Insulating material

Abstract

To provide an insulating material having a low coefficient of thermal expansion and excellent withstand voltage.SOLUTION: An insulating material 100 is provided, where the insulating material 100 includes a first insulating layer 1 made of a first resin composition, and a second insulating layer 2 provided on at least one surface of the first insulating layer 1 and made of a second resin composition, where the first resin composition contains an inorganic filler, and the second resin composition does not contain an inorganic filler.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to insulating materials. [Background technology]

[0002] Flexible printed circuit boards have come into widespread use as electronic devices become smaller and lighter. These flexible printed circuit boards are formed, for example, by laminating a coverlay on a polyimide substrate so as to cover copper wiring patterned on the substrate. For example, Patent Document 1 describes a coverlay including an insulating, flexible, and light-reflective cover film and an adhesive layer laminated on one side of the cover film. In this coverlay, the cover film includes a base layer and a reflective layer laminated on the other side of the base layer. The reflective layer contains a white pigment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-48736 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, coverlays are now also required to have a low coefficient of thermal expansion. To address this issue, one approach is to incorporate a large amount of inorganic filler into the varnish used to form the coverlay. However, there is a problem in that applying and curing a varnish containing a large amount of inorganic filler results in a decrease in withstand voltage.

[0005] An object of the present invention is to provide an insulating material that has a low coefficient of thermal expansion and excellent voltage resistance. [Means for solving the problem]

[0006] According to the present invention, there is provided an insulating material as follows. [1] An insulating material comprising a first insulating layer made of a first resin composition and a second insulating layer made of a second resin composition provided on at least one surface of the first insulating layer, the first resin composition contains an inorganic filler, The second resin composition does not contain an inorganic filler. Insulation material. [2] In the insulating material according to [1], The thickness of the second insulating layer is 0.5 μm or more and 10 μm or less. Insulation material. [3] In the insulating material according to [1] or [2], the first resin composition contains an inorganic filler in an amount of 20% by mass or more and 60% by mass or less relative to the total solid content of the first resin composition; Insulation material. [4] In the insulating material according to any one of [1] to [3], The inorganic filler is silica. Insulation material. [5] In the insulating material according to any one of [1] to [4], The first resin composition contains a polyimide. Insulation material. [6] In the insulating material according to any one of [1] to [5], The second insulating layer is provided on both surfaces of the first insulating layer. Insulation material. [Effects of the Invention]

[0007] According to one aspect of the present invention, an insulating material having a low coefficient of thermal expansion and excellent voltage resistance can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing an insulating material according to a first embodiment of the present invention. [Figure 2] FIG. 4 is a cross-sectional view showing an insulating material according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] [First embodiment] The present invention will be described below by taking an embodiment as an example and referring to the drawings. The present invention is not limited to the content of the embodiment. Note that in the drawings, some parts are illustrated enlarged or reduced in size for ease of explanation.

[0010] (insulation material) 1, the insulating material 100 according to this embodiment includes a first insulating layer 1 made of a first resin composition, and a second insulating layer 2 made of a second resin composition provided on at least one surface of the first insulating layer 1. The insulating material 100 is also provided on a substrate 3. It is necessary that the first resin composition contains an inorganic filler, and the second resin composition does not contain an inorganic filler.

[0011] The inventors of the present invention believe that the reason why the insulating material 100 according to this embodiment has a low coefficient of thermal expansion and excellent withstand voltage is as follows. That is, to reduce the thermal expansion coefficient of the insulating material 100, it is necessary to incorporate a large amount of inorganic filler. However, when a varnish containing a large amount of inorganic filler is applied and cured, the inorganic filler is exposed on the film surface. The inventors speculate that this results in a decrease in withstand voltage. In contrast, in the insulating material 100 according to this embodiment, a second insulating layer 2 containing no inorganic filler is provided on the upper surface of a first insulating layer 1 containing inorganic filler. This prevents the inorganic filler from being exposed on the surface of the insulating material 100, allowing the surface to be smoothed. This improves the withstand voltage of the insulating material 100. As described above, the inventors speculate that the insulating material 100 according to this embodiment has a low thermal expansion coefficient and excellent withstand voltage.

