Oled-Compatible Adhesives Comprising Cyclic Azasilane Water Scavengers

Abstract

A barrier adhesive comprising an adhesive base composed of at least one reactive resin having at least one activatable group, at least one elastomer, optionally at least one adhesive resin, wherein the adhesive base has a water vapour permeation rate after the activation of the reactive resin of less than 100 g/m.sup.2d, preferably of less than 50 g/m.sup.2d, especially less than 15 g/m.sup.2d, further comprising a transparent molecularly dispersed getter material and optionally a solvent, in which the getter material is at least one cyclic azasilane, has very long lag times and can be used over an area for encapsulation of organic electronic structures, since the sensitive structures are not damaged.

Claims

1. A barrier adhesive comprising an adhesive base comprising or composed of: at least one reactive resin having at least one activatable group, at least one elastomer, optionally at least one tackifying resin, where the adhesive base after the activation of the reactive resin especially has a water vapour permeation rate of less than 100 g/m.sup.2d, a transparent molecularly dispersed getter material and optionally a solvent, wherein: the getter material is at least one cyclic azasilane.

2. The barrier adhesive according to claim 1, characterized in that the amount of getter material is at least 0.5% by weight, by weight of the adhesive.

3. The barrier adhesive according to claim 1, wherein: the amount of getter material is not more than 15% by weight.

4. The barrier adhesive according to claim 1, wherein the amount of getter material is 3% to 15% by weight,

5. The barrier adhesive according to claim 1, wherein the activatable group is at least one group selected from the group comprising: cyclic ether groups, especially epoxides and oxetanes, acrylates and methacrylates.

6. The barrier adhesive according to claim 1, wherein the at least one reactive resin contains, as activatable groups, at least one group selected from a glycidyl group and an epoxycyclohexyl group.

7. The barrier adhesive according to claim 1, wherein the at least one azasilane is a compound according to the general formula ##STR00002## where R is a hydrogen, alkyl or aryl radical; X is an alkyl or aryl radical; and, Y is an alkyl or aryl group or an alkoxy group, and where the Y radicals may be the same or different.

8. The barrier adhesive according to claim 7, wherein the reactive resin and azasilane have equivalent groups.

9. The adhesive according to wherein the barrier adhesive comprises at least one of: N-methylaza-2,2,4-trimethylsilacyclopentane, N-butylaza-2,2,4-trimethylsilacyclopentane, N-(2-aminoethyl)-aza-2,2,4-trimethylsilacyclopentane, N-vinylaza-2,2,4-trimethylsilacyclopentane, N-vinylaza-2,2-dimethylsilacyclopentane, or N-glycidylaza-2,2,4-trimethylsilacyclopentane.

10. The barrier adhesive according to claim 1, wherein the adhesive is a pressure-sensitive adhesive.

11. The barrier adhesive according to wherein the barrier adhesive is cured by cationic means.

12. The barrier adhesive according to claim 1 which further comprises a photoinitiator.

13. Adhesive tape comprising a barrier adhesive according to claim 1.

14. A method of encapsulating an assembly found in organic electronics, the method comprising the step of: utilizing the barrier adhesive of claim 1.

15. A method of 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.

16. The method according to claim 15, wherein; the barrier adhesive is in the form of a layer of an adhesive tape.

17. The method according to claim 15, wherein: the adhesive layer, is applied first, and in a subsequent step a cover is applied to the substrate and/or the electronic arrangement.

18. The method according to claim 15, wherein the adhesive layer and the cover are applied together to the substrate and/or the electronic arrangement.

19. The method according to claim 15, wherein the cover fully covers the electronic arrangement.

20. The method according to claim 15, wherein a region of the substrate around the electronic arrangement is also wholly or partly covered by the cover.

Description

[0107] Further details, features and advantages of the present invention are elucidated in detail hereinafter by preferred working examples. The drawings show:

[0108] FIG. 5 an (opto)electronic arrangement according to the prior art in schematic view,

[0109] FIG. 6 a first inventive (opto)electronic arrangement in schematic view,

[0110] FIG. 7 a second inventive (opto)electronic arrangement in schematic view.

[0111] FIG. 5 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.

[0112] In order to encapsulate the electronic structure 3 at the side as well and simultaneously to bond the cover 4 to the atomic arrangement 1 in addition, an adhesive 5 is provided around the periphery of 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.

[0113] The adhesive 5 is one according to the prior art, i.e. an adhesive having a high permeation barrier, which may additionally also be filled with getter material to a high degree. The transparency of the adhesive is irrelevant in this assembly.

[0114] 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.

[0115] FIG. 6 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 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.

[0116] 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.

[0117] FIG. 7 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.

