Adhesive application in flexible packaging industry

First, the application of adhesives

At present, there are three major categories of adhesives commonly used in the flexible packaging industry: solvent-free adhesives, water-based adhesives, and solvent-based adhesives. Developed countries in Europe and the United States attach great importance to environmental protection, and mainly use solvent-free adhesives and water-based adhesives in the composite production of flexible packaging. Most flexible packaging companies in Asia and Africa still use solvent-based adhesives. For example, in Japan, where the flexible packaging industry is more developed, solvent-based adhesives account for over 90% of the market share.

According to incomplete statistics, there are more than 6,000 soft packaging manufacturers in China, mainly concentrated in the Pearl River Delta, the Yangtze River Delta, and parts of Hebei Province and Shandong Province. In these regions, more than 95% of flexible packaging manufacturers use solvent-based adhesives, and less than 5% of companies use environmentally friendly adhesives (solventless and water-based adhesives).

At present, there are nearly 400 manufacturers of adhesives for flexible packaging in China. It is estimated that the annual production of adhesives in China is about 60,000 tons, of which the main one is still solvent-based adhesives. The well-known manufacturers include Zhongshan Kanghe, Zhejiang New Oriental, Shanghai Lianyin, Beijing Gaomeng, Beijing Chemical Research Institute (Northern Chemical Industry Institute), and Jiangsu Jintan. In recent years, some well-known foreign adhesive manufacturers have also increased their investment and development efforts in the Chinese market. They have built factories in China, such as Henkel, Mitsui Takeda, Rohm and Haas, Bright, and other companies. The addition of this product has significantly increased the production and production capacity of adhesives in the domestic market.

Second, the type and characteristics of adhesives

The three types of adhesives commonly used in the flexible packaging industry have their own characteristics and corresponding application areas. The following sections briefly analyze their advantages and disadvantages.

Solvent adhesive

Solvent-based adhesives for flexible packaging are mainly composed of two-component polyester, two-component polyether, two-component polyurethane and alcohol-soluble polyurethane.

(1) Advantages

1 It has a wide range of applicable substrates and basically has good adhesion to the materials commonly used in flexible packaging.

2 The initial tack is good and the composite strength is high.

3 The composite film has high transparency and good flexibility, which meets the requirements of post-processing and product packaging.

4 The properties of heat resistance, cold resistance, medium resistance, etc. are the best among various types of adhesives.

5 Safety, hygiene, no odor, compliance with FDA standards and VOC (organic volatiles) related regulations.

6 It has good operability and relatively low requirements for equipment and operators.

(2) Disadvantages

1 Volatile organic solvents have some harm to the human body and cause some pollution to the environment.

2 Incompletely reacted free TDI (toluene diisocyanate) in some ester-soluble adhesives is harmful to the human body.

3 A small amount of solvent residue in the composite membrane may cause contamination of the contents of the package.

2. Water-based adhesive

Flexible composite water-based adhesives are mainly waterborne polyurethane adhesives and waterborne acrylic adhesives.

(1) Advantages

1 It does not pollute the environment and is conducive to environmental protection.

2 It can be used on medium and high speed machines.

3 No solvent residue, the composite film has high transparency.

4 pairs of aluminum film composite strength is good, will not damage the aluminum layer, it will not cause the aluminum layer transfer.

5 Low glue application (as low as 1.6g/m2), low cost for comprehensive use.

6 has good adaptability to alcohol soluble inks.

(2) Disadvantages

1 is not suitable for heavy packaging and high temperature cooking packaging.

2 The surface properties of the film are relatively harsh and the surface tension requirement is higher than 3.8×10-2N/m.

3 The energy consumption is large, the production efficiency is low, and the composite equipment is required to have strong heating and air extraction capacity (temperature should reach 60-100°C).

4 The attenuation of composite strength over time is evident.

5 The corrosion of composite equipment is more serious.

6 When the composite aluminum film is used, the aluminum plating layer is easily corroded.

3. Solvent-free adhesive

Solvent-free adhesives for flexible packaging use include single-component, two-component, UV-curable, and EB-curable adhesives.

(1) Advantages

1 non-toxic, environmental protection, solvent-free volatilization, will not cause environmental pollution, in line with FDA standards.

