Test substrate for droplet analysis device for inkjet printers

Abstract

This application relates to inkjet printing, devices for analyzing droplet placement accuracy of inkjet printers, and substrates for such test devices. [Solution] In a droplet drop test system for analyzing droplets of printing material, the droplet drop test system includes a test substrate system having a stage for a test substrate, the test substrate being a flexible substrate comprising a material selected to have high contrast in reflected light, the test substrate having a printing material receiving surface that exhibits a neutral response to the printing material, the printing material receiving surface including a transparent film and a base layer adhered to the transparent film, and an imaging device including a light source positioned to illuminate the printing material receiving surface with light matched to the optical properties of the base layer, and a detector that captures an image of the light reflected from the test substrate.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 260,656, filed August 27, 2021, and U.S. Provisional Patent Application No. 63 / 263,721, filed November 8, 2021, both of which are incorporated by reference in their entireties.

[0002] This application relates to inkjet printing, devices for analyzing droplet placement accuracy of inkjet printers, and substrates for such test devices. [Background technology]

[0003] Industrial inkjet printers are used to apply materials to large substrates to form various devices. The substrates can be hard or soft, thick or thin, and made of a variety of materials. The most typical types of substrates used in this way include substrates made of various types of glass, which are processed to produce electronic displays such as televisions and displays for smartphones.

[0004] Inkjet printers use printheads with nozzles that eject and deposit printing material onto a substrate. Today's industrial inkjet printers deposit tiny droplets of printing material onto the substrate with great precision to create precisely placed, tiny or ultra-fine structures. To ensure that droplets are deposited reliably and accurately onto the substrate, the operating characteristics and changes in each nozzle must be known at all times. For this reason, numerous diagnostic modules are often used to measure and track the performance of the nozzles.

[0005] One example of such a diagnostic module is a droplet drop test system. A droplet drop test system is used to test the landing position of droplets ejected from the nozzles of an inkjet printer, and can also be used to test the size of droplets deposited on a substrate. Such data can be stored so that printing can be planned with an understanding of the performance of the print nozzles. Typically, droplets from all of the printer's nozzles are deposited on a test substrate in the droplet drop test system, and the droplets are then photographed to determine where the droplets landed and the size of the droplets.

[0006] An industrial-scale inkjet printer may have hundreds of thousands of printing nozzles, each configured to produce extremely small droplets, for example 5 μm to 10 μm in diameter. To understand the performance of all the nozzles, it is useful to deposit at least one droplet from each nozzle onto a test substrate and photograph the droplet. If the area of ​​the test substrate is not large enough to accommodate droplets from all the nozzles, a first test can be performed using a first subset of nozzles and a first test substrate or a first portion of the test substrate. A second test substrate or a second portion of the test substrate is then prepared and a second test is performed using a second subset of nozzles. This process is repeated until all the nozzles have been tested. Minimizing the number of cycles maximizes the speed at which the print plan is determined. Adjusting the test substrate to have the desired characteristics when testing the droplets maximizes the speed at which the print plan is determined, which in turn helps maximize the throughput of the inkjet printing system. Therefore, there is a need for a test substrate and a drop test system that maximizes the throughput of the drop test and maximizes the test speed. Summary of the Invention

[0007] According to embodiments described herein, there is provided a substrate for an inkjet printer, the substrate comprising a material selected to have high contrast in reflected light and having a print material receiving surface that exhibits a neutral response to the print material.

[0008] According to other embodiments described herein, there is provided a droplet drop test system for analyzing droplets of printed material, the droplet drop test system comprising: a test substrate system having a stage for a test substrate, the test substrate being a flexible substrate comprising a material selected to have high contrast in reflected light, the test substrate having a printing material receiving surface that has a neutral response to the printed material, the printing material receiving surface including a transparent film and a base layer adhered to the transparent film; and an imaging device comprising a light source positioned to illuminate the printing material receiving surface with light matched to the optical properties of the base layer, and a detector for capturing an image of the light reflected from the test substrate.

[0009] According to other embodiments described herein, a method is provided that includes ejecting a plurality of droplets of a printing material from nozzles of a print head of an inkjet printer onto a test substrate, the test substrate comprising a material selected to have high contrast in reflected light and having a printing material receiving surface that exhibits a neutral response when contacted by the printing material, imaging the droplets using light matched to the material of the test substrate so as to reflect from the test substrate with high contrast relative to light reflected from the droplets, and collecting the test substrate using a roll. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is an elevational view of a test substrate according to one embodiment.

