FR3013354A1 - PROCESS FOR PROCESSING MELAMINE FOAM AND LAYER OF COMPOSITE MATERIAL OBTAINED USING THE SAME - Google Patents

Abstract

The invention relates to a process for transforming melamine foam into a layer of a more flexible and thermo-compressible material, while retaining the lightness, fire-resistance and acoustic properties of the starting foam, including mixing with the foam. dry state of flakes (2) of melamine foam with heat-binding elements mainly containing multicomponent heat-binding fibers (1), followed by a thermo-bonding of said mixture in the form of a sheet (4). The invention also relates to the layers of composite material (7) obtained by said method.

Description

The present invention relates to the field of foamed foam materials, and more particularly to a process for recycling these materials. Foam type foam materials of firm or rigid nature, such as open-celled melamine-formaldehyde resin foam, hereinafter referred to as "melamine resin foam" or "melamine foam", have long been used because of their lightness (low density of the order of 10 kg / m3), their acoustic and thermal properties, a certain firmness, characterized by a lift at 40% greater than about 6kPa according to EN ISO 3386-1, and their good fire resistance (non-flammability).

However, the "thermo-hardened" character of the melamine resin foam makes it a material that is difficult to recycle. A known method for recycling pieces of melamine foam (described in particular in patent EP 2000 488 B1) comprises the agglomeration of pieces of melamine resin foam by means of an organic adhesive-type binder. More particularly, said pieces of melamine foam introduced into a mold are impregnated with an isocyanate prepolymer, which after pressing makes it possible to obtain a piece of composite material having a density greater than the starting cellular material (between 15 and 100 kg / m3), and a firmness (called lift) according to EN ISO 3386-1 ranging from about 5 kPa to about 25kPa. The material thus loses its specificity of lightness, and a part of its acoustic properties due to the at least partial sealing of the surface porosity of the foam pieces by the isocyanate impregnating liquid. In addition, such a composite part can hardly be reworked with heat, since it can not be subsequently thermoformed or thermo-compressed.

In addition, the use of isocyanate monomers or oligomers subjects the operator to the risk of exposure to these molecules in the form of aerosol and / or vapor during application, in particular by spraying, as well as to the degradation. These polymers can also expose the end user to residual amounts of unreacted isocyanates in the finished composite products.

A first object of the invention is therefore to overcome the aforementioned drawbacks by proposing a melamine foam-based foam material recycling process which does not use isocyanate-type compounds.

There is also a real need to develop a recycling process of this lightweight cellular material melamine foam, which has a certain firmness, without increasing its density. Another object of the invention is therefore to provide a method for recycling or processing a lightweight foam-based melamine foam material into a heat-compressible material, while retaining its lightweight properties. Moreover, because of its flame retardancy properties and sound absorption properties melamine foam is frequently used in vehicles (trains, cars), aerodynamic systems, buildings.

Thus another object of the invention is to provide a process for converting a foam-based melamine foam material into a softer material, while retaining its acoustic and fire-resistance properties. Another object of the invention is to provide a method for the recycling of such a solid foam-based melamine foam material making it possible to obtain a flexible and light material in the form of a plate or a thin layer that can be stored or transported in rolls. To this end, the present invention relates to a process for converting a melamine foam-based cellular material into a layer of a more flexible and thermo-compressible material, while retaining its properties of lightness, fire resistance and acoustics, comprising the following successive steps: slicing step of pieces of cellular material mainly comprising melamine resin foam to obtain flakes of said cellular material, optional step of eliminating the finest pieces, in particular for removing dust, for example by suction, step of mixing in the dry state of said flakes with heat-binding elements containing structural fibers mainly comprising multi-component heat-binding fibers, preferably bi-component, said multi-component fibers being formed of a central core and a peripheral sheath whose softening temperature or fu sion is lower than that of the core, step of coating said mixture, - thermo-bonding step of the constituents of the mixture by application to said sheet of a treatment temperature which is on the one hand greater than the softening temperature or melting of the peripheral cladding of the multi-component (preferably two-component) heat-binding fibers and, secondly, less than the softening or melting temperature of the central core of said multi-component fibers (preferably two-component fibers). component), to obtain a layer of flexible composite material in which the foam flakes are entangled in a three-dimensional network of said structural fibers. Thus, unlike the method of EP 2 000 488 B1, the heat-binding element melamine foam pieces is not a liquid binder, but a solid binder, mainly comprising fibers, which do not fill or seal the pores on the surface of the pieces of foam, in view of their agglomeration. According to the invention, the mixture of the mouse pieces with the thermo-binder elements is dry. The optional step of removing the finest pieces is especially intended to eliminate dust, for example by suction, advantageously simultaneously with the slicing step. The transformation process according to the invention is advantageously a continuous process. According to a variant of the process, the heat-binding elements comprise, in addition to the heat-binding fibers, polymer particles having a softening or melting temperature lower than the degradation temperature of the melamine resin foam, the temperature of the a thermo-bonding step being greater than the softening or melting temperature of said particles. These heat-binding particles are preferably polymer particles chosen from epoxy, polyester, polypropylene or polyethylene polymers.

