1.Determination of Titanium Dioxide Content: Place the sample in a drying oven at 105°C for 3 hours. Dissolve the sample using sulfuric acid and ammonium sulfate, then add water and hydrochloric acid. Add a piece of aluminum metal to reduce tetravalent titanium. After cooling, use ammonium thiocyanate solution as an indicator and titrate with 0.1 mol/L ferric ammonium sulfate standard solution.
2.Whiteness Measurement: Accurately weigh 2g (accurate to 0.0002g) of the sample, place it in the middle of the lower plate of a grinding machine, add 0.8ml of refined linseed oil, and mix thoroughly until the sample becomes a paste. Use a spatula to spread the paste into a circle approximately 50mm in diameter from the center of the bottom plate. Close with a glass plate and apply about 1kN force, grind four times, each time for 50 revolutions. After each grinding, gather the paste with a spatula and spread it again into a circle. After grinding, store the paste for later use. Prepare the same amount of standard sample in the same manner. Spread both the standard and test samples on a glass plate in the same direction, use a wet film applicator to create opaque strips no less than 25mm wide and contact edges no less than 40mm long. Observe under scattered daylight or artificial light at a 45-degree angle to compare their whiteness. The color of the sample should be not less than, slightly inferior to, or inferior to that of the standard sample.
3.Comparative Hiding Power Test: Weigh 5g of blue paste (accurate to 1mg), place it in the middle of the lower plate of a grinding machine, and add a certain amount of standard pigment sample (accurate to 0.1mg). Mix well, spread into a circle, close with a glass plate, apply 1kN force, and grind four times, each time for 25 revolutions. Prepare a similar paste with the test sample. Choose two standard samples whose color intensity is closest to that of the test sample. Compare their surface color intensity under scattered daylight or artificial light. The relative hiding power of the test sample compared to the standard sample is calculated as 100m0/m1.
4.Oil Absorption Measurement: Weigh 10g of the sample (accurate to 0.1g) and place it on a flat surface. Gradually add refined linseed oil using a burette, not exceeding 10 drops at a time. Continue adding oil until the mixture forms a uniform paste without cracking or crumbling. Record the amount of oil used. All operations should be completed within 20-25 minutes.
5.pH Value Determination of Pigment Water Suspension: Weigh 3g of the sample (accurate to 0.01g) into a high-form weighing bottle, add 27ml of distilled water to prepare a 10% pigment suspension. Shake vigorously for 1 minute, let stand for 5 minutes, remove the stopper, and measure the pH value of the suspension accurately to 0.1 unit.
6.Determination of Volatiles at 105°C: Place the open weighing bottle in a drying oven at 105±2°C for 2 hours, cool in a desiccator, cover, and weigh to an accuracy of 1mg. Place 10±1g of the sample layer at the bottom of the weighing bottle, cover, and weigh accurately to 1mg. Remove the cover, place the weighing bottle and sample in a drying oven at 105±2°C for 1 hour, cool to room temperature in a desiccator, cover, weigh accurately to 1mg, reheat for 30 minutes, and repeat until the difference between two consecutive weighings does not exceed 5mg. Record the lower weight.
7.Residue on Sieve Determination: Disperse the sample in water with dispersing agents, use rotating water flow to centrifuge, rinse fine particles through the sieve, dry coarse particles retained on the sieve, and weigh them. Weigh a certain amount of the sample (accurate to 0.001g) into a suitable volumetric flask, generally 5-50g. Add an appropriate amount of water containing dispersing agents, stir for 30 minutes to disperse the sample into a freely flowing suspension. Use mechanical flushing equipment to adjust the water pressure to 300±20Kpa, rinse continuously for 10 minutes, finally use distilled water if necessary. Dry the residue on the sieve at 105±2°C for 1 hour, cool in a desiccator, weigh accurately to 0.1mg.
8.Water-Soluble Substances Determination: Weigh 10g of the sample (accurate to 0.01g), place it in a beaker, moisten with a few milliliters of water, add 200ml of water, boil for 5 minutes, cool rapidly to room temperature, transfer to a 250ml volumetric flask, dilute to volume, filter repeatedly until clear. Evaporate 50ml of clear filtrate to dryness in a water bath, transfer to a drying oven at 105±2°C, cool in a desiccator, weigh accurately to 1mg, repeat heating and cooling until the difference between two consecutive weighings does not exceed 10% of the final value, which represents the water-soluble substance content.
9.Electrical Conductivity Measurement: Weigh 20±0.01g of pigment sample, transfer to a 400ml beaker, moisten with 4-16g of boiling water, stir well. Slowly add boiling pure water while stirring to form a homogeneous paste, dilute to a total volume of 200g, boil for 5 minutes, cool to about 60°C, filter directly using filter paper, discard the first 10ml of filtrate. Rinse the platinum black electrode with pure water and filtrate, immerse the electrode in the filtrate at 23±0.5°C, position it about 10mm below the liquid surface, read the conductivity value on the conductivity meter (average of five readings).
10.Hiding Power Determination: Weigh 3-5g of the sample (accurate to 0.2g), add 2ml of ink varnish measured by a pipette, place on the frosted glass surface of a planar grinder, mix uniformly with a spatula, apply 5MPa pressure, grind for 100 or 200 revolutions, add remaining ink varnish, mix uniformly, store for later use. Apply the pigment paste evenly on a black-and-white grid board, observe under two 15W fluorescent lamps in a dark box, determine when the black-and-white grid is exactly covered. The relative error of parallel determinations should not exceed 10%, take the average value as the result.
11.Dispersion Evaluation: Grind the test and standard samples simultaneously in a paint mixer under known conditions, measure the dispersion degree at certain intervals using a scraper fineness gauge, plot curves based on these results. Each pigment’s dispersion time or fineness reached after a certain grinding time indicates its relative ease of dispersion. Factors affecting dispersion must be standardized: container capacity and size; nature and volume of glass beads; volume of grinding material (pigment plus dispersing medium); properties of the dispersing medium; grinding time; concentration of pigment in the grinding material. For all pigments, conduct tests at three different grinding concentrations unless the concentration is already known. Keep the total volume of grinding material constant.
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