Polyolefin-based adhesive agent composition

Abstract

The purpose of the present invention is to provide an adhesive agent composition that exhibits excellent heat resistance and good adhesiveness between a polyolefin base material and a metal base material. The present invention pertains to an adhesive agent composition that contains an acid modified polyolefin (A) and a polyfunctional epoxy resin (B) having a tertiary amine in the molecular skeleton, and that satisfies both formulae (1) and (2). (1) The acid modified polyolefin (A) has a weight average molecular weight of 50,000-150,000, a melting point of 60-130°C, and an acid value of 5-40 mgKOH / g. (2) The ratio represented by (epoxy value of polyfunctional epoxy resin (B) having tertiary amine in molecular skeleton / acid value of acid modified polyolefin (A)) is 0.2-0.8.

Description

Polyolefin adhesive composition

[0001] The present invention relates to an adhesive composition using an acid-modified polyolefin and a multifunctional epoxy resin having a tertiary amine in the molecular skeleton, and more particularly to an adhesive composition suitable for bonding an injection-molded polyolefin substrate to a metal substrate.

[0002] Many metal parts are used in fields such as home appliance exterior panels, furniture materials, building interior components, and electrical and electronic components. Plastic parts, particularly polyolefin resin parts, are also used in combination to reduce the weight of parts. Conventionally, it has been difficult to bond high-polarity metal substrates and low-polarity polyolefin resins, so they have been joined by welding, screwing, or the like. Meanwhile, various adhesive compositions for bonding metal substrates and polyolefin substrates have been proposed to improve the efficiency of component manufacturing processes. However, these adhesive compositions must be more resistant to harsh environments, assuming use in a variety of environments. For example, electrical and electronic components are exposed to high-temperature environments due to heat generation during charging and discharging, and therefore there is a demand for adhesive compositions that exhibit high adhesive strength even in high-temperature environments of around 100°C.

[0003] As a composition for bonding a polyolefin resin to a metal substrate, for example, Patent Document 1 discloses a polyolefin adhesive composition modified with an α,β-unsaturated carboxylic acid or a (meth)acrylic acid ester, and Patent Document 2 discloses an adhesive composition in which an isocyanate curing agent is blended with an α,β-unsaturated carboxylic acid or a (meth)acrylic acid ester-modified polyolefin.

[0004] JP 2020-143181 A Patent No. 6673411

[0005] However, Patent Document 1 does not take into consideration unreacted (meth)acrylic acid esters, and the highly polar (meth)acrylic acid esters precipitate on the surface, reducing the affinity with the polyolefin resin, resulting in low adhesive strength at high temperatures. Furthermore, the thermosetting adhesive described in Patent Document 2 has the problem of requiring long-term aging conditions when joining substrates.

[0006] The present invention has been made in light of the problems of the prior art. That is, an object of the present invention is to provide an adhesive composition that exhibits good adhesion and heat resistance between polyolefin substrates and metal substrates. In addition, an object of the present invention is to provide an adhesive composition that exhibits good adhesive strength even under high-temperature, short-time processing conditions such as injection molding. Furthermore, an object of the present invention is to provide an adhesive composition that exhibits good solvent solubility and is easy to use.

[0007] The present inventors conducted extensive research to solve the above-mentioned problems, and as a result, have completed the present invention. Specifically, the present invention comprises the following features: [1] An adhesive composition containing an acid-modified polyolefin (A) and a multifunctional epoxy resin (B) having a tertiary amine in its molecular skeleton, and satisfying all of the following formulas (1) and (2): (1) The acid-modified polyolefin (A) has a weight-average molecular weight of 50,000 to 150,000, a melting point of 60°C to 130°C, and an acid value of 5 mgKOH / g to 40 mgKOH / g; (2) A ratio expressed as (epoxy value of multifunctional epoxy resin (B) having a tertiary amine in its molecular skeleton / acid value of acid-modified polyolefin (A)) is 0.2 to 0.8; [2] The adhesive composition according to [1], wherein the softening point of the adhesive composition is 140°C or higher; and [3] The adhesive composition according to [1] or [2], further comprising an organic solvent (C). [4] The adhesive composition according to any one of [1] to [3], which is used for bonding a polyolefin substrate to a metal substrate. [5] A laminate comprising a polyolefin substrate, the adhesive composition according to any one of [1] to [4], and a metal substrate laminated in this order.

