US3040702A - Vacuum coating apparatus having sealing means formed of membranes and fibers - Google Patents

Description

June 26, 1962 A. ENG ET AL 3,040,702

VACUUM comma APPARATUS HAVING SEALING MEANS FORMED OF MEMBRANES AND FIBERS Filed June 19, 1958 2 ,Sheets-Sheet 1 20 r N 8%, Z; D S- m INVENTORS A! rf Ew June 26, 1962 MN Em 3,040,702

VACUUM COATING APP HAVING SEALING MEANS FORMED OF MEMB ES AND FIBERS Filed June 19, 1958 2 Sheets-Sheet 2 United States Patent 3,ti40,702 VACUUM COATING APPARATUS HAVING SEAL- ING MEANS FORMED 0F MEMBRANES AND FBERS Albert Eng, Brookline, Milo P. I-Inilicka, in, Concord, John S. Light, East Walpole, and Arthur G. Walsh, Weston, Mass, assignors, by mesne assignments, to National Research (Corporation, (Iarnbridge, Mass, a corporation of Massachusetts Filed June 19, 1958, er. No. 743,096 6 Claims. ((11. 118-4fi) This invention relates to an apparatus for the coating of metallic and nonmetallic substrates in a vacuum. 1

A principal object of the present invention is to provide an improved apparatus for the vacuum coating of metallic and nonmetallic substrates.

Another object of this invention is to provide an apparatus for continuous vacuum coating of substrates which permits the introduction and removal of a substrate having varying thicknesses without loss of vacuum.

Another object of this invention is to provide a coating apparatus having seals between chambers with difierent subatmospheric pressures which permit the passage of substrates having torn edges and splices with loose ends without substantial increase in the amount of gas passing through the seal.

Another object of this invention is to provide a coating apparatus comprising a multiplicity of chambers maintained at various degrees of vacuum which permits the movement through the chambers of both a substrate and a substantially thicker driving or threading belt alongside the substrate; and permtis lateral relative movement between the belt and the substrate through seals without loss of vacuum in the chambers.

A still further object of this invention is to provide a continuous vacuum coating apparatus which permits flexible substrates to be threaded without loss of vacuum in any of the chambers through which the substrates pass, and which permits the driving of all guiding rolls at the same speed utilizing the threading means.

Other objects of this invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, references should be had to the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatic schematic view of one preferred embodiment of the invention;

FIG. 2 is a detailed view of one embodiment of the brush portion of this invention which in conjunction with a chamber and coating vapor source not shown achieve the objects of this invention.

FIG. 3 is a detailed cross-section of the brush of 1 16.2.

The vacuum coating of a moving substrate, such as sheet steel, paper or plastic with coating material such as, for example, aluminum is generally carried out in a chamber or compartment maintained under a pressure of less than about .001 mm. Hg. Abs. The desired degree of vacuum is determined in any particular case by the particular material being deposited, the nature of the substrate being coated and various operating factors.

Recently, continuous coating operations have been developed where the substrate to be coated is continuously introduced from the atmosphere into a vacuum, coated and then removed from the vacuum to the atmosphere.

3,04%,702 Patented June 26, 1962 vacuum pumping system a pressure gradient is maintained between the chambers. The requirements of such narrow slots are extremely critical. On one hand, they must not be so large as to cause pumping requirements to become excessive due to leakage of air adjacent to the strip. On the other hand the slots must not be so narrow as to interfere with the passage of the substrate resulting in tearing, jamming or scratching during coating. Where there are variations in thickness along the length or across the width of the substrate, a seal which adjusts to these variations is required to minimize the leak through the seal. Tensioncontrol problems and the frequent low tensile strength of substrate being coated make it highly desirable that no substantial drag upon the substrate is created by the seal.

The apparatus of this invention not only meets these rigorous standards, but also permits belt threading of the substrate through the system without loss of vacuum. Torn and ragged edges present no problem in threading With this invention, and it is possible to thread using one pair of narrow threading belts. In addition the apparatus of this invention is extremely simple, cheap to manufacture and comprises a minimum of. moving parts.

