Polystyrene with methyl carboxylate groups at both ends and its manufacturing method, polyester resin and its manufacturing method, adhesive composition and its manufacturing method, and laminate

Abstract

The present invention aims to provide an adhesive composition using a polyester resin that has higher solubility, lower dielectric constant and dielectric loss tangent compared to the prior art, as well as higher heat resistance, and excellent adhesion to copper foil, polyimide film, and LCP film; a laminate comprising an adhesive layer made of a coated and dried product of the adhesive composition; and a laminate comprising a film obtained by curing the adhesive composition. [Solution] An adhesive composition characterized by containing a polyester resin that contains polystyrene-derived structural units with methyl carboxylate groups at both ends and hydrogenated polybutadiene-derived structural units with hydroxyl groups at both ends, and has a 2% weight loss temperature of 360°C or higher; a laminate comprising an adhesive layer made of a coated and dried product of the adhesive composition; and a laminate comprising a film obtained by curing the adhesive composition.

Description

[Technical Field]

[0001] The present invention relates to polystyrene having methyl carboxylate groups at both ends and a method for producing the same. The present invention also relates to a polyester resin using the polystyrene as a raw material and a method for producing the same. Furthermore, the present invention relates to an adhesive composition containing the polyester resin and a method for producing the same. Furthermore, the present invention relates to a laminate comprising an adhesive layer made of a coated and dried product of the adhesive composition and a laminate comprising a film obtained by curing the adhesive composition. [Background technology]

[0002] With the miniaturization and weight reduction of electronic devices, the applications for bonding electronic components have diversified, and the demand for adhesives to create metal-plastic laminates has increased. Flexible printed circuit boards (hereinafter also called FPCs), which use adhesives, are thin and flexible because they use plastic films as a base material, allowing for space saving and weight reduction. Taking advantage of these characteristics, they are used as connecting cables to connect movable parts of electronic components, between boards, and between units in smartphones, displays, and even in automotive applications. Related products include, for example, flexible copper-clad laminates (hereinafter also called "FCCLs") made by laminating copper foil onto polyimide film, polyethylene naphthalate film, liquid crystal polymer (hereinafter also called "LCP") film, etc., FPCs with electronic circuits formed on FCCLs, FPCs with reinforced plates made by laminating FPCs with reinforcing plates, and multilayer boards made by layering and bonding FCCLs and FPCs.

[0003] Adhesives used to create FCCLs and FPCs require various properties in addition to adhesion, such as dielectric properties like low dielectric constant and low dielectric loss tangent, flexibility, and heat resistance. In particular, for FPCs involving high-speed signal transmission, dielectric properties are crucial for reducing electrical signal transmission loss in the high-frequency range. Conventionally, styrene-based elastomers have been widely used as adhesive materials with the desired dielectric properties. However, conventional styrene-based elastomers have low solubility and handling problems, so there has been a need for materials that can be dissolved at higher concentrations and lower viscosity, and have better handling properties.

[0004] For example, Patent Document 1 proposes an adhesive composition and adhesive sheet using the same, which is a modified polyphenylene ether resin, a styrene elastomer, and a silane coupling agent, that has a sufficiently low relative permittivity and dielectric loss tangent, as well as a high elongation rate even with a high modulus of elasticity. However, there was room for improvement, such as the need to reduce the concentration of the adhesive component to 20% when considering handling properties, and the fact that polyphenylene ether resin has a high melting point (softening point) and is hard at room temperature, so when the blending ratio is set to sufficiently satisfy the desired dielectric properties, the modulus of elasticity increases, but the elongation rate and bending resistance tend to decrease.

[0005] Furthermore, Patent Document 2 proposes an adhesive composition comprising a modified polyphenylene ether resin, a styrene-based elastomer, and an epoxy resin, which has sufficiently low dielectric constant and dielectric loss tangent, as well as the ability to suppress resin flow, and is used as an adhesive sheet and a layered indirect bonding sheet. However, there was room for improvement, such as the need for dissolving equipment such as a pressurized kneader to dissolve the solvent with a solvent usage of 90% by mass or less relative to the solid content, and the low fluidity of the resulting solvent varnish.

[0006] On the other hand, polyester is used in a wide range of applications, including films, PET bottles, fibers, toners, electrical components, adhesives, and sealants, due to its excellent heat resistance, chemical resistance, durability, and mechanical strength. Furthermore, because of its polymer structure, polyester is highly polar and is known to exhibit excellent adhesion to polar polymers such as polyester, polyvinyl chloride, polyimide, and epoxy resins, as well as to metallic materials such as copper and aluminum. Taking advantage of this property, its use as an adhesive for manufacturing FCCL and FPC is being considered.

[0007] For example, Patent Document 3 discloses an adhesive composition containing a polyester resin having a specific glass transition temperature and dielectric loss tangent, which includes structural units derived from polycarboxylic acids and polyhydric alcohols, as a polyester resin that has an even lower dielectric constant and dielectric loss tangent than conventional polyester resins, and is also excellent in initial adhesion after curing and long-term durability in humid and hot environments. Furthermore, Patent Document 4 discloses a polyester, film, and adhesive composition with excellent dielectric properties, such as excellent solvent solubility, heat resistance, and adhesion, and low relative permittivity and dielectric loss tangent, including an adhesive containing a polyester that exhibits desired dielectric properties by lowering the polarity of the polymer by lowering the ester group concentration. However, in all of the disclosed technologies, although the dielectric properties before curing are evaluated, the dielectric properties of the film after curing, which are problematic during mounting, have not been considered. In fact, there are no adhesives using polyester resins that satisfy the recent requirements for dielectric properties (relative permittivity after curing: 3.0 or less and dielectric loss tangent after curing: 0.0035 or less) while also having high heat resistance. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2022-026390 [Patent Document 2] WO2022-255078 publication [Patent Document 3] Japanese Patent Publication No. 2022-051543 [Patent Document 4] Japanese Patent Publication No. 2022-068240 [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to provide polystyrene with a higher rate of methyl carboxylate introduction to both ends compared to the prior art. The present invention also aims to provide an adhesive composition using a polyester resin that has higher solubility, lower dielectric constant and dielectric loss tangent, and higher heat resistance compared to the prior art, and also exhibits excellent adhesion to copper foil, polyimide film, and LCP film. Furthermore, the present invention aims to provide a laminate comprising an adhesive layer made of a coated and dried product of the adhesive composition, and a laminate comprising a film obtained by curing the adhesive composition. [Means for solving the problem]

[0010] However, in view of these circumstances, the inventors conducted extensive research and, as a result, discovered that an adhesive composition containing a polyester resin with specific structural units can solve the above problems, and thus completed the present invention.

[0011] In other words, the present invention is <1> Polystyrene having methyl carboxylate groups at both ends, characterized in that the introduction index of both terminal methyl carboxylate groups shown in (Formula 1) below is 160 or more. (Equation 1) Index of introduction of both ends of methyl carboxylate group = CM group (mol) / St (mol) × Mn CM group (mol) / St (mol): The amount of methyl carboxylate groups per mole of styrene, which are the constituent units of polystyrene with methyl carboxylate groups at both ends. Mn: Number average molecular weight of polystyrene with methyl carboxylate groups at both ends. <2> The chain transfer constant Cs during styrene polymerization at 60°C is 5.0 × 10⁻⁶. -5A method for producing polystyrene with methyl carboxylate groups at both ends, characterized by radical polymerization of a monomer containing styrene and / or a styrene derivative using an initiator that can introduce methyl carboxylate groups in a lower organic solvent. <3> It contains polystyrene-derived structural units of both terminal methyl carboxylate groups as described above, It contains structural units derived from hydrogenated polybutadiene with hydroxyl groups at both ends, A polyester resin characterized by having a 2% weight loss temperature of 360°C or higher. <4> It is characterized by a structural ratio of 10-60:90-40 (by mass) of polystyrene-derived structural units with methyl carboxylate groups at both ends to structural units with hydroxyl groups at both ends derived from hydrogenated polybutadiene. <3> The polyester resin described above, <5> Characterized by containing structural units derived from polyphenylene ether resin with hydroxyl groups at both ends. <3> The polyester resin described above, <6> <1> A method for producing a polyester resin, characterized by including a step of obtaining a polyester resin from raw materials containing polystyrene with methyl carboxylate groups at both ends and hydrogenated polybutadiene with hydroxyl groups at both ends, as described above. <7> <3> An adhesive composition characterized by containing the polyester resin described above and a (meth)acrylate having an isocyanate group, <8> <3> An adhesive composition characterized by containing a double-bonded polyester resin at both ends, which is a reaction product of a polyester resin described above and a (meth)acrylate having an isocyanate group. <9> <3> An adhesive composition characterized by containing the polyester resin described above and a compound having two or more isocyanate groups in one molecule (excluding compounds having a double bond in the same molecule), <10> Characterized by further containing organic peroxides. <7> or <8> The adhesive composition described above, <11> The adhesive composition according to <10>, further comprising a polyphenylene ether resin having double bonds at both ends. <12> The adhesive composition according to <9>, further comprising a polyphenylene ether resin having hydroxyl groups at both ends. <13> The adhesive composition according to any one of <7>, <8>, <9> and <12>, further comprising an organic solvent. <14> A laminate comprising an adhesive layer made of a coated and dried product of the adhesive composition according to any one of <7> to <9>. <15> A laminate comprising a film obtained by curing the adhesive composition according to any one of <7> to <9>. It is.

