Patent Application
20120316269
This application claims the benefit of European Patent Office Application No. 11 447 013.1 filed Jun. 10, 2011, the entire disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of production of flame retardant products comprising at least wood containing particles and/or fibers and at least an organic resin binder system, wherein the method comprises at least the following steps:
a mixing or contacting step in which at least wood containing particles and/or fibers and the organic resin binder system formaldehyde based resin system are mixed or contacted together, and a hardening step in which the mixture of at least wood containing particles and/or fibers and organic binder resin system is hardened.
2. Description of the Related Art
For the manufacturing of products, panels, etc. having flame retardant properties, it is known to add to the organic resin binder (which can be hardened or cured) one or more additives having flame retardant properties.
Attempts have been made to add ammonium polyphosphates to aqueous urea-formaldehyde resin solution or to aqueous urea-melamine-formaldehyde resin solution in order to give flame retardant properties. However, only a low concentration of ammonium polyphosphate can be added, whereby no efficient flame retardant properties can be achieved. Indeed, as soon as the concentration in ammonium polyphosphate is high enough for having some flame retardant properties, the resin starts to be cloud and to precipitate, rendering the resin not suitable for efficiently binding wood containing particles.
U.S. Pat. No. 3,939,107 discloses in a flame retardant of formaldehyde based resin, the use of the reaction product of an ammonium polyphosphate aqueous solution with formaldehyde and caustic, so as to increase the dissolution of the ammonium polyphosphate. Such a use will increase the problem of release of formaldehyde from the manufactured wood panel.
U.S. Pat. No. 3,976,752 relates to the manufacture of water-insoluble ammonium phosphate or polyphosphate as flame retarding agents. The water-insoluble ammonium polyphosphate is prepared by reacting a phosphoric acid with a combined ammoniating and condensing agent. The compound so obtained is water-insoluble. The ammonium phosphate or polyphosphate when used in a sufficient amount for ensuring some flame retardancy will cause the resin to start to be cloudy and to precipitate, rendering the resin not suitable for binding efficiently wood containing particles.
UA80648 discloses the production, of highly condensed ammonium polyphosphate suitable for decreasing the flammability of different classes of polymers. The highly condensed ammonium polyphosphate is prepared by heating a mixture containing ammonium orthophosphate and urea at a temperature of 270° C.-300° C. This highly condensed ammonium polyphosphate is adapted to form a kind of coating or layer in the polymer.
U.S. Pat. No. 3,939,107 discloses a method of production of flame retardant products comprising wood containing particles, an urea-formaldehyde resin and ammonium polyphosphate reacted with formaldehyde.
Panels formed from wood particles and/or fibers bound together by a thermosetting or curable resin binder have in general a low flame resistance, even if the resin binder has been premixed with one or more flame retardant additives. It has been observed that in case of fire, the wood particles and/or fibers form weakening zones. Furthermore, the wood panels are using some organic material or materials which are still in a releasable form, meaning an increase of fire damage due of a release of organic material.
For example, for wood panels, wood particles or fibers are often agglomerated with formaldehyde based binders which remain a good compromise of cost, performance and ease of use for such applications. These binders are thermosetting resins obtained by polycondensation of formaldehyde, urea and, possibly, melamine. Typically, these adhesive compositions contain a substantial molar excess of formaldehyde. Some of this excess is released upon curing of the resin during the manufacture of the panel. However, it is well known that formaldehyde continues to be released from these panels even after the manufacturing process is completed. Thus, formaldehyde in the indoor air has been a major concern for many years.
Such release of organic material (formaldehyde) further increases the risk of fire damage.
Several attempts have been made for many years for reducing formaldehyde emission:
However such attempts were not effective for increasing the flame retardant properties of the panels.
Ammonium polyphosphate is an inorganic salt of polyphosphoric acid and ammonia. The chain length (n) of this polymeric compound is both variable and branched, and can be greater than 1 000. Short and linear chain APPs (n<100) are more water sensitive (hydrolysis) and less thermally stable than longer chain APPs (n>1000), which show a very low water solubility (<0.1 g/100 ml).
