BACKGROUND

[0001] Users are increasingly demanding functionalities beyond merely recognizing a touch to the surface of a touch-sensitive device. Such other functionalities include handwriting recognition and direct note taking (using, for example, a stylus). Such functionalities are generally provided in so-called digitizing systems. Digitizing systems may have position-dependent indicia defected by an image sensor in a stylus, such as an electro-optical (E/O) pen or other image reader, where the position-dependent indicia include an ink.

BRIEF DESCRIPTION OF THE DRAWING

[0002] Features of the present disclosure are illustrated by way of example and not limited in the following figure(s), in which like numerals indicate like elements, in which:

[0003] FIG. 1 is a simplified diagram of an example ink;

[0004] FIG. 2 is a simplified diagram of an example display;

[0005] FIG. 3 is a flow chart of an example of a method of making a printed substrate; and

[0006] FIG. 4 is a line graph of the backscatter reflectance of an example ink. DETAILED DESCRIPTION

[0007] For simplicity and illustrative purposes, the present disclosure is described by referring mainly to an example thereof. In the following description, numerous specific details are set forth in order to provide a thorough

understanding of the present disclosure. It will be readily apparent however, that the present disclosure may be practiced without limitation to these specific details. In other instances, some methods and structures have not been described in detail so as not to unnecessarily obscure the present disclosure. As used herein, the terms "a" and "an" are intended to denote at least one of a particular element, the term "includes" means includes but not limited to, the term "including" means including but not limited to, and the term "based on" means based at least in part on.

[0008] With reference first to FIG. 1 , there is shown a simplified diagram of an example ink 100. The ink 100 may include a carrier 1 10 and a light scattering metallic pigment 120 having a size ranging from about 1 micron to about 3 microns. The light scattering metallic pigment 120 may be present in an amount ranging from about 15 wt. % to about 35 wt. % by weight relative to the total weight of the ink 100. In an aspect, the light scattering metallic pigment 120 may be present in an amount ranging from about 20 wt. % to about 30 wt. % by weight relative to the total weight of the ink 100. The light scattering metallic pigment 120 disclosed herein may be color neutral in the visible wavelength spectrum and may not, noticeably, to the human observer, impact color, such as color-shifting, in the visible wavelength spectrum.

[0009] The light scattering metallic pigment 120 may include any metal that has a reflective surface. In an aspect, the metal may be any metal from the periodic table of elements, including but not limited to, aluminum, magnesium, silver, nickel, copper, iron, titanium, chromium, cobalt, tin, indium, gold, lead, platinum, zinc, and the like. The light scattering metallic pigment may include a metal alloy and a metal oxide. Non-limiting examples of metal oxides include aluminum oxide, antimony trioxide, antimony tetroxide, antimony pentoxide, arsenic trioxide, arsenic pentoxide, barium oxide, bismuth(iii) oxide, bismuth(v) oxide, calcium oxide, cerium oxide, chromium(ii) oxide, chromium(iii) oxide, chromium(iv) oxide, chromium(vi) oxide, cobalt(ii) oxide, cobalt(ii,iii) oxide, cobalt(iii) oxide, copper(i) oxide, copper(ii) oxide, indium oxide, iron(ii) oxide, iron(ii,iii) oxide, iron(iii) oxide, lead(ii) oxide, lead(ii.iv) oxide, lead(iv) oxide, lithium oxide, magnesium oxide, manganese(ii) oxide, manganese(iii) oxide,

manganese(iv) oxide, manganese(vii) oxide, mercury(ii) oxide, nickel(ii) oxide, nickel(iii) oxide, rubidium oxide, silicon dioxide, silver(i) oxide, thallium(i) oxide, thallium(iii) oxide, tin(ii) oxide, tin(iv) oxide, zinc oxide, and combinations thereof. In an aspect, the light scattering metallic pigment includes silver; silver alloys, such as sterling silver; and silver (i) oxide.

[0010] The light scattering metallic pigment 120 may be in any form or shape, such as a particle, a nanoparticle, a flake, a crystal, a powder, and the like. The light scattering metallic pigment 120 may be grown as a crystal having an arithmetical mean roughness Ra of the surface of about 10 nm or less, such as about 9 nm or less, and for example, about 4 nm or less. In an aspect, the light scattering metallic pigment 120 may be a flake, such as a milled flake to achieve a particular size, for example about 1 μιη to about 3 μιη. The light scattering metallic pigment 120 may be a flake having a diffraction grating.

