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Flexible/Stretchable Conductive Coatings, DENATRON
HOME > DENATRON Museum > Get to know DENATRON > Flexible/Stretchable Conductive Coatings, DENATRON
In the development and manufacturing of electronic devices and batteries, stretchable conductive coatings and conductive paints are gaining attention. This article explores the stretchable conductive coatings DENATRON in detail, explaining its key features and applications.
Basics of DENATRON
Conductive coatings often use highly conductive metals, such as silver and copper, or indium tin oxide (ITO), which is known for its high transparency and durability. However, metal films that conduct electricity well are prone to cracking, which interrupts the conductive pathways.
ITO also lacks stretchability and is difficult to process, which is a significant drawback, driving the development of alternative materials. In contrast, DENATRON is based on the conductive polymer PEDOT:PSS. It can be made stretchable, has high conductivity, and can be used in thin films, making it almost invisible once applied. A water- or water/alcohol-based and biocompatible polymer, it is a stretchable conductive coating that is gentle on both the human body and the environment.
Applications
Thanks to its excellent stretchability, conductivity, and transparency, DENATRON can be applied in fields where traditional conductive materials have been challenging to use. Here, we introduce specific applications of DENATRON through case examples.
Sensor Electrodes
Due to its excellent processability and stretchability, DENATRON can be used on curved surfaces that are prone to cracking. The shape can be processed after film formation, making it applicable to 3D switches. Sensor electrodes must be transparent to the extent that they are invisible to maintain the screen's appearance, and DENATRON can provide conductivity without compromising the appearance.
It solves issues such as:
"I want to apply touch sensors using a simple wet process."
"I can't attach a bent touch sensor to a curved surface."
"I'm concerned about visible sensor wiring patterns."
Flexible Displays
With its excellent stretchability, DENATRON can accommodate the bending and curvature of flexible displays. Its high transparency ensures that the display’s visibility is not compromised. Additionally, the Sheet Resistance of the film is 102 to 103 Ω/sq, enabling high-sensitivity touch operations. The film’s physical properties can also be finely customized, making it ideal for attaching touch sensors to flexible, stretchable devices.
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Wearable Electronics
PEDOT:PSS is a safe hydrophilic and biocompatible material. Since there is no concern for metal allergies, it is ideal for electrodes in biosensors that come into direct contact with the human body. By coating fibers, it can also be used for conductive textiles in smart textiles (advanced functional textile materials). Washing durability and other properties can be added through blending technology.
PEDOT:PSS shows no signs of cytotoxicity, and it is a human-friendly material expected to be used in medical applications, such as artificial muscles and artificial retinas.
Features of DENATRON
DENATRON combines stretchability and conductivity, which is difficult to achieve with conventional conductive coatings. In this section, we explain DENATRON’s outstanding features that will contribute to the development of next-generation devices.
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High Transparency
The conductive polymer PEDOT:PSS, which serves as the base for DENATRON, has minimal absorption in the visible light range and can be used as a thin film, resulting in a highly transparent conductive film. Even with a very thin layer, the conductive film formed by applying DENATRON maintains high conductivity without compromising transparency.
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Humidity Independence
DENATRON achieves stable conductivity due to its electronic conduction mechanism, which is unaffected by humidity. Because it is not dependent on humidity, DENATRON is also ideal for devices that require stable performance across a wide range of environments.
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Excellent Processability
One of the key strengths of DENATRON is its compatibility with various printing and coating methods. Whether it is gravure printing, slit coating, or screen printing, DENATRON can be used in the optimal method based on the customer’s shape, size, and application requirements.
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Biocompatibility
PEDOT:PSS is a safe substance that is hydrophilic and reported to have low cytotoxicity. *1 It is free from concerns about metal allergies, making it ideal for applications that come into direct contact with the human body, such as biosensors and smart textiles.
Contact Us for More Information About DENATRON
A major challenge with previous conductive coatings, especially metal films, was that cracks would form when subjected to strain, causing loss of conductivity. However, with the DENATRON SPS series, such concerns are resolved. The DENATRON SPS series uses a highly flexible and stretchable conductive polymer that conforms perfectly to materials that expand and contract, such as rubber, while maintaining stable conductivity.
In the electronics industry, especially in the development of devices such as flexible displays and wearable electronics, the demand for shape-changing devices is rapidly increasing. Conductive materials that can adapt to these changes in shape, such as DENATRON, are supporting this evolution.
Nagase ChemteX will continue to challenge the development of new materials. If you are interested in the DENATRON SPS series, please feel free to contact us.
Basics of Flexible/Stretchable Conductive Coatings (Conductive Paints)
DENATRON is a groundbreaking conductive coating that, unlike conventional conductive materials, maintains its conductivity even when bent or stretched. But what exactly is a flexible/stretchable conductive coating material? In this section, we explain the basics of these materials.
What is Flexible/Stretchable Conductive coatings?
Conventional electronic devices mostly use rigid, inflexible materials. However, next-generation devices, such as flexible displays and wearable sensors, require special materials that can bend and stretch-and still conduct electricity without breaking.
Flexible/stretchable conductive coatings are innovative paints developed to meet these needs by combining flexibility and conductivity. These conductive inks come in several types, using materials such as metal particles, metal wires/mesh, and conductive polymers. Using these inks and applying appropriate treatments makes it possible to impart conductivity to flexible substrates.
