Title of Invention

AN APPARATUS USEFUL FOR THE PREPARATION OF UNIFORM FILMS OF A VISCOUS FLUID

Abstract

An apparatus useful for the preparation of uniform filsm of a viscous fluid which comprises a movable structurally rigid bridge (1 & 2) having a spreading edge (27) characterized in that the said spreading edge being provided with spindles (26) held in eyelet shaped holes (25) the said spreading edge fixed to the said bridge by means (metal brackets) (21 to 24), the said spreading edge being provided with means (rack & pinion, fromt plate) {15 to 20) for vertical movement, the said bridge being movably fixed by means (at lease three ball bearings) (10,11, 12) on rails (13), the said rails being provided with leveling screws (8) at its bottom and spirit level (9) for horizontal leveling, the said rails having at its top a base (6) for holding a substrate (5) between spacers (7), pulleys (3 & 4) being rotatably fixed at both ends of the said rails (13), the endless wire (28) connected (14) to the said bridge to provide horizontal movement, one of the said pulleys being connected to a prime-mover.

Full Text

The present invention relates to an apparatus useful for the preparation of uniform films of a viscous fluid. Presently films of viscous fluids are formed by various methods such as spraying, brushing, settling, roller coating, dipping, flow coating, edge (knife)coating, fluidi2ed bed coating etc. A number of commercial equipments utilizing these techniques are available but suffer from the following drawbacks. In spraying method, there is a lot odf wastage of the material as well as the environmental problems. It necessitates careful +masking of adjacent areas. Brushing is a slow manual process and does not yield good uniform coatings. Gravity settling of powders in a fluid is again a slow process and involves handling of a lot of solvent. Roller coating is dependent on type of surface preferably porous, and the skill of operator . To obtain a good layer by dipping one has to control many variables such as viscosity, solvent concentration, temperatures etc. The amount of the fluid in the dip tank is also an inhibiting factor. Flow coating method is highly dependent on manner in which the object is hung . It tends to from drop beads on edges thereby affecting the uniformity of coating. In edge coating technique for making films, the jerks of the moving parts in the machine affect the uniformity of the layer formed. Fluidized bed coating technique is highly sophisticated techniques and is of very limited application. It is mainly meant for forming uniform layer of solid particles with the help of a gas. The most commonly used mechanical apparatus for making films on flat surfaces employ a straight edge to spread the coating material. The thickness of the coating is controlled by adjust- ment of clearance between the edge and the base surface. Adaptation of the edge coating principle to continuous sheets or webs may require support of a base sheet under the coating edge by a roller (1) as shown in Fig.l of the drawings accompanying this specification. The coating edge has been marked as (2) and coating compound is indicated as (3). The base surface (4) is moved by the roller (1) or any other drive mechanism. The support for base surface can be by an endless rubber blanket as shown in Fig. 2 of the drawings. Endless rubber blanket with the driving rolls is shown as (1) in the figure. Knife is marked as (2), the coating compound is (3) and the base surface is (4). The coating edge (2) can be floating as shown in Fig. 3 of the drawings and depends upon web tension to support the base surface against the edge. Support for the base surface (1) consist of a channel and roll, floating edge is (2) and coating compound being (3). The base surface (4) moves in the direction of roll. An air loaded rubber diaphragm or impingement of a direct air jet for forcing the substrate against the edge are other methods to support the substrate. The contour of the edge may be sharp as shown in Fig 4 of the drawings, or rounded as shown in Fig. 5 of the drawings depending on the characteristics required of layer formed. Sharp edge reduces the penetration of coating into porous surfaces and fills surface unevenness. The rounded edge is good for smoothing heavier coating thicknesses. The spreading edge can also be of flexible spring steel which i3 inclined to substrate surface. A variation in coating edge design permit literally divided coating reservoirs at the knife edge to deposit multicoloured stripes longitudinally on the coated sur- face. To coat molten plastics having good flow characteristics a wire wound blade or roll is also used as spreading edge. Notched spreader blades are used as spreading edge for application of adhesives to floors when laying tiles or linoleum. Some coating equipments