[0012] (First insulating layer) The first insulating layer 1 is a layer made of a first resin composition. The first resin composition must contain an inorganic filler. The inorganic filler can reduce the thermal expansion coefficient of the insulating material 100. Examples of inorganic fillers include silica, alumina, aluminum hydroxide, and magnesium hydroxide. Among these, silica is preferred from the viewpoint of the balance of various physical properties. These may be used alone or in combination of two or more.

[0013] The amount of inorganic filler blended is preferably 20% by mass or more and 70% by mass or less, more preferably 25% by mass or more and 65% by mass or less, and particularly preferably 30% by mass or more and 55% by mass or less, relative to 100% by mass of the solid content of the first resin composition. If the amount of inorganic filler blended is equal to or greater than the lower limit, the thermal expansion coefficient of the insulating material can be further reduced. On the other hand, if the amount of inorganic filler blended is equal to or less than the upper limit, the inorganic filler can be sufficiently dispersed in the first resin composition.

[0014] The first resin composition contains a resin. Examples of the resin include polyimide, polyetherimide, polyamide, polyamideimide, polymethylpentene, polyester, polyetheretherketone, liquid crystal polymer, polyphenylene ether, polyphenylene sulfide, polyolefin, syndiotactic polystyrene, epoxy resin, maleimide resin, phenolic resin, and melamine resin. Among these, polyimide is preferred from the viewpoint of low thermal expansion coefficient and excellent voltage resistance. Furthermore, the polyimide is preferably obtained by curing polyamic acid, which is a polyimide precursor.

[0015] The first resin composition may contain additives and solvents in addition to the inorganic filler and resin. The additives include a curing accelerator and a flame retardant. Examples of the solvent include n-methyl-2-pyrrolidone (N-methylpyrrolidone), diethylene glycol monomethyl ether acetate, cyclohexanone, and methyl ethyl ketone. These may be used alone or in combination of two or more.

[0016] From the viewpoint of withstand voltage, the thickness of the first insulating layer 1 is preferably 10 μm or more and 100 μm or less, more preferably 15 μm or more and 50 μm or less, and particularly preferably 20 μm or more and 30 μm or less.

[0017] (Second insulating layer) The second insulating layer 2 is a layer made of a second resin composition. The second resin composition must not contain an inorganic filler. The second insulating layer 2 is provided on at least one surface of the first insulating layer 1, and is preferably provided on the upper surface of the first insulating layer 1, as shown in FIG. 1 . In this way, the inorganic filler exposed on the upper surface of the first insulating layer 1 can be covered with the second insulating layer 2.

[0018] The second resin composition contains a resin. Examples of the resin include the same resins as those used in the first resin composition. From the viewpoint of interlayer adhesion, it is preferable that the resins used in the first resin composition and the second resin composition are the same type. The second resin composition may contain, in addition to the resin, the additives and solvents used in the first resin composition.

[0019] The thickness of the second insulating layer 2 is preferably 0.5 μm to 10 μm, more preferably 1 μm to 10 μm, even more preferably 1 μm to 5 μm, and particularly preferably 2 μm to 4 μm. If the thickness of the second insulating layer 2 is equal to or greater than the lower limit, exposure of the inorganic filler at the film surface can be more reliably suppressed. On the other hand, if the thickness of the second insulating layer 2 is equal to or less than the upper limit, a low thermal expansion coefficient can be maintained.

[0020] From the viewpoint of the balance between the thermal expansion coefficient and the withstand voltage, the ratio of the thickness of the second insulating layer 2 to the thickness of the first insulating layer 1 (thickness of the second insulating layer 2 / thickness of the first insulating layer 1) is preferably 1 / 20 or more and 1 / 2 or less, more preferably 1 / 15 or more and 1 / 4 or less, and particularly preferably 1 / 10 or more and 1 / 6 or less.

[0021] (substrate) The substrate 3 may be any known substrate, such as a flexible wiring substrate, a rigid wiring substrate, or a semiconductor substrate.

