adhesive composition

Abstract

[Problem] An adhesive composition according to the present invention addresses the problem of providing an adhesive composition that exhibits excellent flexibility as an uncured coating film, excellent wet soldering heat resistance when used as an adhesive for flexible printed circuit boards, and excellent peel strength at high temperatures. [Solution] An adhesive composition comprising a polyisocyanate and a polyester having a glass transition temperature or a melting point that exceeds 80°C.

Description

[Technical Field]

[0001] The present invention relates to an adhesive composition, and more particularly to an adhesive composition that provides excellent flexibility of an uncured coating film and exhibits excellent humid solder heat resistance and peel strength at high temperatures as an adhesive for flexible printed wiring boards. [Background technology]

[0002] A flexible printed circuit board (FPC) is a board with an electrical circuit formed on a base material made by bonding a thin, soft insulating film such as polyimide to a conductive metal such as copper foil with an adhesive. Unlike rigid boards, FPCs are extremely thin and flexible, allowing them to be used in small gaps and bending moving parts of electronic devices, and are therefore used in many of the electronic devices around us, such as personal computers and smartphones. In recent years, more and more FPCs have been installed in automobiles, which means that adhesives are required to be able to adhere at high temperatures.

[0003] Polyesters are widely used as raw materials for resin compositions used in coatings, inks, adhesives, etc. and are generally composed of polycarboxylic acids and polyhydric alcohols. Because they offer flexibility and the ability to freely control molecular weight by selecting and combining polycarboxylic acids and polyhydric alcohols, they are widely used in a variety of applications, including coatings and adhesives.

[0004] Polyester has excellent adhesive properties (peel strength) with metals including copper, and has been used as an adhesive for FPCs when blended with a curing agent (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 9-125043 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0006] However, the polyester resin described in Patent Document 1 is composed solely of a polyester resin having a low glass transition temperature (Tg) of 80° C. or less, and therefore has insufficient peel strength at high temperatures.

[0007] The present invention was made in response to the problems of the prior art. That is, an object of the present invention is to provide an adhesive composition that has excellent flexibility in an uncured coating film (B-stage) and is excellent in humid solder heat resistance and peel strength at high temperatures as an adhesive for flexible printed wiring boards. [Means for solving the problem]

[0008] As a result of extensive investigations, the present inventors have found that the above problems can be solved by the following means, and have arrived at the present invention. That is, the present invention comprises the following configurations.

[0009] An adhesive composition comprising a polyester (A1) having a glass transition temperature or melting point of more than 80°C and a polyisocyanate (B).

[0010] Furthermore, it is desirable to contain a polyester (A2) having a glass transition temperature of 0° C. or lower and a melting point of 80° C. or lower, or which is amorphous.

[0011] The content of the polyester (A2) is desirably 10 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the polyester (A1).

[0012] The content of the polyisocyanate (B) is desirably 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the total of the polyester (A1) and the polyester (A2).

[0013] The adhesive composition can be suitably used for flexible printed wiring boards. [Effects of the Invention]

[0014] The adhesive composition of the present invention has excellent flexibility in the uncured coating film, and as an FPC adhesive it has excellent solder heat resistance in a humid environment and peel strength at high temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of the present invention will be described in detail below, however, the present invention is not limited to this embodiment and can be practiced in various modified forms within the scope of the above description.

[0016] <Polyester (A1)> The adhesive composition of the present invention contains a polyester (A1) having a glass transition temperature or melting point of greater than 80° C. By using a polyester (A1) having a glass transition temperature (Tg) or melting point (Tm) of greater than 80° C., it is possible to improve the humid solder heat resistance and the peel strength at high temperatures. The polyester (A1) has a chemical structure that can be obtained by polycondensation of a polycarboxylic acid component or a polycarboxylic acid ester component with a polyhydric alcohol component, and the polycarboxylic acid component or the polycarboxylic acid ester component and the polyhydric alcohol component each consist of one or more selected components.

