Optical adhesive and laminate for flexible panels

Abstract

This invention provides an optical adhesive and a laminate for flexible panels. The optical adhesive comprises: 100 parts by weight of component (A), a resin prepolymer with straight side chains; 0.02-1 parts by weight of component (B), a crosslinking agent; and 0.005-0.01 parts by weight of component (C), a catalyst. Component (A) is obtained by reacting the following components: 10-40 parts by weight of a soft monomer; 2-15 parts by weight of a hard monomer; 1 part by weight of a hydroxyl-containing monomer; and 0.001-0.03 parts by weight of a thermal initiator, wherein the soft monomer comprises a soft acrylate monomer with straight chains, and the hard monomer comprises an unsaturated ethylene double bond monomer.

Description

Technical Field

[0001] This invention relates to an optical adhesive and a laminate for use in flexible panels. Prior Technology

[0002] Traditionally, glass panels are used as protective layers for various display panels. However, glass panels have disadvantages such as being heavy and easily broken, and they also raise environmental concerns due to their high carbon emissions.

[0003] To address the aforementioned issues, and with the trend towards thinner and lighter displays and electronic devices, flexible materials such as acrylic sheets and polycarbonate sheets are increasingly being used to replace glass sheets as protective layers.

[0004] However, panels using flexible boards as protective layers are prone to delamination or warping (unable to return to flatness) during rolled storage and transportation or when subjected to environmental thermal shock. This may be due to latent changes in the molecules of the adhesive used to bond the panels and the protective layer, or a mismatch between the viscoelasticity and Poisson's ratio of the adhesive and the protective layer.

[0005] Due to the aforementioned possible reasons, thermal stress may easily be generated between the layers of the panel module during bending or high temperature and humidity testing, which may cause interlayer delamination and degrade the quality of the panel module. Summary of the Invention

[0006] The present invention provides an optical adhesive and a laminate for use in flexible panels.

[0007] In some embodiments, an optical adhesive is provided, comprising: 100 parts by weight of component (A), a resin prepolymer with straight side chains; 0.02-1 parts by weight of component (B), a crosslinking agent; and 0.005-0.01 parts by weight of component (C), a catalyst. The prepolymer of component (A) is obtained by reacting a mixture comprising: (a) 10-40 parts by weight of a soft monomer; (b) 2-15 parts by weight of a hard monomer; (c) 1 part by weight of a hydroxyl (-OH) monomer; and (d) 0.001-0.03 parts by weight of a thermal initiator. The soft monomer (a) comprises a straight-chain soft acrylate monomer as shown in formula (I), and the hard monomer (b) comprises an unsaturated ethylene double-bond monomer, wherein n is an integer from 7 to 15. Formula (I)

[0008] In some embodiments, a laminate for a flexible panel is also provided, comprising: the optical adhesive described above; and at least one substrate. The optical adhesive is located on one surface of the substrate. Implementation

[0009] In order to enable those skilled in the art to better understand and implement the objectives, technical features and advantages of the present invention, the following description clarifies the technical features and implementation methods of the present invention and provides further explanation with preferred embodiments. However, the following description is not intended to limit the present invention.

[0010] [Definitions and Explanations]

[0011] <tg>

[0012] In this specification, Tg represents the glass transition temperature.

[0013] <Optical Adhesive> The present invention provides an optical adhesive comprising: (A) a resin prepolymer having straight side chains; (B) a crosslinking agent; and (C) a catalyst.

[0014] In the following cases, the optical adhesive having the above-described structure may be simply referred to as "the optical adhesive of the present invention" or simply as "optical adhesive". Furthermore, the resin prepolymer with straight side chains of component (A) may be simply referred to as "component (A) of the present invention" or simply as "component (A)". Similarly, the crosslinking agent of component (B) may be simply referred to as "component (B) of the present invention" or simply as "component (B)"; and the catalyst of component (C) may be simply referred to as "component (C) of the present invention" or simply as "component (C)".

