Method for producing a barrier layer and carrier body comprising such a barrier layer

Abstract

A method for producing a barrier layer and a carrier body including such a barrier layer are disclosed. In an embodiment the method includes providing a carrier body including a polymer film having at least one polymer, drying the barrier interface, exposing the barrier interface to one reagent gas, or to a plurality of reagent gases which do not chemically react with each other, so that the at least one reagent gas chemically reacts with the at least one polymer at least inside the polymer film in at least one chemical reaction thereby forming the barrier layer, and removing at least one product gas of the at least one chemical reaction.

Claims

1. A method for producing a barrier layer in a polymer film, the method comprising: A) providing a carrier body comprising the polymer film, wherein the polymer film includes at least one polymer, and wherein the polymer film forms a barrier interface of the carrier body; B) drying the barrier interface; C) exposing the barrier interface to one reagent gas, or to a plurality of reagent gases which do not chemically react with each other, so that the at least one reagent gas chemically reacts with the at least one polymer at least inside the polymer film in at least one chemical reaction thereby forming the barrier layer, wherein inside the polymer film means that the at least one reagent gas chemically reacts with the at least one polymer in a depth of the polymer film of at least 10 nm; and D) removing at least one product gas of the at least one chemical reaction, wherein the barrier layer is produced without using H.sub.2O.

2. The method according to claim 1, wherein step C) is performed with a low, first total pressure of at most 100 mbar, wherein in step D) a lower, second total pressure of at most 1 mbar is at least temporally reached, wherein steps C) and D) directly follow each other in a reactor and are directly repeated at least twice, wherein in step C) the barrier interface is exposed to the reagent gas with the first pressure by at least is so that the reagent gas can diffuse into the polymer film, and wherein in step D) the second pressure is applied by at least 2 s so that the at least one product gas can diffuse out of the polymer film.

3. The method according to claim 1, wherein at least method steps C) and D) are performed with a total pressure of at least 500 mbar, wherein step C) is performed with a low, first partial pressure of the reagent gas of at most 50 mbar, wherein in step D) a lower, second partial pressure of the product gas of at most 1 mbar is at least temporally reached, wherein steps C) and D) directly follow on each other and are directly repeated at least four times, and wherein a total exposure time in all method steps C) together is at least 0.5 s.

4. The method according to claim 1, wherein steps C) and D) are repeated at least 20 times.

5. The method according to claim 1, wherein exactly one reagent gas is used, and wherein the reagent gas intentionally only reacts with the polymer.

6. The method according to claim 1, wherein the reagent gas is an organometallic precursor, a metalorganic compound, a halide, a chalcogenide or an organic compound, and wherein the polymer or at least one of the polymers of the polymer film is a polyester, a polycarbonate, a polyaryletherketone, a polyamide, a polyamide-imide, a polyurethane, a polyimide a polylactide, a polyolefin or a polyketide.

7. The method according to claim 6, wherein the reagent gas is (CH.sub.3).sub.3Al, (CH.sub.3).sub.6Al.sub.2 or (C.sub.2H.sub.5).sub.2Zn, wherein the polymer is polyethylene terephthalate, wherein a water content in the barrier layer of the polymer film is at most 0.05% by mass after producing the barrier layer, and wherein a concentration of Al or Zn from the reagent gas which is included into the barrier layer by the chemical reaction gradually decreases in a direction away from the barrier interface towards a substrate of the carrier body.

8. The method according to claim 1, wherein the chemical reaction includes bridge-forming between at least two functional groups, between at least two side chains or between at least one side chain and at least one functional group of subunits comprised of monomers or oligomers of the at least one polymer, the bridges in each case including at least one atom from the reagent gas which is covalently bound to the subunits.

9. The method according to claim 1, wherein in step C) a degree of cross-linking in the barrier layer is increased.

10. The method according to claim 1, wherein a thickness of the barrier layer is between 2 nm and 600 nm inclusive, and wherein the barrier layer is a layer comprising a part of the reagent gas with a concentration of at least 0.02 atom-%.

11. The method according to claim 1, wherein, after producing the barrier layer, the barrier interface is free of a closed layer of a ceramic and/or an oxide and/or a nitride and/or an oxynitride, and wherein by producing the barrier layer a hardness of the barrier interface is changed by a maximum of 20%.

