Plastic material colorants or concentrates overview

Plastics material colorants can sometimes cause nearly as many issues as the materials they are mixed with. It is important to have a solid understanding what potential molding issues to look for when issues such as color swirls, contamination or other potential colorant related issues arrise. Having a solid knowledge of the characteristics that are relevant can sometimes save alot of headache. This is an overview of colorants..their properties, usage and potential defects.

We must first define colorant. Colorants are materials that are almost always made with the the same base as the natural materials they are mixed with. There are several colorant types, the primary categories being pellet, liquid and powder forms. Pellet being the concentrate most commonly used, this article will primarily be aimed towards this method of developing a colorized material.

Pelletized colorants are often called concentrates due to their purpose. Initially the colors themselves start as pigments. These pigments of various colors are often blended together to become a particular color. For instance...a blue pigment can be combined with a yellow pigment to develop a shade of green. This color may require a lighter or darker pigment to become a particular shade of green. When the desired shade has been achieved, this concentrate is blended with a natural powdered base, such as nylon or polypropylene. This completed blend is then extruded and pelletized to be used with natural pellets to mold a specific color. I will describe the process in greater detail in the future... for now, I'll stick with the basics so I can concentrate more on areas that can lead to defects.

Each colorant has a specific ratio. These ratios are often established by the extrusion facility, but these are generally recommendations and there are times when less or more than the recommended ratio is used for cost savings, or better color content. The important thing to remember here is the cost of using too much colorant...as well as the cost of scrap generated by lack of colorant. Best practice dictates that the manufacturer's mixtures be followed. Quite often, this ratio is affixed to the label on the barrel, as well as documented on the Material Safety Data Sheet. The general formula is a virgin-to-concentrate number (in ex: "25:1" is twenty-five pounds of virgin with one pound of color added to it).

Newer age equipment (such as Maguire blenders) do a fantastic job of producing consistent blends. Some of the older equipment, however can be a bit more tricky. The digital equipment is harder to establish just what the proper setpoint should be when first setting up a job. The best method here is to use the manufacturer's color chip in comparison. Readings are taken from parts (NOTE: make sure the press was properly purged and the barrel has had time to heat soak while running several cycles prior to color testing) and compared to the color of the color chip using a McBeth Spectrometer, or similar piece of equipment. This analysis will help you determine if the colorant content is to dark or too light. Once a good read has been established, blender setpoints should be recorded for use in future runs.

Now we'll focus on the key issues regarding color concentrates. I will point out the most common first, then give some rare but equally as aggravating situations to watch for:

One of the first keys to success in molding with colorant is tracking lots. This is often overlooked, but treat colorant with the same precautions as your materials. Some examples of what can happen during an extrusion lot change are as noted:


-Contaminated pellets(poor screw cleaning at extrusion line changeover)

-pellet longs (pellet sizes inconsistent due to end/ beginning of run conditions, or poorly adjusted pelletizers)

-change in pellet size(pellet size changed in diameter or length at changeover

-wrong base material used

-lamination(poor screw clean at changeover while changing base materials)

-change in color (poor blend or improper pigment configuration)

-viscosity changes(too high or low heats, base powder lot change)

Knowing how and when to inspect your concentrates for these conditions is crucial to profitable use of colorant in comparison to precolored materials. Failure to consider these potential factors can lead to an improper diagnosis of a change in molding conditions. One pokayoke that your company should consider is requiring the concentrate supplier to provide a color chip molded from every lot with every new shipment.These chips should be verified for proper color content and visual aesthetics.

Colorant usage can have a profitability factor... but only as long as they are used and analyzed properly.

Plastic Material Problems: Plastics Drying, Defects, Lot Changes, Material Changes, Properties and Solutions

A company's material handling methods and supplier choices can be their best friend or biggest nightmare. This article addresses typical material problems and solutions for approaching issues as they arrise. As I'm sure many of you are well aware, this is a monstrous topic...and my being able to identify and offer solutions to every material topic in a single article are slim to none. I will touch on a few topics at a time, and as time goes by I will expand on these in greater detail.

This particular article will touch on the various issues that plague our daily operations and offer some brief information on potential causes and solutions.

It is important to understand the variety of properties that are associated with different material categories. There are many different grades and types of plastics, and each grade has its own set of rules and potential defects. It is important to always be aware of what type of material you are running and you should always refer to your MSDS when issues arrise that could be directly related to a material issue. A good material supplier performs extensive testing on the materials they produce, and you should always be able to get resource information from them regarding the molding properties associated with the material they are providing you. Some examples of data they should be able to offer you are as follows:

• Mean melt temperature
• Melt Window
• Specific gravity
• Temperature settings (Window
• Potential Problems
• Velocities
• Back Pressure/ Hold Pressure settings
• Mold Temperature setpoints

These are the basic ones of importance...there are others that sometimes need to be addressed as well. You can get some pretty intensive information regarding a specific material's properties from the following website:

http://www.ides.com

Materials sometimes require drying, and even removing the moisture for extended periods beyond manufacturer specs can lead to an array of other problems, such as splay and process variances. It is important to know what the minimum/ maximum drying times for your material should be, and when choosing a dryer you should calculate what the throughput of that dryer will be. There is a throughput calculator on the site that can help you determine this.

Drying temperatures are also important. I've seen situations where a material seemed to be performing incorrectly, and the cause was an individual trying to run at a higher temperature on the dryer for a shorter length of time. Sure, this may work on occasion...but it is not a good approach. Material specifications exist because people put a significant amount of testing and time determining how a material performed optimally. I will say that there are times you can push those specs to their limit...but any such action should be approached with caution and as a sample first. Changing your material procedure can affect your end product's functional, aesthetic and dimensional properties.

Materials that are susceptible to moisture should be considered when there are changes to your normal process. It is important to know what moisture level your material runs best at (moisture analyzer) and one of the first things you should check when moisture-specific defects arrise is the moisture content.

Another thing that can result in a drastic process change is a change from one lot of material to a new lot. I cannot stress how important it is for you to track your lots! There have been a number of times that I have witnessed a huge crisis that was identified as a change in lot properties.

I've just barely scratched the surface on this topic. Material can make or break consistency and profitability in a company. Buying the cheapest does not concrete being the most economic approach. If there are huge variances in your processes (resulting in scrap) that can be resolved by buying a better brand or a specific blend, then this may be the best approach to a long term solution.