US3645233A

US3645233A - Apparatus for successively applying a plurality of coatings to a substrate

Info

Publication number: US3645233A
Application number: US18276A
Authority: US
Inventors: Ralph Ephraim Mishler
Original assignee: Globe Union Inc
Current assignee: Globe Union Inc
Priority date: 1970-03-10
Filing date: 1970-03-10
Publication date: 1972-02-29
Anticipated expiration: 1989-02-28
Also published as: FR2081824A1; DE2107080B2; CA934147A; GB1343027A; CH535479A; FR2081824B1; DE2107080A1; ES387769A1; JPS503511B1; NL7102902A

Abstract

An apparatus for successively applying to the surface of a dielectric substrate, a plurality of parallel microthin coatings with the adjacent edges forming a fine edge overlap, each coating formed from a flowable viscous plastic material having dispersed therethrough particles that exhibit discrete electrical properties so that the adjacent coatings forming the thin line overlapped junction between them have uniform and improved electrical characteristics across the junction between the different plastic materials.

Description

United States Patent Mishler Feb. 29,1972

APPARATUS FOR SUCCESSIVELY APPLYING A PLURALITY OF COATINGS TO A SUBSTRATE Inventor: Ralph Ephraim Mishler, Menomonee Falls, Wis.

Assignee: Globe-Union Inc., Milwaukee, Wis.

Filed: Mar. 10, 1970 Appl. No.: 18,276

U.S. Cl ..ll8/642,l18/412,118/413, 118/415 Int. Cl ..B05c 5/02 FieldofSearch ..l18/411,4l2,4l3,415,DlG. 9, 118/620, 641, 642, 643

References Cited UNITED STATES PATENTS Taylor ..1 18/412 2,695,005 11/1954 Lewin et a1. ..188/413 X 2,573,952 11/1951 Bretherton ..118/412 2,565,036 8/1951 MacDonald ll8/D1G. 9 1,510,465 10/1924 Dittmar ...118/415 X 2,878,779 3/1959 Biedermann et al. ..118/415 X 2,216,594 10/1940 Marchev .L ..1 18/412 X Primary Examiner.lohn P. McIntosh Attorney-John Phillip Ryan, Glenn A. Buse, Donald D. Benton and David T. Terry [5 7] ABSTRACT An apparatus for successively applying to the surface of a dielectric substrate, a plurality of parallel microthin coatings with the adjacent edges forming a fine edge overlap, each coating formed from a flowable viscous plastic material having dispersed therethrough particles that exhibit discrete electrical properties so that the adjacent coatings forming the thin line overlapped junction between them have uniform and improved electrical characteristics across the junction between the different plastic materials.

17 Claims, 6 Drawing Figures PATENTEDFEB 29 I972 SHEET 1 BF 2 INVENTOR RALPH E. MISHLER PAIENTEDFB29 m2 3. 645,233

sum 2 or 2 IN VENTOR RALPH E. MISHLER n3 w im I08 BY g ATTORNEY APPARATUS FOR SUCCESSIVELY APPLYING A PLURALIT Y OF COATINGS TO A SUBSTRATE BACKGROUND OF THE INVENTION This invention relates to an apparatus for coating a substrate from which resistor-type elements, such as linear and nonlinear resistors can be formed for use as components in sophisticated electronic circuitry where the uniformity of quality of the resistor elements is of paramount importance to their function and ability to remain operative over extended periods of time. Such resistor elements require a plurality of coatings of material having different conductive properties by forming on the surface of a substrate, such as a dielectrical substance, a plurality of coatings that are parallel to each other with adjacent coatings in a thin or fine edge-to-edge overlap relationship so that there is a fine edge junction between adjacent coatings. It is important that the resistor elements have a particular edge-to-edge relationship between coatings with the relationship being one of a fine edge overlap in the form of a reversed taper so that there is a distinct line of demarcation on the surface of the coating between the two types of adjacent materials. Such a junction produces parallel strip coatings which exhibit a smooth transition in the change of electrical characteristics from one coating to its adjacent coating. The coating of two or more conductor-type materials having different electrical properties in overlapped edge-to-edge relationship is particularly difiicult where the coatings are microthin and are applied to a thin phenolic resin substrate by striping where adjacent coatings must be deposited so as to have a fine edge junction between the edges of adjacent coatings. For example, striping a substrate with two parallel coatings of a flowable plastic material, one having silver particles therein and the other having carbon particles therein, in an edge junction relationship and curing the plastic coatings forms a basic resistor element having two zones with difierent electrical characteristics from which quality resistor elements can be made.

