For colored polymeric materials, there are two possibilities of introducing colorant: by coloring in the mass of polymer material or the addition of a concentrate which includes the polymer, the colorant and special additives. Both methods have advantages and disadvantages.
Staining bulk polymer preferably used for polymeric materials, some of which characteristics (mechanical strength in continuous operation, incombustibility) rigidly defined. First of all it refers to the polymers constructional purposes. For these polymers, the color itself is not a big deal, since it is determined by international standards.
In case you need to staining polymer for the production of, for example, consumer goods, and color output Party explicitly stated by the customer, it becomes much more difficult to acquire dyes for coloring in the mass at affordable prices to meet the desire of the customer to have its “brand” color, solve emerging issue staining can products using the concentrates.
Consider the advantages and disadvantages of using concentrates:
the need for additional equipment (eg. dispenser premixed, devices for measuring color, etc.)
in the presence of an extruder screw mixing Profile
further training of staff
stringent quality compliance staining
shortness dyeing process
low cost of raw materials
Shipping and storage containers and concentrate containers other
the need for small amounts of concentrate
high flexibility in achieving the desired color
fast delivery of new concentrates manufacturers
quick and easy change of color in the processing device
more features flexible response to higher prices
Having considered all the advantages of using masterbatch coloring, it becomes clear why this process was so widespread.
Requirements for concentrates for coloring plastics.
The following is a list of criteria in accordance with which the concentrate formulation is determined by:
Physical state concentrate
Type a painted polymer
Process parameters polymer processing
The concentration of colorant
Selection of additives, fillers, stabilizers.
After the above will be coordinated position, we can talk about the creation of a specific concentrate. But it is necessary to concentrate characteristics strictly comply with international requirements of the polymer products.
1. Chemical resistance.
The need for chemical resistance concentrates is not always obvious at first glance, but it becomes apparent when get acquainted with the operational requirements for polymer products. According to international standards, the manufacturer of colorants check their resistance to acids (HCl, H2SO4, HNO3), alkalis (NaOH, KOH) and peroxides. The test results cover a wide area of use of colored polymers as polymeric containers, bottles, boxes, films are used in daily life widely. Many products are packaged in polymer containers, have little acidity or alkalinity. Tests peroxides are particularly important. Firstly, unsaturated polyolefins polymerized in the presence of peroxide as a catalyst; Second, modern detergents for textile products contain peroxides.
Chemical resistance is a property of the system as a whole, comprising at least a colorant and a polymer. Because of the large variety of both polymers and colorants, it is impossible to check the chemical resistance of all possible combinations of polymer-colorant. Not excluded is also tested for long-term storage, especially for polymers used as packaging activities. Only testing can determine whether the interaction between the dyed polymer and its container storage conditions for a predetermined time. According to the specific field of use, the requirements for chemical resistance of colored polymeric materials can vary substantially and be very specific. In this connection, only for long-term storage test can determine if all the requirements of the system will be operated as a whole, comprise a polymer and the colorant additives. Predict the behavior of the system by testing its individual parts is impossible.
2. Resistance to the migration of the pigment and discoloration.
Resistance to migration is a common requirement for all colorants. Many of the international rules and regulations prescribe the absence of migration of colored products. It should also distinguish between migration and discoloration of the pigment.
Bleaching effect occurs when the colorant dissolved moves from the volume of the polymeric article to the surface where recrystallizes. Since the pigment by definition is insoluble in the polymer can become discolored only dye dissolved in a polymer. In practice, however, all the organic pigments are soluble in the polymer and therefore may also discolour.
Manifestation of pigment migration are numerous. As pigment. and dissolved in the polymer dye exhibit migration under certain conditions. There are two ways to pigment migration.
Firstly, the pigment migration is observed when the polymeric article comprises a kneader, wherein the limited solubility of many organic pigments. Therefore, the migration of the pigment occurs simultaneously with migration of the kneader volume to surface of the product for this reason, many organic pigments can be used in the plasticizing polymer, such as polyvinyl chloride (PVC) or polyurethane (PU) elastomers.
Another possibility for the migration can occur when a polymeric product does not contain solvents or kneaders, but be in contact with a solvent and (or) a polymer containing a kneader. The solvent and (or) the kneader may partially dissolve the organic colorant on the surface of the article. As a result, the colors will be transferred to a different environment, which is also a migration of pigment.
The bleeding can be a serious problem in the production of packaging polymers, since the liquid content of polymeric packaging often contains a component which is a solvent of the pigment.
3. The shrinkage and warpage.
Any material, including polymers, expanding as the temperature rises. Therefore, the amount of polymer melt will be greater than the volume of the same polymer in the solid state, and cooling the melt shrinkage will occur. Shrinkage is very important feature in the processing of polymers, and should be taken into account, in particular, in the design of the mold. It is known that the polymers have greater shrinkage in the melt flow direction than in the transverse direction. Furthermore, any additives including colorants and fillers to polymers will to some extent affect the shrinkage of the finished product. The amount of shrinkage of the polymeric article in the presence of colorant depends on the chemical structure of the colorant, the polymer type, the particle size of colorant and its concentration. For partially crystallizable polymers, such as polyethylene (PE) or polypropylene (PP), shrinkage depends on the degree of crystallinity.
The processes of shrinkage and warpage of polymer products are closely linked. As already mentioned, the shrinkage is partially crystallizable polymer, such as PE, in the direction of flow of the polymer melt is greater than in the transverse direction, and therefore, after cooling, a symmetrical body of revolution becomes oval and asymmetric rotation body will experience significant distortion or warping. The distortion may also be a polymeric article unevenness, because the polymer has a very low thermal conductivity, and the cooling rate of a thick wall is much lower than the cooling rate of the thin wall. Examples gage polymer article may be for example a bottle crate with a large number of thin and thick walls sidewalls.
Many organic pigments affect shrinkage partially crystallizable polymers as act as nucleation sites; while inorganic pigments do not exhibit such an effect. In practice, the shrinkage caused by organic colorants plays an important role in those cases where the polymer parts are joined, for example, a screw cap, gears, utensils of composite polymers. A common requirement in the use of composite polymers – very good dimensional stability, regardless of color. However, considering the wide palette of colors, you’ll find that this requirement is not feasible for any of them, so the trade-offs between coloring polymers and shrinkage can not be avoided.
Each new chemical substance that appears on the market, must be previously characterized not only by its technical, physical and chemical characteristics, but also for toxicological properties. international standards for testing to assess toxicological risk to humans based on the realities of modern life. Toxicological tests simulate a single contact, and multiple potential human exposure to chemicals. They establish the possible impact on the intrauterine development of the embryo and the possible toxicological risk to the environment.
Toxicological tests include studies aimed at studying:
The data on short-term toxicity provide information about the impact of a possible short-term one-time effects on human health. Acute toxicity is defined as poisoning after a single ingestion, skin contact and inhalation. All toxicological tests investigated the pure substance, but in fact the contact person with a pure colorant is limited only by the stages of production and processing.
Chronic study involves repeated exposure to the test substance to the animals, usually within 90 days (predohranicheskaya toxicity) or two years (chronic toxicity). Chronic solids is studied by adding a substance to an animal feed, and gas – by inhalation. The most important task of long-term tests for admission into the test substances is a risk of cancer.
There are many methods for testing of chemicals for mutagenicity, but only a few of them have received universal recognition. The purpose of such studies – to determine the potential impact of chemicals on the genetic material.
Another problem is the question of the impact of chemicals on the embryonic development and the emergence of pathologies during pregnancy. Experiments with the use of mutagenic substances inside give an answer to this question. Chemical substances. gave a positive test result, are classified as hazardous to the fetus.
effects on reproductive function
Effect of chemicals on human reproduction are also investigated. As in the previous case, the chemicals which are positive in the test are classified as dangerous for the reproductive function.
The purpose of environmental studies is the protection of the environment that has become very topical in recent years. Methods of environmental studies depend on how the chemical enter into the environment. Gaseous substances, for example, are checked by the nature of their impact on the ozone layer, the solids are investigated for possible toxicity to algae, bacteria, fish and other living organisms. The research results presented in the form of security certificates.
Colorants for polymers are substantially insoluble in water and in most cases biologically inert. However, the potential risk of contamination of water colorants can be removed by filtration, sedimentation or adsorption.
It should be noted also that the substance is completely safe for the results of toxicology studies could. nevertheless constitute a danger to the environment. Examples include certain types of fluorine-containing hydrocarbons that are safe for humans, but deplete the ozone layer of the atmosphere.
5. Heat resistance
All manufacturers of polymers provide customers detailed information regarding the characteristics and recommendations for its revision. The processing temperature depends on polymer type and grade of polymer and may vary over a considerable range from 160-200 ° C (PVC) to 320 ° C (polysulfone). At the same time, the processing temperature colored polymers means that the colorant is able to withstand this temperature. in practice this does not cause any particular problems, since the heat resistance of virtually all colorants temperature exceeds 320 ° C.
Heat resistance colorant, also known as heat resistance depends on:
type crystal structure, if the pigment is a crystalline substance
effective concentration of the colorant in the polymer
the type and brand of the polymer to be painted
processing parameters, such as residence time in the extruder. the use of hot runner injection molding system, etc.
presence of additives, e.g., fillers, stabilizers, flame retardants, etc.
It should also distinguish between the heat resistance and heat resistance. Thermal stability of a substance characteristic chemical structure remains unchanged with increasing temperature, while the heat resistant material is characterized by the ability to soften (i.e., to maintain the shape) as the temperature increases.
Thermal stability of the colored polymer, as well as many other features will depend on all components of the system and can not be defined for the polymer in the presence of only one pigment.
In the study of heat-resistant organic colorant stepwise increase the processing temperature to a temperature near which the polymer begins to show signs of discoloration; it is taken as the limit of thermal stability of the colored polymer.
Most of inorganic pigments are the reaction products occurring during high-temperature calcination (700 to 900 ° C). Therefore, heat resistant inorganic pigments are much higher heat resistance of any polymer, and in this case, the determination of heat resistance by direct repetition standard tests lead to incorrect results.
Manufacturers colorants certificates usually indicate two temperatures: pure thermal stability and color tone in the presence of titanium dioxide as a Bleaching Agent reducing the color intensity.
Any discoloration organic matter actually depends not only on the temperature but also on the duration of the test. In the standard test time was 5 min., Which is much longer than the processing time of polymers under normal conditions. From experience we know that the organic colorant can be processed at slightly higher temperatures than indicated in the certificates of thermal stability, due to less processing time.
Another reason for the discoloration may be a heated polymer melt on the hot sprue. Therefore, the time course of polymer sprues should be added at the time of processing of the polymer. The resulting still usually less than the time discoloration. However, usually recommended scrutinize parameter resulting processing time.
Thermal degradation of the organic colorant is possible not only in the production of polymer products, but also in the preparation of the granular masterbatches containing, e.g., fluorescent pigments.
It is important to note that the heat resistant organic colorant added into the polymer depends on the type and grade of polymer.
6. Light and atmospheric resistance
Light fastness of colored polymer material is determined by the ability of the pigment-polymer retains its original color when exposed to sunlight.
Atmospheric resistance is defined as the ability to withstand the colored polymeric material simultaneously or separately to sunlight and atmospheric conditions such as moisture, atmospheric oxygen, industrial pollution.
Simply put, light resistance and atmospheric resistance characterize the stability of colored resin to weather conditions in conjunction with moisture, as moisture is usually one of the most important atmospheric parameters.
Except for a few inorganic pigments, colorants everything under sunlight more or less strongly change the color. Joint effects of light and weather conditions (especially humidity) is usually destructive to the organic colorant, and the colored polymer will destructure.
Some organic colorants exhibit good light fastness, but poor atmospheric resistance. Therefore, their use is restricted for use in products operated outdoors. Certificates colorants typically have detailed information about their light and atmospheric stability.
Typically used two methods to estimate the light and atmospheric resistance:
Investigation of sunlight both in the presence and in the absence of atmospheric moisture on the experimental plants. located in the open air (environmental tests)