ROLLER BALL PEN

Field of Invention The present invention relates to a resistive ink formulation for a roller-ball pen. Particularly, the present invention relates to an ink formulation that is aqueous and can be used in a pen to create controlled resistances within a range, on paper with immense scope of application for educational circuit lessons as well as making paper-based circuitry.

Background and Prior art

Resistors are used in virtually all electronic circuits and many electrical ones. Resistors, as their name indicates resist the flow of electricity, and this function is key to the operation most circuits. Resistance is one of the key factors used in electrical and electronic circuits. Resistance is the property of materials to resist the flow of electricity, and it is governed by Ohm's Law.

Resistance not only depends upon the chemical composition of the material, but on the length, cross sectional area and shape of the device.

The first major categories into which the different types of resistors can be fitted is into whether they are fixed or variable. These different resistor types are used for different applications: Fixed resistors: Fixed resistors are by far the most widely used type of resistor. They are used in electronics circuits to set the right conditions in a circuit. Their values are determined during the design phase of the circuit, and they should never need to be changed to "adjust" the circuit. There are many different types of resistors which can be used in different circumstances and these different types of resistor are described in further detail below. Variable resistors: These resistors consist of a fixed resistor element and a slider which taps onto the main resistor element. This gives three connections to the component: two connected to the fixed element, and the third is the slider. In this way the component acts as a variable potential divider if all three connections are used. It is possible to connect to the slider and one end to provide a resistor with variable resistance.

[Ref: https://www.electronicsnotes.com/articles/electronic_compone nts/resistors/resisto r-types.php].

While making paper-based circuitry, if the user has to use a resistor in making the circuit, the use of a resistor as described above will actually hamper the flexibility of the paper based circuitry. On the other hand, if the user has an access to draw a resistor using a pen, and vary the resistance just by thickening the line trace, it takes paper- circuitry altogether to a different level. The pen which is a very common day-to-day used writing instrument although looks like any ordinary pen but uses a particular type of special ink called the Resistive ink instead of the conventional pigment-based ink. Used in conjunction with the conductive ink pen, the resistive pen may be used to draw resistors on paper for drawing/ sketching or making one’s own circuit and by connecting a power source in a closed loop can allow the passage of electricity through it. Thus, with the application of the conductive ink in a pen to make electrical connections and using the resistive pen to make resistors, one can generate paper circuits, especially to use it as a teaching cum learning tool to understand concepts of parallel and series resistors etc.

US 2012/0020033 A1 highlights the development of a conductive ink application to demonstrate both the conductivity of the ink that is safe to be used on skin and the use of the ink on surfaces other than skin. This application also used the ink to create a circuit between a LED and a power supply, on a piece of paper (300 GSM watercolour paper). However, the ink required to be applied like a paint with a brush which invariable creates non-uniform and think like traces.

US3663276A discloses method of adjusting the resistivity of a thick-film resistor of the type made by screen printing on a substrate a composition comprising metal particles, glass frit, a temporary organic binder and a temporary solvent, drying to remove the solvent, and firing the composition to fuse the glass frit and burn off the binder, said method comprising determining the relationship between the resistivity of the fired composition and the drying time that elapses between screen printing the composition on the substrate and the beginning of the firing cycle, and setting this elapsed time in accordance with a desired resistivity value.

US2795680A discloses a printed resistor comprising a ceramic base, an adherent layer of resistance material consisting of from about 50% to about 95% of cross-linked epoxy resin, from about 50% to about 5% of finely divided conducting particles and from about 25% to about 0% of finely divided non conducting particles deposited upon said base, and terminal contact areas provided at spaced portions of said layer.

“Educational tool for foundation of electricity using conductive pen and carbon ink brush pen”, Translated Paper D. Sakai, S. Kida, K. Harada, H. Shibata; Electr Eng Jpn. 2018;205:3-8 has developed a pen brush with carbon ink that can make resistors. They have shown that both series and parallel connection with the resistances drawn by the carbon ink brush is achieved, however the brush pen requires longer drying time and drying is achieved by heating the substrate at 70°C or maintaining stringent indoor conditions. This limits the user form creating paper resistors.

Accordingly, there is a need to develop a resistive ink that can be used to build a paper resistors with ease and with the application of a roller ball pen. Object of the Invention

It is as object of the present invention to provide a resistive ink formulation that can be drawn on paper by a conventional roller Ball pen.

It is another object of the present invention to provide a resistive ink formulation that is safe and eco-friendly.

It is further an object of the present invention to provide a resistive ink formulation that can be used to build paper resistors and paper based circuits.

It is also an object of the present invention to provide a process for making a safe and eco-friendly resistive ink formulation.

