Molded body, circuit board, and modification method

Abstract

To provide a molding made of a fluorine resin which achieves both adhesion to other material such as metal and electric characteristics inherent to the fluorine resin.SOLUTION: A molding is made of a fluorine resin, wherein in an elemental composition on the surface specified by X-ray photoelectron spectroscopy making carbon, oxygen and fluorine as detection objects, within a limit that the total of the carbon and the oxygen is 100 atom% or less, a content of carbon is 60 atom% or more and 75 atom% or less, a content of oxygen is 25 atom% or more and 35 atom% or less, and a content of oxygen at a position with a depth from the surface of 200 nm, which is specified by X-ray photoelectron spectroscopy making carbon, oxygen and fluorine as detection objects, is 0 atom% or more and 12 atom% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a molded article made of a fluororesin, a circuit board including the molded article made of a fluororesin, and a modification method for modifying the surface of the molded article made of a fluororesin.

Background Art

[0002] In the field of electronic devices, circuit boards are widely used. In particular, in circuit boards used for communication devices, it is desirable to use an insulator having a small dielectric constant and a small dielectric loss tangent in order to achieve high-speed and low-loss communication.

[0003]

[0004] Typical materials having a small dielectric constant and a small dielectric loss tangent include fluororesins. However, since fluororesins have poor adhesion to other materials containing metals, in order to manufacture a circuit board using a fluororesin as an insulator, it is necessary to perform treatments such as imparting adhesiveness to the surface of the fluororesin. For example, Japanese Patent Application Laid-Open No. 2006-128443 (Patent Document 1) discloses a method of treating the surface of a fluororesin molded article with a metal sodium-naphthalene complex solution to impart adhesiveness.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0006] ​

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the surface modification technique using a metal sodium-naphthalene complex solution, not only the surface part contributing to adhesiveness but also a part with a certain depth from the surface is modified, so the electrical properties originally possessed by the fluororesin may be lost. In addition, a substrate material manufactured by impregnating a glass cloth with a fluororesin contains a glass material with inferior electrical properties compared to the fluororesin, so it has been difficult to improve the electrical properties.

[0008] Therefore, in a molded article made of fluororesin, it is required to achieve both adhesiveness to other materials such as metal and the electrical properties originally possessed by the fluororesin. Also, the realization of a circuit board including the molded article is required.

Means for Solving the Problems

[0009] The molded article according to the present invention is Perfluoro a molded article made of fluororesin, and regarding the elemental composition on the surface specified by X-ray photoelectron spectroscopy with carbon, oxygen, and fluorine as detection targets, within the limit that the total content of carbon and oxygen is 100 atomic% or less, the content of carbon is 60 atomic% or more and 75 atomic% or less, and the content of oxygen is 25 atomic% or more and 35 atomic% or less, and the content of oxygen at a position 200 nm deep from the surface specified by X-ray photoelectron spectroscopy with carbon, oxygen, and fluorine as detection targets is 0 atomic% or more and 12 atomic% or less.

[0010] Also, the circuit board according to the present invention is PerfluoroA circuit board including a molded article made of a fluororesin, wherein the elemental composition on the surface of the molded article specified by X-ray photoelectron spectroscopy for detecting carbon, oxygen, and fluorine is such that the total content of carbon and oxygen is 100 atomic% or less, the content of carbon is 60 atomic% or more and 75 atomic% or less, and the content of oxygen is 25 atomic% or more and 35 atomic% or less, and the content of oxygen at a position 200 nm deep from the surface of the molded article specified by X-ray photoelectron spectroscopy for detecting carbon, oxygen, and fluorine is 0 atomic% or more and 12 atomic% or less.

[0011] Further, the modification method according to the present invention is a modification method for modifying the surface of a molded article made of a fluororesin, including a first step of bringing an electron donor into contact with the surface of the molded article, and a second step of bringing a formaldehyde derivative into contact with the surface of the molded article after the first step, wherein the electron donor includes a dispersion in which metallic sodium is dispersed in a solvent and at least one compound selected from the group consisting of 1,3-dialkyl-2-imidazolidinone and crown ether.

[0012] According to these configurations, a molded article in which only the outermost surface portion contributing to adhesiveness is modified, and a circuit board including the same are provided. Thereby, adhesiveness to other materials such as metal and the electrical properties inherent to the fluororesin can be made compatible.

[0013] Hereinafter, preferred embodiments of the present invention will be described. However, the scope of the present invention is not limited by the preferred embodiment examples described below.

