Fluororesin composition and fine foamed fluororesin film using same

Abstract

A fluororesin composition containing (A) and (B) described below, the content of (B) being 10 mass% or more. (A) A fluororesin which contains, as constituent components, a tetrafluoroethylene component and a component other than the tetrafluoroethylene component and which has the greatest heat of fusion in the fluororesin composition. (B) A fluororesin having a lower melting heat than the fluororesin (A).

Description

Technical Field

[0001] The present invention relates to a fluororesin composition and a fine-foamed fluororesin film using the fluororesin composition. Background Art

[0002] The sterilization effect of ultraviolet rays has been studied for a long time. As the light source of ultraviolet rays, low-pressure mercury lamps, xenon lamps, etc. have been the mainstream so far, but in recent years, LEDs that can emit light with wavelengths in this area have been developed, and sterilization equipment equipped with LEDs or sterilization methods using LEDs have been developed. For example, Patent Document 1 describes a fluid sterilization component that irradiates ultraviolet rays to a fluid flowing in a flow path to sterilize the fluid. In order to effectively diffuse the ultraviolet rays irradiated from the light source to a certain area, it is effective to use a reflective material that can effectively and evenly reflect ultraviolet rays. The fluid sterilization component described in Patent Document 1 uses an ultraviolet reflective material in the inner cylinder that forms a cylindrical processing flow path.

[0003] As ultraviolet reflective materials, metal materials, resin materials, etc. are known. As the metal material, for example, aluminum foil for ultraviolet reflective materials showing high reflectivity to ultraviolet rays by controlling aluminum particles is known (Patent Document 2), aluminum reflective parts having a reflective layer or a UV permeable resin layer on the surface of the aluminum material, etc. (Patent Document 3). In addition, as the above-mentioned resin material, it is known that fluorine-based resins or silicone-based resins are made into materials of multilayer laminates, for example, multilayer optical films with two kinds of fluoropolymer materials having different refractive indices, ultraviolet reflective polymer films with two different polymer layers are known (Patent Documents 4 and 5). In addition, sintered compression or porous molded bodies made of polytetrafluoroethylene (PTFE) are also known as ultraviolet reflective materials.

[0004] Fluororesin is rarely degraded by ultraviolet rays. By being made into a foamed film with bubbles and pores of the desired size inside, it can reflect ultraviolet rays, so it is expected to be used as an ultraviolet reflective material in the field of sterilization (Patent Document 6). In order to more effectively reflect ultraviolet rays in the wavelength range used for sterilization, it is necessary to control the size of the bubbles or pores inside to a very fine size. For example, in the case of using a foamed film to realize a reflective film for reflecting ultraviolet rays called UV-C (Ultraviolet C: deep ultraviolet) with a wavelength of 200nm to 280nm, it is necessary to control the size of the bubbles or pores to about 1μm. In addition, the wavelength of sterilizing ultraviolet rays has also been changing more recently, and reflective materials that can more efficiently reflect ultraviolet rays with a short wavelength of 200nm or thereabouts are required.

[0005] As a resin foaming technology, it is known to impregnate a thermoplastic resin with a gas such as carbon dioxide under pressure, then release the pressure to return to normal pressure, and then heat the resin to a softening point or above to foam it. However, in the case of a fluororesin, due to its high crystallization rate and crystallinity, after the pressure is released until the heating and foaming step, the gas is discharged from the resin, which has a problem of being difficult to control to the target fine foaming state.

[0006] As a foaming technology for fluororesin, Patent Document 7 records that carbon dioxide is impregnated into a non-foamed molded body of a resin material containing a crystalline fluororesin and then foamed. However, in this method, a special pressure vessel is required to impregnate the crystalline fluororesin with supercritical carbon dioxide, and industrial mass production is difficult. In addition, Patent Document 8 records a technology for using a foamed fluororesin material as a covering layer of an insulated wire. Specifically, an insulated wire having a foamed insulating layer formed directly or via a hot melt layer on the surface of a conductor is recorded, and the foamed insulating layer is composed of a material formed by mixing an amorphous fluororesin having a glass transition temperature of 80°C to 300°C in a copolymer of tetrafluoroethylene and hexafluoropropylene or a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether. However, in the technology recorded in Patent Document 8, in the formation of the foamed insulating layer, fluorocarbons with high affinity for fluororesin are used to foam from a molten state, which has practical problems from the perspective of global warming. In addition, this method cannot obtain a fine foaming layer that reflects UV-C.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2019-187657

