Adhesives are also called binders, or glue for short. Adhesive refers to a substance that can firmly join two identical or dissimilar materials together. The paste used daily is one of the simplest adhesives. With the development of modern science and technology, as a new type of connecting material, adhesives are used more and more widely in various fields of the national economy.
Adhesives are widely used in the electronics industry, mainly for bonding, sealing, potting, coating, conformal lamination and SMT patches of electronic components. In addition to mechanical fastening, adhesives must also meet the requirements of thermal conductivity, insulation, and adapt to impact-resistant assembly, sealing and protecting substrates. If the adhesive fails, it is very likely to cause the entire equipment to malfunction or even stop running, which will seriously affect the normal use of the user.
Therefore, in the actual application process of the adhesive, we will pay more attention to various physical properties of the adhesive, such as the appearance, density, viscosity, non-volatile content, ph value, curing time, aging, etc. of the adhesive. What are the main physical properties of the adhesive? Woolen cloth? And what is the test method for the physical properties of the adhesive? Let’s look at the adhesive manufacturer CoolThermo for your analysis.
Refers to color, state, macro uniformity, mechanical impurities, etc., which can intuitively assess the quality of adhesives.
a. Pour the adhesive sample into the beaker, stir with a glass rod, and observe whether the glue liquid is uniform and whether it contains other mechanical impurities or coagulation.
b. Pour the adhesive into a vertical bottle obliquely, and observe whether the glue flows evenly from the upper part of the bottle along the wall of the glass bottle.
Density is the mass of substance per unit volume at a specific temperature, and its unit is g/cm, which can reflect the uniformity of adhesive mixing.
a. Gravity equalization method;
b. Hydrometer method;
c. Syringe method.
Viscosity is a property of the adhesive that hinders its relative flow, and it is an important indicator for evaluating the quality of the adhesive.
a. Rotational viscometer method;
b. Viscosity cup method.
For adhesives containing solvents, the non-volatile content of the components must be determined.
Non-volatile content (X%) calculation formula:
Note: G1—the mass of the sample after drying (g) G—the mass of the sample before drying
The pH value can know the acid-base size of the adhesive. The smaller the pH value, the stronger the acidity; the larger the pH value, the stronger the alkalinity. If it contains acidic substances that will cause corrosion of metals, care must be taken when selecting them.
The easiest way to test is with pH paper, but this method is only suitable for water-based or emulsion adhesives and is not accurate enough. The most accurate test is the glass electrode acidity meter method, which is suitable for water-soluble, dry or non-aqueous media and adhesives that can be dissolved, dispersed and suspended in water.
The pot life of an adhesive is the amount of time the formulated adhesive can maintain its usable properties. It is an important industrial index for chemical reactive adhesives and two-component rubber adhesives.
The curing speed of the adhesive is the main data for studying the curing conditions of the adhesive, and it can be used as a simple method to check whether the finished product performance of the adhesive is correct or not.
The storage period of the adhesive is the storage time during which the adhesive can still maintain its operational performance and specified strength under certain conditions.
Chemical resistance is one of the durability indicators of adhesives. The metal samples bonded by adhesives are immersed in a certain test liquid at a certain temperature for a specified period of time, and the reduction in bonding strength measures the chemical resistance of the adhesive.
During the use of the test adhesive, due to the action of various environmental factors and media, the performance of the adhesive will be reduced and destroyed, resulting in aging.
a. Atmospheric aging test: Before the test, install the exposure frame at the designated location, fix the sample on the exposure frame with stainless wire, the distance between the samples is not less than 10mm, and the exposure time of the sample is generally at least one year. It is measured once a month, and the performance of each adhesive tested after aging is compared with that before aging.
b. Atmospheric accelerated aging test: The use of atmospheric accelerated aging test can shorten the test period and improve the test level. The test is carried out on a special aging test machine, which is an automatic insolation device used outdoors and tracking the sun all day long.
c. Damp heat aging test: The simultaneous action of high temperature and high humidity is the main reason for the aging of the adhesive. The damp heat aging test is generally carried out in a thermostat.
d. Artificial simulated climate accelerated aging test: use artificially manufactured simulated aging light source instead of sunlight to conduct accelerated aging test. At present, the test light sources are mainly ultraviolet carbon arc lamps, sunlight carbon arc lamps, and xenon lamps.
e. Salt spray corrosion test: This test is mainly that when the adhesive comes into contact with seawater and steam, the salt spray particles will settle on the bonding parts and quickly absorb moisture and dissolve into an aqueous solution of chloride, thereby infiltrating the inside of the adhesive layer and accelerating electrochemical corrosion. The corrosion of the adhered material caused by aging is caused by the reaction, and the test is mainly carried out in various salt spray corrosion test chambers.
The above is the introduction of the adhesive manufacturer CoolThermo to the main physical properties of the adhesive and its testing methods. If you want to know more about the adhesive, you can contact CoolThermo.