Indian Patents. 277138:FIRE RETARDANT INTUMESCENT HIGH DENSITY RIGID POLYURETHANE FOAM

Title of Invention	FIRE RETARDANT INTUMESCENT HIGH DENSITY RIGID POLYURETHANE FOAM
Abstract	The invention relates to an intumescent fire retardant rigid polyurethane foam having desired particle size adapted for providing a voluminous multi-cellular swollen char with lesser released amount of heat and toxic smokes, comprising polyether polyol, polymeric methane diisocyanate with combination of intumescent fire retardant char forming additives.

Full Text	TECHNICAL FIELD OF THE INVENTION The present invention relates to the rigid polyurethane foam (PUF) having excellent flame resistant property in respect to limiting oxygen index (LOI), heat release rate and smoke evolution properties. More particularly, the invention relates to the unique combinations of different flame retardant (FR) additives and intumescent compounds incorporated into the foam without affecting the physical and mechanical properties of the resultant PUFs. The intumescent flame retardant polyurethane foams of the present invention are characterized by different ways, such as self-extinguishing properties, intumescent properties, and charring properties which respond to provide protection when exposed to fire. The charred foam is an insulator of low combustibility which, at the same time, retards the release of flammable gases from the heated mass. According to this invention the present high density rigid PUF yields strong intumescent char which protects the material inside the rigid PUF. BACKGROUND OF THE INVENTION Rigid polyurethane foam (PUF) has a wide range of applications such as insulation, structural, packaging and so on, because of their higher strength to weight ratio, excellent insulation properties, lower density, excellent dimensional stability, and low water vapor permeability. Now-a-days because of the strict regulations in safety and security in defense, aerospace, military and consumer sectors intumescent PUF plays an important fire retardant packaging material. Generally, flame retardant PUFs are prepared by two methods, viz; (1) incorporating suitable additives into the reactants, (2) modification of the formulation process to incorporate the flame retarding compounds containing functional groups which become chemically bound to the polymer chain. In practice, the use of additives is generally preferred because it is more flexible. There are large numbers of flame retardant additives commercially available in the different category like halogens, phosphorus, inorganic materials, nitrogen based organic materials and so on. The selection of the flame retardants (FR) for suitable application is a major task. Because some of the FR additives leach out and/or migrate towards the surface causing the failure of the mechanical properties and also deteriorate flame retardant properties with time. It has been reported in the literature that in the case of halogenated flame retardants corrosive, toxic gases (dioxins) and smokes are released while combustion, which erode the instruments and pollute the environment. In most of the cases addition of these FR additives lead to inferior mechanical properties (Troitzsch J., 1990, "International Plastics Flammability Handbook", 2nd Ed., Hanser Publishers, New York; Grand, A. F, et al., 2000, Fire Retardancy of Polymeric Materials; Marcel Dekker, Inc., New York). The use of different flame retardant chemicals and intumescent mixtures for inclusion in polyurethane materials such as thermoplastic polyurethane elastomer, polyurethane based paints and coatings, and flexible polyurethane foams have been reported in the literatures based on the intumescent flame retardant chemicals (Wang, J., et al., 2004, J. Appl. Polym. Sci., 91, 1193; Camino, G., et al, 1988, Costa, L. Polym. Degrad. Stab. 20, 271; Camino, G., et al., 1989, Polym. Degrad. Stab. 23, 359; Camino, G., et al., 1991, Polym. Degrad. Stab. 33, 131; Modesti, M., 2002, Polym. Degrad. Stab. 77, 195; Xie, R., 2001, J. Appl. Polym. Sci., 80, 1190; Bian, X-C, et al., 2007, J. Appl. Polym. Sci., 104, 3347; Shi, L., 2006, Polym. Int., 55, 862; Anna, P., et al., 2001, Polym. Degrad. Stab. 74, 423; Ma, Z., et al., 1997, J. Appl. Polym. Sci., 63,1511). It has been observed that the conventional phosphorus-halogen containing flame retardants (e,g chlorophosphate esters) cannot effectively retard the fire at higher temperature (> 500 °C). This is due to their volatilization as well as the insufficient char formation at higher temperatures. US Patent Nos. 3393129, 3535130, 3769074, 3801333, 4831062, 5989706, 0212495 disclose the intumescent products based on the coating and paints. US Patent No. 0209982 describes the intumescent mixtures based on phosphoric acid compound, polyalcohol and polyamide used for the different polymeric foams. US Patent No. 4374207 describes intumescent flexible PUF prepared from a hydrated alumina and low viscosity linear polyester polyol. US Patent No. 3803063 describes intumescent flexible PUF using nitrogen and phosphorous containing compound and polycondensates of polymerized unsaturated fatty acids with aliphatic amine. US Patent No. 4514524 describes intumescent PUFs derived from halogenated flame retardants and water or alcohol soluble urea formaldehyde resins. This prior art deals with fire retardant properties of the flexible PUF prepared by using halogenated FR additives. They have used polyether based polyols having the hydroxy functionality of 2 to 3 and molecular weight of 3000 to 4500. However, it was not known from this prior art that fire retardant properties of rigid PUF based on a polyether based polyol can be prepared using a suitable combination of intumescent char forming additives based mainly on non- halogenated FR additives. Some of the US patents 3574644, 4945015, 5258216, 6228914, 6960388, 7087670 disclose the preparation of the intumescent polymeric materials using intercalated expandable graphite flakes. US Patent Nos. 3934066, 4052526, 4201593, 4210725, 4218502, 4269944, 4542170, 4588523, 4831062, 5387655, 6632442, 6706793 disclose the intumescent compositions which are used for the polyurethane material and other polymeric materials. The application of fire retardant and intumescent char forming materials in rigid PUF is not well-explored. However, none of the patents discloses the unique combination of different additives to achieve specific properties for important special applications. In recent years there has been worldwide serious concern regarding the use of FR additives, which are subjected to the stringent conditions set by statutory government regulations. As a result there is a need for the development of halogen-free flame retardant materials. The environmental friendly FR additives having good flame retarding properties are in particular demand. Recently attention has been directed towards the intumescent type flame retardant systems, as they are quite effective in flame retardance and also do not produce toxic gases in the event of fire. Intumescent compositions of the prior art usually contain an intumescent additives having at least three components, i.e., a carbonific, a spumific, and a catalyst. Good intumescent compositions should be able to at least double their volume (swollen) compared to original size, when they come in contact with a flame. PUFs burn readily when ignited by external heating source, thus they are unsuitable for certain applications in which fire is a hazard. Accordingly, it is desirable to make PUF which are flame retardant or self-extinguishing, and if possible, release less toxic gas and smoke, so as to eliminate or minimize the hazard of fire. The present invention provides the combination of novel fire retardant additives to prepare rigid PUF which can be used in the critical applications like in defense, aerospace, military, automotive, buildings and construction, computer, packaging, rail transport, telecommunication, electrical and electronics, etc. OBJECTIVE OF THE INVENTION The primary objective of this invention is to provide the intumescent high density rigid polyurethane foam having excellent fire retardant, self-extinguishing characteristics, releasing lesser amount of heat and toxic smokes. Another