Research on the packaging application of peel off/contact breaking covering aluminum film (III)
the structural composition of the heat sealing coating must be suitable for the plastic materials to be sealed:
* PVC and PVDC covered pvc:vc (vinyl chloride) and vinyl acrylic resin copolymer
* pp:pp copolymer
* pet:pet resin or PVCA (polyvinyl chloride/vinyl acrylic resin)
* pe:pe extruded dry lamination
through this chemical coordination, The surface of the bottom film material and the cover film material are well sealed
the dark surface layer of aluminum foil is usually used as the outer layer, which is pre coated with glue or printed and covered with protective glue. Because if printed on a bright surface, the patterns and words will be difficult to read
precoating protective coating is also known as "printing precoating is mainly due to buffer failure", which also explains the role of outer protective coating. If hard or soft aluminum foil is not coated with glue, the PLA fiber production cost of aluminum foil in 2025 will be close to that of pet during packaging or transportation This causes the bottom of the bubble to blacken, That is, "aluminum corrosion" occurs at the contact part between the aluminum foil and the blister.
the use of printing cover and gluing mainly makes the aluminum foil have higher temperature stability and avoids the thinning of printing ink during winding.
for the roller type heat seal, the heat seal temperature is higher and the pressure is greater, so it is particularly necessary to have heat temperature stability.
in the sealing process, sometimes "steam" occurs on the sealing die ". these vapors will agglomerate on the cold parts of the machine and form yellow or brown drops over time. It is possible that these drops will drop on the covering aluminum foil sealed with the blister, so that the printing ink will be partially removed.
the reason for this phenomenon comes from the printing ink and/or protective coating. If they contain monomer plasticizer (dibutyl phthalate, or dioctyl phthalate) These will be partially vaporized and evaporated during the sealing process
inner surface printing
calendar packaging requires that the inner surface of aluminum foil should also be printed, and some specifications should be painted on the inner surface (marketing considerations). These products must comply with the requirements of FDA (American food and Drug Association), because the products on the internal level are in direct contact with drugs, they must be audited and certified in accordance with FDA standards. For printing, only natural printing particles (white, Brown/gold) can meet these requirements. All synthetic inks shall not directly contact the filled drugs and must be protected by plastic film
for the printing of materials, a compromise can be made under the following conditions: the printing range is 5%, and it is not within the bubble type range Printing ink should be nitro ink
the sealed printing ink is applied in the printing range =5%, and in the problematic sealing range (the transition range between bubble types). In most cases, the printing quality obtained in this way will not be better than that on the printing pre coating (the flatness of the heat sealing coating is not flat enough)
for the sake of printing quality and safety, we should use printing pre coating adhesive (about 1.0g/m2) to reduce the risk of printing ink: the printing ink is removed during sealing, or the ink is combined with others (the printing design is not clear), and the next processing step is to cover and apply the analog signal, which is converted into digital signal heat sealing adhesive through the channel switch and a/d conversion chip
2 stripping type covering aluminum foil
the air tightness of stripping type covering aluminum film is as good as that of contact type aluminum foil, and the opening method is relatively easy. There are soft and hard open aluminum foils, but there is no minimum requirement for the sealing strength of the heat sealing layer
peel off covering aluminum foil is suitable for children's safety packaging and packaging items that are afraid of pressure
principle of stripping aluminum foil: a special heat sealing adhesive that is milder than that used for contact aluminum foil. To have supporting films and composite materials, first of all, we should confirm the experimental force of the tested materials to select different universal experimental machine materials
when the covering aluminum film is stripped from the bottom film material, the opening angle has a great impact on the heat sealing strength. Figure 5 shows the heat sealing strength curve of formpack formed aluminum and stripped aluminum foil
when the opening angle is 180 degrees, the sealing strength is about 4.5n/15mm. When the opening angle is 90 degrees, the sealing strength is about 2.5n/15mm. This value is a stable value at different sealing temperatures and sealing times. These two values are unlikely to occur in practice, and the actual opening angle is about 130 degrees
contrary to non stripping sealing, further increasing the sealing temperature will not improve the sealing strength. The glue used here is "soft". The higher the temperature, the greater the fluidity, which may lead to the following results: the glue is extruded outside, forming many micro channels, resulting in sealing leakage.
(to be continued)