AU650866B2 - Sliding, anti-blocking and optical quality compositions based on ethylene copolymers of low cristallinity - Google Patents

Abstract

The sliding, anti-blocking and optical quality compositions are comprised of at least one ethylene copolymer having a cristallinity not exceeding 30 %; they are characterized in that they further include an efficient quantity of ethylene-bis-oleamide. Said compositions may be conveniently used for the fabrication of plates with a thickness comprised between 1 and 10 mm approximately, and particularly for the production of films with a thickness comprised between 10 and 500 mu m approximately.

Description

TEXT FOR FOREIGN FILING CASE 5412 SLIPPERY, ANTIBLOCKING AND OPTICAL QUALITY COMPOSITIONS BASED ON ETHYLJENE COPOLYMIERS OF LOW CRYSTALLINITY.

The present invention relates to compositions based on ethylene copolymers of low crystallinity, exhibiting good optical, antiblocking and slip properties, and to industrial articles, especially fibres and sheets, obtained from these compositions.

In the industry for coaverting plastics into films the term 'blocking" refers to the phenomenon of adhesiveness of a film to itself, which can have many causes, especially an excessively high extrusion temperature, but also the very nature of the plastic to be extruded. To avoid this blocking phenomenon during extrusion and then subsequently on the reels of film, and to make it easy to open the polymer sleeve obtained by blow-extrusion, it is usual to add to the polymer 'ft. various additives whose function it is to modify the too, state of the film surface, especially by migration t t 20 towards the surface. This is especially the case with ethylene homopolymers and copolymers. Conventional additives are inorganic fillers such as silica, or got organic ones such as certain unsaturated fatty acid ft ,~,amides containing at least 8 carbon atoms, in particular stearic, oleic, palmitic, erucic, myristic, ft behenic and lauric amides.

*food A~qFor example, European Patent No. 060,178

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2 describes an antiblocking composition based on ethylene polymer containing from 200 to 2500 ppm of talc.

The abovementioned conventional additives are completely satisfactory insofar as the antiblocking function is concerned in the case of ethylene polymers and copolymers of intermediate and high crystallinity, that is to say those whose crystallinity, determined by X-ray diffraction, is at least approximately 30%: this means in particular high density polyethylene (approximately 0.96 to 0.97), radical low density polyethylene (approximately 0.92 to 0.93) and linear low density polyethylene, that is to say copolymers of ethylene and of at least one alpha-olefin containing from 3 to 8 carbon atoms which have a density approximately from 0.91 to 0.95. In fact, in the case of all these polymers, the addition of approximately up to 2% of the abovementioned antiblocking fillers does not have an unfavourable and appreciable effect on other, especially optical and mechanical, properties required in the films.

tilt The situation is completely different in the case of ethylene copolymers of low crystallinity, that is to say those whose crystallinity, determined by X-ray diffraction, is lower than or equal to approximately 30%. In this case, in fact, an Iappreciable deter:ioration in the optical properties of the films is noted, due to the fact that much higher proportions (which can go up to 10%) of the 3 conventional additives would be necessary to reduce the blocking to an acceptable level. In some extreme cases such as, for example, that of a copolymer containing by weight of ethylene and 30% by weight of methyl acrylate, not only are the optical properties greatly degraded but also the blocking remains 25 times higher than the generally accepted level, despite the addition of 10% of a usual antiblocking filler such as talc.

A first problem which the invention is aimed at solving consists therefore in choosing a filler which, when incorporated in an ethylene copolymer of low crystallinity such as defined above, makes it possible to avoid the blocking phenomenon without, however, appreciably deteriorating the optical and/or mechanical properties of the films extruded from this copolymer.

Furthermore, the slippery nature of a thermoplastic is also an important parameter for the conversion industry, where it is necessary to avoid the sticking of the stock in the guidance systems of 8 automatic machines. This slippery nature is generally r evaluated using a static or dynamic friction coefficient on the outer face, which measures the ratio 8 of the traction force to be applied to initiate or maintain the sliding of the two faces to the force which applies them against each other. For a regular use, without difficulties in manufacture, most conversion machines require a coefficient of friction P ~F C 4 on the outer face not exceeding approximately 0.2.

