Polyolefin adhesive composition

Abstract

The present invention provides an adhesive composition which exhibits heat resistance and good adhesiveness with a polyolefin resin base material and a metal base material, and which does not require aging.　Provided is an adhesive composition comprising a modified polyolefin (A) an olefin-α-olefin copolymer (B), wherein: (1) the olefin-α-olefin copolymer (B) is contained at a proportion of 15-85 parts by mass per 100 parts by mass of the modified polyolefin (A); (2) the weight-average molecular weight of the olefin-α-olefin copolymer (B) is not less than 200,000; (3) the melting point of the olefin-α-olefin copolymer (B) is 80-100°C; and (4) the weight-average molecular weight of the modified polyolefin (A) is less than or equal to the weight-average molecular weight of the olefin-α-olefin copolymer (B).

Description

[Technical Field]

[0001] The present invention relates to an adhesive composition using a modified polyolefin and an olefin-α-olefin copolymer, and more particularly to an adhesive composition suitable for bonding a polyolefin resin substrate to a metal substrate. [Background technology]

[0002] Many metal parts are used in fields such as home appliance exterior panels, furniture materials, architectural interior components, and electrical and electronic components. Plastic parts, particularly polyolefin resin parts, are also used in combination to reduce the weight of parts. Due to the difficulty of bonding high-polarity metal substrates and low-polarity polyolefin resin substrates, they have traditionally been joined by welding, screwing, or other methods. Meanwhile, various adhesive compositions have been proposed for bonding metal substrates and polyolefin resin substrates 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 environments of around 25°C and 90°C.

[0003] As a composition for bonding a polyolefin resin substrate 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. Also, 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-143181 [Patent Document 2] Patent No. 6673411 Summary of the Invention Problems to be Solved by the Invention

[0005] However, Patent Document 1 does not take into consideration unreacted (meth)acrylic acid esters, and there is a problem that the highly polar (meth)acrylic acid esters precipitate on the surface, particularly at high temperatures, reducing the affinity with the polyolefin resin substrate, resulting in low adhesive strength at high temperatures. Also, the thermosetting adhesive described in Patent Document 2 has a problem in that it requires long-term aging to complete the curing reaction.

[0006] The present invention was made in response to these problems in the prior art. Specifically, an object of the present invention is to provide an adhesive composition that exhibits good adhesion and heat resistance between a polyolefin resin substrate and a metal substrate, and does not require aging. Additionally, 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 a laminate comprising a polyolefin resin substrate, an adhesive layer made of the adhesive composition, and a metal substrate.

[0007] The present inventors have conducted extensive research to solve the above problems and have completed the present invention, which comprises the following features. [1] An adhesive composition comprising a modified polyolefin (A) and an olefin-α-olefin copolymer (B), and satisfying all of the following requirements (1) to (5): (1) the modified polyolefin (A) is an acid-modified polyolefin, The olefin-α-olefin copolymer (B) is contained in an amount of 15 to 85 parts by mass per 100 parts by mass of the modified polyolefin (A). (2) The weight average molecular weight of the olefin-α-olefin copolymer (B) is 200,000 or more. (3) The melting point of the olefin-α-olefin copolymer (B) is 80°C or higher and 100°C or lower. (4) The weight average molecular weight of the modified polyolefin (A) is equal to or less than the weight average molecular weight of the olefin-α-olefin copolymer (B). (5) The olefin-α-olefin copolymer (B) is a propylene-α-olefin copolymer (excluding the case where the α-olefin in the propylene-α-olefin copolymer is propylene or vinyl acetate). [2] The adhesive composition according to [1], wherein the weight average molecular weight of the modified polyolefin (A) is 70,000 or more but less than 200,000. [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], wherein the acid value of the modified polyolefin (A) is 2 to 50 mgKOH / g. [5] The adhesive composition according to any one of [1] to [4], which is used for bonding a polyolefin resin substrate to a metal substrate. [6] A laminate comprising a polyolefin resin substrate, the adhesive composition according to any one of [1] to [5], and a metal substrate laminated in this order. [Effects of the Invention]

