Tests should confirm weather resistance for fabrics that will be used outdoors.
Photo courtesy Expand A Sign
Verification
SDOs do not only rely on the opinions of experts. To make sure the theories behind a new testing method are valid, the method must itself be tested.
Interlaboratory studies are undertaken to ensure each test method provides repeatable and reproducible results. By having multiple operators in multiple labs perform the same procedure, these studies can identify potential areas for improvement or clarification.
Interlaboratory studies are also used to develop statistics regarding just how consistent the results are likely to be. With this information, a company can make better-educated decisions about selecting a testing method, the number of specimens to test and when to retest them.
Updates
Consistency is key, but standards are not static documents. After a standard is published, experts continue to come together to review it on a regular basis. Its wording might be revised to reduce confusion or a procedure may be updated to allow for a new technology. And occasionally, a better method of testing is discovered.
As with the initial testing method development process, updates are more efficient and more thorough when there is a team in place to share ideas and work. Also, revisions need to be carefully tracked, so there is no confusion about which version of a method is being referenced. There is usually documentation to show exactly which changes were made with each revision.
Testing textiles
The ongoing development of standardized test methods for textiles used in wide-format printing is a worthwhile investment, but can seem overwhelming, as each material requires a slightly different battery of tests depending on its components, production process and specific end use. Overall, though, a few basic categories are of particular importance:
Health and safety
Health and safety tests are often required by law. Even when they are not, they are vital both for ensuring products are satisfactory and for avoiding costly recalls or lawsuits.
Also, health and safety regulations are constantly changing. They vary among countries and even among provinces and states.
With textiles, the applicable flammability and chemical standards will need to be identified for testing. Chemical exposure must be considered both for those involved in manufacturing processes and those using the materials in finished applications.
Standardized testing is important given the development of new textiles for wide-format printing.
Photo courtesy Mimaki
Colourfastness
Colourfastness is the resistance of a material to (a) change in any of its colour characteristics and/or (b) transfer of its colourants to adjacent materials, as a result of the exposure of the material to any environment that might be encountered during the processing, testing, storage or use of that material.
Examples of such environmental exposure can include light, laundering, rubbing, chemicals, heat and other conditions, any of which may cause an unwanted change or transfer of colour.
Colourfastness to crocking (i.e. dry or wet rubbing) is especially relevant to today’s printed textiles. With most types of digital wide-format printing, colour is applied mainly to the surface of the material, where it can prove more fugitive than a dye that is completely absorbed by the fibres (as is the case with dye sublimation).
In a crocking test, a white cloth is rubbed on the surface of the test fabric. As in any laboratory test method, the variables must be controlled as tightly as possible.
The white cloth is meticulously specified in terms of its fibre, yarn and fabric construction. The rubbing motion is also clearly defined in terms of surface area, pressure and stroke length, as each test should be performed in exactly the same manner.
Crocking is performed with both dry and wet cloths. In each instance, the white cloth is evaluated to determine how likely the printing inks are to transfer onto another surface. This test can also evaluate colour loss of the printed material due to rubbing.
Weather resistance
Weathering should be a significant component of any testing program for products that will spend a majority of their time outdoors, as is the case with much printed signage.
Colourfastness is one aspect of weather resistance. Tests should confirm the colour does not fade prematurely due to wind, rain, sunlight or atmospheric contaminants.
Tests must also confirm the structural integrity of the material will remain intact and not become brittle or weak with outdoor exposure. Further, ultraviolet (UV) radiation and mould can pose serious challenges for some textile-based materials.
standardized testing matters