Method for amorphizing crystalline component of crystalline fluororesin

Abstract

The purpose of the present invention is to provide a method for regenerating a crystalline fluororesin.　The problem can be solved by a method for amorphizing a crystalline component of a crystalline fluororesin according to the present invention, which is characterized by comprising bringing an ionic crystal represented by general formula: MaXb (wherein M is an alkali metal, an alkaline earth metal, NH4 or aluminum; X is a halogen element, NO3, CO3, SO4 or PO4; and a and b each are an integer) into contact with the crystalline fluororesin.

Description

A method for converting the crystalline components of crystalline fluororesin into amorphous form

[0001] The present invention relates to a method for converting the crystalline component of a crystalline fluororesin into an amorphous form, and the present invention enables the crystalline fluororesin to be recycled.

[0002] Fluorine resins include polyolefins in which hydrogen atoms are replaced with fluorine atoms. For example, polytetrafluoroethylene (PTFE), commonly known as Teflon (registered trademark), is a CF ２ A resin molded from this polymer chain is an excellent resin that combines various excellent properties such as heat resistance, chemical resistance, weather resistance, and sliding properties (Patent Document 1).

[0003] On the other hand, the crystallized polymer chains of PTFE have high chemical resistance and cannot be decrystallized with chemicals, making it difficult to recycle PTFE as a material using a solvent.

[0004] Furthermore, other than PTFE, difluorocarbon (-CF ２ The same problem exists in crystalline fluororesins containing polymers having hydroxyl groups.

[0005] International Publication No. 2019 / 244433

[0006] Therefore, an object of the present invention is to provide a method for regenerating a crystalline fluororesin.

[0007] The present inventors have conducted extensive research into methods for regenerating crystalline fluororesin, and have surprisingly found that crystalline fluororesin can be regenerated by using ionic crystals. The present invention is based on this finding. Therefore, the present invention provides: [1] a method for amorphizing the crystalline component of a crystalline fluororesin, comprising: ４ or aluminum, and X is a halogen element, NO ３ , CO ３ , S.O. ４ , or P.O. ４[1] A method for amorphizing a crystalline component of a crystalline fluororesin, comprising contacting an ionic crystal represented by the formula (I) with the crystalline fluororesin; [2] The ionic crystal is selected from the group consisting of NaCl, KCl, MgCl, ２ , CaCl ２ , or AlCl ３[3] The method for amorphizing the crystalline component of a crystalline fluororesin according to [1], wherein the ionic crystals are crystals of MaXb or a mixture of these crystals; [3] The method for amorphizing the crystalline component of a crystalline fluororesin according to [1] or [2], wherein the ratio of the number of moles of X contained in the ionic crystals to the number of moles of fluorine atoms contained in the crystalline fluororesin is 0.5 or more; [4] The method for amorphizing the crystalline component of a crystalline fluororesin according to [1] or [2], wherein the crystalline fluororesin is PTFE, PFA, FEP, PCTFE, ETFE, Nafion, or PVdF; [5] The method for amorphizing the crystalline component of a crystalline fluororesin according to [1], wherein the crystalline fluororesin is in powder form; [6] The method for amorphizing the crystalline component of a crystalline fluororesin according to [5], comprising the steps of (a1) mixing the powder of the crystalline fluororesin and crystals of MaXb to obtain a mixture, and (b1) pulverizing the mixture; [7] The method for amorphizing the crystalline component of a crystalline fluororesin according to [6], further comprising the step of (c1) immersing the pulverized mixture obtained in the step (b1) in water to remove the MaXb from the mixture; [8] The method for amorphizing the crystalline component of a crystalline fluororesin according to [5], further comprising the steps of (a2) pulverizing the crystalline fluororesin powder, (b2) pulverizing the MaXb crystals, and (c2) mixing the pulverized powder of the crystalline fluororesin and the pulverized crystals of MaXb; [9] The method for amorphizing the crystalline component of a crystalline fluororesin according to [8], further comprising the step of (d2) immersing the mixture obtained in the step (c2) in water to remove the MaXb from the mixture;

[10] A mixture produced by the method according to [6] or [8];

[11] Crystalline fluororesin particles produced by the method according to [7] or [9];

[12] A molded product obtained by molding the mixture according to

[10] ;

[13] A crystalline fluororesin molded product obtained by immersing the molded product according to

[12] in water to remove the MaXb crystals from the molded product;

[14] A crystalline fluororesin molded product obtained by molding the crystalline fluororesin particles according to

[11] ; and

[15] A method for recycling a crystalline fluororesin, comprising a step of molding the mixture according to

[10] or the crystalline fluororesin particles according to

[11] .

[0008] According to the method of the present invention for converting the crystalline component of a crystalline fluororesin into an amorphous form, the crystalline fluororesin can be recycled.

[0009] 1 is a spectrum showing the results of infrared ATR measurement of Comparative Example 1 and Examples 1 to 4. It is a photograph of the mixed powder and XRD patterns of Comparative Example 1 (a), Example 1 (b), and Example 7 (c). It is a chart showing the results of infrared ATR measurement of the mixed powder of Examples 8 to 14. It is a diagram showing the Tg (A) and DSC curve (B) of the mixed powder of Examples 1 and 3, and Comparative Example 1. It is a photograph (B) showing the moldability of the molded body of Example 5 (A) and the molded body of Comparative Example 2, and a photograph (C) showing the molded body of Example 6 that maintained its shape even after immersion in water. It is a photograph showing the moldability of the molded bodies of Examples 19 to 29. It is a conceptual diagram of contact between a crystalline fluororesin and an ionic crystal. It is a graph showing the 625 / 638 peak ratio by infrared ATR versus the grinding time of the mixture of PTFE and NaCl of Example 30. Photographs (A) of the molded bodies of Comparative Example 3(a), Example 31(b), and Example 32(c) using recycled PTFE products, photographs (B) of the molded body of Comparative Example 3 after being crushed with fingers, and photographs (C) of the molded body of Example 31(f) and the molded body of Example 32(g) after the molded bodies of Example 31(b) and Example 32(c) were respectively fired.

