LASER-MARKABLE SEALING COMPOUNDS WITH OXYGEN ABSORBERS

Abstract

Receptacle closure made of metal, with a sealing insert that is arranged in the receptacle closure in such a way that it comes into contact with the mouth of the receptacle when the receptacle closure is positioned on the receptacle, wherein the sealing insert contains or is made from a sealing compound that includes at least 10% by weight, preferably at least 40% by weight LDPE relative to the total weight of the sealing compound, in particular with butene, hexene or octene as comonomer besides contents of LLDPE and/or OBC and a content of more than 2% by weight of at least one oxygen-absorbing compound, preferably sodium sulfite.

Claims

1. A closure for a receptacle, the closure made of metal with a sealing insert that is arranged in the receptacle closure in such a way that it comes into contact with the mouth of the receptacle when the receptacle closure is positioned on the receptacle, wherein the sealing insert comprises a sealing compound that includes at least 10% by weight LDPE relative to the total weight of the sealing compound, and a content of more than 2% by weight of at least one oxygen-absorbing compound.

2. The closure according to claim 1, in which the sealing compound further includes at least one SEBS or SIBS styrene block copolymer.

3. The closure according to claim 1, in which the sealing compound further includes a content of 5 to 40% by weight oil relative to the total weight of the sealing compound.

4. A closure for a receptacle, the closure made of metal with a sealing insert that is arranged in the receptacle closure in such a way that it comes into contact with the mouth of the receptacle when the receptacle closure is positioned on the receptacle, wherein the sealing insert comprises a sealing compound that includes contents of polyolefin and at least one oxygen-absorbing compound, wherein the closure has a non-zero content of at least one laser marking substance.

5. The closure according to claim 4, in which the laser marking compound is a component of the sealing insert.

6. The closure according to claim 4, in which the laser marking compound comprises metal particles.

7. The closure according to claim 4, in which the closure contains up to 1% by weight, laser marking compound.

8-10. (canceled)

11. The closure according to claim 1, where LDPE is present in said sealing insert in an amount of at least 40% by weight.

12. The closure according to claim 1, said oxygen-absorbing compound comprising sodium sulfite.

13. The closure according to claim 1, said sealing insert further comprising, as one or more comonomers, one or more of butene, hexene, or octene

14. The closure according to claim 1, said sealing insert further comprising, as one or more comonomers, one or more of LLDPE or OBC.

15. The closure according to claim 2, said styrene block copolymer being present in a proportion of 10 to 40% by weight relative to the total weight of the sealing compound.

16. The closure according to claim 3, said oil comprising white oil having a kinematic viscosity at 40 C. of 60 to 150 cSt.

17. The closure according to claim 4, said polylefin comprising LDPE.

18. The closure according to claim 6, said laser marking compound comprising metal particles based on antimony oxide, tin antimony oxide, and/or aluminum.

19. The closure according to claim 7, in which the closure contains up to 0.1% by weight laser marking compound.

Description

[0027] Advantageous embodiments of the invention are defined in the dependent claims.

[0028] The invention provides sealing materials that absorb oxygen for longer than conventional sealing materials suitable for laser marking without sacrificing their sealing effect.

[0029] Surprisingly, it was found that with a combination of laser marking additives with alkali metal sulfites having particular particle sizes (D.sub.90<20 m, measured by laser light scattering) in sealing materials, even laser-engraved QR codes after several weeks of forced aging (i.e. storage at elevated ambient temperature of 38-42 C.) exhibited improved rather than degraded scannability.

[0030] Surprisingly, a large bandwith with tolerated additives and matrices was also found for marking with infrared (IR) laser (wavelength approx. 1064 nm fibre laser/Nd:YAG).

[0031] The invention may be used with a variety of closures that have a full-area seal inserted, particularly crown corks, ringpull caps, aluminium closures, and plastic closures.

