CA2154863C - Powdered varnish and its use for coating the insides of packaging containers and for covering weld seams - Google Patents
Powdered varnish and its use for coating the insides of packaging containers and for covering weld seamsInfo
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- CA2154863C CA2154863C CA002154863A CA2154863A CA2154863C CA 2154863 C CA2154863 C CA 2154863C CA 002154863 A CA002154863 A CA 002154863A CA 2154863 A CA2154863 A CA 2154863A CA 2154863 C CA2154863 C CA 2154863C
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- powder coating
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D167/00—Coating compositions based on polyesters obtained by reactions forming a carboxylic ester link in the main chain; Coating compositions based on derivatives of such polymers
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D163/00—Coating compositions based on epoxy resins; Coating compositions based on derivatives of epoxy resins
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Wood Science & Technology (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Paints Or Removers (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
- Details Of Rigid Or Semi-Rigid Containers (AREA)
Abstract
A powder coating for the coating of packaging container weld seams based on epoxy resins and carboxyl-containing polyesters, wherein 1. the powder coating contains A) at least one polyester having an acid value of 25 to 120 mg of KOH/g and an OH value ~ 10 mg of KOH/g, and B) at least one epoxy resin having an epoxide equivalent weight of 400 to 3000, and 2. the powder coating has such a particle size distribution that a) at least 90% by mass of the powder coating particles have a particle size between 1 and 100 µm, b) the maximum particle size of the powder coating particles for at least 99%
by weight of the particles is ~ 50 µm, c) the average particle size of the powder coating particles is between > 20 and 60µm, and d) the slope of the particle distribution curve at the inflection point is ~ 50.
by weight of the particles is ~ 50 µm, c) the average particle size of the powder coating particles is between > 20 and 60µm, and d) the slope of the particle distribution curve at the inflection point is ~ 50.
Description
POWDER COATING AND THE USE THEREOF FOR THE
COATING OF PACKAGING CONTAINER INTERIORS
AND OF WELD SEAMS
The present invention relates to powder coatings, based on epoxy resins and carboxyl-containing polyesters, for the coating of packaging container interiors and weld seams.
In addition, the present invention relates to the process of coating packaging container interiors and weld seams as well as to the use of the powder coatings.
l0 Packaging containers, such as food cans, two- and three-part beverage cans and others, are provided on the inside with a coating, the purpose of which is on the one hand to protect the contents from contamination by dissolved constituents of the metal sheeting and on the other hand to prevent corrosion of the metal sheeting by aggressive contents.
This coating of the packaging containers takes place in practice mainly by means of organically dissolved coatings.
However, this causes high solvent contamination of the 20 environment on drying of the coating films. Attempts have therefore been increasingly made to replace these coatings by low-solvent or solvent-free coatings. Thus, for example, thermoplastic powder coatings have frequently been used to coat can weld seams. These products are produced from the corresponding thermoplastics by an expensive cold grinding process.
Furthermore, thermosetting powder coatings for the 26766-lOD
coating of weld seams of metal containers used for foodstuffs or beverages are known from EP-B-119,164. These thermosetting powder coatings contain, as binder, a mixture of an aromatic epoxy resin having on average not more than 2 epoxide groups per molecule, and an aromatic epoxy resin having on average more than 2 epoxide groups per molecule. The condensation product of bisphenol A diglycidyl ether with bisphenol A
and/or an acid polyester based on trimellitic anhydride/aliphatic polyol is used as curing agent. However, EP-B-119,164 contains no information on suitable particle sizes and particle size distribution of the powder coatings.
In addition, it is a drawback that these powder coatings are only suitable for the coating of weld seams.
Powder coatings for the coating of can interiors, which contain a polyester having terminal carboxyl groups and an OH value lower than 10 mg of KOH/g as well as an epoxy resin, are known from EP-B-10,805. These powder coatings contain choline derivatives as curing catalyst. The powder coatings have an average particle size between 20 and 150 Vim.
However, EP-B-10,805 contains no information on how to obtain can interior coatings which would provide closed films even at film thicknesses of s 15 Vim. Furthermore, owing to the low OH
value of the polyester, these powder coatings have the drawback of having only poor cross linking. Correspondingly, this system has drying times of 10 to 40 min. at 150 to 220°C
which are unacceptable in practice, while the drying time in modern production lines is not more than 20 to 30 sec. at an object temperature of 260 to 280°C.
COATING OF PACKAGING CONTAINER INTERIORS
AND OF WELD SEAMS
The present invention relates to powder coatings, based on epoxy resins and carboxyl-containing polyesters, for the coating of packaging container interiors and weld seams.
In addition, the present invention relates to the process of coating packaging container interiors and weld seams as well as to the use of the powder coatings.
l0 Packaging containers, such as food cans, two- and three-part beverage cans and others, are provided on the inside with a coating, the purpose of which is on the one hand to protect the contents from contamination by dissolved constituents of the metal sheeting and on the other hand to prevent corrosion of the metal sheeting by aggressive contents.
This coating of the packaging containers takes place in practice mainly by means of organically dissolved coatings.
However, this causes high solvent contamination of the 20 environment on drying of the coating films. Attempts have therefore been increasingly made to replace these coatings by low-solvent or solvent-free coatings. Thus, for example, thermoplastic powder coatings have frequently been used to coat can weld seams. These products are produced from the corresponding thermoplastics by an expensive cold grinding process.
Furthermore, thermosetting powder coatings for the 26766-lOD
coating of weld seams of metal containers used for foodstuffs or beverages are known from EP-B-119,164. These thermosetting powder coatings contain, as binder, a mixture of an aromatic epoxy resin having on average not more than 2 epoxide groups per molecule, and an aromatic epoxy resin having on average more than 2 epoxide groups per molecule. The condensation product of bisphenol A diglycidyl ether with bisphenol A
and/or an acid polyester based on trimellitic anhydride/aliphatic polyol is used as curing agent. However, EP-B-119,164 contains no information on suitable particle sizes and particle size distribution of the powder coatings.
In addition, it is a drawback that these powder coatings are only suitable for the coating of weld seams.
Powder coatings for the coating of can interiors, which contain a polyester having terminal carboxyl groups and an OH value lower than 10 mg of KOH/g as well as an epoxy resin, are known from EP-B-10,805. These powder coatings contain choline derivatives as curing catalyst. The powder coatings have an average particle size between 20 and 150 Vim.
However, EP-B-10,805 contains no information on how to obtain can interior coatings which would provide closed films even at film thicknesses of s 15 Vim. Furthermore, owing to the low OH
value of the polyester, these powder coatings have the drawback of having only poor cross linking. Correspondingly, this system has drying times of 10 to 40 min. at 150 to 220°C
which are unacceptable in practice, while the drying time in modern production lines is not more than 20 to 30 sec. at an object temperature of 260 to 280°C.
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Powder coatings for the coating of can interiors and can lids which contain an epoxy resin and aromatic amines, Lewis acids and acid anhydrides as curing agents, are known from US Patent 4,497,837. The powder coatings have an average particle size between 20 and 150 Vim, preferably 30 to 70 Vim.
The drawback of these systems is the high minimum film thickness of 38 ~m for obtaining coatings which are not excessively porous. Moreover, these powder coatings have the drawback of oven dwell times between 5 and 12 min. being l0 required for the curing of the systems described.
Furthermore, powder coatings which also contain an epoxy resin and aromatic amines, epoxide-amine adducts or acid anhydrides, for the coating of can interiors are known from US
Patent 3,962,486. By using the plasma spray coating process it is possible to produce coatings which, at low film thicknesses of less than 13 Vim, comply with the requirements which are usually specified for interior coatings of foodstuff containers. To ensure applicability by the plasma spray process, only those powder coatings which have a maximum 20 particle size of s 100 um and a sufficiently low melt viscosity should be used.
However, the use of aminic curing agents leads to an inadequate resistance to sterilization of the resultant coatings. It is furthermore a drawback that amine-cured epoxy resins tend to be brittle and have very poor flexibility.
Acid anhydride curing agents have the disadvantage of being strongly irritant, thus requiring special protective measures in the formulation of the powder coatings.
Powder coatings for the coating of can interiors and can lids which contain an epoxy resin and aromatic amines, Lewis acids and acid anhydrides as curing agents, are known from US Patent 4,497,837. The powder coatings have an average particle size between 20 and 150 Vim, preferably 30 to 70 Vim.
The drawback of these systems is the high minimum film thickness of 38 ~m for obtaining coatings which are not excessively porous. Moreover, these powder coatings have the drawback of oven dwell times between 5 and 12 min. being l0 required for the curing of the systems described.
Furthermore, powder coatings which also contain an epoxy resin and aromatic amines, epoxide-amine adducts or acid anhydrides, for the coating of can interiors are known from US
Patent 3,962,486. By using the plasma spray coating process it is possible to produce coatings which, at low film thicknesses of less than 13 Vim, comply with the requirements which are usually specified for interior coatings of foodstuff containers. To ensure applicability by the plasma spray process, only those powder coatings which have a maximum 20 particle size of s 100 um and a sufficiently low melt viscosity should be used.
However, the use of aminic curing agents leads to an inadequate resistance to sterilization of the resultant coatings. It is furthermore a drawback that amine-cured epoxy resins tend to be brittle and have very poor flexibility.
Acid anhydride curing agents have the disadvantage of being strongly irritant, thus requiring special protective measures in the formulation of the powder coatings.
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Finally, powder coatings for the coating of can interiors which contain an epoxy resin and an amine curing agent, are known from US Patent 4,183,974. These powder coatings have an average particle size between 1 and 100 Vim, preferably between 1 and 10 Vim. It is true that the resultant coatings have the required low porosity at film thicknesses as low as s 13 Vim, but the resistance to sterilization of the resultant coatings is in the need of improvement.
Furthermore, it is a drawback that amine-cured epoxy resins tend to be brittle and have very poor flexibility.
Finally, powder coatings for the coating of can interiors which contain an epoxy resin and an amine curing agent, are known from US Patent 4,183,974. These powder coatings have an average particle size between 1 and 100 Vim, preferably between 1 and 10 Vim. It is true that the resultant coatings have the required low porosity at film thicknesses as low as s 13 Vim, but the resistance to sterilization of the resultant coatings is in the need of improvement.
Furthermore, it is a drawback that amine-cured epoxy resins tend to be brittle and have very poor flexibility.
