Adhesive strength, including heat resistance, low temperature resistance, aging resistance and other curing conditions, including temperature and pressure retention time during bonding, and other process properties, including coating fluidity, effective storage period, and other properties, including rust and fire resistance.
Explanation of common performance terms of adhesives
1. Adhesive
According to the description of the American Standard Test Method (ASTM): the substance that can use its adhesion to the surface of various materials to make the same or different materials together is called an adhesive.
2. Performance and requirements of adhesive for shoemaking
A. Appearance
(1) Including the color, color and luster of the adhesive, and whether there is precipitation or delamination;
(2) In general, the lighter the color of the adhesive, the more transparent the more popular; if the color is too dark, it will cause pollution to the light-colored materials and affect the beauty of the shoes;
(3) After the film is dried, the color will gradually become darker with time. If the stability of the adhesive is not good, the speed of color darkening will be faster;
(4) Generally, the color of universal glue is darker than that of grafting glue, and the color of grafting glue is darker than that of PU glue.
B. Viscosity
Generally, the viscosity refers to the resistance generated when the liquid flows, that is, the resistance generated during painting, and the number expressed in a unit is the viscosity; the unit is CPS / 25 ℃ or mpa? S / 25 ℃
(1) High viscosity and poor fluidity; low viscosity and good fluidity;
(2) There is no absolute relationship between viscosity and solid content. For adhesives with high solid content, the viscosity is not necessarily high;
(3) Viscosity has no absolute relationship with what is called "brushability" in general operation. A high viscosity does not mean that the brushability is necessarily poor; the brushability and the volatilization rate of the solvent and the glue of the brush Quantity has a close relationship;
(4) It is best to use different brushing tools for adhesives with different viscosities. For example, adhesives with lower viscosity should use softer brushes with stronger adhesive strength;
(5) When choosing an adhesive, viscosity is an important consideration. For porous materials, if the viscosity of the adhesive used is too low, most of the adhesive will penetrate under the surface of the adhesive. At this time, the phenomenon of under-adhesive will occur. If the viscosity of the adhesive is too high, the penetration is not good, and the drying speed is slow. If the drying time is not enough, it will often affect the bonding effect.
C. Solid content
It is the percentage of solute (non-volatile matter) contained in the unit weight of the adhesive;
Solid content = solute / (solute + solvent) × 100%
(1) The solid content of the adhesive affects its brushability, tack time, adhesion, etc .;
(2) Porous materials should use adhesives with higher solid content, and non-porous materials should use adhesives with lower solid content.
D. operability
In addition to the good adhesive effect, the adhesive must have good operability, which can not only increase the speed of gluing, but also maintain the stability of the adhesive effect and the appearance of the finished product. Adhesives with good operability must meet the following conditions:
(1), easy to apply-increase the glue speed, and the thickness of the glue film is uniform.
(2) Easy to stir-after adding hardener, it is easy to stir evenly.
(3), no brushing-there can be no brushing after the brush is dipped in glue or brushing, so as to avoid the glue sticking to the shoe upper and affecting the appearance of the shoe.
(4) No glue dripping-After the brush is glued, if there is glue dripping, it will also contaminate the shoes and reduce the glue content of the brush.
E. Sticky time:
The adhesive is applied to the surface of the adherend. After the solvent in the adhesive evaporates, a solvent-free adhesive film is formed. This adhesive film remains sticky. At this time, the time when the bonding is well adhered is called the "stickiness maintenance time" "If no bonding is allowed within this time, if bonding is performed after this time, even if sufficient pressure is applied, a satisfactory bonding effect cannot be obtained.
(1) After the adhesive is dried, the laminating and pressing must be completed within the "viscosity maintenance time";
(2) The crystallization speed of the adhesive is related to the viscosity maintenance time. The faster the crystallization speed, the shorter the viscosity maintenance time;
(3) The viscosity maintenance time is related to the thickness of the film, the solid content, and the number of times of gluing;
(4) Generally, the stickiness of universal glue is the longest, the grafting glue is the second, and the PU glue is the shortest.
