JP7282687B2 - OPTICAL TRANSPARENT ADHESIVE SHEET, COMPOSITION FOR MANUFACTURING THE SAME AND FLAT DISPLAY DEVICE USING THE SAME - Google Patents

Description

The present invention relates to an optically transparent adhesive sheet.

Video display modules of electronic devices such as mobile portable devices, computer displays and touch panels are laminated with a glass or plastic film as a surface protective layer. Such a surface protective layer is fixed to the video display module or touch panel by applying a frame-shaped tape or adhesive to the margin outside the video display portion or the active area of the touch panel. As a result, a gap is formed between the active area of the video display portion or touch panel and the surface protective layer.

In order to increase transparency and improve image clarity, there has been a trend in the industry to replace the gap between the image display module or touch panel and the surface protective layer with a transparent material that closely matches the refractive index of these materials. . Exemplary transparent materials include, but are not limited to, optical adhesive films (OCA films), vacuum adhesives, adhesives, silicon gels, and the like. When using an adhesive, for example, if defects occur after laminating the surface protective layer and the image display module, it is difficult to separate and replace the surface protective layer. Silicon gel has reliability problems due to its low adhesion. In contrast, vacuum adhesives (e.g., vacuum adhesive sheets) are capable of re-lamination despite sufficiently high adhesive strength, but are in liquid form with solvents, so uniform It is difficult to apply the solvent properly, and there is a problem that a floating phenomenon occurs due to the residual solvent.

The surface of an adherend such as an image display module, an optical member, or a surface protective layer is sometimes uneven. The surface of the surface protective layer, particularly the surface that comes into contact with an adhesive film or adhesive sheet, generally undergoes a printing step for the purpose of decoration or shading. In some cases, the printed portion causes steps of 10 μm or more in height on the surface of the surface protective layer. One potential problem in laminating a video display module or a touch panel to a surface protection layer using an optical adhesive film is that the optical adhesive film may not conform well to the step, and on the step, Or it can induce a gap around it.

Korean Patent Publication No. 10-2016-0011785 discloses a transparent photocurable pressure-sensitive adhesive composition. There was a problem that the surface of the adherend was lifted up after curing due to the lack of ability to overcome unevenness.

Korean Patent Publication No. 10-2016-0011785

In order to solve the above-mentioned problems, the present invention provides an optically transparent pressure-sensitive adhesive sheet which is excellent in embedding and overcoming unevenness and which minimizes the floating phenomenon from the surface of the adherend after curing. aim.

The present invention provides an optically transparent pressure-sensitive adhesive sheet containing a resin syrup produced by partially polymerizing a (meth)acrylate monomer and a photoinitiator,
The optically transparent pressure-sensitive adhesive sheet has a storage elastic modulus of 1.0×10 ⁶ to 1.0×10 ⁷ Pa at 25° C. and 1 Hz, and 5.0×10 4 to 1.0×10 ⁷ Pa at 70° C. and 1 Hz after primary ultraviolet cross-linking. 5.0×10 ⁵ Pa, and the 25° C. storage elastic modulus increase rate after curing after the secondary UV cross-linking is 10 to 100% of the 25° C. storage elastic modulus after the primary UV cross-linking. To provide a transparent adhesive sheet.

The present invention also provides a composition for producing the optically transparent pressure-sensitive adhesive sheet described above.

Further, the present invention provides a flat panel display device including the above optically transparent adhesive sheet.

The storage modulus of the present invention after primary UV cross-linking is 1.0×10 ⁶ to 1.0×10 ⁷ Pa at 25° C. and 1 Hz, and 5.0×10 ⁴ to 5.0 at 70° C. and 1 Hz. × 10 ⁵ Pa, and the rate of increase in storage elastic modulus at 25°C after curing after the secondary ultraviolet cross-linking satisfies 10 to 100% of the 25°C storage elastic modulus after the primary ultraviolet cross-linking. It is possible to provide an optically transparent pressure-sensitive adhesive sheet which is excellent in part embedding properties and unevenness overcoming properties, and which minimizes the floating phenomenon from the surface of the adherend after curing.

