Process for producing a polymer tape from a powder

Abstract

The invention relates to a process for the production of a non-fibrous drawn polymer tape, said process comprising the steps: a) compacting a polymer powder in a press to form a compacted polymer bed; b) calendering said compacted polymer bed to form an oriented polymer tape; and c) drawing said oriented polymer tape to form a highly oriented polymer tape; characterized in that step a) comprises compacting the polymer powder at a temperature and pressure such that from 0.1 to 20 wt. % of the polymer powder as measured by DSC is melted. The invention also relates to a tape obtainable by the above process, and a monolayer, multilayered material sheet and ballistic resistant article comprising such a tape.

Claims

1. A process for the production of a non-fibrous drawn polymer tape, said process comprising the steps: a) forming a compacted polymer bed by compacting a polymer powder which comprises ultra-high molecular weight polyethylene (UHMWPE) at a temperature and pressure such that from 1 to 20 wt. % of the polymer powder as measured by Differential Scanning Calorimetry (DSC) is melted; b) calendering said compacted polymer bed to form an oriented polymer tape; and c) drawing said oriented polymer tape to form a highly oriented polymer tape.

2. The process according to claim 1, wherein step a) is practiced such that from 1 to 5 wt. % of the polymer powder is melted.

3. The process according to claim 1, wherein the polymer powder is compacted in a double belt press.

4. The process according to claim 1, wherein the polymer powder comprises particles having an average particle size of up to 1000 μm.

5. The process according to claim 4, wherein the UHMWPE powder comprises polyethylene having an intrinsic viscosity greater than 5 dl/g.

6. A non-fibrous drawn polymer tape obtained by the process according to claim 1.

7. A monolayer comprising a plurality of uniaxially aligned non-fibrous polymer tapes, wherein each tape is the non-fibrous drawn polymer tape according to claim 6.

8. A monolayer comprising a plurality of woven non-fibrous polymer tapes, wherein each tape is the non-fibrous drawn polymer tape according to claim 6.

9. A multilayered material sheet comprising a consolidated stack of monolayers, wherein each monolayer is the monolayer according to claim 7.

10. A ballistic resistant article comprising a multilayered material sheet according to claim 9 and a further material sheet, wherein the material of the further material sheet is a metal or metal alloy selected from the group consisting of steel, aluminum, magnesium, titanium, nickel, chromium, and iron, and/or a non-metal selected from the group consisting of ceramic, glass, graphite, and combinations thereof.

11. A process for producing a monolayer comprising: (i) forming a parallel arrangement of tapes by arranging a plurality of the non-fibrous drawn polymer tapes according to claim 6 in parallel such that adjacent tapes partially overlap; and (ii) consolidating the parallel arrangement under pressure and at a temperature such that at least a portion of the polymer forming the tapes melts as determined by DSC.

12. A process for producing a monolayer comprising: (i) forming a woven arrangement of tapes by weaving a plurality of the non-fibrous drawn polymer tapes according to claim 6; and (ii) consolidating the woven arrangement of tapes under pressure and at a temperature such that at least a portion of the polymer forming the tapes melts as determined by DSC.

13. A process for producing a multilayered material sheet comprising: (i) stacking a plurality of the monolayers according to claim 7, and (ii) consolidating the stack of monolayers under pressure and at a temperature such that at least a portion of the polymer of the monolayers melts as determined by DSC.

14. A process for producing a ballistic resistant article comprising: (i) stacking a plurality of the monolayers according to claim 7 together with a further material sheet, wherein the material of the further material sheet is a metal or metal alloy selected from the group consisting of steel, aluminum, magnesium, titanium, nickel, chromium, and iron, and/or a non-metal selected from the group consisting of ceramic, glass, graphite, and combinations thereof, and (ii) consolidating the stack of the monolayers and further material sheet under pressure and at a temperature such that at least a portion of the polymer forming the monolayers melts as determined by DSC.

Description

(1) FIG. 1 shows a comparative DSC curve between UHMWPE powder prior to compaction and tape produced according to Example 1. Temperature is plotted on the X axis and % melted material is plotted on the Y axis. A peak at approximately 130° C. is shown at approximately 5% melted material.

