Functional curing agent instead of polyamide resin for nylon polishing wheel
Polyamide resin with bisphenol A epoxy resin E-44 or 128 as adhesive has been used in the manufacturing process of nylon polishing wheel for many years in China, which has made great contribution to the development of the industry. Polyamide curing agent is widely used because of its light color, good toughness, good dispersion to corundum, silicon carbide and other abrasives, and high adhesive strength to abrasives and nylon. However, there are also natural defects in polyamide resin, which hinders the development of nonwoven polishing wheel industry towards refinement, specialization and high-end.
Therefore, on the basis of keeping the advantages of polyamide and overcoming the defects of polyamide, we have developed a kind of modified amine curing agent mh-3650 / MH-3651, which is specially used for nylon fiber wheel, with high comprehensive cost performance.
1、 Disadvantages of polyamide resin
1. Because of the low temperature resistance and hardness of the system, the instantaneous heating of the interface is easy to exceed the glass transition temperature of polyamide when the nylon fiber wheel is grinded, which leads to the decrease of bonding strength and the adhesion of the glue, which is easy to cause blackening and sanding. Although the friction coefficient and heat value can be reduced by adding lubricant, the heat resistance of glue is also reduced by adding lubricant, so there are still many problems caused by insufficient heat resistance. Especially in autumn and summer when the temperature is high, it is easy to have quality problems.
2. The molecular structure of polyamide is rich in amide bond. Under the action of temperature and water, it is easy to cause molecular chain break and further decrease of colloidal strength, adhesive strength and heat resistance. When the nylon wheel is polished, the instant heating causes the bonding strength to decline rapidly in the wet grinding environment, and the phenomenon of sand falling occurs.
3. The made nylon polishing wheel is placed for a long time in the humid climate. Because the abrasive and nylon are polar molecules, it has a strong water absorption. If the glue also has strong hydrophilicity, the water will penetrate into the bonding interface, which will lead to the failure of bonding. This is due to the lack of hydrophobicity after curing of epoxy adhesive. Therefore, the bonding strength of the fiber wheel placed for a long time in a humid environment will decrease, and the phenomenon of sanding may occur when it is polished on the machine.
2、 Characteristics of mh-3650 curing agent
In view of the defects of polyamide curing agent and the advantages of polyamide curing agent, we developed mh-3650 curing agent for the production of nylon polishing wheel, which has the following characteristics:
1. The molecular structure of surfactant has good dispersibility for silicon carbide, corundum and other abrasives. It is not easy to agglomerate, layer, blacken and scratch the workpiece.
2. Compared with polyamide, it has lower viscosity and better low-temperature operation performance. It can reduce the amount of solvent added and the amount of solvent discharged (PVC). It can reduce the fire level and is more environmentally friendly and efficient.
3. It has almost the same toughness as polyamide.
4. The heat resistance is significantly higher than 650 at least 30 ℃, and the hardness is improved.
5. Compared with polyamide, the water resistance, solvent resistance, wet heat aging resistance and wet bonding ability are greatly improved.
6. The molecular structure of polyamine and long carbon chain has high bonding strength to polar interface such as abrasive and nylon; it does not contain amide bond and is not easy to hydrolyze; it has strong hydrophobicity and obvious "lotus leaf effect" and water is not easy to penetrate into the interface, which ensures the stability of bonding. For example, in the environment with high humidity, without baking nylon and abrasive, mh3650 has higher bonding strength and durability than 650.
7. Low energy consumption, no need to cure after 120 ℃, 80 ℃ for 2 hours has enough degree of cure and hardness.
8. Shorten curing time and improve production efficiency.
9. The ratio range is large, and the curing agent can float up and down by 10%. (experimental verification required)
10. The surface will not appear birch and oil level when it solidifies at room temperature in high humidity environment.
3、 Disadvantages of mh-3650
Curing agents with different molecular structures bring different physical and chemical properties. The operation time of mh-3650 at room temperature is 25-30 minutes. The operation time of 650 is nearly 120 minutes. The more volatile the solvent evaporates before the gel, the higher the gel strength and adhesive hardness. The faster the gel is, the more residual solvents will be, and the slow evaporation of the gel after curing will produce shrinkage stress, reduce the bonding strength, and cause the grinding dust. This is a typical disadvantage of mh-3650. Especially in summer, we should pay special attention to the following ways to effectively avoid this problem:
1. Effectively reduce the environmental temperature of limited space, or reduce the amount of one-time dispensing. Especially in summer.
2. Not only alcohol, but also compound solvent.
2.1 because of the accelerated curing effect of alcohol, it will shorten the gel time, so it is not recommended that all alcohol be used as solvent.
2.2 the operation time can be prolonged by using ketone, benzene, ester solvent or the combination of several solvents. Such as: acetone, cyclohexanone, toluene, xylene, acetate, dimethyl carbonate and so on.
2.3 however, it is necessary to test the solubility of the mixed solvent to the lubricant. The mixed solvent must have good solubility to calcium stearate.
2.4 in particular, it is not recommended to use solvents with slow volatilization speed.
3. After pressing out the cotton sheet, the solvent volatilization is accelerated by the equipment
3.1 increase the air convection speed in the cotton chip area
3.2 evaporate at room temperature for about 10-20 minutes before entering the mold for sealing.
3.3 for large-scale factories, the exhaust fan of tunnel kiln or convection type can be considered to accelerate the volatilization speed.
4. resin recommended 128, do not use E-44 epoxy, 44 high viscosity, gel time is relatively short, will increase the amount of solvent, resulting in more residual gel, affect the bonding strength.
4、 Typical reference formula (for reference only)
1. Participating formula
If silane coupling agent is selected, because the coupling agent with the characteristics of surfactant is quickly dispersed to the interface of nylon and abrasive, epoxy group can react with nylon to form chemical bond, so KH560 is better than KH550; however, to control the dosage, too much coupling agent (& gt; 1%), not only increases the cost, but also decreases the effect of improving the interface bonding strength.
2. Process Description: weigh the glue, prepare the fiber, mix the glue, press the cotton piece, air dry for 20-30 minutes, put it into the mold for finalization, after 8-24 hours at normal temperature, solidify it at 80 ℃ x2h, and then ship it after cooling.
3. Comparison of main parameters:
4. About color and curing degree
4.1 because the activation energy of mh-3650 is low, the reaction activity is high. After setting at room temperature, curing at 80 ℃ for x2 hours has enough curing degree and does not change color, while curing at 80-120 ℃ usually has the possibility of gradually darkening color.
4.2 polyamide 650 belongs to room temperature curing system. Curing at 120 ℃ x2h can achieve a higher degree of curing
4.3 if the mh3651 of the company is used, it does not need to be cured in the oven when the temperature is ≥ 15 ℃, and it can also reach enough curing degree after curing at room temperature for 7-10 days.
In short, as long as according to the change of environment temperature and humidity, pay attention to control the coordination relationship between production process and solvent. On the basis of not increasing the material cost, MH-3650/MH-3651 can produce nylon polishing wheel with better performance than polyamide. At present, the product has done a lot of experiments in many large factories, which proves that it can greatly improve the quality of nylon wheel.
Click to read the original and browse the official website of Henan ant new materials Co., Ltd