TECHNICAL FIELD OF THE INVENTION

The present invention relates to a flexible, flame-retardant material of multilayered structure formed of at least one fabric layer and of at least one Polyvinyl butyral (PVB) coating layer, and its manufacturing method. In particular, the present invention relates to the field of flexible construction materials (such as facade elements) insofar as they can, for example, be used to form a digital printing media, typically for outdoor and indoor advertising, and/or a solar protection material. The digital printing medium can for example be a facade element, a temporary shelter, a billboard, a building wrap, a wallcovering, a display or a suspended ceiling.

PRIOR ART

Digital printing is a method of printing from a digital-based image directly to a variety of media. Digital printing allows for on-demand printing, short turnaround time, and even a modification of the image (variable data) used for each impression. The savings in labor and the ever-increasing capability of digital presses leads to the fact that digital printing has many advantages over traditional methods.

Digital printing is often used in advertising, usually for indoor and outdoor banners and event signage, in trade shows, and in the retail sector at point of sale or point of purchase. It is also used in architecture where the media is a flexible composite material, which conforms to a variety of surfaces. It enables interior and exterior spaces (such as facades) to be transformed, and optionally functions as solar protection. These materials are to fulfil the requirements of more and more strict environmental standards.

Traditionally, these flexible materials comprise coatings made of polyvinyl chloride (PVC). However, nowadays the industry tends to avoid using PVC mainly because of its high chlorine content. There is a need of coatings made of eco-friendly polymers for the environment and for the health of the persons in contact with them.

Polyurethane (PU) and acrylic polymers have been envisaged, but they appear too costly for the majority of applications or do not meet all the performance criteria needed for their respective end use. Therefore, when looking for a composition for coating a flexible material, it is particularly difficult to combine eco-friendly requirements and to respond to technical requirements such as flexibility, flame retardancy, weldability, good printability, good adhesion and abrasion resistance for mechanical performances, as well as cost efficiency. The invention intends therefore to propose a flexible, flame-retardant composite material generally of multilayered structure free of PVC, which renders it capable of being used in applications such as digital printing media, solar protection media or replace traditional PVC- or PU-coated fabrics in automotive applications, while being able to comprise eco-friendly polymers for the environment and for the health of the persons in contact with them

DISCLOSURE OF THE INVENTION

The present invention proposes solving the technical problems described above in relation with the prior art by means of a flexible, flame-retardant composite material comprising: a fabric layer; and at least one impregnated or coated Polyvinyl Butyral (PVB) coating layer, which is integral with said fabric layer; the PVB coating layer containing 20 to 60% by weight of PVB, at least one plasticizer in an amount of 5 to 40%, preferably 5 to 25%, by weight of the coating layer, and at least one flame retardant in a total amount of 5 to 75%, preferably 20 to 65%, by weight with respect to the coating layer.

The amount of the constituents of the coating layer is 100% in total. The constituents are, as will be explained below, the components described above as well as, optionally, other compounds such as other flame retardant(s), UV stabilizer...

According to a preferred embodiment, the flame retardant is a mixture of antimony trioxide Sb20s and at least one halogenated organic compound as flame retardant in a total amount of 5 to 45%, preferably 10 to 40%, by weight with respect to the coating layer, and in a ratio of 0.1 to 5, preferably 0.2 to 3, e.g. 0.33, part of antimony trioxide Sb2C>3 per part of halogenated organic compound.

Thus, the fabric layer is coated or impregnated with a PVB coating layer on at least one side. Typically, the fabric layer is coated on only one side or on its two sides. In the last case, the PVB coating layers on both sides of the fabric layer can be similar or different (different composition and/or color and/or thickness. . .). In a preferred embodiment, the flexible, flame-retardant composite material consists essentially of, preferably consists of the fabric layer and one PVB coating layer.

In a preferred embodiment, the flexible, flame-retardant composite material consists essentially of, preferably consists of the fabric layer and two PVB coating layers (similar or different).

The amount of plasticizer refers to the total amount of plasticizers.

