阅读说明：本技术 通过近红外高光谱成像进行测量的薄膜厚度测量仪 (Film thickness measuring instrument for measuring by near-infrared hyperspectral imaging ) 是由 X·陈 J·王 M·M·毕晓普 C·M·瑟伯 M·本尼迪克特 H·金 E·L·马驰班克斯 于 2020-01-22 设计创作，主要内容包括：本发明教导包含测量整个薄膜厚度的方法。所述方法可以包含形成聚合物薄膜(10)以及用同时采集多个点的空间图像和光谱图像的相机(20)来测量所述薄膜(10)的厚度。所述相机可以从所述薄膜的某条线采集线图像。所述相机可以是高光谱近红外相机。在分析在所述测量步骤期间采集的原始数据时,可以使用经典最小二乘分析来校正所述原始数据的条纹。(The present teachings encompass methods of measuring the thickness of the entire film. The method may include forming a polymer film (10) and measuring a thickness of the film (10) with a camera (20) that simultaneously acquires spatial and spectral images of a plurality of points. The camera may capture a line image from a certain line of the film. The camera may be a hyperspectral near infrared camera. In analyzing the raw data acquired during the measuring step, the fringes of the raw data may be corrected using a classical least squares analysis.)

1. A method, comprising the steps of:

a. obtaining a polymer film, sheet or sheet; and

b. measuring the thickness of the film, sheet or sheet,

wherein the measuring step is performed using a camera that simultaneously acquires both spatial and spectral images of a plurality of points.

2. The method of claim 1, wherein the camera captures a line image from a certain line of the film, sheet or lamina.

3. The method of claim 1, wherein the film, sheet, or sheet has a thickness of 2mm or less.

4. The method of any preceding claim, wherein the camera collects light having a wavelength of 780nm or greater to 2500 nm.

5. The method of claim 4, wherein a light source emitting light having a wavelength of 780nm or greater to 2500nm is positioned on a side of the polymer film, sheet or lamina opposite the camera.

6. The method of claim 5, further comprising the steps of:

the polymer film is formed using a blown film process.

7. The method of claim 6, wherein the blown film process comprises forming a film bubble, and wherein the measuring step is performed on the bubble to determine a thickness of the film forming the bubble.

8. The method of claim 6, wherein the blown film process comprises collapsing a film bubble to produce a flat device (layflat), and wherein the measuring step is performed on the flat device to determine a thickness of the flat device or one or more layers thereof.

Technical Field

In general, the present teachings relate to the measurement of the thickness of a thin film. More particularly, the present teachings relate to hyperspectral cameras and their use for measuring the thickness of thin films.

Background

Polymeric film materials are used in a wide range of products and packaging. These film materials are generally classified as either packaged or unpackaged. The packaging film can be used in food applications, non-food applications, and other applications. Food packaging films can be used, for example, in product bags, baked goods, bread, and candy; for wrapping meat, poultry, seafood or candy; or for box bags or boiling bags. Non-food packaging films may be used, for example, in grocery sacks, blister cloths, envelopes, and industrial liners. Other packaging may include stretch and shrink wrapping. Non-packaging film applications include grocery bags, can liners, agricultural films, construction films, health care films, garment bags, house wrap and even as part of disposable diapers.

In producing these films, it is important to maintain the desired thickness and reduce gauge variation of the film. Providing multiple data points is also important because weak points of the film may be missed when fewer data points are collected.

One method of producing these films is by a blown film process. Systems for measuring the thickness of a film in a blown film process rely on an in-line thickness measuring device to send real-time film thickness to an automated mold or an automated air ring to control gauge variation. Currently, various types of thickness gauge technology are used in the blown film industry.

Historically, gamma backscatter sensors or capacitive sensors have been used on air bubbles in blown film applications to measure total thickness. Transmission sensors (e.g., beta, gamma, x-ray, and near infrared) have been used on collapsed bubbles or two-layer films (also known as flat mounts).

Conventional capacitive sensors must contact the surface of the film to measure thickness. However, touching the film risks tearing the film and has certain limitations because it does not allow measurement of the adhesive film. Recently, compressed air has been used to control the small gap between the capacitive sensor and the surface of the membrane to overcome these disadvantages. However, the scanning speed is very slow and a single position is measured at a time. Therefore, it cannot provide a full film thickness profile. In addition, if used in blown film applications, this requires stable bubbles. Any significant change in the shape of the bubble during production can push the sensor pin into the bubble and cause production failure.