[0008] The adhesive composition of the present invention has excellent adhesion between polyolefin substrates and metal substrates, and is heat-resistant, allowing adhesion even at high temperatures of 100°C, without the need for aging. Furthermore, it exhibits good solvent solubility and is easy to use. Therefore, it is particularly suitable as an adhesive for injection-molded polyolefin resins and metal substrates.

[0009] Fig. 1 is a cross-sectional view showing an example of a laminate of the present invention. Fig. 2 is a diagram showing a test piece for measuring adhesive strength of the present invention. Fig. 3 is a diagram showing how adhesive strength is measured using the test piece.

[0010] In the drawings accompanying this specification, the scale and aspect ratios have been appropriately changed and exaggerated from those of the actual objects for the sake of ease of illustration and understanding.

[0011] The present invention will be described in detail below. <Acid-Modified Polyolefin (A)> The acid-modified polyolefin (A) used in the present invention is not limited, but is preferably at least one of polyethylene, polypropylene, and a propylene-α-olefin copolymer, which has been acid-modified. Furthermore, the acid-modified polyolefin (A) is more preferably polypropylene or a propylene-α-olefin copolymer, and even more preferably a propylene-α-olefin copolymer, which has been acid-modified.

[0012] The propylene-α-olefin copolymer is obtained by copolymerizing propylene as the main component with an α-olefin. As the α-olefin, for example, one or more of ethylene, 1-butene, 1-heptene, 1-octene, 4-methyl-1-pentene, vinyl acetate, etc. can be used. From the viewpoints of adhesiveness and dissolution stability, a copolymer of propylene and 1-butene is particularly preferred. The molar ratio of the propylene component to the α-olefin component in the propylene-α-olefin copolymer is not particularly limited, but the propylene component is preferably 50 mol% or more, and more preferably 70 mol% or more. A molar ratio of the propylene component of 50% or more can exhibit excellent adhesiveness to polyolefin substrates, particularly polypropylene substrates.

[0013] The acid-modified polyolefin (A) used in the present invention may be modified with other modifications. Specific examples include chlorine modification, hydroxyl group modification, etc. Furthermore, from the viewpoints of adhesion to metal substrates and production efficiency, it is particularly preferred that the acid-modified polyolefin (A) is modified only with an acid.

[0014] The acid-modified polyolefin (A) is preferably a polyolefin modified with an α,β-unsaturated carboxylic acid and its acid anhydride. Examples of the α,β-unsaturated carboxylic acid and its acid anhydride include maleic acid, itaconic acid, citraconic acid, and their acid anhydrides. Among these, acid anhydrides are preferred, and maleic anhydride is more preferred. These α,β-unsaturated carboxylic acids and their acid anhydrides can be used alone or in combination of two or more.

[0015] The acid value of the acid-modified polyolefin (A) is 5 mgKOH / g or more from the viewpoint of adhesion between the polyolefin resin substrate and the metal substrate. It is preferably 10 mgKOH / g or more, more preferably 15 mgKOH / g or more, and even more preferably 20 mgKOH / g or more. By adjusting the acid value to be equal to or greater than the lower limit, the adhesive strength at the polyolefin / metal interface is improved, resulting in good metal adhesion in environments at 25°C and 100°C. The upper limit of the acid value is 40 mgKOH / g or less. It is preferably 35 mgKOH / g or less, more preferably 30 mgKOH / g or less, and even more preferably 25 mgKOH / g or less. Adjusting the acid value to be equal to or less than the upper limit improves the molecular weight and cohesive strength, thereby improving adhesive strength. Furthermore, production efficiency is also improved. That is, the acid value is 5 to 40 mgKOH / g, preferably 10 to 35 mgKOH / g, more preferably 15 to 30 mgKOH / g, and even more preferably 20 to 25 mgKOH / g.

[0016] The acid value of the acid-modified polyolefin (A) can be adjusted by the amounts of the α,β-unsaturated carboxylic acid, the acid anhydride of the α,β-unsaturated carboxylic acid, and the radical generator used.

[0017] The weight-average molecular weight (Mw) of the acid-modified polyolefin (A) is 50,000 or more, preferably 60,000 or more, more preferably 80,000 or more, and even more preferably 90,000 or more. It is also 150,000 or less, preferably 140,000 or less, and more preferably 130,000 or less. That is, the weight-average molecular weight (Mw) is 50,000 to 150,000, preferably 60,000 to 140,000, more preferably 80,000 to 130,000, and even more preferably 90,000 to 130,000. By setting the Mw at or above the lower limit, the cohesive strength is improved and excellent adhesive properties can be achieved. By setting the Mw at or below the upper limit, excellent solvent solubility, flowability, and operability are achieved.

