METHOD OF MAKING AN ADHESIVE CABLE-WRAP TAPE

Abstract

The invention relates to a method for producing an adhesive tape (1), in particular a wrapping tape for wrapping around cables in automobiles. A strip-shaped carrier (2) is provided with a UV cross-linkable adhesive coating (5). In addition to an acrylate-based pressure-sensitive adhesive with embedded photoinitiators, the adhesive coating (5) comprises at least one additive. The photoinitiators are activated for cross-linking by irradiation with a UV light source (6) emitting in the range of its activation wavelength. According to the invention, the additive has at least in the range of the activation wavelength of the photoinitiators an absorbance (E) of 0.1 to 0.7, preferably between 0.2 and 0.6.

Claims

1. A method of making an adhesive tape, the method comprising the steps of: providing a substrate strip with a UV-cross-linkable adhesive coating having an application weight of from 15 g/m.sup.2 to 250 g/m.sup.2, the adhesive coating comprising an acrylate-based, pressure-sensitive adhesive with incorporated photoinitiators having an activation wavelength between 250 nm and 320 nm and present in the adhesive coating in a grammage of from 0.05 wt % to 5 wt %, and an additive embodied as a resin admixture present in the adhesive coating in a grammage of up to 40 wt % and having an absorption of 0.1 to 0.7 at least at the activation wavelength of the photoinitiators, and activating the photoinitiators for cross-linking by irradiation with a UV light source that emits in the range of the activation wavelength of the photoinitiators.

2. The method according to claim 1, wherein the additive has an absorption E between 0.2 and 0.6 in the range of the activation wavelength of the photoinitiators.

3. The method according to claim 1, wherein the UV light source irradiates the adhesive coating with a dose of from 15 mJ/cm.sup.2 to 400 mJ/cm.sup.2.

4. The method according to claim 1, wherein an LED-based UV light source is used.

5. The method according to claim 1, wherein the additive is applied in order to increase the adhesion to the substrate strip.

6. The method according to claim 1, wherein the additive embodied as a resin admixture is based on a partially hydrogenated abietic acid ester.

7. The method according to claim 1, wherein the substrate strip is embodied as a textile fabric with a weight per unit area of between 15 g/m.sup.2 and 250 g/m.sup.2.

8. The method according to claim 1, wherein the photoinitiators are provided in the adhesive coating in a grammage of from 0.2 wt % to 5 wt %.

9. The method according to claim 1, wherein the additive is present in the adhesive coating in a grammage of at least 5 wt % and up to 40 wt %.

Description

[0021] The invention is explained in further detail below with reference to a schematic drawing that illustrates only one exemplary embodiment:

[0022] FIG. 1 is a schematic view of an apparatus for carrying out the method according to the invention,

[0023] FIG. 2 is a graph of an absorption spectrum or the measured absorption E over the wavelength for a resin admixture that is frequently used in practice (Foral 85),

[0024] FIG. 3 is a graph of an alternative additive 1 that is used in the context of the invention and its absorption spectrum or absorption E over the wavelength,

[0025] FIG. 4 is a graph like FIG. 3 for an additive 2, and

[0026] FIG. 5 is a graph of an absorption spectrum or, again, the absorption over the wavelength in consideration of the acrylate-based pressure-sensitive adhesive with the incorporated photoinitiators without resin admixture (solid line) and with resin admixture (dashed line).

[0027] FIG. 1 shows an apparatus with the aid of which an adhesive tape 1 can be manufactured. For this purpose, a substrate strip 2 is fed to a coater 3 for hot-melt adhesive. In the coater 3 for the hot-melt adhesive, the hot-melt adhesive is at a temperature of about 100 C. to 150 C. and can be applied to the substrate strip 2 being moved past the nozzle 4 via an output-side nozzle 4 of the coater 3, thereby coating the substrate strip 2.