12. The method according to claim 1, wherein step B) includes heating of the polymer film to a temperature of between 50 C. and 200 C. inclusive, the barrier interface is flushed with a water free gas and/or is evacuated, and wherein a process temperature during step C) is between 70 C. and 160 C. inclusive.

13. The method according to claim 1, wherein the carrier body is a foil consisting of the polymer film, a thickness of the foil is between 40 m and 500 m inclusive, and wherein, after producing the barrier layer, the carrier body is mechanically flexible.

14. The method according to claim 1, wherein a permeability against water vapor and/or oxygen is increased by at least a factor of two by producing the barrier layer.

15. A carrier body comprising: a polymer film of at least one polymer, wherein the polymer film forms a barrier interface of the carrier body; and a barrier layer formed inside the polymer film, wherein, after producing the barrier layer, the barrier interface is free of a closed layer of a ceramic and/or an oxide and/or a nitride and/or an oxynitride, wherein the barrier layer comprises a plurality of bridges between different subunits comprised of monomers or oligomers of the at least one polymer or polymer chain, wherein the bridges include at least one metal atom which is covalently bound to the subunits, and wherein the carrier body is mechanically flexible.

16. The carrier body according to claim 15, wherein the barrier layer is formed inside the polymer film in a depth of the polymer film of at least 10 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A carrier body and a method described in this case will be explained in greater detail hereinafter with reference to the drawing with the aid of exemplified embodiments. Like reference numerals designate like elements in the individual figures. However, none of the references are illustrated to scale. Rather, individual elements can be illustrated excessively large for ease of understanding.

(2) In the drawing:

(3) FIGS. 1, 4 and 7 show schematic sectional views of method steps for producing a carrier body described in this case,

(4) FIG. 2 shows a schematic structural formula of a barrier layer described in this case,

(5) FIG. 3 shows a permeability against oxygen in dependency of the number of cycles used to produce the barrier layer described in this case,

(6) FIGS. 5 and 6 shows a schematic sectional view of an OLED comprising a carrier body described in this case, and

(7) FIG. 8 schematically shows a concentration gradient in the barrier layer described here.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(8) In FIG. 1, method steps for producing a barrier layer 22 in a polymer film 2 are shown. According to FIG 1A, a carrier body 1 is provided. The carrier body 1 is a foil and consists of the polymer film 2. For example, the polymer film 2 is made of polyethylene terephthalate, PET for short, and has a thickness of 50 m, 75 m or 100 m. In particular, the carrier body 1 is a polyester film Melinex 401 CW or Melinex ST 504. An outer boundary surface 10 of the carrier body 1 is identical with a barrier interface 20 to be created by producing the barrier layer 22.

(9) Further, as shown in FIG. 1A, the carrier body 1 is brought into a reactor 3. The reactor 3 is designed to perform processes like ALD or CVD in it. Preferably, all the method steps shown in FIG. 1 are done in the reactor 3 without releasing the carrier body 1 from the reactor 3.

(10) According to FIG. 1B, the boundary surface 10 is dried. In other words, water is removed from the boundary surface 10. For drying, flushing with a drying gas 9 and/or vacuum is applied. The drying gas 9 can be nitrogen with a gas grade of 5.0, which is essentially free of water.

(11) Moreover, a temperature of the carrier body 1 is preferably increased during drying, for example, to about 100 C. With this combination of elevated temperature and low water partial pressure, the boundary surface 10 can be efficiently dried. Further, water is also removed or reduced in concentration in an area of the carrier body 1 near the boundary surface 10. For example, the vacuum or the flushing with the drying gas 9 is maintained for at least 30 s or 120 s.

(12) No cleaning with a plasma like oxygen plasma or ozone plasma is required. On the contrary, by such plasma methods undesired water may be produced near the barrier interface 20.

(13) In the method step of FIG. 1C, the reactor 3 is flooded with a reagent gas 4 together with a carrier gas. The carrier gas is not shown in the figures. The reagent gas 4 is (CH.sub.3).sub.6Al.sub.2 and/or (CH.sub.3).sub.3Al, also referred to as trimethylaluminum or TMA, for short, or the reagent gas 4 is (C.sub.2H.sub.5).sub.2Zn. A first pressure of the reagent gas 4 together with the carrier gas is about 10 mbar, for example.

(14) Thus, the polymer film 2 is exposed to the reagent gas 4 which is at least one reactive organic or inorganic molecule from the vapor phase in the absence of a solvent.

