Patent Publication Number: US-2021172089-A1

Title: Method for producing thread bundle derived from bagworm silk threads spun on the surface of a base material

Description:
TECHNICAL FIELD 
     The present invention relates to a method for producing a thread bundle consisting of foothold silk thread obtained by allowing a bagworm to spin the foothold silk thread onto the surface of a base material. 
     BACKGROUND ART 
     The thread consisting of an insect cocoon or a hair of mammal has been used as an animal fiber for a clothes and the like since long time ago. Especially, silk thread from a silk moth ( Bombyx mori ) larva, namely a silkworm, which is herein often referred to as “silkworm silk thread”, has excellent properties for absorption and desorption of moisture, moisture retention, and heat retention, and also has a unique gloss and a smooth texture. Therefore, the silkworm silk thread is valuable and expensive natural material even today. 
     However, there exist animal fibers in nature having properties comparable or superior to those of silkworm silk thread. Recently, for utilizing an animal fiber having such excellent properties as novel natural material, exploration thereof and research and development thereon are ongoing. 
     A thread from a spider (herein often referred to as “spider thread”) is one material of interest. A spider thread has flexibility and elasticity and has an elastic force up to 5 to 6 times greater than that of polystyrene, and is thus expected to be used as a medical material for surgical suture, for example, and as a special material for emergency ropes, protective clothes, or the like (Non-Patent Literatures 1 and 2). However, mass-production of spider threads is not feasible because mass rearing of spiders and collecting a large amount of thread from spiders are difficult, which also results in a problem of high production cost. An attempt to solve this problem is ongoing by using gene recombination technology to produce a spider thread in a host such as a silkworm or  Escherichia coli  (Patent Literature 1 and Non-Patent Literature 2). However, a silkworm or  Escherichia coli  for spider thread production is a recombinant and is thus allowed to be reared or cultured only in facilities with predetermined equipment, which poses a problem of large maintenance or management burden. Additionally, a liquid spider thread protein expressed in  Escherichia coli  needs to be converted to a fiber, which also causes a problem in that the number of processes increases accordingly. Furthermore, another problem is that the current spider thread spun by a recombinant silkworm is merely comprised in silkworm silk thread at several percentages and cannot be obtained as 100% spider thread which allows 100% of the properties of spider thread to be utilized. 
     There exists an insect called a bagworm (alias “basket worm”). The larvae of moth belonging to the family Psychidae in the order Lepidoptera is collectively referred to as a bagworm and is known to spend the whole larval stages living with a spindle-shaped or cylinder-shaped nest made of pieces of leaves and twigs assembled by thread, as shown in  FIG. 1A , during which the larva usually hide itself inside the nest and move with the nest even for eating. 
     The silk thread spun by the bagworm (herein often referred to as “bagworm silk thread”) has recently been attracting attention as a new animal-fibrous natural material having more excellent properties than the silkworm silk thread and the spider thread. For example, the bagworm silk thread from the bagworm  Eumeta minuscula  has an elastic modulus up to 3.5 times of that of the silkworm silk thread and up to 2.5 times of that of the  Nephila clavata  spider thread, and a very high strength (Non-Patent Literatures 1 and 2). Additionally, the bagworm silk thread not only have a gloss and a shiny appearance comparable or superior to those of the silkworm silk thread but also allow production of much fine, thin and light fabric with a smooth texture compared to the silkworm silk thread because monofiber of the bagworm silk thread has a cross-sectional area only about one-seventh of that of the silkworm silk thread. 
     The bagworm is more advantageous than the silkworm and the spider also in terms of rearing. The bagworm is phytophagous, as is the silkworm. Thus, differently from the spider, which is carnivorous, the bagworm food is easy to procure and can be supplied stably. Additionally, the bagworm is phytophagous similarly to but more advantageously than the silkworm. For example, since the silkworm feeds on only raw leaves of mulberry (species belonging to the genus  Morus , comprising, for example,  M. bombycis, M. alba , and  M. Ihou ) in principle, the region for rearing and season for rearing depend on the supply area of mulberry leaves and the season of mulberry leaf development. In contrast, the bagworm is euryphagous, the specificity for food leaves is low, and many species of the bagworm can feed on leaves of trees of various species. Accordingly, food leaves for the bagworm are easily available, and the bagworm can be raised in any region. Also, the bagworm of some species can feed on leaves of evergreen trees. Thus, differently from mulberries, which are deciduous trees, it is possible to supply food leaves all year round. Moreover, the bagworm is smaller in size than the silkworm and requires a rearing space equal to or less than that required for rearing the silkworm, which makes mass rearing easy. Thus, the cost for rearing can be reduced. 
     Also, the bagworm is superior to the silkworm in terms of productivity. For example, the silkworm spins a large amount of thread only during cocooning and all larvae perform cocooning in the same period. Thus, thread collection periods overlap and labor periods concentrate thereon. However, the bagworms repeatedly spin silk thread for nest building or migrating throughout larval stages. Thus, labor periods can be dispersed by artificially adjusting the thread collection periods. 
     As described above, the bagworm silk thread has properties superior to those of the silkworm silk thread and the spider thread, and also has many advantages for their production, and thus, is expected as a very promising novel natural material. 
     However, the bagworm silk thread has several problems in the practical application thereof. One of them is a problem associated with the characteristics of the bagworm nest. Contaminants, such as pieces of leaves and twigs, are inevitably attached on the surface of the bagworm nest. This is due to the habit of the bagworm incorporating small pieces of twigs and leaves into the nests from the surroundings for camouflage in the process of nest production and expansion. These contaminants need to be completely removed for commercialization of the bagworm silk thread. In conventional method, these contaminants are manually removed from the built nest, or are detached from the nest after the nest is immersed in warm water for a long time to be softened. However, the work of removing these contaminants requires enormous labor. Additionally, complete removal of the contaminants is not possible with existing technologies, resulting in a problem in that only low quality final products can be obtained, due to contamination with a small amount of small pieces of leaves and the like, as well as light-brown staining of the bagworm silk thread with pigments from the contaminants and so on. Decolorization treatment can be performed using a base or an acid to remove the pigments, but can result in a marked decrease in quality such as an impaired strength of the bagworm silk thread. 
     The bagworm silk thread comprises a silk thread called a foothold silk thread, as well as a nest silk thread constituting the nest. As shown in  FIG. 1B , this foothold silk thread is a silk thread spun to be used as a scaffold for preventing the bagworm from falling when the bagworm migrates. The results of the present inventors&#39; studies have revealed that this foothold silk thread is tougher and has excellent mechanical properties than the nest silk thread. Additionally, the foothold silk thread has no contaminant such as pieces of leaves and twigs, differently from the nest silk thread. Accordingly, if the foothold thread can be collected to be utilized, it can serve as a practical bagworm silk thread. 
     However, such a method still has a problem. First, foothold thread is usually spun in the intended direction and in a zigzag pattern, as shown in  FIG. 2A . The bagworm silk thread is spun in the form of a mixture of a fiber component and a paste-like protein covering the surface thereof, and in the case of the foothold silk thread, the foothold silk thread is fixed to the surface of a base material by the paste-like protein (as shown by the arrowheads in the larger circle in  FIG. 2A ) at the turnaround points in the zigzag pattern. This fixation is very strong, and thus, a strong tension is necessary to mechanically peel the foothold silk thread from the base material. In many cases, such an operation also causes the foothold silk thread to be broken around the fixed portion and to be fragmented. Furthermore, the migration of a bagworm is generally difficult to control, and it is possible that a bagworm migrates among the same place back and forth for number of times. As a result, the silk threads spun in a zigzag pattern overlap and entwine one another in the form of a complicated entanglement as shown in  FIG. 2B  that it is even more difficult to collect the silk thread from the base material without damaging the thread. For this reason, foothold silk thread spun on a base material has hitherto never been utilized effectively as a natural fiber material. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: WO2012/165477 
       
