For people who are not engaged in the chemical industry, many chemical things may be unfamiliar to us. If we don't understand polyvinyl chloride processing aids and polymers, we won't know the relationship between them.
Polyvinyl chloride processing aids play an important role in the development of industry. In order to improve the quality of manufactured products, many issues need to be noted. Among them, the compatibility of polyvinyl chloride processing aids with polymers is one of the influencing factors. The compatibility of polyvinyl chloride processing aids with polymers is very important. If the compatibility is poor, it will affect the quality of plastics.
If the two are incompatible or have poor compatibility, the polyvinyl chloride processing aid will precipitate. After precipitation, the polyvinyl chloride processing aid loses its function and also affects the appearance of plastic products. However, this is not always the case. Some do not need good compatibility. For example, the compatibility of lubricants should not be too large, otherwise it will act as a plasticizer and soften the polymer.
The compatibility of polyvinyl chloride processing aids with polymers mainly depends on their structural similarity. For example, plasticizers with strong polarity have better compatibility in polar polyvinyl chloride than those with weaker polarity. Introducing longer alkyl chains into antioxidants and light stabilizers can improve their compatibility with polyolefins.
For some incompatible substances, such as some inorganic fillers that are insoluble in polymers, they need to have good dispersibility. The finer they are, the better they can be dispersed in polymers. Therefore, attention should be paid to the compatibility problem of polyvinyl chloride processing aids and polymers.
Such a relationship is very important in our actual production. Paying more attention to this aspect in production can help us better handle and avoid some problems, so that the production of polyvinyl chloride processing aids can proceed more smoothly.
Perhaps many friends don't know much about polyvinyl chloride processing aids, but from the name above, we can know that this is related to polyvinyl chloride. As a processing aid, its use must play an auxiliary and promoting role. We can take a specific look through analysis.
Blow molding: Blow molding is the most commonly used processing method for making various plastic bottles, ranging from cosmetics bottles of a few cubic centimeters to large containers that can hold several liters of water. The production method of blow molding has a high output, generally able to produce thousands of bottles per hour. Therefore, good demolding ability is crucial. As for end users, the visual effect of the bottle is the key: there can be no fisheyes, no flow marks, and good transparency.
Thermoforming: The thermoforming process is not a direct PVC processing route because the raw material is already a semi-finished product similar to calendered film or extruded film. However, this processing process includes heating the material at a certain temperature. At this temperature, PVC processing aids will help control the physical and mechanical properties of the material.
Extrusion molding: Extrusion molding is the most widely used in PVC processing technology: window frames, window sills, rain gutters, pipes, cables, transparent and opaque sheets, etc. Molding processing will use many different types of extruders. Sometimes even for processing the same product in the same place, multiple extruders such as single screw, parallel twin screw and conical twin screw will be used. Therefore, when designing the formula, the limitations of processing conditions become smaller. Adding acrylic PVC processing aids to the PVC formula is beneficial to achieving the flexibility of using this extruder and controlling the physical properties of the final product.
Rigid foamed PVC: The extrusion process of rigid PVC foamed materials has very strict requirements on the physical and mechanical properties of the melt: if the melt does not have sufficient strength, the bubbles will burst or transfer to the surface, resulting in high density, irregular microcellular structure, and uneven surface.
Injection molding: Injection molding may be the most demanding process for melt viscosity in PVC processing technology. When the wall thickness decreases or the part size increases, the fluidity needs to be increased. In addition, the injection screw provides less shear than the commonly used extruder, so it is necessary to ensure a short solidification and molding time. The quality of demolding is the primary factor for speeding up the injection cycle and increasing production.
Thermoforming: The thermoforming process is not a direct PVC processing route because the raw material is already a semi-finished product similar to calendered film or extruded film. However, this processing process includes heating the material at a certain temperature. At this temperature, PVC processing aids will help control the physical and mechanical properties of the material.
In our actual production, choosing the appropriate polyvinyl chloride processing aid is very important. The type and dosage we choose need to be carefully analyzed. The actual situation is always the standard we follow and change. Chlorinated polyethylene (CPE) and ABS are both additives for PVC products. CPE mainly plays the role of plasticizing and toughening. So, let me introduce the performance and application of ABS.
Performance of ABS:
ABS is synthesized from three chemical monomers: acrylonitrile, butadiene, and styrene. (Each monomer has different characteristics: acrylonitrile has high strength, thermal stability and chemical stability; butadiene has toughness and impact resistance; styrene has easy processing, high gloss and high strength. The polymerization of the three monomers produces a ternary copolymer with two phases, one is the continuous phase of styrene-acrylonitrile, and the other is the dispersed phase of polybutadiene rubber.)
From a morphological point of view, ABS is an amorphous material with high mechanical strength and comprehensive properties of "toughness, tenacity and steel". It is an amorphous polymer. ABS is a general-purpose engineering plastic with various varieties and wide applications. It is also called "general-purpose plastic". (MBS is called transparent ABS). ABS is easy to absorb moisture, with a specific gravity of 1.05g/cm3 (slightly heavier than water), low shrinkage rate (0.60%), stable dimensions, and easy for molding and processing.
The characteristics of ABS mainly depend on the ratio of the three monomers and the molecular structure in the two phases. This gives great flexibility in product design and results in hundreds of different qualities of ABS materials on the market. These different qualities of materials provide different characteristics, such as medium to high impact resistance, low to high gloss and high temperature distortion characteristics. ABS materials have super easy processability, appearance characteristics, low creep and excellent dimensional stability as well as very high impact strength.
ABS is a light yellow granular or bead-shaped opaque resin, non-toxic, tasteless, low water absorption, and has good comprehensive physical and mechanical properties, such as excellent electrical properties, wear resistance, dimensional stability, chemical resistance and surface gloss, and is easy to process and mold. The disadvantages are poor weather resistance, heat resistance, and flammability.
Process characteristics of ABS
2.1 ABS has relatively large moisture absorption and moisture sensitivity. It must be fully dried and preheated before molding and processing (at least 2 hours of drying at 80-90°C), and the moisture content should be controlled below 0.03%.
2.2 The melt viscosity of ABS resin is less sensitive to temperature (different from other amorphous resins). Although the injection temperature of ABS is slightly higher than that of PS, it cannot have a wide temperature increase range like PS. The method of blindly increasing the temperature cannot be used to reduce its viscosity. The method of increasing the screw speed or injection pressure can be used to improve its fluidity. Generally, the processing temperature is preferably 190-235°C.
2.3 The melt viscosity of ABS is medium, which is higher than that of PS, HIPS, and AS. A relatively high injection pressure (500-1000 bar) is required for molding.
2.4 Using medium to high injection speed for ABS material has a better molding effect. (Unless the shape is complex and thin-walled parts require a higher injection speed), air marks are easy to occur at the gate position of the product.
2.5 The mold temperature of ABS is generally adjusted at 25-70°C.
As a chemical raw material, chlorinated polyethylene (CPE) is not common in daily life, and many people don't understand its properties. Next, let me talk about its physicochemical properties:
Chlorinated polyethylene (CPE) is made by chlorinating polyvinyl chloride (PVC) resin and is a new type of engineering plastic. This product is a white or light yellow odorless, tasteless, non-toxic loose granular or powder.
After chlorination of PVC resin, the irregularity of molecular chain arrangement increases, polarity increases, which increases the solubility of the resin and chemical stability, thereby improving the heat resistance of the material and its corrosion resistance to acids, alkalis, salts, oxidants, etc. The mechanical properties of the heat distortion temperature of the resin are improved. The chlorine content is increased from 56.7% to 63-69%, and the Vicat softening temperature is increased from 72-82°C (to 90-125°C). The maximum service temperature can reach 110°C, and the long-term service temperature is 95°C.
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