Ventilation filter and ventilation member

Abstract

A ventilation filter has one main surface and another main surface, and includes a fluororesin porous membrane treated with an oil-repellent agent for oil repellency. When the absorption spectrum is measured through Fourier-transform infrared spectroscopy, the absorbance ratio Rf of the one main surface calculated by Aa / Am and the absorbance ratio Rb of the other main surface are not substantially the same. Aa indicates the absorbance at a peak derived from the oil repellent in the absorption spectrum, and Am indicates the absorbance at a peak derived from a C-F bond in the absorption spectrum.

Description

Ventilation filter and ventilation member

[0001] The present invention relates to a ventilation filter and a ventilation member that are provided with oil repellency.

[0002] A ventilation filter is sometimes attached to the housing of an electronic device or the like to ensure ventilation between the inside and outside of the housing, thereby adjusting the internal pressure of the housing. Some ventilation filters include a type equipped with a porous fluororesin membrane. The porous fluororesin membrane is, for example, a porous polytetrafluoroethylene (hereinafter referred to as "PTFE") membrane. Furthermore, this type of ventilation filter can more reliably prevent foreign matter such as water and dust from entering the housing from the outside, based on the excellent water resistance and dustproof properties of the porous fluororesin membrane. The housing is, for example, the housing of an electronic device such as a smartwatch or a mobile phone.

[0003] Although porous fluororesin membranes have high water resistance, they allow the passage of liquids with low surface tension, such as hydrocarbons such as kerosene and light oil, low-molecular-weight alcohols, surfactants, etc. Therefore, for such applications, porous fluororesin membranes are subjected to an oil-repellent treatment using an oil-repellent agent.

[0004] For example, Patent Document 1 describes that an oil-repellent ventilation filter is obtained by a so-called immersion method in which a porous PTFE membrane constituting the ventilation filter is immersed in an oil-repellent treatment liquid. In the examples of Patent Document 1, a porous PTFE membrane with an average pore size of 1 μm is used.

[0005] JP 2012-236188 A

[0006] In particular, when a sufficient amount of oil repellent is supplied to obtain good oil repellency, the pores of the porous fluororesin membrane constituting the ventilation filter may become clogged, resulting in a decrease in air permeability. For this reason, when high air permeability must be maintained, an oil repellent treatment has been applied to a porous fluororesin membrane with a relatively large pore size. However, depending on the application and required properties of the ventilation filter, it may be necessary to use a porous fluororesin membrane with a small pore size.

[0007] Therefore, an object of the present invention is to provide a ventilation filter that is suitable for suppressing a decrease in air permeability while exhibiting oil repellency, regardless of the pore size of the porous fluororesin membrane.

[0008] After extensive research, the present inventors have found that the above object can be achieved by controlling the distribution of the oil repellent in the porous fluororesin membrane. Conventionally, when a dipping method in which the oil repellent is supplied from both main surfaces is used, as well as when a coating method in which the oil repellent is supplied from only one main surface, the oil repellent has been supplied in excess of the amount required for the main surface to be imparted with oil repellency. According to the inventors' research, in such cases, the amount of oil repellent present on both main surfaces becomes approximately the same.

[0009] The present invention provides a porous fluororesin membrane having one main surface and another main surface, the membrane having been subjected to an oil-repellent treatment with an oil-repellent agent, wherein when an absorption spectrum is measured by Fourier transform infrared spectroscopy, an absorbance ratio R of the one main surface calculated by the following formula (1) is f and the absorbance ratio R of the other principal surface b and a ventilation filter, which are not substantially identical to each other. a / A m ...Equation (1) where A a represents the absorbance at a peak attributable to the oil repellent in the absorption spectrum, and A m indicates the absorbance at the peak derived from the C—F bond in the absorption spectrum.

[0010] From another aspect, the present invention provides a ventilation member comprising: the ventilation filter of the present invention; and a pressure-sensitive adhesive layer bonded to the ventilation filter.

[0011] According to the present invention, it is possible to provide a ventilation filter that is suitable for suppressing a decrease in air permeability while exhibiting oil repellency, regardless of the pore size of the porous fluororesin membrane.

[0012] FIG. 1 is a cross-sectional view schematically showing an example of a ventilation filter of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of the distribution state of an oil repellent in a ventilation filter of the present invention. FIG. 3A is a perspective view schematically showing another example of a ventilation filter of the present invention. FIG. 3B is a cross-sectional view showing a cross-section of the ventilation filter shown in FIG. 3A. FIG. 4A is a perspective view schematically showing an example of a ventilation member of the present invention. FIG. 4B is a cross-sectional view showing a cross-section of the ventilation member shown in FIG. 4A. FIG. 5A is a perspective view schematically showing another example of a ventilation member of the present invention. FIG. 5B is a cross-sectional view showing a cross-section of the ventilation member shown in FIG. 5A. FIG. 6A is a cross-sectional view schematically showing an example of a ventilation member of the present invention attached to an opening in a housing of an electronic device or an opening in an electronic component. FIG. 6B is a cross-sectional view schematically showing another example of a ventilation member of the present invention attached to an opening in a housing of an electronic device or an opening in an electronic component. FIG. 6C is a cross-sectional view schematically showing yet another example of a ventilation member of the present invention attached to an opening in a housing of an electronic device or an opening in an electronic component. FIG. 7A is a schematic cross-sectional view illustrating measurement of the absorption spectrum by FT-IR for a ventilation filter of the present invention. FIG. 7B is a graph showing an example of an absorption spectrum by FT-IR for a ventilation filter of the present invention. FIG. 7C is a graph showing another example of an absorption spectrum by FT-IR for a ventilation filter of the present invention. FIG. 8 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 1. FIG. 9 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 2. FIG. 10 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 3. FIG. 11 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 4. FIG. 12 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 5. FIG. 13 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 6. FIG. 14 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 7. Fig. 15 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 8. Fig. 16 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 9. Fig. 17 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 10.FIG. 18 is a graph showing the absorbance ratio in the thickness direction of the breathable filter of Example 11. FIG. 19 is a graph showing the absorbance ratio in the thickness direction of the breathable filter of Example 12. FIG. 20 is a graph showing the absorbance ratio in the thickness direction of the breathable filter of Example 13. FIG. 21 is a graph showing the absorbance ratio in the thickness direction of the breathable filter of Example 14. FIG. 22 is a graph showing the absorbance ratio in the thickness direction of the breathable filter of Example 15. FIG. 23 is a graph showing the absorbance ratio in the thickness direction of the breathable filter of Example 16. FIG. 24 is a graph showing the absorbance ratio on both main surfaces (measurement of the membrane center is omitted) of the breathable filter of Comparative Example 1. FIG. 25 is a graph showing the absorbance ratio on both main surfaces (measurement of the membrane center is omitted) of the breathable filter of Comparative Example 2. FIG. 26 is a graph showing the absorbance ratio on both main surfaces (measurement of the membrane center is omitted) of the breathable filter of Comparative Example 3. Fig. 27 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 17. Fig. 28 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 18. Fig. 29 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 19. Fig. 30 is a graph showing the absorbance ratio in the thickness direction of the ventilation filter of Example 20.

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings, but is not limited to the following embodiments.

[0014] [Ventilation filter] An example of a ventilation filter of the present embodiment is shown in Fig. 1. The ventilation filter 10 of Fig. 1 includes a porous fluororesin membrane 1 having one main surface 11 and the other main surface 12. The porous fluororesin membrane 1 has been subjected to an oil repellent treatment using an oil repellent agent.

[0015] When the absorption spectrum of the ventilation filter 10 is measured by the ATR (Attenuated Total Reflection) method of Fourier transform infrared spectroscopy (hereinafter referred to as "FT-IR"), the absorbance ratio R f and the absorbance ratio R of the other main surface 12 bThe ATR method is a method for obtaining an absorption spectrum of a sample surface by measuring infrared light totally reflected by the sample surface. The measurement depth in the ATR method is about 1 μm. The absorbance ratio R f and absorbance ratio R b are both calculated by the following formula (1).

[0016] A a / A m ...Formula (1)

[0017] In formula (1), A a indicates the absorbance at the peak attributable to the oil repellent in the absorption spectrum, and A m indicates the absorbance at the peak derived from the C—F bond in the absorption spectrum.

[0018] In this embodiment, the absorbance ratio R f and the absorbance ratio R b The phrase "substantially the same" means that even if there is a slight difference in the absorbance ratio caused by measurement precision or the like, they are considered to be the same. The slight difference in the absorbance ratio caused by measurement precision or the like is, for example, about 0.002, or even 0.0015. In other words, in this embodiment, the absorbance ratio R f and the absorbance ratio R b The phrase "substantially the same" means that the difference in absorbance ratio is 0.0015 or less, more specifically 0.001 or less.

