EP1300506A2 - Textile substrate with improved fire resistance - Google Patents

Abstract

The improved heat and fire resistance textile substrate comprises a flame retardant coating including a polymeric binder, an intumescent composition and a small amount of at least one synergist, chosen from aluminum hydroxide, hydroxide of magnesium, bauhemite, titanium oxide, sodium silicate, zeolites, low-melting glass, clay nanoparticles, borosilicate product, polyamide nanocomposites, polypropylene and polyester. Under the action of a heat source, a double carbon layer is obtained, namely a uniform thin layer on the surface and a cellular layer in depth. The amount of synergistic agent is between 0.2 and 3% by weight relative to the polymeric binder.

Description

The present invention relates to a textile substrate, formed from synthetic yarns or fibers and having a flame retardant coating comprising agents developing an intumescent structure, intended to provide said substrate with improved performance as to its resistance to heat and fire.

The use of agents developing an intumescent structure mixed with other components to a polymeric binder to form a flame retardant system of the support on which is applied said binder is already well known. In particular the document WO 98/22555 relates to a flame-retardant composition applicable to a substrate, including a textile structure. This flame-retardant composition, without halogen, includes a polymeric binder and an intumescent agent which is consisting at least of an acid source agent and of a source agent of carbon (polyhydric carbon compound). To be effective, the acid must be able to dehydrate the polyol. This dehydration should not have place only from a certain temperature or in the presence of a flame, this is why the acid salts are preferably used. The release of acid should take place below the temperature of decomposition of polyhydric material. The relative effectiveness of the different acids will depend on the strength of the acid character. Acid salts most often used are compounds which have a volatile cation, so that the acid can be released in areas of temperature close to the ignition temperature of the material. The carbonaceous polyhydric compound is generally a compound chosen from different classes of carbohydrates and which has a quantity relatively high carbon and many hydroxile sites. The carbonaceous polyhydric compound has the function of developing, in combination with the strong thermodegradable acidic compound, one layer alveolar carbonaceous, capable of forming, when the substrate is subjected to a heat source, a shield for protecting said substrate. It is the principle of indirect fireproofing.

According to document WO 98/22555, the strong acid compound thermodegradable is preferably chosen from the group consisting in phosphoric acids, boric acids, or a salt of these the latter having a volatile cation and in particular polyphosphate ammonium. As for the carbon-containing polyhydric compound, it is same document of a starch or polyhydric alcohol and more preferably pentaerythritol. The relatively high amount of carbon and hydroxile sites contained by said agents promotes the formation of a large alveolar or expanded carbon layer. This are the gases released by the reaction of the strong acid compound thermodegradable with the polyhydric carbon compound which allow the expansion of the carbon layer.

As regards the polymeric binder, according to document WO 98/22555, its choice is not limited to a particular polymer, as long as it fulfills the function of binder of the flame-retardant composition. However, when the polymeric binder is a polyurethane or an acrylic polymer, it necessarily add a fire retardant adjuvant, in particular an inorganic phosphorus compound.

Thus, in a preferred embodiment, the composition flame retardant of the aforementioned document consists of 35 to 45% by weight an acrylic polymer, from 15 to 35% of ammonium polyphosphate, 10 to 15% pentaerythritol and 10 to 30% a flame retardant adjuvant which can be an alumina hydroxide or an organophosphorus compound, this adjuvant always being different and distinct from the constituent compounds the intumescent agent and in particular of the strong acid compound thermally degradable.

The purpose of the above document was to obtain a flame retardant composition, comprising a binder fraction with a binder polymer and an intumescent composition, allowing to keep or improve the properties of the intumescent agent without altering the basic properties of the binding fraction, for example its thermosolvency and / or its resistance to moisture uptake so as to ability to apply to substrates such as textile structures including technical fabrics and obtaining fire resistance improved of these substrates. In this case, such substrates can be either threads of mineral or organic material, of natural origin or synthetic or textile structures, woven, non-woven or knitted fabrics, of the technical fabric type used for example to make blinds, curtains and the like.

The aim that the applicants have set themselves is to propose a textile substrate having improved performance in terms of resistance to heat and fire thanks to a special intumescent system.

