Printing aluminizing properties of the hottest BOP

2022-08-14
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The printing and aluminizing properties of BOPET film and its influencing factors

Abstract: This paper introduces the adhesion mechanism of film Aluminizing and printing, and discusses the surface properties of BOPET film and its influencing factors in order to improve its Aluminizing and printing properties

key words: BOPET attached film aluminized printing surface performance

I. Introduction

in recent years, the biaxial tensile polyester (BOPET) film industry has developed at an amazing speed, and its application scope is also expanding, especially in the field of printing and packaging. Due to its high tensile strength, superior air barrier to offset higher manufacturing costs, good dimensional stability and chemical resistance, Therefore, it has the potential to overwhelm BOPP film. Compared with other non-polar plastic films, BOPET film has a certain polarity, and its aluminum plating and printability are acceptable. However, in order to better improve its adhesion fastness during aluminum plating and printing, it still needs to be surface treated, and sometimes even after a certain surface treatment, it will cause dealumination and deinking after aluminum plating or printing due to other reasons, such as the weak interface layer formed by oil, dust, low molecular substances and other pollution, which will affect its use. Therefore, it is necessary to deal with the dealumination and deinking of BOPET film after aluminizing or printing, which will affect its use. Therefore, it is necessary to make an in-depth discussion and Research on the aluminizing and printing properties of BOPET film and its influencing factors, so as to further expand the application of BOPET film in the field of printing and packaging

simply speaking, the printing or Aluminizing of film is the adhesion of ink or aluminizing layer on the surface of film. Therefore, to improve the printing and aluminizing effect of film, it is required to enhance the adhesion fastness between ink or aluminizing layer and film surface. Next, we will explain how to improve the adhesion between ink or aluminized layer and film from the aspects of adhesion mechanism, surface structure and properties of BOPET film and its influencing factors

II. Adhesion mechanism

1. Intermolecular force and bond energy

intermolecular force and bond energy have an important influence on the adhesion between ink or aluminized layer and plastic film, and are the main factors affecting the adhesion fastness between them. Generalized intermolecular forces include van der Waals forces, chemical bonds and hydrogen bonds

van der Waals force 8. Opening the aperture ring includes orientation force, induction force and dispersion force. The orientation force is the attraction of the permanent dipole moment of polar molecules due to electrostatic interaction, and its action energy is 1.2x 1X104J/mol。 The inducing force is the force generated by the influence of polar molecules on other polar and non-polar molecules, and its action energy is 0.6x 2X104J/mol。 The dispersion force can be regarded as the result of the "instantaneous dipole moment" interaction of molecules, which exists between non-polar molecules, polar molecules and polar and non-polar molecules. The dispersion force is weak, and the dispersion energy of small molecules is generally 0.8x 4X103J/mol[1]。 Generally, the surface of plastic film is non-polar. Even if it has a certain polarity, such as BOPET and BOPA, its polarity is relatively low. The resin component in the ink has a certain polarity, and the aluminum coating is also a polar material with high surface energy. Therefore, there is a weak dispersion force between the plastic film, especially the non-polar plastic film, and the ink or aluminum layer, and there is a lack of strong orientation force, so the adhesion fastness between them is relatively low

chemical bonds include covalent bonds, coordination bonds, etc., with strong bond energy of 4.2x 4X105J/mol[1]。 Most plastic films have good chemical stability and lack of active groups on the surface, so it is usually difficult to have chemical interaction with ink and aluminum layer to form chemical bonds, thus affecting the adhesion between them

hydrogen bond is a weak chemical bond formed by the functional group ah in the molecule and atom B in different molecules. Its bond energy is 2.1x104 ~ 4.2x104j/mol[1], which is much smaller than the energy of chemical bond, which is greater than van der Waals force, but the order of magnitude is the same

2. Surface tension and wettability

the surface is the external area of the object when it exists alone. The outward direction of the material molecules on the surface is different from the situation that the molecules in the non surface area (phase) are in the balance of forces in all directions because they are not attracted by the same molecules. The molecules in the surface area of the material produce an inward contracting force or heat energy due to the unbalanced force, that is, surface tension or surface energy [2]

generally, objects on the earth are in the environment of air (including the vapor of some substances), and the surface tension of liquid is usually measured by liquid (L) in the environment of vapor (air) (V). Therefore, the measured value is actually the interfacial tension between liquid and gas γ LV, but γ The LV value is very close to the liquid surface tension measured in vacuum γ LV。

for printing, the ink is fully spread on the film substrate, that is, complete wetting is the prerequisite for the formation of good adhesion fastness, because only when the ink and the film surface are sufficiently close, the intermolecular distance reaches μ Below m, mutual attraction can be generated between molecules, and the molecular spacing can be further shortened to the distance that can be in the most stable state

when the liquid contacts the solid surface, there are three forces in equilibrium, as shown in the following figure

in the figure: γ S is the surface tension of solid, which is the force of liquid extending on the surface of solid, and has the effect of expanding the interface area between solid and gas

γ L is the surface tension of the liquid

γ SL is the force that reduces the interface area between solid and liquid, which is called the interfacial tension between liquid and solid

