How to improve the high temperature resistance and aging resistance of composite materials is a problem that many practitioners of composite materials are very concerned about.
Depending on the application range and coloring object of the pigment paste, while it is required to have sufficient light resistance, weather resistance, solvent resistance, and migration resistance, it should also have satisfactory heat resistance. After a certain period of time, no obvious hue, color light and color force change occur on the surface of the material, especially in colored pastes such as thermosetting composites, plastics, rubber, and silicone composites, which should have excellent thermal stability, such as for glue The colored paste should have a certain thermal stability at the reaction temperature of the vulcanization process; used for thermosetting composite materials (saturated polyester modified epoxy resin, novolac epoxy resin, halogenated epoxy resin, high temperature curing Saturated polyester resin, vinyl resin, polyurethane resin, etc.) do not change the color light at the processing molding temperature, and have no effect on other physical properties of the finished product. When used as a food packaging material, it does not decompose during the high temperature sterilization process.
Due to the different molding temperatures of different types of resins, such as saturated polyester-modified epoxy resins with a molding temperature of more than 180 degrees and fifteen minutes, and some linear phenolic epoxy resins have a molding temperature of 240 degrees. The molding temperature of saturated polyester resin is generally between 160-200 degrees and 20-45 minutes, and the polyurethane resin is mostly above 240 degrees. The molding temperature of many polyurethane composite materials using closed curing agents is even above 280 degrees, the processing temperature of polytetrafluoroethylene is also 280 degrees, and PEEK and high-temperature POM molding are all above 350 degrees.
The factors that affect the final color effect of composite materials are mainly the following aspects:
1. Including the thermal stability of the molding resin itself. For example, some resins will change color when heated, such as phthalic unsaturated polyester resins, which are prone to yellowing at high temperatures. Polyether-modified epoxy resins, 240 degrees will disperse and pulverize, and most acrylic resins are easy to yellow at high temperatures.
2. By-products such as hydrogen chloride in the reaction of cross-linking assistants will cause discoloration of acid-resistant color pastes, such as sky blue, ultramarine, phenol resins, and polyamide resins. The pigment molecules in the oxidative cyclogen react with the leucochromic body to cause the color light to change.
3. The functional additives are not resistant to temperature and decompose during the molding process.
4. The more important influencing factors are the changes in the structure of the pigment used in the color paste, such as the big red, Ciba Chemical 2BP, and Clariant Chemical's F5RK, which will increase blue light when heated, and when it absorbs water At the same time, it will turn yellow light red, and the A-type phthalocyanine blue will change from red light blue to green blue B-CUPC when it is heated above 220 degrees.
Therefore, changing the molecular structure of the pigment contained in the color paste, improving the temperature resistance of the composite material during the molding process, and the long-term temperature stability of the finished product in the later use process are the key cores.
After cooperating with dyeing agent R & D and production enterprises, we have accumulated technical application experience to improve the high-temperature resistance of the color effect of composite materials.
First, change the molecular structure of the pigment in the colorant, and increase the relative molecular mass of the pigment, such as some conventional pigments, bright red, rose red, the relative molecular mass of the 2030 red and fast yellow 94 yellow used increased from 400-600, 1000-1500, not only the color light is more vivid, the tinting power is high, but also the light resistance (outdoor light resistance) and migration resistance are significantly improved. With the increase in molecular weight, the base melting point has increased significantly, from 250 degrees melting point (the finished product begins to change color to 180 degrees) to 315 degrees melting point (the 240 degree only begins to change color). Thyssen is currently cooperating with the colorant enterprise to develop large molecules. Type pigment products have a relative molecular mass of about 2000-4000, have stronger solvent resistance, more excellent resistance to migration, and have a qualitative leap in color fastness.
Second, the introduction of halogenated atoms in the molecule can change the polarity of the color paste, which can improve the thermal stability. This solution has been very mature in the coloring of raw pulp of polyester and polypropylene fibers.
Third, the molecule has a fused structure.
Fourth, the introduction of polar substituent groups in the molecule, such as cyano and chloro, methoxy, o-chloroacetyl, acetanilide couplers, forming hydrogen bonds within the molecule, increasing the coplanarity of the pigment molecules in the color paste, and reducing The electron density of -N = N-group.
Fifth, the use of high-molecular dispersant to replace the small-molecule wetting agent of the color paste to improve the overall high temperature resistance, anti-free, and solve the problem of precipitation.