AU2017100981B4 - Method, system and apparatus for detecting coating materials on a substrate - Google Patents

Abstract

A printing system 10, that has a printing station 16, 18 for applying a coating material to predetermined areas of a substrate 12, and an applicator 20 for applying one or more indicator materials onto an indicator patch on the substrate 12. The indicator patch overlaps (at least partially) the area intended to be coated with the coating material, wherein the coating material and the indicator material(s) generate a remotely detectible indication when combined. The system 10 also having a detector 28 sensitive to the remotely detectible indication, and positioned such that the indicator patch passes within range, in order to generate an output indicative of the coating material presence, absence, thickness and/or location on the substrate 12. The system 10 is particularly suited to detection of thin, transparent and/or colourless coatings on a substrate

Description

1 2017100981 19 Μ 2017

METHOD, SYSTEM AND APPARATUS FOR DETECTING COATING MATERIALS

ON A SUBSTRATE

Field of the Invention [0001] The invention relates to the application of thin, transparent and/or colourless coatings to an underlying substrate surface. In particular, the invention concerns the application of thin colourless and/or transparent coatings to the surface of a substrate.

Background of the Invention [0002] Coatings are applied for functional and aesthetic reasons on a broad range of products. The application of different ink colours to print a colour image on an underlying substrate is one common example. Each different colour (e.g. cyan, magenta, yellow and black) is applied or printed in accurate registration (i.e. relative position) to maintain image quality. Similarly, other coatings such as surfactants, adhesives and the like often need to be in registration with previously or subsequently printed layers.

[0003] Printing or coating of substrate films will often occur in a continuous roll-to-roll process for high throughput (examples of these printing systems include gravure, flexographic roll-to-roll and rotary screen printing systems). Sheet-fed printing is also common and achieves reasonable throughput. Registration of the various ink layers is normally checked by an automated system but may also be manually checked by offline manual inspection of sample prints. Visually checking samples offline is slow and only provides a statistical indication of the online printing accuracy and consistency. Automated visual inspection systems are online and allow direct feedback to adjust print parameters in real time.

[0004] Some automated systems use non-contact capacitance based sensors or non-contact inductance based sensors. US 7,652,760 describes a system in which the test equipment includes a light reflection sensor and a conductive sensor. Together, the sensors detect the presence and location of a conductive or non-conductive coating. The conductive coating sensor is a non-contact capacitance 2 2017100981 19 Μ 2017 sensor or a non-contact inductive sensor. The light reflection sensor measures levels of light energy reflected from the coated (or uncoated) surface of the print medium. Fluctuations in the sheet stacking step of a sheet-fed process or web flutter in a continuous roll-to-roll process, can reduce the accuracy of detection, particularly when using a capacitance method and even more so when detecting thin coatings. Detecting very thin coatings using the reflectance of a wet substrate versus a dry substrate can be problematic. The quick drying nature of very thin coatings complicates these systems, particularly if there is flutter in the substrate as well.

[0005] To improve coating detection, a functional additive such as an optical brightener, dye or fluorophore may be used. However, the amount of additive needed to facilitate good detection can adversely impact on the behaviour of the coating in the print process. Furthermore, detecting the functional additives other than a dye will require costly, specialised cameras and/or light sources. The dye itself may also be presented at such a low colour intensity so as not to impact the coating’s behaviour, that specialized lighting sources will be required.

[0006] Alternatively, manual testing techniques can be used such as those typically employed to detect coatings containing titanium or zirconium. These coatings are sometimes applied to pre-treat or modify the substrate surface prior to adding subsequent inks or other coatings. One example is the use of organic titanates and organic zirconates to augment adhesion properties, better disperse pigments, promote polymer crosslinking and so on. Hence there are a number of offline spot tests for titanium and zirconium to confirm the presence and extent of these pre-treatments. For example: • Several drops of 10% sulfuric or hydrochloric acid are placed on the substrate surface and spread over the area to be analyzed. A drop of 30% hydrogen peroxide is added to the treated area and the appearance of a yellow colour indicates the presence of titanium. • One or two drops of diluted sulphuric acid or hydrochloric acid solution on the substrate surface are spread over the area to analyzed contact. A drop of 5% solution of the sodium salt of chronotropic acid (4, 5-dihydroxynaphthalene-2,7-disulfonic acid) is added to the treated area. 3 2017100981 19 Μ 2017

The appearance of a reddish-brown colour indicates the presence of titanium. • A drop of 10% hydrochloric acid solution is placed on the substrate surface and spread over the area to analyzed. The acid solution is allowed to partially dry then a 10% solution disodium1,2-dihydroxybenene-3,5-disulfonate is added to the acid-treated area. The appearance of a yellow colour indicates the presence of titanium.