[0017] The polycarboxylic acid component constituting the polyester (A1) is not limited, but the following polycarboxylic acids or their esters and polycarboxylic acid anhydrides can be used. Specific examples of polycarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, adipic acid, sebacic acid, dimer acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, fumaric acid, maleic acid, 5-sodiumsulfodimethylisophthalic acid, trimellitic acid, pyromellitic acid, and esters thereof. Examples of polycarboxylic acid anhydrides include phthalic anhydride, tetrahydrophthalic anhydride, succinic anhydride, trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, and hydrogenated naphthalenedicarboxylic acid. Aromatic polycarboxylic acid components such as naphthalenedicarboxylic acid and terephthalic acid are particularly preferred. The use of aromatic polycarboxylic acids increases Tg and improves peel strength at high temperatures.

[0018] The polyhydric alcohol constituting the polyester (A1) is not particularly limited, but examples thereof include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1-methyl-1,8-octanediol, 2-methyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-n-propyl-1,3-propanediol, and 2,2-di-n-propyl-1, Examples of glycol components that can be used include 3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 2,4-diethyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, polytetramethylene glycol, polypropylene glycol, and other polyalkylene ether glycols; glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, α-methylglucose, mannitol, sorbitol, and dimer diol. One or more of these can be used. Particularly preferred are polyhydric alcohols without long-chain alkyl groups, such as ethylene glycol, 1,2-propanediol, and 1,3-propanediol, and alicyclic polyhydric alcohols, such as 1,4-cyclohexanedimethanol and tricyclodecane dimethanol. The use of these polyhydric alcohols increases Tg and improves peel strength at high temperatures.

[0019] The polyester (A1) may also be copolymerized with a trivalent or higher polycarboxylic acid component and / or a trivalent or higher polyalcohol component. Examples of trivalent or higher polycarboxylic acid components include aromatic carboxylic acids such as trimellitic acid, pyromellitic acid, benzophenonetetracarboxylic acid, trimesic acid, trimellitic anhydride (TMA), and pyromellitic anhydride (PMDA), and aliphatic carboxylic acids such as 1,2,3,4-butanetetracarboxylic acid. These may be used alone or in combination of two or more. Examples of trivalent or higher polyalcohol components include glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, α-methylglucose, mannitol, and sorbitol. These may be used alone or in combination of two or more.

[0020] The polyester (A1) may be copolymerized with a lactone or lactam, such as ε-caprolactone or ε-caprolactam.

[0021] Examples of methods for the polymerization condensation reaction to produce the polyester (A1) include 1) a method in which a polycarboxylic acid and a polyhydric alcohol are heated in the presence of a known catalyst, followed by a dehydration esterification step and then a polyhydric alcohol removal / polycondensation reaction, 2) a method in which an alcohol ester of a polycarboxylic acid and a polyhydric alcohol are heated in the presence of a known catalyst, followed by a transesterification step and then a polyhydric alcohol removal / polycondensation reaction, and 3) a method in which depolymerization is performed. In methods 1) and 2), part or all of the acid component may be replaced with an acid anhydride.

[0022] When producing the polyester (A1), a conventionally known polymerization catalyst can be used, for example, titanium compounds such as tetra-n-butyl titanate, tetraisopropyl titanate, and titanium oxyacetylcetonate, antimony compounds such as antimony trioxide and tributoxyantimony, germanium compounds such as germanium oxide and tetra-n-butoxygermanium, and acetates of magnesium, iron, zinc, manganese, cobalt, and aluminum. These catalysts can be used alone or in combination of two or more.

[0023] Methods for increasing the acid value of the polyester (A1) include, for example, (1) adding a trivalent or higher polycarboxylic acid and / or a trivalent or higher polycarboxylic anhydride after the polycondensation reaction and reacting (acid addition), or (2) intentionally modifying the resin during the polycondensation reaction by applying heat, oxygen, water, or the like. The polycarboxylic acid anhydride used in the acid addition method is not particularly limited, and examples thereof include phthalic anhydride, tetrahydrophthalic anhydride, succinic anhydride, maleic anhydride, trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and ethylene glycol bisanhydrotrimellitate, and these can be used alone or in combination of two or more.

[0024] The acid value of the polyester (A1) is 200 eq / 10 6 g or less, and more preferably 100 eq / 10 6 g or less, more preferably 50eq / 10 6 g or less, particularly preferably 30 eq / 10 6 g or less, most preferably 20eq / 10 6 By setting the resin acid value within the above range, it is possible to expect effects such as a good pot life, improved adhesion to substrates, and improved crosslinkability. Furthermore, the lower the acid value, the more the moisture absorption can be suppressed, and the better the humid solder heat resistance.