Specifically in the present invention the substrate transits a plurality of evacuated chambers, In the lowest pressure chamber the substrate is coated with a vacuum deposited metal film such as aluminum. It is a primary consideration of the present invention that the amount of air that leaks into each chamber be kept to a minimum and that the maximum amount of air pumped out of the system be pumped out at the highest possible pressure. Accordingly, it is preferred that a low leak rate be maintained at each seal, through which the substrate passes in moving between chambers of different pressures. In order to minimize the leak rate, each seal must have a high impedance to the flow of air, i.e. it must create a highly tortuous path which any molecule must negotiate in order to move from one chamber to another. To achieve this minimum leak rate each seal must be such as to adapt at any point to the thicknms of the material passing through at that point.

A preferred method of threading a paper, for example, through a continuous coating apparatus is by the use of belts. A pair of narrow belts with their faces in contact is led through the path in the apparatus which the substrate is to follow. The belts are looped back in opposite directions to make each an endless belt. A leader attached to the substrate is fed between these belts. The belts are moved together, pulling the leader and substrate along. The substrate is thus threaded through the apparatus. After threading, the threading belts normally continue to run along side the substrate being coated.

To insure that the threading belts do not interfere with the substrate after the apparatus is threaded, means are provided to position the substrate and the belts in dilferent though parallel paths. One of the means includes a device to move the belts aside after threading. Another means includes a device for moving the substrate to the side, permitting the belts to run in their initial threading position. Finally, a side extending leader may be used to thread the susbtrate initially. This side-extending leader is attached to one of the edges of the substrate, and protrudes from the edge. It is fed between the threading belts and as it is pulled by the belts, the substrate is threaded through a parallel path, not in contact with the threading belts. complete threading.

The leader is only long enough to permit.

One of the rolls of the apparatus can be the driven member and the belts may be utilized to drive all otherrolls at the same speed. This serves to alleviate the tension on the substrate which, in some instances, may have low tensile strength.

Difiiculty has been encountered in applying this threading method to continuous vacuum coating. Known seal ing means have caused excessive wear of the belts and created tension control problems in the belts as well as in the substrate. Moreover, no suitable seal has been known which permits free lateral relative movement between the belts and the substrate subsequent to threading without loss of vacuum. Torn edges and the buckling of the substrate when pulled from only one side create jamming and tearing at seals normally adequate for continuous coating. The brush-membrane seal of this invention permits free movement during threading without loss of vacuum, thus making the vacuum coating of a substrate a more economical process.

The objects of this invention are achieved by providing a large gap between the moving substrate and a vacuumtight wall which separates the chambers between which the substrate is being passed. The substrate is led through that gap preferably in contact with a roll. From the wall to the substrate extends a'unique combination of bristles and gas-impervious flexible sheets. The bristles are sufliciently stiff so as to extend completely across the gap, contacting the substrate, and sufiiciently flexible so as to bend when in contact with the substrate. The coefficient of friction between the bristle material and the substrate must below. The number of the bristles required per unit length of seal'depends upon the diameter of each individual bristle and the density in which they are held as well as the pressure differential to be achieved.

In addition to the bristles, the gas-impervious nature of the seal is achieved by'interposing across the seal a plurality of gas impervious membranes, which preferably extend from the wall where the bristles are attached to the paper. These gas impervious membranes may be of any material with gas-impervious qualities such as latex, lateximpregnated cloth, polyethylene, polyethylene terephthalate, cellulose, acetate, metal foil or other such gas-impervious flexible sheets. In a preferred embodiment of the seal, the flexible gas-impervious sheet is polyethylene terephthalate, preferred because it does not absorb gases and because of its durability.

Referring now to the figures the invention will be explained in more detail.