The prior art has employed both the spray and doctor blade techniques for coating many types of articles. Such coated articles do not have a sharp junction between coatings; for example, the spray coating of a substrate with two or more parallel strips of sprayable plastic material, each having different electrical properties, produces an edge junction between coatings of a relatively wide band of intermingling of the plastics from each plastic material due to the overspraying of one coating onto the other. This intermingling of the different materials in the case of resistor elements would produce a zone between coatings exhibiting poor electrical properties across the wide band junction of the coatings, thus resulting in a resistor element that exhibits poor electrical resolution when an electric contact element is passed from the surface of one coating to its adjacent coating.

ln like manner, the technique of doctor blade spreading known to the coating art still does not produce a consistent edge abutment of a plurality of adjacent coatings without a relatively wide zone of intermingling of the material of one coating into the other. Although the art teaches many forms of doctor blade spreading of flowable plastic materials on substrates, it does not teach means for obtaining accurate edge overlap contact between two or more adjacent coatings simultaneously applied so that there is a fine edge junction between the materials of the adjacent coats.

SUMMARY OF THE INVENTION The apparatus of this invention overcomes the disadvantages presented in the prior art by providing means for continuously striping on the surface of a dielectric substrate two or more parallel coatings, one after the other, to produce in adjacent coatings a fine and distinct edge overlap, which overlap exhibits a fine line junction between coatings. The substrate is advanced under a first applicator head having a dispensing compartment therein containing a body of flowable plastic material having particles dispersed therein that exhibit discrete electrical characteristics where a first stripe of plastic material is continuously deposited. Upon passage from in under the first applicator head, the substrate passes under a heating means where the plastic material is semicured or made nonflowable. After passage under the heating means, the substrate passes under a second applicator head having a second dispensing compartment therein containing a second body of flowable plastic material having particles dispersed therein that exhibit discrete electrical characteristics, where a second stripe coating is continuously deposited side by side of the first coating and of a thickness substantially equal to the thickness of the first coatings. The apparatus may have as many alternate applicator heads and heating means for heating a deposited coating before entry under the next applicator head as are desired.

Advantageously, the coating apparatus of this invention may provide for suitable roller means such as nip rolls to advance the substrate through its coating operation. Also, suitable edge guide means may be employed to assure that the substrate is in registry with the successive dispensing compartments so that the laydown of the stripes are in a fine reversed tapered edge overlap. It will be appreciated that each compartment is positioned over the surface of the substrate upon which the coating is applied so that the substrate can move under it with the forward wall raised at a distance equal to the thickness of the plastic material to be coated. This allows for a doctor blade means in the forward wall in each applicator head to doctor the surface of the coatings to the desired thickness as the coatings exit from under a compartment. A second roller means may be positioned downstream of the first applicator head so as to assure continuous movement of said substrate through the apparatus, particularly where continuous end-to-end abutted pieces of substrate are fed through the apparatus. The second roller means continues the travel of the substrate when it has passed through the feed rollers until it is out of contact with the flowable plastic material in the last dispensing compartment and is ready to be removed from the apparatus. The second roller means may be vertical in operation, such as an edge contact roller or rollers so that the last stripe of uncured flowable plastic coated on the substrate is not disturbed by roller action. Also, the vertical roller means may assist in maintaining one edge of the substrate against a guide means to assure registry of the surface of the substrate with stripe coating being applied.

Advantageously, the doctoring of the flowable plastic material deposited by each applicator head may be accomplished by a doctor blade that may form a forward wall of a dispensing compartment and can be adjustable so that changes in thickness of the coatings can be made when desired. Also, a micrometer biasing means may be operationally connected to said doctor blade so that the lower edge of the doctor blade may be micrometrically set to produce a microthin coating that is held to close tolerances and which is reproducible. The doctor blade used to form the forward wall of the dispensing compartments also may be bevelled outwardly and upwardly from its inner bottom edge to form a sharp edge. Such an edge form places a minimum of friction on the surface of the coating immediately passing from under a dispensing compartment.

