Method for selecting material of injection-molded article and method for manufacturing injection-molded article

Abstract

The present application relates to a method for selecting an injection-molded article and a method for manufacturing an injection-molded article. An injection-molded article having excellent crack stability can be produced using the material selected using the described selection method without having to manufacture test articles through injection molding.

Claims

1. A method for selecting a material of an injection-molded article, the method comprising: preparing a first specimen, which is a polyethylene sheet having a width of 6 mm, a height of 10 mm and a thickness of 0.3 mm; preparing a second specimen by injection-molding polyethylene in a form of a dog bone having a thickness of 3 mm, a width of 3 mm and an elongation part length of 13 mm; measuring a complex modulus of the first specimen at 25° C.; measuring elongation (A) in a transverse direction of the second specimen and elongation (B) in a longitudinal direction of the second specimen at 25° C. to determine an elongation ratio (A/B); and selecting a polyethylene having the complex modulus of 1.80 GPa or less and the elongation ratio (A/B) of 2.8 or less as a selected polyethylene for injection molding.

2. The method for selecting a material of an injection-molded article according to claim 1, wherein the first specimen is prepared by dissolving polyethylene pellets at 1500 C to 250° C. and subjecting the dissolved polyethylene pellets to a pressing process at a molding pressure of 20 to 25 MPa.

3. The method for selecting a material of an injection-molded article according to claim 1, wherein the complex modulus of the first specimen is measured by applying a displacement of 0.1% at a frequency of 1 Hz to the first specimen in a longitudinal direction of the first specimen at 25° C.

4. The method for selecting a material of an injection-molded article according to claim 1, wherein the second specimen is prepared by an injection molding method with a resin temperature of 190° C. to 250° C., a mold temperature of 40° C. to 60° C. and a molding pressure of 0.6 MPa to 1.2 MPa.

5. The method for selecting a material of an injection-molded article according to claim 1, wherein the elongation ratio (A/B) of the second specimen is calculated by measuring the elongation (A) in the transverse direction and the elongation (B) in the longitudinal direction at an elongation speed of 300 mm/min at 25° C.

6. The method for selecting a material of an injection-molded article according to claim 1, wherein the complex modulus of the selected polyethylene is from 1.3 GPa to 1.80 GPa and the ratio (A/B) of the selected polyethylene is from 1.5 to 2.8.

7. The method for selecting a material of an injection-molded article according to claim 1, wherein the second specimen has an elongation (A) of 1.8 to 2.5 and elongation (B) of 1.25 to 1.45.

8. A method for manufacturing an injection-molded article using polyethylene as a raw material, the method comprising: selecting a polyethylene having a complex modulus in a range of 1.3 GPa to 1.80 GPa, wherein the complex modulus of a first specimen of the polyethylene is measured in a form of a sheet having a width of 6 mm, a height of 10 mm and a thickness of 0.3 mm at 25° C., and having a ratio (A/B) of elongation (A) in a transverse direction and elongation (B) in a longitudinal direction of 1.5 to 2.8 wherein the ratio (A/B) of a second specimen of the polyethylene is measured in a form of a dog bone having a thickness of 3 mm, a width of 3 mm and an elongation part length of 13 mm, and preparing the injection-molded article by injection molding.

9. The method for manufacturing an injection-molded article according to claim 8, wherein the injection molding is carried out at a resin temperature of 190° C. to 250° C., a mold temperature of 40° C. to 60° C. and a molding pressure of 0.6 MPa to 1.2 MPa.

10. The method for manufacturing an injection-molded article according to claim 8, wherein the first specimen is prepared by dissolving polyethylene pellets at 150° C. to 250° C. and subjecting the dissolved polyethylene pellets to a pressing process at a molding pressure of 20 to 25 MPa.

11. The method for manufacturing an injection-molded article according to claim 8, wherein the complex modulus is measured by applying a displacement of 0.1% at a frequency of 1 Hz in the longitudinal direction of the first specimen at 25° C.

12. The method for manufacturing an injection-molded article according to claim 8, wherein the second specimen is prepared by an injection molding method with a resin temperature of 190° C. to 250° C., a mold temperature of 40° C. to 60° C. and a molding pressure of 0.6 MPa to 1.2 MPa.

