WO2000068313A1

WO2000068313A1 - A soft ethylene-alkyl (meth)acrylate copolymer composition

Info

Publication number: WO2000068313A1
Application number: PCT/SE2000/000861
Authority: WO
Inventors: Hans Eklind; Bill Gustafsson
Original assignee: Borealis A/S
Priority date: 1999-05-05
Filing date: 2000-05-04
Publication date: 2000-11-16
Also published as: AU4791600A; SE9901618D0

Abstract

A soft ethylene-alkyl (meth)acrylate copolymer composition is described. The composition is characterised in that the alkyl (meth)acrylate monomer comprises at least 15 % by weight of the ethylene-alkyl (meth)acrylate copolymer, and that the composition comprises a plasticiser which, when present in an amount of 25 % by weight gives a reduction in the Tg of the composition of at least 5 °C and reduces the dynamic shear modulus of the composition by at least 20 % in the temperature range from -60 °C to +30 °C, said plasticiser being selected from the group consisting of alkyl alcoholes; secondary or tertiary alkyl 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.

Description

A SOFT ETHYLENE-ALKYL (METH) ACRYLATE COPOLYMER

COMPOSITION

Technical field

The present invention relates to a soft ethylene- alkyl (meth) acrylate copolymer composition. Technical background Polyvinyl chloride (PVC) is a widely used polymer inter alia because of its excellent properties. It has found various applications such as m wall paper, pipes, films, sheets, profiles, cables, flooring materials, roofing materials, tarpaulins, rainwear apparel, etc. For many applications a soft and flexible material is needed and to this end the PVC is plasticised with a plasticiser. There are concerns, however, in some cases about the use of plasticised PVC and an ambition to substitute it with other polymers. However, this ambition has not been quite successful, and m particular it has been d_-ff__c--lt tc find acceptable substitute polymers for applications where soft and flexible PVC is used. Although many polymers may have an acceptable softness at room temperature, they become rigid and brittle at lower temperatures such as sub-zero temperatures, i.e. below

0°C. There is thus a need for a polymer which may be used as an acceptable substitute for soft PVC and which can be used down to temperatures of the order of -60°C, also m applications where no volume plastic as yet has been found suitable.

Summary of the invention

It is an object of the present invention to provide a soft polymer composition which retains its softness and flexibility at low temperatures. It is another object of the present invention to provide a polymer composition which is flexible and soft and may be used as a substitute for soft PVC. According to the present invention these objects are achieved by a composition comprising an ethylene-alkyl (meth) acrylate copolymer and a plasticiser for the ethylene-alkyl (meth) acrylate copolymer. The present invention thus provides a soft ethylene- alkyl (meth) acrylate copolymer composition, characterised m that the alkyl (meth) acrylate monomer comprises at least 15% by weight of the ethylene-alkyl (meth) acrylate copolymer, and that the composition comprises a plasti- ciser which, when present m an amount of 25 % by weight gives a reduction m the T_g of the composition of at least 5°C and reduces the dynamic shear modulus of the composition by at least 20% m the temperature range from -60°C to +30°C, said plasticiser being selected from the group consisting of alkyl alcoholes; secondary or tertiary alkyl amines; esters of carboxylic acids with at least one carboxylic function; amides of mono- or dicar- boxylic acids; esters of phosphoric acid; organic oils; and mineral oils. Further characteristics and advantages of the present invention appear from the appended claims and the following description. Detailed description of the invention

Generally, and m connection with the present inven- tion the expression "alkyl (meth) acrylate" includes alkyl acrylates as well as alkyl methacrylates . At the present invention the alkyl moiety preferably is an alkyl group with 1-8 carbon atoms, more preferably 1-4 carbon atoms. Particularly preferred ethylene-alkyl (meth) acrylate copolymers of the present invention are ethylene-methyl acrylate and ethylene-methyl methacrylate copolymers. The most preferred ethylene-alkyl (meth) acrylate copolymer is ethylene-metyl acrylate copolymer.

Ethylene-alkyl (meth) acrylate copolymers normally comprise the alkyl (meth) acrylate comonomer in an amount of up to about 10 to 15 % by weight. The present invention differs from such conventional ethylene-alkyl (meth) acrylate copolymers in that it contains the alkyl (meth) acrylate comonomer in a high amount of at least 15 % by weight, preferably at least 20 % by weight and up to about 45 % by weight of the comonomer. More preferably the alkyl (meth) acrylate comonomer comprises about 20-40 % by weight of the copolymer.