[0007] While these tests are effective and relatively simple, they are performed offline, slow and do not allow for real time feedback and adjustment of any printing parameters.

[0008] Any reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

Summary of the Invention [0009] With the above issues in mind, one aspect of the present invention provides a method for detecting a coating material applied to a substrate moving along a feed path, the method comprising: printing one or more indicator materials onto an indicator patch on the substrate, the indicator patch at least partially overlapping an area of the substrate intended to be coated with the coating material, the coating material and the at least one indicator material having properties that generate a remotely detectible indication when combined; and, bringing the indicator patch within range of a detector sensitive to the remotely detectible indication, such that output from the detector is indicative of the coating material presence, absence, thickness and/or location on the substrate.

[0010] In another aspect, the present invention provides a printing apparatus, the apparatus comprising: 4 2017100981 19 Μ 2017 a printing station for applying a coating material to predetermined areas of a substrate; a media feed path for moving the substrate through the printing station; an applicator for applying one or more indicator materials onto an indicator patch on the substrate the indicator patch at least partially overlapping the area intended to be coated with the coating material, wherein the coating material and the at least one indicator material generate a remotely detectible indication when combined; and, a detector positioned adjacent the feed path such that the indicator patch passes within range of the detector, the detector being sensitive to the remotely detectible indication to generate an output indicative of the coating material presence, absence, thickness and/or location on the substrate.

[0011] In yet another aspect, the present invention provides a printing system, the system comprising: a printing station for applying a coating material to predetermined areas of a substrate; an applicator for applying one or more indicator materials onto an indicator patch on the substrate the indicator patch at least partially overlapping the area intended to be coated with the coating material, wherein the coating material and the at least one indicator material generate a remotely detectible indication when combined; and, a detector positioned such that the indicator patch passes within range, the detector being sensitive to the remotely detectible indication in order to generate an output indicative of the coating material presence, absence, thickness and/or location (i.e. registration) on the substrate.

[0012] Preferably the applicator is a droplet ejection device such as an inkjet printhead and the coating material is applied to the substrate at a separate printing station. Preferably the separate printing station is a gravure printing station with at least one print roller paired with an opposing press roller such that the feed path 5 2017100981 19 Μ 2017 passes through the nip of the rollers. The inkjet printhead may be upstream or downstream of the gravure printing station.

[0013] Preferably, the substrate has a print area for images and indicia to be printed, and a test area for test patches of printed coating materials (such as ink), wherein the indicator patch is printed in the test area and the area to be coated with the coating material includes a test patch that overlaps with the indicator patch. Optionally, a plurality of test patches are printed within the indicator patch, each of the test patches printed with different coating materials respectively. Optionally, the coating material is thicker in the test patch than in the print area. Preferably, the test area is adjacent a lateral edge of the substrate (relative to the feed path) and spaced from the print area.

[0014] Preferably, one of the indicator materials is pH sensitive such that the remotely detectible indication corresponds to a change in pH. Preferably, the coating material is colourless, transparent or less than 1 micron thick, in some cases less than 0.5 microns thick, or even less than 100 nanometres thick. Optionally, the remotely detectible indication is a change in reflective properties for incident radiation of particular wavelengths. In some cases, the remotely detectible indication is a colour change in the visible spectrum. Preferably the detector is a vision system with an image sensor sensitive to the remotely detectible indication.

[0015] Preferably, output from the detector is used for feedback control of print parameters relevant to application of the coating material.

[0016] The invention enables a relatively inexpensive and standard vision system to detect the thickness (i.e. ‘coat weight’) and position of thin, transparent and/or colourless coatings that are traditionally difficult to accurately detect using automated methods. This requires a calibration curve to correlate the detected colour intensity with a coat weight, and of course the coating thickness of the test patch should be the same as that of the print area.

