Coating film and method for forming coating film

Abstract

Provided are: a coating film that satisfies the requirements for use in a light irradiation device; and a method for forming the same. The coating film 36 is applied to a surface of a substrate and comprises a thermoplastic elastomer and a pigment. The mass ratio of the thermoplastic elastomer and the pigment is less than 1:2.0. In a tensile test in which a test piece obtained by applying the coating film 36 to a substrate with a width of 10 mm and a length of 40 mm is set in a tension testing machine at a grab distance of 25 mm and measurement is performed at a tensile speed of 25 mm / min, the elongation at break of a test piece (A) composed of the substrate and the coating film 36 is smaller than the elongation at break of a test piece (B) composed of the substrate, and the elongation of the test piece (A) is 40% or more of the elongation of the test piece (B).

Description

Coating film and coating film forming method

[0001] The present invention relates to a coating film applied to the surface of a substrate used in a medical light irradiation device, and a method for forming the same.

[0002] Various medical devices, such as catheters, are known that are inserted into living bodies to perform treatment. Some medical devices require a coating film applied to the surface of a substrate, such as a marker for visually identifying the position within the living body or a light-shielding body for preventing light from being irradiated outside of a predetermined area in a light-irradiating device.

[0003] Known examples of light irradiation devices include devices that irradiate a lesion with light in photodynamic therapy (PDT) or photoimmunotherapy (PIT) using a photoreactive substance with tumor cell selectivity. The light irradiation medical device includes at least a light-emitting irradiator and an elongated member having the light-irradiator at its distal end. The light irradiation device has a balloon at the distal end of the elongated member, and a light irradiator having a light-irradiator is disposed inside the balloon, allowing light to be irradiated through a light-transmitting window provided in the balloon. The light irradiation device can maintain a constant distance between the lesion and the light-irradiator by expanding the balloon, and can fix the position of the light-irradiator relative to the lesion, thereby enabling stable irradiation of the lesion with light.

[0004] To form a light-transmitting window in the balloon, a light-shielding body made of a coating film with low light transmittance is formed on the surface of the balloon, which serves as a base material, in an area other than the light-transmitting window. The coating film is formed, for example, by vapor-depositing a metal on the base material. An example of a light-irradiation device having such a coating film is disclosed in Patent Document 1.

[0005] Japanese Patent Application Laid-Open No. 2005-46640

[0006] The coating film of a light irradiation device must have sufficiently low light transmittance and must also satisfy several other conditions. Because the light irradiation device is inserted into a living body, the coating film must have low cytotoxicity. The coating film must also be water-resistant so that it will not peel off due to water. Furthermore, the coating film must be able to be formed at a temperature that does not deform the substrate. In addition, in order to maintain the flexibility of the substrate when the coating film is applied to the substrate, the coating film must be able to follow the deformation of the substrate when it stretches to a certain extent. A coating film that satisfies these conditions and a method for forming the coating film are needed.

[0007] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a coating film that satisfies the conditions necessary for use in a light-irradiating device, and a method for forming the same.

[0008] (1) A coating film according to the present invention that achieves the above-mentioned object is a coating film applied to the surface of a substrate, the coating film comprising a thermoplastic elastomer and a pigment, the mass ratio of the thermoplastic elastomer to the pigment being less than 1:2.0, and the coating film is such that, in a tensile test performed at a tensile speed of 25 mm / min, a test piece obtained by applying the coating film to the substrate having a width of 10 mm and a length of 40 mm is set in a tensile tester so that the gripping distance is 25 mm, the elongation at break of test piece (A) composed of the substrate and the coating film is smaller than the elongation at break of test piece (B) composed of the substrate, and the elongation of test piece (A) is 40% or more of the elongation of test piece (B).

[0009] A method for forming a coating film according to the present invention (10) that achieves the above-mentioned object includes preparing a first solution by dissolving a pigment in a solvent so that the mass ratio of the thermoplastic elastomer to the pigment is less than 1:2.0, preparing a second solution by dissolving the thermoplastic elastomer in the first solution, and applying the second solution to a substrate and drying the solution to form a coating film, wherein a test piece formed by applying the coating film to the substrate and measuring 10 mm wide and 40 mm long is set in a tensile tester so that the gripping distance is 25 mm, and a tensile test is performed at a tensile speed of 25 mm / min, in which the elongation at break of test piece (A) composed of the substrate and the coating film is smaller than the elongation at break of test piece (B) composed of the substrate, and the elongation of test piece (A) is 40% or more of the elongation of test piece (B).

