WO2003106143A1

WO2003106143A1 - Method of forming packaging using thermoforming inks

Info

Publication number: WO2003106143A1
Application number: PCT/US2002/018198
Authority: WO
Inventors: Robert L. Flowers; Michael A Parrotta
Original assignee: Westvaco Packaging Group, Inc.
Priority date: 2002-06-16
Filing date: 2002-06-16
Publication date: 2003-12-24
Also published as: AU2002314995A1

Abstract

A method of making pre-printed, thermoformed plastic packaging comprising printing a layer of modified, UV-curable thermoforming ink onto a plastic surface, then thermoforming the plastic surface to form a packaging article. The resulting article is characterized by a printed, thermoformed layer in which the ink exhibits substantially no shrinkage, peeling or other deterioration after thermoforming. The process is also suited to a distortion printing method.

Description

METHOD OF FORMING PACKAGING USING THERMOFORMING INKS

[001] FIELD OF INDUSTRIAL APPLICABILITY

[002] The invention provides a method of forming pre-printed, semi-rigid and rigid plastic packaging wherein the plastic surface is thermoformed after being printed with a UV-curable ink. In particular embodiments of this method, a product or consumer item is contained within cavities formed in the packaging surface as a result of the thermoforming process. The resulting packaging product items may be used as product samplers, e.g. for cosmetic formulations. The process may also be used in the manufacture of other types of thermoformable packaging made from plastic substrates, for example creased plastic boxes or cases.

[003] TECHNICAL BACKGROUND OF THE INVENTION

[004] In the development of packaging products and techniques, the use of various types of semi-rigid blister packaging is known. One form of blister packaging is for example used to contain individual doses of medicaments, which may be dispensed by opening the blister. Other'blister packages of varying size may be used to contain sundry articles and materials. One such application is the packaging of cosmetic formulations either in full product size or as samplers. This type of packaging may be required to provide as much product information or advertising as possible in a limited surface area. Additionally, plastic packaging is often the preferred substrate for forming such packaging, as the blisters can be wholly formed out of a single piece of plastic film. Forming blister packaging from plastic film has however been impeded by the inability to print an ink layer either as a sheet of color, text or graphics onto the plastic surface before it is formed. Typically, this type of process results in a brittle printed layer that sh nks, cracks, peels or is otherwise degraded when the plastic is formed into a multi-dimensional surface. The inks conventionally used are screen-printing UV inks. These inks form hard, tough coatings with high gloss, and have been found desirable because they cure quickly and are made of relatively inexpensive components.

[005] Another problem related to the molecular structure of the conventional inks is that oligomers used in such inks are typically cured under conventional mercury vapor UV lamps, which are electrode-type systems ranging from about 400 - 600 watts in output. Another problem observed with conventional UV inks is that typically they cannot be printed by desirable printing methods that can produce a high level of definition and a finely printed image. This is because the inks are of relatively high viscosity, and in order to be used in a high definition process, e.g. flexographic (flexo) printing, they would have to be of much lower viscosity. Thinning the conventional UV inks has not been found to be successful as the printing quality is compromised. Consequently, use of conventional UV curable inks in high quality printing applications has been limited.

[006] These problems are addressed by the various embodiments of the claimed invention, which are described and exemplified below.

[007] SUMMARY OF THE INVENTION

[008] A method has now been discovered for the manufacture of plastic packaging that has been pre-printed with a thermoformable ink that does not peel, flake, lift or decompose during the thermoforming step required to shape such packaging into a container suited to holding various products.

[009] The method comprises printing one or more layers of a UV-curable, pre- polymeric thermoforming ink onto a surface of a thermoformable plastic substrate, the UV-curable prepolymeric thermoforming ink having a molecular functionality of less than about 1.5 and an estimated elongation equal to or greater than about 400%, preferably around 300%; curing the printed surface so formed under ultraviolet light; forming the printed thermoformable plastic substrate into one or more thermoformable blanks; and thermoforming the printed thermoformable plastic substrate into a packaging blister having a thermoformed printed surface in which the printed ink exhibits improved flexibility and substantially no shrinkage.