[0014] As one aspect, the molded article according to the present invention preferably has a fluorine content at a position 200 nm deep from the surface, specified by X-ray photoelectron spectroscopy for detecting carbon, oxygen, and fluorine, of 40 atomic% or more and 67 atomic% or less.

[0015] According to this configuration, the electrical properties inherent to the fluororesin are further maintained, and better electrical properties can be exhibited.

[0016] In one aspect, the molded article according to the present invention is such that the Perfluoro fluororesin preferably contains 95 mol% or more of tetrafluoroethylene units.

[0017] With this configuration, since the molded article is mainly formed of a fluororesin having particularly good electrical properties among fluororesins, even better electrical properties can be exhibited.

[0018] Further features and advantages of the present invention will become clearer from the following description of exemplary and non-limiting embodiments.

Mode for Carrying Out the Invention

[0019] Embodiments of the molded article, circuit board, and modification method according to the present invention will be described. Hereinafter, an example in which a sheet made of a fluororesin is modified to obtain a sheet with a modified surface, and an example in which a circuit board using the modified sheet as a base material is manufactured will be described. Note that the sheet is an example of the molded article.

[0020] 〔Modification Method〕 First, a modification method for modifying a sheet made of a fluororesin to obtain a sheet with a modified surface will be described. Hereinafter, for the sake of distinction, the sheet before being subjected to the modification treatment is referred to as an "unmodified sheet", and the sheet with a modified surface is referred to as a "modified sheet". Also, the sheet refers to a molded article having a thickness that is considerably smaller compared to the spread in the plane direction. The thickness of the sheet is not particularly limited, but can be, for example, 10 μm or more and 2000 μm or less.

[0021] (Configuration of Unmodified Sheet) The unmodified sheet is a conventional sheet made of a fluororesin. The fluororesin is a resin material containing a fluorine-containing monomer as a polymerization unit. The fluororesin in the present embodiment may be polytetrafluoroethylene (PTFE), ethylene tetrafluoride - hexafluoropropylene copolymer (FEP), ethylene tetrafluoride - perfluoroalkoxyethylene copolymer (PFA), ethylene - tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), or a mixture thereof, but is not limited thereto. However, among the fluororesins listed above, it is preferable to use a perfluororesin (PTFE, FEP, and PFA) that exhibits particularly good high-frequency characteristics.

[0022] However, the fluororesin preferably contains 95 mol% or more of tetrafluoroethylene units, and more preferably 97 mol% or more. Fluororesins that meet this condition are typically PTFE and PFA, and PTFE is even more preferable. Note that PTFE may be so-called homopolymer PTFE containing only tetrafluoroethylene as a polymerization unit, or so-called modified PTFE containing polymerization units other than tetrafluoroethylene. The content of tetrafluoroethylene units in the fluororesin can be quantified by, for example, nuclear magnetic resonance (melt 19 F NMR or solid 19 F NMR) or infrared spectroscopy (IR).

[0023] Also, the fluororesin preferably has a melting point of 300 °C or higher, and more preferably 320 °C or higher. The melting point of the fluororesin can be determined, for example, by differential scanning calorimetry (DSC measurement). The measurement conditions for DSC measurement follow the industrial standards (such as ASTM D4894, ASTM D2116, ASTM D3307, etc.) of each fluororesin.

[0024] The unmodified sheet can be manufactured by known methods such as cutting, compression molding, and extrusion molding. For example, a sheet made of PTFE can be obtained by cutting a billet obtained by compression molding a PTFE material into a block shape and then firing it. Also, for example, a sheet made of PFA can be obtained by extrusion molding using a T-die.

[0025] (Procedure of the modification method) The modification method according to this embodiment includes a first step of bringing an electron donor into contact with the surface of the unmodified sheet, and a second step of bringing a formaldehyde derivative into contact with the surface of the sheet after the first step. Through the first step and the second step, the fluorine atoms present on the surface of the unmodified sheet are substituted with oxygen-containing functional groups.

[0026] (1) First step The first step is a step of bringing an electron donor into contact with the surface of the unmodified sheet. Here, the electron donor is a dispersion in which metallic sodium is dispersed in a solvent (hereinafter referred to as "SD". Note that SD is an abbreviation for Sodium Dispersion.), and a mixture containing at least one compound selected from the group consisting of 1,3-dialkyl-2-imidazolidinone and crown ether.

