TW201735984A - Desiccant, sealing structure and organic electroluminescent device effectively suppressing the occurrence of black spots in organic electroluminescent device for a longer period of time - Google Patents

Abstract

The present invention discloses a desiccant, containing adhesive resin and oxide particles dispersed in the adhesive resin. At least a portion of the oxide particles transform into secondary particles. The secondary particles comprise a plurality of primary particles. The average particle size of the oxide particles is lower than 4μm. The specific surface area of the oxide particles is 5 m2/g to 60 m2/g.

Description

Desiccant, sealing structure and organic electroluminescent element

The present invention relates to a desiccant, a sealing structure and an organic electroluminescent element.

The organic EL (Electroluminescence) element generally has a light-emitting portion including a film containing an organic light-emitting material, that is, an organic layer, and a pair of electrodes sandwiching the organic layer. The organic EL element is a self-luminous element that emits light (fluorescent or phosphorescent) by injecting a hole and an electron into a thin film and recombining it to generate an exciton and deactivating the exciton. .

Regarding the organic EL element, it is expected to prevent the generation and growth of the non-light-emitting portion of the organic layer called a black dot. As a main cause of black spots, it is known that water and oxygen have a large influence, and even if a trace amount of water is present, it has a great influence on the generation of black spots.

Therefore, various studies have been conducted on a method of preventing moisture and oxygen from intruding into an organic EL element. For example, a hollow sealing structure in which an organic layer and an electrode are sealed in an airtight container in a dry inert gas atmosphere and a desiccant is enclosed in an airtight container is proposed. For example, Patent Document 1 discloses an organic EL device having a desiccant-containing layer on the inner surface of a sealing cover, the desiccant-containing layer containing a powder of phosphorus pentoxide and a low-temperature curing epoxy-based adhesive.

On the other hand, as a dehumidifying agent, quicklime (calcium oxide) is sometimes used. For example, Patent Document 2 discloses that quicklime preferably contains 50% by mass or more of particles having a particle diameter of 75 μm or more.

(Patent Document) Patent Document 1: Japanese Laid-Open Patent Publication No. 2001-035659. Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-335987.

A main object of the present invention is to provide a desiccant capable of effectively suppressing generation of black spots of an organic EL element for a longer period of time.

In one aspect of the invention, there is provided a desiccant comprising a binder resin and oxide particles dispersed in a binder resin, at least a portion of the oxide particles forming secondary particles comprising a plurality of primary particles, oxide particles The average particle diameter is 4 μm or less, and the specific surface area of the oxide particles is 5 to 60 m ² /g. According to the above desiccant, black spots can be effectively suppressed from occurring in the organic EL element for a longer period of time.

The present invention can also provide a composition for use as a desiccant (application) for preparing a desiccant (application) comprising a binder resin and oxide particles dispersed in a binder resin, oxidizing At least a portion of the particles form a secondary particle comprising a plurality of primary particles, the oxide particles having an average particle diameter of 4 μm or less, and the oxide particles having a specific surface area of 5 to 60 m ² /g.

Further, the oxide particles may have a specific surface area of 5 to 35 m ² /g. When the specific surface area of the oxide particles is in the above range, the water catching performance of the desiccant can be improved. The binder resin may also contain an anthrone resin based on the same viewpoint.

According to another aspect of the present invention, a sealing structure including: a pair of substrates disposed to face each other; a sealant that seals an outer peripheral portion of the pair of substrates; and a desiccant layer on the inner side of the sealant It is disposed between the pair of substrates and includes the aforementioned desiccant.

According to still another aspect of the invention, there is provided an organic EL device comprising: an element substrate; a sealing substrate disposed opposite to the element substrate; a sealant sealing the element substrate and an outer peripheral portion of the sealing substrate; and a laminate Provided on the inner side of the sealant and disposed on the element substrate, and having an organic layer and a pair of electrodes sandwiching the organic layer; a desiccant layer on the inner side of the sealant and disposed on the sealing substrate, And including the aforementioned desiccant.

