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Advantages and Optimization Methods of CO2 Laser Cutting Labels

DATE:2016-11-25READ:


Digital printing technology innovation and development has greatly changed the status of label production and production. With a flexible print design, it is important to easily change the shape of the cut so that the shape fits the matching requirements. Traditionally, label cutting is performed by a mechanical stamper and a slitter blade, in which case a production shift is made by a user to produce a design specification. The high cost of storing multiple dies and complicated logistics work makes it difficult to cut a variety of shapes. Moreover, downtime due to tool change causes a reduction in production efficiency, which often has a decisive impact on operating costs. Laser cutting with a high-speed scanning head turns this work into a very dynamic and simple and flexible process. Cut design can be done anytime, anywhere via software, without interrupting the production line.

One application of laser cutting is the use of CO2 laser beams for high-speed label cutting. Broadly speaking, this application is divided into the type of conversion processing, the industry generally recognized as the definition of a roll of material "processing" to make it into another form of technology. Including cutting labels, porous plastic, paper; for folding carton trimming; characterization of easy to tear type food bags and so on.

Laser processing has many advantages. In addition to being able to digitally and flexibly change new designs at any time, increased throughput from contactless machining is an important benefit that can not be overlooked, especially since labels are becoming thinner and thinner, allowing the user to tailor the required depth Which selectively & quot; kisses & quot; At the same time, the laser cutting process without supplies (ie, no mechanical wear parts), process repeatability (laser does not produce passivation problem). Therefore, the laser, digital, non-contact technology performance advantage is very impressive.

Label market

Market analysts expect a strong CAGR of 6% in the laser cutting market by 2016-2020, driven by emerging markets and end markets such as pharmaceuticals, food / beverage containers, and cosmetics. Although the laser cutting market is growing at a slower rate (less than 1%) compared to traditional machine tools, which are expected to grow faster, the laser cutting market is expected to grow at a faster rate due to the development and evolution of digital printing. Many companies have begun to study the advantages of laser cutting labels.

AB Graphics (AB Plane International, Inc.), from Yorkshire, England, is one such company. The company has been in the past nearly 10 years, began to engage in laser label cutting equipment manufacturing. They see the use of laser cutting equipment equipped with the CO2 laser from the US company Synrad, in contrast to traditional machine tool technology, to show significant processing advantages. "Today, there are many limitations to laser cutting, but the development of digital printing opens up opportunities for laser processing because it is an ideal tool for small-lot custom product processing," said AB Burton's general manager Mike Burton. CAD document design orders, quickly passed to the digital printer terminal, and then digital laser cutting.This end-to-end digital processing tool-saving, the time required for mold, not only to improve the processing speed, also received a larger Of the processing freedom.If there is no laser cutting machine, you can not use a truly cost-effective way to meet the needs of customers for fast batch.

Figure 1: Digicase series of AB Graphics laser label cutting machine.

Laser processing solutions provide a convincing value proposition. It can save customers several to several weeks of tool change downtime, and provides maximum flexibility. Such as, the simplest equipment flat die-cutting machine tool, it is necessary to the cost of cutting tool is more than 100 dollars, new tool design also need to spend several days. Both semi-rotary flexible and rotary die-cutters face similar problems, and the tooling costs of these tools are more expensive. Semi-rotary die-cutting tooling costs hundreds of dollars and requires 3-5 days of delivery time. The cost of full rotary die-cutting tools ranges from $ 1,000 to $ 2,000 and delivery time is about two weeks. Obviously, the delivery time is long, can not meet the rapid design changes on the production capacity caused great constraints. "Laser equipment is now only 1-2% of the label cutting market," Burton added. "This mechanical device is ideal for long-term reprocessing needs and costs 4-8 times lower than laser equipment.Therefore, the cost of laser equipment does not reflect the advantage.However, the HP indigo digital press led to the digital printing "AB Graphic designs and sells the Digilase series of laser label cutters driven by two Synrad 200W CO2 lasers (Figure 1)." The company has been designing and marketing laser marking machines that are driven by two Synrad 200W CO2 lasers (Figure 1 ).

Optimum label laser cutting process

In label cutting applications, it is important to allow the label material to absorb more laser energy as much as possible in order to achieve the highest production efficiency. The use of CO2 lasers enables high-quality cutting of most plastic and paper labels, as these materials absorb the long wavelengths generated by the laser. Except for vinyl labels which are charred and emit noxious gases.

In order to further optimize the label laser cutting process, taking into account some of the specific label materials and how they will absorb CO2 laser emission of different laser wavelengths and other factors. The label sheet contains different layers of material. With backing paper, adhesive-coated plastic or paper labels, and then applied with a layer of protective varnish or composite coating. First of all, the uppermost layer will absorb the most laser energy, so the absorption properties of this layer of material is particularly important. For example, polypropylene labels (typically used as sizing labels) generally have better absorption properties at wavelengths of 10.2 to 10.3 m as compared to conventional 10.6 m laser wavelengths. In this way, the laser power can be adjusted at this level, in order to improve the productivity and processing quality.
Test sample settings

In this particular test, a dynamic triaxial laser marking system, the Flyer 3D, with Synrad's proprietary p250 CO2 laser, enables fast and accurate marking over a wide range of product lines. The field size of the Flyer 3D subsystem is 400x350mm and the focused spot size is 282μm. In the high-speed processing, it is best equipped with high-speed galvanometer scan head system in order to manipulate and control the beam. X-Y plotter for the production level of production, the processing speed is too slow. In addition, the excellent stability of the p250 CO2 laser provides excellent uniformity of label cutting depth, so that even after long processing time, it is possible to maintain constant processing quality.

Figure 2: Typical absorption profile for polypropylene (and biaxially oriented polypropylene) labels.

Using the experimental setup, a Synrad label sheet made of a polypropylene film having a thickness of 0.1 mm was subjected to a cutting test. The p250 laser operates at 50kHz pulse-width modulation (PWM) with 45% duty cycle. This high repetition rate of the pulse together, the material can be continuous cutting. The average power of the scan head is 275W. The laser cutting speed of the label is 4064mm / s at the standard 10.6μm wavelength. Since the absorption rate of the polypropylene label material (Fig. 2) is increased, the cutting speed can be increased by 1.5 times when a laser with a wavelength of 10.2 / 10.3 μm is used. In addition, the energy loss imparted by the polypropylene layer to the backing paper backing is reduced so that the scratches can be reduced to near negligible levels. The label can be easily torn from the backing sheet, and the edges are clean, smooth, and less molten (Fig. 3).

Figure 3: The cut view of the label (see the center of the figure above).

Conclusion

CO2 lasers demonstrate the ability to selectively process applications such as label cutting. In this case, it is necessary to flexibly cut a plurality of materials which are easily changed in shape during processing. Furthermore, by optimizing the CO2 wavelength to match the label material, it is possible to increase the cutting speed and quality compared to a conventional 10.6 μm laser system with a standard wavelength. This has been confirmed not only in the laboratory but also at the production site. According to Burton, AB
For Graphics, "we have witnessed a significant improvement in the quality of our customers' label cutting, and we will mainly produce laser cutting systems with wavelengths of 10.2 μm."

Although this article discusses the advantages of a 10.2 μm laser compared to a 10.6 μm wavelength laser in the processing of polypropylene labels, it is worth noting that CO2 lasers can also operate at a laser wavelength of 9.3 μm, Other types of label film materials are optimized for processing, such as PET materials commonly used in sleeve-type labels. Maximizing the quality and efficiency of the process can be achieved when the wavelength of the laser matches the absorption characteristics of the project-specific film.