CA1077787A

CA1077787A - Abrasion resistant coatings for plastic surfaces

Info

Publication number: CA1077787A
Application number: CA263,623A
Authority: CA
Inventors: John R. Hollahan; Theodore J. Wydeven
Original assignee: National Aeronautics and Space Administration NASA
Current assignee: National Aeronautics and Space Administration NASA
Priority date: 1975-11-21
Filing date: 1976-10-18
Publication date: 1980-05-20
Also published as: AT355321B; DE2650048A1; FR2332313B1; GB1529995A; ATA862876A; JPS5265575A; NL7612893A; IT1072621B; NL184625C; DE2650048C2; JPS5948017B2; US4137365A; NL184625B; FR2332313A1

Abstract

ABSTRACT OF THE DISCLOSURE

Abrasian resistant protective coatings for plastic surfaces such as acrylics, polystyrenes and polycarbonates is provided by the plasma polymerization of at least one member of a group of organosilane compounds selected from a group consisting of vinyltrichlorosilane, tetraethoxyailane, vinyltriethoxysilane, tetravinylsilane, vinyltriacetoxysilane, hexamethyldisilazane, tetramethylasilane, vinyldimethylethoxy-silane, vinyltrimethoxysilane and methyltrimethoxysilane.
Plasms polymerization of these organosilane compounds provides an abrasion resistant protective coating for plastic optical surfaces together with a uniform optically clear layer in the 4,000 to 8,000 angstrom range. The advantages of applying plasma polymerization to the present organosilane compounds is further enchanced by the utilization of an additive gas during plasma polymerization to further increase the abrsion resist-ance of the protective coating.

Description

~L~77787 BACKGROUND OF THE IN~TENTION:
Field of the Invention This invention relates to the utili~ation of plasma polymerization or glow discharge polymerization process to a group o~ organosilane compounds which when plasma polymer-ized provide a superior abrasion resistant protective coating.
The present organosilane abrasion resistant coatings when plasma polymerized provide a uniform and optically clear (4,000 to 8,000 angstroms) protective layer for plastic and plastic optical components. More particularly the present invention relates to the application of plasma polymer-ization processes to a novel group o~ organosilane compounds to provide an abrasion resistant protective coating to a less durable plastic surface by the plasma polymeriæation of at least one member of a group of organosilane compounds selected from a group comprising vinyltrichlorosilane, tetra-ethoxysilane, vinyltriethoxysilane, tetravinylsilane, vinyl-triacetoxysilane, hexamethyldisilazane, tetramethylsilane, vinyldimethylethoxysilane, vinyltrimethoxysilane and methyl-trimethoxysilane.
The plasma polymerization process together with thecompounds o~ the present invention provide not only an optically clear scratch resistant coating for plastic substrates but also eliminate pFoblems with directionality ~, - , .. .. ... . .

~ ~77787 requirements encountered in the coating of plas-tic substra-tes.
Plastic substra-tes coated in accordance with the present inven-tion exhibit a uniform optically clear coating useful in pho~
tographic and other applications where an op-tically clear sur-face is required which posse~ses the properties of abrasion resistance and a uniform coating thickness.
Description of the Prior Art ' .
Synthetic plastic optical componen-ts have generally been made from various organic resins such as acrylics, polystyrenes, poly- ~ -10 carbonates, polymethylmethacrylates, Plexiglas ~ Lexan ~ and , ; other such synthetic resins. Optical components made from trans-parent synthetic resins possess many advantages over glass and crystalline optical ma-terials, such as lower cost of production and their resis-tance to ther~nal shock and mechanical stresses.
Such plastic optical components have however been particularly vulnerable to abrasion, scratching and environmental conditions ``
~7hich results in an impairment if not complete destruction of their optical capabilities.
Various efforts have been made in the art to eliminate or ~ ', retard the impairment of the optical capabilities of transparent :~
plas-tic optical components by the appl;cation of various types of scratch resistant coatings by an array of methods including dip I coating, elec-tronic beam coating, ultraviolet polymerization and 'I the application of coatings by solvent r~r~ing techniques in ,~ which a solvent is evaporated from a coating composition resulting `;
in subsequent coating formation. These coating compositions and ' processes have generally not proven to be an effective method of ' ,, 30 protecting transparent s,ynthetic resins as such processes have res~lted in additional problems relat-ing to uniformity of coating, '~ random adhesion between the coating and substrate, orientation, and directionality requirements between the subs-tra-te _3_ , . , . . ., . ,. .;. ; . , , ~ . :