[0010] The coating film configured as described above is water-resistant and can be formed at a temperature at which the substrate does not deform. Furthermore, when the substrate stretches to a certain extent, the coating film conforms to the deformation and can prevent peeling or tearing from the substrate. Therefore, the coating film has the mechanical and optical properties required for functioning as a light-irradiation device, and also satisfies the properties required for use in a light-irradiation device.

[0011] (2) In the coating film of (1) above, the elongation of the test piece (A) may be 90% or more of the elongation of the test piece (B), which allows the coating film to better follow the elongation of the substrate, and therefore ensures that the coating film returns to its original shape when the substrate stretches and shrinks.

[0012] (3) When the coating film of (1) or (2) above is evaluated according to ISO 10993, the cell attribute strength (IC) is higher than that of a polyurethane film containing 0.25% zinc dibutyldithiocarbamate (ZDBC) as a positive control material B. ５０ This allows the cytotoxicity of the coating film to be weakened to a level necessary for use in a light irradiation device.

[0013] (4) In any one of the coating films (1) to (3) above, the coating film may have a thickness of 60 μm or less, thereby making it possible to reduce the outer diameter of the light irradiation device.

[0014] (5) In the coating film of any one of (1) to (4) above, the light transmittance of the coating film may be 31% or less, thereby enabling the coating film to satisfy its optical performance requirements.

[0015] (6) In the coating film of any one of (1) to (5) above, the thermoplastic elastomer may be a polyurethane elastomer, which allows the coating film to have high conformability to deformation of the substrate.

[0016] (7) In the coating film of any one of (1) to (6) above, the pigment may be titanium oxide, carbon black, or a mixture of titanium oxide and carbon black, thereby making it possible to obtain a white, black, or gray coating film that satisfies the requirements for cytotoxicity strength.

[0017] (8) In the coating film of any one of (1) to (7) above, the substrate may be a balloon made of a light-transmitting material, and the thickness of the balloon may be 30 μm. This allows the biological safety and mechanical and optical properties of the balloon to be satisfied in a light irradiation device having a light irradiator inside the balloon on which the coating film is formed so as to be able to irradiate light in a certain direction.

[0018] (9) In the coating film of any one of (1) to (8) above, the mass ratio of the thermoplastic elastomer to the pigment may be 1:0.5 or less, the thickness of the coating film may be 30 μm or less, the light transmittance of the coating film may be 0%, and the pigment may be carbon black. This makes the coating film highly biologically safe and allows for a small thickness.

[0019] The method for forming a coating film configured as described above can form a coating film that is water resistant, can be formed at a temperature at which the substrate does not deform, and satisfies the properties required for a light irradiation device.

[0020] 1 is an overall view of a light irradiation device having a coating film according to an embodiment of the present invention and an endoscopic device; FIG. 2 is a perspective view of a balloon; and FIG. 3 is an enlarged cross-sectional view of the vicinity of a distal end portion of the light irradiation device inserted into an endoscopic device.

[0021] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For convenience of explanation, the dimensions of the drawings may be exaggerated and may differ from the actual dimensions. Furthermore, in this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant explanations will be omitted. In this specification, the side of the device that is inserted into the living body will be referred to as the "distal side," and the side that is operated will be referred to as the "proximal side."

[0022] The light irradiation device 10 of this embodiment can be configured to be suitable for treatment that approaches tumor cells as an endoscopic system via an endoscopic device 100. As shown in FIG. 1 , the light irradiation device 10 is used, for example, by being inserted into the endoscopic device 100. The type of tumor is not particularly limited. For example, when the light irradiation device 10 is inserted into the endoscope 100 and used as an endoscopic system, it can be applied to tumors occurring in hollow organs such as the esophagus, stomach, small intestine, large intestine, urinary tract, blood vessels, external auditory canal, Eustachian tube, and nasal cavity. The light irradiation device 10 of this embodiment can be used, for example, in photoimmunotherapy, which destroys target cells by irradiating light onto a drug adsorbed on target cells, as taught in Japanese Patent No. 6127045. The target cells are tumor cells, such as cancer cells or cells of precancerous lesions. In this treatment method, a photosensitive substance adsorbed with an antibody that specifically binds only to a specific antigen on the surface of tumor cells and a photosensitive substance that pairs with the antibody is used as the drug. The antibody may be, but is not limited to, panitumumab, trastuzumab, HuJ591, pertuzumab, lapatinib, palbociclib, olaparib, etc. The photosensitizer may be, but is not limited to, a hydrophilic phthalocyanine (IR700) that reacts to near-infrared light with a wavelength of approximately 700 nm. When IR700 is exposed to near-infrared light with a wavelength of approximately 660 to 740 nm, the ligand of the functional group that ensures water solubility is broken, causing a structural change from water-soluble to hydrophobic. This structural change extracts membrane proteins, opening holes in the cell membrane and allowing water to enter the cell, thereby rupturing and destroying tumor cells. Furthermore, IR700 is excited by near-infrared light and emits fluorescence with a wavelength different from the excitation wavelength. For example, when IR700 is excited by near-infrared light with a wavelength around 690 nm, it emits fluorescence with a wavelength around 700 nm. IR700 undergoes a structural change while emitting fluorescence in response to light, and once it has destroyed tumor cells and fulfilled its role as a drug, it no longer emits fluorescence.

