Adhesive

Abstract

The present application can provide an adhesive and its uses which can be applied to flexible devices, can effectively handle repeated deformation and recovery, does not cause defects before and after deformation (e.g., observation of deformation marks), has excellent cuttability and workability, and does not induce lifting, peeling, and / or bubble generation.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0065231 filed on May 27, 2022, and all the contents disclosed in the literature of the Korean patent application are incorporated herein by reference.

[0002] This application relates to adhesives and their uses.

Background Art

[0003] Flexible devices are new concept devices, and examples thereof include so-called foldable devices and rollable devices.

[0004] The adhesive layer applied to a foldable device stretches after being repeatedly folded or loosens after being rolled.

[0005] Therefore, the layer applied to a foldable device is required to effectively follow the repeated deformations, and when the force applied during deformation disappears, it can further recover to its original shape.

[0006] Generally, it is known that the lower the elastic modulus of an adhesive, especially at low temperatures, the more effectively it follows the repeated deformations as described above.

[0007] However, if the elastic modulus of the adhesive layer is too low, the recovery property when the force applied for deformation disappears decreases, and there are problems such as a decrease in cutting performance and workability.

[0008] Therefore, considering cutting performance and workability, it is preferable for the adhesive layer to have an elastic modulus above a certain level. However, it is not easy to obtain an adhesive layer that ensures desired levels of recovery, cutting performance, and workability while effectively following deformations.

[0009] Furthermore, increasing the modulus of elasticity to improve cutability and workability presents a problem: it reduces the peeling force that is fundamentally required of the adhesive layer.

[0010] Therefore, providing an adhesive layer with physical properties suitable for flexible devices is not an easy task. [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] This application relates to an adhesive. One objective of this application is to provide an adhesive suitable for flexible devices. In one example, one objective of this application is to provide an adhesive that can form an adhesive layer that exhibits a low modulus of elasticity at low temperatures, a relatively high modulus of elasticity at high temperatures, and at the same time exhibits an appropriate level of adhesive strength (peel strength).

[0012] This application also aims to provide an adhesive film or flexible device containing the adhesive. [Means for solving the problem]

[0013] In this specification, if the measurement temperature affects any of the physical properties mentioned, unless otherwise specified, the physical properties are those measured at room temperature.

[0014] In this specification, the term "room temperature" refers specifically to a temperature without heating or deheating, and may mean any one temperature within the range of about 10°C to 30°C, for example, about 15°C or higher, 18°C ​​or higher, 20°C or higher, or about 23°C or higher, and about 27°C or lower. Unless otherwise specified, the unit of temperature referred to in this specification is °C.

[0015] In this specification, if the measurement pressure affects any physical property mentioned herein, unless otherwise specified, the physical property shall be the one measured at normal pressure.

[0016] In this specification, the term "atmospheric pressure" specifically refers to pressure under conditions of no pressurization or depressurization, and typically means a pressure of approximately 740 mmHg to 780 mmHg, which is at atmospheric pressure.

[0017] In this specification, if the measured humidity affects any of the physical properties mentioned, unless otherwise specified, the physical properties are those measured at the natural humidity under normal temperature and pressure conditions.

[0018] This application relates to an adhesive. The adhesive of this application may include an acrylic copolymer.

[0019] In this specification, the term copolymer means the result of a polymerization reaction of a monomer mixture. In this specification, the term monomer unit means the state of the monomer after the polymerization reaction.

[0020] In this specification, the term "acrylic copolymer" refers to a copolymer mainly composed of acrylic monomer units. The lower limit of the proportion of acrylic monomer units in the acrylic copolymer may be approximately 50% by weight, 55% by weight, 60% by weight, 65% by weight, 70% by weight, 75% by weight, 80% by weight, 85% by weight, 90% by weight, or 95% by weight, and the upper limit may be approximately 100% by weight, 99% by weight, 98% by weight, 97% by weight, 96% by weight, or 95% by weight. The proportion may be within the range of any one lower limit or greater than or exceeding the aforementioned lower limit; within the range of any one upper limit or less than the aforementioned upper limit; or within the range of any one lower limit or greater than or exceeding the aforementioned lower limit, and any one upper limit or less than the aforementioned upper limit.

[0021] In this specification, the term "acrylic monomer" means acrylic acid, methacrylic acid, or derivatives of said acrylic acid or methacrylic acid (e.g., acrylic acid ester or methacrylic acid ester).

[0022] In this specification, the term (meth)acrylic means acrylic or methacrylic.

[0023] When the acrylic copolymer in the adhesive of the present application is crosslinkable, the acrylic copolymer in the adhesive may be in a state before crosslinking or after crosslinking, and preferably may also be in a crosslinked state. Therefore, the adhesive may contain the crosslinked acrylic copolymer.

[0024] As a result, the present application may relate to an adhesive that contains a crosslinked acrylic copolymer and has a storage elastic modulus, peel force against glass, and haze at a low temperature (-20°C) described later.

[0025] Further, the present application may relate to an adhesive that contains a crosslinked acrylic copolymer, exhibits the temperature-dependent change characteristics of the storage elastic modulus described later, and has the haze described later.

[0026] Further, the present application may relate to an adhesive that contains a crosslinked acrylic copolymer and a compound of Chemical Formula 1 described later.

[0027] The adhesive may contain the acrylic copolymer as a main component. For example, the lower limit of the proportion of the acrylic copolymer based on the total weight of the adhesive may be about 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, 97 wt% or 99 wt%, and the upper limit thereof may be about 100 wt%, 99 wt%, 98 wt%, 97 wt%, 96 wt% or 95 wt%. The proportion may be within the range of any one of the lower limits described above or more than the lower limit; within the range of any one of the upper limits described above or less than the upper limit; or within the range of any one of the lower limits described above or more than the lower limit and any one of the upper limits described above or less than the upper limit. When the adhesive contains components that are not included in the final adhesive layer, such as solvents, the content of the acrylic copolymer is the content in the adhesive excluding the components that are not included in the final adhesive layer.

[0028] The storage elastic modulus and peel strength of the adhesive referred to in this specification are the storage elastic modulus and peel strength in the state where the adhesive composition is crosslinked (i.e., the state where the acrylic copolymer contained in the adhesive composition is crosslinked). Therefore, the above may be the storage elastic modulus and peel strength of the adhesive or the adhesive layer.

[0029] The adhesive of the present application can exhibit a low storage elastic modulus at low temperatures.

[0030] In this specification, the storage elastic modulus is the result measured by the method presented in the following examples.

[0031] For example, the upper limit of the storage elastic modulus of the adhesive at -20°C may be about 100,000 Pa, 98,000 Pa, 96,000 Pa, 95,000 Pa, 94,000 Pa, 93,000 Pa, 92,000 Pa, 90,000 Pa, 88,000 Pa, 86,000 Pa, 85,000 Pa or 84,000 Pa, and the lower limit may be, for example, about 30,000 Pa, 40,000 Pa, 42,000 Pa, 44,000 Pa, 45,000 Pa, 46,000 Pa, 48,000 Pa, 50,000 Pa, 52,000 Pa, 54,000 Pa, 55,000 Pa, 56,000 Pa, 58,000 Pa, 60,000 Pa, 62,000 Pa, 64,000 Pa, 65,000 Pa, 66,000 Pa, 68,000 Pa, 70,000 Pa, 72,000 Pa, 74,000 Pa, 75,000 Pa, 76,000 Pa, 78,000 Pa, 80,000 Pa, 82,000 Pa, 84,000 Pa, 86,000 Pa, 88,000 Pa, 90,000 Pa, 92,000 Pa, 94,000 Pa or 96,000 Pa. The storage elastic modulus at -20°C may be within the range below or less than any one of the above-mentioned upper limits; or within the range above or exceeding any one of the above-mentioned lower limits and below or less than any one of the above-mentioned upper limits.

[0032] The adhesive exhibits a storage modulus within the aforementioned range at low temperatures of -20°C, allowing it to be applied to flexible devices and effectively accommodate repeated deformation and recovery.