TECHNICAL FIELD The present invention relates to an optically transparent pressure-sensitive adhesive sheet, a composition for manufacturing the same, and a flat panel display including the same. The optically transparent pressure-sensitive adhesive sheet of the present invention may be a substrate-free film. The composition of the present invention may also contain a (meth)acrylate syrup, a photoinitiator, and a (meth)acrylate monomer. The optically transparent pressure-sensitive adhesive sheet of the present invention can contain a (meth)acrylic copolymer, a photoinitiator, and an acrylate monomer. It can mean manufactured with the composition. The optically transparent pressure-sensitive adhesive sheet of the present invention produced from the composition has a storage modulus of 1.0×10 ⁶ to 1.0×10 ⁷ Pa at 25° C. and 1 Hz, and 5.0×10 Pa at 70° C. and 1 Hz. ⁴ to 5.0×10 ⁵ Pa, and the 25° C. storage elastic modulus increase rate after curing after the secondary UV cross-linking satisfies 10 to 100% of the 25° C. storage elastic modulus after the primary UV cross-linking. As a result, it is possible to provide excellent step embedding properties and step overcoming properties, and to minimize the floating phenomenon from the surface of the adherend after curing.

The present invention has a storage modulus of 1.0×10 ⁶ to 1.0×10 ⁷ Pa at 25° C. and 1 Hz, and 5.0×10 ⁴ to 5.0×10 ⁵ Pa at 70° C. and 1 Hz, If the 25° C. storage elastic modulus increase rate after curing after the secondary UV cross-linking is less than 10% of the 25° C. storage elastic modulus after the primary UV cross-linking, the cohesive force in the internal adhesive is insufficient, resulting in durability. Defects due to air bubbles occur under the conditions of adhesion, and if it is 100% or more, the cohesive force is excessively increased and the adhesion to the adherend is lowered, thereby impairing the durability. When the 25° C. storage elastic modulus increase rate after curing after the secondary UV cross-linking satisfies 10 to 100% of the 25° C. storage elastic modulus after the primary UV cross-linking, the cross-linking density inside the pressure-sensitive adhesive increases and Durability can be ensured by improving proper cohesion.

The configuration of the present invention will be described in detail below.
(Meth)Acrylate Syrup In the present invention, (meth)acrylate means “acrylate”, “methacrylate”, or both. When the (meth)acrylate syrup is included, it can contribute to the cohesion, adhesion and durability of the pressure-sensitive adhesive.

The (meth)acrylate syrups of the present invention can comprise i) acrylates containing hydroxy groups and ii) monofunctional (meth)acrylate monomers. When i) the acrylate monomer having a hydroxy group is included, it can contribute to improvement of cohesion and adhesion. The type of the i) hydroxy group-containing acrylate is not limited as long as it contains a hydroxy group. Hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 5-hydroxypentyl acrylate, 6-hydroxyhexyl acrylate, 8-hydroxyoctyl acrylate, 2-hydroxyethylene glycol acrylate, and 2-hydroxypropylene glycol acrylate, and the like.

The type of the ii) monofunctional (meth)acrylate monomer is not limited as long as it is a monofunctional monomer known in this field. Specific examples include ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate Acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, sec-butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, n- Octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, tetradecyl (meth)acrylate, acrylic acid, methacrylic acid, 2-(meth)acryloyloxyacetic acid, 3-(meth) acryloyloxypropyl acid, 4-(meth)acryloyloxybutyric acid, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, It can include one or more selected from the group consisting of 8-hydroxyoctyl (meth)acrylate, 2-hydroxyethylene glycol (meth)acrylate, 2-hydroxypropylene glycol (meth)acrylate, and the like. More preferably, it contains one or more selected from the group consisting of ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, isobornyl (meth)acrylate, and cyclohexyl (meth)acrylate.

