Printable flexible overcoat ink composition

Abstract

To provide a digitally printable flexible overcoat ink composition.SOLUTION: The printable flexible overcoat ink composition includes a mixture of a thermoplastic polyurethane (TPU) and a solvent. The mixture has a viscosity of 1 centipoise to 2000 centipoise to allow the mixture to be digitally printed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates generally to ink compositions, and more particularly to printable flexible overcoat ink compositions for printed electronics. [Background technology]

[0002] Printed electronics is an emerging industry that aims to add functionality to even inanimate objects by printing low-cost electronic components. For example, printed electronics can be used to add functionality to clothing, sports equipment, storage containers, etc.

[0003] Unlike traditional electronics, printed electronics are not limited to rigid substrates. Currently available digitally printable conductive inks are generally not flexible, often suffer from low scratch resistance, and may exhibit poor adhesion to the substrate. These factors limit the application of these digitally printable conductive inks to a few areas that require highly robust circuitry.

[0004] For example, conductive circuits for smart packaging must withstand long-distance transportation and rough handling. Although significant efforts have been made to develop flexible conductive inks, few digitally printable products have appeared on the market. Of those that do exist, they lack the high conductivity required for many of these emerging applications. Summary of the Invention

[0005] According to aspects set forth herein, a printable flexible overcoat ink composition and a method for making the same are provided. One disclosed feature of an embodiment is a printable flexible overcoat ink composition comprising a mixture of thermoplastic polyurethane (TPU) and a solvent, the mixture having a viscosity of 1 centipoise to 2000 centipoise to enable the mixture to be digitally printed.

[0006] Another disclosed feature of an embodiment is a printable flexible overcoat ink composition comprising a mixture of thermoplastic polyurethane (TPU) and a solvent, wherein the ratio of TPU to solvent comprises approximately 1:4 to 2:1, and the total solids content of the TPU in the mixture comprises approximately 2 percent to 80 percent.

[0007] Another disclosed feature of an embodiment is a method of making a printable flexible overcoat ink composition, the method including: providing a thermoplastic polyurethane (TPU) dispersion having an average particle size of approximately 10 nanometers to 200 nanometers; providing a solvent in a container, the solvent including at least one of water, ethylene glycol, diethylene glycol, sulfolane, propylene glycol methyl ether acetate, propylene glycol monomethyl ether acetate, di(propylene glycol) methyl ether acetate, (propylene glycol) methyl ether, di(propylene glycol) methyl ether, methyl isobutyl ketone, diisobutyl ketone, butyl acetate, methoxypropyl acetate, or propoxylated neopentyl glycol diacrylate; mixing the TPU dispersion and the solvent in the container to form a mixture of the TPU dispersion and the solvent to a viscosity of 1 centipoise to 2000 centipoise; and allowing the mixture to settle for approximately 30 minutes. [Brief explanation of the drawings]

[0008] The teachings of the present disclosure can be readily understood by considering the following detailed description in conjunction with the accompanying drawings.

[0009] [Figure 1] 1 shows a flow chart of an exemplary method for making a printable flexible overcoat ink of the present disclosure.

[0010] To facilitate understanding, wherever possible, the same reference numbers have been used to designate identical elements that are common to the figures. DETAILED DESCRIPTION OF THE INVENTION

[0011] This disclosure relates to printable flexible overcoat ink compositions and methods for making the same. As mentioned above, printed electronics is an emerging industry aiming to print low-cost electronic components. However, currently available digitally printable conductive inks have drawbacks such as inflexibility, low scratch resistance, and poor adhesion.

[0012] The present disclosure provides solutions to problems associated with digitally printable conductive inks. The present disclosure provides a printable flexible overcoat layer over the delicate conductive traces of printed electronics. In addition to flexibility and digital printability, the printable flexible overcoat ink of the present disclosure provides conformability and strong adhesion to the conductive traces of printed electronics. The printable flexible overcoat ink composition also provides strong scratch resistance.

