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In order to thoroughly implement the important instruction spirit of the practice on the construction of production workers, skill power and safety production, and solidly do a good job in the 23rd national "safety production Month" activities, Xinhui employees are guided to actively tree safety development concept, and constantly improve safety awareness and safety skills. Xinhui Company held the "Xinhui Chemical 2024 Safety Skills PK Competition" on the afternoon of June 29. The safety skills competition has further enhanced the safety awareness of all staff and created a good safety production atmosphere. Through the form of the competition, it also inspires the enthusiasm and enthusiasm of employees to learn safety knowledge. Looking forward to the future, we will continue to strengthen the publicity and training of safety production work and promote the in-depth development of the company's safety production work. Jointly create a safe and harmonious working environment, and contribute safety forces to the high-quality development of enterprises

The flexible packaging two-component polyurethane laminating adhesive consists of a main agent and a curing agent. Precise ratio matching is the foundation for the normal cross-linking and stable formation of the adhesive layer. In production, imbalanced ratios are common latent problems. Even a slight deviation from the standard ratio can lead to a series of lamination quality defects, and most of these defects will only be exposed after curing or during the storage period of the finished product, resulting in extremely high rework costs.    When the curing agent is in excess, there are too many free isocyanate groups inside the adhesive layer. The excess components cannot participate in the cross-linking reaction and will easily absorb water vapor from the air and continue to react, resulting in the laminated film turning white, bubbling, and the surface becoming sticky. At the same time, it will aggravate the problem of residual solvents and unpleasant odors, seriously affecting the safety of food packaging. Long-term storage will also cause the adhesive layer to become brittle and the peel strength to decrease.   Insufficient curing agent is more common. The hydroxyl groups in the main agent cannot fully cross-link, resulting in insufficient cross-linking density of the adhesive layer, and forming a soft bond. The finished product shows poor adhesion, significant reduction in water boiling resistance and low-temperature resistance, and is prone to delamination when bent or pulled during packaging, failing to meet the end-user standards.    The deviation in proportion is mainly caused by calibration errors of the mixing equipment, mistakes in manual weighing, residual substances in the pipelines, etc. During production, it is necessary to regularly calibrate the automatic mixing machine, standardize the manual proportioning process, remove residual glue, eliminate uneven mixing, strictly control the proportioning error range, and ensure the stable cross-linking effect of polyurethane glue and the quality stability of laminated products from the source.  

The aging resistance of the flexible packaging polyurethane laminating adhesive directly determines the long-term storage stability of the composite packaging. During the storage, transportation and end-use processes of flexible packaging, it will continuously be exposed to light, high temperature, oxygen, moisture and oil erosion. If the adhesive has insufficient aging resistance, problems such as yellowing, delamination, blistering, and attenuation of peel strength due to aging failure are likely to occur.    The aging of polyurethane adhesive essentially involves the degradation of molecular chains and oxidative breakage. In a common polyurethane system, ester bonds and amide bonds are subject to long-term exposure to ultraviolet rays and thermal oxidation, resulting in chain segment breakage, a decrease in crosslink density, and gradual brittleness and softening of the adhesive layer. At the same time, hydrolytic aging gradually damages the bonding interface, significantly reducing the bonding force between the film and the aluminum foil, leading to premature failure of the packaging.  Highly resistant to aging polyurethane adhesives mostly adopt modified weather-resistant formulations. By introducing hydrolysis-resistant and ultraviolet-resistant molecular structures, they enhance the antioxidant and anti-hydrolysis capabilities of the adhesive layer, effectively slowing down the aging rate of the adhesive layer. These adhesives are particularly suitable for scenarios such as long-term storage of leisure foods, outer membranes of daily chemicals, and outdoor light-avoidance packaging.   The production end can also improve the aging resistance performance through process optimization. By strictly controlling the uniformity of coating amount, ensuring adequate curing and cross-linking, reducing workshop humidity and residual moisture, and minimizing post-hydrolysis risks, the adhesives can significantly extend the service life of flexible packaging and improve the stability of product shelf life quality. The stable cross-linking structure combined with high-quality weather-resistant formulations can significantly prolong the service life of flexible packaging and enhance the stability of product shelf life quality.  