` ~()'77~7 .:., and origin of the coa-ting composition. Prior art processes have also resulted in expensive coa-ting costs and wide varia-tions in the quality and uniformity of the scratch resistant properties of the coated plastic product.
In some instances the coating compositions and procedu-; res of the prior art have resulted in problems of compatability of the coating material and the substrate to cause in-terference with the optical transmission capabilities at the interface between the plastic substrate and -the coating composition. Other coating techni~ues and compounds employed in -the prior art sacri-; ~ioed the optical ~ualities of the plastic substrate to obtain a surface that was more resistant to abrasion. In addition the coating compositions and techniques for applying coating compo-sitions employed in the prior art have not provided a method for producing a uniform optically clear abrasion resistant coating -transmitting in the L~,000 -to 8,000 angstrom waveleng-th range.
SUMMARY OF THE I~VENT~ON: `
The disadvantages and limitations of the prior art are obviated by the present invention which provides the utilization of plasma polymeriza-tion or glow discharge polymerization proce-sses to a new and useful group of organosilane coating composi-tions which are particularly resistant to environmental condi-` tions and systems in which transparent synthetic resins are sub-jected to abrasive conditions. The abrasion resistance of the present organosilane coa-ting compositions is coupled with advan-tages of efficient application by the utilization of plasna po-lymerization to pr~ide a tenacious, uniform and optically clear ~; coating in the 4,000 to 8,000 angstrom range. The new and use-ful coating compositions are compatible with the acrylic, poly-- 30 styrene, polycarbonate and other synthetic resin surfaces and are well suited .' ' ~.

: ~

~777~7 ., to the plasma polymerization processes of the present invention to provide a uniform abrasion resistant surface.
The organosilane coating compositions which have been found to be particularly useful in providing optically clear coatings for plastic substrates by plasma polymeriza-tion are organosilane compounds from the following group wherein at least one member of the organosilane coating compositions is selected from vinyltrichlorosilane, tetraethoxysilane, vinyltriethoxysilane, tetravinylsilane, vinyltriacetoxysilane, hexamethyldisilazane, tetramethyl-silane, vinyldimethylethoxysilane, vinyltrimethoxysilane and methyltrimethoxysilane.
In accordance with this invention there is provided a method for protecting plastic surfaces which comprises applying a coating to a plastic substrate by plasma poly-merization of an organosilane coating composi~ion consi.sting of at least one organosilane compound selected from the group consisting o~ vinylkrichlorosilane, tetraethoxysilane, vinyltriethoxysilane, tetravinylsilane, vinyltriacetoxy-silane, hexamethyldisilazane, tetramethylsilane, vinyldi-methylethoxysilane, vinyltrimethoxysilane and methyltri- , methoxysilane.
DESCRIPTION OF TH~ PREEERRED EMBODIMENT:
The set up and mechanical operation of the plasma polymeri~ation or glow dischaxge polymerization processes utilized in the application of the organosilane compounds to provide an abrasion resistant coating have been described in U.S. Patent No. 3,847,652, issued November l~, 1974, and entitled, "Method of Preparing Water Purifica-tion Membranes". The present invention utilizes plasmapolymerization processes in the application of a specific class of organosilane compounds which when plasma pol~merized offer superior abrasion resistant optically clear coatings for plastic surfaces.
The organosilane compounds of the present invention provide a particularly useful abrasion resistant coating for plastic optical components together with the advantages of the plasma polymerization process for the application of abrasion resistant coatings to less durable plastic surfaces 4~ such as acrylicst polystyrenes, polycarbonates, Plexiglas~
(polymethylmethacrylate), LexanW and other such synthetic resins. The present organosilane ~ 10'777~37 coa-ting compositions are highly compa-tihle wi-th the plastic substrate and -the plasma polymerizat;on proces6es permits a tena-cious organosilane coating ~hat con~ormally adheres to the sub-strate, including an~irregular plastic substrate. These organo-silane compounds furthermore provide an optically clear abrasion resistant coating in the 4,000 to 8,000 angstroms wavelength range for optical components h~ving a plastic resinous substrate.
The plasma polymerization processes as appli~d to the present ; organos~làne compounds have the furt~er advantage in not impo-sîng directionality requirements between the s~bstrate and the origin of the coating mater~al.
The application of plasma polymerization to the organosilane compounds of the present inven~ion allows a greater array of mono-mers to ~e polymer~zed wh~cn are respon~ive to the polymerization proces8 as a result o~ the hi~h energ~ dosages that a~e availa-ble to promote polymerizat~on ~nd prov~de c~atings having supe-rior mechan~cal stren~th and uniformity o~ coating deposition. The polymer~zation processea ma~ ther~ore be emplo~ed to ~rovide organoxilane coati~gs of c~mpounds that are combined and polyme-rized to provide useful coatin~ ao~pos~t~on~ that are eas~ly appliedto result in a wide var~et~ of optical coat~ngs having a variety of desirable optical c~aracterist~c~.
The organo~ilane c~mp~t~ons of ~he pre~ent ~nvention are highly conformal and compatible w~th s~nthetic plastic sub~trates thereby enabling the~r appl~cation and use ~ith su~rates having m~cro-~tructu~al deta~l suc~ as pr~nted circu~t b~ards and micro- ;-e}eotron~c components. Once polymer~zed the organosilane com-pounds provide a super~or abrasi~n reslstant coating for pl~tic ~urface~ whic~ seals out moisture and ot`her environmental in-~luences. The organo~lane compcsiti~ns of the p~esen* ~nvention may be polymer~zed ~7~787 either alone or in combinations to provide an optically clear coating on plastic surfaces and are set forth in Table I below.

