There are many varieties of practical plastic film for packaging. In the use of many plastic films, there are often cases of mutual penetration and mutual substitution, but the characteristics of various plastic films themselves cannot be ignored. Therefore, it is not easy to correctly select and apply a plastic packaging film. This requires the personnel of the packaging materials industry to understand some of the basic functions of plastic packaging film, mainly for the protection of goods, promotional functions, adaptability to packaging machinery and Other special needs. In addition, economic rationality and adaptability to environmental protection must also be considered.
The protective function of the packaging material is the most important and basic function. It can be said without exaggeration that if the plastic film does not have a reliable protection effect on the packaged goods, it loses its use value as a packaging material. The protective function of plastic film on commodities is multi-faceted. Different products and different packaging forms have different emphasis on the protection function of plastic packaging film.
Reliable mechanical protection consists of preventing the leakage of goods in the package or the damage and contamination of the goods by the entry of foreign substances into the package. The performance index that directly reflects the mechanical protection function of the plastic film is mainly the mechanical strength of the film, such as tensile strength, tear strength, drop impact strength (drop impact) and puncture strength.
Good weld strength is also a necessary condition for plastic film bags to reliably protect goods. If the weld strength is insufficient, the weld will become the Achilles heel of the plastic film bag, and the plastic bag will lose its protection to the product due to the crack of the weld. Ordinary polypropylene biaxially oriented film has good mechanical strength, but because of poor welding properties, biaxially oriented polypropylene single film is generally not used for bag making. The welding performance of plastic film is usually expressed by the weld strength, that is, N/15mm, the higher the weld strength, the better the weldability.
Among the other functions of commodity protection, the most common considerations are barrier properties and shading properties.
Barrier performance refers to the performance of plastic film to prevent the transmission of oxygen, carbon dioxide, nitrogen and other gases as well as aroma, water vapor and other substances. When there is no clear range, it generally refers to the barrier of non-polar gases such as oxygen, carbon dioxide and nitrogen. For many commodities, especially food products, the barrier properties of plastic packaging films are important factors for the long-term and effective storage of the packaged goods. The packaging of fresh fruits and vegetables requires that the film should have moderate air permeability, properly inhibit breathing and allow the packaged articles to maintain a certain metabolism without necrosis, thereby extending the shelf life.
The most commonly used method for the barrier properties of plastic films is to measure the amount of material per unit area through a certain amount of time in a certain temperature and humidity. The barrier property of the plastic film to the aroma, usually after the scented substance is sealed in a film bag, the time required for the aroma to pass through the film bag is measured (the plastic bag is placed in a desiccator, and the time is periodically opened for inspection, and the time at which the fragrance is initially perceived is The longer the fragrance time, the better the barrier properties of the film to the aroma transmission. Shading is also very important for the packaging of some goods. Light, especially ultraviolet light, is an important cause of discoloration, fading, and oxidative deterioration of some substances, so it needs to be taken seriously. The light-shielding property is measured by the light transmittance at a given wavelength, and the light transmittance is high, and the light-shielding property is poor. The effect of the plastic film on the product display is closely related to the light transmittance, haze, gloss, antistatic property and printability of the film itself, and needs to be paid enough attention.
Light transmittance and haze are important indicators for determining the visibility and clarity of the packaged goods, and the relationship between the display effects of the products is particularly large. Both light transmittance and haze are expressed as a percentage. The larger the value of light transmittance, the better the transparency of the film. The larger the haze, the greater the turbidity of the object observed through the film, that is, the sharper the sharpness.
Glossiness is the ability of a plastic film to reflect light when exposed to light, expressed as a percentage of the brightness of the sample reflected in the direction of normal reflection relative to the standard surface. The higher the gloss value, the better the brightness of the film surface.
As we all know, the printing patterns on the packaging can not be ignored for the promotion and display effect of the products. Roughly speaking, the quality of plastic film printing refers to whether the film needs to be surface pretreated before printing. The antistatic property of the plastic film directly affects the dust absorption of the plastic film bag. Good antistatic property, not easy to vacuum; poor antistatic property, easy to vacuum. Vacuuming reduces the transparency, gloss, and clarity of the printed film. Therefore, the good antistatic properties of the plastic film are important for maintaining a good display of the bag for a long time. When a good display effect is desired, a film having good antistatic properties should be selected.
The antistatic property of a plastic film is expressed by surface resistivity or charged half life. The lower the surface resistivity and the shorter the charged half-life, the better the antistatic properties of the film.
With the continuous improvement of production levels, the application of automatic production lines has become increasingly widespread. When using mechanized, high-speed packaging, the packaging film must be highly valued for packaging machinery. The performance index that affects the adaptability of plastic packaging film to packaging machinery is mainly the smoothness and weldability of the film.