[0013] In one embodiment, the printable overcoat ink composition may include a mixture of a thermoplastic polyurethane (TPU) latex dispersion and at least one additional solvent. The mixture of TPU and solvent(s) may be an emulsion that is mixed to have a viscosity that allows for digital printing of the printable overcoat ink composition via an inkjet printhead or an aerosol jet printhead. In one embodiment, the viscosity may be between approximately 1 centipoise and 2000 centipoise.

[0014] TPU may be a type of polyurethane plastic that has properties of elasticity, transparency, and abrasion or scratch resistance. TPU may also be an elastomer composed of a linear segmented block copolymer consisting of hard and soft segments. TPU in its raw form cannot be digitally printed. However, embodiments of the present disclosure allow the TPU to be formulated with a solvent to a desired viscosity, allowing the TPU to be digitally printed (e.g., onto conductive traces on a printed circuit board).

[0015] In one embodiment, the blend may be formed with a TPU having an average diameter of approximately 1 nanometer (nm) to 1000 nm. In one embodiment, the TPU may have an average diameter of approximately 5 nm to 500 nm. In one embodiment, the TPU may have an average diameter of approximately 10 nm to 200 nm.

[0016] In one embodiment, the TPU may be dispersed as a latex dispersion. In other words, the TPU dispersion may comprise a stable dispersion of TPU particles in water. Notably, the TPU does not dissolve in water, but remains in a solid form uniformly dispersed in the solution (e.g., a colloidal dispersion). TPU latex dispersions can be purchased from various vendors, such as Alberdingk Boley Inc. and Covestro, under trade names such as Alberdingk U410, Alberdingk U615, Alberdingk U2101, Bayhydrol U2757, Bayhydrol U2559, and Bayhydrol 2606.

[0017] In one embodiment, the solvent may be a high-boiling-point solvent. The high boiling point of the solvent may allow the mixture of TPU and solvent to remain stable when stored in a cartridge for printing at room temperature. In other words, the high-boiling-point solvent may enable stable printing of the ink in both inkjet printing and aerosol jet printing, ensuring that the mixture does not dry out or evaporate inside the reservoir (e.g., print head). The solvent may be selected from a group of solvents that are compatible with the TPU dispersion (e.g., the solvent does not destroy the TPU dispersion). Examples of solvents that can be used include water, ethylene glycol, diethylene glycol, sulfolane, or any combination thereof.

[0018] In one embodiment, the amount of TPU and solvent in dispersed form in the mixture may have a TPU to solvent ratio of approximately 1:1 to 1:20 for inkjet printers and approximately 10:1 to 1:20 for aerosol jet printers.

[0019] In one embodiment, the amount of TPU to solvent may range from approximately 1:4 to 2:1. In one embodiment, the amount of solid TPU to solvent may have a ratio of approximately 1:8 for inkjet printers and approximately 1:4 for aerosol jet printers. Therefore, the ratio may vary based on whether dispersed or solid TPU is being measured. In one embodiment, the total solids content of the TPU in the mixture may be approximately 1 percent to 60 percent. In one embodiment, the solids content may be approximately 10 percent to 25 percent. In one embodiment, the solids content may be approximately 5 percent to 15 percent.

[0020] In one embodiment, a printable flexible overcoat ink composition can be formulated for an inkjet printhead. For example, the printable flexible overcoat ink composition can be formulated with a 1:2 ratio (e.g., by weight) of TPU dispersion to solvent. The printable flexible overcoat ink composition can have a total solid TPU content of approximately 13 percent by weight. The mixture can be mixed to have a viscosity of approximately 1 centipoise to 40 centipoise.