[0019] The peak due to the C—F bond is at 1150 cm in the absorption spectrum. -1 This peak is known to be caused by the stretching vibration of the C—F bond. The peak due to the C—F bond reflects the amount of fluororesin as well as the oil repellent, and usually the majority of the peak is due to the fluororesin.

[0020] The peak derived from the oil repellent is a peak derived from a bond other than a C—F bond. The peak derived from the oil repellent is, for example, a peak derived from the oil repellent and not from the fluororesin, in other words, a peak derived only from the oil repellent, and specifically may be a peak derived from a bond other than a C—F bond, a C—H bond, and a carbon-carbon bond. The peak derived from the oil repellent may be a peak derived from a structural unit present in the oil repellent but not in the fluororesin, in other words, a peak derived from a bond contained in a structural unit present only in the oil repellent.

[0021] The peak derived from the oil repellent is not particularly limited, and may be a peak derived from at least one functional group selected from the group consisting of a hydroxy group, a carboxy group, an aldehyde group, a carbonyl group, an ester group, and an ether group. The functional group may be a functional group containing a heteroatom, particularly an oxygen atom. The peak derived from the oil repellent may be the largest peak among peaks derived from bonds other than C-F bonds, C-H bonds, and carbon-carbon bonds.

[0022] The peak derived from the oil repellent may be a peak derived from a carboxy group and / or an ether group. The peak derived from a carboxy group may be a peak at 1700 cm -1 ~1740cm -1 Nearby, more widely 1670 cm -1 ~1770cm -1 The peak due to the ether group is present around 980 cm and is due to the stretching vibration of the C=O bond of the carboxyl group. -1 ~990cm -1 Nearby, wider 950 cm -1 ~1100cm -1 This peak is present in the periphery and is derived from the stretching vibration of the C—O bond of the ether group (C—O—C).

[0023] In this embodiment, a predetermined wave number (for example, 1740 cm -1 , 983 cm -1 , 1150 cm -1The term "peaks near a certain wavenumber" refers to not only peaks whose peak tops exist at certain wavenumbers, but also peaks whose midpoints exist at certain wavenumbers. The absorbance of a peak is determined according to the height of the peak top, even if the peak top is shifted from the specified wavenumber.

[0024] Absorbance ratio R of the main surface 11 f and the absorbance ratio R of the main surface 12 b may both be positive values ​​(R f >0 and R b >0). R b >0 means that the oil repellent agent is also present on the main surface 12 of the porous fluororesin membrane 1. f is the absorbance ratio R b is larger than (R f >R b ) or vice versa (R f <R b ) may be used. When applying the oil repellent from only one of the main surfaces, conventionally, an excess of oil repellent has been supplied in order to obtain sufficient oil repellency. For this reason, even when applying the oil repellent from only the main surface 11, for example, the absorbance ratios on both main surfaces 11 and 12 will be substantially the same, as in the case where the film is immersed in the oil repellent and the oil repellent is supplied from both main surfaces. More specifically, taking into consideration slight differences, the excess oil repellent that has reached the main surface 12 may cause the absorbance ratios to be substantially the same, but with a difference of R b is R f In this embodiment, the absorbance ratio of the main surface to which the oil repellent is applied is higher than the absorbance ratio of the main surface to which the oil repellent is not applied. For example, when the oil repellent is applied only from the main surface 11, R f >R b may be established.

[0025] The inventors' investigations have revealed that an excessive supply of oil repellent may slightly increase oil repellency, but may also significantly decrease breathability.

[0026] The oil repellency of the principal surfaces 11 and 12 is not particularly limited, but one of the principal surfaces 11 may have oil repellency that prevents penetration of n-alkane having 15 carbon atoms, in other words, n-pentadecane. f>R b holds true, and one of the main surfaces 11 may have oil repellency that prevents the penetration of n-alkanes having 15 carbon atoms, in other words, n-pentadecane. One of the main surfaces 11 may have oil repellency that prevents the penetration of n-alkanes having 14, 13, 12, 10, 9, and even 8 carbon atoms. A main surface that does not allow the penetration of n-alkanes having a relatively small number of carbon atoms will also not allow the penetration of n-alkanes having a relatively large number of carbon atoms. For example, an oil-repellent surface that does not allow the penetration of n-alkanes having 8 carbon atoms, i.e., n-octane, will not allow the penetration of n-alkanes having 9 to 15 carbon atoms.

[0027] In this embodiment, the maximum pore size and Gurley air permeability of the porous fluororesin membrane can satisfy at least one of the following a) to c): a) maximum pore size of 75 nm or less, Gurley air permeability of 160 sec / 100 mL or less b) maximum pore size of 150 nm or less, Gurley air permeability of 80 sec / 100 mL or less c) maximum pore size of 900 nm or less, Gurley air permeability of 12 sec / 100 mL or less

[0028] In a), the maximum pore size may be 70 nm or less, or even 65 nm or less. In a), the Gurley air permeability may be 150 sec / 100 mL or less, or even 140 sec / 100 mL or less. In b), the maximum pore size may be 140 nm or less, or even 130 nm or less. In b), the Gurley air permeability may be 70 sec / 100 mL or less, or even 60 sec / 100 mL or less. In c), the maximum pore size may be 800 nm or less, or even 750 nm or less. In c), the Gurley air permeability may be 10 sec / 100 mL or less.

[0029] In this embodiment, the Gurley air permeability of the fluororesin porous membrane may be 90 seconds / 100 mL or less, 80 seconds / 100 mL or less, or even 60 seconds / 100 mL or less, and in some cases, 20 seconds / 100 mL or less. The Gurley air permeability is not particularly limited, but may be 1 second / 100 mL or more.

[0030] In this embodiment, the absorbance difference rate between the main surface 11 and the main surface 12 calculated by the following formula (2) may be 4% or more.

[0031] 100×(R f-R b ) / R f ...Formula (2)

[0032] Absorbance ratio R of the main surface 11 f is not particularly limited, but may be, for example, 0.005 or more, or even 0.007 or more. f The upper limit of R f ≦0.050) and 0.040 (R f ≦0.040).

[0033] The upper limit of the absorbance difference rate between the principal surface 11 and the principal surface 12 is, for example, 99%. The upper limit of the absorbance difference rate between the principal surface 11 and the principal surface 12 may be 95%.

[0034] The absorbance ratio at a position 40 to 60% of the thickness of the porous fluororesin membrane 1 from the main surface 11 in the thickness direction of the porous fluororesin membrane 1 is defined as R m In this case, the absorbance ratio R m is 0.0025 or more (R m If the oil repellent treatment is performed not only on the main surface 11 but also on the vicinity of the center of the film, the oil repellency can be stably exhibited. m is 0.005 or more (R m ≧0.005).

[0035] Absorbance ratio R m The upper limit of R m ≦0.030). m The upper limit of is 0.025 (R m ≦0.025).

[0036] R b is 0.001 or more (R b The thickness of the part of the porous fluororesin membrane 1 where the oil repellent agent has permeated is defined as an oil repellent layer. In this case, the oil repellent layer has an absorbance ratio R f and the absorbance ratio R bThe oil-repellent layer may have a thickness equal to that of the porous fluororesin membrane 1 so that the difference in absorbance coefficient calculated by formula (2) is 4% or more.

[0037] R f , R m and R b is R f >R m >R b R m and R b is R m >1.1R b As shown in Figure 2, when the cross section of the fluororesin porous membrane 1 is viewed in the thickness direction, the oil repellent may be distributed in a gradational manner such that the amount of oil repellent gradually decreases from the main surface 11 to the main surface 12.

[0038] Absorbance ratio R of the main surface 11 f and the absorbance ratio R of the main surface 12 b and are substantially the same, the distribution of the oil repellent in the porous fluororesin membrane 1 is not limited to the example shown in Fig. 2. For example, when viewing the cross section of the porous fluororesin membrane 1 in the thickness direction, the oil repellent may be distributed so that the amount of oil repellent decreases from the main surface 11 toward the center and increases slightly from the center toward the main surface 12.

[0039] The porous fluororesin membrane 1 is a membrane formed by stretching a fluororesin membrane to make it porous, typically by biaxial stretching. The porous fluororesin membrane 1 may have countless pores formed during stretching, more specifically, pores that are voids between countless fluororesin fibrils formed during stretching.

[0040] The porous fluororesin membrane 1 may be a single-layer membrane, or a laminated membrane in which multiple layers are stacked.

[0041] Examples of the fluororesin contained in the fluororesin porous membrane 1 include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-ethylene copolymer.

[0042] The fluororesin may be PTFE. That is, the fluororesin porous membrane 1 may be a PTFE porous membrane. A PTFE porous membrane has excellent water resistance and dustproof properties, and therefore, when used in the ventilation filter 10, it has an excellent function of preventing foreign matter such as water and dust from entering the housing from the outside. The housing is, for example, the housing of an electronic device such as a smart watch or a mobile phone.

