阅读说明：本技术 制造导电图案的方法 (Method of manufacturing conductive pattern ) 是由 B·穆伊斯 P·维莱尔特 K·范登博舍 F·科尔迪斯萨拉扎尔 于 2020-04-23 设计创作，主要内容包括：一种在基材上制备导电银图案的方法,所述方法包括以下步骤：—在所述基材上施加银油墨,以形成银图案,以及—在至少50℃的温度和至少50%的相对湿度(RH)下,在一个步骤中烧结所施加的银图案。(A method of preparing a conductive silver pattern on a substrate, the method comprising the steps of: -applying a silver ink on said substrate to form a silver pattern, and-sintering the applied silver pattern in one step at a temperature of at least 50 ℃ and a Relative Humidity (RH) of at least 50%.)

1. A method of preparing a conductive silver pattern on a substrate, the method comprising the steps of:

-applying a silver ink on said substrate to form a silver pattern, and

-sintering the applied silver pattern in one step at a temperature of at least 50 ℃ and a Relative Humidity (RH) of at least 50%.

2. The method of claim 1, wherein the temperature is at least 70 ℃.

3. The method of claim 1 or 2, wherein the relative humidity is at least 80%.

4. The method of any one of the preceding claims, wherein sintering is performed for an amount of time from 1 minute to 200 hours.

5. The method of claim 4, wherein the amount of time is between 30 minutes and 50 hours.

6. The method according to any one of the preceding claims, wherein the silver ink comprises a Dispersion Stabilizing Compound (DSC) having a chemical structure according to formulae I to IV,

wherein

Q represents the necessary atoms to form a substituted or unsubstituted five or six membered heteroaromatic ring;

m is selected from the group consisting of hydrogen, monovalent cationic groups, and acyl groups;

r1 and R2 are independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkaryl, substituted or unsubstituted aralkyl, substituted or unsubstituted aryl or heteroaryl, hydroxyl, thioether, ether, ester, amide, amine, halogen, ketone, and aldehyde;

r1 and R2 may represent the necessary atoms to form a five to seven membered ring;

r3 to R5 are independently selected from: hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkaryl, substituted or unsubstituted aralkyl, substituted or unsubstituted aryl or heteroaryl, hydroxyl, thiol, thioether, sulfone, sulfoxide, ether, ester, amide, amine, halogen, ketone, aldehyde, nitrile, and nitro;

r4 and R5 may represent the necessary atoms to form a five to seven membered ring.

7. The method according to any of the preceding claims, wherein the silver ink comprises a Dispersion Stabilizing Compound (DSC) according to formula I,

formula I

Wherein

M is selected from the group consisting of hydrogen, monovalent cationic groups, and acyl groups; and

q represents the necessary atoms to form a five-membered heteroaromatic ring.

8. The method of claim 7, wherein M in formula I is hydrogen.

9. The method of claim 7 or 8, wherein Q is a five-membered heteroaromatic ring selected from the group consisting of: imidazole; benzimidazole; a thiazole; benzothiazole; oxazole; benzoxazoles; 1,2, 3-triazole; 1,2, 4-triazole; oxadiazole; thiadiazole and tetrazole.

10. The method of any one of claims 6 to 9, wherein the dispersion stabilizing compound is selected from the group consisting of N, N-dibutyl- (2, 5-dihydro-5-thio-1H-tetrazol-1-yl-acetamide, 5-heptyl-2-mercapto-1, 3, 4-oxadiazole, 1-phenyl-5-mercaptotetrazole, 5-methyl-1, 2, 4-triazole- (1,5-a) pyrimidin-7-ol, and S- [5- [ (ethoxycarbonyl) amino ] -1,3, 4-thiadiazol-2-yl ] O-ethylthiocarbonate.

11. The method according to any one of claims 6 to 10, wherein the amount of the Dispersion Stabilizing Compound (DSC) is less than 5wt% relative to the weight of silver in the ink.

12. The method of any preceding claim, wherein the silver ink is a silver inkjet ink or a silver screen printing ink.

13. The method according to any one of the preceding claims, wherein a receptive layer is applied on the substrate prior to applying the silver ink.

14. The method of any preceding claim, wherein the silver ink comprises a liquid carrier selected from the group consisting of 2-phenoxyethanol, propylene carbonate, propylene glycol, n-butanol, and 2-pyrrolidone.

