AU587091B2

AU587091B2 - Process for forming structural coating on vitreous ceramic or porcelain substrate

Info

Publication number: AU587091B2
Application number: AU66286/86A
Authority: AU
Inventors: Alan Don Mcinnes
Original assignee: VAPOCURE INT Pty
Current assignee: VAPOCURE INTERNATIONAL Pty Ltd
Priority date: 1985-12-03
Filing date: 1986-11-26
Publication date: 1989-08-03
Anticipated expiration: 2006-11-26
Also published as: AU6628686A; WO1987003576A1

Description

PROCESS FOR FORMING STRUCTURAL COATING ON VITREOUS CERAMIC OR PORCELAIN SUBSTRATE

This invention relates to the formulation of structural coatings, films and the like. By the invention there is provided an improved product (and process of producing it) , which product displays increased performance in areas related to its structural stability. The invention flows from our discovery that a particular substrate - coated in accordance with the process hereafter defined and described - is not merely provided with coating but, in addition, achieves a dramatic and unexpected improvement in certain functional properties.

The invention finds application in the structural reinforcement, restoration and/or refurbishing of vitreous containers such as bottles of all configurations, types and sizes (for milk, soft drinks, and alcoholic or other beverages), drinking vessels, jars, vases - in fact, glass containers or glass surfaces of any kind and for any purpose. The invention is also appropriate for the structural strengthening of other materials such as porcelain and ceramic ware. Its practical value is thus self-evident.

In one broad aspect, the invention provides a process for forming a structural coating (as herein defined) on a vitreous, ceramic or porcelain substrate thereby protecting and strengthening the substrate comprising the steps of applying a coating material containing free isocyanate groups to the substrate and subjecting the thus-coated substrate to treatment with a drying agent at room temperature, the drying agent being in vapour-phase and being:

(a) ammonia, an amine or an alkanolamine; or

(b) a multi-component agent comprising (i) water and (ii) a further component selected from an amine, alkanolamine or other hydratable compound.

More specifically, the invention provides a process for forming a structural coating (as herein defined) on a glass bottle thereby protecting and strengthening the glass bottle comprising the steps of applying a one component coating material containing free isocyanate groups to the surface of the glass bottle and subjecting the thus-coated bottle to treatment with a drying agent at room temperature, the drying agent being:

(a) in vapour-phase and

(b) a multi-component agent comprising water and an amine.

In a further aspect, the invention provides a structural coating (as herein defined) comprising a coating material containing free isocyanate groups applied to a vitreous, ceramic or porcelain substrate and dried thereon at room temperature by a drying agent in vapour-phase, the drying agent being:

(a) ammonia, an amine or an alkanolamine; or

In a still further aspect, the invention also provides a glass bottle the surface of which is protected and strengthened by a structural coating (as herein defined) , the coating comprising a one component coating material containing free isocyanate groups applied to the surface of the bottle and dried thereon at room temperature by a drying agent, the drying agent being:

(a) in vapour-phase and

(b) a multi-component agent comprising water and an amine.

In the specification, the following is to be understood:-

1. In respect of a structural coating, retentive film or the like which is to be, or has been, subjected to the process of the invention - the term "drying" is to be understood as (i) including within its ambit "curing" and as (ii) indicating that the coating is either free from "tack", insoluble in solvent, possessed of an advanced degree of integrity, or able to withstand reasonable abrasion or pressure without damage. It will also be appreciated that a dry coating may evidence any or all of the foregoing qualities.

2. The expression "substrate" denotes an article or article surface which can be structurally strengthened and/or stabilised by the structural coating of the invention. The substrate is vitreous, ceramic or porcelain in nature.

3. The expression "coating material" denotes a material which, on application to the substrate and treatment with the drying agent, will contribute to the formation of the structural coating of the invention. The material contains isocyanate groups, may be of the one-component type, and may include solvent(s), additive(s) and/or surfactant(s) as required. It may be clear, translucent or opaque.

