The growth of composites in airframes has resulted in aerospace companies taking increased fire protection measures in the design and construction of their aircraft.

This, in turn, has resulted in an increased demand for fire resistantcoatings.

A fire resistant coating, IP9189 from Indestructible Paint Ltd, is a material designed specifically for this purpose and whose benefits have been proven over a period of time. IP9189 is normally used at a dry film thickness of 600 μm.

Because of weight considerations, Indestructible has recently been investigating the possible use of lower film thicknesses to produce the same or better benefits.

In an evaluation carried out recently and described below the company tested two materials, used together and separately, to provide three systems, or processes, with intumescent layers, at film thicknesses of only 350 μm.

This level of film thickness is considered low for the purpose (less than 60% of the original) and would provide significant weight savings if practical.

Process 1

- IP1265 a ceramic modified version of IP9189, designed to provide greater thermal barrier properties with less intumescent activity (catalysed 8:1 by volume with IP1265B+10%IP9064-THIN).

Application:

Two coats of LR2439-123 seal coat were applied, wet on wet, allowing the first coat to penetrate the composite substrate. Dry film thickness was 16 μm after air drying for 30 minutes and force drying for one hour @80ºC. IP1265. Two cross coats were applied and air dried for 40 minutes. The spray process was repeated and air dried for one hour, then force dried for one hour @80ºC to achieve 300-350 μm dry film thickness. Two thin coats, wet on wet, of LR2442-1232-pack low flame spread white finish (catalysed 4:1 by volume with LR2096+5%IP3 reducer) were applied and air dried for 30 minutes then force dried for one hour @80°C providing a dry film thickness of 31μm.

Process 2

-a layer of IP1265 covered with a layer of IP9189.

Application:

LR2439-123 as process 1. Two cross coats of IP1265 were applied and air dried for one hour then force dried for one hour @80°C. Dry film thickness 150-175μm. IP9189. Two cross coats were applied and air dried one hour then force dried for one hour @80ºC to achieve a dry film thickness of 150-175μm. LR2442-123 as process 1.

Process 3

- IP9189 2-pack intumescent coating (catalysed 8:1 by volume with IP9189B + 5% IP9064-THIN).

Application:

LR2439-123asprocess1.
Two cross coats IP9189 were applied and air dried for 40 minutes. The spray process was repeated and air dried for one hour then force dried for one hour @80ºC to achieve a dry film weight of 300-350μm.
LR2442-123 as process 1.

The objectives of the tests were:-

1. To measure substrate temperatures during a flame test on the reverse side of composite test panels coated with the three different systems.

2. To compare the merits of IP9189 intumescent coating with those of IP1265.

Flame test:-

The composite test panels were of carbon fibre epoxy resin (Cytec prepreg Cycom 5215 T650 6K-1355HS) -6” x 3” x 66.4mils.
IP9189 and IP1265 were applied, as described above, to the composite and subjected to two minutes and five minutes burning at 1060ºC.
A propane fuelled Rothenburger Superfire 2 torch provided the heat in the test rig. Otherwise the set-up was as BSX37.
The flame was applied directly on to the coatings for two minutes and five minutes @1060ºC.

Side View

2 minute burn

5 minute burn

Front View

2 minute burn

5 minute burn

• All three systems intumesced and kept the substrate temperature below 350ºC with minimal damage to the substrate.
• All three systems gave similar temperature profiles, but without the coatings the substrate reached 520ºC and showed substantial damage.
• The level of smoke produced increased very slightly from process three to process one but was considerably less than that from the uncoated composite.

• Process 1 gave the most rigid char, process 3 the weakest. Process 1 would appear to have the most potential for with standing burning beyond five minutes.
• The differences between the three systems investigated were small. If the requirement to withstand 1060º C is five minutes or less, then process 3 (IP9189) would be the optimum choice because of the lower level of smoke produced.
• However, if there is a requirement to withstand heat for more than five minutes, process 1 (IP1265) may be preferred because of its more rigid char.
• Process 2 (IP1265/IP9189) had no clear advantages but had the disadvantage of using an additional material.