GB2285259A

GB2285259A - An oil resistant plasticizer for PVC and PVC-rubber blends

Info

Publication number: GB2285259A
Application number: GB9400041A
Authority: GB
Inventors: Joseph Gordon Robinson; Michael William Copson
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-01-04
Filing date: 1994-01-04
Publication date: 1995-07-05
Also published as: GB9400041D0

Abstract

Polyvinyl chloride and blends of polyvinyl chloride and nitrile rubber plasticized with the product by heating a liquid copolymer of butadiene and acrylonitrile with an ethylenically unsaturated compound (e.g. ester) in the presence of an organic peroxide have similar low temperature flexibilities to PVC and to PVC-nitrile rubber blends plasticized with monomeric plasticizers, but they exhibit superior oil resistance and lower plasticizer migration

Description

AN OIL RESISTANT PLASTICIZER FOR PVC AND PVC-RUBBER BLENDS It is common practice to add monomeric plasticizers, such as alkyl phthalates, aryl phosphates and esters of aliphatic acids to PVC and to blends of PVC and nitrile rubber (PVC-NBR) in order to Improv their toughness and processing characteristics. However, these improvements are invariably at the expense of other desirable properties of the PVC and of PVC-nitrile rubber blends. Thus, the plasticized PVC or PVC-NBR blend generally have lower tensile strength and reduced resistance to attack by certain oils and solvents as compared with the unplasticized materials. Moreover, the plasticizer present in derived artefacts may migrate into a substrate with which they are required to make contact in service.

This plasticizer migration can cause unacceptable deterioration in the properties, not only of the PVC or of the PVC-NBR blend, but also of the contacted substrate. For example, stress cracking nay be caused in the case of polycarbonate panels encountered in glazing applications, and impairment of electrical properties in the case of polyethylene used to insulate electric power cables sheathed with a plasticized PVC-NBR blend.

To offset these and other drawbacks associated with the use of monameric plasticizers but retaining the toughness and satisfactory processing and extrusion characteristics of the plasticized PVC and of PVC-NBR blends, the monaneric plasticizers are commonly replaced by so-called polymeric plasticizers such as, for example, polyadipates and esters of poly(ethylene glycol).

This replacement of monomeric plasticizers leads, desirably, to reduced plasticizer migration and to enhanced resistance to the plasticizer being leached out of extrusions and mouldings in contact with oils and solvents. Also, the absorption or inhibition of certain fluids by moulded or extruded artefacts nay be reduced by using polymer plasticizers instead of the conventional mLnomeric plasticizers. On the other hand, however, the low temperature flexibility of PVC and PVC-nitrile rubber compositions is adversely affected by the use of the conventional polymeric plasticizers.

The e present invention provides a means whereby PVC and blends of PVC and nitrile rubber can be plasticized to give, unlike hitherto plasticized PVC and plasticized blends of PVC and nitrile rubber, readily extrudable artefacts with outstanding resistance both to plasticizer migration and to attack by most oils and fuels, and at the same time having the desirable low temperature flexibility like that of PVC and PVC/NBR blends plasticized with monomeric plasticizers. Oil resistance is conventionally and conveniently assessed by measuring the voluble change and changes in hardness, elongation and tensile strength after immersion in ASTM No.l and No.3 oils.

For the purpose of one aspect of the present invention the amount of nitrile rubber taken is preferably in the range 5 parts to 120 parts per 100 parts of PVC polymer, and more preferably in the range 10 parts to 65 parts per 100 parts of PVC polymer. The nitrile rubber has an acrylonitrile content which is preferably in the range 10 parts to 45 parts per 100 parts of rubber and is most preferably in the range 25 parts to 40 parts per 100 parts of rubber. The rubber is taken in fine particulate powder form (ca.0.5nrn) and is desirably cross-linked before blending with the PVC or other constituents of the formulation.

The PVC suitable for this aspect of the present invention, and for the whole invention, may either be a suspension grade or an emulsion prepared grade or a mass polymerised grade or a mixture of any of these grades. The K-value is preferably in the range 45-90 (DIN 53726) and most preferably in the range 50-60.

The amount of plasticizer of the present invention, which is blended with the PVC, is preferably in the range 25 parts to 150 parts per 100 parts of PVC polymer and is more preferably in the range 40 parts to 100 parts per 100 parts of PVC polymer. The plasticizer is constituted of an ethylenically unsaturated organic compound or mixture of such compounds, and a liquid co-polymer of butadiene and acrylonitrile. This mixture is heated in the presence of an organic peroxide (or AZBN or a derivative thereof), preferably during melt mixing of the PVC with the cross-linked nitrile rubber and the other constituents of its formulation employed for making extruded or moulded artefacts.

