GB2264116A

GB2264116A - Process for producing microsphere containing thermosetting resin compositions

Info

Publication number: GB2264116A
Application number: GB9302406A
Authority: GB
Inventors: Douglas Badhams
Original assignee: Balmoral Group Ltd
Current assignee: Balmoral Group Ltd
Priority date: 1992-02-14
Filing date: 1993-02-08
Publication date: 1993-08-18
Also published as: FI930581A; GB9203186D0; NO930519D0; GB9302406D0; NO930519L; FI930581A0

Abstract

A process for producing a composition comprising thermoplastic microspheres dispersed in thermosetting resin, the process comprising the steps of i) dispersing unexpended microspheres in the resin to form a mixture ii) heating the mixture to a temperature greater than the temperature at which the microspheres expand but less than the temperature at which the resin thermosets.

Description

PROCESS FOR PRODUCING MICROSPHERE CONTAINING THERMOSETTING RESIN COMPOSITIONS This invention relates to a process for producing resin compositions containing expanded thermoplastic microspheres.

It is known in fields such as pipe-coating to thermally insulate or corrosion protect pipes with a mixture containing a thermosetting resin composition and expanded thermoplastic microspheres. When using nonthermosetting resin compositions, unexpanded thermoplastic microspheres may be added to the resin or other substrate and expanded, by heating to in excess of the expansion temperature of the microspheres, during the process of application. When using a thermosetting resin composition, however, it is not possible to use the same process because upon heating to the required temperature, rapid exothermic heating occurs resulting in rapid thickening of the mixture, caused by melting of the microspheres, without expansion of -the thermoplastic microspheres. Until now, this has meant that the microspheres must be expanded prior to mixing with the thermosetting resin composition.This causes further difficulties. First, there is caused a health problem of dust created from the expanded microspheres. It is also difficult to mix the very lightweight spheres with the viscous resin composition. Hence it is normally only practical to carry out this mixing in the same place as that at which the resin is produced and not where the composition will be used. Furthermore on transportation the expanded microspheres, being of considerably lower density than the resin, float to the top of the mixture, thereby requiring remixing on site, and subsequently the mixture must be used quickly to prevent reseparation.

This separation means that transportation of the material should be in small units leading to yet further cost increases due to package costs and the like.

According to the present invention there is provided a process for producing a composition comprising expanded thermoplastic microspheres dispersed in thermosetting resin the process comprising the steps of i dispersing unexpanded microspheres in the resin to form a mixture ii heating the mixture to a temperature greater than the temperature at which the microspheres expand but less than the temperature at which the resin thermosets.

As a further embodiment of the present invention there is provided an apparatus for heating the thermosetting resin composition and unexpanded microsphere mixture to a temperature sufficiently high to cause the microspheres to expand, which comprises; pumping the mixture through pipes of small bore such that the mixture is heated rapidly, causing expansion of the microspheres, but without permitting overheating of the mixture which would otherwise cause the microspheres to melt rather than expand.

The above and other aspects of the present invention and their advantages will now be illustrated in greater detail by description of some embodiments of the invention with reference to the accompanying drawings.

Figure 1 shows the application of the invention on a small scale; Figure 2a illustrates schematically a heat exchanger in an application of the present invention on an industrial scale; and Figure 2b being a cross-section along line I-I In Figure 2.

Being of much lower density than an thermosetting resin, expanded microspheres rise to the surface of a mixture of the two and it is thus difficult to maintain a uniform mixture of resin and microspheres. As such, heretofore batches of the mixture have only been prepared and used in relatively small quantities.

Since according to the process of the present invention, the microspheres are not expanded until immediately prior to application, no such problem occurs.

Furthermore, the composition of the mixture is no longer restricted to that which was prepared at the factory, variations in composition may now be made according to local requirements and conditions. Such variations may include varying the ratios of components or incorporating more or less air. Which may be added at any stage in the process prior to curing. The air can be advantageous since it improves the thermal insulation properties of the composition.

Unexpanded thermoplastic microspheres, such as those manufactured by Nobel Industries Sweden, and marketed under the Registered Trade Mark EXPANCEL, are added to a thermosetting resin composition, such as may be routinely used in the art, depending upon the application.

