KR20210119027A - Adhesive composition and adhesive film for foldable display - Google Patents

Abstract

The present invention provides an adhesive composition and an adhesive film for a foldable display. The adhesive composition of the present invention comprises a high molecular weight copolymer and a low molecular weight copolymer. The adhesive film for foldable display comprises a cured product of the adhesive composition, and thus has excellent deformability and resilience, and excellent adhesive force.

Description

Adhesive composition and adhesive film for foldable display {ADHESIVE COMPOSITION AND ADHESIVE FILM FOR FOLDABLE DISPLAY}

The present invention relates to a pressure-sensitive adhesive composition and an adhesive film for a foldable display. Specifically, it relates to an adhesive composition having excellent folding properties and an adhesive film for a foldable display.

An adhesive film for adhering various display members is used in a foldable display. Since such an adhesive film is used in a foldable display, it is required that sufficient deformation is possible by an external force in order to relieve the stress applied to each layer during folding, and there is no problem in that members such as a panel are not broken during folding.

In addition, at the same time, it must be satisfied that there is no lifting in each layer because it has excellent recovery power when unfolding and at the same time maintains adhesive force.

In order to have a property of relieving stress, it is advantageous to use a pressure-sensitive adhesive layer having a low storage modulus, but there is a problem such as a wrinkle during unfolding due to a low recovery force.

In order to solve this problem, conventionally, a free volume agent is added to the pressure-sensitive adhesive layer. By adding a free-volume agent, it was possible to achieve a high strain rate while maintaining recovery, but another problem occurred due to the lower adhesive strength, causing the panel to float.

There is a need for a pressure-sensitive adhesive film having sufficient deformability and recoverability, high adhesion, and excellent optical properties.

An object of the present invention is to provide an adhesive composition having excellent folding properties and an adhesive film for a foldable display.

According to one aspect of the present invention, a high molecular weight copolymer having a weight average molecular weight of 1.5 million to 2.5 million; and a low molecular weight copolymer having a weight average molecular weight of 5,000 to 80,000, wherein the high molecular weight copolymer is more than 80% by weight based on the total weight of the high molecular weight copolymer and the low molecular weight copolymer and 95% by weight %, wherein the high molecular weight copolymer is polymerized from a first monomer mixture comprising a first alkyl (meth) acrylate and a first hydroxy alkyl (meth) acrylate, and the first monomer The mixture is to include the first hydroxy alkyl (meth) acrylate in an amount of 10 to 20 wt %, and the low molecular weight copolymer is a second alkyl (meth) acrylate and a second hydroxy alkyl (meth) It is polymerized from a second monomer mixture containing an acrylate, and the second monomer mixture contains more than 0 and 5 wt% or less of the second hydroxyalkyl (meth)acrylate, and the first alkyl (meth) The acrylate and the second alkyl (meth) acrylate include at least one of alkyl (meth) acrylates having an alkyl group having 8 to 20 carbon atoms, and the first hydroxy alkyl (meth) acrylate and the second The hydroxy alkyl (meth) acrylate is provided with a pressure-sensitive adhesive composition comprising at least one of hydroxy alkyl (meth) acrylate having an alkyl group having 4 to 6 carbon atoms.

According to another aspect of the present invention, there is provided an adhesive film for a foldable display including a cured product of the pressure-sensitive adhesive composition.

The pressure-sensitive adhesive composition according to an embodiment of the present invention can provide an adhesive film for a foldable display that has a sufficient strain for stress relief while maintaining a storage modulus and has excellent adhesive strength and optical properties.

The pressure-sensitive adhesive film for a foldable display including the cured product of the pressure-sensitive adhesive composition according to another embodiment of the present invention has a sufficient strain rate for stress relief while maintaining storage modulus, and has excellent adhesion and optical properties.

1 is a schematic diagram of a cross-section of a specimen prepared for a folding test.

In the present specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

Hereinafter, the present invention will be described in more detail.