[0021] The printable flexible overcoat ink composition can be formulated so that the composition can be digitally printed without clogging the printhead and / or evaporating rapidly from the printhead reservoir. The composition can also remain flexible after printing and curing to protect the conductive traces. Inkjet printer example

[0022] In one embodiment, a mixture of 1.0 grams of Alberdingk U615 and 2.0 grams of ethylene glycol was placed in a glass vial. The mixture was vortexed to thoroughly mix the Alberdingk U615 and ethylene glycol. The mixture was allowed to settle for approximately 30 hours. The mixture had a viscosity of approximately 5 centipoise to 14 centipoise. The mixture was produced to have a total solid TPU content of approximately 13 percent.

[0023] In a second embodiment, a mixture of 1.0 gram of Alberdingk U615 and 1.0 gram of ethylene glycol was placed in a glass vial. The mixture was vortexed to thoroughly mix the Alberdingk U615 and ethylene glycol. The mixture was allowed to settle for approximately 30 hours. The mixture was produced to have a total solid TPU content of approximately 20 percent.

[0024] In a third embodiment, a mixture of 1.0 gram of Alberdingk U2101 and 2.0 grams of ethylene glycol was placed in a glass vial. The mixture was vortexed to thoroughly mix the Alberdingk U2101 and ethylene glycol. The mixture was allowed to settle for approximately 30 hours. The mixture was produced to have a total solid TPU content of approximately 13 percent.

[0025] The mixture was inkjet printed using a Dimatix 2300 printer. The mixture was printed onto the conductive traces on the substrate at a temperature of approximately 25.2 degrees Celsius (°C), a drop mass of 5.6 nanograms (ng), and a speed of 7 meters per second (m / s). The printed overcoat ink was baked in an oven at 120°C for 10 minutes.

[0026] The printed overcoat ink produced a uniform film of material. The printed overcoat ink was found to have high adhesion. The strength of the printed overcoat ink was demonstrated via a folding test and survival of 10+ folding cycles, where one cycle is defined as a 180-degree inward fold and a 360-degree outward fold. The printed overcoat ink was also shown to maintain its integrity after being scratched with the tip of a sharp pair of tweezers. The conductive traces were found to be conductive after the folding test when protected by the printed overcoat ink.

[0027] The mixture was found to still be printable after several hours of use, and no clogging of the inkjet printhead was observed after 3 hours of use. Example of an aerosol jet printer

[0028] In a first embodiment, a mixture of 15.0 grams of Alberdingk U615 and 10.0 grams of diethylene glycol was placed in a glass vial. The mixture was vortexed to thoroughly mix the Alberdingk U615 and diethylene glycol. The mixture was allowed to settle for approximately 30 hours. The mixture had a viscosity of approximately 76.51 centipoise. The mixture was produced to have a total TPU content of approximately 24 percent after a 3:2 dilution.

[0029] In a second embodiment, a mixture of 15.0 grams of Alberdingk U410 and 10.0 grams of diethylene glycol was placed in a glass vial. The mixture was vortexed to thoroughly mix the Alberdingk U410 and diethylene glycol. The mixture was allowed to settle for approximately 30 hours. The mixture was produced to have a total TPU content of approximately 24 percent.

[0030] In a third embodiment, a mixture of 15.0 grams of Alberdingk U615 and 15.0 grams of ethylene glycol was placed in a glass vial. The mixture was vortexed to thoroughly mix the Alberdingk U615 and diethylene glycol. The mixture was allowed to settle for approximately 30 hours. The mixture was produced to have a total TPU content of approximately 20 percent.

[0031] The mixture of the first embodiment in the example aerosol jet printer was printed using an aerosol jet printer with deionized water in the bubbler to prevent the ink from concentrating and thus preventing a film-forming process in the printing system. The mixture printed well in the aerosol jet printer for several hours without clogging. The printing conditions for the aerosol jet printer are provided in Table 1 below. [Table 1] Table 1: Aerosol jet printing conditions

[0032] The printed overcoat ink was printed on several different substrates, including Clearwater carton board, polycarbonate, and polyethylene naphthalate (PEN). The printed overcoat ink was baked in an oven at 120° C. for 10 minutes.

