CA1119902A - Process for coating vitreous article and such coated articles - Google Patents

Abstract

PROCESS FOR COATING VITREOUS ARTICLE, AND SUCH COATED
ARTICLE
ABSTRACT

A method for "hot end" coating of vitreous articles, with refractory magnesium oxide coatings from aqueous solutions of magnesium nitrate, which are applied to the vitreous surface at an elevated temperature to evaporate the water from the solution and pyrolytically decompose magne-sium compound to form a transparent magnesium oxide coating and articles with magnesium oxide and lubricious coating.

Description

The present invention relates generally to reractory "hot" end" coatings for vitreous articles such as glassware, and more particularly to improved method~ for forming magnesium oxide "hot end" coatings upon glassware from aqueous solutions, and to articles 90 coated.
The desirability of forming refractory coatings on vitreous suraces, such as glass, and particularly upon glass~are such as bottles, is well known. Pristine glass is theore~ically an extremely strong substance. However, when, or example, glassware is subiected to high speed processing machines and normal use in which glass is caused to rub against glass, scratches, abrasions, and other physical damage rapidly degrades the surface of the glass thereby providing sîtes for lnitiation of failure throughout the glass. Also, glass i8 subject to attack by various atmo-spheric consitituents, particularly moisture. Accordingly, it ha~ been an accepted practice in the production of glassware to form a refractory, so-called "hot end" coating upon the newly ormed glass, usually at or before the annealing lehr while the glassware is at an elevated tem-perature. After ~ormation o the refractory "hot end"
coating, it i~ conventional practice to thereafter apply a lubriclous "cold end" coa~ing at lower temperatures. "Cold end" coatings conventlonaLly include, or instance, waxy poly~thylene, ~at~y acids, beeswax, ancl other such lubri-clou8 co~positions, elther alone or in com~ination.
The "hot end" coatin~ o which ~he pre~ent invention pertains, di~play particular re~uirements which dis~ingulsh "hot end" coat~n~,s ~rom a number o~ other coatings previously employed upon gla88 ~or various purposes. For instance, thick coa~ings of tin oxide and magnesia hav~ been applied to, or instance, electrical insula~ors. Other thlck coat-ings of tin o~ide have been applied ~o provide electrical conductivity for defrosting o glass surfaces by employing the tin oxide coating as a resistance element. Semi-trans-parent, colored coatings have been utiliæed for decorative purposes and, in some instances, for tinting of glass.
"Hot end" coatings have a number of requirements not met by many known glass coatings. Typically, such coatings should be non-toxic as a coating, and also are desirably formed ~rom compositions which are not in themselves toxic and which do not form toxic by-products. The coatings ~ormed should not change the appearance of the glassware, i.e , are colorless and substantially free of iridescence.
Torque requirements of closur~s should not be altered.
Since glassware is formed at high rates, coatings must be conveniently applied and utilize relatively economlcal solvents and compounds. Further, "hot end" coatings must be resistant to normal handling a~d processing, such as washing, and must tenaciously adhere to the glass to provide a suit-able base ~or lubriclous "cold end" coating.
Contrary to the purpose o~ certain otller gla~ coatlngs, "hot end" coating~ should have hi~h electrical resifltance to ~id ~al~an~c actloll between, for in~tance, container clo~ure~ and other materlals which come in contact with the gla~s under damp condition~. The "hot end" coating l~selE
3hould not ~unction as an electrolyte in contact with metal closures. Thus, it wlll be recognized that "hot end"
coatlngs ~or glassware are a well recogn~zed group o ma~
ter~als ha~ing characterlstics and requîrements distinct ~rom other glass coatings.

