WO2000068314A1

WO2000068314A1 - Elastomeric polymer composition

Info

Publication number: WO2000068314A1
Application number: PCT/SE2000/000863
Authority: WO
Inventors: Eugene Denis; Jan Desimpel; Hans Eklind; Bill Gustafsson; Erik Van Praet
Original assignee: Borealis A/S
Priority date: 1999-05-05
Filing date: 2000-05-04
Publication date: 2000-11-16
Also published as: SE9901619D0; AU4637100A

Abstract

An elastomeric polymer composition is described which is characterised in that it comprises a crosslinkable ethylene-alkyl (meth)acrylate-unsaturated silane terpolymer that has an alkyl (meth)acrylate content of more than 5 mole %, an MFR2.16 at 190 °C, determined according to ISO 1133, Condition D, of at least 0.1 g/10 min, and that the composition has, after having been crosslinked, a hot set, determined according to IEC-811, of less than 400 %.

Description

ELA5TOMERIC POLYMER COMPOSITION

Technical field

The present invention relates to an elastomeπc polymer composition. Technical background For many products elasticity, i.e. the ability to undergo deformation and return to essentially the initial size and form after deformation is desirable or necessary. As examples of such products the following may be mentioned: seals, gaskets, profiles, bellows, bumpers, hoses, tubes, cables, tyres, fenders, membranes, tarpau- lmes, flooring materials, roofing materials, conveyor belts, foamed products, medical devices, building products, automotive products, films, sheets, coatings, etc. To prepare such products elastomeπc materials are used such as crosslmked rubbers and thermoplastic elastomers. However, conventional elastomeπc materials ha e several disadvantages. Thus, elastomeπc rubber materials have to be prepared m specific rubber processing equipment and it is normally not possible e.g. to use equipment for processing of polymers such as polyethylene or polyvmyl chloride. Further, special curing equipment is needed for the curing. Moreover, the curing involves sulphur or peroxides which generate an unpleasant smell. Also, the curing rate is a bottleneck which limits the productivity. To this comes the disadvantage that the resistance of conventional elastomeπc materials to the effects of air, oxygen, ozone and high temperatures as well as to the effects of solvents, like mineral oils and non-polar chemicals, often is rather poor. In view hereof it would be an important progress m the art if an elastomeπc composition could be obtained which overcomes the above disadvantages. Summary of the invention

It is an object of the present invention to alleviate or eliminate the above mentioned drawbacks of the prior art and provide an elastomeπc polymer composition which does not have to be prepared m specific rubber processing equipment, but can be prepared m processing equipment for conventional polymers like polyethylene; which does not need special curing equipment for curing; which does not involve sulphur or peroxides for its curing; where the curing rate does not limit the productivity; and which have excellent resistance to the effects of air, oxygen, ozone and high temperatures as well as to the effects of solvents like mineral oils and non-polar chemicals. These and other objects are achieved according to the present invention by a crosslmkable ethylene-alkyl (meth) acrylate-unsaturated silane terpolymer.

More particularly, the present invention provides an elastomeπc polymer composition, characterised m that it comprises a crosslmkable ethylene-alkyl (meth) acrylate- unsturated silane terpolymer which has an alkyl (meth) - acrylate content of more than 5 mole%, an MFR₂ __ at 190°C, determined according to ISO 1133-1981 (E) , Condition 1, of at least 0.1 g/10 mm, and that the composition has, after having been crosslmked, a hot set, determined according to IEC-811, of less than 400%.

