Causes and Solutions of Wrinkles and Stripes in BOPP Film

The biaxially stretched BOPP film was trimmed, thickness measured, corona treated (or not used), and then taken into the coil. In order to meet the requirements of wide-width high-speed production and automatic roll change, BOPP take-up equipment adopts double-position winder, and the winding method adopts active roll-up by the center, and is equipped with tension and pressure automatic control system. The quality of windings directly affects the finished product yield, second-class product rate, and final profit. In most BOPP production lines, wrinkles and streaks are often encountered and difficult to resolve. For this reason, this paper focuses on the analysis of the causes of wrinkles, streaks, and the introduction of control methods.

Effect of winding tension on wrinkles and stripes and solutions

The winding tension is essentially the elastic elongation of the film caused by the increase of the winding speed. Only by maintaining proper tension, the film can be curled flatly. Improper tension control is the main reason for wrinkles and fringes. Conversely, controlling tension is also the main method to solve wrinkles and streaks. In the tension control parameters, factors such as size, slope, etc., must be controlled not only for each factor but also for the synergistic effect between each other.

1.1 The effect of tension and its solution

The setting of the tension size directly affects the quality of the film roll winding. The larger the tension setting, the more uneven the horizontal distribution and the poorer the flatness of the film. The air entrained by a certain part of the film roll is less likely to be discharged, resulting in wrinkles. The chance of streak defects is greater; the tension setting is too small, the film roll is easy to wrinkle when the film is wound, the film roll hardness is loose, and when the film is cut, the core of the film roll roll is easy to remove the core and it is difficult to wind the film. The BOPP film continues to crystallize after crimping and shrinks. As the diameter of the film roll increases, the longitudinal shrinkage increases as the length of each roll increases. If the film is wound at a constant tension during production, it will cause the film roll to loosen and loosen. A large number of films at the core produce wrinkles and streaks (especially the heaviest O-4000m). Table 1, Table 2 is the actual production of 22μm shrink film tension (roll core 0-4000m tension) size - wrinkles, stripes of rice (same temperature).

Table 1 Effect of Tensile Strength on Film Thickness Wrinkles and Stripes Tension Setting Value (N/m) 70-80 100-110 120-130 140-150 160-170
No. 1 film wrinkle and stripe length, m 1500 1200 800 200 1200
No. 2 film wrinkles and stripe length, m 1500 700 200 1000 1500

Table 1 (different film types) indicates that a certain range of tension should be used when producing films of the same type; different ranges of tension should be used when producing different types of films; Table 2 indicates that constant tension cannot be used in production. The increase in the diameter of the film roll diameter gradually decreases, in order to ensure that the film roll has a shrink space, the hardness of the inner tight external loose.

Table 2 Effect of tension on the wrinkles and fringes of the film after correction The number of film rolls, m 0-4000 4000-8000 8000-12000 12000-16000
Tension setting, N/m 120-130 120-130 120-130 120-130
Wrinkles and stripes length, m 2500 1500 1000 500
Corrected tension setting, N/m 120-130 110-100 100-110 100-110
Corrected wrinkles and streaks length, m 200 180 150 100

1.2 The influence of the office slope and its solution

Under the same conditions, the smaller the slope of the tension curve, the slower the attenuation of tension, the more pronounced the wrinkles and stripes caused by the tension, and the slope can not be too large, otherwise it will easily cause the film roll core string edge, so that the roll core film is crumpled In addition, the hardness of the film roll is loose and unfavorable for the large slitting. The tension curve is shown in the figure below.

1.3 Effect of Formula and Solution

Due to different formulations, the friction coefficient of the film surface is different, the greater the friction coefficient, the more serious electrostatic, resulting in deterioration of the film flatness, resulting in increased opportunities for wrinkles, streaks, and the size of the tension should be properly adjusted when changing the formula. The approximate adjustment is as follows: The double-slip mask tension value is set a little larger; the single-slip mask grease friction coefficient is greater the tension set value is smaller. In addition, different surface heat-seal materials and different additives are used to adjust tension setting values ​​accordingly.

