Definition
A paper tear analyzer is a specialized laboratory instrument used to determine the tear resistance of paper, cardboard and other sheet materials. The measurement results are usually expressed as tear degree or tear index, which reflects the ability of the material to resist tear propagation and is one of the important parameters for evaluating the mechanical strength of the material.
Principle
The working principle of the instrument is based on pendulum energy conversion. During the test, the specimen is clamped in a fixture and an incision is pre-made. The pendulum is released to make it fall, and the kinetic energy of the pendulum is used to tear the specimen from the incision to a certain length. The force required to tear the specimen is calculated by measuring the energy consumed by the pendulum during the tearing process, i.e. the difference between its initial potential energy and the remaining potential energy after tearing. This force value is converted internally by the instrument and finally shows the degree of tear in millinewtons (mN) or Newtons (N). For paper, the tear index is often calculated in conjunction with quantitative calculations, and the relationship can be expressed as:
Tear index = average tear / quantitative
Among them, quantification refers to the mass per unit area, measured in grams per square meter.
Measurement method
The standard testing process usually follows international standards such as ISO 1974 or national standards GB/T 455. First, cut the specified number of specimens along the paper vertically and horizontally. The specimen is clamped into the instrument fixture and a standard length cut is pre-cut using a blade. The pendulum is released to complete the tearing action, and the instrument pointer or sensor records the force value. The average of the longitudinal and transverse test results is calculated separately as the degree of tearing in that direction. If the tear index is to be calculated, the quantification of the specimen must be determined in advance.
Influencing factors
Measurement results are influenced by a variety of factors. The characteristics of the material itself are key, such as fiber type, length, bond strength, and the manufacturing process of the paper. Environmental conditions cannot be ignored, and changes in temperature and humidity will cause changes in fiber moisture content, which will affect its flexibility and strength, so temperature and humidity balance must be carried out under standard temperature and humidity conditions before testing. Operational standardization is also important, and factors such as whether the cutting direction of the specimen is accurate, whether the incision length is consistent, and whether the pendulum release is stable may introduce deviations.
Application:
This instrument is widely used in the production quality control and product development stage of the paper industry to evaluate the tear resistance of various cultural papers, packaging cardboards, household papers, etc. In the field of packaging materials, it is used to test the load-bearing and anti-damage ability of corrugated boxes, paper bags, etc. In addition, it is also used in the research and development and quality inspection of textile non-woven fabrics, plastic films, metal foils and other related sheets, providing basic data for the study of material mechanical properties.
Selection
The measurement range should be considered when selecting an instrument, which should cover the expected tear strength of the material to be measured. The accuracy and resolution of the instrument must meet the requirements of relevant standards for test data. Examine whether the instrument has automatic detection, data storage and transmission functions to meet the needs of modern laboratory informatization. The fixture design of the instrument should be able to securely hold samples of different thicknesses and stiffness, and be easy to operate. At the same time, calibration services, technical support, and certification of compliance with current international and national standards provided by instrument manufacturers are also important bases for ensuring long-term validity and comparability of tests.