Colorant
Colorants, also known as food pigments, are substances that take food coloring as the main purpose to endow food with color and improve food color. At present, there are more than 60 kinds of food colorants commonly used in the world, and 46 kinds are allowed to be used in China, which can be divided into two categories: food synthetic colorants and food natural colorants according to their sources and properties. With the improvement of people’s safety awareness of food additives, the development of natural, nutritious and multifunctional natural colorants has become the development direction of colorants
Introduction
Colorant
Coloring agent
Definition: Any substance that can make the substance show the color required by the design is called a colorant. It can be organic or inorganic, natural or synthetic.
The chemical synthetic pigments allowed to be used in China include amaranth, carmine, red moss, new red, lemon yellow, sunset yellow, indigo, brilliant blue, and various pigments to enhance the dispersibility of the above water-soluble acid pigments in oils.
China allows the use of 45 kinds of natural pigments: beet red, lac red, blueberry red, pepper red, red rice red, etc.
Colorants are mainly divided into pigments and dyes. Pigments can be divided into organic pigments and inorganic pigments according to their structures. Dyes are organic compounds that can be used in most solvents and dyed plastics. They have the advantages of low density, high colouring power and good transparency, but their general molecular structure is small and they are easy to migrate when coloring.
Finished products after coloring
Finished products after coloring
According to the source, the colorants can be divided into two categories: natural colorants and artificial colorants.
Natural colorants are carotenoids extracted or processed from animals, plants and microorganisms. At present, the natural pigments widely accepted and used in the international market mainly include marigold pigment derivatives (lutein) and capsicum pigment derivatives (capsanthin). In addition, natural animals and plants are often used as colorants in China; For example, ginseng stem and leaf powder, marigold powder, purple essence powder, cassava leaf powder, pine needle leaf powder, orange peel powder, acacia leaf powder, carrot, shrimp and crab shell powder, seaweed, etc. are used as colorants for livestock, poultry and aquatic products.
The synthetic colorant is mainly carotenoid. as β- Apo-8-carotal (C30H40O) or β- A-PO-8 carotenoid ethyl ester (C32H44O) and citrin (C33H44O), cantharidin, carmine, carmine, lucondine, etc.
Function introduction
Fundamentals of Feed Coloring
In order to make feed products more catering to users’ traditional habits, feed is generally dyed and processed into light yellow or yellow products. In the process of feed production, the purpose can be achieved by adding common colorants such as lemon yellow in a certain proportion.
Shading Basis
Animals themselves cannot synthesize pigments. The study also found that only carotenoids containing oxygen functional groups (such as hydroxyl, acyl, ketone, etc.) have coloring effect in livestock, poultry and aquatic products. These carotenoids include:
Lutein, lycopene and zeaxanthin. Carotenoids in feed are all in the form of palmitic acid diester. These carotenoids in feed are digested by animals and absorbed in free form, mainly by combining with low-density lipoprotein (LDL); The absorbed carotenoids enter the blood in a free state and enter the skin, egg yolk and other tissues with the blood circulation. Here, carotenoids are re converted into palmitic acid diester and deposited, making skin and egg yolk present the color people like (such as yellow). Different carotenoids deposit in different tissues with different efficiency. Generally, esterified lutein and zeaxanthin deposit better in animal tissues than crystalline lutein and zeaxanthin. Adding fat to the feed can promote the deposition of pigment, and it is found that adding animal fat is more effective than adding vegetable oil. In addition, with the increase of pigment level in feed, the proportion of pigment deposition in animal tissues decreased. It is reported that if each chicken eats 0.3~1.0mg of pigment every day, about 30%~45% of the pigment can be deposited in the egg yolk. If the pigment intake increases to 5mg or more, only 15%~20% can be deposited in the egg yolk. Crustaceans convert carotenoids in plants into prawn nutrients and chicken oil fungus xanthin by eating green plants. Fish feed on a large number of crustaceans and plankton to make their flesh bright. Goldfish and prawns can change the composition of pigment after absorption, such as transforming lutein into astaxanthin, and then depositing in body tissues.
