JP7278967B2 - Optical transparent adhesive sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optically transparent adhesive sheet, a flat panel display device including the same, and a composition for manufacturing the same.

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 produces steps with a height of 10 μm or more 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 that minimizes the floating phenomenon from the surface of the adherend after curing, and has excellent adhesion, step-filling ability, and durability. Its purpose is to

The present invention provides an optically transparent pressure-sensitive adhesive sheet containing a (meth)acrylic copolymer, a photoinitiator, and an acrylate monomer, wherein the optically transparent pressure-sensitive adhesive sheet has a stress relaxation ratio of 0.02 to 0.10, and the stress relaxation ratio after the secondary UV cross-linking at the same temperature as the primary UV cross-linking temperature is 0.3 to 0.6. Provide adhesive sheet.

The present invention also provides a composition comprising a (meth)acrylate resin syrup, which is a resin syrup produced by partially polymerizing a (meth)acrylate monomer, a photoinitiator, and a (meth)acrylate monomer. Thus, a composition for producing the optically transparent pressure-sensitive adhesive sheet described above is provided.

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

The film of the present invention has a stress relaxation ratio of 0.02 to 0.10 after primary UV cross-linking at 70 ° C., and has excellent step embedding properties and step overcoming properties. By designing the stress relaxation ratio after cross-linking to 0.3 to 0.6, it has the effect of minimizing the floating phenomenon from the surface of the adherend. As a result, it is possible to provide an energy-curable substrate-free pressure-sensitive adhesive film with excellent step-filling properties and durability.

TECHNICAL FIELD The present invention relates to an optically transparent adhesive film and a composition for producing the same. The optically transparent pressure-sensitive adhesive film of the present invention may be a substrate-free film. The composition of the present invention may also contain a (meth)acrylate copolymer, a photoinitiator, and a (meth)acrylate monomer. The optically transparent adhesive film of the present invention may contain a (meth)acrylic copolymer, a photoinitiator, and an acrylate monomer. It can mean made of matter. The optically transparent pressure-sensitive adhesive sheet of the present invention produced from the composition has a stress relaxation ratio of 0.02 to 0.10 after primary UV cross-linking at 70° C., which is the same temperature as the primary UV cross-linking. characterized by a stress relaxation ratio of 0.3 to 0.6 after secondary UV cross-linking at a temperature of 100° C., which is characterized by excellent step embedding and step overcoming properties, and a phenomenon of lifting from the surface of the adherend after curing. can be minimized.

The present invention provides a composition comprising a (meth)acrylate resin syrup, which is a resin syrup produced by partially polymerizing a (meth)acrylate monomer, a photoinitiator, and a (meth)acrylate monomer, A composition for producing the optically transparent pressure-sensitive adhesive sheet described above is provided, and the composition of the present invention has a stress relaxation ratio of 0.02 to 0 after primary UV cross-linking at 70°C. .10, and when the stress relaxation ratio after the secondary UV cross-linking satisfies 0.3 to 0.6 at the same temperature as the temperature of the primary UV cross-linking, the cohesion and adhesion in the pressure-sensitive adhesive Also, by improving durability, it is possible to secure step embedding properties and step overcoming properties, and it is possible to minimize the floating phenomenon from the surface of the adherend.

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-1,2- Diphenylethan-1-one (2,2-Dimethoxy-1,2-diphenylethan-1-one) , Diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide ), hydroxycyclohexyl phenyl ketone, hydroxymethyl phenyl propanone , benzoylformic acid, 1,4-dibenzoylbenzene e), benzyl, etc. be done.

