Insulating material

Abstract

An insulating material (100) comprising a first insulating layer (1) that comprises a first resin composition and a second insulating layer (2) that is provided on at least one surface of the first insulating layer (1) and that comprises a second resin composition, wherein the first resin composition contains an inorganic filler, and the second resin composition does not contain an inorganic filler.

Description

Insulation material

[0001] The present invention relates to insulating materials.

[0002] Flexible printed circuit boards have become widely used as electronic devices become smaller and lighter. These flexible printed circuit boards are formed, for example, by laminating a coverlay over copper wiring patterned on a polyimide substrate. For example, Patent Document 1 describes a coverlay including a cover film having insulating, flexible, and light-reflective properties, 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.

[0003] JP 2016-48736 A

[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.

[0006] According to the present invention, there are provided insulating materials 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, wherein the first resin composition contains an inorganic filler, and the second resin composition does not contain an inorganic filler. [2] The insulating material according to [1], wherein the thickness of the second insulating layer is 0.5 μm or more and 10 μm or less. [3] The insulating material according to [1] or [2], wherein the first resin composition contains 20 mass % or more and 70 mass % or less of an inorganic filler relative to the total solid content of the first resin composition. [4] The insulating material according to any of [1] to [3], wherein the inorganic filler is silica. [5] The insulating material according to any of [1] to [4], wherein the first resin composition contains a polyimide. [6] The insulating material according to any one of [1] to [5], wherein the second insulating layer is provided on both surfaces of the first insulating layer.

[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.

[0008] 1A and 1B are cross-sectional views showing an insulating material according to a first embodiment of the present invention, and FIG. 1C is a cross-sectional view showing an insulating material according to a second embodiment of the present invention.

[0009] [First embodiment] Hereinafter, the present invention will be described with reference to the drawings, taking an embodiment as an example. 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] (Insulating Material) As shown in Fig. 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 that 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 voltage resistance is as follows. Specifically, to reduce the coefficient of thermal expansion of the insulating material 100, a large amount of inorganic filler must be blended. 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 believe that this results in a decrease in voltage resistance. In contrast, in the insulating material 100 according to this embodiment, the second insulating layer 2, which does not contain inorganic filler, is provided on the upper surface of the first insulating layer 1, which contains inorganic filler. This prevents the inorganic filler from being exposed on the surface of the insulating material 100, thereby smoothing the surface. This improves the voltage resistance of the insulating material 100. As described above, the inventors believe that the insulating material 100 according to this embodiment has a low coefficient of thermal expansion and excellent voltage resistance.

[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. This 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 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 is equal to or more 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 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. Examples of additives include a curing accelerator and a flame retardant. Examples of solvents 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 resin as that 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. In addition to the resin, the second resin composition may contain 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 for Producing 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. Apparatuses for applying the first resin composition include a bar coater, a curtain coater, a spray coater, a roll coater, and a screen printing machine. The thickness of the applied first resin composition is preferably adjusted so that the thickness of the first insulating layer 1 falls within the aforementioned range.

[0024] In the first drying step, the coating film formed in the first film formation step is dried (hereinafter also referred to as pre-baking) to form a precursor film of the first insulating layer 1. Drying conditions can be set appropriately depending on the type of resin. For example, when the resin is 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 or lower. If this temperature is within the above range, the solvent in the first resin composition can be dried. The drying time is preferably 10 seconds or higher and 45 minutes or lower, more preferably 1 minute or higher and 40 minutes or lower, and particularly preferably 5 minutes or higher and 35 minutes or lower. If this time is within the above 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 coating device for the second resin composition can be the same as the coating device for the first resin composition. The coating thickness of the second resin composition is preferably adjusted so that the thickness of the second insulating layer 2 falls within the aforementioned 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 the drying conditions 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 set appropriately depending on the type of resin. For example, when the resin is 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 or lower. If this temperature is within the above range, the first resin composition and the second resin composition can be properly cured. The curing time is preferably 10 minutes or higher and 300 minutes or lower, more preferably 15 minutes or higher and 200 minutes or lower, and particularly preferably 20 minutes or higher and 100 minutes or lower. If this time is within the above range, the first resin composition and the second resin composition can be properly cured. Note that curing may be performed in one stage, or may be performed in two or more stages. In this manner, the insulating material 100 according to this embodiment can be produced.