The invention also relates to a manufacturing method for forming the flexible, flame retardant composite material according to the invention, wherein said method comprises:

- Providing a fabric layer;

- Providing at least one water-based dispersion of PVB containing the PVB, the plasticizer, at least one crosslinker, and at least one flame retardant, which is preferably a mixture of antimony trioxide and halogenated organic compound;

- Impregnating or coating at least one side of the fabric layer with the water-based dispersion of PVB;

- Curing the thus impregnated or coated fabric layer at a temperature of 100 to 200°C, preferably 100 to 180°C, more preferably 120 to 180°C, even more preferably of 140 to 180°C.

The manufacturing method is surprisingly efficient since, as it is known to the skilled person, providing a coating is much more difficult technically using a water-based product than using an organic solvent-based product.

In the curing step, the crosslinker reacts and is no more present in the PVB coating layer once the reaction is complete.

DETAILED DESCRIPTION OF THE INVENTION

A first object of the invention is the flexible, flame-retardant composite material, which comprises at least one impregnated or coated PVB coating layer. This layer is generally a not a laminated product, which is a different composite material as can be seen easily on the composition material. Actually, laminates having a polymer layer on the outside usually have a plastic or oil-like look and touch. The laminated product is made from the lamination of a solid product composition like a film or foil applied onto the fabric layer or onto an intermediate layer. According to the invention, the manufacturing method is different. The impregnation or coating of the coating layer is made from a liquid composition applied onto the fabric layer or onto an intermediate layer on which thermal treatment for drying and curing is carried out. Advantageously, the impregnation or coating manufacturing method according to the invention is more cost-efficient than lamination and the mechanical resistance of a coating layer manufactured by impregnation or coating is more efficient than the one of a coating layer manufactured by lamination.

According to a preferred embodiment, the composite material has been manufactured by a manufacturing method comprising:

- Providing a fabric layer,

- Providing at least one water-based dispersion of PVB containing the PVB, the plasticizer, at least one crosslinker, and at least one flame retardant, which is preferably a mixture of antimony trioxide and halogenated organic compound;

- Impregnating or coating at least one side of the fabric layer with the water-based dispersion of PVB;

- Curing the thus impregnated or coated fabric at a temperature of 100 to 200°C, preferably 100 to 180°C, more preferably 120 to 180°C, even more preferably of 140 to 180°C.

The fact that the method is as a water-based method can be determined on the thus- obtained composite material. Actually, one could measure the remaining amount of typical dispersing aids/surfactants used in a manufacturing process of water-based dispersions as known to the skilled person. These compounds are still present in the coating film after the curing step, at least to a certain degree. This is different from oilbased methods where the PVB is dissolved.

Polyvinyl butyral (or PVB) is a resin mostly used for applications that require strong binding, optical clarity, adhesion to many surfaces, toughness and flexibility. The major application of PVB is laminated safety glass for automobile windshields in which a protective foil made of polyvinyl butyral acting is bonded between two panels of glass. This results in a large amount of PVB foils to be recycled worldwide. However, this recycling is not an easy task since the waste material to be recycled comprises a plasticizer (roughly one fourth to one third of a plasticizer which is typically TEG-EH (Triethylene Glycol Bis (2-Ethyl Hexanoate) of CAS number 94-28-0 in the case of automotive applications) as well as traces of impurities such as glass, silicone and/or rubber, depending on its grade.

According to the invention, “A and/or B ” means A, or B, or A and B. The use of PVB coatings in the art is always limited to the use of solvent-based system or foils obtained by lamination, which is costly, complicated, and not environmental- friendly.

Advantageously, the flexible, flame-retardant composite material of the invention comprises an eco-friendly PVB coating layer which is a water-based coating obtained by an impregnation or coating manufacturing method.

According to the invention, “multilayer ” means at least two layers according to the invention. At least one intermediate layer (i.e. present between the PVB coating layer and the fabric layer), preferably a polymer-based intermediate layer, can be present. The layer in contact with the outside is preferably the PVB coating layer, but at least one top-coat layer can be optionally present between the PVB coating layer and the outdoor atmosphere. In any case, the layers are adapted to the need in terms of adhesion strength and flame retardancy, in as much as the layers of the composite material are mechanically and/or chemically joined.