Bubbles are a common appearance defect in the production of solvent-free polyurethane adhesive lamination. They can directly cause problems such as voids in the laminated film, decreased peel strength, and uneven light transmission, seriously affecting the qualification rate of flexible packaging products. Unlike solvent-based adhesives, the solvent-free system has no solvent evaporation channels. Once bubbles form, they are difficult to eliminate on their own, so the early process control is particularly crucial.    The primary cause of bubble formation is the air intake during the mixing process. The viscosity of solvent-free two-component adhesives is relatively high. If the mixing speed is too fast or the mixing method is improper, a large amount of air will be entrained into the adhesive liquid. Changing the adhesive bucket, air entering the supply pipeline, and loose pump body seal can also lead to adhesive bubbles, resulting in dense point-like bubbles after coating. Secondly, high humidity in the workshop is the main cause. The isocyanate groups react with water to produce carbon dioxide, which causes the adhesive layer to bubble and turn white.  Incompatibility of process parameters can also cause problems. If the coating temperature is too low, the glue will have poor fluidity and weak defoaming ability, and tiny bubbles will not be able to escape. Insufficient lamination pressure and uneven contact of the pressure rollers will prevent the air between the film layers from being completely expelled, resulting in bubble defects.    Actual production rectification requires a multi-pronged approach, including low-speed and uniform stirring, static defoaming followed by coating, and sealing of the supply system. The temperature and humidity in the workshop should be strictly controlled, avoiding production in high-humidity environments. Reasonably increasing the coating temperature and optimizing the compounding pressure can completely solve the problem of bubbles in solvent-free adhesive lamination, ensuring the flatness and transparency of the lamiantion film.

Solvent residue is a key indicator for the quality inspection of food flexible packaging, directly affecting the safety of the packaging and the odor quality. The solvent-based flexible packaging polyurethane laminating adhesive uses ethyl acetate as the diluent. If the drying and  coating processes are not properly controlled, the residual solvents will remain inside the adhesive layer, causing packaging odors, contaminating the contents, and even triggering food safety inspection non-compliance issues. The main cause of excessive solvent residue lies in the drying process. Insufficient temperature, low wind speed, and excessive film movement in the drying tunnel of the composite production line can prevent the complete  evaporation of solvents in the adhesive layer. The surface adhesive liquid quickly forms a crust, sealing the internal solvents and resulting in hidden residue. At the same time, excessive coating amount and overly thick adhesive layer will significantly increase the difficulty of solvent evaporation, exacerbating the residue problem. The ratio of glue and the quality of raw materials also affect the residual amount. Excessive addition of curing agent, unqualified purity of diluent, presence of impurities such as fusel alcohol and moisture, will reduce the efficiency of solvent evaporation and delay the drying speed of the glue layer. In addition, if the humidity in the workshop is too high and water vapor mixes into the glue layer, it will inhibit the evaporation of the solvent and aggravate the accumulation of residues.  In production control, by using methods such as staged temperature increase in the drying tunnel, matching appropriate machine speed, strictly controlling the coating dryness, and using high-purity solvents, residual substances can be effectively reduced. Additionally, during the curing stage, maintaining a constant temperature can facilitate the secondary evaporation of trace residual solvents, ensuring that the solvent residues in the finished products meet national standards and food packaging safety requirements.

