GB2088400A

GB2088400A - Fire Resistant Coating Compositions

Info

Publication number: GB2088400A
Application number: GB8135270A
Authority: GB
Original assignee: KIN CHUNG LEE
Current assignee: KIN CHUNG LEE
Priority date: 1980-11-24
Filing date: 1981-11-23
Publication date: 1982-06-09
Also published as: GB2088400B

Abstract

A fire resistant composition comprises an alkali metal silicate, especially sodium silicate, and a starch, in a liquid vehicle and optionally containing a film-forming binder, the weight ratio of silicate to starch being in the range 10:1 to 1:50. It is preferred that the vehicle is a paint, especially a water-base latex paint. Fire resistant coating may be made on, for example, brick, expanded polystyrene, steel and wood.

Description

SPECIFICATION Fire Resistant Coating Compositions The present invention relates to fire resistant coating compositions and provides intumescent fire resistant coating compositions and methods of fire-resisting employing said compositions.

It is well known to protect materials by coating them with intumescent coating compositions and numerous such compositions have been proposed over many years (see, for example, UK Patent Specifications Nos 822123, 1095857, 1493478 and 1554538). Ingredients known for use in such compositions number many thousands and include alkali metal silicates (see, for example UK Patent Specification Nos 1493478 and 1554538) and starches (see, for example UK Patent Specification Nos 822123 and 1 095857) but, to the best of the Applicant's knowledge, it has not previously been proposed to employ an alkali metal silicate with a starch as the essential ingredients of an intumescent coating composition.-He has found that such a simple and inexpensive mixture'provides a surprisingly high degree of fire-resistance to building materials such as brick, expanded polystyrene, steelnd wood.

According to a first aspect of the present invention, there is provided a first resistant coating composition an intumescent fire-resistant coating composition comprising an alkali metal silicate and a starch in a liquid vehicle and preferably containing a film-forming binder, the ratio by weight of silicate to starch being in the range 10:1 to 50:1.

According to a second aspect of the present invention, there is provided a method of treating a material to increase its fire resistance, which method comprises applying to said material a fire resistant coating composition of the invention.

One essential component of the coating composition of the invention is an alkali metal silicate. A particularly preferred silicate is sodium silicate, especially in the form commonly known as "water glass".

A second essential component of the coating composition of the invention is a starch. The presently preferred starch is corn starch, although other forms of starch such as wheat starch and potato starch can be used.

The alkali metal silicate and starch are present in a ratio by weight of from 10:1 to 1:50, preferably from 4:1 to 1:3 and especially from 2:1 to 1:1.

The alkali metal silicate and starch are carried in a liquid vehicle which can be either aqueous or non-aqueous and which preferably contains a film-forming binder, especially latex, and/or a pigment, for example titanium-dioxide. The vehicle can be comprised of any water-base or solvent base vehicle used in paints and can be comprised of a water-base or solvent base paint itself provided that said paint vehicle or paint is compatible with the alkali metal silicate, the starch and intended application of the coating composition of the invention. Solvent-base vehicles have advantageous drying properties and suitable solvent-base vehicles include, for example, those based on binders such as polystyrene and solvents such as methylene chloride.Preferred water-base vehicles include those based on a filmforming latex such as those available in the U.K. under the Trade Mark "ROLLS" and in Hong Kong under the Trade Marks "DURO" and "FLYINGTiGER". Lime, usually in an amount of about 1 to 5% by weight, or cement, especially Portland Cement, usually in an amount of 1 to 20% by weight can be included in water-base vehicles to improvide their drying properties.

The amount of liquid vehicle present in the composition of the invention will depend upon the manner in which the composition is to be applied to a material to be rendered fire resistant by the coating composition. Further, the presence of other components in the liquid vehicle and the proportions of such components will also depend upon the intended use of the coating composition of the invention.

The relative and absolute proportions of all the ingredients of the coating composition of the invention readily can be determined by a simple experiment to provide the desired degree of fire resistance.

According to a preferred embodiment of the invention, there is provided an intumescent fire resistant paint comprising sodium silicate and starch in a water-base or solvent-base paint.

A typical fire resistant composition of the invention is an intumescent paint comprising about five parts by weight mineral grade water glass (approx. 40% sodium silicate), about two parts by weight corn starch and one to three parts by weight water-base latex paint and, optionally, titanium dioxide as pigment. This composition is particularly suitable for the formation of a surface coating on building materials such as brick, expanded polystyrene, steel and wood. Suitably, it is applied at a thickness of 0.1 to4mm.

The invention is illustrated in the following non-limiting Examples.

Example 1 An intumescent paint was prepared by thoroughly mixing together the following ingredients: Water Glass* -five parts by weight Corn Starch -two parts by weight *Mineral Grade containing 38% by weight sodium silicate and supplied by Charles Tennant Ltd, London.

The paint was tested for determination of fire resistance according to BS 476: Part 8:1972 (nonload bearing) using a wall of building blocks of aerated concrete and available under the Trade Mark "CELCON". The blocks had a nominal thickness of 75 mm and a density of approximately 640 kilogrammes per cubic metre. The wall was 3 metres high, 3 metres wide and of single block thickness.

The mortar used was three parts building sand to one part cement mixed with clean cold water and without the addition of plasticiser. Four thick coats of the paint were applied by brush to one face of the wall to provide a coating of approximately 4 mm thickness. A drying time of 24 hours was allowed between the application of each coat.

