The principles and misunderstandings about adhesive selection

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Adhesives are an old and young material. As early as thousands of years ago, human ancestors have begun to use adhesives. Many unearthed cultural relics show that our ancestors used natural products such as clay, starch and fragrant pine as adhesives 5,000 years ago; raw lacquer was used as adhesives and paints to make utensils more than 4,000 years ago; 3,000 years ago in the Zhou Dynasty Animal glue has been used as a caulking sealant for wooden boats; the Qin Dynasty two thousand years ago used glutinous rice pulp and lime as mortar to bond the cornerstone of the Great Wall; at the beginning of the last century, the invention of synthetic phenolic resin created the modern development of adhesives history.

Most of the earliest used adhesives were derived from natural substances, such as starch, dextrin, bone glue, fish glue, etc. Only water is used as a solvent, and it is prepared into glue after heating. Because of its single composition and poor applicability, it is difficult to meet the needs of various uses. With the emergence of synthetic polymer compounds, people began to develop synthetic resin adhesives for various bonding occasions. In recent years, with the development of new technologies and new materials, various adhesives with stronger applicability have come out one after another, which has greatly enriched the adhesive market.

1. The role of adhesive

Adhesive, as a substance that closely bonds the same or different materials together, mainly plays the following five functions:

1. Adhesion

Use glue to connect structural components to achieve the purpose of becoming a one-piece structure (this kind of sealant is sometimes called structural sealant;

2. Blocking effect

Prevent the loss of substances (solid, liquid, gas), energy, pressure, heat, etc. in the adhered (sealed) object; prevent the entry of external substances, energy, sound, heat, etc.

3. Buffering

Using the elasticity of the glue, the connecting part will not be damaged under the conditions of bumpy vibration, temperature volume change, external force, etc.

4. Protection

Adhesives with specific properties can protect the joint or the entire object from high and low temperatures, fire, corrosive liquids, mold, high voltage, etc.

5. Decorative effect

Fill and repair the gaps, holes, depressions and other defects left in the construction process, and play the role of modifying the appearance.

2. Selection of adhesive

In the face of various types and varieties of adhesives, how to choose an economical and applicable adhesive and how to operate to achieve the best performance of the product are the voices of the majority of users. Below, we share with you some general principles when choosing adhesives.

1. The principle of function preference

In different application fields, the performance and process requirements of the adhesive are different. According to the characteristics of the material to be adhered and the requirements of the bonding process, one or more of the above five functions should be selected as consideration. key points, such as Table 1 below.

Table 1. Performance and process requirements of automotive adhesives

2. Principles of Economic Applicability

Adhesives used in windshield glass, automobile body and skeleton, floor and skeleton, etc., the basic requirement is bonding/sealing, such as polyurethane, silicone and body weld glue, etc. have similar effects. When the agent is used, its economy should also be considered on the basis of satisfying its basic performance.

3. Principles of reliability and safety

Since many materials are not in a static state after bonding, the reliability and safety of the product under different operating conditions (use conditions and environment) and long-term use (life cycle) should also be considered when selecting adhesives.

4. Other requirements - fire protection, environmental protection

Lightweight is the development trend of many industries, as well as the application of new chemical materials. There are more and more non-metallic materials in vehicles, construction and other industries. For a single car, the amount of glue used in a single car can reach several kilograms to dozens of kilograms. , once there is a fire, it is very easy to burn, so flame-retardant bonding/dense materials will become one of the inevitable trends in development; and the bonding/sealing materials often contain a certain amount of solvent, which will be adhered during the construction process of the adhesive. The materials will volatilize freely during the service (use) period. The light ones are easy to cause discomfort to the personnel at the construction site, and the heavy ones may cause harm to the human body. Therefore, environmentally friendly bonding/sealing materials with no solvent, low precipitation, and no pollution are also used in the adhesive. Adhesive selection is also increasingly important.

3. Use of adhesive

With the diversification of adhesive chemical materials and materials to be bonded/sealed, the choice of glue should also be selected and tested in conjunction with the base material. Most people believe that as long as the glue is selected correctly, the bonding of materials will not fail. question. However, in the actual use of adhesives, many bonding/sealing failures are caused by neglecting the construction process. Therefore, in the use of adhesives, the following problems should also be avoided.

1. Neglecting material properties

Focusing only on production line (takt) requirements, ignoring material properties. For example, compressing each station of an automobile production line for 1 minute may increase the output of hundreds of vehicles, but the adhesive often requires a certain reaction and curing time to achieve the corresponding bonding/sealing effect. For example, the curing characteristics of one-component silicone are that the surface dryness is fast and the depth curing is slow. Generally, the curing depth is 3-5mm in 24 hours. If the normal assembly test or use is carried out in a short period of time, the adhesive layer has not yet reached Its optimum performance and therefore some bond/sealing failures will occur.

2. Neglect the treatment of the substrate surface

The use of adhesives/sealants for the purpose of holding the adherends firmly together. Practice has proved that most adhesives/sealants require surface treatment of the substrate, such as removing dust, oil, moisture, etc. on the surface of the substrate. For molded products, low-molecular-weight substances on the surface should be removed with a solvent; for particularly smooth materials, the surface should be roughened to facilitate the bonding and sealing effect.

3. Ignore the influence of construction environment on the bonding effect

Most bonding/sealing materials have suitable ambient temperature and humidity requirements. In cold or hot environments, even the same product will produce different bonding results. For example, anaerobic locking adhesive will cure very quickly at high temperature (above 25°C), and generally can reach initial solidification within 30 minutes; but its initial solidification speed will be very slow below 5°C, and it will not cure even after 10 hours. The phenomenon.

4. Neglecting personnel training and lax construction process control

Good quality of personnel and construction in strict accordance with the operating guidelines are important conditions for achieving good construction results and one of the important measures to avoid unstable construction quality.

Adhesives should play their best role. One is for selection and the other is for use. If you have other technical questions, you can consult our company's customer service staff for answers~