Shoemaking Technology: Introduction Of Adhesive Technology

1.1 glue:

The quality of the adhesive directly affects the bonding performance of the adhesive parts. The weight of each component must be accurately called (the error is not more than 2-5%).

The amount of adhesive preparation should be determined according to the amount of the coating, and it will be used up in the active period.

In the process of preparation, the special person should be responsible for the detailed batch number, weight, glue temperature and other process parameters.

It must be stirred evenly.

1.2A pre coating process: dilution can reduce the viscosity of adhesives and improve the adhesive property, but prolong the bonding cycle, prolong the curing time, even lead to inconvenient curing and affect the bonding quality. Filling with filler can increase the viscosity of glue and adhesive strength. If the temperature of the preparation is reduced, the method of water bath heating or drying and preheating can be used to make the mixing uniform, which can reduce the viscosity of the glue itself.

A brush method: the general brush is glued to the adhesive surface. The disadvantage is that it is difficult to control the thickness of the adhesive layer and uneven coating.

B scraping method: pour the glue on the adhesive surface and make glue with flat blade or glass rod. The thickness of the adhesive layer is controlled by experience.

Its coating quality is not stable enough, it can only be constructed on the plane adhesive surface.

C roll coating method: using rubber roller to glue the adhesive parts evenly to the glue solution, adjusting the gap or pressure of the rubber roller can control the thickness of the glue layer, the smoother the rubber roller, the more uniform and thinner the glue layer is.

D spraying (electrostatic spraying): in the high voltage electrostatic field, the charged glue drops from the discharge edge of the spray gun on the adhesive surface.

The viscosity of the glue is controlled at 15-40S; the adhesive has dielectric property and the volume resistance is 106-107.Cm. This method can ensure the thickness of the adhesive layer is uniform and the loss of glue liquid is small.

E melting method: hot melt adhesive heating, brush and so on.

2.1 curing methods the curing of adhesives through physical methods, such as solvent evaporation, emulsion condensation and melt cooling and chemical methods.

(1) hot melt adhesive: polymer melt can solidify through cooling after infiltrating the sticky surface.

(2) solution adhesive: with the volatilization of solvent and increasing concentration of solution, it gradually solidified to a certain degree of strength.

(3) emulsion adhesive: as the water in the emulsion gradually penetrates into the porous sticky substance and evaporates, the concentration of the emulsion increases continuously. Finally, due to the effect of surface tension, the polymer colloid particles coagulate.

When the ambient temperature is high, the emulsion is condensed into a continuous adhesive film, while the ambient temperature is low and the minimum film forming temperature (MFT) forms a white discontinuous film.

Emulsion adhesives are mainly copolymers of polyvinyl acetate and its copolymer and acrylate.

(4) polyfunctional monomers or prepolymers of thermosetting adhesives of thermosetting adhesives are polymerized. With the increase of molecular weight, molecular chain changes and crosslinks are formed at the same time, forming insoluble or melted gelation or basic curing.

It is not equivalent to prolonging curing time and raising curing temperature in a certain range. It is difficult to compensate the curing temperature by extending the time.

Because a certain chemical action is required between the adhesive and the surface of the adhesive, this requires high enough temperature to carry out.

It is good for the adhesive to fully infiltrate the surface; it helps remove the low molecular volatiles produced by the curing reaction of the adhesive; it is good for discharging residual solvent in the adhesive layer; it is good for controlling the thickness of the adhesive layer; the adhesive with high viscosity often has thick adhesive layer, and the thickness of the adhesive layer is controlled by adjusting the curing pressure.

After coating for a period of time, this is called pre cure.

The viscosity of the adhesive increases and the pressure is applied to ensure the uniformity of the adhesive layer thickness.

The curing temperature is too low, the crosslinking density of adhesive layer is too low, and the curing reaction is incomplete.

The curing temperature is too high, resulting in the loss of glue or the embrittlement of the adhesive layer, resulting in the decrease of adhesive strength.

Heating is conducive to the molecular diffusion between adhesive and adhesive parts, and is conducive to the formation of chemical bonds.

(1) oven direct heating method: use the blower to make it uniform heat pfer.

(2) external heating method: the heat is quickly pmitted to the inner layer of the adhesive layer, thus greatly reducing the curing time.

Sonic heating method: it is heat cured for viscoelastic adhesives and solventless glue, and is not suitable for thermosetting rigid adhesives.