[0033] The adhesive of this application exhibits a low storage modulus at low temperatures, while simultaneously exhibiting a relatively high storage modulus above a certain level at relatively high temperatures. The storage modulus of an adhesive is a temperature-dependent function, and normally, as the temperature increases, the storage modulus decreases. Therefore, the storage modulus of an adhesive at high temperatures is usually lower than that at low temperatures. However, if the storage modulus of an adhesive is low at low temperatures, the storage modulus at high temperatures also decreases relatively, so the storage modulus at high temperatures of an adhesive with a low storage modulus at low temperatures is lower than that of an adhesive with a high storage modulus at low temperatures.

[0034] However, in this application, along with the low storage modulus at low temperatures, a relatively high storage modulus can be observed at high temperatures. That is, the adhesive of this application can show a relatively gentle slope in the graph of storage modulus with respect to temperature.

[0035] For example, the adhesive of this application may have a rate of change in the elastic modulus calculated by the following formula 1 within a predetermined range. [Formula 1] Change rate of elastic modulus = (M20 - M25) / 45

[0036] In Equation 1, M20 is the storage modulus of the adhesive at -20°C (unit: Pa), and M25 is the storage modulus of the adhesive at 25°C (unit: Pa).

[0037] The upper limit of the rate of change in elastic modulus may be approximately 2500, 2400, 2300, 2200, 2100, 2000, 1900, 1800, 1700, 1600, 1500, 1400, 1300, 1200, or 1100, and its lower limit may be approximately 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, or 1200. The rate of change in elastic modulus may be within the range of any one upper limit or less than any one of the upper limits mentioned above; or it may be above or above any one lower limit and below any one of the upper limits mentioned above.

[0038] An adhesive layer exhibiting the above-described rate of change in elastic modulus can effectively follow repeated deformation and recovery in a foldable device, while maintaining good workability and cutability. However, as mentioned above, an adhesive with a low elastic modulus at low temperatures exhibits a relatively low elastic modulus even at high temperatures, making it difficult to satisfy the above-described rate of change in elastic modulus. In this application, the above-described rate of change in elastic modulus can be satisfied by applying a predetermined acrylic copolymer, as described later, as the acrylic copolymer.

[0039] The lower limit of the storage modulus of the adhesive at 25°C may be approximately 10,000 Pa, 12,000 Pa, 13,000 Pa, 14,000 Pa, 15,000 Pa, 16,000 Pa, 17,000 Pa, 18,000 Pa, 20,000 Pa, 21,000 Pa, 22,000 Pa, 23,000 Pa, 24,000 Pa, 26,000 Pa, 28,000 Pa, 30,000 Pa, 32,000 Pa, 34,000 Pa, 36,000 Pa, or 38,000 Pa, and the upper limit may be, for example, approximately 100,000 Pa, 98,000 Pa, 96,000 Pa, 94,000 Pa, 92,000 Pa Pa, 90,000 Pa, 88,000 Pa, 86,000 Pa, 84,000 Pa, 82,000 Pa, 80,000 Pa, 78,000 Pa, 76,000 Pa, 74,000 Pa, 72,000 Pa, 70,000 Pa, 68,000 Pa, 66,000 Pa, 64,000 Pa, 62,000 Pa, 60,000 Pa, 58,000 Pa, 56,000 Pa, 54,000 Pa, 52,000 Pa, 50,000 Pa, 48,000 Pa, 46,000 Pa, 44,000 Pa, 42,000 Pa, 40,000 Pa, or around 38,000 Pa or 36,000 Pa. The storage modulus at 25°C may be within the range of any one of the aforementioned lower limits or exceeding it; or it may be within the range of any one of the aforementioned lower limits or exceeding it, and any one of the aforementioned upper limits or less than it.

[0040] As described above, the adhesive of this application exhibits a relatively high high-temperature modulus and simultaneously high peeling force. For example, the adhesive may have a room-temperature peeling force to glass within a predetermined range.

[0041] The aforementioned room-temperature peeling force is the peeling force measured at approximately 25°C, and the method for measuring this peeling force is described in the examples.

[0042] The lower limit of the peeling force may be, for example, about 1,700 gf / inch, 1,800 gf / inch, 1,900 gf / inch, 2,000 gf / inch, 2,100 gf / inch, 2,200 gf / inch, 2,300 gf / inch, or 2,400 gf / inch, and the upper limit may be about 5,000 gf / inch, 4,500 gf / inch, 4,000 gf / inch, 3,500 gf / inch, 3,000 gf / inch, 2,800 gf / inch, 2,600 gf / inch, 2,500 gf / inch, or 2,400 gf / inch. The peeling force may be within the range of any one of the lower limits mentioned above or exceeding it; or within the range of any one of the lower limits mentioned above or exceeding it, and any one of the upper limits mentioned above or less.

[0043] Adhesives with such storage modulus and peeling force effectively handle repeated deformation and recovery in flexible devices, do not produce defects before or after deformation (e.g., observation of deformation marks), have excellent cutability and workability, and do not induce lifting, peeling, and / or bubble formation.

[0044] The adhesive can exhibit excellent optical transparency. For example, the upper limit of the haze of the adhesive may be approximately 0.5%, 0.45%, 0.4%, 0.35%, 0.3%, 0.25%, or 0.2%, and the lower limit may be approximately 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, or 0.35%. The haze may be within the range of any one upper limit or less than any one of the upper limits mentioned above; or within the range of any one lower limit or more than any one of the lower limits mentioned above, and within the range of any one upper limit or less than any one of the upper limits mentioned above.

[0045] In this application, a specific acrylic copolymer is applied to form an adhesive with the specific physical properties described above.

[0046] The acrylic copolymer may contain at least alkyl (meth)acrylate units, units of the following chemical formula 3, and polar functional group-containing units. The copolymer may further contain, if necessary, units of the following chemical formula 4 as arbitrary monomer units.

[0047] In the above, the unit refers to the monomer unit.

[0048] [Chemical formula 3] [ka] In chemical formula 3, R1 represents hydrogen or an alkyl group, and R2 represents an alkyl group having 11 to 13 carbon atoms.

[0049] [Chemical formula 4] [ka] In chemical formula 4, R1 represents hydrogen or an alkyl group, and R3 represents an aromatic ketone group or a (meth)acryloyl group.

[0050] The acrylic copolymer containing the monomer units is effective in forming the desired adhesive.

[0051] The acrylic copolymer is formed as a so-called crystalline copolymer in a predetermined proportion of the units of chemical formula 3 and / or polar functional group-containing units, or has properties similar to those of a crystalline copolymer. In this specification, the term crystalline copolymer means a copolymer whose melting point is confirmed within a predetermined range by the DSC (Differential Scanning Calorimeter) measurement method described in the examples of this specification.

[0052] Acrylic copolymers are known as amorphous copolymers. However, when the units of chemical formula 3 are present in a predetermined proportion, and optionally interact with polar functional groups present in a predetermined proportion, such copolymers can exhibit crystalline properties or at least properties similar to crystalline properties. When copolymers exhibiting crystalline properties or properties similar to crystalline properties are applied, adhesives with the aforementioned characteristics can be efficiently formed. Therefore, an adhesive layer exhibiting the elastic modulus and peeling force characteristics described above can be effectively formed through an adhesive to which such a copolymer is applied.

[0053] As the alkyl (meth)acrylate units contained in the copolymer, for example, units derived from alkyl (meth)acrylate having an alkyl group having 1 to 10 carbon atoms can be used. In other examples, the alkyl group may be an alkyl group having 2 to 20 carbon atoms, 3 to 10 carbon atoms, 4 to 10 carbon atoms, 4 to 9 carbon atoms, or 4 to 8 carbon atoms. The alkyl group may be linear or branched, and may be substituted or unsubstituted. In one example, the units can be formed using alkyl (meth)acrylate having a linear or branched, unsubstituted alkyl group as the alkyl group.

[0054] Examples of the alkyl (meth)acrylates mentioned above include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, sec-butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, isononyl (meth)acrylate, n-octyl (meth)acrylate, or isooctyl (meth)acrylate.

[0055] In the acrylic copolymer, the lower limit of the weight percentage of the alkyl (meth)acrylate units may be approximately 10% by weight, 15% by weight, 20% by weight, 25% by weight, 30% by weight, 35% by weight, 40% by weight, 45% by weight, 50% by weight, or 55% by weight, and the upper limit may be approximately 80% by weight, 75% by weight, 70% by weight, or 65% by weight. The percentage may be within a range of any one lower limit or greater than or exceeding the aforementioned lower limit; within a range of any one upper limit or less than the aforementioned upper limit; or within a range of any one lower limit or greater than or exceeding the aforementioned lower limit, and any one upper limit or less than the aforementioned upper limit. Within such a range, the desired adhesive can be effectively formed.

