Photoinitiator, adhesive composition, adhesive film, and method for producing same

Abstract

The present invention provides a photoinitiator including at least one benzophenone group and a urethane bond, an adhesive composition including the photoinitiator, an adhesive film including an adhesive layer including a photocured product of the adhesive composition, and a method for preparing the adhesive film.

Description

TECHNICAL FIELD

[0001] The present application relates to a photoinitiator, an adhesive composition, an adhesive film, and a method for producing the same. BACKGROUND

[0002] An adhesive film can be produced by photo-polymerization by irradiating light to an adhesive composition containing a monomer. A photoinitiator contained in such an adhesive composition functions to initiate a photo-polymerization reaction. SUMMARY

[0003] PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] An object of the present application is to provide a photoinitiator having excellent compatibility with an acrylic resin.

[0005] Further, another object of the present application is to provide an adhesive composition and an adhesive film having excellent durability by containing the photoinitiator, which reduces a total mass loss and a swelling index and increases a gel fraction.

[0006] The objects of the present application are not limited to the above-mentioned objects, and other objects and advantages of the present application not mentioned above can be understood from the following description, and can be more clearly understood from the embodiments of the present application. Also, it is obvious that the objects and advantages of the present application can be achieved by the means indicated in the scope of the claims and combinations thereof.

[0007] TECHNICAL SOLUTION

[0008] To achieve the object, in an example of the present application, a photoinitiator containing at least one benzophenone group and a urethane bond is provided.

[0009] The photoinitiator can contain three or more benzophenone groups.

[0010] In an example of the present application, a compound represented by the following Chemical Formula 1 is provided.

[0011] Chemical Formula 1

[0012]

[0013] In the Chemical Formula 1,

[0014] R 1 , R 2 , and R 3 are each independently , R 4 , R 5 , and R 6 are each independently a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms, in which case, Indicates the location of the connection.

[0015] The R 4 R 5 and R 6 Each can be an alkylene group, either substituted or unsubstituted, having 5 or more but less than 8 carbon atoms.

[0016] The compound can be represented by the following chemical formula 1-1.

[0017] Chemical Formula 1-1

[0018]

[0019] The compound can be used as a photoinitiator.

[0020] In one embodiment of the present invention, an adhesive composition is provided comprising an acrylic resin and a photoinitiator, wherein the photoinitiator is a photoinitiator comprising at least one benzophenone group and an urethane bond, or comprises a compound represented by Formula 1 or a compound represented by Formula 1-1.

[0021] The acrylic resin may include acrylate prepolymers and acrylate monomers.

[0022] The adhesive composition uses the photoinitiator as a first photoinitiator and further comprises an additive containing at least one selected from the group consisting of polyurethane acrylate, multifunctional crosslinking agent, coupling agent, second photoinitiator, and combinations thereof, wherein the second photoinitiator may be different from the first photoinitiator.

[0023] The multifunctional crosslinking agent can be a multifunctional acrylate.

[0024] The coupling agent can be a silane-based coupling agent.

[0025] The second photoinitiator may include at least one selected from the group consisting of benzoin-based photoinitiators, hydroxyketone-based photoinitiators, aminoketone-based photoinitiators, and combinations thereof.

[0026] In one embodiment of the present invention, an adhesive film is provided, comprising an adhesive layer, the adhesive layer comprising a photocurable form of the adhesive composition.

[0027] The gel fraction of the adhesive layer can be 55% to 80%, the swelling index of the adhesive layer can be 12 to 35, the haze of the adhesive layer can be below 0.7, and the colorimeter shows a b... The value can be less than 0.45.

[0028] The thickness of the adhesive layer can be from 50 μm to 250 μm.

[0029] In one embodiment of the present invention, a method for preparing an adhesive film is provided, comprising: a step of preparing an acrylic resin; a step of mixing the prepared acrylic resin with a photoinitiator to prepare an adhesive composition; and a step of photocuring the adhesive composition to form an adhesive layer. The photoinitiator is a photoinitiator containing at least one benzophenone group and an urethane bond, or a compound represented by Formula 1 or a compound represented by Formula 1-1.

[0030] The viscosity of the acrylic resin at 25°C can be from 500 cps to 5000 cps.

