Method for producing an artificial leather with improved flexing endurance properties

Abstract

The present invention relates to a process for production of artificial leather comprising top coat, polyurethane layer and optional substrate layer, said process comprising i) providing a release layer, ii) applying one or more than one layer of a top coat to the release layer to an overall top coat layer thickness in the range from 1 to 500 m, iii) applying first polyurethane system components comprising an isocyanate component (A) and a polyol component (B) to the top coat to form a first polyurethane layer, wherein the isocyanate index of the first polyurethane system components is in the range from 101 to 140, iv) optionally applying further polyurethane system components to the first polyurethane layer to form further polyurethane layers, v) optionally applying a substrate layer to the polyurethane system components, vi) curing the polyurethane system components to form a polyurethane layer, and vii) separating the release layer from the top coat, wherein the overall thickness of the first and optionally further polyurethane layers is in the range from 0.01 to 20 mm and the polyurethane system components are solvent-free. The present invention further relates to an artificial leather obtainable by such a process and to the use of the artificial leather as upper materials for footwear.

Claims

1. A process for producing an artificial leather comprising a top coat, a polyurethane layer and an substrate layer, the process comprising, in the following order: applying at least one layer of a top coat to a release layer to produce an overall top coat layer thickness in the range from 1 to 500 m; applying a first polyurethane system comprising an isocyanate component (A) and a polyol component (B) to the top coat to form a first polyurethane layer, such that an isocyanate index of the first polyurethane system is in the range from 101 to 140; optionally applying a further polyurethane system to the first polyurethane layer to form at least one further polyurethane layer; applying a substrate layer to the first polyurethane layer or to the further polyurethane layers; curing the first polyurethane system and optionally the further polyurethane system to form a second polyurethane layer; and then, separating the release layer from the top coat, to form an artificial leather, wherein the overall thickness of the first and optionally further polyurethane layers is in the range from 0.01 to 20 mm and the first polyurethane system and the further polyurethane system are solvent-free.

2. The process according to claim 1, which is a continuous process.

3. The process according to claim 1, wherein the top coat is formed from an aqueous polyurethane dispersion.

4. The process according to claim 1, wherein the overall thickness of the first and optionally further polyurethane layers is in the range from 0.1 to 10 millimeters.

5. The process according to claim 1, wherein at least one layer of the first polyurethane system and/or the further polyurethane system comprises a blowing agent.

6. The process according to claim 1, wherein at least one layer of first polyurethane system and/or the further polyurethane system comprises a filler.

7. The process according to claim 1, wherein the isocyanate component (A) is a polyisocyanate prepolymer formed by reaction of 4,4-MDI with a polytetrahydrofuran.

8. The process according to claim 1, wherein the polyol component (B) comprises a polytetrahydrofuran.

9. The process according to claim 8, wherein the polyol component (B) comprises the polytetrahydrofuran and 1,4-butanediol.

10. The process according to claim 8, wherein the at least one of the isocyanate component (A) and the polyol component (B) comprises from 40% to 70% by weight of a polytetrahydrofuran, based on the overall weight of components (A) and (B).

11. The process according to claim 1, wherein at least one of the isocyanate component (A) and the polyol component (B) comprises a plasticizer.

12. The process according to claim 1, wherein the applying of the first polyurethane system and optionally the further polyurethane systems occurs by blade coating.

13. The process according to claim 12, wherein a thermally activatable catalyst is present during the applying.

14. The process according to claim 1, wherein the applying of the first polyurethane system and optionally the further polyurethane systems occurs by spraying.

15. The process according to claim 1, wherein the first polyurethane system comprising an isocyanate component (A) and a polyol component (B) is applies directly to the top coat to form the first polyurethane layer, and wherein the isocyanate index of the first polyurethane system is in the range from 110 to 140.

16. The process according to claim 15, wherein the isocyanate index of the first polyurethane system is in the range from 115 to 140.

