NL2023663B1

NL2023663B1 - Weather resistant thermal insulation material

Info

Publication number: NL2023663B1
Application number: NL2023663A
Authority: NL
Inventors: Martinus Johannes Mario Martens Thom; Klaus Brueck Gernot; Matheus Maria Verweerden Theodorus
Original assignee: Lamoral Holding B V
Priority date: 2019-08-19
Filing date: 2019-08-19
Publication date: 2021-03-30
Also published as: WO2021032805A1; EP4017893A1

Abstract

Described is an article comprising a radiation reflective surface, the radiation reflective surface comprising a coating comprising a transparent terpolymer comprising a transparent terpolymer of polytetrafluoroethylene monomers, methyl monomers and hydroxymethyl monomers. The transparent terpolymer provides for an anti-corrosive transparent coating conferring long term stability to reflective materials to be used e.g. as building elements such as roofing panels or roofing tiles. Further the use of such a transparent terpolymer is described for coating a radiation reflective surface of an article.

Description

Weather resistant thermal insulation material The invention relates to a thermal insulation material comprising an outer radiation reflective surface, coated with a protective coating comprising a transparent terpolymer comprising polytetrafluoroethylene monomers, and to the use of such a transparent terpolymer for coating a radiation reflective surface of a thermal insulation material.

Thermal insulation materials comprising an outer radiation reflective surface are used as insulation material that prevent heat transfer by thermal radiation. Such materials reflect radiation heat and prevent transfer from the outer side, where the thermal radiation hits the material, to the opposite inner side. Such materials are radiant barriers, in particular against infrared red (IR), providing reflective insulation. Examples of such materials are insulation materials, such as foam panels, glass wool, stone wool, provided with a radiation reflective surface, such as a metal layer.

The outer reflective surface of such thermal insulation material preferably reflects not only IR radiation, but also visible light and UV radiation. In the building industry, such thermal insulation material is often used indoors, e.g. below roofing surfaces, as it is avoided to expose the radiation reflective surfaces known in the art to environmental conditions such as variable temperatures, humidity, corrosion, (acid) rain etc. It is therefore desired to coat the radiation protective surface with a protective layer to protect the radiation reflective surface from weathering influences and to render such surfaces suitable for outdoors usage.

Fluoropolymer coatings are strong and can form an oxygen barrier to prevent corrosion of the coated material. In the art, many fluoropolymers are known, such as polytetrafluorethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene tetrafluoroethylene (EFTE), copolymers such as tetrafluoroethylene perfluoromethylvinylester (MFA) and terpolymers such as tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer (THV). Because of the strong C-F bond, fluoropolymers have a high chemical inertness and provide a strong oxygen barrier. However, most of the fluoropolymers are not transparent and are therewith not suitable as a transparent coating.

Protective coating materials based on fluoropolymers are known, e.g. polyvinylidene fluoride (PVDF) resin, a copolymer of vinylidene fluoride and tetrafluoroethylene, marketed under the name Kynar® of (Arkema, France). Indeed, PVDF provides an improved lasting performance in coating applications for the building industry. However, it was found that PVDF containing coatings have a limited durability, which is caused by the bond of the vinyl monomers and the absorption profile of PVDF in the IR and UV range. By exposure to thermal radiation, PVDF absorbs IR and UV resulting in heat generation, breakage of the double vinyl bonds and radical formation, leading to deterioration of the polymer cured coating in time. Emission rates, i.e. the radiation that is passed through the coating are undesirably low and become even lower in time.

From US4,710,426 a thermal insulation material is known, however intended to be transmissive of visible light and selectively reflective of infrared radiation. Said material comprises an exterior radiation reflective surface comprising a fluoropolymer comprising vinyl groups, such as Kynar. Because of the presence of vinyl double bonds, such coatings are less sustainable in time.

US2012/301728 describes a thermal insulation material, comprising an exterior reflection surface comprising a coating comprising a transparent fluoropolymer. The coating is prepared by reacting hydroxy-functional fluoropolymers comprising chlorotrifluoroethylene and hydroxybutyl vinyl ether with a polyisocyanate. Again, the presence of vinyl groups renders the coating susceptible to weathering by radical formation from vinyl groups, as well as from the chlorine groups that may break and result in radical formation, deteriorating the coating polymer.