The applicator head may be held by registering and positioning supports that assure alignment of each of the dispensing compartments with the substrate moving under them so that each stripe is deposited with adjacent edges in a fine line overlap.

In order to maintain the substrate in its proper position with respect to the bottom surface of the successively positioned compartments, spring means may be provided at each applicator head to bias the substrate upwardly so that the coating is the proper thickness. Also, the outer walls of each compartment may have its bottom edge tapered downwardly and inwardly to form a sharp edge for dispensing the plastic material onto the surface of the substrate. It is believed that by having the plastic material in highly viscous state, such as for example 1,000 to 50,000 cps., at 10 rpm. on Brookfield Viscosimeter, there is produced a condition of increased flow of the plastic material at the point of doctoring so as to produce a thin line laydown of the edges of the stripe of plastic material to provide, when cured, a fine edge overlap junction between adjacent coatings that has a substantially uniform interfacial reversed taper which produces a smooth transition in the electrical characteristics when going from the surface of one coating across the junction to the surface of the other coating.

It has been found that this range of viscosity of the plastic material effects a reproducible taper in the overlapped edges of adjacent coatings by the uniform sidewise movement of the coating outwardly towards the parallel edges of the substrate. Also, it has been found that where the plastic material is thixotropic, the apparatus of this invention produces a fine edge overlap junction between the adjacent coatings.

It has been found that only sufficient heat need be applied to a stripe coating passing from in under one applicator head to another so that the surface is given a partial curing to make it nonflowable.

The products and the method for producing the products which may be made and carried out by the apparatus of this invention are particularly set forth and described in my application for Letters Patent entitled Production of Resistive Coatings" filed concurrently herewith.

BRIEF DESCRIPTION OF THE DRAWINGS Additional advantages of the apparatus of this invention for applying, successively, a plurality of microthin coatings of flowable plasu'c materials on the surface of a substrate will become apparent from the following description of a preferred embodiment and the accompanying drawings, in which:

FIG. I is a view in elevation having a portion of its view in section as taken on the line 1-1 of FIG. 2 of an apparatus of this invention showing a guide track means and roller means for advancing the substrate, two coating applicator heads with heat curing means therebetween for applying parallel stripe coatings of plastic material, and a vertical edge roller for removing the coating substrate from under the last applicator heads;

FIG. 2 is a plan view of the apparatus shown in FIG. 1 illustrating the position of successively arranged dispensing compartments in the applicator heads in an offset position to apply two stripe coatings with a fine edge overlap;

FIG. 3 is a partial cross-sectional view on the line 3-3 of FIG. 1 showing details of the leaf spring construction for contacting the underside of the substrate when passing under apparatus heads;

FIG. 4 is a view in perspective of an applicator head showing it arranged in registry with a piece of substrate passing under the compartments therein;

FIG. 5 is an exploded view in perspective showing the component parts of one of the applicator heads and its micrometer adjusting means for raising and lowering the doctor blade; and

FIG. 6 is a view in perspective showing the body portion of a second applicator head with its compartment arranged so that it will produce a stripe coating whose edge overlaps the adjacent edge of the first stripe coating produced by the applicator head shown in FIG. 5.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings, numeral 10 represents a coating apparatus for successively and continuously applying to the surface of a substrate or base material 12 flowable plastic conducting coatings in a thin edge overlap relationship to each adjacent coating. The coating apparatus has a guide track 14 upon which the substrate is moved. Guide track 14 is supported by upright members 15 which in turn are anchored to a base 16. The track 14 is in four sections: a feed section 17, coating guide sections 18, heating section 19, and a removal section 20. Roller feed section 17 has edge guide 21 and a raised cover guide plate 22 positioned downstream thereof, both held in position by bolts 23. Coating guide section 19 has a raised guide cover plate 24 held in fixed position by bolts 25. Heating section 19 and removal section 20 each have raised retaining strips or plates 26, one positioned on each side of the track 14 extending lengthwise therewith and covering an edge portion of the parallel edge of the substrate to guide and retain the substrate in the guide track 14 during its advancement through the apparatus. The retaining plates are maintained in position by suitable bolts 28.

