CA1072828A - Electrostatic coating of glass bottles with powder containing epoxide and amidine - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An improved method is disclosed for the coating of glass bottles with transparent plastic film which film will withstand repeated cleaning. The method involves treating clean bottles with a silane size, preheating the bottles and then electro-statically applying a powder lacquer thereto, the powder lacquer containing one or more 1,2-epoxide compounds with at least one epoxide group per molecule and a lower melting point greater than 40°C, and a hardener which is an amidine of the general formula wherein R denotes hydrogen, an alkyl or aryl group, R' denotes a cycloalkyl, heterocycloalkyl or R group, R" denotes an alkyl or aryl substituted alkylene or arylene group X denotes hydrogen or a

Description

~7~82i3 This invention relates to the coating of glass bottles with a transparent plastic and more particularly to an improved method for such coating using a powder varnish of particular composition.
The coating of glass bottles with a firmly adherent, uni-form and transparent plastic film renders these bottles extremely safe in their use for carbonated beverages, such as mineral water, beer, fruit juice beverages, etc., and prolongs their useful life in case of reusable bottles. As a result of being subjected to blows and impacts, but also through heating-up in sunlight or near heat sources, unprotected bottles have frequently exploded in the past, resulting in some cases in serious bodily injury to persons, parti-cularly eye injuries.
Some of the coatings used previously for this purpose had the disadvantage that the ilm turned turbid upon repeated cleaning, which, in the case of thermoplastic materials, may be due to a re-crystallization effect of the plastic:. Such bottles are unattractive in appearance and ~herefore have an undesirable psychological effect on the consumer, ` I
Now, the discovery was made that glass bottles can also be coated without incurring these and other disadvantages while, at the same time, achieving good handling properties, if the following me-thod is used for the coating of glass bottles with a transparent, thermosetting, protective film: First, the clean glass bottles are treated with an aqueous or alcoholic silane size, and dried if neces-- sary and, subsequently, the bottles are heated to a temperature of 180 - 250C. Next, a powder lacquer, which is composed of 1,2 epoxide compounds with at least one epoxide group per molecule and a

