Adhesive compositions, adhesive layers formed therefrom, and optical display devices comprising the same

Abstract

Provided are: an adhesive composition including (i) a (meth)acrylic prepolymer having a hydroxyl group and an alkyl group, and (ii) at least one of an aryl-containing (meth)acrylate, an alicyclic group-containing (meth)acrylate, and a heteroalicyclic group-containing (meth)acrylate, and having a shear viscosity of about 0.04 Pa·s or less at 40℃, wherein an adhesive layer formed from the adhesive composition has a modulus of about 0.3 MPa or less at -20℃ and a peel strength of about 400 gf / in or more; an adhesive layer formed therefrom; and an optical display device including the same.

Description

TECHNICAL FIELD

[0001] The present application relates to an adhesive composition, an adhesive layer formed therefrom, and an optical display device including the same. BACKGROUND

[0002] An optical display device includes a plurality of elements. For example, the plurality of elements can include a display panel, various films, various optical sheets, etc. In the optical display device, the elements are stacked through an adhesive layer rather than simply stacked with each other, thereby ensuring stability while implementing their inherent functions.

[0003] Generally, an optical display device is produced by stacking such elements through an adhesive layer produced separately. The adhesive layer can be produced in the form of a roll by coating an adhesive composition to a predetermined thickness between release films and can be cut to a size and shape suitable for use. However, this method requires additional processes such as a punching process, etc.

[0004] Accordingly, a method of directly spraying an adhesive composition on an element through inkjet printing, and then curing the adhesive composition has been proposed. In this regard, a typical optical clear resin (OCR) composition, which is a liquid adhesive composition including an oligomer and a plasticizer such as isoprene and butadiene serving as a softening component, is used in the art. Due to an increase in viscosity thereof, this type of adhesive composition is applied through a dispensing process rather than an inkjet printing process. However, disadvantageously, the dispensing process takes more time than the inkjet printing process, and the adhesive composition is less likely to achieve a low modulus of flexibility for a foldable or flexible display. To solve these problems, an adhesive composition prepared by reducing the molecular weight of the oligomer or the plasticizer (softening component) or prepared using a reactive diluent monomer having a low viscosity is used in the art. However, this type of adhesive composition is also not suitable for inkjet printing and cannot improve the resistance to bending.

[0005] Background art of the present application is disclosed in Korean Patent Publication No. 10-2007-0055363, etc. SUMMARY

[0006] TECHNICAL PROBLEM

[0007] An aspect of the present application is to provide an adhesive composition suitable for inkjet printing or a dispensing process.

[0008] Another aspect of the present application is to provide an adhesive composition that can achieve an adhesive layer having good flexibility at a low temperature.

[0009] TECHNICAL SOLUTION

[0010] An aspect of the present application relates to an adhesive composition.

[0011] 1. An adhesive composition can include: (i) a (meth)acrylic prepolymer having a hydroxyl group and an alkyl group; and (ii) at least one selected from the group consisting of an aromatic group-containing (meth)acrylate, an alicyclic group-containing (meth)acrylate, and a hetero alicyclic group-containing (meth)acrylate, and has a shear viscosity of about 0.04 Pa-s or less at 40°C, wherein an adhesive layer formed from the adhesive composition has a modulus of about 0.3 MPa or less at -20°C and has a peel strength of about 400 gf / in or more.

[0012] 2. In 1, the adhesive composition can be a solventless liquid adhesive composition.

[0013] 3. In 1-2, the (meth)acrylic prepolymer having a hydroxyl group and an alkyl group can include a (meth)acrylic prepolymer of a monomer mixture including about 10% by weight (wt%) to about 40 wt% of a hydroxyl group-containing (meth)acrylate and about 60 wt% to about 90 wt% of an alkyl group-containing (meth)acrylate.

[0014] 4. In 3, the alkyl group-containing (meth)acrylate can include a compound represented by Formula 1:

[0015] [Formula 1]

[0016]

[0017] (In Formula 1, R1 is hydrogen or a methyl group, R4 is an unsubstituted straight chain or branched C1 to C 10 alkyl group).

[0018] 5. In 1-4, the (meth)acrylic prepolymer having a hydroxyl group and an alkyl group has a weight average molecular weight of about 1,500,000 or less.

[0019] 6. In 1-5, the (meth)acrylic prepolymer having a hydroxyl group and an alkyl group has a shear viscosity of about 0.05 Pa-s or less at 40°C.

[0020] 7. In 1-6, at least one selected from the group consisting of an aromatic group-containing (meth)acrylate, an alicyclic group-containing (meth)acrylate, and a hetero alicyclic group-containing (meth)acrylate can be present in an amount of about 15 parts by weight or more with respect to 100 parts by weight of the (meth)acrylic prepolymer having a hydroxyl group and an alkyl group.

[0021] 8. In 1-7, the (meth)acrylate containing an aromatic group can include at least one selected from the group consisting of benzyl (meth)acrylate and phenoxy ethyl (meth)acrylate.

[0022] 9. In 1-8, the (meth)acrylate containing an alicyclic group can include at least one selected from the group consisting of dicyclopentanyl (meth)acrylate and dicyclopentenyloxyethyl (meth)acrylate.

[0023] 10. In 1-9, the (meth)acrylate containing a heteroalicyclic group can include at least one selected from the group consisting of tetrahydrofurfuryl (meth)acrylate and cyclic trimethylolpropane formal (meth)acrylate.

[0024] 11. In 1-10, the adhesive composition can include at least one selected from the group consisting of an initiator and a plasticizer.

[0025] The adhesive layer according to the present application includes a cured product formed from the adhesive composition according to the present application.

[0026] The optical display device according to the present application includes the adhesive layer according to the present application.

[0027] Advantageous Effects

[0028] The present application provides an adhesive composition suitable for an inkjet printing or a dispensing process.

