Process for making film from low density ethylene hydrocarbon copolymer

• US 4,243,619 A
• Filed: 02/16/1979
• Issued: 01/06/1981
• Est. Priority Date: 03/31/1978
• Status: Expired due to Term

• Current Assignee: Union Carbide Corporation (Dow, Inc.)
• Original Assignee: Union Carbide Corporation (Dow, Inc.)
• Inventors: Fraser, William A., Cieloszyk, Gary S.
• Primary Examiner(s): Thurlow, Jeffery R.
• Application Number:
  US06/012,795
• Time in Patent Office: 690 Days
• Field of Search: 264/176 R, 264/40.1, 264/563-564, 264/565, 264/566, 264/569, 264/237, 264/216, 264/40.6, 264/210.1, 526/128
• US Class Current: 264/40.6
• CPC Class Codes: B29C 48/0012 combined with shaping by internal pressure generated in the material, e.g. foaming
• CPC Class Codes: B29C 48/0017 combined with blow-moulding or thermoforming
• CPC Class Codes: B29C 48/0018 combined with shaping by orienting, stretching or shrinking, e.g. film blowing B29C48/0017 takes precedence
• CPC Class Codes: B29C 48/022 characterised by the choice of material
• CPC Class Codes: B29C 48/10 flexible, e.g. blown foils
• CPC Class Codes: B29K 2023/06 PE, i.e. polyethylene
• CPC Class Codes: B29K 2105/04 cellular or porous
• CPC Class Codes: B29K 2995/0063 Density
• CPC Class Codes: B29K 2995/0073 smooth
• CPC Class Codes: B32B 27/322 comprising halogenated polyolefins, e.g. PTFE
• CPC Class Codes: C08J 2323/08 Copolymers of ethene C08J2323/16 takes precedence
• CPC Class Codes: C08J 5/18 Manufacture of films or sheets
• CPC Class Codes: C08L 23/06 Polyethene
• CPC Class Codes: C08L 23/0815 Copolymers of ethene with aliphatic 1-olefins
• CPC Class Codes: C08L 2666/06 Homopolymers or copolymers of unsaturated hydrocarbons; Derivatives thereof
• CPC Class Codes: Y10S 526/901 Monomer polymerized in vapor state in presence of transition metal containing catalyst
• CPC Class Codes: Y10S 526/904 Monomer polymerized in presence of transition metal containing catalyst at least part of which is supported on a polymer, e.g. prepolymerized catalysts

Abstract

A process for making film from a narrow molecular weight distribution low density ethylene hydrocarbon copolymer, which process comprises extruding said copolymer through a die gap of greater than about 50 mils. The film exhibits an excellent balance of optical and mechanical properties.

Claims

1. A process for forming blown tubular film essentially free of melt fracture from an extrudate formed from molten ethylene hydrocarbon copolymer,

said copolymer having been made from ≧

90 mol percent of ethylene and ≦

10 mol percent of at least one C₃ to C₈ alpha olefin monomer with a transition metal based catalyst and having a narrow molecular weight distribution and a melt index of about ≧

0.1 to about ≦

5.0 and being susceptible to melt fracture in blown tubular film form when extruded into such form through an extrusion die having a die gap of 15 to ≦

45 mils, which comprises extruding said copolymer into such form through an extrusion die having a die gap of greater than about 50 mils and at a drawdown ratio of greater than about 2 to less than about 250.

2. A process as in claim 1 in which said copolymer has a melt index of about >

0.5 to ≦

4.0.

3. A process as in claim 1 in which said copolymer has a density of about ≧

0.912 to ≦

0.940.

4. A process as in claim 3 in which said copolymer has a molecular weight distribution of about ≧

2.7 to ≦

3.6 and a total unsaturation content of about ≧

0.1 to ≦

0.3 C═

C/1000 C atoms.

5. A process as in claim 3 in which said copolymer has a melt flow ratio of about ≧

22 to ≦

36 and a total unsaturation content of about ≧

0.1 to ≦

0.3 C═

C/1000 C atoms.

6. A process as in claim 1 in which said copolymer has a molecular weight distribution of about ≧

2.7 to ≦

3.6.

7. A process as in claim 6 in which the alpha olefin comprises butene-1.

8. A process as in claim 7 in which the die gap is greater than about 50 to less than about 120 mils.

9. A process as in claim 8 in which said gap is greater than about 50 to less than about 90 mils.

10. A process as in claim 1 in which said film is formed at a drawdown ratio of about 25 to less than about 150.

11. A process as in claim 1 in which said copolymer is formed into film having a thickness greater than about 0.1 to about 20 mils.

12. A process as in claim 11 in which said film has a thickness of greater than about 0.1 to about 6.0 mils.

13. A process as in claim 12 in which said film has an ultimate elongation of greater than about 400 percent.

14. A process as in claim 12 in which said film has a puncture resistance of greater than about 7.0 in-lb./mil.

15. A process as in claim 12 in which said film has a tensile impact strength of greater than about 400 to about 2000 ft.-lbs./in³.

16. A process as in claim 12 in which said film has a tensile strength of greater than about 2000 to about 7000 psi.

17. A process as in claim 1 in which said film is formed from a composition comprising

about 99 to 80 weight percent of said ethylene hydrocarbon copolymer and,

about 1 to 20 weight percent of high pressure low density of polyethylene having a melt index of about 0.2 to about 5.0.

18. A process as in claim 17 in which said composition comprises about 2 to about 12 weight percent of said high pressure low density of polyethylene.

19. A process as in claim 18 in which said high pressure low density polyethylene has a melt index of about 0.2 to about 5.0.

20. A process as in claim 18 in which said copolymer has a melt flow ratio of about ≧

22 to ≦

36 and a total unsaturation content of about ≧

0.1 to ≦

0.3 C═

C/1000 C atoms.

21. A process as in claim 20 in which said copolymer has a molecular weight distribution of about ≧

2.7 to ≦

3.6.

22. A process as in claim 21 in which the alpha olefin comprises butene-1.

23. A process as in claim 22 in which the die gap is greater than about 50 mils to less than about 120 mils.

24. A process as in claim 23 in which said die gap is greater than about 50 mils to less than about 90 mils.

25. A process as in claim 1 wherein the extruded copolymer is cooled to form a frost line providing improved optical properties in the film product according to the following relationships:

space="preserve" listing-type="equation">45°

specular gloss=336.4 φ

.sup.-0.664

wherein

φ

is a cooling rate parameter

φ

=τ

(MI)⁰.29 [(Tm-Tc)/Tm]^-1

Tc=resin crystallization temp. (K°

)

Tm=compound temp. (K°

)

MI=resin melt index (grams/10 min.)

τ

=residence time of extrudate between the die and the frost line (sec.), and wherein

τ

is calculated assuming, that to a first approximation, extrudate extension between the die and the frost line height is a constant strain rate deformation, wherein ##EQU2## where FLH=frost line height (cm.)

V₁ =linear nip roll velocity (cm/sec)

V₀ =average linear extrudate velocity at the die exit (cm/sec) and is calculated as

space="preserve" listing-type="equation">V.sub.0 =Q/ρ

mπ

DG

where

Q=extruder output rate (grams/sec)

ρ

m=melt density (grams/cm³)

D=die diameter (cm) and

G=die gap (cm).