WO1997019117A1

WO1997019117A1 - Functional polymers and use thereof in reversible self-cross-linking compositions

Info

Publication number: WO1997019117A1
Application number: PCT/FR1996/001815
Authority: WO
Inventors: Patrice Breant
Original assignee: Elf Atochem S.A.
Priority date: 1995-11-20
Filing date: 1996-11-18
Publication date: 1997-05-29

Abstract

Flame retardant compositions that are thermoplastic at extrusion temperatures (240-270 °C) and cross-linkable below 210 °C, the cross-linking being reversible at certain temperatures, are disclosed. Said compositions include a polymer (A) having anhydride or hydroxyl functions and a bifunctional reagent (B) having either hydroxyl or anhydride functions, respectively, or (i) a function reacting reversibly with (A) and (ii) a function reacting irreversibly with (A). Said compositions are useful for sheathing electric cables.

Description

FUNCTIONAL POLYMERS AND THEIR USE IN REVERSIBLE SELF-CROSSLINKING COMPOSITIONS

Description

The present invention relates to functional polymers and their use in reversible self-crosslinking compositions.

It relates more particularly to reversible crosslinkable polymers (A)

- comprising at least two reactive functions between them,

- which are thermoplastic at extrusion temperatures and, - reticles below extrusion temperatures

Depending on the type of functions, the polymers (A) are for example thermoplastic between 240 and 270 ° C and crosslinked below 210 ° C

These polymers are useful as coextrusion binders for example for manufacturing multilayer films such as polyamide / binder / polyolefin or polyolefin / binder / EVOH / binder / polyolefin (EVOH denotes a copolymer of ethylene and vinyhque alcohol) or polyolefin / binder / SιO _x - PET

They are also useful as an adhesive (or binder) to adhere thermoplastics to the exterior surface of steel tubes that are used for pipelines protected against corrosion. They are also useful as impact reinforcers for polyamides or polyesters.

These polymers, mixed with flame retardant fillers, are useful for the flame retardant coating of electrical cables

The prior art has already described thermoreversible systems US Pat. No. 3,678,016 describes thermoreversible systems in which the pairs of co-reactive functional groups are anhydride / hydroxyl, anhydride / secondary amine, carboxylic acid / vinyl ether These systems are applied to vinyl polymers comprising a monomer which has a reactive functional group as described above and a monomer chosen from aromatic vinyls, esters of (meth) acrylic acids, vinyl esters, alpha-olefins and isobutylene crosslinking agents are either diols, secondary diamines, or divmylesether Only the styrene / maleic anhydride, styrene / hydroxyethyl methacrylate and styrene / N (terbutyl) aminoethyl methacrylate copolymers are exemplified

US Patent 3,933,747 to DOW describes the application of these reactions to styrene / maleic anhydride copolymers (SMA type)

US Patent 4987190A describes the thermoreversible crosslinking of mixtures of polypropylene and polyethylene grafted with maleic anhydride with diols such as 1, 4-methanolcyclohexene

EP 565734 and Patent JP-A-06,057,062 in priority JP 92-209847 disclose ethylene copolymer systems / maleic anhydnde and ethylene graft polymers pa ^r maleic anhydride which are crosslinked thermoréversiblement with polyols in the presence of catalysts as ethylene / acrylic acid copolymers partially neutralized in the form of alkali metal salts US 3,299,184 describes the use of alcoholamine (hydroxylamine type) to crosslink ethylene / bιcyclo- (2,2, 1) -hept2- copolymers ene-5,6- dicarboxylic

EP 158 540 describes adhesive compositions with thermoreversible crosslinking and resulting from the action of a divinylether on a copolymer of an olefin and an unsaturated carboxylic acid or its ester

The prior art has also described non-reversible systems for reinforcing thermoplastics FR 2 629 465 describes saturated polyesters reinforced by a mixture (i) of an ethylene / alkyl (meth) acrylate / epoxidized unsaturated copolymer and (n) of an ethylene / alkyl methacrylate / unsaturated carboxylic acid anhydride copolymer This crosslinking is not reversible