The resin is kept at a temperature at which it is liquid but below that at which the microspheres will expand. Being of similar densities, the resin and unexpanded microspheres mix easily to form a homogeneous mixture which maintains its homogeneity, unlike when the microspheres are already expanded. The mixture may thus be stored or transported.

A small scale apparatus according to the invention is shown in Figure 1. It comprises a first reservoir 6 for storing a mixture of resin and unexpanded microspheres. Preferably the first reservoir 6 is heated to a temperature below which the resin does not cure at an appreciable rate nor the microspheres expand. Typically such a temperature is around 60 C. The mixture in the reservoir 6 should be relatively homogeneous and an agitator (not shown) may be provided. For reasons which will be explained hereinafter, the agitation may advantageously be so vigorous as to entrap air.

Homogenisation is fairly straightforward since the warm resin is of relatively low viscosity and the unexpanded microspheres are of broadly similar density.

The mixture is then transported to a reactor 2.

Any of a large number of transportation mechanisms may be used. In the embodiment shown the mixture is drawn through by a vacuum pump 4. Other suitable arrangement include gravity feed or gas injectors.

The reactor 2 comprises a long and thin bore tube.

In the embodiment shown the reactor 2 comprises a coil of copper tubing. The mixture in the reactor 2 is heated to a temperature sufficient to expand the microcapsules. In the embodiment shown this is by immersion of the reactor 2 in a vessel 3 of boiling water.

In contrast to previous techniques, a homogeneous mixture of resin and microcapsules is obtained.

If the pumping has been by gas-entrainment or there has been vigorous agitation in reservoir 6 a large number of gas-bubbles may be present. This is positively advantageous for insulation since the thermal resistivity of the cured material is further increased by the presence of bubbles.

Where the resin is to be used to provide corrosion protection, it is preferable to pass the mixture through a centrifuge prior to expansion of the microspheres. Air bubbles in the mixture are thus expelled thereby providing a less porous and therefore more corrosion protecting coating.

The mixture may be used directly or drawn off into a second reservoir to allow collection of larger quantities of mixture.

The treated mixture may be used in the usual manner for ex##le, by application using applicator head 5 A large scale device is shown in Figure 2. In this embodiment the reactor comprises a plurality of generally parallel pipes 10 disposed in an outer shell 11.

The pipes are spaced apart by tube plates 12, 13. The apparatus is broadly similar to a tubed boiler, condenser or other heat exchanger and they in fact may be usable.

The untreated mixture is pumped into the pipes through inlet 14, traverses them and exits through outlet 15 to storage or use.

Heating fluid is present in the shell 11.

Typically the heating fluid will comprise water steam air or combustion gases generated by generator 16 and pumped through the shell by a pump 17. Preferably a recirculating heating circuit is employed.

Claims

1. A process for producing a composition comprising thermoplastic microspheres dispersed in thermosetting resin the process comprising the steps of i dispersing unexpanded microspheres in the resin to form a mixture ii heating the mixture to a temperature greater than the temperature at which the microspheres expand but less than the temperature at which the resin thermosets.

2. A process as claimed in claim 1 wherein step ii comprises passing the mixture through means for heating the mixture.

3. A process as claimed in claim 2 wherein the means for heating comprise at least one tube having a ratio of length: outside diameter of 10:1 or greater.

4. A process as claimed in claim 3 wherein the ratio is 25:1 or greater.

5. A process as claimed in claim 4 wherein the ratio is 50:1 or greater.

6. A process as claimed in any one of the preceding claims wherein the means for heating comprise two or more tubes.

7. A process as claimed in any one of the preceding claims further comprising the addition of gas to the mixture preferably not later than the heating step.

8. A process for producing a thermosetting rein composition containing expanded thermoplastic microspheres substantially as illustrated herein by reference to any one of the figures.

A A composItIon obtained by a process as claimed in any one of the preceding claims.

10. Apparatus for performing a process as claimed in any one of claims 1 to 8 comprising: i. a mixer for mixing the resin and the unexpanded microspheres; ii. a heating chamber for heating the mixture; and iii. a pump for pumping the mixture through the heating chamber.

11. Apparatus for performing a process as claimed in any one of claims 1 to 8 substantially as illustrated herein by reference to any one of the Figures.