Sterilizable PVC-free closures

Abstract

The present invention relates to compositions (compounds) which can be used as seal material in vessel caps under sterilization conditions. More specifically, the invention relates to such compositions that are suitable for vessel caps or vacuum caps that can be unscrewed, such as cam screw caps and in particular Press-on/Twist-off caps, and that demonstrate a reduced migration of undesirable substances.

Claims

1. A vessel cap made of metal or plastic for a vessel for receiving foods or beverages, comprising a seal insert made of a seal material which comprises at least three different polymers mixed with further substances, wherein the seal material comprises no polyvinyl chloride (PVC), wherein the seal material is substantially free from components that are liquid at application temperature, wherein the seal material has a Shore A hardness between 40 and 95, wherein the seal material comprises at least three different polymers, wherein the first polymer is a propylene polymer and/or propylene copolymer, the second polymer is a thermoplastic elastomer, and the third polymer is a polyolefin elastomer, wherein the seal material is composed such that the seal insert withstands a sterilization at temperatures of above 100 C. and up to 132 C., and wherein the seal material, in a dynamic mechanical thermal analysis (DMTA), demonstrates a heating curve for the phase angle tan (delta) the inflection point of which lies above the required sterilization temperature.

2. The vessel cap according to claim 1, wherein the inflection point lies in a region of the heating curve, which corresponds to the softening of the seal material on the whole and lies around at least 10 C. above the intended sterilization temperature.

3. The vessel cap according to claim 1, wherein the inflection point lies in a temperature range of the heating curve in which phase transitions of individual components at lower temperatures are already substantially complete.

4. The vessel cap according to claim 1, wherein the seal material, in relation to the total weight of the seal material, comprises a minimum content of 5% by weight of styrene-based block copolymer and a minimum content of 10% by weight of a propylene polymer and/or propylene copolymer.

5. The vessel cap according to claim 1, wherein the vessel cap corresponds to an inner diameter of the vessel opening of more than 2.5 cm.

6. The vessel cap according to claim 1, wherein the vessel cap is a lug screw cap, a cap that can be pressed on and twisted off, a hooded lid, a crimp-on or single-use cap, or a metal cap that can be rolled on.

7. The vessel cap according to claim 1, wherein the seal material is formed such that the seal insert can be used during a heat treatment (with or without pressure) of the filled vessel for the purpose of sterilization (above 98 C.).

8. The vessel cap according to claim 1, wherein the vessel cap, in the closed state, has a gas barrier effect and/or the effect of a pressure relief valve.

9. The vessel cap according to claim 1, wherein the vessel cap, in the closed state, demonstrates vacuum retention.

10. The vessel cap according to claim 1, wherein the Shore A hardness of the seal material is between 40 and 95 and the seal material, in the compression set test similar to ASTM D395-97 method B under the conditions of 22 h/70 C., demonstrates a compression set (CS) of 25-90%.

11. The vessel cap according to claim 1, wherein the seal material contains between 0.1 and 80% of at least one block copolymer, wherein the block copolymer is an interpolymer of ethylene with at least one C.sub.3-C.sub.20 alpha olefin or a copolymer of ethylene with a C.sub.3-C.sub.20 alpha olefin, optionally in combination with other unsaturated monomers.

12. The vessel cap according to claim 11, wherein the block copolymer has a density from 0.85 to 1.1 g/cm.sup.3 and a melt flow index (WI) from 0.01 g/10 min to 1,000 g/10 min, with a production of 5 kg at 190 C.

13. The vessel cap according to claim 11, wherein the block copolymer is formed from an ethylene and an alkene.

14. The vessel cap according to claim 11, wherein the seal material contains between 0.1% and 80% of at least one random copolymer, wherein the random copolymer is a linear interpolymer of ethylene and a C.sub.3-C.sub.20 alpha olefin or a branched interpolymer of ethylene and a C.sub.3-C.sub.20 alpha olefin.

15. The vessel cap according to claim 14, wherein the random copolymer has a density from 0.85 to 1.1 g/cm.sup.3 and a melt flow index (MFI) from 0.15 g/10 min to 100 g/10 min.

16. The vessel cap according to claim 15, wherein the random copolymer comprises two alkenes selected from the group consisting of ethylene, propene, butene, hexene and octene.

17. The vessel cap according to claim 11, wherein the seal material comprises up to 50% of polyolefins.

18. The vessel cap according to claim 1, wherein the seal material has a Shore A hardness from 65 to 90.

19. The vessel cap according to claim 1, wherein the compression set of the seal material under the conditions of 22 h/70 C. is between 55% and 75%.