[0027] SD is one in which sodium is dispersed as fine particles (i.e., solids) in a dispersion solvent, or one in which sodium is dispersed as minute droplets (i.e., liquids) in a dispersion solvent. Here, sodium may be pure metallic sodium or an alloy containing metallic sodium.

[0028] The average particle diameter of sodium (fine particles or droplets) in SD is preferably less than 100 μm, more preferably less than 50 μm, still more preferably less than 30 μm, even more preferably less than 10 μm, and particularly preferably less than 5 μm. The average particle diameter is represented by the diameter of a sphere having a projected area equivalent to the projected area obtained by image analysis of a micrograph.

[0029] The content of metallic sodium in SD is preferably 10 to 45% by mass, more preferably 15 to 25% by mass. The content of metallic sodium may be calculated from the mass ratio of metallic sodium used for manufacturing SD and the dispersion solvent, or may be determined by a method of determining the amount of metallic sodium in SD based on the concentration of the aqueous sodium hydroxide solution specified by neutralization titration after adding the obtained SD to an excessive amount of water to obtain an aqueous sodium hydroxide solution.

[0030] As the dispersion solvent, a known solvent can be used as long as sodium (fine particles or droplets) can be dispersed therein and the reactions proceeding in the first and second steps according to this embodiment are not inhibited. As the dispersion solvent satisfying such requirements, known solvents such as paraffinic solvents (normal paraffinic solvents, cycloparaffinic solvents), aromatic solvents, and heterocyclic compound solvents can be used. Examples of the normal paraffinic solvent include, but are not limited to, normal pentane, normal hexane, normal heptane, normal octane, normal nonane, and normal decane. An example of the cycloparaffinic solvent is cyclopentane, but it is not limited thereto. Examples of the ether solvent include, but are not limited to, tetrahydrofuran, cyclopentyl methyl ether, and 2-methyltetrahydropyran. Examples of the aromatic solvent include, but are not limited to, benzene, toluene, and xylene. An example of the amine solvent is ethylenediamine, but it is not limited thereto. An example of the heterocyclic compound solvent is tetrahydrothiophene, but it is not limited thereto. These solvents may be used alone or as a mixed solvent of two or more kinds.

[0031] As a specific method for generating SD, a known method can be adopted. For example, Japanese Patent Application Laid-Open No. 2007-197787 discloses a method of sequentially mixing metallic sodium (liquid) heated to a temperature equal to or higher than its melting point and a paraffinic solvent using a primary dispersion device and a secondary dispersion device.

[0032] As the primary dispersion device, for example, a stirring device equipped with paddle blades or disk turbine blades can be used, and the stirring device is provided with a jacket through which synthetic heat transfer oil can flow. The stirring device is operated with synthetic heat transfer oil at 105 to 140°C flowing through the jacket to obtain a primary dispersion in which metallic sodium is dispersed in a paraffinic solvent. The average particle diameter of sodium in the primary dispersion is, for example, 20 μm or less.

[0033] As the secondary dispersion device, for example, a device having a rotor and a stator can be used. Blades are provided on both the rotor and the stator, and a shearing force generated between the blades of the rotor and the blades of the stator as the rotor rotates is applied to the object to be processed. When the primary dispersion is supplied to the secondary dispersion device and the secondary dispersion device is operated, a secondary dispersion in which the dispersed particle diameter of metallic sodium is smaller than that of the primary dispersion is obtained. The secondary dispersion is used as the SD.

[0034] In addition, the electron donor according to the present embodiment contains, in addition to the SD, at least one compound selected from the group consisting of 1,3-dialkyl-2-imidazolidinone and crown ether (hereinafter referred to as "predetermined compound").

[0035] 1,3-Dialkyl-2-imidazolidinone is a compound represented by the following formula (1).

Chemical formula

[0036] In formula (1), R 1 and R 2 are the same or different alkyl groups. More specifically, R 1 and R 2 can be a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a sec-butyl group, an iso-butyl group, a tert-butyl group, etc. For example, R 1 and R 2When both are methyl groups, the compound of formula (1) is 1,3 - dimethyl - 2 - imidazolidinone (DMI), and R 1 and R 2 When both are ethyl groups, the compound of formula (1) is 1,3 - diethyl - 2 - imidazolidinone (DEI).

[0037] In formula (1), R 1 and R 2 are preferably selected from the group consisting of a methyl group, an ethyl group, an n - propyl group, and an n - butyl group. Also, in formula (1), it is more preferable that at least one of R 1 and R 2 is a methyl group or an ethyl group, and in formula (1), it is even more preferable that both of R 1 and R 2 are a methyl group or an ethyl group.

