JP7840102B2 - synthetic leather - Google Patents

Description

This invention relates to synthetic leather comprising a laminate containing a base material and a resin layer directly or indirectly provided on one side of the base material.

Synthetic leather is widely used on the surfaces of electronic devices, vehicle and aircraft seats, etc., due to its luxurious appearance, pleasant feel, and high durability. Examples of electronic devices where synthetic leather is used include personal computers, tablet devices, mobile phones, and headphones, with synthetic leather being applied to the cases, covers, and keyboard surfaces of these devices. Examples of vehicles where synthetic leather is used include automobiles and railway cars.

As an example of this type of synthetic leather, a nubuck-like sheet material with a surface dynamic friction coefficient (average surface dynamic friction coefficient MIU) of 0.20 to 0.50 has been proposed (see Patent Document 1).

International Publication No. 2015/136921

Synthetic leather is required to have a moderate degree of slipperiness and excellent surface tactile properties (hereinafter also referred to as "surface touch properties").

In this regard, nubuck-like synthetic leather, as shown in Patent Document 1 above, is not slippery, which tends to make handling products to which synthetic leather is applied (applicable products) such as electrical appliances difficult. On the other hand, if the synthetic leather is slippery, it is easy to drop the applicable product when handling it, which may lead to damage.

This invention was made in view of the above-mentioned problems, and aims to provide synthetic leather with excellent surface touch (having a moderate level of smoothness).

As shown in Patent Document 1 above, conventional synthetic leathers were evaluated based on the average surface dynamic friction coefficient MIU. However, it was difficult to design synthetic leathers with excellent surface touch properties using the average surface dynamic friction coefficient MIU. Therefore, after diligent research, the inventors discovered that by cutting out a fabric from the synthetic leather to rub against the measurement sample, measuring the dynamic friction coefficient Ra using both the sample and the fabric, and evaluating the properties of the synthetic leather based on this dynamic friction coefficient Ra, it is possible to design synthetic leathers with excellent surface touch properties. This led to the completion of the present invention.

In other words, the characteristic configuration of synthetic leather according to one embodiment of the present invention for solving the above problem is:
A synthetic leather comprising a laminate including a base material and a resin layer directly or indirectly provided on one side of the base material,
The aforementioned resin layer comprises a polyether-based polyurethane resin and a polycarbonate-based polyurethane resin.
The laminate is cut to a size of 63 mm x 63 mm, and the surface of the resin layer on the resulting cut piece is rubbed with the same fabric at a load of 500 gf (4.90 N) and a speed of 1000 mm/min. The coefficient of dynamic friction Ra is given by the following formula (1):
0.70≦Ra≦1.00...(1)
The objective is to be configured in such a way that it satisfies the following conditions.

With this synthetic leather configuration, the dynamic friction coefficient Ra satisfies formula (1) above, resulting in a synthetic leather that is neither too slippery nor too slippery, but possesses a moderate degree of slipperiness, thus exhibiting excellent surface touch properties.

In the synthetic leather according to the present invention,
The coefficient of dynamic friction Ra and,
The laminate is cut to a size of 63 mm x 63 mm, and the surface of the resin layer on the resulting cut piece is rubbed with the same fabric at a load of 200 gf (1.96 N) and a speed of 100 mm/min. The coefficient of dynamic friction Rb is given by the following equation (2):
0.6≦Ra/Rb≦0.8...(2)
It is preferable that it be configured to satisfy the following conditions.

According to this synthetic leather configuration, by using a dynamic friction coefficient Rb in addition to the dynamic friction coefficient Ra, and by satisfying the ratio Ra/Rb of the dynamic friction coefficients Ra and Rb in formula (2) above, the synthetic leather exhibits excellent surface touch properties.

In the synthetic leather according to the present invention,
The surface roughness (SMD) of the resin layer is preferably 0.35 to 0.80 μm.

With this synthetic leather configuration, the surface roughness (SMD) of the resin layer is 0.35 to 0.80 μm, resulting in a synthetic leather with excellent surface touch properties.

In the synthetic leather according to the present invention,
It is preferable that minute irregularities with a depth of 7 to 38 μm and spacing of 29 to 120 μm are formed on the surface of the resin layer.

In this synthetic leather configuration, the resin layer has minute irregularities with a depth of 7 to 38 μm and spacing of 29 to 120 μm, resulting in a synthetic leather with excellent surface touch properties.

In the synthetic leather according to the present invention,
Preferably, the resin layer is substantially free of organic solvents.

With this synthetic leather configuration, the resin layer substantially does not contain organic solvents, thus reducing the harmful effects on the body.

Figure 1 is a schematic cross-sectional view showing a synthetic leather according to an embodiment of the present invention. Figure 2 is a schematic cross-sectional view showing the state in which release paper is laminated on the resin layer of synthetic leather during the manufacturing of synthetic leather according to an embodiment of the present invention.

The synthetic leather of the present invention will be described below with reference to the drawings. However, the present invention is not intended to be limited to the configuration described below or the embodiments described later. Note that the actual size relationships of each layer of the synthetic leather in each figure are not strictly reproduced, but are exaggerated as appropriate for ease of explanation. Furthermore, in this specification, the "surface" of the resin layer in synthetic leather refers to the outer surface exposed to the outside on the opposite side of the product to which the synthetic leather is applied when it is provided on the surface of the product to which it is applied.

<Synthetic leather>
Figure 1 is a schematic cross-sectional view showing the structure of synthetic leather 1 according to an embodiment of the present invention. The synthetic leather 1 of this embodiment comprises a laminate 30 including a base material 10 and a resin layer 20 directly or indirectly provided on one side of the base material 10 (the upper side in Figure 1). In this embodiment, the laminate 30 further comprises an adhesive layer 40 between the base material 10 and the resin layer 20 (i.e., the resin layer 20 is indirectly provided on one side of the base material 10), but the synthetic leather of the present invention can also be configured such that the laminate 30 does not include an adhesive layer 40.

(Base material)
Examples of the base material 10 include fibrous base materials and thermoplastic resin films. For example, a fibrous base material is preferred when improving chemical resistance, and a thermoplastic resin film is preferred when improving surface touchability and heat press resistance.