15. The method of any one of the preceding claims, wherein the substrate is a polycarbonate, polyvinyl chloride, polystyrene, or polyester based substrate.

Technical Field

The present invention relates to a method of producing conductive patterns on various substrates.

Background

Over the past few decades, interest has increased in metal printing or coating fluids containing metal nanoparticles due to their unique properties when compared to the bulk properties of a given metal. For example, the melting point of metal nanoparticles decreases with decreasing particle size, making them interesting for printed electronics, electrochemical, optical, magnetic and biological applications.

It is of great interest to produce stable and concentrated metal printing or coating fluids, which can be printed, for example, by inkjet printing, or coated at high speed, because of the ability to produce electronic devices at low cost.

The metal printing or coating fluid is typically a metal nanoparticle dispersion comprising metal nanoparticles and a dispersion medium. Such metal nanoparticle dispersions can be used directly as printing or coating fluids. However, additional ingredients are typically added to the metal nanoparticle dispersion to optimize the properties of the resulting metal printing or coating fluid.

EP-a 2671927 (Agfa Gevaert) discloses a metal nanoparticle dispersion, such as a silver inkjet ink, comprising a specific dispersion medium, such as 2-pyrrolidone, resulting in a more stable dispersion without the use of polymeric dispersants.

Typically, after the metal printing or coating fluid is applied on the substrate, a sintering step, also referred to as a curing step, is performed at elevated temperature to induce/enhance the electrical conductivity of the applied pattern or layer.

The organic components of the metal printing or coating fluid (e.g., polymeric dispersants) can reduce the sintering efficiency and, thus, the conductivity of the applied pattern or layer. Therefore, higher sintering temperatures and longer sintering times are generally required to decompose such organic components.

For substrates that do not resist high temperatures, high temperature sintering is not possible. For this reason, it is often difficult to produce highly conductive patterns on such substrates.

EP-a 3037161 (Agfa Gevaert) discloses a metal nanoparticle dispersion comprising silver nanoparticles, a liquid carrier and a specific dispersion stabilizing compound.

WO2017/139641 (TE Connectivity Corp) discloses a method of producing a conductive silver pattern on a substrate, wherein after drying/annealing the printed silver ink, a humidity treatment is performed. The humidity treatment enables the drying/annealing step to be performed at a lower temperature. However, the "two-step" sintering process introduces additional complexity into the process.

There remains a need for a simplified method of making highly conductive silver patterns on substrates that cannot withstand high sintering temperatures.

Summary of The Invention

It is an object of the present invention to provide a reliable method for producing electrically conductive silver patterns with high conductivity, sufficient adhesion and good resolution on various substrates.

This object is achieved by the method defined in claim 1.

Further advantages and embodiments of the invention will become apparent from the following description and the dependent claims.

Detailed Description

Definition of

The terms polymeric support and foil as used herein refer to a self-supporting polymer-based sheet that may be combined with one or more adhesive layers, such as a primer layer. The support and the foil are usually manufactured by extrusion.

The term layer as used herein is not considered to be self-supporting and is manufactured by coating or spraying it onto a (polymer) support or foil.

PET is an abbreviation for polyethylene terephthalate.

The term alkyl refers to all possible variations for each number of carbon atoms in the alkyl group, i.e. methyl, ethyl, for three carbon atoms: n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl, and tert-butyl; for five carbon atoms: n-pentyl, 1-dimethyl-propyl, 2-dimethylpropyl, and 2-methyl-butyl, and the like.

Unless otherwise specified, substituted or unsubstituted alkyl is preferably C₁-C₆An alkyl group.

Unless otherwise specified, substituted or unsubstituted alkenyl is preferably C₂-C₆An alkenyl group.

Unless otherwise specified, substituted or unsubstituted alkynyl is preferably C₂-C₆Alkynyl.

Unless otherwise specified, a substituted or unsubstituted alkaryl group preferably comprises one, two, three or more C₁-C₆Alkyl phenyl or naphthyl.

Unless otherwise specified, a substituted or unsubstituted aralkyl group is preferably C including an aryl group (preferably phenyl or naphthyl)₁-C₆An alkyl group.

Unless otherwise specified, substituted or unsubstituted aryl is preferably substituted or unsubstituted phenyl or naphthyl.

Cyclic groups include at least one ring structure and can be monocyclic or polycyclic groups, which means one or more rings fused together.

