WO2024157146A1 - Deposition of nanostructured coatings on polymer foams using a partial injection or immersion process - Google Patents

Deposition of nanostructured coatings on polymer foams using a partial injection or immersion process Download PDF

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Publication number
WO2024157146A1
WO2024157146A1 PCT/IB2024/050583 IB2024050583W WO2024157146A1 WO 2024157146 A1 WO2024157146 A1 WO 2024157146A1 IB 2024050583 W IB2024050583 W IB 2024050583W WO 2024157146 A1 WO2024157146 A1 WO 2024157146A1
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Prior art keywords
foam
solution
suspension
foams
solutions
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PCT/IB2024/050583
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French (fr)
Inventor
Federico CAROSIO
Alberto FINA
Chiara PARAVIDINO
Massimiliano GHIRLANDA
Federico STRETTI
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Politecnico Di Torino
Euroguarco S.P.A.
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Publication of WO2024157146A1 publication Critical patent/WO2024157146A1/en

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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
    • C09D5/18—Fireproof paints including high temperature resistant paints
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/36—After-treatment
    • C08J9/365—Coating
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/36—After-treatment
    • C08J9/40—Impregnation

Definitions

  • the subject of the present invention is a process for functional coating of open-cell polymer foams by deposition on said foams of solutions or suspensions of flame-retardant components.
  • opencell polymer foams Due to their excellent physical (e.g. insulating or mechanical) characteristics, opencell polymer foams can be used in many fields: soundproofing/thermal insulation materials for construction and transport, padding for the automobile industry, furnishing and transport. Unfortunately, their high flammability and low thermomechanical fire resistance precludes their use in applications with strict flame-retardant requirements.
  • Flame-retardant properties can be given to polymer foams by adding solid or liquid flame retardants (mainly inorganic/organic salts) or polymeric flame retardants (polymeric FRs), or by copolymerisation of flame retardants with reactive groups during production of the foams.
  • solid or liquid flame retardants mainly inorganic/organic salts
  • polymeric flame retardants polymeric FRs
  • Said solutions involve adding the flame retardant during formulation of the foam.
  • the additives are mixed with the components used to manufacture the foam and are retained in the foam structure (walls) during the expansion process.
  • Said techniques involve impregnating the foam, followed by squeezing to remove the excess solution/suspension and drying (the “one-pot” process).
  • the foam can be dried directly without removing it from the solution/suspension in which it is immersed. In both cases, an initial step designed to activate the surface of the foam can be conducted.
  • the deposition process can be repeated multiple times by depositing different components in each step (the “layer-by-layer” technique), immersing the foam in a first suspension/solution and then in a different solution. After each immersion, the foam is squeezed and washed with deionised water. The process can be repeated until the desired properties have been obtained.
  • WO2016123295 describes the preparation of polyelectrolyte complexes in aqueous phase.
  • WO2016154137 and EP 2 226 364 describe the deposition of coatings using successive processes of adsorption of reagents with opposite electrostatic charges.
  • US20050177950 describes the manufacture of flame barrier systems characterised by a protective fabric and an impregnated foam. The foam is impregnated with a polymer possessing intrinsic flame-retardant properties.
  • WO2019058186 describes the deposition of coatings using processes of self-assembly of components upon removal of the solvent. The processes described involve the complete immersion of the foams in an excess of the solution/suspension/dispersion used to provide the functional properties. The solvent is removed by evaporation. In WO2019058186, the amount of solvent removed is similar to the volume of the foam.
  • a first limitation is represented by the high volume of solution/suspension/dispersion required for each deposition step (typically 2 or 3 times the volume of the foam to be treated). Said limitation is particularly significant, especially in view of the high manufacturing volumes of open-cell foams.
  • a second limitation, relating to layer-by-layer processes, is associated with the large number of depositions required to obtain the desired flame-retardant properties. Both types of deposition involve problems associated with the production of depleted solutions/suspensions, which are difficult to reintroduce into the manufacturing process, so that their correct disposal is necessary. Finally, the foam drying step, needed to consolidate the coating by removing the solvent, involves significant energy use.
  • a flame-retardant treatment for polymer foams employable for thermal insulation and soundproofing is relevant to various industries (construction, vehicles), and in particular, shipyards.
  • SOLAS International Convention for the Safety of Life at Sea
  • IMO International Maritime Organization
  • IMO Resolution A. 472(XII), Chapter II - 2, regulation 23 and 34 The criterion of non-combustibility is evaluated according to standard UNI EN ISO 1182:2020 - Reaction to fire tests for products - Noncombustibility test.
  • the commercial products have very high densities (70-120 kg/m 3 ), involving drawbacks in terms of: higher fuel consumption and production of SO X , CO2 and NO X emissions during navigation; lower stability of the ship (in view of the high weight of the upper decks, the centre of gravity is shifted, a particularly important factor in the case of the latest cruise ships, which can be up to 70 metres high); high panel handling and installation costs.
  • the general principle whereon the invention is based involves exposing the foam to be treated to a solution/suspension containing the main coating components, without completely filling the free volume of the foam, then distributing the solution throughout its entire volume, and finally removing the solvent by evaporation.
  • the object of the invention is therefore a method for functional coating of open-cell polymer foams by deposition of solutions or suspensions of flame-retardant components, characterised by the following steps: a) partly impregnating the foam with solutions or suspensions of flame-retardant components; b) distributing the solution/suspension throughout the entire free volume of the foam; c) removing the solvent; wherein step a) is performed alternatively (i) by partial immersion of the foam in the solution or suspension, or (ii) by partial impregnation effected by injecting the solution or suspension into the foam.
