Smart card, also known as card, is a chip with storage encryption and data processing capability embedded in a plastic film base to make it easy to carry cards, in finance, taxation, public security, transportation, post and telecommunications, communication, services, medical care, insurance, etc. The field has received extensive attention and application.

The process of processing the smart card is a hot pressing process of the multilayer plastic film, and the lamination effect is related to the compatibility between the plastic film material for the card making, the surface state and the cleanliness of the film material.

Thermogravimetric analysis is a thermal analysis technique that measures the mass of a test sample as a function of temperature under temperature control. The contact angle is the outer tangent of the semicircular form naturally formed by the droplet on the solid surface relative to the solid plane. The contact angle measuring instrument can simultaneously measure and calculate the surface tension and surface free energy of the sample.

Surface analysis is the interaction of electrons, photons, ions, atoms, strong electric fields, thermal energy, etc. with solid surfaces to measure the energy spectrum, spectrum, mass spectrum, and spatial distribution of electrons, photons, ions, atoms, and molecules scattered or emitted from the surface. Or a diffraction image to obtain various techniques for information such as surface composition, surface structure, surface electronic state, and surface physicochemical processes.

1 Experimental part

1.1 main raw materials

PETG film materials for card making: Jiangsu Huaxin, Shanghai Dakai; PET printing film: PETF3368 FILM, DuPont; holographic physics anti-counterfeiting film: Shanghai Hongdun Company.

1.2 main equipment and test parameters

Thermal analyzer: Q-100, American TA company, 10~750°C, heating rate 10°C/min, nitrogen 50ML/min; tensile machine: Shenzhen Ruige RGT-0.5, GT114B.1, card inspection- Peel force test; heat sealing machine: GBC3500 Pro Series, 80~100°C, speed 1.2 cm/s; laminating machine: Santong Company YTJ-Z1X8H laminator, preheating 130°C, 10S, 0.5MPa; hot pressing 135 °C, 10S, 1MPa, cold pressure: room temperature 10S, 1MPa; XPS: Thermo Corporation with ESCALAB250 XPS, magnesium aluminum double anode, sample chamber vacuum 3X10 -9 PA", vacuum chamber 2X10 -9 PA" contact angle measuring instrument: DATAPHYSICS OCA20 Video Contact Angle Gauge, Water Drop Test Printer: Xerox DC1255 Printer.

2 Results and discussion

2.1 The influence of the quality of the card body material

In the process of card making, the same card body material is used for each layer of film material, such as PVC material for bearing layer, and PVC material for printing layer and padding layer. Since each layer of plastic film is of the same material, the compatibility between the layers is generally good. But sometimes it also produces a phenomenon of poor salary. Because the adjustment of raw materials, formulas and processing parameters in the production process of the film products will cause fluctuations in the processing properties of the film materials. If the fluctuation range of the influencing factors is too large, it will affect the lamination effect of the film materials, such as long storage time or storage. If the conditions are bad, the aging of the material, oxidative decomposition, etc., will also affect the coring effect of the material. In view of this situation, different analysis methods can be used to determine the cause of the damage to avoid cracking of the card body. For example, the Vicat softening point of the PETG material is 78 ° C. However, in the process of laminating the card, it is difficult to laminate some of the film materials at a laminating temperature of 120 ° C. To find out the reason, the following test method is employed.

2.1.1 Contact Angle Measuring Instrument

The 1# and 5# samples are laminated and do not reflect the actual surface condition.
The average values ​​of the contact angle measurements of the 2#, 3#, and 4# samples are shown in Table 2.
The 3# sample has weaker binding strength and the contact angle measurement is also small, indicating that the surface state is different from the other two samples.

2.1.2 Surface Element Analysis (XPS)

As shown in Table 3, the silicon content in the 3# and 5# samples is lower than that in the #1, 2# and 4# samples, and the oxygen content in the 5# sample is higher than other samples, 3# and The strength of the 5# sample is also weak, indicating that the content of the silicon additive in the 3# and 5# samples has changed or

2.1.3 Thermogravimetric analysis

As shown in Table 4, thermogravimetric analysis showed that the thermal decomposition rate of the 5# sample was higher than that of the other samples.

The contact angle and surface element analysis showed that the surface state and formula composition of the sample were different. The surface of the material was treated by some experiments, such as grinding, corona, etc., but the strength of the breech could not meet the requirements.

Judging from the data obtained from the above test analysis, the reason for the difference in the strength of the erectile strength may be the change of the silicon additive content of the sample of #3, 5# or the oxidative decomposition phenomenon of the sample during the production and storage process, resulting in failure to bond.

2.2 Surface additive effects of film materials

Some thin-film materials, especially high-transparent materials with smooth surface, prevent the friction between the films from damaging the surface of the film during the production process. Some anti-slip agents are often added to the surface of the film. The main component of the anti-slip agent is silicon compounds such as hatred. Anti-slip agents can affect the mutual bridging between materials if the amount of addition is improperly controlled or unevenly distributed on the surface of the film. The table is a heat sealable data for low temperature heat sealing. “The sample is a sample without an anti-slip agent. The sample is a sample with a normal amount of anti-slip agent.” The sample is a sample with twice the anti-slip dose.

