Analysis of laser flexible packaging technology fo

2022-10-18
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Analysis of laser flexible packaging technology for food (Part I)

the emergence of small, sealed CO2 lasers and the development of shorter output wavelength are promoting the growth of film packaging industry

the sealed CO2 laser technology is developing continuously, the performance is improving, the reliability is increasing, the volume is decreasing, and the total cost of the laser is decreasing. As a solid and reliable tool, sealed CO2 lasers are widely used in industry. One of the latest applications is flexible packaging, that is, paper, plastic film and other materials are folded into a preset packaging shape. This paper mainly introduces how the recent progress of CO2 laser technology promotes the rapid growth of food laser flexible packaging market

laser soft packaging technology

the soft packaging used for processing food and beverages can adopt Rockwell hardness test and Brinell hardness test 1 in a variety of forms and shapes, including envelopes, bags, especially the packaging that can be resealed, which has developed rapidly. Most of these packages use film materials, such as polyester (PE), aluminum foil and polypropylene (PP) - usually biaxially oriented polypropylene (BOPP). Usually, these materials should be combined to form a two-layer or multi-layer composite structure. The most common film synthetic materials are double-layer PP and PE rolled together. PE is a barrier layer, which is in direct contact with food. The PP layer with graphics is outside, which is a printing layer. The whole film thickness is about 100 microns, even for bag packaging that can stand up. During the packaging process, the film wound on the drum moves forward continuously due to the rapid rotation of the drum. At this time, laser is used to cut and trim the film, or notch and drill holes on the film. For example, laser scoring can make the packaging bag easy to open, and laser drilling can make the packaging bag breathable

compared with traditional machining methods, the advantage of non-contact laser processing is that there is no tool wear problem and the consistency of products is improved. In addition, flexibility is also very important, because today's product production cycle is very short. Machining, including tool costs, is not suitable for short-term operations, and is not suitable for changing back and forth between different film types and packaging forms. Due to the real-time control of laser parameters, the flexibility of laser processing and packaging can enable producers to obtain consistent scoring results, even when the film thickness changes

it is obvious that in business areas with large output/low profit, such as film packaging, the reliability and total cost of laser are key issues for owners to consider. The small size of lasers is also very important because they can be assembled into packaging equipment. In terms of laser output power, these applications usually require only 30 to 100 watts of power, because the multilayer structural materials to be processed are usually very thin

Figure 1: this small, sealed laser can output 30 watts of power and weighs only 6 kg

these characteristics make today's small CO2 lasers an ideal tool for the folding flexible packaging market. The low-power sealed diamond CO2 laser produced by coherent company has the characteristics of high reliability, low cost per watt and small volume. Its size is as large as an ordinary shoebox (see Figure 1). These foldable waveguide lasers are ideal tools for processing plastic (polypropylene and polyester) films at a processing speed of more than 300 meters per minute (1000 feet per minute). In addition to providing cheap solutions for medium power applications, the small size of the new laser also makes it possible to arrange multiple lasers on a wide drum (such as a 1.5 meter/60 inch wide main drum), thus providing unprecedented processing flexibility for flexible packaging. Moreover, these lasers do not need maintenance, and their service life is between 10000 and 20000 hours, which can fully meet the needs of typical high-yield packaging equipment while ensuring functions

there may also be rust, corrosion and other phenomena. The progress of small CO2 lasers in other output wavelengths is another important factor that has a significant impact on the food flexible packaging market. The reason is that the infrared absorption spectrum of most polymer films contains several peaks. Therefore, small changes in laser wavelength may have a great impact on the absorption coefficient, because the thin films used in flexible packaging are very thin, and usually only a small part of the laser power can be absorbed. Therefore, by adjusting the wavelength to increase the absorption coefficient of the film, the processing speed at a given laser power will be greatly increased

the output wavelength of most CO2 lasers is concentrated at 10.6 microns. However, if wavelength selective optical elements are inserted into the folded cavity structure, other wavelengths, such as 10.2 microns, will be generated. Coherent application laboratory recently studied the effect of commercial 10.2 micron lasers on thermoplastics, and the results were published in document 1. For unexpanded polypropylene film, there is only a small difference in processing speed when using 10.6 and 10.2 micron laser processing. However, for the commonly used BOPP film (micron thickness), the difference is very obvious (see Figure 2)

Figure 2: comparison of cutting speed between 10.2 and 10.6 micron wavelength laser cutting PP

in addition, using different carbon dioxide isotopes can shift the laser output wavelength further, which will have an important impact on other applications. For example, coherent has found that when processing Kapton (polyimide) films commonly used in electronics and other industries, 9.4 micron wavelength laser can produce the best results

(to be continued)

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