A Guide to Using Thermochromic Powder on Ceramics: Printing, Application Methods, Precautions and FAQ

Thermochromic powder (thermochromic pigment), one of iSuoChem's hot selling special effect pigments, has consistently proven popular in the color-changing pigment market. Its application in ceramic products is growing rapidly. We often receive inquiries from customers about how to use thermochromic powder on ceramics. Therefore, we've compiled this blog, drawing on relevant information, over a decade of practical user experience, and our expertise.

This blog will comprehensively explain the application techniques of thermochromic powder on ceramic surfaces, including suitable printing and application methods, detailed procedures, solutions to common problems, and precautions. Whether creating thermochromic ceramic mugs, temperature-indicating cookware, or creative ceramic crafts, mastering the correct application method is crucial. This blog will explain how to select the appropriate thermochromic material, prepare the substrate, apply the color-changing layer, and apply a protective coating to ensure a durable and effective color-changing effect.

1. Thermochromic Powder Basics and Ceramic Application Overview

Thermochromic powder (TCP) is a type of effect pigment that reversibly changes color with temperature. It is a capsule-type pigment prepared from an electron-transfer organic compound system. When the ambient temperature reaches its specific color change temperature, the material's molecular structure undergoes a reversible change, resulting in a different color state. This property provides a new approach to adding value to ceramic products and avoiding market homogeneity and price wars.

1.1 In ceramic applications, TCPs exhibit three basic color change modes:

• Reversibly Color-Colorless type: These display a specific color (such as black) at room temperature. Upon heating, the color disappears, becoming colorless. Upon cooling, the original color returns. For example, 31°C black TCPs appear colorless above 31°C and black below 31°C. (Thermochromic paint black to clear or thermochromic ink black to clear)
• Reversibly Colorless-Color type: These display colorless at room temperature, develop color upon heating, and return to colorless upon cooling. These products are commonly used for high-temperature warnings, such as the 60°C color-developing type.
• Reversible color-shifting powder (color-color type): Displays one color at room temperature, changes to another color upon heating, and returns to its original color upon cooling. This type of powder can create richer color-shifting effects.

Tips: Irreversible thermochromic pigment or irreversible thermochromic ink is also an important thermochromic pigment/ink. But in ceramic industries, we fewly use this type.

• Common color-shifting temperatures in ceramic applications include: 18°C, 22°C, 28°C, 31°C, 33°C, 42°C, 45°C, 50°C, and 65°C. Users can select the appropriate temperature based on the product's intended use. For example, 31-45°C is suitable for beverage cup temperature indication, while 50-65°C is suitable for cookware temperature warning.

Thermochromic powders typically have a particle size between 1 and 10 microns and are encapsulated using microencapsulation technology, which imparts a certain degree of temperature resistance and chemical stability. However, as organic compounds, heat sensitive pigment powders have limited high-temperature resistance. They can withstand temperatures of 230°C for short periods (approximately 10 minutes), but long-term operating temperatures should not exceed 75°C. This characteristic makes the application location of thermochromic powders on ceramics crucial; they should be placed away from direct heat exposure.

Pic#A Thermochromic pigment powder

1.2 In the ceramics industry, thermochromic powders are primarily used in the following products:

• Ceramic mugs, cups: For example, thermochromic ceramic mugs display liquid temperature through color changes to prevent burns.
• Cookware temperature indicators: thermochromic coatings applied to pot handles and other locations indicate the operating temperature.
• Creative ceramic crafts: Artistic ceramics with patterns that change with temperature.
• Anti-counterfeiting labels: Leveraging precise thermochromic properties as a counterfeit prevention measure for high-end ceramic products.

Understanding the basic properties and applications of thermochromic powders is the first step in successfully applying them to ceramic products. Next, it's necessary to select the appropriate application process and material formulation based on specific product requirements.

2. Thermochromic Ink Printing Methods for Thermosensitive Powder on Ceramics

Thermosensitive powders are primarily applied to ceramic surfaces through printing processes. Different printing techniques have their own characteristics, suiting different design requirements and production volumes. Choosing the right printing method is crucial for ensuring the desired color-changing effect, production efficiency, and cost control.