When the base material 10 is a fibrous base material, examples of fibrous base materials include knitted fabrics, woven fabrics, nonwoven fabrics, and other woven materials. For woven materials, it is also possible to use materials that have been coated or impregnated with conventionally known solvent-based or solvent-free (including water-based) polymer solutions (preferably polyurethane resin or its copolymer, or a polymer solution mainly composed of polyurethane resin), and then dry-coagulated or wet-coagulated. Furthermore, the material of the fibers constituting the base material 10 is not particularly limited; examples include conventionally known fibers such as natural fibers, regenerated fibers, semi-synthetic fibers, and synthetic fibers, and two or more of these may be combined. Among these, synthetic fibers are preferred from the viewpoint of heat resistance and light resistance, polyester fibers are more preferred, and polyethylene terephthalate fibers are even more preferred.

When the base material 10 is a thermoplastic resin film, examples of thermoplastic resin films include polyvinyl butyral (PVB), ethylene vinyl acetate (EVA), polyethylene terephthalate (PET), polyurethane (PU), polypropylene (PP), polyacrylate, polyethylene (PE), polycarbonate (PC), polymethyl methacrylate, and polyvinyl chloride. However, from the viewpoint of flexibility, elongation, and adhesion, thermoplastic polyurethane resin films are preferred.

The base material 10 is preferably one with a flat surface on the resin layer 20 side. In this regard, it is preferable to use, for example, knitted fabrics such as jersey knit, rib knit, pearl knit, and smooth knit; woven fabrics such as plain weave, twill weave, and satin weave; or films made of thermoplastic resins such as polyurethane resin, polyethylene terephthalate resin, polyethylene naphthalate resin, polypropylene resin, and polyethylene resin.

The thickness of the base material 10 is preferably 0.05 to 1.5 mm, and more preferably 0.1 to 0.5 mm, from the viewpoint of improving the surface touch, chemical resistance, and heat press resistance of the synthetic leather 1. The base material 10 may also be colored with dyes or pigments.

(Resin layer)
The resin layer 20 contains a polyether-based polyurethane resin and a polycarbonate-based polyurethane resin. The inclusion of both polyether-based and polycarbonate-based polyurethane resins in the resin layer 20 results in the synthetic leather 1 having excellent surface touch properties.

Here, for example, an applied product made of synthetic leather tends to come into frequent contact with human skin (and the oils present in the skin). Furthermore, human skin often has various chemicals (sunscreen, hand cream, disinfectant, etc.) applied to it. Thus, synthetic leather is frequently exposed to these chemicals, and contact with the resin layer of the synthetic leather can cause adverse effects such as swelling, dissolution, and discoloration of the resin layer.

However, by including both a polyether-based polyurethane resin and a polycarbonate-based polyurethane resin in the resin layer 20, it is possible not only to suppress the softening of the resin layer 20 due to heating and pressurization during hot pressing, i.e., to improve heat press resistance, but also to further improve chemical resistance.

As the polyether-based polyurethane resin, a water-based polyether-based polyurethane resin is preferred, and as the polycarbonate-based polyurethane resin, a water-based polycarbonate-based polyurethane resin is preferred. Thus, by using water-based resins for the polyether-based and polycarbonate-based polyurethane resins, the inclusion of organic solvents in the resin layer 20 of the synthetic leather 1 can be suppressed.

The mass ratio (blending ratio) of polyether-based polyurethane resin to polycarbonate-based polyurethane resin, expressed as polyether-based polyurethane resin:polycarbonate-based polyurethane resin, is preferably 20:80 to 80:20, and more preferably 30:70 to 50:50. By keeping the blending ratio within this range, the surface touch, chemical resistance, and heat press resistance of the synthetic leather can be improved.

The total content (in terms of solids) of polyether-based polyurethane resin and polycarbonate-based polyurethane resin in the resin layer 20 is preferably 55 to 93% by mass, and more preferably 70 to 85% by mass. By keeping the total content within this range, the surface touch, chemical resistance, and heat press resistance of the synthetic leather 1 can be improved. The resin layer 20 may also contain polyurethane resins other than polyether-based polyurethane resin and polycarbonate-based polyurethane resin, as well as other resins.

The resin layer 20 preferably further contains a crosslinking agent. Examples of crosslinking agents include carbodiimide-based crosslinking agents, isocyanate-based crosslinking agents, and melamine-based crosslinking agents, but carbodiimide-based crosslinking agents (with a high degree of crosslinking) are more preferred. The crosslinking agent content (in terms of solid content) in the resin layer 20 is preferably 2 to 10% by mass, and more preferably 2 to 5% by mass.

The resin layer 20 may contain additives other than resin and crosslinking agents. Examples of such additives include wettability enhancers, defoamers, pigments, film-forming aids, smoothers, matting agents, fillers, and thickeners. Examples of wettability enhancers include silicone-based surfactants, fluorine-based surfactants, acetylene-based surfactants, and organic solvents. Examples of defoamers include silicone-based surfactants, fluorine-based surfactants, and acetylene-based surfactants. Examples of pigments include inorganic pigments such as titanium dioxide and carbon black, organic pigments, and dyes. Examples of film-forming aids include organic solvents. Examples of smoothers include silicone-based oils, silicone-based powders, fluorine-based resins, and silicone-modified resins. Examples of matting agents include urethane beads and silica particles. Examples of fillers include calcium carbonate. Examples of thickeners include alkaline thickeners and urethane-associative thickeners. The content of additives in the resin layer 20 can be appropriately set to an extent that does not adversely affect the surface touchability, chemical resistance, and heat press resistance of the resin layer 20.

The basis weight (mass of the resin layer 20 per unit area) of the resin layer 20 is preferably 30 g/ ^m² to 150 g/ ^m² , and more preferably 60 g/ ^m² to 80 g/ ^m² . By having a basis weight of 30 g/ ^m² to 150 g/ ^m² for the resin layer 20, the surface touch, chemical resistance, and heat press resistance of the synthetic leather 1 can be improved.

