EP0745002A1

EP0745002A1 - Process for producing lids and/or bottoms of packaging containers, thus produced lids and bottoms and their use for producing packaging containers, in particular foodstuff packages

Info

Publication number: EP0745002A1
Application number: EP95907634A
Authority: EP
Inventors: Udo Dr. Reiter; Manfred Reiman; Peter Dr. Lessmeister; Josef Dr. Rademacher; Tom Mcmurtry
Original assignee: BASF Lacke und Farben AG; PPG Industries Inc
Current assignee: PPG Industries Ohio Inc
Priority date: 1994-02-18
Filing date: 1995-02-01
Publication date: 1996-12-04
Also published as: WO1995022412A1; DE4405170A1; JPH09509100A; BR9506837A

Abstract

A process is disclosed for producing lids and/or bottoms of packaging containers during which a coating powder is applied on the lids and/or bottoms. The process is characterised in that a metal sheet or board is first coated with a primer, then a coating powder is applied on the primer coat and the lids and/or bottoms are cut or punched out of the metal sheet or board either before or after the coating powder is applied. Also disclosed are lids and bottoms produced by this process and their use for producing packaging containers, in particular foodstuff packages.

Description

Process for the production of lids and / or bottoms for packaging containers, the lids and bottoms produced in this way, and their use for the production of packaging containers, in particular for food packaging

The present invention relates to a process for the production of lids and / or bottoms of packaging containers, in which a powder coating is applied to the lids and / or bottoms.

The present invention also relates to the lids and bases produced by this process and their use for the production of packaging containers, in particular for food packaging.

Packaging containers, such as cans, two-part and three-part beverage cans, etc., are provided with a coating on the inside to protect the contents from being affected by detached components of the metal sheet, on the one hand, and to prevent corrosion of the metal sheets by aggressive contents. In practice, this coating is mainly carried out using organically dissolved paints. However, this has a high solvent load on the ur tion when drying the paint films. Attempts are also being made to replace these lacquers with low-solvent or solvent-free lacquers. Thermoplastic powder coatings are often used to cover the weld seam.

What is common to all currently customary methods for the production of can lids or can bases, however, is that the metal sheets are first provided with the desired coating and the already coated sheets or sheets then to the lids and Soils are processed. However, this method has some disadvantages. For example, depending on the resistance requirements to the can lid or can bottom, which differ considerably depending on the contents, the sheets or sheets used must be given a special coating. The can producer must therefore stock a large number of different, coated sheets or plates. This results in high storage costs. Furthermore, the quality of the coated lid is in need of improvement. In particular, an improved adaptation of the coating compositions to the requirements of the customers is desired.

From DE-OS 42 04 266 and DE-OS 40 38 681, for example, powder coatings for the inner coating of packaging containers are now known, which are used in particular for the inner coating of can bodies, but are also used for the coating of can lids and can bases can.

In these two documents, however, there are no indications for first providing metal plates or metal sheets with a primer for the production of the lids or bases, then punching out the lids or bases and first coating the lids or bases with the powder coating. It is disadvantageous in the manufacture of the lids or bases described there that the lids must already be painted by the sheet metal supplier in order to avoid corrosion. Individual painting by the can manufacturer is not possible.

The present invention is therefore based on the object of providing a method for producing can lids and / or can bottoms which enables rational, simple and inexpensive production. Above all, the procedure should enable coating of the cans according to the individual wishes of the can manufacturers. In addition, the coated lids and bottoms should meet the requirements that are usually placed on the inner coating of packaging containers. In particular, the can lids and can bases produced by the process should show good porosity behavior and good adhesion to the substrate. Finally, the coatings should be permanent under the usual pasteurization and sterilization conditions.

This object is surprisingly achieved by a method of the type mentioned at the outset, which is characterized in that a metal sheet or a

Metal plate is first coated with a primer, a powder coating is applied to the primer, and before or after the application of the powder coating, the lids and / or bottoms are cut out or punched out of the metal sheet or the metal plate.