Good smoothness is beneficial to the smooth movement of the film in the packaging machine during packaging, avoiding the damage caused by excessive resistance during its movement. The smoothness of the film can be described by the magnitude of its coefficient of friction. The smaller the coefficient of friction, the better the smoothness performance. The heat welding performance mentioned here refers not only to whether the plastic packaging film can be heat-sealed, or whether it can achieve a sufficiently high welding strength after heat sealing, and it is often required that the plastic packaging film is allowed to be heat-sealed. There is a larger heat seal time interval and a larger heat seal pressure interval. Although some films can be heat-sealed and can obtain high welding strength, the heat sealing conditions are harsh and cannot be well matched with the packaging machinery, and sufficient attention should be paid to this.
The special requirements for packaging films according to the needs of specific commodities are in fact within the scope of some special requirements. Because of their particularity, they are introduced separately. Such requirements include the compatibility of the plastic film with the contents, the adaptability of the plastic film to the environment of use, the dielectric properties, the hygiene, and the restraint.
It is often necessary to consider whether the plastic packaging film will be corroded, dissolved or swelled by the packaged material to lose strength and the plastic film is a chemical reaction between the trivial and the packaged material, causing the performance of the product to be degraded or the package to be damaged.
It is often necessary to consider the high and low temperature resistance of the film, such as refrigeration, especially the use of plastic packaging film for frozen foods, which needs to have good low temperature resistance; plastic packaging film for retort foods needs to have good high temperature resistance.
Products such as integration are easily broken down by static electricity in the package. Therefore, the plastic film selected for such product packaging must have good antistatic properties, and the surface resistivity is generally controlled at about 108 ohms or less.
When packaging food or pharmaceutical products, the selected plastic packaging film must have good hygienic performance and meet the requirements of relevant national health standards to ensure that the plastic film does not cause pollution to the packaged goods.
Packaging restraint is important when using heat shrink packaging and wrapping. Therefore, when selecting such a film, attention should be paid to shrinkage, shrinkage stress, and elastic recovery rate, and should be selected according to the different conditions of the product. Insufficient binding force, packaging (especially collection packaging) is not tight; but if the binding force is too large, it may cause fragile and fragile items to be destroyed.
Under the premise of meeting the above performance requirements, when using plastic packaging film. Try to choose relatively low-priced varieties to save packaging costs, reduce commodity costs, and improve competitiveness. Blindly pursuing the “high-end†of packaging will obviously increase the production cost of goods, and it is meaningless to improve the packaging effect of goods, and must be avoided.
The wide application of plastic packaging materials has made positive contributions to industrial and agricultural production and people's living standards. However, it has also brought about a negative impact on the living environment of human beings and caused a great burden on the environment. Therefore, in the selection of plastic packaging film, in addition to considering the above principles, we should also attach great importance to the adaptability of plastic film to environmental protection.
When selecting plastic film, we must first grasp the characteristics of the product and its basic requirements for packaging. At the same time, we should have a clear understanding of the basic properties and main features of plastic packaging film, especially the commonly used plastic packaging film. In order to choose the ideal plastic packaging film
The protective function of the packaging material is the most important and basic function. It can be said without exaggeration that if the plastic film does not have a reliable protection effect on the packaged goods, it loses its use value as a packaging material. The protective function of plastic film on commodities is multi-faceted. Different products and different packaging forms have different emphasis on the protection function of plastic packaging film.
Reliable mechanical protection consists of preventing the leakage of goods in the package or the damage and contamination of the goods by the entry of foreign substances into the package. The performance index that directly reflects the mechanical protection function of the plastic film is mainly the mechanical strength of the film, such as tensile strength, tear strength, drop impact strength (drop impact) and puncture strength.
Good weld strength is also a necessary condition for plastic film bags to reliably protect goods. If the weld strength is insufficient, the weld will become the Achilles heel of the plastic film bag, and the plastic bag will lose its protection to the product due to the crack of the weld. Ordinary polypropylene biaxially oriented film has good mechanical strength, but because of poor welding properties, biaxially oriented polypropylene single film is generally not used for bag making. The welding performance of plastic film is usually expressed by the weld strength, that is, N/15mm, the higher the weld strength, the better the weldability.
Among the other functions of commodity protection, the most common considerations are barrier properties and shading properties.
Barrier performance refers to the performance of plastic film to prevent the transmission of oxygen, carbon dioxide, nitrogen and other gases as well as aroma, water vapor and other substances. When there is no clear range, it generally refers to the barrier of non-polar gases such as oxygen, carbon dioxide and nitrogen. For many commodities, especially food products, the barrier properties of plastic packaging films are important factors for the long-term and effective storage of the packaged goods. The packaging of fresh fruits and vegetables requires that the film should have moderate air permeability, properly inhibit breathing and allow the packaged articles to maintain a certain metabolism without necrosis, thereby extending the shelf life.
The most commonly used method for the barrier properties of plastic films is to measure the amount of material per unit area through a certain amount of time in a certain temperature and humidity. The barrier property of the plastic film to the aroma, usually after the scented substance is sealed in a film bag, the time required for the aroma to pass through the film bag is measured (the plastic bag is placed in a desiccator, and the time is periodically opened for inspection, and the time at which the fragrance is initially perceived is The longer the fragrance time, the better the barrier properties of the film to the aroma transmission. Shading is also very important for the packaging of some goods. Light, especially ultraviolet light, is an important cause of discoloration, fading, and oxidative deterioration of some substances, so it needs to be taken seriously. The light-shielding property is measured by the light transmittance at a given wavelength, and the light transmittance is high, and the light-shielding property is poor. The effect of the plastic film on the product display is closely related to the light transmittance, haze, gloss, antistatic property and printability of the film itself, and needs to be paid enough attention.