    
     Non-Patent Literature 
     
         
         Non-Patent Literature 1: Shigeyosi Ohsaki, 2002, Sen&#39;i Gakkaishi (Sen&#39;i To Kogyo), 58: 74-78. 
         Non-Patent Literature 2: Kuwana Y, et al., 2014, PLoS One, DOI: 10.1371/journal.pone.0105325 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     A bagworm foothold silk thread spun on a base material is conventionally difficult to be collected and cannot be utilized. A purpose of the present invention is to develop and provide a method in which such a bagworm foothold silk thread can be peeled from a base material with a weak force without being damaged and can be collected as a thread bundle so as to be utilized. 
     Solution to Problem 
     To solve the above-mentioned problems, the present inventors have vigorously made studies, and as a result, have succeeded in enabling a bagworm silk thread spun on a base material to be peeled in the form of a thread bundle from the base material without being damaged, by such a bagworm silk thread is sprayed or coated with a wetting liquid such as ethanol, an aqueous solution, or an organic solvent and peeled with a force of only 15% or less, compared with a negative control with such a wetting liquid not being used. The present invention provides the followings based on the method described above. 
     (1) A method for producing a thread bundle of a bagworm silk thread(s), comprising: wetting liquid applying process of applying a wetting liquid to the bagworm silk thread(s) spun on the surface of a base material; and 
     separation process of separating the bagworm silk thread(s) from the base material, 
     wherein the wetting liquid presents a liquid form at least in the range of 20° C. or more and less than 30° C. under the atmospheric pressure, and is a pure substance or a mixture that does not damage, denature, or dissolve a fibroin protein which is a fiber component of the bagworm silk thread(s). 
     (2) The method according to (1), comprising a spinning process of placing a bagworm on the surface of the base material before the wetting liquid applying process and allowing the bagworm to spin the thread. 
     (3) The method according to (2), further comprising a bagworm collection process of collecting the bagworm together with a nest after the spinning process and before the wetting liquid applying process. 
     (4) The method according to any one of (1) to (3), comprising a washing process of washing the separated bagworm silk thread(s). 
     (5) The method according to any one of (1) to (4), comprising a degumming process of degumming the separated bagworm silk thread(s). 
     (6) The method according to any one of (1) to (5), wherein the wetting liquid is a pure substance or a mixture that has a melting point of less than 20° C. and a boiling point of 30° C. or more and 300° C. or less. 
     (7) The method according to any one of (1) to (6), wherein the wetting liquid is an aqueous solution or an organic solvent. 
     (8) A method for collecting a bagworm silk thread(s) spun on the surface of a base material, comprising: 
     wetting liquid applying process of applying a wetting liquid to the bagworm silk thread(s) spun on the surface of the base material; and 
     separation process of separating the bagworm silk thread(s) from the base material, 
     wherein the wetting liquid presents a liquid form at least in the range of 20° C. or more and less than 30° C. under the atmospheric pressure, and is a pure substance or a mixture that does not damage, denature, or dissolve a fibroin protein which is a fiber component of the bagworm silk thread(s). 
     (9) The method according to (8), wherein the wetting liquid is an aqueous solution or an organic solvent. 
     (10) A bagworm silk thread(s) obtainable by using the method for producing a thread bundle according to any one of (1) to (7) or the method for collecting a bagworm silk thread(s) according to (8) or (9). 
     (11) An unwoven fabric formed of a bagworm silk thread(s) obtainable by using the method for producing a thread bundle according to any one of (1) to (7). 
     The present specification encompasses the contents disclosed in the specification and/or drawings of Japanese Patent Application No. 2018-158762, on which the priority of the present application is based. 
     Advantageous Effects of Invention 
     The method for producing a thread bundle of a bagworm silk thread according to the present invention makes it possible that a bagworm foothold thread spun on the surface of a base material, which was conventionally difficult to be collected, is collected with a weak force without being fragmented. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  shows the appearance of a nest of a bagworm of  Eumeta japonica  ( Eumeta japonica  bagworm).  FIG. 1B  shows the spinning behavior of a  Eumeta japonica  bagworm in migration. This shows how the bagworm moves while spinning a foothold silk thread (as shown by the arrowhead) and hooks its claws onto the spun bagworm silk thread (foothold silk thread) (as shown by the thin arrows). 
         FIG. 2A  is a schematic diagram showing the spun state of the bagworm silk thread (foothold silk thread) spun by a bagworm migrating on the surface of a base material. As shown here, the bagworm foothold silk thread presents a ladder-like zigzag pattern. In the figure, the black arrows indicate the direction in which the bagworm migrates spinning the thread. Additionally, the view in the larger circle is an enlarged view of that in the smaller circle, and the arrowheads in the larger circle indicate a paste-like protein. The foothold silk thread is fixed on the base material at the turnaround points of the zigzag portions corresponding to the steps of the ladder.  FIG. 2B  shows the state of the bagworm silk thread, which is a thread spun on a plastic plate by the  Eumeta japonica  bagworm. This shows how the bagworm silk threads spun in a zigzag pattern are entangled complicatedly. 
         FIG. 3  shows a process flow diagram of a method for producing a thread bundle of a bagworm silk thread according to the present invention. 
         FIG. 4  is the graphs showing the results of a peeling tension evaluation test performed in Example 1. In the graphs, (A), (B), and (C) show the test results of a negative control with no wetting liquid applied thereto, a sample with water applied thereto, and a sample with ethanol (99.5%) applied thereto respectively. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     1. Method for Producing Thread Bundle of Bagworm Silk Thread 
     1-1. Concept 
     The first aspect of the present invention is a method for producing a thread bundle of a bagworm silk thread. The production method according to the present invention is a method in which a thread bundle consisting of an intended bagworm silk thread is obtained by applying a wetting liquid to a bagworm silk thread spun on the surface of a base material and then separating the bagworm silk thread from the base material. The method according to the present invention makes it possible that a foothold silk thread, which has excellent properties but is difficult to collect without being physically damaged and thus, has never been utilized, is efficiently collected without being damaged. 
     1-2. Definition of Terms 
     The following terms frequently used herein are defined as described below. 