According to an embodiment of the present invention, a high molecular weight copolymer having a weight average molecular weight of 1.5 million to 2.5 million; and a low molecular weight copolymer having a weight average molecular weight of 5,000 to 80,000, wherein the high molecular weight copolymer is more than 80% by weight based on the total weight of the high molecular weight copolymer and the low molecular weight copolymer and 95% by weight %, wherein the high molecular weight copolymer is polymerized from a first monomer mixture comprising a first alkyl (meth) acrylate and a first hydroxy alkyl (meth) acrylate, and the first monomer The mixture is to include the first hydroxy alkyl (meth) acrylate in an amount of 10 to 20 wt %, and the low molecular weight copolymer is a second alkyl (meth) acrylate and a second hydroxy alkyl (meth) It is polymerized from a second monomer mixture containing an acrylate, and the second monomer mixture contains more than 0 and 5 wt% or less of the second hydroxyalkyl (meth)acrylate, and the first alkyl (meth) The acrylate and the second alkyl (meth) acrylate include at least one of alkyl (meth) acrylates having an alkyl group having 8 to 20 carbon atoms, and the first hydroxy alkyl (meth) acrylate and the second The hydroxyalkyl (meth)acrylate is provided with a pressure-sensitive adhesive composition comprising at least one of hydroxyalkyl (meth)acrylate having an alkyl group having 4 to 6 carbon atoms.

1. High molecular weight copolymer

According to one embodiment of the present invention, the pressure-sensitive adhesive composition may include a high molecular weight copolymer as a main component. The high molecular weight copolymer can provide a pressure-sensitive adhesive composition having excellent adhesion, which is the basic performance of the pressure-sensitive adhesive, maintaining the storage modulus in a wide temperature range, and having excellent recovery characteristics. By maintaining a high storage modulus at a high temperature, the pressure-sensitive adhesive composition is prevented from being excessively stretched at a high temperature, thereby preventing a bleed-out problem.

The high molecular weight copolymer may have a weight average molecular weight of 1.5 million to 2.5 million, 1.7 million to 2.3 million, or 1.9 million to 210 thousand. When a high molecular weight copolymer having a weight average molecular weight within the above range is used, the internal bonding strength of the pressure-sensitive adhesive composition is excellent, and interpolymer entanglement does not occur, so that the pressure-sensitive adhesive can be applied smoothly.

According to one embodiment of the present invention, the high molecular weight copolymer is, based on the total weight of the high molecular weight copolymer and the low molecular weight copolymer, the pressure-sensitive adhesive in an amount of more than 80% by weight and less than 95% by weight or 85% by weight to 90% by weight. may be included in the composition. When included in the pressure-sensitive adhesive composition in an amount within the above range, the creep strain rate is high, and when applied to a foldable display, bubbles or defects such as lifting and cracking do not occur, so that durability may be excellent.

The high molecular weight copolymer is polymerized from a first monomer mixture comprising a first alkyl (meth) acrylate and a first hydroxy alkyl (meth) acrylate, and the first alkyl (meth) acrylate has 8 carbon atoms. to at least one of alkyl (meth)acrylates having an alkyl group of 20 to 1, wherein the first hydroxy alkyl (meth)acrylate is one of hydroxyalkyl (meth)acrylates having an alkyl group having 4 to 6 carbon atoms. includes more than one species.

When a high molecular weight copolymer is prepared by polymerizing an alkyl (meth) acrylate and a hydroxy alkyl (meth) acrylate having a carbon number within the above range, an adhesive film having an appropriate level of storage modulus can be prepared, and a low temperature When the foldable adhesive film is manufactured by improving the strain and recovery in the area, the folding performance of the adhesive film can be improved.

According to one embodiment of the present invention, the glass transition temperature of the first alkyl (meth) acrylate may be -60 ℃ or less or -100 ℃ to -60 ℃. When an alkyl (meth)acrylate having a glass transition temperature within the above range is used, it is possible to prevent deterioration of deformability due to excessively high storage modulus.

According to one embodiment of the present invention, the glass transition temperature of the first hydroxy alkyl (meth) acrylate may be -30 ℃ or less or -50 ℃ to -30 ℃. When a hydroxyalkyl (meth)acrylate having a glass transition temperature within the above range is used, adhesion and internal bonding strength may increase.

According to one embodiment of the present invention, the first alkyl (meth) acrylate is ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, iso It may include at least one of nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, tetradecyl (meth) acrylate, and isodecyl (meth) acrylate.

According to one embodiment of the present invention, the first hydroxy alkyl (meth) acrylate may include hydroxybutyl (meth) acrylate.