[0038] The 1,3 - dialkyl - 2 - imidazolidinone used in the first step may be commercially available or may be produced by a method known in the art. Such methods include the reaction of N,N’ - dialkylethylenediamine having the corresponding alkyl group with phosgene (formula (2)), the reaction of ethyleneurea with alkyl iodide (formula (3)), etc. However, in the latter case, two alkyl groups R 1 on the nitrogen atom are the same.

Chemical formula

Chemical formula

[0039] Also, the crown ether used in the first step may be commercially available or may be produced by a method known in the art. More specifically, the crown ether can be 18 - crown - 6, 15 - crown - 5, 12 - crown - 4, etc., but is not limited thereto.

[0040] In the electron donor according to this embodiment, the ratio of SD to a predetermined compound is not particularly limited. For example, the molar ratio of sodium to the predetermined compound may be from 1:1 to 1:60.

[0041] The electron donor according to this embodiment may contain a diluting solvent in addition to SD and a predetermined compound. The diluting solvent may be the same solvent as the dispersion solvent of SD or a different solvent.

[0042] The electron donor according to this embodiment preferably contains an ether-based solvent. This is because when the electron donor contains an ether-based solvent, the active species as the electron donor is likely to be uniformly dispersed in the ether-based solvent. Examples of the ether-based solvent include, but are not limited to, tetrahydrofuran, cyclopentyl methyl ether, and 2-methyltetrahydropyran, and tetrahydrofuran is particularly preferred. Typically, two examples are shown for providing an electron donor containing an ether-based solvent. The first example is a method using SD having an ether-based solvent as a dispersion solvent as a raw material. The second example is a method of adding an ether-based solvent as a diluting solvent in addition to SD and 1,3-dialkyl-2-imidazolidinone. According to these methods, it is preferable because the whole electron donor can be obtained as a single-phase liquid. Also, the ether-based solvent and 1,3-dialkyl-2-imidazolidinone are preferably sufficiently dehydrated. Specifically, the ether-based solvent and 1,3-dialkyl-2-imidazolidinone preferably have a water content of 100 ppm or less, more preferably 50 ppm or less.

[0043] Further, the electron donor according to this embodiment may contain additives such as a surfactant and an antioxidant.

[0044] The electron donor according to this embodiment is obtained by mixing SD and a predetermined compound in a reaction vessel and stirring them. At this time, other constituent components such as a diluting solvent may be added to the reaction vessel. As a stirring method, a known method can be used. For example, a method using a magnetic stirrer or a method using a stirring device having a stirring blade is exemplified.

[0045] When SD and a predetermined compound (for example, DMI) are mixed and stirred, eventually the solution in the reaction vessel turns blue. The reason why the solution turns blue is not clear, but as a hypothesis, it is considered that chemical species in which metallic sodium Na is separated into cation Na + and anion Na - are generated. Among these chemical species, anion Na - is an active species that acts as an electron donor. Although these chemical species are unstable, in this system, cation Na + is stabilized by a predetermined compound, and recombination with anion Na - is prevented. Therefore, it is considered that the active species, anion Na - can exist stably at room temperature. It should be noted that there is a reported example in Peng Lei et. al., Org. Lett. 2018, 20, 12, 3439-3442 (Non-Patent Document 1) that the solution turns blue when chemical species in which an alkali metal is separated into a cation and an anion are generated.

[0046] From the above hypothesis, it is considered that the fact that the solution in the reaction vessel turns blue indicates the generation of an electron donor. Therefore, the electron donor used in the first step can be obtained by mixing SD and a predetermined compound in a reaction vessel and stirring until the solution turns blue.

[0047] That is, the predetermined compound is cation Na +Any Lewis base having a coordination ability with respect to [the relevant substance] will do. The inventors of the present invention confirmed that when the Lewis base is at least one compound (predetermined compound) selected from the group consisting of 1,3-dialkyl-2-imidazolidinone and crown ether, the effects of the present invention are actually manifested, and thus completed the present invention. However, it is expected that when other Lewis bases are used, the same kind of effects as those obtained when the predetermined compound is used will be exhibited.

[0048] As a method of bringing the electron donor prepared as described above into contact with the surface of the unmodified sheet, a known method can be adopted. For example, operations such as applying a solution of the electron donor to the surface of the unmodified sheet, spraying a solution of the electron donor onto the surface of the unmodified sheet, and immersing the unmodified sheet in a solution of the electron donor may be performed.

