Paint and Coating Technology

Compatibility of solvents with binders is crucial in coatings and formulation science for several reasons:

1. Proper Dissolution and Stability: The binder (resin or polymer) must dissolve or disperse uniformly in the solvent. Incompatible solvents can cause phase separation, incomplete dissolution, or haziness in the final product.

2. Application Properties: Solvent compatibility affects viscosity, flow, leveling, and sprayability. Incompatible systems may result in poor application performance or surface defects like orange peel, cratering, or sagging.

3. Drying and Film Formation: The evaporation rate of solvents must match the binder system. Incompatibility can cause issues like skinning, poor coalescence, or uneven drying, leading to weak or brittle films.

4. Adhesion and Performance: Poor solvent-binder interaction can reduce adhesion to substrates and negatively impact mechanical and chemical resistance of the cured coating.

5. Shelf Life and Storage: A compatible solvent system ensures good stability over time. Incompatible blends may lead to gelling, phase separation, or sedimentation during storage.

For example: You should choice solvents for epoxy according to its compatibility , polarity and evaporation rate.

8 months ago | [YT] | 3

Paint and Coating Technology

In coating technology, an impact test evaluates a coating’s resistance to mechanical deformation or cracking when subjected to a sudden impact. It is used to assess the flexibility, adhesion, and durability of the coating film.

Purpose in Coatings:

• Determines whether a coating can withstand impact forces (like dropping, striking, or bending) without cracking, delaminating, or losing adhesion.
• Ensures coatings are suitable for surfaces exposed to mechanical stress (e.g., metal structures, machinery, vehicles).

Common Test Method:

ASTM D2794 – Standard Test Method for Resistance of Organic Coatings to the Effects of Rapid Deformation (Impact)

Why It’s Important:

• Ensures coating performance under real-world mechanical abuse.
• Helps predict field durability, especially for industrial, automotive, and protective coatings.

Calculation :

• Mass (m) = 1.5 kg
• Height (h) = 0.65 m
• Gravity (g) = 9.81 m/s²
• 1 Joule = 8.8507 in·lbf

Potential Energy (mgh)


E = mgh = 1.5 X9.81X0.65 = 9.56 Joules


Convert to in·lbf:

9.56X8.8507= 84.57 in·lbf

8 months ago | [YT] | 3

Paint and Coating Technology

Sagging in coatings (like paints or epoxies) refers to the downward flow of the coating after application, leading to uneven film thickness, drips, or runs. It’s a common defect, especially on vertical or inclined surfaces.

Why Sagging Happens

1. Low Viscosity: The coating is too fluid to hold its shape on vertical surfaces.
2. Too High Film Thickness: Applying too thick a layer in one go.
3. Poor Rheology Control: Absence or insufficient use of thixotropic/rheology modifiers.
4. Incorrect Solvent Blend: Slow-evaporating solvents can reduce viscosity too much during application.
5. High Temperature or Humidity: Affects solvent evaporation and viscosity behavior.
6. Substrate Angle or Shape: Steep angles promote sagging more.

How to Cure or Prevent Sagging

1. Optimize Viscosity:
• Increase solids content.
• Reduce solvent load or use faster-evaporating solvents.
2. Add Rheology Modifiers:
• Use fumed silica, urea-modified polyurethanes, or castor oil derivatives.
• For epoxy systems, polyamide resins or thixotropic agents can help.
3. Apply in Thinner Coats:
• Multiple thin coats are better than one heavy coat.
4. Adjust Spray Parameters (if sprayed):
• Reduce fluid pressure or increase atomizing pressure.
• Maintain correct spray distance and technique.
5. Modify Curing Profile:
• Avoid fast curing at high temperatures before solvents can evaporate.
• Allow flash-off time before baking or force drying.
6. Test Using Sag Resistance Test:
• Use a sagging bar (e.g., ASTM D4400) to evaluate your formulation.

8 months ago | [YT] | 4

Paint and Coating Technology

The Cross Hatch Adhesion Test (also known as Cross Cut Test) is a standard method to evaluate the adhesion of paint or coatings to a substrate. It’s commonly used in industrial coatings, quality control, and R&D. Here’s how it’s typically performed:

Standard Reference:

• ISO 2409
• ASTM D3359 (Method B)

Procedure Overview:

1. Surface Preparation:
• Ensure the coated surface is clean and dry.
• The coating should be fully cured before testing.
2. Cutting the Grid:
• Use a cross hatch cutter or a sharp blade to make a series of parallel cuts (usually 6 or 11) spaced at 1 mm or 2 mm intervals depending on coating thickness.
• Make a second set of cuts perpendicular to the first to form a grid pattern.
3. Apply Adhesive Tape:
• Use a pressure-sensitive adhesive tape (e.g., 3M 600 or similar).
• Press the tape firmly over the cut area and smooth it out to remove air bubbles.
• Pull the tape off sharply at a 180° angle.
4. Evaluation:
• Examine the grid for any paint removal.
• Rate the adhesion based on the amount of coating removed using a standardized scale.