[0010] Patent Document 2: International Publication No. 2017 / 158989

[0011] Patent Document 3: Japanese Patent Application Publication No. 2016-042183

[0012] Patent Document 4: Japanese Patent Publication No. 7-507152

[0013] Patent Document 5: Japanese Patent Application Publication No. 2015-165298

[0014] Patent Document 6: International Publication No. 2022 / 064991

[0015] Patent Document 7: Japanese Patent Application Publication No. 2015-34255

[0016] Patent Document 8: Japanese Patent Application Laid-Open No. 5-47221 Summary of the invention

[0017] Problems to be solved by the invention

[0018] The present invention aims to provide a fluororesin composition, which can contain fine bubbles inside the resin composition by gas impregnation and subsequent foaming operation. In addition, one aspect of the present invention aims to provide a fluororesin composition, which can form a fine-foamed fluororesin film that efficiently reflects UV-C by gas impregnation and subsequent foaming operation. In addition, the present invention aims to provide a fine-foamed fluororesin film that can efficiently reflect UV-C, for example, which can be obtained by gas impregnation and subsequent foaming operation.

[0019] Means for solving problems

[0020] The above-mentioned problems of the present invention are solved by the following means. [1]

[0022] A fluororesin composition comprising the following (A) and (B), wherein the content of the above-mentioned (B) is 10 mass % or more.

[0023] (A) A fluororesin comprising a tetrafluoroethylene component and a component other than the tetrafluoroethylene component as constituent components and having the highest heat of fusion in the above-mentioned fluororesin composition.

[0024] (B) A fluororesin having a lower heat of fusion than the fluororesin (A) above. [2]

[0026] The fluororesin composition as described in the above [1], wherein both (A) and (B) are fully fluorinated resins, or both (A) and (B) are partially fluorinated resins. [3]

[0028] The fluororesin composition as described in the above [1] or [2], wherein the total of the transmittance and the total reflectance to ultraviolet rays having a wavelength of 200 nm to 280 nm is 60% or more. [4]

[0030] A finely foamed fluororesin film obtained by foaming the fluororesin composition according to any one of [1] to [3] above. [5]

[0032] The finely foamed fluororesin film as described in the above [4] has an average cell diameter of 1 μm or less. [6]

[0034] The fine-foamed fluororesin film as described in the above [4] or [5] has a total reflectivity of 85% or more with respect to ultraviolet rays having a wavelength of 200 nm to 280 nm. [7]

[0036] The finely-foamed fluororesin film as described in any one of the above [4] to [6], wherein the expansion ratio is 1.05 to 2.00. [8]

[0038] The finely-foamed fluororesin film as described in any one of the above [4] to [7], which is a deep ultraviolet reflecting film.

[0039] In the present invention, "ultraviolet rays" refer to electromagnetic waves having a wavelength shorter than that of visible light. It should be noted that in the present invention, "ultraviolet rays having a wavelength of 200 nm to 280 nm" refer to ultraviolet rays included in deep ultraviolet rays.

[0040] In the present invention, "total reflectance" refers to the sum of "regular reflectance" (specular reflectance) and "diffuse reflectance". In addition, "regular reflectance" refers to the proportion of irradiated light that is regularly reflected in the irradiated light, and "diffuse reflectance" refers to the proportion of irradiated light that is diffusely reflected in the irradiated light.

[0041] Effects of the Invention

[0042] The fluororesin composition of the present invention can contain fine bubbles inside the composition by gas impregnation and subsequent foaming operation. Therefore, for example, a fine-foamed fluororesin film that efficiently reflects UV-C can be formed. In addition, the fine-foamed fluororesin film of the present invention can be obtained by using a fluororesin composition in which a specific type of fluororesin is combined as a raw material, and by gas impregnation and subsequent foaming operation of the composition, and can, for example, efficiently reflect UV-C. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a photograph in lieu of a drawing in which the fine-foamed fluororesin film produced in Example 2 was freeze-fractured in a high vacuum and the cross section was photographed using a scanning electron microscope. DETAILED DESCRIPTION

[0044] Preferred embodiments of the fluororesin composition and finely foamed fluororesin film of the present invention will be described.

