Stick feet with glue

environment

Conditions of use Glue and sealant water should be used in a certain environment, and working conditions have an important influence on bonding performance. In terms of use conditions, there are stress conditions, environmental temperature and humidity, chemical medium conditions, outdoor conditions and so on.

(1) pressure situation. When the adherend is subjected to peeling force and uneven tearing force, an adhesive with good toughness, such as rubber glue and polyurethane adhesive, can be selected; When bearing uniform tearing force and shearing force, you can choose adhesives with higher hardness and strength, such as epoxy adhesive and acrylate adhesive.

(2) Temperature situation. Different glues have different heat resistance. Choose different glues according to different temperatures.

(3) Humidity. Moisture and moisture are unfavorable to the stability of bonding interface, which can be said to be harmful. Due to the small size and high polarity of water molecules, the bonding strength and durability are reduced due to hydrolysis after infiltration and diffusion, which destroys the bonding surface or detaches itself. If the adherend requires good water resistance, choose epoxy adhesive, polyurethane adhesive, etc.

(4) chemical medium. Chemical medium mainly refers to acid, alkali, salt, solvent, etc. Different types of glue and curing conditions have different medium resistance. Therefore, glue and sealant should be selected according to the medium contacted by the adherend.

(5) Outdoor conditions. The conditions of outdoor bonding connectors are complex, and the changes of air temperature, wind and rain, sun exposure and freezing will accelerate the aging of the bonding layer and shorten its life. Therefore, under outdoor conditions, adhesives with high temperature curing and good atmospheric aging resistance should be selected for bonding, such as phenolic acetal adhesive and epoxy nitrile rubber. Silicone sealants is selected as the seal.

Two-component polyurethane adhesive

The good compounding effect of two-component polyurethane adhesive is related to many conditions, among which the change of working environment is also a very important factor. That is to say, with the change of seasonal climate, it is necessary to make some minor adjustments to the gluing process in order to obtain the ideal composite effect.

Simply put, the seasonal climate change that affects the combination is the change of environmental humidity and temperature: specifically, in spring and summer, especially in the rainy season, the relative humidity of the air is relatively high, even reaching saturation, while in autumn and winter, the air is dry and the humidity is relatively low; As far as temperature is concerned, summer is much higher than winter, and the maximum difference between them is nearly 30 ~ 40℃ (here, take the southern region without indoor heating as an example for comparison).

If we don't pay attention to these differences, the following problems are likely to occur when compounding: when the air is humid, the glue is often not cured completely, that is, it is not dry enough, and the residual viscosity is large, and even the wire drawing phenomenon can be observed when peeling off the composite film, especially when the film itself is highly hygroscopic, such as when compounding with nylon film; Secondly, humid air will condense on the glue roller, thus bringing moisture into the glue basin. With the passage of time, the glue gradually changed from transparent to chaotic and white, and even lost its bonding effect. Damp heat and high temperature also make it difficult to preserve glue. If the prepared working glue is not used up in the same day, it will often turn white and agglomerate after being left overnight, forming a gel (jelly-like). On the contrary, when it is cold in winter, the working glue that has not been used up before remains transparent and flowing overnight, and can be used directly on the computer without being mixed into the newly prepared working glue in batches.

On the other hand, when the temperature is low in winter, the glue will become sticky and the leveling will decrease. When the laminating machine is running at high speed, a large number of bubbles are easy to accumulate on the rubber surface and the edge of the top roller in the rubber basin, which leads to the transfer of bubbles and insufficient glue application, which affects the bonding fastness; At the same time, due to poor leveling and dispersion, the appearance effect of the composite film will also become worse. For example, the flow pattern of glue is obvious, and sometimes it is orange peel-like. When used for composite aluminum foil or aluminized film, if there is a large area of Bai Mo or light-colored ink on the printing surface, it is easier to form small white spots and spots; In addition, due to the low temperature in winter, the temperature of the curing room is quite different from the external environment. If the thermal insulation measures are not in place, the heat loss rate is much faster than that in hot summer, which often makes the indoor temperature of curing room not reach the set temperature (generally 50℃). Therefore, the curing effect is also affected. Under the same curing time, the composite fastness may be lower than that in summer.

To analyze the causes of the above phenomenon, it is necessary to understand the influence of moisture and temperature on the adhesive. First of all, for two-component polyurethane adhesives, water can react with NCO groups in the curing agent, just like the main agent, namely polyester/polyether polyol. It is estimated that 1g water can consume 26 ~ 32g curing agent. Of course, this is in terms of pure reaction weight ratio. In practice, the water mixed in the working glue competes with the main agent when it reacts with the curing agent. However, no matter how much water is added in the reaction, it will undoubtedly consume the curing agent, so that the reaction amount with the main agent can not reach the original set working ratio, resulting in incomplete curing and residual viscosity.

The viscosity and reactivity of adhesive are closely related to temperature. The viscosity value given by the adhesive manufacturer is measured with a rotary viscometer at the standard temperature of 25℃, that is to say, the temperature of the working environment is 10 degrees higher than that in summer, and it may be 20 degrees lower than that in winter in cold weather. The viscosity of glue is just the opposite of temperature, that is, the same glue shows low viscosity at high temperature, good fluidity and dispersibility, high viscosity at low temperature and poor leveling. In addition, the cross-linking and curing reaction between the two components of the adhesive is slow at low temperature and fast at high temperature, which is precisely the reason for having a curing chamber (accelerating the curing reaction and improving production efficiency).

In view of this situation, when using two-component polyurethane adhesive for compounding, the following adjustments can be made according to environmental changes: if the air is humid and the temperature is high, the dosage of curing agent should be appropriately increased 10% ~ 20% to make up for water consumption; Often use dry cotton yarn or cloth scraps to suck the condensed water droplets on the laminator to prevent them from falling into the rubber basin; The inexhaustible working glue can be diluted by adding a small amount of solvent, and then sealed and stored. If possible, it can be stored in a small freezer, and the effect is better. When it is used again, it should be thawed in a sealed state and mixed with the newly prepared working glue. When the temperature is low in winter, more solvents can be added to the working rubber solution to reduce the viscosity of the system, improve the leveling dispersion and reduce the generation of bubbles in the rubber basin when working.

However, the concentration of working glue will decrease. If the working concentration is unchanged, a small amount of acetone can be used to replace part of ethyl acetate, that is, the mixed solvent of acetone and ethyl acetate can be used as diluent, and the ratio of the two can be 2: 8 or 3: 7. In addition, when the temperature is low in winter, the temperature of the curing room can be slightly raised to ensure that the actual temperature can meet the requirements, so as not to affect the curing effect.