According to the invention, the top-coat layer if present is for example a clear coat for improving the UV resistance and/or the abrasion resistance. This top-coat layer is typically necessary in applications like artificial leather (e.g. for car interior or furniture) or in applications where PVB would replace a PVC coated fabric in a mechanically challenging application where it sees more wear and tear (e.g. for truck tarpaulins or tents). This top-coat layer is typically made of another coating layer which can be a clear coat. This could also be a PVB or acrylic or polyurethane coating layer or a coating comprised by a mix of multiple of these polymers on top of the PVB coating layer of the composite materi al according to the invention.

According to the invention, “integral with said fabric layer” means that the layers are mechanically and/or chemically joined. This is for example the case when there is no intermediate layer between the fabric layer and the PVB coating layer. But this is also the case when there is a primer or another intermediate layer between the fabric layer and the PVB coating layer, in as much as the primer or PVB coating layer is mechanically and/or chemically joined to both the fabric layer and the PVB coating layer. Accordingly, any such intermediate layer can be present in the composite material.

In the preferred case where the flame retardant is a mixture of antimony trioxide and halogenated organic compound, the weight ratio PVB on antimony trioxide is generally from 2: 1 to 10: 1, preferably from 3: 1 to 7: 1. In the preferred case where the flame retardant is a mixture of antimony trioxide and halogenated organic compound, the weight ratio PVB on (antimony trioxide + halogenated organic compound) is generally from 0.1 : 1 to 4: 1, preferably from 0.5: 1 to 2: 1.

PVB is a polymer of formula (CSHMOI or wherein n is an integer generally of more than 20. It is usually prepared from polyvinyl alcohol by reaction with butyraldehyde. Its CAS number is 915977-69-4.

The PVB originates from original PVB or from recycled PVB.

Preferably, the PVB originates from recycled PVB waste, such as the commercial products Shark Dispersion (from various grades e.g. SX1, XS, FX2, WX2...).. This corresponds advantageously to an eco-responsible approach. The impurities which can be present in the recycled PVB waste are less than 1% by weight. This ability to recycle the waste stream as such is a surprising advantage of the invention, since it is often very difficult to integrate and/or to adapt waste stream from the recycling of goods into the current production cycle of products.

The PVB can also originates from original PVB (which means originating from recycling) such as the commercial products Aquarez PVB (from various grades, e.g. 501, 605, DPS48-36. . .) o.

Antimony trioxide or antimony oxide (III) (IUPAC name) (or antimonious oxide or antimony sesquioxide) of formula Sb20s is an inorganic compound. Its CAS number is 1309-64-4.

In the preferred case where the flame retardant is a mixture of antimony trioxide and halogenated organic compound, the halogenated organic compound is preferably a polyhalogenated organic compound (such as decabromodiphenyl ether or 1,1'- oxybis(2,3,4,5,6-pentabromobenzene) of CAS number 1163-19-5). This compound is mixed with antimony as antimony trioxide. The halogen is chosen from chlorine, bromine, fluorine, iodine, and their mixtures, preferably the halogen is bromine. The fabric according to the invention is a textile material of any type, such as woven materials, knitted materials, warp-knitted materials, non-woven materials, and their mixtures. In a preferred embodiment, the fabric is a rollable fabric. Preferably the fabric is a sheet stocked as a roll, that is to say a structure of low thickness with respect to the other two dimensions of the material. As an example, the thickness can be limited to about. 0.1 to 5 mm, for rolls of about 1 m to 6 m width and a weight from about 30 g/m ² to about 800 m ² . The rolls are assembled when constructing the facade elements typically by welding them along their lengths in particular by High Frequency (HF) welding.

In any case, the fabric can be a mesh fabric or a plain fabric, depending mainly on its final use. The mesh fabric is particularly suitable for a use in outer advertising, for example as building wrap of reduced load.

According to an embodiment, the fabric is a textile-based substrate comprising fibers chosen from the group consisting of polyester, polyamide, polyacrylic, polyethylene, polypropylene, glass, wool, cotton, rayon, linen, bamboo, carbon, steel, copper, and aramide fibers and their mixtures. For example, the polyester can be polyetherterephthalate.

According to the invention, the term “fiber” includes both staple fibers and filaments.

According to one embodiment, the fabric originates from recycled grades (such as recycled polyester from bottle chips) or from renewable resources (such as bamboo, cotton...).

According to the invention, the PVB coating layer comprises at least one flame retardant. Preferably it comprises at least two flame retardants, as a mixture. The mixture is carried out before the manufacturing method or during the manufacturing method, in which case the two flame retardants are not necessarily directly mixed together.