     The term “bagworm” collectively refers to a moth larva belonging to the family Psychidae in the order Lepidoptera, as described above. Moths belonging to the family Psychidae are distributed worldwide and the larva (bagworm) of any species of the moth spends the whole larval stages living in a nest covered with natural materials, such as pieces of leaves and twigs, which are assembled by silk threads spun by the larva itself. Additionally, any species of bagworm has the habit of spinning a foothold silk thread which functions as a scaffold in the intended direction of migration to prevent the bagworm from falling when the bagworm migrates. Accordingly, the species, instar, and gender of bagworms used herein are not limited, as long as that the bagworm is a larva of a moth species belonging to the family Psychidae and that the species has the habit as described above. For example, the family Psychidae comprises the genera  Acanthopsyche, Anatolopsyche, Bacotia, Bambalina, Canephora, Chalioides, Dahlica, Diplodoma, Eumeta, Eumasia, Kozhantshikovia, Mahasena, Nipponopsyche, Paranarychia, Proutia, Psyche, Pteroma, Siederia, Striglocyrbasia, Taleporia, Theriodopteryx, Trigonodoma , etc., and the bagworm used herein may be a species belonging to any genus. Additionally, the instar of the larva may be any instar between the first instar and the last instar. However, a larger bagworm is preferable to obtain a large mass of the bagworm silk thread. For example, among larvae of the same species, a larva in the last instar is more preferable, and a female larva is more preferable than a male larva because the female grows larger than the male. Furthermore, among the family Psychidae, a large species is more preferable. For example,  Eumeta japonica  and  Eumeta minuscula , which are large species, are suitable as species used in the present invention. 
     A bagworm to be used in a method for producing according to the present invention is preferably, but is not limited to, a bagworm keeping a nest. “Keeping a nest” refers to the state in which the bagworm has a nest therewith. As described above, the bagworm lives with its own nest, and exposes only part thereof out of the nest even during eating and moving, as shown in  FIG. 1B , and in principle, the bagworm never exposes its whole body out of the nest throughout the whole larval stage. When the bagworm is artificially separated from the nest and wholly exposed to the outside, the bagworm thus made naked generally minimizes its movement and promptly starts rebuilding a nest for self-protection and to keep itself warm. Accordingly, the reason why a bagworm keeping a nest is suitable is not to make prioritize the behavior of spinning a nest silk thread but rather to make actively spin a foothold silk thread, which is a purpose of the present invention. 
     The term “silk thread” as used herein refers to a thread derived from an insect and made of proteins, which is spun by the insect in a larval or adult stage for the purpose of nest building, migrating, anchoring, cocooning, prey capture, and the like. When the term “silk thread” is simply recited herein, it refers to a general silk thread from an unspecified insect. In case of indicating a silk thread from a particular insect species, the name of the organism is placed before the term “silk thread,” as a “silkworm silk thread” or a “bagworm silk thread.” 
     The term “bagworm silk thread” as used herein refers to a silk thread spun by a bagworm. The “bagworm silk thread” herein encompasses a monofiber, spun fiber, and fiber assembly. The term “monofiber”, which is also referred to as monofilament, is the smallest filament unit constituting fiber components. The monofiber contains a fibroin protein as a main component. The bagworm silk thread and the silkworm silk thread in natural states are spun in the form of bifilament in which two monofibers are joined together by a sericin protein, a gummy material. This bifilament is referred to as a “spun fiber”. The bagworm nest and the silkworm cocoon are constituted with spun fiber(s). Also, a fiber bundle formed by assembling plural spun fibers is referred to as a “fiber assembly (or multifilament)”. In general, this fiber assembly corresponds to a raw silk thread. Furthermore, silk thread obtained by treatment of raw silk thread with an enzyme and a basic chemical such as soap, lye, sodium carbonate, and urea to remove sericin protein is called degummed silk thread. 
     The bagworm silk thread includes two kinds of the silk thread: foothold silk thread and nest silk thread. As described above, the “foothold silk thread” refers to a silk thread spun by a bagworm for the purpose of its migration, which has a function as a foothold (scaffold) for preventing it from falling from a branch, a leaf, or the like. On the other hand, the “nest silk thread” refers to a bagworm silk thread spun for forming a nest, which is spun to assemble pieces of leaves and twigs or to make an internal wall of a nest so that its accommodation space becomes a comfortable environment. A foothold silk thread is intended as a bagworm silk thread in the present invention in view of the purpose. Thus, the expression “bagworm silk thread” herein refers to a foothold silk thread unless otherwise specified. 
     As used herein, a “thread bundle” refers to a silk thread aggregate consisting of a bagworm foothold silk thread(s) alone. A bagworm nest is an aggregate of a bagworm silk thread(s), but usually is a mixture of contaminants of small pieces of twigs, leaves, and the like, and is consisting of a nest silk thread(s). Therefore, it is not the thread bundle according to the present invention. The thread bundle herein is, but is not limited, an aggregate of a foothold silk thread(s) with no contaminant intruded produced through some artificial process. Examples of such thread bundles comprise a thread bundle which a bagworm placed on a base material is allowed to spin. Without limitation, the state of the thread bundle may be, for example, a sheet-like state such as an unwoven fabric in which one or more bagworm silk threads are entwined complicatedly, or may be an assembled state in which one or more bagworm silk threads are reelably held together. 
     A “wetting liquid” refers to a pure substance or a mixture which presents a liquid form at least in the range of 20° C. or more and less than 30° C. under the atmospheric pressure, and does not damage, denature, or dissolve a fibroin protein which is a fiber component of the bagworm silk thread. Accordingly, a pure substance which is in a state other than a liquid state in the above-mentioned temperature range, and a substance in a liquid state which denatures a protein including a strongly acid solvent, a strongly basic solvent, a mixture such as a solution containing protease, or the like are not suitable as a wetting liquid in the present invention. 
     A “pure substance” refers to a chemical substance having certain properties, and examples thereof comprise a simple substance consisting of a single element, and a compound consisting of a plurality of elements. A pure substance in the present invention usually corresponds, but is not limited, to a compound. 
     A “mixture” refers to a substance formed by mixing a plurality of pure substances. A mixture corresponds to, for example, a solution. 
     A wetting liquid may be consisting of any pure substance or a mixture as long as the wetting liquid satisfies the above-mentioned requirements. Examples thereof comprise, but are not limited to, compounds having a melting point (Melting Point: MP) of less than 20° C. and a boiling point (Boiling Point: BP) of 30° C. or more and 300° C. or less under normal temperature (25° C.) and normal pressure (100 kPa). A compound having such properties often has the properties as a “solvent” which can dissolve another compound as a solute. 
     Specific of a compound for wetting liquids are as mentioned below, but a wetting liquid herein is not limited to the examples below. 
