Method and device for joining transfer or laminating film webs

Abstract

A description is given of a method for joining a first and a second film web (2, 2′) of a transfer film or laminating film, wherein the film webs (2, 2′) comprise a thermoplastic carrier film (21) and a decorative layer (23). Formed between the first and second film webs (2, 2′) is a common joining portion (3), in which the first and second film webs (2, 2′) are joined to each other by a welding process. A device for carrying out the method is also described.

Claims

1. A method for joining an end portion of a first film web to an end portion of a second film web, the method comprising: providing a first transfer film to form the first film web, the first transfer film comprising a thermoplastic carrier film, a decorative layer and a separating layer disposed between the carrier film and the decorative layer for facilitating removal of the decorative layer from the carrier film of the first transfer film; providing a second transfer film to form the second film web, the second transfer film comprising a thermoplastic carrier film, a decorative layer and a separating layer disposed between the carrier film and the decorative layer for facilitating removal of the decorative layer from the carrier film of the second transfer film; bringing the end portions of the first and second film webs together, wherein the first and second film webs are aligned in a longitudinal direction and a common joining portion is formed between the first and the second film web; and moving a weld head having two weld tips across the common joining portion in a direction perpendicular to the longitudinal direction to form a double weld seam in the common joining portion, in which the end portions of the first and second film webs are joined to each other by a welding process.

2. A method according to claim 1, wherein the common joining portion is formed as a lap joint.

3. A method according to claim 1, wherein the common joining portion is formed as a butt joint which is covered by a splice film.

4. A method according to claim 1, wherein the first and second film webs are joined to each other by means of ultrasonic welding.

5. A method according to claim 1, wherein the first and second film webs are joined to each other by means of contact welding.

6. A method according to claim 5, wherein an electric heating element is used to form a weld seam.

7. A method according to claim 1, wherein the first and second film webs are joined to each other by means of laser welding.

8. A method according to claim 7, wherein an absorbing layer for laser light is arranged in the joining portion below the first and the second film web.

9. A method according to claim 8, wherein a splice film which absorbs laser light is used as absorbing layer.

10. A method according to claim 1, wherein a continuous weld seam is formed.

11. A method according to claim 1, wherein a discontinuous weld seam is formed.

12. A method according to claim 1, wherein a weld seam is formed in an oscillating shape.

13. A method according to claim 1, wherein the first and second film webs are aligned with one another such that the motifs and/or register marks arranged on the first film web are aligned with the motifs and/or register marks arranged on the second film web in the joining portion registered with a position tolerance better than +/−0.5 mm.

14. A method according to claim 1, wherein a portion of the decorative layer of at least one of the first and second film webs is removed locally in the area of the common joining portion before the weld seam is formed.

15. A method according to claim 1, wherein such a first and second film web are joined to each other which have a separating layer in order to make it easier to detach the decorative layer from the thermoplastic carrier film.

16. A method according to claim 1, wherein such a first and second film web are joined to each other, which webs have an adhesive layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is now explained in more detail with reference to embodiment examples. There are shown in

(2) FIG. 1a a first embodiment example of a device for joining two transfer or laminating film webs in a schematic side view;

(3) FIG. 1b the device in FIG. 1a in a schematic top view;

(4) FIG. 2a the film webs in FIG. 1a joined to each other in a schematic perspective representation;

(5) FIG. 2b the film webs in FIG. 1a joined to each other in a schematic sectional representation;

(6) FIG. 3 a second embodiment example of a device for joining two transfer or laminating film webs in a schematic perspective representation;

(7) FIG. 4a a third embodiment example of a device for joining two transfer or laminating film webs in a schematic sectional representation;

(8) FIG. 4b the film webs in FIG. 4a joined to each other in a schematic sectional representation;

(9) FIG. 5a a first preparation stage of the film end portions for a fourth embodiment example, shown in FIG. 5c, of a device for joining two transfer or laminating film webs in a schematic sectional representation;

(10) FIG. 5b a second preparation stage of the film end portions in FIG. 5a;

(11) FIG. 5c a fourth embodiment example of a device for joining two transfer or laminating film webs in a schematic sectional representation;

(12) FIG. 5d the film webs in FIG. 5c joined to each other in a schematic sectional representation;