2.1 Screen Printing

Screen printing is the most common and stable method for applying thermochromic powders to ceramic surfaces. It is particularly suitable for flat or slightly curved ceramic surfaces. This method transfers thermochromic printing ink to the ceramic surface via a screen, enabling precise control of ink layer thickness, ensuring a distinct and uniform color change.

Specific steps:

• Ink preparation (thermochromic screen printing ink): Mix the thermal pigment powder with a specialized ceramic ink base in appropriate proportions, typically adding 2-20% of the total ink volume. Stir thoroughly before use to prevent settling. If the viscosity is too high, add an appropriate amount of specialized thinner, typically at a 1:1 or 1:2 ratio (ink:thinner).
• Screen selection: A 150-200 mesh screen is recommended. A mesh count that is too low will result in a thick ink layer, affecting drying and adhesion; a mesh count that is too high will result in a thin ink layer, resulting in a less pronounced color change. For finer patterns, consider using a higher mesh count (e.g., 250 mesh).
• Substrate preparation: The ceramic surface should be clean and free of oil and dirt, preferably pre-wiped with alcohol. To improve adhesion, lightly sand the surface or apply a specialized ceramic primer.
• Printing: Pour the prepared thermochromic ink onto the screen and apply the heat reactive ink evenly with a squeegee at an appropriate angle and pressure. It is recommended to use a white or light-colored background to significantly enhance the contrast and visibility of color changes.

Drying and Curing: Select the appropriate drying method based on the ink type:

• Air-drying: Allow to dry naturally at room temperature for 8-12 hours.
• Bake-drying: Bake at 120°C for 5-10 minutes.
• UV Curing: Cures using a UV lamp (if equipped).

Process Advantages:

• Controllable ink layer thickness, pronounced color change.
• Suitable for complex patterns and multi-color printing.
• Relatively low equipment investment, suitable for small to medium-sized batch production.
• Adapts well to ceramic surface shapes.

Precautions:

• The printing environment temperature should be stable to avoid temperature fluctuations that may affect print quality.
• Check the screen for clogging and clean it promptly after each print run.
• Separate screens for different thermochromic inks to avoid cross-contamination.
• Clean the screen and equipment as soon as possible after printing to prevent thermosensitive ink drying.

Pic#B Thermochromic ink for ceramics

2.2 Spraying Method:

The spraying process is suitable for large areas or irregularly curved ceramic products. It achieves a uniform coating and is relatively simple to operate, but material utilization is low.

Key Points:

• Paint Preparation: Mix the thermochromic powder with transparent ceramic paint to make thermochromic paint, typically at a ratio of 2-5%. Use a specialized thinner to adjust the viscosity to a suitable spray consistency, typically using a 1:1 or 1:2 (paint:thinner) ratio.
• Spraying Equipment: Use a spray gun with a 0.8-1.2mm diameter and an air pressure of 2-3 kg/cm². Maintain a distance of 20-30 cm between the spray gun and the ceramic surface, spraying evenly in a cross-coat pattern.
• Thermochromic Coating Control: It is recommended to spray in thin layers, allowing each layer to dry before applying the next. The total thickness should be controlled within 20-30 μm. Too thick a layer will result in drying difficulties and the risk of cracking, while too thin a layer will affect the color change effect.
• Curing: Air drying takes 12-24 hours; oven drying at 80-120°C for 10-15 minutes is recommended. High-temperature ceramic products require curing at 150-180°C.

Applications:

• Temperature indicators on ceramic cookware handles
• Ceramic crafts that change color throughout
• Daily ceramics with large-area thermochromic effects

Advantages and Limitations:

• Suitable for complex surfaces
• Uniform coating, enabling a gradient effect
• High material loss and high cost
• Requires high technical skills, requiring controlled spray distance and speed

2.3 Pad Printing and Transfer Printing Technologies

Pad printing and transfer printing provide effective solutions for ceramic products with unique shapes or high-precision patterns.

Pad Printing Process:

• Use a patterned pad to apply thermochromic ink.
• Transfer the pattern to the ceramic surface.
• Suitable for small-area, multi-color, and curved printing.
• Commonly used for bottom logos on ceramic cups or partial patterns on handles.

