Fibre reinforcements, be they in the physical form of chopped fibres, cords, woven fabrics, fabric mats and so on, have long been used as a means of improving the physicomechanical properties of elastomers and hence also the composite articles constructed in that manner.

A general trend in the preparation of composite materials and articles has been the imposition of increasingly greater demands on the role of the fibre reinforcement.

This in turn has placed an increasing emphasis on the need for excellent bond strengths between the fibre and the elastomer, not only at room temperature but also commonly at elevated temperature. This latter requirement is the case for composite articles that find service in aggressive environments such as vehicle engine bays.

There has been a recent trend in increasing engine- compartment operating temperatures, partly as a result of a reduction in size of engine compartments and also as a result of exploiting higher engine operating temperatures as a means of achieving reduced exhaust emissions.

These factors have led to a real need for improved fibre-to-rubber bonding as used in composite articles such as power transmission belts, which need to maintain excellent performance over a range of operating temperatures.

As the service environment of the composite becomes more aggressive, the use of aramid fibre and hydrogenated nitrile rubber becomes increasingly attractive. In the main this is due to the excellent chemical and physicomechanical properties of these two components.

However, it is well known that these two substrates are not easily bonded together and so various attempts have been made using resorcinol-formalin-latex (RFL) based treatments to improve the bond strength between the fibre and the elastomer. Similar approaches have also been made for other combinations of fibre and elastomer.

Typically these involve the use of"primer" treatments for the fibres, such as epoxies or polyisocyanates, which are applied prior to the"RFL" treatment itself and may be followed by a"cement" treatment to improve further the bonding to the rubber.

Alternatively a two-or three-step"repeated RFL" application can be used to some effect as in US 4,409, 055, US 5,306, 369 and US 5,728, 245.

This invention describes a treatment process for reinforcement fibres, whatever their form, which, when combined with elastomers, results in a composite material with outstanding fibre to rubber bonding characteristics.

It is particularly suitable for the bonding of aramid fibre to HNBR elastomer, though it is also suitable for other fibres such as polyester and nylon and other elastomers, both synthetic and natural, such as styrene butadiene rubber or Standard Malaysian rubber, for example.

According to a first aspect of the present invention, there is provided a method for the bonding of fibres to rubber comprising the steps of: (a) treating the fibres with a primer;

(b) treating the fibres with a resorcinol/formalin/latex preparation ; (c) curing the rubber in intimate contact with the treated fibres, wherein the primer comprises a ring-opened, maleinised polybutadiene and a phenolic derivative comprising electron-withdrawing groups.

According to a second aspect of the present invention, there is provided a primer which comprises a ring-opened, maleinised polybutadiene and a phenolic derivative comprising electron-withdrawing groups.

According to a third aspect of the present invention, there is provided a composition which comprises a primer according to the second aspect of the invention in combination with a resorcinol/formalin/latex preparation.

The fibre treatment process comprises a primer, which can be used separately prior to the RFL treatment, or as a bonding promoter in the RFL preparation itself, followed by an optional cement treatment. The primer treatment can be in the form of an aqueous or an organic solution and is comprised of a novel combination of compounds that afford synergistic properties as a primer (or RFL bonding promoter additive).

The first of the two primer components consists of a ring-opened, maleinised polybutadiene (PBD), the second being a phenolic derivative comprising electron- withdrawing groups. Prior art literature such as US 5,077, 127, US 5,300, 569 and US 5,521, 248 contains examples of the use of these families of bonding promoters individually as rubber-compounding additives, but not as a combination to form a primer, as in the present invention. It has been demonstrated that the

bonding potential of this combination is superior to that of each individual component.

Precisely why the bonding potential of the combined primer components is superior to that of each individual component is unknown. It is possible that the two primer components work synergistically. Alternatively, it is possible that the primer components form a complex or indeed react to generate another chemical species.

The maleinised PBDs are preferably ring-opened by an alcohol to yield half-ester derivatives, although hydrolysis to form a diacid using water is possible.

Examples of the PBD component include the isobutyl half- ester derivative of maleic anhydride adducts of PBD. The preparation of such derivatives is standard in the art, and can be found in US 5,300, 569.

In aqueous form it is possible to form the PBD derivative as an aqueous solution, preferably in distilled (deionised) water, for example using a suitable alkaline hydroxide solution as the solvent. It may be preferable to make the solution with ammoniated or aminated water as the solvent, for example using ammonia, triethylamine or ethanolamine. The solution should be made to a concentration so that the viscosity is of such a consistency to allow ease of handling in a manner preferred by the user, and may for example be in the range 5 and 50 wt%. Thus, a less viscous solution would be more suited to dipping whilst a more concentrated solution would be more suited to application by brushing.

