Adhesive composition

Abstract

The present invention relates to an adhesive composition in which bubble generation is suppressed and which has excellent transparency, adhesiveness, mechanical properties, and long-term reliability.

Description

Adhesive composition

[0001] The present invention relates to an adhesive composition that suppresses bubble generation due to outgassing and exhibits excellent transparency, adhesiveness, mechanical properties, and long-term reliability.

[0002]

[0003] Optically clear adhesives (OCAs) are widely used in the process of bonding glass, LCDs, and display modules containing them, and various studies are being conducted to improve their physical properties. For example, Korean registered patent 10-1288238 discloses an acrylic resin composition that is desirable for an adhesive with excellent durability, which does not cause changes in the appearance of an optical laminate even under high humidity and heat conditions and even when heating and cooling are repeated.

[0004] Recently, due to cost considerations or safety issues related to electric vehicles, there has been an increasing number of attempts to use plastic plates containing polycarbonate (PC), polymethyl methacrylate (PMMA), etc., instead of glass plates. When conventional optical adhesives are applied to these plastic plates, there is a problem of bubbles forming due to the outgassing phenomenon occurring in the plastic material.

[0005] Gases emitted from plastic materials are mainly composed of volatile organic compounds (VOCs), unreacted substances, and moisture, and various methods are being attempted to prevent such gas emissions. For example, to remove air trapped in plastic covers, a method (baking method) has been proposed in which the plastic cover is exposed to high temperatures to maximize gas release and then laminated with an optically clear adhesive (OCA). However, this requires an additional process, which increases costs, and there is a problem where the plastic cover warps due to thermal expansion.

[0006] As another example, an attempt was made to suppress gas release by increasing the hardness of optically clear adhesives (OCAs); however, this leads to a problem where delamination occurs due to reduced adhesive strength. Additionally, while increasing hardness allows for gas release, controlling moisture penetration is difficult.

[0007] Accordingly, there is a need to develop an adhesive composition that suppresses bubble formation due to outgassing and offers excellent transparency, adhesiveness, mechanical properties, and long-term reliability.

[0008]

[0009] The present invention provides an adhesive composition in which bubble generation due to outgassing is suppressed and transparency, adhesiveness, mechanical properties, and long-term reliability are excellent.

[0010]

[0011] The present invention provides an adhesive composition comprising: a monomer mixture comprising an alkyl (meth)acrylate, a cycloaliphatic (meth)acrylate, and a hydroxyl group (meth)acrylate; a polyfunctional (meth)acrylate crosslinking agent; and a silane coupling agent, wherein, based on the total weight of the monomer mixture, the composition comprises 40 to 85 weight% of the alkyl (meth)acrylate, 1 to 8 weight% of the cycloaliphatic (meth)acrylate, and 10 to 40 weight% of the hydroxyl group (meth)acrylate, and, per 100 weight parts of the monomer mixture, the composition comprises 0.05 to 0.2 weight parts of the polyfunctional (meth)acrylate and 0.5 to 2 weight parts of the silane coupling agent, and wherein the viscosity (25°C) of the resin prepared from the monomer mixture is 400 to 20,000 cPs.

[0012]

[0013] The present invention provides an adhesive composition that suppresses bubble formation due to gas outgassing and exhibits excellent transparency, adhesiveness, mechanical properties, and long-term reliability. Since the adhesive composition according to the present invention suppresses bubble formation due to gas outgassing when applied to a plastic substrate under high temperature or high temperature and high humidity conditions, it is suitable for application as an optical adhesive for plastic substrates. Furthermore, since the adhesive composition of the present invention can suppress gas outgassing without a baking process for the plastic substrate, it can reduce costs associated with additional processes and minimize changes in the physical properties of the plastic substrate.