[0025] The number average molecular weight of the polyester (A1) is preferably 5,000 or more and 100,000 or less, more preferably 10,000 or more, and even more preferably 50,000 or less. When the number average molecular weight is within the above range, the polyester (A1) is easy to handle when dissolved in a solvent, and has high cohesive strength after curing, thereby exhibiting excellent peel strength.

[0026] The Tg or Tm of the polyester can be increased to above 80° C. by, for example, introducing a rigid structure such as an aromatic compound or an alicyclic compound, or by increasing the concentration of ester bonds.

[0027] <Polyester (A2)> The adhesive composition of the present invention preferably further contains a polyester (A2) having a Tg of 0°C or lower and a melting point of 80°C or lower or being amorphous. By containing a polyester (A2) having a Tg of 0°C or lower and a melting point of 80°C or lower or being amorphous, flexibility can be imparted to the uncured coating film, and humid solder heat resistance can also be imparted. The Tg of the polyester (A2) is preferably -10°C or lower. Furthermore, being amorphous means that the material does not show a melting peak in the measurement of the melting point described below.

[0028] The content of the polyester (A2) is preferably 10 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the polyester (A1) having a Tg or Tm of more than 80°C. It is more preferably 25 parts by mass or more. Also, it is more preferably 70 parts by mass or less. When the content of the polyester (A2) is within the above range, the flexibility of the uncured coating film, peel strength at high temperatures, and humid solder heat resistance are excellent.

[0029] The acid value of the polyester (A2) is 200 eq / 10 6 g or less, and more preferably 100 eq / 10 6 g or less, more preferably 50eq / 10 6 g or less, particularly preferably 30 eq / 10 6 g or less, most preferably 20eq / 10 6 By setting the resin acid value within the above range, it is possible to expect the effects of improving pot life, substrate adhesion, and crosslinkability. Furthermore, the lower the acid value, the more the moisture absorption can be suppressed, and the more the humid solder heat resistance is improved.

[0030] The number average molecular weight of the polyester (A2) is preferably 5,000 or more and 100,000 or less. It is more preferably 10,000 or more, even more preferably 20,000 or more, and particularly preferably 25,000 or more. When the number average molecular weight is above this value, the polar group concentration is relatively reduced, thereby suppressing moisture absorption and improving humid solder heat resistance. Furthermore, the number average molecular weight is more preferably 50,000 or less. When the number average molecular weight is below this value, the polyester is easy to handle when dissolved in a solvent, retains cohesive strength even before curing, and exhibits flexibility in the uncured coating film.

[0031] The glass transition temperature of the polyester can be set to 0°C or lower and the melting point to 80°C or lower, or the polyester can be made amorphous, for example, by copolymerizing a monomer component having a long-chain alkyl group or a monomer component having an asymmetric structure to disrupt the crystallinity.

[0032] <Polyisocyanate (B)> The adhesive composition of the present invention contains a polyisocyanate (B). The polyisocyanate (B) used in the present invention is not particularly limited as long as it is an isocyanate compound that reacts with a polyester resin and cures.

[0033] Examples of the polyisocyanate (B) include aromatic or aliphatic diisocyanate compounds and trivalent or higher polyisocyanate compounds. These isocyanate compounds may be either low-molecular-weight compounds or high-molecular-weight compounds. Examples include aliphatic diisocyanates such as tetramethylene diisocyanate and hexamethylene diisocyanate; aromatic diisocyanates such as toluene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate; alicyclic diisocyanates such as hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, dimer acid diisocyanate, and isophorone diisocyanate; and trimers of these isocyanate compounds. Also included are compounds containing terminal isocyanate groups obtained by reacting an excess amount of the isocyanate compound with a low-molecular-weight active hydrogen compound such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, or triethanolamine. Further examples include compounds containing terminal isocyanate groups obtained by reacting an excess amount of the isocyanate compound with various polyester polyols, polyether polyols, polyamides, or other polymeric active hydrogen compounds. These isocyanate compounds can be used alone or in combination of two or more. Among these, a trimer of a hexamethylene diisocyanate compound is particularly preferred.