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Currently, "hot end" coatings are generally tin oxide or titanium oxide, formed ~ro~ vapors of anhydrous ti~ or titanium tetrachloride or from aqueous solutions o such compounds. Howe~er, previously "hot end" coatings of tin, titanîum or zirconium oxide have also been formed from organic compounds applied in or from organic solutions.
A number of prior art discusssions exist concerning the ~arious coatings. For lnstance, U.S. Letters Patent 2,165, 819, issued July ll, 1939, discloses an electrical insulator of magnesium titanate suitable for formation on ceramic sub- ;
~tances such as condensors. Magnesium titanate is~disclosed as being suitable for a narrow, and quite speci~ic coating ~: purpose, but does not correlate with the requirements~ of a ~ ~-"hot end":coating. ~ :
U.S. Letters Patent 3,323,889, issued June 6, 1967, : ~ discloses a coa~ing system ~or the purposes o~ the instant:
. ~ : invention, but involves the use of zirconium and titanium ~ oxide as a:"hot end!' coating applied from an organlc solvent solution in con3unction with relatively conventional "cold ~ ;
end" coatings. Many organic~solvents are expensive, oten~ :
: ~lammable, and cau~e objeetionable pollution of the atmo- ~ :
sphere }lowever, U.S. Letters Patent 3j323,889 is pertinent in sett~ng $o~th man~ o the requirements of a "hot end" ~ -:
coating.
U,S, Le~er~ Pa~ent 3,450,57~, issued June 17, 1969, ,......................................................................... ..
1~ co~cerned wlth th~ p~eparation o~ a magnesla coating on re~ractory ~otles. Pre:eerably, ~he pa~en~ t~achQs thç
~orma~ o~ a:thin ~lm o~ metal under seducing conditions and therea~ter~pro~ldin~ oxidiz~n~l condi~ions to ~orm the oxide. Sinterl~g techniques are also disclosed, ' ' . ' ; : :

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U.S. Letters Patent 3, 516, 811, issued June 23, 1970, primarily discloses apparatus for applying "ho~ end" coat-ings in laminar flow conditions, but also contains a fairly comprehensive listing of ~arious prior art patents dealing with "hot end" and "cold end" coatings.
Typical of the hot end coatings discussed by U.S.
Letters Patent 3,516,811 is U.S. Le~ters Patent 3,561,940, issued February 9, 1971, which conce~ns the formation of tin oxîde coatings by the pyrolytic composition of anhydrous stannic tetrachloride vapors in a moisture-free carrier gas.
While tin oxide is a desirable and workable "hot end"
coating, the by-products of the pyrolitic decomposition include hydrochloric acid (upon hydrolysis with atmosp~eric moisture~ w~ich presents serious problems with regard to attack of surrounding equipment and pollution of the atmo~
sphere. Such installations may require expensive scrubbing equipment to remove the unused stannic tetrachloride and hydrochloric acid from the exhaust gases.
U.S. Lette~ Patent 3,694,299, issued Sep~ember 26, ~0 1972, discloses a means for fusing gla~s sheets together utilizing an organo-metallic film Eorming solution in which the metallic constituent may include magnesl.um. However, the solution utilizes volatile and combustible solvents as well a~ re~in~ which would be entirely lnappropriate for use in ~ "hot end" coa~lng compo~ltlon ~or t'he reason~ di~cussed above.
U,S, ~e~ers Patent 3,711,3~2l issued January 16, 1973, d~scloses or~anic sol~ent based composltlons utilizing two s metal compounds, one of which may be a magnesium compound such as magnesium acetate, to form semi-transparent, colored metal oxide coatings. For numerous reasons including trans-parencyJ color, organic solvents, etc., such coatings would not be useul as "hot end" coatings.
U.S. Letters Patent 3,847,583, i~sued November 12, 1974, ~imilarly discloses the use of two metal compounds dissol~ed in an organic solvent to form coatings. Titanit~n oxide and, it is believed, tin oxide, are discussed, and spec~fic mention i8 made that alkali or alkali earth oxides are not operable to fo~m pyrolytically induced oxide coat-ings U.S. ~etters Patent 3,926,103, issued Decem~er 16, 1975, discloses a recovery system for spray solut:ions of ~in compotmds.
Finally, U.S. Letters Patent 3,984,591, issued October 5, 1976, discloses the ormation of metallic oxide coatings from metallic salts utilizing, as a critical ~eature of the invention, aprotic solvents of specified dipolar moments which would be inappropriate for "hot end" coatlngs. Men-tion i8 ~ade of spraying aqueous solutions, but such coat-ings are characteriæed as being readlly removed Ln the form o dust by passing a finger over the coating.
Th~t~, on the basis o the above prior art, th~ only workable "ho~ endl' coa~ings are ~ho~e in~volvlng pyrolytic d~compo~it~on ~rom okJectlonable orgAnlc ~olvent~ or ~rom hallde~. In both ca8e~, ob~ect~onable by-products in the ~orm o~ e~haust ~ume~ are pre~entsd. The better, more economlcal coatings lnvolve pyrolytic decomposition of ~tannic tetrachloride with the resulting ~ormation of h~drochloric acid.