Advantages of the Invention

[0012] The adhesive composition containing a polyester resin using polystyrene having carboxylic acid methyl ester groups at both ends of the present invention is excellent not only in low dielectric constant and low dielectric tangent but also in heat resistance, and further forms a film excellent in adhesiveness and flexibility after curing. In particular, such an adhesive composition is an adhesive for producing a laminate composed of a metal foil and a plastic film, for example, for bonding electronic material members, and is effective as an adhesive for FCCL, coverlay, bonding sheet, etc. used in the production of FPC and the like.

Embodiments for Carrying out the Invention

[0013] <Polystyrene having carboxylic acid methyl ester groups at both ends> The polystyrene having carboxylic acid methyl ester groups at both ends of the present invention has an introduction index of carboxylic acid methyl ester groups at both ends shown by the following (Formula 1) of 160 to 290. (Formula 1) Introduction index of carboxylic acid methyl ester groups at both ends = CM group (mol) / St (mol) × Mn CM group (mol) / St (mol): The amount of methyl carboxylate groups per mole of styrene, which are the constituent units of polystyrene with methyl carboxylate groups at both ends. Mn: Number average molecular weight of polystyrene with methyl carboxylate groups at both ends.

[0014] In the above (Equation 1), the CM group (mol) / St (mol) ratio is measured using a nuclear magnetic resonance (NMR) spectrometer under the following measurement conditions, and calculated using Equation 2 from the peak area of ​​2.9 to 3.3 ppm for the 3 protons of the methyl carboxylate group and the peak area of ​​6.0 to 7.5 ppm for the 5 protons of the styrene benzene ring. (Equation 2) (Peak area for 2.9-3.3 ppm ÷ 3) / (Peak area for 6.0-7.5 ppm ÷ 5). [Measurement conditions] Device: Bruker AVANCEIIIHD Magnetic field strength: 400MHz Total number of times: 16 Solvent: Chloroform-d

[0015] A higher index increases the reactivity of the hydroxyl groups at both ends with the polyol containing hydrogenated polybutadiene in the production of the polyester resin included in the adhesive composition described later, thereby improving heat resistance. An index of 170 or higher further improves heat resistance, and an index of 180 or higher further improves heat resistance. Heat resistance can be evaluated by measuring the thermal decomposition temperature of the resin or by evaluating the solder heat resistance of the laminate.

[0016] In the above (Equation 1), Mn refers to the value obtained by measuring the tetrahydrofuran (hereinafter sometimes abbreviated as THF) soluble portion of polystyrene with methyl carboxylate groups at both terminal ends by gel permittation chromatography (hereinafter also called GPC) under the molecular weight measurement conditions described below. [Molecular weight measurement conditions] Equipment: HLC-8320 manufactured by Tosoh Corporation Column: TSKGELGMHxL×2+TSKGELGUARDCOLUMNHXL―H Measurement temperature: 40℃ Sample concentration: 1.0g / L THF solution Solvent: THF Solution injection volume: 100μL Detection device: Refractive index detector Molecular weight calibration curve: Created using standard polystyrene.

[0017] The weight-average molecular weight (hereinafter sometimes abbreviated as Mw) of the polystyrene with methyl carboxylate groups at both ends of the present invention is preferably 1,000 or more and 20,000 or less. Since the π electrons of the phenyl groups constituting the polystyrene contribute to adhesion with the copper foil, if Mw is 1,000 or more, the proportion of structural units derived from polystyrene with methyl carboxylate groups at both ends of the polyester resin increases, thus improving adhesion. Furthermore, if Mw is 20,000 or less, the properties of the polystyrene portion do not become too strong, the flexibility due to the structural units derived from hydrogenated polybutadiene of the hydroxyl groups at both ends is not impaired, and adhesion can be maintained. The Mw of the polystyrene with methyl carboxylate groups at both ends of the polystyrene is more preferably 1,500 or more and 10,000 or less. The weight-average molecular weight (Mw), like the number-average molecular weight (Mn), is a value measured under the molecular weight measurement conditions described above.

[0018] <Method for producing polystyrene with methyl carboxylate groups at both ends> The method for obtaining polystyrene with methyl carboxylate groups at both ends of the present invention is not limited, but as one embodiment, the present invention uses an initiator capable of introducing methyl carboxylate groups, and the chain transfer constant Cs during styrene polymerization at 60°C is 5.0 × 10⁻⁶. -5 A method of radical polymerization of monomers containing styrene and / or styrene derivatives in a lower organic solvent is employed.

[0019] An example of an initiator capable of introducing methyl carboxylate groups is dimethyl 2,2'-azobis(2-methylpropionate). When dimethyl 2,2'-azobis(2-methylpropionate) is used as an initiator, dimethyl tetramethylsuccinate is generated from a portion of it. Since dimethyl tetramethylsuccinate has a methyl ester group, it participates in transesterification reactions and inhibits the polymerization of polyester resins. Therefore, it is preferable to remove as much dimethyl tetramethylsuccinate as possible that is contained as an impurity in polystyrene with methyl carboxylate groups at both ends. The content of dimethyl tetramethylsuccinate contained as an impurity in polystyrene with methyl carboxylate groups at both ends is preferably 2,000 ppm or less, more preferably 1,000 ppm or less, and particularly preferably 500 ppm or less.

[0020] The chain transfer constant Cs during styrene polymerization at 60°C is 5.0 × 10⁻⁶. ―5 Examples of polymerization solvents include benzene, cyclohexane (hereinafter sometimes abbreviated as CH), toluene, and methylcyclohexane (hereinafter sometimes abbreviated as MCH). On the other hand, the chain transfer constant during styrene polymerization at 60°C is 5.0 × 10⁻⁶. ―5 Examples of larger polymerization solvents include ethylbenzene and xylene. In this invention, the chain transfer constant Cs refers to the value obtained by dividing the chain transfer constant of the organic solvent by the growth rate constant of radical polymerization.

[0021] In the present invention, a styrene derivative refers to a styrene derivative having only one vinyl group and no reactive groups other than the vinyl group. Examples of the styrene derivatives include α-methylstyrene, β-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, pn-butylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene, p-methoxystyrene, and p-phenylstyrene. The proportion of styrene and / or styrene derivatives is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 100% by mass of the raw material monomer component of polystyrene with methyl carboxylate groups at both ends. Furthermore, styrene is preferred from the viewpoint of versatility and handling.

[0022] As long as the effects of the present invention are not hindered, other monomers having only one vinyl group or allyl group, other than styrene and the styrene derivatives, can be used as raw material monomers for polystyrene with methyl carboxylate groups at both ends. In particular, when using monomers having reactive groups other than vinyl groups and allyl groups, such as carboxyl groups, hydroxyl groups, and amino groups, or ester bonds, it is necessary to note that these reactive groups or ester bonds will impart a branched structure to the polyester resin. The proportion of monomers having reactive groups or ester bonds used is usually preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably 1% by mass or less, of the raw material monomer components of polystyrene with methyl carboxylate groups at both ends. Examples of other monomers include acrylic polymerizable monomers such as methyl acrylate, ethyl acrylate, and n-propyl acrylate.

[0023] <Polyester resin> The polyester resin of the present invention is a polyester resin (hereinafter referred to as "(1) polyester resin") that contains structural units derived from polystyrene with methyl carboxylate groups at both ends, and structural units derived from hydrogenated polybutadiene with hydroxyl groups at both ends, and has a 2% weight loss temperature of 360°C or higher.

[0024] [2% weight loss temperature of polyester resins] The polyester resin in (1) above has a 2% weight loss temperature (hereinafter referred to as T d 2 (Sometimes abbreviated as ), but it is 360°C or higher. 370°C or higher is particularly preferred. By setting the temperature to the above 2% weight loss temperature, the heat resistance when made into a substrate can be improved.

[0025] The method for measuring the 2% weight loss temperature of the polyester resin described in (1) above can be determined using a differential thermal-thermogravimetric simultaneous measurement device as follows. Equipment: Rigaku Corporation Thermoplus EVO2TG / DTA8122 Sample quantity: 5 mg of resin Measurement method: The temperature at which 2% of the total weight of the sample decomposes when the temperature is increased from room temperature to 550°C at a rate of 10°C / min under a nitrogen atmosphere.

