Although oriented polypropylene (OPP) is slightly inferior to PET in stiffness, transparency, barrier property, and processability, OPP has lower price than PET and better heat resistance, so OPP has a huge application prospect in food and non-food packaging. . Although its output rate is lower than that of PET, OPP containers can replace glass, PET, and PVC containers with the modification of resins and the continuous development of the technology of the whitening agent and mechanical equipment.
Currently, OPP containers have appeared in the packaging market for bottled water, fruit juices, hot-filled foods, dry powders, and personal hygiene products. They are used in the single-stage injection stretch blow (ISBM) and two-step heating and blowing (SBM) molding machines. Molded, both transparent and strong heat, the price is lower than traditional materials.
Bottle-grade PET typically has a density of 1.35 g/cc and is currently priced at 63 cents per pound, whereas the density of an anti-reflective PP random copolymer used in oriented polypropylene bottles is approximately 0.910 g/cc. 56 cents/lb, which reduces the cost of OPP bottles by 40% compared to PET bottles. Kraft, Glenview, Illinois
R&D manager Surendra, Foods
Mr. Agarawal said that compared with glass bottles, OPP bottles have the advantages of light weight, non-breakable, and easy shipping, and their “real transparency†is the same as that of PET bottles. Therefore, they hope to use OPP bottles to reduce production costs.
The high-speed rotary heated SBM forming machine can produce 60,000 PET bottles per hour. In comparison, the OPP bottle is produced by one-step ISBM equipment, and its efficiency is relatively low, making it limited to children in Asia and South America. Nutrition supplements and medicine bottles are not used in the United States.
Overcoming OPP bottle defects
So far, OPP bottles have not been widely used due to their slower processing speed and poorer physical properties than PET bottles. However, these disadvantages are being overcome by advanced mechanical equipment, optimized preform design, improved PP resin raw materials, and auxiliaries specifically developed for PP bottles.
ExxonMobil's research shows that the use of high-speed machinery and the rational design of OPP preforms allow OPP to match PET in yield, transparency, rigidity, toughness, and sensory. If you use something like Sidel, SIG
High-speed, rotary-heated SBM molding machines manufactured by Corpoplast or other companies, OPP bottles will be extremely competitive.
The disadvantages of PP are:
1. PP is harder to absorb and disperse heat than PET, and the wall thickness of the OPP preform is thicker (in order to achieve the same rigidity, the OPP bottle needs to be thicker than the equivalent PET bottle wall). Therefore, although PP has a lower processing temperature during the preform injection stage (230°C), the blow molding of OPP bottles needs to be done at 130°C. Not only is the energy consumption higher than PET bottles, but the molding and cooling cycles are also Longer, the OPP yield is 25% lower than PET.
2. The processing temperature for OPP stretch blow moulding is narrow, only 5 °C, while PET is 15 °C, which increases the chance of stopping and producing waste products. In addition, the method of stretching OPP is also different. This is because certain parts of the preform, such as the bottom of the bottle and the bottleneck, may be less oriented than the bottle and are more likely to cause fogging. Therefore, in order to make OPP transparent to PET, designers of preforms and OPP bottles must optimize the orientation and draw ratio.
3. The low rigidity of the OPP means that the OPP bottle has lower top load and circumferential strength than the PET bottle. In order to achieve the same rigidity, OPP bottles need to be thicker than the equivalent PET bottles.
4. The oxygen and carbon dioxide permeability of the OPP bottle is about 30 times that of the PET bottle, making it impossible to be a barrier vessel that needs to block CO2 in carbonated beverages unless the coating is co-injected with the barrier resin.
At present, many companies have improved some of the inadequacies of OPP bottles through the research and development of PP. For example, the 3988 can solve problems such as haze (mainly bottleneck and bottom), long preform molding cycle (solved by enhanced PP nucleation), and poor processing stability when blowing. This Millad 3988 antireflection agent has been widely used in the packaging of vitamins, water, tea, juices, detergents, and pharmaceuticals on the OPP bottle market outside of the United States. ExxonMobil, Basell, Atofina, and BP Petrochemicals have also launched the AR-enhanced PP grades. They use a catalyst with a low residual rate to replace peroxide catalysts that can affect the appearance of the bottle, making the OPP bottle highly transparent and flowable. Sex, rigidity and toughness have also reached a good balance, thereby increasing the competitiveness of OPP bottles in the packaging market. Basell has developed a metallocene PP (mPP) for the pull-OPP bottle market. The 18-MFR (melt flow rate of 18g/10min) Metocene X50182 resin has been tried on the Sidel machine, which can reduce the bottle body haze to 1.5% and increase the gloss to 82%. Atofina is also producing mPPs for OPP bottles that can be blended with conventional PP to increase transparency.