  • Step a) can be performed alternatively (i) by partial immersion of the foam in the solution or suspension, or (ii) by partial impregnation effected by injecting the solution or suspension into the foam using suitably distanced injectors, or by simple partial immersion of the foam in the solution or suspension.
  • Other types of technological solutions can also be used to impregnate the foam with the desired amount of solution/suspension, for example by using spatula systems and/or by applying vacuum.
  • Partial impregnation step a) allows the use of a small amount of solution to impregnate the foam.
  • the foam is placed in contact with a volume of solution/suspension smaller than the total volume occupied by the foam.
  • Step b) of distributing the solution/suspension throughout the free volume of the foam can be performed by subjecting the partly impregnated foam to compression cycles at predetermined deformation values or by inverting the partly impregnated foam, or using suction or other similar techniques, so that the solution/suspension comes into contact with all the available surfaces of the foam.
  • the foam volume is not completely filled with the solution/suspension used, and a percentage (e.g. between 97.5% and 25%) of free volume remains in the foam.
  • the partial injection process comprises the following steps:
  • Drying the treated foam in a furnace to remove the solvent used for the solutions/suspensions and consolidate the coating.
  • the temperatures ranging within wide limits (for example between 60 and 150°C, depending on the substrate selected and the coating components), using conventional drying systems of various types. Drying can be performed by simple evaporation of the solvent or by conducting a final compression, for example with about 70-80% deformation, to remove part of the solution/suspension and reduce the amount of solvent to be removed by evaporation.
  • step a) the foam is placed in contact with a volume of solution/suspension smaller than the total volume occupied by the foam, preferably a volume of solution/suspension ranging between 5 and 40% of the total volume occupied by the foam.
  • the partial immersion process takes place (i) by immersing the dry foam so that the level of the solution or suspension typically ranges between 5 and 40% of the total volume of the foam.
  • the partial impregnation process takes place (ii) by injecting the solution or suspension into the dry foam so that the level of the solution or suspension injected typically ranges between 5 and the 40% of the volume of the foam.
  • the compression cycles of step b) can range from 5 to 15 in number, preferably from 8 to 12, and more preferably 10 cycles are used, with the deformation values for each cycle ranging between 10 and 80%, preferably between 25 and 50%, and more preferably being about 50%.
  • the term “about” in this description refers to value ranges of ⁇ 10-15% of the indicated value (45-55% for the value of 50%).
  • Drying can then be performed as described above for the injection method.
  • the foam can be precompressed to a deformation ranging between 10 and 90% before being impregnated.
  • the flame-retardant components employable comprise, but are not limited to, silicates, graphene, graphene oxide, nano-graphite, boron nitride, natural or synthetic clays, zirconium phosphate and derivatives thereof, molybdenum disulphide or other dichalcogenides, sepiolites, carbon nanotubes, halloysites, carbon nano-fibres, silica, alumina, metal oxides, polyhedral oligomeric polysilsesquioxanes, organometallic clusters, and alkali silicates.
  • concentration of said components in the solutions/suspensions can range from 1 to 50% by weight, preferably from 5 to 15% by weight.
  • the solvent can be water or a non-toxic volatile organic solvent, such as alcohols.
  • the preferred solvent is water.
  • the method according to the invention provides a novel type of product based on polymer foam possessing characteristics of noncombustibility and insulation equal to those of the solutions currently used on the market (insulation materials based on rock wool, fibreglass, etc).
  • the foams offer the following advantages over said insulating materials in terms of performance:
  • the coated foams have density values lower than 30 kg/m 3 . This is possible due to the low density of the raw foams.
  • This advantage of the panels according to the invention is significant, enabling the weight of the insulating materials to be reduced by 50% (compared with a panel having a density of 60 kg/m 3 ).
  • a reduction in the density of the insulating material means, for example, in the case of a passenger ferry (length 210 m, 2800 passengers, single car deck), a weight reduction of 280,000 kg, an annual fuel saving of $180,000, a reduction of emissions amounting to 750 tonnes of CO2, and improved stability.
  • the foams used are melamine resin foams marketed by BASF (tradename Basotect UF), having a density of 7 kg/m 3 .
  • the solution of silicates was purchased from Merck (tradename sodium silicate solution, silicate content 40-45% by weight, Merck Product code 1056212500). The solution was used, by dilution, to prepare 10 wt% aqueous solutions. Solutions thus prepared were maintained under mechanical stirring for 4 hours before being used for deposition. The solutions were prepared with ultrapure water (resistivity 18.2 MQ) supplied by a Millipore Direct Q20 device (Milan, Italy).
  • the functional coating is deposited by the following procedure:
  • Multiple compressions multiple compressions are performed, for example from 2 to 10 in number, preferably from 2 to 5, and more preferably from 2 to 4 compressions, with 50% deformation, to bring the solution into contact with the entire volume of the foam.
  • Table 1 evaluation of the amount of coating after deposition.
  • the non-combustibility properties were evaluated by a system constructed according to standard UNI EN ISO 1182:2020.
  • the criteria for the non-combustibility conditions are evaluated according to standard IMO 2010 FTPC Part 1.
  • For each formulation two samples were tested, conditioned for 24 hours in a stove at 60°C and cooled to room temperature in a dryer before testing.
  • the test involves exposing cylindrical samples (diameter 45 mm and height 50 mm) to 750°C in a furnace characterised by an opening in the upper part and an air intake in the lower part.
  • the configuration is such that when the temperature of 750°C is reached in the heated part of the furnace, an airflow is generated from the lower (colder) to the upper (warmer) zone.
  • the sample is placed in the furnace for 30 minutes, monitoring the furnace temperature (T furnace) and the sample surface temperature (T sample).
