Introduction To Dispersants For Plastics

Dispersants are surfactants that have two opposite properties, lipophilicity and hydrophilicity, in the molecule. They can evenly disperse the solid particles of inorganic and organic pigments that are difficult to dissolve in liquids, and at the same time prevent the sedimentation and agglomeration of solid particles, forming the agents needed for stable suspensions.

Product categories:

1. Fatty acids: fatty amides and esters. Stearic acid amides are used in combination with higher alcohols to improve lubricity and thermal stability. The dosage (mass fraction, the same below) is 0.3%-0.8%, and it can also be used as a lubricant for polyolefins. Vinyl bisstearamide, also known as ethylene bisstearamide, is a high melting point lubricant with a dosage of 0.5% to 2%. Stearic acid monoglyceride, tristearic acid glyceride. Oleic acid dosage 0.2% to 0.5%. Hydrocarbon paraffin solid, melting point of 57-70℃, insoluble in water, soluble in organic solvents, poor dispersibility, compatibility and thermal stability in resin, the dosage is generally less than 0.5%.

2. Paraffin:
Although paraffin is an external lubricant, it is a non-polar straight-chain hydrocarbon and cannot wet the metal surface, that is, it cannot prevent polyvinyl chloride and other resins from adhering to the metal wall. Only when used in combination with stearic acid, calcium stearate, etc., can a synergistic effect be exerted.
Paraffin: Solidification point -15–35℃, poor compatibility with resin during extrusion and injection molding, the addition amount is generally 0.3%-0.5%, and excessive addition will deteriorate the processing performance.
Microcrystalline wax: obtained from petroleum refining, with a large relative molecular mass and many isomers, melting point 65-90℃, good lubricity and thermal stability, but poor dispersibility, generally used in an amount of 0.1%-0.2%, preferably used in combination with butyl stearate and higher fatty acids.

3. Metal soaps:
Metal salts of higher fatty acids are called metal soaps, such as barium stearate, which is suitable for a variety of plastics, with a dosage of about 0.5%; zinc stearate is suitable for polyolefins, ABS, etc., with a dosage of 0.3%. Calcium stearate is suitable for general plastics, for external lubrication, with a dosage of 0.2%-1.5%; other stearic acid soaps such as cadmium stearate, magnesium stearate, copper stearate.

4. Low molecular waxes:

Low molecular waxes are a series of oligomers with different properties, which are made from various polyethylene (homopolymers or copolymers), polypropylene, polystyrene or other polymer modified materials, and are cracked and oxidized.
Its main products include five categories: homopolymer, oxidized homopolymer, ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, and low molecular weight ionomer. Among them, polyethylene wax is the most commonly used.
Functions of dispersant products:

1. Improve gloss and increase leveling effect. The gloss actually depends mainly on the scattering of light on the plastic surface (i.e. a certain flatness is sufficient.

2. Prevent floating color and flowery.

3. Improve tinting strength. Note that the tinting strength is not the higher the better in the automatic color matching system.

4. Reduce viscosity and increase pigment loading.

5. Reduce flocculation. This is the case, but the finer the particles, the higher the surface energy, and the higher the adsorption strength of the dispersant is required. However, a dispersant with too high adsorption strength may cause adverse effects on the performance of the coating.

6. Increase storage stability.

7. Increase color development and color saturation.

8. Increase transparency (organic pigments) or hiding power (inorganic pigments).

In our plastic production process, pigment dispersion is a very important production link, which is directly related to the storage, construction, appearance and performance of the plastic film, so the reasonable selection of dispersants is a very important production link.