The prior art has always described reactions between functions carried by different polymers, each polymer carrying different functions

The polymers of the invention have many advantages

They are thermoplastic at extrusion temperatures, so they can be easily shaped according to techniques known to those skilled in the art of thermoplastics, for example at around 240 to 270 ° C. and then cooling below about 200 °. C - 210 ° C they crosslink, that is to say at room temperature and up to 200 or 210 ° C, they have good mechanical properties and excellent dimensional behavior when hot (200 ° C) This property is important for the coating of electric cables to avoid deformation due to the heat given off by the Joule effect or generated by local and occasional short circuits Another advantage is a very good resistance to fire Another advantage is recycling in fact, it is possible to re-extrude production scraps, non-standard materials or recovered materials, whereas this is not possible with the irreversible crosslinked compositions of the PRIOR ART Another advantage is the easy implementation for example, it is not necessary to use peroxides to crosslink

In the field of coating of electric cables, the most commonly used polymers are PVC and polyolefins

In applications where the coating is in direct contact with the electrical conductor, it is customary, to avoid deformation due to heat, to improve the dimensioned heat resistance of the polymers used for example by crosslinking them. is usually obtained by the use of radical initiators such as peroxides These products are generally not very easy to handle, dangerous and give rise, after their reaction, to odorous products which are harmful to the qualities of the coating. It is therefore important to try not to use this type of reagents, while keeping the material the same properties as those resulting from their use

In the event of a fire, or of a significant heat source, it is well known that synthetic polymers and in particular polyolefins are particularly sensitive, flammable materials, flame spreaders and smoke generators It is well known that the use of polyolefins having a fire resistance at least equivalent to that of PVC, is possible by the formulation of these polymers with so-called flame retardant additives

Reversible crosslinked compositions based on polyolefins and containing flame retardants, that is to say both flame retardant and having good dimensional resistance to heat, are not known.

These polymers make it possible to obtain products which are particularly suitable for use as coatings for electric cables, but also as tubes or in the design of objects obtained by molding, forming or filming according to the know-how of those skilled in the art.

The polymers (A) of the invention are only thermplastic at temperatures where the reactions do not take place, for example above 240 ° C. for those which carry hydroxyl functions and anhydride functions of carboxylic acid A very simple way to manufacture these polymers consists of a polymer having a single function, that is to say a single type of function and then adding the other function by grafting at a temperature or the reaction between the functions n does not take place

By way of example, the polymer (A) can carry the functions hydroxyl and carboxylic acid hydroxyl and anhydride of dicarboxylic acid hydroxyl and anhydride of carboxylic acids carboxylic acid and amino carboxylic acid and vinyl ether

For example, if the polymer (A) carries hydroxyl functions and anhydride functions of dicarboxylic acid, during cooling the hydroxyl functions of a chain (i) of polymer (A) reacting with the anhydride functions of dicarboxylic acid another chain (ii) of polymer (A) while the hydroxyl functions of chain (ii) react with the anhydride functions of dicarboxylic acids either of chain (i) or of another chain (iii) causing thus crosslinking.

By way of illustration, the principle of this reversible reaction between an anhydride and a hydroxyl is recalled using the following diagram:

R OH + R - C - C - R R - C - R

2 / \ 3

(I V) O COO R + C OOH

(I I I) (D (l l)

in which R1, R2 and R3 denote polymer chains (A). The reaction moves in direction 1 when the temperature decreases and direction 2 when it increases.

The thermoreversibility is conditioned by the equilibrium constant of the system as defined below which decreases with temperature:

pe ²

K =

(ab-pe) ^* (a-pe)

(pe) represents the quantity of ester (I) or acid (ll) functions formed and (a) and (b) respectively the quantity of anhydride functions (III) and hydroxyl functions (IV) present initially. If R1 or (R2.R3) represents polymer chains, (pe) represents the degree or density of crosslinking of the system (Pe) must be sufficiently large at the working temperatures of the material to give it good dimensional strength and sufficiently low at manufacturing or processing temperatures of the material to give it a thermoplastic character sufficient for good handling