Add reason
Colorant
According to the analysis results of psychologists, 83% of the external information that people receive by feeling comes from vision. It can be seen that the product appearance is important, especially the appearance color. As far as feed products are concerned, the appearance color of feed plays an important role in determining whether users will use a certain feed product or not. For livestock, poultry and aquatic products, especially poultry products, whether consumers are willing to buy and eat, the color of carcass skin and egg yolk are very important factors. The appearance color of livestock, poultry and aquatic products depends on the pigment content and accumulation of the feed taken. The traditional coarse feeding method has a long feeding period, and there are many pigments and gourmet accumulated in the animal body. The final product has a very pleasant appearance and color, which consumers are willing to accept, and the product price is high; On the contrary, due to the rapid development of modern breeding and breeding technology, livestock and poultry. The growth rate of fish and shrimp is very fast, and the feeding period of the product is very short, so the pigment obtained from natural feed is little, the product looks pale, loses its appeal to consumers, and the price is low. To solve this problem, it is obvious that the general demand is for colorants.
Add purpose
The addition and use of colorants are increasingly common in modern feed industry and modern animal husbandry and aquaculture. It has two purposes: first, to change the color of feed through colorants. Especially in the case of increasing use of non-traditional feed materials, add colorants to cover up the bad color of some non-traditional feed materials (such as rapeseed cake), cater to the psychological habits of users, and increase market competitiveness; At the same time, it also plays the role of stimulating appetite and inducing food; The colorants that play this role can be called feed colorants.
Second, improve the color and luster of livestock, poultry and aquatic products through colorants to enhance their commercial value. Such as adding colorants to make broiler skin. The meat quality of poultry egg yolks, milk butter, fish and shrimp and other aquatic products has a brighter, beautiful color and better product quality, catering to consumers’ psychology; The colorants that play this role can be called colorants of aquaculture products.
Influencing factors
Colored food
Main factors affecting the coloring effect of the colorant: The coloring effect of the colorant is affected by many factors. The main influencing factors are as follows:
Pigments are colorants that cannot be dissolved in ordinary solvents, so in order to obtain ideal coloring performance, it is necessary to evenly disperse pigments in plastics by mechanical methods. Inorganic pigments have good thermal stability and light stability, low price, but relatively poor coloring power and high relative density; Organic pigments have high tinting power, bright color, complete chromatography and low relative density. Their disadvantages are that they are inferior to inorganic pigments in terms of heat resistance, weather resistance and hiding power.
The white pigments mainly include titanium dioxide, zinc oxide and lithopone. Titanium dioxide is divided into rutile type and anatase type. The rutile type titanium dioxide has high refractive index, high hiding power, stability and good weather resistance. Carbon black is a commonly used black pigment, which is cheap. In addition, it has the function of ultraviolet protection (anti-aging) and electric conduction for plastics. Different production processes can produce various carbon black with a wide range of particle sizes and different properties. Carbon black is divided into pigment carbon black and rubber reinforcing carbon black according to its use, and pigment carbon black is divided into high pigment carbon black, medium pigment carbon black and low pigment carbon black according to its coloring ability. Carbon black particles are easy to gather. To improve the coloring power of carbon black, it is necessary to solve the dispersion of carbon black.
Pearlescent pigment, also called mica titanium pearlescent pigment, is a kind of mica chip coated with titanium dioxide. According to different colors, it can be divided into three categories: silver white pearlescent pigment, rainbow pearlescent pigment and color pearlescent pigment. The ability to color freely is a major advantage of most plastics. How to use cheap colorants to produce colorful and durable plastic products is also a concern of plastic processors. Colorants can be divided into dyes and pigments. Dyes are organic compounds with strong coloring ability. Although they have bright colors, complete chromatograms, and large coloring power, their heat resistance, light resistance, and solvent resistance are generally poor, and they are easy to seep out or migrate from plastics. Therefore, water-soluble dyes widely used in the printing and dyeing industry are generally not suitable for plastics. Only certain oil soluble and alcohol soluble dyes, such as azo and anthraquinone, can be used when the requirements for heat resistance are not high, Therefore, the colorants used in the plastic industry are mainly pigments. Pigments can be divided into inorganic and organic ones. Inorganic pigment has the advantages of good thermal stability and low price, but its color lacks brightness and transparency, while organic pigment has high color intensity and bright color, but its price is high. Inorganic pigments mainly include titanium dioxide, iron oxide, zinc oxide, chromate, tin compounds, mercury and cadmium, etc. Among them, titanium dioxide is the most widely used white pigment, which is often mixed with other pigments to obtain a series of colors. It has the advantages of chemical inertness, good thermal stability, low price and high coloring strength. Organic pigments mainly include carbon black, azo pigment, phthalocyanine, quinone, isoindole ketone, anthraquinone, thioindigo and various acid-base pigments. Among them, carbon black is the most commonly used black pigment. It has the advantages of low price, good dispersion, and good fluidity. At the same time, it is also a good filling weatherability for electrical conductivity of plastics and anti ultraviolet degradation. Many requirements can be put forward for the ideal colorant, such as bright color, large coloring power, easy to disperse evenly in the plastic without agglutination, high heat resistance without affecting the fluidity of the plastic, without affecting the aging resistance of the resin and other use properties, weather resistance, light resistance, low price and non-toxic, etc. But in fact, we can’t find an excellent colorant, so we can only consider different aspects for different purposes. For example, the decoration of plastic parts is mainly to meet the color requirements; For industrial plastic parts, the influence of colorants on the physical and mechanical properties of products shall be emphatically considered; For hollow containers, focus on the chemical stability of the colorant and its non interaction with the contents; Food packaging materials should focus on non-toxic and tasteless hygiene requirements.
