Pressure-Sensitive Adhesive Based on EPDM

Abstract

The invention relates to a pressure-sensitive adhesive composition containing, as a base polymer, at least one or more solid EPDM-rubbers and adhesive resins, the proportion of adhesive resins being between 30-130 phr. The adhesive composition free of plasticizers.

Claims

1. A pressure-sensitive adhesive which comprises, as base polymer, at least one or more solid EPDM rubbers and tackifier resins, the fraction of the tackifier resins being 30 to 130 phr, wherein the adhesive is plasticizer-free.

2. The pressure-sensitive adhesive as claimed in claim 1, wherein the base polymer consists EPDM rubbers.

3. The pressure-sensitive adhesive as claimed in claim 1, wherein the EPDM rubbers, besides ethylene and propylene, comprise diene ethylidene-norbornene (ENB), dicyclopentadiene or 5-vinyl-2-norbornene.

4. The pressure-sensitive adhesive as claimed in claim 1, wherein the fraction of the tackifier resins is 50 to 120 phr.

5. The pressure-sensitive adhesive as claimed in claim 1, wherein the Mooney viscosity (ML 1+4/125 C.) of the EPDM rubbers, measured according to DIN 53523, is at least 20 to 120.

6. The pressure-sensitive adhesive as claimed in claim 1, comprising at least one liquid EPDM rubber.

7. The pressure-sensitive adhesive as claimed in claim 5, wherein the fraction of the liquid EPDM rubbers is up to 40 wt %.

8. The pressure-sensitive adhesive as claimed in claim 1, consisting of a composition only of solid, or only of solid and liquid, EPDM rubbers and tackifier resin, and optionally againg inhibitors.

9. The pressure-sensitive adhesive as claimed in claim 1, wherein the fractions of all added substances besides EPDM rubbers and tackifier resin do not exceed a total of 5 wt %.

10. An adhesive tape selected from a single-sided adhesive tape and a double-sided adhesive tape, comprising the pressure-sensitive adhesive as claimed in claim 1.

11. The adhesive tape of claim 10, wherein the coat weight (coating thickness) of the pressure-sensitive adhesive is between 10 and 150 g/m.sup.2.

12. The pressure-sensitive adhesive of claim 2, wherein the only polymer present is the EPDM rubbers.

13. The pressure-sensitive adhesive of claim 4, wherein the fraction of the tackifier resins is 60 to 110 phr.

14. The pressure-sensitive adhesive of claim 5, wherein the Mooney viscosity (ML 1+4/125 C.) of the EPDM rubbers, measured according to DIN 53523, is 40 to 90.

15. The pressure-sensitive adhesive of claim 7, wherein the fraction of the liquid EPDM rubbers is between 5 and 35 wt %.

16. The pressure-sensitive adhesive of claim 9, wherein the fractions of all added substances, besides EPDM rubbers and tackifier resin, do not exceed a total of 2 wt %.

17. The pressure-sensitive adhesive of claim 9, wherein the added substances include synthetic rubbers and/or thermoplastic elastomers and/or fillers and/or dyes and/or aging inhibitors.

18. The pressure-sensitive adhesive of claim 16, wherein the added substances include synthetic rubbers and/or thermoplastic elastomers and/or fillers and/or dyes and/or aging inhibitors.

19. The adhesive tape of claim 11, wherein the coat weight is between 15 and 100 g/m.sup.2.

Description

[0099] Further details, objectives, features, and advantages of the present invention will be elucidated in more detail below by reference to a number of figures which represent preferred working examples. In these figures

[0100] FIG. 1 shows a single-sided pressure-sensitive adhesive tape,

[0101] FIG. 2 shows a double-sided pressure-sensitive adhesive tape,

[0102] FIG. 3 shows a carrier-free pressure-sensitive adhesive tape (adhesive transfer tape).

[0103] FIG. 1 shows a single-sidedly adhering pressure-sensitive adhesive tape 1. The pressure-sensitive adhesive tape 1 has an adhesive layer 2 produced by coating one of the above-described PSAs onto a carrier 3. The PSA coat weight is preferably between 10 and 50 g/m.sup.2.

