How do heavy dry goods design the best formula for epoxy?

Epoxy adhesive is one of the most widely used adhesive varieties, the market share is very large. How to design the best formula for epoxy?
In order to design the best formula for epoxy adhesive and achieve the required bonding performance, we must understand the adhesion of epoxy adhesive and the destruction of adhesive

, the relationship between the properties of the adhesive order and the properties of the glue
The performance of the adhesive has a decisive effect on the adhesive performance and is essential to the formulation design of the adhesive

. The performance of the glue layer and interface layer in the joint mainly depends on the structure, performance and curing process of the adhesive, and of course, it is related to the surface structure and properties of the adhesive. The properties of the adhesives discussed in this section refer to the properties of the cured adhesive layer and interface hierarchy.
adhesive properties that affect the properties of the glue are:
01, the strength and toughness of the adhesive. The former is the adhesive's ability to resist external forces, while the latter is the ability to reduce stress concentration and resist crack expansion. Improving the strength and toughness of the adhesive is beneficial to improving the bonding strength of the joint.
02, the mod of the adhesive and the fracture elongation. Both affect the stress distribution of the glue joint. Adhesives with low mods and high fracture elongation greatly increase the bonding strength when the "line is subjected". However, the mod is too low, the fracture elongation rate is too large will often reduce the cohesion strength, but the bit glue strength is reduced. For these two factors that affect the opposite, only by finding the best value under their common influence can we get the best "line force" glue strength.
03, adhesive stability and durability. This is its ability to resist the deterioration and structural damage of the adhesive by its surroundings (temperature, humidity, aging, media erosion, etc.). It is decisive to improve the heat resistance, wet heat resistance, aging resistance, corrosion resistance and safety reliability of the joints. Shear strength (face force) and peeling strength (line force) are obviously two types of properties with different properties. The former belongs to the category of stress, is the material's limit stress (destructive stress); The latter is related to the deformation energy of the adhesive, belongs to the energy category, is the break energy of the material (fracture work). So some people list the peel strength as a toughness parameter. The relationship between the thickness, temperature and test speed of the adhesive layer and the peeling strength was determined, and it was found that these parameters could be conversion, and the number of peeling strength peaks in the curve was related to the number of change points of the adhesive. The relationship between the hardness, mould and bonding properties of epoxy adhesives can be divided into four areas according to the hardness size: non-structural adhesives, flexible adhesives, general structural adhesives and heat-resistant adhesives.
it must be pointed out that the performance of adhesive and bonding performance are interrelated and mutually restricted, only comprehensive consideration, comprehensive trade-off, in order to design the required epoxy adhesive optimal formula.
, to determine the key properties of the required epoxy adhesive mainly according to
01, according to the joint in the force state and size of the adhesive selection adhesive performance. If it is "face force", it is advisable to choose cohesion strength and adhesive strength, good toughness adhesive. If it is "line force", it is advisable to choose adhesives with good toughness, small modality and large fracture elongation. Good toughness adhesives should be used when fatigued or impact loads.
02, according to the nature of the adhesive selected adhesive. Strong brittle materials (e.g. glass, ceramics, cement, stone, etc.) should be used with high strength, hardness and modulation, not easy to deform adhesive. Sheet metal and structural parts, such as tough, high-strength rigid materials, due to the large load and peeling stress, impact and fatigue stress, it is appropriate to use high strength, toughness of structural adhesives, such as epoxy-butyl adhesive. Soft and elastic materials (plastic film, rubber, etc.) generally do not use epoxy. It is also available with flexible epoxy glue. Porous materials (foam, sea damage, etc.) should be used with a large degree of education, flexible good epoxy glue. Materials with low polarity (polyethylene, polypropylene, fluoroplastics, etc.) should be processed by surface bio-active treatment before bonding with epoxy.
03, according to the temperature of use to select adhesive. The glassy temperature Tg of the adhesive should generally be greater than the maximum temperature of use. The temperature of use of universal epoxy adhesives is about -40 to 80 degrees C. Heat-resistant adhesives should be used when the temperature is above 150 degrees C. Low temperature adhesives with good toughness, such as epoxy-polyurethane glue, epoxy-nylon gel, etc., should be used at temperatures below -70 degrees C. Hot and cold cross-change butt head damage is large, it is appropriate to use good toughness of high and low temperature glue, such as epoxy-nylon glue.
04, according to other performance requirements to select adhesive. Such as water resistance, moisture and heat resistance, aging resistance, corrosion resistance, diele thermodyne, etc.
05, according to the process requirements (curing temperature, curing speed, education, tide surface or water curing, etc.) to choose adhesive. Selected adhesives often do not meet all requirements at the same time. This requires correctly determining which properties are the primary (critical) and which are secondary properties of the desired adhesive. And in accordance with the principle of ensuring the main performance, taking into account other performance design adhesive formula.
3. The steps and methods of epoxy adhesive formulation design
First of all, according to the performance of use and the permitted curing process conditions, whether it is possible to use epoxy adhesive, whether there is an advantage in performance price. Then generally follow the steps below to design the recipe.
1, preliminary judgment of the required epoxy adhesive main performance is what, secondary performance is which.
2, in line with the principle of ensuring the main functions, taking into account other functions, according to the structure and performance of the ingredient material and adhesive performance to determine the initial formulation of adhesive (adhesive group and ratio). Costs and the source of the material should also be considered.
(1) first with an epoxy curing system. The theoretical dosage of resins and curing agents is calculated by chemical equivalent. The amount of catalysts and promoters is used in empirical data.
(2) with other additives. Select the initial dosage (ratio) by reference to empirical data or trial matching methods. It is recommended that the selection of ingredient materials should pay attention to the interaction between the ingredients.
3, according to the main function of the best, other functions appropriate principles for the optimization of the initial formula. Such as the use of orthosective regression analysis, and with the help of computer-aided design, after comprehensive trade-offs, and finally decided the best formula.
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