In organic solution it is preferable to use solvents such as toluene, xylene or benzene, perhaps in combination with polar solvents such as acetone or methyl ethyl ketone, to achieve a solution concentration of the polybutadiene derivative that satisfies the particular

viscosity requirements of interest to the user, as described above.

The phenolic derivatives comprise electron- withdrawing groups, and are preferably halogenated.

Examples of the phenolic derivative include 4- chlorophenol and 4-bromophenol, together with the resorcinol/formaldehyde and ethoxylated resorcinol/formaldehyde condensates of said substituted phenols, for example Casabond E (manufactured by Thomas Swan & Co. , UK). This illustrates the fact that the nature of the phenolic derivative (chemical structure and RMM) can vary appreciably and it is not limited to a simple class of compounds.

It is possible to form the phenolic derivatives described above in the form of an aqueous solution, preferably in distilled (deionised) water, through the formation of the alkaline metal salt using a suitable alkaline hydroxide solution. It is preferable to form the quaternary salt of the phenolic derivative via dissolution in ammoniated or aminated water, examples of which include ammonia, triethylamine and ethanolamine.

It is recommended to make the solution of the phenolic derivative to a concentration of between 5 and 50 % although it is more preferable to make the solution concentration in the range 10 and 30% by weight.

It is preferable to prepare the primer with a weight ratio of ring-opened, maleinised polybutadiene to phenolic derivative comprising electron-withdrawing groups in the range 1: 19 to 19: 1.

The second treatment is composed of a resorcinol- formaldehyde-latex condensate (RFL).

The preparation of such RFL's is well known in the art. However, it is useful to state that it is standard practice to prepare such an RFL through the reaction of

resorcinol and formaldehyde in the ratio of 1.0 : 1.2 to 1.0 : 2.0, carried out in an aqueous solution of sodium hydroxide. This is followed by the addition of a controlled amount of latex such that the ratio of RF resin to latex is normally in the range 15-20 parts resin to 100 parts latex, the choice of latex being determined largely by the elastomer the treated fibre is to be bonded to.

As stated earlier the primer treatment can be used as a separate treatment step to the RFL treatment step.

Alternatively, the primer can be used as an additive to the RFL thereby reducing the total number of dipping stages for the fibres. The RFL treatment can be repeated one or more times if desired.

Following the RFL treatment stage, whether or not it contains a primer additive, it is optional to treat the fibres with a final, cement treatment. Cement treatment is standard in the art, and the method disclosed in EP0353473, for example, is particularly suitable. The cement may be composed of an organic solution, preferably in a polar solvent such as methyl ethyl ketone, containing a blend of a blocked isocyanate and a chlorinated rubber. An example of the blocked isocyanate includes butanone oxime blocked oligomeric 4, 4'- diisocyanatodiphenyl methane ; examples of the chlorinated rubber include Pergut S10, a chlorinated polyisoprene manufactured by Bayer.

It is recommended to use the dip treatments according to specific conditions of dip time, drying time and drying temperature and so on, in order to obtain the best possible performance from the treatment systems.

It is also recommended that the fibre be immersed in the primer solution for between 1 and 300 seconds, and preferably for between 60 and 300 seconds; drying of the

dipped fibre is recommended at between 100 and 250 °C for between 60 and 300 seconds.

It is recommended that the RFL, or the RFL containing a primer'additive as a bonding promoter, be used to treat the fibre for between 1 and 300 seconds; drying conditions are recommended as being 2-3 minutes at 200-250 °C if the fibre was pretreated with primer; drying conditions are recommended as being 1-5 minutes at 100- 150 °C followed by 2-3 minutes at 200-250 °C if the fibre was dipped into the RFL containing a bonding promoter additive.

Finally, the treated fibre can be further treated using a cement solution. It is recommended that the immersion time for this stage be in the range 1-60 seconds, and preferably in the range 1-20 seconds.

Drying conditions for this treatment are recommended as being in the range 100-150 °C for 1-5 minutes, where the choice of drying temperature is lower than the deblocking temperature of the blocked isocyanate component of the cement treatment. This completes the treatment of the fibre.