[0045] [Fluororesin composition]

[0046] The fluororesin composition of the present invention (hereinafter also referred to as "the composition of the present invention") contains at least two or more fluororesins. The fluororesin may be a fully fluorinated (perfluoro) resin or a partially fluorinated resin. A fully fluorinated resin refers to a resin in which all hydrogen atoms in the molecule are replaced by fluorine atoms. Examples of such fully fluorinated resins include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFA), tetrafluoroethylene-hexafluoropropylene copolymers (FEP), and the like. In addition, a partially fluorinated resin refers to a resin in which a portion of hydrogen atoms in the molecule are replaced by fluorine atoms, or a copolymer of a fluororesin and a hydrocarbon monomer. Examples of such partially fluorinated resins include polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether-chlorotrifluoroethylene copolymer (CPT), ethylene-tetrafluoroethylene-hexafluoropropylene copolymer (EFEP), and tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer (THV).

[0047] Various additives may be added to these fluororesins within the range not impairing the effects of the present invention, such as heat stabilizers, organic lubricants, organic or inorganic fine particles, antistatic agents, surfactants, antioxidants, and the like.

[0048] The composition of the present invention contains the following fluororesins (A) and (B). Each fluororesin contained in the composition is classified into either of the following (A) and (B) based on its heat of fusion.

[0049] (A) A fluororesin comprising a tetrafluoroethylene component and a component other than the tetrafluoroethylene component as constituent components and having the highest heat of fusion in the above-mentioned fluororesin composition.

[0050] (B) A fluororesin having a lower heat of fusion than the fluororesin (A) above.

[0051] The heat of fusion (crystallization heat of fusion) (J / g) of the above-mentioned fluororesin can be measured by a method generally used for crystalline resins. For example, using a differential scanning calorimeter (DSC), the integral value calculated from the DSC curve and the baseline is obtained, thereby determining the heat of fusion (in the present invention, "heat of fusion" refers to the absolute value of the value (negative value) calculated by DSC). It should be noted that when comparing the heats of fusion of the various fluororesins used, the heats of fusion obtained by unifying the measurement conditions such as the cooling rate are compared.

[0052] When a commercially available fluororesin is used, the heat of fusion described in the product information of the commercial product may be used as the heat of fusion of the fluororesin.

[0053] The above-mentioned (A) is a copolymer containing a tetrafluoroethylene component and components other than the tetrafluoroethylene component. Examples of the above-mentioned copolymer containing a tetrafluoroethylene component and components other than the tetrafluoroethylene component include PFA, FEP, ETFE, CPT, EFEP, THV, etc. In addition, the above-mentioned (A) is a fluororesin having the largest heat of fusion among the fluororesins contained in the composition of the present invention. Therefore, in the composition of the present invention, the above-mentioned (A) is usually one kind of fluororesin.

[0054] The above-mentioned (B) is a fluororesin other than the fluororesin corresponding to the above-mentioned (A) among the fluororesins contained in the composition of the present invention. The above-mentioned (A) is a fluororesin having the largest heat of fusion, and therefore, the heat of fusion of the fluororesin corresponding to the above-mentioned (B) is smaller than the heat of fusion of the fluororesin corresponding to the above-mentioned (A). It should be noted that in the composition of the present invention, the fluororesin corresponding to the above-mentioned (A) is usually one kind.

[0055] When the composition of the present invention contains three or more fluororesins, all fluororesins other than the fluororesin corresponding to the above-mentioned (A) correspond to the above-mentioned (B). That is, the above-mentioned (B) may be one fluororesin or two or more fluororesins. For example, when the composition of the present invention contains two fluororesins having different calorific values, the fluororesin corresponding to the above-mentioned (B) is one, and when the composition of the present invention contains three or more fluororesins having different calorific values, the fluororesins corresponding to the above-mentioned (B) are two or more.