These and other advantages and characterising features of the present invention will appear from the following specification and the appended claims. Detailed description of the invention

Generally, and m connection with the present invention the expression "alkyl (meth) acrylate" includes alkyl acrylates as well as alkyl methacrylates . The alkyl moiety preferably is an alkyl group having 1-4 carbon atoms, such as methyl, ethyl, propyl, and butyl, preferably methyl or butyl . Conventional ethylene-alkyl (meth) acrylate polymers generally comprise the alkyl (meth) acrylate comonomer m a low amount of up to about 10 % by weight. The present invention differs from such conventional ethylene-alkyl (meth) acrylate copolymers m that it is not a copolymer, but a terpolymer containing an unsaturated silane compound as a termonomer, and also m that it contains the alkyl (meth) acrylate comonomer m a high amount of at least 5 mole%, preferably 5-25 mole%. More preferably the alkyl (meth) acrylate comonomer comprises about 9-20 mole% of the polymer. The high alkyl (meth) acrylate comonomer content at the present invention is necessary order to make the polymer composition elastomeπc, i.e. sufficiently soft and flexible. The terpolymer according to the present invention has a melt flow rate (MFR₂ χ_ ) , determined according to ISO 1133, Condition D, of at least 0.1 g/10 mm. Preferably, the melt flow rate lies m the range 0.1-1000 g/10 mm, more preferably 0.2-50 g/10 mm, and most preferably 1-25 g/10 mm.

As indicated above, another characterising feature of the composition according to the present invention is that it has, after having been crosslmked, a hot set, determined according to IEC-811, of less than 400%. Preferably, the hot set is less than 100%. The hot set method of IEC-811 is a way of determining the crosslmkmg degree of a polymer composition. According to the hot set method dumbbell shaped test bars of the material are suspended m a Hereaus oven, and their elon- gation is determined after 15 mm at 200°C and a load of 20 N/cm².

As mentioned above, the ethylene-alkyl (meth) - acrylate-unsaturated silane terpolymer composition of the present invention is crosslmkable. The crosslmkmg at the present invention is by way of hydrolysable silane groups which are incorporated in the ethylene-alkyl (meth) acrylate-unsaturated silane terpolymer according to the invention.

The crosslmkmg of polymers with hydrolysable silane groups is carried out by so-called moisture curing. In a first step, the silane groups are hydrolysed under the influence of water or steam, resulting in the splitting-off of alcohol and the formation of silanol groups. In a second step, the silanol groups are cross- linked by a condensation reaction splitting off water. In both steps, a so-called silanol condensation catalyst is used as a catalyst .

Silanol condensation catalysts include carboxylates of metals, such as tin, zinc, iron, lead and cobalt; organic bases; inorganic acids; and organic acids. In practice dibutyl tin dilaurate (DBTL) is generally used as the silanol condensation catalyst.

At the present invention it is preferred, however, to use a specific silanol condensation catalyst of formula I

ArSO₃H (I)

or a precursor thereof, Ar being a benzene ring substituted with at least one hydrocarbyl radical such that the total number of carbon atoms of the hydrocarbyl radical (s) is 8-20, or a naphthalene ring substituted with at least one hydrocarbyl radical such that the total number of carbon atoms of the hydrocarbyl radical (s) is 4-18, and the catalyst of formula I containing 14-28 carbon atoms in total. This catalyst, as opposed to conventional silanol condensation catalysts such as e.g. DBTL allows crosslinking at ambient temperature such as room temperature .

A silanol condensation catalyst of the above defined type is disclosed m WO 95/17463 for the crosslinking of polymers with hydrolysable silane groups. Witn regard to the silanol condensation catalyst of formula I it is preferred that the hydrocarbyl radical m formula I is an alkyl substituent with 10-18 carbon atoms . The currently most preferred compounds of formula I are dodecyl benzene sulphomc acid and tetrapropyl benzene sulphonic acid.

It is further preferred that the polymer composition includes 0.0001-3% by weight of silanol condensation catalyst.

In the following the crosslmkable silane group containing terpolymer according to the present invention will be described m more detail with regard to its preparation and the unsaturated silane termonomer. The crosslmkable base resin generally is an ethy- lene copolymer or graft polymer which contains hydrolysable silane groups and which is crosslmked under the influence of water and at least one silanol condensation catalyst . Specifically, the crosslmkable polymer is an ethylene-alkyl (meth) acrylate polymer containing cross- linkable silane groups introduced either by copolymensa- tion or graft polymerisation.