Bonding of the treated fibre (fibre, fabric, cord, mat and so on) is recommended to be carried out according to conventional means familiar to those skilled in the art. In essence this consists of placing the treated fibre in intimate contact with the elastomer component of the reinforced composite under construction, and under conditions of elevated temperature and pressure effecting a vulcanisation reaction of the elastomer during which the fibres are bonded to the elastomer. It is preferable that the vulcanisation temperature is such that it is greater than the deblocking temperature of the blocked isocyanate of the cement treatment, in order to bring about the deblocking reaction and hence to maximise the

bonding potential of the treated fibre. The actual conditions of vulcanisation are dictated largely by the type of elastomer used in the composite.

Fibre-reinforced elastomeric artefacts constructed in such a way as has been described, possess excellent fibre-to-rubber bonding characteristics. Artefacts prepared in such a manner may include, but need not be limited to, high performance power transmission belts, conveyor belts, hoses and vehicle tyres. For example, artefacts prepared according to the present invention are found to perform well at elevated temperatures like those encountered in aggressive environments such as vehicle engine bays.

Furthermore, the present invention provides a method and composition for bonding fibres to rubbers that avoids . the use of epoxies as primers; a feature that is welcomed by the Industry.

EXAMPLES Example 1 Aromatic polyamide fabric, measuring 2x8 inches, was dipped into a primer comprising a 50: 50 blend of ca. 20% solids Casabond E (a condensate of resorcinol, formaldehyde and 4-chlorophenol manufactured by Thomas Swan & Co. Ltd) and ca. 20% solids Lithene YS501 (a ring- opened, maleinised polybutadiene, also known as Lithene N4-5000: 25MA HE AQ, manufactured by Synthomer Ltd.).

The primed fabric was dried for 5 minutes at 120 °C.

The fabric was then treated with a resorcinol/formalin/latex solution comprised as follows and being referred to hereafter as the HNBR RFL solution: 10 parts resorcinol ; 6.8 parts 40% formalin; 237.2 parts HNBR latex (Chemisat LCH-7335X) ; 184 parts water. The fabric was then dried at 200 °C for 2 minutes.

The fabric was then treated with a cement solution composed of 10 parts chlorinated rubber (Pergut S10, Bayer); 10 parts butanone oxime blocked oligomeric 4, 4'- diisocyanatodiphenyl methane (Thomas Swan R & D) ; 40 parts toluene ; and 40 parts methyl ethyl ketone.

Following immersion in the cement the treated fabric was dried in an oven for 2 minutes at 120 °C.

The fabric was cut into two 1x8 inch strips that were placed in intimate contact with unvulcanised HNBR compound to form a fabric-rubber-fabric composite. This layered structure was cured at 153 °C for 35 minutes to provide a test-specimen measuring 6x1x0. 25 inches in the rubber/fabric central section and having 1-inch overhangs of fabric at the ends to facilitate tensile testing.

Room temperature tensile-testing was performed (180° angle, 100 mm min-1 cross-head) to determine the fabric- to-rubber bond-strength. The results are provided in Table 1.

Table 1. Example 1 Tensile Testing Results. Maximum Bond-strength/N. per 607 Inch Width Average Bond-strength/N. per 544 Inch Width Failure Mode Totally Cohesive Failure/Rubber Tear

Examples 2-4 Aromatic polyamide fabric of the form described in Example 1 was dipped into a range of primers comprising different blends of ca. 20% solids Casabond E (Thomas Swan & Co. Ltd) and ca. 20% solids Lithene YS501 (Synthomer Ltd.). The primed fabric pieces were dried for 5 minutes at 120 °C.

Each piece of fabric was then treated with the RFL of Example 1, being dried in the manner described in the earlier example and subsequently treated with the cement of Example 1, being dried in the manner described in that example.

The fabric pieces were cut into two lx8-inch strips that were placed in intimate contact with unvulcanised HNBR compound to form fabric-rubber-fabric composites.

Curing was as per Example 1.

Room temperature tensile-testing was performed as per Example 1 to give the results reported in Table 2.

Table 2. Examples 2-4 Tensile Testing Results. Casabond E Example 2 Example 3 Example 4 Content of (20%) (35%) (50%) Primer Max. Bond-87 864 777 strength/N. per Inch Width Ave. Bond-40 371 410 strength/N. per Inch Width Failure Mode Partly Totally Partly Cohesive Cohesive Cohesive

Examples 5 and 6 For Examples 5 and 6, aromatic polyamide fabric samples of the form described in Example 1 were dipped into a range of primers comprising 50: 50 blends of Casabond E (Thomas Swan & Co. Ltd) and the water-based PBD Derivatives (Examples 5 and 6, respectively) listed in Table 3, below.

