GB2526591A

GB2526591A - Conductive carbon ink

Info

Publication number: GB2526591A
Application number: GB1409509.5A
Authority: GB
Inventors: Robert Murray-Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-05-29
Filing date: 2014-05-29
Publication date: 2015-12-02
Also published as: GB201409509D0

Abstract

An ink composition comprises at least one solvent, at least one binder and a conductive additive comprising at least one carbon material of a variety of geometry and size distributions, wherein the conductive material is present in an amount sufficient for the ink, once dry, to be electrically conductive. The ink may further comprise at least one polysaccharide. The solvent base may be water or a non-aqueous solvent. The conductive material preferably comprises a spherical carbon, a plate carbon and a rod carbon. The plate carbon may be graphite, carbon black, activated carbon powder, modified conductive carbon, powdered activated carbon or powdered charcoal. The plate carbon may be graphite nanoplates, graphene, graphene nanoribbons, graphyne or few layer graphene flakes. The rod carbon may be in the form of nanotubes, fibre, chopped fibre, milled fibre or nanohorns. Also disclosed is a biodegradable ink composition.

Description

Field Of Invention

My invention lies in improvements in the art of applying designs and text onto flexible surfaces. in particular, my invention is an improved conductive printing ink whose use creates no environmental problems, is non-toxic, flexible and more conductive than current carbon based formulations.

Background Of The Invention

Presently, most printing is done with inks made of a complex mixture of vinyl resin, plasticizer and one or more pigments derived from hazardous industrial processes that produce a large quantity of harmful chemicals and require volatile solvents to clean.

Flexible inks have different requirements to those inks applied to more rigid substrates, for example paper, board or cartons but are essentially of the same chemical family in terms of their derivatives. Plastisol inks being an example.

Conventional conductive inks, as currently used in the electronics industry for printing circuit boards or repairing circuit breaks, are constructed from copper, silver, conductive polymer, graphite or carbon and are applied using methods such as inkjet printing or by pen. They are designed for high conductivity and generally contain toxic metals and solvents, unsafe for application to the skin and dangerous if inhaled.

inks safe to apply to the skin exist as per US patent 2012/0020033 bLit sLiffer from drying, cracking and poor conductivity.

The present invention differs from these in that it applies a flexible non-toxic conductive ink that can be applied to the skin or any other flexible or rigid surface and has improved conductivity by an order of magnitude.

Moreover, most inks are not biodegradable and some of the components used in conventional printing are hazardous. Printing, in general, generates waste it which often contains hazardous materials, creating disposal, manufacturing and health and safety problems.

The printing industry, seeking ways to reduce printing costs and faced with governmental regulations aims at conserving energy and reducing environmental pollution and has been investigating alternative methods and materials to reduce or eliminate the foregoing problems.

in addition improvements in the methodology in conductive ink formulations are continually being sought and the current invention addresses those issues

Summary Of The Invention

This invention is a biodegradable printing ink that is free of hazardous materials and consists of carbon in a varity of geometries and sizes in order to improve conductivity. It consists essentially of water and naturally occurring colloidal polysaccharides to which are added hinders and one or more conductive materials drawn from tile carbon family that are selected based on their geometry and size distribution. These inks are biodegradable, ellvironmentally 11011-polluting in manufacture and disposal, safe to use, flexible and more conductive than currently available carbon based inks.

Detailed Description Of The Invention

The biodegradable and air-dryable inks of this invention comprise a base of one or more colloidal polysaccharides or other soluble gums, for example, bLit not limited to, gum Arabic, xanthan gum, sodium alginate, carboxy methyl cellulose, starch gum, etc, dissolved ill water to form a viscous colloidal solution. A disbursing agent which is a high saturated fatty oil that is resistant to oxidation is used and can he taken from, bitt not limited to, coconut oil, palm oil, soybean oil, etc, is preferably added to obtain rapid dissolution. Additiollal cross linkillg components can be added to give a degree of "fastness", for example, but not limited to, protein/urea, starch/urea, etc The base then, is a clear and colorless liquid, comprises water, colloidal additive, and dispersing oil, a polymer and a cross linking agent.

