JP7703363B2 - Artificial leather and its manufacturing method - Google Patents

Description

The present invention relates to artificial leather and its manufacturing method.

Artificial leather is suitably used in the fields of clothing, shoes, bags, interior decoration, furniture, seat coverings and interior materials for automobiles, railway vehicles, aircraft, ships, etc., and badge base materials, etc. In these fields, good appearance quality and feel are required, as well as flame retardancy and resistance to physical loads such as abrasion.
The mainstream of artificial leather materials is a nonwoven fabric structure that is impregnated with and adhered to a polymeric elastomer resin. If the constituent fibers are simply physically entangled by needle punching, water jet processing, etc. without impregnating the nonwoven fabric with an elastomer resin, the resulting material will have the disadvantages of not having sufficient strength to withstand the load caused by the liquid flow during dyeing, or being easily damaged when used as artificial leather.

A common technique used by artificial leather manufacturers is to impart a good texture and abrasion resistance by attaching a polymeric elastomer such as polyurethane. For example, artificial leather impregnated with polyurethane is commercially available under names such as Ecsaine (trademark) and Alcantara (trademark). However, because polymeric elastomers such as polyurethane are easily combustible, the attachment of these materials can easily cause problems in that the flame retardancy of the artificial leather itself is reduced.

The following Patent Document 1 discloses an example of compensating for flame retardancy by back-coating a flame retardant on polyurethane-impregnated artificial leather. While this method provides good flame retardancy, it has the drawback that the nonwoven fabric becomes extremely hard, making it difficult to obtain a good feel when used as artificial leather. Another drawback is that the manufacturing process becomes complicated due to the need to apply a flame retardant, which can easily increase costs.

In addition to impregnating and adhering a polymeric elastomer such as polyurethane, a method has been considered in the past to obtain a binder effect to give strength to artificial leather by mixing heat-fusible fibers when manufacturing nonwoven fabric for artificial leather and melting them to bond the main fibers together. For example, in the examples of Patent Document 2 below, fibers with a large fiber diameter and sheath-core type are used as heat-fusible fibers. Since the fusion points of the main fibers are connected via the core fibers, the feel of the nonwoven fabric becomes hard, which is disadvantageous in that it is of poor quality.

In addition, in the method disclosed in Patent Document 3 below, since a process of thermally shrinking the nonwoven fabric is included, the molten lumps of the heat-sealed fibers tend to become large, which can lead to the drawback of poor surface quality. Furthermore, since the molten fibers are generated from ultrafine fiber-generating composite fibers, such as islands-in-the-sea fibers, the molten lumps tend to concentrate at the site of the original composite fiber. From this point of view, the method is prone to the drawback of the molten lumps tending to become large, which is derived from the manufacturing method.

In addition, the following Patent Document 4 proposes a leather-like material composed of a laminated structure containing a fused fiber nonwoven fabric. In this leather-like material, the surface layer is made of ultrafine fibers, and the nonwoven fabric layer containing fused fibers is arranged as an underlying layer, creating a laminated structure. In sheets with such a laminated structure, the fibers on the outermost surface of the surface layer are not held together by fusion or the like, so there remain issues with the abrasion resistance required for artificial leather.

In addition, in the following Patent Document 5, in order to provide an artificial leather that has good texture, high abrasion resistance, cut-off properties, and shape stability without impregnation with a polymer elastomer such as polyurethane resin, a heat-fusible short fiber is mixed in a specific ratio with at least the surface fiber layer of a nonwoven fabric having a multilayer structure of at least two layers, a surface fiber layer and a scrim layer that is a woven or knitted fabric, and then a heat-fusible treatment is performed to produce an artificial leather. Since the obtained artificial leather does not contain polyurethane resin, it has improved resistance to artificial sebum, and if it is made of polyester fibers, it has high recyclability, but there is still room for improvement in terms of abrasion resistance (20,000 times or more in the abrasion resistance test by the Martindale method) and texture (bending value of less than 26 cm in the KES forward bending measurement).

In addition, in the invention described in Patent Document 5, the following Patent Document 6 improves abrasion resistance (40,000 or more times in the Martindale abrasion resistance test) and feel (bending value of less than 24 cm in the KES pure bending measurement) by exposing part of the thermoplastic resin formed by melting the heat-fusible short fibers to the surface of the surface fiber layer in the form of chunks of a specified size. However, as with Patent Document 5, there is room for improvement in terms of specific applications such as car seats, which require both high abrasion resistance and a supple feel.

Furthermore, the following Patent Document 7 describes a fiber laminated sheet consisting of at least two layers including an upper layer base paper and a base fiber layer, the upper layer base paper being a synthetic fiber paper made by a wet papermaking process containing polyester binder staple fibers including a copolymer polyester having a melting point in the range of 210 to 250°C and polyester staple fibers as the main component fiber, the constituent fibers of the upper layer base paper being partially temporarily bonded by the polyester binder staple fibers at the time of papermaking, but being dissociated by hydroentanglement, and after entanglement, being heated at a temperature higher than the drying temperature at the time of papermaking, so that the entangled points are partially softened and bonded, the base fiber layer being selected from at least one of a nonwoven fabric, a nonwoven web, and a woven or knitted fabric, the upper layer base paper and the base fiber layer being laminated, and the fibers constituting both layers being entangled with each other and integrated. Patent Document 7 also describes that the present invention provides a novel fiber laminate sheet that has a soft surface texture and appropriate firmness, stiffness, and breathability when not impregnated with an elastic polymer, and that the present invention provides a fiber laminate sheet that can be used to make artificial leather with a texture similar to that of natural leather when impregnated with an elastic polymer, as well as artificial leather using the same, and synthetic fiber paper used for the same that can easily dissociate and entangle single fibers during hydroentanglement, all at low cost. Therefore, the artificial leather described in Patent Document 7 is limited to one that contains a polymer elastomer such as a water-based polyurethane.
Patent Document 7 also describes that the synthetic fiber paper of the present invention is (1) a synthetic fiber paper in which fibers are weakly bonded to each other by agglutination, (2) a synthetic fiber paper in which the agglutination is released by the pressure of mechanical entanglement and the fibers are redispersed in the thickness direction to form three-dimensional entanglement, and (3) a synthetic fiber paper in which the binder short fibers soften, shrink, and deform during heat treatment after entanglement, bonding the entangled points, thereby improving the peel strength between layers compared to when entangled. In order to achieve the series of actions (1) to (3), the synthetic fiber paper contains polyester short fibers as the main component fiber, and is wet-formed synthetic fiber paper containing binder short fibers that are partially bonded to the main component fiber by weak agglutination at the drying temperature (100 to 120° C.) during papermaking, and that then soften, shrink, and have a bond-developing effect when heated at a temperature of 150 to 180° C., which is higher than the drying temperature during papermaking.
According to these descriptions, the substance that softens and shrinks is the binder short fiber, and therefore Patent Document 7 does not teach that a part of the thermoplastic resin formed by melting the heat-fusible short fiber is exposed on the surface of the surface fiber layer in the form of lumps of a predetermined size, nor does it teach that abrasion resistance or feel is improved.

Special Publication No. 03-080914 Japanese Patent Application Publication No. 07-216756 Special Publication No. 03-016427 Patent No. 4835181 Patent No. 5685003 Patent No. 6118174 Patent No. 4708494

In view of the state of the prior art described above, the problem that the present invention aims to solve is to provide an artificial leather that combines a good feel, high abrasion resistance, and flame retardancy, and a method for producing the same.

In order to solve the above problems, the inventors conducted extensive research and experimentation, and unexpectedly discovered that artificial leather having the following characteristics could solve the problems, leading to the completion of the present invention.

That is, the present invention is as follows.
[1] An artificial leather including at least a surface fiber layer constituting a first surface, the artificial leather having the following characteristics:
(1) The surface fiber layer contains a main fiber and a thermoplastic resin;
(2) The fineness of the main fiber is 0.01 dtex or more and 0.5 dtex or less;
(3) At least a portion of the thermoplastic resin bonds the main fibers;
(4) The thermoplastic resin has the following properties as determined by time-of-flight secondary ion mass spectrometry (TOF-SIMS):
(i) the ratio (71/27) of the ion intensity of the positive ion m/z = 71 (fragment ion: C4H7O) to that of the positive ion m/z = 27 (fragment ion: C2H3) is 0.2 or more and 2.3 or less; and (ii) the ratio (42/25) of the ion intensity of the negative ion m/z = 42 (fragment ion: CNO) to that of the negative ion m/z = 25 (fragment ion: C2H) is 0 or more and 0.5 or less;
(iii) the ratio (104/27) of the ion intensity of the positive ion m/z=104 (fragment ion: C7H4O) to that of the positive ion m/z=27 (fragment ion: C2H3) is 0.2 or more and 1.0 or less; and (5) the number average volume of the thermoplastic resin is 3500 ^μm3 or more and 24000 ^μm3 or less;
The artificial leather has the following properties.
[2] The artificial leather according to [1], wherein the main fiber is a polyester fiber.
[3] The artificial leather according to [1] or [2], wherein the thermoplastic resin is a polyester-based resin.
[4] The artificial leather according to any one of [1] to [3], wherein the volumetric particle density of the thermoplastic resin per unit volume in the surface fiber layer is 0.5× ¹⁰ particles/m ^or more and 5.0× ¹⁰ particles/m or ^less .
[5] The artificial leather according to any one of [1] to [4], wherein the average quotient of the major axis divided by the minor axis when the thermoplastic resin is approximated as an ellipse is 100 or less.
[6] The artificial leather according to any one of [1] to [5], wherein the surface fiber layer is entangled with a scrim layer which is a woven fabric.
[7] The artificial leather described in [6], wherein the scrim layer is made of polyester-based resin fibers.
[8] The artificial leather according to any one of [1] to [7], wherein when the surface is abraded with a pressing load of 12 kPa in accordance with JIS-L-1096 E method (Martindale method), the scrim is not exposed when the abrasion count is less than 50,000.
[9] The artificial leather according to any one of the above [1] to [7], wherein when the surface is abraded with a pressing load of 12 kPa in accordance with JIS-L-1096 E method (Martindale method), the abrasion loss is 21 mg or less after 50,000 abrasion cycles.
[10] the steps of:
(1) mixing a main fiber with a heat-fusible fiber made of a thermoplastic resin having the characteristic (3) as measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) so that the weight ratio of the heat-fusible fiber is 3% or more and 25% or less, entangling the mixture by wet papermaking, and then forming a surface fiber web by a hydroentanglement treatment or a needle punching method; and (2) forming a surface fiber layer by thermal annealing the entangled structure of the obtained surface fiber web at a temperature equal to or higher than the melting point of the heat-fusible fiber and lower than the melting point of the main fiber;
The method for producing the artificial leather according to any one of the above [1] to [9],
[11] The method according to [10], wherein the fiber length of the heat-fusible fiber made of the thermoplastic resin is 2 mm to 90 mm or less.
[12] The method according to [10] or [11], wherein the fiber diameter of the heat-fusible fiber is 0.5 dtex or more and 2.2 dtex or less.
[13] The method according to any one of [10] to [12], wherein the heat-fusible fiber is produced by melt spinning the thermoplastic resin.
[14] The method according to any one of [10] to [13], wherein 95% by weight or more of the resin contained in the heat-fusible fiber is a copolymer of polyester and aliphatic polyether.
[15] The method according to any one of [10] to [14], wherein the melting point of the thermoplastic resin is 130° C. or higher and is 20° C. or higher lower than the melting point of the subject fiber.

