ADHESIVE COMPOUNDS CONTAINING GETTER MATERIALS THAT CAN BE ACTIVATED

Abstract

An adhesive comprising a getter material and optionally a solvent comprising a catalyst activatable by means of an external stimulus for the reaction of the getter material with a permeate can tolerate brief contact with permeates such as moisture in particular before user application, without any significant impairment of getter capacity.

Claims

1. Adhesive comprising a getter material and optionally a solvent, wherein the adhesive comprises a catalyst activatable by means of an external stimulus for the reaction of the getter material with a permeate.

2. Adhesive according to claim 1, wherein the permeate is water.

3. Adhesive according to claim 1, wherein the getter is present in an amount of at least 2% by weight.

4. Adhesive according to claim 1, wherein the amount of catalyst is less than 5% by weight.

5. Adhesive according to claim 1, wherein the external stimulus is UV radiation, a temperature change, microwave radiation or visible light.

6. Adhesive according to claim 1, wherein the catalyst activatable by an external stimulus is a latent acid or a latent base.

7. Adhesive according to claim 1, wherein the adhesive comprises an adhesive base composed of at least one polymer, and at least one tackifying resin.

8. Adhesive according to claim 7, wherein the adhesive base further comprises at least one reactive resin having at least one curable group.

9. Adhesive according to claim 7, wherein the adhesive is a barrier adhesive, and the adhesive base, if a reactive resin is present, has a water vapor permeation rate after curing of less than 100 g/m.sup.2d.

10. Adhesive according to claim 1, wherein the getter material is at least one compound selected from the group consisting of ethoxysilanes.

11. Adhesive according to claim 10, wherein the ethoxysilane additionally comprises at least one polymerizable group.

12. Adhesive according to claim 1, wherein the catalyst is a latent acid or a latent base.

13. Adhesive according to claim 8, wherein the adhesive base optionally comprises a reactive resin and the polymerizable group is polymerizable with those of the reactive.

14. Adhesive according to claim 1, wherein the getter material is at least one compound selected from the group consisting of nonaromatic carbodiimides.

15. Adhesive according to claim 1, wherein the getter material is at least one compound selected from the group consisting of acid- and/or base-hydrolysable esters.

16. Adhesive according to claim 1, wherein the getter material is at least one compound selected from the group consisting of the oxazolidines.

17. Adhesive according to claim 16, wherein the catalyst is a latent base.

18. Adhesive according to claim 1, wherein the getter material is at least one compound selected from the group consisting of the isocyanates.

19. Adhesive according to claim 18, wherein the catalyst is a latent base.

20. Adhesive according to claim 1, wherein the getter material is at least one compound selected from the group consisting of the anhydrides.

21. Adhesive according to claim 20, wherein the catalyst is a latent acid.

22. Adhesive according to claim 8, wherein the at least one curable group is at least one group selected from the group consisting of cyclic ether, vinyl, acrylate, methacrylate, hydroxyl, amino and isocyanate.

23. Adhesive according to claim 1, wherein the adhesive is a pressure-sensitive adhesive.

24. Adhesive tape comprising an adhesive according to claim 1.

25. Method for encapsulation of assemblies in organic electronics, which comprises encapsulating said assemblies with the adhesive of claim 1.

26. Method for applying an adhesive of claim 1 comprising the steps of applying the adhesive to the article to be bonded; activating the getter material by means of an external stimulus.

27. Method according to claim 26, wherein the adhesive comprises a reactive resin and the external stimulus induces not only the activation of the getter material but also the curing of the adhesive.

28. Method for protecting an organic electronic arrangement disposed on a substrate, wherein a cover is applied to the electronic arrangement in such a way that the electronic arrangement is at least partly covered by the cover, wherein the cover is additionally bonded over at least part of the area on the substrate and/or on the electronic arrangement, wherein the bonding is brought about by means of at least one layer of an adhesive according to claim 1.

29. Method according to claim 28, wherein the adhesive takes the form of a layer of an adhesive tape.

30. Method according to claim 28, wherein the adhesive layer, optionally as a constituent of a double-sided adhesive tape comprising further layers, is applied first, and in a subsequent step the cover is applied to the substrate and/or the electronic arrangement.

31. Method according to claim 30, wherein, the adhesive layer and the cover are applied together to the substrate and/or the electronic arrangement.

32. Method according to claim 28, wherein the fully covers the electronic arrangement.

33. Method according to claim 28, wherein a region of the substrate around the electronic arrangement is also wholly or partly covered by the cover.