According to the desiccant according to an aspect of the invention, it is possible to effectively suppress the generation of black spots of the organic EL element for a longer period of time. Since the oxide particles are dispersed in the binder resin, the oxide particles as the water-trapping component can be uniformly dispersed.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

In the present specification, "primary particles" means particles which are integrally formed into a single particle when judged from an apparent geometric form. "Secondary particles" include a plurality of primary particles. Usually, secondary particles are formed by aggregating a plurality of primary particles.

(Drying Agent) An embodiment of the desiccant comprises: a binder resin and oxide particles dispersed in the binder resin.

[Oxide Particles] At least a part of the oxide particles contained in the desiccant form secondary particles including a plurality of primary particles. When the oxide particles form secondary particles, for example, it can be confirmed by observing oxide particles by a scanning electron microscope (SEM) or the like. In the oxide particles contained in the desiccant, for example, 10 to 100% by mass or 50 to 100% by mass of the secondary particles may be formed. According to the findings of the present inventors, the case where the oxide particles form secondary particles contributes to suppressing the generation of black spots. Also, it is difficult for the oxide particles forming the secondary particles to become large in volume, which contributes to achieving sufficient water trapping performance with a smaller volume of desiccant.

The average particle diameter of the oxide particles may be 4 μm or less. When the average particle diameter of the oxide particles is 4 μm or less, it is helpful to suppress generation of black spots in the organic EL element. From the same viewpoint, the average particle diameter of the oxide particles may be 3.9 μm or less or 3.8 μm or less. The lower limit of the average particle diameter of the oxide particles is not particularly limited, and may be, for example, 0.5 μm or more or 1 μm or more. For example, the average particle diameter of the oxide particles can be controlled by adjusting the calcination temperature, the calcination time, the pulverization conditions, and the like of the oxide particles.

In the present specification, the average particle diameter of the oxide particles means the median of the volume distribution measured by a dynamic light scattering particle size analyzer. The average particle diameter is an average particle diameter of the entire oxide particles including the primary particles and the secondary particles, and the average particle diameter is obtained by dispersing the oxide particles in a predetermined dispersant. measuring.

The average particle diameter of the primary particles of the oxide particles is not particularly limited, and may be, for example, 0.5 μm or less or 0.1 μm or less. The average particle diameter of the primary particles of the oxide particles may be 0.01 μm or more. The average particle diameter of the primary particles of the oxide particles may be an average value of the particle diameter (maximum width) of the primary particles existing in the observation field when the oxide particles are observed by an electron microscope or the like.

The oxide particles comprise an inorganic oxide that imparts water trapping properties to the oxide particles. The oxide particles usually contain 80% by mass or more or 90% by mass or more of the inorganic oxide based on the mass of the oxide particles. The desiccant may contain one oxide particle or two or more oxide particles different in composition. The oxide particles include, for example, selected from the group consisting of phosphorus pentoxide (P ₄ O ₁₀ ), magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), barium oxide (BaO), and aluminum oxide (Al ₂ O ₃ ). At least one inorganic oxide in the group formed. The oxide particles may also contain at least one alkaline earth metal oxide selected from the group consisting of magnesium oxide, calcium oxide, cerium oxide, and cerium oxide, and may also contain calcium oxide.

The specific surface area of the oxide particles is 5 to 60 m ² /g, and may be 5 to 35 m ² /g. If the specific surface area is 5 to 60 m ² /g, the desiccant can have more excellent water trapping performance. From the same viewpoint, the specific surface area of the oxide particles may be 10 m ² /g or more or 15 m ² /g or more, or may be 50 m ² /g or less, 40 m ² /g or less, or 35 m ² /g or less.

In the present specification, the specific surface area of the oxide particles means the total specific surface area of the oxide particles including the primary particles and the secondary particles, which are measured by the BET method.

The content of the oxide particles in the desiccant may be 10% by mass or more, 20% by mass or more, or 30% by mass or more based on the total mass of the desiccant. The content of the oxide particles may be 80% by mass or less, 70% by mass or less, or 60% by mass or less.