Because these coatings enable printing on curved or movable parts, which was impossible with traditional conductive materials, they significantly expand the design freedom of electronic devices and smart textiles.
Features of Flexible/Stretchable Conductive Coating
Flexible/stretchable conductive coatings possesses characteristics that other coatings does not. In this section, we explain three major features of flexible/stretchable conductive coatings.
Flexibility
Traditional conductive materials, such as metals, crack or peel when bent or stretched. Additionally, one common method for manufacturing metal electrodes, dry coating by applying powdered electrode materials to metal substrates, is not well suited to 3D shapes. However, flexible/stretchable conductive coating materials can conform to 3D shapes while maintaining conductivity. Among them, the conductive polymer PEDOT:PSS offers superior stability compared with other conductive polymers.
Conductivity
Since flexible/stretchable conductive coating materials can maintain conductivity even when deformed, they are expected to be applied to devices with shapes and structures that were impossible with conventional electronic components. The polythiophene-based conductive polymer PEDOT:PSS allows for the adjustment of conductivity based on the polymerization conditions. Furthermore, its high transparency allows it to add conductivity without affecting the appearance of the device, making it highly applicable to touch panels and displays.
Printability
Flexible/stretchable conductive coatings can be uniformly applied to various substrates using common printing technologies, such as screen printing and inkjet printing. They are also used in wearable sensors that are worn on the human body. DENATRON, based on PEDOT:PSS, does not contain metals. Since there is no concern for metal allergies, it is ideal for wearable sensors that come into direct contact with the human body.
Recommended Product
The DENATRON series offers a variety of products suited to different applications. Among them, we introduce a product that is ideal for flexible/stretchable conductive coatings.
SPS-801
DENATRON SPS-801 is a flexible/stretchable conductive coating. It uses a conductive polymer (PEDOT:PSS), resulting in a high-transparency, low-resistance paste-like paint. Table 1 shows the liquid properties of SPS-801.
| Appearance | Dark blue color |
|---|---|
| Main Components | Conductive material, binder resin, additive |
| Main Solvent | Water-based solvent |
| pH | 2–3 |
| Viscosity | 1,000–3,000 mPa·s |
| Storage Stability（1〜25℃） | More than 4 months |
Table 1. Liquid Properties of SP-801
Before application (in its paste state), it appears dark blue, but after application and film formation, it becomes transparent. The water-based solvents used are solvents with characteristics that dissolve organic compounds such as resins, but have low toxicity. Additionally, it has a viscosity suitable for screen printing, where the paste is extruded from the slit using a squeegee. When stored under proper conditions, it can be stored for more than four months.
To print DENATRON onto the substrate, first, thoroughly stir it using a dispersion mixer (around 1,500 rpm for about 10 minutes). Afterward, set it up in a screen-printing machine for printing. Please refer to the recommended film formation conditions shown in Table 2.
| Recommended Coating Conditions | Squeegee hardness: 70–80°, Squeegee angle: 50–80° |
|---|---|
| Speed | 200–350 mm/s, Clearance: 2–4 mm |
| Mesh | #200–460 |
| Recommended Substrate | Plastics such as polyethylene terephthalate (PET), acrylic resin (PMMA), polycarbonate (PC), or glass |
| Recommended Drying Conditions | Temperature: 80°C–130°C, Drying time: 1–5 minutes |
Table 2. Film Formation Conditions
FAQs
Here are some frequently asked questions and answers from our customers:
How are flexible/stretchable conductive coatings used in industrial applications?
They are used in products that need to stretch and conform to the shape and movement of substrates, such as flexible displays, wearable devices, electronic paper, and flexible displays. Additionally, conductive coatings play an active role in fields where flexible designs are required, such as lithium-ion batteries, solid-state batteries, capacitors, and antistatic films.
What are the representative materials used in flexible/stretchable conductive coatings?
1. Metal particles, metal wires/mesh
Conductivity is imparted by dispersing conductive metal particles, nanowires, or mesh-like metals, such as silver, copper, or ITO, in a solvent.
2. Carbon Nanotubes
Unlike PEDOT:PSS, it is turned into a paint using special dispersants and dispersion machines. Its nano-size gives it high transparency, and it also has excellent weather resistance due to the C-C bonds.
3. Conductive Polymers
There are polythiophene-based, polyacetylene-based, polyaniline-based, and polypyrrole-based polymers. Among them, PEDOT:PSS, composed of PEDOT (Poly(3,4-EthyleneDiOxyThiophene) and PSS (Poly(4-StyreneSulfonate)), is known as the most stable material among the conductive polymers.
What materials can flexible/stretchable conductive coating materials be applied to?
Plastics
They can be used on plastics such as PET, PMMA, TriAcetyl Cellulose (TAC), and PC.
Rubber materials
They can be applied to rubber materials, such as silicone and polyurethane.
Textiles
They can be used on non-woven fabrics and fabrics used in clothing.
Metals
While they can be applied to metals, since metals can rust, it is recommended to use anti-rust measures, such as stainless steel, plating, or resin lining on parts where the liquid comes into direct contact.
Glass
It can exhibit high adhesion to glass substrates and form a uniform conductive layer.
Reference
*1：Biomed. Mater. 4 (2009) 045009, M Asplund et al.
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