[0031] The effects of the invention

[0032] The photoinitiator of the present invention contains a molecular structure compatible with acrylic resins, and can be easily mixed with acrylic resins when preparing photocurable adhesive compositions.

[0033] Furthermore, the photoinitiator of the present invention improves the efficiency of the photoinitiation reaction, thereby increasing the curing density, which in turn increases the gel fraction and reduces the swelling index, thus providing a cured product with excellent durability.

[0034] It should be understood that the effects of the present invention are not limited to those described above, but also include all effects that can be inferred from the structure of the invention as described in the detailed description of the invention or the claims. Detailed Implementation

[0035] Please note that in the following description, only the parts necessary for understanding the embodiments of the present invention are described, and the rest of the description will be omitted without obscuring the gist of the present invention.

[0036] It should be noted that the terms or vocabulary used in this specification and the scope of protection of the invention should not be limited to their commonly understood or dictionary meanings. Rather, they are interpreted in accordance with the principle that inventors may appropriately define the concepts of terms to best describe their invention, and should be interpreted as conforming to the technical concept of the invention. Therefore, the embodiments and structures described in the drawings are merely preferred embodiments of the invention and do not represent all the technical concepts of the invention. It should be understood that, at the time of filing this application, there are many equivalents and modifications that can replace them.

[0037] The present invention will now be described in detail.

[0038] In one embodiment of the present invention, a novel compound represented by the following chemical formula 1 is provided.

[0039] Chemical Formula 1

[0040]

[0041] In the chemical formula 1,

[0042] R 1 R 2 and R 3 Each independently ,

[0043] R 4 R 5 and R 6 Each is independently a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms; in this case, Indicates the location of the connection.

[0044] In one instance, the R 4 R 5 and R 6 Each can be an alkylene group, either substituted or unsubstituted, having 5 or more but less than 8 carbon atoms.

[0045] In one instance, the compound may be represented by the following chemical formula 1-1.

[0046] Chemical Formula 1-1

[0047]

[0048] In one instance, the compound can be used as a photoinitiator.

[0049] In one embodiment of the invention, a photoinitiator comprising at least one benzophenone group and an urethane bond is provided.

[0050] The photoinitiator contains both a benzophenone group with photoinitiating function and an urethane bond with excellent compatibility with acrylic resins. It has excellent efficiency and compatibility in photoinitiation reaction, thus making it easy to prepare adhesive compositions containing acrylic resins.

[0051] Specifically, the photoinitiator may contain more than three benzophenone groups in order to improve the photoinitiation reaction, that is, to increase the photocuring speed and form a denser curing network.

[0052] In one instance, the photoinitiator may be a compound represented by the following chemical formula 1.

[0053] Chemical Formula 1

[0054]

[0055] In the chemical formula 1,

[0056] R1 R 2 and R 3 Each independently ,

[0057] R 4 R 5 and R 6 Each is independently a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms; in this case, Indicates the location of the connection.

[0058] In one instance, the R 4 R 5 and R 6 Each can be an alkylene group, either substituted or unsubstituted, having 5 or more but less than 8 carbon atoms.

[0059] In one instance, the photoinitiator may be a compound represented by the following chemical formula 1-1.

[0060] Chemical Formula 1-1

[0061]

[0062] An example of the present invention provides an adhesive composition comprising an acrylic resin and a photoinitiator.

[0063] The adhesive composition can be used to prepare adhesive films with excellent durability by reducing total mass loss and swelling index and increasing gel fraction.

[0064] The acrylic resin may include acrylate prepolymers and acrylate monomers.

[0065] The acrylate prepolymer can be prepared by partially polymerizing acrylate monomers, and can be additionally photocured by including photocurable sites.

[0066] The acrylate monomers can be derived from unreacted acrylate monomers that did not participate in the formation of the acrylate prepolymer. As described later in the method for preparing the adhesive film, if the acrylate monomers are first partially polymerized and then the acrylate prepolymer is synthesized, a mixture of unreacted acrylate monomers and the synthesized acrylate prepolymer can be obtained. The adhesive composition can be prepared by directly containing a product comprising a mixture of unreacted acrylate monomers and the synthesized acrylate prepolymer. Therefore, the acrylate monomers can be derived from unreacted acrylate monomers generated during the polymerization of the acrylate prepolymer.

