METHOD AND DEVICE FOR BONDING FILM-SHAPED SUBSTRATES

Description

[0001] The present invention relates to a method for bonding film-shaped substrates, wherein one of the substrates has a thermoplastic surface that is softened prior to bonding, and wherein the surface of this substrate opposite the thermoplastic surface is cooled using a cooling roller. Furthermore, the present invention relates to an apparatus for carrying out the method according to the invention and to a composite body obtainable by means of the method according to the invention.

[0002] Those skilled in the art are familiar with a wide variety of methods for bonding film-like substrates, with a variety of adhesives being used to join the substrates. Typically, the adhesive is applied to the surface of a first substrate, and the substrates are then brought into contact with each other under pressure. However, this poses the problem that, to ensure a sufficient bond between the two substrates, the adhesive should wet the surface of the substrate as completely as possible. This also compensates for certain unevenness in the surface of the substrates and prevents the formation of air bubbles during lamination. Therefore, the required adhesive quantities are relatively high to prevent delamination of the product.The use of the required quantities of adhesive entails well-known disadvantages, such as excessive use of resources and the costly disposal and processing of the resulting waste. In view of the increasing scarcity of resources and growing environmental pollution, there is a need for industrial processes that enable responsible and sustainable use of resources and the environment. In view of the disadvantages listed, reducing the amount of adhesive used seems to be an obvious solution. Reducing the amount of adhesive per se proved impractical in initial tests. On the one hand, the products showed an increasing tendency towards delamination and, on the other hand, the formation of air bubbles during lamination could no longer be ruled out. This leads to a severe impairment of the mechanical and optical properties, particularly in transparent products.In order to obtain optically and mechanically resilient products despite a small amount of adhesive, it was therefore necessary to use substrates with smooth surfaces.

[0003] One approach to smoothing the surface of the substrates is to use a thermoplastic substrate whose surface can be smoothed by heat before bonding.

[0004] However, heating the substrate surface to smooth it has the disadvantage that the heated substrate deforms and stretches, making it difficult to guide the substrate during lamination and resulting in a composite that no longer exhibits the desired properties. The prior art proposes various approaches to addressing the problem of substrate deformation.

[0005] US 4,069,081 describes a lamination process in which a protective film is applied to a relatively flexible substrate document, preventing the resulting product from curling. For this purpose, a composite film is provided comprising a protective film made of a robust, transparent, and abrasion-resistant resin and an inner layer of a transparent thermoplastic composite resin, with a certain number of radiant heat-blocking pigments added to the composite resin.The layer of composite resin is heated such that the heat falls directly on the composite resin, and the composite film is laminated to the substrate by passing the composite film and the substrate directly after heating between a first and a second press roll, wherein the adhesive surface of the film is brought into contact with an inner surface of the substrate, while the outer surface of the film faces the first press roll and the outer surface of the substrate faces the second press roll.

[0006] US 2018 / 0162113 relates to the production of a laminated film, in which, in a first coating step, a coating is applied to a first film, the coating comprising a radiation-curing resin; in a lamination step, a second film is laminated to the coating; and in a curing step, during which the coated film is guided between the first and second films, a cured layer is formed. Each of these steps is performed while the first film is guided around a support roller. The support roller may have a temperature control unit for controlling the surface temperature of the roller.

[0007] EP3526042 A1 describes a device for laminating a substrate (4) with a thermoplastic coating material (2), comprising an IR heating device (3) for melting a surface of the coating material, an opposing cooling device (1) which actively cools the opposite surface of the coating material (2), and at least one press roller arrangement (5) which presses the substrate web (4) and the coating material (2) together to produce a hot-melt adhesive bond.To avoid irregularities in the finished product, EP3526042 proposes that the cooling device be designed as a rotationally driven cooling roller (1), around the circumference of which are arranged in succession: - a feed device (2a) for the thermoplastic coating material (2); - one or more IR heaters (3) for heating the surface of the thermoplastic coating material (2) resting on the cooling roller (1); - a feed device (4a) for the substrate web (4); - one or more press rollers (5) for pressing the substrate web (4) against the coating material (2); - and a discharge device (6a) for the laminated product (6). EP3526042 A1 falls under Article 54(3) EPC.