[0033] The printed overcoat ink produced a uniform film of material. The printed overcoat ink was found to have high adhesion. The strength of the printed overcoat ink was demonstrated via a folding test and survival of 10+ folding cycles, where one cycle is defined as a 180-degree inward fold and a 360-degree outward fold. The printed overcoat ink was also shown to maintain its integrity after being scratched with the tip of a sharp pair of tweezers. The conductive traces were found to be conductive after the folding test when protected by the printed overcoat ink.

[0034] It should be noted that the printable flexible overcoat ink composition formulations are provided as examples for inkjet printing and aerosol jet printing. However, the formulation and printable flexible overcoat ink composition can be tailored for any desired digital printing application. For example, the size of the TPU particles, the type of solvent, and the amount of solvent mixed with the TPU can be adjusted to adjust the viscosity for a specific printing application.

[0035] 1 shows a flowchart of an exemplary method 100 for making a printable flexible overcoat ink of the present disclosure. Method 100 can be performed by various devices under the control of a processor, or can be performed manually by a technician using various types of equipment.

[0036] At block 102, the method 100 begins. At block 104, the method 100 provides a thermoplastic polyurethane (TPU) dispersion having an average particle size of approximately 10 nanometers to 200 nanometers in a container. TPU can be purchased from TPU manufacturing vendors under a variety of different trade names. TPU can be a polyurethane plastic having properties of elasticity, transparency, and abrasion or scratch resistance.

[0037] At block 106, the method 100 provides a solvent in a container, the solvent comprising at least one of water, ethylene glycol, diethylene glycol, sulfolane, propylene glycol methyl ether acetate, propylene glycol monomethyl ether acetate, di(propylene glycol) methyl ether acetate, (propylene glycol) methyl ether, di(propylene glycol) methyl ether, methyl isobutyl ketone, diisobutyl ketone, butyl acetate, methoxypropyl acetate, or propoxylated neopentyl glycol diacrylate. The solvent may be a high boiling point solvent so that the mixture of the TPU and solvent can remain stable in the reservoir (e.g., can be stored without rapidly evaporating).

[0038] In one embodiment, the amount of TPU and solvent can vary depending on the type of printing application used to digitally print the printable flexible overcoat ink. For example, for an inkjet printer, the TPU and solvent can be provided in a TPU to solvent ratio of about 1:8. For example, the solvent can be ethylene glycol, and 2 grams of ethylene glycol can be mixed with 1 gram of TPU dispersion.

[0039] In one embodiment, for an aerosol jet printer, the TPU and solvent may be provided in a weight ratio of TPU to solvent of approximately 3: 2. For example, the solvent may be diethylene glycol, and 10 grams of diethylene glycol may be mixed with 15 grams of TPU.

[0040] At block 108, the method 100 mixes the TPU dispersion and the solvent in a container to form a TPU dispersion and solvent mixture having a viscosity of between 1 centipoise and 2000 centipoise. For example, for an inkjet printer, the mixture can be mixed to a viscosity of between approximately 1 centipoise and 40 centipoise. For an aerosol jet printer, the mixture can be mixed to a viscosity of between approximately 1 centipoise and 2000 centipoise.

[0041] In block 110, the method 100 allows the mixture to settle. For example, the mixture may be allowed to settle for approximately 30 minutes. The mixture may then be transferred to a print head and dispensed by a desired printing method. The mixture may be digitally printed onto conductive traces formed on a substrate. For example, a digital printer may have a processor containing instructions related to where the conductive traces are to be placed on the substrate. The processor may control the movement of the print head to dispense the mixture at known locations on the conductive traces. In one embodiment, after the mixture is printed onto the conductive traces, the printed flexible overcoat ink may be cured and dried. However, after curing, the printed flexible overcoat ink may remain flexible and provide protection for the conductive traces.

[0042] It should be noted that the printed flexible overcoat ink is not applied globally across the entire surface of the printed circuit. Rather, the printed flexible overcoat ink of the present disclosure is formulated to be selectively dispensed or printed in specific locations on the printed circuit. Thus, less material is used to reduce costs. Additionally, digitally printing the printed flexible overcoat ink can prevent dispensing the printed flexible overcoat ink in undesired locations on the printed circuit. At block 112, the method 100 ends.