4. The term "structural coating" denotes a coating (such as an organic coating) which functions to protect, strengthen and contain (by envelopment or otherwise) a substrate to which it is applied. The coating is derived from the coating material as above defined, and is effective at reduced thicknesses not previously contemplated, i.e., thicknesses of the order of 10-20 microns. This is not to say that the invention is restricted to coatings and coated substrates where the thicknesses is of this order (it is not so restricted as will be evident hereafter) . What is simply meant is that the coating is effective at such reduced thicknesses. The expression "structural coating" is, for the purposes of this invention, to be understood as synonymous with "retentive film" (or the like) .

5. The expression "drying agent" connotes the chemical compound(s) which effect(s) the curing or drying of the coated material. It may be sometimes

•alternatively referred to, in this text, as a catalytic agent, or simply as a catalyst. The drying (or catalytic) agent may be ammonia, an amine or an alkanolamine. In another form of the invention it may be a multi-component (e.g., two-component) agent comprised of water, as the first component, together with at least one further component selected from an amine or alkanolamine or any other hydratable compound which, in association with the water, will accelerate the desired pathway. It is believed that the water and the further component(s) interact, or interreact, to form an agent of hydrated complex type, which agent is thereby effective in drying the coated material at an accelerated rate - and, in so doing, in structurally strengthening the substrate upon which the material has been coated.

It was of course known to coat glass bottles prior to the present invention. However, the previously known coated bottles have invariably been characterised by coatings of substantial thicknesses and/or have required heat to carry out the coating process. Whilst the thus-coated bottles were reasonably satisfactory performance wise, undue thickness of coating, coupled with a tendency to falter if conditions of storage, transport and usage were other than ideal, tended to make them unattractive to users. In addition, there was clearly scope for refinement and improvement in the coating procedures.

It was likewise known to coat certain substrates with coating vehicles containing curable groups and dry the vehicles in vapour-phase. However, the known procedures were unrelated to the areas of the present invention. The coating of the herein identified substrates in accordance with the herein described process had never been contemplated - nor could the surprising results obtained by the present invention have been envisaged.

As briefly indicated above we have discovered that particular substrates, coated in accordance with the invention, achieve a dramatic improvement in certain functional properties. Specifically, we have discovered that glass bottles, so coated, not only attain these improved properties but, unexpectedly, are able to do so at coating thicknesses not previously considered possible. A glass bottle of, and coated in accordance with, the invention is thus able to achieve a higher level of user acceptance. In^' association therewith, the coatings, being able to be rapidly dried at room temperature, can be applied more efficiently and economically than is the case with thermal application. Still further, the coatings in the present invention are applied as liquid coatings which have substantial practical advantages over powder form coatings which also feature prominently in the prior art.

The present status of the glass bottle industry is such that a uniform level of technology in the art is generally available to manufacturers on a worldwide basis. Thus the same techniques, processes, raw materials, intermediates and the like are being utilized to, produce a similar type of product. A thin protective, structural coating as provided by this invention, possessing a high order of abrasion resistance, enhanced tensile strength and the ability to show excellent adhesion to a cross section of glass or ceramic substrates, opens up enormous possibililities for the glass container industry. When one couples to this the fact that the formulations herein described may be cured at room temperature in a matter of minutes, it will be realised that the invention provides a dramatic advance - capable of industrial implementation on a major scale - in the glass bottle industry.

The structural coating once cured adds increased burst strength to a glass container, lowers the possibility of surface scoring and, in the event of breakage, retains a greater percentage of glass fragments within a close proximity to the point of breakage. A related consequence is that bottles may be made of thinner glass (and thus lighter in weight) with resultant economic advantages.

In the preceding description the structural strengthening of the substrate has been mentioned. Whilst it is emphasised that the specification is not to be construed as bound to any particular theory of operation, it is nevertheless believed that the increase in burst strength of a glass container, coated in accordance with the invention, may be attributable to the following:-

(a) the filling, by the liquid coating material. of all surface cracks_* or other imperfections whereby, on curing, the entire container is structurally strengthened; and

(b) the scavenging of water molecules, from such surface cracks or other imperfections, by the reactive groups contained in the coating material, thus producing a completely anhydrous surface which in turn inhibits the propogation of further surface imperfections.

