US3361109A

US3361109A - Emulsion coating system

Info

Publication number: US3361109A
Application number: US519315A
Authority: US
Inventors: Ellwood J King
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1966-01-07
Filing date: 1966-01-07
Publication date: 1968-01-02
Anticipated expiration: 1985-01-02

Description

" Jam. 2, 196s E. J. KING 3,361,109

EMULSION COATING SYSTEM Filed Jan. 7, 1966 2 Sheets-Sheet 1 Jan. 2, 1968 E. J. KING EMULSION COATING SYSTEM 2 Sheets-Sheet 2 Filed Jan.

United States Patent 3,361,109 EMULSIUN COATING SYSTEM Ellwood J. King, Newbury Park, Calif., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Filed Jan. 7, 1966, Ser. No. 519,315 11 Claims. (Cl. 118-209) ABSTRACT 0F THE DISCLOSURE The present invention relates to an apparatus for producing a uniform coating of coating material on the surface of a substantially planar substrate using a dispensing apparatus for dispensing the coating material toward a means for distributing the coating material on the substantially planar substrate. The means for distributing the coating material has a curved bottom structure lying on and contacting the surface of the substrate and includes an opening through the means for distributing the coating material to allow the coating material to fiow through the opening and onto the surface of the substantially planar substrate. In one embodiment of the invention, the means for distributing -is a spherical shell and in the second embodiment the means for distributing is a trough-shaped member. In both embodiments the opening is preferably away from the area of contact between the curved bottom and the surface of the substrate so as to allow for the coating material to ow to the surface of the substrate. When the apparatus of the present invention is used to coat a disc member, the disc is rotated and the distributing means is moved in a radial direction along the surface of the disc as the disc is rotated. In order to insure a uniform coating of the coating material, either the rotation of the disc -is variable or the radial movement of the distributing means is variable so as to produce a uniform area loading on the disc.

This invention relates to an apparatus for producing a coating of a material, such as an emulsion material, on a substrate. The shape of the substrate is not limited to any particular conguration and may have varying configurations such as a disc, tape or plate. In particular, the present invention relates to an apparatus for producing a very thin uniform coating of the emulsion material on the substrate. Specifically, the present invention relates to an apparatus for producing a coating of the emulsion material on the substrate wherein the coated substrate may be used as a recording medium in a high-resolution recording system.

The emulsions which may be coated by the apparatus of the present invention generally are considered to be of the photographic type. Although the emulsions are generally characterized as of the photographic type, this does not mean that the emulsions may be exposed only by the use of visible light energy. For example, the recording of information on the emulsion coating on the substrate may be produced by sensitizing the emulsion for exposure by energy having wavelengths other than the visible band. For example, the use of infrared or ultraviolet energy may be used to expose a properly sensitized emulsion, and a particularly useful means of exposing the emulsion material is the use of an electron beam. The use of an electron beam for recording has certain advantages, since it is relatively easy to modulate and control the electron beam when compared with other types of energy such as visible light. One difficulty with the use of electron beam recording is that the recording must take place within a partial vacuum. The recording within a partial vacuum gives rise to a relatively complex recording structure and, in addition, requires that the emulsion material is iirmly adhering to the surface of the substrate.

One specic example of a high-resolution recording system uses a substrate having a disc shape which has been coated by the coating apparatus of the present invention with the emulsion material. Information may be recorded on the coated disc by rotating the disc and by exposing progressive portions of the emulsion coating the disc along a spiral path in accordance with the information. The exposing of the progressive portions of the emulsion material in accordance with the information may be accomplished by directing an electron beam toward the rotating coated disc and by modulating the electron beam with the information. The spiral path of the recorded information on the surface of the coated disc may be produced by either moving the disc while rotating relative to the position of the electron beam or by moving the electron beam relative to the rotating disc or by producing a deflection of the electron beam in a radial path as the disc rotates,

After the emulsion material on the coated disc has been exposed at the progressive portions along the spiral path, the emulsion material is developed in a normal photographic manner to produce translucent and opaque areas on the surface of the disc in accordance with the information. The translucent and opaque portions of the developed emulsion material may now be used to reproduce the recorded information using optical techniques. In addition, if it is desired to produce copies of the original` recording, the copies may be produced from the original recording by normal photographic means such as by the use of a contact print or by projection methods.

