Plastic color matching jobs

Definition of plastic color matching

Color matching is to match the favorite color, which meets the color difference requirements of the color card, meets the color desired by customers, is economical, and does not change color in processing and use based on the three basic colors of red, yellow and blue (three primary colors).

In addition, plastic coloring can also give plastics a variety of functions, such as improving the light resistance and weather resistance of plastics; Give plastics some special functions, such as conductivity, antistatic, antibacterial and other special materials; Different colored agricultural land films have the functions of weeding or avoiding insects and raising seedlings. That is, through color matching and coloring, it can also meet some application requirements.

Colorant

Pigment characteristics: pigment is a colorant that cannot be dissolved in ordinary solvents. Therefore, in order to obtain ideal coloring performance, it is necessary to evenly disperse the pigment in plastics by mechanical heating and mixing.

Pigment classification: according to the structure, pigments can be divided into organic pigments and inorganic pigments.

Inorganic pigments:

Advantages: good thermal stability, very good weather resistance, excellent light stability, low price and excellent dispersion performance. For example: titanium dioxide, carbon black, etc.

Titanium dioxide series: mainly including titanium dioxide, zinc oxide and lithopone. Titanium dioxide can be divided into rutile and anatase. Rutile titanium dioxide has high refractive index, high hiding power, stability and good weather resistance.

If titanium dioxide is not dispersed before leaving the factory of the original factory, a large number of black spots will be generated in the color matching process, which belongs to the dispersion not open state. Therefore, it can be used only after dispersion processing with dispersant. The brands of some manufacturers enter the market after processing, and such materials can be used directly. It is mainly used to cover the transmittance of resin and increase whiteness.

Carbon black is a commonly used black pigment, which is cheap, and also has the function of ultraviolet protection (anti-aging) and conduction of plastics. Different production processes can get various carbon black with a wide range of sizes, and the properties are very different.

Carbon black can be divided into pigmented carbon black and rubber reinforcing carbon black according to its use. Pigmented carbon black can be divided into high pigmented carbon black, medium pigmented carbon black and low pigmented carbon black according to its coloring ability. Carbon black particles are easy to aggregate. In order to improve the coloring power of carbon black and solve the dispersion of carbon black, dispersant needs to be added for processing before it can be used.

Disadvantages: the coloring power is relatively poor, the relative density is large, the addition amount is large, and the color is not bright;

It is mainly used to increase the color concentration (generally all kinds of resins can be used according to the needs of color), especially in engineering plastics, such as PA, PC, PBT, POM, PPO, PPS and other materials, as well as non transparent color, gray and other resins.

Organic pigments:

Advantages: high coloring power, bright color, complete chromatography, low relative density and small addition.

Disadvantages: the heat resistance, weather resistance and covering power are not as good as inorganic pigments, the dispersion effect is poor, the transparency is poor relative to dyes, and the price is high.

It is mainly used in POM, PE, PP, TPU, TPE and other crystalline materials and some bright color products (bright color products whose dye brilliance cannot be reached).

Dye:

Advantages: dyes are organic compounds that can be used in most solvents and dyed plastics. They have the advantages of low density, high coloring power and good transparency.

Disadvantages: however, its general molecular structure is small, and it is easy to migrate when coloring (crystalline material) is more expensive than inorganic, and some prices are close to those of organic pigments.

Pearlescent pigment: also known as mica titanium pearlescent pigment, it is a mica wafer coated with titanium dioxide. According to different hues, it can be divided into silver white pearlescent pigments, rainbow pearlescent pigments and color pearlescent pigments.

Note:

When purchasing pigments, you must understand the dye index (C.I) of pigments. C.I is an international collection of dyes and pigments compiled and published by the British dyers Association and the American Textile Chemists and dyers Association. Each pigment has two numbers according to the application and chemical structure category to avoid misunderstandings about pigments with the same molecular structure and different names during procurement, It is also conducive to the management of color and the use of correct pigments, which is convenient to find out the causes in case of problems.

Color matching and coloring process

Color matching and coloring can adopt the method of directly adding toner to resin, the method of extruding toner mixed resin and the method of color masterbatch.

Toner directly adding resin method: after the toner is directly mixed with plastic resin, it is sent to the next product forming process, with short process and low cost, but poor working environment, poor coloring force, poor coloring uniformity and quality stability.

