The invention relates to a process for coating substrates in web form with at least two adhesives (one or two adhesives but two lines, overlapping or alongside one another), to an adhesive tape produced by the process, and to its use.
Self-adhesive articles consist of at least two layers, these being a non-self-adhesive substrate (backing layer) and, applied to it, a pressure-sensitive adhesive. A double-sided self-adhesive tape is generally applied from at least three layers, these being the substrate and the adhesive layers applied to it on either side. There are also products known which on one side of the substrate have two or more adhesive layers, these being applied to the substrate partly or completely overlapping one another or else alongside one another. In this case, for example, the bottom layer of two adhesive layers may serve as an adhesion promoter between the substrate and the upper adhesive layer. In this instance complete overlap of the two adhesive layers is appropriate. There are also adhesive tapes known, however, which have two or more strips of adhesive arranged alongside one another or with only a partial overlap. With different adhesive properties of the adhesive materials used, a multifunctional adhesive tape of this kind is capable of attaching to different materials to be bonded. Additionally such adhesive tapes find use as auxiliary systems in connection with splicing, when ends of two webs of material are joined to one another, or for the purpose of implementing a flying reel changeover of continuous web materials, as in the printing industry, for example.
According to customary processes for producing adhesive tapes a web substrate, produced separately, is coated with the fluid or spreadable adhesive. Coating normally takes place from a solution, for which purpose the pressure-sensitive adhesive is converted into a spreadable consistency with the aid of solvents prior to coating. Depending on the adhesive composition, however, coating may also take place from the melt, solventlessly, in an extrusion process. This process has become established particularly for pressure-sensitive adhesives based on thermoplastic elastomers. Another way of establishing the connection between substrate and pressure-sensitive adhesive is first to apply the pressure-sensitive adhesive to a dehesive medium to form a film thereon and subsequently, in a laminating process, applying the adhesive film to the backing.
All of the processes referred to are also employed for producing adhesive tapes having two or more adhesive layers. Where production takes place from the solution or the melt the coating operations are performed in succession after the lower adhesive layer in each case has dried or cured. Because of the multiplicity of worksteps required, this approach is inconvenient and costly. Multiple coating by a laminating process carries the problem of low dimensional accuracy when one line of adhesive is applied to a previous one.
It is an object of the invention, therefore, to provide a simple and inexpensive process for producing adhesive tapes having two or more adhesive layers.
This object is achieved by a process having the features of Claim 1. By virtue of the fact that the web substrate is first coated over at least part of its area with a first adhesive and thereafter coated over at least part of its area with a further adhesive while the first adhesive is still wet or has not yet cured, the process can be carried out with a minimal number of process stages. The individual coating operations can take place virtually in one work cycle, without the need for otherwise-necessary drying or curing stages in between. Particular advantages arise, moreover, in the case where the adhesives are coated partly or completely over one another. In this case, indeed, there is partial diffusion of the layers into one another, so that the anchoring of the adhesives with one another is substantially better when they are crosslinked on the web. The application with the adhesives in immediate succession can be carried out, moreover, with a high level of dimensional accuracy in terms of the site of application on the substrate or on the adhesive layer applied previously.
In the process the individual adhesive layers, which may be composed of the same or different adhesive compositions, can be applied to the substrate partly or completely overlapping one another or else alongside one another (not overlapping). The substrate may also be coated on one or both sides, it being possible to coat the individual sides with the at least two adhesives over part or all of their area in each case.
The individual adhesives are preferably applied to the substrate in a known way, from a solution, with additional solvents, or from a melt, with thermal heating, in an extrusion process. Depending on the nature of the process and on the adhesives used, customary coating methods are appropriate here, examples being brush application, extrusion, spray application, roll application and/or knife coating. The said processes and methods can also be combined with one another. Thus, for example, it is possible to spray-apply the first adhesive as a solution and to apply the second adhesive as a melt, or else in reverse sequence, to the substrate by means of rolling or knife coating.
