Editor's note: On the afternoon of April 17, the 6 leading QQ groups of the packaging front co-sponsored by the Information Committee of the Guangdong Provincial Association of Packaging and our magazine conducted an online exchange on "water-based glue application" at the same time (total group 121451012; group I: 64311965; II Group: 37848282; Group III: 119411638; Group IV: 116162302; Group V: 256925591), about 1200 people from 6 groups participated online. We are very honored to invite Manager Dow Zhu Jianliang to explain the characteristics of water glue, the current range of use, process control and precautions, and analyze the use of water glue and other examples.
Data show that by 2015, Asia ’s flexible packaging adhesives will reach 260,000 tons, of which solvent-based adhesives account for 67%, water glue 20%, and solvent-free 13%. Water glue will gain more use space in our flexible packaging industry .
1. Lecture by Dow Zhu Jianliang Manager · Water glue application
In the flexible packaging color printing composite industry, water-based adhesives and solvent-free adhesives will be the direction of future development.
In China, with the increase of people's awareness of environmental protection and the importance of food packaging safety, more and more issues have been raised for the color printing packaging industry. Over the years, flexible packaging composite adhesives have continuously undergone technological improvements and innovations. They have gone from an initial ester-soluble adhesive to an alcohol-soluble adhesive to a solventless adhesive, and finally to an aqueous adhesive. development path. Dow Chemical has been committed to the development and promotion of water-based adhesives since the 1990s. In 2003, it achieved true commercial sales in China, and it has begun the rapid development of water-based adhesives in China.
After ten years of development in China, water-based adhesives have become an important part of China's flexible packaging compound adhesives. While fully grasping the operating skills of water-based adhesives, people are discovering more and more unique properties of water-based adhesives.
In order to meet the needs of customers with different applications, Dow Chemical's water-based adhesives have gone from the first-generation single-component water-based adhesive to the second-generation two-component water-based adhesive and the third-generation water-based adhesive. The development process can meet most of the different functional requirements and application requirements of different composite structures.
1.Water glue advantages
In today's low-profit era, water-based adhesives have created great value for users. These values are mainly reflected in the following points:
(1) Excellent product hygiene performance
The water-based adhesive is not toxic in itself. It does not have the problem of solvent residue like solvent-based adhesives, and it does not have the problem of PAA residue of solvent-free adhesives. Food safety performance.
(2) Efficient production efficiency
The operating conditions of high solid content and the requirement of low sizing amount, as well as the incompatibility of water and acrylic acid, cause the moisture to be dried to be easily dried, so its production efficiency can be increased by more than 20% compared with solvent glue. The high molecular weight adhesive design greatly shortens the time required for curing and enables fast shipment.
(3) Good aluminization affinity
The characteristics of the acrylic resin determine the good composite strength between the adhesive and the aluminized layer. The high molecular pre-polymerization degree of the water-based adhesive and the design of the flexible molecular chain further prevent the aluminum composite layer from transferring and causing unqualified composite strength. The problem.
(4) Improve the working environment, reduce pollution, reduce work intensity and avoid the danger of fire
As the water-based adhesive can be directly produced on the machine without dilution, it reduces the labor for the operator to prepare the adhesive, and also avoids the concentration of the solvent in the air at the work site, which is quite beneficial to the operator and also avoids It reduces the discharge of solvents and has no pollution to the environment. Of course, the absence of solvents avoids the danger of fire.
(5) Effectively reduce the occurrence of quality accidents
With water-based adhesive composite products, you can intuitively see the quality of the product. As long as you carefully check the appearance and composite strength of the product when it is offline, it will not cause adverse changes over time, especially The composite strength and appearance, after being left for a period of time, as the adhesive molecules fuse together, the composite strength will increase and the appearance will become better.
2.Successful cases of water glue application
Choosing the right water-based adhesive for different composite structures and final packaging applications is an important step in the successful use of water-based adhesives.
Early water-based adhesives were mainly used in the following areas:
(1) BOPP / ink / MCPP structure
Generally, the water-based adhesive suitable for the structural compounding is a single-component common water-based adhesive. The structured product is widely used in packaging of instant noodles, biscuits, egg yolks, and other dry foods. The main performance characteristics are high composite strength, beautiful appearance, and no occurrence of aluminum plating transfer problems. For aerated packaging such as egg yolk pie, it can effectively reduce the occurrence of packaging leakage.