[0043] The oil repellent may include a fluorine-containing polymer.

[0044] The fluorine-containing polymer may contain a carboxy group. The fluorine-containing polymer is a polymer having a structure represented by the formula: CH2=CR 1 COOR 2 In this case, the polymer may contain a compound represented by the following formula: 1 is a hydrogen atom or a methyl group. 2 is a hydrocarbon group in which at least one hydrogen atom is substituted with a fluorine atom. 2 may be an alkyl group in which at least one hydrogen atom is substituted with a fluorine atom. 2 may have 1 to 20 carbon atoms, or even 3 to 18 carbon atoms.

[0045] R 2 may be a linear fluorine-containing hydrocarbon group. The linear fluorine-containing hydrocarbon group is (i) -R 3 C5F 10 CH2C4F9, or (ii) -R 4 C6F 13 where R 3 and R 4 are each independently an alkylene group having 1 to 12 carbon atoms, preferably 1 to 10, or a phenylene group. The linear fluorine-containing hydrocarbon group represented by (i) or (ii) above is 3 or R 4When R is an alkylene group, it becomes a linear fluoroalkyl group. The above-mentioned "linear" means that the carbon skeleton of the fluorine-containing hydrocarbon group does not have two or more branched ends, and 3 or R 4 This does not mean that a phenylene group is excluded as the alkyl group.

[0046] A linear perfluoroalkyl group (hereinafter referred to as an Rf group, and written as Rf in the formula) is a functional group that exhibits low surface free energy and imparts high oil repellency to the coated surface. In particular, an Rf group having 8 or more carbon atoms (C n F 2n (n is an integer of 8 or more) is known to exhibit excellent oil repellency due to its high crystallinity. However, oil repellent treatment using an oil repellent agent containing an Rf group having 8 or more carbon atoms may significantly reduce the breathability of the fluororesin porous membrane 1. The fluorine-containing polymer may not contain an Rf group having 8 or more carbon atoms. An oil repellent agent having the above (i) or (ii) as the linear fluorine-containing hydrocarbon group can impart sufficient oil repellency for practical use without significantly reducing the breathability, even when it coats the surface of the fluororesin porous membrane 1.

[0047] As shown in the above chemical formula, the linear fluorine-containing hydrocarbon group-containing monomer may have a methacrylate structure or an acrylate structure in the main chain.

[0048] The compound may be represented by the following chemical formula (a): CH2=C(CH3)COOCH2CH2C5F 10 CH2C4F9...(a)

[0049] The compound may be represented by the following chemical formula (b): CH2=CHCOOCH2CH2C6F 13 ...(b)

[0050] As the oil repellent, an oil repellent containing a copolymer containing a linear fluorine-containing hydrocarbon group-containing monomer and a crosslinkable monomer may be used.

[0051] The crosslinkable monomer includes at least one selected from an alkoxy group-containing monomer, a hydroxy group-containing monomer, and a carboxy group-containing monomer. The crosslinkable monomer may have a methacrylate structure or an acrylate structure in the main chain. As the alkoxy group-containing monomer, for example, 3-methacryloxypropyltriethoxysilane can be used. As the hydroxy group-containing monomer, for example, 2-hydroxyethyl methacrylate can be used. As the carboxy group-containing monomer, for example, 2-carboxyethyl methacrylate can be used. The crosslinkable monomer preferably has a copolymerization ratio of 0.1 to 40 mol%, particularly 1 to 10 mol%, so as to suppress melting of the oil repellent at high temperatures and not interfere with imparting oil repellency. Among these, alkoxy group-containing monomers and carboxy group-containing monomers are preferred due to their high crosslinking reactivity, and alkoxy group-containing monomers are particularly preferred.

[0052] The oil repellent may be a polyether-based oil repellent. The fluorine-containing polymer contained in the oil repellent may contain perfluoropolyether. The perfluoropolyether contains an ether group, more specifically, a unit structure represented by -(Rf-O)-.

[0053] Perfluoropolyethers are perfluorinated polyethers that are primarily composed of carbon, fluorine, and oxygen. Perfluoropolyethers have a variety of structures. Perfluoropolyethers may further contain perfluorinated side chains.

[0054] As perfluoropolyethers, for example, perfluoropolyethers commercially available as KRYTOX®, FOMBLIN®, HOSTINERT, and DEMNUM® can be used.

[0055] The perfluoropolyether may have a repeating unit represented by the following chemical formula (c).

[0056]

[0057] In the chemical formula (c), the ratio of m:n represented by m / n is, for example, 2 / 3.

[0058] The perfluoropolyether may have a repeating unit represented by the following chemical formula (d).

[0059]

[0060] In the chemical formula (d), the ratio of m:n:n' represented by m / n / n' is, for example, 40 / 1 / 1.

[0061] The perfluoropolyether may have a repeating unit represented by the following chemical formula (e).

[0062]

[0063] The perfluoropolyether may have a repeating unit represented by the following chemical formula (f).

[0064]

[0065] In the chemical formulas (e) and (f), m is an integer of 1 or more.

[0066] The acrylate-based oil repellent having a perfluoropolyether in the side chain may be represented by the following chemical formula (g).

[0067] CH2=CH2COOCH2CH2NHCOCFCF3-(OCF2CF(CF3)) n -OCF2CF2CF3...(g)

[0068] The methacrylate-based oil repellent having a perfluoropolyether in the side chain may be represented by the following chemical formula (h).

[0069] CH2=CH(CH3)COOCH2CH2NHCOCFCF3-(OCF2CF(CF3)) n -OCF2CF2CF3...(h)

[0070] In the chemical formulas (g) and (h), n is an integer of 1 or more.

[0071] As the oil repellent, an oil repellent containing a copolymer containing a linear fluorine-containing hydrocarbon group-containing monomer and a crosslinkable monomer may be used.

[0072] The oil repellent is not limited to the above. The oil repellent may contain a functional group other than a carboxy group and an ether group. The oil repellent may contain at least one functional group selected from the group consisting of a hydroxy group, an aldehyde group, a carbonyl group, and an ester group.

[0073] In the fluororesin porous membrane 1, the water pressure resistance of the main surface 11 against an aqueous solution of isopropanol (hereinafter referred to as IPA) with a concentration of 30 wt % may be 180 kPa or more. The water pressure resistance against the IPA aqueous solution may be 200 kPa or more. In this specification, according to common usage, the water pressure resistance measured using an aqueous solution instead of water is also referred to as the "water pressure resistance."

[0074] The upper limit of the water pressure resistance against the IPA aqueous solution is, for example, 400 kPa. The upper limit of the water pressure resistance against the IPA aqueous solution may be 350 kPa.

[0075] In the fluororesin porous membrane 1, the water pressure resistance of the main surface 11 to an IPA aqueous solution with a concentration of 30 wt % can be measured using a measuring jig in accordance with the water resistance test method B (high water pressure method) specified in JIS L1092:2009 as follows.

[0076] An example of a measuring jig is a 47 mm diameter stainless steel disk with a 1.0 mm diameter through-hole (with a circular cross section) in the center. This disk has a thickness that is not deformed by the water pressure applied when measuring the water pressure resistance. Measurement of the water pressure resistance using this measuring jig can be carried out as follows.

[0077] The porous fluororesin membrane 1 to be evaluated is fixed to one surface of the measuring jig so as to cover the opening of the through-hole of the measuring jig. The fixing is performed so that the IPA aqueous solution does not leak from the fixed part of the membrane during the measurement of the water pressure resistance. The porous fluororesin membrane 1 can be fixed using double-sided adhesive tape with a water passage hole punched in the center, the shape of which matches the shape of the opening. The double-sided adhesive tape can be placed between the measuring jig and the porous fluororesin membrane 1 so that the periphery of the water passage hole and the periphery of the opening coincide. Next, the measuring jig with the porous fluororesin membrane 1 fixed thereto is set in a testing device so that the surface opposite to the fixing surface of the porous fluororesin membrane 1 becomes the water pressure application surface during measurement, and the water pressure resistance to the IPA aqueous solution is measured according to Water Resistance Test Method B specified in JIS L1092:2009. However, the water pressure resistance is measured based on the water pressure when the IPA aqueous solution comes out from one point on the membrane surface of the porous fluororesin membrane 1. The measured water pressure resistance can be regarded as the water pressure resistance of the main surface 11 of the fluororesin porous membrane 1 to an aqueous solution of IPA with a concentration of 30 wt %. The test device can have the same configuration as the water resistance test device exemplified in JIS L1092:2009 and have a test specimen mounting structure into which the above-mentioned measuring jig can be set.