[0010] [1] Method for amorphizing the crystalline component of a crystalline fluororesin The method for amorphizing the crystalline component of a crystalline fluororesin of the present invention is to form a crystalline fluororesin having a general formula MaXb (wherein M is an alkali metal, an alkaline earth metal, Be, Mg, NH ４ or aluminum, and X is a halogen element, NO ３ , CO ３ , S.O. ４ , or P.O. ４ where a and b are integers) is brought into contact with the crystalline fluororesin. By bringing the ionic crystal into contact with the crystalline fluororesin, -CF of the crystalline component of the crystalline fluororesin is ２ - The chain crystals can loosen and become amorphous.

[0011] <<Crystalline Fluororesin>> The crystalline fluororesin is not particularly limited as long as it is a crystalline resin containing fluorine, and examples thereof include polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), perfluoroethylenepropylene (FEP), polychlorotrifluoroethylene (PCTFE), ethylenetetrafluoroethylene copolymer (ETFE), Nafion (registered trademark), and polyvinylidene fluoride (PVdF).

[0012] The shape of the crystalline fluororesin is not particularly limited as long as it can come into contact with ionic crystals, but from the viewpoint of regenerating the crystalline fluororesin and forming a molded product, a particulate (powder) shape is preferred. The particle size of the particles is not particularly limited as long as it can come into contact with ionic crystals, but the lower limit is, for example, 0.1 μm or more, in one embodiment 0.5 μm or more, in one embodiment 1 μm or more, and in one embodiment 5 μm or more. The upper limit is, for example, 10 mm or less, in one embodiment 5 mm or less, in one embodiment 1 mm or less, in one embodiment 500 μm or less, in one embodiment 100 μm or less, in one embodiment 50 μm or less, and in one embodiment 10 μm or less. The lower limit and upper limit can be appropriately combined. The particle size may be the particle size of a single particle, or the average particle size (D ５０ ) may also be used. The particle size of a single particle can be measured, for example, using an electron microscope. The average particle size can be measured, for example, using a laser diffraction particle size distribution analyzer. Specifically, a particle size accumulation diagram is prepared in accordance with JIS K 1474. The average particle size is determined by drawing a horizontal line on the particle size accumulation diagram from the intersection of the vertical line at the 50% point on the horizontal axis and the particle size accumulation line, and determining the sieve opening (mm) indicated by the intersection.

[0013] The crystalline fluororesin forms crystals before being treated by the method of the present invention. On the other hand, by contacting with ionic crystals, the crystalline component (e.g., CF ２) becomes amorphous. It is preferable to amorphize the crystalline components as thoroughly as possible. However, the effects of the present invention can be obtained and the crystalline fluororesin can be recycled even by amorphizing only the surface of the crystalline fluororesin. Therefore, the proportion of amorphous components in the crystalline fluororesin that can achieve the effects of the present invention is not limited, and is, for example, 1% or more, in some embodiments 5% or more, in some embodiments 10% or more, in some embodiments 30% or more, in some embodiments 50% or more, in some embodiments 70% or more, in some embodiments 80% or more, in some embodiments 90% or more, in some embodiments 95% or more, and in some embodiments 100% or more. In other words, by amorphizing at least a portion of the crystalline fluororesin, the PTFE recycled product can be integrated into a molded product by pressure or the like, as described below. Therefore, the method for amorphizing the crystalline components of the crystalline fluororesin of the present invention may be a method for amorphizing at least a portion of the crystalline components of the crystalline fluororesin.

[0014] Whether or not the crystalline component of the crystalline fluororesin has been made amorphous by the method of the present invention can be confirmed by, but is not limited to, infrared ATR spectroscopy (ATR-IR measurement method) or X-ray diffraction (XRD method).

[0015] <<Crystalline Fluoropolymer Recycled Powder>> The crystalline fluoropolymer recycling method is a recycling method applied to recycled powder of crystalline fluoropolymer. Examples of recycled powder include waste materials after calcination of crystalline fluoropolymer, and pulverized powder of used crystalline fluoropolymer. The particle size of the recycled powder is not particularly limited because it can come into contact with ionic crystals. The lower limit is, for example, 0.1 μm or more, in some embodiments 0.5 μm or more, in some embodiments 1 μm or more, and in some embodiments 5 μm or more. The upper limit is, for example, 10 mm or less, in some embodiments 5 mm or less, in some embodiments 1 mm or less, in some embodiments 500 μm or less, in some embodiments 200 μm or less, in some embodiments 100 μm or less, in some embodiments 50 μm or less, and in some embodiments 10 μm or less. The lower limit and upper limit can be combined as appropriate.

[0016] <<Infrared ATR Spectroscopy>> For example, in infrared ATR spectroscopic analysis, amorphous materials are characterized by CF ２ Symmetric stretching vibration of 1140 cm －１ ~1160cm －１ The peaks present in the graph show a peak shift to the higher wavenumber side. Therefore, the crystalline fluororesin exhibiting the peak shift is judged to have undergone amorphousization. In addition, in infrared ATR spectroscopy, amorphous is ２ Symmetric stretching vibration of 1140 cm －１ ~1160cm －１ In addition to the peak at 1210 cm, a peak at 1210 cm reflects the increase in the specific surface area of ​​the particles due to the miniaturization of the resin. －１ ~1260cm －１ A shoulder peak due to phonons is shown at 1210 cm. －１ ~1260cm －１ In the case of fluororesin that shows a shoulder peak due to phonons at 625 cm in the IR spectrum, it is judged that the crystal is amorphous. －１ Band and 638cm －１ This is reflected in the band ratio. Amorphous materials are thought to have a high density of helical defects. Therefore, the higher the density of helical defects, the more amorphous the crystals of crystalline fluororesin are considered to be.

