KR102691712B1 - Ink composition for forming OLED functional layer - Google Patents

Abstract

The present invention relates to a functional layer forming polymer compound; A first solvent comprising at least one benzene compound represented by Formula 1 and having an ether functional group having a boiling point of 200°C or higher; and a second solvent having a higher boiling point than the first solvent.
The ink composition of the present invention can secure all ink stability, ejection stability, image of the film surface state, and film flatness by using a specific solvent combination suitable for the polymer-type functional layer forming material.

Description

Ink composition for forming OLED functional layer {Ink composition for forming OLED functional layer}

The present invention relates to an ink composition for forming an OLED functional layer, and more specifically, to an ink composition capable of forming a flat OLED functional layer film.

Organic Light-Emitting Diode (OLED) is a semiconductor whose light-emitting layer is made of a film of an organic compound that emits light in response to electric current. Organic light-emitting diodes may generally be composed of a cathode, an anode, and an organic layer positioned between them, such as a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, and a functional layer including an electron injection layer.

The functional layer of the OLED as described above may be formed through a solution process, for example, by printing a pattern through an inkjet process using an ink composition containing a functional layer forming material and a solvent. In order to manufacture the functional layer of OLED using this solution process, ink stability, discharge stability, film drying property, and film surface characteristics must be met at the same time. Ink compositions mostly consist of solvents, and the selection of solvents is very important in order to satisfy the above characteristics.

For this purpose, the solvent used in the ink composition has sufficient solubility in the functional layer forming material to enable inkization of the functional layer forming material and prevent phase separation even after long-term storage, and has a viscosity suitable for stably discharging ink from the nozzle after printing. It must have physical properties such as a high boiling point that does not evaporate quickly during the film drying process and an appropriate surface tension that does not reduce the spreadability of the ink.

In conventional ink compositions for forming OLED functional layers, benzene-based solvents with a high boiling point of 150°C or higher were used. The benzene-based solvent has the advantage of being able to obtain a flat film of the functional layer due to its good solubility in the functional layer forming material.

Meanwhile, if a functional layer forming material in the form of a polymer rather than a monomer is used in the ink composition, the viscosity may increase and profile control may become difficult. When a benzene-based solvent with a high boiling point is used alone for this polymer-type functional layer forming material, the interaction with the polymer material is insufficient, resulting in lower solubility and dispersibility, resulting in an uneven U-shape. There is a disadvantage in that a film surface is formed. If the film surface is not flat, problems such as brightness differences within the pixel, reduced lifespan of the device, and short-circuiting of the device due to electron transfer leakage occur.

Therefore, formulation of specific solvents that can improve film surface properties when forming a functional layer of polymer material is needed.

The present invention provides an ink composition for forming an OLED functional layer that can secure all ink stability, discharge stability, image of the film surface state, and film flatness by using a specific solvent combination suitable for a polymer-type functional layer forming material. It is for.

In order to solve the above problems, the present invention provides a functional layer forming polymer compound; A first solvent comprising at least one benzene compound represented by the following formula (1) and having an ether functional group having a boiling point of 200°C or higher; and a second solvent having a higher boiling point than the first solvent.

[Formula 1]

In Formula 1,

R ₁ is H or C _1-15 alkyl,

R ₂ and R ₃ are each independently H, C _1-15 alkyl or C _1-15 alkoxy,

X ₁ to X ₅ are each independently H, OH, C _1-15 alkyl or C _1-15 alkoxy,

Additionally, the present invention provides an OLED functional layer formed by applying the ink composition to an OLED substrate using an inkjet method and drying it.

The ink composition for forming an OLED functional layer according to the present invention uses a benzene-based solvent with a boiling point of 200°C or higher and an ether functional group as a first solvent along with a functional layer-forming compound in the form of a polymer. Not only does it increase solubility through good interaction, it improves the dispersibility of the polymer compound in the ink, thereby improving ink stability, ejection stability, and surface leveling effect during film drying, and also uses benzene as a second solvent, which has a higher boiling point than the first solvent. By optimizing membrane dryness and flatness by including the system solvent, a functional layer of a flat membrane can be formed.

