Stretchable Polymer Thick Film Carbon Black Composition for a Mountable Heater

Abstract

To provide a stretchable polymer thick-film carbon black composition for wearable heaters.SOLUTION: A polymer thick-film carbon black composition comprises 6-13 wt.% of a conductive carbon black powder, and 87-94 wt.% of an organic medium comprising a thermoplastic polyurethane resin dissolved in an organic solvent. The composition can be used to form a resistance element of heaters in applications that require significant stretching, particularly on substrates that can be greatly elongated and that can be particularly used in wearable garment applications.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention aims at a polymer thick film carbon black composition. More specifically, using the polymer thick film carbon black composition, in applications where significant elongation is required, particularly on a substrate that can be highly stretched and can be used, especially in wearable clothing applications, a heater can be formed. Another method utilizes the process of directly printing on either a woven or knitted fabric clothing substrate to manufacture a stretchable heater.

Background Art

[0002] Polymer thick film (PTF) circuits have been used for a long time as electrical elements. Although they have been used as electrical elements, the use of PTF silver or carbon conductors in highly stretchable applications such as wearable clothing is not common. The ability to be stretchable, exposed to multiple washing and drying cycles, and still maintain conductivity is important. One of the objectives of the present invention is to address the aforementioned requirements and to produce a stretchable PTF ink that can be used in the structure of a functional battery used in a substrate applicable to a fabric that can be used as or in wearable clothing.

[0003] Printing a carbon polymer thick film (PTF) paste can produce a dry film that is considerably more resistive than those made from silver paste. As a result, they are ideal candidates for resistive heating elements in printed electrical resistive heaters. Silver printed circuits can provide low resistance bus bars that supply power to the activated carbon elements with little or no parasitic heating. In many cases, a certain positive temperature coefficient (PTC) of resistance inherent in the carbon formulation is desirable to limit the maximum operating temperature. However, in heaters trying to draw maximum power from a small power source, a strong PTC effect can cause problems. When designed to supply power at the operating temperature, the cold resistance can be very low, and current demand can activate the battery's current limiting circuit, resulting in shutdown. When designed to start reliably at low temperatures, the heater may not supply sufficient power when warm. Low PTC carbon that is stable over the desired operating temperature range is needed.

Summary of the Invention

Means for Solving the Problems

[0004] The present invention provides (a) 6-13 wt% of conductive carbon black powder, and (b) an organic medium of 87-94 wt% containing 10-30 wt% of a thermoplastic polyurethane resin dissolved in an organic solvent, wherein the thermoplastic polyurethane has a percent elongation of at least 200%, the organic medium, and the weight percentage of the thermoplastic polyurethane resin is based on the total weight of the organic medium, and the weight percentages of the conductive carbon black powder and the organic medium are based on the total weight of the composition.

[0005] The present invention further relates to using the composition to form a resistive portion of an article requiring a stretchable heater, such as a heater for wearable clothing. Accordingly, the present invention provides (a) 6-13 wt% of conductive carbon black powder, and (b) An article containing a stretchable heater formed from a polymeric thick film carbon black composition comprising 87 - 94 wt% of an organic medium containing 10 - 30 wt% of a thermoplastic polyurethane resin dissolved in an organic solvent, wherein the thermoplastic polyurethane has a percent elongation of at least 200%, wherein the weight percent of the thermoplastic polyurethane resin is based on the total weight of the organic medium, and the weight percents of the conductive carbon black powder and the organic medium are based on the total weight of the composition.

[0006] In one embodiment, the article is a wearable garment.

Brief Description of the Drawings

[0007]

Figure 1

Embodiments for Carrying Out the Invention

[0008] The present invention relates to a polymeric thick film carbon black composition for use in forming heaters, and in particular for use in highly stretchable circuits such as those where the heater is formed on a fabric for clothing. This is often referred to as wearable electronics. Further, this composition is useful for forming heaters in applications such as heating sheets. The layer of the conductor is printed and dried on a substrate so as to generate a heater, and then the entire circuit is subjected to typical bends / folds that the fabric will receive. Further, as is typical for fabrics, these must be washed and dried regularly, and the conductivity and integrity of the conductor must be maintained.

[0009] In this specification, weight percent is described as wt%.

