SUEDE LIKE ARTIFICIAL LEATHER WITH EXCELLENT STRENGTH AND

ELONGATION PROPERTIES

TECHNICAL FIELD

The present invention relates to a suede-like artificial leather with excellent

strength and elongation properties, and more particularly, to a suede-like artificial leather

which is useful as high durability materials for vehicles, furniture, etc. because it has an

excellent tensile strength and constant load elongation.

Nowadays, an artificial leather made of non-woven fabric with

three-dimensionally crosslinked micro-fibers and polyurethane resin (polyurethane

elastomer) impregnated in the non-woven fabric is widely used as material rapidly

replacing natural leather used for furniture or vehicles because it has a soft touch and

unique appearance similar to those of the natural leather.

Recently, artificial leather having a high functionality, as well as imitating the soft

touch and unique appearance conventionally characteristic of a natural leather, is being

actively developed. Particularly, there is a demand for an artificial leather which

requires form stability so as to have durability against excessive friction and external

force when used for vehicles, furniture, etc. and which has a suitable strength and

elongation so as to make sewing and mounting workability easier as it is to be used for a

flexed region.

As conventional techniques for giving an artificial leather form stability, U.S.

Patent No. 5,112,421, U.S. Laid-Open Patent No. 2005/0009426 Al and so on propose a

method in which a fabric is inserted between web layers made of cotton in the production

of a non-woven fabric so as to have a stable stitching strength and constant load

elongation properties.

However, the above-mentioned method is disadvantageous in that although the

strength is high, the constant load elongation becomes much smaller due to the insertion

of a fabric, which makes manual work, such as a seat mounting, difficult when this

method is applied to furniture or vehicles with a lot of flexed regions.

Meanwhile, Japanese Patent Laid-Open No. 2004-332173 suggests a method of

producing an artificial leather by inserting a stretch knitted or woven fabric made of

polyurethane elastic yarns by a water jet method into the middle of a short fiber web layer

during the production of a non-woven fabric.

However, according to the above-described method, knitted or woven fabrics are

produced only from polyurethane elastic yarns, such that it is difficult to insert by needle

punching. Therefore, bonded pleats are formed because bonding is done using a

water-jet method, thereby making the surface irregular. In addition, the elongation is

excessively high and the strength is weak, which leads to unsatisfactory form stability

such that the fabric may not be used for furniture and vehicles.

As described above, the artificial leathers produced by the conventional methods

have good strength and poor elongation or vise versa, and are not satisfactory in

appearance. Thus, they are unsuitable as artificial leathers for furniture and vehicles lhat

require high durability along with aesthetic appearance.

DISCLOSURE OF INVENTION

(PROBLEM TO BE SOLVED BY THE INVENTION)

It is an object of the present invention to provide an artificial leather which has

strength and elongation so as to improve the sewing and mounting workability of a flexed

region, as well as forming stability against excessive friction and external force by

controlling the strength and elongation of woven and knitted fabrics to be bonded to a

web and adequately realize the strength and elongation of a final product depending on

the strength and elongation of woven and knitted fabrics.

(TECHNICAL SOLUTION)

To achieve the above object, there is provided a suede-like artificial leather

according to the present invention, comprising a composite sheet having polyurethanc

filled therein, the composite sheet comprising: a non-woven fabric of ultrafine short fibers

entangled with each other and having a thickness less than 0.3 denier; and a woven or

knitted fabric placed in the non-woven fabric, entangled with the ultrafine short fibers of

the non-woven fabric, and having an constant load elongation of 10 to 30% at a load of

8kgf, wherein the tensile strength in longitudinal and lateral directions is 35 to 60kgf750iιiiιι

and the constant load elongation in longitudinal and lateral directions is 8 to 25%.

Hereinafter, the present invention will now be described in detail.

Firstly, the suede-like artificial leather of the present invention has a tensile

strength in longitudinal and lateral directions of 35 to 60kgf/50mnι and an constant load

elongation in longitudinal and lateral directions of 8 to 25%.

In a case where the artificial leather is used for materials for furniture, vehicles,

etc., there is required mounting workability for adequately extending the artificial leather

so as to make sewing and mounting works easier, as well as form stability for preventing

too much extension. In terms of form stability, if the constant load elongation is greater

than 25%, the artificial leather continues to be extended during use, thereby damaging the

permanent value of the product. In terms of mounting workability, if the tensile strength

is less than 35kgf/50nim or the constant load elongation is less than 8%, there is a

possibility of damage to the product during mounting, and stress and strain may be

exerted on the worker's body. In addition, if the tensile strength is greater than 60

kgf/50mni, the constant load elongation becomes too low, thereby causing the

above-mentioned problems.

A typical artificial leather consists of ultrafine short fibers of less than 0.3 denier

and a polyurethane elastomer. However, in the present invention, as means for

achieving strength and elongation properties, a woven or knitted fabric having strength

and elongation properties is added as a reinforcing material to the typical artificial leather.