[0078] The average thickness of the porous fluororesin membrane 1 varies depending on the application, but may be 100 μm or less, 75 μm or less, 50 μm or less, or even 25 μm or less. The lower limit of the average thickness of the porous fluororesin membrane 1 is, for example, 3 μm or more.

[0079] The Gurley air permeability can be measured in accordance with the air permeability measurement method B (Gurley method) specified in JIS L1096:2010.

[0080] Even when the size of the fluororesin porous membrane 1 is smaller than the size of a test piece in the Gurley method (approximately 50 mm × 50 mm), the Gurley air permeability can be evaluated by using a measuring jig. An example of the measuring jig is a polycarbonate disk having a thickness of 2 mm and a diameter of 47 mm and a through-hole (having a circular cross section with a diameter of 1.0 mm) at the center. Measurement of the Gurley air permeability using this measuring jig can be carried out as follows.

[0081] The porous fluororesin membrane 1 to be evaluated is fixed to one surface of the measuring jig so as to cover the opening of the through-hole of the measuring jig. The fixing is performed so that, during measurement of the Gurley air permeability, air passes only through the opening and the effective test portion of the porous fluororesin membrane 1 to be evaluated (the portion overlapping with the opening when viewed from a direction perpendicular to the main surfaces 11 and 12 of the fixed porous fluororesin membrane 1), and the fixed portion does not obstruct the passage of air through the effective test portion of the porous fluororesin membrane 1. To fix the porous fluororesin membrane 1, double-sided adhesive tape with a vent hole punched in the center and having a shape matching the shape of the opening can be used. The double-sided adhesive tape may be placed between the measuring jig and the porous fluororesin membrane 1 so that the periphery of the vent hole coincides with the periphery of the opening. Next, the measuring jig with the porous fluororesin membrane 1 fixed thereto is set in a Gurley air permeability tester so that the fixed surface of the porous fluororesin membrane 1 is downstream of the air flow during measurement, and the time t1 required for 100 mL of air to pass through the porous fluororesin membrane 1 is measured. Next, the measured time t1 was calculated based on the effective test area of ​​642 [mm 2 ] as defined in the air permeability measurement method B (Gurley method) of JIS L1096:2010. 2 ], the value t per unit area is calculated by the formula t = {(t1) × (area of ​​the effective test portion of the fluororesin porous membrane 1 [mm 2 ]) / 642 [mm 2 ]}, and the obtained converted value t can be regarded as the Gurley air permeability of the fluororesin porous membrane 1. When the above-mentioned circular plate is used as the measuring jig, the area of ​​the effective test portion of the fluororesin porous membrane 1 is the area of ​​the cross section of the through-hole. It has been confirmed that the Gurley air permeability measured without using a measuring jig for a fluororesin porous membrane 1 that meets the size of the above-mentioned test piece agrees well with the Gurley air permeability measured using the measuring jig after cutting the fluororesin porous membrane 1 into small pieces, that is, that the use of the measuring jig does not substantially affect the measured value of the Gurley air permeability.

[0082] The porosity of the porous fluororesin membrane 1 is, for example, 25% or more. The porosity of the porous fluororesin membrane 1 may be 63% or more. The porosity can be calculated by substituting the mass, thickness, area (area of ​​the main surface) and true density of the membrane into the following formula (3). For example, when the porous fluororesin membrane 1 is a porous PTFE membrane, the true density of PTFE is 2.18 g / cm3 is.

[0083] Porosity (%) = {1 - (mass [g] / (thickness [cm] × area [cm 2 ]×True density [g / cm 3 ]))}×100 ...Formula (3)

[0084] The upper limit of the porosity of the fluororesin porous membrane 1 is, for example, 95%. The upper limit of the porosity may be 90%.

[0085] The main surface 11 of the porous fluororesin membrane 1 may be colored. For example, when the porous fluororesin membrane 1 is a porous PTFE membrane, the porous PTFE membrane is usually white and is easily noticeable when placed in an opening. A conspicuous breathable membrane not only interferes with the design of an electronic device, etc., but also stimulates the user's curiosity and is easily damaged by punctures such as with a writing implement. Coloring the main surface 11 can alleviate the above problems.

[0086] The main surface 11 may be colored black or gray. The fluororesin porous membrane 1 colored black or gray has a relatively low lightness L * If the lightness L is small, the lightness L is not noticeable. * is CIE1976 (L) as defined in JIS Z8781-4:2013. * , a * , b * ) Color space lightness L * is.

[0087] The colorant may be a dye or a pigment, but is preferably a dye from the viewpoint of preventing it from falling off from the fluororesin porous membrane 1. Falling off from the fluororesin porous membrane 1 may cause discoloration of the fluororesin porous membrane 1, or, if the colorant is conductive, damage to electrical circuits or electronic components located near the fluororesin porous membrane 1. Furthermore, when the colorant is a dye or an insulating pigment, the high insulating properties inherent in the fluororesin make it possible to make the fluororesin porous membrane 1 insulating. The insulating properties can be achieved by, for example, a 1×10 14 It is expressed by a surface resistivity of 1×10 Ω / □ or more.15 Ω / □ or more, 1×10 16 Ω / □ or more, even 1×10 17 It may be Ω / □ or more.

[0088] Examples of dyes include azo dyes and oil-soluble dyes, and examples of pigments include carbon black and metal oxides, but the dyes and pigments are not limited to these examples.

[0089] The maximum pore size of the porous fluororesin membrane 1 is, for example, 1000 nm or less. The maximum pore size of the porous fluororesin membrane 1 may be 500 nm or less. A porous fluororesin membrane 1 having a small maximum pore size is advantageous for realizing high water pressure resistance.

[0090] The maximum pore size r of the fluororesin porous membrane 1 can be calculated using the following formula (4) which indicates the limit water pressure resistance value h of water.

[0091]

[0092] In equation (4), T represents the surface tension of water (dyne / cm), and S represents the density of water (g / cm 3 ) g is the gravitational acceleration (cm / sec 2 ) where θ represents the water contact angle with respect to the fluororesin porous membrane 1. The limiting water pressure resistance value h can be measured in accordance with the water resistance test method B (high water pressure method) defined in JIS L1092:2009. In this case, the measuring jig has a through-hole with a diameter of 1.0 mm in the center.

[0093] The maximum pore size of the fluororesin porous membrane 1 may be 300 nm or less. The lower limit of the maximum pore size of the fluororesin porous membrane 1 is, for example, 50 nm. To obtain a fluororesin porous membrane 1 having a maximum pore size equal to or less than a predetermined value, a raw fluororesin porous membrane before being subjected to oil repellent treatment may be selected that has a maximum pore size equal to or less than that value.

[0094] The shape of the ventilation filter 10 is, for example, a polygon including a square and a rectangle, a circle, an ellipse, an irregular shape, or a strip shape when viewed from a direction perpendicular to the main surfaces 11 and 12. However, the shape of the ventilation filter 10 is not limited to the above examples.

[0095] The ventilation filter 10 shown in FIG. 1 is composed of a porous fluororesin membrane 1 .

[0096] [Method of Manufacturing the Ventilated Filter] The following describes a method of manufacturing the ventilation filter 10. The ventilation filter 10 can be manufactured, for example, by the following method.

[0097] First, prepare a raw fluororesin porous membrane. The raw fluororesin porous membrane can be formed by a known method. For example, when the raw fluororesin porous membrane is a PTFE porous membrane, a mixture of PTFE fine powder and a molding aid is extruded and rolled into a sheet, and the molding aid is removed, and then the sheet is stretched to form the membrane. The properties of the PTFE porous membrane can be adjusted by adjusting the rolling conditions and stretching conditions.

[0098] Next, an oil repellent is applied to one main surface of the raw porous fluororesin membrane (application step). In the application step, the oil repellent is preferably applied to the one main surface so that the wet thickness of the oil repellent is no more than twice the thickness of the raw porous fluororesin membrane.

[0099] The oil repellent is preferably applied to one main surface of the raw porous fluororesin membrane at a relatively high concentration. The "relatively high concentration" refers to a treatment liquid, which is a mixture of the oil repellent and a solvent, with a concentration of the oil repellent in the treatment liquid being 0.8 to 10.0 wt %. The oil repellent concentration may be 1.0 to 7.5 wt %.

