1. Overview

Vacuum evaporation of metal films is a new process that evaporates metal on the surface of a film substrate under vacuum conditions to form a composite film. The metal material to be plated can be gold, silver, copper, zinc, chromium, aluminum, etc., among which aluminum is the most commonly used. Coating a very thin layer of metallic aluminum on the surface of plastic film or paper (single or double-sided) is called aluminized film, which is widely used to replace aluminum foil composite materials such as aluminum foil/plastic, aluminum foil /paper etc. used.

Aluminized film has the following characteristics compared with aluminum foil composite materials:

(1) It greatly reduces the amount of aluminum used, saves energy and materials, and reduces costs. Aluminum foil is used for composites The thickness is mostly

7~gpm, while the aluminum layer thickness of aluminized film is about

0.05n, and its aluminum consumption is about

aluminum foil

1/140～1/180, and the production speed can be as high as

450m/min.

(2) It has excellent folding resistance and good toughness, with few pinholes and cracks, and no bending and cracking. Therefore, it is resistant to gas, water vapor,

Improved barrier properties against odors, light, etc.

(3) It has excellent metallic luster, and the light reflectivity can reach

97%; and it can form a colored film through coating treatment, and its decorative effect is that of aluminum foil

Unmatched.

(4) Shielding type can be used for partial aluminum plating to obtain any pattern or transparent window so that the contents can be seen.

(5) The aluminum-plated layer has good electrical conductivity and can eliminate electrostatic effects; its sealing performance is good, especially when packaging powdered products, it will not contaminate the sealing part

to ensure The sealing performance of the packaging.

(6) It has good adaptability to post-processing such as printing and lamination.

Due to the above characteristics, aluminized film has become a new type of composite film with excellent performance, economy and beauty, and has replaced aluminum foil composite materials in many aspects.

Mainly used for vacuum packaging of flavored foods and agricultural products, as well as packaging of medicines, cosmetics, and cigarettes. In addition, aluminized films are also widely used as hot stamping materials and trademark label materials in printing.

2. Coating substrate

The substrates of aluminized films are mainly plastic films and paper.

The vacuum evaporation process has the following requirements for the substrate to be plated:

(1) Good heat resistance, the substrate must be able to withstand the radiant heat and evaporation of the evaporation source The latent heat of condensation of the substance.

(2) The volatile substances produced from the film substrate should be less; for substrates with high hygroscopicity, they should be treated before coating.

(3) The base material should have a certain strength and surface smoothness.

(4) The adhesion to the evaporated layer is good; for non-polar materials such as

PP and PE, surface treatment should be carried out before evaporation to improve the adhesion to the coating.

Accessibility.

Commonly used film substrates include: BOPET, BONY, BOPP, PE, PVC and other plastic films and papers. Among the plastic film base materials, the aluminum-plated film formed of three base materials:

BOPET,

BONY, and BOPP, has excellent gloss and adhesion, and is an excellent aluminum-plated film. Films are widely used as packaging materials and hot stamping materials in printing. Aluminum plating

PE film has poor gloss, but its cost is lower and it is widely used. Aluminized paper formed from a paper base material has a lower cost than aluminized plastic film; it is thinner and cheaper than aluminum foil/paper composite materials; it has good processing performance and is not prone to curling during printing. No creases

marks left. Therefore, it has largely replaced aluminum foil/paper composite materials and is used as inner packaging materials for cigarettes, food, etc., as well as packaging trademark materials.

1. Principle of vacuum evaporation.

Place the substrate to be coated (cylindrical) in a vacuum evaporator, and use a vacuum pump to evacuate the film to a level of 1.3×10-2 ~1.3×10-3Pa, heat the crucible to melt and evaporate the high-purity aluminum wire into gaseous aluminum particles at a temperature of

1200℃~1400℃. A continuous and bright metallic aluminum layer is formed on the surface of the moving film substrate after cooling and reduction. See Figure 14-9 for the schematic diagram of vacuum evaporation metal.

/p>

Figure 14-9 Schematic diagram of vacuum evaporation metal

1-Pump 2-Unwinding 3-Cooling roller 4-Heat insulation mask 5-Source 6-Rewinding

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The thickness of the aluminum coating is controlled by controlling the evaporation rate of metallic aluminum, the moving speed of the film substrate, and the vacuum degree of the coating room. Generally, the thickness of the aluminum coating is

>

25~500nm, the width of the aluminum film is

800mm~2000mm

2. The method of evaporating aluminum on the surface of the substrate is direct evaporation. There are two types: plating method and transfer method.

