UV radiation is intense enough to detach one or more electrons from the polymer molecule, thereby cutting and shortening the polymer chains and causing degradation of the mechanical properties. As a result, the product will become more fragile and brittle, its color will fade, the shine will be lost, the surface of the product will be marred and the molecular weight of the polymer will change.

Maintaining colors outdoors is no simple task

In order to prepare the correct color concentrate that will be optimally compatible for outdoor applications, it is important to take into account the intensity of the UV radiation, other weather conditions and the product’s age, all of which affect the appearance and functionality of the final product. Kafrit is at the vanguard of its field and specializes in customizing color concentrates optimally for the variety of outdoor applications.

Let’s set aside for the moment the familiar adage “don’t judge a book by its cover” and actually focus on the cover. If you look around, you can see numerous plastic products in the outdoor environment: playground equipment, garden furniture, roofs, signage, awnings and a myriad of other examples. Most of these are colorful, are manufactured using a wide variety of processing methods, such as extrusion, injection and blow molding, and are made of a variety of polymers. Color attracts the eye, makes a product stand out, and also conveys a message and decorates our environment. When designing a colorful outdoor product, we want the product to maintain its brilliant color over time, to withstand the ravages of nature, to remain usable over time and provide good value for its cost. This task is challenging and requires manufacturers to invest money and resources.

What is a pigment?

A pigment is a material that affects the color of reflected or transmitted light as the result of wavelength-selective absorption. There are different types of pigments – organic, inorganic, opaque or transparent. The various properties are summarized in Table 1.

Characterizing the pigment

The subject of pigments is very broad. When we want to select the most suitable pigment, we need to address the customer’s product requirements:

• Hue and effects: metallic, pearl, wood, etc.
• UV resistance, manufacturing technology, the raw material and product thickness.
• Regulations applicable to the product: REACH, safety upon contact with food, safe for use with infants and children, etc.
• Manufacturing and usage temperatures.
• Minimal warpage, which may be caused by use of a pigment.
• Required mechanical properties.

Beware of radiation!

Weather is the greatest challenge to an outdoor product – wind, sand, humidity, rain, air pollution and exposure to chemicals and, of course, sun rays are causes of product damage. Sunlight, and particularly ultraviolet (UV) radiation, is the most harmful to plastic.

Illustration 1: The solar spectrum, specifically the UV spectrum

UV radiation is energy emitted from the sun. UV radiation is intense enough to detach one or more electrons from the polymer molecule, thereby cutting and shortening polymer chains and causing degradation of the product’s mechanical properties and eroding the product. As a result, the product will become more fragile and brittle, its color will fade, the shine will be lost, the surface of the product will be marred and the molecular weight of the polymer will change.

Illustration 2: New product (on the left) compared to an old product (on the right) that was exposed to sunlight over a long period

The pigment’s weather resistance

Two terms relate to a pigment’s resistance to UV radiation:

• Light fastness – describes the pigment’s resistance to fading as a result of short-term exposure to light under indoor conditions. The value is defined on a scale of 1-8 for an accelerated weathering test for 1,000 hours.
• Weather resistance – describes the pigment’s resistance to changing weather conditions – rain, snow, heat and humidity, with minimum surface damage over time. The value is defined on a scale of 1-5 for an accelerated weathering test for 3,000 and/or 5,000 hours.

The above pigment properties may be tested in two ways:

1. Full Shade – when the pigment is tested with only a binder and without additives.
2. Tint/Reduction – test of the pigment at a lower concentration and usually with the addition of TiO2.

Another property that is important to test is the pigment’s chemical resistance and how it responds chemically to other materials incorporated in the final product.

When a bright, white, and opaque product is needed, a pigment called TiO2 – titanium dioxide – is usually used. This is a pigment with very high chemical resistance that remains stable under all processing conditions, absorbs UV radiation and slows down the polymer degradation process. White pigment, which is suitable for the color concentrate, is selected while taking into account the required properties of the final product, such as: hydrophilicity / hydrophobicity, weathering resistance, chemical resistance, etc.

Smart pigment preparation

Raw pigment is usually powdery and difficult to measure and work with. Masterbatch suppliers usually do not supply it in its raw form, but rather prepare a color concentrate containing a binder, pigments and additives. Kafrit asks each customer to complete a color matching questionnaire that specifies the requirements the concentrate must meet in terms of hue, use, mechanical and thermal properties, regulatory requirements and more.

In addition to pigments, Kafrit prepares various types of UV additives tailored specifically to client requirements. Integrating the UV protection system into the pigments is a complex process and requires considerable knowledge and many years of experience, particularly for complex applications under harsh outdoor conditions.

A special and specific color adjustment is then performed to ensure compliance with the requirements specified by the customer. The most prevalent test for concentrates intended for outdoor use is the “accelerated weathering” test, which simulates outdoor conditions in terms of radiation, moisture and heat. The test may be performed using a QUV probe at a single wavelength 314 nm (UVB) or 340 nm (UVA) or using a Xenon probe at wavelengths similar to the solar spectrum. The tests are carried out in compliance with ISO 4892-2.

Illustration 3: Different spectra of accelerated weathering testers compared to the solar spectrum

Results of accelerated weathering tests

These tests show how the product will look after having remained in sunlight over short periods of several weeks or months and over several years. These tests may be performed on samples with or without TiO2 (reduction or in full shade).

Illustration 4: Samples after accelerated weathering tests under different configurations

There are also analytical methods, such as FTIR, UV-VIS and the use of a spectrophotometer, that enable measurement and detection of absorption or reflection of tested materials at visible and IR wavelengths. Paint concentrates are usually tested against the standard to show the degree of compliance with the customer’s requirements.

Kafrit customizes color for you

Kafrit diligently develops concentrates customized to the customer’s requirements, while performing in-depth analyses of the various factors. Kafrit has extensive knowledge and a variety of tools enabling it to select the most compatible pigments and UV additives for various applications. The provision of information that is as precise, organized and transparent as possible will help Kafrit tailor the optimal solution!

For additional information: Roy Levi, 054-648-7367, rlevi@kafrit.co.il