[0034] In the adhesive composition of the present invention, the content of polyisocyanate (B) is preferably 0.1 parts by mass or more and 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 1 part by mass or more, per 100 parts by mass of the total of polyester (A1) and polyester (A2). By setting the content of polyisocyanate (B) within the above range, excellent peel strength at high temperatures can be exhibited.

[0035] In addition, in the present invention, organic phosphorus compounds, inorganic flame retardants such as zinc oxide, zinc sulfate, aluminum hydroxide, and barium hydroxide, leveling agents, and colorants such as dyes and pigments can be appropriately blended within a range that does not impair the properties of the adhesive composition of the present invention. [Example]

[0036] The present invention will be described in more detail below with reference to examples. In these examples and comparative examples, "parts" simply refers to parts by mass.

[0037] (1) Measurement of polyester composition 400MHz 1 Using a H-nuclear magnetic resonance spectrometer (hereinafter sometimes abbreviated as NMR), the molar ratios of the polycarboxylic acid components and polyhydric alcohol components that make up the polyester were quantified. Deuterated chloroform was used as the solvent. When the acid value of the polyester was increased by acid post-addition, the molar ratio of each component was calculated by setting the total of the acid components other than the acid component used in the acid post-addition as 100 mol %.

[0038] (2) Measurement of glass transition temperature and melting point Measurement was performed using a differential scanning calorimeter (SII, DSC-200). 5 mg of polyester was placed in an aluminum container with a lid, sealed, and cooled to -50°C using liquid nitrogen. The temperature was then increased to 150°C at a rate of 20°C / min. The glass transition temperature (Tg, unit: °C) was determined by the temperature at the intersection of an extension of the baseline before the endothermic peak (below the glass transition temperature) and a tangent to the endothermic peak (the tangent showing the maximum slope from the rising part of the peak to the peak peak) in the endothermic curve obtained during the temperature increase. In addition, in the same endothermic curve, the temperature at the apex of the crystalline melting peak was taken as the melting point (Tm, unit: ° C.).

[0039] (3) Measurement of number average molecular weight The polyester sample was dissolved and / or diluted with tetrahydrofuran to a resin concentration of approximately 0.5 wt% and filtered through a 0.5 μm pore size polytetrafluoroethylene membrane filter to prepare the measurement sample. The molecular weight was measured by gel permeation chromatography (GPC) using tetrahydrofuran as the mobile phase and a differential refractometer as the detector. The flow rate was 1 mL / min and the column temperature was 30°C. The columns used were Showa Denko KF-802, 804L, and 806L. Monodisperse polystyrene was used as the molecular weight standard.

[0040] (4) Acid value measurement 0.2 g of polyester sample was dissolved in 40 ml of chloroform and titrated with 0.01 N potassium hydroxide ethanol solution to obtain 10% polyester. 6 Equivalents per g (eq / 10 6 g) was determined. Phenolphthalein was used as an indicator.

[0041] The following describes examples of producing adhesive compositions containing the polyester of the present invention, a polyester serving as a comparative example, and a polyisocyanate.

[0042] Production example of polyester (a1) A reactor equipped with a stirrer, condenser, and thermometer was charged with 359 parts of terephthalic acid, 58 parts of dimethyl 2,6-naphthalenedicarboxylate, 67 parts of ethylene glycol, 189 parts of propanediol, 5 parts of trimethylolpropane, and 0.03 mol% tetrabutyl orthotitanate as a catalyst relative to the total acid components. The temperature was raised from 160°C to 220°C over 4 hours, and an esterification reaction was carried out through a dehydration process. Next, the polycondensation reaction process was carried out by reducing the pressure in the system to 5 mmHg over 20 minutes and then raising the temperature to 250°C. The pressure was then reduced to 0.3 mmHg or less, and the polycondensation reaction was carried out for 60 minutes, after which the product was removed. NMR analysis of the resulting polyester (a1) revealed a molar ratio of terephthalic acid / 2,6-naphthalenedicarboxylic acid / ethylene glycol / propanediol / trimethylolpropane of 90 / 10 / 27 / 72 / 1. The glass transition temperature was 89° C. The results are shown in Table 1.

