LOW DENSITY POLYURETHANE FOAM SYSTEMS WITH HIGH SPLIT TEAR

Abstract

Described herein is a polyurethane foam produced in a “one shot process” that has low density, is semi-hard, and displays a high rebound value all while providing superior split tear performance. The polyurethane foam can be used in a “one shot process” to produce a shoe sole, a mid-sole or an insole for a shoe. The shoe sole may be used for forming an outer sole of a sandal type shoe, a midsole of an athletic type shoe, or an insole for insertion into any type of shoe.

Claims

1. A polyurethane foam having a density of 150 to 400 g/L measured according to DIN EN ISO 845, wherein the polyurethane foam is formed by reacting a mixture consisting of: 80 to 50 weight percent (wt. %) of a polyol formulation and 20 to 50 wt. % of an isocyanate prepolymer, wherein the wt. % is based on the total weight of the mixture; wherein the polyol formulation comprises 90 to 98 wt. % of a polytetramethylene ether glycol (PTMEG) with a weight average molecular weight (MWw) of 1800 to 2100, 0.1 to 6 wt. % of expandable microspheres and 0.5 to 3 wt. % of water, wherein the wt. % values for the polyol formulation are based on the total weight of the polyol formulation.

2. The polyurethane foam of claim 1, further comprising a catalyst, a surfactant, a crosslinking agent, and other optional additives as ingredients in the polyol formulation, wherein the catalyst, the surfactant, the crosslinking agent, and other optional additives together bring the wt. % of the polyol formulation to 100 wt. %.

3. The polyurethane foam of claim 1, wherein the isocyanate pre-polymer includes: 40 to 70 wt. % of an isocyanate component having at least 92 wt. % of 4,4′-diphenylmethane diisocyanate; and 30 to 60 wt. % of the PTMEG, based on the total weight of the isocyanate pre-polymer, wherein the NCO value of the isocyanate prepolymer is 15 to 22.

4. The polyurethane foam of claim 1, wherein the polyol formulation has a water content of 0.8 to 2 wt. % based on the total weight of the polyol formulation.

5. The polyurethane foam of claim 1, wherein the polyol formulation has an expandable microspheres content of 0.5 to 5 wt. % based on the total weight of the polyol formulation.

6. The polyurethane foam of claim 1, wherein the polyurethane elastomer foam has a vertical rebound of 55% to 65% measured according to ASTM D2632.

7. The polyurethane foam of claim 1, wherein the polyurethane elastomer foam has an Asker C hardness of 25 to 70 measured according to ASTM D2240.

8. A shoe sole, a mid-sole or an insole formed from the polyurethane foam of claim 1.

9. A method of forming a polyurethane foam according to claim 1, comprising i) preparing a polyol formulation by admixing at room temperature and melting PTMEG at 70° C. overnight and then keeping it at 40 to 50° C. for a better handling and dosing together with other components, i) heating the polyol formulation to a temperature of 40 to 45° C. inside a stirred reactor tank of a polyurethane foam machine, iii) heating an isocyanate prepolymer to a temperature of 30 to 45° C. inside an isocyanate tank of a polyurethane foam machine, iv) admixing the isocyanate pre-polymer with the polyol formulation at atmospheric pressure and pouring the mixture using the polyurethane foam machine into a heated mold with desired shape, and v) closing the mold, allowing the reactants to fill the mold and react for a given demolding time to form a polyurethane foam.

10. The method of claim 9, wherein the polyurethane forming composition has 50 to 80 weight percent of a polyol formulation and 20 to 50 wt. % of an isocyanate prepolymer, wherein the wt. % is based on the total weight of the polyurethane forming composition.

11. The method of claim 9, wherein the heated mold has a temperature of 50 to 60° C. and the demolding time is from 5 to 15 min.

12. The polyurethane foam of claim 1, wherein the polyol formulation has a water content of 1.4 to 2 wt. % based on the total weight of the polyol formulation.

13. The polyurethane foam of claim 1, wherein the polyol formulation has an expandable microspheres content of 1 to 5 wt. % based on the total weight of the polyol formulation.

14. The polyurethane foam of claim 1, wherein the polyurethane elastomer foam has an Asker C hardness of 30 to 55 measured according to ASTM D2240.

15. The polyurethane foam of claim 1, wherein the polyurethane elastomer foam has an Asker C hardness of 35 to 55 measured according to ASTM D2240.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0035] FIG. 1 Shows a split tear test specimen after preparation for test showing position of splits and mark.

EXAMPLES

[0036] The following examples are provided to illustrate various embodiments, but are not intended to limit the scope of the claims. All components purchased from commercial vendors and used as received unless otherwise noted. All percentages are weight percentages (wt. %) based on the total weight of the mixture used to form the polyurethane elastomer foam, unless otherwise noted.

[0037] The components used for preparing the polyurethane elastomer foam of the following Examples are listed in Table 1.

