Since its introduction in 1960, laser technology has quickly found applications in manufacturing. Subsequently, as understanding of the underlying theory deepened, various types of lasers evolved, broadening their range of applications and progressively increasing their scale of use, leading to substantial social and economic benefits.
As one of the cutting-edge technologies, laser technology is an important hallmark of the scientific and technological advances of the 20th century and is an integral part of optoelectronics in the modern information society.
It not only attracts great attention from technologically advanced nations, but also from many developing countries, which invest heavily in it.
Since the 1980s, many governments have incorporated laser technology into their national development plans. For example, the UK's AWE, the US's laser fusion program and Japan's five-year laser research plan.
The implementation of these plans accelerated the development of laser technology, promoting a vibrant and emerging industry.
Simultaneously, the progression of laser technology has significantly driven advancements and improvements across diverse technologies, disciplines and production levels, making a global impact.
Abroad, laser engraved ceramic anilox rollers for flexographic printing have been used for many years, with quality being the key to their success. Laser engraving machines can inscribe continuous, continuous patterns on printing cylinders.
However, for non-continuous patterns, the cost of laser engraved plates and cylinders may be higher. Although the long service life and high printing quality of plates and cylinders can offset the higher cost of plate production, this expense can still slow down the development of laser engraving technology.
Today, quality remains a crucial factor, but the focus has shifted to productivity. Graphics require anilox rolls with a high number of lines and good engraving quality, which takes a considerable amount of time.
To increase quality and reduce costs, laser engraving technology needs to be improved and the speed of laser engraving needs to be increased. Rewarding progress has been made in this regard.
In principle, it is simple to use a laser to engrave a grid pattern onto a ceramic-coated roller. The ceramic roller is placed on a lathe and rotated, a laser beam is focused on the surface of the roller, and the beam moves along the length of the roller, continuously turning on and off.
Consequently, the surface of the roller becomes full of small holes. Grid size and pattern depend on many variable factors.
For coarse grid engraving such as glue rollers, a slight process improvement is sufficient. However, engraving high-quality anilox rolls is a completely different story. Flexo printing shops need anilox rolls that deliver consistent ink performance.
This means that the shape of the grid must be uniform and variations in volume must be minimized. The grid pattern also needs to be regular to ensure even ink transfer, especially when printing solid areas.
Laser engraving is a common technique in laser technology. There are three types of laser engraving: CO2 laser engraving, Nd:YAG laser engraving, and excimer laser engraving. Each of these laser engraving techniques has unique characteristics and advantages, making them suitable for different areas of application.
In the late 1970s, Buekley and Jenkins began developing laser-engraved anilox rolls. Prior to this, most were engraved using CO2 lasers with carbon dioxide gas as the laser medium.
CO2 laser engraved anilox rolls have largely met the development needs of the flexographic printing industry, especially the packaging printing industry.
The successful application of laser-engraved ceramic anilox rollers in flexographic printers can be considered one of the main factors contributing to the rapid development of flexographic printing in recent years.
This allowed flexography to compete with lithography and gravure printing. The CO2 laser engraving machine has gone through three stages of development:
The first generation of carbon dioxide laser engraving machines essentially used lasers as amplified scales of light pens, controlled by a foot pedal, that could be used to replicate handwriting, curvilinear images, and portraits. The laser engraves an image similar to the original on the workpiece. This is a simple and primitive, low-cost CO2 laser engraver.
The second generation of CO2 laser engravers are designed to engrave woodcut images, controlled by a single-chip machine to digitize the light spot line by line on the XY platform. The laser is turned off in the light parts of the original and turned on in the dark parts, thus processing a black and white image.
The diameter of the laser focus is 0.4 mm and the black regions of the image are essentially made up of a series of lines 0.4 mm wide and 2.2 mm deep.
An image can be divided into 550 lines, and the reading head can also perform synchronous scanning. The reading head has an opening of 0.4 mm, composed of a semiconductor light tube and a receiver tube, which receives the reflected light from the image illuminated by the emission tube, and controls the exchange of the CO2 laser after obtaining the limit value through the single-chip machine.