The flame retard materials are generally chosen as known to the skilled person. However, some combinations are particularly advantageous and are part of the invention as preferred embodiments.

According to a less preferred embodiment, the PVB coating layer comprises at least one organic flame retardant.

In one embodiment, the organic flame retardant is a phosphate-based compound usually used as a plasticizer. More generally, the organic flame retardant is generally chosen from the group consisting of ammonium polyphosphate, bisphenol-a-bis(diphenyl phosphate), phosphate plasticizers, isopropyl phenyl phosphate, melamine cyanurate, expandable graphite, melamine polyphosphate, melamine phosphate, 9,10-dihydro-9-oxa-10- phosphaphenanthrenlO-oxide, resorcinol-bis(diphenyl phosphate), red phosphorous; and their mixtures. The organic flame retardant is preferably chosen from the group consisting of ammonium polyphosphate, bisphenol-a-bis(diphenyl phosphate), isopropyl phenyl phosphate, melamine cyanurate, expandable graphite, melamine polyphosphate, melamine phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrenl0-oxide, resorcinol- bis(diphenyl phosphate), red phosphorous, and their mixtures. Two organic flame retardants particularly preferred are ammonium polyphosphate (or APP, CAS number 68333-79-9) (coated or not, preferably coated) and melamine cyanurate (or MCU, CAS number 37640-57-6 or 16133-31-6), used alone or in combination. A combination of these two ingredients corresponds to an embodiment particularly preferred according to the invention. In other words, the organic flame retardant is preferably a mixture of melamine cyanurate (MCU) and ammonium polyphosphate (APP), more preferably a mixture of melamine cyanurate (MCU) and coated ammonium polyphosphate (APP)..

When present, the amount of organic flame retardant is of 0 (excluded) to 20%, preferably 1 to 8%, by weight with respect to the coating layer.

Preferably, the organic flame retardant comprises at least one nitrogen-base flame retardant and at least one phosphorous-based flame retardant. In this case, the total range of these organic flame retardants is from 20 % to 45% by weight of the PVB coating layer.

According to a preferred embodiment, the PVB coating layer further comprises at least one mineral flame retardant, the mineral flame retardant being present in an amount of 0 to 40%, preferably 20 to 40%, more preferably 2 to 35%, by weight with respect to the coating layer. The flame retardant is preferably chosen from aluminum trihydrate, magnesium hydroxide, zinc borate, sodium borate, sodium metaborate, borax, huntite, hydromagnesite, and their mixtures, more preferably aluminum trihydrate, magnesium hydroxide, zinc borate and their mixtures, even more preferably, the mineral flame retardant is aluminum trihydrate.

The CAS number of aluminum trihydrate (or ATH) (or hydrated alumina or aluminum (III) hydroxide or aluminum trihydroxide) is 21645-51-2.

The CAS number of magnesium hydroxide (or magnesium hydroxide or milk of magnesia) is 1309-42-8.

The CAS number of zinc borate differs according to the zinc/boron ratio and the water content. The usual zinc borate has CAS number 12767-90-7. All the variants of zinc borate are also encompassed according to the invention. In the case of the presence of both an organic flame retardant and a mineral flame retardant, the total amount of organic and mineral flame retardants is from 50 to 70%, by weight of the PVB coating layer.

According to a preferred embodiment, the organic flame retardant does not comprise any halogenated compound, since this compound is not allowed in Europe.

According to a preferred embodiment, the flame retardant is a combination of organic flame retardants, e.g. 2 or 3 of them, and one mineral flame retardant. The organic flame retardants are preferably phosphate plasticizer, melamine cyanurate (MCU), and coated ammonium polyphosphate (APP), or melamine cyanurate (MCU), and coated ammonium polyphosphate (APP). The mineral flame retardant is preferably ATH. The 3 or 4 of them are preferably combined together.