[0067] The acrylate monomers may comprise a mixture of more than one.

[0068] The acrylate monomers may be freely used and can be any acrylate monomers that are suitable for use in acrylic adhesives. They may be used in appropriate blends after taking into account known physical properties, the intended use of the adhesive, etc. For example, the acrylate monomers may be 2-ethylhexyl acrylate (2-EHA), isooctyl acrylate (IOA), butyl acrylate (BA), isobornyl acrylate (IBOA), cyclohexyl acrylate (CHA), acrylamide (AAm), 2-hydroxyethyl acrylate (HEA), 4-hydroxybutyl acrylate (HBA), 2-hydroxyethyl methacrylate (HEMA), acrylic acid (AA), 4-hydroxybutyl acrylate (HBA), etc., but are not limited thereto, and may include more than one of them.

[0069] In one example, to further improve the solubility of the photoinitiator containing at least one benzophenone group and urethane bond or the photoinitiator containing the compound represented by Formula 1, the acrylate monomer may be an acrylate monomer substituted with a straight-chain alkyl group having four or more carbon atoms, for example, it may be butyl acrylate (BA), pentyl acrylate (PA), hexyl acrylate, octyl acrylate, decyl acrylate, dodecyl acrylate, octadecyl acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, but is not limited thereto, and may contain more than one of them.

[0070] In one example, the acrylate monomer may comprise at least one selected from the group consisting of soft monomers, hard monomers, functional monomers, and combinations thereof.

[0071] The soft monomer refers to an acrylic monomer with a glass transition temperature (Tg) of less than -50°C, such as ethylhexyl acrylate, isooctyl acrylate (IOA), butyl acrylate (BA), etc., but is not limited to this, and may include more than one of them.

[0072] The hard monomer refers to an acrylic monomer with a glass transition temperature (Tg) that is relatively higher than that of the soft monomer, ranging from -10°C to room temperature. For example, it can be isobornyl methacrylate (IBO(M)A), cyclohexyl methacrylate (CH(M)A), acrylamide (Aam), etc., but is not limited to this, and may include more than one of them.

[0073] Such as acrylate monomers containing strongly activated carboxyl groups or nitrogen-containing acrylate monomers, the functional monomers refer to acrylate monomers containing functional functional groups, for example, hydroxyethyl acrylate (HEA), hydroxybutyl acrylate (HBA), hydroxyethyl acrylic acid (HEAA), hydroxyethyl methacrylate (HEMA), acrylic acid (AA), etc., but not limited to these, and may contain one or more of them.

[0074] The photoinitiator is the same as the photoinitiator described above, and the content that is repeated in the description of the photoinitiator will not be explained again.

[0075] The photoinitiator contains at least one benzophenone group with photoinitiating function and an urethane bond with excellent compatibility with acrylic resins. Especially when it contains three or more benzophenone groups, the portion that can initiate a polymerization reaction after generating free radicals through light irradiation is three or more, thereby allowing for the dense formation of a polymer structure through polymerization. This dense formation of the polymer structure increases the crosslinking density of the photocurable, increases the gel fraction, improves durability and oil resistance, and also achieves excellent optical properties.

[0076] In this specification, "light irradiation" refers to the irradiation of an electronic substrate that can induce a polymerization reaction by influencing a photoinitiator or a polymerizable compound. The electronic substrate can be used in the general sense of microwaves, infrared rays, ultraviolet rays, X-rays and gamma rays, as well as particle beams such as alpha particle beams, proton beams, neutron beams and electron beams.

[0077] Relative to 100 parts by weight of the total acrylic resins, the adhesive composition may contain 0.2 to 5 parts by weight of the photoinitiator comprising at least one benzophenone group and urethane bond, specifically, 0.2 to 3 parts by weight. When the adhesive composition contains the photoinitiator comprising at least one benzophenone group and urethane bond within the aforementioned numerical range, excellent transmittance, haze, and colorimetric properties of the photocured product can be achieved while simultaneously increasing the crosslinking density and gel fraction. Optical properties such as optical properties.

[0078] If the photoinitiator containing at least one benzophenone group and urethane bond is referred to as the first photoinitiator, the adhesive composition may further contain an additive containing at least one selected from the group consisting of polyurethane acrylate, multifunctional crosslinking agent, coupling agent, second photoinitiator, and combinations thereof.

