Additive offers better rubber-to-reinforcement adhesion and eliminates hazardous chemicals.

The challenges of bonding rubber to metal or fabric are well documented, and many of the methods require hazardous compounds to facilitate the process. Hallbond RX-13946-D is a radically new adhesion promoter developed by CPH Ester Solutions (an affiliate of CPH Holding). Lab and field studies show Hallbond improves adhesion between 20% and 200% in many rubber-to-metal and rubber-to-synthetic fiber reactions without hazardous compounds. In fact, for example, dry RX-13946-D added during compounding of EPDM and applied to steel wire achieved adhesion of 187 Newtons of force at 25[degrees]C. Adhesion to polyester cord was even higher, at 212 Newtons. Hallbond delivers increased performance and lower costs in an environmentally friendly additive.

The powdered Hallbond RX-13946-D, which is a single-component 4product, can be used in two ways: It can be added directly to the primary material during compounding, or a liquid formulation of the adhesive can be applied directly to the substrate being adhered to.

Three customers shared their experiences with the new adhesion promoter.

Rubber-to-metal adhesion

A leading manufacturer of industrial hose derived triple benefits when it added Hallbond, including: elimination of pollutants, better rubber-to-metal adhesion, and lower production costs.

The manufacturer needed to bond a natural rubber/SBR blend to brass wire. According to the firm's chief compounder, what originally attracted the company to the new CPH adhesion promoter was the fact that it was in powder form and non-hazardous. The liquid adhesive the manufacturer had been using contained 60% toluene, which both the company and its home state were pleased to eliminate. This state limits the volume of hazardous solvents a manufacturer can use, and the company was approaching its limit.

The hose manufacturer added Hallbond during compounding of the natural rubber/SBR blend from which the cushion is made. In the final analysis, the hose manufacturer found that the new adhesion promoter improved adhesion between the elastomer layer and the surrounding wire. There are no longer any volatile solvents to contend with during production of the product, which reduces the company's volume of hazardous emissions. And the cost of buying and using the new technology is lower than the cost of the earlier toluene-containing product.

Rubber to non-metal adhesion

Hallbond RX-13946-D also promotes adhesion to non-metal reinforcement layers. A leading manufacturer of rubber hoses for industrial applications experienced problems with reinforcing iso-treated, braided polyester yarn layers separating from its NBR hose. This treatment delivered 20 lbs. of adhesion. which was not sufficient for satisfactory performance. Company engineers experimented with RFL-treated polyester yam, which produced improved adhesion performance over the iso-treated yarn (to 40 lbs. of adhesion), but pull tests demonstrated that the initial 40 lbs. quickly fell to 20 lbs.

The engineers added Hallbond RX-13946-D at 5 phr to the NBR compound, which resulted in tests showing 40 lbs. of adhesion for the full length of the test (figure 1).

[FIGURE 1 OMITTED]

In a similar case, a leading global manufacturer of belts and hoses to the automotive and industrial aftermarket had been strengthening its belts with polyester cord pre-treated with a combination of hexamethoxymelamine or hexamethylenetetramine and phenol-formaldehyde condensation product, where the phenol is usually resorcinol. The resin reacts with the fiber and the rubber to produce a firm, reinforcing bond. Other adhesion promoting processes for polyester cord that deliver adequate adhesion results are various resorcinol-formaldehyde (RFL) resin dips that create a bond between the rubber and the polymeric cords during vulcanization. These, however, are very costly processes.

CPH conducted research in which three adhesion formulations were compared, including:

* Compound 1, a melamine-formaldehyde resin with 27% calcium silicate;

* Compound 2, Hallbond RX-13946-D, which was 72% active with 27% calcium silicate; and

* Compound 3, a control formulation using the belt manufacturer's current EPDM/additive formula.

The control (Compound 3) was bonded with polyester cord pre-treated with a melamine-formaldehyde resin and dipped into an additional adhesive compound. The polyester cord used with compounds 1 and 2 was treated with melamine-formaldehyde resin, but not with an additional adhesive.

Each compound was tested at room temperature and after 48 hours at 257[degrees]F. Compound 1 showed adhesion essentially equal to the control. Compound 2, containing Hallbond RX-13946-D, showed adhesion at least 100% greater than Compound 1 and the control. Table 1 summarizes the data.

These results demonstrate clearly that Hallbond RX-13946-D provides a significant increase in adhesive force between EPDM and polyester cord reinforcement over the other two compounds. Force was recorded at 212 Newtons, even greater than the adhesion shown with metal braid reinforcement. The use of this new additive also eliminates the additional production step of dipping the polyester cord into a bonding adhesive.

Table 1--adhesion force comparison

Compound                       Adhesion              Aged adhesion
variable                (Newtons-force)            (Newtons-force)
                       Room temperature    257[degrees]F--48 hours

Melamine A                         95.9                       15.9
Hallbond RX-13946-D               212.2                       63.2
Control                            98.8                       21.7