[0029] The present application provides an adhesive composition which can realize an adhesive layer having good flexibility at a low temperature. DETAILED DESCRIPTION

[0030] BEST MODE

[0031] Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily practice the present application. It should be understood that the present application can be embodied in many different ways and is not limited to the following embodiments.

[0032] Herein, the "viscosity" of the adhesive composition refers to a shear viscosity measured for the adhesive composition using a viscometer at 40°C. In particular, the shear viscosity of the adhesive composition can be measured using a Brookfield viscometer RVDV-II+P CP (spindle #51, 20 rpm) for 0.5 g of the adhesive composition after adjusting the temperature of the adhesive composition to 40°C.

[0033] Herein, the "modulus" refers to a storage modulus G' measured for an adhesive layer formed from the adhesive composition. In particular, the storage modulus is measured in a temperature sweep test mode using a rheometer (ARES, Anton Paar, MCR-501) as a dynamic viscoelasticity instrument under an automatic strain condition at a strain of 1% and at a shear rate of 1 rad / s. The sample for measuring the storage modulus is prepared by stacking a plurality of adhesive layers to form a laminate having a thickness of 400 µm, followed by punching the laminate using a punch machine of 8 mm in diameter. In particular, a normal force of 1 N is applied to the sample using an 8 mm clamp, and the storage modulus on the sample is measured while the temperature is raised from -50°C to 100°C at a heating rate of 5°C / min.

[0034] Herein, the "peeling strength" is a value measured for an adhesive layer formed from the adhesive composition. In particular, the sample for measuring the peeling strength is prepared by adhering a polyethylene terephthalate (PET) film (length x width x thickness: 100 mm x 25 mm x 100 µm) subjected to corona treatment to one surface of the adhesive layer (length x width x thickness: 100 mm x 25 mm x 25 µm), while adhering a glass plate (soda-lime glass) (length x width x thickness: 100 mm x 25 mm x 100 µm) to the other surface of the adhesive layer. The PET film subjected to corona treatment is prepared by subjecting one surface of the PET film to corona treatment twice (total dose: 156 shots) while plasma discharging at 78 shots per treatment. The sample is left at room temperature for 30 minutes, and then fixed to a TA.XT_Plus texture analyzer (Stable Micro Systems). Then, the peeling strength is measured by peeling the entire body of the corona-treated PET film and the adhesive layer from the glass plate at a peeling temperature: 25°C, a peeling angle: 180°, and a peeling rate: 300 mm / min.

[0035] Herein, the "(meth)acryloyl group" can refer to an acryloyl group and / or a methacryloyl group.

[0036] Herein, in the "substituted or unsubstituted", the "substituted" means that at least one hydrogen atom in the corresponding functional group is replaced by a halogen, a hydroxyl group, an amino group, a C1 to C 10 alkyl, C3 to C10 cycloalkyl, C6to C 20 aryl or C7to C 20 arylalkyl group.

[0037] As used herein to designate a specific numerical range, "X to Y" means "greater than or equal to X and less than or equal to Y (X≤ and ≤Y)".

[0038] Hereinafter, an adhesive composition according to one embodiment of the present application will be described.

[0039] The adhesive composition can be applicable to an inkjet printing process or a dispensing process. The inkjet printing process or the dispensing process refers to a process allowing the adhesive composition to be applied to a substrate by an inkjet head at 25 to 50°C, preferably 40°C to form a smooth and uniform adhesive layer, and after curing, a substrate to be bonded to a bonded object by bonding the bonded object to the adhesive layer.

[0040] For the inkjet printing process or the dispensing process, the adhesive composition has a shear viscosity of about 0.04 Pa s or less at 40°C to allow the adhesive composition to be applied to a substrate while ensuring a uniform coating. With this viscosity, the adhesive composition allows effective application by the inkjet printing process while ensuring good spreading on the substrate to form a uniform coating, so that various films and / or display panels of an optical display device can be bonded by the adhesive composition. Preferably, the adhesive composition has a shear viscosity of about 0.005 Pa s to about 0.04 Pa s at 40°C. Within this range, the adhesive composition is applicable to the inkjet printing process or the dispensing process. Further, within this range, the adhesive layer formed by the adhesive composition can ensure flexibility by adjusting the peel strength and modulus at low temperature. For example, the adhesive composition can have a shear viscosity of about 0.005, 0.006, 0.007, 0.008, 0.009, 0.010, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.020, 0.021, 0.022, 0.023, 0.024, 0.025, 0.026, 0.027, 0.028, 0.029, 0.030, 0.031, 0.032, 0.033, 0.034, 0.035, 0.036, 0.037, 0.038, 0.039, or 0.040 Pa s at 40°C.

[0041] The adhesive composition can realize an adhesive layer that exhibits good flexibility at low temperatures. To this end, the adhesive layer formed of the adhesive composition can have a modulus of about 0.3 MPa or less at -20°C and have a peel strength of about 400 gf / in or more. Within these ranges of modulus and peel strength, the adhesive layer has good flexibility at low temperatures to prevent delamination or bubble generation, slight cocking or appearance distortion at 100,000 or more folding cycles at low temperatures. Preferably, the adhesive layer has a modulus of about 0.07 MPa to about 0.3 MPa at -20°C. Preferably, the adhesive layer has a peel strength of about 400 gf / in to about 1500 gf / in.

[0042] For example, the adhesive layer can have a modulus of about 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, or 0.30 MPa at -20°C.

[0043] For example, the adhesive layer can have a peel strength of about 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, or 1500 gf / in.

[0044] To allow the formation of the adhesive layer while ensuring the viscosity, modulus, and peel strength within the above ranges, the adhesive composition includes a (meth)acrylic prepolymer having a hydroxyl group and an alkyl group.