Description

EXAMPLES

(1) The following input materials were used:

(2) Top coat 1: MDI-polyether-based, linear polyurethane in DMF

(3) Top coat 2: waterborne polyurethane coat based on aliphatic isocyanate and polyether

(4) Isocyanate 1: Prepolymer based on monomeric MDI and polytetrahydrofuran with an OH number of 56 mgKOH/g

(5) Polyol 1: Polytetrahydrofuran with an OH number of 56 mgKOH/g

(6) Polyol 2: Polytetrahydrofuran with an OH number of 112 mgKOH/g

(7) Polyol 3: Polyethylene oxide-co-ethylene oxide based on glycerol as starter molecule with an OH number of 28 mg KOH/g

(8) Chain extender (CE): 1,4-butanediol

(9) Catalyst 1 (Cat.1): Jeffcat DPA

(10) Catalyst 2 (Cat.2): acid-blocked diazabicycloundecene in 10% by weight diethylene glycol

(11) Defoamer: MSA antifoam

(12) Foam stabilizer: Dabco DC193

(13) Formulations used were as follow (in parts by weight):

(14) TABLE-US-00001 0 A B C D polyol 1 66 polyol 2 66 64 66 67 polyol 3 15 15 15 15 15 CE 15 15 15 15 15 water 1 1 Cat 1 2 2 2 Cat 2 0.2 0.2 defoamer 0.5 0.5 0.5 stabilizer 1 1 black paste 2 2 2 2 2 isocyanate 1 X X X X X

(15) The artificial leathers were produced as follows (batch process):

(16) A Favini BHT Nara release paper from (please add) is hotplate heated to 70 C. surface temperature. A coat layer about 50 micrometers in thickness is applied using a commercially customary spray gun. The coat consists of 500 ml of Astacin PR aqueous aliphatic PU dispersion mixed with 150 ml of water, 50 ml of Lepton black NB color preparation from BASF and 30 ml of Astacin Hrter CT carbodiimide-based curative from BASF. The curative was suspended in 100 ml of water for better solubility before being added to the mixture. After spraying, the coat layer is allowed to dry for about 3 minutes. Thereafter, an approximately 400 micrometers thick layer of polyurethane reactive system A, which was temperature controlled to 25 C., is applied using a robot-guided spray mix head. Shortly after the PU reactive system was spray applied, Baiksan 0.8 mm is applied as a textile substrate, under slight pressure, to the incompletely cured polyurethane. The polyurethane is subsequently cured directly on the hotplate at 70 C. for about 15 minutes. Thereafter, the final artificial leather can be peeled off the release paper.

(17) Table 1 below shows the properties of the artificial leather obtained from formulation A in the batch process as a function of the isocyanate index:

(18) TABLE-US-00002 TABLE 1 Maximum release force to GB/T 1646-2007 in Specimen Index N/2.5 cm Bally flex 1 90 53 <100 000 (failed) 2 95 22 <100 000 (failed) 3 100 53 <100 000 (failed) 4 105 60 >100 000 5 110 120 >100 000 6 115 149 >100 000 7 120 111 >100 000

(19) The table shows that it needs an isocyanate index of 105 or more to achieve more than 100 cycles in the ASTM D6182 Bally flex test, which is important for footwear upper material in particular. At the same time, the release force between coat layer and polyurethane layer increases significantly for these indices.

Ex. 2 (Continuous Process)

(20) A release paper (Favini BHT Nara) travels at a speed of 8 m/min across a continuous rig for artificial leather production. A commercially customary spray gun was used to apply to the release paper a coating layer about 50 micrometers in thickness. The coating consists of 500 ml of aqueous, aliphatic PU dispersion (BASF Astacin PR) mixed with 150 ml of water, 50 ml of black color preparation (BASF Lepton schwarz NB) and 30 ml of carbodiimide-based curative (BASF Astacin Hrter CT). The curative was suspended in 100 ml of water for better solubility before being added to the mixture. The coating layer dries in the oven into which the material is conveyed after application of the coating and delayed therein for about 3 minutes. Thereafter, an approximately 400 micrometers thick layer of polyurethane reactive system (based on MDI prepolymer and PTHF polyols, temperature controlled at 25 C.) is applied with a robot-guided spray mix head. The material is subsequently led through an oven temperature controlled to 100 degrees only to reemerge from it after about 90 seconds. Thereafter, a textile substrate (Baiksan 0.8 mm Softlin S 100) is applied, under slight pressure, to the still incompletely cured PU. Subsequently the polyurethane is cured in the 3.sup.rd oven at 120 degrees and reemerges from the oven after 4 minutes. Thereafter, the final artificial leather can be peeled off the release paper.

(21) The obtained product of the present invention satisfies typical requirements of upper materials for footwear with regard to flexing endurance, adherence between top coat layer and polyurethane mid-layer and adherence between polyurethane mid-layer and substrate layer.