(1) Direct evaporation method. The substrate is directly evaporated on the surface of the substrate through a vacuum coating machine to form an aluminum coating. Evaporation

The evaporation method has higher requirements on the substrate, especially to form a bright metal film, the substrate must have good surface smoothness

If the paper is used. The surface is rough, so the direct evaporation method must be used. The surface must be coated before aluminum plating. In addition, the base material has less volatile matter during the evaporation process, so the direct evaporation method is suitable. The base material has great limitations. It is mainly suitable for evaporation of plastic films and can also be used for evaporation of paper. However, the quality requirements of paper are high and there are certain limits on the ration of paper.

(2) Transfer method. The metal aluminum layer is transferred to the surface of the substrate with the help of a carrier film (vacuum aluminum plating film) to form an aluminum plating film.

A new process developed on the basis of the evaporation method. It overcomes the limitations of the direct evaporation method on the base material and is especially suitable for aluminum plating on various paper and cardboard

. It can be used for aluminum plating of plastic films.

At present, transfer method has been applied to aluminized products of cloth, fiber, leather and other substrates in my country.

3. Evaporated aluminum process

1. Plastic film aluminum plating process is relatively simple. BOPET, BONY, and film substrates do not require surface treatment before aluminum plating. /p>

It can be evaporated directly. When using non-polar plastic films such as BOPP and PE, the surface of the film needs to be corona treated before evaporation.

The tension reaches

38X10-5N～40X10-5N. When coating, place the roll film in the vacuum chamber, close the vacuum chamber and evacuate. When the degree of vacuum reaches a certain level, the evaporation source is heated to

1400℃~1500℃, and then the aluminum with a purity of

99.9% The metal wire is continuously sent to the high temperature area of ??the evaporation source.

Adjust the unwinding, rewinding speed, wire feeding speed and evaporation amount, and turn on the cooling source. The aluminum wire is continuously melted and evaporated in the high-temperature zone, thereby forming a bright aluminum layer on the surface of the moving film, which is finished after cooling. The aluminized film can be used for printing, composite bags, etc. after being cut according to specifications.

2. Paper evaporation aluminum process. There are two methods of paper aluminum plating: direct aluminum plating and transfer method.

(1) Direct aluminum plating method. The direct aluminum plating method is to first coat the surface of the rolled paper substrate with a layer of glue or a composite layer of PE film, and then directly pass it through a vacuum coating machine. Aluminum plating forms a metallic aluminum film on the surface of the paper, and then the aluminized paper is subjected to moisture regain treatment to complete the product.

If you need to obtain

aluminized paper of different colors, you need to perform coloring treatment on the surface of the aluminized paper.

The direct aluminum plating method mainly has the following characteristics:

① The production process is relatively simple and the cost is low.

②The surface quality and strength of the paper substrate are required to be high. When aluminizing, the moisture content of paper is required to be below

3%. Generally, the moisture content of paper is

6~

7%. Lowering the moisture content will cause Paper is brittle and easy to break. Therefore, paper is required to have higher strength.

③The surface gloss of the product is low and the printing filling effect is poor.

The direct aluminum plating method is generally only suitable for thin paper with a dry weight of less than

30g/m2. Thicker paper is difficult to aluminize. Aluminized paper produced by direct aluminizing method

Although the quality is poor, the cost is low, so it is widely used.

(2) Transfer method; The transfer method to produce aluminized paper is more advanced than the direct aluminum plating method. It transfers the aluminum layer on the surface of the aluminized plastic film to the surface of the paper base to form aluminized paper. First, apply the coating evenly on the plastic film base material, generally using

BOPET film and

BOPP film; then apply the plastic film

film base material Aluminum plating is carried out in a vacuum coating chamber to form a metallic aluminum film layer on the coating surface; then a layer of adhesive is applied to the surface of the aluminum layer of the aluminized plastic film; paper, cardboard or The base material is compounded with it and then separated to separate the paint layer and aluminum layer from the plastic film. The

process flow is shown in Figure

14-10.

Figure 14-10 Transfer method process flow chart

The separated plastic film can be reused. The more times it is reused, the lower the cost of the product. The main features of using the transfer method to produce aluminized paper are as follows:

① The production process is relatively complex and the cost is high.

② It has a wide adaptability to the base material, and any paper or cardboard with a basis weight of

30-600g/m2 is acceptable, and the quality requirements for the base material are not high, and the surface does not need to be

Reapply paint or film.

③The product has good quality and bright surface; because there is a layer of paint outside the aluminum layer, it not only plays a protective role, but also improves the printing adaptability

and the filling effect.

④ Adding pigments to the paint can produce colored aluminized paper.

Because transfer method aluminum plating has the above characteristics, it is increasingly used in the production of aluminized paper