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~1 ~4~ ~3 The aim of the present invention is to make available powder coatings which, with the same chemical composition, are suitable both for weld seam coating and for the coating of packaging container interiors, in particular metal container interiors. In addition, these powder coatings, when used for the coating of packaging container interiors and when applied at film thicknesses as low as s 15 ~,m, should comply with the requirements which are usually specified for can interior coatings. In particular, these interior coatings should not be porous (determined with the aid of a so-called enamel rater test), they should possess good adhesion to the substrate and good flexibility, and they should withstand the customary pasteurization and sterilization conditions. Furthermore, these powder coatings, when used for weld seam coating, should lead to highly flexible coatings which withstand the mechanical deformations incurred in the flanging and of the cans beading. Resistance to sterilization and pasteurization is also required after the deformative treatment.
The powder coating should be curable in the course of the brief drying times which are customary in can coating.
Surprisingly, this aim is achieved by the invention of the parent application which provides a powder coating of the type referred to at the outset, wherein I. the powder coating comprises A) at least one polyester having an acid value of to 120 mg of KOH/g and an OH value z 10 mg of KOH/g and 26766-lOD
B) at least one epoxy resin having an epoxide equivalent weight of 400 to 3000, and II. the powder coating has such a particle size 5a 26766-lOD
~.
21~4~~3 distribution that a) at least 90o by mass of the powder coating particles have a particle size between 1 and 60 um, b) the maxirnum particle size for at least 99o by mass of the powder coating particles is < 100 um, c) the average particle size of the powder coating part icles is between 5 and 20 urn, and d) the slope of the particle distribution curve at the inflection point is greater than or equal to 100.
Furthermore, the invention of the divisional application relates to a powder coating for the coating of packaging container weld seams based on epoxy resins and carboxyl-containing polyesters, wherein I. the powder coating comprises A) at least one polyester having an acid value of 25 to 120 mg of KOH/g and an OH value of a 10 mg of KOH/g, and B) at least one epoxy resin having an epoxide equivalent weight of 400 to 3000, and II. the powder coating has such a particle size distribution that a) at least 90% by mass of the powder coating particles have a particle size between 1 and 100 ~.m, b) the maximum particle size for at least 99% by mass of the powder coating particles is ~ 150 ~.m, c) the average particle size of the powder coating particles is between > 20 and 60 Vim, and d) the slope of the particle distribution curve at the inflection point is >_ 50.
In addition, the invention relates to processes for the coating of packaging container interiors and weld seams A
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in which these powder coatings are applied. The invention finally also relates to the use of the powder coatings for the coating of packaging container interiors and weld seams.
It is surprising, and could not have been foreseen, that the powder coatings according to the invention are suitable, with the same chemical composition, for the coating both of weld seams and of packaging container interiors and that the property profile and hence the use can be regulated simply by establishing a corresponding particle size distribution. At the same time these powder coatings are rapidly curable, simple to handle and simple to apply.
Furthermore, the powder coatings according to the invention, when used for the coating of packaging container interiors, are distinguished by the fact that coatings with a very low film thickness of only s 15 ~m possess the properties required by can manufacturers. In particular, these coatings have the required low porosity at a film thickness as low as s 15 Vim. Moreover, these coatings possess good adhesion, high flexibility and good resistance to pasteurization and sterilization.
Furthermore, the powder coatings according to the invention, when used for weld seam coating, have the advantage of high flexibility, with the result that the weld seam coating is able to follow the deformations of the packaging container on further fabrication without peeling off or cracking. Moreover, it is an advantage that, in contrast to aminic curing agents, the powder coating according to the invention attains good resistance to sterilization.
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The individual components of the powder coatings according to the invention are now elucidated in greater detail below. The polyesters employed in the powder coatings according to the invention (component A) have an acid value of 25 to 120 mg of KOH/g, preferably 30 to 90 mg of KOH/g and particularly preferably 60 to 90 mg of KOH/g, and an OH value of at least 10 mg of KOH/g, preferably at least 15 mg of KOH/g and preferably lower than or equal to 30 mg of KOH/g.
Polyesters having a functionality of z 2 are preferably employed. The number average molecular weights of the polyesters are generally between 1000 and 10,000, preferably between 1500 and 5000. Polyesters approved by the US FDA
(FDA = Food and Drug Administration) are preferably used. The carboxyl- and hydroxyl-containing polyesters can be prepared by conventional methods (cf., for example, Houben Weyl, Methoden der organischen Chemie, [Methods of Organic Chemistry], 4th edition, volume 14/2, Georg Thieme Verlag, Stuttgart 1961 ) .
Aliphatic, cycloaliphatic and aromatic dicarboxylic and polycarboxylic acids, such as phthalic acid, terepthalic acid, isopthalic acid, trimellitic acid, pyromellitic acid, adipic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, acelaic acid, sebacic acid and others, are suitable as the carboxylic acid component in the preparation of the polyesters. The acids can also be used in the form of their derivatives capable of esterification (for example anhydrides) or transesterification (for example dimethyl esters).
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The commonly used diols and/or polyols, for example ethylene glycol, 1,2- and 1,3-propanediol, butanediols, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,6-hexanediol, neopentyl glycol, 1,4-dimethylolcyclohexane, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, ditrimethylolpropane, diglycerol and others, are suitable as the alcohol component in the preparation of the polyesters. The polyesters obtained in this manner can be used either individually or as a mixture of different polyesters.
Any solid epoxy resin having an epoxide equivalent weight between 400 and 3000, preferably between 600 and 900 and particularly preferably between 700 and 800, is suitable as the component B. Epoxy resins based on bisphenol A and/or epoxidized novolak resins are preferably used. The epoxy resins based on bisphenol A generally have a functionality s 2, and the epoxidized novolak resins a functionality of z 2.
Examples of suitable epoxy resins are products commercially available under the following names: Epikote°
154, 1001, 1002, 1055, 1004, 1007, 1009, 3003-4F-10 from Shell Chemie, XZ 86 795* and DER* 664, 667, 669, 662, 642U and 672U
from Dow and Araldite* XB 4393, XB 4412, GT 7072, GT 7203, GT 7004, GT 7304, GT 7097 and GT 7220 from Ciba Geigy.
Epoxy resins approved by the FDA are preferably employed.
The polyester component A is normally used in an *Trade-mark 26766-lOD
amount of 19 to 80% by weight, preferably of 39 to 60% by weight, based on the total weight of the powder coating. The epoxy resin component B is normally used in an amount of 19 to 80% by weight, preferably of 39 to 60% by weight, based on the total weight of the powder coating.
As a further component C, the powder coatings according to the invention contain at least one curing catalyst, normally used in an amount of 0.01 to 5.0% by weight preferably of 0.05 to 2.0% by weight, in each case based on l0 the total weight of the powder coating.
The catalyst used is preferably imidazole, 2-methyl-imidazole, ethyltriphenylphosphonium chloride or another salt of the same compound, a quinoline derivative, such as that described in EP-B-10,805, a primary, secondary or tertiary aminophenol, aluminum acetylacetonate or a salt of toluenesulfonic acid or a mixture of different catalysts listed above.
The carboxyl- and hydroxyl-containing polyester resins available commercially usually already contain the 20 required curing catalyst. Examples of such carboxyl- and hydroxyl-containing polyesters available commercially which are particularly preferably used are the products available commercially under the following brand names: Crylcoat* 314, 340, 344, 2680, 316, 2625, 320, 342 and 2532 from UCB, Drogenbos, Belgium, Grilesta* 7205, 7215, 72-06, 72-08, 72-13, 72-14, 73-72, 73-93 and 7401 from Ems-Chemie and Neocrest*
*Trade-mark 26766-lOD
P 670, P 671, P 672, P 678 and P 662* from ICI.
In addition, the powder coatings according to the invention may also contain 0 to 40% by weight, preferably 15 to 25% by weight, of fillers (component D). Fillers approved by the FDA are preferably used. In general, inorganic fillers, for example titanium dioxide such as Kronos* 2160 from Kronos Titan, rutile R 902 from Du Pont and RC 566 from Sachtleben, barium sulfate and silicate-based fillers, such as talc, kaolin, magnesium aluminum silicates, mica and others are used. Titanium dioxide and fillers of the quartz sand type are preferably used.
Furthermore, the powder coatings according to the invention may also contain, where appropriate, 0.01 to 10% by weight, preferably 0.1 to 2% by weight, based on the total weight of the powder coating, of other auxiliary substances and additives. Examples of these are flow control agents, spraying agents, deaeration agents, such *Trade-mark 26766-lOD
215~8~3 as benzoin, pigments and others.
The preparation of the powder coatings is performed by known methods (cf., for example, product information from BASF
Lacke + Farben AG, "Pulverlacke", ("Powder Coatings"], 1990) by homogenization and dispersion, for example by means of an extruder, worm kneader and others. It is an essential part of the invention that the particle size distribution of the powder coatings, following their preparation, is adjusted to suit the application by grinding and, if appropriate, by screening and sieving.
For use in the coating of packaging container interiors, the particle size distribution (a) is adjusted in such a way that at least 90o by mass of the powder coating particles have a particle size between 1 and 60 um, i.e. d 90 = 1 to 60 Vim.
Preferably 90°s by mass of the powder coating particles have a particle site between 1 and 40 ~m (d 90 = 1 to 40 um) and particularly preferably between 5 and 25 ~m (d 90 = 5 to 25 Vim). For at least 99 o by mass of the particles,~the maximum particle size of the powder coating particles is < 100 Vim, preferably < 60 um and particularly preferably < 40 Vim). In the parent application the average particle size of the powder coating particles is preferably between 5 and 20 Vim, particularly preferably between 5 and 12 ~tm. Furthermore, it is an essential part of the invention that, when the powder coatings are used for the coating of packaging container interiors, the particle size distribution is adjusted in such a way that the slope S of the particle distribution curve at the inflection point is z 100, preferably a 150 and particularly preferably z 200. To obtain coatings having particularly good properties, it is most particularly preferred to use powder coatings in which the slope S of the particle distribution curve at the inflection point is Z 300. However, the production costs of powder coatings increase considerably with increasing slope. The slope S is defined as limit value for f (x2) - f (xi) against zero of (f (x2) - f (xi) ) /lg ( (x2/xi) ) at the inflection point of the particle distribution curve. The particle distribution curve thus represents the plot of the accumulated percentages by mass against the absolute particle diameter (represented logarithmically). Accordingly, for use in the coating of packaging container interiors, suitable powder coatings are in particular those which contain only a small proportion of very fine particles (particle size < 5 Vim) and also a very small proportion of coarse powder coating particles (particle size > 25 ~.m), i.e. they have as narrow a particle size distribution as possible.
