Wet-laid nonwoven fabrics and their manufacturing methods, as well as prepregs and metal-clad laminates.

Abstract

To provide a wet-laminate nonwoven fabric with low dielectric constant and low dielectric loss tangent, a method for manufacturing the same, and a prepreg and a metal-clad laminate. [Solution] A wet-laid nonwoven fabric characterized in that it contains 5% by mass or more and 100% by mass or less of syndiotactic polystyrene, and when the wet-laid nonwoven fabric is extracted with methyl ethyl ketone, the ratio of the mass of the extract to the mass of the nonwoven fabric before extraction is 0% by mass or more and 2.8% by mass or less, and a method for producing the same, and a prepreg comprising the wet-laid nonwoven fabric and a matrix resin composition, and a metal-clad laminate comprising a cured product of the prepreg and a metal foil laminated on one or both sides of the cured product.

Description

[Technical Field]

[0001] This invention relates to wet-laid nonwoven fabrics and methods for producing the same, as well as prepregs and metal-clad laminates. [Background technology]

[0002] As a base material for prepregs used in the manufacture of printed circuit boards with low dielectric constant and low dielectric loss tangent, for example, Patent Document 1 below discloses a meltblown nonwoven fabric containing syndiotactic polystyrene (hereinafter also referred to as "SPS"). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2024 / 202454 [Overview of the project] [Problems that the invention aims to solve]

[0004] The base material of the prepreg is preferably uniform in texture and thin, and in that respect, a wet-laid nonwoven fabric is preferable. However, Patent Document 1 does not disclose the specific composition of a wet-laid nonwoven fabric containing SPS, nor its manufacturing method.

[0005] Given the current state of prior art, the problem that the present invention aims to solve is to provide a wet-laid nonwoven fabric with low dielectric constant and low dielectric loss tangent, a method for manufacturing the same, and a prepreg and a metal-clad laminate. [Means for solving the problem]

[0006] The inventors of this invention, after diligently studying and conducting numerous experiments to solve the aforementioned problems, unexpectedly discovered that the problems could be solved by the following configuration, and thus completed the present invention. In other words, the present invention is as follows: [1] A wet nonwoven fabric, Contains 5% to 100% by mass of syndiotactic polystyrene. A wet nonwoven fabric characterized in that, when the wet nonwoven fabric is extracted with methyl ethyl ketone, the ratio of the mass of the extract to the mass of the nonwoven fabric before extraction is 0% by mass or more and 2.8% by mass or less. [2] The wet nonwoven fabric according to [1], wherein the proportion of the extract is 0% by mass or more and 0.2% by mass or less. [3] A wet nonwoven fabric according to [1] or [2], comprising 60% by mass or more and 100% by mass or less of syndiotactic polystyrene. [4] A wet-laid nonwoven fabric according to any one of [1] to [3] above, comprising 60% by mass or more and less than 100% by mass of syndiotactic polystyrene, and more than 0% by mass and 40% by mass or less of polyphenylene ether. [5] The following steps: A papermaking process to form an undried web by papermaking a slurry containing at least one type of fiber and water; A drying step to obtain a dried web by drying the obtained dried web; and A hot pressing process in which the resulting dried web is subjected to hot pressing; A method for producing a wet nonwoven fabric according to any one of the above [1] to [4], including the above. [6] The method according to [5], wherein the slurry further comprises a surfactant and / or a thickener. [7] The method according to [5] or [6], wherein the average degree of crystallinity of the fibers is 0% or more and 42.5% or less. [8] The method according to any one of [5] to [7], wherein the hot press is performed using a heating element at 100°C to 190°C. [9] The method according to any one of [5] to [8], further comprising the step of washing with a scouring agent and then drying after the hot pressing step.

[10] The method according to [9], wherein the scouring agent is an organic solvent.

[11] The method according to

[10] , wherein the organic solvent is a ketone solvent.

[12] A prepreg comprising a wet nonwoven fabric according to any of [1] to [4] above and a matrix resin composition.

