GB2114579A - Method of reinforcing rubber - Google Patents

Abstract

The invention relates to a method of reinforcing rubber using a phenanthrene/formaldehyde/phenol resin as reinforcing agent. Reinforcement is effected by cross-linking a blend of 100 parts by weight of a rubber (for instance SBR, nitrile or natural rubber), from 5 to 150 parts of a phenanthrene/ formaldehyde/phenol resin, from 1 to 5 parts of a vulcanising agent for the rubber and from 5-to 15 parts per hundred parts of resin of formaldehyde or a formaldehyde donor.

Description

SPECIFICATION Method of reinforcing rubber This invention relates to a method of reinforcing rubber, and particularly relates to reinforcing rubber with a phenanthrene-based resin.

In compounding either natural or synthetic rubbers it is common practice to incorporate a resin which plasticises the rubber and thereby aids processing. After processing,the rubber compound is heated to a temperature at which both the rubber and the resin are cross-linked, to give a vulcancised reinforced rubber. The vulcanisation is achieved by the cross-linking of the rubber and the reinforcement is achieved by the simultaneous cross-linking of the resin.

It has not been usual to use phenol/formaldehyde resins as plasticising/reinforcing agents for rubbers, since these resins and rubbers are, in general, incompatible. However certain alkyl substituted-phenol/formaldehyde resins are sufficiently compatible with rubbers to be able to be used as plasticising/reinforcing agents.

We have discovered that certain resins derived from phenanthrene, phenol and formaldehyde can adequately reinforce rubbers, and in some cases the reinforcement achieved is better than that obtained with conventional plasticising/reinforcing resins. It is therefore an aim of the present invention to provide a method of making a reinforce rubber using phenanthrene phenol/formaldehyde resins.

According to the present invention there is provided a method of making a reinforced rubber, comprising cross-linking a blend of 100 parts of a rubber, from 5 to 1 50 parts of a phenanthrene/phenol/formaldehyde resin, from 1 to 5 parts of a vulcanising agent for the rubber, and from 5 to 1 5 parts per hundred parts of resin of a formaldehyde donor.

In this specification cross-linking is used to denote both the cross-linking of a rubber by a vulcanising agent and curing of a resin. Also all parts and percentages are by weight unless otherwise indicated, and all Registered Trade Marks are indicated by asterisks.

Preferably the cross-linking is achieved by heating the blend, conveniently at a temperature of from 1 20 to 1 80 C, preferably under pressure, conveniently of from about 4 x 106 to 80 x 106 N/m2, for at least ten minutes.

The rubber may be a styrene/butadiene rubber, a nitrile rubber, natural rubber, or a blend of any two or more of them, although other synthetic rubbers may also be employed.

The phenanthrene/phenol/formaldehyde resin peferably has a combined phenol content from 20 to 40% and an average molecular weight from 375 to 925.

Conveniently the resin is made by reacting phenanthrene with a molar excess of formaldehyde or a formaldehyde donor in the presence of an acid catalyst, for instance sulphuric acid, to give a phenanthrene-formaldehyde resin.

Preferably the molar ratio of formaldehyde to phenanthrene is about 3:1 and the resultant resin has an oxygen content from 3 to 8%. Advantageously the phenanthrene formaldehyde resin has an oxygen content from 3.5 to 6%.

The phenanthrene formaldehyde resin is then reacted with a molar excess of phenol in the presence of a strong acid catalyst, for instance p-toluene sulphonic acid. At the end of the reaction the acid catalyst may be neutralised and unreacted starting materials removed by any of the usual techniques, for instance distillation or washing.

The phenanthrene need not necessarily be pure, but it is preferred that it should comprise at least 90% phenanthrene.

The phenol may be phenol itself or any other momonuclear phenol, for instance one of the cresols, or a mixture of phenols.

The formaldehyde donor may be formaldehyde itself, paraform (a solid polymer of formaldehyde and also containing about 13% water) or formalin (a 40% W/V solution of formaldehyde in water). In the rubber blend, the formaldehyde donor may be hexamethylene tetramine (hexamine), although this cannot be used to form the phenanthrene formaldehyde resin.

The vulcanising agent may be a single component, and is usually sulphur although it may also be a peroxide, such as dibenzoyl peroxide, dicumyl peroxide or dilauroyl peroxide.

However, in normal commercial practice an accelerator is also added to the sulphur vulcanising agent to speed up the cross-linking of the rubber by the vulcanising agent. Most commercially available accelerators may be used, but we prefer to use Ancamine* CBS (which is believed to comprise cyclohexyl benzothiazyl sulphenamide), Vulcafor* MBTS (which is dibenzthiazyl disulphide), or Vulcafor ZMBT (which is the zine salt of mercaptobenzthiazole).

The blend may further include other compounds, such as carbon black, inert fillers, stabilisers, lubricants and antioxidants. These compounds are generally used in rubber compositions and their use is well known to persons skilled in the art of rubber compounding and formulating.

The rubber blend of the present invention may be processed and moulded in a similar manner to conventional rubber compositions. The moulding conditions, particularly times and temperatures, are not substantially different from those which would be chosen using conventional reinforcing resins.

The blend may be mixed and homogenised by any of the conventional techniques, for instance using a Banbury mixer or a 2-roll mill. Preferably the blending is carried out at a temperature of from 50 to 90"C, at which temperature the resin plasticises the rubber and thereby promotes mixing, but there is no scorching of the rubber.

The present invention also comprises reinforced rubbers when made according to the method of the present invention, and these reinforced rubbers may be used for any of the purposes for which conventional reinforced rubbers are used.

