The advantages of screen printing in the production of smart labels

Abstract: The advantages, principles, and methods of RFID tagging are discussed. The advantages of screen printing on smart tagging are discussed, and screen printed conductive inks are illustrated.

This paper introduces the advantages, principles and manufacturing methods of RFID tags, discusses the advantages of screen printing in the production of smart tags, and explains the screen printed conductive inks.

As the transponder of the RFID (radio frequency identification) system, the smart tag is the most advanced non-contact sensing technology. It has a series of outstanding advantages, such as large data memory capacity, high data density, good anti-pollution ability and durability, almost no impact on the pollution of water, oil and chemicals, long reading distance, high speed, and good data security performance. and many more. The facts have proved that with the development of RFID and materials technology, smart labels will replace the current popular barcodes and become the new darling of retail, packaging and logistics.

RFID is a non-contact automatic identification technology that automatically recognizes target objects and obtains relevant data by using page signals. The RFID system generally consists of three modules: a smart tag, a reader, and a radio frequency antenna, as shown in FIG. The system works as follows. When a tag is exposed to a radio frequency signal generated by a system reader and transmitted by a radio frequency antenna island port, the internal line generates an induced current and the chip is activated; the chip transmits its own information through the tag's built-in antenna (coil). The radio frequency (RFID) antenna of the RFID system receives the carrier signal sent from the tag and transmits it to the reader via the antenna regulator. The reader then demodulates and decodes the received signal, thereby obtaining the data information contained in the tag.

From the working principle of the RFID system, the reader of the system can read multiple smart tags at the same time, and the identification of the tags is completely non-contact automatic recognition. Without any manual intervention, only a variety of objects to be labeled with smart tags are required. Move through the radio frequency area, as shown in Figure 2. Therefore, using smart tag technology saves the manpower necessary for bar code technology, and at the same time it also improves the sales efficiency of supermarkets, which facilitates consumers and saves consumers time.

The relatively high cost of labels is a bottleneck in the promotion process of smart labels. Market research shows that the unit price of each label currently ranges from about 20 cents to 1 US dollar; generally speaking, for a single item, the acceptable label price is 5 cents. Therefore, the overall promotion of smart labels should be mainly from two aspects: to further improve the performance of the label and reduce the production cost of the label.

The smart tag consists of a (silicon) chip, a built-in antenna (coil), and a substrate, as shown in Figure 3. At present, the performance and price of chips and substrates are basically stable. Therefore, the advantages of various manufacturing methods can only be reflected in the optimization of the manufacturing process of the built-in antenna and the reduction of antenna production costs. Judging from a method, the built-in antenna of the tag is functional and cost-effective. It should meet at least three standards: 1 The antenna should have high electrical performance (impedance); 2 It is easy to install the chip on the antenna. 3 Can produce large quantities and low cost production.

At present, there are mainly three methods for producing smart tag antennas.

Etching method. Also called subtraction production technology. In this method, a flat copper foil is first laminated on a plastic film; then a photosensitive paste is coated on the copper foil, dried, and then lighted through a positive film (pattern having a desired shape); put in a chemical developer; At this point, the photosensitive part of the photoresist is washed away to expose the copper; Finally, an etching bath is put in, and all the copper that is not covered by the photoresist is etched away to obtain a copper coil of a desired shape.

· Coil winding method. The label coil is wound on a winding tool and fixed. At this time, the number of turns of the antenna coil is required to be larger (a typical number of turns is 50 to 1 500 turns). This method is commonly used for labels with a small frequency range (eg, less than 135 kHz) and for market applications where the cost of the label is not considered first.

· Conductive Ink printing method. Also known as additive manufacturing technology. Since the tag antenna has a relatively rough shape, it can be realized by printing (adding) a conductive ink on the substrate. Currently, a screen printing method is mainly used to produce a UHF (Ultra High Frequency) tag antenna.

The advantages of screen printing antenna

Screen Printing Labels The built-in antenna uses conductive ink. Conductive ink is a kind of conductive composite material formed by metal conductive particles (silver, copper, carbon) dispersed in the connecting material. After printed on the substrate, it acts as a wire, an antenna and a resistor. The ink is printed on a flexible or rigid substrate (paper, PVC, PE, etc.) to create a printed circuit, and an antenna printed with conductive ink can receive RFID-specific radio frequency signals. The smart tag built-in antenna using conductive ink screen printing method has many advantages over other methods (such as copper etching method), can be said to be a green, stable, low-cost solution, is a high-volume production of low-cost labels is a The ideal process method has its advantages in the following aspects

1. low cost

A significant advantage of using the method of screen printed conductive ink to make a tag built-in antenna is low cost and easy operation. The low-cost nature of this method is reflected in two aspects.