Heterocyclyl is a cyclic group having at least two atoms of different elements as members of one or more of its rings. The counterpart of a heterocyclic group is a homocyclic group whose ring structure is composed of only carbon. Unless otherwise specified, a substituted or unsubstituted heterocyclic group is preferably a five-or six-membered ring substituted with one, two, three or four heteroatoms, preferably selected from an oxygen atom, a nitrogen atom, a sulfur atom, a selenium atom or a combination thereof.

A cycloaliphatic radical is a non-aromatic, homocyclic radical in which the ring atoms consist of carbon atoms.

The term heteroaryl refers to a monocyclic or polycyclic aromatic ring comprising carbon atoms and one or more heteroatoms, preferably 1-4 heteroatoms, in the ring structure, said heteroatoms being independently selected from nitrogen, oxygen, selenium and sulfur. Preferred examples of heteroaryl groups include, but are not limited to, pyridyl, pyridazinyl, pyrimidinyl (pyrimidyl), pyrazinyl (pyrizyl), triazinyl, pyrrolyl, pyrazolyl, imidazolyl, (1,2,3) -triazolyl and (1,2,4) -triazolyl, pyrazinyl (pyrimidyl), pyrimidinyl (pyrimidyl), tetrazolyl, furanyl, thienyl, isoxazolyl, thiazolyl, isoxazolyl and oxazolyl. Heteroaryl groups may be unsubstituted or substituted with one, two or more suitable substituents. Preferably, the heteroaryl group is a monocyclic ring, wherein the ring contains 1-5 carbon atoms and 1-4 heteroatoms.

The term substituted in, for example, substituted alkyl means that the alkyl group may be substituted with atoms other than those typically present in such groups (i.e., carbon and hydrogen). For example, a substituted alkyl group may include a halogen atom or a thiol group. Unsubstituted alkyl groups contain only carbon and hydrogen atoms.

Unless otherwise indicated, substituted alkyl, substituted alkenyl, substituted alkynyl, substituted aralkyl, substituted alkaryl, substituted aryl, substituted heteroaryl and substituted heterocyclyl are preferably substituted with one or more substituents selected from: methyl, ethyl, n-propyl, isopropyl, n-butyl, 1-isobutyl, 2-isobutyl and tert-butyl, esters, amides, ethers, thioethers, ketones, aldehydes, sulfoxides, sulfones, sulfonates, sulfonamides, -Cl, -Br, -I, -OH, -SH, -CN and-NO₂。

Method for preparing conductive silver pattern

The method for preparing a conductive silver pattern on a substrate according to the present invention comprises the steps of:

-applying a silver ink on a substrate to form a silver pattern, and

-sintering the applied silver pattern in one step at a temperature of at least 50 ℃ and a Relative Humidity (RH) of at least 50%.

The temperature in the one-step sintering process is preferably at least 60 ℃, more preferably at least 70 ℃, and most preferably at least 80 ℃.

The one-step sintering process may also be referred to as a single-step sintering process.

The relative humidity in the one-step sintering process is preferably at least 60%, more preferably at least 70%, most preferably at least 80%.

The "one-step" sintering step according to the present invention enables the formation of highly conductive silver patterns at relatively low temperatures. Such low temperatures make it possible to use substrates which are not resistant to high temperatures, for example polyvinyl chloride (PVC), Polycarbonate (PC) or Polystyrene (PS) substrates.

The advantage of the "one-step" sintering step is a lower complexity of the overall process and a higher yield, for example compared to the "two-step" sintering process disclosed in WO 2017/139641.

Sintering step

The temperature in the one-step sintering process is preferably at least 60 ℃, more preferably at least 70 ℃, and most preferably at least 80 ℃.

The relative humidity in the one-step sintering process is preferably at least 60%, more preferably at least 70%, most preferably at least 80%.

The one-step sintering step according to the present invention enables the formation of highly conductive silver patterns at relatively low temperatures. Such low temperatures allow the use of substrates that are not resistant to high temperatures, such as PCV substrates.

By one-step sintering step is meant that the printed silver is not subjected to additional treatments, such as drying, annealing, heating, prior to the sintering step.

An optional drying step may follow the one-step sintering step.

The amount of time used in the one-step sintering step is 1 minute to 200 hours, preferably 5 minutes to 150 hours, more preferably 10 minutes to 100 hours, most preferably 30 minutes to 50 hours.