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The present inventlon, w~ich provides a heretofore unrecognized and unavailable improvement over previous methods for forming "hot end" coa~ings on glassware, in-volves pyrolyti~ decomposition of solutions of water soluble magnesium compounds which, directly or indirectly, form magnesium oxide ~ontaining coating upon glassware heated above about 450C, preferably between 500-700~C. Particu-larly, magnesium acetate, which provides high quality coatings with innocuous by-products, and also magnesium nitrate which forms a desirable coating with less desirable by-products are preferred, though other magnesium compounds have also been found to be operahle if suficiently wat~r ~oluble.
Accordingly, an advantage of the present invention is to pro~ide a new and improved coating method and refractory coating for gla~sware which adheres strongly to the g~ass-ware and does not substantially alter the appearance of the glassware.
~ nother ad~antage of the present invention i~ to provide a new and improved coating method and coating for gla~sware which displays an affinity for "cold end" coatings and provides both wet and dry lubr~cation with such "cold end" coatlng~.
S~ill another advan~age o the pre~ent lnven~ion i~ ~o provide a new and improved coa~ing method and lmproved coat~ng ~or ~la~w~re whlch coatlng 1~ non-toxic~
The~e and other adv~ntage~ of the presen~ invention will be apparent ~om the ~ollowing de~cription o ~he in~ntion.

According ~o the present invention, "hot end" coatings o~ magnesium ox~de are ~ormed on vîtreous substances such as glassware by applying an aqueous solution of magnesium compounds having specific proper~ie~ to glassware heated to an ele~ated temperature, i.e., a~ove 400C to 450C, and pre~erably a~ove about 550C. Typically, such surfaces are not hea~ed above 7Q0C, but in spec~fîc instances may be heated to hîgher temperatures without adversely affecting the coating in accord with the ins~ant invention. The limi~ing upper temperature depends upon the substrate and the coating and the lower temperature depends upon the coating.
Ma~y of the advantages of the instant invention accrue from the use of aqueous solutions of the magnesium compounds.
E~sentially, the compounds must be wa~er 601uble magnesium compounds. The magnesium compounds are dissolved in a water carrier and are sprayed upon the hot glassware preerably in the form of a mist or ~ine spray of the solution. It is a~so important that ~he magnesium compound decompose to magnesium oxide at the temperatures existing on the surface of the glas~ware and, preferably, after initially melting as t~e di~ol~ed magnesium compound.
While the mechanl6m is not entirely unders~ood, it i8 postulated that the magne~um compound i8 deposite~d a~ a solid upon the heated glassware as the ~ol~ent i9 evaporated ~rom th~ ~olution. Th~ ma~nesium compo~md~ ini~ially meLt and th~n pyrolytically decompos~ to ~orm ma~ne~ium oxide.
Accordingl~ the original magne~i~m compound, or an~ mag-n~um compound other than magnesium oxide ormed during the course o pyrolytic decompo~ition i.s stable at the tempera-ture involved, satis~actory resul~s will not be obtained.