TABLE-US-00001 TABLE 1 Components and Commercial Sources Components Source PolyTHF ® 2000 BASF DABCO ® DC 193 Air Products DABCO ® EG Evonik Expancel 031 DU 40 Akzo Nobel Diethanolamine pure BASF Isocyanate prepolymer ISO 136/26 BASF

[0038] Mechanical properties are determined according to the procedure listed in the following standards in Table 2

TABLE-US-00002 TABLE 2 Test standards of Mechanical properties Specific Item Standards Version information Density DIN EN ISO June 1995 845 Hardness ASTM D2240 Designation: D 2240 - Reference type C Asker C 05 Rebound ASTM D2632 Designation: D2632 - Vertical 01 (Reapproved 2014) Tensile DIN 53504 May 1994 Test type: S1, test strength speed: 500 mm/ min Elongation DIN 53504 May 1994 Test type: S1, test speed: 500 mm/ min Tear ASTM D624 Designation: D 624 - Test type: Die C, strength 00 (Reapproved 2007) test speed: 500 mm/min Compression ASTM D 395 Designation: D 395 - Method B set 03 (Reapproved 2008) Split tear Internal N/A Details are described as below

Split Tear Test Method

[0039] The split tear test is based on the SATRA TM65 (1992), keep the same preparation of test specimens according to article 5, while the sample size was modified to a thickness of 10±1mm and cutting 3 rectangular 25±1mm×160±5mm from the sheet material.

[0040] Procedure is as below;

1 Split one end of each test piece midway between the top and bottom surfaces for a distance of 16±4mm. Then make 4 successive 30 mm portions on specimen as shown in FIG. 1. The cutting tools and method are according to article 6.1 and 6.2.
2 Operate the machine with a jaw separation rate of 100±10mm/min until the split has propagated by each four 30 mm which indicated by the mark in FIG. 1 or has run to the surface. If the split does not propagate along the center of the test specimen but instead reaches the surface before 120 mm (4×30 mm) mark is reached, the value is not counted.
3 Repeat the procedure in above 2 for the other two specimens.

Data Collection & Analysis

[0041] 1 Record the lowest values for each of the four portions of each specimen. Calculate the average value of four lowest value of each specimen and record the results in the unit of N/mm.
2 Report the average value for each sample.

[0042] Table 3 below lists Comparative Examples 1, which include various polyol formulations but exclude expandable microspheres in Comparative Example 1.

[0043] To form the polyurethane elastomer foam of Example 1-6, heat the formulated polyol formulation at their given weight percent (wt. %) to a temperature of 40 to 45° C. inside the stirred reactor tank and heat the isocyanate pre-polymer at its given weight percent (wt. %) to a temperature of 30 to 35° C. in an isocyanate tank of a low pressure machine (Zhejiang Haifeng Shoemaking Equipment Co.,Ltd.). Heat an aluminum mold (test plate mold 200×200×10 mm) to a temperature of 55° C. Admix given parts in the table 3 of the isocyanate pre-polymer with 100 parts by weight of the polyol formulation at atmospheric pressure and pour the admixture using the low pressure machine into the heated aluminum mold. Close the mold, allow the reactants to fill the mold and react for given demolding time in the table 3.

Open the mold and demold the polyurethane elastomer foam. Allow the polyurethane elastomer foam to cure for 24 hours at 25° C. and 50% relative humidity before testing the physical properties of the polyurethane elastomer foam.

TABLE-US-00003 TABLE 3 Comparison of Mechanical Properties of Polyurethane foam of Examples 1 to 6 Against Comparative Example 1 of Polyurethane foam without expandable microspheres Comparative example 1 1 2 3 4 5 6 PTHF ® 2000 96.4 94.9 94.8 94.3 93.7 90.8 92.3 Water 0.8 0.8 1.4 1.4 2.0 1.4 1.4 Expancel 031 DU40 0 1.5 1.0 1.5 1.5 5 1.5 DABCO ® DC 193 (Silicone oil) 0.5 0.5 0.5 0.5 0.5 0.5 0.5 DABCO ® EG (Amine catalyst) 2 2 2 2 2 2 2 Diethanolamine 0.3 0.3 0.3 0.3 0.3 0.3 0.3 pure (Crosslinking agent) MEG (Chain extender) 2.0 Isocyanate prepolymer 49.7 49.7 63.2 63.2 76.5 61.1 77.4 NCO content of Isocyanate 18.0 18.0 18.0 18.0 18.0 18.0 18.0 prepolymer Demolding time (min) 7 7 7 7 10 7 7 Density(g/L) 280 280 280 280 280 280 280 Hardness (Asker C) 36 38 57 55 62 57 53 Rebound(%) 64 63 62 61 58 57 53 Split tear (N/mm) 0.86 1.28 2.05 2.23 2.76 2.6 1.90 Compression set % 14.5 19.3 13.2 14 6.8 19.8 17.4 Tensile strength (N/mm.sup.2) 1.83 1.88 2.42 2.3 2.66 2.06 2.23 Elongation (%) 456.6 447.6 383.6 386.7 411.3 372.4 362.8 Tear strength (N/mm) 6.86 7.09 8.56 8.45 9.94 9.05 8.64

[0044] The properties of Examples 1 and Comparative Examples 1 seen in Table 3 demonstrate that the absence of expandable microspheres has a negative impact on the split tear of the polyurethane foam.