EP3519799A1 - Dispositif et procédé de quantification de propriétés optiques de matériaux transparents - Google Patents

Dispositif et procédé de quantification de propriétés optiques de matériaux transparents

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Publication number
EP3519799A1
EP3519799A1 EP17772423.4A EP17772423A EP3519799A1 EP 3519799 A1 EP3519799 A1 EP 3519799A1 EP 17772423 A EP17772423 A EP 17772423A EP 3519799 A1 EP3519799 A1 EP 3519799A1
Authority
EP
European Patent Office
Prior art keywords
sample
optical
mask
optical properties
light
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.)
Withdrawn
Application number
EP17772423.4A
Other languages
German (de)
English (en)
Inventor
Stephan P. BUSATO
Aleksandr PEREVEDENTSEV
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.)
Eidgenoessische Technische Hochschule Zurich ETHZ
Original Assignee
Eidgenoessische Technische Hochschule Zurich ETHZ
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 Eidgenoessische Technische Hochschule Zurich ETHZ filed Critical Eidgenoessische Technische Hochschule Zurich ETHZ
Publication of EP3519799A1 publication Critical patent/EP3519799A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
    • G01N21/958—Inspecting transparent materials or objects, e.g. windscreens
    • 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
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/8806—Specially adapted optical and illumination features
    • 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
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/8806—Specially adapted optical and illumination features
    • G01N2021/8829—Shadow projection or structured background, e.g. for deflectometry
    • 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
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/8806—Specially adapted optical and illumination features
    • G01N2021/8848—Polarisation of light

Definitions

  • the present application discloses, inter alia, an imaging and measuring device. In addition, the present application discloses an analysis. BACKGROUND
  • the present invention relates to a device and a method for quantifying optical properties of at least partially transparent material samples.
  • the present invention is directed to a versatile, end-user-defined device and method for quantifying optical properties such as, but not limited to, haze, as well as the spatial distribution thereof, for a plurality of material samples.
  • Materials display a wide range of characteristics that depend on, among others, their chemical composition and microstructure. Of these, optical characteristics often play a critical role in determining the suitability of a material for selected applications while, simultaneously, providing insight into related material characteristics such as mechanical, thermal and electrical.
  • Certain optical characteristics may be especially significant for a particular intended use or function of material.
  • the haze characteristics of various materials or compounds thereof are an important aspect of the design of many products. Haze is defined by the American Society for Testing and Materials as "the scattering of light by a specimen responsible for the reduction in contrast of objects viewed through it" (ASTM D1003).
  • Light-transmitting articles such as glass, films and foils are used in a wide variety of fields for the manufacture of products such as screens, containers, packaging materials, coatings, eyewear and optical filters.
  • Much research and development in many industries is focused on controlling and optimizing the haze of the constituent materials, especially in combination with the related optical or other characteristics.
  • materials used in products such as eyewear, packaging and screens may typically require high transmittance and minimal haze values in a specified spectral region for providing users with clear images of the viewed objects.
  • products such as light diffusers as used, for instance, in optical components and photovoltaics may demand low absorbance and, simultaneously, maximal haze.
  • haze is an optical property that has relevance to a wide range of fields.
  • the prior art standard for quantifying haze utilizes a dedicated Haze Meter instrument designed and developed by, most notably, BYK-Gardner GmbH (US Patent 5,760,890).
  • the amount of light transmitted through a material and the amount of light scattered by the same material are measured, and the ratio of scattered light to the total amount of transmitted light yields a haze value for the analyzed material sample.
  • the prior art instrumentation for assessing the haze is limiting in a number of significant aspects. First, it is costly and, arguably, provides limited optical information on the analyzed samples.
  • the instrumentation outputs a single, spatially- and spectrally-averaged value for the analyzed optical characteristics such as haze or transmittance.
  • these aspects necessitate the use of relatively large and maximally homogeneous material samples which may differ from the intended products while, simultaneously, obscuring the effects of, for instance, local microstructure heterogeneities on the optical characteristic of interest. Consequently, a merely subjective, relative estimation of haze is still often performed both during development and manufacturing which incurs the obvious disadvantage of large uncertainties in the evaluation of this important optical characteristic.
  • the present invention provides an inexpensive, versatile, end-user-defined device and method by means of which optical properties of at least partially transparent materials may be measured at different spatial locations on a material sample.
