Method for inspecting joint portion of fluororesin member and method for inspecting fluororesin member

Abstract

The present application provides a new inspection method capable of non-destructive inspection of the internal state of the joint of a fluororesin member. An inspection method for the joint of a fluororesin member, comprising a step (A1) of inspecting the internal state of the joint of a fluororesin member (A1) and a fluororesin member (A2) based on image data obtained by photographing the joint using optical coherence tomography.

Description

Technical Field

[0001] The present invention relates to a method for inspecting a joint portion of a fluororesin member and a method for inspecting a fluororesin member. Background Art

[0002] Fluororesin has excellent heat resistance, abrasion resistance, and chemical resistance, and is widely used in molded products as a representative engineering plastic.

[0003] Patent Document 1 describes a specific method for inspecting an object to be inspected made of fluororesin using ultrasonic waves.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-145559 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] An object of the present invention is to provide a new inspection method capable of non-destructively inspecting the internal state of a joint portion of a fluororesin member or the internal state of a fluororesin member.

[0009] Means for solving problems

[0010] The present invention relates to a method for inspecting a joint of a fluororesin component, comprising a step (A1) of inspecting the internal state of the joint between a fluororesin component (A1) and a fluororesin component (A2) based on image data obtained by photographing the joint using optical coherence tomography.

[0011] It is preferable that at least one of the fluororesin members (A1) and (A2) is a sheet containing a fluororesin.

[0012] It is also preferred that at least one of the fluororesin members (A1) and (A2) is a laminate comprising a sheet containing a fluororesin and a heat-resistant fiber layer.

[0013] The present invention also relates to a method for inspecting a fluororesin member, comprising a step (B1) of inspecting the internal state of the fluororesin member (B1) based on image data obtained by photographing the fluororesin member (B1) using optical coherence tomography.

[0014] The fluororesin member (B1) is preferably a sheet containing a fluororesin.

[0015] The fluororesin member (B1) is preferably a laminate comprising a sheet containing a fluororesin and a heat-resistant fiber layer.

[0016] Effects of the Invention

[0017] According to the present invention, a new inspection method capable of non-destructively inspecting the internal state of a joint portion of a fluororesin member or the internal state of a fluororesin member can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram showing an example of a joining method of fluororesin members.

[0019] Figure 2 This is a schematic diagram showing another example of the joining method of fluororesin members.

[0020] Figure 3 Schematic diagram showing an example of an optical coherence tomography (OCT) apparatus that can be used in the inspection method of the present invention.

[0021] Figure 4 This is an enlarged view showing an example of how a sample is arranged obliquely in an OCT apparatus that can be used in the inspection method of the present invention.

[0022] Figure 5 3 is a diagram showing OCT images obtained in Example 1.

[0023] Figure 6 This is a diagram showing OCT images obtained in Example 2.

[0024] Figure 7 This is a diagram showing OCT images obtained in Example 3.

[0025] Figure 8 This is a diagram showing OCT images obtained in Example 4. DETAILED DESCRIPTION

[0026] The present invention is described in detail below.

[0027] The present invention relates to a method for inspecting a joint of a fluororesin component (hereinafter also referred to as a first inspection method), comprising a step (A1) of inspecting the internal state of a joint between a fluororesin component (A1) and a fluororesin component (A2) based on image data obtained by photographing the joint using optical coherence tomography (OCT).

[0028] According to the first inspection method, the internal state of the joint portion of the fluororesin member can be non-destructively inspected, and thus a full inspection can be performed. Therefore, the quality reliability of the joint body including the joint portion can be improved.

[0029] Furthermore, since precise analysis can be performed based on the image data obtained, it is possible to detect minute internal defects, quantify the state of the bonded interface, and accurately understand the internal state of the bonded portion. This allows for the establishment of objective indicators for determining the quality of the bonded portion, thereby stabilizing the quality of the bonded product.

[0030] Furthermore, because OCT-based imaging can be performed at high speed, the inspection method can be easily introduced at construction sites where fluororesin components are joined. This allows for improved and stabilized quality of the joined components without significantly increasing the number of steps required at the construction site.

[0031] In step (A1), the joint between the fluororesin member (A1) and the fluororesin member (A2) is inspected. The joint may be a joint between the fluororesin member (A1) and the fluororesin member (A2) in a joined body formed by joining the fluororesin member (A1) and the fluororesin member (A2).

[0032] Here, joining means being joined to such an extent that they cannot be separated without mechanical cutting, or a state in which they are joined in this manner.

[0033] The shapes, dimensions, etc. of the fluororesin members (A1) and (A2) may be the same or different.

[0034] The fluororesin members (A1) and (A2) may be separate members or may be located at different locations in the same member.

[0035] The number of fluororesin members (A1) and (A2) is not particularly limited, and may be one or two or more.

[0036] The fluororesin members (A1) and (A2) are members containing a fluororesin.

[0037] The fluororesin members (A1) and (A2) preferably contain fluororesins different from each other.

[0038] Internal defects such as interlayer delamination and cracks are likely to occur at the interfaces between different fluororesins.

[0039] According to the first inspection method, the presence or absence of such internal defects can be inspected.

[0040] Fluororesin members (A1) and (A2) may be molded articles or joined members. Alternatively, one of fluororesin members (A1) and (A2) may be a molded article and the other a joined member. A joined member is a member used to join two or more other members.

[0041] It is one preferred embodiment that at least one of the fluororesin members (A1) and (A2) is a sheet containing a fluororesin, and it is also one preferred embodiment that both are such sheets.

[0042] It is also a preferred embodiment that at least one of the fluororesin members (A1) and (A2) is a laminate comprising a sheet containing a fluororesin and a heat-resistant fiber layer, and it is also a preferred embodiment that both are such laminates.

[0043] The fluororesins constituting the fluororesin members (A1) and (A2), the molded article, the joining member, the sheet, and the laminate are as follows.

[0044] When the fluororesin members (A1) and (A2) are in sheet form, they may be joined in the thickness direction or in the surface direction (direction perpendicular to the thickness direction).

[0045] The fluororesin member (A1) and the fluororesin member (A2) are preferably welded at the joining portion.

[0046] Examples of the joining method of the fluororesin members (A1) and (A2) will be described with reference to the drawings, but the joining method in the present invention is not limited to these examples.

[0047] Figure 1 In the embodiment shown, a sheet 1 containing fluororesin and a sheet 2 containing fluororesin are joined in the thickness direction.

[0048] In this embodiment, for example, the sheet 1 corresponds to the fluororesin member (A1), and the sheet 2 corresponds to the fluororesin member (A2).

[0049] Figure 2 In the embodiment shown in (a), the sheet 3 made of fluororesin is joined to the joining member 5 made of fluororesin, and the joining member 5 is further joined to the sheet 4 made of fluororesin. In other words, the sheet 3 and the sheet 4 are joined in the plane direction via the joining member 5.

[0050] Figure 2 In the embodiment shown in (b), a laminate 6 comprising a sheet 6a containing a fluororesin and a heat-resistant fiber layer 6b is joined to a joining member 5 containing a fluororesin, and the joining member 5 is further joined to a laminate 7 comprising a sheet 7a containing a fluororesin and a heat-resistant fiber layer 7b. In other words, the laminates 6 and 7 are joined in the plane direction via the joining member 5.