[0056] The difference between the heat of fusion of the fluororesin corresponding to (A) and the heat of fusion with the lowest heat of fusion among the fluororesins corresponding to (B) is preferably 5 J / g or more, more preferably 10 J / g or more, and even more preferably 15 J / g or more. It should be noted that there is no particular restriction on the upper limit of the difference between the heat of fusion of the fluororesin corresponding to (A) and the heat of fusion with the highest heat of fusion among the fluororesins corresponding to (B), and the difference is usually 40 J / g or less, and may be 30 J / g or less, or 20 J / g or less.

[0057] In the composition of the present invention, the content of (B) is 10% by mass or more. From the perspective of setting the foaming ratio and average bubble diameter of a fine-foamed fluororesin film produced using the composition of the present invention to a desired range, the content is preferably 15% by mass or more. In addition, the content can be 90% by mass or less, can be 70% by mass or less, preferably 50% by mass or less, more preferably 40% by mass or less, and further preferably 30% by mass or less.

[0058] In addition, when a plurality of fluororesins correspond to the above-mentioned (B), the above-mentioned "content of (B)" means the total content of the plurality of fluororesins corresponding to the above-mentioned (B).

[0059] In the composition of the present invention, the content of (A) may be 10% by mass or more, 30% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 70% by mass or more. In addition, the content is 90% by mass or less, preferably 85% by mass or less.

[0060] In the above (A) and (B), from the viewpoint of compatibility, it is preferred that the fluororesins corresponding to (A) and (B) are both fully fluorinated resins, or that the fluororesins corresponding to (A) and (B) are both partially fluorinated resins.

[0061] The composition of the present invention, when formed into a film having a thickness of 500 μm and not foamed, preferably has a total transmittance and a total reflectance of 60% or more, more preferably 65% ​​or more, and even more preferably 70% or more.

[0062] It should be noted that in this specification, the total reflectivity and transmittance of the deep ultraviolet light of wavelength 200nm~280nm all refer to the average value of the total reflectivity and transmittance under each wavelength (1nm unit) of the wavelength region of the deep ultraviolet light of wavelength 200nm~280nm. The total reflectivity and transmittance of the deep ultraviolet light can be measured by the method described in the following embodiment.

[0063] The composition of the present invention can be used for applications such as deep ultraviolet reflective films, foamed insulating films of printed circuit boards, etc., ultraviolet protective films, antenna cases, and radio wave transmissive bodies.

[0064] It should be noted that the composition of the present invention is preferably used for applications other than forming an insulating coating layer of an insulated wire (not used for forming an insulating coating layer of an insulated wire).

[0065] [Fine-foamed fluororesin film]

[0066] The finely foamed fluororesin film of the present invention (hereinafter also referred to as "the film of the present invention") is a film obtained by finely foaming the above-mentioned composition. In the film of the present invention, bubbles generated by fine foaming are dispersed in the composition.

[0067] The composition of the present invention can suppress the crystallization rate of the composition as a whole by including two or more fluororesins with different heats of fusion, and maintain the crystallinity at a low level, thereby suppressing the detachment of the gas impregnated in the fluororesin. In addition, by molding the composition into a film and subjecting it to a foaming treatment, the fluororesin (B) uniformly dispersed in the fluororesin (A) acts as a good bubble nucleating agent, accelerating the bubble generation rate, and forming a large number of bubbles before the carbon dioxide detaches.

[0068] Figure 1 This is a scanning electron microscope photograph of a cross section of one embodiment of the film of the present invention cut in the thickness direction. Figure 1 The fluororesin film (10) shown is a film composed of a fluororesin composition (1) and has cells (2) therein which are substantially circular in plan view.

[0069] It should be noted that the film of the present invention is not limited to Figure 1 way.

[0070] The shape of the above-mentioned bubble is not particularly limited and can be appropriately designed within the scope of not damaging the effect of the present invention. For example, in the top view of the film cross section, it can be circular, approximately circular, elliptical, or can be a long elliptical shape with acute angles at both ends formed by making the approximate circular arcs face each other. In the present invention or this specification, "bubble diameter" refers to the maximum distance (maximum diameter) between a certain point connecting the periphery of a bubble (the boundary line between the bubble and the resin) and another point. In addition, "average bubble diameter" refers to the average value of the bubble diameter measured for 50 random bubbles. It should be noted that the above-mentioned average bubble diameter can be determined, for example, by the method described in the embodiments.