[0010] Organic medium The organic medium consists of a thermoplastic polypolyurethane resin dissolved in an organic solvent. The polypolyurethane resin must achieve good adhesion to the lower substrate. The polypolyurethane resin must be compatible with the performance of the heater after deformation, washing, and drying cycles and must not have an adverse effect.

[0011] The thermoplastic polypolyurethane resin is 10 - 30 wt% of the total weight of the organic medium. In one embodiment, the thermoplastic polypolyurethane resin is a polyurethane homopolymer. In another embodiment, the polyurethane resin is a polyester - based copolymer. In one embodiment, the thermoplastic polypolyurethane resin is mainly a linear hydroxyl polyurethane.

[0012] The thermoplastic polypolyurethane resin has an elongation of at least 200%.

[0013] The percent elongation is defined in the usual way.

[0014]

Number

[0015] Typically, the polymer resin is added to an organic solvent by mechanical mixing to form a medium. Solvents suitable for use in the polymer thick film composition are recognized by those skilled in the art and include acetic acid and terpenes such as carbitol acetate and α- or β-terpineol, or other solvents such as kerosene, dibutyl phthalate, butyl carbitol, butyl carbitol acetate, hexylene glycol, and high boiling point alcohols, and alcohol esters, and mixtures thereof. Further, it can contain a volatile liquid to promote rapid curing after application to the substrate. In many embodiments of the present invention, solvents such as glycol ethers, ketones, esters, and other solvents with similar boiling points (in the range of 180°C to 250°C), and mixtures thereof can be used. Various combinations of these and other solvents are formulated to obtain the desired viscosity and volatility requirements. The solvent used must solubilize the resin. The solvent can be added to the composition to adjust the viscosity and is considered part of the organic medium.

[0016] In various embodiments, the amount of the organic medium ranges from 87 to 94 wt% based on the total weight of the composition.

[0017] Conductive carbon black composition Many carbon composite coatings contain graphite. It is easy to obtain a high conductivity with a suitable amount of graphite. However, the contact between graphite sheets is easily broken by the thermal expansion of the polymer matrix, and the resistance increases rapidly with temperature. Therefore, highly structured carbon black (CB) powders such as Vulcan (registered trademark) XC-72 and Monarch (registered trademark) 700 (both available from Cabot Corp, Boston, Mass) are used in this composition. When suitably dispersed, carbon black can provide a conductive network that is less likely to break when the matrix expands. A very low level of CB results in a very high resistance and a very high positive temperature coefficient (PTC) of resistance. The electrical resistance generally improves as the amount of carbon black increases until the volume fraction of carbon particles significantly exceeds the percolation threshold of that particular CB. Also, the PTC decreases as the concentration of CB is increased. The improvement becomes smaller as the percolation threshold is passed. However, a very high amount of CB in the dry coating can result in insufficient mechanical properties and crack formation during the drying process. High shear mixing can be used to provide a better dispersion of carbon, lower the percolation threshold, and provide better electrical performance at a lower CB loading. This results in a more crack-resistant and low-PTC formulation. This conductive carbon black composition forms a crack-free coating with an acceptably low resistivity and low PTC when processed using standard PTF blending and roll milling equipment and methods. The amount of conductive carbon black powder ranges from 6 to 13 wt% based on the total weight of the composition. The ratio of the weight of the polyurethane resin to the weight of the conductive carbon black powder ranges from 1.50 to 1.75.

[0018] Yet another process where a surfactant is premixed with the solvent and carbon black can further improve the dispersion, but the surfactant does not burn out when in the paste processed at high temperatures and causes toxicity issues as an unstable compound in the coating that can come into contact with the skin.

[0019] Additional powder Various powders or additives can be added to the PTF composition to improve adhesion, improve rheology, increase low shear viscosity, and thereby improve printability, as long as they do not have a harmful effect on the skin.

[0020] Coating of the PTF composition The PTF carbon black composition, also referred to as a "paste", can be used in wearable clothing or deposited on a substrate that can be applied to a fabric used as wearable clothing. One substrate is a thermoplastic polyurethane substrate such as Bemis ST-604 available from Bemis Associates, Inc., Shirley, MA. Another possible substrate is a thermoplastic polyester such as Hytrel® available from DuPont Co., Wilmington, DE. Also, the substrate can be a sheet of a composite material consisting of a combination of plastic sheets having a permeable coating deposited thereon.

