Several Kinds of Plastic Film Packing Materials

1. Biaxially oriented polypropylene film (BOPP)
BOPP film is formed by the co-extruded polypropylene sheet by particles, then stretched in both directions by the aspect obtained. As the tension of molecular orientation, so the film's physical stability, mechanical strength, better air tightness, high transparency and gloss, tough wear-resistant, is the most widely used print film. Generally used thickness 20 ~ 40 μ m, the most widely used for the 20 μ m. Its main drawback is poor sealing, it is generally used as the outer layer of thin film composite membrane, such as the composite of moisture with polyethylene film, transparency, strength, stiffness and printability than ideal for dress dry food. Since the surface of BOPP film for non-polarity, high crystallinity, surface free energy is low, therefore, poor performance of its printing, ink and adhesive adhesion to the poor, in the printing and composite surfaces prior to the need for treatment.

2. Low-density polyethylene film (LDPE)
Low-density polyethylene film generally use two kinds of blow molding and casting process is made of cast polyethylene film of uniform thickness, but because of higher prices, now rarely used. Blow by blow molding grade polyethylene film PE particles by blowing machine blowing, low cost, the most widely used. Low-density polyethylene film is a translucent, shiny, soft texture film with excellent chemical stability, heat sealing, water resistance and moisture resistance, freeze, can be boiled, its main drawback is that oxygen The barrier is poor, commonly used in the inner layer of thin film composite flexible packaging materials, but also the most widely used, the maximum amount of a plastic packaging film, plastic packaging films accounted for about 40% of consumption.

Since polyethylene does not contain polar groups, namely non-polar surface and high crystallinity, surface free energy is low, therefore, poor performance of the film print, ink and adhesive adhesion to the poor Therefore, in the compound before the need for printing and surface treatment.

3. Polyester film (PET)
Polyester film is polyethylene terephthalate was prepared by extrusion method into thick slices, and then by two-way stretch material made of the film. It is a colorless, transparent, glossy film, excellent mechanical properties, rigidity, high hardness and toughness, puncture resistance, abrasion, high temperature and low temperature, chemical resistance, oil resistance, air tightness and Paul Hong Xing good permeability resistance is a common one composite film substrate, but the higher the price of polyester film, the general thickness of 12 μm, common to do steaming the outer packaging materials, better printability.

4. Nylon membrane (PA)
Nylon film is a very tough film, transparency is good, and good gloss, tensile strength, tensile strength is higher, but also has good heat resistance, cold resistance, oil resistance and organic solvent resistance, abrasion resistance, good puncture resistance, and relatively soft, good oxygen barrier, but poor water vapor barrier, moisture absorption, moisture permeability and large, heat sealing is poor, suitable for rigid packaging materials, mostly used in oily foods, meat, fried foods, vacuum-packed food, cooking food packaging.

5. Cast polypropylene film (CPP)
Cast polypropylene film is produced by cast process polypropylene film, can be divided into ordinary cooking class CPP and CPP two, transparency excellent, uniform thickness, and the performance of vertical and horizontal to the uniform, the general used composite films layer material.

General CPP film thickness is generally between 25 ~ 50μm, and the transparency of the composite OPP good, bright surface, feel strong, general gift bags are used to such material. Meanwhile, the film also has good heat sealing ability. Cooking class CPP film thickness is generally between 60 ~ 80 μ m, the ability of 121 ℃, 30 minutes of high-temperature cooking, oil resistance, good airtightness and high heat seal strength, the inner meat packaging in general are CPP film using cooking class.

6. Aluminum film
Currently the most widely used aluminum metallized polyester film mainly (VMPET) and CPP metallized (VMCPP). Both the characteristics of metallized plastic film, but also has the characteristics of metals, the role of aluminum films shading, anti-ultraviolet radiation, not only extended the shelf life of the contents, but also to improve the brightness and perception of the film, from a certain degree, instead of aluminum foil, with cheap, beautiful and good barrier properties, so, aluminum composite package applications in a wide range, the key used in biscuits and other dry, puffed food packaging, and other pharmaceuticals, cosmetics the packaging.

Metallized polyester generally used as the middle layer of composite packaging materials, because of its beautiful appearance, the most in the high-end packaging applications, such as milk powder, tea bags. CPP metallized compound generally used as packaging sealing layer, commonly used in ordinary small food (eg biscuits) packaging. Basic properties of the plastic film material requirements in the procurement of plastic film material, must be clear plastic film material for the production of what the performance requirements, the following will make a brief introduction.

1. Appearance
Plastic film on the surface should be smooth with no wrinkles or only a small number of live fold, without obvious uneven, black spots, impurities, crystal points and rigid blocks, no stripes, scar, tendons and other ills of violence, no bubbles, pinholes and cracking, aluminum in the aluminum layer should be uniform, not allowed to have significant Bright, yin and yang side and so on. It also requires the film surface clean, no dirt, oil, etc.

2. Specification and deviation
Plastic film width, thickness and deviation should meet the requirements, and should be uniform thickness, horizontal, vertical thickness deviation is small, and the deviation is more evenly distributed. Moreover, aluminum in the aluminum layer should meet the requirements.