[0017] <<X-ray Diffraction Method>> In X-ray diffractometry, an amorphous substance exhibits a broad halo pattern at a diffraction angle 2θ in the range of 33° to 45° in a diffraction pattern detected using CuKα radiation. Therefore, a crystalline fluororesin having a broad halo pattern at a diffraction angle 2θ in the range of 33° to 45° is judged to have undergone amorphization of its crystals.

[0018] Ionic Crystals The ionic crystals are not particularly limited as long as the effects of the present invention can be obtained. Specific examples of the ionic crystals include LiF, NaF, KF, RbF, CsF, FrF, NH ４ F, LiCl, NaCl, KCl, RbCl, CsCl, FrCl, NH ４ Cl, LiBr, NaBr, KBr, RbBr, CsBr, FrBr, NH ４Br、L-、NaI、K-、Rb-、Cs-、Fr-、NH ４ - ４ At、L-O ３ 、NaNO ３ 、KNO ３ 、RLOO ３ 、C3O ３ 、FrOO ３ 、NH ４ No ３ 、 ２ CO ３ 、N ２ CO ３ 、K ２ CO ３ 、 ２ CO ３ 、Cs ２ CO ３ 、Fr ２ CO ３ 、(NH ４ ) ２ CO ３ 、 ２ OO ４ 、N ２ OO ４ 、K ２ OO ４ 、 ２ OO ４ 、Cs ２ OO ４ 、Fr ２ OO ４ 、(NH ４ ) ２ OO ４ 、 ３ 2O ４ 、N ３ 2O ４ 、K ３ 2O ４ 、 ３ 2O ４ 、Cs ３ 2O ４ 、Fr ３ 2O ４ 、(NH ４ ) ３ 2O ４ 、BeF ２ 、MGF ２ 、1F ２ 、SrF ２ 、BF２ 、RaF ２ , BeCl ２ 、MgCl ２ 、CaCl ２ ,SrCl ２ 、BaCl ２ 、RaCl ２ ,BeBr ２ 、MgBr ２ ,CaBr ２ ,Srrr ２ ,BaBr ２ ,RaBr ２ Beea ２ 、MgI ２ ,CaI ２ ,Sry ２ 、BaI ２ ,RaI ２ 、Beat ２ 、MgAt ２ 、CaAt ２ 、Srrt ２ 、Ba At ２ 、Ra At ２ ,Be (No) ３ ) ２ , Mg (NO) ３ ) ２ , Ca (NO) ３ ) ２ ,SA(NOO ３ ) ２ 、Ba(NO ３ ) ２ ,Ra (NO) ３ ) ２ ,BộCO ３ 、MgCO ３ 、CaCO ３ ,SrCO ３ 、BaCO ３ 、RaCO ３ 、BeSO ４ 、MgSO ４ 、CaSO ４ 、SA2SO ４ 、BaSO ４ 、RaSO ４ 、AlF ３ 、AlCl ３ ,AlBr ３ 、Al I ３ 、Al At ３ 、AlPO ４ 、AlPO ４ 、AlPO４ , AlPO ４ , or AlPO ４ In the present invention, a combination of two or more of these ionic crystals can be used. Preferably, NaCl, KCl, MgCl ２ , CaCl ２ , or AlCl ３ or a mixture of these crystals. In the MaXb formula, "a" is, but is not limited to, an integer of 1 to 3, and "b" is an integer of 1 to 3.

[0019] The shape of the ionic crystals is not particularly limited as long as they can come into contact with the crystalline fluororesin, but from the viewpoint of regenerating the crystalline fluororesin and forming a molded product, a particle (powder) shape is preferred. The particle size of the particles is not particularly limited as long as the effects of the present invention can be obtained, but the lower limit is, for example, 1 nm or more, in one embodiment 5 nm or more, in one embodiment 10 nm or more, in one embodiment 50 nm or more, in one embodiment 100 nm or more, in one embodiment 500 nm or more, and in one embodiment 1 μm or more. The upper limit is, for example, 5 mm or less, in one embodiment 1 mm or less, in one embodiment 500 μm or less, in one embodiment 100 μm or less, in one embodiment 50 μm or less, in one embodiment 10 μm or less, and in one embodiment 5 μm or less. The lower limit and upper limit can be appropriately combined. The particle size may be the particle size of a single particle, or the average particle size (D ５０ ) may also be used. The particle size of a single particle can be measured, for example, using an electron microscope. The average particle size can be measured, for example, using a laser diffraction particle size distribution analyzer. Specifically, a particle size accumulation diagram is prepared in accordance with JIS K 1474. The average particle size is determined by drawing a horizontal line on the particle size accumulation diagram from the intersection of the vertical line at the 50% point on the horizontal axis and the particle size accumulation line, and determining the sieve opening (mm) indicated by the intersection.

[0020] The ionic crystals, when formed into fine particles together with the crystalline fluororesin, generate a dipole or a multipole similar thereto within the resin. Although not limited thereto, by generating such a dipole or a multipole similar thereto, the effect of the present invention, i.e., amorphizing the crystalline component of the crystalline fluororesin, can be achieved more efficiently.