[0045] The (meth)acrylic prepolymer having a hydroxyl group and an alkyl group having a weight average molecular weight and / or viscosity within a certain range can ensure the above viscosity range. Here, the "prepolymer" is distinguished from a polymer having a high weight average molecular weight, and any polymer having a weight average molecular weight and / or viscosity within the following range can be included in the prepolymer according to the present application.

[0046] The (meth)acrylic prepolymer having a hydroxyl group and an alkyl group can have a weight average molecular weight of about 1,500,000 or less, for example, about 500,000 to about 1,500,000. Within this range, the adhesive composition can easily achieve the viscosity within the above range and can easily ensure the peel strength and various properties. When the (meth)acrylic prepolymer does not have the weight average molecular weight within the above range, even if having at least one of the aryl group-containing (meth)acrylate, the alicyclic group-containing (meth)acrylate, and the heteroalicyclic group-containing (meth)acrylate selected from the group consisting of, it can be difficult for the adhesive composition to ensure the peel strength and the modulus according to the present application. For example, the (meth)acrylic prepolymer having a hydroxyl group and an alkyl group can have a weight average molecular weight of about 500,000, 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,100,000, 1,200,000, 1,300,000, 1,400,000, or 1,500,000.

[0047] The (meth)acrylic prepolymer having a hydroxyl group and an alkyl group can have a shear viscosity of about 0.05 Pa·s or less, for example, about 0.03 Pa·s to about 0.05 Pa·s at 40℃. Within this range, the adhesive composition can easily achieve the viscosity within the above range and can easily ensure the peel strength and various properties. The viscosity of the (meth)acrylic prepolymer can be measured by the following method. When the (meth)acrylic prepolymer does not have the viscosity within this range, even if having at least one of the aryl group-containing (meth)acrylate, the alicyclic group-containing (meth)acrylate, and the heteroalicyclic group-containing (meth)acrylate selected from the group consisting of, it can be difficult for the adhesive composition to ensure the peel strength and the modulus according to the present application. For example, the (meth)acrylic prepolymer having a hydroxyl group and an alkyl group can have a shear viscosity of about 0.030, 0.031, 0.032, 0.033, 0.034, 0.035, 0.036, 0.037, 0.038, 0.039, 0.040, 0.041, 0.042, 0.043, 0.044, 0.045, 0.046, 0.047, 0.048, 0.049, or 0.050 Pa·s at 40℃.

[0048] In one embodiment, the adhesive composition can be a solventless liquid composition not including a solvent. When the adhesive composition is a solventless adhesive composition, the (meth)acrylic prepolymer has the weight average molecular weight and / or the viscosity within the above range, so that the adhesive composition can easily achieve the viscosity within the range according to the present application.

[0049] The (meth)acrylic prepolymer having a hydroxyl group and an alkyl group can include a (meth)acrylic prepolymer of a monomer mixture including a (meth)acrylic ester having a hydroxyl group and a (meth)acrylic ester having an alkyl group.

[0050] The (meth)acrylic ester having a hydroxyl group can help ensure the peel strength of the adhesive layer. The (meth)acrylic ester having a hydroxyl group can be a C1 to C 10 (meth)acrylic ester. For example, the (meth)acrylic ester having a hydroxyl group can include at least one selected from the group consisting of 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate.

[0051] In the monomer mixture, the (meth)acrylic ester having a hydroxyl group can be present in an amount of about 10 wt% to about 40 wt%, for example, about 10 wt% to about 30 wt%. Within this range, the adhesive composition can also improve the peel strength and durability of the adhesive layer formed therefrom. For example, the (meth)acrylic ester having a hydroxyl group can be present in the monomer mixture in an amount of about 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 wt%.

[0052] The (meth)acrylic ester having an alkyl group can form a matrix of the adhesive layer. Here, the "alkyl group" can refer to an unsubstituted straight-chain or branched C1 to C 10 alkyl group. The (meth)acrylic ester having an alkyl group can include a compound of Formula 1.

[0053] [Formula 1]

[0054]

[0055] (in Formula 1,

[0056] R1 is hydrogen or a methyl group, and

[0057] R4 is an unsubstituted straight-chain or branched C1 to C 10 alkyl group).

[0058] In one embodiment, the (meth)acrylic ester having an alkyl group is a (meth)acrylic ester having an unsubstituted straight-chain or branched C1 to C 10alkyl group. For example, the (meth)acrylate ester containing an alkyl group can include at least one selected from the group consisting of (meth)acrylic acid 2-ethylhexyl ester, (meth)acrylic acid n-butyl ester, (meth)acrylic acid iso-octyl ester, (meth)acrylic acid propyl ester, (meth)acrylic acid t-butyl ester, (meth)acrylic acid iso-butyl ester, (meth)acrylic acid pentyl ester, (meth)acrylic acid hexyl ester, (meth)acrylic acid heptyl ester, (meth)acrylic acid octyl ester, (meth)acrylic acid nonyl ester, and (meth)acrylic acid decyl ester. Preferably, the (meth)acrylate ester containing an alkyl group includes at least one selected from the group consisting of (meth)acrylic acid 2-ethylhexyl ester, (meth)acrylic acid n-butyl ester, and (meth)acrylic acid iso-octyl ester, more preferably (meth)acrylic acid 2-ethylhexyl ester.

[0059] In the monomer mixture, the (meth)acrylate ester containing an alkyl group can be present in an amount of about 60 wt% to about 90 wt%, preferably about 70 wt% to about 90 wt%. Within this range, the adhesive composition can ensure good bending reliability of the adhesive layer at low temperature and high temperature / high humidity. For example, the (meth)acrylate ester containing an alkyl group can be present in the monomer mixture in an amount of about 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, or 90 wt%.

