ADHESIVE TAPE FOR BONDING LOW-ENERGY SURFACES

Abstract

An adhesive tape for bonding low-energy surfaces, comprising a UV cross-linked pressure-sensitive adhesive compound which comprises poly-acrylate, a linear or branched vinyl aromatic block co-polymer and at least one adhesive resin. The UV cross-linking of the pressure-sensitive adhesive compound is the result of irradiation with UV-A-containing light.

Claims

1. An adhesive tape for bonding low-energy surfaces, comprising a UV-cross-linked pressure-sensitive adhesive compound, comprising poly-acrylate, a linear or branched vinyl aromatic block co-polymer, and at least one adhesive resin, wherein the UV cross-linked pressure-sensitive adhesive compound adaped to be cross-linked as a result of irradiation with UV-A-containing light.

2. The adhesive tape of claim 1, wherein the cross-linked pressure-sensitive adhesive compound of the adhesive tape is cross-linkable at a Gardner color scale rating of 1 to 2 to a depth of 150 μm with UV-A-containing light.

3. The adhesive tape of claim 1 wherein the cross-linked pressure-sensitive adhesive compound has an application weight in the range of 20 g/m.sup.2 to 150 g/m.sup.2 and a Gardner color scale rating of 1 to 2.

4. The adhesive tap of claim 1, wherein the adhesive tape further comprises 30-75 percent by weight of the UV cross-linked pressure-sensitive adhesive compound, 2-40 percent by weight of the linear or branched vinyl aromatic block co-polymer, and 4-40 percent by weight of the at least one adhesive resin.

5. The adhesive tape of claim 1, wherein the UV cross-linked pressure-sensitive adhesive compound comprises a UV initiator polymerised into the poly-acrylate chain.

6. The adhesive tape of claim 1, wherein the vinyl aromatic block co-polymer comprises: soft blocks comprising homo- and co-polymers of butadiene, isoprene, ethyl butadiene and partially or fully hydrogenated varieties thereof, and hard blocks comprising homo- and co-polymers of styrene, alpha methyl styrene and their derivatives.

7. The adhesive tape of claim 1, wherein the adhesive resins comprises a hydrocarbon resin, a poly-terpene resin, or both limonene, wherein the resins can be derivatised with phenol.

8. The adhesive tape of claim 1, wherein the crosslinked adhesive tape comprises anti-oxidants, fillers, dyes, rheological additives, or UV protection agents, or any combinations thereof.

9. The adhesive tape of claim 1, wherein the cross-linked pressure-sensitive adhesive compound is adapted to be foamed.

10. A method for producing an adhesive tape for bonding low-energy surfaces, the method comprising: a) melting of a vinyl aromatic block co-polymer and an adhesive resin; b) stirring the vinyl aromatic block co-polymer and the adhesive resin; c) adding a UV cross-linkable pressure-sensitive adhesive compound for producing a blend; d) applying the generated blend of vinyl aromatic block co-polymer, adhesive resin and pressure-sensitive adhesive compound on a sheet material; and e) irradiating the blend with UV-A-containing light to provide a UV cross-linked adhesive tape.

11. The method of claim 10, wherein the blend is completely cross-linked at a Gardner color scale rating of 1 to 2 to a depth of 150 μm with UV-A containing light.

12. The method of claim 10, wherein a complete cross-linking of the blend is obtained using a UV-A-containing light; and the UV cross-linkable pressure-sensitive adhesive compound has an application weight in the range of 20 g/m.sup.2 to 150 g/m.sup.2; and the blend has a Gardner color scale rating of 1 to 2.

13. The method claim 1, wherein a photon energy of the irradiation amounts to 3.26 to 3.94 eV.

14. The method claim 1, wherein the melting of the vinyl aromatic block co-polymer and the adhesive resin is at a temperature between 80-160° C.

15. The method of claim 1 wherein the method for producing the adhesive tape is solvent-free.

16. The adhesive tape of claim 3, wherein the cross-linked pressure-sensitive adhesive compound has an application weight in the range of 70 g/m.sup.2.

