WO2016078968A1

WO2016078968A1 - A method of shielding a substrate, a use of a paint composition for shielding a substrate, and a painted substrate

Info

Publication number: WO2016078968A1
Application number: PCT/EP2015/076206
Authority: WO
Inventors: Antonius Eijkenboom; Hermanus IJDEMA
Original assignee: Pp&C Technology B.V.
Priority date: 2014-11-17
Filing date: 2015-11-10
Publication date: 2016-05-26
Also published as: NL2013823B1; NL2013823A

Abstract

A method of shielding a substrate comprising a source of thoron. The method comprises applying a layer of a paint composition adjacent to the substrate. The paint composition comprises an aqueous emulsion of a non-cross-linkable polymer,and a filler comprising inorganic microbeads; a use of the paint composition for shielding the substrate; a shielded substrate comprising the substrate and adjacent to the substrate a hardened paint layer which is obtainable by hardening a layer of the paint composition.

Description

A METHOD OF SHIELDING A SUBSTRATE,

A USE OF A PAINT COMPOSITION FOR SHIELDING A SUBSTRATE,

AND A PAINTED SUBSTRATE The invention relates to a method of shielding a substrate which substrate comprises a source of thoron. The invention also relates to a use of the paint composition for shielding the substrate. The invention also relates to a shielded substrate comprising the substrate and a hardened paint layer.

Buildings in which people live or work may comprise walls, ceilings or floors which have been constructed from building materials having, for example, a mineral origin. Examples of building materials having a mineral origin are concrete, rock and gypsum. Other building materials of relevance to this invention include, for example, loam, clay, turf, or dung. Such building materials may include small amounts of naturally occurring elements which have a high atomic number and which show a slow radioactive decay with formation of various decay products. When such decay products are gaseous, they may be emitted from the walls, ceilings or floors into the interior of the buildings. Radon and thoron are such gaseous decay products. Radon and thoron are radioactive isotopes.

The emission of radioactive isotopes into the interior of buildings is considered to represent a health risk to people who live or work in such interiors. In particular the emission of thoron is considered dangerous, because thoron has a half-life of about 55 seconds, and may therefore decay to a substantial extent before it is removed from the interior by ventilation, whether natural or forced ventilation. Radon has a half-life about 3.8 days and may be effectively removed from the interior before substantial decay.

There is a desire to find a method of preventing emissions of thoron from walls, ceilings or floors into the interior of buildings. The present invention provides a method of shielding a substrate comprising a source of thoron, which method comprises applying a layer of a paint composition adjacent to the substrate, wherein the paint composition comprises

- an aqueous emulsion of a non-cross-linkable polymer, and

- a filler comprising inorganic microbeads.

The present invention also provides a use of a paint composition for shielding a substrate comprising a source of thoron, wherein the paint composition comprises

- an aqueous emulsion of a non-cross-linkable polymer, and

- a filler comprising inorganic microbeads.

The present invention also provides a shielded substrate comprising

- a substrate comprising a source of thoron, and

- adjacent to the substrate a hardened paint layer which is obtainable by hardening a layer of a paint composition comprising an aqueous emulsion of a non-cross-linkable polymer and a filler comprising inorganic microbeads.

Without wishing to be bound by theory, it is believed that the hardened paint layer provides a barrier to thoron to such an extent that a considerable portion, if not all, of the thoron decays inside the hardened paint layer before it has reached the interior of the building. In this way substantial, if not complete, shielding in respect of thoron is achieved. It is an advantage of the invention that it provides for a hardened paint layer which is sufficiently permeable to moisture from the substrate, with relatively little detriment to the shielding effect in respect of thoron.

The invention may be applied in association with any building in which people spend time, for example, for living or working. Examples of such buildings are domestic houses, offices, factories, workshops and hospitals. The substrate may be any wall, floor or ceiling of such a building, or a portion of such a wall, floor or ceiling. In particular, the substrate may be adjacent to the interior of the building. The substrate may include separation walls, exterior walls and inner walls of cavity walls.

The substrate comprises a source of thoron. Thoron may be designated ²²⁰ n. Sources of thoron may be thorium and/or radium. The substrate may be based on, for example, gypsum, concrete, rock, loam, clay, turf, or dung. The substrate may comprise, for example, blocks, board or plaster. Useful substrates may be formed from, or may comprise, gypsum blocks, gypsum board, gypsum plaster, concrete slabs, or concrete blocks. Typically the substrate as such may exhibit a thoron exhalation rate, expressed in mBq/(m².s), of at least 0.5 mBq/(m².s), in particular at least 1 mBq/(m².s), more in particular at least 2 mBq/(m².s), typically at least 4 mBq/(m².s), and more typically at least 6 mBq/(m .s). In the normal practice of this invention, the substrate as such may frequently exhibit a thoron exhalation rate of at most 5000 mBq/(m².s), in particular at most 2000 mBq/(m².s), more in particular at most 1000 mBq/(m².s), typically at most 800 mBq/(m².s), and more typically at most 600 mBq/(m².s).

As used herein, thoron exhalation rate is as measured by the method known from G. De With, P. De Jong and A. Rottger, "Measurement of thoron exhalation rates from building materials", Health Physics Society, 107 (3) pp. 206 - 212 (2014), wherein the method involves conditioning four 0.15 x 0.15 x 0.15 m³ test samples at 20 °C and 50 % relative humidity as described therein, and arranging the four conditioned samples in the exhalation chamber for exhalation rate measurement under the Standard test conditions as defined therein.

The invention provides for applying a layer of a paint composition adjacent to the substrate. The layer of the paint composition may be applied between the interior of the building and the substrate. Typically, the layer of the paint composition may applied onto the substrate. As an alternative, it may be that the substrate has been covered with a finishing layer, in which case the layer of the paint composition may applied onto the finishing layer, so that the finishing layer is a layer intermediate between the substrate and the layer of the paint composition. Examples of such finishing layers may be wall paper, or wood panelling. It is conceivable that the paint composition is applied in accordance with this invention after the relevant wall, floor or ceiling has been constructed. It is also conceivable that the paint composition is applied before the wall, floor or ceiling has been constructed, for example the paint composition is applied onto gypsum blocks, gypsum board, concrete slabs, or concrete blocks after manufacture of the blocks, the board or the slabs before they are used in the construction of the wall, floor or ceiling.

The paint composition comprises an aqueous emulsion of a non-cross- linkable polymer. Because, the polymer is a non-cross-linkable polymer, the hardening process is basically a physical process comprising the evaporation of water present in the paint composition.

Examples of suitable non-cross-linkable polymers for use in this invention are poly(alkyl acrylate)s, polyurethanes, and poly(alkyl

methacrylate)s. Preferred non-cross-linkable polymers are poly(vinyl acetate)s and, in particular, ethylene/vinyl acetate copolymers.

Preferably, the ethylene/vinyl acetate copolymers comprise monomer units based on vinyl acetate in a quantity of at least 60 %w, more preferably at least 70 %w, and preferably at most 98 %w, more preferably at most 96 %w, based on the weight of the copolymer. Preferably, the ethylene/vinyl acetate copolymers comprise monomer units based on ethylene in a quantity of at least 2 %w, more preferably at least 4 %w, and preferably at most 40 %w, more preferably at most 30 %w, based on the weight of the copolymer. Other monomer units, for example based on propylene, styrene, an alkyl acrylate, or acrylonitrile, may be present, typically in a quantity of at most 10 %w, more typically at most 5 %w, based on the weight of the copolymer. The minimum film forming temperature of the polymer may typically be at least -2 °C, more typically at least 3 °C, and preferably at least 10 °C. In the normal practice of this invention, the minimum film forming temperature of the polymer may typically be at most 20 °C, and more typically at most 15 °C. The minimum film forming temperature may also be referred to by the abbreviation "MFFT". As used herein, the minimum film forming

temperature is as measured according to UNI 8490-14.

The polymer for use in this invention may be supplied in the form of an aqueous emulsion. Such emulsions may comprise water in a quantity in the range of from 20 to 80 %w, more typically from 30 to 70 %w, in particular from 40 to 60 %w, relative to the weight of the aqueous emulsion. Such emulsions may comprise the polymer in a quantity in the range of from 20 to 80 %w, more typically from 30 to 70 %w, in particular from 40 to 60 %w, relative to the weight of the aqueous emulsion. For example, an aqueous emulsion of an ethylene/vinyl acetate copolymer is available from WACKER CHEMIE A.G., Munich, Germany, as VINNAPAS 401 dispersion (WACKER and VINNAPAS 401 are trademarks), from VINAVIL S.p.A., Milan, Italy, as VINAVYL EVA 04 emulsion and VINAVYL EVA 09 emulsion (VINAVIL, VINAVYL EVA 04 and VINAVYL EVA 09 are trademarks), or from

CELANESE Campany as VINAMUL 1404 emulsion or MOWILITH DM 105 emulsion (CELANESE, VINAMUL 1404 and MOWILITH DM 105 are trademarks). For example, an aqueous emulsion of a poly(vinyl acetate) is available from CELANESE Company, as VINAMUL 8481 emulsion.

In accordance with the invention, the paint composition comprises, in addition to the aqueous emulsion of the polymer, a filler comprising inorganic microbeads.

The inorganic microbeads for use in this invention may comprise hollow or solid spherical beads. Typically they have a particle size

distribution, such that - at most 10 %v of the inorganic microbeads represents beads having a diameter of at most 2 μηι, preferably at most 1.5 μηι and more preferably at most 1 μηι;

- at least 50 %v represents beads having a diameter of at most 8 μηι, preferably at most 7 μηι and more preferably at most 6 μηι; and

- at least 90 %v represents beads having a diameter of at most 30 μηι, preferably at most 27 μηι and more preferably at most 24 μηι.

The particle size distribution of the inorganic microbeads as specified herein is as it can be measured according to ASTM F751-83 (1997), typically by using a MULTISIZER 3 COULTER COUNTER analyser, available from Beckman Coulter Nederland B.V., Woerden, The Netherlands (MULTISIZER 3 COULTER COUNTER is a trademark).

The inorganic microbeads may be available and suitably applied in the invention as a gray material, or, preferably, as a white material.

The inorganic microbeads for use in this invention are known in the art. They may be, for example, ceramic microbeads or glass microbeads. Ceramic microbeads are generally crystalline materials, whereas glass microbeads are generally non-crystalline materials. The ceramic microbeads may be commercially available from 3M Company, St Paul, Minnesota, USA (3M is a trademark), under the name ZEEOSPHERES microbeads or

MICROPSHERE microbeads (ZEEOSPHERES and MICROSPHERE are trademarks). Preferred types of ZEEOSPHERES microbeads are designated G-400. Preferred types of MICROSPHERES microbeads are designated W- 610 and W-210. Alternatively, the ceramic microbeads may be hollow alumina silicate based materials, known as cenospheres, which may be available from Plomp Mineral Services B.V., Sleeuwijk, The Netherlands. Hollow glass based microbeads may be commercially available from 3M Company, St Paul, Minnesota, USA, under the trademark 3M GLASS

BUBBLES. In addition to inorganic microbeads, the filler may comprise mica. The use of a filler comprising mica as an additional component may be preferred as paint compositions comprising mica have a relatively high viscosity so that less thickening agent, if any, may be used. The mica may be employed as an additional component substantially without detriment to the thoron shielding capability of the hardened paint layer.

The mica component which may be present in the filler is typically a phyllosilicate mineral having a layered or platy structure. The particle size distribution may be assessed by means of a sieve analysis. For use in this invention, the mica component comprises typically a particle size distribution such that

- at most 0.1 %w of the particles, more typically in the range of from 0.001 to 0.05 %w of the particles, is retained on a 100 MESH sieve;

- using the particles passing the 100 MESH sieve, at most 10 %w of the particles, more typically in the range of from 0.05 to 8 %w of the particles, is retained on a 200 MESH sieve;

- using the particles passing the 200 MESH sieve, at most 15 %w of the particles, more typically in the range of from 0.05 to 12 %w of the particles, is retained on a 325 MESH sieve; and

- more than 80 %w of the particles, preferably in the range of from 85 to 100 %w of the particles, can pass the 325 MESH sieve,

wherein %w is relative to the total weight of the particles subjected to the sieve analysis, and the MESH sieves and the sieve analysis are according to ASTM E1 1.

Suitable mica components for use in this invention are known in the art. Preferably water ground mica 325 mesh may be employed, which is commercially available from Mahlwerk Neubauer-Friedrich Geffers GMBH., Hamburg, Germany, or from IME YS S.A., Paris, France. In addition to inorganic microbeads and optionally mica, the paint composition may comprise other filler materials, such as diatomaceous earth, talc, chalk, or one or more kinds of calcium alumina silicates, such as feldspar. The total quantity of inorganic microbeads and mica, if any, in the filler may typically be at least 40 %w, more typically at least 50 %w, relative to the weight of the filler.

As the paint composition comprises an aqueous emulsion of a polymer, the paint composition comprises water. The paint composition may comprise one or more diluents in addition to water, such as glycols, for example propylene glycol or butylene glycol; glycol ethers, for example propylene glycol phenyl ether, commercially available from Dow Chemical Company under the trademark DOWANOL PPh glycol ether (DOWANOL is a trademark); and ester alcohols, for example 2,2,4-trimethyl-l,3-pentanediol monoisobutyrate, which is commercially available as EASTMAN TEXANOL Ester Alcohol (EASTMAN and TEXANOL are trademarks). Typically, such diluents have a boiling point of at least 150 °C, preferably at least 200 °C, and more preferably at least 220 °C, when measured at a pressure of 0.1 MPa. Such high-boiling diluents have advantageously a relatively low volatility. Typically, such diluents have a boiling point of at most 350 °C, and preferably at most 300 °C, when measured at a pressure of 0.1 MPa.

The paint composition may or may not additionally comprise one or more pigments, surface active components, dispersants, stabilisers, thickening agents, anti foam components, components for pH control, and/or

preservatives, such as anti-bacterial components and fungicides. Dispersants may include dispersants which are available from Elementis Specialties, East Windsor, New Jersey (USA) under the trademark NUOSPE SE W-30.

Thickening agents may include, for example, KELZAN S thickening agent (KELZAN is a trademark) from C P KELCO, Genk, Belgium. Preservatives may include 5-chloro-2-methyl-2H-isothiazol-3-one and/or 2-methyl-2H- isothiazol-3-one, which are available as PREVENTOL preservatives from LANXESS Company, New Delhi, India (LANXESS and PREVENTOL are a trademarks), or as MERGAL K14 preservative from TROY Corporation, Florham Park, New Jersey (USA) (MERGAL K14 and TROY are a trademarks), or as KATHON LX 150 preservative from DOW CHEMICAL Company (KATHON LX150 and DOW CHEMICAL are a trademarks).

The quantity of the various components in the paint composition may be selected within wide ranges. Suitably, the polymer may be present in the paint composition in a quantity in the range of from 10 %w to 40 %w, in particular in the range of from 15 %w to 35 %w, relative to the weight of the paint composition. Water may be present in the paint composition in a quantity in the range of from 10 %w to 40 %w, in particular in the range of from 15 %w to 35 %w, on the same basis. The inorganic microbeads and mica, if any, may be present in the paint composition in a total quantity in the range of from 10 %w to 80 %w, in particular in the range of from 15 %w to 70 %w, on the same basis. The weight ratio of the total quantity of the inorganic microbeads and mica, if any, in the paint composition to the quantity of polymer in the paint composition may typically be in the range of from 0.3 : 1 to 5 : 1, in particular in the range of from 0.4 : 1 to 4 : 1, more in particular in the range of from 0.5 : 1 to 3 : 1. Diluents may or may not be present in the paint composition in a total quantity in the range of from 0 %w to 20 %w, in particular in the range of from 0.1 %w to 15 %w, on the same basis. Fillers, additional to the inorganic microbeads and mica, if any, may or may not be present in the paint composition in a total quantity in the range of from 0 %w to 30 %w, in particular in the range of from 1 %w to 20 %w, on the same basis. Each one of the one or more surface active components, dispersants, stabilisers, thickening components, anti foam components, components for pH control, and preservatives may be present in the paint composition in a quantity in the range of from 0 %w to 5 %w, in particular in the range of from 0.1 %w to 3 %w, on the same basis. Pigments may or may not be present in the paint composition in a total quantity in the range of from 0 %w to 10 %w, in particular in the range of from 0.1 %w to 8 %w, on the same basis.

The paint composition may be prepared by mixing the components, typically by using a high-speed mixer. Additionally, a pebble mill or a ball mill may be employed for homogenizing the composition and/or decrease the particle size. If desired, when an aqueous polymer emulsion is used, water may be added additional to the water already present in the emulsion.

The paint composition may be formed into a layer of the paint composition adjacent to the substrate in any suitable manner. The paint composition may be applied by using a brush or a roller, or the paint composition may be applied by spraying. The hardened paint layer is obtained by hardening the paint composition, as described hereinbefore. The thickness of the layer of the paint composition may be in the range of from 50 to

250 μηι, when measured after drying. One or more of such layers may be applied.

The invention will now be illustrated by means of the following non- limiting working examples.

EXAMPLE 1 (according to the invention)

A paint composition is prepared as follows. The paint composition comprises ethylene/vinyl acetate copolymer as a polymer, which is employed as a polymer emulsion comprising 50 %w polymer and 50 %w water,

ZEEOSPHE ES G-400 microbeads obtained from 3M Company

(ZEEOSPHERES and 3M are trademarks) as ceramic microbeads, 2,2,4- trimethyl-l,3-pentanediol monoisobutyrate as a diluent, NEOSPERSE W-30 dispersant (NEOSPERSE is a trademark) as a dispersant, PREVENTOL preservative (PREVENTOL is a trademark), and additional water. The polymer emulsion is stirred using a high-speed mixer, while the other components are added. The final composition is as specified in Table I.

Samples of the paint composition are applied to 0.15 x 0.15 x 0.15 m³ blocks of gypsum comprising a source of thoron, using a roller, and air dried, to form about 90 - 95 μηι thick hardened paint layers. After storage at ambient conditions for three days and for four months, the blocks of gypsum covered with the hardened paint are subjected to thoron exhalation rate measurements as defined hereinbefore.

Separately, samples of the paint composition are applied to paper sheets of LENETA standard paper type 3NT-4 Regular Bond, available from LENETA Company, Inc., Mahwah, New Jersey (USA) (LENETA is a trademark), using a bar coater, and air dried, to form 100 μηι thick hardened paint layers. These coated paper sheets are used for water vapour permeability measurements according to ASTM F- 1249- 13 using a PERMATRAN-W Model 3/61 test system (PERMATRAN-W is a trademark) available from MOCON, Inc., Minneapolis, Minnesota (USA).

EXAMPLE 2 (according to the invention)

EXAMPLE 1 was repeated, except that the paint composition comprised mica as an additional component. The results are provided in Table I.

EXAMPLE 3 (according to the invention)

EXAMPLE 1 was repeated, except that the paint composition comprised titanium dioxide white pigment and KELZAN S thickening agent (KELZAN S is a trademark) as additional components. The results are provided in the Table.

EXAMPLE 4 (not according to the invention, for comparison)

Thoron exhalation rate measurements and water vapour permeability measurements were carried out on uncoated gypsum blocks and uncoated paper sheets, respectively. The results are provided in Table I. Table

EXAMPLE 5 (according to the invention)

A paint composition was prepared as follows. The paint composition comprised VINAVYL EVA 04 ethylene/vinyl acetate copolymer as the polymer, which was employed as a polymer emulsion comprising 50 %w polymer and 50 %w water (VINAVYL EVA 04 is a trademark), 2,2,4- trimethyl-l,3-pentanediol monoisobutyrate as the diluent, MICROSPHERES W-410 microbeads obtained from 3M Company (MICROSPHERES and 3M are trademarks) as a filler, NEOSPERSE W-30 dispersant (NEOSPERSE is a trademark) as the dispersant, PREVENTOL preservative (PREVENTOL is a trademark) as the preservative, KELZAN S thickening agent (KELZAN is a trademark) as the thickening agent, and additional water. The polymer emulsion was stirred using a high-speed mixer, while the other components were added. The final composition was as specified in Table II.

Samples of the paint composition were applied to 0.15 x 0.15 x 0.15 m³ blocks of gypsum comprising a source of thoron, using a roller, and air dried, to form about 95 μηι thick hardened paint layers. After storage at ambient conditions for three days and for four months, the blocks of gypsum covered with the hardened paint were subjected to thoron exhalation rate measurements as defined hereinbefore. The results were as provided in Table II, which provides the reduction in the thoron exhalation rate relative to the thoron exhalation rate found for uncoated gypsum blocks.

Separately, samples of the paint composition were applied to paper sheets of LENETA standard paper type 3NT-4 Regular Bond, available from LENETA Company, Inc., Mahwah, New Jersey (USA) (LENETA is a trademark), using a bar coater, and air dried, to form 90 μηι thick hardened paint layers. These coated paper sheets were used for water vapour permeability measurements according to ASTM F- 1249- 13 using a

PERMATRAN-W Model 3/61 test system (PERMATRAN-W is a trademark) available from MOCON, Inc., Minneapolis, Minnesota (USA). The results were as provided in Table II. Table II provides the reduction in the thoron exhalation rate (Y in %), relative to the thoron exhalation rate found for uncoated gypsum blocks, which is as calculated by using the mathematical formula

Y = (l - X/A) x 100,

wherein X represents the thoron exhalation rate of the sample tested (in mBq/(m².s)), and A represents the thoron exhalation rate of uncoated gypsum block (in mBq/(m .s)).

EXAMPLE 6 (according to the invention)

EXAMPLE 5 was repeated, except for the difference that the paint composition comprised IME YS WG 325 mica (IMERYS WG 325 is a trademark) as an additional component. Samples of the paint composition were applied to the blocks of gypsum to form about 90 μηι thick hardened paint layers. The results are provided in Table II.

EXAMPLE 7 (not according to the invention, for comparison)

EXAMPLE 5 was repeated, except for the difference that the addition of mica was omitted. Samples of the paint composition were applied to the blocks of gypsum to form about 98 μηι thick hardened paint layers. The results are provided in Table II.

EXAMPLE 8 (not according to the invention, for comparison)

EXAMPLE 4 was repeated. The results are provided in Table II.

Table II

The EXAMPLES demonstrate that the application of this invention in association with a source of thoron leads to a significantly reduced

concentration of thoron in the air present in an area having a wall, ceiling or floor comprising a source of thoron.

Claims

C L A I M S

1. A method of shielding a substrate, which method comprises applying a layer of a paint composition adjacent to the substrate, wherein the substrate comprises a source of thoron and the paint composition comprises

- an aqueous emulsion of a non-cross-linkable polymer, and

- a filler comprising inorganic microbeads.

2. A method as claimed in claim 1, wherein the non-cross-linkable polymer comprises an ethylene/vinyl acetate copolymer.

3. A method as claimed in claim 1 or 2, wherein the ethylene/vinyl acetate copolymer comprises monomer units based on vinyl acetate in a quantity in the range of from 60 %w to 98 %w, in particular in the range of from 70 %w to 96 %w, based on the weight of the copolymer, and comprises monomer units based on ethylene in a quantity in the range of from of 2 %w to 40 %w, in particular in the range of from 4 %w to 30 %w, based on the weight of the copolymer.

4. A method as claimed in any of claims 1 - 3, wherein the non-cross-linkable polymer has a minimum film forming temperature of at least -2 °C, in particular at least 3 °C, and more in particular at least 10 °C, and at most 20 °C, in particular at most 15 °C, wherein the minimum film forming temperature is as measured according to UNI 8490-14.

5. A method as claimed in any of claims 1 - 4, wherein the paint composition comprises the non-cross-linkable polymer in a quantity in the range of from 10 %w to 40 %w, in particular in the range of from 15 %w to 35 %w, relative to the weight of the paint composition.

6. A method as claimed in any of claims 1 - 5, wherein the inorganic microbeads comprise solid spherical beads.

7. A method as claimed in claim 6, wherein the solid spherical beads comprise ceramic microbeads.

8. A method as claimed in any of claims 1 - 7, wherein the inorganic microbeads comprise a particle size distribution, such that

- at most 10 %v of the inorganic microbeads represents beads having a diameter of at most 2 μηι, in particular at most 1.5 μηι and more in particular at most 1 μηι;

- at least 50 %v represents beads having a diameter of at most 8 μηι, in particular at most 7 μηι and more in particular at most 6 μηι; and

- at least 90 %v represents beads having a diameter of at most 30 μηι, in particular at most 27 μηι and more in particular at most 24 μηι, wherein the particle size distribution is as it can be measured according to ASTM F751-83 (1997).

9. A method as claimed in any of claims 1 - 8, wherein the paint composition comprises inorganic microbeads in a total quantity in the range of from 10 %w to 80 %w, in particular in the range of from 15 %w to 70 %w, relative to the weight of the paint composition.

10. A method as claimed in any of claims 1 - 9, wherein the paint composition additionally comprises inorganic microbeads, in particular ceramic

microbeads.

1 1. A method as claimed in any of claims 1 - 10, wherein the source of thoron is thorium or radium.

12. A method as claimed in any of claims 1 - 1 1, wherein the substrate is based on gypsum, concrete, rock, loam, clay, turf, or dung.

13. A method as claimed in any of claims 1 - 12, wherein the substrate exhibits a thoron exhalation rate of at least 0.5 mBq/(m .s), in particular at least 1 mBq/(m².s), more in particular at least 2 mBq/(m².s), typically at least 4 mBq/(m².s), and more typically at least 6 mBq/(m².s).

14. A method as claimed in any of claims 1 - 13, wherein the substrate exhibits a thoron exhalation rate of at most 5000 mBq/(m .s), in particular at most 2000 mBq/(m².s), more in particular at most 1000 mBq/(m².s), typically at most 800 mBq/(m².s), and more typically at most 600 mBq/(m².s).

15. A use of a paint composition for shielding a substrate, wherein the substrate and the paint composition are as defined in any of claims 1 - 14.

16. A shielded substrate comprising

- a substrate as defined in any of claims 1 - 14, and

- adjacent to the substrate a hardened paint layer which is obtainable by hardening a layer of a paint composition as defined in any of claims 1 - 14.