US3494326A - Spin-coating machine - Google Patents

Description

Feb. 10, 1970 L. O. UPTON 3,494,326

SPIK-COATING MACHINE Filed Feb. 1, 1968 S Sheets-Sheet 1 INVENTOR. LEE 0. UPTON 7 L a i u M r n H,

A ATTORNEY Feb. 10, 1970 L. o. UPTON 3,494,325

SPIN-COATING MACkINE Filed Feb. 1, 1968 v 3 Sheets-Sheet 2 I INVENTOR.

/ L LEE 0. uPm/v AT T0 RNEY United States Patent US. Cl. 118-50 1 Claim ABSTRACT OF THE DISCLOSURE An improved device for applying coating solutions to spectacle lenses. The device includes an adjustable lens holder rotatably mounted in a sealed, glass-walled compartment, a coating applicator, and means for introducing filtered, dehumidified air under pressure into the compartment. A vacuum chamber connected to a vacuum device is positioned around said lens holder. When in operation, a controlled air flow is maintained around the vicinity of the spinning lens, as a result of the pressure differential created between the positive pressure within the compartment and the vacuum in the area of the spinning lens. By use of this invention, the problem of speckling or mottling lenses is eliminated. The sealed chamber includes glove means sealingly secured to openings in the chamber wall and permitting operator-manipulation within the chamber. At least one oven is incorporated into the structure defining the compartment and includes plural door means whereby entry into the oven can be from both Within said without the compartment.

Field of the invention Apparatus for spin-coating lenses and filters, including a controlled air flow in the area of the spinning lens.

Description of the prior art Lenses and filters have in the past been spin-coated by depositing on the center of the article to be coated a predetermined amount of the coating material and spinning the lens or filter to produce a thin film, as is shown in British patent specification 571,238. Prior art devices present problems in uniformly coating certain elongated lens shapes especially when the concave side of a lens is being coated. Many of todays lenses, especially those used in womens spectacles, are designed with a short axis and a long axis. As a result, the liquid coating material applied to the surface and spun off at the short axis is picked up along the surface of the long axis as the lens rotates, causing speckling or mottling of the surface along the long axis. By providing a pressure differential in accordance with this invention, a controlled air flow in the area of the spinning lens is produced so that material spun off is drawn clear of the surface to be coated and the problem of speckling or mottling is eliminated.

Summary A spin-coating machine including a sealed compartment and means for introducing filtered, dehumidified, heated air under a positive pressure into said compartment and a vacuum cavity producing a pressure differential in the area of the spinning lens for controlled withdrawal and flow of said air around the spinning lens.

It is an object of this invention to provide an improved device for spin-coating lenses by providing an environment free of dust and water vapor.

It is a further object of this invention to provide an improved device whereby the problem of speckling or mottling of the coated lens is eliminated by a controlled air flow around the spinning lens.

3,494,326 Patented Feb. 10, 1970 Brief description of the drawing FIG. 1 is a perspective view of an embodiment of the invention.

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1 with the operator removed.

FIG. 3 is an enlarged cross-sectional view of the vacuum chamber of the invention.

FIG. 4 is an exploded perspective cross-sectional view of the vacuum chamber as shown in FIG. 3.

FIG. 5 is a top view in diagrammatic form showing the flow of coating material.

FIG. 6 is a diagrammatic view similar to FIG. 5 but showing the lens in a position one-quarter of a revolution from the position shown in FIG. 5.

FIG. 7 is a side view of a spinning lens showing diagrammatically the controlled air flow that results from the invention.

The spin-coating machine of this invention consists of a booth generally indicated by the numeral 10, comprising a sealed compartment 12 supported by bench 14. Compartment 12 is built up from floor 18, side walls 20, 22, rear wall 24, top cover and front wall 27. Front wall 27 facing operator 26 is provided with two vertical glass panels 28 and 30. Separating glass panels 28 and 30 is a vertical metal sheet 32 having formed therein two openings 34 and 36, which are fitted with gauntlets 38 and 39. These may be made of parachute nylon or other light impervious sheet fabric material. Said gauntlets are tightened to operator 26 at the wrists and provide a means whereby operator 26 can extend both hands into the interior of compartment 12 while maintaining said compartment in a sealed condition. Directly above metal sheet 32 carrying gauntlets 38 and 39 is located movable glass cover 40, which slopes backward at an angle of about and is hingedly joined by hinge 41 to top 25 of compartment 12. A sealing material such as foam rubber is applied about the periphery of cover 40 to provide a tight seal between cover 40 and the adjacent edges of the frame in which it sits. Integrally joined to glass panel 28 and top 25 is glass side panel 43 and joined in the same manner to glass panel 30 is glass side panel 45. Located on each side of said gauntlets, so placed to be conveniently reached by said operator, are ovens 44 and 46, constructed of monolithic insulating refractory block-s, and heated by wire-wound heating units. In a typical embodiment said heating units are so positioned on the top and bottom of the oven as to provide for a uniform distribution of heat. Hingedly located on the front and back of said oven is framed door 48 also insulated With a monolithic refractory material. In a typical embodiment, both ovens protrude through rear wall 24 as is shown in FIG. 2. Lenses placed in an oven after being spin-coated, through the front door, can be removed by the operator from the rear door without entering into compartment 12 through either cover 40 or gauntlets 38. Formed in floor 18 intermediate between said gauntlets is aperture 50. Located directly beneath said aperture and symmetrically oriented with respect thereto is spin pan 52 having the general shape of a cylinder.