In the art, roofing materials from polyvinylchloride (PVC) and thermoplastic elastomer olefin (TPO) are also used, but these materials are not transparent and are not or to a very small extent reflective for UV radiation.

Therefore, an improved coating material is desired with improved weathering resistance, emissivity and reflection profile, while still having the protective strength and oxygen barrier characteristics of the known fluoropolymers.

It has now been surprisingly found that terpolymers comprising polytetrafluoroethylene monomers, methyl monomers and hydroxymethyl monomers have such improved emissivity and reflection profiles. Such polymers are fully saturated, i.e. being free of double C=C bonds. The said terpolymers are fully transparent for infra-red and visible light while being extreme UV stable. This means that such coatings are highly resistant against weathering, caused by UV radiation. It was observed that UV is passed through the coating or converted therein into IR. This conversion is without heat generation because of the full transparency of the terpolymer for IR. The radiation that passes through the coating and the IR generated therein are reflected by the radiation reflective surface of the thermal insulation material without heat generation. The radiation arrives at the surface of the reflective material where it bounces away from the reflective material without penetration and concomitant heat generation. Indeed, PVDF is not a fully transparent coating.

Therefore, the invention provides a thermal insulation material comprising an outer radiation reflecting surface, the radiation reflective surface comprising a coating comprising a transparent terpolymer comprising polytetrafluoroethylene monomers, methyl monomers and hydroxymethyl monomers. It was observed that such thermal insulation materials are not only suitable to be used below roofing surfaces, but can be used as roofing surface itself, as these materials are extremely resistant against the above- mentioned environmental conditions and are weathering and waterproof. As the term terpolymer intrinsically means that the polymer is built from three different monomers, the terpolymer attractively consists of polytetrafluoroethylene monomers, methyl monomers and hydroxymethyl monomers, i.e. having the following formula: 1 | it do re CT I. - i Vig 3 abr or wherein n, p, and q can have any natural number, and wherein all the three monomers are incorporated in the polymer. It is to be understood that the sequence of the monomers does not necessarily reflect the sequence as depicted in the formula (wherein a methyl monomer is followed by a polytetrafluoroethylene monomer, followed by a hydroxymethyl). Any sequence between the three building blocks (monomers) can present in the terpolymer, and it is also possible that the polymer comprises a stretch of a number of consecutive identical monomers, i.e. two or more consecutive polytetrafluoroethylene monomers. Two consecutive methyl monomers are also possible and would the form an ethyl monomer.

In fact, the only covalent bonds in the terpolymer are C-C, C-OH, C-F, C-H and C-F bonds. Accordingly, the terpolymer is free from vinyl groups and chlorine groups that are susceptible for radical formation.

In an attractive embodiment, the methyl monomers in the terpolymer are grouped in an even number, i.e. constituting ethyl monomers. In that case, the terpolymer comprises two consecutive methyl monomers, i.e. ethyl monomers, polytetrafluoroethylene monomers and hydroxymethyl monomers.

In another attractive embodiment, the terpolymer has a fluoridisation degree of 15 — 70 mol%, preferably of 25 — 60 mol% and most preferably of 30 — 45 mol% to provide for the envisaged radiation and weathering resistance. The fluoridisation degree can be determined e.g. by scanning electron microscopy, known to the skilled person.

Accordingly, the terpolymer preferably comprises 30 — 85 mol% alkane and hydroxymethyl monomers, more preferably 40 — 75 mol% and most preferably 55 — 70 mol%. The term ‘alkane monomers’ here means either methyl monomers or ethyl monomers. A propyl group would be understood as three consecutive methyl groups, whereas a butyl group would be understood as four consecutive methyl groups, or two consecutive ethyl groups, as the case may be. The skilled person is aware of how to determine the molar percentage of alkane and hydroxymethyl monomers in the terpolymer, and may use a method, such as titration, Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy and mass spectroscopy (MS).