Scanners such as beta, gamma, x-ray and infrared are all single point scanning technologies. Therefore, they also fail to provide a full film thickness profile. Other gauges for measuring the thickness profile of a thin film are very expensive and cannot scan a wide thin film.

Despite efforts to improve film thickness measurement or monitoring of the film (e.g., during production), there is still a need to measure the entire film thickness in real time to better control the process.

Disclosure of Invention

The present invention teaches the use of a simple and compact construction method by which the measurement of the thickness of a sample can be achieved with relatively few components. The measurement can be performed without contacting the sample. The measurement can be made quickly and/or in real time. The measurement may occur in-line (e.g., during the process of forming a film, sheet, or web). The measurement may be performed off-line (e.g., after forming a film, sheet, or web).

The present teachings include a method comprising obtaining a polymer film, sheet, or sheet and measuring the thickness thereof. The measuring step may be performed using a camera that acquires spatial and spectral images of a plurality of points at a time. This may allow for measurement of the overall film thickness and/or generation of a full film thickness profile. The camera may capture a line image from a certain line of the film, sheet or lamella. The line image may comprise about 10 pixels or more, about 20 pixels or more, about 100 pixels or more, or even about 300 pixels or more. The spectral image may comprise about 10 pixels or more, about 20 pixels or more, about 100 pixels or more, or even about 300 pixels or more. The spectral image may, for example, cover the wavelengths of infrared and/or near infrared (e.g., about 800 to 25,000nm, about 12,500 to 400 cm)^-1Or both). The camera may be a hyperspectral camera. The camera may be a hyperspectral near infrared camera. The measuring step may be performed in real time. The measuring step may be performed in the longitudinal direction. The measuring step may be performed in a transverse direction.

The film, sheet or sheet may comprise polyethylene, polypropylene, polyester, nylon, polyvinyl chloride, cellulose acetate, cellophane, semi-embossed film, bioplastic, biodegradable plastic, or combinations thereof. The film may be formed by operations such as blowing, casting, extruding, calendering rolls, solution deposition, skiving, co-extruding, laminating, extrusion coating, spin coating, deposition coating, dip coating, or combinations thereof. The obtaining step may comprise forming the film using a blown film process. The blown film process may include forming film bubbles. The measuring step may be performed on the bubble to determine a thickness of the bubble. Multiple cameras may be mounted around the bubble to measure the entire bubble. A single camera may rotate around the bubble to measure the entire bubble. The blown film process can include collapsing the film bubble to produce a flattened device. The measuring step may be performed on the appliqu e to determine the appliqu or one or more layers thereof.

The present teachings also contemplate the use of a hyperspectral camera to map and calculate the thickness. Streaking of the raw data acquired in the measurement step may be corrected (e.g., using classical least squares analysis).

Thus, the present teachings allow for the measurement of films, sheets or sheets using hyperspectral imaging.

According to a first feature of the present disclosure, a method comprises the steps of: obtaining a polymer film, sheet or sheet; and measuring the thickness of the film, sheet or sheet, wherein the measuring step is performed using a camera that simultaneously acquires both spatial and spectral images of a plurality of points. According to a second feature of the present disclosure, the camera captures a line image from a certain line of the film, sheet or lamella. According to a third feature of the present disclosure, the film, sheet or sheet has a thickness of 2mm or less. According to a fourth feature of the present disclosure, the camera collects light having a wavelength of 780nm or more to 2500 nm. According to a fifth feature of the present disclosure, a light source emitting light having a wavelength of 780nm or more to 2500nm is positioned on a side of the polymer film, sheet or plate opposite to the camera. According to a sixth feature of the present disclosure, the method further comprises the steps of: the polymer film is formed using a blown film process. According to a seventh feature of the present disclosure, the blown film process includes forming a film bubble, and wherein the measuring step is performed on the bubble to determine a thickness of the film forming the bubble. According to an eighth feature of the present disclosure, the blown film process includes collapsing a film bubble to produce a appliqu e, and wherein the measuring step is performed on the appliqu e to determine a thickness of the appliqu e or one or more layers thereof.

Drawings

Fig. 1 is a diagram for measuring the thickness of a thin film using a known scanner.

Figure 2 is a graphical representation of measuring film thickness in accordance with the teachings of the present invention.

FIG. 3 is an illustrative blown film production line and positioning of cameras for making measurements of the film in accordance with the teachings of the present invention.

Fig. 4A and 4B illustrate exemplary positions of a camera for measuring the thickness of a thin film bubble in accordance with the teachings of the present invention.

FIG. 5 is a comparison of measurements made by an x-ray scanner and a hyperspectral NIR camera on a film sample.