[0056] The aforementioned polar functional group-containing unit is a unit formed by monomers having polar functional groups. Such monomers typically contain both polymerizable groups (e.g., carbon-carbon double bonds) and polar functional groups simultaneously.

[0057] Examples of monomers having polar functional groups include hydroxyl group-containing monomers, carboxyl group-containing monomers, and nitrogen-containing monomers. In this application, it is particularly advantageous to use hydroxyl group-containing monomers, but the application is not limited to them.

[0058] Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 2-hydroxypolyethylene glycol (meth)acrylate, or 2-hydroxypolypropylene glycol (meth)acrylate. Examples of carboxyl group-containing monomers include (meth)acrylic acid, 2-(meth)acryloyloxyacetic acid, 3-(meth)acryloyloxypropyl acid, 4-(meth)acryloyloxybutyl acid, acrylic acid dimer, itaconic acid, maleic acid, and maleic anhydride. Examples of nitrogen-containing monomers include (meth)acrylamide, N-vinylpyrrolidone, or N-vinylcaprolactam, but are not limited to these. One or more of the above can be used.

[0059] The weight ratio of the polar functional group-containing units to 100 parts by weight of the alkyl (meth)acrylate units can be adjusted within a range that stably maintains the durability, tackiness, and peeling force of the adhesive layer. For example, the lower limit of the weight ratio of the polar functional group-containing units to 100 parts by weight of the alkyl (meth)acrylate units may be around 1, 5, 10, or 15 parts by weight, and the upper limit may be around 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, or 20 parts by weight.

[0060] The unit of chemical formula 3 is a unit containing a long-chain alkyl group. Such units are present in copolymers in a certain proportion or more and can interact with polar functional groups as needed to impart crystallinity or properties similar to crystallinity to the copolymer.

[0061] In the unit of chemical formula 3, R1 may be hydrogen or an alkyl group having 1 to 4 carbon atoms, specifically hydrogen, methyl, or ethyl.

[0062] In chemical formula 3, R2 is an alkyl group having 11 to 13 carbon atoms, and such alkyl groups may be linear or branched, and may be substituted or unsubstituted. In one example, R2 may be a linear and unsubstituted alkyl group. For example, the units of chemical formula 3 can be formed using lauryl (meth)acrylate and / or tetradecyl (meth)acrylate.

[0063] The lower limit of the weight ratio of the unit of chemical formula 3 to 100 parts by weight of the alkyl (meth)acrylate unit may be approximately 10 parts by weight, 15 parts by weight, 20 parts by weight, 25 parts by weight, 30 parts by weight, 35 parts by weight, 40 parts by weight, 45 parts by weight, or 50 parts by weight, and the upper limit may be approximately 300 parts by weight, 280 parts by weight, 260 parts by weight, 240 parts by weight, 220 parts by weight, 200 parts by weight, 180 parts by weight, 160 parts by weight, 140 parts by weight, 120 parts by weight, 100 parts by weight, 90 parts by weight, 80 parts by weight, 70 parts by weight, 65 parts by weight, 60 parts by weight, 55 parts by weight, or 50 parts by weight. The aforementioned ratio may be within the range of any one lower limit mentioned above, or exceeding it; within the range of any one upper limit mentioned above, or less than it; or within the range of any one lower limit mentioned above, or exceeding it, and any one upper limit mentioned above, or less than it.

[0064] The units of chemical formula 4 that can be included in any monomer unit of an acrylic copolymer are units that have an aromatic ketone group or a (meth)acryloyl group in their side chain.

[0065] Within the adhesive, the aromatic ketone group or (meth)acryloyl group may exist in that state, or in a state after undergoing a hydrogen abstraction reaction or radical reaction described later.

[0066] In units of chemical formula 4, an aromatic ketone group refers to an aromatic ketone group or a substituent containing such an aromatic ketone group that induces hydrogen abstraction from the polymer chain when exposed to electromagnetic waves.

[0067] When exposed to electromagnetic waves, the aromatic ketone group can remove hydrogen atoms from other polymer chains or from other parts of a polymer chain. Such removal can lead to the formation of radicals, which can form crosslinks between polymer chains or within the same polymer chain. The category of such aromatic ketone groups includes, for example, aromatic ketone groups such as benzophenone, acetophenone, or derivatives of anthraquinone.

[0068] Monomers that can derive the unit of chemical formula 4 having an aromatic ketone group include, but are not limited to, 4-benzoylphenyl (meth)acrylate, 4-(meth)acryloyloxyethoxybenzophenone, 4-(meth)acryloyloxy-4'-methoxybenzophenone, 4-(meth)acryloyloxyethoxy-4'-methoxybenzophenone, 4-(meth)acryloyloxy-4'-bromobenzophenone and / or 4-acryloyloxyethoxy-4'-bromobenzophenone.

[0069] In chemical formula 4, the (meth)acryloyl group refers to a (meth)acryloyl group or a substituent containing it that induces free radical polymerization when exposed to electromagnetic waves in the presence of a suitable radical initiator. Such (meth)acryloyl groups can act similarly to the aromatic ketone group upon irradiation with electromagnetic waves.

[0070] The unit of chemical formula 4, in which R3 is a (meth)acryloyl group, can be formed, for example, by preparing a precursor copolymer and then further reacting it with an unsaturated reagent compound to introduce a (meth)acryloyl group. Typically, the introduction of the (meth)acryloyl group involves either (1) a reaction between a nucleophile on the precursor copolymer and an electrophile on the unsaturated reagent compound (i.e., the unsaturated reagent compound contains both an electrophile and a (meth)acryloyl group), or (2) a reaction between an electrophile on the precursor copolymer and a nucleophile on the unsaturated reagent compound (i.e., the unsaturated reagent compound contains both a nucleophile and a (meth)acryloyl group). These reactions between nucleophiles and electrophiles are typically ring-opening reactions, addition reactions, or condensation reactions.

[0071] In such cases, the precursor copolymer has a hydroxyl, carboxylic acid (-COOH), or an anhydride (-O-(CO)-O-) group. If the precursor copolymer has a hydroxyl group, the unsaturated reagent compound often has a carboxylic acid (-COOH), isocyanate (-NCO), epoxy (i.e., oxyranyl), or anhydride group in addition to the (meth)acryloyl group. If the precursor copolymer has a carboxylic acid group, the unsaturated reagent compound often has a hydroxyl, amino, epoxy, isocyanate, azilidinyl, azetidinyl, or oxazolinyl group in addition to the (meth)acryloyl group. If the precursor (meth)acrylate copolymer has an anhydride group, the unsaturated reagent compound often has a hydroxyl or amine group in addition to the (meth)acryloyl group.

[0072] In one example, the precursor copolymer may have a carboxylic acid group, and the unsaturated reagent compound may have an epoxy group. Examples of exemplary unsaturated reagent compounds include, for example, glycidyl (meth)acrylate and 4-hydroxybutyl acrylate glycidyl ether. In another example, the precursor copolymer has an anhydride group, which reacts with unsaturated reagent compounds such as hydroxysubstituted alkyl (meth)acrylates, e.g., 2-hydroxyethyl (meth)acrylate and 3-hydroxypropyl (meth)acrylate. In yet another example, the precursor copolymer has a hydroxyl group, and the unsaturated reagent compound has an isocyanato group and a (meth)acryloyl group. Such unsaturated reagent compounds include, but are not limited to, isocyanatoalkyl (meth)acrylates, e.g., isocyanatoethyl (meth)acrylate.

[0073] The (meth)acryloyl group may, in one example, be represented by the chemical formula CH2=CHR1-(CO)-QL- (where L is a linking group and Q is oxy(-O-) or -NH-). The L therein comprises alkylene, allylene or a combination thereof, and further comprises a precursor copolymer and a specific unsaturated reagent compound that reacts to form a (meth)acryloyl group, selectively comprising -O-, -O-(CO)-, -NH-(CO)-, -NH-, or a combination thereof. In some specific cases, the (meth)acryloyl group is H2C=CHR1-(CO)-O-R6-NH-(CO)-O-R5-O-(CO)- formed by the reaction of a hydroxyl-containing group represented by the chemical formula -(CO)-O-R5-OH of the precursor copolymer with an unsaturated reagent compound which is an isocyanatoalkyl (meth)acrylate represented by the chemical formula H2C=CHR1-(CO)-O-R6-NCO. In the above, R5 and R6 are each independently alkylene groups, for example, alkylenes having 1 to 10 carbon atoms, 1 to 6 carbon atoms, or 1 to 4 carbon atoms. Also, in the above, R1 is methyl or hydrogen.