[0008] The adhesive composition of the present invention has excellent adhesion between polyolefin resin substrates and metal substrates, and is heat resistant, allowing adhesion even under high temperature conditions, and does not require aging. Therefore, it is particularly suitable as an adhesive for injection-molded polyolefin resins and metal substrates. [Brief explanation of the drawings]

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

[0011] 1 polyolefin resin substrate, 2 adhesive composition, 3 metal substrate (aluminum plate) DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below. <Modified polyolefin (A)> The modified polyolefin (A) used in the present invention is not limited, but is preferably at least one of polyethylene, polypropylene, and propylene-α-olefin copolymers modified. Furthermore, the modified polyolefin (A) is more preferably a modified polypropylene or propylene-α-olefin copolymer, and even more preferably a modified propylene-α-olefin copolymer. From the perspective of improving compatibility, it is particularly preferable that the modified polyolefin (A) be modified with the same resin type as the olefin-α-olefin copolymer (B) used. This improves the compatibility between the modified polyolefin (A) and the olefin-α-olefin copolymer (B), resulting in excellent adhesive properties.

[0013] The propylene-α-olefin copolymer is a copolymer of propylene as a main component with an α-olefin. Examples of the α-olefin include ethylene, 1-butene, 1-heptene, 1-octene, and 4-methyl-1-pentene. Hmm One or more of these 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. When the molar ratio of propylene is 50% or more, excellent adhesiveness to polyolefin resin substrates, particularly polypropylene resin substrates, can be exhibited.

[0014] Specific examples of modifications of the modified polyolefin (A) used in the present invention include acid modification, chlorine modification, hydroxyl group modification, etc. Among these, acid modification is particularly preferred from the viewpoints of adhesion between the modified polyolefin (A) and the metal substrate and production efficiency.

[0015] The 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.

[0016] From the viewpoint of adhesion between the polyolefin resin substrate and the metal substrate, the acid value of the modified polyolefin (A) is preferably 2 mgKOH / g or more. More preferably, it is 3 mgKOH / g or more, even more preferably, 5 mgKOH / g or more, and particularly preferably, 7 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, and metal adhesion is improved in environments at 25°C and 90°C. The upper limit of the acid value is preferably 50 mgKOH / g or less. More preferably, it is 45 mgKOH / g or less, even more preferably, 40 mgKOH / g or less, and particularly preferably, 35 mgKOH / g or less. By adjusting the acid value to be equal to or less than the upper limit, the molecular weight is high and the cohesive force is strong, thereby improving adhesive strength. Furthermore, production efficiency is also improved.

[0017] The acid value of the modified polyolefin (A) can be adjusted by the amounts of the α,β-unsaturated carboxylic acid, its acid anhydride, and radical generator used.

[0018] The weight-average molecular weight (Mw) of the modified polyolefin (A) is preferably in the range of 70,000 or more and less than 200,000, more preferably 75,000 to 150,000, even more preferably 80,000 to 130,000, and most preferably 85,000 to 105,000. By setting it to be equal to or greater than the lower limit, good cohesive strength can be achieved, and excellent adhesive properties can be exhibited. On the other hand, by setting it to be equal to or less than the upper limit, excellent dissolution stability, flowability, and operability can be achieved.

[0019] The melting point (Tm) of the modified polyolefin (A) is preferably in the range of 50°C to 130°C, more preferably in the range of 60°C to 125°C. It is even more preferably in the range of 70°C to 120°C, and most preferably in the range of 85°C to 110°C. By setting it to above the lower limit, the resin does not melt even in a high-temperature environment, the cohesive force derived from the crystals is improved, and excellent adhesive properties and heat resistance can be exhibited. Furthermore, by setting it to below the upper limit, excellent dissolution stability and flowability are achieved, and operability during adhesion is improved.

[0020] The heat of fusion (ΔH) of the modified polyolefin (A) is preferably in the range of 5 J / g to 60 J / g, more preferably in the range of 10 J / g to 50 J / g, and even more preferably in the range of 20 J / g to 40 J / g. By making it equal to or greater than the lower limit, the cohesive force derived from crystals becomes good, and excellent adhesive properties can be exhibited. On the other hand, by making it equal to or less than the upper limit, excellent dissolution stability and flowability are achieved, and operability during adhesion is improved.

