CA1077199A - Polymeric film - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A film formed from a copolymer of ethylene and at least one mono-.alpha.-olefine has a combination of impact strength and stiffness which is such that the function is at least 750. The function is preferably at least 1000 and may be several thousands. The film may also have a high tsar strength and good tensile strength.
The copolymer from which the film is formed is preferably one in which the comonomer contains at least 5 carbon atoms. The comonomer content of the polymer is typically in the range from 6.5 up to 30% by weight. The film can be produced by a tubular film technique using a temperature of 170-300°C. a circumferential expansion of 1.2 to 10.0 times and a draw down of 2.5 to 50 times.

Description

Po/Q 27657 The pre~ent invontion relates to fllm~ mado from polymeric materials and is part~cularly concern~d with fllm~ ~ade from olefin~ polymers.
Ac¢ordlng to the pres~t lnvention th~r~ 18 provid~d a film for~od from a copolym~r of othylone with at least one mono-a-ol~fino comonomor, said film boing such t~at th~ iqpact-~tiffhos~ functlon (ae her~inafter do~lned) la at lcast 750.
By impAct-sti~in~ss function i8 meant th~ rolatlon-~hlp:-; I~Pact stren~th(~) X ~Sti~n~ss Modulu~ (MNm 2)-100 F ~Icrons) The impa¢t ~tr~ngth is m~asured according to ; British Standard 2782; 1970, Method 306F. me stif~noss mOdUlU8 18 the 1% s~cant modulus moasurod according to ASTM Method D882-73, uslng te~t ~pocim~ns 10 incho~
by 0.5 lnch and a drawing speed of ons lnch per minut~.
Four msasur~ments are made ln the machine dir~ction and four ln the tran~verse directlon, and ~he geom~tric mean of thc averag~d values 18 taken as the stiffn~ss modulu~.
Tho lmpact-~ti~fh~s~ functlon i8 pref~rably at loa~t 1000, espoclally at loast 1250 ~nd may have ; a value of ffeveral thou~and~, for ~xample 5000.
It wlll be reallsed that tho ~ilm8 0~ the present lnvention posses~ a comblnation of toughness and stlffhess. Thus, films in accordance wlth th~ pr~sent : .
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P~/Q 27657 inventlon havinE a thickness of 30 microns, may have an impact strength as high a3 600 gramm~s. Films of thickness 150 mlcrons can have impact strengths whlch are greater than 1460 gramm~s. The stifi~ess modulus of the films l~ typlcally at least 200 MNm 2 and can be as high as 400MNm 2.
By way of contrast, it may be noted that the i~paot-~tlffnes~ i~Lnction of i?ilms formed from fr~e radical ethylene polymers or copolymers, 18 typlcally in the range 300 to 400.
In addition to an impact-stl~fnes~ ~unction of at least 750, many filmY in accordance with the present lnvention al~o haw a tear strength, (measured a¢cording to British Standard 2782 Method 308B) whlch is at least 5 g/~icron, and may be as high as 35 g/micron, of film thickness in one direction in the film. Preferably the tear strength iB at least 5 g/micron in both the machine and the tran~ver~e direction, and i8 especially at least 7 g1micron in both tho machine and the tran~verse directlon.
Many of the films al~o have a tensile strength at broak (~easur~d according to IS0 Recommendation 1184, 1970 at a ~tralning rate of 500 mm~minute) of at lea~t 20 MN/n~, preferably at lea~t 30 MN/m~.