  • T furnace monitoring the furnace temperature
  • T sample surface temperature T sample surface temperature
  • Table 2 Non-combustibility test results on 10% silicates formulation with partial impregnation. Furnace UNI EN ISO 1182-2020. As shown in Table 2, all the samples obtained with the 10% silicates formulation pass the non-combustibility test.
  • the foams used are melamine resin foams produced by BASF (tradename Basotect G+), having a density of 9 kg/m 3 .
  • the solution of silicates was purchased from Merck (tradename sodium silicate solution, silicate content 40-45%, Merck Product code 1056212500 2.5).
  • Natural montmorillonite (tradename CloNa + ®) was purchased from Southern Clay Products. The solution was used, by dilution, to prepare 10 wt% aqueous solutions. The solutions thus prepared were maintained under mechanical stirring for 4 hours before being used for deposition.
  • the aqueous solution used in this example has a composition by weight of 10% silicates and 1% montmorillonite.
  • the solution was prepared by mixing a 10 wt% aqueous solution of silicates (obtained by diluting the commercial solution) with a 1 wt% solution of montmorillonite and leaving it under mechanical stirring for about 8 hours.
  • the solutions were prepared with ultrapure water (resistivity 18.2 MQ) supplied by a Millipore Direct Q20 device (Milan, Italy).
  • the functional coating is deposited by the following procedure:
  • the mechanical properties were evaluated by subjecting the foams to 10 compression cycles at 25% deformation (deformation rate 100 mm/min) on an INSTRON 5956 dynamometer equipped with a 10 kN load cell and a set-up for porous materials according to ASTM 3574.
  • the non-combustibility properties were evaluated by a system constructed according to standard UNI EN ISO 1182:2020.
  • the criteria for the non-combustibility conditions are evaluated according to standard IMO 2010 FTPC Part 1. For each formulation two samples were tested, conditioned in a stove at 60°C for 24 hours, and then cooled to room temperature in a dryer before testing.
  • the test involves exposing cylindrical samples (diameter 45 mm and height 50 mm) to 750°C in a furnace characterised by an opening in the upper part and an air intake in the lower part.
  • the configuration is such that when the temperature of 750°C is reached in the heated part of the furnace, an airflow is generated from the lower (colder) to the upper (warmer) zone.
  • the sample is placed in the furnace for 30 minutes, monitoring the furnace temperature (T furnace) and the sample surface temperature (T sample). The test is deemed to be passed if:
  • Figure 2 shows the results of a compression on the treated samples, and the images of the samples before (1) and after (2) cyclic deformations.
  • Table 4 Results of non-combustibility test on 10% silicates - 1% CLONa formulation by injection. Furnace UNI EN ISO 1182-2020.
  • a thermal conductivity test is performed by the hot-disk method.
  • the treated foams exhibit a thermal conductivity value of 0.04 W/mK (reference value of untreated foam 0.03 W/mK, maximum value for the application 0.045 W/mK), demonstrating that the deposition of a functional coating does not involve a substantial reduction in the thermal insulation properties of the foams, which maintain thermal conductivity values in line with those of other materials used in the naval field.
  • Open-cell melamine resin foams with a density of 7 kg/m 3 were considered.
  • the density of the melamine resin is estimated at 1.13 g/cm 3 .
  • the panel dimensions are 1200x600x30 mm 3 .
  • the panel volume is 2.16 • 10' 2 m 3
  • the free volume (calculated on the basis of the known panel weight and density of the melamine resin) is 2.15 • 10' 2 m 3 .
  • the partial impregnation process according to the invention characterised by the following steps, was considered: a. Immersion of the sample in a volume of solution/ suspension amounting to 10% of the panel volume. b. Multiple compressions: multiple compressions are performed, for example 2 to 10 compressions with 50% deformation, to bring the solution/suspension into contact with the entire panel volume. c. Drying: the treated foam is placed in a ventilated furnace (Temperature 70°C) to remove the solvent used for the solutions/suspensions and consolidate the coating.
  • the known (total impregnation) procedure characterised by the following steps, was then considered: a. Immersion of the sample in a volume of solution/suspension equal to or greater than the free volume of the sample. b. Removal of the sample from the deposition bath and squeezing by compression to eliminate the excess solution/suspension. The compression removes an excess of solution/suspension equal to the free volume of the panel minus 10% of the total panel volume. The amount of residual solution/suspension before the drying step is therefore the same for both processes.
  • the solution/suspension removed in this step is waste solution/suspension, which cannot be directly reused in the process because the application to the foam in step a) can change its chemical composition, due to deposition of fractions of the active components contained in the solution/suspension. Contaminants released by the foam into the solutions/suspensions may also be present.
  • Drying the treated foam is placed in a ventilated furnace (Temperature 70°C) to remove the solvent used for the solution/suspension and consolidate the coating.
  • Table 5 shows the comparison between the volumes of solution/suspension to be used and the waste volumes for the known processes of impregnation by partial immersion and impregnation by total immersion.
  • the total immersion process involves the use of more solution/suspension than the partial immersion process (15.5 m 3 vs. 1.56 m 3 ) and produces a high volume of waste solution/suspension (amounting to 13.9 m 3 or 13900 litres).
  • Said waste solution/suspension cannot be reused directly in the process because the application to the foam can change its chemical composition, due to deposition of fractions of the active components contained in the solution/suspension. Contaminants released by the foam may also be present.

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Abstract

Disclosed is a process for functional coating of open-cell polymer foams by deposition on said foams of solutions or suspensions of flame-retardant components. The process according to the invention comprises: a) partial impregnation of the foam with solutions or suspensions of flame-retardant components; b) treatment of the partly impregnated foam with compression cycles at predetermined deformation values; c) elimination of solvent by evaporation; wherein step a) is performed alternatively (i) by partial immersion of the foam in the solution or suspension, or (ii) by partial impregnation effected by injecting the solution or suspension into the foam.