[0014]

[0015] The present invention will be described in detail below. However, it is not limited to the following description, and each component may be modified in various ways or selectively combined as needed. Accordingly, it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0016] The term "viscosity" as used in this specification is measured by conventional methods known in the art, for example, using a Brookfield rotational viscometer at room temperature (25°C).

[0017] The adhesive composition of the present invention comprises a monomer mixture comprising an alkyl (meth)acrylate, a cycloaliphatic (meth)acrylate, and a hydroxyl group-containing (meth)acrylate; a polyfunctional (meth)acrylate crosslinking agent; and a silane coupling agent.

[0018]

[0019] monomer mixture

[0020] The adhesive composition of the present invention comprises a monomer mixture comprising an alkyl (meth)acrylate, a cycloaliphatic (meth)acrylate, and a hydroxyl group-containing (meth)acrylate.

[0021] Alkyl (meth)acrylates serve to impart adhesiveness. The alkyl (meth)acrylates may include (meth)acrylic acid esters having linear or branched alkyl groups having 1 to 20 carbon atoms (C1-C20). For example, the alkyl (meth)acrylate having a C1-C20 alkyl group may include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, etc. These may be used alone or in a mixture of two or more. As an example, the alkyl (meth)acrylate may include 2-ethylhexyl (meth)acrylate (EHA).

[0022] The above alkyl (meth)acrylate may be included in an amount of 40 to 85 weight%, for example, 50 to 70 weight%, based on the total weight of the monomer mixture. If the content of the alkyl (meth)acrylate is less than the aforementioned range, the adhesive strength may be reduced, and if it exceeds the aforementioned range, the storage modulus and elongation characteristics may be reduced, and the gas release prevention effect may be reduced.

[0023] Alicyclic (meth)acrylates serve to control adhesive strength. The alicyclic (meth)acrylates may include C3-C20 alicyclic (meth)acrylates. For example, the alicyclic (meth)acrylates may include isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, etc. These may be used individually or in a mixture of two or more. For example, the alicyclic (meth)acrylates may include isobornyl (meth)acrylate (IBOA).

[0024] The above-mentioned cycloaliphatic (meth)acrylate may be included in an amount of 1 to 8 weight%, for example, 3 to 7 weight%, based on the total weight of the monomer mixture. If the content of the cycloaliphatic (meth)acrylate is below the aforementioned range, the adhesive strength to the plastic may decrease, and if it exceeds the aforementioned range, it may become excessively hard and cause lifting.

[0025] Hydroxyl group-containing (meth)acrylates serve to impart hydrophilicity to the adhesive. The above hydroxyl group-containing (meth)acrylates may include C1-C20 alkyl group-containing (meth)acrylates having hydroxyl groups, and C5-C20 cycloalkyl group-containing (meth)acrylates having hydroxyl groups. For example, the above hydroxyl group-containing (meth)acrylate may include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 1,4-cyclohexanedimethanol mono(meth)acrylate, chloro-2-hydroxypropyl (meth)acrylate, diethylene glycol mono(meth)acrylate, etc. These may be used alone or in a mixture of two or more. As an example, the above hydroxyl group-containing (meth)acrylate may include 2-hydroxyethyl (meth)acrylate (HEA).

[0026] The above hydroxyl group-containing (meth)acrylate may be included in an amount of 10 to 40 weight%, for example, 30 to 40 weight%, based on the total weight of the monomer mixture. If the content of the hydroxyl group-containing (meth)acrylate is less than the aforementioned range, the outgassing prevention effect may be insufficient, and if it exceeds the aforementioned range, it may become excessively hard and cause lifting.

[0027] The above monomer mixture may contain the alkyl (meth)acrylate, the alicyclic (meth)acrylate, and the hydroxyl (meth)acrylate in a weight ratio of 10 to 15:1:3 to 10, for example, 10 to 12:1:5 to 8. If the mixing ratio of the alkyl (meth)acrylate to the alicyclic (meth)acrylate is less than the aforementioned range, the adhesiveness may be reduced, and if it exceeds the aforementioned range, an outgassing phenomenon may occur. If the mixing ratio of the hydroxyl (meth)acrylate to the alicyclic (meth)acrylate is less than the aforementioned range, bubbles may be generated, and if it exceeds the aforementioned range, the adhesive strength may be reduced.