The invention will now be described with sequential reference to (i) preferred sub-generic performance features and (ii) specific detailed examples. It is to be understood that, being merely illustrative of the invention, such ensuing description is not to be limitatively construed.

The coating is desirably of the one component (or one pot) type containing free isocyanate groups. The expression "free isocyanate groups" includes within its ambit potentially free such groups, the meaning to be conveyed being that the prepolymer has isocyanate groups which are releasable, or available for reaction with water molecules or any other compound possessing active hydrogen sites (for the purpose of polymer propogation and/or film formation) . Compounds containing free isocyanate groups are to be understood as embracing all such compounds.

Accordingly, comprehended thereby are, not only isocyanates with urethane structure and polyisocyanates, but also those with polyisocyanurate, biuret, allophanate and urea structure.

Particularly preferred isocyanate containing coating materials are toluene diisocyanate (TDI) prepolymers, xylene diisocyanate (XDI) prepolymers (hydrogenated and otherwise) , and blends thereof and based thereon. Others include prepolymers of 4,4*-diisocyanato diphenyl methane (MDI) , trimethyl hexamethylene diisocyanate (TMDI) , hexamethylene diisocyanate (HMDI) , isophorone diisocyanate (IPDI) and appropriate blends thereof.

Certain additives in usually minimal amounts (e.g.. trace quantities to 2%) may also be preferably used in the formulation to achieve the optimum levels of adhesion to the substrate or to modify, as required, the rheological properties of the coating to facilitate in its mode of application. The adhesion promotors are typically silane based compositions, in turn exemplified by -glycidoxy propyl trimethoxy silane. Further additives may include flow promotors/surfactants, wax emulsions and water scavengers, which are respectively exemplified by silicone based compositions, polyethylene wax emulsions and monofunctional isocyanates and molecular sieves. Further additives may include organo metals and inorganic salts in turn respectively exemplified by dibutyl tin dilaurate, lead tetrethyl, titanium acetyl acetonate, dimethyl tin dichloride, stannous and zinc octoates and bismuth nitrate and ferric chloride.

As indicated above the coatings and coated substrates of the present invention are effective at reduced thickness - with resultant advantages as indicated. Typically, but not essentially, the thicknesses may be of the order of 10-20 microns (e.g., 15 microns). However, depending upon particular circumstances and requirements, thicker coatings (e.g., of the order of 40 microns) may be applied. It should also be understood that coated substrates can be recoated to any desired thickness.

As indicated, the drying (or catalytic) agent may be ammonia, an amine or an alkanolamine. Alternatively it may be a multi-component agent with the further components as set forth above. The drying agent effects its treatment in vapour-phase. Where the agent is a multi-component agent, the further component may be first complexed with water molecules as indicated above (to form an agent of hydrated complex type) . The expression "vapour-phase" denotes that the drying agent is in gaseous, vapour, or any other entrained air-borne form (e.g., dispersion, fog or aerosol) in which it is available for reaction. The drying operation does not require heat being carried out at room temperature.

The expression "amine" includes within its ambit not only those of simply primary aliphatic monofunctional structure, but also amines characterised by (i) polyfunctionality and (ii) a more advanced degree of hydrogen substitution. In the case of tertiary amines these may be (a) polyfunctional, (b) aromatic, (c) aliphatic or cycloaliphatic in nature.

The amine itself may be widely exemplified. Thus typical examples are mono compounds such as methylamine, ethylamine, propylamine, isopropylamine and the numerous isomers of butylamine and polyfunctional amines such as hydrazine, ethylene diamine, propylene diamine and diethylene triamine. Further examples are diethylamine, triethyla ine and dimethylethanolamine (DMEA) , and ditertiary amines such as

N,N,N' ,N'-tetramethylethylenediamine (TMEDA) and N,N,N' ,N" ,2-pentamethyl-l,2-propanediamine (PMT) - and, indeed, any combination of such amines, proportioned as required, whereby advantage may be taken of the synergistic effect of such a combination.