[0011] The size and distribution of size of the light scattering metallic pigment 120 may be controlled with high accuracy by using a grown crystal form. In this manner, and with reference to the display 200 depicted in FIG. 2 and the ink 100 depicted in FIG. 1 , the ink 100 and subsequent printed substrate 210 may have a high count of pigment 230 in each printed indicia 220 which may enhance the uniformity of a reflected response and a magnitude of the light scattering effectiveness. The light scattering metallic pigment 120, 230 may have a size smaller than the retinal resolution of the eye and hence may improve invisibility of the pigment to the human eye when printed on a clear substrate 210. A median size (D50) of the light scattering metallic pigment 120, 230 may range from about 0.1 μιη to about 15 μιη, for example, from about 0.5 μιη to about 12 μιη. In an aspect, the light scattering metallic pigment 120, 230 has a size ranging from about 1 μιη to about 5 μιη, for example, from about 1 μιη to about 3 μιη. The median size (D50) may be measured using a laser diffraction type particle size analyzer (LA-950V2) from HORIBA, Ltd.

[0012] A standard deviation oD of diameter D of the light scattering metallic pigment 120, 230 may be about 0.8 μιη or less, for example, about 0.5 μιη or less, and as a further example, μιη or less.

[0013] As shown in FIG. 1 , the light scattering metallic pigment 120, 230 may be combined with a carrier 1 10, such as a clear carrier or clear resin, to form the ink 100. By way of non-limiting examples, the carrier 1 10 may be polyvinyl alcohol, polyvinyl acetate polyvinylpyrrolidone, poly(ethoxyethylene), poly(methoxyethylene), poly(acrylic) acid, poly(acrylamide), poly(oxyethylene), poly(maleic anhydride), hydroxyethyl cellulose, cellulose acetate,

poly(saccharides) such as gum arabic and pectin, poly(acetals) such as polyvinylbutyral, polyvinyl halides) such as polyvinyl chloride and polyvinylene chloride, poly(dienes) such as polybutadiene, poly(alkenes) such as

polyethylene, poly(acrylates) such as polymethyl acrylate, poly(methacrylates) such as poly methylmethacrylate, poly(carbonates) such as poly(oxycarbonyl oxyhexamethylene, poly(esters) such as polyethylene terephthalate,

poly(urethanes), poly(siloxanes), poly(sulphides), poly(sulphones),

poly(vinylnitriles), poly(acrylonitriles), poly(styrene), poly(phenylenes) such as poly(2,5 dihydroxy-1 ,4-phenyleneethylene), poly(amides), natural rubbers, formaldehyde resins, other polymers and mixtures of polymers and polymers with solvents. According to an example, the ink 100 is not visible to the human eye. As such, it should be understood that the depiction of the pigment 120, 230 in FIGS. 1 and 2 are for purposes of illustration and that the pigment 120, 230 may not be visible to the naked eye.

[0014] The carrier 1 10 may be present in an amount ranging from about 60 wt. % to about 95 wt. % by weight relative to the total weight of the ink 100. In an aspect, the carrier 1 10 may be present in an amount ranging from about 65 wt. % to about 90 wt. % by weight relative to the total weight of the ink 100.

[0015] The light scattering metallic pigment 120, 230 may be present in the carrier 1 10 in any loading amount so long as the pigment 120, 230 may randomly orient within the carrier 1 10. In an aspect, the ink 100 may include from about 0.5% by volume to about 90%, for example, from about 5% to about 85%, and as a further example, from about 10% to about 80%, by volume of the light scattering metallic pigment 120, 230 in the ink 100.

[0016] The ink 100 may further include other additives including, but not limited to, anti-clumping agents, anti-curl agents, binders, charge directors, corrosion inhibitors, dispersants, light stabilizers, optical brighteners, polymers, resins, rheology modifiers, UV curable materials, surface-active agents or combinations thereof. In an aspect, the anti-clumping agent may be salicylic acid. The additives may be included within the ink. In another aspect, the additives may coat a portion of a surface of the light scattering metallic pigment, such as coating half of the surface of the light scattering metallic pigment. In another aspect, the additive, such as the anti-clumping agent, may encapsulate the light scattering metallic pigment 120, 230.

[0017] The ink 100 may be applied to a clear substrate 210, such as a plastic film, to form the display 200 as shown in FIG. 2. In an aspect, the ink 100 may be applied to the clear substrate 210 in a pattern of indicia 220. The pattern of indicia 220 may be a dot array, as shown in FIG. 2. A user may utilize an electrical-optical reader, such as an electro-optical pen to read the pattern of indicia 220 on the clear substrate 210 shown in FIG. 2. The ink 100 may be present on the clear substrate 210 in any amount so long as a pattern of indicia 220 is formed. In an aspect, the ink 100 may be present at a thickness ranging from about 1 .5 μιη to about 8 μιη, such as from about 3 μιη to about 5 μιη.