3. Transparency and gloss
The transparent plastic film, its transmittance higher, should generally be more than 92%; while the opaque plastic film, such as albuginea, requires its high brightness, good opacity. In addition, the plastic film should also have good gloss, printing and composite products to ensure bright, beautiful.

4. Physical and mechanical properties
As the plastic film in the complex process of printing and are subject to mechanical forces and, accordingly, requested film material must have certain mechanical strength and flexibility. Physical and mechanical properties of plastic films include tensile strength, elongation at break, tear strength, impact strength, etc. In addition, the metallized aluminum layer on a solid degree should meet the requirements.

5. WVT
Said plastic film material under certain conditions the amount of water vapor through, such as 90% relative humidity, temperature of 30 ℃ in the case, 24 hours a thickness of 25 μ m for each square meter of plastic film, through the The quality of water vapor. It from a certain degree, the film moisture of materials, water vapor permeability of various films of different materials, which determines its scope of application.

6. Oxygen content
Said plastic film material under certain conditions by the amount of oxygen, such as 90% relative humidity, the temperature is 23 ℃ circumstances, 24 hours a thickness of 25 μ m of plastic film, through oxygen per square meter volume. The water vapor permeability of various thin films are also different.

7. Geometric Dimensional stability
Plastic film must have a certain geometric dimensional stability, otherwise, the expansion Lv too large, complex process in the printing and subject to mechanical forces or the role of heat prone of stretch will not only affect overlay accuracy, wrinkles will appear, curl and so on, seriously affect the product quality and production efficiency.

8. Chemical stability
Plastic film in the printing and complex process, we need contact with inks, adhesives and certain organic solvents, which are chemical substances, therefore, plastic film must be exposed to these chemicals have some resistance to resistance, so as not to its impact.

9. Surface Tension
To make the printing ink and adhesive compound used in plastic film with good surface wetting and adhesion between the surface tension of film should be required to achieve a certain standard, otherwise it will affect the ink and adhesive on the surface of the adhesion and bonding, thus affecting the quality of print and composite products. Such as BOPP film and low-density polyethylene film surface tension required to achieve 3.8 × 10-2N / m or more, nylon films, metallized polyester film and polyester surface tension of the general requirements to 4.5 × 10-2N / m or more. In general, the plastic film in the printing or complex to go through before the surface treatment to improve its surface tension, and can smoothly carry out the printing and complex.

Membrane surface characteristics of the impact of printing and composite

1. Molecular structure of non-polar
Under normal circumstances, ink and adhesive plastic film surface is mainly by adsorption and adhesion force between the two elements to achieve. Most of the plastic film packaging materials in the molecular structure of the basic no polar groups or polar groups with only weak, the critical surface tension, inertia strong, is a typical non-polar polymer materials, inks and adhesives the surface wettability and affinity difference between the two is very weak intermolecular forces.

2. Plastic film surface energy
Plastic film is usually very low surface energy, such as the critical surface tension of polyethylene only 3.1 × 10-2N / m, the critical surface tension of polypropylene only 3.4 × 10-2N / m, the surface energy is low, not easy to ink or the adhesive is wet, it is imperative that the critical surface tension of plastic films is greater than or equal to the surface tension of ink or adhesive to ensure the ink or adhesive on the surface is fully wetted.

3. Plastic film crystallinity
Many plastic film is not only smooth, and high crystallinity, molecular state in the thermodynamic stability, with stable chemical properties, ink or adhesive molecules is difficult in its surface diffusion, so that ink, adhesives, etc. in the film surface adhesion very satisfactory results.

4. Weak surface layer
Polyolefin and other films in the processing process, in order to make films with good openings, antistatic, anti-aging, anti-ultraviolet radiation and other properties, often adding a certain amount of additives, such as opening agent, antistatic agent, plasticizer agent, stabilizer, these additives can easily precipitate migration and the formation of oil to the surface, so thin film formed on the surface strength of the weak surface layer is very low, due to the weak cohesive strength of the surface layer than the subject of low cohesive strength more printing and lamination process will adversely affect.

5. Plastic film surface cleanliness if the relatively poor sanitation, clean air is low, the plastic film on the surface vulnerable to absorption of air in the dust, grease and other substances, which would prevent ink absorption properties and the adhesive with the film surface contact with each other, affect their wetting the surface of the plastic film, so the film must be the cleanliness of the surface of attention.
These factors for the adhesion of printing ink fastness, such as bond strength of composite films has a significant impact, therefore, before printing or complex, the general must be carried out on the plastic film surface.

Plastic film used for surface treatment methods include chemical treatment, solvent treatment, coating treatment, flame treatment, corona treatment and ultraviolet irradiation, etc., which present the most commonly used method is corona treatment. Corona discharge treatment is the use of cutting-edge principle, using high-frequency high-voltage or frequency of high pressure on the surface of plastic film processing, so that the surface activation, was porous, increasing the surface area and enhanced ink and adhesive bond strength, At the same time oxidation of the surface of plastic film, plastic film to improve the surface energy, thereby improving the printability of films and composite performance. Because space is limited, since the content of corona treatment to Syria.