[0015] The optical adhesive of the present invention, by means of component (A) having specific components and component (B) controlling the degree of crosslinking of the optical adhesive, enables the optical adhesive to have good anti-creep properties and achieve good stress absorption effect, thereby making it suitable as an adhesive layer for flexible panels or flexible composite boards.

[0016] <(A)Component>

[0017] The present invention (A) comprises a prepolymer of a resin with straight side chains, obtained by reacting the following components: (a) 10-40 parts by weight of a soft monomer, which may be a soft acrylate monomer with straight chains, or a mixture of a soft acrylate monomer with straight chains (first soft monomer) and a soft monomer with a Tg ≦ 0°C (second soft monomer); (b) 2-15 parts by weight of a hard monomer, which may be an unsaturated ethylene double bond monomer or a mixture of an unsaturated ethylene double bond monomer (first hard monomer) and the hard acrylate monomer (second hard monomer); (c) 1 part by weight of a hydroxyl (-OH)-containing monomer; and (d) 0.001-0.03 parts by weight of a thermal initiator.

[0018] [Soft monomer]

[0019] In some embodiments, relative to 1 part by weight of the hydroxyl (-OH) monomer in component (c) of component (A), the soft monomer in component (a) of the present invention may be 10-40 parts by weight, for example 10-30 parts by weight or 10-20 parts by weight.

[0020] In some embodiments, the soft monomer (a) used in component (A) of the present invention may be a soft acrylate monomer with a straight chain, specifically as shown in formula (I): Formula (I) Where n can be an integer from 7 to 15, but is not subject to this restriction.

[0021] In some embodiments, there are no particular limitations on the specific examples of linear soft acrylate monomers, for example, the following groups may be selected: n-octyl (meth)acrylate, n-decyl (meth)acrylate, lauryl (meth)acrylate (LA), myristyl (meth)acrylate, and palmityl (meth)acrylate.

[0022] Based on the view that optical adhesives can have better resistance to creep and better stress absorption, the linear soft acrylate monomer can be lauryl (meth)acrylate (LA), whose structure is shown in formula (I-1). Formula (I-1)

[0023] In some embodiments, in addition to the above-mentioned linear soft acrylate monomer (first soft monomer), the soft monomer (a) of component (A) of the present invention may selectively include a soft monomer (second soft monomer) with a Tg ≦ 0°C. The proportion of the second soft monomer with a Tg ≦ 0°C may be up to 60 wt% of the total soft monomer (i.e., the sum of the first soft monomer and the second soft monomer). That is, the second soft monomer may account for 0 wt% to 60 wt% of the total soft monomer, for example, 0 wt%-50 wt%, 0 wt%-45 wt%, 0 wt%-40 wt%, 0.1 wt%-60 wt%, 0.1 wt%-50 wt%, or 1 wt%-50 wt%.

[0024] In some embodiments, the soft monomer of the present invention with Tg ≦ 0°C is specifically selected from the group consisting of: butyl (meth)acrylate, sec-butyl (meth)acrylate, ethyl (meth)acrylate, 2-ethylhexyl (meth)acrylate (2-EHA), ethoxyethyl (meth)acrylate, and isononyl (meth)acrylate.

[0025] Based on the view that it can make optical adhesives have better resistance to creep and better stress absorption, the soft monomer with Tg≦0℃ can be isooctyl (2-ethylhexyl (meth)acrylate, 2-EHA), whose structure is shown in formula (II). Equation (II)

[0026] [Hard monomer]

[0027] In some embodiments, relative to 1 part by weight of the hydroxyl (-OH) monomer in component (c) of the present invention, the hard monomer in component (b) of the present invention may be 2-15 parts by weight, for example 2-13 parts by weight, 2-10 parts by weight, 3-13 parts by weight or 3-10 parts by weight.

[0028] In some embodiments, the hard monomer (b) used in this invention may be a hard monomer with Tg ≥ 85°C, but is not limited thereto.

[0029] In some embodiments, the hard monomer of component (b) of the present invention (A) may be an unsaturated ethylene double bond monomer.

