Low modulus folded OCA

Abstract

The invention discloses a low-modulus folding OCA (optical clear adhesive), which comprises a light release layer, an optical acrylate pressure-sensitive adhesive layer and a heavy release layer which are sequentially arranged, and the optical acrylate pressure-sensitive adhesive layer comprises the following raw materials in parts by weight: 80-100 parts of polyacrylic resin, 0-20 parts of an active diluent monomer, 0.1-5 parts of a cross-linking agent, 0.01-2 parts of a silane coupling agent and 0.01-5 parts of a photoinitiator. According to the invention, by optimizing the formula composition of the folded OCA and adopting a UV polymerization cross-linking mode, the adhesive has relatively high viscosity while realizing low modulus, and also has relatively high deformation, so that the risk of deformation and warping is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of optical adhesives, and in particular relates to a low-modulus folded OCA. Background Art

[0002] In recent years, with the continuous evolution and upgrading of technology, thinner and lighter, foldable flexible display devices have gradually become popular. With the demand for foldable electronic devices, the functional film materials supporting electronic display devices also need to be developed to be thinner and lighter and foldable. Foldable OCA, which plays a key role in this, is particularly critical.

[0003] The main problems of the existing technology are: the existing conventional optical OCA often has a high modulus and glass transition temperature. Under low temperature conditions, OCA is prone to bending failure due to its high modulus. For folding OCA, in order to reduce the modulus and glass transition temperature, the proportion of hard monomers and functions is relatively small, resulting in low peeling force and poor high temperature resistance, especially the risk of adhesive failure or bending fracture in high temperature and high humidity environments.

[0004] Therefore, in view of the above technical problems, it is necessary to provide a low modulus folded OCA.

[0005] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0006] The object of the present invention is to provide a low modulus folded OCA.

[0007] In order to achieve the above object, a technical solution provided by a specific embodiment of the present invention is as follows:

[0008] The low modulus folding OCA comprises a light release layer, an optical acrylate pressure-sensitive adhesive layer, and a heavy release layer which are arranged in sequence, wherein the raw material composition of the optical acrylate pressure-sensitive adhesive layer comprises, by weight: 80 to 100 parts of polyacrylic resin, 0 to 20 parts of active diluent monomer, 0.1 to 5 parts of cross-linking agent, 0.01 to 2 parts of silane coupling agent, and 0.01 to 5 parts of photoinitiator.

[0009] In one or more embodiments of the present invention, the weight average molecular weight of the polyacrylic acid resin is 1 million to 4 million, preferably 2 million to 4 million, and more preferably 2.5 million to 3 million.

[0010] In one or more embodiments of the present invention, the polyacrylic resin is prepared by 60-90 parts by weight of a soft monomer, 3-15 parts by weight of a hard monomer, 3-20 parts by weight of a functional monomer, and 0-0.005 parts by weight of a chain transfer agent, and 0.01-2 parts by weight of a photoinitiator is used to decompose free radicals under UV light conditions to initiate the polymerization of carbon-carbon double bonds of propylene alkyl ester monomers.

[0011] In one or more embodiments of the present invention, the soft monomer is selected from an alkyl acrylate monomer having an alkyl group with a carbon number of 4-20. Preferably, the alkyl group has a carbon number of 4-16, and more preferably, the alkyl group has a carbon number of 6-12. More preferably, the alkyl group contains any one of a straight chain or a branched chain. More preferably, the soft monomer includes but is not limited to butyl acrylate, isobutyl acrylate, (class A) propylene-2-ethylhexyl ester, (methyl) acrylate n-octyl ester, isodecyl acrylate, ethoxyethoxyethyl acrylate, lauryl methacrylate and lauryl acrylate. Among them, the soft monomer is more preferably a long molecular weight and a relatively low glass transition temperature, such as butyl acrylate, propylene-2-ethylhexyl ester, and ethoxyethoxyethyl acrylate.