[0051] In these embodiments, for example, the sheet 3 , the sheet 4 , the laminate 6 , and the laminate 7 correspond to the fluororesin member ( A1 ), and the joining member 5 corresponds to the fluororesin member ( A2 ).

[0052] The method of joining is not particularly limited, and a conventionally known method can be employed.

[0053] For example, the following method can be mentioned: fluororesin members (A1) and (A2) are superimposed, pressurized as needed, and heated to a temperature not lower than the melting point of the fluororesin constituting at least one of the fluororesin members (A1) and (A2). Figure 1 Appropriately adopt the method shown.

[0054] Another method is to butt-join two or more fluororesin members (A1), arrange a fluororesin member (A2) as a joining member therebetween, apply pressure as needed, and heat to a temperature above the melting point of the fluororesin constituting at least one of the fluororesin members (A1) and (A2). In this method, the fluororesin member (A1) is joined to the fluororesin member (A2) (two or more fluororesin members (A1) are joined via the fluororesin member (A2). This method can be performed, for example, Figure 2 Appropriately adopt the method shown.

[0055] In the above method, at least one of the fluororesin members (A1) may be provided with an inclination (groove) at a portion to be joined.

[0056] In the above embodiment, two or more fluororesin members (A1) are preferably welded via the fluororesin member (A2).

[0057] The inspection in step (A1) is performed based on image data obtained by photographing the bonded portion using OCT. The first inspection method may include the step of photographing the bonded portion using OCT to obtain image data based on the bonded portion.

[0058] OCT is classified into time domain OCT (TD-OCT) and Fourier domain OCT (FD-OCT), and FD-OCT is further classified into spectral domain OCT (SD-OCT) and swept source OCT (SS-OCT).

[0059] In step (A1), any OCT can be used, but SS-OCT is preferred from the viewpoint of high sensitivity and deep measurable depth.

[0060] Examples of the light used in OCT include visible light and infrared light, and near infrared light (NIR) is preferred.

[0061] When inspecting fluororesin components primarily composed of C—F bonds and C—C bonds, near-infrared light can often be used over the entire wavelength range. In cases where the crystal size is small, light with wavelengths in the long-wavelength range of the visible region (600 nm or longer) and the short-wavelength range of the infrared region (5000 nm or less) can also be used.

[0062] Due to the availability of compatible OCT devices, light with a wavelength of 800 to 2000 nm is preferred. Among these, light with a center wavelength of 940 ± 50 nm, 1100 ± 50 nm, 1320 ± 50 nm, and 1750 ± 100 nm is more preferred due to the stability of the light source and the reliability of the sensor.

[0063] Reference Figure 3 An example of an imaging method using an OCT device will be described.

[0064] In the OCT device 10, the light emitted from the light source 11 is separated into two by the spectroscope 12. One light is reflected by the reference mirror 13 and then enters the light detector 14 as a reference light. The other light is incident on the sample (joint) 15, penetrates to a certain depth, and is reflected by the surface of the sample 15 or the internal defect parts such as cracks and interlayer delamination. The reflected light from the sample 15 passes through the spectroscope 12 and enters the light detector 14 as signal light. The light detector 14 detects the interference light generated by the interference of the above-mentioned reference light and the above-mentioned signal light, converts it into a signal and outputs it. The output signal is imaged according to characteristics such as intensity, thereby obtaining an image representing the structure of the sample 15.

[0065] It should be noted that the OCT device and photographing method that can be used in the inspection method of the present invention are not limited to the above.

[0066] In the OCT imaging, the incident angle α of the light from the light source of the OCT device relative to the joint is preferably 3 to 30 degrees. The incident angle α is more preferably 5 degrees or greater, and even more preferably 7 degrees or greater. Furthermore, it is more preferably 30 degrees or less, even more preferably 20 degrees or less, even more preferably 15 degrees or less, and particularly preferably 10 degrees or less.

[0067] By setting the incident angle α within the above range, noise in the image can be reduced, and a signal based on a defect in the joint portion can be made clear.

[0068] The above effect is significant when the near-infrared transmittance of the above-mentioned joint is high, or when the surface of the above-mentioned joint that is the inspection object (the surface on the OCT light source side) and the back surface (the surface opposite to the above-mentioned surface) are parallel.

[0069] The incident angle α is defined as the angle formed by the incident direction of the light and a perpendicular line relative to the surface of the bonding portion. The surface may be a surface on the OCT light source side.

[0070] Figure 4 An example of a method of arranging the sample with an inclination is shown. Figure 4 In the example, the light is incident on the sample 15 at an incident angle α.

[0071] The incident angle α can be adjusted, for example, by adjusting the inclination of a sample stage on which the inspection object serving as a sample is placed.

[0072] When there are two or more parts to be inspected on a single inspection object, multiple OCT optical systems can be prepared to measure the inspection objects simultaneously or sequentially. In this case, even if the slopes of the various parts of the inspection object are different, the angles of incidence α and β can be adjusted within the preferred ranges described above, making this a preferred method. Even when the measurement sites are separated, there is no need to change the specifications of the OCT device, making this a preferred method. Furthermore, even when there are large height differences between the parts of the inspection object, the angles of incidence α and β can be adjusted accordingly for each part, making this a preferred method.

[0073] In the OCT imaging, the intensity of the light incident on the joint is preferably 1 mW to 18 mW. It is more preferably 5 mW or greater, and even more preferably 10 mW or greater. It is more preferably 15 mW or less, and even more preferably 12 mW or less.

[0074] By setting the intensity of the light within the above range, noise in the image can be reduced, and a signal based on a defect in the joint portion can be made clear.

[0075] The above effect is remarkable when the near-infrared transmittance of the bonding portion is high or when the front surface and the back surface of the bonding portion are parallel.

[0076] In this specification, the intensity of the light incident on the joint portion is the intensity of the light at the probe end of the OCT device.

[0077] If the portion of the sample to be measured is close to the sample stage, light that has passed through the sample may be reflected by the sample stage and become a noise source. Therefore, it is preferable to take measures to prevent light that has passed through the sample from affecting the measurement.

[0078] For example, an object reflecting light that has passed through the sample can be placed at least 10 mm away from the portion of the sample to be measured. In this case, it is preferable to support the sample at portions not to be measured (e.g., the ends of the sample) so that the portion to be measured does not overlap with the sample stage.

[0079] Another example is to reflect the light that has passed through the sample in the direction opposite to the probe.

[0080] Another example is placing an object that absorbs or scatters most of the light that has passed through the sample at a position where the light is irradiated.

[0081] The above-mentioned methods can be used in combination as appropriate.

[0082] In step (A1), the internal state of the bonding portion is inspected based on the image data.

[0083] The above-mentioned inspection may be performed using an image obtained from the above-mentioned image data, may be performed by processing the above-mentioned image data, or may be performed by combining the two.

[0084] In step (A1), it is preferred to inspect the interface state between the fluororesin member (A1) and the fluororesin member (A2) inside the joint.

[0085] In addition, when one of the fluororesin components (A1) and (A2) is the above-mentioned laminate and the other is the above-mentioned joining component, the state of the interface between the above-mentioned fluororesin-containing sheet and the above-mentioned joining component, the interface between the above-mentioned heat-resistant fiber layer and the above-mentioned joining component, and the state of the interface between the above-mentioned fluororesin-containing sheet and the above-mentioned heat-resistant fiber layer can also be inspected.

