First, the purpose and significance of large film roll slitting
The slitting process is a very important process. It is a special process connected between the film manufacturer and the downstream printing compound company. Its role is: according to the user's requirements, the large film roll is slit into the precise specifications required by the customer for customers' use .
When slitting and unwinding, the quality of the entire large film roll can be re-checked, and some defects of the large film roll, such as light wrinkles, can be corrected by using the jitter during the slitting of the large film roll. It can also make the slit roll film obtain a good winding state, so that the flatness of the end face meets the printing requirements.
In the national standard GB / T10004--2008, the requirements for the surface roughness of the film roll are not greater than 3mm, and some films have higher requirements for the surface roughness of the slit end surface, which is generally not greater than 2mm.
Second, the reasons affecting the unevenness of the slitting end face
The flatness of the film roll end surface is a very important indicator of film appearance quality. It can affect the stability of the product quality in printing and compounding processes, such as: overprint accuracy, misalignment, and sticky edges.
The reasons for the unevenness of the end face of the slit film roll are:
1. The effect of the quality of the large film roll itself
The quality of large film rolls is inferior, such as large thickness tolerances, cramps, and severe soft wrinkles in the longitudinal direction. Even after slitting and rewinding, satisfactory apparent quality cannot be obtained. Slicing can only improve local problems but not all problems. In order to obtain a good product appearance, on the one hand, appropriate adjustments are made in the slitting process operation. On the other hand, large film rolls must be required to improve their product quality. Demanded film rolls.
2. Impact of the cutting process operation process
Different types of slitting machines, different types of films, and composite films with different material combinations have different methods, methods, and values for setting the slitting process parameters. The performance of the device itself and the intrinsic properties of the film both slit and wind the film Quality has a great impact, so it is not possible to use one process parameter to process all slit film rolls.
The slitting speed and the intrinsic properties of the film, such as the smoothness of the film surface and the large thickness tolerance, etc., have an impact on the regularity of the slitting end face. Rewinding too tightly will also cause the film roll to slide laterally and affect the rewinding of the end face. Too loose will cause air to wind up and cause the end face to be misaligned.
3, the impact of paper tube quality
The quality of the paper core directly affects the quality of the slitting. The straightness, concentricity, strength, and surface finish of the paper core are very important. The wider the paper core, the more difficult it is to ensure straightness and concentricity. The straightness of the core should be within 0.004%, and the surface roughness of the paper core should be less than 0.2um. If the paper core width is more than 1.8m, it is necessary to strengthen the inspection. The paper core must not have any dents or breakage. Otherwise, the unwinding tension will fluctuate due to the quality of the paper tube, which will affect the uniformity of the slitting end surface winding. .
4. The influence of mechanical factors of slitting equipment
Some film rolls have very strict requirements on the uniformity of the end surface. Concave and convex surfaces exceeding 1.5 mm are judged to be unqualified. In addition to the reasons for the large film and slitting process and the quality of the paper tube, it also has a lot to do with the slitting equipment and machinery.
Slitting machine is a device that requires high precision in the operation of the equipment. After a period of operation, the accuracy of some parts has been reduced or damaged, the operation of the equipment is unstable, and the rewinding causes slippage or acceleration and deceleration. The parallelism between the rollers of the rewinding part of the slitting equipment and the level between the equipment and the ground should meet the assembly requirements. The parallelism between the rollers is also one of the key to ensure the uniformity of the slitting end surface. Check and maintain the equipment regularly.
Rewinding gap, tension, to maintain relative coordination, unwinding and rewinding tension is uneven, the gap between the rewinding function and the rewinding tension is inconsistent, it is easy to produce endless rewinding phenomenon. Adjusting the angle between the film and the pressure roller, and reducing the entry of air to reduce the sliding between the films have a great effect on improving the regularity of the end surface. If the rewinding tension is too large, the horizontal tension of the flattening roller is not enough, and it is easy to cause uneven end surface rewinding. If the tension is too small, the rewinding is too loose, and the end surface rewinding unevenness may occur. Therefore, in the slitting process, different diameters of the roll film need to adjust different tension. This is very important to ensure the uniformity of the end face of the roll film.
The winding pressure and speed must be consistent. By adjusting the winding pressure and speed, the end face of the film roll is not uniform. Generally speaking, under high-speed cutting, the longitudinal wrinkle streaks and end layer misalignment are most likely to occur. The cutting speed should be Controlled within a reasonable range.