[13] A metal-clad laminate comprising a cured product of the prepreg according to

[12] , and a metal foil laminated on one or both surfaces of the cured product. Effects of the Invention

[0007] According to the present invention, it is possible to provide a wet-laid nonwoven fabric having a low dielectric constant and a low dielectric loss tangent, a method for producing the same, a prepreg, and a metal-clad laminate. Mode for Carrying Out the Invention

[0008] Hereinafter, modes for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The following embodiment is one aspect of the present invention, and thus the present invention is not limited to only the following embodiment. Therefore, the following embodiment can be implemented with appropriate modifications within the scope of the gist of the present invention.

[0009] One embodiment of the present invention is a wet-laid nonwoven fabric, wherein the wet-laid nonwoven fabric contains 5% by mass or more and 100% by mass or less of syndiotactic polystyrene, and when the wet-laid nonwoven fabric is extracted with methyl ethyl ketone, the ratio of the mass of the extract to the mass of the nonwoven fabric before extraction is 0% by mass or more and 2.8% by mass or less.

[0010] The present embodiment relates to a wet-laid nonwoven fabric. A wet-laid nonwoven fabric is a nonwoven fabric as defined in JIS L 0222:2022, in which short fibers are bonded to form a sheet.

[0011] From the viewpoint of reducing the dielectric constant and dielectric loss tangent, the wet-laid nonwoven fabric of the present embodiment contains 5% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more of SPS. Further, the wet-laid nonwoven fabric of the present embodiment can contain 100% by mass or less, less than 100% by mass, 95% by mass or less, 90% by mass or less, or 85% by mass or less of SPS.

[0012] SPS is a styrenic polymer mainly having a syndiotactic structure. Here, the syndiotactic structure means that the stereochemical structure is a syndiotactic structure, that is, it has a stereostructure in which phenyl groups, which are side chains with respect to the main chain formed from carbon-carbon bonds, are alternately positioned in opposite directions.

[0013] From the viewpoint of improving heat resistance, the wet nonwoven fabric of the present embodiment preferably contains SPS in an amount of 60% by mass or more and less than 100% by mass, and polyphenylene ether (hereinafter also referred to as "PPE") in an amount of more than 0% by mass and 40% by mass or less, more preferably contains SPS in an amount of 70% by mass or more and less than 100% by mass, and PPE in an amount of more than 0% by mass and 30% by mass or less.

[0014] PPE contains phenylene ether units as repeating structural units. The phenylene group in the phenylene ether unit may or may not have a substituent.

[0015] PPE may also contain other structural units other than phenylene ether units. The amount of the other structural units is typically 30% or less, 25% or less, 20% or less, 15% or less, 10% or less, or 5% or less based on the number of all structural units. However, the amount of the other structural units may exceed 30% based on the number of all structural units, as long as the action and effect of the present embodiment are not impaired.

[0016] Specific examples of PPE include poly(2,6-dimethyl-1,4-phenylene ether), poly(2-methyl-6-ethyl-1,4-phenylene ether), poly(2-methyl-6-phenyl-1,4-phenylene ether), poly(2,6-dichloro-1,4-phenylene ether), copolymers of 2,6-dimethylphenol and other phenols (e.g., 2,3,6-trimethylphenol, 2-methyl-6-butylphenol, etc.), and PPE copolymers obtained by coupling 2,6-dimethylphenol with bisphenols, and the like.

[0017] In this embodiment, when the wet-laid nonwoven fabric is extracted with methyl ethyl ketone, the ratio of the extract to the nonwoven fabric before extraction is 0% by mass or more and 2.8% by mass or less, preferably 0% by mass or more and 2.0% by mass or less, more preferably 0% by mass or more and 1.5% by mass or less, even more preferably 0% by mass or more and 1.0% by mass or less, particularly preferably 0% by mass or more and 0.5% by mass or less, and most preferably 0% by mass or more and 0.2% by mass or less. The extract obtained from the wet-laid nonwoven fabric with methyl ethyl ketone may contain various additives such as oils contained in the raw material fibers, and surfactants and thickeners added during the manufacture of the wet-laid nonwoven fabric. These additives increase the dielectric constant and dielectric loss tangent of the wet-laid nonwoven fabric, and by having an extract ratio of 2.8% by mass or less, the wet-laid nonwoven fabric has a low dielectric constant and a low dielectric loss tangent. In order to ensure that the proportion of the extract is between 0% by mass and 2.8% by mass, it is preferable to reduce the amount of surfactants, thickeners, etc. added during the production of the wet nonwoven fabric, and to wash the fabric after the hot pressing process.