The thickness of the resin layer 20 is preferably 20 to 150 μm, and more preferably 50 to 80 μm. A resin layer thickness of 20 to 150 μm improves the surface touch, chemical resistance, and heat press resistance of the synthetic leather 1. Here, the thickness of the resin layer 20 is measured by photographing a vertical cross-section of the synthetic leather 1 using a microscope (Keyence Corporation, Digital HF Microscope VH-8000), measuring the thickness of the resin layer 20 at 10 arbitrary locations in the obtained image (photograph), and calculating the average value of the measurement results.

The resin layer 20 preferably contains substantially no organic solvents. Here, "substantially no organic solvents" means that the organic solvent content in the synthetic leather is 5 ppm by mass or less.

For example, when an organic solvent such as N,N-dimethylformamide (DMF) is used to form the resin layer, there is a risk that the organic solvent may remain in the formed resin layer. If the resin layer contains an organic solvent, the synthetic leather containing this resin layer may cause harm to the body. However, because the resin layer 20 substantially does not contain an organic solvent, the harmful effects on the body of the synthetic leather 1 are suppressed.

(Adhesive layer)
The adhesive layer 40 is placed between the substrate 10 and the resin layer 20 to bond the substrate 10 and the resin layer 20. The adhesive layer 40 contains, for example, a polyurethane resin and a crosslinking agent. Examples of polyurethane resins include water-based polyurethane resins. Examples of crosslinking agents include isocyanate-based crosslinking agents, blocked isocyanate-based crosslinking agents, and carbodiimide-based crosslinking agents. In addition to the polyurethane resin and crosslinking agent, the adhesive layer 40 may also contain additives. Examples of additives include wettability improvers, defoamers, thickeners, fillers, and flame retardants. Examples of wettability improvers include silicone-based surfactants, fluorine-based surfactants, acetylene-based surfactants, and organic solvents. Examples of defoamers include silicone-based surfactants, fluorine-based surfactants, and acetylene-based surfactants. Examples of thickeners include alkaline thickeners and urethane-associated thickeners. Examples of fillers include calcium carbonate. Examples of flame retardants include phosphorus-based flame retardants, bromine-based flame retardants, and antimony trioxide-based flame retardants.

The basis weight (mass of adhesive layer 40 per unit area) of the adhesive layer 40 is preferably 20 g/ ^m² to 150 g/ ^m² , and more preferably 60 g/ ^m² to 80 g/ ^m² . By having a basis weight of 20 g/ ^m² to 150 g/ ^m² for the adhesive layer 40, the adhesive layer 40 can bond the substrate 10 and the resin layer 20 more firmly.

The thickness of the adhesive layer 40 is preferably 20 to 200 μm, and more preferably 50 to 150 μm. A thickness of 20 to 200 μm for the adhesive layer 40 allows for stronger adhesion between the substrate 10 and the resin layer 20. Here, the thickness of the adhesive layer 40 is measured by photographing a vertical cross-section of the synthetic leather 1 using a microscope (Keyence Corporation, Digital HF Microscope VH-8000), measuring the thickness of the adhesive layer 40 at 10 arbitrary locations in the obtained image (photograph), and calculating the average value of the measurement results.

In this invention, a measurement sample and a matching fabric for rubbing the measurement sample are cut from the synthetic leather 1, the dynamic friction coefficient Ra is measured using the measurement sample and the matching fabric, and the properties of the synthetic leather 1 are evaluated based on this dynamic friction coefficient Ra, thereby enabling the design of the synthetic leather 1 to have excellent surface touch properties. Specifically, the synthetic leather 1 is obtained by cutting the laminate 30 to dimensions of 63 mm x 63 mm, and rubbing the surface 21 of the resin layer 20 of the obtained cut piece with the matching fabric at a load of 500 gf (4.90 N) and a speed of 1000 mm/min, and the dynamic friction coefficient Ra is given by the following formula (1):
0.70≦Ra≦1.00...(1)
It is configured to satisfy the following conditions. The "matching fabric" used in this embodiment is obtained separately from the cut pieces by cutting the laminate to dimensions of 200 mm x 200 mm. Hereinafter, "matching fabric" is synonymous. The dynamic friction coefficient Ra is the value obtained by dividing the average value (N) of the frictional force in the force region excluding the peak immediately after moving the cut piece relative to the matching fabric, in a graph plotting the relationship between the force applied to the cut piece when moving the cut piece and the frictional force, by the load (N).

The surface touch properties of the synthetic leather 1 can be improved by having a dynamic friction coefficient Ra of 0.70 or more and 1.00 or less. From the viewpoint of improving surface touch properties, a dynamic friction coefficient Ra of 0.73 or more and 0.94 or less is preferable, and a value of 0.77 or more and 0.87 or less is more preferable.

When measuring the coefficient of dynamic friction Ra, the static friction coefficient Rc, which is measured together with the coefficient of dynamic friction Ra, is preferably between 0.9 and 1.3. Here, the static friction coefficient Rc is the value obtained by dividing the peak friction force (N) immediately after moving the cut piece relative to the fabric, as shown in the graph plotting the relationship between the applied force and the frictional force during the measurement of the coefficient of dynamic friction Ra, by the load (N).

By having a static friction coefficient Rc of 0.9 or higher and 1.3 or lower, the surface touch properties of the synthetic leather 1 can be improved.

In this invention, the properties of the synthetic leather 1 can be evaluated based on the above-mentioned dynamic friction coefficient Ra and the dynamic friction coefficient Rb measured under different conditions, thereby enabling the design of the synthetic leather 1 to have excellent surface touch properties. Specifically, the dynamic friction coefficient Ra of the synthetic leather 1 and the dynamic friction coefficient Rb obtained when the laminate 30 is cut to dimensions of 63 mm x 63 mm and the surface 21 of the resin layer 20 of the obtained cut piece is rubbed with the same fabric at a load of 200 gf (1.96 N) and a speed of 100 mm/ min are given by the following equation (2):
0.6≦Ra/Rb≦0.8...(2)
It is preferable that it be configured to satisfy the following conditions.

