BACKGROUND
A flexible package, such as a package made from a thermoplastic film, can be produced in a process where the film is printed, a package or pouch is produced from the film by shaping the film and overlapping film layers, the package is filled and sealed by crimping using jaws. The jaws can generate a seal applying heat and pressure to a seal region of the package. When the sealing area is printed, even if there is a protective varnish coating or lamination, the geometry of the jaws can cause defects in the printed image areas.
DESCRIPTION OF DRAWINGS
Some examples will be described with reference to the drawings.
FIG. 1 shows a schematic diagram of a system for producing a package from a flexible packaging material according to one example;
FIG. 2 shows different types of flexible packages according to a number of examples;
FIG. 3 shows an enlarged view of a seal region of the package according to one example;
FIG. 4 shows a schematic diagram of a sealing tool according to one example;
FIG. 5 shows a graph for illustrating a profile of a sealing tool according to one example;
FIG. 6 shows a flow diagram of a manufacturing process according to one example.
DESCRIPTION OF EXAMPLES
Different types of consumer goods, such as food products, pharmaceuticals, cosmetics, toys, just to name a few examples, are packaged using thin films or sheets of flexible packaging material, with images such as corporate branding, or product information printed onto the film. The flexible packaging material serves to protect the product from, for example, moisture, oxidation or pathogens, while also providing information to the user regarding the nature and origin of the product contained therein.
Liquid electrophotographic printing (LEP), or electrostatic printing, is one method by which images or information can be printed onto substrates such as paper or plastic. The LEP printing process involves creating an image on a photoconductive surface, applying an ink having charged particles to the photoconductive surface, such that they selectively bind to the image, and then transferring the charged particles in the form of the image to a print substrate.
As used herein, “electrostatic printing” or “electrophotographic printing” generally refers to a process that provides an image that is transferred from a photo imaging substrate either directly or indirectly via an intermediate transfer member to a print substrate. As such, the image is not substantially absorbed into the photo imaging substrate on which it is applied. Additionally, “electrophotographic printers” or “electrostatic printers” generally refer to those printers capable of performing electrophotographic printing or electrostatic printing, as described above. “Liquid electrophotographic printing” is a specific type of electrophotographic printing where a liquid composition is employed in the electrophotographic process rather than a powder toner.
The flexible substrate, to which the liquid electrophotographic ink composition is to be printed (and thus is also referred to herein as the print substrate) may be any material suitable for use in a liquid electrophotographic printing process and suitable for use in a flexible packaging material. The flexible substrate may form the outermost layer of a laminated flexible packaging material or it may form the entire packaging material. The flexible substrate may be transparent, semitransparent or opaque.
In one example, the flexible substrate comprises a film of a polymer, for example a thermoplastic polymer. For example, the flexible packaging material is formed from a PET/PE pre-laminate or from a PET/AI/PE pre-laminate. In another example, the flexible substrate comprises a film of biaxially oriented polypropylene (BOPP), polypropylene (PP), or polyethylene terephthalate (PET). Other suitable polymers will be known in the art and the examples provided above should be seen as non-limiting examples. The flexible substrate may comprise a single-layer or multiple-layer film having a thickness in the range of about 5 μm to about 150 μm, or from about 10 μm to about 20 μm, or of about 12 μm, for example.
The liquid electrophotographic printing (LEP) composition useful for printing on the flexible packaging materials may comprise a colorant or pigment, a polymer resin and a carrier fluid or liquid. The LEP composition may further comprise additives such as charge directors, charge adjuvants, surfactants, viscosity modifiers, emulsifiers and the like. In some examples, the LEP composition may not contain any pigment, or comprise substantially zero pigment and thus be a pigment-free composition, useful in providing a particular transparent gloss or sheen to a printed substrate. The printed packaging material may comprise a primer layer to promote adhesion between the LEP composition and the packaging material, and an overprint varnish covering and protecting the LEP composition. Overprint varnish (OPV) may be applied on surface printed image to protect the LEP printing against chemical and mechanical damage, heat, UV radiation and the like. Another way to protect printed image can be done by lamination, using adhesive and secondary substrate.