[0049] When an electron donor is brought into contact with the surface of the unmodified sheet, fluorine atoms contained in the main chain of the fluororesin (for example, derived from tetrafluoroethylene units) are pulled out from the main chain to generate radicals or anions. An example in the case where the predetermined compound is DMI is shown in Formula (4). These radicals or anions function as reaction points in the subsequent second step.

Chemical formula

[0050] The time (first reaction time) for bringing the electron donor into contact with the surface of the unmodified sheet is not particularly limited, but can be, for example, 10 seconds or more and 20 minutes or less. When the first reaction time is 10 seconds or more, the reaction of Formula (4) easily proceeds sufficiently. Also, when the first reaction time is 20 minutes or less, it is preferable in that it is easy to avoid unnecessary reactions by sodium. The first reaction time is more preferably 30 seconds or more, and even more preferably 60 seconds or more. Also, the first reaction time is more preferably 10 minutes or less.

[0051] The temperature (first reaction temperature) when bringing the electron donor into contact with the surface of the unmodified sheet is not particularly limited, and can be, for example, -20°C or higher and 40°C or lower. When the first reaction temperature is 0°C or higher, it is preferable in terms of cooling efficiency. Also, when the first reaction temperature is 40°C or lower, it is preferable in terms of reactivity. The first reaction temperature is more preferably 0°C or higher, and even more preferably 15°C or higher. Also, the first reaction temperature is more preferably 35°C or lower, and even more preferably 25°C or lower.

[0052] (2) Second step The second step is a step of bringing a formaldehyde derivative into contact with the surface of the sheet after the first step.

[0053] Examples of the formaldehyde derivative used in the second step include, but are not limited to, formaldehyde, paraformaldehyde, and trioxane. Also, the formaldehyde derivative may be a single formaldehyde derivative or a mixture of multiple types of formaldehyde derivatives. The formaldehyde derivative used in the second step preferably contains paraformaldehyde, and more preferably is paraformaldehyde alone.

[0054] As a method of bringing the formaldehyde derivative into contact with the sheet surface in the second step, a known method can be adopted. For example, the sheet after the first step may be immersed in the formaldehyde derivative.

[0055] When bringing the formaldehyde derivative into contact with the surface of the sheet after the first step, a nucleophilic addition reaction occurs in which the radical or anion generated by the reaction of formula (4) acts as a nucleophile. In this reaction, since the same results are obtained regardless of which formaldehyde derivative is used as when using formaldehyde, the case of using formaldehyde will be described as an example below.

[0056] When the above nucleophile undergoes nucleophilic addition to formaldehyde, an alkoxide anion is generated. This alkoxide anion is promptly protonated, ultimately yielding a compound in which a hydroxymethyl group is added to the polymer main chain. Thus, after the first step, the fluororesin reacts with the formaldehyde derivative, and a hydroxymethyl group is introduced into the fluororesin (Formula (5)).

Chemical formula

[0057] The time for contacting the formaldehyde derivative with the surface of the sheet after the first step (the second reaction time) is not particularly limited, and can be, for example, 10 seconds or more and 30 minutes or less. When the second reaction time is 10 seconds or more, the reaction of Formula (5) easily proceeds sufficiently. Also, when the second reaction time is 30 minutes or less, it is preferable in terms of productivity. The second reaction time is more preferably 30 seconds or more, and even more preferably 1 minute or more. Also, the second reaction time is more preferably 20 minutes or less, and even more preferably 10 minutes or less. Note that making the reaction time of the second step longer than the reaction time of the first step is preferable in terms of ensuring the progress of the reaction.

[0058] The temperature when contacting the formaldehyde derivative with the surface of the sheet after the first step (the second reaction temperature) is not particularly limited, and can be, for example, -20°C or more and 30°C or less. When the second reaction temperature is -25°C or more, it is preferable in terms of cooling efficiency. Also, when the second reaction temperature is 30°C or less, it is preferable in terms of productivity. The second reaction temperature is more preferably 0°C or more, and even more preferably 10°C or more. Also, the second reaction temperature is more preferably 25°C or less, and even more preferably 20°C or less.

[0059] The surface of the modified sheet that has undergone the first and second steps contains at least partially the structure of Formula (6).