Peeling and insufficient peeling force are the most common quality problems in the production of flexibe packaging lamination. Most of these issues are closely related to the selection of polyurethane laminating adhesives, coating processes, and substrate conditions. The polyurethane laminating adhesives used in flexible packaging rely on cross-linking bonding to achieve the composite of multiple layers of films. Any improper control at any stage will lead to defects such as delamination, blistering, and peeling during the storage or use of the finished products.    The failure of the substrate surface treatment is the primary cause. The surface tension of polyolefin substrates such as PE and PP is relatively low. If the corona treatment fails or there are residual oil stains and dust on the surface, the polyurethane adhesive cannot form an effective anchoring bond, and the substrate is prone to overall delamination in the later stage. Secondly, the imbalance in the adhesive ratio and uneven mixing of the adhesive will result in incomplete reaction between the resin and the curing agent, insufficient internal cohesion of the adhesive layer, and the occurrence of pseudo-adhesion.  Environmental and process factors are equally crucial. If the humidity in the production workshop is too high, the moisture will consume the curing agent and damage the cross-linking structure. If the curing temperature is too low or the time is insufficient, the adhesive layer cannot form a dense network structure, and the resistance to media and aging performance will significantly decrease. In addition, if the coating thickness is too thin, it will result in insufficient bonding points; if it is too thick, it is prone to internal curing lag, causing local delamination.    To solve this problem, it is necessary to implement control from the source. Regularly test the surface tension of the substrate, strictly follow the standard for glue ratio, control the coating amount and curing parameters, maintain a constant temperature and humidity production environment in the workshop, which can effectively prevent the occurrence of composite delamination defects and stabilize the quality of product lamination.

The steaming and boiling type polyurethane laminating adhesive is a special lamination raw material for high-temperature sterilization food packaging. Relying on the high-crosslinking polyester molecular structure, it can withstand boiling and steaming processes at temperatures above 121℃, and is widely used in the lamination of packaging bags for meat marinated products, pre-prepared foods, and high-temperature sterilization snacks.    This type of adhesive is made by combining high-functional polyester polyol with water-resistant curing agent. The crosslinking density is much higher than that of ordinary dry lamination adhesives. The cured adhesive layer is dense and stable, with strong ability to prevent water vapor and oil from penetrating. After steaming, it will not experience delamination, white spots, or aluminum loss, etc. For high-barrier steaming film structures such as NY/AL/CPP, PET/AL/PE, the bonding is durable and stable, and the attenuation of peel strength is extremely small.  During the production and usage stage, there are strict process requirements. The ratio error of the two-component mixture needs to be controlled within a very narrow range. The shelf life after mixing the glue is relatively short, and it should be prepared as needed to avoid waste due to premature gelation of the glue solution. The coating amount should be moderate. If the coating is too thin, it will not be sufficient for boiling treatment. If the coating is too thick, the curing process will be slow and it is prone to residual odors. It is recommended to maintain a constant temperature and humidity in the curing environment. Only after full cross-linking can it proceed to the boiling test process.    The drawback of this type of product lies in its high cost and poor adaptability to low-temperature freezing. It is only specifically used for high-temperature sterilization packaging. Currently, the industry is constantly improving and modifying the formula to balance the resistance to steaming and the low-temperature toughness, thereby expanding the application scope of integrated packaging for pre-prepared dishes and frozen cooked foods.  

Water-based flexible packaging polyurethane laminating adhesive is an environmentally friendly adhesive that uses water as the dispersion medium and does not contain organic solvents. It is a core green material that replaces traditional solvent-based adhesives. Compared with solvent-free and solvent-based polyurethane adhesives, the greatest advantage of this product is its low VOC content and no risk of flammability or explosion. It completely solves the safety and environmental protection problems in flexible packaging production, and is suitable for strict food packaging safety production standards.    This adhesive system has excellent stability and good coating fluidity. It is compatible with ordinary dry lamination equipment and does not require significant modification of the production line. The enterprise's renovation cost is low. After curing, the adhesive layer has high transparency, does not affect the color effect of the printed film, has excellent yellowing resistance performance, and is not prone to yellowing or fogging problems during long-term storage. It is particularly suitable for high-transparency food, daily chemical, and exquisite flexible packaging.  In terms of performance, water-based polyurethane laminating adhesive has wide adaptability to substrates such as plastic films, paper, and aluminum-coated films, with uniform and gentle adhesion. The laminated film has good flexibility and is less likely to crack or curl. However, its shortcomings are also quite obvious. The curing speed is slow, and the water resistance is relatively weak. It is prone to reduced adhesion in high-humidity environments, and it is not suitable for packaging products that undergo high-temperature boiling.    With the continuous tightening of environmental protection policies, water-based polyurethane laminating adhesives have seen a continuous increase in their penetration rate in the ordinary flexible packaging sector where the load is low and the temperature is normal. They have become the preferred adhesive material for small and medium-sized packaging enterprises in their green production upgrades.