The one-step sintering step is preferably carried out in an oven with relative humidity control. For example, wherein a given temperature and an accurate relative humidity value can be set.

The advantage of the "one-step" sintering step is a lower complexity of the overall process and a higher yield, for example compared to the "two-step" sintering process disclosed in WO 2017/139641.

Silver ink

The silver ink comprises silver particles, preferably silver nanoparticles.

The silver ink may be a flexographic ink, an offset ink, a rotogravure ink, a screen printing ink or an inkjet ink.

The silver ink may further comprise a liquid vehicle, stabilizing compounds, binders, polymeric dispersants, and other additives to further optimize its properties.

Silver particles

The silver ink of the present invention comprises silver particles, preferably silver nanoparticles.

The silver nanoparticles have an average particle size or average particle diameter (measured by transmission electron microscopy) of less than 150 nm, preferably less than 100 nm, more preferably less than 50 nm, most preferably less than 30 nm.

The amount of silver nanoparticles in the ink is preferably at least 5wt%, more preferably at least 10 wt%, most preferably at least 15 wt%, particularly preferably at least 20 wt%, relative to the total weight of the silver ink.

Silver nanoparticles are preferably prepared by the methods disclosed in paragraphs [0044] - [0053] and examples of EP-A2671927.

The silver ink may also comprise silver flakes or silver nanowires.

Dispersion Stabilizing Compound (DSC)

The silver inkjet ink preferably comprises silver nanoparticles, a liquid carrier and a Dispersion Stabilizing Compound (DSC) according to formula I, II, III or IV,

wherein

Q represents the necessary atoms to form a substituted or unsubstituted five-or six-membered heteroaromatic ring;

m is selected from the group consisting of hydrogen, monovalent cationic groups, and acyl groups;

r1 and R2 are independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkaryl, substituted or unsubstituted aralkyl, substituted or unsubstituted aryl or heteroaryl, hydroxyl, thioether, ether, ester, amide, amine, halogen, ketone, and aldehyde;

r1 and R2 may represent the necessary atoms to form a five to seven membered ring;

r3 to R5 are independently selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkaryl, substituted or unsubstituted aralkyl, substituted or unsubstituted aryl or heteroaryl, hydroxyl, thiol, thioether, sulfone, sulfoxide, ether, ester, amide, amine, halogen, ketone, aldehyde, nitrile, and nitro;

r4 and R5 may represent the necessary atoms to form a five to seven membered ring.

The dispersion stabilizing compound is preferably a compound according to formula I,

formula I

Wherein

M is selected from the group consisting of hydrogen, monovalent cationic groups, and acyl groups; and

q represents the necessary atoms to form a five-membered heteroaromatic ring.

M in formula I is preferably hydrogen.

Q is preferably a five-membered heteroaromatic ring selected from the group consisting of imidazole, benzimidazole, thiazole, benzothiazole, oxazole, benzoxazole, 1,2, 3-triazole, 1,2, 4-triazole, oxadiazole, thiadiazole and tetrazole.

Q is more preferably tetrazole.

Some examples of dispersion stabilizing compounds according to the present invention are shown in table 1.

TABLE 1

The dispersion stabilising compound is preferably selected from the group consisting of N, N-dibutyl- (2, 5-dihydro-5-thio-1H-tetrazol-1-yl-acetamide, 5-heptyl-2-mercapto-1, 3, 4-oxadiazole, 1-phenyl-5-mercaptotetrazole, 5-methyl-1, 2, 4-triazolo- (1,5-a) pyrimidin-7-ol and S- [5- [ (ethoxycarbonyl) amino ] -1,3, 4-thiadiazol-2-yl ] O-ethylthiocarbonate.

The dispersion stabilizing compounds according to formulae I-IV are preferably non-polymeric compounds. Non-polymeric compounds as used herein refer to compounds having a molecular weight preferably less than 1000, more preferably less than 500, most preferably less than 350.

The amount of the Dispersion Stabilizing Compound (DSC), expressed in wt% relative to the total weight of silver in the silver ink, is at least 1.0, preferably at least 1.25, more preferably at least 2.0. The amount of the dispersion stabilising compound, expressed in wt% relative to the total weight of silver in the silver ink, is preferably below 10, more preferably below 7.5, most preferably below 5.