The ethylenically unsaturated compound is preferably, but not exclusively, an organic ester of an unsaturated alcohol, such as allyl alcohol, or an organic ester of an unsaturated dicarboxylic acid, such as citraconic acid, itaconic acid, mesaconic acid, maleic acid and furaric acid or their alkyl, aryl, dialkyl or diaryl derivatives. Esters of unsaturated monocarboxylic acids, such as acrylic acid and methacrylic acid, are also suitable for use in the present invention. Examples of such esters are dibutyl naleate, dibutyl ethyl maleate, ethyl hydrogen maleate, diethyl fumarate, dibutyl itaconate, dibutyl citraconate, diallyl phthalate, ethyl acrylate and butyl methacrylate.Unsaturated acids such as maleic acid (or its anhydride), fumaric acid, acrylic acid, itaconic acid and methacrylic acid are also suitable.

The liquid co-polymer of butadiene and acrylonitrile has an acrlonitrile content preferably in the range 20 to 40 parts per 100 parts of the co-polymer and the viscosity (at 50'C) is preferably, but not exclusively, in the range 5 to 300 Poise.

The peroxide suitable for use in the present invention has a halflife of preferably 10 seconds to 300 seconds at 150'C and m6re preferably a half-life of 40 seconds to 150 seconds at 150-C.

Suitable peroxides include tert butyl peroxyisobutyrate; l,l-ditert butyl peroxy-3,5,5-trimethylcyclohexane; l,l-ditert butylperoxycyclohexane; 2,2-ditert butylperoxybutane and tert butylperoxybenzoate. The amount of peroxide (or AZBN) used is in the range 0.01 parts to 10 parts per 100 parts of liquid co-polymer of butadiene and acrylonitrile and preferably 0.05 parts to 3 parts per 100 parts of liquid co-polymer of butadiene and acrylonitrile.

In an illustration of the practice of one aspect of the present invention, the PVC polymer is mixed with the constituents of the plasticizer, viz. the liquid co-polymer of butadiene and acrylonitrile, the ethylenically unsaturated organic compound and the organic peroxide (or AZBN). Next, the cross-linked nitrile rubber powder and the other constituents of the formulation, including a PVC heat stabilizer and, optionally, one or more of the following: a mineral filler, carbon black, a lubricant, a crosslinking co-agent and an antioxidant are thoroughly mixed together.

This mix is then melt-blended on a 2-roll mill or other suitable melt mixer, such as a Buss ko-Kneader, at a temperature typically in the range 130-185'C. The period of mixing is sufficiently long, at a given temperature profile, for at least 8 half-lifes of the peroxide to have elapsed. This time is readily determined by persons skilled in the art. The thoroughly mixed blend of plasticized PVC and nitrile rubber leaving the 2-roll mill, or other type of mixer, is cooled and granulated. These granules are fed to an extruder fram which emerges a PVC-NBR artefact. This artefact has excellent resistance to plasticizer migration, good oil resistance and having low temperature flexibility similar to that of the PVC-NBR blend when plasticized with a monaneric plasticizer (see Examples 1 and 2).

As an alternative to the above procedure the mixture of liquid copolymer of butadiene and acrylonitrile, and the unsaturated organic compound is heated with an organic peroxide for sufficient time (at least 8 half-lifes) to decompose essentially all of the peroxide, at a temperature typically between 80-C and 160*C. The resultant product is then mixed with the PVC to effect its plasticization.

The resultant plasticized PVC is then melt mixed on a 2-roll mill or in a Buss Ko-Kneader with the cross-linked nitrile rubber and the other constituents of the formulation employed. The thoroughly mixed blend is then granulated and extruded as described above to give artefacts having excellent resistance to plasticizer migration, good oil resistance and a similar low temperature fexibility to that of PVC-NBR plasticized with a monomeric plasticizer. In another aspect of the present invention the cross-linked nitrile rubber is anitted fran the fonmulation when a plasticized PVC compound is obtained. This too has good oil resistance and similar low temperature flexibility to that of the PVC plasticized with a monomeric plasticizer.

It is assumed that free radicals are generated when the peroxide is heated in the course of melt mixing on a 2-roll mill or other suitable melt mixer (or in the course of heating during separate PVC plasticization as described above). These free radicals are assumed by us to interact with the unsaturated ester and the liquid copolymer of butadiene and acrylonitrile, thereby promoting their chemical combination and thus forming the plasticizer for PVC and for PVC-NBR blends.It is further assumed that some, at least, of the resultant plasticizer becanes chemically attached through carbon-carbon covalent bonds to the nitrile rubber and to the PVC, a process further promoted by the incorporation of a cross-linking co-agent, such as trimethylolpropane trimethacrylate, triallyl cyanurate and glycol dimethacrylate, in the formulation.

These interpretations of the mechanism of formation of the plasticizer for PVC, PVC-NBR and/or PVC blended or combined with any other rubber or plastic, and illustrated by a chemical reaction scheme shown in Figure 1, are of a speculative nature only and they are not intended to constitute any part of the invention or to limit its scope.

The compression set of the artefacts of the present invention are typically in the range 50% to 70%. However, replacement of sate or all of the PVC in the formulation with chlorinated polyethylene leads to lower values of compression set but without affecting the other desirable properties, particularly the oil resistance and the low temperature flexibility. The chlorine content of the chlorinated polyethylene is preferably in the range 5% to 56% and more preferably in the range 25% to 40%.