(2) KOPP (BOPP) / ink / CPP structure
Because the single-component water-based adhesive has poor composite strength for transparent structures, the structure generally requires a two-component water-based adhesive. This structured product is mainly used in the packaging of foods such as bread, cakes, and rice cakes. The main feature is to effectively reduce the occurrence of air leakage in inflatable packaging, reduce the pollution of residual solvents and the occurrence of odor problems.
The early one-component water-based adhesives had large limitations in use due to their performance limitations. With the development of more and more high-performance water-based adhesives, the market share of water-based adhesives in flexible packaging adhesives has also increased, and various successful new applications have also emerged:
(1) PET / ink / MCPP structure
This structured product is mainly used in candy and back-sealed rice cake packaging. In the early days, this type of product was compounded with solvent glue, and the problem of aluminum transfer was easy to increase the temperature resistance. However, after the problem of aluminum transfer was controlled, the problem of poor temperature resistance was easy to occur. Features of high-performance water-based adhesive It has good heat resistance and is suitable for high-speed packaging without the risk of aluminum plating transfer.
(2) PET (BOPP) / ink / MPET / PE and (BOPP / ink / PE / MPET) / PE structure
The two-layer composite structure can use water-based adhesives, and is mainly used in puffed food, food outer bags, dried fruits, granules or powder medicine packaging. In the outer layer composite application, it has high composite strength and effectively reduces the risk of aluminum plating transfer. In the inner layer composite application, it has high composite strength (especially for products with thin composite PE) and can avoid the impact on the friction coefficient. No odor effect, can meet the requirements of fast delivery.
(3) Two composite structures of potato chip packaging
BOPP19 / MPET12 / PE45: two-layer dry composite, L168 / CR3A = 100: 2 can be used;
(BOPP19 / PE15 / MPET12) / PE (CPP) 25: The first layer is extruded and compounded, and the second layer is dry compounded. L188 / CR3A = 100: 2 can be used.
Advantages of two-component water-based adhesives for potato chip packaging:
Higher composite strength to meet the needs of packaging.
Lower solvent residues to ensure food safety.
No adhesive odor effect to ensure product flavor.
Low slip effect on PE film to ensure smooth production, no fire hazards on the compound site, reducing the impact of solvents on employees.
(4) Frozen food packaging
The main structures of frozen food packaging are PA / PE, BOPP / CPP, and BOPP / PE. The main characteristics are the good low temperature resistance of water-based adhesives, which can effectively reduce the brittle cracking of packaging materials under frozen conditions and improve the heat at low temperatures Seal strength.
(5) Composite of paper products
Because water-based adhesives have good permeability to paper, water-based adhesives have a good compound effect in paper products. Any film and aluminum foil can be compounded with water-based adhesives and paper. Generally, this application uses Two-component high-functional water-based adhesive, the amount of curing agent can be adjusted according to heat resistance requirements. The main features are no solvent residue, high composite strength and lowest cost.
The future development of water-based adhesives mainly considers the convenience of use and the functionality of the product. In terms of convenience, one-component water-based adhesives are a development direction, so it is foreseeable that in the future, one-component water-based adhesives will be suitable for more and more products with composite structures, and their composite properties will also be significantly improved. . In terms of functionality, the performance of two-component water-based adhesives will become stronger and stronger, and will gradually cover the high functional requirements of high thermal shear resistance, high temperature resistance and chemical resistance, and gradually replace the use of solvent-based adhesives. range.
Second, the actual case analysis and discussion submitted by the enterprise
1. Nanguang Solventless Machinery Xu Shengsheng: How to solve the two-component water glue often blocking?
Dow Chemical Zhu Jianliang: There are two main reasons for blocking: One is the problem of the adhesive itself. The more severely designed the adhesive is, the more severe the blocking will be with the prolongation of production time, and the blocking will have to be replaced. Adhesive supplier or adhesive type address. In addition, a reasonable screen version can also reduce the occurrence of such problems. Screens with large openings can usually slow down blocking. The other is poor operation control, the main reason is that after the production is stopped, the version is not timely. Such blocking can be found in production.
Beijing-Li Gong: When using two-component water glue, it is easy to block plates, and single-component is much better.
Soft package consulting Tang Yongqiang: Regarding the problem of blocking, we still have to work hard on the screen roll or production operation and process management. We use water-based glue, blocking is very rare.
Nanguang Solventless Machine Xu Xusheng: How many rollers are generally in line? 160? 200?
Dow Chemical Zhu Jianliang: It is generally recommended to use a 200-line, 32um deep version.
2. Nanguang solvent-free machine Xu Xusheng: After the water-glue compound (two-component), after making the bag, it is easy to wrinkle at the heat seal of the bag after being put for a period of time. What is the reason?