Advantageously, said thermo-binder particles have a particle size of between 50 .mu.m and 500 .mu.m, preferably between 100 .mu.m and 300 .mu.m. The multi-component heat-binding fibers, which represent the majority fraction by weight of the heat-binding elements mixed with melamine foam pieces, are preferably fibers comprising one or more polymers chosen from polyester, polyethylene or polypropylene polymers or a combination of these polymers. Advantageously, said heat-binding fibers have a length of between 10 mm and 50 mm, preferably between 20 mm and 30 mm, and preferably have a linear weight of between 1 decitex and 5 decitex, preferably between 2 decitex and 4 , 5 decitex. The slicing of the pieces of cellular material predominantly comprising melamine resin foam is made from melamine foam blocks or cut-off production or reuse pieces of melamine foam, for recycling. The flakes, obtained in the slicing stage, are advantageously of size between 4 mm and 25 mm, preferably between 6 mm and 12 mm, more preferably between 8 mm and 10 mm. Slicing (and not grinding) the pieces of melamine foam advantageously gives flakes of cellular material of generally polyhedral shape, which ensures better mixing with the fibers and limits the expansion, the flocks interlocking better in each other with these mastered forms. Advantageously, the mixture of said flakes based on melamine foam with the heat-binding elements comprises the following weight proportions: from 70% to 95%, preferably from 75% to 90%, of foam material predominantly formed of resin foam melamine and from 5% to 30%, preferably from 10% to 25%, in heat-binding elements which comprise at least 50% of multi-component fibers, preferably at least 70% of multi-component fibers, preferably at least 90% of multi-component fibers. Below a proportion of heat-binding elements of 5%, the thermo-bonding of all pieces of melamine foam is incomplete to ensure sufficient cohesion of the composite material, and beyond 30% the composite material loses its flexibility (and its lightness) due to too much presence of structural fibers. A preferred blend contains from 75% to 90% melamine foam and from 10% to 25% structural fibers essentially comprising multi-component fibers, such as bi-component fibers, preferably polyester fibers. The thermo-bonding step may be associated with or followed by a step of compressing the web.

The composite material obtained by means of the process described above is in the form of a layer of flexible and thermo-compressible composite material having at least one of the following properties: an equivalent density / of the same order of magnitude as the density of the foam starting material (without compression of the web or with a slight compression during the thermo-bonding step), an acoustic absorption coefficient between 1000 Hz and 6300 Hz, preferably between 1250 Hz and 6300 Hz, higher or equal to that of the starting foam material, for layers of the same thickness, fire resistance properties equivalent to those of the starting foam material, for layers of the same thickness. A preferred layer of flexible and heat-compressible composite material according to the invention is essentially formed of flakes of melamine resin foam and bi-component polyester structure fibers.

Thanks to the properties mentioned above, it can find an interesting use in the fields of thermal and / or acoustic insulation, for building, civil engineering, the construction of vehicles, machines or aerodynamic systems, the most often in the form of panels. The invention will be illustrated by the following examples, in no way limiting, with reference to the appended drawings in which: FIG. 1 schematizes the method according to the present invention; FIG. 2 is a sectional diagram of a layer of composite material obtained by the process according to the invention, the detail of which is shown in FIG. 2A is an enlarged diagram of the constituents of the composite material and the detail of FIG. 2B is an enlarged sectional view of a bi-component fiber; FIG. 3 is a graph showing the measurement results of the acoustic absorption coefficient of several samples of composite material according to the invention, compared with the starting material; FIG. 4 is a graph showing the measurement results of the acoustic absorption coefficient of several samples of composite material according to the invention, compared with other porous or fibrous materials; Figure 5 is a graph showing the measurement results of the acoustic absorption coefficient of several samples of composite material according to the invention coated with a polyurethane film, compared to other porous or fibrous materials.