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For instance, most magnesium compo~mds which are water soluble and include sulfur, i.e., magnesium sulfate hep~a-hydrate MgS04.7H20, and other such magnesium compounds in-cludi~g sulfur, i.e., magnesium thiosulfate MgS203.6H20, magnesium sulphite MgS03.6H20 which form, upon initial decomposition, magnesiu~ sulfate MgS04 (decomposition temperature of about 1124C) are not workable. This temper-ature is above ~hat to which glassware can conventionally be heated. Thus, the final coating is magnesiu~ sulfa~e rather than magnesium oxide and does not display desirable "hot end" coating characteristics. However, such sulfur contain-ing compounds ~ould be expected to provide good results in some instances at higher temperatures with, for instance, ceramics.
Examples of magnesium compounds which meet the above criteria and form worthwhile "hot end" coatings include magnesium acetate, magnesium nitrate, and magnesium formate.
As mentioned earlier, the sulfur containing compounds generally are not decomposable to magnesium oxide under the available temperatures.
Other magnesium compounds such as magnesium benzoate Mg(C7~I502)~ 3H~O, magnesium lactate Mg(C6H507).3H20 magne-~lum citrate MgHC6H07.5H~O and magneslum dicitrate M~,2(C6~507).5H20 appear to be too insoLuble to provlde cLear, adherent coa~lngs. While coatlngs are ~ormed, the coat~ngs tend to be cloudy and water soluble. ~hig appears to be a function o the solubllity of the magne~ium com-pound, ~Iighly soluble magnesium compounds, as discussed abo~e, are believed to form small particles of the compo~md upon the gla~sware whlch partlcles are belleved to immedi-... .

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ately melt into a smooth continuous layer of the compouncl, and then pyrolytically deoompose into magnesium oxide.
Water insoluble or marginally soluble magnesium co~pound~ do not yield the desired results, possibly because of the formation of solid magnesium compouncl particles in the presence of substantial quantities o solvent which do not melt into a smooth layer prlor to pyrolytic decomposition.
Of the magnesium compounds which satisfy the basic criteria, l.e., high water solubility, melting point below the general sur~ace temperature of heated glass, and pyro-lytic decomposition lnto magnesium oxide at the surface temperature of the glass, magnesium acetate is a particular-ly preferred composition having properties significantly superior to those of other of the operable magnesium com-pounds. For instance, magnesium acetate is highly soluble in water, generally employed at between 10 parts by weight of water to one part by weight of magnesium acetate to one part by weight of water to one part by weight of magnesium acetate, and typically at five parts by weight of water to one part by weigh~ of magnesium acetate, and melts at 80C
and decomposes at 323~C, presumably into magneslum oxide.
Upon decomposltion, magnesium acetate forms water and carbon dioxide as by-products. Magnesium oxide, magnesium acetate and th~ by-proclucts are all non-toxic ancl non-corroslve m~ter~al~.
Operably ma~nes~um oxlde ~ormed by applylng ~na~,nes~um aceta~e ~n an aqueous solutlon to reheated glas8ware may be pxocluced a~ surace temperature~ above about 400C to ~50C.
However/ ~he preferred range 1~ between 680C to 700C.

Below about 550C to 60QC, the transparency o~ the coating may become s~mewha~ une~en. A~o~e about 680C to 700C, the "hot end'l coating lubrica~ion quaiities diminish somewhat, particularly when wet. W~th n~wly ~ormed gla~s-ware with i~ternal ~emperatures higher than the sur~ace temperature, lower initial temperature may be operable.
M~gnes~
F ~ Mlgnci~um nitrate ~orms e~cellent coatlngs from aqueous solutions, but forms ~10x by-products upon pyroly~ic decom-posit~on. ~owe~er, magnesium nitrate meLts at 89C and decomposes at 330C ylelding excellent coatings a~ normaL
"hot end" glass coating ~empera~ures.
The resulting magnesium oxide "hot end" coatings in accord with the instant invention should, of course, be thick enough to afford subs~antîal protection to the protec-ted vitreous sur~ace, such as glassware. However, in most instances, the coating should not be thicker than about one wa~elength o light to which it is typically exposed, i.e., about one micron, to avoid wave interference within the coating leading to iridescence. In some instances, coatings may be thicker without otherwise degrading the results.
Iridescence, at times, is considered a desirable appearance.
A1BO, thicker coating4 ~end to be more electrically conduc-a xule, the eQatlng thickne~s ~ay b~ ea~ily co~roll~d by re~lating the ~xpo~ure tlme o~ the hea~ed , ~ gl~sswa~e to a ~iven concen~ration o~ the magne9ium compound aqu~ou~ 801utlon.