[0028] The viscosity (25°C) of the resin prepared from the above monomer mixture may be 400 to 20,000 cPs, for example, 1,000 to 20,000 cPs. If the viscosity of the resin is below the aforementioned range, it may be difficult to control the thickness during coating, making it difficult to obtain a coating film of the desired thickness, and if it exceeds the aforementioned range, the workability of the coating may be reduced, making it difficult to obtain a film of uniform thickness.

[0029] By using the monomer mixture according to the present invention, the modulus (25°C) of the adhesive composition can be controlled to 50,000 to 200,000 Pa, and gas release can be effectively suppressed due to the increased hardness.

[0030]

[0031] crosslinking agent

[0032] The adhesive composition of the present invention includes a polyfunctional (meth)acrylate as a crosslinking agent. The above-mentioned polyfunctional (meth)acrylates are 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, neopentyl glycol adipate di(meth)acrylate, dicyclofentanyl di(meth)acrylate, caprolactone-modified dicyclofentenyl di(meth)acrylate, ethylene oxide-modified di(meth)acrylate, di(meth)acryloxyethyl isocyanurate, allylated cyclohexyl di(meth)acrylate, tricyclodecane dimethanol (meth)acrylate, dimethylol dicyclopentane di(meth)acrylate, and ethylene oxide-modified hexahydrophthalic acid di(meth)acrylate. Difunctional (meth)acrylates such as tricyclodecane dimethanol (meth)acrylate, neopentyl glycol-modified trimethylpropane di(meth)acrylate, adamantane di(meth)acrylate, and 9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene; trifunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, propionic acid-modified dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, trifunctional urethane (meth)acrylate, and tris(meth)acrylates such as tris(meth)acrylate; It may include tetrafunctional (meth)acrylates such as diglycerin tetra(meth)acrylate and pentaerythritol tetra(meth)acrylate; pentafunctional acrylates such as dipentaerythritol penta(meth)acrylate; and hexafunctional (meth)acrylates such as dipentaerythritol hexa(meth)acrylate and caprolactone-modified dipentaerythritol hexa(meth)acrylate. These may be used alone or in a mixture of two or more types. For example, the polyfunctional (meth)acrylate may include hexanediol diacrylate (HDDA).

[0033] The above-mentioned polyfunctional (meth)acrylate may be included in an amount of 0.05 to 0.2 parts by weight, for example, 0.1 to 0.2 parts by weight, per 100 parts by weight of the monomer mixture. If the content of the polyfunctional (meth)acrylate is less than the aforementioned range, the outgassing prevention effect may be insufficient, and if it exceeds the aforementioned range, it may become excessively hard.

[0034]

[0035] Silane coupling agent

[0036] The adhesive composition of the present invention includes a silane coupling agent. The silane coupling agent complements the adhesive strength and effectively suppresses lifting phenomena. In particular, when a hydrophilic silane coupling agent is used, an increase in solubility can also be induced.

[0037] As the above silane coupling agents, tetraethyl orthosilicate, 3-glycidoxypropyl trimethoxysilane, etc., may be used. These may be used alone or in a mixture of two or more.

[0038] The above silane coupling agent may be included in an amount of 0.5 to 2 parts by weight, for example, 0.7 to 1.3 parts by weight, per 100 parts by weight of the monomer mixture. If the content of the silane coupling agent is less than the aforementioned range, the effect of increasing adhesion and preventing outgassing may be insufficient, and if it exceeds the aforementioned range, the solid content value is lowered during photocuring, which may cause outgassing due to unreacted material.