Chemical formula

[0060] The hydroxymethyl group generated by the reaction of formula (5) can form a coordination bond, a hydrogen bond, or both with a mating material such as a metal, and thus becomes a factor that exhibits high adhesiveness to these mating materials. Therefore, when the surface of the modified sheet contains the structure of formula (6), the surface has adhesiveness. In this way, adhesiveness can be imparted to a fluororesin that does not have adhesiveness in the unmodified state through the first step and the second step.

[0061] 〔Configuration of Modified Sheet〕 Next, the configuration of the modified sheet (which is an embodiment of the molded body according to the present invention) obtained by the above-described modification method will be described. The modified sheet according to the present embodiment is a sheet made of a fluororesin, and a functional group derived from a formaldehyde derivative is introduced into the fluororesin constituting the surface thereof. The thickness of the modified sheet is the same as the thickness of the unmodified sheet used as the starting material, and can be, for example, 10 μm or more and 2000 μm or less.

[0062] Regarding the elemental composition on the surface of the modified sheet according to the present embodiment, which is specified by X-ray photoelectron spectroscopy with carbon, oxygen, and fluorine as detection targets, the total content of carbon and oxygen is 100 atomic% or less, and the content of carbon is 60 atomic% or more and 75 atomic% or less, and the content of oxygen is 25 atomic% or more and 35 atomic% or less. In addition, as the remainder other than carbon and oxygen, fluorine derived from the unmodified fluororesin, sodium derived from SD, etc. may be present. The oxygen content on the surface of the modified sheet is higher than the normal oxygen content in the unmodified fluororesin. This is due to the substitution of fluorine atoms with hydroxymethyl groups by the reactions of formula (4) and formula (5). Here, only the contents of carbon and oxygen are mentioned, but these contents are specified by X-ray photoelectron spectroscopy with carbon, oxygen, and fluorine as detection targets as described above, and are not specified by measurements targeting only carbon and oxygen. Also, regarding the content of each element described below, unless otherwise noted, it is specified by X-ray photoelectron spectroscopy with carbon, oxygen, and fluorine as detection targets.

[0063] The measurement of the elemental composition of the surface of the modified sheet by X-ray photoelectron spectroscopy can be carried out, for example, using a scanning X-ray photoelectron spectrometer PHI5000 VersaProbeII manufactured by ULVAC-PHI, Inc., equipped with an argon gas cluster ion gun (Ar + , 10 keV, cluster size 2500 atoms, raster range 3 mm × 3 mm), with AlKα line 1486.6 eV as the X-ray source. Further, as an example, the measurement conditions are such that the capture solid angle is ±20° and the extraction angle is 90°. Note that detecting carbon, oxygen, and fluorine can be achieved by narrow scan analysis in which the binding energy region where peaks attributed to these elements appear is the measurement target.

[0064] That the oxygen content on the surface of the modified sheet is 25 atomic % or more means that the modification on the surface of the modified sheet is sufficient, and at this time, a modified sheet that is easily adherent to a mating material such as a metal can be obtained. Also, that the oxygen content on the surface of the modified sheet is 35 atomic % or less means that the modification is appropriately carried out, and at this time, a modified sheet in which properties such as the electrical properties and heat resistance of the unmodified fluororesin are likely to be exhibited can be obtained. The oxygen content on the surface of the modified sheet is preferably 27 atomic % or more, more preferably 30 atomic % or more. Also, the oxygen content on the surface of the modified sheet is preferably 33 atomic % or less.

[0065] When the fluorine content on the surface of the modified sheet is 5 atomic % or less, it can be said that the modification on the surface of the modified sheet is sufficient. In this case, since a modified sheet that is easily adherent to a mating material such as a metal can be obtained, it is preferable. Note that the fluorine content on the surface of the modified sheet is not particularly limited and may be 0 atomic % or more (above the detection limit). The fluorine content on the surface of the modified sheet is more preferably 5 atomic % or less, and even more preferably 3 atomic % or less.

[0066] The sodium detected on the surface of the modified sheet is due to the SD used in the modification process. The upper limit of the sodium content can be, for example, 10 atomic %. Note that sodium may not remain (even below the detection limit).

[0067] The modified sheet according to the present embodiment has an oxygen content at a position 200 nm deep from the surface (hereinafter referred to as the "predetermined depth") specified by X-ray photoelectron spectroscopy for which carbon, oxygen, and fluorine are detection targets, of 0 atomic % or more and 12 atomic % or less. The fact that the oxygen content at the predetermined depth is 12 atomic % or less indirectly means that excessive modification has not been performed, and a sheet in which performance such as electrical characteristics and heat resistance of the unmodified fluororesin is likely to be exhibited can be obtained. The oxygen content at the predetermined depth is preferably 12 atomic % or less, more preferably 10 atomic % or less. Also, the oxygen content at the predetermined depth is preferably 2 atomic % or more, more preferably 5 atomic % or more.