Rating Scales:

ISO 2409 Scale (0 to 5):

• 0 – No coating removed (best adhesion)
• 5 – More than 65% of the grid area is removed (poor adhesion)

ASTM D3359 Scale:

• 5B – Edges of cuts are smooth; no coating removed
• 4B – Small flakes of coating are detached at intersections
• 0B – More than 65% of area removed

Key Considerations:

• Use appropriate spacing based on coating thickness.
• The substrate and coating type influence results.
• Perform the test in multiple locations for reliability.

8 months ago | [YT] | 1

Paint and Coating Technology

Chemical Resistance Test Method (ISO 2812-4 – Immersion / Spot Test)

1. Test Panel Preparation

• Apply the coating to standard concrete or metal panels (e.g., 150x70 mm).
• Cure the coating fully as per manufacturer specifications.

2. Selection of Test Chemicals

Common chemicals used for floor coatings include:

• Acids: Sulfuric acid, hydrochloric acid
• Bases: Sodium hydroxide
• Solvents: Xylene, ethanol, MEK
• Oils, fuels, cleaning agents

3. Exposure Method

Spotting (ISO 2812-4) – Typical for flooring:

• Place a drop (e.g., 1 mL) of each chemical on the coated surface.
• Cover with watch glass or foil to prevent evaporation.
• Leave for set periods: 1h, 8h, 24h, 72h, or longer depending on requirement.

Immersion (optional for harsher testing):

• Immerse coated panel partially or fully in the chemical.

4. Evaluation of Results (per ISO 4628)

After exposure, remove chemicals, rinse with water, and assess:

• Blistering (ISO 4628-2)
• Discoloration
• Softening
• Cracking or loss of gloss
• Rate damage visually using standard ISO 4628 grading scales.

Optional Tests

• Adhesion test after chemical exposure (ISO 2409 or ASTM D3359)
• Hardness change (ASTM D3363 pencil hardness)
• Gloss loss (ISO 2813)

8 months ago | [YT] | 1

Paint and Coating Technology

Here is a sample report template for ASTM B117 Salt Spray Test that you can adapt for your own testing:

ASTM B117 Salt Spray (Fog) Test Report

1. General Information

Item Description
Test Standard ASTM B117
Client / Project Name [Enter Name]
Sample Description [e.g., Epoxy-coated steel panel]
Sample ID / Code [ID Number]
Coating Type [e.g., Epoxy, Polyurethane]
Coating Thickness [e.g., 80 µm]
Substrate [e.g., Mild Steel]
Number of Samples [e.g., 3 panels]
Date of Test Start [DD/MM/YYYY]
Test Duration [e.g., 240 hours]
Test End Date [DD/MM/YYYY]

2. Test Conditions

Parameter Value
Salt Solution 5% NaCl by weight
Spray Chamber Temp 35 ± 2 °C
pH of Salt Solution 6.5–7.2
Spray Rate 1.0–2.0 mL/hour per 80 cm²
Specimen Angle 15°–30° from vertical
Chamber Type [e.g., Q-Fog SSP600]

3. Evaluation Summary (at Intervals)

Time (Hours) Rust Area (%) ASTM D610 Grade Blistering (ASTM D714) Creepback (mm) Notes / Observations
24
96
240
500
1000

(Fill only up to the duration tested)

4. Visual Evidence

• Attach photographs of specimens at different intervals.
• Mark and highlight any significant corrosion, blisters, or failures.

5. Corrosion Rate Calculation (if applicable)

Use only if mass loss data is available.

Corrosion Rate (mpy) = (534 × W) / (D × A × T)
Where:
W = weight loss (mg)
D = material density (g/cm³)
A = exposed area (in²)
T = time (hours)

6. Conclusion / Assessment

• Performance Rating: [Pass / Fail based on criteria]
• Coating Performance: [Good / Moderate / Poor]
• Remarks: [e.g., Minimal rusting observed after 500 hours. No blistering or creepback beyond 2 mm.]i

8 months ago (edited) | [YT] | 3

Paint and Coating Technology

Paint defect ! Stoving paint putty can fail after heat! What is the solution do you know?

2 years ago | [YT] | 0