Ethylene-alkyl (meth) acrylate copolymers 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 in a tubular reactor or in a stirred tank reactor. When polymerising ethylene-alkyl (meth) acrylate polymers of such high alkyl (meth) acrylate contents as at the present invention, the polymerisation may be troubled by fouling of the polymerisation reactor which manifests itself as unstable and inhomogenous production. To this end it is preferred that measures are taken to inhibit fouling during the polymerisation. These measures preferably include the addition of an adhesion reducing silicon containing compound, e.g. a silane or a silicone compound to the polymerisation reactor, as is disclosed in the international patent application PCT/SE98/01949 , filed on October 28, 1998.

Addition of silicon containing compounds eliminates reactor fouling already at very small amounts of addition to the polymerisation reactor. Generally, it is preferred to add the silicon containing compound in an amount of about 0.001-3 % by weight, more preferably about 0.005-2 % by weight, and still more preferably about 0.01-1 % by weight, such as about 0.1-1 % by weight, based on the weight of the polymer produced. The adhesion reducing silicon containing compound may be added in any suitable way to the reactor, e.g. continuously or batchwise; separately or together with the other polyme- πsation components (e.g. dissolved m a monomer); etc. Preferably the silicon containing compound is added continuously during the polymerisation together with one or more of the monomers to be polymerised. The point of addition of the silicon containing compound is preferably upstream (i.e. on the suction side) of the compressor feeding monomer (s) to the polymerisation reactor.

By the expression "adhesion reducing silicon containing compound" used herein is meant a silicon contain- mg compound that reduces the adhesion between the inner metal surface of the reactor and the polymer produced m the reactor during polymerisation.

In order to exert an adhesion reducing effect it is necessary that the silicon containing compound has affm- lty to the reactor wall material which usually is a metal . The compound should therefore contain one or more polar groups or functions that m some way tend to adhere to the reactor wall surface, i.e. to metal surfaces. Two types of silicon containing compounds that show such affinity are silanes and silicones.

Suitable silane compounds can be represented by the general formula I

R_kSiR ' _mX_n ( i :

where

m is 0 or 1,

k + m + n = 4

R which may be the same or different if more than one such group is present, is an alkyl, arylalkyl, alkylaryl or aryl group containing 1-20 carbon atoms, with the proviso that if more than one R group is present the total number of carbon atoms of the R groups is at most 30; R' is -R"SιR_pX_q, where p is 0-2, q is 1-3, and p + q = 3; R" is - (CH₂) _rY_Ξ (CH₂) _t- where r and t independently are 1-3, s is 0 or 1 and Y is a difunctional heteroatomic group selected from -0- , -S-, -SO-, S0₂ , -NH- , -NR- or -PR-, where R is as defined above;

X which may be the same or different if more than one such group is present, is an alkoxy, aryloxy, alkyl - aryloxy, or arylalkyloxy group containing 1-15 carbon atoms, with the proviso that if more than one X group is present the total number of carbon atoms is at most 40. The alkyl moiety of the R group may be linear or branched .

The alkyl moiety of the X group may be linear or branched. Preferably, each X group has 1-8 carbon atoms, most preferably 1-4 carbon atoms. The most preferred X groups are alkoxy groups selected from methoxy, ethoxy, propoxy, and 1-butoxy.

The groups R and X may include heteroatomic substi- tuents, but this is not preferred. Especially, acid groups or groups that may form acids on hydrolysis, like halogen or carboxylate substituents are not preferred, since the acids may cause corrosion problems m the reactor.

The most preferred silicon containing compound at present is hexadecyl trimethoxy silane, which is commercially available and a liquid at ambient (room) temperature .

As mentioned above, another type of preferred silicon containing compound that may be used is silicones. Silicones is the common denomination for different types of polysiloxanes and have the general formula R'_m(SιR₂0) _nR'_m/ where R and R' can be methyl or phenyl and n is 3, 4 or 5 if m is 0, i.e. when the compounds is cyclic and n is 2 -20 if m is 1 , i.e. if the compound is a straight chain one.