[010] The invention further comprises a range of products that are produced by the process of the invention. Blister packaging products are among the preferred applications for this method. [011]

[012] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[013] The invention comprises printing a modified UV-curable ink onto a plastic substrate before it is thermoformed to provide a novel printed packaging material, in which the ink is thermoformed in conformity with the plastic surface but does not exhibit the aforementioned defects such as shrinkage, peeling or splitting. The ink is a modified epoxy acrylate prepolymer composition, which is preferably modified with polyester or urethane oligomers to enhance its flexibility and adhesion to difficult substrates. Such oligomers include dinners, trimers, tetramers and other co-polymerized sub-units. In addition, the composition may be further modified to provide enhanced viscosity by the addition of monomeric and oligomeric components such as acrylates and methacrylates.

[014] To modify this problem therefore, monomers of acrylate or methacrylate have been added to the prepolymeric inks to reduce viscosity to desired levels and to adjust certain physical properties of the printed layer, such as flexibility and adhesion. Because of these improvements in the ink chemistry, a thinner consistency ink is derived and can be used in fine printing applications. In this respect, it has now been determined that an ink with a minimal total molecular functionality of about 1.5 or less is advantageously used in this invention. As used herein, "molecular functionality" refers to the index representing the number of available crosslinking sites on the oligomers and monomers of the ink composition. A higher molecular functionality, which represents an increased number of such crosslinkable sites, as is evident in conventional inks, increases the cure rate and produces a harder, more brittle coating upon cure. Conventional UV inks have a molecular functionality on the order of about 3.0, which represents an ability for a significant amount of crosslinking, which in turn leads to the formation of a harder layer. The tensile strength and the glass transition temperature, Tg, which is the temperature above which the composition will flow, are also increased relative to the modified inks of this invention. The increased hardness of the conventional ink also reduces elongation and the flexibility of the printed layer. It has now been found that reducing the molecular functionality to reduce the brittleness characteristics and applying the resulting modified ink formulation in a process conducive to even application and rapid cure using high irradiation produces a printed plastic surface in which the ink layer is more elastic, and therefore does not shrink or crack during the thermoforming process. The modified inks used in the invention are characterized by glass transition temperatures that can range from about -15°C to about -60°C. Exemplary inks exhibit glass transition temperatures of less than about -30°C.

[015] The printing process used to apply the thermoforming ink is not limited by the physical or chemical properties of the ink, as is the difficulty with conventional UV-curable inks. As discussed above, conventional UV-curable inks are limited primarily to screen-printing while the thermoforming ink may be applied by that method and a variety of other means. Accordingly, any conventional printing method, whether solvent-, water- or UV-based, may be used to apply the ink. Preferred methods are flexographic, electron-beam lithography and distortion printing. The printing step may further be modified by the use of three-dimensional printing techniques to provide multidimensional images on the printed surface, e.g. holographic or lenticular printing.

[016] An exemplary ink suited for use in the process of the invention is a custom formulation based on an epoxy acrylate prepolymer as the main component, with an addition of acrylate monomers and oligomers to provide a molecular functionality of about 1.3. These inks are produced for example by Environmental Inks (Linthicum, MD). Such a modified ink would not typically be contemplated for use in a high-speed flexographic or lithographic printing process as used in the preferred embodiments of the present invention because of the different chemistry of the formulation in relation to conventional inks.

[017] In certain embodiments of the invention, an overcoating or varnish may be applied atop the one or more ink layers. The varnish is preferably comprised of similar polymeric and prepolymeric components as the ink layer, but lacking pigment ingredients. By such a characterization, the application of a varnish will provide added surface gloss and protection, while at the same time the flexibility of the inked surface is maintained. The varnish may be applied after the one or more thermoforming ink layers is cured, or may be applied after the layers of thermoforming ink have been applied but before they have been cured.

