TRANSPARANT DRAWN ARTICLE

Abstract

The invention relates to a stretched molded article comprising a polymer A and a compound B, wherein the polymer A is a polyamide or a polyolefin and is at least partially oriented and comprises a crystalline phase and a non-crystalline phase, wherein the mass of compound B is from 0.25 to 10 mass % relative to the mass of polymer A, and wherein the compound B has a refractive index (n.sub.B) higher than the isotropic refractive index of polymer A (n.sub.A). The invention further relates to a process for manufacturing such stretch molded article, the use of such stretch molded articles and a product comprising such stretch molded article.

Claims

1. A stretched molded article comprising a polymer A and a compound B, wherein the polymer A is a polyamide or a polyolefin and is at least partially oriented and comprises a crystalline phase and a non-crystalline phase, wherein the mass of compound B is from 0.25 to 10 mass % relative to the mass of polymer A, and wherein the compound B has a refractive index (n.sub.B) higher than the isotropic refractive index of polymer A (n.sub.A).

2. Molded article according to claim 1 wherein n.sub.B is at least 0.01 larger than n.sub.A, preferably at least 0.02, more preferably at least 0.05 and most preferably at least 0.1 larger than n.sub.A.

3. Molded article according to claim 1 wherein the mass of compound B relative to the mass of polymer A is from 0.3 to 8 mass %, preferably from 0.5 to 5 mass %.

4. Molded article according to claim 1, wherein the molded article is a fibre, a tape or a film.

5. Molded article according to claim 1 wherein the at least partially oriented polymer A is semi-crystalline, preferably highly crystalline, preferably the partly oriented polymer A has a heat of fusion of at least 50 J/g, preferably at least 100 J/g, most preferably at least 150 J/g, whereby the heat of fusion is determined by Differential Scanning calorimetry according to ASTM E 793-85.

6. Molded article according to claim 1 wherein the polymer A has a degree of orientation as derived from wide angle X-ray scattering (WAXS) of at least 0.6, preferably 0.7 most preferably at least 0.8.

7. Molded article according to claim 1 wherein the polymer A is a polyolefin, most preferably polymer A is polyethylene or polypropylene.

8. Molded article according to claim 7 wherein polyethylene (PE), is a linear low density polyethylene (LLDPE), low density polyethylene (LDPE), high density polyethylene (HDPE), high molecular weight polyethylene (HMWPE), ultra-high molecular weight polyethylene (UHMWPE) or any combination thereof, preferably the PE is HDPE, HMWPE, UHMWPE or any combination thereof, more preferably the PE has a density of at least 0.92 g/cm.sup.3, preferably of at least 0.93 g/cm.sup.3, more preferably of at least 0.94 g/cm.sup.3, even more preferably of at least 0.95 g/cm.sup.3 and most preferably of at least 0.96 g/cm.sup.3.

9. Molded article according to claim 1 wherein the article has a transmittance of at least 70%, preferably at least 80% and most preferably at least 90% when measured at a film thickness of 0.1 mm and at a wavelength of 550 nm.

10. Molded article according to claim 1 having a tensile strength of at least 0.5 GPa in at least on direction of the molded article.

11. Molded article according to claim 1 wherein part of the compound B is present in the non-crystalline phase of the polymer A, preferably at least 50 mass % of the compound B present in the molded article is present in the non-crystalline phase of polymer A.

12. Molded article according to claim 1 wherein the article is a monoaxial oriented fibre, a monoaxial oriented tape or film or a biaxial oriented tape or film.

13. A process for the production of the stretch molded article according to claim 1 comprising the steps of a) providing polymer A and compound B wherein the mass of compound B relative to the mass of polymer A is from 0.25 to 10 mass % and wherein the compound B has a refractive index (n.sub.B) higher than the isotropic refractive index of the polymer A (n.sub.A), wherein the polymer is a polyamide or a polyolefin, b) molding the polymer A and the compound B into a molded article, c) solid state stretching the molded article in at least one drawing step in at least one direction by a total draw ratio of at least 1.5, preferably of at least 2, more preferably of at least 3, even more preferably at least 5, most preferably of at least 8.

