U.S. patent application number 15/025788 was filed with the patent office on 2016-07-28 for napped artificial leather and production method thereof.
This patent application is currently assigned to KURARAY CO., LTD.. The applicant listed for this patent is KURARAY CO., LTD.. Invention is credited to Tetsuya ASHIDA, Osamu OGAWARA.
Application Number | 20160215444 15/025788 |
Document ID | / |
Family ID | 52742539 |
Filed Date | 2016-07-28 |
United States Patent
Application |
20160215444 |
Kind Code |
A1 |
ASHIDA; Tetsuya ; et
al. |
July 28, 2016 |
NAPPED ARTIFICIAL LEATHER AND PRODUCTION METHOD THEREOF
Abstract
Disclosed is a production method of a napped artificial leather
including the steps of: providing a fiber sheet including a
non-woven fabric of ultrafine fibers with a fineness of 1 dtex or
less that has been impregnated with a first elastic polymer;
napping one or both surfaces of the fiber sheet to form a napped
surface thereon; applying, to the napped surface, a resin solution
containing a second elastic polymer having solubility in a
predetermined solvent; and applying the predetermined solvent to
the surface to which the resin solution is applied. Also disclosed
is a napped artificial leather including a fiber sheet obtained by
impregnating a first elastic polymer into a non-woven fabric that
is an entangled body of ultrafine fibers with a fineness of 1 dtex
or less, wherein the fiber sheet includes, on one or both surfaces
thereof, a napped surface obtained by the ultrafine fibers, and a
second elastic polymer is fixed to basal portions of the napped
ultrafine fibers.
Inventors: |
ASHIDA; Tetsuya; (Osaka-shi,
JP) ; OGAWARA; Osamu; (Osaka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KURARAY CO., LTD. |
Okayama |
|
JP |
|
|
Assignee: |
KURARAY CO., LTD.
Kurashiki-shi, Okayama
JP
|
Family ID: |
52742539 |
Appl. No.: |
15/025788 |
Filed: |
September 24, 2014 |
PCT Filed: |
September 24, 2014 |
PCT NO: |
PCT/JP2014/004868 |
371 Date: |
March 29, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D06N 3/183 20130101;
D06N 3/0004 20130101; D06N 3/0075 20130101; D06N 3/0011 20130101;
D06N 2211/28 20130101; D06N 2213/03 20130101 |
International
Class: |
D06N 3/00 20060101
D06N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2013 |
JP |
2013-205266 |
Claims
1. A production method of a napped artificial leather, comprising
the steps of: providing a fiber sheet including a non-woven fabric
of ultrafine fibers with a fineness of 1 dtex or less that has been
impregnated with a first elastic polymer; napping one or both
surfaces of the fiber sheet to form a napped surface thereon;
applying, to the napped surface, a resin solution containing a
second elastic polymer having solubility in a predetermined
solvent; and applying the solvent to the surface to which the resin
solution is applied.
2. The production method of a napped artificial leather in
accordance with claim 1, wherein the first elastic polymer is an
elastic polymer having insolubility in the solvent.
3. The production method of a napped artificial leather in
accordance with claim 2, wherein the solubility corresponds to a
rate of dissolution in the solvent of 90% or more, and the
insolubility corresponds to a rate of dissolution in the solvent of
10% or less.
4. The production method of a napped artificial leather in
accordance with claim 2, wherein the first elastic polymer is an
elastic polymer that forms a cross-linked structure, and the second
elastic polymer is an elastic polymer that does not form a
cross-linked structure.
5. The production method of a napped artificial leather in
accordance with claim 1, wherein the first elastic polymer is an
aqueous polyurethane, and the second elastic polymer is a
solvent-based polyurethane.
6. The production method of a napped artificial leather in
accordance with claim 1, wherein the ultrafine fibers are
filaments.
7. The production method of a napped artificial leather in
accordance with claim 1, wherein the second elastic polymer has a
weight per area that is 0.001 to 0.05 times a weight per area of
the first elastic polymer.
8. A napped artificial leather comprising a fiber sheet obtained by
impregnating a first elastic polymer into a non-woven fabric that
is an entangled body of ultrafine fibers with a fineness of 1 dtex
or less, wherein the fiber sheet includes, on one or both surfaces
thereof, a napped surface formed by the napped ultrafine fibers,
and further includes a second elastic polymer that is fixed to
basal portions of the napped ultrafine fibers and is unevenly
distributed on a surface layer of the fiber sheet.
9. The napped artificial leather in accordance with claim 8,
wherein the first elastic polymer has insolubility in a
predetermined solvent, and the second elastic polymer has
solubility in the solvent.
10. The napped artificial leather in accordance with claim 9,
wherein the solubility corresponds to a rate of dissolution in the
solvent of 90% or more, and the insolubility corresponds to a rate
of dissolution in the solvent of 10% or less.
11. The napped artificial leather in accordance with claim 8,
wherein the first elastic polymer is an aqueous polyurethane, and
the second elastic polymer is a solvent-based polyurethane.
12. The napped artificial leather in accordance with claim 11,
wherein the aqueous polyurethane has a cross-linked structure, and
the solvent-based polyurethane does not have a cross-linked
structure.
13. The napped artificial leather in accordance with claim 8,
wherein the second elastic polymer is permeated into and unevenly
distributed on the surface layer of the fiber sheet in a form of a
layer or film, and a region where the second elastic polymer is
permeated into and unevenly distributed has an average thickness of
5 to 60 .mu.m.
14. The napped artificial leather in accordance with claim 8,
wherein the ultrafine fibers are filaments.
15. The napped artificial leather in accordance with claim 8,
wherein the second elastic polymer has a weight per area that is
0.001 to 0.05 times a weight per area of the first elastic
polymer.
16. The napped artificial leather in accordance with claim 8,
wherein the napped ultrafine fibers have a nap length of 30 to 200
.mu.m.
Description
TECHNICAL FIELD
[0001] The present invention relates to a napped artificial leather
for use as a surface material for clothing, shoes, articles of
furniture, car sheets, general merchandise, and the like. More
particularly, the invention relates to a napped artificial leather
that has excellent pilling resistance, i.e., that is less likely to
cause pilling, which is a phenomenon in which fibers on the surface
are fuzzed due to friction or the like and the fuzzed fibers are
entangled to form small spherical masses.
BACKGROUND ART
[0002] Napped artificial leathers such as a suede-like artificial
leather and a nubuck-like artificial leather are conventionally
known.
[0003] For example, PTL 1 below discloses a method of producing a
nubuck-like artificial leather that provides dense fluff and fine
creases. Specifically, PTL 1 discloses a method of producing a
nubuck-like artificial leather in which, when an artificial leather
substrate containing an elastic polymer inside an ultrafine
fiber-entangled non-woven fabric is finished into a napped
artificial leather, the following steps are performed in order:
applying a solvent capable of swelling or dissolving the elastic
polymer to one surface of the artificial leather substrate; napping
at least the one surface to form a napped surface; applying the
elastic polymer to the napped surface; and further napping the
surface to which the elastic polymer has been applied.
CITATION LIST
Patent Literature
[0004] [PTL 1] Japanese Laid-Open Patent Publication No.
2007-262616
SUMMARY OF INVENTION
Technical Problem
[0005] The conventional napped artificial leathers tend to cause
pilling. Pilling is problematic in that it degrades the appearance.
It is an object of the present invention to provide a napped
artificial leather having excellent pilling resistance.