[0021] <<Ratio>> In the method of the present invention, the ratio of ionic crystals to crystalline fluororesin is not particularly limited as long as the effects of the present invention can be obtained. From the viewpoint of ensuring that the ionic crystals are in contact with the crystalline fluororesin throughout, the ratio of the number of moles of X contained in the ionic crystals to the number of moles of fluorine atoms contained in the crystalline fluororesin is, for example, 0.1 or more, in some embodiments 0.2 or more, in some embodiments 0.2 or more, in some embodiments 0.3 or more, in some embodiments 0.4 or more, in some embodiments 0.5 or more, in some embodiments 0.6 or more, in some embodiments 0.7 or more, in some embodiments 0.8 or more, and in some embodiments 0.9 or more. The upper limit is also not particularly limited, but is, for example, 2.0 or less, in some embodiments 1.8 or less, in some embodiments 1.6 or less, in some embodiments 1.6 or less, in some embodiments 1.4 or less, and in some embodiments 1.2 or less. The upper and lower limits can be appropriately combined.

[0022] In the method of the present invention, as described above, the effect of the present invention (amorphization of the crystalline fluororesin) is obtained by contacting the crystalline fluororesin with the ionic crystals. However, in order to efficiently obtain the effect of the present invention or to efficiently bring the crystalline fluororesin into contact with the ionic crystals in order to perform molding for purifying the crystalline fluororesin, it is preferable to pulverize the crystalline fluororesin and the ionic crystals. Examples of embodiments of the present invention that include a pulverization step include, but are not limited to, the following first and second embodiments.

[0023] First Aspect A first aspect of the method of the present invention for amorphizing the crystalline component of a crystalline fluororesin includes (a1) a step of mixing the crystalline fluororesin powder and crystals of MaXb to obtain a mixture, and (b1) a step of pulverizing the mixture. That is, this is an aspect in which the crystalline fluororesin and the ionic crystals are mixed and then pulverized. By pulverizing the crystalline fluororesin and the ionic crystals, the contact surface between the crystalline fluororesin and the ionic crystals is increased, allowing the crystals of the crystalline fluororesin to be efficiently amorphized. The lower limit of the particle size of the pulverized particles of the crystalline fluororesin is, for example, 0.1 μm or more, in one aspect 0.5 μm or more, in one aspect 1 μm or more, and in one aspect 5 μm or more. The upper limit is, for example, 10 mm or less, in one embodiment, 5 mm or less, in one embodiment, 1 mm or less, in one embodiment, 500 μm or less, in one embodiment, 100 μm or less, in one embodiment, 50 μm or less, and in one embodiment, 10 μm or less. The lower limit and upper limit can be combined as appropriate. The particle size of the pulverized ionic crystals is not particularly limited as long as the effects of the present invention are obtained, but the lower limit is, for example, 1 nm or more, in one embodiment, 5 nm or more, in one embodiment, 10 nm or more, in one embodiment, 50 nm or more, in one embodiment, 100 nm or more, in one embodiment, 500 nm or more, and in one embodiment, 1 μm or more. The upper limit is, for example, 5 mm or less, in one embodiment, 1 mm or less, in one embodiment, 500 μm or less, in one embodiment, 100 μm or less, in one embodiment, 50 μm or less, in one embodiment, 10 μm or less, and in one embodiment, 5 μm or less. The lower limit and upper limit can be combined as appropriate. The pulverization in the pulverization step (b1) is not particularly limited, and examples thereof include pulverization using a ball mill, rod mill, roller mill, roll mill, bead mill, or mortar.

[0024] Steps (a1) and (b1) of the first aspect of the present invention can produce a mixture of crystalline fluororesin and ionic crystals. In the resulting mixture, the crystalline components of the crystalline fluororesin are amorphized in the areas in contact with the ionic crystals. Although not limited to this, applying force to the crystalline fluororesin using a grinding tool in the grinding step is thought to be useful for amorphizing the crystalline fluororesin. Furthermore, although not limited to this, it is thought that the ionic crystals stabilize the amorphized crystalline fluororesin. The grinding time in step (b1) is not particularly limited as long as the effects of the present invention are obtained, but is, for example, 2 minutes or more, and in one aspect, 5 minutes or more. It is thought that the amorphous components can be increased by increasing the time for mixing and grinding the crystalline fluororesin and ionic crystals.

[0025] The first aspect may further include a step (c1) of immersing the pulverized mixture obtained in step (b1) in water to remove the MaXb from the mixture. This step allows the ionic crystals to be removed from the mixed powder. The mixed powder from which the ionic crystals have been removed can be suitably used for regenerating the crystalline fluororesin.

[0026] Crystalline fluororesin particles can be obtained by steps (a1), (b1), and (c1) of the first aspect of the present invention. The obtained crystalline fluororesin particles can be used as recycled crystalline fluororesin by molding. Steps (a1), (b1), and (c1) can basically be performed at room temperature. However, they can also be performed while heating or cooling.