Description

DEPOSITION OF NANOSTRUCTURED COATINGS ON POLYMER FOAMS USING A PARTIAL INJECTION OR IMMERSION PROCESS
The subject of the present invention is a process for functional coating of open-cell polymer foams by deposition on said foams of solutions or suspensions of flame-retardant components.
Prior art
Due to their excellent physical (e.g. insulating or mechanical) characteristics, opencell polymer foams can be used in many fields: soundproofing/thermal insulation materials for construction and transport, padding for the automobile industry, furnishing and transport. Unfortunately, their high flammability and low thermomechanical fire resistance precludes their use in applications with strict flame-retardant requirements.
The commercial solutions currently employed to extend their field of application involve using flame-retardant additives, which can reduce flammability, but do not guarantee the thermomechanical resistance of the foam under fire conditions. The flame retardants commonly used to protect polymer materials also might involve significant environmental and toxicological problems
(https://www.liebertpub.com/doi/10.1089/ees.2017.0147; Environ Sci Pollut Res, 2018, 25, 24201 DOI: 10.1007/sl 1356-018-24940; Environmental Research, 2017, 158,669 DOI: 10.1016/j.envres.2017.07.022), which have led to a major reduction in consumption of flame retardants, especially halogenated retardants.
Flame-retardant properties can be given to polymer foams by adding solid or liquid flame retardants (mainly inorganic/organic salts) or polymeric flame retardants (polymeric FRs), or by copolymerisation of flame retardants with reactive groups during production of the foams.
Said solutions involve adding the flame retardant during formulation of the foam. The additives are mixed with the components used to manufacture the foam and are retained in the foam structure (walls) during the expansion process.
Recently, techniques for deposition of nanostructured coatings from aqueous phase were proposed as a possible solution that considerably improves the flame-retardant performance of open-cell foams, using sustainable components with limited toxicity.
Said techniques involve impregnating the foam, followed by squeezing to remove the excess solution/suspension and drying (the “one-pot” process). Alternatively, the foam can be dried directly without removing it from the solution/suspension in which it is immersed. In both cases, an initial step designed to activate the surface of the foam can be conducted.
The deposition process can be repeated multiple times by depositing different components in each step (the “layer-by-layer” technique), immersing the foam in a first suspension/solution and then in a different solution. After each immersion, the foam is squeezed and washed with deionised water. The process can be repeated until the desired properties have been obtained.
WO2016123295 describes the preparation of polyelectrolyte complexes in aqueous phase. WO2016154137 and EP 2 226 364 describe the deposition of coatings using successive processes of adsorption of reagents with opposite electrostatic charges. US20050177950 describes the manufacture of flame barrier systems characterised by a protective fabric and an impregnated foam. The foam is impregnated with a polymer possessing intrinsic flame-retardant properties. WO2019058186 describes the deposition of coatings using processes of self-assembly of components upon removal of the solvent. The processes described involve the complete immersion of the foams in an excess of the solution/suspension/dispersion used to provide the functional properties. The solvent is removed by evaporation. In WO2019058186, the amount of solvent removed is similar to the volume of the foam.
Said types of deposition involve intrinsic limitations that limit their commercial development. In said processes, as in GB1499168 A, US 2020/270415 Al and JP2009149721 Al, the foams are completely immersed in aqueous solutions/suspensions/ dispersions to facilitate deposition of a coating by adsorption of the components on surfaces exposed to the solution/suspension/dispersion. A first limitation is represented by the high volume of solution/suspension/dispersion required for each deposition step (typically 2 or 3 times the volume of the foam to be treated). Said limitation is particularly significant, especially in view of the high manufacturing volumes of open-cell foams.
Removal by compression of part of the solution/suspension/dispersion, used to facilitate the drying stage that consolidates the coating, generates large volumes of waste solution/suspension/dispersion (especially in the case of an industrial-scale manufacturing process). Said solution/suspension/dispersion cannot be reused directly in the process because the application to the foam might change its chemical composition, due to deposition of fractions of the active components contained in the solution/suspension/dispersion. In addition, contaminants released by the foam into the solutions/suspensions may also be present.
Management of said solution/suspension/dispersion therefore involves two options:
- reintroduction into the process after continuous chemical analysis of the composition, with optional removal of impurities and replenishment of the coating components. This option requires an online control and a dedicated system able to restore the correct concentration values of each component used for the solutions/suspensions. Said operation is extremely complicated for solutions/suspensions containing more than one component, and dedicated detection systems are therefore required for the different chemical substances used (a technical solution that is not always possible or integrable into an industrial process); or disposal according to current regulations for aqueous solutions/suspensions/dispersions.
Both cases involve a further cost and complicate the applicability of the process at the industrial scale.
A second limitation, relating to layer-by-layer processes, is associated with the large number of depositions required to obtain the desired flame-retardant properties. Both types of deposition involve problems associated with the production of depleted solutions/suspensions, which are difficult to reintroduce into the manufacturing process, so that their correct disposal is necessary. Finally, the foam drying step, needed to consolidate the coating by removing the solvent, involves significant energy use.