Thus, a preferred flame retardant is constituted by, preferably consists in, phosphate plasticizer, melamine cyanurate and ammonium polyphosphate, more preferably phosphate plasticizer, melamine cyanurate and coated ammonium polyphosphate. Another preferred flame retardant is constituted by, preferably consists in, melamine cyanurate and ammonium polyphosphate, more preferably melamine cyanurate and coated ammonium polyphosphate. Another preferred flame retardant is constituted by, preferably consists in, phosphate plasticizer, melamine cyanurate, ammonium polyphosphate and aluminum trioxide, more preferably phosphate plasticizer, melamine cyanurate, coated ammonium polyphosphate and aluminum trioxide. Another preferred flame retardant is constituted by, preferably consists in, melamine cyanurate, ammonium polyphosphate and aluminum trioxide, more preferably melamine cyanurate, coated ammonium polyphosphate and aluminum trioxide.

Phosphate plasticizer can be the compound Addiflam® SR 10 commercialized by STF 2000. APP can be the compound Aflammit® TLP 1630 commercialized by Thor, or Addiflam® Pov APP Eco commercialized by STF 2000. MCU can be the product Addiflam® pow PCU Eco commercialized by STF 2000.

According to this embodiment, when manufacturing the composite material, the compositions comprised generally 100 parts of aqueous PVB dispersion and as flame retardants, as part on top of 100 parts of this resin dispersion 5 to 15, preferably 10 to 15, parts of phosphate plasticizer, 5 to 20 parts, preferably 10 to 15, of melamine cyanurate (MCU), 20 to 40, preferably 30 to 40, parts coated ammonium polyphosphate (APP) and 20 to 45 parts of ATH. The sum of phosphate plasticizer, MCU and coated APP varied between 35 and 75 parts per 100 parts of aqueous PVB dispersion. Any other combinations of organic flame retardants and mineral flame retardant can also be envisaged.

Preferably, as an example, the amount of phosphate plasticizer is 2.5 to 11.5%, the amount of MCU is 2.5 to 14.5%, the amount of coated APP is 10 to 18%, and the amount of ATH is 17.5 to 41.5%, all by weight with respect to the PVB coating layer.

The skilled person can easily adapt the amounts of all the compounds of the coating layer as long as it is within the scope of the invention, in particular of the amounts of the flame retardant(s), totaling 100% by weight of the coating layer.

As known to the skilled person, a plasticizer is a substance added to produce or promote plasticity and flexibility and/or to reduce brittleness. The measure is to be carried out in a relative way, as a comparison of a situation with or without this substance.

Any kind of plasticizer can be used as known to the skilled person.

According to a preferred embodiment, the plasticizer of the PVB coating layer is present in an amount of 5 to 25% by weight of the coating layer. The amount of plasticizer is a total amount, including the halogenated organic compound and any other organic compound acting as plasticizer.

The plasticizer can be present in the PVB as raw material, if the PVB originates from recycled PVB waste. In this case, preferably, the plasticizer originates from recycled PVB waste, and only from PVB waste: there is no further addition of plasticizer. In this case, more preferably, all the plasticizer(s) originate(s) from the recycled PVB. Actually, recycled PVB waste typically comprises around one third to one fourth of plasticizer.

Part of the plasticizer can be chosen from phosphate-based compounds such as triarylphosphates, or such as tris(2-ethylhexyl) phosphate, 2-ethylhexyl diphenyl phosphate, or triphenyl phosphate. These compounds can act as organic fire retardant. This phosphate-based compound plasticizer is preferably used as an additive in small amount of, e.g. from 0 (excluded) to 20 % by weight of the coating layer, not precluding the presence of other plasticizer(s) to comply with the requirements of the invention.

Some halogenated organic compounds can also be used as plasticizers such as chlorinated paraffins. This case does not constitute a preferred embodiment since these compounds are not allowed in Europe.

More generally, the plasticizer is preferably chosen from triethylene glycol (CAS number 112-27-6), triethylene glycol di(2-ethylhexoate) (also known as triethylene glycol bis (2- ethyl hexanoate or 2,2’ -ethylenedi oxy di ethyl bis(2-ethylhexanoate, CAS number 94-28- 0), alkyl phthalate (such as di -2-ethylhexyl phthalate, CAS number 117-81-7), dibutyl maleate (CAS 105-76-0), dibutyl adipate (CAS number 105-99-7), dibutyl sebacate (CAS number 109-43-3), tris(2-ethylhexyl) phosphate (CAS number 78-42-2), 2-ethylhexyl diphenyl phosphate (CAS 1241-94-7), triphenyl phosphate (CAS number 115-86-6), and their mixtures.

