Analysis of Factors Affecting Peel Strength of Extrusion Composite Films
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The extrusion compounding process has many advantages such as low investment, low cost, high production efficiency, and easy operation. Therefore, it occupies a very important position in the composite processing of plastic film. However, in actual production, it is inevitable that such problems will occur. In this paper, we take the most common peel strength difference as an example to discuss and discuss with you.
First, the effect of film substrate on peel strength
1. The effect of the surface treatment effect of the substrate on the peel strength. The coated substrate should be pre-corona treated, and the surface tension after corona treatment should be above 40 dynes, which can improve the adhesion of the substrate to the melt-extruded resin, thereby improving the extrusion composite strength. Therefore, it is necessary to check whether the surface tension of the substrate meets the requirements before production. Once the surface tension is too low, the substrate should be replaced immediately or the substrate should be resurfaced. In addition, the surface tension of the surface-treated film should be uniform, otherwise it will have a certain influence on the peel strength, resulting in uneven peeling strength and inconsistency.
2. The effect of substrate surface cleanliness on peel strength. The surface of the coated substrate should be clean and clean, free from dust and oil. If the surface of the substrate is not clean and adheres to dirt, grease and other contaminants, it will directly affect the adhesion of the molten resin to the surface of the plastic film. Thereby, the bonding strength of the extruded composite film is lowered.
3. The influence of other factors. For some moisture absorbing film materials (such as nylon film), if moisture absorption has occurred, it will also affect the bonding fastness of the extruded composite film. Therefore, the moisture-absorbing film material must be protected from moisture. The nylon film should be wrapped with aluminum foil before use and after use.
Second, the effect of ink on peel strength
1. The effect of ink quality on peel strength.
In the actual production process, sometimes there is a phenomenon that the peeling strength of the parts without ink or ink is good, and the adhesion fastness of the parts with more ink or ink is rather poor, which is because the printing ink used is suitable. Poor properties, poor adhesion between the ink and the substrate, resulting in poor peel strength of the extruded composite film. Once this happens, the appropriate ink should be replaced in time and contact with the ink manufacturer to negotiate and research solutions.
2. The effect of ink drying on peel strength. If the ink is poorly dried, especially when a large amount of solvent such as toluene or butanol is used in the ink, and the temperature of the drying oven is set.
If not, a small amount or a large amount of solvent remains in the ink layer, which may cause delamination of the composite film and deteriorate the peel strength. Therefore, the drying performance of the ink must be strictly controlled during the printing process to ensure that the ink can be sufficiently dried.
In addition, control of process conditions such as printing speed and drying temperature should be taken into account during the printing process, as they also have a certain effect on the volatilization rate of the solvent in the ink. If the printing speed is fast and the temperature of the drying oven of the printing press is relatively low, the solvent in the ink may not be completely evaporated, and the residual solvent will form some small bubbles on the film, so that the bonding fastness of the composite film is lowered. . In general, when setting the temperature of the drying oven, it is necessary to comprehensively consider factors such as the printing speed, the drying speed of the ink, the type of the substrate material, and the size of the printed image.
Third, the effect of extrusion compound resin on peel strength
1. Effect of resin type on peel strength. The extrusion coating composite resin may be polyethylene, polypropylene, EVA, Surlyn, Nucler, Bynel, EVAL, EAA, EMAM or the like. The purpose of extrusion coating is different, and the resin chosen is different. For example, for general-purpose composite plastic bag making, various heat-sealing resins with better heat-sealing properties can be used; for sandwich-extrusion resin, both the same layer and the inner seal layer plastic layer are required to be good. For compatibility, various compatibilizer resins such as Surlyn, Nucle, and Bynelr may be selected depending on the surface layer and the inner sealing layer material. If the resin is improperly selected, it will affect its compatibility with the coated substrate, thus affecting the extrusion composite strength.