By having a ratio of the coefficient of dynamic friction Ra to the coefficient of dynamic friction Rb (Ra/Rb) of 0.6 to 0.8, the surface touch properties of the synthetic leather 1 can be improved.

When measuring the coefficient of dynamic friction Rb, the static friction coefficient Rd, which is measured together with the coefficient of dynamic friction Rb, is preferably between 1.0 and 1.6. Here, the static friction coefficient Rd is the value obtained by dividing the peak friction force (N) immediately after moving the cut piece relative to the fabric, as shown in the graph plotting the relationship between the applied force and the friction force during the measurement of the coefficient of dynamic friction Rb, by the load (N).

By having a static friction coefficient Rd of 1.0 or higher and 1.6 or lower, the surface touch properties of the synthetic leather 1 can be improved.

In synthetic leather 1, the surface roughness (SMD) of the resin layer 20 (surface 21) is preferably 0.35 to 0.80 μm, and more preferably 0.40 to 0.70 μm. Here, the surface roughness (SMD) of the resin layer 20 is measured by using synthetic leather 1 as a sample, attaching this sample to a KES surface tester (KES-FB4-A, manufactured by Kato Tech Co., Ltd.), and moving a wire sensor with a diameter (thickness) of 0.5 mm and a contact width of 5 mm over the sample at a speed of 1 mm/sec while applying a load of 10 gf.

The surface roughness (SMD) of the resin layer 20 being 0.35 to 0.80 μm improves the surface touch properties of the synthetic leather 1.

In the synthetic leather 1, it is preferable that minute irregularities with a depth of 7 to 38 μm and spacing of 29 to 120 μm are formed on the surface 21 of the resin layer 20. Here, the depth and spacing of the minute irregularities are measured by photographing a vertical cross-section of the synthetic leather 1 using a microscope (Keyence Corporation, Digital HF Microscope VH-8000), measuring the depth and spacing of the irregularities on the surface 21 of the resin layer 20 at 10 arbitrary locations in the obtained image (photograph), and calculating the average value of the measurement results.

By forming minute irregularities with a depth of 7 to 38 μm and spacing of 29 to 120 μm on the surface 21 of the resin layer 20, the surface touch properties of the synthetic leather 1 can be improved.

In the synthetic leather 1, the gloss value of the surface 21 of the resin layer 20, measured at an incident angle of 60°, is preferably 0.2 to 0.6. Here, the gloss value of the surface 21 of the resin layer 20 is measured using Microgloss 60°S (manufactured by BYK).

By having a gloss value of 0.2 to 0.6 on the surface 21 of the resin layer 20, the surface touch properties of the synthetic leather 1 can be improved.

In synthetic leather 1, it is preferable that the rigidity of the laminate 30, measured according to JIS L1096 Method A, 45° cantilever method, is 16 to 25 mm in the vertical direction and 14 to 29 mm in the horizontal direction.

The rigidity of the laminate 30 is 16-25 mm in the vertical direction and 14-29 mm in the horizontal direction, which improves the surface touch properties of the synthetic leather 1.

(Manufacturing of synthetic leather)
The synthetic leather 1 of this embodiment can be manufactured by carrying out the following steps. Specifically, a coating liquid for forming a resin layer 20 is applied to the release treatment surface of the release paper 50, and the resin layer 20 is formed by drying and curing (resin layer formation step). After the formation of the resin layer 20, a coating liquid for forming an adhesive layer 40 is applied to the resin layer 20 (i.e., on the side of the resin layer 20 opposite to the release paper 50), and the adhesive layer is formed in a semi-cured state by drying without completely curing (adhesive layer formation step). After the formation of the semi-cured adhesive layer, the base material 10 is placed on the surface of the semi-cured adhesive layer, pressure is applied, and then the semi-cured adhesive is cured by drying, thereby bonding the resin layer 20 and the base material 10 via the adhesive layer 40 (adhesion step). As a result, as shown in Figure 2, a laminate 1' with release paper is obtained in which the release paper 50, resin layer 20, adhesive layer 40, and base material 10 are laminated in this order. Then, the release paper 50 is peeled off the resulting laminate 1' with the release paper attached (i.e., the laminate 30 (synthetic leather 1) with the release paper 50 laminated on the resin layer 20) (peeling step). In this way, synthetic leather 1 can be manufactured by performing the resin layer formation step, adhesive layer formation step, adhesive step, and peeling step.

The release paper 50 used in the peeling process is removably bonded to the resin layer 20 during the manufacturing of the synthetic leather 1. The release paper 50 may remain bonded to the synthetic leather 1 after its manufacture until it is applied to the surface of the product to be treated.

It is preferable that minute irregularities with a depth of 7 to 10 μm and spacing of 30 to 135 μm are formed on the release surface of the release paper 50 (i.e., the surface facing the resin layer 20). Here, the depth and spacing of the minute irregularities are measured by photographing the vertical cross-section of the release paper 50 using a microscope (Keyence Corporation, Digital HF Microscope VH-8000), measuring the depth and spacing of the irregularities on the release surface at 10 arbitrary locations in the obtained image (photograph), and calculating the average value of the measurement results.

Examples of such release paper 50 include Spectra 800 (manufactured by Sappi), FRZ (manufactured by Lintec Corporation), and R331 (manufactured by Lintec Corporation).

In the resin layer formation process, polyurethane resin (polyether-based polyurethane resin and polycarbonate-based polyurethane resin), a crosslinking agent, and other additives are used as raw materials for the resin layer 20. These are mixed to prepare a coating solution, which is then applied to the release surface of the release paper 50 before curing. The solution is then heated at a predetermined temperature for a predetermined time to dry. This forms the resin layer 20 as a cured body. It is preferable to apply the coating solution to the substrate 10 within 24 hours after mixing the polyurethane resin and crosslinking agent.

In the adhesive layer formation process, a water-based polyurethane resin, a crosslinking agent, and other additives are used as raw materials for the adhesive layer 40. These are mixed to prepare a coating solution, which is then applied to the resin layer 20 (i.e., the side of the resin layer 20 opposite to the release paper 50) before it hardens. The solution is then heated at a predetermined temperature for a predetermined time to dry it, preventing complete hardening. This forms a semi-hardened adhesive layer. It is preferable to apply the coating solution to the resin layer 20 within four hours of mixing the polyurethane resin and crosslinking agent. Furthermore, if the synthetic leather 1 does not contain an adhesive layer 40, the adhesive layer formation process can be omitted.

