Explanation of Adhesive (Glue, Adhesive, Adhesive) Bonding Process

Composition of adhesive

1、 Composition of adhesive

The adhesives currently used by Advanced Institute Technology Materials are all synthetic resin adhesives with multiple components, and single component adhesives can no longer meet the requirements in use. Synthetic adhesives are composed of a main agent and auxiliary agents, with the main agent also known as the main material, base material, or adhesive; Auxiliaries include curing agents, diluents, plasticizers, fillers, coupling agents, initiators, thickeners, anti-aging agents, polymerization inhibitors, stabilizers, complexing agents, emulsifiers, etc. Depending on requirements and applications, they can also include flame retardants, foaming agents, defoamers, coloring agents, and mold inhibitors.

1. Main agent

The main agent is the main component of the adhesive, which dominates the bonding performance of the adhesive and is also an important indicator to distinguish the type of adhesive. The main agent is generally composed of one or two, or even three high polymers, requiring good adhesion and wetting properties. The commonly used adhesives are:

·Natural polymer compounds

Such as protein, skin glue, fish glue, rosin, peach glue, bone glue, etc.

2) Synthesis of polymer compounds

① Thermosetting resins, such as epoxy resin, phenolic resin, polyurethane resin, urea formaldehyde resin, organic silicon resin, etc.

② Thermoplastic resins, such as polyvinyl acetate, polyvinyl alcohol and aldehyde resins, polystyrene, etc.

③ Elastic materials such as nitrile rubber, chloroprene rubber, polysulfide rubber, etc.

④ Mixtures or grafts, inlays, and copolymers of various synthetic resins and synthetic rubbers.

2. Additives

In order to meet specific physical and chemical properties, various auxiliary components added are called additives. For example, curing agents are added to form a network or body structure of the main adhesive and increase the cohesive strength of the adhesive layer (they react with the main adhesive and produce cross-linking effects); Adding curing accelerators or catalysts to accelerate curing and reduce reaction temperature; In order to improve the resistance to atmospheric aging, thermal aging, arc aging, ozone aging and other properties, anti-aging agents are added; Adding fillers to give adhesives specific properties and reduce costs; Adding toughening agents to reduce the rigidity of the adhesive layer and increase toughness; In order to improve processability, reduce viscosity, and extend service life, diluents are added. include:

1) Curing agent

Curing agent, also known as hardener, is a component that accelerates the curing of bonding substances through chemical reactions. It is the most important component in adhesives. Its function is to directly or through a catalyst react with the main polymer, and after curing, introduce the curing agent molecules into the resin, transforming the originally thermoplastic linear main polymer into a tough and hard network structure.

There are many types of curing agents, and different resins and requirements require different curing agents to be used. The processability and performance of adhesive bonding are determined by the performance and quantity of the curing agent added.

2) Toughening agent

The active groups of toughening agents directly participate in the curing reaction of adhesives and enter the chain structure of a large molecule ultimately formed in the cured product. After curing, adhesives without toughening agents have brittle properties, are prone to cracking, and have poor practicality. Adhesive agents with toughening agents have good impact strength and peel resistance. Different toughening agents can also reduce their internal stress and curing shrinkage to varying degrees, and improve their low-temperature performance.

Common toughening agents include polyamide resin, synthetic rubber, aldehyde resin, polysulfone resin, etc.

3) Diluent

Diluents, also known as solvents, are mainly used to reduce the viscosity of adhesives, increase their wetting ability, and improve process performance. Some can reduce the activity of adhesives, thereby extending their service life. However, excessive addition can reduce the bonding strength, heat resistance, and medium resistance of the adhesive.

Common diluents include acetone, paint, and other solvents that are compatible with adhesives.

4) Packing material

Fillers generally do not undergo chemical reactions in adhesives. The use of fillers can improve the strength, impact toughness, wear resistance, aging resistance, hardness, maximum operating temperature, and heat resistance of adhesive joints, while reducing linear expansion coefficient, curing shrinkage rate, and cost. Common fillers include copper oxide, magnesium oxide, silver powder, porcelain powder, mica powder, asbestos powder, talc powder, etc.

5) Modifier

Modifiers are components added to improve a certain aspect of adhesive performance to meet special requirements. For example, coupling agents can be added to increase bonding strength, as well as preservatives, mold inhibitors, flame retardants, and stabilizers.

2、 Classification of adhesives

Classify by components

There are many types of adhesives, including urea formaldehyde resin adhesive, polyvinyl acetate adhesive, polyacrylic acid resin adhesive, polyacrylic acid resin, polyurethane adhesive, hot melt adhesive, epoxy resin adhesive, synthetic adhesive, and so on.

1. Organic silicone adhesive

It is a sealing adhesive that has the characteristics of cold resistance, heat resistance, aging resistance, waterproofing, moisture resistance, high tensile fatigue strength, small permanent deformation, and non toxicity. In recent years, this type of adhesive has developed rapidly in China, but currently, the raw materials for organic silicone adhesives in China rely partially on imports.

2. Polyurethane adhesive

It can bond various materials and maintain their physical and chemical properties even at low or ultra-low temperatures after bonding. It is mainly used in the fields of shoemaking, packaging, automobiles, magnetic recording materials, etc.

3. Polyacrylic acid resin

Mainly used in the production of pressure-sensitive adhesives, it is also used in the textile and construction fields.

Adhesive for construction: mainly used for bonding between building decoration, sealing or structures.

4. Hot melt adhesive

According to different raw materials, it can be divided into EVA hot melt adhesive, polyamide hot melt adhesive, polyester hot melt adhesive, polyolefin hot melt adhesive, etc. At present, EVA hot melt adhesive is mainly produced and used in China. The main raw materials for polyolefin adhesives are ethylene series, SBS, and SIS copolymers.

5. Epoxy resin adhesive

Can bond between metals and most non-metallic materials, widely used in construction, automotive, electronics, electrical appliances, and daily household items

6. Urea formaldehyde resin, phenolic resin, melamine formaldehyde adhesive

Mainly used in the wood processing industry, the formaldehyde emissions after use are higher than international standards.

Adhesive for wood processing: used for medium density fiberboard, gypsum board, plywood, particleboard, etc

7. Synthetic adhesive

Mainly used in fields such as wood processing, construction, decoration, automobiles, shoemaking, packaging, textiles, electronics, printing and binding. At present, China imports nearly 200000 tons of synthetic adhesives annually, including hot melt adhesives, organic silicon sealing adhesives, polyacrylic acid adhesives, polyurethane adhesives, and polyvinyl chloride (PVC) plastic adhesives for automobiles. Meanwhile, approximately 20000 tons of synthetic adhesives are exported annually, mainly including polyvinyl acetate, polyvinyl formaldehyde, and pressure-sensitive adhesives.

Classify by purpose

1. Sealing adhesive

Mainly used for connecting doors, windows, and prefabricated components of prefabricated houses. High end sealing adhesives are silicone and polyurethane adhesives, while mid-range adhesives include chloroprene rubber adhesives, polyacrylic acid, etc. In China, organic silicone adhesives and polyurethane sealing adhesives should be the future development direction in the construction adhesive market. Currently, they account for about 30% of the sales volume of construction sealing adhesives.

2. Adhesive for building structures

Mainly used for connecting structural units. For external repairs of reinforced concrete structures, metal reinforcement and fixation, as well as on-site construction, epoxy resin series adhesives are generally considered.

3. Automotive adhesive

There are four types of adhesives, namely for vehicle body, interior decoration, windshield, and chassis.

At present, the annual consumption of automotive adhesives in China is about 40000 tons, among which the most widely used are polyvinyl chloride plastic adhesives, chloroprene rubber adhesives, and asphalt series adhesives.

4. Adhesive for packaging

It is mainly used to make pressure-sensitive adhesive tapes and labels, and to bond the surfaces of packaging materials such as paper, plastic, and metal. The adhesive for paper packaging material is polyvinyl acetate lotion. Adhesives for plastic and metal packaging materials are polyacrylic lotion, VAE lotion, polyurethane adhesive and cyanoacrylate adhesive.

5. Electronic adhesive

The consumption is relatively low, currently less than 10000 tons per year, mostly used for integrated circuits and electronic products. Currently, epoxy resin, unsaturated polyester resin, and organic silicone adhesive are mainly used. We can supply the sealing adhesive for 5-micron thick electronic components ourselves, but the adhesive for 3-micron thick electronic components needs to be imported from abroad.

6. Adhesive for shoemaking

The annual consumption is about 125000 tons, of which 110000 tons are needed for chloroprene rubber adhesives and about 15000 tons are needed for polyurethane adhesives. Due to the use of benzene as a solvent for chloroprene rubber adhesives, which are harmful to human health, their development should be restricted. To meet the development needs of the footwear industry, the use of polyurethane series adhesives will be the direction.

Classify by physical form

1. Sealing glue

1.1 Classification by vulcanization method of sealant

(1) Wet air vulcanized sealant

This type of sealant series is vulcanized with moisture in the air. It mainly includes single component polyurethane, silicone rubber, and polysulfide rubber. The polymer base material contains active functional groups that can react with water in the air to form cross-linking bonds, causing the sealant to sulfide into a network structure.

(2) Chemical vulcanized sealant

Two component polyurethane, silicone rubber, polysulfide rubber, chloroprene rubber, and epoxy resin sealant all belong to this category and are generally vulcanized at room temperature. Some single component chlorosulfonated polyethylene and chloroprene rubber sealants, as well as polyvinyl chloride sol paste sealants, must undergo chemical reactions under heating conditions to complete vulcanization.

(3) Heat transfer variant sealant

Polyvinyl chloride resin dispersed with plasticizers and sealant containing asphalt are two different types of thermal transition systems. Vinyl resin plasticizers are liquid suspensions at room temperature, which harden by being converted into solids through heating; And the rubber asphalt joint sealant is hot-melt.

(4) Oxidation hardening sealant

Surface dry sealant for embedding or installing glass is mainly based on dry or semi dry vegetable oil or animal oil, which can be refined, polymerized, blown or chemically modified.

(5) Solvent volatile solidification sealant

This is a sealant based on a non viscous high polymer after solvent evaporation. This type of sealant mainly includes butyl rubber, high molecular weight polyisobutene, acrylic ester with a certain degree of polymerization, chlorosulfonated polyethylene, and chloroprene rubber sealant.

1.2 Classification by sealant form

(1) Paste like sealant

This type of sealant is mainly used in static joints, with a service life of generally 2 years or more. Usually, three main materials are used: oil and resin, polybutene, and asphalt.

(2) Liquid elastomer sealant

This type of sealant includes liquid polymers that can be vulcanized to form a truly elastic state, and they have the ability to withstand repeated joint deformations. The polymer elastomers used in elastomeric sealants include liquid polysulfide rubber, thiol terminated polypropylene ether, liquid polyurethane, room temperature vulcanized silicone rubber, and low molecular weight butyl rubber. This type of sealant is usually composed of two components, which are mixed together when used.

(3) Hot melt sealant

Hot melt sealant, also known as hot construction sealant. A sealant based on a blend of elastomer and thermoplastic resin. This type of sealant is usually extruded directly into the joint through a certain mouth shape under heating (150-200 ℃). Hot construction can improve the wetting ability of sealant to the adhesive base material, thus having good adhesion to most adhesive base materials. Once placed in the appropriate position, it cools and forms a strong elastic material with minimal shrinkage or film formation. The main materials of hot construction sealant are isobutene polymers, EPDM rubber, and thermoplastic styrene block copolymers. They are usually similar to thermoplastic resins such as EVA EEA、 Polyethylene, polyamide, polyester and other blends.

(4) Liquid sealant

This type of sealant is mainly used for sealing mechanical joint surfaces, replacing solid sealing materials such as solid gaskets to prevent internal fluid leakage from the joint surfaces. This type of sealant is usually made of polymer materials such as rubber, resin, etc. as the main material, supplemented with fillers and other components. Liquid sealant is usually divided into four categories: non drying adhesive type, semi dry viscoelastic type, dry adhesive type, and dry peelable type. Choose according to specific usage location and requirements.

1.3 Classification of performance after sealant construction

(1) Curing sealant

Curing sealant can be divided into two types: rigid sealant and flexible sealant: a) rigid sealant forms a hard solid after vulcanization or solidification, and rarely has elasticity; Some varieties of this type of sealant serve both sealing and bonding purposes, with representative sealants based on resins such as epoxy resin, polyester resin, polyacrylate, polyamide, and polyvinyl acetate. b) Flexible sealant maintains its softness after vulcanization. They are generally based on rubber elastomers. The flexibility changes significantly, and the hardness (Shore A) ranges from 10 to 80. Some varieties of this type of sealant are pure rubber, while most have good adhesive properties.

(2) Non curing sealant

This type of sealant is a soft and solidifying sealant that remains in a non drying state after application. Usually in the form of a paste, it can be applied to the joint with a scraper or brush, and can be combined with many different viscosities and properties of sealants.

2. Classified by adhesive hardening method

The low-temperature hardening code is a; The room temperature hardening code is b; The code for heating hardening is c; Suitable for hardening in various temperature zones with the code d; The solidification code for reaction with water is e; The anaerobic solidification code is f; Radiation (light, electron beam, radiation) curing code g; The code for hot melt cold hardening is h; The code for pressure-sensitive adhesive is i; The coagulation or condensation code is j, and other codes are k.

3. Classified by adhesive and adherend

Multiple material codes are A; The wood code is B; The paper code is C; The natural fiber code is D; The synthetic fiber code is E; Polyolefin fibers (excluding Class E) are designated as F; The metal and alloy code is G; The code for difficult to stick metals (gold, silver, copper, etc.) is H; The code for metal fibers is I, and the code for inorganic fibers is J; The code for transparent inorganic materials (glass, gemstones, etc.) is K; The code for opaque inorganic materials is L; The natural rubber code is M; The code for synthetic rubber is N; The code for difficult to stick rubber (silicone rubber, fluororubber, butyl rubber) is O, the code for hard plastic is P, and the code for plastic film is Q; The code of leather and synthetic leather is R, and the code of foam plastic is S; The code for difficult to stick plastics and films (fluoroplastics, polyethylene, polypropylene, etc.) is T; The code for biological tissues, bones, and dental materials is U; The other codes are V.

4. Adhesive state

The solvent-free liquid code is 1; The organic solvent liquid code is 2; The code for water-based liquids is 3, the code for paste like and paste like liquids is 4, and the code for powder like, granular, and block like liquids is 5; The code for sheet, film, mesh, and strip is 6; The code for filamentous, strip-shaped, and rod-shaped materials is 7.

5. Other adhesives: (not commonly used)

Metal structural adhesive, polymer structural adhesive, photosensitive sealing structural adhesive, other composite structural adhesives

Thermosetting polymer adhesives: epoxy resin adhesive, polyurethane (PU) adhesive, amino resin adhesive, phenolic resin adhesive, acrylic resin adhesive, furan resin adhesive, meta phenolic formaldehyde resin adhesive, dimethyl phenolic formaldehyde resin adhesive, unsaturated polyester adhesive, composite resin adhesive, polyimide adhesive, urea formaldehyde resin adhesive, other polymer adhesives

Sealing adhesive: room temperature vulcanized silicone rubber, epoxy resin sealant, polyurethane sealant, unsaturated polyester, acrylic ester, sealing putty, chloroprene rubber sealant, elastic sealant, liquid sealing gasket, polysulfide rubber sealant, other sealants

Hot melt adhesive: hot melt adhesive strips, rubber granules, adhesive powder, EVA hot melt adhesive, rubber hot melt adhesive, polypropylene, polyester, polyamide, polyurethane hot melt adhesive, styrene hot melt adhesive, new hot melt adhesive, polyethylene and ethylene copolymer hot melt adhesive, other hot melt adhesives

Water based adhesive: acrylic lotion, vinyl acetate lotion, polyvinyl acetal adhesive, lotion adhesive, other water-based adhesives

Pressure sensitive adhesive (sticker): glue, adhesive tape, solvent-free pressure-sensitive adhesive, solvent pressure-sensitive adhesive, cured pressure-sensitive adhesive, rubber pressure-sensitive adhesive, acrylic pressure-sensitive adhesive, other pressure-sensitive adhesives

Solvent based adhesive: resin solution adhesive, rubber solution adhesive, other solvent adhesives

Inorganic adhesives: hot melt inorganic adhesive, natural dry inorganic adhesive, chemical reaction inorganic adhesive, water-based inorganic adhesive, other inorganic adhesives

Thermoplastic polymer adhesive: solid polymer adhesive, solution polymer adhesive, lotion polymer adhesive, monomer polymer adhesive, other thermoplastic polymer adhesive

Natural adhesives: protein adhesives, carbohydrate adhesives, other natural adhesives

Rubber adhesives: silicone rubber adhesive, chloroprene rubber adhesive, nitrile rubber adhesive, modified natural rubber adhesive, chlorosulfonated polyethylene adhesive, polysulfide rubber adhesive, carboxyl rubber adhesive, polyisobutene, butyl rubber adhesive, other rubber adhesives

High temperature resistant adhesives: organic silicone, inorganic adhesives, high-temperature mold resin adhesives, metal high-temperature adhesives, other high-temperature resistant adhesives

Polymer adhesives: nitrile polymer adhesive, polysulfide rubber adhesive, polyvinyl chloride adhesive, polybutadiene adhesive, vinyl chloride adhesive, other polymer adhesives

Repair agents: metal repair agent, high-temperature repair agent, emergency repair agent, wear-resistant repair agent, corrosion-resistant repair agent, plastic repair agent, other repair agents

Medical adhesive, paper adhesive, magnetic adhesive, anti magnetic adhesive, fireproof adhesive, anti quenching adhesive, anti cracking adhesive, animal adhesive, plant adhesive, mineral adhesive, food grade adhesive, and other adhesives.