[0022] (Method of manufacturing insulating material) There are no particular limitations on the method for producing the insulating material 100 according to this embodiment. The insulating material 100 can be produced, for example, by a method including a first film-forming step of applying a first resin composition onto a substrate 3 to form a coating film, a first drying step of drying the coating film formed in the first film-forming step to form a precursor film of the first insulating layer 1, a second film-forming step of applying a second resin composition onto the precursor film of the first insulating layer 1 obtained in the first drying step to form a coating film, a second drying step of drying the coating film formed in the second film-forming step to form a precursor film of the second insulating layer 2, and a curing step of curing the precursor films of the first insulating layer 1 and the second insulating layer 2 to form the first insulating layer 1 and the second insulating layer 2.

[0023] In the first film-forming step, the first resin composition is applied onto the substrate 3 to form a film. Examples of the coating device for the first resin composition include a bar coater, a curtain coater, a spray coater, a roll coater, and a screen printing machine. The coating thickness of the first resin composition is preferably adjusted so that the thickness of the first insulating layer 1 falls within the above-mentioned range.

[0024] In the first drying step, the coating film formed in the first film forming step is dried (hereinafter also referred to as pre-baking) to form a precursor film of the first insulating layer 1. The drying conditions can be appropriately set depending on the type of resin. For example, when the resin is a polyamic acid, which is a precursor of polyimide, the following conditions can be used. The drying temperature is preferably 60° C. or higher and 150° C. or lower, more preferably 70° C. or higher and 140° C. or lower, and particularly preferably 80° C. or higher and 130° C. If the temperature is within this range, the solvent in the first resin composition can be dried. The drying time is preferably from 10 seconds to 45 minutes, more preferably from 1 minute to 40 minutes, and particularly preferably from 5 minutes to 35 minutes. If the drying time is within this range, the solvent in the first resin composition can be dried.

[0025] In the second film-forming step, a second resin composition is applied onto the precursor film of the first insulating layer 1 obtained in the first drying step to form a coating film. The second resin composition application device may be the same as the first resin composition application device. The coating thickness of the second resin composition is preferably adjusted so that the thickness of the second insulating layer 2 falls within the above-mentioned range.

[0026] In the second drying step, the coating film formed in the second film forming step is dried to form a precursor film of the second insulating layer 2. The drying conditions are the same as those in the first curing step.

[0027] In the curing step, the precursor films of the first insulating layer 1 and the second insulating layer 2 are cured to form the first insulating layer 1 and the second insulating layer 2. The curing conditions can be appropriately set depending on the type of resin. For example, when the resin is a polyamic acid, which is a precursor of polyimide, the following conditions can be used. The curing temperature is preferably 140° C. or higher and 250° C. or lower, more preferably 150° C. or higher and 240° C. or lower, and particularly preferably 160° C. or higher and 230° C. If the temperature is within this range, the first resin composition and the second resin composition can be appropriately cured. The curing time is preferably from 10 to 300 minutes, more preferably from 15 to 200 minutes, and particularly preferably from 20 to 100 minutes. If the time is within this range, the first resin composition and the second resin composition can be properly cured. The curing may be carried out in one step or in two or more steps. In this manner, the insulating material 100 according to this embodiment can be produced.

[0028] (Operation and effect of the first embodiment) According to this embodiment, the following effects can be achieved. (1) The inorganic filler exposed on the upper surface of the first insulating layer 1 can be covered with the second insulating layer 2. As a result, an insulating material 100 having a low thermal expansion coefficient and excellent voltage resistance can be obtained.

[0029] [Second embodiment] Next, a second embodiment of the present invention will be described with reference to the drawings. Note that a description of the same configuration as in the first embodiment will be omitted. 2, the insulating material 100A according to this embodiment includes a first insulating layer 1 made of a first resin composition and a second insulating layer 2 made of a second resin composition provided on both surfaces of the first insulating layer 1. The insulating material 100A is also provided on a substrate 3. It is necessary that the first resin composition contains an inorganic filler, and the second resin composition does not contain an inorganic filler.

[0030] The first insulating layer 1, the second insulating layer 2, and the substrate 3 are as described above. The insulating material 100A of this embodiment can be produced by a method that further includes, before the first film-forming step in the method for producing the insulating material 100 described above, a pre-coating film-forming step in which a second resin composition is applied onto the substrate 3 to form a coating film, and a pre-coating film drying step in which the coating film formed in the pre-coating film-forming step is dried to form a precursor film of the second insulating layer 2.

