Things To Look for When Die Cutting Pressure-Sensitive Film

This article highlights a variety of dies available to you and the three things that will influence your ability to be successful when die cutting PSA materials.

Die cutting is a complicated and intricate process. Several variables must come together to produce a good-looking finished label. A rotary, flexible magnetic (mag), flatbed, or laser die, are all viable options for die cutting PSA materials. Choosing the right die depends on your specific needs.

Die Cutting Machine

The Choices:

Rotary Dies

Rotary dies are blades formed from a solid bar of steel. They can be coated through high-tech steel hardening processes, cryogenic treatments, and life-extending coatings to meet certain materials cutting requirements. The rotary dies can do one of two things: they can cut completely through the material and its corresponding release liner (called a metal-to-metal die-cut), or they can cut through the material and down to, but not through, the release liner. Examples include a kiss-cut or a butt-cut.

Magnetic Cylinders and Flexible Dies

Magnetic cylinders and flexible dies are cost-saving alternatives to the traditional solid rotary die. Similar to a steel die, a flexible magnetic die is formed by wrapping stainless steel around a magnetic cylinder. The main difference between a rotary die and a mag or flexible die is cost and durability.

Flatbed Dies

A flat bed die can be used on a roll-to-roll press, or a flatbed die cutting station. The steel tooling is typically mounted into a multiple layer structure, similar to the layers of a sheet of plywood, to support the die and maintain flatness. Material shapes are stamped out utilizing steel rule dies that are adjusted accordingly to varying degrees of hydraulic pressure. One of the biggest advantages of flatbed die cutting is that tooling costs are kept to a minimum. Therefore, the less costly flatbed dies can provide definite value over rotary tooling. Another plus is that on materials over 1/8” in thickness, the vertical cut allows a much tighter tolerance. The tooling causes very little coning (or curvature) of the material used, as opposed to rotary dies. Different combinations of materials are better suited to the process of flatbed die cutting over rotary cutting. It all depends on what specific materials are needed for the project at hand.

Laser Dies

Laser die cutting, or laser digital finishing, is the direct, high-speed laser processing of flexible materials without the use of hard tooling. Laser processing systems are used to cut, score, etch, kiss-cut, and perforate roll- or sheet-fed materials with precision, flexibility, and speed. This non-contact process is an alternative to traditional die cutting and is ideal for applications that feature locations, tolerances, sizes, or material characteristics that would be difficult or cost-prohibitive to process the liner altogether. These elements play an important role in the die cutting process. To be sure your die cutting is successful, be on the lookout for the following influencers:

1. CLEARANCE - This refers to the distance the die blade is set to properly cut through the film and adhesive without deep striking the release liner. To determine the proper clearance, the exact thickness or caliper of the liner material is required.

2. CALIPER CONSISTENCY - If the liner caliper is not consistent when kiss cutting, two things can happen: 1)The die fails to cut completely through the facestock and adhesive, in which case the matrix may pull labels off the web when stripped. 2) The die cuts too deep into the release liner and the web may break or the adhesive may be pushed down into the die strike. This is why the clearance is set to the thickness of the liner and is so important for successful kiss cutting.

Since all die cutting is based on the caliper consistency of the liner, we have outlined below how different liners can affect your die cutting process. Die strikes on the liner should be even and light. Any irregular or inconsistent die strikes should be reviewed with your die company.

Polyester liners provide the best die cutting bases because of their caliper consistency, smoothness, and strength, making them the ideal “anvil,” and thus they can help to limit web breaks, as well as potential problems resulting from human error. These liners are ideal for high-speed roll-form converting. While polyester liners used to cost more than paper, supply constraints in the paper market have brought the cost of paper liners into range with that of polyester. Couple that with the efficiencies realized from fewer web breaks and less waste, and the total applied cost is comparable. 

Polycoated kraft liners (papers with polyethylene or polypropylene applied between the release chemistry and base paper) also provide a smooth cutting surface and can therefore lead to improved die cutting. Polyolefin coatings, in particular, allow for deeper die cutting. Choosing between the two is mostly a function of whether you are converting roll- or sheet-form products.

Similarly, a clay-coated paper liner offers better smoothness than plain papers. The clay provides a smoothness lacking in densified paper liners. Unlike polyester liners, the coated papers are backside printable, which can be an attractive option for some applications. Coated paper liners are best used for sheet-form applications. When a clay-coated liner is used with roll-form converting, they tend to experience more web breaks than polyester.

Densified kraft paper liners may also be used. The 50 lb. densified kraft liner is the industry standard for roll-form applications. The library of dies of most converters is tooled to this liner. Though not as consistent in smoothness or caliper as coated or polyester liners, densified paper liners have some important pluses: they won’t stretch or slide, and they provide excellent registration in addition to backside printability. During hand dispensing, they are generally easier to handle than other liner options.

3. APPARENT DENSITY - In general, the higher the apparent density of the liner, the easier it is to die cut (this means the liner is more densified). However, this does not mean that you cannot use a less dense sheet to die cut, say a machine finish sheet. It just takes the right expertise and the right tooled die for the application and liner.

STAYING SHARP

Other than laser dies, all dies dull. In addition to the general wear and tear of use, some causes include abrasive coatings, heavy coat weight adhesives, or too much pressure on the die during cutting. This is why it is critical to present the intended material to be die cut to your die supplier at the beginning of the process. You should have a discussion with them about the expected footage and the number of revolutions the die will have. Also inquire about what to look for when the die is starting to wear. Routine maintenance is the key to keeping your dies sharp.

Die manufacturers can recommend preferred maintenance schedules and suggest a specific type of die. You can also work with your ink, adhesive, and film suppliers to determine if alternative products are available that may result in less die wear.

FINDING SUCCESS

With so many variables, the best approach is an informed one. Work closely with your die manufacturer and your pressure-sensitive material supplier. By understanding your requirements, they may be able to recommend specific dies for the facestocks, adhesives, and liners being used in your applications that will help you improve your level of success.