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Po/Q 27657 1077~99 The tensile strength at break typically does not exceed 50 MN/~2.
Additionally the film has a r~latively high elongation at break (measured according to IS0 Recommendation 1184, 1970 at a straining rate of 500 mm per minute) of at least 300% and may be a3 h1Eh as 1100%.
All of the foregoing properties (impact ~trength, stiffness modulu~, tear strength, tensile strength at break and % elongation~ are determined at ambient temperature on a sample of the film as prepared.
Particularly preferred films in accordance with the invention combine all of the ~oregoing characteristics.
15 Thus, there is provided a film formed from a copolymer of ethylene with at least one mono--olefine comonomer, said film having an impact-stiffness function of at least 750, a tear ~trength of at lea~t 5 grammes and not more than 35 grammes for each micron of film thicknesR in at least one direction in the film, a tensile strength at break of at least 20 MN/m~
and not more than 50 MN/D~, and an elongation of at least 300% and not more than 1100%, Films in accordance with the present in~ention have a density in the range from 915 up to 935 kg/m3, particularly up to 930 kg/m3, e~pecially up to 925 kg/m3.
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:: -Po/Q 27657 The ~elt flow index of the film (measured at l90DC with a weight of 2.16 kg using the technique of ASTM Method 12~8-62T) is typically from 0.05 up to 0.7, preferably from 0.1 up to 0.3.
In addition to having an impact-stif~hess function of at least 750, it i8 preferred that the films of the present invention also po~ses~ a "~ecol1dary function"
(a8 hereafter defined) of at least 18000.
By "secondary function" is meant the relationship:-I act stren~th ~) X St~ffhess modulus ~MND 2) ~Fil~ thicknes~ (microns)]-5 The secondary function shows les~ var~ation with the thickness of the film than 18 shswn by the `~ impact-stiffnes~ function.
The copolymers from which the fil~s are formed are preferably copolymers of ethylene with a comonomer which i8 at least one mono-a-ole*ine at least 50%
molar of the mono-a-olefine having 5 or more carbon atoms. Although in the preferred copolym~r the co-monomer may include not re than 50~ lar of a mono-a-olefine having less than 5 carbon atoms, ~or e~ample butene-1, it is preferred that ~he comonomer contalns only no-a-olefines having at lea3t 5 carbon atoms. The comonomer conveniently contains not ~ore than 12 carbon atom~, preferably not more than 10 .
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Po/Q 27657 1077~99 and ~peclally not more than 8 carbon ato~. The comonom~r i~ co~veni~ntly a linear mono-a-o~efine, particularly h~xene-1.
The copol~m~r3 l?rom Yhich th~ films are formed typically contain th~ comonomer in an amount of from 6.5 up to 30% by w~ight, of the copolymer, pref~rably from 8.0 up to 27~ by w~ight of tho copolymer. If the ccpolymer i~ a copolymer containing hex~n~-1, the amount Or hoxone-1 18 typlcally from 6.5 up to 16.5% by weight Or the copolymer, preferably from 8.0 up to 15% by weight of the copolymer. If the comonomer 18 pentene-1, the a~ount of p~ntone-1 pr~ent in th~ copolymer i8 fro~ 6.5 up to 20X, pr~i?erably from 7.2 up to 16.5% by wei~ht; if the como~omer ; 15 i~ 4-methylpentcne-1, tho ~ount Or 4-methylpentene-1 pre~ent ln the copolymer i8 from 6.5 up to 18.0%, pr~ferably from 7.2 up to 16.5% by ~elght; and ir tho comono~er i8 decen~-1, the amount o~ doceno-1 pros~nt in the copolymer i~ from 7.5 up to 2~%, preferably i~rom 9 up to 21.5% by woight.
A particularly ~uitable copolym~r from which the fil~ of the prosent invention can be formod i~ a copoly~er of ethylene with a comonomor wh$ch i~ at least one mono-a-olefine, at l~ast 50~ molar ` 25 of the mono--olofine which i9 the comonoD~r ha~ing :' :~ - 6 -.. ~ :.............. .....
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Po/Q 27657 1~77~99 5 or more carbon atomfi, th~ copoly~r ha~lng an ann~aled d~n~ity (a~ hcreina~tor dofined) in the rango from 918 up to 940 kgJ~3, pro~rably from 920 up to 935 ~ m3, an apparent Ylscosity (as h~relna~t~r dofin~d) mcasured at a temperature of 200C and a sh~ar rate of 100 sec 1 in the range rrom 0.5 x ~03 up to 3.0 x 103 NAm 2, pre~erably 1.3 x 103 up to 2.4 x 103 NJm 2, and a viscosity m~sured at a temp-rature of 200C and a atress of 103N/~ which is at least 2A~ (1-6A x 10 ), pre~2rably at least 3.5~e (1-6A x 10 ), and not more than 1000A, preferably not mor* than : 500A, where A 18 th~ apparent vi~coslty at 200C
and a ~hear rate of 100 sec 1.
The term "annealed den~ity~ is used herein to refer to the denslty moasurod as doscrib~d ln ASTM
1928/70, Method A, u8ing a density gradlent column at 23C and ~aking allo~anco for resldual quantitles o~ polymerlsation catalyst to give the ~an~oaled densityH, uslng the ralationship:-Pc e (l-A) p ~ ~8 P8 - APm where 18 tho "annealed donslty~;
p~ i8 the measured denslty of the total polym~r product including catslyst re~ldues;
PB is th~ density of the catalyst ~upport andJor catalyst; and ' ' . .' - ' ' ' '. :