[0086] Furthermore, a compatible layer of the fluororesin members (A1) and (A2) may be formed at the interface between the fluororesin members (A1) and (A2), and the presence and thickness of the compatible layer may be confirmed in the above-mentioned inspection.

[0087] In addition, when at least one of the fluororesin components (A1) and (A2) is the above-mentioned laminate, as described below, a fired layer and an unfired layer may be formed in the above-mentioned sheet containing fluororesin. In the above-mentioned inspection, the presence and thickness of the above-mentioned fired layer and the above-mentioned unfired layer may also be confirmed.

[0088] In addition, when the laminate further includes a heat-melting resin layer described later, the presence or absence and thickness of the layer formed by impregnation of the heat-resistant fibers with the heat-melting resin may be checked.

[0089] The inspection is preferably an inspection for internal defects of the joint.

[0090] Examples of such defects include cracks, delamination, voids, and foreign matter. Furthermore, the absence of a layer that should be present or the lack of a required thickness are also examples of such defects. These defects can be caused by poor joining (welding) or poor molding.

[0091] Modification or voids at the interface of dissimilar materials are likely to occur in the above-mentioned joint, and the above-mentioned defects are likely to occur.

[0092] In the above inspection, it is preferable to determine whether the above defects exist.

[0093] Step (A1) is preferably a step of inspecting the joint portion for internal defects based on the image data, and more preferably a step of inspecting the joint portion for internal cracks and interlayer delamination based on the image data.

[0094] The inspection is performed based on a signal caused by an internal defect of the joint in the image data. In addition, it is preferable to determine whether the defect exists based on the signal caused by the defect.

[0095] As a method for determining whether the above-mentioned defects exist, for example, the following method can be cited: when no signal caused by any of the above-mentioned defects is confirmed in the image obtained by OCT, it is determined that there is no defect; when a signal caused by at least one of the above-mentioned defects is confirmed in the above-mentioned image, it is determined that there is a defect.

[0096] If a defect is detected during the above inspection, the size, shape, orientation, and frequency of occurrence of the defect can be further analyzed. This analysis can easily determine whether the defect is sufficiently severe to degrade the bonding state of the joint. This analysis can be performed, for example, by processing signals generated by the defect.

[0097] The inspection method of the present invention may further include a step (A2) of determining whether the joining state of the fluororesin members (A1) and (A2) in the joining portion is good or not based on the inspection result of the step (A1).

[0098] Step (A2) may be, for example, a step of determining that the bonding state is good when it is determined that there is no defect in step (A1), and determining that the bonding state is poor when it is determined that there is a defect in step (A1).

[0099] Process (A2) can also be the following process: when it is judged that there is no defect in process (A1), and when the degree of defect in the case of being judged to have a defect in process (A1) is below the prescribed standard, it is judged that the bonding state is good; when the degree of defect in the case of being judged to have a defect in process (A1) exceeds the prescribed standard, it is judged that the bonding state is poor.

[0100] The criteria for the degree of defects are not particularly limited and may be appropriately determined based on the required characteristics of the bonded body having the bonded portion. For example, the correlation between the size, shape, orientation, and frequency of defects in the bonded body and the pass / fail data obtained when the bonded body having the bonded portion is subjected to practical testing may be obtained in advance. The permissible range of the size, shape, orientation, and frequency of defects that does not result in a defective bonded state may be determined experimentally, and the criteria may be determined accordingly.

[0101] Next, the fluororesin members (A1) and (A2) used in the first inspection method will be described.

[0102] The fluororesin members (A1) and (A2) contain a fluororesin.

[0103] In this specification, fluororesin is a partially crystalline fluorine-containing polymer, also known as a fluoroplastic. Fluororesin has a melting point, is thermoplastic, and can be either melt-processable or non-melt-processable.

[0104] In this specification, melt-processability refers to the ability to melt and process a polymer using existing processing equipment such as extruders and injection molding machines. Therefore, melt-processable fluororesins typically have a melt flow rate of 0.01 to 100 g / 10 minutes, as measured at a temperature above the crystallization melting point according to ASTM D-1238 and D-2116.

[0105] As used herein, "non-melt-processability" refers to the inability to melt-process a polymer using existing processing equipment such as extruders and injection molding machines. More specifically, "non-melt-processability" refers to the inability to measure the melt flow rate at a temperature above the crystallization melting point according to ASTM D-1238 and D-2116.

[0106] In one preferred embodiment, at least one of the fluororesin members (A1) and (A2) is a molded article containing a fluororesin.

[0107] The melting point of the fluororesin constituting the molded article is preferably 100 to 360°C, more preferably 140 to 350°C, further preferably 160 to 350°C, and particularly preferably 180 to 350°C.

[0108] In the present specification, the melting point of the above-mentioned fluororesin is the temperature corresponding to the maximum value in the heat of fusion curve when the temperature is raised at a rate of 10°C / minute using a differential scanning calorimeter [DSC].

[0109] As the fluororesin which can be used in the above-mentioned molded article, polytetrafluoroethylene [PTFE], tetrafluoroethylene [TFE] / perfluoro(alkyl vinyl ether) [PAVE] copolymer [PFA], TFE / hexafluoropropylene [HFP] copolymer [FEP], ethylene [Et] / TFE copolymer [ETFE], TFE / vinylidene fluoride [VDF] copolymer, Et / TFE / HFP copolymer, polychlorotrifluoroethylene [PCTFE], chlorotrifluoroethylene [CTFE] / TFE copolymer, Et / CTFE copolymer, polyvinylidene fluoride [PVDF], polyvinyl fluoride [PVF], and the like can be given.

[0110] As the fluororesin which constitutes the above-mentioned molded article, at least one selected from the group consisting of PTFE and PFA is preferable, and PTFE is more preferable.

[0111] The above-mentioned PTFE can be a homopolymer PTFE which contains only TFE units, or can be a modified PTFE which contains TFE units and modified monomer units based on a modified monomer which can be copolymerized with TFE, and a modified PTFE is preferable. In addition, the above-mentioned PTFE is preferably a high molecular weight PTFE which has non-melt processability and fibrillation property.

[0112] As the above-mentioned modified monomer, there is no particular limitation as long as it can be copolymerized with TFE, and, for example, perfluoroolefins such as hexafluoropropylene [HFP]; fluorochloroolefins such as chlorotrifluoroethylene [CTFE]; hydrofluoroolefins such as trifluoroethylene, vinylidene fluoride [VDF]; perfluorovinyl ethers; perfluoroalkyl ethylenes; ethylene; fluorine-containing vinyl ethers having a nitrile group; and the like can be given. In addition, the modified monomer used can be one kind, or two or more kinds.

[0113] As the above-mentioned perfluorovinyl ether, there is no particular limitation, and, for example, perfluoro unsaturated compounds represented by the following general formula (1)

[0114] CF2=CF-ORf 1 (1)

[0115] (In the formula, Rf 1 represents a perfluoro organic group) can be given. In the present specification, the above-mentioned "perfluoro organic group" means an organic group in which all of the hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. The above-mentioned perfluoro organic group can have an ether oxygen.