  • An exemplary embodiment of the device comprises three principal elements, namely (i) an illumination means which makes light impinge on a sample, (ii) one or more modulation elements which modify light characteristics prior to and/or following its interaction with a sample and (iii) a measurement means for detecting the characteristics of light that has impinged on the sample.
  • the method and the associated analysis for determining the optical properties for a given sample are based on an evaluation of the changes to the characteristics of the illumination light incurred by its interaction with the material sample.
  • the inventive device uses an illumination means which is arranged such that the illumination light passes a sample reception space wherein the sample can be placed and then impinges into a measurement means.
  • illumination means which is arranged such that the illumination light passes a sample reception space wherein the sample can be placed and then impinges into a measurement means.
  • light is understood to be any part of the electromagnetic radiation spectrum, with the corresponding wavelengths ranging from 0.01 nm (X-ray) to over 10 ⁇ 00 nm (far infrared).
  • the spectral composition of the illumination light covers any part of the visible light spectrum such as, for instance, may be obtained using a light-emitting diode (LED).
  • LED light-emitting diode
  • the spectral composition of the illumination light corresponds to a standardized composition such as that for, for instance, the Commission Internationale de I'Eclairage (CIE) standard illuminants (e.g. ISO 10526:1999/CIE S005/E-1998) or the standardized light sources used in solar simulators (e.g. ASTM E490).
  • the spectral composition of the illumination light covers any wavelength between 0.01 nm and 10 ⁇ 00 nm, such as to characterize optical properties of materials outside the wavelength range of visible light.
  • the inventive device includes a measurement means for quantifying the spatial distribution of the intensity of light that has interacted with - that is, passed through or impinged upon - the material sample.
  • a measurement means for quantifying the spatial distribution of the intensity of light that has interacted with - that is, passed through or impinged upon - the material sample.
  • such measurement means is a digital still camera.
  • the measurement means is a digital video camera.
  • the measurement means is based on photoactive materials such as those used in film for analog still image and video cameras.
  • the measurement means contains any number and type of material or device that is photoactive in a desired wavelength range.
  • the inventive device uses at least one means for modulating the characteristics of light impinging on and/or transmitted through a material sample; such characteristics include, but are not limited to, light intensity, polarization, spectral bandwidth, phase, direction of propagation, duty cycle, as well as the spatial distribution thereof.
  • a preferred embodiment of the inventive device utilizes a mask featuring spatially-modulated transmittance and/or reflectance that, in turn, spatially modulates the intensity of light impinging on a sample.
  • the function of the mask is twofold. Qualitatively, it represents an object, viewing which through a hazy material sample incurs some degree of "reduction in contrast" (ASTM D1003) of its features - that is, a reduction of perceived image quality. Quantitatively, it allows the haze values at different spatial locations on a material sample to be calculated using the analysis described below.
  • an advantage of the inventive device is that additional modulation elements can be employed to extract further spatially-resolved information about the material sample and, if desired, correlate it with other local optical properties such as haze.
  • the inventive device includes an optical polarizer arranged between the illumination means and the sample, in combination with an optical analyzer arranged between the sample and the measurement means, which may be used to yield information on the sample's birefringence and/or microstructure heterogeneity.
  • additional modulation means can be employed to extract further information on the material sample; such modulation means may include, among others, masks, optical filters, polarizers, optical waveplates, lenses, collimators and diffusors.
  • the three principal elements of the inventive device namely the illumination, modulation and measurement means
  • the three elements are placed on a single axis, termed the "optical axis" in the field of imaging and optics, in order to enhance the homogeneity of sample illumination and facilitate measurement, as well as to enable rotational symmetry of the elements around the optical axis.
  • the ability to detect the changes to the optical characteristics of the illumination light incurred by its interaction with a given material sample at different spatial locations on the said sample is provided.
  • the number and position of these locations depend on the number and arrangement of light-sensitive elements present in the measurement means as well as on the geometrical design of the modulation means.
  • a video camera is used as the measurement means, additionally the spatially-resolved optical characteristics of the illumination light can be measured as a function of time.