In the artificial leather according to the present invention, the thermoplastic resin bonding the main fibers having a fineness of 0.01 dtex or more and 0.5 dtex or less has an ion intensity ratio (71/27) of positive ion m/z=71 (fragment ion: C4H7O) to m/z=27 (fragment ion: C2H3) of 0.2 to 2.3, an ion intensity ratio (42/25) of negative ion m/z=42 (fragment ion: CNO) to m/z=25 (fragment ion: C2H) of 0 to 0.5, and an ion intensity ratio (104/27) of positive ion m/z=104 (fragment ion: C7H4O) to m/z=27 (fragment ion: C2H3) of 0.2 to 1.0, and a number average volume of the thermoplastic resin is 3500 ^μm3 to 24000 μm By setting the molecular weight ratio to ³ or less, the fabric will have excellent feel and high abrasion resistance even without the addition of a water-based polyurethane, and will also have excellent flame resistance in that gas generation during combustion can be suppressed.

FIG. 2 is a diagram showing an example of the state of lump resin in a surface fiber layer. FIG. 11 is a diagram showing another example of the state of lump resin in a surface fiber layer. FIG. 11 is a diagram showing another example of the state of lump resin in a surface fiber layer. FIG. 11 is a diagram showing another example of the state of lump resin in a surface fiber layer. FIG. 11 is a diagram showing another example of the state of lump resin in a surface fiber layer. FIG. 11 is a diagram showing another example of the state of lump resin in a surface fiber layer. FIG. 11 is a diagram showing another example of the state of lump resin in a surface fiber layer. FIG. 11 is a diagram showing another example of the state of lump resin in a surface fiber layer. 1 is a photograph, instead of a drawing, showing the results of TOF-SIMS analysis of a cut piece of artificial leather according to one embodiment. 1 is a photograph in place of a drawing showing an example of a cross-sectional image obtained by cutting an artificial leather according to one embodiment and evaluating it by X-ray-CT.

Hereinafter, an embodiment of the present invention will be described in detail.
One embodiment of the present invention is an artificial leather including at least a surface fiber layer constituting a first surface, the artificial leather having the following characteristics:
(1) The surface fiber layer contains a main fiber and a thermoplastic resin;
(2) The fineness of the main fiber is 0.01 dtex or more and 0.5 dtex or less;
(3) At least a portion of the thermoplastic resin bonds the main fibers;
(4) The thermoplastic resin has the following properties as determined by time-of-flight secondary ion mass spectrometry (TOF-SIMS):
(i) the ratio (71/27) of the ion intensity of the positive ion m/z = 71 (fragment ion: C4H7O) to that of the positive ion m/z = 27 (fragment ion: C2H3) is 0.2 or more and 2.3 or less; and (ii) the ratio (42/25) of the ion intensity of the negative ion m/z = 42 (fragment ion: CNO) to that of the negative ion m/z = 25 (fragment ion: C2H) is 0 or more and 0.5 or less;
(iii) the ratio (104/27) of the ion intensity of the positive ion m/z=104 (fragment ion: C7H4O) to that of the positive ion m/z=27 (fragment ion: C2H3) is 0.2 or more and 1.0 or less; and (5) the number average volume of the thermoplastic resin is 3500 ^μm3 or more and 24000 ^μm3 or less;
It is an artificial leather having the above structure.

The main fibers contained in the surface fiber layer constituting the first surface are fibers contained in an amount of 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, based on 100% by mass of the surface fiber layer. The upper limit is not particularly limited, but may be 99% by mass or less.
The main fiber contained in the surface fiber layer constituting the first surface is preferably a polyester-based fiber, a polyamide-based fiber, an acrylic-based fiber or a polyolefin-based fiber from the viewpoints of strength, availability, etc., but as described above, from the viewpoint of providing a recyclable artificial leather that also has flame retardancy, polyester-based fibers are particularly preferred.

As the polyester fibers serving as the main fibers constituting the surface fiber layer, polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactate, copolymers thereof, etc. are preferably used. As the polyamide fibers, nylon, meta-aramid, para-aramid, copolymers thereof, etc. are preferably used. As the acrylic fibers, polymers of acrylic acid esters or methacrylic acid esters, copolymers thereof, etc. are preferably used. As the polyolefin fibers, polyethylene, polypropylene, polybutene, polystyrene, copolymers thereof, etc. are preferably used.

If not only the main fiber but also the thermoplastic resin contained in the surface fiber layer described below and the scrim are made of polyester-based resin, then, for example, used PET can be collected from clothing and beverage bottles, processed into recycled PET resin, and used to manufacture artificial leather. The artificial leather after use (at the end of its life) can then be recycled and processed into, for example, insulation material or filter material, and PET can be recovered from the used insulation material or filter material, making it possible to produce recyclable artificial leather that is suitable for the circular economy.

The main fiber preferably has a fineness of 0.5 dtex or less, more preferably 0.35 dtex or less, and even more preferably 0.2 dtex or less, in order to easily obtain a texture similar to that of natural leather and a suede-like or nubuck-like surface texture. From the viewpoints of production efficiency and production stability during fiber production, the fineness is preferably 0.01 dtex or more, and even more preferably 0.03 dtex or more.
The subject fiber may be a fiber directly spun by a melt spinning method, a fiber obtained by a wet spinning method, or an ultrafine fiber obtained by removing the sea part from a sea-island fiber in which a copolymer polyester is used as the sea part and a regular polyester is used as the island part.

The main fiber does not necessarily have to be composed of only fibers made of a single polymer, but may be a mixture of fibers made of other types of polymers, and the main fiber does not necessarily have to be composed of only fibers having a single fineness, but may be a mixture of fibers having multiple finenesses.
In addition, additives may be mixed into or attached to the main fiber as long as the desired effect is achieved. Additives include titanium oxide, various antioxidants, light fasteners, antistatic agents, flame retardants, softeners, fastness improvers, pigments such as carbon black, dyes, etc.

Additives may be mixed into or attached to the main fiber as long as the desired effect is achieved. Additives include titanium oxide, various oxidation inhibitors, light resistance agents, antistatic agents, flame retardants, softeners, fastness improvers, pigments such as carbon black, dyes, etc.

The thermoplastic resin constituting the surface fiber layer is preferably a polyester resin, an acrylic resin, a polyolefin resin, etc., from the viewpoint of availability. As the polyester resin, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactate, copolymers thereof, etc. are preferably used. From the viewpoint of high abrasion resistance as artificial leather, aromatic polyester is preferable, and from the viewpoint of achieving a further supple texture, copolymers of polyester and aliphatic polyether are more preferable. Among them, polybutylene phthalate resin is preferable, and in particular, copolymers of polybutylene phthalate and aliphatic polyether, and further copolymers of polybutylene phthalate and polytetramethylene ether glycol are preferably used. The term "phthalate" as used herein refers to a general term for benzenedicarboxylic acid compounds. That is, isomers such as 1.2-benzenedicarboxylic acid, 1.3-benzenedicarboxylic acid, and 1.4-benzenedicarboxylic acid can be used in any ratio. The form of the isomers used at any ratio is not particularly specified, and a single isomer can be used, or homopolymers at any ratio can be mixed, or these isomers can be copolymerized. When a copolymer is used, the block/random nature of the comonomer is not particularly limited, and a block copolymer is particularly preferred because the soft segment and hard segment coexist in a moderate manner and because of the simplicity of the manufacturing process. The ratio of the soft segment can be calculated by the following formula.
Presence ratio of soft segments (%)=number of monomer units of soft segments×100/(total number of monomer units of soft segments and hard segments)
The soft segment ratio (%) can be calculated using 1H-NMR, and is preferably 40% or more and 85% or less, particularly preferably 50% or more and 75% or less.
In the copolymer of polybutylene phthalate and polytetramethylene ether glycol, polybutylene phthalate is the hard segment and polytetramethylene ether glycol is the soft segment.

As acrylic resins, polymers of acrylic acid esters or methacrylic acid esters, copolymers thereof, etc. are preferably used. As polyolefin resins, polyethylene, polypropylene, polybutene, polystyrene, copolymers thereof, etc. are preferably used.

The composition of the thermoplastic resin in the artificial leather can be analyzed using TOF-SIMS with sputter cleaning. TOF-SIMS can analyze the elemental composition and chemical structure of the extreme surface of the sample. When a primary ion beam is irradiated onto a sample under ultra-high vacuum, secondary ions are emitted from the extreme surface (1-3 nm) of the sample. By introducing the secondary ions into a time-of-flight (TOF) mass spectrometer, a mass spectrum of the extreme surface of the sample can be obtained. By keeping the amount of primary ion irradiation low, surface components can be detected as molecular ions that maintain their chemical structure and partially cleaved fragments, and information on the elemental composition and chemical structure of the planar direction of the extreme surface can be obtained. By evaluating the fragment intensity of the positive ion m/z = 27 (fragment ion: C2H3) detected from general organic matter, the fragment intensity of the positive ion can be compared relatively. As for negative ions, the fragment intensity of the negative ion can be compared relatively to the m/z = 25 (fragment ion: C2H) detected from general organic matter.

In order to fully exert the desired effect of the present invention, the fragment intensity ratio of the thermoplastic resin measured by TOF-SIMS must be 0.2 or more and 2.3 or less, i.e., the ratio (71/27) of the ion intensity of the polyol, particularly tetramethylene glycol, to the positive ion m/z = 27 (fragment ion: C2H3). If the ion intensity ratio is too low, the content of polyol, particularly tetramethylene glycol, is low, the thermoplastic resin lacks flexibility as a binder for artificial leather, and high quality as artificial leather cannot be obtained. If the ion intensity ratio is too high, the content of polyol, particularly tetramethylene glycol, is high, the binder lacks mechanical strength, and the abrasion resistance as artificial leather cannot be obtained. From these viewpoints, the fragment intensity ratio of the thermoplastic resin measured by TOF-SIMS is preferably 0.8 or more and 2.4 or less, more preferably 1.2 or more and 2.2 or less, in terms of the ratio (71/27) of the ion intensity of the polyol, particularly tetramethylene glycol-derived m/z = 71 (fragment ion: C4H7O) to the positive ion m/z = 27 (fragment ion: C2H3).