The oxide particles containing calcium oxide can be obtained, for example, by the following steps, which comprise the steps of: oxidizing lime (CaO) to obtain slaked lime (Ca(OH) ₂ ), and calcining the hydrated lime to obtain quicklime And crushing the quicklime. The temperature at which the slaked lime is calcined may be 300 to 600 °C. The simmering time can be 1 to 20 hours.

By pulverizing the quicklime, the average particle diameter of the oxide particles can be adjusted to a desired range. For example, the quicklime may be dispersed in a solvent such as heptane and pulverized by a ball mill or the like.

The diameter of the primary particles of the oxide particles containing calcium oxide has a tendency to depend on primary particles of slaked lime. By subjecting the quicklime to a hydrogenation treatment, the diameter of the primary particles of the oxide particles can be adjusted to a desired range.

[Binder Resin] The binder resin is not particularly limited as long as it can disperse oxide particles. When mixing with the oxide particles, a binder resin capable of forming a paste can be used. By using a paste of a desiccant, a desiccant layer in which oxide particles are uniformly dispersed can be easily formed.

The binder resin may, for example, comprise at least one resin selected from the group consisting of polyvinyl chloride resins, phenol resins, anthrone resins, epoxy resins, polyester resins, urethane resins, propylene resins, and olefin resins. The binder resin may also contain an anthrone resin.

The mass ratio of the oxide particles to the binder resin in the desiccant is not particularly limited and may be 1:4 to 4:1 or 1:2 to 2:1. When the mass ratio of the oxide particles and the binder resin is within the above range, the desiccant layer described later tends to be easily formed.

The desiccant may contain, for example, an organic metal compound or a curable resin in addition to the oxide particles and the binder resin.

The desiccant can be produced by a method including a step of mixing the oxide particles and the binder resin. The above mixing operation can be carried out by centrifugal separation or the like. The rotational speed of the centrifugal separation may be, for example, 100 to 3000 rpm. The centrifugation time can be from 1 to 60 minutes.

(Sealing Structure) The sealing structure of the present embodiment includes a pair of substrates disposed to face each other, a sealant that seals the outer peripheral portions of the pair of substrates, and a drying agent disposed inside the sealant between the pair of substrates Agent layer. The desiccant layer may contain the desiccant according to the above embodiment. The desiccant layer may fill the sealed space (the space between the pair of substrates and inside the sealant).

The sealing structure of this embodiment is particularly suitable for use when packaging a device that is susceptible to moisture. As such a device, for example, an organic electronic device such as an organic EL device, an organic semiconductor, or an organic solar cell can be exemplified.

(Organic EL Element) Fig. 1 is a schematic cross-sectional view showing an embodiment of an organic EL element. The organic EL element 1 shown in Fig. 1 is an organic EL element having a so-called hollow sealing structure, and is composed of an element substrate 2, a sealing substrate 3 opposed to the element substrate 2, and a device a laminate on the substrate 2 (the laminate has an organic layer 4 and an anode 5 and a cathode 6 sandwiching the organic layer 4), a sealing agent 8 for sealing the element substrate 2 and an outer peripheral portion of the sealing substrate 3, and a sealant 8 The inner side of the desiccant layer 7 is provided on the sealing substrate 3. The desiccant layer 7 may contain the desiccant of the above embodiment.

In the organic EL element 1, a conventional structure other than the desiccant layer 7 can be used. An example of the organic EL element 1 will be briefly described below.

The element substrate 2 is made of a rectangular glass substrate having insulating properties and light transmissivity. On the element substrate 2, an anode 5 (electrode) is formed of a transparent conductive material, that is, ITO (Indum Tin Oxide). The anode 5 is formed, for example, by forming an ITO film formed on the element substrate 2 by a PVD (Physical Vapor Deposition) method such as a vacuum vapor deposition method or a sputtering method, and performing etching by photolithography. The pattern is shaped to form the anode 5. A part of the anode 5 as an electrode is led out to the end of the element substrate 2 and connected to a drive circuit (not shown).