Toner mixed resin extrusion method: this method has the best effect on the uniformity of resin and color, and can fully disperse pigments in the resin, with accurate color, clean quality and easy processing.

Color Masterbatch method:

It is a granular material with a certain concentration of colorant prepared from colorant, carrier resin, dispersant and other additives. When the product is formed, a certain amount of color masterbatch is added according to the coloring requirements to make the product contain the required coloring dose and meet the coloring requirements.

Color masterbatch can be classified according to the resin to be colored, such as ABS Color Masterbatch, PC Color Masterbatch, PP Color Masterbatch, etc; It can also be classified according to the coloring resin plus process, including injection molding, film blowing and extrusion masterbatch. Because the pigment is pretreated first, the color masterbatch has high coloring power, the dosage can be reduced, the quality is stable, the transportation, storage and use are convenient, and the environmental pollution is greatly reduced.

The dispersant removes the surface air by wetting and penetrating the pigment, disperses the condensate and aggregate into fine, stable and uniform particles, and no longer agglomerates in the processing process. The common dispersant is low molecular weight polyethylene wax, and EVA wax or oxidized polyethylene wax is used for organic pigment and carbon black that are difficult to disperse, The synthetic low molecular weight polyethylene wax is very different from the low molecular weight polyethylene wax produced by polyethylene cracking.

Other additives include coupling agents, antioxidants, light stabilizers, antistatic agents, fillers, etc. the addition amount depends on the requirements and varieties, which is called multi-functional masterbatch. In addition, the addition of brightener is conducive to demoulding of molded products and improving the surface brightness of products.

The performance indexes of Color Masterbatch include color difference, whiteness, yellowness, yellowness, thermal stability, oxygen index, melt flow rate, etc. of course, the fineness, mobility, chemical resistance and toxicity of pigment are also related to the performance of color masterbatch. Some indexes are very important in special applications, such as the fineness of filter pressing value (DF value) of fiber dimension masterbatch.

Color matching management and instruments

The hardware of color matching management includes a colorimeter and a computer for processing the measured data. Colorimeter can be divided into spectrophotometer and color difference meter, which can replace human eyes to measure color and remove the influence of human factors on the measurement results.

Spectrophotometer is used to measure the reflection coefficient of each wavelength on the fully diffuse reflection surface. It can not directly obtain the chromaticity value or color difference, but it can evaluate the chromaticity value and other values through its data processing. Spectrophotometer can be divided into two types: diffraction grating and interference filter. The advanced spectrophotometer with built-in microprocessor has the functions of 0%, 100% automatic correction and magnification increase, so as to improve the accuracy.

The color difference meter is a simple test instrument, that is, to make a filter with light splitting characteristics equal to the color sensitivity of human eyes, and use it to measure the light of the sample. The key is to design a filter with light splitting sensitivity of photoreceptor and can measure the color difference value under a certain light source. The color difference meter has small volume and simple operation, It is more suitable for batch management of the same product with small change in spectral characteristics. The color difference meter with small microcomputer is easy to correct and output multiple color difference values with standard template.

Color matching management software includes spectral inversion curve, color difference formula, conditional isochromatic representation, hiding power representation and haze representation. The spectral reflectance curve is used for the analysis when selecting colorants, but can not be used to judge the consistency of colors. Color difference value is one of the most important indexes in color management, but the color difference obtained by different color difference formulas is different, so the chromaticity system or color difference formula used must be indicated.

The computer color matching instrument has the following functions:

(1) Color matching: establish the database of common pigments (dyes) according to the requirements (prepare the basic color board and input it). Then input the incoming color board into the computer under the software menu, select several candidate pigments on the keyboard, immediately calculate a series of formulas, and list them respectively according to color difference and price for color matching selection;

(2) The formula correction computer lists the formula and other source formulas. When the color difference is unqualified, use the inconsistent reflection curve displayed on the display to directly increase or decrease the pigment amount through the keyboard until the two curves basically coincide to obtain the corrected formula;

(3) Color measurement and color difference control measure the coloring intensity of colorant, whiteness of product, color fastness of product and color difference. Because the computer can quantitatively express the performance index of color, it is conducive to the communication and transmission of information between both parties;

(4) The color sample, formula, process conditions, production date, user and other information in the daily work of color management can be stored in the computer, which is convenient for retrieval, search and reference during modification, convenient and fast, improves work efficiency, and is convenient for confidentiality