5.The irregularity of the cut end face caused by large static electricity increases
Generally, when the surface resistance of the object is greater than 1015 ohms, it is an insulator and does not have antistatic ability. The static electricity accumulation during the film itself and high-speed operation will cause adhesion or drift between the films, resulting in uneven end faces. When the factor of static electricity accumulation during long-distance transportation is not taken into consideration, the surface resistance of the ex-factory film should be below 1013.
At the same time, the workshop environment, climate, management methods, workers' psychological quality, and work mood will also affect the quality of the cut products.
3. Appearance requirements when selecting film rolls
When purchasing film rolls, in addition to confirming the external label specifications production date and shelf life, the following points should be paid attention to:
1.In terms of food safety and hygiene standards, each roll of film is not allowed to have any odor, even the "resin smell" often emphasized by film manufacturers is not allowed, because these odors will seriously affect the taste guarantee of the contents of the packaging bag .
2.The surface of the film roll is not allowed to have severe streaks, and it is also not allowed to have violent tendons and soft wrinkles, because this is a reflection of the accumulation of uneven thickness of the film.It will produce uneven cutting end faces, overprinting, compound misalignment, There are air bubbles or missing coating.
3. The surface of the film roll is also not allowed to have crystal points, black points, bubbles, dirty points, oil stains, etc. that have an impact on the quality of the downstream products. These will affect the appearance quality and composite quality of downstream products.
4. The film roll is not allowed to have internal looseness and external tightness, and it is not allowed to insert newspapers due to the thickness of the material during cutting to achieve a flat surface. The star-shaped wrinkles on the end face caused by internal looseness and external tightness are also not allowed. The reasons for this are due to improper control of the tension attenuation amount during slitting, and improper control of the tension attenuation pressure change or uneven film thickness, bending of the paper core, and contact rollers. Pressure imbalance.
1.Set reasonable process parameters
When cutting with different materials and different composite structures, the setting of process parameters is different, which must be taken seriously by various companies. First of all, it is necessary to understand the basic parameters and characteristics of the slitting material, and secondly, to understand the function of the slitting sliding platform. The sliding platform not only supports the feed roller, but also can perform left-right swing positioning, which is the core part of the unwinding device. Therefore, the sliding platform is required to be flexible, otherwise the slitted roll film will not be cut flat, and the end surface with jagged shapes is prone to film breakage.
2.Selection of slitting blades
The blade should be selected according to the thickness of the slit film and the structure of the rewinding. Generally, double-blades can be used for slitting materials and rewinding structural film thicknesses below 70um, because double-sided blades are relatively soft and suitable for slitting thinner materials. For films over 70um, single-sided blades can be used. The single-sided blades are thicker and more rigid. In the case of high-speed cutting, hard blades are not easy to be displaced. The blades should be placed at 45 °. The angle is large, and the blade gap cannot be fully utilized. If the angle is small, the incomplete cutting is easy to produce burrs.
If a slitter with a 5mm pitch groove is used, the blade should be installed in the middle of the groove when tightening the blade and tightened to prevent the blade from moving during high speed operation. Once the blade and the edge of the groove contact each other, friction occurs during the high-speed operation of the film to generate thermal energy. For a long time, it will cause the surrounding film to soften and heat up, and it will easily cause mutual soft overlap at the end surface, and the film will break during use. .
The irregularity of the end face of the slit film roll must not be too large, and no scratches, adhesions, burrs, or fractures are allowed at the end face.Due to the secondary tear strength in BOPP, BOPA, BOPET and other biaxially stretched films Low, a small gap under the effect of printing compound tension is very easy to tear, resulting in lateral fracture.
The appearance quality of the slit can be judged by seeing, touching and knocking:
Look --- whether the cutting end surface is flat, whether the surface is clean and free of impurities, no black spots, crystal points, colored water marks, etc., whether there are violent tendons, depressions and soft wrinkles.
Touch --- the hand senses the smooth, no burr, no tightness or 'big head and small tail' phenomenon.
Knock --- Tap the roll film by hand to check whether the roll film has the same hardness. If it is the same, the sound is basically the same. You can also use the hardness tester to measure the three points at the left, middle, and right, and then rotate 90 °. If the degree of difference is above 3 °, it means that the film roll is thick and thin.
The slitting process is a special process that carries on and off. Because of the quality of the film and the precision of the slitting equipment, the slitting process, and the operation level, controlling the uniformity of the slitting end face is more complicated. The factors that cause it should be comprehensively analyzed. Have a certain understanding of the performance of the slitting equipment and the characteristics of the slitting film material. The quality of the large film roll must be improved and controlled to continuously improve the psychological quality of the workers and the workers' ability to resist pressure. Cutting quality, cutting out good products for customer needs.