EXAMPLES 1. Starting materials The starting cellular material of the process according to the invention is formed of falling cuttings or melamine foam block recovery, marketed by BASF under the name BASOTECTO G, which are in the form of pieces. of dimension of several centimeters. Structural fibers are known bi-component heat-binding fibers 1. As schematized in FIG. 2B, these bicomponent heat-binding fibers 1 consist here of two concentric parts, namely a central core 11 surrounded by a peripheral sheath. The central core 11 and the peripheral sheath 10 are both made of a polymeric material, for example a polyester. This core 11 and this peripheral sheath have melting, or softening, temperatures which differ from each other. "Softening temperature" or "softening point" means a temperature at which the material reaches a certain degree of softening under standardized conditions. By "melting temperature" or "melting point" is meant the temperature at which a material changes from solid to liquid. In a conventional manner, the core 11 is made of a material with a high softening point, that is to say higher than the softening point of the peripheral sheath. The sheath 10 thus provides the stickiness of these two-component heat-binding fibers, while the core of said fibers participates in the structuring of the three-dimensional network they will constitute. For example, the core 11 has a high temperature softening point of about 200 ° C; the peripheral sheath has a softening point of about 110 ° C.

Moreover, the length of these bicomponent heat-binding fibers 1 is advantageously between 10 mm and 50 mm, and their linear weight is advantageously between 1 and 5 decitex. 2. Process The pieces of melamine foam are introduced into a standard flocculation device, rotary grinder type that ensure a clean cut and not tearing of the material. The device comprises a grid for obtaining a fluffed foam containing flakes of dimensions of approximately between 6 mm and 12 mm. Fine particles and dust are removed as and when suction. The melamine foam flakes 2 obtained after slicing are optionally stored in a specific silo and then directed to a mixing station 3 to include a given proportion of bicomponent polyester 1 heat-binding fibers. In the example illustrating the present invention, the weight proportions flakes of melamine foam / heat-binding fibers are about 80/20. The foam flakes 2 and the fibers 1 are intimately mixed, as homogeneously as possible. The flake + fiber mixture is then subjected to a lay-up operation on a conveyor 6 advancing at a speed of approximately 5 m / min according to an Airlay type process. The layers of coated mixture 4 having a thickness of approximately 30 mm then undergo a heat treatment operation by heating, aiming to raise the core temperature of the mixture to a value sufficient to obtain softening (or melting) and the welding of the two-component heat-binding fibers 1 with each other and with the surrounding materials (fibers, flakes) which touch them. In practice, this treatment temperature is, on the one hand, greater than the melting or softening temperature of the peripheral sheath of the bicomponent heat-binding fibers, and on the other hand, lower than the melting temperature or softening of the central core of said bicomponent heat-binding fibers The treatment temperature is such that a weld occurs at each zone of contact with the peripheral sheath of the two-component heat-binding fibers, this being all the more first to a softening and melting of said sheaths, then to a hardening during cooling.