Particularly preferred drying agents are dimethylethanolamine (DMEA), N,N,N' ,_.^•-tetramethyl- ethylenediamine (TMEDA) and N,N,N' ,N' ,-2-pentamethyl- 1,2-propanediamine (PMT) .

The expression "vapour-phase" has been defined above. Where the drying agent is a multi-component agent, attainment of this phase is desirably achieved by the atomisation of predetermined quantities of water and a selected said further component. The concentration levels, of water and the further component, may be varied in accordance with situational requirements. For instance, the drying may be carried out at 45-85% relative humidity, for example 65%, at a temperature within the range 20-30°C (e.g., 250C) . The concentration of drying (catalytic) agent may vary in accordance with the chosen further component. Thus for DMEA, the concentration is preferably in the range 1200-1800 ppm, for example 1400 ppm. For DMI and TMEDA the respective preferred ranges are 700-900 ppm (more preferably 800) and 800-1000 ppm (more preferably 900) .

The coating material may be applied to the substrate by any conventional means (spraying, dipping, brushing) capable of applying a film/coating on to a surface uniformly and to specific wet film thicknesses. Once applied, the coating material may be treated in accordance with processes previously developed by us. One such process is described in co-pending Australian Patent Application No. 47146/85, the disclosures of which are incorporated, herein, by cross-reference. Another process, the disclosures of which are likewise incorporated by cross-reference, is set forth in co-pending Australian Patent Application No. 23010/83.

Initial tests, carried out on glass containers coated in accordance with the invention, indicate that the surface of such a container has a readily controllable coefficient of friction. Further tests show that the coated glass containers are better able to withstand the vigorous treatment to which glass containers are subjected in conventional asse blyline container-filling and like operations. Thus a coated container, in a moving assemblyline, is less likely to be "popped" from its position or jammed through excess friction. In addition adjoining surfaces of glass containers can be rubbed together for much longer periods under increased pressures without suffering adversely from dulling, chipping, scratching or scoring, such as presently occurs during the transportation of these articles over long distances.

In a further test, a one litre bottle, coated with a structural coating as described herein, was found to display greatly improved levels of fragment reteηtion when dropped on a hard surface from a height of one metre. All these tests will be set forth and explained hereafter.

The coatings of the invention demonstrate remarkably good integrity under a diverse range of exposure conditions. They are completely inert, solvent resistant, and display no change in characteristics after rigorous cleaning (e.g., 20 commercial dishwasher cycles) . The ability of a coated glass container to withstand rigorous cleaning will also be demonstrated hereafter.

A further advantage is demonstrated when a glass container, coated in accordance with the invention, is recycled. Because it is possible to volatilize the coating (e.g., in a melt furnace), uncontaminated glass can once again be available for moulding. Thus the invention involves no loss of re-cyclable glass. Nor is it necessary to separate clear glass from coloured glass.

We now proceed to the specific detailed examples, which demonstrate both (i) the formation of the protective structural coating on the substrate, and (ii) the testing of this protected and strengthened substrate. Where abbreviations requiring possible explanation are employed, such explanation is provided. Where ingredient(s) are commonly known by the trade name(s) under which they are commercially available, the trade names are given. Otherwise, the terminology is the standard terminology of the art.

EXAMPLE 1

A clear coating material, for coating glass bottles, was constituted as follows:- Component Parts by Weight

Toluene Diisocyanate Prepolymers 56.5 Aromatic Hydrocarbon Solven 40.0

(a high flash aromatic naptha commercially available under the trade name "Solvesso 100") Silicone Based Flow Promoter 2.0

(product known commercially as "BYK 300") Silane Based Adhesion Promoter 1.0

(product known commercially as "Silane A 187") Wax Emulsion (polyethylene wax) 0.5

The coating material was sprayed from a - 11 - conventional siphon pot spray gun, at an application viscosity of 18 seconds FORD Cup No. 4, onto a pristine (i.e., newly manufactured) glass bottle rotating on a turntable within a conventional spray booth. The coating was applied to the external surface of the bottle to give a thickness equating to approximately 15 microns dry film.