[0021] Deposition of the PTF carbon black composition on the substrate is typically carried out by screen printing, but other deposition techniques such as stencil printing, syringe dispensing, or coating techniques can be utilized. In the case of screen printing, the screen mesh size controls the thickness of the deposited thick film.

[0022] Generally, the thick film composition includes a functional phase that imparts appropriate functional properties to the composition. For example, the functional phase can include electrically functional powders dispersed in an organic medium that acts as a carrier in the functional phase. Generally, the composition is fired to burn both the polymer and the solvent of the organic medium to impart electrical functional properties. However, in the case of a polymer thick film composition, the polymer portion of the organic medium remains as a constituent of the composition after drying.

[0023] The PTF carbon black composition is processed for a time and at a temperature necessary to remove all of the solvent. For example, the deposited thick film is typically dried by exposure to heat at 130° C. for 10-15 minutes.

[0024] Heater Structure The PTF carbon black composition is printed onto a substrate and dried as described above. One or more layers of the PTF carbon black resistive composition can be printed onto a substrate and dried to form the resistive element of the battery. The conductors to the busses and busbars can be printed before or after the PTF carbon black resistive composition.

[0025] In one embodiment, the substrate can be applied to a fabric that can be used to form a wearable garment. Either side of the substrate can be applied to the fabric, i.e., the side of the substrate with the carbon black coating can be adjacent to the fabric, or the other side of the substrate can be adjacent to the fabric. Thermoplastic polyurethane substrates such as DuPont™ Intexar™ TE11C or Bemis ST-604 adhere to polyester, nylon, and polyurethane or polyvinyl chloride coated fabrics.

[0026] In another embodiment, the carbon black composition can be applied directly to a stretchable permeable fabric. One such nonwoven fabric is made from Evolon® available from Fruedenberg Evolon, Colmar, France. Another permeable substrate that can be used for this type of application is a woven polyester coated with a polyamide, such as Cetus® OS5000U available from Dyneic Co., Ltd., Kyoto, Japan. EXAMPLES

[0027] Examples and Comparative Experiments Example 1 The PTF carbon black composition was prepared as follows. 69 parts by weight of an initial organic medium was used, and 28.50 wt% of Desmocoll® 406 polyurethane (Covestro LLC, Pittsburgh, PA) was prepared by mixing with 71.50 wt% of Dowanol™ DPM dipropylene glycol methyl ether (Dow Co., Midland MI) organic solvent. This mixture was heated at 90 °C for 1 - 2 hours to dissolve all the resins. 12.31 parts by weight of Vulcan® XC - 72 conductive carbon black powder (Cabot Corp, Boston, Mass) was added. Finally, 18.69 parts by weight of Dowanol™ DPM dipropylene glycol methyl ether was added for thinning to bring the composition to a desired viscosity of 70 Pas. The amount of the organic medium containing the solvent added to adjust the viscosity was 87.70 wt%, consisting of 68.03 wt% of the solvent and 19.67 wt% of the polyurethane resin, and the wt% is based on the total weight of the composition. The polyurethane resin was 22.4 wt% of the total weight of the organic medium. The ratio of the weight of the polyurethane resin to the weight of the carbon black was 1.60.

[0028] This composition was mixed in a planetary mixer for 30 minutes and then fed several times to a three - roll mill to provide a good dispersion of the carbon black powder.

[0029] The composition was screen - printed onto a polyester (PET) substrate and dried in a forced - air oven box at 130 o °C for 10 minutes. No crack formation occurred during the drying process. The volume percentage of carbon black in the dried film was 36.6.

[0030] The resistivity of the dried film was 162 Ohms / sq. The PTC index was obtained by measuring the resistance of the film at 25 o °C, 40 o °C and 65 o °C. The PTC resistance factor at 40 o °C (the resistance at 40 o °C divided by the resistance at 25o The ratio to the resistance in C) is 1.06, and 65 o The PTC resistance factor in C (65 o Of the resistance in C, 25 o The ratio to the resistance in C) is 1.18, showing a relatively low PTC.