[0030] In some embodiments, there are no particular limitations on the specific examples of unsaturated ethylene double bond monomers that are the hard monomers of (b) of the present invention. For example, they may be: acrylonitrile, acrylamide, acrylmorpholine, and N-vinyl-2-pyrrolidone (NVP).

[0031] Based on the viewpoint that optical adhesives can have better resistance to creep and better stress absorption, the unsaturated ethylene double bond monomer of the present invention can be N-vinyl-2-pyrrolidone (NVP), the structure of which is shown in formula (III). Equation (III)

[0032] In some embodiments, the hard monomer in component (b) of the present invention, in addition to the aforementioned unsaturated ethylene double bond monomer (first hard monomer), may selectively include a hard acrylic monomer (second hard monomer). In some embodiments, the hard acrylic monomer (second hard monomer) may account for up to 40 wt% of the total hard monomers (i.e., the sum of the first hard monomer and the second hard monomer), that is, the hard acrylic monomer (second hard monomer) accounts for 0 wt% to 40 wt% of the hard monomer in component (b), for example, 0 wt%-30 wt%, 0 wt%-25 wt%, 1 wt%-40 wt%, 1 wt%-35 wt%, or 1 wt%-30 wt%.

[0033] In some embodiments, there are no particular limitations on the specific examples of the hard acrylic monomer (second hard monomer) of the present invention. For example, it can be selected from the group consisting of: tert-butyl (meth)acrylate, butyl methacrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate (IBOA), and methyl (meth)acrylate.

[0034] Based on the viewpoint that optical adhesives can have better resistance to creep and better stress absorption, the hard acrylic monomer (second hard monomer) of the present invention can be isobornyl (meth)acrylate (IBOA), the structure of which is shown in formula (IV). Formula (IV)

[0035] [Hydroxy (-OH) monomers]

[0036] In some embodiments, component (c) of element (A) of the present invention contains a hydroxyl (-OH) monomer, specifically, which may be selected from the group consisting of: hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate (4-HBA), hydroxypentyl (meth)acrylate, and hydroxyhexyl (meth)acrylate.

[0037] Based on the view that it can make the optical adhesive have better resistance to creep and better stress absorption effect, (c) the hydroxyl (-OH) monomer can be hydroxybutyl (meth)acrylate (4-HBA), whose structure is shown in formula (V). Formula (V)

[0038] [Heat initiator]

[0039] The content of the thermal initiator (d) used in component (A) of the present invention is not particularly limited and can be adjusted as needed according to the type and amount of monomer selected and the expected degree of polymerization. In some embodiments, the thermal initiator (d) may be 0.001-0.03 parts by weight relative to 1 part by weight of the hydroxyl (-OH) monomer (c) in component (A) of the present invention.

[0040] In some embodiments, specific examples of the thermal initiator may be selected from, but are not limited to, the group consisting of: azobisisobutyronitrile (AIBN), benzoyl peroxide, cumyl hydroperoxide, dicumyl peroxide, tert-butyl hydroperoxide, tert-butyl monoperoxymaleate, diacetyl peroxide, and dilauroyl peroxide.

[0041] Based on the view that it can make optical adhesives have better resistance to creep and better stress absorption, the thermal initiator can be azobisisobutyronitrile (AIBN), whose structure is shown in formula (VI). Formula (VI)

[0042] <(B) Ingredients>

[0043] Component (B) of this invention is a crosslinking agent used to control the degree of crosslinking of the optical adhesive. Component (B) can be 0.02-1 parts by weight relative to 100 parts by weight of component (A) of this invention.

[0044] Component (B) of the present invention may be selected as needed, depending on the type and amount of other monomers used and the expected degree of crosslinking.

[0045] In some embodiments, specific examples of component (B) of the present invention may be organic peroxides or isocyanates, but are not limited thereto.