The bottle was then placed in a drying chamber and subjected to a gently turbulent air stream (air movement 1.5 metres per second) containing a concentration of DMEA of 1400 ppm at 25°C, 65% relative humidity. After exposure to this treatment for one minute, the chamber was evacuated and fresh air was circulated around the chamber for a post-cure period of three minutes.

The resultant coated bottle exhibits all the improved properties specified heretofore. These will be demonstrated in ensuing Examples. EXAMPLE 2

An opaque white coating material, for coating glass bottles, was constituted as follows:- Component Parts by Weight

Xylene Diisocyanate Prepolymers 50.0 Titanium Dioxide (pigment) 20.0

Inert Grinding Resin for pigment 5.0

("Durasol 310") Ester Solvent ("Corsol EEA") 23.8

Moisture Scavenger for pigment 1.0

("Additive TI") Surfactant ("BYK 300") 0.2

The coating material was sprayed through a conventional siphon pot spray gun, at an application viscosity of 16 seconds FORD Cup No. 4, onto a pristine glass bottle rotating on a turntable within a conventional spray booth. The coating was applied to the external surface of the bottle to give a thickness equating to approximately 15 microns dry film.

The bottle was then placed in a drying chamber and subjected to drying in the manner and under the conditions set forth in Example 1. The finished product was characterised by excellent opacity and an attractive gloss finish. In addition the coated bottle exhibits all the improved properties specified above.

EXAMPLE 3

Introductory:-

Eight pristine glass bottles were removed from a bottle manufacturer's lehr with only the conventional stannic chloride hot end coating applied. Eight identical further bottles were removed from the lehr l>ut, in this instance, a conventional cold end coating of polyethylene wax had also been applied. These bottles will be compared in Example 6 hereafter.

The eight unwaxed bottles were placed on a conveyor line to transport them through a sidedraft spray booth and in front of an electrostic turbo bell applicator. The applicator applied a transparent green coating material constituted as follows:-

Component Parts by Weight

Toluene Disiocyanate Prepolymers 50.0 Aromatic Hydrocarbon Solvent 37.0

(as in Example 1) Methyl Ethyl Ketone Solvent 8.0

Organic Green Dyestuff 1.5

(Savinyl Green G L S) Silicone Based Flow Promoter

(as in Example 1) 2.0

Silane Based Adhesion Promoter 1.0

(as in Example 1) Wax Emulsion (as in Example 1) 0.5

The coating material was applied via the electrostatic turbo bell to give a wet film coating equating to approximately 15 microns dry film. The coated bottles (which had been spun and which also had metal probes inserted) continued on the conveyor line through an air curtain and into a permeation zone. In the zone, controlled conditions of 25©C, 65% relative humidity and 1400 ppm of DMEA (air movement 1.5 metres per second) were maintained.

The transport time of the bottles was arranged to give one minute permeation under these conditions. - 13 - Thereafter, the bottles passed through an air curtain and into a post-cure air movement for a period of three minutes. When removed from the conveyorised line the bottles were completely dry, free of solvent odour and demonstrated the improved properties specified above. EXAMPLE 4

An opaque etched amber coloured coating material was constituted as follows:-

Component Parts by Weight

Xylene Diisocyanate Prepolymers 25.0 Hydrogenated xylene 25.0 diisocyanate prepolymers Aromatic Hydrocarbon Solvent 17.0

(as in Example 1) Methyl Ethyl Ketone Solvent 10.0

Organic Amber Dyestuff 1.5

(derived from Savinyl dye material) Silica 20.0

Silane Based Adhesion Promoter 1.0

(as in Example 1) Wax Emulsion (as in Example 1) 0.5

This coating material was applied in the manner set forth in Example 2. Drying was carried out as per Example 1. Again, the thus coated bottles demonstrated the advantageous properties set forth above. EXAMPLE 5

