Brief Introduction of Colorants for Polyurethane Materials
Polyurethane materials have good colourability. By adding dyes or pigment pastes, polyurethane products with various colors can be manufactured, such as colored polyurethane soft foam, elastomer, synthetic leather, etc. These additives that can make products colored can be called colorants.
Additional effect of dyeing
In addition to using color to provide different visual effects, it also has the following functions for dyeing PU foam products:
① Different colors are used to distinguish polyurethane soft foam products with different densities and functions. Different colors can represent different densities or different kinds of PU soft foam, such as flame retardant sponge, anti-static sponge, etc;
② Brown, red, yellow or black can be used to cover up the yellowing phenomenon of polyurethane, so that the yellowing phenomenon of polyurethane products is not obvious or easy to detect, thus reducing the negative effect to the lowest point.
Colorant selection
There are many kinds of pigments and dyes. Due to the presence of highly reactive NCO groups in the polyurethane reaction system, attention should be paid to whether there are functional groups or compounds in the pigments and dyes that are easy to react with polyurethane raw materials (they are easy to lose their coloring effect after reaction). It is better to choose whether the pigment is suitable for polyurethane system through experiments.
The selection of pigments or dyes generally follows the following principles:
It can be easily dispersed in components;
Can withstand processing temperature;
The influence on material properties shall be as small as possible;
No color shift and pigment precipitation.
For the convenience of use and better dyeing effect, pigments or dyes are usually pre dispersed and dissolved in polyether to make color paste. In the production of color paste, in order to make the powder pigment well dispersed, it is usually necessary to add a wetting and dispersing agent.
Type of color additive
Black pigment
Carbon black, aniline black, titanium black, etc
White pigment
Titanium dioxide, etc
Red pigment
Vulcanizing pot, iron oxide red, lake red, etc
Yellow pigment
Titanium yellow, isoindolinone pigments, etc
Green pigment
Cadmium oxide, phthalocyanine green, orange pigment, chrome red, etc
There is a type of reactive pigment with Reactive brand, and the colors are blue, orange, red, yellow and purple respectively. By mixing 2 or even 3 kinds of color materials and black materials in a certain proportion, various colors of products can be obtained. The polymer chain of the coloring assistant contains hydroxyl groups and chromogenic groups. The coloring group is connected to the polymer network through reaction, and the color is firm without migration and fading.
Inner mold paint is an auxiliary agent with three functions of paint, color paste and release agent. It is evenly sprayed in the mold. After the paint film is dry, the polyurethane sole, self skinning foam, polyurethane soft foam and hard foam products can be molded. After demoulding, the color paint is attached to the molded and solidified products.