[0023] The endoscopic device 100 has an endoscope body 120 connected to a control display unit 110. An operator inserts the endoscope body 120 into a living body and performs various operations. The endoscope body 120 has a long insertion section 121 that is inserted into the living body, and a handle section 122 that is provided at the base end of the long insertion section 121. The handle section 122 has a forceps opening 122b that communicates with an inner cavity 125 of the long insertion section 121. The light irradiation device 10 is inserted into the endoscopic device 100 through the forceps opening 122b of the handle section 122.

[0024] The light irradiation device 10 has a long shaft portion 20 that is inserted into the endoscopic device 100, and a balloon 30 that is provided at the distal end of the shaft portion 20 and exposed at the distal side of the long insertion portion 121. The light irradiation device 10 further has a proximal hub 70 that is provided at the proximal end of the light irradiation device 10. An expansion device 80 that injects a fluid to expand the balloon 30 is connected to the proximal hub 70. As the expansion device 80, for example, an indeflator can be used.

[0025] A light irradiator 90 that emits light in the balloon 30 is inserted into the light irradiation device 10. The light irradiator 90 is exposed proximally from the proximal hub 70 of the light irradiation device 10 and is connected to a light source unit 95 that outputs light. The light irradiator 90 includes a light irradiation unit 92 provided at the distal end of the light irradiator 90 in the longitudinal direction, and an optical fiber connected to the light irradiation unit 92 and extending toward the proximal end of the light irradiation device 90 in the longitudinal direction. For example, the light irradiator 90 is configured with a side-emitting optical fiber that can irradiate light radially outward from the distal end. The light irradiation unit 92 and the optical fiber can be configured such that the diameter of the light irradiation unit 92 is larger than the diameter of the optical fiber in the longitudinal direction of the light irradiator 90.

[0026] As shown in FIG. 2 , the balloon 30 can expand radially between its distal end 31 and proximal end 32. The central portion of the balloon 30 in the longitudinal direction is a straight portion 33 having the same diameter along the longitudinal direction, and both ends of the balloon 30 in the longitudinal direction are tapered portions 34 whose diameter decreases toward the ends. As shown in FIG. 2 , the tapered portion 34 can be hemispherical. Alternatively, the tapered portion 34 may be conical. The balloon 30 is made of an optically transparent material such as nylon or urethane. The thickness of the balloon 30 is, for example, 30 μm.

[0027] The light irradiator 90 described above is disposed inside the balloon 30. The balloon 30 has a light-transmitting window 37 that transmits light from the light irradiator 92 of the light irradiator 90, and a coating film 36 that has a lower transmittance of light from the light irradiator 92 than the light-transmitting window 37. The coating film 36 is formed by applying it to the outer surface of the balloon 30 as a base material. In other words, the balloon 30 includes a film body made of the coating film 36 coated on the outer surface of the balloon 30 as a light-shielding body. The light-transmitting window 37 can transmit light from the light irradiator 92 because the surface of the balloon 30 as a base material is not covered with the coating film 36. In other words, the portion not covered by the light-shielding body is defined as the light-transmitting window 37. The light-transmitting window 37 may be provided over the entire circumferential direction (360 degrees) or over a portion of the circumferential direction (e.g., 180 degrees).

[0028] 3 , the balloon 30 can be inflated by being exposed to the distal end side from a distal opening 125a of the lumen 125 of the endoscopic device 100. The endoscopic device 100 has an endoscope 123 at its distal end, which allows the state of the balloon 30 to be visually confirmed. The proximal end of the balloon 30 is joined to the distal end of the shaft portion 20, which is inserted into the lumen 125 of the endoscopic device 100. A distal tip 35 is provided at the distal end of the balloon 30.