[0068] The elemental composition at a position at a predetermined depth from the surface of the modified sheet can be carried out by adjusting the combination of the output and the sputter time when measuring the elemental composition by X-ray photoelectron spectroscopy. For example, the elemental composition at a position 200 nm deep from the surface can be measured under the same measurement conditions as those for specifying the elemental composition on the surface of the modified sheet, except that the sputter time is changed to 6 minutes. The basis for being able to measure the elemental composition at a position 200 nm deep from the surface by setting the sputter time to 6 minutes is that the theoretical sputter rate of polystyrene is 33.75 nm per minute, and multiplying this by 6 minutes and rounding to one significant figure gives 200 nm (2×10 2 nm).

[0069] The modified sheet according to this embodiment preferably has a fluorine content at a predetermined depth, specified by X-ray photoelectron spectroscopy with carbon, oxygen, and fluorine as detection targets, of 40 atomic % or more and 67 atomic % or less. That the fluorine content at the predetermined depth is 40 atomic % or more directly means that excessive modification has not been performed, and a modified sheet can be obtained in which the performance such as the electrical characteristics and heat resistance of the unmodified fluororesin is more likely to be exhibited. More preferably, the fluorine content at the predetermined depth is 60 atomic % or less, and even more preferably 55 atomic % or less. Also, more preferably, the fluorine content at the predetermined depth is 45 atomic % or more, and even more preferably 48 atomic % or more.

[0070] The modified sheet according to this embodiment preferably has a carbon content at a predetermined depth, specified by X-ray photoelectron spectroscopy with carbon, oxygen, and fluorine as detection targets, of 30 atomic % or more and 60 atomic % or less.

[0071] 〔Configuration of Circuit Board〕 Subsequently, the configuration of the circuit board according to this embodiment will be described. In the circuit board according to this embodiment, copper wiring is formed on the surface of the above-described modified sheet.

[0072] The circuit board according to this embodiment can be manufactured by a method known in the art, except that the above-described modified sheet is used as a material. That is, a material obtained by applying copper plating to the surface of the modified sheet may be used as a raw material, and a conventional method related to the manufacture of the circuit board may be applied.

[0073] As described above, a functional group derived from a formaldehyde derivative is introduced on the surface of the modified sheet, and the hydroxymethyl group of the functional group acts on copper atoms, thereby exhibiting good adhesiveness to copper. Since a fluororesin is a material that is difficult to adhere to other materials containing metal, it has been conventionally difficult to apply copper plating to a fluororesin. However, for a modified sheet obtained by applying the above-described modification method, copper plating can be applied with practically sufficient strength.

[0074] In the modified sheet obtained by applying the above modification method, only the surface portion contributing to adhesiveness is minimally modified, so the good high-frequency characteristics (low dielectric constant and low dielectric tangent) inherent in the fluororesin are maintained at a high level. Therefore, when a circuit board manufactured using the modified sheet as a material is used in a high-frequency device, high-speed and low-loss communication can be realized.

[0075] 〔Other Embodiments〕 Regarding other configurations as well, it should be understood that all the embodiments disclosed in this specification are illustrative in all respects, and the scope of the present invention is not limited thereby. Those skilled in the art will easily understand that appropriate modifications can be made without departing from the spirit of the present invention. Therefore, other embodiments modified without departing from the spirit of the present invention are naturally included in the scope of the present invention.

Examples

[0076] Hereinafter, the present invention will be further described with reference to examples. However, the following examples do not limit the present invention.

[0077] 〔Test 1: Elemental Composition at the Surface and a Predetermined Depth〕 For the modified sheets prepared under the conditions shown below, the elemental composition at the surface and a predetermined depth (a position 200 nm deep from the surface) was measured.

[0078] (Sample) As the untreated sheet, a sheet made of PTFE with a width of 210 mm, a length of 297 mm, and a thickness of 1 mm was used. As the SD, a sodium dispersion with an average particle diameter of sodium of 10 μm or less and a sodium content of 25 to 26% by mass was used. As the formaldehyde derivative, paraformaldehyde added in a THF solvent was used.

