The difference between structural adhesives and non-structural adhesives is mainly reflected in the bonding strength. It is completely differentiated by resin type.
1, the difference in bonding strength
Structural adhesive, with high bond strength, the bond can bear a large load, high shear strength, high uneven tear strength, and the bond can withstand shock, vibration, fatigue, etc. load test. In addition, structural adhesives have certain properties such as heat resistance and weather resistance, and the bonded structural components can work in relatively harsh environments. According to the main components, common structural adhesives include modified phenolic resin, modified epoxy resin, unsaturated resin and other adhesives. PUR hot melt adhesive is a one-component solvent-free hot melt structural adhesive.
Non-structural adhesives generally do not bear any large load, and are used for bonding parts with less stress or for positioning. There are also many varieties of non-structural adhesives, such as polyurethane, neoprene, urea-formaldehyde and other adhesives.
Share: The formula of epoxy resin adhesives cured at room temperature with general amines can only be used for the bonding of non-structural parts. If it is modified, it can become a good structural adhesive.
2. Introduction to the Standard for Structural Adhesives
At present, there is no recognized consensus on the definition, classification and evaluation standards of structural adhesives at home and abroad. Views vary across industries.
(1) The American aviation structural adhesive standard MMM-A-132 divides structural adhesives into four types according to the requirements for heat resistance at different Mach number flight speeds, and evaluates shear, fatigue, creep, aging, T The strength indicators such as type peeling have been specified.
The flight speed corresponding to Type I is below Mach 1, and the strength index at room temperature and 82°C is specified; Type II corresponds to Mach number 1 to 2, and the strength index at room temperature and 149°C is specified; Types III and IV correspond to From Mach 2 or more to about Mach 3, strength indicators at room temperature, 149°C and 260°C are specified. The last three types are high temperature structural adhesives for supersonic aircraft.
The I type is divided into three grades according to different strengths, and the regulations are as follows: the first grade is used for the bonding of the main stress structure, which is a structural adhesive; the second grade is used for the bonding of the secondary stress structure, which is a quasi-structural adhesive; There is no requirement for peel strength and should belong to non-structural adhesives.
(2) There is no national standard for the definition and classification of structural adhesives in my country. Generally, structural adhesives are divided into two categories: high-strength, high-toughness, medium-strength, and medium-toughness according to the force of the bonding object and the bonding strength: main stress The steel-to-steel shear strength of the structural adhesive is greater than or equal to 25MPa, the tensile strength is greater than or equal to 33MPa, and the uneven pull-off strength is greater than or equal to 40kN/m. The shear strength of the adhesive for secondary stress structure is 17-25Mpa, and the non-uniform pull-off strength is 20-50kN/m.
3. Epoxy structural adhesive
Epoxy resin structural adhesive refers to a type of adhesive that adheres to stress-receiving structural parts. In the connection of structural parts, gluing has greater advantages than traditional riveting, screwing and welding. Epoxy resin structural adhesive has high strength and toughness, good comprehensive performance, and high safety and reliability of bonding. The formula design is flexible, the selectivity is large, and it can adapt to various use requirements. It is the most important and most reliable product in structural adhesives. With the improvement of building safety requirements, its importance is becoming more and more known.
a. Epoxy structural adhesives can be divided into four categories according to the curing temperature: high temperature curing, medium temperature curing, room temperature curing and low temperature curing.
(1) High temperature curing epoxy structural adhesives have high temperature, toughness, heat resistance, etc., and are mostly used for bonding of main stress structures;
(2) The medium temperature curing epoxy structural adhesive is mainly a kind of glue developed to meet the needs of the aircraft industry. Since the aluminum alloy begins to show the tendency of grain boundary corrosion above 120 ℃, it will intensify with the increase of temperature. After the grain boundary corrosion The strength and toughness of green alloy will decrease, so the curing condition of the adhesive for bonding aluminum alloy is required not to exceed 130℃/4h;
(3) The application of room temperature curing epoxy structural adhesive is more extensive. The application in the field of civil construction is more important, and it is one of the main varieties of building structural adhesives;
(4) Low temperature curing epoxy adhesive is a new type of adhesive developed in recent years in order to meet the needs of low temperature construction in winter. It can be constructed and cured at 0 °C or even below -10 °C. (A low temperature curing epoxy adhesive developed by Kane KY company, 80 ℃ relatively low temperature curing, does not affect sensitive components, high bonding strength, used in the bonding of camera module structural parts)
b. According to the heat resistance, structural adhesives can also be divided into three types: general type (≤80℃), high temperature resistant type (≥150℃) and medium temperature resistant type (between the former).
4. Construction Adhesives
Construction adhesive is an indispensable material in construction engineering and is widely used. In the process of building decoration and decoration, it is mainly used for sheet bonding, wall pretreatment, wallpaper pasting, ceramic wall and floor tiles, various floors, carpet laying and bonding, etc., which increases waterproofness, sealing, elasticity and impact resistance. It can not only improve the quality of building decoration, increase the beauty and comfort, but also improve the construction process, improve the efficiency and quality of building construction, etc. Due to its wide range of applications, there are many kinds of them, which are classified according to bonding strength and use:
a. Structural type
(1) Building structural adhesives: steel glue, planting glue (anchor glue), pouring glue, carbon fiber reinforcement glue, etc.;
(2) Curtain wall structural adhesive: dry-hanging adhesive, silicone structural adhesive;
b. Unstructured
(1) Adhesive adhesives: floor glue, floor tile glue, wallpaper glue, plastic pipe glue, stone glue, bamboo and wood glue, etc.;
(2) Sealant: polysulfide sealant, butyl sealant, silicone sealant, etc.
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