The application steps of waterborne PU shoe adhesives are as follows:
A. glue adjustment
(1) The density of waterborne PU adhesives is about 1.1g.cm-3. When stored for a long time, precipitation stratification may occur. So shake well before use. According to the usage time of about 2 hours to determine the amount of mixing, in order to avoid waste.
(2) Clean mixing containers and agitators, weigh water-borne PU adhesives and curing agents correctly and place them in containers with a mass ratio of 100:5-6.
(3) Because of the different density, the curing agent will float on the surface after adding people, so the mixing blade should be placed at the bottom of the container at the initial stage of mixing, and then stirred at a low speed to avoid spillover and influence measurement. Then, on the premise of ensuring no spillover, high-speed stirring for more than 10 minutes. Closed reserve, in order to avoid moisture absorption or contamination, the mixing must be really uniform, conducive to the best bonding effect.
B. gluing
(1) The bonded material must be preheated and then glued after its surface is expressed at 40-50 C, which can increase the physical properties of the bonded surface and increase the drying speed. It can also be used to treat the material surface before gluing, which is beneficial to improve the wettability of water-borne PU glue and material, and improve the initial bonding effect.
(2) When gluing, the amount of treatment agent and water-borne glue should be increased at the upper textiles. Otherwise, glue can easily be absorbed by textiles and even lead to underglue.
(3) Choose suitable painting tools according to shoe type, such as paint brush, watercolor pen, etc. When gluing, it should be uniformly coated, non-integrable glue or too thin, to avoid poor drying and glue shortage. In addition, glue spills cause shoe upper contamination and should be immediately used for cleaning cloth.
(4) Solvent-based PU glue is usually used for repairing, which can be bonded after 10 minutes of natural drying, but not water-based PU glue, because local repairing is not easy to dry, which affects the overall bonding effect.
(5) The gluing tool will harden and turn out after a period of time, which makes it inconvenient to use. At this time, it can be washed by MEK soaking.
C. drying
(1) The best drying method of waterborne PU adhesives is to dry at low temperature for a long time, and then use activation lamp to make the temperature reach the optimum bonding temperature before bonding.
(2) The drying temperature is gradual from low to high. It should not be dried directly at high temperature at the beginning, nor should it be cooled and dried again because of insufficient drying. Otherwise, the crust on the surface of the adhesive layer will affect the internal moisture evaporation. It is better to install insulation cover and electric heat pipe on the conveyor belt.
(3) Whether the waterborne PU adhesives are dried or not after coating depends on whether the surface of the adhesives is completely transparent when it comes out of the oven.
D. bonding
(1) The stickiness of waterborne PU adhesives is generally maintained for 3 minutes after they leave the oven. Therefore, the best bonding effect can be obtained by completing the bonding in the shortest time. Otherwise, the temperature of the extended solid decreases at any time, which will affect the bonding effect.
(2) Experience shows that the optimum bonding temperature of waterborne PU adhesives is 48-54 C, which is lower than 45 C, and the viscosity of waterborne PU adhesives decreases obviously; when the bonding temperature is higher than 65 C, the unbonded adhesive layer may lose its viscosity. At the same time, after pressing, the edge line of glue coating is easy to be drawn, and the consistency between materials is not good, or because of the high tension at this place, the degumming and pseudo-bonding are formed.
(3) The last oven outlet should be equipped with thermal insulation cover, so as to avoid the temperature dropping too fast and affect the bonding fastness.
E. pressurization
(1) The length and pressure of pressure depend on the shape and material of shoes. For high tension shoes, the pressing time should be prolonged, generally pressing 1O-12S under 2.5-3MPa.
(2) When pressing, a three-in-one high-pressure press is used to complete one-time pressing. Because the shear force produced by repeated pressing will destroy the bonded surface.
F. finishing
(1) The solvent used in finishing should be avoided to infiltrate into the bonding surface so as to reduce the bonding strength.
(2) If there is a reprocessing process, it should be placed for 24 hours until the reaction of water-borne PU glue is completed, so as to avoid degumming caused by thermal activation.