Solvent-free polyurethane laminating adhesives are the core material for the green upgrade of flexible packaging. They eliminate the use of large amounts of organic solvents in traditional solvent-based adhesives, meeting the dual development requirements of environmental protection and safe production in the packaging industry. They have now been widely applied in the production of snack, frozen food, and seasoning composite films.    The traditional solvent-based glue production process releases VOCs, requires a large amount of waste gas treatment equipment, increases the operating costs of the factory, and the residual solvents pose safety risks to food packaging. The solvent-free system does not contain organic solvents such as ethyl acetate, and the lamination processing has no volatile waste gas. The production environment in the workshop is clean, the investment in waste gas treatment is significantly reduced, the residual solvent content in the finished products is far below the national standard limit, and it is suitable for high-end food and infant supplementary food packaging.  From the perspective of processing performance, the solvent-free two-component polyurethane adhesive does not require drying in an oven. The lamination production line eliminates long sections of drying equipment, significantly reducing equipment energy consumption. At the same time, the production speed can be steadily increased, effectively enhancing the factory's production capacity. After curing, the adhesive has excellent internal cohesion strength, firmly adhering to VMPET and aluminum foil barrier substrates. The laminated product is resistant to boiling water and oil penetration.    This laminating adhesive also has usage thresholds. The ratio of the two components and the coating temperature need to be precisely controlled. An imbalance in the ratio may lead to incomplete curing and insufficient peel strength. Currently, the industry is continuously improving the formula and simplifying the operation process. Solvent-free polyurethane laminating adhesives are gradually becoming the mainstream choice for flexible packaging laminating.  

Flexible packaging polyurethane laminating adhesives are the core auxiliary materials for the production of flexible laminated packaging in industries such as food, cosmetics, and medicine. With excellent adhesion, flexibility, and weather resistance, they have become the preferred adhesive products for laminating various substrates such as films, aluminum foil, and paper. In the industry, based on the raw material structure and system characteristics, they are mainly divided into two mainstream categories: polyester type and polyether type. The performance of these two types is significantly different, and they are suitable for different production scenarios.    Polyester-based polyurethane laminating adhesives are the most widely used. Their molecular chains contain polar ester groups, and the intermolecular forces are strong. They have excellent adhesion to polar substrates such as PET, nylon, and aluminum foil. This type of adhesive has high bonding strength, good heat resistance, outstanding resistance to boiling and aging, and can meet the production requirements for high-temperature sterilization and water-boiling packaging. It is widely used in laminated packaging for high-temperature food. However, it has relatively weak low-temperature toughness and is prone to brittleness in long-term low-temperature environments.  The polyether-based polyurethane laminating adhesive is mainly composed of ether bond structures. Its molecular chain has extremely strong flexibility and excellent low-temperature adaptability. It can maintain stable bonding performance in extremely low temperatures and is not prone to cracking or delamination. At the same time, it has outstanding hydrolysis resistance and is suitable for use in high-humidity and high-humidity environments. It is commonly used in the production of frozen food and fresh flexible packaging. However, its bonding strength and heat resistance are slightly inferior to those of the polyester type, and it is not suitable for high-temperature processing conditions.    Currently, the industry typically selects equipment based on the requirements of the packaging terminals. For high-end laminated packaging, two systems are often combined to balance both high and low temperature performance as well as bonding stability, thus meeting the diverse production needs of flexible packaging.