Spin pan 52 is supported by brace 49 and sealed to the underside of floor 18 of compartment 12 by gasket 51. Located beneath spin pan 52 is electric motor 54 having a rotatable shaft 56 extending through aperture 57 formed in the center of said spin pan. Fixedly at tached to shaft 56 as by set screw 61, is chuck 58, designed to receive lens holder 59 such as that described in US. Patent No. 3,336,902, assigned to the assignee of the instant application.

An electrical speed control device for said rotating haft, not shown, is located on a rear wall of said comlartment within said operators reach, and is capable of lroviding various speeds of rotation of motor 54 within he range of 100 to 4,000 revolutions per minute, as elected by the operator. Secured to floor 18 is mounting lange 60. Positioned in said flange is standard 62 havng pivotally joined thereto arm 64 which has attached hereon clamp 66. Said clamp provides means for se ,urely holding coating solution applicator 68 at the deired elevation and orientation over the lens chuck. Said tpplicator is generally comprised of tank 70 fitted with ilter 71. Tank 70 is fused to stopcock unit 72, which tself is fused to stem 73 having formed therein a suittbly sized orifice 75. A pressure pump, not shown, is :onnected by means of air line 74 to tank 70 by means )f rubber stopper 79. Proper pressure is applied to the iquid in said tank by means of an adjustable manually- )perated pressure reducing valve, now shown. When said ;tockcock is turned on, liquid coating materials are meered by pressure applied to said tank through said air me.

Secured to top 25 is housing 76 which houses a standard 'oom dehumidification unit mounted above a dust filter, )oth not shown. Mounted adjacent to housing 76 is lower 77 operated by motor 82. Said blower pulls air hrough the dust filter and the dehumidifier. The dustfree, dehumidified air is thus blown through an aperture, iot shown, in top 25 onto heating coils 78 mounted on )afile 80. A thermostat, not shown, is provided to control he temperature of the heated air within said compartnent. This mechanism supplies dehumidified, dust-filtered, leated air under a moderate degree of pressure into the :ompartment.

Located beneath said compartment is a suction device, such as a vacuum cleaner indicated by the numeral 82, laving a hose 84 which is connected to a T-joint 87. Formed in said hose beneath said T-joint is suction bycrass vent 86 over which is frictionally fixed rotatable lent cover 88. Attached to T-joint 87 are two suction hoses 90 which are attached to elbows 92. The base of said spin pan has formed therein ducts 94 over which is received elbow 92. So designed to be received by said :lucts 94 is a vacuum chamber, generally indicated by the iumeral 95. Said chamber includes a bottom circular plate 96 having an outer flanged rim 101, a central aperture 97 and two ducts 99 which extend in an opposite direction from said rim and are coupled to ducts 94 in said spin pan. Vacuum chamber 95 has an upper disclike plate 98 having formed therein a central aperture 100 corresponding to aperture 97 on lower plate 96 and having an outer flanged rim 102 which is telescoped over rim 101 on lower plate 96. The vacuum chamber, when connected to the vacuum device as described above, causes a high velocity air flow from the inside of the closed booth over the surface of the spinning lens. The air flow has a large radial component of motion for a purpose which will be described.

A slight positive pressure is maintained within the booth by adjusting the influx of air from blower 77 with relation to the exhaust of air caused by vacuum device 82.

