Plastics/Small Quantities of Masterbatch
I'm looking for small amounts of masterbatch to color my home made ABS filament. The smallest order I can find from a supplier is 25lbs from Clariant, which is enough to color 1 ton of plastic. That's overkill, especially if I want a collection of colors.
I thought maybe I could contact local extruders and plastic processors here in Los Angeles about looking through and picking up any masterbatch left over from finished jobs. There are also some that do color matching and might have small batches from failed attempts.
I was wondering if you could give me any advice on approaching those companies without getting ignored, or handed by the front desk to a sales manager who can't be bothered. Is there a job title I should be looking for to find someone who is more likely to let me come rummage through the dumpster, so to speak? What usually happens to left-over masterbatch?
Thought I'd share this with you
EXTRUSION OF MEDICAL TUBING (Applies to rod in many cases)
Most specifications for medical tubing consist of a drawing of a tube with the material, and dimensions that usually include two of the following three dimensions; inner diameter (ID), outer diameter (OD) and the tubing wall thickness, along with their associated tolerances.
Very few manufacturers or buyers of medical tubing specify other tubing attributes associated with the production of the tubing. It is a common misconception that as long as a lot of tubing is made from the right material and meets the dimensional requirements, it will be the same as, or equivalent to, another lot of tubing either made by the same supplier or potentially made by a different supplier. While this may be true, there is also a good chance that the two lots of tubing may be different. Physical properties such as tensile strength, hoop strength, elongation, bust pressure, surface texture or chemical resistance may all play a critical role in part performance.
Degradation during the extrusion process is one of the things that may affect the physical properties of the end-use medical tube. Polymers are very large molecules that derive their unique and useful properties from their size (molecular weight). Degradation is a breakdown of these large molecules. At some point, polymer degradation results in a change in properties such as tensile strength, brittleness, flexibility, discoloration, etc. It is important to remember that degradation is time/temperature dependant, low temperatures with long residence times and high temperatures and short residence time might both work to produce an acceptable tube meeting your specifications.
Extrusion Process Overview
The extrusion line is a combination of several pieces of equipment and may include a resin drying system if the resin requires drying, the extruder, the die set, the cooling or sizing tank, a take-up device (puller) and a cutter or winder. To achieve consistency in product, one must achieve a consistent process by minimizing variations in output and take-up speeds.
Materials and Drying
Polymer drying is a critical process in extrusion for polymers that are “hygroscopic”, i.e. those that absorb moisture readily from the environment. Hygroscopic polymers must be carefully dried prior to being melt extruded or compounded to prevent them from degrading. Materials used in medical extrusions may be “neat” or “virgin” as produced by the manufacturer, or compounded by a secondary vendor to achieve a color match or special end use requirement such as radiopaque properties. Typically, end users do not specify the physical properties of the material they purchase. This may be because they have little power to dictate to the resin producers due to the low volumes purchased. Material properties that affect the extrusion process are pellet size (bulk density) and pellet configuration (diced spherical or pelletized). Consistent pellet size is more critical than pellet configuration when it comes to feeding the extruder as variations may cause inconsistent output.
The extruder is a melting machine, but must also serve as a pumping machine. It converts solid pellets into a uniform, molten state and forces the material through the die, hopefully at a constant rate. Melting is accomplished through frictional heat generated from the mechanical work of the screw and heat conduction from the heated barrel of the extruder. In a modern extruder, 80% of the energy needed to melt the plastics comes from mechanical energy and 20% from resistance heating. The design of the extrusion screw is critical in achieving uniform melting and pumping of the polymer without over-working (over-heating through excessive shearing) the material. Note that most feed screws are designed for a particular resin family to achieve a consistent output.
The extrusion die sits at the end of the extruder and is the point where the polymer exits into a cooling tank. The die forms the initial shape of the tube. A tubing die set typically consists of two major components; a mandrel or tip that forms the tube ID, and a die, which forms the tube OD. The die and mandrel are typically contained inside the extrusion “head”. The relationship between the die and tube dimension is typically referred to as the draw down ratio. In addition to the draw down ratio, the die set must be designed for the proper draw down balance to achieve minimum shrinkage and proper draw on the wall. That calculation takes into account the dimensions of the Die, Mandrel, and the OD and ID of the tubing.
The use of high draw down ratios significantly improves dimensional tolerances, unfortunately, it also imparts significant orientation and residual stress in the finished tubing. High orientation can significantly increase the tensile strength and reduce the elongation of the tubing in the machine direction, but also may reduce the tubing burst pressure due to the loss in hoop strength. The residual stresses from high drawn down ratios can wreak havoc during subsequent thermal processing such as sterilization, or aging (natural or accelerated). These thermal processes can release the stresses built in during extrusion, causing the tubing to shrink significantly in length and increase in diameter and wall thickness. Physical properties of the extrudate too, are affected by tooling selection.
The drawdown ratio, (DDR), is defined as the ratio of the Die to the O.D. of the tube. It can be calculated using either Areas or Diameters.
The drawdown balance, (DDB), is defined as the ratio of the cross sectional volume of material between the Die and Tip, ( Die Gap) as compared to the cross sectional volume of material in the finished tube, (Wall Thickness). It usually runs between 1.1 as a maximum and .98 as a minimum.
The formula for calculating the DDB is; DDB = ( Die / O.D. / ( Mandrel / I.D.)
Cooling / Sizing
Most extruders cool the polymer as it exits the die using an open cooling tank filled with water. This is typically done in free extrusion or through a vacuum sizing tank. However, in both methods, the polymer cools through contact with water in the cooling tank. The variables that can affect the cooling process include water temperature, the circulation of the water in the tank, the length of the cooling tank and the line speed. All of these variables can affect the physical properties of the tubing, especially if they change or vary over time.
Medical extrusions should not be defined merely by tubing dimensions. Process parameters, equipment and lot-to-lot material variations all play an important role in determining the properties of an extruded tube beyond the physical dimensions and include physical properties such as hoop strength, tensile and elongation, kick resistance and bust pressure to name a few. Manufacturers should take into account the criticality of the application in the finished medical device and the importance of the performance characteristics of that tube in ensuring the proper function of the device. Since it is not possible or practical to specify or even measure every critical characteristic of a given tube, it is desirable to define those that are critical to the end use of your product.
Extruders used in the production of medical extrusions should be capable of consistent steady output - pullers must be capable of holding consistent pulling speed over a wide range of speeds, and sizing tanks must maintain a constant temperature and vacuum settings if used. Consistency is key, and more important than any given setting of temperature, screw speed, pressure, run speed or other process variable.