[0060] The monomer mixture can further include a copolymerizable comonomer with the (meth)acrylate ester containing a hydroxyl group and / or the (meth)acrylate ester containing an alkyl group. Here, the copolymerizable comonomer does not include the (meth)acrylate ester containing an aryl group, the (meth)acrylate ester containing an alicyclic group, and the (meth)acrylate ester containing a hetero alicyclic group. When the monomer mixture includes the (meth)acrylate ester containing an aryl group, the (meth)acrylate ester containing an alicyclic group, and the (meth)acrylate ester containing a hetero alicyclic group, the adhesive composition prepared from the monomer mixture can suffer from high reactivity between the (meth)acrylate ester containing a hydroxyl group and the (meth)acrylate ester containing an alkyl group, thereby making it difficult to implement an inkjet printing process or a dispensing process due to gelation of the adhesive composition. In one embodiment, the (meth)acrylic prepolymer can be free of aryl groups, alicyclic groups, and hetero alicyclic groups.

[0061] The comonomer can include at least one selected from the group consisting of a (meth)acrylic monomer containing phosphorus, a (meth)acrylic monomer containing a silane group, a (meth)acrylic monomer containing an epoxy group, and a (meth)acrylic monomer containing an alkylene oxide group, but is not limited thereto. In the monomer mixture, the comonomer can be present in an amount of about 30 wt% or less, for example, about 0.1 wt% to about 30 wt%. For example, the comonomer can be present in the monomer mixture in an amount of about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 wt%.

[0062] The (meth)acrylic prepolymer having a hydroxyl group and an alkyl group can be prepared by polymerization of the monomer mixture. Here, the polymerization can be performed to secure the weight average molecular weight and / or the viscosity within the ranges described above. For example, the chain transfer agent can be present in an amount of about 50 ppm to about 300 ppm, for example, about 50 ppm to about 200 ppm, with respect to 100 parts by weight of the monomer mixture, at the time of polymerization. The polymerization can be achieved by solution polymerization, suspension polymerization, or the like, but is not limited thereto. The chain transfer agent can include at least one selected from the group consisting of a silane compound, a mercapto compound, a dithioacetate compound, a xanthate compound, and a disulfide compound. Detailed information on these compounds can be readily obtained with reference to typical compounds well known to those skilled in the art.

[0063] On the other hand, the adhesive layer formed of the adhesive composition having a shear viscosity of about 0.04 Pa·s or less at 40℃ has a problem of low peeling strength due to the low viscosity of the adhesive composition allowed to be applied by the inkjet printing process or the dispensing process. In addition, the low viscosity of the adhesive composition can cause the adhesive layer to fail to secure a target modulus at a low temperature. Accordingly, the adhesive layer can exhibit poor flexibility.

[0064] Accordingly, the adhesive composition can include at least one selected from the group consisting of an (meth)acrylate containing an aryl group, an (meth)acrylate containing an alicyclic group, and an (meth)acrylate containing a hetero alicyclic group, in addition to the (meth)acrylic prepolymer having a hydroxyl group and an alkyl group.

[0065] At least one selected from the group consisting of an aryl-containing (meth)acrylate, an alicyclyl-containing (meth)acrylate, and a heteroalicyclyl-containing (meth)acrylate can improve flexibility at a low temperature by increasing the peeling strength of the adhesive layer while securing the modulus and the peeling strength at a low temperature within the scope according to the present application, without affecting the shear viscosity at 40°C secured by the (meth)acrylic prepolymer having a hydroxyl group and an alkyl group.

[0066] At least one selected from the group consisting of an aryl-containing (meth)acrylate, an alicyclyl-containing (meth)acrylate, and a heteroalicyclyl-containing (meth)acrylate can be present in an amount of about 15 parts by weight or more, for example, about 15 parts by weight to about 50 parts by weight, with respect to 100 parts by weight of the (meth)acrylic prepolymer having a hydroxyl group or an alkyl group or a monomer mixture for the (meth)acrylic prepolymer. Within this range, the adhesive composition can secure the viscosity, good peeling strength, and flexibility at a low temperature within the ranges described above. For example, at least one selected from the group consisting of an aryl-containing (meth)acrylate, an alicyclyl-containing (meth)acrylate, and a heteroalicyclyl-containing (meth)acrylate can be present in an amount of about 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 parts by weight, with respect to 100 parts by weight of the (meth)acrylic prepolymer having a hydroxyl group and an alkyl group or a monomer mixture for the (meth)acrylic prepolymer.

[0067] The aryl-containing (meth)acrylate can include a monofunctional (meth)acrylate having an aryl group. The aryl group refers to a monocyclic aryl group, a polycyclic aryl group including a fused aryl group, or a monocyclic aryl group having a sigma bond. For example, the aryl group can include at least one selected from the group consisting of a substituted or unsubstituted C6 to C 50 The aryl group refers to a monocyclic aryl group, a polycyclic aryl group including a fused aryl group, or a monocyclic aryl group having a sigma bond. For example, the aryl group can include at least one selected from the group consisting of a substituted or unsubstituted C6 to C 50 The aryloxy group refers to an oxygen-substituted aryl group. For example, the aryloxy group can include at least one selected from the group consisting of a substituted or unsubstituted C7 to C 50 The arylalkyl group refers to an alkyl group substituted with an aryl group. For example, the arylalkyl group can include at least one selected from the group consisting of a substituted or unsubstituted C7 to C 50 The arylalkoxy group refers to an alkoxy group substituted with an aryl group. For example, the arylalkoxy group can include at least one selected from the group consisting of a substituted or unsubstituted C7 to C The aryl group refers to a monocyclic aryl group, a polycyclic aryl group including a fused aryl group, or a monocyclic aryl group having a sigma bond. For example, the aryl group can include at least one selected from the group consisting of a substituted or unsubstituted C6 to C

[0068] For example, the aryl-containing monofunctional (meth)acrylate can be represented by Formula 2.