     A wetting liquid may be a liquid consisting of a polar molecule (polar solvent). Examples thereof comprise: protic polar solvents such as water (MP: 0° C.; BP: 100° C.), methanol (MP: −96° C.; BP: 64.7° C.), ethanol (MP: −117° C.; BP: 78.3° C.), 1-propanol (MP: −127° C.; BP: 97.2° C.), 1-butanol (MP: −90° C.; BP: 118° C.), glycerin (MP: 17.8° C.; BP: 290° C.), formic acid (MP: 8.3° C.; BP: 100.8° C.), acetic acid (MP: 15° C.; BP: 118° C.), and butyric acid (MP: −7.9° C.; BP: 164° C.); and aprotic polar solvents such as DMSO (MP: 18.5° C.; BP: 189° C.), acetonitrile (MP: −48° C.; BP: 81.6° C.), acetone (MP: −94° C.; BP: 56° C.), dimethylformamide (MP: −61° C.; BP: 153° C.), dimethylsulfoxide (MP: 19° C.; BP: 189° C.), tetrahydrofuran (MP: −108° C.; BP: 66° C.), and 1,1,1,3,3,3-hexafluoro-2-propanol (MP:−3.3° C.; BP:58.2° C.). Other examples comprise an ionic liquid. Here, the values in the parenthesis following each compound indicate a melting point (MP) and a boiling point (BP) under normal temperature and normal pressure (the same applies hereinafter). 
     A wetting liquid may also be a nonpolar liquid consisting of a nonpolar molecule (nonpolar liquid: nonpolar solvent). Examples thereof comprise an oil and many organic solvents (low polarity organic solvents) excluding some. An oil is a compound in a liquid state under normal temperature and normal pressure, and examples thereof comprise a fatty acid represented by the general formula: R—COOH (wherein R is a C 4-8  alkyl group). Specific examples of nonpolar liquids comprise: fatty acids such as valeric acid (valerianic acid: MP: −34.5° C.; BP: 186° C.), caproic acid (hexanoic acid: MP: −3° C.; BP: 205° C.), enanthic acid (heptylic acid, heptanoic acid: MP: −7.5° C.; BP: 223° C.), caprylic acid (octanoic acid: MP: 16.7° C.; BP: 239.7° C.), pelargonic acid (nonanoic acid: MP: 11° C.; BP: 247° C.), palmitoleic acid (hexadecenoic acid: MP: −0.1° C.; BP: 230° C.), linoleic acid (octadecadienoic acid: MP: −5° C.; BP: 229° C.), linolenic acid (octadecatrienoic acid: MP: −11° C.; BP: 278° C.), and arachidonic acid (eicosatetraenoic acid: MP: −49° C.; BP: 169° C.); hexane (MP: −95.3° C.; BP: 68.7° C.); toluene (MP: −95° C.; BP: 110.6° C.); chloroform (MP: −63.5° C.; BP: 61° C.); dichloromethane (MP: −95° C.; BP: 39.8° C.); 1,2-dichloroethane (MP: −35.7° C.; BP: 83.4° C.); trichloroethylene (MP: −86.4° C.; BP: 87° C.); acetone (MP: −94° C.; BP: 56° C.); diethyl ether (MP: −116° C.; BP: 34.6° C.); xylene (MP: −25° C.; BP: 137° C.); carbon tetrachloride (MP: −23° C.; BP: 76.7° C.); methyl acetate (MP: −98° C.; BP: 57° C.); and ethyl acetate (MP: −84° C.; BP: 77° C.). 
     Additionally, in cases where a wetting liquid herein is a mixture, specific examples thereof comprise a solution. Examples of such solutions comprise, but are not limited to: a solution consisting of a polar liquid or nonpolar liquid in which one or more different solutes are dissolved; a colloidal solution or sol in which a colloid is dispersed in a liquid which is a dispersion medium; two or more different liquids (for example, a liquid mixture or the like consisting of different polar liquids); or a combination thereof. Examples of polar solutions comprise: an aqueous solution in which a solute is dissolved in water; and a solution mixture of solvents such as of ethanol and water. Solute in the aqueous solution is not limited. Examples thereof comprise, but are not limited to, a salt, a sugar, and a surfactant. A preferable salt is, but is not limited to, a salt having high solubility. Examples thereof comprise sodium chloride salt, potassium chloride salt, sodium carbonate salt, and sodium hydrogencarbonate salt. The solute concentration of the solution is not particularly limited. For example, it may be equal to solubility. Solute concentration for the solution mixture is also not limited in particular. For example, a liquid mixture of ethanol and water may be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99.5% ethanol. 
     As mentioned above, a pure substance or mixture constituting a wetting liquid is not limited to any type. Considering the easiness of handling (including waste liquid disposal), safety, and purchasing cost, water (including warm water and hot water), an aqueous solution, ethanol, and a liquid mixture thereof are preferable; and an aqueous solution and ethanol are particularly preferable. 
     As used herein, a “base material” refers to a base for collecting a bagworm silk thread. A bagworm placed on the surface of this base material is allowed to migrate, thus spinning a bagworm silk thread on the surface. 
     A material constituting a base material is not limited as long as it can fix a bagworm silk thread on its surface with a paste-like protein. Examples thereof comprise glass (comprising enamel), metal, a synthetic resin (comprising a thermoplastic resin, a thermosetting resin, and a synthetic rubber), ceramic, paper, a piece of plant (comprising, for example, a piece of wood), or a piece of animal (comprising, for example, a piece of bone, seashell, and sponge). However, a base material which is dissolved by a wetting liquid used or causes a reaction such as an oxidation-reduction reaction with a wetting liquid does not fit with the spirit of the present invention in which a bagworm silk thread spun on a base material is collected. Accordingly, a material constituting a base material is desirably a material insoluble in and nonreactive with a wetting liquid used in the present invention. Being “insoluble in a wetting liquid” refers to the property of not being dissolved in a wetting liquid used in the present invention. Additionally, being “nonreactive with a wetting liquid” refers to the property of causing no chemical reaction with a wetting liquid used in the present invention. Accordingly, the material of a base material in the present invention can be vary depending on the type of the wetting liquid used. For example, with a wetting liquid such as water or an aqueous solution, a synthetic resin can be used, such as polyethylene, polypropylene, polystyrene, vinyl acetate, cellulose acetate, acrylic resin, or polycarbonate, but with a wetting liquid such as a low polarity organic solvent, those having solubility therein cannot be used, such as polystyrene, vinyl acetate, cellulose acetate, acrylic resin, polycarbonate, or the like. Glass, ceramic, polypropylene, or the like, which is readily available and relatively inexpensive and has low reactivity, is suitable as the material of a base material. 
     The thickness of a base material used in this process is not limited. The thickness can suitably be determined considering the production cost and rigidity of the base material, the easiness of processing in the subsequent processes, and the like. For example, it is preferable that an average thickness of the base material is 0.5 mm or more, 0.6 mm or more, 0.7 mm or more, 0.8 mm or more, 0.9 mm or more, 1.0 mm or more, 1.2 mm or more, or 1.5 mm or more, and in addition, may be 3.0 mm or less, 2.8 mm or less, 2.5 mm or less, 2.2 mm or less, or 2.0 mm or less. In cases where the base material is consisting of a thin film having an average thickness of less than 0.5 mm, 0.4 mm, 0.3 mm, 0.2 mm, or 0.5 mm, the base material itself does not have enough rigidity to retain a given shape, and thus, the base material may be placed on a suitable support. 
     As used herein, a “support” refers to a member on the surface of which a base material is placed so that rigidity and/or a shape is given to the base material. The support is an optional constituent to be used in the method according to the present invention, and can be used if necessary. The material of the support is not particularly limited as long as it has enough rigidity to retain a given shape. Examples thereof comprise glass, metal, plastic, synthetic rubber or ceramic, or paper, a piece of plant or a piece of animal. 