F. Available time
Before using the adhesive, an appropriate hardener must be added. After the hardener is added, the viscosity first decreases slightly, and then gradually increases until it cannot be applied. This period is the usable time. Generally, the viscosity is increased to the original viscosity. The elapsed time twice is the "usable time"
(1), the usable time is related to the type of adhesive, the type of hardener, the amount of hardener added, temperature and humidity;
(2). The adhesive can be used for a long time, the "dead glue" speed is slow, reducing waste, but if it can be used for too long, the hardening speed is slow, which affects the initial bonding strength;
(3) In general use, due to the different production speeds, the required usable time is also different. The principle of not using it hurriedly should be used. Generally speaking, it is sufficient for more than two hours.
G. Dry
After the adhesive is coated with the adherend, it must be dried until most of the solvent volatilizes before it can produce an excellent adhesion effect. If the adhesive film still contains a large amount of solvent and has not been dried before bonding, not only the initial strength is poor, the remaining Solvents can affect crystal hardening, resulting in poorer post-force.
(1) The drying speed of the adhesive is related to the type of solvent, solid content, and thickness of the coating film;
(2) When applying adhesive, the thickness of the film must be uniform to make the film dry evenly;
(3) The drying temperature should be appropriate.
If the temperature is too high, the drying time can be shortened, but the crystallization of the adhesive will be excessively damaged. The cooling time before bonding must be extended or the initial force will be poor. In addition, it may also cause the plasticizer in the PVC and TPR to move out. If the temperature is too low, if the temperature is too low, the adhesive (especially PU adhesive) will not be thermally activated, and there will be no proper Tack (initial adhesion), and it will not bond.
(4), the temperature in the air should be properly controlled, and maintain good ventilation, otherwise, if the temperature is too high, the water vapor will adhere to the film, causing white fog phenomenon, affecting the adhesion effect;
(5) In the dry box, no matter what kind of heat source is used, it should strive for uniform temperature and proper circulation of heat flow in the box. The heating and temperature control system in the box should be regularly checked, and the box should be measured with a thermometer. The actual temperature inside, and use the surface thermometer to measure the surface temperature of the shoe material.
H. Initial force
The two kinds of adherends to which the adhesive is applied are dried, and the adhesion force immediately after pressing is applied, which is the initial force.
(1) The initial force of the adhesive has an important relationship with the crystallization speed. The faster the crystallization speed, the better the initial force;
(2). Adhesive with strong initial strength, good operability, the next process can be carried out in a short time after laminating and pressing, such as lasting, edging, etc .;
(3) Generally, the initial strength of PU glue is the strongest, followed by grafting glue, and all-round glue is second;
(4) Generally, the type of hardener and its added amount can be adjusted to adjust the initial force of the adhesive.
I. Late power
After the two kinds of adherends are adhered with the adhesive, the adhesive force obtained after being placed for a period of time is called the post-force, which is generally based on one day, and one week or January is the standard: strong post-term force means that the adhesive effect of the adhesive can be Maintain long-term, and have good weather resistance, oil resistance and water resistance, etc. For ordinary plastic shoes, the adhesive life of the adhesive is often the service life of the shoes.
J. Heat resistance
It is the ability of the adhesive to remain intact and resist softening after being bonded and dried in a certain high temperature zone: after the adhered material is adhered, due to the qualitative heating, the packaged transportation or its finished product is used at a high temperature. If the adhesive is not good For heat resistance, the phenomenon of degumming often occurs, especially for materials with high tension, they will naturally peel off when exposed to heat.
(1) The heat resistance of the adhesive is related to the type of adhesive, the type of hardener, the amount of hardener added, etc .;
(2) After the shoe manufacturing is completed, it is best to do the heat resistance test before shipment. Otherwise, after being loaded into the container, the high temperature for a long time may affect the destination.
K. The ability of yellowing resistant adhesives and their films to resist aging and maintain the original color under the influence of sunlight, air, temperature and other factors.
L. Oil and water resistance
After the adhesive is dried, it can resist the intrusion of oil and water and maintain the good adhesion effect.
M. Stability
After the adhesive is manufactured, after a long period of storage, it may change in appearance, viscosity, adhesion, etc. The three properties of the adhesive with good stability will remain unchanged for a certain period of time, or the change will be very slight. The adhesive should be placed in A cool, dry, well-ventilated place.
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