FIG. 1 shows an example of a system for producing a package from a flexible packaging material. The system comprises a roll of packaging material 10 which, in this example, may be a thermoplastic film substrate having a surface printed by LEP with an overprint varnish (OPV) coating. The packaging material 10 can be transported as a film web 12, via a number of rollers 14, to a forming station 16. In the example of FIG. 1, forming station 16 comprises a forming tube 18 and a forming shoulder 20 but other types of forming devices can be used. The fanning station reshapes the film web 12 to have a tubular shape which is closed along a longitudinal seam 22, produced downstream of the forming station, at seam forming unit 26. This “endless” tube of the thermoplastic film is fed to a sealing station 24 where a bottom seam can be generated by sealing jaws 30, 32. This will become the bottom of a new package or pouch. Then a product (not shown) is dispensed into the package and the top of the package can be sealed by a top seal using the same pair of sealing jaws 30, 32 or another pair of sealing jaws. The package is sealed in the region of the seams by application of heat and pressure via the sealing jaws 30, 32. The sealing medium is provided by the material of the thermoplastic film which is at least partially melted during the sealing process. In one example, a pre-laminated structure is used, such as PET/Al/PE, and the PE film is melted as the sealing medium. As soon as the sealing medium has cooled off and cured, the seal is completed. The sealing process may take less than a second.
In one example, the sealing station 24 may comprise two pairs of sealing jaws, a lower pair for forming the top seal of a package that has just been filled; and an upper pair, closer to the forming station 16, for forming the bottom seam of the next package. A cutting device, e.g. a blade, may be provided between the two pairs of sealing jaws to cut and separate subsequent packages.
Whereas a vertical system design is shown in FIG. 1, this is just an example and different system configurations can be contemplated. For example, forming of the package, filling and sealing the package can be performed in an in-line process at a single location or station or it can be distributed across different locations or stations. Whereas FIG. 1 shows an in-line system performing all of the steps of forming, filling and sealing, other systems can provide a pre-forms of the package which is shipped to a customer where the package is filled with a product and sealed.
FIG. 2 shows a number of different package designs according to various examples. One package 40 has a pillow design, including a top seal 42 and a bottom seal 44 which may be formed by a pair of sealing jaws as described with regard to FIG. 1, for example. Another package 50 has a so-called block bottom design including a top seam 52 which may be formed by a pair of sealing jaws. The package has a flat bottom and can stand up. Another package 60 has a so-called gusseted design, including a top seal 62 and a bottom seal 64, which is a variation of the pillow design. Packages 50 and 60 have side folds to provide for additional volume. Each of the seals can be formed by a pair of sealing jaws including grooves and ridges which extend along the length of the seam to generate a “wavy” sealing structure.
An enlarged view of a seal portion of a package 18 is shown in FIG. 3. Package 70 comprises top seal regions 72 and side seal regions 74. Each of the seal regions 72, 74, in the example of FIG. 3, comprises three ridges and three grooves which are shaped according to a sinusoidal of or approximately sinusoidal wave. The grooves each have rounded bottom portions and the ridges have rounded top portions. The shape of the wavy seal regions in explained in further detail with respect to FIG. 4, showing an example of a sealing jaw for producing the seal region.
FIG. 4 shows an example of a sealing jaw 30 which is part of the sealing tool for producing a sealed seam of the package. The sealing jaw 30 comprises an elongate tool plate 34 having a length extending in the direction of the seal to be formed. Support studs 36 are provided at shorter side faces of the plate for mounting the jaw in a sealing tool. The tool plate 34 features a flat surface portion 38 and a wavy profile, including alternating grooves 40 and ridges 42. In the example of FIG. 4, four grooves and four ridges are provided on the tool plate 34 surface. Other numbers of grooves and ridges can be provided, such as two grooves and two ridges, or three grooves and three ridges, or three grooves and four ridges, or four grooves and three ridges etc. In one example, the wavy profile of the tool plate 34 comprises from one to six grooves and from one to six ridges, or from two to four grooves and from two to four ridges. The tool plate 34 can be made from stainless steel iron or another matter which provides a substrate for forming the wavy profile. Teflon coating on the jaws can be applied to avoid stickiness to the sealing surface.