[0079] The polyurethane acrylate can not only improve the cohesiveness and adhesive properties of the photocured product together with the multifunctional crosslinking agent, but also make the molecular structure softer.

[0080] Relative to 100 parts by weight of the total acrylic resins, the adhesive composition may contain 0.1 to 10 parts by weight of the polyurethane acrylate, specifically 0.5 to 3 parts by weight. When the adhesive composition contains the polyurethane acrylate in the range described above, if the content of the polyurethane acrylate is less than 0.1 parts by weight, the cohesive strength and adhesive properties of the UV-cured product can be improved, and the adhesive strength can be appropriately maintained by adjusting the degree of curing while making the molecular structure soft.

[0081] The multifunctional crosslinking agent may be a multifunctional acrylate, for example, it may include at least one selected from the group consisting of hexanediol diacrylate, trimethylolpropane trioxyethyl diacrylate, alkylene glycol diacrylate, dialkylene glycol diacrylate, trialkylene glycol diacrylate, dicyclopentenyl diacrylate, dicyclopentenyloxyethyl diacrylate, neopentyl glycol diacrylate, dipentaerythritol hexaacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and combinations thereof, but is not limited thereto.

[0082] Relative to 100 parts by weight of the total acrylic resins, the adhesive composition may contain 0.001 to 10 parts by weight of the multifunctional crosslinking agent, specifically 0.01 to 3 parts by weight. The inclusion of the multifunctional crosslinking agent in the stated numerical range can suppress bubble formation at high temperatures by improving the cohesiveness of the UV-cured product, achieve excellent adhesion and peel strength by appropriately adjusting the degree of curing, and also contribute to ensuring durability and reliability by suppressing interlayer peeling or warping.

[0083] Furthermore, the cohesive force and adhesive properties of the photocured product after light irradiation can be adjusted according to the amount of the multifunctional crosslinking agent used.

[0084] The coupling agent can also improve heat resistance and moisture resistance by enhancing the adhesion and bonding stability between the UV-cured material and the substrate, thereby improving the bonding reliability when the UV-cured material is placed in a high temperature and / or high humidity environment for a long time.

[0085] The coupling agent may be a silane coupling agent, for example, comprising at least one selected from the group consisting of γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, 3-isocyanate propyltriethoxysilane, γ-acetoacetate propyltrimethoxysilane, and combinations thereof.

[0086] The adhesive composition may contain 0.005 to 5 parts by weight of the coupling agent relative to 100 parts by weight of the total acrylic resins, specifically 0.01 to 3 parts by weight. The inclusion of the coupling agent in the aforementioned numerical range in the adhesive composition can effectively ensure adhesion while also ensuring durability and reliability by suppressing the occurrence of bubbles or peeling.

[0087] The adhesive composition uses the photoinitiator comprising at least one benzophenone group and an urethane bond as a first photoinitiator, and further comprises a second photoinitiator, which is different from the first photoinitiator. The second photoinitiator can adjust the degree of polymerization of the photocured product.

[0088] For example, the second photoinitiator may include at least one selected from the group consisting of benzoin-based photoinitiators, hydroxyketone-based photoinitiators, aminoketone-based photoinitiators, and combinations thereof. Specifically, it may include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin isobutyl ether, acetophenone, dimethylaminoacetophenone, α,α-dimethoxy-α-hydroxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinyl-propane-1-one, 4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)one The group consisting of at least one of the following, but not limited thereto: benzophenone, 4,4'-diethylaminobenzophenone, trichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyl dimethyl ketal, acetophenone dimethyl ketal, oligomeric [2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]acetone] and combinations thereof.

[0089] The adhesive composition may contain 0.01 to 10 parts by weight of the second photoinitiator relative to 100 parts by weight of the total acrylic resins, specifically 0.1 to 5 parts by weight. The inclusion of the second photoinitiator in the range of these values ​​allows the degree of polymerization of the photocurable to be adjusted to a desired level.

[0090] In one embodiment of the present invention, an adhesive film is provided, comprising an adhesive layer comprising a cured adhesive composition.

[0091] The adhesive composition described herein is the same as that described above, and the content that is repeated in the description of the adhesive composition described above will not be repeated.

[0092] The adhesive layer in the adhesive film can be prepared from an adhesive composition.