Until now this result has been achieved by incorporating into the ethylene polymer a mixture of metal salt and of fatty acid and of a saturated fatty amide, for example a mixture of zinc stearate and of erucamide. While being efficient, this solution has the practical disadvantage of making it necessary during the conversion to meter out and monitor two ingredients in very low proportions in relation to the plastic forming the main constituent.

A second problem which the invention is aimed at solving consists therefore in choosing an additive which, when incorporated into an ethylene copolymer of low crystallinity such as is defined above, makes it possible by itself to achieve a coefficient of static or dynamic friction on the outer face not exceeding approximately 0.2.

The present invention is based on the surprising discovery that the two problems set out above can be solved simultaneous3y by incorporating an effective quantity of ethylenebisoleamide containing an i ethylene copolyer of low crystallinity.

A first subject of the present invention relates, therefore, to a slippery, antiblocking and optical quality composition comprising at least one 'Itethylene copolymer with a crystallinity not exceeding *approximately 30%, characterised in that it t a additionally comprises an effective quantity of ethylenebisoleamide of formula: 0 0 ir II

CH

3

(CH

2 7 -CH=CH- (CH 2 7 -C-NH- (CH) 2 -NH-C- (CH 2 7 -CH=CH- (CH 2 7

-CH

3 An effective quantity means a quantity which is sufficient to reduce the blocking and/or the coefficient of dynamic or static friction on the outer face of the composition to a level which is acceptable for the conversion of the said composition as a function of the characteristics of the conversion machine and as a function of the intended final application. In the majority of cases the required properties are: a coefficient of static or dynamic friction on the outer face not exceeding approximately 0.2, a blocking, determined according to the method described below, not exceeding a value of I 1 *described below, not exceeding a value of ~"ti

J

I It approximately 20 g, an optical haze, determined according to ASTM standard D-1003, not exceeding approximately 13%.

20 Among the ethylene copolymers of low crystallinity which can form part of the constitution of the composition according to the invention there may be mentioned especially polar ethylene copolymers which have a comonomer content of at least approximately 0.09 mol per 100 g of copolymer, such as: 6 copolymers of ethylene and of at least one alkyl acrylate or methacrylate whose alkyl group has from 1 to 10 carbon atoms (these including particularly ethylene/methyl acrylate copolymers containing at least 8% by weight of acrylate, copolymers of ethylene and of at least one vinyl ester of a saturated carboxylic acid containing 2 to 6 carbon atoms, such as vinyl acetate or vinyl propionate, ethylene/alkyl (meth)acrylate/unsaturated dicarboxylic acid anhydride terpolymers (comprising up to 15 mol% of (meth)acrylate and up to 3 mol% of anhydride such as maleic anhydride) such as are described in Patent FR-A-2,498,609, ethylene/unsaturated glycidyl monomer copolymers and ethylene/unsaturated ethylenic monomer/unsaturated glycidyl monomer terpolymers comprising up to 50% by weight of a glycidyl monomer such as glycidyl methacrylate and acrylate, mono- and diglycidyl itaconate, mono-, di- and triglycidyl butenetricarboxylate and, if appropriate, up to 45% by weight of an ethylenic monomer such as a vinyl ester of a saturated carboxylic acid containing from 2 to 6 carbon atoms, an acrylate or methacrylate of a saturated alcohol containing from 1 to 8 carbon atoms or an j ttt ester of maleic acid with a saturated alcohol containing from 1 to 18 carbon atoms, such as are

CA

I F/IZ 7 described in Patent FR-A-2,130,279, ethylene/unsaturated dicarboxylic acid anhydride/polyol poly(meth)acrylate copolymers (comprising up to 3 mol% of anhydride, up to 0.4 mol% of polyol poly(meth)acrylate and if appropriate up to 13.6% of alkyl (meth)acrylate) such as are described in Patent EP-A-312,459, ethylene/alkyl (meth)acrylate/unsaturated dicarboxylic acid N-carboxyalkylimide copolymers (comprising up to 14 mol% of alkyl (meth)acrylate, up to 3 mol% of N-carboxyalkylimide and, if appropriate, up to 3 mol% of unsaturated dicarboxylic acid anhydride), these being obtained by reacting an aminoalkylcarboxylic acid with an ethylene/alkyl (meth)acrylate/unsaturated dicarboxylic acid anhydride terpolymer at a temperature of between 150" and 300°C.

