It should be modified by increasing the additives so that the process becomes possible and the required features appear in the final product. In this section, we will mention a summary of the role of each of these items and leave the full explanation to the next chapters.
During the process, PVC is subjected to heat and mechanical stress; As a result, to prevent thermal transformation during the process, it is necessary to add thermal stabilizers to it.
In order to prevent color change and reduce the desired characteristics in the product, optical stabilizers are added to the polymer, to prevent the change caused by ultraviolet radiation.
Materials and types of products made from P. V. C, divided into two groups: “hard PVC” and “soft PVC”. In the latter group, a mixture with a small amount of softening material is called “semi-hard PVC”.
In making the mixture of P. V. Si soft, the most essential and major component of the composition, is the softening agent, which is added after V. Si as well as thermal stabilizer is added to the mixture. Softening materials have a major role in the thermal process in terms of helping the process and lubrication, affecting the product characteristics (softness, flexibility, stretchability, and toughness).
In the compounds of P. V. Si hard, process aids are added to the mixture in order to improve the characteristics of fusion and molten silane, and impact modifiers, p. V. 3 hard against the impact increase.
Lubricants, silane, melt mixture, P. V. They make the process easier and prevent the molten material from sticking inside the machine. These types of additives are divided into two groups: internal lubricants and external lubricants. The first group reduces the viscosity of the molten mixture and the second group prevents the adhesion of the molten material to the process wall.
Fillers and dyes are other additives that are added to mixtures.
The use of fillers, in most cases, has an economic motivation, which is the reduction of the final product doors – although, it also leads to features such as: reduction of shrinkage (shrinkage in films) and increase of hardness.
Fillers such as: fine-grained calcium carbonate and crushed glass fibers, base compounds. V. They make it hard to resist.
By using some fire retardants, it is possible to prevent fire or its spread in the city. V. provided C (this polymer, on its own, has a low flammability rate, but plasticizers – in most cases – do not).
With the help of phosphate softeners and types of chlorinated paraffin, it is possible to improve the resistance to flammability. In order to prevent the unwanted emission of an unpleasant smell (such as the smell of artificial leather) or to give a suitable smell and a good smell to some mixtures of P. V. C, odor control materials can be used. Baby shorts and all kinds of handbags used by women are examples of the use of odor control materials in products produced from P. V. It is thirty.
A large number of softeners are a desirable environment for the growth and type of bacteria; While P. V. C is stable against the growth of all types of microorganisms (bacteria,…). Therefore, the use of antibacterial substances is considered the most appropriate way to deal with these destructive agents.
During the production or use of some products such as molded parts from the foundation. V. Static electric charges are formed on conveyor belts. In this case, the use of anti-static materials to prevent the surface of the part from getting dirty due to the absorption of particles in the air – which in many cases is due to the presence of static electric charges on the surface of the part – or to prevent sparks and fires in Sensitive cases are necessary.
All kinds of additives that are in various combinations. V. Si is used, there are many and it is chosen according to the type of product, process conditions, and also the application. In the continuation of this section, we will introduce and review these materials and how they are used in various products made from pi. V. We will pay thirty.
Softening materials, hard and brittle resin. V. They turn Si into a soft and flexible material. The type and amount of softener has a special importance in the composition of the mixture and has a direct effect on its properties, as well as the characteristics of the process. The ratio of the amount of softener to other ingredients in the mixture. V. C is very important and is used in large quantities in some products. For this reason, it is important to choose a softener in terms of price. If it is not necessary to provide special characteristics in the production of a product, a cheap softener for general use is selected, which in most cases will be of the “phthalate” type. “Di(2-ethylhexyl) phthalate” or its popular form “dioctyl phthalate -D.O.P”, gives universal and suitable properties to the mixture. Some types of phthalates (such as D.O.P.) are included in the “primary plasticizers” group.
Materials with Pi. V. 3 are compatible and are used in a ratio of 25-100 percent (softener/PVC = 25/75-50/50), they are called “primary softeners”. These materials are used for gelling and mixing with p. V. They have enough power.
