HZ info,The study successfully developed a water-based acrylic copolymer emulsion for high-performance renovation of old ceramic tiles. The emulsion achieves superior adhesion to ceramic tile substrates and densification of the coating structure by introducing a diacetone acrylamide (DAAM)/adipate dihydrazide (ADH) room-temperature self-crosslinking system and a silane coupling agent. Application performance tests show that the coating achieves Grade 0 dry adhesion on polished tiles, and the pencil hardness rapidly reaches 2H within 14 days of air drying. Especially in the extreme tests of 75°C heat baking and 100°C boiling water for 4 hours, the film's hardness retention, heat softening resistance, and wet stability are significantly better than market  standards, fully meeting the requirements of high-durability applications such as bathrooms and kitchens.

 Keywords: Tile color change; Acrylic emulsion; Room temperature crosslinking; High hardness; Wet adhesion

1. Research Background and Introduction

1.1 Market-driven and Technical Challenges

With the continuous expansion of existing housing renovation and partial renovation market, the demand for environmentally friendly and efficient old tile renovation solutions has surged. The traditional "re-laying" method has drawbacks such as long construction period, high cost, and the generation of large amounts of construction waste. Water-based tile color change coatings, due to the environmentally friendly and healthy (non-toxic and odorless), convenient construction, and cost-saving advantages, have become an ideal renovation alternative.

 However, tile renovation places extremely stringent requirements on coating performance:

 1. Adhesion Limit Challenge: Polished tiles, vitrified tiles, etc., are low surface energy substrates with dense and smooth surfaces. The coating must have an adhesion level of at least 0 or 1 (GB/T 9286-2021) to ensure that the coating does not peel off due to daily friction or moisture.

2. High Hardness and Durability: Applied in areas such as kitchens and bathrooms, the coating needs to withstand frequent abrasion, moisture erosion, and temperature changes. The coating must have a pencil hardness of H or higher (GB/T 6739-2022) to provide effective scratch resistance and a long   lifespan.

3. Stain and Chemical Resistance: In daily life, the coated surface will inevitably come into contact with stains such as dust, oil, tea, coffee, dish soap, and laundry detergent. Therefore, the coating must have strong resistance to everyday stains (refer to GB/T 23999-2009) to maintain its appearance over long-term use.

 4. Limitations of Single-Component Systems: Currently available single-component acrylic resin coatings generally have a pencil hardness of 2B-HB, far below the H requirement. Furthermore, the hardness decreases significantly after water resistance testing, and they may even blister and peel off, making it difficult to meet high-performance requirements.

1.2 Design Strategy and State of YC-8699 Emulsion

To overcome the aforementioned technical challenges, this study developed YC-8699 emulsion using functional monomer modification technology and constructed a core room-temperature self-crosslinking system:

 Crosslinking Mechanism: Diacetone acrylamide (DAAM) was introduced as a functional monomer, and adipate dihydrazide (ADH) was added as a crosslinking agent after polymerization. The carbonyl group on DAAM reacts with the hydrazide group on ADH at room temperature to form stable acylhydrazone bonds, constructing a high-density polymer network structure, which is key to achieving high hardness and high durability.

Adhesion Enhancement: Silane coupling agents such as vinyltrimethoxysilane were added to the formulation to promote chemical bonding between the coating film and the inorganic ceramic tile substrate, ensuring ideal dry and wet adhesion.

Photo 1 YC-8699 Emulsion

YC-8699 emulsion is a milky white liquid with a bluish sheen (as shown in Photo 1), and has the following typical properties: polymer type is an acrylate-modified copolymer, solids content is 45%, and minimum film-forming temperature (MFFT) is 50°C.

Table 1: Typical Properties of YC-8699 Emulsion

Table 2: Basic Formula for Tile Color Changing Paint

Usage proportion: Mix component A and component B at a proportionof 100:2 (coating:hardener) before use.

2.  YC-8699 Application Performance and Photo Comparison

YC-8699 emulsion was prepared into a two-component tile color-changing coating and tested on polished tiles after sanding. The dry film thickness was approximately 30-40 μm.

2.1 Comparison of Adhesion and Hardness Increase

The hardness and adhesion of the coating film are the primary indicators for evaluating the performance of tile paint.

Table 1: Comparison of Drying Performance (7 days air-drying) of YC-8699 and Market Sample (Two-component)

Table 2: Comparison of pencil hardness increase rate (air drying time)

Photo 2/3:Hardness climbing grid comparison of YC-8699 (left) and market sample (right).