Positioned between feed section 17 and coating guide section 18 is a pair of horizontally disposed top and bottom

nip feed rolls

30 and 32, respectively, whose axis of rotation is normal to the centerline of guide track 14. Feed roll 30 is biased downwardly into contact with roll 32. The feed rolls 30 and 32 are covered with a soft resilient material 34, such as rubber, capable of frictional gripping of the surface of the substrate between them to move it at a constant predetermined speed through the apparatus. The top feed roll 30 operates rotationally in front and

rear bearings

36, 38 on shaft member 40. The front and

rear bearings

36, 38 are maintained in pivot arms, not shown, which provide for the downward biasing of the top feed roll 30 against drive bottom feed roll 32. The bottom feed roll 32 operates rotationally in front and rear bearings, not shown, on drive shaft member 42 with the front and rear bearings maintained in bearing blocks. Drive shaft member 42 and its rearward end has a drive pulley 44 for turning the drive shaft during operation of the feed rolls 30 and 32 so as to move through the apparatus a piece, sheet, or strip of substrate 12 when it is nipped between the rolls (see FIG. 1 and 2).

Positioned in the removal section 20 of guide track 14 is a vertically disposed edge roll 46 for contacting the edge of the substrate as it is passed along guide track 14 to convey the substrate from the apparatus. The roll 46 has a soft surface 48 thereon, such as a rubber coating. The vertical roll 46 has a drive shaft 50 which is operatively connected to a bevel gear arrangement 52 which is in turn operatively connected to a second shaft 54 that is coupled at one end to a drive motor 56 and at the other end to a second drive pulley 58. A drive belt 60 operatively connects feed roll drive pulley 44 with drive pulley 58 so that operation of motor 56 turns feed roll 32 and it contacting roll 30, which is biased thereon, and vertical edge roll 146 at a speed that maintains the passage of the substrate through the apparatus at a constant speed. Positioned opposite from vertical roll 46 is a spring biased roller means 61 that contacts the edge of the substrate and maintains one of its adjacent parallel edges in contact with roll 46 and one of the raised guide and retaining 26 and an edge of the guide cover plate 24. (see FIGS. 1 and 2) Positioned over the guide track 14 in section 23 is a set of heating lamps 62 connected to electrical wiring 64 which is in turn connected to a source of electrical power 66 for providing the necessary heat to effect a partial curing of the surface of the plastic in the stripe coating immediately after the depositing of the first coating and before it passes under the next applicator head.

Located between

guide sections

22 and 23 and removal section 24 are spaced applicator heads 70 and 71, each maintained in a fixed position with relation to guide track 14 by a set of registering and of holding brackets 72, for dispensing successively two coatings of a flowable plastic material onto the surface of the substrate 12 (see FIGS. 2 and 4). The applicator heads 70 and 71 each has a block-shaped body portion 74 with a milled out dispensing compartment, 76 formed in

head

70, and 77 in head 71, and a rectangular slot 78 in the bottom thereof of a size and shape that permits the strip of substrate 12 to pass under the dispensing compartment. The top of the body portion 74 extends forward to form an integral lip or edge 80 that defines therein a U-shaped elongated slot 82 that terminates at the top of front face 84. On each side of elongated slot 82 is a screw receiving hole 85. The bottoms of

compartments

76 and 77 are shaped so as to provide a rectangular opening that is smaller in width than the width of the major portion of the compartment, but of the width of the coating to be applied to the substrate. Each compartment has

outer sidewalls

86 and 88 and backwall 89.

Outer sidewalls

86 and 88, respectively of each of

compartments

76 and 77 at the bottom portion thereof angle towards each other to form a sharply tapered

edge

90 and 92, respectively.