34. Method for encapsulation of assemblies in organic electronics, which comprises encapsulating said assemblies with the adhesive tape of claim 24.

35. Method for applying an adhesive tape of claim 24, comprising the steps of applying the adhesive tape to the article to be bonded; activating the getter material by means of an external stimulus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0121] FIG. 1 illustrates a calcium test for determining breakthrough time,

[0122] FIG. 2 illustrates the time that moisture takes to cover the distance to the calcium, defined as the breakthrough time,

[0123] FIG. 3 illustrates an (opto)electronic arrangement according to the prior art in schematic view,

[0124] FIG. 4 illustrates a first inventive (opto)electronic arrangement in schematic view, and

[0125] FIG. 5 illustrates a second inventive (opto)electronic arrangement in schematic view.

[0126] FIG. 3 shows a first configuration of an organic electronic arrangement 1 according to the prior art. This arrangement 1 has a substrate 2 with an electronic structure 3 disposed thereon. The substrate 2 itself takes the form of a barrier for permeates and hence forms part of the encapsulation of the electronic structure 3. Above the electronic structure 3, in the present case also spaced apart therefrom, is disposed a further cover 4 that takes the form of a barrier.

[0127] In order to encapsulate the electronic structure 3 at the side as well and simultaneously to bond the cover 4 to the electronic arrangement 1 in addition, an adhesive 5 is provided around the periphery alongside the electronic structure 3 on the substrate 2. It is unimportant here whether the adhesive has been bonded first to the substrate 2 or first to the cover 4. The adhesive 5 bonds the cover 4 to the substrate 2. By means of an appropriately thick configuration, the adhesive 5 additionally enables the cover 4 to be spaced apart from the electronic structure 3.

[0128] The adhesive 5 is one according to the prior art, i.e. an adhesive having a high permeation barrier, which may additionally be filled with getter material to a high degree. The transparency of the adhesive is irrelevant in this assembly.

[0129] In the present case, a transfer adhesive tape would be provided in the form of a die-cut part which, because of its delicate geometry, is more difficult to handle than a transfer adhesive tape applied essentially over the full area.

[0130] FIG. 4 shows an inventive configuration of an (opto)electronic arrangement 1. What is shown is again an electronic structure 3 disposed on a substrate 2 and encapsulated by the substrate 2 from beneath. Above and to the side of the electronic structure, the inventive adhesive, for example in the form of a transfer adhesive tape 6, is now disposed over the full area. The electronic structure 3 is thus encapsulated fully by the transfer adhesive tape 6 from above. A cover 4 has then been applied to the transfer adhesive tape 6. The transfer adhesive tape 6 is one based on the inventive transfer adhesive tape as described above in general form and detailed hereinafter in working examples. The transfer adhesive tape, in the version shown, consists only of one layer of an inventive adhesive.

[0131] In contrast to the above configuration, the cover 4 need not necessarily satisfy the high barrier demands, since the barrier is already provided by the adhesive when the electronic arrangement is fully covered by the transfer adhesive tape. The cover 4 may, for example, merely assume a mechanical protective function, but it may also additionally be provided as a permeation barrier.

[0132] FIG. 5 shows an alternative configuration of an (opto)electronic arrangement 1. In contrast to the above configurations, two transfer adhesive tapes 6a, b are now provided, which are identical in the present case, but may also be different. The first transfer adhesive tape 6a is disposed over the full area of the substrate 2. The electronic structure 3 is provided upon and is fixed by the transfer adhesive tape 6a. The composite composed of the transfer adhesive tape 6a and electronic structure 3 is then fully covered by the further transfer adhesive tape 6b, such that the electronic structure 3 is encapsulated from all sides by the transfer adhesive tapes 6a, b. The cover 4 is in turn provided above the transfer adhesive tape 6b.

[0133] In this configuration, therefore, neither the substrate 2 nor the cover 4 need necessarily have barrier properties. They may nevertheless be provided, in order to further restrict the permeation of permeates to the electronic structure 3.

[0134] Especially with regard to FIGS. 4 and 5, it is pointed out that these are schematic diagrams. More particularly, it is not clear from the diagrams that the transfer adhesive tape here, and preferably in each case, has a homogeneous layer thickness. There is therefore no sharp edge formed at the transition to the electronic structure, as appears to be the case in the diagram; instead, the transition is fluid and it is in fact possible for small unfilled or gas-filled regions to remain. If necessary, however, matching to the substrate may also be effected, especially when the application is conducted under reduced pressure. Moreover, the adhesive is subject to different degrees of local compression, and so flow processes can result in a certain degree of compensation for the height differential at the edge structures. The dimensions shown are not to scale either, but instead serve merely for better illustration. Especially the electronic structure itself is generally relatively flat (often less than 1 μm thick).