  • the inventive method allows particular optical characteristic properties of transparent materials to be quantified at a number of spatial locations on a sample using the data obtained from optical measurements performed using the inventive device. a) Haze
  • the analysis involves determining the modulation transfer function (MTF; magnitude vs. spatial frequency /) for the image of the mask at a given spatial location from analysis of the images of (i) the mask in the absence of sample and (ii) the mask viewed through the sample. From the respective modulation transfer functions a "haze spectrum", / (/), for the sample is calculated. For transparent materials the average value of H(f) x 100% over a selected spatial frequency interval essentially matches the optical property "haze" as defined by ASTM D1003. Such analysis can be performed at different spatial locations on the sample placed between the mask and the measurement means in order to obtain spatially-resolved optical property data.
  • MTF modulation transfer function
  • an optical property T of the sample at a given spatial location is determined from analysis of the images of (i) the illuminated sample reception space in the absence of sample and (ii) the illuminated sample. The reduction in measured light intensity incurred by placing the sample in the path of the illumination light is then used to calculate the value of T for the sample.
  • the optical property T is a measure of the sample's transmittance at the corresponding spatial location. Such analysis can be performed at different spatial locations on the sample in order to obtain spatially-resolved optical property data.
  • an optical property R of the sample is determined from the MTF data obtained as described under "a) Haze" as the spatial frequency / at which the magnitude of the MTF for the mask viewed/imaged through the sample reaches a selected low value.
  • the optical property R is a measure for the sample's optical resolution. Such analysis can be performed at different spatial locations on the sample placed between the mask and the measurement means in order to obtain spatially-resolved optical property data.
  • the field of application is determined by variables such as the requirement for spatially-resolved optical information, the specific modulation elements employed, the relative placement of the sample and modulation elements and the spectral properties of the illumination light.
  • variables such as the requirement for spatially-resolved optical information, the specific modulation elements employed, the relative placement of the sample and modulation elements and the spectral properties of the illumination light.
  • Optical properties in the visible light spectral range may typically be of interest in the development and manufacture of packaging materials, for instance films, foils, coatings and containers, for which the degree and homogeneity of optical properties such as transmittance, haze, optical resolution and optical activity is of critical importance.
  • the present invention can be used to spatially characterize such properties while the use of modulation elements such as polarizers and analyzers can additionally correlate them with, for instance, material flow during processing via imaging of the optical birefringence.
  • modulation elements such as polarizers and analyzers can additionally correlate them with, for instance, material flow during processing via imaging of the optical birefringence.
  • using a suitable mask as the modulation means and placing it in or out of contact with the material sample can be used to quantify, respectively, "contact” or “non-contact” haze as may be of interest for a particular application .
  • Similar properties are pertinent to the quality of other transparent materials including, but not limited to, glass plates, films, foils and coatings for buildings, vehicles, greenhouses, optical filters, sporting articles, fashion articles, glasses, protective gear and eyewear.
  • Selected optical properties of such articles can be characterized by the present invention, in which the ability to straightforwardly control the spectral properties of the illumination light via the use of modulation elements such as optical filters can be used to obtain optical property data in the spectral region relevant for the intended applications.
  • modulation elements such as optical filters
  • For suspensions, emulsions and dispersions such as, for instance, found in food products, cosmetics, paints and varnishes, and widely studied and exploited in many branches of life sciences, the homogeneity and stability of said dispersions is of critical importance for the intended applications.
  • the present invention can be used to quantify haze as well as other selected optical properties spatially and/or as a function of time which can be useful for monitoring aging- and/or chemically- induced compositional fluctuations in food products such as mayonnaise, sedimentation in particle- filled fluids, as well as formation of micelles, to state only a few examples. Similar uses of the present invention can be pertinent to the quantification of the optical properties of fog, mist, aerosols, and their deposits on solid and fluid substrates, with exemplary applications including smoke detection and dew point determination.
  • Yet another area of relevance for the present invention is the in-situ monitoring of chemical reactions and physical processes, for instance: curing of resins, crystallization of polymers, aging of materials and products, and rheology of fluids such as, but not limited to, 3-D printing inks.
  • Such processes are often typified by the characteristic corresponding changes in the optical properties such as haze and transmittance, which can be quantified by the present invention.
  • the present invention may be beneficial for optical imaging techniques such as those employed in, for instance, ophthalmology for characterizing human eye lens disorders.
  • optical imaging techniques such as those employed in, for instance, ophthalmology for characterizing human eye lens disorders.