All organic products suffer from degradation over time and therefore require the addition of preservatives. A great deal of preservatives are readily available. Preservatives can be classified as one of two types. Class 1 preservatives refers to those preservatives which are naturally occurring, everyday substances. Class II preservatives refer to preservatives which are synthetically manufactured.

Preservatives maybe antimicrobial preservatives, which inhibit the growth of bacteria or fungi, including mold or they can be antioxidants such as oxygen absorbers, which inhibit the oxidation of product constituents. Common antimicrobial preservatives include sorbic acid and its salts, befizoic acid and its salts, calcium propionate, sodium ilitrite, sulfites (sulfur dioxide, sodium hisulfite, potassium hydrogen sulfite, etc.) and disodium EDIA.

Antioxidants include BHA, BHT, TBHQ and propyl gallate. Other preservatives include ethanol and methylchloroisothiazolinone The base of the present invention should be preserved using only types of preservatives from class 1, class 11 preservatives may also be used but class 1 being preferred.

Examples of class I type preservatives are, hut not limited to, rosemary extract, hops, salt, sLtgar, vinegar, alcohol, diatomaceous earth, oil of cloves, vitamin B, vitamin C and castor oil.

Latex is the stable dispersion (emulsion) of polymer microparticles in an aqueous medium. Latexes may he natural or synthetic. It can he made synthetically by polyrnerizing a monomer such as styrene that has been emulsified with surfactants.

Latex as found in nature is a milky fiLlid found in 10% of all flowering plants (angiosperms). It is a complex emulsion consisting of proteins, alkaloids, starches, sugars, oils, tannins, resins, and gums that coagulate on exposure to air. it is usually exuded after tissue injury. Tn most plants, latex is white, hut some have yellow, orange, or scarlet latex Within the spirit of this invention a naturally-occurring latex, is preferred hut not limited to it and other examples of naturally occurring hinders that could he used would he starch, dextrin, asphalts, manila copal, shellac, malic resins and esters, rosin and limed rosin. The preferred latex is added to the base as a binder. Preferably, the natural latex will occupy preferably about 5 to 95%, and more preferably about 5 to 50%, and more 1referahly, 10 to I 5% of the resulting mixture hy volume and dependant upon the specific application of the resulting end ink.

To this printing composition of hase and hinder is added one or more carbon hased conductive additives.

The conductive material must he capahle of forming a conductive layer when applied.

Examples of such materials include: metals, such as powdered or flake silver, gold or copper; or conductive non-metals, such as carbon. Of these, the various electrically conductive forms of carbon are preferred, for example graphite, carbon black, activated carbon powder, powdered activated carbon, carbon nanotuhes or powdered charcoal.

Because, unlike the metallic material, it is non-toxic, environmentally friendly and readily available, graphite powder or flakes are, in part, preferred.

in principle, it is understood that connectivity of the conducting elements is the main limiting factor to the performance of any conductive ink. This problem has previously been addressed by including as much of the conductive material as possible, in order to maximize connections and therefore the conductivity of a composition. However, the composition must also contain other components and the formation of a matrix to hold the components in place and adhered to the substrate inevitable acts as a limiting factor.

in previous art the material supplied to perform the conductive function has been supplied with tight control over particle size this results in a close packing structure that still leaves a great many voids within the formed conductive matrix once the ink has dried. It is therefore preferred to use a precursor conductive material that has a range of sizes and thereby ensuring the filling' of these voids.

in addition particle geometry plays a large part in the formation of the resultant film of dried ink. Given that most particles included in conductive formulations are roughly spherical then the formation of voids is inevitable. It is one embodiment of the invention that a variety of particle geometries be utilized as well as a variety of particle sizes.