The i) acrylate containing a hydroxy group is contained in an amount of 5 to 20% by weight based on the total weight of the i) acrylate containing a hydroxy group and ii) the copolymer containing a monofunctional (meth)acrylate monomer. If it is less than 5% by weight, there is a risk of deterioration in durability reliability such as cohesive failure under high-temperature and/or high-humidity conditions. Adhesion strength may decrease.

In the present invention, the (meth)acrylate syrup may have a weight average molecular weight of 600,000 or more and 1,000,000 or less, more preferably 600,000 or more and 800,000 or less. When the weight-average molecular weight of the (meth)acrylate syrup of the present invention satisfies the above range, improvement in adhesion properties, wettability and durability can be expected.

Photoinitiator The optically transparent pressure-sensitive adhesive sheet of the invention contains a photoinitiator in order to efficiently induce the reaction of the radically polymerizable group.

The photoinitiator is not particularly limited as long as it is a general initiator capable of initiating photopolymerization by generating radicals upon irradiation with ultraviolet rays or the like, and photopolymerization initiators known in this field can be used. Specific examples include benzoin-based initiators, hydroxyketone-based initiators, aminoketone-based initiators, and/or phosphine oxide-based initiators, and more specifically 2,2-dimethoxy-2-phenylacetophenone. (2,2-Dimethoxy-2-phenylacetophenone), Diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide, Hydroxycyclohexylphenyl ketone, Hydroxymethylphenylpropanone , benzoylformic acid, 1,4-dibenzoylbenzene, benzyl and the like.

The photoinitiator, when mixed with a (meth)acrylate syrup, is from a benzoin-based initiator, a benzophenone-based initiator, a hydroxyketone-based initiator, an aminoketone-based initiator, and/or a phosphine oxide-based initiator. It can contain two or more kinds selected from the group consisting of: Preferably, 2,2-dimethoxy-1,2-diphenylethan-1-one (2,2-Dimethoxy-1,2-diphenylethan-1-one), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (Diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide), hydroxycyclohexylphenyl ketone, hydroxymethylphenylpropanone, benzoylformic acid, 1,4-dibenzoylbenzene, benzyl, benzophenone acryl (VISIOMER6973, Evonik), etc. Two or more selected from can be included.

The amount of the photoinitiator is 0.1 to 5 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the total amount of the acrylate monomer containing the hydroxyl group and the monofunctional (meth)acrylate monomer. 5 to 2 parts by weight.

The photoinitiator is contained in an amount of 0.1 to 5 parts by weight, preferably 0.5 to 2 parts by weight, based on 100 parts by weight of the (meth)acrylate syrup.

When the photoinitiator is within the above range, there is no problem that the effect is slight even though it is added, and physical properties such as durability, reliability and transparency can be improved.

Additives The method for producing the optically transparent pressure-sensitive adhesive sheet of the present invention can be carried out by methods commonly used in this field, except for the methods described above. At this time, molecular weight modifiers, catalysts, etc. used in this field can be used without limitation.

The optically transparent adhesive sheet of the present invention may have a gel fraction of 30 to 70%. When the gel fraction satisfies the above range, the effects of durability, step embedding property and step overcoming property can be improved.

The method of applying the optically transparent pressure-sensitive adhesive sheet of the present invention is not particularly limited, and after applying the optically transparent pressure-sensitive adhesive sheet, it is cured by light irradiation. In the present application, for example, when an ultraviolet irradiation method is applied, the ultraviolet irradiation can be performed using means such as a high-pressure mercury lamp, an electrodeless lamp, or a xenon lamp.

Also, before or after the light irradiation step, a suitable aging step may proceed to induce reaction between the functional groups of the crosslinker in the composition and the thermosetting functional groups of the polymer, and the conditions in the process is not particularly limited as long as an appropriate cross-linking reaction can occur.