[0135] Direct contact of the adhesive with the electronic assembly is not obligatory either. It is also possible for further layers to be disposed in between, for example a thin-layer encapsulation of the electronic assembly or barrier films.

[0136] The thickness of the transfer adhesive tape may include all customary thicknesses, for instance from 1 μm up to 3000 μm. Preference is given to a thickness between 25 and 100 μm, since bonding force and handling properties are particularly positive in this range. A further preferred range is a thickness of 3 to 25 μm, since the amount of substances permeating through the bondline within this range can be kept to a low level merely by virtue of the small cross-sectional area of the bondline in an encapsulation application.

[0137] For production of a transfer adhesive tape of the invention, the carrier of the adhesive tape or the liner is coated or printed on one side with the inventive adhesive from solution or dispersion or in neat form (for example of a melt), or the adhesive tape is produced by (co)extrusion. Alternatively, production is possible by transfer of an inventive adhesive layer by lamination to a carrier material or a liner. The adhesive layer can be crosslinked by means of heat or high-energy beams.

[0138] Preferably, this production process takes place in an environment in which the specific permeate is present only in a low concentration or is virtually not present at all. One example may be a relative air humidity of less than 30%, preferably of less than 15%.

EXAMPLES

Test Methods

Determination of Breakthrough Time (Lifetime Test)

[0139] A measure that was employed for the determination of the lifetime of an electronic assembly was a calcium test. This is shown in FIG. 1. For this purpose, a thin calcium layer 23 of 10×10 mm.sup.2 in size is deposited onto a glass slide 21 under reduced pressure and then stored under a nitrogen atmosphere. The thickness of the calcium layer 23 is about 100 nm. For the encapsulation of the calcium layer 23, an adhesive tape (23×23 mm.sup.2) having the adhesive 22 to be tested and a thin glass slide 24 (35 μm, from Schott) as carrier material are used. For stabilization, the thin glass slide was laminated with a 100 μm-thick PET film 26 by means of a 50 μm-thick transfer adhesive tape 25 to give an acrylate pressure-sensitive adhesive of visually high transparency. The adhesive 22 is applied to the glass slide 21 in such a way that the adhesive 22 covers the calcium mirror 23 with an excess margin of 6.5 mm on all sides (A-A). Because of the impervious glass carrier 24, only the permeation through the pressure-sensitive adhesive or along the interfaces is determined.

[0140] The test is based on the reaction of calcium with water vapour and oxygen, as described, for example, by A. G. Erlat et. al. in “47th Annual Technical Conference Proceedings—Society of Vacuum Coaters”, 2004, pages 654 to 659, and by M. E. Gross et al. in “46th Annual Technical Conference Proceedings—Society of Vacuum Coaters”, 2003, pages 89 to 92. This involves monitoring the light transmission of the calcium layer, which increases as a result of the conversion to calcium hydroxide and calcium oxide. In the test setup described, this is done from the edge, such that the visible area of the calcium mirror decreases. The time until the light absorption of the calcium mirror has halved is referred to as the lifetime. The method covers both the decrease in the area of the calcium mirror from the edge and via point degradation in the area and the homogeneous reduction in the layer thickness of the calcium mirror resulting from full-area degradation.

[0141] The measurement conditions chosen were 60° C. and 90% relative air humidity. The specimens were bonded with a layer thickness of the pressure-sensitive adhesive of 50 μm over the full area and with no bubbles. The degradation of the calcium mirror is monitored via transmission measurements. The breakthrough time (lag time) is defined as that time that the moisture takes to cover the distance to the calcium (cf. FIG. 2). Before attainment of this time, there is only a marginal change in the transmission of the calcium mirror at 60° C./90% r.h. and a slight change at 85° C./85% r.h.

Permeability to Water Vapour

[0142] The determination of the permeability to water vapour (WVTR) is effected to ASTM F-1249. For this purpose, the pressure-sensitive adhesive is applied with a layer thickness of 50 μm to a highly permeable polysulphone membrane (available from Sartorius) which does not itself make any contribution to the permeation barrier. The water vapour permeability is determined at 37.5° C. and a relative humidity of 90% with a Mocon OX-Tran 2/21 measuring instrument.