Positioned in the front face 84 and spaced from each side of

outer walls

86 and 88 are

dowel pins

100 and 102, respectively, and two threaded

screw retaining holes

104 and 106, two other threaded screw retaining holes, not shown, are positioned above

holes

104 and 106. A rectangular holding block 108 defining two bolt holes 110 on one side of the front face of block 108 and two bolt holes 112 on the other side are positioned to mate with threaded screw holes 104 and 106 when bolts 113 are assembled. in like manner there are two holes, not shown, in back of block 108 adapted to receive

dowel pins

100 and 102 when the holding block is assembled to the front face 84 of body portion 74 of one of the applicator heads. The top surface of holding block 108 has a centralized wide slot 114 therein with a U-shaped slotted groove 115 extending from the front face of the block inwardly. On each side of the slotted grove 115 are vertically positioned biasing pins 116 and outboard of each side of wide slot 114 are threaded holes 117 which are in registry with screw receiving holes 85 positioned in edge 80 of body portion 74.

Between holding block 108 and front face 84 is positioned a doctor blade 118. The doctor blade is of an L-shaped configuration having a downwardly projecting portion 119 and a horizontally projecting top portion 120 at right angles to each other. The outer edge of top portion 120 has a second U- shaped slot 122 defined therein while the bottom edge of the downwardly projecting portion 119 has a tapered edge 124. The downwardly projecting portion 119 also forms the front wall for closing the

compartment

76 or 77 when abutted thereto with the tapered edge 124 presenting a sharp edge along the bottom thereof where it meets with front face 84 when the top portion 120 is positioned in wide slot 114 of the holding block 108. In this position the horizontal projecting top portion 120 of the doctor blade is positioned in wide slot 114 with the

U-shaped slots

82 and 122 in registry with slotted groove 115 with bottom surface of the top portion 120 resting on biasing pins 115 when holding block 108 is assembled to front face 84 with the doctor blade 118 therebetween.

Positioned on top of edge 80 is a micrometer holding bar 126 having a centrally disposed micrometer barrel 128 and shaft 130 positioned therein with the shaft extending vertically downward through U-shaped slot 82. The end of shaft 130 has an annular groove 132 therein adapted to be received in and retained by U-shaped slot 122 so that an incremental movement of shaft 130 by turning barrel 128 causes the doctor blade 118 to be moved vertically with biasing by pins 116 thereby assuring that a fine adjustment in height above the top surface of the substrate can be made to produce the desired thickness of coatings on the substrate. The end portion of shaft 130 projects into U-shaped slot 115. Bolt retaining holes 134 are defined hear each end of the micrometer holding bar 126 in register with holes 85 and threaded holes 117 in holding block 108. When bolts 136 of holding bar 126 and bolts 1 13 of holding block 108 are assembled, the micrometer holding bar, the doctor blade, and the holding block are united to the body portion to complete the assembly of the

applicator head

70 or 71. The assembled applicator head is removably retained in a fixed position with respect to track 14 in registering and holding brackets 72 with a set screw 139 assuring that the applicator head 70 is secured therein. The doctor blade 118 is adjusted by bringing bolts 113 to a semitight position so that the doctor blade 118 can be slideably moved up or down between holding block 108 and the front face 84 by the tuming of barrel 128.

Positioned under the bottom of both

applicator head

70 and 71 and normal to the length of guide track 14 are two spring biasing means 140 and 142. Each biasing means has a leaf spring 144 adapted to support the substrate in its proper position with respect to the bottom of dispensing compartments as it passes thereunder so that the flat surface of the substrate is always maintained in the proper relationship against the bottom of each compartment and in spaced relationship with the sharp edges of the doctor blade to provide for a constant doctoring of material on the surface of the substrate that is of uniformly deposited thickness. The spring 144 is held by holding lugs 146 which in turn are attached to the frame of apparatus 10.

in operation, the micrometer barrel 128 is adjusted in each

applicator head

70 and 71 so that the doctor blade 118 is positioned at the desired height above the surface of the substrate passing under each

compartment

76 and 77. When the proper adjustment is set, the screws 113 are tightened to place the doctor blades in each applicator head in a fixed position. With flowable plastic material having the desired electrical characteristics in each of the

compartments

76 and 77 and of such consistency that it will spread evenly when striped to join tapered edges, the motor 56 is energized, and nip feed roll 32, drive roll 30, and edge feed roll 46 are then in continuous operation.