In FIG. 1 there isshown a preferred embodiment of the apparatus of this invention. housing 26 is divided into a multiplicity of vacuum chain: bers 10, 12,14, 16, 18, 20, 22 and 24 by transverse walls 28 which are vacuum tight and are provided with openings in which there are provided seals schematically indicated at 30. Each chamber is connected to a vacuum system (not shown) provided to evacuate the chambers to various degrees of vacuum. Substrate 32 is fed from a supply thereof into the apparatus, through the seals and the various chambers and then out of the apparatus Where it can be rolled up in a known manner. In chamber 18, there is provided a source 34 of coating vapors of the particular substance to be deposited upon the substrate. Where coating by vapor deposition is being efiected the source comprises a crucible 3S filled with the coating metal 36 maintained in the molten state by a surrounding induction coil 37. A water cooled roll 40, with which the substrate 32 is preferably in contact while being coated, is located above the source.

i In the preferred embodiment of FIG. 1, the seals, indicated generally at 39, are all of thesame type and include a roll- 42 and a cooperating curved shroud 44 carrying the novel combination of bristles 46 and impermeable membranes 48 shown in greater detail in FIG. 2. Referring now to FIGS. 2 and 3, the details of an individual seal are illustrated in diagrammatic, fragmentary, enlarged views.

An outer vacuum tight In FIG. 2 one side of the substrate 32 is shown in contact with one of the rolls 42 which is rotatably mounted in the sealed opening 36. a.

On the side of the substrate away from the roll 42, there is provided the brush-membrane holder 44 carried by one of the transverse walls 23 and connected in a gas tight manner thereto. bristles 46 and gas-impervious membranes 48.

The bristles 45 extend from the holder 44 to the substrate 32. The bristles 46 may be of natural or synthetic material, for instance either hogs hair or nylon is suitable. Polytetrailuoroethylene bristles are sometimes preferred. The membranes 48 are maintained in extended relationship from the holder '44, by the surrounding bristles 46 which constitute strength members for the membranes 48. Thus extended, the membranes 48 serve as barriers to the passage ofgas molecules through the extending bristles. The bristles and membranes are preferably mounted in the holder by a cast plastic which forms a solid, vacuumtight connection with the holder 44.

it should be noted that with this arrangement, the maximum permissible thickness which can pass through the seal 3% is almost as large as the gap between the roll 42 a and the holder 44 since the bristles 46 and the membranes are sufficiently flexible so as to freely pass irregularities such as tears, splices, pieces of dirt md the like. On the other hand, the only possible passage for gas through the seal is adjacent to the substrate 32 at the space between the lower edge of the membranes and the substrate 32. This space is extremely small since the membranes preferably contact the substrate. The passage from one membrane to the next is highly tortuous due to the bristles which occupy this space.

In FIG. 3, it is seen that variations 32a in the substrate thickness and the threading belts 50 are easily accommodated by the seal with no substantial passage of gas therethrough. In FIG. 3 the end seal of one of the rolls 42is also shown as comprising a similar combination of bristles 46 and impermeable membranes 48. In this case the membrzmes also contact the end of roll 42. A similar seal is provided for sealing the surface of the roll opposite to that on which the substrate is traveling, as schematically indicated in FIG. 1.

Each seal 36 preferably includes five to fifteen or more impermeable membranes 48 and sufiicient bristles 46 between the membranes to provide a structure of adequate rigidity to maintain the membranes in their sealing position substantially in contact with the substrate 32. With time, the membranes may Wear so that they just miss touching the paper by a few thousandths of an inch. However this small gap has an enormously high impedance to the flow of gas therethrough. This is particularly true as the pressure in the system drops to the region of molecular rather than laminar flow.

In one preferred embodiment of the invention, each seal 30 preferably comprises 12 membranes of polyethylene terephthalate and five clumps of nylon bristles. The membranes are preferably about .001 inch thick and the bristles have diameters of about .003 inch. The gap spanned by the bristles and membranes is about 1 /2 inches and the membranes and bristles are firmly anchored to a support by a thermosetting plastic such as polystyrene. Each clump of bristles is preferably about 20 bristles thick along the direction of travel of the substrate.

The two belts 5t) which are threaded through the apparatus alongside the substrate can serve two functions. First, they can be used to thread the substrate without breaking the vacuum in the system. For this purpose they preferably grip an edge of the substrate or a leader attached to the substrate. The belts can also be used to drive all of the rolls at the same surface speed so as to prevent slippage between the roll surfaces and the substrate. 7

While one preferred embodiment of the invention has been described above, numerous modifications thereof In the holder 44 are mountedmay be made. For example, when sheet steel is being coated rather than paper, the threading belts can be eliminated, if desired, and threading can be accomplished manually. The problem of breaking the web is not so severe with steel as it is with paper. When steel is being coated the brush-membrane seals at the inlet and outlet pumping chambers can be eliminated by the use of barometric liquid seals and the brush-membrane seal of the present invention can be employed only for the lower pressure portions of the system.

