Fire retardant additives and their uses

A composition comprising two or more frits of different melting temperatures and optionally one or more ceramic material or basalt or intumescent substance is provided that may be added to a variety of materials to provides or enhance fire resistance. Such materials include phenolic and polyester resins and sodium silicate.

This invention concerns additive compositions for use in providing or 
enhancing fire resistance of materials and compositions and a method of 
providing or enhancing fire resistance properties for materials and 
compositions. 
If alumina trihydrate is used as an additive to plastics materials, as a 
fire retardant, several difficulties emerge. Alumina trihydrate produces 
water, up to 30% of its weight, at temperatures of 200 degrees C. This 
water turns to steam and blankets burning action. It follows therefore, 
that alumina trihydrate cannot be used in plastics materials which are 
processed at temperatures above 185 degrees C (to leave a safety margin). 
Such plastics materials include polypropylene and polyethylene. 
Secondly, to be effective, levels of 60% by weight and even 64% by weight 
of alumina trihydrate have been used in urethane methacrylate and 
polyesters. Such high amounts of a filling make the resin very difficult 
to work. 
Thirdly, alumina trihydrate is supplied in various grades priced according 
to their micron size. The cheapest is at 25 micron particle size, the 
dearest at about 10 micron. The larger particles are in plate form which 
makes them difficult to disperse in high concentrations, and that can also 
have an adverse effect on surface finish. The smaller particles are 
rounded during processing and disperse more easily but are more expensive 
by a factor of three compared to the larger particles. 
Another popular fire retardant additive is antimony oxide. This material 
contains 3% arsenic and consequently renders any product containing it 
toxic. Antimony oxide works by combining with free halogen but is only 
partially effective, in that it improves existing fire retardant 
properties rather than making materials conform to rigorous tests. 
Antimony oxide is usually used in amounts of 3% by weight, although higher 
amounts may be used in some materials. 
One object of the present invention is to provide an additive composition 
that can be used for the purpose of providing or enhancing fire resistance 
of materials and compositions. 
Another object of the present invention is to provide a method of providing 
or enhancing fire resistance properties for materials and compositions. 
According to one aspect of this invention there is provided an additive 
composition for use in providing or enhancing fire resistance for 
materials and compositions comprising two or more frits and optionally 
ceramic and/or basalt fibres or powder. 
According to another aspect of this invention there is provided a method of 
providing or enhancing fire resistance properties for a material or 
composition comprising adding to said material or composition a 
composition comprising two or more frits and optionally ceramic and/or 
basalt fibres or powder. 
Preferably a combination of frits of different melting points are used in 
the compositions of the invention to provide continuous flow of molten 
frit as temperatures increase. A devitrifying frit is a desirable 
component of the additive of the invention as that tends to solidify after 
melting to provide strength. The frits under fire conditions will melt 
progressively to provide a fused protective layer. A preferred frit 
combination comprises a low melting frit e.g. that starts to melt at about 
450 degrees C. and a high melting or devitrifying frit that starts to melt 
at about 700 degrees C. The preferred weight ratio of low melt frit to 
high melt frit is in the range 1:9 to 1:1, especially 3:7. A typical 
selection of frits may be from those that melt at or about the following 
temperatures: 450 degrees C., 650 degrees C., 850 degrees C. and 1000 
degrees C. The frits used are preferably oven dried, water washed and 
ground prior to inclusion in the compositions of the invention. 
The inclusion of ceramic in fibre or powder form can be used to bind the 
melting frits and also to remain unchanged at temperatures above 1000 
degrees C. Basalt fibre or chopped fibre or powder can also be used in 
place of or in addition to the ceramic material. 
The compositions of the invention may also comprise one or more other fire 
retardant additives. For example an intumescent substance or substances 
may be included in the compositions of the invention, such as alumina 
trihydrate which releases most of its chemically combined water between 
200 and 330 degrees C. to dampen burning and reduce smoke emission or 
hydrated magnesium calcium carbonate which releases its chemically 
combined water and carbon dioxide from 230 degrees C. upwards. For some 
purposes hydrated magnesium calcium carbonate may be preferable to alumina 
trihydrate because it is less expensive to obtain in very finely divided 
form say of the order to 2 to 3.mu. particle size. A preferred composition 
of frits and intumescent substance or substances comprises from 15-50, 
especially 20-30, % by weight of frits and 85 to 50, especially 80-70, % 
by weight of intumescent substance(s). Another example of fire retardant 
additives may be antimony oxide usually used in combination with 
halogenated hydrocarbon, whereby halogen free radicals are produced that 
suppress burning. 
The proportion of frits to ceramic or basalt in a preferred embodiment of 
the invention is about 7:3. 