Preferably, the silane-contammg polymer has been obtained by copolymeπsation of ethylene, an alkyl (meth) acrylate comonomer and an unsaturated silane termonomer compound represented by the formula II

RSιR'_nY_{3 n} (ID

wherein

R is an ethylenically unsaturated hydrocarbyl, hydro- carbyloxy or (meth) acryloxy hydrocarbyl group,

R' is an aliphatic saturated hydrocarbyl group,

Y which may be same or different, is a hydrolysable organic group, and

If there is more than one Y group, these do not have to be identical.

Specific examples of the unsaturated silane compound are those wherein R is vinyl, allyl, isopropenyl, bute- nyl, cyclohexenyl or gamma- (meth) acryloxy propyl; Y is methoxy, ethoxy, formyloxy, acetoxy, propionyloxy or an alkyl- or arylamino group; and R', if present, is a methyl, ethyl, propyl, decyl or phenyl group.

A preferred unsaturated silane compound is repre- sented by formula III

CH₂=CHSi (OA)₃ (III)

wherein A is a hydrocarbyl group having 1-8 carbon atoms, preferably 1-4 carbon atoms.

The most preferred compounds are vinyl trimethoxy- silane, vinyl triethoxysilane, gamma- (meth) acryloxypro- pyltrimethoxysilane and vinyl triacetoxysilane or combinations of two or more thereof. The copolymerisation of the ethylene, the alkyl

(meth) acrylate, and the unsaturated silane compound may be carried out under any suitable conditions resulting in polymerisation of the monomers, e.g. as disclosed in GB 2, 088,831. The silane-containing polymer according to the invention suitably contains more than 0.2 % by weight, preferably 0.2-5.0 % by weight, and more preferably 0.5-3.0 % by weight of the unsaturated silane compound. If using a graft polymer, this may be prepared e.g. by the methods described in US 3,646,155 and US 4,117,195.

The above ethylene-alkyl (meth) acrylate-unsaturated silane terpolymers are produced by radical initiated high pressure polymerisation. Generally, the polymerisation of the monomers is carried out at a temperature of about

100-300°C and at a pressure of about 100-300 MPa in the presence of a radical initiator in a polymerisation reactor. Usually, the polymerisation is carried out continuously, preferably m a tubular reactor, or m an autoclave reactor.

Usually, when polymerising ethylene-alkyl (meth) - acrylate polymers with a high content of alkyl (meth) - acrylate the polymerisation may be troubled by fouling of the polymerisation reactor which manifests itself as unstable and mhomogenous production. To alleviate this problem and inhibit fouling during the polymerisation an adhesion reducing silicon containing compound, e.g. a silane or a silicone compound may be added as an anti- foulmg agent to the polymerisation reactor, as is disclosed m the international patent application PCT/SE98/01949, filed on October 28, 1998. At the present invention it is not necessary to add any such anti- foulmg agent, because the terpolymer of the present invention includes a silane termonomer which avoids fouling and m practice acts as an anti -fouling agent. Although ethylene-alkyl (meth) acrylate polymers, such as ethylene-methyl acrylate polymers general and polymers with a high content of alkyl (meth) acrylate comonomer such as the ethylene-alkyl (meth) acrylate- unsaturated silane terpolymer of the present invention in particular are sufficiently soft and flexible at room temperature, they tend to become increasingly stiff and rigid at lower temperatures such as sub-zero temperatures .

The present invention has solved this problem by adding a plasticiser to the ethylene-alkyl (meth) acrylate polymer composition when desired or necessary. The particular type of plasticiser is not critical to the present invention, but it is preferred that the plasticiser is selected from a particular group of plasticisers .

These preferred plasticisers are selected from the group consisting of: alkyl alcoholes; secondary or tertiary amines; esters of carboxylic acids with at least one carboxylic function; amides of mono- or dicarboxylic acids; esters of phosphoric acid; organic oils; and mineral oils .

These plasticisers result a composition of the desired softness and flexibility both at room temperature and at sub-zero temperatures. In addition they are compatible with the polymer and do not migrate from the polymer or result m exudation.

