表面涂层的附着力与耐久性检测

结论：涂层的失效多数发生在界面，附着力是核心

医疗器械上的涂层有多种作用——防腐、润滑、绝缘、生物活性、外观、标识。

而涂层的失效，多数不是涂层材料本身破坏，而是涂层从基体上脱离 ——起泡、剥离、片状脱落。

所以附着力是涂层的核心指标。 涂层材料再好，附着不牢就会脱落，而脱落的涂层碎片在医疗器械上可能是异物、可能造成基体暴露、也可能使产品失去涂层带来的功能。

涂层的类型与作用

附着力的测量方法

划格法。 在涂层上划出网格，用胶带粘拉，观察脱落程度。简便快速，适合薄涂层的定性或半定量评价。

拉拔法。 用粘接剂把测头粘在涂层上，垂直拉拔，测出脱离时的应力。能给出定量数值。

划痕法。 用针尖以递增载荷划过涂层，测出涂层脱落的临界载荷。适合硬质薄涂层。

弯曲试验。 把涂层件弯曲，观察涂层是否开裂剥离。

冲击试验。 冲击后观察涂层状态。

剪切试验。 对于某些涂层，测剪切方向的结合强度。

方法的选择取决于涂层的类型、厚度、以及关注的失效方式。

附着失效的位置

拉拔或剥离试验后，观察失效发生在哪里：

界面失效。 涂层从基体剥离。说明附着力不足。

内聚失效。 涂层内部破坏。说明附着力大于涂层本身的强度。

混合失效。 两者兼有。

粘接剂失效。 测试用的粘接剂先破坏，说明测出的不是涂层的真实附着力，测试无效。

「粘接剂失效」是拉拔法的常见问题，特别是附着力高的涂层——需要更强的粘接剂，否则测出的只是粘接剂的强度。

耐久性的考察

涂层在使用中会经历多种作用：

磨损。 摩擦导致涂层减薄或磨穿。

清洁与消毒。 化学品对涂层的作用。

灭菌。 高温、辐照对涂层的影响。

温度循环。 涂层与基体的热膨胀差异造成的应力。

湿热。 水汽渗透到界面，削弱附着。

弯曲与变形。 基体变形时涂层的跟随能力。

老化。 涂层材料本身的老化。

「湿热对附着力的影响」是常见的失效途径——水汽渗透到涂层与基体的界面，逐渐削弱结合，这个过程是渐进的，新品测试看不出来。

建议做耐久处理后的附着力复测。

涂层完整性的考察

对于起隔绝作用的涂层（防腐、绝缘）：

针孔。 微小的孔洞使涂层失去隔绝作用。

检测方法。 电火花、电化学、或者染色渗透。

厚度的均匀性。 薄的位置是薄弱点。

边缘与棱角。 涂层在棱角处通常较薄。

孔洞与凹陷处。 涂覆工艺可能覆盖不到。

「棱角处的涂层厚度」是常见的薄弱点，因为多数涂覆工艺在棱角处的覆盖较差，而棱角又常常是受摩擦和碰撞的位置。

失效的分析

涂层失效后，分析的要点：

失效的位置。 在哪个部位、是否有规律。

失效的形式。 起泡、剥离、开裂、磨穿。

界面的状态。 剥离后基体表面的状态，是否有污染或氧化。

基体的表面处理。 涂覆前的前处理是否充分。

涂层的厚度。 是否过厚（内应力大）或过薄。

使用条件。 是否超出涂层的适用范围。

「前处理不充分」是附着失效的常见原因 ——基体表面的油污、氧化层、脱模剂残留都会严重影响附着，而这些在涂覆后从外观上看不出来。

涂层与基体的配合

涂层性能不只取决于涂层本身，还取决于与基体的配合：

基体材料。 不同基体的表面能和反应性不同。

前处理。 脱脂、粗化、活化、底涂。这是附着力的基础。

热膨胀匹配。 涂层与基体的膨胀系数差异大时，温度变化产生界面应力。

厚度。 过厚的涂层内应力大，易剥离。

涂覆工艺。 温度、速度、环境对涂层质量的影响。

「热膨胀系数的差异」在经历温度循环的产品上是实际问题，比如要反复灭菌的器械，每次温度循环都在界面产生应力，累积后导致剥离。

送检准备的建议

提供涂层的类型与成分；说明基体材料与前处理工艺；说明涂层的厚度范围；说明使用环境与接触介质；以及提供足够样品（附着力测试是破坏性的）。

常见的准备不足

信息不全。 材料、工艺、使用环境的信息缺失，导致方案设计缺乏依据。

样品不具代表性。 试制样品或挑选样品，与量产状态有差距。

条件未明确。 测试条件没说清楚，数据的适用范围就不明确。

只看初始值。 忽略了环境和时间作用后的性能变化。

项目不完整。 遗漏了必要的项目，提交时才发现。

这五项在实际委托中出现频率较高，建议在项目启动时逐项确认，因为它们造成的返工成本远高于事前确认所花的时间。

数据的组织与保存

记录的完整性。 条件、方法、设备、样品状态、实测值。

可追溯性。 数据与样品批次、生产批次的关联。

保存期限。 覆盖产品的生命周期。

检索的便利。 需要时能快速定位。

版本的管理。 数据更新时的版本控制。

建议建立统一的数据台账，记录每组数据的来源、条件、适用范围和有效期。数据积累起来之后，后续的产品开发和变更评估都能受益。

我们的做法

做涂层相关检测时，我们建议附着力在耐久处理前后各测一次 ——耐久处理包括清洁循环、灭菌、湿热、温度循环，因为附着力的下降是渐进的，只测初始值反映不出使用中的表现。

失效位置的判断是我们会做的内容 ——界面失效还是内聚失效，指向的原因完全不同，前者指向前处理和界面，后者指向涂层材料本身。

对于起隔绝作用的涂层，完整性检测（针孔）是必做项，因为单个针孔就可能使涂层失去作用。

如果你有涂层产品需要做附着力和耐久性检测，可以把涂层类型和使用条件发过来一起讨论方法，或者直接联系：132 4819 8029。能力范围见服务介绍，送检要求见送检要求，其他问题见常见问题。

English version

Conclusion. Coatings on medical devices serve several purposes: corrosion protection, lubricity, electrical insulation, biological activity, appearance and marking. Coating failure is mostly not destruction of the coating material but separation from the substrate, appearing as blistering, peeling or flaking. Adhesion is therefore the core characteristic. However good the coating material, poor adhesion means it comes off, and detached fragments on a medical device may be foreign bodies, may expose the substrate, and may leave the product without the function the coating provided.

Coating types and purposes. Corrosion protection coatings exclude corrosive media, with integrity, adhesion and corrosion resistance the concerns. Lubricious coatings reduce friction, with lubricity, durability and particulates the concerns. Insulating coatings provide electrical insulation, with dielectric strength, pinholes and integrity the concerns. Bioactive coatings promote osseointegration and similar, with composition, bond strength and degradation the concerns. Antimicrobial coatings inhibit microorganisms, with release, durability and efficacy the concerns. Appearance and marking coatings provide aesthetics and information, with adhesion, wear resistance and cleaning tolerance the concerns. And anodising provides corrosion protection and colour, with thickness, sealing and adhesion the concerns.

Measuring adhesion. Cross-cut testing scribes a grid and lifts it with tape, observing the degree of removal; it is quick and simple and suits qualitative or semi-quantitative assessment of thin coatings. Pull-off testing bonds a stud to the coating and pulls perpendicular, measuring the stress at separation and giving a quantitative value. Scratch testing draws a stylus across the coating under increasing load and identifies the critical load at which the coating detaches, suiting hard thin coatings. Bend testing flexes the coated part and observes cracking or peeling. Impact testing observes coating condition after impact. And shear testing measures bond strength in shear for certain coatings. Method selection depends on coating type, thickness and the failure mode of concern.

Locating adhesion failure. After pull-off or peel testing, observe where the failure occurred. Interfacial failure separates coating from substrate and indicates inadequate adhesion. Cohesive failure occurs within the coating and indicates adhesion exceeding the coating's own strength. Mixed failure shows both. And adhesive failure, where the test adhesive gives way first, means the measured value is not the coating's true adhesion and the test is invalid. Adhesive failure is a common problem in pull-off testing, particularly with strongly adhering coatings: a stronger adhesive is needed, or the result measures only the adhesive.

Examining durability. Coatings experience several actions in service. Wear thins or penetrates the coating through friction. Cleaning and disinfection expose it to chemicals. Sterilisation exposes it to heat or irradiation. Temperature cycling stresses it through differential thermal expansion against the substrate. Damp heat allows moisture to reach the interface and weaken adhesion. Bending and deformation test whether the coating follows the substrate. And ageing affects the coating material itself. Damp heat weakening adhesion is a common failure route: moisture penetrating to the coating-substrate interface progressively weakens the bond, a gradual process invisible in new-product testing. Re-measure adhesion after durability exposure.

Examining coating integrity. For coatings providing a barrier, whether corrosion protection or insulation, pinholes defeat the barrier function. Detection methods include spark testing, electrochemical methods and dye penetration. Thickness uniformity matters, since thin areas are weak points. Edges and corners typically carry thinner coating. And holes and recesses may not be covered by the coating process. Coating thickness at edges is a common weak point, since most coating processes cover corners poorly, and corners are frequently the areas exposed to friction and impact.

Analysing failure. After a coating fails, examine the location, covering where and whether a pattern exists. Examine the form, covering blistering, peeling, cracking or wear-through. Examine the interface condition, covering the substrate surface after peeling and whether contamination or oxidation is present. Examine substrate preparation, covering whether pretreatment before coating was adequate. Examine coating thickness, covering whether it is excessive, producing internal stress, or insufficient. And examine service conditions, covering whether they exceeded the coating's applicable range. Inadequate pretreatment is a common cause of adhesion failure: oil, oxide layers and release agent residues on the substrate severely impair adhesion, and none of them is visible after coating.

How we handle it. For coating work we suggest measuring adhesion both before and after durability exposure, covering cleaning cycles, sterilisation, damp heat and temperature cycling, since adhesion declines gradually and initial values say nothing about behaviour in service. Determining the failure location is something we do as a matter of course: interfacial and cohesive failure point to entirely different causes, the first to pretreatment and the interface and the second to the coating material itself. For barrier coatings, integrity testing for pinholes is a standing item, since a single pinhole can defeat the function.

Send us the coating type and service conditions and we will discuss the method. Phone or WeChat: +86 132 4819 8029.