It is surprising and was not foreseeable that the method according to the invention enables the simple, rational and inexpensive coating of can lids and can bases and thereby leads to coatings which meet the requirements which are usually placed on the inner coating of packaging containers. It is particularly advantageous that the lids or bases are protected from corrosion by applying a primer and are only provided with the inner coating by the can manufacturer. This enables an improved adaptation of the coating means to the individual use of the coated lids or bases by the can manufacturers. For example, the requirements for the coating depend heavily on the product with which the coating is filled after filling of the packaging container is in contact.

The primers and powder coatings used in the process will now be explained in more detail below.

Primers suitable for the method according to the invention are known per se.

In particular, primers are used which contain at least one epoxy resin and at least one phenolic resin. Primers are preferably used which contain at least one epoxy resin based on a reaction product of bisphenol A and epichlorohydrin. The primers preferably contain an epoxy resin with an epoxide equivalent weight of 400 to 5000, preferably from 1500 to 3000. In addition, primers are preferably used which contain at least one phenolic resin based on phenol and / or cresol and formaldehyde, such as e.g. which are commercially available under the names Phenodur PR 285 from Hoechst, Frankfurt and Bakelite 100 from Bakelite, Iserlohn.

The commercially available primers for packaging containers and the commercially available primers for the coating of metal panels or metal strips (so-called coil paints), such as the primer for the board coating EG 03-0823 and the primer for the coil coating, are also examples of the primer for the process according to the invention EG 03-060D from BASF Lacke + Farben AG, Münster.

The primer is usually applied with a layer thickness between 1 and 20 μm, preferably with a layer thickness of 2 to 5 μm. The application takes place with the usual application methods such as for example, dipping, brushing, knife-coating ^', Rollers include, but wherein preferably according to the coil coating process (so-called. coil coating process) is carried out.

Powder coatings which are suitable for the process are described, for example, in the published documents DE-OS-42 04 266 and DE-OS 40 38 681. However, other powder coatings can of course also be used, provided the resulting coatings meet the requirements placed on the inner coating of packaging containers.

It is of particular importance for the method according to the invention that the application of the primer prevents the corrosion of the metal sheets or metal plates and therefore the powder coating must first be applied by the can manufacturer. This enables the powder coating to be individually adapted to the special requirements of the can manufacturer. Furthermore, the binder or the crosslinking agent can be tailored individually to the requirements of the can manufacturer, for example by varying the crosslinking ratios, the epoxide equivalent ratios and the molecular weights of the components.

Powder coatings which have a particle size distribution such that

a) at least 90 percent by mass of the powder coating particles have a particle size between 1 and 60 μm, preferably 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 <100 μm, preferably <60 μm, c) the average particle size of the powder coating particles between 5 and 20 microns, preferably between 5 and

12 μm, lies and

d) the steepness of the grain distribution curve at the turning point is> 100 μm, preferably> 150 μm.

It is further preferred that a powder coating is used which

A) at least one epoxy resin with an epoxy equivalent weight of 300 to 5500 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, preferably from 200 to 300 or

C) at least one polyester with an acid number of 25 to 120 mg KOH / g, preferably 30 to 90 mg KOH / g, as hardener

contains.

In addition, it is preferred that the powder coating used as component A epoxy resins based on bisphenol A and / or epoxidized novolak resins and / or either as component B hardener with 1.8 to 4, preferably <3 phenolic OH groups per Molecule or as component C contains polyester based on terephthalic and / or trimellitic acid and ethylene glycol and / or neopentyl glycol.

Finally, it is preferred that a powder coating be is set who

A) 19 to 80% by weight of epoxy resin component A,

B) 10 to 50% by weight of hardener component B or

C) 19 to 80% by weight of the polyester component C

contains, where the percentages are based on the total weight of the powder coating.

These powder coatings ε; .nd known and in DE-OS 42 04 266, page 3, line 39, to page 6, line 38 and DE-OS 40 38 681, page 3, line 55, to page 5, line 16.

The powder coatings are preferably applied to the lids or bases with a layer thickness of 5 to 30 μm, particularly preferably 10 to 12 μm. The powder coating is preferably applied to that side of the lid or base which, after being fastened with the can body, faces the filling material.