Preferably, the plasticiser is selected from the group consisting of: linear or branched C₈-C₁₈ alkyl alco- holes; linear or branched C -Cι₈ alkyl secondary or tertiary amines,^■ linear or branched C₄-Cι₈ alkyl esters of C₃-C₁₀ dicarboxylic acids; C₄-C₁₈ N-substituted amides of C₁₂-C₁₈ linear monocarboxylic acids or C₆-Cι₀ dicarboxylic acids; alkyl, aryl , alkylaryl, or arylalkyl esters of phosphoric acid where the alkyl moiety is C₆-C₁₈ and the aryl moiety is phenyl ; organic oils like sunflower oil, rape seed oil, terpene oil or soybean oil; and mineral oils like paraffmic oil, aromatic oil and, m particular, naphtenic oil. Among the preferred linear or branched C₈-Cι₈ alkyl alcoholes may be mentioned octanols like 2-ethyl-l-hexa- nol or 1-octanol, 1-decanol and 1-dodecanol, etc.

Among the preferred linear or branched C₄-Cι₈ alkyl secondary or tertiary amines compounds like tπ-n-butyl am e and di-n-hexyl amme may be mentioned.

Among the esters of dicarboxylic acids are esters of aliphatic dicarboxylic acids with 6-10 carbon atoms, such as adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. Preferably, the esters are alkyl esters where the alkyl moiety has 4-18 carbon atoms, such as butyl, pentyl , hexyl , heptyl , octyl , nonyl , decyl , unde- cyl , dodecyl, tπdecyl , etc. Particularly preferred are C₄-C_ι8 alkyl esters of adipic acid.

Among esters of dicarboxylic acids are also esters of aromatic dicarboxylic acids, such as alkyl esters of phthalic acid. As particular examples of alkyl esters of phthalic acid may be mentioned e.g. dimethyl phthalate, diethyl phthalate, dibutyl phthalate (DBP) , dnsobutyl phthalate, dihexyl phthalate, dioctyl phthalate (DOP) , dnsooctyl phthalate, dnsononylphthalate, dnsodecyl phthalate, diundecylphthalate, ditπdecyl phthalate, butyl benzyl phthalate, butyl octyl phthalate, dicapryl phthalate, and dicyclohexyl phthalate. Although these plasticisers may be used at the present invention m view of their physical properties, they are not preferred, but avoided for environmental reasons. As particular examples of preferred esters of dicarboxylic acids may be mentioned dnsobutyl adipate, di (n- heptyl , n-nonyl) adipate , dioctyl adipate [di (2 -ethylhexyl) adipate] , dicapryl adipate, dnsodecyl adipate, dmonyl adipate, di (tridecyl) adipate, dimetyl sebacate, dibutyl sebacate, and di (2 -ethylhexyl) sebacate . Of these dioctyl adipate is a particularly preferred plasticiser.

Among the amides the N-substituted C₄-Cι₈ alkyl amides of C₃-Cι₀ dicarboxylic acids compounds corresponding to those of the above C₄-Cι₈ alkyl esters of C₆-Cι₀ dicarboxylic acids may be mentioned where the amide moiety is selected from butyl amide, pentyl amide, hexyl amide, heptyl amide, octyl amide, nonyl amide, decyl amide, undecyl amide, dodecyl amide, tridecyl amide, etc. The esters of phosphoric acid are preferably selected from alkyl, alkoxy, aryl, alkylaryl , or arylalkyl esters of phosphoric acid. The alkyl or alkoxy moiety of these esters preferably has 6-16 carbon atoms, more preferably 8-14 carbon atoms, and the aryl moiety preferably is phenyl which may be unsubstituted or sub- stituted with Cι-C₄ alkyl och hydroxyl . Particularly preferred examples of esters of phosphoric acid are alkyldiphenyl phosphates, such as metyldiphenyl phosphate, 2-etylhexyl diphenyl phosphate, isodecyl diphenyl phosphate, t-butylphenyl diphenyl phosphate; tributyl phosphate; tricresyl phosphate; triphenyl phosphate; and tributoxiethyl phosphate. As preferred examples of mineral oil may be mentioned aliphatic, aromatic or , preferably, naphtenic

The plasticisers defined and exemplified above may be used alone or m combination with each other.

