Application of the hottest aluminum coating in com

2022-08-02
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Application of aluminum plating film in composite flexible packaging

aluminum plating film is a kind of composite flexible packaging material formed by coating a very thin layer of metal aluminum on the surface of plastic film with a special process. The most commonly used processing method is vacuum evaporation method, which is to melt and evaporate the metal aluminum at high temperature under high vacuum, so that the vapor precipitation of aluminum is accumulated on the surface of plastic film, so that the surface of plastic film has metal luster. As it has the characteristics of both plastic film and metal, it is a kind of packaging material with low price, beautiful appearance, excellent performance and strong practicability. Therefore, aluminized film has been widely used in the packaging of food, medicine, chemical products, such as fast food, tea, coffee and cosmetics. In this paper, the characteristics of aluminized film and its application in dry compounding are briefly introduced

I. characteristics and application of aluminized film

the use of aluminized film in flexible packaging mainly has the following outstanding advantages:

firstly, aluminized film composite products have the characteristics of plastic film; Secondly, a layer of dense "aluminum plating" on the surface has a good barrier effect; At the same time, it is also bright in appearance, thus beautifying the packaging effect of products; In addition, it replaces the aluminum foil composite packaging to a certain extent, thus reducing the packaging cost

(1) the aluminized film has excellent metallic luster and good reflectivity, giving people a feeling of richness and luxury. Using it to package goods can beautify goods and improve the grade of goods

(2) the aluminized film has excellent gas resistance, moisture resistance, light shielding and fragrance retention. It not only has strong resistance to oxygen and water vapor, but also can block almost all ultraviolet, visible and infrared rays, and can prolong the storage life and shelf life of the contents. Therefore, for food, drugs and other products that need to extend the storage life, It is a good choice to use aluminized film as packaging, which can prevent food or contents from corruption and deterioration due to moisture absorption, oxygen permeability, light exposure and other reasons. In addition, the aluminized film also has fragrance retention and small fragrance transmission rate, which can keep the fragrance of the contents for a long time. Therefore, the aluminized film is an excellent barrier packaging material. They only need to find a supplier

(3) aluminized film can also replace aluminum foil to some extent, but the amount of aluminum is greatly reduced, which not only saves energy and materials, but also reduces the cost of a common mechanical testing equipment for commodity packaging

(4) the aluminized layer on the surface of the aluminized film has good conductivity and can eliminate the electrostatic effect. Therefore, it has good sealing performance, especially when packaging powdery goods, it can ensure the sealing of the packaging, thus greatly reducing the incidence of leakage

because of its outstanding advantages in the above aspects, the application of aluminum coating is becoming more and more extensive, and it has become a very common packaging material in the flexible packaging industry. There are many kinds of aluminized films. At present, the most widely used aluminized films are polyester aluminized film (VMPET) and CPP aluminized film (VMCPP). Polyester aluminized film (VMPET) is generally used as a kind of intermediate layer that needs to be packaged. Because of its beautiful appearance, it is most used in high-end packaging, such as milk powder, tea and other packaging bags. CPP aluminum plating film (VMCPP) is generally used as the heat sealing layer of composite packaging, and is commonly used in the packaging of ordinary small food (such as biscuits)

I. Basic Performance of aluminized film

1. Appearance. The surface of the aluminized film shall be flat and smooth, without folds or only a small amount of flexible folds, without obvious unevenness, obvious impurities and rigid blocks, without defects such as spots, bubbles, missing plating holes, etc., and no obvious bright strips, yin and Yang surfaces, etc

2. The thickness of aluminized film shall be uniform, the horizontal and vertical thickness deviation shall be small, and the deviation distribution shall be relatively uniform. There are no obvious ribs on the drum, otherwise it is easy to wrinkle when compounding

3. Thickness of aluminum coating. The thickness of the aluminized layer is directly related to the barrier property of the aluminized film. With the increase of the thickness of the aluminized layer, the transmittance of oxygen, water vapor and light gradually decreases, and accordingly, the barrier property of the aluminized film is also improved. Therefore, the thickness of the aluminum coating should meet the standard requirements, and the coating should be uniform, otherwise the expected barrier effect will not be achieved

4. The aluminized layer has strong adhesion and good firmness, otherwise it is easy to dealuminate and cause quality problems. During the processing of high-quality vacuum aluminizing film, a certain amount of primer shall be coated on the aluminized surface of the aluminized substrate film to improve the adhesion between the aluminized layer and the substrate film, so as to ensure that the aluminized layer is firm and not easy to fall off; Then, a two-component polyurethane adhesive shall be coated on the aluminized layer as the top coating to protect the aluminized layer from wear

5. Physical and mechanical properties. As the aluminized film is subject to mechanical force in the composite process, it is required to have certain mechanical strength and flexibility, and should have good tensile strength, elongation, tear strength, impact strength, excellent folding resistance and toughness, so as to ensure that it is not easy to appear bending, folding, fracture and other phenomena in the composite process

6. Moisture permeability. Moisture permeability indicates the water vapor permeability of the aluminized film under certain conditions, which reflects the moisture resistance of the aluminized film to a certain extent. For example, the moisture permeability of 12 um thick polyester aluminized film (VMPET) is between 0.3 g/M2 · 24h and 0.6 g/M2 · 24h (temperature 30 ℃, relative humidity 90%); The moisture permeability of CPP aluminized film (VMCPP) with a thickness of 25 um is between 1.0 g/M2 · 24h and 1.5 g/M2 · 24h (temperature 30 ℃, relative humidity 90%)