[0118] In this configuration, 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.

[0119] Especially with regard to FIGS. 6 and 7, it is pointed out that these are schematic diagrams. More particularly, it is not clear from the drawings 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.

[0120] 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 m thick).

[0121] 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.

[0122] The thickness of the transfer adhesive tape may include all customary thicknesses, for instance from 1 m up to 3000 m. Preference is given to a thickness between 25 and 100 m, since bonding force and handling properties are particularly positive in this range. A further preferred range is a thickness of 3 to 25 m, 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.

[0123] 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.

[0124] 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 is a relative air humidity of less than 30%, preferably of less than 15%.

EXAMPLES

Test Methods

[0125] Unless noted otherwise, the measurements are conducted under test conditions of 231 C. and 505% relative air humidity.

Determination of Breakthrough Time (Lifetime Test)

[0126] 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 1010 mm.sup.2 in size is deposited onto a glass plate 21 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 (2323 mm.sup.2) having the adhesive 22 to be tested and a thin glass slide 24 (35 m, from Schott) as carrier material are used. For stabilization, the thin glass slide was laminated with a 100 m-thick PET film 26 by means of a 50 m-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 slide 24, only the permeation through the pressure-sensitive adhesive or along the interfaces is determined.

[0127] 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 ProceedingsSociety of Vacuum Coaters, 2004, pages 654 to 659, and by M. E. Gross et al. in 46th Annual Technical Conference ProceedingsSociety 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.

[0128] 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 m over the full area and with no bubbles. The degradation of the calcium mirror is monitored via transmission measurements. The breakthrough time is defined as that time that moisture takes to cover the distance to the calcium (cf. FIG. 2). Before attainment of this time, there is only a slight change in the transmission of the calcium mirror, then a distinct rise.

Permeability to Water Vapour (Water Vapour Permeation Rate)

[0129] 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 m to a highly permeable polysulfone 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 an OX-Tran 2/21 measuring instrument.

Molecular Weight

[0130] The molecular weight determinations of the number-average molecular weight M.sub.n and the weight-average molecular weight 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, 5, 10.sup.3 , ID 8.0 mm50 mm. For separation, the columns used were PSS-SDV, 5, 10.sup.3 and 10.sup.5 and 10.sup.6 each with ID 8.0 mm300 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

[0131] 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.

[0132] 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

[0133] The tackifying resin softening temperature is determined by the standard methodology, which is known as the Ring & Ball method and is standardized in ASTM E28.

[0134] 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.

[0135] 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 determinations.

Measurement of Haze and Transmission

[0136] The HAZE value describes the proportion of the light transmitted which is scattered forward at wide angles by the sample being irradiated. Thus, the HAZE value quantifies the opaque properties of a layer which disrupt clear transparency.

[0137] The transmission and the haze of the adhesive are determined analogously to ASTM D1003-11 (Procedure A (Byk Haze-gard Dual hazemeter), D65 standard illuminant) at room temperature on a 50 m-thick layer of the adhesive. No correction of interfacial reflection losses is done.

[0138] Since correct application on the measuring instrument is important in the case of thin transfer adhesive tapes, in order not to distort the measurement result, an auxiliary carrier was used. The carrier used was a PC film from GE Plastics (Lexan 8010 film, thickness 125 m).

[0139] This carrier met all the criteria (smooth planar surface, very low haze value, high transmission, high homogeneity) for planar attachment of the adhesive tape specimen to the measurement channel.

Adhesive Layers

[0140] 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. The adhesive layer thickness after drying was 505 m. Drying was effected in each case firstly 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).

[0141] Raw materials used:

TABLE-US-00001 Sibstar 62M SiBS (polystyrene-block-polyisobutylene block copolymer) from Kaneka with block polystyrene content 20% by weight. Also contains some diblock copolymers. Uvacure 1500 cycloaliphatic diepoxide from Cytec ((3,4- epoxycyclohexane) methyl 3,4- epoxycyclohexylcarboxylate) Escorez 5300 a fully hydrogenated hydrocarbon resin from Exxon (Ring and Ball 105 C., DACP = 71, MMAP = 72) Polyacrylate acrylate copolymer formed from 2-hydroxyethyl acrylate, 2-ethylhexyl acrylate and C-17 acrylate, M.sub.n = 884 000 g/mol N-methylaza-2,2,4-trimethylsilacyclopentane from SIM6501.4 Gelest triarylsulfonium cationic photoinitiator from Sigma-Aldrich hexa- fluoroantimonate The photoinitiator has an absorption maximum in the range of 320 nm to 360 nm and was in the form of a 50% by weight solution in propylene carbonate.

