Multiple calender process for forming non-fibrous high modulus ultra high molecular weight polyethylene tape
View Patent ↗A multi-calender process for forming a high modulus, high strength component for use in ballistic-resistant articles. The process includes forming ultrahigh molecular weight polyethylene powder into a uniform sheet at a low pressure. Multiple calender units mold and draw the uniform sheet into a non-fibrous, monolithic, ultra high molecular weight polyethylene tape. The multi-calender process and subsequent draw stages stretch the non-fibrous UHMWPE tape to a total draw of at least 100 to 1 to produce a high modulus, high strength UHMWPE component with a modulus of 1,400 grams per denier or greater. The multi-calender process of the present invention enables production of a high-strength, high-modulus UHMWPE component for ballistic-resistant articles and other applications at significantly higher rates and at a lower unit cost.
1. A process for continuously producing a highly oriented non-fibrous ultra high molecular weight polyethylene tape comprising:
feeding particles of ultra high molecular weight polyethylene into a forming device, said forming device including an upper and lower rotating belt;
applying pressure from said upper and lower rotating belts to said polyethylene particles between said upper and lower rotating belts to remove a substantial amount of air from said polyethylene particles and to bond said polyethylene particles into a continuous sheet;
heating said continuous sheet to a temperature near the melting point of said polyethylene;
rolling and stretching said heated sheet in a first calender unit to form a partially oriented polyethylene web;
rolling and stretching said partially oriented polyethylene web in at least one additional calender unit to form a fully oriented polyethylene web; and
drawing said fully oriented polyethylene web to form said highly oriented non-fibrous ultra high molecular weight polyethylene tape, said UHMWPE polyethylene tape including a modulus of at least 1,400 grams per denier.
2. The process of claim 1 wherein said pressure from said upper and lower rotating belts is between 2 and 20 kg/cm 2 .
3. The process of claim 1 wherein said partially oriented sheet at the exit of said first calender unit includes a density of at least 0.93 gm/cm 3 .
4. The process of claim 1 wherein said ultra high molecular weight polyethylene particles include a viscosity-average molecular weight of between 800,000 to 4,500,000.
5. The process of claim 1 wherein said UHMWPE polyethylene tape includes
a denier of 6,000 or greater;
a width of at least 1.0 inch;
a thickness of between 0.0015 and 0.004 inch; and
a width to thickness ratio of at least 400:1.
6. The process of claim 1 wherein said ultra high molecular weight polyethylene tape is drawn to a total draw ratio of 100:1 or greater.
7. The process of claim 1 wherein said ultra high molecular weight polyethylene particles include
a crystallinity of at least 76%; and
a heat of fusion of 220 joules/gram or greater.
8. The process of claim 1 wherein said partially oriented polyethylene at the exit of said first calender includes a density of at least 0.89/cm 3 .
9. The process of claim 1 wherein said tape includes intermediate stages of
a friable sheet formed from light pressing of UHMWPE particles;
a partially oriented UHMWPE sheet formed from calendering said friable sheet in said first calender unit;
a fully oriented UHMWPE sheet formed from calendering said partially oriented UHMWPE sheet in said second calender unit; and
a highly oriented UHMWPE tape formed from drawing said fully oriented UHMWPE sheet under carefully controlled tension and carefully controlled temperature to a total draw ratio of 100:1 or greater.
10. The process of claim 9 wherein said tension in drawing said fully oriented UHMWPE sheet is between 0.5 and 5.0 grams per denier.
11. The process of claim 9 wherein said temperature of calendering is between 132° C. and 143° C.
12. The process of claim 9 wherein said pressing is at a temperature between 132° C. and 138° C.
13. The process of claim 1 wherein said tape is a monolithic structure.
14. The process of claim 1 wherein each of said first and said additional calender units stretch the polyethylene sheet to a total draw ratio of between 2 and 7.
15. The process of claim 1 wherein each of said calender units includes
a pair of nip rolls including a first nip roll and a second nip roll; and
said first nip roll runs at a different speed than said second nip roll.
16. The process of claim 1 wherein the speed of said fully oriented polyethylene web exiting said additional calender unit is between 4 and 18 meters per minute.
17. A process for producing a highly oriented non-fibrous ultra high molecular weight polyethylene tape including the steps of:
providing an ultra high molecular weight polyethylene powder having a viscosity-average molecular weight of between 800,000 to 4,500,000;
pressing said polyethylene powder at a temperature lower than the melting point of said polyethylene powder to form a friable polyethylene sheet and remove air from said friable sheet;
calendering said friable polyethylene sheet between a first set of calender rolls to form a partially oriented polyethylene sheet;
calendering said partially oriented polyethylene sheet between at least one additional set of calender rolls to form a fully oriented polyethylene sheet; and
drawing said fully oriented polyethylene sheet to form a highly oriented polyethylene tape of substantially rectangular cross-section and having a modulus of at least 1,400 gpd.
18. The process of claim 17 wherein said friable polyethylene sheet, said partially oriented polyethylene sheet, and said highly oriented polyethylene tape are maintained in a monolithic state and not subjected to slitting or splitting.
19. The process of claim 17 including
an efficiency defined by weight of first grade tape produced divided by weight of polyethylene powder input; and
said efficiency is at least 95%.