Hereinafter, terms or words used in this specification and claims should not be construed as limited to their usual or dictionary meanings, and the inventor appropriately defines the concept of terms in order to explain his or her invention in the best way. It must be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it can be done.

One embodiment of the present invention relates to an ink composition for forming an OLED functional layer comprising a combination of a polymeric functional layer material and a solvent suitable therefor.

Specifically, the ink composition of the present invention includes a functional layer forming polymer compound (a); A first solvent (b) containing at least one benzene compound having an ether functional group having a boiling point of 200°C or higher; and a second solvent (c) with a higher boiling point than the first solvent.

The functional layer forming polymer compound (a) is a main component of the OLED functional layer formed using the ink composition for forming the OLED functional layer according to the present invention, and is capable of exhibiting semiconductor properties, that is, the energy of the conduction band and the valence band. It refers to an organic semiconductor compound with a gap in the range of 0.1 to 4 eV.

The OLED functional layer refers to the Hole Injection Layer (HIL), Hole Transfer Layer (HTL), Electron Transfer Layer (ETL), and Electron Injection Layer, which constitute the OLED device. EIL) and an emission layer (EML), and the functional layer forming material may vary depending on the type of functional layer to be formed.

In one embodiment of the present invention, the functional layer forming polymer compound may include a unit represented by the following formula (3):

[Formula 3]

In Formula 3 above,

L1 is direct bonding; Substituted or unsubstituted phenylene group; Substituted or unsubstituted naphthylene; Substituted or unsubstituted biphenylylene; Substituted or unsubstituted divalent fluorene; or substituted or unsubstituted divalent carbazole,

l1 is an integer from 1 to 10,

Ar1 and Ar2 are the same or different from each other, and are each independently substituted or unsubstituted aryl; Or substituted or unsubstituted heteroaryl,

R1 to R8 are the same as or different from each other, and are each independently hydrogen; heavy hydrogen; halogen; hydroxy; cyano; Substituted or unsubstituted alkyl; Substituted or unsubstituted cycloalkyl; Substituted or unsubstituted alkoxy; Substituted or unsubstituted aryl; Or substituted or unsubstituted heteroaryl,

r4, r6 and r8 are each integers from 1 to 4,

r5 and r7 are each integers from 1 to 3,

When r4 is 2 or more, the 2 or more R4 are the same or different from each other,

When r5 is 2 or more, the 2 or more R5 are the same or different from each other,

When r6 is 2 or more, the 2 or more R6 are the same or different from each other,

When r7 is 2 or more, the 2 or more R7 are the same or different from each other,

When r8 is 2 or more, the 2 or more R8 are the same or different from each other,

When l1 is 2 or more, the 2 or more L1 are the same or different from each other,

n is the number of repetitions of the unit and is an integer from 1 to 10,000.

As the unit represented by Formula 3 includes a curing group in the spiobifluorene core, steric hindrance is minimized and the degree of curing of the polymer compound containing it can be increased. In addition, it has solvent resistance (solvent orthogonality), making a solution process possible.

In one embodiment of the present invention, the unit represented by Formula 3 may be selected from one or more of the following structures.

In the above structure,

n is the number of repetitions of the unit and is an integer from 1 to 10,000.

Additionally, the terminal group of the functional layer forming polymer compound may be hydrogen.

In one embodiment of the present invention, the number average molecular weight of the functional layer forming polymer compound may be 5,000 to 1,000,000 g/mol, specifically 5,000 to 300,000 g/mol. In addition, the functional layer forming polymer compound has a molecular weight distribution of 1 to 10, specifically a molecular weight distribution of 1 to 3.

