Polyplastics Co,.Ltd.

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Coloring methods

At first, the types of coloring methods are explained.
Following 4 types of coloring methods are used for plastics. Coloring in black is usually done by means of either a masterbatch or a compounding method, while plastic materials of other colors are mainly made by means of a surface-coating method where color matching is relatively easy.

This is a coloring method in which plastic material to be colored is mixed with so-called "masterbatch" which is the colored material of a high pigment content. Masterbatches can be handled easily, and the depth of color can also be easily controlled by the amount of masterbatches to be added. They are often used for coloring in black or gray. Depending on the kinds of pigments, however, it is sometimes difficult to make masterbatches, or to match up to the colors wanted by customers.

This is a method to make colored pellets by means of mixing pigment with the pellets of natural color and then extruding the mixture. The highest consistency in color is the most important advantage of this method. However, this is usually the most expensive coloring method, since it is inevitably accompanied by extrusion process.

In this method, organic solvent in which pigment is dispersed is sprayed on the surfaces of natural pellets to be colored to form colored coating. Since colored pellets can be easily available by this method, this method is very popular among customers, and used most widely particularly for colorful moldings. Handling is also easy, but the dispersion of pigment by this method is slightly inferior to that by compounding method.

This is a method to just mix pellets and pigment prior to molding. The handling is not so easy and the cleaning after the molding is also troublesome. The dispersion of pigment is poor, and the consistency of color is not good either. Although this method is applicable if only pigment is available, actually this method is not used so often because of the reasons mentioned above.

Effect of coloring on properties

The effect of pigment on the properties of moldings depends on the type and the amount of pigment added. There are two types of pigments i.e. organic and inorganic, and inorganic metal compounds are mainly used for the resin of high melting point such as engineering plastics. We recommend that ratio of natural color material to masterbatch is 20 to 1 in the case of masterbatch method. Since pigment is basically foreign matter contaminating molded products, it never has any good influence on their properties. However, since the amount of pigment added is very limited and its particle size is very small, it does not happen that the properties of the moldings are badly spoiled by the addition of pigment.

The effect of coloring on each property is summarized below for your reference.

(1) Mechanical property
Slight reduction in strength and some reduction in tenacity may possibly be induced by coloring. The comparison between DURACON M90-44 natural and colored (red and yellow) is shown below as an example.

Properties of DURACON M90-44 (Colored material is a blend of M90-44 and masterbatch M90-07)

Property Unit Natural Red Yellow
Tensile strength MPa 62.5 61.1 61.0
Tensile elongation % 35.5 26.8 27.0
Flexural strength MPa 86.6 79.5 80.5
Flexural modulus of elasticity MPa 2500 2280 2310
Charpy impact strength kJ/m2 5.8 6.4 6.0

Also, please note that the reduction in mechanical properties tends to become more significant, when glass-fiber reinforced plastic is colored in white by the addition of white pigment made of titanium compounds to increase whiteness.

(2) Heat resistance
Coloring does not affect the heat resistance of resin itself. However it is possible that the amount of decomposition products from the added pigment increases in high temperature environment.

(3) Friction and wear property
Basically no change is anticipated in this property. However, when polyethylene is used as the base resin of masterbatch to facilitate high carbon content, molding material blended with such masterbatch is inevitably contaminated with considerable amount of polyethylene. In such a case, frictional property may possibly be deteriorated due to the phenomenon of delamination etc. Therefore, it is necessary to use masterbatch whose base resin is same as that of molding material, in order to prevent such problems. For masterbatch which is suitable for our material, please make inquiry to our sales offices or through HP.

(4) Weather resistance
Weather resistance largely depends on color. However, this is not caused by the change in the property of resin, but rather caused by the degree of the absorption of light energy which is different color by color. Data on the weather resistance color by color are summarized in the following pages for your reference.

Weather resistance of DURACON Weather resistance of DURANEX

(5) Electrical property
There is hardly any change in electrical properties between natural and colored material. The electrical properties of black material is, however, somewhat different from those of natural material due to the effect of carbon black added, except for electrically conductive grades and antistatic grades.

Other topics in the form of Q&A

(Q) Are there harmful heavy metals contained in chemicals used as pigment?

(A) It is not possible to answer this question simply by yes or no, since this depends on the kind of pigment. If the molding material in question is our product, please contact our sales offices, or inquire through our HP, notifying us, at the some time, the kinds of the metals of your concern, and the grades and color numbers of our material. Then we will answer your question after our investigation and confirmation.

(Q) Is it possible to guess the composition of pigment from the color of plastic material?

(A) It is impossible from the practical view point. It is very rare that only one kind of pigment is used, and usually several kinds of pigments are used in combination. Therefore the kinds of pigments contained can not be identified only from the color.

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