The standard softener of this group -D.O.P- has features such as: gelling, compatibility with foundation. V. Thirty-four has relatively few features and only by using it, many desired and desired features can be achieved.
In exceptional cases (such as to aid in gelation or chemical sponge production), a mixture of “alkyl aryl phthalates” (such as butyl benzyl phthalate-B.B.P.) is used with other softeners. Because the degree of volatility of “B.B.P” is relatively high, it should not be used as the main plasticizer.
Softeners that are compatible with P. V. C is low, they are called “secondary softeners”. These materials are usually used together with primary softeners. In addition to “aliphatic dicarboxylic esteracids” and “heavy aliphatic alcohols”, “dicarboxylic aromatic esteracids” and “long-chain aliphatic alcohols” are also in the group of secondary softeners.
Due to low polarity and weakness in surrounding PVC particles and dissolving them, these softeners require more heat and longer gelation time.
Another group of P softeners. V. C are “polymeric softeners”, which are among the most important secondary softeners and because of their compatibility with p. V. C is low, they are commonly used together with primary softeners. The viscosity of polymer softeners is high, and accordingly, the viscosity of the mixture made from them will also be high.
Liquid chlorinated paraffins are also in the group of secondary softeners. The products made using this softener are resistant to fire and petroleum products. Liquid chlorine paraffin if it contains 50-60% chlorine, with pi. V. C is better suited. If the amount of chlorine in the chlorinated paraffin is low, it should be less in the mixture. V. 3 is used; Because if the amount of chlorine is low, the compatibility of this softener will also be low. From now on, we will identify the most important types of softening materials.
Types of phthalates
The most important and diverse group of softeners are “phthalic acid esters”, which are mainly used in making vinyl compounds. These materials have favorable compatibility, suitable process behavior, low volatility, desirable thermal and optical stability, and finally, a cheap price – compared to other comparable materials.
“Butyl”, “hexyl”, “octyl”, “nonyl”, “decyl” and “benzyl” alcohols are the most common types of alcohol used in the production of sterphthalates. The structure of aliphatic alcohols may be in the form of a straight chain or a branched chain. Typically, a mixture of various isomers and a set of different alcohols is used instead of a single alcohol.
In general, increasing the molecular weight of the alcohol used in ester production produces these characteristics: low volatility, poor compatibility, low solubility in the resin, and increased oil extraction.
The decrease in molecular weight also causes the following changes:
High volatility of plasticizer, desirable compatibility, higher solubility in resin, and improvement of plasticizer properties at low temperature.
Types of phosphates
If the production of a mixture of P. V. Considering the stability against the flame, the use of “phosphoric acid” is suggested. The most important and common phosphates are: “tributyl phosphate”, “tri(2-ethylhexene) phosphate”, “cresyl diphenyl phosphate”, “triphenyl phosphate” and “tricresyl phosphate”.
Features such as: low volatility and fire resistance to the desired extent, “triaryl phosphates” are used to make various types of conveyor belts resistant to the spread of fire from P mixtures. V. Si contains this substance, it is suitable.
If the type of softener is changed from “triaryl aromatic” to “trialkyl aliphatic”, the flexibility will increase at low temperature, in this case, the chemical stability and flame resistance will also decrease.
Reminder: when using these types of softeners, their negative effect on the strength of barium/cadmium stabilizers should be kept in mind, and this deficiency should be compensated for by strengthening the stabilizer system; Or use another stabilizer.
Types of epoxy
Epoxy softeners greatly increase the thermal and optical stability of the mixture and are used as auxiliary stabilizers.
These types of materials together with many metal stabilizers (such as cadmium and zinc) create an intensifying effect. Epoxy oils are not toxic and their volatility is low. “Alkyl epoxy stearate monoester and tallate” achieve desired flexibility at low temperature.
From the reaction between a “dihydric alcohol” (glycol) and a “dicarboxylic acid”, high molecular weight polyester is produced. Some types of this type of polyester with a monocarboxylic acid create a “polymeric softener”.