In the bonding process, the substrate 10 is laminated onto a semi-cured adhesive layer. The resulting laminate is then pressurized at a predetermined pressure for a predetermined time, and subsequently aged at a predetermined temperature for a predetermined time to cure the semi-cured adhesive layer. This results in a laminate 1' in which the release paper 50, resin layer 20, adhesive layer 40, and substrate 10 are laminated in that order.

Furthermore, if the synthetic leather 1 does not contain an adhesive layer 40, a laminate is obtained in which the release paper 50, resin layer 20, and base material 10 are laminated in that order by directly laminating the base material 10 onto the resin layer 20. In this case, after applying the coating liquid for forming the resin layer 20 onto the base material 10, the base material is laminated and heated at a predetermined temperature for a predetermined time to dry. This results in a laminate 1' in which the release paper 50, resin layer 20, and base material 10 are laminated in that order.

In the peeling process, the release paper 50 is peeled off from the laminate 1' with the release paper attached. This yields the synthetic leather 1.

As described above, the synthetic leather 1 of this embodiment has a resin layer 20 containing a polyether-based polyurethane resin and a polycarbonate-based polyurethane resin, and the dynamic friction coefficient Ra of the laminate 30 satisfies 0.70 to 1.00. As a result, the synthetic leather 1 has moderate slipperiness, excellent surface touch, and also excellent chemical resistance and heat press resistance.

To verify the surface touch properties, chemical resistance, and heat press resistance of the synthetic leather of the present invention, synthetic leather (Examples 1-8) possessing the characteristic configuration of the present invention was prepared. For comparison, synthetic leather (Comparative Examples 1-7) lacking some or all of the characteristic configuration of the present invention was also prepared.

[Example 1]
As shown in Table 1, Spectra800 (manufactured by Sappi, with a texture depth of 7 μm and a texture spacing of 30 μm) was used as the release paper. A coating solution for forming a resin layer was prepared by mixing the following based on the formulation in Table 1: polyether-based polyurethane resin I (DS-450 (manufactured by DIC Corporation), water-based), polycarbonate-based polyurethane resin I (DS-300 (manufactured by DIC Corporation), water-based), wettability enhancer (BYK-3455 (manufactured by BYK Corporation)), defoaming agent (TEGO Formex 800 (manufactured by EVONIC Corporation)), pigment (carbon black), film-forming aid (1,3-butanediol (Tokyo Chemical Industries, Ltd.)), crosslinking agent I (highly crosslinked carbodiimide crosslinking agent (V-02-L2, Nisshinbo Chemical Inc.)), and thickener I (Borchi Gel A LA (manufactured by Borchers Corporation)). In Table 1, "-" indicates that the component is not included.

Before the obtained coating solution hardened (specifically, before 24 hours had elapsed after contacting the water-based polyether-based polyurethane resin and water-based polycarbonate-based polyurethane resin with the crosslinking agent), the coating solution was applied to the release surface of the release paper using a comma coater to a coating thickness of 140 μm (solid content of 70 g/ ^m² ). After application, the coating was dried by heating in a dryer at a heating temperature of 80°C for 5 minutes to form a resin layer as a hardened body.

The coating solution for forming the adhesive was prepared by mixing a polycarbonate/polyether polyurethane resin (DA-700 (manufactured by DIC Corporation), water-based), a wettability enhancer (BYK-3455 (manufactured by BYK Corporation)), an antifoaming agent (TEGO Formex 800 (manufactured by EVONIC Corporation)), a crosslinking agent III (isocyanate crosslinking agent (BAYHYDUR XP2655, manufactured by Covestro Corporation)), and a thickening agent II (Borchi Gel 0626 (manufactured by Borchers Corporation)) based on the formulation in Table 1.

Before the obtained coating solution hardened (specifically, within 4 hours after contacting the water-based polyurethane resin with the crosslinking agent), the coating solution was applied to the resin layer using a comma coater to a coating thickness of 170 μm (solid content of 70 g/ ^m² ). After application, the coating solution was dried using a drying oven at a heating temperature of 80°C for 4 minutes to prevent complete hardening, thereby forming a semi-cured adhesive layer.

On the obtained semi-cured adhesive layer, as shown in Table 1, a 44-gauge circular knit smooth PET33T/36f (33dtex/36f polyethylene terephthalate fiber) (number of needles per inch (2.45 cm) of knitting machine) was placed and pressed at a pressure of 4 kgf/ ^cm² for 1 minute. The resulting laminate was aged at 50°C for 48 hours to cure the semi-cured adhesive layer, thereby bonding the resin layer and the substrate via the adhesive layer. After that, the synthetic leather of Example 1 was produced by peeling off the release paper. Table 1 shows the depth and spacing of the minute irregularities on the release surface of the release paper used, measured using the measurement method described above.

[Examples 2, 3, and 5]
Synthetic leathers for Examples 2, 3, and 5 were prepared in the same manner as in Example 1, except that the proportions of polyether-based polyurethane resin I and polycarbonate-based polyurethane resin I were changed as shown in Table 1.

[Example 4]
As shown in Table 1, the synthetic leather of Example 4 was prepared in the same manner as in Example 3, except that crosslinking agent II (carbodiimide crosslinking agent (V-02, Nisshinbo Chemical Co., Ltd.)) was used instead of crosslinking agent I (highly crosslinked carbodiimide crosslinking agent (V-02-L2, Nisshinbo Chemical Co., Ltd.)) as the crosslinking agent.

[Example 6]
As shown in Table 2, the synthetic leather of Example 6 was prepared in the same manner as in Example 3 (see Table 1), except that FRZ (Lintec Corporation, with a surface depth of 10 μm and a surface spacing of 125 μm) was used as the release paper instead of Spectra 800 (Sappi). Table 2 shows the results of measuring the depth and spacing of the minute surface irregularities on the release paper used, using the measurement method described above. In Table 2, "-" indicates that the component was not included.