A co-polymer of vinyl chloride and vinyl acetate may also be employed instead of PVC polymer in the practice of the present invention. The vinyl acetate of suitable co-polymers is preferably in the range 2-10 mole % By substituting a liquid co-polymer of butadiene and styrene or other butadiene-based liquid co-polymer or butadiene-based graft co-polymer for the liquid co-polymer of butadiene and acrylonitrile component used in the above preparation of PVC plasticizers, by heating with an unsaturated organic ester (or other class of unsaturated organic compound) in the presence of an organic peroxide, as described above, further plasticizers within the scope of the present invention are obtained.

PVC (or PVC-NBR) plasticized with one or more of these plasticizers has superior oil resistance and excellent resistance to plasticizer migration. Moreover, it has a low temperature flexibility similar to that of PVC plasticized with dioctyl phthalate or other monaneric plasticizer.

Example 1 One hundred parts by weight of PVC powder having a K-value of 64, 40 parts of a cross-linked powdered nitrile rubber, 30 parts of liquid butadiene-acrylonitrile co-polymer of viscosity 100 Poise at 50'C, 30 parts of diethyl naleate, 0.15 parts of organic peroxide having a half-life of 30 seconds at 160 C, 12 parts of powdered chalk, 1.5 parts of tribasic lead sulphate, 1.5 parts of carbon black and 0.8 parts of calcium stearate were dry powder blended.

The powder blend was then melt mixed in a 2-roll mill at 160'C for 4 minutes. The hide, upon removal fran the mill, was cooled to ambient temperature and granulated. The granules were fed into an extruder fran which emerged a strip of rectangular cross-section & m x 25mm. The properties of the strip were as follows: Ultimate tensile strength (mPa) ........ 15.8 Elongation at break (%) ...... 430 Hardness (Shore A-) ........... 83 Tear strength (KN/m) ............. 56 Compression set after 22 hours &commat; 70'C (%) ...... 64 Brittle temperature ( C) -35 Fluid ageing, 168 hours at 100 C ASTM No.l Oil Tensile strength (% change) ............. +8.5 Elongation (% change) .............. -4 Hardness (degree change) ...................... +9 Volume swell (%) .. . . . .. ... -6.8 Fluid ageing, 168 hours at.10QC ASTM No.3 Oil Tensile strength (% change)... ........+3 Elongation (% change). . ............-5.5 Hardness (degree change) .......... +5.2 Volume swell (%) ............... +6.3 Example 2 - Comparative Example The procedure desscribed in Example 1 was repeated except that 50 parts of dioctyl phthalate were used instead of the plasticizer of the present invention. The change in properties of the extruded strip after oil immersion tests are given below.

Fluid ageing 168 hours # 100 C - ASTM No.1 Oil Tensile strength (% change).. ................+18 Elongation (% change) ............... ............. -20 Hardness (degree change).... ... .. ....+22 Volume swell (%) ...................... -26 Fluid ageing 168 hours # 100 C - ASTM No.3 Oil Tensile strength (t change) ............ +31 Elongation (% change) ................ -13 Hardness (degree change) ....................... +22 Volume swell (%) .................. -15

Claims

WHAT I CLAIM IS:

1 A polymer composition comprising a mixture of 100 parts by weight of poly(vinyl chloride) and of fran 20 to 150 parts by weight of a plasticizer obtained by heating a liquid co-polymer of a diene monomer and a vinyl monomer, with an ethylenically unsaturated ester in the presence of an organic peroxide at a temperature of not less than 80 C and for sufficient time for the peroxide to be essentially all decomposed.

2 A polymer composition according to Claim 1 wherein 5 parts to

120 parts by weight of a cross-linked nitrile rubber having an acrylonitrile content of between 10% and 45% by weight is blended with the 100 parts by weight of PVC.

3 The liquid co-polymer according to Claims 1 and 2 has a viscosity of less than 350 Poise at 50"C.

4 The diene monomer content of the liquid co-polymer according to Claims 1 to 3 is in the range 45% to 85% by weight.

5 The diene monomer constituent of the liquid co-polymer according to Claims 1 to 4 is butadiene.

6 The diene monomer constituent of the liquid co-polymer according to Claims 1 to 4 is isoprene.

7 The diene monomer constituent of the liquid co-polymer according to Claims 1 to 4 is chloroprene.

8 The diene monomer constituent of the liquid co-polymer according to Claims 1 to 4 is a mixture of any of the diene monomers according to Claims 5 to 7.

9 The vinyl monomer constituent of the liquid co-polymer according to Claims 1 to 3 is acrylonitrile or derivative thereof.

l: The vinyl monomer constituent of the liquid co-polymer according to Claims 1 to 3 is styrene or a styrene derivative.

ii The vinyl monomer constituent of the liquid co-polymer according to Claims 1 to 3 is methyl methacrylate.

12 The vinyl monomer constituent of the liquid co-polymer is a mixture of any of the vinyl monomers according to Claims 9 to 11.

13 Extruded, moulded or calendered artefacts whenever obtained using the composition according to any of the preceeding Claims.