CA2226956A1 - Powder coating and its use for the internal coating of packing containers - Google Patents
Powder coating and its use for the internal coating of packing containers Download PDFInfo
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- CA2226956A1 CA2226956A1 CA002226956A CA2226956A CA2226956A1 CA 2226956 A1 CA2226956 A1 CA 2226956A1 CA 002226956 A CA002226956 A CA 002226956A CA 2226956 A CA2226956 A CA 2226956A CA 2226956 A1 CA2226956 A1 CA 2226956A1
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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
- C09D163/00—Coating compositions based on epoxy resins; Coating compositions based on derivatives of epoxy resins
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G59/00—Polycondensates containing more than one epoxy group per molecule; Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups
- C08G59/18—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing
- C08G59/182—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing using pre-adducts of epoxy compounds with curing agents
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G59/00—Polycondensates containing more than one epoxy group per molecule; Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups
- C08G59/18—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing
- C08G59/40—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing characterised by the curing agents used
- C08G59/62—Alcohols or phenols
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G59/00—Polycondensates containing more than one epoxy group per molecule; Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups
- C08G59/18—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing
- C08G59/40—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing characterised by the curing agents used
- C08G59/62—Alcohols or phenols
- C08G59/621—Phenols
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- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
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- Wood Science & Technology (AREA)
- Paints Or Removers (AREA)
Abstract
The present invention concerns a powder coating based on epoxy resins and phenolic hardeners, in particular for the internal coating of packing containers, and containing: 1) at least one epoxy resin with an epoxideequivalent weight of between 300 and 5500; and at least one hardener with more than one phenolic hydroxyl group per molecule and a hydroxyl-equivalent weight, relative to phenolic OH groups, of between 100 and 500; the powder coating having a grain size distribution such that: a) at least 90 mass % of the powder coating particles have a particle size of between 1 and 60 .mu.m; b) the maximum particle size of the powder coating particles for at least 99 mass % of the particles is <= 100 .mu.m; c) the average particle size of the powder coating particles is between 5 and 20 .mu.m; and d) the slope of the grain distribution curve at the inflection point is >= 100; and 2) a lubricant, preferably in an amount of <= 2 wt.%.
Description
CA 022269~6 1998-02-12 Powder coating and its use for internal coating of packaging containers The present invention relates to powder coat-ings, in particular for internal coating of packaging containers, based on epoxy resins and phenolic hardeners, and to a process for the [sic] their preparation.
The present invention moreover relates to a process for internal coating of pac};aging containers, and to the use of the powder coatings.
Packaging containers, such as, for example, preserve cans, two- and three-component drinks cans and the like, are provided with a coating on the inside, on the one hand to protect the contents from deterioration due to constituents of the sheet metal being dissolved out, and on the other h~nd to avoid corrosion of the sheet metal by aggressive contents.
In practice, packaging containers are coated in this way mainly by means of organically dissolved coatings. However, this results in an increased pollu-tion of the environment by solvents during drying of the coating films. Attempts are therefore increasingly being made to replace these coatings with low-solvent or solvent-free coatings. Thus, for example, thermo-plastic powder coatings are often already used for covering can weld seams. These products are produced from the corresponding thermoplastics by expensive cold grinding.
Thermosetting powder coatings for covering the weld seams of metal containers employed for holding foodstuffs or drinks are known from EP-B-119164. These thermosetting powder coatings comprise, as a binder, a mixture of an aromatic epoxy resin having on average not more than 2 epoxide groups per molecule and an aro-matic epoxy resin having on average more than 2 epoxide groups per molecule. The condensation product of the diglycidyl ether of bisphenol A with bisphenol A, CA 022269~6 1998-02-12 having an equivalent weight, based on phenolic hydroxyl groups, of 220 to 280 or an acid polyester or a mixture thereof is employed as the hardener.
These powder coatings are employed only for covering the weld seams of packaging containers.
EP-B-119164 contains neither indications of also employing these powder coatings for internal coating of packaging containers, nor indications of how these powder coatings are to be modified for use as internal protective coatings. In particular, EP-B-119 164 con-tains no information on particle sizes and particle size distributions of the powder coatings. However, the use of these powder coatings of EP-B-119 164 with a particle size distribution customary for powder coat-ings leads to coatings which have too high a porosity at the low coating thicknesses of < 15~m customary for internal coating finishes.
Thermosetting solvent-containing and solvent-free coating agents for coating car bodies, machinery, plant and containers, comprising an epoxy resin having more than one 1,2-epoxide group per molecule and a polyol having more than one phenolic OH group per molecule as well as other customary auxiliaries and additives are furthermore known from DE Patent 23 12 409.
For the production of automotive topcoats, according to DE Patent 23 12 409 a powder coating having a particle size of not more than 0.044 mm is applied in a dry-film thickness of 25 ~m. Neither the particle size nor the particle size distribution of the powder coating particles is reported for powder coat-ings which are suitable for the production of internal coatings on packaging containers. Nor does DE Patent 23 12 409 contain any indication that the particle size and particle size distribution are to be adjusted specifically according to the intended use of the powder coatings. However, powder coatings having a maximum particle size of 44 ~m and a conventional CA 022269~6 1998-02-12 particle size distribution are unsuitable for the production of internal coatings for packaging con-tainers in the conventional low coating thickness of S 15 ~m, since the resulting coatings have too high a porosity.
Powder coatings for internal coating of cans comprising an epoxy resin and a hardener are further-more disclosed by US Patent 3,962,486. Catalytic hardeners, aromatic amines, epoxy-amine adducts and acid anhydrides are mentioned as typical hardeners in US Patent 3,962,486, whi:Le phenolic hardeners are not mentioned. Coatings which meet the requirements usually imposed on internal coatings of foodstuffs packaging even at low coating thicknesses of less than 13 ~m can be produced by using the plasma spray coating process.
To ensure that application by means of the plasma spray process is possible, only powder coatings which have a maximum particle size of < 100 ~m and a sufficiently low melt viscosity may be employed. However, the par-ticle size distribution of the powder coatings used isnot characterized in more detail in US Patent 3,962,486.
A disadvantage of the powder coatings described in US Patent 3,962,486 is the inadequate resistance of the resulting coatings to sterilization due to the use of aminic hardeners. It is furthermore a disadvantage that epoxy resins hardened with amines tend to become brittle and have very poor elasticities. Acid anhydride hardeners have the disadvantage that they are highly irritating, and special safety precautions are there-fore required during formulation of the powder coatings.
Powder coatings for internal coating of cans, which likewise comprise an epoxy resin and an amine hardener, are furthermore known from US Patent 4,183,974. These powder coatings have mean particle sizes of between 1 and 100 ~m, preferably between 1 and 10 ~m. Although the resulting coatings already display CA 022269~6 1998-02-12 the required low porosity at coating thicknesses of < 13 ~m, the resistance of the resulting coatings to sterilization is in turn in need of improvement. It is furthermore a disadvantage that epoxy resins hardened with amines tend to beccme brittle and have very poor elasticities.