[0012] In one or more embodiments of the present invention, the hard monomer includes but is not limited to methyl acrylate, vinyl acetate, styrene, methyl methacrylate, ethyl methacrylate, acrylamide, N,N-dimethylacetoacetamide, isopropyl methacrylate, cyclohexyl methacrylate, isobutyl methacrylate, isobornyl methacrylate, isobornyl acrylate, tetrahydrofuran methacrylate, and cyclohexyl acrylate.

[0013] In one or more embodiments of the present invention, the functional monomer includes but is not limited to a monomer containing a hydroxyl group, a monomer containing a carboxyl group, a monomer containing an amide group, a monomer containing an epoxy group, and a monomer containing nitrogen. Preferably, the functional monomer can be 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, acrylic acid, methacrylic acid, acrylamide, glycidyl acrylate, N,N-diethylacrylamide, N-vinyl pyrrolidone, etc.

[0014] In one or more embodiments of the present invention, the photoinitiator includes one or more of benzoin and its derivatives, benzil and its derivatives, acetophenone and its derivatives, α-hydroxyalkyl acetophenone, α-aminoalkyl acetophenone, and acylphosphine oxide photoinitiators. Preferably, the commercially available brands are one or more of 651, 184, and TPO.

[0015] In one or more embodiments of the present invention, the active diluent monomer is selected from: acryloyl morpholine (ACMO), isooctyl acrylate (2-EHA), isodecyl acrylate (IDA), lauryl acrylate (LA), hydroxyethyl acrylate (HEA), styrene (St), vinyl acetate (VA), N-vinyl pyrrolidone (NVP), butyl acrylate (BA), hydroxypropyl acrylate (HPA), hydroxyethyl methacrylate (HEMA), glycidyl methacrylate (GMA), isobornyl methacrylate (IBOMA), isobornyl acrylate (IBOA), tetrahydrofuran acrylate (THFA).

[0016] In one or more embodiments of the present invention, the crosslinking agent is selected from: phenoxyethyl acrylate (POEA), tripropylene glycol diacrylate (TPGDA), dipropylene glycol diacrylate (DPGDA), 1,6-hexanediol diacrylate HDDA, ethylene glycol dimethacrylate (EGDMA).

[0017] In one or more embodiments of the present invention, the silane coupling agent is selected from: γ-aminopropyl triethoxysilane, γ-2,3-glycidoxypropyl trimethoxysilane, γ-methacryloxypropyl trimethoxysilane. Preferably, the silane coupling agent is brand KH-560.

[0018] In one or more embodiments of the present invention, the chain transfer agent is selected from dodecanethiol nDDm.

[0019] Compared with the prior art, the low modulus folded OCA of the present invention adopts UV polymerization cross-linking method, so that the adhesive has high viscosity while achieving low modulus and high deformation, which greatly reduces the risk of deformation and warping. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0021] Example 1

[0022] Preparation of acrylate resin:

[0023] 88 parts of butyl acrylate BA, 7 parts of 2-hydroxyethyl acrylate HEA, 5 parts of cyclohexyl acrylate CHA, and 0.05 parts of photoinitiator 184 were weighed; 0.005 parts of chain transfer agent dodecanethiol nDDM were added into a reaction kettle and stirred evenly; polymerization reaction was carried out under UV light under nitrogen protection; the reaction was terminated when the viscosity of the reaction liquid reached 10000-12000 cps to obtain the polyacrylic resin.

[0024] Weigh 100 parts of polyacrylic resin, 0.10 parts of photoinitiator 184, 0.1 parts of silane coupling agent KH-560, and 0.1 parts of 1,6-hexanediol diacrylate HDDA; add them into a container and stir evenly; apply them on the release layer of the PET release film with a coating thickness of 25 μm; cover and protect with the PET release film, and after UV light curing, the low modulus optical acrylate pressure-sensitive adhesive layer is obtained.

[0025] Example 2

[0026] Based on Example 1, the amount of transfer agent dodecanethiol nDDm was adjusted to 0.002.

[0027] Example 3

[0028] Based on Example 1, the amount of transfer agent dodecanethiol nDDm was adjusted to 0.

