Ion beam process for deposition of highly abrasion-resistant coatings

Abstract

An ion beam deposition method is provided for manufacturing a coated substrate with improved abrasion resistance, and improved lifetime. According to the method, the substrate is first chemically cleaned to remove contaminants. In the second step, the substrate is inserted into a vacuum chamber, and the air in said chamber is evacuated. In the third step, the substrate surface is bombarded with energetic ions to assist in the removal of residual hydrocarbons and surface oxides, and to activate the surface. <DEL-S DATE="20010724" ID="DEL-S-00001">Alter<DEL-E ID="DEL-S-00001"> <INS-S DATE="20010724" ID="INS-S-00001">After <INS-E ID="INS-S-00001">the substrate surface has been sputter-etched, a protective, abrasion-resistant coating is deposited by ion beam deposition. The ion beam-deposited coating may contain one or more layers. Once the chosen thickness of the coating has been achieved, the deposition process on the substrates is terminated, the vacuum chamber pressure is increased to atmospheric pressure, and the coated substrate products having improved abrasion-resistance are removed from the vacuum chamber. The coated products of this invention have utility as plastic sunglass lenses, ophthalmic lenses, bar codes scanner windows, and industrial wear parts that must be protected from scratches and abrasion.

Description

FIELD OF THE INVENTIONThis invention relates generally to a process for depositing coatings which protect a substrate from wear and abrasion. More particularly, the invention relates to a process for protecting such substrates as plastic sunglass lenses, ophthalmic lenses, bar codes scanner windows, and industrial wear parts from scratches and abrasion.BACKGROUND OF THE INVENTIONThere are numerous prior art methods for coating substrates to improve their performance, e.g. lifetime, abrasion wear resistance and similar properties. For example, consider the case of plastic sunglass lenses or plastic prescription eyewear. Due to the ease of scratching plastic, abrasion-resistant coatings are deposited onto the surface of plastic lenses. These hard outer coatings increase the useful life of the lenses. To make such coatings marketable, the process for depositing these hard coatings must be inexpensive, reliable and reproducible.Plastic lenses sold into the ophthalmic lens market are lar...

AI Technical Summary

Benefits of technology

The invention provides an improved method for deposition of an abrasion-resistant coating onto substrates. More particularly, this invention provides an ion beam deposited coating to the surface of a substrate which is highly adherent, and exhibits greatly improved wear resistance and environmental durability. Still more particularly, this invention provides a low cost and efficient process for mass-producing coated substrates with improved wear resistance and superior lifetime. The method is especially useful for applying an abrasion-resistant coating to the surface of plastic optical substrates, such as lenses.

Problems solved by technology

This is particularly true for the case of polycarbonate which is very subject to abrasion.

However, improved abrasion resistance of coated lenses is still a major problem in the ophthalmic lens industry.

Current commercial plastic lenses have abrasion resistance characteristics which are poor compared to glass.

The performance of these plasma polymers is often only marginally better than that of the polysiloxane and acrylic spin and dip coatings, and the performance of these coatings does not approach the performance of glass.

These films are often quite soft and are not useable as protective coatings except on extremely soft substrates.

These plasma systems are not readily scaled to a throughput required for mass production nor are they easily operated in a reproducible, controlled fashion in a production environment.

The RF plasma process also suffers in that the deposition process, and the properties of the resultant coating are dependent on whether the substrate to be coated is an electrical conductor or insulator.

This reduces the flexibility of the process for use in production.

Additionally, systems with large area electrodes are not widely available.

For example, there are no readily available commercial parallel plate RF deposition systems having large electrodes, i.e. at least one meter in diameter.

(1) difficulty in pre-cleaning of substrates prior to deposition;

(2) adhesion of the protective, abrasion-resistant coating;

(3) permeation of the coatings by water vapor and oxygen;

(4) fabrication of coherent, dense coatings;

(5) control of coating properties during a deposition run and batch-to-batch variation of coating characteristics;

(6) coating thickness control and reproducibility of thickness;

(7) part-to-part and batch-to-batch control of coating uniformity;

(8) difficulty in coating substrates of complex geometry or configuration; and

(9) production readiness and ability to scale-up the deposition process for mass production.

The first problem encountered by both methods is the difficulty in pre-cleaning the substrates prior to deposition of the adhesion layer or abrasion-resistant film.

This pre-cleaning technique suffers from low cleaning rate, and re-contamination of the substrate by sputtered contaminants which are deposited back onto the substrate.

This atom packing density is maximized by a high degree of ion bombardment during film growth, which is not easily attainable or optimized by the plasma polymerization methods of the prior art.

Regarding the control of the coating properties within a single deposition run, and from batch-to-batch, it is well known that control is difficult with the plasma deposition methods.

This decrease results in a change in the properties of the deposited coating, i.e. hardness, stress and hydrogen concentration.

Because the size and shape of the particular part to be coated, and its method of fixturing influence the plasma uniformity and plasma density around the part, it is difficult to predict and control deposition thickness uniformity across multiple parts coated within a single coating run using the plasma deposition methods of the prior art.

While the plasma deposition methods offer high deposition rates, it is difficult to reproducibly control deposition rate, deposition thickness and deposition uniformity across large areas with plasma deposition methods.

Because of the interdependence of process variables such as pressure, gas flow rate, power, and substrate bias, accurate control of deposition thickness is difficult.

Thus, it is very difficult to manufacture coating layers with thickness less than 0.1 micron, and with run-to-run thickness variation of less than approximately 10%.

This is a significant disadvantage of the plasma deposition techniques of the prior art for the deposition of optical coatings, especially those requiring the use of multiple, thin layers of varying refractive index, such as antireflection coatings.

Finally, because of the sensitivity of the plasma deposition processes to substrate geometry, it is often impossible to coat parts of complex geometry or configuration.

These electrically insulating industrial machine parts are especially difficult to coat uniformly by the plasma deposition methods.

All of the difficulties above combine to make mass production of protective, abrasion-resistant coatings on a variety of substrates by the plasma deposition processes of the prior art very problematic indeed.

It is believed that RF equipment is not commercially available which approaches this level of scale.

However, one major disadvantage to prior art ion beam deposition processes, e.g. for deposition of DLC films, is their relatively low deposition rate which leads to long production times for thick coatings, and hence high production cost.

These large voltages are difficult to control and become problematic in a production environment.

In addition, the coatings manufactured by this method are opaque and not useable for applications where a transparent coated product is required.

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