Therefore not only are a range of roughly spherical particles are utilized but so are fibers and plates.

Examples of fibers that could he used are, hut not limited to, carbon nanotLihes, milled carbon fibers, chopped carbon fibers, carbon nanohorns, graphene ribbons, etc. Carbon fibers are made primarily by the graphitic carbonization of precursor materials these are predominantly synthetic fibers or petroleum pitch. The precursors of the fibers produce materials with variable conductivities which is dependant on the degree of graphentisation and therefore the more conductive fiber types are preferred. Carbon fibres are normally in the size range of 5-iD micrometers in diameter and are therefore suitable for most printing applications where smaller size ranges are reqLlired carbon nanotLihe, for example, can be used.

Plate like structures include, for example, hut not limited to, graphene, graphitic nanoplates, graphene ribbons, few layer graphene flakes, etc. Having perfect surface morphology or crumpled form is not a necessary prerequisite as the function of the plates is to interconnect the other particles within the composition.

Therefore the conductive additive to the ink is composed of conductive carbon particles in the form of spheres, plates and fibers of a variety of size, suitable to the application.

Carbon materials as supplied or synthesized may or may not have sufficient intermix or size in order to perform the required function sufficiently with in the ink composition. it therefore maybe necessary to preprocess the carbon materials prior to the addition of the conductive additive to the ink formulation. Preprocessing consists of thorough mixing and or further reduction of the component parts. This can be achieved by a variety of means for example but not limited to, dry milling, dry grinding, shear mixing, wet milling, wet grinding, etc. The preferred method is wet grinding in an arrangement whereby shear is the predominant force for example a Retsch KM I mortar grinder.

in addition the polymer component of the ink may he preprocessed by coating it with conductive materials or by using an inherently conductive polymer, for example, PEDOT:PSS.

The percentage by weight of the varioLls forms of carbon are preferably 50-90% graphite particles, 15-50% rods or fibres and 1-15% plates, more preferably 60-80% graphite particles, 20-40% rods or fibres and 1-10% plates and are preferably 60-70% graphite particles, 20-25% rods or fibres and 1-5% plates. The size distribution will he dependant on the particular application but should be arranged with that guidance that it be a variety of sizes.

The preprepared condLictive additive is added to the base to include at least 30% by weight of the conductive material, based on the wet weight of the composition. More preferably, the composition contains at least 35%, still more preferably from 35 to 70% by weight of the conductive composition. Most preferably, the composition contains from to 63%, especially from 50 to 63%, by weight of the conductive material.

Once prepared the base material and the conductive material are mixed together to ensure homogenization in, for example a blade type mixer. Once mixed the ink is then passed through a 3-roll mill preferably 5 times to ensure adequate dispersion.

In use, the ink formulation is applied by conventional printing procedures, spray application, brush application or inkjet printing.

From the above it can he readily seen that the separation of base and conductive additive as a formulation convention allows for the use of any additive within the base and equally any base for use with the conductive additive. It should therefore not be seen as beyond the scope of this ifivention should the base be changed for use with the conductive additive or vice versa.

Examples

Example 1

To 500mL of conductive additive add 70 ml of water and mix thoroughly, heat mixture to 1000 C., add to 240 ml of clear base, mix in 40 ml of natural latex, add 1 g of urea and mix at low speed until the urea is dissolved.

Example 2

To 500 mL of conductive additive, add 240 ml of clear base, mix in 25 ml of natural latex, add Sg of casein and 1 g of urea, mix at slow speed until urea is dissolved.

Example 3

To 500mL of conductive additive, add to 240 ml of clear base, mix in 55 ml of natural latex, add 2 g of urea and mix at low speed until urea is dissolved.

The clear base comprises 98.5% water, 1% sodium alginate, and 0.5% palm oil by weight.

The conductive additive comprises % by weight of 60% graphite powder at 5 micrometers, 25% milled carbon fiber at ISO micrometers and 5% graphene at 45 micrometers. The resulting mix was wet ground for 16 hours in 500mL of water.