This object is perfectly achieved by the textile substrate of the invention which, in known manner, includes a flame retardant coating, which comprises a polymeric binder and an intumescent composition.

Characteristically, according to the invention, the coating flame retardant further comprises a small amount of at least one synergy, chosen from aluminum hydroxide, magnesium, bauhemite, titanium oxide, sodium silicate, zeolites, low melting point glass, clay nanoparticles, borosilicate product, nanocomposites of polyamide, polypropylene and polyester so to obtain, under the action of a heat source, a double layer carbonaceous, namely a uniform thin layer on the surface and a layer alveolar in depth.

Of course, aluminum hydroxide and magnesium hydroxide are commonly used as flame retardants. Such additives, subjected to a heat source, degrade following a reaction endothermic by releasing water. This degradation leads thanks to dilution of the gases, an increase in the minimum ignition time and a decrease in heat output. However, to achieve an effect significant, the material to be protected must be loaded with a quantity important of such additives. For example in document US 6,150,448, a metal hydroxide such as aluminum hydroxide or magnesium is used in combination with red phosphorus and ammonium polyphosphate, but at the rate of 60 to 150 parts of metal hydroxide per 100 parts by weight of the polymeric binder, to know an ethylene-vinyl-acetate-acrylate copolymer.

On the contrary, in the present case, the quantity of synergy, implemented, according to the present invention, is in quantity reduced, for example between 0.2 and 3% by weight relative to the polymeric binder. This amount is so small that the improvement in performance cannot be explained by the water release caused by the degradation of this synergistic agent.

Without trying to explain precisely the reasons for the improvement brought by this small amount of synergistic agent, the applicants specify that they were able to observe by microscope analyzes scanning electronics only when the polymer binder is loaded non only ammonium polyphosphate but also an amount reduced by at least one synergistic agent, for example hydroxide aluminum, a carbonaceous double layer is formed, namely a uniform thin layer on the surface and a layer consisting of cells in depth. It would be the thin surface layer that would limit gas transfers to the flame. In addition, the synergistic agent containing a metal atom, an X-ray analysis of the elements constituting the carbon layer following the thermal degradation of the sample showed a very high concentration of the metal at level of the uniform surface thin layer, which strengthens the cohesion of the intumescent system.

Thus the synergistic agent in small quantities allows to lead to a ceramic structure on the surface of the carbon layer. The hydroxide alumina or aluminum, titanium oxide, sodium silicate, zeolites, low melting point glasses, clay nanoparticles, borosilicate product, polyamide nanocomposites, polypropylene and polyester acting as a ceramising agent improve the mechanical properties of the carbonaceous residue, while the charges minerals play the role of cement by improving the cohesion of the layer carbon.

Preferably, the polymeric binder being an acrylic polymer, the textile substrate is formed from polypropylene yarns or fibers or polyester. It should be noted in particular that the implementation, as synthetic material, polyamide is not at all suitable with the use of an acrylic polymer as a polymeric binder.

Preferably, in the aforementioned case, the intumescent composition includes an ammonium polyphosphate as the acid salt.

The overall preferred proportion of ammonium polyphosphate and the synergistic agent relative to the polymeric binder is between 10 and 20%, the percentage of 15% being an optimum compromise in terms of outcome and cost.

As for the proportion by weight of the flame retardant coating by relative to the entire textile substrate, it can be between 20 and 70%, a proportion of the order of 40% being preferred.

The present invention will be better understood on reading the description of several exemplary embodiments of a nonwoven based on polypropylene fibers and polyester fibers and a coating flame retardant based on an acrylic polymer binder, polyphosphate ammonium as the acid salt of the intumescent composition and a reduced amount of at least one synergistic agent.

The textile substrate which one seeks to improve the fire resistance, according to the invention, is formed of threads or fibers. He can therefore be a woven, knitted or non-woven article. In the examples given below, it is, preferably but not exclusively, a nonwoven, for example needled as used in floor coverings. In addition, the threads or fibers are made of a synthetic material which is hot-melt that is to say that it melts from a certain temperature then degrades under the effect of heat. Preferably it is son or polypropylene or polyester fibers.