(15) In order to save reagent gas 4, the reagent gas 4 is preferably introduced only during a short pulse, for example, with a pulse length of between 100 ms and 200 ms. A fraction of the reagent gas 4, relative to the carrier gas, is preferably around 20 volume-%. The reagent gas 4 is schematically indicated by a hatching.

(16) According to FIG. 1D, the boundary surface 10 is exposed to the reagent gas 4 for a comparably long time. The exposure time is preferably around 30 s. This method step is optional and could be replaced by a longer taking method step as shown in conjunction with FIG. 1C. By means of the comparably long exposure time, it can be ensured that the reagent gas 4 not only reaches the boundary surface 10 but also diffuses into the polymer film 2 of the carrier body 1 to a sufficient depth. The diffusion depth is preferably at least 10 nm or 20 nm or 40 nm and/or at most 600 nm or 400 nm or 250 nm, for example, around 50 nm.

(17) The diffusion depth is the depth in which a concentration of the reagent gas 4 in the polymer film 2 has dropped to 1/e or about 37%, relative to a concentration of the reagent gas 4 directly at the boundary surface 10. Depending on the material of the polymer film 2, the reagent gas 4 and its partial pressure, and a temperature of the carrier body 1, the exposure time should preferably be adjusted to obtain the desired diffusion depth.

(18) As the reagent gas 4 is very reactive, the reagent gas 4 undergoes a chemical reaction with the polymer of the polymer film 2 as explained in more detail in the context of FIG. 2 below. Because of said chemical reaction, a cross-linking in the polymer of the polymer film 2 is increased. Furthermore, the reagent gas 4 is consumed to some extent and a product gas 5 is produced. In FIG. 1D, the product gas 5 is schematically indicated by crosses. The product gas 5 is an alkyl like methane, for example. Due to the product gas 5 present in the polymer film 2, the chemical reaction between the polymer and the reagent gas 4 and/or a further diffusion of reagent gas 4 into the polymer film 2 is hindered. Thus, after some time the chemical reaction is disrupted.

(19) As is shown in FIG. 1E, the remaining reagent gas 4 and the at least one product gas 5 are removed by evacuation. This method step continues until a lower, second pressure is reached. The lower, second pressure is, for example, a factor of 1000 smaller than the first pressure in order to qualitatively remove the gases 4, 5. By way of example, the second pressure is 0.01 mbar.

(20) During the method steps of FIGS. 1C, 1D and 1E, an elevated temperature is set. Particularly, the temperature is between 100 C. and 120 C. With this temperature, an improved diffusion of the reagent gas 4 into and of the product gases 5 out of the carrier body 1 can be achieved while maintaining short time intervals for the method steps according to FIGS. 1D and 1E. If the temperature is decreased or increased, the time intervals for the method steps 1D and 1E should accordingly be adapted.

(21) In order to achieve a sufficient cross-linking in the barrier layer 22 and, thus, the desired impermeability against oxygen and/or water vapor, the method steps of FIGS. 1C, 1D and 1E are repeated, compare FIGS. 1F, 1G and 1H. Other than shown, these method steps can be repeated more than twice. Particularly because of the removal of the at least one product gas 5, the cross-linking and the forming of the barrier layer 22 can be enhanced.

(22) All the method steps as shown in FIG. 1 are preferably done in the stated order without any intermediate steps. The method is performed without the use of water and preferably with only one reagent gas 4. No additional layer like a ceramic layer is applied to the boundary surface 10.

(23) FIG. 2 shows schematic structural formulas of the polymer.

(24) In FIG. 2A, three subunits comprised of monomers or oligomers of three polymer chains with a length n of the untreated polymer are shown. The polymer is polyethylene terephthalate as used in connection with FIG. 1. There is no or no significant cross-linking between the polymer chains. Because of the lack of cross-linking, the polymer can be regarded as a kind of sponge with a considerable number of small cavities. Through such cavities, diffusion of gases like oxygen and water occurs at a comparably high rate. In other words, in particular said cavities result in the typically high permeability of polymer films.

(25) In FIG. 2B, the modified polymer in the barrier layer 22 produced with the described method is shown. In very brief, by means of an electrophile attack, Al.sup.3+ from the reagent gas is covalently attached to the carbonyl oxygen of the polymer. The carbonyl carbon is nucleophilicly attacked by CH.sub.2.sup.2 and CH.sub.3.sup.. Thus, a cross-linking between the polymer chains is achieved by bridges 24, the bridges 24 include the metal of the precursor of the reagent gas. As other products of the chemical reaction like methane are removed and, thus, are of no greater importance in the present case, these products are not highlighted in connection with FIG. 2.

