GB2539177A

GB2539177A - Method and apparatus

Info

Publication number: GB2539177A
Application number: GB1508503.8A
Authority: GB
Inventors: Michael Conway Trevor
Original assignee: Optimal Tech Ltd
Current assignee: Optimal Tech Ltd
Priority date: 2015-05-18
Filing date: 2015-05-18
Publication date: 2016-12-14
Also published as: GB201508503D0

Abstract

The method comprises advancingly moving substrates, such as ophthalmic lenses, in a batch on a carrier through process vessels which perform respective functions, and reversingly moving the batch at one or more intervals back to at least one of the vessels to perform at least one of the functions again. The coating may be anti-scratch. The ophthalmic lenses may be organic. The functions may comprise ultrasonic cleaning, or primary or de-ionized water rinsing. Also claimed is an apparatus for applying a coating to substrates comprising a driving device for moving a carrier carrying a batch of substrates, process vessels for performing respective functions, and a control system which drives the carrier advancingly through the vessels, and at one or more intervals drives the carrier reversingly to at least one of the vessels.

Description

Method and Apparatus This invention relates to a method of, and apparatus for use in, applying a coating to substrates.

s Machines designed to apply anti-scratch coatings to organic substrates, such as ophthalmic lenses, traditionally run the substrates through a series of in-line process vessels in batches. A batch of ophthalmic lenses generally comprises at least several lenses, some machines having batch sizes of several hundreds, but the coating process is usually the same, with batches being indexed through the io machine at 5-minute intervals typically.

Preparation of the lenses in these 'hard coating' machines is in water-based detergents and rinse tanks. Ultrasonic transducers provide the necessary mechanical scrubbing action through cavitation of the liquid. Filtration in the is process vessels removes particles from the liquids. Drying is either with infrared (IR) heaters or warm air. Coating often requires different index-matched lacquers and a primer undercoat. The primer undercoat requires a dedicated curing oven (IR or warm air) before the top coat can be applied. The top coat is pre-cured in ovens, which are usually a repeat of the preceding drying ovens. It is this complexity that would make an automatic version of the traditional machine commercially unviable for a batch size of two or so.

A conventional machine is shown in Figure 1 of the accompanying drawings. This moves the batches along stage-by-stage from left to right through several process stages described in the table therebelow.

A problem to be solved by the present invention was to fill a niche in the market for a machine that would deliver that comprehensive process, but for only 20 lenses per hour and market-acceptable build cost. For using the traditional process one could simply provide smaller vessels, but the cost of individual pumps, heaters, ultrasonic generators and the like would have to be the same owing to the fact that the quantity of process vessels would have to be the same.

According to one aspect of the present invention, there is provided a method of applying a coating to substrates, comprising mainly advancingly moving said substrates in a batch on a carrier through a series of process vessels performing respective functions, and reversingly moving such batch at one or more intervals so as to perform at least one of said functions again in at least one of said process vessels dedicated to said at least one of said functions.

According to another aspect of the present invention, there is provided apparatus for use in applying a coating to substrates, comprising a driving device arranged to move a carrier for carrying a batch of substrates, a series of process vessels serving to perform respective functions, and a control system arranged to drive said carrier advancingly through said vessels but at one or more intervals to drive said carrier reversingly to at least one of said vessels.

It is possible to use the same stock vessels as in a bigger machine, but which are too big for what would be used in a conventional smaller machine, because the larger stock vessels can each receive at least two of the present smaller batches.

Thus, at least one single vessel can be used for double processing. This is made possible by software which cycles that vessel between cleaning and filtration for more than one batch at a time. The manufacturing cost saving for heating, filtration, ultrasonic generators, pipework and controls are significant. The machine is also more compact.

The present machine can have a batch size of only two lenses, which would make it commercially unviable, owing to the cost of manufacturing and the return on investment, if a conventional multi-vessel process was used.

The present machine can use the same dryers as a bigger machine so that it is possible to utilise an upstream side of a first dryer to dry the lenses after cleaning and a downstream side to cure a primer coat. This is again made possible by the control software, which moves the lenses back up the machine after primer application rather than downstream to a dedicated dryer.

By grouping the coating vessels together it is possible to save space and to replace, e.g. three, individual automatically opening lids with one single lid covering all three coating vessels.

In order that the invention may be clearly and completely disclosed, reference is made, by way of example, to the accompanying drawings in which:-Figure 1 shows diagrammatically a side elevation of a per se known machine for coating organic ophthalmic lenses; with therebelow a table of processes carried out in the machine and times therefor.

s Figure 2 shows diagrammatically a side elevation of a machine according to the present invention for coating organic ophthalmic lenses; with therebelow a table of processes carried out in the machine and times therefor.

The processes 1 to 17 and process times given in the table below Figure 1 are typical in the prior art for processing 60 lenses per hour in batches of 6 lenses.

The processes 1 to 11 and process times given in the table below Figure 2 are for processing 20 lenses per hour in batches of 2 lenses. The processes include washing, applying of primer, curing of primer, hard coating, and pre-curing of the hard coating, before exiting the machine for final curing.

The stages 2a and 2b are for ultrasonic cleaning. During cleaning the batch is cycled between ultrasonic cavitation and filtration. The global time and the toggle time are set in the process menu. Typically the batch is pulsed each cycle for 60 seconds. Total immersion in NaOH (or KOH) is for 10 minutes with regular intervals of cleaning and particulate removal.

The stages 3a and 3b are for primary water rinsing. This is performed in a constantly filtered rinse tank and, when lenses enter it, a solenoid valve opens to allow supply water to enter the tank and displace existing water, thus preventing chemical build-up. The purge time and the global time are independently programmable.

The stages 4a and 4b are for de-ionized water rinsing. The water flows through s this tank at, say, 9001itres/hour, which is capable of a tank change every 50 seconds. During rinsing the batch is cycled between ultrasonic cavitation and filtration. The global time and the toggle time are set in the process menu. Each batch can be pulsed each cycle for 60 seconds and achieve 5 tank changes of de-ionized water at 0.07p.S (microsiemens).

Claims

CLAIMS1. A method of applying a coating to substrates, comprising mainly advancingly moving said substrates in a batch on a carrier through a series of process vessels performing respective functions, and reversingly moving such batch at one or more intervals so as to perform at least one of said functions again in at least one of said process vessels dedicated to said at least one of said functions.
2. A method according to Claim 1, wherein said coating is an anti-scratch coating.
3. A method according to Claim 1 or 2, wherein said substrates are organic.
4. A method according to any preceding Claim, wherein said substrates are ophthalmic lenses.
5. A method according to any preceding Claim, wherein at least one of said functions is selected from at least one of cleaning and rinsing.
6. A method according to Claim 5, wherein said cleaning is ultrasonic cleaning.
7. A method according to Claim 5 or 6, wherein said rinsing is at least one of primary water rinsing and de-ionized water rinsing.
8. Apparatus for use in applying a coating to substrates, comprising a driving device arranged to move a carrier for carrying a batch of substrates, a series of process vessels serving to perform respective functions, and a control system arranged to drive said carrier advancingly through said vessels but at one or more intervals to drive said carrier reversingly to at least one of said vessels.
9. A method of applying a coating to substrates, substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.
10. Apparatus for use in applying a coating to substrates, substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.