Figure 6 shows the CLS based stripe removal process on a 1 mil film.

Figure 7 shows the CLS based stripe removal process on a 0.5 mil film.

Figure 8 shows a film thickness map based on CLS analysis.

Detailed Description

As required, detailed embodiments of the present teachings are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the teachings of the invention that may be embodied in various and alternative forms. The drawings are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present teachings.

In general, and as will be appreciated from the following description, the present teachings relate to methods and apparatus for measuring the thickness of a material (e.g., film, sheet, web, etc.). The measurements can provide a through thickness profile of the article. Providing a thickness profile may allow defects to be discovered or may ensure that the material meets the required specifications. The measurements may allow for adjustments during processing. This may allow for modifications in forming the material without stopping the manufacturing process. The thickness measurement may be used to provide automatic feedback (e.g., to bring the thickness back to a target value in a control system). The measurement may occur online during manufacturing. The measurement may occur after the material has been formed (e.g., offline). It is contemplated that the present teachings can also be used to measure or detect the crystallinity of a material. The present teachings can also be used to measure or detect impurities and/or foreign particles in a material.

Although referred to herein as a film for simplicity, it is within the scope of the teachings that the methods and apparatus are capable of measuring films having a thickness of about 250 micrometers or less (e.g., in the range of about 1 to about 250 micrometers), sheets having a thickness of about 250 micrometers or more and/or about 2000 micrometers or less, sheets having a thickness of about 2mm, and the like. The film may be a thin, continuous polymeric material. The sheet may be a thicker polymer material than the film. Where reference is made herein to films, it is contemplated that the discussion also relates to and/or encompasses these other articles for making measurements.

The film to be measured may be transparent. The film may be translucent. The film may be opaque. The film may be clear. The film may be coloured. The film may be flexible. The membrane may be rigid. The film may have different properties depending on the application. The films may provide hardness, toughness, performance on automated packaging equipment, robust processability, or combinations thereof. The film may meet desired puncture, secant modulus, tensile yield point, tensile break point, dart impact strength, Elmendorf tear strength (Elmendorf tear strength), gloss, haze, and the like, or combinations thereof. The film may be capable of acting as a barrier to gas, liquid or moisture. The membrane may alternatively be permeable. The thin film may act as a separator. The films may be used in a variety of applications including, but not limited to, packaging, plastic bags, labels, architectural construction, landscaping, electrical manufacturing, photographic film, stock film (e.g., for movies), and the like, or combinations thereof. For example, the film may be used as a heat shrinkable film, a cover or protective film, an embossed film, or a laminating film.

The film to be measured may be formed of or comprise a polymeric material. The film may comprise a polyethylene resin, such as Low Density Polyethylene (LDPE), Linear Low Density Polyethylene (LLDPE), metallocene linear low density polyethylene (mLLDPE), Ultra Low Density Polyethylene (ULDPE), Very Low Density Polyethylene (VLDPE), Medium Density Polyethylene (MDPE), high molecular weight HDPE (hmwhdpe), High Density Polyethylene (HDPE), or combinations thereof. The film may comprise polyethylene terephthalate (PET). The film may comprise polyethylene terephthalate glycol (PETG). The film may comprise a polypropylene resin. The film may comprise a polypropylene homopolymer or a polypropylene copolymer. Exemplary homopolymers include homopolymer polypropylene (hPP), random copolymer polypropylene (rcPP), impact copolymer polypropylene (hPP + at least one elastomeric impact modifier) (ICPP) or high impact polypropylene (HIPP), high melt strength polypropylene (HMS-PP), isotactic polypropylene (iPP), syndiotactic polypropylene (sPP), and combinations thereof. Examples of homopolymer propylene that may be used in the teachings of the present invention include homopolymer propylene commercially available from LyondellBasell Industries (e.g., Pro-fax PD702), Braskem (Braskem) (e.g., D115A), and Nordic chemical (e.g., WF 420 HMS). The film may comprise a propylene-a-olefin interpolymer. The propylene- α -olefin interpolymer may have substantially isotactic propylene sequences. The propylene- α -olefin interpolymer comprises a propylene-based elastomer (PBE). By "substantially isotactic propylene sequences" is meant sequences having isotactic triads (mm) as measured by 13C NMR: about 0.85 or greater; about 0.90 or greater; about 0.92 or greater; or about 0.93 or greater. The membrane may comprise an EPDM material. The film may comprise a polyvinyl chloride (PVC) resin. The film may comprise a nylon resin (e.g., PA 6). The film may comprise a polyester. The film may comprise a polypropylene-based polymer, Ethylene Vinyl Acetate (EVA), polyolefin plastomer, polyolefin elastomer, olefin block copolymer, Cyclic Olefin Copolymer (COC), ethylene acrylic acid, ethylene methacrylic acid, ethylene methyl acrylate, ethylene ethyl acrylate, ethylene butyl acrylate, isobutylene, polyisobutylene, maleic anhydride grafted polyolefin, ionomer of any of the foregoing, or a combination thereof. The film may comprise polyvinylidene chloride (PVDC), ethylene vinyl alcohol (EVOH), Polystyrene (PS) resins, High Impact Polystyrene (HIPS), polyamides (e.g., copolyamides (CoPA)), or combinations thereof. The film may be formed of cellulose acetate, cellophane, semi-embossed film, bio-plastic, and/or biodegradable plastic, and the like, or combinations thereof.