[0018] The thickness of the wet nonwoven fabric in this embodiment is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 60 μm or less, and particularly preferably 40 μm or less, from the viewpoint of increasing the wiring density when used as a printed circuit board. The thickness of the wet nonwoven fabric can also be 5 μm or more, or 10 μm or more.

[0019] The basis weight of the wet nonwoven fabric in this embodiment is preferably 133 g / m², from the viewpoint of achieving both thinness and resin impregnation. 2 More preferably 67 g / m 2 μm or less, more preferably 40 g / m² 2 The following is particularly preferred: 27 g / m 2 The following applies:

[0020] The dielectric constant of the wet nonwoven fabric of this embodiment at 10 GHz is preferably 2.0 to 4.0, more preferably 2.0 to 3.5, and even more preferably 2.0 to 3.0, from the viewpoint of reducing transmission loss when used as a printed circuit board and suppressing skew by reducing the dielectric constant difference with the matrix resin.

[0021] The dielectric loss tangent of the wet nonwoven fabric in this embodiment at 10 GHz is preferably 0.003 or less, more preferably 0.002 or less, and even more preferably 0.001 or less, from the viewpoint of reducing transmission loss when used as a printed circuit board.

[0022] The nonwoven fabric of this embodiment is produced by the following process: A papermaking process to form an undried web by papermaking a slurry containing at least one type of fiber and water; A drying step to obtain a dried web by drying the obtained undried web; and A heat pressing step in which the resulting dried web is heat-pressed; It can be manufactured by a manufacturing method that includes [specific details]. In other words, another embodiment of the present invention is such a manufacturing method.

[0023] The fibers used in the papermaking process should be selected such that the final wet-laid nonwoven fabric contains 5% to 100% SPS by mass. Either a single type of fiber or a mixture of two or more types of fibers may be used.

[0024] The thickness (i.e., fiber diameter and fineness) and cross-sectional shape of the fibers are not particularly limited, as long as they can achieve the desired thickness, basis weight, etc. Furthermore, the fibers may have different thicknesses and cross-sectional shapes.

[0025] The length of the (short) fibers is not particularly limited and can be appropriately selected within a range of, for example, 1 mm to 20 mm.

[0026] The average crystallinity of the fibers is preferably 42.5% or less, more preferably 41.5% or less, even more preferably 40.5% or less, and particularly preferably 39.5% or less. By setting the average crystallinity of the fibers to 42.5% or less, the raw material fibers can be sufficiently bonded together without adding a binder, thus preventing an increase in dielectric loss tangent due to the presence of a binder. Furthermore, the crystallinity of the fibers is 0% or more, and from the viewpoint of suppressing shrinkage in the hot pressing process, it is preferably 37.0% or more, more preferably 37.5% or more, and even more preferably 38.0% or more. The average crystallinity is the weighted average of the crystallinity of one or more types of fibers used as raw materials, weighted by their mass.

[0027] The fibers may be manufactured by any method, for example, by wet spinning, dry spinning, or melt spinning. For fibers containing SPS, it is preferable to use fibers manufactured by melt spinning from the viewpoint of productivity.

[0028] From the viewpoint of improving the dispersibility of fibers, the slurry preferably contains a surfactant and / or a thickener.

[0029] The apparatus used for papermaking is not particularly limited, and any known apparatus can be used.

[0030] The drying method in the drying process can be, for example, using a Yankee dryer or a hot air dryer.

