Thread Content
1. Definition: Color matching is based on the three basic colors of red, yellow, and blue, to match colors that are pleasing to the eye, meet the color difference requirements of the color card, are economical, and do not discolor during processing and use. 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 certain special functions, such as conductivity and antistatic properties ； Different colored agricultural mulch films have functions such as weeding, insect repelling, and seedling cultivation. That is, certain application requirements can also be achieved through color matching. 2. Colorants: Colorants are mainly divided into two types: pigments and dyes. Pigments are colorants that are insoluble in ordinary solvents. Therefore, to obtain ideal coloring properties, mechanical methods need to be used to disperse the pigments evenly in the plastic. According to the structure, it can be divided into organic pigments and inorganic pigments. Inorganic pigments have excellent thermal stability and light stability, low price, but relatively poor tinting power and high relative density. ； Organic pigments have high tinting power, bright colors, complete color spectrum, and low relative density. The disadvantages are that they are not as good as inorganic pigments in terms of heat resistance, weather resistance, and hiding power. Dyes are organic compounds that can be used in most solvents and dyed plastics. They have the advantages of low density, high tinting power, and good transparency. However, their general molecular structures are small and they are prone to migration during coloring. There are three main types of white pigments: titanium dioxide, zinc oxide, and zinc-barium white. Titanium dioxide is divided into two structures: rutile type and anatase type. Rutile type titanium dioxide has high refractive index, high hiding power, stability and good weather resistance. Carbon black is a commonly used black pigment and is cheap. In addition, it also has UV protection (anti-aging) and conductive effects on plastics. Different production processes can produce various carbon blacks with a wide range of particle sizes, and their properties vary greatly. Carbon black is divided into pigment carbon black and rubber reinforcing carbon black according to its use. Pigment carbon black is further 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 aggregation. To improve the tinting power of carbon black, the dispersion of carbon black must be solved. Pearlescent pigment, also called mica-titanium pearlescent pigment, is a titanium dioxide-coated mica wafer. According to different hues, they can be divided into three categories: silver-white pearlescent pigments, rainbow-type pearlescent pigments, and colored pearlescent pigments. When purchasing pigments, you must understand the dye index (CI) of the pigment. CI is an international compilation of dyes and pigment varieties jointly compiled and published by the British Colorists Association and the American Textile Chemists and Colorists Association. Each pigment has two numbers according to application and chemical structure category. This avoids misunderstandings about pigments with the same molecular structure and different names during purchase, and is also helpful for management and finding reasons during use. 3. Color matching and coloring process: Color matching can be done by directly adding the toner to the resin or the masterbatch method. After the toner is directly mixed with the plastic resin, it is sent to the next step of the product forming process. The process is short and the cost is low, but the working environment is poor, the tinting power is poor, and the coloring uniformity and quality stability are poor. The masterbatch method is to prepare colorant, carrier resin, dispersant, and other auxiliaries into pellets with a certain concentration of colorant. When molding the product, a certain amount of masterbatch is added according to the coloring requirements so that the product contains the required amount of colorant and meets the coloring requirements. 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 processing technology, and there are three categories of masterbatch: injection molding, blown film, and extrusion grade. Because the pigments are pre-treated first, the masterbatch has high tinting power, the dosage can be reduced and the quality is stable. It is easy to transport, store and use, and the environmental pollution is greatly reduced. The dispersant removes surface air by wetting and penetrating the pigment, and 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 blacks 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 method. Other additives include coupling agents, antioxidants, light stabilizers, antistatic agents, fillers, etc. The amount added depends on the requirements and variety, and is called a multifunctional masterbatch. Adding a brightener, for example, is beneficial to the demoulding of molded products and improves the surface brightness of the products. The performance indicators of the masterbatch include color difference, whiteness, yellowness, yellowing degree, 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 performance of the masterbatch. Some indicators are very important in specialized applications, such as the fineness of the filter press value (DF value) of the fiber-grade masterbatch. 4. Color matching management and instrument color matching management hardware include colorimeter and computer for processing the measured data. Colorimeter can be divided into two types: spectrophotometer and colorimeter, which measure color instead of the human eye and remove the influence of human factors on the measurement results. The spectrophotometer is used to measure the reflection coefficient of each wavelength on a completely diffuse reflecting surface. It cannot directly obtain the chromaticity value or color difference, but it can evaluate the chromaticity value and other various numerical values through its data processing. Spectrophotometers can be divided into two types: diffraction gratings and interference filters. The advanced spectrophotometer with built-in microprocessor has functions such as 0% and 100% automatic correction and magnification increase, thereby improving accuracy. A colorimeter is a simple testing instrument, which is to make a filter with spectral characteristics equal to the color sensitivity of the human eye and use it to measure light on a sample. The key is to design a filter that has the spectral sensitivity characteristics of the photoreceptor and can measure the color difference value under a certain light source. The colorimeter is small in size and easy to operate. It is more suitable for batch management of the same product with small changes in spectral characteristics. A colorimeter with a small computer can easily use a standard sample to calibrate and output multiple color difference values. The color matching management software includes spectral reversal rate curve, color difference formula, conditional isochromatic representation, hiding power representation and haze representation. The spectral reflectance curve is used for analysis when selecting colorants and cannot be used to judge color consistency. Color difference value is one of the most important indicators in color management, but the color difference calculated by different color difference formulas is different, so the colorimetric system or color difference formula used must be indicated. 5. Computer color matching: The use of computers for coloring formulas and their management has been successfully used in plastic coloring. The computer color matching instrument has the following functions: (1) Color matching Establish a database of commonly used colors (dyes) according to requirements (prepare basic color plates and input them). Then input the incoming color palette into the computer under the software menu, click on several candidate pigments on the keyboard, and immediately calculate a series of formulas, and list them in order of color difference and price for color selection. ； (2) Formula correction. Correct the formula listed on the computer and formulas from other sources. When the color difference is unqualified, use the inconsistent reflection curve displayed on the monitor to directly increase or decrease the amount of pigment through the keyboard until the two curves basically coincide, and the corrected formula is obtained. ； (3) Color measurement and color difference control Measure the coloring 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 performance indicators of color, it is conducive to the communication and transmission of information between both parties. ； (4) Information such as color samples, formulas, process conditions, production dates and users in daily work of color management can be stored in the computer, which is convenient for retrieval, search and reference for modification. It is convenient and fast, improves work efficiency, and facilitates confidentiality.