For use in the coating of weld seams, the particle size distribution (b) is adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 1 and 100 ~,m. Preferred powder coatings are those in which at least 90% by mass of the powder coating particles have a particle size between 5 and 100 ~,m. In this case the slope S, defined above, of 26766-lOD
21~~g63 the particle distribution curve at the inflection point can also be below 100. The slope is usually > 50, preferably >
100. For at least 99o by mass of the particles, the maximum particle size of the powder coating particles is c 150 um, preferably < 100 um. In the divisional application the average particle size of the powder coating particles is preferably between ~ 20 and 60 um, particularly preferably between 25 and 40 urn.
Accordingly, the powder coatings used for the coating of packaging container interiors are in principle also suitable for use in the coating of weld seams. However, powder coatings preferred for use in the coating of weld seams are those which contain a high proportion of coarse powder coating particles.
The ad~ustrnent of the particles size distribution of the power coating is carried out in each case with the aid of suitable grinding aggregates, if appropriate in combination with suitable screening and sieving equipment, e.g. using a fluidized bed opposed yet rnill (AFG) from Alpine, Augsburg, in combination with an ultra-fine classifier from Alpine, Augsburg.
The packaging containers which are coated with the powder coatings according to the invention, can be made of a variety of materials, can be of a variety of sizes and shapes and can be produced by various processes. However, metal containers in particular are coated by the powder coatings according to the invention. These metal containers can be prepared by first rolling and then folding back the metal plate. The end pieces can then be affixed to the cylinder produced in this way. The powder coatings according to the invention are used for the coating of the weld seam as well as for the coating of the can body interiors, which generally are already provided with a bottom.
In addition, the interiors of deep-drawn metal containers can also be coated with the powder coatings according to the invention. The powder coatings are of course also suitable for the coating of can lids and can bottoms.
The packaging containers can be made from a variety of materials, such as aluminum, black plate, tin plate, and various ferrous alloys which are provided, if necessary, with a passivation coat based on nickel, chromium and tin compounds.
Containers of this type are usually used as containers for foodstuffs and beverages, such as beer, juices, fizzy drinks, soups, vegetables, meat dishes, fish dishes, vegetables, but also, for example, for pet foods. Application is carried out by known methods, for example those described in US Patent 4,183,974. The electrostatic charging of the powder coating particles is carried out by friction (triboelectricity). Application of the powder coating particles is performed with the aid of special spray heads, known to a person skilled in the art.
For the coating of packaging container interiors, the powder coatings are normally applied at a film thickness of s 15 um, preferably of 10 to 14 Vim. Even at these low film thicknesses, the coatings comply with the requirements 26766-lOD
normally specified for such films. The powder coatings can of course also be applied in higher film thicknesses. For the coating of weld seams, the powder coatings are normally applied at a film thickness of s 200 Vim, preferably s 80 Vim.
The packaging containers whose weld seam or interior have been coated with the powder coating according to the invention, are subsequently heat-treated in order to cure the powder coating.
This heat treatment can be performed in a variety of ways. To this end the containers in practice are often passed through a continuous-heating oven. In general, the powder coatings cure fully at object temperatures between 230 and 350°C within 5 to 30 sec. The continuous-heating oven can be operated at constant temperature or at a temperature profile set to suit the particular circumstances.
The working examples given below elucidate the invention in greater detail. All parts and percentages are by weight, unless expressly stated otherwise. The preparation of the powder coatings was carried out in each case by weighing all components in canisters, premixing them in a premixer, homogenizing the mixture by means of an extruder at 60 to 80°C, cooling it as rapidly as possible and adjusting it to the desired particle size distribution using grinding aggregates.
Example 1 The following components were processed to give powder coating 1:
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500 parts of a commercial polyester containing a crosslinking catalyst, having an acid value of 35 mg of KOH/g and an OH value of 15 mg of KOH/g (commercial product Grilesta P 7401 from Ems-Chemie), 248 parts of a commercial epoxidized novolak resin having an epoxide equivalent weight (EEW) of 700 (commercial product DER 672 U from Dow), 50 parts of a commercial epoxy resin based on bisphenol A having an EEW of 800 (commercial product Epikote 3003-4F-10 from Shell Chemie), 200 parts of a finely divided silicate filler of the quartz sand type, and 2 parts of a fluidization auxiliary agent based on pyrogenic silicic acid.
Using grinding aggregates, the particle size distribution was adjusted in such a manner that at least 90%
by mass of the powder coating particles have a particle size between 1 and 25 ~m (d 90 = 1 to 25 Vim). For at least 99% by mass of the particles, the maximum particle size is s 100 Vim, the average particle size is bout 9 Vim. The slope S is 250.
This powder coating 1 was applied to a can body (diameter of opening 73 mm, length of body = 110 mm) using suitable equipment, baked for 30 sec. at an object temperature of 280°C
and then subjected to an enamel rater test: The coated can was immersed in a Cu/Cd standard solution S475 (conductance 2.2 ~ 0.2 mS/cm) and connected as cathode. A voltage of 6.3 V
was applied for a period of 30 sec. and the amperage was 26766-lOD
measured. The amperage I = 5 mA was not exceeded at a film thickness as low as 15 Vim. In addition, this powder coating 1 was applied to a tinned can body (deposit of 2.8 mg/m2) at a film thickness of 15 ~m and baked for 30 sec. at an object temperature of 280°C. The coating obtained in this way was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake, (visual) adhesion and flexibility were tested after sterilization. The results are summarized in Table 1.
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Table 1: Test results of the powder coating coat 1 (film thickness 15 Vim, d 90= 1-25 Vim) 3% 3% 2%
untreated3) H20 NaCl4) HAcS) lactic acid 6 ) H20 uptake - none none none none Adhesionl) Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 T-Bend2) TO TO TO TO TO
Key to Table 1:
1) adhesion testing by the crosshatch method (DIN 53151) 2) testing by the ECCA (European Coil Coating Association) procedures 3) examination of the untreated coating prior to sterilization 4) test medium = 3% aqueous sodium chloride solution 5) test medium = 3% aqueous acetic acid 6) test medium = 2% aqueous lactic acid 26766-lOD
Example 2 Powder coating 2 was prepared in a manner similar to that of Example 1 from the components listed in Example 1. In contrast to Example 1, the particle size distribution was adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 1 and 100 ~m (d 90 = 1 to 100 Vim). The maximum particle size of at least 99% by mass of the particles is < 150 Vim, the average particle size is about 35 Vim. The slope S is 100. This powder coating 2 was applied to a can body (diameter of opening 73 mm, length of body = 110 mm), baked for 30 sec. at an object temperature of 280°C and then subjected to the enamel rater test described in Example 1: A minimum film thickness of 35 ~m was required to maintain the amperage I < 5 mA.
Furthermore, this powder coating 2 was applied to a tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at a film thickness of 80 Vim, using suitable spray equipment, and was baked for 30 sec. at an object temperature of 280°C. The coating obtained in this manner was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake (visual), adhesion and flexibility were tested after sterilization. The results are summarized in Table 2.
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Table 2: Test results of the powder coating coat 2 (film thickness 80 Vim, d 90 = 1-100 ~,m) 3% 3% 2%
untreated3) H20 NaCl4) HAcS) lactic acid 6) H20 uptake - none none none none Adhesionl) Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 T-Bend2) TO TO TO TO TO
Key to Table 2:
1) adhesion testing by the crosshatch method (DIN 53151) 2) testing by the ECCA (European Coil Coating l0 Association) procedures 3) examination of the untreated coating prior to sterilization 4) test medium = 3% aqueous sodium chloride solution 5) test medium = 3% aqueous acetic acid 6) test medium = 2% aqueous lactic acid 26766-lOD
~'~ 548 ~ ~
Example 3 The following components were processed to give powder coating 3:
600 parts of a commercial polyester containing a crosslinking catalyst, having an acid value of 35 mg of KOH/g and an OH value of 15 mg of KOH/g (commercial product Grilesta* P 7401 from Ems-Chemie), 250 parts of a commercial epoxy resin based on l0 bisphenol A having an EEW of 600 (commercial product DER 692 from Dow), 48 parts of a master batch of 10 parts of a flow control agent based on an oligomeric acrylate in 90 parts of a commercial epoxy resin based on bisphenol A having an EEW
of 800 (commercial product E 3003-4F-10 from Shell Chemie), 100 parts of a finely divided silicate filler of the quartz sand type, and 20 2 parts of a fluidization agent of the pyrogenic silicic acid type.
*Trade-mark 23 Using grinding aggregates, the particle size distribution was adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 1 and 25 ~m (d 90 = 1 to 25 um). The maximum particle size for at least 99% by weight of the particles is s 100 um, the average particle size is about 11 um. The slope S is 200.
This powder coating 3 is applied to a can body (diameter of opening 73 mm, length of body = 110 mm) by means of spray aggregates, is baked for 30 sec. at an object temperature of 280°C and then subjected to the enamel rater test described in Example 1: the amperage I = 5 mA was not exceeded at a film thickness of less than 15 Vim. In addition, this powder coating 3 was applied with the aid of spray aggregates to a tinned can body (deposit of 2.8 mg/m2) at a film thickness of 15 ~m and was baked for 30 sec. at an object temperature of 280°C. The coating obtained in this way was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake, adhesion and flexibility were tested after sterilization. The results are summarized in Table 3.
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Table 3: Test results of the powder coating coat 3 (film thickness 15 ~.m d 90 = 1-25 ~.m) 3% 3% 2%
untreated4) H20 NaClS) HAc6) lactic acid 7) H20 uptakel) - mod. mod strong strong Adhesion2) Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 T-Bend3) TO TO TO TO TO
Key to Table 3:
(mod. -moderate) 1) visual assessment: examination for turbidity or similar 2) adhesion testing by the crosshatch method (DIN 53151) 3) testing by the ECCA (European Coil Coating Association) procedures 4) examination of the untreated coating prior to sterilization 5) test medium = 3% aqueous sodium chloride solution 6) test medium = 3% aqueous acetic acid 7) test medium = 2% aqueous lactic acid 26766-lOD
Example 4 Powder coating 4 was prepared in a manner similar to that of Example 3 from the components listed in Example 3. In contrast to Example 3, the particle size distribution was adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 1 and 100 ~m (d 90 = 1 to 100 Vim). The maximum particle size for at least 99% by mass of the particles is < 150 Vim, the average particle size is about 40 Vim. The slope S is 90. This powder coating l0 4 was applied to a can body (diameter of opening 73 mm, length of body = 110 mm), was baked for 30 sec. at an object temperature of 280°C and then subjected to the enamel rater test described in Example 1: A minimum film thickness of 35 ~m was required to maintain the amperage I < 5 mA.
