US 3394678 A
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Description (OCR text may contain errors)
United States Patent 3,394,678 APPARATUS FOR VACUUM COATING Richard H. Edwards, Concord, and Charles dA. Hunt,
Oriuda, Calif., assignors, hy mesne assignments, to Air Reduction Company, incorporated, a corporation of New York Filed Dec. 23, 1966, Ser. No. 604,386 8 Claims. (Cl. 118-49.!)
This invention relates generally to an apparatus for coating a substrate and more particularly, it relates to an improved apparatus for applying a coating to a continuous strip of material which evolves gases upon exposure to a vacuum.
Conventional methods of coating a substrate with a metal alloy, metal, organic polymer, or an inorganic substance generally include the steps of vaporizing an evaporant within a chamber maintained under vacuum and then continuously exposing the substrate to the vapor thus formed so that the evaporant will be deposited thereupon in the form of a coating. Frequently, the substrate is in the form of a continuous web of plastic, paper or other organic material. Several forms of desirable substrate materials, for example, low grade paper such as kraft paper, contain substantial amounts of occluded gases and other volatile materials which are evolved from the substrate upon exposure to vacuum conditions. For purposes of the present discolsure, all volatile materials present in the substrate which may be evolved from the substrate upon exposure to a vacuum are defined as occluded gases. The presence of occluded gases in the substrate is undesirable in that they mask or cover the surface of the substrate thereby interfering with the adherence of the evaporant to the surface of the substrate and further tend to dull the finish of the coating. A further disadvantage resulting from the generation of occluded gases is that they increase the difiiculty of providing a sufiiciently high vacuum within the coating chamber to enable high evaporant fiow rates and good coating characteristics.
A method used commercially to minimize the undesirable effects of the presence of occluded gases in the substrate is to place a thin coating of an organic material upon one surface of the substrate and then to expose this coated surface through a suitable aperture, generally in the form of a window, to the vapor cloud within the coating chamber. The coating chamber is generally maintained at a pressure of about 1 micron of mercury absolute. The substrate acts as a diaphragm across the aperture thereby sealing the gassy back side of the substrate from the coating chamber. thus facilitating the maintenance of a vacuum within the coating chamber. To further minimize the passage of gas from the gassy back side of the substrate around the edges of the substrate and through the aperture and thus improve the vacuum within the coating chamber, the longitudinal edges of the strip material may be positioned to slightly overlap the edges of the aperture. This overlap, however, produces a substantial uneoated border along the longitudinal edges of the substrate, generally in the order of as to 1 inch, and represents a significant amount of wasted material. To prevent scratching of the coating the coated side of the material must not be allowed to touch the wall of the aperture between the compartments, therefore the strip is suspended slightly above the frame providing a 3,394,678 Patented July 30, 1968 p we . finite gap between the strip and the frame. This gap provides a passage for the gases evolved from the gassy back side of the substrate to pass around the material through the aperture and into the coating chamber. Thus, as a result of the aforementioned difiiculties it has been heretofore impractical to establish a vacuum of less than about 1 micron of mercury within the coating chamber and simultaneously reduce the amount of uncoated border along the edges of the substrate resulting from the overlap previously described.
A main object of the present invention is to provide an improved apparatus for coating a substrate with an evaporant. A more particular object is to provide an improved means of applying an evaporant coating to a continuous strip substrate which gives off a gas upon exposure to a vacuum. A still further object is to provide an improved means of exposing a continuous strip of substrate to a coating chamber wherein high vacuum conditions are maintained. Other objects and advantages of the invention will become apparent through reference to the following description and accompanying drawings which show an illustrative embodiment of this invention in which:
FIGURE 1 is a diagrammatic cross-sectional elevational view of a preferred embodiment of a coating apparatus in accordance with this invention;
FIGURE 2 is a fragmentary top view of a portion of the embodiment illustrated in FIGURE 1 taken along line 2-2;
FIGURE 3 is an enlarged fragmentary sectional view taken along the line 3-3 of FIGURE 2, and
FIGURE 4 is an enlarged fragmentary sectional view similar to that of FIGURE 3 of an alternate embodiment of a coating apparatus in accordance with this invention.
Briefly, a preferred embodiment of this invention includes a first chamber 11 containing therein in a continuous strip substrate 12 to be coated. The first chamber 11 is preferably maintained at an absolute pressure of between about and about 500 microns of mercury. A second chamber 13 is provided which is separated from the first chamber by a common wall 15. The second chamber 13 is preferably maintained at an absolute pressure of about 0.2 micron of mercury. A vapor source 17 generally including a means for evaporating an evaporant is maintained within the chamber 13. An aperture 19 is provided in the common wall 15 thereby providing communication between the chambers and permitting exposure of the strip substrate 12 to the evaporant vapors within the coating chamber. In accordance with the present invention, the aperture 19 is formed such that the width of the aperture in the direction normal to the movement of the substrate is slightly wider than the width of the substrate. A sealing means 22 is positioned about the aperture 19 which includes a plurality of parallel spaced guide members 23 oriented about the aperture 19 to receive and position the strip substrate 12 in relation to the aperture 19 to minimize the gas leakage between the first chamber 11 and the second chamber 13.