objective of this invention is to provide mechanically stable voluminous (approximately double than unburnt foam) multi-cellular swollen char after burning without affecting the material inside the PUF. SUMMARY OF THE INVENTION The present invention reports the preparation of intumescent fire retardant rigid PUF using suitable polyols, diisocyanates and a proper combination of suitable fire retardant additives. This specialty PUFs, on burning provides a voluminous multi-cellular swollen char with lesser release of heat and smokes. DETAILED DESCRIPTION OF THE INVENTION Intumescent fire retardant compounds are characterized by their foaming and char- forming properties. The phenomenon of intumescent fire retardance is based on the production from the reagents of gaseous materials which expand the sample into charred carbonaceous foam on heating. The charred foam is an insulator of low combustibility which, at the same time, retards the release of flammable gases from the heated mass. The present invention relates to the intumescent flame retardant high density rigid polyurethane foam prepared by one-shot, molding method. The composition of the foam forming mixtures (Table 1) comprises of Polyol, Isocyanate, Catalyst, Chain extender, Cross-linking agents, Blowing agents, Surfactants, Fillers and the unique combinations of flame retardant additives, which impart the intumescing char when ignited. The rigid PUF prepared by polyol based either on polyether or polyester, polyisocyanate and blowing agents. Physical as well as chemical blowing agents can be used in the preparation of PUFs. Water is one of the most widely used chemical blowing agents. It reacts with diisocyanate and then generates gaseous carbon dioxide and polyurea. This in-situ prepared carbon dioxide inflates reactant mixture; as a result, a cellular structure is formed. The widely used physical blowing agents are chlorofluorocarbons (CFCs), hydro chlorofiuorocarbons (HCFCs), fluorocarbons (FCs), and low boiling hydrocarbons (HCs). The formation of polyurethane is based on the reaction of diisocyanate with polyol. The reaction is exothermic in nature and the reaction heat can be used to form a cellular structure by the evaporation of physical blowing agents present in the reaction formulation. The polyether based polyol of this invention is selected from the polyoxyalkylene polyether polyols, are generally prepared by the reaction of an alkylene oxide, such as ethylene oxide, 1, 2-propylene oxide with a polyhydric initiator or starter. The polyhydric initiator or starter can be, for example, glycerol, trimethylolethane, trimethylolpropane, triethanolamine, aromatic diamines, sucrose, sorbitol, etc. The polyethers used in the present invention preferably have molecular weight of about 400 to about 700 g/mol and an average hydroxy functionality of about 3 to 8. The low molecular weight compounds containing hydroxyl groups, or amino groups, or thiol groups or carboxyl groups are used as chain extenders or cross-linking agent to form branched or three-dimensional network structure. Examples of such compounds include ethylene glycol, 1,2-and 1,3-propylene glycol, 1,4- and 2,3-butylene glycol, 1,5-pentane diol, 1,6-hexane diol, 1,8-octane diol, neopentyl glycol, glycerol, trimethylol propane, trimethylol ethane, 1,2,6-hexane triol, pentaerythritol, mannitol and sorbitol. The organic polyisocyanates include toluene diisocyanate (TDI), methylenediphenyldiisocyanate (MDI) (in the form of pure as well as crude), modified MDI and TDI, prepolymers of MDI and TDI, polymeric diphenyl methane diisocyanate (PMDI). The blowing agents comprise of water alone or water in combination with other conventional physical blowing agents such as n-pentane, cyclopentane, isopentane, butane, isobutane, hexane, heptane, HCFC 141b, HCFC 142b, HCFC 134a, HCFC 245fa, HFC 134a, HFC 152a, HFC 245fa and HFC 365mfc. The catalyst includes tertiary amines such as N-alkyl morpholamine, N, N'- dialkyl cyclohexylamines, (where the alkyl groups are methyl, ethyl, propyl, butyl, etc.) also dimethyl hexahydroaniline, diethylhexa hydroaniline, N, N, N', N", N"pentamethyl diethylenetriamine, N, N'-diethyl aminoethanol, N, N-dicyclohexylamine, triethyl amine, tributylamine, triamylamine, pyridine, quinoline, dimethyl piperidine, and organometalic compounds including those of bismuth, lead, tin, titanium, iron, antimony, mercury, zinc, nickel, cerium, molybdenum, vanadium, copper, manganese, zirconium, etc., examples of which include stannous octoate, dibutyltin dilaurate, bismuth nitrate, lead benzoate, lithium acetate, ferric chloride, thorium nitrate, triphenyl aluminum. They are used as blowing catalysts as well as sometimes gelling catalyst. The surfactants employed for the desirable uniform cell structure include paraffins, fatty alcohols, silicone oils and dimethylpolysiloxanes. According to this invention the suitable combination of the flame and intumescent fire retardant additive comprises of a halogenated phosphate ester, nitrogen and phosphorus containing compound, intercalated expandable graphite flakes, triazine compounds and its derivatives, polyhydroxy compounds and hydrated silicates. A suitable nitrogen and phosphorus containing compound is ammonium phosphate, ammonium polyphosphate, melamine phosphate, melamine polyphosphate, ethylenediamine phosphate, ammonium dihydrogen phosphate, aluminum orthophosphate, piperazine phosphate, guanidine phosphate, phosphoric ester polyols or urea phosphate. Suitable polyhydroxy compounds used are pentaerythritol, dipentaerythritol, polyethylene glycol and phosphoric ester- based polyols. The amount of flame and intumescent fire retardant additive combination used in the foam is an amount effective to give the combined reduction of flame retardant and mechanically stable with carbonaceous char properties desired by the user. The combined weight of the flame retardant additive combination is typically about 10 to 50 php weight percent of the total weight of the polyol in the formulation. The present invention provides the flame retardant rigid PUF with intumescent mixtures, which produce physically strong and voluminous multi-cellular carbonaceous swollen char during burning [as shown in Figure 1 (a & b)]. The importance of this mechanism is that because of the formation of intumescent char, the bulk of the material will not be affected by the flame. In addition, this solid char layer protects the remaining polymer from the heat of combustion, thus it limits the heat and mass transfer and access of oxygen to the polymer. The flame cannot spread further due to dearth of oxygen and fuel. In this way it retards the degradation of PUF and reduces smoke production and evolution of toxic gases during burning. The obtained char is stable at higher temperature (550 °C) and gives higher value of the limiting oxygen index (LOI) (approx. 33 %). Further aspect of the present invention is to provide the particle size and surface treatment of the FR additives which play a crucial role in fire resistant and mechanical properties of PUF. This intumescent fire retardant additive having the particle size is in the range from 5 to 200 urn and FR surface is coated with reactive functional group to have better compatibility with the polymer matrix. The particle size and surface treatment of the FR additives play a crucial role in density and mechanical properties of PUF. The physico-mechanical properties of polymer improved with addition of fillers having low particle size and/or suitable surface modification. Lower particle size increases the interfacial interaction (more aspect ratio) between filler with polymer matrix. Modification of the surface of the additive via specific functional group improves the compatibility with the polymer matrix. A significant advantage in the foams produced in the present invention is that they swell or intumesce and char when exposed to flame and form an insulating fire-retardant barrier between the flame and the unburnt portions of the foam. The char formed on the foam after exposure to heat provides a high resistance to heat flow between the heat source and the foam surface. In addition, foam of this invention inhibits the formation of hot or flaming droplets which can cause