The fragment intensity ratio of the thermoplastic resin measured by TOF-SIMS must be 0.2 or more and 1.0 or less, i.e., the ratio of the ion intensity of the aromatic m/z = 104 (fragment ion: C7H4O) to the positive ion m/z = 27 (fragment ion: C2H3) (104/27). If this ion intensity ratio is less than 0.2, the amount of hard segments in the thermoplastic resin decreases, and the mechanical strength required as a binder for artificial leather is not obtained, so abrasion resistance cannot be expressed. On the other hand, if this ion intensity ratio is greater than 1.0, the amount of hard segments becomes too large, impairing the flexibility required as a binder for artificial leather, and sufficient surface quality cannot be obtained. From these viewpoints, the fragment intensity ratio of the thermoplastic resin measured by TOF-SIMS is preferably the ratio of the ion intensity of aromatic m/z = 104 (fragment ion: C7H4O) to the positive ion m/z = 27 (fragment ion: C2H3) (104/27), which is 0.4 or more and 0.9 or less, and more preferably 0.5 or more and 0.8 or less.

The fragment intensity ratio of the thermoplastic resin measured by TOF-SIMS must be such that the ratio (42/25) of the ion intensity of the negative ion m/z=25 (fragment ion: CH) to the isocyanate-derived m/z=42 (fragment ion: CNO) is 0 or more and 0.5 or less. If it is in this range, it will be substantially free of urethane, and will therefore have excellent recyclability and flame retardancy as an artificial leather.

The thermoplastic resin does not necessarily have to be composed of only a single polymer, and may be a mixture of multiple types of polymers.
In addition, this thermoplastic resin may contain or have attached thereto additives, such as titanium oxide, various antioxidants, light resistance agents, antistatic agents, flame retardants, softeners, fastness improvers, pigments such as carbon black, dyes, etc., as long as the desired effect is achieved.
The melting point of the thermoplastic resin is preferably 130°C or higher, and 20°C or higher lower than the melting point of the main fiber. Considering the detachment of the thermoplastic resin from the artificial leather during dyeing, the melting point of the thermoplastic resin is preferably 130°C or higher. The melting point is preferably 140°C or higher, and more preferably 150°C or higher. When bonding the main fibers together with the thermoplastic resin, the melting point of the thermoplastic resin needs to be lower than that of the main fiber. Furthermore, when the thermoplastic resin is a mixture of multiple polymers, it is preferable that the thermoplastic resin with the highest melting point has a melting point 20°C or higher lower than the melting point of the main fiber with the lowest melting point. Regarding the range of the melting point, if it is within the above range, the abrasion resistance and appearance quality described in the present application can be achieved, but from the viewpoint of maintaining particularly good appearance quality, it is preferable that the melting point is 30°C or lower, more preferably 40°C lower.

It is preferable that the thermoplastic resin is exposed on the surface of the surface fiber layer in a block shape. When it is exposed on the surface, the main fibers present on the surface are sufficiently held by resin fusion, and the fibers are less likely to fall off or break, improving the abrasion resistance of the artificial leather. It is also preferable that part or all of the thermoplastic resin bonds the main fibers together. When the thermoplastic resin bonds the main fibers together, the main fibers can be held together, the fibers are less likely to fall off or break, and the artificial leather has satisfactory abrasion resistance and strength.

It is also preferable that the thermoplastic resin is present in a block shape in the cross section of the surface fiber layer. If it is present on the surface and in a block shape in the cross section, the main fibers are sufficiently held together by the resin fusion, the abrasion resistance of the artificial leather is improved, the density of the surface fiber layer is increased, and the luxurious, moist texture characteristic of artificial leather can be expressed.

In this embodiment, the thermoplastic resin must bond the main fibers together and have a number-average volume of 3500 μm ³ or more and 24000 μm ³ or less. If the number-average volume exceeds 24000 μm ³ , the probability that the same heat-fusion point resin will bond multiple main fibers increases, which is likely to cause the material to feel rough to the touch, and the material cannot exhibit a satisfactory sense of luxury as artificial leather. On the other hand, if the volume is less than 3500 μm ³ on average, the size is not sufficient to bond the main fibers together, and the material cannot exhibit abrasion resistance. The number-average volume is preferably in the range of 4000 μm ³ or more and 22000 μm ³ or less, more preferably 6000 μm ³ or more and 20000 μm ³ or less.

The volumetric density of the thermoplastic resin in the surface fiber layer is preferably 0.5×10 ¹² pieces/m ³ or more and 5.0×10 ¹² pieces/m ³ or less. When the number of thermoplastic resins per unit volume is 0.5×10 ¹² pieces/m ³ or more, a plurality of main fibers can be bonded with a plurality of heat fusion point resins, and when worn, the fiber bundles are less likely to fall off, and wear resistance can be exhibited. On the other hand, when the number of thermoplastic resins per unit volume is 5.0×10 ¹² pieces/m ³ or less, the surface fiber layer does not become too hard, and a supple, luxurious feel required for artificial leather can be obtained. The volumetric density of the thermoplastic resin per unit volume in the first surface fiber layer is preferably 0.6×10 ¹² pieces/m ³ or more and 3.0×10 ¹² pieces/m ³ or less, more preferably 0.8×10 ¹² pieces/m ³ or more and 1.5×10 ¹² pieces/m ³ or less.

It is preferable that the thermoplastic resin isotropically bonds the main fibers when viewed from any angle in three dimensions. Specifically, it is preferable that the average value of the quotient (long axis/short axis ratio) obtained by dividing the long axis by the short axis when the thermoplastic resin in the surface fiber layer is approximated as an ellipse is 100 or less. If the average value of the quotient obtained by dividing the long axis by the short axis when the thermoplastic resin is approximated as an ellipse is 100 or less, the heat-sealing resin is sufficiently melted when bonding the main fibers, the adhesive strength is high, and high abrasion resistance can be obtained. The long axis/short axis ratio is more preferably 30 or less, and even more preferably 10 or less. Since it is preferable that the thermoplastic resin is close to a perfect sphere (quotient value 1), there is no particular limitation, but the average value of the quotient obtained by dividing the long axis by the short axis when the thermoplastic resin is approximated as an ellipse may be 1 or more.

Another embodiment of the present invention is a method for producing a process comprising the steps of:
(1) mixing a main fiber with a heat-fusible fiber made of a thermoplastic resin having the characteristic (3) as measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) so that the weight ratio of the heat-fusible fiber is 3% or more and 25% or less, entangling the mixture by wet papermaking, and then forming a surface fiber web by a hydroentanglement treatment or a needle punching method; and (2) forming a surface fiber layer by thermal annealing the entangled structure of the obtained surface fiber web at a temperature equal to or higher than the melting point of the heat-fusible fiber and lower than the melting point of the main fiber;
The method for producing the artificial leather includes the steps of:

The artificial leather of this embodiment may include a scrim layer. In that case, the scrim layer is preferably a woven or knitted fabric from the viewpoint of stabilizing the production of the papermaking sheet in the papermaking process and increasing the mechanical strength of the obtained artificial leather, as it functions as a core material. The material of the scrim layer is preferably the same polymer system as the main fiber in terms of color uniformity in dyeing, and in the case of knitted fabrics, single knits knitted with a gauge of 22 to 28 are preferable. In the case of woven fabrics, higher dimensional stability and strength can be achieved than in knitted fabrics, so they are even more suitable. The yarns constituting the woven fabric may be monofilament or multifilament. The single fiber fineness of the yarns is preferably 5.5 dtex or less in terms of ease of obtaining a flexible artificial leather using an entangled sheet. As the form of the yarns constituting the woven fabric, raw multifilament yarns such as polyester and polyamide, or textured yarns that have been subjected to false twist processing, etc., are preferably twisted with a twist number of 0 to 3000 T/m. The multifilament may be a normal one, and for example, 33 dtex/6f, 55 dtex/24f, 83 dtex/36f, 83 dtex/72f, 110 dtex/36f, 110 dtex/48f, 167 dtex/36f, 166 dtex/48f, etc. of polyester, polyamide, etc. are preferably used. The threads constituting the woven fabric may be long multifilament fibers. In order to obtain an artificial leather that is soft and has excellent mechanical strength, the weaving density of the threads in the woven fabric is preferably 30 threads/inch or more and 150 threads/inch or less, more preferably 40 threads/inch or more and 100 threads/inch or less. In order to provide good mechanical strength and a suitable texture, the basis weight of the woven fabric is preferably 20 g/ ^m2 or more and 150 g/ ^m2 or less. In addition, the presence or absence of false twist processing in the woven fabric, the number of twists, the single fiber fineness of the multifilament, the weaving density, etc. contribute to the entanglement with the constituent fibers of the main fiber layer, the flexibility of the artificial leather, as well as mechanical properties such as seam strength, tear strength, tensile strength/elongation, and stretchability, and may be appropriately selected depending on the target physical properties and applications.

The length of the main fiber in step (1) is not particularly limited, but is preferably 2.5 mm or more and 90 mm or less. If the length of the main fiber is within this range, hydroentanglement with the scrim layer will be sufficient. If the length of the main fiber is 2.5 mm or less, the entanglement effect with the scrim layer will not be fully expressed in the entanglement step, and relative peeling will easily occur between the main fiber layer and the scrim layer, which may cause quality defects such as poor adhesion and poor appearance. The length of the main fiber is more preferably 2.5 mm or more and 20 mm or less, and even more preferably 3 mm or more and 10 mm or less.

The length of the heat-sealing fibers made of a thermoplastic resin is preferably 2.0 mm or more and 90 mm or less. When a scrim layer is used, if the length of the heat-sealing fibers is within this range, the water flow entanglement with the scrim layer is sufficient, and the heat-sealing fibers can be bonded to the main fiber and the scrim when they are melted. If the length of the heat-sealing fibers is 2.0 mm or less, the entanglement effect with the scrim layer is not fully expressed in the entanglement process, and the heat-sealing fibers cannot be bonded to the main fiber and the scrim when they are melted, which may cause quality defects such as poor adhesion and poor appearance. The length of the main fiber is more preferably 2.5 mm or more and 20 mm or less, and even more preferably 3 mm or more and 10 mm or less.