[0093] The adhesive film has a low swelling index and a high crosslinking density, thus enabling it to contain an adhesive layer with increased gel fraction, excellent durability, and high permeability.

[0094] Specifically, the gel fraction of the adhesive layer can be 55% to 80%, and the swelling index of the adhesive layer can be 15 to 35.

[0095] The adhesive layer can achieve both excellent durability and excellent optical properties, making it suitable for use as an adhesive film for thin-film sensors.

[0096] The haze of the adhesive layer of the automotive adhesive film can be below 0.7, and the haze of the adhesive layer in the colorimeter is b. The value can be less than 0.45.

[0097] In this specification, "haze" refers to the degree of opacity of a transparent sample due to light scattering from its surface.

[0098] In this instruction manual, "b in the colorimeter" "Value" refers to the comparison value when blue and yellow are set as an axis after measuring the color difference of a product using a device that measures color differences. The higher the value, the closer it is to yellow. The smaller the value, the closer it is to blue.

[0099] The thickness of the adhesive layer can be from 50μm to 250μm. Forming the adhesive layer to a thickness within this range can effectively cover the height difference of the display panel.

[0100] It may also include a release film laminated on at least one side of the adhesive layer.

[0101] The release film can be formed by appropriately treating one side of at least one selected from the group consisting of polyethylene terephthalate film, polytetrafluoroethylene film, polyethylene film, polypropylene film, polybutene film, polybutadiene film, vinyl chloride copolymer film, polyurethane film, ethylene-vinyl acetate film, ethylene-propylene copolymer film, ethylene-ethyl acrylate copolymer film, ethylene-methyl acrylate copolymer film, and polyimide film.

[0102] The release agent used in the release treatment can be alkyd, silicone, fluorine, unsaturated polyester, polyolefin or wax release agent, etc. Among them, from the perspective of heat resistance, alkyd, silicone or fluorine release agents are preferred, but not limited to these.

[0103] The adhesive layer can be formed by stacking on at least one side of the release film, and the adhesive layer can be inserted between at least two release films, such as a first release film and a second release film.

[0104] In one embodiment of the present invention, a method for preparing an adhesive film is provided, comprising: a step of preparing an acrylic resin; a step of mixing the prepared acrylic resin with a photoinitiator containing at least one benzophenone group and an urethane bond to prepare an adhesive composition; and a step of photocuring the adhesive composition to form an adhesive layer.

[0105] The adhesive film described above can be prepared according to the method for preparing the adhesive film. The acrylic resin and the photoinitiator containing at least one benzophenone group and an urethane bond in the method for preparing the adhesive film are as described above and will not be repeated.

[0106] In the method for preparing the adhesive film, the viscosity of the acrylic resin at 25°C can be from 500 cps to 5000 cps, specifically from 1000 cps to 4000 cps. Specifically, the acrylic resin comprises an acrylate prepolymer and acrylate monomers. The viscosity of the acrylic resin can be adjusted according to the degree of partial polymerization of the acrylate prepolymer. The acrylate prepolymer can be synthesized by partially polymerization with the viscosity adjusted to the aforementioned range. Excellent durability and oil resistance, as well as excellent optical properties, can be achieved by increasing the gel fraction and crosslinking density of the adhesive layer formed therefrom.

[0107] As described above, in the method for preparing the adhesive film, the adhesive composition can be prepared by mixing the photoinitiator containing at least one benzophenone group and urethane bond as the first photoinitiator with the acrylic resin and the first photoinitiator, and by adding an additive containing at least one selected from the group consisting of polyurethane acrylate, multifunctional crosslinking agent, coupling agent, second photoinitiator, and combinations thereof. Detailed descriptions of the first photoinitiator, second photoinitiator, polyurethane acrylate, multifunctional crosslinking agent, and coupling agent have been described above and will not be repeated.

[0108] As an acrylic resin comprising a paste-like mixture of the acrylate prepolymer obtained by partial polymerization as described above and the unreacted acrylate monomers, the adhesive composition can also be prepared by mixing and diluting monomers to accommodate subsequent photocuring. The viscosity of the adhesive composition at 25°C can be from 500 cps to 5000 cps. The viscosity of the adhesive composition within this range allows for uniform dispersion and coating onto the release film, thereby improving workability.