17. The adhesive tape of claim 7 wherein the hydrocarbon resin comprises hydrocarbon resin selected from the group consisting essentially of a non-hydrogenated carbohydrate resin, a partially hydrogenated carbohydrate resin, a selectively hydrogenated carbohydrate resin, a fully hydrogenated carbohydrate resin; a C5 monomer resin, a C5/C9 monomer resin, and a C9 monomer resin.

18. The adhesive tape of claim 7, wherein the poly-terpene resin comprises a poly-terpene resin selected from the group consisting essentially of an alpha pinene resin, a beta-pinene resin, and a delta-limonene.

19. The method of claim 3, wherein the cross-linked pressure-sensitive adhesive compound has an application weight in the range of 70 g/m.sup.2.

Description

DETAILED DESCRIPTION OF EMBODIMENTS

[0043] Sample embodiments of the present disclosure are described in connection with the description of the test-set-up outlined below.

[0044] Shear Strength Test (SAFT):

[0045] A sample strip (width: 25 mm) consists of an adhesive compound layer laminated onto an etched PET film (thickness: 50 μm). The sample strip is glued onto a stainless steel plate (previously cleaned with benzine) in an overlapping pattern to create a bonded surface of 25 mm×25 mm. Subsequently, the sample strip is pressed securely onto the surface using a spatula. The sample strip is vertically subjected to a weight of 1 kg, and this arrangement is suspended in a convection oven. Subsequent heat treatment starts at a temperature of 40° C. and is increased to 160° C. at 0.5 K/min. The test result is concluded by the temperature where the sample strip drops off. If the strip does not drop off at 160° C., the result is over 160° C. The value indicated corresponds to the mean value of three measurements.

Peel Strength on Steel and Poly-Ethylene (PE):

[0046] The 180° peel strength measurement is performed in accordance with DIN ISO 1939 at standard atmosphere conditions (23° C., 50% relative humidity). A substrate is wiped off with a cloth soaked with benzine. Once the benzine has evaporated, a sample strip of a width of 25 mm is applied onto the substrate (adhesive compound laminated onto an etched PET film, thickness: 50 μm). Then, a roller (weight: 5 kg) is run twice across the sample strip (5 m/min). The specimen thus produced is conditioned at standard atmosphere conditions (23° C., 50% humidity) for 24 hours . Then, the force is measured that has to be exerted at a peel-off angle of 180° at a speed of 300 mm/min in order to peel the sample strip off of the substrate. The value indicated corresponds to the mean value of three measurements.

[0047] For example, stainless steel (according to the Afera standard 4001) or poly-ethylene (test plates by the company Rocholl) can be used as a substrate.

[0048] After the peel strength measurement, the fracture pattern is evaluated. In this context, AF stands for adhesion fracture with the substrate, CF stands for cohesion fracture and AFCa stands for adhesion fracture with the etched PET film. If the fracture pattern is CF, i.e. when the adhesive compound is fractured in itself, this indicates insufficient cross-linking of the adhesive compound.

[0049] 90° Peel Strength on Painted Metal Sheets:

[0050] The 90° peel strength measurement on painted metal sheets is performed in accordance with DIN ISO 1939 at standard atmosphere conditions (23° C., 50% relative humidity). The painted metal sheet consists in a metal sheet with a three-layer paint structure: filler, base paint and clear varnish: 2K-clear varnish Supermar by the company Axalta, drying conditions: 20 min at 140° C.

[0051] The sample strip is a PE foam adhesive tape, having a poly-ethylene foam as the backing (Alveolit TMA SRZ 801 by the company Sekusui Alveo), which is pre-treated with corona irradiation on both sides and that the adhesive film is laminated onto (application weight: 70 g/m.sup.2, on siliconised PET film).

[0052] The painted metal sheet is wiped off with a cloth soaked with benzine. Once the benzine has evaporated, one side of the sample strip of (width: 25 mm) is applied after removing the siliconised PET film. The PET film on the rear side is replaced by a non-siliconised, etched PET film (thickness: 50 μm). Then, a roller is run over the compound (weight: 5 kg, 5 m/min). The specimen is conditioned at standard atmosphere conditions (23° C., 50% humidity) for 24 hours, then the force is measured that has to be exerted at a peel-off angle of 90° at a speed of 100 mm/min in order to peel the sample strip or the adhesive tape off of the substrate. The value indicated corresponds to the mean value of three measurements.