The textile substrate has a flame retardant coating, which is composed of a polymeric binder, which acts as a carbon source agent, and an intumescent composition containing at least one acid salt, coating which is applied to the nonwoven while it is under the form of a paste, being applied for example to the doctor blade.

The paste intended to form this coating is prepared under the following conditions. We start with an acrylic polymer. It is more generally a copolymer, capable of containing units of acrylic acid, methacrylic acid, acrylonitrile, acrylamide, acrylic ester of formula CH ₂ = CH - COO - R, with R designating hydrocarbon chains which can contain up to eight carbons.

In a specific embodiment, we started with a resin type A acrylic. This preliminary acrylic resin has been diluted with water in the proportion of 40%. We successively added an agent wetting at the critical micellar concentration and, as the acid salt, ammonium polyphosphate powder. This powder has been dispersed by performing a bubble removal by the action of ultrasound. Possibly this dispersion can take place in a micro-grinder. Anti-foaming agent is optionally added, then a thickening agent to obtain the flame retardant composition comprising acrylic resin and poly ammonium phosphate in the form of a paste, which is applied with a doctor blade on one side of the nonwoven, which is then dried in an oven or an oven at a temperature of the order of 120 ° C., in order to obtain the crosslinking or polymerization of the resin. The amount of paste applied on the textile substrate is determined according to the proportion by weight flame retardant coating with respect to the entire textile substrate. This proportion can be between 20 and 70%. However for applications such as floor coverings or items of furniture, this proportion is preferably of the order of 40%.

As for the proportion of acid salt relative to the polymeric binder, as regards the acrylic polymer / ammonium polyphosphate pair, this proportion is between 10 and 20%, preferably of the order 15%. Certainly a higher amount of ammonium polyphosphate can increase the fire resistance properties, but in a way that is not significant in view of the additional cost that this increase causes. So the 15% percentage is an optimum compromise in term of result and cost.

The performance in terms of improvement of the fire retardancy properties of two nonwovens was tested, one formed from polypropylene fibers and the other from polyester fibers, both comprising a flame retardant coating without synergistic agent. . According to the principle of indirect fireproofing, it is the fireproofing coating which forms a shield intended to protect the textile material. To assess the fire resistance provided by the flame retardant coating, it is checked whether the presence of this coating decreases the heat flow released when the textile substrate is subjected to an incident radiant heat flux of a value of 30 kW / m ² . The samples are arranged horizontally; the textile substrate is exposed directly to the heating resistance of a calorimeter cone. The calorimeter cone tests are carried out according to ASTME 1354-90 or ISO 5660.

The polypropylene nonwoven web, making 550 g / m ² , releases a heat flow of 230kw / m ² when it is uncoated and a heat flow of 165kw / m ² when it has a flame retardant coating of the order 40%.

The polyester nonwoven web, of the order of 450 g / m ² , uncoated releases a heat flow rate of 285kw / m ² and the same sheet coated with flame retardant coating releases a heat flow rate of 153kw / m ² .

So we see that the presence of the flame retardant coating, composed of acrylic binder and ammonium polyphosphate, without synergistic agent, proves to be quite effective in terms of flow reduction calorific, more particularly when the textile substrate is composed of polyester yarns or fibers, for which the reduction in heat flow is close to 50%, being close to 30% for yarns or fibers polypropylene.

The above values are maximum flow values It should be noted that the heat output depends on the value of the incident radiant heat flux. Figures 1 and 2 illustrate this development of the heat flow as a function of time for the coated nonwoven (A), for the non-coated nonwoven (B) and also for the coating alone (C), being a polyester nonwoven (1) for FIG. 1 and a nonwoven polypropylene (2) for Figure 2.

It emerges from the examination of these two figures that the flame retardant coating composed of a binder of acrylic polymer and ammonium polyphosphate, without synergistic agent, makes it possible to reduce the normal calorific flow of a nonwoven nonwoven coated with polyester (B1) and polypropylene (B2) fibers, subjected to an incident radiant heat flux of a value of 30kw / m ² . However, it is noted that the ignition of the polyester coated nonwoven (A1) is early compared to the uncoated nonwoven (B1). This characteristic is specific to the implementation of an intumescent system. The applicants wish to emphasize that this early ignition time leads to the rapid formation of the carbon layer of the intumescent system, which has the advantage of rapidly limiting heat transfers. This is, according to the applicants, the reason why the maximum heat output released for the ply of coated polyester fibers (A1) is lower than that of the ply of uncoated polyester fibers (B1). However, the ignition time should not, however, be too fast. It is preferable that it remains longer than 20 seconds.