[0071] The film of the present invention can make the impregnated gas finely foamed by uniformly dispersing the above-mentioned (B) in the fluororesin of the above-mentioned (A), and can form a form containing the generated fine bubbles. The average bubble diameter of the bubbles is preferably 1 μm or less, more preferably 0.8 μm or less, further preferably 0.5 μm or less, and further preferably 0.4 μm or less. In addition, the average bubble diameter of the bubbles is usually 0.01 μm or more, preferably 0.05 μm or more, and preferably 0.06 μm or more. It should be noted that the above-mentioned bubbles can be independent bubbles or continuous bubbles.

[0072] In the film of the present invention, the expansion ratio is preferably 1.05 or more, more preferably 1.10 or more. In addition, the expansion ratio can also be 2.00 or less. If fine foaming is considered, it is preferably 1.60 or less, more preferably 1.50 or less, also preferably 1.30 or less, and also preferably 1.25 or less. In the present invention or this specification, the expansion ratio refers to the ratio (P / Q) of the density (P) of the resin composition constituting the film itself to the density (bulk density, Q) of the film (film having bubbles). It should be noted that the units of density P and density Q are the same. The density (bulk density) of the film of the present invention can be measured, for example, by the water displacement method (JIS K7112: 1999).

[0073] The film of the present invention can be appropriately set in thickness according to the purpose. For example, it can be 50 μm or more, 100 μm or more, or 300 μm or more. In addition, the film thickness can be 1000 μm or less, 800 μm or less, or 600 μm or less. It should be noted that the film thickness refers to the film thickness after the foaming treatment. For example, in the case where the film thickness changes before and after the foaming treatment due to the high foaming ratio, the film thickness of the resin film provided for the foaming treatment can be appropriately set so that the film thickness after the foaming treatment is within the above-mentioned preferred range.

[0074] For example, when the film of the present invention is used as a deep ultraviolet reflection film, the film thickness is preferably 100 μm or more, more preferably 200 μm or more, and further preferably 400 μm or more from the aspect of deep ultraviolet reflection efficiency. In addition, from the aspect of processability of the reflection film, the film thickness is preferably 1000 μm or less, more preferably 800 μm or less, and further preferably 600 μm or less.

[0075] The film of the present invention preferably has a total reflectivity of 50% or more, more preferably 60% or more, more preferably 70% or more, more preferably 80% or more, further preferably 85% or more, and further preferably 90% or more for deep ultraviolet rays of 200nm to 280nm when the film thickness is 500μm. The film of the present invention is also excellent in total reflectivity for deep ultraviolet rays of short wavelength side, for example 200nm to 220nm.

[0076] The film of the present invention having excellent reflective performance for deep ultraviolet rays of 200nm to 280nm is used, for example, as a reflective film for a deep ultraviolet light source, thereby being able to efficiently reflect the deep ultraviolet rays irradiated from the light source. Therefore, for example, for deep ultraviolet light emitted from a mercury lamp or a metal halide lamp, a barrier discharge lamp, a deep ultraviolet LED, etc., it is possible to reflect light that deviates from the irradiation object, and effectively utilize the deep ultraviolet rays without omission. The unit combining such a light source with a reflective film can be suitable for water sterilization equipment, space sterilization equipment, equipment for sterilizing the surface of medical supplies or daily necessities, various processed products or foods, etc.

[0077] Furthermore, since the film of the present invention prevents transmission of deep ultraviolet rays by highly reflecting deep ultraviolet rays, it can also be used as a shielding film for protecting substances exposed to deep ultraviolet rays, for example.

[0078] Furthermore, the film of the present invention having fine bubbles in the film has excellent dielectric properties and can therefore be suitably used for antenna cases, insulating coating films, radio wave transmitting films, and the like.

[0079] [Method for producing film of the present invention]

[0080] Next, the method for producing the film of the present invention will be described.