Summary of the Invention

The following disclosure presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

In an aspect of the present invention, there is provided a resistive ink formulation comprising carbon black, an adhesive, glycerol and water.

In another aspect of the present invention, there is provided a process for making the resistive ink formulation as described herein, the process comprising the steps of: a. mixing the adhesive, water and glycerol to obtain a homogeneous white colour solution; b. adding carbon black to the homogeneous white colour solution of step (a) to obtain a black solution mixture; and c. homogenizing the black solution mixture of step (b) and centrifuging the mixture to remove trapped air bubbles to obtain the resistive ink formulation.

In a further aspect of the present invention, there is provided a use of the resistive ink formulation as described herein in building paper circuits.

In yet another aspect of the present invention, there is provided a method of drawing paper resistors, the method comprising the steps of: a. filling the the resistive ink formulation as described herein in a roller ball point pen; b. drawing resistive lines on the paper with the roller ball point pen, characterized in that the resistive lines are the paper resistors and resistance is attained at two ends of the lines drawn.

Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

Brief Description of Accompanying Drawings

Figure 1 illustrates drawing resistors with the resistive ink on paper Figure 2 illustrates replacing a physical resistor with a resistive line drawn on paper

Figure 3 illustrates drawing a simple circuit on paper

Figure 4 illustrates drawing a complex circuit on paper

Figure 5 illustrates drawing a variable resistor using the resistive pen

Figure 6 illustrates Powder XRD of carbon black material

Figure 7 illustrates FESEM of Carbon black material

Figure 8 illustrates plot depicting shear stress vs shear rate of the resistive ink formulation

Figure 9 illustrates plot of resistance as a function of line length Figure 10 illustrates (a) representative 20 lines, (b) optical image of one line 10, (c) resistance of line 10

Figure 11 the plot of resistance vs time in minutes

Detailed Description of Invention

The present invention relates to a resistive ink formulation.

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding, but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents.

All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments belong. Further, the meaning of terms or words used in the specification and the claims should not be limited to the literal or commonly employed sense but should be construed in accordance with the spirit of the disclosure to most properly describe the present disclosure. The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising" used herein specify the presence of stated features, integers, steps, operations, members, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, components, and/or groups thereof.

The present disclosure will now be described more fully with reference to the accompanying drawings, in which various embodiments of the present disclosure are shown. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the various embodiments set forth herein, rather, these various embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the present disclosure.

The present invention provides a novel ink formulation that is aqueous and allows to design conventional type roller-ball point pen with the ability to realize the functionality of resistance on paper. The ink of the invention can be used in a variety of pens, typically the roller-ball type which allows the flow of ink by the rolling ball when friction is applied through the paper during the act of writing. In one embodiment, the ink of the invention can be used as GEL inks, providing superior performance.

This ink formulation not only can be used with a writing instrument of a roller ball type pen, but also is aqueous in nature. Thus, it is skin-safe, child safe and can be used on paper with the ease of a conventional writing instrument. Typically, ink formulation of the kind of resistive inks are available for various printing processes such as screen printing or inkjet printing or also available as paints that can be applied using a brush or a lamitube squeeze. The novelty of the ink formulation described here is that the ink composition comprises one or more component material that is resistive in nature, one or more dispersing agents, and a liquid medium made up of one or more water/water-based liquids as solvent. Typically ink formulations of the kind available in prior art are non-aqueous.

Another aspect of the ink is the room-temperature, quick drying characteristics of the resistive ink wherein the functionality of the ink is achieved without any post-treatment including heat treatment. Hand-drawn paper resistors are not only useful for making resistors on paper, but also can be used to verify the text book circuit diagram by drawing the circuits on paper and evaluating them by the user, thus eliminating the cognitive gap between the logical layout of the electronic drawing and the practical/physical layout.

The present invention relates to a resistive ink formulation comprising carbon black, an adhesive, glycerol and water.

The resistive ink formulation comprises 10-15% by weight of carbon black, 20-45% by weight of an adhesive, 15-20% by weight of glycerol and 20-60% by weight of water.

The resistance of the line trace drawn with the resistive ink is ~20- 50 K Ohm /cm. The viscosity of the resistive ink formulation is -830 mPa.s at 20 Shear Rate.

The ink formulation is suitable for a roller-ball pen and can be hand written like any conventional pen. The line traces are resistive and the resistance can be varied either by increasing the length of the line trace or by widening the line to a rectangular box. The ink formulation has good flow characteristics akin to conventional writing pens and the drying time is < 5 min. One of the key applications of the resistive pen is that it would be used in the educational kit for paper circuitry being developed by the same group. Hence, water as solvent and glycerol as humectant which is both safe and easily available was chosen for the ink formulation. Acylate adhesive was used as a binder.

