Adhesive (Cooked Glue) Formula And Production Process

Pasteurizer

Industrial caustic soda (NaOH) is available in the form of crystals, rods, flakes and 30% NaOH aqueous solution. As long as the purity is qualified, any state of caustic soda can be used. The amount of caustic soda is added to the oxidized starch and stirred for 20 minutes until the starch solution becomes translucent paste. If the amount of caustic soda is too large, the glue solution will have high fluidity, good transparency and long storage time, but the alkali content in the corrugated paper gluing will also increase, and the corrugated paper box will easily turn yellow, causing the ink on the surface of the corrugated paper box to change color; if the amount of caustic soda is small, after 20 minutes of addition, it will always be white or milky white paste, not transparent and not sticky. A part of caustic soda solution should be added as appropriate to make it a translucent glue solution. If the amount of caustic soda is small, the adhesive will not gelatinize well, the adhesion is poor, and it is easy to thicken. From actual observation, the amount of caustic soda used is generally about 12% of starch, which is more appropriate.

Oxidants

Among starch adhesives, commonly used oxidants include hydrogen peroxide, sodium hypochlorite, potassium permanganate, etc. Potassium permanganate is used as an oxidant, and the dosage is easy to control. The quality of the finished starch adhesive is also stable, but the color of the starch adhesive is dark coffee or brown-black. The starch adhesive made by sodium hypochlorite and hydrogen peroxide as oxidants is light yellow in color, but the quality of starch adhesive made by sodium hypochlorite is unstable during use, and chlorine is decomposed, which makes the operator feel eye discomfort; starch adhesive made by hydrogen peroxide often produces a lot of foam during use, and defoaming agents need to be added. In addition, sodium hypochlorite is easy to decompose under sunlight or high temperature, reducing its hypochlorite content. In application, its exact content should be kept under control at all times and the dosage should be increased appropriately. From the analysis of use, the use of hydrogen peroxide as an oxidant is stable in quality, small in dosage, low in cost, and fast in reaction, making it an ideal material for use as an oxidant.

When making cold-made high-strength quick-drying starch adhesive, oxidation reaction plays a key role. If oxidation is appropriate (the viscosity is 60-80 seconds after adding caustic soda for 20-40 minutes), the starch solubility is improved, the film-forming ability is good, and the bonding force is strong; if oxidation is insufficient, the macromolecules are less degraded, and its properties are the same as those of starch. After adding caustic soda, it does not become thin for a long time, and even cannot be stirred (adding caustic soda for more than 40 minutes, the viscosity is higher than 100 seconds). In this case, an oxidant needs to be added for secondary oxidation. If oxidation is excessive, the starch ring structure opens, the viscosity is too low, and even loses its bonding ability (the viscosity is lower than 40 seconds after adding caustic soda for 20 minutes). Therefore, special attention should be paid to the use of oxidant content and ratio.

Temperature also plays a certain role in the oxidation process. The higher the temperature, the faster the oxidation. In summer, the oxidation reaction generally takes 10-15 minutes, in spring and autumn, it takes 15-20 minutes, and in winter, it takes about 30 minutes. The oxidation reaction time is extended, the oxidation is complete, and the product quality is stable, but too long a time will affect the production cycle.

The specific amount of oxidant changes with the starch. The amount of starch is small, and the amount of oxidant is also small. The amount of sodium hypochlorite (10%) is about 28% of starch, the content of hydrogen peroxide (27.5%) is about 4% of starch, and the amount of potassium permanganate is about 2% of starch. The method to judge whether the oxidation is appropriate is to add caustic soda and stir for 20-40 minutes, and measure the viscosity of about 60 seconds (in summer). In this way, the finished product is stored for about 2 hours, and the viscosity is about 50 seconds, and it stabilizes at 40±10 seconds after one day. In addition, the temperature is low in winter, and the amount of oxidant should be appropriately increased. The temperature is high in summer, the reaction is fast, and the amount should be appropriately reduced.

Strong-setting catalyst (desiccant)

The main factor that distinguishes the cold-made high-strength and fast-drying series of starch adhesives from other adhesives is the use of "strong-setting catalysts". Strong-setting catalysts are formed by the polymerization reaction of several salts and organic and inorganic compounds. In the production process of adhesives, as long as the time and amount are appropriate, they not only accelerate the reaction speed, but also react chemically with the oxygen in the air through the polymer after sizing, and quickly flocculate and crystallize, which accelerates the adhesive film formation speed, shortens the carton drying time, and improves the strength of the cardboard. Therefore, the bonding speed (initial bonding, full bonding, and fiber destruction) of this adhesive is several times higher than that of similar starch glues. In addition, the cardboard has high hardness and good stiffness. The amount of strong-setting catalyst used in the adhesive is less than 5kg per ton of water, which will not play its due role. If the amount of water used per ton is higher than 15kg, the adhesive film formation is too fast, and the cardboard is prone to degumming. Therefore, the proportion of the addition should be strictly controlled. The normal dosage standard is 6-12kg/ton of water.