Moreover, powder coatings which are based on epoxy resins and which, after appropriate adjustment of the particle size distribution of the powder coating particles, are suitable both for internal coating of packaging containers and for covering weld seams are known from German Patent Application P 40 38 681.3.
These powder coatings contain, as hardeners, polyesters containing carboxyl groups. The use of phenolic hardeners is not described in this patent application.
Finally, powder coatings based on epoxy resins and phenolic hardeners are known. Such coatings are suitable for coating packaging containers. However, the properties are still not to be regarded as being satisfactory, in particular as regards the flexibility, the transparency of the coating and the processing speed.
The present invention is thus based on the object of providing powder coatings which meet the requirements usually imposed on internal coatings for cans, even when low coating thicknesses of < 15 ~m are applied, when said powder coatings are used for inter-nal coating of packaging containers. In particular, these internal coatings should not be porous (deter-mined with the aid of the so-called enamel rater test), should display good adhesion to the substrate, should have a high elasticity, and should be stable under the customary pasteurization and sterilization conditions.
The powder coatings should in this case be hardenable over the short drying times customary in the coating of cans.
This object is achieved, surprisingly, by a powder coating based on epoxy resins and phenolic CA 022269~6 1998-02-12 hardeners, in particular for internal coating of packaging containers, comprising 1.) at least one epoxy resin having an epoxide equivalent weight of from 300 to 5500 and at least one hardener having more than one phenolic hydroxyl group per molecule and a hydroxyl equivalent weight, based on the phenolic OH groups, of from 100 to 500, the powder coating having a particle size distribution such that a) at least 90 per cent by weight of the powder coating particles have a particle size of between 1 to [sic] 60 ~m, b) the maximum particle size of at least 99 per cent by weight of the powder coating particles is < 100 ~m, c) the mean particle size of the powder coating particles is between 5 to [sic] 20 ~m and d) the gradient of the particle distribution curve at the point of inflexion is > 100.
and 2) a lubricant, preferably in an amount of < 2% by weight.
The invention furthermore relates to processes for internal coating of packaging containers, in which these powder coatings are applied.
The invention finally also relates to the use of the powder coatings for internal coating of packag-ing containers.
It is surprising and was not foreseeable that the profile of properties and therefore the intended use of powder coatings based on epoxy resins and phenolic hardeners and lubricants can be controlled specifically by establishing a specific particle size distribution. The powder coatings according to the invention also can be hardened quickly, are easy to handle and are easy to apply, have a good processing speed, good flexibility and transparency after coating.
CA 022269~6 1998-02-12 Moreover, the powder coatings according to the invention are distinguished by the fact that coatings having only very low coating thicknesses of S 15 ~m have the properties required for internal coatings by can manufacturers. In particular, these coatings have the required low porosity even at a low coating thickness of S 15 ~m. Moreover, these coatings are distinguished by good adhesion, high flexibility and a good resistance to pasteurization and sterilization.
The individual components of the powder coat-ings according to the invention will now first be explained below in more detail.
The epoxy resins employed in the powder coat-ings according to the invention are solid epoxy resins having an epoxide equivalent weight of from 300 to 5500. Aromatic, aliphatic and/or cycloaliphatic epoxy resins are suitable. Aromatic epoxy resins based on bisphenol A and/or bisphenol F and/or epoxy resins of the novolak type are preferably employed. The epoxy resins based on bisphenol A or bisphenol F which are particularly preferably employed have an epoxide equivalent weight of from 500 to 2000. Epoxy resins of the novolak type which are particularly preferably employed have an epoxide equivalent weight of from 500 to 1000.
Epoxy resins based on bisphenol A or bisphenol F in general in this context have a functionality of not more than 2, and epoxy resins of the novolak type have a functionality of in general at least 2. However, the epoxy resins based on bisphenol A or bisphenol F also can be brought to a functionality of more than 2 by branching, for example by means of trimethylolpropane, glycerol, pentaerythritol or other branching reagents.
Other epoxy resins, such as, for example, alkylene glycol diglycidy:L ethers or branched secondary products thereof, epoxy resins based on bisphenol A or F which have been rendered flexible with alkylene glycols or the like, can of course also be employed.
CA 022269~6 1998-02-12 Mixtures of various of the epoxy resins mentioned are furthermore also suitable.
Suitable epoxy resins are, for example, the products obtainable commercially under the following names: EpikoteR 159, 1001, 1002, 1055, 1004, 1007, 1009 and 3003-4F-10 from Shell-Chemie, XZ 86 795 and DERR
664, 667, 669, 662, 642U and 672U from Dow, and AralditR, GT 6064, GT 7072, GT 7203, GT 7004, GT 7304, GT 7097 and GT 7220 from Ciba Geigy.
FDA-approved epoxy resins are preferably employed here.
Suitable hardener components are all the solid compounds having more than one phenolic OH group, preferably 1.8 to 4, particularly preferably < 3, especially preferably 1.8 to 2.2 phenolic OH groups per molecule, and a hydroxyl equivalent weight, based on the phenolic OH groups, of from 100 to 500, preferably from 200 to 300.
Hardeners based on bisphenol A and/or bisphenol F are preferably employed as the hardener. The condensation product of the diglycidyl ether of bisphenol A or bisphenol F with bisphenol A or bisphenol F, in par-ticular the condensation product having an equivalent weight, based on the phenolic hydroxyl groups, of from 220 to 280, is particularly preferred as the hardener.
These condensation products are usually prepared by reaction of, in general, excess bisphenol with a bis-phenol diglycidyl ether in the presence of a suitable catalyst. The condensation product is preferably prepared by reaction of t:he diglycidyl ether with the bisphenol in a weight ratio of from 0.5 to 2. These hardeners based on said condensation products of the bisphenol diglycidyl ether with a bisphenol in general have a functionality of not more than 2, it being possible in turn to establish higher functionalities by using branching reagents.
Furthermore, the reaction products of bisphenols with epoxy resins of the novolak type are also suitable as hardeners. These hardeners are preferably obtained by reaction of the epoxy resin with the bisphenol in a weight ratio of from 0.5 to 2 in the presence of a suitable catalyst.
The phenolic hardeners described in DE-PS-23 12 409 in column 5, line 2 to column 6, line 55, for example, are suitable. These polyphenols correspond to the following general formulae OH
X X
- X
H - O ~ X OH
X~ ~X
CA 022269~6 1998-02-12 O CH,- f H - CHI- O ~ A ~ O - H
OH
~C
x o - CH~-CH-CHr-O ~ ~ ~ o ~ H
~
X
in which A is a divalent hydrocarbon radical having from 1 to 6 C atoms or the radicals O O
Il 11 -C-, -O-, -S-, -~S-, -S-, or ~
Il 11 O O
X is a hydrogen [lacuna] or alkyl having 1 to 4 C atoms n assumes a mean value of from 1 to 9, preferably from 2 to 7, and y assumes a value of 0 or 1.
Furthermore, the phenolic hardeners described in DE-A-30 27 140 can also be employed.
Hardeners modified with branching agents and/or hardeners which have been rendered flexible are of course also suitable. Mixtures of various hardeners of those mentioned can also be employed.