The above test was carried out using a flame retardant coating composed exclusively, as main components, of a polymer type A acrylic as a polymer and polyphosphate binder ammonium as the acid salt.

According to the invention, the addition to the polymeric binder of a low amount of a synergistic agent increases the performance of the textile substrate of the invention in terms of resistance to heat and fire. This synergistic agent, in small proportions, preferably understood between 0.2 and 3% by weight relative to the polymeric binder, is chosen from aluminum hydroxide, magnesium hydroxide, titanium oxide, sodium silicate, zeolites, low melting point glass, nanoparticles clay, borosilicate product, polyamide nanocomposites, polypropylene and polyester so as to obtain, under the action of a heat source, a carbonaceous double layer, namely a uniform thin layer on the surface and a deep alveolar layer.

Tests carried out by the applicants show that the replacement of a certain amount of acid salt, in particular ammonium polyphosphate, with synergistic agent, in particular aluminum hydroxide, increases the fire performance of the samples submitted to an incident radiant heat flux with a value of 3Okw / m ² . This increase may be a function of the particle size of the synergist charge. The finer this particle size and the greater the decrease in energy illumination, but correspondingly the more the ignition time decreases. Scanning electron microscope analyzes show the formation of a double carbon layer, namely a uniform thin layer on the surface and a layer consisting of deep cells. We therefore obtain a honeycomb carbon structure associated with a ceramization system. The presence of the thin layer on the surface limits gas transfers to the flame.

In addition, the X-ray analysis of the elements constituting the layer carbonaceous following the degradation of the sample makes it possible to note a concentration of metal in the thin layer on the surface of the sample, when the synergist contains a metal atom.

A comparative study was carried out using various agents synergy which are all mineral additives, namely hydroxide aluminum, bauhemite, zinc borate, titanium oxide, talc, sodium silicate and calcium carbonate, said additives being works with a type A acrylic polymer as a polymeric binder and the ammonium polyphosphate as the acid salt of the intumescent system.

In the first part of the study, we sought to assess what is the influence of these mineral charges on the fire behavior of polymeric binder. The grain size of the mineral fillers being identical, these were dispersed simultaneously with the acid salt within the polymeric binder, according to the protocol described above. Mineral fillers are introduced in partial substitution for the acid salt, specifically ammonium polyphosphate.

The fire performances were assessed by measuring two parameters, namely on the one hand the maximum heat flow values and on the other hand the ignition time, obtained during the combustion of the coating films according to the different formulations using uses type A acrylic resin, acid salt and each of the mineral fillers. The results are obtained in Table 1 below.

It appears from the examination of this table that the presence of charges mineral within the coating film has consequences for both the minimum ignition time or ignition time and on the maximum value of heat flow. If we consider that the minimum ignition time must be greater than 20 seconds, talc and calcium carbonate are mineral charges which are a priori to be avoided.

In order to select the most effective mineral fillers from the other five charges, we measured the speed evolution energy acceleration as a function of time (Figure 3).

The curves in Figure 3 show that the introduction of charges mineral in partial substitution of ammonium polyphosphate influences the fire retardancy properties of coating films. Compared to the coating film formed exclusively with the resin type A acrylic and ammonium polyphosphate, films coating with different mineral fillers have a speed energy acceleration which is reduced by around 8 to 20% in depending on the nature of the mineral filler; which leads us to think that there does have an interaction between the mineral charge and the acid salt during of the thermal degradation phase.

In another part of the study, we sought to highlight evidence of this possible interaction between mineral charges and salt acid and especially to assess the ability of this interaction to enhance the stability of the intumescent structure. For this we measured the evolution of thermal degradation of the acid salt in the presence of the various mineral charges as a function of temperature. The obtained results are shown in Figure 4.