[0008] WO 2016 / 026918 describes a method for bonding two substrates, wherein a first film-shaped substrate containing at least one thermoplastic is transported by means of a supporting conveyor belt through a heating zone in which the substrate is heated such that the surface of the substrate is converted into a softened state, the substrate is brought together with a second substrate during and / or immediately after heating, wherein the second substrate is coated with an adhesive with a layer weight of 0.01 to 4 g / m², and the two substrates are bonded together under pressure. To ensure that only the surface of the substrate to be bonded is converted into a heated state, it is proposed to cool the surface not to be bonded.However, the described process has the disadvantage that the use of the conveyor belt only allows for indirect cooling of the substrate, which leads to increased energy consumption. Furthermore, there is only a limited choice of materials for the conveyor belt itself, as it cannot be heated to prevent the belt from stretching in the tensile direction.

[0009] US 5,582,669 describes a method and apparatus for applying a protective coating to an image-bearing medium. A heated roller and an actively cooled chill roller are arranged to form a gap through which the protective coating applied to a mesh and the image-bearing medium are passed. A temperature gradient between the layers of the mesh and the medium stimulates adhesion between the surface of the protective coating and the image, while simultaneously avoiding common problems during lamination, such as waving and curling of the substrates.

[0010] US 2011 / 041981 describes a laminating station for laminating a film or material layer to a web of cardboard or paperboard. The laminating station comprises a pressure roller and a cooling roller. A nip is formed between the rollers, pressing the material layer or film and the cardboard web together. The film or material layer rests against the cooling roller behind the nip for a predetermined angular interval. A shoe press roll is used as the pressure roller.

[0011] The methods described in the prior art have the disadvantage that their implementation is limited in terms of materials and implementation. Either special resins must be used or complex process setups are required to ensure dimensionally stable lamination of flexible substrates, even with small amounts of adhesive. Therefore, the object of the present invention is to provide a method that allows the dimensionally stable lamination of flexible substrates with small amounts of adhesive.

[0012] It has surprisingly been found that this object is achieved by a method in which a first surface of a substrate is heated, while the side opposite this surface is cooled by means of a cooling roller. Therefore, a first subject of the present invention is a method for bonding substrates, comprising Providing a film-shaped first substrate having a thermoplastic surface; guiding the first substrate (3) around a drivable cooling roller (1) with which the first substrate (3) is in contact, the cooling roller rotating in the feed direction; providing a second substrate, to the surface of which an adhesive is applied; and bringing the first and second substrates together under pressure, wherein the thermoplastic surface of the first substrate (3) is in a softened state upon joining, the surface of the first substrate (3) opposite the softened surface is cooled by means of a rotating cooling roller (1), the thermoplastic surface of the first substrate (3) is converted into a softened state by heating, wherein the heating is carried out by means of at least one heating element (2) which is arranged opposite the cooling roller (1), and the distance between the at least one heating element (2) and the cooling roller (1) is variable

[0013] It has surprisingly been found that by cooling the surface opposite the thermoplastic surface using a cooling roller, deformation of the substrate can be prevented without requiring a reduction in the process speed. The use of a cooling roller also offers the advantage that the surface of the roller with which the surface of the substrate to be cooled is in contact can be cooled directly, thus avoiding unnecessary energy losses. In contrast, the use of a conveyor belt, as proposed in the prior art, has the disadvantage that the conveyor belt itself can only be cooled indirectly, making effective cooling of the substrate surface difficult.

[0014] Softened state in the context of the present invention refers to a state in which the thermoplastic surface of the first substrate can be plastically deformed without changing the dimensional dimensions of the substrate.

[0015] Film-shaped or film in the sense of the present invention refers to a very thin material produced in webs for gluing or packaging, preferably made of metal or plastic.

[0016] According to the method according to the invention, the surface of the first substrate opposite the heated surface of the first substrate is cooled by means of a rotating cooling roller, wherein the first substrate is guided around the cooling roller. The contact area between the cooling roller and the first substrate can be adjusted as required. The cooling roller is actively driven, as this minimizes the risk of the substrate being stretched during the process. Therefore, the cooling roller is an actively driven cooling roller. Particularly preferably, the cooling roller is operated at web speed to avoid any deformation of the substrate. No special requirements are placed on the coolant used in the cooling roller within the scope of the method according to the invention. In a preferred embodiment, the cooling roller is operated with a liquid coolant, in particular water.