[0011] [Diagram 2] FIG. 1 is an elevation view of a droplet drop test system according to one embodiment.

[0012] [Diagram 3] 1 is a flow chart outlining a method according to one embodiment;

[0013] [Figure 4A] FIG. 13 is an elevational view of a test substrate according to another embodiment.

[0014] [Figure 4B] FIG. 13 is an elevational view of a test substrate according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Described herein is a test substrate for testing the deposition of printed material from an inkjet printer.

[0016] The test substrate surface that receives the printing material is adapted to correlate the behavior of the printing material when deposited on the test substrate with the behavior of the printing material when deposited on a non-test substrate. For example, the test substrate can be configured such that the change in droplet width when a droplet of the printing material is deposited on the test substrate is similar to the change in droplet width when a droplet of the printing material is deposited on a non-test substrate. In some cases, the test substrate is configured such that the droplet of the printing material is fixed when the droplet contacts the test substrate. For example, it may be desirable to know the behavior of the droplet deposited on the product substrate, such as the behavior of the droplet in terms of reaction such as spreading, in order to know the exact size of the droplet ejected from the nozzle of the printer. The known spreading behavior can be applied to know the exact size of the droplet to know the result of depositing the droplet from the nozzle on the product substrate. In such cases, a test substrate having a printing material receiving surface that the droplet is fixed when it contacts is useful to determine the exact size of the droplet.

[0017] Droplets dispensed onto a test substrate can also be used to evaluate how the nozzle dispenses the droplets onto the substrate. The nozzle position when dispensing the droplets is known or known, and the droplet position on the substrate is also known. Comparing these two positions determines how the nozzle dispenses the droplets onto the substrate. Alternatively, the predicted droplet position on the test substrate based on the expected performance of the dispensing nozzle is compared to the actual position of the dispensed droplet to determine adjustments. The droplet size information and droplet placement information can be used to control the droplet dispense from the nozzle to achieve accurate droplet size and placement on the substrate.

[0018] The test substrate also interacts with light in a manner that provides optimal high contrast reflected light for imaging of droplets deposited on the test substrate, and the optical properties of the test substrate are typically matched to the light used for imaging so that micron-level details of the droplets can be resolved by the imaging system.

[0019] The test substrate described herein is configured to image the side of the substrate that receives the droplets. Thus, the droplets are dropped onto the print material receiving surface, and the substrate is positioned so that the print material receiving surface faces the imaging unit to capture an image of the droplets. The test substrate may be a tape-like or ribbon-like structure that passes through a test zone where the droplets are dropped and then through an imaging zone where an image of the droplets is captured. To optimize imaging, the test substrate is generally made of a material selected to have a high contrast in reflected light. The material may be homogeneous or the test substrate may have a layered structure. Depending on the type of material being imaged, the material may include a pigment that reflects a desired frequency of light selected to optimize imaging of the droplets of the print material. For example, if the print material is transparent or colorless and clear, the material of the test substrate may include a reflective material so that the droplets can be imaged using the refractive properties of the droplets. If the print material has a color such as black, white, red, etc., the material of the test substrate may be black or white or another color selected to have a high contrast with the droplets of the print material.

[0020] The print material receiving surface may be a surface-treated test substrate surface. For example, a chemical composition that has a neutral reaction when contacted by the print material may be applied to the surface of the test substrate. In general, the properties of the print material receiving surface are selected to have a neutral reaction when contacted by the print material, and are selected to have optical properties that support clear and sharp imaging of the droplets at very high resolution or magnification, for example 400 nm per pixel. The material of the test substrate is similarly selected to have optical properties that support clear and sharp imaging, and the light used is also selected so that the optical properties of the test substrate interact with the optical properties of the droplets themselves to provide clear and sharp high-resolution images of the droplets.

[0021] As used herein, "neutral response" means that the droplet does not substantially change in shape or composition when it contacts the receiving surface. The droplet has a contact angle of about 90 degrees with the receiving surface. In some cases, the droplet may spread a little when it contacts the receiving surface, but the surface material is selected so that the contact angle of the droplet with the surface is about 75 degrees or more. The contact angle can be measured according to the ASTM-D7334 standard for contact angles. As of this writing, D7334 is in its 8th edition published in 2013. D7334 is a standard practice method for contact angles based on the contact angle measurement method D5725, which was withdrawn by ASTM in 2010, citing the TAPPI contact angle test method T458cm-14 published in 2009. Any of the above methods can be used to measure the contact angle.

