Which is better CPP or Bopp?

BOPP film

It is a very important flexible packaging material with a wide range of applications. BOPP film is colorless, odorless, odorless, non-toxic, and has high tensile strength, impact strength, rigidity, toughness and good transparency. The surface energy of BOPP film is low, and corona treatment is required before gluing or printing. However, after corona treatment, BOPP film has good printing adaptability and can be overprinted to obtain exquisite appearance, so it is often used as the surface layer material of composite film. BOPP film also has shortcomings, such as easy accumulation of static electricity and no heat seal-ability. On a high-speed production line, BOPP film is prone to static electricity, so it is necessary to install static electricity remover. In order to obtain a heat-sealable BOPP film, heat-sealable resin glue, such as PVDC latex, EVA latex, etc., can be coated on the surface of the BOPP film after corona treatment, solvent glue, or extrusion coating or The method of co-extrusion and compounding produces heat-sealable BOPP film. 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 induced tear strength of BOPP film is improved after stretching, but the secondary tear strength is very low. Therefore, no cuts should be left on both ends of the BOPP film, otherwise the BOPP film will be easily torn during printing and lamination. After BOPP is coated with self-adhesive, sealing tape can be produced, which is a market with a large amount of BOPP.

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BOPP film can be produced by tube film method or flat film method. The properties of BOPP films obtained by different processing methods are different. The BOPP film produced by the flat film method has a large stretch ratio (up to 8-10), so the strength is higher than that of the tube film method, and the uniformity of the film thickness is also better.

In order to obtain a better overall performance, it is usually produced by a multi-layer composite method during use. BOPP can be compounded with many different materials to meet the needs of special applications. 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.

CPP film

It has the characteristics of good transparency, high gloss, good stiffness, good moisture resistance, excellent heat resistance, and easy heat sealing. CPP film is printed and bagged, and is suitable for: clothing, knitwear and flower packaging bags; document and photo album film; food packaging; and metallized film for barrier packaging and decoration. Potential uses also include: food packaging, candy packaging (twisted film), pharmaceutical packaging (infusion bag), replacing PVC in photo albums, folders and documents, synthetic paper, self-adhesive tape, business card holders, ring folders And standing bag composite material.

CPP has excellent heat resistance. Since the softening point of PP is about 140°C, this type of film can be used in hot filling, retort bags, aseptic packaging and other fields. Coupled with excellent resistance to acid, alkali and grease, it becomes the first choice for bread product packaging or laminate materials. It is safe in contact with food, has excellent performance, does not affect the flavor of the food inside, and can choose different grades of resin to obtain the required characteristics.

As mentioned above, the production process of cast film generally adopts the T-die method. The characteristics of this method are:

(1) The casting method eliminates the film blowing stage of the tube film method, which is easy to drive and has less waste;

(2) In the production by casting method, the chemical molecules are arranged in an orderly manner, so it is beneficial to improve the transparency, gloss and thickness uniformity of the film, and is suitable for advanced packaging;

(3) The casting part adopts electric up and down swing and back and forth movement structure, which is easy to operate;

(4) The corona part is air-cooled and water-cooled, and the product is not easy to deform.

The extruder first melts the raw material resin, and the molten resin is cast on the cooling roller with a smooth surface through the die to quickly cool into a film. After thickness measurement, traction, corona treatment, and flattening, cut off the thicker edge material, unfold and wind it into a film roll again.

The main points of CPP cast film production process

The T-type head is one of the key production equipment. The design of the head should make the material flow out evenly along the entire width of the lip. There is no dead angle in the flow channel inside the head, and the material mold has a uniform temperature. It needs to consider the material rheology. Many factors including behavior. To use precision machining heads, the gradual reduction manifold hanger heads are commonly used. The surface of the cooling roller should be finished, the surface roughness should not be greater than 0.15mm, the speed should be stable, and the dynamic balance performance should be good to avoid longitudinal thickness fluctuations. Use β-ray or infrared thickness gauge to monitor film thickness to achieve satisfactory thickness tolerance. To produce a qualified cast film, not only must the raw material be adjusted, but also the processing conditions must be mastered.

The biggest influence on film performance is temperature. As the temperature of the resin increases, the longitudinal (MD) tensile strength of the film increases, the transparency increases, and the haze gradually decreases, but the transverse (TD) tensile strength of the film decreases. The suitable temperature is 230&#;250&#;. The air knife on the cooling roll makes the film and the surface of the cooling roll form a thin air layer, so that the film is uniformly cooled, thereby maintaining high-speed production. The adjustment of the air knife must be appropriate. Excessive air volume or improper angle may make the thickness of the film unstable or not stick to the roll, causing wrinkles or patterns to affect the appearance quality. The temperature of the cooling roll increases, the stiffness of the film increases, and the haze increases.

