1, heat distortion temperature
The heat distortion temperature (full load heat distortion temperature, English abbreviation: HDT) refers to a predetermined load (1.81 N/) of a rectangular resin sample of a certain size in a heat-conducting liquid medium immersed at a heating rate of 120 ° C / h. Mm2 or 0.45 N/mm2), the temperature at which the deformation amount of the midpoint of the sample reaches a predetermined value corresponding to the height of the sample. It should be noted that the values ​​of the heat distortion temperature determined by different load values ​​are different and there is no comparability, so the value of the heat distortion temperature must be determined to indicate the specified load value (ie the standard used). The heat distortion temperature is one of the main indicators for measuring the heat resistance of plastics (resins). Nowadays, most of the plastic (resin) products in the world have the index of heat distortion temperature as the product quality index, but it is not the highest. The use temperature, the maximum use temperature should be determined according to a combination of factors such as the force of the product and the requirements of use.
There are many standards for measuring the heat distortion temperature. The common ones in China are: China National Standard (GB), American Society for Testing and Materials (ASTM), International Organization for Standardization (ISO), European Community Standards, etc., as required by various standards. The method, unit system, etc. are different, so the test results are also different. For example: a well-known foreign brand of phenolic epoxy vinyl ester resin product heat distortion temperature ASTM test typical value: 149-154 ° C, GB measured value: 137 ° C; 898 resin GB measured value: 155 ° C.
2, Martin heat
The Martin heat test method is one of the methods for testing the heat resistance of plastics (resins). Proposed by Martin in 1924, it was officially used in Germany for phenolic plastic testing in 1928. Later, other hard plastics also used this test method. It is widely used in Europe and the former Soviet Union. In 1970, China also issued the national standard for this test method, which became one of the national standards for testing plastics (resins) established in China in the early days, so it has a long history in China.
Martin heat-resistant temperature refers to the temperature at which the specimen bends under a certain bending moment and in a certain constant-speed heating environment. When the specified deformation amount is reached, the temperature is reached.
3. Analysis of heat distortion temperature and Martin heat resistance
The heat distortion temperature and Martin heat resistance are both methods for testing the heat resistance of plastics (resins), but due to the essential difference of the test methods, there is no comparability and no conversion formula.
Because Martin's heat-resistant temperature measurement is the application of cantilever beam bending moment, the operation is not convenient; and the applied bending moment value is large, so that the initial deflection of many plastics after loading is very considerable, so the scope of application is limited, generally used for Hard plastic. In addition, it uses air as the heat transfer medium to distribute the temperature unevenly, and the heat transfer to the sample is slow, so the heating rate should not be too fast. All this, so that this method has not been adopted in many countries, has been gradually eliminated in our country.
Therefore, when testing the heat resistance of plastic (resin), it is not possible to compare the heat resistance of Martin with the heat distortion temperature. At the same time, it should be noted that they are not the maximum use temperature of plastic (resin). The maximum use temperature of plastic (resin) should be determined according to factors such as the force of the product and the requirements of use.
In addition, the thermosetting resin is annealed, which is what we call daily heating, which will increase the heat distortion temperature and Martin heat resistance. Generally, the annealing treatment can increase the heat distortion temperature by 10 °C, which indicates the thermosetting property in daily use. The post-heating treatment of the resin is still necessary.
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