[018] After the ink and optionally, the varnish layers are applied, the printed surface is exposed to an ultraviolet (UV) light source for curing. The curing step preferably follows immediately after coating; for example in a high-speed, in-line operation, the printed surface is exposed to the UV light source almost immediately, typically within up to 3 seconds. Curing speeds in an in-line operation may range from about 100 feet per minute (fpm) to in excess of 300 feet per minute. At speeds of up to 300 feet per minute, for example, the time lapse between printing and curing is almost instantaneous. This compares favorably with the screen-printing process dictated by conventional UV curable inks, in which the line speeds are necessarily much lower, on the order of 100 fpm or less.

[019] In still another embodiment of the invention, a primer layer may be applied between the surface of the plastic substrate and the ink layer. In such an embodiment, the primer is applied before the ink layer is printed. In this manner, the risk of premature transfer of the ink layer and blocking after printing is minimized.

[020] Suitable plastic substrates for practicing the invention may be selected from any known thermoplastic polymer material. Examples of such substrates include APET, PET-G, polypropylene (PP), polycarbonate, polyesters, polyacrylates, polystyrene and PVC, however any other suitable plastic substrate may be used. The substrate may be a monolayer material, but polylaminates made a combination of substrates may also be used.

[021] The UV irradiation used to cure the printed plastic substrate is suitably delivered by microwave-activated lamps, which output a peak irradiation higher than the output of conventional UV lamps. In fact, conventional electrode-type UV lamps, which have an intensity of at most about 1 watt/cm², do not provide sufficient irradiation to cure the flexible inks of the present invention. Preferably, lamps usable in the invention are electrodeless microwave- activated UV lamps having a peak irradiation intensity of from about 4.5 to about 5.5 watts/cm², such as are manufactured by Fusion Inc. These lamps produce an irradiation output of approximately 5 times the intensity of conventional UV lamps.

[022] The UV lamp used in the process of the invention may also be doped to alter its spectral output while still producing light of a wavelength within the UV range. For example, the lamps may be doped to produce rapid and efficient curing results for white and opaque inks in one range, for blues and violets in another wavelength range, and in a third wavelength range for other colors.

[023] In a preferred embodiment, the printed, cured plastic substrate is thermoformed after printing. Any known means of thermoforming may be used, and the conditions optimized to suit the type of plastic and the thickness of the substrate. Typically, the sheet of printed plastic substrate is unrolled, flattened and then passed between heated platen on a press-mold machine. To the surfaces of the platen are attached die configured to form the desired shape in the thermoformed article. With the application of heat and optionally, an amount of positive pressure via the die, the sheet is deformed to form cavities. There are no extraordinary limitations on the forming temperature, however the temperature should be high enough to allow deformation of the plastic substrate with the application of minimal to moderate pressure, but low enough to avoid distortion or melting. Once the cavities have been formed, the sheet may be run through a chiller to slightly reduce the temperature of the sheet. It should be noted that in an in-line operation, the chiller step may be omitted as only a slight reduction in temperature is necessary and this cooling may be accomplished as the sheet moves along the line.

[024] The cavities formed in the thermoforming process are next filled at a dispensing unit. The nature and consistency of the material being filled is not intended to be limited in any way. For example, a cosmetic such as a lipstick formulation may be heated to a flowing consistency in a melting tank to which a dispenser is attached, and the formulation dispensed into the cavities then cooled. Alternatively, a cold fill product may be dispensed.

[025] The filled cavities are sealed preferably by laminating a film by any suitable means over the surface of the filled product. The film is adhered to the plastic substrate in the areas surrounding the cavities, preferably by heat sealing. At this point in an in-line process, the plastic substrate is still in the form of a continuous sheet, which is not cut or otherwise separated until after the filled package has been fully formed, and so the entire sheet is over- laminated with the film. In a manual process, hand sheets may be processed to this point before being cut into the individual thermoformed articles (e.g. blister packages), or the thermoformed articles may be formed and/or printed separately before filling.

