WO1997012931A1 - Sealing material for mechanically sealing closures - Google Patents

Abstract

The present invention pertains to sealing materials for mechanically sealing closures, made from polymer mixtures comprising the following: A) at least one metallocene-free polyolefin; B) a polypropylene random copolymer; C) (optionally) a synthetic rubber; D) (optionally) fillers; and E) (optionally) further additives. Also disclosed are processes for producing mechanically sealing closures using the claimed polymer mixture as an inner inlay on the closure surface, and mechanically sealing closures of this type.

Description

Sealing compounds for mechanically sealing closures

Field of the Invention

The invention relates to sealing compounds for mechanically sealing, in particular thin-lip closures, consisting of polymer mixtures PM, comprising A) at least one metallocene-free polyolefin homopolymer, B) a polypropylene random copolymer, C) optionally a synthetic rubber, D) optionally at least one Filler ε and E) optionally other additives.

State of the art

It has long been known to provide vessel closures, in particular for vessels containing food, such as crown caps or screw closures, on their inner side facing the vessel with an elastic sealing element which, when the vessel is closed, between the latter and the closure is pressed in and the tightness is guaranteed.

Whereas in the past the inlays of crown corks or bottle screw caps were mainly made from pressed cork, which was optionally also coated with a thin plastic or aluminum foil, the sealing element has been made from a synthetic polymer mixture for a long time. However, only polymer blends that are durable and resistant enough and at the same time have the required elasticity are suitable for this.

In practice, this is mainly polyvinyl chloride used; Polyethylene and mixtures of the aforementioned polymers with polyvinyl acetate and vinyl acetate-ethylene copolymers have also been used. The production of vascular occlusions using such polymer mixtures is described, for example, in DE-AS 20 33 064 and DE-A-30 21 488.

However, these known polymer mixtures still have considerable disadvantages. The use of polyvinyl chloride or other halogen-containing plastics leads to ever increasing difficulties in the elimination and rendering harmless as well as in the recycling of the used vascular occlusions that get into the household garbage. In the conventional combustion treatment of domestic waste, acid-containing gases are produced from halogen-containing plastics, the release of which into the environment is harmful. The additions of low molecular weight plasticizers (for example phthalic diesters), which are indispensable for the adjustment of the required sealing properties, are also not harmless for reasons of health care, since these plasticizers are partly released again from the polyvinyl chloride and via the food and beverages contained in the container can get into the human body. For this reason, the plasticizer content of such polymer materials is limited by appropriate regulations.

The polyethylenes which have also been used hitherto have not been found to be a sealing material in particular because temperature fluctuations or damaged vessel mouths have to be taken into account, which place high demands on the elasticity of the sealing materials. Polyethylene was also considered to be unusable because the tightness was not considered sufficient for carbonated beverages. In the as yet unpublished German patent application 195 29 230.8, compositions are described, preferably consisting of a) at least one polyolefin produced using catalysts from the group of metallocenes, b) at least one polypropylene copolymer, c) at least a synthetic rubber, d) optionally fillers and e) optionally further additives, which are necessary as an inner insert in a sealing element for vessels

Ensures tightness, no harmful substances, in particular no halogen-containing constituents and no low-molecular plasticizers containing ester groups, and also contains vascular closures, particularly when pasteurizing the contents of the container, and withstand the stress conditions.

The polypropylene copolymers b) described in German patent application 195 29 230.8 are preferably mixtures of polypropylene random copolymers and polypropylene homopolymers. In the case of such mixtures, the individual components of the polypropylene random copolymer and polypropylene homopolymer have to be carefully and therefore laboriously coordinated with one another in order to avoid malfunctions in the compounding of the mixture components, such as incomplete melting of a mixture component become. Such disturbances lead to loss of properties in the sealing compounds, such as pressure loss or leaks in the vascular occlusions, due to inhomogeneities in the polymer mixture.

Therefore, there was still a need for easy-to-use polymer mixtures for sealing closures, such as those in the German patent application 195 29 230.8 meet the criteria.

Surprisingly, it was found that when pure polypropylene random copolymers are used as mixture component b) in the polymer mixtures described in German patent application 195 29 230.8, on the one hand the high level of properties required for sealing compounds is set, and on the other hand to the use of metallocene catalysts in the Production of the polyolefin component (s) a) can be dispensed with. The specific restriction of the polyolefin component (s) a) according to German patent application 195 29 230.8 is therefore no longer necessary.