[0046] In some embodiments, examples of organic peroxides include: tetrahydrofuran peroxide, ethylene glycol dimethyl ether peroxide, benzoyl peroxide, methyl ethyl ketone peroxide, triacetone triperoxide, acetyl peroxide nitrate, diethylene oxides, peracetic acid, ether peroxide, and cumene hydroperoxide, etc.

[0047] In some embodiments, the isocyanate may be a monoisocyanate or a polyisocyanate, among which examples of polyisocyanates include toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (H12MDI), and lysine diisocyanate (LDI).

[0048] In some embodiments, component (B) of the present invention may also be a commercially available product, such as Desmodur® N3200 (biuret form of hexamethylene diisocyanate) manufactured by Covestro Inc.

[0049] <(C) Ingredients>

[0050] The component (C) of this invention is a catalyst, and the component (C) may be 0.005-0.01 parts by weight relative to 100 parts by weight of component (A) of this invention.

[0051] In some embodiments, based on environmental considerations, component (C) of the present invention may be an organometallic catalyst; specifically, component (C) of the present invention may be a tin-free catalyst.

[0052] In some embodiments, the components (C) of the present invention may also be commercially available products, such as Borchi® Kat 0243 (a tin-free catalyst of metal carboxylates) and Borchi® Kat 15 (a tin-free catalyst of zinc neodecanoate) manufactured by Borchers (Milliken) Inc.

[0053] [Laminated materials for flexible panels]

[0054] Some embodiments of the present invention may also provide a laminate for a flexible panel, comprising: an optical adhesive; and at least one substrate. The optical adhesive may be located on one surface of a substrate or sandwiched between two substrates to form a three-layer laminate structure.

[0055] In some embodiments, the substrate material may be selected from the group consisting of: polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET), polyvinyl chloride (PVC), thermoplastic polyurethane elastomer (TPU), and styrene-acrylonitrile copolymer (AS) and polyimide (PI).

[0056] [Examples and Comparative Examples]

[0057] The following examples illustrate the present invention in more detail, but the present invention is not limited to these examples.

[0058] [Synthesis Examples 1-7 of Resin Prepolymers with Straight Side Chains]

[0059] First, according to Table 1, weigh 10% of the monomer combination and 25% of the solvent (ethyl acetate) into a three-necked flask, and then attach a reflux tube and a burette. Then, add the remaining 90% of the monomer combination, azobisisobutyronitrile as a thermal initiator, and the remaining 75% of the solvent (ethyl acetate) dropwise over an 8-hour feeding time. After the addition is complete, stir the reaction mixture at about 80°C at a rate of 200 rpm and reflux for 40 hours. Then, stop heating and add 2,6-dibutyl-p-cresol as a terminator. After cooling, stop stirring to obtain a mixture containing resin prepolymers (1) to (7).

[0060] Here, the linear soft acrylate monomer (first soft monomer) is lauryl methacrylate (LA); the soft monomer with Tg≦0℃ (second soft monomer) is isooctyl methacrylate (2-EHA); the unsaturated ethylene double bond monomer (first hard monomer) is N-vinyl-2-pyrrolidone (NVP) and the hard acrylate monomer (second hard monomer) is isobornyl methacrylate (IBOA); the hydroxyl (-OH) monomer system is hydroxybutyl methacrylate (4-HBA); and the thermal initiator is azobisisobutyronitrile (AIBN).

[0061] [Table 1] Synthesis Examples (1) (2) (3) (4) (5) (6) (7) reactants Weight (g) reactants Linear soft acrylate monomers (first soft monomers) LA 0 95.1 190.4 228.1 285.2 380.2 190.4 Soft monomers with Tg≦0℃ (second soft monomers) 2-EHA 291.3 218.6 145.7 116.6 72.9 0 145.7 Unsaturated ethylene double bond monomer (first hard monomer) NVP 77.8 77.8 77.8 77.8 77.8 77.8 92.91 Hard acrylic monomer (second hard monomer) IBOA 21.7 21.7 21.7 21.7 21.7 21.7 0 Hydroxyl (-OH) monomers 4-HBA 22.3 22.3 22.3 22.3 22.3 22.3 22.3 thermal initiator AIBN 0.105 0.105 0.105 0.105 0.105 0.105 0.105 solvent EA 964.3 964.3 964.3 964.3 964.3 964.3 964.3 Terminator BHT 1.65 1.65 1.65 1.65 1.65 1.65 1.65 Total (g) 1379 1401 1424 1432 1446 1468 1468 Solid content (%) 30.08 31.19 32.28 32.68 33.31 34.31 31.95 Mixtures (products) containing resin prepolymers (1) (2) (3) (4) (5) (6) (7)