Polyurethane laminating adhesives are the core material in the production of flexible packaging lamination. Temperature, as a crucial environmental and process parameter, directly affects the curing reaction of the adhesives, the coating effect, and the quality of the laminated products. It is an important factor in controlling the yield rate of flexible packaging production.    Excessive low temperature will significantly inhibit the molecular movement of the adhesive, slow down the cross-linking reaction between isocyanate and hydroxyl groups, and cause a substantial decrease in the curing rate. In a low-temperature environment, the adhesive does not cure completely, the initial adhesion force is weak, the curing period is significantly prolonged, and it is very likely to cause the delamination and debonding of the flexible packaging lamination film. At the same time, the residual active groups will also cause the failure of subsequent bonding and seriously affect the stability of the product.  Excessive temperature can also have negative effects. High temperature can cause the adhesive to cure too quickly, resulting in uneven coating, blistering of the adhesive layer, and formation of a crust. This disrupts the uniformity of the adhesive layer. At the same time, rapid curing causes the adhesive layer to generate internal stress. Coupled with the difference in thermal expansion and contraction coefficients between the film and the adhesive layer, the finished product becomes brittle, the peel strength decreases, and the release agent in the film is more likely to be released, further reducing the quality of the lamination.    In industrial production, the flexible packaging polyurethane laminating adhesive needs to be compatible with a reasonable temperature range. The conventional curing temperature is generally 40–50℃. Precise control of the temperature parameters can ensure that the adhesive fully cross-links, stabilize the bonding strength, avoid defects such as delamination and brittleness, and is a key process point for ensuring the quality of flexible packaging products.  

Polyurethane laminating adhesives are the core materials in the production of flexible packaging lamination. Their bonding strength, curing effect, and product stability are influenced by multiple factors, directly determining the lamination quality and service life of flexible packaging products. The key influencing factors mainly lie in the formulation, environment, substrate, and construction process.    The formulation ratio of the adhesive itself is the fundamental key. The ratio of the main agent to the curing agent in the two-component polyurethane laminating adhesive, as well as the NCO content, directly affect the effect of the cross-linking reaction. An imbalanced ratio will lead to incomplete curing and a decrease in adhesion force. At the same time, the viscosity and solid content of the adhesive determine the uniformity of coating. An excessively high viscosity is prone to cause uneven coating, while an excessively low viscosity will result in insufficient coating volume, thereby affecting the firmness of the lamination.    The environmental temperature and humidity have a significant impact on the curing process. The curing of polyurethane relies on the cross-linking reaction of isocyanates. In a high-humidity environment, the moisture in the air will react with the curing agent, consuming the effective components and causing problems such as bubbles, whitening, and re-adhesion, which will damage the stability of the composite layer. Low temperatures will significantly slow down the curing rate and prolong the curing time; high temperatures will shorten the opening time of the glue and cause coating defects.  The condition of the base material and the construction process are equally crucial. If the surface energy of the base material such as films and aluminized films is insufficient, or if dust and oil stains are adhered to the surface, it will reduce the wetting property and adhesion of the glue, and pre-treatment with corona discharge and plasma can effectively improve the bonding effect. In addition, improper process parameters such as coating thickness, compounding speed, and curing conditions can cause uneven bonding, delamination and detachment, significantly reducing the quality of the finished flexible packaging products.

In the production of flexible packaging lamination, most people focus on the coating amount, ratio and initial adhesion effect of polyurethane laminating adhesives, but often overlook the core role of the curing process. In fact, the curing of flexible packaging polyurethane laminating adhesives is a crucial step that determines the quality of the laminating products, and directly affects the performance and service life of the packaging.    The curing process of polyurethane laminating adhesives is essentially a molecular cross-linking reaction. Only when the adhesives are fully cured can they transform from a soft adhesive state to a high-strength gel layer, forming a stable bonding structure. The cured gel layer has excellent peel strength, heat resistance, and chemical resistance, which can effectively prevent problems such as delamination, blistering, and debonding in flexible packaging. It is suitable for sealing and preservation requirements of food and daily chemical packaging. If the curing is not thorough, the molecular cross-linking of the gel layer is incomplete. Even if the initial bonding is good, it is prone to be affected by temperature and humidity in the future, resulting in a decrease in bonding force.  The curing effect is restricted by three factors: temperature, time, and environmental humidity. If the temperature is too low or the curing time is insufficient, the reaction will not be complete; if the humidity is too high, it will damage the cross-linking structure of the adhesive layer and cause defects such as whitening and brittleness. In production, it is necessary to strictly control the curing temperature and the aging duration to meet the lamination requirements of different material films.    In summary, curing is the final critical process for shaping the bonding performance of polyurethane laminating adhesives. Only by attaching importance to the control of the curing process and making precise adjustments to the production parameters can the performance of the adhesives be maximized, ensuring the stable quality and improved qualification rate of flexible packaging products.