The film may comprise one or more additives. For example, the film may comprise one or more plasticizers, antioxidants, colorants, slip agents, anti-blocking additives, UV stabilizers, IR absorbers, anti-static agents, processing aids, flame retardant additives, cleaning compounds, blowing agents, degradable additives, color concentrates, and the like, or combinations thereof.

In an exemplary process, the extruded film material may be formed using a blown film extrusion process. The process may include extruding a tube of molten polymer through a die and expanding the polymer to form thin bubbles. The bubbles can be compressed and then rolled, cut into sheets, and the like.

In more detail, polymer pellets, resin, raw materials, and/or other materials may be charged into a hopper. The input material is then directed into an extruder unit and melted. The polymer melt was extruded through an annular slot die. Air is introduced into the center of the mold to inflate the tube into bubbles. The air ring may cool the hot film by blowing air on the inner and/or outer surface of the bubble. The bubbles may then be directed upward toward one or more rollers where they are then collapsed or flattened. The collapsed tube is then directed through one or more idler rollers. The collapsed tube may be delivered to a winder to wind the film into a roll. The process can produce a flat film.

The properties of the material and/or the appearance of the material may depend on the processing method and/or conditions. The film may be free or at least substantially free of wrinkles. This may be the result of a collapsing process from a circular shape to a flat shape. The film may have optical properties that are affected by the type of raw materials and/or the melt quality of the extruder. During the production process (e.g. the blow-moulding process), the mechanical properties of the film may be affected by the orientation of the molecular structure. The mechanical properties may be influenced by the raw materials used. During the production process, the thickness of the film may be affected by the temperature profile.

While the present teachings are discussed in the context of blown films, it is within the scope of the present teachings to use other film production methods. The methods and elements disclosed herein are also compatible with measuring films, sheets, and the like produced by casting, extrusion, calendering rolls, solution deposition, skiving, coextrusion, lamination, extrusion coating, spin coating, deposition coating, dip coating, and the like, or combinations thereof.

The present teachings relate to measuring the thickness of a film, sheet, or web or the like. With these teachings, a thickness profile can be derived to provide a measurement of thickness along an area of a film, sheet, web, or the like. The present teachings can be used to measure any thickness of a thin film. For example, the methods and apparatus discussed herein may be used to measure film thickness of about 1 micron or greater, about 10 microns or greater, or about 100 microns or greater. The methods and apparatus discussed herein may be used to measure film thicknesses of about 100m or greater, about 50m or greater, or about 1m or greater.

The present teachings may include using hyperspectral imaging to determine the thickness and/or thickness profile of a film, sheet, etc. Hyperspectral imaging can be used to provide these measurements without contacting the sample. Hyperspectral imaging can be used to determine how light interacts with a measured item. Hyperspectral imaging can measure the reflection, emission, and/or absorption of electromagnetic radiation. Hyperspectral imaging may also be referred to as chemical imaging because a system may be set up to map the uniformity of chemical composition. Hyperspectral imaging can collect and process information from the entire electromagnetic spectrum. Hyperspectral imaging a spectrometer can be used to examine how light behaves in a film, sheet, etc. Spectrometers can be used to identify materials based on their spectral characteristics or spectra. Obtaining a thickness profile can be achieved by obtaining both spectral and spatial information at the same time in each measurement. These measurements can be provided in real time, allowing data to be obtained quickly.