The woven or knitted fabric is an important component for allowing the artificial leather

product of the present invention to achieve strength and elongation properties.

More importantly, the strength and elongation properties of the product differ

greatly depending on the warp and weft density of the non- woven or knitted fabric to be

inserted as a reinforcing material and the constant load elongation thereof. Particularly.

it is very important to entangle the ultrafine short fibers in the non- woven fabric integrally

with the woven or knitted fabric in order to achieve satisfactory appearance and physical

properties. In case of production by a needle punching method, the warp and weft

densities of the woven or knitted fabric are preferably 20 to 100 yarns/inch. If the

density is less than 20 yarns/inch, it is too weak to adequately function as the reinforcing

material, thereby degrading the tensile strength of the product. If the density is greater

than 100 yarns/inch, there is a greater possibility of damage to the reinforcing material

while a needle is passing through meshes of the woven or knitted fabric. In this case, the

constant load elongation of the reinforcing material is reduced, thereby also deteriorating

the constant load elongation of the product.

Additionally, the constant load elongation, measured under a load of 8kgf, of the

woven or knitted fabric applied to the present invention is 10 to 30%. The constant load

elongation of the woven or knitted fabric is the factor that has the most influence on the

constant load elongation of the product. As for a typical artificial leather comprising a

non-woven fabric only, consisting of ultrafine short fibers and polyurethane filling

material and having no reinforcing material therein, its constant load elongation is too

large, so the elongation is not suitable for applications as materials for vehicles or

furniture, etc. Thus, as one of the methods for achieving an constant load elongation, a

woven or knitted fabric is inserted and interposed, which makes the constant load

elongation of the woven or knitted fabric very important. The constant load elongation

of the woven or knitted fabric tends to become smaller when the woven or knitted fabric

is coupled to a non- woven fabric. Therefore, in order to have an constant load

elongation of greater than 8% and less than 25%, it is most preferable that the woven or

knitted fabric has the aforementioned constant load elongation.

Additionally, the woven or knitted fabric used in the present invention may consist

of one or two or more of yarns selected from the group consisting of a polyethylene

terephthalate yarn, a polytrimethylene terephthalate yarn, a polyamide yarn, a

polyurethane yarn, a polyethylene yarn and a polypropylene yarn. Moreover, the yarn

comprising the woven or knitted fabric is a filament yarn or staple yarn.

The reinforcing woven or knitted fabric may be entangled to a short fiber web

layer of a non-woven fabric by a needle punching method, or crosslinked thereto by a

high pressure water jet.

The production of a suede-like artificial leather of the present invention having

excellent strength and elongation properties is accomplished by the following series of

process steps.

Concretely, a woven or knitted fabric having an constant load elongation of 10 to

30% measured under a load of 8kgf is prepared, and then an ultrafme short fiber web

having a thickness of less than 0.3 deniers after dissolution or separation is prepared,

thereby bonding the woven or knitted fabric layer and the ultrafine web layer by a needle

punching method. A needle whose number of needle barbs is one or less is used in order

to prevent damage to the woven or knitted fabric layer, and the probability of contact with

the woven or knitted fabric is minimized by adjusting the angle of the barbs. A

punching density required for bonding is preferably 1500 to 3000 times per unit area of

lαif. The density of the composite sheet with the woven or knitted fabric bonded therein

should fall within the range of 0.200 to 0.250g/ciif.

The ultrafine short fibers of less than 0.3 deniers used in the present invention may

consist of one or two or more of a polyamide polymer, a polyester polymer, polyolefin

polymer, and a polyurethane polymer.

A 3 to 15% concentration water soluble polymer solution of polyvinyl alcohol or

carboxymethylcellulose is padded and dried on the composite sheet of the non-woven

fabric and the woven or knitted fabric so as to have the amount of 5 to 20% by weight

with respect to the weight of the fibers. This process is effective for preventing the touch

of the final product from being hard resulting from the polyurethane resin being

excessively bonded with the fibers converted into a bundle of fine fibers in the later

process of impregnating polyurethane resin.

Next, a polyurethane wet impregnating treatment is carried out on the composite

sheet. The polyurethane elastomer used in this step is easily dissolved in a

straight-chained polymer material consisting of macroglycol, diisocyanate and a low

molecular weight diol or diamine, or in some crosslinking polymer materials such as

dimethylformamide (hereinafter, refer to as "DMF").

The macroglycol used in the present invention may include polyether glycol,

polyester glycol, polyether polyester copolymer glycol, polycarbonate glycol and the like.

The low molecular weight diols in the present invention may include

4,4'-butandiol, ethylene glycol and the like. It also may use a chain extender of diamine

base such as methylene-bis-(4,4'-phenylamine). An impregnating solution is made by

adding a detergent, pigments, functional particles and the like to such a DMF solution of

polyurethane elastomer and diluting the resulting solution.