  • Artificial Intelligence is another field of relevance, where the present invention may be used to enhance an intelligent machine's capability of perceiving its environment through optical imaging and analysis.
  • Additional areas of application for the present invention include those involving imaging with electromagnetic radiation outside the range of visible light.
  • X-ray radiation is used, as in radiography and tomography
  • the corresponding haze, transmittance and resolution measurement is adjuvant for instance, but not limited to, in medical diagnostics and research, in non-destructive testing and evaluation of engineering materials and objects, in scientific diffraction and scattering analyses and in civilian and military security and safety scanning appliances.
  • infrared light is employed - such as, but not limited to, in thermal imaging as used in civil, mechanical and electrical engineering, as well as in civilian and military reconnaissance - haze
  • transmittance and resolution measurements can be exploited to determine the properties of the material located between the radiating source and the measurement means.
  • FIG. 1 represents an embodiment of the inventive device, including the illumination, modulation and measurement means.
  • FIG. 2 represents various embodiments of "knife-edge" masks used as the modulation means.
  • FIG. 3 represents selected aspects of the analysis used for quantifying optical properties of material samples illuminated through a mask modulation element.
  • an illumination means 11 is a light source arranged such that its output is detected by the measurement means 16.
  • the illumination means 11 is an incandescent lamp or an LED emitting visible light.
  • a preferred embodiment for the measurement means 16 is a digital image capturing device such as a digital still camera, while a digital video camera represents another embodiment which may be advantageous for monitoring selected optical properties as a function of time.
  • a material sample 14 is arranged such that the light from the illumination means 11 can be made impingent on it. In one embodiment a material sample in solid, liquid or gas form is used.
  • the material sample is enclosed within a transparent container such as a glass cuvette.
  • a means for determining optical characteristics such as haze and resolution hereafter termed a "mask" 13 is used to spatially modulate the intensity of light impinging on the sample 14.
  • the sample is placed in direct contact with the mask featuring spatially-modulated transmittance.
  • the sample is separated from said mask by, for instance, a layer of air or immersion fluid.
  • one end of the sample is physically separated from said mask by, for instance, a wedge while the other end of the sample is in contact with the mask.
  • haze In terms of, for instance, haze, a choice of these embodiments may be used to determine, respectively, "contact” haze, “non-contact” haze or the increase in haze as a function of distance between the material sample and the object viewed through it.
  • the described elements are arranged on a single axis, hereafter termed the "optical axis" 17, as depicted for the exemplary configuration in FIG. 1.
  • optical axis Such arrangement may be used to facilitate measurement by improving the homogeneity of sample illumination and enabling rotational symmetry of the elements around the optical axis.
  • both illumination and detection means are placed, for instance, at selected locations above the material sample, in which case the mask placed below the sample preferably features spatially-modulated reflectance in order to spatially modulate the intensity of illumination light re-transmitted through the sample.
  • the two above-described embodiments of the inventive device allow, respectively, "transmission” or “reflection” haze to be determined for a given material sample, with the corresponding values commonly showing quantitative differences.
  • a particular embodiment may be selected in order quantify optical properties pertinent to the intended application of said material sample.
  • Additional modulation elements 12 and 15 may be placed between the illumination and/or measurement means and the sample 14.
  • modulation means 12 and 15 as well as mask 13 may be chosen in order to quantify selected optical properties.
  • a diffuser is used as the modulation means 12 in order to obtain maximally homogeneous distribution of illumination light impingent on the sample.
  • optical filters are used as the modulation means 12 and/or 15 in order to, for instance, eliminate any possible fluorescence from the sample or define the spectral range within which selected optical properties are determined.
  • a polarizer is used as the modulation means 12 and an analyzer, with its transmission axis oriented orthogonal to that of the polarizer, is used as the modulations means 15, thereby allowing optical birefringence to be imaged for the sample.
  • the aforementioned mask 13 employed in the present invention for quantifying optical properties such as haze and resolution can be realized in several embodiments.
  • the common feature of these is spatially modulated transmittance and/or reflectance of the mask, that is to say that the mask features at least two areas of non-identical transmittance and/or reflectance.
