It has long been thought that aluminum foils are ideal barrier layers for laminated packaging film structures that require low moisture vapor and oxygen transmission rates. In fact, both flat-plate aluminum foil moisture vapor transmission rate (MVTR) and oxygen transmission rate (OTR) are close to zero. Because of these characteristics, they have traditionally been used in paper/polyethylene/foil/polyethylene (PPFP) constructions, while the paper on the outer layer can be printed and coated to improve its aesthetic appearance.
The common ingredients in foods packaged in the PPFP format are ingredient powders, seasonings, soups, rice, toasted breads, stuffing ingredients, dried cheese and nutritional/energy drinks, and sweets. These foods require packaging not only to ensure that they are not degraded, but also to have good puncture resistance, because many foods have sharp edges and corners. In a highly competitive market, saving costs is also an important aspect to consider.
Alternatives to aluminum foil
At present, the development of metallized thin film technology provides processors and end users with an alternative to metal flakes. Metal-coated polypropylene (MOPP) films now allow processors and end-users to develop “metal-free sheet†packages that are more barrier-free, aesthetically pleasing, puncture-resistant, and economical than aluminum foil structures. The advantages. Toray Plastics USA's new metallized OPP product is an ultra-thin 45-gauge film called PCF-2. This film is made with proprietary technology and may be a thinner MOPP film currently available in the packaging industry.
A significant advantage of the film is that it can produce a larger area per pound of film. 45-gauge, compared to 36,000 square inches per pound for commonly used 0.000285-inch metal foil and 41,100 square inches per pound for popular 0.00025-inch foil The ultra-thin MOPP film can produce 68,200 square inches per pound per pound. Although the yield of fine films is higher per pound—more than 65% of thinner aluminum foil—its moisture vapor transmission rate (MVTR) and oxygen transmission rate (OTR) are very low. At 100 degrees Fahrenheit and 90% relative humidity (RH), the typical MVTR is only 0.01 g/100 in 2 /day, while at 73 degrees Fahrenheit and 0% RH, the OTR is 1.5 ml/100 sq. Inches/day.
Bonding
A common problem faced by processors is the delamination of traditional PPFP structures after repeated processing. This is often the case in food packaging in retail environments. However, new MOPP films that can now be used can help overcome this problem. Compared to conventional corona-treated PP, it can provide better metal adhesion and stronger bond strength between non-metal lamination and extrusion lamination or coating. The metal adhesion strength of the new MOPP film exceeds 400 g/in, and the delamination phenomenon in general cases becomes impossible.
The new metallized film not only provides better metal adhesion than the traditional PPFP structure, but also has better adhesion than the extrusion lamination and the non-metallic surface of the coated film. For example, the adhesive strength of a non-metallic surface of a new MOPP film was tested using a layer of extrusion coated low density polyethylene (LDPE). The measured adhesive strength was 477 g/in, which is almost 30% higher than that of the conventional MOPP structure of 369 g/in. At the same time, the new MOPP film offers better puncture resistance than the PPFP structure, even though they are thin.
Flexibility
The initial nature of the new MOPP film has advantages over the traditional PPFP structure. After repeated operations and handling, the advantages of the new MOPP film may even become more apparent. Unlike pinholes that are formed only after a few minutes after the foil is bent, the MOPP film retains its barrier properties after repeated bending. To simulate the real environment that this type of repetitive flexing may encounter, TomyPlastics USA tested a new ultra-thin MOPP film and a sample of a traditional PPFP structure sampled using a Gelbo tester.
The Gelbo tester consisted of two 90 mm diameter sampleable mandrels, one movable and one fixed, with a relative distance of 180 mm at the beginning of each cycle. The sample being tested is bent using repeated twisting and rolling of the film, typically 45 cycles per minute. Depending on the sample tested, the severity and number of test strokes may vary, and color tinting is used to determine whether there is a pinhole in the entire white-based twisted film using colored turpentine.
Through testing, Toray's new MOPP film can withstand repeated "twist" and "rolling" cycles, with no pinholes and loss of barrier properties for at least 16 cycles. The traditional PPFP structure can not withstand several cycles, and repeated distortions will quickly deteriorate the situation.
Another important advantage of the new MOPP film is that it can maintain its beautiful appearance for a long period of time even under conditions exceeding the normal processing strength. The aluminum foil cannot recover creases and wrinkles, and it cannot be restored after any deformation. This makes the food packaging look old. On the other hand, the new MOPP film packaging is flexible and can recover any distortions caused during processing and handling, so it can maintain its original appearance and charm no matter how many times it is processed by customers or store employees.
Aluminum cost limit
In terms of economy, the new MOPP film has advantages over the traditional PPFP structure because food manufacturers can use the same weight of film to produce more packages, and another reason is the consideration of aluminum prices. Aluminum and aluminum alloys are growing at a higher rate than polypropylene. In addition, the continuing high demand for aluminum materials in the U.S. market will lead to higher prices. The result is that the price gap between aluminum and polypropylene will increase.
In order to reduce the cost of traditional PPFP structures, processors are turning to finer gauge metal sheets. However, the initial barrier to the substrate does not help much, even making pinholes more likely to occur during normal processing. On the other hand, short-term and long-term barrier properties of the new MOPP film do not increase with thickness. In fact, the new 45-gauge membrane has the same barrier properties as the 80-gauge MOPP membrane.
Compared to the traditional PPFP structure, the newly emerged MOPP film represents an important advancement of technology, and it can provide all the advantages mentioned above.
There are raceways on the inner and outer rings of angular contact ball bearings, and the inner and outer rings can be displaced relative along the axial direction of the bearing. These bearings are particularly suitable for combined loads, i.e. loads that act in both the radial and axial directions. The axial load bearing capacity of angular contact ball bearings increases with the increase of contact angle α. The contact angle is the angle between the contact point connection between the ball and the raceway in the radial plane and the perpendicular line of the bearing axis.
The types of angular contact ball bearings are divided into: α=15° angular contact ball bearings (70000C type); α=25° angular contact ball bearings (70000AC type); α=40° angular contact ball bearings (70000B type); Back-to-back paired double angular contact ball bearings [70000C(AC, B)/DB type]; Face-to-face paired double angle contact ball bearings [70000C(AC, B)/DF type]; Tandem Paired Double Angular Contact Ball Bearings [70000C (AC, B)/DT Type]; Double row angular contact ball bearings with ball notch (00000 type); Double row angular contact ball bearings without ball notch (type 00000A); Double row angular contact ball bearing without ball notch, one side with dust cap (00000A-Z type); Double row angular contact ball bearings without ball notch, with dust caps on both sides (00000A-2Z type); Double row angular contact ball bearing with sealing ring on one side without ball notching (00000ARS type); Double row angular contact ball bearings with sealing rings on both sides without ball notching (00000A-2RS type); Four-point angular contact ball bearings (QJ0000 type), a total of 13 types
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