[0116] As the above-mentioned perfluorovinyl ether, for example, perfluorovinyl ethers represented by Rf 1Perfluoro(alkyl vinyl ether) [PAVE] represents a perfluoroalkyl group having 1 to 10 carbon atoms. The perfluoroalkyl group preferably has 1 to 5 carbon atoms.

[0117] Examples of the perfluoroalkyl group in PAVE include perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, and perfluorohexyl. Perfluoropropyl vinyl ether [PPVE] in which the perfluoroalkyl group is perfluoropropyl is preferred.

[0118] Examples of the perfluorovinyl ethers include Rf in the general formula (1): 1 A substance which is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, Rf 1 is the following formula:

[0119] [Chemistry 1]

[0120]

[0121] (wherein m represents 0 or an integer of 1 to 4) and Rf 1 is the following formula:

[0122] [Chemistry 2]

[0123]

[0124] (wherein n represents an integer of 1 to 4) and the like.

[0125] The perfluoroalkylethylene is not particularly limited, and examples thereof include perfluorobutylethylene [PFBE] and perfluorohexylethylene.

[0126] As the fluorine-containing vinyl ether having a nitrile group, CF2=CFORf is more preferred. 2 CN (where Rf 2 represents an alkylene group having 2 to 7 carbon atoms in which an oxygen atom may be inserted between two carbon atoms) a fluorine-containing vinyl ether.

[0127] The modifying monomer in the modified PTFE is preferably at least one selected from the group consisting of PAVE and HFP, and more preferably PAVE.

[0128] In the above-mentioned modified PTFE, the modified monomer unit is preferably in the range of 0.0001 to 1 mass %. As the lower limit of the content of the modified monomer unit, it is more preferably 0.001 mass %, further preferably 0.01 mass %, and particularly preferably 0.05 mass %. As the upper limit of the content of the modified monomer unit, it is more preferably 0.5 mass %, further preferably 0.3 mass %.

[0129] In this specification, the content of each monomer unit constituting the fluororesin can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis depending on the type of monomer.

[0130] The standard specific gravity (SSG) of the PTFE is preferably 2.140 or more, more preferably greater than 2.150, further preferably 2.160 or more, and is preferably 2.210 or less.

[0131] The standard specific gravity (SSG) can be measured by a water displacement method in accordance with ASTM D 4895-89.

[0132] The melting point of the PTFE is preferably 324-350°C, more preferably 327-347°C. The melting point is the temperature corresponding to the maximum value in the melting curve shown below, where at least one endothermic peak appears in the range of 324-347°C. This melting point is obtained when the temperature of PTFE, which has not been heated to a temperature of 300°C or higher, is increased at a rate of 10°C / minute using a differential scanning calorimeter (DSC).

[0133] Examples of PAVE in the PFA include those represented by the above formula (1), and among these, perfluoro(methyl vinyl ether) [PMVE], perfluoro(ethyl vinyl ether) [PEVE], and perfluoro(propyl vinyl ether) [PPVE] are preferred.

[0134] The above-mentioned PFA is not particularly limited, but preferably the molar ratio of TFE unit to PAVE unit (TFE unit / PAVE unit) is 70 / 30 or more and less than 99.5 / 0.5. A more preferred molar ratio is 70 / 30 or more and 98.9 / 1.1 or less, and a further preferred molar ratio is 80 / 20 or more and 98.5 / 1.5 or less. The above-mentioned PFA may be a copolymer consisting only of TFE and PAVE, and is also preferably a copolymer in which the monomer unit from the monomer capable of copolymerizing with TFE and PAVE is 0.1 to 10 mol%, and the total of TFE unit and PAVE unit is 90 to 99.9 mol%. As monomers capable of copolymerizing with TFE and PAVE, HFP, CZ 1 Z 2 =CZ 3 (CF2)nZ 4 (Where Z 1 , Z 2 and Z 3 are the same or different, representing a hydrogen atom or a fluorine atom, Z 4 represents a hydrogen atom, a fluorine atom or a chlorine atom, and n represents an integer from 2 to 10), and a vinyl monomer represented by CF2=CF-OCH2-Rf 11(Where Rf 11 represents a perfluoroalkyl group having 1 to 5 carbon atoms), and the like.

[0135] The melting point of PFA is preferably 180-340° C., more preferably 230-330° C., and even more preferably 280-320° C. The melting point is the temperature corresponding to the maximum value in the heat of fusion curve when the temperature is increased at a rate of 10° C. / min using a differential scanning calorimeter (DSC).

[0136] The melt flow rate (MFR) of the PFA is preferably 0.1 to 100 g / 10 minutes, more preferably 0.5 to 90 g / 10 minutes, and even more preferably 1.0 to 85 g / 10 minutes.

[0137] The shape of the molded article is not particularly limited, and may be in the form of a film, sheet, block, rod, pipe, tube, belt, wire, or the like, but is preferably in the form of a sheet.

[0138] The molded article is preferably a sheet composed of the fluororesin, more preferably a sheet composed of PTFE.

[0139] The fluororesin-containing sheet is preferably made of PTFE and has an average specific gravity of 2.175 or greater, more preferably greater than 2.175, further preferably 2.178 or greater, and preferably 2.210 or less.

[0140] The average specific gravity herein refers to the specific gravity of the entire fluororesin-containing sheet. When a portion (layer) having a lower specific gravity is formed in the fluororesin-containing sheet by heating, the average specific gravity also refers to the overall specific gravity including the lower specific gravity layer.

[0141] The average specific gravity of the sheet can be measured by a water displacement method. The shape and size of the measurement sample are not particularly limited, and for example, a sample of about 2 cm in length and 2 cm in width cut from the sheet can be measured.

[0142] The above-mentioned sheet composed of PTFE and having an average specific gravity of 2.175 or more is composed of high-crystallinity PTFE, thereby having excellent low-reagent permeability. This high-crystallinity PTFE sheet can be obtained, for example, by the method described in PCT / JP98 / 01116, which comprises compression molding PTFE powder, rotating the resulting PTFE molded article, and then cutting the resulting article into sheets to obtain the high-crystallinity PTFE sheet.

[0143] The thickness of the fluororesin sheet varies depending on the intended use, but is generally 1 to 4 mm, and is approximately 2 to 4 mm when used as a backing sheet.

[0144] The molded article is preferably a laminate comprising the sheet containing the fluororesin and a heat-resistant fiber layer, and more preferably a laminate comprising a sheet containing PTFE and a heat-resistant fiber layer.

[0145] Examples of the heat-resistant fiber constituting the heat-resistant fiber layer include glass fiber, carbon fiber, polyamide-imide fiber, and boron nitride fiber. Among them, glass fiber and carbon fiber are preferred.

[0146] The heat-resistant fiber layer is preferably composed of a knitted fabric of the heat-resistant fibers, and more preferably composed of a woven fabric of the heat-resistant fibers.

[0147] The heat-resistant fiber layer is preferably composed of at least one selected from the group consisting of glass cloth and carbon cloth, and more preferably composed of glass cloth.

[0148] The glass cloth is preferably a woven fabric of glass yarn. The glass yarn may be bulked or unbulked (straight yarn). From the perspective of obtaining a glass cloth having excellent adhesion and flexibility to the fluororesin-containing sheet (and the heat-melting resin layer described later), the glass yarn is preferably bulked.

