CH435095A - Method for closing sterilizable containers - Google Patents

Description

       

  
 



  Method for closing sterilizable containers
It is known to use packaging of any kind, such as. B.



  To close bags, cans and wrappings by heat sealing. In this case, the padk material, which consists of a thermoplastic or is coated with such a plastic, is welded at the seam by applying pressure and heat.



  When using packaging films coated with a thermoplastic, it is important for a perfect closure that both of the mutually facing sides of the packaging film are coated with the thermoplastic. Only in isolated cases, when a low strength weld is sufficient, is it possible to seal a coated on an uncoated material.



   Also known are cans which are deep-drawn from polyethylene-coated aluminum foil and closed with a cover film also covered with polyethylene, the cover film being sealed onto an outwardly directed edge flange of the lower part of the can.



   However, none of these packagings are suitable for filling goods. especially foodstuffs that are subjected to high temperature sterilization, since the thermoplastic layers are insufficiently resistant to the effects of the sterilization temperatures. Sterilization-proof cans are covered on the inside with a burn-in load, i.e. a plastic that has been hardened by burning. These cans are closed by flanging the lid with the edge of the can with the interposition of a sealing compound, usually based on rubber.



   The present invention relates to a method for closing sterilizable metal containers which are coated on their inside with a plastic that has been cured by baking. According to the invention, the lid, which is also coated with a hardened plastic, is sealed with the aid of a thermoplastic onto an edge flange of the container using heat and pressure, the sides of the lid and container, which are coated with the hardened plastic, facing each other.



   As thermoplastic plastics for the hot seals; treatment come polyolefins, z. B. polyethylene, vinyl resins and polyamides in question. A copolymer of ethylene and vinyl acetate with a vinyl acetate content of 18-40%, which has good adhesion to stoving enamels, has proven particularly suitable. The thermoplastic can be applied by applying a solution with subsequent drying or the molten mass, e.g. B. by spraying. It can be applied to both parts to be welded, i.e. St. on the flange of the container and the edge of the lid. However, it is preferably only applied to a part, e.g. B. applied the lid. In this case, the heating during sealing takes place preferably only from the non-coated side.



   But it is also possible to work without prior application of the hot-dip liquid and in such a way that the same immediately before closing the container in the form of a round wire of z. B. 0.8-1.2 mm diameter or a ring, with a rectangular cross-section of z. B. 0.05-0.50 mm thick and 3.0-0.5 mm wide between the Siegeiränder (flanges) of the container and lid is placed. The welding takes place in a known manner by applying pressure and heat.



   Certain amounts of resins, plasticizers, stabilizers, wax and paraffin can be added in the usual way to the thermoplastics used for sealing.



   To coat the container with a hardenable plastic come the known stoving enamels, z. B. based on phenolic and / or epoxy resin in question.



   Examples
1. An aluminum strip 0.1 mm thick was painted with a conventional can paint (epoxy-modified phenolic resin) and baked. The layer thickness of the paint was 5-7 / 1000 mm. A container 1 was produced from this material by deep drawing and a lid 2 was punched out.



   At the edge of the lid, a xylene solution of a copolymer of ethylene and vinyl acetate with a content of 28% of the latter was applied to the lacquer side and dried in warm air, so that a coating 4 with a thickness of 200-400 / 1000 mm was created (Fig. 1 ). This lid was welded onto the flange 3 of the container 1, namely at a tool temperature of 200-2300 C, a specific pressure of 30 Kp / cm2 and a sealing time of 2 seconds. Better results were achieved if the heat was only supplied from below, from the side of the flange 3 of the container. The container closed in this way (FIG. 3) was sterilized for 30 minutes at 1210 ° C. and the strength of the sealed seam was then tested by drilling into the container and pressing it off.

   The container only burst open at an internal pressure of 2.5-3.5 atmospheres.



   2. The container and lid were produced as in Example 1, but not coated with hot-sealing compound, this was placed in the form of a wire 5 with a diameter of 1.2 mm between the lid 2 and the container flange 3 (FIG. 2). The sealing temperature, pressure and time were chosen to be the same, with heat being supplied from both sides. The test of the container (Fig. 3) was carried out in the manner described in Example 1 and showed the same result.


    

Claims (1)

PATENT CLAIM A method for closing sterilizable metal containers which are coated on their inside with a hardened plastic material, characterized in that the lid, which is also coated with a hardened plastic material, is attached to an edge flange of the container with the aid of a thermoplastic material using pressure and heat is sealed, with the sides of the lid and container coated with the hardened plastic facing each other. SUBCLAIMS 1. The method according to claim, characterized in that the thermoplastic is a copolymer of ethylene and vinyl acetate with a vinyl acetate content of 18-40%. 2. The method according to claim or claim and dependent claim 1, characterized in that the thermoplastic is applied to only one of the parts to be sealed together. 3. The method according to dependent claim 2, characterized in that the heat is supplied during the Ver seal only from the side not coated with thermoplastic. 4. The method according to claim or claim and dependent claim 1, characterized in that the thermoplastic is placed in the form of a ring between the parts to be sealed.