2. Effect of resin melt index (MI) on peel strength. Melt index (MI) refers to the weight value of the resin melt passing through a standard capillary at 10 ° min under a certain temperature and a certain pressure, expressed in grams / 10 min. The melt index (MI) is an index of the fluidity of the resin. Generally, the higher the melt index (MI) of the resin, the better the fluidity, and the lower the viscosity of the molten film, the greater the adhesion. In the extrusion compounding process, it is not preferable to use a resin having a too small melt index (MI). If the melt index (MI) of the resin is small and its molecular weight is large, the fusion property is relatively poor, and it cannot be well bonded to the substrate to be coated, so that the peeling fastness is lowered. For example, when extrusion bonding is carried out using LDPE resin, an LDPE resin having a melt index (MI) of 4 to 7 g/1Omin is generally used.
3. Effect of resin density on peel strength. The smaller the density of the resin, the higher the content of the branch, the easier the surface is activated, the greater the adhesion, and the better the improvement of the peel strength.
4. The effect of additives and moisture content in the resin on the peel strength. The additives in the resin, especially the lubricant, have a great influence on the peel strength of the extruded composite film. For example, when using LDPE resin for extrusion compounding, an extrusion coating grade containing no or little lubricant should be used. Resin particles, such as 1C7A from Beijing Yanshan Petrochemical Company and 1C8A from Shanghai Jinshan Petrochemical Company. In addition, if the amount of moisture contained in the resin is relatively large, plasticization may occur during the extrusion compounding process, thereby affecting the peel strength of the composite film.
Fourth, the effect of extrusion compounding process on peel strength
1. The effect of extruder temperature on peel strength. The control of extruder barrel temperature and T-die temperature is extremely important and is the key and core of the extrusion compounding process. The temperature is too low, the resin is poorly plasticized, and it is not well mixed with the substrate when it is cast from the die, so that the peeling fastness is lowered; the temperature is high, the melting of the molten film is more sufficient, and the surface generates polar molecules to the substrate. The greater the affinity, the higher the peel strength. However, the temperature should not be too high, otherwise the resin will be easily decomposed, and it may burn the substrate, and it will also generate smoke and pollute the working environment. In general, the temperature of the extruder barrel is usually controlled between 150 ° C and 340 ° C, and the temperature of the T mold is usually controlled at about 310 ° C - 340 ° C, depending on the extrusion of the composite equipment and the resin used. Set the details.
2. Effect of resin temperature on peel strength. The high temperature of the resin facilitates the wetting and penetration of the molten plastic film on the coated substrate, thereby facilitating the improvement of the composite strength, but too high causes decomposition, generally not exceeding 350 °C. If the temperature at which the resin and the substrate are pressed is too low and the surface of the resin is insufficiently oxidized, the resin temperature should be appropriately increased.
3. The effect of air gap on peel strength. The air gap is the distance from the extrusion die to the composite cooling steel roll, the contact line of the pressure roll. Due to the existence of the air gap, the surface of the hot melt film will be oxidized with oxygen in the air, and the peeling fastness of the oxidized hot melt film when being coated with the plastic film will be greatly improved. The size of the air gap also has a great influence on the extrusion peel strength. The air gap is too small, the surface of the resin is not sufficiently oxidized, resulting in poor extrusion strength. The air gap is large, and the hot melt film is in contact with air for a long time. The degree to which the surface of the membrane is oxidized by oxygen in the air is more severe. Increasing the polarity gene, the greater the adhesion of the resin to the surface of the substrate, which is beneficial to the improvement of the composite strength. However, if the air gap is too large, the heat loss of the hot melt film is too large, the temperature is lowered too much, and the temperature at the time of recombination is too low, which in turn causes a decrease in peel strength, and the heat sealability also deteriorates. Therefore, the size of the air gap should be adjusted according to the actual situation when extrusion compounding. Generally, the air gap is controlled between 50mm and 100mm.
4. The effect of composite pressure on peel strength. The composite pressure is small, and the adhesion between the molten resin and the substrate is not tight, and the peeling fastness is lowered. However, the composite pressure is not too great, otherwise the substrate is easily deformed by compression.