If the internal additives of the raw material precipitate on the surface of the cooling roller, the machine must be shut down for cleaning to avoid affecting the appearance of the film. The cast film is relatively soft, and the pressure and tension must be adjusted according to factors such as film thickness and production speed during winding. Otherwise, it will produce ripples and affect the flatness. The choice of tension depends on the tensile strength of the product. Generally, the greater the winding tension, the product after winding is less likely to experience roll slack and deviation, but it is prone to ripples at the beginning of the winding, which affects the smoothness of the roll. On the contrary, the winding tension is small and the initial effect is good, but the more the winding is, the more the film is slack and the deviation occurs. Therefore, the tension should be moderate and the tension should be kept constant.

Process characteristics of multi-layer co-extruded cast film:

In order to improve film performance, reduce costs, and meet user requirements for multiple uses and high performance, multilayer composite films have developed rapidly, especially in developed countries where living standards are relatively high, environmental protection is emphasized, and food shelf life and quality are required to be extended. Multi-layer copolymerized cast film is also one of the multi-layer films, which has changed the problems and drawbacks of CPP film products that have single performance and cannot meet the requirements of the market.

1. Universal type: Multi-layer copolymerized cast film can be used for different purposes and designs, such as bread packaging, clothing (especially underwear, pants) packaging, fruit packaging, etc. on automatic packaging machines, or used with BOPP after printing The film is compounded into a BOPP/CPP two-layer film, which is used for packaging of clothing and dry food (such as fast food noodle bags, bowl covers, etc.). The general-purpose structure is copolymer PP/homo PP/co PP or homopolymer.

2. Metallized type: The surface of the product is required to have strong adhesion to the vapor-deposited metal (such as aluminum), and it can still maintain good dimensional stability and rigidity after vapor deposition. The other surface has a lower heat sealing temperature and Higher heat sealing strength, metalized structure is also PP copolymer/homo polymer PP/PP copolymer.

3. Cooking type: Two-layer copolymerized CPP used for cooking, which can withstand cooking and sterilization at 120&#; and 15MPa pressure. It not only maintains the shape and flavor of the internal food, but the film will not crack, peel or bond, and has excellent dimensional stability. It is often compounded with nylon film or polyester film, and is packaged with soup foods, meatballs, and dumplings. For food or processed frozen food before eating, the cooking type three-layer PP film structure is co-PP/co-PP/co-PP.

4. High-temperature cooking type: packaging roasted chicken, roasted ribs and jam, beverages need to be 121-135 &#; high temperature sterilization three-layer copolymer CPP film, of which copolymer PP requires better performance than the general cooking type copolymer PP. In addition to the three-layer film, there are also five-layer packaging with cast barrier properties. Its structure is: PP/adhesive/PA/adhesive/copolymer PE; PP/adhesive/PA/adhesive/EVA; PP /Adhesive/EVOH/Adhesive/PE; PP/Adhesive/EVOH/Adhesive/EVA; PP/Adhesive/EVOH/Adhesive/PP.

OPP film is a kind of polypropylene film. Because the production process is multi-layer extrusion, it is called co-extrusion oriented polypropylene film (Oriented Polypropylene Film). If there is a process of biaxial stretching in the processing, it is called Biaxially Oriented Polypropylene Film. Compared with the co-extrusion process, the other is called Casting Polypropylene Film, which is relatively thick.

OPP film

The current applications in packaging include self-adhesive labels, in-mold labels, winding labels and wet glue point labeling. The latter is mainly used in beverage and alcohol labeling abroad. In the past few years, it has gradually been introduced into the Chinese market from Europe, and its application fields include food, chemical, and daily chemical products. In addition, OPP is applied to shrink film like PE and PVC film. The advantages are high transparency, good gloss, high shrinkage and shrinkage stress, but poor heat sealing performance and heat sealing strength, high shrink temperature, and narrow range.

