged with a voltage of about 10 to about 150 kV to create an electrostatic charge of the flock fibers 20 as they exit the gun 14 and an electrostatic field between the gun nozzle and to build the earthed object 24 to be flocked.

Of course, in order to protect the operator 22, there are those parts of the gun that are under the high voltage Parts come into contact, made of electrically insulating material. Of course, the pistol can also be stationary or reciprocally mount in a mechanical holder, which is actuated accordingly, so that the pistol does not need to be held in the hand by the operator. This arrangement is particularly advantageous when there is no need to manually move the pistol to clear facing or recessed areas of the Object to flock.

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When flocking certain objects, e.g. the inner walls of cylindrical objects, it is advisable to use the flocks spread out radially. For this purpose, an arm star 90 can be built into the nozzle 62, which according to FIG. 4 a Component # 2 carries a small diameter. The component 92 protrudes axially outward relative to the arm star and carries a diffuser 94, which in the present case is designed as a removable and displaceable conical body. Is located the diffuser 94 on the component 92, it is arranged exactly in the middle of the air stream expelling the fibers from the nozzle. Thus, the diffuser causes the fibers in the air stream opposite the exit end of the nozzle along a conical surface be thrown outwards. The closer one moves the diffuser 94 along the component 92 to the arm star 90, the more the diffuser spreads the fibers emitted by the gun.

The diffuser and its holder only serve to give the spray of fibers the desired shape, however not to electrically influence the flock fibers. In view of this, these parts consist of an electrical non-conductive material.

In carrying out the method, the fibers are dispensed from the container 12 to the trough 34, where a large part of the fibers are aligned in the longitudinal direction and from which they enter the venturi 40. The conveying air flow then picks up the fibers and transports them through the gun 14, where they are electrostatically charged. The air flow further aligns the fibers so that they are dispensed from the gun in the aligned condition. The charged fibers are blown through the electrostatic field 25 with the aid of the gun and deposited on the adhesive film on the object 24. Here, the air flow gives the fibers 20 such a speed that those fibers which do not get caught on the adhesive film are blown past the article 24 to be collected for reuse, or that they rebound and re-enter

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the electrostatic field 25 enter to focus on the object to be deposited where they are held by the adhesive film can be. This prevents fibers that do not bond with the adhesive film from physically connecting become entangled with the fibers held in place by the adhesive, and therefore no areas of high fiber density are created which are used for the Tend to peel off.

The method according to the invention was applied, for example, to electrostatic way of flocking automobile sun visors; the sun visors were covered with an adhesive film and then coated with nylon fibers about 1 mm long, weighing 3 deniers and having a resistance of 1 χ 10 ohms flocked. The fibers were fed through the sieve 31, which was 12 meshes per inch with the brush 32 in contact with the screen and rotating at 47 rpm. The fibers were fed into the venturi 40 at a rate of about 95 g / min while the air flow of the venturi tube was about 85 ltr / min. As the fibers were being dispensed from the gun 14, tension was applied of 80 kV is applied to electrodes 76. Under these conditions, the sun visors were very uniform and dense flake coating.

Claims :

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Claims (1)

EXPECTATIONS 1; Process for the electrostatic application of a coating made of flake fibers on an adhesive coated Surface, characterized in that dry flake fibers with the action of gravity a length of about 0.25 to about 6.5 mm and a weight of about 1.5 to about 30 denier in compliance with a regulated Throughput rate are fed to a Venturi tube that a transport air flow with a throughput rate from about 55 to about 285 ltr / min is passed through the venturi to entrain the fibers therein the fibers along with the air flow through and per se in a substantially continuous flow channel along this channel extending electrodes are moved past in order to charge the fibers electrostatically, and that It causes the air flow and the electrostatic charge of the fibers towards the fibers from the electrodes move the surface to be flocked so that the fibers are held in place by the adhesive on the surface. 2. The method according to claim 1, characterized in that the fibers resistance values of about 5 χ 10 to about 5 χ 10 Have ohms. 3. The method according to claim 1, characterized in that the speed of the air flow transporting the fibers is about 600 to about 1500 m / min. 4. A method of electrostatically depositing a coating of flake fibers onto one coated with an adhesive Area, characterized in that dry flake fibers under the action of gravity in compliance a controlled throughput rate are fed to a Venturi tube that an air stream in compliance a regulated flow rate through the venturi 70984 1/0969 -ie- is directed to pick up and entrain the fibers that the air flow and the fibers through one substantially continuous channel of a tubing and an electrostatic Charge gun are directed so that the air stream and fibers exit the gun, causing the fibers to pass through the air flow is thrown off in the direction of the surface, and that the fibers are electrostatically charged and aligned as they exit the pistol using electrodes attached to the pistol in such a way that they extend generally parallel to the direction of movement of the air stream and fibers within the gun to it to allow the airflow and fibers to flow through the gun in a substantially uninterrupted manner. ö. The method according to claim 4, characterized in that the throughput rate of the air stream is about 55 to about 285 ltr / min and that the fibers have a length of about 0.25 to about 6.5 mm, a weight of about 1.5 to about 30 denier and
Have ohms. Denier and resistance values from about 5 10 to about 5 χ 10 6. The method according to claim 4, characterized in that the fibers under the action of gravity in compliance fed at a controlled throughput rate through a sieve to a trough which is open at the top and inclined downwards and that the trough is vibrated to align a substantial portion of the fibers in the longitudinal direction and feeding the fibers from the trough out of the venturi. 709841/0969