According to one embodiment of the present invention, the first monomer mixture comprises 10 wt% to 20 wt%, 15 wt% to 20 wt%, or 18 wt% to 20 wt% of the first hydroxy alkyl (meth)acrylate can be included as When the high molecular weight copolymer is polymerized with a monomer mixture containing hydroxyalkyl (meth)acrylate in an amount within the above range, the storage stability may be excellent and adhesion to the adherend may be excellent.

According to one embodiment of the present invention, the first monomer mixture contains the first alkyl (meth)acrylate in an amount of 80 wt% to 90 wt%, 80 wt% to 85 wt%, or 80 wt% to 82 wt% can do.

2. low molecular weight copolymer

According to one embodiment of the present invention, the pressure-sensitive adhesive composition further comprises a low molecular weight copolymer. The low molecular weight copolymer can improve deformability and recovery by acting as a free volumizing agent, and specifically, it has fewer functional groups, acts as a branched chain in the high molecular weight copolymer, and can give an effect of increasing adhesion.

The low molecular weight copolymer may have a weight average molecular weight of 5,000 to 80,000, 10,000 to 60,000, or 30,000 to 50,000. When using a low molecular weight copolymer having a weight average molecular weight within the above range, it is possible to provide excellent deformability and recovery, and less entanglement with the high molecular weight copolymer to provide an adhesive film having an appropriate level of storage modulus. .

The low molecular weight copolymer is polymerized from a second monomer mixture including a second alkyl (meth)acrylate and a second hydroxyalkyl (meth)acrylate, and the second alkyl (meth)acrylate has 8 carbon atoms. to at least one of alkyl (meth) acrylates having an alkyl group of 20 to 1, wherein the second hydroxy alkyl (meth) acrylate is one of hydroxy alkyl (meth) acrylates having an alkyl group having 4 to 6 carbon atoms. includes more than one species.

The second alkyl (meth) acrylate and the second hydroxy alkyl (meth) acrylate may be the same as or different from the first alkyl (meth) acrylate and the first hydroxy alkyl (meth) acrylate, respectively.

When a low molecular weight copolymer is prepared by polymerizing an alkyl (meth) acrylate and a hydroxy alkyl (meth) acrylate having a carbon number within the above range, a low glass transition temperature when acting as a branched chain in a high molecular weight copolymer By having it, it can serve as a free volume agent and at the same time give an effect of increasing adhesion.

According to one embodiment of the present invention, the glass transition temperature of the second alkyl (meth)acrylate may be -60 ℃ or less or -100 ℃ to -60 ℃. In the case of using an alkyl (meth)acrylate having a glass transition temperature within the above range, it is possible to prevent an increase in storage modulus by having a low glass transition temperature when acting as a branched chain in a high molecular weight copolymer.

According to one embodiment of the present invention, the glass transition temperature of the second hydroxyalkyl (meth)acrylate may be -30 °C or less or -50 °C to -30 °C. In the case of using a hydroxyalkyl (meth)acrylate having a glass transition temperature within the above range, an increase in storage modulus can be prevented by having a low glass transition temperature when acting as a branched chain in a high molecular weight copolymer. .

According to one embodiment of the present invention, the second alkyl (meth) acrylate is ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, iso It may include at least one of nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, tetradecyl (meth) acrylate, and isodecyl (meth) acrylate.

According to one embodiment of the present invention, the second hydroxy alkyl (meth) acrylate may include hydroxybutyl (meth) acrylate.

According to an embodiment of the present invention, the second monomer mixture contains the second hydroxyalkyl (meth)acrylate in an amount of greater than 0 to 5% by weight, 1% to 5% by weight, or 1% to 3% by weight. may include When the low molecular weight copolymer is polymerized with a monomer mixture containing hydroxyalkyl (meth)acrylate in an amount within the above range, the bonding strength with the high molecular weight copolymer may be excellent, and when the pressure-sensitive adhesive composition is molded into an adhesive film Stress relaxation performance can be improved.

According to one embodiment of the present invention, the second monomer mixture is 95 wt% or more and less than 100 wt% of the second alkyl (meth)acrylate, 95 wt% to 99 wt% or 97 wt% to 99 wt% may include

3. Other

According to one embodiment of the present invention, the pressure-sensitive adhesive composition is selected from a crosslinking agent, a silane coupling agent, a silicone additive, an adhesion imparting agent, a catalyst, a UV stabilizer, a UV blocker, an initiator, a dye, a pigment, an organic-inorganic particle, and an ionic salt It may further include one or more additives.

