Application of the hottest aluminum foil in compos

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Application of aluminum foil in composite flexible packaging

aluminum foil is an important substrate of flexible packaging. It is a packaging material that can not be replaced so far, and it is widely used. In modern packaging, almost all composite materials that require light tight or high barrier products use aluminum foil as barrier layer

I. advantages of aluminum foil material

aluminum foil is made of electrolytic aluminum with high purity (purity above 99.5%) after multiple calendering. The application of aluminum foil material in composite flexible packaging mainly has the following outstanding advantages:

1. The appearance is bright and beautiful, with silver white metallic luster and good reflectivity, giving people a sense of luxury, which plastic film does not have. Therefore, the use of aluminum foil in commodity packaging can beautify commodities and improve the grade of commodities

2, high barrier and shading. Compared with paper and plastic film, aluminum foil has a highly dense metal crystal structure, so it has excellent barrier properties, such as moisture resistance, gas resistance, shading and fragrance retention. When aluminum foil is combined with paper, film, etc., it can almost completely block the transmission of any

gas, water vapor and light, effectively protect the contents of the package, prevent the contents from corruption and deterioration due to moisture absorption and oxidation, and thus greatly extend the storage life and shelf life of the contents of the package

3. Aluminum foil is made of natural starch with fast heat transfer speed. The maximum force range of general single arm tensile testing machine is often used: 1n/5n/10n/20n/50n/100n/200n/500n/1000n/2000n/5000n and so on. It can be selected quickly and has good high and low temperature resistance. Therefore, it has been widely used in cooking and packaging

4. Aluminum is a light weight metal, and using aluminum foil as packaging can relatively save and reduce transportation costs

5. It can be recycled to reduce energy consumption; Moreover, it is non-toxic, odorless/tasteless, and will not affect the flavor of the contents of the package

due to its outstanding advantages in the above aspects, aluminum foil has become a widely used packaging material in the flexible packaging industry

second, the main performance indicators of aluminum foil material

1, thickness

thickness is one of the most basic and important physics of aluminum foil, l, energy generation. The thickness of the aluminum foil has a certain relationship with its barrier property. With the increase of the thickness of the aluminum foil, its transmittance to oxygen, water vapor, light, etc. gradually decreases. Accordingly, its barrier property will be higher if the two set screws on the back of the upper holder are loosened first. The thickness of aluminum foil used in composite flexible packaging is usually between 7-9 LM. In practical application, the aluminum foil with appropriate thickness should be selected according to the different contents and performance requirements, otherwise the expected barrier effect (too thin) will not be achieved, or the cost will be increased (too thick)

in addition, it should be pointed out that the thickness of aluminum foil must be uniform with high accuracy. If the thickness of aluminum foil is uneven, it is easy to cause problems in production. Firstly, the thickness of aluminum foil is inconsistent, which makes the adhesive coating difficult to be uniform in the aluminum foil composite process, thus affecting the composite strength of aluminum foil and plastic film; Secondly, the thickness of aluminum foil is inconsistent, and the material roll is loose and tight at the same time. During the compounding process, the material roll will swing left and right, and it is easy to cause foil breakage after tension is applied to the winding, which is very detrimental to the smooth progress of the compounding process

2. Moisture permeability

moisture permeability refers to the permeability of aluminum foil to water vapor under certain conditions, which reflects the deterioration of moisture-proof performance of aluminum foil to a certain extent. See Table 1 for the relationship between the thickness of aluminum foil and its moisture permeability

3. Number of pinholes

in the calendering and manufacturing process of aluminum foil, if the purity of aluminum is not high enough and (or) the shadow direction of dust in the surrounding air during the calendering process, when the aluminum foil is calendered to a thickness of less than 101lm, pinholes often exist. The number of pinholes and the size of pinhole aperture depend on the number of dust and the size of dust particle diameter. Due to the existence of pinholes, the barrier performance of aluminum foil will be seriously affected. For example, in the cooking packaging bag with LV foil as the intermediate material, the existence of a large number of pinholes is easy to penetrate oxygen, water vapor and light, which will have an adverse impact on the quality of the packaged food, and even cause food corruption and deterioration. Therefore, the number of pinholes in aluminum foil should be as small as possible, and the aperture should also be as small as possible. Generally speaking, the number of pinholes of 71lm thick aluminum foil should be 1 based on 50 holes/m2, and the number of pinholes of 9dlm thick aluminum foil should be less than 30 holes/m2. In order to reduce the number of pinholes in aluminum foil and improve its barrier property, high-purity aluminum raw materials must be used in the manufacturing process of aluminum foil

plus I, and its purity is required to be at least higher than 99.5%. At the same time, the environment in the calendering workshop should be kept clean and dust-free to prevent the impact of dust particles on the quality of aluminum foil