The molecular weight was measured by GPC using chlorobenzene as a solvent, and the number average molecular weight (Mn) and weight average molecular weight (Mw) were measured, and the molecular weight distribution is calculated by dividing the weight average molecular weight (Mw) by the number average molecular weight (Mn). , that is, it means weight average molecular weight (Mw)/number average molecular weight (Mn).

In the ink composition according to an embodiment of the present invention, the content of the functional layer forming compound is 0.1 to 10% by weight, specifically 0.3 to 7% by weight, and more specifically 0.5 to 3% by weight, based on the total weight of the composition. It may be %. When the content of the functional layer forming material satisfies the above range, the thickness of the OLED functional layer manufactured by the inkjet method can be appropriately adjusted.

On the other hand, ink containing a polymer-type functional layer forming material increases the viscosity and makes profile control difficult, resulting in the formation of an uneven U-shaped film surface.

To overcome this problem, in the present invention, a solvent that can increase the interaction with the polymeric functional layer forming material is used in the ink composition.

Specifically, the first solvent included in the ink composition of the present invention may include one or more benzene compounds having an ether functional group of the following formula (1).

[Formula 1]

In Formula 1,

R ₁ is H or C _1-15 alkyl,

R ₂ and R ₃ are each independently H, C _1-15 alkyl or C _1-15 alkoxy,

X ₁ to X ₅ are each independently H, OH, C _1-15 alkyl or C _1-15 alkoxy,

Since the first solvent of this structure has a benzene core, it has a good interaction with the aromatic molecular structure of the functional layer-forming polymer compound, thereby increasing the solubility of the polymer compound. In addition, since the ether functional group is bonded to the side chain of the benzene ring, intermolecular solvation is possible, allowing the polymer compound used as a functional forming material to be well dispersed in the ink and leveling when drying the film. It is highly effective and can increase flatness.

In one embodiment of the present invention, the boiling point of the first solvent may be 200°C or higher, for example, 200°C to 300°C. If the boiling point of the first solvent is lower than 200°C, the ejection stability of the ink is unstable and may evaporate quickly before going through the vacuum drying process after printing, resulting in uneven film formation.

In one embodiment of the present invention, representative examples of benzene-based compounds having an ether functional group that can be used as the first solvent include the following compounds:

In the ink composition according to an embodiment of the present invention, the content of the first solvent is 50 to 99% by weight, specifically 60 to 99% by weight, and more specifically 70 to 95% by weight, based on the total amount of the composition. It can be. When the content of the first solvent satisfies the above range, sufficient solubility of the functional layer forming material is secured, and clogging of the nozzle during the inkjet process can be prevented.

Meanwhile, the benzene-based compound having an ether functional group used as the first solvent has the possibility of drying faster than desired during the inkjet process, so it is advantageous to mix the first solvent with a second solvent having a higher boiling point. .

Accordingly, the ink composition of the present invention further includes a second solvent having a higher boiling point than the first solvent, thereby optimizing film drying properties and flatness.

In one embodiment of the present invention, the high boiling point second solvent may include one or more benzene compounds having an alkyl, ester, ether, or alcohol functional group represented by the following Chemical Formula 2a or 2b:

[Formula 2a]

[Formula 2b]

In Formula 2,

Y ₁ and Y ₂ are each independently C _1-15 alkyl, substituted or unsubstituted ester (-COO-), substituted or unsubstituted ether (-O-), or substituted or unsubstituted alcohol (R-OH ), and

X ₁ to X ₅ are each independently H, OH, C _1-15 alkyl, or C _1-15 alkoxy.

Specific examples of compounds having the structure of Formula 2a or 2b include isobutyl salicylate, 2-phenylethyl isovalerate, and 2-phenylethyl isobutyrate. , butyl benzoate, pentyl benzoate, hexyl benzoate, phenyl ether, dibenzyl ether, ethyl 4-methoxybenzoate ), ethyl 4-ethoxybenzoate, dimethyl phthalate, diethyl phthalate, decyl benzene, nonyl benzene, 3-phenoxybenzyl Examples include alcohol, isobutyl salicylate, etc., and these compounds can be used alone or in combination of two or more.