[0026] The ratio of polystyrene with methyl carboxylate groups at both ends and hydrogenated polybutadiene with hydroxyl groups at both ends that constitutes the polyester resin of (1) above is preferably 10-60:90-40 by mass ratio, taking into account the production volume and weight-average molecular weight of the polyester resin having hydroxyl groups at both ends described later. By keeping it within this range, a polyester resin with an excellent balance between improved film strength and adhesion due to structural units derived from polystyrene with methyl carboxylate groups at both ends and flexibility due to structural units derived from hydrogenated polybutadiene with hydroxyl groups at both ends is obtained. Preferably, the ratio is 15-55:85-45 by mass ratio, and more preferably 20-50:80-50.

[0027] [Polyester resin with hydroxyl groups at both ends] The polyester resin (1) used in the adhesive composition of the present invention hardens by a crosslinking reaction via terminal hydroxyl groups to form a film. Therefore, in addition to the design that takes into account the balance between adhesion and balance described above, it is preferable for the polyester resin (1) used in the present invention to include a polyester resin having hydroxyl groups at both ends in order to obtain a film that satisfies the desired effect. Although the polyester resin having hydroxyl groups at both ends can be sufficiently produced even in the above proportion, it can usually be increased by increasing the number of moles of hydrogenated polybutadiene with terminal hydroxyl groups relative to the number of moles of polystyrene with terminal methyl carboxylate groups.

[0028] The polyester resin may contain structural units of polyphenylene ether resin with hydroxyl groups at both ends, as described later. The inclusion of polyphenylene ether structural units in the polyester resin allows for control of tensile properties. From the viewpoint of balancing elongation at break and peel strength, the content of the polyphenylene ether structural units with hydroxyl groups at both ends relative to the total polyester resin is preferably 0.1 to 2% by weight.

[0029] The polyester resin preferably has an ester group concentration of 400 eq / g or less. A low ester group concentration reduces the polarity of the polymer, resulting in low dielectric properties. The ester group concentration is preferably 300 eq / g or less, and more preferably 200 eq / g or less.

[0030] [Method for calculating ester group concentration] The reciprocal of the weight-average molecular weight of the units generated from each acid component and each glycogen component is 2 × 10⁻¹⁰. 6 The ester group concentration was calculated using a factor of 1 / 2. For example, in the case of a polyester resin consisting of polystyrene (Mw 3,250) and GI-3000 (Mw 7,080) with methyl carboxylate ester groups at both ends, considering the methanol (molecular weight 32) that is eliminated, the weight-average molecular weight of the generated unit is Mw = (3,250 + 7,080 - 32 × 2) = 10,266, so the ester group concentration is 195 eq / 10 6 It is calculated as g. Here, the product unit consisting of glycol (Chemical Formula 1 below) and polystyrene with methyl carboxylate groups at both ends (Chemical Formula 2 below) refers to Chemical Formula 3 below.

[0031] [ka]

[0032] [ka]

[0033] [ka]

[0034] [Crystallization of polyester resins] The polyester resin of the present invention is preferably amorphous from the viewpoint of organic solvent solubility and solution stability. An amorphous resin is a resin that has a glass transition temperature but no melting point. The presence or absence of crystallinity can be confirmed by the presence or absence of an endothermic peak due to crystal melting using a differential scanning calorimeter, which is used to measure the glass transition temperature as described later.

[0035] [Glass transition temperature of polyester resins (hereinafter sometimes abbreviated as Tg)] The Tg of the polyester resin of the present invention is preferably -50 to 0°C, more preferably -40 to -15°C, and particularly preferably -35 to -25°C. Because the polyester resin of the present invention contains polybutadiene with hydroxyl groups at both ends, it retains its flexibility even after curing.

[0036] The method for measuring Tg is as follows: Tg is determined by measuring it using a differential scanning calorimeter. Equipment: DiscoveryDSC25 manufactured by TA Instruments Japan Co., Ltd. Sample quantity: 10 mg of resin Measurement method: Under a nitrogen atmosphere, the temperature was raised to 150°C (first heating), maintained at that temperature for 10 minutes, then cooled to -100°C at a rate of 10°C / min, maintained at that temperature for 10 minutes, and then heated again at a rate of 10°C / min (second heating). Glass transition temperature: In the DSC curve obtained during the second heating, the glass transition temperature was defined as the temperature midway between the temperature indicated by intersection 1 and intersection 2, where intersection 1 is the point where the line extending the baseline on the low-temperature side towards the high-temperature side intersects with the tangent line showing the maximum slope between the rising part of the peak and the peak apex, and intersection 2 is the point where the line extending the baseline on the high-temperature side towards the low-temperature side intersects with the tangent line showing the maximum slope between the rising part of the peak and the peak apex.

[0037] [Dielectric properties of polyester resins] (Relative permittivity (sometimes abbreviated as Dk below)) The dielectric constant of the polyester resin of the present invention at a temperature of 23°C and a relative humidity of 50% RH at a frequency of 10 GHz is preferably 2.8 or less, more preferably 2.6 or less, particularly preferably 2.5 or less, and even more preferably 2.4 or less. By achieving the above dielectric constant, the transmission speed when used as a substrate can be maintained and transmission loss can be suppressed. (Dielectric loss tangent (hereinafter sometimes abbreviated as Df)) The dielectric loss tangent of the polyester resin of the present invention at a temperature of 23°C and a relative humidity of 50%RH at a frequency of 10GHz is preferably 0.0035 or less, and more preferably 0.0030 or less. By achieving the above dielectric loss tangent, transmission loss when the material is made into a substrate can be suppressed.

[0038] Polyester resins have terminal hydroxyl groups that increase the dielectric loss tangent, but because the ester group concentration and terminal hydroxyl group concentration are sufficiently low, the dielectric loss tangent before curing is also kept low.

[0039] The relative permittivity and dielectric loss tangent can be determined by the cavity resonator perturbation method using a network analyzer (Keysight Technologies N5224B) and a cylindrical cavity resonator (Kanto Electronics Applied Development CP531). If the polyester resin is highly tacky and difficult to prepare as a standalone sample, the measurement can be performed with the resin inserted into a PTFE tube, and the dielectric properties of the polyester resin alone can be calculated by subtracting the PTFE tube's weight.

[0040] Thus, in the present invention, a polyester resin with a very low dielectric loss tangent can be obtained compared to conventional materials. Furthermore, since a polyester resin with a very low dielectric loss tangent can suppress transmission loss in the high-frequency range, it is extremely useful as a raw material for adhesives used in bonding electronic material components and the like.

[0041] [Weight-average molecular weight (Mw) of polyester resins] The Mw of the polyester resin of the present invention is preferably 10,000 to 400,000, more preferably 20,000 to 350,000, and particularly preferably 20,000 to 300,000. An Mw higher than 10,000 results in good adhesion and prevents problems such as the polyester resin in the adhesive layer flowing and seeping out during press processing when manufacturing flexible laminates such as FCCL and FPC. Furthermore, an Mw lower than 400,000 allows the solution viscosity during application to be maintained within an appropriate range, resulting in a uniform coating film.

[0042] <Method for manufacturing polyester resins> The method for obtaining the polyester resin of the present invention is not limited, but as one embodiment, a method is preferred that includes the step of obtaining the polyester resin from raw materials containing polystyrene with methyl carboxylate groups at both ends and hydrogenated polybutadiene with hydroxyl groups at both ends.

[0043] [Materials other than polystyrene with methyl carboxylate groups at both ends] [Hydrogenated polybutadiene with hydroxyl groups at both ends] Hydrogenated polybutadiene with hydroxyl groups at both ends is a hydrogenated form of polybutadiene with hydroxyl groups at both ends, and is a compound having a polymerization chain derived from butadiene and hydroxyl groups at both ends of that polymerization chain. The polymerization chain derived from butadiene can act as an elastomer, and by having such a polymerization chain, it is possible to impart adhesion and flexibility to polyester resins. Hydrogenated polybutadiene with hydroxyl groups at both ends preferably has an average of 1.8 to 2.5 hydroxyl groups in the molecule. Having 1.8 or more hydroxyl groups in the molecule allows for high molecular weight production without stopping the polymerization of the polyester resin, while having 2.5 or less suppresses gelation of the polyester resin due to crosslinking, making it easier to obtain the excellent effects of the present invention.

[0044] Hydrogenated polybutadiene with hydroxyl groups at both ends can be used as is from the market. Examples of commercially available hydrogenated polybutadiene with hydroxyl groups at both ends include NISSO-PB(registered trademark) GI-1000, GI-2000, GI-3000 (all trade names, manufactured by Nippon Soda Co., Ltd.) and KRASOL(registered trademark) HLBH-P2000, HLBH-P3000 (all trade names, manufactured by Crayvalley). These can be used individually or in combination of two or more, depending on the amount of hydroxyl groups in the molecule.

[0045] The manganese content of hydrogenated polybutadiene with hydroxyl groups at both ends is preferably 500 to 100,000, more preferably 700 to 50,000, and most preferably 900 to 10,000, from the viewpoint of balancing viscosity and adhesive strength.