FDA-approved hardeners are preferably employed here.
The epoxy resin component is usually employed in the powder coatings according to the invention in an amount of from 29 to 80% by weight, preferably from 39 to 60% by weight, in each case based on the total weight of the powder coating.
CA 022269~6 1998-02-12 The hardener component is usually employed in the powder coatings according to the invention in an amount of from 10 to 50% by weight, preferably from 15 to 90%
by weight, in each case based on the total weight of the powder coating.
The powder coatings according to the invention comprise, as a further component, at least one harden-ing catalyst, usually in an amount of from 0.01 to 5.0%
by weight, preferably from 0.05 to 2.0% by weight, in each case based on the total weight of the powder coating.
The catalyst is advantageously imidazole, 2-methylimidazole, ethyltriphenylphosphonium chloride or another salt thereof, a quinoline derivative, as described, for example, in EP-B-10805, a primary, secondary or tertiary aminophenol, aluminium acetyl-acetonate or a toluenesulphonic acid salt, or a mixture of various of the catalysts mentioned.
The commercially available hardeners containing hydroxyl groups usually already comprise a hardening catalyst.
Examples of such commercially available hardeners containing hydroxyl groups which are prefer-ably employed are the products available commercially under the following names: D.E.H.R 81, D.E.H.R 82 and D.E.H.R 84 from Dow, Hardener XB 3082 from Ciba Geigy and EpikureR 169 and 171 from Shell-Chemie.
The powder coatings according to the invention can furthermore also comprise from 0 to 55% by weight, preferably from 15 to 25% by weight, of fillers.
FDA-approved fillers are preferably employed.
Inorganic fillers, for example titanium dioxide, such as, for example, Kronos 2160 from Kronos Titan, Rutil R 902 from Du Pont and RC 566 from Sachtleben, barium sulphate and fillers based on silicate, such as, for example, talc, kaolin, magnesium aluminium silicates, mica and the like, are usually employed. Titanium CA 022269~6 1998-02-12 dioxide and fillers of the quartz sand type are pre-ferably employed.
The powder coatings according to the invention can furthermore also comprise, if appropriate, from 0.01 to 10% by weight, preferably from 0.1 to 2% by weight, based on the total weight of the powder coating, of other auxiliaries and additives. Examples of these are levelling agents, flow aids, deaerating agents, such as, for example, benzoin, pigments or the like.
For use for internal coating of packaging containers, the particle size distribution is adjusted so that at least 90 per cent by weight of the powder coating particles have a particle size of between 1 and 60 ~m, that is to say d 90 = 1 to 60 ~m. Preferably, 90 per cent by weight of the powder coating particles have a particle size between 1 and 40 ~m (d 90 = 1 to 40 ~m), and particularly preferably between 5 and 25 ~m (d 90 = 5 to 25 ~m). The maximum size of the powder coating particles for at least 99 per cent by weight of the particles is < 100 ~m, preferably < 60 ~m and particularly preferably < 40 ~m). The mean particle size of the powder coating particles is between 5 to [sic] 20 ~m, particularly preferably between 5 to [sic]
12 ~m. It is furthermore essential to the invention that, when the powder coatings are used for internal coating of the packaging containers, the particle size distribution is adjusted so that the gradient S of the particle distribution curve at the point of inflexion is 2 100, preferably 2 150 and particularly preferably 2 200. To achieve coatings having particularly good properties, powder coatings in which the gradient S of the particle size distribution curve at the point of inflexion is 2 300 are especially preferably employed.
The gradient S is defined here as the limiting value for f(x2) - f(x1) tending to zero of (f(x2) - f(x1))/log ((x2/x1)) at the point of inflexion of the particle distribution curve. The particle CA 022269~6 1998-02-12 distribution curve here is the plot of the cumulative percentages by weight (f(x)) against the absolute particle diameter (x), the particle diameter being plotted on a logarithmic scale and the cumulative S percentages by weight on a linear scale. For use as an internal coating on packaging containers, powder coat-ings which have both only a low proportion of very fine particles (particle size c 5 ~m) and at the same time also only a very low proportion of coarse powder coat-ing particles (particle size > 25 ~m), i.e. as narrowas possible a particle size distribution, are thus particularly suitable.
The particular particle size distribution of the powder coatings is adjusted with suitable grinding units, if appropriate in combination with suitable sifting and sieving devices, for example with fluidized bed countercurrent mills (AFG) from Alpine, Augsburg, in combination with Turboplex extra-fine sifters from Alpine, Augsburg.
Also essential to the invention is the addition of lubricant. This lubricant is added, in accordance with the invention, in amounts of less than 2% by weight. Additions of less than 1% by weight are pre-ferred. The range which has proven optimum is that from 0.1 to 0.6% by weight. Lubricants employed are propy-lene waxes, modified polyethylene waxes and acid amides.
In addordance with the invention, the propylene waxes are preferably employed in micronized form. Such waxes are obtainable commercially, inter alia, under the designation Hoechst-Wachs pp. 230, Hoechst-Wachs C, Hoechst-Wachs C Mikropulver PM and Hoechst-Wachs R 31.
The polyethylene waxes are, as a general rule, polytetrafluoroethylene-modified waxes. These are obtainable commercially, inter alia, under the desig-nations Hoechst-Wachs PED 121, 191, 136, 153, 261, 521, 522, and also Hostalup H 12 and Hostalup H 22.
CA 022269~6 1998-02-12 The acid amides which can be employed in accor-dance with the invention include, above all, erucamide and oleamide.
The addition of the lubricants according to the invention achieves surprising, unexpected properties, especially when the powder coatings are used for the interior coating of packaging containers. The coatings obtained are, in particular, highly flexible and surface scratch-resistant. The corrosion protection properties are also improved. Finally, the material according to the invention, as a coating, exhibits an outstanding transparency. It is possible, furthermore, to achieve crosslinking in between 10 seconds and a number of minutes at temperatures between 21 and 350~.
The powder coatings are prepared by the known methods (compare, for example, product information from BASF Lacke & Farben AG, "Pulverlacke", 1990) by homo-genization and dispersion, for example by means of an extruder, screw kneader and the like. It is essential to the invention that, after their preparation, the powder coatings are adjusted by grinding and, if appropriate, by sifting and sieving to a particle size distribution appropriate for the intended use.
In accordance with the invention the lubricant is preferably extruded and ground together with the powder coating material. This procedure makes it possible, in accordance with the invention, to obtain especially good profiles of properties. Otherwise to grind [sic] can be followed, if desired, by sifting and by application by means of corona units or tribo-electric charging. The result of a powder coating prepared and applied in the manner described is a surprising high level of matting, surface hardness, flexibility and adhesion promotion.
The packaging containers which are coated with the powder coatings according to the invention can be made of the most diverse materials, may have the most diverse sizes and shapes and may have been produced by CA 022269~6 l998-02-l2 various processes. In particular, however, metallic containers are coated with the powder coatings accord-ing to the invention. These metallic containers may have been produced by first rolling sheet metal and then joining it by folding back the edge. The end pieces can then be attached to the cylinder thus formed. The powder coatings according to the invention are employed for internal coating of the can bodies, which in general already have a base. Deep-drawn metal containers can furthermore also be coated on the inside with the powder coatings according to the invention.