[0104] Provided additionally (not shown) may be a release film, which covers and protects the adhesive layer 2 before the pressure-sensitive adhesive tape 1 is used. The release film is then removed before use from the adhesive layer 2.

[0105] The product construction shown in FIG. 2 shows a pressure-sensitive adhesive tape 1 with a carrier 3, coated on both sides with a PSA and therefore having two adhesive layers 2. The PSA coat weight per side is in turn preferably between 10 and 200 g/m.sup.2.

[0106] With this embodiment as well, at least one adhesive layer 2 is preferably lined with a release film. In the case of a rolled-up adhesive tape, this one release film may optionally also line the second adhesive layer 2. However, it is also possible for a plurality of release films to be provided.

[0107] It is possible, furthermore, for the carrier film to be provided with one or more coatings. Moreover, only one side of the pressure-sensitive adhesive tape may be furnished with the inventive PSA, and a different PSA may be used on the other side.

[0108] The product construction shown in FIG. 3 shows a pressure-sensitive adhesive tape 1 in the form of an adhesive transfer tape, in other words a carrier-free pressure-sensitive adhesive tape 1. For this construction, the PSA is coated single-sidedly onto a release film 4, to form a pressure-sensitive adhesive layer 2. The PSA coat weight here is customarily between 10 and 100 g/m.sup.2. This pressure-sensitive adhesive layer 2 is optionally also lined on its second side with a further release film. For the use of the pressure-sensitive adhesive tape, the release films are then removed.

[0109] As an alternative to release films it is also possible for example to use release papers or the like. In that case, however, the surface roughness of the release paper ought to be reduced, in order to realize a PSA side that is as smooth as possible.

[0110] In order to enhance the cohesive properties of the PSA, it may also be crosslinked with the methods described above and, in particular, through the addition of peroxides, the addition of a sulfur vulcanizing system, or with irradiation with high-energy radiation. This has positive effects on properties, in particular, such as the holding power or the micro-shear travel, whereas properties such as the peel adhesions tend to fall.

Test Methods

[0111] Unless otherwise indicated, the measurements are carried out under test conditions of 231 C. and 505% relative humidity.

Softening Point

[0112] The figures for the softening point T.sub.s of oligomeric and polymeric compounds, such as of the resins, for example, are based on the ring & ball method according to DIN EN 1427:2007 with corresponding application of the provisions (investigation of the oligomer sample or polymer sample instead of bitumen, with the procedure otherwise retained); the measurements are made in a glycerol bath.

Storage

[0113] Before the tests described below, the specimens are stored for at least 24 hours at 23 C. and 50% relative humidity.

Peel Adhesion

[0114] The peel strength (peel adhesion) was tested in a method based on PSTC-1.

[0115] A strip of the pressure-sensitive adhesive tape, 2 cm wide, consisting of a PET film 23 m thick and etched with trichloroacetic acid and of an adhesive coating applied thereto and 50 m thick is adhered to the test substrate in the form of an ASTM steel plate by being rolled on back and forth five times using a 4 kg roller.

[0116] The surface of the steel plate is cleaned with acetone beforehand. The plate is clamped in, and the self-adhesive strip is peeled from its free end on a tensile testing machine at a peel angle of 180 and a speed of 300 mm/min (or with the other specified speeds), and a determination is made of the force needed to achieve this. The measurement results are reported in N/cm and are averaged over three measurements and reported with standardization to the width of the strip in N/cm.

[0117] The initial peel adhesion (peel adhesion to ASTM steel) was measured immediately after bonding and not more than 10 minutes after bonding. The peel adhesion on alternative substrates (e.g., polypropylene (PP)) was determined in accordance with the methodology above, by changing the bonding substrate.

Micro-Shear Travel Measurement

[0118] The measurement setup is illustrated in FIG. 4.