The pieces of dielectric substrate to be coated are continuously fed flatwise on the track 14 of feed section 17 with each piece being pushed longitudinally of the bed with the forward edge of each piece in engagement with the rearward edge of the next preceding piece while the feed rolls 30 and 32 continuously advance the pieces one by one into coating guide section 18, being held in a predetermined position by spring biased roller mechanism 61. The top surface of the pieces of substrate, after passing through the coating guide section 18, passes under applicator head 70 where the top surface of the substrate receives a first stripe coating of plastic material, (designated A in FIG. 2 of the drawings) and then passes through heating section 19 where the surface of the coating is partially heat cured by heat lamps 62, and then under applicator head 71 where it receives a second stripe coating B parallel to the first and the edge of the substrate with one edge overlapping the adjacent edge of the first coating to form a thin overlap. Spring biasing means and 142 maintain the substrate in its proper relationship with the bottom of applicator heads 70 and 71, and the sharp edge 124 of the doctor blade 1 18 assures that each coating is of the proper thickness.

The tapered bottom edges outer walls of

compartments

76 and 77 cause the plastic materials to be applied to the surface of the substrate with sharply defined edges, and the doctor blade 118 assures a smooth even thickness in each coating so that a precise and sharp electrical junction line C therebetween is formed. Upon curing of the stripe coatings, the electrical characteristics across the junction were found to be of high quality exhibiting excellent resolution and a smooth transition in changing from the electrical characteristics of one surface to the other. The knife edge doctor blade produces an even thickness coating as the dielectric strip passes frogn under each

applicator head

70 and 71 with the feed rolls 30 and 32 and the edge roll 56 assuring that the strip is fed at a constant continuous rate through the coating operation. After the strip has been coated and passed from the apparatus, it is then cured to set the coatings on the substrate.

1t will be appreciated that the registering and holding plates 72 are so arranged with respect to the guide track that a multiple number of different applicator heads may be used depending upon the width of the stripe coatings desired. Also, any number of applicator heads may be used depending on the number of different stripings desired with of course heating means being applied to the stripe coating to semicure it before the next parallel coating is applied.

In forming a conductive element from which small resistors can be made, a strip of dielectric substrate of about 20 mils in thickness and about 1% inches wide may have a laydown of a first stripe of plastic about three-eighth inch wide having conductive silver particles therein and a second stripe of plastic about one-half inch wide having carbon particles therein with their adjacent edges in a thin reversed tapered overlap so that upon curing there are provided two parallel strips of plastic material having different electrical properties with a thin edge overlap junction therebetween separating the materials of different electrical characteristics. From such coated substrate can be cut crescent-type resistor elements oriented so that the ends of the resistor elements are in the stripe with the silver particles while the center of the crescent elements forms from the stripe having the carbon particles.

Also, it is appreciated that the apparatus of this invention can produce a variety of thicknesses by adjustment of the doctor blade on each applicator head. Substrates of as little as mils in thickness may be used and suitable multiple stripings have been found to be produced when the thicknesses of the stripings are from about 0.5 to about 10 mils. It has been found that plastic materials having viscosities of from about 1,000 to 50,000 cps. at 10 rpm. on a Brookfield viscosimeter with an advancement of the substrate of speeds of from about 20 to about 60 feet per minute produce excellent strip coatings having a fine line reverse taper between adjacent coatings. It will be appreciated that the speed of advancement and the viscosity of the plastic material are interrelated so as to produce the desired reversed tapered junction between adjacent coatings. Also, excellent results are obtained when the plastic material is in a thixotropic state, for it is believed that there is an edge flow of the plastic material as the substrate passes from under its respective compartment and doctor blade to produce a uniform tapering of the edges of the stripe coating so that the second stripe coating will produce a reverse taper to provide a junction in adjacent coatings of a unifonn reversed tapered overlap. Such a contact produces true, fine line junction between the adjacent edges of the stripes which brings excellent resolution and a smooth transitional change of characteristics between stripe coatings with the result that a better resistor element is made than has been produced heretofore in the art.