However, the powder coatings are of course also suit-able for coating can lids and can bases.
The packaging containers can be made of the most diverse materials, such as, for example, aluminium, black sheet, tin sheet and various iron alloys, which are provided, if appropriate, with a passivating coating based on compounds of nickel, chromium and tin.
Containers of this type are usually used as containers for foodstuffs and drinks, for example for beer, juices, carbonated drinks, soups, vegetables, meat dishes, fish dishes and vegetables, but also, for example, for animal foods.
The application is carried out by known methods, such as are described, for example, in US Patent 4,183,974.
Electrostatic charging of the powder coating particles is effected here by friction (triboelectricity). The powder coating particles are applied with the aid of special spray heads known to those skilled in the art.
The powder coatings according to the invention can of course also be applied by the known process of electro-static assistance.
For internal coating of packaging containers, the powder coatings are usually applied in a coating thickness of S lS ~m, preferably of from 10 to 14 ~m.
Even at these low coating thicknesses, the coatings meet the requirements usually imposed on such CA 022269~6 1998-02-12 films. However, the powder coatings can of course also be applied in higher coating thicknesses.
The packaging container, the inside of which has been provided with the powder coating according to the invention, is then subjected to a heat treatment for hardening the powder coating. This heat treatment can be carried out in various ways. In practice, the containers are often conveyed through a tunnel oven for this purpose. During this operation, the powder coatings in general harden completely at object temperatures of between 230 and 350~C within a period of from 5 to 30 seconds. The tunnel oven here can be operated at a constant temperature, or can have a temperature profile adjusted to suit the particular circumstances.
The invention will now be explained in more detail with the aid of working examples. All the data on parts and percentages here are weight data, unless expressly stated otherwise. The powder coatings were in each case prepared by weighing all the constituents into canisters and premixing them in a premixer, and homogenizing the mix at 60 to 80~C by means of an extruder, cooling it as quickly as possible and adjusting it to the desired particle size distribution with grinding units.
Example 1 The following components were processed to give powder coating 1:
580 parts of commercially available epoxidized novolak resin having an EEW of 500 (commercial product D.E.RR 692U from Dow), 270 parts of commercially available hardener, contain-ing OH groups, based on bisphenol A having a hydroxyl equivalent weight of 250 (commercial product D.E.H.R 82 from Dow), 5 parts of commercially available levelling agent based on an oligomeric acrylate, CA 022269~6 l998-02-l2 143 parts of finely divided silicate-based filler of the quartz sand type and 2 parts of fluidization auxiliary based on pyrogenic silica or aluminium oxide.
SThis powder mixture is etruded [sic] and ground together with erucamide. In two experiments, an amount of 0.2% by weight and 0.5% by weight was added.
Using grinding units, the particle size distribution was adjusted so that at least 90% by weight of the powder coating particles have a particle size of between 1 and 25 ~m (d 90 = 1 to 25 ~m). The maximum particle size of at least 99 per cent by weight of the particles is < 100 ~m, and the mean particle size is 9 ~m. The gradient S at the point of inflexion of the particle distribution curve is 250.
tinplate panels were coated by means of corona charging with a) powder coating containing 0.2% erucamide b) powder coating containing 0.5% erucamide and the coating was crosslinked for 3 minutes in an oven at 220~C. Club cans, i.e. fish preserve cans, were stamped from the panels and sterilized for half an hour at 128~C. The media tested were:
- water, - 2% strength ~actic acid solution and - 3% strength acetic acid solution.
The result shows that the powder coating without erucamide fractures on punching (brittle) and acquires a milky appearance. The can also shows corrosion. The powder coating with 0.2% of lubricant is highly flexible and lends itself well to punching but shows a milky appearance with 2% strength lactic acid. With 0.5% of lubricant there are no concerns of this nature.
The results can be seen from the following table.
CA 02226956 l998-02-l2 L
Sterilization: ~ h 128~C
no +0.2% +0.5%
lubricant erucamide erucamide in H20 2% strength lactic acid + + ++
5% strength lactic acid + ++ ++
The present invention moreover relates to a process for internal coating of pac};aging containers, and to the use of the powder coatings.
Packaging containers, such as, for example, preserve cans, two- and three-component drinks cans and the like, are provided with a coating on the inside, on the one hand to protect the contents from deterioration due to constituents of the sheet metal being dissolved out, and on the other h~nd to avoid corrosion of the sheet metal by aggressive contents.
In practice, packaging containers are coated in this way mainly by means of organically dissolved coatings. However, this results in an increased pollu-tion of the environment by solvents during drying of the coating films. Attempts are therefore increasingly being made to replace these coatings with low-solvent or solvent-free coatings. Thus, for example, thermo-plastic powder coatings are often already used for covering can weld seams. These products are produced from the corresponding thermoplastics by expensive cold grinding.
Thermosetting powder coatings for covering the weld seams of metal containers employed for holding foodstuffs or drinks are known from EP-B-119164. These thermosetting powder coatings comprise, as a binder, a mixture of an aromatic epoxy resin having on average not more than 2 epoxide groups per molecule and an aro-matic epoxy resin having on average more than 2 epoxide groups per molecule. The condensation product of the diglycidyl ether of bisphenol A with bisphenol A, CA 022269~6 1998-02-12 having an equivalent weight, based on phenolic hydroxyl groups, of 220 to 280 or an acid polyester or a mixture thereof is employed as the hardener.
These powder coatings are employed only for covering the weld seams of packaging containers.
EP-B-119164 contains neither indications of also employing these powder coatings for internal coating of packaging containers, nor indications of how these powder coatings are to be modified for use as internal protective coatings. In particular, EP-B-119 164 con-tains no information on particle sizes and particle size distributions of the powder coatings. However, the use of these powder coatings of EP-B-119 164 with a particle size distribution customary for powder coat-ings leads to coatings which have too high a porosity at the low coating thicknesses of < 15~m customary for internal coating finishes.
Thermosetting solvent-containing and solvent-free coating agents for coating car bodies, machinery, plant and containers, comprising an epoxy resin having more than one 1,2-epoxide group per molecule and a polyol having more than one phenolic OH group per molecule as well as other customary auxiliaries and additives are furthermore known from DE Patent 23 12 409.
For the production of automotive topcoats, according to DE Patent 23 12 409 a powder coating having a particle size of not more than 0.044 mm is applied in a dry-film thickness of 25 ~m. Neither the particle size nor the particle size distribution of the powder coating particles is reported for powder coat-ings which are suitable for the production of internal coatings on packaging containers. Nor does DE Patent 23 12 409 contain any indication that the particle size and particle size distribution are to be adjusted specifically according to the intended use of the powder coatings. However, powder coatings having a maximum particle size of 44 ~m and a conventional CA 022269~6 1998-02-12 particle size distribution are unsuitable for the production of internal coatings for packaging con-tainers in the conventional low coating thickness of S 15 ~m, since the resulting coatings have too high a porosity.
