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US-12624134-B2 - Polymer composition for caps and closures

US12624134B2US 12624134 B2US12624134 B2US 12624134B2US-12624134-B2

Abstract

Polyethylene composition has a density of 949-955 kg/m 3 and a melt index MI 2 between 15 and 40 g/10 min, and comprises a low molecular weight fraction (A) and a high molecular weight fraction (B), wherein the amount of (A) is 52-58 wt % based on the weight of (A)+(B), and the melt index MI 2 of (A) is 200-600 g/10 min. Injection moulded articles, preferably caps or closures, made from the composition are also described.

Inventors

  • Pascale Godon
  • Luc Marie Ghislain Dheur

Assignees

  • INEOS EUROPE AG

Dates

Publication Date
20260512
Application Date
20211216
Priority Date
20201222

Claims (19)

  1. 1 . A polyethylene composition having a density of 949-955 kg/m 3 and a melt index MI 2 between 15 and 40 g/10 min, which comprises a low molecular weight fraction (A) and a high molecular weight fraction (B), wherein the weight fraction of (A) is 52-58 wt % based on the weight of (A)+(B), the melt index MI 2 of (A) is 200-600 g/10 min, and the high molecular weight fraction (B) has a density of 918-928 kg/m 3 .
  2. 2 . The composition according to claim 1 , which has an MI 2 of 19 to 37 g/10 min.
  3. 3 . The composition according to claim 1 , which has a density of 950-954 kg/m 3 .
  4. 4 . The composition according according to claim 1 , which has a molecular weight distribution (measured by GPC analysis) Mw/Mn of 5-10.
  5. 5 . The composition according to claim 1 , which has a SHI (1,100) of 2.5-8.
  6. 6 . The composition according to claim 1 , wherein the weight fraction of (A) is 53-57 wt %.
  7. 7 . The composition according to claim 1 , wherein the low molecular weight fraction (A) has an MI 2 of between 250 and 550 g/10 min.
  8. 8 . The composition according to claim 1 , wherein the high molecular weight fraction (B) has a density 920-926 kg/m 3 .
  9. 9 . The composition according to claim 1 , which has a density of 950 to 954 kg/m 3 , an MI 2 of between 20 and 35 g/10 min, a SHI (1,100) of between 2.5 and 8 and an Mw/Mn between 5 and 10.
  10. 10 . An injection moulded article comprising the composition as defined in claim 1 .
  11. 11 . The article according to claim 10 which is a cap or closure.
  12. 12 . The composition according to claim 1 , which has an MI 2 of 20 to 35 g/10 min.
  13. 13 . The composition according to claim 1 , which has an MI 2 of 22 to 32 g/10 min.
  14. 14 . The composition according to claim 1 , which has a density of 951-953 kg/m 3 .
  15. 15 . The composition according according to claim 1 , which has a molecular weight distribution (measured by GPC analysis) Mw/Mn of 7-10.
  16. 16 . The composition according to claim 1 , which has a SHI (1,100) of 3-6.
  17. 17 . The composition according to claim 1 , wherein the weight fraction of (A) is 54-56 wt %.
  18. 18 . The composition according to claim 1 , wherein the low molecular weight fraction (A) has an MI 2 of between 300 and 500 g/10 min.
  19. 19 . The composition according to claim 1 , which has a density of 950 to 954 kg/m 3 , an MI 2 of between 22 and 32 g/10 min, a SHI (1,100) of between 3 and 6 and an Mw/Mn between 7 and 10.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is the U.S. national phase of International Application No. PCT/EP2021/086246 filed Dec. 16, 2021, which designated the U.S. and claims priority to EP 20216471.1 filed Dec. 22, 2020, the entire contents of each of which are hereby incorporated by reference. The present invention relates to novel ethylene polymer compositions and to articles made therefrom, particularly articles made by injection moulding such as caps and closures. Injection moulding may be used to make a wide variety of articles including articles having relatively complex shapes and a range of sizes. A particularly important application is in the manufacture of caps and closures for food and drink applications, such as for bottles containing carbonated or non-carbonated drinks, or for non-food applications such as containers