METHOD OF MAKING A PRODUCT WITH COMPOSITE BODY AND RUBBER SURFACE

Abstract

A composite product is made by forming an object body comprising a mixture of rubber crumb and binder having a first temperature-dependent cure rate. A surface layer of a vulcanizable rubber compound having a second temperature-dependent cure rate is brought into contact with the object body, and the surface layer and the object body are simultaneously cured at different temperatures so as to match said first and second cure rates such that the surface layer adheres to the object body.

Claims

1. A method of making a composite product, comprising: forming an object body comprising a mixture of rubber crumb and binder having a first temperature-dependent cure rate; preparing a surface layer of a vulcanizable rubber compound having a second temperature-dependent cure rate; bringing said object body and surface layer into contact; and simultaneously curing the surface layer and said object body at different temperatures so as to match said first and second cure rates such that the surface layer adheres to the object body.

2. A method as claimed in claim 1, wherein the vulcanizable rubber compound surface layer is formed by Banbury roll mill or extrusion mixing and sheeting to form the preform sheet.

3. A method as claimed in claim 2, wherein the vulcanizable rubber compound preform sheet is applied to a bottom platen of a mold and the rubber crumb and binder is poured into a cavity of the mold over the preform sheet.

4. A method as claimed in 3, wherein the binder is pre-polyurethane.

5. A method as claimed in claim 4, wherein the temperature of the bottom is about 10-20 C. hotter than the cavity of the mold.

6. A method as claimed in claim 5, wherein the preform sheet is about 1-3 mm thick.

7. A method as claimed in claim 5, wherein the bottom platen is maintained at a temperature of 140-150 C. and cavity of the mold is maintained at a temperature of 130-140 with a temperature differential of at least 10 C. between the bottom platen and the cavity of the mold.

8. A composite product, comprising: an object body comprising a mixture of at least 95% rubber crumb and binder; and a surface layer of a vulcanizable rubber compound adhering to the object body.

9. A composite product as claimed in 8, wherein the binder is pre-polyurethane.

10. A composite product as claimed in claim 9, wherein the preform sheet is about 2 mm thick.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] This invention will now be described in more detail, by way of example only, with reference to the accompanying drawings:

[0016] FIG. 1 shows the process steps involved in making a composite body in accordance with an embodiment of the invention;

[0017] FIG. 2 is a block diagram of the specific example embodiment described;

[0018] FIG. 3 illustrates a side view of a product made by a conventional method; and

[0019] FIG. 4 illustrates a side view of a product made by a method contemplated by the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0020] An example of a specific embodiment is described. A landscaping tile 20 is made by preparing at step 10 a mixture 25 of 1-5% polyurethane pre-polymer binder and 95-99% cured rubber particles, typically tire crumb.

[0021] At step 11 a layer of natural or synthetic rubber based compound 30, for example, NR or SBR elastomer, is prepared for vulcanizing in a Banbury mixer and calendered to 2 mm thickness to form a preform sheet of vulcanizable rubber. It is then laid into the cavity of a mold 35. The preferred thickness is 2 mm as it is found this thickness helps the skin resist penetration of the cured rubber particles in the slurry without being economically unrealistic. However an acceptable range is 1-3 mm. The thickness of the preform sheet could vary depending on the requirements of the final product as discussed above.

[0022] At step 12, 8-10 lbs. of the mixture 25 prepared in step 10 is then poured into the mold cavity 35 over the layer of natural or synthetic rubber and levelled to form the object body.

[0023] At step 13, the preform sheet and the object body are cured together in the mold under pressure, typically in excess of 2000 psi hydraulic pressure. The cure rates of the surface layer and object body are matched by controlling the temperature. Typically the mold has a bottom platen maintained at a temperature of 140-150 C. and a cavity containing the object body maintained at a temperature of 130-140 C. with a temperature differential of at least 10 C. between the bottom platen and the cavity of the mold. The cure time is 8-10 mins.

[0024] These parameters ensure that the surface compound cure rate is set such that the surface layer cures simultaneously with the object body. This ensures that a bond forms between the layers without delamination or interstitial gas bubbles. The polyurethane polymerization produces gas so if the cure is not synchronized gas will pool between the layers and cause delamination.

[0025] The cure times and temperatures are a specific instance where a 2 mm skin is adhered to a 19-25 mm body. If the temperatures are increased, the cure times shorten or lengthen with a decrease. It will be understood that a differential may need to be applied and the amount of the differential may change depending whether the temperature is hotter or colder than the specific embodiment described above. One skilled in the art will understand that a rheometer cure meter times and temperatures for the two substrates can be determined at specific temperatures and mold temperatures chosen depending on where the cure curves intersect in time. Normal adjustments will have to be taken into effect for the thicknesses of the substrates due to the poor heat transfer rates from the mold surface to the center of the composite.

[0026] Embodiments of the invention permit the manufacture of products including matting and landscaping features where a surface distinguishable from the object body is applied during the formation of the body. An example of such a feature would be a landscaping patio tile. The object body typically comprises in excess of 95% by weight of the object is typically produced from a slurry of rubber particulate (crumb) and a binding agent. The binding agent can, for example, consist of a polyurethane pre-polymer binder, or other binder as may be known in the art.

[0027] FIG. 3 illustrates a side view of a product made by a conventional method. The delamination can be seen between the surfaces of 25 and 30. The gap where gas accumilated between the surfaces has prevented adhesion.

[0028] FIG. 4 illustrates a side view of a product made by a method contemplated by the present invention. It can be seen there is no delamination between the surfaces of 25 and 30. The absence of a gap between the surfaces indicates successful adhesion.