[0018] The melting point (Tm) of the acid-modified polyolefin (A) is 60°C or higher, preferably 70°C or higher, and more preferably 80°C or higher. It is also 130°C or lower, preferably 120°C or lower, more preferably 110°C or lower, and even more preferably 100°C or lower. That is, the melting point (Tm) of the acid-modified polyolefin (A) is 60 to 130°C, preferably 70 to 120°C, more preferably 80 to 110°C, and even more preferably 80 to 100°C. By setting the melting point at or above the lower limit, the crystal-derived cohesive force is improved, and excellent adhesive properties can be exhibited. Furthermore, by setting the melting point at or below the upper limit, excellent solvent solubility and flowability are achieved, and operability during adhesion is improved.

[0019] The method for producing the acid-modified polyolefin (A) is not particularly limited, and examples thereof include a radical graft reaction (i.e., a reaction in which radical species are generated on a polymer that becomes a main chain, and an unsaturated carboxylic acid and an acid anhydride are graft-polymerized using the radical species as a polymerization initiation point).

[0020] The radical generator is not particularly limited, but examples thereof include organic peroxides and azonitriles, and it is preferable to use an organic peroxide. Examples of the organic peroxide include, but are not particularly limited to, di-tert-butyl peroxyphthalate, tert-butyl hydroperoxide, dicumyl peroxide, benzoyl peroxide, tert-butyl peroxybenzoate, tert-butylperoxy-2-ethylhexanoate, tert-butyl peroxypivalate, methyl ethyl ketone peroxide, di-tert-butyl peroxide, lauroyl peroxide, and examples of the azonitrile include azobisisobutyronitrile and azobisisopropionitrile.

[0021] As the acid-modified polyolefin (A), commercially available products may be used, such as the "MODIC" series manufactured by Mitsubishi Chemical Corporation, the "ADMER" series and "UNISTOR" series manufactured by Mitsui Chemicals, Inc., the "HARDLEN" series manufactured by Toyobo Co., Ltd., the "UMEX" series manufactured by Sanyo Chemical Industry Co., Ltd., and the "AUROLEN" series manufactured by Nippon Paper Industries Co., Ltd.

[0022] <Polyfunctional Epoxy Resin (B) Having a Tertiary Amine in the Molecular Skeleton> The polyfunctional epoxy resin (B) having a tertiary amine in the molecular skeleton used in the present invention is not particularly limited as long as it has a tertiary amine in one molecule and is a compound having a polyfunctional epoxy group.

[0023] Examples of the polyfunctional epoxy resin (B) having a tertiary amine in the molecular skeleton used in the present invention include tetrafunctional ones such as N,N,N',N'-tetraglycidyl-m-xylylenediamine and diaminodiphenylmethane tetraglycidyl ether, and trifunctional ones such as triglycidyl-p-aminophenol. These can be used alone or in combination of two or more.

[0024] The epoxy groups of the polyfunctional epoxy resin (B) having a tertiary amine in its molecular skeleton used in the present invention must be at least difunctional, preferably at least trifunctional, preferably up to pentafunctional, and more preferably up to tetrafunctional, in order to crosslink with the acid-modified polyolefin (A). From the viewpoint of storage stability, trifunctional epoxy resins are preferred. That is, the epoxy groups of the polyfunctional epoxy resin (B) are di- to pentafunctional, preferably tri- to tetrafunctional, and more preferably trifunctional.

[0025] The epoxy value is preferably 300 mgKOH / g or more, more preferably 400 mgKOH / g or more, and even more preferably 500 mgKOH / g or more, and is preferably 800 mgKOH / g or less, more preferably 700 mgKOH / g or less, and even more preferably 600 mgKOH / g or less. That is, the epoxy value is preferably 300 to 800 mgKOH / g, more preferably 400 to 700 mgKOH / g, and even more preferably 500 to 600 mgKOH / g.

[0026] The number of tertiary amines must be 1 or more, preferably 2 or more, and is preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less. That is, the number of tertiary amines is 1 or more, preferably 2 to 5, more preferably 2 to 4, and even more preferably 2 to 3.

[0027] <Adhesive Composition> The adhesive composition of the present invention is a composition containing an acid-modified polyolefin (A) and a polyfunctional epoxy resin (B) having a tertiary amine in the molecular skeleton.