excessive damage even though the flame has been extinguished or inhibited. This kind of intumescent char has low thermal conductivity and high oxidation resistance, so that it not only affords protection to the material present inside by virtue of its low thermal conductivity, but its surface reaches a high temperature and thus re-radiates a large fraction of the incident heat load. The present invention is now demonstrated by way of illustrative non limiting examples. The following specific examples will serve further to illustrate the practice and advantages of this invention. BRIEF DESCRIPTION OF THE ACCOMPANING DRAWINGS Fig.1 (a) and (b) show the images of unburnt and burnt intumescent fire retardant rigid PUF, respectively. Fig. 2 shows graphically the thermal insulation test of different rigid PUF samples (prepared in this invention as well as of a couple of commercial reference samples) illustrating rise in temperature in 25 mm PUF sample. Fig. 3 shows graphically the thermal insulation test of different rigid PUF samples (prepared in this invention as well as of a couple of commercial reference samples) illustrating thickness of the char produced when one of the faces of the test piece was heated to 800 °C in a flame. EXAMPLE 1 The process for the preparation of the rigid PUF is as follows: all of the ingredients (as shown in Table 1) except isocyanate, were first well mixed in a plastic container. Then isocyanate was added into the container with vigorous stirring for 20 seconds. The resulting mixture was poured into a mold, which is used to produce the rigid PUF. After the preparation the foams were kept in an oven at 70 °C for 24 h to complete the polymerization reaction. The particle size of flame retardants is very important since physical properties of the resulting products are significantly affected. Generally, the finer the particle size of fillers impart better properties of the resultant products. It is preferred to use flame retardants having an average particle size of less than 30 microns, and especially about 10 microns or less. The intumescent mixture for the rigid polyurethane foam produced in this invention is very efficient, and renders excellent retardant to flame, heat and smoke. Table 2 summarizes the different physical, mechanical and fire retardant properties of rigid PUF prepared in this invention. Table 3, Table 4, Figure 2 and 3 show the comparative results of rigid PUF and commercial reference sample (Reference 1 and 2). EXAMPLE 2 The rigid PUF is characterized by following various tests. The density of the PUF samples was measured according to ASTM D 1622-03. The mechanical properties such as compressive strength at 10% strain in parallel to foam rise direction was performed according to ASTM D 1621-00. The morphology of the PUF samples was studied with a JEOL, JSM 5800 scanning electron microscope, Japan. The thermal conductivity of the PUFs was tested between two plates on a guarded hot plate apparatus as per ASTM C 177-97. The thermal stability of PUF was examined on a thermogravimetry analysis (TGA), (Q50, TA Instruments, USA) under nitrogen environment at a heating rate of 20 °C /min. The flame retardant properties of the PUF were determined by Limiting Oxygen Index (LOI) according to the ASTM D-2863 test. This LOI expresses the minimum percentage of oxygen in a flowing mixture of oxygen and nitrogen required to support flaming combustion. A higher value of LOI indicates a lesser probability of burning since a greater amount of oxygen would be required to support combustion. Therefore, the LOI of 21.0 means that combustion can be supported in air (content of oxygen in air is about 21%) whereas the LOI of 31.0, indicates that the relative amount of oxygen in the environment of the sample must be considerably greater than what is found in air, to support combustion. The char yields (CY) of the foams were measured on a muffle furnace at 550°C for 30 min. The cone calorimeter test is also used to indicate flammability or lack of it with respect to a test sample and measured according to ASTM E-1354. In this test, the objective is to determine the ignition time, heat release rate, amount of smoke released, amount of mass loss at the fixed or varied heat flux. To achieve this objective, at high intense heat, the foam should have a minimum heat release rate, minimum smoke evolution and greater the ignition time. The smoke density was measured as per ASTM D 2843-04. The smoke generated in the process of burning of sample is measured by the change of light intensity. The size of the PUF specimen was 100 x 100 x 12 mm3 (length x width x thickness). The maximum smoke density was measured from the curves of peak maxima of the light absorption vs time. This smoke density rating represents the total amount of smoke present in the chamber for the 4 min time and was measured by using the equation; Smoke density rating = A/T x 100 Where, A and T are the area under the curve of light absorption vs. time and total area of the curve respectively. WE CLAIM 1. An intumescent fire retardant rigid polyurethane foam having desired particle size adapted for providing a voluminous multi-cellular swollen char with lesser released amount of heat and toxic smokes, comprising polyether polyol, polymeric methane diisocyanate with combination of intumescent fire retardant char forming additives. 2. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1, wherein said fire retardant intumescent additives comprise of the combination of: (a) acid forming additives selected from the group comprising of halogenated phosphate ester, ammonium phosphate, ammonium polyphosphate, ammonium pentaborate, melamine phosphate, melamine polyphosphate, ethylenediamine phosphate, ammonium dihydrogen phosphate, aluminum orthophosphate, piperazine phosphate, guanidine phosphate, phosphoric ester polyols or urea phosphate, expandable graphite flakes, melamine compounds and its derivatives; (b) char promoting agents selected from the group comprising of pentaerythritol, dipentaerythritol, polyethylene glycol and starch, sucrose, glycerol, trimethylol propane, and phosphoric ester-based polyols; (c) gas forming additives selected from the group comprising of melamine, chlorinated paraffin, chlorophosphate ester, urea, melamine formaldehyde resins, dicyandiamide; and (d) inorganic based additives selected from the group comprising of antimony oxide, alumina trihydrate, zinc borate, ammonium polyphosphate, ammonium pentaborate, red phosphorus, low melting glasses, calcium carbonate, silicates, and glass powder. 3. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1, wherein said density is preferably ranging from 200 to 450 kg/m3. 4. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1, wherein said percentage of limiting oxygen index ranges from 29-35%. 5. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1, wherein said intumescent fire retardant additive having the particle size is preferably ranging from 5 to 200 urn. 6. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1, wherein said fire retardant intumescent char forming additives is preferably ranging from 5 to 50 parts per hundred of polyol by weight. 7. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1, wherein said fire retardant intumescent acid forming additives range from 5 to 30 parts per hundred of polyol by weight. 8. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1, wherein said char promoting agents range preferably from 1 to 25 parts per hundred of polyol by weight. 9. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1, wherein said fire retardant intumescent gas forming additives range preferably from 1 to 30 parts per hundred of polyol by weight. 10. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1, wherein said fire retardant intumescent inorganic additives range preferably from 1 to 25 parts per hundred of polyol by weight. The invention relates to an intumescent fire retardant rigid polyurethane foam having desired particle size adapted for providing a voluminous multi-cellular swollen char with lesser released amount of heat and toxic smokes, comprising polyether polyol, polymeric methane diisocyanate with combination of intumescent fire retardant char forming additives.