For the relatively saturated and homogeneous daily chemical products in the market, appearance is everything. The first impression determines the purchase behavior of consumers. 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. Their squeeze resistance must match the bottle body. At the same time, the transparent bottle body is suitable for adhesives and The transparency of the label surface material puts forward stringent requirements. Compared with paper labels, OPP labels have the advantages of transparency, high strength, moisture resistance, and resistance to falling off. Although the cost is increased, it can get a good label display and use effect. With the development of domestic printing technology and coating technology, the production of self-adhesive film labels and printed film labels is no longer a problem. It is foreseeable that the use of domestic OPP labels will continue to increase.

Definition

 

What is BOPP Film?

BOPP stands for &#;Biaxially Oriented Polypropylene&#;,  which refers to a film made from polypropylene that is stretched in both vertical and horizontal directions. Its production involves extruding molten polypropylene through a narrow die to form a sheet or thick film, which is then stretched in both directions (longitudinally and laterally) in a special stretcher at specific temperatures and speeds. The film is subsequently cooled or heat-treated and processed (e.g., corona treatment, coating) to achieve its final form.

BOPP film is characterized by its excellent transparency, high strength, durability, superior stretchability, and water resistance. It is commonly used for making food packaging bags, gift wrapping, and printing materials.

What is CPP Film?

CPP film, also known as Cast Polypropylene film or unstretched polypropylene film, primarily comprises polypropylene as its main processing material. Depending on its application, CPP film can be categorized into General CPP (GCPP), Metalize CPP (MCPP), and Retort CPP (RCPP) among others.

CPP is a polypropylene (PP) film produced in the plastics industry through the cast extrusion process. Unlike BOPP (Biaxially Oriented Polypropylene) film, it is a non-oriented film. Strictly speaking, CPP film has some orientation in the longitudinal direction (MD). By rapidly cooling on a chill roll, the film acquires excellent clarity and smoothness.

CPP film has good moisture resistance, heat sealing properties, and antistatic properties, and is commonly used for making bread bags, vegetable bags, stationery bags, etc.

 

 

Differences Between BOPP and CPP

 

Manufacturing Process

BOPP film is produced by forming polypropylene granules into sheets, which are then biaxially stretched at high temperatures. Biaxial stretching means that the film is stretched in both longitudinal and lateral directions to achieve improved physical properties.

CPP film is also made from polypropylene granules formed into sheets, but it is typically stretched in only one direction, usually longitudinally. This results in better performance in the longitudinal direction of the film.

 

 

Physical Properties

BOPP film: Exhibits high transparency and gloss, excellent ink and coating adhesion, and good stretchability.

CPP film: Due to unidirectional stretching, it may be slightly less transparent than BOPP but has better longitudinal stretching and tear resistance. CPP film features good transparency, high gloss, stiffness, moisture barrier, excellent heat resistance, barrier properties, and mechanical adaptability, suitable for high-temperature cooking and low-temperature heat sealing. Additionally, its resistance to acids, alkalis, and fats makes it a preferred material for bread packaging and composite materials. It is safe for food contact and does not alter the flavor of the contents, with different grades of resin available to achieve desired properties.

Application Fields

BOPP film: Widely used in food packaging, printing, tapes, labels, and other areas, especially those requiring high transparency.

CPP film: Typically used in food packaging.

Heat Sealing Performance

BOPP film: Generally has poor heat sealing performance and requires the addition of a heat-seal coating during manufacturing.

CPP film: Due to its unidirectional stretching, it usually has better heat sealing performance and does not require an additional heat-seal coating.

Film Characteristics

BOPP film: Usually thinner and may require increased thickness for certain specific applications.

CPP film: Relatively thicker, usually with better moisture barrier properties.

Here is a comparative analysis table of BOPP and CPP films across various dimensions:

Feature/Attribute BOPP Film CPP Film Material Composition Biaxially oriented polypropylene Cast polypropylene Manufacturing Process Biaxial orientation (longitudinal and transverse) Casting (uniaxial orientation) Physical Properties High strength, high transparency Good flexibility and transparency, lower barrier properties Heat Resistance Good heat resistance Slightly lower heat resistance than BOPP Applications Widely used in food packaging, labels, cigarette packaging, etc. Commonly used in clothing packaging, stationery packaging, flower packaging, etc. Printing and Processing Suitability Requires corona treatment to improve printability Better direct printability Environmental Friendliness Recyclable, environmentally friendly Also recyclable, environmentally friendly Cost Relatively higher due to more complex production processes Lower cost due to simpler production processes Market Demand High demand, especially in the food and pharmaceutical packaging industries Growing demand, particularly in non-food packaging areas

 

Types of BOPP and CPP Films

 

Types of BOPP Films

 

Heat Sealable Film

Heat-sealable film is one of the basic varieties of BOPP film, mainly used for printing, composite bag-making, or wrapping packaging. It is divided into single-sided heat-sealable film and double-sided heat-sealable film. The single-sided heat-sealable film, after printing patterns on the non-heat-sealable layer, is laminated with PE, BOPP, and aluminum foil to make bags for packaging food, tea, beverages, etc.