use sequential coating edges of different designs to achieve better finish in stages. The object of the present invention is to provide details of an apparatus useful for the preparation of uniform films of a viscous fluid. The present invention describes an apparatus which is different from the ones available and uses the edge and base in a manner that there are almost no jerks during formation of films and uniform films of the fluids involving a solution, hot melt, homogeneous mixture of liquid reactants or a slurry are obtained. The method which we devised to overcome the above mentioned problems and to make uniform films of the viscous fluids involves spreading technique. For this a simple apparatus has been fabricated. The details of such an apparatus for the preparation of uniform films of viscous fluids is not described in the published literature or any the patent to the best of knowledge of the patentees. The present invention provides an apparatus as shown in Fig. 6 (a & b) of the drawings accompanying this specification useful for the preparation of uniform films of a viscous fluid which comprises a movable but structurally rigid bridge (2), a spreading edge (27) that may be a wedge or roller, a geared electric motor or any other driving mechanism for uniform speed of the bridge, base of the apparatus (6) for holding substrate (5) with two lengthwise side spacers (7), fixed rails (13), set of ball bearings (10,11,12) for smooth movement and to avoid jerks in horizontal and vertical direction, rack and pinion arrangement, (15-20) for up-down movement of the wedge, dual spring loading (21-24) of the wedge to take care of micro non-uniformities, wire and pulley arrangement (3,4,14) for movement of bridge parallel to the substrate and the base. Accordingly, the present invention provides an apparatus useful for the preparation of uniform films of a viscous fluid which comprises a movable structurally rigid bridge (1&2) having a spreading edge (27) characterized in that the said spreading edge being provided with spindles (26) held in eyelet shaped holes (25), the aid spreading edge fixed to the said bridge by means (metal brackets)(21 to 24), the Said spreading edge being provided with means (rack & pinion, front plate)(15 to 20) for vertical movement, the said bridge being movably fixed by means (at lease three ball bearings)(10,11,12) on rails (13), the said rails being provided with leveling screws (8) at its bottom and spirit level (9) for horizontal leveling, the said rails having at its top a base (6) for holding a substrate (5) between spacers (7), pulleys (3&4) being rotatably fixed at both ends of the said rails (13), the endless wire (28) connected (14) to the said bridge to provide horizontal movement, one of the said pulleys being connected to a prime-mover. The detailed working of the present invention described above is given with reference to the Fig. 6 (a&b) of the drawings. The movable bridge (2) carrying a spreading edge (27) which may be an edge or a roller of materials that are wetted by the fluid used, moves uniformly along the base (6) of the apparatus by means of a geared electric motor or any other driving mechanism which can give a smooth uniform speed. Substrate (5) held fast on the base of the apparatus with two spacers(7) attached to its top surface on which the spreading edge moves. The viscous fluid is poured lengthwise in front of the spreading edge on the substrate at the starting point. It is spread by the edge(27) on the substrate in the form of a thin uniform film as the bridge moves. The thickness of the layer is determined by the spacers. The base of the apparatus is a rigid flat piece fitted with leveling screws (8) and spirit level(9) that help to keep it and the substrate perfectly horizontal. The rigidity of the base takes care of the surrounding micro shocks and vibrations. On the sides of the base are provided rails (13) on which the bridge moves. The bridge is made rigid by joining two metal end plates (2), one on either side of the base, with three metal rods(l). The end plates are fitted with ball bearings (10-12) in a special arrangement as wheels that move along the rails (13). Each set of bearings on either side consists of five balls bearings. Three of these ball-bearings(12) engage part of the rails and stop any movement in vertical direction. Other two bearing (1Q&11) are there to take care of movement of bridge in horizontal direction. The bridge is left to move smoothly in both forward and backward directions along the length of the base. The height of the spreading edge (27) the substrate is adjusted by means of rack and pinion (15-18) arrangement. The spreading edge is fitted horizontally at the two ends by metal brackets (24). The spindles (26) of the edge are supported freely in eyelets (25) and edge is also spring