The terpolymer preferably comprises 3 — 40 mol%, preferably 10 - 30 mol% hydroxymethyl monomers. In another embodiment, the terpolymer comprises up to 2 mols, more preferably up to 1 mol% hydroxymethyl monomers. Expressed differently, the terpolymer preferably has an OH number, or hydroxyl value, of 10 - 150 mg KOH /g terpolymer, preferably of 20 - 120 mg KOH/g terpolymer, more preferably of 30 - 100 mg KOH/g terpolymer, even more preferably of 30 - 60 mg KOH/g terpolymer, and still even more preferably of 50 — 55 mg KOH/g terpolymer. The hydroxyl value is defined as the number of milligrams of potassium hydroxide required to neutralize the acetic acid taken up on acetylation of one gram of the terpolymer. The hydroxyl value is a measure of the content of free hydroxyl groups in the terpolymer, expressed in units of the mass of potassium hydroxide (KOH) in milligrams {mg} equivalent to the hydroxyl content of one gram of the terpolymer. The analytical method used lo determine the hydroxyl value traditionally involves acetylation of the free hydroxy! groups of the terpolymer with acetic anhydride in pyridine solvent, After completion of the reaction, water is added, and the remaining unreacted acetic anhydride is converted to acetic acid and measured by titration with potassium hydroxide.

The above hydroxyl value, or content of hydroxymethyl monomers in the terpolymer renders the terpolymer soluble in a polar organic solvent, and allows for crosslinking of the polymer with a stable crosslinker, known in the art.

Suitable organic solvents are e.g. ketones and acetals, such as 2-butanon, ethylbenzene, cyclohexanone, butyl acetate, ethyl acetate ethanol, butanol or propanol, a saturated hydrocarbon solvent such as xylene or toluene, an alcohol solvent such as ethanol propanol or butanol.

The above numbers for fluoridisation degree, alkane and hydroxymethyl monomer content and hydroxyl value, clearly define the terpolymer by way of relative content of the different monomers.

The transparent terpolymer is preferably solvent-based, to allow application of the polymer onto the radiation reflective material by spraying or other known techniques. The majority of fluoropolymers are however hardly soluble in organic solvents. Perfluoroalkoxy

(PFA) has a high degree of transparency, but has a low solubility, rendering it impossible for application of thin layers onto a substrate. The hydroxyl groups of the terpolymer of the invention makes the terpolymer more readily soluble in organic solvents such as xylene, ethylbenzene and 2-butanon, also known as methylethylketone (MEK). The more hydroxyl 5 groups, the more soluble the polymer is. The terpolymers as described herein are very suitable in view of solubility, transparency, UV resistance and inertness for IR and visible light. Suitable terpolymers are e.g. Lamoral 100 — series.

The solubility makes the polymers particularly suitable to be coated on surfaces, e.g. by roll-to-roll converting/coating or any other suitable technique, known to the skilled person.

In another attractive embodiment, the coating further comprises a polyisocyanate, crosslinking the terpolymer. A polyisocyanate hardens, or cures, the coating by reacting with the hydroxyl groups to produce polyurea. By crosslinking the terpolymer, a coating of the envisaged qualities is obtained. Said crosslinking preferably occurs while the terpolymer is coated on the substrate surface, i.e. the thermal insulation material, therefore curing on the said substrate surface after application thereon.

The skilled person is aware of suitable polyisocyanates for use in crosslinking the terpolymer of the invention. Preferably, the polyisocyanate comprises a diisocyanate, more preferably an aliphatic diisocyanate. Polyisocyanates comprising double C=C bonds or cyclic structures are less preferred, as these are less stable and may lead to less weather durability of the cured terpolymer coating. Hexamethylene diisocyanate is one of the preferred aliphatic diisocyanates. Accordingly, a suitable diisocyanate is Lamoral C20 (Lamoral, The Netherlands).

In particular, the weight ratio between the fluoropolymer and the polyisocyanate, based on dry weight, is 5 - 25:1, preferably 10 - 20:1.

In an attractive embodiment, the crosslinked terpolymer of the thermal insulation material has a density of 0.9 — 1.4 g/m2. The glass transition temperature of the cured terpolymer is preferably 180 - 210°C.

Particularly, the coating of the article described herein has a thickness of 1 - 10 um, in particular of 2 - 5 um.

The radiation reflective surface preferably reflects at least 80% of the radiation (i.e. UV, visible light and IR). Such materials are suitable as reflective insulation materials. However, the radiation reflective surface preferably has a reflectivity for UV, visible light and IR of at least 90%, preferably at least 95%, 96%, 97%, 98%, 99% or even 100%.

The coating is impermeable for oxygen, vapour and water, and is therefore optimally suitable to be applied to a radiation reflective surface of an article according to the invention, wherein the radiation reflective surface is corrosion sensitive, such as a metal surface. The coating renders the substrate, in particular the metal weather and waterproof.

The radiation reflective surface preferably comprises a metal.

In an attractive embodiment, the article of the invention is a building element, in particular chosen from the group, consisting of roofing tiles, roofing panels, wall elements, thermal insulation panels, thermal insulation wool, such as stone wool or glass wool, in particular provided with a radiation reflective surface of e.g. metal. The thermal insulation material is preferably waterproof, in particular as a result of the terpolymer coating applied thereon.

In another aspect, the use of a transparent terpolymer as described above for coating an outer radiation reflective surface of thermal insulation material, in particular as described above is disclosed.

The invention further relates to a method for coating an outer radiation reflective surface with a terpolymer as defined herein, comprising the steps of a. preparing a 15 — 35 w/w% solution of a mixture of 1: 10 - 40 polyisocyanate : terpolymer on weight basis in an organic solvent; b. applying the mixture on the reflective surface; and c. allowing the mixture to cure on the reflective surface. A 15 — 30 w/w% solution is made by mixing, on weight basis, 1 weight part polyisocyanate with 10 to 40 weight parts of the terpolymer in a suitable solvent such as 2- butanon. To this end, both the polyisocyanate and the terpolymer may be provided as separate mixtures and combined together. The solutions can be in a high concentration and be diluted to the envisaged values. For example, the isocyanate can be provided as a 20 w/w% in 2-butanon, and the terpolymer can be provided in a concentration of 40 w/w®% in 2-butanon or ethyl benzene or xylene, and both can be mixed in a 1:10 ratio, resulting in a 34 w/w% solution that can be further diluted to 20 -25 w/w% in e.g. acetone. Such solution can optimally be used for spray application on envisaged surfaces.

The invention will now be further explained by way of the following non limiting examples.

Preparation of samples Terpolymers of tetrafluoroethylene monomers, methyl monomers and hydroxymethyl monomers as described above (Lamoral series 100, Lamoral Coatings, The Netherlands), as solution in methylethylketone, having a solids content of 40% and a density of 0.9-1.0 kg/l (at 20°C) is mixed with hexamethylene diisocyanate Lamoral C20 (Lamoral Coatings, The Netherlands) a solution in methylethylketone, having a solids content of 20% and a density of 0.8-0.9 kg/l (at 20°C), in a weight ratio of 10:1. This mixture was diluted with acetone to 15-30% solids. Several substrates were used, varying from plain aluminium foil (50 um thickness) and plain PET film.

Sheets having a size varying from DIN A4 (210 x 297 mm) to DIN A6 (105 x 148 mm) were cut from the above-mentioned samples and were placed on the rubber surface of a hand coater set (K101 Hand Coater, RK PrintCoat Instruments Ltd., UK). A set of K-bars (RK PrintCoat Instruments Ltd., UK) with a closed wound from the firm RK Printcoat instruments were used to apply desired coating weights in g/m.

When using K-bar no 2 with a closed wound wire diameter of 0.15 mm, the wet film deposit is approximately 12 um leading to a dry film deposit of approximately 3 um when using a solids content of 25%.

To remove the solvent, an air dryer with an outlet temperature of 80°C was used for one minute and the samples were afterwards placed in an oven at 80°C for 5 minutes.

In view of variation in applied coating thickness due to pressure, speed, solids etc. in the manual coating application, the actual coating thickness on several samples of a coated PET film was measured according to ISO 19840, wherein the coating thickness was measured with an Elcometer 456 Ferro layer thickness meter with a Ferro probe (iso 19840). The Elcometer measures the coating thicknesses on metal substrates with an accuracy of 1%. The thickness of coating and substrate was measured and compared with the thickness of the substrate to calculate the coating thickness, see table A.

Table A: correlation between theoretical and actual applied coating thickness Sample | average coating coating thickness | deviation deviation thickness(u) measured theory (Mu) (u) % according to ISO 19840 4 109 [1 B Fw [sme [wer The coated samples were stored at ambient temperature for 7 days to reach final cure.

UV, Visible and IR transmittance UV, visible and IR transmittance was measured by coating a polyester film as described above and measuring the transmittance with UV-VIS spectrophotometer LISR- 3100 (Shimadzu, Japan) with the settings shown in table B below.

The Polyester film was coated with several coating thicknesses of Lamoral 100 series + C20 as described above. Coating thickness measured was done according to Iso 19840 and Transmission curves obtained as in figure 1.

It can be concluded that the coating is UV stable and protects the film from UV impact, while the difference in IR transmission between a coated film versus an uncoated film is negligible. This means that the coating is inert for radiation from 400 nm and above (visible and IR).

Reflection — aluminium foil Reflection was measured by coating plain Aluminium foil (50 um) with Lamoral 100 + C20 series with a thickness of 3 um as described above and measuring the transmittance with UV-VIS spectrophotometer LISR-3100 (Shimadzu, Japan) with the settings shown in the table B. The reflection was measured and compared with a blanco uncoated aluminium foil sample. The reflection data, shown in figure 2, show that there is no significant difference in reflection over the full range from UV (300-400), visible (400-700) and Infrared (2700 nm) between coated and uncoated aluminium foil. This means that the coating does not disturb or interfere with solar radiation -especially the IR radiation - that is reflected from the aluminium foil. This means that the coating is an ideal radiant barrier coating, e.g. for keeping roofs cool by an optimized radiant reflection.

A similar reflection test was done with the above coated aluminium foil over the visible and infrared spectrum and compared with TPO (Versify™, Dow Chemical Company, US). The measurements were performed in conformity with the ASTM E903-96 standard on a Perkin Elmer Lambda 1050 in combination with the 150mm InGaAs Integrating Sphere at TNO, Netherlands. The measurements were performed in the 300 — 2500 nm range in steps of 5nm, see figure 4. The detector switch from InGaAs (NIR) to PMT (UV-Vis) occurred at 860nm. The lamp switch took place at 320nm. The baseline was set against a calibrated white Spectralon standard (barium sulphate).The reflection was measured by placing the samples facing the lamp.

It can be clearly seen from figure 4 that the reflectivity of TPO is low in the infrared spectrum, whereas the Lamoral coated aluminium as a reflectance of 95% or even more in this spectrum.

Table B settings UV-VIS spectophotometer

Wavelength Range (nm.): 200,00 to 1200,00 … Auto Sampling Interval: Disabled [Instrument Properties]

Instrument Type: UV-3600 Series MeasuringMode: Transmittance source Lamp: AO Light Source Change Wavelength: 29500nm DetectorUnit: External(2Detectors) Detector Change Wavelength: 850,00nm | Grating Change Wavelength: _850,00nm S/R Exchange: Normal

Stair Correction: Disable [Attachment Properties] Attachment: Nome | [Operation] Threshold: : 0,001 Average: Disabled [Sample Preparation Properties] Dilution: Additional Information: :

Acid corrosion test Several solutions of H:SO4 were prepared with a pH of 2, 3, 4, 5 by diluting a concentrated H2SO,4 solution (98%) with demineralised water. Coated aluminium foil as described above was contacted with vapour of the above solutions or brought in direct contact therewith as follows.

The acid solutions were kept in a glass container of 10 ml. The opening was covered with the aluminium foil. On top of the foil, a cap was placed to close the container tightly to avoid water or other molecules to evaporate during the test. For the vapour test, the containers were kept with the foil and lid up, allowing contact of the vapour of the acid solution with the foil. For the direct contact test, the containers were put upside down, bringing the foil in direct contact with the acid solution. This was done for a period of 4 days in an oven at 40°C. The results are shown in table C. Table C: Acid corrosion test coating type test type 3 4 5 Corrosion on scale 0 to 5 (O=none, 5=all the way through) Coated vapour 0 0 0 Droplet test Drops of a H2SO, solution having a pH of 1,64 were contacted with both uncoated aluminium foil, and coated as described above, having a coating thickness of 3 um. Already after 4 hours at ambient temperature, the uncoated foil was fully corroded and etched away while the coated sample was not corroded or etched even after 24 hours, see figure 3.

