Beginning in 2020, an outbreak caused by a new coronavirus will ravage the country. Because the mask can effectively block the invasion of droplets, blood, body fluids and secretions, and block the spread of the virus, it has become a necessity of life at this stage. Demand has surged, and mask resources are very scarce across the country. Masks are difficult to find in many places. Many manufacturers have increased the production of mask machines in an emergency, but they have ignored the mask printing process in the production process. The surface printing of masks requires molds and a large amount of ink. The molds cannot be in place in time. A large amount of ink printing has a great impact on the environment, resulting in a large number of whiteboard masks on the market (no masks with any information). Non-printed masks flowed into the market, giving some unscrupulous merchants an opportunity; in addition, some inferior masks were rampant in the market, which was extremely harmful to consumers' health.
How to solve the problem of mask recognition and anti-counterfeiting becomes the most important. The best way to solve this kind of problem is to make it easy and quick for the mass consumer to identify the mask information, and know what can be bought and what cannot be bought. For enterprises, it is urgent to further improve the quality control and brand building of the mask production process.
The importance of logos to products and brands is self-evident. The traditional marking method mainly uses ink coding technology, but the biggest disadvantage of this technology in the current process of producing masks is the inflexibility and environmental pollution, which also causes the large-scale expansion of masks in special periods to meet production requirements.
Laser applications can solve the above problems well. The flexible production of lasers has been used in large quantities in various industries at present. Compared with inks, it is more environmentally friendly and highly recognizable. It has been recognized and used by many food companies. Huagong Laser has carried out related process development and experiments in response to the current mask market identification problem, and launched a new laser ink-free printing technology that can solve the high-quality identification of mask products, improve the overall quality of the product, and enhance the brand influence of the mask.
01 Principles of laser marking for medical protective masks
Material properties
Medical protective mask is a non-woven material, which is composed of oriented or random fibers. It is usually a multilayer structure, usually referred to as SMS structure (2 layers of S layer and 1 layer of M layer). At present, the highest number of layers in China is 5 layers, namely SMMMS (2 layers S layer and 3 layers M layer). S represents a spunbond, M represents a barrier layer or a meltblown layer M (Meltblown), both of which are composed of polypropylene (PP). The M layer uses meltblown nonwoven fabric as the filter layer. Because its fibers are randomly distributed and have complex three-dimensional porosity, the biggest feature is that it consists of ultrafine fibers. The fiber has a large specific surface area and a strong adsorption capacity for particles. The spray filter material fibers are randomly distributed, forming a large number of minute pores, and the pores are uniformly distributed, the filtration resistance is small, and the filtration efficiency is high, which makes the filtering performance of the non-woven medical protective mask far superior to the traditional gauze mask.
SMS non-woven fabric uses polypropylene PP (with natural bacteriostatic and hydrophobic properties) as the main raw material, and the fiber diameter can reach 0.5-10um. These ultra-fine fibers with unique capillary structure increase the number of fibers per unit area and surface area, so that Meltblown cloth has good air filterability and is a good mask material. Therefore, the laser marking surface is a non-woven fabric made of S-layer polypropylene.
Laser marking
Like all medical and health products, anti-counterfeiting marks are an important part of mask products.
Today, compared to traditional ink printing technology, laser marking has the characteristics of non-toxicity, pollution-free, high efficiency, high definition, high precision, and abrasion resistance. It has technically solved one of the traditional ink printing technologies. Series of questions. It can be said that laser marking technology has been escorting the medical industry since its birth.
The principle of laser marking technology is mainly to irradiate the surface of the material with a laser with a high energy density, so that the surface of the material is vaporized to expose deep substances, or a chemical reaction that changes the color of the surface of the material under the effect of light irradiation , Leaving permanent markings. Since laser processing is non-contact processing, the tool does not directly cause friction with the surface of the workpiece, so the laser processing speed is extremely fast, the area affected by heat of the processing object is small, and no noise is generated. Since the energy of the laser beam and the speed of the beam can be adjusted, laser processing can be applied to different levels and ranges.
At present, there are two recognized laser processing principles: laser thermal processing and photochemical processing (also known as cold processing).
When a short-wavelength ultraviolet laser is applied to a polymer, it directly breaks the chemical bond of the material, so that the material fragments are discharged in small particles or gaseous manner, so as to achieve the purpose of stripping and removing the material, thereby generating smooth, clear and easily identifiable marks inside the material . Since most of the energy is used to destroy chemical bonds, very little energy is converted into thermal energy, which can basically eliminate the change of the heat affected zone (HAZ) and surrounding materials, and ensure that the materials will not be deformed by heat.
Cold processing (ultraviolet) photons with high load energy can break chemical bonds in materials (especially organic materials) or surrounding media, causing non-thermal process destruction of materials. This kind of cold processing is of special significance in laser marking processing, because it is not thermal ablation, but rather does not produce cold peeling that is assisted by "thermal damage" and breaks chemical bonds. Therefore, it does not affect the inner layer and nearby areas of the processed surface layer. Generates heating or thermal deformation.
Because the heat generated by the hot processing light source will cause damage to the outer and middle surfaces of the mask, which will have a greater impact on the filterability of the mask, a "cold processing" UV laser is used to mark the surface of the mask.
02 Impact factor of laser marking on medical protective masks
Laser marking speed
The laser marking speed is the distance of the laser scanning per unit time. The action time of the laser and the material can be controlled by changing the marking speed.
The above is the change of the effect of different marking speeds on the surface of the material. As can be seen from the figure, the marking speed adopted by Huagong Laser this time is from 2000mm / s to 5000mm / s, and the effect changes from the yellowish color to the moderate effect. When the marking speed is slow, the interaction time between the laser beam and the unit area of the material is longer, the carbonization of the laser beam and the surface material of the material is more severe, and the thermal effect is increased, resulting in a yellowing of the marking effect and a thicker outline of the marking. When the marking speed is gradually accelerated, the time for the laser beam to interact with the material is reduced, so that the degree of carbonization of the laser beam and the material on the surface layer of the material is reduced. When the marking speed is a specific value, the carbonization is more moderate and the best is obtained. Contrast.
Laser frequency
The laser repetition frequency is the number of laser beams emitted per unit time. When the marking speed is constant, it affects the spot overlap rate. Figure 2 (b) has a yellower marking effect than Figure 2 (a). Analyze the reason. Under the same laser power, the peak power of 6OKHZ laser is the highest. During the same time, the energy of the laser beam absorbed by the material increases, and the thermal effect increases and turns yellow.
Fill line spacing
Filling line spacing refers to the distance between two adjacent filling lines when filling the text or pattern to be marked with lines. The line spacing is too small, the marking time is long, and the thermal influence of the material is serious, which causes the contour lines to stick together, and the marking effect is poor.
03Effects of laser marking on masks of medical protective masks
In order to test the impact of laser marking on the core index of the mask, the filtering performance, we performed a strict filtration rate and performance test on the laser marked material. The conclusion of the test was that the marked material had There is almost no impact on performance.