Solution to Problem
[0006] An aspect of the present invention relates to a production
method of a napped artificial leather, including the steps of:
providing a fiber sheet including a non-woven fabric of ultrafine
fibers with a fineness of 1 dtex or less that has been impregnated
with a first elastic polymer; napping one or both surfaces of the
fiber sheet to form a napped surface thereon; applying, to the
napped surface, a resin solution containing a second elastic
polymer having solubility in a predetermined solvent; and applying
the predetermined solvent to the surface to which the resin
solution is applied.
[0007] Another aspect of the present invention relates to a napped
artificial leather including a fiber sheet obtained by impregnating
a first elastic polymer into a non-woven fabric that is an
entangled body of ultrafine fibers with a fineness of 1 dtex or
less, wherein the fiber sheet includes, on one or both surfaces
thereof, a napped surface obtained by the ultrafine fibers, and
further includes a second elastic polymer that is fixed to basal
portions of the napped ultrafine fibers and is unevenly distributed
on a surface layer of the fiber sheet. Such a napped artificial
leather has excellent pilling resistance.
Advantageous Effects of Invention
[0008] According to the present invention, it is possible to obtain
a napped artificial leather having high pilling resistance.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a schematic cross-sectional view, in the thickness
direction, of a napped artificial leather according to an
embodiment of the present invention.
[0010] FIG. 2 is an SEM image showing a cross section, in the
thickness direction, of a napped artificial leather obtained in
Example 1, showing the vicinity of a surface layer.
DESCRIPTION OF EMBODIMENT
[0011] First, a napped artificial leather according to an
embodiment of the present invention will be described with
reference to the drawings. FIG. 1 is a schematic diagram of a cross
section, in the thickness direction, of a napped artificial leather
10 according to the present embodiment.
[0012] As shown in the schematic cross-sectional view in FIG. 1,
the napped artificial leather 10 includes a non-woven fabric 1 that
is an entangled body of ultrafine fibers 1a with a fineness of 1
dtex or less. The non-woven fabric 1 is formed as a fiber bundle,
for example. A first elastic polymer 2 is provided in the internal
voids of an inner layer of the non-woven fabric 1. The first
elastic polymer 2 imparts fullness to the non-woven fabric 1. The
outer side of the non-woven fabric 1 has a napped surface S on
which napped ultrafine fibers 1a are present. Also, a second
elastic polymer 3 is fixed to the basal portions of the napped
ultrafine fibers.
[0013] The napped artificial leather according to the present
embodiment will now be described in detail, in conjunction with an
exemplary production method thereof.
[0014] The napped artificial leather of the present embodiment can
be obtained by a production method including the steps of:
providing a fiber sheet including a non-woven fabric of ultrafine
fibers with a fineness of 1 dtex or less that has been impregnated
with a first elastic polymer; napping one or both surfaces of the
fiber sheet to form a napped surface thereon; applying, to the
napped surface, a resin solution containing a second elastic
polymer having solubility in a predetermined solvent; and applying
the predetermined solvent to the surface to which the resin
solution is applied.
[0015] In the production method of a napped artificial leather
according to the present embodiment, first, a fiber sheet is
produced by impregnating a first elastic polymer into a non-woven
fabric that is an entangled body of ultrafine fibers with a
fineness of 1 dtex or less.
[0016] In the production of the non-woven fabric, first, a fiber
web of ultrafine fiber-generating fibers is produced. Examples of
the production method of the fiber web include a method involving
melt-spinning ultrafine fiber-generating fibers and directly
collecting the resultant fibers as filaments (continuous fibers)
without intentionally cutting them, and a method involving cutting
the resultant fibers into staples and subjecting them to a known
entangling treatment. Here, "filaments" are fibers that have not
been subjected to cutting. From the viewpoint of sufficiently
increasing the fiber density, the length of the filaments is
preferably 100 mm or more, more preferably 200 mm or more. The
upper limit for the length of the filaments is not particularly
limited, and may be several meters, several hundred meters, several
kilometers, or longer, and continuously spun. Among these, it is
particularly preferable to produce a filament web of ultrafine
fiber-generating fibers from the viewpoint of obtaining a napped
artificial leather that is less likely to cause falling out of
fibers and has excellent pilling resistance. In the present
embodiment, the production of a filament web of ultrafine
fiber-generating fibers will be described in detail as a
representative example.
[0017] Here, "ultrafine fiber-generating fiber" refers to a fiber
that forms an ultrafine fiber with a small fineness as a result of
being subjected to a chemical or physical post-treatment after
being spun. Specific examples thereof include an island-in-the-sea
composite fiber in which an island component polymer serving as a
domain different from a sea component polymer serving as the matrix
is dispersed in the sea component polymer on the fiber cross
section, and the sea component is later removed to form a fiber
bundle-like ultrafine fiber composed mainly of the island component
polymer; and a strip/division-type composite fiber in which a
plurality of different resin components are alternately disposed
around the periphery of a fiber to form a petaline shape or a
superposed shape, and the fiber is divided as a result of the resin
components being stripped from the fiber by a physical treatment,
thereby forming a bundle-like ultrafine fiber. The use of the
island-in-the-sea composite fiber can prevent damage to the fibers
such as cracking, bending, and breaking during an entangling
treatment, which will be described below. In the present
embodiment, the formation of ultrafine fibers by using the
island-in-the-sea composite fiber will be described in detail as a
representative example.
[0018] The island-in-the-sea composite fiber is a multicomponent
composite fiber composed of at least two polymers, and has a cross
section on which an island component polymer is dispersed in a
matrix composed of a sea component polymer. A filament web of the
island-in-the-sea composite fiber is formed by melt-spinning the
island-in-the-sea composite fiber and directly collecting the
resultant fiber as a filament on a net without cutting it.
[0019] The island component polymer is not particularly limited so
long as it is a polymer capable of forming an ultrafine fiber.
Specific examples thereof include polyester resins such as
polyethylene terephthalate (PET), polytrimethylene terephthalate
(PTT), polybutylene terephthalate and an elastic polymer or
modified products thereof with isophthalic acid or the like;
polyamide resins such as polyamide 6, polyamide 66, polyamide 610,
polyamide 12, an aromatic polyamide, a semi-aromatic polyamide, an
elastic polymer or modified products thereof; polyolefin resins
such as polypropylene; and polyurethane resins such as a polyester
polyurethane. Among these, polyester resins such as PET, PTT, PBT
and modified polyesters thereof are preferable in that they are
easily shrinkable by a heat treatment and thus can provide a napped
artificial leather having fullness. Also, polyamide resins such as
polyamide 6 and polyamide 66 are preferable in that they can
provide an ultrafine filament having hygroscopicity and pliability
as compared with those obtained by polyester resins, and thus can
provide a napped artificial leather having fluffiness and a soft
texture.
[0020] As the sea component polymer, a polymer having higher
solubility in a solvent or higher decomposability by a
decomposition agent than those of the island component polymer is
selected. Also, a polymer having low affinity for the island
component polymer and a smaller melt viscosity and/or surface
tension than the island component polymer under the spinning
condition is preferable in terms of the excellent stability in
spinning of the island-in-the-sea composite fiber. Specific
examples of the sea component polymer satisfying such conditions
include a water-soluble polyvinyl alcohol resin (water-soluble
PVA), polyethylene, polypropylene, polystyrene, an
ethylene-propylene copolymer, an ethylene-vinyl acetate copolymer,
a styrene-ethylene copolymer, and a styrene-acrylic copolymer.
Among these, the water-soluble PVA is preferable in that it can be
removed by dissolution by using an aqueous medium without using an
organic solvent and thus has a low environmental load.
[0021] The island-in-the-sea composite fiber can be produced by
melt spinning in which the sea component polymer and the island
component polymer are melt-extruded from a multicomponent fiber
spinning spinneret. The temperature of the multicomponent fiber
spinning spinneret is not particularly limited so long as it is a
temperature at which melt spinning can be performed and is higher
than both the melting points of the sea component polymer and the
island component polymer, but is usually selected from the range of
180 to 350.degree. C.
