Printing process and smart label printing

The rapid development of printing technology stems from the large increase in the demand for information in society. The use of printing methods for copying graphic and textual information can reduce production costs, increase production efficiency, and result in a uniform print format that is aesthetically pleasing and durable. With the development of technology, the printing process can be applied to various printing materials. In addition to text lines, dots can also be superimposed to obtain continuous color tuning graphics. The development of electronic industry and ink technology has opened up new areas for printing processes, such as the printing production of PCB printed circuit boards and emerging RFID smart electronic tags.

First, smart electronic tags

Smart Label is also known as a radio frequency identification (RFID) tag, which is the crystallization of high technology such as electronics and computers. Smart tags include RFID tags, concealed or exposed trademark protection indicators, or sensors that indicate the status of the product.

The electronic tag is mainly composed of a chip and an antenna. The chip is mainly used for receiving and transmitting data, and is read through a radio frequency signal sent by a reader. The reader is connected with an antenna and a computer network to form an electronic module, and the reader sends from it. The special signal of the antenna is given to the electronic tag in a specific area, and the feedback information is processed and transmitted to the computer network so that the management personnel can obtain the special information of the product. RFID smart labels meet higher and more complete information needs in many aspects such as production, storage, transportation, quality assurance, anti-counterfeiting, and management. Compared with traditional bar code labels, it has many functions and good anti-counterfeiting effect.

At present, the antennas of electronic tags are mostly made by punching and etching, which has a high cost and hinders their popularization and use. The manufacture of antennas by printing conductive inks is the best choice in terms of material cost, material consumption, and production efficiency, which can greatly increase the production efficiency and reduce production costs.

The printing of smart labels at the present stage also includes the printing of surface bar code information, which is a supplementary means adopted to prevent the labels from being damaged and cannot be read. In this sense, the printing of RFID is both a category of label printing and a type of circuit printing. The production process has strict requirements for printing, mainly in several aspects: First, the precise printing position; The strict amount of ink (printing) adhesion, such as the thickness of the conductive paste film and the number of conductive particles are strictly controlled; Another factor is the size of the print resolution. Selecting the printing process can be comprehensively considered in terms of the size of the printing, the surface properties of the printing material, the adhesion properties of the ink or the printing material, the cost, and the characteristics of the process.

The functional conductive ink used in circuit printing is also called printed material. It is to add conductive metal powders, metal oxide powders and other carriers to UV inks, flexographic water-based inks or special offset inks to make inks conductive. Of course, similar to traditional printing inks, printing materials also have complex rheological properties and influence the printing process to a large extent. Due to the characteristics of the production process, the printing materials are resistant to solvents, light, and friction.

Second, the printing process comparison

The current printing methods can be classified into two types: traditional printing and digital printing. Offset printing, gravure printing, embossing, and screen printing are conventional printing methods. Press printing is used. Digital printing methods such as ink jet printing and electrophotography are non-pressure printing processes. Graphics are directly transferred from the computer to printing materials.

Offset printing is the most common method of application. 80% of publications are printed using offset printing. Its wide range of printing materials, such as paper, cardboard, metal, plastic, etc. can be printed. The number of prints can range from 500 to 1 million, fast and efficient.

Preprinted sensitized plate, printing according to the principle of repulsion of oil and water, forming graphics on the plate partially covering the ink, the blank part covers the distribution of water, the ink is first transferred to the blanket, and then transferred to the blanket Printing materials. The viscosity of the ink is very large, about l-50Pa.s, and the polarity is small.

Another way of offset printing is waterless offset printing. The blank on the plate consists of a silicone resin that does not absorb ink during printing. Since there is no "water" effect, the operation in production is more convenient, the quality is more stable, and the printing accuracy is higher. The ink film thickness obtained by printing is about 0.5-3 μm.

Offset printing has the advantages of efficiency, precision, and resolution for coil printing. However, the offset ink film has a small thickness and does not meet the requirements of line printing. Of course, this can be accomplished by repeated printing multiple times, but this poses new challenges for fine line register control. Newer, more conductive inks can also achieve the required impedance performance at a smaller thickness. .

Flexographic printing is mainly used for packaging and decorating printing. Printing materials include paper, cardboard (especially printed on corrugated cardboard), and plastic films. This is a direct printing method. Using a photosensitive photosensitive resin plate of 1 to 5 mm in thickness, printing on a web, is fast and efficient. The viscosity of the ink is between 0.01 and 0.1 Pa.s. Water based inks, solvent based inks and UV cured inks can be used. However, the flexographic resolution is low, usually about 60L/cm, fine printing up to 80L/cm, ink film thickness 6~8μm, suitable for antenna printing requirements.

With the development of thin-plate technology, the resolution and printing accuracy of flexographic printing have also increased. The inadequacies are: The imprint appears on the edge of the imprint, which is caused by the deformation of the imprint caused by the pressure of the printing process. The appearance of the imprint makes the edge of the line imprinted irregularly, which affects the accuracy of the ink adhesion and the impedance of the line, making it easy to produce waste products.

Gravure printing is also the main packaging publishing method, accounting for approximately 18% of the market. It has a large print resistance, up to 500,000 prints, and a wide range of printing materials such as thin paper, cardboard, plastic film, etc. The ink has a viscosity of about 10 to 50 mPa.s. The solvent ink is mainly used. The resolution is related to the engraving of the reticulate cavities, laser engraved up to 1000 L/cm, and the ink film thickness is between 8 and 12 μm. However, due to its high printing pressure, there are difficulties in RFID antenna printing.