[0017] By providing a small indicator patch of material (or materials) that reacts with the coating material to generate an indication that is more easily detectable, the use of sophisticated visions systems and lighting arrangements is unnecessary. Similarly, the slow process of manual, off-line inspection is avoided and replaced with the high throughput of inline detection by an automated vision system.

[0018] In some embodiments, the substrate is a transparent film with the indicator material on one side and an opacifying layer applied to an opposing side of 6 2017100981 19 Μ 2017 the film, the opacifying layer at least partially overlapping the indicator patch and coloured to enhance visual detection of the colour resulting from the colour change. Preferably, the opacifying layer is white.

[0019] Optionally, the transparent film is a continuous web extending between a feed roll and an uptake roll, the continuous web being printed as it is fed from the feed roll to the uptake roll such that an optical detector, positioned downstream of the printing station, detects any changes in the colour of the indicating patch.

[0020] Optionally, the substrate is an individual sheet such that a series of these individual sheets move along a sheet feed path past a station (for example, offset printing, intaglio printing or screen printing) at which the individual sheets are printed with the coating such that an optical detector is positioned downstream of the station for detecting any changes to the colour of the indicating patch.

[0021] Preferably the indicator material is a phenol red solution. Preferably the phenol red solution is 20% by volume phenol red in 80% ethanol. In a further preferred form, the phenol red solution includes a resin to promote binding to the substrate. Optionally, the resin is selected such that it increases the thickness of the indicator material on the indicator patch. This better enables the indicator patch to be printed in a well-defined, discrete shape.

[0022] Preferably the coating is an organic titanate or organic zirconate.

[0023] Preferably, the optical detector includes a CCD (charge coupled device) array or CMOS image sensor that is sensitive to light in the visible spectrum. Preferably, the optical detector is incorporated into an automated vision system for detecting the thickness and registration of all coatings printed on the substrate including inks that are not colourless, transparent or less than 0.5 microns thick.

[0024] In some embodiments, the substrate is a base material from which a security document or token is formed. Optionally, the substrate is a transparent polymer film used as the base material to form a banknote. In some forms, the banknote has at least one opacifying layer applied to a portion of the transparent polymer film to form a window or half window. Preferably, the banknote incorporates one or more security features.

Brief Description of the Drawings 7 2017100981 19 Μ 2017 [0025] The invention will now be described by way of example only, by reference to the following preferred embodiments illustrated in the accompanying drawings, in which:

Figure 1 is a schematic section view of a printing system according to the present invention; and,

Figure 2 is a schematic plan view of a continuous web printed by the system of Figure 1.

Detailed Description of Preferred Embodiments

Security Document or Token [0026] As used herein the term security documents and tokens includes all types of documents and tokens of value and identification documents including, but not limited to the following: items of currency such as banknotes and coins, credit cards, cheques, passports, identity cards, securities and share certificates, driver's licenses, deeds of title, travel documents such as airline and train tickets, entrance cards and tickets, birth, death and marriage certificates, and academic transcripts.

[0027] The invention is particularly, but not exclusively, applicable to security documents or tokens such as banknotes or identification documents such as identity cards or passports formed from a substrate to which one or more layers of printing are applied. The diffraction gratings and optically variable devices described herein may also have application in other products, such as packaging, toys or novelty items.

Device or Feature or Security Device or Feature [0028] As used herein the term security device or feature includes any one of a large number of security devices, elements or features intended to protect the security document or token from counterfeiting, copying, alteration or tampering. Security devices or features may be provided in or on the substrate of the security document or in or on one or more layers applied to the base substrate, and may take a wide variety of forms, such as security threads embedded in layers of the 12 security document; security inks such as fluorescent, luminescent and δ 2017100981 19 Μ 2017 phosphorescent inks, metallic inks, iridescent inks, photochromic, thermochromic, hydrochromic or piezochromic inks; printed and embossed features, including relief structures; interference layers; liquid crystal devices; lenses and lenticular structures; optically variable devices (OVDs) such as diffractive devices including diffraction gratings, holograms and diffractive optical elements (DOEs).