In one example, the grooves have a curved cross-section in a bottom region thereof, and the ridges have a curved cross-section in a top region thereof. The curved cross-section of the grooves and the curved cross-section of the ridges may have the same or approximately the same radius of curvature. The curved cross-section of the grooves and the curved cross-section of the ridges may have a radius of curvature of about 0.5 to 2 mm.
The sealing jaw 30 shown in FIG. 3 may be used in combination with a further mating sealing jaw (not shown) wherein the pair of sealing jaws are part of a sealing tool. Each sealing jaw 30 comprises a surface having a wavy profile, wherein the sealing jaws of one pair have complementary profiles, including grooves and ridges which, when the two jaws are brought together, engage with each other. In this and other examples, a depth of the grooves of one sealing jaw may correspond to a height of the ridges of the mating sealing jaw; and a pitch of the grooves of one sealing jaw may correspond to a pitch of the ridges of a mating with heating jaw. In this and other examples, the pitch may be in the range of about 1 to 3 mm. In this and other examples, a depth of the grooves of one sealing jaw may correspond to a height of the ridges of a mating sealing jaw wherein the depth and the height are in the range of about 0.3 to 0.8 mm. In this and other examples, the ratio between the depth of the grooves and a pitch of the grooves may be in the range of about 1:10 to 1:3.
In this and other examples, the radius of curvature of the grooves at the bottom portion of the grooves and the radius of curvature of the ridges at the top of the ridges may be about 1.5 to 2.5 of the depth of the grooves or about 1/10 to ¾ of the pitch of the grooves. In this and other examples, the grooves and the ridges may form a sinusoidal or approximately sinusoidal profile on the respective jaw surfaces.
The sealing jaw 30 shown in FIG. 4 is used in combination with a corresponding meeting sealing jaw having a wavy profile which complements the profile of the sealing jaw 30 wherein the pair of sealing jaws is part of a sealing station or sealing tool. The sealing tool further comprises a heating device coupled with one or both of the sealing jaws. The heating device may be integrated at least partially into one or both of the sealing jaws. The sealing tool, which in FIG. 1 is schematically shown at 24, further comprises a mechanism for moving the sealing jaws towards each other and apart. For forming the seal, the sealing jaws, either one or both, are heated and moved towards each other, with part of the packaging material placed in the nip between the pair of sealing jaws. Accordingly, when closing the sealing jaws over the packaging material, the sealing jaws apply pressure and heat to the packaging material so as to at least partially melt the material and seal the packaging material in a seal region. As a result, a wavy sealed seam region is generated, an example of which is shown in FIG. 3.
The wavy profile of the sealing jaws avoids grooves and ridges having sharp edges and hence avoids damaging the printed packaging material during sealing. For example, packaging material which is printed by LEP technology, even if an over print varnish is provided, is vulnerable to heat sealing using grooved jaws having sharp edges because the LEP chemistry is sensitive to high temperatures and the grooved jaws' sharp geometry, along with the pressure applied. Mechanical movement of ink and over print varnish can be generated which may be visible on the final package. To avoid any optical defects in printed images and color patches caused by the sealing jaws, the wavy profile of the sealing jaws may be used, an example of which is shown in FIG. 4. Due to the rounded contour of the grooves and ridges, damaging any printed images and/or over printed varnish can be avoided or at least reduced to a degree that it is no longer perceivable. Performance tests have shown that the sealing jaws having the wavy profile can achieve very good and reliable sealing results.