Winding pressure effects on wrinkles and stripes and solutions

The winding pressure is essentially to exclude the air entrained during the winding process, so that the film layer and the layer maintain an appropriate space, so that the shrinkage margin exists when the film is aged. Improper pressure control is also a major cause of wrinkles and stripes. Conversely, controlling pressure is also the main method to solve wrinkles and streaks. In the pressure control parameters, factors such as size, slope, etc., are required to control not only each factor but also the synergistic effect between each other.

2.1 The effect of pressure and its solution

In general, the film is easily entrained in the air during the winding process. If too much air is entrained, the large film roll shrinks due to the subsequent crystallization of the film during the aging treatment, so that the entrained excess air cannot be discharged, and the film roll will be presented. More wrinkles and streaks. Therefore, it is important to set the pressure. The pressure setting is too large, although it helps to eliminate air during winding, the possibility of wrinkle and streaking defects is reduced; but the pressure is too high, the film may stick together, which is not conducive to large slitting; when the pressure is set too low, the film is rolled Large amount of air into the film rolls easily and vertical stripes. Thus, a specific pressure is used for producing each film, and the pressure can be appropriately adjusted according to the hardness of the film roll. Its specific situation is shown in Table 3.

Table 3 Effect of pressure size on film wrinkles and streaks Film roll diameter, mm 200 400 600 800
Pressure 1 setting, N/m 80 78 76 74
Wrinkles and stripes length, m 200 160 100 50
Pressure 2 setting, N/m 50 48 46 44
Wrinkles and stripes length, m 1000 600 600 400
Pressure 2 setting, N/m 60 58 56 54
Wrinkles and stripes length, m 250 200 150 100

2.2 Influence of pressure gradient and solution

Under the same conditions, the smaller the slope of the pressure curve, the slower the pressure decay, the greater the pressure on the film roll, the smaller the space between the film layer and the layer, the more easily the films stick together, which is not conducive to slitting: the more inclined the pressure curve Larger, the smaller the pressure on the film roll, the more difficult it is to discharge the air inside the film roll, and the wrinkles and streaks are more likely to be formed on the film. For this reason, in the production of different films, different, suitable pressure curves are required.

Effect of Production Temperature on Wrinkles, Stripes and Solutions

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

Table 4 Effect of Air Temperature on Film Wrinkles and Fringes Temperature, °C 20-22 24-26 28-30 36-38
The original tension setting, N/m 120-130 120-130 120-130 120-130
Original pressure setting, N/m 60 60 60 60
Original wrinkles and stripe length, m 2500 2000 1500 2800
Corrected tension setting, N/m 150-160 130-140 120-128 80-90
Revised pressure setting, N/m 66 64 60 56
Revised wrinkles and stripe length, m 380 320 250 400

The effect of cumulative thickness on wrinkles, fringes, and solutions usually results in poor film thickness at the time of starting or converting, localized unevenness, and poor flatness, making the large film roll inexhaustible during aging, resulting in more wrinkles. Stripe defects, for which it is necessary to optimize the film thickness from time to time in production.

Effect of production rate on wrinkles, striations, and solutions Generally, the slower the production rate under the same winding tension and pressure conditions, the harder the film roll hardness, and the longer the length of wrinkles and stripes. See Table 5 for details.

Table 5 Effect of Production Rate on Wrinkles and Stripes Production Rate, kg/h 540 690 780 830
Wrinkles and stripes length, m 2000 1000 500 100

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

Other influencing factors

Film thickness, setting of traction attenuation coefficient, matching condition of each traction roller speed, surface smoothness of the traction roller, parallelism of the expanding wheel, flattening effect, whether the winding roller is deformed, or the like.

Other influencing factors

From the above discussion, we can see that wrinkles and streaks are affected by factors such as tension, pressure, formula, cumulative thickness, and production rate, and all factors are mutually restrictive. In production, conditions must be met according to actual conditions.

Wang Sheng
(Zhanjiang Packaging Materials Enterprise Co., Ltd.)

Reprinted from: Guangdong Packaging