Substrate [0029] As used herein, the term substrate refers to any underlying surface for supporting one or more coatings of functionalised fluid such ink, adhesive and so on. It may be a media substrate for use in a printing system, such as the base material from which packaging, labelling, a security document or token is formed. The base material may be paper or other fibrous material such as cellulose; a plastic or polymeric material including but not limited to polypropylene (PP), polyethylene (PE), polycarbonate (PC), polyvinyl chloride (PVC), polyethylene terephthalate (PET), biaxially oriented polypropylene (BOPP); or a composite material of two or more materials, such as a laminate of paper and at least one plastic material, or of two or more polymeric materials.

Transparent Windows and Half Windows [0030] As used herein the term window refers to a transparent or translucent area in the security document compared to the substantially opaque region to which printing is applied. The window may be fully transparent so that it allows the transmission of light substantially unaffected, or it may be partly transparent or translucent partially allowing the transmission of light but without allowing objects to be seen clearly through the window area.

[0031] A window area may be formed in a polymeric security document which has at least one layer of transparent polymeric material and one or more opacifying layers applied to at least one side of a transparent polymeric substrate, by omitting least one opacifying layer in the region forming the window area. If opacifying layers are applied to both sides of a transparent substrate a fully 13 transparent window may be formed by omitting the opacifying layers on both sides of the transparent substrate in the window area. 9 2017100981 19 Μ 2017 [0032] A partly transparent or translucent area, hereinafter referred to as a "halfwindow", may be formed in a polymeric security document which has opacifying layers on both sides by omitting the opacifying layers on one side only of the security document in the window area so that the "half-window" is not fully transparent, but allows some light to pass through without allowing objects to be viewed clearly through the half-window.

[0033] Alternatively, it is possible for the substrates to be formed from an substantially opaque material, such as paper or fibrous material, with an insert of transparent plastics material inserted into a cut-out, or recess in the paper or fibrous substrate to form a transparent window or a translucent half-window area.

Opacifying Layers [0034] One or more opacifying layers may be applied to a transparent substrate to increase the opacity of the security document. An opacifying layer is such that LT < L0, where L0 is the amount of light incident on the document, and LT is the amount of light transmitted through the document. An opacifying layer may comprise any one or more of a variety of opacifying coatings. For example, the opacifying coatings may comprise a pigment, such as titanium dioxide, dispersed within a binder or carrier of heat-activated cross-linkable polymeric material. Alternatively, a substrate of transparent plastic material could be sandwiched between opacifying layers of paper or other partially or substantially opaque material to which indicia may be subsequently printed or otherwise applied.

[0035] Referring to the figures, a substrate 12, in the form of a continuous web extending between a feed roller and an uptake roller (not shown), is printed with images and indicia 30 at a number of print stations for each of the different inks and other coatings. One of the print stations is shown in Figure 1. It has a gravure print roller 18 paired with an opposing press roller 22 for printing a coating that is colourless, transparent and/or thin (i.e. less than 1 micron but often less than 0.5 microns and in some cases less than 100 nm). The print controller 16 adds the coating material (such as ink, adhesive or another type of functionalised fluid) to the surface of the gravure roller 18 in a controlled manner to achieve the desired coating weight (i.e. coating thickness). 10 2017100981 19 Μ 2017 [0036] The surface of the gravure roller 18 is etched so that the coating is applied in the required parts of the print area 32 on the substrate 12. Along one edge of the substrate 12 is a test area where test patches 34, 36, 38 and 40 for each coating are printed. These test patches are used to check the coating weight and registration using an inline, automated vision system 28.

[0037] In Figure 1, the optical detector is a camera with CCD array or CMOS image sensor. The camera’s field of view 44 scans the test area of the substrate 12 as it moves along the feed path 14 in the feed direction 26. From the colour levels and position of the test patches 34, 36, 38 and 40, the automated vision system 28 can determine if the coating weight and registration are within specified tolerances. Output from the vision system can be used for real-time feedback control of the gravure controller 16.

[0038] To improve the accuracy of the vision system, the camera 28 is paired with a backing 24 positioned on the other side of the feed path 14. The backing 24 provides a stable background, particularly for translucent or transparent substrates 12. In some cases, the backing 24 is not reflective but a light source (such as a light box) to provide the optimum background colour or surface for the camera 28.

[0039] Optionally, or additionally, an opacifying layer can be applied to the opposite of the web 12 in the test area. Typically the opaque coating is white.

[0040] While Figure 1 shows a single camera 28, it will be appreciated that the vision system may use several cameras to detect both sides of the substrate web 12 if required.