Flexible packaging polyurethane laminating adhesives are the core materials for the lamination of food, daily chemical, and pharmaceutical flexible packaging. Their aging resistance directly determines the service life and safety of the packaging products, and is also a key indicator for evaluating the bonding quality. In general, high-quality two-component polyurethane flexible packaging adhesives possess excellent comprehensive aging resistance and can be adapted to most normal temperature, conventional storage, and mild outdoor usage scenarios.  The aging resistance of this type of adhesive is mainly reflected in aspects such as heat resistance, resistance to high and low temperatures, and weather resistance. The dense and cross-linked structure formed after curing has strong stability. Under normal conditions, it can withstand temperature fluctuations and moisture erosion. Long-term use is unlikely to cause problems such as delamination, cracking, or debonding. High-quality products can undergo aging tests for more than 8,000 hours, meeting the long-term storage requirements for packaging. At the same time, it has excellent low-temperature toughness and will not harden and crack due to low temperatures. It is suitable for cold chain transportation scenarios.    However, its aging resistance has some shortcomings. Under long-term exposure to strong ultraviolet rays, high temperature and high humidity conditions, the polyurethane molecular chains are prone to degradation, resulting in aging phenomena such as yellowing of the adhesive layer and decreased bonding strength. In addition, inferior single-component adhesive has a faster aging rate due to insufficient crosslinking degree. By optimizing the raw material ratio, adding weather-resistant additives, and improving the curing process, the anti-aging ability can be significantly enhanced, further meeting the usage requirements of complex working conditions for flexible packaging.  

Flexible packaging polyurethane laminating adhesives are the core materials for film laminating and flexible packaging production. The bonding effect directly affects the sealing, durability and safety of the packaging products. To avoid problems such as delamination, blistering and poor curing, and to ensure production quality and construction safety, the following five key points need to be paid special attention to when using them.  1. Strictly control the mixing ratio. This adhesive is mostly two-component, and the main agent and curing agent must be mixed in the standard proportion. It is strictly forbidden to increase or decrease the dosage at will. After mixing, fully stir for 10-15 minutes, let it stand to eliminate bubbles, and then use. An imbalanced ratio or uneven stirring will result in incomplete gelation of the adhesive and a decrease in bonding strength. 2. Do a good job in surface treatment of the substrate. Before bonding, thoroughly clean the dust, oil stains, and moisture on the surface of the film, aluminum foil, etc., to ensure the substrate is dry and clean. Impurities on the substrate will block the bonding of the adhesive, easily causing quality defects such as glue spots and delamination after bonding. 3. Strictly control the construction temperature and humidity environment. The suitable construction temperature is 5-35℃. High humidity in the environment will cause the adhesive to absorb water and deteriorate, affecting the curing effect. At the same time, avoid direct blowing of the air onto the adhesive surface to prevent rapid formation of a crust on the surface of the glue and reduce the bonding performance. 4. Follow the construction time specification. The mixed glue has a fixed applicable period. It should be prepared in small amounts and used as soon as possible to avoid the increase of glue viscosity and failure due to long-term storage. After bonding, it is necessary to control the temperature and humidity for curing according to the standard to ensure the stability of bonding. 5. Standardize storage and safe operation. The glue should be stored in a cool, dry, and shaded place away from fire sources, heat sources, and acid and alkali chemicals. The remaining glue should be sealed and stored, marked with usage information, and prevent the mixing of deteriorated glue. At the same time, take proper construction protection measures to ensure operational safety.  