  • the function of the mask is to generate a spatial pattern of light intensities, originating from the specific spatially-modulated optical properties of said mask, which is made to impinge upon, and be transmitted through, a material sample. Viewing said pattern of light intensities through a material sample would reduce the sharpness of transitions between adjacent individual elements of the pattern compared with the case when no material sample is placed between the illuminated mask and the measurement means. As will be shown below, the degree of this reduction in the perceived sharpness of the light pattern can be correlated with the optical properties such as haze and resolution for the material sample used.
  • a mask 13 comprises an array of "knife-edge" elements, wherein a knife- edge is understood to be any means for providing a step function, also known as the Heaviside step function, in transmittance and/or reflectance.
  • a knife-edge array mask features maximally abrupt transitions between areas with, for instance, 0% transmittance and 100% transmittance, although the absolute transmittance values may vary depending on the specific mask used.
  • Note that other embodiments for the mask 13 may be realized; for instance, in another embodiment a mask features a graduated, rather than abrupt, spatial transition between areas of the mask featuring different transmittance and/or reflectance.
  • a particular criterion may be formulated by the end-user of the inventive device in order to distinguish the two types of edge modulation elements.
  • a knife-edge modulation element may be selected to be expressed as a spatial gradient in transmittance and/or reflectance (dl/dx) > 250 %/mm across said edge element, wherein / is transmitted and/or reflected light intensity and x is position on said element.
  • FIG. 2 depicts several embodiments of knife-edge array masks in terms of the arrangement and orientation of the constituent knife-edge elements. Keeping in mind that the perceived sharpness of light pattern features generated by a mask is determined perpendicular to the constituent knife-edge elements, the orientation of said elements is dictated by the specific requirements for imaging the spatial distribution of selected optical properties.
  • the knife-edge elements are arranged in a stripe pattern.
  • the knife-edge elements are arranged in a "checkerboard" pattern.
  • the knife-edge elements are arranged in a concentric pattern.
  • the knife-edge elements are arranged in a radial pattern.
  • Quantitative analysis of selected optical properties of transparent materials using the present invention is based on determining changes in the characteristics of illumination light incurred by its interaction with a given material sample.
  • a knife-edge array mask such as one of a selection depicted in FIG. 2 is used to generate a spatial pattern of light intensities which is then transmitted through a material sample as depicted for an exemplary device configuration in FIG. 1.
  • the details of quantitative analysis of selected optical properties, namely haze, transmittance and resolution, for this exemplary embodiment are given below with reference to FIG. 3. It is emphasized, however, that the analysis below is also applicable for other embodiments of the inventive device utilizing, for instance, a "graduated" edge array mask as the modulation means.
  • digitized images of the mask itself and the mask viewed through a material sample are converted to, for instance, grayscale in order to generate a single scale for the detected light intensities prior to performing the above-described image analysis.
  • said digitized images are analyzed in their original color space, in which case for color images the above- described analysis is preferably performed separately for the individual components constituting said color space.
  • image processing may be performed by any of the available computer software packages.
  • Optical properties the quantitative analysis of which is described below, are determined for the spectral range given by both the spectral distribution of light impinging on the sample and the spectral sensitivity of the measurement means. Those skilled in the art may optimize both according to the specific optical property data requirements.
  • Modulation transfer function hereafter abbreviated as MTF and expressed as magnitude vs. spatial frequency /, is the magnitude response of an optical system to sinusoids of different spatial frequencies.
  • MTF thus specifies the amplitude/contrast reduction of a sinusoidal pattern after passing through a hazy - that is, "dull/milky" to quote the terminology used in the prior art (US Patent 5,760,890) - material sample as a function of periodicity of the sinusoidal input. It is further noted that while in practice most inputs are not sinusoidal, they can nevertheless be represented by a sum of sinusoidal components using Fourier transform.
  • analysis of haze involves determining the MTF for images of a knife-edge - that is, the light pattern generated by it - obtained in two configurations: (i) the knife-edge in the absence of sample and (ii) the knife-edge viewed through a material sample.
  • Representative light intensity distribution 30 and MTF 32 data corresponding to the two above-described configurations are shown schematically in FIG. 3. Such analysis is performed for a single selected location on the knife-edge and the sample, and any number of said locations can be analyzed in order to obtain spatially-resolved optical property data.
  • MTF data from light intensity distributions for knife-edge 30 or "graduated edge" 31 embodiments of the mask modulation means can be straightforwardly extracted using the widely-known open-source computer software ImageJ.