[0041] If the coatings are transparent, colourless and/or thin, the camera 28 has difficulty seeing these test patches 40 and hence fails to accurately gauge the coating weight and registration. Additives such as fluorophores or brighteners can improve detection but these can affect other properties of the coating or require particular lighting. Alternatively, there are manual, offline methods of checking the coating weight and registration but this is detrimental to throughput and does not allow direct feedback as discussed above. 11 2017100981 19M2017 [0042] The Applicant addresses these issues by applying an indicator patch 42 of indicator material selected to create an easily detected indication when combined with the coating material. The indicator patch 42 need only be a small portion of the test area and will not affect the print area 32. Any suitable applicator 20 can be used to apply the indicator material, and hence there is no need for an additional gravure roller. Although, the applicator can also be a separate gravure roller if desired. In some cases, the substrate may be ‘pre-printed’ with the indicator material in a separate process and/or location. A droplet ejection device such as an inkjet printhead 20 is simpler and more compact. It will be appreciated that the inkjet printhead 20 may be upstream or downstream of the gravure print roller 18 relative to the feed direction 26, but must of course be upstream of the camera 28. Adding the indicator material after the coating to be detected can provide a more readily detectible indication as the reagent(s) that change colour are not partially masked or obscured by the coating.

[0043] The system 10 may use a number of different indicator materials applied to different indicator patches 42 for different test patches 40, or applied to the same indicator patch 42. Each indicator patch 42 can encompass several test patches 40 or the single test patch 40 for a particular coating material.

[0044] Suitable indicator materials may be pH sensitive so that a pH change and associated colour change occurs when added to the coating material. Other suitable indicator materials may include the reagents discussed above (sulfuric or hydrochloric acid, hydrogen peroxide, sodium salt of chronotropic acid (4, 5-dihydroxynaphthalene-2,7-disulfonic acid), and disodiuml ,2-dihydroxybenene-3,5-disulfonate solution) to detect coatings containing titanium or zirconium. To further improve detection, the coating weight in the test patch 40 can be greater than that applied in the print area 32. However, in some cases, the weight of the test patch can only be increased marginally because of the nature of the ink used (low viscosity, high solvent). Similarly, other types of inks that need to be deposited at very low concentrations use dilute solutions to help achieve the ‘thinness’ required. Other types of inks used elsewhere, (e.g. PEDOT-PSS) have coating weights limited by cost and solubility. Hence, the skilled worker will understand that dilute inks may not allow much scope to change the gravure cylinder engraving depth and 2017100981 19 Μ 2017 12 significantly increase the weight of the ink but a marginal increase used in conjunction with the detection system described in this invention provides easier detection.

[0045] However with other types of inks, with higher solid content, higher coat weights (e.g. 1 micron thickness) are possible. The print area is printed using shallow gravure cells while the test patch can be printed using the deeper (volume) cells.

[0046] The skilled addressee will readily recognise many variations and modifications to the described embodiments, which do not depart from the spirit and scope of the broad inventive concept.

Claims (5)

1. Claims

   1. A printing system, the system comprising: a printing station for applying a coating material to predetermined areas of a substrate; an applicator for applying one or more indicator materials onto an indicator patch on the substrate the indicator patch at least partially overlapping the area intended to be coated with the coating material, wherein the coating material and the at least one indicator material generate a remotely detectible indication when combined; and, a detector positioned such that the indicator patch passes within range, the detector being sensitive to the remotely detectible indication in order to generate an output indicative of the coating material presence, absence, thickness and/or location on the substrate.
2. 2. A printing system according to claim 1 wherein the applicator is a droplet ejection device such as an inkjet printhead and the coating material is applied to the substrate at a separate printing station.
3. 3. A printing system according to claims 1 or 2 wherein the substrate has a print area for images and indicia to be printed, and a test area for test patches of printed coating materials (such as ink), wherein the indicator patch is printed in the test area and the area to be coated with the coating material includes a test patch that overlaps with the indicator patch.
4. 4. A printing system according to claims 1, 2 or 3 wherein the coating material is colourless, transparent or less than 1 micron thick, in some cases less than 0.5 microns thick, or even less than 100 nanometres thick.
5. 5. A printing system according to any one of claims 1 to 4 wherein the remotely detectible indication is a change in reflective properties for incident radiation of particular wavelengths.