Dow Chemical Zhu Jianliang: If wrinkling occurs at the heat seal of the bag, it is caused by poor temperature resistance of the adhesive. Usually, the shrinkage of the composite film after heat sealing is inconsistent, the adhesive does not adhere well, and layered wrinkles appear.
Beijing-Li Gong: After long time, water-based acrylic glue will have the problem of strength attenuation.
Dow Chemical Zhu Jianliang: There is no problem of attenuation. The characteristic of water glue is that the longer it is placed, the better the composite strength. I still have samples for more than ten years here, and the composite strength is still very good.
Soft bag service Jia Junliang: "There is no problem of attenuation, the characteristic of water glue is the longer it is placed." This is the relative composite strength for different material structures, right?
Nanguang Solventless Machinery Xu Huansheng: Ours is NY complex PE.
Dow Chemical Zhu Jianliang: NY / PE needs to use our mid-functional water glue.
3. Chen Sheng of Oriental Resin: What are the better water glue brands at present? What is the system? What are the main applications?
Dow Chemical Zhu Jianliang: At present, the main system of water glue is acrylic system, and there are some water-based polyurethane systems.
Soft bag service Jia Junliang: The future development direction should be water-based polyurethane.
Dow Chemical Zhu Jianliang: The system performance of waterborne polyurethane will be higher than acrylic, but the cost of waterborne polyurethane system will be higher. The main problem is the grafting of hydrophilic groups of polyurethanes and the use of curing agents. In fact, we also have adhesives for water-based polyurethane systems. The development process is earlier than water-based acrylic systems and is available abroad.
Dongfang Resin Chen Sheng: I think the biggest problem of polyurethane hydrogel is that it is easy to hydrolyze. The glue produced just now is good, but it is troublesome after hydrolysis for a period of time. This problem does not exist in acrylic system.
4. Chaoan Color Printing: How to avoid the quality accident of aluminized products due to moisture residue?
Dow Chemical Zhu Jianliang: This is an old problem, which often happened before, but it is almost gone now. The main causes of moisture residue are the following:
(1) The amount of glue is too large, which makes it difficult to dry. It is recommended to control the gluing amount to 1.8 ~ 2.2gsm.
(2) The glue is not uniform due to a bad scraper.
Xiaochen: The unevenness of the scraper causes unevenness. Can the uniform roller make it even?
Dow Chemical Zhu Jianliang: It is easy to see when this problem occurs. Because the water glue is white, you can observe the uniformity of the white on the screen roller before production. If the unevenness is required, the scraper must be adjusted. Can not be solved with a rubber roller.
(3) Poor drying of the oven or excessively fast composite cars.
In short, proper inspection can completely avoid this problem. Remember a few points: check the uniformity of the screen roller before starting, check the dryness of the film from the oven when starting, and check the initial adhesion after starting.
5. A soft bag: What is the shelf life after water-glue compound? Some companies have delaminated after three months after water-glue compound?
Dow Chemical Zhu Jianliang: The shelf life of water-glue compound is very long, there is no specific data on how long it is, and it will never appear that the compound strength decreases when it is left for 2 to 3 years. If delamination occurs after being left for 3 months after compounding, there must be other problems. At present, our company has not encountered this problem.
6. A soft bag: How to properly clean the network cable roller after using water glue?
Dow Chemical Zhu Jianliang:
The first step is to prepare 2kg of water in a plastic bucket with water.
In the second step, raise the scraper and keep the dampening plate.
In the third step, remove the remaining glue.
In the fourth step, press down the scraper, and at the same time, slowly rinse the screen roller with a bucket until the flowing water becomes transparent.
Step 5: Raise the scraper and dry the screen roller with a clean cloth.
Cleaning is complete. Rinse the screen roller with ethyl acetate one time before the next boot.
7. Li Gong: It is said that if the water-based acrylic system is used to make bag products, is it still risky when heat-sealed? If controlled?
Dow Chemical Zhu Jianliang: In fact, water glue has no risk to three sides sealing and back sealing. I have some customers who use water glue to make bags directly without any problems. Water glue can fully meet the requirements of bag making. Note that the zipper bag is not suitable for water glue. Mainly at the two ends of the zipper due to high temperature and pressure, delamination. Of course, also pay attention to the use of the product, high temperature cooking and repacking water glue is not suitable. Liquid pouches are also not recommended.