In order to obtain the maximum density and resolution of the information recorded on the disc, the spot size of the electron beam is maintained as small as possible and an emulsion material is used which has a grain which is ultrafine. In addition, it is desirable to maintain a very thin uniform coating of the emulsion material on the substrate. The use of a very thin uniform coating of emulsion material helps to lower the effect of the emulsion material on the electron beam during the recording of the information and on the light beam during the reproduction of the information. Specifically, the uniformity of the coating helps to eliminate any effects in the recording and reproduction due to variations of thickness on the different beams of energy. Also, maintaining a very thin coating of the emulsion material reduces the spreading effect of the emulsion material on the various beams of energy used in recording and reproducing and helps to maintain a high-resolution recording of the information.

It is to be appreciated that the above method of exposing the `emulsion material coated on the substrate is illustrative only and that properly sensitized emulsion material may also be exposed by other forms of energy such as visible light or infrared or ultraviolet energy. Prior art apparatus for coating emulsion material has not been able to produce the desired very thin uniform coating of emulsion material onthe substrate. It has, therefore, been difficult to use substrates, as coated by the prior art apparatus, as a recording medium in highresolution recording systems. The present invention is directed to an apparatus for Coating a substrate, such as a disc, plate or tape, with an emulsion material so that the coating of emulsion material across the surface of the substrate is very thin and uniform.

The emulsion material is applied to the surface of the substrate in a wet state, but the present invention applies the emulsion material in an extremely uniform manner and controls the thickness of the emulsion material in the wet state to a desired value. As the emulsion material dries, it shrinks to significantly reduce the thickness of the emulsion material. However, the relationship of the wet to dry state of the emulsion material follows a constant pattern which may be reproduced in succeding coatings with a high degree of accuracy.

As an example, the emulsion material may have a relationship of its thickness from the wet to diy state by a constant factor such as a factor of 38. rfhis would mean that the emulsion material as applied by the apparatus of the present invention to the surface of the substrate shrinks by a factor of 38 times from its wet to dry thickness. As a specific example, the deposition of a wet lm of emulsion material of a thickness of 0.0075 inch produces a dry film of emulsion material of a thickness of approximately 0.0002 inch, which is approximately 5 microns thick.

Although the use of a S-micron layer of emulsion material on the surface of a substrate produces excellent results when information is recorded by progressively exposing the emulsion material, the apparatus of the present invention can produce coatings of emulsion material on the surface of a Isubstrate having dry thicknesses thinner or thicker than 5 microns. Specifically, the apparatus of the present invention produces a coating of an emulsion material on the surface of a substrate wherein the emulsion material has a high degree of uniformity across the surface of the substrate and wherein the em-ulsion material has a controlled thickness which may be quite small in comparison to prior art emulsion coatings.

The present invention generally produces the uniform coating of the emulsion material by first maintaining a controlled flow of emulsion material from a dispensing apparatus. The emulsion material flows into a means for providing a uniform distribution of the emulsion material across local areas of the surface of a substrate. The dispensing apparatus and distribution means provide a coating station and the substrate is moved relative to the coating :station to produce a uniform coating of emulsion material across the surface of the substrate. In order to control the uniformity and thickness of the coating of the emulsion material, the present invention maintains very close control of three particular operating conditions. These conditions are: First, the flow rate of the emulsion material from the dispensing apparatus must be accurately maintained. Second, the velocity of the substrate which is being coated relative to the coating station must be accurately controlled. Third, and most important, means must be provided for producing a high degree of distribution uniformity across at least local areas of the substrate.

Maintaining a control over the flow rate of the emulsion from the dispensing apparatus is generally not a diicut problem. For example, a glass separatory funnel may be suspended over the substrate and the rate of flow of emulsion material from the funnel may be easily controlled by a value structure. This type of funnel and value structure is corrunon in laboratory use. The valve structure is generally set to produce a constant rate of flow of emulsion material. The rate of flow is generally measured in drops per second. It may be desirable sometimes to control the setting of the valve structure s0 as to produce a non-uniform rate of ow of emulsion material.

The control of the relative velocity `of the substrate in relation to the coating station is again not a particularly diicult problem. For example, if the substrate is a tape which is moving on a longitudinal direction, the tape may be maintained at a constant velocity by a capstan drive system. The coating station, for example, may be suspended over the tape and when the tape is moved at a constant velocity, of course, the relative velocity between the coating station and the tape is maintained at a constant value.