On the upper surface of the anode 5, a film including an organic light-emitting material, that is, an organic layer 4, is laminated by a PVD method such as a vacuum deposition method or a resistance heating method. The organic layer 4 may be formed of a single layer or a plurality of layers having different functions. The organic layer 4 in the present embodiment has a four-layer structure in which a hole injection layer 4a, a hole transport layer 4b, a light-emitting layer 4c, and an electron transport layer 4d are sequentially laminated from the anode 5 side. The hole injection layer 4a is formed, for example, of copper phthalocyanine (CuPc) having a film thickness of several tens of nanometers. The hole transport layer 4b is, for example, bis[N-(1-naphthyl)-N-phenyl]benzidine having a film thickness of several tens of nanometers, Formed by α-NPD). The light-emitting layer 4c is formed, for example, of tris(8-hydroxyquinoline)aluminum (Alq ₃ ) having a film thickness of several tens of nanometers. The electron transport layer 4d is formed, for example, of lithium fluoride (LiF) having a film thickness of several nanometers. Further, the laminate in which the anode 5, the organic layer 4, and the cathode 6 to be described later are laminated in this order constitutes a light-emitting portion.

On the upper surface of the organic layer 4 (electron transport layer 4d), a cathode 6 (electrode) which is a metal thin film is formed by a PVD method such as a vacuum deposition method. The material of the metal thin film may, for example, be a metal monomer having a small work function such as Al (aluminum), Li (lithium), Mg (magnesium) or In (indium) or Al-Li (aluminum-lithium) or Mg- An alloy such as Ag (magnesium-gold) having a small work function. The film thickness of the cathode 6 is, for example, tens of nanometers to several hundreds of nanometers (preferably 50 nm to 200 nm). A part of the cathode 6 is led out to the end of the element substrate 2 and connected to a drive circuit (not shown).

The sealing substrate 3 is disposed to face the element substrate 2 via the organic layer 4, and the outer peripheral portions of the element substrate 2 and the sealing substrate 3 are sealed by the sealant 8. As the sealant, for example, an ultraviolet curable resin can be used. Further, the desiccant layer 7 is provided inside the sealant 8 and on a part of the sealing substrate 3 or on the entire sealing substrate 3. The desiccant layer 7 is formed by applying the desiccant of the above-described embodiment. The film thickness of the desiccant layer 7 is formed to be 1 to 300 μm.

(Manufacturing Method of Organic EL Element) First, a laminate in which an organic layer 4 or the like (an electrode is not illustrated) is laminated on the element substrate 2.

Next, the desiccant of this embodiment is applied onto the separately prepared sealing substrate 3 using a coater to form a desiccant layer 7. Further, the sealant 8 is applied in such a manner as to surround the desiccant coated on the sealing substrate 3 using a coater. These operations are preferably carried out in a glove box that has been replaced with nitrogen having a dew point of -76 °C.

Next, the element substrate 2 on which the organic layer 4 or the like is laminated and the sealing substrate 3 are bonded together. The organic EL element 1 of the present embodiment is produced by irradiating the bonded substrates with UV (ultraviolet rays) and heating to about 80 ° C for sealing.

(Embodiment) Hereinafter, the present invention will be more specifically described based on examples. However, the invention is not limited to the embodiments.

1. Synthesis of Oxide Particles [Oxide Particles 1] Commercially available oxide particles were used as the oxide particles 1. The oxide particles 1 did not form secondary particles. The oxide particles 1 had an average particle diameter of 2.5 μm and a specific surface area of 2.5 m ² /g. Dispersing an oxide particle in a dispersing agent (alcohol) to prepare a dispersion for measurement, and using the dispersion to pass a dynamic light scattering particle size analyzer to obtain a median volume distribution as an average of oxide particles Record the particle size. Further, the oxide particles were dried at 120 ° C for 8 hours or more under reduced pressure to 500 Pa or less, and then only the isotherm adsorption line on the nitrogen adsorption side in the liquid nitrogen temperature was obtained. The isothermal adsorption line was analyzed by the BET method to determine the specific surface area of the oxide particles. The average particle diameter and specific surface area of other oxide particles were also measured in the same manner.

