An important link in the production of corrugated board

The preparation and control of adhesive is one of the important links in the production of corrugated board, and it is very important for how to obtain the best adhesive strength, production efficiency and economic benefits. The author's statistics on the cardboard waste products of the unit show that about 80% of the waste products are directly or indirectly related to the bonding failure. This article tries to start with the bonding theory and discuss the parameters that affect bonding in order to achieve the best bonding effect.

There are many formulas for starch adhesives, but there are four basic components: starch, water, sodium hydroxide (NAOH), and borax, which are mostly prepared by the double-groove method. The functions of each component are as follows:

starch

Laked starch is a dilute starch dispersion that acts as a carrier, suspends and transports particles, controls the penetration of moisture and adhesives into the paper sheet, and contributes to the formation of wet bond strength. The dosage is about 17% of the total starch.

Raw starch is an insoluble granule with a diameter of 10-25 μm. When heated to a certain gel temperature, it absorbs water and expands to gel.

water

It forms a flowing liquid and acts as a dispersant for starch solutions, providing moisture to the gel.

Borax

1. Interact with carrier starch, help to retain moisture in the agent, and help uniform gelation of powder-dissolving particles;
2. Increase stickiness, improve adhesive viscosity stability;
3. Play a buffering role when adding NaOH to avoid destroying starch;
4. It forms a network complex polymer with starch gel and generates high viscosity, which contributes to the formation of binding force. The dosage is about 1.2-1.8% of the starch dosage. Do not add too much, otherwise it will increase the cohesive strength and make the adhesive become like rubber.

Alkali (NaOH)

1. It is a strong base, which combines with the hydroxyl group of starch in the solution to destroy the hydrogen chain, reduce the gelatinization temperature of starch, and maintain it between 63-66 ℃;
2. Helps the adhesive to wet the wet paper surface, so that the adhesive has good contact with the paper and penetrates into the paper sheet. If the gelation temperature is too high, it will inevitably consume more heat to make it gelatinize; if it is too low, it will be partially gelled before use, affecting the work and bonding quality of the gluing system.

Urea Hydrogen Peroxide

Hydrogen peroxide acts as a bleaching agent, oxidizing modifier and increases fluidity. Urea enhances the plasticity of the adhesive and achieves a certain waterproof effect.

Thermosetting resin

It can be cured into granular structural material in the adhesive at high temperature, which greatly improves the physical strength of the cardboard, and provides the possibility of low weight and high strength of corrugated cardboard.

Before discussing the failure of bonding, it must be pointed out that the bonding process of the adhesive in different sections is not the same, so the control of bonding in different sections is different.

On a single-sided machine, the adhesive on the top of the corrugated paper is combined with the tissue under high pressure, and penetration occurs at the same time, and its thickness generally does not exceed 1/4 of the thickness of the paper. After the paperboard comes out of the two corrugated roller press area, the starch may not be completely gelatinized, and the gelatinization process is completed by the residual heat of the cardboard conveying bridge. On the double-sided machine, on the one hand, the preheater cannot preheat the panel excessively, otherwise the starch will gel prematurely;
On the other hand, the curing of the adhesive adopts the heating method, the temperature of the hot plate (drying part) is usually around 180 °, and the temperature is controlled by the movement of the canvas pressed on the freely rotating support roller (for floating type The veneer device of the hot plate technology controls the temperature through the number of high-speed hot plates). On the single-sided machine, the corrugated forming adopts high-pressure heating method; on the veneer machine, in order to protect the corrugated from being damaged, high pressure cannot be applied.

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