[0149] Bulking, also known as bulking or texturing, is a process used to increase the volume of fibers. In the case of glass yarn, this is accomplished by feeding the yarn into a high-speed air jet nozzle at a constant draw-out speed and then taking it up at a slower speed to create a turbulent air flow that contacts the yarn, causing it to open and bulk.

[0150] The bulked glass yarn is preferably formed by twisting glass filaments. The average diameter of the glass filaments is preferably 2 to 10 μm, more preferably 4 to 7 μm, and the number of twisted glass filaments is preferably 200 to 6000, more preferably 400 to 2400. For example, the glass yarn may be one of the commonly known nominal diameters (codes) for glass staple fibers, such as D, DE, E, and G.

[0151] The bulked glass yarn may be a single yarn or a plurality of yarns may be twisted together to form a twisted yarn.

[0152] The count (linear weight) of the bulked glass yarn is preferably 30 to 200 tex, more preferably 50 to 100 tex.

[0153] To ensure strong adhesion between the glass cloth and the hot-melt resin layer, the bulkiness of the bulked glass yarn is preferably 101% or greater, more preferably 103% or greater, and even more preferably 105% or greater. The upper limit of the bulkiness is not particularly limited, but is, for example, 200%. To process the glass yarn into a woven fabric, the upper limit of the bulkiness is preferably 150%, more preferably 130%, and even more preferably 120%.

[0154] The bulkiness is a value obtained from the ratio of the count (linear weight) of the glass yarn subjected to bulking to the count (linear weight) of the glass yarn before bulking.

[0155] Here, the count (linear weight) of the bulked glass yarn is the mass of the glass yarn per unit length, and the count (linear weight) of the glass yarn before bulking is determined by the thickness of the glass filaments and the total number of filaments.

[0156] The above-mentioned woven fabric can be a fabric (woven cloth) or a braided fabric, and the above-mentioned glass yarn is woven or braided to produce it. As means for weaving or braiding the above-mentioned glass yarn, for example, means using a well-known loom or braiding machine can be cited. Specifically, means for weaving glass fibers using a jet loom (for example, an air jet loom or a water jet loom), a shuttle loom or a rapier loom can be cited. After the warping process and the sizing process of the glass yarn, as the weaving method (weaving method) of the fabric, for example, plain weave, satin weave, square weave, twill weave, twill weave, leno weave, triaxial weave or horizontal weave can be cited. In addition, as the braiding method (weaving method) of the braided fabric, for example, horizontal weaving such as plain needle weaving, rib weaving or double reverse weaving, vertical weaving such as single comb warp plain weaving, single comb warp velvet weaving, heavy warp weaving, lace mesh weaving, float weaving, terry weaving, etc. can be cited. Knitting can be performed using a known flat knitting machine or vertical knitting machine such as a multi-cam circular knitting machine, a circular knitting machine, or a Corden knitting machine. Among these, a fabric (woven fabric) woven by a diagonal weave is preferred.

[0157] The glass cloth is preferably composed of warp yarns and weft yarns. In the case of using the glass yarn that has been bulked, the glass yarn that has been bulked is preferably used for at least one of the warp yarns and the weft yarns. More preferably, the glass yarn that has been bulked is used for one of the warp yarns and the weft yarns, and the glass yarn that has not been bulked is used for the other. By bringing the exposed surface of the bulked glass yarn into contact with the sheet containing fluororesin of the laminate, the glass cloth is firmly bonded to the sheet containing fluororesin. Furthermore, by using the bulked glass yarn in at least one of the warp yarns and the weft yarns, the glass cloth has better flexibility and is less likely to be damaged when the laminate is bent.

[0158] When the glass cloth is composed of the bulked glass yarn and the unbulked glass yarn, the mass ratio of the bulked glass yarn to the unbulked glass yarn is preferably 100 / 0 to 10 / 90, more preferably 100 / 0 to 40 / 60.

[0159] The thickness of the glass cloth can be selected according to the intended purpose, and may be, for example, 0.03 to 3.0 mm. When used as a backing sheet, it is preferably 0.1 to 0.5 mm.

[0160] The laminate preferably further comprises a heat-fusible resin layer. The heat-fusible resin melts during heat fusion and can be impregnated into the heat-resistant fiber layer. Consequently, the heat-fusible resin layer and the heat-resistant fiber layer are firmly bonded. Furthermore, the heat-fusible resin layer exhibits excellent adhesion to the fluororesin-containing sheet, enabling the fluororesin-containing sheet and the heat-resistant fiber layer to be firmly bonded via the heat-fusible resin layer.

[0161] A film or sheet of a heat-melting resin can be used in the heat-melting resin layer. As the heat-melting resin, any resin capable of heat-melting with the sheet containing the fluororesin can be used. Examples include olefin resins having a melting point close to that of the fluororesin; aromatic resins such as PPS, PES, and PEEK; and heat-melting fluororesins such as TFE-PAVE copolymers (PFA) and TFE-hexafluoropropylene copolymers (FEP). Among these, heat-melting fluororesins are preferred, particularly PFA and FEP, which are preferred for use as backing sheets, with PFA being more preferred.

[0162] The thickness of the heat-meltable resin layer may be appropriately selected depending on the intended purpose. For example, when used as an adhesive layer between the fluororesin-containing sheet and the heat-resistant fiber layer in a backing sheet, the thickness may be approximately 10 to 300 μm.

[0163] The sheet containing fluororesin, the heat-fusible resin layer and the heat-resistant fiber layer are preferably stacked in sequence. In other words, the sheet containing fluororesin and the heat-resistant fiber layer are preferably bonded via the heat-fusible resin layer. The heat-fusible resin layer has excellent adhesion to the sheet containing fluororesin and to the heat-resistant fiber layer. Therefore, by adopting the above-mentioned stacking sequence, a laminate in which the sheet containing fluororesin and the heat-fusible resin layer, as well as the heat-fusible resin layer and the heat-resistant fiber layer are firmly bonded can be obtained. Depending on the purpose, a layer of unfired PTFE particles can be provided between the sheet containing fluororesin and the heat-fusible resin layer. When a layer of unfired PTFE particles is provided, the melting energy (heat of fusion) of the unfired PTFE is preferably less than 65 J / g. Regarding the melting energy (heat of fusion), when the temperature of PTFE without a heating history to a temperature of 300°C or higher is increased at a rate of 10°C / minute using a differential scanning calorimeter [DSC], at least one endothermic peak appears in the range of 324°C to 347°C. This melting energy (heat of fusion) is a melting energy (heat of fusion) of 290°C to 350°C calculated from the melting curve.

[0164] However, if the sheet containing the fluororesin and the heat-resistant fiber layer are sufficiently firmly bonded to each other, there is no problem even if the PTFE fine particle layer is not included.

[0165] In the above-mentioned laminate, it is more preferred that the sheet containing fluororesin, the above-mentioned heat-meltable resin layer and the above-mentioned heat-resistant fiber layer are stacked in order, the sheet containing fluororesin is directly bonded to the above-mentioned heat-meltable resin layer, and the above-mentioned heat-meltable resin layer is directly bonded to the above-mentioned heat-resistant fiber layer.