[0053] After measuring, the fracture pattern is evaluated. Here, AF stands for adhesion fracture in respect of the paint.

[0054] Gardner Color Scale:

[0055] The Gardner color scale provides a reference table for the yellow tint of resin. A corresponding Gardner color scale ranges from 1 to 18 and is either determined by means of a color comparison with cobalt chloride solutions of different concentrations or by means of spectroscopic methods according to DIN EN 4630 at 380-720 nm. 1 means crystal clear, 3 is slightly yellow, 5 is yellow to amber colored. Significant yellow tint in the visible range may also be taken into account as a point of reference for the absorption of UV light in the UV-A range (320 to 400 nm) to determine the degree of absorption due to its spectral vicinity. Adhesive resin manufacturers provide the Gardner color scale rating of a solution of the resin in toluene (50%) in the data sheet. A significant difference can be seen in particular between the color reference ratings 4 and 5. Whilst color reference rating 4 still results in yellow-tinted adhesive compounds, resins associated with the reference rating 5 already produce noticeably darker adhesive compounds.

Materials

[0056]

TABLE-US-00001 Gardner product name brief description color scale company acResin 204 UV UV acrylate hotmelt, based on EHA and BA crystal clear BASF SE Kraton D 1161 linear SIS, 15% styrene share, 17% diblock crystal clear Kraton share Dercolyte A 115 poly-terpene resin based on α-pinene 5 DRT Piccolyte S 115 poly-terpene resin based on β-pinene 4 Pinova Sylvares 6100 poly-terpene resin, styrene modified, end 3 Kraton block resin Sylvares TR M 115 poly-terpene resin 3 Kraton Regalite R 1090 carbohydrate resin, hydrogenated 1 Eastman Regalite R 1125 carbohydrate resin, hydrogenated 1 Eastman Novares PURE 85 carbohydrate resin, aromatic 1 Rütgers AS Novares Foral 85 E Colophony ester resin, hydrogenated 2 Eastman

[0057] Production of the Adhesive Compounds and Coating

[0058] In an aluminium container set into a heating block, a styrene block co-polymer and resin are melted and stirred at a temperature of 165° C. until a uniform, clear melt is formed. Subsequently, it is cooled down to 150° C., and UV acrylate hotmelt is added until a quasi-homogeneous white mixture is formed.

[0059] The mix is coated onto siliconised polyester film in a hotmelt coating device between two rollers (temperature: 145° C.). The gap setting between the two rollers is selected such that the resulting application amount is 70 g/m.sup.2. The coating step is followed by a cooling step. A cloudy transfer film is obtained, which is used for measuring. The clouding shows that it is a blend adhesive compound. Subsequently, the transfer films are irradiated under UV light. Two types of irradiation are carried out:

[0060] UV-C: Irradiation with a UV mini laboratory dryer BE 7/1 laboratory irradiation device by the company Beltron. Set at full UV intensity, belt speed: 6 m/min.

[0061] UV-A: Irradiation in a Honle LEDcube100 irradiation chamber with a Honle LEDpowerdrive 40 controller, wavelength 365 nm, duration: 20 seconds.

[0062] The irradiation intensities in both devices are measured using the same UV measurement device, i.e. the Power Puck II by the company EIT Instrument Markets Group. In this, the intensities were measured separately for UV-C, UV-B and UV-A. The different irradiations for the durations listed resulted in the following intensities:

TABLE-US-00002 intensities according to Power Puck II in mJ/cm.sup.2 UV-C UV-B UV-A UV-A 0 0 3738 UV-C: 58 192 216

[0063] The examples B1 to B5 show the adhesive compound compositions of the different specimens:

TABLE-US-00003 amounts specified in percent by weight B1 B2 B3 B4 B5 UV acrylate acResin acResin acResin acResin acResin hotmelt 204 UV 204 UV 204 UV 204 UV 204 UV 52% 52% 52% 52% 52% styrene Kraton D Kraton D Kraton D Kraton D Kraton D block 1161 1161 1161 1161 1161 copolymer 19.5% 19.5% 19.5% 19.5% 19.5% adhesive Sylvares Sylvares Sylvares Sylvares Regalite R resin 1 6100 6100 6100 6100 1090 4% 4% 4% 4% 14.25% adhesive Regalite R Piccolyte Novares Sylvares Regalite R resin 2 1090 S 115 PURE 85 TR M115 1125 12.25% 24.5% AS 24.5% 14.25% 24.5% adhesive Regalite R resin 3 1125 12.25%