[0022] In some cases, the print material receiving surface may be a material coated on the test substrate. In other examples, the print material receiving surface may be an opaque, semi-transparent, colored, and / or reflective film surface. The test substrate may be a reflective material, such as a metal film or foil, and may be surface treated to provide a uniform print material receiving surface throughout that exhibits a neutral response when the print material contacts it. In general, when imaging is performed from the print material receiving surface side of the test substrate, the test substrate is configured to obscure structures beneath the test substrate so as not to impair the image. In this sense, the test substrate may be opaque or non-transparent or minimally transmissive to light, so that features of the imaging surface beneath the test substrate are not resolved in the image.

[0023] The test substrate is typically thin enough to be easily wound onto a spool, and configured to allow continuous printing and imaging cycles to be performed using one long test substrate. The test substrate is also typically thin enough to be flexible and to be held stationary against a flat surface during printing and imaging. The test substrate is typically chucked to a vacuum surface during printing and imaging, and the test substrate herein is thin enough to be flat against such a vacuum surface under the use of a nominal pressure differential. In this specification, the thickness of the test substrate is, by way of example, 50 μm to 100 μm, or about 2 mils to 4 mils.

[0024] The print material receiving surface is generally made of a low surface energy material such as a biaxially oriented polymeric material, and the material deposited on the print material receiving surface is a hydrophobic material. Suitable materials have a surface energy of less than about 35 dynes / cm, for example, about 20 dynes / cm to 30 dynes / cm, more particularly 21 dynes / cm to 26 dynes / cm, 21 dynes / cm to 23 dynes / cm, etc. In one example, the print material receiving surface has a surface energy of 22 dynes / cm. Examples of such materials include polyolefin materials (PO) such as polyethylene (PE) and polypropylene (PP), polyester materials such as polyethylene terephthalate (PET), and silicone-based (polysiloxane-based) materials such as polydimethylsiloxane (PDMS). Fluorinated polymers such as polytetrafluoroethylene (PTFE), polytrifluoroethylene (P3Fet or PTrFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polyhexafluoropropylene (PHFP), fluorinated ethylene polymer (FEP), polychlorotrifluoroethylene (CTFE), etc. can also be used. Other polymers such as styrene butadiene rubber (SBR), natural latex rubber, polyisobutylene (PIB), etc. can also be used. The print material receiving surface can be a composite PE material, a composite PP material, a composite PET material, a composite or non-composite ("pure") silicone material, or a mixture, copolymer, or multipolymer thereof. Hydrophobic self-assembled monolayer (SAM) materials such as PDMS, methyl-terminated organosilanes, fluoroalkylsilanes, etc. can be used to form a coating suitable for use as the print material receiving surface of the test substrate described herein. In one example, the print material receiving surface is a silicone-based film or a silicone-based coating.

[0025] In some cases, the print material receiving surface may be made of an environmentally stable material that does not change substantially when exposed to ambient conditions, such as air, room temperature, ambient light, etc. Specifically, the print material receiving surface should slowly change in surface energy when exposed to ambient conditions. For example, a material that changes the surface energy of a test substrate by less than about 1 dyne / cm / hour when the test substrate is exposed to ambient conditions for more than about 24 hours can be used as a print material receiving surface. A more stable material, for example a material that changes surface energy by about 5 dynes / cm / day or less, will provide improved results, and a material that changes surface energy by about 1 dyne / cm / day or less will provide even better results.

[0026] As described above, the test substrate can have a layered structure. FIG. 1 is an elevational view of a test substrate 100 according to one embodiment. The test substrate 100 has a print material receiving surface 102 and a base layer 104. Thus, the test substrate 100 is a two-layer substrate. The print material receiving surface 102 is made of a material that exhibits a neutral reaction to the print material deposited thereon. As used herein, "neutral reaction" means that a drop of the print material placed on the print material receiving surface does not substantially flow, move, or change shape or composition. In one embodiment, the drop has a contact angle with the print material receiving surface of about 90 degrees, such as about 75 degrees or more. In another embodiment, the drop has a contact angle of about 105 degrees or less. If the print material is a hydrophobic material, a print material receiving surface with a low surface energy, as described above, will exhibit the above-mentioned neutral reaction.