The additive may be added to impart necessary properties to the pressure-sensitive adhesive composition, and may be added without limitation as long as it is generally used in the art.

The crosslinking agent may be added to facilitate bonding of the high molecular weight copolymer and the low molecular weight copolymer, and specifically, an isocyanate-based crosslinking agent may be used.

The silane coupling agent and the adhesive force-imparting agent may be added to adjust the adhesive force of the pressure-sensitive adhesive, and the silicone additive may be added to adjust the release/peel strength and the adhesive force of the pressure-sensitive adhesive.

Catalysts and initiators may be added to control the curing rate and degree of curing and further curing, and UV stabilizers and blockers may be added for light durability and reliability of the pressure-sensitive adhesive.

Dyes and pigments may be added to control the permeability of the pressure-sensitive adhesive, organic-inorganic particles may be added to control the storage modulus of the pressure-sensitive adhesive and to facilitate handling, and ionic salts may be added to control the dielectric constant and static electricity generation of the pressure-sensitive adhesive can be added.

When the total weight of the high molecular weight copolymer and the low molecular weight copolymer is 100 parts by weight, the additive may be included in the pressure-sensitive adhesive composition in an amount of 0.01 to 10 parts by weight.

In addition, the pressure-sensitive adhesive composition may further include a solvent to have a viscosity of about 500 cp to 1500 cp, which is an appropriate level of viscosity for coating. As the solvent, a commonly used solvent may be used, and specifically, an organic solvent such as ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, and acetone may be used.

When the total weight of the high molecular weight copolymer and the low molecular weight copolymer is 100 parts by weight, the solvent may be included in an amount of 300 to 600 parts by weight.

4. Manufacturing method

According to one embodiment of the present invention, the pressure-sensitive adhesive composition comprises the steps of preparing a high molecular weight copolymer and a low molecular weight copolymer; and preparing a mixture comprising the high molecular weight copolymer, the low molecular weight copolymer, and a solvent; can be manufactured through

The high molecular weight copolymer may be prepared by polymerization of a first monomer mixture, and the low molecular weight copolymer may be prepared by polymerization of a second monomer mixture.

The polymerization reaction comprises the steps of preparing a monomer mixture; purging with nitrogen gas; and preparing a copolymer by adding a polymerization additive and stirring.

The monomer mixture may be prepared by mixing the monomer component and the solvent. The monomer component may include alkyl (meth) acrylate and hydroxy alkyl (meth) acrylate as described above, and the solvent is not particularly limited and those widely used in the art may be used, specifically Ethyl acetate, methyl ethyl ketone, acetone, etc. can be used.

Next, side reactions can be prevented by purging the prepared monomer mixture with nitrogen gas to remove dissolved oxygen in the mixture.

After that, a copolymer can be prepared by adding a polymerization additive and stirring. The polymerization additive may include at least one of an initiator, a chain transfer agent, and an antioxidant.

The initiator may serve to initiate the polymerization reaction itself, the chain transfer agent may serve to help the initiated reaction proceed in a chain to extend the chain length of the copolymer, and the antioxidant may serve to extend the chain length of the copolymer after the polymerization is completed. It can be added to improve storage stability by preventing oxidation.

The molecular weight of the copolymer can be controlled by adding the polymerization additive and controlling the stirring time. That is, as the reaction is carried out for a long time, the copolymer having a higher molecular weight is polymerized. Thus, the pressure-sensitive adhesive composition can be prepared by mixing the thus prepared high molecular weight copolymer and the low molecular weight copolymer with a solvent, and as described above, the additive It can also be prepared by adding

According to another embodiment of the present invention, there is provided an adhesive film for a foldable display comprising a cured product of the adhesive composition.

The pressure-sensitive adhesive film for a foldable display may be manufactured by a process of applying and curing the pressure-sensitive adhesive composition, but is not limited thereto and may be manufactured using the pressure-sensitive adhesive composition according to a method widely used in the art.

Specifically, the pressure-sensitive adhesive film for a foldable display may include: forming a coating film by coating the pressure-sensitive adhesive composition; And the step of thermosetting; can be prepared through.