[0046] Of the hydrogenated polybutadienes with hydroxyl groups at both ends, GI-3000 (Mn 5,660, Mw 7,080) is the most preferred, considering the number-average molecular weight, weight-average molecular weight, and the amount of hydroxyl groups in the molecule.

[0047] In the preparation of polyester resins, a polyol that can react with polystyrene having methyl carboxylate groups at both ends (hereinafter also referred to as "other polyols") may be used in combination with hydrogenated polybutadiene with hydroxyl groups at both ends.

[0048] From the viewpoint of flexibility, the ratio of hydrogenated polybutadiene with hydroxyl groups at both ends is preferably 70% by mass or more, and more preferably 80% by mass or more, based on the total amount of polyol (total of hydrogenated polybutadiene with hydroxyl groups at both ends and other polyols). The polyol may consist only of hydrogenated polybutadiene with hydroxyl groups at both ends. The content of other polyols is preferably 0 to 30% by mass, or more preferably 0 to 20% by mass, based on the total amount of polyol.

[0049] Other polyols include, for example, dimer ols, bisphenol skeleton-containing monomers, aliphatic polyhydric alcohols, alicyclic polyhydric alcohols, aromatic polyhydric alcohols, polyester resin polyols, polyether polyols, polyacrylate polyols, polycarbonate polyols, polysiloxane polyols, polyisoprene polyols, and polyolefin polyols. These other polyols may be used individually or in combination of two or more.

[0050] In the present invention, the compounds constituting the polyester resin preferably contain dimer ols as other polyols. Examples of dimer ols include dimer ols which are reduced forms of dimer acids mainly having 36 to 44 carbon atoms derived from oleic acid, linoleic acid, linolenic acid, erucic acid, etc., and hydrogenated versions thereof. Among these, hydrogenated versions are preferred from the viewpoint of suppressing gelation during the production of the polyester resin.

[0051] When dimer ols are included as other polyols, the content of dimer ols relative to the total polyol is preferably 0.1 to 20% by mass. Furthermore, the content of dimer ols relative to the total polyester resin is preferably 0.5 to 15% by weight. The presence of dimer ols tends to promote the reaction between polystyrene with methyl carboxylate groups at both ends and hydrogenated polybutadiene with hydroxyl groups at both ends, and if the amount is too high, the dielectric loss tangent tends to deteriorate.

[0052] In the preparation of polyester resins, condensed polycyclic aromatic compounds of dimer acids and polycarboxylic acids may be used in combination. Examples of dimer acids include dimer acids with 36 to 44 carbon atoms derived from oleic acid, linoleic acid, linolenic acid, erucic acid, etc., and their hydrogenated products. Among these, hydrogenated products are preferred from the viewpoint of suppressing gelation during the production of polyester resins. Examples of condensed polycyclic aromatic compounds of polycarboxylic acids include naphthalenedicarboxylic acid, dimethyl naphthalenedicarboxylic acid, and anthracenedicarboxylic acid. Among these, naphthalenedicarboxylic acids are preferred from the viewpoint of price and availability, and dimethyl naphthalenedicarboxylic acid is more preferred from the viewpoint of reactivity. These can be used individually or in combination of two or more.

[0053] When dimer acids and condensed polycyclic aromatic compounds are used in combination, their content relative to the total polyester resin is preferably 0.5 to 15% by weight. The presence of dimer acids and condensed polycyclic aromatic compounds tends to increase the resin strength, but too much tends to worsen the dielectric loss tangent.

[0054] <Process for obtaining polyester resin> Since polycondensation by transesterification between polymer terminal functional groups is generally unreactive, it is preferable to use an organic solvent that can act as a compatibilizer between polycarboxylic acids, such as polystyrene with methyl carboxylate groups at both ends, and polyols, such as hydrogenated polybutadiene with hydroxyl groups at both ends, in order to promote the reaction between the two. Furthermore, a catalyst that promotes the transesterification reaction can also be used in combination. Polycondensation can be carried out by distilling off the by-product methanol while keeping the organic solvent that can act as a compatibilizer in the system. Subsequently, volatile components including the organic solvent are distilled off under reduced pressure to obtain a polyester resin with a high molecular weight and hydroxyl groups at the ends.

[0055] As the organic solvent, it is preferable to use one or a mixture of two or more aromatic organic solvents selected from toluene, xylene, solvent naphtha, Solvesso®, etc. Xylene is particularly preferred from the viewpoint of solubility of polystyrene with methyl carboxylate groups at both ends and hydrogenated polybutadiene with hydroxyl groups at both ends, and the transesterification reaction temperature. The amount of organic solvent used should be such that it can be adjusted to a viscosity that can promote the reaction. Preferably, the amount of organic solvent used is 10 to 50 parts by mass per 100 parts by mass of solute. The compatibilization effect is sufficiently exhibited when the amount of organic solvent used is 10 parts by mass or more, and the transesterification reaction is promoted when it is 50 parts by mass or less.

[0056] As catalysts to promote transesterification reactions, for example, titanium compounds such as tetra-n-butyl titanate, tetraisopropyl titanate, and titanium oxyacetyl cetonate; 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, aluminum, etc., can be used. These catalysts can be used individually or in combination of two or more.

[0057] The typical transesterification reaction between polystyrene with methyl carboxylate groups at both ends and hydrogenated polybutadiene with hydroxyl groups at both ends and other raw material compounds is carried out at a temperature of 140-220°C for a reaction time of 2-8 hours. The typical polycondensation reaction is carried out at a temperature of 160-240°C for a reaction time of 2-10 hours.

[0058] <Adhesive composition> The adhesive compositions of the present invention will be described in order below. The embodiments of the adhesive compositions of the present invention can be broadly classified into the following two types. <1> Adhesive composition using a crosslinking system via double bonds with (meth)acrylate having isocyanate groups. <2> Adhesive composition utilizing a urethane bond crosslinking system using compounds having two or more isocyanate groups in one molecule (excluding compounds having a double bond in the same molecule).

[0059] <1> Adhesive composition using a crosslinking system via double bonds with (meth)acrylate having isocyanate groups. [(meth)acrylate having an isocyanate group] The present invention as described above <1> The adhesive composition may further contain, in addition to the polyester resin of (1) above, a (meth)acrylate having an isocyanate group.

[0060] Examples of (meth)acrylates having an isocyanate group include methacryloyl isocyanate, 3-isopropenyl-α,α-dimethylbenzyl isocyanate, and 2-isocyanate ethyl methacrylate.

[0061] Furthermore, the (meth)acrylate having the isocyanate group may be a commercially available product. For example, there is the Karenz (registered trademark, omitted hereafter in this paragraph) series (manufactured by Resonac Corporation), specifically Karenz MOI, Karenz AOI, Karenz MOI-EG, Karenz BEI, Karenz MOI-BP, Karenz MOI-BM, Karenz MOI-EM, etc. In the present invention, Karenz AOI or Karenz MOI is preferred from the viewpoint of reactivity and low dielectric properties.

[0062] The amount of (meth)acrylate having an isocyanate group added is usually 0.1 to 10 parts by mass per 100 parts by mass of the polyester resin of (1), and 0.3 to 6 parts by mass is preferred from the viewpoint of dielectric properties and crosslinkability.

[0063] Furthermore, the present invention <1> The adhesive composition may also include a terminal double-bond polyester resin, which is a reaction product of the polyester resin of (1) and a (meth)acrylate having an isocyanate group. The terminal double-bond polyester resin can be obtained as a solution, for example, by reacting the polyester resin of (1) and a (meth)acrylate having an isocyanate group in the presence of an organic solvent at 100 to 180°C. In this case, a catalyst such as a titanium compound may be used to promote the reaction between the polyester resin and the (meth)acrylate having an isocyanate group, and a polymerization inhibitor such as 2,6-di-tert-butyl-p-cresol (hereinafter also referred to as BHT) may be used to suppress the reaction of the double bond.

[0064] The introduction of double bonds to the ends of polyester resins can be confirmed by measuring the hydroxyl value before and after the reaction.

[0065] [Organic peroxide] Furthermore, the present invention <1> The adhesive composition may further contain an organic peroxide if it contains the (meth)acrylate having an isocyanate group or the terminal double bond polyester resin. Examples of organic peroxides include di-t-butyl peroxide, 2,5-dimethyl-2,5-di(t-butyl peroxide)hexane, 2,5-dimethyl-2,5-di(t-butyl peroxide)hexyne-3, and α,α'-di(t-butyl peroxy)diisopropylbenzene. One or more organic peroxides can be used in combination. The content of the organic peroxide is usually 0.1 to 10 parts by mass, preferably 1 to 5 parts by mass, per 100 parts by mass of the total of the polyester resin of (1), the (meth)acrylate having an isocyanate group, the terminal double bond polyester resin, and the double-bonded polyphenylene ether resin described later.