[0069] [Formula 2]

[0070]

[0071] (In Formula 2,

[0072] R1is hydrogen or methyl,

[0073] s is an integer from 0 to 10, and

[0074] R2is a substituted or unsubstituted C6to C 50 aryl group or a substituted or unsubstituted C6to C 50 aryl group or a substituted or unsubstituted C6to C

[0075] For example, R2may be phenylphenoxyethyl, phenoxyethyl, benzyl, phenyl, phenylphenoxy, phenoxy, phenylethyl, phenylpropyl, phenylbutyl, methylphenylethyl, propylphenylethyl, methoxyphenylethyl, cyclohexylphenylethyl, chlorophenylethyl, bromophenylethyl, methylphenyl, methylethylphenyl, methoxyphenyl, propylphenyl, cyclohexylphenyl, chlorophenyl, bromophenyl, phenylphenyl, biphenyl, terphenyl, quaterphenyl, anthryl, naphthyl, triphenylenyl, methylphenoxy, ethylphenoxy, methylethylphenoxy, methoxyphenoxy, propylphenoxy, cyclohexylphenoxy, chlorophenoxy, bromophenoxy, biphenylyloxy, terphenylyloxy, quaterphenylyloxy, anthryloxy, naphthyloxy, and triphenylenyloxy.

[0076] Specifically, the aryl group-containing mono-functional (meth)acrylate can include at least one selected from 2-phenylphenoxyethyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenyl (meth)acrylate, phenoxy (meth)acrylate, 2-ethylphenoxy (meth)acrylate, benzyl (meth)acrylate, 2-phenylethyl (meth)acrylate, 3-phenylpropyl (meth)acrylate, 4-phenylbutyl (meth)acrylate, 2-(2-methylphenyl)ethyl (meth)acrylate, 2-(3-methylphenyl)ethyl (meth)acrylate, 2-(4-methylphenyl)ethyl (meth)acrylate, 2-(4-propylphenyl)ethyl (meth)acrylate, 2-(4-(1-methylethyl)phenyl)ethyl (meth)acrylate, 2-(4-methoxyphenyl)ethyl (meth)acrylate, 2-(4-cyclohexylphenyl)ethyl (meth)acrylate, 2-(2-chlorophenyl)ethyl (meth)acrylate, 2-(3-chlorophenyl)ethyl (meth)acrylate, 2-(4-chlorophenyl)ethyl (meth)acrylate, 2-(4-bromophenyl)ethyl (meth)acrylate, 2-(3-phenylphenyl)ethyl (meth)acrylate, 4-(biphenyl-2-yloxy)butyl (meth)acrylate, 3-(biphenyl-2-yloxy)butyl (meth)acrylate, 2-(biphenyl-2-yloxy)butyl (meth)acrylate, 1-(biphenyl-2-yloxy)butyl (meth)acrylate, 4-(biphenyl-2-yloxy)propyl (meth)acrylate, 3-(biphenyl-2-yloxy)propyl (meth)acrylate, 2-(biphenyl-2-yloxy)propyl (meth)acrylate, 1-(biphenyl-2-yloxy)propyl (meth)acrylate, 4-(biphenyl-2-yloxy)ethyl (meth)acrylate, 3-(biphenyl-2-yloxy)ethyl (meth)acrylate, 2-(biphenyl-2-yloxy)ethyl (meth)acrylate, 1-(biphenyl-2-yloxy)ethyl (meth)acrylate, 2-(4-benzylphenyl)ethyl (meth)acrylate, 1-(4-benzylphenyl)ethyl (meth)acrylate, or structural isomers thereof.

[0077] Preferably, the aryl group-containing (meth)acrylate includes at least one selected from benzyl (meth)acrylate and phenoxyethyl (meth)acrylate.

[0078] The alicyclic group-containing (meth)acrylate can include a compound having a C3 to C 10 The mono(meth)acrylate of a single ring or multiple rings. For example, the alicyclic group-containing (meth)acrylate can include a compound represented by Formula 3.

[0079] [Formula 3]

[0080]

[0081] (in formula 3,

[0082] R1is hydrogen or methyl,

[0083] s is an integer of 0 to 10, and

[0084] R3is substituted or unsubstituted C3to C10cycloalkyl, substituted or unsubstituted C3to C10cycloalkenyl, substituted or unsubstituted C3to C10cycloalkoxy, or substituted or unsubstituted C3to C10cycloalkenyloxy.

[0085] In particular, R3may include at least one selected from dicyclopentyl and dicyclopentenyloxy.

[0086] Preferably, the (meth)acrylate containing an alicyclyl group can include at least one selected from dicyclopentyl (meth)acrylate and dicyclopentenyloxyethyl (meth)acrylate.

[0087] The (meth)acrylate containing a heteroalicyclic group can include a C3to C10alicyclic group having a heteroatom (e.g., oxygen, sulfur, nitrogen, preferably oxygen) in the atoms constituting the ring. 10 The (meth)acrylate containing a heteroalicyclic group can include at least one selected from tetrahydrofurfuryl (meth)acrylate and cyclotrimethylolpropane methylal (meth)acrylate.

[0088] The adhesive composition is a photocurable adhesive composition and can further include an initiator. The initiator can include a photopolymerizable initiator.

[0089] The photopolymerizable initiator can be selected from any kind of photopolymerizable initiator capable of inducing polymerization of the following free radical polymerizable compound by irradiation with light or the like during the curing process. For example, the photopolymerizable initiator can be a benzoin, a hydroxyketone, an amino ketone, or a phosphine oxide photoinitiator.