(13) FIG. 6a a fifth embodiment example of a device for joining two transfer or laminating film webs in a schematic sectional representation;

(14) FIG. 6b the film webs in FIG. 6a joined to each other in a schematic sectional representation;

(15) FIG. 7a a sixth embodiment example of a device for joining two transfer or laminating film webs in a schematic sectional representation;

(16) FIG. 7b the film webs in FIG. 7a joined to each other in a schematic sectional representation;

(17) FIG. 8 the film end portions welded to each other in the layer structure a schematic sectional representation;

(18) FIG. 9a a sectional view of a film-welded joint magnified 10 times;

(19) FIG. 9b a sectional view of a film-welded joint magnified 20 times.

DETAILED DESCRIPTION OF THE INVENTION

(20) FIGS. 1a and 1b show a device 1 for joining or splicing two transfer or laminating film webs 2 and 2′ by means of ultrasonic welding in a schematic representation. In the embodiment example shown in FIGS. 1a and 1b the films are transfer films formed as hot stamping films.

(21) The tape-shaped film webs 2 and 2′ are provided on feed rollers 2v and fed to supporting devices 4 and 4′ which fix the end portions of the film webs. The film webs are present as film reels which in the device 1 are joined to form larger film reels. The films are multilayer bodies which comprise a thermoplastic carrier film and a decorative layer which can be detached from the carrier film and is formed as a transfer layer. The films can have further layers, for example a separating layer arranged between the carrier film and the transfer layer which makes it easier to detach the transfer layer from the carrier film. Reflective layers and protective layers can further be provided as described further below in FIG. 8.

(22) The supporting device 4 is immovably joined to an adjusting device 4j. The supporting device 4 is adjustable in the x and y direction by means of the adjusting device 4j, whereby the positions of the two film webs 2 and 2′ can be adjusted relative to each other. With the adjusting device 4j the two film webs 2 and 2′ can be aligned with each other such that the motifs and/or register marks arranged on the first film web 2 are aligned with the motifs and/or register marks arranged on the second film web 2′ registered with a position tolerance less than +/−0.5 mm and form a lap joint 3, in which they are arranged one on top of the other. In the lap joint 3, the film webs 2 and 2′ lie on an anvil 5, which is arranged below an ultrasonic welding head 6. The ultrasonic welding head 6 comprises an ultrasonic transducer 6w, an amplitude transformer 6a and a sonotrode 6s.

(23) A high-frequency alternating current is transmitted to the ultrasonic transducer 6w from which a mechanical ultrasonic oscillation is generated with the aid of the piezo-electric or the magnetostrictive effect. The ultrasonic oscillation is transmitted to the sonotrode 6s via the amplitude transformer 6a. The amplitude of the ultrasonic oscillation and the impedance matching are influenced by the shape and mass of the amplitude transformer 6a. The sonotrode 6s can be produced from steel, aluminum or titanium.

(24) In the embodiment example represented in FIGS. 1a and 1b the sonotrode 6s has two tips spaced apart from one another. By the lowering of the ultrasonic welding head 6 the two tips of the sonotrode 6s come to rest against the film web 2 lying on top in the lap joint 3 and transmit the ultrasonic oscillations to the film material. The anvil 5 forms a counter bearing for the sonotrode 6s. The ultrasonic oscillations are thus transmitted under pressure to the film webs 2 and 2′ to be joined, which are arranged one on top of the other in the lap joint 3 on the anvil 5. The areas of the film webs 2 and 2′ which are in contact with the sonotrode 6s heat up as a result of the internal friction caused by the ultrasound and merge together.

(25) The lowered ultrasonic welding head 6 can be moved across the longitudinal axis of the film webs 2 and 2′ such that a double seam can be produced from two parallel weld seams 3n due to the two tips of the sonotrode 6s (see FIGS. 2a and 2b), which seams extend over the entire width of the film webs 2 and 2′.

(26) It has surprisingly been shown that a durable and resilient welded joint occurs although the aforementioned further layers are arranged between the two carrier films in the lap joint 3 such that the two carrier films are not in direct contact. It was to be expected that wax in particular would act as a separation means also during ultrasonic welding by melting as a result of the energy input and would prevent a lasting welded joint. Further below in FIG. 8 a possible mechanism of action is described which leads to the resilient welded joint.