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' ,' , . ' , ~, P~/Q 27657 ~a77~99 A is the weight fraction of th~ catalyst support and/or cataly~t in the pol~er as calculated ~rom the a~h levels.
me "apparent viscosity of the polym~r is meaAured using a capillary viscometer and ls defined by the relationship~ ~ r4P
' 8Ql' where ~ i5 the apparent viscosity in Nsm 2;
r is the die radius in mm;
P is the pressure drop across the d~e $n Nm 2 a 1~ the volume flow rate in mm3sec 1; and 1 i8 the length of the die in m~.
The viscosity at a stress of 10 ~/m~ i8 convenlently measured using the cone and plate technique.
Films ln accordance with the present invention have a combination of properties which makes them particularly suitable for use in heavy duty fllm applications, such as, for example, sacks for fertilisers, tarpaulins, carrier bags and liners for refuse container~
The films of the present invention can be for~ed by any film forming technique such a~ extrusion through a slot die or by a tubular film technique. A particularly convenient technique of producing the films of the in~ention i~ by extrusion of a polymer through an annular die and inflating the extrudate.
~ore particularly, a film i~ obtained by extruding a copolymer of ethylene with at least one mono-a-olefine .. . .

~77199 Po/Q 27657 comonomer through an annular die maintained at a temperature in the range from 170 to 300C, blowing the extrudate to give a circumferential expansion of from 1.2 up to 10.0 ti~es, and a draw down (as hereinafter defined) of from 2.5 up to 50 times.
By "draw down" i8 meant the ratio:-die ~a~
~inal film thickness ~he die temperature 18 preferably in the range 200 to 250C, the circumferential eexpansion i~ con-veniently up to 5.0 times especlally from 1.3 up to 3.0 times and the draw down 18 preferably ~rom 5 up to 30 times.
me film production process will now be de~cribed with reference to the accompanying drawing which is a diagrammatic representation of a system suitable for the production of a tubular film.
In the drawing, an extrusion machine 1 is provided with an up~ardly aIigned annular die 2. An air pipe 3 passes through the die 2. A cooling ring 4, provided wlth a number of alr lnlets S, i8 secured above the dle 2, the cooling rlng 4 and die 2 being separated by an insulating plate 6.
Se~eral pair~ of guide rolls 7 are located above the cooling ring 4 and directly above the guide rolls 7 is located a pair of nlp rolls 8. Between the nip ' . ' . : ~

