Green Environmental Adhesives

In China, soft composite packaging materials refer to packaging films or packaging bags made of plastic films, paper and aluminum foil, and bonded together with adhesives. Taking it as the final product, it has led to the rise and development of the plastic film manufacturing industry, gravure ink manufacturing industry, gravure printing machinery and composite machinery manufacturing, bag making and cutting machinery manufacturing, and compound adhesive manufacturing. Formed a complete flexible packaging industry system. China's flexible packaging industry system is a sunrise industry that started from the mid-70s of the last century, the rapid development in the mid-1980s, and the early 1990s.

At present, China's soft composite packaging materials, the total annual output value of up to 80 billion yuan, production of nearly 4 million tons in food, medicine, cosmetics, household chemicals, chemical products, pesticides, feed, seeds, In the fields of cleaning products, disinfection products, medical equipment, and clothing, it has been widely used and closely linked to people's daily life. About 80% of these flexible composite packaging materials are produced by a dry composite process. In this dry composite process, dry compound adhesives must be used.

Among these types of adhesives, benzene-type and non-benzene-type single-component pressure-sensitive adhesives were first used in China. Since the 1980s, a large number of single-component or double-use lipid solvents have been used. Polyurethane adhesive components, the beginning of this century, alcohol solvent single-component or two-component polyurethane adhesives, as well as water-based polyacrylate adhesives. In addition to the dry compound method, since the second half of the 1970s, China has developed a flexible composite packaging material that is produced by extrusion coating or extrusion. In the last decade, a solvent-free composite process has emerged. And co-extrusion compounding process. None of these four process methods require the use of any solvent media type of adhesive. At present, products produced by these four processes account for about 20% of all flexible composite packaging materials.

From this it can be seen that at present in China, a large part of the soft composite packaging materials is produced using a dry compounding process. Each year, approximately 40,000 tons of "solvent-based" adhesives are used, roughly estimated throughout the year. The total consumption of organic solvents is not less than 60,000 tons, while the only adhesive material that actually produces adhesives is only 25,000 tons. With more and more attention to health, safety, environmental protection, resource conservation, and green ecology, people are increasingly concerned about the negative impact of the consumption of such large amounts of organic solvents. The consumption of such a large amount of organic solvents each year causes serious waste on the one hand and does not meet the scientific development concept of conservation, rationality and sustainable development. Because of the organic solvent, it only plays the role of uniformly coating the compound onto the surface of the base film in the dry compounding, and then it must be dried 100% by dry exhaust to drive it to the atmosphere. go with. Fundamentally, it has no effect on the fastness, heat resistance and dielectric resistance of composite materials. If there are other ways to evenly apply the rubber to the surface of the base film, then you can save the organic solvent and it is more in line with the spirit of "doing everything right." The second aspect also caused a waste of money and increased production costs. Based on the current price of about 8,000 yuan per ton of solvent, the amount of solvent consumed each year in the country is as high as 480 million yuan, which is comparable to the method that does not use organic solvents. In contrast, only the cost of adhesives will be more than 40% higher. In the third aspect, the discharge of a large amount of organic solvents, in addition to causing unpleasant smells or irritating human respiratory organs and causing discomfort to the human body in the production plant, is considered as all emissions to the outside, but also causes pollution to the atmosphere. Destroy the ecological balance of the earth and threaten human survival and security. Therefore, in recent years, the topic of green environmental protection adhesives has attracted more and more attention of people in the industry. This is a gratifying phenomenon of human progress and technological development.

As mentioned above, adhesives using organic solvents as media are used extensively in dry composite processes. Organic solvents are flammable, explosive, irritating to humans and even toxic. They are emitted to the outdoors to pollute the atmosphere and damage the environment. To harm the ecological balance, this adhesive certainly does not meet the requirements of environmental protection. Therefore, the application of this type of product has been increasingly questioned and restricted in the increasingly stringent environmental protection regulations in the past decade or so. In fact, many years ago we opposed the use of benzene, isopropanol, and chlorinated alkane solvents that are clearly toxic to the human body, and in particular, single-component pressure-sensitive adhesives that oppose benzene-based solvents. Since the second half of last year, benzene-based solvents in food packaging bags have exceeded the standard of standards, which has aroused people’s great concern. The cry for health, safety, and reliability of food packaging bags is also rising. This will inevitably lead to a topic of green environmental protection. .