It will also be appreciated that many different types, sizes, and shapes of dielectric substrates can be simultaneously striped with a plurality of parallel coatings in accordance with the apparatus of this invention. Among the suitable forms of dielectric substrates are ceramics, glass, various types of plastic materials, and the like. The substrate may be in the form of pieces, sheets, films, or any other form that has a flat surface with the capability of receiving and holding the coatings applied thereto. Also, the surface of the dielectric substrate may have a group of indexing holes therein for registering the surface of the substrate with the striping of the coatings thereon so that the parallel coatings will always appear in the exact position on the substrate. Also, indexing units of resistor elements from the body of the coated substrate.

It has been found that the reversed tapered overlap between adjacent edges of said parallel stripe coatings produces a transition zone extending lengthwise on the top surface of the substrate with distinct lines of demarcation at the end of the taper portion to provide substantially linear edges, one on the surface of adjacent parallel stripe coatings and the other on the bottom of the stripe coating that is in contact with the top surface of the substrate. Thus, the reversed taper with its sharp lines of demarcation provides a transitional zone for effecting smooth change from the electrical characteristics of one stripe coating to the coating adjacent to it.

It has also been found that the alignment of the parallel edges of the substrate with the compartment outer walls that form the overlapped edge of the adjacent stripe coating particularly is effective when the registry of the edges of the outer wall is from substantial alignment to about 0.005 inch in overlap position. Such an alignment of the compartment in the one applicator head with another or the positioning of the compartment with respect to the parallel edges of the substrate so that reverse feed of the substrate after one coat has been applied produces the aforesaid positional alignment of the stripe coatings with the desired reversed interfacial tapered overlap.

It will be appreciated that any type of heat curing means may be used to partially cure the top surface of the stripe coating so that its surface is in a hardened or flowable state before it passes under the next applicator head. The heat curing means may be accomplished by heating lamps, ovens or by blowing heated air over the surface of the plastic stripe. lnfrared heating lamps are particularly efiective for inducing the partial cure.

It will be further appreciated that many changes, modifications and additions may be made to the apparatus of this in vention in which only a preferred embodiment has been illustrated and described.

What is claimed is: I

1. An apparatus for depositing successively a plurality of parallel microthin stripe coatings on the surface of a dielectric substrate with adjacent edges of the coatings having a thin edge overlap comprising: roller means for continuously advancing at a constant rate said dielectric substrate, in operational contact with said dielectric substrate before and after said coatings are applied, under a plurality of successively spaced compartments positioned in relationship to each other so as to produce a thin edge overlap between coatings, each compartment adapted to hold a body of gravity flowable plastic material containing conductive particles dispersed therethrough having discrete electrical characteristics, said compartments having sidewalls having inwardly and downwardly bevelled edges at the line of contact of deposited plastic material so that there are formed sharply defined outer edges on the stripe coating as it passes out of contact with said body of flowable plastic material; a discharge opening in the bottom of each said compartment for supplying a quantity of said flowable plastic material in contact with the surface of said advancing substrate to effect a depositing in succession of a plurality of stripe coatings thereon; heating means positioned between adjacent compartments for providing a partial curing to upper surface of a coating after deposited and before another coating is applied to said substrate; and doctor blade edge means in each of said compartments for doctor-ing an even thickness to said coatings on the surface of said substrate as it passes out of contact with said body of flowable plastic material.

2. The apparatus of claim 1 in which said doctor blade edge means includes micrometer biasing means adapted to adjust its height in relationship with the top surface of the substrate for providing said microthin coating.

3. The apparatus of claim 1 in which said doctor blade edge means forms the forward wall in each of said compartments and is adjustable to vary the thickness of said coatings as desired.

4. The apparatus of claim 1 in which said plurality of successively spaced compartments are two, one adapted to deposit a wider stripe of coating than the other.

5. The apparatus of claim 1 in which said heating means is positioned directly above said advancing substrate for partially heat curing the deposited stripe coating.

6. The apparatus of claim 5 in which said heating means are infrared heating lamps.

7. The apparatus of claim 1 in which said means for advancing said dielectric substrate is a pair of horizontally placed advancing rolls having their axis of rotation normal to the axis of said substrate and positioned for feeding the forward ends of rectangular-shaped pieces of substrate having parallel edges in succession under said compartments and an edge contacting roll that removes said substrate from under the last of said successively spaced compartments when the rearward end of said substrate has passed through said advancing rolls.