Among these compounds, compounds having an ester or ether functional group have excellent selectivity for polymeric functional layer forming materials and can be used more advantageously.

In the ink composition according to an embodiment of the present invention, the high boiling point second solvent is 0.3 to 50% by weight, specifically 1 to 40% by weight, and more specifically 3 to 30% by weight, based on the total amount of the composition. It may be included in % content. When the content of the second solvent satisfies the above range, it is possible to ensure membrane drying properties and prevent the possibility of the membrane becoming uneven due to a difference in drying speed with the first solvent.

The ink composition of the present invention, which uses a specific combination of the first solvent and the second solvent as described above together with a polymer-type functional layer material, has ink stability that maintains the ink in a stable state without solid content precipitation and phase separation in the cartridge for a long time, Ink discharge stability, in which ink is stably discharged from the nozzle of the inkjet equipment, film drying property that does not evaporate quickly for a sufficient period of time after inkjet printing, and a uniform film is formed without surface irregularities during the drying process after film formation, forming pixels. It can simultaneously satisfy the surface characteristics of the ink drying film being formed flatly with the same thickness.

In particular, the ink composition using the specific solvent combination of the present invention suppresses the formation of a U-shaped non-flat film that can occur from ink containing a polymer material, thereby reducing brightness steps within the pixel, reducing the lifespan of the device, Short-circuiting of devices due to electron transfer leakage can be minimized.

Therefore, the present invention provides an OLED functional layer formed by applying the above-described ink composition for forming an OLED functional layer to an OLED substrate by an inkjet method and then drying it.

Specifically, the OLED functional layer includes a printing process of applying an ink composition in which the functional layer material is dissolved to an area where pixels dividing pixels are patterned to a certain size, and a drying process of evaporating the solvent of the applied ink composition. It can be formed through . The method of applying and drying the ink composition can be performed according to a conventional inkjet method without any particular restrictions.

The film flatness of the OLED functional layer is defined by the following equation using the center thickness of the functional layer formed from the ink filled in the pixel, the maximum thickness and the minimum thickness between the pixel and the partition wall. It can be calculated by 1.

[Equation 1]

In the above equation,

H _max is the maximum thickness of the functional layer film in the pixel,

H _min is the minimum thickness of the functional layer film within the pixel,

H _center is the central thickness of the functional layer film within the pixel.

The smaller the flatness value calculated from Equation 1, the more consistent the overall thickness of the film is (i.e., the flatter the film), and the functional layer formed from the ink composition according to the present invention can exhibit excellent flatness of less than 0.3. there is.

Hereinafter, the operation and effects of the invention will be described in more detail through specific examples of the invention. However, this is presented as an example of the invention, and the scope of the invention is not limited by this in any way.

Examples 1 to 20

As shown in Table 1 below, 1,4-bis(methoxymethyl)benzene or (4-methoxybenzyl) methyl ether having a boiling point of 200° C. or higher as the first solvent, And as a second solvent, any one of isobutyl salicylate, 2-phenylethyl isovalerate, 2-phenylethyl isobutyrate, hexyl benzoate, and dibenzyl ether having a higher boiling point than the first solvent in a ratio of 7:3. It was mixed. 0.7 parts by weight of any one of the functional layer forming polymer compounds 1 to 4 below was added to 100 parts by weight of the resulting mixed solvent, and then stirred for 60 minutes to prepare an ink composition for forming an OLED functional layer.

<Functional layer forming polymer compound>

Comparative Examples 1 to 8:

As shown in Table 1 below, an ink composition for forming an OLED functional layer was prepared by carrying out the same process as Example 1, except that a single solvent with a high boiling point was used rather than a solvent combination.

Experiment example:

The following four items were evaluated for the ink compositions prepared in Examples and Comparative Examples.