Edible colouring agent
1. Food colorants: Food additives with the main purpose of food coloration are called colorants, also called pigments.
2. According to the source, it can be divided into two categories: food synthetic colorants and food natural colorants.
3. By structure: food synthetic colorants can be divided into azo colorants and non azo colorants;
4. Natural food colorants can be divided into pyrrole, polyene, ketone, quinone and polyphenol.
5. According to the solubility of colorants, it can be divided into fat solubility and water solubility.
Hazard introduction
Production enterprises are prohibited to add colorants and sweeteners, and long-term consumption of such products will seriously endanger human health. The quality supervision department reminds consumers to recognize the brand when purchasing jam products. Jam is an auxiliary food made from one or more fruits through pretreatment, crushing or pulping, sugar concentration and other processes. The quality supervision department inspected 19 batches of jam products produced by 18 enterprises, 13 batches were qualified, and the sampling qualification rate was 68.4%. The result of spot check shows that the quality of jam products sold in Jiangxi market is worrying. According to the introduction of the quality supervision department, the first major problem of unqualified products is the illegal addition of colorants. Among the 6 batches of unqualified products in this spot check, all of them are prohibited to add the colorant lemon yellow, and the 3 batches of products are prohibited to add the colorant carmine. Colorants are added to the product mainly to make the product bright and conducive to product sales; The second is the illegal addition of sweeteners. Among the 6 batches of unqualified products in this spot check, 3 batches of products are prohibited to add sweetener saccharin sodium. This is mainly because some enterprises use saccharin sodium to replace sugar production in order to save costs. Long term consumption of jam products with excessive colorants and sweeteners will endanger the health of consumers.
Safety of food synthetic colorants
There are 10 kinds of synthetic colorants allowed to be used in China. Natural colorants are mainly plant colorants, which are not only safe. Moreover, many natural colorants have certain nutritional value and physiological activity. Such as those widely used in fruit juice drinks β- Carotene colorants are not only provitamin A, but also have obvious anti-oxidation, anti-aging and other health functions. GB2760-2011 lists them as food additives that can be used appropriately in various foods according to production needs. Monascus red pigment, which is used for coloring various foods, also has obvious hypotensive effect. With the improvement of people’s awareness of the safety of food additives, the development of natural, nutritious and multifunctional natural colorants has become the development direction of colorants [1].
Plastic application
The coloring of plastics is mainly inorganic and organic pigments, which are required to have high coloring strength and brightness; Good transparency or covering, dispersion, weather resistance, thermal stability, chemical stability, electrical function, environmental protection performance, etc. Coloring force. The coloring power directly determines the amount of colorant. Generally speaking, the coloring power of organic pigments is much higher than that of inorganic pigments as the particle size of colorant decreases. When color pigments and white pigments are used together, the coloring power can be significantly improved. Nowadays, organic pigments and ultra-fine particles are widely used and developed. Dispersion. Only when colorants are easily dispersed uniformly in the form of tiny particles in polymers, can they obtain good coloring effects. Because the pigment contains many aggregated particles, it must be dispersed with high shear force to break the large aggregate to form a small aggregate to achieve the required particle fineness, so as to obtain the ideal optical effect. The pigment can be processed into a certain practical form, such as masterbatch, by means of surface treatment of pigment, which can effectively improve the dispersion of pigment. In addition, some additives can also improve the dispersion of colorants. Light and weather resistance. Generally speaking, inorganic pigments have good light stability. Among organic colorants, phthalocyanine, quinacridone, dioxazine, isoindolinone and other organic pigments have excellent light resistance, which can be compared with inorganic pigments; Dyes such as anthraquinone and ketone also have good light resistance. Migration resistance. There are three main types of migration of colorants: 1) solvent extraction, i.e. color bleeding in water and organic solvents; 2) Contact and migration, causing pollution of adjacent objects; 3) The surface frosting is mainly caused by the gradual crystallization and precipitation of colorant due to its high solubility in polymer during thermal processing and low solubility at room temperature. Inorganic pigments dispersed in polymers are generally heterogeneous and will not cause frost spraying, while organic pigments have different solubility in polymers and other organic substances, and are relatively easy