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As discussed above, the magnesium compound should be applied to a reheated surface at a~ least about ~00C, preferably between 550C and 700C, though higher tempera-tures are suitable for coating purposes. In most instances though, the vitreous surface may be adversely affected by higher temperatures, though certain vitreous surfaces, such as ceramic, may be heated to quite elevated ~empera~ures.
Somewhat lower temperatures may be employed with newly formed glass. Each magnesium compound suitable for forming 10 magnesium oxide coatings in accord wi~h the instant invention of course display dîffering melting points and pyrolytic decomposition points. Accordingly, optimum temperatures may vary somewhat from compound ~o compound~ though the above specified tcmperatures are generally operable. For instance, magnesium acetate is preferably applied to reheated surfaces between 680C and 700C, though good results may be obtained outside of thls range.
The concentratlon of the magnesium compoun~ in aqueous solution i8 not critical. Of course, more dilute solutions 20 require e~aporation of greater quantities of water and accordingly cool the glassware surface more. As a rule, between about 10% to S0% by weight of magnesium compound to wei~ht o ~olution ha~ been ~o~md to be a desirable opera~-Lng ran~e, though no~ a crLtical r~nge. Preferably about mldpoint o~ thi~ range Ls employed, ~ 'Lt should be noted ~ha~ the solublllty oE the magnesium r~' compound ln water i9 an lndependent eon~ideration rom ~ha~
J 0~ the actual concentration o the magnesium compounds ln solution w~en applied to vitreous surfaces. Thus, compo~nds 30 which marginallyr dissol~e at the above-~pecified concentra-:
r, .:

tion are not necessarily desirable coating compounds. As the water evaporates, solid particles of the magnesium co~pound is of course Xormed on the vitreous surface. This result can be prematurely accomplished in near sa~urated solutions of magnesium compounds. Accordingly, while not ~irmly established, it i8 believed that the more highly soluble magnesium compounds operable in the instant inven-tion do not orm solid particles until but small amounts o~
water remain thereby minlmizing the concurrent exi~t~nce of ~olid matter and solution and leading to melting of the particles to orm an initial coating.
It is contemplated that the magnesium oxide coatings formed in accordance with the instant invention will be further coated with lubricious "cold end" coatings as are well known in the art. Generally, this is accomplished by spraying the lubriciou~ coatings, usually as aqueous 501u-tions, onto the vitreous surfaces after, in the case of glassware, annealing i~ 6ub6tantially complete. Vapors of organic lubricious materials may also be employed to ac-compli3h the coating. "Cold end" coatings are well known inthe art. Typically ~uch coatings include one or more lubri-cious constituent~ such as waxy polyolefins such as poly-ethylene having a molecular ~s~ght between 1000 and 2000, ~atty acid~ ~uch as oleic, palmitic, ~tearic, lauric, or mlxtureA thereo~, alkali metal salts o~ atty aci.d~, beeswax and polyvinyL alcohol. Such "cold end" coatings ar~ well known in the art and are applicable to ~he magneslum ox-Lde coatln~s in a~cord with ~he instant invention.
A more detailed appreciation o the invention will be 0 galned from the ~ollowLng examples.

~P~ 2 Example 1 An aqueous solution of magnesium acetate tetrahydrate was prepared by adding one part by weight o the magnesium acetate compound to five parts by weight of water. A glass-ware article (bottle) was heated to provide a surface te~perature of about 640C. The solution of magnesium acetate ~as sprayed at a flow rate of about .5 grams per second while the glassware was rotatled upon a turntable a~
78rpmO Approxima~ely 16 revolutions o.E the glassware bottle occurred during an application. A clear, transparent coating of magnesium oxide was formed on the bottle. There-after, when the glassware had cooled to 120C, a com~ercial "cold end" coating, i.e., GLAS-LUBE 1000 available from Crown Chemical Company, diluted by a factor of 100 by weight in distilled water was sprayed at the rate of 1 gram of "cold end" coating solution per second for a period of 5 revolution~ of the glassware on the turntable as discussed above. The thus coated article with both "hot end" and ; "cold end" coatings was tested for lubrication both wet and dry. Under both conditions lubrLcatlon was found to be excellent when two such glassware articles were manually rubbed togethes.
, ~xample 2 A ~Las8ware article was coated utilizlng the same technlques and compo~l~ions A~ in ~xample l with the excep-tion that the article was pa~sed through a coa~in~ hood at a rate of about .~ ~et per second wh~Le the aqueous solution o~ magnesium acetate was sprayed onto the ar~icle through `` ~our nozzles arranged to provlde unl~orm coverage o~ the bottle on one pass through the coated hood. Results sub-:,:

~antially iden~ical to those of Example 1 were obtained.
Numerous other simîlar examples o~ coating o~ magnesium acetate were carried out wi~h the following observations;
excellent coatings were observed utiLizing between about 10~/o by weight (actually '~.1%~ of ~agnesium acetate to water to 50~ by weight o~ magnesium acetate to water; technical grades o~ magnesium acetate and ordinary tap water were ~ound to be entirely workable; and a preferred range of 550C to 700C was established, and a particularly preferred range being 680C to 700C was noted, ~or reheated glass with the lubrication degrading somewhat, particularly when wet at higher temperatures, and the appearance o the coat-ing degraded somewhat at lower tempera~ures.

Example 3 4.1 part~ by weight of water and 1 part by weight of magnesium nitrate hexahydrate were mixed to provide a s tion of magnesium nitrate. The thus prepared solution of aqueous magnesium nitrate was applied to a glassware article utilizing substantially identical conclitions as those em-ployed in Example 1. The reQulting "hot end" coat.ing wastran~parent and attractive in appearance, and the article a~ter "cold end" coatln~ prov-Lded good lubricatlon both dry and wet wh~n testetl ln a manner identical to that utili2ed in Ex~mple 1.
~ ther test~ with magneslum nikrate were conduc~ed with coating results substantially equal to those obtained wi.~h ma~ne~ium acetate, though lubrica~ion qualities were poorer utilizing more dilute solutions, and were marginal at about 10% by weight and below o magnesium nitrate to water solu-tions.

E ample 4 4.4 parts by weight of water and 1 part by weight ofmagnesium formate were mixed to form an aqueous solution of magnesi~m formate. The thus ormed aqueous solution of magnesium formate was applied to a glassware articl~ heated to a temperature of abou~ 660C to 680C as described in Example 1, An attractive transparent coating was formed.
"Cold end" coating was applied as described in Example 1 and the article tested for lubricity. Lubrici.ty was found to be good when dry and air wet. In general, magnesium formate was found to be an acceptable and desirabl~ "hot end" coat-ing material.

Example 5 Ten parts by weight of water and 1 part by weight of magnesium sulfate were mixed to form a magnesium sulfate aqueous solution. The thus formed aqueous solution of ; magnesium sulfate was applied to a glassware ar~icle heated to about 720C and the article was otherwise treated and coated as described in Example 1. The "hot end't coating was spotty, the article, including additional "coLd end'l coat-lng, displayed poor lubricity. It ls believed ~hat magne-; ~ium Elulate o~mecl the coatin~. Thu~, at the temperatures normnLl~ employed wl~h glas~ware, magnesium ~ul~ate was outlcl to be ~msa~ actory as havlng a decomposition point (abou~ 112~aC) above that o~ the working range o most ~la~sware.

F~ample 6 3.3 parts by welght of water was mixed with 1 part byweight of magne~ium benzoate. The magnesium benzoate did not entirely dissolve in the water. The magnesium benzoate solution formed; which was more di~u~e than the lnitîal consitituen~s, was decanted and applied to a glassware article heated to a te~perature of about 640~C in ~he manner described in Example 1. The resulting "hot end" coating was cloudy. Ater applying a "cold end" coating as descrlbed ln Exa~ple 1, ~he article was tested for lubricity. The results were poor because of poor adhesion of the "hot end" coating.
It was found that the l'hot end" coating would wash of~ in water. It is believed ~hat magnesium benzoate is not suf-ficiently soluble to form a clear, adherent coating asrequired of the magnesium compound in accord with the in stant ;nvention. Sim;lar results were obtained with mag-nesium ~actate, magnesium citrate, and magnesium dicitrate, all o which required decanting utillzing similar amounts of ; water and magnes~um compounds.
From the above description, it will be apparent that the instant inven~ion discloses an advantageous means for providing "hot end" coatings upon glassware. Aqueous coat-ings so;utions of magnesium compounds are much easier to utilize and yield less troublesome by-products than the anhydrou~ compounds previously employed in many instances.
Further, one ~killed in the art can, wlth little eort, identi~y ma~neslum compound~ ~uitable or u~e in the in~tant lnvention. Such compouncls are hlghly soluble ln water, i.e., ~orm ~olution~ o~ a~ leaa~ 50~/0 by ei~l~, and preer-~bly much h~gher~ of the ma~rle~u~ compound in water, dl~-play melting point below ~ha~ o ~he ~urace to be coated and pyro~ytic decomposltiorl point to magnesi.um oxide below the temperature oP the sur~ace to be coated but above the melting point o the magnesi~ compound~. Actual ~esting is ~7 easily accomplished by substituting various solutions in a coating hood.
In operation, it is preferred to conduct the vitreous articles, and particularly newly formed glassware, ~hrough a coating hood in which the aqueous solution of magnesi~n compound is applied to ~he bottle as a fine mist or spray.
Surface temperatures of the glassware and concentration of the aqueous magnesium solution are not critical wi~hin broad limits but do generally influence the nature of the "hot end" coating. Eighly dilute solutions, of course, may cause objectionable cooling Qf the unannealed articles.
Although only several specific examples and em~odiments of the present invention have been presented in detail, those skilled in the art will recognize numerous changes and modifications within the scope of the invent~on. Such changes may be made without departing from the scope of the in~ention, as defined by the following claims.

