RFID Technology and Screen Printing Analysis

There is a big difference between the printing of smart labels and the printing of traditional labels. At present, the printing technology of traditional labels in our country has a very high level. There are many experienced companies in the trademark printing industry, and many well-designed and high-quality products are also produced. The product, but for the smart tag, some people think that it has nothing special, just use a plain label to cover it with a beautiful coat, which is not difficult for high-quality label printing companies, but simply adding The smart label of a beautiful coat, whose high added value is worrying, otherwise it will cause the first, from the definition of the smart label, smart, is a radio frequency circuit composed of chips, antennas, etc.; and the label is printed by the label Make RF circuits have a commercial outerwear. From a printing point of view, the emergence of smart labels will bring higher gold content to traditional label printing. The chip layer of smart labels can be packaged and printed with materials such as paper, PE, PET, and even textiles to make self-adhesive stickers, paper cards, hanging labels, or other types of labels. The chip is the key to the smart label, which is determined by its special structure and cannot withstand the pressure of the printing press. Therefore, in addition to ink-jet printing, it is generally used to print the surface layer first, and then combine with the chip layer and die-cut process.

(1) Printing method. Printing is the first choice for screen printing, because the screen printing of integrated circuit boards, membrane switches and other aspects of the printing quality is unmatched by other printing methods. In smart label printing, conductive inks are used, and the preferred screen for printing conductive ink is nickel foil perforated mesh. It is a kind of high-tech wire mesh. It is not a wire mesh woven from general metal or nylon wire, but a foil mesh drilled from nickel foil. The mesh is hexagonal and can also be formed by electrolytic forming. Hole shape. 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, and can resolve circuit line intervals of 0.1 mm and have high positioning accuracy. 0.01mm. You can also choose 61-100T/cm silk screen solvent printing, printing conductive ink using 60 degrees temperature drying.

(2) The application of conductive ink. Conductive ink is a kind of special ink. It can add conductive carrier to UV ink, flexographic water-based ink or special offset ink to make the ink conductive. Conductive inks are mainly composed of conductive fillers (including metal powders, metal oxides, non-metals, and other composite powders), linkers (mainly synthetic resins, photosensitive resins, low-melting-point organic glass, etc.), additives (mainly dispersants, and adjustments). Agents, thickeners, plasticizers, lubricants, inhibitors, etc.), solvents (mainly aromatics, alcohols, ketones, esters, alcohol ethers, etc.). The ink is a kind of functional ink. There are mainly conductive inks such as carbon paste and silver paste in printing. Carbon paste ink is a liquid type thermosetting ink. It has the function of protecting copper foil and conducting current after film curing. It has good conductivity and low resistance force. It is not easy to oxidize, stable performance, acid, alkali and chemical resistance. Erosion of solvents; with strong wear resistance, anti-wear, good thermal shock resistance and so on. Silver paste ink is a one-component ink composed of ultra-fine silver powder and thermoplastic resin. It can be used on PET, PT and PVC sheets. It has strong adhesion and hiding power, can be cured at low temperature, and has controllable Conductivity and very low resistance. In addition, conductive nanometer carbon ink can be added to ink to make conductive ink, and metal powder (such as silver powder) in conductive ink can also be made into nanometer silver powder to make conductive ink. This conductive ink not only prints the film layer. Thin and uniform smooth, excellent performance, but also can save a lot of material.

In smart label printing, conductive inks are mainly used to print RFID antennas, replacing traditional metal foils produced by foiling or etching. It has two main advantages. First of all, the traditional metal foil made by the foiling method or etching method has a complicated process and a long time for the production of the finished product. The application of the conductive ink to print the antenna is a high-speed printing method, which is efficient and fast, and is a printed antenna. The fastest and cheapest method of choice in the circuit. Today, conductive inks have begun to replace etched antennas at various frequency bands, such as ultra-high frequency bands (860 to 950 MHz) and microwave frequency bands (2450 MHz). Antennas printed with conductive ink can be compared to traditionally etched copper antennas. In addition, conductive inks It is also used to print sensors and circuit prints in smart labels. Secondly, metal foils fabricated using conventional foiling or etching methods consume wasted metal materials at a relatively high cost, while the cost of raw materials for conductive inks is lower than that of conventional metal antennas. This has a great impact on reducing the production costs of smart labels. significance.

(3) unique process requirements. Smart label printing has unique requirements for the production process, and it should mainly pay attention to high yield, thick paper printing and composite processing.

In terms of high yield, since the value of the smart label itself is many times higher than that of an ordinary printed label, it brings high profits to the enterprise, and high yield of printed matter is particularly important. In particular, many products require multi-color UV ink printing, glazing, and gluing. Most of the large-volume labels are also processed by roll-to-roll or no-interface printing. Due to the large number of processing operations, the number of finished products has increased. Screening difficulty.

For thick paper printing, in the paperboard processing, it must be noted that the equipment must have good printability for 350-gram-thick paperboard, and the tension of the paper tape should be kept stable in the paper-card printing to ensure that the accumulated printing overlay error is minimized. Therefore, if each frame is overprinted, but the space between the frames has a large error, it will cause troubles for the compounding and die-cutting process after the smart label is printed.

As for composite machining, it is a key process in the processing of smart labels. In the composite processing, not only does the size between each label not change due to tension, but also for film materials, it takes into account the tensile deformation caused by the label spacing Increase and make appropriate adjustments.

