JP3408260B2 - Apparatus and method for producing sheets of material - Google Patents

Description

Detailed Description of the Invention

The present invention relates to an apparatus for producing a sheet of material. An apparatus in which the coating is applied to the article as a liquid curtain is disclosed in GB1281512. The device includes a nozzle for supplying liquid to the tip through a liquid contact, a conductive surface, and a device for charging the conductive surface with a high voltage. The two reaction liquids associate to form a curtain as they separate from the tip and fall by gravity. When the conductive surface is charged to a high voltage, an electrostatic field is added to the liquid at the tip, promoting mixing of the two liquids. Curtain coating devices have the disadvantage that they act only downwards because the curtains fall by gravity. Moreover, they can only work with liquids that are relatively viscous, for example a few poises. Furthermore, they are only suitable for forming relatively thick coatings, for example 60 microns and above. Another device for producing sheets is a groove die. They are,
Due to the coating, it has the drawback of having to be placed very close to the article to be coated, for example a distance of 10 microns. This also means that unless the device is large, it can only be used with liquids which are not relatively viscous, for example a few poises or less, and also from Swiss Patent No. 454613 a liquid coating mixture can be applied by means of a meniscus or wavy coating technique. It is known to apply a flat layer to a liquid, the liquid being coated from a slit-like hole located near the moving layer to be coated and an electric field being applied to the liquid mixture supplied to the hole and to the back side of the layer. Is maintained between the electrically conductive element and the conductive element. In a conventional meniscus or corrugated coating device, the layer is advanced near the feed surface of the coating mixture and the liquid level is raised to form a meniscus or wave to adhere the liquid to the layer. This requires precise control of liquid level to avoid separation of coating waves from the bed. Swiss Patent 4546
According to No. 13, the precision with which the liquid level is controlled in the meniscus or wavy coating is due to the resulting simplification of the water level control device, if the electrostatic field forms a liquid meniscus or wave between the hole and the layer. Can be less stringent.

Hole widths of 0.1, 0.3, 0.5 and 0.9 mm are disclosed and described as being at a distance of 0.5 and 0.7 mm from the layer. Pore-to-layer spacing is an important requirement in determining coating speed and liquid mixture deposition layer thickness. In particular, if a high coating speed is adopted, the hole / layer spacing is reduced, the deposited layer thickness is increased, and the pore / layer spacing is reduced again. In another technique, European Patent No. 186993 describes a device for producing a spray of particles. The device includes a nozzle having a passage for supplying liquid to the tip through a liquid contact, a conductive or semi-conductive surface, and a device for charging a high voltage to the conductive or semi-conductive surface. The passageway is provided with a through hole which ends in a groove in the tip or is separated from the tip by a discharge surface. According to the present invention, a passage for supplying liquid to a tip through liquid contact, a conductive or semi-conductive surface,
A device for charging a passage, a conductive or semi-conductive surface to a high voltage, having a through hole which terminates in the groove at the tip or is separated from the tip by a discharge surface, the groove having a width of at least 250 microns. , And most of the liquid is static by the high voltage
It is made into a sheet by electric force and kept in the sheet.
To the groove with a flow rate such that the sheet shape is ejected from the groove
An apparatus for producing a sheet of material is provided having a feeding apparatus .

According to the present invention, the liquid is supplied to the tip portion and a strong electric field is generated almost at the tip portion. Thereby providing a method of making a sheet of material that is jetted from the tip. Compared to the meniscus or wavy coating device of Swiss Patent No. 454613, the device and method of the present invention forms a liquid as a sheet which is electrostatically attracted when it passes between the nozzle groove and the target. Maintained as. In the present invention, the liquid is first drawn to the pointed portion by the electrostatic field, and is thinned to the film or sheet by the acceleration force applied by the electric field. Normal,
The liquid has a specific resistance in the range of 5 × 10 ⁶ to 5 × 10 ¹⁰ . The device can be used with or without electric field modifying electrodes. Without electrodes, the electric field accelerates the sheet throughout the target. The sheet is preferably jetted under the force of gravity.