The present invention also relates to reversible crosslinkable compositions comprising these polymers (A) and optionally products (B), flame retardant fillers (C) of inert polymers (D), that is to say reacting neither with (A) nor with (B), anti oxidants, anti UV, etc

These compositions make it possible to obtain p ^r oduιts qu ^{1 which} are particularly suitable for being used as coatings for electric cables, but also as tubes or in the design of objects obtained by molding, forming or filming according to the know-how of the people of the art The present invention also relates to these objects as well as electrical cables whose coating comprising the compositions of the invention

By way of example of polymers (A), mention may be made of polymers (A1) carrying hydroxyl functions which are grafted with dicarboxylic acid anhydrides and polymers (A2) carrying anhydrous dicarboxylic acid functions which grafted with monomers carrying hydroxyl functions

The hydroxyl functions of (A1) can be provided by copolymerized or grafted monomers. Examples of polymers (A1) that may be mentioned are: copolymers of ethylene, vinyl alcohol and optionally vinyl acetate (that is to say the ethylene-vinyl acetate copolymers partially or completely hydrolyzed),

- copolymers of ethylene, optionally of a vinyl ester of saturated carboxylic acid such as for example vinyl acetate grafted or copolyméπsés with a hydroxyalkyl (meth) acrylate such as hydroxyethyl (meth) acrylate ,

- copolymers of ethylene, optionally of an ester or an unsaturated carboxylic acid salt such as for example an alkyl (meth) acrylate or a zinc (meth) acrylate grafted or copolymerized with a (meth) acrylate hydroxyalkyl such as hydroxyethyl (meth) acrylate,

- polyethylene, polypropylene, copolymers of ethylene and an alpha olefin, EPR and EPDM rubbers, styrene / butadiene / styrene (SBS) or styrene / ethylene-butene / styrene (SEBS) block copolymers or styrene / isoprene / styrene (SIS), all of these polymers being grafted with hydroxy (meth) acrylate such as hydroxyethyl (meth) acrylate

The unsaturated dicarboxylic acid anhydrides which are grafted onto these polymers (A1) can be chosen from maleic anhydride, itaconic anhydride, citraconic anhydride or tetrahydrophthalic anhydride

The anhydride dicarboxylic acid functions of (A2) can be provided by copolymerized or grafted monomers

Examples of polymers (A2) that may be mentioned

copolymers of ethylene, optionally of a vinyl ester of saturated carboxylic acid such as for example vinyl acetate, grafted or copolyméπsés with a dicarboxylic acid anhydride msature such as for example maleic anhydride,

- copolymers of ethylene, optionally of an ester or an unsaturated carboxylic acid salt such as for example an alkyl (meth) acrylate or a zinc (meth) acrylate grafted or copolymerized with an acid anhydride unsaturated dicarboxylic such as for example maleic anhydride,

- polyethylene, polypropylene, copolymers of ethylene and an alpha olefin, EPR and EPDM rubbers, styrene / butadiene / styrene (SBS) or styrene / ethylene-butene / styrene (SEBS) or styrene block copolymers / isoprene / styrene (SIS), all these polymers being grafted with unsaturated dicarboxylic acid anhydrides such as for example maleic anhydride

The hydroxyl functions which are grafted onto these polymers (A2) can come from the grafting of a hydroxyalkyl (meth) acrylate such as hydroxyethyl (meth) acrylate.

These graftings are carried out according to techniques known to those skilled in the art, generally by radical initiation, in the molten state or in an appropriate solvent or even even in the solid state.

The graft can be previously dispersed in a polymer (D) and the radical initiator, for example (D) can be a polyethylene

Advantageously, the polymers (A) are copolymers (A2) of ethylene of an alkyl (meth) acrylate and of maleic anhydride grafted with hydroxyethyl (meth) acrylate.