A clear coating material was constituted as follows:-

Component Parts by Weight

Xylene Diisocyanate Prepolymers 28.25

Hydrogenated Xylene Diisocyanate 28.25

Prepolymers Aromatic Hydrocarbon Solvent 40.00

(as in Example 1) Silicone Based Flow Promoter 2.00

(as in Example 1) Silane Based Adhesion Promoter 1.00

(as in Example 1) Wax Emulsion (as in Example 1) 0.5 The coating material was applied as per Example 1. In this instance drying was carried out using PMT at a concentration of 800 ppm. The other drying conditions (temperature etc) were as in Example 1. The coated bottles again exhibited the advantages of the invention.

EXAMPLE 6

The burst strength properties of the two groups of bottles referred to in Example 3 were compared by subjecting them to the AGR Ramp Pressure test using an GR Ramp Pressure Tester. Before carrying out the test, the bottles were subjected to a seven minute run on an GR Line Simulator. The results are tabulated below.

Notes:- 1. AGR is a recognised abbreviation, in the art, for American Glass Research.

2. An AGR Line Simulator is a standard apparatus which enables an observer to approximate the effect upon bottles of the type of treatment to which bottles are subjected during their lifetime in normal conveyor-type filling operations etc. The longer the simulation time, the more severe the treatment.

3. The ramp pressure test/tester are also well known in the art. The test is carried out with the bottles filled with water. The tester progressively increases pressure with time until failure (breakage) occurs. The pressure at failure is recorded. - 15 - TABLE II PRESSURE AT FAILURE (POUNDS PER SQUARE INCH)

Bottle 1. Tin Chloride 2. Tin Chloride % Improvement

Plus P. E. Wax Plus Coating Col . 2 Over of the Col 1

Invention

1. 291.5 574. 4 97 .0

2. 335.0 490 . 2 46 . 3

3. 364.0 475 .7 30 .7

4. 226. 3 575.8 154.4

5. 268. 3 571.5 113.0

6. 332. 1 481.5 45.0

7. 277 .0 510 .5 84. 3

8 . 206.0 452. 5 119 .7

AVERAGE 287 .5 PS I 516 .5 PSI 79 .6

The bottles of the first column (not coated in accordance with the invention) give an average failure pressure of 287.5 psi. However, the second column (bottles coated in accordance with the invention) shows an average failure pressure of 516.5 psi. This represents a very substantial improvement in performance and thus clearly demonstrates a dramatic increase in burst strength.

EXAMPLE 7

Fragment retention: A bottle, coated in accordance with Example 1 and recoated to give a dry film thickness of 35-40 microns, was filled with water and released from a height of 1.5 metres so as to land on a steel plate of 6 mm thickness. The test called for the plate to be set at an angle of 4° to the ground such that the resulting rebound would be directed at a length of soft carpet. The purpose was to ensure only one direct impact per drop.

A control bottle (not coated in accordance with the invention) was similarly filled and tested.

The control bottle disintegrated on impact with total loss of contents. The bottle of the invention exhibited no discernible structural breakage. EXAMPLE 8

Bottles coated in accordance with the invention exhibit excellent slip characteristics (in the art called lubricity). This is demonstrated by a standard test in which three bottles are arranged pyramidally - two below, one above - and tilted until the top bottle is induced to slide. The results obtained when the test was applied to three groups of bottles (two control groups, one group of bottles of the invention) are tabulated below:-

TABLE III

LUBRICITY/SLIP ANGLE

Bottle Type Slip Angle Degrees

Pristine Flint Glass 30 - 35

Standard Wax Treated Glasslδ - 20

Bottle Coated as per Example 2 11 - 13

By appropriate variation, the result with bottles coated in accordance with the invention can of course be adjusted as required. The improved characteristics shown by the bottles of the invention can eliminate the need for stearate or other lubricating sprays that are currently used to facilitate the movement of bottles on conveyor filling lines.