[0066] The present invention as described above <1> The adhesive composition may contain a (meth)acrylate having an isocyanate group, or a terminal double bond polyester resin, and may further contain a co-crosslinking component that can be co-crosslinked with the terminal double bond polyester resin. By co-crosslinking, durability (tensile strength) and heat resistance can be improved compared to cases where co-crosslinking is not performed, so an adhesive layer with a good balance of adhesion, durability and heat resistance can be obtained. Examples of co-crosslinking components include triallyl isocyanurate, monoalkyldiallyl isocyanurate, phosphorus substituent-containing diallyl isocyanurate, and modified polyphenylene ether resins having double bonds at both ends. Among these, modified polyphenylene ether resins with double bonds at both ends are preferred.

[0067] [Polyphenylene ether resin with double bonds at both ends] The double-bonded polyphenylene ether resin has at least one ethylenically unsaturated bonding group, such as a (meth)acryloyl group or a vinylbenzyl group, at both ends of the polyphenylene ether resin.

[0068] Specific examples of polyphenylene ether resins with double bonds at both ends include OPE-2St (a modified polyphenylene ether resin having vinyl benzyl groups at both ends), OPE-2EA (a modified polyphenylene ether resin having acryloyl groups at both ends, both manufactured by Mitsubishi Gas Chemical Company), and NORYL® SA9000 (a modified polyphenylene ether resin having methacryloyl groups at both ends, manufactured by SABIC Corporation).

[0069] <2> Adhesive composition utilizing a urethane bond crosslinking system using compounds having two or more isocyanate groups in one molecule (excluding compounds having a double bond in the same molecule). [Compounds having two or more isocyanate groups in one molecule] The present invention as described above <2> The adhesive composition may further contain, in addition to the polyester resin of (1) above, a compound having two or more isocyanate groups in one molecule (excluding compounds having a double bond in the same molecule).

[0070] Examples of the aforementioned compounds 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, or trimers of these isocyanate compounds. In the present invention, trimers of hexamethylene diisocyanate and isophorone diisocyanate are preferred from the viewpoint of reactivity and low dielectric properties. It is also possible to use a combination of trimers of hexamethylene diisocyanate and isophorone diisocyanate.

[0071] Furthermore, commercially available compounds can also be used. Specific examples include TORONATE (registered trademark, hereinafter omitted, manufactured by VENCOREX) IDT70B and HDT, and Desmodur (registered trademark, hereinafter omitted, manufactured by Sumika Covestro Urethane) N3300.

[0072] The amount of added compound having two or more isocyanate groups per molecule (NCOG) relative to the mass of the polyester resin (OHG) and the mass of the polyphenylene ether resin with hydroxyl groups at both ends of the co-crosslinking component described later (SAG) is preferably within the range of Formula 3, derived from the hydroxyl group equivalent of the polyester resin (OHE), the polyphenylene ether resin with hydroxyl groups at both ends (SAOHE), and the isocyanate equivalent of the compound having two or more isocyanate groups per molecule (NCOE), from the viewpoint of dielectric properties, crosslinkability, and the time-dependent stability, also known as the pot life, of the adhesive composition.

[0073] (Formula 3) 0.8<(NCOG / NCOE)÷(OHG / OHE+SAG / SAOHE)<1.2

[0074] The present invention as described above <2> The adhesive composition, if it contains the aforementioned compound, may further contain a co-crosslinking component that can be co-crosslinked with a hydroxyl-terminated polyester resin. By co-crosslinking, durability (tensile strength) and heat resistance can be improved compared to when co-crosslinking is not performed, so an adhesive layer with a good balance of adhesion, durability, and heat resistance can be obtained. Examples of co-crosslinking components include 1,3,5-benzenetriol, 1,4-benzenediol, and hydroxyl-modified polyphenylene ether resins. Among these, polyphenylene ether resins with hydroxyl-terminated polyphenylene ethers are preferred.

[0075] [Polyphenylene ether resin with hydroxyl groups at both ends] Specific examples of the aforementioned polyphenylene ether resin with hydroxyl groups at both ends include NORYL® SA90 (a modified polyphenylene ether resin having hydroxyl groups at both ends, manufactured by SABIC Corporation).

[0076] [organic solvent] The present invention as described above <1> , <2> The adhesive composition may further contain an organic solvent in which the polyester resin is soluble. By including the organic solvent, the viscosity of the adhesive composition when applied to the substrate can be adjusted to an appropriate range, making it easier to handle when forming the coating film.

[0077] As the aforementioned organic solvent, for example, aromatic organic solvents such as xylene used in the production of polyester resins are preferred, but alicyclic hydrocarbon organic solvents such as methylcyclohexane and ethylcyclohexane; ketone organic solvents such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcoholic organic solvents such as methyl alcohol, ethyl alcohol, isopropyl alcohol, and isobutyl alcohol; ester organic solvents such as ethyl acetate and n-butyl acetate; acetate organic solvents such as cellosolve acetate and methoxyacetate; or mixtures of two or more of these organic solvents can also be used. The amount of organic solvent used is not particularly limited and should be an amount that can be adjusted to achieve the optimal viscosity when coating the adhesive composition of the present invention. Preferably, the amount of organic solvent used is 50 to 160 parts by mass per 100 parts by mass of solute.

[0078] The present invention as described above <1> , <2> The adhesive composition can be adjusted to a viscosity that is easy to handle by dissolving it in the amount of organic solvent described above. In this invention, a viscosity that is easy to handle is 12 Pa·s or less, more preferably 6 Pa·s or less. It is also 100 mPa·s or more, and more preferably 400 mPa·s or more.

[0079] The present invention as described above <1> , <2> The Mw of the double-bonded polyphenylene ether resin and the hydroxyl-grouped polyphenylene ether resin (collectively referred to as modified polyphenylene ether resin) that can be included in the adhesive composition is preferably 1,000 to 4,000, from the viewpoint of compatibility with polyester resins and step-following ability when heat-curing (pressing) the substrate and the wiring pattern side of a wired resin substrate, which has a wiring pattern, via the adhesive layer.

[0080] The present invention as described above <1> , <2> The content of modified polyphenylene ether resin in the adhesive composition is 3 to 60 parts by mass, preferably 4 to 50 parts by mass, based on 100 parts by mass of the total of the polyester resin and modified polyphenylene ether resin of the present invention. By limiting the content of modified polyphenylene ether resin to 60 parts by mass or less, good flexural resistance can be achieved. Furthermore, by limiting the content of modified polyphenylene ether resin to 3 parts by mass or more, heat resistance can be further improved. Polyphenylene ether resin may be used alone or in combination of two or more types.

[0081] The present invention as described above <1> , <2> In addition to the components listed above, the adhesive composition may also contain, depending on the desired effect and purpose, conjugated diene polymers such as butadiene polymers, styrene elastomers such as ethylene-ethylenebutylene-styrene block copolymers and styrene-ethylenepropylene-styrene block copolymers, and modified styrene elastomers.

[0082] Furthermore, the present invention <1> , <2> The adhesive composition may contain other components besides those listed above for the purpose of further improving its functionality. Examples of other components include inorganic fillers, coupling agents such as silane coupling agents, UV inhibitors, antioxidants, plasticizers, fluxes, flame retardants, colorants, dispersants, emulsifiers, de-elasticizing agents, diluents, defoaming agents, ion trapping agents, leveling agents, catalysts, and the like. The content of other components is preferably 70% by mass or less of the total amount of the adhesive composition of the present invention, more preferably 0.05 to 60% by mass, particularly preferably 0.1 to 50% by mass, and even more preferably 0.2 to 40% by mass. As inorganic fillers, LCP fillers are preferred, such as XYDAR(registered trademark) LF-31P and LF-31FP manufactured by ENEOS Corporation.

[0083] An adhesive layer is a layer consisting of a coated and dried adhesive composition formed on a base film or metal foil, in which at least the organic solvent has almost evaporated and the layer has lost its fluidity (generally called the "B stage" in this technical field). In this invention, a layer that has been partially cured as necessary during the manufacturing process (cured in a later process) is also referred to as an adhesive layer. Examples of laminates comprising an adhesive layer include coverlay films, resin-coated copper foil, and bonding sheets. A coverlay film is a laminate in which it is difficult to separate the base film from the adhesive layer. A resin-coated copper foil is a laminate in which it is difficult to separate the copper foil from the adhesive layer. On the other hand, a bonding sheet is a laminate in which an easily peelable release film is used as the base film, and the release film is peeled off before bonding. A bonding sheet may also have an adhesive layer between two release films. When the laminate comprising an adhesive layer is a coverlay film or resin-coated copper foil, a release film used for bonding sheets may be laminated on the surface of the adhesive layer as needed for storage, etc.

[0084] Examples of base films used for coverlay films include polyimide films, polyether ether ketone films, polyphenylene sulfide films, aramid films, polyethylene naphthalate films, liquid crystal polymer films, polyethylene terephthalate films, polyethylene films, polypropylene films, polymethylpentene films, and fluororesin films. Among these, polyimide films, polyethylene naphthalate films, and liquid crystal polymer films are preferred from the viewpoint of adhesion and electrical properties, with polyimide films and liquid crystal polymer films being even more preferred.