In addition, this powder coating 4 was applied to a tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at a film thickness of 80 ~m and was baked for 30 sec. at an object temperature of 280°C. The coating obtained in this manner was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in 20 various test media. Water uptake (visual), adhesion and flexibility were tested after sterilization. The results are summarized in Table 4.
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Table 4: Test results of the powder coating coat 4 (film thickness 80 ~.m, d 90 = 1-100 ~.m) 2% (siC) 3% 3%
untreated3) H20 NaCl4) HAcS) lactic acid 6) H20 uptake - mod. mod. strong strong Adhesionl) Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 d2) T2 T2 T2 T3 T3 B
T
en -Key to Table 4:
(mod. - moderate) 1) adhesion testing by the crosshatch method (DIN
53151) 2) testing by the ECCA (European Coil Coating Association) procedures 3) examination of the untreated coat prior to sterilization 4) test medium = 3% aqueous sodium chloride solution 5) test medium = 3% aqueous acetic acid 6) test medium = 2% aqueous lactic acid 26766-lOD
Example 5 Powder coating 5 was prepared from the following components:
400 parts of a commercial polyester containing a crosslinking catalyst, having an acid value of 80 mg of KOH/g, an OH value of about 2o mg of KOH/g, synthesized from terepthalic acid, trimellitic acid, adipic acid, ethylene glycol and neopentyl glycol (commercial product Grilesta V 72-6 from Ems-Chemie), 400 parts of a commercial epoxy resin based on bisphenol A, having an EEW of 750 (commercial product XB
4393 from Ciba Geigy), 100 parts of titanium dioxide of the rutile type, 93 parts of a finely divided silicate filler of the quartz sand type, 5 parts of a flow control agent based on an oligomeric acrylate, and 2 parts of a fluidization auxiliary agent based on Si02.
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Using grinding aggregates, the particle size distribution was adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 5 and 15 ~m (d 90 = 5 to 15 Vim). The maximum particle size for at least 99% by mass of the particles is s 100 um, the average particle size is about 8 Vim. The slope S is 250.
This powder coating 5 was applied to a can body (diameter of opening 73 mm, length of body = 110 mm), was baked for 30 sec. at an object temperature of 280°C and then subjected to the enamel rater test described in Example 1:
The amperage I = 5 mA was not exceeded at a film thickness of less than 15 Vim.
In addition, this powder coating 5 was applied to a tinned can body (deposit of 2.8 mg/m2) at a film thickness of um and was baked for 30 sec. at an object temperature of 280°C. The coating obtained in this manner was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake (visual), adhesion and flexibility were tested after sterilization. The results are summarized in Table 5.
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Table 5: Test results of the powder coating coat 5 (film thickness 15 ~,m, d 90 = 5-15 ~.m) 3% 3% 2%
untreated3) H20 NaCl4) HAcS) lactic acid 6) H20 uptake - none none none none Adhesionl) Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 d2) TO TO TO TO TO
T
B
-en Key to Table 5:
1) adhesion testing by the crosshatch method (DIN
53151) 2) testing by the ECCA (European Coil Coating Association) procedures 3) examination of the untreated coat prior to sterilization 4) test medium = 3% aqueous sodium chloride solution 5) test medium = 3% aqueous acetic acid 6) test medium = 2% aqueous lactic acid 26766-lOD
Example 6 Powder coating 6 was prepared in a manner similar to that of Example 5 from the components listed in Example 5. In contrast to Example 5, the particle size distribution was adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 1 and 100 ~,m (d 90 = 1 to 100 ~,m). The maximum particle size for at lest 99% by mass of the particles is s 150 ~.m, the mean particle size is about 40 Vim. The slope S is 100. This powder coating 6 was applied to a can body (diameter of opening 73 mm, length of body = 110 mm), was baked for 30 sec. at 280°C and then subjected to the enamel rater test described in Example 1: A
minimum film thickness of 25 ~m is required to maintain the amperage I < 5 mA.
In addition, this powder coating 6 was applied to a tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at a film thickness of 80 ~.m and was baked for 30 sec. at an object temperature of 280°C. The coating obtained in this manner was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake (visual), adhesion and flexibility were tested after sterilization. The results are summarized in Table 6.
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Table 6: Test results of the powder coating coat 6 (film thickness 80 ~.m, d 90 - 1-100 /gym) 3% 3% 2%
untreated3) H20 NaCl4) HAcS) lactic acid 6 ) H20 uptake - none none none none Adhesionl) Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 d2) TO TO TO TO TO
B
T
en -Key to Table 6:
1) adhesion testing by the crosshatch method (DIN
53151) l0 2) testing by the ECCA (European Coil Coating Association) procedures 3) examination of the untreated coating prior to sterilization 4) test medium = 3% aqueous sodium chloride solution 5) test medium = 3% aqueous acetic acid 6) test medium = 2% aqueous lactic acid 26766-lOD
In addition, pack tests were carried out on cans whose weld seams were coated with powder coating 6 (application by means of suitable spray aggregates, curing for 30 sec. at an object temperature of 280°C, film thickness 60 -80 Vim, coating of the can interiors with a conventional, commercial spray paint). The foodstuff cans were filled with water, 3% acetic acid and 2% lactic acid and sealed. The cans were sterilized for 30 min. at 1.6 bar and 128°C and then stored at 37°C.
l0 No damage to the coating was apparent after 6 months' storage.
Example 7 The following components were processed to give powder coating 7:
425 parts of a commercial polyester containing an esterification catalyst, having an acid value of 80 mg of KOH/g and an OH value of 20 mg of KOH/g (commercial product Grilesta V 72-6 from Ems-Chemie), 20 475 parts of a commercial epoxy resin based on bisphenol A, having an EEW of 800 (commercial product XZ
86795 from Dow) , 50 parts of talc, 48 parts of a master batch of 10 parts of a flow control agent based on an oligomeric acrylate in 90 parts of the abovementioned commercial polyester having an acid value of 80 mg of KOH/g and an OH value of 20 mg of KOH/g, and 26766-lOD
2 parts of a fluidization auxiliary agent based on pyrogenic silicic acid.
Using griding aggregates, the particle distribution was adjusted in such a way that 90% by mass of the powder coating particles have a particle size between 1 and 25 ~m (d 90 = 1 to 25 Vim). The maximum particle size for at least 99% by mass of the particles is s 100 Vim, the average particle size is about 14 um. The slope S is 200. This powder coating 7 was applied to a can body (diameter of opening 73 mm, length l0 of body = 110 mm), baked for 30 sec. at an object temperature of 280°C and then subjected to the enamel rater test described in Example 1: A minimum film thickness of 15 ~m is required to maintain an amperage I < 5 mA.
In addition, this powder coating 7 was applied to a tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at a film thickness of 30 ~m and baked for 30 sec. at an object temperature of 280°C. The coating obtained in this manner was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake (visual), adhesion and 20 flexibility were tested after sterilization. The results are summarized in Table 7.
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Table 7: Test results of the powder coating coat 7 (film thickness 30 Vim, d 90 = 1-25 Vim) 3% 3% 2%
untreated3) H20 NaCl4) HAcS) lactic acid 6) H20 uptake - strong strong strong strong Adhesionl) Gt 0 Gt 0 Gt 2 Gt 0 Gt 2 d2) TO TO TO TO TO
T
B
-en Key to Table 7:
1) adhesion testing by the crosshatch method (DIN
53151) 2) testing by the ECCA (European Coil Coating Association) procedures 3) examination of the untreated coating prior to sterilization 4) test medium = 3% aqueous sodium chloride solution 5) test medium = 3% aqueous acetic acid 6) test medium = 2% aqueous lactic acid 26766-lOD
Example 8 Powder coating 8 was prepared in a manner similar to that of Example 7 from the components listed in Example 7. In contrast to Example 7, the particle size distribution was adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 1 and 100 ~m (d 90 = 1 to 100 Vim). The maximum particle size for at least 99% by mass of the particles is s 150 Vim, the average particle size is bout 35 Vim. The slope S is 150. This powder coating 8 was applied to a can body (diameter of opening 73 mm, length of body = 110 mm), baked for 30 sec. at an object temperature of 280°C and then subjected to the enamel rater test. A
minimum film thickness of 35 ~m is required to maintain the amperage I < 5 mA.
In addition, this powder coating 8 was applied to a tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at a film thickness of 80 ~m and baked for 30 sec. at an object temperature of 280°C. The coating obtained in this manner was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake (visual), adhesion and flexibility were tested after sterilization. The results are summarized in Table 8.
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Table 8: Test results of the powder coating coat 8 (film thickness 80 Vim, d 90 = 1-100 Vim) 3% 3% 2%
untreated3) H20 NaCl4) HAcS) lactic acid 6) H20 uptake - strong strong strong strong Adhesionl) Gt 0 Gt 0 Gt 2 Gt 0 Gt 2 T-Bend2) T2 T2 T3 T3 T4 Key to Table 8:
1) adhesion testing by the crosshatch method (DIN
53151) 2) testing by the ECCA (European Coil Coating Association) procedures 3) examination of the untreated coating prior to sterilization 4) test medium 3% aqueous sodium chloride solution =
5) test medium 3% aqueous acetic acid =
6) test medium 2% aqueous lactic acid =
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~1 ~4~ ~3 The aim of the present invention is to make available powder coatings which, with the same chemical composition, are suitable both for weld seam coating and for the coating of packaging container interiors, in particular metal container interiors. In addition, these powder coatings, when used for the coating of packaging container interiors and when applied at film thicknesses as low as s 15 ~,m, should comply with the requirements which are usually specified for can interior coatings. In particular, these interior coatings should not be porous (determined with the aid of a so-called enamel rater test), they should possess good adhesion to the substrate and good flexibility, and they should withstand the customary pasteurization and sterilization conditions. Furthermore, these powder coatings, when used for weld seam coating, should lead to highly flexible coatings which withstand the mechanical deformations incurred in the flanging and of the cans beading. Resistance to sterilization and pasteurization is also required after the deformative treatment.