While this invention has been shown and described with respect to a detailed embodiment thereof, it will he understood by those skilled in the art that changes in form and detail thereof may be made without departing from the scope of the claims of the invention.

Claims

Claims 1 claim: 1. A biodegradable ink composition comprising: at least one biodegradeable solvent base, at least one biodegradable binder, and a conductive additive comprising of at least one carbon material of a variety of geometry and size distributions wherein the conductive material is present in sufficient amount that the ink, once dry, is electrically conductive.
2. A ink composition comprising: at least one solvent, at least one binder, and a conductive additive comprising of at least one carbon material of a variety of geometry and size distributions wherein the conductive material is present in sufficient amount that the ink, once dry, is electrically conductive.
3. A biodegradable ink of claim I, wherein the composition comprises: a base of water and at least one polysaccharide, a biodegradable binder, and a conductive additive, the ink by volume containing from 10 to 90% base, from 5 to 40% binder, and from 0.2 to 90% conductive additive.
4. A ink of claim 2, wherein the composition comprises: a base of water and at least one polysaccharide, at least one binder, and a conductive additive, the ink by volume containing from i 0 to 90% base, from 5 to 40% hinder, and from 0.2 to 90% conductive additive.
5. A ink of claim 2, wherein the composition comprises: a base of at least one non aqueous solvent, a binder and a conductive additive, the ink by volume containing from to 90% base, from 5 to 40% binder, and from 0.2 to 90% conductive additive.
6. The ink according to claim I, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon in a range of sizes ranging from 4 nanometers to 150 micrometers.
7. The ink according to claim 2, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon in a range of sizes ranging from 4 nanometers to 150 micrometers.
8. The ink according to claim 3, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon in a range of sizes ranging from 4 nanometers to i 50 micrometers.
9. The ink according to claim 4, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon in a range of sizes ranging from 4 nanometers to 150 micrometers.
10-The ink according to claim 5, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon in a range of sizes ranging from 4 nanometers to 150 micrometers.
11. The ink according to claim 1, wherein the polysaccharide is gum arabic, guar gum, xanthan gum, hypromellose, agar, an alginate, carageenan, methylcellulose, hydroxymethyl cellulose, pectin, acacia, or gum tragacanth -
12. The ink according to claim 1, wherein the biodegradable binder is natural latex, Poly Vinyl Acetate, Poly Vinyl Alcohol, Poly Lactic Acid, cellulose, chitosan, glycolide polymers, caprolactone polymers, hydroxybutyric acids, polyanhydrides, polyphosphozanes or polyphosphoesters.
13. The ink according to claim 1, wherein the spherical carbon is in the form of graphite, carbon black, activated carbon powder, modified conductive carbons, powdered activated carbon, or powdered charcoal.
14. The ink according to claim 1, wherein the plate carbon is in the form of graphite nanoplates, graphene, graphene nanoribbons, graphyne, or few layer graphene flakes.IS. The ink according to claim 1, wherein the rod carbon is in the form of carbon nanotubes, carbon fibre, chopped carbon fibre, milled carbon fibre, or carbon nanohorns.16. The ink according to claim 1, wherein the spherical, rod or plate carbon is in the size range of 4 nanometers to 150 micrometers.17. The ink according to claim 1, wherein the ink comprises at least 30% by weight of the conductive material, based on the wet weight of the ink.18. The ink according to claim 1, wherein the ink contains at least 35% by weight of the conductive material.19. The ink according to claim 1, wherein the ink contains from 45 to 63% by weight of the conductive material.20. The conductive additive according to claim 1, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the spherical carbon can range within the composition from 5 to 90% of the weight of the conductive additive. a21. The conductive additive according to claim I, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the rod carbon can range in the composition from 5 to 90% of the weight of the conductive