Adhesive market analysis

Adhesion is the application of a substance with a bonding effect on the surface of two identical or different substances, so that they are firmly bonded together. We call the bonding agent a medium substance called adhesive. With the rapid development of the packaging industry in China, people are increasingly deepening the development and use of adhesives, and the material selection and preparation process of adhesives are undergoing major changes. The most obvious change is that starch binders are rapidly replacing epoxides and synthetic resins and occupy more and more market share.

The paper packaging industry is the industry with the widest range of adhesives and the largest amount of use. It involves many processes such as corrugated board processing, cladding, laminating, carton bonding, and bonding of other paper products. Among them, the highest amount of adhesive used for corrugated board processing and cladding is about 90% of the total amount of adhesives used in the entire packaging industry. This article will focus on the analysis of the development trend of these two types of adhesives.

At present, most of the adhesives for corrugated board processing are homemade thermosetting type starch adhesives. Only a handful of manufacturers with inadequate equipment or cold-formed corrugating technology use synthetic resins and oxidized starch binders.

Heat-curable starch binders are made by cardboard manufacturers themselves using starch, caustic soda, and borax, and they promote gelatinization of the binder by high temperatures to achieve a cardboard-bound adhesive. Due to the continuous improvement of the line speed of corrugated board and the better performance of the base paper, the quality requirements of adhesives have also changed. The main trends are as follows:

Increased binder solids

Starch adhesives for corrugated cardboard lines, high solids content, relatively low moisture content, and less amount of glue ensure the adhesion of the paperboard, so it can speed up the drying speed of paperboard bonding and ensure high-speed operation. Quality stability. High solid content binders have less moisture change during paperboard processing and can reduce board warpage. Once the speed of the high-speed wide corrugated board machine reaches 200m/min or more, the solid content of the adhesive must be high. The high solid content binder powder ratio is usually between 2.5:1 to 3:1. The solid content of the adhesive should also be determined according to the equipment and material conditions. Some plant equipment has poor accuracy, slow speed, and easy penetration of the base paper. If high solid content adhesives are used, it will cause debonding and sticking of cardboard. Problems such as explosion and explosion.

Faster tack time

Tacking time refers to the time required for the adhesive to begin to produce adhesive force between the adhesive layer and its tackiness can damage the paper surface fiber. The shorter initial tacking time is to ensure that the cardboard is completely bonded and improved. The key to speed. To make the initial viscosity of the starch adhesive as soon as possible, there are four methods:

In the production of corrugated board, increase the paper warm-up area (that is, increase the wrap angle on the preheater)
Adding a cross-linking agent to the adhesive improves the initial tack and reduces the water ratio in the adhesive formulation. That is, increasing the solid content of the adhesive. When the adhesive is produced, the borax is added to the main body and the carrier tank respectively. The former accounts for the latter. More than two-thirds of the added amount is preferred

Low viscosity

The lower the viscosity of the adhesive, the better the flowability. The fluidity determines the permeability of the adhesive, the uniformity of the sizing, and the amount of glue, which directly affect the speed, board bonding, board flatness, and hardness. The viscosity of a general pit machine should be between 30-40S (measured with a 4# cup). The viscosity of the paste machine should be between 45-65S. For the understanding of the fluidity of starch binders, there is a wrong point to be clarified, that is, the higher the proportion of powder in the binder, the worse the fluidity, in fact, this is incorrect, by adjusting the adhesive formulation process High solid content adhesives also maintain a very low viscosity.

The gelatinization temperature drops

The gelatinization temperature is the initial temperature needed to convert the starch binder into a paste. The gelatinization temperature of the starch binder is one of the key factors for maintaining high-speed production. The conditions for the production of high-speed wide-width corrugated cardboard require that the gelatinization temperature of the starch binder must be low, otherwise the vehicle speed is difficult to mention.

To solve the gelatinization temperature problem of starch binders, in addition to adjusting the amount of caustic soda and the method of heating, the appropriate addition of some additives can also achieve the same effect. Gelatinization temperature can not be too low, too low will cause the adhesive during the cycle of gelatinization and affect the adhesive fluidity, should be adjusted according to seasonal changes in adhesive formulations, low temperature weather can be reduced gelatinization temperature To 55-60°C, the gelatinization temperature can be increased to 61-66°C in hot weather.