[0029] A tubular body 40 having a lumen 41 along the longitudinal direction is disposed inside the balloon 30. The tubular body 40 extends along the longitudinal direction inside the shaft portion 20. Inside the shaft portion 20 and outside the tubular body 40 is an inflation lumen 21 through which a fluid for inflating the balloon 30 flows.

[0030] A light irradiator 90 is inserted into the lumen 41 of the tubular body 40. The light irradiator 90 is a side-emitting optical fiber that can irradiate light radially outward all around, and has a light irradiating portion 92 at its tip that can irradiate light in the radial direction. The tubular body 40 is made of a light-transmitting material to allow light from the light irradiating portion 92 to pass through.

[0031] Light from the light irradiation unit 92 is transmitted through the light-transmitting window 37 of the balloon 30 and irradiated to the outside. Portions of the balloon 30 other than the light-transmitting window 37 are covered with the coating film 36, resulting in low transmittance of light from the light irradiation unit 92. To selectively irradiate light from the light irradiation unit 92 only to the lesion and its surrounding area, the coating film 36 is required to have optical properties that require a sufficiently low light transmittance. Furthermore, the coating film 36 is required to have mechanical properties such as the ability to deform in response to the expansion and contraction of the balloon 30, as well as water resistance and abrasion resistance when the balloon 30 is inserted into a living body. In addition, since the coating film 36 is used in the light irradiation device 10, which is inserted into a living body, it must also be biologically safe.

[0032] The coating film 36 formed on the balloon 30, which is the substrate, will now be described in detail. The coating film 36 is made of a thermoplastic elastomer and a pigment. In this embodiment, a polyurethane elastomer is used as the thermoplastic elastomer. However, the thermoplastic elastomer is not limited to polyurethane elastomer; other thermoplastic elastomers such as polystyrene elastomer and polyamide elastomer can also be used.

[0033] The pigment is not particularly limited as long as it can color the coating film 36, but in this embodiment, titanium oxide is used as a pigment to color the film white, and carbon black is used as a pigment to color the film black. Also, by mixing titanium oxide and carbon black, the coating film 36 can be colored gray. Other pigments may also be used, such as phthalocyanine blue or phthalocyanine green.

[0034] As an example of the coating film 36, a coating film 36 was formed on a substrate with the composition and thickness shown in Table 1. The transmittance marked with * is the transmittance estimated from the measured reflectance.

[0035]

[0036] The coating film 36 is formed as follows. First, the thermoplastic elastomer and pigment that form the coating film 36, as well as a solvent for dissolving them, are prepared. First, the pigment is dissolved in a solvent to prepare a first solution. Next, a thermoplastic elastomer is dissolved in the solution (first solution) obtained by dissolving the pigment in the solvent to prepare a second solution. By first dissolving the pigment in a solvent and then dissolving the thermoplastic elastomer, the pigment can be easily dispersed in the solvent. Tetrahydrofuran (THF) can be used as the solvent. As shown in Table 1, the mass ratio of the thermoplastic elastomer to the pigment ranged from 1:1.0 to 1:2.0 when the pigment was titanium oxide, and from 1:0.4 to 1:0.5 when the pigment was carbon black. Furthermore, when titanium oxide and carbon black were mixed, the mass ratio of the thermoplastic elastomer to the pigment was 1:1.0. The mixing ratio of titanium oxide to carbon black was 100:1. The thermoplastic elastomer and pigment are dissolved in a solvent to prepare a solution. The solution is formulated so that when the mass ratio of the thermoplastic elastomer to the pigment is 1:1.0, the thermoplastic elastomer is 10 mass %, the pigment is 10 mass %, and the solvent is 80 mass %.

[0037] Once the solution is prepared, it is applied to a substrate. The substrate for the coating film 36 in Table 1 is a PET film. The solution is applied by dipping. The film thickness of the coating film 36 can be adjusted by adjusting the lifting speed and number of dipping operations. The lifting speed for dipping is, for example, 0.5 mm / s, and the number of dipping operations is, for example, one time.

[0038] After the solution is applied to the substrate, the coating film 36 is dried. The boiling point of the solvent, THF, is 66°C, and it can be dried at room temperature. The solvent used to form the coating film 36 may be other than THF, as long as it can be dried at a low temperature between room temperature and 60°C. This allows the coating film 36 to be formed without deforming the substrate. Specifically, the solvent may be THF, methanol, hexane, or the like.