More particularly, the coating process is performed within an enclosure 25 defined by a wall 27 of suitable material such as steel. The enclosure 25 is partitioned by the wall 15 which divides the enclosure 25 into the upper and lower chambers 11 and 13.
As illustrated in FIGURE 1, an evaporant material 31 3 is vaporized in a crucible 33 positioned beneath the aperture 19. The crucible 33 may be constructed of a suitable inert material and may be fed with evaporant material by a suitable feeder such as a vibrational feeder. The feeder 35 is mounted upon a pedestal 37 which is so positioned that the material expended from the feeder 35 will fall into the crucible 33. To vaporize the evaporant 31 within the crucible 33 an electron gun 39, energized by a power supply 41, is positioned within the lower chamber 13 of the enclosure 25. Any suitable electron gun may be utilized in accordance with known techniques. One suitable electron gun such as illustrated in FIGURE 1, is described in United States Patent No. 3,177,535, issued Apr. 13, 1965.
To facilitate the vaporization of the evaporant, the lower chamber 13 is evacuated by means of a vacuum pump to a pressure of about 0.2 micron of mercury absolute. The upper compartment 11 is maintained by a vacuum pump 47 at a pressure of about to 500 microns of mercury absolute.
The substrate 12 may take the form of any suitable material such as plastic containing volatile plasticizer or moisture, or wrapping paper, e.g., kraft paper. Preferably, the paper is previously coated on the side upon which the evaporant coating is to be applied with an organic coating, e.g., polyethylene, polypropylene, Saran and coating resins, in order to provide a smooth surface upon which the evaporant may be deposited. The substrate is conveniently supplied in the form of a supply roll 49, which may be supported within the enclosure 25, as shown in FIGURE 1, or which may be supported externally to the enclosure 25 and introduced into the chamber 11 through a suitable vacuum seal. The substrate 12 is withdrawn from the supply roll 49 and passed longitudinally through the sealing means 22 across the aperture 19 in order to expose the substrate to the evaporant vapor cloud generated within the compartment 13. The substrate 12 is fed over a positioning member in the form of a first idler roller 51 and is then passed between the parallel rails 23 in a manner to be hereinafter more clearly described. After passing between the guide rails 23, the substrate 12 is fed over a second positioning means in the form of second and third idler rollers 53 and and out of the chamber through a vacuum seal 57 in the wall 27. The vacuum seal 57 permits removal of the coated material from the chamber 11 without destroying the vacuum therein.
As determined by the coating desired, as will be later considered, the lowermost surface of the idler rollers 51 and 53 may be located either slightly above the upper surface of the passage defined by rails 23 or slightly below this surface. The rollers are spaced from the aperture 19 in the longitudinal direction of travel of the substrate.
In this preferred embodiment, the aperture 19 is shown in the form of a rectangular window, however, other suitable shapes may be used in accordance with this invention. The longitudinal sides of the aperture 19 are parallel to the direction of movement of the substrate 12 and, as previously mentioned, are spaced apart ata distance slightly greater than the width of the substrate in order that the entire surface of the substrate will be exposed to the evaporant vapors as shown in FIGURES 2 and 3.
To minimize the leakage of gases from the upper chamber 11 to the lower chamber 13, the sealing means 22 includes parallel rails 23 secured to the wall 15 adjacent to the edges of the aperture 19 by suitable fasteners 58. The rails 23, as illustrated in FIGURE 3, are provided with a longitudinal groove 59 forming a downwardly facing retaining surface 61 which extends inwardly of the aperture 19 as shown in FIGURE 3. The rails 23 preferably extend longitudinally beyond the aperture 19 so that the substrate 12 may be positioned as shown in FIGURE 2. A clearance space 63 is provided between the surface 61 and the upper face of the wall 15 which is slightly greater than the thickness of the substrate 12. It has been found that a clearance space of approximately 0.05 inch is satisfactory for most applications.
In operation, the strip substrate is stored upon the supply roll 49. The substrate is passed about the idler roll 51 and through the passage defined by the rails 23 directly above tl-e aperture 19. The substrate is then passed over the rollers 53 and 55 and is passed out of the chamber 11 through the seal 57. Suitable drive means, not shown, are provided for withdrawing the substrate 12 from the supply roll 49 at a uniform rate in order to provide a coating on the substrate of uniform thickness. The supply roll is preferably provided with a suitable brake, not shown, in order that the substrate will be maintained in a taut condition during exposure to the evaporant vapors. As clearly shown in FIGURE 3, the downward surface of the substrate 12 is exposed to the vapor cloud of evaporant within the lower chamber 13 so that when properly positioned between the rails 23, no portion of the edges of the substrate masked by the edges of the aperture.