[0109] The diluent monomer can be any known substance that does not impair the desired physical properties; for example, acrylate monomers can be used.

[0110] In the method for preparing the adhesive film, the adhesive composition can be photocured by irradiation with activation energy rays. Photocuring caused by photopolymerization can be further performed by irradiating the adhesive composition with activation energy rays.

[0111] In this specification, "activation energy rays" refers to the collective term for particle beams such as microwaves, infrared rays, ultraviolet rays, X-rays, gamma rays, as well as alpha particle beams, proton beams, neutron beams, and electron beams.

[0112] In one example, the method for preparing the adhesive film further includes the step of coating the adhesive composition onto a release film, which may include the step of irradiating the upper part of the release film with light to photocur the adhesive composition to form an adhesive layer.

[0113] Specifically, the step of coating the adhesive composition onto the release film can be performed by using tools such as a barcode coating machine to coat the release film, followed by irradiating the upper part of the release film with light for photocuring to prepare the adhesive layer.

[0114] The adhesive layer formed by the method described above can have a gel fraction of 55% to 80%, a swelling index of 12 to 35, a haze of less than 0.7, and a colorimeter with a b... The value can be less than 0.45. The adhesive layer is formed transparently, and its transmittance, haze, and colorimetric properties (b) are measured. It has excellent optical properties, high gel content, and excellent durability.

[0115] Hereinafter, embodiments will be described in detail to specifically illustrate the present invention. However, the embodiments of the present invention can be modified into many other forms, and the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments in this specification are provided to more fully illustrate the present invention to those skilled in the art.

[0116] Preparation Example

[0117] Preparation Example 1: Preparation of partially polymerized acrylic resin (A)

[0118] In a 1L reactor with reflux nitrogen and a cooling device set up for easy temperature adjustment, 66 parts by weight of butyl acrylate (BA), 14 parts by weight of cyclohexyl acrylate (CHA), and 20 parts by weight of 4-hydroxybutyl acrylate (HBA) were added and partially polymerized to obtain a slurry with a viscosity of 3500 cps. The partially polymerized acrylic resin (A) had a weight-average molecular weight of 2,550,000.

[0119] Example

[0120] Example 1: Synthesis of photoinitiator containing 3 benzophenone groups and urethane linkage

[0121] A solution of 253 g of HDI trimer (hexamethylene-1,6-diisocyanate) dissolved in 100 g of butyl acetate was prepared and placed in a 2 L reactor and stirred at room temperature. Next, a solution of 307 g of 4-hydroxybenzophenone (BPOH) and 940 g of butyl acetate was added dropwise to the 2 L reactor while monitoring for heating. The temperature was then raised to 100 °C, stirred for 20 hours, and cooled to room temperature. After the reaction was complete, the reaction solution was transferred to a tray and dried in an oven at 120 °C for 3 days to remove butyl acetate, yielding a light brown to yellow solid photoinitiator containing benzophenone and urethane bonds. The obtained photoinitiator has the structure of the following chemical formula 1-1 (…). 1 H-NMR: 27H(m, 7.02~7.96ppm), 6H(s, 3.95ppm), 6H(s, 3.32ppm), 24H(m, 1.39~2.0ppm)).

[0122] Chemical Formula 1-1

[0123]

[0124] Example 2

[0125] A partially polymerized acrylic resin (A) prepared in Preparation Example 1 was used as a reference for 100 parts by weight. An adhesive composition was prepared by combining 0.03 parts by weight of hexanediol diacrylate as a multifunctional crosslinking agent, 0.3 parts by weight of coupling agent (KBM 403, manufactured by Shin-Etsu), 0.3 parts by weight of photoinitiator (Irgacure 651, manufactured by Ciba Specialty Chemicals), and 0.5 parts by weight of the photoinitiator synthesized in Example 1. A coating liquid with a viscosity of 2000 cps (25°C standard) was prepared from this composition. The prepared coating liquid was then applied to a release-treated polyethylene terephthalate film (XD500P, Toray Advanced Materials, thickness: 75 μm) using a barcode coating machine, and the thickness after UV curing was 125 μm. The film was then cured by irradiation with a UV lamp for 5 minutes to prepare an adhesive film.