[0029] Example 4

[0030] On the basis of Example 3, 2-hydroxyethyl acrylate HEA was replaced with hydroxypropyl acrylate HPA.

[0031] Example 5

[0032] On the basis of Example 3, 2-hydroxyethyl acrylate HEA was replaced with hydroxybutyl acrylate HBA.

[0033] Example 6

[0034] Based on Example 5, butyl acrylate BA was replaced with isooctyl acrylate EHA.

[0035] Example 7

[0036] Preparation of acrylate resin:

[0037] Weigh 88 parts of butyl acrylate EHA, 5 parts of hydroxybutyl acrylate HBA, 7 parts of cyclohexyl acrylate CHA, and 0.05 parts of photoinitiator 184; stir evenly; perform polymerization reaction under UV light protection in a nitrogen environment; terminate the reaction when the viscosity of the reaction liquid reaches 10000-12000 cps to obtain the polyacrylic resin.

[0038] Weigh 100 parts of polyacrylic resin, 0.10 parts of photoinitiator 184, 0.1 parts of silane coupling agent KH-560, and 0.1 parts of 1,6-hexanediol diacrylate HDDA; add them into a container and stir evenly; apply them on the release layer of the PET release film with a coating thickness of 25 μm; cover and protect with the PET release film, and after UV light curing, the low modulus optical acrylate pressure-sensitive adhesive layer is obtained.

[0039] Example 8

[0040] Preparation of acrylate resin:

[0041] Weigh 90 parts of butyl acrylate EHA, 6 parts of hydroxybutyl acrylate HBA, 4 parts of 1-vinyl-2-pyrrolidone acrylate NVP, and 0.05 parts of photoinitiator 184; stir evenly; carry out polymerization reaction under UV light in a nitrogen protection environment; terminate the reaction when the viscosity of the reaction liquid reaches 10000-12000cps to obtain the polyacrylic resin.

[0042] Weigh 100 parts of polyacrylic resin, 0.10 parts of photoinitiator 184, 0.1 parts of silane coupling agent KH-560, and 0.1 parts of 1,6-hexanediol diacrylate HDDA; add them into a container and stir evenly; apply them on the release layer of the PET release film with a coating thickness of 25 μm; cover and protect with the PET release film, and after UV light curing, the low modulus optical acrylate pressure-sensitive adhesive layer is obtained.

[0043] Comparative Example 1

[0044] Weigh 90 parts of butyl acrylate EHA, 6 parts of hydroxybutyl acrylate HBA, 4 parts of acrylamide AM, and 0.05 parts of photoinitiator 184; stir evenly; perform polymerization reaction under UV light protection in a nitrogen environment; terminate the reaction when the viscosity of the reaction liquid reaches 10000-12000 cps to obtain the polyacrylic resin.

[0045] Weigh 100 parts of polyacrylic resin, 0.10 parts of photoinitiator 184, 0.1 parts of silane coupling agent KH-560, and 0.1 parts of 1,6-hexanediol diacrylate HDDA; add them into a container and stir evenly; apply them on the release layer of the PET release film with a coating thickness of 25 μm; cover and protect with the PET release film, and after UV light curing, the low modulus optical acrylate pressure-sensitive adhesive layer is obtained.

[0046] Comparative Example 2

[0047] Weigh 90 parts of butyl acrylate EHA, 6 parts of hydroxybutyl acrylate HBA, 4 parts of isobornyl acrylate, and 0.05 parts of photoinitiator 184; stir evenly; perform polymerization reaction under UV light protection in a nitrogen environment; terminate the reaction when the viscosity of the reaction liquid reaches 10000-12000 cps to obtain the polyacrylic resin.

[0048] Weigh 100 parts of polyacrylic resin, 0.10 parts of photoinitiator 184, 0.1 parts of silane coupling agent KH-560, and 0.1 parts of 1,6-hexanediol diacrylate HDDA; add them into a container and stir evenly; apply them on the release layer of the PET release film with a coating thickness of 25 μm; cover and protect with the PET release film, and after UV light curing, the low modulus optical acrylate pressure-sensitive adhesive layer is obtained.