Powder coatings for internal coating of cans comprising an epoxy resin and a hardener are further-more disclosed by US Patent 3,962,486. Catalytic hardeners, aromatic amines, epoxy-amine adducts and acid anhydrides are mentioned as typical hardeners in US Patent 3,962,486, whi:Le phenolic hardeners are not mentioned. Coatings which meet the requirements usually imposed on internal coatings of foodstuffs packaging even at low coating thicknesses of less than 13 ~m can be produced by using the plasma spray coating process.
To ensure that application by means of the plasma spray process is possible, only powder coatings which have a maximum particle size of < 100 ~m and a sufficiently low melt viscosity may be employed. However, the par-ticle size distribution of the powder coatings used isnot characterized in more detail in US Patent 3,962,486.
A disadvantage of the powder coatings described in US Patent 3,962,486 is the inadequate resistance of the resulting coatings to sterilization due to the use of aminic hardeners. It is furthermore a disadvantage that epoxy resins hardened with amines tend to become brittle and have very poor elasticities. Acid anhydride hardeners have the disadvantage that they are highly irritating, and special safety precautions are there-fore required during formulation of the powder coatings.
Powder coatings for internal coating of cans, which likewise comprise an epoxy resin and an amine hardener, are furthermore known from US Patent 4,183,974. These powder coatings have mean particle sizes of between 1 and 100 ~m, preferably between 1 and 10 ~m. Although the resulting coatings already display CA 022269~6 1998-02-12 the required low porosity at coating thicknesses of < 13 ~m, the resistance of the resulting coatings to sterilization is in turn in need of improvement. It is furthermore a disadvantage that epoxy resins hardened with amines tend to beccme brittle and have very poor elasticities.
Moreover, powder coatings which are based on epoxy resins and which, after appropriate adjustment of the particle size distribution of the powder coating particles, are suitable both for internal coating of packaging containers and for covering weld seams are known from German Patent Application P 40 38 681.3.
These powder coatings contain, as hardeners, polyesters containing carboxyl groups. The use of phenolic hardeners is not described in this patent application.
Finally, powder coatings based on epoxy resins and phenolic hardeners are known. Such coatings are suitable for coating packaging containers. However, the properties are still not to be regarded as being satisfactory, in particular as regards the flexibility, the transparency of the coating and the processing speed.
The present invention is thus based on the object of providing powder coatings which meet the requirements usually imposed on internal coatings for cans, even when low coating thicknesses of < 15 ~m are applied, when said powder coatings are used for inter-nal coating of packaging containers. In particular, these internal coatings should not be porous (deter-mined with the aid of the so-called enamel rater test), should display good adhesion to the substrate, should have a high elasticity, and should be stable under the customary pasteurization and sterilization conditions.
The powder coatings should in this case be hardenable over the short drying times customary in the coating of cans.
This object is achieved, surprisingly, by a powder coating based on epoxy resins and phenolic CA 022269~6 1998-02-12 hardeners, in particular for internal coating of packaging containers, comprising 1.) at least one epoxy resin having an epoxide equivalent weight of from 300 to 5500 and at least one hardener having more than one phenolic hydroxyl group per molecule and a hydroxyl equivalent weight, based on the phenolic OH groups, of from 100 to 500, the powder coating having a particle size distribution such that a) at least 90 per cent by weight of the powder coating particles have a particle size of between 1 to [sic] 60 ~m, b) the maximum particle size of at least 99 per cent by weight of the powder coating particles is < 100 ~m, c) the mean particle size of the powder coating particles is between 5 to [sic] 20 ~m and d) the gradient of the particle distribution curve at the point of inflexion is > 100.
and 2) a lubricant, preferably in an amount of < 2% by weight.
The invention furthermore relates to processes for internal coating of packaging containers, in which these powder coatings are applied.
The invention finally also relates to the use of the powder coatings for internal coating of packag-ing containers.
It is surprising and was not foreseeable that the profile of properties and therefore the intended use of powder coatings based on epoxy resins and phenolic hardeners and lubricants can be controlled specifically by establishing a specific particle size distribution. The powder coatings according to the invention also can be hardened quickly, are easy to handle and are easy to apply, have a good processing speed, good flexibility and transparency after coating.
CA 022269~6 1998-02-12 Moreover, the powder coatings according to the invention are distinguished by the fact that coatings having only very low coating thicknesses of S 15 ~m have the properties required for internal coatings by can manufacturers. In particular, these coatings have the required low porosity even at a low coating thickness of S 15 ~m. Moreover, these coatings are distinguished by good adhesion, high flexibility and a good resistance to pasteurization and sterilization.
The individual components of the powder coat-ings according to the invention will now first be explained below in more detail.
The epoxy resins employed in the powder coat-ings according to the invention are solid epoxy resins having an epoxide equivalent weight of from 300 to 5500. Aromatic, aliphatic and/or cycloaliphatic epoxy resins are suitable. Aromatic epoxy resins based on bisphenol A and/or bisphenol F and/or epoxy resins of the novolak type are preferably employed. The epoxy resins based on bisphenol A or bisphenol F which are particularly preferably employed have an epoxide equivalent weight of from 500 to 2000. Epoxy resins of the novolak type which are particularly preferably employed have an epoxide equivalent weight of from 500 to 1000.
Epoxy resins based on bisphenol A or bisphenol F in general in this context have a functionality of not more than 2, and epoxy resins of the novolak type have a functionality of in general at least 2. However, the epoxy resins based on bisphenol A or bisphenol F also can be brought to a functionality of more than 2 by branching, for example by means of trimethylolpropane, glycerol, pentaerythritol or other branching reagents.
Other epoxy resins, such as, for example, alkylene glycol diglycidy:L ethers or branched secondary products thereof, epoxy resins based on bisphenol A or F which have been rendered flexible with alkylene glycols or the like, can of course also be employed.
CA 022269~6 1998-02-12 Mixtures of various of the epoxy resins mentioned are furthermore also suitable.
Suitable epoxy resins are, for example, the products obtainable commercially under the following names: EpikoteR 159, 1001, 1002, 1055, 1004, 1007, 1009 and 3003-4F-10 from Shell-Chemie, XZ 86 795 and DERR
664, 667, 669, 662, 642U and 672U from Dow, and AralditR, GT 6064, GT 7072, GT 7203, GT 7004, GT 7304, GT 7097 and GT 7220 from Ciba Geigy.
FDA-approved epoxy resins are preferably employed here.
Suitable hardener components are all the solid compounds having more than one phenolic OH group, preferably 1.8 to 4, particularly preferably < 3, especially preferably 1.8 to 2.2 phenolic OH groups per molecule, and a hydroxyl equivalent weight, based on the phenolic OH groups, of from 100 to 500, preferably from 200 to 300.
Hardeners based on bisphenol A and/or bisphenol F are preferably employed as the hardener. The condensation product of the diglycidyl ether of bisphenol A or bisphenol F with bisphenol A or bisphenol F, in par-ticular the condensation product having an equivalent weight, based on the phenolic hydroxyl groups, of from 220 to 280, is particularly preferred as the hardener.
