Adhesive is a type of ancient and young material. Thousands of years ago, human ancestors began using adhesives. Many unearthed cultural relics show that our ancestors used clay, starch, cedar and other Natural product as adhesives 5000 years ago; More than 4000 thousand years ago, raw lacquer was used as adhesive and coating to manufacture tools; 3000 years ago, the Zhou Dynasty used animal glue as a joint sealant for wooden ships; Two thousand years ago, the Qin Dynasty used glutinous rice slurry 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 opened up the modern development history of adhesives.

The earliest adhesives used were mostly derived from natural substances such as starch, dextrin, bone glue, fish glue, etc. Using only water as a solvent and heating it to prepare a gel, it is difficult to meet the needs of various uses due to its single component and poor applicability. With the emergence of synthetic polymer compounds, people have begun to develop synthetic resin adhesives for various bonding occasions. In recent years, with the development of new technologies and materials, various adhesives with stronger applicability have successively emerged, greatly enriching the adhesive market.

1、 Adhesive action

Adhesive, as a substance that tightly binds the same or different materials together, mainly plays the following five roles:

Bonding effect

Using adhesive to connect structural components to achieve the goal of becoming an integrated structure (this type of sealant is sometimes referred to as structural sealant;

Blocking effect

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

Buffering effect

By utilizing the elasticity of the adhesive, the connecting part will not be damaged under conditions such as turbulence, vibration, temperature and volume changes, and external forces.

Protective effect

Adhesives with specific properties can protect the connecting parts or the entire object from high and low temperatures, fires, corrosive liquids, mold, high voltages, and other damages.

Decorative effect

Fill and repair gaps, holes, depressions and other defects left during the construction process to enhance the appearance.

2、 Selection of adhesive

Facing the diverse types and varieties of adhesives, how to choose an economical and applicable adhesive, and how to operate it to achieve the best performance of the product are the voices of the majority of users. Below, we will share with you some general principles for selecting adhesives.

Functional preference principle

In different application fields, the performance and process requirements of adhesives vary, and selection should be based on the characteristics of the adhesive material and the requirements of the bonding process.

Principle of economic applicability

The basic requirement for adhesives used in windshield glass, car body and frame, floor and frame, and other areas is adhesion/sealing, such as polyurethane, silicone, and body weld adhesive, which have similar effects. Therefore, when selecting adhesives, while meeting their basic performance, their economy should also be considered.

Principles of reliability and safety

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

Other requirements - fire prevention, environmental protection

Lightweight is a development trend in many industries, as well as the application of new chemical materials. There are more and more non-metallic materials in industries such as vehicles and construction. For a single car, the amount of adhesive used can reach several kilograms to dozens of kilograms. Once caught on fire, it is very easy to burn, so flame-retardant adhesive/sealing materials will become one of the inevitable trends in development; Moreover, adhesive/sealing materials often contain a certain amount of solvent, which can evaporate freely during the construction process of the adhesive and during the service (use) period of the adhesive material. Light cases can cause discomfort to personnel on the construction site, while heavy cases may pose a threat to human health. Therefore, environmentally friendly adhesive/sealing materials that are solvent-free, low precipitation, and pollution-free are becoming increasingly important in the selection of adhesives.

3、 Adhesive usage

With the diversification of chemical materials for adhesives and the materials to be bonded/sealed, the selection of adhesives should also be combined with the selection and testing of substrates. Most people believe that as long as the adhesive is selected correctly, the bonding of materials will not be a problem. However, in the actual use of adhesives, many bonding/sealing failures are caused by neglecting the construction process. So, in the use of adhesives, the following issues should also be avoided.

Neglecting material properties

Focusing solely on production line (rhythm) requirements and neglecting material characteristics. For example, compressing each workstation of an automotive production line for 1 minute may increase the production of hundreds of vehicles, but adhesives often require a certain reaction curing time to achieve the corresponding bonding/sealing effect. For example, the curing characteristics of single component silicone are fast surface drying and slow deep curing. Generally, the curing depth within 24 hours is 3-5mm. If normal assembly tests or use are carried out in a short period of time, the adhesive layer has not yet reached its optimal performance, which will result in certain bonding/sealing failures.

Neglecting the treatment of the substrate surface

The purpose of using adhesive/sealant is to firmly bond the adherend together. Practice has proven that the vast majority of adhesives/sealants require surface treatment of the substrate, such as removing dust, oil, moisture, etc. from the surface of the substrate. For products that have been molded, solvents should also be used to remove low molecular substances from the surface; For materials that are particularly smooth and clean, the surface needs to be roughened to facilitate bonding and sealing effects.

Neglecting the impact of construction environment on bonding effect

Most bonding/sealing materials have appropriate environmental temperature and humidity requirements. When working in cold or overheated environments, even the same product can produce different bonding effects. For example, anaerobic locking adhesive will solidify quickly at high temperatures (above 25 ℃), and generally can achieve initial solidification within 30 minutes; But its initial solidification rate will be very slow below 5 ℃, and even the phenomenon of not curing after 10 hours may occur.

Neglecting personnel training and lax control of construction processes

Good personnel quality and strict adherence to operating guidelines are important conditions for achieving good construction results, as well as one of the important measures to avoid unstable construction quality.