[0100] Methods that can apply the oil repellent at a relatively high concentration include, for example, slot die coating, gravure coating, spin coating, and bar coating. In particular, slot die coating and gravure coating are preferred because they allow easy control of the wet thickness of the oil repellent and are easy to handle. The dip coating method (impregnation method) is a method in which the oil repellent is applied to both main surfaces of the raw fluororesin porous membrane. According to the dip coating method, the oil repellent is permeated almost uniformly throughout the raw fluororesin porous membrane, so that in the ventilation filter 10, the absorbance ratio R f and the absorbance ratio R of the other main surface 12 b It is difficult to distribute the oil repellent so that there is a difference between

[0101] In the slot die coating method, the wet thickness of the oil repellent (flow rate / line speed) is determined by specifying the amount of oil repellent discharged per unit coating width (flow rate) and the line speed. In the slot die coating method, the wet thickness of the oil repellent is, for example, 5 to 100 μm. The lower limit of the wet thickness of the oil repellent may be 10 μm. The upper limit of the wet thickness of the oil repellent may be 80 μm or 70 μm.

[0102] In the gravure coating method, the wet thickness of the oil repellent is determined by specifying the gravure roll speed. In the gravure coating method, the wet thickness of the oil repellent is, for example, 5 to 100 μm. The lower limit of the wet thickness of the oil repellent may be 10 μm. The upper limit of the wet thickness of the oil repellent may be 80 μm or 70 μm.

[0103] According to the above manufacturing method, the oil repellent applied to the one principal surface in the application step penetrates into the original porous fluororesin membrane, but is prevented from penetrating into the entire original porous fluororesin membrane. f and the absorbance ratio R of the other main surface 12 b The oil repellent can be distributed so that there is a difference between

[0104] Next, another example of the ventilation filter of the present invention is shown in Figures 3A and 3B. Figure 3B shows a cross section of the ventilation filter 20 shown in Figure 3A. The ventilation filter 20 in Figures 3A and 3B further includes a support layer 2 that supports the porous fluororesin membrane 1.

[0105] 3A and 3B , the support layer 2 is disposed on the main surface 12 side of the porous fluororesin membrane 1. However, the support layer 2 may also be disposed on the main surface 11 side of the porous fluororesin membrane 1. The support layer 2 may also be disposed on both the main surface 11 and the main surface 12 side of the porous fluororesin membrane 1.

[0106] 3A and 3B , the shape of the support layer 2 corresponds to the shape of the fluororesin porous membrane 1 when viewed in a direction perpendicular to the main surfaces 11 and 12, and is specifically circular. However, the shapes of the fluororesin porous membrane 1 and the support layer 2 are not limited to the above example. In the ventilation filter 20 including the support layer 2, the fluororesin porous membrane 1 can be reinforced and handleability can be improved.

[0107] The support layer 2 has a net-like or mesh-like form and is breathable in the thickness direction. The breathability of the support layer 2 is usually higher than that of the porous fluororesin membrane 1. The support layer 2 ensures the strength and rigidity of the breathable filter 20, improves handling, and has the function of suppressing damage when the breathable filter 20 is attached to the housing of an electronic device or the like and when the breathable filter 20 is in use.

[0108] The material constituting the support layer 2 is not limited, and examples thereof include metals such as aluminum and stainless steel, resins such as polyolefins (polyethylene, polypropylene, etc.), polyesters (polyethylene terephthalate, etc.), polyamides (aliphatic polyamides, aromatic polyamides, etc.), and composite materials thereof.

[0109] The material constituting the support layer 2 is typically a polyolefin-based nonwoven fabric.

[0110] [Method for manufacturing a ventilation filter] The ventilation filter 20 can be manufactured, for example, by laminating a support layer 2 on the main surface 12 side of the fluororesin porous membrane 1 of the ventilation filter 10 manufactured by the above-mentioned method for manufacturing the ventilation filter 10. Lamination of the ventilation filter 10 and the support layer 2 can be performed using various bonding methods, such as thermal lamination, heat welding, ultrasonic welding, or bonding with an adhesive or pressure-sensitive adhesive.

[0111] [Ventilation member] An example of a ventilation member of the present invention is shown in Figures 4A and 4B. Figure 4B shows a cross section of the ventilation member 30A shown in Figure 4A. The ventilation member 30A comprises the ventilation filter 10 or 20 and a pressure-sensitive adhesive layer 3 bonded to the ventilation filter 10 or 20. Figures 4A and 4B show an example in which the ventilation member includes a ventilation filter 20.

[0112] In the ventilation member 30A, the pressure-sensitive adhesive layer 3 is disposed on the main surface 11 side of the porous fluororesin membrane 1. However, the pressure-sensitive adhesive layer 3 may also be disposed on the main surface 12 side of the porous fluororesin membrane 1. Figures 5A and 5B show another example of the ventilation member of the present invention. Figure 5B shows a cross section of the ventilation member 30B shown in Figure 5A. In the ventilation member 30B, the pressure-sensitive adhesive layer 3 is disposed on the support layer 2 on the main surface 12 side of the porous fluororesin membrane 1. The pressure-sensitive adhesive layer 3 may also be disposed on both the main surface 11 side and the main surface 12 side.

[0113] 4A to 5B , the shape of the pressure-sensitive adhesive layer 3 corresponds to the shape of the peripheral edge of the ventilation filter 20 when viewed from a direction perpendicular to the main surfaces 11 and 12, and is specifically ring-shaped. In this case, the pressure-sensitive adhesive layer 3 can be used as an attachment margin for the ventilation filter 20. However, the shapes of the ventilation filter 20 and the pressure-sensitive adhesive layer 3 are not limited to the above example, as long as they can be attached to an opening in the housing of an electronic device or an opening in an electronic component.

[0114] The ventilation member 30 (30A, 30B) may be attached to an opening in the housing of an electronic device or an opening in an electronic component with the pressure-sensitive adhesive layer 3 so that the main surface 11 of the fluororesin porous membrane 1 faces outward, or may be attached to an opening in the housing of an electronic device or an opening in an electronic component with the main surface 11 of the fluororesin porous membrane 1 facing inward.

[0115] 6A and 6B are cross-sectional views schematically showing examples in which a ventilation member 30 is attached to an opening of a housing of an electronic device or an opening of an electronic component so that the main surface 11 of the porous fluororesin membrane 1 faces outward. In Fig. 6A, the ventilation member 30A is attached to the opening 51 of the housing or electronic component 5 with a pressure-sensitive adhesive layer 3 so that the main surface 11 of the porous fluororesin membrane 1 faces outward. In Fig. 6B, the ventilation member 30B is attached to the opening 51 of the housing or electronic component 5 with a pressure-sensitive adhesive layer 3 so that the main surface 11 of the porous fluororesin membrane 1 faces outward.

[0116] Fig. 6C is a cross-sectional view schematically showing an example in which a ventilation member 30 is attached to an opening in the housing of an electronic device or an opening in an electronic component so that the main surface 11 of the porous fluororesin membrane 1 faces the interior. In Fig. 6C, the ventilation member 30A is attached to the opening 51 of the housing or electronic component 5 by the pressure-sensitive adhesive layer 3 so that the main surface 11 of the porous fluororesin membrane 1 faces the interior. The embodiment of Fig. 6C is intended for applications in which a liquid is held inside the housing 5 (for example, an ink cartridge).

[0117] The manner in which the ventilation member 30 is attached to the opening of the housing of an electronic device or the like or the opening of an electronic component is not limited to the above-described example, and various other manners are possible.

[0118] The adhesive layer 3 may be, for example, a double-sided adhesive tape.

[0119] [Method for manufacturing ventilation member] The ventilation member 30 can be manufactured, for example, by bonding the pressure-sensitive adhesive layer 2 to the main surface 11 side of the fluororesin porous membrane 1 of the ventilation filter 10 or 20 manufactured by the method for manufacturing the ventilation filter 10 or 20 described above.

[0120] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples shown below.

[0121] First, the method for evaluating the ventilation filter produced in this example will be described.

[0122] [Measurement of absorption spectrum by FT-IR] Using an FT-IR measurement device (4700 manufactured by Thermo Electron and Quest manufactured by SPECAC), the absorption spectrum was measured by the reflection method (ATR method) at a wave number of 650 cm. -1 ~4000cm -1 , resolution 4.0cm -1 The absorption spectrum was measured with an accumulation count of 64. From the obtained absorption spectrum, the absorbance A at the peak due to the oil repellent agent was a , and the absorbance A at the peak derived from the C—F bond m Using the above, the absorbance ratio R of one of the main surfaces is calculated by the following formula (1): f and the absorbance ratio R of the other principal surface b and was calculated.

[0123] When the peak derived from the oil repellent is a peak derived from a carboxy group, the absorbance A a As a result, 1700 cm -1 ~1740cm -1 When the peak derived from the oil repellent agent is a peak derived from an ether group, the absorbance A a As a result, 980 cm -1 ~990cm -1 The absorbance of the nearby peak was used. m As for height, it is 1150 cm. -1 The absorbance of a nearby peak was used.

[0124] A a / A m ...Formula (1)

[0125] The absorbance difference ratio between one principal surface and the other principal surface is calculated as the absorbance ratio R f and R b was used to calculate using the following formula (2).