Chemical Formula and structure: [NH4PO3]n
APP is a stable, non-volatile compound. In contact with water, APP slowly gets hydrolysed to monoammonium phosphate (orthophosphate). Higher temperatures and prolonged exposure to water will accelerate the hydrolysis. Long chain APP starts to decompose at temperatures above 300° C. to polyphosphoric acid and ammonia. Short chain APP will begin to decompose at temperatures above 150° C.
CA1054918 discloses particle board comprising Ammonium polyphosphate as a fire-retardant agent. Such ammonium polyphosphate is not a formaldehyde catcher.
It has now been discovered that by pretreating the wood containing particles or fibers so that said particles or fibers are associated to specific modified ammonium polyphosphate, the panels using said pretreated wood particles or fibers had increased fire resistance properties, especially increased fire retardant properties. Such properties are quite important, as giving more time to people for leaving a building in fire.
The method of the invention is a method of production of flame retardant products, said products comprising at least:
In this method, at least a part of the wood containing elements to be mixed with the organic resin binder system are treated, prior to being mixed with the said organic binder system, with an aqueous composition comprising at least a reaction product (MAPP) of a reagent selected from the group consisting of melamine, urea and mixtures thereof with an ammonium polyphosphate compound selected from the group consisting of ammonium polyphosphate having a water solubility at 25° C. greater than 0.5 g/100 ml, ammonium polyphosphate has a weight average particle size of less than 50 μm, and combinations thereof. In this method, the composition is selected from the group consisting of aqueous solution, aqueous suspension and a mix thereof, wherein the weight ratio ammonium polyphosphate/reagent used for the preparation of the reaction product is comprised between 1:1 and 25:1. Advantageously the weight ratio ammonium polyphosphate/reagent use for the preparation of the reaction product is between 2:1 and 15:1, and preferably between 5:1 and 12:1. For example, during the reaction, the weight ratio ammonium polyphosphate/reagent used for the preparation of the reaction product is controlled so as to be comprised between 1:1 and 25:1, advantageously between 2:1 and 15:1, and preferably between 5:1 and 12:1.
Advantageously, the MAPP is at least the reaction product of ammonium polyphosphate with melamine (possibly with some urea). In case some melamine is used together with urea for the preparation of the reaction product MAPP, the weight ratio melamine/urea is advantageously greater than 1:1, preferably greater than 2:1, and most preferably comprised between 4:1 and 25:1.
The reaction product MAPP advantageously has a water solubility at 25° C. greater than 2 g/100 ml, preferably greater than 10 g/100 ml, more preferably greater than 20 g/100 ml, and most preferably is comprised from 25 g to 70 g/100 ml, and in particular may be from 50 g to 70 g/100 ml. The said reaction product can also be a mixture of MAPPs with different values for n in the APP of formula I which is/are reacted with the reagent and/or with different water solubility at 25° C.
The APP used for the preparation of the MAPP is advantageously a compound of formula 1, with n being less than 20, preferably less than 10, such as comprised between 2 and 7. The APP can also be a mix of compounds of formula 1, in this case “n” is the weight average of the different n values for the different compounds of formula 1. The APP is most preferably substantially free of any compounds of formula I with n greater than 10. Preferably, the APP mixes comprise less than 25% by weight of compound of formula I with n equal to 1.
Preferably, prior to bonding the wood containing elements, such as wood fibers and/or wood particles together by use of an organic resin binder system, such as a thermosetting organic resin, the wood containing elements are treated with an aqueous composition comprising the reaction product MAPP, especially with an aqueous solution comprising modified ammonium polyphosphate, mentioned hereafter as MAPP, and then dried so as to reduce the water content to less than 5% by weight, advantageously to less than 3% by weight.
The method of the invention is suitable for the wood panels in which wood particles or fibers are agglomerated with formaldehyde based binders which remain a good compromise of cost, performance and ease of use for such applications. These binders are thermosetting resins obtained by polycondensation of formaldehyde, urea and/or melamine.
