EP0847425A1

EP0847425A1 - Container closure coated with a powder coating

Info

Publication number: EP0847425A1
Application number: EP96930109A
Authority: EP
Inventors: Peter Nüssen; Leonidas Kiriazis
Original assignee: PPG Industries Inc
Current assignee: PPG Industries Inc
Priority date: 1995-08-28
Filing date: 1996-08-27
Publication date: 1998-06-17
Also published as: DE19531559A1; WO1997008253A1; JPH11511491A

Abstract

The present invention concerns a container closure preferably comprising a coated metal or plastics material and a sealing element, the coating being a powder coating based on epoxy resins and carboxyl group-containing polyesters or phenolic hardeners, and/or based on polyolefins, and/or based on copolymers and ionomers which comprise carboxyl or anhydride groups or groups which can be hydrolyzed to form carboxyl groups.

Description

Powder-coated container closure

The present invention relates to container closures coated with powder coating, in particular closures for beverage bottles.

Container closures are provided with a coating, on the one hand to protect the contents from being affected by detached components of the metal sheet, and on the other hand to avoid corrosion of the metal sheet by aggressive contents.

In practice, this coating is mainly carried out using organically dissolved paints. However, this results in a high solvent load in the environment when drying the paint films. In addition, the previously common paints must be specially adapted to the sealing element, since conventional paints are not readily compatible with the sealing compounds.

Usually, the sheets are first coated with lacquer and then punched. The cut edges are exposed. The corrosion protection of such closures is therefore not sufficient. The present invention has for its object to provide container closures that are coated with lacquers that are compatible with the sealing elements without modification or special process measures in the coating. In addition, the paint should ensure improved edge protection. Furthermore, when used for the coating of packaging containers, these lacquers should also meet the requirements that are usually placed on closure coatings when applied with thin layers of <15 μm. In particular, these coatings should not be porous (determined using the so-called Enamelrat test), show good adhesion to the substrate, have high elasticity and be stable under the usual pasteurization and sterilization conditions. Furthermore, these paints should lead to coatings with high elasticity that can withstand the mechanical deformations without damage. Resistance to sterilization and pasteurization is also required.

This object is surprisingly achieved in that the paint is a powder paint based on epoxy resins and carboxyl-containing polyesters or phenolic hardeners and / or on the basis of polyethylene and / or on the basis of copolymers, terpolymers, graft copolymers and ionomers, the carboxyl or anhydride groups or groups which can be hydrolyzed to carboxyl groups.

The invention also relates to methods for producing container closures. Here, the closure is formed from a substrate, preferably metal, then a powder coating with a layer thickness of j <15 μm and then a sealing element is applied.

It is surprising and was not foreseeable that the powder coatings according to the invention are suitable for coating container closures and that the property profile and thus the application can be controlled simply by setting an appropriate grain size distribution. These powder coatings can be hardened quickly, are easy to handle and easy to apply.

In addition, the powder coatings according to the invention are characterized in that coatings with only a very small layer thickness of <. 15 μm have the properties required at the outset. In particular, these coatings have the required low porosity even with a small layer thickness of <15 μm. In addition, these coatings are characterized by good adhesion and good resistance to pasteurization and sterilization.

Furthermore, the powder coatings according to the invention have the advantage that the coatings have a high degree of flexibility, so that the coating layer can follow deformations without detachment or cracking.

The individual components of the powder coating materials according to the invention will now be explained in more detail below.

The polyesters used in the powder coatings according to the invention have an acid number of 25 to 120 mg KOH / g, preferably 30 to 90 mg KOH / g and particularly preferably 60 to 90 mg KOH / g and an OH number of at least 10 mg KOH / g, preferably of at least 15 mg KOH / g and preferably < _^ 30 mg KOH / g. Polyesters with a functionality> _ 2 are preferably used. The number average molecular weights of the polyesters are generally between 1000 and 10000, preferably between 1500 and 5000. FDA-approved (FDA = Food and Drug Administration) polyesters are preferably used. The polyesters containing carboxyl groups and hydroxyl groups can be prepared by the customary methods (cf., for example, Houben Weyl, Methods of Organic Chemistry, 4th Edition, Volume 14/2, Georg Thieme Verlag, Stuttgart 1961).