[0022] The fineness of the island-in-the-sea composite fiber is not
particularly limited, but is preferably 0.5 to 10 dtex, more
preferably 0.7 to 5 dtex. An average area ratio between the sea
component polymer and the island component polymer on the cross
section of the island-in-the-sea composite fiber is preferably 5/95
to 70/30, more preferably 10/90 to 50/50. The number of domains of
the island component on the cross section of the island-in-the-sea
composite fiber is not particularly limited, but is preferably
about 5 to 1000, more preferably about 10 to 300, from the
viewpoint of the industrial productivity.
[0023] The molten island-in-the-sea composite fiber discharged from
the spinneret is cooled by a cooling apparatus, and is further
drawn out and attenuated with a high-velocity air stream at a
velocity corresponding to a take-up speed of 1000 to 6000 m/min by
a suction apparatus such as an air jet nozzle so as to have a
desired fineness. Then, the drawn and attenuated filaments are
piled on a collection surface of a movable net or the like, thereby
obtaining a filament web. Note that, in order to stabilize the
shape, a part of the filament web may be further pressure-bonded by
pressing the filament web if necessary. The weight per area of the
filament web thus obtained is not particularly limited, but is
preferably in the range of 10 to 1000 g/m.sup.2, for example.
[0024] Then, the obtained filament web is subjected to an
entangling treatment, thereby producing an entangled web.
[0025] Specific examples of the entangling treatment for the
filament web include a treatment in which a plurality of layers of
filament webs are superposed in the thickness direction by using a
cross lapper or the like, and subsequently needle-punched
simultaneously or alternately from both sides such that at least
one barb penetrates the web.
[0026] In addition, an oil solution, an antistatic agent, or the
like may be added to the filament web in any stage from the
spinning step to the entangling treatment of the island-in-the-sea
composite fiber. Furthermore, if necessary, the entangled state of
the filament web may be densified in advance by performing a
shrinking treatment in which the filament web is immersed in warm
water at about 70 to 150.degree. C. The fiber density may be
increased by performing hot pressing after needle punching so as to
provide shape stability. The weight per area of the entangled web
thus obtained is preferably in the range of about 100 to 2000
g/m.sup.2.
[0027] If necessary, the entangled web may be subjected to a
treatment for increasing the fiber density and the degree of
entanglement by heat shrinking the entangled web. Specific examples
of the heat shrinking treatment include a method involving bringing
the entangled web into contact with water vapor, and a method
involving applying water to the entangled web, and subsequently
heating the water applied to the entangled web by using hot air or
electromagnetic waves such as infrared rays. If necessary, hot
pressing may be performed. By performing hot pressing, it is
possible to further densify the entangled web that has been
densified by the heat-shrinking treatment, fix the shape of the
entangled web, and smooth the surface thereof.
[0028] The change in the weight per area of the entangled web
during the heat-shrinking treatment step is preferably 1.1 times
(mass ratio) or more, more preferably 1.3 times or more and 2 times
or less, further preferably 1.6 times or less, as compared with the
weight per area before the shrinking treatment.
[0029] Then, the sea component polymer is removed from the
island-in-the-sea composite fiber in the entangled web that has
been densified, thereby obtaining an ultrafine filament non-woven
fabric that is an entangled body of fiber bundle-like ultrafine
filaments. As the method for removing the sea component polymer
from the island-in-the-sea composite fiber, a method involving
treating the entangled web with a solvent or decomposition agent
capable of selectively removing only the sea component polymer can
be used without any particular limitation. Specifically, in the
case of using the water-soluble PVA as the sea component polymer,
for example, it is preferable to use hot water as the solvent. In
the case of using a modified polyester that is easily decomposed by
alkali as the sea component polymer, it is preferable to use an
alkaline decomposition agent such as an aqueous sodium hydroxide
solution.
[0030] In the case of using the water-soluble PVA as the sea
component polymer, it is preferable to remove the water-soluble PVA
by extraction until the removal rate of the water-soluble PVA
becomes about 95 to 100 mass % by treating the web in hot water at
85 to 100.degree. C. for 100 to 600 seconds. Note that the
water-soluble PVA can be efficiently removed by extraction by
repeating a dip-nipping treatment. The use of the water-soluble PVA
is preferable in terms of a low environmental load and reduced
generation of VOCs since the sea component polymer can be
selectively removed without using an organic solvent.
[0031] The fineness of the ultrafine fiber formed in this manner is
preferably 1 dtex or less, more preferably 0.001 to 1 dtex, further
preferably 0.002 to 0.2 dtex.
[0032] The weight per area of the ultrafine filament non-woven
fabric thus obtained is preferably 140 to 3000 g/m.sup.2, more
preferably 200 to 2000 g/m.sup.2. The apparent density of the
ultrafine filament non-woven fabric is preferably 0.45 g/cm.sup.3
or more, more preferably 0.55 g/cm.sup.3 or more in that a dense
non-woven fabric can be formed, thus obtaining a non-woven fabric
with fullness. Although the upper limit is not particularly
limited, the apparent density is preferably 0.70 g/cm.sup.3 or less
in that a pliable texture can be obtained and excellent
productivity can also be achieved.
[0033] In the production of a napped artificial leather according
to the present embodiment, a first elastic polymer is impregnated
into the internal voids of the ultrafine filament non-woven fabric
before or after generating an ultrafine fiber from an ultrafine
fiber-generating fiber such as an island-in-the-sea composite
fiber. The first elastic polymer imparts shape stability and
fullness to the non-woven fabric.
[0034] Specific examples of the first elastic polymer include
polyurethane, an acrylic resin elastic polymer, an acrylonitrile
resin elastic polymer, an olefin resin elastic polymer, and a
polyester resin elastic polymer. As the first elastic polymer, it
is preferable to use an elastic polymer having low solubility in a
solvent for dissolving a second elastic polymer, which will be
described below, and it is more preferable to use an elastic
polymer having low solubility in the solvent as a result of forming
a cross-linked structure after being solidified. As such an elastic
polymer having low solubility in the aforementioned solvent, it is
preferable to use an aqueous polyurethane that forms a cross-linked
structure after being solidified.
[0035] An aqueous polyurethane refers to a polyurethane emulsion,
or a polyurethane that is solidified from a polyurethane dispersion
dispersed in an aqueous solvent. The aqueous polyurethane usually
has insolubility or low solubility in an organic solvent, and forms
a cross-linked structure after being solidified. When the emulsion
has thermal gelation properties, the emulsion particles are
thermally gelled without migration, thus making it possible to
evenly apply the first elastic polymer to the fiber-entangled
body.
[0036] Examples of the method for impregnating the first elastic
polymer into the non-woven fabric include a dry method in which an
emulsion, dispersion or solution containing the first elastic
polymer is impregnated into an entangled web before generating an
ultrafine fiber or a non-woven fabric after generating an ultrafine
fiber, followed by drying and solidification, and a method in which
the solidification is performed by a wet method. Here, in the case
of using an elastic polymer such as an aqueous polyurethane that
forms a cross-linked structure after being solidified, a curing
treatment in which the polymer is heat-treated after being
solidified and dried may be performed in order to promote
crosslinking, if necessary.
[0037] Examples of the method for impregnating the emulsion,
dispersion or solution of the first elastic polymer include
dip-nipping in which a treatment of nipping by a press roll or the
like to achieve a predetermined impregnated state is performed once
or a plurality of times, bar coating, knife coating, roll coating,
comma coating, and spray coating.