loaded in vertical direction for allowing the edge height to adjust vertically to any non-uniform- ity of the substrate. This consists of springs (23), rod (22) fixed to the edge and guide-holes in metal brackets (21) fixed to front plate (20) of the bridge. These holes guide the rods (23) during vertical movement. This further ensures that the edge keeps riding on the spacers without any intervening gaps during spreading thereby further improving the uniformity of the film formation. There are two freely rotating pulleys (3 & 4) fixed on one side of the base at either end. The shaft of the pulleys is fitted with ball bearings for smooth movement. The line joining the center of the pulleys are parallel to the rails. A straight wire (28) is put on the pulleys so as to allow a linear motion of a point on the wire. When the pulleys are rotated a point on the wire moves in a perfect straight line parallel to the rails. The bridge is connected at one point of the wire between the pulleys for movement of the bridge and it covers more than the length of the substrate. One of the pulleys is driven by constant speed electric motor or any other drive mechanism. The construction of various parts, their assembly and detailed working of the present invention as described above results in a mechanical spreading apparatus for the preparation of uniform films of a viscous fluid. The thickness of the films can be adjusted from 10 to 250 µm depending on viscosity of the fluid. The uniformity of the films is within ± 5% of the total thickness. Uniform films are important for processing of devices where precise control of parameters essential. Viscous fluid can either a solution, hot melt, homogeneous mixture of liquid reactants or a slurry etc. Scope of making uniform films has increased immensely with advancement of electronic industry and demand for better finish. Liquid crystal displays, electroluminescent displays, audio and video tapes and other coatings with special materials are the applications that require highly uniform films where the present apparatus can be gainfully employed. We claim: (1) An apparatus useful for the preparation of uniform films of a viscous fluid which comprises a movable structurally rigid bridge (1&2) having a spreading edge (27) characterized in that the said spreading edge being provided with spindles (26) held in eyelet shaped holes (25), the aid spreading edge fixed to the said bridge by means (metal brackets)(21 to 24), the said spreading edge being provided with means (rack & pinion, front plate)(15 to 20) for vertical movement, the said bridge being movably fixed by means (at lease three ball bearings)(10,11,12) on rails (13), the said rails being provided with leveling screws (8) at its bottom and spirit level (9) for horizontal leveling, the said rails having at its top a base (6) for holding a substrate (5) between spacers (7), pulleys (3&4) being rotatably fixed at both ends of the said rails (13), the endless wire (28) connected (14) to the said bridge to provide horizontal movement, one of the said pulleys being connected to a prime-mover. (2) An apparatus as claimed in claim 1 wherein the movable structurally rigid bridge is made by joining two end plates with three rods or pipes. (3) An apparatus as claimed in claims 1-2 wherein the spreading edge may be a roller or wedge. (4) An apparatus as claimed in claims 1-3 wherein the base (6) is a rigid flat piece. (5) An apparatus as claimed in claims 1-4 wherein the spacers (7) used are of wire or a flat tape for control of uniformity and thickness of the film. (6) An apparatus as claimed in claims 1-5 wherein a set of three or more ball bearings, one running against vertical surface and other two against horizontal surface of the rails is used on either side of the bridge. (7) An apparatus as claimed in claims 1-6 wherein rack and pinion arrangement is used for vertical movement of the wedge (27) to adjust with the thickness of the substrate and the film. (8) An apparatus as claimed in claims 1-7 wherein the wedge (27) is supported at its ends by spindles (26) held in eyelet shaped holes (25) in support brackets (21,24) and is spring loaded (22,23) in vertical direction. (9) An apparatus useful for the preparation of uniform films of a viscous fluid substantially as herein described with reference to figs 6(a&b) of the drawings accompanying this specification.

Documents:

2372-del-1995-abstract.pdf

2372-del-1995-claims.pdf

2372-del-1995-complete specification (granted).pdf

2372-del-1995-correspondence-others.pdf

2372-del-1995-correspondence-po.pdf

2372-del-1995-description (complete).pdf

2372-del-1995-drawings.pdf

2372-del-1995-form-1.pdf

2372-del-1995-form-2.pdf

2372-del-1995-form-3.pdf

2372-del-1995-form-4.pdf

2372-del-1995-form-9.pdf

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