The sealing compounds for vessel closures according to the invention are accordingly polymer mixtures PM of:

A) at least one metallocene-free polyolefin,

B) a polypropylene random copolymer, C) optionally a synthetic rubber,

D) optionally fillers, and

E) optionally further additives.

The polymer mixtures PM according to the invention preferably contain 15 to 85% by weight, particularly preferably 25 to 60% by weight, of metallocene-free polyolefin A), 15 to 35% by weight, particularly preferably 20 to 30% by weight. % of the polypropylene random copolymer B), 0 to 25% by weight, particularly preferably 5 to 20% by weight, of the synthetic rubber C), 0 to 20% by weight, particularly preferably 5 to 20% by weight. % Fillers D) and 0 to 5% by weight, particularly preferably 0.1 to 5% by weight, further additives E). The data in% by weight relate to the polymer mixture PM in its entirety. Implementation of the invention

The blend components

The metallocene-free used according to the invention

Polylolefins A) are preferably homopolymers and / or copolymers of ethylene and / or propylene, with the exception of polypropylene random copolymers. Worth mentioning are low density polyethylenes (LDPE), linear low and linear very low density polyethylene (LLDPE or VLDPE) medium density (MDPE), and preferably high density polyethylene (HDPE).

Furthermore, copolymers of ethylene can be used as component A) with one or more comonomers, such as, for example, alpha-olefins, vinyl esters, such as vinyl acetate or vinyl propionate, vinyl alkyl ethers, such as vinyl methyl ether, and also unsaturated mono- and dicarboxylic acids, their salts, anhydrides or Esters such as acrylic acid, maleic acid, maleic anhydride or diethyl maleate.

These polyolefins are commercially available, for example, under the brand names Escorene®, Lupolen®, Lotader®, Laqctene®, Orevac®, Dowlex®, Lucalen®, Primacor®, Surlyn®, Admer®, Novatec®, Sclair® and Stamylan® .

The polypropylene random copolymers B) are statistical copolymers of 90 to 99% by weight, preferably 93 to 99% by weight of propylene and 1 to 10% by weight, preferably 1 to 7% by weight. % of further comonomers, in each case based on the total weight of the monomers used.

Such statistical copolymers B) have a non-uniformity U = Mw / Mn, where Mw stands for the weight-average molecular weight and Mn for the number-average molecular weight, in the range from 2 to 10, preferably in the range from 3 to 6. The melt index MFI 230 degrees C / 2.16 kg according to DIN 53 735 of the copolymer B) is in the range between 1 and 10 g / 10 min, preferably between 4 and 15 g / 10 min. Such polypropylenes B) and methods for their production are known. They can be produced, for example, by the polymerization process described in DE-A-37 30 022 using a Ziegler-Natta catalyst. The propylene copolymers B) are, for example, in a gas phase polymerization process at temperatures between 20 and 160

Degree C and at pressures between 1 and 100 bar producible. The molecular weights of the polymers can be adjusted by generally known measures, for example using molecular weight regulators, such as e.g. Hydrogen.

Suitable comonomers for the propylene in the propylene copolymers are, for example, ethylene and alpha-mono-olefins with 4 to 12 carbon atoms, in particular ethylene and alpha-mono-olefins with 4 to 6 carbon atoms, such as butene-1,4-methyl-pentene -1, hexene-1, n-octene-1, n-decene-1 ε and n-dodecene-1. Polypropylene-random copolymers B) composed of 96 to 99% by weight of propylene and 1 to 4% by weight of ethylene, in each case based on the total weight of the monomers used, are particularly suitable, such polypropylene random Copolymers B) generally have a non-uniformity U between 3 and 6 and a melt index MFI (230 degrees C / 2.16 kg according to DIN 53 735) between 5 and 9 g / 10 min. Such polypropylene copolymers B) have a melting range of about 135 to 155 degrees C (determined by DSC). Polypropylene random copolymers B) composed of 90 to 97% by weight of propylene, 2 to 5% by weight of ethylene and 1 to 6% by weight of butene-1, each based on the total weight of the monomers used, are also particularly suitable ren, which is a non-uniformity U between 3 and 6, have a melt index MFI (230 degrees C / 2.16 kg) between 4 and 8 g / 10 min and a melting range between 120 and 140 degrees C (measured by DSC). The polypropylene random copolymers described are available, for example, under the trade name Novolen® 3520 LX from BASF AG.