  • a haze spectrum / (/) 33 for the material sample ' then calculated according to the formula MTF ' sa7n pi e v ⁇ a m ask
  • an optical property T for the sample is determined for any location on a material sample illuminated via any part of the mask that features unmodulated - that is, spatially homogeneous - non-zero transmittance. T in percent (%) units is then calculated according the formula _ I sample via mask ⁇
  • I sample via mask and ⁇ mask are the light intensities detected for, respectively, the mask imaged though a material sample and the mask imaged in the absence of sample.
  • an optical property R is determined from the MTF data obtained for the knife-edge imaged through a material sample as described in a) Haze.
  • R is given by the spatial frequency / at which the magnitude of the MTF - which commonly decreases with increasing / as exemplified in 32 in FIG. 3 - reduces to a selected low value.
  • Such analysis is performed for a single selected location on the knife- edge and the sample, and any number of said locations can be analyzed in order to obtain spatially- resolved optical property data.
  • haze and transmittance referred to in the examples below and expressed in percent (%) were determined using an embodiment of the inventive device and analysis as well as using a dedicated commercial haze meter Haze-Gard Plus (BYK-Gardner GmbH, Germany) operated in adherence to the ASTM D1003 standard and routinely calibrated using transmittance standards.
  • Haze standards referred to in the examples below featuring nominal haze values of 4.79, 10.30, 20.20 and 30.40% (AT-4741, AT-4742, AT-4743 and AT-4744 respectively) were obtained from BYK- Gardner GmbH, Germany.
  • Polyethylene (PE) referred to in the examples below was the linear-low- density polyethylene (LLDPE) resin DOWLEXTM 2552E obtained from The Dow Chemical Company, USA. As expected for a rapidly-crystallizing semicrystalline polymer, its visual appearance after typical melt-processing is dull/milky, indicative of appreciable haze.
  • the additive referred to in the examples below is a so-called "clarifying agent” 1 ,2,3-trideoxy-4,6:5,7-bis-0-[(4-propylphenyl)methylene]-nonitol (Millad NXTM 8000) obtained from Milliken Chemical, USA.
  • Polypropylene (PP) referred to in the examples below is the isotactic polypropylene (iPP) Pro-fax PH350 resin obtained from
  • Neat PE as well as the PE/additive blends referred to in the examples below were compounded for 5 minutes in a mini-twin-screw extruder (Xplore® MC 15; DSM, The Netherlands) operated at 220 °C and 40 rpm under a nitrogen blanket.
  • PE/additive blends exhibit haze values different from those of neat PE when processed under identical conditions.
  • Circular plaque samples (1 mm thickness, 26.6 mm diameter) referred to in the examples below were prepared by injection molding of neat PE and PE/additive blends using a micro injection molder (Xplore® IM 12; DSM, The Netherlands) into a mold kept at room temperature.
  • Thin films of PE and PP were fabricated by compression molding at 210 °C and 235 °C, respectively, followed by quenching and consolidation in a water-cooled (7 °C) press. Mold plates were lined with polyimide to provide maximally smooth film surfaces. Spacers were placed between the mold plates to provide the desired film thickness.
  • Photographic imaging referred to in the examples below was performed with the inventive device configured according to FIG. 1 , using a light-emitting diode (XM-L T6 Cool White; Cree, USA) as the illumination means 11 , a laser-cut apertured stainless steel sheet (0.1 mm thickness, grid pattern similar to 22 in FIG. 2 comprising 2 mm wide stripes separated by 2 mm wide gaps) as the mask 13, corresponding specifically to a "knife-edge array mask" in the description above, and a digital still camera (EOS 6D; Canon, Japan) as the measurement means 16.
  • a light-emitting diode XM-L T6 Cool White; Cree, USA
  • a laser-cut apertured stainless steel sheet 0.1 mm thickness, grid pattern similar to 22 in FIG. 2 comprising 2 mm wide stripes separated by 2 mm wide gaps
  • EOS 6D digital still camera
  • 8-bit RGB photographic images were saved in raw ('Canon CR2') format and subsequently converted to 8-bit grayscale format using Adobe Photoshop CS6 software (default conversion settings; 'Gray Gamma 1 .8' profile) available from Adobe Systems Inc., USA.