A method of coating the pressure-sensitive adhesive composition is not particularly limited, and for example, a coating film may be formed using a method such as comma coating, slot die coating, bar coating, blade coating, and the like.

After forming the coating film, thermosetting may be performed to manufacture an adhesive film for a foldable display. The thermal curing may be performed in an oven, and may be performed by thermal curing at a temperature of about 100° C. to 200° C. for 1 minute to 10 minutes. In the thermal curing process, drying is performed together and the solvent may be removed by evaporation.

According to one embodiment of the present invention, the adhesive film for a foldable display may have a thickness of 10 to 100 μm. When the thickness is within the above range, the stress applied to the pressure-sensitive adhesive film during folding may be sufficiently alleviated, and the storage modulus may be appropriate to facilitate handling of the pressure-sensitive adhesive film.

According to one embodiment of the present invention, the adhesive film for a foldable display may have a haze of 0.5% or less, 0.48% or less, or 0.4% or less. When the haze is within the above range, optical properties required for the foldable display may be excellent.

According to an embodiment of the present invention, the adhesive film for a foldable display has an adhesive strength of 500 gf/in or more, 550 gf/in or more, 600 gf/in or more, 700 gf/in or more, or 750 gf/in to 1000 gf. It can be /in. If the adhesive force is within the above range, the interface may not be detached when it is applied to a foldable display and folded.

According to one embodiment of the present invention, the adhesive film for a foldable display may have a storage elastic modulus at -30°C of 10 ⁴ Pa to 10 ⁶ Pa or 10 ⁵ Pa to 10 ⁶ Pa. When it has a storage modulus within the above range, the foldability may be excellent and steaming may not occur.

According to one embodiment of the present invention, the adhesive film for a foldable display may have a creep strain rate of 80% or more or 80% to 99% at -20°C. Creep strain is a measure of the degree to which the adhesive film is deformed when stress is applied, and may be a ratio of the adhesive film deformed immediately after applying a stress to the adhesive film, that is, strain. When the creep strain rate is within the above range, the stress applied to the pressure-sensitive adhesive film may be sufficiently relieved, and thus the deformability may be excellent.

If the adhesive film has the same storage modulus, the adhesive film having a high creep strain may have better foldability.

According to one embodiment of the present invention, the adhesive film for a foldable display may have a recovery rate of 80% or more or 81% to 85% at -20°C. The recovery rate is measured by measuring the strain (creep strain) of the adhesive film deformed immediately after applying a force, and measuring the strain (post strain) that is not recovered after a certain time after removing the force. It can be calculated according to Equation 1 below.

[Equation 1]

Recovery (%) = (Creep Strain - Post Strain) / Creep Strain * 100

As the recovery rate is higher, the pressure-sensitive adhesive layer may be flexibly deformed even in the process of repeating folding and unfolding applied to a foldable display. In addition, since the cohesive force is adequate, the role of the adhesive film may be smoothly performed, and wrinkles may not occur when applied to a foldable display.

Hereinafter, embodiments will be described in detail to describe the present invention in detail. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention is not to be construed as being limited to the embodiments described below. The embodiments of the present specification are provided to more completely explain the present invention to those of ordinary skill in the art.

manufacturing example 1, 5: Preparation of high molecular weight copolymer

To a 1L reactor in which nitrogen gas was refluxed and a cooling device was installed to facilitate temperature control, monomers having the composition shown in Table 1 below were added, and 400 g of ethyl acetate was added as a solvent. Then, nitrogen gas was purged for 1 hour to remove oxygen. Next, after uniformly mixing while maintaining the temperature of the reactor at 62° C., azobisisobutyronitrile (AIBN) as a reaction initiator at a concentration of 400 ppm and n-dodecylmercaptan (n-DDM) as a chain transfer agent at a concentration of 400 ppm and the mixture was polymerized for 4 hours to prepare a copolymer having a weight average molecular weight shown in Table 1 below.

manufacturing example 2, 3, 4, 6: low molecular weight Preparation of copolymer

To a 1L reactor in which nitrogen gas was refluxed and a cooling device was installed to facilitate temperature control, monomers having the composition shown in Table 1 below were added, and 400 g of ethyl acetate was added as a solvent. Then, nitrogen gas was purged for 1 hour to remove oxygen. Next, after uniformly mixing while maintaining the temperature of the reactor at 62 °C, azobisisobutyronitrile (AIBN) as a reaction initiator at a concentration of 2000 ppm and n-dodecylmercaptan (n-DDM) as a chain transfer agent at a concentration of 2000 ppm The mixture was polymerized for 30 minutes to prepare a copolymer having a weight average molecular weight shown in Table 1 below.