[0049] Table 1: Example and comparative example feeding table

[0050] Proportion Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Comparative Example 1 Comparative Example 2 2-EHA 88 88 90 90 90 BA 88 88 88 88 88 HEA 7 7 7 HBA 7 7 5 6 6 6 HPA 7 CHA 5 5 5 5 5 5 7 NVP 4 AM 4 IBOA 4 184 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 nD 0.005 0.002 0 0 0 0 0 0 0 0

[0051] Performance Testing

[0052] Test Item 1:

[0053] 180° peel strength test of acrylic pressure-sensitive adhesive layer

[0054] According to the ASTM D3330 method, the sample was made into 300mm long and 25mm wide, and rolled back and forth on the glass with a 2kg rubber roller for three times. After being placed at a temperature of 23°C and a humidity of 50% RH for 20 minutes, it was tested with a tensile tester. The peeling was carried out at a peeling angle of 180° and a peeling speed of 300mm / min, and the 180° peeling force was tested.

[0055] Test Item 2:

[0056] Shear modulus and creep recovery: The film is stacked into a test sample with a thickness of 0.9mm to 1.1mm (such as 1.0mm), and a cylinder with a diameter of 8mm is punched out and used as a sample. Anton Paar rheometer MCR 102e is used, and the test standard is ASTM D4440-15. The temperature is scanned from -40℃ to 100℃ at 2℃ / min, and the sample oscillates at a frequency of 1Hz and a shear strain of 0.1%. The shear storage modulus (G') at different temperatures is recorded. The maximum value of the loss factor tanδ is the Tg of the material.

[0057] Creep recovery: Fixed temperature such as 25℃, apply 10KPa stress for 600s. Remove the external force and test the OCA recovery curve for 600s. The maximum deformation is recorded as Creep, and the creep recovery rate is (maximum value - minimum value) / maximum value.

[0058] Test Item 3:

[0059] Molecular weight and molecular weight distribution: Gel permeation chromatograph Agilent 1260Infinity, test standard GB / T21863-2008

[0060] Test Item 4:

[0061] Gel fraction of film: accurately weigh 0.3-05g of film, record it as m1, dissolve it in enough ethyl acetate for 24 hours, filter it with a 200-mesh filter, record it as m2, and dry it at 150℃ for 30 minutes, record it as m3. The gel fraction is (m3-m2) / m1.

[0062] Test Item 5:

[0063] Dynamic bending test: A 25μm thick adhesive pressure-sensitive adhesive layer is laminated between two 50μm polyimide (PI) sheets and then cut into 25mm wide and 125mm long dimensions. The sample is mounted in a dynamic folding device with a temperature control of 85℃*85%RH and two folding stages, which rotate from 180° (flat state) to 0° (folded state) and are cycled 200,000 times at a rate of 6 cycles / min. If there is no fracture or delamination of the composite structure after the cycle, the observed sample passes the dynamic folding test.

[0064] Table 2: Performance results of examples and comparative examples

[0065]

[0066]

[0067] Through the data of Examples 1, 2, and 3, it is found that increasing the polymer molecular weight can improve the cohesive strength and bending performance of the film. Increasing the polymer molecular weight to above 260W can significantly improve the film performance. Of course, the existing polymer molecular weight is not necessarily the optimal result, and the polymer molecular weight can be further increased by adjusting the initiator light intensity.

[0068] Through the data of Examples 3, 4, and 5, it is found that the addition of monomers containing hydroxyl functional groups can improve the high temperature rheological properties of the adhesive layer. At the same time, the use of hydroxybutyl acrylate with a lower glass transition temperature can reduce the glass transition temperature of the polymer without affecting the cohesive strength, thereby reducing the shear modulus of the adhesive layer.

[0069] From the data of Examples 5, 6, and 7, it is found that the shear modulus of the adhesive layer can be further reduced by adjusting the glass transition temperature of the soft monomer, but this will also affect the bonding properties of the adhesive layer. Therefore, the glass transition temperature of the adhesive layer cannot be too low.