[0039]

[0040] Photoinitiator

[0041] The adhesive composition of the present invention may include a photoinitiator. As the photoinitiator, any photoinitiator used in the relevant technical field may be used without special limitations. The photoinitiator may be included in an amount of 0.01 to 0.5 parts by weight, for example, 0.01 to 0.2 parts by weight, per 100 parts by weight of the monomer. If the content of the crosslinking agent is less than the aforementioned range, polymerization and crosslinking proceed insufficiently, and the outgassing prevention effect may be insufficient; if it exceeds the aforementioned range, the molecular weight of the resin becomes excessively small and becomes excessively hard, which may cause lifting.

[0042]

[0043] The adhesive composition of the present invention can be prepared by a manufacturing method comprising the steps of: mixing a monomer comprising an alkyl (meth)acrylate, a dicycloal (meth)acrylate, and a hydroxyl group-containing (meth)acrylate, and a photoinitiator (step 1); irradiating the mixture with UV light to produce a resin (step 2); and mixing a polyfunctional (meth)acrylate, which is a crosslinking agent, and a photoinitiator into the resin (step 3).

[0044]

[0045] The present invention will be explained in more detail below through examples. However, the following examples are intended only to aid in understanding the present invention and do not imply that the scope of the present invention is limited to these examples in any way.

[0046]

[0047] [Examples 1-5: Preparation of Adhesive Compositions]

[0048] According to Table 1 below, the resin component was introduced into a reactor, and dissolved oxygen was removed by injecting nitrogen for 30 minutes, after which UV was irradiated using a low-pressure UV lamp (Philips TL-8W). The reaction was terminated while observing an increase in viscosity after the polymerization reaction began. Termination of the reaction was performed by turning off the low-pressure UV lamp and injecting air. The adhesive composition of each example was prepared by uniformly mixing a crosslinking solution with the resin prepared above (viscosity (25 ℃) 1,500 cps, solid content 10%).

[0049]

[0050] [Comparative Example 1-5: Preparation of Adhesive Composition]

[0051] The adhesive compositions of each comparative example were prepared in the same manner as the examples, except for those according to Table 2 below.

[0052]

[0053]

[0054]

[0055]

[0056] EHA: 2-ethylhexyl acrylate

[0057] IBOA: Isobornyl acrylate

[0058] HEA: 2-hydroxyethyl acrylate

[0059] HDDA: Hexanediol diacrylate

[0060] Photoinitiator: Benzyl dimethyl ketal

[0061] Silane coupling agent 1: Tetraethyl orthosilicate (TEOS)

[0062] Silane Coupling Agent 2: 3-glycidoxypropyl trimethoxysilane

[0063]

[0064] [Physical Property Evaluation]

[0065] The physical properties of the adhesive compositions of each example and comparative example were evaluated according to the following method, and the results are shown in Tables 3 and 4 below.

[0066]

[0067] Transparent adhesive tape manufacturing

[0068] The adhesive compositions of each example and comparative example were applied to a thickness of 400 μm on a release film, and after covering with a release film, 2,100 mJ / cm² 2 Transparent adhesive tapes of each example and comparative example were prepared by UV irradiation.

[0069]

[0070] Gel content (Gel%)

[0071] The transparent adhesive tapes of each example and comparative example were immersed in ethyl acetate for at least 24 hours, filtered, and dried in a 120°C oven for 30 minutes, after which the gel content was evaluated based on the rate of mass change before and after immersion.

[0072]

[0073] Solid content (NV%)

[0074] After drying the transparent adhesive tapes of each example and comparative example in a forced circulation oven at 120°C for 30 minutes, the solid content was evaluated based on the rate of change in mass before and after drying.

[0075]

[0076] adhesiveness

[0077] A transparent adhesive tape of each example and comparative example was adhered to a 25 μm PET film, cut to a width of 1 inch, adhered to soda-lime glass, and left for 24 hours to prepare specimens. The adhesive strength was evaluated by performing a 180° Peel test at room temperature at a speed of 300 mm / min using a UTM instrument (Salt, ST-1003).