additive.22. The conductive additive according to claim 1, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the plate carbon can range in the composition from 01 to 90% of the weight of the conductive additive.23. The ink according to claim 2, wherein the polysaccharide is gum arabic, guar gum, xanthan gum, h ypromellose, agar, an alginate, carageenan, meth ylcell ulose, hydroxymethyl cellulose, pectin, acacia, or gum tragacanth.24. The ink according to claim 2, wherein the biodegradable binder is natural latex, Poly Vinyl Acetate, Poly Vinyl Alcohol, Poly Lactic Acid, cellulose, chitosan, glycolide polymers, caprolactone polymers, hydroxybutyric acids, polyanhydrides, 1olypl1osphozanes or pol yphosphoesters - 25. The ink according to claim 2, wherein the spherical carbon is in the form of graphite, carbon black, activated carbon powder, modified conductive carbons, powdered activated carbon, or powdered charcoal.26. The ink according to claim 2, wherein the plate carbon is in the form of graphite nanoplates, graphene, graphene nanoribbons, graphyne, or few layer graphene flakes.27. The ink according to claim 2, wherein the rod carbon is in the form of carbon nanotubes, carbon fibre, chopped carbon fibre, milled carbon fibre, or carbon nanohorns.28. The ink according to claim 2, wherein the spherical, rod or plate carbon is in the size range of 4 nanometers to 250 micrometers.29. The ink according to claim 2, wherein the ink comprises at least 30% by weight of the conductive material, based on the wet weight of the ink.30. The ink according to claim 2, wherein the ink contains at least 35% by weight of the conductive material.3i. The ink according to claim 2, wherein the ink contains from 45 to 63% by weight of the conductive material.32. The conductive additive according to claim 2, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the spherical carbon can range within the composition from 5 to 90% of the weight of the conductive additive.33. The conductive additive according to claim 2, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the rod carbon can range in the composition from 5 to 90% of the weight of the conductive additive.34. The conductive additive according to claim 2, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the plate carbon can range in the composition from 01 to 90% of the weight of the conductive additive.35. The ink according to claim 3, wherein the polysaccharide is gum arabic, guar gum, xanthan gum, hypromellose, agar, an alginate, carageenan, methylcellulose, hydroxymethyl cellulose, pectin, acacia, or gum tragacanth.36. The ink according to claim 3, wherein the biodegradable hinder is natural latex, Poly Vinyl Acetate, Poly Vinyl Alcohol, Poly Lactic Acid, cellulose, chitosan, glycolide polymers, caprolactone polymers, hydroxybutyric acids, polyanhydrides, 1olypl1osphozanes or pol yphosphoesters - 37. The ink according to claim 3, wherein the spherical carbon is in the form of graphite, carbon black, activated carbon powder, modified conductive carbons, powdered activated carbon, or powdered charcoal.38. The ink according to claim 3, wherein the plate carbon is in the form of graphite nanoplates, graphene, graphene nanoribbons, graphyne, or few layer graphene flakes.39. The ink according to claim 3, wherein the rod carbon is in the form of carbon nanotubes, carbon fibre, chopped carbon fibre, milled carbon fibre, or carbon nanohorns.40. The ink according to claim 3, wherein the spherical, rod or plate carbon is in the size range of 4 nanometers to 350 micrometers.4i -The ink according to claim 3, wherein the ink comprises at least 30% by weight of the conductive material, based on the wet weight of the ink.42. The ink according to claim 3, wherein the ink contains at least 35% by weight of the conductive material.43. The ink according to claim 3, wherein the ink contains from 45 to 63% by weight of the conductive material.44. The conductive additive according to claim 3, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the spherical carbon can range within the composition from 5 to 90% of the weight of the conductive additive.45. The conductive additive according to claim 3, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the rod carbon can range in the composition from 5 to 90% of the weight of the conductive additive.46. The conductive additive according to claim 3, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the plate carbon can range in the