[0062] [Preparation of optical adhesive]

[0063] Examples 1 to 6 and Comparative Examples 1 to 5

[0064] First, according to the contents of Tables 2 and 3, 300 g (approximately 90-100 g of solid) of mixtures (1) to (7) containing resin prepolymer, 1.86 g of 1% catalyst (Borchi® Kat 0243) and different weights of crosslinking agent (Desmodur® N3200) were weighed and placed into beakers and stirred evenly to obtain the optical adhesives (A) to (K) of Examples 1 to 6 and Comparative Examples 1 to 5.

[0065] The optical adhesives (A) to (K) were applied to release film H350A (manufactured by Nan Ya Plastics Industrial Co., Ltd., model: NYN YA Release Film H350A) using a wet coating method. The coating machine speed was 0.3-0.5 m / min, and the air duct temperature was set at 65℃ / 80℃ / 90℃-120℃. Afterwards, the film was dried using an oven. On the opposite side of the bonding surface between the optical adhesives of Examples 1 to 6 and Comparative Examples 1 to 5 and the release film H350A, release film L150A (manufactured by Nan Ya Plastics Industrial Co., Ltd., model: NYN YA Release Film L150A) was laminated and wound-cured at 50℃ for 24 hours to obtain a three-layer structure of release film H350A-optical adhesive-release film L150A. Remove the release film sandwiched between the two sides of the optical adhesive to obtain a thin film (100 μm thick) made of optical adhesive (A) to (K). Various physical properties of the optical adhesive are measured by the method described below, and the results are summarized in Tables 2 and 3.

[0066] [Poisson's ratio test] Poisson's ratio (γ) is determined at room temperature by bonding the aforementioned optical adhesives (A) to (K) into a universal tensile testing machine and obtaining (E) Young's modulus and (G) shear modulus according to the "Application of the finite element method in the tensile-shear test of adhesive technology" (doi: 10.1016 / S0143-7496(01)00012-4) proposed by A. Öchsner et al., which describes the "method for performing shear force tests and the calculation of Poisson's ratio". The result is calculated using the following formula:

[0067] [Relaxation Time (Anti-Subtraction Capability) Measurement]

[0068] At room temperature, the films formed by the aforementioned optical adhesives (A) to (K) are bonded to a tensile testing machine, stretched to 50% and fixed for 15 minutes. After relaxation, the recovery time required for the adhesive is measured, and the result is taken as the "relaxation time", with the unit being "seconds".

[0069] [Peel Adhesion Test]

[0070] One side of the film (100 μm thick) formed by the aforementioned optical adhesives (A) to (K) was bonded to a 1.0 mm support material, and the other side was bonded to a transparent PI film (manufactured by Lusheng Technology Co., Ltd., model: MCF025), resulting in a sample with a width of 24±0.5 mm. The transparent PI film was stretched and peeled at a constant speed of 300 mm / min, with parameters set according to ASTM D3330, thereby measuring the peel adhesion of the optical adhesives (A) to (K).