Suitable carboxylic acid components for the production of the polyesters are aliphatic, cycloaliphatic and aromatic di- and polycarboxylic acids, e.g. Phthalic acid, terephthalic acid, isophthalic acid, trimellitic acid, pyromellitic acid, adipic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, acelainic acid, sebacic acid and others. The acids can also be used in the form of their esterifiable derivatives (e.g. anhydrides) or their transesterifiable derivatives (e.g. dimethyl ester).

The diols and / or polyols usually used are suitable as alcohol components for the production of the polyesters, e.g. Ethylene glycol, 1,2-and 1,3-propanediol, butanediols, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,6-hexanediol, neopentyl glycol, 1,4-dimethylolcyclohexane, glycerol, trimethyloiethan, trimethylolpropane, pentaerythritol, ditrimethylolpropane, diglycerol and others.

The polyesters thus obtained can be used individually or as a mixture of different polyesters.

All solid epoxy resins with epoxy equivalent weights between 400 and 3000, preferably between 600 and 900 and particularly preferably between 700 and 800 are suitable as epoxy resins. 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 <_ 2, the epoxidized novolak resins have a functionality> 2. Suitable epoxy resins are, for example, the products available commercially under the following names: Epikote ^ύ 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 Araldit XB 4393, XB 4412, GT 7072, GT 7203, GT 7004, GT 7304, GT 7097 and GT 7220 from Ciba Geigy.

FDA-approved epoxy resins are preferably used.

The polyester component is usually used in an amount of 19 to 80

% By weight, preferably from 39 to 60% by weight, based on the total weight of the

Powder coating.

The epoxy resin component is usually used in the powder coatings according to the invention in an amount of 19 to 80% by weight, preferably 39 to 60% by weight, based on the total weight of the powder coating.

Suitable hardener components are all solid compounds with more than one phenolic OH group, 1.8 to 4, preferably 2 to 3 and particularly preferably <3 phenolic OH groups per molecule and a hydroxyl equivalent weight, based on phenolic OH groups, 100 to 500, preferably 200 to 300. Those based on bisphenol-A and / or bisphenol-F are preferably used as hardeners. The condensation product of the diglycidyl ether of bisphenol-A or bisphenol-F with bisphenol-A or bisphenol-F is particularly preferred as the hardener, in particular the condensation product with an equivalent weight of 220 to 280 based on phenolic hydroxyl groups. These condensation products are usually prepared by reaction of generally excess bisphenol with a bisphenol diglycidyl ether in the presence of a suitable catalyst. The condensation product is preferably prepared by reacting the diglycidyl ether with the bisphenol in a weight ratio of 0.5 to 2. These hardeners based on these condensation products of the bisphenol diglycidyl ether with a bisphenol generally have a functionality of at most 2, with the use of branching reagents again higher functionalities can be set.

The reaction products of bisphenols with epoxy resins of the novolak type are also suitable as hardeners. These hardeners are preferably obtained by reacting the epoxy resin with the bisphenol in a weight ratio of 0.5 to 2 in the presence of a suitable catalyst.

For example, the phenolic hardeners described in DE-PS 23 12409 in column 5, line 2 to column 6, line 55 are suitable. These polyphenols correspond to the following general formulas

A is a divalent hydrocarbon radical with 1 to 6 carbon atoms or the radicals

O O

-c- -o- -s- -s-s- -S-, or -S-

O O

x is a hydrogen or alkyl having 1 to 4 carbon atoms n an average value of 1 to 9, preferably 2 to 7 and y assumes a value of 0 or 1.

The phenolic hardeners described in DE-OS 30 27 140 can also be used.

Of course, hardeners modified with branching reagents and / or flexible hardeners are also suitable. Mixtures of different hardeners can also be used. FDA-approved hardeners are preferred.

According to the invention, in addition to the epoxy resin-based powder coatings mentioned, particularly preferred are polyethylene compounds which can be obtained, for example, under the name Lupolen ^R (to be obtained from BASF AG). Polyethylenes of this type can be obtained by radical polymerization of ethylene at high pressures (1500 to 3000 bar) or by coordinative Polymerization can be produced with the help of catalysts at low pressures. Depending on the polymerization conditions, polymers of different densities (0.90 to 0.97 g / cm ³ ) and different molar mass are formed. Polyethylenes are usually characterized by densities and melt indices. By polymerizing ethylene with polar monomers, such as vinyl acetate, acrylates, acrylic acid or non-polar α-olefins such as butene (-1), hexene (-1) etc., copolymers can be obtained with targeted changes in the polymer structure. According to the invention, preference is given to those polyethylenes which are produced by low-pressure polymerization, such as, for example, the Lupolen cited above.