     The shape and size of a base material used in this process are not limited. For example, the shape may be a sheet-like or plate-like planar shape, or may be a three-dimensional shape, and is preferably a planar shape, considering the easiness of separating the base material from the bagworm silk thread. Additionally, the surface condition of base material is preferably, but is not limited to, smooth surface from which bagworm silk thread can be easily separated rather than that which is rough surface to which the thread can be strongly fixed. The size of the base material can be that which is selected as necessary, and in view of the fact that the foothold silk thread is a bagworm silk thread spun during migration, the lower limit is preferably a size equal to or greater than the size of the bagworm and the body length of the bagworm. For example, the long axis or the major axis can be 1 cm or more, 2 cm or more, 3 cm or more, 4 cm or more, or 5 cm or more. Additionally, the size of the base material is not limited to any upper limit, but in cases where the long axis or the major axis is 10 cm or more, 15 cm or more, 20 cm or more, 25 cm or more, or 30 cm or more, it is more preferable to allow a plurality of bagworms to spin threads. 
     1-3. Method 
     The process flow diagram of this aspect is shown in  FIG. 3 . As shown in this Figure, the method according to the present aspect comprises: a wetting liquid applying process (S 0103 ) and a separation process (S 0104 ) as essential processes; and a spinning process (S 0101 ), a bagworm collection process (S 0102 ), a washing process (S 0105 ), and a degumming process (S 0106 ) as optional processes. Each of the processes will be described below in flow order. 
     1-3-1. Spinning Process 
     The “spinning process” (S 0101 ) is a process of placing a bagworm on the surface of a base material or placing a bagworm together with a base material and allowing the bagworm to spin a thread. This process is an optional process in the present invention. This process is performed before the wetting liquid applying process mentioned below. 
     “Placing a bagworm on the surface of a base material” refers to positioning both of them such that the bagworm can touch the surface of the base material. For example, the bagworm may be directly placed on the arranged base material, or be placed so that the bagworm can migrate to reach the base material. Specific examples of the latter option comprise a case in which a bagworm is placed on the bottom of a lidless wide-mouthed plastic container, and then, a base material is used as a lid for the container. The bagworm prefers a higher position and accordingly migrates along the inner sidewall of the wide-mouthed plastic container to reach the undersurface of the base material corresponding to the ceiling of the container, followed by spinning a foothold silk thread while migrating on the base material. The arrangement of the base material on which a bagworm silk thread is spun is not particularly limited. As mentioned above, the base material may be arranged on the ceiling of a container, or may be arranged on the wall thereof. It is convenient to arrange the base material on a portion other than the bottom as such because feces defecated by a bagworm fall on the bottom and the surface being spun on is not contaminated by the feces. 
     In this regard, the species and the number of the bagworm to be placed are not limited. For example, one bagworm or a plurality of bagworms may be placed at one time per base material onto which the bagworm silk thread is to be spun. Additionally, the species or age of the bagworm to be placed are not limited. In cases where a plurality of bagworms are placed, the individuals may be of the same species and the same age, or may be a mixture of bagworms of different species or different ages. 
     The period of time for this process is not particularly limited. The process period depends on species and age of the bagworm, and the number of individuals to be used, but in any case, the process may usually be continued until a necessary amount of thread is spun on a base material. For example, when one last instar bagworm of  Eumeta japonica  is used to spin a thread onto a circular base material having a diameter of 9 cm, the bagworm is allowed to spin for 1 day or more, 2 days or more, 3 days or more, 4 days or more, 5 days or more, 6 days or more, or 7 days or more. As described above, the bagworm foothold silk thread is spun while the bagworm migrates, and thus, the amount of the obtained silk thread is in proportion to the migration distance of the bagworm in principle. Therefore, by using a plurality of bagworms to spin, time of the spinning process is shorter than that by using a single bagworm to spin. In addition, the bagworm is not allowed to eat food while spinning, and thus, the bagworm often stops spinning in this process. In such a case, the bagworm may be exchanged for a new one to continuously maintain the spinning process. 
     It is recommended that the temperature and humidity in this process be constant or with little change so that the amount of thread spun by a bagworm per unit time can be larger. It is preferable that the temperature is around 20° C., for example, ranges from 15° C. to 25° C., or from 18° C. to 22° C., and that the humidity is around 50%, for example, ranges from 40% to 65%, or from 45% to 60%. There is no limit about light and dark period during this process, and it may have only a light period, or may have cyclical light and dark periods. For example, the cycle may be such that, in 24 hours, the light period is 6 hours to 18 hours, 7 hours to 17 hours, 8 hours to 16 hours, 9 hours to 15 hours, 10 hours to 14 hours, 11 hours to 13 hours, or 12 hours, and the rest is the dark period. 
     1-3-2. Bagworm Collection Process 
     The “bagworm collection process” (S 0102 ) is a process of collecting the bagworm used in the spinning process together with the nest, and is an optional process in the present invention. A purpose of this process is to separate the bagworm no longer required from the base material and collect it after the spinning process. 
     After the spinning process, the spun foothold silk thread and the bagworm which has spun the thread coexist on the base material. In principle, however, the bagworm is not needed in the subsequent wetting liquid applying process. In addition, when the liquid to be used is applied to a bagworm in the wetting liquid applying process, it is possible that the bagworm silk thread is stained with an undesirable color by the bodily fluid of the bagworm and the extract from dead leaves and the like used for the nest. Thus, this process is an optional process, but is preferably performed after the spinning process. 
     The method for collecting a bagworm from the base material is not limited. Any method for separating a bagworm from the base material can be utilized. For example, the bagworm in contact with the base material may be peeled away together with the nest. However, for purposes of the present invention, it is preferred that the damage to the bagworm silk thread is as low as possible. For example, the bagworm may be induced to spontaneously leave the base material. Specific examples of such a method comprise a method in which, utilizing the feature of the bagworm, which migrates to a higher place, the container is turned upside down so that the position of the base material can be changed from the ceiling to the bottom. After the bagworm migrates to the inner sidewall of the container, the base material can be collected. Another method is heating of the base material. The bagworm spontaneously leaves the base material to escape from high temperature, and thus, the base material can be collected after the migration. The heating temperature may be ordinary temperature or more and the temperature without the damage of the bagworm silk thread and melting the base material. For example, the temperature may be 30° C. or more, 33° C. or more, 35° C. or more, 38° C. or more, 40° C. or more, 42° C. or more, 45° C. or more, 48° C. or more, or 50° C. or more, and 80° C. or less, 75° C. or less, 70° C. or less, 65° C. or less, 60° C. or less, or 55° C. or less. 