3, the standard for electronic tags is;

(1) High sensitivity (high Q value)

(2) High decoding rate (standard decoding rate is 1%)

(3) Low reactivation rate after decoding (revival rate should be 0 in 10 minutes)

(4) Adhesiveness is good

(5) The overall softness of the soft tag is better. Although the standard is dead, but to produce a qualified label, we must do high-tech, fine craftsmanship. The technology for producing electronic anti-theft soft tags is not a single technology and process, and its technology and process are a combination of many aspects. It includes electronics/circuitry, mechanical control, chemistry/chemicals, and printing.

4, electronic tag technology parameters are as follows:

Label parameters

Specifications 38mmX42mm, 30mmX37mm, 50mmX50mm and so on.

Thickness 10 wire

Frequency 8.2M up and down offset 0.1

Q value 153

No decoding rate 1/10000

Resurrection rate 1/1000

Fifth, the basic principle of radio frequency tag reading and writing equipment

Radio frequency tag reading and writing equipment is one of the two important components of RFID systems (tags and readers). According to the features of the specific functions, there are some other popular names such as: Reader, Interrogator, Communicator, Scanner, and Reader. And Writer), a programmer, a reading device, a portable readout device, an AEI device (automatic equipment identification device), and the like.

Under normal circumstances, radio frequency tag reading and writing equipment should be designed according to the read and write requirements of radio frequency tags and application requirements. With the development of radio frequency identification technology, radio frequency tag reading and writing equipment has also formed some typical system implementation modes. The focus of this chapter is also to introduce the implementation principle of this reader/writer.

The reader/writer is corresponding to the radio frequency tag reading/writing device. The reader/writer transmits the command to the radio frequency tag through the spatial channel between the reading device and the radio frequency tag. The radio frequency tag makes the necessary response after receiving the command from the reader/writer. This realizes radio frequency identification. In addition, in radio frequency identification application system, under normal circumstances, contactless collection of radio frequency tag data realized by a reader/writer or tag information written by a reader/writer into a radio frequency tag is to be returned in an application system or from Application system, this forms the interface API (Application Program Interface) between the radio frequency tag reading and writing device and the application system program. Under normal circumstances, the reader/writer is required to be able to receive commands from the application system, and respond according to the commands of the application system or the agreed protocol (returning the collected tag data, etc.).

VI. RF Antennas in Smart Tags

The type of RF antenna must be chosen so that its impedance matches the free space and ASIC. Directional antennas have less radiation patterns and return loss interference. The access control system can use short-range passive tags. In an RF device, the matching between the antenna and the tag chip becomes more severe when the operating frequency is increased to the microwave region. The goal of the antenna is to transmit maximum energy into and out of the tag chip. This requires careful design of the antenna and the free space and the matching of its attached tag chips. The frequency bands considered are 435 MHz, 2.45 GHz and 5.8 GHz for use in retail merchandise.

1, the antenna must:

(1) It is small enough to be attached to the required items;

(2) There is directionality of omnidirectional or hemispherical coverage;

(3) Providing the largest possible signal to the tag's chip;

(4) Regardless of the direction of the object, the polarization of the antenna can match the reader's interrogation signal;

(5) Robust;

(6) Very cheap.

(7) The main considerations when choosing an antenna are:

a, the type of antenna;

b. Antenna impedance:

c. The performance of the RF applied to the item;

d. RF performance when there are other items around labeled items.

2. Possible choices

There are two ways of using this: 1) The tagged item is placed in a warehouse, there is a portable device, may be handheld, asks for all items, and they are required to give information feedback information; 2) Install a reader at the door of the warehouse Set up, ask and record entries and exits. Another major choice is active tags or passive tags.

3, optional antenna

In the RFID system with 435 MHz, 2.45 GHz and 5.8 GHz frequencies, there are several types of optional antennas. See the table below. They focus on the size of the antenna. The gain of such a small antenna is limited, the magnitude of the gain depends on the type of radiation mode, the omnidirectional antenna has a peak gain of 0 to 2 dBi, and the directional antenna has a gain of 6 dBi. The gain size affects the antenna's range of action. The first three types of antennas in the table below are linearly polarized, but a microstrip antenna can make a circularly polarized, logarithmic spiral antenna only circularly polarized. Since the directionality of the RFID tag is not controllable, the card reader must be circularly polarized. A circularly polarized tag antenna can generate a strong signal of 3dB.

4, impedance problems

For maximum power transmission, the input impedance of the chip after the antenna must match the output impedance of the antenna. The antenna is designed to match the impedance of 50 or 70 ohms, but the antenna may be designed to have other characteristic impedances. For example, a slot antenna can be designed with an impedance of several hundred ohms. The impedance of a folded dipole can be 20 times that of a standard half-wave dipole. The lead-out point of the printed patch antenna can provide a wide range of impedance (usually 40 to 100 ohms). The type of antenna is selected so that its impedance can be matched with the input impedance of the tag chip. Another problem is that other objects close to the antenna can reduce the return loss of the antenna. For omnidirectional antennas, such as double dipole antennas, this effect is significant. Changing the spacing between the dipole antenna and a ketchup did some actual measurements, showing some changes, and other objects had similar effects. In addition, the dielectric constant of the object, not the metal, changes the resonant frequency. A plastic bottle of water reduces the minimum return loss frequency by 16%. When the distance between the object and the antenna is less than 62.5mm,