The maintenance of the constant velocity between the substrate and the coating station does present problems when coating a substrate which has the shape of a disc. The coating of the emulsion material on the disc may be accomplished by suspending the coating station above the disc as the disc rotates and by then moving the coating station radially so as to produce a spiral path between the coating station and the rotating disc. When the rotation of the disc is maintained at a vconstant rate, then the velocity between the coaing station and the disc varies in acordance with the radial position between the coating station and the disc. When the rate of ow of emulsion material from the `dispensing apparatus is maintained at a constant rate, then the unit area loading of the emulsion material on the surface of the disc would vary in accordance with the radial position between the coating station and the disc.

The varying of the unit area loading of the emulsion material on the surface of the disc would produce a nonunform layer of emulsion material. The non-uniformity of the thickness of the emulsion material on the surface of the disc may be corrected in various Ways. For example, one embodiment of the invention corrects for the non-uniformity of the thickness of emulsion material by varying the spacing between adjacent turns `along the spiral path produced by the relative rotational and radial movement between the coating station and the disc. The variation of the spacing of the turns along the spiral path is designed so that the unit area loading of the emulsion material on the surface of the disc is constant at all points along the spiral path of the coating station relative to the disc. Another embodiment of the invention corrects for the non-uniformity of the thickness of the emulsion layer by varying the rotational rate of the disc so as to produce a constant velocity between the coating station and the disc and to achieve a constant unit area loading of the emulsion material. A third method which may be used to correct for the non-uniformity of the thickness of the emulsion material would be to regulate the rate of flow of emulsion material from the dispensing apparatus so as to produce a constant unit area loading of the emulsion material on the rotating disc.

The third condition for producing a uniform thin emulsion coating on the surface of the substrate is in the use of a means for assuring a high degree of uniform distribution of the emulsion material across local areas of the surface of the substrate. Prior art methods do not spread the emulsion material evenly over the surface of the substrate. For example, if the dispensing apparatus would merely drop the emulsion material on the surface of the substrate, this would produce an uneven thickness of the emulsion material on the surface of the substrate due to the periodic dropping of the emulsion material. The emulsion material does not have the consistency to cornpletely spread out evenly over the surface of the substrate, but rather tends to stay lumped up at places where the drops of emulsion material fall on the surface of the substrate. Prior art methods of leveling the coating of emulsion m-aterial which use such means as brushes, Scrapers, etc., produce coatings which are adequate for normal photographic purposes, but which would be inadequate for use in a high-resolution recording system. Moreover, due to the desirability of maintaining a very thin coating of emulsion material on the surface of the substrate, any non-uniformity in the very thin coating has a relatively larger effect than with a thicker coating. For example, a 2-micron variation in a S-micron coating is a 40% variation, whereas a 2-micron variation in a 100- micron coating is only a 2% variation.

The present invention, therefore, incorporates novel means to uniformly distribute the emulsion material on the surface of the substrate and, in addition, to act as a hydraulic lter so as to smooth out the flow of the emulsion material from the dispensing apparatus. For example, when the apparatus of the present invention is used for coating a disc, an upper chamber is lled with emulsion material and is supported over the disc. As mentioned above, a valve arrangement controls the rate of flow of the emulsion material from the dispensing apparatus at a particular value. A light spherical shell is supported under and moves with the dispensing apparatus to continuously receive the flow and store a small amount of the emulsion material from the dispensing tank. The light spherical shell is arranged so that it lightly rests on the surface of the disc and it is attached to the same support as the dispensing apparatus so that a xed relationship is achieved between the dispensing apparatus and the spherical shell. A small opening in the bottom of the light spherical shell extends from the inside of the shell to the bottom surface and the opening is off-center from the point of contact between the surface of the disc an-d the spherical shell to allow emulsion material to drain onto the surface of the disc.

The emulsion material which drains through the opening in the spherical shell forms a smooth meniscus ring approximately centered about the contact point between the disc and the spherical shell. The size of the opening in the spherical shell is selected so as to produce a particular thickness of the emulsion material on the surface of the disc and to maintain a desired head of emulsion material in the spherical shell when the rate of flow of emulsion material from the dispensing apparatus is set at a desired value and taking into account the relative velocity between the spherical shell and the rotating disc. Although the flow characteristics from the dispensing apparatus are periodic, for example, 2 drops of emulsion material per second, the llow characteristics from the bottom of the spherical shell to the surface of the disc are Very smooth and uniform. The spherical shell, therefore, acts as a hydraulic lilter to smoothout llow irregularities from the dispensing tank. In addition, the flow of the emulsion material through the opening in the spherical shell wets the area as dened by a meniscus ring around the contact point between the spherical shell and the disc so as to uniformly distribute the emulsion material across a local area of the disc. The spherical shell, therefore, uniformly distributes the emulsion material to the surface of the disc and produces a uniform coating across the entire surface of the disc after the spherical shell makes a complete spiral path.