     Incidentally, the collected bagworm can be fed and then reused in the method for producing according to the present invention. 
     1-3-3. Wetting Liquid Applying Process 
     The “wetting liquid applying process” (S 0103 ) is a process of applying a wetting liquid to a bagworm silk thread spun on the surface of a base material, and is the most important essential process in the present invention. 
     The method for applying wetting liquid is not limited. Any method can be used as long as by which the bagworm silk thread on the surface of a base material is sufficiently wetted with a wetting liquid. For example, the method comprises a method for spraying, splashing, or spreading a wetting liquid onto the surface of a base material having a bagworm silk thread spun thereon, and a method for immersing a base material having a bagworm silk thread spun thereon in a wetting liquid. 
     After the wetting liquid is applied, it is preferably retained for a predetermined time. This is in order to ensure the time for the wetting liquid to sufficiently permeate between the base material and the bagworm silk threads. The length of the “predetermined time” herein is not limited in particular. The time depends on the amount of a wetting liquid to be applied and the applying method, and usually may be from 1 second to 1 hour, from 1 minute to 40 minutes, from 2 minutes to 30 minutes, from 3 minutes to 20 minutes, from 4 minutes to 15 minutes, or from 5 minutes to 10 minutes, after the application. 
     The temperature of a wetting liquid used in this process is not limited in particular as long as the temperature does not damage, denature, or dissolve the bagworm silk thread. The temperature is usually be in the range of room temperature, for example, from 1° C. to 35° C., from 5° C. to 32° C., from 10° C. to 30° C., from 12° C. to 27° C., from 15° C. to 25° C., or from 18° C. to 20° C., when the wetting liquid has a melting point of less than 1° C. and a boiling point of more than 35° C. In general, however, a wetting liquid has higher reactivity at a higher temperature, and thus, it is preferable in this process that the temperature of the wetting liquid is higher. For example, if the wetting liquid is an aqueous solution, the liquid temperature under the atmospheric pressure is preferably 35° C. or more, 38° C. or more, 40° C. or more, 42° C. or more, 45° C. or more, 48° C. or more, 50° C. or more, 52° C. or more, 55° C. or more, 58° C. or more, 60° C. or more, 62° C. or more, 65° C. or more, 68° C. or more, 70° C. or more, 72° C. or more, 75° C. or more, 78° C. or more, 80° C. or more, 82° C. or more, 85° C. or more, 88° C. or more, 90° C. or more, 92° C. or more, 95° C. or more, or 98° C. or more. Incidentally, the wetting liquid can be heated before and/or during this process. 
     1-3-4. Separation Process 
     The “separation process” (S 0104 ) is a process of separating a bagworm silk thread spun on the surface of the base material from a base material after the wetting liquid applying process. It is an essential process in the present invention. The method for separating a bagworm silk thread from the base material is not limited. The wetting liquid applying process decreases the bonding force between the base material and the bagworm silk thread, and thus, both can be separated with a relatively weak tension. For example, the method comprises a method of holding a bagworm silk thread with the end and ripping off or peeling from a base material, a method for jetting air or liquid with high pressure into the bonding surface between a base material and the bagworm silk thread so that the bagworm silk thread can be peeled away, a method for sucking a bagworm silk thread and peeling away from a fixed base material, a method for immersing a base material in liquid and separating both with a liquid pressure or the like from the liquid flow caused by shaking the base material, by stirring the liquid, or the like. If a liquid is used in this process, the liquid is preferably, but is not limited to, the wetting liquid used in the wetting liquid applying process. In particular, water is suitable. This process makes it possible to obtain a bagworm foothold silk thread spun on the surface of a base material, which was difficult to be collected with a conventional method without damaging the thread. 
     1-3-5. Washing Process 
     The “washing process” (S 0105 ) is a process of washing the bagworm silk thread separated in the separation process. This process is an optional process and may be performed if necessary. 
     The wetting liquid used in the wetting liquid applying process remains on the surface of the bagworm silk thread obtained from the separation process. If the wetting liquid used is a solution or a low polarity organic solvent, and is dried and stuck to the surface of a bagworm silk thread, the bagworm silk thread can be deteriorated or discolored over time. Therefore, it is preferable that the wetting liquid used is completely removed by washing in this process. By this process, part of the feces or the like attached to the bagworm silk thread can be removed simultaneously even when they are present. 
     A washing solution used for washing in this process is not limited. If the wetting liquid used is a polar liquid, an aqueous solution, or a colloidal solution, a liquid suitable as a washing solution is water (comprising warm water). If the wetting liquid used is a nonpolar liquid such as a low polarity organic solvent, another highly volatile solvent with high affinity to the low polarity organic solvent is suitable as a washing solution. For example, when toluene or benzene is used in the wetting liquid applying process, other xylene or ethanol can be used as a washing solution. 
     The washing method is not limited as long as the wetting liquid used in the wetting liquid applying process can be removed from the bagworm silk thread. The bagworm silk thread may be sprayed with the washing solution or immersed in the washing solution. 
     The number of washes is not limited. The wash can be performed once or plural times. The term “plural times” as used herein refers to, for example, 2 to 20 times, 2 to 15 times, 2 to 10 times, 2 to 7 times, 2 to 5 times, 2 to 4 times, or 2 to 3 times. In general, the wash is preferably performed plural times. If the wash is performed plural times, the washing solution to be used at each time may be the same or different. Also, the washing methods may be the same or different. After the wash, the thread may be left to be naturally dried, or the washing solution may be separated and removed by centrifugation using a dehydrator or the like. 
     1-3-6. Scouring Process 
     The “degumming process” (S 0106 ) is a process of degumming a thread bundle consisting of a bagworm foothold silk thread produced in this process. This process is an optional process and may be performed if necessary. 
     The term “degumming” refers to removing a sericin-like gummy substance (paste-like protein) from the bagworm silk thread to obtain a fibroin fiber. 
     A method for degumming a bagworm silk thread is not limited in particular as long as a gummy substance can be removed without weakening the strength of the fiber component of the silk thread. For example, any degumming method for a silkworm silk thread can be applied. In a method for degumming a silkworm silk thread, 0.01 mol/L to 0.1 mol/L, 0.03 to 0.08 mol/L, or 0.04 to 0.06 mol/L of sodium carbonate solution is used as a degumming solution, and the solution can be used in the same manner also in the degumming process in the present method. The obtained bagworm silk thread may be boiled in the sodium carbonate solution, a degumming solution, for 1 second to 1 hour, 5 seconds to 30 minutes, 10 seconds to 15 minutes, 20 seconds to 10 minutes, or 30 seconds to 5 minutes. 