The device is capable of producing thinner sheets than that produced by curtain coating devices, and may use relatively viscous liquids, for example preferably with a minimum viscosity of 5 poises. In a special example, Dyna-clear [trade name, a coating liquid commercially available from Chemical Coatings Ltd. of Canada, used as a vehicle body dustproof coating,
This liquid has a component based on an acrylic resin and a melamine formaldehyde resin mixed in an ester solvent, and the total non-volatile component is about 70%. ]
Has a viscosity of 10 poise, and the tip length is 1 cm per minute.
Form a sheet with a minimum flow rate of 20cc. Another special example Evo
In stic (trade name), an adhesive having a viscosity of 100 poise forms a sheet at a minimum flow rate of 6 cc per 1 cm of the tip length per minute. In choosing a suitable liquid and flow rate for use in the present invention, due consideration must be given to viscoelastic actuation of the liquid. For example, Dynaclea is easily formed into a sheet at a flow rate of 20cc per cm of tip length, while Newtonian liquids, such as viscous mineral oil at 10 poise, produce more sheet flow than Dynaclea. Need.

The distance between the nozzle and the target is not a strict requirement because the liquid is reliably formed and ejected as a sheet. The normal distance between the nozzle and the target is
It is never smaller than 4 mm, for example 2 cm. However, if the electric field is kept large enough at the tip, for example by increasing the voltage, it is possible to place the nozzle, for example, 12 cm from the target without damaging the sheet. In contrast to the jetting device, the sheet is only formed for a constant viscosity when the liquid flow rate is much higher than the jetting flow rate. The higher the viscosity, the lower the actual flow rate for producing the sheet. Nevertheless, at high viscosities, the flow rate for producing sheets is significantly higher than that which produces jets at the same viscosities. In injectors, the width of the grooves is narrower, making it impractical to achieve the high flow rates required at constant viscosity to produce sheets. Moreover, as the flow rate increases, the quality of the jets deteriorates to the point of completely obscuring the interest of studying the effect of the further increase, where a nozzle with a wide width is needed. Since the particles are jetted, according to previously published research, the normal groove width is 20 to 1
A typical example of 95 microns has been found to be 125 microns.

The only purpose of increasing the groove width is to increase the liquid flow rate. With a groove width of 195 microns, the flow rate is also increased to a level where the properties of relatively less jetted ligaments are significantly inferior. The jetting technique does not require a wide groove, and the use of a wide groove suitable for jetting tends to result in an uneven distribution of liquid along the groove, especially if the jet is not directed for a vertical drop. As the flow rate increases, the quality of the jet decreases. The flow rate at which the jet still has some value is about 20% of the flow rate from the (very poor) jet to sheet formation. Compared to a groove die, the device according to the invention has a groove width that is significantly larger and independent of the thickness of the liquid sheet. This means that it is not necessary to use the high pressures required for groove dies. Gravity feed can be used. Maximum pressure is approximately 1.4 kg / cm ² (20 psi). This allows the device to be constructed of plastic or plastic composites instead of the large stainless steel devices required in the prior art.

The grooves are preferably undivided to facilitate the production of sheets of uniform thickness. In addition, the conductive or semi-conductive surface and the discharge surface are separated, the conductive or semi-conductive surface is in the inner passage and the discharge surface is non-conductive to facilitate the production of films of uniform thickness. Since the discharge surface is non-conductive, a voltage gradient develops there, creating an electric field that accelerates the liquid across the discharge surface. A somewhat stable thin sheet is obtained from this device. Embodiments of the present invention will be described below with reference to the drawings. The device shown in FIG.
It consists of two parts 2, 4 fixed together by bolts through a through hole 6 shown in FIG. 3 and a sandwiched gasket 8 (the hole is shown in part 2 but not in part 4). It has not been). The gasket defines the width of the groove 10 and the portion 2,
4 is sealed together except the groove. A particularly preferred material for the gasket is melexex sheet. The width of the groove is shown in a large scale, which is different from the other parts in the drawing. Nevertheless, the grooves are at least about 250 microns and are large compared to those used in electrostatic atomization where the ligaments are produced electrohydrodynamically. Due to the atomization the flow rate is much higher for a given viscosity of the liquid.

Behind the groove, both parts are distribution gallery
12 is formed. The cavity 12 is connected to the cylindrical supply passage 14 of the part 2. The distribution cavity 12 is large compared to that required for atomization, where the liquid supplied through the passages 14 is evenly distributed in the grooves. Since the liquid is distributed evenly along the groove, the liquid flows through the groove, that is, FIG.
The pressure drop as it flows downwards at is large compared to the pressure drop along the cavity 12, ie to the left and to the right in FIG. The parts 2 and / or 4 can be made of a conductive material for connecting to a high voltage generator (not shown). However, it is preferred to make both parts from an insulating or semi-insulating material. An example of a semi-insulating material is a paper / phenol formaldehyde resin, for example from Tufnol Kite. Conductive or semi-conductive surface 1
6 is provided by a conductive material (eg metal) inside the groove 10 or at the conductive material 18 inlet to the portion 18 and is connected at 20 to an electrical terminal.