[0074] In the unit of chemical formula 4, R1 may be hydrogen or an alkyl group having 1 to 4 carbon atoms, specifically hydrogen, methyl, or ethyl.

[0075] When the unit of chemical formula 4 is included, the lower limit of the weight ratio of the unit of chemical formula 4 to 100 parts by weight of the alkyl (meth)acrylate unit is 0 parts by weight, 0.001 parts by weight, 0.003 parts by weight, 0.005 parts by weight, 0.007 parts by weight, 0.009 parts by weight, 0.01 parts by weight, 0.015 parts by weight, 0.02 parts by weight, 0.025 parts by weight, 0.03 parts by weight, 0.035 parts by weight, 0.04 parts by weight, 0.045 parts by weight, 0.05 parts by weight, 0.055 parts by weight, 0.0 The ratio may be approximately 6 parts by weight, 0.065 parts by weight, 0.07 parts by weight, 0.075 parts by weight, 0.08 parts by weight, 0.085 parts by weight, 0.09 parts by weight, or 0.1 parts by weight, and its upper limit may be approximately 5 parts by weight, 4.5 parts by weight, 4 parts by weight, 3.5 parts by weight, 3 parts by weight, 2.5 parts by weight, 2 parts by weight, 1.5 parts by weight, 1 part by weight, 0.5 parts by weight, 0.3 parts by weight, 0.1 parts by weight, 0.08 parts by weight, 0.06 parts by weight, 0.04 parts by weight, or 0.02 parts by weight. The ratio may be within the range of any one lower limit or higher than any one of the lower limits mentioned above; within the range of any one upper limit or lower than any one of the upper limits mentioned above; or within the range of any one lower limit or higher than any one of the lower limits mentioned above, and any one upper limit or lower than any one of the upper limits mentioned above. The desired adhesive layer can be effectively formed by irradiation with electromagnetic waves at such a ratio.

[0076] The acrylic copolymer may contain other monomer units in addition to the monomer units described above, as long as this does not impair the purpose (for example, as long as it does not impair the crystallinity of the copolymer).

[0077] In one example, the acrylic copolymer contained in the adhesive may be a crystalline acrylic copolymer. As previously stated, the term crystalline copolymer means a copolymer whose melting point is confirmed within a predetermined range by the DSC (Differential Scanning Calorimeter) measurement method described in the examples of this specification.

[0078] In one example, the upper limit of the melting point of the acrylic copolymer, as confirmed by the method, may be approximately -20°C, -25°C, -30°C, -35°C, or -40°C, and the lower limit may be approximately -100°C, -95°C, -90°C, -85°C, -80°C, -75°C, -70°C, -65°C, -60°C, -55°C, -50°C, or -45°C. The melting point may be within the range of any one lower limit or greater than or exceeding the aforementioned lower limit; within the range of any one upper limit or less than the aforementioned upper limit; or within the range of any one lower limit or greater than or exceeding the aforementioned lower limit and any one upper limit or less than the aforementioned upper limit. An acrylic copolymer having such a melting point can effectively form the desired adhesive.

[0079] The specific composition of the crystalline acrylic copolymer is not particularly limited. In one example, the crystalline acrylic copolymer may be a copolymer containing at least the three types of units mentioned above (alkyl (meth)acrylate units, units of chemical formula 3, and polar functional group-containing units). However, not all of the acrylic copolymers mentioned above exhibit crystalline properties. For an acrylic copolymer to exhibit crystalline properties, it is necessary that the units of chemical formula 3 are present in a certain level or higher among the aforementioned units. In a crystalline acrylic copolymer, the lower limit of the weight ratio of the units of chemical formula 3 to 100 parts by weight of alkyl (meth)acrylate units may be around 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 parts by weight, and the upper limit may be around 300, 250, 200, 150, 100, 90, 80, 70, 60, or 50 parts by weight. The aforementioned ratio may be within the range of any one of the aforementioned lower limits or exceeding it; or it may be within the range of any one of the aforementioned lower limits or exceeding it, and any one of the aforementioned upper limits or less than it.

[0080] In a crystalline acrylic copolymer, the lower limit of the ratio (A / B) of the weight of the unit of chemical formula 3 (A) to the weight of the polar functional group-containing unit (B) may be approximately 1.5, 2, 2.5, or 3, and the upper limit may be approximately 10, 9, 8, 7, 6, 5, 4, or 3. The ratio may be within the range of any one of the aforementioned lower limits being greater than or greater than the lower limit; within the range of any one of the aforementioned upper limits being less than or equal to the upper limit; or within the range of any one of the aforementioned lower limits being greater than or greater than the lower limit and any one of the aforementioned upper limits being less than or equal to the upper limit.

[0081] In a crystalline acrylic copolymer, the polar functional group-containing unit may be a hydroxyl group-containing unit. In one example, a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having a predetermined range of carbon atoms can appropriately form the crystalline acrylic copolymer. Although the reason is not clear, it is thought that the interaction between the alkyl group (R2) of the unit of chemical formula 3 and the hydroxyalkyl group contributes to the crystallinity of the acrylic copolymer. The lower limit of the carbon number in the hydroxyalkyl group may be around 3 or 4, and the upper limit may be around 10, 9, 8, 7, 6, 5, or 4. The carbon number may be within the range of any one of the aforementioned lower limits or exceeding it; within the range of any one of the aforementioned upper limits or less than it; or within the range of any one of the aforementioned lower limits or exceeding it, and any one of the aforementioned upper limits or less than it.

[0082] In a crystalline acrylic copolymer, the lower limit of the proportion of alkyl (meth)acrylate units may be about 20% by weight, 25% by weight, 30% by weight, 35% by weight, 40% by weight, 45% by weight, 50% by weight, 55% by weight, or 60% by weight, and the upper limit may be about 70% by weight, 65% by weight, or 60% by weight. The proportion may be within a range of any one of the lower limits mentioned above, or within a range of any one of the upper limits mentioned above, or within a range of any one of the lower limits mentioned above, or within a range of any one of the lower limits mentioned above, or any one of the upper limits mentioned above, or within a range of any one of the lower limits mentioned above, or any one of the upper limits mentioned above, or within a range of any one of the lower limits mentioned above, or within a range of any one of the upper limits mentioned above. Within such a range, the desired adhesive layer can be effectively formed.

[0083] Although the reason is not clear, it is thought that the acrylic copolymer acquires crystallinity and its melting point is determined by the interactions and regularity of each monomer unit contained in the aforementioned proportions.

[0084] As the acrylic copolymer, a copolymer with a weight-average molecular weight above a certain level can be used. In this specification, weight-average molecular weight means the polystyrene equivalent value measured by GPC (gel permeation chromatography). Unless otherwise specified, the unit of weight-average molecular weight is g / mol. The lower limit of the weight-average molecular weight of the copolymer may be around 1 million, 1.1 million, 1.2 million, 1.3 million, 1.4 million, 1.5 million, 1.6 million, 1.7 million, 1.8 million, 1.9 million, or 2 million, and the upper limit may be around 5 million, 4 million, 3 million, 2.5 million, or 2 million. The weight-average molecular weight may be within the range of any one of the lower limits mentioned above or exceeding it; within the range of any one of the upper limits mentioned above or less; or within the range of any one of the lower limits mentioned above or exceeding it, and any one of the upper limits mentioned above or less.

[0085] The lower the weight-average molecular weight of the copolymer, the greater the change in physical properties after crosslinking. However, if the weight-average molecular weight is too low, it is disadvantageous in terms of durability under high temperature and / or high humidity conditions. Nevertheless, in the case of this application, by using the specific copolymer described above, the desired adhesive layer can be effectively formed even while maintaining the weight-average molecular weight at an appropriate level.