[0031] The method of heat pressing in the heat pressing process can be a method of applying pressure to the drying web by at least one heating element, such as using a heat press machine or using a calender roll.

[0032] In hot pressing, the temperature of the heating element is preferably 100°C or higher, more preferably 150°C or higher, and even more preferably 170°C or higher, from the viewpoint of sufficiently bonding the fibers together to suppress breakage and fuzzing. Furthermore, the temperature of the heating element is preferably 195°C or lower, more preferably 190°C or lower, and even more preferably 185°C or lower, from the viewpoint of improving the impregnation of the matrix resin without crushing the voids in the wet nonwoven fabric.

[0033] The manufacturing method for the wet nonwoven fabric of this embodiment, from the viewpoint of reducing the additives contained in the wet nonwoven fabric to achieve lower dielectric constant and dielectric loss tangent, includes the following steps after the hot pressing process: Washing process: After washing with scouring agent, drying is performed. It can further include

[0034] The scouring agent can be, for example, an alkaline aqueous solution containing a textile scouring agent mainly composed of a surfactant, or an organic solvent. The organic solvent can be a ketone solvent, a glycol solvent, or a hydrocarbon solvent, but a ketone solvent is preferred from the viewpoint of removing additives and suppressing deterioration of the physical properties of the fibers. Examples of ketone solvents include acetone, methyl ethyl ketone, and methyl isobutyl ketone.

[0035] The drying method in the washing process may be the same as or different from the drying method in the drying process.

[0036] A further embodiment of the present invention is a prepreg comprising the wet nonwoven fabric and a thermosetting matrix resin composition. The matrix resin composition may include at least one thermosetting resin selected from the group consisting of epoxy resins, cyanate ester resins, bismaleimide resins, polyphenylene ether resins, hydrocarbon resins, and bismaleimide-triazine resins (BT resins).

[0037] A further embodiment of the present invention is a metal-clad laminate comprising a cured prepreg and a metal foil laminated on one or both sides of the cured prepreg. Examples of the metal foil include aluminum foil and copper foil. [Examples]

[0038] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples.

[0039] The following describes the measurement and evaluation methods for the various characteristics used in the examples. <Evaluation Method> (1) Extract amount (%): The ratio of the mass of the extract to the mass of the nonwoven fabric before extraction when the wet nonwoven fabric is extracted with methyl ethyl ketone (%) 50 mg of wet nonwoven fabric and 1 mL of methyl ethyl ketone were added to a glass sample bottle and immersed and extracted at 25°C for 30 minutes. The wet nonwoven fabric was removed, rinsed with 1 mL of methyl ethyl ketone, and the methyl ethyl ketone used for immersion and rinsing was evaporated to dryness at 25°C. If fibers were visually confirmed in the residue after evaporation to dryness, the residue was redissolved in methyl ethyl ketone, filtered through a syringe filter, and evaporated to dryness again. The mass of the residue after evaporation to dryness (mg) was divided by the mass of the wet nonwoven fabric before extraction (50 mg), and multiplied by 100 to calculate the ratio (%) of the mass of the extract to the mass of the nonwoven fabric before extraction when the wet nonwoven fabric was extracted with methyl ethyl ketone.

[0040] (2) Fiber diameter (μm) Using a scanning electron microscope (Hitachi Science Systems, Ltd. SEMEDX3TypeN), we imaged cross-sections of 10 arbitrary fibers, measured the diameter of each fiber, and calculated the average value.