The polyethylenes are semi-crystalline plastics. Depending on the polymerization conditions, polyethylenes with different degrees of branching are formed. The less branched the macromolecules are, the higher the crystalline fraction and thus the density. The level of the crystalline fraction and the crystallite thicknesses determine the melting behavior, i.e. the melting temperature and the heat of fusion of the polyethylenes. The mechanical properties depend directly on the crystallinity and density as well as on the molar mass. Rigidity and hardness increase with increasing density. In the case of copolymers, stiffness and hardness decrease with increasing comonomer content due to falling crystallinity. Accordingly, the degrees of branching and the crystalline fraction are to be controlled according to the invention in such a way that the preferred hardness ranges are achieved.

The copolymers, terpolymers, graft copolymers and ionomers which can be used according to the invention can be used with the proviso that they contain carboxyl or anhydride groups or groups which form carboxyl groups are hydrolyzable and have that the melt index of the polymers measured at 190 ° C. and a load of 2.16 kg between 0.1 and 30 g / 10 min, preferably between 0.2 and 25 g / 10 min and particularly preferably between 0 , 5 and 20 g / 10 min.

Suitable copolymers or terpolymers can be prepared by copolymerizing olefin, preferably ethylene or propylene and α, β-unsaturated carboxylic acids such as e.g. Acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid and fumaric acid, the corresponding anhydrides or the corresponding esters or sharks with 1 to 8 carbon atoms in the alcohol residue, e.g. Methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, heptyl, octyl and 2-ethylhee esters of the acids listed. The corresponding salts of the listed carboxylic acids, such as the sodium, potassium, lithium, magnesium, calcium, zinc and ammonium salts, can also be used. The carboxylic acids and their anhydrides are preferably used.

Further monomers which can be copolymerized with olefin, preferably ethylene or propylene and the unsaturated carbonyl compounds, can also be used in the copolymerization. For example, α-olefins with 3 to 10 carbon atoms, vinyl acetate and vinyl propionate are suitable.

The amounts of the monomers used are chosen so that the corresponding polymer has a carboxyl group content of 0.1 to 30% by weight, preferably 2 to 20% by weight, and that the content of olefin units, preferably ethylene or propylene units in the Polymer up to 99.9% by weight

%, preferably between 75 and 95% by weight.

Suitable graft copolymers can be prepared by grafting at least one polymer from the group of the polyolefins with up to 10

% By weight, preferably up to 5% by weight, based on the total weight of the Monomers, at least one monomer from the group of (α, β-unsaturated carboxylic acids, their anhydrides, their esters or salts in the presence or absence of peroxides.

The ionomers used can be prepared by the copolymerization of olefin and possibly further monomers with salts et, β-unsaturated carboxylic acids already described above or by partial neutralization of the above-described carboxylic acid-containing co-, ter- and graft polymers with salts, oxides and hydroxides of Sodium, potassium, lithium, magnesium, calcium, zinc and ammonium. The neutralization can be carried out in the melt or in the solution. The amount of basic compound is chosen so that the degree of neutralization of the polymer is between 0.1 and 99, preferably between 0.1 and 75% and very particularly preferably between 0.1 and 40%.

The polyolefins, copolymers, terpolymers, graft copolymers and ionomers mentioned can optionally be processed together with those mentioned on epoxy resins to form powder coatings and used for the container closures according to the invention.

As a further component, the powder coating materials of the invention contain at least one curing 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 material.

Advantageously, the catalyst is 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, aluminum acetylacetonate or a toluenesulfonic acid salt or a mixture of various of these Catalysts. The commercially available polyester resins containing carboxyl groups and hydroxyl groups usually already contain the necessary curing catalyst.

Examples of such commercially available carboxyl- and hydroxyl group-containing polyesters, which are used with particular preference, are the products commercially available under the following brand names: Crylcoat 314, 340, 344, 2680, 316, 2625, 320, 342 and 2532 from UCB, Arzneimittelbos , Belgium, Grilesta 7205, 7215, 72-06, 72-08, 72-13, 72-14, 73-72, 73-93 and 7401 from Ems-Chemie as well as Neocrest P 670, P 671, P 672, P 678 and P 662 from IQ.

Furthermore, the powder coatings can also contain 0 to 40% by weight, preferably 15 to 25% by weight, of fillers. FDA-approved fillers are preferred.