These multiple bonds form, in the resulting composite product layer, a three-dimensional network that retains and traps including foam flakes. This heating phase is effected, for example, in a heat-bonding furnace 5 using hot air produced from a gas-burner type heat source. For example, the heating temperature applied to the mixture is between 130 and 170 ° C. Simultaneously in advance of the conveyor 6 in the oven 5 and the heat treatment, compression of the material can be performed. On leaving the oven, and cooling, the layer of agglomerated product 7 is cut to the desired width and length, and is packable in the form of rolls or plates. The result obtained is a light material with a density ranging from 8 kg / m3 to 35 kg / m3 with good flexibility (see below). 3. Tests and Comparisons The tests carried out on the various layers of agglomerated melamine foam (Examples 1 to 5), according to the method of the invention described above, in comparison with various other materials including the melamine foam Basotect® G The samples tested are as follows: Example 1: Density 11.4 kg / m3 - Thickness 30 mm for acoustic tests Thickness 53 mm for the lift test Example 2: Density 12 kg / m3 thickness 30 mm Example 3: density 14 kg / m3-thickness 30 mm Example 4: density 20 kg / m3-thickness 35 mm Example 5: density 23 kg / m3-thickness 32 mm Comparative example 6: melamine foam Basotect® G: density 10.1 kg / m3 - thickness 30 mm for acoustic tests thickness 50 mm for the lift test The tests carried out firstly show that it is possible to produce an agglomerate product of melamine foam presenta a density (11.4 to 14 kg / m 3) which can be equivalent to the starting material (10.1 kg / m 3): see table 1 below for example 1. The material obtained without compression, or with a moderate compression during the thermo-bonding step therefore has lightness properties equivalent to those of the starting material. Density and lift The lift of a foam can be likened to the measurement of the hardness of the foam. The higher the lift, the more the foam is "hard". The measurement corresponds to defining the weight necessary to compress the foam by 25%, 40% and 70% of its initial thickness (the more a foam is hard the more it will take a significant weight to crush it by a given percentage). The lift was measured according to standard NF EN ISO 3386-1. The comparison between the agglomerated material according to the invention (Example 1) and the starting BASOTECTO G melamine foam is presented in Table 1 below. Characteristic Unit Ex. Comp. 6 Example 1 Net density kg / m3 10.1 11.4 Bearing at 25% kPa 4.7 0.7 Bearing at 40% kPa 7.4 1.7 Bearing at 70% kPa 19.5 7 Table 1 The comparison values of the lift of the two products shows that the BASOTECTO agglomerate according to the invention is much more flexible than the BASOTECTO G starting, while the two products have a comparable density. Fire resistance The 11 kg / m3 agglomerated material, 35 mm thick (example 1), obtained a fire classification M1 according to the standard NFP 92-501: 1995, as is the BASOTECT® G starting. This is the most difficult test to meet for the Ml classification, and it was not easy to obtain such a good performance after having also fundamentally transformed the structure of the starting melamine foam and having it introduced fibers of different chemical nature. This result therefore confirms the non-flammability of the composite material obtained by the process according to the present invention. Acoustical properties The results presented in FIGS. 3 to 5 relate to measurements of the sound absorption of different materials using an impedance tube, according to the PSA D45 5430 standard. The spectra in third octave of absorption of these figures represent the absorption in% as a function of the central bands of one-third octave: the higher the percentage of absorption, the higher the product is performing. Comparisons made on layers of materials of identical thickness (30 mm) show that the agglomerated products according to the present invention (ex.2 and ex.3) have an absorption coefficient equivalent (to within a few percent) to that of the starting material (eg comp 6). For somewhat higher thicknesses (32 mm for Example 5, and 35 mm for Example 4) the acoustic results are even better, the absorption of a material being a function of its thickness, the absorption coefficient exceeding 90% between 1600 Hz and 6300 Hz for the latter material (Example 4).

Comparison with other porous or fibrous materials The composite material agglomerated according to the process of the invention (see dotted curves in FIG. 4) has much better absorption performance than a composite material of polyurethane foam (PU) with two-component polyester thermobonding fibers made according to the same process in the same thickness of 30 mm (see in Figure 4 the curve "PU 27 kg / m3"). With regard to other fibrous or porous products conventionally used for the acoustic absorption treatment (see in FIG. 4 the curve PU 28: PU foam 28 kg / m3 - thickness 30 mm, and the curve PU 30: PU foam 30 kg / m3- thickness 30 mm, and the felt curves (cotton felt 1600g / m2 - thickness 25 mm or 64 kg / m3), and wadding (polyester wadding 1600g / m2 thickness 37 mm or 43 kg / m3), it has good performance at low frequencies, and we note a good behavior on the frequency band from 2000 to 6300 Hz which is interesting to treat in particular the human voice (800 Hz - 4000 Hz) in the premises receiving the public or the staff.

Polyurethane film-coated materials Polyurethane film is very often used in coating (applied by heat-sealing) on fibrous and porous materials to ensure a seal (important in machines or vehicles) and to modify and adapt sound absorption of the product. Although the material according to the invention (Examples 2 (12 kg / m3) and Example 5 (23 kg / m3) coated with a polyurethane film has good absorption performance at low frequencies (due in particular to the effect in these frequencies), it is especially above 1000 Hz and up to 6300 Hz that it makes the difference with the other materials tested, and is better than the other products in the two densities tested (see Figure 5). Thermo-Compression Test The composite material agglomerated according to the process of the invention is thermocompromable (thermocompression is a process which makes it possible to shape products based on thermoplastics, by first heating them in order to soften the material, then place them in a cold mold that will freeze the material to its shape.) The resulting part, at a furnace temperature of about 185 ° C, a heating time of 500 s and a press time of 120 s, does not have a great rigidity for an initial fiber content of 20% by weight but retained the shape of the mold. If necessary the rigidity of the final piece can be increased by increasing the percentage of bi-component fibers in the initial mixture. In view of the above properties and performance, including flexibility, low density, good weight / acoustic performance / fire performance, fire resistance, thermocompression ability, the composite material obtained according to the method of the present invention finds interesting uses in the following areas: Acoustic absorption in the building including for public buildings; Acoustic absorption in vehicles or machines and especially those requiring a good fire classification (railway example requiring a classification of type M1). Comfort products requiring a good fire rating.