[0039] When the coating film 36 was formed under the conditions in Table 1, if the mass ratio of the thermoplastic elastomer to the pigment was 1:2.0, powder formed on the surface and the coating film 36 was not formed sufficiently. Therefore, the mass ratio of the thermoplastic elastomer to the pigment that forms the coating film 36 needs to be less than 1:2.0.

[0040] In order to reduce the outer diameter of the light irradiation device 10, it is desirable that the thickness of the coating film 36 be as small as possible while still satisfying certain optical properties. Under the conditions shown in Table 1, when the pigment is carbon black, the coating film 36 can have a thickness of 30 μm or less and achieve a sufficiently low transmittance. Furthermore, when the pigment is titanium oxide, the mass ratio of the thermoplastic elastomer to the pigment is 1:1.2, and the thickness of the coating film 36 is 60 μm, the light transmittance is 9%. When the mass ratio of the thermoplastic elastomer to the pigment is 1:1.0, and the thickness of the coating film 36 is 15 μm, the light transmittance is 31%. When the mass ratio of the thermoplastic elastomer to the pigment is 1:1.5, and the thickness of the coating film 36 is 14 μm, the light transmittance is 27%. Furthermore, when the pigment is a mixture of titanium oxide and carbon black, the mass ratio of the thermoplastic elastomer to the pigment is 1:1.0, and the thickness of the coating film 36 is 12 μm, the light transmittance is 8%. These results indicate that by setting the thickness of the coating film 36 to 60 μm or less, it is possible to set the light transmittance to at least 31% or less, thereby ensuring sufficient optical properties of the coating film 36. Furthermore, by setting the thickness of the coating film 36 to 30 μm or less (more preferably 22 μm or less), it is possible to deform in accordance with the expansion and contraction of the balloon 30, which is the base material, and to sufficiently ensure the mechanical properties of the balloon 30, such as water resistance, abrasion resistance, and ease of insertion and removal, when the balloon 30 is inserted into the forceps channel of an endoscope or inserted into a living body.

[0041] The coating film 36 must have low cytotoxicity in order to ensure the aforementioned biological safety. The strength of cytotoxicity is determined by IC ５０ It can be evaluated by IC value. ５０ The value is the concentration (%) of the test solution that inhibits the colony formation rate by 50% (the average value of the colony counts in the control group or the solvent control group is taken as 100%). In this embodiment, the evaluation was carried out in accordance with ISO 10993-5 (2009); Biological evaluation of medical devices - Part 5: Tests for in vitro cytotoxicity. The titanium oxide used in the coating film 36 in Table 1 was IC ５０ The IC value is 78 to 100%. Carbon black is not cytotoxic, so ５０In contrast, in this embodiment, the IC value of the positive control material B (polyurethane film containing 0.25% zinc dibutyldithiocarbamate (ZDBC)) was 100% or more. ５０ The value of the coating 36 in Table 1 was 60%. ５０ Since the cytotoxicity (value) was 60% or more, it was confirmed that the cytotoxicity was weaker than that of the polyurethane film containing 0.25% zinc dibutyldithiocarbamate (ZDBC) as the positive control material B.

[0042] The coating film 36 of this embodiment contains a thermoplastic elastomer, and therefore is flexible and can expand and contract in accordance with the expansion and contraction of the balloon 30. That is, the coating film 36 is adaptable to the deformation of the balloon 30, which serves as the base material. Furthermore, the coating film 36 has high adhesion to the base material, and can increase abrasion resistance in vivo. Furthermore, the coating film 36 contains a thermoplastic elastomer, and therefore is water-resistant. Therefore, the coating film 36 can satisfy the mechanical properties described above.

[0043] Tensile tests were carried out on a substrate having the coating film 36 and a substrate not having the coating film 36. First, a test piece (A) was prepared in which the coating film 36 was applied to a substrate having a width of 10 mm and a length of 40 mm, and a test piece (B) was prepared in which only the substrate having a width of 10 mm and a length of 40 mm was formed. Each of these test pieces was set in a tensile tester so that the gripping distance was 25 mm, and measurements were made at a tensile speed of 25 mm / min.

[0044] The results of the tensile tests on the three test pieces (A) and the three test pieces (B) are shown in Table 2.