[0041] (3) Degree of crystallinity of fibers (%), and average degree of crystallinity (%) Using a differential scanning calorimeter DSC7000X manufactured by Hitachi High-Tech Science Corporation, the sample was heated at a rate of 10°C / min to a temperature exceeding its melting point. For the exothermic peak originating from crystallization, with a peak top around 140°C in the resulting chart, the peak area in the region showing a change in heat quantity was measured from the differential curve to determine the low-temperature crystallization enthalpy ΔH c(J / g). Further, for the endothermic peak derived from crystal melting having a peak top around 270°C to 285°C in the obtained chart, the peak area was measured in a region with a heat quantity change from the differential curve to obtain the crystal melting enthalpy ΔH m (J / g). Note that ΔH c , ΔH m are both positive values. The crystallinity of the fiber was calculated by the following formula, assuming that the enthalpy of melting when SPS is completely crystallized is 53 J / g. Crystallinity (%) = 100 × (ΔH m −ΔH c ) / 53 The average crystallinity of n types of fibers was calculated by the following formula, where C i (%) is the crystallinity of the i-th fiber and x i is the mass ratio thereof.

Math

[0042] (4) Area shrinkage ratio before and after hot pressing (%) When S0 is the area before hot pressing and S1 is the area after hot pressing, the area shrinkage ratio was calculated by the following formula. Area shrinkage ratio (%) = 100 × (S0 - S1) / S0

[0043] (5) Thickness of wet-laid nonwoven fabric (μm) Measurement under a 5 N load using an external micrometer (0 to 25 mm) specified in JIS B 7502:1994 was performed on 10 points randomly selected from the wet-laid nonwoven fabric, and the arithmetic average value was taken as the thickness of the wet-laid nonwoven fabric.

[0044] (6) Basis weight of wet-laid nonwoven fabric (g / m 2 ) One rectangular sample (size 5 cm × 20 cm) was collected from the wet-laid nonwoven fabric, and the mass of the sample was measured. Thereafter, the value converted to the mass per 1 m 2 (a value obtained by multiplying by 100) was taken as the basis weight of the wet-laid nonwoven fabric.

[0045] (7) Dielectric constant and dielectric loss tangent of wet nonwoven fabric at 10 GHz The dielectric constant and dielectric loss tangent of wet-laid nonwoven fabrics at 10 GHz were measured using the cavity resonance method. A network analyzer (N5230A, Agilent Technologies) and a cavity resonator (Cavity Resornator CP series, Kanto Electronics Applied Development Co., Ltd.) were used as the measurement equipment.

[0046] <Fiber production> [Fibers 1-6] Using pellets containing 75% by mass of SPS (Zarec® 90ZC, manufactured by Idemitsu Kosan Co., Ltd.) and 25% by mass of PPE (Zylon® S203A, manufactured by Asahi Kasei Corporation), or pellets containing only SPS, the raw materials were extruded through a spinneret at 295°C in a melt spinning machine, and the undrawn yarn was wound up. In order to adjust the fiber diameter, the number and diameter of holes in the spinneret, as well as the polymer discharge rate and winding speed, were appropriately changed in the production of each fiber.

[0047] For fibers 2-4, the undrawn yarns were drawn at a preheating temperature of 115°C and a draw ratio of 1.13 times, and then heat-set at 125°C, 150°C, and 175°C, respectively.

[0048] The obtained fibers were cut to approximately 5 mm to produce fibers 1 to 6. The production conditions and physical properties of fibers 1 to 6 are shown in Table 1 below.

[0049] [Table 1]

[0050] [Example 1] A slurry was formed by mixing and dispersing the fibers according to the fiber composition shown in Table 2 below, and then a fiber web was formed by a wet process. The formed fiber web was passed between a pair of calender rolls heated to 160°C, and after heating and pressurizing the fiber web, it was allowed to cool, which deformed the undrawn fibers 1 and bonded the constituent fibers of the fiber web together, thereby producing a wet nonwoven fabric. In this embodiment, the wet-laid nonwoven fabric maintained its sheet form, but because the fibers were not sufficiently bonded together, some fuzzing occurred.

[0051] [Example 2] A wet-laid nonwoven fabric was prepared in the same manner as in Example 1, except that the temperature of the calender rolls was set to 180°C at both the top and bottom.

[0052] [Example 3] A wet-laid nonwoven fabric was prepared in the same manner as in Example 2, except that the web was sandwiched between two polyester films during the heat-pressing process.