[0018] The ink 100 may be cured using ultraviolet light, visible light, infrared, electron beam, or the like. Curing may proceed in an inert or ambient atmosphere. In an aspect, the curing step may utilize an ultraviolet light source having a wavelength of about 395 nm. The ultraviolet light source may be applied to the ink 100 at a dose ranging from about 200 mJ to about 1000 mJ, for example ranging from about 250 mJ to about 900 m J, and as a further example from about 300 m J to about 850 m J. In an aspect, the ink 100 may be cured in a short period of time, for example substantially instantaneously, in order to decrease the possibility of the light scattering metallic pigments 1 10, 230 reorienting in the carrier in a flat orientation due to the effect of gravity, which would provide for a less scattered irradiance when subjected to an electronic reader.

[0019] The ink 100 may not impart a noticeable color shift when applied in a pattern of indicia 220 to a substrate 210, such as on the display 200. A color shift of C* <= 2.0 is considered invisible to the eye, referring to the L*a*b* color space. The indicia may occupy about 8.9% of the display at 100 micron diameter. The aggregate color shift for such a display may be about C* 0.35, which is negligible.

[0020] With reference now to FIG. 3, there is shown a flow diagram of an example method 300 of making a printed substrate. In the method 300, at block 310, an ink 100 including a carrier 1 10 and light scattering metallic pigments 120, 230 having a size from about 1 micron to about 3 microns may be made. In addition, at block 320, a pattern of indicia 220 may be applied onto a clear substrate 210 using the ink 100. Moreover, at block 330, the applied pattern may be cured.

[0021] EXAMPLES

[0022] Example 1 - An ink having about 25 wt.% by weight loading of silver microflakes (commercially available from Tokusen USA, Inc.) and about 75 wt.% by weight loading of a ultraviolet light curable clear carrier (FR Force Transparent White, commercially available from FlintGroup) was prepared. The silver microflakes had an across flake size ranging from 1 μιη to 3 μιη. The ink (M13SA0S) was continually mixed to ensure uniform dispersion of the flakes until applied by flexographic printing to a clear substrate.

[0023] The backscatter reflectance was measured, as shown in FIG. 4, using a Cary 7000 reflectometer. The incidence of near IR light (850 nm) onto a clear substrate was varied from 0° to 70° by incrementing the sample angle theta. The detector angle was held constant at 10° relative to the instruments collimated 850 nm source irradiance. At this position, the backscatter reflection at an angle that is 10° past the source radiance was measured. The measurement was continuously taken as the sample was rotated clockwise from an initial normal orientation relative to the light source. [0024] As shown in FIG. 4, the black dashed line is the optimal diffuse backscatter reflectance of white paper. The ink M13SA0S is shown in the thick solid line having a backscatter reflectance of about 0.33 % at an angle of 0°, and a backscatter reflectance of greater than 0.08% at an angle of about 45°. Curves for the backscatter reflection at 850 nm of silver micro-flakes ranging size from 2 urn to 7 urn (M27A05) and silver nano-flakes ranging from 300 nm to 500 nm (N300SA05) are shown in FIG. 4 additionally. It should be noted that all three of these micro and nano metallic pigments provided performance above the thin horizontal line across the plot located at 0.05% reflectance. This is the threshold diffuse/backscatter reflection necessary for robust operation of a digital EO-pen at a 45 degree tilt relative to the surface it is trying to detect ink marked indicia with.

[0025] One will note from FIG. 4 that the silver micro-flakes ranging in size from 2 urn to 7 urn (M27A05) actually perform better than the silver micro-flakes ranging in size from 1 urn to 3 urn (M13SA0S) for equivalent loading by weight (25%) formulations compared in FIG. 4. The silver micro-flakes ranging in size from 1 urn to 3 urn (M13SA0S) based ink may be used despite this fact because its smaller size flakes are less visible to the EO-pen/display users eye due to their significantly smaller size.

[0026] Although described specifically throughout the entirety of the instant disclosure, representative examples of the present disclosure have utility over a wide range of applications, and the above discussion is not intended and should not be construed to be limiting, but is offered as an illustrative discussion of aspects of the disclosure.

[0027] What has been described and illustrated herein is an example of the disclosure along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. Many variations are possible within the spirit and scope of the disclosure, which is intended to be defined by the following claims - and their equivalents - in which all terms are meant in their broadest reasonable sense unless otherwise indicated.