Preferably, the (meth) acrylate is chosen from methyl (meth) acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate and 2-ethylhexyl acrylate The amount of (meth) acrylate can represent up to 40% by weight of the copolymer, the amount of maleic anhydride can be between

0.5 and 5% by weight of the copolymer The product (B) comprises at least two functions which do not react with each other at the extrusion temperatures of (A) but which react reversibly with the functions of (A) to cause a reversible crosslinking The product (B) is thermoplastic or melted at the extrusion temperatures of (A) Product (B) can be either a molecule or a polymer

It is recommended to choose the product (B) so that it remains with the polymer (A) when it is heated to de-crosslink and return to the thermoplastic state before cooling to crosslink again, that is to say to avoid the loss by diffusion or exudation volatility When we choose (B) from molecules, preferably selected low-volatility products in this middle way of ^the e exemp products (B) include

- the above polymers (A1) and (A2), these polymers not being grafted with the second function and provided that there are at least two functions per polymer chain - polyols containing amino functions to crosslink polymers

(A) having anhydride functions, for example tπs (hydroxymethyl) - aminomethane

As regards the crosslinking kinetics of the polymer (A) on itself possibly in mixture with (B) and in particular of the anhydrous / hydroxyl reaction, it can be advantageously modified by the use of suitable additives acting either catalysts are as activators of the reaction They are generally basic products like salts of carboxylic acids, tertiary amines or mineral bases It can also be products with acid character like carboxylic acids or organic sulfonic acids (like paratoluenesulfonic acid) or LEWIS acids or acids such as tin salts, boric acid or acids containing phosphorus or their derivatives, such as dilauratedibutyltin, orthoboric acid or phosphoπque acid respectively The flame-retardant fillers (C) are generally mineral fillers suitable for the use of the material. xample, magnesium hydroxide, aluminum hydroxide, boemithe, the various hydrotalcites, calcium carbonate The effectiveness of these additives can be enhanced by their mixing The effectiveness of these flame-retardant fillers can also be improved by the joint incorporation of products such as antimony tπoxide or zinc hydroxystannate or zinc stannate used at suitable levels For this type of additive, a suitable fire resistance in polyolefins is generally obtained for an overall mass content greater than 60% by weight of A + C + possibly (B + D).

The additives providing improved fire resistance can also be so-called intumescent systems comprising polyols such as pentaerythritol and products carrying nitrogen or phosphorus functions such as for example ammonium polyphosphate or melamine cyanurate. The effectiveness of these systems can also be improved by the joint use of additives such as antimony oxide or different zeolites. For this type of additive, a suitable fire resistance is generally obtained for an overall mass content greater than 30% by weight of A + C + possibly (B + D).

Fire resistance can also, when the circumstances of use of the final material allow, be improved by the use of halogenated derivatives such as decabromodiphenyloxide or decabromodiphenyl generally in combination with products such as antimony oxide. For this type of additive, a suitable fire resistance is generally obtained for an overall mass content greater than 10% by weight of A + C + possibly (B + D).

The flame retardant additives can be introduced at the same time as the polymer (A) and optionally (B), and (D) or subsequently under conditions and with methods compatible with the crosslinking kinetics, that is to say at high temperature. Their thermal stability must be sufficient not to induce untimely decomposition.

The compositions of the invention may also include anti oxidants, anti UV, pigments, carbon black, etc.

Those skilled in the art easily determine the amounts of A, B, C and D as a function of the crosslinking rate sought, that is to say of the mechanical properties and the degree of fireproofing. The quantities of (A) and (B) also depend on the quantity of functions which they contain. The grafting of the polymer (A) is carried out according to the usual techniques in solution or in the molten state. The graft can be introduced in the solid state diluted in a powder of polymer (D) such as for example polyethylene. The optional polymer (B) can be introduced as such into (A) or in the form of a masterbatch, for example diluted in (D). The compositions of the invention are prepared by the usual methods of the thermoplastics industry. The mixing can be carried out in an internal mixer, an extruder, a twin cylinder or a calender at a suitable temperature. Typically, mixing is carried out on a calender at a temperature of 250 ° C. The mixtures are easily calenderable which demonstrates their thermoplasticity at this temperature

The product is then placed in the form of 2 mm thick plates in a press at 250 ° C., then the test pieces necessary for the evaluation tests are cut out with a punch.

