The quality of polyester chips not only affects the quality of PET filament, but also affects the normal production of POY, FDY filament spinning. Therefore, to prepare high-quality filament products, polyester chips must be strictly selected.
Filament-level slices should meet the following requirements in terms of conventional indicators:
1.Characteristic viscosity number
In order for the product to have appropriate physical and mechanical properties and POY/ FDY spinning smoothly, the polyester chips are required to have an appropriate molecular weight. The methods for measuring molecular weight and distribution are complicated, so the intrinsic viscosity number is used to express the molecular weight.
The intrinsic viscosity of slices used for PET filament depends on the product variety. The intrinsic viscosity of commonly used slices is 0.64~0.66. It increases with the increase of molecular weight and can be converted by the following formula:
【ç】=KMɑ
In the formula: [ç]——intrinsic viscosity number;
K——coefficient (when measured with o-chlorophenol or phenol-tetrachloroethane mixture, K takes the constant 1.27x10-4);
M——Weight average molecular weight;
Ɑ——Constant (generally 0.86).
2. Melting point
Melting point (softening point) refers to the temperature at which polymer chains can move freely. Filament production requires polyester chips with a melting point of approximately 260°C.
3.Diethylene glycol content
The content of diethylene glycol in polyester affects the melting point of slices, hue and dyeing of finished products. The required content is less than 1.3% and evenly distributed.
4. Agglomerated particles
The agglomerated particles in polyester chips mainly include polymer oxidation gels, titanium dioxide agglomerates, catalyst precipitates, and high melting point substances and carbides generated on the reactor wall. These impurities not only increase the load on the melt pre-filter or component filter layer, but also easily lead to lint and breakage. The number of aggregated particles (20 ìm > diameter > 10 ìm) per milligram of slice is required to be ≤0.4. Due to the uneven distribution of agglomerated particles, multiple tests are required.
5.Terminal hydroxyl content
The high content of terminal hydroxyl groups indicates a broad molecular weight distribution and poor spinnability. When the finished product is used in hot conditions, the degradation of polyester macromolecules will be accelerated. The terminal hydroxyl content is required to be less than 30mmol/106mg.
6.Titanium dioxide content
The purpose of adding titanium dioxide to polyester chips is to make the fiber matt. The addition amount is 0.3~0.5%, which can produce a better semi-matting effect. On the premise of achieving good matting effect, the content of TiO2 should be as low as possible, evenly distributed and fine particles.
7.Ash content
Refers to inorganic metal salts other than TiO2 in slices. High content indicates that there are many impurities in the slices and the spinning performance of the slices is poor. The general requirement is less than 0.1%.
8.Iron
High iron content will cause the fiber to turn yellow and deteriorate the color, so the content is required to be less than 3ppm.
9.Hue
The hue of polyester chips not only affects the hue of the finished fiber, but also affects the spinning performance of the chips. Generally, the hue value of the slice is required to be less than 3.
Post time: Jul-05-2024