[0043] It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unprecedented alternatives, modifications, variations, or improvements may be made by those skilled in the art, which are intended to be encompassed by the following claims. Another aspect of the present invention may be as follows. [1] A printable flexible overcoat ink composition, comprising: A composition comprising a mixture of thermoplastic polyurethane (TPU) and a solvent, the mixture having a viscosity of 1 centipoise to 2000 centipoise to enable the mixture to be digitally printed. [2] The printable flexible overcoat ink composition according to [1], wherein the viscosity of the mixture is approximately 1 centipoise to 40 centipoise so that it can be dispensed through an inkjet printhead. [3] The printable flexible overcoat ink composition according to [2], wherein the total solids content of the TPU in the mixture is approximately 1 percent to 60 percent. [4] The printable flexible overcoat ink composition according to [1], wherein the viscosity of the mixture is approximately 1 centipoise to 2000 centipoise so that it can be dispensed through an aerosol jet print head. [5] The printable flexible overcoat ink composition according to [4], wherein the total solids content of the TPU in the mixture is approximately 1 percent to 80 percent. [6] The printable flexible overcoat ink composition according to [1], wherein the TPU comprises a TPU dispersion. [7] The printable flexible overcoat ink composition according to [6], wherein the ratio of the TPU dispersion to the solvent is approximately 1:1 to 1:20 for an inkjet printhead. [8] The printable flexible overcoat ink composition according to [6], wherein the ratio of the TPU dispersion to the solvent is approximately 10:1 to 1:20 for an aerosol jet printing head. [9] The printable flexible overcoat ink composition according to [1], wherein the solvent comprises a high-boiling point solvent.

[10] The printable flexible overcoat ink composition according to [9], wherein the high-boiling point solvent comprises at least one of water, ethylene glycol, diethylene glycol, sulfolane, propylene glycol methyl ether acetate, propylene glycol monomethyl ether acetate, di(propylene glycol) methyl ether acetate, (propylene glycol) methyl ether, di(propylene glycol) methyl ether, methyl isobutyl ketone, diisobutyl ketone, butyl acetate, methoxypropyl acetate, or propoxylated neopentyl glycol diacrylate.

[11] A printable flexible overcoat ink composition, comprising: 1. A composition comprising a mixture of thermoplastic polyurethane (TPU) and a solvent, wherein the ratio of the TPU to the solvent is between approximately 1:4 and 2:1, and wherein the total solids content of the TPU in the mixture is between approximately 1 percent and 80 percent.

[12] The printable flexible overcoat ink composition according to

[11] , wherein the mixture has a viscosity of approximately 1 centipoise to 40 centipoise so that it can be dispensed through an inkjet printhead.

[13] The printable flexible overcoat ink composition according to

[12] , wherein the total solids content of the TPU in the mixture is approximately 1 percent to 60 percent.

[14] The printable flexible overcoat ink composition according to

[11] , wherein the mixture has a viscosity of approximately 1 centipoise to 2000 centipoise so that it can be dispensed through an aerosol jet print head.

[15] The printable flexible overcoat ink composition according to

[14] , wherein the total solids content of the TPU in the mixture is approximately 1 percent to 80 percent.

[16] The printable flexible overcoat ink composition according to

[11] , wherein the TPU comprises a TPU dispersion.

[17] The printable flexible overcoat ink composition according to

[16] , wherein the ratio of the TPU dispersion to the solvent is approximately 1:1 to 1:20 for an inkjet printhead.

[18] The printable flexible overcoat ink composition according to

[16] , wherein the ratio of the TPU dispersion to the solvent is approximately 10:1 to 1:20 for an aerosol jet printing head.