[0021] The method for producing the 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 in a polymer that will become the main chain, and an unsaturated carboxylic acid and an acid anhydride are graft polymerized using the radical species as a polymerization initiation point).

[0022] The radical generator is not particularly limited, but examples thereof include organic peroxides and azonitriles, and it is preferable to use organic peroxides. The organic peroxide is not particularly limited, but examples thereof include di-tert-butyl peroxyphthalate, tert-butyl hydroperoxide, dicumyl peroxide, benzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxypivalate, methyl ethyl ketone peroxide, di-tert-butyl peroxide, lauroyl peroxide, etc., and examples of the azonitrile include azobisisobutyronitrile and azobisisopropionitrile.

[0023] As the 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 "AUROLENE" series manufactured by Nippon Paper Industries Co., Ltd.

[0024] <Olefin-α-olefin copolymer (B)> The olefin-α-olefin copolymer (B) used in the present invention means a random copolymer containing an α-olefin as a comonomer, which is unmodified. The comonomer is not limited to, but examples thereof include, but are not limited to, ethylene, propylene, 1-butene, 1-heptene, 1-octene, and 4-methyl-1-pentene. Hmm One or more of these can be used. Of these, 1-butene is preferred. As the main component of the olefin-α-olefin copolymer (B), polyethylene, polypropylene, etc. can be used. Of these, polypropylene is preferred. The main component of the olefin-α-olefin copolymer (B) refers to a component that accounts for 50 mol % or more of the total copolymer components. The olefin-α-olefin copolymer (B) used in the present invention is particularly preferably a propylene-α-olefin copolymer.

[0025] The propylene-α-olefin copolymer is a copolymer of propylene as a main component with an α-olefin. Examples of the α-olefin include ethylene, 1-butene, 1-heptene, 1-octene, and 4-methyl-1-pentene. Hmm One or more of these can be used. 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. When the propylene molar ratio is 50% or more, excellent adhesion to polyolefin resin substrates, particularly polypropylene resin substrates, can be achieved.

[0026] The weight-average molecular weight (Mw) of the olefin-α-olefin copolymer (B) is 200,000 or more, preferably in the range of 200,000 to 1,300,000. It is more preferably in the range of 300,000 to 1,200,000, even more preferably in the range of 400,000 to 1,100,000, and most preferably in the range of 500,000 to 1,000,000. By ensuring that the Mw is equal to or greater than the lower limit, the cohesive strength is improved and excellent adhesive properties can be achieved. By ensuring that the Mw is equal to or less than the upper limit, the solubility in organic solvents is improved and the dissolution stability is improved.

[0027] The melting point (Tm) of the olefin-α-olefin copolymer (B) is in the range of 80°C to 100°C, preferably in the range of 80°C to 90°C. By setting it to be equal to or higher than the lower limit, the cohesive force derived from crystals becomes good, and excellent adhesive properties can be exhibited. On the other hand, by setting it to be equal to or lower than the upper limit, excellent dissolution stability and flowability are achieved, and operability during adhesion is improved.

[0028] The heat of fusion (ΔH) of the olefin-α-olefin copolymer (B) is preferably in the range of 20 J / g to 70 J / g, more preferably in the range of 25 J / g to 60 J / g, and even more preferably in the range of 30 J / g to 50 J / g. By making it equal to or greater than the lower limit, the cohesive force derived from crystals becomes good, and excellent adhesive properties can be exhibited. On the other hand, by making it equal to or less than the upper limit, excellent dissolution stability and flowability are achieved, and operability during adhesion is improved.

[0029] <Adhesive composition> The adhesive composition of the present invention contains the above-mentioned modified polyolefin (A) and olefin-α-olefin copolymer (B).