In general, inorganic fillers, e.g. titanium dioxide, e.g. Kronos 2160 from Kronos Titan, Rutil R 902 from Du Pont and RC 566 from Sachtleben, barium sulfate and silicate-based fillers, such as Talc, kaolin, magnesium aluminum silicates, mica etc. used. Titanium dioxide and fillers of the quartz sand type are preferably used.

In addition, the powder coatings can if necessary. 0, 01 to 10 wt. -%, preferably 0.1 to 2 wt .-%, based on the total weight of the powder coating, contain other auxiliaries and additives. Examples of these are leveling agents, flow aids, deaerating agents, such as e.g. Benzoin, pigments etc.

The powder coatings are produced using the known methods (cf., for example, product information from BASF Lacke + Farben AG, "powder coatings", 1990) by homogenizing and dispersing, for example by means of an extruder, screw kneader, etc. It is essential to the invention that the powder coatings are adjusted to a grain size distribution adapted to the intended use by grinding and, if appropriate, by screening and sieving.

For use in coating the container closures, the particle size distribution (a) is set so that at least 90 percent by mass of the powder coating particles have a particle size between 1 and 60 μm, ie d 90 = 1 to 60 μm. 90% by mass of the powder coating particles preferably have a particle size between 1 and 40 μm (d 90 = 1 to 40 μm) and particularly preferably between 5 and 25 μm (d 90 = 5 to 25 μm). The maximum particle size of the powder coating particles is at least 99% by mass of the particles _ <100 μm, preferably _ <60 μm and particularly preferably <40 μm). The average particle size of the powder coating particles is between 5 and 20 μm, particularly preferably between 5 and 12 μm. Furthermore, it is essential to the invention that when the powder coating materials are used, the particle size distribution is adjusted so that the slope S of the particle distribution curve at the turning point is> 100, preferably> 150 and particularly preferably> 200. In order to achieve coatings with particularly good properties, powder coatings are very particularly preferably used in which the steepness S of the grain distribution curve is 300 at the turning point. However, the manufacturing costs of powder coatings increase sharply with increasing steepness. The slope S is defined as the limit for f (x ₂ ) - f (Xi) towards zero of (f (x ₂ ) - f (xj)) / lg ((x ₂ / xι) at the point of inflection of the grain distribution curve represents the plot of the cumulative mass percent against the absolute grain diameter (shown logarithmically).

For the use as a coating of container closures, powder coatings are therefore particularly suitable, which only have a small proportion have very fine particles (particle size <5 μm) and at the same time only a very small proportion of coarse powder coating particles (particle size> 25 μm), ie have the narrowest possible particle size distribution.

The respective particle size distribution of the powder coating is adjusted using suitable grinding units, if necessary in combination with suitable screening and screening devices.

The container closures, which are coated with the powder coatings according to the invention, can consist of a wide variety of materials, have a wide variety of sizes and shapes and have been produced by various processes. In particular, however, metallic closures are coated with the powder coatings according to the invention. These metal closures can have been produced by first forming sheet metal into a container closure. The powder coatings are used both for covering the edges and for the exterior and interior coating of the closures.

The powder coatings are applied by known methods, as described, for example, in US Pat. No. 4,183,974. The powder coating particles are electrostatically charged by friction (triboelectricity). The powder coating particles are applied using special spray heads known to those skilled in the art.

For coating the container closures, the powder coatings are usually applied in a layer thickness of <_15 μm, preferably from 10 to 14 μm. Even with these small layer thicknesses, the coatings meet the requirements usually placed on such films. Of course, the powder coatings can also be applied in higher layer thicknesses. The container closure is then subjected to a heat treatment to harden the powder coating. This heat treatment can be done in different ways. In practice, the container closures are conveyed through a continuous furnace, for example. The powder coatings generally cure completely at object temperatures between 230 and 350 ° C. within a time of 5 to 30 s. The continuous furnace can be operated at a constant temperature or have a temperature profile that is set according to the respective circumstances.

After coating the inside, the sealant is applied. The sealants commonly used today are readily compatible with the powder coating, which is not the case with previously used wet coatings.

Styrene-butadiene-styrene rubber is preferably used as the sealing compound. These also contain oils, polyolefins, erucic acid amide and stabilizers. In a preferred embodiment, the sealing compound which can be used according to the invention contains 20 to 68% by weight, preferably 30 to 50% by weight of styrene-butadiene-styrene rubber, 80 to 20% by weight of polyolefins, preferably 30 to 50% by weight 10% by weight of white oil, 0 to 0.8% by weight of erucic acid amide and 0 to 1.2% by weight of stabilizers.