[0017] According to the invention, the first substrate and the second substrate are brought together under pressure. The substrates can be brought together in a conventional manner known to those skilled in the art, for example using a laminating unit. This is preferably a laminating unit that is integrated into the cooling roller arrangement or is formed separately from it. The two substrates are preferably brought together by exerting uniform pressure across the entire width of the substrates. In a particularly preferred embodiment, the substrates are brought together by bringing the second substrate together with the first substrate resting on the cooling roller. It was surprisingly found that the dimensional stability of the first substrate in particular could be increased in this way.

[0018] The thermoplastic surface of the first substrate is converted into a softened state by heating, wherein the heating takes place by means of at least one heating element arranged opposite the cooling roller. In a preferred embodiment, the at least one heating element is arranged around the periphery of the cooling roller. In a preferred embodiment, the at least one heating element comprises a series of separate heating elements, preferably IR radiators. The number of individual heating elements is determined by the diameter of the cooling roller and is preferably at least 3, more preferably 3 to 15, particularly preferably 3 to 10, in particular 3 to 5. In a particularly preferred embodiment, the separate heating elements are arranged around the periphery of the cooling roller.In a further preferred embodiment, the various heating elements of the at least one heating element are arranged around at least a quarter of the periphery of the cooling roller, particularly preferably around at least half of the periphery. Most preferably, the various heating elements are arranged around the entire periphery of the cooling roller, it being clear to the person skilled in the art that the arrangement is such that the process flow and / or other components are not impaired. It has proven particularly advantageous if the at least one heating element is arranged in spatial proximity to the point in the process at which the first substrate and the second substrate are brought together, preferably with the aid of a laminating unit. Therefore, an embodiment in which the at least one heating element is arranged in spatial proximity to the laminating unit is particularly preferred.It has surprisingly been found that in this way the substrate surface of the first substrate can be converted into a softened state such that a resilient bond is achieved between the first substrate and the second substrate. Those skilled in the art are aware of a number of measures for heating the thermoplastic surface of a substrate, for example by means of hot air or electromagnetic radiation. It has proven particularly advantageous to carry out the heating using IR radiation, since this allows a surprisingly homogeneous heating of the surface to be achieved. Therefore, an embodiment of the method according to the invention is preferred in which the thermoplastic surface of the first substrate is converted into a softened state by heating using IR radiation.

[0019] The process according to the invention is particularly characterized by the fact that, despite only a small amount of adhesive, it yields laminated substrates characterized by excellent bond strength. Therefore, an embodiment is preferred in which the layer weight of the adhesive on the surface of the second substrate is less than 2 g / m 2 , preferably less than 1 g / m 2 , particularly preferably 0.1 to 0.7 g / m 2 .

[0020] Furthermore, the process according to the invention is characterized in that, in contrast to processes described in the prior art, no special requirements are placed on the adhesive used. Rather, conventional adhesives known to those skilled in the art can be used. Therefore, an embodiment is preferred in which the adhesive applied to the second substrate is selected from thermoplastic adhesives or crosslinking adhesives in solvent-based, aqueous, or solvent-free form, whereby both one-component and two-component systems can be used.The adhesive is particularly preferably selected from the group consisting of adhesives based on thermoplastic polymers, such as polyurethanes, ethylene-vinyl acetate, or polyacrylates; solvent-based adhesives such as acrylate adhesives; 1-component or 2-component polyurethane adhesives; silane-crosslinking adhesives; reactive hot melt adhesives such as 1-component polyurethane adhesives, epoxyamine adhesives, and radiation-crosslinking adhesives. Adhesives based on polyurethanes, ethylene-vinyl acetate, or polyacrylates are particularly preferred. Polyurethane adhesives are particularly used in the present process.

[0021] The method according to the invention is particularly suitable for laminating film-shaped substrates. Even though non-film-shaped substrates such as wood-based materials or metal sheets can be used as the second substrate, the second substrate is preferably also a film-shaped substrate, which is preferably selected from the group consisting of thermosetting or thermoplastic plastics, organic polymers and metals and metal alloys. For example, the second substrate can be a film-shaped substrate based on aluminum or an aluminum alloy or a plastic film. In a preferred embodiment, the second substrate is selected from the group consisting of aluminum coated with polyethylene or polypropylene, biaxially stretched polyamide, biaxially stretched polyethylene terephthalate, oriented polypropylene and oriented polyethylene.