Flexible packaging polyurethane laminating adhesives are the core materials for the composite processing of packaging in industries such as food, cosmetics, and medicine. With excellent comprehensive performance, they have become the mainstream bonding materials in the soft packaging industry. Their core features include six prominent aspects.  1. The bonding strength is high and the stability is good. It can firmly adhere to various flexible packaging substrates such as plastics and aluminum foil. The initial adhesion is strong and the final bonding is long-lasting. The composite product is not prone to delamination or blistering. 2. Excellent temperature resistance. It can be adapted to scenarios of low-temperature refrigeration and high-temperature sterilization. The adhesive layer does not soften or crack, and it is suitable for various cold and hot processing techniques. 3. Outstanding resistance to media. It can withstand erosion from substances such as acids, alkalis, oils, and moisture. It is suitable for special packaging scenarios such as sauces, cooked foods, and oily foods. 4. Excellent flexibility. After curing, the adhesive layer has excellent elasticity. It can follow the bending and stretching of flexible packaging, meet the usage requirements of packaging transportation, folding, and compression, and is not prone to cracking or falling off. 5. Wide process compatibility. It covers various types such as solvent-based, solvent-free, and water-based. The coating is uniform and the leveling is good. It is suitable for high-speed composite production lines and has high production efficiency. 6. Green, safe and environmentally friendly. Compliant products have no harmful substances such as benzene, and low VOC emissions. They comply with food contact safety standards, are non-toxic and odorless, meet the requirements of green packaging development, and are applicable to various food and daily product packaging.  

The composite strength is the core indicator for evaluating the bonding performance of flexible packaging polyurethane laminating adhesives. It directly determines the inter-layer stability of the composite film and is the key to preventing packaging problems such as delamination, glue separation, and bulging. It is widely used in the production of flexible packaging in fields such as food, cosmetics, and medicine. The industry usually uses the T-type peel strength as the testing standard. The peel strength of qualified products should be no less than 100 N/m to ensure the usability and storage reliability of the packaging.    The adhesive formula is the key internal factor influencing the strength of the composite. Polyurethane laminating adhesives consist of a main agent and a curing agent. The ratio of NCO (nitrile carbon-oxygen) groups to OH (hydroxyl) groups is crucial. The optimal industrial ratio range is 1.05:1 to 1.2:1. An imbalanced ratio will result in insufficient cross-linking reaction, decreased cohesion within the adhesive layer, directly reducing the composite strength, and may also cause abnormal curing, boiling delamination and other problems. At the same time, the molecular weight of the polyol and the structure of the resin will also affect the toughness and adhesion of the adhesive layer, determining the peel resistance and tensile strength of the composite film.  The production process and the environment are the key external factors. Insufficient surface tension of the substrate and failure to perform corona treatment will weaken the adhesion of the adhesive layer.Uneven coating thickness and inappropriate curing temperature and time will result in incomplete cross-linking and curing. In addition, the humidity in the workshop has a significant impact. In a high-humidity environment, water molecules will consume the active groups of the curing agent, destroying the network structure of the adhesive layer, causing the adhesive layer to become brittle and significantly reducing the composite strength.    In actual production, it is necessary to precisely control the ratio of the adhesive solution, optimize the coating and curing process, strictly control the temperature and humidity in the workshop, and cooperate with the activation treatment of the substrate surface. This will fully release the adhesive's bonding performance, stably enhance the bonding strength of the composite, and ensure the quality of the flexible packaging products.

The flexible packaging polyurethane laminating adhesive, with its strong bonding strength, excellent flexibility, and excellent heat resistance and weather resistance, is widely used in the laminating process of food and daily necessities flexible packaging. The proper usage techniques are crucial for preventing problems such as delamination, blistering, and wrinkling, and ensuring the quality of the packaging.    Base material pre-treatment is the foundation for a strong bond. Before the operation, it is necessary to thoroughly clean the dust, oil stains and moisture on the surface of the film, aluminum foil and other base materials, keeping the surface clean and dry. At the same time, the operation needs to be adjusted according to the characteristics of the base material. For soft films, they should be gently flattened to avoid stretching deformation, ensuring that the bonding surface is flat and free of defects, and creating conditions for the uniform adhesion of the glue.  Precise glue dispensing and uniform coating are the core steps. For two-component adhesive, it is necessary to strictly follow the standard ratio for mixing, accurately weigh the ingredients, and thoroughly stir to avoid any deviation in the ratio that could lead to failure of curing or reduced adhesion. During coating, control the thickness of the glue layer to be uniform, avoiding uneven thickness that may cause local bubbling or detachment. Adapt the coating to the production line speed to ensure a continuous and stable coating process.    Controlling the fixed temperature and humidity levels and the details of the curing process is of utmost importance. The working environment must be maintained at a constant temperature and humidity, with a suitable temperature and constant humidity. The environment should be dry, moist, well-ventilated and stable. After the adhesive layer is laminated, it needs to be dried according to the process requirements, allowing the solvents to completely evaporate, and then rolled up and left to stand still. The finished product needs to be left to cure for a sufficient period to achieve complete solidification. During this process, it is necessary to avoid squeezing and bending to maximize the peel strength and stability of the laminated film and extend the service life of the flexible packaging.