The present invention also discloses a process for making the resistive ink formulation as described herein. The process comprises the steps of: a. mixing the adhesive, water and glycerol to obtain a homogeneous white colour solution; b. adding carbon black to the homogeneous white colour solution of step (a) to obtain a black solution mixture; c. homogenizing the black solution mixture and centrifuging the mixture to remove trapped air bubbles to obtain the resistive ink formulation.

The mixing and homogenizing of the solution are done at room temperature. It may be emphasized that homogenization is the key and intricate step in the ink formulation after choosing the right resistive material and hence, the process need be carried out such that there are no large/ agglomerate particles visible to naked eye.

The ink is formulated in such a way that is designed to fill in the barrel of a conventional roller-ball pen cartridge which allows the ink to flow via a roller- ball tip on to the paper during the act of writing. The intricate steps involved in the process of ink formulation with suitable choice of material components which renders the ink as a resistive ink for roller ball pen to be used for paper circuits are novel. The inventive merit and non-obviousness reside in making a judicious choice of components for the ink formulation.

The present invention also relates to the use of the resistive ink formulation as described herein in building paper circuits. The present invention further relates to a method of drawing paper resistors, the method comprising the steps of: a. filling the the resistive ink formulation in a roller ball point pen; and b. drawing resistive lines on the paper with the roller ball point pen, characterized in that the resistive lines are the paper resistors and resistance is attained at two ends of the lines drawn.

The advantages and applications of the present resistive ink are as follows:

(a) Novel ink formulation with resistive and writing properties.

(b) Typically designed for using in roller ball pens of any kind. Ease of using a conventional roller-ball Pen for writing/ drawing/ creating resistors.

(c) The Resistive ink formulation has room temperature, quick drying characteristics, without the requirement of any post-treatment including heat-treatment to display the functionality of the ink.

(d) Resistive ink is eco-friendly, skin-safe and child safe to be used for drawing or making paper based resistors.

(e) The resistive ink formulation is easily scalable for bulk production, without affecting the resistive properties of the resistive line traces.

(f) The ink formulation can be used as a ‘gel’ ink providing superior performance of writing while maintaining the resistive functionality.

(g) The ink formulation allows Resistors to be created on paper by means of a roller-ball pen thereby allowing the user to comprehend the physical layout of the circuit diagram.

(h) The ink formulation allows ‘Hand created resistors’ from a typical roller ball pen enhancing the students tinkering ability to create their very own circuit path.

(i) The Resistive Ink formulation in the form of a resistive pen, in conjunction with a conductive pen allows for easy prototype-testing on paper prior to actual circuit designing (j) The Resistive ink formulation of the Resistive Ink pen is capable of drawing line traces of varying length and width on paper thereby replacing the physical resistors.

(k) The ink formulation is relatively inexpensive, affordable and accessible even to one and all.

In one implementation, the resistive ink can be used for drawing resistors as shown in Figure 1. The resistance can be measured across the resistor lines.

In another implementation, the resistive ink may be used for replacing a physical resistor with a resistive line drawn on paper as shown in Figure 2. In Figure 2 is it seen that the physical resistor is replaced with a resistive line drawn with the resistive ink.

In another implementation, the resistive ink may be used for drawing a simple circuit on paper as shown in Figure 3. In a further implementation, the resistive ink may be used for drawing a complex circuit on paper to show charging and discharging of a capacitor as shown in Figure 4.

In yet another implementation, the resistive ink may be used for drawing a variable resistor using the resistive pen as shown in Figure 5. From Figure 5 it is evident that by measuring the voltage across CG, the user would have made his/her variable resistor using the resistive pen on paper by calculating, VCD, VDE, VEF and VFG·

For the above-mentioned figures, the following reference numerals are used for the components shown in the Figures: paper substrate (1),

LED (2), capacitor (3), conductive lines (4), battery (5) physical resistor (A) resistive line drawn with the resistive ink (B)

The present invention is now being illustrated by way of non-limiting examples. The examples are intended to be purely exemplary of the invention and should therefore not be considered to limit the invention in any way. Efforts have been made to ensure accuracy with respect to numbers used, but some experimental errors and deviations should be accounted for.

Examples

Materials and methods

Carbon black ENSACO250G is purchased from Imerys Graphite & Carbon Switzerland Ltd. White adhesive (Fevicol MR) is purchased from Pidilite Industries Ltd. Glycerol is purchased from Fisher Scientific. In-house DI water from plant was used. OV5 homogenizer from Velp Scientifica was used to mix and homogenize the ink contents for ink formulation. Formulated ink was filled into a roller-ball pen for application as a resistor pen.