[0126] Example 3

[0127] Except that the photoinitiator used as the photoinitiator in Example 2 in Example 1 was replaced with 0.8 parts by weight instead of 0.5 parts by weight, the adhesive film was prepared under the same conditions and methods as in Example 2.

[0128] Example 4

[0129] Except that the photoinitiator used as the photoinitiator in Example 2 in Example 1 was replaced with 1.0 part by weight instead of 0.5 parts by weight, the adhesive film was prepared under the same conditions and methods as in Example 2.

[0130] Example 5

[0131] Except that the photoinitiator used as the photoinitiator in Example 2 in Example 1 was replaced with 1.0 part by weight instead of 0.5 parts by weight, and the multifunctional crosslinking agent used in Example 2 was not used, the adhesive film was prepared under the same conditions and methods as in Example 2.

[0132] Comparative example

[0133] Comparative Example 1

[0134] The adhesive film was prepared under the same conditions and methods as in Example 2, except that 0.5 parts by weight of the common photoinitiator 2,4,6-tri(4-benzoylphenoxy)-1,3,5-triazine (BPT, 2,4,6-tri(4-benzoylphenoxy))-1,3,5-triazine was used instead of the 0.5 parts by weight of the photoinitiator used in Example 2.

[0135] Comparative Example 2

[0136] Except that 0.5 parts by weight of the common photoinitiator Omnipol BP was used instead of 0.5 parts by weight of the photoinitiator used in Example 2 as the photoinitiator in Example 1, the adhesive film was prepared under the same conditions and methods as in Example 2.

[0137] Comparative Example 3

[0138] Except that 0.8 parts by weight of the common photoinitiator Omnipol BP was used instead of 0.5 parts by weight of the photoinitiator of Example 1 used as the photoinitiator in Example 2, the adhesive film was prepared under the same conditions and methods as in Example 2.

[0139] Comparative Example 4

[0140] Except that 1.0 part by weight of the common photoinitiator Omnipol BP was used instead of 0.5 parts by weight of the photoinitiator of Example 1 used as the photoinitiator in Example 2, the adhesive film was prepared under the same conditions and methods as in Example 2.

[0141] Comparative Example 5

[0142] Except that the photoinitiator used as the photoinitiator in Example 2 in Example 1 was replaced with 0.1 parts by weight instead of 0.5 parts by weight, the adhesive film was prepared under the same conditions and methods as in Example 2.

[0143] Experimental Example

[0144] Experimental Example 1: Evaluation of solubility of photoinitiator

[0145] To confirm dissolution, add 1% by weight of the photoinitiator synthesized according to Example 1 and the common photoinitiator BPT (2,4,6-tri(4-benzoylphenoxy)-1,3,5-triazine) relative to the total weight of the organic solvents or monomers shown in Table 1 below and stir for 1 hour.

[0146]

[0147] EHA: 2-Ethylhexyl acrylate, BAM: n-Butyl acrylate, IBOA: Isobornyl acrylate. In Table 1, if the photoinitiator is dissolved in an organic solvent or monomer and is transparent to the naked eye, it is represented by O; if it is opaque, it is represented by X.

[0148] Referring to Table 1, it can be confirmed that the photoinitiator prepared according to Example 1, which contains at least one benzophenone group and an urethane bond, dissolves in all the organic solvents shown in Table 1, and its solubility in BAM of acrylic acid monomers is particularly excellent.

[0149] However, it can be confirmed that BPT, as a common photoinitiator that does not contain at least one benzophenone group and urethane bond, is soluble in toluene and cyclohexanone, but insoluble in acrylic acid monomers and other organic solvents.

[0150] Experimental Example 2: Evaluation of physical properties of adhesive film

[0151] The physical properties of the adhesive films prepared according to the embodiments and comparative examples were measured by the following methods, and the measured values ​​are shown in Table 2 below.

[0152] a) Measuring gel fraction

[0153] The cured adhesive composition (adhesive) was cut into 5cm × 5cm pieces and placed in a polyethylene bottle for weight measurement (a). Next, ethyl acetate was added to the polyethylene bottle to fully soak the adhesive, and the bottle was left at room temperature for 24 hours. Then, the adhesive and ethyl acetate mixture from the polyethylene bottle was poured onto a 14cm × 14cm wire mesh (weight: b) and hung on the mesh. The wire mesh with the adhesive was then dried in an oven at 110°C for 2 hours and its weight was measured (c). Finally, the measured weights a, b, and c were substituted into General Formula 1 below to determine the gel fraction (unit: %).

