Guida completa al controllo della differenza di colore in plastica: controllo preciso dalla fonte al prodotto finito

People don't think about the really small details in the production of plastic. If the production consistency is really poor, people think it's production mistakes. People see the difference in production and have a hard time trusting the difference even if it is from different plastic, a production gloss finishing, or some other production details. If a consumer loses trust they will complain, and leave bad reviews. Your reputation and good reviews will disappear. People in the plastic industry have lost a lot of money because they have ignored color differences that people see and they avoid poor production.

These papers will be the first of a series of documents that will try to contain the color variations of plastic in a realistic way from the selection of raw materials to the final variations on the product.

Key Impacts and Ideas of Color

Difference in plastic color in terms of industrial production is always about plastic being produced and plastic being produced.

Basic Color Space Theory

As some different types of plastic contain different types of color, it is necessary to assess them based on the color space systems (such as the CIE Lab). These systems include:

● L: Lightness from black to white.

● A: The spectrum that includes red and green.

● B: The spectrum that includes yellow and blue.

A color difference (measurement) is commonly described as ΔEab. This indicates how close a sample is to a reference. The larger the ΔE, the greater the difference is and the more easily it can be noticed.

In manufacturing:

● ΔE ≤ 1.0 is considered an extremely tight control.

● ΔE between 1.0–2.0 is acceptable for many industrial applications.

● ΔE above 3.0 can be seen with the human eye.

This depends on the subject, the client, the industry, or the type of products.

We perceive color based on different lighting, the angle of the light, and the background. All these variances exist when it comes to visual examination and vary the light source. It is for this reason that visual inspections can be extremely unreliable and a formal testing method is needed.

All concerns above are intended to mitigate disputes which are primarily based on visual observations. It also helps create a 'common language' between customers, quality insurance, and production.

Main Reasons for Color Differences in Plastics

The reasons for color differences in plastics are not random. It is caused by:

● Variation in raw materials

● In the homogeneity of pigment dispersion

● Fluctuation of processing temperature

● Injection speed variations

● Machine variations

● Environmental changes

Any of these factors can cause color differences individually, but in combination, can cause color differences that are pronounced in plastics.

A difference in color can lead to:

● Customer complaints

● Rework or scrap

● Damage to brand image

● Increase production costs

Like some may think, managing color difference in production is a straightforward task. It is a multi-step process; and for this to be achieved, the causes of the color differences must be dealt with on a chain from the supply to production.

Variation in Raw Materials (The Source of the Color Differentiation)

The raw materials contribute to the theory of color stability. A natural resin, even without the added pigment, has a base color. ABS, PP, or PC from different batches may have slight differences in transparency or brightness, and in the Masterbatch these differences become more obvious.

The color masterbatch can also have variations. If the pigment has a nonuniform concentration, the color of the masterbatch may be different due to poor dispersion. As a side note, pigment suppliers may change the raw pigment source without notifying the customer, which can lead to color changes.

Coloration can be affected by storage conditions. In hygroscopic polymers (for example nylon) storage can lead to moisture absorption and this may change the processability, appearance and surface. The mixing process of resins (for example, a different grade of resin) without adequate prior testing can lead to resin contamination and processability issues.

This is why checking raw materials is important, and for each and every shipment, there must be a standard of measurement to determine value. Should base resin fall outside the parameters, it is possible to intervene and modify the production plan before mass molding is undertaken.

Variations in Processing Technology (Most Important Production Parameter)

Variability in raw material processing can cause problems around the final product, even if the raw materials in question, are consistent and uniform. Considerations, such as injection mold temperatures, screw speed, and the holding and cooling times, can all impact the final product and the coloration that is desired.

An example would be for the barrel, where the temperatures are too high, and yellowing and loss of a pigment may occur. In this scenario, the mixture is too cold, and therefore, is not mixed and results in poor and uneven coloration. If injection speeds are controlled, this could somehow also influence the coloration and even cause a desired or undesired change in gloss.

In high production environments, the primary problem is that the uniformity of the mold design and the processing technologies are not uniform. Process Variables may be systematically altered to improve molding or decrease flash regardless of the final product's color. These changes, seemingly small, cause deviations in the production of colored plastics.

The production of colored plastic needs certain unchanging process variables. One condition to achieve the targeted color, the variables are recorded, process variables are held constant, and in the mold design, color shift is documented.

Equipment Issues (Often Overlooked Issues)

The importance of the equipment in color stability is often underestimated. Mixing efficiency is reduced by a defective screw. A temperature sensor that is poorly calibrated gives bad readings. The heating bands may not heat evenly.

While these issues are not guaranteed to cause equipment malfunction immediately, they erode the reliability of equipment over extended periods of use. Take, for instance, uneven heating of the barrel. Overheating occurs in certain spots and alters the behavior of the pigment. This is something an operator may miss, but those around will surely notice the color variation.

Little things like calibrations and maintenance are often forgotten about. Not doing preventive maintenance on the equipment and systems that manage the heat and mixing parts is a guarantee that you are going to get inconsistent colors. Stable machines will provide you with stable colors.

Humans and the surroundings.

In most scenarios human mistakes are possible, even in industrial environments, however there are strategies to manage it. An operator may overdraft or undermine a masterbatch, may not dry it, or may not mix it for a sufficiently homogeneous time, and all of these scenarios are capable of producing a color change. Besides, it is plausible that there are different references, and as a consequence, different operators will have different perspectives on the color.

A very high environmental humidity level can change the behavior of a material, and this is an example of how the surroundings can influence this. Also, insufficient lighting in areas where colors are compared can lead to different perceptions regarding the shade.

A standard operating procedure and a clearly defined process will minimize the reliance on personal elements. The purpose of a clearly defined process is to eliminate ambiguity and center the focus on the elements that can be measured, thus avoiding the reliance on personal elements.

Picking and Getting the Colorimeter Ready

The difference between amateurs and professionals in color measurement is their use of objectives.

Choosing the Right Tools

When determining color, selecting proper instruments is critical, especially when the instruments are a colorimeter and a spectrophotometer. Instruments used for color measurement should be adaptable and appropriate for the material's surface characteristics. For the measurement of high-gloss plastics, the measurement geometry should be designed to account for and diminish the influence of reflection.

The measurement should also take into consideration the appropriate optical geometry in the presence of high-gloss and textured surfaces so that a representative measurement is obtained. In color measurement, incorporating a D65 and other standard light sources for simulating daylight is crucial. Additionally, for the sake of easy traceability, the measurement device should have data storage and data exporting capabilities.

Choosing a color measurement device because of a lower cost, can result in a higher overall cost for measurement in the future. This device also determines the control decision's measurement accuracy.

Training of the Personnel

Training to correctly initiate the measurement of the colorimeter is critical. Before measuring, a standard measurement should be taken after cleaning the measurement standard. The measurements should be recorded in the identical positional coordinates and angles.

Training of measurements taken, will assist in decreasing the variation of measurements.

To ensure accuracy and consistency, certain steps must be followed. The collection and aggregation of measurement data at specified and distinct time intervals improves the measurement standard.

Key Areas for Managing Color Variation

Control of color variation must be done throughout the production process and not just at the end.

Control of Incoming Raw Materials

The incoming inspection is the first point of control for a batch. Each batch is recorded, and one example is compared to the reference sample. Detection of a variation allows the necessary adjustments to be made prior to the commencement of large scale production.

Proper storage and clear identification of a batch minimizes the risk of mixing. Records of supplier performance are useful in assessing the temporal stability of McGavock.

Pre-production Adjustment and First Sample Approval

Trial samples should be produced and compared to the standard prior to mass production. Adjustments to the masterbatch ratio can also be made, if needed, in addition to adjustments to the process settings.

The approved first sample is the reference for the batch. This sample should be kept as the standard for a certain period of time, and a detailed record of the parameters should be kept.

Ongoing Monitoring During Production

The color of the first sample must also be monitored. Neglected routine monitoring can lead to the emergence of new problems.

Although end-of-shift checks can be helpful, continuing and adjusting during production is better. If ΔE values rise, it is better to figure out the reason early, since a correction is better than wasting time and doing unnecessary work later.

Product inspection and shipping

Before we ship any products, we first need to do a sample inspection of the products to make sure each unit is within the allowed limits of the total number of products to be produced. Inspections are done in a lit inspection area where the light is arranged to see all the products well.

Final confirmation provides protection to the manufacturer and the customer. If any problems are found during the inspection and the products are found to have any undesirable characteristics, the production records are sufficient to identify the source of the problem.

Data management and abnormal behavior

When the production parameters are set in the system, color regulation is a matter of guesswork.

Data Management System

When recording a batch, a control record should be made, specifying the batch number of raw materials, processing parameters, and color measurement results. The digital system makes it possible to create a record for a batch and its parameters. Due to the nature of the data stored in the digital system, a prediction of what will happen next can be made by looking at what has happened in the past.

Even with the same production parameters and the same production machine, if the color measurement results deviate, this is a good indication that the machine needs to be checked and adjustments made. The data also allows to inform the Client objectively, and the presence of records in the negotiations makes it easier and more professional.

Abnormal Behavior Management

When there's a chance to change a color, the process must be controlled without delay. If the change goes beyond pre-adjusted tolerances, production will be blocked. Changes must be made to separate all modifications in the batch from the unchanged batch.

A complete inspection must be performed to evaluate the raw materials, process parameters, and production apparatus.

The documentation of interventions illustrates the problem and helps to prevent it from recurring. If changes are made to the raw materials that cause the desired color to be achieved again, the color must be verified to be within compliance before any further modifications may proceed.

Problem Identification and Solutions

Despite the variations, the problems that cause the color of a product to change are usually the same

Color Shift from Raw Materials

If an entire batch of products is produced in a color that is either a tad bit lighter or a tad bit darker than the desired color, the reason is most likely the raw materials. This issue could possibly be resolved by a simple change to the masterbatch ratio.

Without testing, trying to change a ratio can be a pretty big risk. That’s why testing is a better option before making changes to a material composition, rather than trying to resolve big problems down the line.

Changes in Color Due to Change in Processing Parameters

If the color gradually shifts during a production cycle, it is most likely caused by the uneven distribution of heat or pressure.

Most of the time, a problem like this can be solved through heater adjustments or changes in the heating cycle.

When it comes to the processing of materials, it is important to maintain the same parameters. If the parameters have to change, the whole system can become unbalanced.

Assessing Effects and Achievements

The introduction of a color control system in some factories has led to a positive outcome in the reduction of production waste, a decrease in the number of customer complaints, and an increase in the uniformity of production.

While the reduction of production waste is an outcome of the introduction of new technology, the introduction of new technology is not the most important change. Making the most significant changes is a combination of establishing systematic process control, monitoring the less significant aspects of the system, and adjusting the process as the system is developed.When factories manage color better, control raw materials, and change process parameters, they typically achieve small ΔE values and more uniform quality of their products.

In removal of unsatisfactory systems ΔE, rejection and returns from customers express the system’s efficiency and quality. The less returns from customers and the smaller ΔE value, the more efficient the system is.

Errors and their risk regarding plastic color discrepancies

One of the mistakes is trusting BTE (Blind Taste Estimation) solely. People tend to have different perceptions and can be affected psychologically.

Not the degree, but the faults and small variations in color can lead to making of increasing integral defects.

Risks include uncalibrated instruments and raw materials mixed incorrectly.

Records and documentation of all steps is the best example of your understatement of the risks and quality reliability you demonstrate.

For a long duration that is consistent, plastic color quality variations are the same.The color of the raw materials used to create plastic is monitored consistently to ensure proper quality control.

The raw materials used to create plastic and the end products are evaluated based on the quality of the color control. Buyers determine the plastic's quality based on the level of control and consistency.

Answers to Your Frequently Asked Questions About Plastic Color Measurement

Q 1: What level of ΔEab is acceptable for plastic products?

The acceptable value for ΔE averages is based on the value of the specific product. For high-end consumer products, the ΔE value is expected to be < 1.0, whereas, for industrial components, the ΔE value acceptable is > 2.0. Prior to production, it is best to consult the customer on specific values.

Q2: What action should be taken if differences in color arise due to changing batches of raw materials?

Conduct mini-test runs before the start of any production. Depending on the formulation, adjustments may be required. Always compare to the approved reference sample.

Q3: Do the temperatures while processing the plastic affect the colors of the pigments in the plastic?

Yes, temperatures can affect the pigments' dispersion and stability, leading to significant color changes from too low or too high processing temperatures.

Q4: Why is it that the color of plastic can be stable for a long time?

It depends on the choice of pigments. Pigments that provide resistance to light and heat must be used. Where the product is expected to be used outdoors, it is necessary to include some UV stabilizers and other light stabilizers to protect the color.

Q5: Is a visual control of the color of the plastic sufficient?

No, visual control alone is not enough. For a rigorous and systematic evaluation, some color measuring instruments are necessary.