EXAMPLES

(2) Methods of Measurement

(3) Tensile properties, e.g. tensile strength and tensile modulus of the adhesive tape and of the tapes and of films according to this invention were defined from tensile testing. The width and thickness of the tapes were measured with a micrometer having an accuracy of 1 μm for the thickness and with a Vernier caliper with 100 μms accuracy for the width. The cross section area was obtained by multiplying width and thickness and expressed as square mm (mm.sup.2). Clamping was done in such a way that clamping damage was prevented, e.g. was done by draping the ends of the tapes around a circular bar, thus allowing load introduction by the capstan effect. The encircling around the circular bar was 180 degree and then the bar was clamped with mechanical means. A nominal gauge length of the tape of 440 mm and a crosshead speed of 50 mm/min were chosen. Tensile strength was obtained by measuring the breaking force, expressing it in newton and dividing that breaking force by the cross section area. The resulting breaking stress in N/mm.sup.2 is identical to a stress expressed in MPa (1 MPa=1 N/mm.sup.2). A modulus was obtained by adding reflective markers on the tape and measuring elongation (increase of distance between the markers) with optical means. The strain was then obtained by dividing the distance increase by the original distance. A modulus was obtained by dividing the stress difference by the according strain. Typically the modulus was obtained at a strain of about 0.15%, where initial setting of the specimens in the clamps and straightening was completed, but non-linearites occurring at higher strains were not yet present. Intrinsic Viscosity (IV) is determined according to ASTM-D1601/2004 at 135° C. in decalin, the dissolution time being 16 hours, with DBPC as anti-oxidant in an amount of 2 g/I solution, by extrapolating the viscosity as measured at different concentrations to zero concentration. There are several empirical relations between IV and Mw, but such relation is highly dependent on molar mass distribution. Based on the equation Mw=5.37*10.sup.4 [IV].sup.1.37 (see EP 0504954 A1) an IV of 4.5 dl/g would be equivalent to a Mw of about 422 kg/mol. Differential Scanning calorimetry (DSC) was performed according to DIN EN ISO 11357-3 using standard heat flux DSC of Mettler Toledo. Samples of 1-5 mg mass were weighed with a precision balance and encapsulated in (crimped) aluminium pans of known mass. An identical empty pan was used as a reference. Nitrogen was purged at a rate of 50 ml min′. Heating-cooling-heating cycles in the range 0 to 200° C. at a rate of 10K/min were applied. The % melted polymer was calculated by comparing the DSC curve for polymer powder prior to compacting against that of a compacted powder bed, by the following procedure: i. Carrying out DSC of polymer powder prior to compaction ii. Carrying out DSC of compacted powder bed iii. Plotting curves of % melted material against temperature for i. and ii, normalized for 100% mass of each sample iv. Subtracting the curve of i. from the curve of ii. to give % difference in melted material v. Reading the % increase in material at the peak present below the melting temperature of the polymer powder.

(4) For ultra-high molecular weight polyethylene powder, the polymer powder used in the examples, this peak occurs between 125 and 137° C.

Example 1

(5) UHMWPE powder GUR2014 was obtained from Ticona, Germany. DSC was carried out on the powder as described in the method section.

(6) A powder bed of UHMWPE powder was compacted in a double belt press at a pressure of 4 MPa and a temperature above 142° C. The aerial density of the powder bed was 1 kg per square meter. A sample of the compacted powder bed was subjected to DSC as described in the method section. The DSC curve was compared with the DSC curve for the polymer powder as described in the method section, and the % melted polymer was calculated. An increase in melted polymer of 5% was shown at the peak in the comparative DSC curve at approximately 130° C.

(7) The resulting compacted polymer bed was compressed between two calendar rolls at a temperature of 135° C., to a thickness of 270 μm and subsequently was drawn with a factor 10 in an oven at 147° C. and then it was drawn again in another oven with a factor 2.5 at a temperature of 150° C. The resulting oriented tape had a thickness of 42 μms, a tensile strength of 1.7 GPa, a tensile modulus of 115 GPa and a width of 35 cm. The tape was slit to 2 mm in width.