[0081] Figure 1 The film of the present invention shown is a film formed by molding the composition of the present invention into a film shape, impregnating carbon dioxide, and further heating to form fine bubbles inside. By using the composition of the present invention as a resin material constituting the film, it is possible to effectively suppress the gas from escaping before foaming, and in addition, the above (B) acts as a good bubble nucleating agent to accelerate the bubble generation rate, so that the film can be finely foamed inside. An example of a method for obtaining such a film formed with a large number of fine bubbles is described.

[0082] The production method exemplified here includes the following steps: a gas sealing step of impregnating a film composed of the composition of the present invention with a gas (inert gas such as carbon dioxide, nitrogen, and rare gas) under high pressure; and a heating and foaming step of heating after the pressure is released to generate bubbles inside the resin.

[0083] In the gas sealing step, the film composed of the resin composition of the present invention is exposed to gas for preferably 1 hour to 100 hours, more preferably 2 hours to 48 hours, preferably under a pressure condition of 1 MPa to 20 MPa, more preferably 3 MPa to 10 MPa, to seal the gas in the resin film. For example, an autoclave or a pressure vessel can be suitably used in the gas sealing step.

[0084] In the heating foaming step, the film after the gas sealing step is preferably heated at a temperature of 120° C. to 300° C., more preferably 150° C. to 250° C., for preferably 0.1 minute to 3 minutes, more preferably 0.5 minute to 2 minutes. By going through this step, a reflective film having desired fine bubbles or pores inside the resin film can be obtained.

[0085] When gas is sealed in a resin film composed of a single-component fluororesin under high pressure, due to the high crystallization rate and crystallinity of the fluororesin, the gas will be discharged from the resin after the pressure is released and before the heating and foaming process, making it difficult to control the target fine foaming state. In particular, in the manufacturing site of fluororesin films that are not laboratory-scale but large-scale, it is sometimes difficult to shorten the time from pressure release to the heating and foaming process. In addition, the gas is quickly released from the resin, so it is easy to produce deviations in gas concentration in the resin film before the heating and foaming process is about to be carried out, which may also be the cause of deviations in the reflectivity of deep ultraviolet rays in the surface of the resin film obtained by the subsequent heating and foaming.

[0086] In contrast, the composition of the present invention is a composition containing fluororesins with different calorific values ​​of fusion, so compared with a composition consisting of a single-component fluororesin, it is possible to suppress the crystallization rate of the composition as a whole and maintain a low degree of crystallinity. Therefore, even if the film after the gas sealing process is not quickly subjected to the heating and foaming process, the target finely foamed fluororesin film can be obtained. For example, the time spent from pressure relief to the heating and foaming process can be set to 1 minute to 240 minutes, 5 minutes to 120 minutes, or 10 minutes to 60 minutes. In addition, the composition of the present invention maintains a low degree of crystallinity as described above, so it is believed that the deviation of the gas concentration in the resin film before the heating and foaming process is about to be performed can be suppressed, and the deviation of the reflectivity of deep ultraviolet rays in the surface of the resin film can be suppressed.

[0087] Example

[0088] Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to these embodiments.

[0089] <Manufacturing method>

[0090] [Example 1]

[0091] 80 parts by mass of Neoflon (manufactured by Daikin Industries, Ltd., trade name: Neoflon FEP NP-40, MFR: 1) and 20 parts by mass of A-PFA (manufactured by DuPont Mitsui & Co., Ltd., amorphous PFA 959HP-Plus) were put into a twin-screw extruder (Φ25 mm) for kneading to obtain a compound (mixture). After that, the above compound was put into a single-screw extruder (Φ20 mm) to prepare a fluororesin composition, which was molded into a thickness of 500 μm and a width of 300 mm to obtain a resin film (hereinafter also referred to as "pre-foaming film"). Next, a film with a thickness of 160 μm, a width of 290 mm, and a basis weight of 55 g / m 2 An olefin-based nonwoven fabric (manufactured by Japan Vilene Co., Ltd.: FT300 grade) was used as a separator, and the resin film and the nonwoven fabric were overlapped and rolled up to obtain a roll A.

[0092] Thereafter, the roll A was placed in a pressure vessel, the interior of the pressure vessel was pressurized to 5.2 MPa with carbon dioxide, and the carbon dioxide was allowed to permeate into the resin film for 24 hours.