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~3i7Z~28 melting range having a lower temperature greater than 40C plus hardeners as well as additives, is applied electrostatically. In this case, the hardener being used consists of amidines of the gener-al formula R R
R - C - C - R
R' - N
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wherein R denotes hydrogen, an alkyl or aryl group, R' denotes a cy-cloalkyl, heterocycloalkyl, or R group, R" denotes an alkyl or aryl sùbstituted or unsubstituted alkylene or arylene group, X denotes hydrogen or a R
R - C - N
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R C - N
R R' Subsequently, the film is cured by supplying additional heat if ne-cessary.
The protective film applied in this way i9 highly elastic and possesses excellent adhesion so that no glass fragments can pene-trate to the outside in the event of fracture of the glass or burst-ing of the bottle. In the event of destruction of the glass bottle, the shape of the bottle is fully preserved. The resulting kinetic energy is dissipated through stretching and heating-up of the plastic coating.
A particular advantage consists of the stability of the ` .' .
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~7Z~2~3 coating in the presence of hot, alkaline rinsing liquors, in which the bottles are cleaned prior to being filled with a particular bev-erage. This is particularly true in the case of reusable bottles which are subjected to an intensive cleaning operation prior to each filling.
The advantage of the coating according to the invention consists of the fact that, even after repeated rinsing in hot, alka-line liquor, there is no softening of the material and no loss of adhesion. Nor are there any visual changes in the appearance of the coating.
- Glass bottles coated in this way can be used as containers for carbonated beverages without hazards upon breakage or bursting.
If used as reusable bottles, the useful life-span of coated bottles is considerably longer than that of unprotected bottles which, as a result of motion, suffer slight damage or severe superficial wear due to rub~ing against sharp edges and due to rinsing operations in hot li~uors.
Before applying the actual coating, th0 cleaned bottles are treated with an aqueous or alcoholic silane size. The silanes used in this treatment contain groups which belong to two different func-tional types. On the one hand, these groups consist of alkoxy groups, especially methoxy and ethoxy groups which reac~ with the OH groups of the glass surface, and, on the other hand, of organic groups with functional groups which can react either with the 1,2-epoxide com-pounds, such as amino groups, or with the hardener, e.g. epoxy groups, ~` glycidyl groups, etcO, such as y-aminopropyl-trimethoxy silane, .
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glycidyloxypropyl-triethoxy silane, etc. It is also possible to use mixtures of the same functional groups, i.e. mixtures of groups which react with epoxy groups or groups which react with the hardeners.
The treatment of the bottles may, for example, consist of dipping in-to or spraying with the sizing agent. The bottles treated in this way can subsequently be dried separately. The drying can also be accomplished through simultaneous heating of the bottle to 180- 250&, i.e. to a temperature such as the one prevailing in the manufacture of the bottles during the cooling process.
The application of the powder lacquers described below to the heated glass bottles is carried out according to commonly known methods, e.g. through electrostatic powder spraying; however, other methods such as dip coating in powder or electrostatic dip coating in powder etc. may also be used.
The instant melting of the powder, whose melting point oc-curs in the region around 100C, gives rise to the excellent, trans-parent levelling of the film.
If the inherent heat capacity is not sufficient for the curing process, additional heat may be supplied, even after the powder lacquer has been applied, until the cross-linking reactlonis ocmpleted.
The ~lass bottles coated in this way are cured at a temper-ature in the region of 140 - 240C, preferably at 180 - 200 C.
The compounds which are suitable for the preparation of the fine-grained mixtures which are to be used as powder lacquers consist of 1,2-epoxide compounds with at least one 1,2-epoxide group per mDle-cu18 and a melting range having a lower temperature greater than 4PC.
Compounds which possess these characteristics comprise, on the one .. ~ . . .
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hand, polyepoxide compounds which are solid at 40 C and below, which include compounds of higher molecular weight (so-called solid resins), and compounds which, as a result of their symmetric structure or the size of the carbon groups attached to the 1,2-epoxide group, are solid; on the other hand, they comprise compounds which were prepared through the reaction between liquid 1,2-epoxide compounds with more than one epoxide group per molecule and primary or secondary amines in such quantities that the adduct contains, on the average, still at least one 1,2-epoxide group per molecule (so-called adduct hardeners).
The 1,2-epoxide hardeners can be both saturated and unsat-urated, as well as aliphatic, cycloaliphatic, aromatic, orheterocyclic.
Furthermore, they may contain substituents which do not cause inter-fering secondary reactions under the mixing and reaction conditions.
Substituents which do not cause interfering secondary reactions in-clude, for example, alkyl or aryl substituents, hydroxyl groups,ether groupings, and similar substituents. Compounds which are suitable belong to the following classes of substances: epoxides of singly or multiply unsaturated hydrocarbons, halogen-containing epoxides, .. . epoxy ethers of single or multiple al.cohols and phenols, epoxy esters of single or polybasic acids, as well as N-containing epoxides.
. Of the solid resins, 1,2-epoxide compounds with more than one epoxide group per molecule, whose epoxy equivalent weight is be-tween 500 to 1000, are preferred for this application. These include, for example, the solid polymeric polyglycidyl polyethers of 2,2-bis-(4-hydroxyphenyl)-propane which are obtained, for example, through the reaction of 2,2-bis-(4-hydroxyphenol)-propane with epichlorohydrin in molar ratios of 1:1.9 to 1.2 (..in the presence of an alkali hydro--.
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~C~7;~3Z8 xide in an aqueous medium). Polymeric polyepoxides of this type can also be obtained through the reaction of a polyglycidyl ether of 2,2-bis-(4-hydroxyphenyl)-propane with less than an equimolecular quantity of divalent phenol, preferably in the presence of a catalyst such as a tertiary amine, a tertiary phosphine, or a quaternary phos-phonium salt. The polyepoxide may also consist of a solid epoxidized polyester which is obtained, for example, through the reaction of a polyhydric alcohol and/or a polybasic carboxylic acid or its anhydride with a low-molecular-weight polyepoxide. Examples of such polyepo-xides of low molecular weight include the liquid diglycidyl ether of2,2-bis-(4-hydroxyphenyl)-propane diglycidylphthalate, diglycidylte-trahydrophthalate, diglycidylhexahydrophthalate, diglycidyladipate, diglycidylmaleate, and the 3,4-epoxycyclohexylmethyl ester of 3,4-epoxycyclohexane carboxylic acid.
Mixtures of solid polyepoxides may also be used, e.g. a mixture of a polyepoxide whose melting point occurs between 120 and 160C and a polyepoxide with a melting point between 60 and 80C (the melting point is determined according to the mercury method o Durrans). Suitable mixtures contain between 30 and 50% by weight of a solid polyglycidyl ether of 2,2-bis-(4-hydroxyphenyl)-propane of an equivalent weight between 1650 and 2050 and a melting point of 120 to 160~, and between 50 and 70% by weight of a solid polyglycidyl poly-ether of 2,2-bis-(4-hydroxyphenyl)-propane of an equivalent weight between 450 and 525 and a melting point of 60 to 80C.
If a high epoxy functionality is desirable, then the poly-glycide ether of 1,1,2,2-tetra-(4-hydroxyphenyl)-ethane represents a preferable polyepoxide.