Hyperspectral imaging may involve instruments that decompose incident light into spectra. The instrument may be a spectrometer, a hyperspectral camera, a hyperspectral sensor, or a combination thereof. The incident light may be provided by a light source. During measurement of the film, a light source may be positioned on the side of the film being measured opposite the camera to allow the camera to measure light transmitted through the film. The light source may be positioned on the same side of the film as the camera to allow the camera to measure the light reflected by the film. The light source may be integrated into the camera or attached thereto. It is contemplated that two or more cameras may be used with a single light source or multiple light sources. For example, the light source may be positioned in one place with the camera positioned on the opposite side of the light source. A film or portion of a film may be positioned between each camera and the light source, which may allow for multiple films to be measured at one time or multiple portions of the same film to be measured at one time.

The light source may emit any type of light that may be received, detected, resolved, captured, and/or analyzed by a hyperspectral imaging instrument (e.g., a spectrometer, a hyperspectral camera, and/or a hyperspectral sensor). Although referred to herein as a hyperspectral camera, it should be understood that this also encompasses a hyperspectral sensor and/or a spectrometer. The light source may emit light and/or radiation having a wavelength in the electromagnetic spectrum. The light source may emit light and/or radiation having a wavelength in a range encompassing values of about 10nm or greater, about 410nm or greater, about 710 or greater, or about 780 or greater. The light source may emit light and/or radiation having a wavelength of about 1mm or less, about 50,000nm or less, or about 2500nm or less. The light source may emit ultraviolet radiation and/or light. The light source may emit visible light. The light source may emit Near Infrared (NIR) radiation and/or light. The light source may emit infrared radiation and/or light.

The camera may receive light from the light source to provide spatial information, spectral information, or both in each measurement. The hyperspectral camera may measure a plurality of spectra. The spectra can be used to form an image. Thus, the hyperspectral camera can capture information as a set of images. These images may be combined to produce a three-dimensional hyperspectral cube or data cube. The data cube may be assembled by stacking successive scan lines. The hyperspectral data cube may contain absorption spectrum data for each image pixel.

The camera may measure a thickness point of the film in an image (e.g., a line image). The image may comprise a plurality of pixels. The hyperspectral camera may measure a plurality of spectra within a spectral range of the hyperspectral camera, creating a full spectrum for each pixel. The hyperspectral camera may measure the spectrum along the electromagnetic spectrum. The spectrum may have wavelengths ranging over values of about 10nm or greater, about 410nm or greater, about 710 or greater, or about 780 or greater. The spectrum may have a wavelength of about 1mm or less, about 50,000nm or less, or about 2500nm or less. The spectral image may have a wavelength in the ultraviolet range. The spectral image may have a wavelength in the visible range. The spectral image may have wavelengths in the Near Infrared (NIR) range. The spectral image may have a wavelength in the mid-infrared range. The spectral image may have a wavelength in the infrared range.

The hyperspectral camera may measure each pixel in an image (e.g., a line image) and provide spectral features for each pixel. The number of pixels measured may depend on the camera used. For example, the line image may include about 10 or more pixels, about 20 or more pixels, about 100 or more pixels, about 200 or more pixels, or about 300 or more pixels. The line image may include about 1000 or less pixels, about 800 or less pixels, or about 500 or less pixels. The higher the number of pixels and the closer the camera is to the sample, the higher the spatial resolution. This may mean that the resolution is higher when compared to measuring the same sample size, or that a larger sample can be measured at the same resolution.

The camera for enabling hyperspectral imaging may use one or more modes of operation. For example, a line imaging mode or a push-broom mode may provide the necessary measurements and/or data to derive a thickness profile for the sample. In the push-broom mode, a line image may be taken from a certain line of the sample in each frame or picture. The light from each spot, where the size may be determined by the distance between the camera and the sample, the camera lens, and the camera itself, may be dispersed by the optics in front of the camera such that each frame has both one dimension (i.e., the spatial dimension) and another dimension (i.e., the spectral dimension). Although discussed herein as line images, it is also contemplated that other measurements of shape are possible and within the teachings of the present invention. For example, the camera may capture an area having a rectangular shape, a circular shape, an elliptical shape, a polygonal shape, an amorphous shape, or a combination thereof at a time.

In general, the camera and/or sensor may comprise a suitable optical system using mirrors and lenses. For example, the hyperspectral camera and/or sensor may include a scanning mirror, optics, a dispersive element, imaging optics, a detector or detector array, or a combination thereof. The camera used may depend on the number of pixels desired for each measurement. The camera used may depend on the measured spectrum. For example, to measure or provide a spectral image in the near infrared range, a hyperspectral NIR camera may be used. The camera may be a Short Wave Infrared (SWIR) camera. The camera may comprise means for moving charge, such as a Charge Coupled Device (CCD).