Examples 2 and 3

(8) A 25 cm length of 2 mm wide tape was laid on a metal plate of 25×30 cm covered with silicon paper. A second identical tape was laid on top such that 100% of the surface of the first tape was covered. Two such samples were prepared and consolidated under a pressure of 4 MPa and temperature of 127° C. for 15 minutes. The consolidated samples were removed.

(9) Adhesion was measured by a peel test. Samples were placed in a tensile tester and a T-test was performed over a length of 100 mm. The tensile tester was a Zwick Z005, using 8253 2.5 kN clamps with 15 mm grip to grip and due to the curve 30 mm distance between the clamping contact points. The speed was 50 mm/min. The results are summarised in Table 1.

Comparative Experiments 1 and 2

(10) Endumax® TA23 UHMWPE tape, Teijin, the Netherlands was purchased. The tape was produced by a process wherein, during compaction of the polymer powder bed no polymer in the powder bed was melted. A 25 cm length of 2 mm wide tape was laid on a metal plate of 25×30 cm covered with silicon paper. A second identical tape was laid on top such that 100% of the surface of the first tape was covered. Two such samples were prepared and consolidated separately under a pressure of 4 MPa and temperature of 127° C. for 15 minutes. The consolidated samples were removed and a peel test was conducted on each as described for Examples 2 and 3, as described in the method section. The average of the two results is 0.1 N. The results are summarised in Table 1.

(11) TABLE-US-00001 TABLE 1 % melted material at peak 125 to Peeling Force Sample 137° C. by comparative DSC (N) Ex. 2 5 0.2273 Ex. 3 5 0.2135 Comp. 0 0.097 Ex. 1 Comp. 0 0.101 Ex. 2

(12) The results indicate that a tape produced according to the Examples, i.e. with 5% melting of the powder in the polymer powder bed as shown by DSC comparison with the polymer powder, has approximately double the adhesion of the tape of the Comparative Experiments, i.e. representing the prior art.

Comparative Experiment 3

(13) UHMWPE powder GUR168 was obtained from Ticona, Germany. DSC was carried out on the powder as described in the method section.

(14) A compacted polymer bed was produced by placing 15.6 g polymer powder in a 40*180 mm mould. The powder was placed in a Fontijne T1000 press wherein the temperature was increased over 30 minutes such that the temperature of the material was measured at 11TC, after which the press was closed and the material subjected to a pressure of 350 kN for 5 minutes. After pressing, the mould was cooled to 35° C. DSC was carried out on the compacted polymer bed as described in the method section. The % melted material was calculated by comparison with the DSC for the GUR168 polymer powder.

(15) The compacted polymer bed was preheated to 130° C. for 3 minutes before being passed through calendars to produce a tape with a thickness of approximately 500 μm, retaining 40 mm width.

(16) The Calendared tapes were cut into strips and two strips were placed with an overlap of 50 mm length. The thickness of the overlapped portion was measured and metal strips 50 μm thinner than the overlapped tapes was placed either side such that during pressing, only the overlapped portion is pressed. The overlap of the strips was pressed at 800 kN at 130° C. (preheating to 123° C.) for 60 minutes, then cooled under force to 50° C.

(17) Adhesion was measured by a peel test. Samples were placed in a tensile tester and a T-test was performed over a length of 100 mm. The tensile tester was a Z1474-2, using 1 kN pneumatic grips, with a preload of 1 N and a speed of 5 mm/min. The results are summarised in Table 2.

Examples 4 and 5

(18) Comparative Experiment 3 was repeated, except that that in the Fontijne T1000 press, the temperature of the material was measured at 128° C. (Example 4) and 138° C. (Example 5) rather than 11TC. % melted material for each Example was calculated in the same way as for Comparative Experiment 5. A peel test was for each Example was carried out the same way as for Comparative Experiment 5.

(19) TABLE-US-00002 TABLE 2 % melted material at peak 125 Peeling Force Sample to 137° C. by comparative DSC (N/mm.sup.2) Ex. 4 0.43 0.03 Ex. 5 2.56 0.14 Comp. 0 Fell apart - no adhesion Ex. 3 measureable

(20) The results indicate that by applying higher temperatures during compaction of the polymer powder bed, a larger degree of melting occurs. As a result, the peeling force required to separate two strips of calendared material consolidated together also increases.