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How should I colour match black, white, red, yellow and special coloured materials?

2022-07-29 Page view : 31 views


How to prepare extra white plastic

To match a bright white products, the primary choice of the bottom tone with blue titanium dioxide (should be chosen to use the chlorination process to produce titanium dioxide, its small particle size, uniform molecular weight distribution), because the bottom tone with blue titanium dioxide with white, will give people a sense of freshness, on the contrary, if you choose a large particle size, the bottom tone with yellow titanium dioxide, no matter what methods are used to adjust the colour light can not reach the bright pure white.

Titanium dioxide because of the whiteness is not enough, in the plastic coloring often add additives to whiten. A very small amount of blue and purple pigment or fluorescent whitening agent can be added to whiten the titanium dioxide whitening effect is as follows: the common and simplest method is to use fresh green carved white block, the effect of its whitening marketed as magnetic white; with fluorescent whitening effect is the best, but its cost is the highest.


How to formulate extra black plastic

When formulating special black products with carbon black, attention should be paid to the problem of carbon black colour light. In incident light, carbon black with a small particle size is usually more bluish than carbon black with a large particle size, but in transmitted light (transparent tinting) and when spinning grey it is brownish. If you wish to obtain a black and shiny plastic product, choose a low structured carbon black with a small particle size. This is because when colouring carbon black, blackness is mainly based on light absorption, so the smaller the particle size, the higher the degree of light absorption, the weaker the light reflection and the higher the blackness. After selecting the above-mentioned carbon black varieties, special attention needs to be paid to the dispersion of the carbon black in order to obtain satisfactory colouring results. Only by solving the problem of carbon black dispersion can the highest carbon black colouring power be achieved.

After oxidation, the introduction of polar groups such as -OH, -COOH, all increase the dispersion of the carbon black, therefore there is a volatile fraction indicator in the performance index of carbon black, the higher the value, the higher the degree of oxidation.

In any case, carbon black always has some yellow light, so you can use the blue colouring, the amount of 8% to 10%, so that the black black of the preparation of the ebony degree greatly increased. The pigment used is generally blue 15: if the blue colouring agent is used on the basis of toning and then toning with purple or red, the black colouring may be even blacker.


How to formulate grey plastic

When formulating grey with carbon black, attention should be paid to the issue of carbon black colour light, carbon black particle size is small, when added to titanium dioxide with yellow tones of grey; carbon black particle size is large, when added to titanium dioxide, will get with blue tones of grey. Titanium dioxide particle size and particle size distribution and titanium dioxide light also has a great relationship, titanium dioxide particle size with yellow light, small particle size with blue light. Therefore, the first thing to do is to clarify the relationship between carbon black and titanium dioxide particle size and tone, otherwise the wrong tone, and then adjust the pigment, will be more and more complex.

Grey products colour matching after the determination of carbon black and titanium dioxide, sometimes also need to use other colours to mix the colour to meet the user’s requirements, because the pigment added less, so should choose some coloring power low species, such as iron oxide (pigment yellow 119, pigment red 101), metal oxides (pigment yellow 53, pigment brown 24), which can make the colour matching system colour stability better.


How to formulate plastic for outdoor use

(1) Dark coloured plastic products for outdoor use.

Outdoor plastic products such as chairs for stadiums, steel cable sheathing for bridges, building materials, advertising boxes, crates and plastic car parts must have good light and weather resistance as they are used outdoors for long periods of time. Inorganic pigments generally have good light stability and can be used to match the colour of plastic products for outdoor use, but are limited by their low colouring power.

When preparing dark-coloured outdoor products, we must firstly choose a colouring agent with good light and weather resistance, and secondly use as little or no titanium dioxide in the product as possible, so that the pigment concentration in the product is as high as possible. In addition, there is a sufficient amount of UV absorbers and anti-oxidants in the colouring formula to ensure that the resin does not change colour.

(2) Light coloured plastic products for outdoor use.

Light-coloured plastic products are made by adding a large amount of titanium dioxide and a small amount of pigment. As most organic pigments are added to titanium dioxide, the weather resistance and heat resistance will be reduced to varying degrees, and the impact of light-coloured varieties is even greater due to the small amount of pigment added. Another organic pigment is used in light-coloured varieties because of its high colouring power, so it is used in light-coloured varieties with a small amount of addition, which can cause colour differences in production and colour deviations when used.

Light coloured varieties should be modulated with inorganic pigments, mainly using their advantages of good heat resistance and low colouring power. The inorganic pigments available are pigment yellow 119 (iron oxide), pigment yellow 53 (metal oxide), pigment brown 24 (metal oxide), pigment brown 184 (bismuth vanadate), pigment red 01 (iron oxide), pigment blue 29 (ultramarine), pigment green 8 (cobalt blue), pigment brown 50 (cobalt green).