Unit: g Preparation Example 1 Preparation 2 Preparation 3 Preparation 4 Preparation 5 Preparation 6 EHA 60 79 77 60 - - LA 20 20 20 40 - - BA - - - - 80 80 4-HBA 20 One 3 - - - HEA - - - - 20 20 Molecular Weight 2 million 40,000 40,000 40,000 2 million 40,000

In the table above, EHA is ethylhexyl acrylate, LA is lauryl acrylate, BA is butyl acrylate, 4-HBA is 4-hydroxybutyl acrylate, and HEA is hydroxyethyl acrylate.

Example 1 and 2 and comparative example 1 to 7: Preparation of pressure-sensitive adhesive composition and pressure-sensitive adhesive film

100 g of a mixed copolymer comprising the copolymer prepared in Preparation Example with the composition shown in Table 2 below, 0.07 g of TKA-100, an isocyanate-based crosslinking agent, and 100 g of ethyl acetate, using a mechanical stirrer (IKA) for 30 minutes A pressure-sensitive adhesive composition was prepared by stirring and uniformly mixing.

After leaving the pressure-sensitive adhesive composition prepared above at room temperature for 10 minutes to remove bubbles generated during mixing, the pressure-sensitive adhesive composition was applied on the film using an applicator to form a coating film, and then dried at a temperature of 140 ° C. using a Matisse oven for 3 minutes. and curing to prepare an adhesive film having a thickness of 25 μm.

high molecular weight copolymer low molecular weight copolymer Example 1 90 g of the copolymer of Preparation Example 1 10 g of the copolymer of Preparation Example 2 Example 2 90 g of the copolymer of Preparation Example 1 10 g of the copolymer of Preparation Example 3 Comparative Example 1 100 g of the copolymer of Preparation Example 1 - Comparative Example 2 98 g of copolymer of Preparation Example 1 2 g of the copolymer of Preparation Example 2 Comparative Example 3 95 g of the copolymer of Preparation Example 1 5 g of the copolymer of Preparation Example 3 Comparative Example 4 80 g of the copolymer of Preparation Example 1 20 g of the copolymer of Preparation Example 2 Comparative Example 5 90 g of the copolymer of Preparation Example 1 10 g of the copolymer of Preparation Example 4 Comparative Example 6 90 g of the copolymer of Preparation Example 1 ATBC 10 g Comparative Example 7 90 g of the copolymer of Preparation Example 5 10 g of the copolymer of Preparation Example 6

In Table 2, ATBC is acetyl tributyl citrate.

Experimental example 1: Measurement of adhesion

The adhesive films prepared in Examples 1 and 2 and Comparative Examples 1 to 7 were cut into 1 inch * 6 inch size and attached to glass, and then left at room temperature for 24 hours. After standing, the adhesive force was measured at a speed of 300 mm/min using a TA texture analyzer (Stable micro systems, TA-XT plus) according to ASTM D3330.

Experimental example 2: Measurement of storage modulus

A laminate was prepared by overlapping the adhesive films prepared in Examples 1 and 2 and Comparative Examples 1 to 7 to have a total thickness of 1 mm, and then the storage modulus was measured with an Advanced Rheometric Expansion System G2 (TA) device. Specifically, an adhesive film laminate having a thickness of 1 mm was placed between parallel plate fixtures having a diameter of 8 mm, and then measured at a temperature of -30°C at 1 Hz and 5%.