[0166] When the heat-melting resin layer and the heat-resistant fiber layer are laminated so as to be in contact with each other, it is preferred that a layer be formed on the surface of the heat-resistant fiber layer that contacts the heat-melting resin layer, wherein the heat-melting resin is impregnated between the heat-resistant fibers. This allows for a more secure bond between the heat-resistant fiber layer and the heat-melting resin layer. The layer impregnated with the heat-melting resin is formed, for example, by allowing the melted heat-melting resin to impregnate between the heat-resistant fibers and solidify during heat fusion.

[0167] In the case where a woven fabric of the bulked glass yarn, i.e., a glass cloth, is used as the heat-resistant fiber layer, it is preferable that the bulked glass yarn be exposed on the surface of the glass cloth that is to be in contact with the hot-melt resin layer. It is more preferable that a layer in which the hot-melt resin is impregnated between the bulked glass yarns be formed on the surface to be in contact. It is further preferable that a layer in which the hot-melt resin is impregnated between the bulked glass yarns and between the glass filaments that constitute the bulked glass yarn be formed on the surface to be in contact. By these configurations, the glass cloth and the hot-melt resin layer are more firmly bonded. The layer in which the hot-melt resin is impregnated is formed, for example, by impregnating the hot-melt resin between the glass yarns (and between the glass filaments) and solidifying the hot-melt resin that is melted at the time of heat welding.

[0168] In the laminate, one of the particularly preferable modes is that the laminate is formed so that the hot-melt resin layer is in contact with the glass cloth, the glass cloth is woven by diagonal weaving, the bulked glass yarn is used in at least one of the warp and weft of the glass cloth, and the bulked glass yarn is exposed on the surface of the glass cloth that is to be in contact with the hot-melt resin layer.

[0169] In the laminate, one of the particularly preferable modes is that the bulked glass yarn is twisted to constitute the bulked glass yarn, and a layer in which the hot-melt resin is impregnated between the bulked glass yarns and between the glass filaments is formed on the surface of the glass cloth that is to be in contact with the hot-melt resin layer.

[0170] The fluorine resin-containing sheet can be subjected to a heat treatment before the lamination. By this, the fluorine resin-containing sheet can be flattened, and the lamination with other layers can be easily performed.

[0171] The temperature of the heat treatment is preferably 100 to 320°C.

[0172] The time of the heat treatment is preferably 1 to 30 minutes.

[0173] The laminate can be manufactured, for example, by a method in which the fluorine resin-containing sheet, the film or sheet of the hot-melt resin, and the woven fabric of the heat-resistant fiber are overlaid and subjected to heat welding.

[0174] As specific conditions, for example, the conditions described in International Publication No. 00 / 10805, International Publication No. 2019 / 082582, and the like can be employed.

[0175] In the laminate obtained by the above-described manufacturing method, a fired layer and an unfired layer can be formed in the fluororesin-containing sheet. The fired layer is a layer that melts during the heat-welding process and is formed in the portion of the fluororesin-containing sheet on the heat-resistant fiber layer side (heating side). The unfired layer is a layer that does not melt during the heat-welding process. Typically, the fired layer is transparent, and the unfired layer is white and opaque.

[0176] It is also one of the preferred embodiments that one of the fluororesin members (A1) and (A2) is a joining member composed of a fluororesin.

[0177] The melting point of the fluororesin used in the bonding member is preferably 100 to 360°C, more preferably 140 to 350°C, further preferably 160 to 350°C, and particularly preferably 180 to 320°C.

[0178] The melting point of the fluororesin is a temperature corresponding to the maximum value in the heat of fusion curve when the temperature is increased at a rate of 10° C. / min using a differential scanning calorimeter (DSC).

[0179] Examples of fluororesins that can be used for the above-mentioned joining members include polytetrafluoroethylene [PTFE], tetrafluoroethylene [TFE] / perfluoro(alkyl vinyl ether) [PAVE] copolymer [PFA], TFE / hexafluoropropylene [HFP] copolymer [FEP], ethylene [Et] / TFE copolymer [ETFE], TFE / vinylidene fluoride [VDF] copolymer, Et / TFE / HFP copolymer, polychlorotrifluoroethylene [PCTFE], chlorotrifluoroethylene [CTFE] / TFE copolymer, Et / CTFE copolymer, polyvinylidene fluoride [PVDF], and polyvinyl fluoride [PVF].

[0180] The fluororesin in the bonding member is preferably at least one selected from the group consisting of modified PTFE, PFA, and FEP, more preferably at least one selected from the group consisting of PFA and FEP, and even more preferably PFA.

[0181] The fluororesin in the above-mentioned joining member may be a perfluororesin.

[0182] The modified PTFE comprises TFE units and modified monomer units, and the content of the modified monomer units is preferably 0.05 to 0.7% by mass relative to the total monomer units. The modified monomer is preferably at least one selected from the group consisting of PAVE and HFP.

[0183] The melt viscosity of the modified PTFE is preferably 1×10 8 ~15×10 8 Pa·s.

[0184] The melt viscosity η is measured using a dynamic viscoelasticity measuring apparatus (trade name: PDS-II, manufactured by Rheometrics).

[0185] Examples of PAVE in the PFA include those represented by the above formula (1), and among these, perfluoro(methyl vinyl ether) [PMVE], perfluoro(ethyl vinyl ether) [PEVE], and perfluoro(propyl vinyl ether) [PPVE] are preferred.

[0186] The above-mentioned PFA is not particularly limited, but preferably the molar ratio of TFE unit to PAVE unit (TFE unit / PAVE unit) is 70 / 30 or more and less than 99.5 / 0.5. A more preferred molar ratio is 70 / 30 or more and 98.9 / 1.1 or less, and a further preferred molar ratio is 80 / 20 or more and 98.5 / 1.5 or less. The above-mentioned PFA may be a copolymer consisting only of TFE and PAVE, and is also preferably a copolymer in which the monomer units from monomers copolymerizable with TFE and PAVE are 0.1 to 10 mol%, and the total of TFE units and PAVE units is 90 to 99.9 mol%. As monomers copolymerizable with TFE and PAVE, HFP, CZ 1 Z 2 =CZ 3 (CF2)nZ 4 (Where Z 1 , Z 2 and Z 3 are the same or different, representing a hydrogen atom or a fluorine atom, Z 4 represents a hydrogen atom, a fluorine atom or a chlorine atom, and n represents an integer from 2 to 10), and a vinyl monomer represented by CF2=CF-OCH2-Rf 11 (Where Rf 11 represents a perfluoroalkyl group having 1 to 5 carbon atoms), and the like.

[0187] The melting point of PFA is preferably 180-340° C., more preferably 230-330° C., and even more preferably 280-320° C. The melting point is the temperature corresponding to the maximum value in the heat of fusion curve when the temperature is increased at a rate of 10° C. / min using a differential scanning calorimeter (DSC).

[0188] The melt flow rate (MFR) of the PFA is preferably 0.1 to 100 g / 10 minutes, more preferably 0.5 to 90 g / 10 minutes, and even more preferably 1.0 to 85 g / 10 minutes.