The artificial leather of the present embodiment may include at least a surface fiber layer constituting a first surface, and for example, in the case of an artificial leather consisting of a surface fiber layer and a scrim layer, the first surface (upper surface) becomes the surface (front surface), and the back surface of the scrim layer becomes the second surface (lower surface). In addition, in the case of an artificial leather of the present embodiment consisting of three layers of a surface fiber layer/scrim layer/back fiber layer, the back surface of the back fiber layer becomes the second surface.
In addition, in the case of adopting a structure of a surface fiber layer/scrim layer/back fiber layer as one aspect of this embodiment, the material constituting the back fiber layer is not particularly limited, but from the viewpoint of exhibiting good recyclability, it is preferable that it is the same as the main fiber and/or thermoplastic resin of the surface fiber layer. In addition, when the back fiber layer is included, it may be different from the surface fiber layer, for example, by adding a flame retardant, to add desired properties.

A preferred method for producing the artificial leather of this embodiment is to heat treat a nonwoven fabric structure having a surface fiber layer formed by mixing at least one type of main fiber and a fully meltable heat-fusible fiber having a melting point 20° C. or more lower than the melting point of the main fiber, thereby melting the heat-fusible fiber and forming a lump of thermoplastic resin in the surface fiber layer.
The heat-fusible fibers are preferably full-melt fibers so that the molten resin has a sufficient number of points at which the main fibers are fused together. Compared with sheath-core fibers using a low-melting thermoplastic resin in the sheath or side-by-side fibers using a low-melting thermoplastic resin on only one side, full-melt fibers have many points at which the main fibers are bonded together and a large amount of fusion components in the fusion parts, so that the fusion strength is sufficient. In addition, the fusion points are not continuously present in the vicinity of each other via the heat-fusible fibers, so that the feel is likely to be soft.

The resin component contained in the heat-sealable fiber is preferably 95% or more, but additives may be mixed in or attached as long as the desired effect is achieved. Additives include titanium oxide, various oxidation inhibitors, light resistance agents, antistatic agents, flame retardants, softeners, fastness improvers, pigments such as carbon black, dyes, etc. The preferred range of the resin component contained in the heat-sealable fiber is 96% or more, more preferably 97% or more.

The heat-sealing fiber does not necessarily have to be composed of a single polymer, and may be a mixture of multiple polymers. In terms of high fusion strength and uniformity in dyeing, it is preferable to use the same polymer system as the main fiber. The heat-sealing fiber may be a fiber directly spun by a melt spinning method, a fiber obtained by a wet spinning method, or an ultrafine fiber obtained by removing the sea component from a sea-island fiber using a copolymer polyester as the sea component and a regular polyester as the island component. In terms of the size of the lumpy thermoplastic resin after melting, the fineness of this heat-sealing fiber is preferably 0.5 dtex or more and 2.2 dtex or less. If the fineness is 2.2 dtex or less, the lumpy thermoplastic resin after melting is uniformly dispersed on the surface of the surface fiber layer, resulting in excellent appearance quality and feel. The fineness of the heat-sealing fiber is more preferably 0.6 dtex or more and 2.0 dtex or less, and even more preferably 0.7 dtex or more and 1.5 dtex or less.

Additives may be mixed into or attached to the heat-sealed fibers as long as the desired effect is achieved. Additives include titanium oxide, various oxidation inhibitors, light resistance agents, antistatic agents, flame retardants, softeners, fastness enhancers, pigments such as carbon black, dyes, etc.

Methods for forming the surface fiber layer include using the main fibers and/or heat-fusible fibers in the form of short fibers and entangling the fibers to form a nonwoven structure using a papermaking method, a carding method, an air-laying method, or the like.
From the viewpoints of uniform dispersion of the constituent fibers and ease of use of ultrafine fibers, it is particularly preferred that the surface fiber layer be formed by a papermaking method.

In addition, in this embodiment, the inter-layer entanglement can be performed using a hydroentanglement method called the spunlace method, a needle punch method, or the like, but when a scrim layer is used, the hydroentanglement method is preferred because it does not destroy the structure of the woven or knitted fabric that is the scrim layer.

The above thermoplastic resins can be evaluated by cutting the artificial leather vertically and observing it with an optical microscope or electron microscope, or by measuring three-dimensional images with CT or MRI. It is necessary to accurately evaluate the position, density, shape, and size of the heat-sealed resin not only on the surface of the surface fiber layer, but also inside it. This can be accurately analyzed and evaluated by performing continuous image analysis of the cross section in X-ray CT as described in the examples, taking the steps to properly process the images, and then performing mathematical analysis.

The nonwoven fabric for artificial leather obtained by the above method can be used as suede- or nubuck-like artificial leather by raising the surface of the surface fiber layer and dyeing it. The raising can be performed by a known method such as buffing with sandpaper. In this case, if the raising is performed before the heat-fusible fibers of the surface fiber layer are heat-fusible, a suede-like surface texture can be obtained. On the other hand, if the raising is performed after the heat-fusible fibers are heat-fusible, a nubuck-like surface texture can be obtained.

There are no particular limitations on the dyeing process. For example, when the main fiber is a polyester fiber, disperse dyes are generally used. The dyeing method can be a conventional method well known to dye processing companies, and for artificial leather, a liquid flow dyeing machine is preferably used in terms of uniform dyeing. The artificial leather dyed in this way is reduced and washed by soaping or in the presence of a chemical reducing agent to remove excess dye. There are no particular limitations on the conditions for reduction and washing, and basic reducing agents and acidic reducing agents can be used without any particular limitations in accordance with conventional methods.

In the present embodiment, the heat fusion (heat annealing) treatment can be performed using a drum dryer, a contact dryer such as a calendar roll, a biaxially stretching film stretcher, or an air-through dryer such as a pin tenter dryer. The (heat annealing) treatment temperature is at least 5°C higher than the melting point of the thermoplastic resin, preferably at least 10°C higher, and is 240°C or lower. If the difference between the treatment temperature and the melting point of the thermoplastic fiber is less than 5°C, a sufficient heat fusion effect may not be obtained. If the treatment temperature exceeds 240°C, the polyester fiber may melt, and the surface quality and abrasion resistance may not be fully expressed.

When the heat fusion occurs in the thermal annealing treatment, it is preferable to relax the nonwoven fabric structure. By performing the heat fusion while sagging and shrinking the surface fiber web entangled with the scrim layer in the MD and CD directions, the entangled structure is in a relaxed state, i.e., the main fibers are fixed in a non-tensioned state. This makes it possible to obtain artificial leather with high abrasion resistance and texture compared to the conventional technology method in which heat fusion is performed while tensing and shrinking using a pin tenter.

The thickness of the artificial leather of this embodiment is preferably 0.40 mm to 1.50 mm. By making the thickness of the artificial leather within the range of 0.40 mm to 1.50 mm, the thickness of the ultrafine fiber layer can be sufficiently ensured while maintaining sufficient fusion points per unit area and entanglement between the fibers in the ultrafine fiber layer on the surface, thereby achieving both a soft feel and sufficient stretchability.

The weight per unit area of the artificial leather of this embodiment is preferably 100 g/m ² to 400 g/m ^2. By setting the weight per unit area to 100 g/m ² to 400 g/m ² , it is possible to achieve both a soft feel and appropriate hardness.

The artificial leather of this embodiment preferably has good abrasion resistance for use as artificial leather, in that when the surface is abraded with a pressure load of 12 kPa in accordance with JIS-L-1096 E method (Martindale method), the scrim is not exposed after less than 50,000 abrasion cycles.

Similarly, the artificial leather of this embodiment preferably has good abrasion resistance for use as artificial leather, in accordance with JIS-L-1096 E method (Martindale method), and when the surface is abraded with a pressure load of 12 kPa 50,000 times, the abrasion loss is preferably 21 mg or less.

The artificial leather of this embodiment preferably exhibits flame retardancy of grade 4 or higher in a flammability test conforming to the US Federal Motor Vehicle Safety Standard "FMVSS No. 302". By maintaining flame retardancy of grade 4 or higher, it is possible to clear the flame resistance standards used in automobile applications, aircraft applications, etc., and the range of applications that can be applied when used as artificial leather can be expanded.

The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to these examples. The physical properties used in the examples were measured by the following methods.

(1) TOF-SIMS Measurement Pretreatment The artificial leather was cut into a piece 5 mm wide and 10 mm long to prepare a sheet-like sample. 9.7 ml of Quetol 812, 3.7 ml of MNA, 6.6 ml of DDSA, and 0.34 ml of DMP-30 manufactured by Nissin EM were mixed to prepare a resin composition, which was then vacuum degassed. The epoxy resin prepared with the sample was then filled into a silicon embedding plate and cured in a thermostatic chamber at 60°C for three days. The composite of the obtained sample and the cured epoxy resin was removed, and a cross section of the sample was prepared using a cryomicrotome (Ultracut-UCT manufactured by Leica).

(2) TOF-SIMS Measurement The cross section of the artificial leather sample was cleaned of surface contamination using a gas cluster beam (GCIB), and then TOF-SIMS measurement was performed. Spectra were extracted from the thermoplastic resin region in the measured image, and the ion intensities of m/z = 27 (fragment ion: C2H3), m/z = 71 (fragment ion: C4H7O), and m/z = 104 (fragment ion: C7H4O) for positive ions, and m/z = 25 (fragment ion: C2H) and m/z = 42 (fragment ion: CNO) for negative ions were obtained.
The same measurement was repeated for five regions identified as thermoplastic resin regions by the following method, and the arithmetic average was taken as the ionic strength, and the ratio was calculated. However, regions that clearly did not show the above-mentioned spectrum were excluded as they were determined not to be thermoplastic resin regions.
To identify the thermoplastic resin region, the cross section of the sample prepared by a cryomicrotome is measured by an atomic force microscope, and the location of the thermoplastic resin is identified from the shape characteristics. The epoxy resin is observed as the matrix with the largest area, and the cross section of the thread is observed as a fixed shape such as a circle or ellipse. The thermoplastic resin component is observed as an amorphous region. When analyzing the thermoplastic resin, in order to avoid the influence of the epoxy resin or the thread, the analysis is performed by selecting a location 2 μm or more away from the interface between the thermoplastic resin and the epoxy resin, and from the interface between the thermoplastic resin and the thread.