OPP bottle advantages
Canada’s Container Corp. (CCC) is one of the few companies in North America that produces OPP bottles. The company’s CEO, Norman
Mr. Gottlieb said that the comprehensive cost and environmental advantages prompted CCC to enter the OPP bottle market several years ago. He described CCC's EnviroClear bottle as a "single polymer" packaged product. The OPP bottle, PP bottle cap, and PP sleeve tag all use recycled PP materials. Gottlieb also said that standard PP caps can effectively mask the atomization defects of the OPP bottleneck. In addition, CCC also studied the moisture barrier, processability, and hot-fillability of OPP bottles. They used 250kg, 500cc, and 600cc OPP beverage bottles for general-purpose preforms for dry powder packaging (requiring vapor barriers such as low-temperature deposits) and hot-filled foods (prices were 35% lower than heat-resistant PET bottles). about).
The OPP bottle has excellent heat resistance and can withstand temperatures of 205°C during hot filling. Non-heat-resistant PET bottles can only withstand temperatures of 160°C to 170°C during hot filling. In addition, PET bottles also require the use of vacuum trays to prevent collapse when the hot-filling temperature exceeds 180°C. When the bottle wall is thickened, the production rate is slowed, resulting in a 20% increase in production costs.
Single-layer OPP bottles can be used in a variety of hot-filled food markets, especially when hot filling temperatures are high (180°C to 205°C), resulting in juices, jams, pectins, pickled products, and sauces. The barrier and non-barrier packaging of foods such as juice and ketchup opened up the market.
OPP bottles are cheap. PET and OPP bottles need to increase the gas barrier layer. Although the cost of barrier materials used in PET bottles and OPP bottles is basically the same, the price advantage of OPP bottles themselves makes them more attractive in the market of gas barrier plastic bottles.
Three production methods
In order to solve the problem of low output of OPP, Bekum
America and CCC restructured their PET molding machines to make OPP bottles. They believe that in the PET bottle series equipment, the eight-cavity and eight-cavity linearly heated SBM system is the most cost-effective equipment for producing medium-capacity OPP bottles.
CCC designed a series of linearly heated SBM patented devices for OPP bottles. The company's EnviroClear (also can produce PET) molding machine is manufactured by a Chinese partner company and has a variety of types from two to eight chambers. Among them, the four-cavity molding machine produces 900 bottles per hour per cavity, and the company's next-generation device production speed is expected to increase to 1,100 bottles per hour. Currently, CCC can supply preforms and SBM equipment (made in China) with up to 32 cavities at a price that is 40% to 80% lower than locally manufactured equipment. In addition, the company also has machines for making open bottles.
CCC believes that optimizing preform design is critical. The company designed the preform to be 50% more stretchable than PET and the transparency was greatly improved.
The OCP bottle series produced by CCC mainly includes open bottles such as salad dressings, pickles and dry powders, as well as squeezable containers for shampoos, mouthwashes and medicines. In order to increase the top load and the cycle strength, CCC injects nitrogen into the mouth of the OPP bottle after filling.
Bekum America's modified design of its heated SBM machine (such as the dual chamber RBU-225) allowed it to switch between PET bottles and PP bottles. A few years ago, Bekum America specially designed the first fully electric heated SBM machine for PP. This six-chamber SB-6 machine has a rated production capacity of 7200 bottles/hour, which is only slower than the PET machine with the same number of chambers. 15 %.
PTI has proposed another manufacturing method. The company believes that the best way to fully reflect the price advantage of OPP bottles is to produce at a constant rate of 1,000 bottles per hour per cavity on a high-speed, rotary-heated SBM machine. At this speed, PTI has simulated 24g production on a Sidel machine on a computer.
OPP bottle process, and estimated that the unit cost of this OPP bottle is 10 cents lower than PET bottle. If the OPP bottle's previous production rate (600 bottles per hour per hour) is followed, the unit cost will exceed the PET bottle.
Strict process control can increase the output of OPP bottles. In production, if the blowing is insufficient within the temperature range of OPP, it will cause insufficient stretching, leading to a low transparency of the preform. If the processing temperature is too high, the bottle body, the bottle neck and the bottom of the bottle may be atomized, or the material Uneven distribution in the bottle walls and sticky bottles interfere with downstream operations. In the past, PTI used laboratory research and Virtual Prototyping software to predict the effect of adding preforms to increase the heat absorption rate of PET preforms. They also produced air cooling and water cooling models to accelerate PET bottles. Processing. Now, they have successfully used these technologies for the production of OPP bottles, so that the target productivity (more than 1000 bottles per cavity per hour) becomes feasible. PTI uses a masterbatch rapid heating additive developed by Colormatrix. According to Colormatrix, auxiliaries that increase the heating rate of PET preforms are also suitable for OPP preforms.