[0086] The acrylic copolymer may have a molecular weight distribution within a predetermined range. Furthermore, the acrylic copolymer may preferably be crosslinked with an appropriate crosslinking agent based on the molecular weight distribution and included in the adhesive. The molecular weight distribution is the value obtained by dividing the number-average molecular weight (Mn) by the weight-average molecular weight (Mw) (Mw / Mn). Generally, a smaller molecular weight distribution indicates a smaller proportion of components with relatively small molecular weights and relatively large molecular weights relative to the average molecular weight within the copolymer, resulting in a more uniform copolymer composition and stable rheological properties such as elastic modulus. However, properties suitable for flexible devices include mutually conflicting properties such as conformability to deformation and recovery, conformability to deformation, cutability, and reliability. Therefore, to ensure stable performance of such properties, it may be necessary to adjust the molecular weight distribution depending on the type of crosslinking agent applied.

[0087] In one example, when the acrylic copolymer is crosslinked with a thermal crosslinking agent described later, the lower limit of the molecular weight distribution may be approximately 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, or 5.0, and the upper limit may be approximately 10, 9.5, 9, 8.5, 8, 7.5, 7, 6.5, 6, or 5.5. The molecular weight distribution may be less than or equal to any one of the upper limits mentioned above, or greater than or equal to any one of the lower limits mentioned above, or less than or equal to any one of the upper limits mentioned above and greater than or equal to any one of the lower limits mentioned above. An acrylic copolymer with such a molecular weight distribution is suitable for forming the desired type of adhesive when crosslinked with a thermal crosslinking agent described later. It is preferable that such types of acrylic copolymers be crosslinked solely by the thermal crosslinking agent. For example, when the acrylic copolymer is crosslinked solely by the thermal crosslinking agent, or when the thermal crosslinking agent and the radical crosslinking agent are applied simultaneously, it is preferable that the ratio (A / B) of the weight of the thermal crosslinking agent (A) to the weight of the radical crosslinking agent (B) used is below a certain level. For example, the upper limit of the weight ratio A / B may be around 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, 0.01, 0.009, 0.008, 0.007, 0.006, 0.005, 0.004, 0.003, 0.002, 0.001, 0.0009, 0.0008, 0.0007, 0.0006, 0.0005, 0.0004, 0.0003, 0.0002, or 0.0001, and its lower limit may be around 0. The ratio A / B may be less than or equal to any one of the upper limits mentioned above, or it may be less than or equal to any one of the upper limits mentioned above and greater than or equal to any one of the lower limits mentioned above. Acrylic copolymers with such a molecular weight distribution are suitable for forming the desired type of adhesive when crosslinked with a radical crosslinking agent described later.

[0088] In one example, when the acrylic copolymer is crosslinked with a so-called radical crosslinking agent, the lower limit of the molecular weight distribution may be around 0.5, 1, 1.5, or 2, and the upper limit may be around 3, 2.8, 2.6, or 2.4. The molecular weight distribution may be less than or equal to any one of the upper limits mentioned above, or greater than or equal to any one of the lower limits mentioned above, or less than or equal to any one of the upper limits mentioned above and greater than or equal to any one of the lower limits mentioned above. An acrylic copolymer with such a molecular weight distribution is suitable for forming a type of adhesive intended to be crosslinked with a so-called radical crosslinking agent. It is preferable that such a type of acrylic copolymer is crosslinked only with the radical crosslinking agent. For example, when the acrylic copolymer is crosslinked only with the radical crosslinking agent, or when the thermal crosslinking agent and the radical crosslinking agent are applied simultaneously, it is preferable that the ratio (C / D) of the weight of the thermal crosslinking agent (C) to the weight of the radical crosslinking agent (D) used is below a certain level. For example, the upper limit of the weight ratio C / D may be around 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, 0.01, 0.009, 0.008, 0.007, 0.006, 0.005, 0.004, 0.003, 0.002, 0.001, 0.0009, 0.0008, 0.0007, 0.0006, 0.0005, 0.0004, 0.0003, 0.0002, or 0.0001, and its lower limit may be around 0. The ratio C / D may be less than or equal to any one of the upper limits mentioned above, or it may be less than or equal to any one of the upper limits mentioned above and greater than or equal to any one of the lower limits mentioned above. Acrylic copolymers with such a molecular weight distribution are suitable for forming the desired type of adhesive when crosslinked with a radical crosslinking agent described later.

[0089] Methods for adjusting the molecular weight distribution of acrylic copolymers are known, and the molecular weight distribution can be controlled through one or more methods selected from, for example, the use of molecular weight modifiers, adjustment of initiator proportions, and / or adjustment of polymerization time.

[0090] The adhesive may contain the compound of the following chemical formula 1. An adhesive containing such a compound can effectively satisfy the desired properties.

[0091] [Chemical formula 1] [ka] In chemical formula 1, X is carbon or nitrogen, and R1 to R3 are each independently hydrogen, alkyl group, or hydroxyl group. When X is nitrogen, R4 is absent, and at least one of R1 to R3 is a hydroxyl group. If R4 is present in chemical formula 1, it may be a substituent of the chemical formula 2 below.

[0092] [Chemical formula 2] [ka] In chemical formula 2, R5 is a single bond, an oxygen atom, -L1-C(=O)-L2-, -L1-C(=O)-O-L2-, or -L1-OC(=O)-L2-; R6 is an alkylidene group or an alkylene group; R7 is a single bond, -OC(=O)-, -C(=O)-, or -C(=O)-O-; R8 and R9 are independently hydrogen or an alkyl group, and n is a number in the range of 0 to 10.

[0093] In chemical formula 2, if R7 is a single bond or -C(=O)-O-, then R9 does not exist. Also, in chemical formula 2, L1 and L2 are independently a single bond, an alkylidene group, or an alkylene group.

[0094] In chemical formula 1, when X is carbon, R1 to R3 may each be independently hydrogen or an alkyl group. The alkyl group may have 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Such alkyl groups may have a linear or branched structure and may be optionally substituted with one or more substituents.

[0095] In chemical formula 2, R5 may, in one example, be an oxygen atom, -C(=O)-, -C(=O)-O-, or -OC(=O)-.

[0096] The aforementioned terms alkylidene group is a divalent residue formed in alkanes by the removal of two hydrogen atoms from one carbon atom, and alkylene group is a divalent residue formed in alkanes by the removal of hydrogen atoms from two different carbon atoms.

[0097] In chemical formula 2, the alkylidene group R6 may be an alkylidene group having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Such alkylidene groups may have a linear or branched structure and may be optionally substituted with one or more substituents.

[0098] In chemical formula 2, the alkylene group R6 may be an alkylene group having 2 to 20 carbon atoms, 2 to 16 carbon atoms, 2 to 12 carbon atoms, 2 to 8 carbon atoms, or 2 to 4 carbon atoms. Such an alkylene group may have a linear or branched structure and may be optionally substituted with one or more substituents.

[0099] In chemical formula 2, R8 may be hydrogen or an alkyl group, and the alkyl group may be an alkyl group having 1 to 20 carbon atoms, 4 to 20 carbon atoms, 6 to 20 carbon atoms, 6 to 16 carbon atoms, 6 to 12 carbon atoms, or 6 to 8 carbon atoms. Such alkyl groups may have a linear or branched structure and may be optionally substituted with one or more substituents (e.g., alkyl groups).

[0100] In chemical formula 1, when X is nitrogen, R1 and R2 may independently be hydrogen or an alkyl group, where the alkyl group may have 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Such alkyl groups may have a linear or branched structure and may be optionally substituted with one or more substituents.

[0101] In chemical formula 1, if X is nitrogen, R3 may be a hydroxyl group.

[0102] When X is carbon in chemical formula 1, n in chemical formula 2 may be 0 or not. If n is not 0, the lower limit of n may be 1, 2, or 3, and the upper limit may be 10, 9, 8, 7, 6, 5, 4, or 3. If n is not 0, it may be less than or equal to any one of the upper limits mentioned above, or greater than or equal to any one of the lower limits mentioned above, or less than or equal to any one of the upper limits mentioned above and greater than or equal to any one of the lower limits mentioned above.

