Analysis of Factors Affecting Adhesive Peel Strength
1. Effect of substrate surface tension
Because the surface tension of the polyurethane adhesive is about 40 dyne, the surface of the adhered substrate must reach about 40 dyne, so that there is a prerequisite for bonding. If the substrate to be adhered is metal, it is a high-energy surface in terms of its material quality, but its cleanliness and oxidation must be taken into account. The penetration of the adhesive to its surface should be kept close to zero, that is, it should not be fully wetted.
If the substrate to be bonded is a plastic film, then the corona treatment effect is very important, especially for some materials that are structurally low surface energy, such as PE, PP, etc., must have sufficient surface activation to make It becomes a high surface energy surface that can be used for compounding.
2. The influence of the chemical structure of the substrate
1 Macromolecule plastic film, in terms of its macromolecular structure, has polarity and non-polarity. Polyester and nylon are polar molecules, and PE and PP are non-polar molecules. Polyurethane adhesive belongs to polar molecules. Because of its good wettability with materials for polar molecular structures. Of course, the wetting of materials with non-polar molecular structures is not good. If wet non-polar molecular adhesives are used, the wettability is improved, but the adhesive force is mainly dependent on the intermolecular dispersion. The dipolar orientation of the polar molecules, as well as the hydrogen bonding forces between the polar groups, does not exist, and as a result, the adhesion is greatly reduced. In order to obtain a high-strength bonding effect, it is necessary to treat non-polar molecular materials on the surface to have polar groups, increase the surface polarity, and increase the surface tension. A polar adhesive is used for bonding. The highly polar molecules have a high cohesive energy and a large intermolecular force, and they have a strong adhesive strength to polar adherends, for example, a polyester type has a greater adhesive strength than a polyether type polyurethane.
2 Migration and Bonding Pressure: Many high polymer materials contain various plasticizers, antioxidants, slip agents, antistatic agents, and the like. These auxiliaries are easily migrated from the inside of the polymer. The small molecule auxiliaries migrated out and accumulate at the interface will affect the bonding strength between the adhesive and the adhered material. When a certain pressure is applied to the adhesive surface during bonding, the adhesive can more easily fill the pits on the surface of the adherend, increasing the contact surface and peeling strength. When the viscosity of the adhesive is small, pressurization causes the adhesive to flow excessively, resulting in a lack of adhesive. Less pressure should be applied or after the viscosity rises, pressure can be applied to higher viscosity or solid adhesives. The ultimate goal is to increase the peel strength of the composite structure.
3. The influence of the weak interface layer
The weak interface layer is due to the substrate, adhesive and low molecular weight substances or various impurities in the environment through the dialysis, adsorption on the interface to produce a dense layer, affecting the mutual contact between the adhesive substrate, and their adsorption of the substrate The force is greater than the adhesive force of the adhesive, forming an adsorption layer of low molecular weight at the interface, adsorbing the molecules of the adhesive and greatly reducing the adhesive force. Some failed bonding in the production practice is caused thereby. .
Therefore, we now particularly emphasize that manufacturers must conduct serious tests on the purchase of raw materials and comply with national or international standards. In the actual processing should be more appropriate. Pay attention to the control of the production process. Effectively monitor the product to prevent problems during use.
4. The amount of glue applied
The amount of glue used to determine the thickness of the adhesive layer, the key is to ensure uniform coating, no bubbles and no defects. If the adhesive layer is too thin, the adhesive cannot fill holes in the surface of the material, and voids occur, the peel strength cannot be guaranteed naturally. The depth, shape, and actual working concentration of the gluing screen roller determine the amount of glue applied. If the roller is squeegee, the angle of the blade will also affect the amount of glue. Instead of the squeegee transferring the glue, the pressure of the sizing roller directly affects the sizing amount. Therefore, if you want to obtain products with high strength and apparent quality, you should do a good job from all aspects.
5. Influence of temperature and humidity
This is a more general concept. There are two aspects: “The binder in high temperature will degrade to a certain extent, and the adhesive performance will be reduced. Higher temperatures will also cause the film layer to deform and reduce the cohesive energy. The temperature will make the adhesive further cross-linked, so that the migration and volatilization components will escape, will change the performance of the adhesive.Hydricity is too high, some polymer materials, especially polyurethane adhesives containing ester bonds in the humidity environment Hydrolysis will lose strength and hardness, so the actual glue has certain limitations on the temperature, which requires the flexible packaging manufacturers to strictly carry out the process operation.In this regard, it is obvious that the glue is cooked at high temperature, such as delamination after cooking. , ink transfer and other quality phenomena; the actual operating environment temperature and humidity effects, two-component adhesive operation generally require ambient temperature at 21-23 °C, relative humidity at 40%, too high temperature and humidity will affect the product quality Humidity is easy to form a layer of water vapor on the surface of the product, affecting the bond strength and affecting the peel strength.Especially, now the rainy season is approaching, flexible packaging companies should note that Glue seal, a solvent storage, in order to prevent the ingress of moisture because the moisture is too large, the curing agent consume a certain impact strength.
6. Effect of two-component polyurethane glue coating process
Talking about process problems is more complicated. This is also a general concept. Different composite structures should have different process control issues. This requires us to have rich practical experience. Mainly on the process of temperature control, the choice of network roller and the amount of glue control, material compatibility. The temperature control includes composite temperature and aging temperature. Cable roller selection includes how much and depth of cable. General composite light packaging OPP/PE, OPP/CPP, PET/CPP, PET/VMPE/PE structure, glue control can be 2 to 2.5; if compound cooking packaging structure: PET/AL/NY/CPP PET/AL/CPP, etc., require a gluing amount of 4.5-5.5 grams, which is also the key to ensure peel strength. The compatibility issues on the material include: ink, glue, materials, solvents and other aspects. If you use a high-temperature cooking bag, the problem of using table printing inks or peeling strengths that are not resistant to high temperatures cannot be discussed. Therefore, this fully demonstrates that the deeper issues such as technology and awareness now appear to be very important.
In the actual use of the two-component adhesive, attention must be paid to the link problem in order to achieve a good composite effect, and the experience of the peel strength must be well summarized in practical work.
(author/Chen Quandong)
Flexible Packaging Weekly
Ningbo XISXI E-commerce Co., Ltd , https://www.petspetskitty.com