When the apparatus of the present invention is used to produce a coating of emulsion material on the surface of a substrate such as a plate or a tape, the means for uniformly distributing the emulsion material to the surface of the substrate is a trough having a cylindrical bottom surface. When used to produce a thin uniform coating of emulsion material on a tape, the trough sits across and contacts the tape along a line. The trough may be maintained in a stationary position while the tape is moved underneath the trough using conventional means such as a capstan drive. One or more dispensing apparatuses are supported above the trough and dispense a llow of emulsion material into the trough. The trough has a slit opening which extends from the inside of the trough to the bottom surface of the trough, and the slit opening is substantially parallel to the contact line between the bottom of the trough and the tape.

The slit opening in the trough allows the emulsion material to drain onto the surface of the tape, and, in addition, allows the emulsion material to form a meniscus along the cylindrical 'bottom surface of the trough to evenly distribute the emulsion material across the tape as the tape moves relatively to the trough. As with the spherical shell, the trough contains a head of emulsion material so that the trough acts as a hydraulic filter to smooth out the irregular flow of emulsion material from the dis-` pensing apparatus. Again, the wetting of the cylindrical bottom surface of the trough as defined by the meniscus produces the even distribution of the emulsion material across the tape.

A clearer understanding of the invention will be had with reference to the drawings, wherein:

FIGURE 1 is a block diagram of a first embodiment of the invention for producing a uniform thin coating of emulsion material on the surfrace of a disc;

FIGURE 2 is a block diagram of a second embodiment of the invention for producing a uniform thin coating of emulsion material on the surface of a disc;

FIGURE 3 is a detail view of the spherical shell of either FIGURE 1 or FIGURE 2 and the surface of the disc;

FIGURE 4 is a diagram of a means for removing the spherical shell from the surface of the disc without disturbing the uniformity of the coating of the emulsion material;

FIGURE 5 is a block diagram of an embodiment of the invention for producing a uniform thin coating of an emulsion material on the surface of a tape; and

FIGURE 6 is a detail view of the trough of FIGURE 5 and the surface of the tape.

In FIGURE l, a first embodiment of the present invention is shown for producing a uniform thin coating of an emulsion material on the surface of a disc 10. The disc 10 is rotated in a counter-clockwise direction, as shown by an arrow 12, by a motor 14, at a slow rate so that centrifugal forces are kept at a low value and do not play any part in the coating of the surface of the disc 10. The rotation of the disc ltl by the motor 14 is shown schematically in FIGURE 1 and it is to be appreciated that any appropriate method of driving the disc 10 from the motor 14 may be used. A dispensing apparatus 16 having an upper chamber 18 is positioned over the disc 10. The upper chamber 18 is lled with emulsion material 20 and the rate of flow of the emulsion material 20 from the dispensing apparatus is controlled by a valve 22.

The dispensing apparatus 16 is supported above the disc 10 by upper and lower arm supports 24 and 26. The upper and lower arm supports 24 and 26 extend from a rigid .post 28. In addition, a flexible arm 30 extends from the lower arm 26 to support a spherical shell 32. The spherical shell is positioned under the end of dispensing apparatus 16 to receive the flow of emulsion material 20 from the dispensing apparatus 16. The spherical shell 32 rests on the surface of the disc 10 and has a small opening 34 extending from the inside of the spherical shell to the bottom surface of the spherical shell at a point behind the point of contact between the spherical shell 32 and the disc 10.

A cam 3'6 is affixed to the lower end of the post 28 to produce a rotation of the post 28 with a rotation of the cam 36. The rotation of the post 28 also produces a corresponding rotation of the dispensing tank 16 and spherical shell 32, both of which are connected to the post 28. The cam 36 is driven by a wheel 38 which frictionally engages the cam. The wheel is rotated in a clockwise direction, as shown by the arrow 40, by the motor 14. The clockwise rotation of the Wheel 38 produces a counter-clockwise rotation of the cam 316 as shown by the arrow 42. The wheel 38 is maintained in contact with the cam 36 through all positions of the cam by appropriate mechanical means as shown schematically by the spring 44. It is to be noted that although the driving of the wheel 38 by the motor 14 is shown schematically, any appropriate mechanical drive means may be used to produce the rotation of the wheel 33.