Full Text

TECHNICAL FIELD OF THE INVENTION
The present invention relates to the rigid polyurethane foam (PUF) having excellent
flame resistant property in respect to limiting oxygen index (LOI), heat release rate and
smoke evolution properties. More particularly, the invention relates to the unique
combinations of different flame retardant (FR) additives and intumescent compounds
incorporated into the foam without affecting the physical and mechanical properties of
the resultant PUFs. The intumescent flame retardant polyurethane foams of the present
invention are characterized by different ways, such as self-extinguishing properties,
intumescent properties, and charring properties which respond to provide protection
when exposed to fire. The charred foam is an insulator of low combustibility which, at
the same time, retards the release of flammable gases from the heated mass. According to
this invention the present high density rigid PUF yields strong intumescent char which
protects the material inside the rigid PUF.
BACKGROUND OF THE INVENTION
Rigid polyurethane foam (PUF) has a wide range of applications such as insulation,
structural, packaging and so on, because of their higher strength to weight ratio, excellent
insulation properties, lower density, excellent dimensional stability, and low water vapor
permeability. Now-a-days because of the strict regulations in safety and security in
defense, aerospace, military and consumer sectors intumescent PUF plays an important
fire retardant packaging material.
Generally, flame retardant PUFs are prepared by two methods, viz; (1) incorporating
suitable additives into the reactants, (2) modification of the formulation process to
incorporate the flame retarding compounds containing functional groups which become
chemically bound to the polymer chain. In practice, the use of additives is generally
preferred because it is more flexible. There are large numbers of flame retardant additives
commercially available in the different category like halogens, phosphorus, inorganic
materials, nitrogen based organic materials and so on.
The selection of the flame retardants (FR) for suitable application is a major task.
Because some of the FR additives leach out and/or migrate towards the surface causing
the failure of the mechanical properties and also deteriorate flame retardant properties
with time. It has been reported in the literature that in the case of halogenated flame
retardants corrosive, toxic gases (dioxins) and smokes are released while combustion,
which erode the instruments and pollute the environment. In most of the cases addition of
these FR additives lead to inferior mechanical properties (Troitzsch J., 1990,
"International Plastics Flammability Handbook", 2nd Ed., Hanser Publishers, New York;
Grand, A. F, et al., 2000, Fire Retardancy of Polymeric Materials; Marcel Dekker, Inc.,
New York).
The use of different flame retardant chemicals and intumescent mixtures for inclusion in
polyurethane materials such as thermoplastic polyurethane elastomer, polyurethane based
paints and coatings, and flexible polyurethane foams have been reported in the literatures
based on the intumescent flame retardant chemicals (Wang, J., et al., 2004, J. Appl.
Polym. Sci., 91, 1193; Camino, G., et al, 1988, Costa, L. Polym. Degrad. Stab. 20, 271;
Camino, G., et al., 1989, Polym. Degrad. Stab. 23, 359; Camino, G., et al., 1991, Polym.
Degrad. Stab. 33, 131; Modesti, M., 2002, Polym. Degrad. Stab. 77, 195; Xie, R., 2001,
J. Appl. Polym. Sci., 80, 1190; Bian, X-C, et al., 2007, J. Appl. Polym. Sci., 104, 3347;
Shi, L., 2006, Polym. Int., 55, 862; Anna, P., et al., 2001, Polym. Degrad. Stab. 74, 423;
Ma, Z., et al., 1997, J. Appl. Polym. Sci., 63,1511).
It has been observed that the conventional phosphorus-halogen containing flame
retardants (e,g chlorophosphate esters) cannot effectively retard the fire at higher
temperature (> 500 °C). This is due to their volatilization as well as the insufficient char
formation at higher temperatures.
US Patent Nos. 3393129, 3535130, 3769074, 3801333, 4831062, 5989706, 0212495
disclose the intumescent products based on the coating and paints.
US Patent No. 0209982 describes the intumescent mixtures based on phosphoric acid
compound, polyalcohol and polyamide used for the different polymeric foams.
US Patent No. 4374207 describes intumescent flexible PUF prepared from a hydrated
alumina and low viscosity linear polyester polyol.
US Patent No. 3803063 describes intumescent flexible PUF using nitrogen and
phosphorous containing compound and polycondensates of polymerized unsaturated fatty
acids with aliphatic amine.
US Patent No. 4514524 describes intumescent PUFs derived from halogenated flame
retardants and water or alcohol soluble urea formaldehyde resins. This prior art deals with
fire retardant properties of the flexible PUF prepared by using halogenated FR additives.
They have used polyether based polyols having the hydroxy functionality of 2 to 3 and
molecular weight of 3000 to 4500. However, it was not known from this prior art that fire
retardant properties of rigid PUF based on a polyether based polyol can be prepared using
a suitable combination of intumescent char forming additives based mainly on non-
halogenated FR additives.
Some of the US patents 3574644, 4945015, 5258216, 6228914, 6960388, 7087670
disclose the preparation of the intumescent polymeric materials using intercalated
expandable graphite flakes.
US Patent Nos. 3934066, 4052526, 4201593, 4210725, 4218502, 4269944, 4542170,
4588523, 4831062, 5387655, 6632442, 6706793 disclose the intumescent compositions
which are used for the polyurethane material and other polymeric materials.
The application of fire retardant and intumescent char forming materials in rigid PUF is
not well-explored. However, none of the patents discloses the unique combination of
different additives to achieve specific properties for important special applications.
In recent years there has been worldwide serious concern regarding the use of FR
additives, which are subjected to the stringent conditions set by statutory government
regulations. As a result there is a need for the development of halogen-free flame