Among the ethylene copolymers of low I I crystallinity falling within the scope of the present invention there may also be mentioned copolymers of ethylene and of at least one alpha-olefin containing from 3 to 8 carbon atoms, whose density is not higher than 0.910, such as: copolymers of density approximately between 0.905 S 25 and 0.910 in accordance with European Patent No. 070,220, copolymers of density approximately between 0.890 AL>- Io 7020 a 8 and 0.905, generally comprising from 6 to 10 mol% of alpha-olefin, copolymers of density approximately between 0.860 and 0.890, such as especially: polyolefin rubbers marketed by Mitsui under the trademark Tafmer®, consisting of copolymers of 78 to 92 mol% of ethylene and 8 to 22 mol% of an alpha-olefin chosen from propylene and 1-butene, having a density of 0.860 to 0.890, having a residual crystallinity of 1 to 14%, a crystalline melting temperature J of 75 0 C, which have a geometric mean molecular mass of 60 to 120 kg/mol and a polydispersity index of between 2.2 and 2.7, polyolefin rubbers consisting of ethylene/propylene and/or 1-butene copolymers having a melt index of approximately between I 0.3 and 15 dg/min and a density approximately between 0.865 and 0.885, comprising from 77 I' to 91 mol% of units derived from ethylene and from 9 to 23 mol% of units derived from propylene and/or 1-butene, characterised by a crystalline melting temperature J of approximately between 100" and 125C.

Subsidiarily these polyolefin rubbers according to the invention may be characterised by at least one of the I ~1 t

I'\

following elements: a polydispersity index of approximately between 3.5 and 15, preferably approximately between 4 and 8, a geometric mean molecular mass (defined as shown below) of approximately between and 70 kg/mol, a relationship between the density d and the content x (expressed in mol%) of units derived from propylene and from 1butene which is expressed by the double equation: 0.9084 s d 0.002 x s 0.918 *4 4 p *p.4 S9 #5 p pr p i4 p 4r 444.: p a residual crystallinity (determined according to the method described below) of approximately between 3 and The crystalline melting temperature J means the temperature determined at the maximum of the melting curve after crystallisation obtained by 20 subjecting the copolymer sample to the following threestage process: melting at the rate of 8°C per minute from up to 150*C, then crystallisation at the rate of 8°C per minute 25 from 150°C to 10°C, then again melting at the rate of 8"C per minute from i.-1 ,hi i J-- 0 C up to 150 0

C.

The residual crystallinity is determined by X-ray diffraction on a copolymer sample which has been subjected to cooling at the rate of 5°C per hour from 190°C to room temperature.

The geometric mean molecular mass is defined by the mathematical relationship: i=N log 10 Mg E W i log 1 0

M

i i=l where Wi is the weight fraction of material of mass Mi and N is the number of fractions eluted using permeable gel chromatography.

Such polyolefin rubbers can be obtained by a process consisting in copolymerising, at a temperature approximately from 160 to 270 0 C and at a pressure approximately from 400 to 850 bars, a gas stream containing approximately from 18 to 42% by volume of ethylene and approximately from 58% to'82% of propylene 20 and/or 1-butene, in the presence of a Ziegler-type I'.oo catalyst system comprising, on the one hand, at least one compound of a transition metal of groups IVB, VB, VIB and VIII of the Periodic Classification and, on the other hand, at least one organoaluminium compound and, 25 if appropriate, in the presence of at least one chain 1 i transfer agent. The catalyst system may additionally r" i I? ,r comprise at least one aluminium or magnesium halide. To obtain the copolymers which have the characteristics described above and in which the molar ratio of units derived from propylene/units derived from 1-butene exceeds 0.5, the composition of the gas stream subjected to the copolymerisation will be preferably such that the propylene/1-butene volume ratio exceeds approximately 0.3, depending on the nature of the catalyst system employed. The choice of the latter, in fact, has an influence, known to the specialist, on the relative reactivity of ethylene, propylene and 1-butene in the copolymerisation and consequently on the tendency for the units derived from propylene or else the units derived from 1-butene to be preferentially incorporated into the macromolecular chain.