When the amount of dispersion stabilizing compound relative to the total weight of the silver is too low, the stabilizing effect may be too low, while too high an amount of dispersion stabilizing compound may adversely affect the conductivity of the coating or pattern obtained with the silver ink.

Polymeric dispersants

The silver ink may comprise a polymeric dispersant.

Usually, polymeric dispersants contain so-called anchor groups in a part of the molecule, which adsorb on the silver particles to be dispersed. In another part of the molecule, the polymeric dispersant has a polymer chain that is compatible with the dispersion medium (also referred to as the liquid vehicle), as well as all the ingredients present in the final printing or coating fluid.

Polymeric dispersants are typically homopolymers or copolymers prepared from acrylic, methacrylic, vinylpyrrolidone, vinyl butyral, vinyl acetate, or vinyl alcohol monomers.

It is also possible to use the polymeric dispersants disclosed in EP-A2468827, which have a decomposition of 95% by weight at temperatures below 300 ℃, as measured by thermogravimetric analysis.

However, in a preferred embodiment, the metal nanoparticle dispersion comprises less than 5wt%, more preferably less than 1 wt%, most preferably less than 0.1 wt% of polymeric dispersant relative to the total weight of the dispersion. In a particularly preferred embodiment, the dispersion does not contain a polymeric dispersant at all.

It has been observed that the presence of polymeric dispersants may negatively affect the sintering efficiency.

Liquid carrier

The silver ink preferably comprises a liquid carrier.

The liquid carrier is preferably an organic solvent. The organic solvent may be selected from alcohols, aromatic hydrocarbons, ketones, esters, aliphatic hydrocarbons, higher fatty acids, carbitols, cellosolves and higher fatty acid esters.

Suitable alcohols include methanol, ethanol, propanol, 1-butanol, 1-pentanol, 2-butanol, tert-butanol.

Suitable aromatic hydrocarbons include toluene and xylene.

Suitable ketones include methyl ethyl ketone, methyl isobutyl ketone, 2, 4-pentanedione, and hexafluoroacetone.

Diols, glycol ethers, N-dimethylacetamide, N-dimethylformamide may also be used.

Mixtures of organic solvents can be used to optimize the properties of the metal nanoparticle dispersion.

Preferred organic solvents are high boiling solvents. High-boiling organic solvents as referred to herein are solvents having a boiling point higher than that of water (> 100 ℃).

Preferred high boiling solvents are shown in table 2.

TABLE 2

Particularly preferred high boiling solvents are 2-phenoxyethanol, propylene carbonate, propylene glycol, n-butanol, 2-pyrrolidone, and mixtures thereof.

The silver ink preferably comprises at least 25 wt%, more preferably at least 40 wt% of 2-phenoxyethanol based on the total weight of the silver ink.

Additive agent

To optimize printing properties, and also depending on the application for which it is used, additives (e.g., reducing agents, wetting/leveling agents, dewetting agents, rheology modifiers, adhesives, adhesion promoters, wetting agents, jetting agents, curing agents, biocides, or antioxidants) may be added to the above-described silver inks.

The silver ink may comprise a surfactant. Preferred surfactants are Byk 410 and 411 (both solutions of modified urea), and Byk 430 (solutions of medium polarity polyamide modified with polymeric urea).

The amount of the surfactant is preferably 0.01 to 10 wt%, more preferably 0.05 to 5wt%, most preferably 0.1 to 0.5 wt% with respect to the total amount of the silver ink.

It may be advantageous to add small amounts of metals of mineral acids or compounds capable of generating such acids to the silver ink, as disclosed in EP-a 2821164. A layer or pattern formed from such a silver ink was observed to have higher conductivity.

Higher conductivities can also be obtained when the silver ink contains a compound according to formula X, as disclosed in EP-a 3016763,

wherein

X represents an essential atom for forming a substituted or unsubstituted ring.

Particularly preferred compounds according to formula X are ascorbic acid or isoascorbic acid derivative compounds.

Base material

The substrate may be glass, paper or a polymeric support.

The substrate as used herein is also referred to as a support.

Preferred polymeric supports are substrates based on polycarbonate, polyethylene terephthalate (PET) or polyvinyl chloride (PVC).

The support may provide one or more layers to improve adhesion, absorption or diffusion of the applied conductive inkjet ink, screen printing ink or flexographic printing ink.

The polymer support preferably provides a so-called primer layer to improve the adhesion of the applied conductive inkjet ink, screen printing ink or flexographic printing ink. Such underlayers are usually based on vinylidene copolymers, polyesters or (meth) acrylates.