θ Is the contact angle. When the three forces reach equilibrium

when θ When approaching 0 ℃, cos θ At this time, the wettability of liquid to solid reaches the maximum value. For ink and film, close contact is achieved in this case. It can be seen from the above formula that the wettability and adhesion can be improved by increasing the surface tension of the film, reducing the surface tension of the ink or reducing the interfacial tension between them. This is why we need to carry out surface treatment on the film before printing and aluminizing to improve its surface tension

3. diffusion effect

for printing, when the solubility parameters of resin and solvent in ink are similar to those of film, they are easy to be miscible. When they are in close contact with each other, under the influence of molecular thermal motion (micro Brownian motion), long-chain molecules and their chain segments will undergo diffusion movement, forming an intertwined interface layer between polymers, thereby improving the adhesion between them

4. mechanical action

the adhesion fastness between the smooth plastic film surface and the inking and aluminizing layers is not good, because the contact area between them is relatively small, and there is a lack of necessary mechanical anchoring effect. When the film surface is treated to have appropriate roughness, on the one hand, the effective bonding area between the ink and aluminum layer and the film surface is increased; On the other hand, the ink and aluminum powder condensed during vacuum aluminum plating can enter the pits and pores on the rough film surface, so the ink resin and aluminum powder are mechanically embedded in the pores, forming many tiny mechanical connection points, and firmly "anchoring" the ink and aluminum layer on the film surface [3]. However, too rough surface is not conducive to adhesion, because when the surface is too rough, the wettability of printing ink becomes poor, and printing ink and aluminum powder cannot completely fill the pores, causing adhesion defects, but reducing the adhesion

III. surface structure performance of BOPET film and its influence on film printing and aluminizing performance

from the above analysis of adhesion mechanism, it can be seen that the surface structure and performance of BOPET film directly affect the performance and effect of subsequent processing such as aluminizing, printing and compounding. The following are from the surface polarity and tension, surface roughness, friction coefficient Film interface layer and other aspects to explain the performance characteristics of its surface and its influence on its printing and aluminizing properties

1. surface polarity and surface tension

the molecular structure of the material itself determines the size of the material polarity, and the surface tension of the material is related to its surface polarity. The greater the polarity, the greater the surface tension. Pet macromolecular chain contains polar group ester group. Therefore, the surface of BOPET film has certain polarity, and its surface tension is larger than that of general non-polar plastic films such as BOPP. The surface tension of BOPET film without surface treatment can reach 40 ~ 42 dyne/cm [4]. When the film is used for printing, in order to make the ink completely infiltrate (wet) the film surface, the surface tension of the film is required to be equal to or greater than the surface tension of the ink. Therefore, during printing, the surface tension of the film is required to be at least greater than 38 dyne/cm [5]. For vacuum aluminum plating, due to the high surface energy of the aluminum surface, the surface polarity and surface tension are large, and its surface often contains hydroxyl groups, while the surface of BOPET film is due to the existence of ester groups, It also has a certain polarity, so on the one hand, the film is combined with the aluminum layer by van der Waals force; On the other hand, in the BOPET thin-film fluid field, pet is in a plane layered aggregation state, and its benzene ring lies flat in the direction of the film surface. The existence of benzene ring forms a redundant electronic system, which is superimposed with the electron cloud on the outer layer of aluminum atom to form a valence bond [6]

practice has proved that in general, untreated BOPET film can meet the requirements of printing and aluminizing. However, in order to further increase the adhesion fastness between ink and aluminum layer and film, BOPET film usually needs to be surface treated. There are 1 reasons for the film surface The latest standard surface treatment methods include corona treatment, plasma treatment, chemical treatment, photochemical treatment, flame treatment, coating treatment, etc. Corona treatment is the most widely used one. The functions of corona treatment are as follows: ① discharge between the electrode and the corona treatment roll through the electrode to ionize the air and form ozone and nitrogen oxide. At the same time, high-energy electrons and ions attack the surface of the film, breaking its chain molecules, producing free radicals, and reacting with the corona products of the air to produce polar groups such as hydroxyl and carbonyl, which improves the surface tension and polarity of the film. ② High energy electron and ion implantation films produce micro concave dense holes on the surface of the plastic film, roughening the surface of the film and increasing the surface activity. The wetting tension of the film surface is related to the intensity of corona treatment. The intensity of corona treatment is related to the electrode voltage and the gap between electrode and corona roller. The electrode voltage is high, the distance between the electrode and the corona roller is small, and the corona treatment effect is strong; It is related to whether there is - 40 ~ + 130 ℃ air between the film and corona roll. If there is air between the film roll, the back of the film will also be treated; It is related to the cleanliness of corona roll and electrode surface. If the corona roll and electrode surface are dirty, the effect of corona treatment will be weakened

the addition of additives may also have a certain impact on the polarity and surface tension of the film surface. The commonly used additive in BOPET film is anti adhesion agent, usually silicon dioxide. The silicon oxygen bond in silicon dioxide has strong polarity, and the surface of silicon dioxide particles often adsorbs a certain amount of combined water and hydroxyl. Therefore, silicon dioxide particles have high surface energy, so the silicon dioxide particles exposed on the surface of the film help to increase the polarity and surface tension of the film surface, which is conducive to aluminum plating and printing. Sometimes, in order to improve the compatibility between silica particles and pet, promote its application in PE

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