In use, liquid is supplied to the passage 14 and flows from the distribution cavity 12 to the groove 10. The liquid in the groove 10
Contact a conductive or semi-conductive surface 16 connected to the output of a high voltage generator (not shown). Ignoring any electrodes here, if surface 16 is connected to the negative terminal of the high voltage generator, the other terminal is grounded and positive ions are transferred to surface 16.
Therefore, the liquid escapes from the liquid and a negative charge remains on the liquid. A discharge surface 22 is provided in front of the groove 10 and liquid flowing out of the groove flows to the tip portion 24 thereover. Flowing over the discharge surface helps to even out and stabilize the flow along the nozzle, making the sheet thinner. The liquid is sufficiently conductive that a strong electric field occurs at the tip 24 when it is covered with liquid. The formation of the sheet depends on having a sufficiently strong electric field. 2 cm from the target with the nozzle grounded
When placed at a distance of, a voltage range of 35-40 kv is sufficient. The advantage of this device is that without the electrode 25, there is an electric field across the nozzle to the target and the sheet can be under control.

In another embodiment, an electrode 25 is provided near the nozzle to change the electric field. The electrodes are tubes of semi-insulating material that form a sheath on the conductive core. The semi-insulating material is
It has a specific resistance in the range of 5 × 10 ¹⁰ to 5 × 10 ¹² .
Examples of such materials are soda glass, for example paper / phenol-formaldehyde resin composites from Tafnol-Kite, melamine-formaldehyde polymerized polymers. Electrical connection to each electrode is made by the conductive core. As described in European Patent No. 186983, the semi-insulating sheath increases the electrical stress between the nozzle and the electrode beyond what is possible without the sheath. Typically, electrode 25 is at ground potential or the same polarity as the nozzle, but at a lower voltage. It has been found that the position with respect to the electrode 25 is such that the electric field at the nozzle is largely defined by the potential difference between the electrode 25 and the nozzle and that the sheet is projected through the electrode and onto the target. This has the advantage that the distance between the nozzle and the target is not constant.

In another embodiment where the majority of the parts 2, 4 are insulating or semi-insulating, a conductive or semi-conductive surface is inserted at the tip of the part 4 and the tip 24 becomes conductive. Sheet formation is related to flow rate when using a liquid of a particular viscosity. Using a liquid with a viscosity of about 20 poises greater than that normally used for nozzles with 3 cm tips and curtain coating equipment or groove dies, the flow rate to obtain a spray of acceptable quality was about 10 cc / m 2. On the contrary, the minimum flow rate at which the transition to sheet formation occurred was 50 cc / m. This higher flow rate can be accommodated by using a wider groove 10 than the widest groove necessary to accommodate the flow rate required for atomization. It is impractical to use conventional atomizing nozzles at such high flow rates. The extremely high pressure required has two effects. One is to deform or damage the nozzle. The other is about 7-1.
At discharge pressures above 05 kg / cm ² (10 to 15 psi),
The liquid is to dissolve enough air so that the bubbles form a sheet as they exit the nozzle.

In order to easily produce a sheet of constant thickness, the width of the groove is practically kept as accurate as possible. It is practicable to support the walls of the groove by separate fingers in the gasket 8. However, such fingers have also been found to interfere with the uniformity of the sheet and the grooves 10 are not split, as can be seen in FIG. This makes the parts 2, 4 much larger than would be required for a sprayer. The use of the ejection surface 24 is preferred but not necessary. Two-part 2 and 4, as shown in FIG. 3, so as to define a tip 24 having a groove 10 on the tip during, has the form of the same tip. Although such a device appears to have two tips, it acts as one tip forming a sheet when the channels are connected by liquid.
In another embodiment, not shown, the conductive or semi-conductive 16 is properly placed at the tip of the ejection surface and the tip 24 becomes conductive or semi-conductive.

The tip of the illustrated nozzle is flat and straight. The tip is curved, for example circular, in the direction in which the cross section of FIG. 1 is rotated about the vertical axis to the right or left of the tip 24.
Or it may be a partial circle. In this example, the groove 10 is annular or a part thereof. In addition, the tip is placed in the plane of the gasket or sheet, for example, the tip portion
It can also be curved by rotating the cross section shown in FIG. 1 around a horizontal axis away from 4. Such a device is shown in FIG. It has a convex quadrant tip, which exhibits the property that the width of the sheet produced on a flat target is varied by varying the voltage applied to surface 16. In another embodiment, the convex tip in FIG. 5 is concave, resulting in a complete inward circle.