retardant materials. The environmental friendly FR additives having good flame retarding
properties are in particular demand. Recently attention has been directed towards the
intumescent type flame retardant systems, as they are quite effective in flame retardance
and also do not produce toxic gases in the event of fire. Intumescent compositions of the
prior art usually contain an intumescent additives having at least three components, i.e., a
carbonific, a spumific, and a catalyst. Good intumescent compositions should be able to
at least double their volume (swollen) compared to original size, when they come in
contact with a flame.
PUFs burn readily when ignited by external heating source, thus they are unsuitable for
certain applications in which fire is a hazard. Accordingly, it is desirable to make PUF
which are flame retardant or self-extinguishing, and if possible, release less toxic gas and
smoke, so as to eliminate or minimize the hazard of fire.
The present invention provides the combination of novel fire retardant additives to
prepare rigid PUF which can be used in the critical applications like in defense,
aerospace, military, automotive, buildings and construction, computer, packaging, rail
transport, telecommunication, electrical and electronics, etc.
OBJECTIVE OF THE INVENTION
The primary objective of this invention is to provide the intumescent high density rigid
polyurethane foam having excellent fire retardant, self-extinguishing characteristics,
releasing lesser amount of heat and toxic smokes.
Another objective of this invention is to provide mechanically stable voluminous
(approximately double than unburnt foam) multi-cellular swollen char after burning
without affecting the material inside the PUF.
SUMMARY OF THE INVENTION
The present invention reports the preparation of intumescent fire retardant rigid PUF
using suitable polyols, diisocyanates and a proper combination of suitable fire retardant
additives. This specialty PUFs, on burning provides a voluminous multi-cellular swollen
char with lesser release of heat and smokes.
DETAILED DESCRIPTION OF THE INVENTION
Intumescent fire retardant compounds are characterized by their foaming and char-
forming properties. The phenomenon of intumescent fire retardance is based on the
production from the reagents of gaseous materials which expand the sample into charred
carbonaceous foam on heating. The charred foam is an insulator of low combustibility
which, at the same time, retards the release of flammable gases from the heated mass.
The present invention relates to the intumescent flame retardant high density rigid
polyurethane foam prepared by one-shot, molding method. The composition of the foam
forming mixtures (Table 1) comprises of Polyol, Isocyanate, Catalyst, Chain extender,
Cross-linking agents, Blowing agents, Surfactants, Fillers and the unique combinations of
flame retardant additives, which impart the intumescing char when ignited.
The rigid PUF prepared by polyol based either on polyether or polyester, polyisocyanate
and blowing agents. Physical as well as chemical blowing agents can be used in the
preparation of PUFs. Water is one of the most widely used chemical blowing agents. It
reacts with diisocyanate and then generates gaseous carbon dioxide and polyurea. This
in-situ prepared carbon dioxide inflates reactant mixture; as a result, a cellular structure is
formed. The widely used physical blowing agents are chlorofluorocarbons (CFCs), hydro
chlorofiuorocarbons (HCFCs), fluorocarbons (FCs), and low boiling hydrocarbons
(HCs). The formation of polyurethane is based on the reaction of diisocyanate with
polyol. The reaction is exothermic in nature and the reaction heat can be used to form a
cellular structure by the evaporation of physical blowing agents present in the reaction
formulation.
The polyether based polyol of this invention is selected from the polyoxyalkylene
polyether polyols, are generally prepared by the reaction of an alkylene oxide, such as
ethylene oxide, 1, 2-propylene oxide with a polyhydric initiator or starter. The polyhydric
initiator or starter can be, for example, glycerol, trimethylolethane, trimethylolpropane,
triethanolamine, aromatic diamines, sucrose, sorbitol, etc. The polyethers used in the
present invention preferably have molecular weight of about 400 to about 700 g/mol and
an average hydroxy functionality of about 3 to 8.
The low molecular weight compounds containing hydroxyl groups, or amino groups, or
thiol groups or carboxyl groups are used as chain extenders or cross-linking agent to form
branched or three-dimensional network structure. Examples of such compounds include
ethylene glycol, 1,2-and 1,3-propylene glycol, 1,4- and 2,3-butylene glycol, 1,5-pentane
diol, 1,6-hexane diol, 1,8-octane diol, neopentyl glycol, glycerol, trimethylol propane,
trimethylol ethane, 1,2,6-hexane triol, pentaerythritol, mannitol and sorbitol.
The organic polyisocyanates include toluene diisocyanate (TDI),
methylenediphenyldiisocyanate (MDI) (in the form of pure as well as crude), modified
MDI and TDI, prepolymers of MDI and TDI, polymeric diphenyl methane diisocyanate
(PMDI).
The blowing agents comprise of water alone or water in combination with other
conventional physical blowing agents such as n-pentane, cyclopentane, isopentane,
butane, isobutane, hexane, heptane, HCFC 141b, HCFC 142b, HCFC 134a, HCFC 245fa,
HFC 134a, HFC 152a, HFC 245fa and HFC 365mfc.
The catalyst includes tertiary amines such as N-alkyl morpholamine, N, N'- dialkyl
cyclohexylamines, (where the alkyl groups are methyl, ethyl, propyl, butyl, etc.) also
dimethyl hexahydroaniline, diethylhexa hydroaniline, N, N, N', N", N"pentamethyl
diethylenetriamine, N, N'-diethyl aminoethanol, N, N-dicyclohexylamine, triethyl amine,
tributylamine, triamylamine, pyridine, quinoline, dimethyl piperidine, and organometalic
compounds including those of bismuth, lead, tin, titanium, iron, antimony, mercury, zinc,
nickel, cerium, molybdenum, vanadium, copper, manganese, zirconium, etc., examples of
which include stannous octoate, dibutyltin dilaurate, bismuth nitrate, lead benzoate,