[026] While the process is most economically carried out as an in-line process in which rolls of plastic substrate material are printed and then thermoformed before cutting to form individual blister packages, the process may also be performed by printing pre-cut hand sheets. Additionally, while in a preferred embodiment the printing step is carried out before the thermoforming step, the package may first be formed and then printed, if necessary. A technique such as distortion printing or flexo printing may be used.

[027] The invention therefore provides a method of manufacturing plastic packaging, in particular blister packaging that may be printed and then thermoformed without deterioration of the printed layer, as was heretofore known in the art. This improvement allows manufacture of plastic packaging articles not having a flat surface but having a formed, multi-dimensional printed plastic surface. Advantageously, such products can be manufactured in-line in a high-speed process. Examples of packaging that may be produced by the process of this invention include, but are not limited to, cosmetics samplers, which may stand alone or be incorporated into any thermoformed article such as a bottle hanger, bottle cap or magazine insert, and unit dose blister packaging for pills or pharmaceutical preparations. In one embodiment, the blister packaging may be formed as a spray blister from a material that is sufficiently pliable to allow the formed blister to be pressed or squeezed to dispense the blister contents. To form this type of packaging, a capillary or dispensing tube may also be thermoformed adjacent to an in flow communication with the blister before the filling and sealing steps. The package formed by this combination of elements provides for spraying or squirting of the package contents through the capillary by squeezing the blister. The process may also be used in the manufacture or detailing of other articles such as face for appliances (e.g. plates forming the control panels) and automobile parts.

[028] EXAMPLES

[029] Various aspects of the claimed invention are illustrated by the following examples.

[030] Example 1 [031] The physical properties of a conventional screen-printable UV ink were compared to a customized UV-curable ink formulation such as is used in the present invention. The particular composition of the ink formulations of the invention allow them to be used in printing techniques other than screen printing, for example in a flexo printing process. The modified ink included a combination of oligomeric additives and an epoxy acrylate medium. The results of the comparative evaluation are presented in Table 1.

Table 1 - Performance Characteristics of UV Curable Inks

b - A modified epoxy acrylate having effective amounts of low T_g acrylate and methacrylate monomers and oligomers, manufactured by Environmental Inks.

[032] Example 2

[033] In the manufacture of a thermoformed blister package in the form of a single use cosmetic sampler according to the invention, a roll of polypropylene plastic substrate is unwound and printed on a flexographic printing press with a pre-set graphic design. A single color of modified ink formulation, as characterized in Table 1 , is applied in one pass as the sheet is fed through a flexographic printing press. Once past the printing press, the printed ink layer is exposed to a UV curing light beam emitted from a microwave-activated UV lamp (Fusion Inc.) having a peak irradiance emittance range of from about 4.5 to about 5.5 watts/cm². The cured sheet is then re-wound. In a subsequent inline thermoforming and filling operation, the sheet is unwound, printed side down and flattened by passing it through a series of rollers. The sheet is then passed between opposed weighted platen, the inner face of each plate being fitted with die shaped to provide depressions of from roughly I inch by ^ΛA inch in shape across the surface of the sheet. After this step, the sheet is passed through a chiller blowing ambient or slightly cooled air to slightly reduce the temperature of the plastic material. The resulting thermoformed sheet is formed with the printed layer of thermoformed ink on the reverse of the side exposed to the die.

[034] The sheet is passed to a dispensing station. At this point, a tank carrying a heated lipstick composition is injected into each depression. Immediately following this dispensing step, a cover film is laminated over the entire sheet and heat-sealed. In this manner, the depressions containing the product are sealed. After lamination, the sheet is fed through a cutting station where it is diced into separate rectangular cosmetic samplers; each comprised of a cavity filled with the lipstick formulation.