The present invention thus also provides a method for producing panels comprising wood particles/fibers and a formaldehyde resin, having increased fire resistance (increased fire retardant properties), and having also a reduced emission or release of formaldehyde after the thermosetting step.
In the present application, “wood containing elements” or “wood containing particles and fibers” or “wood particles and/or fibers” mean in the present specification particles and fibers produced or prepared from wood and/or wood residues, cellulose containing particles and fibers, and particles from paper, cardboard, and the like. The wood containing particles and fibers can be mixed with other particles and fibers, such as with glass fibers, glass beads, hollow glass beads, etc.
By “wood-based panels” it is herein meant to include particle board panels, MDF (medium density fiber board panels) and plywood, it being understood that such wood-based panels can possibly contain particles and fibers which are not wood containing particles and fibers.
The method of the invention has advantageously one or more of the following characteristics, and more advantageously a combination of more of two of the following characteristics:
Likewise, the method may include a method for treating at least the outer surface, as well as the inner surface of wood containing elements, advantageously at least partly the outer surface and the inner surface, with the composition. This included method comprises the following steps for treating the wood containing elements with the said aqueous composition comprising the reaction product:
The invention also relates to a flame retardant product comprising at least:
Advantageously, the hardened organic resin binder system is a thermoset hardened formaldehyde based resin system, while the quantity of reaction product associated to the wood containing elements is sufficient for reducing the formaldehyde emission by at least 50% with respect to the same product except that it does not contain said reaction product within one month after the thermosetting of the formaldehyde based resin system.
The product of the invention can have one or more of the characteristics disclosed for the method of the invention.
The wood containing elements, such as particles and/or fibers, are advantageously wood containing elements adapted for the manufacture of particle boards, medium density fibreboards and plywood boards (PB, MDF, PW). The flame retardant formaldehyde laden products are then advantageously selected from the group consisting of particle boards, medium density fiber boards and plywood (PB, MDF, PW).
Various aqueous compositions have been prepared by mixing in water different ammonium polyphosphate with, melamine, possibly urea, possibly followed by partial or complete reaction between ammonium polyphosphate with melamine and/or urea. The solution or suspension were prepared so as to have a solid content comprised between 50 and 75%, such as a solid content of about 60%.
The following ammonium polyphosphates [NH4PO3]n have been used as starting material:
APP1: [NH4PO3]n with n having as average value about 10 and a P2O5 weight content of about 60%, the weight average particle size being comprised between 5 μm and 20 μm
APP2: [NH4PO3]n with n having as average value about 20 and a P2O5 weight content of about 65%, the weight average particle size being comprised between 5 μm and 20 μm
APP3: [NH4PO3]n with n having as average value about 30 and a P2O5 weight content of about 69%, the weight average particle size being comprised between 5 μm and 20 μm
APP4: [NH4PO3]n with n having as average value about 5 and a P2O5 weight content of about 69%, the weight average particle size being comprised between 5 μm and 20 μm. The compound is substantially free of compounds [NH4PO3]n with n greater than or equal to 10.
APP5: [NH4PO3]n with n having as average value about 3 and a P2O5 weight content of about 69%, the weight average particle size being comprised between 5 μm and 20 μm. The compound is substantially free of compounds [NH4PO3]n with n greater than or equal to 8.
APP6: [NH4PO3]n with n having as average value about 4 and a P2O5 weight content of about 70%, the weight average particle size being comprised between 5 μm and 20 μm. The compound is substantially free of compounds [NH4 PO3]0 with n greater than or equal to 8.
APP7: [NH4PO3]n with n having as average value about 2.5 and a P2O5 weight content of about 70%, the weight average particle size being comprised between 5 μm and 20 μm. The compound is substantially free of compounds [NH4PO3]n with n equal to 1 and free of compounds [NH4 PO3]n with n greater than or equal to 5.