• Le borate de zinc, le carbonate de calcium , le talc qui accélèrent la dégradation du système dès 350°C ;
• L'hydroxyde d'aluminium et la bauhémite qui ralentissent la dégradation dès 400°C, température correspondant à celle de l'achèvement de la croissance de la structure intumescente pour le liant polymère acrylique de type A ;
• Le silicate de sodium et l'oxyde de titane qui conduisent à une diminution de la vitesse de dégradation des systèmes respectivement de 170° à 500°C et de 170° à 350°C.

The analysis of the different curves makes it possible to distinguish three types of curves depending on the loads, namely:

• Zinc borate, calcium carbonate, talc which accelerate the degradation of the system from 350 ° C;
• Aluminum hydroxide and bauhemite which slow degradation from 400 ° C, temperature corresponding to that of the completion of the growth of the intumescent structure for the acrylic polymer binder type A;
• Sodium silicate and titanium oxide which lead to a decrease in the rate of degradation of the systems from 170 ° to 500 ° C and from 170 ° to 350 ° C respectively.

These results confirm the existence of an interaction between mineral fillers and acid salt.

The next part of the study consisted in analyzing the influence of mineral charges on the morphology of the intumescent structure. This has was carried out using a scanning electron microscope. The examined samples were obtained by degrading the coating films under an oxidizing atmosphere, for 15 minutes at 400 ° C, temperature of formation of the intumescent structure when using a resin type A acrylic as a polymeric binder.

This study made it possible to highlight correlations between the morphological characteristics of the intumescent structure and the thermal stability of systems combining different loads mineral and ammonium polyphosphate.

Ammonium polyphosphate associations and respectively zinc borate, calcium carbonate or talc degrade stability thermal systems. In the presence of type A acrylic resin, they lead to the formation of an unexpanded structure.

Ammonium polyphosphate associations and respectively bauhemite, aluminum hydroxide, titanium oxide, sodium silicate allow to slow down the degradation rate of the systems. In presence of type A acrylic resin, they lead to the formation of an expanded cellular structure, associated with a ceramization of area.

It could be hypothesized that said mineral charges have a certain capacity to form bridges between the chains of ammonium polyphosphate, thus forming complexes promoting the formation of a stable alveolar system.

The next part of the study consisted in assessing the influence of mineral charges on the fire behavior of the coated textile substrate. This part of the study was carried out with a non-woven fabric substrate polypropylene whose flame retardant coating is composed of type A acrylic resin as polymer binder, polyphosphate ammonium as the acid salt. Three formulations were selected for flame retardant coating, with 2% mineral filler respectively aluminum hydroxide, zinc borate and titanium oxide.

Table 2 below presents the fire performance of the different samples tested in terms of ignition time and heat flow. The last column of the table indicates the morphology of the intumescent structure. % APP % of mineral charges % fiber Minimum ignition time Heat output Morphology of the intumescent structure 12% 60% 30 seconds 210 kw.m ^-2 10% 2% aluminum hydroxide 59% 35 seconds 165 kw.m ^-2 Cellular system, surface glass 10% 2% zinc borate 58% 29 seconds 250 kw.m- ² Unexpanded system 10% 2% titanium oxide 61% 31 seconds 180 kw.m ^-2 Compact, low-expansion honeycomb system

It follows from the results obtained that the fire performance of coated textile substrates are directly related to the morphology of the intumescent structure. It is the acrylic resin formulation of type A, ammonium polyphosphate and aluminum hydroxide which leads to the maximum reduction in heat flow for a polypropylene nonwoven. The intumescent structure composed of a alveolar system combining surface ceramisation constitutes obviously the most effective heat shield.

In the next part of the study, we tried to optimize the action aluminum hydroxide and acid salt, examining on the one hand the influence of the granulometry of aluminum hydroxide and on the other hand the proportion of acid salt relative to the hydroxide aluminum.

Table 3 below groups together the fire performances of the samples tested as a function of the particle size of the aluminum hydroxide, in a flame-retardant coating composed of 85% of acrylic resin of type A, of 13% of ammonium polyphosphate. and 2% aluminum hydroxide. It appears from this comparison for a particle size of 45 and 12 μm respectively that it has an impact both on the minimum ignition time or ignition time and on the heat flow rate. To facilitate the representation of the results, the evolution of the energy acceleration rate as a function of the time of these samples was also measured (FIG. 4). It is found that the presence of aluminum hydroxide leads to an increase in the ignition time and a decrease in the speed of energy acceleration. However, the fact that aluminum hydroxide has a particle size of 12 μm minimizes the impact of this additive, compared to the particle size of 45 μm. This phenomenon is probably due to the presence of agglomerates within the dispersion. It is therefore preferable not to use too small a particle size.