When a static sample or film is being measured, the camera may be translated in one or more directions to acquire a true two-dimensional chemical map. In the case where the sample or film is moving, for example, if the measurement is performed on-line, the motion of the sample may allow a two-dimensional chemical map to be acquired. The movement of the sample may be performed at a preset speed. The camera may be in a fixed position. The camera may be moving. If a moving sample is measured, the cameras may be moved in the same direction or in different directions. For example, the camera may be moved in a direction generally perpendicular to the direction of movement.

One or more hyperspectral cameras and light sources may be employed when a film, sheet, web, or the like is being formed. The measurement may be performed in real time. This may allow for adjustments to be made to the process or one or more process parameters (e.g., if the film does not meet desired specifications, then changes must be made). The measurements may allow troubleshooting or determining which areas of the process need to be adjusted to provide a film that meets specifications.

One or more hyperspectral cameras and light sources may be positioned at different points along the line to ensure that the film meets the required specifications throughout the process. For example, in a blown film process, a hyperspectral camera may be mounted outside the bubble while a light source is mounted on the internal bubble cooling tube to directly measure the monolayer of film. The camera may measure the bubble thickness vertically (i.e., in the longitudinal direction), horizontally (i.e., in the lateral direction), or both. If measured in the longitudinal direction, a line image is generated in the longitudinal direction, which may be helpful for determining the thickness variation and/or the crystallization process, especially during the cooling process of the gas bubbles. If measured in the cross direction, gauge variations near the die exit can be measured. Such measurements may allow for rapid feedback to the blown film line control system. It is possible that two or more cameras may be used to provide measurements of the bubbles. For example, two or more cameras may be positioned around the diameter of the bubble. For example, three or more cameras, four or more cameras, or even six or more cameras may be used. Such a camera may be stationary. It is also contemplated that one or more of the cameras may be translatable or movable. For example, the camera may be mounted to a rotating platform to scan (e.g., rotate about) the bubble. The camera may be capable of translating in the direction of movement of the bubble or film production process. The camera may be able to move in any direction that will provide a valuable measurement.

In a blown film process, one or more cameras may be positioned after the bubble collapses, forming a flat device. The hyperspectral camera may be positioned at some point in the process after the nip roll. The light source may be positioned on the opposite side of the film so that the light waves travel through the film to the camera. This may allow for the thickness of the appliqu e to be measured to determine if there are any wrinkles in the appliqu e, to determine if there are any flaws (e.g., bubbles, tears, thickness inconsistencies) in the appliqu e, to determine if there are any foreign particles or entrapment within the appliqu e, or a combination thereof.

The positioning of the camera and light source in-line or during the manufacturing process is not limited to blown film processes. The camera and light source may be positioned, for example, before or after a lamination process, an extrusion process, a cutting process, a sheeter stacking process, a molding process, a stretching process, a winding process, a cooling and/or quenching process, a heating process, etc., or combinations thereof.

One or more cameras may alternatively or additionally be used to measure films, sheets, etc. in an off-line environment. The sample may be measured after the material is made, cut, removed from the processing equipment, or a combination thereof. The film may be positioned on a translation stage or other linear movement mechanism, for example to measure the sample. The film may be held in place (e.g., between two or more elements that tension the film) and measurements taken. The film or a portion thereof may be measured while being rolled or may be unwound for measurement.

When multiple pixels and spectra are measured at once, data can be generated to identify the thickness of the film along the line. This data can be used to generate a thickness profile for the thin film. Since the absorbance is linearly or directly proportional to the thickness of the material (and to the concentration of the sample), by measuring the absorbance, the thickness of the material can be determined.

Interference or fringes may be present when the data is acquired and plotted. These fringes may hinder the interpretation and analysis of the transmission spectrum from the film sample. For example, the fringes may be caused by wavelength-dependent constructive and/or destructive interference of light traveling through the film and light reflected by two parallel film surfaces (e.g., in the case of a flat device). To minimize thickness prediction errors due to such striations, one or more mathematical methods may be used. One approach may be to use Classical Least Squares (CLS). The CLS algorithm is based on matrix operations that can be used to process hundreds of spectra almost instantaneously. The CLS method assumes that the sample spectrum is a linear combination of the spectra of its components. Fringe-free spectra can be obtained by averaging multiple spectra to cancel out their fringes or by measuring films with rough surfaces. The fringes can then be considered as spectral residuals. Because of the intrinsic symmetry of the fringes, their spectral contributions may cancel out when sufficient fringe cycles are involved.