20. The vessel cap according to claim 1, wherein the seal material contains between 5% and 70% of SEBS and between 10% and 50% of a propylene(co)polymer.

21. The vessel cap according to claim 20, wherein the seal material comprises between 20% and 50% of SEBS, and up to 25% of polyethylene, up to 50% of PP, and /or up to 50% of PP-based elastomer.

22. The vessel cap according to claim 1, wherein the seal material comprises a polyester.

23. A vessel for beverages or foods, comprising the vessel cap according to claim 1.

Description

5. DETAILED DESCRIPTION OF THE INVENTION

(1) The compositions according to the invention generally comprise at least one polymer, usually two chemically and physically different polymers, and additionally a third polymer that is chemically and physically different from the two aforementioned polymers; are suitable for a pasteurizing, in particular also for a sterilizing, post-treatment (at temperatures above 100 C. and up to 132 C.), and/or have a Shore A hardness between 40 and 95, preferably 45 to 90, more preferably between 50 and 85 (in particular between 70 and 85), both under the conditions of 30 min/20 C. and 24 h/20 C. and have a compression set CS (in percent, similarly to ASTMD 395-97, method B under the conditions of 22 h/70 C.) between 40 and 95, more specifically between 50 and 90, preferably between 50 and 80, particularly preferably between 50 and 70, and specifically between 50 and 60. Here, it is desirable in accordance with the invention for the CS under the conditions of 22 h/20 C. to lie below 20, and under the conditions of 22 h/100 C. to lie below 95, specifically below 90 and particularly preferably between 80 and 90.
5.1 Preferred Embodiments with 3 Polymers

(2) In some preferred embodiments, the PVC-free sealing compound is a mixture that comprises at least three different plastics, which will be referred to hereinafter as plastic 1, plastic 2 and plastic 3.

(3) The PVC-free composition according to the invention preferably comprises plastic 1 plastic 2 plastic 3 optionally plastic 4, optionally at least one liquid component optionally at least one lubricant optionally at least one stabilizer, optionally at least one pigment, and/or optionally at least one filler.

(4) At least one plastic in this embodiment is a substantially non-resilient, thermoplastic polymer. A typical example is polypropylene (PP).

(5) The other plastics are then preferably resilient thermoplastic polymers and/or thermoplastic elastomers.

(6) A distinction is usually made between two types of resilient thermoplastics: (A) block copolymers and (B) elastomer alloys.

(7) Plastic 1, plastic 2 and/or plastic 3 may be block copolymers or polymer alloys. In the context of the present invention, the terms plastic 1, plastic 2 and plastic 3 are to be understood broadly. Plastic 1, plastic 2 and plastic 3 may be pure substances (for example a block copolymer, a homopolymer, etc.) or may be mixtures (for example a polymer blend, a polymer alloy, etc.). If plastic 1, 2 and/or 3 is/are a polymer blend or a polymer alloy, the PVC-free composition according to the invention comprises more than three different types of polymer.

(8) It has now surprisingly been found that the problem addressed by the present invention can be solved in preferred embodiments of the invention by a PVC-free composition which comprises plastic 1, plastic 2 and plastic 3, which are appropriately selected in a targeted manner from the large number of aforementioned, known plastics.

(9) Plastic 1 is preferably a polymer (or a polymer mixture), which primarily has the properties of a thermoplastic. In very preferred embodiments, plastic 1 is a conventional thermoplastic, for example polypropylene or a similar polyolefin.

(10) In contrast hereto, plastic 2 is preferably a thermoplastic elastomer. In a particularly preferred embodiment, plastic 3 is a material such as SEBS.

(11) In accordance with the invention, plastic 3 is preferably a resilient thermoplastic, which constitutes a balanced compromise between an elastomer and a thermoplastic. In a specific embodiment, plastic 2 is an olefin copolymer.

(12) In a preferred embodiment of the invention, the composition according to the invention comprises no compounds of which the polymeric main components consist of 39-40% of ethylene octene block copolymer and 45-60% of ethylene octene random copolymer, in particular if a content of up to 10% PP is additionally present.

(13) In certain embodiments of the invention, the primary polymer component is a thermoplastic elastomer or a resilient thermoplastic, in particular selected from SEBS, propylene-based elastomers and terpolymers.

(14) A preferred embodiment of the present invention is illustrated schematically in FIG. 1.