Light colours

How to prepare light coloured transparent plastic

The formulation of light coloured transparent products requires first of all that the resin itself is transparent and colourless, for example polypropylene and clear styrene. It is important to choose a colourant with good transparency and consistent colour light. Generally speaking, inorganic pigments with poor transparency cannot be applied. The varieties with good transparency in organic pigments are: pigment yellow 139 (isoindolinone), pigment yellow 199 (anthraquinone), pigment red 149 (perylene system), pigment red 254 (diketone-pyrrole-pyrrole), pigment blue 15:1 (phthalocyanine), pigment green 36 (phthalocyanine) and pigment brown 41 (condensed azo).


How to formulate pearlescent plastic

The proportion of pearlescent pigment added in plastic injection moulded products is generally 1%, in extruded film products it is 4%~8%, depending on the thickness of the plastic film. Similarly in co-extrusion compounding, the pearlescent content in the pearlescent layer should be increased accordingly, the addition amount is 5%~10% according to the thickness of the plastic pearlescent layer.

(1) Pay attention to the choice of pearlescent and organic pigments.

The use of pearlescent pigments in plastic processing generally requires attention to the following points: the transparency of the coloured resin should be good; as far as possible, use pigments with good transparency (such as organic pigments) and solvent dyes; they cannot be used with titanium dioxide, and in order to achieve a certain covering power, small-sized pearlescent pigments can be used at the same time, and high covering power pigments should be avoided as far as possible; when pearlescent pigments are applied to outdoor plastic products, consideration should be given to When pearlescent pigments are used in outdoor plastic products, the weather resistance of pearlescent pigments should be considered.

(2) Pay attention to the pearlescent pigment processing and moulding process.

When injection moulding, the back pressure is increased to improve the mixing of the screw, so as to improve the dispersion of the pearlescent pigment. The processing temperature during injection moulding is generally chosen at the upper limit of the recommended use temperature range of the resin, so as to ensure the dispersion of the pearlescent powder.

The surface finish of the mould is very important. The more polished the mould, the more uniformly oriented and smoothly pearlescent colour can be obtained.

The design of the mould gate is also very important. The choice of a single gate reduces the mould outflow line more than multiple gates. Gates should normally be chosen in thick places away from flow barriers and the distance between the end of the gate and the runner system should be as small as possible to reduce the uneven distribution of pearlescent pigments and the haphazard arrangement caused by differences in fluid resistance.

As the pearlescent pigment exists in the form of flakes, the particle size of the pigment will become smaller and the pearlescent effect will be reduced due to the shearing force during the plastic processing. A larger aspect ratio and a suitable fineness of filter mesh are used to increase the pressure of the machine head, so as to reduce the damage of the pearlescent pigment by the shearing force during the processing as much as possible.

When using pearlescent pigments in PMMA, PC and PA systems, prior drying must be carried out. When using gold and bronze pearlescent pigments in PVC plastics, care must be taken as they contain free iron ions, which accelerate the decomposition of PVC resins. Silvery white pearlescent pigments can yellow in some pigment products, so the use of anti-yellowing products is recommended.

Gold and Silver

How to formulate gold and silver plastic

The pigments used in silver plastic products are actually aluminium powders. Aluminium pigments produce a very bright blue-white specular reflective light, as the aluminium surface strongly reflects the entire visible spectrum, including blue light.

Aluminium powders are available in different varieties for use in plastics. The average diameter of the particles is 5μm, which has excellent colouring and covering power; the average diameter of the particles is 20~30μm, which can be used together with coloured pigments; the average diameter of the particles is 330μm, which has an extra coarse shimmering effect.

The melting point of aluminium powder is 660°C, but when in direct contact with air at high temperatures, the surface is oxidised to a greyish-white colour, so surface treatment of aluminium powder covered with a protective silicon oxide film can make it heat, weather and acid resistant.

The pigment used in the gold plastic products is copper powder, which is easy to oxidise at high temperatures, and its weather resistance is not good, and it will be darkened for a long time outdoors. If the surface of the copper powder is treated with a protective silicon oxide film, the heat resistance, weather resistance and acid resistance can be greatly improved. After the silicon oxide treatment, the masterbatches will not darken under high temperature injection.

In order to formulate a special metallic effect, a small amount of organic pigments with better transparency and similar colour and light can be added, but it should be noted that if too much titanium dioxide and pearlescent powder and other substances are added to the formula, it will also make the product dark.

As metallic pigments are generally in the form of flakes, the use of metallic pigments and pearlescent pigments is more likely to produce mould flow lines in the injection moulding process, affecting the appearance of the plastic product. The following methods can be used to reduce or minimize the above situation: using large particle size metallic pigments, increasing the amount of metallic pigments added, choosing resins with high viscosity, increasing the injection aperture and increasing the injection speed.

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