The powder coating should be curable in the course of the brief drying times which are customary in can coating.
Surprisingly, this aim is achieved by the invention of the parent application which provides a powder coating of the type referred to at the outset, wherein I. the powder coating comprises A) at least one polyester having an acid value of to 120 mg of KOH/g and an OH value z 10 mg of KOH/g and 26766-lOD
B) at least one epoxy resin having an epoxide equivalent weight of 400 to 3000, and II. the powder coating has such a particle size 5a 26766-lOD
~.
21~4~~3 distribution that a) at least 90o by mass of the powder coating particles have a particle size between 1 and 60 um, b) the maxirnum particle size for at least 99o by mass of the powder coating particles is < 100 um, c) the average particle size of the powder coating part icles is between 5 and 20 urn, and d) the slope of the particle distribution curve at the inflection point is greater than or equal to 100.
Furthermore, the invention of the divisional application relates to a powder coating for the coating of packaging container weld seams based on epoxy resins and carboxyl-containing polyesters, wherein I. the powder coating comprises A) at least one polyester having an acid value of 25 to 120 mg of KOH/g and an OH value of a 10 mg of KOH/g, and B) at least one epoxy resin having an epoxide equivalent weight of 400 to 3000, and II. the powder coating has such a particle size distribution that a) at least 90% by mass of the powder coating particles have a particle size between 1 and 100 ~.m, b) the maximum particle size for at least 99% by mass of the powder coating particles is ~ 150 ~.m, c) the average particle size of the powder coating particles is between > 20 and 60 Vim, and d) the slope of the particle distribution curve at the inflection point is >_ 50.
In addition, the invention relates to processes for the coating of packaging container interiors and weld seams A
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in which these powder coatings are applied. The invention finally also relates to the use of the powder coatings for the coating of packaging container interiors and weld seams.
It is surprising, and could not have been foreseen, that the powder coatings according to the invention are suitable, with the same chemical composition, for the coating both of weld seams and of packaging container interiors and that the property profile and hence the use can be regulated simply by establishing a corresponding particle size distribution. At the same time these powder coatings are rapidly curable, simple to handle and simple to apply.
Furthermore, the powder coatings according to the invention, when used for the coating of packaging container interiors, are distinguished by the fact that coatings with a very low film thickness of only s 15 ~m possess the properties required by can manufacturers. In particular, these coatings have the required low porosity at a film thickness as low as s 15 Vim. Moreover, these coatings possess good adhesion, high flexibility and good resistance to pasteurization and sterilization.
Furthermore, the powder coatings according to the invention, when used for weld seam coating, have the advantage of high flexibility, with the result that the weld seam coating is able to follow the deformations of the packaging container on further fabrication without peeling off or cracking. Moreover, it is an advantage that, in contrast to aminic curing agents, the powder coating according to the invention attains good resistance to sterilization.
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The individual components of the powder coatings according to the invention are now elucidated in greater detail below. The polyesters employed in the powder coatings according to the invention (component A) have an acid value of 25 to 120 mg of KOH/g, preferably 30 to 90 mg of KOH/g and particularly preferably 60 to 90 mg of KOH/g, and an OH value of at least 10 mg of KOH/g, preferably at least 15 mg of KOH/g and preferably lower than or equal to 30 mg of KOH/g.
Polyesters having a functionality of z 2 are preferably employed. The number average molecular weights of the polyesters are generally between 1000 and 10,000, preferably between 1500 and 5000. Polyesters approved by the US FDA
(FDA = Food and Drug Administration) are preferably used. The carboxyl- and hydroxyl-containing polyesters can be prepared by conventional methods (cf., for example, Houben Weyl, Methoden der organischen Chemie, [Methods of Organic Chemistry], 4th edition, volume 14/2, Georg Thieme Verlag, Stuttgart 1961 ) .
Aliphatic, cycloaliphatic and aromatic dicarboxylic and polycarboxylic acids, such as phthalic acid, terepthalic acid, isopthalic acid, trimellitic acid, pyromellitic acid, adipic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, acelaic acid, sebacic acid and others, are suitable as the carboxylic acid component in the preparation of the polyesters. The acids can also be used in the form of their derivatives capable of esterification (for example anhydrides) or transesterification (for example dimethyl esters).
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The commonly used diols and/or polyols, for example ethylene glycol, 1,2- and 1,3-propanediol, butanediols, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,6-hexanediol, neopentyl glycol, 1,4-dimethylolcyclohexane, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, ditrimethylolpropane, diglycerol and others, are suitable as the alcohol component in the preparation of the polyesters. The polyesters obtained in this manner can be used either individually or as a mixture of different polyesters.
Any solid epoxy resin having an epoxide equivalent weight between 400 and 3000, preferably between 600 and 900 and particularly preferably between 700 and 800, is suitable as the component B. Epoxy resins based on bisphenol A and/or epoxidized novolak resins are preferably used. The epoxy resins based on bisphenol A generally have a functionality s 2, and the epoxidized novolak resins a functionality of z 2.
Examples of suitable epoxy resins are products commercially available under the following names: Epikote°
154, 1001, 1002, 1055, 1004, 1007, 1009, 3003-4F-10 from Shell Chemie, XZ 86 795* and DER* 664, 667, 669, 662, 642U and 672U
from Dow and Araldite* XB 4393, XB 4412, GT 7072, GT 7203, GT 7004, GT 7304, GT 7097 and GT 7220 from Ciba Geigy.
Epoxy resins approved by the FDA are preferably employed.
The polyester component A is normally used in an *Trade-mark 26766-lOD
amount of 19 to 80% by weight, preferably of 39 to 60% by weight, based on the total weight of the powder coating. The epoxy resin component B is normally used in an amount of 19 to 80% by weight, preferably of 39 to 60% by weight, based on the total weight of the powder coating.
As a further component C, the powder coatings according to the invention contain at least one curing catalyst, normally used in an amount of 0.01 to 5.0% by weight preferably of 0.05 to 2.0% by weight, in each case based on l0 the total weight of the powder coating.
The catalyst used is preferably imidazole, 2-methyl-imidazole, ethyltriphenylphosphonium chloride or another salt of the same compound, a quinoline derivative, such as that described in EP-B-10,805, a primary, secondary or tertiary aminophenol, aluminum acetylacetonate or a salt of toluenesulfonic acid or a mixture of different catalysts listed above.
The carboxyl- and hydroxyl-containing polyester resins available commercially usually already contain the 20 required curing catalyst. Examples of such carboxyl- and hydroxyl-containing polyesters available commercially which are particularly preferably used are the products available commercially under the following brand names: Crylcoat* 314, 340, 344, 2680, 316, 2625, 320, 342 and 2532 from UCB, Drogenbos, Belgium, Grilesta* 7205, 7215, 72-06, 72-08, 72-13, 72-14, 73-72, 73-93 and 7401 from Ems-Chemie and Neocrest*
*Trade-mark 26766-lOD
P 670, P 671, P 672, P 678 and P 662* from ICI.
In addition, the powder coatings according to the invention may also contain 0 to 40% by weight, preferably 15 to 25% by weight, of fillers (component D). Fillers approved by the FDA are preferably used. In general, inorganic fillers, for example titanium dioxide such as Kronos* 2160 from Kronos Titan, rutile R 902 from Du Pont and RC 566 from Sachtleben, barium sulfate and silicate-based fillers, such as talc, kaolin, magnesium aluminum silicates, mica and others are used. Titanium dioxide and fillers of the quartz sand type are preferably used.
Furthermore, the powder coatings according to the invention may also contain, where appropriate, 0.01 to 10% by weight, preferably 0.1 to 2% by weight, based on the total weight of the powder coating, of other auxiliary substances and additives. Examples of these are flow control agents, spraying agents, deaeration agents, such *Trade-mark 26766-lOD
215~8~3 as benzoin, pigments and others.
The preparation of the powder coatings is performed by known methods (cf., for example, product information from BASF
Lacke + Farben AG, "Pulverlacke", ("Powder Coatings"], 1990) by homogenization and dispersion, for example by means of an extruder, worm kneader and others. It is an essential part of the invention that the particle size distribution of the powder coatings, following their preparation, is adjusted to suit the application by grinding and, if appropriate, by screening and sieving.
For use in the coating of packaging container interiors, the particle size distribution (a) is adjusted in such a way that at least 90o by mass of the powder coating particles have a particle size between 1 and 60 um, i.e. d 90 = 1 to 60 Vim.
Preferably 90°s by mass of the powder coating particles have a particle site between 1 and 40 ~m (d 90 = 1 to 40 um) and particularly preferably between 5 and 25 ~m (d 90 = 5 to 25 Vim). For at least 99 o by mass of the particles,~the maximum particle size of the powder coating particles is < 100 Vim, preferably < 60 um and particularly preferably < 40 Vim). In the parent application the average particle size of the powder coating particles is preferably between 5 and 20 Vim, particularly preferably between 5 and 12 ~tm. Furthermore, it is an essential part of the invention that, when the powder coatings are used for the coating of packaging container interiors, the particle size distribution is adjusted in such a way that the slope S of the particle distribution curve at the inflection point is z 100, preferably a 150 and particularly preferably z 200. To obtain coatings having particularly good properties, it is most particularly preferred to use powder coatings in which the slope S of the particle distribution curve at the inflection point is Z 300. However, the production costs of powder coatings increase considerably with increasing slope. The slope S is defined as limit value for f (x2) - f (xi) against zero of (f (x2) - f (xi) ) /lg ( (x2/xi) ) at the inflection point of the particle distribution curve. The particle distribution curve thus represents the plot of the accumulated percentages by mass against the absolute particle diameter (represented logarithmically). Accordingly, for use in the coating of packaging container interiors, suitable powder coatings are in particular those which contain only a small proportion of very fine particles (particle size < 5 Vim) and also a very small proportion of coarse powder coating particles (particle size > 25 ~.m), i.e. they have as narrow a particle size distribution as possible.
For use in the coating of weld seams, the particle size distribution (b) is adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 1 and 100 ~,m. Preferred powder coatings are those in which at least 90% by mass of the powder coating particles have a particle size between 5 and 100 ~,m. In this case the slope S, defined above, of 26766-lOD
21~~g63 the particle distribution curve at the inflection point can also be below 100. The slope is usually > 50, preferably >
100. For at least 99o by mass of the particles, the maximum particle size of the powder coating particles is c 150 um, preferably < 100 um. In the divisional application the average particle size of the powder coating particles is preferably between ~ 20 and 60 um, particularly preferably between 25 and 40 urn.