[0027] The contact angle during droplet deposition is related to the spreading behavior of the droplets. In inkjet printing, droplets of printing material are deposited on a substrate and it is desired that the droplets spread and merge to form a film with no gaps. In such a case, the droplets are deposited at a maximum pitch that allows the droplets to spread and form a film with no gaps. The film thus formed is of a minimum thickness, i.e. the minimum thickness that can be formed on the substrate without gaps using the particular printing material. If necessary, a pitch narrower than the maximum pitch can be used to form a film thicker than the minimum thickness.

[0028] A droplet that spreads upon deposition generally has a contact angle with the substrate surface of less than 90 degrees. This angle is measured as the angle between the substrate surface and the tangent of the droplet surface at the edge of contact between the droplet and the substrate surface. The lower the contact angle, the higher the dot gain will generally be. If the spreading behavior of the droplet on the substrate surface is known, i.e. the gain factor of the droplet size on the substrate surface is known, it may be desirable to know the exact size of the droplet ejected from the print nozzle of the inkjet printer so that the droplet size on the substrate can be predicted. In such a case, the print material receiving surface of the test substrate is configured to have a neutral response to the print material, so that the droplet size is not affected by the interaction of the droplet with the print material receiving surface. In another example, the substrate throughput can be maximized by maximizing the number of droplets that can be densely packed on the test substrate in one measurement cycle.

[0029] The print material receiving surface may be transparent, partially transparent, translucent, partially opaque, or opaque. If the majority of the print material is made of an organic material that is substantially immiscible with water, the print material receiving substrate may be hydrophobic. The selection of a material for the print material receiving surface that has a neutral reaction to the print material depends on the print material to be deposited. For example, for print materials with a high proportion of acrylate monomers, the print material receiving surface may be made of a silicone-based material.

[0030] As the underlayer, a polymeric material film or a metal film or foil can be bonded to the material that will be the print material receiving surface. Thus, two films can be bonded together to form a test substrate, i.e. the underlayer can be applied as a coating on the print material receiving film, or the print material receiving material can be adhered and solidified to the underlayer film or foil. The underlayer can also be a polymeric or metal material that is not in the form of a film or foil, and these materials can be applied to the print material droplet receiving film by jetting, plasma deposition, CVD, evaporation deposition, or other suitable deposition methods. The print material receiving material can also be applied to the underlayer using these methods. These materials can also be applied by inkjet printing. That is, a test substrate for an inkjet printer can be made using an inkjet printer.

[0031] If an underlayer is used, it is generally a light blocking or light absorbing layer that reduces or substantially eliminates light transmission through the test substrate. Underlayers may be opaque, partially opaque, or translucent, and are generally used to reduce background optical noise to improve imaging of print material deposited on a print material receiving surface.

[0032] Metals such as aluminum, silver, chromium, etc., can be applied to the polymeric film to provide a reflective background for imaging the printed material deposited thereon. Such metals can be deposited on the polymeric film by sputtering, plasma spraying, or vapor deposition processes. The thickness of the metal is typically selected to reduce the light transmission of the underlayer, thereby reducing noise captured when an image of the deposited printed material is captured by an imaging device. The metal need only be thick enough to be nearly opaque (e.g., optical density 2.5 or greater, where optical density is defined as the logarithm of the light intensity of the incident light divided by the light intensity of the transmitted light). Alternatively, the metal need only be thick enough to reduce the light transmission to a level where a sufficiently clear image of the deposited printed material can be obtained. Such underlayers can be considered semi-transparent and can have an optical density as low as 1 (i.e., having 90% "opacity" or 10% "transmission"). For aluminum, a thickness of 120 nm is typically opaque, but thicknesses as low as 50 nm can be used effectively in some cases. Typically, the metal layer is at least about 50 nm thick, e.g., at least about 100 nm, at least about 120 nm, etc. Using a thicker metal layer, e.g., 500 nm thick, may provide little additional benefit and may even come at the expense of increased film stiffness. Mylar-type materials can be used as test substrates.

