Laser markable microporous material

1. A microporous material having improved laser marking capability, the microporous material comprising:

(a) a polyolefin matrix;

(b) finely divided, substantially water-insoluble filler distributed throughout the matrix, said filler comprising siliceous material and from 3 to 20 weight percent of titanium dioxide, based on the microporous material, said siliceous materiai being at least 50 weight percent of said filler;

(c) a network of interconnecting pores communicating throughout the microporous material, the pores constituting 10 to 80 percent by volume of the microporous material;

(d) 4 to 10 weight percent, based on the microporous material, of a particulate contrast enhancing material, other than titanium dioxide, that is distributed throughout the matrix;

and wherein the particulate contrast enhancing material comprises reduced tungsten oxide, tin antimony oxide, tin antimony gray Cassiterite or mixtures thereof.

2. The microporous material of claim 1 , wherein the polyolefin matrix material comprises a mixture of

(a) 1 to 99 weight percent of substantially linear, ultrahigh molecular weight polyethylene; and

(b) 99 to 1 weight percent of high density polyethylene.

3. The micro porous material of claim 2 , wherein the polyolefin matrix material further comprises a thermoplastic organic polymer different from polyethylene.

4. The microporous material of claim 3 , wherein the thermoplastic organic polymer is selected from the group consisting of poly(tetrafluoroethylene), polypropylene polycarbonates, polyethylene terephthalate, glycol-modified polyethylene terephthalate, polyamides, polyurethanes, copolymers of ethylene and propylene, copolymers of ethylene and acrylic acid, copolymers of ethylene and methacrylic acid, and mixtures thereof.

5. The microporous material of claim 3 , wherein the particulate contrasting enhancing material further comprises a thermoplastic organic polymer coated with antimony oxide and/or reduced tungsten oxide.

6. The microporous material of claim 1 , wherein the filler further comprises non-siliceous materials different from the titanium dioxide.

7. The microporous material of claim 1 , wherein the sum of the weight percent of the titanium dioxide comprising the microporous material and the weight percent of the contrast enhancing material comprising the microporous material is at least 7 weight percent based on total weight of the microporous material.

8. The microporous material of claim 1 , wherein the titanium dioxide is present in an amount ranging from 3 to 15 weight percent.

9. A multilayer article comprising:

(a) at least one layer of the microporous material of claim 1 in the form of a sheet; and

(b) at least one transparent layer of polymeric material different from the polyolefin matrix material of the microporous material of layer (a) that is affixed to a surface of the sheet.

10. The multilayer article of claim 9 , wherein the sum of the weight percent of the titanium dioxide comprising the microporous material and the weight percent of the contrast enhancing material comprising the microporous material is at least 7 weight percent based on total weight of the microporous material.

11. The multilayer article of claim 9 , wherein the titanium dioxide is present in an amount ranging from 5 to 15 weight percent.

12. The multilayer article of claim 11 , wherein the contrast enhancing material also is present as a component of the transparent layer of polymeric material affixed to a surface of the microporous material sheet.

13. The multilayer article of claim 9 wherein the article is a document selected from the group consisting of national identification cards, health insurance cards, institutional identification cards, entitlement cards, loyalty cards, driver's licenses, passports, membership cards, credit cards, banking cards, medical information cards, and security cards.