Useful primers for this purpose are well known in the art and include, for example, polymers of vinylidene chloride, such as vinylidene chloride/acrylonitrile/acrylic acid terpolymers or vinylidene chloride/methyl acrylate/itaconic acid terpolymers.

Other preferred subbing layers include a binder based on a polyester-polyurethane copolymer. In a more preferred embodiment, the polyester-polyurethane copolymer is an ionomeric polyester polyurethane, preferably using polyester segments based on terephthalic acid and ethylene glycol and hexamethylene diisocyanate. A suitable polyester-polyurethane copolymer is Hydran ™ APX 101H from DIC Europe GmbH.

The application of subbing layers is well known in the art of making polyester supports for silver halide photographic films. The preparation of such a base layer is disclosed, for example, in US 3649336 and GB 1441591.

The acid generating compound may be added to the primer layer on the support as disclosed in WO 2015/000932. Preferred primers comprise copolymers of vinylidene chloride, acrylate and itaconic acid.

In a preferred embodiment, the dry thickness of the bottom layer is not more than 0.2 μm, or preferably not more than 200 mg/m²。

Another preferred support is a transparent conductive oxide based support. Such supports are typically glass or polymer supports on which a layer or pattern of Transparent Conductive Oxide (TCO) is provided. Examples of such conductive oxides are ITO (indium tin oxide), ZnO, SnO₂Or doped oxides, such as ZnO: and Al.

A particularly preferred TCO is ITO.

A preferred paper based support is a Powercoat HD paper substrate, a substrate designed for printed electronic products by Arjowiggins Creative Papers.

Multiple metal layers or patterns (i.e., stacks of patterned or unpatterned layers) may be applied to the substrate. Thus, references to supports in the method of making a metal layer or pattern also include previously applied metal layers or patterns.

Receiving layer

In a preferred embodiment, a receptive layer is applied to the substrate, and then a silver ink is applied to the receptive layer.

Such a preferred method comprises the following steps.

-applying a receiving layer on the substrate.

-applying the above-mentioned silver ink on at least a part of the receiving layer, thereby forming a silver pattern, and

-sintering the silver pattern.

The receptive layer may be applied to the substrate as a coating that covers substantially the entire substrate. A silver ink is then applied over at least a portion of the receptive layer.

However, the receiving layer may also be applied imagewise to the substrate.

For example, a receptive layer may be applied to the substrate in accordance with the first image. Silver ink is then applied over at least a portion of the first image.

Preferably, the receptive layer is printed slightly wider than the silver ink to ensure improved adhesion, resolution and effective curing.

This can be achieved with minimal use of additional ink, since with high positioning accuracy of the ink jet device one can create the necessary pattern of the receiving layer (first image) by simple "thickening" or "widening" of the silver pattern (e.g. silver circuit). This can be done quite easily in a digital workflow.

The receiving layer is preferably applied to the substrate by ink jet printing as a UV curable ink jet ink.

UV curable inkjet inks are preferred in order to obtain a receptive layer with sufficient roughness Rz and to achieve sufficient adhesion of the receptive layer on various substrates. The resulting Rz can be optimized by adjusting the diffusion properties of the inkjet ink, or by adjusting the UV curing parameters.

Although UV curable inkjet inks are preferred, thermally curable inks can also be used and similar rough layers can be obtained by adjusting the thermal curing parameters.

The roughness Rz of the receiving layer is preferably 1 μm to 75 μm, preferably 2 μm to 60 μm, more preferably 5 μm to 50 μm.

The roughness Ra of the receiving layer is preferably 0.5 μm to 20 μm, more preferably 1 μm to 15 μm, and most preferably 2 μm to 10 μm.

It has been observed that the insertion of a receptive layer having a roughness of 1-75 μm between the substrate and the metal pattern results in improved adhesion of the pattern and better printing resolution of the pattern.

The thickness of the receptive layer is preferably 10 μm to 500 μm, more preferably 20 μm to 350 μm, and most preferably 30 μm to 250 μm.

Preferred white receptive layers and white UV curable inkjet inks for preparing such white receptive layers are disclosed in EP-a 18171221.7 (filed 08-05-2018).