5. The effect of the surface temperature of the cooled steel roll on the peel strength. The cooling roller adopts a steel roller with a surface chrome plating, which functions to remove the heat of the molten resin film, so that the bonded composite film is immediately cooled and solidified to form a strong cohesive force, so that the molten film is coated. The substrate is firmly adhered and shaped, and no relative displacement is generated, thereby ensuring good peel strength. Therefore, the temperature of the surface of the cooled steel roll has a certain influence on the peel strength of the extruded composite film. If the surface temperature of the cooling steel roll is too high, the cooling setting effect is not good, and the extrusion composite film may be wrinkled, so that the composite fastness is lowered; but if the surface temperature of the cooling steel roll is too low and the cooling rate is too fast, It also causes a decrease in the composite strength. In general, the surface temperature of the chill roll is controlled to be optimal around 30'C. Moreover, the surface of the chill roll must be smooth, and the surface temperature distribution should be uniform, so as to ensure the uniform cooling effect of the extruded composite film, thereby ensuring the consistency of the bonding fastness and the peel strength.
6. The influence of the surface state of the silicone rubber pressure roller on the peel strength. The function of the silicone rubber pressure roller is to press the substrate and the molten resin film to the cooling roller with a certain pressure, and the substrate and the molten film are pressed and bonded, and cooled and solidified. The silicone rubber pressure roller is made by coating 20-25mm thick silicone rubber on the outer surface of the steel roller. The hardness of the silicone rubber is generally 80-85 Shore hardness, and the surface of the silicone rubber pressure roller The hardness should be uniform, so as to ensure that the overall pressure is kept uniform and uniform, so as to ensure uniform and constant peeling fastness of the extruded composite product.
7. The effect of composite line speed on peel strength. In the case of a certain amount of extrusion, that is, the speed of the extrusion main motor does not change, the faster the composite line speed, the thinner the composite layer, the temperature of the hot melt film will decrease, and the heat on the coated substrate will decrease. The drilling force of the molten resin is lowered, which in turn causes a decrease in peel strength. Conversely, the composite line speed is reduced, the thickness of the composite layer is increased, and the composite strength is also increased, but it affects the production speed. Therefore, in the production process, it is necessary to control the appropriate production speed according to the actual situation, not only to ensure the production schedule, but also to ensure the extrusion peel strength and composite quality.
8. The effect of the thickness of the extrusion coating on the peel strength. In extrusion compounding, the extruded molten film mainly acts as a thermal bond. If the thickness of the extrusion coating layer is too thin, the heat and strength are insufficient, and the peel strength is lowered. Generally, the thickness of the coating layer is required. Controlled above 18-20μm.
9. The effect of winding tension on the peel strength. The winding tension can be appropriately larger, that is to say, the winding should be wound as much as possible, so as to avoid the decrease of the bonding fastness caused by the wrinkling and delamination of the composite film. Since they are compounded together during winding, the two materials do not immediately produce strong adhesion, and the composite fastness is not so good. When the winding tension is properly increased, the winding is smooth and compact, and it is not easy to produce. Shrinkage, after cooling and setting, the composite fastness will be better.
10. The influence of equipment tooling on peel strength.
In daily production, attention should also be paid to the maintenance and maintenance of the tooling equipment to ensure that the equipment is in good operating condition. This is the basic condition for ensuring the smooth progress of the extrusion compound production. Always check the surface of the silicone rubber press roller for any abnormal phenomena such as scribes, pits, and bumps that affect normal production. Once it is found, it should be repaired or replaced in time. In addition, we must also pay attention to keep the cleaning of each tooling clean, remove dust, sundries or oil stains adhering to the surface in time, and always check the surface of the silicone rubber pressure roller for any scribes, pits and bumps that affect normal production. Abnormal phenomena such as injury, so as not to affect the peel strength of the composite product.