A flame-retardant treatment for polymer foams employable for thermal insulation and soundproofing is relevant to various industries (construction, vehicles), and in particular, shipyards. In fact, the International Convention for the Safety of Life at Sea (SOLAS) states that no structural or insulation materials used for a ship’s structures shall be combustible, according to the directives issued by the International Maritime Organisation (International Maritime Organization, IMO) (IMO Resolution A. 472(XII), Chapter II - 2, regulation 23 and 34). The criterion of non-combustibility is evaluated according to standard UNI EN ISO 1182:2020 - Reaction to fire tests for products - Noncombustibility test. Said property is not currently guaranteed by any of the polymer foams on the market and limits their application in the field of naval insulating materials. Currently known solutions, which involve the use of inorganic materials such as rock wool or calcium silicates, present various limitations on both the manufacture of the insulating panel and its properties during its period of service, because of the high density and fibrous composition of the materials. The commercial products have very high densities (70-120 kg/m3), involving drawbacks in terms of: higher fuel consumption and production of SOX, CO2 and NOX emissions during navigation; lower stability of the ship (in view of the high weight of the upper decks, the centre of gravity is shifted, a particularly important factor in the case of the latest cruise ships, which can be up to 70 metres high); high panel handling and installation costs.
Moreover, the preponderant use of rock wool panels based on mineral fibres not only involves the known toxicity risks of fibrous inorganic materials, but also problems during panel manufacture: cutting and assembly operations can damage the panel, which disintegrates due to its fibrous structure. This behaviour becomes increasingly problematic as panel density is reduced, to the point that panels with a density lower than 60 kg/m3 are practically unusable.
There is consequently a need for improved methodologies which produce insulating materials that overcome the limitations of the currently available solutions.
Description of the invention
A method has now been found whereby flame-retardant properties considerably superior to the state of the art are given to organic or hybrid organic/inorganic porous polymer substrates, guaranteeing the thermomechanical resistance of the foam for several minutes under fire conditions, using a fast, highly efficient process. Using the proposed technology, characteristics of non-combustibility can be obtained for the treated foams; a condition that is not currently achievable using techniques based on adding flame retardants to the mass.
The general principle whereon the invention is based involves exposing the foam to be treated to a solution/suspension containing the main coating components, without completely filling the free volume of the foam, then distributing the solution throughout its entire volume, and finally removing the solvent by evaporation.
The object of the invention is therefore a method for functional coating of open-cell polymer foams by deposition of solutions or suspensions of flame-retardant components, characterised by the following steps: a) partly impregnating the foam with solutions or suspensions of flame-retardant components; b) distributing the solution/suspension throughout the entire free volume of the foam; c) removing the solvent; wherein step a) is performed alternatively (i) by partial immersion of the foam in the solution or suspension, or (ii) by partial impregnation effected by injecting the solution or suspension into the foam.
Step a) can be performed alternatively (i) by partial immersion of the foam in the solution or suspension, or (ii) by partial impregnation effected by injecting the solution or suspension into the foam using suitably distanced injectors, or by simple partial immersion of the foam in the solution or suspension. Other types of technological solutions can also be used to impregnate the foam with the desired amount of solution/suspension, for example by using spatula systems and/or by applying vacuum.
Partial impregnation step a) allows the use of a small amount of solution to impregnate the foam. In fact, in step a), the foam is placed in contact with a volume of solution/suspension smaller than the total volume occupied by the foam.
Step b) of distributing the solution/suspension throughout the free volume of the foam, can be performed by subjecting the partly impregnated foam to compression cycles at predetermined deformation values or by inverting the partly impregnated foam, or using suction or other similar techniques, so that the solution/suspension comes into contact with all the available surfaces of the foam.
After compression step b), the foam volume is not completely filled with the solution/suspension used, and a percentage (e.g. between 97.5% and 25%) of free volume remains in the foam.
In one embodiment, the partial injection process comprises the following steps:
1. Injecting a known volume of solution/suspension containing the coating components. One, two or more types of solutions/suspensions can be injected simultaneously or sequentially.
2. Multiple compressions, typically up to about 50% deformation (non-critical value), to bring the solution into contact with the entire volume of the foam. This step can be performed in a mould suitable to contain the foam or simply on a rigid surface, in view of the ability of some types of foam to retain the volume of solution/suspension injected.
3. Drying the treated foam in a furnace, to remove the solvent used for the solutions/suspensions and consolidate the coating. The temperatures, ranging within wide limits (for example between 60 and 150°C, depending on the substrate selected and the coating components), using conventional drying systems of various types. Drying can be performed by simple evaporation of the solvent or by conducting a final compression, for example with about 70-80% deformation, to remove part of the solution/suspension and reduce the amount of solvent to be removed by evaporation.
In step a), the foam is placed in contact with a volume of solution/suspension smaller than the total volume occupied by the foam, preferably a volume of solution/suspension ranging between 5 and 40% of the total volume occupied by the foam.
In one embodiment, the partial immersion process takes place (i) by immersing the dry foam so that the level of the solution or suspension typically ranges between 5 and 40% of the total volume of the foam.
In another embodiment, the partial impregnation process takes place (ii) by injecting the solution or suspension into the dry foam so that the level of the solution or suspension injected typically ranges between 5 and the 40% of the volume of the foam.
The compression cycles of step b) can range from 5 to 15 in number, preferably from 8 to 12, and more preferably 10 cycles are used, with the deformation values for each cycle ranging between 10 and 80%, preferably between 25 and 50%, and more preferably being about 50%. The term “about” in this description refers to value ranges of ± 10-15% of the indicated value (45-55% for the value of 50%).
Drying can then be performed as described above for the injection method.
In one embodiment of the process according to the invention, the foam can be precompressed to a deformation ranging between 10 and 90% before being impregnated.