Molecular Weight

[0143] The molecular weight determinations of the number-average molecular weights M.sub.n and the weight-average molecular weights M.sub.w were made by means of gel permeation chromatography (GPC). The eluent used was THF (tetrahydrofuran) with 0.1% by volume of trifluoroacetic acid. The measurement was made at 25° C. The precolumn used was PSS-SDV, 5μ, 10.sup.3 Å, ID 8.0 mm×50 mm. For separation, the columns used were PSS-SDV, 5μ, 10.sup.3 and 10.sup.5 and 10.sup.6 each with ID 8.0 mm×300 mm. The sample concentration was 4 g/l; the flow rate was 1.0 ml per minute. Measurement was effected against polystyrene standards.

MMAP and DACP

[0144] MMAP is the mixed methylcyclohexane/aniline cloud point which is determined using a modified ASTM C 611 method. Methylcyclohexane is used in place of the heptane used in the standard test method. The method uses resin/aniline/methylcyclohexane in a ratio of 1/2/1 (5 g/10 ml/5 ml), and the cloud point is determined by cooling a heated clear mixture of the three components until complete cloudiness has just set in.

[0145] The DACP is the diacetone cloud point and is determined by cooling a heated solution of 5 g of resin, 5 g of xylene and 5 g of diacetone alcohol to the point at which the solution turns cloudy.

Ring & Ball Softening Temperature

[0146] The tackifying resin softening temperature is determined by the standard methodology, which is known as the Ring and Ball method and is standardized in ASTM E28.

[0147] The tackifying resin softening temperature of the resins is determined using a Herzog HRB 754 Ring and Ball tester. Resin specimens are first crushed finely with a mortar and pestle. The resulting powder is introduced into a brass cylinder open at the base (internal diameter in the upper part of the cylinder 20 mm, diameter of the base opening of the cylinder 16 mm, height of the cylinder 6 mm) and melted on a hot stage. The filling volume is chosen such that the resin after melting fills the cylinder fully without excess.

[0148] The resulting specimen together with the cylinder is placed into the sample holder of the HRB 754. The equilibration bath is filled with glycerol if the tackifying resin softening temperature is between 50° C. and 150° C. At lower tackifying resin softening temperatures, it is also possible to work with a water bath. The test balls have a diameter of 9.5 mm and weigh 3.5 g. In accordance with the HRB 754 procedure, the ball is arranged above the test specimen in the equilibration bath and placed onto the test specimen. 25 mm beneath the base of the cylinder is a collector plate, and 2 mm above the latter is a light barrier. During the measurement process, the temperature is increased at 5° C./min. In the temperature range of the tackifying resin softening temperature, the ball begins to move through the base opening of the cylinder until it finally comes to rest on the collector plate. In this position, it is detected by the light barrier and the temperature of the equilibration bath at this time is registered. A double determination takes place. The tackifying resin softening temperature is the average from the two individual measurements.

Adhesive Layers

[0149] For production of adhesive layers, various adhesives were applied from a solution to a conventional liner (siliconized polyester film) by means of a laboratory spreading instrument and dried. The adhesive layer thickness after drying is 50±5 μm. Drying was effected in each case first at RT for 10 minutes and at 120° C. in a laboratory drying cabinet for 10 minutes. The dried adhesive layers were each laminated on the open side immediately after drying with a second liner (siliconized polyester film with lower release force).

Raw Materials Used

[0150]

TABLE-US-00001 Sibstar 62M SiBS (polystyrene-block-polyisobutylene block copolymer) from Kaneka with block polystyrene content 20% by weight. Also contains some diblock copolymer. Tuftec P 1500 SBBS with 30% block polystyrene content from Asahi. The SBBS contains about a 68% diblock content. HBE-100 hydrogenated bisphenol A diglycidyl ether from ECEM Escorez 5300 a fully hydrogenated hydrocarbon resin from Exxon (Ring and Ball 105° C., DACP = 71, MMAP = 72) Escorez 5600 hydrogenated hydrocarbon resin having a softening point of 100° C. from Exxon Ondina G 17 white oil composed of paraffinic and naphthenic components from Shell Polyacrylate acrylate copolymer formed from 2-hydroxyethyl acrylate, 2-ethylhexyl acrylate and C-17 acrylate, M.sub.n = 884 000 g/mol Glycidoxypropyltriethoxysilane triethoxysilane with glycidyl epoxide group [4-(2-hydroxytetradecyloxy)- cationic photoinitiator from Sigma-Aldrich phenyl]phenyliodonium The photoinitiator has an absorption maximum in the hexafluoroantimonate range of 320 nm to 360 nm and was in the form of a 50% by weight solution in propylene carbonate. Titanium (IV) isopropoxide catalyst for the hydrolysis of alkoxysilanes (Sigma- Aldrich)

