Introduction: Colorants are the most important raw material in color matching, and color matching professionals must fully understand them and be able to apply them flexibly. It is economically feasible to meet the price in use, because the economy of color matching is very important, and the customer’s request is always a cheap and good product. This article shares a piece of knowledge about plastic color matching, and the content is for your reference:
Color matching is based on the three basic colors of red, yellow, and blue (three primary colors), to match the color that is pleasing, meets the color difference requirements of the color card, meets the color that customers want, is economical, and does not change color during processing and use. In addition, plastic coloring can also give plastics many functions, such as improving plastics light resistance and weather resistance; giving plastics some special functions, such as electrical conductivity, antistatic properties, antibacterial properties and other special materials; different colored agricultural mulches can kill weeds or insects , Nursery seedlings, etc. That is, the requirements of certain applications can be met through color matching and coloring.
Pigments and dyes
Pigment characteristics: Pigments are colorants that cannot be dissolved in common solvents. Therefore, to obtain ideal coloring properties, it is necessary to uniformly disperse the pigments in the plastic by methods such as mechanical heating and kneading.
Pigment classification: According to structural pigments, it can be divided into organic pigments and inorganic pigments.
Advantages: good thermal stability, very good weather resistance, excellent light stability, low price, superior dispersion performance. For example: titanium dioxide, carbon black, etc.
Titanium Dioxide Series
There are mainly three kinds of titanium dioxide, zinc oxide and lithopone. Titanium dioxide has two structures: rutile and anatase. Rutile titanium dioxide has high refractive index, high hiding power, stability, and good weather resistance. If titanium dioxide is not dispersed when it leaves the factory, a large number of black spots will be produced during the color matching process. It belongs to the unopened state of the dispersion, so it can be used after dispersion processing with a dispersant. Some manufacturers’ brands enter the market after processing , Such materials can be used directly. It is mainly used to cover the transmittance of resin and increase the whiteness.
It is a commonly used black pigment with low price. In addition, it has the effect of UV protection (anti-aging) and electrical conductivity on plastics. Different production processes can obtain various carbon blacks with a wide range of particle sizes, and their properties vary greatly. Carbon black can be divided into pigment carbon black and rubber reinforcement carbon black according to its purpose. Pigment carbon black can be divided into high pigment carbon black, medium pigment carbon black and low pigment carbon black according to its coloring ability. Carbon black particles are prone to agglomeration. To improve the coloring power of carbon black, and to solve the dispersibility of carbon black, it is necessary to add a dispersant for processing before it can be used.
Disadvantages: relatively poor coloring power, high relative density, large addition amount, and not bright colors;
Mainly used: to increase the color density (generally all kinds of resins are available according to the color needs), especially for engineering plastics with good superior performance, such as: PA, PC, PBT, POM, PPO, PPS, etc. Among materials, non-transparent colors, gray and other resins.
Advantages: high tinting strength, bright color, complete chromatogram, low relative density, small addition amount.
Disadvantages: Inferior to inorganic pigments in terms of heat resistance, weather resistance and hiding power, poor dispersion effect, poor transparency relative to dyes, and higher prices.
Mainly used in: POM, PE, PP, TPU, TPE and other crystalline materials and some bright (bright color products that cannot be achieved by dyes) products.
Advantages: Dyes are organic compounds that can be used in most solvents and dyed plastics. The advantages are low density, high coloring power, and good transparency.
Disadvantages: But its general molecular structure is small, and it is easy to migrate during coloring (crystalline material). The price is more expensive than inorganic, and the price of some is close to that of organic pigments.
Also called mica titanium pearlescent pigment, it is a kind of mica wafer coated with titanium dioxide. According to different hue, it can be divided into three types: silver-white pearlescent pigments, rainbow pearlescent pigments, and colored pearlescent pigments.
When buying pigments, you must understand the dye index (CI) of the pigment. CI is an international collection of dyes and pigments compiled and published by the British Dyers Association and the American Textile Chemists and Dyeers Association. Each type of pigment is based on application and chemistry. The structure category has two numbers to avoid misunderstandings of the same molecular structure and different names when purchasing, and it is also conducive to color management during use and the use of correct pigments to find the cause when problems occur.
Color matching process
Color matching and coloring can adopt the method of adding toner directly to the resin, the method of mixing the toner with resin and the method of masterbatch.