composition from 0.3 to 90% of the weight of the conductive additive.47. The ink according to claim 4, wherein the polysaccharide is gum arabic, guar gum, xanthan gum, h ypromellose, agar, an alginate, carageenan, meth ylcell ulose, hydroxymethyl cellulose, pectin, acacia, or gum tragacanth.48. The ink according to claim 4, wherein the biodegradable binder is natural latex, Poly Vinyl Acetate, Poly Vinyl Alcohol, Poly Lactic Acid, cellulose, chitosan, glycolide polymers, caprolactone polymers, hydroxybutyric acids, polyanhydrides, 1olypl1osphozanes or pol yphosphoesters - 49. The ink according to claim 4, wherein the spherical carbon is in the form of graphite, carbon black, activated carbon powder, modified conductive carbons, powdered activated carbon, or powdered charcoal.50. The ink according to claim 4, wherein the plate carbon is in the form of graphite nanoplates, graphene, graphene nanoribbons, graphyne, or few layer graphene flakes.51. The ink according to claim 4, wherein the rod carbon is in the form of carbon nanotubes, carbon fibre, chopped carbon fibre, milled carbon fibre, or carbon nanohorns.52. The ink according to claim 4, wherein the spherical, rod or plate carbon is in the size range of 4 nanometers to 450 micrometers.53. The ink according to claim 4, wherein the ink comprises at least 30% by weight of the conductive material, based on the wet weight of the ink.54. The ink according to claim 4, wherein the ink contains at least 35% by weight of the conductive material.55. The ink according to claim 4, wherein the ink contains from 45 to 63% by weight of the conductive material.56. The conductive additive according to claim 4, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the spherical carbon can range within the composition from 5 to 90% of the weight of the conductive additive.57. The conductive additive according to claim 4, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the rod carbon can range in the composition from S to 90% of the weight of the conductive additive.58. The conductive additive according to claim 4, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the plate carbon can range in the composition from 0.4 to 90% of the weight of the conductive additive.59. The ink according to claim 5, wherein the polysaccharide is gum arabic, guar gum, xanthan gum, hypromellose, agar, an alginate, carageenan, methylcellulose, hydroxymethyl cellulose, pectin, acacia, or gum tragacanth.60-The ink according to claim 5, wherein the biodegradable binder is natural latex, Poly Vinyl Acetate, Poly Vinyl Alcohol, Poly Lactic Acid, cellulose, chitosan, glycolide polymers, caprolactone polymers, hydroxybutyric acids, polyanhydrides, polypliosphozanes or pol yphosphoesters - 61. The ink according to claim 5, wherein the spherical carbon is in the form of graphite, carbon black, activated carbon powder, modified conductive carbons, powdered activated carbon, or powdered charcoal.62. The ink according to claim 5, wherein the plate carbon is in the form of graphite nanoplates, graphene, graphene nanoribbons, graphyne, or few layer graphene flakes.63. The ink according to claim 5, wherein the rod carbon is in the form of carbon nanotubes, carbon fibre, chopped carbon fibre, milled carbon fibre, or carbon nanohorns.64. The ink according to claim 5, wherein the spherical, rod or plate carbon is in the size range of 4 nanometers to 550 micrometers.65. The ink according to claim 5, wherein the ink comprises at least 30% by weight of the conductive material, based on the wet weight of the ink.66. The ink according to claim 5, wherein the ink contains at least 35% by weight of the conductive material.67. The ink according to claim 5, wherein the ink contains from 45 to 63% by weight of the conductive material.68. The conductive additive according to claim 5, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the spherical carbon can range within the composition from 5 to 90% of the weight of the conductive additive.69. The conductive additive according to claim 5, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the rod carbon can range in the composition from 5 to 90% of the weight of the conductive additive.70. The conductive additive according to claim 5, wherein the conductive material is a conductive additive comprising: a spherical carbon, a plate carbon and a rod carbon such that the plate carbon can range in the composition from 05 to 90% of the weight of the conductive additive.