Transfer Printing Technology:

• Print the thermochromic ink onto a specialized transfer film.
• Transfer the pattern to the ceramic surface via heat press or water transfer.
• Enables complex patterns and high-resolution images.
• Suitable for large-scale, standardized production.

Pic#C Thermochromic ink for ceramics

Table Comparison of Printing Methods

Choosing the appropriate printing method requires comprehensive consideration of product design, production volume, cost, and quality requirements. In actual production, multiple printing processes are often combined to achieve optimal results and economic benefits, depending on the specific parts and functional requirements of the ceramic product.

Pic#D Thermochromic ink printing

3. Preparation and Curing Process for Thermochromic Ceramic Coatings

The successful application of thermochromic powders to ceramic products requires not only the appropriate printing method but also a scientific and rational coating preparation and curing process. This step is directly related to the stability of the thermochromic effect, the durability of the coating, and the safety of the product.

3.1 Preparation of Thermochromic Ceramic Coatings

The preparation of thermochromic ceramic coatings is a key step in the application process, and its quality directly determines the color-changing performance and physical properties of the final product. Depending on the application requirements, thermochromic ceramic coatings can be prepared in either oil-based or water-based systems.

Preparation Method for Oil-Based Thermochromic Ceramic Coatings:

• Substrate Selection: Select a dedicated ceramic coating resin as the base material to ensure good adhesion to the ceramic surface and temperature resistance.
• Pigment Addition: Slowly add the thermochromic pigment powder to the base material, typically at a level of 2-5% by weight of the colorant component. Constant stirring should be performed during addition to prevent the formation of agglomerates.
• Dispersion Grinding: Transfer the mixed material to a dispersion grinder, add zirconium beads as the grinding media, and grind at 1000-2000 rpm until the fineness does not exceed 20 μm. This step is crucial to ensuring uniform pigment dispersion.
• Viscosity Adjustment: Adjust the viscosity of the coating using the appropriate diluent according to the printing/spraying method. Oil-based systems typically use a dedicated diluent, but water-based systems can also be customized and diluted with water.
• Curing: The prepared coating should be allowed to stand for 12-24 hours to allow the components to fully blend and eliminate any bubbles introduced during stirring.

Preparation of Water-Based Thermochromic Ceramic Coating:

• Select a water-based ceramic coating resin as the base.
• Use a water-based dispersant to evenly disperse the thermochromic powder.
• Add 3-10% of the total formulation.
• Adjust the viscosity with deionized water.
•  Add an appropriate amount of defoamer and leveling agent.

Precautions:

• Avoid using highly polar solvents such as methanol and ethanol, as these may penetrate the microcapsule wall and impair the color-changing properties.
• Thermochromic powder should not be mixed with common pigments (such as titanium dioxide and carbon black), as this will mask the color-changing effect.
• The stirring speed should be kept to a minimum to avoid damaging the microcapsule structure of the thermochromic pigment powder.
• The preparation process should be carried out in a well-ventilated area, and operators must wear protective equipment.

Constructing a Multi-Layer Coating System

For thermochromic ceramic products that are intended for long-term use or food contact (such as cookware and tableware), a multi-layer coating system is recommended to protect the thermochromic layer while ensuring product safety. Typical three-layer construction method:

Base layer (ceramic coating):

• Sandblast the ceramic surface to a roughness of 2-5μm Ra.
• Preheat the substrate to 40-70°C.
• Spray the ceramic primer and topcoat.
• Cure at 200-280°C to form the base ceramic coating.

Intermediate layer (thermochromic layer):

• Laser polish the cured ceramic coating to increase surface energy.
• Spray or print the prepared thermochromic ceramic coating.
• Select the appropriate drying method (air drying, oven drying, or UV curing) based on the coating type.
• Coating thickness is controlled at 15-25μm.

Top Layer (Transparent Protective Layer):

• Spray a transparent ceramic coating onto the surface of the thermochromic layer.
• Coating thickness: Approximately 10-15 μm.
• Cure at 150-180°C.
• A UV-curable layer can be added to increase surface hardness.