[0079] (Example) According to the procedure shown in the above embodiment, a modified sheet was prepared using an electron donor (Na:DMI = 1:6) containing SD and DMI. Both the first step and the second step were carried out at room temperature, with the first reaction time being 1 minute and the second reaction time being 10 minutes. In the obtained modified sheet, when the measured values of the elemental composition on the surface were measured with carbon, fluorine, oxygen, nitrogen, and sodium as the detection targets, they were 67.7 atomic% carbon, 0.8 atomic% fluorine, 22.4 atomic% oxygen, 5.0 atomic% nitrogen, and 4.0 atomic% sodium. On the other hand, the measured values of the elemental composition at a position 200 nm deep from the surface were 41.2 atomic% carbon, 49.3 atomic% fluorine, 5.0 atomic% oxygen, 0.7 atomic% nitrogen, and 3.7 atomic% sodium. When calculated by limiting it to the three elements of carbon, fluorine, and oxygen, the elemental composition on the surface was 72.7 atomic% carbon, 1.1 atomic% fluorine, and 26.2 atomic% oxygen, and the elemental composition at a position 200 nm deep from the surface was 42.2 atomic% carbon, 52.8 atomic% fluorine, and 5.0 atomic% oxygen. The preparation conditions and the measurement conditions of the elemental composition not specifically mentioned were the same as those in the above embodiment.

[0080] (Comparative Example) As a comparative example, a commercially available modified sheet was used. The modified sheet of the comparative example was obtained by contacting the surface of the unmodified sheet with a solution containing sodium and naphthalene and then washing the surface with water. In the modified sheet of the comparative example, when calculated by limiting the elemental composition on the surface to the three elements of carbon, fluorine, and oxygen, it was 72.0 atomic% carbon, 5.1 atomic% fluorine, and 22.9 atomic% oxygen. Also, the elemental composition at a position 200 nm deep from the surface was 64.5 atomic% carbon, 19.0 atomic% fluorine, and 16.5 atomic% oxygen.

[0081] [Test 2: Measurement of Adhesion Strength] After copper plating was performed on the modified sheets of each of the examples and comparative examples under the same conditions, the adhesion strength between the modified sheet and copper was measured in accordance with JIS C 6481, except that the width of the sample was set to 5 mm. The adhesion strength of the modified sheet of the example was 0.64 N / mm, and the adhesion strength of the modified sheet of the comparative example was 0.15 N / mm. According to the modification method of the example, it was shown that good adhesiveness to copper can be imparted to the fluororesin.

Industrial Applicability

[0082] The present invention can be used, for example, for a circuit board for a high-frequency device.

Claims

1. A molded article made of perfluororesin, Regarding the elemental composition of the surface as determined by X-ray photoelectron spectroscopy detecting carbon, oxygen, and fluorine, the carbon content is 60 atomic % or more and 75 atomic % or less, and the oxygen content is 25 atomic % or more and 35 atomic % or less, with the total content of carbon and oxygen being 100 atomic % or less; A molded article having an oxygen content of 0 atomic % or more and 12 atomic % or less at a position 200 nm deep from the surface, as determined by X-ray photoelectron spectroscopy detecting carbon, oxygen, and fluorine.

2. 2. The molded article according to claim 1, wherein the fluorine content at a position 200 nm deep from the surface, as determined by X-ray photoelectron spectroscopy detecting carbon, oxygen, and fluorine, is 40 atomic % or more and 67 atomic % or less.

3. 3. The molded article according to claim 1, wherein the perfluororesin contains 95 mol % or more of tetrafluoroethylene units.

4. A circuit board including a molded body made of perfluororesin, The elemental composition on the surface of the molded body, as determined by X-ray photoelectron spectroscopy detecting carbon, oxygen, and fluorine, is such that the carbon content is 60 atomic % or more and 75 atomic % or less, and the oxygen content is 25 atomic % or more and 35 atomic % or less, with the total content of carbon and oxygen being 100 atomic % or less; A circuit board in which the oxygen content at a position 200 nm deep from the surface of the molded body, as determined by X-ray photoelectron spectroscopy detecting carbon, oxygen, and fluorine, is 0 atomic % or more and 12 atomic % or less.

5. A method for modifying a surface of a fluororesin molded body, comprising the steps of: a first step of contacting an electron donor with a surface of the molded body; A second step of contacting a formaldehyde derivative with the surface of the molded body after the first step, The method for modifying a substrate, wherein the electron donor comprises a dispersion in which metallic sodium is dispersed in a solvent, and at least one compound selected from the group consisting of 1,3-dialkyl-2-imidazolidinone and crown ether.

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