EXAMPLE 9

Refurbishing : Three groups of unblemished 750 ml bottles, six in each group, were set up as follows:-

Group A were subjected to no preliminary treatment (these are designated as standard bottles) . Group B were provided with a 25 cm scratch, made with a glass cutter, midway between the shoulder and heel of the bottles. Group C were similarly scratched and were additionally coated, to a thickness equivalent to 30 microns dry film, with the coating of Example 5. The bottles were then subjected to the AGR ramp pressure test as explained and described in Example 6.

2 The results, in kg/cm ar :ee ttaabbuullaatteedd bbeellooww::--

STD SCRATCH SCRATCH & COAT

A B C

1. 26 .0 8.5 21.8

2. 33. 1 26.1 30.5

3. 13.9 14.8 22.0

4. 41.0 14.7 15.9

5. 27 .0 20.1 20.6

6. 33. 5 17.2 17.3

Aver age 29.1 16.9 21.4 The above results demonstrate a substantial improvement of the bottles in Column C as compared with the bottles in Column B. Bottles coated in accordance with the invention were thus able to significantly approximate their original properties.

EXAMPLE 10

A batch of bottles coated in accordance with Example 2 (XDI) was treated as follows:-

(a) Immersion in 2% caustic soda at 85°C for 15 minutes.

(b) Immersion in 6% caustic soda at 85θc for 15 minutes.

No changes in gloss, colour or adhesion were detected.

This example demonstrates that bottles coated in accordance with the invention will be able to withstand the type of vigorous cleaning to which they would be subjected in ordinary usage. Washing with caustic soda is orthodox practice in breweries for the cleaning of used beer bottles.

EXAMPLE 11

A batch of bottles coated in accordance with Example 4 (amber glass) was treated as follows:-

(a) 100% brandy immersion (approximately 37% alcohol) for four hours at 2QOC. Results :-

( i) No colour change compared to standard.

( ii) No loss in gloss compared to standard.

(iii) No loss in adhesion compared to standard after half hour recovery.

( iv) No blistering, film degredation or softening.

(b) 100% industrial methylated spirits under watch glass for four hours at 20oc.

Results:-

( i) No colour change compared to standard.

( ii) No loss in gloss compared to standard.

(iii) Slight softening of the coating was noticed initially; recovery was rapid.

This example demonstrates that bottles coated in accordance with the invention should be satisfactory for the liquor market.

EXAMPLE 12

Scratch resistance and glass strength are directly related (bottles actually decrease in strength due to abrasion during handling and transportation). A scratch in the surface of a bottle creates a weak point and any breakage will commence at that point. Scratch resistance is measured by rubbing two bottles together under increasing increments of pressure. The result is the pressure at which a scratch is noticed on either of the bottles. The minimum standard for bottles is 18 kg, i.e., at less than 18 kg a bottle is rejected.

A test - the static compression scratch test - was carried out on (i) two control (prior art) bottles and (ii) two bottles coated in accordance with Example 5. In the static compression scratch test, the two bottles are placed one on top of the other and a static weight is placed on top of the bottles for one minute. The surface is then examined for coating removal and glass scratching.

With the control bottles, scratching appeared in the range 40-60 kg. However, with the bottles coated in accordance with the invention, no scratches were apparent at maximum equipment loading of 110 kg. EXAMPLE 13

In this example, which is related to Example 6, two batches, each of six bottles, were subjected to five minutes exposure on an AGR Line Simulator and then subjected to the AGR Ramp Pressure test. The bottles of the first batch (B) were conventionally coated with (i) stannic chloride and (ii) the wax product known commercially as "Valspex". The bottles of the second batch (C) were coated with (i) stannic chloride and (ii) in accordance with Example 1. The results are set forth below:- SURFACE TREATMENT

(B; ) Stannic (C) Stannic % Improvement

Chlor ide Chlor ide (C) over (B) plus plus

Valspex Coating of Example 1

Bottle No . P. S. I . P. S . I .