TABLE 3: PBD Backbone Amine Degree Pendent Molecular Used to of Ester Weight Form Maleinisation Group Salt Example 5 5000 20 wt% Butanol Ethanolamine Example 5 5000 20 wt% Butanol Ammonia The primed fabric pieces were dried for 5 minutes at 120 °C. Each piece of fabric was then treated with the RFL of Example 1, being dried in the manner described in the earlier example and subsequently treated with the cement of Example 1, being dried in the manner described in that example.

The fabric pieces were cut into two lx8-inch strips that were placed in intimate contact with unvulcanised HNBR compound to form fabric-rubber-fabric composites.

Curing was as per Example 1.

Room temperature tensile-testing was performed as per Example 1 to give the results reported in Table 4.

Table 4. Examples 5 and 6 Tensile Testing Results. PBD Derivative in Primer Example 5 Example 6 Max. Bond-strength/N. per 352 777 Inch Width Ave. Bond-strength/N. per 240 410 Inch Width Failure Mode Partly Partly Cohesive Cohesive

Examples 7-9 For Examples 7 to 9, respectively, aromatic polyamide fabric samples of the form described in Example 1 were dipped into the primer described in Example 1.

The immersion time of the fabric in the primer was varied as described in Table 5 below.

TABLE 5 : Fabric Immersion Time <BR> <BR> n Prn me es Example 7 1 Example 8 3 Example 9 5 The primed fabric pieces were dried for 5 minutes at 120 °C. Each piece of fabric was then treated with the RFL of Example 1, being dried in the manner described in the earlier example and subsequently treated with the cement of Example 1, being dried in the manner described in that particular example.

The fabric pieces were cut into two lx8-inch strips that were placed in intimate contact with unvulcanised HNBR compound to form fabric-rubber-fabric composites.

Curing was as per Example 1.

Room temperature tensile-testing was performed as per Example 1 to give the results reported in Table 6.

Table 6. Examples 7-9 Tensile Testing Results. Example 7 8 9 Max. Bond-strength/N. 623 326 598 per Inch Width Ave. Bond-strength/N. 425 189 383 per Inch Width Failure Mode Mainly Partly Partly Cohesive Cohesive Cohesive

Examples 10-12 For Examples 10 to 12, respectively, aromatic polyamide fabric samples of the form described in Example 1 were dipped into the primer described in Example 1, namely a blend of a phenolic derivative and a PBD derivative. The immersion time of the fabric in the primer was maintained at 5 minutes for all three examples in question.

TABLE 7: Fabric Drying Conditions (Dipped In Primer) Example 10 2 mins @ 120 °C Example 11 5 mins @ 120 °C Example 12 2 mins @ 200 °C The drying conditions for the dipped fabric was varied as described in Table 7 above. Each piece of fabric was then treated with the RFL of Example 1, being dried in the manner described in the earlier example and subsequently treated with the cement of Example 1, being dried in the manner described in that particular example.

The fabric pieces were cut into two lx8-inch strips that were placed in intimate contact with unvulcanised HNBR compound to form fabric-rubber-fabric composites.

Curing was as per Example 1.

Room temperature tensile-testing was performed as per Example 1 to give the results reported in Table 8.

Table 8. Examples 10-12 Tensile Testing Results. Example 10 11 12 Max. Bond-strength/N. 642 712 533 per Inch Width Ave. Bond-strength/N. 418 492 341 per Inch Width Failure Mode Mainly Totally Partly Cohesive Cohesive Cohesive

Examples 13-15 For Examples 13 to 15, respectively, aromatic polyamide fabric samples of the form described in Example 1 were treated with one of three primers based on that described in Example 1, namely a blend of a phenolic derivative and a PBD derivative. The three primers of the present examples varied according to their overall concentration in an aqueous medium, as described in Table 9 below: TABLE 9: Primer Concentration (wt% solids) Example 13 37 Example 14 20 Example 15 15 The drying conditions for the three examples were standardised at 5 minutes at 120 °C. Each piece of fabric was then treated with the RFL of Example 1, being dried in the manner described in the earlier example and subsequently treated with the cement of Example 1, being dried in the manner described in that particular example.

The fabric pieces were cut into two lx8-inch strips that were placed in intimate contact with unvulcanised HNBR compound to form fabric-rubber-fabric composites.