Polyurethane, polyester, polyolefin, polyamide, phenolic, melamine or other types of open-cell foams can be used. The flame-retardant components employable comprise, but are not limited to, silicates, graphene, graphene oxide, nano-graphite, boron nitride, natural or synthetic clays, zirconium phosphate and derivatives thereof, molybdenum disulphide or other dichalcogenides, sepiolites, carbon nanotubes, halloysites, carbon nano-fibres, silica, alumina, metal oxides, polyhedral oligomeric polysilsesquioxanes, organometallic clusters, and alkali silicates. The concentration of said components in the solutions/suspensions can range from 1 to 50% by weight, preferably from 5 to 15% by weight.
The solvent can be water or a non-toxic volatile organic solvent, such as alcohols. The preferred solvent is water.
The method according to the invention possesses the following advantages over known techniques for giving flame-retardant properties:
1. Use of water-based solutions and suspensions containing non-toxic components, the use whereof is preferable to adding flame retardants in the mass.
2. Use of a minimum volume of solution/ suspension to obtain a functional coating because the foam volume is not entirely filled with the solution/suspension used. This reduces the use of solution per panel volume treated, and potentially eliminates the production of residues of depleted solution/suspension of the active components, which would otherwise require disposal.
Unlike the solutions known in the state of the art for thermal insulation/soundproofing in the naval field, the method according to the invention provides a novel type of product based on polymer foam possessing characteristics of noncombustibility and insulation equal to those of the solutions currently used on the market (insulation materials based on rock wool, fibreglass, etc). The foams offer the following advantages over said insulating materials in terms of performance:
1. Lower density than inorganic materials: the coated foams have density values lower than 30 kg/m3. This is possible due to the low density of the raw foams. This advantage of the panels according to the invention is significant, enabling the weight of the insulating materials to be reduced by 50% (compared with a panel having a density of 60 kg/m3). A reduction in the density of the insulating material (from 60 to 30 kg/m3 for the known solutions and the polymer foams produced with the technology respectively) means, for example, in the case of a passenger ferry (length 210 m, 2800 passengers, single car deck), a weight reduction of 280,000 kg, an annual fuel saving of $180,000, a reduction of emissions amounting to 750 tonnes of CO2, and improved stability.
2. Easy industrial manufacture: polymer foams coated using the technology according to the invention have exhibited excellent workability by hot cutting or with conventional tools. The foams are flexible and reversibly compressible, so that they can be handled in the conventional manufacturing process without any particular precautions. Moreover, shaping and cutting operations do not involve the release of inorganic fibres or powders.
The invention is described in greater detail in the examples below.
Example 1 Partial impregnation by partial immersion (i)
Materials
The foams used are melamine resin foams marketed by BASF (tradename Basotect UF), having a density of 7 kg/m3. The solution of silicates was purchased from Merck (tradename sodium silicate solution, silicate content 40-45% by weight, Merck Product code 1056212500). The solution was used, by dilution, to prepare 10 wt% aqueous solutions. Solutions thus prepared were maintained under mechanical stirring for 4 hours before being used for deposition. The solutions were prepared with ultrapure water (resistivity 18.2 MQ) supplied by a Millipore Direct Q20 device (Milan, Italy).
Methods
The functional coating is deposited by the following procedure:
1. Immersion of the sample in a volume of solution amounting to 25% of the total volume of the sample.
2. Multiple compressions: multiple compressions are performed, for example from 2 to 10 in number, preferably from 2 to 5, and more preferably from 2 to 4 compressions, with 50% deformation, to bring the solution into contact with the entire volume of the foam.
3. Drying: the treated foam is placed in a ventilated furnace (Temperature 70°C) to remove the solvent used for the solutions/suspensions and consolidate the coating.
Table 1: evaluation of the amount of coating after deposition.
Figure imgf000009_0001
Characterisation
The non-combustibility properties were evaluated by a system constructed according to standard UNI EN ISO 1182:2020. The criteria for the non-combustibility conditions are evaluated according to standard IMO 2010 FTPC Part 1. For each formulation two samples were tested, conditioned for 24 hours in a stove at 60°C and cooled to room temperature in a dryer before testing. The test involves exposing cylindrical samples (diameter 45 mm and height 50 mm) to 750°C in a furnace characterised by an opening in the upper part and an air intake in the lower part. The configuration is such that when the temperature of 750°C is reached in the heated part of the furnace, an airflow is generated from the lower (colder) to the upper (warmer) zone. The sample is placed in the furnace for 30 minutes, monitoring the furnace temperature (T furnace) and the sample surface temperature (T sample). The test is deemed to be passed if:
• Loss of mass < 50%
• Flame duration < 10s
• T furnace increase < 30°C
• T sample increase < 30°C
Results
The non-combustibility criteria according to the directives of standard IMO 2010 FTPC Part 1 were applied. The table shows the results for each foam treated.
Table 2: Non-combustibility test results on 10% silicates formulation with partial impregnation. Furnace UNI EN ISO 1182-2020.
Figure imgf000009_0002
As shown in Table 2, all the samples obtained with the 10% silicates formulation pass the non-combustibility test.
Example 2 Partial impregnation by partial injection (ii)
Materials
The foams used are melamine resin foams produced by BASF (tradename Basotect G+), having a density of 9 kg/m3. The solution of silicates was purchased from Merck (tradename sodium silicate solution, silicate content 40-45%, Merck Product code 1056212500 2.5). Natural montmorillonite (tradename CloNa+®) was purchased from Southern Clay Products. The solution was used, by dilution, to prepare 10 wt% aqueous solutions. The solutions thus prepared were maintained under mechanical stirring for 4 hours before being used for deposition. The aqueous solution used in this example has a composition by weight of 10% silicates and 1% montmorillonite. The solution was prepared by mixing a 10 wt% aqueous solution of silicates (obtained by diluting the commercial solution) with a 1 wt% solution of montmorillonite and leaving it under mechanical stirring for about 8 hours. The solutions were prepared with ultrapure water (resistivity 18.2 MQ) supplied by a Millipore Direct Q20 device (Milan, Italy).