Generally, the silane or the silicone used should be a liquid, m order to be easily fed into the reactor, but also m order to form a thin film layer on the reactor walls .

Although ethylene-alkyl (meth) acrylate copolymers, such as ethylene-methyl acrylate copolymers in general and copolymers with the high content of comonomer as prescribed by the present invention in particular are sufficiently soft and flexible at room temperature, they become increasingly stiff and rigid at lower temperatures such as sub-zero temperatures. This property precludes their use as a substitute for plasticised PVC, because such a substitute must be soft and flexible not only at room temperature, but also at sub-zero temperatures, such as -20°C to -30°C to be of practical use. Thus, ethylene- methyl acrylate copolymers (EMA) e.g. are soft and flexi- ble at normal room temperature, but quite rigid at temperatures of about -20°C to -25°C.

The present invention has solved this problem and achieved a non-PVC polymer composition which is soft and flexible both at room temperature and at lower, sub-zero temperatures by combining an ethylene-alkyl (meth) - acrylate copolymer with a certain plasticiser selected from a particular group of plasticisers . It has thus surprisingly been found that while an increase in comonomer contents only leads to a relatively minor change in the glass transition temperature (T_g) of a few degrees centigrade, the addition of a plasticiser according to the present invention m an amount of 25 % by weight of the total composition will lead to a decrease in the glass transition temperature of at least 5°C and to a reduction of the dynamic shear modulus of at least 20% in the temperature range from -60°C to +30°C.

It is to be noted that not all compounds that are generally known as plasticisers in connection with other polymers, such as e.g. PVC are acceptable as plasticisers at the present invention. Only plasticisers from the group defined above and m the claims may be used at the present invention. These plasticisers result in a com- position 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 in exudation. As mentioned above, the plasticiser used in the composition of the present invention is 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.

Preferably, the plasticiser is selected from the group consisting of: linear or branched C₈-C₁₈ alkyl alcoholes; linear or branched C₄-Cι₈ alkyl secondary or ter- tiary amines; linear or branched C₄-Cι₈ alkyl esters of Cs-Cio dicarboxylic acids; C -Cι₈ 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 C₃-Cι₈ and the aryl moiety is phenyl; organic oils like sunflower oil, rape seed oil, terpene oil or soybean oil; and mineral oils like paraffinic oil, aromatic oil and, in particular, naphtenic oil.

Among the preferred linear or branched C₈-Cι₈ alkyl alcoholes may be mentioned octanols like 2-ethyl-l- hexanol or 1-octanol, 1-decanol and 1-dodecanol, etc.

Among the preferred linear or branched C₄-Cι₈ alkyl secondary or tertiary amines compounds like tri-n-butyl amine and di-n-hexyl amine 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 , tridecyl , etc. Particularly preferred are C₄-Ci₈ 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 dicar- boxylic acids may be mentioned dnsobutyl adipate, di (n- heptyl, n-nonyl) adipate, dioctyl adipate [dι(2-ethyl- hexyl) adipate] , dicapryl adipate, dnsodecyl adipate, dmonyl adipate, dι(tπdecyl) 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 C₆-C₁₀ dicarboxylic acids compounds corresponding to those of the above C₄-Cι₈ alkyl esters of C₆-C₁₀ 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, tπdecyl 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 substituted with O_.-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-butyl- phenyl diphenyl phosphate; tributyl phosphate; tricresyl phosphate; triphenyl phosphate; and tributoxiethyl phosphate .

As preferred examples of mineral oil may be men- tioned aliphatic, aromatic or, preferably, naphtenic oils .

The plasticisers according to the present invention as defined and exemplified above may be used alone or in combination with each other. The amount of the plasticiser used should be that required to obtain the desired softness and flexibility of the final polymer composition. Preferably, the content of the plasticiser is 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 melt flow rate at a load of 2.16 kg according to ISO 1133, Condition D (MFR₂) of the composition of ethylene-alkyl (meth) acrylate copolymer according to the invention should lie in the range 0.05-40 g/10 min, pre- ferably 0.1-20 g/10 min.