[0038] Note that the first elastic polymer may further contain a
colorant such as a dye or a pigment, a coagulation regulator, an
antioxidant, an ultraviolet absorber, a fluorescent agent, an
antifungal agent, a penetrant, an antifoaming agent, a lubricant, a
water-repellent agent, an oil-repellent agent, a thickener, a
filler, a curing accelerator, a foaming agent, a water-soluble
polymer compound such as polyvinyl alcohol or carboxymethyl
cellulose, inorganic fine particles, and a conductive agent, so
long as the effects of the present invention are not impaired.
[0039] The content ratio of the first elastic polymer is preferably
0.1 to 60 mass %, more preferably 0.5 to 60 mass %, particularly
preferably 1 to 50 mass %, relative to the mass of the ultrafine
fiber, in terms of the good balance between the fullness and the
pliability or the like of the resulting napped artificial
leather.
[0040] In this manner, a fiber sheet that is a non-woven fabric of
ultrafine fibers with a fineness of 1 dtex or less that has been
impregnated with the first elastic polymer is obtained. The fiber
sheet thus obtained is sliced into a plurality of pieces or ground
in a direction perpendicular to the thickness direction so as to
regulate the thickness thereof if necessary, and is subsequently
napped by being buffed on at least one surface by using abrasive
paper such as sand paper or emery paper. The number of the abrasive
paper is preferably about 120 to 800, more preferably about 320 to
600. In this manner, a napped surface obtained by napping one or
both surfaces of the fiber sheet is formed.
[0041] The thickness of the napped fiber sheet is not particularly
limited, but is preferably 0.2 to 4 mm, more preferably 0.5 to 2.5
mm.
[0042] Next, a resin solution containing a second elastic polymer
having solubility in a predetermined solvent is applied to the
napped surface of the fiber sheet thus obtained, and subsequently
the second elastic polymer is solidified.
[0043] The second elastic polymer soluble in a predetermined
solvent is an elastic polymer that is dissolved in the
predetermined solvent in a later step, and subsequently solidified
from the dissolved state. As the second elastic polymer, it is
possible to use any elastic polymer having solubility in a
predetermined organic solvent without any particular
limitation.
[0044] Specific examples of the second elastic polymer include
polyurethane, an acrylic resin elastic polymer, an acrylonitrile
resin elastic polymer, an olefin resin elastic polymer, a polyester
resin elastic polymer that have solubility in a predetermined
organic solvent. As the second elastic polymer, it is possible to
use an elastic polymer having solubility in a predetermined organic
solvent, and also an elastic polymer that does not form a
cross-linked structure after being solidified and thus has
solubility in the predetermined organic solvent. As such an elastic
polymer having solubility in the predetermined organic solvent, it
is preferable to use a solvent-based polyurethane that does not
form a cross-linked structure after being solidified.
[0045] The solvent-based polyurethane having solubility in an
organic solvent refers to a polyurethane obtained by reacting, at a
predetermined molar ratio, at least one polymer diol selected from
polyester diol, polyether diol, polycarbonate diol and the like
having an average molecular weight of, for example, 500 to 3000, at
least one diisocyanate selected from aromatic, cycloaliphatic, and
aliphatic diisocyanates such as 4,4'-diphenyl methane diisocyanate,
isophorone diisocyanate and hexamethylene diisocyanate, and at
least one low-molecular weight compound having two or more active
hydrogen atoms. If necessary, the polyurethane may be used as a
polymer composition to which a polymer such as a synthetic rubber
or a polyester elastomer is added. The solvent-based polyurethane
can easily form a high elongation film as compared with the aqueous
polyurethane that forms a cross-linked structure.
[0046] The solubility in a predetermined solvent corresponds to a
rate of dissolution of preferably 70% or more, more preferably 90%
or more, the rate of dissolution being obtained by immersing an
elastic polymer sheet having a thickness of, for example, 100 .mu.m
in a predetermined solvent at room temperature for 24 hours,
subsequently filtrating the solvent, drying the resulting residue,
measuring the mass, and using the following expression: Rate of
dissolution (%)=(1-Weight of residue/Weight of sheet before
immersion in solvent).times.100. Meanwhile, the insolubility in a
predetermined solvent corresponds to a rate of dissolution of
preferably 30% or less, more preferably 10% or less.
[0047] The method for applying a resin solution containing the
second elastic polymer to the napped surface of the fiber sheet
include gravure coating, bar coating, knife coating, roll coating,
comma coating, and spray coating.
[0048] The second elastic polymer is applied to the napped surface
of the fiber sheet by applying a resin solution containing the
second elastic polymer to the napped surface of the fiber sheet,
and, if necessary, drying and solidifying the resin solution.
[0049] The second elastic polymer may also further contain a
colorant such as a dye or a pigment, a coagulation regulator, an
antioxidant, an ultraviolet absorber, a fluorescent agent, an
antifungal agent, a penetrant, an antifoaming agent, a lubricant, a
water-repellent agent, an oil-repellent agent, a thickener, a
filler, a curing accelerator, a foaming agent, a water-soluble
polymer compound such as polyvinyl alcohol or carboxymethyl
cellulose, inorganic fine particles, a conductive agent and the
like, so long as the effects of the present invention are not
impaired.
[0050] The content ratio of the second elastic polymer relative to
the mass of the fiber sheet is preferably 0.00001 to 0.01 mass %,
more preferably 0.0001 to 0.001 mass %, from the viewpoint of
achieving a good balance between the fullness and pliability or the
like of the resulting napped artificial leather and appropriately
constraining the napped fibers. An excessively high content ratio
of the second elastic polymer tends to give rise to a hard surface
and generation of fine creases.
[0051] Note that the weight per area of the second elastic polymer
is preferably 0.0001 to 0.1 times, more preferably 0.001 to 0.05
times the weight per area of the above-described first elastic
polymer from the viewpoint of achieving a good balance between the
fullness and pliability or the like of the artificial leather and
appropriately constraining the napped fibers.
[0052] Next, a solvent for dissolving the second elastic polymer is
applied to the surface to which the second elastic polymer has been
applied. By this step, at least a part of the second elastic
polymer that has been applied to the napped surface of the fiber
sheet is dissolved and sunk in the direction of the inner layer,
and dried and solidified. Then, the second elastic polymer is fixed
to the basal portions of the napped ultrafine fibers present on the
napped surface. In particular, it is preferable that the second
elastic polymer is fixed to the basal portions of the napped
ultrafine fibers and is present in the form of a thin film or layer
on the surface layer of the napped surface of the fiber sheet.
Then, as a result of the basal portions of the ultrafine fibers
present on the napped surface being constrained by the second
elastic polymer, the ultrafine fibers become less likely to fall
off and less likely to stick out from the inside to the outside
even when the napped surface is rubbed. As a result, it is possible
to suppress the occurrence of pilling in which the detached fibers
and the sticking-out fibers form fuzz balls due to the rubbing of
the surface.
[0053] Examples of the method for applying the solvent for
dissolving the second elastic polymer to the surface to which the
second elastic polymer has been applied include, but are not
particularly limited to, gravure coating, bar coating, knife
coating, roll coating, comma coating, and spray coating.
[0054] As the solvent for dissolving the second elastic polymer,
any solvent having solubility to dissolve the second elastic
polymer simply by being applied can be used without any particular
limitation. Such a solvent may be selected as appropriate according
to the type of the second elastic polymer. Specific examples
thereof include ketones such as cyclohexanone and methyl ethyl
ketone (MEK), N,N-dimethylformamide (DMF), dimethyl acetamide
(DMA), N-methyl pyrrolidone, dimethyl sulfonamide (DMSO), in the
case of dissolving a solvent-based polyurethane, for example. A
solvent mixture obtained by mixing the above-described solvents at
a predetermined ratio may be used, or a poor solvent of the first
elastic polymer may be mixed.