The photos compare the scratch resistance of YC-8699 (left) and the market sample (right) after 1 to 7 days of air drying, as determined by pencil hardness testing. YC-8699 exhibits less coating peeling and  scratches at each stage compared to the market standard sample (right), demonstrating its faster hardness build-up and stronger adhesion, especially with a final hardness of 2H, far exceeding the competitor's F grade.

Discussion: As shown in Photo 2 and 3, the crosslinking system of YC-8699 (left) enables it to reach a

high hardness of 2H after 14 days of air drying, while the market standard sample (right) only reaches an F grade, a difference of two grades. This high hardness is attributed to the dense polymer network constructed by the DAAM/ADH crosslinking system at room temperature, effectively improving the coating's scratch resistance and abrasion resistance.

2.2 Extreme Durability: Heat and Water Resistance

Durability is crucial for the long-term use of tile coatings in humid and high-temperature environments such as kitchens and bathrooms.

Table 3: Heat Resistance Hardness Comparison (Oven 75°C/10min)

Photo 4/5: Hardness comparison of YC-8699 (left) and market sample (right) after baking at 75°C.

The photos show the scratches after baking at 75°C for 10 minutes using a pencil H-grade test. The scratches on YC-8699 (left) are significantly shallower, with less coating damage. This visually demonstrates that the coating structure of YC-8699 exhibits excellent heat softening resistance and maintains high mechanical strength even at high temperatures.

Table 4: Extreme Hot Water Boiling Resistance Comparison (100°C boiling water for 4 hours)

Comparison of adhesion after water bath and boiling at 100°C.

Photo 6 shows the test conducted in a 100°C thermostat water bath; Photo 7 shows that after boiling for 4 hours, the coating residue rate of YC-8699 (left) in the cross-cut area was significantly higher than that of the market sample (right). This strongly demonstrates that the high-density cross-linked structure of YC-8699 can effectively resist water molecule penetration and thermal swelling, ensuring wet adhesion and structural integrity under extreme humid and hot conditions.

Discussion: As shown in photo 4/5 and 6/7, the cross-linked network of YC-8699 endows the coating

with the ability to resist extreme environments. Especially after boiling for 4 hours, the standard coating was severely softened and swollen ("easily scratched with a fingernail"), while YC-8699 only "slightly softened," a key technological breakthrough that meets the demanding requirements of washrooms and bathrooms. 

2.3 Stain Resistance and Chemical Corrosion Resistance

Table 5: Stain (Dust) Resistance Comparison (Washed after 7 Da  s of Curing)

Photo 8 shows the national standard gray sample; Photo 9 shows that after 7 days of curing with liquid dust coating, the residual dirt on the surface of YC-8699 (left) is significantly lower than that of the market standard sample (right); Photo 10 shows the comparison after washing, with the YC-8699 surface being cleaner.

Discussion: As shown in Table 5 and Photo 8/9/10, the higher reflectivity of the YC-8699 coating and the less visible dust residue indicate that its coating surface is denser and smoother, less prone to dust adsorption, and easier to clean than competing products.

Photo 11/12: Daily Stain Resistance

Photo 11 shows a scenario where the coating is soaked in various household stains such as coffee, tea, and vinegar; Photo 12 shows that after the stains were completely cleaned, there was no obvious stain residue on the surface of the YC-8699 sample.

Discussion: YC-8699 exhibits excellent resistance to common household stains such as coffee,tea, and vinegar (see photo 11/12), meeting the anti-stain requirements for daily use.

3. Conclusion

The cross-linked acrylic emulsion YC-8699, specifically developed for tile color changing, successfully achieved a comprehensive improvement in coating performance through a highly efficient DAAM/ADH room temperature cross-linking network.

YC-8699 has the following core advantages:

1. Ultra-high hardness: The hardness can reach 2H after 14 days of drying, far exceeding that of competing products (F grade), providing excellent scratch resistance.

2. Excellent heat resistance: 75°C. High hardness retention after high-temperature baking, exhibiting excellent heat softening resistance.

3. Ultimate water resistance: Under extreme conditions of boiling in water at 100°C for 4 hours, the wet structure of the coating film remains intact, with wet adhesion and stability significantly superior to market standards.

4. Overall durability: Superior performance in both abrasion resistance and stain resistance.

The successful development of YC-8699 emulsion provides strong technical support for the high

performance and high durability of water-based ceramic tile color-changing coatings, and contributes to the national strategy of old building renovation.