Accordingly, the powder coatings used for the coating of packaging container interiors are in principle also suitable for use in the coating of weld seams. However, powder coatings preferred for use in the coating of weld seams are those which contain a high proportion of coarse powder coating particles.
The ad~ustrnent of the particles size distribution of the power coating is carried out in each case with the aid of suitable grinding aggregates, if appropriate in combination with suitable screening and sieving equipment, e.g. using a fluidized bed opposed yet rnill (AFG) from Alpine, Augsburg, in combination with an ultra-fine classifier from Alpine, Augsburg.
The packaging containers which are coated with the powder coatings according to the invention, can be made of a variety of materials, can be of a variety of sizes and shapes and can be produced by various processes. However, metal containers in particular are coated by the powder coatings according to the invention. These metal containers can be prepared by first rolling and then folding back the metal plate. The end pieces can then be affixed to the cylinder produced in this way. The powder coatings according to the invention are used for the coating of the weld seam as well as for the coating of the can body interiors, which generally are already provided with a bottom.
In addition, the interiors of deep-drawn metal containers can also be coated with the powder coatings according to the invention. The powder coatings are of course also suitable for the coating of can lids and can bottoms.
The packaging containers can be made from a variety of materials, such as aluminum, black plate, tin plate, and various ferrous alloys which are provided, if necessary, with a passivation coat based on nickel, chromium and tin compounds.
Containers of this type are usually used as containers for foodstuffs and beverages, such as beer, juices, fizzy drinks, soups, vegetables, meat dishes, fish dishes, vegetables, but also, for example, for pet foods. Application is carried out by known methods, for example those described in US Patent 4,183,974. The electrostatic charging of the powder coating particles is carried out by friction (triboelectricity). Application of the powder coating particles is performed with the aid of special spray heads, known to a person skilled in the art.
For the coating of packaging container interiors, the powder coatings are normally applied at a film thickness of s 15 um, preferably of 10 to 14 Vim. Even at these low film thicknesses, the coatings comply with the requirements 26766-lOD
normally specified for such films. The powder coatings can of course also be applied in higher film thicknesses. For the coating of weld seams, the powder coatings are normally applied at a film thickness of s 200 Vim, preferably s 80 Vim.
The packaging containers whose weld seam or interior have been coated with the powder coating according to the invention, are subsequently heat-treated in order to cure the powder coating.
This heat treatment can be performed in a variety of ways. To this end the containers in practice are often passed through a continuous-heating oven. In general, the powder coatings cure fully at object temperatures between 230 and 350°C within 5 to 30 sec. The continuous-heating oven can be operated at constant temperature or at a temperature profile set to suit the particular circumstances.
The working examples given below elucidate the invention in greater detail. All parts and percentages are by weight, unless expressly stated otherwise. The preparation of the powder coatings was carried out in each case by weighing all components in canisters, premixing them in a premixer, homogenizing the mixture by means of an extruder at 60 to 80°C, cooling it as rapidly as possible and adjusting it to the desired particle size distribution using grinding aggregates.
Example 1 The following components were processed to give powder coating 1:
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500 parts of a commercial polyester containing a crosslinking catalyst, having an acid value of 35 mg of KOH/g and an OH value of 15 mg of KOH/g (commercial product Grilesta P 7401 from Ems-Chemie), 248 parts of a commercial epoxidized novolak resin having an epoxide equivalent weight (EEW) of 700 (commercial product DER 672 U from Dow), 50 parts of a commercial epoxy resin based on bisphenol A having an EEW of 800 (commercial product Epikote 3003-4F-10 from Shell Chemie), 200 parts of a finely divided silicate filler of the quartz sand type, and 2 parts of a fluidization auxiliary agent based on pyrogenic silicic acid.
Using grinding aggregates, the particle size distribution was adjusted in such a manner that at least 90%
by mass of the powder coating particles have a particle size between 1 and 25 ~m (d 90 = 1 to 25 Vim). For at least 99% by mass of the particles, the maximum particle size is s 100 Vim, the average particle size is bout 9 Vim. The slope S is 250.
This powder coating 1 was applied to a can body (diameter of opening 73 mm, length of body = 110 mm) using suitable equipment, baked for 30 sec. at an object temperature of 280°C
and then subjected to an enamel rater test: The coated can was immersed in a Cu/Cd standard solution S475 (conductance 2.2 ~ 0.2 mS/cm) and connected as cathode. A voltage of 6.3 V
was applied for a period of 30 sec. and the amperage was 26766-lOD
measured. The amperage I = 5 mA was not exceeded at a film thickness as low as 15 Vim. In addition, this powder coating 1 was applied to a tinned can body (deposit of 2.8 mg/m2) at a film thickness of 15 ~m and baked for 30 sec. at an object temperature of 280°C. The coating obtained in this way was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake, (visual) adhesion and flexibility were tested after sterilization. The results are summarized in Table 1.
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Table 1: Test results of the powder coating coat 1 (film thickness 15 Vim, d 90= 1-25 Vim) 3% 3% 2%
untreated3) H20 NaCl4) HAcS) lactic acid 6 ) H20 uptake - none none none none Adhesionl) Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 T-Bend2) TO TO TO TO TO
Key to Table 1:
1) adhesion testing by the crosshatch method (DIN 53151) 2) testing by the ECCA (European Coil Coating Association) procedures 3) examination of the untreated coating prior to sterilization 4) test medium = 3% aqueous sodium chloride solution 5) test medium = 3% aqueous acetic acid 6) test medium = 2% aqueous lactic acid 26766-lOD
Example 2 Powder coating 2 was prepared in a manner similar to that of Example 1 from the components listed in Example 1. In contrast to Example 1, the particle size distribution was adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 1 and 100 ~m (d 90 = 1 to 100 Vim). The maximum particle size of at least 99% by mass of the particles is < 150 Vim, the average particle size is about 35 Vim. The slope S is 100. This powder coating 2 was applied to a can body (diameter of opening 73 mm, length of body = 110 mm), baked for 30 sec. at an object temperature of 280°C and then subjected to the enamel rater test described in Example 1: A minimum film thickness of 35 ~m was required to maintain the amperage I < 5 mA.
Furthermore, this powder coating 2 was applied to a tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at a film thickness of 80 Vim, using suitable spray equipment, and was baked for 30 sec. at an object temperature of 280°C. The coating obtained in this manner was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake (visual), adhesion and flexibility were tested after sterilization. The results are summarized in Table 2.
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Table 2: Test results of the powder coating coat 2 (film thickness 80 Vim, d 90 = 1-100 ~,m) 3% 3% 2%
untreated3) H20 NaCl4) HAcS) lactic acid 6) H20 uptake - none none none none Adhesionl) Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 T-Bend2) TO TO TO TO TO
Key to Table 2:
1) adhesion testing by the crosshatch method (DIN 53151) 2) testing by the ECCA (European Coil Coating l0 Association) procedures 3) examination of the untreated coating prior to sterilization 4) test medium = 3% aqueous sodium chloride solution 5) test medium = 3% aqueous acetic acid 6) test medium = 2% aqueous lactic acid 26766-lOD
~'~ 548 ~ ~
Example 3 The following components were processed to give powder coating 3:
600 parts of a commercial polyester containing a crosslinking catalyst, having an acid value of 35 mg of KOH/g and an OH value of 15 mg of KOH/g (commercial product Grilesta* P 7401 from Ems-Chemie), 250 parts of a commercial epoxy resin based on l0 bisphenol A having an EEW of 600 (commercial product DER 692 from Dow), 48 parts of a master batch of 10 parts of a flow control agent based on an oligomeric acrylate in 90 parts of a commercial epoxy resin based on bisphenol A having an EEW
of 800 (commercial product E 3003-4F-10 from Shell Chemie), 100 parts of a finely divided silicate filler of the quartz sand type, and 20 2 parts of a fluidization agent of the pyrogenic silicic acid type.
*Trade-mark 23 Using grinding aggregates, the particle size distribution was adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 1 and 25 ~m (d 90 = 1 to 25 um). The maximum particle size for at least 99% by weight of the particles is s 100 um, the average particle size is about 11 um. The slope S is 200.
This powder coating 3 is applied to a can body (diameter of opening 73 mm, length of body = 110 mm) by means of spray aggregates, is baked for 30 sec. at an object temperature of 280°C and then subjected to the enamel rater test described in Example 1: the amperage I = 5 mA was not exceeded at a film thickness of less than 15 Vim. In addition, this powder coating 3 was applied with the aid of spray aggregates to a tinned can body (deposit of 2.8 mg/m2) at a film thickness of 15 ~m and was baked for 30 sec. at an object temperature of 280°C. The coating obtained in this way was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake, adhesion and flexibility were tested after sterilization. The results are summarized in Table 3.
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Table 3: Test results of the powder coating coat 3 (film thickness 15 ~.m d 90 = 1-25 ~.m) 3% 3% 2%
untreated4) H20 NaClS) HAc6) lactic acid 7) H20 uptakel) - mod. mod strong strong Adhesion2) Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 T-Bend3) TO TO TO TO TO
Key to Table 3:
(mod. -moderate) 1) visual assessment: examination for turbidity or similar 2) adhesion testing by the crosshatch method (DIN 53151) 3) testing by the ECCA (European Coil Coating Association) procedures 4) examination of the untreated coating prior to sterilization 5) test medium = 3% aqueous sodium chloride solution 6) test medium = 3% aqueous acetic acid 7) test medium = 2% aqueous lactic acid 26766-lOD
Example 4 Powder coating 4 was prepared in a manner similar to that of Example 3 from the components listed in Example 3. In contrast to Example 3, the particle size distribution was adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 1 and 100 ~m (d 90 = 1 to 100 Vim). The maximum particle size for at least 99% by mass of the particles is < 150 Vim, the average particle size is about 40 Vim. The slope S is 90. This powder coating l0 4 was applied to a can body (diameter of opening 73 mm, length of body = 110 mm), was baked for 30 sec. at an object temperature of 280°C and then subjected to the enamel rater test described in Example 1: A minimum film thickness of 35 ~m was required to maintain the amperage I < 5 mA.
In addition, this powder coating 4 was applied to a tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at a film thickness of 80 ~m and was baked for 30 sec. at an object temperature of 280°C. The coating obtained in this manner was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in 20 various test media. Water uptake (visual), adhesion and flexibility were tested after sterilization. The results are summarized in Table 4.