[0126] 100×(R f -R b ) / R f ...Formula (2)

[0127] Fig. 7A is a schematic cross-sectional view illustrating measurement of absorption spectra by FT-IR. Specifically, as in the case of the porous fluororesin membrane 1 shown in Fig. 7A, the measurement was performed on a porous fluororesin membrane that had been cleaved in a direction parallel to one main surface 11 and the other main surface 12 at a position 40 to 60% of the thickness of the porous fluororesin membrane 1 in the thickness direction of the porous fluororesin membrane 1 from the main surface 11. The cleavage was performed by sandwiching one main surface and the other main surface of the porous fluororesin membrane with double-sided tape, respectively, and tearing the double-sided tape so as to separate them from each other.

[0128] As shown in Fig. 7A, a measurement point 21 was set on the main surface 11 of the porous fluororesin membrane 1. Of the opposing surfaces that emerged when the porous fluororesin membrane 1 was cut, a measurement point 22 was set on the surface closer to the main surface 11. Of the opposing surfaces, a measurement point 23 was set on the surface closer to the main surface 12. A measurement point 24 was set on the main surface 12 of the porous fluororesin membrane 1. That is, in the ventilation filter of this example, the absorbance ratio R f means the absorbance ratio at the measurement point 21 in Fig. 7A. The absorbance ratio R m means the absorbance ratio at measurement points 22 and 23 in Figure 7A. If the absorbance ratios at measurement points 22 and 23 do not match, the average value can be used as the absorbance ratio at a position 40 to 60% of the thickness of the membrane. The absorbance ratio R of the other main surface of the porous fluororesin membrane b means the absorbance ratio at measurement point 24 in FIG. 7A.

[0129] Figure 7B shows an example of an absorption spectrum by FT-IR. Figure 7B shows an example in which the oil repellent contains a fluorine-containing polymer including a polymer having a compound represented by the following chemical formula (a) as a monomer, and the fluororesin porous membrane is a PTFE porous membrane. Note that Figure 7B corresponds to Example 7, which will be described later.

[0130] CH2=C(CH3)COOCH2CH2C5F 10 CH2C4F9...(a)

[0131] Figure 7C shows another example of an absorption spectrum by FT-IR. Figure 7C shows an example in which the oil repellent contains a fluorine-containing polymer including a polymer having a compound represented by the following chemical formula (g) as a monomer, and the fluororesin porous membrane is a PTFE porous membrane. Note that Figure 7C corresponds to Example 20, which will be described later.

[0132] CH2=CH2COOCH2CH2NHCOCFCF3-(OCF2CF(CF3)) n -OCF2CF2CF3...(g)

[0133] 7B and 7C show the absorbance at the measurement point 21 in FIG. 7A. From the absorption spectrum in FIG. 7B, a peak (1700 cm ) derived from a carboxy group is observed. -1 ~1740cm -1 Absorbance A of the peak (existing in the vicinity) a , and a peak due to a C—F bond (1150 cm -1 Absorbance A of the peak (existing in the vicinity) m From the absorption spectrum of FIG. 7B, a peak (980 cm) derived from an ether group is observed. -1 ~990cm -1 Absorbance A of the peak (existing in the vicinity) a , and a peak due to a C—F bond (1150 cm -1 Absorbance A of the peak (existing in the vicinity) m The absorbance A a and A m From the above, the absorbance ratio R of one main surface of the porous fluororesin membrane in the ventilation filter can be calculated by the following formula (1). f and the absorbance ratio R of the other principal surface b The absorbance difference rate of the porous fluororesin membrane in the ventilation filter can be calculated using the following formula (2).

[0134] A a / A m ...Formula (1)

[0135] 100×(R f -R b ) / R f ...Formula (2)

[0136] [Oil repellency] In accordance with the oil repellency test (AATCC 118 method), the oil repellency of one main surface of the fluororesin porous membrane was tested by the following method. In the oil repellency test, the fluororesin porous membrane was placed on a piece of paper with the side to be tested facing up, and a drop of linear alkane was dropped on the membrane using a dropper, and it was confirmed whether the membrane was wetted after 30 seconds. Then, the oil repellency was evaluated by the linear alkane with the smallest number of carbon atoms among the linear alkanes that did not wet the membrane. For example, if the linear alkane was hexane (CH 14) the oil repellency was expressed as C6. In Table 1 described later, there are indications of "C10△" and "C10×". "C10△" indicates that C11 is definitely present, but it is not clear whether C10 is present. "C10×" indicates that C11 is definitely present, but C10 is almost infeasible.

[0137] [Gurley Air Permeability] The Gurley air permeability was evaluated by the method described above.

[0138] [Air permeability reduction rate] The air permeability reduction rate was determined as the reduction ratio of the air permeability of the ventilation filter to the air permeability of the original fluororesin porous membrane before the oil repellent treatment. The air permeability is proportional to the reciprocal of the Gurley air permeability. Therefore, when the Gurley air permeability of the original fluororesin porous membrane is defined as B1 and the Gurley air permeability of the ventilation filter is defined as B2, the air permeability reduction rate of the ventilation filter can be calculated using the following formula (5):

[0139] 100×{(1 / B1)-(1 / B2)} / (1 / B1)...Formula (5)

[0140] [Water Pressure Resistance Against IPA Aqueous Solution] The water pressure resistance against an IPA aqueous solution was evaluated by the method described above.

[0141] [Porosity] The porosity was evaluated by the method described above.

[0142] [Maximum Pore Diameter] The maximum pore diameter of the raw fluororesin porous membrane before the oil repellent treatment was calculated by the method described above.

[0143] [Preparation of raw fluororesin porous membrane] (raw PTFE porous membrane A) 100 parts by mass of PTFE fine powder (manufactured by Daikin Industries, F121) and 20.5 parts by mass of isoparaffin hydrocarbon (manufactured by ExxonMobil, Isopar M) as molding aid are uniformly mixed, and the obtained mixture is compressed using a cylinder, and then ram extrusion is carried out to form a sheet.Then, the sheet-like mixture is rolled to a thickness of 0.4 mm through a pair of metal rolls, and further heated at 150 ° C to dry and remove the molding aid, to form a sheet molded body.Then, the sheet molded body is stretched in the longitudinal direction (rolling direction) at a stretching temperature of 300 ° C and a stretching ratio of 4 times, and then stretched in the transverse direction at a stretching temperature of 150 ° C and a stretching ratio of 25 times, and further calcined at 400 ° C, to obtain raw PTFE porous membrane A.The average thickness of the obtained raw PTFE porous membrane A is 50 μm, the maximum pore size is 120 nm, and the porosity is 77.9%. The water pressure resistance against an IPA aqueous solution was 106 kPa, and the Gurley air permeability B1 was 30 seconds / 100 mL.

[0144] (Original PTFE porous membrane B) 100 mass parts of PTFE fine powder (Daikin Industries, F121) and 20.5 mass parts of isoparaffin hydrocarbon (ExxonMobil, Isopar M) as molding aid are uniformly mixed, and the mixture obtained is compressed using a cylinder, and then ram extrusion is carried out to form sheet.Then, the sheet-like mixture is rolled to a thickness of 0.2 mm through a pair of metal rolls, and then heated at 150 ℃ to dry and remove molding aid, and form sheet molding body.Then, the sheet molding body is stretched in longitudinal direction (rolling direction) at a stretching temperature of 300 ℃ and a stretching ratio of 4 times, and then stretched in transverse direction at a stretching temperature of 150 ℃ and a stretching ratio of 40 times, and then calcined at 400 ℃, to obtain original PTFE porous membrane B. The resulting raw PTFE porous membrane B had a thickness of 5 μm, a maximum pore size of 150 nm, a porosity of 76%, a water pressure resistance to an IPA aqueous solution of 100 kPa, and a Gurley air permeability B1 of 1.4 seconds / 100 mL.

[0145] (Original PTFE porous membrane C) 100 mass parts of PTFE fine powder (manufactured by AGC, CD123E) and 20.5 mass parts of isoparaffin hydrocarbon (manufactured by ExxonMobil, Isopar M) as molding aid are uniformly mixed, and the obtained mixture is compressed by cylinder, and then ram extrusion is carried out to form sheet.Then, the sheet-like mixture is rolled to a thickness of 0.2 mm through a pair of metal rolls, and then heated at 150 ° C to dry and remove molding aid, and form sheet molding body.Then, the sheet molding body is stretched in longitudinal direction (rolling direction) at a stretching temperature of 150 ° C and a stretching ratio of 4 times, and then stretched in transverse direction at a stretching temperature of 150 ° C and a stretching ratio of 20 times, and then calcined at 400 ° C, to obtain original PTFE porous membrane C. The resulting raw PTFE porous membrane C had a thickness of 5 μm, a maximum pore size of 700 nm, a porosity of 89%, a water pressure resistance to an IPA aqueous solution of 40 kPa, and a Gurley air permeability B1 of 3 seconds / 100 mL.