[0031] Example 2 The PTF carbon black composition was prepared as follows. 84.2 parts by weight of an initial organic medium was used, and 20.50 wt% of Desmocoll® 530 / 1 polyurethane (Covestro LLC, Pittsburgh, PA) was prepared by mixing with 79.50 of diethylene glycol monoethyl acetate (Eastman Chemical Co., Kingsport, Tenn.) organic solvent. This mixture was heated at 90 °C for 1 - 2 hours to dissolve all the resin. 10.80 parts by weight of Vulcan® XC - 72 conductive carbon black powder (Cabot Corp, Boston, Mass) was added. Finally, 5.00 parts by weight of diethylene glycol monoethyl acetate was added for thinning to bring the composition to a desired viscosity of 70 Pas. The amount of the organic medium containing the solvent added to adjust the viscosity is 89.2 wt%, consisting of 71.94 wt% of the solvent and 17.26 wt% of the polyurethane resin, and wt% is based on the total weight of the composition. The polyurethane resin was 19.4 wt% of the total weight of the organic medium. The ratio of the weight of the polyurethane resin to the weight of the carbon black was 1.60.

[0032] This composition was mixed in a planetary mixer for 30 minutes and then subjected to a three - roll mill several times to provide a good dispersion of the carbon black powder.

[0033] The composition was screen - printed onto a polyester (PET) substrate and dried in a forced - air oven box at 130 o C for 10 minutes. No crack formation occurred during the drying process. The volume percentage of carbon black in the dried film was 36.6.

[0034] The resistivity of the dried film was 187 Ohms / sq. The PTC index was obtained by measuring the resistance of the film at 25 o °C, 40 o °C and 65 o °C. The PTC resistance factor at 40 o °C (the ratio of the resistance at 40 o °C to the resistance at 25 o °C) was 1.14, and the PTC resistance factor at 65 o °C (the ratio of the resistance at 65 o °C to the resistance at 25 o °C) was 1.28, indicating a relatively low PTC.

[0035] Example 3 The PTF carbon black composition was prepared as follows. 58.50 parts by weight of an initial organic medium was used, and 20.50 wt% of Desmocoll® 530 / 1 polyurethane (Covestro LLC, Pittsburgh, PA) was prepared by mixing with 79.50 of diethylene glycol monoethyl acetate (Eastman Chemical Co., Kingsport, Tenn.). This mixture was heated at 90 °C for 1 - 2 hours to dissolve all the resins. 7.00 parts by weight of Vulcan® XC - 72 conductive carbon black powder (Cabot Corp, Boston, Mass) was added. Finally, 34.50 parts by weight of diethylene glycol monoethyl acetate was added for thinning to bring the composition to a desired viscosity of 70 Pas. The amount of the organic medium containing the solvent added to adjust the viscosity was 93.00 wt%, consisting of 81.01 wt% of the solvent and 11.99 wt% of the polyurethane resin, and the wt% is based on the total weight of the composition. The polyurethane resin was 12.9 wt% of the total weight of the organic medium. The ratio of the weight of the polyurethane resin to the weight of the carbon black was 1.71.

[0036] The composition was mixed in a planetary mixer for 30 minutes and then subjected to a three-roll mill several times to provide a good dispersion of carbon black powder.

[0037] The composition was screen-printed onto a polyester (PET) substrate and dried in a forced-air oven at 130 o °C for 10 minutes. No crack formation occurred during the drying process. The volume percentage of carbon black in the dried film was 35.

[0038] The resistivity of the dried film was 179 Ohms / sq. The PTC index was obtained by measuring the resistance of the film at 25 o °C, 40 o °C and 65 o °C. The PTC resistance factor at 40 o °C (the ratio of the resistance at 40 o °C to the resistance at 25 o °C) was 1.11, and the PTC resistance factor at 65 o °C (the ratio of the resistance at 65 o °C to the resistance at 25 o °C) was 1.24, indicating a relatively low PTC.

[0039] Example 4 The PTF carbon black composition was prepared as follows. 66.07 parts by weight of an initial organic medium was used, and 27.50 wt% of Desmocoll® 406 polyurethane (Covestro LLC, Pittsburgh, PA) was prepared by mixing with 72.50 wt% of Dowanol™ DPM dipropylene glycol methyl ether (Dow Co., Midland MI) organic solvent. This mixture was heated at 90 °C for 1 - 2 hours to dissolve all the resin. 12.00 parts by weight of Vulcan® XC - 72 conductive carbon black powder (Cabot Corp, Boston, Mass) was added. 0.06 parts by weight of a surfactant was added. Finally, 18.17 parts by weight of Dowanol™ DPM diethylene glycol monoethyl acetate was added for thinning to bring the composition to the desired viscosity of 70 Pas. The amount of the organic medium containing the solvent added to adjust the viscosity was 87.40 wt%, consisting of 69.23 wt% of the solvent and 18.17 wt% of the polyurethane resin, and the wt% is based on the total weight of the composition. The polyurethane resin was 20.7 wt% of the total weight of the organic medium. The ratio of the weight of the polyurethane resin to the weight of the carbon black was 1.51.