[0055] While the amount of application of the solvent for
dissolving the second elastic polymer may be adjusted as
appropriate according to the balance between the desired texture
and properties, the thickness or the like, it is preferable that
the solvent is applied in an amount of preferably about 1 to 50
g/m.sup.2, more preferably about 5 to 30 g/m.sup.2. When the amount
of application of the solvent is too large, the second elastic
polymer tends to be excessively dissolved and excessively permeated
into the inner layer. When the amount of application is too small,
the second elastic polymer will not be sufficiently dissolved, and
thus, it tends to be difficult for the basal portions of the napped
ultrafine fibers to be sufficiently fixed.
[0056] In the napped artificial leather of the present embodiment,
it is preferable that the second elastic polymer 3 has permeated
into the fiber sheet and fixed to the basal portions of the napped
ultrafine fibers 1a, and is unevenly distributed in the form of a
thin film or layer on the surface layer of the napped surface 1a of
the fiber sheet, as shown in the SEM image of FIG. 2, for example.
An average thickness of the portion where the second elastic
polymer is present in the form of a thin film or layer is
preferably 5 to 60 .mu.m, more preferably 10 to 40 .mu.m, from the
viewpoint of obtaining a pliable napped artificial leather. When
the portion where the second elastic polymer is present is too
thick, the surface layer portion tends to be hard, or fine creases
tend to be formed on the surface. When the portion where the second
elastic polymer is present is too thin, the effect of the napped
ultrafine fibers in fixing the second elastic polymer tends to be
reduced, resulting in a reduction in the pilling suppressing
effect.
[0057] In the napped artificial leather of the present embodiment,
an average ratio of the thickness of the portion where the second
elastic polymer is present, relative to the thickness of the fiber
sheet, is preferably 1 to 20%, more preferably 5 to 10%. When the
ratio of the thickness of the portion where the second elastic
polymer is present relative to the thickness of the fiber sheet is
too high, the fiber sheet tends to have a hard texture.
[0058] In this manner, a napped artificial leather of the present
embodiment is obtained. The length of the napped fibers of the
napped artificial leather according to the present embodiment is
not particularly limited, but is preferably 1 to 500 .mu.m, more
preferably 30 to 200 .mu.m, from the viewpoint of providing a
napped artificial leather having fine short fibers resembling those
of a natural nubuck leather. Note that the length of the napped
fibers can be determined, for example, by capturing a
cross-sectional image with a scanning electron microscope (SEM) in
a state in which the napped fibers on the surface of the napped
artificial leather are manually raised, measuring the length of
arbitrarily selected 50 fibers, the length extending from the
entangled surface, which is the basal portion, to the upper end
thereof, and calculating an average value thereof.
[0059] The apparent density of the napped artificial leather
according to the present embodiment is preferably 0.4 to 0.7
g/cm.sup.3, more preferably 0.5 to 0.6 g/cm.sup.3, from the
viewpoint of achieving a good balance between pliability and
fullness. Furthermore, the weight per area of the napped artificial
leather according to the present embodiment is preferably 150 to
1000 g/m.sup.2, more preferably 200 to 600 g/m.sup.2, from the
viewpoint of achieving a good balance between pliability and
fullness.
[0060] Note that the napped artificial leather of the present
embodiment is dyed as needed. A suitable dye is selected as
appropriate according to the type of the ultrafine fibers. For
example, when the ultrafine fibers are formed from a polyester
resin, it is preferable that the napped artificial leather are dyed
with a disperse dye. Specific examples of the disperse dye include
benzene azo-based dyes (e.g., monoazo and disazo), heterocyclic
azo-based dyes (e.g., thiazole azo, benzothiazole azo, quinoline
azo, pyridine azo, imidazole azo, and thiophene azo),
anthraquinone-based dyes, and condensate-based dyes (e.g.,
quinophthalone, styryl, and coumarin). These are commercially
available as dyes with the prefix "Disperse", for example. These
may be used alone or in a combination of two or more. As the dyeing
method, it is possible to use a high-pressure jet dyeing method, a
jigger dyeing method, a thermosol continuous dyeing machine method,
a dyeing method using a sublimation printing process, and the like
without any particular limitation.
[0061] The napped artificial leather of the present embodiment may
be further subjected to a flexibilizing treatment by crumpling or a
relaxing treatment to adjust the texture, or a finishing treatment
such as a reverse seal brushing treatment, an antifouling
treatment, a hydrophilization treatment, a lubricant treatment, a
softener treatment, an antioxidant treatment, an ultraviolet
absorber treatment, a fluorescent agent treatment and a flame
retardant treatment.
[0062] Since the napped fibers that have been once napped are fixed
to the surface of the fiber sheet by the second elastic polymer,
the napped fibers are less likely to be pulled out even when dyeing
or a relaxing treatment is performed.
[0063] In this manner, a napped artificial leather of the present
embodiment that has been adjusted such that the ultrafine fibers
whose basal portions are constrained by the elastic polymer are
present on the napped surface is obtained. Such a napped artificial
leather can suppress the occurrence of pilling in which the
detached fibers or the sticking-out fibers form fuzz balls even
when the napped surface is rubbed.
EXAMPLES
[0064] Hereinafter, the present invention will be described in
further detail by way of examples. It should be appreciated that
the scope of the present invention is by no means limited by the
examples.
Example 1
[0065] Ethylene-modified polyvinyl alcohol as a thermoplastic resin
serving as a sea component and isophthalic acid-modified PET as a
thermoplastic resin serving as an island component were molten
separately. Note that the ethylene-modified polyvinyl alcohol had
an ethylene unit content of 8.5 mol %, and a degree of
polymerization of 380 and a saponification degree of 98.7 mol %.
The isophthalic acid-modified PET had an isophthalic acid unit
content of 6.0 mol % and a melting point of 110.degree. C. Then,
each of the molten resins was supplied to a multicomponent fiber
spinning spinneret having many nozzle holes disposed in parallel
for forming a cross section on which 25 island component portions
having uniform cross-sectional areas were distributed in the sea
component. At this time, the molten resins were supplied by
adjusting the pressure such that the mass ratio between the molten
resin serving as a sea component and the molten resin serving as an
island component satisfies Sea component/Island component=25/75.
Then, molten resin strands having a cross section with an
island-in-the-sea structure were discharged from the nozzle holes
set at a spinneret temperature of 260.degree. C.
[0066] Then, the molten resin strands discharged from the nozzle
holes were stretched by suction by an air jet nozzle suction
apparatus with an air stream pressure regulated so as to provide an
average spinning speed of 3700 m/min, and thereby to spin
island-in-the-sea composite filaments with a fineness of 2.1 dtex.
The spun island-in-the-sear composite filaments were continuously
piled on a movable net while being suctioned from the back side of
the net. The piled amount was regulated by regulating the movement
speed of the net. Then, in order to suppress the fuzzing on the
surface, the island-in-the-sea composite filaments piled on the net
were softly pressed with a metal roll at 42.degree. C. Then, the
island-in-the-sea composite filaments were removed from the net,
and allowed to pass between a grid-patterned metal roll having a
surface temperature of 75.degree. C. and a back roll, thereby hot
pressing the fibers with a linear load of 200 N/mm. In this manner,
a filament web having a weight per area of 34 g/m.sup.2 and in
which the fibers on the surface were temporarily fused in a grid
pattern was obtained.
