& nbsp; & nbsp; & nbsp; The main components of two-component acrylic adhesive include isocyanates, polyols, hydroxyl containing polyethers, polyesters and epoxy resins, fillers, catalysts, and solvents.
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  & nbsp; & nbsp; & nbsp; & nbsp; Isocyanates commonly used in polyurethane adhesives are divided into aliphatic isocyanates and aromatic isocyanates. Aromatic isocyanates use inexpensive benzene and toluene as raw materials, so they have developed rapidly and currently dominate. Among them, there are toluene diisocyanate (TDI), diphenylmethane 1,4-diisocyanate (MDI), polymethylene polyisocyanate (PAPI), isophorone diisocyanate (IP DI), etc.
  & nbsp; & nbsp; & nbsp; & nbsp; There are three main types of polyester polyols used in the preparation of polyurethane adhesives: polyester polyols, poly (caprolactone), and polycarbonate diols. Dehydration and condensation of dicarboxylic acids and diols (or mixtures of diols and triols), often with excess diols, to obtain polyester polyols with hydroxyl end groups; Open the lactone ring with e-lactone in the presence of an initiator to prepare linear poly (8-monolactone) and polyols with hydroxyl end groups; Polyhexamethylene carbonate diol is produced by heating 1,6 monodiols and diphenyl carbonate under nitrogen protection, followed by ester exchange and high vacuum condensation. Polyester polyols are commonly prepared from polyols and dicarboxylic acids in general adhesive production plants.
  & nbsp; & nbsp; & nbsp; & nbsp; Polyether polyols are formed by ring opening polymerization of low relative molecular weight polyols, polyamines, or compounds containing active hydrogen with oxidized olefins under the action of catalysts. Commonly used ones include polyoxypropylene glycol, polyoxypropylene triol, polyoxypropylene castor oil polyol, polytetramethylene glycol, etc. The specific physical properties of polyether polyols are introduced in the formula.
  & nbsp; & nbsp; & nbsp; Catalysts are required for the NCO/OH reaction and NCO/H2O reaction in the preparation of polyurethane adhesives. Common catalysts include organotin catalysts (such as dibutyltin dilaurate and stannous octoate) and tertiary amine catalysts (such as trimethylenediamine, triethanolamine, triethylamine, etc.).
  & nbsp; & nbsp; & nbsp; In order to adjust the viscosity of the adhesive and facilitate process operation, solvents are often added during the preparation or formulation process. The solvent used for polyurethane adhesives should not contain active hydrogen compounds (such as water, alcohols, etc.) that can react with - NCO. Therefore, polyurethane adhesives require a higher purity of the solvent than general industrial products. The commonly used solvents mainly include esters (such as ethyl acetate), ketones (such as butanone), aromatic hydrocarbons (such as toluene), tetrahydrofuran, etc.
  & nbsp; & nbsp; & nbsp; Chain extenders and crosslinkers. Chain extenders are molecules containing two active functional groups, such as 1,4-butanediol, 2,3-1,1-diol, diethylene glycol, etc. Their main function is to increase the length of PU molecular chains without forming crosslinks. Crosslinking agents are molecules containing two or more active functional groups, such as low relative molecular weight multifunctional compounds containing hydroxyl or amino groups, such as glycerol, trimethylolpropane, sorbitol, polyamines, etc. The dosage of chain extenders and crosslinkers affects the ratio of polyurethane hard and soft segments, and directly affects the performance of polyurethane adhesive products.
  & nbsp; & nbsp; A certain amount of water is generally adsorbed on the surface of the filler, which is easy to react with isocyanate group to generate polyurea and carbon dioxide, and gel will be formed during storage. Therefore, the fillers in polyurethane adhesives should be pre treated with high temperature to remove moisture or treated with coupling agents. Some fillers, such as zinc oxide and slot carbon black, can also react with isocyanates, so attention should be paid when selecting them. Suitable fillers for polyurethane adhesives include talc powder, clay, barite powder, mica powder, calcium carbonate, calcium oxide, asbestos powder, diatomaceous earth, titanium dioxide, aluminum powder, iron powder, iron black, iron yellow, chromium trioxide, corundum powder, and diamond powder.
  & nbsp; & nbsp; Adhesion promoter (coupling agent): In order to improve the adhesion of polyurethane adhesive to the substrate, 0.5% to 2% of organic silicon or titanium ester coupling agent can be added to the adhesive solution. Commonly used functional silanes include r-aminopropyltrimethoxysilane, N_phenyl-r-aminopropyltrimethoxysilane, r-ureidopropyltrimethoxysilane, etc.
  & nbsp; & nbsp; Ionizing reagent is a key raw material for water-based polyurethane to have good water dispersibility or self emulsification, used to reduce or eliminate external surfactants, which is not commonly found in polyurethane synthesis. Ionizing reagents can be classified into cationic and anionic types based on the different charges carried by the ionic groups contained in the reagents.
  & nbsp; & nbsp; At present, anionic emulsifiers are widely used and have good effects. Anionic functional groups mainly include carboxyl and sulfonic acid groups, which are generally combined in diols or diamine chain extenders and introduced into the polyurethane main chain through reactions between hydroxyl or amino groups and the same NcO group. The commonly used ionization reagents currently include dimethylolpropionic acid (DMPA) and 5-sulfonylisophthalic acid sodium (5-SSI PA).
  & nbsp; & nbsp; To prevent thermal oxidation, photo aging, and hydrolysis of polyurethane adhesives, other additives such as antioxidants, light stabilizers, and hydrolysis stabilizers should be added. In order to control the fluidity of the adhesive during the glue application process, thixotropic agents such as gas-phase white carbon black can be added. To improve the initial viscosity and viscosity of the adhesive, thickening resin can be added. To improve the hardness of the adhesive layer, a small amount of plasticizer can be added. To prevent the adhesive from being invaded by microorganisms, insecticides can be added, and pigments can also be added for coloring.