FIELD OF THE INVENTION

The present invention relates to a flame retardant agent comprising at least two components among ammonium sulphate, at least one phosphate, and at least one urea resin. In particular, said flame retardant agent finds advantageous application in fireproof materials, for example for the production of chipboard panels, plastics, resins, and paper matrices.

BACKGROUND ART

The laminate chipboard industry traditionally uses mono ammonium phosphate (MAP) as a flame retardant, with the possibility of adding borates or alumina trihydrate (ATH) as a smoke suppressant agent.

This compound is added in large quantities and can even reach up to 30% by weight with respect to the chipboard panel. The fire retardant action of the panel is a result of the low amount of heat absorbed combined with the high capacity of MAP to form a superficial layer on the surface that prevents or delays flames from spreading. In order to guarantee homogeneity of the panel and prevent the formation of bubbles or visible stains which would cause an aesthetic problem, MAP is generally used in powder form. From an industrial point of view, this can lead to packing problems in the plants during the retardant distribution step, which is why a coarse powder is used in an attempt to limit these effects. Furthermore, the acidic nature of MAP (pH 4-5) can interfere with the setting process of the glues used in the panel, thus accelerating the reaction (acid catalysis).

In the past, alternative formulations have been proposed, with a greater capacity for heat absorption, by mixing different liquid components or by mixing powders. However, liquid flame retardants pose more problems in terms of preservability, storage, and transport, making them less preferable than a solid formulation. On the other hand, a solid mixture in powder form may pose said packing problems, together with the possibility of de-mixing over time, causing uneven areas in the final panels and therefore with fire-protection problems (known as 'hot spots').

The addition of urea formaldehyde resins, or of reagents that lead to the formation of said resin, brings certain benefits, as these resins have excellent thermal absorption and their breakdown produces inert gases which promote removal of oxygen from the flame, thus counteracting the combustion. In the field of flame retardants, one example is given by US4552803, wherein a mixture of powders containing an ureidic reagent is added to a liquid containing an aldehyde. By heating the mixture, it is possible to obtain ureidic resin with the other components trapped inside and, after grinding, a homogeneous powder is obtained to be used as a retardant. However, in addition to said problems with powders, the problem of the formaldehyde trapped inside the resin remains, being promoted by the presence of other components which are external therefrom. With respect to laminate panels, there are increasingly stringent limits on the amount of formaldehyde which may be present, as a result of the glues used, due to its toxicity and carcinogenicity (EN 717-1 and related). The presence of free formaldehyde inside the flame retardant therefore causes not only a safety problem for the operators, but also a problem in terms of compliance with legal limits and for end users.

The object of the present invention is therefore to provide a product which has an adequate flame retarding ability, which is safe for use in terms of health, and likewise both advantageous in terms of production and economical.

SUMMARY OF THE INVENTION

Said object has been achieved by a flame retardant agent, as stated in Claim 1.

The present invention furthermore relates to a fireproof material comprising said flame retardant agent.

In another aspect, the present invention concerns the use of the fireproof material, as disclosed above, for fireproofing a chipboard panel or other wood-based element usable in joinery or the building industry, or for fireproofing plastic or paper objects.

In a further aspect, the present invention concerns a chipboard panel or other wood- based element usable in joinery or the building industry, fireproofed with the fireproof material as disclosed above.

The characteristics and advantages of the present invention will become apparent from the following detailed description and the embodiments provided for illustrative and non-limiting purposes.

DETAILED DESCRIPTION OF THE INVENTION

The invention therefore relates to a flame retardant agent comprising at least two of ammonium sulphate, at least one phosphate, and at least one urea resin. The term "ammonium sulphate" means monoammonium sulphate, diammonium sulphate or a mixture thereof.

The term "at least one phosphate", means monocalcium phosphate, dicalcium phosphate, tricalcium phosphate, phosphorite, polyphosphate, monoammonium phosphate, diammonium phosphate, triammonium phosphate, struvite, or a mixture thereof. Preferably, said at least one phosphate is monoammonium phosphate, diammonium phosphate, triammonium phosphate, or a mixture thereof.