Several sealing stages with intermediate pumping ports can be provided around the periphery of any single sealing roll rather than having the stages separated as illustrated in FIG. 1. These seals can be straight rather than curved, as illustrated, although the combination of the roll and brush-membrane seal is much preferred. While the membrane and bristles have been described as having substantially the same length, the membranes can be slightly shorter than the bristles due to the fact that the closely packed group of bristles has a very low Reynolds number with a consequent high impedance to the flow of gas therethrough.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An apparatus for continuously coating a substrate comprising a vacuum coating chamber in which a source of coating vapors is provided and at least one transition vacuum chamber in position between the coating chamber and the atmosphere to which a substrate to be coated is passed as it proceeds from the atmosphere to the coating chamber, said apparatus containing a multiplicity of rotatably supported rolls provided to support the substrate through its path, a driven endless belt provided to drive the rolls, said endless belt passing between the transition chamber along-side the substrate, and a plurality of seals between the chambers through which the substrate and the endless belt extend, at least some of said seals comprising a plurality of bristles filling the gap between the moving substrate and an adjacent wall separating the chambers, and a plurality of gas-impervious, flexible membranes which are transverse to the substrate and are held at an angle to, and in substantial contact with, the substrate by said bristles.

2. In a continuous vacuum coating machine comprising a plurality of sequentially arranged vacuum chambers, a source of coating vapors provided in one of the vacuum chambers and means provided for introducing a substrate into and through the vacuum chambers, for passing the substrate over the source, and for removing the substrate subsequent to coating, the improvement which comprises vacuum seals formed of a plurality of brush-membrane combinations, each such combination including a brush-membrane holder attached, in vacuum tight manner to a wall of the chamber, and a multiplicity of bristles extending from said holder to said substrate and a plurality of gas-impervious membranes extending from said holder transverse to said substrate, said membranes being held in gas sealing position by said bristles.

3. An apparatus for continuously coating a substrate comprising a high vacuum coating chamber in which a source of coating vapors is provided and at least two transition vacuum chambers in position between the high vacuum coating chamber and the atmosphere to which a substrate to be coated is passed as it proceeds from the atmosphere to the high vacuum coating chamber, at least three seals along the path or" the substrate from the atmosphere to the high vacuum coating chamber, each of said seals comprising at least five flexible impermeable membranes and a plurality of bristles holding said membranes spaced apart and in substantial contact with the substrate.

4. The apparatus of claim 3 wherein each said seal includes a roll and a cooperating coaxial shroud spaced from the roll, said membranes extending generally radially from the shroud toward the roll and substantially spanning the gap between the shroud and the roll.

5. The apparatus of claim 3 wherein each said seal includes a roll having said sealing membranes and said bristles contacting surfaces of said roll substantially along the entire length of the surface of said roll and contacting said substrate and in addition the ends of said roll so that said membranes and bristles substantially circumscribe said roll including the extremities thereof operating to gas seal said ends.

6. In acontinuous vacuum coating machine comprising a plurality of sequentially arranged vacuum chambers wherein a source of coating vapors is provided in one of the vacuum chambers and means are provided for introducing a substrate into and through the vacuum chambers, for passing the substrate over the source, and for removing the substrate subsequent to coating, the improvement which comprises vacuum seals formed of a plurality of alternate layers of bundles of flexible fibers and thin membranes, said membranes being no more than a few thousandths of an inch thick, said fibers and membranes being attached at one end to a holder, the other end of the fibers and membranes engaging the substrate, said membranes being held in gas sealing position by said fibers.

References Cited in the file of this patent UNITED STATES PATENTS 1,799,375 Jones Apr. 7, 1931 2,382,432 McManus et al Aug. 14, 1945 2,384,500 Stoll Sept. 11, 1945 2,963,001 Alexander Dec. 6, 1960 FOREIGN PATENTS 469,310 Great Britain July 22, 1937

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