(27) FIGS. 2a and 2b show the film webs in FIG. 1 joined to each other in a schematic perspective representation and in a schematic sectional representation respectively. The film webs 2 and 2′ are joined to each other by a double seam, formed from two weld seams 3n.

(28) As an alternative to the double seam made of two rectilinear parallel single seams other double seams can also be realized if the ultrasonic welding head 6 is rotatable about its longitudinal axis (z axis, corresponding to the direction of lowering). The two tips of the sonotrode 6s can thereby also be rotated during the rectilinear movement of the ultrasonic welding head 6 across the longitudinal axis or direction of travel of the film webs 2, 2′ such that an oscillating double seam is formed from two parallel, non-rectilinear single seams. Depending on the value of the movement and rotation speed, the resulting, in particular complex, shape, in particular also the density of the crossing connecting seams, i.e. their respective distance from one another, can be controlled. The oscillating double seam can in particular have a shape similar to a guilloche. Such a close-packed double seam can have increased strength, in particular against tensile forces during processing and/or during the reeling of the film webs 2, 2′. It is likewise possible to equip the sonotrode with more than two tips, with the result that either rectilinear parallel multiple seams or, as described above, correspondingly even more complex non-rectilinear multiple seams are formed.

(29) It is likewise possible to combine the multiple seams with the previously described width variations of the seam and/or seam interruptions.

(30) FIG. 3 shows a second embodiment example of the device 1, in which the sonotrode 6s is formed as a rotating sonotrode and the anvil 5 as a rotating anvil. The representation of the device in FIG. 3, which is essentially formed like the device in FIG. 1, is limited to the sonotrode and the anvil to simplify the representation.

(31) FIG. 4a shows a schematic cut section of a third embodiment example of the device 1, which is essentially formed like the device in FIG. 1. The two film webs 2 and 2′ abut directly against one another forming a butt joint and are covered in the joining portion by a splice 7. Like the carrier film of the two film webs, the splice T can consist of a thermoplastic material. It can, for example, be fed to the device 1 as a tape which is cut to the width of the film webs after welding. As shown in FIG. 4b, a double seam can be provided which is formed from two weld seams 3n. The advantage of this embodiment example is that the two weld seams 3n are formed directly between the thermoplastic materials which can be welded to each other, with the result that the weld seams are formed with optimal tensile strength.

(32) FIGS. 5a to 5d show an embodiment in which the end portions of the film webs 2 and 2′ are each bent or folded by 90° and thus form a folding portion 2f or 2f′. Increased strength thereby occurs in one of the weld seams 3n because the carrier films of the two film webs lie one on top of the other as a result of the folding over in the folding portion and the carrier films engage with one another or interlock contrary to the direction of a subsequent tensile loading.

(33) FIGS. 6a and 6b show a further embodiment example in which contact welding is provided as the joining process. Instead of the ultrasonic welding head in FIG. 1, a contact welding head 8 is provided which, on its underside facing the lap joint, has two wire- or tape-shaped heating elements 8h spaced apart from one another which, when the contact welding head 8 is lowered onto the film webs 2 and 2′ to be joined, form two weld seams 3n by local thermal melting of the carrier films. Mixed layers also form in the weld seams, as described further below in FIG. 8.

(34) FIGS. 7a and 7b show a further embodiment example in which the film webs 2 and 2′ are joined to one another by laser welding. In the embodiment example two laser welding heads 9 spaced apart from one another are provided which enable the film webs 2 and 2′ which are to be joined to be heated linearly. For this, the laser welding heads 9 can be formed to be displaceable along the seam axis or non-displaceable laser welding heads with an optical beam deflection can be provided. The upper side of the supporting device facing the laser welding heads 9 is formed transparent for the laser radiation used. The two film webs 2 and 2′ form a butt joint below which an absorbing layer 10 for the laser radiation formed as a black splice film is arranged. The anvil 5 is arranged below the splice film. The two film webs 2 and 2′ are advantageously aligned such that the carrier film lies on the splice film.