[0064] The examples B1 to B5 are compared to the comparative samples VB1 to VB3. Specimens of the comparative samples VB1 to VB3 have the following formulation:

TABLE-US-00004 amounts specified in percent by weight VB1 VB2 VB3 UV acrylate hotmelt acResin 204 acResin 204 acResin 204 UV UV UV 100% 80% 52% styrene block co- Kraton D polymer 1161 19.5% adhesive resin 1 Foral 85 E Sylvares 20% 6100 4% adhesive resin 2 Dercolyte A 115 24.5%

[0065] Test Results

[0066] Following irradiation of the specimens with UV-A light or UV-C light, the shear strength (SAFT) of the examples B1 to B5 and the comparative samples VB1 and VB3 showed the following values (specimens=transfer films):

TABLE-US-00005 Irradiation type SAFT in ° C. B1 UV-C 46 B1 UV-A >160 B2 UV-C 40 B2 UV-A >160 B3 UV-C 40 B3 UV-A 124 B4 UV-C 40 B4 UV-A 104 B5 UV-C 46 B5 UV-A >160 VB1 UV-C >160 VB1 UV-A >160 VB2 UV-C 40 VB2 UV-A 94 VB3 UV-C 40 VB3 UV-A 54

[0067] Following irradiation of the specimens with UV-A, the peel strength on steel and polyethylene, respectively, showed the following values (specimens=transfer films):

TABLE-US-00006 peel strength peel strength on steel fracture on PE fracture Irradiation type [N/2.5 cm] pattern [N/2.5 cm] pattern B1 UV-A 46 AF 27 AF B2 UV-A 31 AFCa 16 AF B3 UV-A 47 AFCa 15 AF B4 UV-A 36 AFCa 10 AF B5 UV-A 38 AFCa 21 AF VB1 UV-A 29 AF 8 AF VB2 UV-A 40 CF 7 CF VB3 UV-A 45 AFCa 37 CF

[0068] The values of the 90° peel strength on painted metal sheets of the examples B1 and VB1 derive from the table copied in below (specimens=PE foam adhesive tape):

TABLE-US-00007 Peel strength on painted metal sheets fracture Irradiation type [N/2.5 cm] pattern B1 UV-A 65 AF VB1 UV-A 24 AF

[0069] In the examples B1 to B5, the irradiation with UV-C results in low SAFT values of about 40° C. This shows that the adhesive compounds were not, or in any case only hardly, cross-linked subject to this irradiation. The adhesive bond may slide off much more easily when weight is applied.

[0070] The SAFT values are much higher subject to irradiation under UV-A conditions (above 100° C. to 160° C.). This indicates that the adhesive compound was cross-linked by the irradiation.

[0071] In the comparative samples VB2 and VB3, also under UV-A conditions only low SAFT below 100° C. values are realised, i.e. no sufficient cross-linking is achieved. This can also be seen from the CF fracture pattern in the peel strength on steel and poly-ethylene.

[0072] The comparative sample VB1, which includes a pure acrylate hotmelt adhesive compound, does cross-link subject to UV-A light (high SAFT value), the peel strengths on low-energy surfaces such as poly-ethylene or painted metal sheets, however, are much less than in the examples B1 to B5.

[0073] Comparative sample VB3 involves a strongly yellow-tinted resin with a Gardner color scale rating of 5. Here, no cross-linking occurs even under UV-A conditions. This is because the UV light cannot penetrate deeper due to the heavy tint and therefore fails to effect cross-linking.

[0074] Sample B1 cross-links very well subject to UV-A irradiation and exhibits high peel strength on poly-ethylene and painted metal sheets.

[0075] It turns out that the formulations B1 to B5 can be sufficiently cross-linked using UV-A light irradiation and that therefore the adhesive tapes that can be generated in this fashion offer very favourable bonding strengths on low-energy surfaces.

[0076] As far as applicable, all individual features shown in the sample embodiments can be combined and/or exchanged without leaving the scope of the disclosure.