As the disc 10 is rotated by the motor 14 in the counterclockwise direction, the dispensing apparatus 1.6 and the spherical shell 32 are moved in a radial arc across the disc 10'. The valve 22 is adjusted to produce a flow of emulsion material 2G from the upper chamber 18. The emulsion material 2G contained in the upper chamber 18 flows through the lower tubing portion of the dispensing apparatus 16 and falls into the spherical shell 32. The emulsion material 20 drains from the spherical shell 32 through the opening`34 onto the surface of the dise 10. The emulsion material Ztl spreads out over the bottom surface of the spherical shell 32 and forms a meniscus ring between the spherical shell 32 and the surface of the disc l0. The meniscus ring generally has a circular 7 shape surrounding the contact point between the spherical shell 32 and the surface of the disc 10. Actually, once the emulsion material 20 starts to flow from the opening 34, the spherical shell 32 rides on a thin iilm of emulsion material rather than directly contacting the surface of the disc 16.

As the disc 10 rotates and the spherical shell 32 moves on a radial arc, the flow of emulsion material 20 from the spherical shell 32 forms a spiral path wherein each turn in the spiral path has a relation with the preceding turn so as to produce a uniform distribution of the emulsion material `across the surface of the disc 10. A partial covering of the emulsion material 46 is shown in FIGURE 1 on the surface of the disc 10. The spherical shell 32 produces the distribution of the emulsion material at localized areas on the surface of the disc 16 by spreading out the emulsion material and, in addition, the spherical shell 32 acts as a hydraulic filter to smooth out the flow `of the emulsion material from the dispensing apparatus 16. In order for the spherical shell 32 to properly act as a hydraulic filter, it is desirable to maintain a proper head of emulsion material in the spherical shell.

It is to be appreciated that as the dispensing apparatus 16 and the spherical shell 32 move in a radial arc across the surface of the disc 10, the relative velocity between the spherical shell 32 and the disc 10 varies in accordance with the particular radial position of the spherical shell. This is assuming that the disc 10 is rotated at a constant speed as shown in FIGURE 1. Since the time for each revolution of the disc 10 is constant, the amount of emulsion material fiowing from the spherical shell 32 tO the surface of the disc 10 would also be constant for each revolution of the disc. The constant deposition of emulsion material for each revolution would produce a non-uniform distribution of the emulsion material across the surface of the disc since the area to be covered varies with each radial position.

In order to eliminate the non-uniformity of the layer of emulsion material on the disc 10, the cam 36 provides for a variation in the spacing between each adjacent turn along the spiral path of the spherical shell. In this manner, as the spherical shell approaches the inner portion of the disc 10, the spacing between each spiral turn increases so that the emulsion material has a constant area to cover for each revolution of the disc 10. The unit area loading `of the disc 10 is, therefore, maintained constant so as to eliminate the problem of non-uniformity. One problem with the embodiment of FIGURE 1 is that when the spacing between adjacent turns along the spiral path of the spherical shell 32 increases as the spherical shell moves in toward the center of the disc 10, the emulsion material must, therefore, spread radially over a larger distance as the spherical shell moves toward the center of the disc 10. The additional spreading of the emulsion material may be unsatisfactory if the emulsion material does not have the necessary flow characteristics to spread the emulsion material uniformly. This problem could be overcome by maintaining an equal spacing between the adjacent turns along the spiral path of the spherical shell Ibut by regulating the flow of the emulsion material from the dispensing apparatus 16 into the shell 32. Another method of maintaining a uniform coating of emulsion material on the surface of the disc 1li, is shown in FIGURE 2.

In FIGURE 2, elements which have the same structure and serve the same purpose as those shown in FIGURE l are given the same reference character. In FIGURE 2 the disc 16 is rotated in the counter-clockwise direction, as shown by the arrow 12, by a motor 14, through a variable speed drive. The variable speed drive will be described later. The dispensing apparatus 16 has an upper chamber 18 which is filled with the emulsion material. The ilow of the emulsion material from the upper chamber 18 is controlled by the valve 22. The dispensing apparatus 16 is rigidly supported by the upper and

lower support varms

24 and 26 which extend from the post 28. The emulsion material flows into the spherical shell 32 which is flexibly supported from the lower support arrn 26 by the member 30. The emulsion material 20 in the spherical shell 32 drains through the opening 34 to coat the surface of the disc 10 along a spiral path as shown by partial coating In FIGURE 2, the disc 10 is driven at a changing rate of revolution through an intermediate drive 50. The intermediate drive 50 is shown in a schematic fashion, but it may be any conventional type which produces a continuously controlled rotational `output with a -constant rotational input.

