If you want the cardboard to have high adhesive strength, please remember the key data of the adhesive formula

The quality of adhesive is a key factor affecting the bonding strength of corrugated cardboard. The selection and use of adhesives by packaging enterprises have become rational and mature, with a trend towards diversification, environmental protection, and low prices. At present, the main adhesives used are various forms of starch adhesives. Starch adhesives made from wheat, corn, or potatoes have the advantages of a wide range of raw materials, easy processing, good bonding strength, moisture resistance, and no secondary pollution. In addition, there are polyvinyl alcohol (PVA) and polyvinyl acetate lotion (PVAC lotion).

1. Corn starch can be used to prepare many adhesives with different quality characteristics due to different formulations

Under normal circumstances, adhesive with high adhesion and good permeability produces cardboard with high adhesion strength, while the opposite is true. The cardboard produced with hot glue has better adhesion strength than cold glue, and it is more pronounced in winter. To ensure the adhesive strength of the cardboard, it is necessary to use good raw and auxiliary materials, adjust the adhesive ratio according to the actual production situation, control the mixing time, mix the adhesive evenly, and use good water quality as much as possible.

To reduce costs, starch adhesives should be used as much as possible instead of synthetic resin adhesives. Corn starch, for example, can be used to prepare adhesives with different quality characteristics due to different formulations. This type of adhesive is made from substances such as water, starch, sodium hydroxide, and a small amount of borax through chemical reactions. The proportions prepared by various cardboard box manufacturers are not the same. Usually, in a water to powder ratio of 1:5, sodium hypochlorite, corn starch, sodium hydroxide, and borax are gradually added in an orderly manner according to the origin and quality of the starch (chemicals must be dissolved and diluted to the required concentration). After uniform stirring and several adjustments, the ideal adhesive can be prepared.

2. The preparation procedure and method have a direct impact on the quality of the adhesive, and some components even have a significant impact.

The protein content of starch does not exceed 0.5%, and excessive protein content is prone to coagulation and clumping, reducing viscosity.

The amount of borax used accounts for about 0.5% of the total amount, and excessive or insufficient amounts can lead to a decrease in adhesive strength.

Sodium hydroxide acts as a gelatinizing agent to decompose insoluble starch molecules and form a uniform, transparent, and sticky starch paste with water. However, the amount of sodium hydroxide must be strictly controlled. Excessive use and strong alkalinity can damage the paper fibers, and when the relative temperature in the air is high, it can cause the cardboard box to absorb moisture, turn yellow, and degumm; Insufficient dosage can cause prolonged starch oxidation time, uneven starch paste, and decreased viscosity. The pH value of the prepared adhesive should be between 7.5 and 8.5.

The concentration of sodium hydroxide (dissolved and diluted to 10%) also has a significant impact on the quality of the adhesive. If the concentration is too high, the reaction during gelatinization is strong, causing the gluing machine to shake the glue, resulting in the appearance of floral glue on the corrugated peak of the lamination, which causes the cardboard to open and the adhesive strength to decrease.

3. The control of adhesives mainly includes three aspects: viscosity, gelatinization temperature, and solid content.

If the viscosity is too high, the flowability will be poor, the glue consumption will increase, and the core paper will absorb too much water, making the cardboard soft; When it is too small, it can also cause excessive water absorption and easily lead to loss of adhesion, resulting in poor adhesion.

The temperature at which starch adhesive begins to thicken and exhibits adhesive properties due to the gradual gelatinization of raw starch in the adhesive material, known as gelatinization temperature.

The gelatinization temperature varies for different qualities of starch, and should be adjusted according to actual production. This is mainly achieved by changing the time of sodium hydroxide. Increasing the gelatinization temperature can appropriately reduce the amount of sodium hydroxide used, and vice versa.

The general gelatinization temperature in summer is 57-59 ℃, and in winter, it is necessary to lower the gelatinization temperature to reduce the heat generated by the adhesive gelatinization, which is conducive to bonding. Generally, it is 55-57 ℃. The solid content also has a significant impact on bonding ability, viscosity, and curing time.