The third generation of CO2 laser engravers replace the single chip with a personal computer in the control system, so they are also known as microcomputer controlled CO2 laser engravers.
It uses a CCD camera to read 512*512 pixels and their grayscale levels at once. The dithering method is used to convert 256 grayscale levels into the black point density of the area, greatly compressing the information capacity, overcoming the brightness and grayscale levels of the image, solving the problem of enlarging and reducing the image and completing the reading of three large-scale, multi-dimensional images, as well as the storage and processing of multiple image information.
Efforts are constantly made to improve the quality of laser engraved ceramic anilox rolls, so that the quality of flexo printing products can reach or even surpass offset and gravure printing.
Therefore, by improving the precision of plate making by strictly demanding the fineness (line number) and ink storage capacity of ceramic anilox rollers, after several years of exploration and effort, Nd:YAG laser engraved ceramic anilox rollers were finally released around 1996.
Nd:YAG lasers are made by doping the substrate of yttrium aluminum garnet (Y3AL3O12) with neodymium oxide (Nd 2 Ó 3 ). The activated ions are also neodymium ions, with an output wavelength of 1.06um.
Due to Nd:YAG's narrow fluorescence spectral line, high quantum efficiency and good thermal conductivity, it is the only solid-state laser capable of continuous operation among the three types of solid-state lasers and is commonly used in laser thermal processing.
The excimer laser is a high-power, high-efficiency ultraviolet laser. It plays an important role in the microfabrication of ceramics, polymers and other materials due to its diverse characteristics. With the continued growth of microfabrication and high precision demands since the advent of the excimer laser, it has been highly valued by countries around the world.
The European Community's Eureka Plan (EREKA), the Japanese government's Advanced Manufacturing and Mechatronics Towards the 21st Century (AMMTRI), as well as China's 863 Program and Super 863 Program all prioritize the development of excimer lasers, which has progressed rapidly .
The mechanism of excimer laser writing: Excimer laser writing is a direct photochemical process on materials. The mechanism by which the excimer laser interacts with the processed material is called ablation, including photo-induced bond breaking and product explosion.
When the photon energy of the excimer laser is greater than the chemical bond energy of the polymer, the chemical bond is broken, the specific volume of a small area on the surface of the material increases suddenly, and when the bond breaking rate exceeds a certain limit , the surface fragments detach, completing the attack.
The advent and evolution of excimer lasers have provided powerful tools for a wide range of industrial applications and scientific research.
Given their wavelength in the ultraviolet and deep ultraviolet spectrum, high pulse energy and photon energy, high repetition rate, and narrow pulse width, most metals and nonmetals strongly absorb ultraviolet light. This absorption allows excimer lasers to perform tasks that other laser heat treatments cannot, thus expanding the range of applications of laser processing.
As the stability and reliability of excimer lasers have improved in recent years, they have found broad applications in biomedical science, materials science, microfabrication, and photochemistry.
After analysis, it is evident that YAG lasers excel in processing metallic materials, while CO 2 lasers are superior for non-metallic materials. Excimer lasers, on the other hand, have an advantage in microfabrication and high-precision tasks.
The use of Nd:YAG laser engraving technology in the production of flexographic printing rolls has significantly improved the performance of engraved products and stimulated advances in laser engraving technology itself. As technology in this area continues to mature, we anticipate even greater achievements in the future.
Looking at the current state of global laser engraving technology, CO 2 laser engraving, YAG laser engraving and excimer laser engraving demonstrate their unique strengths as well as certain shortcomings.
The coordinated operation of these three processing methods, expanding the product variety and improving the performance of engraved products, are undoubtedly the best choices for the current laser engraving processing of ceramic anilox rollers.
Therefore, laser engraving equipment suppliers typically provide CO2 and YAG lasers in their packaging, while high-precision engraving must utilize excimer lasers. Excimer laser engraving processing is the main research direction for high-precision manufacturing.