[0085] Such base films are commercially available, and examples of polyimide films include Kapton (registered trademark, manufactured by Toray DuPont Co., Ltd.), Xenomax (registered trademark, manufactured by Toyobo Co., Ltd.), Upirex S (registered trademark, manufactured by Ube Industries, Ltd.), and Apical (registered trademark, manufactured by Kaneka Corporation). Examples of polyethylene naphthalate films include Theonex (registered trademark, manufactured by Teijin DuPont Films Ltd.). Examples of liquid crystal polymer films include Copolymen (registered trademark, Ningbo JUJIA New Materials Technology Co., Ltd.), Vexter (registered trademark, manufactured by Kuraray Co., Ltd.), Viac (registered trademark, manufactured by Ise Murata Manufacturing Co., Ltd.), and Pericure LCP (Chiyoda Integre Co., Ltd.). The base film can also be made by forming the relevant resin into a film of the desired thickness. The copper foil used in the resin-coated copper foil is not particularly limited, but electrolytic copper foil, rolled copper foil, etc., are preferred.

[0086] Examples of base films (release films) used in bonding sheets include polyethylene terephthalate film, polyethylene film, polypropylene film, silicone release-treated paper, polyolefin resin coated paper, polymethylpentene film, and fluororesin film. While there are no particular limitations as long as the film is peelable, release-treated polyethylene terephthalate film is preferred in terms of availability, cost, and processability during coating and lamination.

[0087] Such release films are commercially available, and you can use Lumirror (registered trademark, manufactured by Toray Film Processing Co., Ltd.), Toyobo Ester (registered trademark) Film (manufactured by Toyobo Co., Ltd.), Aflex (registered trademark, manufactured by AGC Inc.), Opulan (registered trademark, manufactured by Mitsui Chemicals Tohcello Co., Ltd.), etc.

[0088] One method for producing a laminate having an adhesive layer is to apply the adhesive composition to the surface of a base film or copper foil, and then dry it to produce a laminate having an adhesive layer.

[0089] The reaction to introduce terminal double bonds may be carried out, for example, during the drying of the adhesive layer. The drying conditions are designed appropriately according to the type and amount of organic solvent used in the coating solution, the thickness of the coating solution application, and differences in drying equipment, and are not particularly limited. Drying is carried out, for example, at a temperature of 40 to 150°C for 30 minutes to 3 hours under atmospheric pressure. A drying temperature of 40°C or higher makes it easier to prevent deterioration of electrical properties due to residual organic solvent, and a drying temperature of 150°C or lower makes it easier to obtain the adhesive layer. Specifically, the laminate coated with the adhesive composition is passed through a furnace where hot air drying, far-infrared heating, and high-frequency induction heating are performed.

[0090] <Laminate comprising a film obtained by curing an adhesive composition> The laminate comprising the film includes a film obtained by curing an adhesive composition or adhesive layer, and a base film or copper foil in contact with at least one surface of the film.

[0091] The film in this invention can be obtained by curing an adhesive composition or adhesive layer. Here, curing refers to crosslinking via terminal hydroxyl groups in the adhesive or adhesive layer, crosslinking by polymerization of terminal double bonds, or crosslinking via both terminal hydroxyl groups and terminal double bonds. The film exhibits the effects of low dielectric properties, excellent adhesion, and excellent heat resistance.

[0092] [Glass transition temperature (Tg)] The film's Tg is preferably -50 to 0°C, more preferably -40 to -10°C, and particularly preferably -30 to -20°C. The polyester resin used in this invention contains polybutadiene with hydroxyl groups at both ends, and therefore retains its flexibility after curing.

[0093] [Dielectric properties] The dielectric properties of a film depend on the magnitude of the dipole moment in the adhesive components that make up the film, and it is known that the presence of polar groups with a large dipole moment, such as hydroxyl groups, enhances the dielectric properties. In the case of a crosslinking system between carboxyl groups and epoxy groups in conventional adhesive compositions (carboxyl group-containing polyester resin + epoxy crosslinking agent), the carboxyl groups, which have little adverse effect on the dielectric loss tangent, react with the epoxy groups to generate hydroxyl groups before and after curing, so the dielectric loss tangent generally increases after curing. On the other hand, in the adhesive composition of the present invention, since the terminal hydroxyl groups of the polyester resin are primary hydroxyl groups, it can be easily cured with a compound having two or more isocyanate groups in one molecule, and the amount of hydroxyl groups remaining in the film can be reduced as much as possible. Therefore, the low dielectric properties of the film after curing can be made equal to or better than those of the film before curing. As a result, the film in the present invention has low dielectric properties and low dielectric loss tangent.

[0094] In particular, the film of the present invention exhibits excellent electrical properties at high frequencies. Specifically, in a preferred embodiment, the relative permittivity (ε) of the film of the present invention in the frequency range of 1 to 80 GHz is 3 or less, when the film can be crosslinked by a reaction between a polyester resin having hydroxyl groups at both ends and a compound having two or more isocyanate groups in one molecule, or when a (meth)acrylate having isocyanate groups can be crosslinked by introducing terminal double bonds via the terminal hydroxyl groups of the polyester resin, or simultaneously with the introduction of terminal double bonds, using a radical polymerization initiator such as an organic peroxide. Furthermore, in a more preferred embodiment of the film of the present invention, the dielectric loss tangent (tanδ) in the frequency range of 1 to 80 GHz is 0.0035 or less, in an even more preferred embodiment it is 0.0030 or less, and in a particularly preferred embodiment it is 0.0025 or less. Because the relative permittivity (ε) and dielectric loss tangent (tanδ) of the film of the adhesive composition of the present invention in the frequency range of 1 to 80 GHz are within the above ranges, electrical signal loss in the high frequency range of 3 GHz or higher can be reduced.

[0095] [Adhesion] The adhesive composition of the present invention has sufficient adhesion to both the roughened and glossy surfaces of the copper foil forming the wiring of the FPC, so the film of the present invention can be bonded to a copper foil surface with low roughness. Therefore, the film of the present invention is less affected by roughness, and thus transmission loss (transmission loss due to the skin effect) can be reduced. Furthermore, the film of the present invention has sufficient adhesion to polyimide film and LCP film used as substrate materials for FPCs.

[0096] Adhesion can be evaluated by measuring the 180° peel strength (N / cm) using the method described later. A higher peel strength value indicates better adhesion to the substrate. The peel strength can be evaluated by curing a laminate with adhesive layers on both sides of the substrate under a pressure of 0.04 MPa (curing at 165°C for 1 hour, then at 175°C for 1 hour), cutting it into 1 cm wide strips, fixing the strips to a plastic plate using double-sided tape, and performing a 180° peel test (tensile speed 20 mm / min) using a Tensilon test machine (RTC-1150A, A&D Corporation) in an environment of 25°C. Specifically, in a preferred embodiment, the adhesive composition can be crosslinked by a reaction between a polyester resin having hydroxyl groups at its terminals and a compound having two or more isocyanate groups in one molecule, or a (meth)acrylate having isocyanate groups can be crosslinked by introducing terminal double bonds via the terminal hydroxyl groups of the polyester resin, or simultaneously with the introduction of terminal double bonds, using a radical polymerization initiator such as an organic peroxide. In this composition, the 180° peel strength against the roughened copper foil surface and the 180° peel strength between the roughened copper surface and the polyimide film is 4 N / cm or more, in a more preferred embodiment it is 6 N / cm or more, and in a particularly preferred embodiment it is 8 N / cm or more.

[0097] The film in this invention can be cured by a crosslinking reaction of an adhesive composition or adhesive layer using two main crosslinking systems. <1> The adhesive composition is cured by introducing terminal double bonds into a polyester resin by reacting a (meth)acrylate having an isocyanate group with the terminal hydroxyl groups of the polyester resin, or by crosslinking with a radical polymerization initiator such as an organic peroxide simultaneously with the introduction of terminal double bonds. <2> The adhesive composition is cured by reacting a terminal hydroxyl group polyester resin with a compound having two or more isocyanate groups in one molecule (excluding compounds having a double bond in the same molecule).

[0098] Furthermore, the film in this invention is the above <1> The manner and the above <2> Adhesive compositions of the following forms can be used in combination.

[0099] The aforementioned <1> , <2> The curing of the adhesive composition using the crosslinking system can be performed by coating the adhesive composition onto a substrate and then raising the temperature to 40-200°C.

[0100] In a laminate comprising a film, the film thickness is preferably 5 to 100 μm, more preferably 10 to 70 μm, and even more preferably 10 to 50 μm. The base film and film thickness are selected according to the application, but the base film tends to become thinner in order to improve electrical properties.

[0101] <Flexible copper-clad laminate> The flexible copper-clad laminate has at least one laminated structure in which a base film and copper foil are bonded together via the film. Since the film has excellent adhesion to the copper foil, the flexible copper-clad laminate of the present invention has excellent shape stability.