Table 4 groups the fire performances of the samples according to the proportion of aluminum hydroxide relative to the acid salt; respectively 1, 2 and 5% of aluminum hydroxide replacing the 15% of ammonium polyphosphate. It is found that the formulation which has the best fire performance contains from 1 to 2% of aluminum hydroxide, 13 to 14% of acid salt and 85% of acrylic resin of type A.

The last part of the study consisted in analyzing the composition of the intumescent structure obtained during the combustion of the nonwoven of coated polypropylene and especially the distribution of aluminum.

Analysis X revealed an enrichment of aluminum on the surface of intumescent structure. This increased concentration of atoms metallic surface increases when the charge rate increases. This observation confirms the observation of ceramization phenomena in surface of the intumescent structure.

Ceramization is at the origin of the limitation of the diffusion of gases flammable to the flame and diffusion of oxygen to the material. In addition, the presence of concentrated aluminum on the surface strengthens the cohesion of the alveolar system.

A second study was carried out using, as a binder polymer, a type B acrylic resin. This study made it possible to validate the fact that the use of a small amount of synergistic agent, in partial substitution of the acid salt, improved the fire performance. However, the most effective substitution depends on the type of resin used.

Table 5 below shows that the use of 2% sodium silicate is more efficient than 2% aluminum hydroxide in terms of heat flow rate for a type B acrylic resin.

Additional tests have been carried out using no longer a single agent of synergy but two or even three agents of synergy, chosen according to their particular contribution to the system intumescent.

Thus aluminum hydroxide or bauhemite helps promote the expansion of the carbon layer and sodium silicate helps promote the formation of the thin surface layer, the whole slowing down the rate of degradation of the intumescent system to low temperature. Tables 6 and 7 show the results thus obtained.

Claims (9)

Textile substrate with improved heat and fire resistance comprising a flame retardant coating, which comprises a polymeric binder and an intumescent composition, characterized in that the flame retardant coating also comprises a small amount of at least one synergistic agent, chosen among aluminum hydroxide, magnesium hydroxide, bauhemite, titanium oxide, sodium silicate, zeolites, glass with low melting point, clay nanoparticles, borosilicate product, polyamide nanocomposites, polypropylene and polyester so as to obtain, under the action of a heat source, a double carbon layer, namely a uniform thin layer on the surface and a cellular layer in depth. Substrate according to Claim 1, characterized in that the quantity of synergistic agent used is between 0.2 and 3% by weight relative to the polymeric binder. Substrate according to either of Claims 1 and 2, characterized in that the polymeric binder being an acrylic polymer, the textile substrate is formed from threads or fibers of polypropylene or polyester. Substrate according to one of claims 1 to 3 characterized in that the intumescent composition contains at least one ammonium polyphosphate. Substrate according to claim 4 characterized in that the overall proportion of ammonium polyphosphate and synergistic agent relative to the polymeric binder is between 10 and 20%, preferably 15%. Substrate according to one of Claims 1 to 5, characterized in that the proportion by weight of the flame-retardant coating relative to the whole of the textile substrate is between 20 and 70%, preferably of the order of 40%. Substrate according to Claim 1, characterized in that , the textile substrate being formed from polypropylene yarns or fibers, the flame-retardant coating is composed of around 85% of type A acrylic polymer, of around 13 with 14% of type A polyphosphate and of the order of 1 to 2% of aluminum hydroxide. Substrate according to claim 1 characterized in that the flame retardant coating contains at least two synergistic agents, chosen from aluminum hydroxide, sodium silicate and bauhemite. Substrate according to Claim 8, characterized in that the flame-retardant coating is composed of around 85% of type B acrylic polymer, around 11% of aluminum hydroxide, 2% of sodium silicate and 2% aluminum hydroxide or bauhemite.

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