Knowledge of plastic color matching
Plastic color matching
Color matching is in red, yellow, blue (three primary colors) on the basis of three basic colors, with a favorite, in line with the color card color difference requirements, in line with the customer hope to get the color, economic and in processing, use color. In addition, plastic coloring can also give plastic a variety of functions, such as improving plastic light resistance and weather resistance; Give plastic some special functions, such as electrical conductivity, antistatic, antibacterial properties and other special materials; Different color mulch film has the effect of weeding or avoiding insects, seedling and so on. That is, through color matching can also achieve certain application requirements.
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 disperse pigments evenly in plastics by means of mechanical heating and mixing.
Pigments are classified into organic pigments and inorganic pigments according to their structure.
Advantages: good thermal stability, very good weather resistance, excellent light stability, low price, excellent dispersion performance. For example: titanium dioxide, carbon black and so on.
Titanium dioxide series
There are mainly titanium dioxide, zinc oxide, zinc barium white three kinds. Titanium dioxide rutile type and anatase type two types of structure, rutile type titanium dioxide refractive index is high, high covering power, stability, good weather resistance. If titanium dioxide is not dispersed when the original factory leaves the factory, there will be a large number of black spots in the color matching process, which belongs to the state of dispersion and is not opened. Therefore, dispersant is needed for dispersing processing before it can be used. After processing, some manufacturers' brands enter the market, and such materials can be directly used. Mainly used to cover the transmittance of resin and increase the whiteness.
It is commonly used black pigment with low price. In addition, it has ultraviolet protection (anti-aging) effect and electric conductivity effect on plastics. Different production processes can get a wide range of different carbon black particle sizes, with very different properties. According to the use of carbon black is divided into pigmented carbon black and rubber reinforced with carbon black, pigmented carbon black according to the coloring ability and divided into high pigmented carbon black, medium pigmented carbon black and low pigmented carbon black. Carbon black particles are prone to aggregation. To improve the coloring power of carbon black and to solve the dispersion of carbon black, dispersants should be added for processing before use.
Disadvantages: relatively poor coloring, relatively high density, large amount of addition, not bright color;
Mainly used in: used to increase the color concentration (according to the color needs generally all kinds of resin can), especially in engineering plastics has a good superior performance, such as: PA, PC, PBT, POM, PPO, PPS and other materials and non-transparent color, gray resin.
Advantages: high tinting power, bright color, complete chromatography, small relative density, small amount of additives.
Disadvantages: heat resistance, weather resistance and hiding power are not as good as inorganic pigments, poor dispersion effect, poor transparency compared with dyes, and the price is higher.
Mainly used in: POM, PE, PP, TPU, TPE and other crystalline materials and part of the bright color (dye brightness can not reach the bright color products) products.
Advantages: dyestuffs are organic compounds that can be used in most solvents and stained plastics. The advantages are low density, high tinting power and good transparency.
Disadvantages: However, its general molecular structure is small, and it is easy to migrate when colouring (crystalline material) is more expensive than inorganic material, and part of the price is close to that of organic pigment.
Also known as titanium mica pearlescent pigment, it is a titanium dioxide coated mica chip. According to the different hue, it can be divided into three kinds of silver and white pearlescent pigments, rainbow pearlescent pigments and color pearlescent pigments.
Buy paint, must understand the pigment dye index (C.I), C.I is dyed by the UK association and the American association of textile chemists and dyeing house et.al. The publication of the international assembly, dyes, pigments varieties each pigment according to application category and chemical structure, there are two number, avoid purchases for the same molecular structure, different term pigment happen misunderstanding, also is advantageous to the use of color management, and use the right paint is convenient to find the problems of the reasons.
2. Color matching and coloring process
Color matching and coloring can be directly added to toner resin, toner mixed resin extrusion method and color masterbatch method.
Method of adding toner directly to resin:
After mixing toner and plastic resin directly, it is sent to the next product forming process, with short process, low cost, but poor working environment, poor coloring power, poor coloring uniformity and poor quality stability.
