Testing the adhesion properties of the topcoat will ensure the successful performance of the product.
In order to meet the growing expectations of today's discerning customers, highly sophisticated surface finishes for multi-layered furniture-style upholstery systems are becoming more common rather than the exception in all sectors of the woodworking industry. These finishing trends call for the use of glazes, stains, toners and other high-performance coatings. With these finishing systems, finishers need to be more vigilant in testing to ensure that the bonding properties of the system used successfully meet product performance expectations.
Adhesion is a very broad topic, and much attention is paid to the adhesive properties of coatings in the formulator's laboratory; however, from the applicator's perspective, adhesion is often overlooked or misunderstood. From a terminator perspective, I intend to provide a working knowledge of coating adhesion and methods of testing coating adhesion integrity.
Adhesion is the ability of a coating to adhere to a substrate, known as "substrate adhesion," and the ability of a coating to adhere to multiple layers of coatings in a system, known as "intercoat adhesion."
mechanical and chemical bonding
Two factors affect the ability of a coating to adhere to a surface: mechanical adhesion and chemical adhesion.
Mechanical bonding occurs by the coating adhering to the abrasive scratch profile of the surface and by flowing around the fibers of the substrate to mechanically secure the film to the surface. Deeper and larger sanding profiles will increase coating adhesion, while shallower profiles and smoother surfaces hinder the ability of the coating to adhere adequately.
Chemical adhesion refers to the ability of a coating to adhere to the chemistry of the paint formulation. Various components of coating chemistry affect adhesion. The coating needs to have sufficient wetting properties to penetrate into the pores of the surface and wet around the fibers of the substrate. The solvent mixture of the paint system allows the paint to burn into coats within the system. The resinous nature of the coating varies and affects the ability to adhere.
As a general rule for increasing the scale of coating technologies, from lacquer or conversion varnish, to two-component polyurethane to polyester, the adhesive performance will increase significantly.
However, it cannot be assumed that all products in each category are equal in performance. Each product exhibits its own specific adhesive properties. The finisher is ultimately responsible for verifying that the selected coating system meets the necessary adhesion requirements for each specific finishing project. The same coating system will also exhibit varying degrees of chemical adhesion on various wood species and substrates. The resins and bitumen and oils in the wood will significantly affect the chemical adhesion ability of the coating. Keeping in mind all the different factors that affect bond performance, finishers need to make a sound decision about the coating system to use.
然后应编写详细的完工时间表和标准操作程序，并获得涂料供应商代表的签名。为了验证所选涂层系统是否牢固和牢固，整理器需要始终在生产前对薄膜进行充分的粘合测试。
评估粘连的三个程序
有三种不同的方法来评估涂层与基材分离的耐受性，并提供不同的薄膜粘附分析：交叉影线测试，刮擦附着力测试和拉脱测试。
刮擦测试方法利用加重的平衡梁，其具有附接到梁的圆形触针或环。将具有干燥饰面薄膜的面板推到触针下面，并且使光束装载增加的重量，直到从衬底上刮下饰面。评估者使用去除薄膜所需的重量（千克），为涂层的粘合性赋予一个值。该程序遵循美国标准测试方法（ASTM）-D2197，D2248，D2454,5178，取决于待测试的涂层和基材。完整的测试方法可以在ASTM网站www.astm.org上找到。
木材工业中第二种也是常用的测试方法是交叉切割刀具测试。使用便宜的交叉切割刀具测试套件，该测试快速且简单。使用交叉影线切割器将格子图案切割到最终薄膜中直至基板。然后在每个方向上对角刷刷试验区域五次，以除去任何松散的薄膜饰面颗粒。
然后将用于测试粘合性的特殊胶带牢固地施加在交叉影线测试区域上，并通过将胶带从测试区域拉回来快速移除，以显示测试胶带剥离的涂层量。然后将交叉影线的测试区域与（ASTM）标准D3002和D3359进行视觉比较。
在标准中有五个图表，其中包含不同程度的胶片拉脱的视觉图表。ASTM 5B类说明没有代表最高粘附水平的薄膜拉脱。ASTM 1B类说明了35％至65％的薄膜被去除，代表了最差的附着力。2B-4B类表示落在1B类和5B类之间的不同程度的粘合。According to这种视觉比较的性质，结果有时是主观的，并且不具有与该测试相关的数值的确定性。
The third method utilizes a hydraulic pull-off Tester to measure the tensile stress in pounds per square inch (psi) required to separate the coating in a direction perpendicular to the substrate. To perform this test we use a DeFelsko Positest Adhesion Tester following ASTM D4541. Secure the metal loading dolly perpendicular to the surface of the dry film with the aid of a CA (cyanoacrylate or "super glue") adhesive or an adhesive provided by the manufacturer.
While the adhesive is curing, the trolley is attached to the hydraulic pullout device with hydraulic pressure applied and increased until the trolley pulls the coating away from the substrate. The gauge on the Tester shows the pressure (psi) required to separate the coating from the substrate.
The result is a definitive number of adhesive properties that can be imparted to the coating. Due to variations in the density of the wood substrate, different readings may be obtained on different areas of the test panel. The expected acceptable high-low ranges of pull-off pressure should be met and the adhesive value of the coating should be specified.
Based on our research, no standard of expected pull-off pressure has been found for various types of coatings applied to various substrates, and it is up to the finisher to determine the specific coating system being evaluated.
How long should the curing time be before testing the bond? It is recommended to inspect the coating after initial cure and after long-term cure. The coating manufacturer's recommendations should be followed regarding when to perform an adhesion test. When testing, factors such as the number of mils applied, ambient air drying or force cure drying method and type of coating need to be considered.
Usually, a second test should be done after 30 days. As the coating continues to cure, the adhesive properties will change. As the coatings continue to crosslink, some coatings will improve adhesion, while other coating systems will exhibit reduced adhesion due to differential shrinkage between substrates or coatings within the system.
Guards should never be allowed to prevent substandard adhesion. A major product glitch can lead to bankruptcy and cost you, the Terminator, and your work.