[0028] The adhesive composition of the present invention contains the acid-modified polyolefin (A) and the multifunctional epoxy resin (B), and thus its softening point appears higher than the melting point of the base acid-modified polyolefin (A). When a conventional epoxy resin, i.e., an epoxy resin other than the multifunctional epoxy resin (B) having a tertiary amine in its molecular skeleton, is used, a simple crosslink with the acid-modified polyolefin is formed, and therefore no inflection point appears higher than the melting point of the acid-modified polyolefin (A). The mechanism of action is not particularly limited, but is presumed to be due to the interaction between the tertiary amine in the molecular skeleton of the multifunctional epoxy resin (B) having a tertiary amine and the carboxylic acid moiety in the molecular skeleton of the acid-modified polyolefin.

[0029] The compounding ratio of the acid-modified polyolefin (A) to the polyfunctional epoxy resin (B) having a tertiary amine in its molecular skeleton is in the range of 0.2 to 0.8, where the ratio is expressed as the epoxy value of the polyfunctional epoxy resin (B) having a tertiary amine in its molecular skeleton / the acid value of the acid-modified polyolefin (A). It is preferably 0.3 to 0.7, more preferably 0.4 to 0.6. If the ratio is less than the lower limit, the interaction between the tertiary amine and the carboxylic acid moiety in the molecular skeleton of the acid-modified polyolefin does not occur, the resin behaves as a thermoplastic resin, the crosslinking of the resin composition does not proceed sufficiently, and the adhesive strength in a high-temperature environment is poor. If the ratio exceeds the upper limit, a high-density crosslinked product is formed, the resin behaves as a simple thermosetting resin, and the resin does not soften sufficiently, resulting in poor adhesive strength in a high-temperature environment.

[0030] The softening point of the adhesive composition according to the present invention is preferably 140°C or higher, more preferably 145°C or higher, and even more preferably 150°C or higher. It is also preferably 190°C or lower, more preferably 185°C or lower, and even more preferably 180°C or lower. That is, the softening point is preferably 140°C to 190°C, more preferably 145 to 185°C, and even more preferably 150 to 180°C. If the softening point is too high, the adhesive composition will not soften sufficiently during injection molding, resulting in reduced adhesive properties. On the other hand, if the softening point is too low, the heat resistance will decrease and the adhesive composition will flow at the molding temperature during injection molding, preventing sufficient adhesive properties from being achieved.

[0031] The softening point of the adhesive composition of the present invention is a value measured by the method described in the examples.

[0032] The adhesive composition of the present invention may be blended with various other additives such as tackifiers, plasticizers, flame retardants, pigments, and antiblocking agents, as long as the performance of the present invention is not impaired.

[0033] The adhesive composition of the present invention has excellent adhesive properties even without the addition of a curing accelerator. Although the mechanism of action is not particularly limited, it is presumed that the nitrogen atom of the tertiary amine in the molecular skeleton of the polyfunctional epoxy resin (B) of the present invention has catalytic activity, resulting in reactivity with the acid-modified polyolefin (A). It is presumed that this reactivity allows the crosslinking reaction to proceed sufficiently even when the adhesive composition does not contain a curing accelerator.

[0034] Therefore, it is preferable that the adhesive composition of the present invention contains substantially no curing accelerator, that is, the content of the curing accelerator is preferably less than 1 part by mass (solid content equivalent) per 100 parts by mass (solid content equivalent) of the acid-modified polyolefin (A), more preferably less than 0.7 parts by mass, even more preferably less than 0.5 parts by mass, and most preferably no curing accelerator at all.

[0035] The curing accelerator is used for the purpose of accelerating the reaction between the acid-modified polyolefin (A) and the polyfunctional epoxy resin (B) having a tertiary amine, and examples thereof include tertiary amine curing accelerators, tertiary amine salt curing accelerators, and imidazole curing accelerators. Specific examples thereof include N,N-dimethylaminopyridine and N-methylimidazole.

[0036] The adhesive composition of the present invention may further contain an organic solvent to the extent that the performance of the present invention is not impaired. The organic solvent is not particularly limited as long as it dissolves or disperses the acid-modified polyolefin (A) and the polyfunctional epoxy resin (B) having a tertiary amine in its molecular skeleton. Examples include low-polarity solvents such as aliphatic hydrocarbons and alicyclic hydrocarbons, and high-polarity solvents such as alcohol-based solvents, ether-based solvents, ketone-based solvents, and ester-based solvents. From the viewpoint of storage stability, it is preferable to use a low-polarity solvent and a high-polarity solvent in combination. The content ratio of the high-polarity solvent to the low-polarity solvent is preferably 50 / 50 to 3 / 97 (mass ratio), more preferably 45 / 55 to 5 / 95, and even more preferably 40 / 60 to 10 / 90.