[Example 7]
As shown in Table 2, the synthetic leather of Example 7 was prepared in the same manner as in Example 3 (see Table 1), except that R331 (Lintec Corporation, with a texture depth of 8 μm and a texture spacing of 42 μm) was used as the release paper instead of Spectra 800 (Sappi Inc.).

[Example 8]
As shown in Table 2, the synthetic leather of Example 8 was prepared in the same manner as in Example 3 (see Table 1), except that a thermoplastic polyester polyurethane resin (TPU) film (hardness 85A) was used as the base material instead of PET 33T/36f circular knit smooth 44 gauge.

[Comparative Example 1]
As shown in Table 2, the synthetic leather of Comparative Example 1 was prepared in the same manner as in Example 1 (see Table 1), except that polycarbonate-based polyurethane resin I was not used, and instead 100 parts by mass of polyether-based polyurethane resin I was used.

[Comparative Example 2]
As shown in Table 2, the synthetic leather of Comparative Example 2 was prepared in the same manner as in Example 1 (see Table 1), except that polyether-based polyurethane resin I was not used, and instead 100 parts by mass of polycarbonate-based polyurethane resin I was used.

[Comparative Example 3]
As shown in Table 3, the synthetic leather of Comparative Example 3 was prepared in the same manner as in Example 3 (see Table 1), except that R86M (Lintec Corporation, with a surface depth of 37 μm and a surface spacing of 750 μm) was used as the release paper instead of Spectra 800 (Sappi). Table 3 shows the results of measuring the depth and spacing of the minute surface irregularities on the release surface of the release paper used, using the measurement method described above. In Table 3, "-" indicates that the component was not included.

[Comparative Example 4]
As shown in Table 3, the synthetic leather of Comparative Example 4 was prepared in the same manner as in Example 3 (see Table 1), except that TPD130 (Lintec Corporation, with a texture depth of 3 μm and a texture spacing of 160 μm) was used as the release paper instead of Spectra800 (Sappi Inc.).

[Comparative Example 5]
As shown in Table 3, DE-90 (manufactured by Dai Nippon Printing Co., Ltd., with a texture depth of 68 μm and a texture spacing of 1800 μm) was used as the release paper. The coating solution for forming the resin layer was prepared by mixing polycarbonate polyurethane resin II (Crisbon S-705 (manufactured by DIC Corporation), non-aqueous type), N,N-dimethylformamide (DMF) as an organic solvent, and carbon black as a pigment, based on the formulation in Table 3.

Before the obtained coating solution hardened, it was applied to the release surface of the release paper so that the solid content was 70 g/ ^m² . After application, it was dried by heating at a heating temperature of 80°C for 5 minutes to form a resin layer as a hardened body.

The coating solution for forming the adhesive was prepared by mixing polycarbonate-based polyurethane resin III (Crisbon TA-205FT (manufactured by DIC Corporation), non-aqueous type) with N,N-dimethylformamide (DMF) as an organic solvent, based on the formulation in Table 3.

Before the obtained coating solution hardened, it was applied to the resin layer so that the solid content was 70 g/ ^m² . After application, the coating solution was partially dried by heating at 80°C for 4 minutes to prevent it from hardening completely, forming a semi-cured adhesive layer.

As shown in Table 3, a 28-gauge polyester tricot 84T/36f was layered on the obtained semi-cured adhesive layer as a substrate, and pressurized at a pressure of 4 kgf/ ^cm² for 1 minute. The resulting laminate was aged at 50°C for 72 hours to cure the semi-cured adhesive layer, thereby bonding the resin layer and the substrate via the adhesive layer. Subsequently, the synthetic leather of Comparative Example 5 was produced by peeling off the release paper.

[Comparative Example 6]
As shown in Table 3, the synthetic leather of Comparative Example 6 was prepared in the same manner as in Comparative Example 5, except that T-FLAT (manufactured by Dai Nippon Printing Co., Ltd., with a relief depth of 4 μm and a relief spacing of 45 μm) was used instead of DE-90 (manufactured by Dai Nippon Printing Co., Ltd.) as the release paper.

[Comparative Example 7]
As shown in Table 3, R231 (Lintec Corporation, with a texture depth of 7 μm and a texture spacing of 38 μm) was used as the release paper. The coating solution for forming the resin layer was prepared by mixing polyether-based polyurethane resin II (DLU (Covestro Corporation), water-based), water-based silicone resin (MF56 (Shin-Etsu Silicone Co., Ltd.)), pigment (carbon black), defoaming agent (formex800 (Evonic Corporation)), and wettability enhancer (BYK-3455 (BYK Corporation)) based on the formulation in Table 3.

Before the obtained coating solution hardened, it was applied to the release surface of the release paper so that the solid content was 70 g/ ^m² . After application, it was dried by heating at a heating temperature of 80°C for 5 minutes, thereby forming a resin layer.

The coating solution for forming the adhesive was prepared in the same manner as in Example 1 (see Table 1), as shown in Table 3.

Before the obtained coating solution hardened, the coating solution was applied to the resin layer in the same manner as in Example 1 (see Table 1) so that the solid content was 70 g/ ^m². After application, the layer was heated at a heating temperature of 80°C for 4 minutes to form a semi-cured adhesive layer.

On the obtained semi-cured adhesive layer, a substrate similar to that of Example 1 (see Table 1) was placed, as shown in Table 3. By applying pressure and aging in the same manner as in Example 1, the resin layer and the substrate were bonded via the adhesive layer. Subsequently, the release paper was peeled off to produce the synthetic leather of Comparative Example 7.