In one example, a packaging material including a PET/PE pre-laminate was surface printed using LEP technology and an over print varnish. A package was produced by overlapping two layers of the packaging material and sealing the packaging material in a sealing area, using sealing jaws such as those shown in FIG. 4. In a comparative example a similar seal region has been produced using sealing jaws having sharp edges at the bottom of the grooves and the top of the ridges. The surface printed packaging material was sealed at an elevated temperature of about 180° C., applying a pressure of about 450,000 Pa, for a time of about 1 sec, in both the example and the comparative example. Depending on the composition and the thickness of the packaging material, different temperature ranges and different pressure ranges can be selected, including temperatures in the range of 150 to 200° C. and pressures in the range of 200,000 to 600,000 Pa (2-6 bar).
To verify the sealing quality, a package according to the example and a package according to the comparative example underwent a number of tests to compare the performance, e.g. having regard to sealing bond strength at elevated temperatures, drop test, leak test, and pasteurization. For example, in a drop test, the package was filled with 200 ml water, sealed and dropped from a height of 1.8 m. The package then was visually inspected for leaks in the sealing area wherein no defects could be observed. In another test, packages filled with water underwent a pasteurization process at 95° C. for one hour. Again, no degradation of the sealed seam region could be observed after the pasteurization process. The tests revealed that the bond strength of the example was at least as good as or even better than the bond strength of the comparative example. Further, using the sealing jaws having the wavy profile, e.g. as shown in FIG. 4, the printing on the packaging material was not damaged in the sealing area; whereas, in the comparative example, image defects could be observed where the sharp edges of the sealing jaws displaced the ink distorting the printed image or even scraped or scratched off part of the printing. Using wavy jaws avoids mechanical ink movement and yields higher-quality output after sealing is made.
FIG. 5 shows a schematic diagram for illustrating an example of a wavy profile of the sealing jaws. In the example of FIG. 5, the profile has a sinusoidal or approximately sinusoidal cross-section. Assuming that line S represents the flat surface portion 38 of the tool plate 34 of the sealing jaw, the wavy profile illustrated in FIG. 5 comprises grooves 50 and ridges 52. In the example FIG. 5, an amplitude A correspondence to a depth of a groove; a pitch P illustrates a distance between two neighboring ridge tops; and a radius R represents a parameter of the curvature at the ridge top. In the example FIG. 5, the depth of a groove has the same amplitude as the height of a ridge; the pitch of neighboring ridges is the same as the pitch of neighboring grooves; and the radius of curvature at the ridge top is the same as the radius of curvature at the groove bottom. Some examples of the parameters amplitude A, pitch P, and radius R are: 0.3 mm<A<0.8 mm; 1 mm<P<3 mm; and 0.5 mm<R<2 mm. The absolute values, among others, will depend on the size and nature of the package to be sealed. Also the number of grooves and ridges will depend on the size and nature of the package and on the intended bonding strength.
FIG. 6 shows a flow diagram of one example of a process of producing a package from a flexible packaging material. The process starts in block 62 by providing two layers of the flexible packaging material. In block 64 the two layers are overlapped to form a seal region. In block 66 the seal region of the two layers is inserted between two sealing jaws, including a first jaw having a first jaw surface and a second jaw having a second jaw surface wherein the respective jaw surfaces arranged opposite to each other. The first jaw surface includes a plurality of grooves and the second jaw surface includes a plurality of ridges, the grooves and ridges extending along the length of the seal region. The respective grooves and ridges can be provided in a wavy surface profile, such as the one shown in FIG. 4. In block 68, the two sealing jaws are moved towards each other to close the jaws, so as to engage the grooves and ridges of the respective opposite jaw surfaces, with the packaging material they between, and to apply heat and pressure to the seal region of the packaging material to create a wavy seal structure in the seal region. The wavy seal structure includes grooves and ridges corresponding to the grooves and ridges of the jaw surfaces, wherein the grooves and ridges in their bottom and top regions have curved cross-sections.
Patent Application
20190177021