The invention is now explained in more detail below with the aid of exemplary embodiments:

example 1 A large number of crown caps were coated with an epoxyphenol powder coating in accordance with the application by means of corona charging and crosslinked in an oven at 220 ° C. for 40 seconds. The crown caps were then provided with a sealant and used to close beer bottles.

The sealing compound consists of a polyethylene-free PVC-free composition.

Example 2

Crown caps were applied with a powder coating consisting of ethylene-propylene rubber copolymers, which is grafted with maleic anhydride, by means of corona charging and brought above the melting temperature of the powder coating using a continuous furnace (> 150 ° C).

The crown cap was used with a polypropylene-containing sealant to close mineral water bottles.

Claims

claims

1. Container closure consisting preferably of metal or plastic coated with paint and a sealing element, characterized in that the paint is a powder coating

- On the basis of epoxy resins and carboxyl-containing polyesters or phenolic hardeners and / or

- On the basis of polyolefin and / or - On the basis of copolymers and ionomers, the carboxyl or

Have anhydride groups or groups that are hydrolyzable to carboxyl groups.

2. Container closure according to claim 1, characterized in that

1.) the powder coating

A) at least one epoxy resin with an epoxy equivalent weight of 300 to 5500, preferably 400 to 3000 and

B) at least one hardener with more than one phenolic hydroxyl group per molecule and a hydroxyl equivalent weight, based on phenolic OH groups, from 100 to 500 or

C) contains at least one polyester with an acid number of 25 to 120 mg KOH / g and an OH number> 10 mg KOH / g and

2.) the powder coating has such a particle size distribution that a) at least 90 percent by mass of the powder coating particles have a particle size between 1 and 60 μm,

b) the maximum particle size of the powder coating particles is at least 99% by mass of the particles _ <100 μm,

c) the average particle size of the powder coating particles is between 5 and 20 μm and d) the slope of the grain distribution curve at the inflection point is> _ 100.

3. Container closure according to claim 1 or 2, characterized in that the powder coating has such a particle size distribution that

a) at least 90 percent by mass of the powder coating particles have a particle size between 1 and 40 μm, b) the maximum particle size of the powder coating particles for at least 99 percent by mass of the particles is <60 μm, c) the average particle size of the powder coating particles is between 5 and 12 μm and d) the steepness of the grain distribution curve at the turning point> _. 150 is.

4. Container closure according to claim 1 to 3, characterized in that the powder coating such

Grain size distribution has that

a) at least 90 percent by mass of the powder coating particles have a particle size between 5 and 25 μm, b) the maximum particle size of the powder coating particles for at least 99

Mass percentage of the particles is <_ 40 μm, c) the average particle size of the powder coating particles is between 5 and 12 μm and d) the slope of the grain distribution curve at the inflection point is> 200.

5. Container closure according to one of claims 2 to 4, characterized in that the powder coating contains as component B epoxy resin based on bisphenol-A and / or epoxidized novolak resins.

6. Container closure according to one of claims 2 to 5, characterized in that the powder coating as component A epoxy resins based on bisphenol-A and / or bisphenol-F with an epoxy equivalent weight of 500 to 2000 and / or epoxy resins of the novolak type with an epoxy equivalent weight contains from 500 to 1000.

7. Container closure according to one of claims 2 to 5, characterized in that the powder coating contains as component B hardener with a hydroxyl equivalent weight, based on phenolic OH groups, from 200 to 300.

8. Container closure according to one of claims 2 to 7, characterized in that the powder coating as component B contains a hardener with 1.8 to 4, preferably 1.8 to 2.2 phenolic hydroxyl groups per molecule.

9. Container closure according to one of claims 2 to 8, characterized in that the powder coating contains as component B a hardener based on bisphenol-A and / or bisphenol-F.

10. Container closure according to one of claims 1 to 9, characterized in that the powder coating

A) 29 to 80 wt .-%, based on the total weight of the powder coating, the epoxy resin component A and B) 10 to 50 wt .-%, based on the total weight of the powder coating, the hardener component B.

11. Process for the production of container closures, characterized in that the closure is formed from a substrate, preferably metal, onto which a powder coating according to one of claims 1 to 10 is applied with a layer thickness <^ 15 μm and then a sealing element is applied.

12. Use of the container closure according to one of claims 1 to 10 for closing beverage bottles.