The TOF-SIMS measurement conditions used are as follows.
(Measurement conditions)
Equipment used: nanoTOF (ULVAC-PHI)
Analysis software: WinCadenceN (ULVAC-PHI, Inc.)
Primary ion: _Bi32 ⁺
Acceleration voltage: 30 kV
Ion current: Approximately 0.1 nA (as DC)
Bunching: Yes Analysis area: 50 μm x 50 μm
Analysis time: 30 minutes Detected ions: positive and negative ions Neutralization: positive ion electron gun + Ar monomer ion, negative ion electron gun

(Cleaning conditions)
Sputter ion: GCIB (Ar ₂₅₀₀₊ )
Acceleration voltage: 20 kV
Ion current: 5nA
Sputtering area: 600 μm × 600 μm
Sputtering time: 30 seconds/cycle

(3) Number average volume (μm ³ ), volume number density (10 ¹² particles/m ³ )
[Image measurement using X-ray CT]
The observation of the mass of the heat fusion point was performed using an X-ray CT device (Rigaku Corporation's "High Resolution 3D X-ray Microscope Nano3DX") to observe the entire thickness direction of the artificial leather, and a three-dimensional image was taken so that the center of the thickness direction cross section was the center point of the observation area. The image measurement was performed using copper as the X-ray target under the conditions of an X-ray tube voltage of 40 kV, a tube current of 30 mA, an exposure time of 12 seconds/sheet, and a spatial resolution of 1.08 μm/pixel. Using the same operation, 1000 images were taken per 180 degrees of rotation angle to obtain three-dimensional measurement data.

[Image processing method, analysis method, and method for calculating the arithmetic mean value of the quotient obtained by dividing the major axis by the minor axis when approximating an ellipse]
The detailed process of processing and analyzing the three-dimensional measurement data obtained above will be described below. The image analysis software used was ImageJ (version: 1.51j8) (National Institutes of Health, USA).
(i: Image rotation) The three-dimensional image is rotated so that the plane direction of the artificial leather coincides with the plane direction consisting of the xz axes, and the thickness direction of the artificial leather coincides with the y axis.
(ii: Trimming) Trim the three-dimensional image into a rectangular parallelepiped. In this case, the y-axis is set to a range that includes the entire thickness and does not include excessive space outside the film. Regarding the x-axis and z-axis, after the y-axis range is determined, the maximum range is taken so that no pixels outside the measurement field of view are included within the trimmed rectangular parallelepiped.
(iii: Setting of axes) The number of pixels in the x-axis direction of the trimmed image is set to x0, the number of pixels in the y-axis direction to y0, and the number of pixels in the z-axis direction to z0.
(iv: Filtering) A median filter is applied with a radius of 2 pix.
(v: Region division) The Otsu method is applied to divide the regions. At this time, in order to clarify the difference between light and dark, the pixel brightness value is set so that the air portion not containing the artificial leather is set to 0 and the main fiber portion constituting the artificial leather is set to 255.
(vi: Segmentation) The image processing method segmentation is applied to pixels with a brightness value of 255. A structure in which the number of pixels (pix) of a three-dimensionally connected region with a brightness value of 255 is 10,000 or less is regarded as noise, and its brightness value is changed to 0 and removed.
(vii: Noise Removal) Of the pixels with a luminance value of 0, pixels with a luminance value of 0 that are three-dimensionally surrounded by pixels with a luminance value of 255 are regarded as noise, and their luminance values are changed to 255 and removed.
(viii: Calculation of porosity) A two-dimensional original image of the xz plane is cut out from the three-dimensional image at a thickness of 1 pix in the thickness direction, and the porosity on that plane is calculated using the following formula:
The porosity is calculated as the number of pixels with a brightness value of 0 divided by the total number of pixels.
(ix: Thickness distribution of porosity) The above (viii) is carried out for all y data to obtain the distribution of porosity in the y-axis direction.
(x: Calculation of the size of high-luminance pixels) The size of a pixel with a luminance value of 255 is calculated by the Thickness method. This results in a three-dimensional image in which the luminance value of each pixel is the diameter value of the largest sphere that fits in that location. The Thickness method is a method described in the literature "A new method for the model-independent assessment of thickness in three-dimensional images" by T. Hildebrand and P. Ruesgsegger, J. of Microscopy, 185 (1996) 67-75, and can be executed, for example, by BoneJ Thickness, a plug-in for the image analysis software ImageJ. Furthermore, in the image obtained here, structures of 12 μm or less are regarded as main fibers and are removed as objects of analysis, so the image brightness value of the brightness value of the number of pixels corresponding to 12 μm or less is changed to 0.
(xi: binarization) The image obtained in (x) above is binarized by setting all pixels whose luminance value is not 0 to 255 and leaving pixels whose luminance value is 0 as 0.
(xii: Particle analysis) A three-dimensional particle analysis is performed on the image obtained in (xi) above. A three-dimensional continuous part with a brightness value of 255 is considered to be one particle, and the central coordinates (XC, YC, ZC) of each particle and the number of pixels of the continuous structure are calculated.
(xiii: Definition of the front surface, scrim layer, and back surface) In the data of the porosity distribution obtained in (ix) above, a range of 95% is used for analysis (the outermost surfaces of the front surface and back surface are excluded from the analysis), so the y-axis value on the surface of the artificial leather where the porosity is 0.95 or more is the furthest from the front side is defined as y1. In the case where a scrim layer is included, the portion where the porosity value in (viii) above and fibers with a fineness of 100 dtex or more appear is defined as the end of the front side, and its coordinate is y2.
(xiv: Calculation of the sum of the number of pixels and data analysis) Of all the particles found in (xii) above, for particles whose coordinate values satisfy y1<YC<y2, the number of particles and the sum of the number of pixels of the particles are found.
Number average volume (μm ³ )=sum of pixel numbers of particles*p*p*p÷number of particles Volume number density (10 ¹² particles/m ³ )=number of particles÷(|y2-y1|*p*x0*p*z0*p)
Here, p is the pixel size (m/pix), which is the actual size (m) of one pixel (pix).
(xv: Calculation of the average value of the quotient obtained by dividing the major axis by the minor axis when approximating an ellipse and data analysis) Three-dimensional particle analysis is performed on the image obtained in (xi) above. A three-dimensional continuous part with a brightness value of 255 is regarded as one particle, and each particle is approximated as an elliptical sphere. The three axes of the elliptical sphere are designated, in order from the larger one, as the major axis, middle axis, and minor axis. The average value of the quotient obtained by dividing the major axis by the minor axis when approximating each particle as an ellipse is calculated using the following formula:
The calculation was made by dividing the major axis by the minor axis = major axis length/minor axis length.
However, when the major axis of the approximated ellipsoid is greater than the minimum axis of the rectangular parallelepiped to be analyzed, it is excluded as an error and the aspect ratio is set to 0. The average aspect ratio is calculated using the following formula:
Average major axis divided by minor axis = sum of major axis divided by minor axis of particles ÷ (total number of particles - total number of particles excluded)
The calculation was done as follows.

(4) Explanation of the structure of heat fusion points The state of the lump resin and its determination will be explained with reference to the drawings. FIG. 1 is an example where the lump resin is exposed on the surface of the surface fiber layer but does not bond the main fibers, and FIG. 2 is an example where the lump resin is exposed on the surface and bonds the main fibers. FIG. 3 is an example where the lump resin is not exposed on the surface but bonds the main fibers, FIG. 4 is an example where the lump resin is exposed on the surface and bonds the main fibers, and FIG. 5 is an example where the lump resin is exposed on the surface but does not bond the main fibers. FIG. 6 is an example where the heat fusion fiber is not melted, and is not called lump resin. FIG. 7 is an example where sheath-core fiber is used as the heat fusion fiber, and the heat fusion fiber retains its fibrous shape, and is not called lump resin. FIG. 8 is an example where the lump resin is exposed on the surface but does not bond the main fibers. In the drawings, 1 is the main fiber, 2 is lump resin, 3 is unmelted resin, and 4 is sheath-core fiber.
The phrase "the main fibers are bonded to each other" used herein means that at least two main fibers penetrate the interior of the block resin (thermoplastic resin) and are physically bonded to each other.

(5) Fineness Ten randomly selected points on the front or back fiber layer sample of the artificial leather were photographed with a microscope at a magnification of 2500 times, and the diameters of the fibers at 50 points were measured, and the average value thereof was calculated as the average fiber diameter. The fineness [dtex] of the main fiber was calculated by converting the obtained average fiber diameter and the density of the main fiber.
In addition, artificial leather was immersed in ethanol, wrapped in a gelatin capsule, and freeze-dried in liquid nitrogen. The capsule was cut with a knife, and the cut cross section of the sample returned to room temperature was observed using a scanning electron microscope (JSM-5610 manufactured by JEOL Ltd.) under conditions of WD = 10 mm and magnification of 200 times. The thickness of the woven yarns constituting the scrim layer was measured at five points on each of the 20 obtained images, and the fineness of the woven yarns constituting the scrim layer was determined by measuring the thickness.
The fineness of the heat-fused fiber is the fineness of the raw fiber, and was evaluated using a scanning electron microscope. Specifically, an adhesive carbon tape was attached on an evaluation stage, 0.05 g of the raw short fiber was placed on the tape, and the excess heat-fused fiber was removed with an air duster to obtain a sample. The sample was observed under conditions of WD = 10 mm and magnification of 200 times, and the thickness was measured at five points on each of 20 images obtained.

(6) Melting point The melting point of the heat-fusible fiber was determined by placing 3 mg of the heat-fusible fiber in a nitrogen atmosphere, heating it from 25° C. to 250° C. at a rate of 10° C./min using aluminum as a reference substance with a DSCQ100 manufactured by TA Instruments, and then rapidly cooling it. The fiber was then heated for the second time under the same conditions, and the top of the endothermic peak that appeared was taken as the melting point.

(7) Abrasion resistance and abrasion loss The sample surface was abraded with a pressure load of 12 kPa according to the method specified in JIS-L-1096 E method (Martindale method). The evaluation criteria for this test method were the number of abrasions until the sample surface layer was abraded and the scrim was exposed, and the evaluation was divided into the following evaluation criteria (grades).
(Evaluation Criteria)
XX: After 5,000 abrasion cycles, significant fiber loss occurred and evaluation was not possible.
x: The scrim is exposed after less than 30,000 abrasion cycles.
Δ: The scrim is exposed after 30,000 or more and less than 40,000 abrasion cycles.
◯: The scrim is exposed after 40,000 or more and less than 50,000 abrasion cycles.
⊚: The scrim is exposed after 50,000 or more abrasion cycles.
In addition, a sample of artificial leather (a perfect circle with a diameter of 40 mm) specified in JIS-L-1096 E method (Martindale method) was abraded 50,000 times with a pressure load of 12 kPa, and the weight change [mg] was evaluated as the abrasion loss. The measurement was carried out three times, and the arithmetic average was used as the result.

