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WO2020044027A1 - Phosphorescent coating and inspection method - Google Patents

Phosphorescent coating and inspection method Download PDF

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Publication number
WO2020044027A1
WO2020044027A1 PCT/GB2019/052383 GB2019052383W WO2020044027A1 WO 2020044027 A1 WO2020044027 A1 WO 2020044027A1 GB 2019052383 W GB2019052383 W GB 2019052383W WO 2020044027 A1 WO2020044027 A1 WO 2020044027A1
Authority
WO
WIPO (PCT)
Prior art keywords
coating
coating composition
wavelengths
range
wavelength
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/GB2019/052383
Other languages
French (fr)
Inventor
William Robert Cooper
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
LUMINOUS TECHNOLOGIES Ltd
Luminous Tech Ltd
Original Assignee
LUMINOUS TECHNOLOGIES Ltd
Luminous Tech Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by LUMINOUS TECHNOLOGIES Ltd, Luminous Tech Ltd filed Critical LUMINOUS TECHNOLOGIES Ltd
Publication of WO2020044027A1 publication Critical patent/WO2020044027A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
    • B05D5/06—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain multicolour or other optical effects
    • B05D5/065—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain multicolour or other optical effects having colour interferences or colour shifts or opalescent looking, flip-flop, two tones
    • 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
    • C09D5/22—Luminous paints
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/0838—Aluminates; Silicates
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/54—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing zinc or cadmium
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/56—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing sulfur
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7706—Aluminates
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/77064—Aluminosilicates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D2201/00—Polymeric substrate or laminate
    • B05D2201/02—Polymeric substrate
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D2601/00—Inorganic fillers
    • B05D2601/02—Inorganic fillers used for pigmentation effect, e.g. metallic effect
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/59—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing silicon
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/59—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing silicon
    • C09K11/592—Chalcogenides
    • C09K11/595—Chalcogenides with zinc or cadmium
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/61—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing fluorine, chlorine, bromine, iodine or unspecified halogen elements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G01N21/645—Specially adapted constructive features of fluorimeters
    • G01N21/6456—Spatial resolved fluorescence measurements; Imaging

Definitions

  • the invention relates to a phosphorescent coating composition and a method of inspecting a surface to which the coating has been applied.
  • the surfaces of industrial articles such as those of composite structures, metallic surfaces, articles made of plastics etc. may be provided with protective coatings.
  • the performance of such coatings, and thus the performance or working lifetime of the underlying surface, may rely on the quality of the protective coating and of its initial application.
  • a protective coating may be less effective or may prematurely degrade if it is unevenly applied or if it is discontinuous, or if the underlying surface has not been suitably prepared.
  • Protective coatings may therefore require inspection, to assess their integrity. This may be required not only during or after initial application, but also during the lifetime of the coated surface.
  • damage to a surface coating may be caused by underlying structural failure, and the manner or pattern of coating damage can yield vital information.
  • One approach to facilitate the inspection of protective coatings is to dope the coating with a luminescent dye or pigment, for example as described in WO02/28973 of Luminous
  • luminescent“inspection coatings” may also be used as a primer or undercoat, whereby visible luminescence is indicative of gaps in a further top coat.
  • a coating composition having a non-volatile component comprising particulate material in an amount of 10wt% or less of the non-volatile component, wherein at least 80wt% particulate material is phosphorescent pigment.
  • a relatively low total particulate content gives rise to commensurately low detrimental impact, or essentially no detrimental impact, on the performance of the coating formulation (as regards for example flow characteristics, shelf life, wettability, surface adhesion and the like); and of the resulting coating on a surface (durability, longevity etc.).
  • a high proportion of the particulate material is phosphorescent pigment and, when excited, the non-phosphorescent particulate material causes only limited scattering and/or absorption of phosphorescence emitted by the phosphorescent pigment.
  • the coating composition may accordingly be used to form a coating from which phosphorescence can be observed for a longer period than conventional inspection coatings.
  • non-volatile component we refer to the components which remain when the coating composition has been applied to a surface and formed into a coating, for example by drying, polymerising, curing and/or setting.
  • the term does not include components such as solvents or curing/polymerisation reaction products, flow agents and the like, which may evaporate in use. That is to say, the coating composition results in a coating having a total particulate content, and phosphorescent pigment content as disclosed herein. In some cases, all or substantially all (e.g. 95wt%, 98wt%, 99wt% or more) of the coating composition is non volatile.
  • the coating composition may have a non-volatile component with a total particulate content of 8wt% or less, or 5wt% or less.
  • the coating composition may have a non-volatile component comprising between 1 and 10wt%, or between 1 and 8wt%, or between 1 and 6wt%, or 1 and 5wt% or particulate material.
  • the coating composition may have a non volatile component comprising between 2 and 8wt% or 2 and 6wt% of particulate material.
  • At least 85wt%, 90wt%, 95wt%, 98wt% or 99wt% of the particulate material may be phosphorescent pigment.
  • the particulate material of the coating composition may consist essentially of phosphorescent pigment.
  • pigment we refer to a particulate material which is substantially insoluble in the remaining components of the coating composition.
  • a dye is a soluble material and dyes are typically provided in solution in coating compositions. Most dyes are based on organic or organometallic compounds.
  • Phosphorescent pigment is preferred in the present invention since it is less prone to migration into and leaching from the resulting coating and, for inorganic phosphors in particular, less prone to decomposition over time.
  • Pigment (including the phosphorescent pigment) is present in the coating composition to modify the optical properties of the resulting coating.
  • a pigment may selectively absorb or scatter one or more, or a range of wavelengths of light and thereby impart a colour to the coating composition.
  • a phosphorescent pigment absorbs and emits light.
  • a phosphorescent pigment may typically absorb light at a first wavelength or range of wavelengths and emit light at a second wavelength or range of wavelengths.
  • phosphorescence i.e. light emitted by a phosphorescent material following absorption of light
  • phosphorescence is associated with a so-called“forbidden” quantum mechanical transition from an excited state to a lower energy state, following absorption of light from the same or another lower energy resulting in an“allowed” transition to an initial excited state.
  • the coating composition may comprise a suspension of or a dispersion of the
  • phosphorescent pigment (and/or any other pigment present).
  • the phosphorescent pigment may comprise an insoluble inorganic compound, such as a sulphide (e.g. zinc, cadmium, calcium), a silicate or aluminosilicate (e.g. of an alkaline earth element such as calcium, strontium, magnesium etc.) or a fluorite (e.g. of an alkaline earth element).
  • a sulphide e.g. zinc, cadmium, calcium
  • silicate or aluminosilicate e.g. of an alkaline earth element such as calcium, strontium, magnesium etc.
  • a fluorite e.g. of an alkaline earth element
  • Such materials may be doped (typically to an amount of around 1-50 ppm, or around 5 ppm or 10 ppm) with an element to act as an activator.
  • sulphides may be doped with copper or silver; europium doped aluminates or samarium doped fluorites are also known phosphorescent
  • Non-stoichiometric materials in the same general classes of materials are also known to phosphoresce.
  • the phosphorescent material or materials can be selected for a particular purpose, depending on the environmental conditions that the coating is intended to withstand, the required phosphorescent lifetime of the pigment material, the intensity of phosphoresce, chemical compatibility with the coating composition and the like.
  • the aforementioned are provided as examples only and phosphorescent pigment materials having the required phosphorescent properties for a particular purpose can be readily selected by the skilled person.
  • sulphide-based phosphorescent pigments such as zinc sulphide based pigments
  • these materials are readily available in small (ca. 15 micron) particle size and have good water-tolerance.
  • aluminates/aluminosilicates such as strontium aluminates may be used.
  • the invention is not limited to inorganic phosphorescent pigment, and the phosphorescent pigment may include an organic material which is insoluble in the coating composition, or a phosphorescent dye-impregnated or dye-stained particulate/ powered solid.
  • Suitable particulate solids include alumina, silica, titanium oxide, a zeolite or the like.
  • the coating composition may comprise one or more types of phosphorescent pigment.
  • the phosphorescent pigment may have an average particle size of less than or around 500 microns, 300 microns or 150 microns.
  • the average particle size may be between around 0.01-500 microns, or 0.01 to 300 microns or 0.01 to 150 microns, or 0.01 to 50 microns, or 0.01 to 20 microns.
  • the average particle size may for example be around 10-15 microns.
  • each may have the same, or a different average particle size or particle size distribution.
  • the total particulate content of the coating composition may comprise one or more particulate materials other than phosphorescent pigment.
  • Such particulate material may include one or more of; a further non-phosphorescent pigment, a filler, a sacrificial material such as particles of a metallic material (e.g. zinc), an anti-fouling material (present to impart a surface texture or chemical properties to the final coating which supresses fouling); and the like. Some particulate materials may perform more than one of these functions.
  • the particulate material may comprise at least 85wt%, 90wt%, 95wt%, 98wt% or 99wt% pigment (including said phosphorescent pigment).
  • the particulate material present in the coating composition may consist essentially of pigment.
  • the coating composition may have a non-volatile component comprising 10wt% or less of pigment, wherein at least 80wt% of the pigment is phosphorescent pigment.
  • the coating composition may be curable; i.e. it may undergo a chemical curing reaction at ambient temperature, or exposure to heat and/or light (e.g. UV light).
  • the coating formulation may comprise a matrix component, wherein the phosphorescent pigment and any further particulate material is dispersed in the matrix component.
  • the matrix component may make up the great majority or substantially all of the non-volatile component.
  • the coating composition may therefore comprise a matrix component and particulate material dispersed or suspended therein in an amount of 10wt% or less of the matrix component, wherein at least 80% of the particulate material is phosphorescent pigment.
  • the matrix component may be a curable resin, or a mixture of two or more resins.
  • the matrix component may comprise a natural or synthetic resin.
  • the matrix component may for example be an alkyd resin, or an epoxy resin or a polyurethane resin.
  • a curing reaction may cross-link between polymeric species within the resin matrix component. Polymerisation or further polymerisation may also occur.
  • the matrix component may comprise a polymerisable matrix component, including for example one or more monomeric or oligomeric components, or a polymeric or resinous component which, in use reacts to form a higher MW component.
  • the coating composition may be a settable or dryable coating composition.
  • the coating composition may comprise a thermoplastics matrix which may be applied at an elevated temperature and be allowed to set after application.
  • the coating composition may comprise a solvent, which evaporates over time (or with the application of heat) to leave a coating comprising the remaining non-volatile components in use.
  • the coating composition may comprise a suspension or emulsion of an acrylic polymer, a latex, an alkyd resin or a nitrocellulose resin in a solvent, such as water.
  • a coating composition may form a coating by a combination of setting, drying, polymerising and/or curing.
  • the coating composition may comprise a multi-part matrix component, for example a mixture of two or more matrix materials, such as resins, polymers, monomer solutions/suspensions or the like. These and other components of the coating composition can be mixed in any order, with each other and/or with the particulate material and pigment disclosed herein.
  • a multi-part matrix component for example a mixture of two or more matrix materials, such as resins, polymers, monomer solutions/suspensions or the like.
  • the coating composition may comprise additional components.
  • solvent may be present, and the coating composition may comprise one or more further additives, such as a rheological or flow agent, a dye, or a catalyst or initiator may be added to facilitate curing or polymerisation.
  • the coating composition may be provided in a liquid form. That is to say that the coating composition may be liquid at the ambient temperatures in which it is to be used, such as room temperature.
  • the coating composition may be formulated to be applied in any suitable manner, including painting, rolling, dipping, spraying etc.
  • the dye may be beneficial for the dye to have limited or no absorption in the wavelength range of the phosphorescence emitted by the phosphorescent pigment, and/or in the wavelength range required to excite or“charge” the phosphorescent pigment. It may in some circumstances be beneficial for the coating composition not to comprise dye.
  • the coating composition may be a solid or powder, and may in use be heated so as to melt the matrix component and form a surface coating (e.g. in powder coating applications).
  • Particulate material may in such embodiments be present in solid dispersion, and would not undergo a phase change during melting of the matrix component.
  • the invention extends to a coating on a substrate, the coating having particulate material dispersed therein, in an amount of 10wt% or less of the coating, wherein at least 80wt% of the particulate material is phosphorescent pigment.
  • the coating may be obtained or obtainable by applying the coating composition of the first aspect to the substrate and curing, polymerising, drying and/or setting the coating formulation.
  • the coating may consist of the non-volatile components of the coating formulation from which it is made, the composition of which is disclosed herein.
  • the coating may be applied to a wide range of substrates, including for example metals and composite materials, such as carbon fibre composite or glass fibre reinforced composite.
  • the coating has utility in a range of industries, including aerospace, shipping and renewable energy, for structural inspection.
  • the coating may comprise a matrix component, wherein the phosphorescent pigment and any further particulate material is dispersed in the matrix component.
  • Composite materials typically comprise a reinforcement material (such as carbon fibre or glass fibre) embedded in a matrix material (such as epoxy or polyurethane).
  • the coating may comprise a matrix material of the same class of matrix material, or indeed the same matrix material, as that of the substrate.
  • the coating may be a top coat, or may be an undercoat or primer coat, in use itself covered by at least one further cosmetic and/or protective coating.
  • the invention extends in a third aspect to a coated substrate, such as a surface of an industrial article such as a wind turbine blade or aerospace structural component etc., having thereon a coating of the second aspect and, optionally, at least one further coating layer (such as an opaque or substantially opaque top coat) thereon.
  • the coating may be transparent or translucent. At least at the wavelength or in the wavelength range at which the phosphorescent pigment phosphoresces, the coating is beneficially transparent or translucent.
  • the coating may be transparent or translucent at the wavelength or in the wavelength range at which the phosphorescent pigment phosphoresces and/or at the wavelength or in the wavelength range at which excitation of the
  • phosphorescent pigment occurs (e.g. in the UV range).
  • a transparent/translucent coating may be derived from a transparent/translucent coating composition, but this is not always the case since the light transmission properties of the material may change during curing, polymerisation, setting or drying.
  • a transparent or translucent coating we refer to the degree to which light can pass through the coating material, and may be described in terms of the absorbance of the coating.
  • Absorbance is a dimensionless measure of the intensity of light passing through a medium over a certain path length given by equation (1)
  • A log 10 where A is Absorbance, k is intensity of incident light and / is the intensity of light having passed along a defined path length.
  • A may be below 1 (i.e. / is around at least 50% of k) or below 0.3 (i.e. / is around at least 50% of /o), or below around 0.125 (i.e. / is around at least 75% of /o), or below around 0.05 (i.e. / is around at least 90% of k) or below around 0/001 (i.e. / is around at least 98% of /o).
  • coating thickness can vary depending on its use, coating thickness is typically between around 0.1 mm to 2 mm. A coating thickness may for example be around 0.3 mm. Accordingly, in use of a transparent or translucent coating (as described in further detail below) a large proportion of the phosphorescence is observable.
  • the coating disclosed herein may phosphoresce for a prolonged period after excitation. This is dependent on multiple parameters, including the type of phosphorescent pigment, the transparency of the coating or matrix material and the presence of other components, such as other particulate material, dye and the like. However, in general term the
  • phosphorescence is more prolonged for coatings with a lower absorbance and wherein the phosphorescent pigment makes up a higher percentage of the total amount of particulate material present.
  • the rate of decay of the coating disclosed herein may be expressed in terms of the luminance observable after a predetermined time following excitation as a proportion of the observable luminance immediately after excitation has occurred. For example, around 30% of the initial phosphorescence may still be observed up to around 2-4 seconds following excitation, or around 1 to 10 minutes, or around 1 to 30 minutes or 1 to 60 minutes or in some embodiments up to 4 to 8 hours, or up to around 10 to 20 hours following excitation.
  • a method of inspecting a surface comprising:
  • Regions of the acquired image that do not show any phosphorescence are indicative of regions in which the coating has not been applied, or which have degraded over time.
  • intensity variations may be indicative of thickness variations in the coating.
  • the coated surface may be irradiated with light having a first wavelength or range of wavelengths. Phosphorescence may be emitted from the coating at a second wavelength or range of wavelengths.
  • the first and second wavelengths or range of wavelengths may not overlap, or may have minimal overlap.
  • the first wavelength/wavelength range may be in the ultraviolet region (i.e. wavelengths between around 10-400 nm).
  • the first wavelength may be around 365 nm, which may be emitted by an LED source as known to one skilled in this technical field.
  • the second wavelength/wavelength range may be in the visible region (i.e. wavelengths between around 380 to 750 nm).
  • Irradiating light may have a first wavelength range having a peak at least around 100 nm, or 200 nm or 400 nm apart from the peak in the second wavelength range, such that there is minimal overlap therebetween.
  • the coated surface may be irradiated by a (typically electric) light source.
  • a (typically electric) light source Any suitable light source may be used, such as an LED light source, an incandescent bulb (or bulbs), a fluorescent lamp or the like.
  • the light source may be in the form of a“flash” as used for photographic applications, for example.
  • the light source may be integral to imaging apparatus for acquiring the said image.
  • the irradiation may be across a broad range of wavelengths.
  • a typically“UV lamp” comprising an incandescent or fluorescent bulb also emits at least some light in the visible range.
  • the coated surface may be irradiated by sunlight.
  • the phosphorescent pigment may be excited by UV light in the sunlight during daylight hours, enabling the
  • This methodology can be used for example for routine structural inspection of suitably coated external surfaces of structures such as wind turbines, aircraft and the like.
  • An image of the coated surface may be acquired with any suitable imaging apparatus, for example a camera or digital camera apparatus comprising a CCD.
  • the method may be formed with non-specialist equipment, such as found in off the shelf hand held cameras, mobile telephones and the like.
  • the method may comprise irradiating the coated surface, allowing a period of time to elapse, and then acquiring an image.
  • the period of time may be of the order of milliseconds, seconds or in some cases longer (tens of seconds or minutes).
  • the imaging apparatus is capable of detecting light emitted by the light source, allowing a period of time to elapse between irradiation and image acquisition avoids the acquired image including scattered or reflected light from the light source, which might otherwise reduce the contrast or quality of the acquired image.
  • the light source and the imaging apparatus may be introduced sequentially. This may in some cases obviate the need to use specialist imaging apparatus and/or light sources.
  • the coated surface may be irradiated by sunlight during the day and images acquired during the night.
  • the method may comprise acquiring one or more images whilst irradiating the coated surface.
  • the light source may emit light at a third wavelength or range of wavelengths, which includes the first wavelength or at least overlaps with the first range of wavelengths.
  • the imaging apparatus may be capable of detecting light at a fourth wavelength of range of wavelengths, which includes the second wavelength or at least overlaps with the second range of wavelengths.
  • the coated surface may be irradiated for any suitable period of time, depending on the phosphorescent pigment used, the required intensity of emission or the technical application.
  • the coated surface may be irradiated for a short period, of the order of milliseconds, or tens or hundreds of milliseconds (e.g. as might result from a light source used in flash photography).
  • the method may comprise repeatedly irradiating over such timescales and then acquiring an image.
  • the method may comprise acquiring more than one image.
  • the method may comprise more than one step of irradiating the coated surface.
  • More than one (i.e. multiple) images may be overlaid in this way to improve sensitivity.
  • the images may be overlaid using a reference point in the images, for example a marker sign, to allow for relatively short exposure times for each acquired image.
  • a large surface may be“scanned” by acquiring multiple images.
  • the method may comprise irradiating and then acquiring two or more images, or irradiating and image acquisition may alternate.
  • the relatively long period over which phosphorescence is emitted may facilitate longer exposure times or the acquisition of multiple images, to improve sensitivity.
  • the phosphorescent coating may be a top coat, or the surface may be provided with the phosphorescent coating and one or more additional opaque coatings that“mask” the phosphorescent coating.
  • the method may therefore be used“positively” to acquire images of the phosphorescent outer coating, for example to assess the completeness of the phosphorescent coating.
  • the method may alternatively (or subsequently) be used “negatively” to acquire images to assess the completeness of an outer coating covering the phosphorescent coating.
  • the method may be applied during, or immediately after application of the of each said coating (so as to inform whether further such coating(s) need to be applied in selected areas).
  • the method may be used to inspect a coated surface at a later time, for example to detect whether an outer coating has degraded (e.g. due to weathering, defects in the underlying structure, impact damage and the like).
  • the method may comprise applying the coating composition of the first aspect to a surface, e.g. by painting, rolling, dipping, spraying, powder coating or the like.
  • the method may further comprise curing, polymerising, drying or setting the applied coating composition.
  • the method may comprise in a fifth aspect coating a surface with a coating composition according to the first aspect;
  • the acquired image may then inform whether further coating composition needs to be applied, in some embodiments before the coating composition has cured, polymerised, set or dried.
  • the method may further comprise applying one or more further opaque coatings over the coated surface.
  • the method may comprise irradiating and imaging, wherein the acquired image may inform whether further opaque coating needs to be applied. Irradiation and imaging may be conducted during the process of applying said opaque coating.
  • the method may comprise mixing one or more components of the coating composition in situ (i.e. immediately prior to application to the surface). For example, two or more resins may be mixed, or the phosphorescent pigment may be mixed with a resin or other matrix material, and/or a catalyst or initiator may be added to a matrix material.
  • Figures 1-6 show examples of methods of inspecting a coated surface.
  • Figures 7(a) and (b) show a method of structural inspection of a wind turbine.
  • Figure 8 shows luminance data acquired from Examples 1 and 2.
  • Figure 1 shows a substrate 1 having a surface 3 to which a coating comprising a phosphorescent pigment, as disclosed herein, has been applied.
  • the coating may for example comprise ZnS:Cu pigment dispersed in polyurethane matrix.
  • the quality of the coating can be inspected by irradiating with a UV light source 7 for a period of time, which excites phosphorescent pigment in the coating.
  • the phosphorescent pigment will emit phosphorescence 11 for several minutes, during which time an image of the surface 3 can be acquired by a standard digital camera 9.
  • UV lamps such as fluorescent UV lamps and LEDs
  • the UV light source 7 may therefore be switched off before the camera 9 takes a photograph of the surface, as shown in Figure 2, to avoid the capture of scattered or reflected light in the acquired image of the surface.
  • the image intensity can highlight regions that have not been coated, as well as thicker or thinner regions of the phosphorescent coating 3.
  • the image intensity may be empirically calibrated, for a given light source, distance from the coated surface, period of illumination, irradiating light intensity and image acquisition parameters and so forth.
  • a threshold image intensity can be set, indicative of acceptable coating thickness, for example.
  • Image processing software may be used to filter out regions below the threshold image intensity, as will be known to one skilled in the art.
  • a longer period may be allowed to pass between irradiation ( Figure 1) and image acquisition ( Figure 2).
  • a surface with a polyurethane coating and ZnS:Cu pigment might be irradiated for 1-2 minutes and an image acquired 5 minutes after the UV light source 7 is turned off.
  • the method may be used to detect defects in the coating 5, as shown in Figures 4 and 5.
  • the UV light source 7 is used to irradiate the coated surface 3 as described above, and an image of the phosphorescence 11 is acquired by the camera 9.
  • a defect 13 e.g. as might result from environmental degradation or impact damage
  • Further coating 15 may then be selectively applied, over the defect.
  • the method may also be used to detect defects in an opaque top coat.
  • a top coat 17 such as a conventional pigmented paint or lacquer, provided for example with Ti0 2 pigment to block visible light.
  • the top coat 17 acts as a“mask” over the coating 5.
  • the surface can be inspected as previously, by irradiating with UV light and then acquiring an image. Depending on the nature of the top coat 17, it may be more or less transparent to UV light, or opaque to UV light; but in any case, it is opaque to visible light. Accordingly, phosphorescence is only detected by the camera 9 through defects 19 in the top coat 17.
  • Using the coating 5 in a“negative” manner in this way is of particular utility for detecting cracks in the top coat, which may be indicative of structural defects in the underlying substrate 1.
  • Wind turbine blades must be periodically inspected over time, in case of fracture of the carbon fibre composite structures from which they are typically formed.
  • Figure 7 shows another example of an inspection method, in which wind turbine blades 21 of a turbine 23 are provided with a coating 5 and a top coat 17 as described above.
  • multiple images may be acquired and data overlaid.
  • Software may be used to reduce blurring and compensate for movement of the turbine (e.g. swaying of the tower) over time.
  • Visual reference markers may be applied to the turbine 23 to assist in this process.
  • a dispersion of pigment at 60wt% in Shellsol was mixed with a resinous vinyl composition, to disperse the pigment in the composition.
  • the composition was then cured to form a thin (300 micron) PVC film having pigment dispersed through the polymer matrix at around 30wt%.
  • the film was then calendared with an adhesive, and an opaque backing layer to one side, and top layer to the other side, of the pigment-containing layer.
  • Luminance data were obtained from the resulting flexible sheets, using a Minolta LS100 Luminance meter, according to DIN67510.
  • Example 1 All of the pigment present in Example 1 was strontium aluminate.
  • the pigment used in Example 2 included strontium aluminate and Chartreuse yellow pigment, in the ratio 9:1 (by weight).
  • the luminance data is set out in Figure 8, which plots detected phosphorescence in millicandela per sq. metre vs time (on a logarithmic scale).

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Abstract

Disclosed is a coating composition and a method of use. The composition has a non-volatile component comprising particulate material in an amount of 10wt% or less of the non-volatile component, wherein at least 80wt% particulate material is phosphorescent pigment. The low total particulate content has low or no detrimental impact on the coating performance. A high proportion of the particulate material is phosphorescent pigment and, when excited, phosphorescence can be observed for a longer period than for conventional inspection coatings.

Description

PHOSPHORESCENT COATING AND INSPECTION METHOD
FIELD OF THE INVENTION
The invention relates to a phosphorescent coating composition and a method of inspecting a surface to which the coating has been applied.
BACKGROUND TO THE INVENTION
The surfaces of industrial articles, such as those of composite structures, metallic surfaces, articles made of plastics etc. may be provided with protective coatings. The performance of such coatings, and thus the performance or working lifetime of the underlying surface, may rely on the quality of the protective coating and of its initial application.
For example, a protective coating may be less effective or may prematurely degrade if it is unevenly applied or if it is discontinuous, or if the underlying surface has not been suitably prepared.
Protective coatings may therefore require inspection, to assess their integrity. This may be required not only during or after initial application, but also during the lifetime of the coated surface.
In some cases, damage to a surface coating may be caused by underlying structural failure, and the manner or pattern of coating damage can yield vital information.
One approach to facilitate the inspection of protective coatings is to dope the coating with a luminescent dye or pigment, for example as described in WO02/28973 of Luminous
Technologies Ltd. This approach allows the pigment or dye to be irradiated (for example in the UV range) and the emitted luminescence detected (for example in the visible range), thereby providing a contrast between coated and uncoated surface regions. Such luminescent“inspection coatings” may also be used as a primer or undercoat, whereby visible luminescence is indicative of gaps in a further top coat.
Existing coatings of this general type typically suffer from short luminescence lifetimes, with emitted light decaying in under a second in many cases. In turn, this reduces the sensitivity of the inspection methods and may necessitate the use of specialised camera equipment or higher proportions of pigments or dyes.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a coating composition having a non-volatile component comprising particulate material in an amount of 10wt% or less of the non-volatile component, wherein at least 80wt% particulate material is phosphorescent pigment.
A relatively low total particulate content gives rise to commensurately low detrimental impact, or essentially no detrimental impact, on the performance of the coating formulation (as regards for example flow characteristics, shelf life, wettability, surface adhesion and the like); and of the resulting coating on a surface (durability, longevity etc.). A high proportion of the particulate material is phosphorescent pigment and, when excited, the non-phosphorescent particulate material causes only limited scattering and/or absorption of phosphorescence emitted by the phosphorescent pigment. The coating composition may accordingly be used to form a coating from which phosphorescence can be observed for a longer period than conventional inspection coatings.
By non-volatile component, we refer to the components which remain when the coating composition has been applied to a surface and formed into a coating, for example by drying, polymerising, curing and/or setting. The term does not include components such as solvents or curing/polymerisation reaction products, flow agents and the like, which may evaporate in use. That is to say, the coating composition results in a coating having a total particulate content, and phosphorescent pigment content as disclosed herein. In some cases, all or substantially all (e.g. 95wt%, 98wt%, 99wt% or more) of the coating composition is non volatile.
The coating composition may have a non-volatile component with a total particulate content of 8wt% or less, or 5wt% or less. The coating composition may have a non-volatile component comprising between 1 and 10wt%, or between 1 and 8wt%, or between 1 and 6wt%, or 1 and 5wt% or particulate material. The coating composition may have a non volatile component comprising between 2 and 8wt% or 2 and 6wt% of particulate material. At least 85wt%, 90wt%, 95wt%, 98wt% or 99wt% of the particulate material may be phosphorescent pigment. The particulate material of the coating composition may consist essentially of phosphorescent pigment.
By pigment we refer to a particulate material which is substantially insoluble in the remaining components of the coating composition.
In contrast a dye is a soluble material and dyes are typically provided in solution in coating compositions. Most dyes are based on organic or organometallic compounds.
Phosphorescent pigment is preferred in the present invention since it is less prone to migration into and leaching from the resulting coating and, for inorganic phosphors in particular, less prone to decomposition over time.
Pigment (including the phosphorescent pigment) is present in the coating composition to modify the optical properties of the resulting coating. For example, a pigment may selectively absorb or scatter one or more, or a range of wavelengths of light and thereby impart a colour to the coating composition.
A phosphorescent pigment absorbs and emits light. A phosphorescent pigment may typically absorb light at a first wavelength or range of wavelengths and emit light at a second wavelength or range of wavelengths. As will be known to the skilled addressee,
phosphorescence (i.e. light emitted by a phosphorescent material following absorption of light) is associated with a so-called“forbidden” quantum mechanical transition from an excited state to a lower energy state, following absorption of light from the same or another lower energy resulting in an“allowed” transition to an initial excited state.
The coating composition may comprise a suspension of or a dispersion of the
phosphorescent pigment (and/or any other pigment present).
The phosphorescent pigment may comprise an insoluble inorganic compound, such as a sulphide (e.g. zinc, cadmium, calcium), a silicate or aluminosilicate (e.g. of an alkaline earth element such as calcium, strontium, magnesium etc.) or a fluorite (e.g. of an alkaline earth element). Such materials may be doped (typically to an amount of around 1-50 ppm, or around 5 ppm or 10 ppm) with an element to act as an activator. For example, sulphides may be doped with copper or silver; europium doped aluminates or samarium doped fluorites are also known phosphorescent materials. Non-stoichiometric materials in the same general classes of materials are also known to phosphoresce. The phosphorescent material or materials can be selected for a particular purpose, depending on the environmental conditions that the coating is intended to withstand, the required phosphorescent lifetime of the pigment material, the intensity of phosphoresce, chemical compatibility with the coating composition and the like. The aforementioned are provided as examples only and phosphorescent pigment materials having the required phosphorescent properties for a particular purpose can be readily selected by the skilled person.
It has been found that sulphide-based phosphorescent pigments, such as zinc sulphide based pigments, are suitable for use in inspection coatings. These materials are readily available in small (ca. 15 micron) particle size and have good water-tolerance. Where greater sensitivity maybe required, aluminates/aluminosilicates such as strontium aluminates may be used.
The invention is not limited to inorganic phosphorescent pigment, and the phosphorescent pigment may include an organic material which is insoluble in the coating composition, or a phosphorescent dye-impregnated or dye-stained particulate/ powered solid. Suitable particulate solids include alumina, silica, titanium oxide, a zeolite or the like.
The coating composition may comprise one or more types of phosphorescent pigment.
The phosphorescent pigment may have an average particle size of less than or around 500 microns, 300 microns or 150 microns. The average particle size may be between around 0.01-500 microns, or 0.01 to 300 microns or 0.01 to 150 microns, or 0.01 to 50 microns, or 0.01 to 20 microns. The average particle size may for example be around 10-15 microns.
Where more than one type of phosphorescent pigment is present, each may have the same, or a different average particle size or particle size distribution.
The total particulate content of the coating composition may comprise one or more particulate materials other than phosphorescent pigment. Such particulate material may include one or more of; a further non-phosphorescent pigment, a filler, a sacrificial material such as particles of a metallic material (e.g. zinc), an anti-fouling material (present to impart a surface texture or chemical properties to the final coating which supresses fouling); and the like. Some particulate materials may perform more than one of these functions. The particulate material may comprise at least 85wt%, 90wt%, 95wt%, 98wt% or 99wt% pigment (including said phosphorescent pigment). The particulate material present in the coating composition may consist essentially of pigment.
Accordingly, the coating composition may have a non-volatile component comprising 10wt% or less of pigment, wherein at least 80wt% of the pigment is phosphorescent pigment.
The coating composition may be curable; i.e. it may undergo a chemical curing reaction at ambient temperature, or exposure to heat and/or light (e.g. UV light).
The coating formulation may comprise a matrix component, wherein the phosphorescent pigment and any further particulate material is dispersed in the matrix component. The matrix component may make up the great majority or substantially all of the non-volatile component.
The coating composition may therefore comprise a matrix component and particulate material dispersed or suspended therein in an amount of 10wt% or less of the matrix component, wherein at least 80% of the particulate material is phosphorescent pigment.
The matrix component may be a curable resin, or a mixture of two or more resins.
The matrix component may comprise a natural or synthetic resin. The matrix component may for example be an alkyd resin, or an epoxy resin or a polyurethane resin.
A curing reaction may cross-link between polymeric species within the resin matrix component. Polymerisation or further polymerisation may also occur.
The matrix component may comprise a polymerisable matrix component, including for example one or more monomeric or oligomeric components, or a polymeric or resinous component which, in use reacts to form a higher MW component.
The coating composition may be a settable or dryable coating composition. For example the coating composition may comprise a thermoplastics matrix which may be applied at an elevated temperature and be allowed to set after application. The coating composition may comprise a solvent, which evaporates over time (or with the application of heat) to leave a coating comprising the remaining non-volatile components in use. For example, the coating composition may comprise a suspension or emulsion of an acrylic polymer, a latex, an alkyd resin or a nitrocellulose resin in a solvent, such as water.
In some cases a coating composition may form a coating by a combination of setting, drying, polymerising and/or curing.
The coating composition may comprise a multi-part matrix component, for example a mixture of two or more matrix materials, such as resins, polymers, monomer solutions/suspensions or the like. These and other components of the coating composition can be mixed in any order, with each other and/or with the particulate material and pigment disclosed herein.
The coating composition may comprise additional components. For example solvent may be present, and the coating composition may comprise one or more further additives, such as a rheological or flow agent, a dye, or a catalyst or initiator may be added to facilitate curing or polymerisation.
The coating composition may be provided in a liquid form. That is to say that the coating composition may be liquid at the ambient temperatures in which it is to be used, such as room temperature. The coating composition may be formulated to be applied in any suitable manner, including painting, rolling, dipping, spraying etc.
Where dye is present it may be beneficial for the dye to have limited or no absorption in the wavelength range of the phosphorescence emitted by the phosphorescent pigment, and/or in the wavelength range required to excite or“charge” the phosphorescent pigment. It may in some circumstances be beneficial for the coating composition not to comprise dye.
The coating composition may be a solid or powder, and may in use be heated so as to melt the matrix component and form a surface coating (e.g. in powder coating applications). Particulate material may in such embodiments be present in solid dispersion, and would not undergo a phase change during melting of the matrix component.
In a second aspect the invention extends to a coating on a substrate, the coating having particulate material dispersed therein, in an amount of 10wt% or less of the coating, wherein at least 80wt% of the particulate material is phosphorescent pigment.
The coating may be obtained or obtainable by applying the coating composition of the first aspect to the substrate and curing, polymerising, drying and/or setting the coating formulation. Thus, the coating may consist of the non-volatile components of the coating formulation from which it is made, the composition of which is disclosed herein.
The coating may be applied to a wide range of substrates, including for example metals and composite materials, such as carbon fibre composite or glass fibre reinforced composite.
The coating has utility in a range of industries, including aerospace, shipping and renewable energy, for structural inspection.
The coating may comprise a matrix component, wherein the phosphorescent pigment and any further particulate material is dispersed in the matrix component.
Composite materials typically comprise a reinforcement material (such as carbon fibre or glass fibre) embedded in a matrix material (such as epoxy or polyurethane). In use with composites, the coating may comprise a matrix material of the same class of matrix material, or indeed the same matrix material, as that of the substrate.
The coating may be a top coat, or may be an undercoat or primer coat, in use itself covered by at least one further cosmetic and/or protective coating. Thus, the invention extends in a third aspect to a coated substrate, such as a surface of an industrial article such as a wind turbine blade or aerospace structural component etc., having thereon a coating of the second aspect and, optionally, at least one further coating layer (such as an opaque or substantially opaque top coat) thereon.
The coating may be transparent or translucent. At least at the wavelength or in the wavelength range at which the phosphorescent pigment phosphoresces, the coating is beneficially transparent or translucent. The coating may be transparent or translucent at the wavelength or in the wavelength range at which the phosphorescent pigment phosphoresces and/or at the wavelength or in the wavelength range at which excitation of the
phosphorescent pigment occurs (e.g. in the UV range).
A transparent/translucent coating may be derived from a transparent/translucent coating composition, but this is not always the case since the light transmission properties of the material may change during curing, polymerisation, setting or drying.
By a transparent or translucent coating, we refer to the degree to which light can pass through the coating material, and may be described in terms of the absorbance of the coating. Absorbance is a dimensionless measure of the intensity of light passing through a medium over a certain path length given by equation (1)
(1) A = log10 where A is Absorbance, k is intensity of incident light and / is the intensity of light having passed along a defined path length.
For a path length of 1 mm, A may be below 1 (i.e. / is around at least 50% of k) or below 0.3 (i.e. / is around at least 50% of /o), or below around 0.125 (i.e. / is around at least 75% of /o), or below around 0.05 (i.e. / is around at least 90% of k) or below around 0/001 (i.e. / is around at least 98% of /o).
[ The terms“transparent” and“translucent” may be considered to be unclear, so I have included these paragraphs to illustrate how we might further define them if ultimately required. Please let me know if this is a reasonable way we could describe the transparency of the coatings, and whether these figures are representative. ]
Whilst it must be appreciated that coating thickness can vary depending on its use, coating thickness is typically between around 0.1 mm to 2 mm. A coating thickness may for example be around 0.3 mm. Accordingly, in use of a transparent or translucent coating (as described in further detail below) a large proportion of the phosphorescence is observable.
The coating disclosed herein may phosphoresce for a prolonged period after excitation. This is dependent on multiple parameters, including the type of phosphorescent pigment, the transparency of the coating or matrix material and the presence of other components, such as other particulate material, dye and the like. However, in general term the
phosphorescence is more prolonged for coatings with a lower absorbance and wherein the phosphorescent pigment makes up a higher percentage of the total amount of particulate material present.
The rate of decay of the coating disclosed herein may be expressed in terms of the luminance observable after a predetermined time following excitation as a proportion of the observable luminance immediately after excitation has occurred. For example, around 30% of the initial phosphorescence may still be observed up to around 2-4 seconds following excitation, or around 1 to 10 minutes, or around 1 to 30 minutes or 1 to 60 minutes or in some embodiments up to 4 to 8 hours, or up to around 10 to 20 hours following excitation.
According to a fourth aspect of the invention there is provided a method of inspecting a surface, comprising:
providing the surface with a coating according to the second aspect;
irradiating the coated surface so as to excite phosphorescent pigment in the coating; and acquiring an image of phosphorescence emitted from the coated surface.
Regions of the acquired image that do not show any phosphorescence are indicative of regions in which the coating has not been applied, or which have degraded over time.
Moreover, intensity variations may be indicative of thickness variations in the coating.
By“excite” we refer to the process by which light is absorbed by the phosphorescent pigment during its irradiation, causing electrons in the pigment to move to an excited quantum mechanical state.
The coated surface may be irradiated with light having a first wavelength or range of wavelengths. Phosphorescence may be emitted from the coating at a second wavelength or range of wavelengths.
The first and second wavelengths or range of wavelengths may not overlap, or may have minimal overlap.
The first wavelength/wavelength range may be in the ultraviolet region (i.e. wavelengths between around 10-400 nm). For example, in some embodiments, the first wavelength may be around 365 nm, which may be emitted by an LED source as known to one skilled in this technical field. The second wavelength/wavelength range may be in the visible region (i.e. wavelengths between around 380 to 750 nm). Irradiating light may have a first wavelength range having a peak at least around 100 nm, or 200 nm or 400 nm apart from the peak in the second wavelength range, such that there is minimal overlap therebetween.
The coated surface may be irradiated by a (typically electric) light source. Any suitable light source may be used, such as an LED light source, an incandescent bulb (or bulbs), a fluorescent lamp or the like. The light source may be in the form of a“flash” as used for photographic applications, for example. The light source may be integral to imaging apparatus for acquiring the said image.
The irradiation may be across a broad range of wavelengths. For example, a typically“UV lamp” comprising an incandescent or fluorescent bulb also emits at least some light in the visible range.
The coated surface may be irradiated by sunlight. For example, the phosphorescent pigment may be excited by UV light in the sunlight during daylight hours, enabling the
phosphorescence to be detected at night. This methodology can be used for example for routine structural inspection of suitably coated external surfaces of structures such as wind turbines, aircraft and the like.
An image of the coated surface may be acquired with any suitable imaging apparatus, for example a camera or digital camera apparatus comprising a CCD. The method may be formed with non-specialist equipment, such as found in off the shelf hand held cameras, mobile telephones and the like.
The method may comprise irradiating the coated surface, allowing a period of time to elapse, and then acquiring an image.
The period of time may be of the order of milliseconds, seconds or in some cases longer (tens of seconds or minutes).
For example, where the imaging apparatus is capable of detecting light emitted by the light source, allowing a period of time to elapse between irradiation and image acquisition avoids the acquired image including scattered or reflected light from the light source, which might otherwise reduce the contrast or quality of the acquired image.
In some circumstances, e.g. when inspecting confined spaces, it may be desirable for the light source and the imaging apparatus to be introduced sequentially. This may in some cases obviate the need to use specialist imaging apparatus and/or light sources.
Similarly, in some circumstances, the coated surface may be irradiated by sunlight during the day and images acquired during the night. The method may comprise acquiring one or more images whilst irradiating the coated surface.
The light source may emit light at a third wavelength or range of wavelengths, which includes the first wavelength or at least overlaps with the first range of wavelengths.
The imaging apparatus may be capable of detecting light at a fourth wavelength of range of wavelengths, which includes the second wavelength or at least overlaps with the second range of wavelengths.
Where images are acquired during irradiation of the surface advantageously there is no overlap between the third and fourth wavelength/wavelength ranges.
The coated surface may be irradiated for any suitable period of time, depending on the phosphorescent pigment used, the required intensity of emission or the technical application.
In some cases, the coated surface may be irradiated for a short period, of the order of milliseconds, or tens or hundreds of milliseconds (e.g. as might result from a light source used in flash photography). The method may comprise repeatedly irradiating over such timescales and then acquiring an image.
The method may comprise acquiring more than one image. The method may comprise more than one step of irradiating the coated surface.
More than one (i.e. multiple) images may be overlaid in this way to improve sensitivity. In some cases, the images may be overlaid using a reference point in the images, for example a marker sign, to allow for relatively short exposure times for each acquired image.
A large surface may be“scanned” by acquiring multiple images.
The method may comprise irradiating and then acquiring two or more images, or irradiating and image acquisition may alternate.
The relatively long period over which phosphorescence is emitted may facilitate longer exposure times or the acquisition of multiple images, to improve sensitivity. The phosphorescent coating may be a top coat, or the surface may be provided with the phosphorescent coating and one or more additional opaque coatings that“mask” the phosphorescent coating. The method may therefore be used“positively” to acquire images of the phosphorescent outer coating, for example to assess the completeness of the phosphorescent coating. The method may alternatively (or subsequently) be used “negatively” to acquire images to assess the completeness of an outer coating covering the phosphorescent coating.
The method may be applied during, or immediately after application of the of each said coating (so as to inform whether further such coating(s) need to be applied in selected areas). The method may be used to inspect a coated surface at a later time, for example to detect whether an outer coating has degraded (e.g. due to weathering, defects in the underlying structure, impact damage and the like).
The method may comprise applying the coating composition of the first aspect to a surface, e.g. by painting, rolling, dipping, spraying, powder coating or the like.
The method may further comprise curing, polymerising, drying or setting the applied coating composition.
The method may comprise in a fifth aspect coating a surface with a coating composition according to the first aspect;
irradiating the coating composition on the surface so as to excite phosphorescent pigment in the coating composition; and
acquiring an image of phosphorescence emitted therefrom.
The acquired image may then inform whether further coating composition needs to be applied, in some embodiments before the coating composition has cured, polymerised, set or dried.
The method (of the fourth or fifth aspect) may further comprise applying one or more further opaque coatings over the coated surface. Similarly, the method may comprise irradiating and imaging, wherein the acquired image may inform whether further opaque coating needs to be applied. Irradiation and imaging may be conducted during the process of applying said opaque coating. The method may comprise mixing one or more components of the coating composition in situ (i.e. immediately prior to application to the surface). For example, two or more resins may be mixed, or the phosphorescent pigment may be mixed with a resin or other matrix material, and/or a catalyst or initiator may be added to a matrix material.
It is to be understood that further features of any of the aspects of the invention disclosed herein correspond to further features of any other of the aspects of the invention disclosed herein.
DESCRIPTION OF THE DRAWINGS
Example embodiments of the invention will now be described with reference to the following drawings in which:
Figures 1-6 show examples of methods of inspecting a coated surface.
Figures 7(a) and (b) show a method of structural inspection of a wind turbine.
Figure 8 shows luminance data acquired from Examples 1 and 2.
DETAILED DESCRIPTION
Figure 1 shows a substrate 1 having a surface 3 to which a coating comprising a phosphorescent pigment, as disclosed herein, has been applied. The coating may for example comprise ZnS:Cu pigment dispersed in polyurethane matrix.
The quality of the coating can be inspected by irradiating with a UV light source 7 for a period of time, which excites phosphorescent pigment in the coating.
The phosphorescent pigment will emit phosphorescence 11 for several minutes, during which time an image of the surface 3 can be acquired by a standard digital camera 9.
UV lamps, such as fluorescent UV lamps and LEDs, typically emit light across a range of wavelengths, including in the visible range at which standard digital camera CCDs are able to detect. The UV light source 7 may therefore be switched off before the camera 9 takes a photograph of the surface, as shown in Figure 2, to avoid the capture of scattered or reflected light in the acquired image of the surface. The image intensity can highlight regions that have not been coated, as well as thicker or thinner regions of the phosphorescent coating 3.
The image intensity may be empirically calibrated, for a given light source, distance from the coated surface, period of illumination, irradiating light intensity and image acquisition parameters and so forth. A threshold image intensity can be set, indicative of acceptable coating thickness, for example. Image processing software may be used to filter out regions below the threshold image intensity, as will be known to one skilled in the art.
Semi-quantitative applications are also possible, whereby a series of images may be acquired over time, whereby the intensity of phosphorescence in regions of the surface provided with thinner coating falls sooner than for regions having a thicker coating.
Alternatively, a longer period may be allowed to pass between irradiation (Figure 1) and image acquisition (Figure 2). For example, a surface with a polyurethane coating and ZnS:Cu pigment might be irradiated for 1-2 minutes and an image acquired 5 minutes after the UV light source 7 is turned off.
It may be convenient for the UV light source 7 to remain on during image acquisition. In this case (Figure 3), it is beneficial for the camera 9 to be insensitive to wavelengths of light emitted by the light source 7.
The method may be used to detect defects in the coating 5, as shown in Figures 4 and 5. The UV light source 7 is used to irradiate the coated surface 3 as described above, and an image of the phosphorescence 11 is acquired by the camera 9. A defect 13 (e.g. as might result from environmental degradation or impact damage) will show as a dark region in the corresponding acquired image. Further coating 15 may then be selectively applied, over the defect.
The method may also be used to detect defects in an opaque top coat. As shown in Figure 6, a top coat 17 such as a conventional pigmented paint or lacquer, provided for example with Ti02 pigment to block visible light. The top coat 17 acts as a“mask” over the coating 5. The surface can be inspected as previously, by irradiating with UV light and then acquiring an image. Depending on the nature of the top coat 17, it may be more or less transparent to UV light, or opaque to UV light; but in any case, it is opaque to visible light. Accordingly, phosphorescence is only detected by the camera 9 through defects 19 in the top coat 17. Using the coating 5 in a“negative” manner in this way is of particular utility for detecting cracks in the top coat, which may be indicative of structural defects in the underlying substrate 1.
Wind turbine blades must be periodically inspected over time, in case of fracture of the carbon fibre composite structures from which they are typically formed.
Figure 7 shows another example of an inspection method, in which wind turbine blades 21 of a turbine 23 are provided with a coating 5 and a top coat 17 as described above.
Any exposed undercoat, formed from the phosphorescent coating 5, is“charged up” (i.e. excited) by UV in sunlight during daylight hours. Long phosphorescent emission times of 4-8 hours are made possible when substantially all particulate material present in the coating is phosphorescent pigment. This enables images to be acquired overnight (Figure 7b), in which any defects or cracks will show as detected phosphorescence.
Where increased sensitivity is required, multiple images may be acquired and data overlaid. Software may be used to reduce blurring and compensate for movement of the turbine (e.g. swaying of the tower) over time. Visual reference markers may be applied to the turbine 23 to assist in this process.
Examples
A dispersion of pigment at 60wt% in Shellsol was mixed with a resinous vinyl composition, to disperse the pigment in the composition. The composition was then cured to form a thin (300 micron) PVC film having pigment dispersed through the polymer matrix at around 30wt%. The film was then calendared with an adhesive, and an opaque backing layer to one side, and top layer to the other side, of the pigment-containing layer.
A high weight percent of pigment was used to improve S:N for the purposes of the luminescence readings
Luminance data were obtained from the resulting flexible sheets, using a Minolta LS100 Luminance meter, according to DIN67510.
All of the pigment present in Example 1 was strontium aluminate. The pigment used in Example 2 included strontium aluminate and Chartreuse yellow pigment, in the ratio 9:1 (by weight).
The luminance data is set out in Figure 8, which plots detected phosphorescence in millicandela per sq. metre vs time (on a logarithmic scale).
Data were also obtained for a sample“example 3” comprising and 8:2 ratio of strontium aluminate to Chartreuse yellow. The phosphorescence was observed for around 2-3 seconds before falling below a level measurable using the luminance meter. Not data for this sample are not shown in Figure 8, since the sampling rate of the luminance meter was 10 seconds.
The intensity of the detected phosphorescence from example 1 remained consistently above that of example 2, throughout the testing period. Whilst a small difference in intensity (around 10%) might be attributable to the higher wt% of phosphorescent pigment in example 1 , the data presented in table 8 show a far greater difference. The absolute amount of phosphorescent pigment present also cannot account for the far lower intensity observed for example 3. These data illustrate that extended phosphorescence emitted from a clear coating may substantially increase by limiting the proportion of non-phosphorescent pigment present.

Claims

1. A coating composition having a non-volatile component comprising particulate
material in an amount of 10wt% or less of the non-volatile component, wherein at least 80wt% particulate material is phosphorescent pigment.
2. The coating composition of claim 1 , wherein at least 95wt% of the coating
composition is non-volatile.
3. The coating composition according to claim 1 or claim 2, wherein at least 90wt%, of the particulate material is phosphorescent pigment.
4. The coating composition of any preceding claim, wherein the phosphorescent
pigment comprises one or more insoluble inorganic compound, selected
independently from; a sulphide, a silicate, an aluminosilicate and/or a fluorite.
5. The coating composition according to claim 4, wherein the phosphorescent pigment comprises zinc sulphide and/or a strontium aluminate.
6. The coating composition according to any preceding claim, wherein the particulate material comprises at least 85wt% pigment, of which at least 80wt% is
phosphorescent pigment.
7. The coating composition according to any preceding claim, wherein the coating composition is curable.
8. The coating composition according to any preceding claim, comprising a matrix component and the particulate material dispersed in the matrix component.
9. The coating composition according to claim 8, wherein the matrix component
comprises an alkyd resin, an epoxy resin or a polyurethane resin.
10. The coating composition according to any one of claims 1-6, wherein the coating composition is settable or dryable.
11. A coating on a substrate, the coating having particulate material dispersed therein, in an amount of 10wt% or less of the coating, wherein at least 80wt% of the particulate material is phosphorescent pigment.
12. A coating on a substrate obtained or obtainable by applying the coating composition according to any one of claim 1-10 the substrate and curing, polymerising, drying and/or setting the coating formulation.
13. The coating according to claim 11 or 12, comprising a matrix component, wherein the particulate material is dispersed in the matrix component.
14. A coated substrate, having thereon a coating according to claim 11 or 12.
15. A coated substrate according to claim 14, wherein the substrate comprises a
composite material, the composite material comprising a reinforcement material embedded in a matrix material.
16. The coated substrate according to claim 15, when dependent on claim 13, the
coating matrix material is the same material as the coating matrix material.
17. The coating or coated substrate according to any one of claims 11 to 16, wherein the coating is transparent or translucent.
18. A method of inspecting a surface, comprising:
providing the surface with a coating according to claim 11 or claim 12;
irradiating the coated surface so as to excite phosphorescent pigment in the coating; and
acquiring an image of phosphorescence emitted from the coated surface.
19. The method of claim 18, comprising irradiating the coated surface with light having a first wavelength or range of wavelengths and wherein the phosphorescence is emitted from the coating at a second wavelength or range of wavelengths; wherein the first and second wavelengths or range of wavelengths do not overlap, or have minimal overlap.
20. The method of claim 19, wherein the first wavelength or range of wavelengths is in the ultraviolet region and the second wavelength or range of wavelengths is in the visible region.
21. The method of any one of claims 18 to 20, comprising irradiating the surface with an
LED light source.
22. The method of any one of claims 18 to 21 , comprising irradiating the coated surface, allowing a period of time to elapse, and then acquiring an image.
23. The method of claim 22, comprising irradiating the surface using sunlight, and
acquiring the image during the night.
24. The method of any one of claims 18 to 21 , comprising acquiring one or more images whilst irradiating the coated surface.
25. The method of claim 24, wherein the light source emits light at a third wavelength or range of wavelengths, which includes the first wavelength or at least overlaps with the first range of wavelengths; and
using imaging apparatus to acquire the image, wherein the imaging apparatus is capable of detecting light at a fourth wavelength of range of wavelengths, which includes the second wavelength or at least overlaps with the second range of wavelengths.
PCT/GB2019/052383 2018-08-28 2019-08-23 Phosphorescent coating and inspection method Ceased WO2020044027A1 (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115785815A (en) * 2021-09-13 2023-03-14 古德里奇公司 Monitoring low ice adhesion coatings
JP2023092395A (en) * 2021-12-21 2023-07-03 日鉄ケミカル＆マテリアル株式会社 Crack detection method
CN120961407A (en) * 2025-10-20 2025-11-18 上海交通大学 A method for preparing a three-dimensional surface high-density non-connected phosphorescent speckle coating
KR102923609B1 (en) * 2022-11-11 2026-02-04 세메스 주식회사 Substrate processing apparatus including coating film and inspection method of coating film for substrate processing apparatus

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002028973A1 (en) 2000-10-03 2002-04-11 Luminous Technologies Ltd Luminescent paint
EP1550550A1 (en) * 2002-09-12 2005-07-06 Nippon Sheet Glass Co.,Ltd. Articles coated with luminescent film
US8298441B1 (en) * 2007-05-22 2012-10-30 The Sherwin-Williams Company Method for incorporating water soluble, reactive, phosphorescent pigments into a stable waterborne coating through pH buffering
EP2679986A2 (en) * 2012-06-25 2014-01-01 The Boeing Company System and method for improved visual detection of protective coatings
WO2015092761A1 (en) * 2013-12-20 2015-06-25 Universidade Do Porto Composition and method for wood or derivatives of wood
EP3263672A1 (en) * 2015-02-26 2018-01-03 Tateyama Kagaku Industry Co., Ltd. Transparent phosphorescent materials, and metallic products coated with transparent phosphorescent materials

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1231254A1 (en) * 2001-02-07 2002-08-14 Agfa-Gevaert Preparation of ZnS particles doped with copper
EP2480625A4 (en) * 2009-09-21 2013-04-03 Univ Georgia NEAR-INFRARED DOPED PHOSPHORES HAVING A ZINC, GERMANIUM AND GALLATE MATRIX
ES2551759B1 (en) * 2014-05-20 2016-09-09 Universidad De Cantabria Manufacturing procedure for long-lasting phosphorescent tissues and tissues derived from it

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002028973A1 (en) 2000-10-03 2002-04-11 Luminous Technologies Ltd Luminescent paint
EP1550550A1 (en) * 2002-09-12 2005-07-06 Nippon Sheet Glass Co.,Ltd. Articles coated with luminescent film
US8298441B1 (en) * 2007-05-22 2012-10-30 The Sherwin-Williams Company Method for incorporating water soluble, reactive, phosphorescent pigments into a stable waterborne coating through pH buffering
EP2679986A2 (en) * 2012-06-25 2014-01-01 The Boeing Company System and method for improved visual detection of protective coatings
WO2015092761A1 (en) * 2013-12-20 2015-06-25 Universidade Do Porto Composition and method for wood or derivatives of wood
EP3263672A1 (en) * 2015-02-26 2018-01-03 Tateyama Kagaku Industry Co., Ltd. Transparent phosphorescent materials, and metallic products coated with transparent phosphorescent materials

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115785815A (en) * 2021-09-13 2023-03-14 古德里奇公司 Monitoring low ice adhesion coatings
JP2023092395A (en) * 2021-12-21 2023-07-03 日鉄ケミカル＆マテリアル株式会社 Crack detection method
JP7770905B2 (en) 2021-12-21 2025-11-17 日鉄ケミカル＆マテリアル株式会社 Crack Detection Method
KR102923609B1 (en) * 2022-11-11 2026-02-04 세메스 주식회사 Substrate processing apparatus including coating film and inspection method of coating film for substrate processing apparatus
CN120961407A (en) * 2025-10-20 2025-11-18 上海交通大学 A method for preparing a three-dimensional surface high-density non-connected phosphorescent speckle coating

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