[0032] The seal is preferably permanently attached to the closure, but it may also be provided as a disc fitted in the closure.

[0033] The seal according to the invention provided in the closure guarantees scannability with commercially available smartphone cameras.

[0034] Preferred additives for the laser marking include: [0035] Aluminium-based additives (metal particles), [0036] Additives based on antimony oxide and/or tin antimony oxide.

[0037] The additives for the laser marking are used in quantities that are harmonised with the requirements of the seal. Typical embodiments contain <1% by weight laser marking additive. Often, smaller contents are sufficient, e.g. 0.1%, or <0.01%, or even just <0.005%.

[0038] White pigments such as titanium dioxide (TiO.sub.2) may be contained, but do not have to be used, particularly with progressive cloudiness/white discolouration of the seal during use, good contrast is maintained even without the addition of the pigment, allowing scannability. The addition enables a consistent appearance for the entire period of use of the closure system, and better visualisation or look.

[0039] In all cases, sealing compounds of the invention contain a polyolefin component, preferably in a quantity of 30 to 80% by weight relative to the total quantity of sealing compound. In preferred embodiments, the polyolefin component consists mainly of LDPE. In other embodiments, it contains, usually additionally, (co-)polyolefins such as HDPE, LLDPE, PP, propylene-ethylene copolymers, copolymers with contents of butene, octene and the like.

[0040] Preferred embodiments of the sealing compounds contain styrene block copolymers such as OBCs and SBCs, mostly in quantities of 10 to 40% by weight relative to the total quantity of sealing compound.

[0041] Preferred embodiments of the invention contain 5 to 40% by weight medicinal white oil in the sealing compound. If SBS is used, an SBS/white oil proportion greater than 2:1 is preferred: if SEBS and/or SEEPS is/are used, a proportion greater than 0.7:1 is preferred.

[0042] In preferred embodiments of the invention, the sealing compound contains up to 20% by weight EVA relative to the total quantity of sealing compound.

[0043] The oxygen absorbing compound content preferably consists of sodium sulfite, and is generally above 2% by weight, preferably from 3 to 20% by weight Na.sub.2SO.sub.3, particularly preferably 4 to 15% by weight sodium sulfite, here too relative to the total quantity of sealing compound.

[0044] TiO.sub.2 or other white pigments (e.g., Ba.sub.2SO.sub.4) may be used as the pigment.

[0045] The following recipes according to the invention are particularly suitable for the use stated in each case:

TABLE-US-00001 Twist crown % Med. white oil 31 SEBS (styrene cont. 29-33%) 25 LLDPE 15 Na.sub.2SO.sub.3 10 LDPE 10 coPP 8 Additives 0.7 TiO2 0.3 100.0

TABLE-US-00002 Pry-off crown % LDPE 40.5 SBS (29-31% styrene cont.) 22 Med. white oil 11 LLDPE 18 Na.sub.2SO.sub.3 8 TiO.sub.2 0.300 Stabilisers 0.2 100.0

TABLE-US-00003 Ringpull 1 % LDPE 76.5 LLDPE 15 Na.sub.2SO.sub.3 8 TiO.sub.2 0.3 Stabilisers 0.2 100

TABLE-US-00004 Ringpull 2 % LDPE 81.5 OBC 10 Na.sub.2SO.sub.3 8 Stabilisers 0.2 TiO.sub.2 0.3 100

[0046] In all cases, the scavenger content is significantly higher than in WO 2022/174887; surprisingly, the expected problems with reading/scanning due to cloudiness or the like did not arise, even though the sodium sulfite used here (particle size D.sub.90<20 m, measured by laser light scattering) is similar to the sodium sulfite according to WO2022/174887.

[0047] The aforementioned laser marking additives could be added to all of the recipes named above in the quantities required for marking, up to 1% by weight, without loss of the sealing effect. Even without said laser marking additives, the sealing compounds described above are suitable for the purposes disclosed in WO 2022/174887.