[0033] A test substrate has less than 80% light transmission at the relevant wavelengths when the overall optical density is greater than about 0.1. The lower the light transmission (the higher the optical density), the better the results when the test substrate is used for imaging. For example, a light transmission of less than 10% and an optical density of greater than about 1, or even a light transmission of less than about 0.001% and an optical density of greater than about 5, will provide better results. The optical density of the test substrate may be entirely due to the undercoat layer, entirely due to the print material receiving surface, or due to a combination of properties of the two layers. The adhesive layer and other layers may also contribute to the optical properties (e.g., optical density) of the test substrate. It should be noted that imaging of the droplets on the test substrate can be performed using visible or non-visible light, such as ultraviolet or infrared light, as described herein. The test substrate is configured to have high contrast in reflected light at the wavelength or spectral range used for imaging. Thus, the combination of the printing material receiving surface, underlayer, and other layers are selected to reflect and absorb light of specific wavelengths or ranges such that the light reflected from the test substrate and droplets has high contrast in the imaging wavelength range. That is, the light reflected from the droplets will be much brighter (more intense, more power dense) in the imaging wavelength range than the light reflected from the area of ​​the test substrate surrounding the droplets. Contrast levels of 60%, 80%, and 90% result in improved imaging of the droplets.

[0034] In one example, the droplets can be imaged with minimal reflected light from the test substrate and with maximum reflected light from the test substrate. In such an example, a contrast between light and dark areas of greater than 60% helps maximize imaging accuracy. In this case, the contrast can be calculated from the grayscale values ​​of the digital image, with white pixels having a grayscale value of 256 and black pixels having a grayscale value of 0. The contrast is calculated as (light value - dark value) / 256. Thus, if the white area has a grayscale value of 256, a dark area value of 100 or less would result in a contrast of 60%. In this case, the higher the contrast, the better. Of course, a lower contrast can be used, but with reduced imaging accuracy.

[0035] FIG. 2 is an elevational view of a liquid drop test apparatus 200 according to one embodiment. The liquid drop test apparatus 200 uses a test substrate as described herein. A housing 202 supports the function of the liquid drop test apparatus 200. The housing 202 has a stage 204 that receives print material and positions a test substrate 206 to be imaged. The test substrate 206 may be any of the test substrates described herein. The test substrate is supplied as a supply roll 208, unwound within the housing 202, fed to the stage 204 for printing and imaging, and collected on a take-up roll 210 after use. Once the test substrate has been used up, the supply and take-up rolls are replaced and a new test substrate supply roll is installed.

[0036] The stage 204 is typically accompanied by a mechanism for securing the test substrate. Often, a mechanism for applying a vacuum at the surface of the stage 204 is used. As described above, the test substrate 206 is thin enough to be flexible enough to adhere to the stage 204 in response to the application of a vacuum. If the test substrate is too thick, the vacuum application will not close the gap between the stage 204 and the test substrate as it traverses the stage 204 and the test substrate will be too large to be "chucked" properly. A test substrate having a thickness as described herein will typically traverse the stage 204 with a small gap of about 2 mm or less, if the stage width is adequate, such that the vacuum application will secure the test substrate 206 to the stage 204. When the vacuum is released, the test substrate 206 generally disengages from the stage 204. In some cases, the liquid drop test apparatus 200 is configured to apply a positive pressure to the stage to disengage the test substrate 206 from the stage 204.

[0037] The test substrate 206 is secured to the stage 204 during printing and imaging. After imaging, the test substrate 206 is released from the stage 204, and the supply roll 208 and take-up roll 210 are rotated to advance the test substrate 206 such that an unused area of ​​the test substrate 206 is positioned on the stage 204. The housing 202 may optionally include a tensioning device that holds the test substrate 206 spaced above the stage 204 for vacuum chucking. The housing 202 may also include a processing unit (not shown) that solidifies droplets printed on the test substrate 206 before the used portion is wound onto the take-up roll 210.

[0038] A schematic of the stage 204 is shown below. The edges of the stage 204 may be chamfered to allow the test substrate 206 to rest smoothly on the surface of the stage 204. Guide rollers may be used to reduce the angle at which the test substrate 206 contacts the stage 204, reducing bending of the test substrate 206 and contact pressure on the test substrate 206. This may also reduce the gap between the test substrate 206 and the stage 204 if the test substrate 206 does not fit tightly to the stage 204.