[Measurement of dynamic friction coefficient Ra and static friction coefficient Rc]
A fabric was prepared by cutting a synthetic leather (laminated) to dimensions of 200 mm x 200 mm. The area of the synthetic leather (laminated) other than the area where the fabric was cut was cut to 63 mm x 63 mm to prepare a sample piece. Separately, a 63 mm x 63 mm piece of felt was prepared, and the surface of the base material of the sample was attached to this felt using double-sided tape. The fabric was placed on an Autograph AG-IS (manufactured by Shimadzu Corporation) with the resin layer facing upwards, and the resin layer of the sample was placed on top of the resin layer of the fabric. Friction was applied to the fabric by moving the sample on the felt (i.e., on the sample) at a load of 500 gf (4.90 N) and a speed of 1000 mm/min, and the force applied to the sample and the frictional force were measured. In the graph plotting the relationship between the obtained force and frictional force, the static friction coefficient Rc was measured by dividing the peak frictional force (N) immediately after moving the sample by the load (N), and the kinetic friction coefficient Ra was measured by dividing the average value (N) of the frictional force in the force region excluding the peak immediately after moving the sample by the load (N). The results are shown in Tables 4, 5, and 6.

[Measurement of kinetic friction coefficient Rb and static friction coefficient Rd]
The dynamic friction coefficient Rb and static friction coefficient Rd were measured in the same manner as the methods for measuring the dynamic friction coefficient Ra and static friction coefficient Rc described above, except that the load was changed from 500 gf (4.90 N) to 200 gf (1.96 N) and the speed was changed from 1000 mm/min to 100 mm/min. The results are shown in Tables 4, 5, and 6.

[Calculation of the coefficient of dynamic friction Ra / coefficient of dynamic friction Rb]
Using the dynamic friction coefficients Ra and Rb obtained above, the ratio Ra/Rb was calculated. The results are shown in Tables 4, 5, and 6.

[Measurement of mean surface kinetic friction coefficient MIU using conventional method]
Synthetic leather was cut to dimensions of 63 mm x 63 mm to prepare sample pieces. These samples were mounted on a KES surface testing machine (KES-FB4-A, manufactured by Kato Tech Co., Ltd.), and a 10 mm square piano wire sensor was placed on the sample. With a load of 50 gf applied to the sensor, it was moved across the sample at a speed of 1 mm/sec, and the force and frictional force applied to the sample were measured. In the graph plotting the relationship between the obtained force and frictional force, the average value (N) of the frictional force in the region excluding the peak immediately after the sensor was moved was divided by the load (N) to measure the average surface kinetic friction coefficient MIU. The results are shown in Tables 4, 5, and 6.

[Measurement of surface roughness (SMD)]
Based on the surface roughness (SMD) measurement method described above, the surface roughness (SMD) of the resin layer of synthetic leather was measured. The results are shown in Tables 4, 5, and 6.

[Measurement of depth and spacing of minute irregularities]
Based on the method for measuring the depth and spacing of micro-irregularities described above, the depth and spacing of micro-irregularities on the surface of the resin layer of synthetic leather were measured. The results are shown in Tables 4, 5, and 6.

[Measurement of gross value]
Based on the method for measuring the gloss value of the resin layer surface described above, the gloss value of the resin layer surface was measured at an incident angle of 60°. The results are shown in Tables 4, 5, and 6.

[Measurement of rigidity and softness]
The stiffness and flexibility of the synthetic leather were measured based on the method for measuring the stiffness and flexibility of the laminate (synthetic leather) described above. The results are shown in Tables 4, 5, and 6.

[Evaluation of contamination by organic solvents]
The DMF content as an organic solvent in synthetic leather was measured in accordance with ISO TS 16189 and evaluated according to the following criteria. The results are shown in Tables 4, 5, and 6.
A: The amount of organic solvent remaining is below the detection limit (5 ppm by mass) B: The amount of organic solvent remaining is greater than 5 ppm by mass

[Evaluation of surface touch properties]
A trained panelist touched the surface of the synthetic leather resin layer with their bare hands and evaluated the tactile sensation according to the following criteria. The results are shown in Tables 4, 5, and 6.
A: Moderately slimy B: Slightly weak or strong sliminess C: Significantly weak or strong sliminess

[Evaluation of slipperiness (slipperiness)]
When a product (applicable item) is covered with synthetic leather (during use), it is undesirable for the synthetic leather to be either too slippery or too non-slippery. If it is too slippery, the product (applicable item) covered with synthetic leather may easily slip off, increasing the risk of damage to the applicable item inside. Also, when handling the applicable item by hand, it may slip, making it difficult to work with. On the other hand, if it is too non-slippery, dirt may easily adhere to the surface of the applicable item (synthetic leather), it may become difficult to put the applicable item in and out of bags or cases, and the surface of the applicable item (synthetic leather surface) may be easily scratched. Therefore, the slipperiness of the synthetic leather was evaluated assuming that the product is covered with synthetic leather. Synthetic leather was cut to a size of 63 mm x 63 mm. The resulting cut piece was placed on the surface (top surface) of a board tilted at a 40-degree angle from the horizontal plane, with the surface of the resin layer of the cut piece (the surface exposed during use) in contact with it. A constant load ( 200 gf (1.96 N) ) was applied to the cut piece while supporting it with a hand to prevent it from slipping. The board used was an OLFA Cutting mat (manufactured by OLFA Corporation) made of polyvinyl chloride (PVC) resin material. Next, the hand was released from the position where the cut piece was supported as described above, and the time (in seconds) required for the cut piece to slide downwards for a distance of 30.0 cm was measured as the required time. For cut pieces that did not slide to a distance of 30.0 cm after 10.0 seconds, the required time was determined to be 10.0 seconds, and the distance slid within 10.0 seconds was measured as the braking distance (distance traveled). Furthermore, if the vehicle slid more than 30.0 cm within 10.0 seconds, the braking distance was determined to be 30.0 cm. The measured time taken and braking distance were evaluated according to the following criteria. The results are shown in Tables 4, 5, and 6.
A: The required time is between 2.0 seconds and 10.0 seconds, and the braking distance up to 10.0 seconds is 20.0 cm or more (excellent slipperiness).
B: The required time is 2.0 seconds or more and 10.0 seconds or less, and the braking distance until 10.0 seconds have elapsed is 2.0 cm or more and less than 20.0 cm (good slipperiness)
C: The required time is less than 2.0 seconds, or the braking distance is less than 2.0 cm (too much or too little slippage, i.e., poor slipperiness).