lithium acetate, ferric chloride, thorium nitrate, triphenyl aluminum. They are used as
blowing catalysts as well as sometimes gelling catalyst.
The surfactants employed for the desirable uniform cell structure include paraffins, fatty
alcohols, silicone oils and dimethylpolysiloxanes.
According to this invention the suitable combination of the flame and intumescent fire
retardant additive comprises of a halogenated phosphate ester, nitrogen and phosphorus
containing compound, intercalated expandable graphite flakes, triazine compounds and
its derivatives, polyhydroxy compounds and hydrated silicates. A suitable nitrogen and
phosphorus containing compound is ammonium phosphate, ammonium polyphosphate,
melamine phosphate, melamine polyphosphate, ethylenediamine phosphate, ammonium
dihydrogen phosphate, aluminum orthophosphate, piperazine phosphate, guanidine
phosphate, phosphoric ester polyols or urea phosphate. Suitable polyhydroxy compounds
used are pentaerythritol, dipentaerythritol, polyethylene glycol and phosphoric ester-
based polyols. The amount of flame and intumescent fire retardant additive combination
used in the foam is an amount effective to give the combined reduction of flame retardant
and mechanically stable with carbonaceous char properties desired by the user. The
combined weight of the flame retardant additive combination is typically about 10 to 50
php weight percent of the total weight of the polyol in the formulation.
The present invention provides the flame retardant rigid PUF with intumescent mixtures,
which produce physically strong and voluminous multi-cellular carbonaceous swollen
char during burning [as shown in Figure 1 (a & b)]. The importance of this mechanism is
that because of the formation of intumescent char, the bulk of the material will not be
affected by the flame. In addition, this solid char layer protects the remaining polymer
from the heat of combustion, thus it limits the heat and mass transfer and access of
oxygen to the polymer. The flame cannot spread further due to dearth of oxygen and fuel.
In this way it retards the degradation of PUF and reduces smoke production and evolution
of toxic gases during burning. The obtained char is stable at higher temperature (550 °C)
and gives higher value of the limiting oxygen index (LOI) (approx. 33 %).
Further aspect of the present invention is to provide the particle size and surface
treatment of the FR additives which play a crucial role in fire resistant and mechanical
properties of PUF. This intumescent fire retardant additive having the particle size is in
the range from 5 to 200 urn and FR surface is coated with reactive functional group to
have better compatibility with the polymer matrix.
The particle size and surface treatment of the FR additives play a crucial role in density
and mechanical properties of PUF. The physico-mechanical properties of polymer
improved with addition of fillers having low particle size and/or suitable surface
modification. Lower particle size increases the interfacial interaction (more aspect ratio)
between filler with polymer matrix. Modification of the surface of the additive via
specific functional group improves the compatibility with the polymer matrix.
A significant advantage in the foams produced in the present invention is that they swell
or intumesce and char when exposed to flame and form an insulating fire-retardant
barrier between the flame and the unburnt portions of the foam. The char formed on the
foam after exposure to heat provides a high resistance to heat flow between the heat
source and the foam surface. In addition, foam of this invention inhibits the formation of
hot or flaming droplets which can cause excessive damage even though the flame has
been extinguished or inhibited. This kind of intumescent char has low thermal
conductivity and high oxidation resistance, so that it not only affords protection to the
material present inside by virtue of its low thermal conductivity, but its surface reaches a
high temperature and thus re-radiates a large fraction of the incident heat load.
The present invention is now demonstrated by way of illustrative non limiting examples.
The following specific examples will serve further to illustrate the practice and
advantages of this invention.
BRIEF DESCRIPTION OF THE ACCOMPANING DRAWINGS
Fig.1 (a) and (b) show the images of unburnt and burnt intumescent fire retardant rigid
PUF, respectively.
Fig. 2 shows graphically the thermal insulation test of different rigid PUF samples
(prepared in this invention as well as of a couple of commercial reference samples)
illustrating rise in temperature in 25 mm PUF sample.
Fig. 3 shows graphically the thermal insulation test of different rigid PUF samples
(prepared in this invention as well as of a couple of commercial reference samples)
illustrating thickness of the char produced when one of the faces of the test piece was
heated to 800 °C in a flame.
EXAMPLE 1
The process for the preparation of the rigid PUF is as follows: all of the ingredients (as
shown in Table 1) except isocyanate, were first well mixed in a plastic container. Then
isocyanate was added into the container with vigorous stirring for 20 seconds. The
resulting mixture was poured into a mold, which is used to produce the rigid PUF. After
the preparation the foams were kept in an oven at 70 °C for 24 h to complete the
polymerization reaction. The particle size of flame retardants is very important since
physical properties of the resulting products are significantly affected. Generally, the
finer the particle size of fillers impart better properties of the resultant products. It is
preferred to use flame retardants having an average particle size of less than 30 microns,
and especially about 10 microns or less.
The intumescent mixture for the rigid polyurethane foam produced in this invention is
very efficient, and renders excellent retardant to flame, heat and smoke. Table 2
summarizes the different physical, mechanical and fire retardant properties of rigid PUF
prepared in this invention. Table 3, Table 4, Figure 2 and 3 show the comparative results
of rigid PUF and commercial reference sample (Reference 1 and 2).