The photoinitiator is selected from the group consisting of polyfunctional benzoyl compound-based initiators, benzophenone-based initiators, benzoin-based initiators, hydroxyketone-based initiators, aminoketone-based initiators, and/or phosphine oxide-based initiators. It can contain two or more kinds. In the polyfunctional benzoyl compound-based initiator, benzoylformic acid and Coronate-HXR react 100% at an equivalent ratio of 1:1 to form a polyfunctional benzoyl compound through a urethane bond reaction. Preferably, polyfunctional benzoyl compounds, benzophenone acryl (VISIOMER6973, Evonik), 2,2-dimethoxy-1,2-diphenylethan-1-one (2,2-Dimethoxy-1,2-diphenylethan-1-one) , Diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide, Hydroxycyclohexyl phenyl ketone, Hydroxy methyl phenyl propanone yl propanone ), Two or more selected from the group consisting of benzoylformic acid, 1,4-dibenzoylbenzene, and/or benzyl may be included.

The amount of the photoinitiator is 0.2 to 4 parts by weight, preferably 0.2 to 4 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.

Also, the photoinitiator is contained in an amount of 0.2 to 4 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, isocyanate cross-linking agents, catalysts, etc. used in this field can also be used without limitation.

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.

Provided is a flat panel display comprising an optically transparent adhesive-free substrate film formed from the optically transparent adhesive-free substrate composition of the present invention.

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
30% by weight of 2-ethylhexyl acrylate (2-EHA) monomer and 25 wt. %, isobornyl acrylate (IBOA) monomer 30% by weight, and 2-hydroxyethyl acrylate (2-HEA) monomer 10% by weight. After purging with nitrogen gas for 1 hour, the temperature was maintained at 80°C. After uniformly mixing the monomer mixture, 1.0 part by weight of DMPA (2,2-Dimethoxy-2-phenylacetophenone) was added as a photoinitiator. After that, the mixture was stirred and irradiated with a UV lamp (10 mW) to produce a (meth)acrylate syrup having a solid content of 25%.

Production Examples 2-4
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 of (Meth)acrylate Syrup The weight average molecular weight and molecular weight distribution of (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 1-6 and Comparative Examples 1-4
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, and then the pressure-sensitive adhesive composition was prepared.

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.

Test example 2. Adhesion Evaluation The release film on one side of the pressure-sensitive adhesive sheet produced in Examples or Comparative Examples was peeled off, and the 38 μm PET film and the pressure-sensitive adhesive surface were corona-treated and joined, after which the width was 25 mm and the length was 100 mm. Cut to produce test pieces. Next, the release film attached to the PET/adhesive layer structure is peeled off, and the adhesive sheet is adhered to the alkali glass using a 2 kg roller according to JIS Z 0237. Alkali glass with an adhesive sheet was pressure-bonded in an autoclave (50° C., 5 atm) for about 20 minutes and stored for 1 hour under constant temperature and humidity conditions (23° C., 50% relative humidity). (manufactured by Stable Microsystems, UK), the peel force is measured while peeling the pressure-sensitive adhesive sheet from the alkali glass at a peel speed of 300 mm/min and a peel angle of 180 degrees.

In addition, the PET adhesion strength is measured by the same method except that PET is adhered to glass by using a double-faced tape on alkali glass as an adherend. The results are shown in Table 3 below.

Test example 3. Stress relaxation ratio (S/R ratio) evaluation Pressure-sensitive adhesive sheets produced in Examples or Comparative Examples Measuring instrument: Rheometer MCR-302, PP25 (25 mmΦ)
Measurement conditions: Strain 25%, Axial force 1N
Thickness 500 μm (5 sheets of 100 μm stacked)
Temp: 70°C (stabilization 10min)
After stabilization, when measuring, check the elastic modulus at 70°C for 1 sec and the elastic modulus after 300 sec S/R Ratio = 70°C elastic modulus for 300 sec/70°C elastic modulus for 1 sec
A is the S/R ratio after the first UV cross-linking, and B is the S/R ratio after the second UV cross-linking. The results are shown in Table 3 below.

Test example 4. Step embedding property The release PET on one side of the adhesive film prepared by the above method was peeled off and bonded to a polyethylene terephthalate film (PET100) having a thickness of 100 µm to prepare an adhesive film with a PET100 base 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. The evaluation results are shown in Table 3 below.