Examples of synthetic rubbers C) which can be used are styrene-butadiene-styrene block copolymers (SBS rubber), styrene-butadiene copolymers, styrene-isoprene-styrene block copolymers (SIS rubbers) and / or styrene-isoprene copolymers. Suitable SBS and SIS rubbers are described, for example, in DE-A-16 92 059 and in US Pat. No. 3,779,965. These are block copolymers of type A-B-A which contain polystyrene as block A and polybutadiene or polyisoprene as block B. Suitable SBS chewing pads consist, for example, of 30 to 60% by weight of polystyrene end segments and correspondingly 40 to 70% by weight of central segments made of polybutadiene or polyisoprene. Such SBS block copolymers and styrene-butadiene copolymers are available, for example, from Fina under the trade name Finaprene®. Furthermore, synthetic rubber C) ethylene-propylene copolymers EPM can be used, which are amorphous and which are crosslinked, for example, with the help of peroxides. Terpolymers of ethylene, propylene and a diene EPDM can also be used as synthetic rubber C), the EPDM types being able to be crosslinked both peroxidically and with sulfur accelerator systems. For the EPM and EPDM types, see, for example, Ullmann's Encyclopedia of Industrial Chemistry, 4th edition, volume 13, pages 619 to 621, Verlag Chemie, Weinheim, New York, 1977.

Preferred synthetic rubbers C) are butyl rubber. schuke used, which preferably consist of copolymers of 95 to 99.5 mol% isobutene and 0.5 to 5 mol% isoprene. Such butyl rubbers C) are obtained, for example, by cationic copolymerization of isobutene and isoprene in methyl chloride as the solvent and with aluminum chloride as the catalyst at -100 ° C.

The butyl rubbers C) generally have a double bond content of about 0.5 to 3 mol%, which is suitable for peroxidic or sulfur-induced crosslinking. The weight-average molecular weights Mw of the uncrosslinked butyl rubber C) are approximately 150,000 to 400,000 daltons with a non-uniformity U of approximately 3. For the butyl rubbers C), see, for example, Ullmann's Encyclopedia of Industrial Chemistry, loc. eit., pages 621 to 623.

Advantageously, the polymer mixtures according to the invention also contain fillers D), with preference

FDA-approved fillers are used. Examples of inorganic fillers D) include inorganic types: titanium dioxide types, such as titanium dioxide, barium sulfate, silicates, such as magnesium or aluminum silicates, quartz sands, talc, kaolin, mica, amorphous and pyrogenic silicas, calcium carbonate, diatomaceous earth . Titanium dioxide and fillers of the talcum type are preferably used.

If appropriate, further additives E) are present in the polymer mixtures PM according to the invention. These include internal and external lubricants, anti-blocking agents, stabilizers, antioxidants, pigments, crystallization aids and the like. These additives are used in the manufacturing, processing, packaging and application. agile amounts in the form of powder, powder, pearls or incorporated directly into one of the mixture components. More details on the amounts usually used and examples of suitable additives can be found, for example, in Gachter-Müller, Kunststoffadditive, Carl-Hanser Verlag.

It is particularly advantageous if the polymer mixtures PM according to the invention contain up to 0.5% by weight, based on the polymer mixture, of lubricants and up to 0.2% by weight of antiblocking agents and, if appropriate, antioxidants and other processing stabilizers. Suitable lubricants are fatty acids, such as stearic and oleic acids, silicone oils, such as polydimethylsiloxane and polymethylsiloxane. Other examples are waxes and

Silicas to achieve certain flow behavior. Primary and secondary fatty acid amides, such as erucasaureamide or oleic acid amide, are preferably used as lubricants. The antioxidants and processing stabilizers primarily serve to protect against daylight and UV light and against heat. Accordingly, UV light and heat stabilizers are used in particular. For example, sterically hindered amines are used as UV stabilizers. Sterically hindered phenols, for example, are used as heat stabilizers. Phenol derivatives are preferably used as antioxidants.