  • Modulation transfer functions (MTF) referred to in the examples below were calculated from photographic images of "knife-edge" transitions using the open-source software ImageJ (ImageJ with SE_MTF_2xNyquist.jar plugin; National Institutes of Health, USA). Spatial frequency units reported in the examples below and expressed in line pairs per millimeter (Ip/mm) are related to the dimensions of the knife-edge array mask and are thus independent of the specific imaging hardware and device configuration used.
  • a polarizer as the modulation means 12 was placed between the illumination means 11 and the sample 14, and an analyzer as the modulation means 15 was placed between the sample 14 and the camera 16.
  • Polarizer 12 and analyzer 15 were aligned such as to provide orthogonal orientation of their respective transmission axes.
  • Each of the four haze standards obtained from BYK-Gardner GmbH, was individually placed on top of the knife-edge array mask, illuminated through the mask from below and photographed from above. Additionally, the mask was photographed under identical conditions but without a haze standard placed on top. Modulation transfer functions (MTF) were calculated for a "knife edge" transition in the central part of the images, and the haze spectrum //(/) for each standard was calculated therefrom. Haze, as the average value of //(/) x 100 over the spatial frequency / interval of 5-10 Ip/mm was calculated to be 4.9, 10.2, 22.0 and 32.9% for the four standards. Haze determined according to ASTM D1003 using a commercial Haze-Gard Plus haze meter obtained from BYK-Gardner GmbH was found to be 4.8, 10.3, 20.3 and 30.5% respectively.
  • MTF Modulation transfer functions
  • Example 2 Neat polyethylene was injection molded to yield a plaque sample of 1 mm thickness and 26.6 mm diameter. The sample was placed on top of the knife-edge array mask, illuminated through the mask from below and photographed from above. Additionally, the mask was photographed under identical conditions but without the plaque sample placed on top. Modulation transfer functions (MTF) were calculated for "knife-edge" transitions at five spatial locations on the images, and the corresponding haze spectra //(/) for the sample were calculated therefrom. Haze, as the average value of //(/) x 100 over the spatial frequency / interval of 5-10 Ip/mm, was calculated to be 90.1 ⁇ 1 .3%. Haze determined according to ASTM D 1003 was found to be 91 .4%.
  • MTF Modulation transfer functions
  • Example 4 Polyethylene was compounded with 0.25% w/w of the additive and injection molded to yield a plaque sample as in Example 2. Haze, determined as in Example 2, was found to be 23.5 ⁇ 4.2%. Haze determined according to ASTM D1003 was found to be 34.5%.
  • Example 4
  • Example 2 Polyethylene was compounded with 2% w/w of the additive and injection molded to yield a plaque sample as in Example 2. Haze, determined as in Example 2, was found to be 39.6 ⁇ 4.7%. Haze determined according to ASTM D1003 was found to be 56.3%.
  • haze values obtained in Examples 1-4 are compiled in Table 1 . Noted are the relatively large, up to 18% of the overall average value, deviations in haze for the PE and
  • PE/additive plaque samples These are likely to originate from processing issues resulting in, for instance, surface irregularities and microstructure heterogeneities, thus emphasizing the importance of spatially-resolved optical property measurements which cannot be straightforwardly performed using the conventional haze meter instrument.
  • inventive device/method haze meter (ASTM D1003)
  • Transmittance values were calculated for the unmasked regions in the central part of the images obtained in Examples 2, 3 and 4 and were found to be 93, 92 and 88% respectively. Transmittance values determined by the haze meter were found to be 83, 81 and 74% respectively. For comparison purposes, the obtained transmittance values are compiled in Table 2.
  • inventive device/method haze meter (ASTM D1003)
  • Resolution values were calculated from the MTF data obtained in Examples 1 , 2, 3 and 4 as the value of spatial frequency f (Ip/mm) at which the magnitude of the MTF for a given sample reduces to a selected low value, hereafter denoted as MTF 0 .
  • the selected MTF 0 values were 0.5 and 0.05.
  • the same analysis was performed for the knife-edge array mask in the absence of any sample placed on top. The obtained resolution values are compiled in Table 3.
  • optical properties can be defined, as may be required for particular applications of the inventive device and method, and quantified by mathematical manipulation of haze or transmittance or optical resolution values, or combinations thereof, calculated as disclosed above.