[0093] Next, the roll A was taken out from the pressure vessel, and while removing the diaphragm, the resin film permeated with carbon dioxide was continuously supplied to a hot air circulation foaming furnace set at 210° C. with a residence time of 1 minute in the foaming furnace to foam it. It should be noted that the time from taking the roll A out of the pressure vessel to heating the resin film at 210° C. was about 30 minutes. The heated resin film was referred to as the resin film of Example 1 (hereinafter also referred to as the “foamed film”).

[0094] It should be noted that the film thickness of Example 1 (resin film after heating) was measured using a micrometer (trade name: anti-cooling liquid micrometer, model: MDC-25MX, manufactured by Mitutoyo Co., Ltd.), and the film thickness was substantially the same before and after the foaming treatment. The same is true for the following Examples and Comparative Examples.

[0095] [Examples 2 to 8]

[0096] Resin films (films before and after foaming treatment) of Examples 2 to 8 were obtained in the same manner as in Example 1 except that the compounding composition of the fluororesin composition was changed to the composition described in the following Table 1. The detailed information of the fluororesin is as follows.

[0097] -Fluororesin-

[0098] ·FEP-1: Neoflon FEP NP-40, MFR = 1, manufactured by Daikin Industries, Ltd., tetrafluoroethylene-hexafluoropropylene copolymer

[0099] ·FEP-2: Neoflon FEP NP-30, MFR=3, manufactured by Daikin Industries, Ltd., tetrafluoroethylene-hexafluoropropylene copolymer

[0100] ·A-PFA: Amorphous PFA959HP-Plus, MFR=2, manufactured by DuPont Mitsui & Co., Ltd., tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer

[0101] ETFE-1: Neoflon ETFE EP-521, MFR = 11-13, manufactured by Daikin Industries, Ltd., ethylene-tetrafluoroethylene copolymer

[0102] ETFE-2: Neoflon ETFE EP-620, MFR = 12-18, manufactured by Daikin Industries, Ltd., ethylene-tetrafluoroethylene copolymer

[0103] ·PFA-1: Neoflon PFA AP-230, MFR=2, manufactured by Daikin Industries, Ltd., tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer

[0104] The heat of fusion (J / g) of each fluororesin is the heat of fusion (absolute value) measured using a differential scanning calorimeter (DSC-60A, manufactured by Shimadzu Corporation) at a heating temperature of 10° C. / min.

[0105] [Comparative Examples 1 to 3]

[0106] A resin film (film before foaming treatment) with a thickness of 500 μm composed of the fluororesin described in Table 1 below was overlapped with a diaphragm and wound to form a roll in the same manner as in Example 1, and carbon dioxide was permeated in a pressure vessel at 5.2 MPa for 24 hours. The resin film was supplied to a heating circulation foaming furnace in the same manner as above, and the film thickness was measured in the same manner as above to obtain resin films (film after foaming treatment) of Comparative Examples 1 to 3. It should be noted that the time from taking out the resin film from the autoclave to heating at 210° C. was the same as in Example 1.

[0107] The films of Examples 1 to 8 and Comparative Examples 1 to 3 were used to evaluate the average cell diameter, expansion ratio, deep ultraviolet transmittance, and deep ultraviolet reflectance as follows. The obtained results are summarized in Table 1 below.

[0108] <Evaluation method>

[0109] [Average bubble diameter]

[0110] The average bubble diameter in the films (films after foaming treatment) of Examples 1 to 8 was obtained by freezing and cutting each film in a high vacuum, observing the cross section using a scanning electron microscope (model: JSM-6390LV, manufactured by JEOL Ltd.), and randomly measuring the maximum diameter of 50 bubbles from the obtained data to calculate the average value. The obtained average bubble diameter values ​​are shown in Table 1 below.

[0111] [Foaming ratio]

[0112] The density (P) of the films before foaming treatment and the density (Q) of the films after foaming treatment of Examples 1 to 8 and Comparative Examples 1 to 3 were measured by the water displacement method (JIS K 7112: 1999). The foaming ratio (P / Q) was calculated from the obtained density (P) and (Q). The results are shown in Table 1 below.

