Opp film is a kind of polypropylene film. Because the production process is multilayer extrusion, it is called co-extrusion oriented polypropylene film.
If there is a process of biaxial stretching in processing, it is called biaxial stretching oriented polypropylene film bopp film.
Compared with the co-extrusion process, the other is called cast polypropylene film cast polypropylene.
Opp: unidirectional stretching
Bopp: biaxial stretching, horizontal and vertical stretching.
Cpp: cast film, no stretching.
I. OPP film
OPP: Oriented polypropylene (film), stretchable polypropylene, which is a kind of polypropylene.
OPP main products:
1. OPP tape: based on polypropylene film, it has the advantages of high tensile strength, light weight, non-toxic, tasteless, environmental protection, wide application range, etc.
2. OPP bottle: light weight, low cost, improved transparency, good heat resistance, suitable for hot filling.
In recent years, two-way polypropylene (OPP) transparent bottles have become the substitute for PET bottles. At present, the applications in packaging include self-adhesive label, in-mold label, winding label and wet glue point label, the latter is mainly used in beverage and alcohol labeling abroad, and the adhesive self-adhesive label and in-mold label are gradually introduced from Europe to China market in recent years, and their application fields include food, chemical industry, daily chemical products and so on.
In addition, OPP, like PE and PVC films, should be used for shrink films, with the advantages of high transparency, good gloss, high shrinkage rate and shrinkage stress, but poor heat sealing performance and strength, high shrinkage temperature and narrow range.
For daily chemical products with relatively saturated and homogeneous market, appearance is everything, and the first impression determines consumers' buying behavior. Shampoo, shower gel, detergent and other products are used in warm and humid bathrooms and kitchens. Labels are required to withstand moisture without falling off, and their extrusion resistance must match the bottle body. At the same time, transparent bottles put forward strict requirements for the transparency of adhesives and label materials.
3. OPP label: Compared with paper label, it has the advantages of transparency, high strength, moisture resistance, and not easy to fall off. Although the cost has increased, it can get good label display and use effect. With the development of domestic printing technology and coating technology, it is no longer a problem to produce self-adhesive film labels and printed film labels. It can be predicted that the usage of OPP labels in China will continue to increase.
Because the label itself is made of PP, which can be well combined with the surface of PP/PE container, it has been proved that OPP film is the best material for in-mold labels at present, which has been widely used in the field of food and daily chemical in Europe and gradually spread to China, and more and more users have begun to pay attention to or adopt in-mold labeling technology.
Second, BOPP film
BOPP: biaxially oriented polypropylene is also a kind of polypropylene.
Commonly used BOPP films include: ordinary biaxially oriented polypropylene, heat-sealed biaxially oriented polypropylene, cigarette packaging film, biaxially oriented polypropylene pearl film, biaxially oriented polypropylene metallized film, matte film, etc.
The main uses of various films are as follows:
1. Ordinary BOPP film
Usage: mainly used for printing, bag making, adhesive tape and compounding with other substrates.
2. BOPP heat sealing film
Usage: mainly used for printing, bag making, etc.
3. BOPP cigarette packaging film
Usage: used for high-speed cigarette packaging.
4. BOPP pearl film
Usage: used for packaging printed food and daily necessities.
5. BOPP metallized film
Usage: used as vacuum metal plating, radiation, anti-counterfeiting substrate, food packaging.
6. BOPP extinction film
Usage: used for packing boxes of soap, food, cigarettes, cosmetics, pharmaceutical products, etc.
7. BOPP antifogging film
Usage: used for packaging vegetables, fruits, sushi, flowers, etc.
BOPP film is a very important flexible packaging material, which is widely used. BOPP film is colorless, odorless, tasteless and nontoxic, and has high tensile strength, impact strength, rigidity, toughness and good transparency. The surface energy of BOPP film is low, so corona treatment is needed before gluing or printing. However, after corona treatment, BOPP film has good printing adaptability, and can be printed in color to get a beautiful appearance, so it is often used as the surface material of composite film.
BOPP film also has some shortcomings, such as easy accumulation of static electricity and no heat sealing property. In the high-speed production line, BOPP membrane is easy to generate static electricity, so it is necessary to install static eliminator. In order to obtain the heat-sealable BOPP film, the surface of BOPP film can be coated with heat-sealable resin glue, such as PVDC latex and EVA latex, or coated with solvent glue, and the heat-sealable BOPP film can also be produced by extrusion coating or coextrusion.
The film is widely used in the packaging of bread, clothes, shoes and socks, as well as the cover packaging of cigarettes and books. The initial tear strength of BOPP film is improved after stretching, but the secondary tear strength is very low. Therefore, there should be no notches on both ends of BOPP film, otherwise the BOPP film is easy to tear when printing and laminating. BOPP can be coated with adhesive to produce sealing tape, which is a large market for BOPP.
BOPP film can be produced by tube membrane method or flat membrane method. The properties of BOPP films obtained by different processing methods are also different. Due to the large stretch ratio (up to 8-10), the strength of BOPP film produced by flat film method is higher than that of tube film method, and the uniformity of film thickness is better.
In order to obtain better comprehensive performance, multilayer composite method is usually used in the process of use. BOPP can be compounded with many different materials to meet special application needs. For example, BOPP can be compounded with LDPE(CPP), PE, PT, PO, PVA, etc. to obtain high gas barrier, moisture barrier, transparency, high and low temperature resistance, cooking resistance and oil resistance. Different composite films can be applied to oily food.
Third, cast polypropylene
CPP: It has the characteristics of good transparency, high gloss, good stiffness, good moisture resistance, excellent heat resistance and easy heat sealing.
Cast polypropylene has been printed and bagged, which is suitable for: clothing, knitwear and flower packaging bags; Documents and photo album films; Food packaging; And metallized films suitable for barrier packaging and decoration. Potential uses also include: food packaging, candy packaging (twisted conjunctiva), medicine packaging (infusion bag), replacing PVC, synthetic paper, adhesive tape, business card holder, ring folder and standing bag composite materials in the fields of photo albums, folders and documents.
CPP has excellent heat resistance. Because the softening point of PP is about 140℃, this kind of film can be used in hot filling, retort pouch, aseptic packaging and other fields. In addition, it has excellent acid resistance, alkali resistance and grease resistance, making it the first choice for bread product packaging or laminating materials. Its contact with food is safe, and its demonstration performance is excellent, which will not affect the flavor of the contained food, and different grades of resin can be selected to obtain the required characteristics.
As mentioned above, the production process of cast film generally adopts the T-shaped die method, which is characterized by:
(1) The casting method omits the film blowing stage of the tube membrane method, which is easy to start and has less waste;
(2) During the production by tape casting, the chemical molecules are arranged orderly, so it is beneficial to improve the transparency, luster and thickness uniformity of the film, which is suitable for advanced packaging;
(3) The casting part adopts electric up-and-down swinging and back-and-forth moving structure, which is easy to operate;
(4) The corona part is air-cooled and water-cooled, so the product is not easy to deform.
Firstly, the extruder melts the raw resin, and the molten resin is cast on the cooling roller with smooth surface through the die and quickly cooled into a film. After thickness measurement, traction, corona treatment and flattening, the leftover material with thicker edge is cut off, and then it is unfolded and rolled into a film roll again.