The composition according to the invention may obviously comprise a mixture of two or more copolymers such as are described above. Besides one or more such copolymers, the composition may also comprise another thermoplastic polymer in the case of which the blocking, slip and optical property problems are usually solved by means of other additives, such as especially: an ethylene polymer or copolymer with a crystallinity which is higher than 30%, such as, for example, high density polyethylene (approximately 0.96 to 0.97), radical low density polyethylene (approximately 0.92 to

S

9 9 9. 0 9 *9 9 99 9'' .9i 9 9 9 999 9999 12 0.93) and copolymers of ethylene and of at least one alpha-olefin containing from 3 to 8 carbon atoms, which have a density approximately from 0.91 to 0.95, a propylene polymer or copolymer comprising at least 85 mol% of units derived from propylene and not more than 15 mol% of units derived from ethylene or from an alpha-olefin containing from 4 to 8 carbon atoms.

The ethylene copolymer of low crystallinity forming part of the constitution of the composition according to the invention generally has a melt index determinedat 190°C under 2.16 kg according to ASTM standard D-1238 of approximately between 0.1 and 10 dg/min. The same applies in the case of the ethylene polymer or copolymer of a crystallini.ty which is higher than 30% which may be present as a mixture with the ethylene copolymer of low crystallinity.

The proportion of ethylenebisoleamide to be 20 incorporated into the composition according to the S, invention depends on a number of parameters, 4,,d especially: the nature and the proportion of the comonomers present with ethylene in the copolymer of low crystallinity, the melt index of the copolymer of low q t crystallinity, t the thickness of the measurement specimen, iot let 13 the level of the required properties (blocking, slip, optical haze) and the property compromise which is accepted as a function of the method of conversion of the composition and of the intended application of the converted article.

The choice of the proportion of ethylenebisoleamide is within the reach of the specialist, taking into account the following general indications: in most cases it is recommended to employ a proportion of ethylenebisoleamide which is proportionately higher: the lower the crystallinity of the ethylene copolymer, that is to say the higher the comonomer content and when the comonomer is an alpha-olefin the lower the density, the higher the melt index of the ethylene copolymer of low crystallinity, the lower the value expressing the required 20 slip characteristic, according to the method described below.

In the case of the majority of ethylene copolymers of low crystallinity the required properties can be reached by means of the use of not more than 0.8% by weight, preferably approximately 0.1 to 0.6% by weight, of ethylenebisoleamide relative to the ethylene copolymer of low crystallinity.

Although the additional use of conventional

I

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14 additives presents the disadvantages recalled in the preamble of the present description, in some cases, if desired, it will be possible to add to the composition according to the invention: at least one conventional antiblocking additive such as silica, talc or saturated fatty amide, preferably in a proportion not exceeding approximately 1% by weight of the composition, and/or at least one slip-improving additive such as a fatty acid metal salt (for example zinc stearate), a saturated fatty amide (for example erucamide) or ethylenebisstearamide, preferably in a proportion not exceeding approximately 1% by weight of the composition.

In addition, the composition according to the invention may comprise, in a manner which is known per se, at least one conventional additive for ethylene copolymers, such as: 20 an antioxidant such as, for example, a sterically hindered phenol, a mercaptan or a phosphorite, ultraviolet radiation absorbers such as Ssubstituted benzophenones, substituted phenylbenzotriazoles and sterically hindered amines, t- extinguishers such as nickel complexes, an inorganic or organic pigment such as zinc oxide or titanium oxide.