[0071] [Test of Thermal Warpage Deformation under High Temperature and High Humidity]

[0072] As mentioned above, after fabricating the three-layer structure of release film H350A - optical adhesive (A) to (K) of Examples 1 to 6 and Comparative Examples 1 to 5 - release film L150A, release film L150A was removed and a transparent PI film was laminated on that surface. Then, release film H350A was removed and polymethyl methacrylate (PMMA) support material was laminated on that surface to create a laminate with a length of 76.4 mm. The laminate was placed on a metal substrate and subjected to a high temperature and high humidity environment of 85°C / 85% for 4 hours. The deformation of the laminate was measured, and the result is the "thermal warpage deformation under high temperature and high humidity" of optical adhesive (A) to (K). [Table 2] Example Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Mixture containing resin prepolymer (3) (3) (4) (5) (6) (7) NVP as a percentage of total weight (wt.%) 17.0 17.0 16.7 16.2 15.5 20.6 IBOA percentage of total weight (wt.%) 4.7 4.7 4.7 4.5 4.3 0 4-HBA percentage of total weight (wt.%) 4.9 4.9 4.8 4.6 4.4 4.9 2-EHA percentage by weight (wt.%) 31.8 31.8 25.0 15.2 0.0 32.3 LA percentage of total weight (wt.%) 41.6 41.6 48.9 59.4 75.7 42.2 Catalyst (1%) weight (g) 1.86 1.86 1.86 1.86 1.86 1.86 Crosslinking agent (g) 0.15 0.23 0.23 0.23 0.23 0.23 Optical adhesive (A) (B) (C) (D) (E) (F) Poisson's ratio 0.43 0.43 0.47 0.48 0.49 0.42 Relaxation time (seconds) 32 40 38 30 25 59 180° peel adhesion (>10 N / in) 11.3 15.5 15.0 14.3 12.8 10.5 Peel-off test (failure interface) OCA-PI OCA-PI OCA-PI OCA-PI OCA-PI OCA-PI High temperature and high humidity warping deformation (<0.1 mm) 0 0 0 0 0 0 [Table 3] Comparative example Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Mixture containing resin prepolymer (1) (2) (3) (3) (3) NVP as a percentage of total weight (wt.%) 18.8 17.9 17.0 17.0 17.0 IBOA percentage of total weight (wt.%) 5.3 5.0 4.7 4.7 4.7 4-HBA percentage of total weight (wt.%) 5.4 5.1 4.9 4.9 4.9 2-EHA percentage by weight (wt.%) 70.5 50.2 31.8 31 31.8 LA percentage of total weight (wt.%) 0.0 21.8 41.6 41.6 41.6 Catalyst (1%) weight (g) 1.86 1.86 1.86 1.86 1.86 Crosslinking agent (g) 0.23 0.23 0.37 0.07 0.5 Optical adhesive (G) (H) (I) (J) (K) Poisson's ratio 0.43 0.41 0.41 0.46 0.38 Relaxation time (seconds) 420 73 51 20 68 180° peel adhesion (>10 N / in) 17.4 17.0 13.5 8.3 9.7 Peel-off test (failure interface) OCA-PI OCA-PI OCA-PI OCA OCA-PI High temperature and high humidity warping deformation (<0.1 mm) 2.3 0.4 0.2 0 0.3 Based on the results in Tables 2 and 3, it can be seen that compared to the optical adhesives (A) to (F) of this invention, optical adhesives (G) to (H) use fewer linear soft acrylate monomers, resulting in longer relaxation times and greater thermal warpage deformation under high temperature and humidity. Optical adhesive (I) uses more crosslinking agents, resulting in greater thermal warpage deformation under high temperature and humidity compared to optical adhesives (A) to (F) of this invention, and also a longer relaxation time. Furthermore, optical adhesives (J) to (K) use fewer crosslinking agents, resulting in poorer peel test results compared to optical adhesives (A) to (F) of this invention, and also exhibiting a longer relaxation time.

[0073] Furthermore, as shown in Tables 2 and 3, the peel test results indicate that after bonding optical adhesives (A) to (K) with polymethyl methacrylate (PMMA) and polyimide (PI) and then performing the peel test, optical adhesive (J) left residue on both the PI and PMMA sides (the cross-linking degree of the optical adhesive was too small, resulting in cohesion failure in the optical adhesive layer), while the other optical adhesives did not leave residue on the PI side (the failure interface was at the OCA (optical clear adhesive)-PI interface).