[0037] Examples of aliphatic hydrocarbons include hexane, heptane, octane, and decane. Examples of alicyclic hydrocarbons include cyclohexane, cyclohexene, methylcyclohexane, and ethylcyclohexane. Examples of alcohol-based solvents include methanol, ethanol, isopropyl alcohol, butanol, pentanol, hexanol, and propanediol. Examples of ether-based solvents include ethylene glycol mono-n-butyl ether, ethylene glycol mono-iso-butyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-iso-butyl ether, triethylene glycol mono-n-butyl ether, and tetraethylene glycol mono-n-butyl ether. Examples of ketone-based solvents include acetone, methyl isobutyl ketone, methyl ethyl ketone, pentanone, hexanone, cyclohexanone, isophorone, and acetophenone. Examples of ester-based solvents include methyl acetate, ethyl acetate, butyl acetate, methyl propionate, and butyl formate.

[0038] Among the organic solvents described above, the low-polarity solvent is preferably an alicyclic hydrocarbon such as methylcyclohexane, and the high-polarity solvent is preferably a ketone-based solvent such as methyl ethyl ketone, with a mixed solvent of methylcyclohexane and methyl ethyl ketone being more preferred. These organic solvents are preferably contained in an amount of 80 to 2,000 parts by mass per 100 parts by mass of the total amount of (A) and (B). The range is more preferably 90 to 1,600 parts by mass, even more preferably 100 to 1,200 parts by mass, and particularly preferably 110 to 800 parts by mass. Within the above ranges, the solution state tends to be good.

[0039] <Laminate> The laminate of the present invention is obtained by laminating a polyolefin substrate and a metal substrate with the adhesive composition of the present invention.

[0040] As a lamination method, conventionally known injection molding techniques can be used. For example, although not particularly limited, the adhesive composition is applied to the surface of a metal substrate using an appropriate application means such as a roll coater or bar coater, and then dried. After drying, a polyolefin resin can be injection molded onto the layer of the adhesive composition (adhesive layer) formed on the surface of the metal substrate to obtain a laminate. The thickness of the adhesive layer formed from the adhesive composition is not particularly limited, but is preferably 0.5 to 30 μm, more preferably 1.0 to 25 μm, and even more preferably 1.0 to 20 μm.

[0041] In a conventional injection molding technique, for example, molding is performed by injecting a polyolefin resin into a mold in which a metal substrate is set. More specifically, when a screw-type hot melt molding applicator is used, the polyolefin is heated and melted at about 160 to 280°C and injected into the mold through an injection nozzle. After a certain cooling time, the laminate can be removed from the mold to obtain the laminate.

[0042] The type of hot melt molding applicator is not particularly limited, but examples include ST2 manufactured by Nordson, vertical extrusion molding machine IMC-18F9 manufactured by Imoto Manufacturing Co., Ltd., and THX5S manufactured by Nissei Plastics Co., Ltd.

[0043] <Polyolefin substrate> The polyolefin substrate may be appropriately selected from conventionally known polyolefin resins. For example, without particular limitation, polyethylene, polypropylene, ethylene-propylene copolymer, etc. can be used. Among these, the use of polypropylene is preferred. While without particular limitation, the thickness is preferably 100 to 500 μm, more preferably 150 to 400 μm, and even more preferably 200 to 300 μm. Note that pigments and various additives may be blended into the polyolefin substrate as needed.

[0044] <Metal Substrate> The metal substrate is not particularly limited, and various metals and alloys thereof, such as aluminum, copper, steel, chromium, zinc, duralumin, and die-cast metals, can be used. Furthermore, the metal substrate can take any shape, such as a metal foil, rolled steel plate, panel, pipe, can, or cap. Generally, aluminum is preferred from the viewpoint of workability. Furthermore, although it varies depending on the intended use, it is generally used in the form of a sheet having a thickness of 0.01 to 10 mm, preferably 0.02 to 5 mm. Furthermore, the surface of these metal substrates may be previously surface-treated or may remain untreated. In either case, the same effect can be achieved.