[0103] In chemical formula 1, when X is carbon, R1 to R3 may each be independently hydrogen or alkyl groups. In this case, one of R1 to R3 may be hydrogen and the remaining two may be alkyl groups. In this case, the alkyl groups may have 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Such alkyl groups may have a linear or branched structure and may be substituted with one or more substituents. Furthermore, when one of R1 to R3 is hydrogen and the remaining two are alkyl groups, the number of carbon atoms in the two alkyl groups may be different or the same.

[0104] When X is carbon in chemical formula 1 and n is 0 in chemical formula 2, R5 in chemical formula 2 may be -L1-C(=O)-L2-, -L1-C(=O)-O-L2-, or -L1-OC(=O)-L2-, in which case L1 and L2 may each be independently an alkylene group or an alkylidene group. The alkylidene group may be an alkylidene group having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms, and the alkylene group may be an alkylene group having 2 to 20 carbon atoms, 2 to 16 carbon atoms, 2 to 12 carbon atoms, 2 to 8 carbon atoms, or 2 to 4 carbon atoms. Such alkylene groups or alkylidene groups may have a linear or branched structure and may be substituted with one or more substituents.

[0105] In chemical formula 1, X is carbon, and in chemical formula 2, n is 0. In chemical formula 2, R7 may be -OC(=O)-, -C(=O)-, or -C(=O)-O-.

[0106] When X is carbon in chemical formula 1 and n in chemical formula 2 is 0, R8 and R9 in chemical formula 2 may each be independently hydrogen or an alkyl group, or independently an alkyl group. In such cases, the alkyl group may have 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Such alkyl groups may have a linear or branched structure and may be substituted with one or more substituents. Furthermore, when R8 and R9 are independently alkyl groups, their carbon numbers may be the same or different.

[0107] If X is carbon in chemical formula 1 and n in chemical formula 2 is not 0, then R5 in chemical formula 2 may be -L1-C(=O)-L2-, -L1-C(=O)-O-L2-, or -L1-OC(=O)-L2-, in which case L1 and L2 may each be single bonds.

[0108] If X is carbon in chemical formula 1 and n in chemical formula 2 is not 0, then the alkylidene group R6 in chemical formula 2 may be an alkylidene group having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms, and the alkylene group may be an alkylene group having 2 to 20 carbon atoms, 2 to 16 carbon atoms, 2 to 12 carbon atoms, 2 to 8 carbon atoms, or 2 to 4 carbon atoms. Such alkylene or alkylidene groups may have a linear or branched structure and may be optionally substituted with one or more substituents.

[0109] If X is carbon in chemical formula 1 and n in chemical formula 2 is not 0, then R7 in chemical formula 2 may be -OC(=O)-, -C(=O)-, or -C(=O)-O-.

[0110] When X is carbon in chemical formula 1 and n in chemical formula 2 is not 0, R8 and R9 in chemical formula 2 may each be independently hydrogen or an alkyl group, or independently an alkyl group. In such cases, the alkyl group may have 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Such alkyl groups may have a linear or branched structure and may be substituted with one or more substituents. Furthermore, when R8 and R9 are independently alkyl groups, their carbon numbers may be the same or different.

[0111] In the adhesive, the compound of chemical formula 1 may be included in an amount of 0.1 to 50 parts by weight per 100 parts by weight of the acrylic copolymer. Within this range, the adhesive layer can exhibit the desired storage modulus and peel strength and other properties. The proportion may be, in other examples, about 0.2 parts by weight or more, about 0.3 parts by weight or more, about 0.4 parts by weight or more, about 0.5 parts by weight or more, 0.6 parts by weight or more, 0.7 parts by weight or more, 0.8 parts by weight or more, 0.9 parts by weight or more, 1 part by weight or more, 2 parts by weight or more, 3 parts by weight or more, 4 parts by weight or more, 5 parts by weight or more, 6 parts by weight or more, 7 parts by weight or more, 8 parts by weight or more, 9 parts by weight or more, or 10 parts by weight or more, or about 45 parts by weight or less, 40 parts by weight or less, 35 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, 20 parts by weight or less, about 15 parts by weight or less, or 10 parts by weight or less.

[0112] The adhesive may further contain a crosslinking agent. The crosslinking agent may react with the acrylic copolymer to embody a crosslinked structure.

[0113] The type of crosslinking agent is not particularly limited, and general crosslinking agents such as isocyanate compounds, epoxy compounds, aziridine compounds, and metal chelate compounds can be used. These types of crosslinking agents are so-called thermal crosslinking agents that realize a crosslinked structure by the application of heat, and are different from the radical crosslinking agents described later. Specific examples of isocyanate compounds include one or more selected from the group consisting of tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, tetramethylxylene diisocyanate, naphthalene diisocyanate, and reaction products with any one of the above polyols (e.g., trimethylolpropane); specific examples of epoxy compounds include ethylene glycol diglycidyl ether, triglycidyl ether, and trimethylolpropane triglycidyl One or more compounds selected from the group consisting of ethers, N,N,N',N'-tetraglycidylethylenediamine, and glycerin diglycidyl ethers are included; specific examples of aziridine compounds include, but are not limited to, one or more compounds selected from the group consisting of N,N'-toluene-2,4-bis(1-aziridinecarboxamide), N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), triethylenemelamine, bisisophthaloyl-1-(2-methylaziridine), and tri-1-aziridinylphosphine oxide. Furthermore, specific examples of metal chelate compounds include, but are not limited to, compounds in which polyvalent metals such as aluminum, iron, zinc, tin, titanium, antimony, magnesium, and / or vanadium are coordinated to acetylacetone or ethyl acetoethyl, etc.

[0114] In the adhesive layer, the lower limit of the weight ratio of the crosslinking agent to 100 parts by weight of the acrylic copolymer may be approximately 0.01 parts by weight, 0.02 parts by weight, about 0.03 parts by weight, about 0.04 parts by weight, about 0.05 parts by weight, 0.06 parts by weight, 0.07 parts by weight, 0.08 parts by weight, or 0.09 parts by weight, and the upper limit may be approximately 10 parts by weight, 9 parts by weight, 8 parts by weight, 7 parts by weight, 6 parts by weight, 5 parts by weight, 4 parts by weight, about 3 parts by weight, about 2 parts by weight, about 1 part by weight, about 0.8 parts by weight, about 0.6 parts by weight, about 0.4 parts by weight, about 0.2 parts by weight, about 0.15 parts by weight, about 0.1 parts by weight, 0.09 parts by weight, 0.08 parts by weight, or 0.07 parts by weight. The aforementioned proportion may be within the range of any one lower limit above or above the aforementioned lower limit; within the range of any one upper limit above or below the aforementioned upper limit; or within the range of any one lower limit above or above the aforementioned lower limit, and any one upper limit above or below the aforementioned upper limit. By selecting the content of the crosslinking agent to crosslink the acrylic copolymer at an appropriate level within the aforementioned content range, the desired adhesive can be effectively formed.

[0115] The adhesive layer may contain a crosslinking agent of a different type from the thermal crosslinking agent, and may include a so-called radical crosslinking agent. Such a crosslinking agent embodies a crosslinked structure through a radical reaction. Examples of such radical crosslinking agents include so-called polyfunctional acrylates, such as 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, and hydroxypivalic acid. Neopentyl glycol di(meth)acrylate, dicyclopentanyl di(meth)acrylate, caprolactone-modified dicyclopentenyl 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, ethylene oxide-modified hexahydrophthalate di(meth)acrylate, tricyclodecane dimethanol(meth)acrylate, neopentyl glycol-modified trimethylpropane di(meth)acrylate, adamantane di Difunctional acrylates such as (meth)acrylate or 9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene; trifunctional 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 or tris(meth)acryloxyethyl isocyanurate; tetrafunctional acrylates such as diglycerin tetra(meth)acrylate or pentaerythritol tetra(meth)acrylate;Examples include, but are not limited to, pentafunctional acrylates such as propionic acid-modified dipentaerythritol penta(meth)acrylate; and hexafunctional acrylates such as dipentaerythritol hexa(meth)acrylate, caprolactone-modified dipentaerythritol hexa(meth)acrylate, or urethane(meth)acrylate (e.g., reaction products of isocyanate monomers and trimethylolpropane tri(meth)acrylate).

[0116] In the adhesive layer, the radical crosslinking agent may also be present in an appropriate proportion depending on the purpose. For example, it may be included in an amount of 0.01 to 10 parts by weight or 0.01 to 5 parts by weight per 100 parts by weight of the acrylic copolymer.