[0074] As can be seen from the above results, the optical adhesive of some embodiments of the present invention has good anti-creep properties (low "relaxation time") and stress absorption effect (low "high temperature and high humidity warping deformation"), and can be appropriately applied to flexible panels, etc.

[0075] Although the technical content of the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any modifications and refinements made by those skilled in the art without departing from the spirit of the present invention should be included within the scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims. [ ]< / tg>

Claims

1. An optical adhesive, comprising: 100 parts by weight of component (A), wherein component (A) is a resin prepolymer with straight side chains; 0.02-1 parts by weight of component (B), which is a crosslinking agent; and 0.005-0.01 parts by weight of component (C), which is a catalyst; wherein component (A) is obtained by reacting the following components: (a) 10-40 parts by weight of a soft monomer, which includes a linear soft acrylate monomer as shown in formula (I); Formula (I) wherein n is an integer from 7 to 15; (b) 2-15 parts by weight of a hard monomer, which includes an unsaturated ethylene double bond monomer; (c) 1 part by weight of a hydroxyl (-OH) monomer; and (d) 0.001-0.03 parts by weight of a thermal initiator; wherein the catalyst is a tin-free catalyst; The hydroxyl (-OH) monomer is selected from the group consisting of: hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxypentyl methacrylate, and hydroxyhexyl methacrylate.

2. The optical adhesive as described in claim 1, wherein, The (a) soft monomer of component (A) accounts for 10-20 parts by weight relative to 1 part by weight of hydroxyl (-OH) monomer.

3. The optical adhesive as described in claim 1, wherein, The hard monomer of component (b) accounts for 2-10 parts by weight relative to 1 part by weight of hydroxyl (-OH) monomer.

4. The optical adhesive as described in claim 1, wherein, The soft monomer further includes: a soft monomer with Tg≦0℃, the soft monomer with Tg≦0℃ accounting for at most 60 wt% of the total weight of the (a) soft monomer.

5. The optical adhesive as described in claim 4, wherein, The soft monomer with Tg≦0℃ accounts for 0.1 wt%-50 wt% of the total weight of (a) soft monomer.

6. The optical adhesive as claimed in claim 1, wherein the rigid monomer further comprises: A rigid acrylic monomer, wherein the rigid acrylic monomer accounts for at most 40 wt% of the total weight of the (b) rigid monomer.

7. The optical adhesive as claimed in claim 6, wherein the hard acrylic monomer accounts for 1 wt% to 40 wt% of the (b) hard monomer.

8. The optical adhesive as described in claim 1, wherein, The unsaturated ethylene double bond monolith is selected from the group consisting of: acrylonitrile, acrylamide, acrylmorpholine, and N-vinyl-2-pyrrolidone.

9. The optical adhesive as described in claim 6, wherein, The rigid acrylic monomer is selected from the group consisting of: tributyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate and methyl methacrylate.

10. The optical adhesive as described in claim 1, wherein, The linear soft acrylate monomer shown in formula (I) is selected from the group consisting of: (meth)acrylate n-octyl acrylate, (meth)acrylate n-decyl acrylate, (meth)acrylate lauryl acrylate, (meth)acrylate myristyl acrylate and (meth)acrylate palmitate.

11. The optical adhesive as described in claim 4, wherein, The soft monomer system with Tg≦0℃ is selected from the group consisting of: n-butyl (meth)acrylate, dibutyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, ethoxyethyl (meth)acrylate, and isononyl (meth)acrylate.

12. A laminate for use in flexible panels, comprising: The optical adhesive as described in any one of claims 1 to 11; And at least one substrate; wherein the optical adhesive is located on one surface of the substrate; wherein the material of the substrate is selected from the group consisting of: polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET), polyvinyl chloride (PVC), thermoplastic polyurethane elastomer (TPU), and styrene-acrylonitrile copolymer (AS) and polyimide (PI).