Water-based polyurethane adhesives for shoes Progr
20 century, accompanied by the proliferation of a variety of machinery, shoe-making industry from hand manufacturing to a high degree of mechanization, assembly-line direction of rapid development. Create changes in the way of the natural products of traditional adhesives can not meet the production needs. Synthetic adhesives become the main types of shoe adhesives.
in the new production conditions, shoe adhesives should have the following properties:
(1) of the different crystalline yoga materials should have a high adhesive strength, in particular, require a high peel strength;
(2 ) bonding the beginning of a high viscosity to meet the needs of the production line;
(3) sizing technique is simple and easy to operate, be used for adjustable;
(4) adequate heat resistance, water resistance good bonding and lasting.
20 century, 30’s, an ordinary neoprene adhesive, represented the first generation of shoe adhesives, basically meeting the needs of the shoe-making production requirements at that time, for footwear made a great contribution to industrialization. With the PVC artificial leather, PU synthetic leather in the shoe industry in the large-scale use, as ordinary neoprene adhesive adhesive composite equipment materials for these poor results to methyl methacrylate (MMA) grafted neoprene adhesives and solvent-based polyurethane adhesive to represent the second generation of shoe adhesives, and have pairs of synthetic materials because of their excellent performance bonding as adhesives used in shoe-making industry, the main species. Occupy more than a long-term system of three types of adhesives used in shoe adhesives most of the market, and that three types of adhesives used in benzene solvent enormous global environment pollution, the toxicity caused by a large number of shoe workers in multiple diseases, the problem with the environmental awareness and the strengthening of security awareness has become increasingly attracted attention. Because of environmental regulations on the use of the provisions of benzene increasingly stringent, third-generation non-solvent benzene homologue ordinary neoprene, neoprene and polyurethane adhesive graft adhesive replacement to traditional products, although the third-generation shoe adhesive resolved benzene pollution and poisoning problems, they can not fundamentally resolve the adhesive caused by the use of organic solvents, volatile organic compounds (VOC). Beginning of the 20th century, 90’s, Europe and the United States set strict standards for volatile organic compounds to facilitate the complete fourth-generation environment-friendly adhesive for shoes there, mainly non-solvent-based and water-based adhesive.
In China, the footwear industry in the late 20th century has become an important export-processing industries, high-end products are mainly used for export of these products are currently used as part of the total environment-friendly adhesives, and most of the third generation of product benzene solvent adhesive. Therefore, the fourth-generation shoe adhesives in China’s vast development space. This paper introduces the water-based polyurethane adhesives in the shoe industry in the application and future prospects.
1., water-based polyurethane adhesive
1.1 Overview of water-based polyurethane adhesive
polyurethane water-based polyurethane adhesive is soluble in water or dispersed in water to form the adhesive. Polyurethane compounds according to the different particle size dispersed in water, water-based polyurethane can be divided into three categories, polyurethane solution (particle size 0001μm, appearance and transparent), polyurethane dispersions (particle size 0001 ~ 01μm, translucent appearance), polyurethane emulsion ( particle size 01μm, appearance of turbidity). Practical applications, mainly for water-based polyurethane polyurethane emulsion, dispersion.
with both water-based polyurethane adhesive hardness adjustable resistance, and good low temperature toughness, the characteristics of solvent-based polyurethane, but also has flame-retardant, odor small, do not pollute the environment, the advantages of easy operation, its environmental performance, has become a Polyurethane Adhesive future development directions. Waterborne Polyurethane research work began in the 20th century, 50’s, 70 years to achieve commercial production. At present, the United States and Europe in order to comply with near-stringent environmental laws, water-based polyurethane production and use are increasing. In China, the expansion of international trade cooperation with the water-based polyurethane adhesive is bound to occupy a significant market share for its own development to provide adequate conditions.
1.2 the characteristics of water-based polyurethane adhesive
(1) most of the water-based polyurethane adhesive does not contain NCO groups, which rely mainly on intramolecular polar groups generated cohesion and adhesion to curing;
( 2) In addition to the polymer thickener plus, the impact of water-based polyurethane adhesives are an important factor in the viscosity of ionic charge, core-shell structure latex particle size, etc.;
(3) the viscosity of water-based polyurethane adhesives in general by water-soluble thickener and water to adjust;
(4) water-based polyurethane adhesives dry slowly, wetting of the substrate surface hydrophobicity poor;
(5) water-based polyurethane adhesive can be mixed with a variety of water-based resins to improve the performance of or reduce costs;
(6) water-based polyurethane adhesives smell is small, easy to operate, easy to clean up adhesive residue.
1.3 Classification of water-based polyurethane adhesive
(1) single-component thermal plastic, curing in the form of film-forming water evaporation;
(2) two-component thermosetting type, curing by adding cross-linking agent , heat cured to achieve pouch desired intensity;
(3) one-component heat-type, containing the latent cross-linker, cross-linked resins when heated so that played a role in adhesion.
2,. waterborne polyurethane classification and the preparation of waterborne polyurethane
2.1 Classification of
waterborne polyurethane is water-based polyurethane adhesives, coatings and other applications forms the basis, according to the nature of the hydrophilic groups can be divided into: ” br> (1) anionic water-based polyurethane, in order to contain carboxyl chain extender or chain extender containing sulfonate ion or the introduction of carboxylic acid ion;
(2) Cationic Water-based polyurethane, generally refers to the main chain or side chain of water-based polyurethane containing ammonium ion;
(3) non-ionic water-based polyurethane, that is, the molecule does not contain ionic groups of the waterborne polyurethane;
(4) mixed type, polyurethane resin, both the molecular structure of ionic and non-ionic hydrophilic group or chain segment.