In preferred embodiments, said at least one phosphate is monoammonium phosphate. The term "at least one urea resin" means a resin obtained from the reaction between urea and formaldehyde, and for this reason it is often also called urea-formaldehyde resin. Resins with different solubility are obtained according to the degree of polymerisation. For the purposes of the present invention, lower degrees of polymerisation (short-chain/oligomer, preferably methylene urea) are preferred, since they are more water-soluble. Accordingly, in preferred embodiments, said degree of polymerisation is not higher than 6. Suitable resins may be those described, for example, in US4378238. As an alternative to the resin described, resins derived from the reaction of an aldehyde, such as formaldehyde or acrolein, may be used with an amine reactant, such as urea, thiourea, guanidine, dicyandiamide, or melamine.

More preferably, said urea resin is water-soluble or partially water-soluble. In fact, as ammonium sulphate and phosphate are soluble compounds, said preferred form offers the possibility of dissolving the flame retardant agent for industrial applications sorequiring.

Preferably, said flame retardant agent comprises ammonium sulphate and at least one phosphate.

As will be seen in the examples given below, it has surprisingly been found that ammonium sulphate advantageously increases overall heat absorption capacity, has a lower decomposition temperature than that of the flame, and guarantees, at the same time, a slightly less acidic pH, which therefore interferes less with the setting process of the glues used in the panel.

Also, advantageously, ammonium sulphate is an extremely easy component to handle and store, as well as economical and safe for humans.

Preferably, said agent is in a dry solid form, since such a form allows said agent to be easily handled, stored, transported, and metered.

The term "dry solid form" means that the flame retardant agent contains neither liquid components nor solvents, except in negligible amounts (<5%). Higher percentages are possible but not advisable due to possible packing problems and poor flowability.

Indeed, the agent may also have a concentrated or diluted liquid form.

Preferably, said flame retardant agent is in the form of powder, tablet, mini-tablet, micro-tablet, granule, micro-granule, pellet, micro-pellet, multiparticulate, micronised particulate, or a mixture thereof.

More preferably, said flame retardant agent is in the form of micro-granules.

In preferred embodiments, said flame retardant agent is in the form of micro-granules having a D ₅₀ particle-size distribution of 100-3000 pm. For the purposes of the present invention, this parameter is measured through a granulometric screening by sieving with suitable sieves arranged in series, each one of which retains the solid fraction whose granules are larger in size than the sieve holes.

In more preferable embodiments, said microgranules have a D ₅₀ particle-size distribution of 100-2000 pm.

Even more preferable are the embodiments wherein said flame retardant agent is in the form of micro-granules having a D ₉₀ particle-size distribution of 200-3000 pm, and even further again of 300-2000 pm. Even further preferable are the embodiments wherein said flame retardant agent is in the form of micro-granules having a D ₉ o particle-size distribution of 500-1500 pm, and even further preferably of 600-1300 pm.

The particle sizes stated above have proved to be particularly advantageous, since on the one hand they allow suitable mixing of the flame retardant of the invention with any other ingredients to form a fireproof material, and on the other hand they facilitate uniform application of the fireproof material. Smaller particle sizes make processability of the granules considerably more complex, especially with respect to uniformity and homogeneity of the formulation in the final granules. Larger particle sizes, meanwhile, cause application problems on the surfaces to be made fireproof.

Preferably said ammonium sulphate and at least one phosphate are in a weight ratio of 10: 1 to 1 : 10, more preferably 5: 1 to 1 :5.

Indeed, it has been observed that a greater amount of ammonium sulphate increases the ability of the flame retardant agent to absorb heat, while a greater amount of phosphate increases the ability of the flame retardant agent to form the crust that prevents or delays the flame from spreading. Therefore, the weight ratio may be chosen according to application requirements.

In other embodiments, said flame retardant agent comprises at least one urea resin. It has surprisingly been observed that this resin reacts on the flame and contributes, with the at least one phosphate, to the formation of a surface layer. Furthermore, the pH of the resin varies within a range of 6-7, thereby reducing the impact on the setting of the glues used for panels.

In preferred embodiments, the flame retardant agent comprises a water-soluble or partially water-soluble urea resin, wherein the starting formaldehyde content is less than 0.5%, preferably less than 0.1%. Higher percentages are possible but not advisable due to possible problems of toxicity and consequent decline in value of the end product. Indeed, it has been observed that, by pushing the reaction between urea and formaldehyde to completion, a resin is obtained that, advantageously, no longer contains formaldehyde in an unreacted form, which would therefore be freely released into the environment.

Preferably, said urea resin is in an amount of up to 50 wt% based on the weight of the flame retardant agent, more preferably 10-40 wt%.

In other embodiments, the flame retardant agent comprises ammonium sulphate and at least one urea resin, said agent being in a dry solid form.