(26) According to FIG. 2C, without removal of the other products individual reactions between the TMA and the PET occur too, similar to what is shown in FIG. 2B. However, in particular because of the other products of the reaction and higher dose of TMA if supplied in a single and very high dose the cross-linking is hindered. Exposed to air and, thus, with the influence of water, the Al forms Al(OH).sub.x which is only able to form weak hydrogen bonds. Hence, without the removal of the product gases the chemical reaction of FIG. 2B is suppressed and the described barrier layer is not formed. Instead, as indicated in FIG. 2C, the polymer may be destroyed to a certain extent. Therefore, supply of multiple smaller doses of the reagent with intermediate product removal are preferred.

(27) In FIG. 3, the effect of the barrier layer 22 is illustrated. An oxygen transmission rate, OTR for short, of a PET Melinex ST 504 foil processed with TMA at 120 C. as described in connection with FIG. 1 is shown. The OTR is drawn against the number N of cycles. In other words, the method steps according to FIGS. 1C to 1E have been repeated N times. The OTR is measured in cm.sup.3 (STP) per m.sup.2 and day and bar, cm.sup.3 (STP)/(m.sup.2 d bar), wherein d stands for day and STP stands for Standard Temperature and Pressure. The measurement was done with a PSt.sub.9 sensor from PreSens Precision Sensing GmbH, Germany.

(28) Up to about 50 cycles, the OTR exponentially falls by about four orders of magnitude. The logarithmic ordinate scale should be noted. An expected drop of the OTR with a higher number N of cycles could not be resolved in the measurement.

(29) In FIG. 4 it is illustrated that the produced carrier body 1 with the finished barrier layer 22 is mechanically flexible and remains intact in a roll-to-roll process with different rolls 8. Thus, the produced carrier body 1 can easily be applied to different manufacturing procedures with a high production volume and with simplified handling.

(30) Thus, the exposure of a polymeric carrier body 1 to vapors of highly reactive precursors like trimethyl aluminum, diethyl zinc and so on for a duration of time largely exceeding exposures typical of an ALD or MLD process allows diffusion, chemical binding, consumption of latent H.sub.2O, and cross-linking of the polymer chains. The dosing duration, i.e., the number of pulses, pulsing times, and exposure times, determines the depth of diffusion into the polymer film 2 and the degree of cross-linking. The resulting organic/inorganic

(31) hybrid material in the sub-surface region of the boundary surface 10 of the polymeric carrier body 1 shows significant improvement of the barrier properties in comparison to the untreated polymer, while at the same time maintaining a large degree of crack resistance upon mechanical bending of the substrate.

(32) A comparison between the carrier body 1 of FIG. 1 processed with the described method on the one hand and processed with a conventional ALD method on the other hand reveals the following results:

(33) Thin film coatings with 5 nm to 50 nm thickness of Al.sub.2O.sub.3 produced with conventional ALD result in significant improvement of the barrier properties against oxygen of more than 4 orders of magnitude in comparison to the untreated reference samples. However after bending the samples ten times over a radius of 10 cm, the permeation increases again by two to three orders of magnitude. Thus, by multiple bending the effect of the ALD layer to permeability has nearly vanished.

(34) Samples treated with the infiltration method as described in connection with FIG. 1 with five to 50 infiltration cycles improve the barrier properties gradually from one to four orders of magnitude, compare FIG. 3. Bending of the sample results in slight a loss of barrier properties of only one order of magnitude at a maximum, confirming an enhanced mechanical flexibility of the resulting subsurface barrier layer 22.

(35) The infiltration method described here is significantly distinct from the standard ALD or MLD process in terms of processing as well as resulting material: First, the method described here is neither an ALD nor a MLD process as it does not follow the principles of chemisorbed surface reactions that are controlled temporally through pulse/purge steps. Second, ALD/MLD processes require two precursors and, third, result in a distinct surface coating. The infiltration method described here preferably uses only one precursor, though the use of multiple precursors or reagent gases is possible, and binding sites below the surface are the targets of the described chemical reaction.

(36) The infiltration process described here may be further extended to substitution of typical metal-organic precursors with organic reagents such as fluorinated compounds for combining hydrophobicity and cross-linking in the sub-boundary surface and boundary surface area of the polymer film 2 and of the carrier body 1.