EXAMPLE 2
The rigid PUF is characterized by following various tests. The density of the PUF
samples was measured according to ASTM D 1622-03. The mechanical properties such
as compressive strength at 10% strain in parallel to foam rise direction was performed
according to ASTM D 1621-00. The morphology of the PUF samples was studied with a
JEOL, JSM 5800 scanning electron microscope, Japan. The thermal conductivity of the
PUFs was tested between two plates on a guarded hot plate apparatus as per ASTM C
177-97. The thermal stability of PUF was examined on a thermogravimetry analysis
(TGA), (Q50, TA Instruments, USA) under nitrogen environment at a heating rate of 20
°C /min.
The flame retardant properties of the PUF were determined by Limiting Oxygen Index
(LOI) according to the ASTM D-2863 test. This LOI expresses the minimum percentage
of oxygen in a flowing mixture of oxygen and nitrogen required to support flaming
combustion. A higher value of LOI indicates a lesser probability of burning since a
greater amount of oxygen would be required to support combustion. Therefore, the LOI
of 21.0 means that combustion can be supported in air (content of oxygen in air is about
21%) whereas the LOI of 31.0, indicates that the relative amount of oxygen in the
environment of the sample must be considerably greater than what is found in air, to
support combustion.
The char yields (CY) of the foams were measured on a muffle furnace at 550°C for 30
min. The cone calorimeter test is also used to indicate flammability or lack of it with
respect to a test sample and measured according to ASTM E-1354. In this test, the
objective is to determine the ignition time, heat release rate, amount of smoke released,
amount of mass loss at the fixed or varied heat flux. To achieve this objective, at high
intense heat, the foam should have a minimum heat release rate, minimum smoke
evolution and greater the ignition time. The smoke density was measured as per ASTM D
2843-04. The smoke generated in the process of burning of sample is measured by the
change of light intensity. The size of the PUF specimen was 100 x 100 x 12 mm3 (length
x width x thickness). The maximum smoke density was measured from the curves of peak
maxima of the light absorption vs time. This smoke density rating represents the total
amount of smoke present in the chamber for the 4 min time and was measured by using
the equation;
Smoke density rating = A/T x 100
Where, A and T are the area under the curve of light absorption vs. time and total area of
the curve respectively.

