Novachem
Contact: Frank Winner
1450 Barnum
Bridgeport, CT 06610
U.S.
Phone: 800-762-3984
Fax: 203-367-0647
SuperNova Chemical Purging Compounds
The SuperNova family of high-performance purging compounds consists of three general-purpose grades used for purging low, normal and high-viscosity resins in all types of processing equipment, and two specialty grades: SuperNova CX for purging into clear polycarbonate and clear acrylic, and SuperNova XB for use with Extrusion Blow Molding systems. All SuperNova grades are odor-free, free of toxic or hazardous ingredients, and certified as safe for incidental food-contact applications under FDA regulations.
Free Samples of SuperNova Chemical Purging Compounds are available. Call toll-free, 1-800-762-3984 and ask to discuss a sample evaluation program with one of our Technical Sales representatives.
* For most normal purging situations, click on the SuperNova link button (left) to learn about SuperNova Chemical Purging Compound and the SuperNova LT and SuperNova HT varieties, all available in Ready-Mix or Concentrate forms.
* For purging situations where the next production resin will be clear polycarbonate or clear acrylic, click on the SuperNova CX link button (left) to learn about our polyolefin-free grade, available in Ready-Mix or Concentrate, that avoids post-purge clouding.
* If you operate Extrusion Blow Molding systems, click on the SuperNova XB link button (left) to learn about our product specifically formulated for use in extrusion blow molding systems.
Novapurge Chemical Purging Compounds
The Novapurge family of high-performance purging compounds is our original line of purge products based on ammonia chemistry. It consists of three general-purpose grades used for purging low, normal and high-viscosity resins in most processing situations, and two forms of concentrate. The Novapurge products are more economical than the SuperNova products, but they are less operator-friendly (due to the odor of ammonia) and they are not FDA Certified.
* For most normal purging situations, click on the Novapurge R/M link button (above left) to learn about Novapurge NP-1500, NP-2500 and NP-3500 Chemical Purging Compounds in Ready-Mix form.
* If you prefer a Concentrate (add your own carrier resin) click on the Novapurge Conc. link button (above left) to learn about the Novapurge powdered and pelletized concentrates.
Who We Are...
Purging is NOVACHEM's only business. Our purge products provide unsurpassed purging performance for all thermoplastic materials in all types of processing systems including injection molding, extrusion and blow molding equipment. Our expert staff is ready to discuss your purging needs - for dark-to-light color changes, material changes, or removal of degraded resins - and to recommend the best product, review procedures optimized for your systems, and work with you to obtain the best possible results.
Q: How can we tell if a purging compound might be useful in our situation?
A: Think about your dark to light color changes and your material changes. From the last good part in the starting resin or color to the first good part in the new resin or color, do any of these transitions take 45 minutes or more? If so, a good purging compound may help improve your productivity.
Also, think about your startups. Do you lose time and good production material because of specking, gels or streaking on startup? If you do, chances are you should be using a purging compound on shutdown.
Finally, do you tear down equipment frequently for manual cleaning because of excessive black specks? Implementation of a preventive maintenance program based on a high-performance purging compound may make such tear-downs a thing of the past.
Q: What kinds of purging compounds are available, and what kind of purging compound should we use?
A: There are three basic classes of purging compound: Physical, Abrasive and Chemical. Physical purging compounds rely on such things as differences in melt viscosity and surfactant/lubricant effects to remove polymer resin from production equipment. Abrasive purging compounds rely on the "polishing" action of minerals or abrasive resins (like acrylics) to clean the internal surfaces of equipment. Chemical purging compounds rely on active molecules to break down polymer chains into smaller segments thus reducing the effective melt viscosity and rendering the residual material comparitively easy to push out of the system.
Which type you should use depends largely on how challenging your purging situation is. In general, lots of purging products (even just a stiff polyethylene or some cracked cast acrylic) will suffice for a straightforward color change in an injection molding machine running a commodity resin. But if you have a tough-to-remove color, or a wide difference in stiffness between resins, or there is degraded material in your system -- or if you are operating a large and/or complex system like a hot-runner manifold or an extrusion blow molding system -- or if you are processing engineering grade or exotic resins -- then you almost certainly need a high-performance purging product. This probably means a chemical purging compound.
Q: How are chemical purging compounds different?
A: With other types of purging compounds, you usually just run the material through the system until you think that everything is more or less clean. With chemical purging compounds, you typically flush the system with some stiff resin to remove the bulk of the production material, then you fill the system with one system volume of the purging compound and then slow or stop the screw for a period of time known as the "heat soak" period. This is when the chemistry does its job.
So, in a nutshell, if you use a low-performance physical or abrasive purging compound the cost per pound will be low but you'll use a whole lot of pounds to get good results -- if you can get them at all! With a high performance chemical purging compound you will pay somewhat more per pound but you'll use far less -- only about one system volume -- so the cost per purge will be very competitive, especially if you get good results!
Q: Why do we have to wait for a "heat soak" period when we purge?
A: These are chemical purging compounds. Their effectiveness depends on a series of chemical decomposition reactions to break down the residue of production material and to dislodge and suspend particles of degraded material. The more vigorously these reactions proceed, the more effective the purge will generally be. The strength of any chemical reaction is a direct function of available energy (in this case, HEAT), and heat is the product of time at temperature. So to accomplish an effective purge you have to keep the temperatures up in known troublesome areas and give the purging compound time to do its job.
Q: Do we need to worry about these "chemicals" hurting our equipment?
A: Not a bit. Different products use different chemistries, but all of them are safe for use with normal materials of construction in plastics processing equipment. In fact, NOVACHEM's products incorporate a "chemical lasso" the captures hydrogen chloride gas (a common degradation product of PVC and other chlorinated polymers) so that hydrochloric acid (which can damage equipment) will not form.
Q: OK, so the equipment is safe. How about the operator?
A: The operator is safe, too. Some chemical purging compounds (including NOVACHEM's Novapurge products) employ ammonia-based chemistry. Now, exposure to excessive amounts of ammonia can't be good for you and good exhaust ventilation is important (refer to the Novapurge MSDS for details), but the issue is managable. In the case of SuperNova Chemical Purging Compound, there are no hazardous or toxic ingredients used in its manufacture. In fact, this product line is certified as compliant with the FDA's regulations governing incidental food contact applications. Only some carbon dioxide and some water vapor escape into the environment. Your operators can breathe easy!
Q: How do we figure out what product grade is right for us?
A: The very best way is to contact Novachem and discuss the details of your situation with one of our Technical Sales Representatives. The initial considerationin grade selection will be to ensure that the carrier resin of the grade chosen will be appropriate for the melt viscosities of the current and succeeding production resins. For example, the basic SuperNova Chemical Purging compound grades (LT, regular grade and HT) have polyethylene carriers that span a wide range of melt viscosities. So if you have a very low viscosity production resin (like flexible PVC, LDPE or EVA) you might need to use the LT grade. If you have a "normal" sort of resin -- from ABS to Nylon to Polycarbonate -- you would use our regular grade. (In fact, the regular grade is used in about 80% of all situations. It usually works best for all resins processed up to 550°F (288°C).) If you are running a very high viscosity resin, like Polysulfone, or Rigid PVC of a Shore D hardness rating greater than 80, or a polypropylene with a Melt Index of 2, then you may need to use the HT grade.
There are other considerations (beyond processing temperatures) that can affect grade selection. For example, if you are working with polycarbonate you may not wish to use a grade that has a polyethylene carrier resin (as all three basic SuperNova grades do) because unacceptable post-purge clouding can result from the immiscibility of PC and polyolefins like PE. You may therefore opt to use SuperNova CX which contains no polyolefin resins.
Equipment issues also come into play. If you are running an extrusion blow molding system, you may find SuperNova XB to be your best bet. It is formulated just for EBM equipment. However, the XB grade is not appropriate for use with heat sensitive materials, so if you are blow molding PVC you will need to choose a different grade.
If this all seems a bit complicated -- it is! So unless you are very certain of your needs it's REALLY IMPORTANT that you contact Novachem so we can work on grade selection with you.
Q: Should we use a Ready-Mix purge product or would we be better off with a Concentrate?
A: There are a couple of things to think about here. First, if chemical purging compounds are new to you it's best to start with a Ready-Mix. It takes one of the variables out of the situation and makes it easier for all concerned to evaluate results and work our way up the learning curve.
Once you are familiar with the behavior of the product, and provided that you have an appropriate carrier resin available, you may wish to try a concentrate. (Take a look at the Mixing Instructions for guidance on what constitutes an appropriate carrier resin.) You will then have to do some mixing (more time and effort in your shop), but pound for pound you will probably save about 10% on cost.
The other situations where concentrates really shine are cases where the purging compound is used as part of a regular preventive maintenance program in well-maintained equipment. In these cases it may be appropriate to reduce the percentage of concentrate in your purging blend, thus realizing additional cost reduction. You should contact Novachem for guidance if you are thinking of going this route.
Q: How much purging compound will we need to clean our system?
A: We consider it important that when you begin the purging process you have enough purging material on hand for two complete purges. That way if the first purge surprises us by breaking loose a large amount of contamination (in the form of carbon or degraded resin), or if it leaves just a trace of color behind, you'll be able to finish up with a second purge.
Since a purge requires one full system volume of material (plus a bit) you should have on hand at least two system columes (plus two bits :-) ). For example, if your system holds about 8 lbs. of resin you should have ready at hand a little more than 16 lbs. of purging compound -- lets say 18 to 20 lbs. By "system volume" we mean the amount of material required to fill the system, from the top of the feed throat to the discharge of the nozzle, die(s) or head(s). For injection molding systems this turns out to just be the equivalent of the ounce rating of the barrel (at 16 fl. oz. to the pound). For other more complex systems you will have to develop an estimate based on your experience and familiarity with the equipment.
In the case of injection molding systems equipped with hot runner manifolds or injection blow molding systems, you should have at hand five system volumes of purging material rather than two.
In the case of extrusion blow molding systems equipped with accumulators you should add two to three times the accumulator capacity to the system volume, since you will be cycling the accumulator two or three times during the course of each purge procedure.
Q: What resin should we use for flushing, and how much will we need?
A: The flushing that is done before putting the purging compound into the system is critical to the success of any purge. The key thing to remember about the flushing resin is that it must have a melt viscosity greater than or equal to that of the production resin.
Our favorite flushing material is a high density polyethylene with a Melt Index of 0.7 (according to ASTM D1238). Like all HDPE's, it tolerates heat well, and since it is a common blow molding grade it's widely available. At that Melt Index it is stiff enough to displace most resins but not so stiff that it presents its own problem of removal from the system.
If you haven't got a fractional-melt HDPE, another clean, heat-tolerant resin will do as long as it is at least as stiff as the production material. You should contact Novachem for guidance if you are not sure whether your flushing resin will do the job.
In most cases, anywhere from one to four system volumes of flushing resin should be used. The exceptions to this "rule of thumb" would include such cases as systems running carbon black (or other colorants know to be very difficult to purge) or systems with highly complex downstream plumbing (e.g., multiple head extrusion blow systems). For these cases you should flush until, in the operators judgement, the bulk of the previous production material has been removed from the system.