The double-sided heat-sealable film is directly heat-sealed into shaped packaging for food, textiles, audio-visual products, poker, etc. All of these require the film to have good heat-sealing performance. In addition, with the high-speed packaging, BOPP heat-sealable film is also required to have high slip performance, low-temperature instantaneous heat-sealing performance, and better heat-sealing strength. To adapt to different types of packaging machines, the film is required to have a wide heat-sealing temperature range (60-135°C).

In the production of BOPP heat-sealable film, the selection of surface materials is key, including the type of heat-sealing material, production adaptability, heat-sealing temperature, heat-sealing layer thickness, heat-sealing strength, etc. At the same time, appropriate additives should also be selected to improve other properties of the film, such as slipperiness, antistatic properties, stiffness, optical properties, etc.

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Anti Fog Film

The issue of condensation in food packaging affects the preservation and appearance of food, while also providing favorable conditions for microbial growth, leading to food spoilage. The emergence of BOPP anti-fog film addresses this problem, not only preventing condensation but also possessing antibacterial properties, widely used in the packaging of fresh fruits and vegetables.

Characteristics of BOPP anti-fog film:

• Good anti-fog effect (can prevent fogging in both cold and hot conditions), excellent gloss and transparency, good printability;
• Good water vapor barrier properties, maintaining the moisture content of fruits and vegetables, preventing dehydration and shrinkage;
• Suitable oxygen permeability, maintaining the respiration of fruits and vegetables;
  Suitable surface friction coefficient;
• Can have heat sealing properties;
• Contains antibacterial substances, providing antibacterial function;
• Good flexibility, adhering closely to the packaged items;
• More environmentally friendly than PVC.

 

 

Ultra-thin High Matte Film

With the improvement of people&#;s living standards, ordinary packaging can no longer meet the needs of people&#;s lives, and the demand for paper-plastic soft packaging in the market is increasing. To meet this requirement, many manufacturers have developed various new products, among which BOPP matte film is one.

It appears like paper and silk, noble and elegant, with good printing and laminating performance, low gloss and high haze on the surface, good antistatic and easy folding properties. It is mainly used for paper-plastic lamination of books, advertising brochures, gift bags, etc., and can also be laminated with other substrates for packaging of food, clothing, and crafts.

BOPP matte film requires good effects, uniform mattness, fine surface, excellent haze performance; good printing and laminating performance on the non-matte side, smooth surface adhesion; good stiffness, minimizing thickness for easy lamination processing; excellent mechanical properties, good durability; no defects in appearance, especially in combination with dark paper; good performance of UV ink or hot stamping processing on the matte side, etc.

For easy lamination processing and low-cost considerations, BOPP matte film thickness should be as thin as possible. Currently, the thickness of domestic BOPP matte film can reach 15um, and abroad there is BOPP matte film with good performance and a thickness of 12um.

To achieve a thin thickness of BOPP matte film, good matte effect, and adapt to wide-format, high-speed production, the selection of main and matte materials, and control of production process conditions are key, and attention should also be paid to the reasonable match of additives, to produce BOPP matte film with low gloss, high haze, good stiffness, antistatic, easy folding, and fine surface.

 

 

Twist Film

Used for twist wrapping of candies, chocolates, beef jerky, preserved fruits, and snacks, replacing environmentally unfriendly PVC twist films and expensive cellophane twist packaging. Film characteristics: good twistability; good stiffness, strong rigidity; high gloss; and good aluminum plating performance.

Straw Packaging Film

Directly used for transparent heat-seal packaging of straws. Film characteristics: good optical properties, suitable friction coefficient, and heat-seal strength.

Release Film

Used as a silicone oil release film for the protection of plasters, labels, silent adhesive tapes, and other adhesive-backed products. Film characteristics: good thermal dimensional stability; high stiffness; flawless appearance.

Barrier Protection Film

Used for winding and molding isolation protection of fishing rods, golf clubs, and other industrial products. Film characteristics: good thermal dimensional stability; high tensile strength; flawless appearance.