14. Use of a compound B with a refractive index n.sub.B as a clarifying agent for a stretch molded article comprising at least partially oriented polymer A with an isotropic refractive index n.sub.A, wherein n.sub.B is larger than n.sub.A.

15. An article comprising a molded article according to claim 1, preferably the article is a ballistic resistant article, a visor, a car part, a windshield, a window or a radome.

Description

EXPERIMENTAL

[0068] HDPE samples containing between 0.5 and 5 mass % of a compound B were prepared by blending the respective amounts in a co-rotating twin screw extruder at 160 C. The extrudates were cooled in a water bath at room temperature, air dried and pelletized into granules. Subsequently, isotropic sheets of approximately 1.0 mm thickness were produced by compression moulding at 160 C. Dumbbell-like samples with gauge dimensions 1.20.2 cm were then cut from the compression-moulded sheets. These dumbbell-like samples were subsequently drawn to various draw ratios at 80 C. in air using a Zwick Z100 tensile tester at a crosshead speed of 100 mm/min. The thickness of the drawn samples was calculated by weighing, assuming a density equal to 0.96 g/cm.sup.3. Refractive index of the isotropic sheets comprising 0-5 mass % of compound B were 1.50+/0.01 whereas the therefrom drawn samples had refractive indices of 1.54+/0.01.

[0069] Young's modulus, strength and transmittance of the tapes after uniaxial drawing were measured and are reported in Table 1. It is observed that the mechanical properties are maintained upon addition of the additive.

[0070] Furthermore can the influence of the solid state DR and the content of compound B on the transmittance of the films be observed in table 1. It is found that the transmittance as a function of DR exhibits a maximum and that its absolute value increases with increasing additive content. A high transmittance was achieved at draw ratios of 10 to 20 which correspond to maximum Young's modulus and strength of 20 GPa and 0.65 GPa, respectively.

TABLE-US-00001 TABLE 1 B [mass n.sub.B HoF X.sub.cw X.sub.cd Modulus Strength Thickn. Transm. Comp. B %] DR [J/g] [%] [%] [GPa] [GPa] [m] @550 nm [%] Comp. A BZT 1 1.575 1 170.2 65.5 60.7 0.5 0.044 500 Example 1 BZT 1 1.575 15 198.8 68.8 71.0 11.6 0.431 120 81 Comp. B BZT 2 1.575 1 168.0 62.9 60.0 0.3 0.046 500 Example 2 BZT 2 1.575 10 62.3 8.1 0.370 160 90 Example 3 BZT 2 1.575 15 197.8 66.4 70.6 12.6 0.469 120 90 Example 4 BZT 2 1.575 20 67.5 18.2 0.643 100 89 Example 5 BZT 5 1.575 20 100 90 Example 6 CO 2 1.533 10 160 87 Example 7 OS 2 1.576 10 160 88 Comp. C 1 166.4 65.3 59.3 0.4 0.048 500 Comp. D 10 65.1 6.9 0.343 160 50 Comp. E 15 205.2 68.9 73.3 12.5 0.447 120 53 Comp. F 20 71.4 18.9 0.657 100 46 Comp. G PO 2 1.473 10 160 53 Comp. H FX-5911 2 1.36 10 160 39

[0071] It is well-known that the drawn films might suffer from surface light scattering, thus resulting in a loss of transmittance. In an additional measurement a few drops of paraffin oil were coated on the surface of the drawn HDPE films of example 2, 4 and comparative B. The films were subsequently sandwiched between two glass slides. A further slight improvement of transmittance in the range of 2 and 4% in optical transmittance upon coating with a low viscous fluid is observed. Highly transparent drawn HDPE films with a truly glass-like appearance (transmittance >90%) could be obtained.