  • R samp i e and R mask are the resolutions of the sample and the mask, respectively.
  • C may be used as a measure for the optical property "clarity".
  • PE and PE/additive plaque samples from Examples 2, 3 and 4 were photographed between crossed polarizers with the knife-edge array still in place. The corresponding photographs are shown in Image 1 (left to right: PE, PE / 0.25% additive, PE / 2% additive; mask stripes oriented horizontally).
  • Microstructure inhomogeneities were evidenced as distinct birefringence patterns in the images of PE/additive blend samples. If desired, such images may be superimposed onto the corresponding images of the samples illuminated through the knife-edge array mask without the use polarizers, thereby allowing local optical properties to be correlated with the relative degree of birefringence for the same location. Such analysis may be used to elucidate the relation between specific optical properties such as haze and microstructure inhomogeneity in these samples.
  • Haze was measured for polyethylene (PE) and polypropylene (PP) thin films fabricated by compression molding as a function of increasing separation distance between the knife-edge array mask and said films.
  • the samples were illuminated through the mask from below and photographed from above. Spacers of predetermined thickness were placed between the sample and the mask in order to incrementally and homogeneously vary the distance between them, and individual images were acquired. It was ensured that the near-distance depth of field of the imaging optics exceed the sum of sample thickness and the highest separation distance used - that is, both the mask and the samples were in focus in all of the acquired images. Additionally, an image of the mask was acquired under identical conditions but without any sample placed on top.
  • Modulation transfer functions were calculated for "knife-edge" transitions at three spatial locations on the images, and the corresponding haze spectra //(/) for the sample were calculated therefrom. Haze, as the average value of //(/) x 100 over the spatial frequency / interval of 5-10 Ip/mm, was calculated for each sample at each separation distance, with the obtained values compiled in Table 5, wherein the thicknesses d of the analyzed films are also indicated.
  • Such analysis may be used to specifically quantify "contact” and/or "non-contact” optical properties for a given material sample in order to determine its suitability for envisaged applications.
  • “contact” optical properties may be particularly relevant for materials used in laminates while “non- contact” optical properties may be of particular interest for materials used in containers.

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Abstract

La présente invention concerne un dispositif et un procédé associé pour quantifier des propriétés optiques d'échantillons de matériau au moins partiellement transparents. Dans un mode de réalisation, la présente invention concerne un dispositif et un procédé polyvalents pour quantifier des propriétés optiques telles que, mais sans limitation, un trouble, un facteur de transmission et une résolution, ainsi que leur distribution spatiale, pour une pluralité d'échantillons de matériau. Le procédé de détermination des propriétés optiques pour un échantillon donné peut être basé sur une évaluation des changements des caractéristiques de la lumière d'éclairage consécutifs à son interaction avec ledit échantillon.
EP17772423.4A 2016-09-29 2017-09-26 Dispositif et procédé de quantification de propriétés optiques de matériaux transparents Withdrawn EP3519799A1 (fr)

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Publication number Priority date Publication date Assignee Title
DE29511344U1 (de) 1995-07-13 1996-11-14 Byk-Gardner GmbH, 82538 Geretsried Vorrichtung zur Messung von optischen Kenngrößen transparenter Materialien
US5621520A (en) * 1996-05-13 1997-04-15 Northrop Grumman Corporation Transparency inspection method for blurriness in vehicle windscreens with elastomeric liners
DE19741384A1 (de) * 1997-09-19 1999-03-25 Heuft Systemtechnik Gmbh Verfahren zum Erkennen von diffus streuenden Materialien, Verunreinigungen und sonstigen Fehlern bei transparenten Gegenständen
DE19930688A1 (de) * 1999-07-02 2001-01-04 Byk Gardner Gmbh Vorrichtung und Verfahren zur Bestimmung der Qualität von Oberflächen
US6900884B2 (en) * 2001-10-04 2005-05-31 Lockheed Martin Corporation Automatic measurement of the modulation transfer function of an optical system
DE102009040642B3 (de) * 2009-09-09 2011-03-10 Von Ardenne Anlagentechnik Gmbh Verfahren und Vorrichtung zur Messung von optischen Kenngrößen transparenter, streuender Messobjekte
CN104165753B (zh) * 2014-08-01 2017-02-01 京东方科技集团股份有限公司 透明显示屏的检测装置和检测方法

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