8. Jinan-Packaging: How much does the initial viscosity need to reach when producing one-component water glue?
Dow Chemical Zhu Jianliang: The initial adhesion depends on the structure. Single-component BOPP / MCPP usually has an initial adhesion of about 0.4-0.6N. Without ink transfer, the final composite strength is about 1.5N.
9. Color printing packaging: Does water glue require humidity in the workshop? What is the principle of curing?
Dow Chemical Zhu Jianliang: There is no requirement on the humidity in the workshop, but the humidity will affect the drying speed. Generally, the drier the weather conditions, the faster the recombination speed. Under normal conditions, composite light packaging, water-glue compounding can be 20% faster than solvent glue compounding. Up to 50% faster in dry conditions.
The principle of curing is that hydrocolloid does not rely on cross-linking reaction, it is formed by pre-polymerized high molecular weight self-crosslinking (winding). Water glue cannot be stored for reasons. Only when degradation occurs will problems occur. The same is true for single components. The single component has no late chemical reaction, which is why water glue does not have the problem of compound strength attenuation like solvent glue.
10. Guangdong Zhuo Printing Xiaozhuo: What are the reasons for the poor adhesion between the glue and the aluminized layer?
Dow Chemical Zhu Jianliang: There are many reasons for poor adhesion: insufficient dyne on the aluminized surface; other additives are adhered to the surface of the aluminized layer; too small amount of glue causes poor adhesion; compound temperature or compound pressure is insufficient; off time Too short or insufficient curing time; improper choice of adhesive. Generally, the strength of water glue and aluminized layer is poor, which is the problem.
Guangdong Zhuo Printing Xiaozhuo: How long is the maturation time?
Dow Chemical Zhu Jianliang: Generally, the single component is more than 6h and the two component is more than 12h at 40 ~ 45 ℃, depending on the application.
11. Color printing packaging: Are all products made by water glue sticky? How much peel strength can be achieved? The water glue you mentioned should be a single-component acrylic system by default?
Dow Chemical Zhu Jianliang: Water glue is sticky. This is its characteristic and does not affect temperature resistance. If solvent glue has such stickiness, it must be heat sealed and layered.
Color printing packaging: Does not affect temperature resistance, but will affect peel strength.
Oriental resin Chen Sheng: Water glue needs to adhere to the substrate by stickiness, otherwise it will not stick, which is different from the solvent-based mechanism.
Soft bag consultation Tang Yongqiang: Water glue is more or less sticky, but it will obviously improve over time. Initial peeling (downward) 0.6 ~ 0.8N. It reaches 1.05N after 1h in the natural environment.
Dow Chemical Zhu Jianliang: It is difficult to say the strength, depending on the structure and materials: BOPP (PET) / MCPP (CPP), generally around 1.5N, BOPP (PET) / MPET, generally around 1.5-2.5N, (PET / MPET) / PE, generally around 3.0-4.5N. Water glue is now generally acrylic.
Soft bag consultation Tang Yongqiang: After curing for 5 ~ 6h, it can reach 1.3 ~ 1.4N (single component) composite aluminized structure.
12. Color printing packaging: How much can the cost of water glue reach? How much can be saved compared with alcohol-soluble, ester-soluble and solvent-free?
Dow Chemical Zhu Jianliang: The cost of water glue is generally 0.06 ~ 0.08 yuan / m2, solvent glue is generally 0.1 ~ 0.12 yuan / m2, and solvent-free is generally 0.04-0.05 yuan / m2. The cost competitive advantage of solvent-free is obvious. But overall, the three types of glue have their own advantages, for example, water glue is better in terms of safety.
Color printing packaging: water glue does not need to worry about solvent residues and workers' health and safety, workshop safety, no odor.
Dow Chemical Zhu Jianliang: Water glue has no hazardous substances, no process risks, and the quality of the product is more intuitive.
13. Guangdong Zhuo Printing Xiaozhuo: Is the compound pressure inversely related to the amount of glue?
Dow Chemical Zhu Jianliang: There is no relationship between compound pressure and sizing amount. Usually the magnitude of the compound pressure is related to the compound appearance. Of course, the amount of glue is also related to the appearance. The control of the sizing amount is mainly related to the operating concentration and the depth of the screen roller, and it is also related to the hardness of the sizing roller, the angle of the doctor blade, the surface tension of the substrate and the compound speed.
Third, the conclusion
The application of water glue has been in China for more than ten years. From the initial questioning, to the widespread application of water-based acrylic systems, to the successful development of water-based polyurethane systems, the technology of water glue production and use has continued to mature. It is foreseeable that with the deeper understanding of water glue, this environmentally friendly product will be used more widely and comprehensively.
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