to migrate. The difficulty of migration of organic pigments is closely related to the types of polymers and other additives, especially plasticizers and softeners. Experiments show that, generally speaking, the mobility of inorganic salts of organic acids is relatively small; The mobility of higher molecular weight is smaller than that of lower molecular weight. Heat resistance. Excellent heat stability is an important indicator of plastic colorants. Most inorganic pigments have good heat resistance, which can basically meet the requirements of plastic processing, while organic colorants have poor heat resistance. Due to the different chemical structures of various resins and plastics, different heating temperatures (above the softening point) are required during processing and molding. The temperature will directly affect the selection of colorants, so that their coloring will not change significantly at the specified temperature. The characteristics of resin structures are different, and the requirements for colorants are also different. Table 1 shows the processing and molding temperatures of resin plastics and the requirements for colorants. The processing temperature of other resins is 350 ℃ for fluororesin; Acrylate resin, 180-200 ℃; Silicone resin, 180 ℃; Phenolic resin, 150-160 ℃; Epoxy resin, 150 ℃; Cellulose plastics 180 ℃, etc. Suitable colorants can be selected according to different temperatures. Chemical stability. Due to the different use environments of plastics, the chemical resistance of colorants should be fully considered. For example, PVC and other chlorinated polymers are easy to decompose to produce hydrogen chloride, which may have a greater impact on the coloring effect and color fastness of colorants. Therefore, PVC and other chlorinated polymer products must use acid resistant colorants; For example, the influence of other additives such as antioxidants, hindered amine light stabilizers and dispersants in some plastic products on pigments can not be ignored. Electrical performance. Polyvinyl chloride, polyethylene and other plastics are largely used as the insulation layer or sheath of wires and cables. These application fields require that colorants have good electrical insulation performance. Some colorants will lead to the decline of electrical insulation performance after being added. Generally speaking, the reason for the decline of electrical insulation performance is mainly due to the residual electrolyte on the surface of the pigment, not the pigment itself, Therefore, some pigments containing soluble salts are not suitable for coloring plastic products such as wires and cables. Generally, carbon black, titanium dioxide, chrome yellow, phthalocyanine blue and other pigments have good electrical performance. Environmental performance. With the increasingly strict environmental protection regulations at home and abroad, many products put forward strict requirements on the toxicity of plastic colorants, and the toxicity of colorants has attracted more and more attention. Today, the United States, the European Union and other countries have clearly restricted the use of heavy metals, mainly including cadmium, lead, selenium and other colorants; Germany and other countries have also issued laws and regulations to restrict the use of some aromatic amine dyes and organic pigments. At present, there are still a large number of toxic colorants in production and use in China. To completely replace them, they still face challenges in terms of technology and cost.
Test method
1 Color performance (tinting power)
1.1 Importance of color performance in plastic coloring
Color performance is the most basic performance of plastic colorants. Color performance refers to tinting power, hue, and hiding power, which are the first characteristics to evaluate the tinting performance. Coloring force refers to a measure of the coloring depth of plastics given by colorants. Coloring force can be quantified as an absolute value or a relative value compared with other colorants. Hue refers to the basic color of pigment. In chromaticity, it can be expressed by hue, lightness and saturation. Color performance is an important performance index of colorants in plastic coloring, which determines the color quality, coloring cost and stability of coloring process of plastic products.
1.2 Determination of colouring power of pigments in plastics
(1) Test equipment: roll rotation of two roll plastic mill: 25 rpm, rotational speed ratio: 1:1.2, chrome plating on roll surface. The plate press can be heated and cooled. Two stainless steel mirror panels, inner frame: square frame, 0.5mm thick. (2) The test material consists of PVC resin, plasticizer, stabilizer, titanium dioxide and pigment. (3) The test method is to control the surface temperature of the roller at 160 ℃, and the thickness of PVC sheet is 0.4 mm; Plasticizing time: 7-8 minutes; Tablet pressing: press at 165 ℃~170 ℃ for 1 minute and then keep the pressure and cool quickly. (4) Color measurement: measure the standard color value and calculate the K/S value. The pigment tinting force test can compare the difference between the two tinting forces with its standard sample. When the two have the same tinting force. High density polyethylene, low density polyethylene and polypropylene can also be used for testing.