(8) Texture Evaluation The dyed artificial leather samples obtained were cut into 25 cm squares, arranged on a table with the surface facing up, and 20 subjects (10 men and 10 women, 2 subjects per age group ranging from 20s to 60s) were blindfolded and asked to carry out a test to check the texture along the raised surface. At the same time, a similar texture test was also carried out on natural suede, and a sensory evaluation was carried out on the following evaluation criteria for the suppleness of the surface and the sense of luxury, with a maximum score of 5 (suede being 5 points), and the scores were rounded off to the nearest 1 decimal place.
(Evaluation Criteria)
◯: The average score of the sensory evaluation is 4.0 points or more. △: The average score of the sensory evaluation is 3.0 points or more and less than 4.0 points. ×: The average score of the sensory evaluation is less than 3.0 points.

(9) Flame retardancy: Measurement was carried out based on the US Federal Motor Vehicle Safety Standard "FMVSS No. 302." In this measurement, the grade was determined according to the following evaluation criteria.
(Evaluation Criteria)
Grade 5: The burning part does not reach the burning speed range.
Grade 4: Burning length less than 50 mm and burning time less than 60 seconds.
Grade 3: The average burning speed is less than 50 mm/min, and the sample is completely burned.
Grade 2: The average burning speed is 50 mm/min or more and less than 100 mm/min, and the sample is completely burned.
Grade 1: The average burning speed is 100 mm/min or more, and the sample is completely burned.

(10) Reduced viscosity (ηsp / c)
The reduced viscosity (ηsp/c) is measured as follows. 0.35 g of the resin that is the raw material of the thermally fused fiber is added to 0.25 deciliters of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), and stirred at room temperature for 3 hours using a magnetic stirrer to prepare a diluted solution. The obtained diluted solution is added to an Ubbelohde viscosity tube (tube diameter: 0.03), and the falling time of the diluted solution and the HFIP solvent is measured in a water bath adjusted to 25°C ± 0.1°C to obtain the specific viscosity (ηsp). After the measurement, the diluted solution is weighed and dried in an oven at 120°C for 1 hour, and the polymer concentration C (g/dl) is calculated from the obtained solid content. The specific viscosity (ηsp) is divided by the polymer concentration C (g/dl) to obtain the reduced viscosity ηsp/c. The solvent and the amount of solvent may be changed depending on the type of the resin that is the raw material of the thermally fused fiber.

A method for producing the resin that is the raw material for the thermal adhesive resin will be described below.
[Resin Production Example 1]
Polycondensation reaction was carried out using dimethyl terephthalate, 1,4-butanediol, and polytetramethylene glycol to obtain a polyester polyether block copolymer elastomer. Specific experimental conditions are shown below. 1000g of dimethyl terephthalate, 650g of 1,4-butanediol, and 8.3g of tetrabutoxytitanium (IV) were added to a 5L autoclave reactor equipped with a dispensing machine manufactured by Shibata Chemical Industry Co., Ltd., and after sufficient nitrogen replacement, the reactor was pressurized to 2 atm with nitrogen, and then the reactor was reacted at 250°C for 5 hours under a rotating condition of 50 rpm to carry out a polycondensation reaction, thereby obtaining a prepolymer. Next, 1210g of polytetramethylene glycol having a number average molecular weight of 2000 was added, and the polycondensation reaction was continued at 250°C for 2 hours while reducing the pressure to 0.01 atm. The reactor was returned to room temperature and pressure, and then removed from the reactor to obtain a polyester polyether block copolymer elastomer resin 1. This polyester polyether block copolymer elastomer resin 1 had a melting point of 182° C. and a reduced viscosity of 3.0 dl/g.

[Resin Production Example 2]
Polycondensation reaction was carried out using dimethyl terephthalate, dimethyl isophthalate, 1,4-butanediol, and polytetramethylene glycol to obtain a polyester polyether block copolymer elastomer. Specific experimental conditions are shown below. 780 g of dimethyl terephthalate, 220 g of dimethyl isophthalate, 650 g of 1,4-butanediol, and 8.3 g of tetrabutoxytitanium (IV) were added to a 5L autoclave reactor equipped with a dispensing machine manufactured by Shibata Chemical Industry Co., Ltd., and after sufficient nitrogen replacement, the reactor was pressurized to 2 atm with nitrogen, and then reacted at 250°C for 5 hours under a rotating condition of 50 rpm to carry out a polycondensation reaction to obtain a prepolymer. Next, 500 g of polytetramethylene glycol having a number average molecular weight of 2000 was added, and the polycondensation reaction was continued at 250°C for 2 hours while reducing the pressure to 0.01 atm. The temperature and pressure were returned to normal temperature and normal pressure, and the reactor was removed from the reactor to obtain a polyester polyether block copolymer elastomer resin 2. This polyester polyether block copolymer elastomer had a melting point of 170° C. and a reduced viscosity of 2.3 dl/g.

[Resin Production Example 3]
Polycondensation reaction was carried out using dimethyl terephthalate, dimethyl isophthalate, 1,4-butanediol, and polytetramethylene glycol to obtain a polyester polyether block copolymer elastomer. Specific experimental conditions are shown below. 740 g of dimethyl terephthalate, 260 g of dimethyl isophthalate, 650 g of 1,4-butanediol, and 8.3 g of tetrabutoxytitanium (IV) were added to a 5L autoclave reactor equipped with a suction machine manufactured by Shibata Chemical Industry Co., Ltd., and after sufficient nitrogen replacement, the reactor was pressurized to 2 atmospheres with nitrogen and reacted at 250°C for 5 hours under 50 rpm suction conditions to carry out a polycondensation reaction, thereby obtaining a prepolymer. Next, 750 g of polytetramethylene glycol having a number average molecular weight of 2000 was added, and the polycondensation reaction was continued at 250°C for 2 hours while reducing the pressure to 0.01 atmosphere, and the temperature and pressure were returned to normal, and the reactor was removed from the reactor to obtain a polyester polyether block copolymer elastomer resin 3. This polyester polyether block copolymer elastomer resin 3 had a melting point of 155° C. and a reduced viscosity of 3.0 dl/g.

[Resin Production Example 4]
Polycondensation reaction was carried out using dimethyl terephthalate, dimethyl isophthalate, 1,4-butanediol, and polytetramethylene glycol to obtain a polyester polyether block copolymer elastomer. Specific experimental conditions are shown below. 770 g of dimethyl terephthalate, 230 g of dimethyl isophthalate, 650 g of 1,4-butanediol, and 8.3 g of tetrabutoxytitanium (IV) were added to a 5L autoclave reactor equipped with a centrifuge manufactured by Shibata Chemical Industry Co., Ltd., and the reactor was fully substituted with nitrogen, and then pressurized with nitrogen to 2 atm. The reactor was rotated at 50 rpm and reacted at 250°C for 5 hours to carry out a polycondensation reaction to obtain a prepolymer. Next, 1120 g of polytetramethylene glycol having a number average molecular weight of 2900 was added, and the polycondensation reaction was continued to obtain a polyester polyether block copolymer elastomer resin 4. The melting point of this polyester polyether block copolymer elastomer resin 4 was 163°C, and the reduced viscosity was 2.9 dl/g.

[Resin Production Example 5]
Polycondensation reaction was carried out using dimethyl terephthalate, 1,4-butanediol, and polytetramethylene glycol to obtain a polyester polyether block copolymer elastomer. Specific experimental conditions are shown below. 1000 g of dimethyl terephthalate, 650 g of 1,4-butanediol, and 8.3 g of tetrabutoxytitanium (IV) were added to a 5L autoclave reactor equipped with a centrifuge (manufactured by Shibata Chemical Co., Ltd.), and the reactor was fully substituted with nitrogen, and then pressurized with nitrogen to 2 atm. The reactor was rotated at 50 rpm and reacted at 250°C for 5 hours to carry out a polycondensation reaction to obtain a prepolymer. Next, 2400 g of polytetramethylene glycol having a number average molecular weight of 2000 was added, and the polycondensation reaction was continued to obtain a polyester polyether block copolymer elastomer resin 5. The melting point of this polyester polyether block copolymer elastomer resin 5 was 160°C, and the reduced viscosity was 4.4 dl/g.

[Resin Production Example 6]
Polycondensation reaction was carried out using dimethyl terephthalate, dimethyl isophthalate, ethylene glycol, and polytetramethylene glycol to obtain a polyester polyether block copolymer elastomer. Specific experimental conditions are shown below. 800g of dimethyl terephthalate, 200g of dimethyl terephthalate, 450g of ethylene glycol, and 8.3g of tetrabutoxytitanium (IV) were added to a 5L autoclave reactor equipped with a diverter manufactured by Shibata Chemical Industry Co., Ltd., and after sufficient nitrogen replacement, the reactor was pressurized to 2 atm with nitrogen, and reacted at 250°C for 5 hours under diverter conditions of 50 rpm to carry out a polycondensation reaction to obtain a prepolymer. Next, 780g of polytetramethylene glycol having a number average molecular weight of 2900 was added, and polycondensation reaction was continued to obtain a polyester polyether block copolymer elastomer resin 6. The melting point of this polyester polyether block copolymer elastomer resin 6 was 171°C, and the reduced viscosity was 3.1 dl/g.

[Resin Production Example 7]
Polybutylene succinate was obtained by polycondensation reaction of succinic anhydride and 1,4-butanediol. 500g of succinic anhydride, 500g of 1,4-butanediol, 1.3g of tetrabutoxytitanium (IV) as catalyst, and 0.8g of toluene-4-sulfonic acid were added to a 2L autoclave reactor equipped with a rotary extruder manufactured by Shibata Chemical Industry Co., Ltd., and the reactor was pressurized to 2 atm with nitrogen, and reacted at 270°C for 6 hours under rotary extrusion conditions of 50 rpm to obtain polybutylene succinate resin 7. The obtained polybutylene succinate resin 7 had a melting point of 115°C and a reduced viscosity of 1.9 dl/g.

The method for producing the heat-fusible fibers will now be described.
[Fiber manufacturing example 1]
Resin 1 was dried in a dehumidifying dryer at a drying temperature of 80°C for 8 hours, and then melt-extruded in a single-screw extruder at an extrusion temperature of 230°C. The resin was extruded from a spinneret having 400 nozzles and a nozzle diameter of 0.15 mm at a spinning temperature of 250°C and an output rate of 0.05 g/min per hole. The filaments were cooled by applying cooling air at 20°C and a wind speed of 0.5 m/s to a position approximately 100 mm to 900 mm below the spinneret, and then wound at a winding speed of 1000 m/min to obtain a multifilament having a fineness of 200 dtex/400 filaments.
50 of the obtained multifilaments were bundled together to form a tow, which was then cut to a fiber length of 5 mm with a rotary cutter at a cutting speed of 80 m/min and a cutting tension of 0.01 g/d to obtain a heat-fusible fiber made of resin 1 having a fineness of 0.5 dtex.