[0027] Second Aspect A second aspect of the method of the present invention for amorphizing the crystalline component of a crystalline fluororesin includes (a2) a step of pulverizing the crystalline fluororesin powder, (b2) a step of pulverizing the MaXb crystals, and (c2) a step of mixing the pulverized crystalline fluororesin powder and the pulverized MaXb crystals. That is, in this aspect, the crystalline fluororesin and the ionic crystals are pulverized and then mixed. By pulverizing the crystalline fluororesin and the ionic crystals, the contact surface between the crystalline fluororesin and the ionic crystals is increased, allowing the crystals of the crystalline fluororesin to be efficiently amorphized. The lower limit of the particle size of the pulverized particles of the crystalline fluororesin is, for example, 0.1 μm or more, in one aspect 0.5 μm or more, in one aspect 1 μm or more, and in one aspect 5 μm or more. The upper limit is, for example, 10 mm or less, in one embodiment, 5 mm or less, in one embodiment, 1 mm or less, in one embodiment, 500 μm or less, in one embodiment, 100 μm or less, in one embodiment, 50 μm or less, and in one embodiment, 10 μm or less. The lower limit and upper limit can be combined as appropriate. The particle size of the pulverized ionic crystals is not particularly limited as long as the effects of the present invention are obtained, but the lower limit is, for example, 1 nm or more, in one embodiment, 5 nm or more, in one embodiment, 10 nm or more, in one embodiment, 50 nm or more, in one embodiment, 100 nm or more, in one embodiment, 500 nm or more, and in one embodiment, 1 μm or more. The upper limit is, for example, 5 mm or less, in one embodiment, 1 mm or less, in one embodiment, 500 μm or less, in one embodiment, 100 μm or less, in one embodiment, 50 μm or less, in one embodiment, 10 μm or less, and in one embodiment, 5 μm or less. The lower limit and upper limit can be combined as appropriate. The pulverization in the pulverization steps (a2) and (b2) is not particularly limited, and examples thereof include pulverization using a ball mill, rod mill, roller mill, roll mill, bead mill, or mortar.

[0028] A mixture of crystalline fluororesin and ionic crystals can be obtained by steps (a2), (b2), and (c2) of the second aspect of the present invention. In the obtained mixture, the crystalline component of the crystalline fluororesin is amorphized at the portion in contact with the ionic crystals. Although not limited, applying force to the crystalline fluororesin using a grinding tool in the grinding step is thought to be useful for amorphizing the crystalline fluororesin. Furthermore, although not limited, it is thought that the ionic crystals stabilize the amorphized crystalline fluororesin. The grinding time in steps (a2) and (b2) is not particularly limited as long as the effects of the present invention can be obtained, but is, for example, 2 minutes or more, and in one embodiment, 5 minutes or more. Furthermore, the mixing time in step (c2) is also not particularly limited as long as the effects of the present invention can be obtained, but is, for example, 2 minutes or more, and in one embodiment, 5 minutes or more. It is thought that the amorphous component can be increased by increasing the time for grinding and mixing the crystalline fluororesin and ionic crystals.

[0029] The second aspect may further include a step (d2) of immersing the mixture obtained in the step (c2) in water to remove the MaXb from the mixture. This step allows the ionic crystals to be removed from the mixed powder. The mixed powder from which the ionic crystals have been removed can be suitably used for regenerating crystalline fluororesin. The steps (a2), (b2), (c2), and (d2) may basically be performed at room temperature. However, they may also be performed while heating or cooling.

[0030] Crystalline fluororesin particles can be obtained by steps (a2), (b2), (c2), and (d2) of the second aspect of the present invention. The obtained crystalline fluororesin particles can be used as recycled crystalline fluororesin by molding. Although not limited to this, it is believed that the amorphous portions of the crystalline fluororesin serve as a foothold for integration by pressure or the like during molding. It is also believed that the amorphous portions stabilized by ionic crystals promote molding.

[0031] Molded Articles Molded articles can be obtained by molding the mixtures obtained in steps (a1) and (b1) of the first embodiment and the mixtures obtained in steps (a1), (b2), and (c2) of the second embodiment. The molding method can be any molding method commonly used in this field, and includes, but is not limited to, compression molding, injection molding, hydroforming, ram extrusion, patinated extrusion, calendaring, impregnation coating, and extrusion.

[0032] <<Crystalline Fluororesin Molded Article>> The above-mentioned molded article can be immersed in water to remove ionic crystals from the molded article. The molded article from which the ionic crystals have been removed is a crystalline fluororesin molded article.

[0033] The crystalline fluororesin molded article of the present invention can also be obtained by molding the crystalline fluororesin particles obtained by steps (a1), (b1), and (c1) of the first embodiment, or the crystalline fluororesin particles obtained by steps (a2), (b2), (c2), and (d2) of the second embodiment. The molding method can be any molding method commonly used in this field, including, for example, compression molding, injection molding, hydroforming, ram extrusion, pasted extrusion, calendaring, impregnation coating, and extrusion molding. Furthermore, after obtaining a molded article by the above method, the molded article may be further calcined as needed. The calcination method and calcination time can be adjusted appropriately depending on the desired molded article. Calcination can smooth the surface of the recycled crystalline fluororesin molded article. Preferably, the molded article obtained by molding the mixture obtained in steps (a1) and (b1) of the first embodiment is immersed in water to remove ionic crystals from the molded article, and then calcined. It is believed that by performing compression or other molding in the presence of crystalline fluororesin and ionic crystals, the powder interfaces and grain boundaries were bonded well, and the molded body after firing had the smooth surface characteristic of crystalline fluororesin molded bodies, making it possible to regenerate the crystalline fluororesin.

[0034] <<Method for recycling crystalline fluororesin>> The method for recycling crystalline fluororesin of the present invention includes a step of molding the mixture obtained in the first embodiment or the second embodiment. The method for recycling crystalline fluororesin of the present invention includes a step of molding the crystalline fluororesin particles obtained in the first embodiment or the second embodiment.

[0035] <<Action>> In the present invention, the mechanism by which crystalline fluororesin is made amorphous by ionic crystals has not been analyzed in detail, but can be presumed as follows. However, the present invention is not limited to the following presumption. It is presumed that by mixing and pulverizing the crystalline fluororesin and ionic crystals, from a microscopic viewpoint, as shown in FIG. 7, the ionic crystals penetrate into the crystals of the crystalline fluororesin or adhere to the surface. -CF in the crystalline fluororesin ２ - is -CF in the adjacent polymer chain ２ Due to the orientation effect, a strong crystal is formed (Figure 7). If ionic crystals are present here, it is presumed that the ionic crystals penetrate into the crystals of the crystalline fluororesin or adhere to the surface, significantly reducing the crystallinity. The reduction in the crystallinity of the crystalline fluororesin is evident from the high wavenumber shift of the 1150 peak in IR and the significant reduction in the main peak in XRD in the examples described below. It is also presumed that the phonon peak in IR increases as the non-surface area increases due to the miniaturization of the crystalline fluororesin caused by the adhesion of ionic crystals.

