The processing of thermoplastics and/or their end-use performance can be greatly enhanced through the use of additives. Some additives are already present in commercial resins, yet significant benefits can be derived from further modification of those compound. Furthermore, use of the additives affords the processor an opportunity to tailor the material to a specific application.
Processing aid type additives improve productivity of the machinery through reduction of internal friction (lubricants), changing polymer morphology (nucleating agents), removing excessive heat (endothermic blowing agents), or suppressing thermal decomposition during processing (antioxidants).
Other type of additives enhance esthetics (blowing agents, optical brighteners), or performance properties of the final parts (antistatic agents, ultra-violet light stabilizers).
Modification of the properties of the polymers through the addition of those various chemicals is economically preferable to the introduction of new plastic. Additives are frequently introduced to the process through compounding; however, the most economical way is to add those directly to the process through the use of liquid dispersions or concentrates.
Following is a summary of the additive dispersions available from Riverdale Color. This is the list of standard products; custom-tailored blends are also available.
Lubricant & Slips are processing aid additives. They reduce internal and external friction in the molten polymer. The flow of material become less constricted, and melt fracture less likely. This results in the shear heat reduction, better packing and better quality of the parts. Frequently lubricants function also as mold release agents, thus allowing for faster cycle times in injection molding. As slips they allow for better assembly of plastic parts before filling operations.
There are several classes of lubricants; Five of them are available from Riverdale Color:
- SL-69 - Silicone Type
- SL-86A - Fatty Ester
- SL-87 - Stearate Amide
- SL-100 Fatty Amide
- AST-145 - Functions as an Antistat and Lubricant
Chemical Blowing Agents (CBA) are used in plastics for variety of reasons: weight reduction of the parts, removal of the sink marks and for nucleation in direct gassing. While stable at ambient temperature, CBAs decompose during processing and yield significant amounts of gases and small amounts of solid residue. Different applications call for different classes of CBAs.
Azodicarbonamide type CBA provide vigorous foaming action and are frequently the most economical. Endothermic CBAs allow the best control over decomposition rates, and better quality of the parts. In some cases, combination of the two types gives the best results. There are other classes of CBAs, but they are not used as frequently as those mentioned previously.
Riverdale Color manufactures the following dispersions of CBAs
- LBA-92 (Azodicarbonamide type) for polyolefins, HIPS, ABS, PPO, etc.
- LBA-131 & 136 (Endothermic CBA) for polyolefins, HIPS, ABS, PPO, etc.
- LBA-39 (combination) for polyolefins, HIPS, ABS, PPO, etc.
Ultraviolet Light Stabilizers are used in order to protect plastic parts from the degradative effect of the sunlight exposure. There are two types of commercial UV Light Stabilizers; UV Absorbers and Free Radical Scavengers. The former absorb UV light and prevent it from causing degradation. The latter deactivate free radicals that are formed on initial stages of exposure and then regenerate themselves. Thus Free Radical Scavengers, (most frequently, these are Hindered Amine type Light Stabilizers, or HALS) are the most efficient type of stabilizers. HALS are widely used in order to protect polyolefines and other opaque thermoplastics. UV Absorbers are used in combination with HALS for stabilization of styrenic polymers and other applications; they are also used for transparent plastics (PVC, etc.)
Three types of UV Light Stabilizers are offered by Riverdale Color in form of liquid dispersions:
- LST-100 - HALS Dispersion for polyolefins
- LST-292 - HALS/UVA Blend for ABS, PPO and polyolefins.
- LST-302 - UVA Dispersion for transparent engineering materials (PC, PET, etc)
- LST-303 - UVA Dispersion for transparent polyolefin parts.
Nucleating agents raise crystallization temperature and speed of semi-crystalline polymers by changing their morphology. This results in an increase of thermal conductivity, which leads to faster cooling of the plastic parts. Substantial increase in productivity is thus achieved. Other potential benefits are improvement in optical clarity of translucent resins (such as polypropylene) and in some cases increase of the mechanical strength of the material.
Three types of Nucleating Agents are manufactured by Riverdale Color in form of liquid dispersions:
- ABM-114 - Clarifier for Polyolefins
- ABM-129 - for polyolefins
- ABM-136 - for polyolefins, PET and PA
Antistatic agents are used in plastics in order to prevent a buildup of static electric charge on the surface of plastic parts. This charge is normally formed during production and handling of those parts. It will tend to attract dust from the ambient air, thus subtracting from esthetic value of the part. This problem is especially objectionable in consumer-oriented products, such as packaging, i.e. plastic bottles. Antistats will facilitate dissipation of the static charge thus significantly reducing dust accumulation.
Frequently, the use of antistats gives the processor some additional benefits, such as better mold release. Antistats are recommended to be used in polyolefines, HIPS, ABS, polyamides and other resins.
Three types of Liquid Antistats are offered by Riverdale Color in form of liquid dispersions:
- AST-141 - for polyolefins
- AST-142 - for HIPS, ABS and some engineering resins
- AST-145 - for polyolefines and PVC
A great variety of antioxidants are commercially available to the plastics compounders and processors. Those are introduced to the resins in order to stabilize them and prevent decomposition on processing and also to extend service life of the final parts.
In most cases, material suppliers would provide sufficient stabilization package with the resin. However, there are situations when the plastic undergoes unusually high level of exposure to heat (i.e. extrusion blow molding of large parts) or multiple passes through the equipment (i.e. reprocessing). Then it is advisable to introduce additional antioxidant to the process.
For those applications we offer antioxidant blend:
- LAO-315 - for polyolefins and styrenic polymers.
- LAO-312 - Heat processing stabilizer