1.3 How to correctly apply the coloring force index for plastic coloring
(1) When the same pigment is used for coloring different plastics, its color performance, tinting power and other indicators are different. Strictly speaking, its application quality must be mentioned when referring to the color performance of pigment in plastic coloring.
(2) Standard depth In colorimetry, the absolute depth of the pigment can be judged by the color depth of the sample prepared under standard conditions, and expressed by the amount necessary to reach a certain color depth. It is expressed as standard depth, 1/3 standard depth and 1/25 standard depth. This representation method can be directly expressed by the color light continuous depth map designed by Schmelzer.
(3) The maximum absorption wavelength of the colorant determines its color, and the absorption capacity at the maximum absorption wavelength determines its tinting power. However, the coloring power is not only related to its chemical structure, but also to the dispersibility of pigments. The better the dispersibility of pigment, the higher its tinting power. (4) Pigment tinting power and color matching are of great significance. For example, the varieties with high tinting power (organic pigments) should be selected when preparing dark tones, and the varieties with low tinting power (inorganic pigments) should be selected when preparing light tones. When a pigment is lacking in color matching, or the price is expensive, other colors of the same color can be used instead, but the amount required to make the same color when the two pigments are different in coloring power is different.
2 Thermal stability
2.1 Importance of heat stability to plastics coloring
For various types of plastic resins, according to their equipment, process conditions and product requirements, the processing temperature ranges from 120 ℃ to 350 ℃/5 minutes. For example, soft and rigid PVC is generally 170 ℃~200 ℃, low-density and high-density polyethylene, polystyrene is 200 ℃~280 ℃, while polypropylene, polyaniline, ABS and polycarbonate are 250 ℃~330 ℃.
The heat stability of pigment refers to that under a certain temperature and within a certain time, the pigment will not have obvious color light, coloring force and performance changes. The thermal changes of pigments in plastics are composed of the following factors: (1) pigments are decomposed due to thermal chemical structure, for example, azo pigments are discolored due to thermal azo group breakage; (2) Chemical interaction between pigments and additives in plastic resin; (3) The pigment is dissolved in the resin when heated; (4) When the pigment is heated, its particle size changes.
The pigment has excellent heat stability, which can prevent the pigment from discoloring due to decomposition or crystal change under heat. The heat stability is an important application performance index of pigment used for plastic coloring.
2.2 Test method for thermal stability of pigments for plastics
2.2.1 Test equipment Single screw extruder: L/D=24; Injection molding machine.
2.2.2 Test the plastic degradation of raw pigment (HDPE, PP, PS, etc.). Test concentration: pigment concentration is 0.1%, 0.05%, 0.025%, 0.005% respectively; The corresponding titanium dioxide is 1%.
2.2.3 The test method can extrude the quantitative pigment mixture into uniform particles in a single screw extruder according to the concentration in (2). In the injection molding machine, according to a certain constant time and at intervals of 200 ℃, 220 ℃, 240 ℃, 260 ℃, 280 ℃ and 300 ℃, gradually manufacture the sample plate and test it. Assessment: After the color plate is cooled for 16 hours, test the color plate, and the color difference E=3 is the thermal stability of the concentration.
2.3 How to correctly apply heat stability index of pigment for plastic coloring
(1) The thermal stability index of pigment in plastic processing is related to its concentration
The thermal stability of some pigments varies greatly at different concentrations. For example, C.I. Pigment Purple 23 is used for HDPE coloring, and its concentration is less than 0.025%, and its thermal stability is only 200 ℃, while its concentration is more than 0.1%, and its temperature is only 260 ℃. (2) The thermal stability index of pigment in plastic processing is related to the application of material decomposition. The thermal stability index of pigment in a certain application and at a certain concentration is not equal to its index in other solutions. For example, C.I. Pigment Purple 23 can withstand 260 ℃/4 hours when dyeing polyester stock solution. Therefore, the pigment can only be selected after careful test under these conditions. (4) The heat resistance index of pigment in plastic processing is generally related to the addition concentration of titanium dioxide, and the heat resistance index will decline after adding titanium dioxide. (5) The heat resistance index of the coloring resin itself is related to the concentration of titanium dioxide. (5) The influence of the thermal stability of the coloring resin itself on the discoloration such as yellowing due to thermal degradation when the resin is heated, which will also affect the heat resistance index of the pigment used in plastics.
