Analysis Of The Causes And Solutions Of Unevenness In The Slitting Process Of Large Film Rolls

Analysis of the Causes and Solutions of Unevenness in the Slitting Process of Large Film Rolls

I. Purpose and Significance of Slitting Large Film Rolls

The slitting process is a crucial step that serves as a link between film manufacturers and downstream printing and composite enterprises. Its role is to precisely cut large film rolls into the specified dimensions required by customers based on their needs.

During the slitting and unwinding process, the quality of the entire large film roll can be rechecked. By leveraging the jitter during slitting, certain defects in the large film roll, such as slight wrinkles, can be corrected. This process also ensures that the slitted film maintains a good winding state, meeting the flatness requirements for printing.

According to the GB/T10004-2008 standard, the requirement for the unevenness of the appearance end face of a film roll should be no more than 3mm. Some films may have even higher requirements, generally not exceeding 2mm.

II. Factors Affecting the Unevenness of the Slitting End Face

The flatness of the film roll end face is a critical indicator of the film's appearance quality. It can affect the stability of product quality in printing and composite processes, such as accurate overprinting, misalignment, and edge adhesion.

The main reasons for the unevenness of the slitting end face are as follows:

Impact of the Quality of the Large Film Roll Itself:

Poor quality of the large film roll, such as large thickness variations, wrinkles, and severe longitudinal soft wrinkles, even after slitting and rewinding, cannot achieve satisfactory visual quality. Slitting can address local issues but cannot change the overall problems. To obtain a good appearance, adjustments must be made in both the slitting process and the quality of the large film roll. Only when the quality of the large film roll meets the requirements can a visually satisfying film roll be obtained through slitting.

Influence of Slitting Process Operation Techniques:

Different types of slitting machines, film types, and combinations of composite films have different settings, methods, and values for slitting process parameters. The performance of the equipment and the intrinsic properties of the film have a significant impact on the quality of film slitting, and, therefore, a one-size-fits-all approach cannot be used for all film rolls.

Effect of the Quality of the Paper Core:

The quality of the paper core directly affects the slitting quality. Factors such as straightness, concentricity, strength, and surface smoothness of the paper core are crucial. Wide paper cores are more challenging to ensure straightness and concentricity. Good-quality paper cores should have a straightness within 0.004% and a surface roughness less than 0.2um. Paper cores with a width above 1.8m should undergo special inspections, and any dents or damage on the paper core are not allowed, as it could cause fluctuations in unwinding tension, affecting the evenness of the slitting end face.

Impact of Mechanical Factors of the Slitting Equipment:

Some film rolls have strict requirements for the evenness of the end face. Mechanical factors of the slitting equipment, such as the parallelism between the various rollers in the slitting section and the horizontal alignment between the equipment and the ground, are critical. Regular inspections and maintenance of the equipment are necessary to ensure proper functioning. Maintaining coordination between winding clearances and tension is crucial, as uneven tension during unwinding and winding can result in uneven end faces. Adjusting the angle between the film and the pressure roller and minimizing air entry can significantly improve the evenness of the end face. Different diameters of film rolls may require different tension adjustments during the slitting process.

Increased Unevenness Caused by Electrostatics:

When the surface resistance of an object exceeds 10^15 ohms, it is considered an insulator without anti-static capabilities. The film itself and static accumulation during high-speed operation can lead to film adhesion or drifting, resulting in uneven slitting end faces. The surface resistance of the film should ideally be below 10^13 to mitigate the effects of static electricity during long-distance transport.

Other Factors Affecting Appearance Quality:

Factors such as the workshop environment, climate, management methods, and workers' psychological qualities and emotions can also influence the quality of slitting products.

III. Appearance Requirements When Selecting Film Rolls

When purchasing film rolls, in addition to confirming external labels, specifications, production dates, and shelf life, attention should be focused on the following points regarding the appearance of film rolls:

Odor:

According to food safety and hygiene standards, film rolls should not have any odor, even the often-emphasized "resin smell." Such odors can significantly impact the taste protection of the packaged bag contents.

Surface Conditions:

The film roll's surface should not have severe streaks, wrinkles, or depressions. These issues indicate uneven thickness and can lead to uneven slitting end faces, inaccurate overprinting, misalignment in lamination, and coating with bubbles or missing areas.

Defects Affecting Downstream Products:

The film roll's surface should be free of crystal points, black spots, bubbles, dirt, oil stains, or any defects that could affect the appearance quality and lamination quality of downstream products.

Internal and External Tightness:

The film roll should not exhibit internal looseness and external tightness. Artificially inserting newspaper during slitting due to uneven material thickness is also not allowed. Star-shaped wrinkles caused by internal looseness and external tightness are also prohibited. These issues arise from improper tension attenuation control during slitting, inadequate control of pressure changes, uneven film thickness, bending of the paper core, and imbalanced contact roller pressure.

IV. Recommendations

Set Reasonable Process Parameters:

Different materials and composite structures require different slitting process parameter settings. Understanding the basic parameters and characteristics of the slitting material is crucial. Additionally, understanding the role of the sliding platform in slitting is important, as it supports the perforation roller and can be used for left and right swing positioning. Therefore, the sliding platform requires flexibility; otherwise, the slitted film may be uneven, with a jagged end face.

Choose the Right Slitting Blades:

Blades should be selected based on the thickness of the slitting film and the structure of the rewind. For materials with a film thickness below 70um and composite structures, double blades can be used. These blades are softer and suitable for slitting thinner materials. For film thicknesses above 70um, single blades with strong rigidity are preferred. When installing blades, they should be placed at a 45° angle. A larger angle may result in inefficient use of the blade, while a smaller angle may lead to incomplete slitting with jagged edges.