     It is convenient to use a degumming solution such as a sodium carbonate solution as a wetting liquid used in the wetting liquid applying process, since the same degumming solution is subsequently used in the degumming process, and a washing process before the degumming process is not necessary. After being treated in this process, the silk thread may be washed in the same manner as in the washing process. 
     After the degumming process, the collected bagworm silk thread may be dried. The drying method is not limited in particular as long as the amount of the wetting liquid, washing solution, or degumming solution remaining on the bagworm silk thread can be reduced without denaturing or deteriorating the foothold silk thread. For example, the method comprises a natural drying method (comprising sun drying) in which the thread is exposed to external air to vaporize the wetting liquid, washing solution, or degumming solution, an air drying method in which a blowing device or the like is used to blow the thread with warm air or cold air; a dehumidification drying method in which a dehumidifying agent is placed together in a hermetically sealed space for a given period of time, a heat drying method in which the wetting liquid, washing solution, or degumming solution is evaporated and dried by heating; a decompression drying method in which evaporation is performed by degasification with a vacuum pump or the like in a container; or combinations thereof. 
     2. Bagworm Silk Thread and Unwoven Fabric Constituted Therewith 
     2-1. Overview 
     The second aspect of the present invention is a foothold silk thread of a bagworm silk thread and an unwoven fabric constituted therewith. A bagworm silk thread and an unwoven fabric according to the present invention are obtained using the method for producing a thread bundle according to the first aspect. 
     2-2. Constitution 
     A thread bundle obtained by the method according to the first aspect is often in the form of an unwoven fabric in which the bagworm silk threads are superposed one on another lengthwise and crosswise on the surface of a base material when the thread bundle is spun on the surface of the base material without any control of the movement of the bagworm. Accordingly, the bagworm silk thread peeled from the surface of a base material in the method for producing a thread bundle according to the first aspect can itself be utilized as an unwoven fabric. Furthermore, the foothold silk thread obtained by the method according to the first aspect can be made into an unwoven fabric by an existing method for producing an unwoven fabric. Without limitation, a spun lace method or a needle-punching method can be utilized as an existing method for producing an unwoven fabric. 
     Alternatively, when the bagworm silk thread is peeled from the surface of a base material with generating a correct end or when the thread is reeled from the correct end pulled off from the state of a peeled unwoven fabric, the thread can be obtained as a long bagworm silk thread. 
     EXAMPLES 
     Example 1 
     (Purpose) 
     A peeling tension evaluation test verifies that the method for producing a thread bundle according to the present invention can easily collect a bagworm silk thread (foothold silk thread) spun on a base material, which was difficult to be collected with a conventional method. 
     (Material) 
     As a bagworm, a last instar larva of  Eumeta japonica  ( Eumeta japonica  bagworm) collected at an orchard in Tsukuba, Ibaraki, Japan was used. Additionally, an acrylic plate, which was approximately 30 cm 2 , was used as a base material. 
     (Method) 
     A sufficient amount of food leaves was fed to a bagworm used in each of the Examples until the day before that spinning process was performed. 
     The bagworm was allowed to spin a thread on the surface of an acrylic plate as a base material by placing the bagworm on the acrylic plate erected vertically and by allowing the bagworm to climb along the wall surface of the acrylic plate. 
     After a bagworm silk thread was sufficiently spun on the surface of the acrylic plate, water (pure water), aqueous solutions of 30%, 50%, and 70% ethanol, and 99.5% ethanol, a few drops each, were dripped on the site for evaluation using a syringe. A negative control was a bagworm silk thread having no wetting liquid applied thereto (a wetting liquid-unapplied sample). 
     Next, the peeling tension evaluation test used in the present Example is described. As shown in  FIG. 2A , the bagworm foothold silk thread presents a ladder-like zigzag pattern. This foothold silk thread is fixed to the surface of a base material at the turnaround points (referred to as “fixed points”) in a zigzag portion (herein referred to as a “zigzag block”) corresponding to the steps of a ladder shown in the broken line ellipse in  FIG. 2A . When the foothold silk thread is being peeled away, the tension exhibits a peak at a fixed point in each zigzag block because the largest force is needed at the fixed point, but once being peeled, the tension is relaxed down to the initial value of zero because the foothold silk thread is not fixed to the base material to the next fixed point. At this next fixed point, a large tension is needed in the same manner when the thread is peeled away, but the tension becomes the initial value immediately after the peeling. When the foothold silk thread is being peeled away, this cycle is repeated between every zigzag block. In the peeling tension evaluation test, one end of a bagworm foothold silk thread spun on the surface of a base material is fixed to a load cell of a tensile tester, and then, the bagworm silk thread is peeled off at a constant speed, with variations in the tension being continuously recorded, thus the process of releasing the adhesion at the fixed points to sequentially unbend the zigzag foothold thread into a linear form can be measured as the relationship between a peeled length (pulled off distance) and a tension. 
     Each wetting liquid was applied to a bagworm silk thread and the sufficient wetting of which was verified, and then, one end of the bagworm silk thread on each acrylic plate was pulled off and fixed to the load cell of the tensile tester. The fixed bagworm silk thread was peeled off at a constant speed (100 μm/sec), with variations in the tension being continuously recorded on the load cell. This measurement was made using a tensile tester (a small tabletop tester, EZ Test, from Shimadzu Corporation). 
     In this Example, the total of peak areas per zigzag block obtained in the peeling test was divided by the peeled length to calculate a peeling energy per unit peeled length. In order to minimize the influence of differences between bagworm individuals used in the spinning process on the adhesive force, the result obtained from when each wetting liquid was used was normalized with the peeling energy of a negative control (wetting liquid unapplied sample), in which a foothold silk thread is spun by the same bagworm individual, and was evaluated and compared in percentage (%) assuming that the peeling energy for the negative control was 100. 
     (Result) 
     The results are shown in  FIG. 4  and Table 1. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 EtOH Concentration 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 H 2 O 
                 30% 
                 50% 
                 70% 
                 99.5% 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Relative value (%) 
                 29 
                 11 
                 7 
                 10 
                 6 
               