[0119] Flat pieces measuring 10 mm50 mm were cut from the adhesive tape a, and the resulting adhesive tape specimen (71) was adhered to a polished, heatable steel test plate (72), which was 13 mm wide and had been cleaned with acetone, the bonding taking place such that the longitudinal direction of the adhesive tape specimen was oriented in the transverse direction of the steel plate, the bond area had dimensions of lw=13 mm10 mm, and the adhesive tape protruded beyond the steel plate on one side by a section of length z=2 mm. For fixing, a 2 kg steel roller was then rolled over the adhesive tape six times at a speed of 10 m/min. On the side of the adhesive tape (71) facing away from the steel plate (72), the adhesive tape (71) was reinforced, flush with the edge protruding by the section of length z beyond the steel plate, with a stable adhesive strip (73) (dimensions 4 mm25 mm; PET film carrier 190 m thick), which served as a support for a travel sensor (not shown). The arrangement thus prepared was suspended perpendicularly in such a way that the section of length z of the adhesive tape specimen (71) that protruded beyond the steel plate (72) pointed upward. The steel test plate (72) with the adhered sample (71) was heated to 40 C., and the adhesive tape specimen (71) for measurement was loaded at the lower end with a weight (75) of 100 g by means of a clamp (74) at the time t0=0. The travel sensor measured the deformation of the sample under shear over a period of 15 minutes (beginning at t0) at a temperature of 40 C. and a relative atmospheric humidity of 505%.

[0120] The result reported is the shearing distance in m after 15 minutes (maximum value; distance travelled by top edge of the sample downward during the measurement). The shear travel thus measured is a quantitative measure of the crosslinking status of the sample submitted to measurement.

[0121] The intention of the text below is to illustrate the invention using a number of examples, without thereby wishing to subject the invention to unnecessary restriction.

Preparation of the PSAs

[0122] The pressure-sensitive adhesives (PSAs) set out in the examples were homogenized as solvent-based compositions in a kneading apparatus with a double-sigma kneading hook. The solvent used was benzine (mixture of hydrocarbons). The kneading apparatus was cooled by means of water cooling.

[0123] First of all, in a first step, the solid EPDM rubber was pre-swollen with a third of the total amount of benzine and with the aging inhibitor and, optionally, fillers at 23 C. for 48 hours. This preliminary batch, as it is called, was then kneaded for 15 minutes. The resin was subsequently added in three equal-sized portions. After the first two additions, kneading took place for 10 minutes in each case, and for 40 minutes after the third addition. The liquid EPDM rubber or the plasticizers were then added, and kneading was continued for 10 minutes. After that, the second third of benzine was added and kneading took place for 20 minutes, before the last third of the total amount of benzine was incorporated with kneading for 30 minutes. The final solids content is 35 wt %.

Production of the Test Specimens

[0124] The PSA was coated onto a PET film, 23 m thick and etched with trichloroacetic acid, by means of a coating knife on a commercial laboratory coating bench (for example from the company SMO (Sondermaschinen Oschersleben GmbH)). The benzine was evaporated off in a forced air drying cabinet at 105 C. for 10 minutes. The slot width during coating was adjusted so as to achieve a coat weight of 50 g/m.sup.2 following evaporation of the solvent. The films freed from the solvent were subsequently lined with siliconized PET film and stored pending further testing at 23 C. and 50% relative humidity.

TABLE-US-00001 Inv. Inv. Inv. Inv. Inv. Inv. Raw material Type Mooney viscosity Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Vistalon 6602 EPDM 49% 25 (ML 1 + 4 125 C.) 25.00 ethylene Vistalon 2502 EPDM 55% 80 (ML 1 + 4 125 C.) 30.00 ethylene Keltan 69500 EPDM 44% 65 (ML 1 + 4 125 C.) 20.00 35.00 30.00 ethylene Vistalon 5601 EPDM 69% 72 (ML 1 + 4 125 C.) 0.00 ethylene Royalene 563 EPDM 57% 75 (ML 1 + 4 125 C.) 25.00 ethylene Royalene 547 EPDM 57% 80 (ML 1 + 4 125 C.) 25.00 ethylene Ondina 933 Liquid paraffinic white oil Trilene 67 Liquid EPDM 15.00 20.00 25.00 25.00 25.00 Oppanol B10N Liquid polyisobutylene Indopol H6000 Liquid polybutene Regalite R 1100 Hydrogenated 48.00 48.00 48.00 48.00 48.00 48.00 HC resin Irganox 1726 Aging inhibitor 2.00 2.00 2.00 2.00 2.00 2.00 100.0 100.0 100.0 100.0 100.0 100.0