The amount of the plasticiser, when present, should be that required to obtain the desired softness and flexibility of the final polymer composition. The content of the plasticiser is from 0 up to 50 % by weight, pre- ferably 5-50 % by weight, more preferably 5-30 % by weight, most preferably 10-30 % by weight, based on the total weight of the composition.

The composition of the present invention may further include a filler. Although there is no particular restriction on the choice of filler, it is preferably selected from inorganic fillers. As examples of particularly preferred fillers may be mentioned calcium carbonate, kaolin, talc, Mg(OH)₂, and Al(OH)₃. The total amount of filler, when present, is up to 60 % by weight, pre- ferably up to 40 % by weight, based on the weight of the total composition.

In order to alleviate or inhibit any problems with scorch during processing (extrusion) of the polymer composition of the present invention it may also include a so-called scorch retarding agent. As an example of such agents may be mentioned silane compounds of the general formula IV

R^SiR^X, _n)_m (IV) wherein R¹ is a monomfunctional hydrocarbyl group having 13-30 carbon atoms, or a difunctional hydrocarbyl group having 4-24 carbon atoms,

R² which may be the same or different, is a hydrocarbyl group having 1-10 carbon atoms, X which may be the same or different, is a hydrolysable organic group,

m is 1 or 2 ; as disclosed in EP 0 449 939.

It should be understood that the composition of the present invention may also include conventional addi- tives, such as stabilisers, crosslinking agents, coagents, process aids, etc. The total content of such additives, when present, is up to 10 % by weight, preferably up to 5 % by weight, based on the weight of the total composition. It should be understood that the sum of the percentages of all the components present in the ethylene- alkyl (meth) acrylate polymer composition of the invention is 100%.

In order to exhibit the desired elastomeric pro- perty, i.e. softness and flexibility, the terpolymer should have a low crystallinity . Preferably, the crystal - unity of the present terpolymer is lower than 23 % by weight, determined by heating a sample of the terpolymer from -90°C to +125°C at a rate of 10°C/min, cooling the sample to -90°C at a rate of 10°C/min, and finally reheating the sample to +150°C at a rate of 10°C/min. The melting peak between 0°C and 100°C in the second melting scan is integrated and the integrated value is divided with a reference value of 290 J/g°K and multiplied by 100 to obtain the weight percentage crystallinity.

Further, in order to achieve desired elastomeric properties it is preferred that the terpolymer of the present invention has a tensile modulus, determined according to ISO 527-2 (1 mm/min) , of less than 30 MPa. For many applications the softness of the polymer composition is of importance, and it is preferred that the polymer composition of the present invention has a Shore A hardness, determined according to ISO 868, of less than 85. Having thus described the present invention above it will now be illustrated by way of a non-limiting example. In the example all percentages and parts are by weight, unless otherwise stated.

Example

An ethylene-methyl acrylate-vinyl trimethoxysilane terpolymer was prepared by radical initiated high pressure polymerisation in a high pressure tubular reactor. The resulting elastomeric terpolymer contained 9 mole% (31 % by weight) of methyl acrylate, 1 % by weight of vinyl trimethoxysilane and had an MFR_2.16 of 10 g/10 min, a melt temperature of 71°C, a crystallinity of 7 % by weight, a Shore A hardness of 53, a flexibility in terms of the dynamic shear modulus (determined according to ISO 6721-2A, 23°C) of 4.2 MPa, and a tensile modulus of 2.4 MPa. The terpolymer was mixed with dodecyl benzene sul- phonic acid (a silane condensation catalyst) in a Brabender kneader at 120°C and 40 rpm for 10 min. Then the composition was compression moulded into a 2 mm thick plaque which was immersed in a water bath at 60°C for 18 h. The crosslinked plaque was removed from the water bath and the hot set of the crosslinked composition was determined as defined earlier. The composition had a hot set value of 60% which indicates that it was sufficiently crosslinked. The terpolymer of the Example may be mixed with different additives as described earlier, if necessary or desired, in order to prepare different products using the elastomeric composition of the present invention. Examples of such products are seals, gaskets, profiles, bel- lows, bumpers, hoses, tubes, cables, tyres, fenders, membranes, tarpaulines, flooring materials, roofing materials, conveyor belts, foamed products, medical devices, building products, automotive products, films, sheets, coatings, etc. The terpolymer of the present invention may also act as a modifying polymer to enhance the properties (e.g. impact strength, tensile strength, compression set, creep resistance, and upper service temperature) of different plastics and rubbers.