TABLE I
Code C mical Name VTCS vlnyltr~ch~orosilane TES ; ~ etraethoxysilane ~TES v~nyltriethoxysilane TVS tetravinylsilane VTAS vinyltriacetoxysilane HMDSZ hexamethyldisilazane TMS tetramethyls~lane VDMES vinyldimethylethoxysilane VTMS v~nyltrimethoxysilane ::
MTMS methyltrimethoxysilane The organosilane coating composit~on~ o~ the present in-vention are polymer~zed E~y a plasma polymeriz~tic)n process to im~
part superior a~ra~ion resistance to the pla~tic substrate. Re- :
pr~sentative condit~on~ under which an o~ganos~lane compound, such as vinyltrimethox~s~1ane, is deposited as a coatlng upon a plasti~
` substrate by plasma polymer~zat~on is set fort~ in Table II below.

: TA~LE I~

Compound ~ P~es~ure~ .Flow- ~3~n~~ ower ~ è~Time ~torrJ Mo~omer Argon ~atts) (secs) vinyltrimethoxy-silane 0.264 5 14.5 30 l~OD

vinyltrimethoxye~ ...
~ilane 0.254 5 lS.0 30 2000 vinyltrimethoxy-~ilane 0.260 5 14.5 30 3000 : The conditions as set forth in Ta~le I-~ utllize~ an inert atmosphere, wh~ch generally c~n range ~rom about 0.05 to about _ 0.~ torr, wherein argon is us~d in plasma polymerization alth~u~h other gases and mixtures t~ereof ma~ be employed. The conditions as set forth in Tabhe H II can also be employed in the plasma ;~
polymerization of other organosilane compounds wh~ch ", .~ :, ,,, , , ;