[0053] [Example 4] A wet-laid nonwoven fabric was prepared in the same manner as in Example 3, except that after hot pressing, it was washed with hot water at approximately 90°C and dried at 150°C for 30 minutes.

[0054] [Example 5] A wet-laid nonwoven fabric was prepared in the same manner as in Example 3, except that after hot pressing, it was washed with methyl ethyl ketone at room temperature and dried at 150°C for 30 minutes.

[0055] [Example 6] A wet-laid nonwoven fabric was prepared in the same manner as in Example 1, except that the temperature of the calender rolls was set to 200°C at both the top and bottom. The wet-laid nonwoven fabric in this example was partially film-like.

[0056] [Example 7] A wet-laid nonwoven fabric was prepared in the same manner as in Example 1, except that fiber 1 and fiber 3 were used as the fibers, and the calender roll temperature was set to 100°C for the upper roll and 180°C for the lower roll.

[0057] [Example 8] A wet-laid nonwoven fabric was prepared in the same manner as in Example 1, except that fibers 5 and 6 were used as the fibers, and the calender roll temperature was set to 100°C for the upper roll and 200°C for the lower roll.

[0058] [Comparative Example 1] A wet-laid nonwoven fabric was prepared in the same manner as in Example 3, except that the amount of thickener added to the slurry was doubled.

[0059] [Reference example 1] We attempted to produce a wet-laid nonwoven fabric in the same manner as in Example 1, except that we used fibers 1 and 4 as the fibers and set the calender roll temperature to 100°C for the upper roll and 180°C for the lower roll. However, the sheet failed to maintain its shape during heat pressing, making it impossible to produce a wet-laid nonwoven fabric.

[0060] The results are shown in Table 2 below. [Table 2] [Industrial applicability]

[0061] Because the wet-laid nonwoven fabric of the present invention has a low dielectric constant and a low dielectric loss tangent, it can be suitably used as a base material for printed circuit boards for high-speed transmission.

Claims

1. It is a wet-laid nonwoven fabric, Contains 5% to 100% by mass of syndiotactic polystyrene. A wet-type nonwoven fabric characterized in that, when the wet-type nonwoven fabric is extracted with methyl ethyl ketone, the ratio of the mass of the extract to the mass of the nonwoven fabric before extraction is 0% by mass or more and 2.8% by mass or less.

2. The wet nonwoven fabric according to claim 1, wherein the proportion of the extract is 0% by mass or more and 0.2% by mass or less.

3. A wet-laid nonwoven fabric according to claim 1 or 2, comprising 60% by mass or more and 100% by mass or less of syndiotactic polystyrene.

4. A wet-laid nonwoven fabric according to claim 1 or 2, comprising 60% by mass or more and less than 100% by mass of syndiotactic polystyrene, and more than 0% by mass and 40% by mass or less of polyphenylene ether.

5. The following steps: A papermaking process to form an undried web by papermaking a slurry containing at least one type of fiber and water; A drying step in which the obtained undried web is dried to obtain a dried web; and A hot pressing step is performed on the resulting dried web; A method for producing a wet nonwoven fabric according to claim 1 or 2, including the method described above.

6. The manufacturing method according to claim 5, wherein the slurry further comprises a surfactant and / or a thickening agent.

7. The manufacturing method according to claim 5 or 6, wherein the average degree of crystallinity of the fibers is 0% or more and 42.5% or less.

8. The manufacturing method according to claim 5 or 6, wherein the hot press is performed using a heating element with a temperature of 100°C or higher and 190°C or lower.

9. The method according to claim 5 or 6, further comprising the step of washing with a scouring agent and then drying after the hot pressing step.

10. The method according to claim 9, wherein the scouring agent is an organic solvent.

11. The method according to claim 10, wherein the organic solvent is a ketone-based solvent.

12. A prepreg comprising the wet nonwoven fabric according to claim 1 or 2 and a matrix resin composition.

13. A metal-clad laminate comprising a cured prepreg according to claim 12 and a metal foil laminated on one or both sides of the cured prepreg.

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