2.2 Preparation of waterborne polyurethane
Preparation of waterborne polyurethane using the general synthetic resin emulsion is different from the special method. Low-polymer-diol (or polyol), and two pre-isocyanate reaction, made of a certain molecular weight or high molecular weight prepolymer polyurethane resin, can be used after the phase transfer method of dissolved or emulsified in water. Polyurethanes are generally hydrophobic in nature, preparation of water-based polyurethane can be used outside the emulsion method and self-emulsification. Outside the emulsion method is the presence of the emulsifier, the polyurethane prepolymer or polyurethane emulsion in water, organic solvents mandatory. Self-emulsifying process of law is introduced in the preparation of hydrophilic polyurethane composition, without added emulsifiers. Preparation of waterborne polyurethane
the first steps for preparation of polyurethane or prepolymer. Commonly used method is the pre-polymer dispersion method, this method prepared for the terminal NCO prepolymer-based polyurethane, the molecular weight of this prepolymer is not, you can direct emulsification under shear stress. Of water involved in the pre-polymer reaction, the equivalent of chain extender to prepolymer to chain growth, forming high molecular weight polyurethane. In order to improve the performance of latex, but also on the part of the NCO groups to be closed, made of polyurethane emulsion closed, when the heat treatment after film-forming emulsion, NCO re-opened, and polyurethane and the substrate on the reaction of active hydrogen to produce cross-linked.
3, water-based polyurethane adhesive in the shoe industry the application of polyurethane adhesive for shoes
excellent low temperature properties, low curing temperature, good flexibility, for many materials infiltration and adhesion is good. Commonly used in the request at room temperature, fast curing and bonding with the softness occasions, especially suitable for bonding with a different coefficient of expansion of dissimilar materials. Main varieties of solvent type and water-based two broad categories.
3.1 Water-based polyurethane adhesive for shoe application
waterborne polyurethane adhesives in the shoe-making process was originally used primarily to meet the requirements of laws and regulations. One-component waterborne polyurethane thermal plastic adhesive curing, mainly after the water evaporation emulsion film, relying on film and the substrate to achieve between the bonding effect of physical adsorption. Because they do not use organic solvents, shoe production process and the final product are in line with environmental and safety requirements. With the traditional solvent-based polyurethane adhesive compared to its disadvantages are also obvious. Slow evaporation of water, which increases the production process in the energy, shoe-making raw yoga materials are mostly hydrophobic film is not prone to continuous, so that the bonding part of the water resistance is poor, often in the form of physical adsorption to the bonding strength can not make the satisfactory.
order to improve the bonding strength, to meet production needs. Two-component thermosetting adhesive started large-scale use. This adhesive, when used, by adding cross-linker,pvc mat, the formation of NCO groups with the substrate active hydrogen chemical cross-linking, so that bonding strength increased significantly. This cross-linking agent used in adhesives are mainly applicable to water-based system, esters isocyanate cross-linking agent, add the amount of general-based agent (water-based polyurethane) and about 10% of adding cross-linking agent, the adhesive must be mixed evenly. Equipped with a good adhesive for a period of application of restrictions, must be present with the current use, and quickly run out. Europe and the United States is currently using this type of shoe-making enterprises are mainly polyurethane adhesive.
3.2 Water-based polyurethane adhesive for shoes, the latest progress of
20 end of the century, researchers began a reactive one-component waterborne polyurethane research, such as water-based polyurethane adhesive can be used in the footwear industry. The main reaction mechanism of such adhesive is as follows: 35 ~ 95 ℃, the isocyanate-terminated polyurethane prepolymer (A) dispersed in waterborne polyurethane dispersion (B), the reaction is no different after the dispersion of residual isocyanate. Under normal circumstances, the pre-polymer (A) dispersed in water, they are unable to form a stable dispersion. In this study, the aqueous polyester dispersion (B) can make pre-polymer (A) dispersion stability. It is inferred that the pre-polymer (A) part of the isocyanate group and water-based polyurethane dispersion (B) functional groups such as hydroxyl reaction to form a gel-based or polyurethane (A) / polyurethane (B) graft polymer. The pre-polymer (A), another part of the isocyanate groups reacting with water to form amino compounds, such amino compound immediately prepolymer isocyanate reaction, through its own chain extender to form interpenetrating networks, and nuclear [PU (B)] — Shell [polyurethane (c)] structures. Therefore, the final dispersion included graft polymers, interpenetrating networks, core-shell structure.
in this type of adhesive, the peel strength can reach as high 559kN / m, heat-resistant temperature of 125 ℃, but as an important indicator of shoe adhesives, tack strength can reach 0964kN / m. Such adhesives are still in the research stage, with the synthetic method of continuous improvement, with its excellent performance and simplicity of the process performance, polyurethane adhesive for shoes will become the dominant species.
4, the conclusions
countries around pouch world have laid down strict environmental regulations, people’s lives and health and product safety and increasing awareness of organic solvent-based adhesives will withdraw from the field of shoe production, and in the environment-friendly adhesives, water-based Polyurethane adhesives and hot melt adhesives for the footwear adhesive bonding become the world’s manufacturers to work together. Water-based polyurethane adhesives
shoe Research progress
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