Light transmittance and haze are important indicators for determining the visibility and clarity of the packaged goods, and the relationship between the display effects of the products is particularly large. Both light transmittance and haze are expressed as a percentage. The larger the value of light transmittance, the better the transparency of the film. The larger the haze, the greater the turbidity of the object observed through the film, that is, the sharper the sharpness.
Glossiness is the ability of a plastic film to reflect light when exposed to light, expressed as a percentage of the brightness of the sample reflected in the direction of normal reflection relative to the standard surface. The higher the gloss value, the better the brightness of the film surface.
As we all know, the printing patterns on the packaging can not be ignored for the promotion and display effect of the products. Roughly speaking, the quality of plastic film printing refers to whether the film needs to be surface pretreated before printing. The antistatic property of the plastic film directly affects the dust absorption of the plastic film bag. Good antistatic property, not easy to vacuum; poor antistatic property, easy to vacuum. Vacuuming reduces the transparency, gloss, and clarity of the printed film. Therefore, the good antistatic properties of the plastic film are important for maintaining a good display of the bag for a long time. When a good display effect is desired, a film having good antistatic properties should be selected.
The antistatic property of a plastic film is expressed by surface resistivity or charged half life. The lower the surface resistivity and the shorter the charged half-life, the better the antistatic properties of the film.
With the continuous improvement of production levels, the application of automatic production lines has become increasingly widespread. When using mechanized, high-speed packaging, the packaging film must be highly valued for packaging machinery. The performance index that affects the adaptability of plastic packaging film to packaging machinery is mainly the smoothness and weldability of the film.
Good smoothness is beneficial to the smooth movement of the film in the packaging machine during packaging, avoiding the damage caused by excessive resistance during its movement. The smoothness of the film can be described by the magnitude of its coefficient of friction. The smaller the coefficient of friction, the better the smoothness performance. The heat welding performance mentioned here refers not only to whether the plastic packaging film can be heat-sealed, or whether it can achieve a sufficiently high welding strength after heat sealing, and it is often required that the plastic packaging film is allowed to be heat-sealed. There is a larger heat seal time interval and a larger heat seal pressure interval. Although some films can be heat-sealed and can obtain high welding strength, the heat sealing conditions are harsh and cannot be well matched with the packaging machinery, and sufficient attention should be paid to this.
The special requirements for packaging films according to the needs of specific commodities are in fact within the scope of some special requirements. Because of their particularity, they are introduced separately. Such requirements include the compatibility of the plastic film with the contents, the adaptability of the plastic film to the environment of use, the dielectric properties, the hygiene, and the restraint.
It is often necessary to consider whether the plastic packaging film will be corroded, dissolved or swelled by the packaged material to lose strength and the plastic film is a chemical reaction between the trivial and the packaged material, causing the performance of the product to be degraded or the package to be damaged.
It is often necessary to consider the high and low temperature resistance of the film, such as refrigeration, especially the use of plastic packaging film for frozen foods, which needs to have good low temperature resistance; plastic packaging film for retort foods needs to have good high temperature resistance.
Products such as integration are easily broken down by static electricity in the package. Therefore, the plastic film selected for such product packaging must have good antistatic properties, and the surface resistivity is generally controlled at about 108 ohms or less.
When packaging food or pharmaceutical products, the selected plastic packaging film must have good hygienic performance and meet the requirements of relevant national health standards to ensure that the plastic film does not cause pollution to the packaged goods.
Packaging restraint is important when using heat shrink packaging and wrapping. Therefore, when selecting such a film, attention should be paid to shrinkage, shrinkage stress, and elastic recovery rate, and should be selected according to the different conditions of the product. Insufficient binding force, packaging (especially collection packaging) is not tight; but if the binding force is too large, it may cause fragile and fragile items to be destroyed.
Under the premise of meeting the above performance requirements, when using plastic packaging film. Try to choose relatively low-priced varieties to save packaging costs, reduce commodity costs, and improve competitiveness. Blindly pursuing the “high-end†of packaging will obviously increase the production cost of goods, and it is meaningless to improve the packaging effect of goods, and must be avoided.
The wide application of plastic packaging materials has made positive contributions to industrial and agricultural production and people's living standards. However, it has also brought about a negative impact on the living environment of human beings and caused a great burden on the environment. Therefore, in the selection of plastic packaging film, in addition to considering the above principles, we should also attach great importance to the adaptability of plastic film to environmental protection.
When selecting plastic film, we must first grasp the characteristics of the product and its basic requirements for packaging. At the same time, we should have a clear understanding of the basic properties and main features of plastic packaging film, especially the commonly used plastic packaging film. In order to choose the ideal plastic packaging film
Yugong Machinery Manufacturing Factory , http://www.gybiomassmachine.com