Preparation of silver ink

The preparation of silver inks typically involves adding the liquid carrier and other ingredients to the silver particles by using homogenization techniques (e.g., stirring, high shear mixing, sonication, or combinations thereof).

The silver particles are typically pastes or highly concentrated dispersions of silver nanoparticles from which the silver ink is prepared.

A preferred process for the preparation of silver nanoparticles is disclosed in EP-A2671927.

It has been observed that better results may be obtained when all or part of the dispersion stabilizing compound is added during the process of preparation of the silver nanoparticles. Due to their adsorption onto the silver nanoparticles, the dispersion stabilizing compound added during the preparation of the silver nanoparticles will at least partially remain in the final silver nanoparticle dispersion, even if one or more washing steps have been performed in the preparation process.

The homogenization step may be carried out at elevated temperatures up to 100 ℃. In a preferred embodiment, the homogenization step is carried out at a temperature equal to or lower than 60 ℃.

Ink jet printing apparatus

Various embodiments of an apparatus for creating a conductive pattern or receptive layer by ink jet printing may be used.

In a lithographic apparatus, a support is provided on a plate. Droplets of silver inkjet fluid are ejected from the print head onto a support.

The print head typically scans back and forth across a moving support (y-direction) in the transverse direction (x-direction). Such bidirectional printing is called multi-pass printing.

Another preferred printing method is the so-called single pass printing method, wherein the print head or a plurality of staggered print heads cover the entire width of the support. In such a single pass printing method, the print head is typically held stationary while the support is conveyed below the print head (y-direction).

To obtain maximum dot placement accuracy, the print head is placed as close to the support surface as possible. The distance between the print head and the support surface is preferably less than 3 mm, more preferably less than 2 mm, most preferably less than 1 mm.

Since the distance between the print head and the support surface may affect the dot placement accuracy, it may be advantageous to measure the thickness of the support and adjust the distance between the print head and the support surface based on the measurement of the support thickness.

The distance between the fixed print head and the surface of the support mounted on the printing device may also vary across the support due to, for example, undulations of the support or other irregularities of the surface of the support. It may therefore also be advantageous to measure the surface topography of the support and compensate for differences in the measured surface topography by controlling the so-called firing time of the droplets of curable fluid on the support or by adjusting the distance between the print head and the surface of the support. An example of a measuring device that measures the surface topography of a lithographic support is disclosed in ISO 12635:2008 (E).

In a preferred embodiment, the inkjet printing device has a pressing means, for example a vacuum chamber below the support, to press the support in a so-called pressing area, for example by vacuum. In a more preferred embodiment, the support is pressed against the support by independently operating pressing means, e.g. a plurality of vacuum chambers under the support, which are independently controlled to increase the vacuum pressure on the support, so that more than one pressed area is created on the support. The compaction of the support enhances the drop placement and positional accuracy of the ejected drops.

Printing head

UV-curable inkjet inks and silver inkjet inks can be jetted by one or more print heads through a nozzle in a controlled manner to eject small droplets of the ink onto the surface of an ink-receiving layer that is moving relative to the one or more print heads.

A preferred print head for use in an inkjet printing system is a piezoelectric head. Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied thereto. The application of the voltage changes the shape of the piezoelectric ceramic transducer in the printhead, creating a void, which is then filled with ink. When the voltage is removed again, the ceramic expands to its original shape, ejecting a drop of ink from the print head. However, the inkjet printing method according to the present invention is not limited to piezoelectric inkjet printing.

Preferred print heads eject drops having a volume of 50 pL or less, for example 35 pL or 25 pL or less. It has been observed that droplets with a larger volume result in a higher roughness of the printed receiving layer.

Another preferred print head is a through-flow piezoelectric inkjet print head. A through-flow piezoelectric inkjet print head is a print head in which a continuous flow of liquid is circulated through the liquid channel of the print head to avoid condensation in the liquid that may cause interference effects in the flow and poor drop placement. The quality of the conductive pattern on the support can be improved by avoiding poor drop placement by using a through-flow piezoelectric inkjet print head. Another advantage of using such a through-flow printhead is that the viscosity limit of the curable fluid to be ejected is higher, widening the range of variations in the composition of the fluid.

Inkjet print heads typically scan back and forth in a lateral direction across the surface of a moving ink-receiving layer. Typically the inkjet print head does not print on the way back. Bi-directional printing is preferred for achieving high area throughput. Another preferred printing method is by a "single pass printing process" which can be performed by using a page wide inkjet print head or a plurality of staggered inkjet print heads covering the entire width of the ink-receiving layer surface. In a single pass printing process, the inkjet print head is typically held stationary and the substrate surface is transported beneath the inkjet print head.