1. 246.25 348. 32 41. 4

2. 247.50 348. 32 40.7

3. 230 .00 297.19 29.2

4. 197.50 527.28 166.9

5. 236.25 369 .09 56.2

6 . 237.50 420.23 76.9

To tal 1395.00 2310.43 -

Average 232.50 385. 1 65 .6

NOTE : - Bottle 4 survived the upper limit of the test equipment.

The results show that the bottles coated in accordance with the invention achieve a dramatic improvement in burst strength.

With the coating materials and drying agents widely variable within the hereinbefore defined parameters, it will be appreciated that the foregoing examples could be considerably expanded. However, the examples set forth (which are representative of treatments and tests carried out in the development of the invention) should be sufficient to clearly illustrate the invention and the advantages thereof.

In non-limiting summary, the invention thus provides for the protection and structural strengthening of vitreous and other substrates. This permits the manufacturer to lower the mass of his base material while improving its burst strength and fragment retention characteristics. The coating material may be applied and cured within processing times of short duration (of the order of five minutes) under room temperature conditions. It is believed that, by the invention, a substantive advance in the art has been achieved.

Claims

THE CLAIMS :

1. A process for forming a structural coating (as herein defined) on a vitreous, ceramic or porcelain substrate thereby protecting and strengthening the substrate comprising the steps of applying a coating material containing free isocyanate groups to the substrate and subjecting the thus-coated substrate to treatment with a drying agent at room temperature, the drying agent being in vapour-phase and being:

(a) ammonia, an amine or an alkanolamine; or

2. A process as claimed in claim 1 wherein the coating material is a one component coating material containing free isocyanate groups and is selected from toluene diisocyanate prepolymers and blends thereof, and xylene diisocyanate prepolymers and blends thereof.

3. A process as claimed in claim 1 or 2 wherein the drying agent is a multi-component agent comprised of water and an amine.

4. A process as claimed in any one of claims 1 to 3 wherein the amine is selected from DMEA, TMEDA and PMT.

5. A process as claimed in claim 3 or 4 wherein the amine is DMEA and drying is carried out at a concentration of DMEA of 1200-1800 ppm, at a relative humidity of 45-85% and a temperature of 20-25^QC.

6. A process as claimed in any one of the preceding claims wherein the substrate is a vitreous container.

7. A process as claimed in claim 6 wherein the vitreous container is a glass bottle.

8. A process for forming a structural coating (as herein defined) on a glass bottle thereby protecting and strengthening the glass bottle comprising the steps of applying a one component coating material containing free isocyanate groups to the surface of the glass bottle and subjecting the thus-coated bottle to treatment with a drying agent at room temperature, the drying agent being:

(a) in vapour-phase and (b) a multi-component agent comprising water and an amine.

9. A process for forming a structural coating (as herein defined) on a substrate thereby protecting and strengthening the substrate, said process being substantially as herein described with reference to any one of the foregoing examples thereof.

10. A substrate having a structural coating (as herein defined) formed thereon, the substrate being thereby protected and strengthened, the structural coating being formed by a process as claimed in any one of the preceding claims.

11. A structural coating (as herein defined) comprising a coating material containing free isocyanate groups applied to a vitreous, ceramic or porcelain substrate and dried at room temperature thereon by a drying agent in vapour-phase, the drying agent being:

(a) ammonia, an amine or an alkanolamine; or

12. A structural coating as claimed in claim 11 substantially as herein described with reference to any one of the foregoing examples thereof.

13. A glass bottle the surface of which is protected and strengthened by a structural coating (as herein defined), the coating comprising a one component coating material containing free isocyanate groups applied to the surface of the bottle and dried thereon at room temperature by a drying agent, the drying agent being:

(a) in vapour-phase and

(b) a multi-component agent comprising water and an amine.

14. A glass bottle as claimed in claim 13 substantially as herein described with reference to any one of the foregoing examples thereof.

15. Any novel process set forth herein, or any novel substrate set forth herein, or any novel coating set forth herein, the said process, substrate or coating being substantially as herein described.