Polypropylene is produced by polymerization from gas after cracking of petroleum at high temperature under the action of catalyst.Films with different properties can be obtained according to different film-forming processing methods, Common films mainly include plain BOPP, matte BOPP, pearlize film, heat seal BOPP film etc.The printing and pouch-making properties of these films are analyzed in detail in this article.

1. Plain BOPP film

Amorphous or partially crystalline films above the softening point are stretched in vertical and horizontal directions, when BOPP film is processed, The surface area of the film is increased, the thickness is reduced and the gloss and transparency are greatly improved. At the same time, due to the orientation of tensile molecules, its mechanical strength, air tightness, moisture barrier, cold resistance and other aspects have been greatly improved.

Properties of BOPP films

Properties of BOPP films includes high tensile strength, high elastic modulus, but low tear strength; Good rigidity, outstanding extensibility and resistance to bending fatigue; High heat and cold resistance, the operating temperature can be as high as 120℃,The cold resistance of BOPP is also higher than that of ordinary PP films; High surface gloss, good transparency, suitable for all kinds of packaging materials with stable BOPP chemical property, In addition to strong acids, such as fuming sulfuric acid, nitric acid has a corrosive effect on it, insoluble in other solvents, only some hydrocarbons have swelling effect on it. Excellent water resistance, is one of the best moisture resistance materials, water absorption rate < 0.01%; The printability is poor, so the surface corona treatment must be carried out before printing, and the printing effect is good after processing;Anti-static agents need to be added when it is applied to the production of film resin due to the Static electricity.

Biaxially oriented polypropylene film (BOPP) is generally a multi-layer co-extruded film, which is made of polypropylene particles co-extruded into sheets and then stretched in both vertical and horizontal directions. Due to the orientation of the stretched molecules, this film has good physical stability, mechanical strength, air tightness, high transparency and gloss, toughness and wear resistance and is a widely used printed film.Generally, the thickness is 20 ~ 40 μm, the most widely used is 20 μm. The main disadvantage of BOPP film is poor heat sealing.Therefore, it is generally used as the outer layer of composite film, After compounding with polyethylene film, it stands out for moisture resistance, transparency, strength, stiffness and good printing, which is suitable for holding dry food.Because the surface of the BOPP film is non-polar with high crystallinity and low surface free energy, its printing performance is poor, and the adhesion to the ink and adhesive is poor and surface treatment is required before printing and lamination.

2. Matte BOPP film

Matte film is a low gloss (gloss less than 15%) high haze into diffuse reflection extinction effect of plastic matte products, with paper-like appearance, printing color realistic reproduction and feel comfortable. Matte film is a film made by biaxial stretching using matte masterbatch in a single surface layer. The matte film surface looks like paper and natural products, mainly used for book, periodical, annual report cover, cardboard and other paper lamination.

Compared with plain BOPP, matte BOPP has the following characteristics: the matte surface can play a shading role and the surface gloss is greatly reduced.If necessary, the matting layer can be used as sealing layer; The matting surface has good smoothness, and the film roll is not easy to stick because of the surface roughing. The tensile strength of the matte film is slightly lower than that of the general film and the thermal stability is also slightly worse than that of the ordinary BOPP.

Matte heat sealed BOPP film has the characteristics of tensile resistance, wrinkle resistance, stable performance etc., which is widely used in cosmetics, daily necessities, toys, stationery and catering industries in various items packaging, mainly plays a dust-proof, moisture-proof, decorative role, the same is to reduce packaging costs, improve packaging grade and effect.

3. Pearlize film

The white opaque BOPP pearlize film has a silk-like texture and a soft and pleasing pearl luster, low density, excellent flatness, gas barrier, which can be widely used in dried fruits, ice cream, candy, high-grade soap, gifts and other direct packaging, at the same time, it is also a better printing base, It is not necessary to make a full plate primer when carrying out surface printing, therefore,BOPP pearlize film is favored, Compared with ordinary BOPP films, BOPP pearl films have three typical characteristics: a pearlescent luster, good shading,(especially for UV light barrier) and low density.

PP is the raw material, adding CaCO₃, pearlite pigment and rubber modifier, After mixing,  Pearl film is made.In the process of biaxial stretching, PP resin molecules are stretched, the CaCO₃ particles are stretched and distances are created between them, thus forming a pore bubble, so the pearl film is a microporous foam film, the density is about 0.7 g / cm³.

4.Heat sealed BOPP film

Heat sealed film is divided into one side heat sealed film and both sides heat sealed film, It is formed by biaxial stretching of heat sealing masterbatch on the surface.It is mainly used in heat sealed packaging of food, medicine and other electrical components.

Both sides heat sealed film

The film is of ABC structure and both sides of A and C are heat sealing layers, which is mainly used as packaging materials for food, textiles, audio and video products.

One side heat sealed film

The film is ABB structure and the A layer is the heat sealing layer. After the design is printed on the B side, it is laminated with PE, BOPP and aluminum foil to make bags, which are used as high-end packaging materials for food, beverage and tea.

The heat-sealed BOPP film is processed by biaxial stretching. It is three-layer structure: one side heat seal, the other side can be corona surface.Moreover, it can be printed and used as double-sided heat seal. This product has good flatness, good lamination and printing performance, suitable for high-speed packaging and printing composite packaging.