[0043] Production examples of polyesters (a2) to (a11) Polyesters (a2) to (a11) were synthesized by changing the types and blending ratios of raw materials in accordance with the production example for polyester (a1). For polyester (a2), ε-caprolactone was added after the polymerization reaction was completed, and the mixture was reacted at 200°C for 30 minutes to perform post-addition. For polyester (a3), trimellitic anhydride was added after the polymerization reaction was completed, and the mixture was reacted at 230°C for 30 minutes to perform post-addition. The compositional analysis values, melting point (Tm), and glass transition temperature (Tg) of each polyester are listed in Table 1. PTMG1000 is polytetramethylene ether glycol (average molecular weight 1000). In Table 1, cases where the melting point (Tm) was not observed are indicated by "-".

[0044] [Table 1]

[0045] Example 1 An adhesive composition was produced by blending 80 parts (solids) of polyester (a1) with a solids concentration of 50% dissolved in toluene, 20 parts (solids) of polyester (a2) with a solids concentration of 50% dissolved in toluene, and 2 parts of Sumidur N3300 (manufactured by Sumika Covestro Urethane Co., Ltd.) as polyisocyanate. The resulting adhesive composition was evaluated for peel strength, humid solder heat resistance, and flexibility of the uncured coating film. The results are shown in Table 2.

[0046] Examples 2 to 14, Comparative Examples 1 to 4 Adhesive compositions were prepared in accordance with Example 1, but the types and blending ratios of raw materials were changed as shown in Table 2, and various evaluations were carried out. The results are shown in Table 2.

[0047] Peel strength (adhesion) The adhesive compositions prepared in each of the above examples were applied to a 12.5 μm thick polyimide film (Apical®, manufactured by Kaneka Corporation) to a dry thickness of 25 μm, and then dried at 140°C for 3 minutes. The adhesive film (B-stage product) obtained in this manner was bonded to an 18 μm thick rolled copper foil (BHY series, manufactured by JX Metals Corporation). The bonding was performed by pressing the shiny side of the rolled copper foil against the adhesive layer at 160°C under a pressure of 2 MPa for 30 seconds to bond the foil. The foil was then heat-treated at 170°C for 3 hours to cure the film, yielding a sample for peel strength evaluation. Peel strength was measured by a 180° peel test at 125°C, with the film pulled at a tensile speed of 50 mm / min. This test indicates the adhesive strength at 125°C. <Evaluation criteria> 〇: 0.3N / mm or more △: 0.1N / mm or more and less than 0.3N / mm ×: 0.1N / mm or less

[0048] Humidified solder heat resistance A sample was prepared in the same manner as for the peel strength evaluation. This sample was cut into a 2.0 cm x 2.0 cm piece, and left to absorb moisture for two days in a temperature and humidity environment of 40°C and 80%. The sample was then floated in a molten solder bath at 260°C, and the time until swelling occurred was measured. <Evaluation criteria> ○: No swelling for 60 seconds or more △: Swelling occurs after 30 seconds or more but less than 60 seconds ×: Swelling occurs in less than 30 seconds

[0049] Flexibility of uncured coating The adhesive compositions prepared in each of the above examples were applied to a 12.5 μm thick polyimide film (Apical (registered trademark), manufactured by Kaneka Corporation) so that the thickness after drying would be 25 μm, and then dried for 3 minutes at 140° C. The adhesive film (B-stage product) thus obtained was bent 90° to check whether cracks occurred in the coating film and evaluated. <Evaluation criteria> ○: No cracks △: Bending marks present ×: Cracks present

[0050] [Table 2] [Industrial Applicability]

[0051] The adhesive composition of the present invention exhibits excellent flexibility of the uncured coating film, solder heat resistance in a humid environment, and peel strength at high temperatures, making it suitable as an adhesive composition for FPCs exposed to high temperatures, such as automotive FPCs.

Claims

1. An adhesive composition for flexible printed wiring boards, comprising a polyester (A1) having a glass transition temperature or melting point of more than 80°C and a polyisocyanate (B), and further comprising a polyester (A2) having a glass transition temperature of 0°C or lower and a melting point of 80°C or lower or being amorphous.

2. 2. The adhesive composition for flexible printed wiring boards according to claim 1, wherein the content of the polyester (A2) is 10 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the polyester (A1).

3. 3. The adhesive composition for flexible printed wiring boards according to claim 1, comprising 0.1 parts by mass or more and 10 parts by mass or less of the polyisocyanate (B) per 100 parts by mass of the total amount of the polyester (A1) and the polyester (A2).

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