Extrusion method of toner mixed resin:
This method has the best effect on the uniformity of resin and color. It can fully disperse the pigment in the resin. The color is accurate, the quality is clean and easy to be processed.
Color masterbatch method:
Is a colorant and carrier resin, dispersant, other additives prepared into a certain concentration of colorant granule, product molding according to the coloring requirements, add a certain amount of color masterbatch, make the product contains the required coloring dose, to meet the coloring requirements.
Color masterbatch can be classified according to the resin to be colored, such as ABS, PC, PP masterbatch, etc. Can also be added by coloring resin process classification, injection molding, blown film, extrusion stage three categories of master. The color masterbatch has higher coloring power, lower dosage and stable quality, convenient transportation, storage and use, and lower environmental pollution.
Dispersant on the surface of a pigment wetting, penetration to exclude air, scatter agglomerations, aggregate into tiny, stable and uniform particles, and are no longer together, in the machining process commonly used dispersant for low molecular weight polyethylene wax, for difficult to disperse organic pigments and carbon black by EVA wax or oxidized polyethylene wax, synthetic low molecular weight polyethylene and polyethylene wax cracking the legal system of low molecular weight polyethylene wax have very big difference. Other auxiliaries have coupling agents, antioxidants, light stabilizer, antistatic agents, fillers, depending on the requirements and varieties and the amount of addition, known as multifunctional masterbatch, such as adding brightener, is conducive to mold products and improve 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, migration, chemical resistance and toxicity of pigment are also related to the performance of color masterbatch. Some indexes are very important for special purposes, such as the pressure filtration value (DF value) fineness of fiber masterbatch.
3. Color matching management and instruments
The hardware of color matching management includes a colorimeter and a computer that processes the measured data. The colorimeter can be divided into two kinds: spectrophotometer and chromometer, which can replace the human eye to measure color and remove the influence of human factors on the determination results.
The spectrophotometer is used to measure the reflection coefficient of each wavelength to the complete diffuse surface. The chromaticity value or chromatic aberration cannot be obtained directly, but the chromaticity value and other various values can be evaluated by its data processing. Spectrophotometers can be divided into two types: diffraction grating spectrophotometry and interference filter spectrophotometry. Advanced spectrophotometer with built-in microprocessor, with 0%, 100% automatic correction and multiplier increase, so as to improve the accuracy.
Color difference meter is a kind of simple test instrument, which made a piece with the human eye color sensitivity is equal to the spectral characteristics of filter, use it to metering model, the key is to design a light sensor spectral sensitivity characteristics of color difference and can in some kind of light source and optical filter, color difference meter small volume, simple operation, more suitable for the same product of spectral properties change little batch management, with a small computer color difference meter, easy to use standard template for multiple color correction and output value.
The color matching management software has spectral inversion curve, color difference formula, condition color representation, covering force representation and haze representation. Spectral reflectance curves are used to analyze the selection of colorants and cannot be used to determine the consistency of colors. The color difference value is one of the most important indexes in color management, but the color difference obtained by different color difference formula is different, so the color system or color difference formula used must be indicated.
4. Computer color scheme
The formulation and management of the color mixing by computer have been successfully applied to the plastic color matching.
The computer color matching device has the following functions:
1) According to the requirements of color matching, the database of commonly used color (dyeing) materials is established (basic color plate is prepared and input). Then input the swatch into the computer under the software menu, point out several candidate pigments in the keyboard, and immediately calculate a series of formulas, and list them in order of color difference and price respectively, for color matching selection;
2) Formula Correction The computer lists the formula and formula from other sources. If the color difference is not qualified, the inconsistent reflection curve displayed on the display can be used to directly increase or decrease the amount of pigment through the keyboard until the two curves basically coincide to obtain the corrected formula;
3) Color measurement and color difference control measure the color intensity of colorant, whiteness of products, color fastness of products and color difference. Since the computer can quantitatively express the performance index of color, it is beneficial to the communication and transmission of information between the two parties.
4) Color management The color sample, formula, process conditions, production date and user information in daily work can be stored in the computer for easy retrieval, search and as a reference for modification, convenient and fast, improve work efficiency, and easy to keep secret.