Application of the hottest adhesives in packaging

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The application of various adhesives in the packaging industry (Part I)


adhesives have been used in the packaging industry for nearly a century. It is a kind of substance that can firmly bond various solid materials together by the action of interface, also known as adhesive or adhesive, which is called "adhesive" for short. In the packaging industry, there are many kinds of bonded materials. Different types of materials, such as metal, strive to restore your economy. For the testing of some materials, we should still pay attention to some dynamic materials, paper, composite films, etc. of our company. Their physical and chemical properties are different, which has a great impact on the bonding strength. Therefore, different adhesives and bonding processes should be selected according to different materials. With the development of the packaging industry, the consumption of adhesives has maintained a high level. The annual consumption of adhesives in the global packaging industry accounts for about 35% of the total consumption of adhesives. Therefore, it is speculated that the packaging industry may be the largest consumption market of adhesives

1 foamed alkali adhesive

the chemical name of foamed alkali is sodium silicate, which is a colorless crystal or white powder. It is fused by quartz sand and sodium carbonate. It is alkaline when dissolved in water. The transparent slurry solution is called "water glass". The viscosity of the water glass solution increases significantly after the gradual loss of water, and then hardens. Therefore, it can be used as an adhesive. Foam alkali is an early adhesive used in packaging industry. Mainly used in carton industry

1.1 advantages and disadvantages of foamed alkali adhesive. It has been widely used in the industry for many years. But at the same time, it has the disadvantages of deliquescence in case of moisture, slow bonding speed and aggravating cartons, so it is not suitable for rapid packaging and high-quality packaging; Moreover, it has high alkali content and is easy to be alkaline, so the sealing ring or combined gasket should be replaced in time for paper corrosion; According to the use of the machine and the service life of the oil, it will pollute the environment. According to some manufacturers' reports, since the pH value of the paper is 7, it is a neutral substance, while the foam alkali is weakly alkaline. Using it as the adhesive for high-grade wine boxes will make the paper weakly alkaline. However, alkaline substances will have a certain impact on the electrochemical aluminum foil, ink, gold powder and silver powder used for bronzing, and have a certain chemical reaction. In particular, they are easy to react with the metal powder in the electrochemical aluminum foil, which makes the original bright electrochemical aluminum foil lose its original luster, and the color completely turns into antique yellow, thus affecting the beauty of the packaging carton. Over time, it will also make the ink layer on the printed matter lose luster. Therefore, it is better not to use foamy alkali as adhesive in cartons and carton pastes, because it will have a great impact on the beauty of packaging. As for what kind of adhesive to use, we must first analyze the physical and chemical properties of the adhesive. And the influence of acid and alkali on paper, ink, electrochemical aluminum foil, gold powder, silver powder and film covering

1.2 development trend of foamed soda

at present, foamed soda has been listed as an adhesive prohibited to be used in cartons and carton products internationally. However, the adhesive synthesized by foam alkali and other substances is a new development trend. For example, the high-quality mixture of Paohua alkali and various organic adhesives (starch, dextrin, etc.) can enhance its viscosity and overcome the shortcomings of slow bonding speed of Paohua alkali. At present. It has also been reported that PVA adhesive can be modified by using foamed alkali to prepare adhesive with excellent performance

2 use of starch adhesive

because of its high strength, light weight, no corrosion, no pollution and low cost, starch adhesive is widely used in corrugated board, carton production, automatic labeling and other packaging fields to replace it. It has been used for many years. Since the 1970s, China has successively developed various types of starch adhesives for packaging, such as gelatinized starch adhesive, oxidized starch adhesive, composite starch adhesive, esterified starch adhesive, and grafting starch adhesive. Among them, oxidized starch adhesive is the most widely used

2.1 advantages and disadvantages of starch adhesive and its comparison with bubble alkali

relevant national departments have long stipulated (gb-5034-85) that starch adhesive or other adhesives with the same bonding effect shall be used for processing corrugated board, and sodium silicate shall not be used. Compared with foamed alkali, starch adhesive has the advantages of high bonding strength, light weight, no corrosion, low cost and easy manufacture. At present, according to the use of adhesives in the packaging industry, starch adhesives occupy a considerable proportion in the bonding of paper packaging materials and paper containers. More than ten years have passed. So far, in China's carton packaging industry, foamed soda is mainly used, and starch adhesive is rarely used. The main reason is that the natural drying speed of starch adhesive is too slow. This is because starch is a natural polymer with glucose as the structural unit, which is composed of amylose and amylopectin. Amylose is essentially a linear polymer. A large number of hydroxyl groups make the polymer have strong hydrophilicity

in foreign countries, starch adhesives for corrugated boxes are mainly used on forming machines, which are equipped with automatic drying devices, so they do not have the problem of slow drying speed. Since the packaging in China is still relatively backward when I stretch the sample at a constant speed to the cutting edge, few manufacturers use the automatic drying line of the forming machine in the production of cartons. Moreover, China's carton factories are mainly small factories of township enterprises, and there are still some difficulties in establishing automatic drying lines, which seriously affects the universal promotion of starch adhesives. Therefore, at present, there are still most corrugated box manufacturers, especially some single machine and small manual carton factories, which continue to use the traditional foam alkali as the adhesive. Starch glue is usually prepared by heating, which has high production cost and short shelf life. In addition, the more representative is the cold starch adhesive, which is first made into powder packaging products by the adhesive factory, and then prepared and used by the carton factory. The principle is to oxidize starch. After centrifugation, drying, and then adding fillers; The production cost of this process is low, but it is inconvenient to use. The prepared starch glue needs to be used up the same day. It cannot be stored, and the quality of the glue is unstable. Therefore, so far, the domestic general small and medium-sized carton factories still use foamed soda

(to be continued)

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