1 Overview
Alpha-cyanoacrylate adhesives are an attractive class of structural adhesives. It was discovered by the United States Eastman Company in 1955 when it synthesized vinyl compounds. In 1959, the United States Eastman Kodak Corporation began production marketing. Due to its great chemical activity, it can be cured in a very short time, even within seconds, and is thus regarded as an instant dry adhesive.
The alpha cyanoacrylate originally produced was alpha-cyanoacrylic acid methyl ester, and the grade was Eastman 910. Later Eastman Corporation developed a series of products such as Eastman 910 FS, Eastman 910 EM, Eastman 910 HMT, and the like.
At present, 2500 to 3,000 tons of various cyanoacrylate adhesives are sold worldwide. More than 90% of them are ethyl cyanoacrylates due to their excellent adhesiveness, long shelf life, and high productivity.
There are six major cyanoacrylate manufacturing companies worldwide, including The Loctite Corporation and National Starch (Permabond) in the United States, Henkel AKG in Germany, East Asia Synthetic Chemical Industry Corporation in Japan, Sumitomo Chemical Industry Corporation, and Alpha Techno.
China began to develop cyanoacrylate adhesives from the 1960s. Before 1979, the development was slow and the annual output was less than 10 tons. Products are alpha-cyanoacrylate (502 glue) and a small amount of methyl α-cyanoacrylate (501 glue), butyl α-cyanoacrylate (medical, 504 glue).
Since 1979, it has developed rapidly. There are more than 30 research and development units, mainly Beijing Chemical Plant, Zhejiang Huangyan Organic Chemical Plant, and Shandong Yuwang Industrial Corporation Yucheng Chemical. In 1993, it produced about 400 tons. Xi'an Chemical Research Institute is engaged in the research and development work in this area, and it also has small batch production.
2. Method
The industrially widely used production method is the addition condensation reaction of the corresponding cyanoacetate with formaldehyde, followed by heating and depolymerization to obtain α-cyanoacrylate.
In the manufacturing process, dibutyl phthalate or dioctyl phthalate can be used as an accelerator; polymethyl methacrylate, polyacrylate, polycyanoacrylate or cellulose derivatives can be used for tackifying Agent. Cyanoacrylate monomers are highly polymerizable, so inhibitors or stabilizers must be added during production and product storage.
The polymerization inhibitor can be divided into two types of anionic and radical polymerization inhibitors. The former include metaphosphoric acid, maleic acid, maleic anhydride, alkyl sulfonic acid, phosphorus pentoxide, iron(III) chloride, cerium oxide, 2,4,6-trinitrophenol, thiol, alkyl sulfur Acyl, alkyl sulfone, alkyl sulfoxide, alkyl sulfite, sultone, sulfur dioxide and sulfur trioxide.
The latter includes hydroquinone, catechol and derivatives of the above compounds. General products contain 0.001 to 0.01% sulfur dioxide, 0.05% hydroquinone, 3 to 4% plasticizer, and 3 to 10% tackifier.
3. Performance
The rapid development of cyanoacrylate is due to its unique set of advantages:
(1) Easy to use. It is a one-component, solvent-free adhesive that does not require an additional catalyst. It can be cured at room temperature in a matter of minutes or even seconds without heating or pressure. It is easy to use in automated assembly lines. The surface of the adherend does not require special treatment.
(2) Use less. The cyanoacrylate has low viscosity, easy spreading, and small amount of use per unit area, requiring only one or two drops.
(3) High bonding strength and wide application range. Instant adhesives can exert their strong adhesion in the presence of weak base materials such as water (moisture), alcohols, etc. instantaneously due to rapid anionic polymerization.
Because the cyanoacrylate molecules contain highly electronegative groups such as -CN and a COOR, the reaction proceeds smoothly. In the first step, due to the presence of cations, double bonds are formed between the carbon-carbon bonds, and the two molecules are bound by the double bonds, and the molecules are repeatedly formed to generate macromolecular compounds. The poly-α-cyanoacrylate thus obtained has extremely strong cohesive force and adhesive force to various adherends. In addition to polyethylene, polypropylene, polytetrafluoroethylene and other inert materials, a variety of metals and non-metals can be used to glue them, such as steel a aluminum, metal and other chin, phenolic, polyvinyl chloride, polyacrylate and other plastic parts And glass wood, leather, rubber, etc., can still be used for bonding of human tissues such as surgery and dentistry.
(4) The adhesive layer has good transparency and air tightness and is suitable for optical instruments.
There are also some shortcomings of cyanoacrylate:
1 Curing speed is too fast and should not be used in large areas.
2 Glued metal, glass and other surfaces, poor resistance to moisture, water, and polar solvents. A 3 adhesive layer is more brittle, and when it is bonded to a rigid material, it has poor impact resistance and resistance to expansion.
4 The heat resistance is not high enough and the operating temperature is -50-70°C.
5 more expensive.
The R of the ester group differs in its physical properties.
4. Uses
In view of the above-mentioned advantages and disadvantages, cyanoacrylate adhesives can be used for bonding equipment, instrument parts, bonded strain gauges, arts and crafts, glue vulcanized rubber seals and sashes, temporary processing fixed, positioning, machine repair, The repair of utensils and other aspects. Absorption adhesives are used abroad for sand mould manufacture (for metal casting) and have a tensile strength of 2.76 MPa.
In addition, high-purity α-cyanoacrylate is basically non-toxic to human body, and the α-cyanobutyl acrylate adhesive sterilized by high temperature of 120-150°C is greatly developed in clinical application based on animal experiments, such as Wound closure, ophthalmic surgery tissue cementation, organ transplantation, surgical reshaping, and evasion prevention.
The fast curing and easy use of α-cyanoacrylate has brought many benefits to home users, so it is increasingly accepted as a household adhesive.