These condensation products are usually prepared by reaction of, in general, excess bisphenol with a bis-phenol diglycidyl ether in the presence of a suitable catalyst. The condensation product is preferably prepared by reaction of t:he diglycidyl ether with the bisphenol in a weight ratio of from 0.5 to 2. These hardeners based on said condensation products of the bisphenol diglycidyl ether with a bisphenol in general have a functionality of not more than 2, it being possible in turn to establish higher functionalities by using branching reagents.
Furthermore, the reaction products of bisphenols with epoxy resins of the novolak type are also suitable as hardeners. These hardeners are preferably obtained by reaction of the epoxy resin with the bisphenol in a weight ratio of from 0.5 to 2 in the presence of a suitable catalyst.
The phenolic hardeners described in DE-PS-23 12 409 in column 5, line 2 to column 6, line 55, for example, are suitable. These polyphenols correspond to the following general formulae OH
X X
- X
H - O ~ X OH
X~ ~X
CA 022269~6 1998-02-12 O CH,- f H - CHI- O ~ A ~ O - H
OH
~C
x o - CH~-CH-CHr-O ~ ~ ~ o ~ H
~
X
in which A is a divalent hydrocarbon radical having from 1 to 6 C atoms or the radicals O O
Il 11 -C-, -O-, -S-, -~S-, -S-, or ~
Il 11 O O
X is a hydrogen [lacuna] or alkyl having 1 to 4 C atoms n assumes a mean value of from 1 to 9, preferably from 2 to 7, and y assumes a value of 0 or 1.
Furthermore, the phenolic hardeners described in DE-A-30 27 140 can also be employed.
Hardeners modified with branching agents and/or hardeners which have been rendered flexible are of course also suitable. Mixtures of various hardeners of those mentioned can also be employed.
FDA-approved hardeners are preferably employed here.
The epoxy resin component is usually employed in the powder coatings according to the invention in an amount of from 29 to 80% by weight, preferably from 39 to 60% by weight, in each case based on the total weight of the powder coating.
CA 022269~6 1998-02-12 The hardener component is usually employed in the powder coatings according to the invention in an amount of from 10 to 50% by weight, preferably from 15 to 90%
by weight, in each case based on the total weight of the powder coating.
The powder coatings according to the invention comprise, as a further component, at least one harden-ing catalyst, usually in an amount of from 0.01 to 5.0%
by weight, preferably from 0.05 to 2.0% by weight, in each case based on the total weight of the powder coating.
The catalyst is advantageously imidazole, 2-methylimidazole, ethyltriphenylphosphonium chloride or another salt thereof, a quinoline derivative, as described, for example, in EP-B-10805, a primary, secondary or tertiary aminophenol, aluminium acetyl-acetonate or a toluenesulphonic acid salt, or a mixture of various of the catalysts mentioned.
The commercially available hardeners containing hydroxyl groups usually already comprise a hardening catalyst.
Examples of such commercially available hardeners containing hydroxyl groups which are prefer-ably employed are the products available commercially under the following names: D.E.H.R 81, D.E.H.R 82 and D.E.H.R 84 from Dow, Hardener XB 3082 from Ciba Geigy and EpikureR 169 and 171 from Shell-Chemie.
The powder coatings according to the invention can furthermore also comprise from 0 to 55% by weight, preferably from 15 to 25% by weight, of fillers.
FDA-approved fillers are preferably employed.
Inorganic fillers, for example titanium dioxide, such as, for example, Kronos 2160 from Kronos Titan, Rutil R 902 from Du Pont and RC 566 from Sachtleben, barium sulphate and fillers based on silicate, such as, for example, talc, kaolin, magnesium aluminium silicates, mica and the like, are usually employed. Titanium CA 022269~6 1998-02-12 dioxide and fillers of the quartz sand type are pre-ferably employed.
The powder coatings according to the invention can furthermore also comprise, if appropriate, from 0.01 to 10% by weight, preferably from 0.1 to 2% by weight, based on the total weight of the powder coating, of other auxiliaries and additives. Examples of these are levelling agents, flow aids, deaerating agents, such as, for example, benzoin, pigments or the like.
For use for internal coating of packaging containers, the particle size distribution is adjusted so that at least 90 per cent by weight of the powder coating particles have a particle size of between 1 and 60 ~m, that is to say d 90 = 1 to 60 ~m. Preferably, 90 per cent by weight of the powder coating particles have a particle size between 1 and 40 ~m (d 90 = 1 to 40 ~m), and particularly preferably between 5 and 25 ~m (d 90 = 5 to 25 ~m). The maximum size of the powder coating particles for at least 99 per cent by weight of the particles is < 100 ~m, preferably < 60 ~m and particularly preferably < 40 ~m). The mean particle size of the powder coating particles is between 5 to [sic] 20 ~m, particularly preferably between 5 to [sic]
12 ~m. It is furthermore essential to the invention that, when the powder coatings are used for internal coating of the packaging containers, the particle size distribution is adjusted so that the gradient S of the particle distribution curve at the point of inflexion is 2 100, preferably 2 150 and particularly preferably 2 200. To achieve coatings having particularly good properties, powder coatings in which the gradient S of the particle size distribution curve at the point of inflexion is 2 300 are especially preferably employed.
The gradient S is defined here as the limiting value for f(x2) - f(x1) tending to zero of (f(x2) - f(x1))/log ((x2/x1)) at the point of inflexion of the particle distribution curve. The particle CA 022269~6 1998-02-12 distribution curve here is the plot of the cumulative percentages by weight (f(x)) against the absolute particle diameter (x), the particle diameter being plotted on a logarithmic scale and the cumulative S percentages by weight on a linear scale. For use as an internal coating on packaging containers, powder coat-ings which have both only a low proportion of very fine particles (particle size c 5 ~m) and at the same time also only a very low proportion of coarse powder coat-ing particles (particle size > 25 ~m), i.e. as narrowas possible a particle size distribution, are thus particularly suitable.
The particular particle size distribution of the powder coatings is adjusted with suitable grinding units, if appropriate in combination with suitable sifting and sieving devices, for example with fluidized bed countercurrent mills (AFG) from Alpine, Augsburg, in combination with Turboplex extra-fine sifters from Alpine, Augsburg.
Also essential to the invention is the addition of lubricant. This lubricant is added, in accordance with the invention, in amounts of less than 2% by weight. Additions of less than 1% by weight are pre-ferred. The range which has proven optimum is that from 0.1 to 0.6% by weight. Lubricants employed are propy-lene waxes, modified polyethylene waxes and acid amides.
In addordance with the invention, the propylene waxes are preferably employed in micronized form. Such waxes are obtainable commercially, inter alia, under the designation Hoechst-Wachs pp. 230, Hoechst-Wachs C, Hoechst-Wachs C Mikropulver PM and Hoechst-Wachs R 31.
The polyethylene waxes are, as a general rule, polytetrafluoroethylene-modified waxes. These are obtainable commercially, inter alia, under the desig-nations Hoechst-Wachs PED 121, 191, 136, 153, 261, 521, 522, and also Hostalup H 12 and Hostalup H 22.