Moreover this material, as demonstrated, is easily obtained from recycled melamine foam, and is then able to be recycled itself.

Claims (14)

REVENDICATIONS1. Process for converting a melamine foam-based cellular material into a layer of a more flexible and thermo-compressible material, while retaining its properties of lightness, fire resistance and acoustics, comprising the following successive steps: - step slicing pieces of cellular material mainly comprising melamine resin foam to obtain flakes (2) of said cellular material, - optional step of removing the finest pieces, dry mixing step of said flakes (2 ) with thermolating elements comprising structural fibers mainly comprising multi-component, preferably bi-component, heat-binding fibers (1), said multi-component fibers being formed of a central core (11) and a sheath (10) device whose softening or melting temperature is lower than that of the core (11), topping step of said mixture, step of th ermo-bonding the constituents of the mixture by applying to said web (4) a treatment temperature which is on the one hand greater than the softening or melting temperature of the peripheral sheath of the multi-component heat-binding fibers and on the other hand, lower than the softening or melting temperature of the central core of said multi-component fibers, to obtain a layer of flexible composite material (7) in which the foam flakes (2) are entangled in a three-dimensional network of said structural fibers. 2. Method according to claim 1, characterized in that the heat-binding elements comprise, in addition to the heat-binding fibers, polymer particles having a softening or melting temperature lower than the degradation temperature of the melamine resin foam. the temperature of the thermobonding step being greater than the softening or melting temperature of said particles. 3. Method according to one of claims 1 or 2, characterized in that the multi-component heat-binding fibers (1) are fibers comprising one or morepolymers chosen from polyester, polyethylene or polypropylene polymers or a combination of these polymers . 4. Method according to any one of the preceding claims, characterized in that the heat-binding fibers (1) have a length of between 10 mm and 50 mm, preferably between 20 mm and 30 mm, and preferably have a weight linear between 1 decitex and 5 decitex, preferably between 2 decitex and 4.5 decitex. 5. Method according to any one of the preceding claims, characterized in that the heat-binding particles are polymer particles selected from epoxy polymers, polyester, polypropylene or polyethylene. 6. Process according to any one of the preceding claims, characterized in that the heat-binding particles have a particle size of between 50 μm and 500 μm, preferably between 100 μm and 300 μm. 7. Method according to any one of the preceding claims, characterized in that the flakes (2) are of size between 4 mm and 25 mm, preferably between 6 mm and 12 mm, more preferably between 8 mm and 10 mm . 8. Process according to any one of the preceding claims, characterized in that the mixture of said flakes based on melamine foam with the heat-binding elements comprises the following weight proportions: from 70% to 95%, preferably from 75% to 90%, of cellular material predominantly formed of melamine resin foam and from 5% to 30%, preferably from 10% to 25%, of heat-binding elements which comprise at least 50% of multi-component fibers, preferably at least 50% by weight. less than 70% of multi-component fibers, more preferably at least 90% of multi-component fibers. 9. Process according to any one of the preceding claims, characterized in that the flakes of cellular material are of generally polyhedral shape. 10. Method according to any one of the preceding claims, characterized in that the thermo-bonding step is associated with or followed by a compression step of the web. 11. Layer of flexible and thermo-compressible composite material (7) obtained by means of a method according to any one of the preceding claims, having an equivalent density / of the same order of magnitude as the density of the starting foam material. . 12. Layer of flexible and thermo-compressible composite material (7) obtained by means of a method according to any one of claims 1 to 10 having an acoustic absorption coefficient between 1000 Hz and 6300 Hz, preferably between 1250 Hz and 6300 Hz, greater than or equal to that of the starting foam material, for layers of the same thickness. 13. Layer of flexible composite material (7) and thermo-compressible obtained by means of a method according to any one of claims 1 to 10 having fire resistance properties equivalent to those of the starting foam material, for layers of the same thickness. 14. Layer of flexible and thermo-compressible composite material according to any one of claims 11 to 13, characterized in that it is essentially formed of flakes of melamine resin foam and fibers of polyester structure bicomponent.