[0040] This composition was mixed in a planetary mixer for 30 minutes and then fed several times to a three - roll mill to provide a good dispersion of the carbon black powder.

[0041] The composition was screen - printed onto a polyester (PET) substrate and dried in a forced - air oven box at 130 o °C for 10 minutes. No crack formation occurred during the drying process. The volume percentage of carbon black in the dried film was 37.

[0042] The resistivity of the dried film was 122 Ohms / sq. The PTC index was obtained by measuring the resistance of the film at 25 o °C and 40 o °C. The PTC resistance factor at 40 o °C (40 oThe resistance in C, 25 o (the ratio to the resistance in C) was 1.2, showing a relatively low PTC.

[0043] Comparative Experiment A The PTF carbon black composition was prepared as follows. 61.07 parts by weight of an initial organic medium was used, and 27.50 wt% of Desmocoll® 406 polyurethane (Covestro LLC, Pittsburgh, PA) was mixed with 72.50 wt% of Dowanol™ DPM dipropylene glycol methyl ether (Dow Co., Midland MI) organic solvent. This mixture was heated at 90 °C for 1 - 2 hours to dissolve all the resins. 13.00 parts by weight of Vulcan® XC - 72 conductive carbon black powder (Cabot Corp, Boston, Mass) was added. 0.06 parts by weight of a surfactant was added. Finally, 25.33 parts by weight of Dowanol™ DPM diethylene glycol monoethyl acetate was added for thinning to bring the composition to the desired viscosity of 70 Pas. The amount of the organic medium containing the solvent added to adjust the viscosity was 86.40 wt%, consisting of 69.61 wt% of the solvent and 16.79 wt% of the polyurethane resin, and wt% is based on the total weight of the composition. The polyurethane resin was 19.4 wt% of the total weight of the organic medium. The ratio of the weight of the polyurethane resin to the weight of the carbon black was 1.29.

[0044] This composition was mixed in a planetary mixer for 30 minutes and then fed several times to a three - roll mill to provide a good dispersion of the carbon black powder.

[0045] The composition was screen - printed onto a polyester (PET) substrate and dried in a forced - air oven box at 130 o °C for 10 minutes. Cracking occurred during the drying process. The volume percentage of carbon black in the dried film was 40.8. Cracking occurred when the relative amount of carbon black was higher.

[0046] Comparative Experiment B The PTF carbon black composition was prepared as follows. 69 parts by weight of an initial organic medium was used, and 28.50 wt% of Desmocoll® 406 polyurethane (Covestro LLC, Pittsburgh, PA) was mixed with 71.50 wt% of Dowanol™ DPM dipropylene glycol methyl ether (Dow Co., Midland MI) organic solvent. This mixture was heated at 90 °C for 1 - 2 hours to dissolve all the resin. 4.45 parts by weight of Vulcan® XC - 72 conductive carbon black powder (Cabot Corp, Boston, Mass) and 11.1 parts by weight of graphite were added. Finally, 35.93 parts by weight of Dowanol™ DPM dipropylene glycol methyl ether was added for thinning to bring the composition to a desired viscosity of 70 Pas. The amount of the organic medium containing the solvent added to adjust the viscosity was 84.45 wt%, consisting of 67.77 wt% of the solvent and 16.68 wt% of the polyurethane resin, where wt% is based on the total weight of the composition. The polyurethane resin was 19.7 wt% of the total weight of the organic medium. The ratio of the weight of the polyurethane resin to the total weight of the carbon black and graphite was 1.07.

[0047] This composition was mixed in a planetary mixer for 30 minutes and then fed several times to a three - roll mill to provide a good dispersion of the carbon black powder.

[0048] The composition was screen - printed onto a polyester (PET) substrate and dried in a forced - air oven box at 130 o °C for 10 minutes. No crack formation occurred during the drying process. The volume percentage of carbon in the dried film was 37.5.