This multi-layer design offers the following advantages:

• The transparent protective layer completely isolates the thermochromic material from food contact, meeting food safety requirements.
• The base ceramic coating provides excellent adhesion and temperature resistance.
• The protective layer protects the thermochromic layer from abrasion and chemical attack.
• It does not affect the observation of the thermochromic coating's color change.

Table: Multi-layer Coating System

Pic#E thermochromic ink supplier + thermochromic pigment supplier - iSuoChem thermochromic mugs

3.2 Curing Process and Technology

The curing process has a crucial impact on the final performance and color-changing effect of the thermochromic ceramic coating. Improper curing conditions may result in reduced color-changing performance or coating defects.

Common Curing Methods:

• Air-Drying: Dry naturally at room temperature. Curing typically takes 8-24 hours. Suitable for small-batch production or experimental applications. The ambient temperature should be maintained between 15-30°C and the humidity below 70%.
• Hot-Air Curing: Set the oven temperature between 80-120°C. Curing takes 5-15 minutes. Heating should be ramped up in stages to avoid sudden temperature changes that may cause coating defects. Ensure proper ventilation to remove solvent vapors.
• UV Curing: Uses ultraviolet light for curing. Curing takes a few seconds to several minutes. Suitable only for UV-curing coatings containing photoinitiators. Highly efficient and suitable for continuous production.
• Infrared Curing: Uses infrared radiation for heating. Curing is fast and energy-efficient. Precise control of radiation intensity and duration is required.

Key Control Parameters:

• Temperature Control: The processing temperature of thermochromic ceramic coatings should be kept below 200°C, preferably not exceeding 180°C. High temperatures can impair the pigment's color-changing properties, especially in the decolorized state, where thermal stability is particularly poor.
• Time Management: Exposure time to high temperatures should be minimized, preferably no more than 10 minutes at 230°C.
• Heating Rate: A gradual heating process is recommended to avoid thermal shock that can cause cracking or blistering in the coating.
• Ventilation: Maintain good ventilation during the curing process, especially when using solvent-based coatings.

For specialized applications, such as ceramic cookware, the curing process requires more precise control. Patent CN107760068A states that when applying a thermochromic indicator coating on the surface of cookware, the transparent ceramic protective layer should be cured at 150-180°C. This relatively mild curing condition helps preserve the properties of the thermochromic material while ensuring the coating's durability.

Through scientific coating preparation and precise curing control, ideal color-changing effects and a long service life can be achieved in thermochromic ceramic products.

4. Precautions for Applying thermochromic Powder to Ceramics

Successfully applying thermochromic powder to ceramic products requires not only mastering the correct process but also paying attention to a number of key factors to ensure stable, safe, and reliable product performance. The following are special considerations for using thermal pigment powder to ceramics, covering aspects such as material selection and process control.

4.1 Material Selection and Storage Tips

Thermochromic Powder Type Selection:

• Select the appropriate color-changing type based on the product's intended use: achromatic (color changes from colored to colorless), chromogenic (colorless to colored), or color-changing (color A changes to color B).
• Select a color-changing temperature that matches the intended use: 31-45°C is commonly used for products that come into contact with the human body; 50-65°C is used for high-temperature warnings.
• Consider the contrast of the color change: dark colors (such as black and blue) typically change more noticeably than light colors.

Substrate Compatibility:

• Thermochromic inks/pigments are suitable for a variety of substrates: paper, fabric, metal, glass, ceramic, plastic, etc.
• The ceramic surface should be smooth and clean, and sandblasted or primed if necessary to improve adhesion.
• Avoid direct application on porous or highly absorbent ceramics, as this may result in uneven color change.

Storage Conditions:

Thermochromic inks/pigments are suitable for a variety of substrates: paper, fabric, metal, glass, ceramic, plastic, etc. Materials should be stored in a sealed, dry, dark place away from direct sunlight.

Ideal storage temperature: 5-30°C, relative humidity below 60%. Unused thermochromic inks/paints should have their openings sealed to prevent solvent evaporation and moisture intrusion. Follow the "first-in, first-out" principle to avoid performance degradation caused by prolonged storage.