Low volatility and stability against solvent extraction, among other positive features, and high viscosity, low solubility rate, poor softening at low temperature, and finally, expensive price are negative features of this type of softener.
Various types of polymer softeners are used in oil-resistant compounds and in the formulation of non-conductive electrical devices (at high temperatures).
In addition to the mentioned items, there are currently various types of softeners available, the use of which depends on the expected characteristics of the product:
Trimethylate and pentaerythritol esters (for product application at high temperature) and benzoate esters with high solubility (for making flooring) are examples of special softeners.
Characteristics of P mixture. V. Si, as a result of contact with heat and light, is transformed and its positive physical characteristics are also reduced. During the process and high temperature, the molecules of P. V. thirty are broken; A double bond is formed, and hydrogen chloride is released; The substance also changes its color.
To prevent the change of P. V. C. and to protect it from the effects of high temperature during the process, as well as its immunity from the negative effects of light waves in the conditions of use, the stabilizing system is added to the mixture; to stop the progress of decomposition. In this way, the polymer tolerates the high temperature during the process without losing its important characteristics – especially the color change – and can be processed without any difficulty.
Hundreds of types of stabilizers – and their combinations – in foundation mixtures. V. Thirty are used. In the choice of stabilizer, the most important factor is the compatibility and harmony between the price and the effect of the substance on the stability of the mixture.
The main characteristics and important characteristics of the process, such as: glazing, silane behavior, lubrication, the possibility of reaction with other compounds in the mixture, and finally, how and the degree of stability of the final product, should be taken into consideration in the examination and selection of materials, and the answer Suitable for the following questions:
Will the stabilizer make the mixture dark or cloudy? Will it cause coloring? Or what will be its light stability, toxicity, smell and electrical characteristics?
Knowing the characteristics of the most important types of stabilizers used in soil mixtures. V. The following can be helpful in finding the right answer.
These types of stabilizers are divided into two groups, “tin mercaptides” and “tin carboxylates”. Organotin mercaptides are the most effective thermal stabilizers of vinyl compounds. In the common industrial methods of some countries such as the United States, this material alone is used in the mixing of foundation. V. Soft C is used. The major and important advantages of this type of stabilizer; Desired thermal resistance in the long term and stability and transparency of the primary color. Negative features such as: weak light stability, unpleasant smell of the mixture, high price, and also, the tendency to color (formation of metal sulfide colors) in contact with lead, antimony or cadmium salts, diminish the advantages of this material. make However, the use of some tin stabilizers is permitted for the manufacture of products that come into contact with food.
But in the second group, i.e. tin carboxylates, only dialkyl tin derivatives have technical value and practical importance. The main difference and superiority of tin carboxylate over mercaptide is its good light stability. This feature has made these materials suitable for outdoor applications (in the open air-sunlight) such as window profile production.
Barium/cadmium and barium/cadmium/zinc stabilizers
Barium/cadmium soaps usually contain a mixture of barium/cadmium salts with fatty acids: laurates, stearates and myrestates. In the zinc-containing system, an organic salt of the metal (in most cases, zinc octetate) is usually involved. Both systems are common and abundant in Pi compounds. V. Soft and hard C are used. The use of these stabilizers in the mixture is often accompanied by auxiliary stabilizers (such as organic phosphite or an epoxy compound). These two systems, if they have auxiliary stabilizers, not only increase the thermal stability, but also improve the resistance of the composition against atmospheric factors.
Clear compounds are made with liquid barium/cadmium stabilizers, and zinc-based soap systems are not suitable for very clear applications.
The mentioned systems, although they are diverse and effective, but at the same time have limitations that make their use with caution:
Due to the presence of cadmium and the formation of yellow cadmium sulfate (as a result of contact with sulfur-containing compounds), coloring occurs, which despite zinc-containing stabilizers counteracting this phenomenon, coloring can lead to glazing on the walls of the process devices. be made
Due to toxicity, cadmium stabilizers are not used in the production of products that come into contact with food, and over time their use has faced serious limitations.
Lead compounds are widely used in the production of products used in electrical and electronic industries and parts that require long-term thermal stability. In electrically non-conductive tools, lead chloride is insoluble and non-ionizable due to the interaction of the polymer and the lead stabilizer, and as a result, after the stabilization process, the electrical resistance remains intact.
“Lead phosphite 2 games” also has desirable stability against light, and for this reason, it is used for the production of products that are placed in the open air.
Toxicity, turbidity of product color and coloring (due to the formation of lead sulfide) when in contact with sulphurous materials are the main limitations in the use of lead stabilizers.
non-metallic (organic) stabilizers
These materials are the auxiliary stabilizers that we mentioned earlier under the titles: epoxy compounds and organic phosphites. This group has an aggravating effect on metal stabilizers. These compounds are never used alone and are always used together with other metal stabilizers to increase the efficiency of the mixture.
In graph 1-2, the amount of yellowness in the mixture tip – with and without the use of auxiliary stabilizer – is compared.
According to the graph, the amount of yellowness in the mixture without auxiliary stabilizer is much higher at different times – that is, thermal transformation has taken place to a greater extent.
In this test, the mixture is placed inside an oven that has a temperature of 180 degrees Celsius; Then, using the “ASTM-D1925-70” standard test method, the degree of yellowness is measured at different times.
The amount of yellowing or thermal change in the mixture containing both stabilizers (main, auxiliary) is far less than the mixture containing only the main stabilizer.
According to the diagram, “phenyl didecyl phosphite” increases the thermal stability of the mixture compared to other phosphite auxiliary stabilizers.
This type of stabilizer is used in special mixtures for making food packaging containers, as well as in making parts and tools for various medical applications; Like the movie P. V. Si (soft and hard) for packaging purposes, all kinds of bottles produced from pi. V. 3, and flexible pipes, which are widely used in various branches of medical engineering.
The most important types of non-toxic stabilizers are mixtures of organic salts of calcium and magnesium, calcium and zinc, or calcium/magnesium/zinc, which are mainly combined with organic materials such as epoxy compounds. In general, determining the type and amount of stabilizer consumption is related to the national regulations and standards of the countries that supervise the production of health products. The effective role of informal stabilizers is far less than barium/cadmium or lead systems.
The role and type of lubricants in foundation mixtures. V. C can be summarized as follows:
The external lubricant reduces the amount of friction between the mixture and the metal surface of the process machines and prevents it from sticking to the surfaces of the process machines during the process.
The internal lubricant reduces the intensity of intermolecular and interparticle friction, as well as melt viscosity and heat generated during the mixing process.
The materials that have the mentioned set of properties are called “internal/external lubricants”, and the group that provides part of the mentioned properties is called “internal lubricant” or “external lubricant”, depending on the case.
The most important factor in determining the type of performance of the lubricant is its compatibility with the foundation. V. It is thirty.
A suitable and desired external lubricant, with little compatibility, and a desirable internal lubricant, with high compatibility with the base resin. V. It is thirty.
Paraffin, paraffin oil, polyethylene wax, fatty acid, fatty amides and steracids, alcohol and metal soap are chemical compounds that are used as lubricants. The selection of the type and amount of lubricant in the formulation, in a complex way, depends on the following factors:
- Components of the mixture
- The type of process, in this case, choosing the right lubricant in calendrical mixtures, is very important.
- The finishing operation that is performed on the product after the process. (For example, in the special mixtures for the production of films on which printing is done, lubricants that do not penetrate the surface should be used.
- The difference or the same performance of the lubricant, with other components of the mixture – especially with stabilizers.
For example, some stabilizers also have a self-lubricating effect; Or they are affected by the strengthening feature of some lubricants. Also, a stabilization effect can be seen in a number of lubricants.
In a vinyl compound, some of the softener is absorbed into the filler; For this reason, in formulations that have a large amount of filler and with small particles, the amount of softener is added; But the particles whose surfaces are covered with stearate will need less softener than uncoated particles.
In mixtures of P. V. C hard, the degree of compatibility of the lubricant with process aids and impact modifiers is of particular importance. In this case, the most important method of selecting the type and amount of lubricant is the “guess and error” method.
Among the most common materials that are used as base lubricants. V. C hard, are used, can be: metal stearates and levarts, stearic acid, fatty alcohols, paraffin waxes, stearmontane waxes, low molecular weight polyethylene, mineral oils, and organic stearates. cited.
Fillers are solid and relatively ineffective materials that are added to the foundation mixture in order to improve some characteristics and reduce the price. V. 3 are added. If the amount of filler is small, the improvement of physical properties will be insignificant. The use of fillers – in large quantities – leads to an increase in the hardness of the product; But it reduces tensile strength and elongation at break point. Using a large number of fillers leads to a reduction in the price of the product; Because the specific weight of these materials is different from all types of resin. V. There are more softeners and due to their use, the specific weight of the mixture also increases; As a result, the final price of the product – weight price – is reduced.
Checking the price, processability, physical properties (tear strength, tensile strength, material durability, surface quality, …) are effective factors in determining the amount and type of filler in the mixture.
While pointing out that calcium carbonate with a specific gravity of nearly 2.7 is the most important filler for foundation mixtures. V. It is counted as thirty, we will get acquainted with this substance and other fillers.
As mentioned, calcium carbonate – both coated and uncoated – is one of the most important fillers in thermoplastic mixtures and widely used in the construction of foundation mixtures. V. It has thirty. The coating type of this filler has a positive effect on the processability and electrical properties of the mixture, and it is commonly used in the cable industry.
Coated calcium carbonate, in contact with the stabilizer in the mixture, has an aggravating effect, which, if used, reduces the consumption of stabilizers due to the increased thermal stability of the mixture.
In general, the use of calcium carbonate in the foundation mixture. V. Soft C has these features:
- Good distribution – especially in the case of coated type
- Easy process and not having a negative impact in the form of little wear on the machine, tools and process devices
- Less absorption of softener and other mixture additives – in the coated type
- Reduce the use of white pigments
- Improvement of electrical and dielectric properties
- Reduction of convection (wrinkling in the case of films and sheets) and glazing – in the coated type
- Reducing the price of the final product (in the section related to the economic review, it is stated how to estimate the volumetric price of the mixture, by studying it, you will find out the effect of the weight part, volumetric mass, and also the weight price of each component in the unit price of the product win).
Like P mixtures. V. Si soft, calcium carbonate as a filler in soil mixtures. V. Hard Si is also used – of course, of the coated type and with a fine particle size.
According to new surveys and researches, the use of impact-resistant materials in the mixture provides the possibility of increasing the use of filler in the mixture.
The use of coated calcium carbonate in the foundation mixture. V. Hard cement leads to an increase in stiffness and a decrease in convection and glazing, and the extrusion process – if this filler is used – is easier.
Sedimentary calcium carbonate, mainly in the mixture of P. V. Hard Si is used and due to its small particle size and higher degree of purity – compared to other filling materials – it causes less erosion in process devices and machine tools. This filler increases the modulus of elasticity; But it does not have much effect on other mechanical properties. Ground natural limestone, which is another type of calcium carbonate filler, is commonly used in two processes: the production of foundation sponge due to its characteristics such as the desired amount of particle size distribution and the absorption of a small amount of oil. V. Si and coating and immersion are used.
Soot as a filler and color in the foundation mixture. V. It has 3 uses and protects the product against ultraviolet radiation.
This filler is used in the manufacture of pi products. V. Hard steel (such as profiles and sheets) is used.
In various ways of making the mixture of pi. V. C hard, choosing the right resin, stabilizer, and lubricant, is of particular importance; But if these materials are used, the product that will be obtained will be weak and fragile. Therefore, it is necessary to make the product strong and resistant to impact. Impact modifiers are used for this purpose.