[0022] The first substrate is characterized in particular by its thermoplastic surface. In a preferred embodiment, the first substrate is a substrate consisting of or comprising polyolefins, polyvinyl chlorides, ethylene copolymers, polyesters, polyethers, and / or polyamides. Particular preference is given to using polyethylene, polypropylene, polyvinyl chlorides, or ethylene copolymers, especially polyethylene and polypropylene.

[0023] Multilayer substrates can also be used as the first and / or second substrate in the process according to the invention, as long as the first substrate has a thermoplastic surface and the second substrate has a surface to which an adhesive can be applied. Multilayer substrates can be used, for example, as multilayer films with a core layer made of an oxygen barrier material. Common oxygen barrier materials such as vinylidene chloride copolymers with various comonomers, such as vinyl chloride (VC-VDC copolymer) or methyl acrylate (MA-VDC copolymer), and polyamides and ethylene-vinyl alcohol copolymer (EVOH), can be used. In a particularly preferred embodiment, coextruded, oriented polypropylenes and / or coextruded ethylene-vinyl alcohol films are used.

[0024] Preferably, the substrates used are each film-shaped. Therefore, an embodiment is preferred in which the first and / or second substrates have a thickness of 2 to 100 µm, preferably 4 to 80 µm.

[0025] Within the scope of the present invention, it was surprisingly found that deformation of the first substrate, in particular in the feed direction, can be prevented by cooling the surface opposite the heated surface. Improved dimensional stability of the first substrate could be achieved in particular when the substrate was guided over a cooling roller and the temperature difference between the surface of the roller and the environment was at least 10 K, preferably at least 15 K. Therefore, an embodiment of the method according to the invention is preferred in which the temperature difference between the surface of the cooling roller and the environment is at least 10 K, preferably at least 15 K. The method according to the invention has the further advantage that the advantageous temperature differences can be adjusted using conventional coolants, such as water.

[0026] A further object of the present invention is a device for carrying out the method according to the invention, the device comprising the following: a feed device for a film-shaped first substrate, the substrate having a thermoplastic surface; a feed device for a second substrate, to the surface of which an adhesive is applied; a rotationally drivable cooling roller which is in contact with the first substrate (3) and around which the first substrate is guided; at least one heating element for heating the thermoplastic surface of the first substrate, the at least one heating element being arranged opposite the cooling roller, and means for bringing the first and second substrates together, the distance between the at least one heating element (2) and the cooling roller (1) being variable.

[0027] In a preferred embodiment, the device has more than one heating element, which are arranged at least partially around the periphery of the cooling roller. In a preferred embodiment, the at least one heating element comprises a series of separate heating elements, preferably IR radiators. The number of individual heating elements is determined by the diameter of the cooling roller and is preferably at least 3, more preferably 3 to 15, particularly preferably 3 to 10, in particular 3 to 5. In a particularly preferred embodiment, the separate heating elements are arranged around the periphery of the cooling roller. In a further preferred embodiment, the various heating elements of the at least one heating element are arranged around at least a quarter of the periphery of the cooling roller, particularly preferably around at least half the periphery.Most preferably, the various heating elements are arranged around the entire periphery of the cooling roller, it being clear to those skilled in the art that the arrangement is such that the process flow and / or other components are not impaired. It has proven particularly advantageous if the at least one heating element is arranged in spatial proximity to the point in the process at which the first substrate and the second substrate are brought together, preferably with the aid of a laminating unit. Therefore, an embodiment in which the at least one heating element is arranged in spatial proximity to the laminating unit is particularly preferred. In this way, homogeneous heating of the surface of the first substrate can be ensured during the ongoing process, without the web speed of the substrate having to be slowed down or adjusted in any other way.Particularly preferably, the at least one heating element is an IR heating element.

[0028] The temperature required to convert the thermoplastic surface of the first substrate into a softened state can vary depending on the substrate used. Therefore, the distance between the at least one heating element and the thermoplastic surface of the first substrate is variable. The at least one heating element of the device according to the invention is preferably arranged such that the distance between the heating element and the cooling roller can be reduced or increased. For embodiments in which more than one heating element is used, the distance between the individual heating element and the cooling roller is preferably individually controllable.