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72~3~28 Epoxidized polybutadienes may also be used for this purpose.
As was already mentioned above, adduct hardeners are also suitable for the process in accordance with the present invention, in addition to the so-called solid resins. Solid adduct hardeners of this kind can, for example, be prepared from liquid polyepoxides of multiply unsaturated hydrocarbons, such as vinylcyclohexene, dicyclo-pentadiene, etc., epoxy ethers of polyhydric alcohols and phenols etc., and aliphatic~ cycloaliphatic, and aromatic diamines. For such an adduct to be suitable, the melting point has to be above 40C in this case also.
In the same way as the pure epoxide compounds can be used in the process according to the present invention, so can their mix-tures, such as mixtures of mono and polyepoxides.
Suitable cyclic amidines, i.e. imidaæoline derivatives in accordance with the present invention, include 2-methylimidazoline, 2,4-dimethylimidazoline, , . .

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,, ~CI 728~3 2-ethylimidazoline~ 2-ethyl-4-methylimidazoline, 2-ben~yl-imidazoline, 2-phenyl-imiclazoline, 2-phenyl-~-methylimidazoline, 2-(o-tolyl)-imidazoline, 2-(p-tolyl)-imidazoline, 1,4-tetramethylene-bis-imidazoline, 1,1,3-trimethyl-1,4-tetramethylene-bis-imidazoline, 1,3,3-trimethyl-1,4-tetramethylene-bis-imidazo~ine, 1,1,3-trimethyl-1,4-tetramethylene-bis-4-methylimidazoline, 1,3,3-trimethyl-1,4-tetramethylene-bis-4-methylimidazoline, 2-(m-pyridyl)-imidazoline, 2-(p-pyridyl)-imidazoline, 1~ 1,2-phenylene-bis-imidazoline, 1,3-phenylene-bis-imidazoline, 1,4-phenylene-bis-imidazoline, 1,4-phenylene bis-4-methyl-imidazoline, etc. Mixtures of these imidazollne derivatives may also be used in accordance with the present invention.
Of these groups of imidazolines, 2-phenyl-imidazoline is preferred. These compounds may be used as sole hardeners or cross-linking a~ents for the 1,2-epoxide compounds.

The above imidazoline deri~vatives are used in such quantities that concentrations of 4-12% by weight, preferably 6-8% by weight, relative to the total quantity of powder lacquer are obtained.

