DE1720114A1 - Seals for container closures - Google Patents

Description

seals for container closures The invention relates to manufacture of seals for container closures, for example for crown closures, rolled on Screw closures> screw closures with preformed thread and nose closures, and in particular sealing compounds suitable for this purpose.

Seals or inserts are made from a wide variety of materials such as cork and cardboard and the so-called cast or molded Gaskets made from selected plasticized polyvinyl chloride.

Thermo # plastic ones that are not plasticized for these purposes are also used Substances such as polyethylene and copolymers of ethylene are used, it has now been found that one seals with good sealing properties from certain thermoplastic Block copolymers, namely thermoplastic styrene-butadiene and Vinyl pyridine butadiene block copolymers and from mixtures of thermoplastic styrene-butadiene block copolymers with thermoplastic Can produce olefin polymers.

With the invention, demzufolog seals for container closures Proposed from thermoplastic material, which consists of a block copolymer of styrene and butadiene or a mixture comprising (a) a block copolymer of styrene and butadiene and (b) an olefin polymer, as an olefin polymer are in the following hydrocarbon polymers with at least one C-C double bond including the hopopolymers and nischpolymers derived therefrom.

Furthermore, sealing compounds for the manufacture of the invention of closure seals which include an olefin polymer and a block copolymer Contains styrene and butadiene. after all, container closures are also used with the mixture old proposed the seals of the invention.

The styrene butadiene block copolymers which are suitable for the purposes of the invention are preferably characterized in that they contain about 20% to about 40% styrene and at each end of the polymer chain there are styrene branches, and are im generally by condensation of butadiene with styrene in the presence of a lithium alkyl catalyst manufactured. Such styrene-butadiene block copolymers useful in the invention include Compounds in which the blocks derived from butadiene have a saturated carbon chain contain as a backbone on which there are vinyl substituents. The styrene-butadiene block copolymers can be hydrogenated or non-hydrogenated. Typical styrene-butadiene block copolymers are those known under the trade names "The rmoplastic", "Kraton" and "Pharos" Products.

These copolymers must not be used with the copolymers of styrene and Butadiene can be confused with the statistical distribution of the monomers in the chain, which are known as synthetic rubber and are not thermoplastic, and also not with the hard, highly impact-resistant materials such as styrene-butadiene graft copolymers or mixtures of polystyrene and butadiene polymers.

The vinyl pyridine-butadiene block copolymers are essentially accurate so constructed and described in British Patent 1,032,150. These polymers, which contain less than 40% i.e. about 25 to 35% vinylpyridine are hydrochlorinated, i.e. the vinylpyridine blocks are partly in the form of hydrochlorides, whereby the Polymers are resistant to both oils and solvents0 These polymers are therefore particularly advantageous because the seals made from them are oil and are solvent-resistant.

The olefin polymer used in the blends can, for example consist of polystyrene or polyethylene, with low density polyethylene being preferred will. Olefin copolymers such as ethylene / vinyl acetate copolymers can also be used will. The olefin polymer may be partially crosslinked (e.g., by treatment with high-energy rays), but it must be thermoplastic to the point that it can be deformed when heated. Preferably, the mixtures contain up to 25% by weight olefin polymer and at least 75% by weight styrene-butadiene block-poly. meres.

By changing the proportions of olefin polymer to block copolymer in the mixture can the physical properties of a manufactured from it Seal can be modified. This is extremely beneficial for various purposes Seals with different properties are required. For example Seals are desirable in which only a low opening resistance of the lid or a high pressure holding capacity or good resistance to steam sterilization or solvent resistance, for example against Xthanol in closures for packaging containing alcohol such as beer bottles.

For the production of seals and their insertion in container filter closures many processes are known. In the britisoben patent specification 1 112 023 describes a method in which one preformed insert made of solid thermoplastic elastic material inserted into a container closure, which is heated so far that the system bafteta on it and the insert then with it brings a balt forest temple under pressure into the desired yorm, wobble the closure is optionally further heated. Such a process is called "cold forming" designated. In other methods, the thermoplastic sealant is in the Container closure introduced, which can optionally be preheated, and then heated for simultaneous or subsequent deformation. Depending on the profile of the die, flat or profiled seals can be produced.

The D1 ohtungen from the mixtures according to the invention can according to a any of the known methods can be prepared. In order to prior to molding the Apply the exact amount of sealant required to the seal It is advantageous if the seal is in the form of pellets or ßoheiben is present. Such. Soheiben or pellets can stoffverarbei through the usual plastic processing process can be produced, for example, by using the thermoplastic Material to one thin dc or tape pressed and then out of it the panes are knocked out or cut out in some other way. You can also get the crowd Extrude in the form of a rod and then into small pieces or pellets cut. Sealing compound can be used for the production of seal-shaped seals a propellant can be incorporated.

