1. Definitions of terms
In the fields of coatings, inks, adhesives, and various chemical additives, "solids content" is a fundamental physical parameter that describes the composition of a product. It usually refers to the percentage of the mass of non-volatile substances remaining in the total sample mass after the volatile components (such as water, solvents, etc.) are removed by heating and volatilization under specified conditions.
In practical application, there are many equivalent or similar expressions of this term, and its connotations need to be distinguished according to the specific context:
Total solids content/total solids: The most widely used refers to the sum of all non-volatile substances in the sample.
Non-volatile content: commonly found in the standards of coatings, resins and other film-forming substances, its measurement conditions (temperature, time) have strict regulations to simulate the actual drying process.
Solid content/solid content: a more common abbreviation in industrial production and quality inspection.
It should be clear that the determination of solid content is the total amount of all non-volatile components such as resins, pigments, fillers, additives, etc., which is not equivalent to the content of active ingredients or active substances in the product. The latter usually requires determination by other chemical analysis methods.
2. Standard testing methods and technical points
The principle of determination of solids content is relatively uniform, and the core is to remove volatile components from the sample by physical methods and perform weighing calculations. The standard methods of various industries at home and abroad are based on this principle, but there are differences in the specific operating conditions.
1. Classic oven constant weight method
This is the oldest and most recognized benchmarking method, which has been adopted by many national standards. The basic operation process is to put a certain mass of samples in a weighing vessel with a constant weight and dry them to a constant weight at a specified temperature (such as 105℃ ± 2℃) to a constant weight (i.e., the difference in mass between two consecutive weighing weights does not exceed the specified value, such as 0.001g). The calculation formula is as follows:
Solids content (%) = (sample mass after drying / sample mass before drying) × 100%
The method is highly accurate and repeatable, but it is time-consuming, often taking hours.
2. Infrared rapid assay
In order to meet the demand for rapid quality inspection in modern production, rapid moisture/solids content analyzers based on infrared or halogen heating technology are widely used. These instruments use an annular heating tube to heat the sample quickly and evenly, and integrate a high-precision balance for real-time weighing, which automatically calculates and displays the results in minutes. Although it is fast and convenient, it is often calibrated against the oven method to ensure data consistency.
3. Other assay methods
In addition to the above mainstream methods, refractometer method (indirectly estimating soluble solids by measuring the refractive index) and Karl Fischer method (calculating solids after determining moisture) will also be used according to sample characteristics and industry habits.
3. Main reference standards
Solids content determination must be carried out in accordance with the corresponding national, industry or international standards to ensure data comparability and reliability. The following table lists some of the important criteria in these areas:
| Standard type | Standard number | Standard Name (Field) |
| Chinese national standards | GB/T 1725 | Coatings, varnishes and plastics Determination of non-volatile content -1 |
| Chinese national standards | GB/T 2793 | Determination of non-volatile content of adhesive-4 |
| International standards | ISO 3251 | Coatings, varnishes and plastics – determination of non-volatile content -4 |
| Industry approach | — | Printing and dyeing auxiliaries solid content determination method (often refer to GB/T 23883, etc.) |
4. Application in coatings, inks and related fields
As a basic indicator, solid content runs through the whole process of product research and development, production, quality control and cost accounting.
1. Coatings industry
In coating formulations, solids content directly affects the construction performance, film thickness and final cost of the product. For example, the solid content of architectural latex paint is related to its coverage power and consumption per square meter; The solid content of industrial anti-corrosion coatings is closely related to the dry film thickness that can be achieved by one coating. During production, monitoring the solids content of each batch of resin, emulsion, or finished coating is a critical step in ensuring formulation accuracy and batch-to-batch consistency.
2. Ink industry
For printing inks, solids content is an important parameter to control ink viscosity, transferability, drying speed, and gloss of prints. Too high solids content may lead to poor ink fluidity and poor transfer; Too low may cause problems such as slow drying and insufficient color saturation. Precise control of solids content is crucial for ensuring the stability of the printing process and the quality of printed materials.
3. Textile printing and dyeing auxiliaries
In the textile industry, all kinds of slurries, coating adhesives, and finishing agents (such as softeners and waterproof agents) need to be calibrated for their solid content. This is not only related to the effective application of additives, but also directly related to the sizing rate, weight gain rate and functional finishing effect of textiles. For example, when preparing slurry at a specified concentration, it must be accurately calculated and fed based on the solids content of the slurry and the solids content required by the process.
4. Quality and cost control
From an economic point of view, solids content is a direct bridge between the price of liquid products and the cost of solid active matter. The purchaser can calculate the actual cost of the active ingredient per unit mass by solids content. On the production side, fluctuations in solid content may lead to instability in raw material consumption, so its detection is an important part of internal cost control.
5. Testing precautions and common instruments
In order to ensure the accuracy of the test results, it is necessary to pay attention to the following during operation: the sample should be uniform and representative; The weighing process should be fast to prevent solvent volatilization; The temperature and time of the oven method must be strictly controlled; Use a dryer to cool and prevent sample moisture absorption; The parallel test results should be within the allowable error range.
Commonly used testing instruments include:
Precision electronic balances:The basis of weighing is usually required to be 0.001 g.
Electric blast drying oven:The core equipment of the oven method.
Infrared/Halogen Fast Solids Content Tester:For rapid inspection on the production floor.
In summary, solids content is a fundamental and key technical parameter in the field of coatings, inks and related chemicals. A deep understanding of its definition, proficiency in standard testing methods, and effective application in production and quality control practices play a fundamental role in ensuring stable product quality, optimizing process formulations, and achieving precise cost control.