In the preferred case where the flame retardant is a mixture of antimony trioxide and halogenated organic compound, the weight ratio (PVB + plasticizer) on antimony trioxide is generally from 2: 1 to 10: 1, preferably from 3: 1 to 9: 1.

In the preferred case where the flame retardant is a mixture of antimony trioxide and halogenated organic compound, the weight ratio (PVB + plasticizer) on (antimony tri oxide + halogenated organic compound) is generally from 0.5: 1 to 5: 1, preferably from 0.8: 1 to 4: 1.

According to a particularly preferred embodiment, the PVB of the PVB coating layer is partially crosslinked, which means that it still has remaining thermoplastic properties.

Typically, this crosslinking has been obtained when a crosslinker, preferably chosen from blocked isocyanate water-compatible compounds, was present in the compositions before its manufacture e.g. by curing. Generally, the crosslinker is no more present in the PVB coating layer.

Generally, when the composite material is to be used outdoor, the PVB coating layer preferably further comprises at least one compound chosen from UV filters, UV absorbers, UV stabilizers and their mixtures. The UV filters can be chosen from liquid cyanoacrylates UV absorbers, 2-ethylhexyl 2-cyano-3,3-diphenylacrylates (such as one of the commercial products Uvinul 3039, UV-3039 and Omnistab UV 3039) and their mixtures. The UV absorbers can be chosen from benzotriazoles like the one of CAS number 3896-11-5 (such as one of the commercial products Comax UV-126, Riasorb UV-326, MPI UV-absorber 326 and Tinuvin 326). The UV stabilizers can be chosen from benzophenones like the one of CAS number 1843-05-6 (such as one of the commercial products Comax UV-181, Riasorb UV-531 and MPI UV-81 (531)).

The composite material is generally compatible with usual pigments and inks used in digital and screen printing, including water-based inks such as latex-inks or sublimations inks, solvent-based or mild-solvent based inks as well as UV-curable inks.

The flame retardancy is measured according to the standard DIN 4102-1 May 1998. The composite material of the invention must at least pass the level B2, preferable the level B 1. The flexibility is measured by the standard DIN EN ISO 32100. This standard describes the bally-flex test including a detailed description of the equipment to be used. For the examples, a Bally flexometer for 20000 cycles was used.

The adhesion is measured according to the standard DIN 53357.

The weldability is not measured according to a standard, as known to the skilled person, since the measurement depends on the machine which is used. The skilled person is capable to determine the conditions of use so that to know is the composite material can be considered weldable.

The abrasion resistance is measured by a Martindale test. This test and the equipment is described in standard DIN EN ISO 12947.

A second object of the invention is the manufacturing method of the flexible, flameretardant composite material of the invention.

The impregnation is usually carried out by coating the fabric with the water-based dispersion. The coating is usually carried out by deposit of a water-based dispersion on the fabric layer using for example knife coating or roller coating or padding technique. The liquid coating allows more flexibility of the manufacturing method. The liquid coating penetrates into the fabric and in between the filaments and fibers of the yams of the fabric.

This is different from a lamination process where two or more rolls are combined into one with the help of heat and pressure and/or additional adhesives in order to make integral a textile layer and a coating film.

The lamination process is generally such that a separate production step of solid films is needed; the film has to match the width of the textile; the laminated film sits more or less on the very top of the textile so the bond between the laminated film and the textile less intimate compared to a coated textile. This is why this lamination process is outside the scope of the invention.

As already explained, the use of a water-based dispersion helps also to use eco- responsible compounds. The water-based dispersion preferably does not comprise any halogen except from the one(s) in relation to the antimony trioxide in the preferred case where the flame retardant is a mixture of antimony trioxide and halogenated organic compound.