Widespread use of paste additives

In order to increase the waterproof and moisture resistance of cardboard, further increase the speed of cardboard lines, and improve the bonding of cardboard, the addition of some additives to the paste has begun to be widely used in the packaging industry.

Cladding adhesives are also known as adhesives for paperboard or adhesives for veneers. Currently, there are three types of adhesives: silicates, synthetic resins, and starch adhesives.

Changes in the use of adhesives for cladding

Paosite, also known as sodium silicate or water glass, is a soluble silicate. Water glass as a corrugated paperboard adhesive has been used in China since the 1930s. Its adhesive strength is acceptable, but it also has major defects such as slow drying speed, easy efflorescence, moisture absorption, and damage to carton performance. . Therefore, since 1985, it has been banned from use by the national foreign trade authority.

Synthetic resin adhesives are made by adding polyvinyl alcohol to water and dissolving and stirring, and incorporating polyvinyl acetate emulsion. The resin adhesive has many advantages such as convenient operation, harmless to the human body, quick drying and curing, high adhesive strength and long storage period. However, its shortcomings are also very obvious, mainly due to the shortage of material sources, high costs, and large energy consumption. As a result, its original market share is gradually being squeezed by starch binders.

In contrast, starch binders are the most desirable binders. They are formulated with starch as the main raw material and other auxiliary materials. It has the advantages of fast initial adhesion, firm bonding, good water resistance, low cost, and environmental protection. The preparation method of the starch binder is an oxidation method, which is characterized in that the starch is oxidized by an oxidant such as hydrogen peroxide and sodium hypochlorite to be degraded and then gelatinized. However, what is slightly lacking is that the PH value reaches about 12, which has a certain corrosive effect on human skin.

The development trend of coating adhesive for starch

Two different product prices

With the deepening of people's understanding of starch adhesives, the use of starch adhesives in coated surfaces shows two distinctly different trends. One is a low-solids, low-priced adhesive with a solids content of less than 10%, a price of about 500 yuan/ton, and a slow drying speed. It is suitable for poor paper quality and uses a manual single-side coating or low-velocity coating. Machine-faced factory use. Since the solid content is very low, in order to ensure the bonding quality, the amount of glue is generally large, so the drying after coating is slow, and cardboard softness, warping and the like are prone to occur. Therefore, the product is limited to the use of some low-grade products in China. The other type is high solids and high-priced adhesives with a solid content of more than 18% and a price of 700-900 yuan/ton. Its characteristics are excellent adhesion, fast drying speed, small amount of glue, and high hardness of the cardboard after covering, without bending. It is suitable for use in factories where the quality of the base paper is good and the product quality is high.

Two different ways of using

In the Pearl River Delta and some of the Yangtze River Delta, where the packaging industry is developed, due to the large number of packaging manufacturers and the developed traffic, the glue is usually purchased directly from professional adhesive manufacturers, thus avoiding the cumbersome process of preparing glue and thus Some unstable factors brought about. In other parts of the country, due to the decentralized packaging companies, and the small scale, basically the use of raw materials purchased to prepare their own way.

Two different methods of preparation

At present, there are three different methods for the preparation of starch binders: hot preparation, cold preparation, and oxidation followed by pasting. The hot process is carried out in a reactor with a stirrer and a sandwich water bath (or steam bath). Both the oxidation and gelatinization of the starch are carried out under heating conditions. The whole process of the thermal method is always under heating, so the preparation time is short. Thermal adhesives are easy to agglomerate, storage time is not long, foam is prone to occur during use, and the preparation process is difficult to control. Only a few professional adhesive manufacturers use them.

The cold production method is simpler than the hot method, does not consume energy, and has a considerable market share in the Mainland. However, the cold method also has some drawbacks. For example, the preparation time is about 1-2 hours. The materials and production process are greatly affected by climate factors. The factory needs to arrange professionals to prepare glue.

The preparation method of first oxidizing and then gelatinizing is to prepare the oxidized starch from the professional starch by a professional manufacturer, and then the packaging company adds a certain amount of caustic soda and borax to prepare a glue. The most difficult-to-control oxidation process in adhesive formulation is done by professional manufacturers. Packaging companies can simply add a certain proportion of oxidized starch, caustic soda and borax to make glue. The method for preparing the glue does not need to be prepared by a person, the time is shortened to 15 minutes, and the quality of the formulated glue is very stable, and is being used by more and more manufacturers.

Source: Export Goods Packaging