[0030] The adhesive composition of the present invention contains 15 to 85 parts by mass of olefin-α-olefin copolymer (B) per 100 parts by mass of modified polyolefin (A). The olefin-α-olefin copolymer (B) is preferably contained in an amount of 20 parts by mass or more, more preferably 25 parts by mass or more, and particularly preferably 30 parts by mass or more per 100 parts by mass of modified polyolefin (A). By ensuring that the amount is equal to or greater than the lower limit, the cohesive strength of the high molecular weight component is improved, thereby enabling excellent adhesive properties to be exhibited. Furthermore, the olefin-α-olefin copolymer (B) is preferably contained in an amount of 80 parts by mass or less, more preferably 75 parts by mass or less, and particularly preferably 70 parts by mass or less per 100 parts by mass of modified polyolefin (A). By ensuring that the amount is equal to or less than the upper limit, the effect of improving the adhesive strength at the olefin / metal interface by the modified polyolefin (A) is exhibited, enabling excellent adhesive properties to be exhibited even when the resin softens in a high-temperature environment. Furthermore, excellent dissolution stability is also achieved.

[0031] The weight-average molecular weights of the modified polyolefin (A) and the olefin-α-olefin copolymer (B) satisfy the relationship of weight-average molecular weight of (A)≦weight-average molecular weight of (B). Preferably, the weight-average molecular weight of (A)<weight-average molecular weight of (B). By satisfying this relationship, it is possible to achieve both the effect of improving metal adhesion due to the modifying component and the effect of improving adhesive strength due to the cohesive force of the high-molecular-weight component.

[0032] When the weight average molecular weight of the modified polyolefin (A) and the olefin-α-olefin copolymer (B) satisfies the relationship of (A) weight average molecular weight < (B) weight average molecular weight, the difference between the weight average molecular weights of (A) and (B) is preferably 10,000 or more, more preferably 100,000 or more, even more preferably 200,000 or more, and most preferably 300,000 or more, and is preferably 500,000 or less, more preferably 480,000 or less, and even more preferably 450,000 or less.

[0033] The sum of the weight average molecular weights of the modified polyolefin (A) and the olefin-α-olefin copolymer (B) is preferably 450,000 or more, more preferably 500,000 or more, and even more preferably 550,000 or more, and is preferably 700,000 or less, more preferably 650,000 or less, and even more preferably 620,000 or less.

[0034] In addition to the modified polyolefin (A) and the olefin-α-olefin copolymer (B), the adhesive composition of the present invention may contain various additives such as tackifiers, plasticizers, flame retardants, pigments, and antiblocking agents, as long as the performance of the present invention is not impaired.

[0035] The adhesive composition of the present invention is capable of forming an adhesive layer that exhibits high adhesive strength without blending a curing agent, and therefore, it is preferable that the adhesive composition of the present invention contains substantially no curing agent.

[0036] In the adhesive composition of the present invention, the content of the curing agent is preferably less than 1 part by mass per 100 parts by mass of the solid content of the adhesive composition. Less than 0.5 parts by mass is more preferred, less than 0.1 parts by mass is even more preferred, and it is most preferred that no curing agent is included. If the content of the curing agent is too high, not only is it less economical, but the self-condensation reaction between the curing agents may reduce the conformability to the substrate and the long-term storage stability may be poor.

[0037] Here, the curing agent refers to a known curing agent that reacts with the modified polyolefin resin to form a crosslinked structure, and examples thereof include isocyanate compounds, epoxy compounds, carbodiimide compounds, and oxazolin compounds.

[0038] The adhesive composition of the present invention may further contain an organic solvent (C) 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 modified polyolefin (A) and the olefin-α-olefin copolymer (B). Examples of the organic solvent 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 50-3 / 50-97 (mass ratio), more preferably 45-5 / 55-95, and even more preferably 40-10 / 60-90.

[0039] Aliphatic hydrocarbons include hexane, heptane, octane, and decane. Alicyclic hydrocarbons include cyclohexane, cyclohexene, methylcyclohexane, and ethylcyclohexane. Alcohol-based solvents include methanol, ethanol, isopropyl alcohol, butanol, pentanol, hexanol, and propanediol. 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. Ketone-based solvents include acetone, methyl isobutyl ketone, methyl ethyl ketone, pentanone, hexanone, cyclohexanone, isophorone, and acetophenone. Ester-based solvents include methyl acetate, ethyl acetate, butyl acetate, methyl propionate, and butyl formate.