7. Oxygen permeability. The oxygen permeability represents the oxygen permeability of the aluminized film under certain conditions. It reflects the resistance of the aluminized film to oxygen. For example, the oxygen permeability of the 25 um thick polyester aluminized film (VMPET) is about 1.24 ml/㎡ · 24h (temperature 23 ℃, relative humidity 90%)

8. Surface tension. In order to make the printing ink and composite adhesive have good wettability and adhesion on the surface of the aluminized film, it is required that the surface tension of the aluminized film should reach a certain standard, otherwise the adhesion and adhesion of the printing ink and adhesive on its surface will be affected, thus affecting the quality of the printed matter and composite products. For example, the surface tension of polyester aluminized film (VMPET) shall be more than 45 dynes, and at least more than 42 dynes

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III. precautions in dry composite application

in the composite process of aluminized film, the following problems should be paid attention to:

1. Select appropriate adhesive

at present, the common two-component polyurethane adhesive is most widely used in dry composite. However, due to its small relative molecular weight and strong molecular activity, It is easy to penetrate into the aluminized layer and damage the adhesion fastness of the aluminized layer; In addition, the initial adhesion of the common adhesive is generally high, and the solvent release is poor. The adhesive liquid is easy to penetrate into the aluminized layer and damage the aluminized layer. After curing, due to the influence of the residual solvent, the bonding strength will decline, and even the aluminized layer will migrate. Therefore, if the common adhesive is still used in the composite aluminized film products, various quality problems will inevitably occur, such as poor composite strength Aluminum coating migration, "spots" and other faults. Therefore, it is better to use special adhesives for aluminum coating in the composite processing of aluminum coating to avoid or reduce the occurrence of such failures. For example, yh501s of GAOMENG and pu-2975 of Zhejiang New Oriental ink Co., Ltd. have excellent bonding effect on aluminum coating. Compared with ordinary adhesives, the special adhesive for aluminum plating film has moderate molecular weight, uniform molecular weight distribution, low initial bonding force, good solvent release and good coating performance. Therefore, it can well ensure the quality of composite products for aluminum plating film

2. The amount of glue should be appropriate.

too small amount of glue will certainly affect the composite fastness, resulting in poor composite strength and easy peeling. However, if the amount of glue is too large, it will not only increase the cost, but also prolong the curing time, which is prone to the migration of the aluminized layer. Therefore, the amount of glue should be controlled within an appropriate range. Generally speaking, during the composite processing of aluminum plating film, the amount of curing agent should be appropriately reduced when preparing the glue solution, so as to improve the flexibility of the glue film, maintain good flexibility and extensibility, and prevent the migration of aluminum plating layer. In addition, it is necessary to ensure the uniformity of gluing, otherwise it is easy to have "spots"

4. Control of drying temperature

during the composite processing of aluminum coating, the drying temperature of the drying channel should be appropriately increased, for example, by 5 ~ 10 ℃, so that ethyl acetate volatilizes more thoroughly, so as to ensure that the adhesive is fully dried, reduce the residue of solvent, and prevent the transfer of aluminum coating, especially in high temperature and high humidity weather

5. Control the tension control

during the composite processing of aluminum coating, it is necessary to control the unwinding tension of aluminum coating. The automatic unwinding tension can be used, and the tension should not be too large. Otherwise, the aluminum coating will stretch under the action of large tension, resulting in elastic deformation, and the aluminum coating on it will become loose accordingly, and the adhesion will be reduced, and the aluminum coating may fall off

6. Control of curing temperature and time

generally speaking, aluminized film composite products should not be cured at low temperature for a long time. During the curing process, the curing temperature should be appropriately increased and the curing time should be shortened. Generally, the curing temperature should be controlled between 50~60 ℃, so that the adhesive molecules can be solidified quickly, so that there is not enough activity time and ability, and its penetration damage to the aluminized layer can be reduced, It is conducive to ensuring and improving the quality of composite products$ Page break $

IV. common problems and solutions in dry composite application

1. Migration of aluminized layer of aluminized film after composite

cause of problem:

(1) the quality of aluminized film itself is relatively poor, and the bonding firmness between aluminized layer and base film is relatively poor. The imported aluminized film has a layer of primer on the vacuum aluminized surface of the base film to improve the adhesion of the aluminized layer, and then vacuum aluminized on the primer, and then coated with two-component polyurethane glue as the top coating on the aluminum layer to protect the aluminized layer from falling off. The aluminized layer of this aluminized film has good firmness and is not easy to fall off. However, the domestic common aluminized film is easy to fall off because it does not use primer, which has low adhesion and is not very firm

(2) the selected adhesive is inappropriate

(3) the curing time of composite film is too long

(4) the amount of glue applied is too large, the adhesive is not dry enough, and the residual solvent gradually penetrates into the aluminized layer, resulting in the migration of the aluminized layer

(5) if the tension is not properly controlled, the base film of the aluminized film will undergo elastic deformation under large tension, which will affect the adhesion of the aluminized layer, which is also one of the factors that promote the migration of the aluminized layer of the aluminized film

solution:

(1) replace the aluminum coating with good quality

(2)

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