[0117] The aforementioned radical crosslinking agent is not considered an essential component.

[0118] In addition to the above-mentioned components, the adhesive may also contain appropriate additives as needed, such as radical initiators, ultraviolet absorbers, light stabilizers, plasticizers, and / or crosslinking catalysts.

[0119] The method for forming the adhesive in this application is not particularly limited. For example, an adhesive composition containing the components that form the adhesive (such as a copolymer and a crosslinking agent) can be formed by applying an appropriate crosslinking method, taking into account the type of acrylic copolymer and / or crosslinking agent applied to the composition. For example, if the acrylic copolymer and / or crosslinking agent is of a type that is crosslinked by the application of heat, an appropriate heat can be applied to form a crosslinked product; if it is of a type that is crosslinked by irradiation with electromagnetic waves, an appropriate electromagnetic wave can be irradiated to form a crosslinked product; and other crosslinking methods can also be applied.

[0120] Such adhesives can exhibit the aforementioned elastic modulus and / or peeling force characteristics.

[0121] The thickness of such adhesives in this application is not particularly limited and may have the thickness of a normal adhesive, taking into consideration the intended use.

[0122] For example, the adhesive may have an appropriate thickness within the range of approximately 5 μm to 100 μm.

[0123] This application also relates to an adhesive film or optical laminate comprising a base film and an adhesive layer formed on one or both sides of the base film. In the case of an optical laminate, the base film may be an optical film. The adhesive layer may contain the adhesive described above.

[0124] The adhesive layer of this application can be formed on one or both sides of a base film to form an adhesive film, or it can be formed on one or both sides of the base film, which is an optical film, to form an optical laminate.

[0125] In this case, the type of base film that can be used is not particularly limited. Typically, a base film applicable to the formation of an adhesive film can be used as the base film.

[0126] For example, the base film can be, but is not limited to, PET (poly(ethylene terephthalate)) film, PTFE (poly(tetrafluoroethylene)) film, PP (polypropylene) film, PE (polyethylene) film, polyimide film, polyamide film, COP (cyclic olefin polymer) 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 / or polyimide film.

[0127] The thickness of the base film is not particularly limited and may have an appropriate thickness within a range suitable for the purpose.

[0128] When an optical film is used as the base film, there are no special restrictions on the type of optical film. For example, the optical film may be a polarizing film, a polarizing plate, or a phase difference film. In such cases, the optical film may have a thickness within an appropriate range depending on the purpose.

[0129] The adhesive film or optical laminate may further include, if necessary, a release film or protective film to protect the adhesive layer until use.

[0130] This application also relates to a flexible device comprising an adhesive layer, adhesive film, or optical laminate containing the adhesive. There are no particular limitations on the application mode of the adhesive layer, adhesive film, or optical laminate containing the adhesive in the device. For example, the adhesive layer can be used in so-called OCA (Optically Clear Adhesive) or OCR (Optically Clear Resin) applications in the device, and therefore the application mode of the adhesive layer, adhesive film, or optical laminate may be the same as that of a normal OCA or OCR application.

[0131] In such cases, in one example, the flexible device may include a display panel and the adhesive layer, adhesive film, or optical laminate present on one or both sides of the display panel. In such cases, the display panel may be configured to be folded or rolled through one or more folding or rolling axes.

[0132] Other elements constituting the flexible device described above are not subject to any special restrictions, and known components of flexible devices can be used without limitation. [Effects of the Invention]

[0133] This application provides an adhesive that can be applied to flexible devices and effectively handle repeated deformation and recovery, without causing defects before and after deformation (e.g., observation of deformation marks), with excellent cutability and workability, and without inducing lifting, peeling, and / or bubble formation.

[0134] This application can also provide an adhesive layer containing the adhesive, an adhesive film or optical film containing the same, and a flexible device such as a foldable device or a rollable device. [Brief explanation of the drawing]

[0135] [Figure 1] This figure shows the structure of the test specimen used in the dynamic folding test. [Figure 2] This diagram shows the process of performing a dynamic folding test. [Figure 3] This diagram shows the process for evaluating the cuttability of adhesives. [Modes for carrying out the invention]

[0136] The present application will be described in detail below based on examples and comparative examples, but the scope of this application is not limited to the following examples.

[0137] 1. Evaluation of the storage modulus The storage modulus was evaluated using ARES G2 (Advanced Rheometric Expansion System G2) (TA Corporation). Test specimens were prepared by cutting an adhesive layer with a thickness of approximately 0.8 mm into a circle with a diameter of approximately 8 mm. The adhesive layer was prepared by overlapping adhesive layers with a thickness of approximately 25 μm to achieve the aforementioned thickness of approximately 0.8 mm. The storage modulus at the measurement temperature was evaluated for the test specimen using a parallel plate fixture with a diameter of approximately 8 mm. During the evaluation, the evaluation conditions were a frequency of 1 Hz and a strain of 5%, and measurements were taken while increasing the temperature from -40°C to 90°C at a rate of approximately 10°C / min.

[0138] 2. Evaluation of peeling force Test specimens were prepared by cutting the adhesive film to be measured (structure of release film / adhesive layer / base film) into rectangles approximately 25 mm wide and 100 mm long. Next, the release film was peeled off, and the adhesive layer was applied to soda-lime glass using a 2 kg roller according to the provisions of JIS Z 0237, and left at room temperature for one day. After that, the peeling force was measured while peeling the adhesive layer at room temperature with a peeling angle of 180 degrees and a peeling speed of 0.3 m / min using a Texture Analyzer (TA) equipped by Stable Micro Systems.

[0139] 3. Measuring haze Haze was measured by applying an adhesive approximately 25 μm thick to a 0.5 mm thick soda-lime glass using a 2 kg roller according to JIS Z 0237, leaving it at room temperature for one day, and then measuring it. A COH-400 instrument (Nippon Denshoku Co., Ltd.) was used for measurement, and the evaluation was performed using a D65 standard light source.

[0140] 4. Evaluation of weight-average molecular weight The weight average molecular weight (Mw) and molecular weight distribution were measured using GPC (Gel Permeation Chromatograph), and the measurement conditions were as follows. When measuring the weight average molecular weight, the measurement results were converted using standard polystyrene (manufactured by Aglient system) for preparing the calibration curve. The molecular weight distribution was the value (Mw / Mn) obtained by dividing the weight average molecular weight (Mw) by the number average molecular weight (Mn) determined by the above method.

[0141] <GPC Measurement Conditions> Measuring instrument: Aglient GPC (Aglient 1200 series, U.S.) Columns: Two PL Mixed B columns connected in series Column temperature: 40 °C Eluent: THF (Tetrahydrofuran) Flow rate: 1.0 μL / min Concentration: ~1 mg / mL (100 μl injection)

[0142] 5. Dynamic Folding Test The dynamic folding test was carried out by manufacturing a test piece as shown in Fig. 1. A laminate was manufactured by sequentially laminating a polyimide film 200 with a thickness of about 50 μm having a hard coating layer 100 formed on both sides, an adhesive layer 300, a polarizing plate 400, an adhesive layer 300, and a display panel 500 as shown in Fig. 1, and then cutting it into a rectangular shape with a horizontal length of about 7.8 cm and a vertical length of about 17 cm to manufacture a test piece. Next, as shown in Fig. 2, the test piece was sandwiched between parallel plates at 5 mm intervals and folded back and forth 200,000 times at -20 °C. After collecting the samples, defects such as the generation of bubbles, floating / lifting / peeling, and cracks in the hard coating layer in the samples were visually observed. When even one of the above defects occurred, it was evaluated as NG, and when none of the defects occurred, it was evaluated as PASS.

[0143] 6. Cutting Property Test The cutability was evaluated using test pieces 400 prepared by cutting a laminate containing an adhesive layer 300 between two release films (light liner, heavy liner) 100 and 200, as shown in Figure 3, so that the horizontal and vertical lengths were each 10 cm. As shown in Figure 3, the length L of the excess adhesive generated during cutting was measured, and if the length was 100 μm or more, it was evaluated as NG, and if it was less than 100 μm, it was evaluated as PASS.