[0090] The initiator can be present in an amount of about 0.0001 parts by weight to about 5 parts by weight, specifically about 0.001 parts by weight to about 3 parts by weight, more specifically about 0.001 parts by weight to about 1 part by weight, with respect to 100 parts by weight of the monomer mixture or the (meth)acrylic prepolymer. Within this range, the initiator allows complete curing of the adhesive composition without deteriorating the light transmittance of the adhesive film due to the residual initiator and can reduce bubble generation while ensuring good reactivity. For example, the initiator can be present in an amount of about 0.0001, 0.005, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, or 5 parts by weight, with respect to 100 parts by weight of the monomer mixture or the (meth)acrylic prepolymer.

[0091] The adhesive composition initiator can also include a crosslinking agent.

[0092] The crosslinking agent can increase the mechanical strength of the adhesive layer by increasing the degree of crosslinking of the adhesive composition.

[0093] The crosslinking agent can include a multifunctional (meth)acrylate as a crosslinking agent capable of being cured by actinic radiation. For example, the crosslinking agent can include difunctional (meth)acrylates such as 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, neopentyl glycol adipate di(meth)acrylate, dicyclopentyl di(meth)acrylate, caprolactone-modified dicyclopentenyl di(meth)acrylate, oxirane-modified di(meth)acrylate, di(meth)acryloyloxyethyl isocyanurate, allylated cyclohexyl di(meth)acrylate, tricyclodecane dimethanol (meth)acrylate, dimethylol dicyclopentane di(meth)acrylate, oxirane-modified hexahydrophthalic acid di(meth)acrylate, tricyclodecane dimethanol (meth)acrylate, neopentyl glycol-modified trimethylpropane di(meth)acrylate, adamantane di(meth)acrylate, and 9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene; trifunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, propionic acid-modified dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, trifunctional urethane (meth)acrylates, and tri(meth)acryloyloxyethyl isocyanurate; tetrafunctional (meth)acrylates such as diglycerol tetra(meth)acrylate and pentaerythritol tetra(meth)acrylate; pentafunctional (meth)acrylates such as dipentaerythritol penta(meth)acrylate; and hexafunctional (meth)acrylates such as dipentaerythritol hexa(meth)acrylate, caprolactone-modified dipentaerythritol hexa(meth)acrylate, and urethane (meth)acrylates (e.g., a reaction product of isocyanate monomers and trimethylolpropane tri(meth)acrylate), but are not limited thereto.

[0094] The crosslinking agent can optionally be present in an amount of about 5 parts by weight or less, specifically about 0.001 parts by weight to about 5 parts by weight, specifically about 0.003 parts by weight to about 3 parts by weight, specifically about 0.005 parts by weight to about 1 parts by weight, with respect to 100 parts by weight of the monomer mixture or the (meth)acrylic prepolymer. Within this range, the adhesive composition can ensure good peel strength while improving reliability. For example, the crosslinking agent can optionally be present in an amount of about 0, 0.001, 0.005, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, or 5 parts by weight, with respect to 100 parts by weight of the monomer mixture or the (meth)acrylic prepolymer.

[0095] The adhesive composition can further include an additive.

[0096] The additive can be selected from typical additives for an adhesive composition well known to those skilled in the art. For example, the additive can include at least one selected from pigments, UV absorbers, leveling agents, antistatic agents, and silane coupling agents, but is not limited thereto.

[0097] The adhesive composition can be prepared by polymerizing a monomer mixture for a (meth)acrylic prepolymer using an initiator, and further adding at least one selected from an aryl-containing (meth)acrylate and an alicyclic group-containing (meth)acrylate to the same. The initiator, the crosslinking agent, and the additive can be further added to the adhesive composition.

[0098] Next, an adhesive layer according to one embodiment of the present application will be described.

[0099] The adhesive layer includes a cured product formed of the adhesive composition according to the embodiment of the present application.

[0100] The cured product can be prepared by applying the adhesive composition to a substrate, and then curing with light. The curing can include UV irradiation at a wavelength of 300 nm to 400 nm and at a dose of about 200 mJ / cm 2 to about 3,000 mJ / cm 2 , using a typical UV lamp such as a low-pressure lamp, a metal halide lamp, or the like, in an oxygen-free state. The UV irradiation can be performed once or multiple times.

[0101] The adhesive layer can have a modulus of about 0.3 MPa or less at -20°C. For example, the adhesive layer can have a modulus of about 0.07 MPa to about 0.3 MPa at -20°C. Within this range, the adhesive layer can show good flexibility at low temperatures for use in a foldable display.

[0102] The adhesive layer can have a modulus of about 0.2 MPa or less, for example, about 0.01 MPa to about 0.2 MPa at 25°C. Within this range, the adhesive layer can exhibit good flexibility at room temperature and good peel strength to the adherend to prevent the adherend from being peeled.

[0103] The adhesive layer can have a modulus of about 0.001 MPa or more, for example, about 0.001 MPa to about 0.1 MPa at 80°C. Within this range, the adhesive layer can exhibit good flexibility and durability at high temperature.

[0104] The adhesive layer can have a peel strength of about 400 gf / in or more. Within this range of peel strength, the adhesive layer has good flexibility at low temperature to prevent delamination or bubble generation, slight warping or appearance distortion after 100,000 or more folding cycles at low temperature. Preferably, the adhesive layer has a peel strength of about 400 gf / in to about 1500 gf / in.

[0105] The adhesive layer is optionally transparent and suitable for optical display devices. In one embodiment, the adhesive layer can have a single transmittance of about 80% or more, for example, about 80% to about 100% in the visible spectrum (e.g., at wavelengths of 380 nm to 800 nm).

[0106] The adhesive layer can have a thickness of about 10 μm to about 100 μm, specifically, about 10 μm to about 50 μm. Within this range, the adhesive layer can achieve foldability while ensuring peel strength to the adherend.