[0036] The present invention will be specifically described below with reference to examples, but these examples are not intended to limit the scope of the present invention.

[0037] Example 1 In this example, a mixed powder was obtained using PTFE (polytetrafluoroethylene, manufactured by Sigma-Aldrich, particle size: 1 μm) as the crystalline fluororesin and NaCl (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) as the ionic crystal. The molar ratio of NaCl to fluorine atoms contained in PTFE was 0.5, and the mixture was pulverized using a planetary ball mill (P-7, manufactured by Fritsch). The balls used were made of zirconia and had a diameter of 15 mm. The mixture was pulverized at an automatic rotation speed of 700 rpm at room temperature for 8 hours to obtain a particle size D５０ A mixed powder having a particle size of 35 μm (measurement of agglomerates of the pulverized powder by optical microscope) was obtained.

[0038] In this example, PTFE and NaCl were mixed in a mortar to obtain a mixed powder. The mixture was mixed and pulverized for 5 minutes in a mortar at a molar ratio of 1 to the fluorine atoms contained in PTFE. ５０ A mixed powder having a particle size of 35 μm (measurement of agglomerates of the pulverized powder by optical microscope) was obtained.

[0039] In this example, PTFE and NaCl were used and mixed in a mortar to obtain a mixed powder. The particle size D was measured in the same manner as in Example 2, except that the molar ratio of NaCl to fluorine atoms contained in PTFE was 0.5. ５０ A composite powder having a particle size of 50 μm (measurement of agglomerates of the pulverized powder by optical microscope) was obtained.

[0040] Example 4 In this example, PTFE and NaCl were separately pulverized and then mixed to obtain a mixed powder. PTFE and NaCl were pulverized using a planetary ball mill. The pulverization was carried out at an automatic rotation speed of 700 rpm at room temperature for 8 hours, and the PTFE powder had a particle size D ５０ 35 μm (value of agglomerates of pulverized powder measured by optical microscope), NaCl powder has a particle size D ５０ The powders were each 35 μm in size (measured by optical microscopy for the aggregates of the pulverized powder). The resulting PTFE was placed in a sample cell so that the molar ratio of NaCl to fluorine atoms contained therein was 0.5, and mixed for 5 minutes using a vortex mixer to obtain a mixed powder.

[0041] Example 5 In this example, a molded body was produced from a mixed powder of PTFE and NaCl. 0.8 g of the mixed powder obtained in Example 2 was compressed at room temperature using a hydraulic press at a pressure of 20 MPa to produce a molded body. The pressure during compression was not controlled and decreased to 17 MPa.

[0042] Example 6 The compact obtained in Example 5 was placed in a petri dish containing water and left for 12 hours, followed by filtration and drying to obtain a compact from which NaCl had been removed from the mixed powder. It was confirmed that the obtained compact maintained the shape of the compact obtained in Example 5.

[0043] Example 7 In this example, a molded body was produced from a mixed powder of PTFE and NaCl, and then NaCl was removed from the molded body. The mixture was mixed and pulverized using a planetary ball mill (P-7, manufactured by Fritsch) at a molar ratio of NaCl to fluorine atoms contained in PTFE of 0.5. The mixture was pulverized at an automatic rotation speed of 700 rpm for 8 hours to obtain a particle size D ５０ A composite powder with a particle size of 35 μm was obtained. The mixed powder was compressed at room temperature to form a compact. The resulting compact was then placed in a petri dish containing water and left for 12 hours, after which it was filtered and dried. It was confirmed that the dried compact maintained its shape.

[0044] Examples 8 to 18 In these examples, a composite powder was obtained by mixing the ionic crystals for 5 minutes in a mortar, with the ratio of the number of moles of X contained in the ionic crystals to the number of moles of fluorine atoms contained in PTFE being 0.5.

[0045] In this comparative example, a powder was produced using only a crystalline fluororesin without using ionic crystals. The powder was obtained in the same manner as in Example 1, except that NaCl was not used.

[0046] Comparative Example 2 In this comparative example, a molded body was produced using a powder of only the crystalline fluororesin. 0.8 g of the powder obtained in Comparative Example 1 was compressed at room temperature using a hydraulic press to produce a molded body. It was confirmed that the molded body crumbled when removed from the press base.

[0047] [Evaluation] The physical properties of the powders obtained in the examples and comparative examples were evaluated under the following measurement conditions.

[0048] [Infrared ATR Measurement] The state of polymer chains near the powder surface was determined by obtaining a spectrum using a Fourier transform infrared spectrophotometer by the attenuated total reflection method. The measurement conditions were as follows: FT-IR: FT-IR 4700 manufactured by JASCO; Single reflection ATR attachment: (JASCO ATR PRO ONE); Internal reflection element: Diamond; Incident angle: (45°); Resolution: 1 cm －１ ・Detector: TGS type ・Number of integrations: 32