Screen printing is a stencil printing method. First, the screen is stretched over the screen frame. After the exposure is printed, the graphic part of the printing plate can penetrate the ink, and the blank part is covered by the photosensitive resin. When printing, the ink is Under the pressure of the squeegee, a graphic is formed on the substrate through the screen. Screen printing inks have a viscosity of between 0.1 and 10 Pa.s, and inks of different thicknesses can be formed by printing, ranging from 200 nm to 100 μm. The disadvantage of screen printing is that its maximum resolution is small, usually below 50L/cm, and its printing speed is small compared with other printing methods. But for the etching production of circuit boards, screen printing can greatly improve the efficiency.

Screen printing is arguably the preferred method for printing RFID antennas. The print quality of screen printing in integrated circuit boards, membrane switches, etc. is unmatched by other printing methods. In smart label printing, conductive inks are used, and the preferred screen for printing current conductive inks is a nickel foil perforated screen. The net is drilled from nickel foil, and the mesh is hexagonal. It can also be made into a round hole by electrolytic forming. The entire mesh surface is even and thin, which can greatly improve the stability and precision of imprinting. It is effective for printing high-tech products such as conductive inks, wafers, and integrated circuits. It can resolve circuit line intervals of 0.1 mm and the positioning accuracy can be improved. 0.01mm.

Inkjet printing is the fastest growing printing method in recent years, and its versatility is incomparable with other printing methods. This pressureless method can spray digital information from a computer directly onto any shape of material. The ink system is relatively complex and the ink used can be water-based, hot-melt, or UV-curable, with a viscosity of about 10 mPa.s.

Inkjet printing is divided into continuous inkjet and drop-on-demand inkjet. On-demand ink-jet ink droplets can be under 5 pl, which means that the ink droplets have a diameter of 2 lμm and a very high resolution can be achieved. Of course, there is a deviation in the ink ejection position in this manner, and small ink droplets that affect the printing quality appear in the blank portion, resulting in an edge effect.

Electrostatic photography, also known as electrostatic replication or laser printing technology, is another major electronic printing technology. Of course, no advantages have yet been discovered for smart label production.

Third, the printing process application

The advantages of using a printed method for making a tag antenna can be summarized as follows:

1. Low cost and easy operation

With the printing method, the production volume is large, the time is saved, and the number of processes is less.

2. Faster printing speed by rotating method can greatly increase production efficiency and ink transfer ability

Such as Swedish Stork Print company for the smart label antenna coil printing Rotary ScreenIntegration (RSI) screen printing label production line, can be printed continuously 500,000 meters without shutdown.

3. "Green" and environmental protection

Traditional etching and other processes have the waste discharged, causing greater pollution to the environment. The printing technology uses conductive ink to print directly on the substrate, with little or no use of chemical reagents, with the advantages of “green” and environmental protection.

4. Flexible and diverse substrate selection

Conductive inks can be printed on various substrates to produce the desired antenna. If screen printing with “universal printing method” is adopted, the choice of label substrate will be more flexible.

5. Rich label style, good stability and reliability

Printing technology can allow the antenna to have a variety of design styles, capable of printing multiple styles of antennas. Thus, the style of the produced label is rich, allowing the labelled object to have different surface shapes, such as the surface of the object with different curvatures and angles. In addition, printed conductive ink antennas are also able to withstand higher external mechanical stress. The smart tag antenna produced by printing conductive ink has the characteristics of viscous fluid and has better elasticity. When the label is bent under pressure, it shows better performance and reliability.

According to a survey conducted by The Electronicdocument Systems Foundation, 71% of companies surveyed believe that in the next few years, digital printing will be the main method of RFID-based electronic label printing. 19% of companies think that flexo will be adopted. Of course, the most popular method at present is screen printing. Companies such as IBM, Printronix, and Zebra have also developed some solutions for RFID printers.

Such as Printronix's RFID printer - SL5000r MP2, it can provide Gen 2 RFID that truly meets the requirements of the EPCglobal Gen specification. These printers integrate EPC global Gen 2 CertifiedHardware RFID Smart coding technology to meet many application requirements and global frequency requirements. This series of printers all have intelligent RFID tag management capabilities that can identify and slam RFID tags that do not meet the standards and prevent them from entering the supply chain. These printers print ready-made RFID tags and generate bar codes on the front. However, compared with other printing methods, screen printing and ink jet printing are difficult to meet the market demand in the next few years. With the improvement of RFID technology, barcode printing with complementary functions will no longer be used. The printing technology still solves the antenna production problem.

In previous years, Manroland had studied whether the antenna of a transceiver could be directly printed on a substrate. Studies have shown that using offset or other printing methods, suitable conductive inks or adhesives based on metal or conductive polymers can be printed directly. As early as Drupa 2004, Manroland demonstrated the use of RFID-based RFID-based RFID antennas. This way the antenna is combined with the substrate and can only be removed by destroying it. The use of special inks on printing presses is simple and effective. At the same time, transceivers can also be taken into account during the design of the packaging. The antenna is printed directly on the substrate. Of course, an important premise is to measure the function of the circuit in the next procedure by means of measurement. Therefore, Manroland considers it as a prerequisite for the development of direct printed RFID antennas. At present, Siemens AG in Germany is using screen printing, gravure printing