The heat sealing was started from 80 °C with GBC 3500 Pro Series heat sealing machine, and the heat sealing effect was recorded. The heat sealing effect was expressed by the effective ratio of the area of ​​the elastic area. The effective elastic area was fully covered by the PET thermal cover, and the PET was sealed after heat sealing. It can't be peeled off without damage, and the effective area of ​​the fit is divided by the total area of ​​heat seal. Make 5 pairs of 210mmX150mm samples for each temperature, take the average value, then increase the temperature by 5°C. Repeat the above steps until the PET of each group reaches the effective bog in the field. Record the temperature at this time and use the temperature to pay the effective salary. The area ratio is plotted, and the heat seal performance curves of each group of samples are obtained, as shown in Fig. 1.

As can be seen from Figure 1, the greater the amount of anti-slip agent, the greater the effect on the salary strength, the higher the temperature required to achieve the same heat-sealing effect. At the same heat-sealing temperature, the greater the amount of anti-slip agent , the weaker the Hehe strength between the films.

SIMS, XPS, AFM and other test methods can be used to quantitatively or semi-quantitatively analyze the surface of the film. At the same time, combined with the actual heat-sealing effect, the appropriate amount of anti-slip agent can be found to avoid the phenomenon that the inter-membrane strength is unqualified.

2.3 The impact of the printing process

Many card-making film materials require surface printing or printing patterns, and then the card is pressed. Most of the ink or anti-cavitation agent in the printing process is a small molecule solvent. The properties are relatively stable, not easy to decompose, and some are not volatile. If these small molecules are not cleaned during the lamination process, the film will not be very good. Hehe. To prevent the addition of PDMS polydimethylsiloxane to the film-attached printing roller during film printing of personalized information, if the amount is too large, the bond strength between the film materials is reduced.

Table 6 Effect of PDMS dosage on the adhesion strength of PET film

Taking PET film on Xerox DC1255 printer for printing images and laminating heat seals as an example: the amount of PDMS in the printer is controlled at a higher level and normal level, respectively, and the PET film is printed on the same pattern as the unprinted PET film. The card body material is pressed under the same conditions, and each card is made into 5 cards. The three groups of sample cards are subjected to peeling test, and the minimum force value is recorded: see Table 6

The fact that the film was broken during the peel test indicated that the film had been firmly tied to the body of the card. It can be seen from Table 6 that the salary strength between the unprinted film material and the card body is the best, and when the amount of PDMS is increased, the Hehe strength is lowered, eventually resulting in unsatisfactory salary strength. Therefore, when printing or printing, it is important to control the amount of inert additive.

Test methods such as SIMS, XPS, etc. can be used to determine the presence of excess contaminants on the surface of the material.

Some important or statutory documents require physical anti-counterfeiting means. Holographic printing, as an anti-counterfeiting printing method, has been widely used in anti-counterfeiting technology. A large number of membrane embossing holograms are now used. In order to make the embossed hologram easy to view under white light, a layer of aluminum or oxide or sulfide is deposited on the film of the pressed rainbow hologram during the plating process. In the case of improper control, the film will be polluted, affecting the strength of the bond between the films.

The PETG film with the holographic printing pattern and the ordinary PETG film were respectively made with the PET film under the same card-making conditions, and the peeling force test was performed, as shown in Table 7. It can be seen from Table 7 that the strength of the Hertz bond between the holographic printing and the anti-counterfeiting is reduced.

Table 7 Effect of Holographic Printing on the Peel Strength of Films

The surface residue of the holographic film can be tested by SIMS, XPS, etc., and the surface treatment of the holographic film is determined to be clean according to the actual lamination effect. An obvious problem is that the degree of cleanliness of the surface of the holographic film is directly proportional to the strength of the embossing. Therefore, in the production process of the holographic film, it is an important problem to minimize the surface contamination of the holographic film and keep the surface of the film clean.

Since the plastic film is an insulator, it is easy to accumulate static electricity, causing easy adsorption of dust, deterioration in printing or printing quality, and affecting the quality of the final card body. Sometimes it is possible to solve the problem of printing static electricity by spraying antistatic liquid on the back of the film or applying an antistatic layer. However, this treatment is likely to cause surface contamination in a high temperature and high humidity environment in summer. This is because the main component of the antistatic film or the antistatic agent is a substance having a hydrophilic group, or a water-soluble substrate such as polyvinyl alcohol. Excessive exposure of this substance to hot flashes, such as in summer, can cause deliquescence of this coating, and some additives will precipitate on the surface of the material, affecting the Hep strength.

Table 8 compares the results of lamination with a PETG card body and a normal PET and PETG card body after exposure to a water-soluble antistatic coating for 2 days in a high temperature and high humidity environment in summer. It can be seen from the table that the precipitation of the antistatic agent has a great influence on the erection strength of the film, so it is necessary to pay attention to moisture and heat when using such a material with an antistatic agent or an antistatic coating. The surface tension test can be used to judge whether or not the surface of the material is contaminated by the anti-hydrophilic electrostatic agent. Since the water-soluble substance contaminates the surface, the surface of the material tends to become hydrophilic, and the surface tension has a large surface tension. Variety.

3, summary

Smart cards belong to the high-tech industry. The processing of smart cards includes various fields such as plastic processing technology, printing technology and anti-counterfeiting technology. Any improper handling of any technical link will result in poor card lamination. In the process of making smart cards, It is necessary to understand the relevant properties of each material used, pay attention to the factors affecting the lamination fastness of the card body, adopt the relevant testing methods, and combine the actual lamination effect to find the appropriate materials and processing techniques to produce the requirements. Smart card.

(Text / Forensic Center of the First Institute of Public Security, Wang Cheng)

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