[0102] One method for manufacturing flexible copper-clad laminates involves, for example, making surface contact between a copper foil or base film and the adhesive layer of a laminate containing an adhesive layer, performing room-temperature lamination or heat lamination at 20°C to 150°C, and then curing the adhesive layer by a curing treatment. The curing treatment conditions can be, for example, 100°C to 200°C, 30 minutes to 6 hours, and 0.01 to 50 MPa.

[0103] <Application> The adhesive composition of the present invention exhibits excellent low dielectric constant and low dielectric loss tangent, particularly low dielectric loss tangent. The film obtained by curing the adhesive composition also exhibits excellent low dielectric constant and low dielectric loss tangent, as well as excellent flexibility and heat resistance, and low elastic modulus, making it effective for bonding substrates made of various materials such as resins and metals. In particular, it is suitable as an adhesive for making laminates of metal foil and plastic film, for example, as an adhesive used for bonding electronic material components. Examples of "electronic material components" in the present invention include flexible printed circuit boards, coverlays, bonding sheets, etc. As for materials made by bonding electronic material components, flexible laminates such as flexible copper-clad laminates and flexible printed circuit boards are preferred. A flexible laminate is, for example, a laminate in which "flexible substrates / films / conductive metal layers made of copper, aluminum, or alloys thereof" are sequentially laminated, and the adhesive composition of the present invention can be used as the adhesive constituting the film. In addition to the above-mentioned layers, the flexible laminate may further contain other insulating layers, other adhesive layers, and other conductive metal layers. [Examples]

[0104] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. Unless otherwise specified, all values ​​indicated by "parts" and "%" below are on a mass basis.

[0105] <Synthesis of polystyrene (PS) with methyl carboxylate groups at both ends> (Example 1) In a reaction vessel equipped with a thermometer, stirrer, reflux column, dropping funnel, and nitrogen inlet tube, 50 parts by mass of toluene was charged as an organic solvent. Under reflux of toluene, 100 parts by mass of styrene (St) and 24 parts of dimethyl 2,2'-azobis(2-methylpropionate) as an initiator were added dropwise over 5.0 hours to carry out radical polymerization.

[0106] After maintaining the temperature under reflux for 60 minutes following the end of dropwise addition, the reflux column was changed to a distillation system, and distillation was carried out to 170°C. Subsequently, the initiator decomposition product, dimethyl tetramethylsuccinate, was distilled under reduced pressure until it was less than 1,000 ppm. The reaction product was then removed to obtain polystyrene (PS-1) with methyl carboxylate groups at both ends. The results for Mn, Mw, CM group (mol) / St (mol), and the index of introduction of methyl carboxylate groups at both ends of the obtained PS-1 are shown in Table 1.

[0107] Examples 2-7, Comparative Example 1 Polystyrene (PS-2) to (PS-7) and (PS-9) with methyl carboxylate groups at both ends were synthesized in the same manner as (PS-1), except that the solvent type, solvent amount, and initiator amount used in the synthesis were changed as shown in Table 1. The results for Mn, Mw, CM group (mol) / St (mol), and the introduction index of both ends of the methyl carboxylate group for the obtained PS-1, PS-7, and PS-9 are shown in Table 1.

[0108] Example 8 In a pressure-resistant reactor equipped with a thermometer, stirrer, dropping pump, and nitrogen inlet tube, 30 parts by mass of cyclohexane was charged as an organic solvent, and the temperature was raised to 120°C under pressure. 100 parts by mass of styrene (St) and 30 parts of dimethyl 2,2'-azobis(2-methylpropionate) as an initiator were added dropwise over 5.0 hours to carry out radical polymerization, and the reactor was kept warm for 60 minutes after the end of the dropwise addition. After returning to atmospheric pressure, (PS-8) was synthesized in the same manner as (PS-1). The results for Mn, Mw, CM group (mol) / St (mol), and the indices of both ends of the methyl carboxylate group of the obtained PS-8 are shown in Table 1.

[0109] [Table 1]

[0110] CM group (mol) / St (mol): Molar amount of methyl carboxylate groups per mole of styrene, which are constituent units of polystyrene with methyl carboxylate groups at both ends. CM group amount × Mn: Index of introduction of methyl carboxylate groups at both ends = CM group (mol) / St (mol) × Mn

[0111] (Examples 9-20), (Comparative Example 2) <Synthesis of polyester resin (A-1)> In a reaction vessel equipped with a thermometer, stirrer, reflux column with a pre-filled toluene fractionator, and nitrogen inlet tube, 25 parts by mass of xylene as the organic solvent, polystyrene (PS-1) with methyl carboxylate groups at both ends, and hydrogenated polybutadiene with hydroxyl groups at both ends, NISSO-PB(registered trademark) GI-3000 (manufactured by Nippon Soda Co., Ltd.), as shown in Table 2, were charged. After purging the inside of the reaction vessel with nitrogen, the temperature was increased while stirring. When the temperature inside the reaction vessel reached 140°C, tetraisopropyl titanate (trade name: Orgatics(registered trademark) TA-10, manufactured by Matsumoto Fine Chemical Co., Ltd.) was added as a catalyst, and the temperature inside the reaction vessel was further raised to 160°C to 170°C. The by-product (methanol) was removed from the system under xylene reflux, and the transesterification reaction proceeded for 6 hours.

[0112] Subsequently, the fractional distillation apparatus was removed, and the system was changed to a distillation system. Xylene was removed by distillation, and after the internal temperature reached 190°C, the pressure inside the reaction vessel was reduced to further increase the molecular weight. A polyester resin (A-1) was obtained after a 4-hour reduced-pressure reaction.

[0113] <Synthesis of polyester resins (A-2) to (A-13)> Polyester resins (A-2) to (A-13) were synthesized in the same manner as (A-1), except that the types and quantities of raw materials were changed as shown in Table 2.

[0114] <Preparation of organic solvent varnishes (B-1) to (B-13) for polyester resins> The obtained polyester resins (A-1) to (A-13) were each dissolved using organic solvents prepared with the methyl ethyl ketone (MEK) and methylcyclohexane (MCH) ratios shown in Table 2, to obtain the organic solvent varnishes (B-1) to (B-13) of the polyester resins (A-1) to (A-13). Furthermore, it was confirmed that the varnishes had a handleable viscosity, as shown in Table 2.

[0115] [Table 2]

[0116] PS: Polystyrene with methyl carboxylate groups at both ends GI3000: Hydrogenated polybutadiene with hydroxyl groups at both ends (Product name: GI-3000, manufactured by Nippon Soda Co., Ltd.) P2033: Dimer All (Product name: Pripol® 2033, manufactured by Cargill) TA: Tetraisopropyl titanate (Product name: TA-10, manufactured by Matsumoto Fine Chemical Co., Ltd.) SA90: Polyphenylene ether resin with hydroxyl groups at both ends (Product name: NORYL® SA90, manufactured by SABIC Corporation)

[0117] <Evaluation of physical properties of polyester resins> [Preparation of resin films using polyester resins for evaluating glass transition temperatures (Dk, Df)] Polyester resin organic solvent varnishes (B-1) to (B-13) were coated onto a release film to a thickness of 25 μm after drying, and then dried (dried at 130°C for 10 minutes). The resulting resin film was then covered with another release film.

[0118] [Measurement of Dk and Df] The produced resin film was peeled from the release film and used for the measurement of Dk and Df at 10 GHz. The measurement was performed by the cavity perturbation method using a network analyzer (Keysight Technologies N5224B) and a cylindrical cavity resonator (Kanto Electronics Application Development CP531) under the environment of 25 °C and 50% RH relative humidity.

[0119] [Measurement of glass transition temperature (Tg)] The produced resin film was peeled from the release film and used for the measurement of the glass transition temperature. The measurement was performed using a differential scanning calorimeter (DSC25 manufactured by TA Instruments) at a measurement temperature of -100 to 150 °C and a measurement rate of 10 °C / min.

[0120]

[0119] [Measurement of glass transition temperature (Tg)] The produced resin film was peeled from the release film and used for the measurement of the glass transition temperature. The measurement was performed using a differential scanning calorimeter (DSC25 manufactured by TA Instruments) at a measurement temperature of -100 to 150 °C and a measurement rate of 10 °C / min.

[0120] [Measurement of acid value and hydroxyl value] It was measured according to the provisions of JIS K0070.

[0121] [Measurement of 2% weight loss temperature] The produced resin film was peeled from the release film and used for the measurement of the 2% weight loss temperature. The measurement was performed using a differential thermal - thermogravimetric simultaneous measurement device (Thermoplus EVO2 TG / DTA8122 manufactured by Rigaku Corporation) under a nitrogen atmosphere, heating from room temperature to 550 °C at 10 °C / min.