CA 022269~6 1998-02-12 The acid amides which can be employed in accor-dance with the invention include, above all, erucamide and oleamide.
The addition of the lubricants according to the invention achieves surprising, unexpected properties, especially when the powder coatings are used for the interior coating of packaging containers. The coatings obtained are, in particular, highly flexible and surface scratch-resistant. The corrosion protection properties are also improved. Finally, the material according to the invention, as a coating, exhibits an outstanding transparency. It is possible, furthermore, to achieve crosslinking in between 10 seconds and a number of minutes at temperatures between 21 and 350~.
The powder coatings are prepared by the known methods (compare, for example, product information from BASF Lacke & Farben AG, "Pulverlacke", 1990) by homo-genization and dispersion, for example by means of an extruder, screw kneader and the like. It is essential to the invention that, after their preparation, the powder coatings are adjusted by grinding and, if appropriate, by sifting and sieving to a particle size distribution appropriate for the intended use.
In accordance with the invention the lubricant is preferably extruded and ground together with the powder coating material. This procedure makes it possible, in accordance with the invention, to obtain especially good profiles of properties. Otherwise to grind [sic] can be followed, if desired, by sifting and by application by means of corona units or tribo-electric charging. The result of a powder coating prepared and applied in the manner described is a surprising high level of matting, surface hardness, flexibility and adhesion promotion.
The packaging containers which are coated with the powder coatings according to the invention can be made of the most diverse materials, may have the most diverse sizes and shapes and may have been produced by CA 022269~6 l998-02-l2 various processes. In particular, however, metallic containers are coated with the powder coatings accord-ing to the invention. These metallic containers may have been produced by first rolling sheet metal and then joining it by folding back the edge. The end pieces can then be attached to the cylinder thus formed. The powder coatings according to the invention are employed for internal coating of the can bodies, which in general already have a base. Deep-drawn metal containers can furthermore also be coated on the inside with the powder coatings according to the invention.
However, the powder coatings are of course also suit-able for coating can lids and can bases.
The packaging containers can be made of the most diverse materials, such as, for example, aluminium, black sheet, tin sheet and various iron alloys, which are provided, if appropriate, with a passivating coating based on compounds of nickel, chromium and tin.
Containers of this type are usually used as containers for foodstuffs and drinks, for example for beer, juices, carbonated drinks, soups, vegetables, meat dishes, fish dishes and vegetables, but also, for example, for animal foods.
The application is carried out by known methods, such as are described, for example, in US Patent 4,183,974.
Electrostatic charging of the powder coating particles is effected here by friction (triboelectricity). The powder coating particles are applied with the aid of special spray heads known to those skilled in the art.
The powder coatings according to the invention can of course also be applied by the known process of electro-static assistance.
For internal coating of packaging containers, the powder coatings are usually applied in a coating thickness of S lS ~m, preferably of from 10 to 14 ~m.
Even at these low coating thicknesses, the coatings meet the requirements usually imposed on such CA 022269~6 1998-02-12 films. However, the powder coatings can of course also be applied in higher coating thicknesses.
The packaging container, the inside of which has been provided with the powder coating according to the invention, is then subjected to a heat treatment for hardening the powder coating. This heat treatment can be carried out in various ways. In practice, the containers are often conveyed through a tunnel oven for this purpose. During this operation, the powder coatings in general harden completely at object temperatures of between 230 and 350~C within a period of from 5 to 30 seconds. The tunnel oven here can be operated at a constant temperature, or can have a temperature profile adjusted to suit the particular circumstances.
The invention will now be explained in more detail with the aid of working examples. All the data on parts and percentages here are weight data, unless expressly stated otherwise. The powder coatings were in each case prepared by weighing all the constituents into canisters and premixing them in a premixer, and homogenizing the mix at 60 to 80~C by means of an extruder, cooling it as quickly as possible and adjusting it to the desired particle size distribution with grinding units.
Example 1 The following components were processed to give powder coating 1:
580 parts of commercially available epoxidized novolak resin having an EEW of 500 (commercial product D.E.RR 692U from Dow), 270 parts of commercially available hardener, contain-ing OH groups, based on bisphenol A having a hydroxyl equivalent weight of 250 (commercial product D.E.H.R 82 from Dow), 5 parts of commercially available levelling agent based on an oligomeric acrylate, CA 022269~6 l998-02-l2 143 parts of finely divided silicate-based filler of the quartz sand type and 2 parts of fluidization auxiliary based on pyrogenic silica or aluminium oxide.
SThis powder mixture is etruded [sic] and ground together with erucamide. In two experiments, an amount of 0.2% by weight and 0.5% by weight was added.
Using grinding units, the particle size distribution was adjusted so that at least 90% by weight of the powder coating particles have a particle size of between 1 and 25 ~m (d 90 = 1 to 25 ~m). The maximum particle size of at least 99 per cent by weight of the particles is < 100 ~m, and the mean particle size is 9 ~m. The gradient S at the point of inflexion of the particle distribution curve is 250.
tinplate panels were coated by means of corona charging with a) powder coating containing 0.2% erucamide b) powder coating containing 0.5% erucamide and the coating was crosslinked for 3 minutes in an oven at 220~C. Club cans, i.e. fish preserve cans, were stamped from the panels and sterilized for half an hour at 128~C. The media tested were:
- water, - 2% strength ~actic acid solution and - 3% strength acetic acid solution.
The result shows that the powder coating without erucamide fractures on punching (brittle) and acquires a milky appearance. The can also shows corrosion. The powder coating with 0.2% of lubricant is highly flexible and lends itself well to punching but shows a milky appearance with 2% strength lactic acid. With 0.5% of lubricant there are no concerns of this nature.
The results can be seen from the following table.
CA 02226956 l998-02-l2 L
Sterilization: ~ h 128~C
no +0.2% +0.5%
lubricant erucamide erucamide in H20 2% strength lactic acid + + ++
5% strength lactic acid + ++ ++
Claims (14)
1. Powder coating based on epoxy resins and phenolic hardeners, in particular for internal coating of packaging containers, comprising 1) at least one epoxy resin having an epoxide equivalent weight of from 300 to 5500 and at least one hardener having more than one phenolic hydroxyl group per molecule and a hydroxyl equivalent weight, based on the phenolic OH groups, of from 100 to 500 comprises [sic], the powder coating having such a particle size distribution, where a) at least 90 per cent by weight of the powder coating particles have a particle size of between 1 and 60 µm, b) the maximum particle size of the powder coating particles is ~ 100 µm for at least 99 per cent by weight of the particles, c) the mean particle size of the powder coating particles is between 5 and 20 µm and d) the gradient of the particle distribution curve at the point of inflexion is ~ 100 and 2) a lubricant, preferably in an amount of ~ 2% by weight.
2. Powder coating according to Claim 1, characterized in that it has a particle size distribution such that a) at least 90 per cent by weight of the powder coating particles have a particle size of between 1 and 40 µm, b) the maximum particle size of powder coating particles is ~ 60 µm for at least 99 per cent by weight of the particles, c) the mean particle size of the powder coating particles is between 5 and 12 µm and d) the gradient of the particle distribution curve at the point of inflexion is ~ 150.
