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Waterborne Method

Update Time:2011-05-27   Writer:Arima
, Waterborne materials used
1. Polyol oligomers
Preparation of water-based polyurethane adhesive commonly used in the oligomer are generally polyether polyols, polyester diols majority, sometimes using polyether triol, low-branching polyester polyols, polycarbonate diols and other small species oligomer polyol.
Compliant Polyurethane good low-temperature, water resistance, and the common polyethylene oxide propylene glycol (PPG) more expensive than polyester glycol is low, therefore, research and development of China's most water-based polyurethane to polyethylene glycol to propylene oxide major oligomeric polyol raw materials. By the ether glycol obtained PTMEG polyurethane mechanical strength and resistance to hydrolysis are good, but their higher prices, limit its widespread application.
Polyester polyurethane, high strength, good adhesion, but because of its hydrolysis resistance of polyester polyether worse than that, it is commonly used in the polyester raw material obtained water-based polyurethane, the storage stability of the short.
2. Isocyanate
Preparation of polyurethane emulsion commonly used diisocyanates are TDI, MDI and other aromatic diisocyanate and IPDI, HDI, H12MDI other aliphatic, alicyclic diisocyanate. By the aliphatic or alicyclic diisocyanate made of polyurethane, hydrolysis resistance than aromatic isocyanate polyurethane made good, and thus water-based polyurethane product storage stability. Foreign high-quality polyester polyurethane are commonly used aliphatic or alicyclic isocyanate raw materials, and our variety and prices of raw materials by the restrictions, most only diisocyanate TDI as raw materials.
More methylene polyphenyl polyisocyanate generally used for the preparation of vinyl isocyanate polyurethane dispersion and emulsion.
3. Chain extender
Waterborne often used chain extender, which can be introduced in the hydrophilic ionic groups have a variety of chain extenders, chain extender in addition to special classes, but often also used 1,4 - butanediol, ethylene glycol, a diethylene glycol, hexanediol, ethylenediamine, diethylenetriamine amine chain extender. The amine and isocyanate higher reactivity than water, diamine chain extenders can be mixed in water or made into imine, emulsifying the same time in the chain extension reaction.
4. Water
Water is the main medium water-based polyurethane adhesive, to prevent water in the Ca2 +, Mg2 + and other anionic impurities on the stability of water-based polyurethane, the water used to prepare water-based polyurethane is generally distilled or deionized water. In addition to the polyurethane used as solvents or dispersion medium, water or reactive important raw materials, synthetic water-based polyurethane prepolymer method currently mainly distributed in the polyurethane prepolymer with water at the same time, water is also involved in chain extension. As water or diamine chain extender, in fact, most of the waterborne polyurethane polyurethane - urea emulsion (dispersion), polyurethane - urea greater than that of pure polyurethane cohesion and adhesion,
The water resistance of urea bond better than the urethane bond.
5. Hydrophilic chain extender
Hydrophilic chain extender is to introduce hydrophilic groups of the chain extender. Such chain extenders are only used in the preparation of waterborne polyurethane special materials. Such chain extenders are often carboxyl, sulfonate or secondary amino group, when its binding to the polyurethane molecule, so that the PU chain can be ionized with functional groups.
(1) carboxylic chain extenders
Dimethylol propionic acid referred to DMPA, the full name of 2,2 - dimethylol propionic acid, also known as α, α-double-propionic acid, commonly used at home and abroad is a polyurethane emulsion hydrophilic chain extender, Early in the sixties and seventies in Germany, the United States and other countries for the preparation of polyurethane emulsion. Chengdu, China in the early 90's factory has been able to small batch production. The chain extender is a white crystalline, high melting point, storage stability, because of its small molecular weight (Mw134), less able to provide adequate amount of carboxyl content. DMPA is a preparation method: the synthesis of formaldehyde and dimethylol propionaldehyde propionaldehyde, hydrogen peroxide and then into two propionic acid.
Dihydroxy alcohol half esters and half-ester is the product of binary anhydride, usually alcohol and anhydride molar ratio of 1:1, a carboxylic acid anhydride is esterified, while retaining the other carboxyl group. Half-esters used in polyurethane emulsion preparation of chain extender, generally used for small molecule alcohols glycerol or glycerol oligomers, such as glycerol, low molecular weight polyether triol. This would generate the dihydroxy compounds containing carboxyl. Triol molecular weight generally between about 100 to 2000. Can be used to prepare a half-ester acid anhydride and maleic anhydride (maleic anhydride), phthalic anhydride (phthalic anhydride), succinic anhydride, glutaric anhydride.
It normally takes half an ester made.
Carboxylic chain extenders also amino acids such as H2N (CH2) 4 CH (COOH) NH2, two amino acid so on.
(2) sulfonate diamine chain extender B-based sodium, 1,4 - butanediol -2-- and its derivatives such as sodium sulfonate waterborne polyurethane can be used as chain extender. 1,4 - butanediol -2-- sodium from 2 - ene -1,4 - butanediol and derived from sodium bisulfite addition, the same, 2 - ene -1,4 - butanediol oxidation ethylene or propylene oxide condensation product with sodium bisulfite adduct is also used as chain extender.
(3) chain extender containing cationic tertiary amine based polyol is a class of two commonly used cationic polyurethane emulsion chain extender, the reaction by quaternary ammonium or acid and, chains generated in the tertiary amine quaternary ammonium ion, with a hydrophilic effect. Among them, N-methyl diethanolamine most commonly used.
Diethylenetriamine and epichlorohydrin amine reaction products is also a special cationic chain extender:
6. As salts
Broadly speaking, those who can form ionic groups of compounds can be referred to as salt reagents. Agent is a salt with carboxyl, sulfonate groups, tertiary amine or urea groups in the reaction of the polymer salt or ionic groups generated reagents. Anionic polyurethane emulsion into a common salts are sodium hydroxide, ammonia, triethylamine. Salt formation reaction is as follows:
Cationic polyurethane emulsion as salts are HCI, CH3COOH and other acids, CH3I, (CH3) 2SO4, epichlorohydrin and other alkylating agents.
Urea-based and ring lactone, methyl lactone, anhydride reaction in alkaline conditions, can be connected in the polyurethane chain sulfonate or carboxyl groups. Can also sulfomethylated or ammonia methylation obtained with ionic groups of the polyurethane.
7. Solvent
Preparation of the polyurethane emulsion, sometimes very prepolymer viscosity, resulting in mixing difficulties, and the prepolymer in water emulsion to be stirred, low viscosity, is conducive to rapid mixing. Raise the temperature of the prepolymer, although the viscosity can be reduced, but when the prepolymer emulsion temperature is not conducive to fine particle size to ensure a stable emulsion. Therefore, in order to reduce the viscosity of the dispersion prepolymer benefit, amount of organic solvent can be added. The solvent can be acetone, methyl ethyl ketone, dioxane, N, N-dimethylformamide, N-methyl pyrrolidone and other water-soluble (hydrophilic) organic solvents and other hydrophobic solvent toluene. Taking into account the cost, operational and other factors,
The most commonly used acetone and methyl ethyl ketone. In general, in the preparation of a stable emulsion, can also be low by vacuum distillation, the boiling point solvent removed from the emulsion to reduce the smell of water-based polyurethane can be made solvent residue is small The smell almost no organic solvent. If the little amount of solvent can not be removed. Polyurethane dry, a small amount of residual volatile solvents with low boiling point to accelerate the film drying time, and the presence of a small amount of high boiling point solvent can make a smooth film, which more commonly used in the coatings industry.