The composition of the present invention may further include fillers. Although there is no particular restriction on the choice of filler, it is preferably selected from inorganic fillers. As examples of particularly pre- ferred 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, preferably up to 40 % by weight, based on the weight of the total composition. When the composition comprises a filler the MFR value of the copolymer should be selected at the upper end of the range defined above to make blending of the copolymer and the filler easier.

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, pre- ferably 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 m the composition of the invention is 100%.

Having thus described the present invention above it will now be illustrated by way of some non-limitatmg examples. In the examples all percentages and parts are by weight, unless otherwise stated. In the examples the softness or flexibility of the compositions was determined m terms of the the dynamic shear modulus of the composition at different temperatures according to ISO 6721-2A. The modulus was measured with a Dynamic Mechanical Thermal Analysis device (DMTA; bending head, frequency = 1 Hz, 2°C/mιn) . Compositions acceptable as a substitute for soft PVC should have a modulus of at most about 30 MPa at a temperature of 0-25°C and at most about 200 MPa at a temperature of -30°C. Example 1

This example illustrates the increase in flexibility of ethylene-methyl acrylate copolymers by increasing the comonomer content or by using a plasticiser.

The flexibility of an ethylene-alkyl (meth) acrylate copolymer can be increased m primarily two ways: either by increasing the comonomer content or by adding a compatible plasticiser. The consequence of increasing the comonomer content is that the flexibility improves above the glass transition temperature (T_g) . However, the T_g itself is affected only to a minor extent by an increase of the comonomer content of ethylene-alkyl (meth) acrylate copolymers. On the other hand, the addition of a compatible plasticiser provides an overall improved flexibility, i.e. also the T_g is reduced. These findings are demonstrated by the experiments described below.

As a first reference an ethylene-methyl acrylate copolymer containing 25% by weight of methyl acrylate and having an MFR₂ of 0.4 g/10 mm was prepared. This reference copolymer was denominated as EMA1.

As a second reference another ethylene-methyl acrylate copolymer containing 30% by weight of methyl acrylate and having an MFR₂ of 5 g/10 mm was prepared. This reference copolymer was denominated as EMA2.

An ethylene-methyl acrylate copolymer according to the present invention was prepared the following way. A mixture of 75 % by weight of EMA1 and 25 % by weight of dioctyl adipate (DOA) plasticiser was prepared m a

Brabender kneader (temperature = 150°C; mixing time = 10 mm) . This copolymer was denominated as EMA1+PLA.

The dynamic shear modulus of the polymers described above (EMA1, EMA2 , and EMA1+PLA) was determined with a DMTA device as described above. The results appear from Figure 1.

It is evident from Figure 1 when comparing the dynamic shear modulus graph for EMA1 with that of EMA2 that an increase of the comonomer content only improves the flexibility of the polymer at temperatures above the T_g. However, when a plasticiser is added, as the polymer EMA1+PLA this results also in a reduction of the T_g and an overall improvement of the flexibility. This is evident when comparing the dynamic shear modulus graph of EMA1+PLA with the graphs of EMA1 and EMA2 Figure 1. Example 2

As mentioned earlier, the plasticiser of the present invention, when present an amount of 25 % by weight, gives a reduction the T_g of at least 5°C and also reduces the dynamic shear modulus of the composition by at least 20% the temperature range from -60°C to +30°C. To illustrate this the following experiment was made.

The EMA1 of Example 1 was used as a reference and referred to as Composition A. Four compositions according to the present invention, Compositions B-E, were prepared by compounding 75 % by weight of EMA1 with 25 % by weight of different plasticisers a Brabender kneader (tern- perature = 150°C; mixing time = 10 mm) . Composition B contained a naphtenic mineral oil plasticiser with the trade name Nyflex 222 B from Nynas, Sweden. Composition C contained an aliphatic mineral oil plasticiser with the trade name Nypar 20 from Nynas, Sweden. Composition D contained a dioctyl adipate plasticiser with the trade name Plastomoll DOA from BASF, Germany. Composition E contained an isodecyldiphenyl phosphate plasticiser with the trade name Santicizer 148 from Solutia, Belgium. Composition F, which was a reference composition, contained a plasticiser with the trade name Sunigum P7395 from Goodyear, USA (believed to be a terpolymer of butyl acrylate-styrene-acrylonitrile) .

The dynamic shear modulus of Compositions A-F was determined with a DMTA device as described above. The results are shown Table 1.