[0040] Among the organic solvents mentioned 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 even more preferred. The organic solvent (C) is preferably contained in an amount of 80 to 2000 parts by mass per 100 parts by mass of the total amount of components (A) and (B). The amount is more preferably 90 to 1600 parts by mass, even more preferably 100 to 1200 parts by mass, and particularly preferably 110 to 900 parts by mass. Within this range, the solution state tends to be good.

[0041] <Laminate> The laminate of the present invention is obtained by laminating a polyolefin resin substrate, the above-described adhesive composition of the present invention, and a metal material in this order.

[0042] As a lamination method, conventionally known injection molding techniques can be used. For example, an adhesive composition can be 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 that, 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.

[0043] A conventionally known injection molding technique is, for example, a method of molding by injecting a polyolefin resin into a mold in which a metal substrate is set. More specifically, when using a screw-type hot melt molding applicator, 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.

[0044] The type of applicator for hot melt molding is not particularly limited, but examples include the ST2 manufactured by Nordson and the vertical extrusion molding machine IMC-18F9 manufactured by Imoto Manufacturing Co., Ltd.

[0045] <Polyolefin resin substrate> The polyolefin resin substrate may be appropriately selected from conventionally known polyolefin resins. For example, polyethylene, polypropylene, ethylene-propylene copolymer, etc. can be used. Among them, polypropylene is preferred. The thickness is not particularly limited, but is preferably 100 to 500 μm, more preferably 150 to 400 μm, and even more preferably 200 to 300 μm. Pigments and various additives may be blended into the polyolefin resin substrate as needed.

[0046] <Metal base material> 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 substrate can take any shape, such as metal foil, rolled steel plate, panel, pipe, can, or cap. Generally, aluminum is preferred from the viewpoint of workability. Although the thickness 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. [Example]

[0047] 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 mass".

[0048] (1) Measurement of weight-average molecular weight The weight-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.

[0049] (2) Measurement of melting point (Tm) and heat of fusion (ΔH) 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, Q-2000) by heating from -50°C to 200°C at a heating rate of 20°C / min, subsequently cooling from 200°C to -50°C at a heating rate of 20°C / min, and then heating again from -50°C to 200°C at a heating rate of 20°C / min, and measuring the top temperature and area of ​​the melting peak when melted.

[0050] (3) Measurement of acid value (unit: mgKOH / 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 modified polyolefin was dissolved in 100 g of xylene adjusted to 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 (mgKOH / g).

[0051] (4)Dissolution stability The adhesive compositions produced in the examples were dissolved in a methylcyclohexane / methyl ethyl ketone mixture (weight ratio: 9 / 1) to form a resin solution with a solid content of 20% by mass. The solution was stored at 25°C for 2 weeks (14 days), and the presence or absence of haze was visually inspected and evaluated according to the following criteria. ○: No haze occurs in the resin solution. ×: The resin solution is hazy.

[0052] (5) Adhesive strength <Creating laminates for test specimens> A five-layer laminate consisting of an aluminum plate (100 μm thick) / adhesive composition layer (20 μm thick) / polyolefin resin substrate (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 (weight ratio: 9 / 1) to obtain a 20% solids concentration, yielding an adhesive composition solution. The adhesive composition solution was then applied to an aluminum plate at room temperature using an applicator so that the adhesive composition would have a thickness of 20 μm after drying, and the solvent was evaporated in a hot air dryer at 120°C for 2 minutes. The aluminum plate was then fixed inside a mold for adhesion testing so that the adhesive composition layer on the aluminum plate came into contact with the molten polyolefin resin, and the polyolefin resin substrate to be molded measured 25 mm × 10 mm × 300 μm thick. Polypropylene (Prime Polymer Co., Ltd., Prime Polypro J107G, MFR: 30 g / 10 min) was used as the polyolefin. Next, using a vertical injection molding machine (THX5S manufactured by Nissei Plastics Co., Ltd.), the molten polyolefin resin was injected and molded. The molding conditions were a molding resin temperature of 240°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 a five-layer laminate of adhesive strength test pieces (aluminum plate / adhesive composition layer / polyolefin resin substrate / adhesive composition layer / aluminum plate) was obtained, in which the molded polyolefin resin substrate was sandwiched between aluminum plates coated with the adhesive composition.