[0146] (Original PTFE porous membrane D) To a PTFE dispersion (PTFE powder concentration 40% by mass, PTFE powder average particle size 0.2 μm, nonionic surfactant content 6 parts by mass per 100 parts by mass of PTFE), 1 part by mass of a fluorochemical surfactant (MEGAFAC F-142D, manufactured by DIC Corporation) was added per 100 parts by mass of PTFE. Next, a long polyimide film (thickness 125 μm) was immersed in the PTFE dispersion and pulled out, and a coating film of the PTFE dispersion was formed on the film. At this time, the thickness of the coating film was set to 20 μm using a measuring bar. Next, the coating film was heated at 100 ° C. for 1 minute, and then at 390 ° C. for 1 minute, thereby evaporating and removing the water contained in the dispersion, and bonding the remaining PTFE particles together to obtain a PTFE membrane. After repeating the above immersion and heating two more times, a PTFE membrane (thickness 25 μm) was peeled off from the polyimide film. Next, the peeled cast membrane was rolled in the MD direction (longitudinal direction) and further stretched in the TD direction (width direction). Rolling in the MD direction was carried out by roll rolling. The rolling ratio (area ratio) was 2.0 times, and the temperature (roll temperature) was 170 ° C. The stretching in the TD direction was carried out using a tenter stretching machine. The stretching ratio in the TD direction was 2.0 times, and the temperature (temperature of the stretching atmosphere) was 300 ° C. The thickness of the obtained raw PTFE porous membrane D was 10 μm, the maximum pore size was 60 nm, the porosity was 30%, the water pressure resistance against an IPA aqueous solution was 200 kPa, and the Gurley air permeability B1 was 75 seconds / 100 mL.

[0147] Examples 1 to 8 The original porous PTFE membrane A was used as the original porous fluororesin membrane.

[0148] As the oil repellent treatment liquid, a mixture of an oil repellent agent α containing a polymer having a compound represented by the following chemical formula (a) as a monomer, and a solvent was prepared.

[0149] CH2=C(CH3)COOCH2CH2C5F 10 CH2C4F9...(a)

[0150] The solvent was added so that the concentration of the oil repellent agent α in the oil repellent treatment liquid was 1.7% by weight (Examples 1 to 3), 3.7% by weight (Examples 4 to 6), and 7.1% by weight (Examples 7 and 8). The solvent was a mixed solution of 1,1,2,2-tetrafluoroethoxy-1-(2,2,2-trifluoro)ethane (hereinafter referred to as HFE-347pc-f) (manufactured by AGC, AE-3000) and meta-xylene hexafluoride (hereinafter referred to as MX-HF). The mixing ratio, expressed by volume, was HFE-347pc-f:MX-HF = 3:1.

[0151] Next, the prepared oil-repellent treatment liquid was applied to one main surface of the raw PTFE porous membrane A. Then, it was dried at 60 to 70°C. The oil-repellent treatment liquid was applied by adjusting the discharge rate from the coater so that the wet thickness of the oil-repellent treatment liquid was 70 μm (Examples 1 and 4), 40 μm (Examples 2, 5, and 7), or 30 μm (Examples 3, 6, and 8). In this way, the ventilation filters of Examples 1 to 8 were obtained.

[0152] Examples 9 to 11 The original porous PTFE membrane A was used as the original porous fluororesin membrane.

[0153] As the oil repellent treatment liquid, a mixture of an oil repellent agent β containing a polymer having a compound represented by the following chemical formula (b) as a monomer, and a solvent was prepared.

[0154] CH2=CHCOOCH2CH2C6F 13 ...(b)

[0155] The solvent was added so that the concentration of the oil repellent β in the oil repellent treatment liquid was 3.7% by weight (Examples 9 and 10) and 4.8% by weight (Example 11). The same solvent as in Examples 1 to 8 was used.

[0156] Next, the prepared oil-repellent treatment liquid was applied to one main surface of the raw PTFE porous membrane A. By adjusting the discharge amount from the coating machine, the treatment was carried out so that the wet thickness of the oil-repellent treatment liquid was 70 μm (Example 9), 60 μm (Example 10), and 56 μm (Example 11). In this way, the ventilation filters of Examples 9 to 11 were obtained.

[0157] Example 12 The original porous PTFE membrane B was used as the original porous fluororesin membrane.

[0158] A mixture of oil repellent agent α and a solvent was prepared as the oil repellent treatment liquid. The solvent was added so that the concentration of oil repellent agent α in the oil repellent treatment liquid was 1.0 wt %. The same solvent as in Examples 1 to 8 was used.

[0159] Next, the prepared oil repellent treatment liquid was applied to one main surface of the raw PTFE porous membrane B. By adjusting the discharge amount from the coating machine, the treatment was carried out so that the wet thickness of the oil repellent treatment liquid becomes 11 μm. Thus, the ventilation filter of Example 12 was obtained.

[0160] Example 13 The original porous PTFE membrane C was used as the original porous fluororesin membrane.

[0161] A mixture of oil repellent agent α and a solvent was prepared as the oil repellent treatment liquid. The solvent was added so that the concentration of oil repellent agent α in the oil repellent treatment liquid was 3.0 wt %. The same solvent as in Examples 1 to 8 was used.

[0162] Next, the prepared oil repellent treatment liquid was applied to one main surface of the raw PTFE porous membrane C. By adjusting the discharge amount from the coating machine, the treatment was carried out so that the wet thickness of the oil repellent treatment liquid becomes 33 μm. Thus, the ventilation filter of Example 13 was obtained.

[0163] Examples 14 and 15 The original porous PTFE membrane D was used as the original porous fluororesin membrane.

[0164] In Example 14, a mixture of oil repellent agent α and a solvent was prepared as the oil repellent treatment liquid. The solvent was added so that the concentration of oil repellent agent α in the oil repellent treatment liquid was 1.0 wt %. The same solvent as in Examples 1 to 8 was used.

[0165] In Example 15, a mixture of oil repellent β and a solvent was prepared as the oil repellent treatment liquid. The solvent was added so that the concentration of the oil repellent β in the oil repellent treatment liquid was 1.0 wt %. The same solvent as in Examples 1 to 8 was used.

[0166] Next, in Examples 14 and 15, the prepared oil repellent treatment liquid is coated on one main surface of the original PTFE porous membrane D. By adjusting the discharge amount from the coating machine, the wet thickness of the oil repellent treatment liquid is carried out to be 17 μ m. Thus, the ventilation filter of Examples 14 and 15 is obtained.

[0167] The oil-repellent treatment liquid was applied so that the wet thickness of the oil-repellent treatment liquid was 81 μm (Comparative Example 1) and 60 μm (Comparative Example 2). Other than this, the ventilation filters of Comparative Examples 1 and 2 were obtained in the same manner as in Examples 7 and 8.

[0168] Example 16 The original porous PTFE membrane A was used as the original porous fluororesin membrane.

[0169] As the oil-repellent treatment liquid, a mixture of an oil-repellent agent γ containing perfluoropolyether having a repeating unit represented by the following chemical formula (d) and a solvent was prepared.

[0170]

[0171] In the chemical formula (d), the ratio of m:n:n' represented by m / n / n' is, for example, 40 / 1 / 1.

[0172] The solvent was added so that the concentration of the oil repellent agent γ in the oil repellent treatment liquid was 10.0% by weight. The solvent used was the same as in Examples 1 to 8.

[0173] Next, the prepared oil repellent treatment liquid is coated on one main surface of the raw PTFE porous membrane A. By adjusting the discharge amount from the coating machine, the treatment is carried out so that the wet thickness of the oil repellent treatment liquid becomes 50 μ m. Thus, the ventilation filter of Example 16 is obtained.

[0174] Comparative Example 3 A ventilation filter of Comparative Example 13 was obtained in the same manner as in Example 16, except that the oil repellent treatment liquid was applied so that the wet thickness of the oil repellent treatment liquid was 80 μm.

[0175] Examples 17 and 18 The original porous PTFE membrane A was used as the original porous fluororesin membrane.

[0176] As the oil-repellent treatment liquid, a mixture of an acrylate-based oil-repellent agent δ having perfluoropolyether in the side chain, represented by the following chemical formula (g), and a solvent was prepared.

[0177] CH2=CH2COOCH2CH2NHCOCFCF3-(OCF2CF(CF3)) n -OCF2CF2CF3...(g)

[0178] In the chemical formula (g), n ranges from 1 to 12, and is about 6 on average.

[0179] The solvent was added so that the concentration of the oil repellent δ in the oil repellent treatment liquid was 4.0% by weight. The solvent used was the same as in Examples 1 to 8.