Table 1

Dynamic shear modulus m MPa for Comp'ositions A-F mperature A B o D E F

(°C)

-90 1150 1220 1080 1130 800 1040

-60 950 750 740 290 390 810

-30 330 76 110 37 67 330

0 28 12 12 12 14 23

30 10 5 5 4 5 7

Tg (°C) -25 -32 -30 -50 -40 -13

As is evident from Table 1, the dynamic shear modu- lus, i.e. the flexibility both at high and low temperatures is better for Compositions B-E according to the invention than for the reference Composition A without any plasticiser and the reference Composition F with a plasticiser outside the present invention. To achieve a dynamic shear modulus at room temperature of 10 MPa or less without the use of a plasticiser would require an ethylene-methyl acrylate copolymer with a content of more than 30-35 % by weight of methyl acrylate comonomer. However, such a high content of comonomer would not lead to a similar decrease in glass transition temperature (T_g) and thus would not give an equal decrease in low temperature modulus. By the combination of the ethylene-alkyl (meth) acrylate copolymer and selected plasticiser according to the invention the dynamic shear modulus (flexibility) can be easily controlled and this is an important advantage of the inven- tion. Furthermore, the phosphoric acid ester plasticisers of the invention result in the added advantage of improving the flame retardancy of the composition.

Claims

1. A soft ethylene-alkyl (meth) acrylate copolymer composition, c h a r a c t e r i s e d m that the alkyl (meth) acrylate monomer comprises at least 15% by weight of the ethylene-alkyl (meth) acrylate copolymer, and that the composition comprises a plasticiser which, when present m an amount of 25 % by weight gives a reduction the T_g of the composition of at least 5°C and reduces the dynamic shear modulus of the composition by at least 20% m the temperature range from -60°C to +30°C, said plasticiser being selected from the group consisting of alkyl alcoholes; secondary or tertiary alkyl 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.

2. A soft ethylene-alkyl (meth) acrylate copolymer composition as claimed m claim 1, wherein the plasticiser is selected from the group consisting of linear or branched C₈-Cι₈ alkyl alcoholes; linear or branched C₄-Cι₈ alkyl secondary or tertiary amines; linear or branched C₄-Cι₈ alkyl esters of C₆-Cι₀ dicarboxylic acids; C₄-Cι₈ N-substituted amides of Cι₂-Cι₈ linear mono- carboxylic acids or C_e-C₁₀ dicarboxylic acids; alkyl, aryl, alkylaryl, or arylalkyl esters of phosphoric acid where the alkyl moiety is C₃-Cι₈ and the aryl moiety is phenyl; sunflower oil, rape seed oil, terpene oil or soybean oil; and paraffimc oil, aromatic oil and napht-

3. A soft ethylene-alkyl (meth) acrylate copolymer composition as claimed m claim 2, wherein the plasticiser comprises a C₄-Cι₈ alkyl ester of adipic acid.

4. A soft ethylene-alkyl (meth) acrylate copolymer composition as claimed m claim 3, wherein the plasti- ciser comprises dioctyl adipate.

5. A soft ethylene-alkyl (meth) acrylate copolymer composition as claimed m claim 2, wherein the plasticiser comprises an alkyldiphenyl phosphate.

6. A soft ethylene-alkyl (meth) acrylate copolymer composition as claimed m any one of the preceding claims, wherein the alkyl (meth) acrylate monomer comprises at least 20 % by weight of the ethylene-alkyl - (meth) acrylate copolymer.

7. A soft ethylene-alkyl (meth) acrylate copolymer composition as claimed m any one of the preceding claims, wherein the ethylene-alkyl (meth) acrylate copolymer is an ethylene-methyl acrylate copolymer.

8. A soft ethylene-alkyl (meth) acrylate copolymer composition, wherein the plasticiser comprises 5-50 % by weight of the total weight of the composition.

9. A soft ethylene-alkyl (meth) acrylate copolymer composition, wherein the composition further comprises up to 60 % by weight of a filler.

10. A soft ethylene-alkyl (meth) acrylate copolymer composition, wherein the composition further comprises up to 10 % by weight of at least one additive selected from the group consisit g of stabilisers, crosslmkmg agents, coagents, and process aids.