[0045] This application claims priority based on Japanese Patent Application No. 2023-195075, filed on November 16, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-195075, filed on November 16, 2023, are incorporated herein by reference.

[0046] Examples will be given below to explain the present invention more specifically, but the present invention is not limited to these examples. The measured values ​​described in the examples were measured by the following methods. In the examples and comparative examples, "parts" simply refers to "parts by mass" and "%" refers to "% by weight."

[0047] (1) Measurement of Weight-Average Molecular Weight The number-average molecular weight in the present invention is a value measured by gel permeation chromatography (hereinafter referred to as GPC, standard substance: polystyrene resin, mobile phase: tetrahydrofuran, column: Shodex KF-802 + KF-804L + KF-806L, column temperature: 30°C, flow rate: 1.0 ml / min, detector: RI detector) manufactured by Shimadzu Corporation.

[0048] (2) Measurement of Melting Point (Tm) The melting point and heat of fusion in the present invention are values ​​measured using a differential scanning calorimeter (hereinafter referred to as DSC, manufactured by TA Instruments Japan, Ltd., Q-2000) from the top temperature and area of ​​the melting peak when the sample is heated and melted at a rate of 20°C / min, cooled to form a resin, and then heated and melted again.

[0049] (3) Measurement of Acid Value (unit: mg KOH / g) The acid value in the present invention refers to the amount of KOH required to neutralize 1 g of a sample, and was measured in accordance with the test method of JIS K0070 (1992). Specifically, 1 g of acid-modified polyolefin was dissolved in 100 g of xylene adjusted to a temperature of 100°C, and then titrated at the same temperature with a 0.1 mol / L potassium hydroxide ethanol solution [trade name "0.1 mol / L ethanolic potassium hydroxide solution," manufactured by Wako Pure Chemical Industries, Ltd.] using phenolphthalein as an indicator. The amount of potassium hydroxide required for the titration was converted to mg to calculate the acid value (mg KOH / g).

[0050] (4) Softening Point Measurement The adhesive composition was dissolved in methylcyclohexane / methyl ethyl ketone = 9 / 1 (weight ratio) to obtain an adhesive composition solution with a solids concentration of 20%. Next, the adhesive composition solution was applied to a 150 μm thick Teflon® sheet at room temperature using an applicator so that the adhesive composition coating thickness after drying would be 15 μm, and the solvent was evaporated in a hot air dryer at 120 °C for 2 minutes. A 15 mm x 3 mm piece was then cut out, the adhesive composition was removed from the Teflon® sheet, and the softening point was measured using a thermomechanical analyzer (TMA7100, manufactured by Hitachi High-Tech Science Corporation). The measurement conditions were a nitrogen atmosphere, a measurement temperature range of -50 °C to 250 °C, a tensile load of 20 mN, and a heating rate of 10 °C / min. The softening point was determined as the intersection of the tangent obtained from the baseline before the second inflection point on the high-temperature side of the obtained curve and the tangent obtained from the baseline after the inflection point.

[0051] (5) Solvent solubility at 25°C A resin solution prepared by dissolving the adhesive composition in a 9 / 1 (weight ratio) mixture of methylcyclohexane and methyl ethyl ketone to a solid content of 20% by mass was stored at 25°C for 2 weeks (14 days), and the presence or absence of haze or residual solvent was visually inspected. ∘: No haze or residual solvent was observed in the resin solution. ×: Haze or residual solvent was observed in the resin solution.

[0052] (6) Adhesive Strength <Laminate Preparation> A five-layer laminate consisting of an aluminum plate (100 μm thick) / adhesive composition layer (20 μm thick) / polyolefin resin (300 μm thick) / adhesive composition layer (20 μm thick) / aluminum plate (100 μm thick) was prepared by the method described below. First, the adhesive composition was dissolved in methylcyclohexane / methyl ethyl ketone = 9 / 1 (weight ratio) to obtain a 20% solids concentration, thereby obtaining an adhesive composition solution. Next, the adhesive composition solution was applied to an aluminum plate at room temperature using an applicator so that the adhesive composition coating thickness after drying would be 20 μm. The solvent was evaporated in a hot air dryer at 120 °C for 2 minutes, and then the aluminum plate was heat-treated at 140 °C for 2 hours to cure, obtaining an aluminum plate laminated with the adhesive composition. Next, the adhesive composition layer on the aluminum plate was brought into contact with the molten polyolefin resin, and the molded polyolefin resin was fixed inside an adhesion test mold so that it had a size of 25 mm x 10 mm x 300 μm. Polypropylene (Prime Polypro J107G, manufactured by Prime Polymer Co., Ltd., MFR: 30 g / 10 min) was used as the polyolefin. Then, using a vertical injection molding machine (THX5S manufactured by Nissei Plastics Co., Ltd.), the polyolefin resin was injected and molded. The molding conditions were a molding resin temperature of 240°C, a mold temperature of 90°C, a molding pressure of 50 MPa, a cooling time of 20 seconds, and an injection speed of 30 mm / sec. The molded product was removed from the mold, and an adhesive strength test piece (aluminum plate / adhesive composition layer / polyolefin resin / adhesive composition layer / aluminum plate) was obtained in which the molded polyolefin resin was sandwiched between aluminum plates coated with the adhesive composition.