[0049] The resistivity of the dry film was 150 Ohms / sq. The PTC index was obtained by measuring the resistance of the film at 25°C, 40°C, and 65°C. The PTC resistance factor at 40°C (the ratio of the resistance at 40°C to the resistance at 25°C) was 2.2, and the PTC resistance factor at 65°C (the ratio of the resistance at 65°C to the resistance at 25°C) was 2.9, showing a relatively high PTC due to the presence of graphite. The description of the claims at the time of filing is shown below. [Claim 1] (a) 6 to 13 wt% of conductive carbon black powder, and (b) an organic medium of 87 to 94 wt% containing 10 to 30 wt% of a thermoplastic polyurethane resin dissolved in an organic solvent, wherein the thermoplastic polyurethane has a percent elongation of at least 200%, and an organic medium, wherein the weight percentage of the thermoplastic polyurethane resin is based on the total weight of the organic medium, and the weight percentages of the conductive carbon black powder and the organic medium are based on the total weight of the composition, a polymer thick film carbon black composition. [Claim 2] The polymer thick film carbon black composition according to claim 1, wherein the ratio of the weight of the polyurethane resin to the weight of the conductive carbon black powder is in the range of 1.50 to 1.75. [Claim 3] The polymer thick film carbon black composition according to claim 1, wherein the thermoplastic polyurethane resin is selected from the group consisting of polyester-based polymers, urethane homopolymers, and mainly linear hydroxyl polyurethanes. [Claim 4] The polymer thick film carbon black composition according to claim 3, wherein the thermoplastic polyurethane resin is mainly linear hydroxyl polyurethane. [Claim 5] (a) 6 to 13 wt% of conductive carbon black powder, and An article containing a stretchable heater having a resistive element formed from a polymer thick film carbon black composition, the composition comprising an organic medium of 87 - 94 wt% containing 10 - 30 wt% of a thermoplastic polyurethane resin dissolved in an organic solvent, the thermoplastic polyurethane having a percent elongation of at least 200%, the weight percent of the thermoplastic polyurethane resin being based on the total weight of the organic medium, and the weight percents of the conductive carbon black powder and the organic medium being based on the total weight of the composition. [Claim 6] The article according to claim 5, wherein the ratio of the weight of the polyurethane resin to the weight of the conductive carbon black powder is in the range of 1.50 - 1.75. [Claim 7] The article according to claim 5, wherein the thermoplastic polyurethane resin is selected from the group consisting of polyester - based polymers, urethane homopolymers, and predominantly linear hydroxyl polyurethanes. [Claim 8] The article according to claim 7, wherein the thermoplastic polyurethane resin is predominantly linear hydroxyl polyurethane. [Claim 9] The article according to any one of claims 5 - 8, wherein the article is a wearable garment. [Claim 10] An article containing a stretchable heater having a polymer thick film carbon black resistive element, wherein the ratio of the weight of the polyurethane resin to the weight of the carbon black is in the range of 1.50 - 1.75. [Claim 11] The article according to claim 10, wherein the thermoplastic polyurethane resin is predominantly linear hydroxyl polyurethane. [Claim 12] The article according to claim 10 or 11, wherein the article is a wearable garment.

Claims

1. A stretchable heater having a resistive element formed from a polymer thick film carbon black composition contained in an article, wherein the polymer thick film carbon black composition comprises (a) 6 to 12.60 wt% of conductive carbon black powder, and (b) 10 to 30 wt% of a thermoplastic polyurethane resin dissolved in an organic solvent, in an amount of 87 .40 to 94 wt% of an organic medium, wherein the thermoplastic polyurethane has a percent elongation of at least 200 %, and an organic medium, the weight percentage of the thermoplastic polyurethane resin is based on the total weight of the organic medium, and the weight percentages of the conductive carbon black powder and the organic medium are based on the total weight of the composition, the ratio of the weight of the polyurethane resin to the weight of the conductive carbon black powder is in the range of 1.50 to 1.75, the article is a wearable garment, the article.

2. The article according to claim 1, wherein the thermoplastic polyurethane resin is selected from the group consisting of polyester-based polymers, urethane homopolymers, and linear hydroxyl polyurethanes.

3. The article according to claim 2, wherein the thermoplastic polyurethane resin is linear hydroxyl polyurethane. ​

Images