3 Dispersibility
3.1 Importance of dispersibility to plastics coloring
The dispersibility of pigments refers to the dispersibility of pigments in the coloring process. Because most plastic home processes are melt extrusion processes, the shearing force of pigments in the melt extrusion process is much smaller than that of pigments in the ink processing process in roller grinding and pigments in the coating processing process in sanding. Therefore, the dispersibility of pigments in plastics is another important indicator of pigments in plastics.
The dispersibility not only affects the tinting force and shade, but also affects the tinting appearance due to uneven dyeing due to poor dispersion, production streaks or color spots, and more seriously affects the mechanical properties of the finished products. Pigments with good dispersibility can obtain an ideal brilliance, brightness and transparency of plastic products. Therefore, the dispersibility of pigments is of great significance for plastic coloring.
When pigment is used in chemical fiber spinning, its dispersibility is more important. Due to the high melt pressure in the spinning process, the filter screen has to be replaced frequently, which wastes a lot of materials and labor and makes the equipment stop for a long time. More seriously, production cannot be carried out normally.
3.2 Determination method of color dispersibility
3.2.1 Test method
(1) Determination of dispersibility of pigments
Test method: take half of the diluted PVC sheet according to the method for determining the colouring power of pigments in plastics, control the surface temperature of the roller to 130 ℃, the thickness of the PVC sheet is 0.3mm, and the plastic refining time is 7-8 minutes. Tablet pressing temperature: 165~170 ℃; After 1 minute of tablet pressing time, keep the pressure and cool down quickly. Assessment: the dispersibility is calculated by the increase of coloring force after mixing under two different shear stress conditions. Grade 5 is the best and Grade 1 is the worst.
(2) Pigment filtration performance test
Pigment filtration performance (pressure index) is a measurement of the amount of pigment agglomeration and oversized particles in pigment dispersion. The increase of melt pressure in the extruder caused by pigment blocking the filter screen is expressed in kg/cm2/min.
3.2.2 Test equipment
Single screw extruder L/D=25, compression ratio: 1:3
The filter screen assembly shall be in the following specified order: 60100325, 60, 20 mesh, melt pressure sensor, placed between the screw end and the filter screen (range: 0kg/cm2~25kg/cm2)
3.2.3 Test concentration: polypropylene mixture with pigment content of 3%.
3.2.4 Test method:
Set extrusion temperature: 200 ℃ for conveying section, 240 ℃ for other sections, and extrusion capacity: 53g/min. Add the sample mixture into the extruder. When the sample mixture comes in and goes out, record the pressure P0. Record the pressure P60 within 60 minutes of continuous operation. The pigment filter pressure index DF can be calculated using the following formula: DF=(P60-P0)/60 DF value is less than 0.15, indicating that the pigment dispersion is good.
3.3 How to correctly apply pigment dispersibility index for plastic coloring
3.3.1 Effect of pigment dispersibility on plastic products
The dispersibility of pigments has a direct impact on the optical properties of plastic products. The color depth of plastic products is related to the dispersibility, the transparency increases with the decrease of pigment particle size, and the hue is also related to the dispersibility.
3.3.2 Dispersion of pigments in plastics and other effects
The dispersibility of pigments in plastics is related to other important factors besides the dispersibility of pigments themselves.
Characteristic use
The application of plastic materials and products in the world today has involved all walks of life, all aspects, and even every family. More and more business people are involved in the production and sales of plastic products. What kind of colorant should be used for plastic products has also become a topic of discussion among people in the plastic industry.
1 Types of plastic colorants
The types of plastic colorants can be divided into four categories according to their physical forms: powder colorants – toner; Paste colorant color paste; Liquid colorant; Solid color additive – color master batch. Among them, powder colorants and solid colorants are widely used. Therefore, the other two colorants are not discussed in this paper.
2 Characteristics of various colorants
2.1 Characteristics of toner coloring
The method of directly coloring plastic particles with toner (pigment or dye) and an appropriate amount of powder additives is also called dry coloring.
Its advantages are good dispersion, low cost and small batch operation. Because it saves the consumption of human and material resources in the processing of other colorants, such as color masterbatch and color paste, the cost is low, and the buyer and seller are not limited by the quantity. It is not possible to make 1~2kg color masterbatch, but the color powder can be arbitrarily designated according to needs, which is very convenient to prepare. Coloring with toner, compared with other pelleting coloring, the processed resin undergoes less than one degradation process, which is conducive to reducing the aging of plastic products and increasing their service life.
However, the biggest disadvantage is that pigments will fly during transportation, storage, weighing and mixing, causing pollution and seriously affecting the working environment. With the requirements of environmental protection and ISO9000 indicators of enterprises, toner coloring is more and more limited. However, for coloring with special effects, using toner directly mixed with coloring has some effects that cannot be achieved by masterbatch coloring. For example, some pigment powders with poor heat resistance and fear of shearing are used to make color masterbatch. Because they endure high temperature for a long time and are subjected to shearing in color masterbatch processing equipment for a long time, the coloring effect will be significantly weakened, such as pearlescent color powder, fluorescent powder and luminous powder. The pearlescent effect of colored plastics made of color masterbatch with pearlescent powder is about 10% less than that of plastics directly mixed with pearlescent powder for coloring, and injection molded products are also prone to streamline scars and seams. When manufacturing such color masterbatch, corresponding measures shall be taken to minimize the temperature, time and shear degree of color masterbatch heated during processing (instead of twin-screw granulator, single screw granulator, etc.).
Another headache for users of dry dyeing is that the hopper of the extruder is not easy to clean. The toner used for coloring is attached to the inner wall of the barrel (even on the screw) under the action of white oil and other wetting agents. When it is necessary to change the materials, cleaning the material cylinder becomes a problem for the on-site operators, which takes time and materials, and gets half the result with twice the effort. However, the use of color masterbatch has no such problem.
In addition, the pigment powder is used for coloring. Since the pigment powder is evenly distributed in the resin to be colored, its dispersivity is good. This conclusion can only be applied to injection molding products, especially thick wall products, but not to blown film and spinning products. Because the toner has not been pretreated in general, when it is mixed with the resin, it can not be guaranteed that the molecules of the pigment powder and the colored pigment molecules can work together well – full combination – only by the distance from the feed inlet, screw, to the outlet of the extruder and the short plasticizing mixing time. However, this “sandwich” phenomenon will be covered up in thick wall products, which is obvious in blown film and spinning products. Therefore, the coloring method of the latter is still based on color masterbatch.
In addition, due to the different production date and batch number of color powder manufacturers, color powder of the same brand also has a certain color difference. Even if users insist on using the same formula, it is difficult to achieve the color consistency of injection molding products between batches in the processing process. In the production process, color masterbatch can compensate for the color difference of each batch of color powder through midway sampling, inspection and adjustment. Relatively speaking, The repeatability of color masterbatch is obviously better than that of color powder.
Because of the limitations of toner used for coloring plastic products, it is challenged by other colorants. However, due to the relatively low production cost, color fixing and matching are not limited by the amount. For SMEs and private enterprises in developing countries, if they want to participate in the fierce market competition, the use of toner has certain economic benefits, especially for some products with single color sample, large output and low color requirements, such as PVC doors and windows EVA sole, etc., is still in favor of it, so toner colorant cannot completely exit the stage.
2.2 Coloring characteristics of color masterbatch
In order to overcome the disadvantages of toner coloring and improve the quality of plastic products, with the continuous development of the plastic industry and the continuous innovation and breakthrough of the types of plastic resins, additives, plastic products processing equipment and processes, masterbatch coloring, another way of plastic coloring, has been widely used, and masterbatch coloring technology has also been constantly improved in application and practice.
The so-called masterbatch refers to the use of a certain process and corresponding equipment, under the action of auxiliaries, to mix pigments (or dyes) into the carrier, through heating, plasticizing, stirring, and shearing, finally to fully combine the molecules of pigment powder and carrier resin, and then to make particles similar to the size of resin particles. This high concentration colorant is called color masterbatch, and its function is similar to that of “saccharin”. When it is used, only a small proportion (1%~4%) needs to be added to the resin to be colored to achieve the purpose of coloring the resin.
Compared with pigment coloring, masterbatch coloring has the following obvious advantages:
(1) The problem of environmental pollution caused by the flying toner is improved. The color change is easy in the use process, and the extruder hopper does not need to be specially cleaned. It is very convenient.
(2) Strong pertinence and correct color matching. As the color masterbatch manufacturing factory has reasonably selected pigments (dyes), additives, processing equipment and processing technology according to the performance of the applicable resin in the manufacturing process, and timely corrected and supplemented the color differences that may be caused by different batches of toner in the production process, and then inspected them when leaving the factory, it can ensure that the color of the two batches of color masterbatch with the same brand remain relatively stable.
(3) Compared with making plastic parts after batch resin dry dyeing and granulation, the use of color masterbatch can reduce the resin property aging caused by secondary processing of plastic products, which is conducive to the improvement of the service life of plastic products.
The biggest advantage of using color masterbatch is that the color masterbatch is fully mixed with the carrier resin under the action of additives during the processing. When it is used, it is placed in the resin to be processed in a certain proportion, and the color masterbatch quickly enters into the role of recognizing “relatives” with the resin. Affinity — the compatibility is obviously better than the toner coloring, so it is more appreciated by the manufacturers of film and spinning products.
Of course, color masterbatch coloring also has its limitations. Due to the small amount of addition and short processing time of plastic products, the dispersion of color masterbatch is often inferior to that of color powder due to the limitation of the length diameter ratio of the extruder screw. More than one manufacturing process, the dyeing cost must be higher than the toner dyeing. When the performance of the carrier in the color masterbatch is different from that of the resin to be colored, the surface of plastic products often has undispersed spots, color spots and patterns. Therefore, the use of color masterbatch is limited due to its compatibility and dispersion.
3 Selection of general color masterbatch and special color masterbatch
It is precisely because masterbatch coloring has many advantages over toner coloring. With the development of plastic product processing industry, especially the establishment of many joint ventures and the improvement of the coloring requirements of export products, masterbatch coloring gradually takes the leading position. According to the classification of the applicability of masterbatch, it can be divided into general masterbatch and special masterbatch.
3.1 Special color masterbatch
In the production of masterbatch, the same resin as the resin to be dyed is selected as the carrier, and high concentration pigments (dyes) are added. Under the effect of additives, the colorant specially suitable for this resin is made by heating, plasticizing, mixing and extruding granulation, which is called special masterbatch. The concentration of special color masterbatch can be high or low, and the general addition amount is between 1% and 4%.
3.2 Universal color masterbatch
The main difference between the universal color masterbatch (also known as the “universal color masterbatch”) and the special color masterbatch is that although the universal color masterbatch also uses a certain resin as the carrier, it can be used for coloring other resins except the carrier resin, so it is called the universal color masterbatch.
For the so-called universal color masterbatch, the following measures are generally taken (some manufacturing plants simply do not use resin as the carrier, but use high melting point propylene wax as the carrier): firstly, resin with low melting point and high melt index is selected as the carrier of universal color masterbatch, such as PE or EVA; Secondly, the ratio of pigment powder in color masterbatch shall be as high as possible, so the general color masterbatch must be high concentration color masterbatch, and the amount used in injection molding products is generally 1%. Since there are very few different media carriers in the color masterbatch (generally about 20% after deducting the factors of additives), when it is diluted in the resin to be colored with a ratio of 1%, the content of different resins in the plastic product is 0.2kg/100=2g/kg. In order to make the universal color masterbatch combine well with other types of resins to be colored (good affinity), other measures have been taken in the universal color masterbatch, such as adding more special coupling agents, extending the internal mixing time, etc., which are conducive to improving the wide applicability of the universal color masterbatch.
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3.3 Selection principle
Which color masterbatch is appropriate? Is universal color master most appropriate? Let’s analyze from the aspects of manufacturing plants, dealers, users, economic benefits, convenience, product effects, etc.
From the perspective of manufacturing plants, in order to produce universal color masterbatch, pigments with high heat resistance grade and wide application range must be selected. After the temperature resistance grade of pigment powder reaches a certain level, the cost of pigments will increase by 50%~100% for every 10 ℃~20 ℃ increase. When the universal color masterbatch made of a certain high-temperature resistant pigment is used for coloring the high melting point resin, it is used as a material, while the tree finger used for low melting point such as LDPE increases the residual value.
In addition to the coloring and color deviation mentioned above, due to the small addition ratio and relatively poor dispersion, the plastic products are prone to appear patterns, color spots and color spots on the surface, which still lead to brittle skin and other phenomena due to the disharmony of materials, especially for the plastic parts with large area and complex thin-wall shape. At this time, special color masterbatch shall be used as far as possible, and the color masterbatch with low concentration shall be selected, The dispersibility of the product can be improved by increasing the addition amount (1 ∶ 20, 1 ∶ 10 special color masterbatch can be selected).
It can be seen from the above analysis and comparison that the general color masterbatch and the special color masterbatch have their own advantages, but the special color masterbatch is still superior to the general color masterbatch in terms of coloring effect and product performance. It is recommended that after the user has determined the type of resin to be colored, the special color masterbatch is preferred.