The examples given below are for illustrative purposes only to enable a better understanding of the invention, and are not be construed as limiting in any way the scope of the invention.

EXAMPLES Preparation of Phenanethrene/Formaldehyde Resin Sulphuric acid (49.9g, 0.5 mole), water 32.5g) and paraformaldehyde (25.9g, 0.75 mde) were charged into a flanged flask supported in an oil bath held at 11 0,C. The flask was fitted with a stirrer, reflux condenser and thermocouple. The contents were stirred at 1 75 rpm until the paraformaldehyde had dissolved and the mass temperature had reached 100"C.

Molten phenanthrene (44.6g, 0.25 mole) was added from a heated funnel (at about 100"C), after which the stirrer speed was increased to 340 rpm. After about 3 hours the reaction was stopped by the addition of 250ml distilled water. 1,2-dichloroethane (200ml) was added, followed by a further 250ml distilled water. The organic layer was separated from the aqueous layer and washed firstly with a 10% solution of sodium carbonate and secondly with water until the washings were neutral. The organic solution was heated to 100"C and nitrogen passed therethrough to remove the 1,2-dichloroethane and leave a brown phenanthrene-formaldehyde resin having molecular weight of 466 and an oxygen content of about 1.1 %.

A similar resin was prepared, but using 28g of water originally. This resin had a molecular weight of 857 and an oxygen content of about 1.6%.

Preparation of Phenanethrene/Formaldehyde/Phenol Resin A resin prepared as described above and phenol were placed in a flask. The molar ratio of the resin to phenol was either 0.5:1 or 2.5:1. The flask was heated to 100 C to melt the mixture of resin and phenol. 1 part of p-toluene sulphonic acid per 100 parts of resin was added to the mixture which was maintained at 1 00'C for 24h. The properties of the phenolated resins thus produced are shown in Table 1 below.

Preparation of Blends for Vulcanising 100 parts of a nitrile rubber (Breon*652) were masticated for 3 minutes at room temperature on a 15 cm diameter 2-roll mill. 10 or 50 parts of phenolated resin No. 3 (Table 1) were mixed with the rubber for about 1 5 minutes at a nip temperature of about 60"C. Zinc oxide (5 parts), stearic acid (1.5 part) and Vulcafor* MBTS (1.5 parts) were milled into the rubber over a period of about 10 minutes. The nip temperature was reduced to about 50"C and hexamine (5 parts) and sulphur (1.5 parts) were added. Mixing was continued for a further 1 5 minutes before removal of the blend from the mill.

Vulcanisation of the Blends Approximately 75g of each blend were pressed into 1 5 cm square plaques of thickness 3.5mm and vulcanised at 150"C for 40 minutes at a pressure of 1,000 p.s.i. in a hydraulic press. The vulcanised plaques were cooled to room temperature and the ultimate tensile strength, tear strength and elongation at break determined according to B.S. 2782. The hardness of the plaques was determined according to B.S. 903.

The properties of the plaques are given in Table 2 below wherein they are compared with commercially available rubber reinforcing resins. These data show that, unlike other rubber reinforcing resins, phenolated phenanthrene-formaldehyde resins provide a high level of reinforcement without causing a reduction in the elongation (elasticity) of the vulcanised rubber. As this is a desirable result it can be seen that the present invention provides a useful method of reinforcing rubber.

TABLE 1 Properties of Phenolated Phenanthrene Formaldehyde Resins Phenanthrene/formaldehyde resin used Phenol:Resin Combined Phenol No. (oxygen content %) molar ratio Content (%) 1 1.1 0.5:1 35.0 2 1.1 2.5:1 20.0 3 1.6 0.5:1 37.0 4 1.6 2.5:1 22.8 Table 2. Properties of nitrile rubber vulcanizates containing phenanthrene-formaldehyde-phenol resin cured at 150 C for 40 minutes Resin Tear 100% 200% 300 % Ultimate Elongation content Hardness Strength Modulus Modulus Modulus Tensile at break Resin (p.h.r.) (IRHD) (N.mm-1) (N.mm-2) (N.mm-2) (N.mm-2) (N.mm-2) (%) - BLANK++ 50.5 12.0 0.9 0.5 - 1.5 473 PhFP 10 85.7 13.4 1.0 0.7 0.6 2.3 400 PhFP 50 90.0 32.8 2.6 2.0 2.1 12.8 440 Cellobond* H, 859 50 93.0 66.0 7.5 6.0 5.8 25.5 411 TFP 50 96.0 74.0 8.9 6.3 - 14.6 258 Cellobond* H.859 is commercial resin.

TFP is a toluene-formaldehyde-phenol resin.

++No resin or hexamine in the formulation.

Claims (7)

1. A method of making a reinforced rubber, comprising cross-linking a blend of 100 parts of a rubber, from 5 to 1 50 parts of a phenanthrene/phenol/formaldehyde resin, from 1 to 5 parts of a vulcanising agent for the rubber and from 5 to 1 5 parts per hundred parts of resin of a formaldehyde donor.

2. A method according to claim 1, wherein the cross-linking is achieved by heating the blend while maintaining the blend under pressure.

3. A method according to either one of Claims 1 and 2, wherein the rubber in the blend is selected from the group consisting of sytrene/butadiene, nitrile, natural rubbers and blends thereof.

4. A method according to any one of the preceding claims, wherein the resin has an average molecular weight from 375 to 925 and a combined phenol content from 20 to 40%.

5. A method according to any one of the preceding claims, wherein the vulcanising agent is a sulphur vulcanising agent.

6. A method of making a reinforced rubber according to claim 1, substantially as hereinbefore described.

7. A reinforced rubber made according to the method of any one of the preceding claims.