[0028] (Effects of 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. As shown in FIG. 2, an 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 that 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 according to 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 of applying a second resin composition onto the substrate 3 to form a coating film, and a pre-coating film drying step of drying the coating film formed in the pre-coating film-forming step to form a precursor film of the second insulating layer 2.

[0031] (Effects of the Second Embodiment) According to the present embodiment, it is possible to achieve the same effect as the effect (1) of the first embodiment, as well as the following effect (2): (2) An insulating material 100A having further improved withstand voltage and elongation can be obtained.

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

[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 at all. The materials used in the examples and comparative examples are as follows. (Resin) Polyamic acid solution: Polyamic acid solution obtained in Preparation Example 1 below (Inorganic filler) Inorganic filler: Silica, trade 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, a reflux condenser, and a thermometer was charged with 0.5 g of 4,4-oxydianiline, 4 g of dimer diamine (PRIAMINE 1075 manufactured by 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. While blowing nitrogen into the reaction vessel at 0.1 mL / sec, the mixture was heated and stirred at 50° C. for approximately 3.5 hours. After confirming that the salt had dissolved, the mixture was further stirred at room temperature for 24 hours to synthesize polyamic acid, a precursor of polyimide, and a polyamic acid solution (solid content: 20% by mass) was obtained. This polyamic acid itself is in the form of a solution and can be used as is as a varnish for application to 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 three-roll mill to obtain a first resin composition. The polyamic acid solution obtained in Preparation Example 1 was used as a second resin composition. The first resin composition was applied to a substrate (PET film, thickness 40 μm) and then prebaked at 120°C for 10 minutes to form a precursor film for a first insulating layer (thickness: 20 μm). The second resin composition was then applied to the precursor film for the first insulating layer and then prebaked under the same conditions as above to form a precursor film for a second insulating layer (thickness: 3 μm). Next, a heat curing treatment was performed at 150°C for 60 minutes, followed by a further heat curing treatment at 180°C for 30 minutes, whereby the polyamic acid underwent ring-closing polymerization to obtain a polyimide. The first insulating layer and the second insulating layer were then formed to produce an insulating material.

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

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

[0038] 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), prebaked 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, whereby the polyamic acid underwent ring-closing polymerization to obtain polyimide, and a second insulating layer (thickness: 23 μm) was formed, thereby producing an insulating material.

[0039] [Evaluation of Insulating Materials] Evaluation of the insulating materials (voltage resistance, thermal expansion coefficient, elongation) was performed using 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) Voltage Resistance Using the obtained insulating materials as samples, a voltage of 0.5 kV / sec was applied to a predetermined area in the thickness direction of the insulating material, the conducted voltage was measured, and the dielectric breakdown strength was calculated. The voltage resistance was then evaluated according to the following criteria. AA: The dielectric breakdown strength is 450 kV / mm or more. A: The dielectric breakdown strength is 400 kV / mm or more and less than 450 kV / mm. B: The dielectric breakdown strength is 350 kV / mm or more and less than 400 kV / mm. C: 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: AA: Thermal expansion coefficient is 80 x 10 －６ A: The thermal expansion coefficient is less than 80 x 10 mm / °C. －６ mm / ℃ or more 100×10 －６ C: The thermal expansion coefficient is less than 100 x 10 －６ mm / °C or more. (3) Elongation The obtained insulating material was cut into a predetermined size to prepare a sample, and the elongation was measured using an autograph manufactured by Shimazu Corporation at a tensile speed of 5 mm / min. The elongation was then evaluated according to the following criteria. AA: The elongation is 5% or more. A: The elongation is 3% or more but less than 5%. B: The elongation is 1% or more but less than 3%. C: The elongation is less than 1%.

[0040]

[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.

[0042] REFERENCE SIGNS LIST 1...first insulating layer 2...second insulating layer 3...substrate 100, 100A...insulating 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, wherein the first resin composition contains an inorganic filler, and the second resin composition does not contain an inorganic filler.

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

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

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

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

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

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