Understanding Back Slitting Process of Bopp Packaging Films

Understanding Back Slitting of Bopp Films

Biaxially oriented polypropylene (Bopp) films are widely used for packaging applications due to their strength, clarity, and versatility. As continuous sheets produced through extrusion and orientation processes, Bopp films need to be slit to customized widths to meet the specific requirements of end-use applications.

Back slitting is a common slitting method for Bopp films and other web materials such as paper, foil, and labels. It refers to slitting the material from the backside as it moves past the slitting device. Back slitting provides certain advantages over conventional slitting from the top side.

What is Back Slitting?

In back slitting, rotating slitters make incisions on the underside of the continuously moving Bopp film. The slitting blades are positioned underneath the web material, with their sharp edges making cross-direction cuts as the film passes over them. This effectively divides the wide parent roll into multiple narrow rolls or strips.

Back slitting machines hold the film web stable above one or more sets of circular slitter blades or knives mounted on rotating shafts. Precise control over slitter speed and position enables clean, accurate slits as per the required widths and spacings between slits.

Benefits of Back Slitting Bopp Films

Compared to overhead slitting, the underside slitting approach offers following benefits for Bopp film converters and end-users:

• Minimizes dust and debris generation
• Provides higher quality slit edges
• Easy and efficient finished roll handling
• Simple automation of the process
• Enables slitting fragile and delicate materials
• Allows easier removal of trim scrap

The underside position of the slitting station also gives better access for maintenance and blade changes. The simple web path reduces overall machine footprint.

Key Components of Back Slitting Machines

Bopp film back slitting equipment comprises following main components:

• Unwind unit - Holds large parent roll of Bopp film and controls its speed and tension
• Web guiding system - Uses sensors and automatic controls for centering and aligning the web
• Slitting station - Circular knife blades accurately slit film from underside
• Rewinding system - Winds slit strips smoothly and cleanly onto individual cores
• Control unit - Microprocessor based automated control for setting parameters and monitoring operations

Modern back slitting machines also include features like touchscreen HMI, predictive maintenance diagnostics, and remote connectivity. The latest IoT enabled systems can monitor key parameters in real-time and analyze historical data to optimize processes and productivity.

How Does Back Slitting Work?

The back slitting process involves following sequence of steps:

1. Large master roll of Bopp film is loaded on the unwind stand
2. Web guiding system aligns film and guides it towards the slitter
3. Circular blades slit film from below at high speeds
4. Slit strips proceed over support rollers to individual winding shafts
5. Automated rewinding of slit rolls onto cores
6. Continuous operation with automatic splicing new master rolls

Efficient systems maintain optimal web tension and alignment throughout the process. The rewind unit may include contactless winding to ensure perfect roll quality with zero scratches or debris. Some back slitters also have built-in inspection systems and automated rejection of defective portions.

Types of Back Slitting Machines

Based on design and slitting method, common types of Bopp film back slitters include:

Razor Slitters

Use ultra-sharp disposable blades for a single-pass cut. Low cost blades provide good initial cut quality. However, require frequent blade changes and closer operator supervision.

Shear Slitters

Rotating circular shear blades provide multiple shearing actions for a clean cut. Durable shear wheels provide longer life. Needs proper blade maintenance and sharpening cycles.

Score Slitters

Combination of oscillating score blade and shear circular blade allows depth-controlled weakening of film. Subsequent snapping produces a fuzz-free slit edge. Useful for films prone to edge unraveling.

Laser Slitters

Precise computer-controlled laser beams slice through Bopp films without contact. Achieves very fine and complex slitting patterns without wear or debris. High equipment cost but very low operating cost.

Importance of Quality Back Slitting

Back slitting is a critical intermediate process that impacts quality as well as productivity in Bopp film converting environments. Poor slitting can result in following defects:

• Variations in slit width
• Rough, uneven edges
• Fraying, unraveling
• Dimensional instability, curling
• Scratches, debris
• Telescoping of finished rolls

High performance back slitting machines can overcome these issues through precise process control and automation features. Some also include advanced vision inspection systems to detect defects and immediately initiate corrective actions minimizes wastage.

With growing demand for Bopp films across flexible packaging sector, reliable and efficient back slitting process is essential for meeting discerning customer requirements as well as staying competitive. Investing in reliable, high quality slitting systems is imperative for long-term success.

Future Evolution of Bopp Film Back Slitting

Back slitting technology continues to evolve with following emerging trends in Bopp film converting industry:

• Complete workflow automation from order entry to finished roll handling
• Improved operator safety mechanisms
• Increased standardization of components for reduced changeover times
• Roll-to-roll laser micro slitting capability
• Self-diagnostics and predictive maintenance through IoT integration
• Specialized slitters for newer variant films like Bopp digital lamination grade, super high barrier films etc.

With a sharper focus on quality, productivity and sustainability - smart back slitting solutions will be vital for future success of Bopp film converters.

FAQs

What is back slitting of Bopp films?

Back slitting refers to slitting Bopp films and other web materials like paper, foil, etc. from the underside as they move past rotating circular knife blades. It divides large parent rolls into multiple strips or narrow rolls by making incisions on the backside of the continuously running web.

Why choose back slitting over overhead slitting?

Key benefits of back slitting Bopp films include reduced dust/debris generation, superior slit quality, easy roll handling, simple automation, and better access for maintenance. It also allows slitting of delicate materials and easy removal of trim waste.

What are the main components of Bopp film back slitting machines?

Major components are unwinding system, web guiding system, underside slitting station with circular blades, automated rewinding system for slit rolls, and microprocessor control unit for setting parameters and monitoring the process.

How can quality issues be avoided in back slitting?

Investing in high performance back slitting machines with features like precision process control, automated inspection systems, and self-diagnostics can overcome defects related to slit quality, uneven edges, curling, telescoping, etc. Proper blade maintenance is also essential.