Film Adhesion Test Method and Test Instrument

 The adhesion of the coating film refers to the ability of the coating film and the surface of the object to be attached to each other. Adhesion between materials.

The adhesion of the coating film is one of the important indicators to test the performance of the coating film, and the prerequisite for the coating to play a protective and decorative role is that the coating film should be able to adhere firmly to the surface of the coated object for a long time.

The adhesion mechanism of the coating film is generally divided into two forms: mechanical adhesion and chemical adhesion. Among them, the mechanical adhesion depends on the properties of the coated substrate (roughness, porosity, etc.) and the mechanical strength of the solid coating; The focus refers to the mutual attraction between the molecules of the coating film and the substrate interface, which depends on the physical and chemical properties of the coating film and the substrate. For the explanation of the adhesion mechanism of the coating film, it is generally believed that the chemical adhesion is more realistic.

There are many methods and instruments for measuring the adhesion of coating films. If the purpose of the measurement and the "force" to be measured can be preliminarily clarified before the measurement, and a reasonable test method and test instrument should be selected accordingly, it will be convenient for various measurement methods. Compare and effectively evaluate the adhesion properties of coating films.

1 Test method of coating film adhesion

Table 1 lists the classification and technical characteristics of the current coating film adhesion test methods at home and abroad. This article intends to focus on the key points of the test methods and instrument application characteristics of the circle drawing method, the cross cutting method, the pulling method and the twisting method.

1.1 Circle method

my country's national standard GB/T1720-1998 and Japanese industrial standard JIS K6894 respectively make clear technical regulations on the evaluation of coating film adhesion performance by overlapping circular rolling line scratch method, which has become a long-term traditional test in CHINA, Japan and other Asian countries method.

This method has strict requirements on test instruments such as the hardness of the stylus, the wear resistance and penetration of scratches, the quality of the load weight, and the stability of the worktable when it moves; the identification and grade of the peeling position of the coating film after scratches Evaluation seems to be difficult.

1.2 Cross cut method

In the early 1970s, European countries such as Britain and Germany first adopted the method of cross-cutting the coating film with a standard grid knife to directly observe the bonding ability between the coating film and the substrate. In standards such as ISO 2409-1972, DIN 53151, BS 3900 and ASTM, different regulations are made on the number of cutting blades and cutting distance, and a manual or electric cross-hatch adhesion Tester has been developed.

我国国家标准 GB/T 9286-1988(等效采用 ISO 2409-1972)中规定：划格图形每一方向的切割数为6或11，每一方向的切割间距均应满足1或2 mm要求，并对切割方法与评价方式做出严格的规定，明确指出涂膜切割表面的评价，应与有关说明和附图进行对比，并According to对比的结果来定级。

应用实践表明，十字切割法操作简单，穿透性好，便于直观涂膜与底材的粘结能力。但相比之下，这种方法不够严格，如测定时的用力大小、刀刃的锋利程度、划痕深度等都将会对测定结果产生影响；而且测定时针对不同性质、不同厚度的涂膜，其切割间距应有所选择。

1.3  拉开法

拉开法是用适当的粘结剂把一个不锈钢的圆柱形测头与待测试样的膜面粘合，再把仪器套在测头上，匀速扭动仪器旋转，以测定并从表盘上读出涂膜被扭开时所需扭矩(kg-cm)，计算出测头底面积的扭转应力，即为被测涂膜的扭开附着力。

表1  涂膜附着力试验方法分类及其技术特征

1.4  扭开法

扭开法的优点是便于施工现场和小面积样板上测试，且不受涂膜底材形状的限制，不仅在平面上，而且可在垂直或斜面上试验，携带也比较方便；缺点是采用的粘结剂需要充分固化，一般需要6 h，而且粘结剂需用现配，增加了工作量。再者，因测头扭掉的涂膜面积大小不尽一致，则会影响测定结果的一致性。迄今这种方法并未被人们重视和推广应用。

2  涂膜附着力的测试仪器

表2列出涂膜附着力试验方法国内外主要标准及部分配套测试仪器。这里拟重点叙述采用十字切割法和粘结力挖开法标准的典型仪器和国外新型仪器的技术性能与应用特征。

2.1  划格附着力试验仪

德国BYK公司生产的511(系列)型划格测试器，符合多项试验方法标准，备有单面6刃或11刃和圆周式六面6刃或11刃两种形式，多种规格的切割刀具，其切割间距分别为1、1.5、2和3 mm，各自对应的膜厚范围如表3。

表2  涂膜附着力试验方法标准及测试仪器

表3  切割间距与试验膜厚范围

ERICHSEN公司研制的430型自动划格附着力试验仪，实现了压力可调、自动划格的功能，有效地避免了手动划格操作中压力和切割速度等人为因素对测定结果的影响，不仅可做单行、多行，还可完成星形或楔形的划格试验。

2.2  拉开附着力试验仪

近年，英国ELCOMETER公司和德国ERICHSEN公司分别推出试验原理和结构形式相同，而测力范围略有差异的106型和525型粘结拉开式附着力试验仪，并在1995年北京国际涂料展览会上展出，它们均符合ISO、ASTM和BS等多项试验方法标准要求。这些新型仪器不需电源，适于生产车间和施工现场测试。其中，106型备有0.05～28 N/mm2五档可供选择的测力量程，并标注了N/mm2和lb/in2两种形式的测力单位。试验证明，这类仪器测定准确，数据可靠，具有乐观的推广应用前景。

2.3  耐石击附着力测试仪

The ESP-10 single impact Tester developed by BYK is used for the stone impact resistance test of multi-layer coating systems such as automotive coatings, and the test complies with BMW standards. The impact tool is a wedge-shaped cutter head, which is placed under the coated test piece with a slight spring pressure, and is continuously shot by a bullet, and the compressed air at a pressure of 3 bar (3×105 Pa) accelerates the bullet. Because the instrument is portable, testing can be performed in a freezer or outside the laboratory.

references

［1］ Institute of Standardization, Ministry of Chemical Industry. Compilation of Chemical Industry Standards. Volume 9. Coatings and Pigments［M］. (Part 2). 1991

［2］ Department of Science and Technology, Ministry of Machinery Industry. Coating Technology Training Textbook (Part 2). 1983

［3］ Research Institute of Tianjin Construction Instrument Testing Machine Company. Lecture Notes on Coating and Coating Testing Technology. 1992

［4］He Duoxiang. Talking about Coating Adhesion and Its Determination Method［J］. Chinese Paints. 1995.3