; In order to improve the levelling propertie~ o~ the lacquers, so-called levelling agents are added in their .~ . .
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preparation. These agents may consist of chemical com-pounds or mixtures thereof of greatly varying chemical nature, such as polymers or monomeric compounds, acetals, such as polyvinylformal, polyvinylacetal, polyvinylaceto-butyral, or di-2-ethylhexyl-i-butyraldehyde-acetal, di-2-ethylhexyl-n-butyraldehyde-acetal, diethyl-2-ethylhexanal-acetal, di-n-butyl-2-ethyl hexanal-acetal, di-i~butyl-2-ethylhexanal~
acetal, di-2-ethyl-hexyl-acetaldehyde-acetal, etc., ethers, such as polymeric polyethylene glycols and polypropylene glycols, copolymers of n-butylacrylate and vinylisobutyl ether, ketone-aldehyde condensation resins, solid silicone - resins, or also mixtures of zinc soaps, ~atty àcids, and aromatic carboxylic acids, etc. Moreover, products such as ~o~aflow* are commercially availa~ble for this purpose;
their chemical nature is not known to consumers; all that is known about it is that it represents a complex, p~lymeric fluid which is effective. These levelling agents can be present in the charges at concentr~tions of 0.2-0.5~ by weight, relative to the total quantity o~ powder lacquer.
' The concentrations of other commonly used constitu-ents of the powder lacquer mixture, such as dyes which are soluble in the 1,2-epoxidè compounds, stabilizers, etc., .
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~7;~:i!328 may vary over a wide range relative to the quantity of ].,2-epoxide compound plus hardener. The concentrations may be chosen in accordance with the quality requirements of the coatings.

Prior to their use, the constituents of the powder lacquer are thoroughly mixed at temperatures below the curing temperatures, extruded, and subsequently ground. As far as practical applications are concerned, one should try to achie~e a particle size of less than 100 ~, with the 10 . maximum in the particle size distribution prefPrably between 30 and 50 ~.

Depending on the wear of the bottles, the film thickness of the cured coatings can be adjusted to 50 -: 250 ~m.

General Description of the Method Used : Uncoated and clean glass bottles were first coated , with a roughly monomolecular-layer of aqueous or alcoholic ' - y-aminopropyl-triethoxy silan,e solution (l.S~ by weight) at . room tempera~ure 9 and subsequently dried.
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The 1,2-epoxide compounds used, which possessed the special characterlstics and which in practice are usually referred to as epoxide resins, were mixed in the speci-fied ratios with the imidazoline derivatives, which acted both as cross-linking agent and as hardener, and with the levelling a~ent, and were extruded and subsequently ground.
The particle size of the powder constituents was less than 100 ~m. The frequency distribution of the particle size had its maximum in the region from 30 - 50 ~m. Next, these fine-grained mixtures were applied to the preheated glass bottles through electrostatic powder spraying, and were sub-sequently`cured at the specified or unspecified temperatures and times. The properties of the coats obtained were in-vestiya~ed ln tests specified below.

Exam~le 1:
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Powder lacquer was prepared from 2-phenyl-imidazoline plus the specified epoxidè resin, as well as a small amount of added levelling agent, using the following~ratios:

Composition of the Powder Lacquer Solid epoxide resin, based on an adduct of 2,2-bis-~4-hydroxyp~enyl)-propane (Dian) and epichlorohydrin, which -.` . ` . ~ . , . :- .: . :
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~7Z82~3 was subjected to HCl-cracking and, subsequently was allowed to react with additional Dian, and which according to the manufacturer had an epoxide equivalent weight of 900 - 1000, which corresponds to an epoxide value of 0.10 - 0.11, and a melting region of 90 - 100 C : 93.5% by weight 2-phenyl-imidazoline : 6.0% by weight levelling agent, which is commercially available under the name of Modaflow* : 0.5% by weight This formulation was applied to glass bottles heated to 200C and cured for 5 minutes at 180C. The coated bottles were subjected to the following tests:

a. Visual evaluation : The surface had a shiny, smooth appearance b. Film thickness : 60 - 70~m.

c. Bursting pressure : The bottles burst at an inside pressure o 22 - 26 atmospheres, resulting in a fine fragmentation pattern.