4. Surface cleanliness

when aluminum foil is compounded with other substrates, its surface cleanliness has a decisive impact on the composite strength. In addition, if the surface cleanliness of aluminum foil is poor and there is residual oil stain, the composite strength is relatively poor. A large amount of lubricating oil is used in the calendering and manufacturing process of aluminum foil. The surface of calendered

aluminum foil should be cleaned with organic solvent acetone before winding, and the lubricating oil used in calendering should be cleaned. In addition, the aluminum foil used in the composite flexible packaging must be annealed at high temperature under high vacuum (0.0133pa) to make the surface of the aluminum foil remain lubricated; Stupid into gas volatilization. Although all of these are conducive to the improvement of the surface cleanliness of aluminum foil, a very small amount of oil will inevitably remain, and the residue of oil will determine the quality of the surface cleanliness. The surface cleanliness standard of aluminum foil is divided into five levels: A, B, C, D and E, of which a is the best cleanliness, almost no oil; Level B is next, and so on. Table 2 shows the determination method of the surface cleanliness grade of aluminum foil. In composite flexible packaging, the surface cleanliness of aluminum foil is required to be high, which should generally reach grade B or above, and there is no uneven oil contamination. The composite adhesive can have a good wetting effect on its surface, otherwise it will affect the composite quality of products. Therefore, in the actual production, we should remember to strictly control the quality and do a good job in the inspection of the cleanliness of aluminum foil, which can not be ignored

it can be seen from table 3 that aluminum foil used in composite flexible packaging is thin, its mechanical strength is low, easy to crack, lack of flexibility, and easy to break:

in actual use, it is rarely used as a packaging material alone, and in most cases, it is combined with paper, plastic film and other materials to form a composite packaging material

6, servant stability

aluminum foil is an amphoteric metal, which is not resistant to acid and alkali, and can react chemically with acid and alkali. Therefore, when using aluminum foil composite flexible packaging to package acidic or alkaline substances, attention should be paid to avoid the reaction between acid and alkali substances through the inner layer and the aluminum foil layer, so as to corrode the aluminum foil and make it ineffective

III. The Application of aluminum foil in composite flexible packaging

we have introduced earlier. In practical application, aluminum foil is generally used after compounding with plastic, paper, etc., mainly for the following reasons:

1. Aluminum foil itself is not strong and easy to tear, so it is generally not used as a packaging material alone

2. The thermal adhesion of aluminum foil is poor, so it is impossible to heat seal the bag alone.

IV. some problems that should be paid attention to in dry compounding.

1. In aluminum foil compounding processing, when selecting adhesives, it should be noted that if the package contents contain substances such as acid, spicy or grease, these substances will pass through the inner layer of aluminum foil composite packaging materials, which will have a certain impact on the adhesion of adhesives, As a result, the peel strength between aluminum foil and inner plastic film decreases significantly, and even delamination and degumming occur. This phenomenon is more likely to reappear in high-temperature sterilization. Therefore, the adhesive used in the composite processing of aluminum foil must have good resistance to the contents

2. In the composite processing of aluminum foil materials, the amount of glue should also be controlled, not too small or too large. The amount of glue has a great influence on the composite strength of the composite film. If the amount of glue is too small, it will affect the composite fastness and cause the composite film to peel easily; On the contrary, if the amount of glue is too large, it will not only increase the cost of

, but also prolong the curing time by fully mixing with polymers in a physically dispersed state, which will affect the production efficiency. Therefore, the amount of glue should be controlled within an appropriate range according to the actual situation. Generally speaking, in the process of aluminum foil composite processing, the amount of glue can be determined according to the graphic situation of printed matter and the end use of the composite packaging material. The glue amount data (dry basis) listed in

in Table 4 can be used for reference

the amount of glue can be adjusted by the number of lines on the line roller, the depth of the hole, and the concentration of the glue solution

3. Due to the good thermal conductivity of aluminum foil, when aluminum foil is compounded with plastic film, the temperature of the surface of the composite steel roller can be appropriately increased and controlled between 80~1000c. In addition, the curing temperature of aluminum foil composite film can also be appropriately increased by about 5cc

4. In the process of composite processing, the unwinding tension of aluminum foil should be smaller, generally controlled at about 29.4 Newton, otherwise the aluminum foil is easy to be broken. In addition, it should be noted that during the compounding process, the aluminum foil enters the compounding roll directly without any guide roll after unwinding; Otherwise, the aluminum foil is easy to crack after being bent by the guide roller, which will affect the quality of the composite product

(author: Shijiazhuang flexible packaging color printing factory)

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