Preferably, the PVB originates from recycled PVB waste. The water-based dispersion comprises at least one crosslinker generally chosen from blocked isocyanates (such as one of the commercial products Imprafix 2794XP, Trixene BI2021 and Trixene BI201), isocyanates (such as one of the commercial products Desmodur DN and Easaqua XD 401), carbodiimides (such as one of the commercial products Desmodur XP 2802, Picassian XL-732, Picassian XL-702 and Picassian XL- 725), and their mixtures, preferably heat-activated crosslinkers such as blocked isocyanates and carbodiimides, more preferably blocked isocyanates. The amount of crosslinker in the water-based dispersion is preferably from more than 0% and up to 20%, preferably from 1 to 16%, more preferably from 4% to 14%, by weight based on the weight of the PVB polymer in the water-based dispersion. Within a given range, the skilled person is capable to adapt the crosslinking ratio according to the needs thereof. Typically, as known to the person skilled in the art, the amount of crosslinker also depends on the molecular structure of the PVB, more particularly the amount and distance between the hydroxyl groups -OH, which are the potential reaction points for the crosslinker.

According to a preferred embodiment, a drying step is carried out after the impregnation step and before the curing step. In practice, the curing step is generally carried out in an oven or the like, and the temperature rise in the oven to reach the curing temperature is carried out in the oven, which constitutes the drying step. The drying step is carried out as known to the skilled person, for example at 100°C in an oven. The curing step makes the crosslinker chemically react with the PVB layer, hence it is no longer present in the fully cured coating layer.

The invention and the benefits that flow from it will be clearer upon reading the following figures and examples, given to illustrate the invention and not to limit it in any way.

BRIEF DESCRIPTION OF THE FIGURES

The way of carrying out the invention as well as the advantages thereof will become apparent from the following description, made by way of non-limiting indication and with the aid of the accompanying drawings, in which:

Figure 1 is a perspective view of a flexible sheet constituting a first embodiment of the invention.

Figure 2 is a perspective view of a flexible sheet constituting a second embodiment of the invention. Figure 3 is a cross section of a first apparatus for the manufacture of a flexible sheet according to the invention.

Figure 4 is a cross section of a second apparatus for the manufacture of a flexible sheet according to the invention.

Figure 5 is a cross section of a third apparatus for the manufacture of a flexible sheet according to the invention.

DETAILED DESCRIPTION OF THE FIGURES

Identical numbers denote identical parts.

Figure 1 is a perspective view of a flexible sheet 1 constituting a first embodiment of the invention. The flexible sheet 1 comprises a fabric layer 11 coated on both sides by a PVB coating layer 10.

Figure 2 is a perspective view of a flexible sheet 2 constituting a second embodiment of the invention. The flexible sheet 2 comprises a fabric layer 11 coated on both sides by a PVB coating layer 10, the side to be in contact with the outdoor atmosphere being further coated by a top-coat layer 12. This top-coat layer 12 is a clear coat.

Figure 3 is a cross section of a first apparatus 3 for the manufacture of a flexible sheet 39 according to the invention. The apparatus 3 can typically be used for both mesh fabrics and plain fabrics, especially fabrics of large width. The arrows indicate the direction of circulation of the sheet. A fabric 29 is unwound from a roll 28, and further guided by rolls 33. The fabric is impregnated in a bath 30 of liquid PVB present in a container 31. Two scrapers 22 remove excess 32 of PVB which fall down in the bath. The coated fabric 36 is then guided, optionally passed next to a nozzle 20 which blows air by micro jets to clean the holes in the coated fabric 36 if necessary (for example in the case of a mesh fabric if the holes of the mesh fabric are of dimension less than 5 mm), to an oven 25 which allows the drying and crosslinking and thus leads to obtaining the flexible sheet 29. The flexible sheet 29 comprises no crosslinker once the heat-induced chemical reaction is complete.

Figure 4 is a cross section of a second apparatus 4 for the manufacture of a flexible sheet 40 according to the invention. The apparatus 4 can typically be used for mesh fabrics. The arrows indicate the direction of circulation of the sheet. The fabric 29 is unwound from the roll 28, further impregnated in the bath 30 of liquid PVB present in the container 31 and guided by the transfer roll 42 which transfers the coating onto the mesh fabric 29. The following rollers 34 transfers the liquid coating between both sides of the mesh fabric back and forth and ensure an equal, uniform coating of both sides and the inner surface of the mesh fabric. The coated fabric 37 is then guided optionally passed next to a nozzle 21 which blows air by micro jets to clean the holes in the coated fabric 37 if necessary (for example if the holes of the mesh fabric are of dimension less than 3 mm), to an oven 26 which allows the drying and crosslinking and thus leads to obtaining the flexible sheet 40.