cb When the composition according to the invention is intendEl for special applications such as, for example, the manufacture of films for ca..ricultural use, which must offer a sufficient resistance to some climatic conditions (exposure to ultraviolet or infrared radiation), it may additionally comprise an effective quantity of one or more additives capable of providing these special properties, for example: approximately from 1 to 15% by weight of dehydrated kaolinite, in accordance, for example, with Patent US-A-4,075,784, with a view to forming a barrier to infrared radiation, approximately from 0.5 to 4% by weight of iron oxide of gamma crystallographic form, in accordance, for example, with Patent FR-A-2,347,405, with a view to manufacturing a thermal opaque film, a mixture of approximately from 10 to 200 ppm of an ionic iron salt and approximately from 10 to 1000 ppm of sulphur, in accordance, for example, with Patent FR-A-2,199,757, with a view to manufacturing a photodegradable film, ,zinc oxide, in accordance, for example, with Patent EP-A-006,049, with a view to manufacturing a transparent film for packaging products capable of being damaged by ultraviolet radiation, a mixture of biodegradable particles such as natural starch and of a substance capable of _;FLc~ c ^cr

B

16 undergoing autooxidation to form a peroxide and/or a hydroperoxide, in accordance, for example, with Patent FR-A-2,252,385.

The compositions according to the invention can be prepared by any means permitting the dispersion of ethylenebisoleamide and, if appropriate, the other additives in the ethylene copolymer of low crystallinity. It is thus possible to employ an internal mixer, an extruder or a calender, the mixing temperature being advantageously below 200°C and preferably at least 120 0

C.

The compositions according to the invention find advantageous applications for the manufacture of sheets with a thickness of approximately between 1 and 10 mm and, above all, for the manufacture of films with a thickness of approximately between 10 and 500 pm.

Sheets comprising a composition according to the invention can be obtained by compression and injection moulding techniques. Films comprising a composition S: 20 according to the invention can be obtained by extrusion through a flat die or else by blow-extrusion at a ij temperature which is preferably approximately between 100*C and 180°C and with a blow ratio preferably approximately between 1.5 and The examples below are given by way of illustration without limiting the present invention.

EXAMPLES 1 and 2 ,r A copolymer with a melt index (determined at till III'.: -i 17 190"C under 2.16 kg according to ASTM standard D-1238) of 2.5 dg/min, containing 84.5% of ethylene and 15.5% by weight of methyl acrylate is considered. This copolymer has a crystallinity, determined by X-ray diffraction, of 19%. X parts by weight of ethylenebisoleamide are added to 100 parts by weight of this copolymer by mixing in a twin-screw Brabender mixer operating at a temperature of 110°C and 150°C and at a speed of 40 rev/min. The mixture obtained is then extruded into film with a thickness of 50 pm on a Troester B 30 extruder under the following conditions: temperature profile: 120*C to 170 0

C,

die diameter: 40 mm, gap: 1 mm, blow ratio: screw speed: 90 revolutions per minute, haul-off speed: 4 metres per minute.

The following are measured on the film obtained: 20 the optical haze H, expressed as a percentage and V Sdetermined according to the method of NF standard T 54 111, the blocking B, expressed in grams and determined according to the following method, described with reference to the attached figure. A sample of film is placed between two rectangular plates (2) and 100 mm x 76 mm in size. The ends and of the film extending beyond the plates are

IY

v *1 -;iiiopened and fastened to the outer part of the plates with an adhesive. The two plates are placed horizontally between the jaws and of a tensile testing machine. The upper plate is connected to the upper jaw of the machine by means of a chain permitting the plate to move in all directions (Figure la). The plate is then moved vertically at a speed of 36 mm per minute. In a first stage (Figure Ib) the method consists in determining the force F, needed to separate the two film layers. The second stage (Figure Ic) consists in determining the force F 2 to be applied to move the plate once the two film layers are separated. The blocking B is defined by the relationship B F 1

-F

2 The table below shows the properties obtained as a function of the quantity X of ethylenebisoleamide.

EXAMPLES 3 to 6 (Comparative) t t

~I~

The operating procedure of Example 1 is reproduced with the same copolymer but with ethylenebisoleamide replaced with: a talc marketed by Talcs de Luzenac under the name 100 MOOS (Examples 3 and 4), ethylenebisstearamide (Examples 5 and 6).