TABLE-US-00002 PA PP fresh 4.2 3.9 4.2 9.6 9.4 8.1 [N/cm] 300 mm/min 5.2 6.3 5.4 7.6 8.7 7.7 [N/cm] PA ASTM steel 30 mm/min 15.0 5.6 5.9 8.9 8.1 8.0 [N/cm] 3 mm/min 2.9 6.7 8.2 2.1 1.6 3.0 [N/cm] MST max 63 44 47 349 221 266 1N [m] MST min 40 26 28 301 173 208 [m]

[0125] By liquid is meant that the starting materials are liquid at room temperature (softening point less than 60 C. or 400 C., respectively).

[0126] Indopol H6000: polyisobutene-polybutene copolymer

[0127] Regalite R 1100: hydrogenated hydrocarbon resin with a softening point of 100 C. from Eastman

[0128] Irganox 1726: phenolic antioxidant with sulfur-based function of a secondary antioxidant

TABLE-US-00003 Comp. Comp. Comp. Comp. Raw material Type Mooney viscosity Ex. 1 Ex. 2 Ex. 3 Ex. 4 Vistalon 6602 EPDM 49% ethylene 25 (ML 1 + 4 125 C.) Vistalon 2502 EPDM 55% ethylene 80 (ML 1 + 4 125 C.) 25.50 25.50 Keltan 69500 EPDM 44% ethylene 65 (ML 1 + 4 125 C.) 25.50 25.50 Vistalon 5601 EPDM 69% ethylene 72 (ML 1 + 4 125 C.) 20.00 Royalene 563 EPDM 57% ethylene 75 (ML 1 + 4 125 C.) Royalene 547 EPDM 57% ethylene 80 (ML 1 + 4 125 C.) Ondina 933 Liquid paraffinic 20.00 white oil Trilene 67 Liquid EPDM Oppanol B10N Liquid polyisobutylene 20.00 Indopol H6000 Liquid polybutene 20.00 Regalite R 1100 Hydrogenated HC resin 52.50 52.50 52.50 52.50 Irganox 1726 Aging inhibitor 2.00 2.00 2.00 2.00 100.0 100.0 100.0 100.0

TABLE-US-00004 PA PP fresh [N/cm] 8.7 3.4 0.1 0.2 300 mm/min [N/cm] PA ASTM steel 30 mm/min [N/cm] 3 mm/min [N/cm] MST max 1N [m] >2000 851 156 156 MST min [m] 790 109 109

[0129] Inventive examples 1 to 6, irrespective of the EPDM rubber used, show the very good properties of the compositions of the invention.

[0130] In particular, the PSAs, with peel adhesions of >3.0 N/cm, combine good bond strength on low-energy substrates (polypropylene) with a sufficient shear strength (micro-shear travel <500 m).

[0131] Comparative examples 1 and 2 do display a very good peel adhesion, as a result of the addition of paraffinic plasticizers. For many applications, however, the shear strength is not sufficient. As described in the prior art, the plasticizers which can be used include polymeric plasticizers such as polyisobutylenes of polybutylenes. As a result of the polymeric character, these plasticizers do not weaken the shear strength. Comparative examples 3 and 4 therefore exhibit good micro-shear travel figures. In the case of these formulations, however, the peel adhesion on low-energy surfaces is too low. All in all, only the compositions of the invention exhibit both good peel adhesion and high shear strength.