FIGURE 2 also includes an additional feature in that the dispensing apparatus 16 and spherical shell 32 move along a direct radial line across the surface of the disc 10 as opposed to the radial arc `of FIGURE 1. The radial drive for the spherical shell 32 and dispensing apparatus 16 of FIGURE 2 is accomplished through the use of a screw drive including a screw 58 which is threaded through a lower portion 60 of the post 28. The screw S8 is driven in a counter-clockwise direction, as shown by the arrow 62, by the drive 50. The screw has a helical thread which is designed to produce a spiral path of the spherical shell 32 across the disc 10. For the particular embodiment of FIGURE 2 the spiral path has a constant spacing between adjacent turns along the spiral path.

As the spherical shell 32 moves across the disc 10, the emulsion material 20 flows through the opening 34 and wets an area as defined by a meniscus ring surrounding, the contact point between the bottom of the spherical shell 32 and the surface of the disc 10. The spherical shell 32, therefore, produces an even distribution of the emulsion material on the surface of the disc 10, and, in addition, the spherical shell serves as a hydraulic lter to smooth the flow of the emulsion material from the dispensing apparatus 16. The disc 10 is driven by the motor 14 through the intermediate drive 50 so that the relative velocity between the disc 10 and the spherical shell 32 is maintained at a constant value, notwithstanding the radial position of the spherical shell 32. The constant velocity relationship between the spherical shell and the disc 10 provides that the unit area loading of the emulsion material on the surface of the disc remains constant for all radial positions of the spherical shell.

In FIGURE 3, a detail view is shown of the relationship between the spherical shell 32 and the disc 10 of either FIGURE l or FIGURE 2 during the coating of the emulsion material 20 on the surface of the disc. The same reference characters are used as those for FIGURES l and 2. As can be seen in FIGURE 3, the lower portion of the dispensing apparatus 161 includes a tube which drops emulsion material 20 into the spherical shell 32. It is desirable to have the emulsion material 20 build up a head in the spherical shell 32 so that individual drops of emulsion material from the dispensing apparatus 16 do not disturb the liow of the emulsion material out of the spherical shell 32. When the head of emulsion material in the spherical shell 32 has a proper value, the spherical shell 32 operates as a lhydraulic filter so as to smooth the flow of the emulsion material from the dispensing apparatus 16.

The emulsion material 20 ows out of the spherical shell 32 through the opening 34. The size of the opening 34 is designed to produce the correct flow of emulsion material 20 in accordance with the desired thickness of the coating of emulsion material on the surface of the disc 10. The relative velocity and other factors between the spherical shell 32 and the disc 10` are adjusted so as to produce the desired thickness of emulsion material. As can be seen in FIGURE 3, as the emulsion material flows from the spherical shell 32 through the opening 34, the emulsion material spreads over an area as defined by a meniscus ring 64. The meniscus ring, therefore, has

9 essentially a circular configuration, since it surrounds the contact point between the spherical shell 32 and the disc 10. The formation of the meniscus ring controls the distribution of the emulsion material over a width equal to the diameter of the circular configuration of the meniscus ring. In this manner, the emulsion material is controlled to be evenly distributed over a localized area of the disc 10 and as the disc 10 rotates relative to the spherical shell 32, a uniform coating of the emulsion material is produced on the surface of the disc 10. The production of the meniscus ring around the bottom of the spherical shell, therefore, controls the uniform distribution of the emulsion material over a localized area.

Although FIGURES 1 and 2 illustrate the coating of the disc 10 starting at the outside of the disc and moving in toward the center of the disc, it may be desirable to reverse the above procedure and initiate the coating of the disc 10 from the inside of the disc to the outside. This may be accomplished by merely reversing the drive to the dispensing apparatus 16 and the spherical shell 32. The coating of the disc 10 with emulsion material from the inside of the disc to the outside of the disc may have certain advantages over the systems shown in FIGURES 1 and 2. For example, as shown in FIGURE 4 wherein similar items have similar reference characters to those shown in FIGURES 1 and 2, a disc 10` is rotated by the motor 14 and the spherical shell 32 has produced a uniform coating 46 on the surface of the disc 10.