Manufacture of the sealing compounds and the mechanically sealing closures from them

The polymer mixtures PM used in accordance with the present invention are first produced by mechanical

Mixing the mixture components A) to E), which are melted and homogenized in an extruder in a subsequent processing step. The polymer mixtures PM forming the sealing compounds leave the exit opening of the extruder as plastic strands which are immediately cut into individual pieces behind the exit opening. These pieces are applied to the inside of the punched metal fasteners while still plastic. The closure to be coated with the sealing compound is understood to mean all parts of the packaging material which are connected to the body of the packaging, such as, for example, crown caps for beer, fruit juice and lemonade bottles, metallic closures for bottles and glasses, and others Metallic closures for cans, buckets, fibers and other containers which are common in the packaging industry. In addition to crown caps, aluminum twist locks, cam twist locks and CRIMP closures.

Accordingly, the present invention also relates to packaging containers with a metallic closure, the closure containing sealing compounds as a constituent part, which are composed of the polymer mixtures PM according to the invention.

Such closures have the particular advantage that, compared to the usual polyvinyl chloride sealants, the sealants are halogen-free, have no plasticizer migration and have good resistance to solvents and chemicals, good resistance under the conditions of pasteurization and the like Have sterilization and good adhesion to the substrates coated with adhesive lacquers. Furthermore, the components of the polymer mixture PM which form the sealing compounds can be mixed homogeneously in the thermoplastic state without problems and easily available. From an environmental point of view, the sealing compounds according to the invention are particularly advantageous since they contain no harmful substances, in particular no halogen-containing constituents and no low-molecular constituents containing ester groups, and the sealing compounds enable a largely solvent-free process for the manufacture of closures of packaging containers.

The invention is explained in more detail below on the basis of exemplary embodiments. Unless otherwise expressly stated, all information on parts and percentages relate to weight data.

Examples

Example 1: Preparation of the polymer mixture PMI

A mechanical sealant PMI is made from the following components by mechanical mixing and extrusion:

46.296 parts of a high-density polyethylene (HDPE: MFI

(180 degrees C / 5 kg): 25) 28,000 parts of a polypropylene random copolymer (MFI (180 degrees C / 5 kg): 15)

12,000 parts of a butyl rubber (Mooney (125 degrees C, ML8): 70-80) 8,000 parts of filler (talc)

5,000 parts of a polybutylene (molecular weight: 600 daltons)

0.704 parts of other additives divided into: 0.280 parts of titanium oxide pigment (rutile)

0.100 parts of antioxidant (sterically hindered

Phenol) 0.220 parts lubricant (amide wax) 0.100 parts UV stabilizer (sterically hindered

Amine), and 0.004 part of carbon black pigment

Example 2: Crown cork production and properties of the crown corks containing the sealing compounds containing the polymer mixtures PM _/ coated according to the invention as bottle closures

On a crown cork punch type PTC27 from Sacmi, Imola, Italy, metal sheets coated with adhesive on one side are processed into crown corks.

In a second step, ready-to-use crown caps are produced on a PM1200 and PM250 system from Sacmi, Imola, Italy, for the introduction of the polymer mixture PMI that makes up the sealant.

The test runs trouble-free and at optimal speed, the crown caps show good adhesion between adhesive varnish and sealant in laboratory tests. At pasteurization temperatures of up to 80 degrees C, the sealing compounds have a pressure maintenance of at least 8 bar.

Claims

Claims: 1. Sealing compound for mechanically sealing closures for vessels, consisting of polymer mixtures PM, composed of: A) at least one metallocene-free polyolefin, B) a polypropylene random copolymer, C) optionally a synthetic rubber, D) optionally fillers, and E) optionally further additives. 2. Dichtεmaεεen for mechanically sealing Schlüεεe according to claim 1, characterized in that the polymer mixtures PM 15 to 85 wt .-% of component A), 15 to 35 wt .-% of component B), 0 to 25 wt .-% Component C), 0 to 20 wt .-% of component D) and 0 to 5 wt .-% of component E). 3. Dichtungsmaεεen for mechanically sealing closures according to claim 1, characterized in that the polymer mixtures PM 25 to 60% by weight of component A), 20 to 30% by weight of component B), 5 to 20% by weight of the Component C), 5 to 20 wt .-% of component D) and 0.1 to 5 wt .-% of component E). 4. Method for producing a mechanically sealing closure, preferably made of metal or plastic, in particular for bottles or glasses. characterized in that the polymer mixture PM according to one of claims 1 to 3 is applied as an inner insert to the closure surface. Packaging container with a mechanically sealing closure, preferably made of metal or plastic, in particular for bottles or glasses, characterized in that the polymer mixture PM according to one of claims 1 to 3 is applied as an inner insert to the closure surface.