[0189] The FEP is not particularly limited, but preferably comprises a copolymer having a molar ratio of TFE units to HFP units (TFE units / HFP units) of 70 / 30 or greater and less than 99 / 1. A more preferred molar ratio is 70 / 30 or greater and 98.9 / 1.1 or less, and an even more preferred molar ratio is 80 / 20 or greater and 97 / 3 or less. The FEP is also preferably a copolymer having 0.1 to 10 mol% monomer units derived from monomers copolymerizable with TFE and HFP, and a combined TFE and HFP unit content of 90 to 99.9 mol%. Examples of monomers copolymerizable with TFE and HFP include PAVE and alkyl perfluorovinyl ether derivatives.

[0190] The melting point of FEP is preferably 150-320° C., more preferably 200-300° C., and even more preferably 240-280° C. The melting point is the temperature corresponding to the maximum value in the heat of fusion curve when the temperature is increased at a rate of 10° C. / min using a differential scanning calorimeter (DSC).

[0191] The MFR of the FEP is preferably 0.01 to 100 g / 10 min, more preferably 0.1 to 80 g / 10 min, further preferably 1 to 60 g / 10 min, particularly preferably 1 to 50 g / 10 min.

[0192] In this specification, the content of each monomer unit constituting the fluororesin can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis depending on the type of monomer.

[0193] The method for joining fluororesin members using the joining member containing fluororesin is not particularly limited, and a conventionally known method can be employed. For example, a method based on the method described in Japanese Patent Application Laid-Open No. 2004-189939 can be employed.

[0194] The first inspection method can easily inspect the internal condition of a fluororesin member's joint, and is therefore useful for adjusting joining (welding) conditions, etc. Furthermore, since the internal condition of a fluororesin member's joint can be inspected at high speed and non-destructively, it can be used to determine whether the joint is in good condition, etc., at a construction site where fluororesin members are being joined.

[0195] The first inspection method is particularly suitable for inspecting the joints between backing sheets during the installation of backing sheets for lining various containers, tanks, pipes, etc.

[0196] The present invention also relates to a method for inspecting a fluororesin component (hereinafter also referred to as a second inspection method), comprising a step (B1): inspecting the internal state of the fluororesin component (B1) based on image data obtained by photographing the fluororesin component (B1) using optical coherence tomography (OCT).

[0197] According to the second inspection method, it is possible to non-destructively inspect the internal state of the fluororesin member, and thus it is possible to perform a full number inspection. Therefore, it is possible to improve the quality reliability of the fluororesin member.

[0198] In addition, since it is possible to perform a precise analysis based on the obtained image data, it is possible to detect a fine internal defect or the like, to numerically express the state of a lamination interface in the case where the member is a laminate, and to accurately grasp the internal state of the fluororesin member. Therefore, it is possible to set an objective index for determining whether the fluororesin member is good or not, and it is possible to achieve stabilization of the quality of the fluororesin member.

[0199] In addition, since it is possible to perform imaging based on OCT at high speed, it is easy to introduce the above-described inspection method into a production site of the fluororesin member. Therefore, it is possible to achieve improvement and stabilization of the quality of the fluororesin member without significantly increasing the number of processes at the production site.

[0200] In the process (B1), the fluororesin member (B1) is taken as an inspection object. The fluororesin member (B1) is a member containing a fluororesin.

[0201] The fluororesin member (B1) can be a molded product or a joined member, and is preferably a molded product.

[0202] It is one of preferable modes that the fluororesin member (B1) is a sheet containing a fluororesin.

[0203] It is one of preferable modes that the fluororesin member (B1) is a laminate provided with a sheet containing a fluororesin and a heat-resistant fiber layer.

[0204] As the fluororesin constituting the fluororesin member (B1), the above-described molded product, the above-described joined member, the above-described sheet, and the above-described laminate, the same as described in the fluororesin members (A1) and (A2) can be adopted.

[0205] The inspection of the process (B1) is performed based on image data obtained by photographing the fluororesin member (B1) using OCT. The second inspection method can include a process of photographing the above-described member using OCT to obtain image data based on the member.

[0206] The kind of OCT and light rays that can be adopted in the process (B1), the OCT device, and the basic photographing method are the same as described in the process (A1).

[0207] In the OCT imaging in step (B1), the incident angle α of the light from the light source of the OCT device with respect to the member is preferably 3 to 30 degrees. The incident angle α is more preferably 5 degrees or greater, and even more preferably 7 degrees or greater. Furthermore, it is more preferably 30 degrees or less, even more preferably 20 degrees or less, even more preferably 15 degrees or less, and particularly preferably 10 degrees or less.

[0208] By setting the incident angle α within the above range, noise in the image can be reduced, and a signal based on a defect of the component can be made clear.

[0209] The above effect is significant when the near-infrared transmittance of the above-mentioned component is high, or when the surface to be inspected (the surface on the OCT light source side) and the back surface (the surface opposite to the above-mentioned surface) of the above-mentioned component are parallel.

[0210] The definition and adjustment method of the incident angle α are as described in step (A1).

[0211] In the OCT imaging in step (B1), the intensity of the light incident on the member is preferably 1 mW to 18 mW. The intensity of the light is more preferably 5 mW or greater, and even more preferably 10 mW or greater. Furthermore, the intensity is more preferably 15 mW or less, and even more preferably 12 mW or less.

[0212] By setting the intensity of the light within the above range, noise in the image can be reduced, and a signal based on a defect of the component can be made clear.

[0213] The above effect is remarkable when the near-infrared transmittance of the member is high or when the front surface and back surface of the member are parallel.

[0214] In this specification, the intensity of the light incident on the above-mentioned member refers to the intensity of the light at the probe end of the OCT device.

[0215] When the portion of the sample to be measured is close to the sample stage, it is preferable to take measures in the same manner as described in step (A1) so that light passing through the sample does not affect the measurement.

[0216] In step (B1), the internal state of the fluororesin member (B1) is inspected based on the image data.

[0217] The above-mentioned inspection may be performed using an image obtained from the above-mentioned image data, may be performed by processing the above-mentioned image data, or may be performed by combining the two.

[0218] When the fluororesin member (B1) is the above-mentioned laminate, it is preferred that the interface state between the sheet containing the fluororesin and the heat-resistant fiber layer be inspected in step (B1).

[0219] In addition, when the fluororesin member (B1) is the above-mentioned laminate, as described below, a fired layer and an unfired layer may be formed in the above-mentioned sheet containing fluororesin. In the above-mentioned inspection, the presence and thickness of the above-mentioned fired layer and the above-mentioned unfired layer may also be confirmed.

[0220] In addition, when the laminate further includes a heat-melting resin layer described later, the presence or absence and thickness of the layer formed by impregnation of the heat-resistant fibers with the heat-melting resin may be checked.

[0221] The inspection is preferably an inspection for internal defects of the member.

[0222] Examples of such defects include cracks, delamination, voids, and foreign matter. A layer that should be present is absent, or a layer that does not have the required thickness is also one such defect. Such defects can be caused by poor molding.

[0223] When the fluororesin member (B1) is a laminate, modification or voids are likely to occur at the interface between different materials, and the above-mentioned defects are likely to occur.

[0224] In the above inspection, it is preferable to determine whether the above defects exist.

[0225] The step (B1) is preferably a step of inspecting the member for internal defects based on the image data, and more preferably a step of inspecting the member for internal cracks and interlayer delamination based on the image data.

[0226] The inspection may be performed based on a signal caused by an internal defect of the component in the image data. Furthermore, the presence or absence of the defect is preferably determined based on the signal caused by the defect.

