Causes and solutions of wrinkles and stripes in th

2022-09-23
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Causes and solutions of wrinkles and stripes in BOPP film

after biaxial stretching, BOPP film is subject to trimming, thickness measurement, corona treatment (or not), and then enters winding. In order to meet the requirements of wide width and high-speed production and automatic roll change, BOPP winder adopts duplex winder, the winder adopts central active winding, and is equipped with automatic tension and pressure control system. The quality of winding directly affects the yield, second-class yield and final profit of the film. In most BOPP production lines; Wrinkles and stripes are often encountered and difficult to solve. Therefore, this paper focuses on the causes of wrinkles and stripes and introduces the control methods

the effect of winding tension on wrinkles and stripes and its solutions

the essence of winding tension is the elastic elongation of the film caused by the increment of winding speed. Only by maintaining an appropriate tension, the film can be rolled flatly. Improper tension control is the main cause of wrinkles and stripes. On the contrary, good tension control is also the main way to solve the defects of wrinkles and stripes. In tension control parameters, size, slope and other factors are involved. We should not only control each factor, but also pay attention to the synergy between them

1.1 influence of tension size renewable plastic granulator equipment manufacturers encounter huge business opportunities. At present, the recycling rate of waste plastics in China is not high and the solutions are

the setting of tension size directly affects the quality of film winding. The larger the tension setting is, the more uneven the horizontal distribution is, the worse the film flatness is, the more difficult the air involved in a part of the film roll is to be discharged, and the greater the chance of wrinkles and stripes; The set value of tension is too small, the roll core of the film coil is easy to wrinkle during winding, and the hardness of the film coil is too loose. During large slitting, the roll core of the film coil is easy to lose its core and is difficult to roll. However, BOPP film still has the tendency of continuous crystallization and shrinkage after crimping, and the longitudinal shrinkage increases with the increase of the length of each coil with the increase of the coil diameter. If the film is reeled with constant tension in production, it will cause the film coil to be tight outside and loose inside, and a large number of films at the roll core of the film coil will produce wrinkles and stripe defects (especially the heaviest o-4000m). Table 1 and table 2 are actual production 22 μ M shrink film tension (roller core 0-4000m tension) - the number of meters of wrinkles and stripes (at the same temperature)

Table 1 Effect of tension on film thickness wrinkles and stripes

tension setting value (n/m)

length of No. 1 film wrinkles and stripes, m 1500 1200 800 200 1200

length of No. 2 film wrinkles and stripes, m 1500 700 200 1000 1500

Table 1 (different film models) shows that the tension within a specific range should be used when producing the same type of film; When producing different types of films, the tension in different ranges should be used; Table 2 shows that constant tension cannot be used in production, and the tension value should gradually decrease as the diameter of the film coil increases, so as to ensure that the film coil has contraction space and the hardness reaches internal tightness and external looseness

Table 2 Effect of tension size on film wrinkles and stripes after correction

film roll meter, m

tension setting, n/m

wrinkle and stripe length, m 2500 1500 1000 500

tension setting value after correction, n/m

wrinkle and stripe length after correction, m 200 180 150 100

1.2 influence and solution of tension gradient

under the same conditions, the smaller the gradient of tension curve, the slower the tension attenuation, The more obvious the wrinkles and stripes caused by high tension, and at the same time, the slope should not be too large, otherwise it is easy to cause the roll core to cross edge, so that the roll core film is wrinkled. In addition, the hardness of the roll is too loose to be conducive to large slitting, and its tension curve is shown in the figure below

1.3 influence of formula and solutions

due to different formulas, the friction coefficient of the film surface is different. The larger the friction coefficient is, the more serious the static electricity is, resulting in the poor flatness of the film, thus increasing the chances of wrinkles and stripes. Generally, when changing the formula, the tension should be adjusted appropriately. Roughly adjust as follows: set the tension value of double sliding facial mask a little higher; The single sliding surface, especially the load instigating mechanism, should avoid the entry of dust as much as possible. The dust cover should often cover the film. The larger the friction coefficient of grease, the smaller the set value of tension. In addition, the set value of tension should be adjusted accordingly for different surface heat sealing materials and additives

effect of winding pressure on wrinkles and stripes and solutions

the essence of winding pressure is to eliminate the multi gas involved in the winding process, so that the film layer and layer maintain appropriate space, so that there is shrinkage allowance during film aging treatment. Improper pressure control is also a main reason for wrinkles and stripes. On the contrary, controlling pressure well is also the main way to solve the defects of wrinkles and stripes. In the pressure control parameters, size, slope and other factors are involved. We should not only control each factor, but also pay attention to the synergy between them