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1~7Z~Z~3 The plastic coat held the frag-ments completely together.

d. Test in the washing machine : The washing liquor used in the test consisted of a Calgonite*/
sodium hydroxide solution (0.25/2.5~ by weight), and was allowed to act upon the bottles for 5 minutes at`85C. The total time of the run through the washing machine was 30 minutes.
Afte~ards, the plastic showed no adverse changes.

, e. Test in the line simulator. The temperature of the bottles was 80C : In this case, the bottles were first filled with water of a temperature of 80C, and were sub-sequently allowed to stand for 10 minutes in a water bath of a *Calgonite = bottle cleanser based on the sodium salt of a polyphosphate-- ~trade mark ) - ' ~

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, : . . . , . :: . -~7Z~3~8 temperature of 80C. After that, the heated bottles were teste~ in the line simulatcr for 1 minute.

In the region below the neck of the bottle, no abrasions could be detected on the plastic coating after the test.

5 x 1 minute runs in the line simulator : In this case, the above test was repeated five times.

No damage could be detected.

.
f. Impact test (cohesion of fr~ments) : The impact test was carried out using an impact energy of 73 kg cm.

In this case, a steel ball of a ,"~. v diameter of 80 mm was ~llowed to drop from a height of 350 mm onto 1 ~

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~7Z~3213 a horizontal empty bottle lying in a 120 guide piece. The bottles fractured and were de-formed by the impact; however, they were preserved as a coherent body without glass fragments penetrating to the outside.

g. In order to evaluate the lacquer under the action of a piercing load, the "piercing test using electronic data acquisition" according to DIN* 53 373 was carried QUt.
On the basis of the results of this test, the Elexibility and resistance of a plastic film became evident.

The thickness o~ the films ranged from 115 to 138 ~m.
The followin~ test conditions were used:

type of specimen : plane film testing machine : Dynatester test temperaturè : 24~C
relative humidity : 70%
~piercing object : semisphere . ..

20 *DIN = Deutsche Industrie Norm (German Industrial Standards).
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, ~7'~8ZI!3 Results of 10 tests test force FS : 1~.17 kg testing energy Ws : 2.67 kg cm piercing energy W~es ~.05 kg cm deformation LS : 5.08 mm Example 2:
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Powder lacquer.was prepared from 2-phenyl-imidazoline plus the specified epoxide resin, as well as a small amount of added levelling agent, using the following ratios:

Composition of the ~owder Lacquer .

Solid epoxide resin (same as in Example 1): 93.5% by weight 2-phenyl~imidazoline o 6.0% by weight levelling agent (same as in Example 1) : 0.5% by weight .

This formulation was applied to glass bottles which had a temperature o~ approximately 2~.0C at the time of application. No subsequent curing was carried out.
.
The tests of the coated bottles were carried out as described in Example l; the same results as in Example 1 were obtained.

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Example _3:

Powder lacquer was prepared from 1,4-tetramethylene-bis-imidazoline plus the specified epoxide resin, as well as a small amount of adcled levelling agent, using the following ratios:

Composition of the Powder Lacquer Solid epoxide resin (same as in ExaMple 1): 94.0% by weight 1,4-tetra-methylene bis-imidazoline : 5.5% by weight levelling a~ent (same as in Example 1) : 0.5~ by weiyht This formulation was applied to glass bottles which had been heated to 200C. No subsequent curing was carried out. The following tests were subsequently carried out:

a. Visual evaluation : The sur~ace had a shiny, smooth ` appearance.

b. Film thickness : 70 ~ 80 ~m.
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c. Bùrsting pressure : The bottles burst at an inside pressure of 20 - 24 atmospheres, , i8 ` . .-- ~ ~ .
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~7;28Z8 resulting in a fine fragmentation pattern. The plastic coat held the fragments together.

d. Test in the washing machine : The test was carried out in accordance with Example ld.