Turning now to the drawings, FIG. 1 illustrates a common method for measuring the thickness of a film 10. The measurement is performed using a scanner 12 (e.g., a near infrared thickness scanner) as the film travels in the direction of the large arrow. Each measurement made by the scanner 12 is a single point measurement 14. Because the film 10 is moving, the scanner 12 is only able to provide thickness information along the zig-zag path 16 on the surface of the film 10.

FIG. 2 illustrates the measurement of the thickness of the film 10 using a hyper-spectral near-infrared camera 20. As the film travels in the direction of the large arrow, the camera 20 measures a plurality of points 22 across the cross machine direction (CD direction) of the film to obtain a thickness measurement. Thus, as compared to fig. 1, the camera 20 is able to take a line image in the CD direction at any given time, which provides a full film thickness profile, rather than a film thickness profile at a single point or along a zig-zag pattern.

Fig. 3A and 3B illustrate exemplary uses of hyperspectral NIR cameras during the production of films. The example in fig. 3A shows a blown film line 30. In the process, resin or other material 32 is introduced into a hopper 34. The material is delivered through an extruder 36. The extrusion of the molten material is performed through a die 38 to form bubbles 40. The introduction of air takes place through a hole present in the centre of the mould 38 for blowing the bubble 40. The film is cooled by an air ring 42 mounted on top of the mold 38. The bubble 40 continues its upward travel until it reaches the collapsing frame 44 and passes through rollers 46 which flatten the bubble to create a double layer film or flat device 48. The lay-flat member 48 is conveyed through idler roller 50 until it is wound into a roll of film 52.

The thickness of the film may be measured at one or more points in the process. As shown, the thickness of the bubble-forming film can be measured by the hyperspectral NIR camera 20. The hyperspectral NIR camera 20 may measure the thickness of the bubble 40 vertically (machine direction or MD) or horizontally (cross direction or CD). This may be a useful tool to understand thickness variations and crystallization processes during bubble cooling when measuring bubble thickness in the MD. When measuring the CD, it can measure gauge changes near the die exit, which can provide fast feedback to the blown film line control system. NIR light 24 is present within the bubble, mounted on the internal bubble cooling tube, to provide the light source needed for the camera 20 to capture the measurement. The thickness of the appliqu e 48 is also measured by the hyperspectral NIR camera 20 and the NIR light 24 positioned on the opposite side of the appliqu e 48.

Fig. 4A and 4B show a possible setup for a lateral (CD) gauge for measuring bubbles 40 using a hyperspectral NIR camera 20 and NIR light 24 inside the bubble, mounted on an internal bubble cooling tube. Fig. 4A illustrates a plurality of fixedly mounted hyperspectral NIR cameras 20 that can measure the entire bubble 40 in real time. Although shown as four cameras, it is contemplated that any number of cameras may be used (e.g., three cameras, four cameras, six cameras). FIG. 4B illustrates the hyperspectral NIR camera 20 scanning the bubble 40 over a rotating platform.

Illustrative examples

The following examples are provided to illustrate the teachings of the present invention, but are not intended to limit its scope.

Example 1

To illustrate the advantages of using a hyperspectral NIR camera for measurement of films, the hyperspectral NIR camera was compared to an x-ray scanner and a full film surface profiler in three separate tests. Table 1 shows the results of each test.

For the case performed, an x-ray scanner is available from the skunkend technologies corporation (ScanTech). The scan speed of the x-ray scanner was 2 inches/second and 1024 measurements were reported in the CD direction. The full thin film surface profiler is a non-contact capacitive sensor available from SolveTech technology corporation. Each sensor has a width of 1 inch. For case 1, 6 sensors were used. For case 2, 60 sensors were used. For case 3, 216 sensors were used. The hyperspectral NIR camera is an SPECIM SWIR hyperspectral NIR camera, each line image having 384 pixels, measuring 450 frames/sec at a wavelength between 1000 and 2500 nm.

In case 1, a6 inch wide film was measured at a film speed of 25 fpm. In case 2, a 60 inch wide film was measured at a film speed of 500 fpm. In case 3, a 216 inch wide film was measured at a film speed of 1000 fpm.

Table 1:

table 1 shows the advantages of hyperspectral NIR cameras over other technologies. In this study, the x-ray scanner measured only 0.1% of the full film thickness. In the machine direction (MD direction), x-rays will be reported after a significant time interval. For example, reporting MD position thickness takes 108 seconds. In addition, on high speed film lines, x-rays report the average thickness of a long film strip (e.g., 0.2 inches wide and 21 inches long in case 3). The running average of the thickness may already smooth out some of the variations.