Figure 5 is a cross section of a third apparatus 5 for the manufacture of a flexible sheet 41 according to the invention. The apparatus 5 can typically be used for plain fabrics. The arrow indicates the direction of circulation of the sheet. The fabric 29 is unwound from the roll 28, and the liquid PVB 30 is spread onto the fabric 29 using a doctor blade 24. During the knife coating step, the fabric 38 is stabilized by a support roll 35. Afterwards it enters an oven 27 which allows the drying and crosslinking and thus leads to obtaining the flexible sheet 41.

EXAMPLES

8 examples, among which 3 comparative examples and 5 examples according to the invention, were carried out.

First, the components of the compositions of the 8 different PVB coating layers are summarized in Tables 1 and la below, and the related ratios when needed in Table 2 below.

These 8 compositions were used in a manufacturing corresponding the one disclosed in Figure 3. The 6 first compositions used the same fabric layer which is made of woven PES spun yam and has a weight per area of about 125 g/m2. The 7 ^th composition used other fabric layer: 100% PET mesh fabric HOg/qm coated both side (the weight after coating was 250 g/qm). The 8 ^th composition used still another fabric: 100% PET fabric 200 g/qm, closed structure (the weight after coating was 450 g/qm).

The drying was carried out for 1 minute at 80 °C followed by a curing step for 2 minutes at 150°C.

The properties of the thus obtained composite materials were tested according to the standard, except weldability which was measured using a stationary high frequency (HF-) welding machine manufacturesd by Forsstrom, Sweden, model type Forsstrom XP 160. Pressure: 3,0 kg/cm ² Welding time: 6s. Welding current: 0,55 A. Cooling time: 8 seconds. The results are summarized in Table 3 below. Table 1 : composition (part on top of 100 parts of resin dispersion)

Where Comp means comparative and Inv means Invention Table la: composition (in % in the dried coating before curing)

Table 2: ratios (Sb as Sb ₂ C>3, Br as the brominated organic compound)

Where Comp means comparative, Inv means Invention and N/A means not applicable or not defined (not calculable)

Examples 1 to 6 relate to use of the same flame retardant component (brominated organic compound + antimony trioxide), according to a first embodiment of the invention.

It can be seen that examples 1 and 2 were carried out modifying only the content of crosslinker (blocked isocyanate, cells in bold), examples 3 and 4 were carried out modifying only the content of the flame retardant component (brominated organic compound + antimony trioxide, cells in bold), some ATH as mineral flame retardant being present, and examples 5 and 6 were carried out modifying only the content of the flame retardant component (brominated organic compound + antimony trioxide, cells in bold), no mineral flame retardant being present.

Examples 2, 4 and 6 (respectively “Inv 2”, “Inv 4” and “Inv 6”) correspond to cases according to the invention wherein all the ratios PVB on Sb, PVB on (Sb + Br), (PVB + plasticizer) on Sb and (PVB + plasticizer) on (Sb + Br) are inside the preferred ranges.

Comparative example 1 (“Comp 1”) correspond to a case where the composite material does not comprise any crosslinker during the manufacturing process; therefore, the PVB is not partially crosslinked.

Comparative example 3 (“Comp 3”) correspond to a case where the composite material does not comprise any flame retardant component comprising Br/Sb2O3.

Comparative example 5 (“Comp 5”) correspond to a case where the composite material does not comprise any flame retardant component comprising Br/Sb2O3.

Examples 7 and 8 (respectively “Inv 7” and “Inv 8”) relate to use of another mixture of flame retardant (phosphate plasticizer + melamine cyanurate + coated ammonium phosphate + ATH), according to a second embodiment of the invention.

Table 3: results of the tests It can be seen that examples 2, 4, 6, 7 and 8 according to the invention are the only examples fulfilling all the requirements in particular in terms of flame retardant properties.

Comp 1 shows a good weldability. However, due to the lack of crosslinker, the coating is not durable enough and shows not sufficient adhesion to the textile substrate. Comp 3 demonstrates that even a high load of a mineral flame retardant like ATH is not sufficient in order to get the desired flame retardancy properties.

If no Sb ₂ O ₃ nor ATH is present, nor any other flame retardant according to the invention, Comp 5 demonstrates that it is not possible to get the desired flame retardancy properties.