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Po/Q 27657 ~077199 rolls 8 and a wind up roll 9, are located a series of guide rolls 10.
In ~orming a film, an ethylene copolymer is pas~ed through the extru~ion machine 1 and the die 2, which is maintained at a suitable temperature, for example 210C.
A tubular extrudate 11 is formed and this is stretched in a linear direction, as a result of the relative rates of extrusion and of wind up, and i8 also expanded circumferentially by air pas~ed into the extrudate through the air pipe 3. The extrudate ~s cooled b~
a~r ~rom the cooling ring 4 and forms a bubble 12.
The bubble 12 is flattened by the guide rolls 7, drawn off through the nip rolls 8 and wound up on the wind `~ 15 up roll 9.
m e position of the cooling ring 4 may be varied : from that shown and in particular the cooling ring , 4 may be spaced apart from the die 2, in which ca3e the circumferential expan~ion of the extrudate 11 to give the bubble 12j may occur wholly or partially ,~ within the cooling ring 4.
. In another variation, the guide rolls 7 are replaced : by a pair of upwardly converging bubble guide plates.
Other variations in the apparatus and technique used .~ 25 are possible as is known in the art.

.. - 10 -~ Po/Q 27657 In order that the present lnvention may more readily be understood, various embodimonts thoreof are d~crib~d in the following examples whlch are lllustratlve of the ~nvention.
EXAMPLE$ 1 T0 10 Four ~thyl~ne-hoxon~-1 copolymers having dirferent charactoristics and on~ ethyleno-but2ne-1 copolyDer w~re iormed into film using an upwardly oxtrudlng laboratory, tubular film extrusion unlt, having conventional air coolin~ facilities for the ~ubble, und~r the following conditlons.
m~ oxtruder had a 1.5 inch dia~eter 8cr~w, with a length to diamot~r ratio of 18:1, and ~a oporated at ~elt and dio temperaturee of 230C.
The die wa~ of 76.2 mm diamot~r and had an annular die gap of 1m~. The film was blo~n to gi~ a circum-rorential oxpanslon o~ 2.5:1 and rllms o~ 3~, 90, 100 and 150 microns thicknoss ~oro produced. The unit wa~ operat~d at a rate of 10 kg/hour. The chara¢teri~tlcs of the polymer~ used ar~ summarlsed in Tablo 1, and ~n Tablo 2 aro ~et out the propertle~
o~ the fil~ produced, together with propertle~
0~ film8 formod in a similar manner u~ing a free radlcal polyethylene o~ melt flow lndox 0.3 and anncaled den~ity 924 kg~3.

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~ . Po/Q 27657 ~077~99 Note~ to Table 1 a) Annealed d~nslty is measured by ASTM 1928/70, M~thod A, at 23C and includ~s a corr~ction for tho pr~nce of catalyst re~idu~s.
b) Ma~surcd U31ng $n~ra-red technlqu~s u~ing a math~matical compari~on of the absorbanco ~ur~e from 1310 to 1430 cm 1 with two ~tandard polg-ethylene~ of known methyl count. A corroction WaB then made i'or those met~yl groups whlch are ends o~ molecules by substracting the m~thyl count o~ a linaar ethylene homopolymer made using the ~ame catalyst system and ha~ing sub-8tantlally the same Molecular Welght dlstribution .. and th~ ~ame M@I. In Polymor E, the comono~cr .
i8 buten~-1.
c) M~asured at 1gOC with a weight of 2.16 kgm u8ing the technique of ASTM ~ethod 1238O62T.
d) Measured at 200C, UBing a caplllary vlscometer havlng a dle 32 mm in l~ngth and 2 mm in diametcr ;~.
and a viscomoter barrel dlameter of 22.2 mm, u~ing the rolationship:

8Ql e) M~asured at 200C, using a cone and plate technlque Wlth Q 5 cm diamater cone ha~ing a 4 cone : 25 angle on a Wei~senberg Rheogoniometer typ~
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Po/Q 27657 1077~99 f) Mea~ured by the tochnique of ASTM M~tho~ D2289 at a draw rate of 20 in~he~ per se¢ond with a test specimen according to British Standard 903 Part A2 but with an effective gauge length of 0.75 inch (instead of ono in~h), the t~t ~pecim~n having been annealed b~ immer~ion in water at 100C ~or on~ hour and then allo~ing the w~ter and specim~n to cool to ambiont t~mporatura.
g) Determined a~ indlcated under note (b),but no correction ~a~ mado for moth~l group~ whl~h are the end of molecules.
h) The optical don~ity por cm of a mouldod samplo of approximate thlcknoss 0.020 lnch 18 doter~inod at 910 cm 1. The sample 1~ brominated by i~mor~lon in liquid bromin~ at room t~mperaturo ~or 20 minuto~, and the 8Emple i~ drled overnight.
Th~ optlcal den~ity per cm of the samplo is ag~in d~termlned at 910 cm 1. Tho difforenco betwe~n the two optical donsitlea iB ~U~ to un~aturatlon and thls dl~eronce X 0.126 gl~8 ~inyl grOUp8 per 1000 carbon atoms.

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; 5 . : ' ' :., .~: ' ' ' ' ' ' `' ~ ' . ~ ' --- 1077~9 Po/Q 27657 Notes to Table 2 * Thi8 polymer i8 a com~ercially availabl~ free radlcal poly~thyl~ne polymer o~ m~lt flow lnd~x 0.3 and annealed d~nsity 924 ~ m3.
i) Impact strength was measurod accordlng to Brltish Standard 27~2, 1970, MRthod 306F.
J) Dct~rmined ac¢ording to British Stand~rd 27B2;
1970 Method 308B.
k) MD m~ans Machine Direction.
TD moans Transvorso Direction.
l) Tonsile measurements on th~ films wero carri~d and m) out on sp~cimens 10 mm wide by the method descrlbed in IS0 Rocom~ndation 11~4, 1970, at a straining rato of 500 mm per minute.
n) Th~ film st1r~noss values quotod are the 1%
~ocant moduli moasur~d according to ASTM Method D882-73. Four test speci~ens, 10 in&hes by 0.5 lnch are u~d ln both the transverse and the machlne dire¢tlon. A drawing speod o~
one inch per mlnute l~ employed. Tho figure ~uotod i8 the g~ometric mean of the averagod valuos measured in the transvcr~o and machine ; dlrections.
p) The relatlon~hip:
Face ~ act 8tr~n~ith (~3 x [Sti~rhesa Modulus (MNm c 88 m crons -100]

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Po/Q 27657 ~77 ~99 q) The relationship:-Face i~Dact strenoth (~) X Stiffne8B M~dulus (MNm 2) LFilm thickness (microns)3-5 Polymer A was formed into film of thickness 150 microns at a ratc of 23 kg/hour using a larger ~xtruder to that used in Examples 1 to 10. The extruder had a 63.5 mm dlsmeter ~crew with a length to diameter ratio of 25:1 and a 3:1 compre~sion ratio. The melt and die te~peratures were both 200C and the ~ilm w08 bl~wn to give a circumferential expQnsion of

2.0:1. All other conditions were as de~cribed in kxamples 1 to 10. m~ ~ilm obtain~d had ths i'ollowing prop0rtie~:
I2pact strength (i) 1460 g Tear Strength (~) MD(k) 8.1 g/m~cron TD(k) 11.9 g/mlcron Tensile str~ngth (l) MD(k) 33.3 MNm 2 at break TD(k) 32.9 MNm 2 . Elongation to Break (m) MD(k) 670~
TD(k) 760%
Stifi~ess Modulu~ (n) 240 MNm 2 I~pact-stiffness $unction (p) 1365 Secondary function (q) 27700 (i) to (q) are a8 dei~ined in the notes to Tabl~ 2.