The optically transparent pressure-sensitive adhesive sheet of the present invention is, for example, a polarizing film, a retardation film, an anti-glare film, a light viewing angle compensation film, or a brightness enhancement film. can be used for attachment to adherends such as display panels.

In particular, the optically transparent pressure-sensitive adhesive sheet of the present invention can be preferably used for flexible display devices.

As for the method for producing the optically transparent pressure-sensitive adhesive sheet, any method known in this field can be used without limitation.

A flat panel display comprising an optically transparent pressure-sensitive adhesive sheet formed from the optically transparent pressure-sensitive adhesive sheet composition of the present invention is provided.

More preferably, the flat panel display device is a flexible display device.
Hereinafter, the present invention will be described in more detail using examples and comparative examples. However, the following examples are intended to illustrate the present invention, and the present invention is not limited by the following examples, and can be variously modified and changed.

Production Example: Production of (meth)acrylate syrup Production Example 1
50% by weight of 2-ethylhexyl acrylate (2-EHA) monomer and isobornyl acrylate (IBOA) monomer were placed in a 1 L reactor equipped with a cooling device for circulating nitrogen gas and facilitating temperature control. After charging a monomer mixture consisting of 40% by weight of polymer and 10% by weight of 2-hydroxyethyl acrylate (2-HEA) monomer, nitrogen gas was purged for 1 hour to remove oxygen, and then heated to 80°C. maintained. After the monomer mixture was uniformly mixed, 1 part by weight of 1-Hydroxy-cyclohexyl-phenyl-ketone was added as a photoinitiator when the total weight of the monomer mixture was 100 parts by weight. After that, the mixture was stirred and irradiated with a UV lamp (10 mW) to produce an acrylic syrup having a solid content of 25%.

Production Examples 2-5
A (meth)acrylate syrup was prepared in the same manner as in Preparation Example 1, but with the composition shown in Table 1 below.

Test example 1. Evaluation of Weight Average Molecular Weight and Molecular Weight Distribution The weight average molecular weight and molecular weight distribution of the (meth)acrylate syrup were measured using GPC under the following conditions. For preparation of the calibration curve, the measurement results were converted using standard polystyrene of Agilent system.

<Conditions for measuring weight average molecular weight>
Measuring instrument: Agilent GPC (Agilent 1200 series, USA)
Column: PL Mixed B two connected Column temperature: 40°C
Eluent: Tetrahydrofuran Flow rate: 1.0 mL/min
Concentration: ~1 mg/mL [0094] (100 μL injection)

Examples 1-7 and Comparative Examples 1-3
The contents of the (meth)acrylate syrup and the photoinitiator of the Preparation Example were mixed according to the composition shown in Table 2 below to prepare an adhesive composition.

The prepared pressure-sensitive adhesive composition was applied to a release film coated with a silicone release agent to a thickness of 150 μm, and the release film was bonded thereon to prepare a pressure-sensitive adhesive sheet. After that, after the primary UV irradiation, the sheet was completed.

The storage modulus of the pressure-sensitive adhesive sheet was measured at 25°C and 70°C using a viscoelasticity measuring device (MCR-301, Anton Paar). More specifically, the size of the adhesive layer sample is 30 mm in length × 30 mm in width, and after bonding the measurement sample to the Glass Plate and adhering it to the measurement tip, the frequency is 1.0 Hz in the temperature range of -30 to 100 ° C. Measurement was performed under the conditions of a deformation of 2% and a temperature increase rate of 5°C/min, and obtained by reading the measured values at 25°C and 70°C. Table 2 below shows the measurement results of the storage elastic modulus after the first UV curing and the storage elastic modulus after the second UV curing.

