One of the big doubts of many friends who have just started or want to be engaged in the production of pigment masterbatches is the requirements for the production of pigment masterbatches. To explain this problem, let's start with the requirements for colorants for masterbatches.
The colorant used in the color master batch must pay attention to the matching relationship between the colorant, plastic raw materials and additives. The selection points are as follows:
1. The pigment cannot react with the resin and various additives, and has strong solvent resistance, small migration, and good heat resistance. That is to say, the masterbatch cannot participate in various chemical reactions. For example, carbon black can control the curing reaction of polyester plastic, so carbon black material cannot be added to polyester.
Due to the high molding temperature of plastic products, the color material should not decompose and discolor under the molding heating temperature. Generally, inorganic pigments have better heat resistance, while organic pigments and dyes have poor heat resistance, which should be paid enough attention to when selecting colorants.
2. The dispersibility and tinting strength of the pigment should be good. When the colorant is not uniformly dispersed, it will affect the appearance of the product; when the colorant has poor tinting strength, the amount of the colorant will increase and the material cost will increase. The dispersibility and tinting strength of the same colorant in different resins are not the same, so pay attention to this when selecting the colorant.
The particle size of the pigment is also related to the dispersibility. The smaller the particle size of the pigment, the better the dispersibility and the stronger the tinting strength.
3. Other properties of colorants should be understood. For example, for plastic products used in food and children's toys, the colorants are required to be non-toxic; for plastic products used in electrical appliances, colorants with good electrical insulation should be selected; For outdoor plastic products, pigments with good weathering resistance should be selected.
The process requirements of pigment masterbatches production are very strict, and the wet process is generally used. The pigment masterbatch is made by water phase grinding, phase inversion, water washing, drying and granulation. Only in this way can the product quality be guaranteed.
In addition, while the pigment is being ground, a series of tests should be carried out, such as measuring the fineness of the sanding slurry, measuring the diffusivity of the sanding slurry, measuring the solid content of the sanding slurry, and measuring the fineness of the color paste.
There are four methods for the production process of masterbatch:
1. Ink method
As the name implies, it is a production method of ink color paste in the production of pigment masterbatch, that is, through three-roll grinding, a low molecular protective layer is coated on the surface of the pigment. The ground fine paste is mixed with the carrier resin, then plasticized by a two-roll plasticizer (also called a two-roll open mill), and finally granulated by a single-screw or twin-screw extruder.
2. Washing method
The pigment, water and dispersant are sanded to make the pigment particles smaller than 1 μm, and the pigment is transferred into the oil phase by the phase transfer method, and then dried to obtain the pigment masterbatches. An organic solvent and a corresponding solvent recovery device are required for phase inversion.
3. Knead law
After mixing the pigment and the oily carrier, the pigment is washed from the water phase into the oil phase by kneading by taking advantage of the lipophilic feature of the pigment. At the same time, the surface of the pigment is covered by an oily carrier to stabilize the dispersion of the pigment and prevent the pigment from agglomerating.
4. Metal soap method
After the pigment is ground, the particle size reaches about 1 μm, and the soap solution is added at a certain temperature, so that the surface layer of each pigment particle is evenly wetted by the soap solution, forming a layer of saponification solution. The saponified layer on the surface chemically reacts to form a protective layer of metal soap (magnesium stearate), so that the finely ground pigment particles will not cause flocculation and protect a certain fineness.