Definition
A softness tester is a specialized testing device used to quantify the soft properties of materials. It simulates the mechanical behavior of human touch, applies bending or extrusion to specimens such as paper, textiles, nonwovens, films and certain composites, and measures their ability to resist deformation, so as to obtain physical parameters that characterize the softness of the material, such as softness value, bending stiffness or bending force. The instrument plays a key role in quality control, product development, and standard compliance verification.
Principle
The core working principle of the instrument is based on the theory of bending deformation in classical mechanics. Typically, a specimen that has been cut to size is placed between the test head and the sensor platform in a specific geometry. The test head, controlled by a drive mechanism, exerts pressure on the specimen at a constant speed, causing it to bend or sink into a slit. The sensor monitors changes in force and displacement in real time. When the specimen is bent to a preset depth or angle, the maximum force value or integral force value recorded is the softness-related index. The basic mechanical relationship can be approximated as the relationship between the moment of material resistance to bending and the bending deformation, and for the simple model, the bending stiffness D can be derived from the formula D = E × I Partly reflected, where E is the elastic modulus of the material and I is the moment of inertia of the section. The instrument measures the macroscopic expressiveness of this resistance.
Measurement method
The measurement process must strictly follow relevant national or international standards, such as GB/T 8942, ISO 2493 or TAPPI T543. First, the samples are balanced under standard temperature and humidity conditions to eliminate environmental disturbances. Subsequently, a rectangular specimen of the specified size is prepared using a standard cutting knife. Place the specimen exactly in the designated position on the test bench to ensure it is flat and wrinkle-free. The test procedure is initiated, and the indenter is pressed down at the speed specified by the standard, allowing the specimen to pass through a fixed-width slit or create a specific bend. The instrument automatically records the change curve of the force value throughout the process and calculates the softness value, usually expressed in millinewtons (mN) or grams (gf). Each sample is tested with multiple specimens, and the final results are averaged to ensure reliability.
Influencing factors
The accuracy and repeatability of measurement results are affected by a variety of factors. The properties of the material itself are fundamental factors, including the fiber structure, thickness, quantitation, elastic modulus of the substrate, and whether it has been treated with softeners. Environmental conditions, especially ambient temperature and relative humidity, affect the moisture content and mechanical state of materials, so standard testing requires them to be performed in laboratories with constant temperature and humidity. Instrument parameter settings, such as drop pressure speed, slit width, indenter shape, and specimen size, must be consistent with the selected test standard. Operational normatives, such as specimen placement direction, flatness, and consistent clamping, can also introduce deviations. In addition, the specimen's pretreatment history, such as storage time and conditions, should also be taken into account.
Applications
The application of softness testers runs through the material research and development and quality control process of multiple industries. In the paper industry, it is used to evaluate the soft feel of tissue paper, toilet paper, napkins, wrapping paper, and other products, and is a key test item to enhance the consumer experience. In the field of textiles and nonwovens, instruments are used to test the softness of materials such as nonwovens, wipes, and garment interlinings. In the film and flexible packaging industry, it can be used to evaluate the tactile feel of certain flexible packaging materials. In addition, in scientific research institutions and quality inspection departments, the instrument is used for the development of new materials, process improvement research, and product conformity determination according to trade standards.
Equipment selection considerations
When choosing the right softness tester, a comprehensive evaluation is required. First of all, the main test material type and the standard system to be followed should be clarified to ensure that the testing principle, range, accuracy and accessories of the instrument meet the standard requirements. The core parameters include the range and resolution of the force sensor, the accuracy of displacement control, the test speed range, and the adjustability of the slit width. The instrument's software should support the required standard test flow and provide clear data logging and curve analysis capabilities. The long-term stability of the equipment, the ease of calibration, and the manufacturer's technical support and service capabilities are also important considerations. At the same time, consider the sample throughput of the laboratory and choose manual, semi-automatic, or fully automatic models to suit different efficiency needs. The user-friendly interface and the completeness of the training help ensure the standardization and efficiency of testing.