The wall was conditioned according to BS 476 (Supra) and positioned so that the coated face closed the front opening of a gas fired furnace. The furnace was operated to produce the time/temperature relationship in the exposed face as required by the British Standard and temperatures on both faces were monitored by thermocouples located on the exposed and unexposed faces according to the British Standard.

The test was carried out by an independent and officially approved testing laboratory in the U.K.

and the observations and conclusions of the observer of the test are set forth below:- Observations The following observations were made during the test.

Time (minutes) from start of test Observations 00 Test commenced 05 intumescence of the paint on the exposed face very pronounced. The exposed face had taken on a glassy appearance.

05-200 Very little change was observed on either face. The wall steamed from the unexposed face until 200 minutes approximately, but there was little bowing of the wall and few cracks appeared. No smoking was observed. When steaming ceased, unexposed face temperatures began to rise.

300 Insulation failure occurred (one fixed thermocouple on the unexposed face showed a rise of 1 800C above ambient).

Time (minutes) from start of test Observations 300 The test was terminated. There was no integrity or stability failure.

305 The specimen was removed from the furnace. The exposed face was cracked and well impregnated with a glassy coat (5 mm into the blockwork).

The time/temperature data obtained from the test is set forth in the accompanying graph, in which time in hours is piotted as the abscissa and temperature in OC is plotted as the ordinate.

Conclusion The coated CELCON Block wall tested was found to have a fire resistance according to BS 476: Part 8: 1972 (non-loadbearing) of 300 Minutes with: INSULATION 300 MINUTES INTEGRITY 300 MINUTES STABILITY 300 MINUTES Example 2 A paint was prepared as in Example 1 and two thick coats were applied to 3/8" plywood substrate to form a coating of approximately 600 grams per square metre. The coated substrate was classified for surface spread of flame in accordance with BS 476: Part 7:1971, Section 2 by exposure to thermal radiation using the apparatus specified in that British Standard. The test was conducted by the same independent laboratory which conducted the test reported in Example 1.

There was no surface spread of flame on any specimen under the conditions of the test although bubbling and discolouration were noted. The official classification accorded to the coated substrate was the highest (Class 1) under the British Standard.

Example 3 A paint was prepared as described in Example 1 and a single coating of the paint was applied to plywood, softboard and expanded polystyrene substrates each measuring approximately 20x 1 50 mm.

The coating was allowed to dry at room temperature and then each specimen was burned with a gas flame for 60 seconds. The test was carried out by an independent and officially approved testing laboratory in Hong Kong and the following results were reported: Control Sample Coated prepared specimen plywood charred and burned coating blistered, and did not burn softboard burn after 5 secs. coating blistered, and did not burn expanded melt and burn after coating blistered and melted, but polystyrene 5 secs did not burn.

The same laboratory applied a single coating of the paint to steel plate and allowed it to dry at room temperature. The coating was then sprayed with 3% salt solution. After 36 hours, the coating was stripped from the steel plate and the surface of the plate examined. There was no sign of rust on the steel plate.

Example 4 Similar results to those reported in Examples 1, 2 and 3 above were obtained when the paint composition was modified by the inclusion of water-base latex paint and/or Portland Cement. The latex paint improved the covering performance and the Portland Cement decreased the drying time.

Claims

1. An intumescent fire resistant coating composition comprising an alkali metal silicate and a starch in a liquid vehicle, the ratio by weight of silicate to starch being in the range 10:1 to 50:1.

2. A composition as claimed in Claim 1, containing a film-forming binder.

3. A composition as claimed in Claim 1 or Claim 2, wherein the alkali metal silicate is sodium silicate.

4. A composition as claimed in Claim 3, wherein the sodium silicate in the form of water glass.

5. A composition as claimed in any one of the preceding Claims, wherein the starch is corn starch.

6. A composition as claimed in any one of the preceding Claims wherein the liquid vehicle is a water-base paint.

7. A composition as claimed in any one of Claims 2 to 6 wherein the binder is a film-forming latex.

8. A composition as claimed in any one of the preceding Claims containing lime and/or cement in an amount sufficient to improve the drying properties thereof.

9. A composition as claimed in Claim 8 wherein the composition contains lime in an amount of 1 to 5% by weight.

10. A composition as claimed in Claim 8 wherein the composition contains cement in an amount of 1 to 20% by weight.

11. A composition as claimed in Claim 10 wherein the cement is Portland Cement.

12. A composition as claimed in any one of the preceding Claims wherein the said ratio of silicate to starch is 4:1 to 1:3.

13. A composition as claimed in Claim 12 wherein said ratio of silicate to starch is 2:1 to 1:1.

14. A composition as claimed in Claim 6 comprising about five parts by weight mineral grade water glass containing approximately 40% sodium silicate, about two part by weight corn starch and one to three parts by weight water-base latex paint.

1 5. A composition as claimed in Claim 1 and substantially as hereinbefore described.

1 6. A method of treating a material to increase its fire resistance, which method comprises coating the material with a composition as claimed in any one of the preceding Claims.

1 7. A method as claimed in Claim 1 6 wherein the material is coated with a composition as claimed in any one of Claims 1 to 14 to a thickness of 0.1 to 4 mm.

18. A method as claimed in Claim 16 or Claim 17, wherein said material is a building material selected from brick, expanded polystyrene, steel and wood.

1 9. A method as claimed in Claim 1 6 substantially as hereinbefore described.