The composite sheet is dipped in the impregnating solution, then the polyυrethane

is coagulated in an aqueous solution, washed in hot water at 50 to 8O ⁰ C so as to

completely removing temporary filled water soluble polymer, and then dried. The content

of the polyurethane after drying is preferably 20 to 50% by weight with respect to the

weight of the composite sheet

Continuously, the fibers are converted into a bundle of fine fibers by removing the

dissolution component (sea component) with a solvent or aqueous solution of sodium

hydroxide which is capable of dissolving or separating the dissolution component.

In case that the dissolution component (sea component) is a copolymeiϊzed

polyester, the sea component is decomposed by a continuous or discontinuous

arrangement method with a 5 to 15% aqueous solution of sodium hydroxide. In case

that the dissolution component is polyethylene or polystyrene, the sea component is

removed by treating with toluene, perchloroethylene or trichloroethylene.

For example, the copolymerized polyester of the sea component is completely

decomposed and removed by treating with a 10% aqueous solution of sodium hydroxide

at 100°C for 5 to 10 minutes. At this time, although the thickness of the composite sheet

constructed of the non- woven fabric and the woven or knitted fabric is decreased to some

degree because their dissolution component (sea component) is removed, the form of the

composite sheet is kept well by the structure of the woven or knitted fabric, the degree of

longitudinal elongation caused by a mechanical tensile force is not large and the apparent

density of the surface of the composite sheet is improved.

Next, the surface of the thusly obtained composite sheet of the leather form is

buffed by a buffing machine equipped with a sand paper of a proper roughness to thus

form raised fibers on the surface and then fluffs are shagged. The roughness of the sand

paper is selected according to its use. Typically, it is preferable to use the sand paper of

150 to 400 meshes.

The composite sheet of the leather form with the fluffs formed therein is dyed

according to its use. In case that the used fiber comprises nylon-6, it is typically dyed

with a metal complex dye or milling type acid dye. In case of polyester, it is dyed with a

disperse dye in a high pressure rapid dyeing machine.

Finally, a softening and functional agent treatment is carried out on the dyed

product, to thus make a composite suede-like artificial leather of high grade.

The artificial leather produced by the present invention makes sewing and

mounting workability on a flexed region easier, as well as having form stability that

provides durability against external force because the strength and elongation properties

are very excellent, that is, the tensile strength is 35 to 60kgf and the constant load

elongation measured under a load of 8kgf is 8 to 25%. The artificial leather of the present

invention is suitable as high durability material for furniture, vehicles, etc that require

shape stability.

In the present invention, various physical properties of the composite sheet for

artificial leather are determined as follows.

^• Thickness and Fineness (denier) of ultrafine fiber

A sample of a cross-section of the composite sheet for artificial leather is taken

and a preparation process such as gold coating is applied thereto. The cross sectional

photograph of the sample is taken at a constant magnification by a scanning electron

microscope (SEM) analyzer. The diameter of one strand of the ultrafine fibers shown on

the photograph is evaluated and converted into an actual value, and then the fineness is

obtained through the following formula.

Fineness (denier) = 9 π D ² p/4000

In this formula, π is the ratio of the circumference of a circle to the diameter, D

is the diameter of the cross section of the ultrafine fiber, and p is the density (g/cm ³ ) of

the ultrafine fiber. The applied density of nylon is 1.14 and the applied density oϊ

polyethylene terephthalate is 1.38.

^• Constant load elongation (%)

Three test pieces each having a width of 50mm and a length of 250mm are cut out

from a composite sheet of a suede-like artificial leather and from a woven or knitted

fabric in the longitudinal and transverse directions and a display line of 100mm is marked

along their center areas. These test pieces are mounted on a fatigue tester (*) at a clamp

distance of 150mm and a 78.4N (8kg) load (including the load of the lower clamp) is

carefully suspended on the test pieces for 10 minutes. With the load being suspended for

10 minutes, the length between the display lines (E ₀ ) is obtained and the constant load

elongation is calculated by the following formula;

Constant load elongation (%) = f ₀ - 100

In this formula, to designates the length between the display lines (mm) after

suspending the load of 8kg for ten minutes. * As the fatigue tester, 'Marlens fatigue

tester' is used.

^■ Tensile Strength (Kgf/50ιnm)

Five test pieces, each having a 50mm width and a 250mm length, are taken out of

a sample, respectively, in the longitudinal and transverse directions.

Upper portions of the test pieces are gripped on a Densiron type or its equivalent

tensile strength tester, an appropriate initial load is applied thereto so that the test pieces

are upright and consistent with a horizontal line, thereby providing a clamp distance of

15O-ODi.