The powder coating can be applied to the primer before or after the lids or bases have been cut or punched out. First, the primed sheets or sheets are preferably coated with the powder coating. After the powder coating has hardened, the lids or bases are then cut out or punched out.

The application takes place according to known methods, such as are described, for example, in US Pat. No. 4,183,974. The powder coating particles are electrically charged by friction (triboelectricity). The application is carried out with special, the Spray heads known to those skilled in the art.

The powder coatings are usually cured at object temperatures between 230 and 350 ° C for a period of 5 to 30 s. In practice, the

Coated parts for curing the powder coatings are frequently conveyed through a continuous furnace. The continuous furnace can be operated at a constant temperature or have a temperature profile that is set according to the respective circumstances.

The metal sheets or metal strips used to manufacture the can lids or can bottoms can consist of a wide variety of materials, such as aluminum, black plate, tin plate and various iron alloys, which may have a passivation layer based on nickel or chromium - And tin connections can be provided.

The lids or bottoms produced by the method according to the invention can be used for the production of packaging containers for a wide variety of applications, such as for the packaging of food and beverages, e.g. for beer, juices, lemonades, soups, vegetables, meat dishes, fish dishes, but also for animal feed etc.

The invention is now explained in more detail below with the aid of exemplary embodiments. All information on parts and percentages are weight information unless expressly stated otherwise. example 1

A powder coating 1 was produced from the following components:

400 parts of crosslinking catalyst containing commercially available polyester with an acid number of 80 mgKOH / g, an OH number of about 20 mgKOH / g, built up from terephthalic acid, trimellitic acid, adipic acid, ethylene glycol and neopentyl glycol (commercial product Grilesta V 72-6 from Ems-Chemie),

400 parts of commercially available epoxy resin based on bisphenol-A with an EEW of 750 (commercial product GT 6064 from Ciba Geigy),

100 parts of rutile-type titanium dioxide,

93 parts of finely divided silicate filler of the quartz sand type,

5 parts of leveling agent based on oligomeric acrylate

and

2 parts of fluidizing agent based on Si0 ₂ .

The particle size distribution was adjusted with grinding units so that at least 90 percent by mass of the powder coating particles have a particle size between 5 and 15 μm (d 90 = 5 to 15 μm). The maximum particle size for at least 99% by mass of the particles is £ 100 μm, the average particle size is 8 μm. The slope S is 250.

Made of an aluminum coil coated with universal Epoxy / phenol-based primers (commercial product EG 03-060D or EG 03-0823 from BASF Lacke + Farben AG, Münster), layer thickness 2 - 3 μm, are used to punch out the can lid.

The lids obtained in this way are coated at the can manufacturer with the thermosetting powder coating 1 with a layer thickness of 10-12 μm and baked completely cross-linking (object temperature 200 ° C., 2 min).

The lids obtained in this way are used to close cans filled with various filling goods. The cans are stored at 37 ° C for 1 year. Then the cans are opened and the top coating is assessed.

The following results were achieved for the lids coated with powder coating 1:

Product rating

* Mineral water no damage to the paint film, no blistering, no blushing, cross cut GtO

* Tap water no damage to the paint film, no blistering, no blushing, cross cut GtO

* 1% lactic acid no damage to the paint film, no blistering, no blushing, cross-cut Gtl

* 0.5% cysteine no damage to the paint film, no blistering, no blushing, cross cut GtO * 3% acetic acid no damage to the paint film, + 2% NaCl no blistering, no

Blushing, cross cut Gtl

Example 2

The following components were processed into powder coating 2:

580 parts of commercially available epoxidized novolak resin with an EEW of 500 (commercial product D.E.F-S '642U from Dow)

270 parts of commercially available OH group-containing hardener based on bisphenol A with a hydroxyl equivalent weight of 250 (commercial product D.E.H S2 from Dow)

5 parts of a commercial leveling agent based on an oligomeric acrylate,

143 parts of finely divided silicate filler of the quartz sand type and

2 parts of fluidizing agent based on pyrogenic silica or aluminum oxide.