When the rollers 51 and 53 are spaced slightly above the surface 61 of the guide rails 23, as in the illustrated embodiment, they provide an upward pull upon the taut substrate and urge the upper surface of the substrate against the retaining surface 61 to provide a more effective seal between the chambers 11 and 13. The positioning of the rollers 51 and 53 above the level of the retaining surface 61 also provides a slight clearance between the downwardly facing surface of the substrate and the wall 15, thereby preventing scratching of the coated substrate during passage of the substrate over the aperture 19. As previously mentioned, in certain applications it may be desirable to position the rollers 51 and 53 slightly below the surface 61 so as to provide a slight clearance between the surface of the substrate and the rails.
As previously mentioned, the rollers 51 and 53 are longitudinally spaced from the aperture 19 thereby causing the substrate 12 to be spaced slightly above the wall 15 for a distance extending on both sides of the aperture 19. This relation between the substrate and the wall 15 before and after passing over the aperture improves the seal between the compartments 11 and 13 since in order for a molecule of gas to pass from the upper to the lower chamber, it must be traveling in a path substantially parallel to the wall 15 for the distance between the roller and the aperture. The number of molecules having such a path is exceedingly small at the pressure levels at which the illustrated embodiment is operated.
The evaporant 31 is fed into the crucible 33 by the feeder 35 and vaporized therein by the electron gun 39 thereby producing a vapor cloud 67. The vapor thus formed rises through the lower chamber 13 and is deposited upon the substrate 12 forming a coating thereon.
As previously mentioned, the lower face of the substrate 12 upon which the evaporant is disposed, is preferably coated with an organic polymer to reduce the amount of gas emitted therefrom and to provide a smooth surface upon which the coating may be deposited. The back or uncoated surface of the substrate gives off a. considerable amount of occluded gases into the upper chamber 11. The gas given off by the upper surface of the material is removed by the pump 47 and the upper chamber 11 is maintained at a pressure of between about 50 and about 500 microns of mercury absolute.
As previously mentioned, the pump 45 is operated to maintain the lower compartment at a pressure of less than 1 micron, preferably about 0.2 micron of mercury absolute. The unique construction of the guide rails 23 and the location of the rollers 51 and 53 with respect thereto provides a relativelygas-tight seal between the upper and lower chambers 11 and 13, thereby minimizing the flow of occulded gas evolved from the substrate from the chamber 11 through the aperture 19 into the chamber 13. This unique sealing means permits the practical maintenance of a very low pressure of the order of 0.2 micron of mercury or less within the chamber 13. This order of vacuum is highly desirable in that improved adherence of the coating to thesubstrate and brightness of the coating are possible at high evaporant flow rates.
The alternate embodiment illustrated in FIGURE 4 is particularly adapted for use with substrates such as kraft paper which evolve a very significant amount of occluded gases during coating. During the coating of such substrates significant amounts of occluded gases are evolved from the uncoated back surface of the paper, a small but measurable portion of which pass from the chamber 11 about the longitudinal edge of the substrate 12 into the chamber 13. As these gases pass about the edge of the substrate they are trapped or gettered by the rising evaporant and contaminate the evaporant as it is applied to the sub strate. In this connection, it has been found that when such gases become gettered to the evaporant, a relatively wide, brown or grey colored border is produced along the longitudinal coated edge of the substrate.
The alternate embodiment illustrated in FIGURE 4 comprises a pair of spaced guide rails 23a similar to the rails 23 of the previously discussed embodiment. The rails are secured to the wall 150 about the aperture 19a in a manner similar to that illustrated in FIGURES 1 through 3 inclusive. To vent the occluded gases which pass about the longitudinal edges of the substrate a pair of deflection vanes 71 are provided which are secured to the wall 150 and positioned adjacent the edges of the substrate 120. Each of the vanes are preferably constructed from a thin sheet of metal such as stainless steel. In the preferred embodiment, the vanes 71 are formed outwardly away from the substrate 120 so as not to interfere with the deposition of the evaporant thereon, however other vane configurations may be used without departing from the scope of this invention. The ends of the vanes 71 are provided with upwardly projecting support arms 73 which may be secured to the wall a. The upper edges of the deflecting vanes 71 are positioned parallel to and adjacent the longitudinal edge of the substrate 120 and are preferably spaced inwardly approximately V4 of an inch from the edge thereof. The edges of the vanes 71 are spaced as close as practicable to the surface of the substrate in order to prevent as much gas as possible from contaminating the evaporant coating. It has been found that good results are obtained when the vanes are spaced approximately of an inch along the edges of the substrate. Thus, the gases which pass about the longitudinal edge of the substrate are deflected away from the rising evaporant and are quickly removed from the chamber 13 by the vacuum pump 45.