(35) If the contact welding head 8 is equipped with two or more heating elements 8h or the laser welding head 9 is equipped with two or more laser beams, the generation of complex, in particular oscillating, multiple seams with increased strength can thus also be produced by rotating the contact welding head 8 about its longitudinal axis or in the case of the laser welding head 9 by rotating the laser welding head 9 about its longitudinal axis or by correspondingly adjusting the optical beam deflection. It is also possible here to combine the multiple seams with the previously described width variations of the seam and/or seam interruptions.

(36) With reference to a schematic sectional representation, FIG. 8 shows the layer structure of two film webs 2 and 2′ welded to each other and the formation of the weld seams 3n in detail.

(37) The two film webs 2 and 2′ are formed as multilayer bodies. A waxy separating layer 22, a transfer layer 23 and an in particular metallic reflective layer 24 are arranged on a carrier film 21, which can be formed for example from polyester, in particular PET (PET=polyethylene terephthalate). The reflective layer can, fore example, be formed from metals such as aluminum, copper, chromium or from HRI layers (HRI=high refractive index) such as e.g. ZnS or TiO.sub.2 or from a multilayer system over the whole surface or textured, e.g. by partial metallization or demetallization. Combinations of these are likewise possible. An adhesive layer can be provided for example as a further layer.

(38) As tests have shown, mixed structures are formed in the weld seams 3n, wherein the carrier films 21 form a continuous joining layer in which clusters of the remaining layers are incorporated. As FIGS. 9a and 9b show, the strata have become mixed. Although the mixed layer is not as homogeneous as the carrier film, it still has sufficient tensile strength to enable the film to be stamped or laminated, as described further above.

(39) As experiments with different welding, processes have shown, although the tensile strength of a conventional splice is not achieved, the minimum demand to be placed on a splice, of a tensile strength of more than 13 N/cm, is achieved. The tensile strength was, in each case, determined using a Zwick testing machine.

(40) The following tensile strengths were found for an ultrasonic welded joint for films made of PET with a seam width of 0.8 mm depending on the material thickness: PET 19 μm: 215 N/cm PET 50 μm: 47.0 N/cm

(41) With a thickness of 9 μm the starling material has a tensile strength of 40-45 N/cm.

(42) Conventional splice tape coated with adhesive has a tensile strength of 30-40 N/cm. With a conventional splice and a 19 μm thick PET film a tensile strength of 35-45 N/cm is achieved.

(43) The splice of the above-mentioned PET material welded according to the invention had a tensile strength of 15-25 N/cm, which is sufficient for the further processing of the joined film webs in a roll-to-roll process.

(44) In a further experiment, film webs of a hot stamping film were joined by ultrasonic welding with a seam width of 0.6-1.0 mm, wherein the tensile strength per seam was 12-19 N/cm.

(45) With a hot stamping film with pigmented adhesive a tensile strength of only 3.0 N/cm per seam was achieved for the same seam width of 0.6-1.6 mm.

(46) Further experiments were carried out to determine the influence of the seam width and the welding process: ultrasonic welding (per 0.5-mm seam): 4.1 N/cm ultrasonic welding (per 1-mm seam); 8.5 N/cm impulse welding or contact welding (per 1.6-mm seam): 12.8 N/cm.

(47) Clearly the width of the weld seam has the decisive influence on the tensile strength of the weld seam.

(48) The following demands were placed on the joint between the two film webs 2 and 2′:

(49) As was further shown, the following results could be achieved, when joining film webs of a hot stamping film with a total thickness of approximately 19 μm: production of a joint registered with +/−0.5-mm tolerance; maximum width of the joint 3 mm; application of the joint, i.e. thickness of the joint not greater than when formed using splice tape; adhesion so good that the film withstands the tensile forces arising in a typical application machine; length of the joint: in the range of from 10 to 650 mm.

LIST OF REFERENCE NUMBERS

(50) 1 Device for joining film webs 2, 2′ Film web 2f, 2f′ Folding portion 2v Feed roller 3 Lap joint 3n Weld seam 4, 4′ Supporting device 4j Adjusting device 5 Anvil 6 Ultrasonic welding head 6a Amplitude transformer 6s Sonotrode 6w Ultrasonic transducer 7 Splice film 8 Contact welding head 8h Heating element 9 Laser welding head 10 Absorbing layer 21 Carrier film 22 Separating layer 23 Transfer layer 24 Metal layer