Heat-Sealable Aluminum Film

Can be directly used for heat-seal bag packaging of food, replacing CPP aluminum composite film.

Low-Static Film

Suitable for packaging electronic components. Surface resistivity is less than 10^10Ω.

UV-Resistant Film

Used for transparent packaging of products that require protection against ultraviolet rays or for outdoor use.

Antibacterial Film

Used for packaging cooked meats, seafood, and liquid foods. It is a new type of functional material that has antibacterial and bacteriostatic effects, but is non-toxic to humans.

High Transparency Film

Used for the production of high transparency adhesive tapes and the lamination of paper products. Haze is less than 0.3%.

Low Migration Film

Reduces the migration of additives, maintaining good optical performance of the film during its packaging life without contaminating the packaged items, meeting the hygiene requirements for food and pharmaceutical packaging.

Temperature-Resistant Flame-Retardant Film

Used in fields requiring temperature resistance and flame retardance, such as the drying and curing of circuit boards or electronic components.

Label Film

Used as wrap-around labels for bottled beverages. Film characteristics: good printing performance, high stiffness, high whiteness, high gloss, low static electricity, and good slipperiness.

 

 

Types of CPP Films

 

Lamination Grade

Laminated with printed BOPP film or BOPET film to form a BOPP/CPP (or BOPET/CPP) two-layer film, used for clothing and dry food packaging. The typical structure is heat-sealable PP/homopolymer PP/copolymer or homopolymer PP.

Based on the heat-sealing temperature, it can be classified into standard heat-sealable film (heat-sealing temperature 135°C), low-temperature heat-sealable film (heat-sealing temperature 120-130°C), and ultra-low temperature heat-sealable film (heat-sealing temperature below 120°C). By selecting different materials for the heat-sealing layer, the heat-sealing temperature of CPP can be reduced to below 100°C.

Aluminized Grade

CPP film has good barrier properties against water vapor permeation, but its barrier performance against oxygen permeation is relatively poor. After vacuum aluminum metallization, the film&#;s oxygen barrier properties are significantly improved. Metalized products have excellent light-shielding, decorative, and barrier properties and show good adaptability in post-processing such as printing and lamination, meeting requirements for heat resistance, chemical resistance, abrasion resistance, oxidation resistance, and high barrier properties.

The product surface requires a strong adhesion strength to the vapor-deposited aluminum, maintaining good dimensional stability and rigidity after metallization. The other surface should have a lower heat-sealing temperature and higher heat-sealing strength. The structure of the aluminized grade CPP film is copolymer PP/homopolymer PP/copolymer PP.

Retort Grade

Laminated with barrier films such as PA or aluminum foil for packaging products that require high-temperature retort sterilization, commonly used for foods containing fats or sauces. Retort-grade CPP films can generally be classified into an ordinary retort, medium-high temperature retort, and high-temperature retort. Ordinary retort withstands temperatures below 121°C, medium-high temperature retort withstands 121°C to 135°C for 130 minutes, and high-temperature retort withstands 135°C for 30 minutes. Retort-grade CPP films use random copolymer PP material, while high-temperature retort-grade CPP films use block copolymer PP material.

 

 

Printing Grade

CPP films with higher stiffness can be used alone for the outer packaging of food, clothing, sanitary napkins, flowers, etc., after printing and bag making. Depending on the requirements, the film features high transparency, antistatic properties, and customer-specified friction coefficients.

Other Functional Films

Antistatic CPP films are produced by adding an antistatic masterbatch.

High-rigidity CPP films are produced by adding rigidity-enhancing masterbatch and controlling the processing and molding temperature to increase the film&#;s rigidity, suitable for direct printing and used for packaging paper towels or twist wrapping.

Anti-fog CPP films

Anti-freeze CPP films are produced by blending and modifying with POE to improve resistance to low temperatures and are suitable for refrigerated and frozen food packaging.

Co-extruded films with PE

 

Conclusion

 

In this blog, we have explored the unique characteristics and applications of BOPP and CPP films, both of which are widely used in the packaging industry.

BOPP is renowned for its high strength and transparency and is primarily used in food packaging, labels, and cigarette packaging. Its production process, involving biaxial stretching, contributes to its superior physical properties and heat resistance.

On the other hand, CPP stands out for its flexibility and direct printability, making it particularly suitable for packaging apparel, stationery, and floral products. While both films are environmentally friendly and recyclable, BOPP tends to be more costly due to its complex production process, in contrast to CPP, which is more economical to produce.

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