Curing was as per Example 1.

Room temperature tensile-testing was performed as per Example 1 to give the results reported in Table 10.

Table 10. Examples 13-15 Tensile Testing Results. Example 13 14 15 Max. Bond-strength/N. 449 705 748 per Inch Width Ave. Bond-strength/N. 261 483 520 per Inch Width Failure Mode Partly Mainly Mainly Cohesive Cohesive Cohesive

Examples 16-18 For Examples 16 to 18, respectively, polyester or aromatic polyamide fabric samples of the form described in Example 1 were treated with the bonding agents listed in the table below, whereby the bonding agents were used as an additive to an RFL treatment. The RFL treatment used for the aramid in Example 16 was as per Example 1.

The vinyl-pyridine- (VP) based RFL, hereafter referred to as"VP-RFL", was used for the polyester and nylon in Examples 17 and 18 and was prepared according to standard procedures using the following composition: 33. Opbw resorcinol, 48.6pbw 37% formaldehyde solution, 2.8pbw 32% sodium hydroxide solution, 732. Opbw Pliocord VP latex (Goodyear), 893.6pbw water and 28.8pbw 33% ammonium hydroxide solution.

TABLE 11: Fabric Treatment Details Fabric Initial RFL Treatment RFL Cement Primer 1 treatment Treatment Treatment 16 Aramid None 20 pbw Primer None As per as per Example Example 1 1 in 80 pbw RFL Cement as per Example 1 17 Polyester None 702 pbw Primer VP-RFL None as per Example 1 in 1000 pbw VP-RFL 18 Nylon None 100 pbw Primer VP-RFL None as per Example 1 in 100 pbw VP-RFL The dipping and drying conditions for the three examples were in accordance with conditions used by those familiar with the art. Following treatment the fabric pieces were cut into two lx8-inch strips that were placed in intimate contact with unvulcanised rubber as described in the table below and cured to form fabric-rubber-fabric composites using the conditions appropriate for the type of rubber. The HNBR used was as per Example 1; the styrene butadiene rubber compound (SBR, grade 142S) was supplied by RAPRA.

Room temperature tensile-testing was performed as per Example 1 to give the results reported in Table 12.

Table 12. Examples 16-18 Tensile Testing Results.

Example 16 17 18 Rubber the Fabric HNBR SBR SBR was Cured Onto Max. Bond-strength 668 571 461 /N. per Inch Width Ave. Bond-strength 386 431 243 /N. per Inch Width Failure Mode Mainly Some Fibres Partial Cohesive Retained in Fabric Rubber Failure Example 19 For Example 19, aromatic polyamide fabric samples of the form described in Example 1 were treated with the bonding agents listed in the table below. The bonding agents were applied in a manner standard to those familiar with the art.

The primer for Example 19 was composed of the following materials: a 1: 1 (solids) mixture comprising a solution of a modified, maleinised polybutadiene and a phenolic derivative.

The modified, maleinised polybutadiene consisted of the iso-butyl mono-ester of a maleinised polybutadiene which has an original number average molecular weight (Mn) of between 4000 and 5000 and was maleinised to 20 wt%.

The phenolic derivative consisted of the condensate of a mixture of 37% formaldehyde solution, resorcinol and 4-chlorophenol in the ratio 735: 650: 616 by weight.

Following appropriate processing to obtain a dry product the condensate was dissolved to form a solution in methyl ethyl ketone and toluene.

The RFL treatment used for the current example was as per Example 1 (HNBR-RFL). The cement used was as per Example 1.

TABLE 13: Fabric Treatment Details Fabric Primer RFL Cement Treatment Treatment Treatment Example Aramid Phenolic HNBR-RFL as As per 19 Derivative and PBD per Example Example 1 Derivative in 1 Cement Methyl Ethyl Ketone/Toluene

The dipping, drying and curing conditions, onto HNBR compound, were in accordance with conditions used by those familiar with the art.

Following treatment the fabric pieces were cut into two lx8-inch strips that were placed in intimate contact with unvulcanised HNBR as per Example 1 and cured to form fabric-rubber-fabric composites. Room temperature tensile-testing was performed as per Example 1 to give the results reported in Table 14.

Table 14. Example 19 Tensile Testing Results. Example 19 Max. Bond-strength/N. per 496 Inch Width Ave. Bond-strength/N. per 293 Inch Width Failure Mode Partial Cohesive Failure