[Oxide Particles 2] A quicklime powder (purity: 99% by mass) having a specific surface area of 17.1 m ² /g was dispersed in a solvent (heptane) and pulverized by a ball mill. After the pulverization, distillation was carried out to remove the solvent, and oxide particles 2 were obtained. Observation of the oxide particles 2 by a scanning electron microscope (SEM) revealed that almost all of the oxide particles formed secondary particles containing a plurality of primary particles. The oxide particles 2 had an average particle diameter of 2.5 μm and a specific surface area of 5.3 m ² /g.

[Oxide Particles 3] A slaked lime powder (purity: 73.2% by mass) having a specific surface area of 47 m ² /g was placed in a crucible furnace, and calcined at a temperature of 450 ° C for 3 hours to prepare a raw lime powder. The obtained quicklime powder was dispersed in a solvent (heptane) and pulverized by a ball mill. After the pulverization, the solvent is removed to obtain oxide particles 3. Observation of the oxide particles 3 by a scanning electron microscope (SEM) revealed that almost all of the oxide particles formed secondary particles containing a plurality of primary particles. The oxide particles 3 had an average particle diameter of 3.8 μm and a specific surface area of 34.6 m ² /g.

[Oxide Particles 4] A slaked lime powder (purity: 73.2% by mass) having a specific surface area of 47 m ² /g was placed in a crucible furnace, and the pressure was set to 5 × 10 ^-3 Pa or less by a vacuum pump, and 450 ° C was used. The temperature was calcined for 3 hours to prepare oxide particles 4. The oxide particles 4 form secondary particles containing a plurality of primary particles. The oxide particles 4 had an average particle diameter of 4.1 μm and a specific surface area of 82.5 m ² /g.

[Oxide Particles 5] A slaked lime powder (purity: 73.3 mass%) having a specific surface area of 35 m ² /g was placed in a crucible furnace, and the pressure was set to 5 × 10 ^-3 Pa or less by a vacuum pump, and 450 ° C was used. The temperature was calcined for 3 hours to prepare oxide particles 5. The oxide particles 5 form secondary particles containing a plurality of primary particles. The oxide particles 5 had an average particle diameter of 5 μm and a specific surface area of 76.1 m ² /g.

[Oxide particles 6] A slaked lime powder (purity: 73.3 mass%) having a specific surface area of 35 m ² /g was replaced with a slaked lime powder having a specific surface area of 15 m ² /g (purity: 74.7 mass%), and other than oxidation The oxide particles 6 were prepared in the same manner as the particles 5 . The oxide particles 6 form secondary particles comprising a plurality of primary particles. The oxide particles 6 had an average particle diameter of 5 μm and a specific surface area of 68.9 m ² /g.

[Oxide Particles 7] A slaked lime powder (purity: 73.3 mass%) having a specific surface area of 35 m ² /g was replaced with a slaked lime powder having a specific surface area of 12 m ² /g (purity: 74.2% by mass), and other than oxidation The oxide particles 7 were prepared by the same preparation method of the particles 5 . The oxide particles 7 form secondary particles comprising a plurality of primary particles. The oxide particles 7 had an average particle diameter of 5 μm and a specific surface area of 67.2 m ² /g.

2. The preparation of the desiccant was carried out by mixing the oxide particles 1 to 7 and the fluorenone resin in a mass ratio of 1:1, and centrifugally stirring at 1000 rpm for 5 minutes, thereby obtaining Example 1 shown in Table 1. 2 and the desiccants of Comparative Examples 1 to 5.