1) Ink stability evaluation

The ink composition was stored in a sealed ink cartridge at 25° C., atmospheric pressure, and air conditions for one month, and the ink condition was evaluated with the naked eye.

<Evaluation criteria>

○: Very stable state with no solid precipitation or phase separation.

X: Solid content precipitation and phase separation occur

2) Discharge stability evaluation

After filling the ink composition into the inkjet equipment, 10 pℓ (picoliter) droplets were discharged, and the discharge image was observed with the naked eye through the equipment camera.

<Evaluation criteria>

○: Droplets are discharged stably for more than 20 minutes without shaking.

Δ: The droplet is somewhat shaken or the straightness is somewhat poor.

X: No droplets are ejected

3) Membrane image evaluation

After filling the ink composition into the ink cartridge, the ink composition was inkjet printed on the pixel area of the OLED substrate. Subsequently, it was dried at room temperature using vacuum drying equipment, and then heat-dried at 230°C.

The surface image of the formed film was observed through an optical microscope.

<Evaluation criteria>

○: Membrane surface is clean

X: The membrane surface is opaque, the roughness is not uniform, or a white spot due to the aggregation of the solid precipitation/phase separation or the aggregation of the solids is generated.

<Example>

4) Membrane flatness evaluation

Using surface analysis equipment (optical profiler, Nano View E1000, Nanosystem), the center thickness of the functional layer formed from the ink filled in the pixel, the maximum thickness and minimum thickness between the pixel and the partition were measured. Measurements were made, and the flatness was calculated according to Equation 1 below.

[Equation 1]

<Evaluation criteria>

○: Calculated flatness value is less than 0.3

Δ: Calculated flatness value is 0.3 or more to less than 0.5

X: Calculated flatness value is 0.5 or more

The ink compositions obtained in the examples and comparative examples and the evaluation results of the compositions are shown in Table 1 below.

[Table 1-1]

[Table 1-2]

As can be seen in Table 1, an ink composition containing a functional layer forming material in the form of a polymer is mixed with a first solvent having an ether functional group having a boiling point of 200°C or higher and a second solvent having a boiling point higher than the first solvent. While Examples 1 to 20 used were satisfactory ink stability, discharge stability, image of the film surface state, and film flatness, Comparative Examples 1 to 8 using a single solvent with a high boiling point showed poor film flatness.

As the specific parts of the present invention have been described in detail above, it is clear to those skilled in the art that these specific techniques are merely preferred embodiments and do not limit the scope of the present invention. something to do. Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (14)

A functional layer-forming polymer compound containing a unit represented by the following formula (3);
A first solvent comprising at least one benzene compound represented by the following formula (1) and having an ether functional group having a boiling point of 200°C or higher; and
An ink composition for forming an OLED functional layer comprising a second solvent having a higher boiling point than the first solvent:
[Formula 1]

In Formula 1,
R ₁ is H or C _1-15 alkyl,
R ₂ and R ₃ are each independently H, C _1-15 alkyl or C _1-15 alkoxy,
X ₁ to X ₅ are each independently H, OH, C _1-15 alkyl or C _1-15 alkoxy;
[Formula 3]