WE CLAIM
1. An intumescent fire retardant rigid polyurethane foam having desired particle size
adapted for providing a voluminous multi-cellular swollen char with lesser
released amount of heat and toxic smokes, comprising polyether polyol,
polymeric methane diisocyanate with combination of intumescent fire retardant
char forming additives.
2. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1,
wherein said fire retardant intumescent additives comprise of the combination of:
(a) acid forming additives selected from the group comprising of halogenated
phosphate ester, ammonium phosphate, ammonium polyphosphate, ammonium
pentaborate, melamine phosphate, melamine polyphosphate, ethylenediamine
phosphate, ammonium dihydrogen phosphate, aluminum orthophosphate,
piperazine phosphate, guanidine phosphate, phosphoric ester polyols or urea
phosphate, expandable graphite flakes, melamine compounds and its derivatives;
(b) char promoting agents selected from the group comprising of pentaerythritol,
dipentaerythritol, polyethylene glycol and starch, sucrose, glycerol, trimethylol
propane, and phosphoric ester-based polyols;
(c) gas forming additives selected from the group comprising of melamine,
chlorinated paraffin, chlorophosphate ester, urea, melamine formaldehyde resins,
dicyandiamide; and
(d) inorganic based additives selected from the group comprising of antimony
oxide, alumina trihydrate, zinc borate, ammonium polyphosphate, ammonium
pentaborate, red phosphorus, low melting glasses, calcium carbonate, silicates,
and glass powder.
3. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1,
wherein said density is preferably ranging from 200 to 450 kg/m3.
4. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1,
wherein said percentage of limiting oxygen index ranges from 29-35%.
5. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1,
wherein said intumescent fire retardant additive having the particle size is
preferably ranging from 5 to 200 urn.
6. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1,
wherein said fire retardant intumescent char forming additives is preferably
ranging from 5 to 50 parts per hundred of polyol by weight.
7. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1,
wherein said fire retardant intumescent acid forming additives range from 5 to 30
parts per hundred of polyol by weight.
8. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1,
wherein said char promoting agents range preferably from 1 to 25 parts per
hundred of polyol by weight.
9. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1,
wherein said fire retardant intumescent gas forming additives range preferably
from 1 to 30 parts per hundred of polyol by weight.
10. The intumescent fire retardant rigid polyurethane foam as claimed in claim 1,
wherein said fire retardant intumescent inorganic additives range preferably from
1 to 25 parts per hundred of polyol by weight.

The invention relates to an intumescent fire retardant rigid polyurethane foam having
desired particle size adapted for providing a voluminous multi-cellular swollen char with
lesser released amount of heat and toxic smokes, comprising polyether polyol, polymeric
methane diisocyanate with combination of intumescent fire retardant char forming
additives.

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Patent Number

277138

Indian Patent Application Number

76/KOL/2010

PG Journal Number

47/2016

Publication Date

11-Nov-2016

Grant Date

11-Nov-2016

Date of Filing

28-Jan-2010

Name of Patentee

SECRETARY, DEPARTMENT OF ATOMIC ENERGY

Applicant Address

Anushakti Bhavan, C.S.M. Marg, Mumbai 400 001, India

Inventors:

#	Inventor's Name	Inventor's Address
1	THIRUMAL, M.	RUBBER TECHNOLOGY CENTRE, INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
2	SINGHA, NIKHIL, K.	RUBBER TECHNOLOGY CENTRE, INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
3	KHASTGIR, D.	RUBBER TECHNOLOGY CENTRE, INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
4	MANJUNATH, B. S.	RTDS, BARC, MUMBAI
5	NAIK, Y. P.	PRODUCT DEVELOPMENT DIVISION, BARC, MUMBAI

PCT International Classification Number

C08K13/02

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA