A method and a system for monitoring curing of a coating film

Abstract

Systems and methods for monitoring curing of an energy curable film are provided The system comprises a pulsable infrared radiation source (1, 2, 10) arranged to emit an infrared beam directed towards the ultraviolet light-activated film, the infrared beam having a wavelength between 2 and 14 µm; a lens (3, 4, 11) arranged to focus the infrared beam after the infrared beam is reflected from the ultraviolet light-activated film; two narrow bandpass infrared filters (5, 6, 12, 13) arranged to filter the infrared beam after the infrared beam passes through the lens, each filter configured to transmit a respective wavelength range of light; and two detectors (7, 8, 14, 15) arranged to detect light transmitted by a respective filter.

Description

[0001] A METHOD AND A SYSTEM FOR MONITORING CURING OF A COATING FILM

[0002] TECHNICAL FIELD

[0003] The invention relates to a method and a system for monitoring curing of an object's coating, in particular of a coating layer or energy-curable film subjected to curing under UV or electron beam radiation.

[0004] BACKGROUND ART

[0005] Curing mechanisms via polymerization / crosslinking through the energy input from UV light sources have become widely accepted. Energy curable materials, including layers such as films or coatings are cured using energy from sources including UV radiation or electron beams. By using light-activated photo initiators, the carbon double bonds present in the liquid paint phase are broken and a polymerization reaction is initiated. The individual monomers and oligomers are linked to form long-chain polymers. During the so-called "cross-linking" process triggered, for example by UV radiation, the paint increasingly solidifies until it is completely cured. Products that are not fully cured possess hazardous materials that can inflict health problems. Also, in the case of industrial coatings, a set of quality problems are connected in regards to adhesion to the substrate, emission behaviour and long-term stability are also big issues determined by curing quality. The physical and chemical resistance properties of products that are not full cured are poorer. Therefore, a described monitoring system also provides material and energy savings, lower CO2 emissions. For example, by monitoring curing, it is possible to adjust the UV lamps to the correct power level and reduce the power consumption of curing systems.

[0006] UV curing technology offers a significant improvement in the production of durable printed products, for example to produce furniture and floor coverings, and prints on packaging and labels. LED UV curing offers faster and more energy efficient production. However, to maintain the required standards, the quality of the cured product needs to be checked quickly and accurately to ensure that the finished product is durable and safe to use. Without quick and accurate monitoring of curing, there is a risk of significant wastage of sub-standard product because of the rapid speed of production. Furthermore, if there is any delay in detection of a sub-standard product there is an increase in the "down time" of the production process to allow for the required adjustments and maintenance.

[0007] Current state of the art I industry standard is to do post-production monitoring of drying or cross-linking of paints and varnishes in laboratory conditions by bringing the to-be-tested samples to a laboratory (FTIR, mass spectroscopy).

[0008] The curing process may be monitored using reflectance measurement systems. Such systems are based on emitting certain wavelengths from a radiation source directed to a coating and measuring reflected radiation to evaluate the degree of curing of a coating layer. European patent No. : EP2664910 discloses a monitoring device comprising of a light source, an optical filter and an optical detector. The monitoring device may monitor curing processes, such as ultraviolet (UV) curing processes to determine the progression of the level of cure of a light- activated material to a substrate. The light source emits light toward a light-activated material, such as a film, and / or a substrate. The optical filter is positioned so that a wavelength of the light is transmitted through the optical filter after the light is reflected off of the substrate and / or the film. The optical detector is positioned to detect the light that is transmitted through the optical filter. The described system has only one measurement channel, one IR filter and the beam is transmitted through the same IR filter twice, also no background compensation is present in the described solution which is instrumental because it dramatically increases measurement uncertainty. It has been found that a one channel measurement system is sensitive to multiple factors including film thickness and absorption. For applications where curing is of film having a thickness of only a few micrometres, a small change in film thickness will cause uncertainty. Furthermore, under UV curing, a film's optical and mechanical features change. Due to an increase in refraction index, the reflectivity of film increases in the wide spectral range and in the specific wavelengths of curing control. It has been found that a specific signal can be perturbed by a non-specific signal. This non-specific signal arises due to beam reflectance from the IR filter-air interface. Spectroscopy based on single-channel measurements requires spectral post-processing.

[0009] PCT patent publication no. : W02007 / 078949 discloses a spectroscopic sensor for measuring flat sheet products. A combination of spectrometers and single-channel detectors and filters together with a broad band source of illumination is used to measure multiple properties of a static, flat sheet product. The described sensor arrangement can measure properties of the static sample under observation, for instance the weight, thickness or components of the material being sensed.

[0010] However, there remains a need to monitor the dynamic process of curing of a moving product quickly, accurately and "in-line" during the curing process. The curing process to which the present invention relates is carried out in an industrial setting and so the method and system for monitoring curing must be suitable for use in a high-speed, high-performance printing / coating / spraying line. It has been found that current methods to measure properties of a static product are too slow for measurement of a fast-moving product and are not suitable to accurately measure the physical and chemical properties that change during curing. The use of a highly sensitive spectrometer is not suitable for in-line measurement of the dynamic curing process of a fast-moving product. It must also be further considered that the method and system for monitoring curing should not interfere with the high speed process; for example, when used to monitor curing of a web or sheetfed product. The present invention is dedicated to overcoming the mentioned shortcomings and for producing further advantages over the prior art.

[0011] SUMMARY OF THE INVENTION

[0012] Fundamental absorbency bonds of multiatomic compounds, so-called "fingerprints" are located in the middle infrared (MIR) region of spectra. They are much stronger than that in the near infrared (NIR) region, where absorbency is caused only by harmonic or combination vibrations. The system and method according to the invention is based on real-time differential absorbency monitoring, measurement and evaluation between liquid and cured coating film, for example, but not limited to, lacquer films, adhesive coatings, and paint coatings.

[0013] The system according to the invention is configured to determine a level (100%-fully cured, 0%- liquid film) of curing of an energy curable materials, including layers such as films or coatings that are cured using energy from sources including UV radiation or electron beams. It is understood that the present invention applies to all energy curable materials and reference to ultraviolet light-activated film (also referred to herein as a "coating film") is intended to also include layers, films and coatings that are cured by electron beam radiation. The level of cure is determined in real-time immediately after and / or during the curing process, (during and / or after UV light source illumination). This real-time measurement is carried out "in-line" and does not interfere or delay the movement of the energy curable material or the curing process. The level of cure is determined based on the detected infrared light reflected off the ultraviolet light activated film at two different wavelengths. It is understood that the present invention can also be applied to other energy curable films, such as electron beam curable films. Reference to a film is understood to refer to a layer, including a paint layer, a coating, a resin layer, an ink layer, or a layer of adhesive. The system according to the invention comprises one or more infrared radiation sources; which are preferably pulsable infrared thermal sources, which may optionally each comprise an integrated parabolic mirror. It is understood that alternative configurations of the invention can make use of comparable optical systems to replace the integrated parabolic mirror. Advantageously, the mirror significantly increases density of infrared radiation preferably by a factor of 15X for the focal point and this increases sensitivity of the whole system. Optionally, the mirror increases the density of infrared radiation by a factor of between 10X and 20X. The system further comprises one or more infrared lenses, narrow bandpass infrared filters, and detectors.

[0014] The method comprises of measuring reflectance of one or more middle infrared (MIR) wavelength infrared light beams, in the region of 2-14 pm, or preferably 6-12 pm, wavelength. These wavelengths are sensitive to the film absorptivity changes under UV radiation. An infrared beam comprising a first and a second wavelength in this range reflects off the energy curable / ultraviolet light-activated film. As the film cures, a signal associated with the first wavelength increases whereas a signal associated with the second wavelength decreases. Optionally, the signal change at the first wavelength and the signal change at the second wavelength can diverge or converge but monitoring the ratio of transmittance between the first and second wavelength can provide the required information on the level of curing - i.e. the stage of the curing process. The method comprises measuring a relation between these signals which indicates the level of curing of the film. The present invention obtains a high sensitivity of measurement. The background correction is performed during signal post-processing.

[0015] It is understood that the present invention applies to all energy curable materials and reference to ultraviolet light-activated film (also referred to herein as a "coating film") is intended to also include layers, films and coatings that are cured by electron beam radiation.

[0016] Having two distinct measurements at two close wavelengths minimizes the negative influence of surface pre-treatment, film thickness, substrate material, and temperature.

[0017] In view of the above, from a first aspect, the present disclosure relates to a system for monitoring curing of an ultraviolet light-activated (energy curable) film. The system comprises: at least one pulsable infrared thermal source, optionally with an integrated parabolic mirror, arranged to emit at least one infrared beam directed towards the ultraviolet light-activated (energy curable) film, the at least one infrared beam having a wavelength between 2 and 14 pm (i.e., mid-infrared wavelengths); at least one lens (an infrared concentration lens) arranged to focus the at least one infrared beam after the at least one infrared beam is reflected from the ultraviolet light-activated (energy curable) film; at least two narrow bandpass infrared filters arranged to filter the at least one infrared beam after the at least one infrared beam passes through the at least one lens, each filter configured to transmit a respective wavelength range of light (resulting in two infrared beams with different wavelengths - a first wavelength and a second wavelength); and at least two detectors (e.g. a pyroelectric optical detector or any other detector which can produce an electrical signal based on incident infrared light) arranged to detect light transmitted by a respective filter (a first detector detects light at the first wavelength and a second detector detects light at the second wavelength).

[0018] Preferably, the energy curable film is an ultraviolet light-activated film. Optionally, the energy curable film is an electron beam curable film.

[0019] Preferably, the or each infrared thermal source is pulsable at 5-100Hz.

[0020] More preferably, the or each infrared thermal source is pulsable at 5-15Hz.

[0021] Preferably, the or each infrared thermal source is pulsable at 5-15Hz by electrical pulses.

[0022] Preferably, the or each infrared thermal source is modulated up to 100Hz. It has been found that a pulsable infrared thermal source is well-suited to in-line measurement because the material to be cured moves past the detector at speed. The apparatus provides pulsed light which is advantageous because a series of infrared beams can be emitted at intervals towards the energy curable film to provide (at the required intervals) a measure of the level of curing. The detector of the present invention is used to continually monitor the curing process of a fast-moving web or sheet of material in real-time - i.e. multiple measurements are taken in any given time period. The present invention carefully balances the requirements of signal strength, signal to noise ratio, accuracy and speed of measurement to achieve a system and method configured to accurately and efficiently measure curing of an energy curable film.

[0023] Preferably, the first wavelength and the second wavelength are between 7 and 9 pm; optionally, between 8 and 9 pm.

[0024] As such, the invention independently measures two wavelengths of mid-infrared light after they have been reflected from the film using two separate detectors, i.e. the invention uses two independent measurement channels. For each measurement, a signal is generated, resulting in a signal for each wavelength. These two signals can then be used to determine a level of cure of the film (i.e. how cured is the film from a scale of liquid (0%) to solid (100%)). The invention uses differential spectroscopy / absorbency measurement of two mid-infrared close wavelengths, preferably with a difference less than 750nm in wavelength and preferably, each with an opposite impact in signal response. The source may advantageously have a parabolic mirror which provides improved S / N ratio. The invention advantageously eliminates variation due to film thickness, substrate material, temperatures, and environment, as both measurements are performed at the same time.

[0025] In a first embodiment, the system comprises two wideband 2-14 pm pulsable infrared thermal sources, wherein a first source is arranged to emit a first infrared beam, and a second source is arranged to emit a second infrared beam; two infrared concentration lenses, wherein a first lens is arranged to focus the first infrared beam, and a second lens is arranged to focus the second infrared beam; two narrow bandpass infrared filters, wherein a first filter is arranged to filter the first infrared beam after passing through the first lens, and a second filter is arranged to filter the second infrared beam after passing through the second lens, wherein the first filter is configured to transmit a first wavelength range of light, and the second filter is configured to transmit a second wavelength range of light; and two infrared pyroelectrical optical detectors, wherein a first detector is arranged to receive light transmitted by the first filter, and a second detector is arranged to receive light transmitted by the second filter.

[0026] In this first embodiment, the system comprises two wideband 2-14 pm pulsable infrared thermal sources. In this embodiment, infrared beams reflected from the film are focused by separate lenses, filtered by separate filters (the first filter passes the first wavelength, and the second filter passes the second wavelength), and detected by separate detectors.

[0027] In a second embodiment, a first filter of the at least two narrow bandpass infrared filters is arranged to transmit a first wavelength range of light to a first detector of the at least two detectors, and reflect a remaining portion of the beam; and a second filter of the at least two narrow bandpass infrared filters is arranged to filter the remaining portion of the beam and transmit a second wavelength range of light to a second detector of the at least two detectors.

[0028] In this second embodiment, the two wavelengths of mid-infrared light are achieved by the first filter. The first filter acts as a filter, but also as a beamsplitter. The first filter transmits at the first wavelength but reflects everything else. The light reflected from the first filter is then filtered by the second filter at the second wavelength. In this embodiment, there is only one source. As such, only one lens is required. The first filter is positioned at a 45-degree angle to the focused beam, transmitting light at the first wavelength through to the first detector, and sending the remaining portion of the beam 90 degrees to the focused beam, to the second filter which is positioned at a 0-degree angle to the remaining portion of the beam. The second filter then transmits at the second wavelength through to the second detector. The second embodiment is advantageous because using a single infrared source and a first filter to act as both a filter and a beam splitter eliminates any variation between multiple sources caused by degradation at different rates and ensures that the infrared source is effectively synchronised for both measurement channels. This increases the accuracy of the measurement of the level of curing.

[0029] Preferably, the at least one infrared radiation source comprises an integrated parabolic mirror. More preferably, the at least one infrared radiation source is a pulsable infrared thermal source. Preferably, wherein each integrated parabolic mirror increases the density of infrared radiation by a factor of 10-20X for a focal point. More preferably, wherein each integrated parabolic mirror increases the density of infrared radiation by a factor of 15X for a focal point. It is understood that alternative optical systems to the parabolic mirror could be used to increase the density of infrared radiation.

[0030] Preferably, each infrared thermal source is configured for an angular spectrum of between 5-25 degrees of infrared radiation; more preferably, each infrared thermal source is configured for an angular spectrum of between 10-20 degrees of infrared radiation. Most preferably, each infrared thermal source is configured for an angular spectrum ofl5 degrees of infrared radiation.

[0031] Preferably, where each infrared thermal source comprises a solid-state hot plate on a thin dielectric membrane, where the membrane is located on a micro-machined silicon substrate, where a random structure radiation-emitting layer consists of black platinum deposited on a heater, and the whole system has a low thermal mass. More preferably, each infrared thermal source comprises a thin film evaporation membrane and a low mass to ensure pulsable modulation wherein the source is integrated with a beam concentrator. The configuration of the present invention allows for the size of the device to be small enough for "in-line" use - i.e. the device does not interfere with the industrial process that it is used to monitor. Furthermore, the system and method uses a pulsable infrared source to ensure that the sensitivity and speed is suitable to provide a measurement signal from a moving energy curable film both quickly and accurately. The apparatus provides pulsed light which is advantageous because a series of infrared beams can be emitted at intervals towards the energy curable film to provide (at the required intervals) a measure of the level of curing.

[0032] Preferably, each infrared pyroelectric detector comprises a single crystalline lithium tantalate, LiTaO3, element formed as a very thin plate capacitor. It is understood that other suitable infrared detectors could be used with the system of the present invention.

[0033] Optionally, the at least one infrared radiation source comprises an integrated parabolic mirror, and further optionally each integrated parabolic mirror increases density of infrared radiation by a factor of 15X for a focal point.

[0034] It has been found that the use of a parabolic mirror or an equivalent optical system provides a significant improvement in the signal to noise ratio.

[0035] Preferably, the infrared radiation source is a pulsable infrared thermal source. The infrared radiation source is configured to generate and direct an intensity-modulated infrared beam towards the energy curable film. Preferably, the infrared radiation source is configured to generate and direct an electrically modulated infrared beam towards the energy curable film.

[0036] Preferably, the beam comprises at least a first spectral band and a second spectral band.

[0037] Preferably, the narrow bandpass infrared filters have peak transmission between 50-90%.

[0038] More preferably, the narrow bandpass infrared filters have peak transmission greater than 80%.

[0039] Optionally, the narrow bandpass infrared filters have peak transmission greater than 65%.

[0040] It has been found that the filter is a key component of the present invention because its transmissivity (T) must be sufficiently high to ensure that the signal-to-noise (S / N) ratio supports the precise measurement of the curing level as is required. The S / N ratio has been found to depend on the characteristics of the system components including the infrared radiation source, the filter, and the detector. The S / N ratio is also a factor that is considered in the data acquisition system of the present invention. The present invention makes use of a low-power infrared radiation source and so a higher filter transmission allows more light to reach the detector and so achieves the accurate measure of curing. Without the correct transmission by the filter, a highly sensitive detector would be required to avoid a significant reduction in the accuracy of the measure of curing.

[0041] Preferably, the narrow bandpass filters have a halfwidth of about 100-250 nanometres. More preferably, the narrow bandpass filters have a halfwidth of about 100-150 nanometres. From a second aspect, the present disclosure relates to a method for monitoring curing of an energy curable film, the method comprising: emitting at least one infrared beam from at least one pulsable infrared thermal source, optionally with an integrated parabolic mirror, the at least one infrared beam being directed towards the energy curable film, the at least one infrared beam having a wavelength between 2 and 14 pm; focusing the at least one infrared beam using at least one lens (e.g. an infrared concentrating lens), after the at least one infrared beam is reflected from the energy curable film; filtering the at least one infrared beam after the at least one infrared beam passes through the at least one lens using at least two narrow bandpass infrared filters, each filter configured to transmit a respective wavelength of light; detecting the light transmitted by the filters using at least two detectors (e.g. a pyroelectric optical detector or any other detector which can produce an electrical signal based on incident infrared light), each detector arranged to detect light transmitted by a respective filter; determining a first signal (e.g. a voltage value) based on the light detected at a first detector of the at least two detectors; determining a second signal (e.g. a voltage value) based on the light detected at a second detector of the at least two detectors; and determining a level of cure of the energy curable film based on the first signal and the second signal.

[0042] Preferably, the energy curable film is an ultraviolet light-activated film. Optionally, the energy curable film is an electron beam curable film.

[0043] Preferably, the or each infrared thermal source is pulsable at 5-100Hz.

[0044] More preferably, the or each infrared thermal source is pulsable at 5-15Hz.

[0045] Preferably, the or each infrared thermal source is pulsable at 5-15Hz by electrical pulses.

[0046] Preferably, the or each infrared thermal source is modulated up to 100Hz.

[0047] The apparatus provides pulsed light which is advantageous because a series of infrared beams can be emitted at intervals towards the energy curable film to provide at the required intervals a measure of the level of curing.

[0048] Preferably, the method comprises filtering the at least one infrared beam after the at least one infrared beam passes through the at least one lens using at least two narrow bandpass infrared filters, each filter configured to transmit a respective wavelength of light wherein the wavelength of light is between 7 and 9 pm; more preferably between 8 and 9 pm.

[0049] It has been found that the selected wavelength interval demonstrates enhanced responsiveness for particular applications, such as UV curing of components for floor or furniture panels. However, alternative critical wavelengths have also been identified for alternative printing applications.

[0050] In a first embodiment, the emitting comprises simultaneously emitting two infrared beams from two pulsable infrared thermal sources, wherein a first source emits a first infrared beam, and a second source emits a second infrared beam; the focusing comprises focusing the first infrared beam using a first lens, and focusing the second infrared beam using a second lens; the filtering comprises using a first filter to filter the first infrared beam after passing through the first lens, and a second filter to filter the second infrared beam after passing through the second lens, wherein the first filter is configured to transmit a first wavelength range of light, and the second filter is configured to transmit a second wavelength range of light; and the detecting comprises using a first detector to receive light transmitted by the first filter, and a second detector to receive light transmitted by the second filter.

[0051] In a second embodiment, the filtering comprises using a first filter of the at least two narrow bandpass infrared filters to transmit a first wavelength range of light to a first detector of the at least two detectors, and reflect a remaining portion of the beam; and a second filter of the at least two narrow bandpass infrared filters to filter the remaining portion of the beam and transmit a second wavelength range of light to a second detector of the at least two detectors.

[0052] It is understood that in the context of the present invention "film" refers to any layer or coating applied, which also includes an adhesive layer or paint layer.

[0053] It will be appreciated that reference to "one or more" includes reference to "a plurality".

[0054] Within this specification, the term "about" means plus or minus 20%, more preferably plus or minus 10%, even more preferably plus or minus 5%, most preferably plus or minus 2%.

[0055] Within this specification embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended and will be appreciated that embodiments may be variously combined or separated without parting from the invention. For example, it will be appreciated that all preferred features described herein are applicable to all aspects of the invention described herein and vice versa.

[0056] Other features of the disclosure are described below and recited in the appended claims. Dependent features of the system claims may be equally applied to the equivalent method claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Features of the invention believed to be novel and inventive are set forth with particularity in the appended claims. The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes exemplary embodiments, given in non-restrictive examples, of the invention, taken in conjunction with the accompanying drawings, in which:

[0058] Fig. 1 shows a schematic representation of a system according to the invention.

[0059] Fig. 2 shows the spectral distribution of black body source at different source temperatures.

[0060] Fig. 3 shows the characteristic transmittance spectrum of a commercial narrow bandpass infrared filter.

[0061] Fig. 4 shows Infrared Transmittance of calcium Fluoride. Usage of lenses manufactured of this material ensures the cut-off long-range spectrum of the narrow bandpass filter (Fig.3).

[0062] Fig. 5 shows a schematic representation of a system according to the invention.

[0063] Fig. 6 shows the change of signal and signal ratio for different curing states at different conveyor speeds with a measure of signal strength (y-axis) for varying curing level and conveyor speed (x-axis).

[0064] Fig. 7 shows the change of ratio (Chl / Ch2) for different curing states at different conveyor speeds with the ratio baseline and ratio Chl / Chl (y-axis) for varying curing level and conveyor speed (x-axis).

[0065] Figure 8 shows an alternative schematic representation of the system of Figure 5 according to the invention.

[0066] Preferred embodiments of the invention will be described herein below with reference to the drawings. Each figure contains the same numbering for the same or equivalent element.

[0067] DETAILED DESCRIPTION OF THE INVENTION

[0068] It should be understood that numerous specific details are presented in order to provide a complete and comprehensible description of the invention embodiment. However, the person skilled in art will understand that the embodiment examples do not limit the application of the invention which can be implemented without these specific instructions. Well-known methods, procedures and components have not been described in detail for the embodiment to avoid misleading. Furthermore, this description should not be considered to be constraining the invention to given embodiment examples but only as one of possible implementations of the invention. With reference to Fig. 1, in one embodiment a system according to the invention comprises two pulsable middle infrared wavelength thermal sources (1, 2) each optionally comprising an integrated parabolic mirror to concentrate the infrared radiation onto the detector. In some examples, the integrated parabolic mirror significantly increases density of infrared radiation by a factor of 15X for a focal point and in such a way to increase the sensitivity of the whole system. More generally, the sensitivity of the system may be increased by concentrating the infrared radiation onto the detector include using light concentrators such as lenses or curved mirrors (which may include parabolic or ellipsoidal mirrors). Concentrating the infrared radiation onto the detector increases the signal to noise ratio and increases the sensitivity of the sensor system. Some embodiments of the present invention use an integrated parabolic mirror to provide an infrared source with an integrated light concentrator. The system further comprises at least two infrared lenses (3, 4), two narrow bandpass infrared filters (5, 6) each possessing different spectral features, such as different wavelengths in the range of 6-10um, maximum transmittance (T) >80%, half bandwidth <200nm, and two infrared pyroelectric optical detectors (7, 8). In alternative embodiments of the present invention, the two narrow bandpass infrared filters (5, 6) each possessing different spectral features have a maximum transmittance (T) between 50% and 90% and a half bandwidth (HW) between 100-250nm with preferred embodiments having a half bandwidth (HW) between 100-150nm. The system of the present invention examines only a very narrow range of the spectral line because, by identifying a specific bandwidth where change is detectable for the specific ink / coating of the energy curable film, it is possible to monitor the curing process quickly and accurately, such that the system and method are particularly advantageous for rapid or real-time inline monitoring of the dynamic curing process.

[0069] The sensor input / output signals are processed in millisecond (ms) time intervals which enables the system to provide fast response times in relation to emergency signaling based on changes in the curing level calculation. A set of differential absorbency spectroscopy methods, signal post-processing, storage / retrieval and statistical algorithms are used in a unique combination.

[0070] Differential spectroscopy methodology is essential in the invention because of complex mixtures of chemical elements in the medium (oligomers, monomers, pigments, photoinitiators, etc.). All of these multiatomic compounds have different spectral absorbency and reflectance features in the IR region. Due to so called interferences they can influence the measurements specific for curing process C=C bond change under UV radiation.

[0071] A dual channel differential measurement methodology allows the elimination of non-essential chemical fingerprints, instrumental noise, possible interferences (or any other disturbances) from chemical mixtures. It has also been found that the method and device of the present invention reduces the impact of temperature and of coating film thickness on the accurate measurement of the level of curing.

[0072] This is particularly important when testing industrial coatings, which contain many chemical components (complex mixtures).

[0073] Signal post-processing will be described below.

[0074] Sampling of infrared sensor reading with 24-bit delta-sigma analog-to-digital converter, i.e. ADC, which achieves 130dB signal-to-noise ratio, i.e. SNR. Measuring differential signal from the IR sensor (7, 8) allows dynamic adjustment of built in gain amplifier, which allows change of dynamic range on the fly depending on the signal strength using built in buffer for impedance matching across data acquisition path.

[0075] Deduplicative high resolution time-series methods are used for storing / retrieving measurement data.

[0076] Statistical algorithms used in the invention:

[0077] • Moving Averages: This technique smooths data by averaging a fixed number of data points, which helps to reduce random noise.

[0078] • Kalman Filtering: A robust probabilistic technique that factors in sensor noise and combines data from multiple sensors to develop a dynamic model of the data.

[0079] • Wavelet Denoising: This technique decomposes the data into different frequency components and then reconstructs it, filtering out the noise.

[0080] The two pulsable infrared thermal sources (1, 2) each operate in the same and wide spectral IR range. The emitted wavelength range of each thermal source (1, 2) is much wider than the wavelength that reaches the infrared pyroelectric detectors (7, 8). The pulsable infrared thermal sources (1, 2) are configured to emit infrared light towards an energy curable coating, such as an ultraviolet light-activated coating during a curing process to measure the ultraviolet-activated film or a substrate. The infrared thermal sources (1, 2) are preferably micro-machined thermal infrared emitters, but also can be other infrared sources, such as a laser. The IR source design provides a true broadband black body radiation characteristic concentrated from 2 to 14 pm, with high emissivity and a long lifetime, at low cost. The emissive power and spectrum of each source is a function of source temperature, as shown in Fig.2. The pulsable infrared thermal sources (1, 2) have low power consumption and can be modulated extremely fast, up to 100Hz. Each infrared source is constructed of a solid-state hot plate on a thin dielectric membrane. This membrane is located on a micro-machined silicon substrate. The radiation-emitting layer consists of black platinum deposited on the heater. Due to the random structure of the platinum layer, the infrared radiation has a very broad spectrum, close to that of an idealized blackbody radiator. The whole system has a low thermal mass, which enables fast modulation. However, an emitter with standard cap without reflector has a wide angular radiation distribution of about 100 degrees. So, for a detector located at a distance of even a few centimetres only a small part of radiation reaches the detector.

[0081] Each infrared thermal source with an optional integrated parabolic mirror (1, 2) allows a very narrow angular spectrum, such as 15 degrees of infrared radiation, thus radiation is transferred at macroscopic distances (even tens of centimetres). Each infrared thermal source (1, 2) is pulsable at 5-15Hz by electrical pulses. It is understood that the rapid in-line measurement of the present invention can be achieved with each infrared thermal source (1, 2) being pulsable at 5-lOOHz.

[0082] The lenses (3, 4) have high-transmittivity in the IR range of 6-12 nm and works like a cut-off filter for long-range spectrum (more than 12 pm). This long-range transmittance of commercial infrared filters is a common feature and should be eliminated (Fig.3). The lenses (3, 4) are optical concentrators, which have a focal length of 25mm for concentration of infrared radiation in small, e.g. 2x2mm2sensitive area of detector. The infrared lenses (3, 4) are produced from materials like silicon, germanium, zinc selenide, barium fluoride, calcium fluoride etc., which are transparent to infrared wavelength. Calcium fluoride is the most preferable material for better spectral filtering of infrared radiation.

[0083] The narrow bandpass infrared filters (5, 6) have peak transmission (T) in the range 50-90%, preferably greater than 80%, and are key components of the system according to the invention, bandpass halfwidth is <200nm fitting the peculiarities of absorbency bands of film, responsible for the curing. The narrow bandpass filters are selected very precisely to cover (i.e. to provide the sensitivity to) the curing absorption band In case of an acrylate lacquer, paint, laminate, and resin films containing acrylic bonds, the halfwidth of filter is about 100 nanometres. Filters are produced by the vacuum sputtering of multilayer structure on the silicon or germanium substrate. The narrow bandpass infrared filters (5, 6) are positioned so that the wavelengths of the radiation source are transmitted through the optical filters (5, 6) after the two beams of infrared light are reflected off the substrate at an ultraviolet light activated film during the curing process.

[0084] Each reflected infrared light wavelength is separately spectrally filtered and concentrated into a detector (7, 8). Each infrared pyroelectric detector (7, 8) comprises a sensitive key component - single crystalline lithium tantalate (LiTaO3) elements formed as a very thin plate capacitor. Lithium tantalate is a pyroelectric crystal whose ends become oppositely charged when heated.

[0085] The method comprises measuring in real-time reflectance of two middle infrared wavelengths (MIR) - the wavelength of the reflected infrared light at the ultraviolet light activated film.

[0086] Two beams of MIR wavelength light are emitted from the thermal infrared sources (1, 2) simultaneously. Each beam is reflected at the ultraviolet light activated film-substrate boundary and at the air-ultraviolet light activated film boundary. Each reflected beam is passed through a separate concentration lens (3, 4). The beams are concentrated to pass through a separate optical filter (5, 6) and into a separate optical detector (7, 8). Both optical filters (5, 6) are such that one filter (5) filters out one wavelength from the wide band emitted from a first thermal infrared sources (1) to be passed into a first optical detector (7) through a first concentration lens (3) and another filter (6) filters out another wavelength from the wide band emitted from a second thermal infrared sources (2) to be passed into a second optical detector (8) through a second concentration lens (4). In another example the thermal infrared sources (1, 2) can be replaced by a single thermal infrared source wherein a reflected beam would be gathered by separate concentration lenses (3, 4) to pass through separate optical filters (5, 6) and into separate optical detectors (7, 8).

[0087] Both wavelengths are different and within the range of 2-14 pm, preferably 6-12 pm. Both wavelengths are sensitive to the film curing under UV radiation, but with opposite impact in the signal response - the signal at a first wavelength increases whereas at a second wavelength the signal decreases. For example, it has been found to be particularly advantageous for certain applications to select first and second wavelengths in the range between 7 and 9 pm; preferably, between 8 and 9 pm. The method comprises measuring the relation between these two signals. It has also been shown that, in alternative embodiments of the present invention, the signal change at the first wavelength and the signal change at the second wavelength can diverge or converge but monitoring the ratio of transmittance between the first and second wavelength can provide the required information on the level of curing - i.e. the stage of the curing process. The measurement is started with a liquid phase coating film and progresses until the coating film is hardened under UV curing. In this way obtaining high sensitivity of measurement. It has been found that measurement of the change in the ratio between the signal at a first wavelength for which the signal increases and a second wavelength for which the signal decreases offers a very accurate indication of the level of curing. The change in the signal at the respective wavelength may not be a substantial change but the change in the ratio is greater and so detectable more quickly and accurately. By detecting a change in the relationship between the two signals more quickly and accurately, any changes required to modify the curing process can be made more quickly and accurately. For example, it is possible for a threshold alarm to be set whereby a user is alerted to a change in UV curing performance.

[0088] Under curing of lacquer, optical constants of the film changes. These changes influence all spectra and cause the nonspecific change at the measured wavelengths as well. Elimination of this non-specific change is called background correction. The background correction is performed automatically. Operation at two close wavelengths (where d (delta)= difference is <750 nanometers) allows the elimination of negative influence of surface pre-treatment, film thickness, temperature and whether there is a matt or gloss surface finish. Both infrared thermal sources (1, 2) emit light at an angle between 0° and 60° with respect to an axis normal to the substrate and the ultraviolet light-activated film. Preferably, both infrared thermal sources (1, 2) emit light at an angle between 0° and 20° with respect to an axis normal to the substrate and the ultraviolet light-activated film. Most preferably, both infrared thermal sources (1, 2) emit light at an angle of 10° with respect to an axis normal to the substrate and the ultraviolet light-activated film.

[0089] Both optical filters (5, 6) and both optical detectors (7, 8) are positioned at an angle between 0° and 70° with respect to an axis normal to the substrate and the ultraviolet light-activated film. Preferably, both optical filters (5, 6) and the optical detector (7, 8) are positioned at an angle between 0° and 20° with respect to the axis normal to the substrate and the ultraviolet light-activated film. Most preferably, both optical filters (5, 6) and the optical detector (7, 8) are positioned at an angle of 10° with respect to the axis normal to the substrate and the ultraviolet light-activated film.

[0090] The optical detectors (7, 8) each comprise a pyroelectric (or other detector sensitive in the determined spectral region) to translate the detected infrared light from the ultraviolet light activated film into respective voltage values. The respective voltage values correspond with relative concentrations of monomers and oligomers in the ultraviolet light-activated film and the level of cure directly relates to the concentration of the monomers and the oligomers in the ultraviolet light-activated film, which is indicative of a transmission of light in an infrared wavelength region. It is understood that reference to an ultraviolet light-activated film is given as an example of the present invention and the system and method can also be used to determine the level of curing of other energy curable film, such as an electron beam curable film. Reference in the description to a film is understood to refer to any curable coating or layer, including an adhesive layer, a resin layer, an ink layer, or paint layer.

[0091] With reference to Fig. 5, in a further embodiment, a system according to the invention comprises a pulsable infrared thermal source (10) optionally comprising an integrated parabolic mirror. As discussed above, the mirror advantageously significantly increases density of infrared radiation by a factor of 15X for the focal point and in such a way which increases the sensitivity of the whole system. The system further comprises an infrared lens (11), narrow bandpass infrared filters (12, 13), and infrared pyroelectric optical detectors (14, 15). Infrared filter (13) is oriented at 0 degrees of incidence relative to the IR beam, whereas filter (12) is oriented at 45 degrees of incidence relative to the IR beam. Filter (12) transmits a narrow band at wavelength Al and reflects the rest of wideband radiation at an angle 45 degrees to the filter (or 90 degrees to the incident IR beam). Filter (13) is the narrow bandpass transmission filter at wavelength A2. The coefficient properties of the beamsplitter to the first detector (14) is 100% and to the second detector (15) is 70-80%. The method comprises measuring reflectance of middle infrared (MIR) wavelength infrared light beams, in the region of 2-14 pm, preferably 6-12 pm, wavelength. After reflectance from the substrate (17) coated with polymer film (16), the beam is split into two separate beams (channels) using infrared filter (12). Filter (12) is manufactured specifically to transmit IR radiation at a first wavelength sensitive to UV curing Al at an incidence angle of 45 degrees and reflect the rest of the radiation which falls outside the transmission bandwidth of the filter (12). The radiation reflected from filter (12) is filtered by filter (13) at a second wavelength sensitive to UV curing A2. Both wavelengths Al and A2 are sensitive to the film absorptivity changes under UV radiation, but with opposite impact in the signal response. The signal at first wavelength Al increases whereas at second wavelength A2 the signal decreases. The method comprises measuring the relation between these signals Al, A2. The measurement of liquid phase to solid phase (i.e. cured) allows the curing level to be calculated. The background correction is performed during signal post-processing.

[0092] Infrared thermal source (10) emits light at an angle between 0° and 60° with respect to an axis normal to the substrate (17) and the ultraviolet light-activated film (16). Preferably, the infrared thermal source (10) emits light at an angle of about 20° with respect to an axis normal to the substrate (17) and the ultraviolet light-activated film (16).

[0093] IR source (10) is a micro-machined thermal infrared emitter. The design provides a true black body radiation characteristic from 2 to 14 pm (as shown in Fig.2), high emissivity and a long lifetime. It has a low power consumption and the source can be modulated extremely fast. The or each infrared thermal source is modulated up to lOOHz.The construction of an infrared source consists of a solid-state hot plate on a thin dielectric membrane. This membrane is located on a micro-machined silicon substrate. The radiation-emitting layer consists of black platinum deposited on the heater. Due to the random structure of the platinum layer, the infrared radiation has a very broad spectrum from, close to that of an idealized blackbody radiator. The whole system has a low thermal mass, which enables fast modulation. The integrated metal mirror (parabolic optics integrated with the emitter) allows a very narrow angular spectrum of IR radiation; thus, radiation could be transferred at macroscopic distances (even tens centimetres). The IR emitter is pulsable at 5-100Hz; preferably, at 5-15Hz by electrical pulses

[0094] The reflected IR radiation from the surface with coated lacquer or ink film (16) is spectrally filtered (12, 13) and concentrated into the detectors (14,15). The radiation sensitive key components of the detectors (14, 15) are single crystalline lithium tantalate (LiTaO3) elements formed as a very thin plate capacitor. Lithium tantalate is a pyroelectric crystal whose ends become oppositely charged when heated. Detectors (14,15) are integrated with amplifiers and thermal compensation schemes. The pyroelectric detector is robust in construction and its performance well suited to the present invention. Important components of the sensor include the narrow bandpass infrared filters (12, 13). The transmittance maximum of filter and bandpass width should fit the peculiarities of absorbency bonds of the film (16), obtained from FTIR spectra analysis. Filters (12, 13) are produced by the vacuum sputtering of a multilayer structure on the silicon or germanium substrate. The narrow bandpass infrared filter (12) in Fig.5 is oriented at an angle of incidence 45 degrees to the reflected IR radiation beam and has peak transmission >80% at wavelength Al. In alternative embodiments, the narrow bandpass infrared filter has peak transmission in the range 50-90%. The filter (13) is oriented at 0 degrees to the reflected IR radiation beam and has high (>80%) peak transmittance at wavelength A2. Both filters (12, 13) are important components of the system. According to embodiments of the invention, bandpass halfwidth for lacquer film is about lOOnm fitting the peculiarities of the absorbency bonds of film, responsible for the curing. The narrow bandpass filters are selected very precisely to cover the absorption bond sensitive to curing. Filters are produced by the vacuum sputtering of multilayer structure on the silicon or germanium substrate. The narrow bandpass infrared filters (12, 13) are positioned so that the radiation of the infrared source is transmitted through the optical filters (12, 13) after infrared light is reflected from the lacquer film (16). Preferably, optical filter (12) is oriented at 45 degrees relative to the IR beam, whereas filter (13) is oriented at 0 degrees relative to the IR beam. Filter (12) has a double function. It serves as a filter at wavelength Al and also as a beamsplitter, reflecting the rest of the IR radiation not transmitted at wavelength Al (Fig.3). The reflectivity of the filter (12) at wavelength A2 is preferably more than 99%.

[0095] As described above in relation to the system shown in Fig. 1, for concentration of IR radiation in a small, e.g. 2x2mm2sensitive area, it is necessary to use optical concentrators (lenses or reflectors). Infrared lenses may be produced from IR transparent materials like silicon, germanium, zinc selenide, barium fluoride, calcium fluoride etc., which are transparent to infrared wavelength. Calcium fluoride is most preferable material for better spectral filtering of infrared radiation. The transmittance spectrum of calcium fluoride is presented in Fig.4.

[0096] Referring to Figure 8, an alternative schematic of Figure 5 (the beamsplitter embodiment) working on transmittance through the substrate (17') is shown. This embodiment in Fig.8 is for the measurement of energy curable film in transmittance mode. The substrate (17) and / or film (16') in Figure 8 should be transmissive material in the spectral range of measurements. The configuration shown in Figures 5 and 8 comprises a dual function component (12, 12') that acts as a beamsplitter and a narrow bandpass filter. As shown in Figure 8, the system comprises a pulsable infrared source (10') with integrated lens. The infrared radiation is passed to the substrate / film (16', 17'), transmitted through and passed to an infrared lens (11') and further through the narrow bandpass infrared filter dual component (12') that acts as a narrow band pass filter (NBF) and a beamsplitter. The NBF / beamsplitter (12') in this embodiment is oriented at 45 degrees of incidence relative to the reflected infrared beam. The dual component band pass filter and beamsplitter (12') transmits a narrow band at a first wavelength and reflects the rest of wideband radiation at an angle of 45 degrees (in this embodiment) to the filter (13') (or at 90 degrees to the incident IR beam). The beam is split so that a reflected beam passes to a narrow bandpass infrared filter (13') to reach a first infrared pyroelectric optical detector (14'). The transmitted beam passes to a second infrared pyroelectric optical detector (15'). The coefficient properties of the dual component beamsplitter to the first detector (14') is 100% and to the second detector (15') is 70-80%. It has been found that the arrangement shown in Figure 8 is particularly advantageous for the monitoring of curing because of the improved signal to noise ratio, which makes quick and accurate detection to monitor curing of a moving sample possible. Furthermore, the removal of the requirement for an additional filter reduces the complexity of the arrangement whilst ensuring that a detectable signal is produced.

[0097] Testing to determine curing level (100%-fully cured, 0%-liquid film) of an ultraviolet light-activated film

[0098] The improvement of the present invention is shown with respect to Figures 6 and 7 and the test data set out in Table 1 showing that the specific selected wavelengths are sensitive to the film absorptivity changes under UV radiation. As previously described, an infrared beam comprising a first and a second wavelength reflects off an ultraviolet light-activated film and each beam is detected to give a signal (Chl / Ch2). Testing was carried out with multiple runs at each indicated curing stage and conveyor speed. Data was gathered for curing of Lacquer Furniture and ink on photopaper.

[0099] As shown in Figure 6, as the film cures, a signal associated with the first wavelength increases whereas a signal associated with the second wavelength decreases. The method and device of the present invention measures the ratio (Chl / Ch2), which is the relation between these signals to indicate the level of curing of the film. The present invention obtains a high sensitivity of measurement because there is a significant and measurable change in the ratio before, during and after curing. In the example shown in Figure 6, the signal associated with the first wavelength increases whereas a signal associated with the second wavelength decreases. However, in alternative embodiments of the present invention, the signal change at the first wavelength and the signal change at the second wavelength can diverge or converge but monitoring of the ratio of transmittance between the first and second wavelength can provide the required information on the level of curing - i.e. the stage of the curing process.

[0100] [Table 1]

[0101] Table 1 sets out the results of testing carried out to assess the accuracy of the present invention in determining the level of curing at different conveyor speeds. The results are shown in Figure 6. It has been demonstrated that the careful selection of wavelength and signal processing produces an accurate measure of the curing state regardless of the conveyor speed. It can be seen from Figure 6 that by using differential spectroscopy / absorbency measurement of two midinfrared close wavelengths, preferably with a difference less than 750nm in wavelength, each wavelength has an opposite impact in signal response before and after curing. It has been found that measurement of the change in the ratio between the signal at a first wavelength for which the signal increases and a second wavelength for which the signal decreases offers a very accurate indication of the level of curing. With reference to Table 1 and Figure 6 it can be seen that there is a significant ratio change before and after curing.

[0102] Referring to Figures 6 and 7, it has been found that both wavelengths Al and A2 are sensitive to the film absorptivity changes under UV radiation, but with an opposite impact in the signal response (ChlPP and Ch2PP - PP meaning Peak to Peak signal). It can be seen from Figure 6 that ChlPP signal response decreases with curing and Ch2PP signal response increases with curing (regardless of conveyor speed). The method of the present invention comprises measuring the relation between these signals Al, A2 as shown in Figure 7 to provide an accurate and rapid measure of curing level.

[0103] It can be seen from Figure 7 that the ratio of signal response changes significantly after curing and that this is not significantly affected by conveyor speed. There is a dramatic drop in signal ratio when curing is applied. The ratio was found to decrease by approximately 45.56% during the curing process. The present invention was shown to be accurate in detecting a significant shift in the material's properties due to UV curing. It was observed that the signal ratio after UV curing was relatively consistent, which shows that the UV curing process stabilises the signal response - i.e. the signal ratio ChlPP / Ch2PP. The test data collected indicates that the present invention is suitable for providing an accurate real-time indication of curing level.

[0104] Although numerous characteristics and advantages together with structural details and features have been listed in the present description of the invention, the description is provided as an example fulfilment of the invention. Without departing from the principles of the invention, there may be changes in the details, especially in the form, size and layout, in accordance with most widely understood meanings of the concepts and definitions used in claims. It is therefore intended that such changes and modifications are covered by the appended claims.

[0105] There follows a list of numbered features describing particular aspects and features of the present invention. Where a feature refers to one or more earlier numbered features those features may be considered in combination.

[0106] 1. A system for monitoring curing of a coating film comprising a thermal beam source, and a detector for detecting the reflected thermal beam characterised in that the system comprises two middle infrared wavelengths infrared thermal sources (1, 2) configured to emit different wavelengths within range of 6-12 pm and each comprising of an integrated parabolic mirror, and in that the system further comprises two infrared concentration lenses (3, 4), two narrow bandpass infrared filters (5, 6) each possessing different spectral features, and two infrared pyroelectric optical detectors (7, 8).

[0107] 2. The system according to feature 1, where each infrared thermal sources (1, 2) comprises a solid-state hot plate on a thin dielectric membrane, where the membrane is located on a micro-machined silicon substrate, where a random structure radiation-emitting layer consists of black platinum deposited on a heater, and the whole system has a low thermal mass. The system according to any previous feature, where each infrared pyroelectric detector (7, 8) comprises a single crystalline lithium tantalate (LiTaO3) element formed as a very thin plate capacitor. The system according to any previous feature, where each integrated parabolic mirror increases density of infrared radiation by a factor of 15X for a focal point. The system according to any previous feature, where each infrared thermal source (1, 2) is configured for angular spectrum of 15 degrees of infrared radiation. The system according to any one of the previous features, where the infrared lenses (3, 4) have high-transmittivity in the IR range of 6-12 pm and are cut-off filters for long- range spectrum above 10pm. The system according to any one of the previous features, wherein the narrow bandpass infrared filters (5, 6) have peak transmission >80%. The system according to any one of the previous features, where the narrow bandpass filters (5, 6) have halfwidth of about 100 nanometres. The system according to any one of the previous features, where both infrared thermal sources (1, 2) are configured to emit light at an angle between 0° and 45°, preferably at an angle between 0 -20°, most preferably at an angle of 10° with respect to an axis normal to a substrate and an ultraviolet light-activated film. The system according to any one of the previous features, where both narrow bandpass infrared filters (5, 6) and both infrared pyroelectric optical detector (7, 8) are positioned at an angle between 0° and 45°, preferably at an angle between 0-20°, and most preferably at an angle of 10° with respect to the axis normal to the substrate and the ultraviolet light-activated film. A method for monitoring curing of a coating film comprising emitting a thermal beam from a thermal beam source to a film being cured and detecting the reflected thermal beam reflected from the film being cured, characterised in that two beams of different middle infrared wavelength light are emitted from thermal infrared sources (1, 2) simultaneously where both wavelengths are different and within the range of 6-12 pm where signal at first wavelength increases whereas signal at second wavelength decreases, each reflected beam is passed through a separate infrared concentration lens (3, 4), each concentrated beam is passed through a separate optical filter (5, 6) and into separate pyroelectric optical detector (7, 8) for translating the detected infrared light from the ultraviolet light activated film-substrate boundary and the air-ultraviolet light-activated film boundary into respective voltage values, where the respective voltage values correspond with relative concentrations of monomers and oligomers in the ultraviolet light-activated film and the level of cure directly relates to the concentration of the monomers and the oligomers in the ultraviolet light-activated film, the concentration of polymerization of the monomers and the oligomers indicative of a transmission of light in an infrared wavelength region, the method further comprises measuring relation between the two signals of the reflected wavelengths, where the measurement is stated with liquid phase coating film and progresses until the coating film is hardened under UV curing, eliminating nonspecific change at the measured wavelengths, where the reflectance of the wavelength of the reflected infrared light at the ultraviolet light activated film-substrate boundary and at the air-ultraviolet light activated film boundary is in real-time. The method for monitoring curing of a coating film according to feature 12, where both infrared thermal sources (1, 2) emit light at an angle between 0° and 45°, preferably at an angle between 0 -20°, most preferably at an angle of 10° with respect to an axis normal to a substrate and an ultraviolet light-activated film. The method for monitoring curing of a coating film according to feature 12 or 13, where both narrow bandpass infrared filters (5, 6) and both infrared pyroelectric detector (7, 8) are positioned at an angle between 0° and 165°, preferably at an angle between 0-20°, and most preferably at an angle of 10° with respect to the axis normal to the substrate and the ultraviolet light-activated film. The method for monitoring curing of a coating film according to feature 12 or 13, where the signal post processing is performed in millisecond time interval for fast reaction times to emergency signaling like change in the curing level and both signals are used on dual channel measurements.

Claims

23CLAIMS1. A system for monitoring curing of an energy curable film, the system comprising: at least one pulsable infrared radiation source (1, 2, 10) arranged to emit at least one infrared beam directed towards the energy curable film, the at least one infrared beam having a wavelength between 2 and 14 pm; at least one lens (3, 4, 11) arranged to focus the at least one infrared beam after the at least one infrared beam is reflected from the energy curable film; at least two narrow bandpass infrared filters (5, 6, 12, 13) arranged to filter the at least one infrared beam after the at least one infrared beam passes through the at least one lens, each filter configured to transmit a respective wavelength range of light; and at least two detectors (7, 8, 14, 15) arranged to detect light transmitted by a respective filter.

2. The system according to claim 1 : i) wherein the energy curable film is an ultraviolet light-activated film; and / or ii) wherein each pulsable infrared radiation source (1, 2, 10) comprises a solid-state hot plate on a thin dielectric membrane, where the membrane is located on a micro-machined silicon substrate, where a random structure radiation-emitting layer consists of black platinum deposited on a heater, and the whole system has a low thermal mass; and / or iii) wherein the or each infrared radiation source is pulsable at 5-100Hz; preferably, the or each infrared radiation source is pulsable at 5-15Hz; or iv) wherein the or each infrared thermal source is modulated up to 100Hz.

3. The system according to any previous claim, wherein each infrared pyroelectric detector (7, 8, 14, 15) comprises a single crystalline lithium tantalate, LiTaO3, element formed as a very thin plate capacitor.

4. The system according to any previous claim, wherein the at least one infrared radiation source comprises an integrated parabolic mirror, and optionally wherein each integrated parabolic mirror increases density of infrared radiation by a factor of 15X for a focal point.

5. The system according to any previous claim, wherein each infrared radiation source (1, 2, 10) is configured for an angular spectrum of 15 degrees of infrared radiation.

6. The system according to any one of the previous claims, where the at least one lens (3, 4, 10) has high-transmittivity in the IR range of 6-10 pm and is a cut-off filter for long-range spectrum above 10pm.

7. The system according to any one of the previous claims, where the narrow bandpass infrared filters (5, 6) have peak transmission between 50-90%; preferably, wherein the narrow bandpass infrared filters have peak transmission greater than80%.

8. The system according to any one of the previous claims, wherein the narrow bandpass filters (5, 6) have a halfwidth between 100-250 nanometres; preferably, wherein the narrow bandpass filters have a halfwidth of about 100-150 nanometres.

9. The system according to any one of the previous claims, where the at least one infrared radiation source (1, 2) is configured to emit light at an angle between 0° and 60°, preferably at an angle between 0° and 20°, most preferably at an angle of 10° with respect to an axis normal to a substrate and the energy curable film.

10. The system according to any previous claim, wherein the system comprises: two pulsable infrared radiation sources (1, 2) arranged to emit wideband 2-14 pm infrared radiation, wherein a first source (1) is arranged to emit a first pulsable infrared beam and a second source (2) is arranged to emit a second pulsable infrared beam; two infrared concentration lenses (3, 4), wherein a first lens (3) is arranged to focus the first pulsable infrared beam and a second lens (4) is arranged to focus the second pulsable infrared beam; two narrow bandpass infrared filters (5, 6), wherein a first filter (5) is arranged to filter the first infrared beam after passing through the first lens (3), and a second filter (6) is arranged to filter the second infrared beam after passing through the second lens (4), wherein the first filter (5) is configured to transmit a first wavelength range of light, and the second filter (6) is configured to transmit a second wavelength range of light; and two infrared pyroelectrical optical detectors (7, 8), wherein a first detector (7) is arranged to receive light transmitted by the first filter (5), and a second detector (8) is arranged to receive light transmitted by the second filter (6).

11. The system according to claim 10, wherein both narrow bandpass infrared filters (5, 6) and both detectors (7, 8) are positioned at an angle between 0° and 45°, preferably at an angle between 0° and 20°, and most preferably at an angle of 10° with respect to the axis normal to the substrate and the energy curable film.

12. The system according to any of claims 1 to 9, wherein a first filter (12) of the at least two narrow bandpass infrared filters is arranged to transmit a first wavelength range of light to a first detector (15) of the at least two detectors, and reflect a remaining portion of the beam; and a second filter (13) of the at least two narrow bandpass infrared filters is arranged to filter the remaining portion of the beam and transmit a second wavelength range of light to a second detector (14) of the at least two detectors.

13. The system according to claim 12, wherein the first filter (12) is arranged to be oriented at an angle of 45 degrees to the at least one infrared beam after it has passed through the at least one lens.

14. The system according to claim 12 or 13, wherein the first filter (12) has a peak transmission between 50-90% at the first wavelength range of light; preferably, wherein the first filter has a peak transmission greater than 80%.

15. The system according to any of claims 12 to 14, wherein the first filter (12) has a reflectivity greater than 99% at the second wavelength range of light.

16. The system according to any of claims 12 to 15, wherein the second filter (13) is arranged to be orientated at an angle of 0 degrees to the remaining portion of the beam.

17. The system according to any of claims 12 to 16, wherein the second filter (13) has a peak transmission between 50-90% at the second wavelength range of light; preferably, wherein the second filter has a peak transmission greater than 80%.

18. A method for monitoring curing of an energy curable film, the method comprising: emitting at least one pulsable infrared beam from at least one infrared radiation source (1, 2, 10), the at least one pulsable infrared beam being directed towards the energy curable film, the at least one pulsable infrared beam having a wavelength between 2 and 14 pm; focusing the at least one infrared beam using at least one lens (3, 4, 11), after the at least one infrared beam is reflected from the energy curable film; filtering the at least one infrared beam after the at least one infrared beam passes through the at least one lens using at least two narrow bandpass infrared filters (5, 6, 12, 13), each filter configured to transmit a respective wavelength of light; detecting the light transmitted by the filters using at least two detectors (7, 8, 14, 15), each detector arranged to detect light transmitted by a respective filter; determining a first signal based on the light detected at a first detector of the at least two detectors (7, 8, 14, 15); determining a second signal based on the light detected at a second detector of the at least two detectors (7, 8, 14, 15); and determining a level of cure of the energy curable film based on the first signal and the second signal.

19. The method according to claim 18: i) wherein the energy curable film is an ultraviolet light-activated film; and / orii) wherein the or each infrared radiation source is pulsable at 5-100Hz; preferably, the or each infrared radiation source is pulsable at 5-15Hz; or iii) wherein, the or each infrared thermal source is modulated up to 100Hz. iii) comprising filtering the at least one infrared beam after the at least one infrared beam passes through the at least one lens using at least two narrow bandpass infrared filters, each filter configured to transmit a respective wavelength wherein the wavelength is between 7 and 9 pm; optionally, each filter configured to transmit a respective wavelength wherein the wavelength is between 8 and 9 pm.

20. The method according to claim 18 or claim 19, wherein the first and second signals correspond to relative concentrations of monomers and oligomers in the energy curable film and the level of cure is related to the concentration of the monomers and the oligomers in the energy curable film, which is indicative of light transmission in the infrared wavelength region.

21. The method according to any of claims 18 to 20, wherein the method is performed in realtime as the ultraviolet light-activated film is cured, transitioning from a liquid phase energy- curable film to a hard energy curable film.

22. The method according to any of claims 18 to 21, wherein the determining a level of cure step is performed within a millisecond time interval.

23. The method according to any of claims 18 to 22, wherein: the emitting comprises simultaneously emitting two pulsable infrared beams from two infrared radiation sources (1, 2), wherein a first source (1) emits a first pulsable infrared beam and a second source (2) emits a second pulsable infrared beam; the focusing comprises focusing the first infrared beam using a first lens (3) and focusing the second infrared beam using a second lens (4); the filtering comprises using a first filter (5) to filter the first infrared beam after passing through the first lens (3), and a second filter (6) to filter the second infrared beam after passing through the second lens (4), wherein the first filter (5) is configured to transmit a first wavelength range of light, and the second filter (6) is configured to transmit a second wavelength range of light; and the detecting comprises using a first detector (7) to receive light transmitted by the first filter (5), and a second detector (8) to receive light transmitted by the second filter (6).

24. The method according to any of claims 18 to 22, wherein the filtering comprises using a first filter (12) of the at least two narrow bandpass infrared filters to transmit a first wavelength range of light to a first detector (15) of the at least two detectors, and reflect a remaining portion of the beam; and a second filter (13) of the at least two narrow bandpass infrared filters to filter27 the remaining portion of the beam and transmit a second wavelength range of light to a second detector (14) of the at least two detectors.

Images