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Claims (13)

The claims defining the invention are as follows:

1. A method for forming protective, refractory coatings upon vitreous articles comprising, positioning a vitreous article heated to an elevated temperature within a coating location, applying a solution of a magnesium com-pound upon the surface of the heated vitreous article, evaporating the solvent from the magnesium compound solution at the surface of the vitreous article, and pyrolytically decomposing the magnesium compound at the surface of the vitreous article to form a continuous, adherent and substan-tially transparent coating comprising magnesium oxide upon the surface of the vitreous article.

2. A method for coating vitreous articles as set forth in Claim 1 in which the solution of magnesium compound is an aqueous solution.

3. A method for coating vitreous articles as set forth in either of Claims 1 or 2 in which the surface of the article is at a temperature above 400°C.

4 . A method for coating vitreous articles as set forth in either of Claims 1 or 2 in which the magnesium compound is melted after the solvent is substantially evaporated to form a coating of magnesium compound upon the vitreous article surface and thereafter is pyrolyzed to form the coating of magnesium oxide.

5. A method for coating vitreous articles as set forth in Claim 2 in which the magnesium compound is highly soluble in water, has a melting point below the surface temperature of the vitreous article, and a pyrolytic decomposition point below the surface temperature of the vitreous article and above the melting point of the magnesium compound.

6. A method for coating vitreous articles as set forth in either of Claims 1 or 2 in which the magnesium compound is selected from the group consisting of magnesium acetate, magnesium nitrate and magnesium formate.

7. A method for coating vitreous articles as set forth in either of Claims 1 or 2 in which the magnesium acetate is applied as a solution comprising between 10% and 50% by weight of magnesium acetate relative to the solvent.

8. A method for coating vitreous articles as set forth either of Claims 1 or 2 in which the magnesium refractory coating is between about .1 micron and 1 micron thick.

9. A method for coating vitreous articles as set forth in Claim 1 in which the vitreous article is cooled after formation of the magnesium oxide coating and a second lubri-cious coating is applied thereto at a lower temperature.

10. A method for coating vitreous articles as set forth in any of Claims 1, 2, and 9 in which a lubricious coating including at least one compound from the group consisting of waxy polyolefins beeswax, fattys acids, alkali metal salts of fatty acids, and polyvinyl alcohols is applied to the magnesium refractory coating.

11. A vitreous article having protective and lubricious coatings thereon, said articles comprising, a vitreous sur-face, a transparent, refractory coating comprising magne-sium oxide adhered directly to the surface, and a lubri-cious coating of an organic compound adhered to the refractory coating.

12. A coated vitreous article as set forth in Claim 11 in which the lubricious coating includes at least one constituent selected from the group consisting of waxy polyolefins, beeswax, fatty acids, alkali matal salts of fatty acids, and polyvinyl alcohols.

13. A coated vitreous article as set forth in Claim 11;
in which the magnesium refractory coating is between .1 micron and 1 micron thick.