The receptive layer may be applied in a single pass of a multi-pass printing process. A multi-pass printing process may be preferred to achieve sufficient thickness of the receptive layer.

Application of

By using the method according to the invention, a highly conductive metal layer or pattern can be achieved on substrates that are not resistant to high temperatures, such as Polycarbonate (PC), Polyethylene (PE), polypropylene (PP), Polymethacrylate (PMMA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene, nylon-6, polyester, polyvinyl chloride (PVC) or Polystyrene (PS).

Industrial applications requiring high productivity and reliability can benefit from the use of Ag inkjet inks developed herein. Applications such as the manufacture of RFID antennas for smart packaging, sensors for point-of-care diagnostics, and capacitive touch sensors.

With this method, a highly conductive pattern can be provided on an FR-4 substrate that is commonly used for PCB production.

Examples

Material

Unless otherwise noted, all materials used in the following examples are readily available from standard sources, such as ALDRICH CHEMICAL co. (belgium) and ACROS (belgium). The water used was deionized water.

Measuring method

Of silver coatingsElectrical conductivity of

Measuring the surface resistance of the silver coating using a four-point collinear probe (SER). The surface resistance or sheet resistance is calculated by the following formula:

SER = (π/ln2)*(V/I)

wherein

SERSurface resistance of the layer expressed in Ω/square;

pi is a mathematical constant, approximately equal to 3.14;

ln2 is a mathematical constant equal to the natural logarithm of the value 2, approximately equal to 0.693;

v is the voltage measured by the voltmeter of the four-point probe measuring device;

i is the source current measured by the four-point probe measurement device.

For each sample, six measurements were made at different positions of the coating and the average was calculated.

Silver content of the coatingM _Ag (g/m²) Determined by WD-XRF.

The conductivity of the coating was then determined by calculating the conductivity as a percentage of the bulk conductivity of the silver using the following formula:

whereinσ _AgIs the specific conductivity of silver (equal to 6.3X 10)⁷ S/m)，σ _{Coating layer}Is the specific conductivity of the Ag coating,ρ _Agis the density of silver (1.049X 10)⁷ g/m³)。

Viscosity measurement

Unless otherwise stated, the viscosity is at 25 ℃ for 1000 s^-1Is measured using a commercially available viscometer, for example, with a DHR-2 rheometer (double-walled ring) from TA Instruments.

Example 1

As shown in table 3, a silver screen printing ink SI-P2000, commercially available from Agfa Gevaert NV, was screen printed on different substrates using a P150 screen printing screen.

Lexan substrates are all polycarbonate substrates commercially available from Tekra.

The Makrofol substrates are all polycarbonate substrates commercially available from Covestro.

Autostat CT7 is a polyester substrate commercially available from MacDermid.

Sintering of printed silver is carried out in a "one-step" or "two-step" process.

In the "one-step" sintering process, the printed silver was treated at high temperature and relative humidity as shown in table 3.

In a "two-step" sintering process, as disclosed in WO2017/139641, the printed silver is subjected to a heat treatment (known as drying/annealing) in a first step at low RH and then to a heat treatment in a second step at high RH.

The electrical conductivity measured as described above after sintering is shown in table 3.

TABLE 3

As is clear from the results of table 3, the conductivity obtained with the one-step sintering process resulted in a higher conductivity than the two-step sintering process.

Furthermore, it has been observed that the use of a two-step sintering process often results in cracking of the printed silver pattern, which is not the case when a one-step sintering process is used.

Example 2

Silver inkjet ink SI-J20X was printed on the substrates shown in table 4 using a Ceraprnter (available from Cerrpop and equipped with a Konica Minolta 30 pL printhead KM1024i LHE).

Mylar A is a polyester substrate commercially available from Dupont.

Powercoat HD is a paper substrate designed for high definition patterning and is commercially available from Arjowiggins Creative Papers.

The printed silver inks were subjected to a "one-step" sintering process using the conditions shown in table 4.

TABLE 4

It is clear from the results of table 4 that in the one-step sintering process, good electrical conductivity at low temperatures (e.g. 85 ℃) is only obtained at high relative humidity (e.g. 85%).