[0180] Next, the prepared oil-repellent treatment liquid was applied to one main surface of the raw PTFE porous membrane A. By adjusting the discharge amount from the coater, the treatment was carried out so that the wet thickness of the oil-repellent treatment liquid was 54 μm in Example 17 and 72 μm in Example 18. In this way, the ventilation filters of Examples 17 and 18 were obtained.

[0181] Examples 19 and 20 The original porous PTFE membrane A was used as the original porous fluororesin membrane.

[0182] As the oil-repellent treatment liquid, a mixture of a solvent and a methacrylate-based oil-repellent agent ε having perfluoropolyether in the side chain, represented by the following chemical formula (h), was prepared.

[0183] CH2=CH(CH3)COOCH2CH2NHCOCFCF3-(OCF2CF(CF3)) n -OCF2CF2CF3...(h)

[0184] In the chemical formula (h), n ranges from about 3 to 8, and is about 6 on average.

[0185] The solvent was added so that the concentration of the oil repellent agent ε in the oil repellent treatment liquid was 4.0 wt %. The same solvent as in Examples 1 to 8 was used.

[0186] Next, the prepared oil-repellent treatment liquid was applied to one main surface of the raw PTFE porous membrane A. By adjusting the discharge amount from the coating machine, the treatment was carried out so that the wet thickness of the oil-repellent treatment liquid was 54 μm in Example 19 and 72 μm in Example 20. In this way, the ventilation filters of Examples 19 and 20 were obtained.

[0187] The evaluation results for the ventilation filters of the Examples and Comparative Examples are shown in Tables 1 and 2 below.

[0188]

[0189]

[0190] As shown in Tables 1 and 2, in the ventilation filters of the examples, the absorbance ratio R f and the absorbance ratio R of the other principal surface b Since the absorbance difference ratio is not the same as the absorbance difference ratio, sufficient oil repellency is exhibited and the decrease in air permeability is also suppressed. On the other hand, in the ventilation filter of the comparative example, although a certain degree of oil repellency was ensured, the air permeability was significantly reduced compared to the example. This is thought to be because the pores of the PTFE porous membrane in the comparative example were clogged by excess oil repellent. Thus, in the ventilation filter of the example, the oil repellency was exhibited and the decrease in air permeability was suppressed regardless of the pore diameter of the fluororesin porous membrane.

[0191] The absorbance ratios of one of the main surfaces of Example 7 and Example 9 were approximately the same. However, Example 9, which used the oil repellent β, showed a more suppressed rate of decrease in air permeability than Example 7, which used the oil repellent α. The absorbance ratios of one of the main surfaces of Example 14 and Example 15 were approximately the same. However, Example 15, which used the oil repellent β, showed a more suppressed rate of decrease in air permeability than Example 14, which used the oil repellent α.

[0192] Examples 1 to 12 and 14 to 20, which had relatively small maximum pore sizes, exhibited high oil repellency and had a smaller rate of decrease in air permeability than Example 13, which had a relatively large maximum pore size. The maximum pore size of the porous fluororesin membrane of Example 13 exceeded 500 nm, just like before the oil repellent treatment. Furthermore, in Examples 1 to 12 and 14 to 20, the maximum pore size after the oil repellent treatment was maintained at 500 nm or less.

[0193] 8 to 30 are graphs showing the absorbance ratio in the thickness direction of the ventilation filters of Examples 1 to 16, Comparative Examples 1 to 3, and Examples 17 to 20. In Figures 8 to 30, the horizontal axis corresponds to the symbols of the measurement points in Figure 7A. In Figures 8 to 30, the vertical axis corresponds to the absorbance ratio calculated by the above formula (1). Note that in Comparative Examples 1 to 3, the absorbance ratio R f and the absorbance ratio R b The slight difference between the absorbance ratio R and the absorbance ratio R is 0.0015 or less, more specifically, 0.001 or less. f and the absorbance ratio R b are considered to be substantially the same.

[0194] In each example, R f >0 and R b >0 and R f >R b In Examples 1, 4 to 6, and 8, R f >R m >R b As shown in Figures 24 to 26, in Comparative Examples 1 to 3, a sufficient amount of oil repellent was supplied to the porous PTFE membrane, so that the oil repellent was present on both main surfaces of the porous PTFE membrane to the same extent, and R f >R b In Comparative Examples 1 to 3, it is presumed that the excess oil repellent caused clogging of the pores of the porous PTFE membrane, resulting in a significant decrease in the air permeability of the ventilation filter.

[0195] In Examples 2 to 3 and 12 to 20, it was difficult to cut the porous fluororesin membrane in the direction parallel to one principal surface and the other principal surface. m In Comparative Examples 1 to 3, R m Although the measurement of the oil repellent was omitted, it was observed that the oil repellent was distributed almost uniformly in the thickness direction, and therefore the oil repellent was distributed to the same extent from one main surface to the other main surface.

[0196] Although measurement was omitted, the maximum pore size of the porous fluororesin membrane after application of the oil repellent agent was smaller than the maximum pore size of the original porous fluororesin membrane.

[0197] The technology disclosed in this specification can be used to provide waterproofing to electronic devices such as mobile phones, laptops, electronic organizers, digital cameras, and game consoles. However, the application of the technology disclosed in this specification is not limited to electronic devices. The technology disclosed in this specification can also be used to provide waterproofing to products that do not have audio functions, such as the housings of automobile parts such as sensors, switches, ECUs, and power conditioners (FCPCs).

Claims

1. A porous fluororesin membrane having one main surface and the other main surface and having been subjected to an oil repellent treatment with an oil repellent agent, When the absorption spectrum was measured by Fourier transform infrared spectroscopy, The absorbance ratio R of the one principal surface calculated by the following formula (1) f and the absorbance ratio R of the other principal surface b are not substantially identical to Ventilated filter. A a / A m ...Formula (1) Here, A a represents the absorbance at a peak attributable to the oil repellent in the absorption spectrum, and A m indicates the absorbance at the peak derived from the C—F bond in the absorption spectrum.

2. R f >0 and R b The ventilation filter according to claim 1, wherein the ρ is 0.

3. R f >R b and 3. The ventilation filter according to claim 1, wherein the one main surface has oil-repellent properties that prevent penetration of n-alkanes having 15 carbon atoms.

4. 3. The ventilation filter according to claim 1, wherein the maximum pore size of the porous fluororesin membrane and the Gurley air permeability of the porous fluororesin membrane satisfy at least one of the following a) to c): a) Maximum pore diameter 75 nm or less, Gurley air permeability 160 seconds / 100 mL or less b) Maximum pore diameter 150 nm or less, Gurley air permeability 80 seconds / 100 mL or less c) Maximum pore diameter 900 nm or less, Gurley air permeability 12 seconds / 100 mL or less

5. 3. The ventilation filter according to claim 1, wherein the porous fluororesin membrane has a Gurley air permeability of 90 seconds / 100 mL or less.

6. The absorbance difference rate between the one principal surface and the other principal surface calculated by the following formula (2) is 4% or more. The ventilation filter according to claim 1 or 2. 100×(R f -R b ) / R f Formula (2)

7. R f >R m >R b The ventilation filter according to claim 1 or 2, which satisfies the above. Here, R m is the absorbance ratio at a position 40 to 60% of the thickness of the porous fluororesin membrane from the one main surface in the thickness direction of the porous fluororesin membrane.

8. 3. The ventilation filter according to claim 1, wherein the porous fluororesin membrane is a porous polytetrafluoroethylene membrane.

9. The ventilation filter according to claim 1 or 2, wherein the oil repellent agent includes a fluorine-containing polymer.

10. The fluorine-containing polymer is CH 2 =CR 1 COOR 2 10. The ventilation filter according to claim 9, comprising a polymer having a compound represented by the following formula as a monomer: Here, R 1 is a hydrogen atom or a methyl group, and R 2 is a hydrocarbon group in which at least one hydrogen atom is substituted with a fluorine atom.

11. 10. The ventilation filter according to claim 9, wherein the fluorine-containing polymer comprises perfluoropolyether.

12. 3. The ventilation filter according to claim 1, wherein the one main surface of the porous fluororesin membrane has a water pressure resistance of 180 kPa or more against an aqueous solution of isopropanol having a concentration of 30% by weight.

13. 3. The ventilation filter according to claim 1, wherein the porosity of the porous fluororesin membrane is 63% or more.

14. 3. The ventilation filter according to claim 1, wherein the maximum pore size of the porous fluororesin membrane is 500 nm or less.

15. The air filter according to claim 1 or 2, further comprising a support layer that supports the porous fluororesin membrane.

16. The ventilation filter according to claim 1 or 2; a pressure-sensitive adhesive layer bonded to the ventilation filter.