[0154] Formula 1

[0155] Gel fraction = ((cb) / a) × 100

[0156] b) Swelling index

[0157] Formula 2

[0158] Swelling index = Weight of swollen gel (g) / Weight of gel (g)

[0159]

[0160] Referring to Table 2, the adhesive films prepared according to Examples 2 to 5 show a gel fraction of 55% to 80% and a swelling index of 12 to 35, confirming that they exhibit a higher gel fraction and a lower swelling index compared to Comparative Examples 1 to 5. Therefore, it can be confirmed that a curing density with increased curing can be obtained using a photoinitiator containing at least one benzophenone group and an urethane bond.

[0161] The present invention has been described above with reference to the embodiments, but the present invention is not limited to the embodiments disclosed in this specification. It should be understood that, within the scope of the technical concept of the present invention, various modifications can be implemented by those skilled in the art. Furthermore, even if the effects of the structure of the present invention are not explicitly described in the foregoing description of the embodiments, the effects predictable from the related structures should be acknowledged.

Claims

1. A photoinitiator characterized by, contains at least one benzophenone group and a urethane bond.

2. Photoinitiator according to claim 1, characterized in that The photoinitiator contains three or more benzophenone groups.

3. A compound characterized by comprising: is represented by the following Chemical Formula 1, Chemical Formula 1: ， in the Chemical Formula 1, R 1 , R 2 , and R 3 are each independently , R 4 , R 5 , and R 6 each independently is a substituted or unsubstituted alkylenyl group having a carbon atom number of 1 to 20, in which case, represents the position of attachment.

4. The compound of claim 3, wherein R 4 , R 5 , and R 6 each independently is a substituted or unsubstituted alkylenyl group having 5 or more and 8 or less carbon atoms.

5. The compound of claim 3, wherein the compound is represented by the following Chemical Formula 1-1, Chemical Formula 1-1: 。 6. The compound of claim 3, wherein The compound is used as a photoinitiator.

7. An adhesive composition characterized by comprising: an acrylic resin and a photoinitiator, the photoinitiator is the photoinitiator according to claim 1 or 2, or contains the compound according to any one of claims 3 to 6.

8. The adhesive composition according to claim 7, characterized in that, The acrylic resin contains an acrylate-based prepolymer and an acrylate-based monomer.

9. The adhesive composition according to claim 7, characterized in that: the adhesive composition contains the photoinitiator as a first photoinitiator, and further contains an additive containing at least one selected from the group consisting of a polyurethane acrylate, a multifunctional crosslinking agent, a coupling agent, a second photoinitiator, and combinations thereof, the second photoinitiator is different from the first photoinitiator.

10. The adhesive composition of claim 7, wherein The multifunctional crosslinking agent is a multifunctional acrylate.

11. The adhesive composition of claim 7, wherein The coupling agent is a silane-based coupling agent.

12. The adhesive composition of claim 7, wherein The second photoinitiator includes at least one selected from the group consisting of a benzoin-based photoinitiator, a hydroxyketone-based photoinitiator, an aminoketone-based photoinitiator, and combinations thereof.

13. An adhesive film, characterized by an adhesive layer containing a photocured product of the adhesive composition according to any one of claims 7 to 12.

14. The adhesive film according to claim 13, wherein The adhesive layer has a gel fraction of 55 to 80%, a swelling index of 12 to 35, a haze of 0.7 or less, and a b value of less than 0.45 in a color difference meter.

15. The adhesive film of claim 14, wherein, The adhesive layer has a thickness of 50 μm to 250 μm.

16. A method for producing an adhesive film characterized by comprising: comprising: a step of producing an acrylic resin; a step of mixing the produced acrylic resin with a photoinitiator to produce an adhesive composition; and a step of photocuring the adhesive composition to form an adhesive layer, the photoinitiator is the photoinitiator according to claim 1 or 2, or contains the compound according to any one of claims 3 to 6.

17. The method of claim 16, wherein the adhesive film is prepared by a method comprising: The viscosity of the acrylic resin at 25°C is 500 cps to 5000 cps.

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