[0113] [Deep UV Total Reflectance]

[0114] The Φ60 standard integrating sphere was installed in a spectrophotometer (trade name: U-4100, manufactured by Hitachi High-Tech Co., Ltd.), and the total reflectivity of each film (film before and after foaming treatment) was measured in the deep ultraviolet region of wavelength 200nm to 280nm, when the total reflectivity of the Spectralon standard reflector (Labsphere, white, model: USRS-99-010) was 100%. The reflectivity of each 1nm wavelength was read from the obtained chart (measurement result), and the arithmetic average of the total reflectivity (81 measured values ​​(%)) in the above-mentioned deep ultraviolet region was obtained as the "deep ultraviolet total reflectivity". The results of the deep ultraviolet total reflectivity of each foaming treated film of Examples 1 to 8 and Comparative Examples 1 to 3 are shown in Table 1 below.

[0115] [Deep UV transmittance]

[0116] A Φ60 standard integrating sphere was mounted on a spectrophotometer (trade name: U-4100, manufactured by Hitachi High-Technologies Co., Ltd.), and light of each wavelength was irradiated from the front side of the film before the foaming treatment in Examples 1 to 8 and Comparative Examples 1 to 3, and the ratio of the amount of light captured by the detector when the amount of irradiated light was set to 100% was taken as the transmittance (%). The transmittance of each 1 nm wavelength was measured in the deep ultraviolet region of wavelengths of 200 nm to 280 nm, and the arithmetic average of 81 measured values ​​was calculated as the "deep ultraviolet transmittance".

[0117]

[0118] Even when the fluororesin film using one fluororesin was impregnated with carbon dioxide and foamed, a sufficient amount of desired fine bubbles could not be formed in the film, and the deep ultraviolet total reflectivity of the film after the foaming treatment was less than 50% (Comparative Examples 1 to 3).

[0119] In contrast, the fluororesin film using a plurality of fluororesins with different melting heats can form the desired fine bubbles in the film by impregnation with carbon dioxide for foaming treatment, and the foaming ratio is significantly improved by the foaming treatment. In addition, the total value of the transmittance and total reflectance of deep ultraviolet rays with a wavelength of 200nm to 280nm of these resins before the foaming treatment is high, so the absorptivity of the deep ultraviolet rays is suppressed to a low level, and further, after the foaming treatment, the deep ultraviolet total reflectance shows a reflectivity of more than 85% (Examples 1 to 8).

[0120] The present invention has been described in conjunction with its embodiments, but the applicant believes that, unless otherwise specified, the present invention is not limited to any details in the description and should be broadly interpreted without violating the spirit and scope of the invention as shown in the appended claims.

[0121] This application claims the priority based on Japanese Patent Application No. 2022-135178 filed in Japan on August 26, 2022, the contents of which are incorporated herein by reference as a part of the contents described in this specification.

[0122] Explanation of symbols

[0123] 10 Fluororesin film

[0124] 1 Fluororesin composition

[0125] 2 Bubbles

Claims

1. A fluororesin composition comprising the following (A) and (B), wherein the content of (B) is 10% by mass or more, (A) a fluororesin comprising a tetrafluoroethylene component and a component other than the tetrafluoroethylene component as constituent components and having the highest heat of fusion in the fluororesin composition; (B) A fluororesin having a lower heat of fusion than the fluororesin (A).

2. The fluororesin composition according to claim 1, wherein The (A) and (B) are both fully fluorinated resins, or the (A) and (B) are both partially fluorinated resins.

3. The fluororesin composition according to claim 1 or 2, wherein The total of the transmittance to ultraviolet rays having a wavelength of 200 nm to 280 nm and the total reflectance is 60% or more. 4 . A finely foamed fluororesin film obtained by foaming the fluororesin composition according to claim 1 . 5 . The finely foamed fluororesin film according to claim 4 , wherein the average cell diameter is 1 μm or less.

6. The fine-foamed fluororesin film according to claim 4 or 5, which has a total reflectivity of 85% or more to ultraviolet rays having a wavelength of 200 nm to 280 nm.

7. The finely-foamed fluororesin film according to any one of claims 4 to 6, which has an expansion ratio of 1.05 to 2.

00. 8 . The finely-foamed fluororesin film according to claim 4 , which is a deep ultraviolet reflecting film.

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