Characterization of the carbon sample

Powder XRD of Carbon Material: The carbon sample was characterized by powder X-ray diffraction (XRD) on a Rigaku MiniFlex 600 at 30 kV and 10 mA using Cu Ka (l= 1.54059 A) as the radiation source. The data are collected at 2Q ranging from 20° to 80° at a rate of 2° per min. Powder XRD pattern of carbon consists of two clear reflections at 2Q, 23° and 43° and another shallow reflection at 72°. All reflections are broad indicating disorder nature of the carbon. The 23° and 43° reflections correspond to (002) and (100) planes, respectively as shown in Figure 6 ( Reference : N. Munichandraiah, Adv. Mat. Lett. 2014, 5(4), 184-190).

FESEM of Carbon material: The morphology of the carbon material, as obtained was observed by FESEM. It is confirmed from the FESEM image that the particles are compressed, non-uniform and non-spherical in shape and their size is about 10 + 5 nm. These small particles were agglomerated with each other and formed the irregular size of particles in size range 30-100 nm (Figure 7).

Preparation of ink formulation

For making carbon ink formulation, first 40.81 wt% of white adhesive (Fevicol MR), 30.61 wt% of DI water and 16.32 wt% glycerol was weighed and mixed in 100 ml plastic jar. After getting homogeneous white color solution, 12.24 wt% of carbon black was added in solution and mixed by spatula. After mixing of carbon material with solution, whole mixture was homogenized by homogenizer. The process of homogenization was carried out in two parts considering the heat generation in the process of homogenization. This two-phase homogenization is essential to have a uniform homogeneity of the carbon particles into the binder-solvent mixture. The process of homogenization is carried out at room temperature under standard lab conditions, and can generate small air bubbles to be trapped in the mixture. The trapped air is removed by mixing the ink in the centrifugal mixture. After proper mixing, smooth, viscous and glossy shining carbon black ink is obtained that is resistive in nature. The ink is filled in an ink barrel of any standard roller-ball pen with which a 0.7 to 1 mm line width thickness of line is drawn. The resistance of the line trace on paper is ~20- 50 K Ohm / cm.

Characterization of ink formulation

Shear stress and shear rate for the resistive ink is measured using Rheometer MCR102. Typically for low to medium viscous inks ‘Concentric Cylinder’ measuring system is preferred which requires atleast 20 ml of ink. Alternatively, one can use a CP -25-2 measuring system with a diameter of 25 mm and an angle of 2 degree.

Measurement of viscosity is carried out by measuring the shear stress as a function of shear rate using rotational shear from 1 to 100 rotations per second. The plot of shear stress vs shear rate is linear, which is typical for Newtonian fluids. The slope of the line of Shear stress vs shear strain gives the viscosity of the ink in mPas.s. Alternatively the viscosity is estimated directly as a function of the rotational stresses in rotations per second generated by the Rheometer. A plot of viscosity as a function of shear stress is shown in Figure 8, wherein the measured viscosity is -830 mPa.s at 20 Shear Rate.

Resistance of the ink formulation was measured as a function of length of line drawn. It was observed that the resistance of the resistive ink formulation shows a linear trend indicating that by varying the line length (or the thickness) the resistance of the paper resistance can be varied. Figure 9 shows the line trace study of the roller ball pen ink on a paper wherein 20 lines traces are made and the resistance across the line trace.

As a representative, the image of all the 20, 3 cm lines are shown in Figure 10(a). Figure 10 (b) shows the optical image of line 10 (circled by red line). Resistance across all the 20 line traces was measured for a period of about 9 days. The bar plot of resistance of line no. 10 is shown in figure 10 (c). The average R for all the lines is - 20-50 KOhm/cm.

Further, the resistance value of 100 line traces of two pens were drawn on paper by separate users with the resistive ink pen. It may be noted that as per protocol developed by the present inventors, all ink formulations in the ink pen are tested for their writability and flow by making at least 100 line traces of 3 cm each and measuring the resistance across the two ends. The resistance (R) is measured across the line trace using a two probe multimeter. The average resistance for the lines drawn is - 20-50 KW. The purpose of the above data is to show that line traces made by different users also have an average of 20-50 KOhm /cm. Resistance of the ink formulation was also calculated as a function of time. At least eight lines of 3 cm each were made using the resistive ink pen on a normal writing paper and resistance R value was measured using a multimeter over time. It is observed that the R value stabilized after 5 minutes although the functionality is obtained even after 2 minute (Figure 11). The average resistance for the examples shown above is ~ 20-50 KW/cm which is obtained after 5 mins (the drying time of the ink on paper) at room temperature without the aid of any external post-treatment. The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the invention, in addition to those described herein, will become apparent to those skilled in the art from the foregoing description and accompanying figures. Such modifications are intended to fall within the scope of the appended claims. The invention is, therefore, to be limited only by the terms of the appended claims along with the full scope of equivalents to which the claims are entitled.