In operation, a substrate 12a such as kraft paper is positioned between the rails 23a in a manner similar to that of the previously discussed embodiment. The vanes 71 slightly overlap the lower surface of the substrate 120 by approximately /4 of an inch. The small amount of occluded gases which pass about the edges of the substrate are deflected by the deflection vanes away from the vapor cloud and withdrawn from the chamber thereby minimizing the gettering effect of the evaporant as it is deposited upon the substrate. The vanes 71 substantially eliminate the colored border resulting from the gettering of occluded gases by the evaporant; however, the vanes 71 produce a slight uncoated border of approximately V4 of an inch along the edge of the substrate. This slight uncoated border represents relatively little wasted material and is a substantial improvement over the prior art. Thus, a method and apparatus have been described for continuously coating gassy materials by high vacuum evaporation.
Although specific embodiments of this invention have been shown and described, it will be understood that the details of the invention shown may be altered without departing from the spirit-of this invention.
Various of the features of the invention are set forth in the following claims.
What is claimed is:
1. Apparatus for applying a coating on a substrate that evolves occluded gases when exposed to a vacuum comprising, a first chamber adapted to be maintained at a press re between about 50 and 500 microns of mercury absolute and a second chamber adapted to be maintained at less than about 1 micron of mercury absolute, a wall separating said first and said second chambers formed to define an aperture therethrough providing communication between said first and second chambers, a source of substrate material in said first chamber, means for passing said substrate material across said aperture, means in said second chamber for vaporizing an evaporant material which is deposited upon the substrate which is exposed to the second chamber through said aperture, and sealing means for maintaining said substrate in sealing relation to the longitudinal edge portions of the aperture including parallel spaced guide members forming an extension of said wall extending into said first chamber and disposed adjacent said longitudinal edge portions, said guide members having sealing surfaces extending away from said wall and inwardly of the aperture for engagement with the substrate material, thereby minimizing the gas leakage betweensaid first and second chambers.
2. The apparatus of claim 1 which further comprises means for maintaining said first chamber at a pressure of between about 50 and 500 microns of mercury absolute, means for maintaining said second chamber at a pressure less than about 1 micron of mercury absolute, and where- 'in said guide members each have a longitudinally extending groove adapted to receive and retain one longitudinal edge of said substrate thereby orienting said substrate in relation to said aperture to seal said aperture thereby minimizing the gas leakage between said first and second chambers.
3. The apparatus of claim 2 wherein said guide members are in the form of a pair of parallel guide rails positioned parallel to the axis of motion of said substrate and positioned adjacent the aperture defining means, each of said guide rails having said longitudinally extending groove on one face thereof to receive the longitudinal edge of said substrate and displaying an L-shaped configuration in transverse cross section thereby orienting and retaining said substrate in spaced relation to said aperture while scaling said aperture for minimizing the gas leakage between said first and second chambers.
4. The apparatus .of claim 3 which further comprises positioning members positioned upon opposite sides of said aperture in the direction of travel of said substrate, the engaging surfaces of said positioning members being spacially mounted a greater distance from said wall than said substrate when said substrate is positioned by said guide rails, whereby the surface of said substrate is positioned from said wall and within the path defined by said guide rails to seal said aperture and to minimize the gas leakage between said first and said second chambers.
5. The apparatus of claim 4 wherein said positioning members are in the form of idler rollers positioned upon opposite sides of said aperture in the direction of travel of said substrate and transversely oriented thereto, the engaging surfaces of said idler rollers being spacially mounted a greater distance from said wall than said substrate when said substrate is positioned by said guide rails, whereby when said substrate is passed over said idler rollers and through said guide rails the surface of said substrate is positioned from said wall and within the path defined by said guide rails to seal said aperture and to minimize the gas leakage between said first and second chambers.
6. The apparatus of claim 1 which further comprises a plurality of deflecting vanes disposed within said second chamber and positioned inwardly of and spaced substantially adjacent to the longitudinal edges of the substrate.
7. The apparatus of claim 6 wherein said deflecting vanes are longitudinally shaped and have a flared portion outwardly directed for deflecting any leakage gas away from the path of the evaporant material.
8. The apparatus of claim 7 wherein said guide members each have a longitudinally extending groove adapted to receive and retain one longitudinal edge of said substrate.
References Cited 8 Alexander 1l849 X Steinfeld 1l7 107 .1 X McGraw 118-49 Simons ll8--49.1 Koller 118 -49 X Strong 118-49 X Hersh 118-411 X Herrick 117107.1 X
MORRIS KAPLAN, Primary Examiner.