[0144] 7. Evaluation of melting point and glass transition temperature The melting point was measured using a measurement method equipped with a Differential Scanning Calorimeter (DSC). A DSC2500 (TA Corporation) was used. Approximately 10 mg of the sample (polymer) was sealed in a dedicated pan, and the melting point and glass transition temperature were measured by observing the endothermic and exothermic temperatures under an N2 atmosphere with a heating rate of 10°C / min and a cooling rate of -10°C / min. The measurement temperature range was from -120°C to 200°C. The conditions were as follows: First, the sample was cooled from room temperature (approximately 30°C) to -120°C at a rate of approximately -10°C / min, and then heated to 200°C at a heating rate of 10°C / min (primary heating). Afterward, it was cooled again to -120°C at a rate of approximately -10°C / min, and then heated to 200°C at a heating rate of 10°C / min (secondary heating). The melting point was evaluated during the secondary heating.

[0145] Manufacturing Example 1. Manufacturing of copolymer (A) A monomer mixture was added to a 1 L reactor equipped with a cooling device that allowed for easy temperature control and reflux of nitrogen gas. The monomer mixture consisted of n-butyl acrylate (BA), lauryl acrylate (LA), and 4-hydroxybutyl acrylate (HBA) in a weight ratio of 6:3:1 (BA:LA:HBA). After adding the monomer mixture and an appropriate amount of ethyl acetate, the reactor was purged with nitrogen gas for 1 hour to remove oxygen, and the reactor temperature was maintained at approximately 62°C. The mixture was homogenized, and a reaction initiator (AIBN: Azobisisobutyronitrile) was added at approximately 400 ppm, followed by n-dodecyl mercaptan at approximately 400 ppm to initiate the reaction. The reaction was allowed to proceed for approximately 6 to 7 hours to produce a polymer (copolymer (A)). The weight-average molecular weight of the copolymer (polymer) (A) was approximately 2 million, and its molecular weight distribution was approximately 4.5. Furthermore, the melting point of the copolymer (polymer) (A) was approximately -43°C.

[0146] Manufacturing Example 2. Manufacturing of Copolymer (B) Copolymer (polymer) (B) was produced in the same manner as in Production Example 1, except that a monomer mixture of ethylhexyl acrylate (EHA), lauryl acrylate (LA), and 4-hydroxybutyl acrylate (HBA) in a weight ratio of 4:4:2 (EHA:LA:HBA) was used. The weight-average molecular weight of copolymer (polymer) (B) was approximately 2 million, and the molecular weight distribution was approximately 3.5. The melting point of copolymer (polymer) (B) was approximately -42°C.

[0147] Manufacturing Example 3. Manufacturing of Copolymer (C) Copolymer (polymer) (C) was produced in the same manner as in Production Example 1, except that a monomer mixture of n-butyl acrylate (BA), lauryl acrylate (LA), and 4-hydroxybutyl acrylate (HBA) in a weight ratio of 58:40:2 (BA:LA:HBA) was used. The weight-average molecular weight of copolymer (polymer) (C) was approximately 2 million, and the molecular weight distribution was approximately 3.5. The melting point of copolymer (polymer) (C) was approximately -42°C.

[0148] Example 1. An adhesive composition was prepared by blending approximately 0.07 parts by weight of isocyanate crosslinking agent (TKA-100, Needfill Co.), approximately 10 parts by weight of TEG-EH (triethylene glycol bis(2-ethylhexanoate)), and a catalytic amount of catalyst with 100 parts by weight of copolymer (polymer) (A) of Production Example 1. Typically, a catalyst that promotes the urethane reaction between hydroxyl groups and isocyanate groups was used as the catalyst. The adhesive composition was diluted with a solvent (ethyl acetate) to an appropriate viscosity and mixed in a mechanical stirrer for at least 15 minutes. After maintaining at room temperature to remove air bubbles, the mixture was applied to a release film (release PET (poly(ethylene terephthalate)) using a comma coater, and then maintained at 140°C for approximately 3 minutes to form an adhesive layer with a thickness of approximately 25 μm.

[0149] Example 2. Except for using DEHA (Diethylhexyl adipate) instead of TEG-EH (triethylene glycol bis(2-ethylhexanoate)), an adhesive layer with a thickness of approximately 25 μm was formed in the same manner as in Example 1.

[0150] Comparative Example 1. Except for not applying TEG-EH (triethylene glycol bis(2-ethylhexanoate)), an adhesive layer with a thickness of approximately 25 μm was formed in the same manner as in Example 1.

[0151] Comparative Example 2. Except for using IPMS (isopropyl myristate) instead of TEG-EH (triethylene glycol bis(2-ethylhexanoate)), an adhesive layer with a thickness of approximately 25 μm was formed in the same manner as in Example 1.

[0152] Comparative Example 3. Except for using TEC (triethyl citrate) instead of TEG-EH (triethylene glycol bis(2-ethylhexanoate)), an adhesive layer with a thickness of approximately 25 μm was formed in the same manner as in Example 1.

[0153] Comparative Example 4. Except for using ATBC (Acetyl Tributyl citrate) instead of TEG-EH (triethylene glycol bis(2-ethylhexanoate)), an adhesive layer with a thickness of approximately 25 μm was formed in the same manner as in Example 1.

[0154] Comparative Example 5. Except for using copolymer (B) from Production Example 2 instead of copolymer (A) from Production Example 1, and not using TEG-EH (triethylene glycol bis(2-ethylhexanoate)), an adhesive layer with a thickness of approximately 25 μm was formed in the same manner as in Example 1.

[0155] Comparative Example 6. Except for using copolymer (C) from Production Example 3 instead of copolymer (A) from Production Example 1, and not using TEG-EH (triethylene glycol bis(2-ethylhexanoate)), an adhesive layer with a thickness of approximately 25 μm was formed in the same manner as in Example 1.

[0156] The evaluation results for storage modulus, haze, peel strength, dynamic folding test, and cutability of the adhesive layers of the examples and comparative examples are summarized in Table 1 below.

[0157] In Table 1 below, G'(-20) is the storage modulus at -20°C, G'(25) is the storage modulus at 25°C, ΔG is the change in modulus confirmed by formula 1, and DF is the result of the folding test.

[0158] In Table 1, the unit of storage modulus is Pa, and the unit of peeling force is gf / inch.

[0159] [Table 1]

Claims

1. Containing a crosslinked acrylic copolymer, The acrylic copolymer comprises alkyl (meth)acrylate units, units of the following chemical formula 3, and polar functional group-containing units. The alkyl (meth)acrylate unit has a linear or branched alkyl group having 1 to 10 carbon atoms. The aforementioned polar functional group-containing unit is a unit derived from a hydroxyl group-containing monomer, The acrylic copolymer comprises 10 to 300 parts by weight of the unit of chemical formula 3 and 1 to 100 parts by weight of the polar functional group-containing unit per 100 parts by weight of the alkyl (meth)acrylate unit. and, - The storage modulus at 20°C is 100,000 Pa or less, the storage modulus at 25°C is 10,000 Pa or more, the peeling force to glass is 1,700 gf / inch or more, and the haze is 0.5% or less. Furthermore, adhesives whose rate of change in elastic modulus according to the following formula 1 is 2500 or less: [Chemical formula 3] In chemical formula 3, R1 represents hydrogen or an alkyl group, and R2 represents an alkyl group having 11 to 13 carbon atoms. [Formula 1] Change rate of elastic modulus = (M20 - M25) / 45 (Here, M20 is the storage modulus of the adhesive at -20°C, and M25 is the storage modulus of the adhesive at 25°C.)

2. The adhesive according to claim 1, wherein the peeling force to glass is 1,800 gf / inch or more.

3. The adhesive according to claim 2, wherein the acrylic copolymer has a weight-average molecular weight of 1 million or more.

4. The adhesive according to any one of claims 1 to 3, wherein the acrylic copolymer contains the alkyl (meth)acrylate units in a proportion of 10% to 80% by weight.

5. A base film; and an adhesive film comprising an adhesive according to any one of claims 1 to 3 formed on one or both sides of the base film.

6. An optical film; and an optical laminate comprising an adhesive according to any one of claims 1 to 3 formed on one or both sides of the optical film.

7. A display panel configured to be able to fold or roll through one or more folding or rolling axes; and A flexible device comprising an adhesive according to any one of claims 1 to 3, which is present on one or both sides of the display panel.

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