In this case too, the plastic showed no adverse changes after the specified time.

e. Test in the line simu-lator. Tests in accordance with Example le. : The plastic coating showed onl~
slight abrasions. No further damage was detected after 5 x 1 minute runs.

.
; f. Impact test (cohesion of frag-ments). Test in accordance with Example 1 : The bottles broke and ware deformed '-- 19 - ~'. :' . ~ .

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.. . : . . . . . . : ~: . .. . . - -~72~2~3 by the impact; however, they were preserved as a coherent body.

Example 4:
-Powder lacquer was prepared from 2-phenyl-4-methyl-imidazoline plus the specified epoxide resin, as well as a small amount oE added levelling agent, using the following ratios:

Composition of the ~owder Lacquer Solid epoxide resin (same as in Example 1): 94.5~ by weight 10. 2-phenyl-4-methyl-imidazoline : 5.0~ by weight levelling agent (same as in Example 1) : 0.5% by weight .~ This formulation was applied to glass bottles of a temperature of 200C. Subsequently, these coats were cured for 10 minutes at 200C and subjected to the following tests: . :
, ~ a. Visual evaluation : The surface had a shiny, smooth ~ , appearance.
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: ' :~721~2~3 b. Film thickness . 60 - 80 ~m.

c. Burstin~ pressure : The bottles burst at an inside pressure of 20 - 24 atmospheres, resulting in a fine fragmentation pattern. The plastic coating allowed no fragments to penetrate~
to the outside.

d. Test in the washing machine : Test in accordance with ~xample ld. No adverse changes were de-; tected after the testing period.
. .

e. Test in the line simulator. Tests lS - in accordance with Example le : With the exception of a few slight abrasions, the coating was com-pletely preserved.

After 5 x 1 minute runs, no fur-ther damage o~ the pla tic film ~ was detected.

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d. Impact test (cohesion of the fragments). Test in accordance with .5 Example lf . : The bottles fractured and were deformed by the impact; however, they wPre preserved as a coherent body.

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Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for coating a glass bottle with a transparent, thermosetting protective film by applying a powder lacquer composed of at least one 1,2-epoxide compound with at least one 1,2-epoxide group per molecule and a melting range having a lower temperature greater than 40°C, plus hardeners as well as additives, and by curing the film at increased temperatures, characterized in that the clean glass bottle is first treated with an aqueous or alcoholic silane size, and subsequently heated to a temperature of 180-250°C, the powder lacquer is applied electrostatically to form a film on the bottle, the hardener being at least one amidine of the general formula wherein R denotes hydrogen, an alkyl or aryl group, R' denotes a cy-cloalkyl, heterocylcloalkyl, or R group, R" denotes an alkyl or aryl substituted or unsubstituted alkylene or arylene group, and X denotes hydrogen or a group in an amount of 4-12% by weight relative to total quantity of powder lacquer, and the film is cured.

2. The method according to claim 1, further characterized in that the coated glass bottle is cured at a temperature in the region of 140-240°C.

3. The method according to claim 2, further characterized in that the coated bottle is cured at a temperature of 180-200°C.

4. The method according to claim 2, further characterized in that 2-phenyl-imidazoline is used as the cyclic amidine.

5. The method according to claims 1, 2 or 4 further characterized in that the cyclic amidine is used in a concentra-tion of 6-8% by weight relative to the total quantity of powder lacquer.

6. The method according to claims 1, 2 or 4, further characterized in that dyes are added to the powder lacquer which dyes are soluble in the 1,2-epoxide compound.

7. The method according to claim 1, 2 or 4, further characterized in that the coating of the glass bottle with powder lacquer is carried out by dip coating or electrostatic dip coating.

8. A coated glass bottle with a transparent, thermo-setting protective film, manufactured according to claim 1.