The mechanical properties of the material produced and used are evaluated by measuring the dynamometric properties such as elongation at break (AR) and resistance to break (RR) according to ISO R 527 / 1A on test pieces, having the shape of dumbbells of dimensions 105 ^* 10 ^* 4 mm ^Λ 3, recommended by the ISO standard in reference, subjected to a traction speed

The dimensional resistance to heat is evaluated by the elongation under hot load of a test piece of ISO R 527 type. The typical test temperature is 200 ° C. and the test piece is subjected to an initial stress of 2 bars for 15 min

The variation in elongation measured relative to the initial length of the specimen defines a quantity also called creep resistance Typically, a material having good dimensional resistance to heat, such as a crosslinked polyethylene, exhibits creep resistance at 200 ° C., after 15 min, less than 100% A poorly crosslinked product lengthens by more than 100%, which can lead to a rupture of the test piece by excessive reduction in its section A product that is too crosslinked does not lengthen a rupture of the specimen can occur due to poor mechanical properties, in particular a low breaking strength

The fire resistance is evaluated by measuring the oxygen index (IOL) as defined in standard ASTM D2863-70 on test pieces in the form of bars of 80 ^* 10 ^* 4 mm ³ A product has good behavior on fire for an IOL greater than 30

Examples (the proportions are in% by weight) We exemplify the grafting of HEA (hydroxyethyl acrylate) on a polymer containing "maleic anhydride" copolymerized functions

The grafting was carried out on a twin-screw contra-rotating extruder type BRABENDER ZKS at a screw speed of 60 revolutions per minute with a temperature profile of 150-230-250 ° C (respectively feed hopper / extruder body / outlet) The graft was previously dispersed on a polyethylene powder LLDPE (50/50) as well as the radical initiator (DHBP) (ditertiobutyl hexane peroxide) separately (5/95) The products were dried beforehand overnight in vacuum at 80 ° C. The graftable polymer (LOT 3410) is an ethylene / butyl acrylate / maleic anhydride (82/15/3) copolymer with a melt flow index at 190 ° C. under 2 16 kg of 6 3 dg / min

The final compositions are indicated below, the amount of polymer (A) is the complement to 100%

The thermoreversibility is demonstrated by measuring the meit-index (in dg / min) of these products at different temperatures ^•

Crosslinking at 200 ° C is demonstrated by the creep test at this temperature under a load of 2 bars measured by the elongation obtained after

15 min The products were previously loaded, in several installments, to a final content of 60% magnesium hydroxide on BRABENDER ZSK at a temperature profile of 260/260/260 ° C

Cross-linking is obtained by a sufficient content of grafted HEA. Product R has good mechanical properties, it is thermoplastic at 260 ° C. and has the properties of a cross-linked product at 200 ° C. All these products have an IOL of 30

Claims

claims

1. Reversible crosslinkable polymers (A) comprising at least two reactive functions with each other, which are thermoplastic at extrusion temperatures and crosslinked below extrusion temperatures

2. Polymers according to claim 1 chosen from - polymers (A1) carrying hydroxyl functions and which are grafted with an ^ ydπdes of dicarboxylic acids

- polymers (A2) carrying anhydride dicarboxylic acid functions and which are grafted with monomers carrying hydroxyl functions

3. Reversible crosslinkable compositions comprising at least one polymer (A) of claims 1 or 2, optionally a product (B) having at least two functions not reacting with each other at the extrusion temperatures of A but reacting reversibly with the functions of (A) to cause a reversible crosslinking, possibly a flame-retardant filler (C) and possibly a polymer (D) reacting neither with (A) nor with (B)

4. Composition according to claim 3 in which the product (B) is chosen from the polymers (A1) and (A2) of claim 2 and the polyols containing amino functions such as tπs (hydroxymethyl) -amιnomethane

5. Electric cables with a coating comprising the compositions of claims 1 to 4

6. Tubes, molded object or films comprising the compositions of claims 1 to 4

Coextrusion binder or adhesive comprising the compositions of claims 1 to 4