[0067] Next, an oil solution mixed with an antistatic agent was
sprayed to the surface of the obtained filament web. Then, 10
sheets of the filament web were stacked by using a cross lapper
apparatus to form a superposed web with a weight per area of 340
g/m.sup.2, and an oil solution for preventing the needle from
breaking was further sprayed thereto. Then, the superposed filament
web was needle-punched, thereby performing a three-dimensional
entangling treatment. Specifically, the stacked body was
needle-punched at a density of 3300 punch/cm.sup.2 alternately from
both sides by using 6-barb needles with a distance of 3.2 mm from
the needle tip to the first barb at a punching depth of 8.3 mm. The
area shrinkage by the needle punching was 18%, and the weight per
area of the entangled web after the needle punching was 415
g/m.sup.2.
[0068] The obtained entangled web was densified by being subjected
to a heat-moisture shrinking treatment. Specifically, water at
18.degree. C. was uniformly sprayed in an amount of 10 mass % to
the entangled web, and the entangled web was heat-treated by being
stood still in an atmosphere with a temperature of 70.degree. C.
and a relative humidity of 95% for 3 minutes with no tension
applied, thereby heat-moist shrinking the entangled web so as to
increase the fiber density. The area shrinkage by the heat-moisture
shrinking treatment was 45%, and the densified entangled web had a
weight per area of 750 g/m.sup.2 and an apparent density of 0.52
g/cm.sup.3. Then, for further densification, the entangled web was
pressed with a dry-heat roll, thereby adjusting the apparent
density to 0.60 g/cm.sup.3.
[0069] Next, an emulsion of the first elastic polymer with a solid
content concentration of 30% was impregnated into the densified
entangled web. Note that the first elastic polymer was an aqueous
polyurethane composed mainly of a polycarbonate/ether polyurethane
capable of forming a cross-linked structure after being solidified
and having a rate of dissolution of 5% in a solvent mixture
described below. Then, the impregnated emulsion of the first
elastic polymer was dried in a dryer machine at 150.degree. C.,
thereby solidifying the aqueous polyurethane in the densified
entangled web.
[0070] Next, the entangled web to which the aqueous polyurethane
had been applied was immersed in hot water at 95.degree. C. for 20
minutes, thereby removing the sea component contained in the
island-in-the-sea composite filaments by extraction. Then, the
entangled web was dried in a dryer machine at 120.degree. C.,
thereby obtaining a fiber sheet that included a non-woven fabric of
ultrafine filaments with a fineness of 0.08 dtex and to which the
aqueous polyurethane had been applied. The mass ratio of the
non-woven fabric to the aqueous polyurethane in the fiber sheet was
87/13. Then, the fiber sheet was sliced into halves in the
thickness direction, and the surface thereof was napped by being
buffed with sand paper with a number of 600.
[0071] Next, as a solution containing the second elastic polymer, a
solution of a solvent-based polyurethane substantially completely
soluble in a solvent mixture of 5% DMF and 95% cyclohexanone was
prepared as follows.
[0072] 260 parts by mass of polyester diol with a number-average
molecular weight of 2000, 620 parts by mass of polyhexylene
carbonate with a number-average molecular weight of 2000, 580 parts
by mass of polybutylene adipate with a number-average molecular
weight of 2000, 540 parts by mass of polytetramethylene glycol with
a number-average molecular weight of 2000, 217 parts by mass of
ethylene glycol, 1149 parts by mass of diphenyl
methane-4,4'-diisocyanate, and 10100 parts by mass of DMF were
charged into a reactor, and allowed to react under a stream of
nitrogen, to produce a polyurethane solution with a weight-average
molecular weight of 360000. Note that the polyester diol with a
number-average molecular weight of 2000 contained an equimolar
mixture of N-methyldiethanolamine and 3-methyl-1,5-pentane diol as
the diol component and sebacic acid as the dicarboxylic acid
component.
[0073] Then, cyclohexanone was added to the polyurethane solution
to adjust the solid content to 5%. Then, the polyurethane solution
with a solid content of 5% was applied in an amount of 11 g/m.sup.2
to the outer side of the napped surface of the fiber sheet by using
a 200-mesh gravure coater, and subsequently dried. At this time,
the weight per area ratio of the solvent-based polyurethane to the
aqueous polyurethane provided earlier (solvent-based
polyurethane/aqueous polyurethane) was 0.012 times.
[0074] Then, the solvent mixture of 5% DMF and 95% cyclohexanone
for dissolving the solvent-based polyurethane was applied in an
amount of 10 g/m.sup.2 to the outer side of the napped surface of
the non-woven fabric by using a 200-mesh gravure coater, and
subsequently dried.
[0075] Then, the napped artificial leather was scalded in hot water
at 80.degree. C. for 20 minutes to relax the leather with the hot
water, and subsequently dyed into black by using a high-pressure
jet dyeing machine (circular dyeing machine from HISAKA WORKS,
LTD.).
[0076] In this manner, a dyed napped artificial leather that
included a non-woven fabric of ultrafine filaments with a fineness
of 0.08 dtex and had a napped surface on one surface was obtained.
FIG. 2 shows an SEM image showing a cross section, in the thickness
direction, of the napped artificial leather obtained in Example 1.
The obtained napped artificial leather had a thickness of 0.6 mm, a
weight per area of 350 g/m.sup.2, and an apparent density of 0.58
g/cm.sup.3. The length of the napped fibers was about 80 .mu.m. The
second elastic polymer was permeated into the fiber sheet, was
fixed to the basal portions of the napped ultrafine fibers, and was
unevenly distributed in the forms of a layer on the surface layer
of the fiber sheet. The average thickness of that layer was 25
.mu.m.
[0077] Then, the obtained napped artificial leather was evaluated
for the pilling resistance, the surface appearance, and the texture
in the following manner. The results are summarized in Table 1.
[Pilling Resistance]
[0078] Testing was performed by using a Martindale abrasion tester
in accordance with ISO 12945-2, and evaluation was made according
to the following grading criteria.
[0079] 5: No change was observed.
[0080] 4: Slight surface fuzzing and/or fuzz balls formed in some
portions of the surface were observed.
[0081] 3: Medium level of surface fuzzing and/or medium level of
pilling, and fuzz balls with various sizes and densities appearing
in some portions of the test strip surface were observed.
[0082] 2: Clear surface fuzzing and/or clear pilling, and fuzz
balls with various sizes and densities were observed in most
portions of the test strip surface.
[0083] 1: Dense surface fuzzing and/or significant pilling, and
fuzz balls with various sizes and densities covering the entire
surface of the test strip were observed.
[Surface Appearance]
[0084] The appearance of the obtained napped artificial leather was
observed visually, and evaluated according to the following
criteria.
[0085] 3: Nubuck-like, fine short fibers were observed.
[0086] 2: Suede-like, somewhat coarse napped fibers were observed,
or some creases were observed on the surface.
[0087] 1: The nap length was clearly uneven, or creases were
prominently observed.
[Texture]
[0088] The obtained napped artificial leather was bent, and the
differences in elasticity and flexibility compared with a napped
natural leather were evaluated according to the following
criteria.
[0089] 3: A texture with a good balance between fullness and
flexibility, close to the texture of the napped natural leather,
was observed.
[0090] 2: A texture harder than that of the napped natural leather
was observed.
[0091] 1: A texture with poorer fullness than that of the napped
natural leather was observed.