As can be seen from FIGS. 3 and 5, the tip 2
4 results in a large curvature at the opposite tip. This is to prevent corona discharge caused by a large electric stress generated from the tip that ends in a sharp corner. Examples of liquids used in the device are polyurethane adhesives, polyesters, water insoluble paints, moisture curable polymers, polymer melts, blown foams. The above devices and methods are useful in a variety of applications where a liquid coating is applied to a sheet-like target. One such application is to draw lines on the ground, for example to draw lane markings on roads or to define parking places in parking lots. In this example, the device can be conveniently moved so that when moving over the surface to be marked, the coating material can be applied in sheet form to the ground to draw a continuous line.

[Brief description of drawings]

FIG. 1A is a cross-sectional view of an apparatus for manufacturing a sheet embodying the present invention showing a liquid supply passage, and FIG. 1B is a partially enlarged detailed view of FIG. 1A.

2 is a partial cross-sectional view of the device of FIG. 1 showing the electrical connections.

3 is a partial plan view of the device of FIG.

FIG. 4 is a sectional view similar to FIG. 1 of another embodiment.

FIG. 5 is an assembled plan view of yet another embodiment of the present invention.

[Explanation of symbols]

2 parts 4 pieces 6 through holes 8 Gaskets 10 grooves 12 distribution cavities 14 passage 16 Conductive or semi-conductive surface 18 Conductive material 20 electrical terminals 22 Discharge surface 24 tip 25 electrodes

Continued front page    (72) Inventor Stuyuart Cliver Aude               British country. Checker. Double-way               7.4 K. Runcorn. The hee               Su (No other address is displayed)

Claims (14)

(57) [Claims] 1. A nozzle having a passage for supplying liquid to a tip through a conductive or semi-conductive surface with which the liquid contacts, the passage having at least 25 at the tip.
A device having a passage having a width of 0 micron or terminating in a groove separated from the tip end thereof by only a discharge surface, and having a device for charging the conductive or semiconductive surface to a high voltage, further comprising: Is formed into a sheet form by the electrostatic force due to the high voltage , and is maintained in that form,
It has a device for supplying fluid to the groove at a flow rate such that it is ejected in a sheet form from the nozzle, and the liquid is ejected from the nozzle as a sheet having a length of 4 mm or more. Equipment for producing sheets of the material of interest. 2. An apparatus for making a sheet of material according to claim 1, wherein the grooves have a width of at least 500 microns. 3. A device for producing a sheet of material according to claim 1 or 2, characterized in that the grooves are not divided. 4. The conductive or semi-conductive surface is divided into a discharge surface, the conductive or semi-conductive surface is in the passage, and the discharge surface is non-conductive. An apparatus for producing a sheet of the material according to any one of claims 1 to 3. 5. An apparatus for producing a sheet of material according to any one of claims 1 to 4, characterized in that the tip is curved. 6. An apparatus for producing a sheet of material according to claim 5, wherein the tip is flat in the plane of the sheet. 7. An apparatus for producing a sheet of material as claimed in any one of the preceding claims, characterized in that the tip ends at two opposite ends with a large radius of curvature. 8. A liquid is supplied to the tip of the nozzle and
Generating a strong electric field at the tip of the nozzle, the liquid flow rate and the electric field intensity, the same liquid with a sufficient magnitude to be drawn to the section pointed shape by the strong electric field, the liquid
Method for producing a sheet of material, comprising spraying a thin sheet from the tip of the nozzle by the acceleration by the electric field. 9. A method of making a sheet of material according to claim 8 including spraying the sheet onto a target. 10. The method of making a sheet of material according to claim 9, wherein the sheet is deposited on the target while the tip is moved away from the target. 11. A method of manufacturing a sheet of material according to claim 9 or 10, wherein the target is located at a distance of at least 4 mm from the tip. 12. A liquid is supplied to the tip of a nozzle to generate a strong electric field at the tip, and the flow rate and electric field strength of the liquid are such that the liquid is at least 4 mm from the tip in advance.
A method of making a sheet of material characterized by being large enough to be jetted as a sheet by electrostatic forces to a distance. 13. A method of making a sheet of material according to claim 12, wherein the sheet is jetted onto a target spaced at a distance of at least 4 mm from the tip. 14. A method of making a sheet of material according to claim 13 wherein the sheet is deposited on the target while moving the edges away from the target.