Analysis of Substrate Surface Treatment to Prevent Corrosion

Surface preparation is a necessary first stage treatment of the substrate prior to any coating or plating. The performance of a coating can be greatly influenced by its ability to adhere properly to the substrate. It has generally been established that proper surface preparation is an important determinant of the success of any surface treatment.

The presence of even minute amounts of surface contaminants such as oil, grease and oxides can reduce the adhesion of coatings to substrates and reduce the useful life of many materials. The surface treatment significantly increases the durability of the bond, especially once exposed to moisture. This is because invisible chemical contaminants such as chlorides and sulfates can attract moisture through the coating system, causing premature failure. Here, we'll look at the basics of surface preparation and how it can be used to avoid premature failure.

What is surface treatment?

Surface preparation or preparation refers to a series of operations including cleaning, removal of loose material, and physical and/or chemical modification of the surface to which adhesive is to be applied. It is a method of treating a surface to increase its attractiveness to coatings. It can be mechanical or chemical, and its importance to the success of the coating cannot be overstated. In plastic bonding, the purpose of surface treatment is to increase surface polarity, increase surface wetting and create sites for bonding.

Reasons for surface preparation

There are many reasons for surface treating materials. Surface preparation is intended to improve bond strength to metal surfaces, but important reasons for surface preparation prior to bonding are:

• Eliminates or stops the formation of weak layers on substrate surfaces

• To better enhance the degree of molecular interaction between the adhesive or primer and thus between the substrate surface

• To optimize the adhesion formed on the interface to confirm sufficient initial joint strength and joint strength within the joint life

• Generate specific surface microstructures on substrates

Surface treatments are used on metals and plastics to change their surface properties for:

• Decoration and Reflectivity

• Improved hardness and wear resistance

• Corrosion protection

• A base that enhances the adhesion of various treatments such as paints or sensitive coatings for printing

• cut costs

metal surface treatment

Preparing the surface of a metal object involves several steps. It is impossible to obtain a high quality adhesive without cleaning (and sanding) the metal surface. Metals have high-energy surfaces that absorb oil and different pollutants from the atmosphere.

The required surface preparation steps are as follows:

1. Cleaning: use solvents or other chemicals

2. Elimination of loose material

3. Enhanced anti-corrosion

4. start up

5. Surface Hardening: Can be mechanical hardening or chemical hardening, used to strengthen the surface

Better use effective liquid systems to clean metal surfaces by vapor degreasing. This treatment is followed by grit blasting to prolong the adhesive contact by roughening the metal surface. Chemical etching removes the weakly bonded oxide from the metal surface and forms an oxide that is firmly bonded to most components.

plastic surface treatment

Polymers inherently have lower surface energies than metals (assuming they are free of contaminants). Therefore, they tend to develop poor adhesion. However, there are currently chemical, physical and holistic treatment strategies that can improve adhesion. These include:

• Chemical modification techniques, including those that sometimes require wet or chemical reactions. These include wet etching, grafting, acid-induced oxidation and plasma polymerization.

• Physical surface treatment strategies, including corona discharge, ion beam or electron beam, photon beam (laser, UV and X-ray), plasma discharge and flame oxidation.

• Bulk strategies involving additives, blending or recrystallization, all of which affect plastic properties.

Some technologies are limited in their scope of use. For example, chemical treatment (acid-induced oxidation) is a common technique for imparting adhesion to plastic surfaces. Plasma treatment is limited to smaller parts and assemblies. Flame and corona treatments are effective on continuous films (often referred to as "webs") and plastic sheets, often run at high speeds.

Surface treatment method

Any surface preparation requires the completion of one, two or all of the following:

• degreasing or cleaning

• physical therapy or abrasion

• chemical treatment

• start up

In some cases, if the substrate is to be used in a severely hostile environment, it may also be primed to confirm superior durability.

degrease or clean

This involves removing all traces of oil and grease from the surface of the substrate to be fixed, which cannot be overemphasized for the importance of forming a strong bond. Degreasing can be done using steam or ultrasonic degreasing, spraying, immersion and scrubbing strategies and should be used even if the substrate appears clean.

1. Vapor Degreasing: In vapor degreasing, objects are immersed in trichlorethylene (TCE) or perchlorethylene vapors, although these vapors are pure, uncontaminated solvents. As the vapor condenses on the part, the contaminants are dissolved, dripping and dispensing the condensed solvent. Once the vapor degreasing unit is not available, wipe the surface of the joint with a material soaked in trichlorethylene and allow it to evaporate completely from the surface of the joint. These solvents are hazardous in every liquid and vapor form and need to be vented into the working environment.

2. Scrubbing: involves scrubbing the joint surface with a detergent solution. During scrubbing, the metal is dipped or sprayed into an alkaline degreaser, rinsed with a clean hot liquid, and then dried completely with hot air, steam, or ambient air.

3. 超声波除油：超声波除油可为微小的元素提供很好的效果。TCE，丙酮和氯化物以及四氯乙烯是用于超声波脱脂的溶剂。

为了验证已脱脂表面的清洁度，使用了水或达因液体。如果一滴水在表面上形成一层，那么它就不会受到污染。如果液滴保持其形状，则表面应继续脱脂。

磨损

粗糙的粗糙表面有时会形成比非常抛光的表面更强的粘合力，这主要是由于较大的粘合接触面积。适当磨损的表面不得包含任何光滑或抛光的区域。在进行磨损处理之后，应进行第二次脱脂处理，以确保除去了松散的颗粒。磨损包括喷砂（常用的技术），钢丝刷，砂磨和磨料擦洗。喷砂处理可去除表面沉积物，例如锈蚀，锈蚀或轧制水垢从金属表面。如果无法使用喷砂工具，或者金属太稀薄，无法抵抗喷砂处理，请使用钢丝刷，研磨剂或砂纸清洁组合表面。在准备之前，应使用剥离剂将涂漆的表面一直剥离到基材，否则粘合接头将不牢固。

有时，只需要对基板进行少量损坏即可。塑料砂粒，核桃壳或苏打碳酸氢盐将清洁基材或带走之前的涂层。有时，研磨剂会被加压水推动。（在了解行业向湿磨料喷砂的转变中发现这项技术的优势）

化学处理

化学处理是通过化学方法处理清洁表面以提高其附着力的方法。溶剂清洗需要始终在化学处理之前进行，通常应在两者之间进行中间清洗。单独进行脱脂，或在脱脂后进行磨损且更脱脂，足以用于多种粘合。为了获得很大的强度，可重复性和抗变质性，需要化学或电解预处理。在化学溶液的制备过程中应格外注意，以确保正确配比形成足够的结合强度所需的元素。解决方案应用程序中的曝光时间重要性无庸赘述。如果应用程序太短，则无法充分激活表面。另一方面，溶液的过度暴露会形成一层化学反应产物，这会干扰粘合键的形成。

为了进行适当的化学处理，一种快速而肮脏的测试是在物体表面放一小滴水，并注意水是否扩散。如果这样的话，它与表面形成的接触角应该很小。有一些特殊的流体，称为“达因液体”，可以相当准确地包围材料表面的表面能的数值。

底漆

Adhesive primers are usually dilute solutions of the adhesive in organic solvents. Apply this solution to the adherend (or adhesive film) to form a dry film with a thickness of 0.0015 to 0.05 mm. Initiation has the following effects:

• Improve wetting

• Protects adherend surfaces from oxidation when cleaning surfaces

• it helps to inhibit corrosion

• It is used as a barrier coating to stop adverse reactions between the adhesive and the adherend

• It holds the adhesive film or adherend in place throughout the assembly process

The use of primers provides additional versatility in production planning, high reliability of joints, less stringent curing conditions and greater latitude in choice of adhesive system.

Atmospheric Plasma Technology Atmospheric plasma technology is a newer surface treatment technology used to clean surfaces to be bonded that is similar to corona treatment. Plasma surface treatment allows virtually unlimited surface modification. Materials can be in any size, from nanoscale parts to endless sheets in serial production. A wide variety of materials can be treated using plasma surface technology, including glass, metals, metalloids, rubber and polymers.

Factors Affecting Surface Preparation

To put surface treatments into perspective, the interface of the adherend with the organic material (i.e., the adhesive) should be considered in terms of various factors ranging from style to fabrication. Joint design, adhesive selection and process should also be carefully considered. These factors are mutually beneficial. The use of a good surface finish is of little value once an unsuitable adhesive is used. In this case, the bond was improperly handled, or the joint design involved peeling or cleaving stress. Proper surface preparation ensures that the weakest link in an adhesive joint is between the layers of adhesive or organic material and not at the interface within the adherend. Rapid depletion of active chemicals in immersion baths, or buildup of foreign matter in plating baths that can increase a weak boundary layer is also cause for concern. Safety is also an important issue, as surface preparation uses many toxic chemicals that can pose a threat to workers if not handled properly.