8. The apparatus of claim 1 in which said substrate is a ceramic strip.

9. The apparatus of claim 8 in which said substrate is glass.

10. The apparatus of claim 1 in which said substrate is a flexible plastic material.

11. The apparatus of claim 1 in which the substrateis a thin phenolic resin.

12. The apparatus of claim 1 in which said flowable conductive plastic material is a homogeneous mixture of a curable plastic substance and conductive particles having a viscosity of from about 3,000 to 50,000 cps. at rpm. on a Brookfield viscosimeter.

13. The apparatus of claim 12 in which said flowable plastic material is thixotropic.

14. The apparatus of claim 1 in which said edge means for doctoring each of said coatings is positioned from about 0.5 to about 10 mils above the surface of the advancing substrate.

15. The apparatus of claim 1 in which said means for continuously advancing the dielectric substrate advances it at a speed of from about to about 60 feet per minute.

16. The apparatus of claim 1 in which each of said plurality of compartments are removably held in a registering and holding means thereby permitting a variety of different groupings of compartments to be used capable of coating a plurality of different widths of stripe coatings with different compartment groupings.

17. An apparatus for depositing successively two microthin stripe coatings having positioned parallel to each other a reversed interfacial tapered overlap between adjacent coatings on the surface of a thin flat dielectric substrate having parallel edges comprising: guide track means for supporting and guiding a flat elongated dielectric substrate along its parallel edges; nip roller means for continuously advancing at a constant rate said dielectric substrate; two successively spaced applicator means each having a compartment therein, each compartment adapted to hold a body of gravity flowable plastic material containing conductive particles dispersed therethrough having discrete electrical characteristics and dispense a succession of parallel stripe coatings containing such particles, said compartments each having outer sidewalls, a rearward wall, and a forward wall; each sidewall having inwardly and downwardly bevelled edges at the line of contact of deposited plastic material so that there are formed sharply defined outer edges on the stripe coating as it passes out of contact with said body of flowable plastic material; means for registering and guiding the surface of said substrate into contact with said flowable plastic materials; means for adjusting said forward wall to doctor a desired even thickness of said parallel stripe coatings; radiant heat curing means positioned between said spaced applicator means for producing a partial cure to the surface of said deposited stripe coating before the next stripe coating is deposited; and edge roller means for continuing the removal of said coated substrate from contact with said last applicator means.

Claims

1. An apparatus for depositing successively a plurality of parallel microthin stripe coatings on the surface of a dielectric substrate with adjacent edges of the coatings having a thin edge overlap comprising: roller Means for continuously advancing at a constant rate said dielectric substrate, in operational contact with said dielectric substrate before and after said coatings are applied, under a plurality of successively spaced compartments positioned in relationship to each other so as to produce a thin edge overlap between coatings, each compartment adapted to hold a body of gravity flowable plastic material containing conductive particles dispersed therethrough having discrete electrical characteristics, said compartments having sidewalls having inwardly and downwardly bevelled edges at the line of contact of deposited plastic material so that there are formed sharply defined outer edges on the stripe coating as it passes out of contact with said body of flowable plastic material; a discharge opening in the bottom of each said compartment for supplying a quantity of said flowable plastic material in contact with the surface of said advancing substrate to effect a depositing in succession of a plurality of stripe coatings thereon; heating means positioned between adjacent compartments for providing a partial curing to upper surface of a coating after deposited and before another coating is applied to said substrate; and doctor blade edge means in each of said compartments for doctoring an even thickness to said coatings on the surface of said substrate as it passes out of contact with said body of flowable plastic material.

8. The apparatus of claim 1 in which said substrate is a ceramic strip.

9. The apparatus of claim 8 in which said substrate is glass.

11. The apparatus of claim 1 in which the substrate is a thin phenolic resin.

12. The apparatus of claim 1 in which said flowable conductive plastic material is a homogeneous mixture of a curable plastic substance and conductive particles having a viscosity of from about 3,000 to 50,000 cps. at 10 r.p.m. on a Brookfield viscosimeter.

15. The apparatus of claim 1 in which said means for continuously advancing the dielectric substrate advances it at a speed of from about 20 to about 60 feet per minute.