Development of Fast Solid Acrylic Structural Adhesive (I)

Fast-curing acrylate adhesives are also known as reactive acrylic adhesives or second-generation acrylate adhesives. Quick set acrylic structural adhesive (adhesive structural a adhesives) was developed in the 1970s by the United States Du Pont (Du Pont) company developed a new type of adhesive, put on the market in 1975. Since 1950, the first generation dhesive (FGA) has been developed, so the fast-curing acrylate adhesive is often referred to as the second generation of the second generation adhesive (SGA). After the emergence of ultraviolet curing or electron beam curing acrylate adhesive. The third generation of the third generation adhesive (referred to as TGA). The above may be collectively referred to as modified acrylate adhesives, or reactive acrylate adhesives. Since the second-generation acrylic adhesive has outstanding performance and is a unique type, it is an ideal type of adhesive, and it has partially replaced other types of adhesives, and it has become a leader in structural adhesives.

The excellent properties of fast-curing acrylate adhesive make it more and more widely used. The continuous improvement of the varieties and the gradual improvement of performance have increased the prospects.

1. Characteristics and Application of Fast Solid Acrylic Structure Adhesive

1.1. Acrylic Adhesive Features

Fast-curing acrylate adhesives have many unique features compared to air-cured adhesives. Their main features are as follows.

1 Rapid curing at room temperature can be cured in tens or even ten minutes. Positioning time can be up to ten seconds

2 easy to use two-component, without accurate measurement, can be mixed after use, can also be two components separately coated, and then laminated.

3 The surface treatment is simple and does not require strict surface treatment. It can be used for oil surface bonding. Even if a thin oil layer is attached, it has greater strength.

4 High Adhesive Strength The room temperature shear strength of bonded metal is 20 MPa. Good toughness, high peel strength and impact strength.

5 Shrinking 100% Reactive Polymerization Curing

6 good temperature resistance, low temperature, good high temperature performance, can be used in -40-150 °C.

7 Durability Good resistance to heat and humidity and atmospheric aging.

8 Good resistance to media, good oil resistance, good water resistance
9 versatile for many materials have a good bonding performance, can be dissimilar materials bonding

10 Disadvantages Odor and short shelf life.

1.2 Use of Fast Solid Acrylic Structure Adhesives

Because the fast-curing acrylate structural adhesive has the remarkable characteristics of rapid solidification at room temperature, high strength, good toughness, oily surface bonding, strong adaptability, and simple process, it is widely used in aerospace, aviation, automobiles, machinery, ships, etc. Electronic, electrical, instrumentation, construction, furniture, toys, railway vehicles, civil engineering, arts and crafts and other industries, structural bonding, small parts assembly, large parts assembly, emergency repair, anti-seepage plugging, nameplate paste and so on. In the cutting-edge technology and high-tech aspects have also been better applied.

2. Composition and preparation of fast solid acrylic adhesive

2.1 Composition The fast-curing acrylate structural adhesive consists of acrylic monomers or prepolymers, elastomers, toughening resins, initiator accelerators, stabilizers, thickeners, thixotropic agents, and the like.

(1) Monomer The reactive monomer used is a monofunctional monomer, a polyfunctional monomer, or a prepolymer. The commonly used monomer is mainly methyl methacrylate. Other monomers such as styrene, vinyl acetate, acrylamide, vinyl toluene, methyl styrene, etc. are also added to improve performance.

(2) Elastomers and some elastomers added by the toughening resin participate in the reaction during the free radical polymerization of the glue liquid to produce graft copolymers; some form "islands" structures, thereby increasing the toughness and impact resistance. Sex, fatigue resistance, durability and bond strength. At the same time, the addition of the elastomer can also adjust the viscosity and reduce the shrinkage at the time of curing. Therefore, it is very important to select the elastomer that is compatible with the monomer. Commonly used elastomers include chlorosulfonated polyethylene, nitrile rubber, chloroprene rubber, acrylic rubber, polyether rubber, SBS, and the like. Can also add ABS, MBS, MBAS and other engineering plastics.

(3) Initiator initiators are usually peroxides, with benzoyl peroxide (BPO), t-butyl hydroperoxide (BHP), cumene hydroperoxide (CHP), methyl ethyl ketone peroxide (MEKP), Dicumyl peroxide and the like, in which cumene hydroperoxide and tert-butyl hydroperoxide are superior to other peroxides in terms of reactivity, safety and storage stability, especially cumene hydroperoxide at room temperature Under the liquid, easy to handle, easy to use, cheap. The reference amount of initiator is from 0.2% to 5.0% by mass.

(4) Accelerator Accelerators are substances that react with organic peroxides to produce active free radicals at room temperature. The so-called reducing agents form a strong oxidation-reduction initiation system with organic peroxides. Commonly used accelerators are amines, thioureas, metal organic compounds, ketones, sulfur compounds, phosphorus compounds, and the like. The gum compounds mainly include N,N-dimethylaniline, N,N-diethylaniline, NN-dimethyl-p-methylaniline, n-butyraldehyde-aniline condensate 808, and butyraldehyde-n-butylamine condensate. 833, triethylamine, benzyldimethylamine, DMP-30. The thiourea compounds mainly include thiourea, ethylenethiourea (NA-22), trimethylthiourea, tetramethylthiourea, and phenylthiourea. The metal organic compound should include cobalt naphthenate, cobalt naphthenate, cobalt acetate, manganese antimonate, octanoic acid and vanadium acetylacetonate. Acetyl acetone, benzoylacetone, and dibenzoylacetone are the main types of ketones. The sulfur compounds mainly include dodecyl mercaptan and α-hydroxybutyl benzothiazole. The phosphides are mainly tris(α-ethylhexyl) phosphate and triphenylphosphine. The reference amount of accelerator is 0.04%-4% (mass).

(5) Stabilizers In order to ensure that polymerization is not initiated immediately after the addition of the initiator to the monomers, and storage stability at room temperature is maintained, stabilizers such as hydroquinone, p-phenol, p-methoxyphenol, and 264 (BHT) and nitro compounds. Alkali metal salts, zinc salts, nickel salts, and ammonium salts of some organic and inorganic acids can also improve storage stability. The reference amount of stabilizer is 0.1%-0.5% (mass).

(6) Other additives Thickeners, thixotropic agents, fillers, pigments, etc. may be added as needed. The addition of fumed silica gives the solution a thixotropy. In order to reduce the inhibition of air and volatilization of low-boiling monomers, a small amount of paraffin can be added to the glue. Adding polyethylene powder with a particle size of 0.1 mm to the glue liquid can increase the peel strength. Adding a silane coupling agent such as vinyltriethoxysilane (WD-20, A-151), γ-(methacryloyloxy)propyltrimethoxysilane (KH-570), etc. can improve the water resistance SVD and adhesive strength, its small WD-20 can also inhibit the metal corrosion effect of methacrylic acid in glue. The addition of sulfonyl chloride promotes the curing of the adhesive. It is also possible to add film formers such as polystyrene and polymethyl methacrylate. Adding an appropriate amount of unsaturated polyester and methacrylic diester can speed up the curing process.