[0031] (Operation and effect of the second embodiment) According to this embodiment, it is possible to achieve the same effect as the effect (1) in the first embodiment, as well as the following effect (2). (2) The insulating material 100A can be obtained with improved voltage resistance and elongation.

[0032] [Modification of the embodiment] The present invention is not limited to the above-described embodiment, and includes modifications and improvements within the scope of achieving the object of the present invention. For example, in the above-described embodiment, the insulating material 100 is produced using two coating liquids, a first resin composition and a second resin composition, but this is not limiting. For example, the insulating material 100 may be produced using a resin composition in which the inorganic filler precipitates and separates into two layers. [Example]

[0033] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. As shown below. (resin) Polyamic acid solution: Polyamic acid solution obtained in Preparation Example 1 below (inorganic filler) Inorganic filler: Silica, product name "SC2500-SQ", manufactured by Admatechs Co., Ltd. (solvent) Solvent A: n-methyl-2-pyrrolidone (N-methylpyrrolidone), manufactured by Sakamoto Pharmaceutical Co., Ltd. Solvent B: Cyclohexanone, manufactured by Sanyo Chemical Industries, Ltd.

[0034] [Preparation Example 1] A 1 L four-neck separable flask equipped with a stirrer, reflux condenser, and thermometer was charged with 0.5 g of 4,4-oxydianiline, 4 g of dimer diamine (PRIAMINE 1075, Croda Japan), 6.2 g of 2,2',3,3',5,5'-hexamethyl[1,1'-biphenyl]-4,4'-diyl bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate), and 32 g of n-methyl-2-pyrrolidone. The mixture was heated and stirred at 50 °C for 3.5 hours while blowing nitrogen into the reaction vessel at 0.1 mL / sec. After confirming the salt dissolution, the mixture was stirred at room temperature for an additional 24 hours to synthesize polyamic acid, a precursor to polyimide. This polyamic acid solution (solids content: 20% by weight) was obtained. This polyamic acid itself is a solution and can be used as a varnish for coating copper foil.

[0035] [Example 1] 71% by mass of the polyamic acid solution obtained in Preparation Example 1, 14% by mass of inorganic filler, 3% by mass of solvent A, and 12% by mass of solvent B were mixed and dispersed using a triple roll mill to obtain a first resin composition. The polyamic acid solution obtained in Preparation Example 1 was used as a second resin composition as it was. The first resin composition was applied onto a substrate (PET film, thickness 40 μm), and then pre-baked at 120° C. for 10 minutes to form a precursor film of a first insulating layer (thickness: 20 μm). The second resin composition was then applied onto the precursor film of the first insulating layer, and prebaked under the same conditions as above to form a precursor film of the second insulating layer (thickness: 3 μm). Next, a heat curing treatment was performed at 150°C for 60 minutes, and then a heat curing treatment was performed again at 180°C for 30 minutes, whereby the polyamic acid was subjected to ring-closing polymerization to obtain a polyimide, which formed the first insulating layer and the second insulating layer, thereby producing an insulating material.

[0036] [Example 2] In the same manner as in Example 1, a first resin composition and a second resin composition were obtained. The second resin composition was applied onto a substrate (PET film, thickness 40 μm), and then pre-baked at 120° C. for 10 minutes to form a precursor film of a second insulating layer (thickness: 3 μm). Next, the first resin composition was applied onto the precursor film of the second insulating layer, and then pre-baked under the same conditions as above to form a precursor film of the first insulating layer (thickness: 20 μm). The second resin composition was then applied onto the precursor film of the first insulating layer, and prebaked under the same conditions as above to form a precursor film of the second insulating layer (thickness: 3 μm). Next, a heat curing treatment was performed at 150°C for 60 minutes, and then a heat curing treatment was performed again at 180°C for 30 minutes, whereby the polyamic acid was subjected to ring-closing polymerization to obtain a polyimide, which formed the first insulating layer and the second insulating layer, thereby producing an insulating material.