The coating amount is the core parameter in the laminating adhesive compounding process of flexible packaging. It directly determines the bonding strength, appearance quality and durability of the packaged products, and is a key link in improving the quality and reducing the consumption of flexible packaging production. In the industry, the dry basis coating amount is used as the unified measurement standard. The setting of the coating amount is not a fixed value. It needs to be precisely adjusted according to the type of substrate, packaging purpose and post-processing technology to meet the requirements of different production scenarios.    Conventional flexible packaging has clear classification standards for coating amounts. Ordinary transparent lightweight packaging does not have special process requirements and can meet basic bonding needs with a relatively low coating amount. For multi-color printing films, aluminum-coated films, etc., in composite scenarios, due to the poor surface flatness of the substrate, the coating amount needs to be appropriately increased to avoid delamination and false adhesion problems. For special packaging such as boiling and high-temperature steaming, as well as packaging for corrosive contents, a higher coating amount is required to fully ensure the performance of the composite structure in withstanding high temperatures and chemical erosion.  The precise control of the coating amount is of vital importance for product quality. Insufficient coating will result in incomplete coverage of the adhesive layer, problems such as composite bubbles, low peel strength, and failure of heat sealing, and the finished product is prone to delamination and damage. On the other hand, excessive coating will not only cause waste of adhesive, increase production costs, but also lead to accumulation of the adhesive layer, uneven winding, and easy occurrence of warping and stickiness after curing, which will affect the appearance and usage experience of the packaging.    In actual production, it is necessary to precisely control the coating amount through the selection of network roller types and the adjustment of equipment speed. At the same time, it is necessary to dynamically adjust according to the characteristics of the substrate and the purpose of the finished product. Under the premise of ensuring the quality of the composite, energy conservation and consumption reduction can be achieved, and the overall qualification rate and stability of flexible packaging products can be improved.

The volatility of flexible packaging polyurethane laminating adhesives is a key indicator that affects the quality, production safety, and environmental compliance of packaging products. It is mainly manifested as the release of volatile organic compounds (VOCs) during the production curing process, directly impacting the safety of food packaging and the production environment in the workshop. Currently, the mainstream adhesives in the industry are divided into solvent-based, water-based, and solvent-free categories, with significant differences in volatility.    Traditional solvent-based polyurethane laminating adhesives use organic solvents such as ethyl acetate as the carrier, and they have extremely strong volatility. During the coating and curing processes, the organic solvents will rapidly evaporate. If the ventilation is insufficient, it will easily cause the accumulation of waste gas in the workshop, posing potential safety hazards. At the same time, incomplete evaporation will lead to excessive solvent residues, causing packaging odors, film blistering, and decreased bonding strength, which does not meet the safety standards for food packaging.  Water-based polyurethane laminating adhesive uses water as the dispersion medium and contains almost no organic solvents. The volatility is significantly reduced, resulting in low VOC emissions, mild odor, and higher safety. However, its volatility is greatly affected by temperature and humidity. High temperatures accelerate the evaporation of water, which may cause the adhesive layer to form a crust. Low temperatures and high humidity will delay the evaporation, thereby affecting the compounding efficiency.   The solvent-free polyurethane laminating adhesive has a solid content close to 100%, with no solvent evaporation and no residues. It is a low-volatile green product. With the tightening of environmental protection policies, the industry is vigorously promoting this type of product, strictly controlling the evaporation of free monomers and meeting the production needs of high-end flexible packaging. Controlling the volatility of adhesive and choosing low-volatile products has become an inevitable trend for the green development of the flexible packaging industry.