[0045]

[0046] As a result of the tensile test, the average elongation at break of test piece (A) composed of the substrate and coating film 36 was 28.099 mm, while the average elongation at break of test piece (B) composed only of the substrate was 28.904 mm. In other words, test piece (A) composed of the substrate and coating film 36 had a smaller elongation at break than test piece (B) composed of the substrate. Here, elongation refers to the elongation rate of the balloon at each pressure, expressed as a percentage. Furthermore, elongation at break refers to the elongation rate at which the test piece breaks, expressed as a percentage. In other words, the elongation is the value obtained by subtracting the gripping distance of the test piece before tension from the gripping distance of the test piece at break, dividing the value by the gripping distance of the test piece before tension, and multiplying by 100.

[0047] The ratio of the smallest elongation at break of test specimen (A), 27.664 mm / 25,000 mm x 100, to the largest elongation at break of test specimen (B), 29.437 mm / 25,000 mm x 100, was 93.98% (approximately 94%). Therefore, the elongation at break of test specimen (A) relative to the gripping distance before pulling was in a range of 90% or more of the elongation at break of test specimen (B). Therefore, the elongation at break of test specimen (A) was in a range of 90% or more of the elongation at break of test specimen (B). If such a coating film 36 is formed on a balloon as a substrate, when the balloon is expanded and deflated in vivo, the coating film 36 will expand in accordance with the expansion of the balloon, and will also expand in accordance with the contraction of the balloon when the balloon is deflated and removed from the body, without interfering with the folding of the balloon.

[0048] To confirm the mechanical properties of the substrate, the following test was conducted. A balloon made of nylon 12 was prepared as the substrate. Two balloons made of nylon 12 were prepared: Balloon D, with an outer diameter of 20 mm and a length of 45 mm, and Balloon E, with an outer diameter of 15 mm and a length of 45 mm. Both Balloon D and Balloon E were uncoated, not coated with coating film 36. Balloons D and E were inflated using an indeflator at pressures of 0.5 atm increments, and their elongation was measured. Here, elongation refers to the balloon's elongation rate at each pressure, expressed as a percentage. Furthermore, elongation at rupture refers to the elongation rate at which the balloon ruptures (bursts), expressed as a percentage. In other words, the outer diameter of the balloon (before tensioning) at atmospheric pressure (1.0 atm) is taken as 0% and represents the amount of elongation until burst. Balloons D and E were designed to have rated diameters (outer diameters) of approximately 20 mm and approximately 15 mm, respectively, at 2.0 atm.

[0049] For example, an example of balloon D had a diameter of 18.467 mm at atmospheric pressure (1.0 atm) and a diameter of 19.787 mm at normal operating pressure (2.0 atm). Balloon D expanded to a diameter of 21.567 mm at 5.0 atm but burst at 5.5 atm. Therefore, the maximum expanded diameter of balloon D was 21.567 mm, and balloon D stretched 16.79% based on its diameter at atmospheric pressure. Furthermore, balloon D stretched 7.15% based on its diameter at normal operating pressure. Therefore, it can be seen that the ratio of the stretch at normal operating pressure to the maximum expanded diameter of balloon D was approximately 42.58%. An example of balloon E had a diameter of 14.696 mm at atmospheric pressure (1.0 atm) and a diameter of 15.533 mm at normal operating pressure (2.0 atm). Balloon E expanded to a diameter of 17.475 mm at 8.0 atm but burst at 8.5 atm. Therefore, the maximum expanded diameter of Balloon E was 17.475 mm, and Balloon E stretched 18.91% of its diameter at atmospheric pressure. Furthermore, Balloon E stretched 5.70% of its diameter at normal operating pressure. Therefore, the ratio of the elongation at normal operating pressure to the maximum expanded diameter of Balloon E was approximately 30.14%. From the above, it was found that a balloon without coating 36 stretches more than 30% of its maximum expanded diameter at normal operating pressure. The coating 36 is required to adapt to the deformation of the balloon as a substrate and not peel or tear from the balloon. Therefore, a substrate with coating 36 is required to be able to adapt to an elongation of more than 30%. On the other hand, the applied coating 36 causes the substrate with coating 36 to have a smaller elongation at rupture than a substrate without coating 36. Therefore, the elongation at break of a substrate having the coating film 36 relative to the outer diameter of the original balloon (diameter (outer diameter) of the balloon at atmospheric pressure) is smaller than that of a substrate not having the coating film 36, and it can be said that the elongation of the substrate having the coating film 36 relative to the outer diameter of the original balloon is sufficient as long as it is 30% or more of the elongation at break of a substrate not having the coating film 36 relative to the outer diameter of the balloon before stretching.In fact, balloon F, made of nylon 12 and measuring 15 mm in outer diameter and 45 mm in length and having coating 36, exhibited an elongation at normal operating pressure of more than 40% of the elongation at maximum expanded diameter of balloon E. More specifically, balloon F had a diameter of 13.679 mm at atmospheric pressure (1.0 atm) and a diameter of 14.737 mm at normal operating pressure (2.0 atm). Balloon F expanded to a diameter of 17.152 mm at 7.0 atm but burst at 7.5 atm. Balloon F elongated 7.73% at normal operating pressure, based on its diameter at atmospheric pressure. Therefore, the ratio of the elongation of balloon F at normal operating pressure to the elongation at maximum expanded diameter of balloon E was approximately 40.90%. Therefore, it can be said that the elongation at rupture of balloon F with coating 36 relative to the original balloon outer diameter is sufficient if it is 40% or more of the elongation at rupture of balloon E with coating 36 relative to the original balloon outer diameter. According to this configuration, in the light irradiation device 10 having the balloon 30, when the balloon 30 is placed inside a living body and expanded, the coating film 36 can effectively function as a light blocking body.