[0028] The substrate is a substrate strip 2 that is embodied as a textile fabric and has a weight per unit area of between 50 g/m.sup.2 and 250 g/m.sup.2. After coating the substrate strip 2 with an adhesive coating 5 in this manner, the adhesive coating 5 is cross-linked by a UV light source 6 that is above the continuously coated substrate strip 2. It will be readily understood that the adhesive coating 5 is provided on the side of the substrate strip 2 facing the UV light source 6. The light source 6 is an LED-based light source. In fact, a large number of LEDs or UV-LEDs are implemented here. In principle, however, the UV light source 6 can also make use of for example a mercury vapor lamp. That is not shown, however.

[0029] The substrate strip 2 that has been provided with the adhesive coating 5 moves beneath the UV light source 6 at a speed of from 10 m/min to 100 m/min or more. The adhesive coating 5 is irradiated by the UV light source 6 at a UV dose in the range from 150 mJ/cm.sup.2 to 500 mJ/cm.sup.2. The UV light source 6 emits, inter alia or largely, in the range of the activation wavelength for the photoinitiators that are incorporated into the adhesive coating 5. The activation wavelength lies primarily in the range between 250 nm and 260 nm but can reach up to 320 nm, depending on the photoinitiator used.

[0030] The adhesive coating 5 has at least one additive in addition to an acrylate-based pressure-sensitive adhesive with the incorporated photoinitiators. As an additive, the invention makes use of a resin admixture based on a merely partially hydrogenated abietic acid ester. After the substrate strip 2 has been provided with the adhesive coating 5, the adhesive tape 1 manufactured in this manner can be wound up or cut in the longitudinal direction if a fabric web is being fed to the coater 3 here as the substrate strip 2. This is known in detail.

[0031] FIG. 2 shows an absorption spectrum of an additive or resin admixture that is used in practice and according to the prior art. This is an abietic acid ester-based resin that has been hydrogenated and is sold under the trade name Foral 85. It can be seen that, in the range of the activation wavelength between 250 nm and 260 nm that is relevant for the activation of the photoinitiators within the adhesive coating 5 and represented by corresponding limits, the absorption E is virtually zero, so the known resin admixture Foral 85 according to the prior art is practically completely transmissive or transparent in this range and nonabsorptive.

[0032] In contrast, the resin admixtures of the invention shown in FIGS. 3 and 4 that are based on the only partially hydrogenated abietic acid ester have values for the absorption E of approximately 0.6 at 250 nm and approximately 0.2 at 260 nm in the relevant range of the activation wavelength between 250 nm and 260 nm. FIG. 3 illustrates the additive 1 or the absorption E thereof over the wavelength. FIG. 4 shows a diagram that is comparable to that of FIG. 3 for the additive 2. That is, the relevant additive 1 or 2 according to the invention is provided with an absorption E of 0.1 to 0.7 or 0.2 to 0.6 in the range of the activation wavelength between 250 nm and 260 nm of the photoinitiators of the adhesive coating 5.

[0033] Finally, FIG. 5 shows a comparison of the UV-cross-linkable acrylate-based pressure-sensitive adhesive with the incorporated photoinitiators and without resin admixture (solid) with the same pressure-sensitive adhesive in consideration of the inventive resin admixture according to additive 1 (dashed line). It can be seen here again that, in the relevant range of the activation wavelength between 250 nm and 260 nm, the absorption and, consequently, the absorption has increased compared to the situation without resin admixture due to the additive or the resin admixture based on the only partially hydrogenated abietic acid ester. Nevertheless, proper cross-linking of the incorporated photoinitiators in the pressure-sensitive adhesive 5 continues to be observed and achieved unchanged in the context of the invention. This can be attributed substantially and primarily to the emission spectrum of the UV LEDs used, on the one hand that is for example more homogeneous compared to mercury vapor lamps and to the slightly increased UV dose in comparison to the prior art according to EP 1 548 080 B1 on the other hand.

[0034] Additives 1 and 2 are each rosin admixtures based on a partially hydrogenated abietic acid ester. Additive 1 corresponds to the product YT311 from the company Yser, whereas additive 2 denotes the product YT321 from that company.