[0122] [Table 3]

[0123] Ester group concentration: 2 × 10 times the reciprocal of the weight - average molecular weight of the units formed from polystyrene with carboxylic acid methyl ester groups at both ends, hydrogenated polybutadiene with hydroxyl groups at both ends, and dimer diol 6 times * in Table 3 means that the tackiness (adhesiveness) of the sample was too strong to measure the relative permittivity and dielectric loss tangent.

[0124] [Manufacturing example of adhesive composition] (Examples 21 - 32), (Comparative Example 3) In a flask equipped with a thermometer, stirrer, reflux column, and nitrogen inlet tube, 151 parts by mass of the above-mentioned organic solvent varnish of polyester resin (B-1) (95 parts by mass as polyester resin) were added to 10 parts by mass of MEK varnish containing 50% polyphenylene ether resin SA90 (trade name: NORYL® SA90, manufactured by SABIC) as a co-crosslinking component, and 9.1 parts by mass of a trimer of isophorone diisocyanate (trade name: TORONATE IDT70B, manufactured by VENCOREX), a compound having two or more isocyanate groups in one molecule, and the mixture was homogeneously mixed to obtain adhesive composition (C-1).

[0125] Adhesive compositions (C-2) to (C-13) were obtained in the same manner as in (C-1), except that the organic solvent varnish of the polyester resin used, the organic solvent varnish of the co-crosslinking component, and the compound having two or more isocyanate groups in one molecule were changed as shown in Table 4.

[0126] [Table 4]

[0127] SA90: Modified polyphenylene ether resin with hydroxyl groups at both ends (Product name: NORYL® SA90, manufactured by SABIC Corporation) IDT: Trimer of isophorone diisocyanate (Trade name: TORONATE IDT70B, manufactured by VENCOREX)

[0128] <Film Evaluation> [Film preparation for evaluating Dk, Df, and glass transition temperature] Adhesive compositions (C-1) to (C-13) were coated onto a release film to a thickness of 25 μm after curing. A B-stage film was obtained by pre-treatment (drying at 100°C for 20 minutes), which was then covered with another release film. A curing treatment (curing at 165°C for 1 hour, then curing at 175°C for 1 hour) was performed to produce a film.

[0129] [Measurement of Dk and Df] The fabricated films were subjected to Dk and Df measurements at 10 GHz after the release film was removed. The Dk and Df measurements were performed in the same manner as for resin films. The dielectric properties required are those of recent times (relative permittivity after curing: 3.0 or less and dielectric loss tangent after curing: 0.0035 or less).

[0130] [Measurement of glass transition temperature] The prepared films were subjected to glass transition temperature measurement after the release film was removed. The glass transition temperature was measured in the same manner as for the resin film.

[0131] [Measurement of 2% weight loss temperature] The prepared films were subjected to 2% weight loss temperature measurement after the release film was removed. The 2% weight loss temperature was measured in the same manner as for the resin film.

[0132] [Fabrication of polyimide film / copper foil adhesion laminate for evaluation] Adhesive compositions (C-1) to (C-13) were coated onto a release film to a cured thickness of 25 μm, pre-treated (dried at 100°C for 20 minutes), transferred to the unroughened surface of a low-roughness copper foil for high-frequency applications, covered with a polyimide (hereinafter sometimes abbreviated as PI) film, and cured under a pressure of 0.04 MPa (cured at 165°C for 1 hour, then at 175°C for 1 hour) to obtain a laminate. Laminates were also obtained using the same method with copper foil and LCP film instead of polyimide film. [Film thickness] 25μm [Copper Foil] Untreated Electrolytic Copper Foil CF-T9DA-SV-18 (Manufactured by Fukuda Metal Foil Powder Co., Ltd., Thickness 18μm, Surface Roughness Rz 0.7μm) [Polyimide film] Kapton® EN (manufactured by Toray DuPont Co., Ltd., 50 μm thickness) [LCP ​​film] Copolymen (registered trademark, Ningbo JUJIA New Material Technology Co., Ltd.)

[0133] [Adhesion] Each laminate obtained for adhesion evaluation was cut into 1 cm wide strips to serve as test specimens. The test specimens were fixed to a plastic plate using double-sided tape and evaluated using a Tensilon test machine (RTC-1150A, A&D Corporation) at a temperature of 25°C using a 180° peel test (tensile speed 20 mm / min). Note that the required 180° peel strength level for substrates in recent years is 4 N / cm or higher.

[0134] <Evaluation Results> The evaluation results are summarized in Table 5.

[0135] [Table 5]

[0136] Tables 1, 2, and 3 show that polyester resins (Examples 9-20) having structural units derived from polystyrene with methyl carboxylate groups at both ends (Examples 1-8) and structural units derived from hydrogenated polybutadiene with hydroxyl groups at both ends that satisfy the requirements of the present invention exhibit excellent low dielectric constant and low dielectric loss tangent, particularly low dielectric loss tangent, and also have excellent heat resistance. Furthermore, Table 4 shows that adhesive compositions (Examples 21-32) that satisfy the requirements of the present invention, by using polyester resins (Examples 9-20) having structural units derived from polystyrene with methyl carboxylate groups at both ends and structural units derived from hydrogenated polybutadiene with hydroxyl groups at both ends that satisfy the requirements of the present invention, and compounds having two or more isocyanate groups in one molecule as raw materials, exhibit excellent handling properties while using less organic solvent and containing a higher concentration of adhesive components compared to conventional technologies. Furthermore, as shown in Table 5, the films obtained by curing these adhesive compositions (Examples 21-32) also exhibited excellent low dielectric constant, low dielectric loss tangent, and heat resistance, as well as a good balance between the handling properties of the adhesive composition and the adhesion of the film obtained by curing the adhesive composition. On the other hand, a polyester resin (Comparative Example 2) having structural units derived from polystyrene with methyl carboxylate groups at both ends (Comparative Example 1) and structural units derived from hydrogenated polybutadiene with hydroxyl groups at both ends (Comparative Example 2) showed a 2% weight loss temperature below 360°C, indicating poor heat resistance. Furthermore, the film obtained by curing an adhesive composition containing Comparative Example 2 (Comparative Example 3) also showed poor heat resistance.

Claims

1. Polystyrene having methyl carboxylate groups at both ends, characterized in that the introduction index of both methyl carboxylate groups at both ends, as shown in (Formula 1) below, is 160 or higher. (Equation 1) Index of introduction of both ends of methyl carboxylate group = CM group (mol) / St (mol) × Mn CM group (mol) / St (mol): The amount of methyl carboxylate groups in moles per mole of styrene in the constituent units of polystyrene with methyl carboxylate groups at both ends. Mn: Number average molecular weight of polystyrene with methyl carboxylate groups at both ends.

2. The chain transfer constant Cs during styrene polymerization at 60°C is 5.0 × 10⁻⁶. －５ A method for producing polystyrene with methyl carboxylate groups at both ends, characterized by radical polymerization of a monomer containing styrene and / or a styrene derivative using an initiator capable of introducing methyl carboxylate groups in a lower organic solvent.

3. The structural unit comprises polystyrene-derived structural units of both terminal methyl carboxylate groups as described in claim 1, It contains structural units derived from hydrogenated polybutadiene with hydroxyl groups at both ends, A polyester resin characterized by having a 2% weight loss temperature of 360°C or higher.

4. The polyester resin according to claim 3, characterized in that the ratio of structural units derived from polystyrene with methyl carboxylate groups at both ends to structural units derived from hydrogenated polybutadiene with hydroxyl groups at both ends is 10 to 60:90 to 40 (by mass).

5. The polyester resin according to claim 3, characterized in that it contains structural units derived from polyphenylene ether resin with hydroxyl groups at both ends.

6. A method for producing a polyester resin, characterized by comprising the step of obtaining a polyester resin from raw materials containing polystyrene with methyl carboxylate groups at both ends and hydrogenated polybutadiene with hydroxyl groups at both ends, as described in claim 1.

7. An adhesive composition characterized by containing the polyester resin described in claim 3 and a (meth)acrylate having an isocyanate group.

8. An adhesive composition characterized by containing a polyester resin with double bonds at both ends, which is a reaction product of a polyester resin described in claim 3 and a (meth)acrylate having an isocyanate group.

9. An adhesive composition characterized by containing the polyester resin described in claim 3 and a compound having two or more isocyanate groups in one molecule (excluding compounds having a double bond in the same molecule).

10. The adhesive composition according to claim 7 or 8, further characterized by containing an organic peroxide.

11. The adhesive composition according to claim 10, further comprising a polyphenylene ether resin with double bonds at both ends.

12. The adhesive composition according to claim 9, further comprising a polyphenylene ether resin with hydroxyl groups at both ends.

13. The adhesive composition according to any one of claims 7, 8, 9, and 12, further comprising an organic solvent.

14. A laminate comprising an adhesive layer made of a coated and dried product of the adhesive composition according to any one of claims 7 to 9.

15. A laminate comprising a film obtained by curing the adhesive composition according to any one of claims 7 to 9.

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