In Formula 3 above,
L1 is direct bonding; Substituted or unsubstituted phenylene group; Substituted or unsubstituted naphthylene; Substituted or unsubstituted biphenylylene; Substituted or unsubstituted divalent fluorene; or substituted or unsubstituted divalent carbazole,
l1 is an integer from 1 to 10,
Ar1 and Ar2 are the same or different from each other, and are each independently substituted or unsubstituted aryl; Or substituted or unsubstituted heteroaryl,
R1 to R8 are the same as or different from each other, and are each independently hydrogen; heavy hydrogen; halogen; hydroxy; cyano; Substituted or unsubstituted alkyl; Substituted or unsubstituted cycloalkyl; Substituted or unsubstituted alkoxy; Substituted or unsubstituted aryl; Or substituted or unsubstituted heteroaryl,
r4, r6 and r8 are each integers from 1 to 4,
r5 and r7 are each integers from 1 to 3,
When r4 is 2 or more, the 2 or more R4 are the same or different from each other,
When r5 is 2 or more, the 2 or more R5 are the same or different from each other,
When r6 is 2 or more, the 2 or more R6 are the same or different from each other,
When r7 is 2 or more, the 2 or more R7 are the same or different from each other,
When r8 is 2 or more, the 2 or more R8 are the same or different from each other,
When l1 is 2 or more, the 2 or more L1 are the same or different from each other,
n is the number of repetitions of the unit and is an integer from 1 to 10,000. The ink composition for forming an OLED functional layer according to claim 1, wherein the first solvent has a boiling point of 200°C to 300°C. The method of claim 1, wherein the first solvent is p-anisaldehyde dimethyl acetal, 1,4-bis(methoxymethyl)benzene, (4) -Methoxybenzyl) methyl ether ((4-methoxybenzyl) methyl ether), or a mixture of two or more thereof, an ink composition for forming an OLED functional layer. The ink composition for forming an OLED functional layer according to claim 1, wherein the second solvent includes one or more benzene compounds having an alkyl, ester, ether, or alcohol functional group represented by the following formula 2a or 2b:
[Formula 2a]

[Formula 2b]

In Formula 2,
Y ₁ and Y ₂ are each independently C _1-15 alkyl, substituted or unsubstituted ester (-COO-), substituted or unsubstituted ether (-O-), or substituted or unsubstituted alcohol (R-OH ), and
X ₁ to X ₅ are each independently H, OH, C _1-15 alkyl, or C _1-15 alkoxy. The method of claim 4, wherein the second solvent is isobutyl salicylate, 2-phenylethyl isovalerate, 2-phenylethyl isobutyrate, butyl benzoate. Butyl benzoate, pentyl benzoate, hexyl benzoate, phenyl ether, dibenzyl ether, ethyl 4-methoxybenzoate, ethyl 4-ethoxybenzoate, dimethyl phthalate, diethyl phthalate, decyl benzene, nonyl benzene, 3-phenoxybenzyl alcohol, iso An ink composition for forming an OLED functional layer containing butyl salicylate or a mixture of two or more thereof. delete The ink composition for forming an OLED functional layer according to claim 1, wherein the unit represented by Formula 3 is selected from one or more of the following structures:






In the above structure,
n is the number of repetitions of the unit and is an integer from 1 to 10,000. The ink composition for forming an OLED functional layer according to claim 1, wherein the functional layer forming polymer compound has a number average molecular weight of 5,000 to 1,000,000 g/mol. The ink composition for forming an OLED functional layer according to claim 1, wherein the functional layer forming polymer compound is contained in an amount of 0.1 to 10% by weight based on the total amount of the composition. The ink composition for forming an OLED functional layer according to claim 1, wherein the first solvent is contained in an amount of 50 to 90% by weight based on the total amount of the composition. The ink composition for forming an OLED functional layer according to claim 1, wherein the second solvent is included in an amount of 0.3 to 50% by weight based on the total amount of the composition. An OLED functional layer formed by applying the ink composition according to claim 1 to an OLED substrate using an inkjet method and drying it. The OLED functional layer of claim 12, wherein the OLED functional layer satisfies a film flatness value of less than 0.3 calculated by Equation 1 below:
[Equation 1]

In the above equation,
H _max is the maximum thickness of the functional layer film in the pixel,
H _min is the minimum thickness of the functional layer film within the pixel,
H _center is the central thickness of the functional layer film within the pixel. The method of claim 12, wherein the OLED functional layer includes a hole injection layer (HIL), a hole transfer layer (HTL), an electron transfer layer (ETL), and an electron injection layer that constitute the OLED device. An OLED functional layer including an Electron Injection Layer (EIL), an Emission Layer (EML), or a combination of two or more thereof.