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Table 4: Test results of the powder coating coat 4 (film thickness 80 ~.m, d 90 = 1-100 ~.m) 2% (siC) 3% 3%
untreated3) H20 NaCl4) HAcS) lactic acid 6) H20 uptake - mod. mod. strong strong Adhesionl) Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 d2) T2 T2 T2 T3 T3 B
T
en -Key to Table 4:
(mod. - moderate) 1) adhesion testing by the crosshatch method (DIN
53151) 2) testing by the ECCA (European Coil Coating Association) procedures 3) examination of the untreated coat prior to sterilization 4) test medium = 3% aqueous sodium chloride solution 5) test medium = 3% aqueous acetic acid 6) test medium = 2% aqueous lactic acid 26766-lOD
Example 5 Powder coating 5 was prepared from the following components:
400 parts of a commercial polyester containing a crosslinking catalyst, having an acid value of 80 mg of KOH/g, an OH value of about 2o mg of KOH/g, synthesized from terepthalic acid, trimellitic acid, adipic acid, ethylene glycol and neopentyl glycol (commercial product Grilesta V 72-6 from Ems-Chemie), 400 parts of a commercial epoxy resin based on bisphenol A, having an EEW of 750 (commercial product XB
4393 from Ciba Geigy), 100 parts of titanium dioxide of the rutile type, 93 parts of a finely divided silicate filler of the quartz sand type, 5 parts of a flow control agent based on an oligomeric acrylate, and 2 parts of a fluidization auxiliary agent based on Si02.
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Using grinding aggregates, the particle size distribution was adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 5 and 15 ~m (d 90 = 5 to 15 Vim). The maximum particle size for at least 99% by mass of the particles is s 100 um, the average particle size is about 8 Vim. The slope S is 250.
This powder coating 5 was applied to a can body (diameter of opening 73 mm, length of body = 110 mm), was baked for 30 sec. at an object temperature of 280°C and then subjected to the enamel rater test described in Example 1:
The amperage I = 5 mA was not exceeded at a film thickness of less than 15 Vim.
In addition, this powder coating 5 was applied to a tinned can body (deposit of 2.8 mg/m2) at a film thickness of um and was baked for 30 sec. at an object temperature of 280°C. The coating obtained in this manner was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake (visual), adhesion and flexibility were tested after sterilization. The results are summarized in Table 5.
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Table 5: Test results of the powder coating coat 5 (film thickness 15 ~,m, d 90 = 5-15 ~.m) 3% 3% 2%
untreated3) H20 NaCl4) HAcS) lactic acid 6) H20 uptake - none none none none Adhesionl) Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 d2) TO TO TO TO TO
T
B
-en Key to Table 5:
1) adhesion testing by the crosshatch method (DIN
53151) 2) testing by the ECCA (European Coil Coating Association) procedures 3) examination of the untreated coat prior to sterilization 4) test medium = 3% aqueous sodium chloride solution 5) test medium = 3% aqueous acetic acid 6) test medium = 2% aqueous lactic acid 26766-lOD
Example 6 Powder coating 6 was prepared in a manner similar to that of Example 5 from the components listed in Example 5. In contrast to Example 5, the particle size distribution was adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 1 and 100 ~,m (d 90 = 1 to 100 ~,m). The maximum particle size for at lest 99% by mass of the particles is s 150 ~.m, the mean particle size is about 40 Vim. The slope S is 100. This powder coating 6 was applied to a can body (diameter of opening 73 mm, length of body = 110 mm), was baked for 30 sec. at 280°C and then subjected to the enamel rater test described in Example 1: A
minimum film thickness of 25 ~m is required to maintain the amperage I < 5 mA.
In addition, this powder coating 6 was applied to a tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at a film thickness of 80 ~.m and was baked for 30 sec. at an object temperature of 280°C. The coating obtained in this manner was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake (visual), adhesion and flexibility were tested after sterilization. The results are summarized in Table 6.
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Table 6: Test results of the powder coating coat 6 (film thickness 80 ~.m, d 90 - 1-100 /gym) 3% 3% 2%
untreated3) H20 NaCl4) HAcS) lactic acid 6 ) H20 uptake - none none none none Adhesionl) Gt 0 Gt 0 Gt 0 Gt 0 Gt 0 d2) TO TO TO TO TO
B
T
en -Key to Table 6:
1) adhesion testing by the crosshatch method (DIN
53151) l0 2) testing by the ECCA (European Coil Coating Association) procedures 3) examination of the untreated coating prior to sterilization 4) test medium = 3% aqueous sodium chloride solution 5) test medium = 3% aqueous acetic acid 6) test medium = 2% aqueous lactic acid 26766-lOD
In addition, pack tests were carried out on cans whose weld seams were coated with powder coating 6 (application by means of suitable spray aggregates, curing for 30 sec. at an object temperature of 280°C, film thickness 60 -80 Vim, coating of the can interiors with a conventional, commercial spray paint). The foodstuff cans were filled with water, 3% acetic acid and 2% lactic acid and sealed. The cans were sterilized for 30 min. at 1.6 bar and 128°C and then stored at 37°C.
l0 No damage to the coating was apparent after 6 months' storage.
Example 7 The following components were processed to give powder coating 7:
425 parts of a commercial polyester containing an esterification catalyst, having an acid value of 80 mg of KOH/g and an OH value of 20 mg of KOH/g (commercial product Grilesta V 72-6 from Ems-Chemie), 20 475 parts of a commercial epoxy resin based on bisphenol A, having an EEW of 800 (commercial product XZ
86795 from Dow) , 50 parts of talc, 48 parts of a master batch of 10 parts of a flow control agent based on an oligomeric acrylate in 90 parts of the abovementioned commercial polyester having an acid value of 80 mg of KOH/g and an OH value of 20 mg of KOH/g, and 26766-lOD
2 parts of a fluidization auxiliary agent based on pyrogenic silicic acid.
Using griding aggregates, the particle distribution was adjusted in such a way that 90% by mass of the powder coating particles have a particle size between 1 and 25 ~m (d 90 = 1 to 25 Vim). The maximum particle size for at least 99% by mass of the particles is s 100 Vim, the average particle size is about 14 um. The slope S is 200. This powder coating 7 was applied to a can body (diameter of opening 73 mm, length l0 of body = 110 mm), baked for 30 sec. at an object temperature of 280°C and then subjected to the enamel rater test described in Example 1: A minimum film thickness of 15 ~m is required to maintain an amperage I < 5 mA.
In addition, this powder coating 7 was applied to a tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at a film thickness of 30 ~m and baked for 30 sec. at an object temperature of 280°C. The coating obtained in this manner was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake (visual), adhesion and 20 flexibility were tested after sterilization. The results are summarized in Table 7.
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Table 7: Test results of the powder coating coat 7 (film thickness 30 Vim, d 90 = 1-25 Vim) 3% 3% 2%
untreated3) H20 NaCl4) HAcS) lactic acid 6) H20 uptake - strong strong strong strong Adhesionl) Gt 0 Gt 0 Gt 2 Gt 0 Gt 2 d2) TO TO TO TO TO
T
B
-en Key to Table 7:
1) adhesion testing by the crosshatch method (DIN
53151) 2) testing by the ECCA (European Coil Coating Association) procedures 3) examination of the untreated coating prior to sterilization 4) test medium = 3% aqueous sodium chloride solution 5) test medium = 3% aqueous acetic acid 6) test medium = 2% aqueous lactic acid 26766-lOD
Example 8 Powder coating 8 was prepared in a manner similar to that of Example 7 from the components listed in Example 7. In contrast to Example 7, the particle size distribution was adjusted in such a way that at least 90% by mass of the powder coating particles have a particle size between 1 and 100 ~m (d 90 = 1 to 100 Vim). The maximum particle size for at least 99% by mass of the particles is s 150 Vim, the average particle size is bout 35 Vim. The slope S is 150. This powder coating 8 was applied to a can body (diameter of opening 73 mm, length of body = 110 mm), baked for 30 sec. at an object temperature of 280°C and then subjected to the enamel rater test. A
minimum film thickness of 35 ~m is required to maintain the amperage I < 5 mA.
In addition, this powder coating 8 was applied to a tinned (deposit of 2.8 mg/m2) panel (size 20 x 20 cm2) at a film thickness of 80 ~m and baked for 30 sec. at an object temperature of 280°C. The coating obtained in this manner was subjected to a sterilization test (30 min., 1.6 bar, 128°C) in various test media. Water uptake (visual), adhesion and flexibility were tested after sterilization. The results are summarized in Table 8.
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Table 8: Test results of the powder coating coat 8 (film thickness 80 Vim, d 90 = 1-100 Vim) 3% 3% 2%
untreated3) H20 NaCl4) HAcS) lactic acid 6) H20 uptake - strong strong strong strong Adhesionl) Gt 0 Gt 0 Gt 2 Gt 0 Gt 2 T-Bend2) T2 T2 T3 T3 T4 Key to Table 8:
1) adhesion testing by the crosshatch method (DIN
53151) 2) testing by the ECCA (European Coil Coating Association) procedures 3) examination of the untreated coating prior to sterilization 4) test medium 3% aqueous sodium chloride solution =
5) test medium 3% aqueous acetic acid =
6) test medium 2% aqueous lactic acid =
26766-lOD
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A powder coating for the coating of packaging container weld seams based on epoxy resins and carboxyl-containing polyesters, wherein I. the powder coating comprises A) at least one polyester having an acid value of 25 to 120 mg of KOH/g and an OH value ~ 10 mg of KOH/g, and B) at least one epoxy resin having an epoxide equivalent weight of 400 to 3000, and II. the powder coating has such a particle size distribution that a) at least 90% by mass of the powder coating particles have a particle size between 1 and 100 µm, b) the maximum particle size of the powder coating particles for at least 99% by weight of the particles is ~ 150 ~m, c) the average particle size of the powder coating particles is between > 20 and 60 µm, and d) the slope of the particle distribution curve at the inflection point is ~ 50.
2. The powder coating as claimed in claim 1, which has such a particle size distribution that a) at least 90% by mass of the powder coating particles have a particle size between 5 and 100 µm, b) the maximum particle size of the powder coating particles for at least 99% by mass of the particles is ~ 100 µm, c) the average particle size of the powder coating particles is between 25 and 40 µm, and d) the slope of the particle distribution curve at the inflection point is > 100.