In further embodiments, the flame retardant agent comprises at least one phosphate and at least one urea resin, said agent being in a dry solid form.

In preferred embodiments, said flame retardant agent consists essentially of at least two of ammonium sulphate, at least one phosphate, and at least one urea resin, said agent preferably being in a dry solid form. The term "consists essentially of means that at least two of ammonium sulphate, at least one phosphate, and at least one urea resin, are the sole components present which play an active role in the containment or prevention of flames spreading, since the other components are solely formulant agents, inert agents or fluidifying agents.

In other preferred embodiments, said flame retardant agent consists of at least two of ammonium sulphate, at least one phosphate, and at least one urea resin, said agent preferably being in a dry solid form. The present invention furthermore relates to a fireproof material comprising said flame retardant agent.

Preferably, said flame retardant agent is in an amount of up to 98 wt% based on the weight of the fireproof material, and preferably 50-95 wt%.

In preferred embodiments, said flame retardant agent is in an amount of 70-95 wt% based on the weight of the fireproof material.

Preferably, this said fireproof material further comprises at least one smoke suppressant agent.

Said smoke suppressant agent may be alumina trihydrate, zinc borate, antimony trioxide, antimony pentoxide, sodium antimonate, zinc hydroxystannate, zinc stannate, molybdenum trioxide, ammonium molybdate, magnesium oxide, zinc oxide, zinc molybdate, ferrocene, or a mixture thereof.

In preferred embodiments, said smoke suppressant agent is alumina trihydrate, zinc borate, or a mixture thereof.

Preferably, said smoke suppressant agent is in an amount of up to 15 wt% based on the weight of the fireproof material, and more preferably 1-10 wt%.

In preferred embodiments, said smoke suppressant agent is in an amount of 2-7 wt% based on the weight of the fireproof material.

Preferably, said fireproof material is in dry solid form.

The term "dry solid form" means that the fireproof material contains neither liquid components nor solvents, except in negligible amounts (<5%). Higher percentages are possible but not advisable due to possible packing problems and poor flowability.

Preferably, said fireproof material is in the form of powder, tablet, mini-tablet, micro tablet, granule, micro-granule, pellet, micro-pellet, multiparticulate, micronised particulate, or a mixture thereof.

In preferred embodiments, said fireproof material is in the form of micro-granules having a D ₅₀ particle-size distribution of 100-3000 pm. For the purposes of the present invention, this parameter is measured through a granulometric screening by sieving with suitable sieves arranged in series, each one of which retains the solid fraction whose granules are larger in size than the sieve holes.

In preferred embodiments, said micro-granules have a D ₅₀ particle-size distribution of 100-2000 pm. The fireproof material can be obtained by a preparation process comprising the following steps:

- mixing at least two of ammonium sulphate, at least one phosphate, and at least one urea resin, which have been preliminarily ground, and, in case, additives (smoke suppressant agent, inert agents or fluidifying agents) in a granulator,

- granulating into micro-granules, by adding water,

- drying the micro-granules and optionally sieving them to obtain the desired particle size.

In this way, a uniform material is obtained, without any packing problems, which is stable over time and has great heat absorption capacity.

In another aspect, the present invention concerns the use of the fireproof material, as disclosed above, for fireproofing a chipboard panel or other wood-based element usable in joinery or building industry, or for fireproofing plastic or paper objects.

In a further aspect, the present invention concerns a chipboard panel or other wood- based element usable in joinery or the building industry, fireproofed with the fireproof material as disclosed above.

It should be understood that all the possible combinations of the preferred aspects of the components of the flame retardant agent, the fireproof material, the chipboard panel and the preparation and uses disclosed above are described herein and therefore are also preferred.

It is also to be understood that all aspects identified as favourable and advantageous for the flame retardant agent and the components thereof, should be deemed to be similarly preferable and advantageous also for the fireproof material, the chipboard panel, the preparation, and the uses disclosed above.

Below are working examples of the present invention provided for illustrative purposes. EXAMPLES

Comparative example.

5.00 kg MAP was processed in the granulator as in Example 1. 14,381 mg sample was analysed with an STA to assess heat absorption and residue; heat absorbed: 366 J/g, surface layer: 47.3%

Example 1.

1.25 kg MAP was mixed in a batch granulator with 3.75 kg ammonium sulphate. During mixing, by acting on the rotation speed of the granulator body and the inner bar, water is added slowly until micro-granules are formed. The product is unloaded, dried in an oven and sieved within a range of 0.5 to 1.2 mm. 10,336 mg sample was analysed with an STA to assess heat absorption and residue; heat absorbed: 1131 J/g, surface layer: 8.7%

It was observed that the heat absorption capacity was 3.09 times higher than in the comparative example with MAP only.