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~~ Po/Q 27657 ~077199 EXAMPLES 12 T,0 16 Copolymers of ethylene with pentene-1~ decene-1 or 4-methylpentene-1 wore ~ormed into film following the procedure o~ Exampl~s 1 to 10 with th~ exceptions that the melt and die temp~rature~ wero 225C and, when forming film of 30 microns thickn~ss, the clrcum-farential oxpansion was 3.0:1.
The characteristics of the polymers used are ~ummaris~d in Table 3 and in Table 4 ar~ s~t out the propertl-~ o~ tho nl~ produced `
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Claims (17)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A film formed from a copolymer of ethylene with at least one mono-.alpha.-olefine comonomer wherein the film has an impact strength and a stiffness modulus which are such that an impact-stiffness function of the film as defined by the relationship has a value of at least 750.

2. The film of Claim 1 having an impact strength and a stiffness function which are such that the impact-stiffness fuction has a value of at least 1000.

3. The film of Claim 1 which has a stiffness modulus of from 200 MNm-2 up to 400 MNm-2.

4. The film of Claim 1 which has a tear strength of at least 5 g/micron of film thickness in both the machine and the transverse direction in the film.

5. The film of Claim 4 which has a tear strength Or at least 7 g/micron of film thickness in both the machine and the transverse direction in the film.

6. The film Or Claim 1 which has a tensile strength at break, measured at a straining rate Or 500 mm/minute, which is at least 20 MN/m2 up to 50 MN/m2.

7. The film of Claim 1 which has an elongation at break, measured at a straining rate of 500 mm/minute, which is from 300 up to 1100%.

8. The film of Claim 1 which has an impact strength and a stiffness modulus which are such that the relationship has a value of at least 18000.

9. The film of Claim 1 which is formed from a copolymer of ethylene and a comonomer which contains only mono-.alpha.-olefines having at least 5 carbon atoms.

10. The film of Claim 9 which is formed from a copolymer which contains from 6.5 up to 30% by weight of the copolymer of comonomer.

11. The film of Claim 10 which is formed from a copolymer which contains from 6,5 up to 16,5% by weight of the copolymer of hexene-l.

12. The film of Claim 1 which is formed from a copolymer of ethylene with a comonomer which is at least one mono-.alpha.-olefine, wherein at least 50% molar of the mono-.alpha.-olefine which is the comonomer has 5 or more carbon atoms, and the copolymer has an annealed density in the range from 918 up to 940 kg/m3, an apparent viscosity measured at a temperature of 200°C and a shear rate of 100 sec-1 in the range 0.5 x 103 up to 3.0 x 103 Nsm-2 and a viscosity measured at a temperature of 200°C and a stress of 103 N/m2 which is at least 2Ae (1.6A x 10-3) and not more than 1000A, where A is the apparent viscosity at 200°C and a shear rate of 100 sec-1.

13. A fertiliser sack, tarpaulin, carrier bag or liner for a refuse container which is formed from the film of Claim 1.

14. A process for the production of a polymeric film which comprises extruding a copolymer of ethylene with at least one mono-.alpha.-olefine comonomer through an annular die, maintaining the die temperature in the range from 170°C to 300°C, blowing the extrudate to give a circum-ferential expansion of from 1.2 up to 10.0 times and drawing the extrudate to give a draw down of from 2.5 up to 50 times.

15. The process of Claim 14 which comprises extruding a copolymer which is a copolymer of ethylene with a comonomer which is at least one mono-.alpha.-olefine, wherein at least 50% molar of the mono-.alpha.-olefone which is the co-monomer is a mono-.alpha.-olefine which has 5 or more carbon atoms, and the copolymer has an annealed density in the range from 918 up to 940 kg/m3, an apparent viscosity measured at a temperature of 200°C and a shear rate of 100 sec-1 in the range from 0.5 x 103 up to 3.0 x 103 Nsm-2, and a viscosity measured at a temperature of 200°C
and a stress of 103 N/m2 which is at least 2Ae (1.6A x 10-3) and not more than 1000A, where A is the apparent viscosity at 200°C and a shear rate of 100 sec-1.

16. The process of Claim 14 which includes blowing the extrudate to give a circumferential expansion of up to 5.0 times.

17. The process of Claim 14 which includes drawing the extrudate to give a draw down of from 5 up to 30 times.