2.1 influence of pressure and solutions

generally, the film is easy to be involved in the air during the winding process. If too much air is involved, the large film will shrink during the aging treatment due to the subsequent crystallization of the film, so that the involved excess air cannot be discharged, and the film will show more wrinkles and stripe defects. Therefore, it is very important to set the pressure. The pressure setting is too large, although it helps to eliminate air during winding, the possibility of wrinkles and stripes becomes smaller; However, if the pressure is too high, the films may stick together, which is not conducive to large slitting; If the pressure is set too small, the amount of air involved in the roll is large, and the roll is prone to loose and longitudinal stripes. Therefore, specific pressure should be used in the production of each film, and its pressure can be appropriately adjusted according to the hardness of the film roll. See Table 3 for details

Table 3 Effect of pressure on film wrinkles and stripes

roll diameter, mm 200400600800

set value of pressure 1, n/m 80787674

wrinkle and stripe length, m 20016010050

set value of pressure 2, n/m 50484644

wrinkle and stripe length, m 1000600600600 400

set value of pressure 2, n/m 60585654

wrinkle and stripe length, M 250 200 150 100

2.2 influence and solution of pressure gradient

under the same conditions, the smaller the gradient of pressure curve, the slower the pressure attenuation, the greater the pressure on the film roll, the smaller the space between the film layers, and the easier the film is to stick together, which is not conducive to slitting: the greater the gradient of pressure curve, the smaller the pressure on the film roll, the harder the air in the film roll is to be discharged, and the easier the film is to produce wrinkles and stripes. Therefore, different and appropriate pressure curves are needed to produce different films in production

influence of production temperature on wrinkles and stripes and solutions

climate change seriously affects the tightness of the film roll, which is directly related to the probability of wrinkles and stripes. Generally, when the temperature decreases, the tension and pressure should be increased to make the film roll harder; When the temperature rises, the tension and pressure are reduced, making the hardness of the roll loose. See Table 4 for its influence (roll core 0-4000m)

Table 4 Effect of air temperature on film wrinkles and stripes

temperature, ° C 20-22 24-26 28-30 36-38

original tension setting value, n/m 120-130 120-130 120-130 120-130

original pressure setting value, n/m 60 60 60 60

original wrinkles and stripes length, m 2500 2000 1500 2800

recently revised tension setting value, n/m 150-160 130-140 120-128 80-90

revised pressure setting value, N/Jinan gold testing machine is cheap m 66646056

the length of wrinkles and stripes after revision, m 380320250400

the influence of cumulative thickness on wrinkles and stripes and its solutions

generally, the film thickness is poor when starting up or changing production, and local parts are prone to uneven and poor flatness, which makes the large film roll unable to exhaust air during aging, resulting in more wrinkles and stripes defects, Therefore, the film thickness should be optimized from time to time in production

effect of production rate on wrinkles and stripes and solutions

generally, under the same winding tension and pressure, the slower the production rate is, the harder the roll hardness is, and the longer the wrinkles and stripes are produced. See Table 5 for details

Table 5 Effect of production rate on wrinkles and stripes

production rate, kg/h 540690780830

length of wrinkles and stripes, m 2000 1000 500 100

the above table shows that different production rates should adopt different winding tension and pressure; The lower the production rate, the lower the winding tension and pressure should be used

other influencing factors

film thickness, setting of traction attenuation coefficient, matching of speed of each traction roller, surface finish of traction roller, parallelism and flattening effect of expansion wheel, whether the winding roller is deformed, etc

other influencing factors

from the above discussion, it can be seen that wrinkles and stripe defects are affected by factors such as tension, pressure, formula, cumulative thickness, production rate and so on. All factors restrict each other, and the conditions should be adjusted according to the actual situation in production

Wang Sheng

(Zhanjiang Packaging Materials Enterprise Co., Ltd.)

reprinted from: Guangdong packaging

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