(37) In FIG. 5, the carrier body 1 with the barrier layer 22 is used as a carrier and as an encapsulation for a flexible OLED device 100. The OLED 100 comprises an organic layer sequence 6 which is arranged between two electrodes 7. During operation of the OLED 100, light is generated in the organic layer sequence 6. The mechanically flexible electrodes 7 might be formed of a transmissive material like a transparent conductive oxide, for example, indium tin oxide or zinc oxide, or like a thin metal film. The organic layer sequence 6 is arranged between the two carrier bodies 1, which in each case are a polymer foil.

(38) Other than is shown in FIG. 5, the barrier layer 22 can be present at only one side of the carrier body 1, as is also possible in all other exemplary embodiments. In FIG. 5, the barrier layer 22 is symbolically separated from the remaining parts of the carrier bodies 1 by a dashed line although the barrier layer 22 is not a separately applied layer but an integral part of the polymer film 2.

(39) In FIG. 6, a sectional view of another exemplary embodiment of an OLED 100 is shown. The OLED 100 comprises a first carrier body is which is a carrier of the OLED 100. The first carrier body is is a polymer foil consisting of the polymer film 2a. On both sides of the polymer film 2a, one of the barrier layers 22 is formed. Onto this first carrier body la, the organic layer sequence 6 and the two electrodes 7 are formed.

(40) Afterwards, for encapsulation of the organic layer sequence 6, the second carrier body 1b is formed. For example, a material for the second carrier body 1b is applied in liquid form and then cured to form the second polymer film 2b. Thus, the carrier body 1b can be made of a polymeric lacquer. Then, the barrier layer 22 is formed in the second polymer film 2b, in the same way as described in connection with FIG. 1. With the forming of the barrier layer 22 in the second polymer film 2b, it is possible that the barrier 22 in the first carrier body 1a on a side remote from the organic layer sequence 6 increases in thickness.

(41) In FIG. 7, another method for producing the barrier layer 22 is shown. According to FIG. 7, an apparatus as described in the document DE 10 2012 207 172 A1 is used. Thus, the carrier body 1 and, hence, the polymer film 2 are treated with a rotating head 11 comprising a plurality of gas outlet openings 12. Through these gas outlet openings 12, the reagent gas 4 and the drying gas 9 are alternatingly applied to the polymer film 2. By adjusting a forward speed of the polymer film 2 and a rotational velocity of the rotating head 11, a number of cycles of the method steps of applying the reagent gas 4 and of removing the product gas by means of the drying gas 9, for example, can be set. Thus, a thickness of the barrier layer 22 to be created can be set, too.

(42) The method of FIG. 7 can be performed with the pressures and temperatures as described in connection with FIG. 1. However, preferably normal pressure (about 1013 mbar) is chosen so that the barrier layer can be produced outside a reactor and by means of a roll-to-roll method. For example, a partial pressure of the reagent gas is between 0.5 mbar and 50 mbar in each case, particularly around 5 mbar. Moreover, a high number of repetitions of the method steps is applied but a small exposure time in each single step. The exposure time is long enough to ensure that the reagent gas 4 can diffuse and adhere at least into the topmost polymer layers of the polymer film 2.

(43) Other than shown, more than one reagent gas4 can be used. Further, it is possible to use higher or even lower pressures than stated in the previous paragraph.

(44) FIG. 8 illustrates a concentration c of a constituent of the reagent gas in the finished barrier layer 22. In context of FIG. 1, the constituent is Al or Zn. The concentration c of said constituent gradually decreases in a direction away from the barrier interface 20. A maximum concentration c is reached near the barrier interface 20. A thickness d of the barrier layer 22 is the region in which the concentration c of said constituent is above 1/e of the maximum concentration.

(45) Carrier bodies and polymer films described here can be used for electronic devices and high-end products like OLEDs to perform a cost-efficient encapsulation. Moreover, it is also possible to use such barrier layers, in particular comparably thin barrier layers with a thickness of just a couple of nanometers, in lower-cost products, for example, as packaging material for food. Further, composite carrier bodies can be used in which the barrier layer is applied to only a part of a surface and another part of a surface is covered with a metal, for example.

(46) The invention is not limited by the description using the exemplified embodiments. Rather, the invention includes any new feature and any combination of features included in particular in any combination of features in the claims, even if this feature or this combination itself is not explicitly stated in the claims or exemplified embodiments.