Anti-oxidation commonly used in polyurethane hot melt adhesives

During the use of polyurethane hot melt adhesive, it needs to be heated and melted, and kept in a molten state for extrusion. Therefore, under the action of long-term heat and oxygen, the polymer chains of its main components such as matrix polymer, tackifier, wax, etc., the carbon-hydrogen bond is easily broken, and a chain oxidation reaction occurs, causing the relative molecular weight to decrease, making the adhesive Viscosity and color change, affecting the use of glue. The glue should maintain viscosity stability during use, so as to keep the glue extrusion and coating amount uniform, and keep the color unchanged. The chain process of oxidation greatly reduces the heat aging speed, prevents the deterioration of the glue and the reduction of the bonding strength, etc.

What are the requirements for antioxidants used as adhesives:
The following requirements should be met:
1. Good compatibility with adhesives, preferably compatibility;
2. Good inhibition and anti-oxidation performance;
3. Does not affect the process and physical and mechanical properties of the adhesive;
4. Stable storage, no discoloration, delamination, gelation, deterioration, etc. of the adhesive;
5. Non-toxic or low toxicity, less polluting;
6. The source is easy and the price is reasonable.

What are the commonly used antioxidants for polyurethane hot melt adhesives? There are mainly two types;
One is a chain transfer agent, which forms a stable free radical by itself while giving an active hydrogen atom, such as N-phenyl-β-naphthylamine;

Features of N-phenyl-β-captylamine: light gray powder, gradually turning gray-red when exposed to air or sunlight, relative density 1.20, melting point 108°C, insoluble in water, flammable, highly toxic, regarded as Carcinogens; should be used as little or as little as possible. It can be replaced by its N, N, N', N'-tetraphenylaminomethane, its characteristics: off-white powder or amber liquid, melting point range 29-36 ° C, three-dimensional structure content ≥ 35%, this antioxidant effect High, low pollution and coloring. Compared with other amine antioxidants, its outstanding advantages are small migration, low pollution, slight toxicity, good heat resistance and oxidation resistance, and can completely replace N-phenyl-β-naphthylamine, And better performance.

The other is sterically hindered phenols, which are characterized by one or two larger tert-butyl groups at the ortho position of the Phenolic hydroxyl group, using steric hindrance and a higher conjugation system to make the phenols generated after chain transfer Free radical stabilization, such as 2,6-di-tert-p-cresol. Usually the amount of antioxidants is 0.1% to 1.5%, generally not more than 2%. Antioxidants are mainly phenols and phenol derivatives.

2,6-Di-tert-butyl-p-cresol: The pure product is white crystal, the color turns yellow when exposed to light, and gradually deepens, the relative density is 0.8937, and the melting point is 70°C. Soluble in dry benzene, toluene, methanol, ethanol, isopropanol, butanone, carbon tetrachloride, petroleum ether, insoluble in dry water and dilute alkali solution, flammable, non-toxic, used as a non-polluting antioxidant, effective Inhibit air oxidation, thermal degradation and copper damage, and have a protective effect on thermal aging. 4,4'-Thiobis(3-methyl-6-tert-butyl)phenol, white or light yellow powder, relative density 1.06-1.12, melting point 161-164°C. Soluble in ethanol, ether, acetone, benzene, slightly soluble in petroleum ether, gasoline, insoluble in water. Low toxicity, as a non-polluting antioxidant, low volatility, high-efficiency anti-oxidation, excellent thermal stability and weather resistance.

The antioxidant used in a good hot melt adhesive is a highly efficient antioxidant with excellent thermal stability and weather resistance. It has the characteristics of insoluble in water, low toxicity, good heat resistance & oxygen resistance.