[0050] As described above, (1) the coating film 36 according to this embodiment is a coating film 36 applied to the surface of a substrate, the coating film 36 comprising a thermoplastic elastomer and a pigment, the mass ratio of the thermoplastic elastomer to the pigment being less than 1:2.0, and the coating film 36 is applied to a substrate having a width of 10 mm and a length of 40 mm. A test piece of the coating film 36 is placed in a tensile tester with a gripping distance of 25 mm and measured at a tensile speed of 25 mm / min. In this test, the elongation at break of test piece (A) consisting of the substrate and the coating film 36 is smaller than the elongation at break of test piece (B) consisting of the substrate, and the elongation of test piece (A) is 40% or more of the elongation of test piece (B). The coating film 36 thus configured is water-resistant and can be formed at a temperature that does not deform the substrate. Furthermore, the coating film conforms to the deformation of the substrate when it is stretched to a certain extent, preventing peeling or tearing from the substrate. From these facts, the coating film 36 can satisfy the properties required for use in the light irradiation device 10 while having the mechanical and optical properties required for the light irradiation device 10 to function.

[0051] (2) In the coating film 36 of (1) above, the elongation at break of the test piece (A) may be 93.5% or more of the elongation at break of the test piece (B). This allows the coating film 36 to better follow the elongation of the substrate, and therefore ensures that the coating film 36 returns to its original shape when the substrate stretches and shrinks.

[0052] (3) In the coating film 36 of (1) or (2) above, when the coating film 36 is evaluated in accordance with ISO 10993, the cell attribute strength (IC) is higher than that of a polyurethane film containing 0.25% zinc dibutyldithiocarbamate (ZDBC) as a positive control material B. ５０ This allows the cytotoxicity of the coating film 36 to be weakened to a level necessary for use in the light irradiation device 10.

[0053] (4) In any one of the coating films 36 described above in (1) to (3), the coating film 36 may have a thickness of 60 μm or less. This allows the outer diameter of the light irradiation device to be reduced.

[0054] (5) In any one of the coating films 36 described above in (1) to (4), the light transmittance of the coating film 36 may be 31% or less. This allows the coating film 36 to satisfy its optical performance requirements.

[0055] (6) In any of the coating films 36 described above in (1) to (5), the thermoplastic elastomer may be a polyurethane elastomer, which allows the coating film 36 to have a high ability to conform to deformations of the substrate.

[0056] (7) In any of the coating films 36 described above in (1) to (6), the pigment may be titanium oxide, carbon black, or a mixture of titanium oxide and carbon black, thereby making it possible to obtain a white, black, or gray coating film 36 that satisfies the requirements for cytotoxicity strength.

[0057] (8) In any of the coating films (1) to (7) above, the substrate may be a balloon 30 made of a light-transmitting material, and the thickness of the balloon 30 may be 30 μm. This allows the biological safety and mechanical and optical properties of the balloon 30 to be satisfied in the light irradiation device 10 having the light irradiator 90 inside the balloon 30 on which the coating film 36 is formed so as to be able to irradiate light in a certain direction.

