What is the tensile orientation of biaxially oriented polypropylene?

Here are some common plastic films: polyethylene film PE film is the most used plastic packaging film, accounting for more than 40% of the total plastic film consumption. Although the appearance and strength of PE film are not ideal, it has good toughness, moisture resistance and heat sealing performance, and it is convenient to process and shape, so it is widely used. 1, low density polyethylene film. LDPE film produced by LDPE film extrusion blow molding and T-die method is a flexible and transparent film, non-toxic and tasteless, and its thickness is generally 0.02 ~ 0. 1? L it has good water resistance, moisture resistance, drought resistance and chemical stability. Widely used in general moisture-proof packaging of food, medicine, daily necessities, metal products and frozen food packaging. However, for articles with high hygroscopicity and moisture resistance, it is necessary to use films and composite films with better moisture resistance for packaging. LDPE film has high air permeability, no fragrance and poor oil resistance, so it can't be used to package easily oxidized food, flavor food and oily food. However, it is breathable, so it can be used for fresh-keeping packaging of fruits, vegetables and other fresh items. LDPE film has good thermal adhesion and low-temperature heat sealability, and is often used as the adhesive layer and heat sealing layer of composite film, but it cannot be used as the heat sealing layer of retort pouch due to its poor heat resistance. 2. High density polyethylene film. HDPE film is a tough translucent film with milky white appearance and poor surface gloss. The tensile strength, moisture resistance, heat resistance, oil resistance and chemical stability of HDPE film are better than those of LDPE film, and it can also be heat sealed, but its transparency is not as good as that of LDPE film. Can HDPE be made to a thickness of 0.0 1? L is a film, which looks very similar to tissue paper and feels comfortable. It is also called paper-like film. It has good strength, toughness and openness. In order to enhance the paper pattern and reduce the cost, a small amount of light calcium carbonate can be added. HDPE imitation paper film is mainly used to make various shopping bags, garbage bags, fruit packaging bags and various food packaging bags. Because of its poor air tightness and no fragrance, the shelf life of packaged food is not long. In addition, HDPE film can be used as the heat sealing layer of retort pouch due to its good heat resistance. 3. Linear low density polyethylene film. LLDPE film is a newly developed new variety of polyethylene film. Compared with LDPE film, LLDPE film has higher tensile and impact strength, especially tear strength and puncture resistance. Under the same strength and performance as LDPE film, the thickness of LLDPE film can be reduced to 20 ~ 25% of LDPE film, thus greatly reducing the cost. Even if it is used as a heavy packaging bag, its thickness is only 0. 1? L can meet the requirements and can replace the expensive high-molecular-weight polyethylene. Therefore, LLDPE is very suitable for daily necessities packaging, frozen food packaging, and is also widely used in heavy packaging bags and garbage bags. Polypropylene film PP film can be divided into unstretched film and biaxially stretched film. The two films are quite different in performance and should be regarded as different films. 1, unstretched polypropylene film. The unstretched polypropylene film includes blown polypropylene film (IPP) produced by extrusion blow molding method and extruded cast polypropylene film (CPP) produced by T-die method. The transparency and toughness of PP film are poor; And has high transparency and good toughness. The cast polypropylene has better transparency and gloss, and its appearance is close to cellophane. Compared with PE film, unstretched polypropylene film has better transparency, luster, moisture resistance, heat resistance and oil resistance; High mechanical strength, good tear resistance, puncture resistance and wear resistance; And is non-toxic and tasteless. Therefore, it is widely used in the packaging of food, medicine, textiles and other items. However, its drought resistance is poor, and it is brittle at 0 ~ 10℃, so it cannot be used for the packaging of frozen food. The unstretched polypropylene film has high heat resistance and good heat sealing performance, so it is often used as the heat sealing layer of retort pouch. 