               
                   
               
            
           
         
       
     
     In  FIG. 4 , the horizontal axis indicates the peeled length (mm), and the vertical axis indicates the peel tension (N). As shown in  FIG. 4(A) , the negative control required a relatively strong peeling tension of 0.003 to 0.004 N at each fixed point per zigzag block. In contrast, in the case where water was applied, the peeling tension was approximately 0.001 N, showing a decrease to approximately ¼ of that for the negative control, as shown in FIG.  4 (B). Furthermore, when ethanol (99.5%) was applied, it was revealed, as shown in  FIG. 4(C) , that the peeling tension was 0.0001 to 0.0002 N, showing a dramatic decrease to approximately 1/20 to 1/40 of that for the negative control. 
     As shown in Table 1, the peeling energy was decreased to approximately 30% of that for the negative control when water was applied to a base material and a bagworm silk thread. When ethanol (99.5%) was applied, the peeling energy was decreased to 6% of that for the negative control, exhibiting a more marked effect than water. This effect of ethanol was also maintained at various concentrations when an aqueous ethanol solution, a solution mixture of ethanol and water, was used. At any of the concentrations, the effect was verified as higher than that of water. 
     Example 2 
     (Purpose) 
     A peeling tension evaluation test verifies that the method for producing a thread bundle according to the present invention can be used with the other wetting liquid other than water and ethanol. 
     (Method) 
     The basic procedures and basic operation were performed as in Example 1. The wetting liquids used here were: methanol (MeOH) as a polarity monovalent alcohol; 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as a polarity halogen-containing organic solvent; dimethylsulfoxide (DMSO) as a polarity sulfur-containing organic solvent; carbon tetrachloride as a low polarity halogen-containing organic solvent; glycerin as a polarity trivalent alcohol; furthermore, an aqueous solution of sodium chloride having a concentration of 0.05 M (NaCl aq); and an aqueous solution of 0.05 M sodium carbonate (Na 2 CO 3  aq) widely used in a degumming process for a silkworm silk thread. 
     (Result) 
     The results are shown Table 2. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                   
                 Carbon 
                   
                 0.05M 
                 0.05M 
               
               
                   
                 MeOH 
                 HFIP 
                 DMSO 
                 Tetrachloride 
                 Glycerin 
                 Na 2 CO 3   
                 NaCl 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Relative value (%) 
                 11 
                 13 
                 13 
                 6 
                 14 
                 6 
                 11 
               
               
                   
               
            
           
         
       
     
     As shown in Table 2, with any wetting liquid, the peeling energy was decreased to 15% or less of that for the negative control. Additionally, a high effect was verified with any of the liquids, showing that half or less of the peeling energy for the water-applied sample was sufficient. 
     All publications, patents, and patent applications cited herein should be incorporated herein by reference in their entirety.