2 Operational safety, no need to take fire, explosion-proof measures.

3 The amount of glue is small and the compounding process is simple. The compound speed can reach 200-300m/min.

4 Save energy. After the glue is applied, it is not necessary to heat and dry it through the drying tunnel, and it will not increase energy consumption due to waste gas incineration or recycling.

5 Composite products have no solvent residue or migration problems, so they will not cause contamination of the contents and are more suitable for food packaging.

6 The solid content can reach 100%, and the user's comprehensive use cost is low.

(2) Disadvantages

1 The solventless composite equipment has a large investment, and the coating system is more complicated and requires a heating device.

2 The viscosity of glue is high, and the storage time after mixing is short.

3 Low initial viscosity and long curing time.

4 The requirements for the precision of the tension system of the composite equipment are high, and the operation level of the operator is also required to be high.

5 The flatness and thickness of the composite substrate are more stringent, and the surface tension of the film is greater than 3.8×10-2N/m.

6 The decay of composite strength over time is more pronounced.

7 When compounding some packaged products with higher quality requirements (pesticide bags, high-temperature cooking bags, etc.), their performance and compound quality cannot reach the level of ester-soluble polyurethane adhesive.

Third, the domestic adhesive market stability and innovation

The overall situation of the domestic and foreign flexible packaging industry is that each adhesive product has its own market, but the development direction is to use safety and environmental protection products to produce green packaging.

1. Coexistence of various adhesive products

(1) Solvent-based adhesives have a dominant position in the domestic market due to their excellent softness, low temperature and retort resistance, ease of handling, and wide applicability, and other adhesives cannot be temporarily replaced.

(2) In practical applications, there are still some practical problems that cannot be solved temporarily, such as solvent-free adhesives, hot-melt adhesives, and water-based adhesives. 1 The dry composite equipment in the domestic flexible packaging industry is currently only suitable for solvent-based adhesives. If a composite device is to be replaced, a large amount of funds will be required and a large amount of resources will be wasted. 2 Environmentally-friendly adhesives have a certain degree of performance. The limitations; 3 additional heat energy consumption is also a waste of environmental resources, but also cause pollution to the environment.

(3) The flexible packaging industry has begun to pay attention to environmental protection. Only by radically changing the emission of harmful substances in raw and auxiliary materials such as adhesives, inks, solvents, and films, can we fundamentally achieve the goal of environmental protection packaging.

(4) The harm of solvents to the environment has not yet been conclusive. In the international arena, Japan and European and American countries are still controversial on this issue, and some solvent-based adhesives have passed FDA certification and VOC regulations.

2. Environmentally friendly adhesives are the development direction
It is undeniable that the domestic adhesive market is an inevitable trend toward environmental protection. In 2004, manufacturers of water-based adhesives seized the opportunity of rising prices in the international oil market. They have made considerable progress in the market for environmentally friendly adhesives, but they only use one-component water-based adhesives, mainly for composite structures. Simpler lightweight package. Solvent-free adhesives have not made much progress due to factors such as equipment.

However, we must also realize that for a long period of time in the future, solvent-based adhesives will still be the mainstream products in the domestic market, and will be improved in environmental protection: First, the development of some transitional, solvent-based adhesives Adhesive products, such as low-solvent residue adhesives, aliphatic polyurethane adhesives, alcohol-soluble adhesives, etc., and second, solvent-free composite devices with lower development costs and simple operation.

Some adhesive manufacturers in China are very concerned about the development of environmentally friendly adhesives and have carried out relevant technical reserves. As long as the domestic market is mature, they can be produced at any time to meet the needs of customers. For example, Zhongshan Kanghe Chemical Co., Ltd. developed a two-component solvent-free adhesive KH-FS762/KH-1762 as early as 2003, and in 2004 it independently developed KH-WB607 (for paper/plastic composite) and KH-WB608 (for plastic/plastic composite) one-component waterborne adhesives. At the same time, Kanghe Chemical also introduced KH-LS800/3800 ultra-low solvent residual polyurethane adhesive to meet the environmental protection requirements of domestic flexible packaging manufacturers and end users at this stage. In addition, Kanghe Chemicals is actively cooperating with mechanical equipment manufacturers and is committed to the application of solvent-free adhesives on ordinary dry laminators, and has made breakthroughs.

With the development of technology, it is believed that in the future, domestic environmentally friendly adhesives will surely make greater progress and will play a positive role in promoting environmental protection.