The compositions of the invention may be added to a variety of materials 
such as polymers, paints and sodium silicate. Suitable polymers include 
polyesters, phenolic resins, polyurethanes and other thermosetting resins 
and thermoplastics. If, however, alumina trihydrate is to be included in 
the additive composition, the composition cannot be used on materials 
processed at 200 degrees C. or more preferably at 185 degrees C. or more. 
In a phenolic resin, for example, the proportion of an additive composition 
of the invention comprising frits and ceramic or basalt to resin may be 
from 3:7 to 1:4. 
The frits additive with intumescent substance, such as hydrated magnesium 
calcium carbonate or alumina trihydrate or a mixture thereof, may be added 
to dough moulding compounds, such as of the phenolic or polyester type to 
be used with glass reinforcement. Preferably the ratio of frits to 
intumescent is about 1:4. 
For addition to phenolic resin frit/intumescent substance mix ratio in the 
range of from 7:3 to5:5 may be used. the preferred ratio of that mix to 
phenolic resin being in the range of 3:7 to 4:6. 
The action of heat on a resin which contains an additive composition 
according to the invention has the following effect. The resin or plastic 
materials burns and the frit in the first temperature band melts and 
combines with the char. The second frits then melts and so on. The 
substrate and burning material are encapsulated by the molten frits thus 
starving the fire of oxygen. The ceramic or basalt or both, if present, 
insulate and stiffen the molten mass to prevent excessive running. They 
also contribute greatly to stability at high temperatures. 
Since the particle size of the frits and ceramic can be controlled they are 
suitable for use with alumina trihydrate in its course form. The particles 
fill the gaps between the alumina trihydrate plates to give a better 
finish. The plates of alumina trihydrate act as a suspension agent for the 
frits/ceramic mix. The water produced in the form of steam has a 
beneficial effect on the frits, which are water soluble, aiding in the 
coating action. 
The addition of mixes to sodium silicate has a beneficial effect, in that 
the frits tend to plasticise the sodium silicate under increasing 
temperature conditions, this counteracts the embrittlement and powdering 
of the sodium silicate normally encountered in these conditions. The 
inclusion of frits in an intumescent seal or paint formula would 
constitute an improvement. 
It is preferred to use a mix of frits and intumescent substance, such as 
hydrated magnesium calcium carbonate or alumina trihydrate or a mixture 
thereof, say in the ratio of 3:7 to 1:1, preferably 4:6, with sodium 
silicate and by varying the ratio of the frit mix to sodium silicate 
materials suitable for different uses may be obtained. At a ratio about 
1:1 the resultant mixture has a paint consistency at a ratio of aboiut 
7:13 the mixture has adhesive properties and at a ratio of about 1:4 the 
mixture is in a gel form. 
The frit composition of the invention may be used to make sealant say for 
around fire doors or windows. The preferred sealant will swell when heated 
and stop any gaps around doors or windows. 
For a sealant paste a frit combination containing intumescent with sodium 
silicate say in the ratio of 3:7 to 4:6, preferably 7:13 by weight may be 
used as a base to which is added a char agent, such as mica, ammonium 
polyphosphate and an inorganic gelling agent. The resultant paste is one 
which will harden in situ. 
By using polyvinylacetate in place of the sodium silicate, a resilient 
sealant may be produced that will swell and harden when heated. 
Another possible use of the aditive composition of the invention is in the 
production of sheets or boards made by compression of chips of wood with a 
binder. Thus, the binder may be a composition comprising phenolic resin or 
sodium silicate solution containing ceramics such as carborundum, and 
frits, preferably three frits having different melt temperatures. 
A further use of the additive composition of the invention may be as an 
adhesive. The preferred adhesive will be based on sodium silicate solution 
containing a catalyst of phenolic resin and the composition of the 
invention. Such an adhesive may be used in circumstances where fire 
resistance is important. 
For example, the adhesive may be used for bonding facing sheets, such as of 
melamine, to a base material, such as chipboard. Then under fire 
conditions, the adhesive can provide a protective shield for the base 
material even when the facing sheet has been burnt off. 
Another particular use is as an adhesive for attaching a brake lining to 
its carrier. Indeed brake linings may be made from the same composition, 
the ceramic material preferably being slag fibre and shot, such as 
produced as waste from power stations. The brake linings material may 
comprise additional strengthening components, such as carbon fibre or 
thermoplastics material e.g. KEVLAR (trade name). 