3. The powder coating as claimed in claim 1, which comprises A) at least one polyester having an acid value of 30 to 90 mg of KOH/g and an OH value of 15 to 30 mg of KOH/g, and B) at least one epoxy resin having an epoxide equivalent weight of 600 to 900.
4. The powder coating as claimed in claim 1, which comprises, as component B, an epoxy resin based on bisphenol A
or an epoxidized novolak resin.
or an epoxidized novolak resin.
5. The powder coating as claimed in claim 1, which comprises, as component A, a polyester based on terephthalic or trimellitic acid and ethylene glycol or neopentyl glycol.
6. The powder coating as claimed in claim 1, wherein the powder coating comprises A) 19 to 80% by weight, based on the total weight of the powder coating, the polyester component A and B) 19 to 80% by weight, based on the total weight of the powder coating, of the epoxy resin component B.
7. A process for the coating of packaging container interiors, wherein a powder coating as claimed in any one of claims 1 to 5 is applied at a film thickness of < 15 µm.
8. A process for the coating of packaging container weld seams, wherein a powder coating as claimed in any one of claims 1 to 6, is applied.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4038681.3 | 1990-12-05 | ||
| DE4038681A DE4038681A1 (en) | 1990-12-05 | 1990-12-05 | POWDER LACQUER AND THE USE THEREOF FOR THE INTERNAL COATING OF PACKAGING CONTAINERS AND FOR WELDING SEALING |
| CA002096643A CA2096643C (en) | 1990-12-05 | 1991-11-06 | Powdered varnish and its use for coating the insides of packaging containers and for covering weld seams |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002096643A Division CA2096643C (en) | 1990-12-05 | 1991-11-06 | Powdered varnish and its use for coating the insides of packaging containers and for covering weld seams |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2154863A1 CA2154863A1 (en) | 1992-06-06 |
| CA2154863C true CA2154863C (en) | 1999-09-07 |
Family
ID=6419573
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002096643A Expired - Fee Related CA2096643C (en) | 1990-12-05 | 1991-11-06 | Powdered varnish and its use for coating the insides of packaging containers and for covering weld seams |
| CA002154863A Expired - Fee Related CA2154863C (en) | 1990-12-05 | 1991-11-06 | Powdered varnish and its use for coating the insides of packaging containers and for covering weld seams |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002096643A Expired - Fee Related CA2096643C (en) | 1990-12-05 | 1991-11-06 | Powdered varnish and its use for coating the insides of packaging containers and for covering weld seams |
Country Status (12)
| Country | Link |
|---|---|
| EP (1) | EP0560792B1 (en) |
| AT (1) | ATE117713T1 (en) |
| BR (1) | BR9107149A (en) |
| CA (2) | CA2096643C (en) |
| DE (2) | DE4038681A1 (en) |
| DK (1) | DK0560792T3 (en) |
| ES (1) | ES2070520T3 (en) |
| IE (1) | IE65595B1 (en) |
| NO (1) | NO932022L (en) |
| PT (1) | PT99685B (en) |
| WO (1) | WO1992010551A1 (en) |
| YU (1) | YU47456B (en) |
Families Citing this family (23)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2711036B2 (en) * | 1991-10-11 | 1998-02-10 | 日本ペイント株式会社 | Powder coatings and raw materials for powder coatings |
| DE4308977A1 (en) * | 1993-03-20 | 1994-09-22 | Grohe Kg Hans | Sanitary article with a coated surface and process for its manufacture |
| US5888623A (en) * | 1993-03-20 | 1999-03-30 | Hans Grohe Gmbh & Co. Kg | Sanitary article or plumbing fitting with a coated surface and a print image applied thereto and a process for making the same |
| DE4405170A1 (en) * | 1994-02-18 | 1995-08-24 | Basf Lacke & Farben | Process for the production of lids and / or trays for packaging containers, the lids and bottoms thus produced and their use for the production of packaging containers, in particular for food packaging |
| DE19523084A1 (en) * | 1995-06-26 | 1997-04-03 | Basf Lacke & Farben | Aqueous powder coating dispersion for packaging containers |
| DE19531585A1 (en) * | 1995-08-28 | 1997-03-06 | Basf Lacke & Farben | Powder coating and its use for the interior coating of packaging containers |
| DE19531559A1 (en) * | 1995-08-28 | 1997-03-06 | Basf Lacke & Farben | Powder-coated container closure |
| DE19607914A1 (en) | 1996-03-01 | 1997-09-04 | Basf Lacke & Farben | Powder coating for packaging containers |
| ZA973692B (en) | 1996-05-17 | 1997-11-25 | Dexter Corp | Extrusion coating compositions and method. |
| US6270855B1 (en) | 1996-05-17 | 2001-08-07 | The Valspar Corporation | Powder coating compositions and methods |
| US6472472B2 (en) | 1996-05-17 | 2002-10-29 | The Valspar Corporation | Powder coating compositions and method |
| US6458439B1 (en) | 1996-05-17 | 2002-10-01 | The Valspar Corporation | Extrusion coating compositions and method |
| DE19632426C2 (en) * | 1996-06-14 | 1999-02-04 | Basf Coatings Ag | Process for coating metal strips |
| EP0844913B1 (en) * | 1996-06-14 | 2002-09-25 | BASF Lacke und Farben AG | Metal strip coating process |
| JP3266818B2 (en) * | 1996-11-28 | 2002-03-18 | 神東塗料株式会社 | Steel plate weld finish method |
| DE19705962A1 (en) * | 1997-02-17 | 1998-08-20 | Hoechst Ag | Spherical, colored polyester particles, process for their preparation and their use for powder coatings |
| DE19705961A1 (en) * | 1997-02-17 | 1998-08-20 | Hoechst Ag | Spherical, possibly crosslinkable at low temperatures polyester particles, processes for their preparation and their use for powder coatings |
| EP0943658A1 (en) * | 1998-03-19 | 1999-09-22 | Ticona GmbH | Spherical, dyable polyester particles, process for their production and their use for high resolution toners |
| US5994462A (en) * | 1998-06-11 | 1999-11-30 | The Dexter Corporation | Solid coating compositions for powder and extrusion applications |
| DE10126651A1 (en) | 2001-06-01 | 2002-12-12 | Basf Coatings Ag | Use of copolymers with diphenylethylene units as emulsifiers for the production of powder slurry and coating powder for use in coating materials, adhesives and sealants, e.g. for painting cars |
| US6806302B2 (en) | 2001-06-13 | 2004-10-19 | E. I. Du Pont De Nemours And Company | Process for the continuous production of liquid, pigmented coating compositions |
| DE102006001529A1 (en) | 2006-01-12 | 2007-07-26 | Basf Coatings Ag | Powder coating suspensions (powder slurries) and powder coatings, process for their preparation and their use |
| GB2564454A (en) * | 2017-07-11 | 2019-01-16 | Rapid Powders Ltd | A method, treated or modified polymer and article of manufacture |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4183974A (en) * | 1974-01-02 | 1980-01-15 | W. R. Grace & Co. | Container coating method |
| DE2621656A1 (en) * | 1976-05-15 | 1977-12-01 | Dynamit Nobel Ag | HAARDABLE POWDER-FORM COATING COMPOSITIONS |
| EP0136263A3 (en) * | 1983-08-25 | 1986-07-30 | Vernicolor AG Lack- und Farbenfabrik | Duroplastic powder lacquer, metallic container with a welded joint coated with a duroplast and method of coating the surface of a metallic container welded joint |
| FR2577231B1 (en) * | 1985-02-08 | 1987-09-11 | Charbonnages Ste Chimique | PROCESS FOR THE PREPARATION OF POWDER COATING COMPOSITIONS BASED ON AN EPOXY RESIN AND A CARBOXYL POLYESTER |
| IT1231772B (en) * | 1989-08-02 | 1991-12-21 | Hoechst Sara Spa | PROCEDURE FOR THE COATING OF SUBSTRATES THROUGH HIGH TEMPERATURE AND SHORT TIME THERMOSETTING POWDER PAINTS. |
-
1990
- 1990-12-05 DE DE4038681A patent/DE4038681A1/en not_active Withdrawn
-
1991
- 1991-11-06 AT AT91919415T patent/ATE117713T1/en not_active IP Right Cessation
- 1991-11-06 BR BR919107149A patent/BR9107149A/en not_active IP Right Cessation
- 1991-11-06 CA CA002096643A patent/CA2096643C/en not_active Expired - Fee Related
- 1991-11-06 WO PCT/EP1991/002099 patent/WO1992010551A1/en not_active Application Discontinuation
- 1991-11-06 DE DE59104444T patent/DE59104444D1/en not_active Revoked
- 1991-11-06 CA CA002154863A patent/CA2154863C/en not_active Expired - Fee Related
- 1991-11-06 ES ES91919415T patent/ES2070520T3/en not_active Expired - Lifetime
- 1991-11-06 EP EP91919415A patent/EP0560792B1/en not_active Revoked
- 1991-11-06 DK DK91919415.9T patent/DK0560792T3/en active
- 1991-12-02 IE IE418191A patent/IE65595B1/en not_active IP Right Cessation
- 1991-12-03 YU YU188891A patent/YU47456B/en unknown
- 1991-12-04 PT PT99685A patent/PT99685B/en not_active IP Right Cessation
-
1993
- 1993-06-03 NO NO93932022A patent/NO932022L/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| NO932022D0 (en) | 1993-06-03 |
| ES2070520T3 (en) | 1995-06-01 |
| CA2096643C (en) | 2000-01-04 |
| ATE117713T1 (en) | 1995-02-15 |
| DK0560792T3 (en) | 1995-05-29 |
| PT99685B (en) | 1999-05-31 |
| CA2096643A1 (en) | 1992-06-06 |
| BR9107149A (en) | 1993-11-16 |
| IE65595B1 (en) | 1995-11-01 |
| PT99685A (en) | 1992-11-30 |
| CA2154863A1 (en) | 1992-06-06 |
| NO932022L (en) | 1993-07-05 |
| IE914181A1 (en) | 1992-06-17 |
| DE4038681A1 (en) | 1992-06-11 |
| EP0560792B1 (en) | 1995-01-25 |
| YU188891A (en) | 1994-01-20 |
| YU47456B (en) | 1995-03-27 |
| WO1992010551A1 (en) | 1992-06-25 |
| DE59104444D1 (en) | 1995-03-09 |
| EP0560792A1 (en) | 1993-09-22 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |