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Definition of adhesive

Through the adhesion of the interface and the cohesion of the material, the natural or synthetic, organic or inorganic material that can connect two or more parts or materials together is collectively referred to as an adhesive (adhesive).

① Adhesion (adhesion): refers to the state where two surfaces are joined together by chemical force, physical force or both

② The adhesive must first adhere to the surface of the adherend.

Cohesion: that is, the state in which the particles within a single substance are joined together by the primary valence bond force (including ionic bond, covalent bond, coordination bond, metal bond, etc.

Adhesive requirements

① Regardless of the state, it should be liquid when applied

② The surface of the adherend can be completely spread and fully wetted

③ It must be able to transform the liquid into a solid or gel state in some way to form a tough and stable glue layer

④ It should have a certain strength after curing

⑤ It can withstand temperatures above 0℃ and withstand the test of a certain period of time

Classification of adhesives

Classification according to appearance: solvent emulsion type (water-based); paste or paste; solid type; film type

According to the curing method: water-based evaporation type, solvent evaporation type, hot melt type, chemical reaction type, pressure sensitive type

Basic composition of adhesive

The basic composition of the adhesive: the components of the adhesive include base material, curing agent, solvent, plasticizer, filler, coupling agent, crosslinking agent, accelerator, toughener, tackifier, thickener, diluent, Anti-aging agents, polymerization inhibitors, flame retardants, initiators, photosensitizers, defoamers, preservatives, stabilizers, complexing agents, emulsifiers

Types of base material: base material is the main component, main agent or main polymer of the adhesive, which has a bonding effect

① Commonly used organic compounds: thermosetting synthetic resins: phenolic resin, epoxy resin, amino resin, polyurethane resin, unsaturated polyester and acrylic resin

② Thermoplastic synthetic resin: rubber base material, natural polymer material, water-based latex, base material

③ Rubber base adhesive

The selection principle of the adhesive base material: according to the object of the adhesive application, the application occasion and the performance of the application
.
At the same time, the molecular structure of the molecular base material is closely related to the bonding performance
.

① The polarity of polymer materials is related

② Crystallization performance of polymer materials

③ Molecular weight of polymer materials

Curing agent (hardener): Make the ground state raw material undergo a chemical reaction to undergo polymerization, polycondensation, or cross-linking to convert it into a linear polymer or a network polymer.
It is a substance with mechanical strength and stability for the adhesive joint
.

Choice of curing agent:

①It is best to be a liquid, non-toxic, colorless, and odorless substance

②The curing agent and the cured object should react smoothly, with less heat release, in order to reduce the cohesion of the adhesive layer

③Heat resistance, choose a curing agent with more reactive groups in the molecule

④Toughness, choose curing agent with longer molecular chain

Adhesive solvent: refers to the liquid that can reduce the intermolecular force of certain solids or liquids, and disperse the dissolved substances into a homogeneous system of molecules or ions.
Commonly used solvents are liquid substances with low viscosity
.
There are mainly aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, esters, alcohols, ketones, acids, ethers, terpene olefins, amides and water
.
However, most organic solvents have certain toxicity, flammability, explosiveness, pollution to the environment, hidden dangers to safety, and harm to the human body
.

The role of solvent:

① The medium of the polymerization reaction: the reaction is gentle and the temperature is easy to control

② Dissolving base material: preparing solvent-based adhesives

③ Thinner: dilute the adhesive to make it reach a certain viscosity, which is good for wetting and easy to coat

④ Adjust the volatilization speed of the adhesive

⑤ Prevent gelation and increase storage stability

⑥ Surface cleaning agent before bonding

⑦ Direct bonding, some plastics

⑧ Reduce costs and improve efficiency

Choice of adhesive solvent:

① Polarity: Choose a solvent with the same or similar polarity as the base material (the principle of similar compatibility)

② Solubility parameter (related to polarity): the solubility parameter of the solvent is similar to that of the polymer matrix

③ Solvent volatility: Choose a solvent with appropriate volatility or a mixed solvent of fast and slow
.
Solvent volatilizes too fast: the surface of the glue is easy to form a film, and the solvent under the film is not easy to volatilize; the solvent volatilizes too slowly: the surface drying time is slow, which affects the work efficiency

④ The choice of solvent should consider price, toxicity and source

The role of softener: it is a component that is not cost-effective for SBS.
Its role is to adjust hardness, fluidity, and reduce costs.
Oil-extended SBS can make compounding and processing easier
.
The most commonly used is naphthenic oil.
Aromatics have deep color, are toxic, and cannot be used.
Paraffin oil cannot improve physical properties and can also cause ejection
.
The domestic Karamay KN series of environmentally friendly naphthenic oils (such as KN4010, etc.
) are of high quality
.

Types of softeners: According to the hydrocarbon composition, it can be divided into three types: paraffin-based, cycloalkyl, and aromatic

Features of softener:

① Paraffin-based rubber oil: good oxidation resistance and light stability, but relatively poor emulsification, compatibility, and low temperature properties

② Naphthenic rubber oil: has the advantages of both paraffin and aromatic bases, moderate emulsification and compatibility, non-polluting, non-toxic, and a wide range of applications

③ Aromatic rubber oil: good compatibility, large filling volume, low price, and high strength of the rubber product obtained
.
But the color is deep, toxic, and pollute the environment

Definition of plasticizer: It is a substance that reduces the glass transition temperature and melting temperature of polymer compounds, improves the brittleness of the adhesive layer, and enhances the melt fluidity
.

The role of plasticizer:

① Disperse the active groups of polymer compounds, weaken the intermolecular force, thereby reducing the interaction between molecules

② Increase the heat, elongation and cold resistance of the polymer compound, reduce its cohesive strength, elastic modulus and heat resistance

Choice of plasticizer:

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Initiator: A substance that can decompose to produce free radicals under certain conditions.
Generally, an initiator is added to compounds containing unsaturated bonds.
Commonly used initiators include dibenzoyl peroxide, cyclohexanone peroxide, and isopropyl peroxide benzene, azobisisobutyronitrile and the like
.

Promoter (catalyst): a substance that can reduce the decomposition temperature of the initiator or accelerate the reaction between the curing agent and the resin rubber
.

Anti-aging agent: A substance that can delay the aging of polymer compounds.
For the adhesive used under high temperature and exposure to the sun, it is easy to aging and deteriorate, so an anti-aging agent is added when preparing the glue
.

Thickener: an adhesive with low viscosity, a substance that increases its viscosity

Polymerization inhibitors and stabilizers: substances that prevent or delay the self-crosslinking of polymers and monomers containing unsaturated bonds (hydroquinone) during storage
.