[Fiber manufacturing example 2]
Except for discharging at a discharge rate of 0.07 g/min per hole, a multifilament having a fineness of 280 dtex/400 filaments was obtained in the same manner as in Production Example 1. The obtained multifilament was cut under the same cutting conditions as in Production Example 1 to obtain a heat-fused fiber made of Resin 1 having a fineness of 0.7 dtex.

[Fiber manufacturing example 3]
Except for discharging at a discharge rate of 0.11 g/min per hole, a multifilament having a fineness of 440 dtex/400 filaments was obtained in the same manner as in Production Example 1. The obtained multifilament was cut under the same cutting conditions as in Production Example 1 to obtain a heat-fused fiber made of Resin 1 having a fineness of 1.1 dtex.

[Fiber Production Example 4]
Except for discharging at a discharge rate of 0.11 g/min per hole, a multifilament having a fineness of 440 dtex/400 filaments was obtained in the same manner as in Production Example 1. The obtained multifilament was cut under the same cutting conditions as in Production Example 1, except for a fiber length of 8 mm, to obtain a heat-fused fiber made of Resin 1 having a fineness of 1.1 dtex.

[Fiber Production Example 5]
Except for discharging at a discharge rate of 0.18 g/min per hole, a multifilament having a fineness of 720 dtex/400 filaments was obtained in the same manner as in Production Example 1. The obtained multifilament was cut under the same cutting conditions as in Production Example 1 to obtain a heat-fused fiber made of Resin 1 having a fineness of 1.8 dtex.

[Fiber Production Example 6]
Except for using Resin 2 synthesized in Resin Production Example 2 and setting the discharge rate per hole to 0.10 g/min, a multifilament having a fineness of 400 dtex/400 filaments was obtained in the same manner as in Production Example 1. The obtained multifilament was cut under the same cutting conditions as in Production Example 1 to obtain a heat-fused fiber made of Resin 2 having a fineness of 1.0 dtex.

[Fiber Production Example 7]
Except for using Resin 3 synthesized in Resin Production Example 3 and setting the discharge rate per hole to 0.10 g/min, a multifilament having a fineness of 400 dtex/400 filaments was obtained in the same manner as in Production Example 1. The obtained multifilament was cut under the same cutting conditions as in Production Example 1 to obtain a heat-fused fiber made of Resin 3 having a fineness of 1.0 dtex.

[Fiber Production Example 8]
Except for using Resin 3 as the resin and setting the discharge rate per hole to 0.10 g/min, a multifilament having a fineness of 400 dtex/400 filaments was obtained in the same manner as in Production Example 1. The obtained multifilament was cut under the same cutting conditions as in Production Example 1, except for setting the fiber length to 3 mm, to obtain a heat-fused fiber made of Resin 3 having a fineness of 1.0 dtex.

[Fiber Production Example 9]
Except for using Resin 4 and setting the discharge rate per hole to 0.10 g/min, a multifilament having a fineness of 400 dtex/400 filaments was obtained in the same manner as in Production Example 1. The obtained multifilament was cut under the same cutting conditions as in Production Example 1 to obtain a heat-fused fiber made of Resin 4 having a fineness of 1.0 dtex.

[Fiber Production Example 10]
Except for using Resin 4 as the resin and setting the discharge rate per hole to 0.14 g/min, a multifilament having a fineness of 560 dtex/400 filaments was obtained in the same manner as in Production Example 1. The obtained multifilament was cut under the same cutting conditions as in Production Example 1, except for setting the fiber length to 7 mm, to obtain a heat-fused fiber made of Resin 4 having a fineness of 1.4 dtex.

[Fiber Production Example 11]
Except for using Resin 5 and setting the discharge rate per hole to 0.10 g/min, a multifilament having a fineness of 400 dtex/400 filaments was obtained in the same manner as in Production Example 1. The obtained multifilament was cut under the same cutting conditions as in Production Example 1 to obtain a heat-fused fiber made of Resin 5 having a fineness of 1.0 dtex.

[Fiber Production Example 12]
The resin synthesized in Resin Production Example 6 was used, dried in a dehumidifying dryer at a drying temperature of 80°C for 8 hours, melt-extruded in a single-screw extruder at an extrusion temperature of 250°C, extruded from a spinneret with 400 nozzles and a nozzle diameter of 0.15 mm at a spinning temperature of 260°C and an output of 0.10 g/min per hole, cooled by blowing cooling air at 20°C and a wind speed of 0.5 m/s at a position about 100 mm to 900 mm below the spinneret, and wound at a winding speed of 1000 m/min to obtain a multifilament with a fineness of 400 dtex/400 filaments. The obtained multifilament was cut under the same cutting conditions as in Production Example 1 to obtain a heat-melting fiber 12 made of a resin 6 with a fineness of 1.0 dtex.

[Fiber Production Example 13]
Except for discharging at a discharge rate of 0.50 g/min per hole and cooling the filaments by applying cooling air at a speed of 0.9 m/s, a multifilament having a fineness of 2000 dtex/400 filaments was obtained in the same manner as in Production Example 1. The obtained multifilament was cut under the same cutting conditions as in Production Example 1 to obtain a heat-fused fiber made of Resin 1 having a fineness of 5.0 dtex.

[Fiber Production Example 14]
The resin used was Resin 7, which was dried at 60°C for 8 hours, melt-extruded at 180°C with a single-screw extruder, extruded from a spinneret with 400 nozzles and a nozzle diameter of 0.15 mm at a spinning temperature of 190°C and a discharge rate of 0.10 g/min per hole, cooled by blowing cooling air at 20°C and a wind speed of 0.5 m/s at a position about 100 mm to 900 mm below the spinneret, and wound at a winding speed of 1000 m/min to obtain a multifilament having a fineness of 400 dtex/400 filaments. The obtained multifilament was cut under the same cutting conditions as in Production Example 1 to obtain a heat-fused fiber made of 1.0 dtex polybutylene succinate.

[Example 1]
Polyethylene terephthalate fibers with a single fiber fineness of 0.15 dtex and a melting point of 255°C were produced by the direct spinning method, and cut to a length of 5 mm to form the main fiber. The fibers (short fiber fineness of 0.5 dtex, fiber length of 5 mm) produced in fiber production example 1 were used as the heat-fusible fibers. These short fibers were dispersed in water so that the weight ratio of the main fiber:heat-fusible fiber was 90:10 to form a slurry. A papermaking method was used to produce a papermaking sheet for surface fiber with a basis weight of 130 g/ ^m2 from this slurry. In addition, polyethylene terephthalate fibers with a single fiber fineness of 0.15 dtex and a melting point of 255°C were produced by the direct spinning method, and cut to a length of 5 mm to form the main fiber. These short fibers were dispersed in water so that the weight ratio of the main fiber:heat-fusible fiber was 97:3 to form a slurry. A papermaking method was used to produce a papermaking sheet for back fiber with a basis weight of 50 g/ ^m2 from this slurry. These two layers were laminated with a woven scrim having a basis weight of 100 g/ ^m2 and made of 166 dtex/48f polyethylene terephthalate fiber, with the sum of the MD and CD weave densities being 120 (threads/2.54 cm), to form a three-layer structure of surface fiber layer/scrim layer/back fiber layer. The three-layer laminate was entangled by spraying a high-speed water stream using a straight-flow spray nozzle, and then dried at 130°C for 5 minutes using an air-through dryer to obtain a three-layer nonwoven fabric.

The surface of the surface fiber layer of the obtained nonwoven fabric was buffed with 400 mesh sandpaper to give a nap treatment, and then the nonwoven fabric was slackened in a biaxial stretching tester X4HDHT manufactured by Toyo Seiki Seisakusho so that the shrinkage rate in the MD and CD directions was 5%, and the center and four corners of both sides were fixed with compressed air grips. The nonwoven fabric was then thermally annealed at 190°C for 5 minutes in a chamber to obtain a nonwoven fabric for artificial leather. Next, the fabric was dyed at 130°C using a blue disperse dye (BlueFBL: manufactured by Sumitomo Chemical) in a liquid flow dyeing machine and reduced and washed at 80°C to obtain a suede-like artificial leather. The manufacturing conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Example 2]
A suede-like artificial leather 2 was obtained in the same manner as in Example 1, except that the heat-fusible fibers were the fibers (short fiber fineness: 0.7 dtex, fiber length: 5 mm) produced in Fiber Production Example 2. The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Example 3]
A suede-like artificial leather 3 was obtained in the same manner as in Example 1, except that the thermally fusible fiber was changed to the fiber produced in Fiber Production Example 3 and the basis weight of the surface fiber sheet was changed to 140 g/ ^m2 . The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Example 4]
Suede-like artificial leather 4 was obtained in the same manner as in Example 1, except that the heat-fusible fiber was changed to the fiber produced in Fiber Production Example 4, the weight ratio of the surface fiber sheet was main fiber:heat-fusible fiber = 94:6, and the basis weight of the surface fiber sheet was 130 g/ ^m2 . The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Example 5]
A suede-like artificial leather 5 was obtained in the same manner as in Example 1, except that the fibers produced in Fiber Production Example 5 were used as the heat-fusible fibers and the basis weight of the surface fiber sheet was 80 g/ ^m2 . The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Example 6]
Suede-like artificial leather 6 was obtained in the same manner as in Example 1, except that the fibers produced in Fiber Production Example 6 were used as the heat-fusible fibers, the basis weight of the surface fiber sheet was 110 g/ ^m2 , the weight ratio of the surface fiber layer was main fiber:heat-fusible fiber = 92:8, and the thermal annealing temperature was 180° C. The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Example 7]
Suede-like artificial leather 7 was obtained in the same manner as in Example 1, except that the fibers produced in Fiber Production Example 7 were used as the heat-fusible fibers, the basis weight of the surface fiber sheet was 120 g/ ^m2 , and the thermal annealing temperature was 165° C. The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Example 8]
Suede-like artificial leather 8 was obtained in the same manner as in Example 1, except that the fibers produced in Fiber Production Example 8 were used as the heat-fusible fibers, the weight ratio of the surface fiber layer was main fiber:heat-fusible fiber = 91:9, and the thermal annealing temperature was 165° C. The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Example 9]
Suede-like artificial leather 9 was obtained in the same manner as in Example 1, except that the fibers produced in Fiber Production Example 9 were used as the heat-fusible fibers, the weight ratio of the surface fiber layer was main fiber:heat-fusible fiber = 93:7, and the thermal annealing temperature was 170° C. The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Example 10]
A suede-like artificial leather 10 was obtained in the same manner as in Example 1, except that the fibers produced in Fiber Production Example 10 were used as the heat-fusible fibers, the basis weight of the surface fiber sheet was 110 g/ ^m2 , the weight ratio of the surface fiber layer was main fiber:heat-fusible fiber = 95:5, and the thermal annealing temperature was 170° C. The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Example 11]
A suede-like artificial leather 11 was obtained in the same manner as in Example 1, except that the fibers produced in Fiber Production Example 11 were used as the heat-fusible fibers and the thermal annealing temperature was set to 170° C. The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Example 12]
A suede-like artificial leather 12 was obtained in the same manner as in Example 1, except that the fibers produced in Fiber Production Example 12 were used as the heat-fusible fibers and the thermal annealing temperature was 180° C. The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Comparative Example 1]
A suede-like artificial leather 13 was obtained in the same manner as in Example 1, except that the heat-fusible fibers were all-fusible type heat-fusible staple fibers Casven 8000 (manufactured by Unitika Ltd.) having a single fiber fineness of 0.7 dtex and a length of 5 mm. The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Comparative Example 2]
A suede-like artificial leather 14 was obtained in the same manner as in Example 1, except that the heat-fusible fibers were fully fusible heat-fusible staple fibers Casven 8000 (manufactured by Unitika Ltd.) having a single fiber fineness of 1.1 dtex and a length of ⁵ mm, and the surface fiber sheet had a basis weight of 110 g/m2. The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Comparative Example 3]
Suede-like artificial leather 15 was obtained in the same manner as in Example 3, except that the thermal annealing temperature was 130° C. The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Comparative Example 4]
A suede-like artificial leather 16 was obtained in the same manner as in Example 1, except that the fibers produced in Fiber Production Example 13 were used as the heat-fusible fibers and the basis weight of the surface fiber sheet was 140 g/ ^m2 . The production conditions and evaluation results of the obtained artificial leather are shown in Table 1 below.