Methods
A support able to hold 5 syringes to conduct the injections on 10 lines, making a total of 50 injection points, was devised. For each injection point two separate injections are performed at different heights (2 and 4 cm) as shown in Figure 1.
The functional coating is deposited by the following procedure:
1. Injection of a volume of solution amounting to about 37% of the total volume of the foam.
2. Multiple compressions: multiple compressions with 50% deformation are performed to bring the solution into contact with the entire volume of the foam.
3. Final compression at 70-80% deformation, to remove part of the excess solution/suspension.
4. Drying: the treated foam is placed in a ventilated furnace (temperature 70°C) to remove the solvent used for the solutions/suspensions and consolidate the coating.
Two sets of foams were produced from two samples to evaluate whether the functional properties were maintained following cyclic compressions. The sheet produced (final density 26 kg/m3) was sampled to produce samples to be tested with a furnace constructed according to UNI EN ISO 1182:2020 (evaluation of non-combustibility characteristics, a crucial property for application in the field of naval insulation materials). Table 3: evaluation of amount of coating after deposition.
Figure imgf000011_0001
Characterisation
The mechanical properties were evaluated by subjecting the foams to 10 compression cycles at 25% deformation (deformation rate 100 mm/min) on an INSTRON 5956 dynamometer equipped with a 10 kN load cell and a set-up for porous materials according to ASTM 3574.
The non-combustibility properties were evaluated by a system constructed according to standard UNI EN ISO 1182:2020. The criteria for the non-combustibility conditions are evaluated according to standard IMO 2010 FTPC Part 1. For each formulation two samples were tested, conditioned in a stove at 60°C for 24 hours, and then cooled to room temperature in a dryer before testing.
The test involves exposing cylindrical samples (diameter 45 mm and height 50 mm) to 750°C in a furnace characterised by an opening in the upper part and an air intake in the lower part. The configuration is such that when the temperature of 750°C is reached in the heated part of the furnace, an airflow is generated from the lower (colder) to the upper (warmer) zone. The sample is placed in the furnace for 30 minutes, monitoring the furnace temperature (T furnace) and the sample surface temperature (T sample). The test is deemed to be passed if:
• Loss of mass < 50%
• Flame duration < 10s
• T furnace increase < 30°C
• T sample increase < 30°C
Results
Figure 2 shows the results of a compression on the treated samples, and the images of the samples before (1) and after (2) cyclic deformations.
As reported in Figure 2, after cyclic deformation, the foam retains its characteristic mechanical properties and recovers its initial shape.
The non-combustibility of the treated foams and of the foams treated and subjected to cyclic compression was evaluated according to UNI ISO 1182, applying the directives of standard IMO 2010 FTPC Part 1. Table 4 shows the results obtained.
Table 4: Results of non-combustibility test on 10% silicates - 1% CLONa formulation by injection. Furnace UNI EN ISO 1182-2020.
Figure imgf000012_0001
As shown in Table 4, all the samples obtained pass the test. The samples subjected to deformation by compression not only maintain the mechanical properties characteristic of the reference foam, but also pass the non-combustibility test with all parameters within the normal range, indicating that the coating deposited guarantees adequate protection of the foam and maintains its properties despite the repeated compression force.
A thermal conductivity test is performed by the hot-disk method. The treated foams exhibit a thermal conductivity value of 0.04 W/mK (reference value of untreated foam 0.03 W/mK, maximum value for the application 0.045 W/mK), demonstrating that the deposition of a functional coating does not involve a substantial reduction in the thermal insulation properties of the foams, which maintain thermal conductivity values in line with those of other materials used in the naval field.
The following main conclusions can be drawn from the results obtained:
1. The formulation used and the modification of the injection process enable a more homogeneous deposition to be obtained.
2. All the samples obtained from the sheet pass the test according to the UNI EN ISO 1182:2020 criteria. The final density is 26 kg/m3, well below the value of the insulating materials on the market.
Example 3 Partial impregnation process according to the invention by immersion, and total impregnation process
The volumes of solution/suspension required for impregnation, and the amount of waste solution/suspension, are evaluated.
Open-cell melamine resin foams with a density of 7 kg/m3 were considered. The density of the melamine resin is estimated at 1.13 g/cm3. The panel dimensions are 1200x600x30 mm3. The panel volume is 2.16 • 10'2 m3, and the free volume (calculated on the basis of the known panel weight and density of the melamine resin) is 2.15 • 10'2m3.
The partial impregnation process according to the invention, characterised by the following steps, was considered: a. Immersion of the sample in a volume of solution/ suspension amounting to 10% of the panel volume. b. Multiple compressions: multiple compressions are performed, for example 2 to 10 compressions with 50% deformation, to bring the solution/suspension into contact with the entire panel volume. c. Drying: the treated foam is placed in a ventilated furnace (Temperature 70°C) to remove the solvent used for the solutions/suspensions and consolidate the coating.
The known (total impregnation) procedure, characterised by the following steps, was then considered: a. Immersion of the sample in a volume of solution/suspension equal to or greater than the free volume of the sample. b. Removal of the sample from the deposition bath and squeezing by compression to eliminate the excess solution/suspension. The compression removes an excess of solution/suspension equal to the free volume of the panel minus 10% of the total panel volume. The amount of residual solution/suspension before the drying step is therefore the same for both processes. The solution/suspension removed in this step is waste solution/suspension, which cannot be directly reused in the process because the application to the foam in step a) can change its chemical composition, due to deposition of fractions of the active components contained in the solution/suspension. Contaminants released by the foam into the solutions/suspensions may also be present. c. Drying: the treated foam is placed in a ventilated furnace (Temperature 70°C) to remove the solvent used for the solution/suspension and consolidate the coating.