[0058] (9) In the coating film 36 of any one of (1) to (8) above, the mass ratio of the thermoplastic elastomer to the pigment is 1:0.5 or less, the thickness of the coating film 36 is 30 μm or less, the light transmittance of the coating film 36 is 0%, and the pigment may be carbon black. This makes the coating film 36 highly biologically safe and allows the coating film 36 to have a small thickness.

[0059] (10) In this embodiment, the method for forming the coating film 36 includes preparing a first solution in which a pigment is dissolved in a solvent so that the mass ratio of the thermoplastic elastomer to the pigment is less than 1:2.0, preparing a second solution in which a thermoplastic elastomer is dissolved in the first solution, and applying the second solution to a substrate and drying the coating film, wherein a test piece formed by applying the coating film 36 to a substrate having a width of 10 mm and a length of 40 mm is set in a tensile tester so that the gripping distance is 25 mm, and a tensile test is performed at a tensile speed of 25 mm / min, in which the elongation at break of test piece (A) composed of the substrate and the coating film is smaller than the elongation at break of test piece (B) composed of the substrate, and the elongation of test piece (A) is 40% or more of the elongation of test piece (B). This method for forming the coating film 36 thus configured is capable of forming a coating film 36 that is water-resistant, can be formed at a temperature that does not deform the substrate, and satisfies the properties required for a light irradiation device.

[0060] The present invention is not limited to the above-described embodiment, and various modifications can be made by those skilled in the art within the technical concept of the present invention.

[0061] This application is based on Japanese Patent Application No. 2023-187768 filed on November 1, 2023, the disclosures of which are incorporated herein by reference in their entirety.

[0062] REFERENCE SIGNS LIST 10 Light irradiation device 20 Shaft portion 21 Expansion lumen 30 Balloon 36 Light blocking body 37 Light-transmitting window portion 40 Tubular body 41 Lumen 100 Endoscopic device 122 Handle portion 125 Lumen

Claims

1. A coating film applied to the surface of a substrate, the coating film being composed of a thermoplastic elastomer and a pigment, the mass ratio of the thermoplastic elastomer to the pigment being less than 1:2.0, and in a tensile test performed by setting a test piece formed by applying the coating film to the substrate having a width of 10 mm and a length of 40 mm in a tensile tester with a gripping distance of 25 mm, and measuring the tensile speed at 25 mm / min, the elongation at break of test piece (A) composed of the substrate and the coating film is smaller than the elongation at break of test piece (B) composed of the substrate, and the elongation of the test piece (A) is 40% or more of the elongation of the test piece (B).

2. The coating film according to claim 1, wherein the elongation of the test piece (A) is 90% or more of the elongation of the test piece (B).

3. When the coating film was evaluated according to ISO 10993, the cell attribute strength (IC) was higher than that of a polyurethane film containing 0.25% zinc dibutyldithiocarbamate (ZDBC) as a positive control material B. ５０ 3. The coating film according to claim 1 or 2, wherein the resistance (i.e., the resistance to moisture) is weak.

4. The coating film according to claim 1 or 2, wherein the coating film has a thickness of 60 μm or less.

5. The coating film according to claim 1 or 2, wherein the light transmittance of the coating film is 31% or less.

6. The coating film according to claim 1 or 2, wherein the thermoplastic elastomer is a polyurethane elastomer.

7. The coating film according to claim 1 or 2, wherein the pigment is titanium oxide, carbon black, or a mixture of the titanium oxide and the carbon black.

8. The coating film according to claim 1 or 2, wherein the substrate is a balloon made of a light-transmitting material, and the thickness of the balloon is 30 μm.

9. A coating film according to claim 1 or 2, wherein the mass ratio of the thermoplastic elastomer to the pigment is 1:0.5 or less, the thickness of the coating film is 30 μm or less, the light transmittance of the coating film is 0%, and the pigment is carbon black.

10. A method for forming a coating film comprising: preparing a first solution in which a pigment is dissolved in a solvent so that the mass ratio of the thermoplastic elastomer to the pigment is less than 1:2.0; preparing a second solution in which the thermoplastic elastomer is dissolved in the first solution; and applying the second solution to a substrate and drying the second solution; wherein a test piece formed by applying the coating film to the substrate having a width of 10 mm and a length of 40 mm is set in a tensile testing machine so that the gripping distance is 25 mm, and a tensile test is performed at a tensile speed of 25 mm / min, in which the elongation at break of test piece (A) composed of the substrate and the coating film is smaller than the elongation at break of test piece (B) composed of the substrate, and the elongation of test piece (A) is 40% or more of the elongation of test piece (B).

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