[0049] [XRD Measurement] The powders obtained in the examples and comparative examples were filled into an airtight holder that was not exposed to the atmosphere in a glove box purged with sufficiently dried Ar gas (dew point -60°C or lower), and XRD measurement was carried out under the following measurement conditions.・Device name: MiniFlex600 / cx Desktop X-ray Diffraction Device (Rigaku Corporation) ・Radiation source: CuKα ・Tube voltage: 40 kV ・Tube current: 15 mA ・Measurement method: Focusing method (reflection method) ・Optical system: Multilayer mirror divergent beam method (CBO-α) ・Detector: Semiconductor one-dimensional detector ・Input Soller slit: Soller slit 2.5° ・Long limiting slit: 10 mm ・Receiving Soller slit: 2.5° ・Input slit: DS: 1.250° ・Receiving slit: 13.0 mm (open) ・Measurement range: 2θ = 10 to 60° ・Step width: 0.02° ・Scan speed: 10.0° / min

[0050] [Melting point (Tm) and glass transition temperature (Tg)] Using a thermogravimetric-differential scanning calorimetry (TG-DSC) measuring device (NETZSCH, STA449F3 Jupiter), approximately 8 mg of sample was placed in a platinum pan for measurement, heated to 700°C at 10°C / min, held at 700°C for 10 minutes, and then cooled to 30°C at 10°C / min. The melting point (Tm) was calculated from the peak apex of the crystalline melting peak.

[0051] [Moldability] The molded products of Examples 5, 6, and Comparative Example 2 were crushed with fingers to check whether the molded product shape was maintained.

[0052] [Water Contact Angle] The water contact angle was measured using a fully automatic contact angle meter (DM-501Hi, manufactured by Kyowa Interface Science Co., Ltd.). The surface temperature of the surface-treated steel sheet was set to 20°C ± 1°C, and distilled water at 20°C ± 1°C was used. A 2 μl droplet of distilled water was dropped onto the surface of the surface-treated steel sheet, and the contact angle was measured 1 second later by the θ / 2 method. The arithmetic mean of the contact angles of 5 drops was taken as the water contact angle.

[0053] [Solution Resistance] Two molded bodies were prepared and immersed in 1 M hydrochloric acid or 1 M aqueous sodium hydroxide solution for 4 hours, respectively, and the solution resistance was confirmed by checking the change in weight before immersion and after the liquid was removed after immersion.

[0054] The results of each example are explained below.

[0055] Infrared ATR Measurements of Examples 1 to 4 and Comparative Example 1 As shown in FIG. 1, the infrared ATR spectrum of the powder obtained in Comparative Example 1 shows that CF ２ 1140 cm originating from symmetric stretching vibration －１ ~1160cm －１ In other words, in Comparative Example 1, it was considered that the PTFE polymer chains in the powder after pulverization were crystallized. On the other hand, in the infrared ATR spectra of the mixed powders obtained in Examples 1 to 4, a peak was observed at CF ２ The peak due to the symmetric stretching vibration was shifted to the higher wavenumber side. ２ It was thought that the crystal state due to the －１ ~1260cm －１ A shoulder peak due to phonons appearing in the amorphous part of the PTFE polymer appeared. Therefore, the amorphous component of the polymer chain increased in the PTFE in the mixed powder.

[0056] <XRD Spectra of Examples 1 and 7, and Comparative Example 1> As shown in Figure 2, in the XRD spectrum of the powder of Comparative Example 1, a sharp peak at 2θ = 18°, which is attributable to the crystallization of the PTFE polymer chain, was observed (Figure 2(a)). Therefore, in Comparative Example 1, the results of infrared ATR and XRD showed that the PTFE polymer chain of the powder after pulverization was crystallized. In the XRD spectrum of the mixed powder obtained in Example 1, the intensity of the peak appearing at 2θ = 18°, which indicates crystallization, decreased (Figure 2(b)). Therefore, CF ２ It was thought that the crystals derived from the above-mentioned crystalline structure were loosened. Furthermore, in the XRD spectrum of the powder obtained in Example 7, a broad peak was observed around 2θ = 38°. This was an amorphous peak observed in polymers, and it was thought that the crystals had become amorphous (Figure 2(c)).

[0057] Infrared ATR Measurements of Examples 8 to 14 In the infrared ATR spectra of the mixed powders obtained in Examples 8 to 14, CF ２ The peak of the symmetric stretching vibration shifts to the higher wavenumber side, 1210 cm －１ ~1260cm －１ A shoulder peak due to phonons appeared at 1210 cm (Fig. 3). Therefore, it was confirmed that the amorphous components of the polymer chains on the powder surface also increased in the powders containing PTFE mixed with various crystals. Although not shown in Fig. 3, the mixed powders obtained in Examples 15 to 18 also showed a peak at 1210 cm －１ ~1260cm －１ A shoulder peak due to phonons was observed, suggesting that the amorphous component of the polymer chains was increasing.

[0058] <<Melting Point (Tm) and Glass Transition Temperature (Tg)>> There was almost no difference in the Tg of the powders of Example 1 and Example 3. Furthermore, the DSC spectra of Examples 4, 5, and Comparative Example 1 showed a peak at around 345 ° C due to a phase change of the PTFE polymer chain. This is thought to indicate that the ratio of amorphous components on the powder surface to the entire powder is small, or that the amorphous components themselves do not affect the thermal behavior. Furthermore, the powders of Examples 4 and 5 and the powder of Comparative Example 1 exhibited different behaviors in the peaks appearing above 500 ° C. This is thought to be due to the fact that the inclusion of NaCl in the powder had some effect on the thermal decomposition behavior.

[0059] <<Moldability>> The molded bodies of Example 5 (FIG. 5A) and Example 6 (FIG. 5C) maintained their molded shapes, but the molded body of Comparative Example 2 (FIG. 5B) broke into pieces when crushed with fingers.

[0060] <Water Contact Angle> The water contact angles of the mixed powders of Examples 2 to 5 were 122.4±7.8°, 108.8±3.6°, 104.2±0.5°, and 131.3±1.5°, respectively. All of these values ​​were equal to or greater than the literature value of 106 for the water contact angle of PTFE, and these mixed powders maintained the water repellency, which is one of the properties of PTFE.