13. The method for manufacturing an injection-molded article according to claim 8, wherein the elongation (A) in the transverse direction and the elongation (B) in the longitudinal direction are measured at an elongation speed of 300 mm/min at 25° C.

14. The method for manufacturing an injection-molded article according to claim 8, wherein the polyethylene has elongation (A) in the transverse direction of 1.8 to 2.5 and elongation (B) in the longitudinal direction of 1.25 to 1.45.

15. The method for manufacturing an injection-molded article according to claim 8, wherein the injection-molded article is a crucible.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The FIGURE is a view showing results of measuring complex moduli and ratios of elongation in the transverse direction to elongation in the longitudinal direction in Examples and Comparative Examples of the present invention.

MODE FOR INVENTION

(2) Hereinafter, the present application will be described in more detail by way of examples according to the present application and comparative examples that do not comply with the present application, but the scope of the present application is not limited by the examples as set forth below.

(3) In order to evaluate crack stability of injection-molded articles made of seven types of polyethylene, the complex modulus and the ratio of elongation in the transverse direction and elongation in the longitudinal direction were measured from polyethylene as follows.

(4) 1. Measurement of Complex Modulus

(5) Polyethylene pellets were dissolved at 200° C. and the dissolved polyethylene pellets were applied to a pressing process at a molding pressure of 20 to 25 MPa to prepare a specimen in the form of a sheet having a width of 6 mm, a height of 10 mm and a thickness of 0.3 mm.

(6) The complex modulus was measured by applying a displacement of 0.1% at a frequency of 1 Hz to the specimen at 25° C. using Q800, a dynamic mechanical analyzer (DMA) from TA instruments. The measurement results were shown in Table 1 below.

(7) 2. Determination of Ratio of Elongation in the Transverse Direction to Elongation in the Longitudinal Direction

(8) Polyethylene was injection-molded by an injection molding method with a resin temperature of about 230° C., a mold temperature of about 50° C. and a molding pressure of about 0.9 to 1.0 MPa to prepare a specimen in the form of a dog bone having a thickness of 3 mm, a width of 3 mm, and an elongation part length of 13 mm.

(9) Using a universal testing machine (UTM), the specimen was elongated to the breaking point in the transverse direction and the longitudinal direction at an elongation speed of 300 mm/min at 25° C., and elongation in the transverse direction and elongation in the longitudinal direction (B) were measured. The measurement results were shown in Table 1 below.

(10) 3. Crack Stability Test

(11) Polyethylene was injection-molded by an injection molding method with a resin temperature of about 230° C., a mold temperature of about 50° C. and a molding pressure of about 0.9 to 1.0 MPa to manufacture a crucible having a top surface diameter of 30 cm, a bottom surface diameter of 27 cm and a height of 36 cm.

(12) The crucible manufactured by injection molding was filled with water and treated with a lid so as to prevent water from leaking during a drop process, and then, it was observed whether or not cracks were generated on the bottom surface and side surface of the crucible by dropping the crucible 10 times from a 2M height to the bottom surface and the side surface, respectively. Observation results were shown in Table 1 below, where notation criteria are as follows.

(13) O: cracks were found on both side and bottom surfaces of crucible.

(14) X: cracks were not found on the side surface or the bottom surface of crucible.

(15) TABLE-US-00001 TABLE 1 Bending Complex Yield elastic Elongation modulus Crack strength modulus Elongation ratio (GPa) occurrence (MPa) (MPa) Example 1 Transverse direction 1.345 1.84 1.73 X 24.8 932-1030 Longitudinal direction 2.47 25.8 2 Transverse direction 1.435 2.04 1.70 X 24.8 Longitudinal direction 2.93 26.4 Comparative 1 Transverse direction 1.37 1.80 1.83 ◯ 25.3 Example Longitudinal direction 2.47 27.0 2 Transverse direction 0.56 3.51 1.9 ◯ 23.3 Longitudinal direction 1.963 26.2 3 Transverse direction 0.536 2.89 1.73 ◯ 23.6 Longitudinal direction 1.549 26.3 4 Transverse direction 0.514 1.45 1.86 ◯ 25.4 Longitudinal direction 0.743 27.1 5 Transverse direction 0.603 2.91 1.70 ◯ 23.5 Longitudinal direction 1.753 24.9