[Comparative Example 5]
A suede-like artificial leather 17 was obtained in the same manner as in Example 1, except that the fibers produced in Fiber Production Example 14 were used as the heat-fusible fibers and the heat annealing temperature was set to 130° C. The production conditions and evaluation results of the obtained artificial leather are shown in the following Table 1. No heat-fusible points were detected in the artificial leather.

[Comparative Example 6]
Polyethylene terephthalate fibers having a single fiber fineness of 0.15 dtex and a melting point of 255°C were produced by a direct melt spinning method, and cut to a length of 5 mm to form main fibers. The main fibers were dispersed in water to form a slurry. A papermaking sheet for surface fibers having a basis weight of 130 g/ ^m2 was produced from the slurry by a papermaking method. Also, polyethylene terephthalate fibers having a single fiber fineness of 0.15 dtex and a melting point of 255°C were produced by a direct melt spinning method, and cut to a length of 5 mm to form main fibers. The main fibers were dispersed in water to form a slurry. A papermaking sheet for back fibers having a basis weight of 50 g/ ^m2 was produced from the slurry by a papermaking method. These two layers were laminated with a woven scrim having a basis weight of 100 g/ ^m2 and made of 166 dtex/48f polyethylene terephthalate fiber, with the sum of the MD and CD weave densities being 120 (threads/2.54 cm), to form a three-layer structure of surface fiber layer/scrim layer/back fiber layer. The three-layer laminate was entangled by spraying a high-speed water stream using a straight-flow spray nozzle, and then dried at 130°C for 5 minutes using an air-through dryer to obtain a three-layer nonwoven fabric.

The surface of the surface fiber layer of the obtained nonwoven fabric was buffed with 400 mesh sandpaper to perform a nap raising treatment, and then a polyether-based water-dispersed polyurethane emulsion ("Evaphanol AP-700" manufactured by Nicca Chemical Co., Ltd.) was mixed as a polymeric elastomer impregnation liquid at 9 mass % relative to the polymeric elastomer impregnation liquid, and _sodium sulfate ( _Na2SO4 ) was mixed as an impregnation aid at 3 mass % relative to the polymeric elastomer impregnation liquid, and the nonwoven fabric having a raised three-layer structure was impregnated with this impregnation liquid so that the adhesion rate relative to the weight of the fabric was 130%. The fabric was then heated and dried at 130°C using a pin tenter dryer to obtain an artificial leather fabric.
Next, the fabric was dyed at 130°C using a blue disperse dye (BlueFBL: manufactured by Sumitomo Chemical) in a liquid flow dyeing machine, and reduced and washed at 80°C to obtain a suede-like artificial leather. The manufacturing conditions and evaluation results of the obtained artificial leather are shown in Table 1 below. The heat-sealed points were evaluated by X-ray CT in the same manner as in Example 1, but the points were sufficiently smaller than the volume of the heat-sealed resin, and structures of 12 μm or less were treated as noise as described in (Operation x: Calculation of the size of high-brightness pixels), so evaluation could not be performed. Note that the average size of 30 adhesion points derived from the polyether-based water-dispersed polyurethane emulsion when observed at a magnification of 2000 times using the SEM used to evaluate the fineness was 4 μm or less in diameter.

In the artificial leather of the present invention, the thermoplastic resin bonding the main fibers having a fineness of 0.01 dtex or more and 0.5 dtex or less has an ion intensity ratio of positive ion m/z=71 (fragment ion: C4H7O) to positive ion m/z=27 (fragment ion: C2H3) of 0.2 to 2.3 in TOF-SIMS measurement, an ion intensity ratio of negative ion m/z=42 (fragment ion: CNO) to negative ion m/z=25 (fragment ion: C2H) of 0 to 0.5, and an ion intensity ratio (104/27) of positive ion m/z=104 (fragment ion: C7H4O) to positive ion m/z=27 (fragment ion: C2H3) of 0.2 to 1.0 inclusive, and the number average volume of the thermoplastic resin in the first surface fiber layer is 3,500 μm when the aggregate size of the thermoplastic resin is measured by X-ray-CT. Since the surface area of the artificial leather of the present invention is from ¹⁰⁰⁰ to 24,000 ^μm3 , the artificial leather has excellent feel and high abrasion resistance even without adding water-based polyurethane. If the main fiber and thermoplastic fiber used are polyester-based fibers and do not contain elastic polymers such as water-based polyurethane, the artificial leather has excellent flame resistance in that gas generated during combustion can be suppressed. Furthermore, the artificial leather of the present invention can be suitably used not only as a material for car interiors, but also in the fields of seat covering materials and interior materials for railway cars, aircraft, ships, etc., clothing, shoes, bags, smartphone cases, interiors, furniture, etc.

1 Main fiber 2 Lump resin 3 Unmelted resin (heat-fused fiber)
4. Sheath-core fibers

Claims (12)

An artificial leather comprising at least a surface fiber layer constituting a first surface, the artificial leather having the following characteristics:
(1) The surface fiber layer contains a main fiber and a thermoplastic resin;
(2) The fineness of the main fiber is 0.01 dtex or more and 0.5 dtex or less;
(3) At least a portion of the thermoplastic resin bonds the main fibers;
(4) The thermoplastic resin has the following properties as determined by time-of-flight secondary ion mass spectrometry (TOF-SIMS):
(i) the ratio (71/27) of the ion intensity of the positive ion m/z = 71 (fragment ion: C4H7O) to that of the positive ion m/z = 27 (fragment ion: C2H3) is 0.2 or more and 2.3 or less; and (ii) the ratio (42/25) of the ion intensity of the negative ion m/z = 42 (fragment ion: CNO) to that of the negative ion m/z = 25 (fragment ion: C2H) is 0 or more and 0.5 or less;
(iii) the ratio (104/27) of the ion intensity of the positive ion m/z=104 (fragment ion: C7H4O) to that of the positive ion m/z=27 (fragment ion: C2H3) is 0.2 or more and 1.0 or less; and (5) the number average volume of the thermoplastic resin is 3500 ^μm3 or more and 24000 ^μm3 or less;
and
The subject fiber is a polyester fiber, and
The thermoplastic resin is a polyester-based resin, and
the volumetric particle density of the thermoplastic resin per unit volume in the surface fiber layer is 0.5×10 ^particles /m ^or more and 5.0×10 ^particles /m or ^less ;
Artificial leather. 2. The artificial leather according to claim 1 , wherein the thermoplastic resin is approximated as an ellipse, and an average quotient of the major axis divided by the minor axis is 100 or less. 3. The artificial leather according to claim 1, wherein the surface fiber layer is intertwined with a scrim layer which is a woven fabric. The artificial leather according to claim 3 , wherein the scrim layer is made of polyester-based resin fibers. The artificial leather according to any one of claims 1 to 4 , wherein when the surface is abraded with a pressing load of 12 kPa in accordance with JIS-L-1096 E method (Martindale method), the scrim is not exposed when the abrasion number is less than 50,000. The artificial leather according to any one of claims 1 to 5 , wherein when the surface is abraded with a pressing load of 12 kPa in accordance with JIS-L-1096 E method (Martindale method), the abrasion loss is 21 mg or less after 50,000 abrasion cycles. The following steps:
(1) mixing a main fiber with a heat-fusible fiber made of a thermoplastic resin having the characteristic (3) as measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS) so that the weight ratio of the heat-fusible fiber is 3% or more and 25% or less, entangling the mixture by wet papermaking, and then forming a surface fiber web by a hydroentanglement treatment or a needle punching method; and (2) forming a surface fiber layer by thermal annealing the entangled structure of the obtained surface fiber web at a temperature equal to or higher than the melting point of the heat-fusible fiber and lower than the melting point of the main fiber;
The method for producing the artificial leather according to any one of claims 1 to 6 , comprising: The method according to claim 7 , wherein the fiber length of the heat-fusible fiber made of the thermoplastic resin is 2 mm to 90 mm. The method according to claim 7 or 8 , wherein the fiber diameter of the heat-fusible fiber is 0.5 dtex or more and 2.2 dtex or less. The method according to any one of claims 7 to 9 , wherein the heat-fusible fibers are produced by melt spinning the thermoplastic resin. The method according to any one of claims 7 to 10 , wherein 95% by weight or more of the resin contained in the heat-sealable fibers is a copolymer of polyester and aliphatic polyether. The method according to any one of claims 7 to 11 , wherein the melting point of the thermoplastic resin is 130°C or higher and is lower than the melting point of the subject fiber by 20°C or higher.

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