[0061] <<Solution Resistance>> The solution resistance (weight ratio after immersion to before immersion) of Example 6 was 96.5% and 95.2% when immersed in 1 M hydrochloric acid and 1 M sodium hydroxide aqueous solution, respectively. It was found that the mixed powder maintained the acid resistance and alkali resistance, which are one of the properties of PTFE.

[0062] Examples 19 to 29 In these examples, compacts were produced using the mixed powders obtained in Examples 8 to 18. The procedures of Examples 5 and 6 were repeated to obtain compacts, except that the mixed powders obtained in Examples 8 to 18 were used. Compacts were obtained with all of the mixed powders, and the compacts maintained their shape even after immersion in water ( FIG. 6 ).

[0063] Example 30 The powder obtained in Example X was measured for IR and found to have a peak at 638 cm －１ 625 cm for the peak intensity －１The ratio of the peak intensities of the PTFE main chain and the PTFE peak was calculated. This ratio represents the point where the winding direction of the helical structure of the PTFE main chain changes, i.e., the density of helical defects. It was confirmed that the density of helical defects increases with the milling time.

[0064] Comparative Example 3, Examples 31 and 32 In these examples, sintered and crushed fluororesin powder (hereinafter also referred to as "PTFE recycled product") (particle size D ５０ The following samples were prepared using a PTFE recycled product (particle size: 153.5 μm). Comparative Example 3: A molded product produced by hydraulically pressing a PTFE recycled product. Example 31: A molded product produced by mixing and grinding a PTFE recycled product together with NaCl in a planetary ball mill for 2 hours, removing the NaCl by washing, and then hydraulically pressing. Example 32: A molded product produced by mixing and grinding a PTFE recycled product together with NaCl in a planetary ball mill for 2 hours, then hydraulically pressing, and removing the NaCl by washing.

[0065] Each sample retained its apparent shape after molding (Fig. 9A). However, the molded product of Comparative Example 3 was brittle and crumbled when crushed with fingers (Fig. 9B). It resembled glass wool with very short fibers and easily returned to powder (Fig. 9B). On the other hand, the molded products of Examples 31 and 32 maintained their shape (Fig. 9A(b) and 9A(c)). The molded products of Examples 31 and 32 were sintered in air on aluminum strips. First, the temperature was raised from 22°C to 370°C over 360 minutes and held there for 10 minutes. The temperature was then lowered to 320°C and held there for 50 minutes, after which the temperature was lowered from 320°C to 22°C over 300 minutes. Example 31 hardened and sintering progressed (Fig. 9C(f)). Example 32 had a smaller volume, but a solid with a smooth surface was obtained, which was then recycled to PTFE (Fig. 9C(g)).

[0066] The method of the present invention for converting the crystalline component of a crystalline fluororesin into an amorphous form can be used as a method for regenerating the crystalline fluororesin.

Claims

1. A method for amorphizing the crystalline components of a crystalline fluororesin, comprising the steps of: ４ or aluminum, and X is a halogen element, NO ３ , CO ３ , S.O. ４ , or P.O. ４ wherein a and b are integers), with the crystalline fluororesin.

2. The ionic crystals are NaCl, KCl, MgCl ２ , CaCl ２ , or AlCl ３ 2. The method for amorphizing the crystalline component of the crystalline fluororesin according to claim 1, wherein the crystalline component is a crystal of the above or a mixture of these crystals.

3. A method for amorphizing the crystalline component of a crystalline fluororesin according to claim 1 or 2, wherein the ratio of the number of moles of X contained in the ionic crystal to the number of moles of fluorine atoms contained in the crystalline fluororesin is 0.5 or more.

4. A method for amorphizing the crystalline component of a crystalline fluororesin according to claim 1 or 2, wherein the crystalline fluororesin is PTFE, PFA, FEP, PCTFE, ETFE, Nafion, or PVdF.

5. The method for converting the crystalline component of a crystalline fluororesin into an amorphous form according to claim 1, wherein the crystalline fluororesin is in the form of a powder.

6. A method for amorphizing the crystalline component of the crystalline fluororesin according to claim 5, comprising: (a1) mixing the powder of the crystalline fluororesin with crystals of MaXb to obtain a mixture; and (b1) pulverizing the mixture.

7. A method for amorphizing the crystalline component of a crystalline fluororesin according to claim 6, further comprising the step of (c1) immersing the pulverized mixture obtained in step (b1) in water to remove the MaXb from the mixture.

8. A method for amorphizing the crystalline component of the crystalline fluororesin according to claim 5, comprising: (a2) a step of pulverizing the powder of the crystalline fluororesin; (b2) a step of pulverizing the MaXb crystals; and (c2) a step of mixing the pulverized powder of the crystalline fluororesin and the pulverized crystals of MaXb.

9. The method for amorphizing the crystalline component of a crystalline fluororesin according to claim 8, further comprising the step (d2) of immersing the mixture obtained in step (c2) in water to remove the MaXb from the mixture.

10. A mixture produced by the method of claim 6 or claim 8.

11. Crystalline fluororesin particles produced by the method of claim 7 or claim 9.

12. A molded body obtained by molding the mixture according to claim 10.

13. A crystalline fluororesin molded article, in which the molded article according to claim 12 is immersed in water to remove the MaXb crystals from the molded article.

14. A crystalline fluororesin molded product obtained by molding the crystalline fluororesin particles according to claim 11.

15. A method for regenerating a crystalline fluororesin, comprising a step of molding the mixture according to claim 10 or the crystalline fluororesin particles according to claim 11.

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