The volumes of solution/suspension to be used, and the volumes of waste solution/suspension per panel for each process, together with the volume used and the volume of waste produced during a 24-hour manufacturing batch, assuming productivity of 30 sheets/hour (total no. of sheets manufactured 720), were evaluated, and are shown in Table 5. Table 5
Figure imgf000014_0001
Table 5 shows the comparison between the volumes of solution/suspension to be used and the waste volumes for the known processes of impregnation by partial immersion and impregnation by total immersion.
As shown in Table 5, the total immersion process involves the use of more solution/suspension than the partial immersion process (15.5 m3 vs. 1.56 m3) and produces a high volume of waste solution/suspension (amounting to 13.9 m3 or 13900 litres).
Said waste solution/suspension cannot be reused directly in the process because the application to the foam can change its chemical composition, due to deposition of fractions of the active components contained in the solution/suspension. Contaminants released by the foam may also be present.
It is therefore evident that the process of impregnation with partial immersion is innovative and involves a technical advantage essential for industrialisation.

Claims

1. Method for functional coating of open-cell polymer foams by deposition on said polymer foams of solutions and/or suspensions of flame-retardant components characterised by the following steps: a) partly impregnating the foam with solutions or suspensions of flame retardant components; b) treatment of the partially impregnated foam with compression cycles at predetermined deformation values; c) removing of the solvent by evaporation wherein step a) is performed alternatively (i) by partial immersion of the foam in the solution or suspension, or (ii) by partial impregnation effected by injecting the solution or suspension into the foam.
2. Method according to claim 1 wherein step a) is carried out (i) by immersing the dry foam so that the level of the solution or suspension ranges between 5 and 40% of the total volume of the foam.
3. Method according to claim 1 wherein step a) is carried out (ii) by injecting the solution or suspension into the dry foam so that the level of the solution or suspension injected ranges between 5 and 40% of the total volume of the foam.
4. Method according to any one of claims 1-3 wherein the foam is pre-compressed to a deformation ranging between 10 and 90% before being impregnated.
5. Method according to any one of claims 1-4 wherein step b) is carried out by subjecting the partially impregnated foam to compression cycles at predetermined deformation values.
6. Method according to claim 5 wherein the compression cycles of step b) range from 5 to 15 in number.
7. Method according to any one of claims 1 to 6 wherein the deformation values for each cycle range from 10 to 80%, preferably from 25 to 50%.
8. Method according to any one of claims 1 to 7 wherein step c) is carried out by treatment at temperatures ranging between 60 and 200°C.
9. Method according to any one of claims 1 to 8 wherein step c) comprises a final compression step up to deformation values ranging from 50 to 85%, followed by drying at a temperature ranging between 50 and 80°C.
10. Method according to any one of claims 1 to 9 wherein the foams are organic- inorganic hybrid foams or organic foams selected from polyurethane, polyurea, polyester, polyolefin, polyamide, phenolic resin and melamine resin foams.
11. Method according to claim 10 wherein the foam is a melamine resin.
12. Method according to any one of claims 1 to 11 wherein the flame-retardant components in solution/suspension are selected from silicates, graphene, graphene oxide, nanographite, boron nitride, natural or synthetic clays, zirconium phosphate and derivatives thereof, molybdenum disulphide or other dichalcogenides, sepiolites, carbon nanotubes, halloysites, carbon nanofibres, silica, alumina, metal oxides, polyhedral oligomeric polysilsesqui oxanes and organometal clusters, preferably alkali silicates.
13. Open-cell polymer foams obtainable by the method according to claims 1-12.
PCT/IB2024/050583 2023-01-23 2024-01-22 Deposition of nanostructured coatings on polymer foams using a partial injection or immersion process WO2024157146A1 (en)

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1353388A (en) * 1970-07-29 1974-05-15 Bayer Ag Process for impregnating foams
GB1499168A (en) * 1976-11-01 1978-01-25 Hairlok Ltd Flame resistant foams
US4885263A (en) * 1987-03-23 1989-12-05 Swiss Aluminium Ltd. Ceramic foam filter and process for preparing same
EP0451535A1 (en) * 1990-03-14 1991-10-16 Illbruck Production S.A. Method for producing an article from a melamin resin foam
JPH05230271A (en) * 1992-02-17 1993-09-07 Sanwa Kako Kk Method and apparatus for injecting chemical into foam
JP2009149721A (en) * 2007-12-19 2009-07-09 Achilles Corp Flame retardant polyurethane foam
US20200270415A1 (en) * 2017-09-12 2020-08-27 Basf Se Phyllosilicate-impregnated melamine-formaldehyde foam

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1353388A (en) * 1970-07-29 1974-05-15 Bayer Ag Process for impregnating foams
GB1499168A (en) * 1976-11-01 1978-01-25 Hairlok Ltd Flame resistant foams
US4885263A (en) * 1987-03-23 1989-12-05 Swiss Aluminium Ltd. Ceramic foam filter and process for preparing same
EP0451535A1 (en) * 1990-03-14 1991-10-16 Illbruck Production S.A. Method for producing an article from a melamin resin foam
JPH05230271A (en) * 1992-02-17 1993-09-07 Sanwa Kako Kk Method and apparatus for injecting chemical into foam
JP2009149721A (en) * 2007-12-19 2009-07-09 Achilles Corp Flame retardant polyurethane foam
US20200270415A1 (en) * 2017-09-12 2020-08-27 Basf Se Phyllosilicate-impregnated melamine-formaldehyde foam

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