for cosmetics or pharmaceuticals. Important properties of the polymer to be injection moulded are its rheology, stiffness, environmental stress crack resistance (ESCR) and organoleptic properties, requirements for all of which need to be satisfied at the same time. Injection moulded articles, particularly caps and closures, may be in contact with aggressive food and non-food media and/or subject to external stress, e.g. when used as a cap for a carbonated soft drink, and for such applications a high ESCR is therefore desirable. High ESCR values are generally obtained with polyethylenes of lower density and/or lower melt index. On the other hand, injection moulded articles also require a high stiffness as this allows a reduction in wall thickness while maintaining good dimensional stability. Stiffness generally increases as density increases. It is also important in injection moulding that the polymer melt has the appropriate rheological properties, i.e. a flowability within certain limits to ensure that the final product properties are desirable. Certain applications, particular those in which the injection moulded article is larger or longer, require especially good flowability so that the polymer is able to flow to all areas of the mould when injected. Also, the higher the flow rate of the polymer melt, the greater the speed at which it can be injected into the mould and the shorter the processing time, which improves productivity. For improving the flow properties, polyethylenes with broader molecular weight distribution or with higher melt index are typically chosen. However, polymers with higher melt index tend to yield products having poor ESCR. Different applications may require a different balance of ESCR and processability. Monomodal polyethylenes are known commercially for use as caps or closures, an example being the Ineos product Rigidex® HD5226EA, which has a density of 953 kg/m3 and an MI2 of 26 g/10 min. Bimodal polyethylenes are also well known for such applications, as they can provide a better balance of properties. WO 2007/130515 discloses polyethylene compositions suitable for caps and closures having a density of 950-960 kg/m3 and a MI2 of at least 1 g/10 min, preferably 1-2 g/10 min. All the inventive Examples have an MI2 of 2 g/10 min or less. EP 1655338A discloses a polyethylene composition for caps and closures which has an MI2 of 0.1 to 100 g/10 min and a specific relationship between SHI1/1000 and log MI2. All the inventive Examples have an MI2 of 11 g/10 min or less and a density of at least 961 kg/m3, as well as an MI2 of the low molecular weight (LMW) fraction below 60 g/10 min. EP 1655336A also discloses a polyethylene composition for caps and closures having an MI2 of 0.1 to 100 g/10 min, preferably below 15 g/10 min. All the inventive Examples have an MI2 of about 1-2 g/10 min. WO 2011/004032 discloses a bimodal polyethylene composition for caps and closures having a density of 940-960 kg/m3 and a MI2 of 0.5-50 g/10 min, preferably 0.5-2.2 g/10 min. All the inventive Examples have an MI2 of 2 g/10 min or less. WO 2004/031291 and WO 2007/018720 disclose bimodal polyethylene compositions for injection moulding having an MI2 of 2-200 g/10 min, most preferably 4-10 g/10 min. All the inventive Examples have an MI2 of 11 g/10 min or less, and most contain at least 65 wt % of the LMW fraction. WO 2007/140114 discloses bimodal polyethylene compositions for injection moulded living hinges having an MI2 of 10-70 g/10 min, most preferably 45-55 g/10 min. Although the broadest disclosure suggests that the lower molecular weight ethylene component, which has an MI2 no higher than 150 g/10 min, can comprise as little as 30 wt % of the composition, the Examples all contain at least 75 wt % of the lower molecular weight ethylene component. WO 2007/140114 discloses bimodal polyethylene compositions for injection moulded articles such as containers, having an MI2 of 30-75 g/10 min, most preferably 45-55 g/10 min. The Examples have MI2 values above 45 g/10 min and densities below 948 kg/m3. WO 00/071615 closes bimodal polyethylene compositions for i