[0053] <Adhesion Strength> The adhesive strength between the aluminum plates of the five-layer laminate was measured using a tensile tester. The ambient temperature during measurement was set to 25°C or 100°C, the peeling speed was 300 mm / min, and the tensile strength when peeled using a T-peel method was taken as the adhesive strength, and the adhesive strength unit was N / 25 mm. The results are shown in Table 1. (Judgment) ⊚: 30 N / 25 mm or more ◯: 20 N / 25 mm or more but less than 30 N / 25 mm ×: Less than 20 N / 25 mm

[0054]

[0055] Production Examples of Acid-Modified Polyolefin (A) Production Example 1, Acid-Modified Polyolefin (A) A-1 To a 1 L autoclave, 100 parts by mass of a propylene-butene copolymer ("Tafmer (registered trademark) XM7090" manufactured by Mitsui Chemicals, Inc.), 150 parts by mass of toluene, 3 parts by mass of maleic anhydride, and 1 part by mass of di-tert-butyl peroxide were added, and the mixture was heated to 140 ° C. and stirred for an additional 3 hours. Thereafter, the resulting reaction liquid was cooled and poured into a container containing a large amount of methyl ethyl ketone to precipitate a resin. Thereafter, the liquid containing the resin was centrifuged to separate and purify the acid-modified propylene-butene copolymer graft-polymerized with maleic anhydride, (poly)maleic anhydride, and low-molecular-weight substances. Thereafter, the mixture was dried under reduced pressure at 70°C for 5 hours to obtain a maleic anhydride-modified propylene-butene copolymer (A-1, acid value 5 mgKOH / g, weight average molecular weight 90,000, Tm 90°C) which is an acid-modified polyolefin.

[0056] Production Example 2, Acid-Modified Polyolefin (A) A-2> A maleic anhydride-modified propylene-butene copolymer (A-2, acid value 20 mgKOH / g, weight average molecular weight 110,000, Tm 70°C), which is an acid-modified polyolefin, was obtained by the same procedure as in Production Example 1, except that the propylene-butene copolymer (Tafmer (registered trademark) XM7090 manufactured by Mitsui Chemicals, Inc.) used in Production Example 1 was changed to a propylene-butene copolymer (Tafmer (registered trademark) XM7070 manufactured by Mitsui Chemicals, Inc.), the amount of maleic anhydride charged was changed to 16 parts by mass, and the amount of di-tert-butyl peroxide charged was changed to 0.5 parts by mass.

[0057] Production Example 3, Acid-Modified Polyolefin (A) A-3> A maleic anhydride-modified propylene-butene copolymer (A-3, acid value 25 mgKOH / g, weight average molecular weight 60,000, Tm 90°C), which is an acid-modified polyolefin, was obtained in the same manner as in Production Example 1, except that the amount of maleic anhydride charged was changed to 20 parts by mass and the amount of di-tert-butyl peroxide charged was changed to 5 parts by mass.

[0058] Production Example 4, Acid-Modified Polyolefin (A) A-4 Production Example 1 was repeated except that the propylene-butene copolymer (Tafmer (registered trademark) XM7090 manufactured by Mitsui Chemicals, Inc.) used in Production Example 1 was replaced with an unfunctionalized polypropylene having a melting point of 160°C (J-105G manufactured by Prime Polymer Co., Ltd.), the amount of maleic anhydride charged was changed to 10 parts by mass, and the amount of di-tert-butyl peroxide charged was changed to 4 parts by mass, to obtain a maleic anhydride-modified polypropylene (A-4, acid value 8 mgKOH / g, weight average molecular weight: 150,000, melting point 155°C).