(15) 5.1.1 Relationships Between Plastic 1, Plastic 2 and Plastic 3

(16) The selection of the plastics 1, 2 and 3 according to the invention can differ considerably depending in part on the field of application. Nevertheless, at least one of the relationships listed below between plastics 1, 2 and 3 is applicable irrespective of the type of vessel cap.

(17) In preferred embodiments of the invention, a number, or even all, of the following relationships apply:

(18) Minimum Temperature at which Plastic Deformation is Possible:

(19) plastic 1<plastic 3<plastic 2

(20) Glass Transition Temperature (T.sub.g),

(21) plastic 1>plastic 3>plastic 2

(22) Shore A Hardness,

(23) plastic 1>plastic 3>plastic 2

(24) Modulus of Elasticity

(25) plastic 1>plastic 3>plastic 2

(26) Compression Set (22 h/70 C.)

(27) plastic 1>plastic 3>plastic 2

(28) 5.1.2 Selection Of Plastic 1, Plastic 2 and Plastic 3

(29) Plastic 1, plastic 2 and plastic 3 are preferably known, commercially available plastics. On the basis of the above details concerning compression set, Shore A hardness, glass transition temperature, etc., a person skilled in the art is able to identify suitable, commercially obtainable plastics, polymers, polymer alloys, etc.

(30) The following trade products can be considered for example as plastic 1: metallocene-catalyzed polypropylene, such as Metocene HM; and other polyolefins, for example PE, LDPE.

(31) Inter alia, the following trade products can be considered for plastic 2: SEBS, for example Taipol or Kraton; OBCs such as Infuse.

(32) Inter alia the following trade products can be considered for plastic 3: resilient thermoplastics, for example POEs such as Engage, Vistamaxx.

(33) 5.1.3 Quantities

(34) The proportions by weight of plastic 1, 2 and 3 in the PVC-free composition according to the invention may vary depending on use.

(35) The proportion by weight of plastic 1 typically lies in a range from above 0% by weight to 80% by weight, in relation to the total weight of the PVC-free composition according to the invention. The proportion by weight of plastic 1 preferably lies in a range from 10% by weight to 70% by weight, in relation to the total weight of the PVC-free composition according to the invention. The proportion by weight of plastic 1 most preferably lies in a range from 10% by weight to 50% by weight, in relation to the total weight of the PVC-free composition according to the invention.

(36) The proportion by weight of plastic 2 typically lies in a range from above 0% by weight to almost 100% by weight, more specifically up to 70% by weight, in relation to the total weight of the PVC-free composition according to the invention. The proportion by weight of plastic 2 preferably lies in a range from 10% by weight to 50% by weight, in relation to the total weight of the PVC-free composition according to the invention. The proportion by weight of plastic 2 most preferably lies in a range from 20% by weight to 35% by weight, in relation to the total weight of the PVC-free composition according to the invention.

(37) The proportion by weight of plastic 3 typically lies in a range from 10% by weight to 50% by weight, in relation to the total weight of the PVC-free composition according to the invention. The proportion by weight of plastic 3 preferably lies in a range from 15% by weight to 40% by weight, in relation to the total weight of the PVC-free composition according to the invention. The proportion by weight of plastic 3 most preferably lies in a range from 20% by weight to 40% by weight, in relation to the total weight of the PVC-free composition according to the invention.

(38) A person skilled in the art understands that the sum of the % by weight of plastic 1, plastic 2 and plastic 3 may at most be 100% by weight. If the sum of the % by weight of plastic 1, plastic 2 and plastic 3 is less than 100% by weight, the PVC-free composition comprises further components.

(39) 5.1.4 Further Optional Components

(40) The composition according to the invention may optionally comprise a liquid component, such as white oil, in particular in the case of compounds that comprise a thermoplastic elastomer, such as SEBS. Such compounds may be suitable for sterilization, but are less suitable for fatty filled contents.

(41) The composition according to the invention may further comprise lubricants. The purpose of the lubricant is to reduce the twist-off resistance.

(42) Conventional components, such as stabilizers, pigments, fillers and the like may additionally also be provided in conventional small proportions.

(43) 5.1.5 Exemplary Embodiments

Exemplary Embodiment 1

(44) TABLE-US-00001 plastic 1 polypropylene 10% by weight plastic 2 olefin block copolymer 48.8% by weight plastic 3 polyolefin elastomer 40% by weight lubricant 0.6% by weight stabilizer 0.3% by weight pigment 0.3% by weight
Shore A hardness (24 h/20 C.)=78
CS (22 h/70 C.)=59

(45) This sealing compound is extremely suitable for fat-containing filled contents and can be pasteurized, but cannot be sterilized. It can be used at counterpressure up to 98 C., without counterpressure up to a maximum of 105 C.