[035] It is believed that the present invention includes many other embodiments that may not be herein described in detail, but would nonetheless be appreciated by those skilled in the art from the disclosures made. Accordingly, this disclosure should not be read as being limited only to the foregoing examples or only to the designated preferred embodiments.

Claims

CLAIMSWe claim:

1. A method of making thermoformed plastic packaging having a preprinted, thermoformed surface, the method comprising the steps of:

a) printing one or more layers of a UV curable, prepolymeric thermoforming ink onto a surface of a thermoformable plastic substrate, the UV curable prepolymeric thermoforming ink having a molecular functionality of less than about 1.5, a glass transition temperature, T_g, of from about -15°C to about -60°C, and an elongation equal to or greater than about 400%;

b) curing the printed surface so formed under ultraviolet light using a microwave-activated UV lamp;

c) forming the printed thermoformable plastic substrate into one or more thermoformable blanks; and

d) thermoforming the printed thermoformable plastic substrate into a packaging blister having a thermoformed printed surface in which the printed ink exhibits substantially no shrinkage.

2. The method of claim 1 further comprising applying a varnish layer over the one or more layers of UV-curable thermoforming ink.

3. The method of claim 2 wherein the varnish layer is applied before the one of more layers of thermoforming ink is cured.

4. The method of claim 1 wherein the printing process is a distortion printing, flexographic, or electron-beam lithographic process.

5. The method of claim 4 further comprising applying one or more ink layers using a technique that produces a multi-dimensional effect on the printed surface.

6. The method of claim 1 wherein the thermoforming UV curable ink has a glass transition temperature of less than or equal to -30°C.

7. The method of claim 1 wherein the step of curing is completed using one or more microwave-activated UV lamps each doped to produce a spectral output in correlation to the ink color.

8. The method of claim 1 wherein the ultraviolet lamp is an electrodeless microwave-activated UV lamp.

9. The method of claim 8 wherein the peak irradiance emitted from the UV lamp is from about 4.5 to about 5.5 watts/cm².

10. The method of claim 1 wherein the curing is effected at a cure rate of greater than 100 feet per minute up to about 300 feet per minute.

11. The method of claim 1 wherein a UV-curable varnish is overcoated atop the printed surface of the plastic substrate.

12. The method of claim 10 wherein the UV-curable varnish is selected from the group consisting of acrylates.

13. The method of claim 1 wherein the UV curable, prepolymeric thermoforming ink is printed in a holographic configuration to provide a multi-dimensional printed effect.

14. The method of claim 1 wherein the printed thermoformable plastic substrate is cut to form individual blanks for thermoforming into packaging blisters.

15. The method of claim 1 wherein the thermoformable plastic substrate is selected from the group consisting of polyolefins and polyesters.

16. The method of claim 15 wherein the thermoplastic substrate is selected from the group consisting of APET, PET-G, PP, polycarbonate, polyacrylates, polystyrene, PVC and polylaminates thereof.

17. The method of claim 1 wherein the thermoforming process includes selectively applying a vacuum or pressure to deform selected areas of the heated blank to form a desired shape.

18. The method of claim 17 wherein the deformed areas are formed as raised blisters or depressions on the printed surface of the thermoplastic material.

19. The method of claim 1 wherein the surface of the thermoplastic substrate is selectively printed to provide an unprinted region forming said raised blister or depression, such that the raised blister or depression forms a transparent pocket through which the contents may be viewed.

20. The method of claim 18 further including filling the deformed area with a product.

21. The method of claim 20 wherein the product is cold filled.

22. The method of claim 20 wherein product is a cosmetic formulation.

23. The method of claim 18 further including thermoforming a capillary adjacent to and in flow communication with a blister.

24. The method of claim 20 wherein the filled blister is sealed by laminating it over with a heat sealable film.

25. A product formed by the process of claim 1.

26. A product formed by the process of claim 2.

27. A product formed by the process of claim 4.

28. A product formed by the process of claim 23.

29. A product formed by the process of claim 24.