In the recording systems which use discs coated with emulsion material as shown in FIGURE 4, the inner portion of the emulsion coating is not usable. When the spherical shell 32 is producing the coating of emulsion material at the inner portion of the disc 10, as shown by the portion 66, the flow of emulsion material from the dispensing tank may be regulated so as to produce the desired uniformity. This can be seen wherein the characteristics of the coating 46 over the portion 66 is non-uniform. Since the portion 66 is not used during recording, the adjustment of the flow of emulsion material would not produce any adverse effects on the recording of information on the emulsion layer 46. The coating apparatus of the invention is, therefore, adjusted to produce a uniform coating over the remaining portion of the disc 10.

The coating of the disc with emulsion material from the inside o-f the disc to the outside of the disc may also have an advantage in that it is easier to remove the spherical shell from the sur-face of the disc without disturbing the coating of emulsion material at the outside of the disc. For example, as the spherical shell 32 moves toward the outside of the disc it may engage a separating platform 68 which gently lifts the spherical shell away from the surface of the disc 10. If the flow of emulsion material to the spherical shell 32 is also shut off at the proper time, the emulsion material within the spherical shell will complete the coating of the disc 10 at the same time as the spherical shell reaches the outside edge of the disc. The separating platform 63 would then lift the spherical shell slowly olf the rotating disc so that there is no sharp discontinuity in the coating of emulsion material and also so that the coating of emulsion material is produced well to the edge of the disc 10l without running over the side of the disc 10.

In FIGURE 5, an embodiment of the invention is shown for producing a coating of emulsion material on a tape 100. The coating apparatus of FIGURE includes a plurality of dispensing

apparatus

102, 104 and 106 which are similar to dispensing tank 16 of FIGURES 1 and 2. The dispensing

apparatus

102, 104 and 106 are all filled with emulsion material 108 and the ow of the emulsion material 103 from the dispensing apparatus is controlled by

valves

110, 112 and 114. The dispensing

apparatus

102, 104 and 106 are supported above the tape 101i by upper and

lower support arms

116 and 118 which extend between a pair of

posts

120 and 122. Posts 120 10 and 122 are maintained in a stationary position by

support platforms

124 and 126.

A light trough structure 128 is supported by a pair of

arms

130 and 132 which extend from the

posts

120 and 122. The trough 128` is supported so as to lightly contact the tape and so as to extend across the tape 100 beneath the dispensing

apparatus

102, 104 and 106. The trough has a cylindrical bottom surface and endwalls 134 and 136 so as to retain the emulsion material 1018 owing into the trough 128. The emulsion material 108 in the trough 128 flows through a slit 138i in the bottom of the trough 128 so as to produce a coating 140 of emulsion material on the surface of the tape 100. The tape 100 is moved in the direction as shown by the arrow 142 at a constant rate so as to produce the uniform coating of emulsion material on the surface of the tape. It is to be appreciated that the slit 13S may be replaced by a plurality of separate openings similar to the openings 34 shown in FIGURES 1 and 2.

FIGURE 6 illustrates in more detail the relationship between the trough 128 and the tape 100 of FIGURE 5. As shown in FIGURE 6, the emulsion material 108 flows from the dispensing apparatus 102 and the other dispensing apparatus into the trough 12S. In order to smooth out the flow of the emulsion material from the dispensing apparatus, it is desirable to maintain a head of emulsion material within the trough 123. In this manner, the trough 128 acts as a hydraulic lter for the emulsion material flow to the surface of the tape 100. The emulsion mate rial 108 flows from the trough 128 through the slit 138 to the surface of the tape 100. The emulsion material llows between the bottom surface of the trough and the tape until the adherence of the emulsion material is sufcient to produce a pair of meniscuses 144 substantially paralleling the line of contact between the bottom surface of the trough and the tape. The production of the pair of meniscuscs 144 controls the area over which the emulsion material is distributed so as to provide for a uniform distribution of the emulsion material on the surface of the tape 100. The movement of the tape then provides a uniform coating 140 of emulsion material on the -surface of the tape 100.

Although various embodiments of the invention have been shown which illustrate different means for producing a uniform thin coating of emulsion material on a substrate, it is to be appreciated that other adaptations and modifications of the invention may be made. The inven tion, therefore, is only to be limited by the appended claims.