[Evaluation of chemical resistance]
The following substances were used as chemicals: sunscreen (Banana Boat Sunscreen SPF-30), hand cream (Cucina Fruits and Passion Hand), olive oil (Extra Virgin Olive Oil), and oleic acid (reagent, manufactured by Nakalai Tex Co., Ltd.). 0.05 g of each chemical was applied to a 2 cm x 2 cm area on the surface of the resin layer of synthetic leather. After application, the area was left to stand for 24 hours at 22°C x 55% RH, and the appearance of the resin layer was evaluated according to the following criteria. The results are shown in Tables 4, 5, and 6.
A: No change in the appearance of the resin layer surface. B: Slight swelling is observed on the surface of the resin layer. C: Severe swelling is observed on the surface of the resin layer. D: The surface of the resin layer has dissolved.

[Evaluation of heat-resistant pressability]
Using an air-driven fully automatic transfer press HP-4536A-12 (manufactured by HASHIMA Corporation), synthetic leather was placed on the stage with the resin layer facing upwards, and pressed for 15 seconds at a heating temperature of 120°C and a pressure of 6 MPa. After pressing, the surface appearance of the pressed resin layer was observed with a magnifying glass and evaluated according to the following criteria. The results are shown in Tables 4, 5, and 6.
A: The resin layer is not affected by the unevenness of the substrate, and the surface is flat. B: The resin layer is slightly affected by the unevenness of the substrate, and there are slight irregularities on the surface. C: The resin layer is affected by the unevenness of the substrate, and there are irregularities that are visible to the naked eye. D: The resin layer is affected by the unevenness of the substrate, and there are irregularities similar to those of the substrate.

The synthetic leathers of Examples 1 to 8, whose surface dynamic friction coefficient Ra was 0.70 to 1.00, received a surface touch evaluation of "A" or "B," indicating a certain level of surface touch performance.

The synthetic leathers of Examples 1-8 received a slipperiness rating of "A" or "B," indicating a certain level of slipperiness. Of the synthetic leathers in Examples 1-8, Examples 1-3 and 5-8 received a heat-press resistance rating of "A" or "B," indicating a certain level of heat-press resistance. Furthermore, comparing Examples 3 and 4, which had the same resin layer formulation except for the type of crosslinking agent, the synthetic leather of Example 3, which used a relatively high-crosslinking type carbodiimide crosslinking agent, showed superior heat-press resistance compared to Example 4, which used a relatively low-crosslinking type carbodiimide crosslinking agent. On the other hand, when comparing Examples 3 and 4, they showed similarly excellent slipperiness.

Examples 2 and 3, where the mass ratio of polyether-based polyurethane resin to polycarbonate-based polyurethane resin was 60:40 to 40:60, showed superior surface touch properties compared to Example 1 (80:20) and Example 5 (20:80). Examples 2, 3, and 5-8, with a mass ratio of 60:40 or higher, showed superior heat-press resistance compared to Example 1 (80:20). Examples 2-8, with a mass ratio of 60:40 or higher, showed superior slipperiness compared to Example 1 (80:20).

In the synthetic leathers of Examples 1 to 8, the residual amount of DMF as an organic solvent was 5 ppm by mass or less, thus suppressing harmful effects on the body.

In the synthetic leathers of Examples 1 to 8, the depth of the minute irregularities on the release surface of the release paper used for production was within the range of 7 to 10 μm, and the spacing was within the range of 30 to 125 μm, demonstrating that synthetic leather with excellent surface touch properties can be produced.

In contrast, the synthetic leathers in Comparative Examples 1-7 received a "C" rating for surface touch properties, indicating inferior surface touch characteristics.

No correlation was found between the average surface dynamic friction coefficient (MIU) of the conventional method and surface touch properties, indicating that it is difficult to define synthetic leather with excellent surface touch properties using the average surface dynamic friction coefficient (MIU).

The results above demonstrate that synthetic leather containing a polyether-based polyurethane resin and a polycarbonate-based polyurethane resin in its resin layer, with a dynamic friction coefficient Ra of 0.70 to 1.00, possesses excellent surface touch properties, as well as excellent chemical resistance and heat press resistance.

The synthetic leather of the present invention is suitably usable for cases, covers, and keyboard surfaces of electronic devices such as personal computers, tablet devices, mobile phones, and headphones, as well as for the surfaces of seats in automobiles, railway vehicles, aircraft, etc. In particular, it is suitably usable for the surfaces of covers for notebook computers and tablet devices.

1 Synthetic leather 10 Base material 20 Resin layer 30 Laminate 40 Adhesive layer 50 Release paper

Claims (4)

A synthetic leather comprising a laminate including a base material and a resin layer directly or indirectly provided on one side of the base material,
The aforementioned resin layer comprises a polyether-based polyurethane resin and a polycarbonate-based polyurethane resin.
The surface of the resin layer has minute irregularities with a depth of 7 to 20 μm and spacing of 29 to 120 μm.
The rigidity of the aforementioned laminate, measured according to JIS L1096 Method A, 45° cantilever method, is 16 to 25 mm in the vertical direction and 14 to 29 mm in the horizontal direction.
The laminate is cut to a size of 63 mm x 63 mm, and the surface of the resin layer on the resulting cut piece is rubbed with the same fabric at a load of 500 gf (4.90 N) and a speed of 1000 mm/min. The coefficient of dynamic friction Ra is given by the following formula (1):
0.70≦Ra≦1.00...(1)
Synthetic leather constructed to satisfy the requirements. The coefficient of dynamic friction Ra and,
The laminate is cut to a size of 63 mm x 63 mm, and the surface of the resin layer on the resulting cut piece is rubbed with the same fabric at a load of 200 gf (1.96 N) and a speed of 100 mm/min. The coefficient of dynamic friction Rb is given by the following equation (2):
0.6≦Ra/Rb≦0.8...(2)
The synthetic leather according to claim 1, configured to satisfy the requirements. The synthetic leather according to claim 1 or 2, wherein the surface roughness (SMD) of the resin layer is 0.35 to 0.80 μm. The synthetic leather according to any one of claims 1 to 3, wherein the resin layer substantially does not contain an organic solvent.