TABLE-US-00001 TABLE 1 Weight per area ratio between Evaluation
results polymer Solvent Fiber Nap Pilling Surface Example First
elastic Second elastic elastic bodies application length length
resistance appearance Texture No. polymer polymer (Second/First)
step mm .mu.m (5 to 1) (3 to 1) (3 to 1) 1 Aqueous Solvent based
0.012 Performed filament 80 5 3 3 polyurethane polyurethane 2
Aqueous Solvent-based 0.012 Performed 51 80 5 3 3 polyurethane
polyurethane 3 Solvent-based Solvent-based 0.012 Performed filament
60 5 2 3 polyurethane polyurethane 4 Aqueous Solvent-based 0.025
Performed filament 40 5 2 3 polyurethane polyurethane 5 Aqueous
Solvent-based 0.004 Performed filament 180 4 3 3 polyurethane
polyurethane 6 Aqueous Solvent-based 0.0012 Performed filament 300
4 2 3 polyurethane polyurethane 7 Aqueous Solvent-based 0.05
Performed filament 20 5 2 3 polyurethane polyurethane Com. Aqueous
Solvent-based 0.012 Not filament 20 3 2 3 Ex. 1 polyurethane
polyurethane performed Com. Aqueous Aqueous 0.012 Performed
filament 300 4 2 3 Ex. 2 polyurethane polyurethane Com. Aqueous --
-- Performed filament 400 3 2 3 Ex. 3 polyurethane
Example 2
[0092] Using ethylene-modified polyvinyl alcohol as a thermoplastic
resin serving as a sea component and isophthalic acid-modified PET
as a thermoplastic resin serving as an island component, an
island-in-the-sea composite fiber was melt-spun such that the mass
ratio between the sea component and the island component satisfied
Sea component/Island component=25/75, then stretched, crimped and
cut, thereby obtaining short fibers (staples) of island-in-the-sea
composite fibers with a fineness of 2.1 dtex and an average fiber
length of 51 mm.
[0093] Then, the obtained short fibers were formed into a
cross-lapped web by using a webber, and needle-punched at a density
of 700 punch/cm.sup.2 by using a needle punching machine, to obtain
an entangled web with a weight per area of 407 g/m.sup.2.
[0094] Then, a napped artificial leather including a non-woven
fabric having a napped surface on one surface was obtained in the
same manner as in Example 1 except that the entangled web with a
weight per area of 407 g/m.sup.2 obtained as above was used in
place of the entangled web with a weight per area of 415 g/m.sup.2
used in Example 1. The obtained napped artificial leather had a
thickness of 0.6 mm, a weight per area of 340 g/m.sup.2, and an
apparent density of 0.57 g/cm.sup.3. The length of the napped
fibers was about 80 .mu.m. The second elastic polymer was permeated
in the fiber sheet, was fixed to the basal portions of the napped
ultrafine fibers, and was unevenly distributed in the form of a
layer on the surface layer of the fiber sheet. The average
thickness of that layer was 25 .mu.m.
[0095] Then, the obtained napped artificial leather was evaluated
in the same manner as in Example 1. The results are shown in Table
1.
Example 3
[0096] A napped artificial leather including a non-woven fabric
having a napped surface on one surface was obtained in the same
manner as in Example 1 except that the solvent-based polyurethane
used as the second elastic polymer in Example 1 was impregnated as
the first elastic polymer into the densified entangled web such
that the mass ratio of the modified PET to the solvent-based
polyurethane was 87/13 instead of impregnating the emulsion of the
aqueous polyurethane as the first elastic polymer in Example 1. The
obtained napped artificial leather had a thickness of 0.6 mm, a
weight per area of 350 g/m.sup.2, and an apparent density of 0.58
g/cm.sup.3. The length of the napped fibers was about 60 .mu.m. The
second elastic polymer was permeated into the fiber sheet, was
fixed to the basal portions of the napped ultrafine fibers, and was
unevenly distributed in the form of a layer on the surface layer of
the fiber sheet. The average thickness of that layer was 22
.mu.m.
[0097] Then, the obtained napped artificial leather was evaluated
in the same manner as in Example 1. The results are shown in Table
1.
Example 4
[0098] A napped artificial leather including a non-woven fabric
having a napped surface on one surface was obtained in the same
manner as in Example 1 except that the weight per area ratio of the
solvent-based polyurethane to the aqueous polyurethane
(solvent-based polyurethane/aqueous polyurethane) was changed from
0.012 times used in Example 1 to 0.025 times. The obtained napped
artificial leather had a thickness of 0.6 mm, a weight per area of
350 g/m.sup.2, and an apparent density of 0.58 g/cm.sup.3. The
length of the napped fibers was about 40 .mu.m. The second elastic
polymer was permeated into the fiber sheet, was fixed to the basal
portions of the napped ultrafine fibers, and was unevenly
distributed in the form of a layer on the surface layer of the
fiber sheet. The average thickness of that layer was 35 .mu.m.
[0099] Then, the obtained napped artificial leather was evaluated
in the same manner as in Example 1. The results are shown in Table
1.
Example 5
[0100] A napped artificial leather including a non-woven fabric
having a napped surface on one surface was obtained in the same
manner as in Example 1 except that the weight per area ratio of the
solvent-based polyurethane to the aqueous polyurethane
(solvent-based polyurethane/aqueous polyurethane) was changed from
0.012 times used in Example 1 to 0.004 times. The obtained napped
artificial leather had a thickness of 0.6 mm, a weight per area of
350/m.sup.2, and an apparent density of 0.58 g/cm.sup.3. The length
of the napped fibers was about 180 .mu.m. The second elastic
polymer was permeated into the fiber sheet, was fixed to the basal
portions of the napped ultrafine fibers, and was unevenly
distributed in the form of a layer on the surface layer of the
fiber sheet. The average thickness of that layer was 15 .mu.m.
[0101] Then, the obtained napped artificial leather was evaluated
in the same manner as in Example 1. The results are shown in Table
1.
Example 6
[0102] A napped artificial leather including a non-woven fabric
having a napped surface on one surface was obtained in the same
manner as in Example 1 except that the weight per area ratio of the
solvent-based polyurethane to the aqueous polyurethane
(solvent-based polyurethane/aqueous polyurethane) was changed from
0.012 times used in Example 1 to 0.0012 times. The obtained napped
artificial leather had a thickness of 0.6 mm, a weight per area of
350 g/m.sup.2, and an apparent density of 0.58 g/cm.sup.3. The
length of the napped fibers was about 300 .mu.m. The second elastic
polymer was permeated into the fiber sheet, was fixed to the basal
portions of the napped ultrafine fibers, and was unevenly
distributed in the form of a layer on the surface layer of the
fiber sheet. The average thickness of that layer was 10 .mu.m.
[0103] Then, the obtained napped artificial leather was evaluated
in the same manner as in Example 1. The results are shown in Table
1.
Example 7
[0104] A napped artificial leather including a non-woven fabric
having a napped surface on one surface was obtained in the same
manner as in Example 1 except that the weight per area ratio of the
solvent-based polyurethane to the aqueous polyurethane
(solvent-based polyurethane/aqueous polyurethane) was changed from
0.012 times used in Example 1 to 0.05 times. The obtained napped
artificial leather had a thickness of 0.6 mm, a weight per area of
355 g/m.sup.2, and an apparent density of 0.59 g/cm.sup.3. The
length of the napped fibers was about 20 .mu.m. The second elastic
polymer was permeated into the fiber sheet, was fixed to the basal
portions of the napped ultrafine fibers, and was unevenly
distributed in the form of a layer on the surface layer of the
fiber sheet. The average thickness of that layer was 45 .mu.m.
[0105] Then, the obtained napped artificial leather was evaluated
in the same manner as in Example 1. The results are shown in Table
1.