(1) Screen printing process. First of all, the investment in the introduction of screen printing equipment is much cheaper than the introduction of copper etching equipment. In addition, since there is no need for additional investment in the screen printing process due to environmental protection requirements, the maintenance cost of production and equipment is lower than that of the copper etching method. In fact, maintaining the copper etching line and handling the waste (such as the residue in the chemical etching tank) itself requires a very expensive fixed cost, and thus also increases the single piece cost of the tag.

(2) conductive ink. First of all, from the material cost, the conductive ink is cheaper than the etching metal coil; in addition, from the material consumption, the etching process consumes a lot of metal, and the conductive ink printing antenna or circuit is fast and low cost. efficient.

2. Easy to operate

As an additive manufacturing technique, screen printing technology is itself an easy-to-control, one-step process compared to subtractive manufacturing techniques such as etching. In the screen printing process, there are no technical problems such as ink balance in the offset printing, replacement of the blanket, ink emulsification, and adjustment of the ink fountain key, so that it has an easy operation.

3. "Green

From the above description we can see that the copper etching process must use photosensitive adhesives and other chemical reagents. These chemicals have a strong erosive effect, and the generated waste and effluents cause great pollution to the environment. The screen printing technology uses conductive ink to directly print on the substrate without the use of chemical reagents, thus having the advantages of “green” and environmental protection.

Of course, the use of coiled copper technology to make antennas is also a "green" and environmentally friendly manufacturing process. But if you consider the cost factor of the label, the winding method is obviously inferior to screen printing.

4. Flexible substrate selection

Screen printing can print conductive inks on almost any substrate to produce the desired antenna. Therefore, the selection of label substrates is also more flexible and diverse. Substrates that can be used as smart labels include polyester, polyimide, ABS engineering plastics, PVC (polyvinyl chloride), polyethylene, polypropylene, polycarbonate, (paper) cardboard, and the like. When making a label, which material to choose depends on the specific application.

In contrast, copper etching technology can only use substrates with high corrosion resistance, ie highly aggressive substrates (such as polyester) that can tolerate the chemicals used in the etching process. It is worth mentioning that the price of such substrates may also be more expensive than the substrate selected by screen printing. For example, the polyester used in the copper etching process is much more expensive than the paper substrate used in the ticket system of the screen printing bus system.

5. Rich label style, good stability and reliability

Using screen printing technology allows the antenna to have a variety of design styles, capable of printing multiple styles of antennas. Thus, the style of the produced tag is rich, allowing the tagged 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.

In fact, since the screen-printed conductive ink (or conductive paste) is formed by dispersing conductive metal particles in a thermoplastic polymer adhesive or resin, the smart tag antenna thus obtained has the characteristics of a viscous fluid. Better elasticity. When the label is bent under pressure, the performance and reliability of the screen-printed smart label at this time, the etched smart label and the EAS (electronic anti-theft) label produced by the aluminum etching are all high.

About screen printing conductive ink

After the screen printing ink is dried, since the distance between the conductive particles I becomes smaller, the free electrons move along the direction of the applied electric field to form an electric current and have good conductivity. For printed smart tags with built-in antennas, a good conductive ink formulation requires good printability and has the characteristics of strong adhesion, low resistivity, low curing temperature, and stable electrical conductivity after printing.

Faced with the revolutionary changes in packaging, retailing, and logistics that RFID smart labels will bring and the broad application prospects of conductive inks in this label, some companies at home and abroad have also made outstanding achievements in the research and development of conductive inks. For example, in foreign countries, Flint Ink Corporation of the United States has conducted xt-bL in a variety of radio frequency bands for lines printed with conductive ink and copper-etched lines. High-speed pages such as 860-950 M Hz, 2 450 MHz microwaves, and 13.56 MHz high frequencies have all been tested and received very good results. The United States Parelec has also succeeded in printing smart tag antennas. Parmod conductive ink was developed. For different applications, some of the performance parameters of the circuit coil printed by Parmod ink under different screen printing methods are shown in Table 1. In China, for example, Shanghai Baoyin Electronic Materials Co., Ltd. has introduced a series of conductive inks (conductive pastes); Wuhan Sanlai Technology Co., Ltd. has also introduced water-based conductive inks.

summary

Smart tags have been added to the packaging of goods by numerous retailers due to advanced technology and convenient management, in order to track the flow of goods in real time, which has great market potential and wide prospects. In the process of the promotion and application of smart labels, how to reduce the cost of labels and improve performance is a top priority. The use of appropriate conductive inks to print conductive coils on the substrate by screen printing as a smart tag's built-in antenna is undoubtedly an important way to reduce the cost of smart tags. With the maturing of radio frequency technology and electronic packaging technology and the introduction of excellent conductive ink formulations, screen printing will play an increasingly important role in promoting high-performance, low-cost applications for smart labels.

Author: Fan Xiaoping Reprinted from: RFID World Network