Exemplary Embodiment 2

(46) TABLE-US-00002 plastic 1 polypropylene 26% by weight plastic 2 SEBS 27% by weight plastic 3 polyolefin elastomer 38% by weight adhesion promoter polyester 8% by weight lubricant 0.5% by weight stabilizer 0.2% by weight pigment 0.3% by weight

(47) This sealing compound is suitable for PT caps. It is suitable for fatty filled contents and can be sterilized.

(48) Shore A (24 h/20 C.)=78

(49) CS (22 h/70 C.)=69

Exemplary Embodiment 3

(50) TABLE-US-00003 plastic 1 polypropylene 35% by weight plastic 2 olefin block copolymer + 44% by weight SEBS plastic 3 polyolefin elastomer 20% by weight lubricant 0.5% by weight stabilizer 0.5% by weight
Shore A (24 h/20 C.)=90

(51) This embodiment is suitable for fatty filled contents and can be sterilized. It is suitable for PT caps.

(52) 5.2 Preferred Embodiments with Plastics 1 and 2

(53) In other preferred embodiments, the third plastic can be omitted and is then often replaced by a component that is liquid at the application temperature (typically RT), in particular an oil extender.

(54) Such embodiments generally contain (in relation to the total weight of the sealing compound) at least 5% by weight of a thermoplastic elastomer, preferably based on styrene. Styrene-based block copolymers, such as SBS, SEBS, SIBS, are preferred. The compound particularly preferably contains at least 5% by weight of a styrene ethylene butylene styrene block copolymer (SEBS) and a minimum content of 10% of a polyolefin polymer. PP or HDPE are suitable as polyolefin components, even when mixed with LDPE and/or LLDPE.

(55) Such sealing compounds often contain significant quantities of oil, up to more than 50% by weight, but preferably between 5% by weight and 50% by weight and particularly preferably between 35% by weight and 50% by weight.

(56) White oil (with suitable viscosity, for example viscosity 70) is the most preferred oil component.

(57) These sealing compounds can be pasteurized and can usually also be sterilized.

(58) 5.2.1 Exemplary Embodiment 4

(59) A preferred embodiment according to this aspect of the invention has the following composition:

(60) TABLE-US-00004 plastic 1 polypropylene + LDPE 25% by weight plastic 2 SEBS 33% by weight oil component white oil 40% by weight lubricant 1% by weight stabilizer 1% by weight
Shore A (24 h)=68
CS (22 h/70 C.)=27

(61) These embodiments are particularly suitable for seal inserts that do not come into contact with fat-containing filled contents. It can be used for PT caps and can be sterilized.

(62) 5.3 Embodiments with Just One Plastic

(63) Most compounds with just one polymer (besides a lubricant, stabilizer and the like) are not suitable for the purposes of the invention. Compounds with a non elastomeric thermoplastic (for example most of the PP types) as the only polymer are too hard and are not resilient enough. By contrast, compounds with an elastomeric thermoplastic or thermoplastic elastomer are too soft.

(64) An exception is constituted by poly(ethylene-co-propylene)-based compounds, which can be processed with contents of conventional lubricants, etc., to form a sealing compound according to the invention.

(65) The poly(ethylene-co-propylene) forms the primary component of the sealing compound, which preferably has no (or only very minor) contents of other polymers.

(66) These polymers have a density (ISO 1183) from 0.8 to 1.0, preferably 0.86 to 0.9 g/cm, and specifically approximately 0.88 g/cm, and a melt flow rate (MFR, ISO 1133) from 10 to 40, preferably 25 to 29 g/10 min, in particular approximately 27 g/10 min.

(67) Seal inserts produced therefrom are hard (Shore D (15 see, ISO 868) in the range of 25-30, in particular of approximately 28), can be used for fatty filled contents, and are suitable for PT caps. They can also be sterilized.

(68) The suitability for sterilization can be ascertained on the seal material by appropriate tests.

(69) A prediction of this suitability is possible by means of the known dynamic mechanical thermal analysis (DMTA). In principle, the heating curve for the phase angle (tan) delta is determined for this purpose, of which the inflection point should lie sufficiently (generally at least 10 C.) above the intended sterilization temperature.