Kha nang chiu thoi tiet cua PC gia cuong va co che
Polycarbonate (PC) noi tieng voi do trong suot xuat sac, do ben va dap cao va tinh on dinh kich thuoc, duoc su dung rong rai trong dien tu va thiet bi dien, chieu sang o to, vo den chieu sang ngoai troi, mu bao hiem va cac linh vuc khac. Tuy nhien, PC nguyen chat co mot van de noi bat trong su dung ngoai troi lau dai: tia cuc tim (UV) gay ra hien tuong ngã vang, nut be mat va suy giam dang ke tinh chat co hoc, tuc la kha nang chiu thoi tiet khong du. Thong qua gia cuong bang soi thuy tinh ket hop voi chat on dinh UV va chat on dinh nhiet, tuoi tho cua PC trong moi truong ngoai troi co the duoc cai thien dang ke. Bai viet nay danh gia co he thong kha nang chiu thoi tiet cua PC gia cuong va cung cap giai phap chon vat lieu cho ung dung ngoai troi.
Co che lao hoa cua PC: tai sao PC gia cuong can chu y den kha nang chiu thoi tiet
Nguyen nhan co ban khien PC bi suy giam ngoai troi la cac don vi cau truc bisphenol A (BPA) trong chuoi phan tu cua no dac biet nhay cam voi tia cuc tim trong dai 290-315 nm. Chieu xa UV gay ra su phan huy quang oxy hoa cac chuoi phan tu PC, tao ra goc phenoxy va cau truc quinoid, ve mat vi mo bieu hien la ngã vang dan, vet nut vi mo tren be mat (ran) va giam do bong. Khi lao hoa tang len, khoi luong phan tu giam va do ben va dap giam manh tu muc PC nguyen chat ban dau (khoang 600-900 J/m, Izod co khia) xuong duoi 100 J/m.
PC gia cuong soi thuy tinh (nhu PC+GF10 hoac PC+GF20) them soi thuy tinh vao nen. Ban than soi thuy tinh tuong doi on dinh voi UV, nhung be mat tiep giap giua soi thuy tinh va nen PC la vung yeu: chieu xa UV de gay bong tach be mat tiep giap va lan truyen vet nut vi mo. Do do, kha nang chiu thoi tiet cua PC gia cuong khong nhat thiet tot hon PC nguyen chat; nguoc lai, no doi hoi cong thuc bao ve UV nghiem ngat hon.
Giai phap cai thien kha nang chiu thoi tiet cua PC gia cuong
Cac giai phap hien duoc cong nhan la hieu qua de cai thien kha nang chiu thoi tiet cua PC gia cuong bao gom: them chat hap thu UV (UVA) lam tuyen phong thu dau tien, hap thu nang luong UV co hai va chuyen hoa thanh nhiet de tan bien; them chat on dinh anh sang amin can tro (HALS) de loai bo cac goc tu do da hinh thanh va cat dut phan ung day chuyen quang oxy hoa; lop phu be mat (nhu lop phu cung dong ran bang UV hoac mang ma nhom) de tao rao can vat ly; va ap dung quy trinh ep phun hai lop de ket hop lop be mat PC on dinh UV voi loi PC gia cuong.
Vat lieu PC gia cuong duoc cai tien day du bang cac giai phap tren co the giu chenh lech mau DeltaE trong pham vi 3,0 trong thu nghiem lao hoa nhan tao gia toc (tieu chuan ISO 4892, buong lao hoa ho quang xenon trong 1.000-2.000 gio), va ty le duy tri do ben va dap co the duy tri tren 70%. Theo cac thu nghiem phoi nhiem ngoai troi thuc te, o mien nam Trung Quoc (phoi nhiem UV cao), tuoi tho cua PC gia cuong on dinh UV co the dai gap 3-5 lan so voi PC gia cuong thong thuong, dat thoi han su dung ngoai troi 5-8 nam.
So sanh hieu suat ngoai troi cua PC gia cuong voi ASA va PMMA
Trong ung dung ngoai troi, cac vat lieu canh tranh chinh cua PC gia cuong bao gom ASA, PMMA va hop kim ASA/PC. Ban than ASA co kha nang chiu thoi tiet xuat sac va co the dat tuoi tho ngoai troi hon 5 nam ma khong can on dinh UV bo sung; PMMA (acrylic) co kha nang chiu thoi tiet tot nhat nhung do ben va dap thap hon nhieu so voi PC gia cuong. Uu diem noi bat cua PC gia cuong la giu duoc loi the do ben va dap cao trong khi cung cap kha nang chiu thoi tiet tot, cho phep che tao mot chi tiet co thanh mong hon hoac cau truc chuc nang tich hop phuc tap hon so voi ASA.
Huong dan chon vat lieu cho ung dung ngoai troi cua PC gia cuong
Khi chon PC gia cuong cho cac tinh huong ngoai troi, khuyen nghi tuan theo cac nguyen tac sau: Xac nhan tuoi tho du kien cua san pham va yeu cau giu mau: thay doi chenh lech mau o san pham mau toi (den, xam dam) it de nhan thay, nen yeu cau ve on dinh UV co the thap hon mot chut so voi san pham mau sang va trong suot. Xac nhan co can cap chong chay hay khong: vo thiet bi dien tu ngoai troi thuong yeu cau cap chong chay UL94 V-0, va cong thuc chong chay va cong thuc on dinh UV can duoc toi uu phoi hop. Xac nhan ham luong soi thuy tinh: PC+GF10 hoac PC+GF20 duoc khuyen nghi cho cac chi tiet vo ngoai troi, vi ham luong soi thuy tinh cao hon (tren GF30) co the gay noi soi be mat va tap trung ung suat lam tram trong them lao hoa UV.
Cuoi cung, hay chon cac thuong hieu va ma vat lieu truong thanh da vuot qua hon 1.000 gio thu nghiem lao hoa nhan tao theo tieu chuan ASTM D4329 hoac ISO 4892-2, va danh gia can than du lieu thu nghiem lao hoa cua nha cung cap.