Known base polymers for the adhesive layer include natural rubbers and synthetic rubbers, polyacrylates, block copolymers containing polystyrene block functions, polyethylene-vinylacetates, and polyurethanes. They are generally used in combination with additions such as resins and plasticizers and/or or other auxiliaries, examples being antioxidants, UV stabilizers or rheological additives and also fillers. In combination with the substrate employed, the adhesive critically determines the pressure-sensitive adhesion properties of the self-adhesive article, such as bond strength, peel release, redetachability, et cetera.
Suitable non-adhesive substrate materials include any materials in web form, examples being papers, woven fabrics, nonwovens, polymeric films or elastomers, each in different thicknesses, structures and polymer compositions.
According to one particular preferred embodiment of the invention, after the substrate has been coated with the adhesives, at least one release material layer, lining the adhesives, is applied. Release material layers of this kind, typically composed of PE or silicone-coated plastic or paper, are removed from the adhesive tape before it is employed for its intended bonding application, and serve to protect the adhesive layer and to prevent unwanted sticking. With particular preference in this context the at least two adhesive strips are applied alongside one another or partly overlapping on the substrate and are each lined with a release material layer which covers the corresponding adhesive strips. There may also be only one single release material layer, subdivided by a perforation seam.
The invention further provides an adhesive tape produced by the process of the invention, comprising a substrate in web form and at least two strips of adhesive arranged completely, partially or not overlapping one another on the substrate. According to one preferred embodiment the adhesive tape comprises at least one release material layer lining the at least two adhesive strips, and, where adhesive strips are arranged alongside one another or partly overlapping, they are preferably each lined with a release material layer.
Adhesive tapes of this kind can be used with particular advantage as a splicing system for joining ends of material webs, especially for implementing flying reel changeovers in continuous web materials.
Further advantageous embodiments of the invention are subject-matter of the other dependent claims.
The invention is illustrated below in exemplary embodiments with reference to the associated drawings, in which:
According to the embodiment depicted, coating with the adhesives 12 and 14 takes place by spray application of their solutions. For this purpose the adhesives 12 and 14 are in solution in a suitable solvent, which may be an organic solvent or water. The corresponding solutions are each located in a vessel 22 or 24 respectively, which connects by line to a nozzle 26 or 28 respectively. The nozzles 26 and 28 are preferably designed as nozzles corresponding to a desired application width of the respective adhesive 12, 14. The desired spray profile can additionally be limited by baffles which though not shown here are disposed below the nozzles 26 and 28.
The spraying stations for the adhesives 12 and 14, which are situated in direct succession, apply the second adhesive 14 when the first adhesive 12 has still not dried. The drying and, where appropriate, polymerization/crosslinking of the two adhesives 12 and 14 instead takes place only in a downstream heating tunnel 30, through which the coated substrate 10′ passes. The polymerization of the adhesive monomers may also take place here, where appropriate. Alternatively there is electron beam crosslinking.
Alternatively to the implementation shown in
According to
In the coating plants shown in FIGS. 1 to 3 a unitary application method has been chosen in each case for the adhesives 12 and 14. It will be appreciated that the different processes can also be combined with one another. For example, the first adhesive 12 can be applied to the substrate 10 by spray application from solution, and the second adhesive 14 by means of the knife-coating technique shown in
Additionally, coating of the adhesive side with a release material can take place in the same production stage, following application of the second adhesive 14.
In all of the exemplary embodiments shown the two coating stations for the two adhesives 12 and 14 are placed so closely in succession that the second adhesive 14 is applied “wet on wet” to the as-yet undried, uncured or unpolymerized first adhesive 12. The effect of this is to concentrate the coating process in terms of both time and location, with considerable cost savings. The curing of the adhesive layers 12 and 14 may take place in each case in a unitary station 30, 44 or 54. In the case of partial or complete overlap of the two adhesive layers 12 and 14, furthermore, improved anchoring of the adhesives to one another is produced.
Solvent-borne adhesives should never be applied beneath melts or beneath solvent-free systems in general, since these adhesives do not dry. Conversely, lower layers can be cured with electron beams, thermally or by UV—with UV on one side and only to a coat thickness of about 1 mm.
A plan view of the adhesive tape 100 following removal of the release material layer 56 is shown in
The product 100 depicted in
Number | Date | Country | Kind |
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10 2004 053 189.7 | Nov 2004 | DE | national |