4.2 Key Process Control Points:

Temperature Management:

Processing temperatures must be kept below 200°C, with an optimal range of 120-180°C. High-temperature exposure time should be minimized, with no more than 10 minutes at 230°C. Avoid localized overheating and use uniform heating. For multi-layer coating systems, control the curing temperature of each layer to prevent overheating of the underlying layer.

Solvents and Additives:

• Avoid using highly polar solvents (such as methanol and ethanol), as they can damage the microcapsule structure.
• Use a dedicated diluent in the recommended ratio (usually 1:1 or 1:2).
• In epoxy resin systems, carefully select the curing agent to avoid polyamine curing agents, which can cause discoloration failure.
• In PVC systems, avoid using phosphorus-containing stabilizers and plasticizers, as they can cause residual color.

Equipment Selection:

• Avoid using high-shear equipment (such as internal mixers and kneaders), as they can damage the microcapsules.
• For screen printing, a 150-200 mesh screen is preferred.
• For spraying, use a 0.8-1.2mm diameter spray gun with an air pressure of 2-3 kg/cm².
• Use stainless steel or plastic containers and tools to avoid metal contamination.

5. Application Cases of thermochromic Ceramics

5.1 Thermochromic Ceramic Mugs:

Thermochanging ceramic mugs are one of the most common and widely accepted applications on the market. These products typically use a thermochromic pigment powder between 31-45°C. When hot water is poured into the mug, the pattern or color changes, providing a visual indication of the water temperature and preventing burns.

5.2 Cookware Temperature Indicator Coating:

The thermochromic indicator coating on cookware surfaces, described in patent CN107760068A, represents a typical example of a functional application. By applying a thermochromic coating to locations such as pot handles, users can intuitively understand the pot's temperature and avoid overheating.

5.3 Anti-Counterfeiting Authentication Marking:

High-end ceramic products (such as precious porcelain) utilize the precise thermochromic properties of thermochromic pigments to create anti-counterfeiting markings. Consumers can verify the authenticity of the product through a simple temperature change test.

5.4 Creative Art Ceramics:

Artists and designers use thermal color changing powder to create interactive ceramic artworks, creating dynamic visual effects through temperature changes, adding interest and engagement to the work.

6. Development Directions:

6.1 Three-Color and Four-Color thermochromic Powders:

Combining thermochromic powders with different color-changing temperatures can create a richer range of temperature-responsive effects. For example:

The low temperature zone (31°C) displays one color change; the medium temperature zone (45°C) adds a second color change; and the high temperature zone (60°C) triggers a third color change.

This blend of three-color thermochromic powders can be used to indicate different temperature levels.

Pic#F  iSuoChem Three-Color thermochromic technology

6.2 Environmentally Responsive Smart Ceramics:

Combining thermochromic technology with other functional materials to develop smart ceramic products that respond comprehensively to environmental conditions: thermochromic + Light-sensitive: Responding simultaneously to changes in temperature and light.

With advances in materials science and printing technology, the application areas of thermochromic ceramic products will continue to expand. iSuoChem is also actively developing various cosmetic-grade and food-grade thermochromic powders. This will continue to be a future research and development trend.

FAQ - Common Problems and Solutions:

Unclear color change effect:

Possible Causes: Insufficient thermochromic powder added, too thin an ink layer, inappropriate background color.

Solution: Increase the thermochromic pigment powder content to 5-20%; increase Increase the number of printing/spraying cycles; use a white or light-colored background.

Poor Adhesion:

Possible Causes: Insufficient ceramic surface preparation, incomplete curing, material mismatch.

Solution: Enhance surface cleaning and roughening; adjust curing temperature and time; use a ceramic-specific primer.

Rapid Color Loss:

Possible Causes: Overheating, UV exposure, chemical attack.

Solution: Strictly control process temperature; add UV absorbers; avoid strong acid or alkaline environments.

Color Retention:

Possible Causes: Partial irreversible changes caused by excessive temperature, material quality issues.

Solution: Lower operating temperature; replace high-quality thermochromic materials; check for incompatible substances.

By paying attention to these key considerations, the success rate and quality stability of thermochromic ceramic products can be greatly improved.