[0151] The copolymer selected was a polystyrene-block-polyisobutylene block copolymer from Kaneka. The proportion of styrene in the overall polymer is 20% by weight. Sibstar 62M was used. The molar mass M.sub.w is 60 000 g/mol. The glass transition temperature of the polystyrene blocks was 100° C. and that of the polyisobutylene blocks −60° C. The tackifying resin used was Escorez 5300 (Ring and Ball 105° C., DACP=71, MMAP=72) from Exxon, a fully hydrogenated hydrocarbon resin, or Escorez 5600 (softening point 100° C.), a hydrogenated hydrocarbon resin. These raw materials and optionally the alkoxysilane were dissolved in a mixture of toluene (300 g), acetone (150 g) and 60/95 special boiling point spirit (550 g), so as to give a 50% by weight solution.

[0152] Subsequently, a catalyst was added to the solution. The catalyst took the form of a 50% by weight solution in propylene carbonate. The photolatent catalyst has an absorption maximum in the range of 320 nm to 360 nm.

[0153] The exact composition of the individual examples V1 and V2 and of K1 and K2 can be found in Table 1.

TABLE-US-00002 TABLE 1 Example: K1 K2 V1 V2 pts. by pts. by pts. by pts. by wt. wt. wt. wt. Sibstar 62M 37.5 HBE-100 20 20 Escorez 5600 100 100 Escorez 5300 37.5 Ondina G17 25 25 Tuftec P 1500 100 100 Polyacrylate — 75 Glycidoxypropyltriethoxysilane 5 Triethoxyoctylsilane 10 5 Titanium (IV) isopropoxide 0.3 [4-(2-hydroxytetradecyloxy)- 0.3 0.1 0.1 phenyl]phenyliodonium hexafluoroantimonate

[0154] The specimens were introduced into a glovebox. Some of the specimens were laminated without bubbles with a rubber roller onto a glass substrate which had been subjected to calcium vapour deposition. This was covered with the second PET liner and a ply of a thin glass was laminated on. This specimen was used for the lifetime test.

[0155] The results of the moisture permeation measurement of the adhesives and the breakthrough times determined for water in the calcium test before and after the activation of the catalyst and hence of the getter, and after the samples had been exposed to water, are shown in Table 2.

TABLE-US-00003 TABLE 2 K1 K2 V1 V2 WVTR/g m.sup.−2d.sup.−1 33 12 34 678 Lag time.sup.1/h 10 0 150 0 Lag time.sup.2/h 150 470 150 0 Lag time.sup.3/h 145 480 0 0 .sup.1fresh adhesive tape (catalyst not activated by UV light), Ca test at 60° C./90% rh .sup.2fresh adhesive tape, activation of the catalyst with UV light, Ca test at 60° C./90% rh .sup.3after the sample had been exposed to H.sub.2O at 23° C./50% rh for 1 day, drying again in an inert atmosphere, activation of the catalyst with UV light. Ca test at 60° C./90% rh.

[0156] For Comparative Example V1, a noninventive, i.e. non-switchable, catalyst was used. The sample has a certain lag time which does not change as a result of irradiation with UV light. The getter is not switchable. In the case of Inventive Example K1, the lag time changes significantly. In Example K1, the lag time after the activation of the catalyst and hence of the getter by UV radiation is 15 times higher than before the activation. K2 is an example of a combined activation of the getter and curing of the reactive resin. The adhesive does not have any lag time before activation/curing. The activation/curing results in achievement of a long lag time.

[0157] Once the nonactivated samples had been exposed to moist air for one day, the noninventive sample V1 shows that the getter had been used up and had already reacted with the water, and so the lag time had fallen to zero. In the case of the inventive samples K1 and K2, in contrast, the nonactivated getter did not react with the water present in the moist air during the one day. The lag time of the samples was essentially identical to that of a sample that had not been exposed to moist air. Even though the samples had thus been exposed to water vapour, this did not have any effect on their efficacy as getters, since the getter function had not yet been activated.

[0158] Comparative example V2 shows that a sample having a high WVTR does not have a measurable lag time.