In the case of a full film surface profiler, although it reports the full film surface, it is limited by the width of the sensor. The sensor width may be 1 inch wide, but may be customized to 1/2 inches. In case 1, if an 1/2 inch sensor is used, it would report only 6 thickness bands or 12 thickness bands, which is not very useful. In case 3, this may not be economically feasible due to the need for 216 sensors.

For a hyperspectral NIR camera, it measures the entire film surface in the MD direction at a very fast sampling rate (2 milliseconds per measurement). Even in case 3, it would report an average area of 0.6 inches by 0.4 inches on the film.

Example 2

X-ray scanning is a common method for measuring thickness, although it has drawbacks as mentioned. FIG. 5 shows the results of a 0.05mm (2 mil) high density polyethylene film (Dow Elite 5960G) 6 inches wide measured by an x-ray scanner and a hyperspectral NIR camera. The results match well, confirming that using a hyperspectral NIR camera provides an accurate measurement of the thickness of the film. In fig. 5, the gray dashed line represents the thickness measured by the hyperspectral NIR camera, and the black solid line represents the thickness measured by the x-ray scanner.

Example 3

Using a hyperspectral NIR camera, two film spectra were obtained: one film spectrum had a thickness of 2 mils and one film spectrum had a thickness of 0.5 mils. The data are plotted in fig. 6 and 7, respectively, showing wavelength and absorbance. The raw data is shown as the indicated lines. However, there are spectral fringes in the data. To overcome such streaks, Classical Least Squares (CLS) analysis is used, assuming that the sample spectrum is a linear combination of the spectra of its components. Thus, the fringes are considered as spectral residuals. This is satisfied because the fringes have an intrinsic symmetry whose spectral contribution should cancel out when sufficient fringe cycles are involved, since the fringes encountered have a high periodicity. The corrected spectra (without streaks) are shown as black bold lines in fig. 6 and 7 using CLS analysis. The spectral residual after CLS fitting is shown as a gray line at the bottom of the plots in fig. 6 and 7. FIG. 8 shows a plot of film thickness based on CLS analysis on a 15cm by 50cm (6 inches by 20 inches) film. The scale bar represents the CLS response, with response 1 corresponding to 0.05mm (2 mils).

As can be appreciated, variations of the above teachings can be employed. For example, the present teachings are not limited to blown film or blown film processes. The present teachings can be used to measure other polymeric substrates besides films, sheets and sheets. Other calculations or methods of removing streaks from the data may be used. For example, methods of minimum sum, averaging adjacent spectra, non-linear regression (e.g., non-linear fitting algorithms), and the like may be used.

While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. In addition, features of different implemented embodiments may be combined to form further embodiments of the invention.

Any numerical value recited herein includes all values from the low value to the high value in increments of one unit provided that there is a separation of at least 2 units between any low value and any high value. By way of example, if the value specifying the amount of a component or a process variable (e.g., temperature, pressure, time, etc.) is, for example, 1 to 90, preferably 20 to 80, more preferably 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32, etc. be expressly enumerated in this specification. For values less than one, one unit is considered to be 0.0001, 0.001, 0.01, or 0.1, as appropriate. These are only examples of what is specifically intended, and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

Unless otherwise indicated, all ranges are inclusive of the two endpoints and all numbers between the endpoints. The use of "about" or "approximately" in connection with a range applies to both ends of the range. Thus, "about 20 to 30" is intended to encompass "about 20 to about 30", including at least the endpoints specified.

The disclosures of all articles and references, including patent applications and publications, are incorporated by reference for all purposes. The term "consisting essentially of … …" when used to describe a combination is intended to encompass the identified element, ingredient, component or step as well as other elements, ingredients, components or steps that do not materially affect the basic and novel characteristics of the combination. The use of the terms "comprises" or "comprising" to describe combinations of elements, components, or steps herein also contemplates embodiments that consist essentially of, or even consist of, those elements, components, or steps.

A plurality of elements, components, assemblies or steps may be provided by a single integrated element, component, assembly or step. Alternatively, a single integrated element, component or step may be divided into separate plural elements, components or steps. The disclosure of "a" or "an" to describe an element, ingredient, component or step is not intended to exclude additional elements, ingredients, components or steps.

The relative positional relationships of elements depicted in the drawings are part of the teachings herein, even if not described verbally. Further, the geometries shown in the figures, even if not verbally described, are within the scope of the teachings (although not intended to be limiting).