Comparative Example 1
[0106] A napped artificial leather including a non-woven fabric
having a napped surface on one surface was obtained in the same
manner as in Example 1 except that the step of applying the solvent
mixture performed in Example 1 was omitted. The obtained napped
artificial leather had a thickness of 0.6 mm, a weight per area of
350 g/m.sup.2, and an apparent density of 0.58 g/cm.sup.3. The
length of the napped fibers was about 20 .mu.m, but exhibited
uneven nap and had prominent small creases on the surface. Although
the second elastic polymer was fixed to the upper portions and the
basal portions of the napped ultrafine fibers and unevenly
distributed in the form of a layer on the surface layer of the
fiber sheet, the permeation of the second elastic polymer in the
thickness direction of the fiber sheet was not observed.
[0107] Then, the obtained napped artificial leather was evaluated
in the same manner as in Example 1. The results are shown in Table
1.
Comparative Example 2
[0108] A napped artificial leather including a non-woven fabric
having a napped surface on one surface was obtained in the same
manner as in Example 1 except that an emulsion of an aqueous
polyurethane that was the same as the one used as the first elastic
polymer in Example 1 was applied instead of applying the
solvent-based polyurethane as the second elastic polymer in Example
1. The obtained napped artificial leather had a thickness of 0.6 mm
and a weight per area of 350 g/m.sup.2. The length of the napped
fibers was about 300 .mu.m. The second elastic polymer was
discontinuously fixed to the upper portions of the napped ultrafine
fibers, and the permeation of the second elastic polymer in the
thickness direction of the fiber sheet was not observed. Also, a
partial detachment was observed during dyeing.
[0109] Then, the obtained napped artificial leather was evaluated
in the same manner as in Example 1. The results are shown in Table
1.
Comparative Example 3
[0110] A napped artificial leather including a non-woven fabric
having a napped surface on one surface was obtained in the same
manner as in Example 1 except that a solvent mixture that was the
same as the one used in Example 1 was applied, without applying the
second elastic polymer. The obtained napped artificial leather had
a thickness of 0.6 mm and a weight per area of 350 g/m.sup.2. The
length of the napped fibers was about 400 .mu.m.
[0111] Then, the obtained napped artificial leather was evaluated
in the same manner as in Example 1. The results are shown in Table
1.
[0112] All of the napped artificial leathers obtained in Examples 1
to 7 had grade 4 or above according to the pilling resistance
grading criteria, and had high pilling resistance. Note that since
Example 3 used the solvent-based polyurethane soluble in the
solvent as the first elastic polymer, the application of the
solvent caused the first polymer to be partially dissolved, and as
a result, a somewhat hard texture with fine creases on the surface
was observed. The napped artificial leather obtained in Example 6,
which had a low weight per area ratio of the solvent-based
polyurethane to the aqueous polyurethane, exhibited a weak
constraint on the napped ultrafine fibers and thus had grade 4,
which was somewhat low, according to the pilling resistance grading
criteria. The napped artificial leather obtained in Example 7,
which had a high weight per area ratio of the solvent-based
polyurethane to the aqueous polyurethane, had a somewhat hard
surface, and as a result, fine creases were observed on the
surface.
[0113] On the other hand, the napped artificial leather of
Comparative Example 1, in which the step of applying the solvent
mixture for dissolving the solvent-based polyurethane to the outer
side of the napped surface was omitted, had grade 3 according to
the pilling resistance grading criteria. The napped artificial
leather of Comparative Example 2, in which the aqueous polyurethane
insoluble in the solvent was applied to the outer side of the
napped surface instead of applying the solvent-based polyurethane,
had grade 2 according to the surface appearance grading criteria.
From the results of Example 1 and Comparative Examples 1 and 2, it
can be seen that, in order to improve the pilling resistance and
obtain fine nubuck, the elastic polymer needs to be dissolved in
the solvent and be permeated in the direction of the inner layer so
as to be solidified at the basal portions of the ultrafine fibers.
The napped artificial leather obtained in Comparative Example 3, in
which the application of the elastic polymer was omitted and only
the solvent was applied, had a long nap length and exhibited an
uneven nap.
[0114] The production method of a napped artificial leather
described in detail thus far includes the steps of: providing a
fiber sheet including a non-woven fabric of ultrafine fibers with a
fineness of 1 dtex or less that has been impregnated with a first
elastic polymer; napping one or both surfaces of the fiber sheet to
form a napped surface thereon; applying, to the napped surface, a
resin solution containing a second elastic polymer having
solubility in a predetermined solvent; and applying the solvent to
the surface to which the resin solution is applied. With this
production method of a napped artificial leather, the second
elastic polymer provided in the surface layer of the napped surface
is dissolved and permeated in the direction of inner layer by
application of the solvent, and subsequently solidified by
evaporation of the solvent, and thereby fixed to the vicinity of
the basal portions of the napped ultrafine fibers. Then, the napped
ultrafine fibers are constrained by the second elastic polymer, and
thus become less likely to be detached or to stick out to the
outside even when the napped surface is rubbed. As a result, it is
possible to suppress the occurrence of so-called pilling in which
ultrafine fibers are detached or stick out by the surface being
rubbed, and the ultrafine fibers are entangled to form masses.
[0115] Preferably, the first elastic polymer that is
pre-impregnated into the fiber sheet is an elastic polymer having
insolubility in the solvent. When the first elastic polymer is
soluble in the solvent, the first elastic polymer is also
dissolved, together with the second elastic polymer, by the
application of the solvent. Accordingly, the texture becomes hard,
for example, and it tends be difficult to control the product
quality control.
[0116] It is preferable that the first elastic polymer is an
elastic polymer that forms a cross-linked structure, and the second
elastic polymer is an elastic polymer that does not form a
cross-linked structure, since the first elastic polymer is less
likely to be dissolved in the above-described solvent and the
second elastic polymer is likely to be dissolved in the
solvent.
[0117] The first elastic polymer is preferably, for example, an
aqueous polyurethane, and the second elastic polymer is preferably
a solvent-based polyurethane, since the resulting napped artificial
leather has well-balanced properties, and an aqueous polyurethane,
in general, forms a cross-linked structure and thus has low
solubility, whereas a solvent-based polyurethane does not form a
cross-linked structure and thus has high solubility.
[0118] It is preferable that the ultrafine fibers are filaments in
that the ultrafine fibers tend not to fall off.
[0119] It is preferable that the second elastic polymer has a
weight per area that is 0.0001 to 0.05 times a weight per area of
the first elastic polymer, from the viewpoint of improving the
pilling resistance while preventing the texture from becoming too
hard.
[0120] A napped artificial leather includes a fiber sheet obtained
by impregnating a first elastic polymer into a non-woven fabric
that is an entangled body of ultrafine fibers with a fineness of 1
dtex or less, wherein the fiber sheet includes, on one or both
surfaces thereof, a napped surface formed by the napped ultrafine
fibers, and further includes a second elastic polymer that is fixed
to basal portions of the napped ultrafine fibers and is unevenly
distributed on a surface layer of the fiber sheet. Such a napped
artificial leather has excellent pilling resistance.
[0121] It is preferable that the napped ultrafine fibers have a nap
length of 30 to 200 .mu.m since a napped artificial leather have
fine short fibers resembling those of a natural nubuck leather can
be obtained.
INDUSTRIAL APPLICABILITY
[0122] A napped artificial leather obtained by the present
invention can be preferably used as a skin material for clothing,
shoes, articles of furniture, car sheets, general merchandise, and
the like.
REFERENCE SIGNS LIST
[0123] 1a . . . Ultrafine fibers [0124] 1 . . . Non-woven fabric
[0125] 2 . . . First elastic polymer [0126] 3 . . . Second elastic
polymer [0127] 10 . . . Napped artificial leather [0128] s . . .
Napped surface
* * * * *