Experimental Example 1 Evaluation of Gel Fraction (%) The polarizing plates with optically transparent adhesive-free base films produced in Examples 1 to 7 and Comparative Examples 1 to 3 were cured at 23° C. and 65% RH for 1 day. About 0.25 g of the pressure-sensitive adhesive layer is attached to a precisely weighed 250-mesh wire mesh (100 mm×100 mm), and the layer is surrounded so that the gel does not leak out. After accurately measuring the weight with a precision balance, the wire mesh is immersed in an ethyl acetate solution for 3 days. The immersed wire mesh is taken out, washed with a small amount of ethyl acetate solution, dried at 120° C. for 24 hours, and weighed. Using the measured weight, the gel fraction was calculated using Equation 1 below.

[In the formula, A is the weight of the wire mesh (g), B is the weight of the wire mesh to which the pressure-sensitive adhesive layer is attached (B-A: weight of the adhesive, g), and C is the weight of the wire mesh dried after immersion (C- A: weight of gelled resin, g)].

Experimental Example 2: Evaluation of step embedding properties The pressure-sensitive adhesive compositions prepared according to the compositions of Examples 1 to 7 and Comparative Examples 1 to 3 were applied on a release film coated with a silicone release agent to a thickness of 150 µm. A release film was adhered thereon to prepare an adhesive sheet, which was then subjected to primary UV irradiation and then secondary UV irradiation treatment to complete the sheet. The release PET on one side of the pressure-sensitive adhesive film prepared by the method described above was peeled off, and the film was laminated to a polyethylene terephthalate film (PET100) having a thickness of 100 μm to prepare a pressure-sensitive adhesive film having a PET100 substrate bonded to one side. A test piece was obtained by cutting this into a length of 50 mm and a width of 40 mm. Next, a polyethylene terephthalate film (PET50) having a thickness of 50 μm was cut into a frame having a length of 40 mm, a width of 30 mm and a width of 5 mm. A 50-μm-thick frame made of cut PET50 was placed on PET100 from which the remaining one-sided release PET had been peeled off, and joined so as to be sandwiched between other PET100 (structure of PET100/adhesive/PET50/PET100). After this was autoclaved for 20 minutes under an atmosphere of 50° C. and a pressure of 0.5 MPa, a sample was prepared by irradiating 3 J with a metal halide lamp. Then, it was left in an atmosphere of 80° C. for 24 hours, and the inner portion of the 50 μm-thick frame was visually observed to evaluate the embeddability of the 50 μm-thick step as follows.

○: No bubbles mixed △: Some bubbles ×: Many bubbles Experimental Example 3: Evaluation of durability (heat resistance, moist heat resistance) Peel off the release film on one side of the optically transparent adhesive sheet manufactured in the same manner as above, and corona treat the 40 μm COP film and the adhesive surface to bond the adhesive sheet to a size of 90 mm × 170 mm. After cutting and peeling off the release film, a test piece was prepared by adhering to a glass substrate (110 mm×190 mm×0.7 mm). At this time, the applied pressure was 5 kg/cm ² , and clean room work was performed so as not to generate air bubbles or foreign matter. For heat resistance, observe the presence or absence of air bubbles or peeling after standing at a temperature of 100°C for 500 hours. was observed.

<Evaluation Criteria>
◎: No bubbles or peeling ○: Bubbles or peeling <5 △: 5 ≤ bubbles or peeling <10 ×: 10 ≤ bubbles or peeling The results of physical properties measured for the composition are summarized in Table 3 below. was described.

The storage modulus of the present invention is 1.0×10 ⁶ to 1.0×10 ⁷ Pa at 25° C. and 1 Hz, and 5.0×10 ⁴ to 5.0×10 ⁵ Pa at 70° C. and 1 Hz, and 2 In the case of the optically transparent pressure-sensitive adhesive sheets of Examples 1 to 7, the rate of increase in storage elastic modulus at 25° C. after curing after the second UV cross-linking satisfies 10 to 100% of the 25° C. storage elastic modulus after the first UV cross-linking. , Excellent durability means that it has excellent adhesion, and the adhesion is improved, and it is also excellent in step embedding and step overcoming effects. I confirmed that there is