The powder coating was made by all

Components were weighed into cans, premixed in a premixer, homogenized at 60 to 80 ° C. using an extruder, cooled as quickly as possible and adjusted to the desired particle size distribution using milling units. The grain size distribution was adjusted so that at least 90 percent by mass of the powder coating particles have a particle size between 1 and 25 μm (d 90 = 1 to 25 μm). The maximum particle size for at least 99 percent by mass of the particles is <100 μm, the average particle size is 9 μm. The slope S at the inflection point of the grain distribution curve is 250.

Canned food lids are punched out of a steel coil coated with a universal primer based on epoxy / phenol (commercial product EG 03-060D or EG 03-0823 from BASF Lacke + Farben AG), layer thickness 2 - 3 μm.

The lids thus obtained are coated at the can manufacturer with the thermosetting epoxy / phenol-based powder coating with a layer thickness of 10 - 12 μm and baked in completely cross-linking (200 ° C object temperature, 2 min).

The following results were achieved for the lids coated with powder coating 2: Product rating

* Chicken soup no damage to the paint film, no blistering, no blushing, cross cut GtO

* Pea porridge no damage to the lacquer film, no blistering, no blushing, cross cut GtO

* Beer no damage to the paint film, no blistering, no blushing, cross-hatching GtO

* Tomato ketchup no damage to the lacquer film, no blistering, no blushing, cross-hatching GtO, slight red coloring of the film

* black Johannis¬ no damage to the lacquer berry film, no blistering, no blushing, cross-cut GtO, light violet color of the film

Claims

claims

1. A process for the production of lids and / or bottoms of packaging containers, in which a powder coating is applied to the lids and / or bottoms, characterized in that a metal sheet or a metal plate is first coated with a primer, onto the primer Powder coating is applied and before or after the application of the powder coating the lids and / or bottoms are cut out or punched out of the metal sheet or the metal plate.

2. The method according to claim 1, characterized in that the layer thickness of the powder coating on the lid or the bottom between 5 and 30 microns, preferably between 10 and 12 microns.

3. The method according to claim 1 or 2, characterized gekenn¬ characterized in that a primer based on at least one epoxy resin and at least one phenolic resin is applied.

4. The method according to any one of claims 1 to 3, characterized in that a primer is applied, the

(A) at least one epoxy resin which is based on a reaction product of bisphenol A with epichlorohydrin and / or has an epoxide equivalent weight of 400 to 5000, preferably 1500 to 3000, and

(B) at least one phenolic resin based on phenol and / or cresol and formaldehyde contains.

5. The method according to any one of claims 1 to 4, characterized in that the powder coating is applied to the side of the lid or bottom, which faces the contents after fastening with the can body.

6. The method according to any one of claims 1 to 5, characterized in that a powder coating is used which has such a grain size distribution that

a) at least 90 percent by mass of the powder coating particles have a particle size between n, 1 and 60 μm, preferably 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 <100 μm, preferably <60 μm,

c) the average particle size of the powder coating particles is between 5 and 20 μ, preferably between

5 and 12 μm, lies and

d) the steepness of the grain distribution curve at the turning point _> 100 μm, preferably>. 150 μm.

7. The method according to any one of claims 1 to 6, characterized in that a powder coating is used, the

A) at least one epoxy resin with an epoxy equivalent weight of 300 to 5500 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, preferably from 200 to 300 or

contains.

8. The method according to any one of claims 1 to 7, characterized in that the one used

Powder coating as component A epoxy resins based on bisphenol A and / or epoxidized novolak resins and / or either as component B hardener with 1.8 to 4, preferably <3 phenolic OH groups per molecule or as component C polyester based on terephthalate and / or contains trimellitic acid and ethylene glycol and / or neopentyl glycol.

9. The method according to any one of claims 1 to 8, characterized in that a powder coating is used, the

A) 19 to 80% by weight of epoxy resin component A,

B) 10 to 50% by weight of hardener component B or

C) 19 to 80% by weight of the polyester component C

10. Lids and / or bottoms for packaging containers, characterized in that they have been produced according to a method according to one of claims 1 to 9.

11. Use of the lid and / or bottoms according to claim 10 for the manufacture of packaging containers, in particular packaging containers for food packaging.