5. Primer (AC system)
Effect on Peel Strength During the extrusion compounding process, in order to enhance the viscosity, the primer may be applied to the substrate, and then compounded with a resin such as polyethylene or polypropylene. After the primer is applied, the thermal bond fastness between the extruded hot melt resin and the coated substrate can be greatly improved, thereby improving the peel strength of the extruded composite film.
1, the correct choice of primer (AC agent). There are many types and grades of extrusion primers, which can be roughly divided into two types: water-based and solvent-based. The aqueous type primer has a polyethyleneimine primer, and the solvent-based primer has a primer primer, an isocyanate primer, and the like. The aqueous type primer is generally used for a material which does not contain water and has a low composite strength, and the solvent type primer is generally used for a material having a large moisture content and a high composite strength. Therefore, the appropriate primer should be selected according to the actual situation to ensure the quality of the extruded composite product.
2. The influence of the coating amount and coating condition of the primer on the peel strength. In addition to the correct choice of primer, the viscosity of the primer must be properly adjusted to ensure good wetting of the substrate to be coated, to provide a proper coating weight, and to ensure adequate peel strength. Generally, the amount of the primer applied is between 0.1 and 0.5 g/m2 (dry solids). In addition, it is necessary to ensure the uniformity of the coating of the primer, and to ensure uniformity of the bonding force between the molten resin and the substrate to be coated, so that the peeling strength of the extruded composite film is kept constant.
3. The effect of the quality of the primer on the peel strength. The primer also has a certain storage and use period. If the primer has exceeded the service life or has deteriorated within the service life, it will inevitably affect its function and affect the peel strength of the extruded composite film. .
4. The effect of the dry state of the primer on the peel strength. If the undercoating agent is insufficiently dried, a part of the solvent or water remains, thereby affecting the adhesion fastness of the extruded composite film, resulting in a decrease in peel strength. Therefore, when it is found that the primer is poorly dried, the speed of the compounding line should be appropriately lowered, and at the same time, the drying temperature and the amount of ventilation can be increased to ensure that the primer can be sufficiently dried.
6. Environmental sanitation in the workshop
The effect on the peeling strength The environmental sanitation in the workshop also has a certain influence on the quality of the extruded composite products. If the environmental sanitation is relatively poor, there are a lot of dust, impurities and other particles in the air, and these particles will adsorb to the surface of the substrate, or Falling on the cooling steel roll, the silicone rubber press roll, and each of the guide rolls, etc., all of which affect the closeness of the molten resin film to the substrate during the compounding, so that the composite film is contaminated with foreign matter and affects the peel strength of the composite film. Therefore, we must pay attention to keep the environment in the workshop clean and hygienic.
Seven, the conclusion
In the previous section, we briefly analyzed and introduced some of the main influencing factors of the peeling strength of the extruded composite film. In view of the above situation, we should also pay attention to the following matters in actual production:
1. Strengthen the quality inspection of various raw and auxiliary materials (including film, ink, resin, primer, etc.), strictly control, and lay the foundation for improving the quality of composite film.
2. According to the nature of the package contents and the quality requirements of the composite film, select the appropriate primer to control the coating amount and drying temperature, so that the primer can be fully dried to ensure the composite quality.
3. In actual production, the extrusion process parameters should be adjusted and controlled according to the specific conditions of resin, substrate and equipment to ensure the product quality of the composite film. Before extrusion compounding, it is necessary to fully understand and master the properties and main indicators of the resin used, and adjust the production process and temperature based on this, especially to strictly control the extrusion temperature of each working section of the extruder. To ensure uniform plasticization of the resin, quantitative extrusion from the machine head, and good adhesion to the substrate.
4. Pay attention to the maintenance and maintenance of equipment and tooling, ensure the continuity and regularity of the production process, reduce the incidence of failures, improve product quality, and ensure high quality, high yield and low consumption.
5.pay attention to maintain the environmental sanitation in the warehouse and workshop, to ensure clean and clean, and should have good ventilation conditions, to avoid the impact of foreign matter such as dust, sand and other impurities on the composite process and composite strength.