[0078]

[0079] Transmittance, turbidity

[0080] Two sheets of soda-lime glass were laminated using the transparent adhesive tape of each example and comparative example to prepare specimens with a glass / transparent adhesive tape / glass structure. After leaving each specimen for 24 hours, transmittance and turbidity were measured using a transmittance meter (BYK, Haze Guard-i).

[0081]

[0082] Modulus

[0083] The transparent adhesive tapes of each example and comparative example were fabricated into disc shapes with a diameter of 8 mm and a thickness of 1 μm, and then analyzed using a rheometer (Anton Paar, MCR 302-CMK).

[0084]

[0085] Long-term reliability

[0086] Specimens with a Glass / transparent adhesive tape / Glass structure were prepared by laminating two sheets of Soda-lime glass using the transparent adhesive tapes of each example and comparative example. After storing each specimen for 1,000 hours under each condition, haze and turbidity were analyzed. Long-term reliability was evaluated as good when haze was 99% or higher and turbidity was 1% or lower.

[0087]

[0088] Bubble generation suppression power

[0089] Each specimen was prepared by sequentially laminating the PC surface of a PC / PMMA co-extruded sheet, the transparent adhesive tapes of each example and comparative example, and soda-lime glass. After leaving each specimen for 24 hours, long-term reliability was evaluated by placing it in a constant temperature and humidity chamber at 85°C and 85% RH and observing for bubble formation for one week. 10 x 10 cm 2 The number of large bubbles (diameter 300 μm or more) and small bubbles (diameter less than 300 μm) within the specimen was measured, and it was evaluated as good if no bubbles were generated.

[0090]

[0091]

[0092]

[0093]

[0094]

[0095] As shown in Tables 3 and 4 above, the adhesive compositions of Examples 1-5 according to the present invention exhibited excellent physical properties across all measured items. On the other hand, Comparative Examples 1 and 2, in which the content of the silane coupling agent falls outside the scope of the present invention; Comparative Examples 3 and 4, in which some of the three monomers are used at amounts outside the scope of the present invention; and Comparative Example 5, in which no (meth)acrylate containing alicyclic compounds is included, exhibited inferior physical properties compared to the Examples across all measured items. In particular, in the case of the adhesive compositions of the Comparative Examples, it can be confirmed that a large number of bubbles are generated due to outgassing.

[0096]

[0097] The present invention provides an adhesive composition in which bubble generation due to outgassing is suppressed and transparency, adhesiveness, mechanical properties, and long-term reliability are excellent.

Claims

1. A monomer mixture comprising alkyl (meth)acrylates, alicyclic (meth)acrylates, and hydroxyl-containing (meth)acrylates; a polyfunctional (meth)acrylate crosslinking agent; and a silane coupling agent, comprising Based on the total weight of the monomer mixture, the mixture comprises 40 to 85 weight% of the alkyl (meth)acrylate, 1 to 8 weight% of the alicyclic (meth)acrylate, and 10 to 40 weight% of the hydroxyl (meth)acrylate. Based on 100 parts by weight of the monomer mixture, the composition comprises 0.05 to 0.2 parts by weight of the polyfunctional (meth)acrylate and 0.5 to 2 parts by weight of the silane coupling agent, An adhesive composition having a viscosity (25°C) of 400 to 20,000 cPs of a resin prepared from the above monomer mixture.

2. An adhesive composition according to claim 1, wherein the monomer mixture comprises the alkyl (meth)acrylate, the alicyclic (meth)acrylate, and the hydroxyl (meth)acrylate in a weight ratio of 10 to 15: 1: 3 to 10.

3. An adhesive composition according to claim 1, wherein the modulus (Modulus, 25 ℃) is 50,000 to 200,000 Pa.

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