In contrast, the storage modulus of the present invention is 1.0×10 ⁶ to 1.0×10 ⁷ Pa at 25° C. and 1 Hz, and 5.0×10 ⁴ to 5.0×10 ⁵ Pa at 70° C. and 1 Hz. In the case of Comparative Examples 1 and 2, the rate of increase in storage elastic modulus at 25° C. after curing after the secondary UV cross-linking does not satisfy 10 to 100% of the 25° C. storage elastic modulus after the primary UV cross-linking, Durability was poor. It was confirmed that the durability was poor and the adhesive strength was lowered, so that there was almost no effect of embedding the stepped portion and of overcoming the stepped portion. In addition, Comparative Example 3, which did not satisfy the primary UV storage elastic modulus, had poor step embedding properties and durability due to a decrease in reaction rate due to a low amount of light.

The storage modulus of the present invention after primary UV cross-linking is 1.0×10 ⁶ to 1.0×10 ⁷ Pa at 25° C. and 1 Hz, and 5.0×10 ⁴ to 5.0 at 70° C. and 1 Hz. × 10 ⁵ Pa, and the rate of increase in storage elastic modulus at 25°C after curing after the secondary ultraviolet cross-linking satisfies 10 to 100% of the 25°C storage elastic modulus after the primary ultraviolet cross-linking. It is possible to provide an optically transparent pressure-sensitive adhesive sheet which is excellent in part embedding properties and unevenness overcoming properties, and which minimizes the floating phenomenon from the surface of the adherend after curing.

Claims (8)

An optically transparent pressure-sensitive adhesive sheet containing a resin syrup produced by partially polymerizing a (meth)acrylate monomer and a second photoinitiator,
The resin syrup prepared by partially polymerizing the (meth)acrylate monomer includes an acrylate monomer containing a hydroxyl group, a monofunctional (meth)acrylate monomer, and a first photoinitiator ,
The resin syrup has a weight average molecular weight of 600,000 or more and 1,000,000 or less,
The second photoinitiator is 2,2-dimethoxy-1,2-diphenylethan-1-one, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, benzoylformic acid, 1,4-dibenzoylbenzene, Benzyl, containing two or more selected from the group consisting of benzophenone acryl,
The optically transparent pressure-sensitive adhesive sheet has a storage elastic modulus of 1.0×10 ⁶ to 1.0×10 ⁷ Pa at 25° C. and 1 Hz, and 5.0×10 4 to 1.0×10 ⁷ Pa at 70° C. and 1 Hz after primary ultraviolet cross-linking. 5.0×10 ⁵ Pa,
Storage elastic modulus after curing after secondary UV cross-linking is 1.9×10 ⁶ to 6.7×10 ⁶ Pa at 25° C. and 1 Hz,
An optically transparent pressure-sensitive adhesive sheet having a 25° C. storage modulus increase rate after curing after secondary UV cross-linking of 10 to 100% of the 25° C. storage modulus after said primary UV cross-linking. 2. The optically transparent adhesive sheet according to claim 1, wherein the optically transparent adhesive sheet has a gel fraction of 30 to 70%. The hydroxy group-containing acrylate monomer according to claim 1 , comprising 5 to 20% by weight based on the total weight of the resin syrup prepared by partially polymerizing the (meth)acrylate monomer. Optical transparent adhesive sheet. The optically transparent pressure-sensitive adhesive sheet according to claim 1, wherein the (meth)acrylate monomer is monofunctional. Claim 1, wherein the second photoinitiator is contained in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the resin syrup produced by partially polymerizing the (meth)acrylate monomer. The optically transparent pressure-sensitive adhesive sheet according to . The second photoinitiator is contained in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the total amount of the hydroxyl group-containing acrylate monomer and the monofunctional (meth)acrylate monomer. The optically transparent pressure-sensitive adhesive sheet according to claim 1 . A flat panel display comprising the optically transparent adhesive sheet of claim 1. The flat panel display device of claim 7 , wherein the flat panel display device is a flexible display device.