25 The properties obtained as a function of the quantity X of additive are shown in the table below.

19

TABLE

Examples 1 2 3 4 5 6 X 0.25 0.75 1.0 5.0 0.25 0.75 B 20 15 180 20 60 H 10.3 8.8 15.6 49.4 9.3 14.9 It EXAMPLE 7 A copolymer with a melt index (determined at 190"C under 2.16 kg according to ASTM standard D-1238) of 0.3 dg/min, containing 84.5% by weight of ethylene and 15.5% by weight of methyl acrylate, is considered.

This copolymer has a crystallinity of 19%. 0.5% by weight of ethylenebisoleamide are added to 100 parts of this copolymer by mixing under the conditions of Example 1. The mixture obtained is then extruded into film with a thickness of 180 pm under the conditions of Example 1.

The following are measured on the film obtained: a dynamic friction coefficient, determined according to NF standard T 54 112, equal to 0.06, a blocking, determined according to the method described in Example 1, equal to 6 g.

EXAMPLES 8 to k r v The operating procedure of Example 7 is reproduced with the same copolymer but with ethylenebisoleamide replaced with: 1% of zinc stearate (Example in this case the dynamic friction coefficient is equal to 0.87 and the blocking is equal to 8 g, 0.5% of ethylenebisstearamide (Example in this case the dynamic friction coefficient is equal to 1.20 and the blocking is equal to 30 g, a mixture of 1% of talc, 0.25% of ethylenebisstearamide and 1% of zinc stearate (Example 10): in this case the dynamic friction coefficient is equal to 0.87 and the blocking is equal to 5 g.

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Claims (9)

1. Slippery, antiblocking and optical quality composition comprising at least one ethylene copolymer with a crystallinity not exceeding characterised in that it additionally comprises an effective quantity of ethylenebisoleamide and has an optical haze according to ASTM standard D 1003 not exceeding 13%.

2. Composition according to Claim 1, characterised in that the ethylene copolymer is a polar copolymer of ethylene which has a comonomer content of at least 0.09 mol per 100 g of copolymer.

3. Composition according to Claim 2, characterised in that the polar copolymer of ethylene is chosen from the copolymers of ethylene and of at least one alkyl acrylate or methacrylate whose alkyl group has from 1 to 10 carbon atoms, the copolymers of ethylene and of at least one vinyl ester, ethylene/alkyl (meth)acrylate/unsaturated dicarboxylic acid anhydride terpolymers, ethylene/unsaturated glycidyl monomer copolymers and ethylene/unsaturated ethylenic monomer/unsaturated glycidyl monomer terpolymers, ethylene/unsaturated dicarboxylic acid anhydride/polyol poly(meth)acrylate copolymers and ethylene/alkyl (meth)acrylate/unsaturated dicarboxylic acid N- S° carboxyalkylimide copolymers.

4. Composition according to Claim 1, characterised in that the ethylene copolymer is a copolymer of ethylene and of at least one alpha-olefin containing from 3 to 8 carbon atoms, whose density is not higher than 0.910g/cm3. Composition according to any one of Claims 1 to 4, characterised in that it additionally comprises an ethylene polymer or copolymer with a crystallinity which is higher than 30% or a propylene polymer or copolymer.

I' 22

6. Composition according to any one of Claims 1 to 4, characterised in that the ethylene copolymer has a melt index of between 0.1 and 10 dg/min.

7. Composition according to any one of Claims 1 to 6, characterised in that it comprises not more than 0.8% by weight of ethylenebisoleamide relative to the ethylene copolymer with a crystallinity not exceeding

8. Composition according to any one of Claims 1 to 7, characterised in that it additionally comprises at least one additive chosen from antiblocking agents, slip-improving additives, antioxidants, ultraviolet radiation absorbers, extinguishers and inorganic and organic pigments.

9. Film with a thickness of between 10 and 500 Im, obtained from a composition according to any one of Claims 1 to 8. DATED this 3rd day of May, 1994. ATOCHEM o WATERMARK PATENT TRADEMARK ATTORNEYS THE ATRIUM 290 BURWOOD ROAD o HAWTHORN VICTORIA 3122 AUSTRALIA i t'