[0227] As a method for determining whether the above-mentioned defects exist, for example, the following method can be cited: when no signal caused by any of the above-mentioned defects is confirmed in the image obtained by OCT, it is determined that there is no defect; when a signal caused by at least one of the above-mentioned defects is confirmed in the above-mentioned image, it is determined that there is a defect.

[0228] If a defect is detected during the above inspection, the size, shape, orientation, and frequency of occurrence of the defect can be further analyzed. This analysis can easily determine whether the defect is sufficiently severe to render the component defective. This analysis is performed, for example, by processing signals generated by the defect.

[0229] The second inspection method may further include a step (B2) of determining whether the fluororesin member (B1) is a non-defective product based on the inspection result of the step (B1).

[0230] Step (B2) may be, for example, a step of judging a member determined to be non-defective in step (B1) as a good product and judging a member determined to be defective in step (B1) as a defective product.

[0231] Process (B2) may also be a process in which components judged to be non-defective in process (B1) and components whose degree of defects among components judged to be defective in process (B1) is below a prescribed standard are judged to be good products, and components whose degree of defects among components judged to be defective in process (B1) exceeds a prescribed standard are judged to be defective products.

[0232] The criteria for the degree of defects are not particularly limited and may be appropriately determined based on the required characteristics of the component. For example, the criteria may be determined by preliminarily correlating the size, shape, orientation, and frequency of defects of a component with data on whether the component passes or fails practical tests using the component as a part. The tolerance ranges for the size, shape, orientation, and frequency of defects that do not result in a defective product may be determined experimentally.

[0233] The second inspection method can easily inspect the internal state of a component, and therefore is useful for adjusting molding and lamination conditions. Furthermore, since it can perform high-speed non-destructive inspection of the internal state of a component, it can be used for sorting good and bad parts during component manufacturing and for component acceptance inspection.

[0234] The second inspection method can be suitably used to inspect the internal condition of fluororesin components before joining or sheets containing fluororesin before lamination. In particular, it can be suitably used to inspect sheets containing fluororesin (raw material sheets) and the resulting backing sheets (laminated bodies) in the manufacture of backing sheets for linings of various containers, tanks, and pipes.

[0235] The second inspection method can also be suitably used to inspect the internal condition of portions other than the joined portions in a joined body of fluororesin members.

[0236] Example

[0237] Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

[0238] Example 1

[0239] A PTFE sheet (melting point: 328°C) having a thickness of 1 mm, a length of 90 mm, and a width of 20 mm was overlapped with a PFA sheet (melting point: 304°C) having a thickness of 1 mm, a length of 60 mm, and a width of 10 mm, leaving a clamped portion at the time of a peeling test, and a heat treatment was performed at 320°C for 5 minutes under atmospheric pressure to obtain a sample.

[0240] The heat-treated portion of the sample was photographed using OCT under the following conditions. The obtained OCT image is shown in Figure 5 . In the OCT image, a clear white line was not confirmed at the interface between the PTFE and the PFA.

[0241] A T-type peeling test was performed using the sample by the following method, and the peeling strength was 17 N / 10 mm.

[0242] <OCT photographing>

[0243] OCT device: Swept Sys-02 (Systems Engineering Co., Ltd.)

[0244] Scan laser light source for OCT: center wavelength 1310 nm, peak width 100 nm, scan rate 50 kHz, coherence length 12 mm, light output 18 mW (probe end 13 mW)

[0245] Photographing conditions: brightness 100, contrast 30

[0246] <T-type peeling test>

[0247] A T-type peeling test was performed using a tensile testing machine (Tensilon, manufactured by ORIENTEC Co., Ltd.) at 25°C at a peeling speed of 20 mm / minute, and the peeling strength (maximum value) was measured.

[0248] Example 2

[0249] A sample was obtained in the same manner as in Example 1, except that the temperature of the heat treatment was changed to 310°C.

[0250] The heat-treated portion of the sample was photographed using OCT in the same manner as in Example 1. The obtained OCT image is shown in Figure 6 . In the OCT image, a fine white line was confirmed at the interface between the PTFE and the PFA.

[0251] A T-type peeling test was performed using the sample in the same manner as in Example 1, and the peeling strength was 1 N / 10 mm.

[0252] Example 3

[0253] A sample was obtained in the same manner as in Example 1, except that the temperature of the heat treatment was changed to 300°C.

[0254] The heat-treated portion of the sample was photographed using OCT in the same manner as in Example 1. The obtained OCT image is shown in FIG. Figure 7 In the above OCT image, a thin white line is confirmed at the interface between PTFE and PFA.

[0255] A T-type peel test was conducted using the sample in the same manner as in Example 1. The peel strength was 1 N / 10 mm.

[0256] Example 4

[0257] A sample was obtained in the same manner as in Example 1 except that the temperature of the heat treatment was changed to 295°C.

[0258] The heat-treated portion of the sample was photographed using OCT in the same manner as in Example 1. The obtained OCT image is shown in FIG. Figure 8 In the above OCT image, a thick white line is confirmed at the interface between PTFE and PFA.

[0259] A T-type peel test was conducted using the above sample in the same manner as in Example 1. As a result, when the sample was placed in the testing machine, PTFE and PFA peeled off.

[0260] The results of Examples 1 to 4 show that, in the OCT image, when no clear white line is confirmed at the interface between PTFE and PFA, the two are firmly bonded; on the other hand, when a white line is confirmed at the above interface, the two are not bonded or the bonding is insufficient.

[0261] Furthermore, no defects of 10 μm or more, such as cracks, delamination, voids, foreign matter, absence of a layer that should be present, or a layer that does not have the required thickness, were observed in the PTFE sheets and PFA sheets used in Examples 1 to 4.

[0262] Explanation of symbols

[0263] 1, 2: Sheets containing fluororesin

[0264] 3, 4: Sheets containing fluororesin

[0265] 5: Joint components containing fluororesin

[0266] 6, 7: Laminated body

[0267] 6a, 7a: Sheets containing fluororesin

[0268] 6b, 7b: Heat-resistant fiber layer

[0269] 10: OCT device

[0270] 11: Light Source

[0271] 12: Spectroscope

[0272] 13: Reference Mirror

[0273] 14: Light detector

[0274] 15: Sample

Claims

1. A method for inspecting a joint of a fluororesin member, comprising the steps of: inspecting an internal state of the joint between two fluororesin members based on image data obtained by photographing the joint using optical coherence tomography (OCT); The OCT uses light with a central wavelength of 1100±50nm, 1320±50 or 1750±100nm. the two fluororesin members contain fluororesins different from each other, The fluororesin is at least one selected from the group consisting of polytetrafluoroethylene and tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymers, Whether or not the adhesion between the two fluororesin members is sufficient is determined by whether or not a clear white line is observed at the interface between the fluororesins in the two fluororesin members.

2. The inspection method according to claim 1, wherein: At least one of the two fluororesin members is a sheet containing fluororesin.

3. The inspection method according to claim 1 or 2, wherein: At least one of the two fluororesin members is a laminate including a sheet containing a fluororesin and a heat-resistant fiber layer.

4. The inspection method according to claim 1 or 2, wherein: The internal state of the joint is at least one selected from the group consisting of cracks, delamination, voids, foreign matter, the absence of a layer that should be present, and a layer that does not have a required thickness.

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