[0053] <Adhesive 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 90°C, the peel speed was set to 300 mm / min, and the tensile strength when peeled using the T-peel method was taken as the adhesive strength, which was expressed in units of N / 25 mm. The adhesive strength at 25°C was used to evaluate the adhesion between the polyolefin resin substrate and the metal substrate, and the adhesive strength at 90°C was used to evaluate the heat resistance, and the results were evaluated according to the following criteria. ◎:30N / 25mm or more 〇: 15N / 25mm or more and less than 30N / 25mm ×: Less than 15N / 25mm

[0054] Modified polyolefin (A) manufacturing example <Production Example 1, Modified Polyolefin (A)PO-1> A 1-L autoclave was charged with 100 parts by weight of propylene-1-butene copolymer (Mitsui Chemicals, Inc., "Tafmer® XM7090"), 150 parts by weight of toluene, 3 parts by weight of maleic anhydride, and 1 part by weight of di-tert-butyl peroxide. The mixture was then heated to 140°C and stirred for an additional 3 hours. The resulting reaction mixture was then cooled and poured into a container containing a large amount of methyl ethyl ketone to precipitate the resin. The resin-containing solution was then centrifuged to separate and purify the acid-modified propylene-1-butene copolymer graft-polymerized with maleic anhydride, (poly)maleic anhydride, and low-molecular-weight substances. The mixture was then dried under reduced pressure at 70°C for 5 hours to obtain an acid-modified polyolefin, maleic anhydride-modified propylene-1-butene copolymer (PO-1, acid value 5 mg KOH / g, weight-average molecular weight 90,000, Tm 90°C, ΔH 30 J / g).

[0055] <Production Example 2, Modified Polyolefin (A)PO-2> A maleic anhydride-modified propylene-1-butene copolymer (PO-2, acid value 5 mg KOH / g, weight-average molecular weight 90,000, Tm 80°C, ΔH 30 J / g), an acid-modified polyolefin, was obtained in the same manner as in Production Example 1, except that the propylene-1-butene copolymer (Mitsui Chemicals, Inc., "Tafmer (registered trademark) XM7090") used in Production Example 1 was replaced with a propylene-1-butene copolymer (Mitsui Chemicals, Inc., "Tafmer (registered trademark) XM7080").

[0056] <Production Example 3, Modified Polyolefin (A)PO-3> A maleic anhydride-modified propylene-1-butene copolymer (PO-3, acid value 20 mg KOH / g, weight-average molecular weight 110,000, Tm 70°C, ΔH 25 J / g), an acid-modified polyolefin, was obtained by the same procedure as in Production Example 1, except that the propylene-1-butene copolymer (Mitsui Chemicals, Inc., "Tafmer (registered trademark) XM7090") used in Production Example 1 was replaced with a propylene-1-butene copolymer (Mitsui Chemicals, Inc., "Tafmer (registered trademark) XM7070"), 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 4, Modified Polyolefin (A)PO-4> A maleic anhydride-modified propylene-1-butene copolymer (PO-4, acid value 19 mg KOH / g, weight-average molecular weight 75,000, Tm 90°C, ΔH 25 J / g), an acid-modified polyolefin, was obtained in the same manner as in Production Example 1, except that the amount of maleic anhydride added was changed to 13 parts by mass and the amount of di-tert-butyl peroxide added was changed to 3 parts by mass.

[0058] Example 1 100 parts by mass of PO-1 was used as component (A), and 50 parts by mass of S-1, 450 parts by mass of methylcyclohexane, and 50 parts by mass of methyl ethyl ketone (solids concentration: 20% by mass) were mixed as component (B) to obtain the adhesive composition of Example 1. Details of the adhesive composition of Example 1 and the evaluation results are shown in Table 1.

[0059] <Examples 2 to 7 and Comparative Examples 1 to 4> The amounts of components (A) and (B) were changed as shown in Table 1, and adhesive compositions of Examples 2 to 7 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1. Details of these adhesive compositions and the evaluation results are shown in Table 1. The organic solvent (methylcyclohexane / methyl ethyl ketone = 90 / 10 (mass ratio)) was adjusted so that the solids concentration was 20 mass %.