ExxonMobil conducted a computer simulation of the OPP bottle production on a rotary heated stretch blow molding machine. The company used a modified Sidel machine, a special preform design and a specially developed PP resin PP9505E1. The 30-MFR material had a haze of 6% at 1 mm thickness and an elastic modulus of 166,000 psi, and the resulting OPP bottle had a haze of less than 2%.
ExxonMobil produced 750cc PET bottles and OPP bottles of the same shape and weight, and used a computer to simulate the molding process of OPP preforms in a 48-chamber tool and then compared the two. The comparison results show that: OPP preforms are wider and longer than PET preforms, and the composite draw ratio is low. The axial and radial stretch balance is excellent. The thickness of OPP preforms is thinner, which can increase the heating and cooling rate; OPP bottle The dropping speed of the blank is faster than that of the PET bottle in the free falling mode, and the cycle of using the robot to pick and place the two types of bottle blanks is substantially equal. It can be seen that the molding cycle of the OPP bottle is shorter than that of the PET bottle. On the Sidel testing machine, the OPP bottle can be blow molded with maximum capacity; the sensory characteristics of the OPP bottle is the same as that of the PET bottle; the top load strength of the OPP bottle is slightly less than that of the same weight PET bottle. Low, but can fully meet the requirements of multiple applications; OPP bottles have lower drop impact strength than PET bottles, but for single-layer refrigerated OPP bottles, the strength is sufficient.
Sipa claims that their "one-step, half-process" integrated ISBM molding machine is an effective way to produce OPP bottles. This device first injects the preforms, and then sends the preforms through a robot and a linear conveyor to the blow molding process. The FX20/80E model machine designed by Sipa for OPP bottles has a production capacity of 30,000 bottles/hour. It uses a special screw and a redesigned heating oven. OPP bottles produced with FX20/80E have excellent transparency and evenly distributed bottle wall thicknesses. According to Sipa, the FX20/80E can handle OPP preforms for easy loading and unloading and rapid heating, and the produced OPP bottles can be used for water, milk or other hot filling applications.
The one-step ISBM system designed by Nissei ASB for OPP bottles, ASB-650EX3, is mainly used in fields that require vapor barrier or must withstand autoclave temperature (such as medical packaging). The system includes a special screw, a pretreatment station for processing preforms, and independent valves and timers that control the blowing of each cavity.
OPP barrier bottle arrival
The Chicago-based PPPI company (Pechiney Plastics Packaging Inc., now a subsidiary of Alcan) has improved the Sidel rotary heated SBM forming machine to produce three-layer PP/EVOH/PP directional barrier bottles. PPPI has modified the surface of the PP so that the PP can be firmly attached to the EVOH barrier layer without the need for an adhesive layer. Their Gamma Clear transparent bottles are available in 16 ounces and 26 ounces. The 26-ounce bottle is a wide-mouth bottle (63mm) with a temperature resistance of 205°C and a lower price than glass and PET.
PPPI's goal is to replace glass bottles in applications that require long storage times, good oxygen barrier properties, and high hot-filling temperatures with OPP barrier bottles. In the 800 million bottle/year 26-ounce container market, OPP bottles are cheaper than glass bottles. The company predicts that by 2005, OPP bottles will be industrialized. In the design of PET bottles, the use of vacuum discs and gripping designs allows hot filling at temperatures up to 180°C. However, OPP bottles do not need these special designs to withstand higher hot-filling temperatures (195°C), thereby increasing labeling space and increasing sales advantages. Therefore, PPPI believes that their PP/EVOH bottles have great potential in the sauce, apple juice and other hot-fill packaging markets.
Kortec is evaluating the potential of multi-layer OPP containers. The company believes that multi-layer OPP containers are merely replacing, rather than replacing, barrier PET containers. They predict that heat-resistant OPP containers will enter the packaging field for hot canned foods, coexisting with glass containers and metal cans. In addition, the OPP Barrier Bottle utilizes its transparent properties to replace stainless steel tanks.
Another route to manufacturing OPP barrier containers is to use existing PET bottle coating technology (plasma, flame, or corona treatment). PPG Industries announced that its epoxy-amine film, the Bairocade, can improve the oxygen barrier of OPP bottles at a cost similar to that of coated PET. Therefore, Bairocade is expected to achieve industrial use on OPP bottles. By changing the formulation and thickness of the coating, it is possible to achieve or exceed the same oxygen barrier properties as barrier PET containers.
CCC developed a patented technology for adding oxygen barrier immersion coatings to OPP bottles. The immersion coating process is simple and flexible, ideal for small volume, non-spherical and special shaped OPP bottles. Currently, CCC has launched a coating device that processes 3,600 to 5,600 OPP bottles annually.
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