What is claimed is:

1. In an apparatus for producing a uniform coating of a coating material on the surface of a substantially planar substrate,

a dispensing apparatus containing the coating material and including means for directing the coating material toward the surface of the substantially planar substrate,

first means having a curved bottom lying on and con tacting the surface of the substantially planar substrate and having an upper area operatively coupled to the dispensing apparatus to store the coating material directed toward the surface of the substrate and having an opening extending from the upper area to the curved bottom of the first means at a point other than any contact point between the curved bottom and the surface of the substantially planar substrate to produce a uniform distribution. of the coating material on the surface of the substantially planar substrate over a local area by forming a meniscus surrounding the contact on the curved bottom of the first means, and

means for producing a relative movement between the rst means and the substrate to produce a coating of the coating material on the surface of the substantially planar substrate.

l l 2. The apparatus of claim 1 wherein the first means is a spherical shell contacting the surface of the substrate at a single point and wherein the opening extends to the bottom surface of the shell at the point other than the contact point and wherein the meniscus forms :a ring substantially centered around the contact point.

3. The apparatus of claim 1 wherein the rst means is a trough having a cylindrical bottom surface contacting the surface of the substrate along a line and wherein the opening extends to the bottom surface of the trough away from the contact line and wherein the meniscus forms a pair of substantially parallel lines on either side of the contact line.

4. In an apparatus for producing a uniform coating of a coating material on the surface of a disc,

a dispensing apparatus containing the coating material and including means for directing the coating material toward the surface of the disc,

rst means lying on the surface of the disc and operatively coupled to the dispensing tank to receive the coating material directed toward the surface of the disc for smoothing the flow of the coating material from the dispensing apparatus and for producing a uniform distribution of the coating material on the surface of the disc over a local area, and

means for producing a preprogramed relative movement between the first means and the disc to produce a uniform coating of the coating material on the surface of the disc.

5. In an apparatus for producing a uniform coating of a coating material on the surface of a disc,

first means having a curved bottom surface lying on the surface of the disc and having an upper area operatively coupled to the dispensing apparatus to store the coating material directed toward the surface of the disc and having an opening extending from the upper area to the curved bottom surface of the first means to produce a uniform distribution of the coating material on the surface of the disc over a local area by forming a meniscus on thc curved bottom surface of the first means,

second means operatively coupled to the disc to produce a preprogramed rotation of the disc, and

third means operatively coupled to the first means to produce a preprogramed radial motion of the first means across the surface of the disc lfor uniformly coating the surface of the disc along a spiral path.

6. The apparatus of claim 5 wherein the first means is a spherical shell.

7. The apparatus of claim 5 wherein the third means provides a preprogramed variation in the spacing between adjacent turns along the spiral path.

8. The apparatus of claim 5 wherein the second means provides a preprogramed variation in the speed of rotation of the disc.

9. In an apparatus for producing a uniform coating of a coating material on the surface of a tape,

a dispensing apparatus containing the coating material and including means for directing the coating material toward the surface of the tape,

first means having a curved bottom surface lying on and contacting the surface of the tape and having an upper area operatively coupled to the dispensing apparatus to store the coating material directed toward the surface of the tape and having an opening extending from the upper area to t-he curved bottom surface of the rst means away from the contact between the curved bottom and the surface of the tape to produce a uniform distribution of the coating material on the surface of the tape by forming a meniscus on the curved bottom surface of the rst means around the contact between the curved bottom and the surface of the tape, and

means operatively coupled to the tape for longitudinally moving the tape to produce a coating of the coating material on the surface of the tape.

10. The apparatus of claim 9 wherein the first means is a trough extending across the tape.

11. In an apparatus for producing a uniform coating of a coating material on the surface of a substrate and having a dispensing apparatus containing the coating material and with the dispensing apparatus including means for directing the coating material toward the surface of the substrate,

a spherical shell having a curved bottom surface lying on the surface of the substrate and having an upper area to be operatively coupled to the dispensing tank for storing the coating material directed toward the surface of the substrate and having an opening extending from the upper area to the curved bottom surface for producing a uniform distribution of the coating material on the surface of the substrate over a local area by forming a meniscus on the curved bottom surface.

References Cited UNITED STATES PATENTS 1,197,723 9/1916 Edison 118-321 1,609,218 11/1926 Storck 118-401 2,167,727 8/1939 Rosebush 118-401 2,179,221 11/1939 Schneider 118-218 2,961,821 11/1960 Marzocchi et al. 118-401 X 3,201,275 8/1965 Herrick 118-401 X CHARLES A. VVLLMUTH, Primary Examiner.

R. I. SMITH, Assistant Examiner.