[0060] [Table 1]

[0061] The olefin-α-olefin copolymers (B) used in Table 1 are as follows: S-1: Mitsui Chemicals "Tafmer (registered trademark) XM7080", propylene-1-butene copolymer, weight average molecular weight 520,000, melting point 80°C, ΔH 40J / g S-2: Mitsui Chemicals "Tafmer (registered trademark) XM7090", propylene-1-butene copolymer, weight average molecular weight 520,000, melting point 90°C, ΔH 45 J / g

[0062] Other olefin-α-olefin copolymers used in Table 1 are as follows: S-3: Mitsui Chemicals "Tafmer (registered trademark) XM7070", propylene-1-butene copolymer, weight average molecular weight 520,000, melting point 70°C, ΔH 35 J / g S-4: Clariant "Ricosene (registered trademark) PP1602", ethylene-propylene copolymer, weight average molecular weight 50,000, melting point 65°C, ΔH 15 J / g

[0063] As is clear from Table 1, Examples 1 to 7 exhibited good adhesive strengths at 25°C and 90°C, as well as good dissolution stability at 25°C. In contrast, Comparative Example 1 contained a small amount of olefin-α-olefin copolymer (B), resulting in weak cohesive strength, decreased adhesive strength at 90°C, and poor heat resistance. Comparative Example 2 contained a large amount of olefin-α-olefin copolymer (B), resulting in poor adhesive strength at the polypropylene (polyolefin resin substrate) / aluminum (metal substrate) interface. High adhesive strength was achieved at 25°C due to the high cohesive strength, but at 90°C, the resin softened, reducing the contribution of cohesive strength. This resulted in a decrease in adhesive strength at 90°C and poor heat resistance. Furthermore, dissolution stability deteriorated due to aggregation of the olefin-α-olefin copolymer (B). Comparative Example 3 contained a low melting point of the olefin-α-olefin copolymer (B), resulting in a decrease in adhesive strength at 90°C and poor heat resistance. In Comparative Example 4, the weight average molecular weight of the modified polyolefin (A) was higher than the weight average molecular weight of the olefin-α-olefin copolymer (B), and the weight average molecular weight and melting point of the olefin-α-olefin copolymer (B) were low, resulting in a decrease in adhesive strength at 90°C and poor heat resistance. [Industrial Applicability]

[0064] The adhesive composition of the present invention has good adhesion and heat resistance between polyolefin resin substrates and metal substrates. In addition, it exhibits good adhesive strength even under high-temperature, short-time processing conditions such as injection molding. Therefore, 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.

Claims

1. An adhesive composition comprising a modified polyolefin (A) and an olefin-α-olefin copolymer (B), and satisfying all of the following requirements (1) to (5): (1) The modified polyolefin (A) is an acid-modified polyolefin, and the olefin-α-olefin copolymer (B) is contained in an amount of 15 to 85 parts by mass per 100 parts by mass of the modified polyolefin (A). (2) The weight average molecular weight of the olefin-α-olefin copolymer (B) is 200,000 or more. (3) The melting point of the olefin-α-olefin copolymer (B) is 80° C. or higher and 100° C. or lower. (4) The weight average molecular weight of the modified polyolefin (A)≦the weight average molecular weight of the olefin-α-olefin copolymer (B). (5) The olefin-α-olefin copolymer (B) is a propylene-α-olefin copolymer (excluding the case where the α-olefin in the propylene-α-olefin copolymer is propylene or vinyl acetate).

2. 2. The adhesive composition according to claim 1, wherein the weight average molecular weight of the modified polyolefin (A) is 70,000 or more but less than 200,000.

3. The adhesive composition according to claim 1 or 2, further comprising an organic solvent (C).

4. 3. The adhesive composition according to claim 1, wherein the modified polyolefin (A) has an acid value of 2 to 50 mgKOH / g.

5. 3. The adhesive composition according to claim 1, which is used for bonding a polyolefin resin substrate to a metal substrate.

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

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