Hardness is the most basic and important physical parameter of TPE. In many cases, it is the different softness of materials that determines the brilliant application of TPE in all walks of life. Therefore, we must understand some basic knowledge of TPE hardness.
The generalized TPE includes THE TPES(TPR) of SEBS substrate, as well as TPU, TPEE, TPV, TPO, etc. This article discusses the most commonly used TPE, namely THE TPES of SEBS substrates.
This kind of TPE has three kinds of units: Shorea, ShoreD, and ShoreC(OO, Q, etc.).Among them, Shao's hardness A is the most common, Shao's hardness C and Shao's hardness D are occasionally used.
The three hardness units shall have different test durometers. According to the principle of physical pressure, the main difference between the three durometers is in the shape of the presser foot. The sCLERometer A has A needle-like pin, but A blunt one. The Sclerometer D has A needle-like pin but is sharper. The C-foot of the shaw durometer has an arc surface.
In addition, there is a VLRH expression method to measure the hardness of ultra-soft TPE, and this hardness unit is rarely seen, occasionally encountered in some foreign material physical properties data. The following is a schematic diagram of hardness conversion for these different hardness units.
In most cases, the hardness of TPE is expressed in terms of Shaw hardness A. It is necessary to discuss some details that should be paid attention to in the measurement of Shaw hardness A.
The thickness of the test piece shall be 0.25 inches, i.e. 6.35 mm, at least not less than 6mm; Length not less than 35mm; The width shall not be less than 15mm. If the thickness of the test piece is not so thick, multiple test pieces may be overlapped in parallel, but not more than four pieces.
It is required that the test pieces should be stored at a temperature of 18~28℃ for 5 hours before measurement. (The temperature of the specimen itself or the environment will have an impact on the measurement results. If the hardness of the specimen is too hard in winter, it will be too soft in summer or if the specimen is not cooled enough just after it comes out.)
The measurement is divided into immediate reading and reading after 5 seconds. Instant reading refers to the reading immediately after the pin is pressed on the specimen. The 5-second reading refers to the reading after the pressure needle is fully applied to the specimen and then extended for 5 seconds. At present, the industry mostly uses 5-second delay reading, measurement data is relatively accurate.
For the same hardness, the specimen thickness is different, giving people a different feeling of hardness. For example, the TPE material of the same 70 degrees is made into 1mm thick flakes, which will be easier to bend and feel soft. And make it a 1-centimeter thick plank, the bend can be more difficult, the feeling can slant hard.
Due to the error of measurement or the error of weight distribution in each group during batching, there will be certain hardness fluctuation in different batches of TPE adhesive produced. Hardness is generally considered to be a reasonable tolerance range within ±3A.
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