○: No air bubbles mixed in. △: Slight air bubbles. ×: Many air bubbles. Test Example 5. Durability (heat and humidity resistance)
The release film on one side of the pressure-sensitive adhesive sheet produced in Examples or Comparative Examples is peeled off, and the 40-μm COP film and the pressure-sensitive adhesive surface are subjected to corona treatment and joined together to cut the pressure-sensitive adhesive sheet into a size of 90 mm×170 mm. After 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 stress relaxation ratio after the primary UV cross-linking at 70° C. of the present invention is 0.02 to 0.10, and the stress relaxation after the secondary UV cross-linking at the same temperature as the temperature of the primary UV cross-linking. The optically transparent pressure-sensitive adhesive sheets of Examples 1 to 6 satisfying the ratio of 0.3 to 0.6 exhibit very excellent durability, and excellent durability means excellent adhesion. It means that it has an improved adhesion, and it was confirmed that the step embedding property and the step overcoming property are also excellent.

It was confirmed that the optically transparent pressure-sensitive adhesive sheets of Examples 1 to 6 exhibited very excellent durability, improved adhesive strength, and excellent effect of embedding unevenness.

On the other hand, the stress relaxation ratio after the primary UV cross-linking at 70° C. of the present invention is 0.02 to 0.10, and the stress relaxation ratio after the secondary UV cross-linking at the same temperature as the temperature of the primary UV cross-linking. In Comparative Examples 1 to 4, which did not satisfy the stress relaxation ratio of 0.3 or more, durability was poor, and in Comparative Examples 1 and 2, step embedding was also poor.

The film of the present invention has a stress relaxation ratio of 0.02 to 0.10 after primary UV cross-linking at 70 ° C., and has excellent step embedding properties and step overcoming properties. By designing the stress relaxation ratio after cross-linking to 0.3 to 0.6, it has the effect of minimizing the floating phenomenon from the surface of the adherend. As a result, it is possible to provide an energy-curable substrate-free pressure-sensitive adhesive film with excellent step-filling properties and durability.

Claims (9)

An optically transparent pressure-sensitive adhesive sheet containing a (meth)acrylate syrup, which is a resin syrup produced by partially polymerizing a (meth)acrylate monomer, and a photoinitiator,
The (meth)acrylate syrup, which is a resin syrup prepared by partially polymerizing the (meth)acrylate monomer, contains an acrylate monomer containing a hydroxyl group and a monofunctional (meth)acrylate monomer,
The photoinitiators include benzophenone acryl, 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), Hydroxycyclohexyl phenyl ketone, Hydroxymethyl phenyl propanone ), benzoylformic acid, 1 ,4-Dibenzoylbenzene (1,4-Dibenzoylbenzene), and one or more selected from the group consisting of benzyl, and a polyfunctional benzoyl compound-based initiator,
The optically transparent pressure-sensitive adhesive sheet has a stress relaxation ratio of 0.02 to 0.10 after primary UV cross-linking at 70° C., and after secondary UV cross-linking at the same temperature as the primary UV cross-linking. An optically transparent pressure-sensitive adhesive sheet characterized by having a stress relaxation ratio of 0.3 to 0.6. The optically transparent pressure-sensitive adhesive sheet according to claim 1, wherein the (meth)acrylate syrup, which is a resin syrup produced by partially polymerizing the (meth)acrylate monomer, further contains a photoinitiator. 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. The photoinitiator is contained in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the (meth)acrylate syrup, which is a resin syrup prepared by partially polymerizing the (meth)acrylate monomer. The optically transparent pressure-sensitive adhesive sheet according to claim 1. The photoinitiator is contained in an amount of 0.1 to 5 parts by weight when the total of the acrylate monomer containing the hydroxyl group and the monofunctional (meth)acrylate monomer is 100 parts by weight. The optically transparent pressure-sensitive adhesive sheet according to claim 2 . A composition comprising a (meth)acrylate resin syrup, which is a resin syrup prepared by partially polymerizing a (meth)acrylate monomer, a photoinitiator, and a (meth)acrylate monomer, wherein the composition comprises , a composition for producing 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 8, wherein the flat panel display device is a flexible display device.