Example 2.

1.50 kg MAP was mixed in a batch granulator with 3.50 kg ammonium sulphate. The mixture was processed in the granulator as in Example 1. 11,865 mg sample was analysed with an STA to assess heat absorption and residue; heat absorbed: 793 J/g, surface layer: 14.0%

It was observed that the heat absorption capacity was 2.17 times higher than in the comparative example with MAP only.

Example 3.

750 g finely ground urea-formaldehyde resin was mixed in a batch granulator with 1.25 kg MAP, 2.75 kg ammonium sulphate and 250 g alumina trihydrate, as a smoke suppressant agent. The mixture was processed in the granulator as in Example 1. 14,672 mg sample was analysed with an STA (Standard Thermal Analyzer) to assess heat absorption and residue; heat absorbed: 995 J/g, surface layer: 18.75%

It was observed that the heat absorption capacity was 2.72 times that of the comparative example with MAP only.

Example 4.

1.50 kg finely ground urea-formaldehyde resin was mixed in a batch granulator with 1.75 kg MAP, 1.50 kg ammonium sulphate and 250 g alumina trihydrate, as a smoke suppressant agent. The mixture was processed in the granulator as in Example 1. 11,539 mg sample was analysed with an STA to assess heat absorption and residue; heat absorbed: 633 J/g, surface layer: 22.1%.

It was observed that the heat absorption capacity was 1.73 times that of the comparative example with MAP only.

From the foregoing and from the results achieved, an unexpected, significant increase was demonstrated in the heat absorption of the materials according to the invention with respect to known materials comprising MAP only.

Example 5.

Assessment of the reaction to fire of a wooden product treated with the product obtained in Example 3

The fire classification of materials and building products is highly structured. Italian legislation (Ministerial Decree dated 10 March 2005) subdivides building materials into six Euroclasses:

Al, A2, B, C, D, E; a seventh class (F) encompasses products that, even if not intrinsically hazardous, have not yet been classified. Hazard levels increase from category Al to category E.

The materials of class A2, B, C, D, E are in turn subdivided into subclasses, based on predispositions to:

• to produce smoke, meaning the ability to emit vapours or particles;

• to produce falling droplets, meaning the ability to release flaming droplets of molten material.

There are three levels of smoke release: sl, s2, s3 (the letter 's' stands for smoke); the amount of smoke increases from level 1 to level 3. Products intended for flooring (where the emission of smoke is particularly hazardous) may not be s3 class.

There are also three levels which classify falling droplets: dO, dl, d2 (the letter 'd' stands for droplets); level dO means no falling droplets; level dl means that the falling of droplets is short-lived; level d2 means persistent falling droplets.

Products installed along the escape routes (entrances, corridors, stairways, ramps, passageways in general) must necessarily belong to certain classes, also depending on the intended use thereof (wall, ceiling, floor). Droplets falling from ceilings is particularly hazardous: glowing droplets falling from overhead cause fire to spread rapidly and create damage to people trying to escape.

Preparation of samples

6 chipboard panels were prepared having a thickness of 20 mm and density of 640 kg/ m ³ , where 3 panels have dimensions 500 mm x 1500 mm and 3 panels have dimensions 1000 mm x 1500 mm.

The panels were prepared by mixing the product obtained in Example 3, with chips and resin, and subsequently hot-pressing. Tests carried out

A fire reaction test was carried out on the panels, according to the instructions of a test known as the Single Burning Item (SB I) test, compliant with standard UNI EN 13823. The SBI test is a method to determine the reaction and the fire behaviour of building products when they are exposed to heat aggression from a single source of heat (reproduced using a cast iron container supplied with burning propane through a tube). The sample is mounted on a trolley positioned in a sort of chimney, with a smoke/fume extractor hood mounted on top. The reaction of the sample to heat was monitored instrumentally and visually. The rate of heat and smoke released was measured instrumentally.

Results

The values measured after the test was carried out by a certified body are shown below:

The chipboard panels treated with the product according to the invention were found to meet the requirements for Euroclass B - s2, dO, i.e. the fireproof material according to the invention was found to be a Euroclass B product which is suitable for walls or ceilings, produces little smoke, does not produce flaming droplets, and may also be employed in escape routes.