Experimental example 3: Measurement of creep strain

A laminate was prepared by overlapping the adhesive films prepared in Examples 1 and 2 and Comparative Examples 1 to 7 to have a total thickness of 1 mm, and then the creep strain (%) was measured with a DHR (TA) instrument. Specifically, after placing an adhesive film laminate with a thickness of 1 mm between parallel plate fixtures having a diameter of 8 mm, a stress of 10,000 Pa was applied for 600 seconds at a temperature of -20 ° C. was measured with

Experimental example 4: Measure your recovery rate

The adhesive films prepared in Examples 1 and 2 and Comparative Examples 1 to 7 were overlapped to have a total thickness of 1 mm, and then at a temperature of -20 ° C, a force of 10,000 Pa was applied using a parallel plate fixture having a diameter of 8 mm for 600 seconds. After applying to the adhesive film overlapped for a while, removing the force and measuring the strain that is not recovered after 600 seconds, referred to as the post strain (%), the recovery rate was calculated according to Equation 1 below.

[Equation 1]

Recovery (%) = (Creep Strain - Post Strain) / Creep Strain * 100

Experimental example 5: haze measurement

The haze of the adhesive films prepared in Examples 1 and 2 and Comparative Examples 1 to 7 was measured according to JIS K 7105-1 standard using a haze meter (COH-400, Nippon Denshoku Co., Ltd.).

Experimental example 6: dynamic folding test

Specimens were prepared by laminating the adhesive films prepared in Examples 1 and 2 and Comparative Examples 1 to 7 in a 2 Set_Stack Up structure. Specifically, a pressure-sensitive adhesive film is attached to a simulating panel having a size of 7.8 cm * 14 cm, a polarizing film is laminated, and the pressure-sensitive adhesive film is attached once again, and then a polyimide film having a hard coating layer on both sides (thickness 50 μm) was laminated to prepare a specimen. 1 shows a schematic cross-sectional view of the specimen.

The prepared specimen was sandwiched between parallel plates having an interval of 5 mm, and a folding test was performed at 25° C. in which it was folded and unfolded 100,000 times.

After the test, the occurrence of bubbles in the specimen, lifting, and cracks in the hard coating layer were visually observed. If there was no bubble generation or lifting and no cracks in the hard coating layer, it was marked as O, and if bubbles or lifting or cracks in the hard coating layer were observed, it was marked as X.

Experimental example 7: static folding test

After preparing a specimen in the same manner as in Experimental Example 6, the specimen was folded in half, sandwiched between parallel plates having a spacing of 5 mm, and left at 60° C. and 90% RH for 20 days.

After that, the specimens were collected and the degree of bubble generation, the degree of lifting, and the formation of wrinkles were visually observed. If there was no bubble generation or lifting and no wrinkles, it was marked as O, and if bubbles, lifting, or wrinkles were observed, it was marked as X.

The results evaluated in Experimental Examples 1 to 7 are shown in Table 3 below.

adhesion storage modulus creep strain recovery rate haze dynamic folding static folding unit gf/in Pa % % % - - Example 1 760 2.8*10 ⁵ 96.3 81 0.48 O O Example 2 760 2.8*10 ⁵ 80.1 82 0.35 O O Comparative Example 1 900 2.9*10 ⁵ 71.9 80 0.26 X O Comparative Example 2 840 2.9*10 ⁵ 74.2 81 0.3 X O Comparative Example 3 810 2.9*10 ⁵ 73.6 80 0.28 X O Comparative Example 4 not measurable not measurable not measurable not measurable 2.7 not measurable not measurable Comparative Example 5 730 2.5*10 ⁵ 91.3 81 0.87 not measurable not measurable Comparative Example 6 380 2.4*10 ⁵ 97.1 78 0.21 X O Comparative Example 7 850 8.0*10 ⁵ 37.3 83 0.52 X X

Referring to Table 3, it can be seen that Examples 1 and 2 both have low storage modulus, high creep strain at low temperature, and excellent recovery rate, thereby having good physical properties when folded.

On the other hand, in the case of Comparative Examples 1 to 3 containing an excessive amount of the copolymer of Preparation Example 1 corresponding to the high molecular weight copolymer, the storage modulus can be achieved at a similar level, but the creep strain rate is low and the deformation characteristics are inferior to the dynamic folding test As a result, it can be confirmed that bubbles, floating, and cracks in the hard coating layer are observed.

In addition, in the case of Comparative Example 4, the copolymer of Preparation Example 2, which is a low molecular weight copolymer, was included in an excessive amount, causing phase separation, excessive haze, and inferior optical properties, and other physical properties could not be measured.

In Comparative Example 5, since the copolymer of Preparation Example 4, which is a low molecular weight copolymer polymerized from a mixture not containing hydroxyalkyl (meth)acrylate, did not include a reactive group to be crosslinked, phase separation and haze occurred.