Now, in our packaging industry, there is not only a guiding ideology for the development of green adhesives, but also specific adhesive products known as green, such as water-based polyacrylate adhesives, alcohol-soluble Polyurethane adhesives, water-based polyurethane adhesives, and solvent-free polyurethane adhesives, as well as solvent-free adhesive resins. The emergence of these adhesives undoubtedly overcomes the shortcomings of solvent-based adhesives in terms of hygiene and safety and green environmental protection, and also provides conditions for reducing production costs. However, from a true, fundamental sense of the purpose of green environmental protection, the author believes that only solvent-free adhesives are worthy of the title of green environmental protection.

First, take a look at water-based polyacrylate adhesives.

This kind of adhesive replaces the organic solvent with water, water has inexhaustible resources advantages and very low price advantages, but also has the characteristics of non-flammable, non-explosive, odorless, harmless to the human body and safety and health Compared with organic solvent type adhesives, it is a big step forward in terms of environmental protection and health and safety.

However, to make the water-based polyacrylate adhesive really have storage stability and cold-resistance and freeze-resistance, it needs to be truly industrially applicable. Its entire contents are not only water and polyacrylate. Simple two, it must also use polymerization initiators, emulsifiers, PH regulators, stabilizers and cold-resistant antifreeze and many other additives. Although the content of these additives is not very high, but whether they are green and environmentally friendly, and whether they are safe and hygienic, we still don’t know. In the application of some of these products, we said that if diluted, we cannot use pure water to hedge. It should be diluted with water containing isopropanol. In this regard, because isopropanol is an organic solvent, it is not only explosive and explosive, but also harmful to health. There is still a gap between it and the real sense of health and safety and environmental protection.

Next, take a look at alcohol-soluble polyurethane adhesives.

Compared with the widely used ester-soluble polyurethane adhesives, it only uses ester-soluble ethyl acetate solvent instead of ethanol instead of alcohol, which is still an organic solvent-based adhesive. Agent. I personally think that this is not enough to show that alcohol-soluble polyurethane adhesives are hygienic, safe and environmentally friendly adhesives. On the contrary, they may be less hygienic and safer than ester-soluble polyurethanes, and the harm to human health is even more serious. Because, first, a curing agent containing a polyisocyanate group (ie, -NCO) must be protected with an extremely reactive isocyanate group with an end capper in an alcohol solvent so that it will not be protected as uncapped. The -NCO group rapidly reacts with the hydroxyl group (i.e., -OH) in ethanol to lose the function of cross-link curing. The end-capping agent, most of which has a strong chemical odor, is also toxic to the human body. If it is used improperly, it will damage human health, so it is not safe and green. Secondly, with respect to the use of ethanol instead of ethyl acetate to make alcohol-soluble polyurethane adhesives, which of the two organic solvents is more hygienic and safer and greener? More and more information and signs show that ethyl acetate is better than ethanol!

The human understanding of this issue is probably similar to that of humans in the process of understanding the harmful effects of smoking on human health. Forty or fifty years ago, humans did not think that smoking would cause harm to their health. Many people use cigarettes as fashionable clothes. With the development and advancement of modern medicine, social epidemiology statistics, and analytical chemistry, humans have gradually realized that not only does smoking harm health, but passive smoking is also harmful. It can damage fetal development in particular and shorten the life span of people. It also produces lung cancer. The main reason. Therefore, in the last two decades, the world has launched a wave of anti-smoking, restrictions on tobacco production, prohibiting the sale of tobacco to minors, prohibiting smoking in public places, and restricting the sale of tobacco to young people. The United Nations has also introduced a non-smoking convention.

Similarly, the history of human drinking has been four or five thousand years. Especially in China, we have a profound culture of wine. However, no one has ever studied the harm of alcohol to human health. Four or five years ago, the author saw a report saying that the scientific discovery in the United States of America that alcohol has a serious damage effect on human health is based on the fact that alcohol (ie, ethanol) is inhaled into the body, under the action of oxidases. Will be oxidized to produce acetaldehyde:

O
(Oxidation) ‖
2CH3CH2OH + O2 --→ 2CH3-C-H + 2H2O
(alcohol) (oxygen) (acetaldehyde) (water)
American scientists believe that acetaldehyde, like formaldehyde, is a carcinogenic substance, so ethanol is not non-toxic.
Of course, from the point of view of the chemical reaction, acetaldehyde will be further oxidized to become acetic acid, and acetic acid can also be esterified with alcohol to further generate esters. If esterification of acetic acid with ethanol occurs, the final product is a stable ethyl acetate, also known as ethyl acetate:
O O
‖ (Oxidation) ‖
2CH3-CH + O2 --→ 2CH3-C-OH
(Acetaldehyde) (Oxygen) (Acetic Acid)

O O
‖ (Esterification) ‖
CH3-C-OH + HO-CH2-CH3 --→ CH3-C-O-CH2-CH3 + H2O
(Acetate) (Ethanol) (Ethyl Acetate) (Water