[19] The printable flexible overcoat ink composition according to

[11] , wherein the solvent comprises at least one of water, ethylene glycol, diethylene glycol, sulfolane, propylene glycol methyl ether acetate, propylene glycol monomethyl ether acetate, di(propylene glycol) methyl ether acetate, (propylene glycol) methyl ether, di(propylene glycol) methyl ether, methyl isobutyl ketone, diisobutyl ketone, butyl acetate, methoxypropyl acetate, or propoxylated neopentyl glycol diacrylate.

[20] A method for producing a printable flexible overcoat ink composition, comprising: providing a thermoplastic polyurethane (TPU) dispersion having an average particle size of approximately 10 nanometers to 200 nanometers; providing a solvent in the container, the solvent comprising at least one of water, ethylene glycol, diethylene glycol, sulfolane, propylene glycol methyl ether acetate, propylene glycol monomethyl ether acetate, di(propylene glycol) methyl ether acetate, (propylene glycol) methyl ether, di(propylene glycol) methyl ether, methyl isobutyl ketone, diisobutyl ketone, butyl acetate, methoxypropyl acetate, or propoxylated neopentyl glycol diacrylate; mixing the TPU dispersion and the solvent in the container to form a mixture of the TPU dispersion and the solvent with a viscosity of 1 centipoise to 2000 centipoise; and precipitating the mixture.

Claims

1. 1. A printable flexible overcoat ink composition comprising:

1. A composition comprising a mixture of thermoplastic polyurethane (TPU) and a solvent, the mixture having a viscosity of 1 centipoise to 2000 centipoise to enable digital printing of the mixture, the weight ratio of the TPU to the solvent being approximately 1:1 to 1:20 for inkjet printheads and approximately 10:1 to 1:20 for aerosol jet printheads, the solvent being a high-boiling solvent selected from at least one of ethylene glycol, diethylene glycol, sulfolane, propylene glycol methyl ether acetate, propylene glycol monomethyl ether acetate, di(propylene glycol) methyl ether acetate, (propylene glycol) methyl ether, di(propylene glycol) methyl ether, methyl isobutyl ketone, diisobutyl ketone, butyl acetate, methoxypropyl acetate, and propoxylated neopentyl glycol diacrylate, and the composition is free of water.

2. 10. The printable flexible overcoat ink composition of claim 1, wherein the viscosity of the mixture to be dispensed through the inkjet printhead is between approximately 1 centipoise and 40 centipoise.

3. The printable flexible overcoat ink composition of claim 2, wherein the total solids content of the TPU in the mixture is approximately 1 percent to 60 percent.

4. The printable flexible overcoat ink composition of claim 1 , wherein the total solids content of the TPU in the mixture is approximately 1 percent to 80 percent.

5. 1. A printable flexible overcoat ink composition comprising:

1. A composition comprising a mixture of thermoplastic polyurethane (TPU) and a solvent, wherein the weight ratio of the TPU to the solvent is approximately 1:4 to 2:1, the total solids content of the TPU in the mixture is approximately 1 percent to 80 percent, and the solvent is a high-boiling solvent selected from at least one of ethylene glycol, diethylene glycol, sulfolane, propylene glycol methyl ether acetate, propylene glycol monomethyl ether acetate, di(propylene glycol) methyl ether acetate, (propylene glycol) methyl ether, di(propylene glycol) methyl ether, methyl isobutyl ketone, diisobutyl ketone, butyl acetate, methoxypropyl acetate, and propoxylated neopentyl glycol diacrylate, and wherein the composition is water-free.

6. 6. The printable flexible overcoat ink composition of claim 5, wherein the mixture has a viscosity of approximately 1 centipoise to 2000 centipoise for dispensing through an aerosol jet printhead.

7. 6. The printable flexible overcoat ink composition of claim 5, wherein the mixture has a viscosity of approximately 1 to 40 centipoise for dispensing through an inkjet printhead.

8. The printable flexible overcoat ink composition of claim 7, wherein the total solids content of the TPU in the mixture is approximately 1 percent to 60 percent.

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