The invention also encompasses sealants consisting of (a) a Block copolymer of styrene and butadiene or a vinylpyridine-butadine block copolymer and (b) an olefin polymer, the latter preferably made of polyethylene, especially low density polyethylene, plyatyrol or ethylene / vinyl acetate copolymers consists.

These blends preferably contain up to 25% by weight of olefin polymer (b) and at least 75% by weight of block copolymer (a).

The invention is illustrated in more detail by the following examples.

Beiapiel 1 Boin styrene-butadiene block copolymer (commercial product "Pharos 103 "from the Shell Chemical Company) with a styrene content of about 30% and styrene components at each end of the polymer chain was extruded into a rod and then into small cylindrical pellets cut.

The pellets were placed in heated crown locks and this is then carried out under a row of radiant heaters. After the material Anything warmed up enough was turned into the desired sealing profile with a cold molding die shaped. The crown locks thus obtained were excellent Sealing @ and pressure holding capacity.

Example 2 10 parts of low density polyethylene were mixed with 90 parts of the styrene @ butadiene @ block @ copolymer described in Example 1 mixed and the mixture is then shaped into a thin film. The film became discs cut out and inserted into aluminum caps of the "rolled on" type, which were then heated. The softened polymer mixture was then cooled with a Stamp to the seal form described in the German patent application P 16 07 860.7 presses. The closures obtained had excellent sealing properties and good pressure retention and turned off easily.

Example 3 20 parts of low density polyethylene and 80 parts of "Pharos 103 "were dry blended and extruded into a 1 cm diameter rod. A pellet was removed from the stick cut and in the middle of one heated roll-up closure with a diameter of 31.5 mm. The closure with the Pellet was heated further and the seal then as in example? with a shaped chilled stamp.

Example 4 20 parts by weight of polystyrene and 80 parts by weight of the in The styrene-butadiene block copolymers described in Example 1 were mixed in a Banbury mixer mixed. The mixture became one after rolling on a two-roll mill Pressed foil. Discs were cut from the film and heated Roll-up closures made of aluminum. The closure with the disk was heated and deform the disc with a cooled punch. The closures indicated excellent sealing properties, good pressure holding properties for acidic Packs and a low opening resistance.

Example 5 In the same manner as in Example 4, a mixture was made made of 20% by weight of partially cross-linked low-density polyethylene (by irradiation with high-energy electrons networked up to 10 megaras). and 80% by weight of the example 1 described styrene-butadiene block copolymers produced.

From this mixture, sealing gaskets were applied to the in example 1 as described above. They showed an excellent seal and Pressure holding capacity and a low opening resistance.

Example 6 80 parts by weight of the styrene-butadiene block copolymers described in Example 1 were mixed with 20 parts by weight of low density polyethylene and made into one Rod of 1 ci diameter extruded. Pellets were cut from the data stick and placed in sealing caps.

After heating to soften the pellets, they were impact molded formed into thin slices with a cold stamp. The lock is the disk was then heated, whereby the disk by the "elastic memory" the Mases partly returned to the pellet form. The pellet or the disc was then formed into the desired seal with a cold stamp.

Claims (9)

Claims 1. Seals for container closures made of thermoplastic Runststoff, characterized in that the thermoplastic material consists of a block copolymers of styrene and butadiene or vinyl pyridine and butadiene or one Blend of a block copolymer of styrene and butadiene with an olefin polymer consists. 2. Seals according to claim 1, characterized in that you use block copolymers of styrene and butadiene contains 20 to 40% styrene and at each end of the polymer chain has a styrene section. 3. Seals according to claim X and 2, characterized in that the Block copolymers of styrene and butadiene are composed of a hydrogenated copolymer. 4. Seals according to claim 1 to 3, characterized in that the olefin polymer made from polyethylene, polystyrene, or ethylene / vinyl acetate copolymer consists. 5. Thermoplastic compounds for the production of seals for container closures, characterized in that they a) at least 75% by weight of a thermoplastic material contain that 1) a block copolymer of styrene and butadiene or 2) is a block copolymer of vinylpiridine and butadiene, and b) up to 25% by weight 1) Polystyrene, 2) an ethylene-vinyl acetate copolymer or 3) a polyethylene lower density. 6. Thermoplastic compositions according to claim 5, characterized in that that component a) is a Brock copolymer of styrene and butadiene with 20 to 40 % By weight where there are styrene segments at each end of the polymer chain. 7. Thermoplastic compositions close to claim 5 to 6, characterized in that that component a) is a block copolymer of styrene and butadiene which hydrogenates has been. 8. Thermoplastic compositions naoh claim 5 to 7, characterized in that that component b) is a crosslinked low-density ethylene ethylene. 9. Process for the production of container closures with sealing cables according to patent .... ... (patent registration G 45 014 Ivc / 39b), characterized that a thermoplastic composition according to claim 5 to 8 in the form of a pellet introduces into the locking sleeve, compressed to a thin disc, by renewed Warming can partially return to the original shape and finally to that deformed the desired sealing profile.