[0039] Additionally, the materials of the test substrates are typically selected for ease of use with the liquid drop test apparatus. For example, the materials are typically selected so that the test substrates do not substantially adhere to each other while wound on the supply roll. The materials are also typically selected so that they can be handled without deformation, chafing, or degradation, and in the case of layered materials, to avoid delamination. Layer adhesion can be achieved using optically compatible adhesives such as Canada balsam, optically inactive or optically neutral pressure sensitive adhesives, curable (UV, heat, etc.) adhesives, or other optically benign methods of bonding the layers together.

[0040] 3 is a flow chart outlining a method 300 according to one embodiment. At 302, a test substrate is obtained having a print material receiving surface that includes a material selected to reflect incident light with high contrast and that exhibits a neutral response when contacted by a print material. The test substrate can be any of the test substrates described herein and is selected to support imaging of a particular print material with light, which is again selected based on the test substrate and print material.

[0041] At 304, droplets of print material are ejected from nozzles in the printhead of the inkjet printer onto the test substrate. The droplets may be as small as 10 pL, and the material of the test substrate is typically selected such that the droplets do not substantially change shape or composition upon contact with the print material receiving surface of the test substrate. The droplets typically exhibit a contact angle of about 90 degrees upon contact with the print material receiving surface, but in any event the contact angle is about 75 degrees or greater, thereby maximizing the number of droplets that can be deposited on the test substrate.

[0042] At 306, the deposited droplets are imaged using light matched to the material of the test substrate such that it reflects off the test substrate with high contrast to the light reflected from the droplets. The image may be a photographic image captured by a camera or CCD imager, or it may be an intensity image or the like that may be captured using a line scanner or photosensor array configured to produce a sharp and clear image with a resolution of up to 400 nm per pixel such that droplet characteristics can be resolved from the image.

[0043] At 308, a roll is used to advance and withdraw the test substrate. The test substrates herein combine rotational and imaging droplet interaction properties as described above. In some cases, the test substrate has a printing material receiving surface to which a droplet of printing material is fixed upon contact.

[0044] In some cases, a multi-layer test substrate may be used. FIG. 4A is an elevational view of a test substrate 400 according to another embodiment. The test substrate 400 has a base layer 402, a printing material receiving surface 404, a printing material receiving surface support layer 406 in contact with the printing material receiving surface 404 and disposed between the base layer 402 and the printing material receiving surface 404, and an adhesive layer 408 between the base layer 402 and the printing material receiving surface support layer 406. In this case, the printing material receiving surface support layer 406 provides structural strength to the test substrate 400 and optimizes the handling of the test substrate in a liquid drop test analyzer such as the liquid drop test device 200. The printing material receiving surface 404 is generally as described above, being a thin coating of a material selected to have a neutral reaction to the printing material deposited thereon. The printing material receiving surface support layer 406 may be any flexible material, typically a polymeric material such as a polyolefin material (PE, PP) or a PET material. The adhesive layer 408 is applied to a thickness selected to provide strong adhesion without affecting the imaging of the print material. In general, the thickness of the test substrate described above can be about 50 μm or less, and the thickness of the print material receiving surface 404 in combination with the base layer 402 can be 10 μm or less. In one example, the print material receiving surface support layer 406 has a thickness of 23 μm to 25 μm, and the adhesive layer 408 has a thickness of about 15 μm to 18 μm.

[0045] FIG. 4B is an elevational view of a test substrate 450 according to another embodiment. The test substrate 450 includes the test substrate 400 as a component, but with the addition of one or more layers of a backing structure 452. In this example, the backing structure 452 is a layer of a transparent polymeric material. The backing structure can be transparent, partially transparent, semi-transparent, partially opaque, or opaque, and can be selected to reduce the light transmission of the test substrate 450. For example, the backing structure 452 can have a first optical density and the underlayer 402 can have a second optical density, with the combined optical density of the underlayer 402 and the backing structure 452 being a function of the first optical density and the second optical density. The use of a backing structure such as the backing structure 452 allows the underlayer 402 to be thinner, providing advantages in the cost and physical properties of the test substrate 450. In one example, the underlayer is a metal layer as described above, and the backing structure 452 is a transparent polymeric film such as PET.