[0029] Within the scope of the present invention, it has proven particularly advantageous if the first substrate is guided over only one cooling roller, whereby the size and diameter of the roller can be adapted to the respective requirements, since in this way the cooling roller simultaneously serves as a support roller for the substrate. Nevertheless, alternative embodiments are also preferred in which the device according to the invention has more than one cooling roller, i.e., the first substrate is guided around more than one cooling roller.

[0030] As feed devices, conventional means such as rollers and conveyor belts, in particular rollers, are preferably used in the device according to the invention.

[0031] The device according to the invention is intended in particular for laminating film-shaped substrates. Therefore, an embodiment is preferred in which the cooling roller is part of the means for bringing together the first and second substrates, and the means further comprises one or more rollers for pressing the second substrate against the first substrate resting on the cooling roller. In this way, the additional supporting effect of the cooling roller can be utilized when bringing the substrates together, and a good smoothing of the surface of the first substrate can be achieved while simultaneously maintaining its shape. In a particularly preferred embodiment, the heating elements and the rollers for pressing the second substrate are each arranged over half the circumference of the cooling roller.

[0032] In an alternative preferred embodiment, it has proven advantageous if the means for bringing the first and second substrates together is designed independently of the cooling roller. In this way, it is possible to operate the cooling roller independently of the web speed of the substrates. Therefore, an embodiment of the device according to the invention is preferred in which the means for bringing the first and second substrates together is designed independently of the cooling roller and the means has one or more rollers for bringing the first and second substrates together. Furthermore, in this embodiment, the means for bringing the first and second substrates together is preferably arranged downstream of the cooling roller in the process direction, wherein the means is also arranged at a distance from the cooling roller.The distance between the center and the cooling roller should not be too large to avoid heat loss from the thermoplastic surface and stretching in the feed direction of the first substrate. The preferred embodiment allows for variable adjustment of the cooling roller rotation speed independent of the web speed. In a particularly preferred embodiment, the cooling roller rotation speed is therefore higher or lower than the web speed. In a particularly preferred embodiment, the cooling roller rotates at 90 to 110% of the web speed.

[0033] In a preferred embodiment of the device according to the invention, the cooling roller has means for receiving a coolant. The coolant can be selected according to the respective temperature requirements. The coolant is particularly preferably water.

[0034] The present invention further provides a composite body which is obtained by means of the method according to the invention or using the device according to the invention. The composite body is preferably a multi-layer, flexible film. In a particularly preferred embodiment, the first substrate is a flexible thermoplastic film and the second substrate is selected from the group consisting of paper, metal, plastic or multi-layer substrates. In a preferred embodiment, the composite body is a composite body in which the first substrate is polypropylene or polyethylene and the second substrate is a film-shaped substrate based on aluminum or plastic, in particular oriented polypropylene or oriented polyethylene, which are bonded with a polyurethane-based adhesive.The present invention is explained in more detail with reference to the figures provided, which are not to be understood as a limitation of the inventive concept.

[0035] Figure 1shows an embodiment in which the cooling roller is formed as part of the means for bringing the first and second substrates together. The first substrate (3) is guided around a rotating cooling roller (1) and is in contact with it. For this purpose, the device can have one or more further rollers (7) which press the first substrate against the cooling roller. The first substrate is guided past the heating elements (2) arranged around the cooling roller (1) in such a way that the thermoplastic surface of the first substrate (3) faces the heating elements (2), wherein the thermoplastic surface of the first substrate (3) is converted into a softened state. The softened surface of the first substrate (3) is brought together with a second substrate (4) in such a way that the adhesive located on the surface of the second substrate (4) is located between the first substrate (3) and the second substrate (4).For this purpose, the first substrate and the second substrate are guided past a roller (6) that rotates in the opposite direction to the cooling roller (1) and presses the second substrate (4) against the first substrate (3) resting on the cooling roller (1). After passing through the roller (6), the laminated product (5) can be fed to a winding system.