In prior art spin-coating devices, serious problems resulted when attempts were made to uniformly coat elongated lens shapes, which are currently employed in a majority of womens spectacles. The problem is especially acute when coating the concave side of the elongated lens. As is shown diagrammatically in FIGS. and 6, the liquid coating material which is applied to the center of the spinning lens can result in an uneven coating. As the lens is spinning the coating material deposited on the center of the lens is spread out radially until spun off by centrifugal force at the edge of the lens. In FIG. 5 the letters 2: are intended to represent droplets of coating material flung ofi the short axis of the spinning lens. When a lense spins at 3600 revolutions per minute, a

complete revolution is made in 1, of a second, and the thin liquid coating centrifugally thrown from the center of the lens to its periphery at short axis s is picked up by long axis l as it passes through the air of a second later. In FIGS. 5 and 6 the arrow lettered D ind cates the direction of rotation of the spinning lens. This results in speckling or mottling of the surface along the long axis, represented by the letter x in FIG. 6. By use of the instant invention, the problem of speckling the surface along the long axis has been overcome. By providing a positive pressure within the booth and suction concentric to the spinning lens, two important results are obtained. First, the dry, filtered, dehumidified air under positive pressure within the compartment prevents the introduction of dust and water vapor within the booth which would, if present, prevent high quality coatings, and, second, the controllable pressure differential results in a controlled air flow which carries away droplets of the coating material spun olf the surface along the short axis as is shown diagrammatically in FIG. 7 before speckling or mottling of the surface along the long axis can result. In FIGS. 3 and 7 the arrows labelled F indicate the direction of the controlled air flow resulting from the pressure differential. When in operation, the pressure differential is controlled by means of vent 86, previously described, over which is frictionally fixed rotatable vent cover 88. While I am, at present, uncertain as to the reason the radial air flow entirely eliminates the redepositing of liquid droplets along the long axis of the lens, exhaustive tests have shown that in fact no such droplets are re-deposited. Although it is not my intention to be restricted to a particular theory, it is believed that the flow of air over the surface of the lens tends to lift the droplets just enough that they clear the long axis and are then carried olf by the force of the flowing air before the droplet can redeposit on the spinning lens. The pressure differential is adjusted to produce an air flow over the spinning lens having a velocity fast enough to carry away droplets flung off at the surface along the short axis before being picked up at the surface along the long axis.

Operation Lenses to be coated are placed within the compartment through cover 40. Coating material is placed within tank 70 by access through the same cover 40. With a supply of uncoated lenses within said compartment and with said tank filled with a coating material, the cover is closed. Further access into said compartment is accomplished by the operator inserting his hands through gauntlets 38 and 39. A lens to be coated is placed on said lens holder, washed by squirting a lens cleaning solution from a squeeze botle, and rotated at 3600 revolutions per minute until dry. Coating applicator 68 is then positioned over the center of the lens, the stopcock is then turned one-half a turn, and a predetermined amount of coating material is deposited on the lens by a regulated pressure applied along air line 74 as previously described. The lens is then spun at 3600 revolutions per minute until evenly coating and partially dried, removed and placed on a rack, which is not shown, and the rack, when filled, is placed within one of said ovens, which has been preheated, and baked. The oven is then cooled and the coated lenses are removed by an operator from the rear of the oven. The speed at which a lens is spun, baking time, baking temperature, cooling time and cooling temperature are factors which are dependent on the nature of the coating solution used and are no part of the present invention.

I claim:

1. A spin-coating machine comprising:

(a) a generally sealed compartment;

(b) an adjustable lens holder mounted on a .motor driven vertically disposed shaft and adapted to secure a horizontally arranged lens;

(c) nozzle means located in an upper portion of the chamber, in general alignment with said shaft whereby coating fluid may be dispensed centrally upon the upper face of said lens;

(d) means providing a flow of filtered, dehumidified and heated air into said compartment and directed generally centrally upon said coated surface;

(e) means to effect a vacuum in said chamber and comprising a conduit system having an intake which includes a pair of horizontally arranged concentric ring-plate elements disposed respectively above and below said secured lens and the internal diameters of which approximate the diameter of said lens, whereby said air flow is drawn peripherally from said lens;

(f) at least one oven means incorporated into the structure defining said chamber and including door means on both inner and outer oven walls whereby said oven may be entered from both within and external of said chamber;

(g) glove means sealingly secured to openings in a wall of said chamber whereby an operator may manipulate both the structure and lens within said chamber without breaking the chamber seal.

References Cited UNITED STATES PATENTS 11/1935 Huebner 11852 X 3 1937 Fritsche 11852 10/ 1945 Campbell 11852 12/1951 'Rowell 11852 X 9/ 1960 Charron. 8/1964 Cheroff et al. 117-201 9/ 1966 Matthews. 2/1969 Balain et a1 118-52 FOREIGN PATENTS 5/ 1944 France. 5/ 1933 Germany.

US. Cl. X.R.

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