The initial load refers to a load required to flatten unnatural wrinkles or bends.

Especially, the initial load for an unspecified fabric is set to 1.96 N (200gf).

The load (kgf/50mm) required for tearing for the five test pieces are measured at a

pulling speed of 200200 ini/min and averaged.

(ADVANTAGEOUS EFFECT)

The present invention makes sewing and mounting workability on a flexed region

easier, as well as having form stability that provides durability against external force

because the strength and elongation properties are very excellent.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail with reference to

examples, but not limited thereto.

Example 1

A sea-island type composite continuous fiber having a total thickness of 75

deniers convertible into a bundle of fine fibers was prepared from 70% by weight of

polyethylene terephthalate as a fiber-forming component and 30% by weight of

copolymer polyester as an extraction component through spinning and drawing processes.

At this time, the monofilament of the continuous fiber has a denier of 3.1 and has 16

ultrafine fibers (fiber-forming component) therein. The continuous fiber was crimped

and set at 170 ^° C in order to give it a suitable constant load elongation.

The thusly obtained composite fiber was used as warp and weft in the production

of a woven fabric by twisting it at 650 twists per meter in a twisting machine. The warp

and weft were produced into a woven fabric which had a warp density of a 70 yarns/inch

and a weft density of 70 yarns/inch. The constant load elongation in the length

(longitudinal) direction of the woven fabric was 20%, and the constant load elongation in

the width (lateral) direction thereof was 22%.

Meanwhile, a short fiber having a length of 51mm, a monofilament fineness of 2.5

deniers and 36 ultrafine fibers (fiber-forming component) in the monofilament was

prepared from 70% by weight of polyethylene terephthalate as a fiber-forming component

and 30% by weight of copolymer polyester as an extraction component through spinning

and crimp cutting processes. The above-mentioned short fibers formed a web by a

carding, cross-lapping process, and this web was combined to the woven fabric b>

needle-punching during the preparation of a non- woven fabric, thereby forming a

composite sheet. Then, the composite sheet of the non-woven fabric and the woven

fabric was padded and dried in a 10% aqueous solution of polyvinyl alcohol so as to have

the amount of 10% by weight with respect to the weight of the fibers. Afterwards, the

composite sheet was dipped in a 15% impregnating solution prepared by diluting a

polyurethane elastomer of the polyether-polyester copolymer glycol type in

dimethylformamide (DMF). Then, the polyurethane was coagulated in the aqueous

solution, washed in a 7O ⁰ C hydrothermal solution for completely removing polyvinyl

alcohol polymer, and dried. The content of polyurethane after the drying step was found

to be 35% by weight. The composite sheet of the leather form constructed of the

above-mentioned fibers and polyurethane was converted into a bundle of fine fibers by

continuously treating it in a 10% aqueous solution of sodium hydroxide at 100 ⁰ C for

completely removing the sea component, i.e., copolymer polyester, so that only the island

component, i.e., the component of polyester fine fibers, was left. Then, a part of the

ultrafine fibers was cut out and raised by carrying out buffing treatment using a #240 grit

sand paper in order to obtain fluffs, thereby producing a composite sheet of a leather form

with excellent strength and elongation properties. Next, the obtained sheet was dyed

with a disperse dye having an excellent fastness in a high pressure rapid dyeing machine.

Then the sheet was reduced, cleared, and dried. Continuously, water repellent and

antistatic agent treatment and fluff tip softening treatment were carried out to thus prepare

a suede-like composite sheet for artificial leather. The physical properties of the thus

obtained composite sheet for artificial leather were evaluated and the result was shown in

Table 2.

Examples 2 to 3 and Comparative Examples 1 and 2

Except that the type and fineness of the warp and weft used in the production of a

woven fabric are changed as in Table 1, a composite sheet for artificial leather was

prepared in the same manner as that in Example 1. The physical properties were

evaluated and shown in Table 2.

<Table 1> Preparation Conditions

<Table 2> Result of Evaluation of Physical Properties of Composite Sheet of Suede-like

Artificial Leather

Comparative Comparative

Classification Example 1 Example 2 Example 3 Example 1 Example 2

Tensile strength

(longitudinal direction x lateral 55x56 46x43 48x45 30x29 60 x 56 direction) (kgf/50fliπi)

Constant load elongation

(longitudinal 11 x 14 19x24 15x17 28x30 4x5 direction x lateral direction) (%)

* The longitudinal direction is a warp direction of a woven or knitted fabric constituting

the composite sheet for a suede-like artificial leather, and the lateral direction is a weft

direction of the woven or knitted fabric.

INDUSTRIAL APPLICABILITY

The present invention makes sewing and mounting workability on a flexed region

easier, as well as having form stability that provides durability against external force

because the strength and elongation properties are very excellent.

Due to this, the present invention is useful as materials for furniture and vehicles

requiring durability.