1. Dispersion of polypropylene masterbatch in polypropylene fiber

The polypropylene fibers with various colors are caused by the uniform dispersion of pigment particles in the polypropylene fibers. The key is that the pigment particles are fully refined and uniformly distributed (mixed) in the polypropylene fibers. Refinement dispersion is to fully refine the pigment particles and distribute (mix) uniformly in the polypropylene fiber. Refinement and dispersion is to break the agglomerates or agglomerates of pigments to minimize the particles, and the key lies in uniform dispersion. The effect of dispersion affects the color, transparency, luster, fiber strength, elongation, and aging resistance of colored polypropylene fibers. , electronegative rate, etc. are affected.

Generally speaking, the particle size of the pigment dispersed is less than 1um can be used for fibers or ultra-thin films, while more than 5um will lead to dull fiber surface, more than 10um will cause spots and streaks on the fiber surface, and with the increase of particle size. The breaking strength and elongation of large fibers continue to decrease. The finer the particle size, the stronger the tinting strength and the better the dispersibility. At the same time, the smaller the particle size, the larger the surface, resulting in an increase in the covering power.

Because the pigment particles have three types: primary particles, agglomerates and agglomerates, and the general commercial pigment particles are larger than agglomerates (about 75-250um), they must be dispersed. The so-called pigment dispersion is to agglomerate The process of body crushing and refining.

The dispersion of pigments is first to wet the pigment with a wetting agent and coat it on the surface of the pigment to reduce the cohesion between the pigments and reduce the energy required to break the pigment agglomerates. The free movement (impact stress) of the pigment agglomerates and the shear stress of the surrounding medium break the agglomerate particles. After the pigment is dispersed and refined, the particle size decreases, the surface area increases, and the surface free energy of the pigment also increases. The oxidized pigment is unstable, so further coating treatment is required on the surface of the pigment to reduce the newly formed interfacial surface energy to prevent re-agglomeration, and then the pigment is mixed and dispersed in the melt, and the wetted and pulverized pigment is uniformly dispersed. Disperse and distribute into the material that needs to be colored.

        Second, polypropylene masterbatch performance and quality requirements

       1. Performance requirements of polypropylene masterbatch

Polypropylene is a pure hydrocarbon, and the molecular chain contains tertiary carbon atoms. When heated and exposed to light, the molecules at the tertiary carbon atoms are easily cracked, which deteriorates the quality of polypropylene. Therefore, the masterbatch is required to be produced in high temperature spinning. It is easy to diffuse, does not damage the fiber quality, does not fade the fiber, has excellent light resistance, abrasion resistance, solvent resistance, and can withstand strict spinning drafts.

     (1) The pigments used in the heat-resistant color masterbatch are basically required to withstand the temperature in the production process of polypropylene fibers and keep their performance stable. The temperature resistance temperature is generally required to be above 270 to 280 °C.

    (2) Pigments for dispersive masterbatches should have excellent dispersibility, and should be uniformly dispersed in the masterbatches, and the dispersant used will not reduce the quality of polypropylene fibers. Otherwise, high-quality dope dyed fibers cannot be produced, and the operation is also unstable, and it is easy to break or produce abnormal fibers when the fibers are drawn.

    (3) Brightness Polypropylene dope dyeing has various uses, among which it is used for bed cover base fabric and knitted fabrics, requiring bright hues. Because organic pigments are brighter and brighter, and are easy to color, organic pigments should be used for the above purposes.

    (4) Lightfastness Some pigments have photosensitivity under the action of light, which makes the colored fibers fade and become brittle, and the lightfastness of pigments is basically related to its chemical structure, so when making masterbatches, full attention should be paid to the lightfastness of pigments , When lightfast pigments need to be used, you can consider adding a UV absorber.

    (5) The pigment used in the stable color masterbatch should have excellent stability to the colored polypropylene fiber. That is to say, when the pigmented fiber polymer is exposed to heat, light or high temperature for a long time, the pigment will not react with the fiber to form new chemical groups to reduce the performance of the polymer. Therefore, the purest possible pigments should be selected in the masterbatch, without impurities such as iron, copper, lead and other salts, to ensure the excellent physical properties of the colored polypropylene fibers.

    (6) Water resistance, dry cleaning resistance, oil resistance, and coloring polypropylene fiber products are inevitably washed with water or solvent dry cleaning after use and are exposed to oils, especially when used in carpets, so the colorants used should be It has good washing resistance, dry cleaning resistance and oil resistance.

       2. Quality requirements of polypropylene masterbatch

The quality index of color masterbatch includes many contents. For example, the appearance size is generally 2㎜×(3～4)㎜, the pigment particle size in the masterbatch is less than 1 um, more than 90%, the melting point, DF value, MI value, heat and weather resistance characteristics, etc. These indicators are the common concerns of color masterbatch factories and polypropylene fiber factories.

    (1) Filtration performance Fiber-grade color masterbatch is used to characterize the quality of color masterbatch. Its value is called DF value. If the value is small, the replacement cycle of filter components during the spinning process is relatively long, and the DF value of polypropylene masterbatch is generally required. Less than 2.0×105Pa·cm2/g.

    (2) The melting point polypropylene masterbatch dispersant adopts low molecular weight polyethylene wax, so its melting point is between 110 and 120 °C; and the pigment generally has a high melting point, which exceeds the spinning temperature of polypropylene fiber, so the color masterbatch is in the thermal analysis spectrum. There are two endothermic peaks on it. However, the melting point of the color masterbatch cannot characterize the quality of the color masterbatch. Some enterprise standards stipulate that the melting point is 130-160 °C.

    (3) Melt flow index (MI value) The MI of polypropylene chips is mainly used to characterize its molecular weight, which determines the processing and finished product performance after the chips are formed into fibers. The masterbatch contains pigments, dispersants and low molecular weight carriers. Polyethylene wax, so the MI level cannot be used to express its own molecular weight, and it will change due to different pigments and varieties. Therefore, the MI of the color masterbatch is not a control index of the color masterbatch, but can only be used as a reference when spinning. The MI of the selected masterbatch for spinning is slightly larger than that of the original color chip, which is beneficial to the mixing of the two with similar particle sizes. The general requirement is MI value (15-30) g/30min.

    (4) The heat resistance index of heat-resistant masterbatch refers to that the masterbatch and polypropylene chips are spun at different temperatures in a certain proportion in a period of 5 to 10 minutes, and the degree of color change is observed. The change of color can be evaluated by a gray sample card or a color sample card for evaluating discoloration. When the total color difference value ⊿E≤3, the temperature is the heat resistance temperature of this color masterbatch, generally requiring a heat resistance of 270-300 ℃, the color change is grade 4.