As indicated earlier, the elastomeric polymer composition according to the present invention is superior to conventional crosslinked rubbers or thermoplastic elastomers in that a) it is easier to make and causes less pollution than conventional crosslinked rubbers or thermoplastic elastomers, because it is made of free flowing pelleted raw materials instead of powdery raw materials; b) it gives a larger choice of production equipment, because it is not restricted to production in equipment for rubber processing. Equipment for the processing of polyethylene or PVC may be used e.g.; c) it is easy to crosslink by moisture curing, instead of vulcanisation involving peroxide or sulphur as in the curing of rubber. This means that there are no problems with peroxide or sulphur smell or rest products; d) the moisture curing (silane crosslinking) does not require any special curing equipment as curing may be performed in ambient humid air; e) the moisture curing gives less problems with scorch and permits a wider process window because of the possibility to use higher temperatures; f) higher productivity is possible, because the crosslinking operation is no bottleneck; g) it has a very good ageing resistance, i. e resistance to air, oxygen and ozone and high temperatures, because the elastomer contains no carbon-to-carbon double bonds ; h) it has a very good resistance to solvents such as mineral oils and other non-polar chemicals; i) it has a higher melting temperature than e.g. EPR; j ) it contains no corrosive by-products; k) it has good adhesion to various substrates; 1) it has high compatibility with fillers and additives .

Claims

1. An elastomeric polymer composition, c h a r a ct e r i s e d m that it comprises a crosslmkable ethylene-alkyl (meth) acrylate-unsaturated silane terpolymer which has an alkyl (meth) acrylate content of more than 5 mole%, an MFR₂ __ at 190°C, determined according to ISO 1133, Condition D, of at least 0.1 g/10 mm, and that the composition has, after having been crosslinked, a hot set, determined according to IEC-811, of less than 400%.

2. An elastomeric polymer composition as claimed m claim 1, wherein the alkyl (meth) acrylate comonomer is an alkyl acrylate monomer with the alkyl moiety selected from Cι-C₄ alkyl groups.

3. An elastomeric polymer composition as claimed m claim 2, wherein the alkyl moiety is methyl or butyl.

4. An elastomeric polymer composition as claimed in any one of the preceding claims, wherein the unsaturated silane termonomer is a vinyl tπalkoxysilane monomer.

5. An elastomeric polymer composition as claimed in claim 4, wherein the vinyl trialkoxysilane monomer has the general formula III

CH₂=CHSι (OA)₃ ⁽HI⁾ wherein A is a hydrocarbyl group having 1-8 carbon atoms.

6. An elastomeric polymer composition as claimed m any one of the preceding claims, wherein the unsaturated silane termonomer comprises 0.2-5 % by weight of the ethylene-alkyl (meth) acrylate-unsaturated silane terpolymer.

7. An elastomeric polymer composition as claimed in any one of the preceding claims, wherein the terpolymer has an alkyl (meth) acrylate content of 5-25 mole%.

8. An elastomeric polymer composition as claimed m any one of the preceding claims, wherein the terpolymer has a crystallinity of less than 23 % by weight.

9. An elastomeric polymer composition as claimed in any one of the preceding claims, wherein the composition has a tensile modulus, determined according to ISO 527-2, of less than 30 MPa.

10. An elastomeric polymer composition as claimed m any one of the preceding claims, wherein the composition has a Shore A hardness, determined according to ISO 868, of less than 85.