2. Biaxially oriented polypropylene. Compared with unstretched polypropylene film, BOPP film mainly has the following characteristics: ① transparency and gloss are improved, which can be comparable to cellophane; ② The mechanical strength increases, but the elongation decreases; (3) the cold resistance is improved, and it will not become brittle when used at -30 ~-50℃; ④ The water permeability and air permeability are reduced by about half, and the permeability of organic vapor is also reduced to some extent; ⑤ Single film cannot be directly heat sealed, but it can be improved by coating adhesive and compounding with other plastic films. BOPP film is a new packaging film developed to replace cellophane. It has the characteristics of high mechanical strength, good toughness, good transparency and gloss. Its price is about 20% lower than cellophane. Therefore, cellophane has been replaced or partially replaced in the packaging of food, medicine, cigarettes and textiles. However, it has great elasticity and cannot be used for kink packaging of candy. BOPP membrane is widely used as the base material of composite membrane. Composite films made of plastic films such as BOPP film and aluminum foil can meet the packaging requirements of various articles and have been widely used. PVC film PVC film can be divided into soft film and hard film. The soft PVC film has good elongation, tear strength and cold resistance; Easy to print and heat seal; Can be made into a transparent film. Soft PVC film can not be used in food packaging because of the smell and migration of plasticizer. The soft PVC film produced by internal plasticization method can be used to package food. Generally speaking, PVC soft film is mainly used for industrial products and non-food packaging. Rigid PVC film, commonly known as PVC cellophane. High transparency, good rigidity, good toughness and stable kink; Good air tightness, fragrance retention and moisture resistance; Excellent printing performance, and can be made into non-toxic films. It is mainly used for kink packaging of candy, packaging of textiles and clothing, and packaging film of cigarettes and food packaging boxes. However, rigid PVC has poor cold resistance and is fragile at low temperature, so it is not suitable for frozen food packaging materials. PS film has high transparency and gloss, beautiful appearance and good printing performance. Low water absorption and high permeability to gas and water vapor. The unstretched polystyrene film is hard and brittle, and its elongation, tensile strength and impact strength are low, so it is rarely used as a soft packaging material. Biaxially stretched polystyrene (BOPS) films and heat absorbing films are mainly used for packaging. The physical and mechanical properties of BOPS films prepared by biaxial stretching, especially the elongation, impact strength and toughness, have been significantly improved, and the original transparency and gloss have been maintained. The good air permeability of BOPS film makes it very suitable for packaging fresh foods such as fruits, vegetables, meat, fish and flowers. Polyvinylidene chloride film PVDC film is a flexible, transparent and high barrier film. Excellent moisture resistance, air tightness and fragrance retention; And has excellent acid resistance, alkali resistance, chemical resistance and oil resistance; The unstretched PVDC film can be heat sealed, which is very suitable for packaging food and can keep the flavor of food unchanged for a long time. Although PVDC film has good mechanical strength, it is poor in rigidity, too soft and sticky, and poor in operability. In addition, PVDC has strong crystallinity, its film is easy to be perforated or microcracked, and its price is also high. Therefore, at present, PVDC films are rarely used in the form of single-layer films, but mainly used to make composite films. The performance of ethylene-vinyl acetate polymer film EVA film is related to the content of vinyl acetate (VA). The higher the VA content, the better the elasticity, stress cracking resistance, low temperature resistance and heat sealing performance of the film. When the content of VA reaches 15%~20%, the performance of the film is close to that of soft PVC film. The lower the VA content, the smaller the elasticity of the film, and the closer the performance is to LDPE film. Generally, the content of VA in EVA film is 10%~20%. EVA film has good low-temperature heat sealing performance and inclusion sealing performance, and is an excellent sealing film, which is often used as the heat sealing layer of composite film. EVA film has poor heat resistance, the highest use temperature is 60℃, poor air tightness, easy adhesion and peculiar smell. Therefore, single-layer EVA film is generally not directly used for packaging food. PVA membrane can be divided into water-resistant membrane and water-soluble membrane. The water-resistant film is made of PVA with polymerization degree above 1000, which is completely saponified. The water-soluble film is made of partially saponified PVA with low polymerization degree. Water-resistant PVA film is mainly used for packaging. PVA film has good transparency and gloss, and is not easy to accumulate static electricity and absorb dust, so it has good printing performance. Excellent air tightness and fragrance retention in dry state, good oil resistance; Good mechanical strength, toughness and stress cracking resistance; Can be heat sealed; PVA film has high moisture permeability, strong water absorption and unstable size. Therefore, polyvinylidene chloride coating, also known as K coating, is usually used. The coated PVA film can also maintain very good air tightness, fragrance retention and moisture resistance under high humidity, which is very suitable for packaging food. PVA film is often used as the barrier layer of