Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reissue Patent
1998-03-25
2001-07-24
Padgett, Marianne (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S562000, C427S563000, C427S577000, C427S579000, C427S527000, C427S530000, C427S523000
Reissue Patent
active
RE037294
ABSTRACT:
FIELD OF THE INVENTION
This 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 INVENTION
There 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 largely coated by acrylic and polysiloxane dip-coatings or spin coatings. These coatings significantly improve the abrasion resistance of the lens compared to the uncoated lens. 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. The industrial goal is to obtain plastic lenses which exhibit the same abrasion resistance as glass lenses. Current commercial plastic lenses have abrasion resistance characteristics which are poor compared to glass. Therefore, when purchasing lenses, one must choose between glass, which is very abrasion resistant but is heavier, or plastic which is lighter but much less abrasion-resistant.
Other coatings have been suggested for plastic substrates, including lenses. Most of these coatings are so-called “plasma polymers” which are largely produced by creating a plasma from siloxane precursor gases. The substrates are exposed to the plasma, but they are not biased to cause energetic ion bombardment. 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.
Other coating processes have been suggested in which energetic ion bombardment is caused by mounting the substrates on the powered electrode in a radio frequency (RF) plasma system and exposing the parts to the plasma, thereby creating a negative bias on the substrate surface. The resultant coatings are often more abrasion resistant than the “plasma polymers”. 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. Furthermore, if the substrate is an insulator, the thickness of the substrate strongly influences the deposition process energetics and the properties of the resultant coating. This means that for production coating of insulating substrates of different size and shape, e.g. plastic lenses, it may be necessary to have different coating processes for each type of substrate. 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.
The following references illustrate prior an coating processes in which plasmas are used in direct contact with the surface of the substrate:
Rzad et. al., U.S. Pat. No. 5,156,882, describe a method of preparing a transparent plastic article having an improved protective stratum thereon. The protective stratum is deposited by plasma enhanced chemical vapor deposition (PECVD).
Balian et. al., U.S. Pat. No. 5,206,060, describe a process and device for depositing thin layers on a substrate using a plasma chemical vapor deposition (PCVD) technique. The substrate must be made conductive, and is used as an electrode in the PCVD process.
Reed et. al., U.S. Pat. No. 5,051,308, describe an abrasion-resistant article and a method for producing the same. The article includes a plastic substrate and a gradational coating applied by a PECVD process.
Devins et. al., U.S. Pat. No. 4,842,941, also describe an abrasion-resistant article and a method for making the same. The article includes a polycarbonate substrate, an interfacial layer of an adherent resinous composition on the substrate, and an abrasion-resistant layer applied on top of the interfacial layer by PECVD.
Brochot et. al., U.S. Pat. 5,093,153 describe a coated object comprising a glass substrate coated with an organomineral film by a PECVD process.
Bonet et al., U.S. Pat. No.
5
,
093
,
152
, describe a plasma polymerization method for making a coating of composition SiC
0-5
N
0.3-0.8
O
1.3-2.5
H
0.5-1.2
on plastic optical substrates, by placing the substrate in the afterglow of a plasma and injecting a silicon
-
containing material near the surface of the substrate.
Kubacki, U.S. Pat. No. 4,096,315, describes a low-temperature plasma polymerization process for coating an optical plastic substrate with a single layer coating for the purpose of improving the durability of the plastic.
Enke et. al., U.S. Pat. No. 4,762,730, describe a PECVD process for producing a transparent protective coating on a plastic optical substrate surface.
All of the prior art plasma deposition methods for application of wear and abrasion-resistant coatings suffer from one or more of the following deficiencies and shortcomings:
(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.
These shortcomings are highlighted in the following review of the two preferred prior art methods for deposition of abrasion-resistant coatings on plastic optical substrates: plasma polymerization and biased RF plasma deposition.
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. Typically substrates are pre-cleaned in an inert gas or glow discharge (plasma) prior to deposition. 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.
One of the key requirements for a protective coating on a variety of substrates, including optics, is the need to provide a barrier to moisture, oxygen, and other environmental elements. This requires formation of a coating structure with optimal atom packing density. 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. For the case of deposition of electrically insulating coatings on electrically conductive substrates by the biased RF plasma technique, i
Galvin Norman D.
Kimock Fred M.
Knapp Bradley J.
Petrmichl Rudolph H.
Brothers Coudert
Diamonex Incorporated
Padgett Marianne
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