~777~37 are set forth in Table I to provide optically clear abrasion resistant coatings for plastic ~lbstrates. The time of depo-sition, power and atmosphere may be varied to accommodate the thickne3s of the coating de~ired or the particular type or combina-tion of monomers employed. In addit1on the gaseous environment may also be varied to impart various characteristics to the coating as will be discu~sed more fully hereinafter.
The pr~ent invent~on ~ll be furt~er de~cribed by way of the ollo~ing example to more conveniently set forth the conditions and operation of the present invent~on which i~ no~ intended to limit the scope or applica~ ty of t~e ~nvention.
... .....
EXAMPL~ r An abrasion re~i~tant ~ptically clear coating of vinyltri-methoxysilane is applied ~o;a portion of Lexan ~ by p:Lasma po-lymerization. Plasma polymerizat~on of vinyltrimethoxysilane coating on a portion of the Lexan ~ is deposited for 1300 seconds in an argon atmosphere at 0.2$0 torr. total pressure and at a power setting o~ 30 ~atts. These c~ndit~ons may be conveniently summarized as:
Run No. P~e~sure Flo~ _ Power Time (torr) Monomer Argon ~watts) (secs) VTMS-3A,B 0.260 5 l~.5 30 1300 A~ter depositing vin~ltr~methoxysilane over a portion of the Lexan ~ substrate a diamond stylu~ or scribe is drawn over the coated and uncoated portions of the Lexan ~ substrate to test the ; abrasion resistance o~ the vinyl~rimethoxysilane coating. The stylus is mounted so that t~e di~mond chip contacted the Lexa ~
sur~ace and the stylu~ rested at a 45~ angle about a freely moving pi-v~* point while the Lexan ~ ~ample i8 drawn under the stylus a~ an incident pressure at the diamond chip o about 7 to lQ grams . The .. . -. . ...
., ,. ~ , .,.: .. i :' ' ' . J , ' ' 10777~37 Lexan R sample exhibited scratch lines on the uncoated por-tion of the Lexan R which are not exhibited over on to the vinyltrimethoxysilane coated portion o~ the LexanR. The vinyltrimethoxysilane coating is uni~orm and optically clear and provides a superior coating for the prot~ction of plastic optical elements such as lenses, prisms and other components and elements that are particularl~ adapted for optical uses.
While the Example has described the use of an inert ga-seous atmosphere such as argon, the preferred e~bodiment of the present invention con~emplates emplo~ing variou~ other -~ases in the plasma polymerizat~on processes asuch as an atmo~phere of oxygen, nitr~gen, ammonia, water vapor; sulfur dioxide and mixtures thereof. Plasma polymerization in the presence of such gases results not onl~ in -the polymerization of the organosilane compounds but also resulta in the incor-poration o~ a portion o~ the gas to provide additoinal bonds of Si-0, Si-N and Si~S ~ond~ wh~ch are kno~n to be re~rac~
tory and impart add~tional strength to t~e coating composi-tion. The util~zation and selection of add~tl~e gases may be made on the basis o~ desire~ organosilane bonds to enhance the selection of opt~call~ clear plast~c coating compo~itions having de~irable optical and du~able characteristic6 and as a ~urther means o~ suppl~menting the abrasion resistance o~
the organos~}ane comp~s~tions o~ the present învention. These o~ganosilane compounds provide superi~r abras~on resistant coatings which exhibit a h~h degree of mechanical st~ngth and uniformity of coating that may be modified to suit parti-cular requirements by not only combining various organosilane compounds but also by utilizing var~ou~ gaseous atmospheres i.n carrying out the plasma polymerization process of the present invent;on. These plasma polymerization processes furthermore allow a great variety of monomers to be ~(:P7'~787 polymerized because of the wide range o~ power available to provide a selection of a Yariety of desirable optical characteristics to be achîeved through the selection and combination of optical coating compcsition~ and plastic substrate ~aterials.
It will be appreoiated that ~e present invention can be implemented in di~fkrent ~a~s by those skilled in the art to suit particular requirements which are within the ~aope of th~s invent~n and whioh are included within the appended cl~ims, ' ' - .. ;

,~
:~ r .. :

Claims

CLAIMS:

1. A method for protecting plastic surfaces which comprises applying a coating to a plastic substrate by plasma polymerization of an organosilane coating composition consisting of at least one organosilane compound selected from the group consisting of vinyltrichlorosilane, tetra-ethoxysilane, vinyltriethoxysilane, tetravinylsilane, vinyltriacetoxysilane, hexamethyldlsilazane, tetramethylsilane, vinyldimethylethoxysilane, vinyltrimethoxysilane and methyl-trimethoxysilane.

2. The method of claim 1 which further comprises employing a gas during plasma polymerization of said organo-silane coating composition wherein said gas is selected from the group of gases comprising oxygen, nitrogen, ammonia, water vapor, sulfur dioxide and mixtures thereof.

3. The method of claim 1 wherein said plasma poly-merization is initiated in an inert gaseous atmosphere under a pressure of about 0.05 to about 0.6 torr.

4. The method of claim 3 wherein said inert gaseous atmosphere is argon.

5. A method for applying a uniform optically clear abrasion resistant coating to a plastic substrate comprising the plasma polymerization of an organosilane coating composi-tion consisting of at least one organosilane compound selected from the group consisting of vinyltrichlorosilane, tetraethoxysilane, vinyltriethoxysilane, tetravinylsilane, vinyltriacetoxysilane, hexamethyldisilazane, tetramethylsilane, vinyldimethylethoxysilane, vinyltrimethoxy-silane and methyltrimethoxysilane.

6. The method of claim 5 which further comprises employing a gas during plasma polymerization of said organosilane compound wherein said gas is selected from the group of gases comprising oxygen, nitrogen, water vapor, ammonia, sulfur dioxide and mix-tures thereof.

7. The method of claim 5 for applying an optically clear abrasion resistant coating wherein said coating transmits in about the 4,000 to 8,000 angstrom wavelength range.

8. The method of claim 5 wherein said plasma poly-merization is initiated in a gaseous atmosphere of argon under a pressure of about 0.05 to about 0.6 torr.

9. The method of claim 8 wherein said organosilane compound is vinyltrimethoxysilane.