3. Powder coating according to Claim 1, characterized in that it has a particle size distribution such that a) at least 90 per cent by weight of the powder coating particles have a particle size of between 5 and 25 µm, b) the maximum particle size of the powder coating particles is ~ 40 µm for at least 99 per cent by weight of the particles, c) the mean particle size of the powder coating particles is between 5 and 12 µm and d) the gradient of the particle distribution curve at the point of inflexion is ~ 200.
4. Powder coating according to one of Claims 1 to 3, characterized in that it comprises, as component A
[sic], epoxy resins based on bisphenol A and/or bis-phenol F and/or epoxidized novolak resins.
[sic], epoxy resins based on bisphenol A and/or bis-phenol F and/or epoxidized novolak resins.
5. Powder coating according to one of Claims 1 to 4, characterized in that it comprises, as component A
[sic], epoxy resins based on bisphenol A and/or bisphenol F having an epoxide equivalent weight of from 500 to 2000 and/or epoxy resins of the novolak type having an epoxide equivalent weight of from 500 to 1000.
[sic], epoxy resins based on bisphenol A and/or bisphenol F having an epoxide equivalent weight of from 500 to 2000 and/or epoxy resins of the novolak type having an epoxide equivalent weight of from 500 to 1000.
6. Powder coating according to one of Claims 1 to 5, characterized in that it comprises, as component B
[sic], a hardener having a hydroxyl equivalent weight, based on the phenolic OH groups, of from 200 to 300.
[sic], a hardener having a hydroxyl equivalent weight, based on the phenolic OH groups, of from 200 to 300.
7. Powder coating according to one of Claims 1 to 6, characterized in that it comprises, as component B
[sic], a hardener having from 1.8 to 4, preferably ~ 3, phenolic hydroxyl groups per molecule.
[sic], a hardener having from 1.8 to 4, preferably ~ 3, phenolic hydroxyl groups per molecule.
8. Powder coating according to one of Claims 1 to 7, characterized in that it comprises, as component B
[sic], a hardener based on bisphenol A and/or bisphenol F.
[sic], a hardener based on bisphenol A and/or bisphenol F.
9. Powder coating according to one of Claims 1 to 8, characterized in that it comprises A) from 29 to 80% by weight, based on the total weight of the powder coating, of epoxy resin component A [sic] and B) from 10 to 50% by weight, based on the total weight of the powder coating, of hardener component B
[ s i c ] .
[ s i c ] .
10. Powder coating according to one of Claims 1-0 [sic], characterized in that the proportion of lubricant is ~ 1, preferably 0.1 - 0.6% by weight.
11. Powder coating according to one of Claims 1-10, characterized in that lubricants used are acid amides, polypropylene wax, modified polyethylene wax.
12. Process for preparing a powder coating based on epoxy resins and phenolic hardeners, in particular for internal coating of packaging containers, characterized in that a powder coating comprising 1) at least one epoxy resin having an epoxide equivalent weight of from 300 to 5500 and at least one hardener having more than one phenolic hydroxyl group per molecule and a hydroxyl equivalent weight, based on the phenolic OH groups, of from 100 to 500 comprises [sic], the powder coating having a particle size distribution such that a) at least 90 per cent by weight of the powder coating particles have a particle size of between 1 and 60 µm, b) the maximum particle size of the powder coating particles is ~ 100 µm for at least 99 per cent by weight of the particles, c) the mean particle size of the powder coating particles is between 5 and 20 µm and d) the gradient of the particle distribution curve at the point of inflexion is ~ 100 and 2) a lubricant, preferably in an amount of ~ 2% by weight, are [sic] extruded and ground.
13. Process for internal coating of packaging containers, characterized in that a powder coating according to one of Claims 1 to 9 is applied in a coating thickness of ~ 15 µm.
14. Use of powder coatings according to one of Claims 1 to 9 for internal coating of packaging containers.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19531585A DE19531585A1 (en) | 1995-08-28 | 1995-08-28 | Powder coating and its use for the interior coating of packaging containers |
| DE19531585.5 | 1995-08-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2226956A1 true CA2226956A1 (en) | 1997-03-06 |
Family
ID=7770566
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002226956A Abandoned CA2226956A1 (en) | 1995-08-28 | 1996-08-27 | Powder coating and its use for the internal coating of packing containers |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0847427A1 (en) |
| JP (1) | JPH11511490A (en) |
| KR (1) | KR19990044235A (en) |
| CN (1) | CN1198767A (en) |
| BR (1) | BR9610296A (en) |
| CA (1) | CA2226956A1 (en) |
| DE (1) | DE19531585A1 (en) |
| WO (1) | WO1997008257A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19829790A1 (en) * | 1998-07-03 | 2000-01-05 | Gkn Automotive Ag | A lacquer containing powdered lacquer particles useful for corrosion protection of motor vehicle drive parts |
| DE10029548C2 (en) * | 2000-06-15 | 2002-07-04 | Basf Coatings Ag | Self-crosslinking powder coating based on epoxy resins and its use |
| DE10152829A1 (en) * | 2001-10-25 | 2003-05-15 | Basf Coatings Ag | Powdery coating material and functional coatings for high long-term use temperatures |
| US20090136737A1 (en) * | 2005-07-11 | 2009-05-28 | John Ring | Powder coating materials |
| CN101709195A (en) * | 2009-12-25 | 2010-05-19 | 广州擎天实业有限公司 | Pure epoxy powder coating for coating bakelite board and preparation method thereof |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4038681A1 (en) * | 1990-12-05 | 1992-06-11 | Basf Lacke & Farben | POWDER LACQUER AND THE USE THEREOF FOR THE INTERNAL COATING OF PACKAGING CONTAINERS AND FOR WELDING SEALING |
| DE4204266C2 (en) * | 1992-02-13 | 1996-04-18 | Basf Lacke & Farben | Powder coating and process for the interior coating of packaging containers |
-
1995
- 1995-08-28 DE DE19531585A patent/DE19531585A1/en not_active Withdrawn
-
1996
- 1996-08-27 CA CA002226956A patent/CA2226956A1/en not_active Abandoned
- 1996-08-27 KR KR1019980701471A patent/KR19990044235A/en not_active Application Discontinuation
- 1996-08-27 WO PCT/EP1996/003769 patent/WO1997008257A1/en not_active Application Discontinuation
- 1996-08-27 CN CN96196590A patent/CN1198767A/en active Pending
- 1996-08-27 JP JP9509851A patent/JPH11511490A/en active Pending
- 1996-08-27 EP EP96930968A patent/EP0847427A1/en not_active Ceased
- 1996-08-27 BR BR9610296A patent/BR9610296A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| EP0847427A1 (en) | 1998-06-17 |
| DE19531585A1 (en) | 1997-03-06 |
| CN1198767A (en) | 1998-11-11 |
| JPH11511490A (en) | 1999-10-05 |
| BR9610296A (en) | 1999-03-16 |
| MX9801566A (en) | 1998-05-31 |
| KR19990044235A (en) | 1999-06-25 |
| WO1997008257A1 (en) | 1997-03-06 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Dead |