[0046] However, other materials can be used as the light blocking material. For example, a paint layer can be coated on the film that will receive the print material. The paint layer can function as a base layer that blocks or reduces the light transmitted through the test substrate. In another example, the paint layer can function as a back structure and be coated on the back of a base layer (which can be metal or other material). The paint layer can be opaque, partially opaque, or translucent, white, black, or any color that blocks light in the desired way, and can be coated on any component of the test substrate by jetting, slot die coating, ribbon coating, or coextrusion. In another example, pigments can be added to the various polymer layers described above to reduce the light transmission of the test substrate. For example, in some cases, the back structure can be a colored polymeric material such as white PET or black PET. The black material can absorb the incident light and thus help achieve high contrast with the reflected light. The colored material can scatter the incident light, which reduces the contrast, and thus help achieve high contrast with the reflected light.

[0047] While embodiments in accordance with one or more aspects of the present invention have been described above, other embodiments not specifically described in this disclosure may be devised without departing from the basic scope of the disclosure, which scope is defined by the following claims.

Claims

1. 1. A substrate for an inkjet printer, the substrate comprising a printing material receiving surface that exhibits a neutral response to printing material, the printing material receiving surface comprising a material selected to have high contrast in reflected light, a reflective base layer, and a printing material receiving surface support layer disposed between the printing material receiving surface and the base layer.

2. The substrate of claim 1 , wherein the substrate is opaque.

3. The substrate of claim 1 , wherein the printing material has a contact angle with the printing material receiving surface of 75 degrees or greater.

4. The substrate of claim 1 , wherein the print material receiving surface is a transparent film.

5. The substrate of claim 1 having a thickness of 150 μm or less.

6. The substrate of claim 1 , wherein the print material receiving surface is comprised of an environmentally stable material.

7. The substrate of claim 1 , wherein the print material receiving surface is a clear coating.

8. The substrate of claim 7 , wherein the reflective underlayer comprises a metal film.

9. The substrate of claim 8 , wherein the print material receiving surface is a hydrophobic polymeric material.

10. The substrate of claim 1 , wherein the printing material receiving surface is a polymeric material layer, the base layer includes a metal film coated on the printing material receiving layer, and the polymeric material layer is adhered to the base layer.

11. The substrate of claim 1 further comprising a pigment.

12. 1. A droplet drop test system for analyzing droplets of print material, the droplet drop test system comprising: a test substrate system including a stage for a test substrate, the test substrate being a flexible substrate comprising a material selected to have high contrast in reflected light, the test substrate having a printing material receiving surface that exhibits a neutral response to the printing material, the test substrate including a transparent film providing the printing material receiving surface, a base layer, and a printing material receiving surface support layer disposed between the transparent film and the base layer; an imaging device comprising a light source positioned to illuminate the printing material receiving surface with light matched to the optical properties of the substrate, and a detector for capturing an image of light reflected from the test substrate; A droplet drop test system comprising:

13. 13. The liquid drop test system of claim 12, wherein the stage is coupled to a vacuum source for holding the test substrate fixedly in a flat orientation relative to the stage.

14. 13. The liquid drop test system of claim 12, wherein the printing material has a contact angle with the printing material receiving surface of 75 degrees or greater.

15. 15. The liquid drop test system of claim 14, wherein the print material receiving surface is made of an environmentally stable material.

16. 13. The liquid drop test system of claim 12, wherein the underlayer is a reflective film.

17. 13. The liquid drop test system of claim 12, wherein the transparent film is a hydrophobic film and the underlayer is a metal coating on the hydrophobic film.

18. The liquid drop test system according to claim 12, wherein the printing material receiving surface is a surface-treated surface of the test substrate.

19. 13. The droplet drop test system of claim 12, wherein the light is also matched to the optical properties of the printing material and the printing material receiving surface such that the light reflected from the test substrate provides a clear image of a droplet of printing material deposited on the printing material receiving surface.

20. 1. A method, comprising: ejecting a plurality of droplets of a printing material from nozzles of a printhead of an inkjet printer onto a test substrate, the test substrate comprising a material selected to have high contrast in reflected light and having a printing material receiving surface that exhibits a neutral response when contacted by the printing material; imaging the droplet with light matched to the material of the test substrate so as to reflect from the test substrate with high contrast to light reflected from the droplet; recovering the test substrate using a roll; A method comprising:

21. 21. The method of claim 20, wherein the printing material has a contact angle with the printing material receiving surface of 75 degrees or greater.

22. 21. The method of claim 20, wherein the test substrate comprises a base layer, the print material receiving surface is a transparent material, and the base layer is a reflective material.

Images