3. It was evaluated that a film having a transparent conductive material was formed on the element substrate by a sputtering method to have a film thickness of 140 nm. The ITO film is etched by photolithography to form a predetermined pattern shape, thereby forming an anode. Use resistance heating. Copper phthalocyanine (CuPc) was formed on the upper surface of the formed anode to form a film having a film thickness of 70 nm, thereby forming a hole injection layer, and bis[N-(1-naphthyl) was formed on the upper surface of the hole injection layer. -N-phenyl]benzidine (α-NPD) forms a film having a film thickness of 30 nm to form a hole transport layer, followed by tris(8-hydroxyquinoline)aluminum (Alq ₃ ) on the upper surface of the hole transport layer A film having a film thickness of 50 nm was formed to form a light-emitting layer. Next, lithium fluoride (LiF) was formed on the upper surface of the light-emitting layer to form a film having a film thickness of 7 nm, thereby forming an electron transport layer, and aluminum was physically deposited on the surface of the electron transport layer at a film thickness of 150 nm to serve as a cathode. Thereby, a laminate in which an anode, an organic layer (hole injection layer/hole transport layer/light-emitting layer), an electron transport layer, and a cathode are laminated in this order is formed on the element substrate. Next, in a glove box replaced with nitrogen having a dew point of -76 ° C, the desiccant of each of the examples or the comparative examples was applied to the central portion of the sealing substrate by a coater to form a desiccant layer. Further, a sealant composed of an ultraviolet curable resin is applied onto the sealing substrate so as to surround the applied desiccant by a coater. Then, the element substrate and the sealing substrate are bonded to each other such that the laminate, the desiccant layer, and the sealant are located inside. In this state, the outer peripheral portion of the element substrate and the sealing substrate is sealed by irradiation with ultraviolet rays and heating to 80° C., whereby an organic EL element having a hollow sealing structure in which a desiccant is provided in an airtight space surrounded by the sealant is obtained. The obtained organic EL device was placed in a high-temperature and high-humidity environment of 85 ° C and 85% RH, and the change in the light-emitting area ratio with respect to the elapsed time was followed.

Fig. 2 is a graph showing the relationship between the light-emitting area ratio and the elapsed time of the organic EL element in a high-temperature and high-humidity environment. The organic EL device including the desiccant of Examples 1 and 2 showed a light-emitting area ratio of 80% or more after 500 hours passed, and the light-emitting area ratio was maintained at 75% or more after 1000 hours passed. On the other hand, in the organic EL device including the desiccant of Comparative Examples 1 to 5, the light-emitting area ratio was lowered to less than 80% at the time point of 500 hours elapsed. From the results, it is understood that the desiccant of the present invention can sufficiently suppress the generation of black spots in the organic EL element.

1‧‧‧Organic EL components
2‧‧‧ element substrate
3‧‧‧Seal substrate
4‧‧‧Organic layer
4a‧‧‧ hole injection layer
4b‧‧‧ hole transport layer
4c‧‧‧Lighting layer
4d‧‧‧Electronic transport layer
5‧‧‧Anode
6‧‧‧ cathode
7‧‧‧Drying agent layer
8‧‧‧Sealant

Fig. 1 is a schematic cross-sectional view showing an organic EL device according to an embodiment of the present invention. Fig. 2 is a graph showing the relationship between the light-emitting area ratio and the elapsed time of the organic EL element in a high-temperature and high-humidity environment.

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Claims (5)

A desiccant comprising a binder resin and oxide particles dispersed in the binder resin; wherein at least a portion of the foregoing oxide particles form secondary particles, the secondary particles comprising a plurality of primary particles; the foregoing oxide particles The average particle diameter is 4 μm or less; and the specific surface area of the oxide particles is 5 to 60 m ² /g. The desiccant according to claim 1, wherein the oxide particles have a specific surface area of 5 to 35 m ² /g. The desiccant according to claim 1 or 2, wherein the binder resin comprises an anthrone resin. A sealing structure comprising: a pair of substrates arranged to face each other; a sealant sealing an outer peripheral portion of the pair of substrates; and a desiccant layer disposed inside the sealant and on the pair of substrates The desiccant of any one of claims 1 to 3 is included. An organic electroluminescence device comprising: an element substrate; a sealing substrate disposed opposite to the element substrate; a sealant sealing the outer peripheral portion of the element substrate and the sealing substrate; and a laminate having the seal An inner side of the agent and disposed on the element substrate, and having an organic layer and a counter electrode sandwiching the organic layer; and a desiccant layer on the inner side of the sealant and disposed on the sealing substrate, and The desiccant of any one of claims 1 to 3 is included.