APP8: [NH4PO3]n with n having as average value about 3.5 and a P2O5 weight content of about 70%, the weight average particle size being comprised between 5 μm and 20 μm. The compound is substantially free of compounds [NH4PO3]n with n greater than or equal to 5.
urea: (NH2CONH2), with a weight average particle size comprised between 100 μm and 2000 μm.
MAPP(X): reaction product of APPX (with X being an integer between 1 and 8) with melamine, said reaction being carried out in an aqueous medium, at a sufficient temperature comprised between 20° C. and 200° C. (advantageously at a temperature comprised between 20° C. and 100° C.) and, if required or desired, under pressure, for a time required for having the partial or complete reaction of the APPX present.
MAPP(X)u: reaction product of APPX (with X being an integer between 1 and 8) with melamine and urea, said reaction being carried out in an aqueous medium, at a sufficient temperature comprised between 200° C. and 400° C. and under pressure, for a time required for having the partial or complete reaction of the APPX present.
The following table gives the composition of the several solutions or suspensions (“S”) which were prepared. In said table, M designates the weight ratio between APPX and melamine before any reaction between APPX and Urea, T represents the weight ratio urea/melamine when urea is used, and P designates the percentage of reaction product (MAPPX) present in the solution or suspension, expressed as weight percentage of APPX having reacted with melamine.
When mixtures of APPX's are used, the percentage of a compound APPX is the percentage by weight of said compound with respect to the total weight of the APPX's used for the preparation of the solution or suspension.
The solution or suspension can contain one or more additives, such as surfactant, phosphoric acid, boric acid, borax, etc.
For the production of the panels, the wood particles were treated with the solutions/suspensions of example 1. After being dipped and mixed, the particles were dried. The weight content MAPPX (product of the reaction of melamine with APPX) and/or MAPPXu (product of the reaction of melamine with APPX in presence of urea) in the wood particles was in a first set of tests 125 kg per ton wood particles, in a second set of tests 175 kg per ton wood particles and in a third set of tests 200 kg per ton wood particles.
In a further set of tests, the wood particles mixed into a solution or suspension containing APPX and melamine (possibly in presence of some urea) were submitted to a heat treatment for initiating a reaction for producing MAPPX, so as to have about all the APPX converted into MAPPX.
The particle board panels were prepared in a lab-scale hot press, the panel having the following characteristics:
The boards thus manufactured were tested on strength (Internal Bond test, according to EN319, expressed in MPa or N/mm2) and on formaldehyde content (perforator test according to EN 120 and expressed in mg of formaldehyde per 100 g of board), swelling (water resistance according to EN319), flexion test according to EN310, and flame resistance (according to Norm NFP 92-501 “Essai par rayonnement d'un épiradiateur” “Radiation test with epiradiator”). The flame resistance can be measured with an test apparatus adapted to submit the material to be tested to a constant source of radiant heat in a controlled chamber. A description of said apparatus is given in CCC2008—Challenges for Civil Construction Torres Marques et al, FEUP, Porto 2008—“Fire reaction behavior of flame retardant modified epoxy polymer mortars”—maria C. Ribeiro et al, www.dist.unina.it/proc/2008/CCC/links/T5/T5-22.pdf.
The various panel boards have been tested. The panel boards with the fire resistance additive conformed to the commercial requirement, namely a formaldehyde content in mg CH2O per 100 g of less than about 3 (such as less than 2 mg for panels using MAPPXu, i.e. a reduction of more than 50% with respect to the formaldehyde content of the boards free of MAPPX or MAPPXu); an high internal Bond Strength (more than 0.9 MPa, a low swelling (less than 7%, such as less than 5%), a high flexion modulus (higher than 28 MPa) and a flame retardant characteristic (norm M1, with an increase of more than 30% of the start of the flame time following the radiation with respect to the start of the flaming time for the panel boards free of MAPPX or MAPPXu).
| Number | Date | Country | Kind |
|---|---|---|---|
| 11 447 013.1 | Jun 2011 | EP | regional |