[0059] <Multifunctional Epoxy Resins (B) Having a Tertiary Amine in the Molecular Skeleton> Epoxy resin (B-1): TETRAD-X, manufactured by Mitsubishi Gas Chemical Company, Inc., epoxy value: 545 mg KOH / g, number of tertiary amines: 2 Epoxy resin (B-2): jER630, manufactured by Mitsubishi Chemical Corporation, epoxy value: 572 mg KOH / g, number of tertiary amines: 1 <Multifunctional Epoxy Resins (E) Having No Tertiary Amine in the Molecular Skeleton> Epoxy resin (E-1): YX4000H, manufactured by Mitsubishi Chemical Corporation, epoxy value: 292 mg KOH / g, number of tertiary amines: 0 Epoxy resin (E-2): HP-6000, manufactured by DIC Corporation, epoxy value: 224 mg KOH / g, number of tertiary amines: 0

[0060] As is clear from Table 1, Examples 1 to 6 exhibited good adhesive strengths at both 25°C and 100°C. In contrast, Comparative Example 1 contained a small amount of epoxy resin (B-2), resulting in no softening point and weak cohesive strength at 100°C, resulting in reduced adhesive strength. Comparative Example 2 contained a large amount of epoxy resin (B-2), resulting in reduced affinity with polypropylene and reduced adhesive strength. Comparative Examples 3 and 4 used multifunctional epoxy resins (E-1) and (E-2) that did not contain tertiary amines, resulting in no softening point and poor curing reaction, resulting in weak cohesive strength at 100°C and reduced adhesive strength. Comparative Example 5 used an acid-modified polyolefin with a melting point of 155°C, resulting in poor solvent solubility at 25°C, making adhesion evaluation impossible.

[0061] The adhesive composition of the present invention has good adhesion and heat resistance between polyolefin substrates and metal substrates. In addition, it can exhibit good adhesive strength even under high-temperature, short-time processing conditions such as injection molding. Laminates of polyolefin resin substrates and metal substrates formed from the adhesive composition of the present invention can be widely used in fields such as home appliance exterior panels, furniture materials, building interior components, and electrical and electronic components.

[0062] 1 Polyolefin resin 2 Adhesive composition 3 Metal substrate

Claims

1. An adhesive composition containing an acid-modified polyolefin (A) and a multifunctional epoxy resin (B) having a tertiary amine in its molecular skeleton, and satisfying all of the following formulas (1) and (2): (1) the weight average molecular weight of the acid-modified polyolefin (A) is 50,000 or more and 150,000 or less, the melting point is 60°C or more and 130°C or less, and the acid value is 5 mgKOH / g or more and 40 mgKOH / g or less, and (2) the ratio represented by (epoxy value of the multifunctional epoxy resin (B) having a tertiary amine in its molecular skeleton / acid value of the acid-modified polyolefin (A)) is 0.2 or more and 0.8 or less.

2. The adhesive composition according to claim 1, wherein the softening point of the adhesive composition is 140°C or higher.

3. The adhesive composition according to claim 1, further comprising an organic solvent (C).

4. The adhesive composition according to claim 1, wherein the acid-modified polyolefin (A) is at least one of polyethylene, polypropylene and a propylene-α-olefin copolymer that has been acid-modified.

5. The adhesive composition according to claim 4, wherein the α-olefin is at least one selected from the group consisting of ethylene, 1-butene, 1-heptene, 1-octene, 4-methyl-1-pentene, and vinyl acetate.

6. The adhesive composition according to claim 1, wherein the acid-modified polyolefin (A) is a polyolefin that has been acid-modified with an α,β-unsaturated carboxylic acid or its acid anhydride.

7. The adhesive composition according to claim 1, wherein the multifunctional epoxy resin (B) is at least one selected from the group consisting of N,N,N',N'-tetraglycidyl-m-xylylenediamine, diaminodiphenylmethane tetraglycidyl ether, and triglycidyl-p-aminophenol.

8. The adhesive composition according to claim 1, wherein the content of the curing accelerator is less than 1 part by mass (converted into solids) per 100 parts by mass (converted into solids) of the acid-modified polyolefin (A).

9. The adhesive composition according to claim 1 or 2, which is used for bonding a polyolefin substrate to a metal substrate.

10. A laminate comprising a polyolefin substrate, the adhesive composition according to claim 1 or 2, and a metal substrate laminated in this order.

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