Claims

CONCLUSIONS

A thermal insulation material comprising an external radiation-reflecting surface, the radiation-reflecting outer surface comprising a coating comprising a transparent terpolymer of polytetrafluoroethylene monomers, methyl monomers and hydroxymethyl monomers.

The thermal insulation material of claim 1, wherein the terpolymer comprises polytetrafluoroethylene monomers, ethyl monomers and hydroxymethyl monomers.

Thermal insulation material according to claim 1 or 2, wherein the terpolymer has a fluorization degree of 15-70 mol%, preferably 25-60 mol% and most preferably 30-45 mol%.

Thermal insulation material according to any of the preceding claims, wherein the terpolymer comprises 30-85 mole% alkane and hydroxymethyl monomers.

Thermal insulation material according to any of the preceding claims, wherein the terpolymer comprises 3 - 40 mole%, preferably 10 - 30 mole% of hydroxymethyl monomers.

Thermal insulation material according to any of the preceding claims 1-4, wherein the terpolymer comprises up to 2 mole%, preferably up to 1 mole% of hydroxymethyl monomers.

Thermal insulation material according to any of the preceding claims, wherein the terpolymer has an OH number of 10 - 150 mg KOH / g terpolymer, preferably 20 - 120 mg KOH / g terpolymer, more preferably 30 - 100 mg KOH / g terpolymer, even more preferably 30-60 mg KOH / g terpolymer.

Thermal insulation material according to any of the preceding claims, wherein the terpolymer is cross-linked.

The thermal insulation material of claim 8, wherein the coating further comprises a polyisocyanate that cross-links the terpolymer.

The thermal insulation material of claim 9, wherein the polyisocyanate comprises diisocyanate.

The thermal insulation material of claim 10, wherein the diisocyanate comprises an aliphatic diisocyanate.

The thermal insulation material of claim 11, wherein the diisocyanate comprises hexamethylene diisocyanate.

Thermal insulation material according to any of the preceding claims, wherein the weight ratio between the terpolymer and the isocyanate, based on dry weight, is 5-25: 1.

Thermal insulation material according to any of the preceding claims 8-13, wherein the cross-linked terpolymer has a density of 0.9-1.4 g / m.

Thermal insulation material according to any of the preceding claims 8-14, wherein the cross-linked terpolymer has a glass transition temperature of 180-210 ° C.

Thermal insulation material according to any of the preceding claims, wherein the coating has a thickness of 1 - 10 µm.

Thermal insulation material according to claim 16, wherein the coating has a thickness of 2-5 m.

Thermal insulation material according to any of the preceding claims, wherein the radiation reflecting surface reflects at least 80% of the radiation.

The thermal insulation material of claim 18, wherein the radiation is IR radiation, visible light and UV radiation.

Thermal insulation material according to any of the preceding claims, wherein it is opaque to visible light.

A thermal insulation material according to any of the preceding claims, wherein the radiation reflecting surface is susceptible to corrosion.

A thermal insulation material according to any of the preceding claims, wherein the radiation reflecting surface comprises a metal.

23. Thermal insulation material according to any of the preceding claims, wherein the thermal insulation material is a building element.

24. Thermal insulation material according to claim 23, selected from the group consisting of roof tiles, roof plates, wall elements, thermal insulation plates and thermal insulation wool.

A thermal insulation material according to any of the preceding claims, wherein the thermal insulation material is waterproof.

Use of a transparent terpolymer as defined in any one of claims 1 to 15 for coating an externally radiation reflecting surface of a thermal insulation material.

The use of claim 26, wherein the radiation reflecting surface is defined in any of claims 16-25.

A method for coating an external radiation reflective surface as defined in any one of claims 16 to 25, comprising the steps of: a. Preparing a 15-35% strength by weight solution of a mixture of 10:40 polyisocyanate: terpolymer by weight in an organic solvent; b. Applying the mixture to the reflective surface; c. Allow the mixture to harden on the reflective surface.