Another example of using frits is in the construction of a laminate 
comprising an outer skin formed by heat and pressure where a glass cloth 
has been impregnated with a liquid settable resin, such as phenolic, 
containing frits of different melt temperatures together with a binding 
heat stable, fibre, such as ceramic mullite fibre, and optionally alumina 
trihydrate. The skins of impregnated cloth are place on either side of a 
ceramic paper, combination basalt, ceramic and glass fibre paper, glass 
cloth treated with vermiculite or indeed any heat resistance barrier 
material. When this laminate is pressed under heat and with any number of 
interleaved sheets the settable resin migrates into the barrier material 
to produce a solid sheet. 
When flame is applied to the laminate the settable resin burns to protect 
the substrate, the barrier material providing stability. 
The surface of the laminate may be covered with melamine sheet either plain 
or patterned or real wood veneer when flamne is applied, the frits/ceramic 
help to form a char and prevent spread of flame. This moulded laminate, 
flat or three dimensional, can then be adhered to a substrate, such as a 
door, using sodium silicate containing the same frits, ceramic fibre and 
optionally alumina trihydrate previously mentioned to make a high heat 
performance adhesive. 
The substrate can be rigidized sheet of ceramic fibre which is in turn 
adhered with the adhesive described, to a heat resistance sound deadening 
core made from say basalt fibre or rockwool rigidized or non-rigidized. 
The construction may be repeated about the centre line. 
For thirty minute rating the pressed laminates adhered and/or mechanically 
fixed to a basalt or rockwool core is sufficient. For sixty minute rating 
the rigidized ceramic board may be introduced, and for extended times the 
ceramic board can be increased in thickness and a ceramic non-rigid 
blanket can be used instead of the rockwool/basalt core. For light weight 
constructions a phenolic foam core or a foam made from the adhesive 
mentioned can be used. 
A foamed vermiculite clay can be included in the adhesive to produce a 
lightweight, highly insulating core. Alternatively a core can be made by 
using woodchip as a filler to the adhesive to make a high heat resistance 
chipboard core to a door, building panel or partition.

This invention will now be further described by means of the following 
examples. 
EXAMPLE 1 
A polyester resin containing 20% by weight of alumina trihydrate and 16% by 
weight of frits and 4% by weight of ceramic powder was found to have 
enhanced fire resistance. 
EXAMPLE 2 
A phenolic resin containing 30% by weight of a mixture of frits (80% by 
weight) and ceramic powder (20% by weight) passed BS 476 part 8 90 minutes 
fire resistance test. 
EXAMPLE 3 
A mix containing antimony oxide 3% by weight, one frit at a low temperature 
melt band at 10% by weight, one frit at a high temperature melt band (of 
approximately 1100 degrees C.) at 60% by weight and ceramic at 27% by 
weight made up a casting or injection material which was suitable for use 
with a phenolic or sodium silicate binder as well as other materials 
including thermosets and thermoplastics. 
EXAMPLE 4 
A mix containing antimony oxide 3% by weight, one frit at a low temperature 
melt band at 7% by weight, one frit at a high temperature melt band (of 
approximately 1100 degrees C.) at 45% by weight and alumina trihydrate at 
45% by weight made a mix suitable for polyesters and other materials 
including thermosetting resins whose processing is not done above 185 
degrees C. 
EXAMPLE 5 
A basic powder mix was produced from 40% by weight of a combination of a 
low melting frit (450 degrees C.) and a high melting (devitrifying) frit 
(700 degrees C.) in the weight ratio of 3:7 and 60% of hydrated magnesiums 
calcium carbonate. 
An adhesive composition was produced by adding 35% by weight of the powder 
mix to 65% by weight of sodium silicate. 
EXAMPLE 6 
A paint-like composition was produced by adding 50% by weight of the powder 
mix of Example 5 to 50% by weight of sodium silicate. 
EXAMPLE 7 
A gel-like composition was produced by adding 20% by weight of the basic 
powder mix of Example 5 to 80% by weight of sodium silicate. 
EXAMPLE 8 
A powder mix of 70% by weight of low melting frit (450 degrees C.) and 
devitrifying frit (700 degrees C.) in the ratio of 3:7 and 30% by weight 
of hydrated magnesium calcium carbonate was prepared and then added to 
phenolic resin in the weight ratio of 3:7 to produce a mouldable material. 
EXAMPLE 9 
Dough moulding compounds for use with glass fibre reinforcement were 
prepared based on phenolic resin and on polyester resin. In both cases a 
powder mix of 20% by weight frits (low and high melting in a ratio of 3:7) 
and 80% by weight of hydrated magnesium calcium carbonate were added to 
the resin. 
EXAMPLE 10 
A sealant paste was produced from the following ingredients in the amounts 
stated: 
EXAMPLE 11 
A resilient sealant was produced in the same way as in Example 10 except 
that polyvinyl acetate was used instead of sodium silicate.