[0107] Next, an optical display device according to one embodiment of the present application will be described.

[0108] The optical display device can include the adhesive layer according to the embodiments of the present application. The adhesive layer can adhere various adherends present in the optical display device, for example, optical films including display panels, polarizing plates, polarizing sheets, retardation films, etc., various elements including reflective films, brightness enhancement films, etc.

[0109] The optical display device can include various display devices including flexible displays, flexible display devices, etc. that require flexibility.

[0110] Inventive Modes

[0111] Next, the present application will be described in more detail with reference to some examples. However, it should be noted that these examples are provided only for illustration and should not be construed in any way as limiting the present application.

[0112] Example 1

[0113] A monomer mixture for a (meth)acrylic prepolymer of 100 parts by weight as listed in Table 1, 100 ppm of an initiator (Irgacure 651, 2,2-dimethoxy-2-phenylacetophenone, BASF), and 100 ppm of a chain transfer agent (n-decyl mercaptan) were mixed in a reactor. After 30 minutes of replacement of dissolved oxygen in the reactor with nitrogen, the mixture was irradiated with UV light using a low-pressure mercury lamp for several minutes. The irradiation was continued until the (meth)acrylic prepolymer had a viscosity of 0.038 Pa-s at 40°C. The polymerization of the monomer mixture was completed by cooling the reactor while purging with air for 30 minutes, thereby preparing a (meth)acrylic prepolymer (weight average molecular weight: 1,000,000). The viscosity was measured by a method of measuring shear viscosity.

[0114] A liquid adhesive composition was prepared by adding 30 parts by weight of benzyl acrylate, 0.3 parts by weight of Irgacure 127, and 0.2 parts by weight of TPO as an initiator, 0.2 parts by weight of a crosslinking agent (HDDA) to 100 parts by weight of the prepared (meth)acrylic prepolymer (copolymer of acrylic monomers).

[0115] Examples 2 to 6

[0116] Liquid adhesive compositions were prepared in the same manner as in Example 1, except that the components of each adhesive composition were changed to those listed in Table 1. In Table 1, "-" means that the corresponding component is not present.

[0117] Comparative Examples 1 to 4

[0118] Liquid adhesive compositions were prepared in the same manner as in Example 1, except that the components of each adhesive composition were changed to those listed in Table 2. In Table 2, "-" means that the corresponding component is not present.

[0119] Each of the adhesive compositions prepared in the examples and comparative examples was evaluated for the properties listed in Tables 1 and 2. The results are shown in Tables 1 and 2.

[0120] (1) Viscosity (unit: Pa-s): The shear viscosity of the adhesive composition was measured. Specifically, after adjusting the temperature of the adhesive composition to 40°C, the shear viscosity of the adhesive composition was measured with respect to 0.5 g of the adhesive composition using a Brookfield viscometer RVDV-II+P CP (spindle #51, 20 rpm).

[0121] (2) Peeling strength (unit: gf / in): The peeling strength with respect to an adhesive layer formed of the adhesive composition was measured. A release polyethylene terephthalate (PET) film was placed on a coating layer formed by coating the adhesive composition on a PET release film to a thickness of 25 μm using a doctor blade. The adhesive layer (thickness: 25 μm) was formed by curing the adhesive composition using a low-pressure mercury lamp at 200 mJ / cm 2 under and a metal halide lamp at 2,000 mJ / cm 2 under irradiation.

[0122] The sample was prepared by adhering a corona-treated PET film to an exposed surface of the adhesive layer from which a PET release film was peeled off. The sample was cut to a size of 10 cm x 2.5 cm (length x width). Then, the remaining PET release film was removed from the sample, which was in turn adhered to a glass plate (soda-lime glass) through the adhesive layer to prepare a sample for measuring the peeling strength. The corona-treated PET film was prepared by subjecting one surface of a PET film to corona treatment twice (total dose: 156 shots) while plasma discharge was 78 shots per treatment.

[0123] The sample was left at room temperature for 30 minutes and then fixed to a TA.XT_Plus texture analyzer (Stable Micro Systems). Then, the peeling strength was measured by peeling off the entirety of the corona-treated PET film and the adhesive layer from the glass plate at a peeling temperature: 25°C, a peeling angle: 180°, and a peeling rate: 300 mm / min.

[0124] (3) Modulus (unit: MPa): A release polyethylene terephthalate (PET) film was placed on a coating layer formed by coating the adhesive composition on a PET release film to a thickness of 25 μm using a doctor blade. The adhesive layer (thickness: 25 μm) was formed by curing the adhesive composition using a low-pressure mercury lamp at 200 mJ / cm 2 under and a metal halide lamp at 2,000 mJ / cm 2 under irradiation.

[0125] The modulus was measured using a rheometer (ARES, Anton Paar, MCR-501) as a dynamic viscoelasticity instrument in a temperature sweep test mode under an automatic strain condition of 1% of strain and in a shear rate of 1 rad / s. The sample for measuring the storage modulus was prepared by stacking a plurality of adhesive layers to form a laminate having a thickness of 400 μm, followed by punching the laminate using a punch machine of 8 mm in diameter. In particular, a normal force of 1 N was applied to the sample using an 8 mm clamp, and the storage modulus on the sample was measured while the temperature was raised from -50°C to 100°C at a heating rate of 5°C / min.