[0036] Figure 2shows an embodiment of the device according to the invention, in which the means for bringing the first substrate and the second substrate together is designed independently of the cooling roller. The first substrate (3) is guided around a rotatingly driven cooling roller (1) and is in contact with it. For this purpose, the device can have one or more further rollers (7) which press the first substrate against the cooling roller. The first substrate (3) is guided past the heating elements (2) arranged around the cooling roller (1) in such a way that the thermoplastic surface of the first substrate (3) faces the heating elements (2), wherein the thermoplastic surface of the first substrate (3) is converted into a softened state.The softened surface of the first substrate (3) is joined to a second substrate (4) in such a way that the adhesive on the surface of the second substrate (4) is located between the first substrate (3) and the second substrate (4). For this purpose, the first substrate (3) and the second substrate (4) are guided through a roller group (6a, 6b) which has rollers rotating in opposite directions and which presses the second substrate (4) against the first substrate (3). After passing through the roller group (6a, 6b), the laminated product (5) can be fed to a winding system.

Claims

1. A method for bonding substrates, comprising: providing a first substrate (3) in film form, which substrate has a thermoplastic surface; guiding the first substrate (3) around a drivable cooling roller (1) with which the first substrate (3) is in contact, wherein the cooling roller rotates in the feed direction; providing a second substrate (4), on the surface of which an adhesive is applied; and, joining the first and the second substrate under pressure, wherein the thermoplastic surface of the first substrate (3) is in a softened state during the joining process, wherein the surface of the first substrate (3) opposite the softened surface is cooled by means of a rotating cooling roller (1); and, wherein the thermoplastic surface of the first substrate (3) is converted into a softened state by heating, wherein the heating is carried out by means of at least one heating element (2) which is arranged opposite the cooling roller (1), and wherein the distance between the at least one heating element (2) and the cooling roller (1) is variable.

2. The method according to claim 1, wherein the at least one heating element (2) is an infrared (IR) heating element.

3. The method according to one or more of claims 1 or 2, characterized in that the layer weight of the adhesive on the second substrate (4) is less than 2 g / m2, preferably less than 1 g / m2.

4. The method according to one or more of the preceding claims, characterized in that the adhesive applied to the second substrate (4) is selected from thermoplastic adhesives or crosslinking adhesives in solvent-containing, aqueous or solvent-free form.

5. The method according to one or more of the preceding claims, characterized in that the first substrate (3) is a substrate consisting of or comprising polyolefins, polyvinyl chlorides, ethylene copolymers, polyesters, polyamides and / or polyethers.

6. The method according to one or more of the preceding claims, characterized in that the second substrate (4) is a substrate in film form which is preferably selected from the group consisting of thermosetting and thermoplastic plastics materials, organic polymers and metals and metal alloys.

7. An apparatus for carrying out a method according to one or more of claims 1 to 6, characterized in that the apparatus comprises the following: - a feed device for a first substrate (3) in film form, the substrate having a thermoplastic surface, - a feed device for a second substrate (4), on the surface of which an adhesive is applied, - a rotatably drivable cooling roller (1) which is in contact with the first substrate (3) and around which the first substrate is guided; - at least one heating element (2) for heating the thermoplastic surface of the first substrate (3), the at least one heating element (2) being arranged opposite the cooling roller (1), and - means for joining (6) the first and the second substrate (3, 4), the distance between the at least one heating element (2) and the cooling roller (1) being variable.

8. The apparatus according to one or more of claims 7, characterized in that the cooling roller (1) forms part of the means for joining (6) the first and the second substrate (3, 4), and the means (6) also has one or more rollers for pressing the second substrate against the first substrate resting on the cooling roller.

9. The apparatus according to one or more of the preceding claims, characterized in that the means (6) for joining the first and the second substrate is formed independently of the cooling roller (1), and the means has one or more rollers (6a, 6b) for joining the first and the second substrate.

10. The apparatus according to claim 9, characterized in that the means for joining (6) the first and the second substrate is arranged behind the cooling roller (1) in the process direction, the means preferably being arranged at a distance from the cooling roller (1).

11. The apparatus according to one or more of claims 9 or 10, characterized in that the rotational speed of the cooling roller (1) is higher or lower in comparison with the web speed.

12. The apparatus according to one or more of the preceding claims, characterized in that the cooling roller (1) has means for receiving a coolant, the coolant preferably being water.