composite film, and its composite film is mainly used for packaging fast food, meat products, cream products and other foods. PVA monolayer film is also widely used in the packaging of textiles and clothing. Water-soluble PVA film can be used for measuring and packaging chemical products such as disinfectants, detergents, bleaches, dyes and pesticides. And washing bags for patients' clothes. , can be used directly in the water, do not need to open. Nylon membrane There are two kinds of nylon membrane: biaxially stretched membrane and unstretched membrane, among which biaxially stretched nylon membrane (bone) is used more. The unstretched nylon film has outstanding elongation and is mainly used for deep drawing vacuum packaging. Nylon film is a very tough film, which is non-toxic, tasteless, transparent, shiny, difficult to accumulate static electricity and has good printing performance. Its mechanical strength is high, its tensile strength is three times that of PE film, and its wear resistance and puncture resistance are excellent. Nylon film has good heat resistance, sweat resistance and oil resistance, but it is difficult to heat seal. In the dry state, nylon membrane has good air tightness, but high moisture permeability and strong water absorption. In high humidity environment, the dimensional stability is poor and the air tightness drops sharply. Therefore, polyvinylidene chloride coating (KNY) or composite with PE film is often used to improve its waterproof, moisture-proof and heat-sealing properties. This NY/PE composite film is widely used in food packaging. Nylon packaging is widely used to make composite films, and also used as the base material of aluminized films. Nylon film and its composite film are mainly used for packaging greasy food, general food, frozen food and cooked food. The unstretched nylon film can be used for vacuum packaging of seasoned meat, succulent meat and other foods because of its high elongation. EVAL film, an ethylene-vinyl alcohol polymer film, is a new type of high barrier film developed in recent years, which has good transparency, excellent oxygen resistance, fragrance retention and oil resistance. However, its hygroscopicity is very strong, which reduces its barrier performance. EVAL film is usually a composite film made of moisture-proof materials, which is used to package meat products and fast food, such as sausages and ham. EVAL monolayer film can also be used to package fiber products and wool products. Polyester film BOPET is the most widely used in polyester film. PET film is a kind of packaging film with good comprehensive properties. Has good transparency and luster; Good air tightness and fragrance retention; The moisture resistance is moderate, and the moisture permeability decreases at low temperature. PET film has excellent mechanical properties, its strength and toughness are the best among all thermoplastics, and its tensile strength and impact strength are much higher than ordinary films. Suitable for secondary processing such as printing and paper bags. PET film also has excellent heat resistance, cold resistance, chemical resistance and oil resistance. But not resistant to strong alkali; It is easy to carry static electricity, and there is no proper anti-static method. Pay attention to packing powdery articles. PET film is very difficult to heat seal, and its price is relatively high at present. It is rarely used as a single film, and most of it is compounded with PE or PP film with good heat sealing performance or coated with polyvinylidene chloride. This composite film based on PET film is the most ideal material for mechanized packaging operation, which is widely used in food packaging such as cooking, baking and freezing. Polycarbonate film PC film is odorless and nontoxic, and its transparency and luster are similar to cellophane, and its strength is equivalent to that of PET film and bone sensitive film, especially its impact strength is outstanding. PC film has excellent fragrance retention, good air tightness and moisture resistance, and good ultraviolet penetration resistance. Its oil resistance is good; Heat resistance and cold resistance are also very good. Can be cooked and sterilized at high temperature and high pressure; Low temperature resistance and frost resistance are better than those of PET film. However, its heat sealability is poor. PC film is an ideal food packaging material, which can be used to package cooked food, frozen food and seasoning food. At present, because of its high price, it is mainly used for the packaging and aseptic packaging of tablets. Cellulose acetate membrane CA membrane is transparent, shiny and smooth. Large stiffness, stable size, difficult to accumulate electricity and good processability; Easy adhesion and good printability. And has water resistance, folding resistance and durability. CA film has high air permeability and moisture permeability, and can be used for "breathing" packaging of vegetables and fruits. CA film is often used as the outer layer of composite film because of its good appearance and easy printing. Its composite film is widely used in the packaging of drugs, food, cosmetics and other items.