In the case of Comparative Example 6, it was confirmed that the adhesive strength was very low, including acetyl tributyl citrate, which was used as a free volumetric agent, and the interface was detached as a result of the dynamic folding test.

In the case of Comparative Example 7, including the copolymers of Preparation Examples 5 and 6, which are copolymers polymerized from a mixture containing an alkyl (meth)acrylate and hydroxyalkyl (meth)acrylate having a small number of carbons, the glass transition temperature is too high It can be seen that the dynamic folding and static folding evaluation results are inferior because the storage modulus is high and the creep strain is low.

Summarizing the above results, in the case of an adhesive film comprising the pressure-sensitive adhesive composition of the present invention and a cured product thereof, the adhesive strength and optical properties are excellent, and at the same time, the storage modulus is low, so the deformation performance is excellent and the recovery power is also excellent, so it is applied to a foldable display. It can be seen that even when folded, deformation and recovery occur smoothly and adhesive strength can be maintained.

Claims (12)

high molecular weight copolymers having a weight average molecular weight of 1.5 million to 2.5 million; and a low molecular weight copolymer having a weight average molecular weight of 5,000 to 80,000; as a pressure-sensitive adhesive composition comprising:
The high molecular weight copolymer is included in an amount of more than 80% by weight and less than 95% by weight based on the total weight of the high molecular weight copolymer and the low molecular weight copolymer,
The high molecular weight copolymer is polymerized from a first monomer mixture comprising a first alkyl (meth) acrylate and a first hydroxy alkyl (meth) acrylate,
The first monomer mixture comprises 10 wt% to 20 wt% of the first hydroxy alkyl (meth)acrylate,
The low molecular weight copolymer is polymerized from a second monomer mixture comprising a second alkyl (meth) acrylate and a second hydroxy alkyl (meth) acrylate,
The second monomer mixture is to include the second hydroxy alkyl (meth) acrylate in an amount of more than 0 and 5% by weight or less,
The first alkyl (meth) acrylate and the second alkyl (meth) acrylate include at least one of alkyl (meth) acrylates having an alkyl group having 8 to 20 carbon atoms,
The first hydroxy alkyl (meth) acrylate and the second hydroxy alkyl (meth) acrylate include at least one of hydroxy alkyl (meth) acrylate having an alkyl group having 4 to 6 carbon atoms.
adhesive composition.
According to claim 1,
The glass transition temperature of at least one of the first alkyl (meth) acrylate and the second alkyl (meth) acrylate is -60 ° C. or less.
According to claim 1,
The glass transition temperature of at least one of the first hydroxyalkyl (meth)acrylate and the second hydroxyalkyl (meth)acrylate is -30°C or less.
According to claim 1,
At least one of the first alkyl (meth) acrylate and the second alkyl (meth) acrylate is ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) ) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, tetradecyl (meth) acrylate and isodecyl (meth) acrylate containing one or more phosphorous pressure-sensitive adhesive composition.
According to claim 1,
At least one of the first hydroxy alkyl (meth) acrylate and the second hydroxy alkyl (meth) acrylate is a pressure-sensitive adhesive composition comprising hydroxybutyl (meth) acrylate.
According to claim 1,
The pressure-sensitive adhesive composition further comprises at least one additive selected from a crosslinking agent, a silane coupling agent, a silicone additive, an adhesion imparting agent, a catalyst, a UV stabilizer, a UV blocker, an initiator, a dye, a pigment, an organic-inorganic particle, and an ionic salt phosphorous pressure-sensitive adhesive composition.
An adhesive film for a foldable display comprising a cured product of the adhesive composition according to claim 1 .
8. The method of claim 7,
An adhesive film for a foldable display that has a thickness of 10 to 100 μm.
8. The method of claim 7,
An adhesive film for foldable displays with a haze of 0.5% or less.
8. The method of claim 7,
Adhesive film for foldable displays with an adhesive strength of 500 gf/in or more.
8. The method of claim 7,
An adhesive film for foldable displays with a creep strain of 80% or more at -20℃.
8. The method of claim 7,
An adhesive film for a foldable display having a storage elastic modulus at -30°C of 10 ⁴ Pa to 10 ^{6 Pa.}

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