[0126] (4) Flexibility (at -20°C): The laminate was prepared by stacking a PET film (thickness: 50 µm), an adhesive layer (thickness: 25 µm), and a PET film (thickness: 50 µm), and adhered by a roller, and then the laminate was left to stand at room temperature for 12 hours. Then, the laminate was cut into a sample having a size of 140 mm x 70 mm (length x width), which was in turn fixed to a flexible tester (CFT-2000, Covotech Co., Ltd.) by an adhesive (4965, Tesa Co., Ltd.). Here, the PET film was subjected to corona treatment and the adhesive layer was adhered to one surface of the PET film subjected to corona treatment. The sample was subjected to 100,000 folding cycles in the longitudinal direction of the sample at -20°C such that the bent portion of the sample had a radius of curvature of 3 mm at a folding rate of 30 cycles per minute, wherein 1 cycle refers to the operation of folding the sample to have a radius of curvature, maintaining the sample in the folded state for 1 second, and then unfolding the adhesive film back to 180°. After 100,000 folding cycles, the sample that suffered from delamination, bubble generation, slight cocking, or surface deformation was rated as x, and the sample that did not suffer from delamination, bubble generation, slight cocking, or surface deformation was rated as o.

[0127] (5) Inkjet printing processability: The thin release film was adhered to a coating layer formed by depositing each of the adhesive compositions prepared in the examples and comparative examples by an inkjet head, followed by irradiation with UV light at 800 mJ / cm 2 Irradiation with UV light to form a cured adhesive layer, which was in turn evaluated by the naked eye by measuring its thickness. A sample having a smooth appearance and uniform thickness to be used as an adhesive layer was rated as o, and a sample having a rough appearance and non-uniform thickness was rated as X.

[0128] [Table 1]

[0129]

[0130]

[0131] [Table 2]

[0132]

[0133] * EHA: 2-ethylhexyl acrylate (LG Chemical)

[0134] * HBA: 4-hydroxybutyl acrylate (Osaka Organic Chemical Industry Ltd)

[0135] * HEA: 2-hydroxyethyl acrylate (LG Chemical)

[0136] * 1: Benzyl acrylate

[0137] * 2: Phenoxyethyl acrylate

[0138] * 3: Tetrahydrofurfuryl acrylate

[0139] * 4: Dicyclopentyl acrylate

[0140] * 5: Lauryl acrylate

[0141] * 6: Methyl acrylate

[0142] * HDDA: 1,6-hexanediol diacrylate

[0143] * TMPTA: Trimethylolpropane triacrylate

[0144] As shown in Table 1, the adhesive composition according to the present application is suitable for a dispensing process or an inkjet printing process and an adhesive layer formed of the adhesive composition has a smooth appearance and a uniform thickness while ensuring good flexibility at low temperature.

[0145] On the contrary, as shown in Table 2, the adhesive composition of Comparative Example 1 not satisfying the viscosity range of the present application shows poor inkjet printing processability and poor flexibility at low temperature. The adhesive compositions of Comparative Examples 2 to 4 not containing at least one selected from the group consisting of an aryl-containing (meth)acrylate, an alicyclic group-containing (meth)acrylate, and a hetero alicyclic group-containing (meth)acrylate cannot have a peel strength within the range according to the present application and a modulus at -20℃, thereby showing poor flexibility at low temperature.

[0146] It should be understood that various modifications, changes, variations, and equivalents can be made without departing from the spirit and scope of the present application.

Claims

1. An adhesive composition comprising: (i) A (meth)acrylic acid prepolymer having hydroxyl and alkyl groups, wherein the (meth)acrylic acid prepolymer does not contain aryl, alicyclic, or heterocyclic groups; and (ii) Selected from at least one of aryl-containing (meth)acrylates, alicyclic (meth)acrylates, and heterocyclic (meth)acrylates. The adhesive composition has a shear viscosity of 0.04 Pa·s or less at 40°C. in, The adhesive layer formed from the adhesive composition has a modulus of 0.3 MPa or less at -20°C and a peel strength of 400 gf / in or greater. The (meth)acrylic prepolymer having hydroxyl and alkyl groups comprises a (meth)acrylic prepolymer of a monomer mixture containing 10 wt% to 40 wt% of hydroxyl-containing (meth)acrylates and 60 wt% to 90 wt% of alkyl-containing (meth)acrylates. The (meth)acrylic acid prepolymer having hydroxyl and alkyl groups has a weight-average molecular weight of 1,500,000 or less. In this embodiment, relative to 100 parts by weight of the (meth)acrylate prepolymer having hydroxyl and alkyl groups, at least one selected from aryl (meth)acrylates, alicyclic (meth)acrylates and heterocyclic (meth)acrylates is present in an amount of 15 parts by weight or more.

2. The adhesive composition according to claim 1, wherein, The adhesive composition is a solvent-free liquid adhesive composition.

3. The adhesive composition according to claim 1, wherein, The alkyl-containing (meth)acrylates include compounds represented by Formula 1: [Formula 1] In Formula 1, R1 is hydrogen or methyl and R4 is an unsubstituted straight-chain or branched C1 to C4 chain. 10 alkyl.

4. The adhesive composition according to claim 1, wherein, The (meth)acrylic prepolymers having hydroxyl and alkyl groups have a shear viscosity of 0.05 Pa·s or less at 40°C.

5. The adhesive composition according to claim 1, wherein, The aryl-containing (meth)acrylates include at least one selected from benzyl (meth)acrylate and phenoxyethyl (meth)acrylate.

6. The adhesive composition according to claim 1, wherein, The alicyclic (meth)acrylate includes at least one selected from dicyclopentyl (meth)acrylate and dicyclopentenyl oxyethyl (meth)acrylate.

7. The adhesive composition according to claim 1, wherein, The heterocyclic (meth)acrylates include at least one selected from tetrahydrofurfuryl (meth)acrylate and cyclotrimethylolpropane methyl acetal (meth)acrylate.

8. The adhesive composition according to claim 1 further comprises: at least one selected from the group consisting of an initiator and a crosslinking agent.

9. An adhesive layer comprising a cured product formed from an adhesive composition according to any one of claims 1 to 8.

10. An optical display device comprising the adhesive layer according to claim 9.

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