[0037] [Comparative Example 1] In the same manner as in Example 1, a first resin composition was obtained. The first resin composition was applied onto a substrate (PET film, thickness: 40 μm), then pre-baked at 120°C for 10 minutes, heat-cured at 150°C for 60 minutes, and then further heat-cured at 180°C for 30 minutes, causing the polyamic acid to undergo ring-closing polymerization, obtaining polyimide, and forming a first insulating layer (thickness: 23 μm), thereby producing an insulating material.

[0038] Comparative Example 2 The polyamic acid solution obtained in Preparation Example 1 was used as a second resin composition as it was. The second resin composition was applied onto a substrate (PET film, thickness: 40 μm), then pre-baked at 120°C for 10 minutes, heat-cured at 150°C for 60 minutes, and then further heat-cured at 180°C for 30 minutes, causing the polyamic acid to undergo ring-closing polymerization, obtaining polyimide, and forming a second insulating layer (thickness: 23 μm), thereby producing an insulating material.

[0039] [Insulation material evaluation] The insulating materials were evaluated (voltage resistance, thermal expansion coefficient, and elongation) by the following methods. The results are shown in Table 1. Table 1 also shows the blending compositions and layer configurations of the resin compositions in the examples and comparative examples. (1) Withstand voltage The obtained insulating material was used as a sample, and a voltage of 0.5 kV / sec was applied to a predetermined area in the thickness direction of the insulating material, and the conducting voltage was measured to calculate the dielectric breakdown strength.The withstand voltage was then evaluated according to the following criteria. ◎: Dielectric breakdown strength is 450 kV / mm or more. ◯: The dielectric breakdown strength is 400 kV / mm or more and less than 450 kV / mm. △: The dielectric breakdown strength is 350 kV / mm or more and less than 400 kV / mm. ×: The dielectric breakdown strength is less than 350 kV / mm. (2) Thermal expansion coefficient The obtained insulating material was cut into a predetermined size to prepare a sample, and the thermal expansion coefficient was measured in accordance with IPC TM-650 2.4.24C. ​​The thermal expansion coefficient was evaluated according to the following criteria. ◎: Thermal expansion coefficient is 80 x 10 -6 It is less than mm / ℃. ○: Thermal expansion coefficient is 80×10 -6 mm / ℃ or more 100×10 -6 It is less than mm / ℃. ×: Thermal expansion coefficient is 100×10 -6 mm / ℃ or more. (3) Growth rate The obtained insulating material was cut into a predetermined size to prepare a sample, and the elongation was measured at a tension speed of 5 mm / min using an autograph manufactured by Shimazu Co., Ltd. The elongation was evaluated according to the following criteria. ◎: The elongation rate is 5% or more. ◯: The elongation rate is 3% or more and less than 5%. △: The elongation rate is 1% or more and less than 3%. ×: The elongation rate is less than 1%.

[0040] [Table 1]

[0041] As is clear from the results shown in Table 1, the insulating materials according to the present invention (Examples 1 and 2) were good in all of the results of withstand voltage, thermal expansion coefficient, and elongation. Therefore, it was confirmed that the insulating materials according to the present invention have a low thermal expansion coefficient and excellent withstand voltage. [Explanation of symbols]

[0042] 1...First insulating layer 2...Second insulating layer 3...Substrate 100,100A...insulation material

Claims

1. An insulating material comprising: a first insulating layer made of a first resin composition; and a second insulating layer made of a second resin composition provided on at least one surface of the first insulating layer, the first resin composition contains an inorganic filler, The second resin composition does not contain an inorganic filler. Insulation material.

2. 2. The insulating material according to claim 1, The thickness of the second insulating layer is 0.5 μm or more and 10 μm or less. Insulation material.

3. The insulating material according to claim 1 or 2, The first resin composition contains an inorganic filler in an amount of 20% by mass or more and 70% by mass or less relative to the total solid content of the first resin composition. Insulation material.

4. The insulating material according to claim 1 or 2, The inorganic filler is silica. Insulation material.

5. The insulating material according to claim 1 or 2, The first resin composition contains a polyimide. Insulation material.

6. The insulating material according to claim 1 or 2, The second insulating layer is provided on both surfaces of the first insulating layer. Insulation material.

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