Toner is directly added to resin method:
After the toner is directly mixed with the plastic resin, it is sent to the next product forming process, which has short procedures and low cost, but the working environment is poor, the coloring power is poor, the color uniformity and quality stability are poor.
Toner mixed resin extrusion method:
This method has the best effect on the uniformity of the resin and color, and can make the pigment fully dispersed in the resin, with accurate color, clean quality, and easy processing.
The colorant, carrier resin, dispersant, and other auxiliary agents are formulated into pellets of a certain concentration of colorant. When the product is formed, a certain amount of masterbatch is added according to the coloring requirements to make the product contain the required colorant to meet the coloring requirements.
Color masterbatch can be classified according to the resin to be colored, such as ABS masterbatch, PC masterbatch, PP masterbatch, etc.; it can also be classified according to the coloring resin addition process, including injection molding, blown film, and extrusion masterbatches. . The color masterbatch has high tinting strength due to the pretreatment of the pigment first, 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 agglomerates and agglomerates into fine, stable and uniform particles, and no longer agglomerates during processing. The commonly used dispersant is low molecular weight polyethylene wax. For organic pigments and carbon black that are difficult to disperse, EVA wax or oxidized polyethylene wax is used. There is a big difference between synthetic low molecular weight polyethylene wax and low molecular weight polyethylene wax made by polyethylene cracking. Other auxiliaries include coupling agents, antioxidants, light stabilizers, antistatic agents, fillers, etc., depending on the requirements and varieties, called multifunctional masterbatch, and if the brightener is added, it is beneficial to molded products Demould and improve the surface brightness of the product.
The performance indicators of the color masterbatch include color difference, whiteness, yellowness, yellowness, thermal stability, oxygen index, melt flow rate, etc. Of course, the fineness, migration, chemical resistance, and toxicity of the pigment are also related to the color masterbatch. Particle performance is related, and some indicators are very important in special applications, such as the filter pressure value (DF value) fineness of fiber-grade masterbatch.
Color matching management and instruments
The hardware for color matching management includes a color meter and a computer for processing the measured data. Colorimeters can be divided into two types: spectrophotometer and colorimeter, which replace the human eye to measure color and remove the influence of human factors on the measurement results.
The spectrophotometer is used to measure the reflection coefficient of each wavelength to the completely diffuse reflection surface. The chromaticity value or chromatic aberration cannot be obtained directly, but the chromaticity value and various other values can be evaluated through data processing. Spectrophotometers can be divided into two types: diffraction gratings and interference filters. The advanced spectrophotometer with built-in microprocessor has the functions of 0%, 100% automatic correction and magnification increase, thereby improving the accuracy.
The colorimeter is a simple test instrument, that is, to make a filter with spectral characteristics equal to the color sensitivity of the human eye, and use it to measure the sample. The key is to design a photoreceptor with spectral sensitivity characteristics and can The filter used to measure the color difference value under a certain light source. The color difference meter is small in size and easy to operate. It is more suitable for batch management of the same product with small changes in the spectroscopic characteristics. The color difference meter with a small microcomputer is easy to use a standard model. Correct and output multiple color difference values.
The color matching management software has spectroscopic reverse rate curve, color difference formula, conditional color representation, hiding power representation and haze representation. The spectral reflectance curve is used for analysis when selecting colorants and cannot be used to judge the consistency of colors. The color difference value is one of the most important indicators 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.
Computer color matching
Computer toning formula and its management have been successfully used in plastic color matching.
The computer color matching instrument has the following functions:
1) Color matching: Establish a database of commonly used colors (dyeing) materials according to requirements (preparation and input of basic color palettes). Then enter the incoming color palette into the computer under the software menu, click on several candidate pigments in the keyboard, and immediately calculate a series of formulas, and list them in order of color difference and price for color matching;
2) Formula correction: The computer lists formulas and formulas from other sources. When the color difference is unqualified, use the inconsistent reflection curve displayed on the display to directly increase or decrease the amount of pigment through the keyboard until the two curves basically overlap, and the revised formula is obtained;
3) Color measurement and chromatic aberration control Measure the color strength of the colorant, the whiteness of the product, the color fastness of the product, and the color difference. Since the computer can quantitatively express the color performance index, it is conducive to the communication and transmission of information between the two parties;
4) Color management The color samples, formulas, process conditions, production dates and users in daily work can be stored in the computer, which is convenient for retrieval, search and reference when modifying, convenient and fast, improve work efficiency, and facilitate confidentiality