[0142] The polyacrylate was prepared by the following method:

[0143] A 2 I glass reactor of a conventional type for free-radical polymerizations was charged with 40 g of 2-hydroxyethyl acrylate, 240 g of 2-ethylhexyl acrylate, 120 g of C17 acrylate (three branched chains with C.sub.3, C.sub.4 chain segments, BASF SE), 133 g of 69/95 special boiling point spirit and 133 g of acetone. After nitrogen gas had been passed through the reaction solution while stirring for 45 minutes, the reactor was heated to 58 C. and 0.2 g of Vazo 67 (from DuPont) was added. Subsequently, the external heating bath was heated to 75 C. and the reaction was conducted constantly at this external temperature. After 1 h of reaction time, 50 g of toluene were added. After 2.5 h, dilution was effected with 100 g of acetone. After 4 h of reaction time, another 0.2 g of Vazo 67 was added. After 7 h of polymerization time, dilution was effected with 100 g of 60/95 special boiling point spirit, and after 22 h with 100 g of acetone. After 24 h of reaction time, the polymerization was stopped and the reaction vessel was cooled to room temperature. The molecular weight M.sub.n was 884 000 g/mol.

[0144] The copolymer selected was a polystyrene-block-polyisobutylene block copolymer from Kaneka. The proportion of styrene in the overall polymer was 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 & Ball 105 C., DACP=71, MMAP=72) from Exxon, a fully hydrogenated hydrocarbon resin. The reactive resin selected was Uvacure 1500 from Dow, a cycloaliphatic diepoxide. These raw materials and optionally the cyclic azasilane (Example K1) 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.

[0145] Subsequently, a photoinitiator was added to the solution. The photoinitiator took the form of a 50% by weight solution in propylene carbonate. The photoinitiator has an absorption maximum in the range of 320 nm to 360 nm.

[0146] The exact composition of the individual examples can be found in Table 1.

TABLE-US-00002 TABLE 1 K1 V1 V2 pts. pts. pts. Example: by wt. by wt. by wt. Sibstar 62M 37.5 37.5 Uvacure 1500 20 20 20 Escorez 5300 37.5 37.5 Polyacrylate 75 SIM6501.4 5 5 Triarylsulfonium 0.1 0.1 0.1 hexafluoro- antimonate

[0147] The specimens were introduced into a glovebox. Some of the specimens were laminated without bubbles with a rubber roller on to 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 was followed by curing through the cover glass by means of UV light (dose: 80 mJ/cm.sup.2; lamp type: undoped mercury source). This specimen was used for the lifetime test.

[0148] The results of the moisture permeation measurement of the base adhesives (V2) and an acrylate adhesive (V1) without addition of a water scavenger are shown in Table 2.

TABLE-US-00003 TABLE 2 V2 V1 WVTR/g 9 673 m.sup.2d.sup.1

[0149] This shows that adhesive V2, by contrast with V1, shows a very low WVTR value (less than 100 g/m.sup.2d, preferably less than 50 g/m.sup.2d, especially less than 15 g/m.sup.2d). If these results are compared with the barrier properties achieved, it is found that only adhesives V2 and K1 have a breakthrough time (lag time) with less than 100 g/m.sup.2d.

[0150] The breakthrough times determined for water in the calcium test are listed in Table 3 below:

TABLE-US-00004 TABLE 3 Designation K1 V1 V2 Lag time 1150 0 750 60 C./90% r.h. Lag time 190 0 155 85 C./85% r.h.

[0151] Comparison of V2 and K1 shows that the addition of the cyclic silazanes can distinctly improve the barrier effect (determined via the lag time).

[0152] Compatibility of the Adhesives with OLEDs and Cathode Material (Calcium)

[0153] Known transparent getters were incorporated were incorporated into an adhesive in a proportion of 5% by weight. The reactivity of these water scavengers is so great that the calcium surface was attacked even in the calcium test. If cyclic azasilanes are used, as shown here in K1, the calcium remains unaffected. This is recorded in the photographs in FIG. 3.

[0154] OLED compatibility was demonstrated for the cyclic azasilanes, by bonding such adhesives on unencapsulated polymeric OLEDs and storing them at 60 C./90% r.h. for 150 h. As a counter-example, a standard organic water scavenger (Incozol) showed clear damage (dark spots). The results are reproduced in FIG. 4.

[0155] Table 4 summarizes the observations once again.

TABLE-US-00005 TABLE 4 V2 + 5% V2 + 5% Bonding to K1 Incozol* DBAPTS* Calcium no damage severe severe damage damage OLED no damage many dark many dark cathode spots spots (barium- aluminium) *Incozol: bis-oxazolidine water scavenger from Incorez *DBAPTS: dimethylbutylideneaminopropyltriethoxysilane