[0070] From the data of Example 8 and Comparative Examples 1 and 2, it is found that the monomer with too high glass transition temperature will affect the glass transition temperature of the adhesive layer. Therefore, the monomer selection should be a monomer with a lower glass transition temperature or an ethoxylated or propoxylated modified monomer to further reduce the overall glass transition temperature.

[0071] The invention increases the molecular weight of the polymer, improves the cohesive strength and shear creep performance of the polymer, increases the maximum deformation of the OCA without affecting the creep recovery performance, and reduces the risk of bending and fracture. At the same time, hydroxyl functional monomers and hard monomers with lower glass transition temperatures are introduced to make the OCA adhesive have low modulus at low temperatures and high modulus at high temperatures, and the bonding performance meets higher requirements.

[0072] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0073] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A low modulus folding OCA, comprising a light release layer, an optical acrylate pressure-sensitive adhesive layer, and a heavy release layer arranged in sequence, wherein the raw material composition of the optical acrylate pressure-sensitive adhesive layer includes, by weight: 80 to 100 parts of polyacrylic resin, 0 to 20 parts of active diluent monomer, 0.1 to 5 parts of cross-linking agent, 0.01 to 2 parts of silane coupling agent, and 0.01 to 5 parts of photoinitiator.

2. The low modulus folded OCA according to claim 1, characterized in that: The weight average molecular weight of the polyacrylic acid resin is 1 million to 4 million.

3. The low modulus folded OCA according to claim 2, characterized in that: The polyacrylic resin is prepared from 60-90 parts by weight of soft monomers, 3-15 parts by weight of hard monomers, 3-20 parts by weight of functional monomers and 0-0.005 parts by weight of chain transfer agents, and is obtained by initiating polymerization of carbon-carbon double bonds of propylene alkyl ester monomers by decomposing free radicals in 0.01-2 parts by weight of photoinitiator under UV light conditions.

4. The low modulus folded OCA according to claim 3, characterized in that: The soft monomer is selected from alkyl acrylate monomers having an alkyl group with 4 to 20 carbon atoms.

5. The low modulus folded OCA according to claim 3, characterized in that: The hard monomers include, but are not limited to, methyl acrylate, vinyl acetate, styrene, methyl methacrylate, ethyl methacrylate, acrylamide, N,N-dimethylacetoacetamide, isopropyl methacrylate, cyclohexyl methacrylate, isobutyl methacrylate, isobornyl methacrylate, isobornyl acrylate, tetrahydrofuran methacrylate, and cyclohexyl acrylate.

6. The low modulus folded OCA according to claim 3, characterized in that: The functional monomers include, but are not limited to, monomers containing hydroxyl groups, monomers containing carboxyl groups, monomers containing amide groups, monomers containing epoxy groups, and monomers containing nitrogen.

7. The low modulus folded OCA according to claim 1 or 3, characterized in that: The photoinitiator includes one or more of benzoin and its derivatives, benzil and its derivatives, acetophenone and its derivatives, α-hydroxyalkylacetophenone, α-aminoalkylacetophenone, and acylphosphine oxide photoinitiators.

8. The low modulus folded OCA according to claim 1, characterized in that: The active diluent monomer is selected from the group consisting of acryloylmorpholine, isooctyl acrylate, isodecyl acrylate, lauryl acrylate, hydroxyethyl acrylate, styrene, vinyl acetate, N-vinyl pyrrolidone, butyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, glycidyl methacrylate, isobornyl methacrylate, isobornyl acrylate, and tetrahydrofuran acrylate.

9. The low modulus folded OCA according to claim 1, characterized in that: The crosslinking agent is selected from the group consisting of phenoxyethyl acrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, 1,6-hexanediol diacrylate, and ethylene glycol dimethacrylate.

10. The low modulus folded OCA according to claim 1, characterized in that: The silane coupling agent is selected from: γ-aminopropyltriethoxysilane, γ-2,3-glycidoxypropyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane.

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