Light blocking articles having opacifying layers
A light-blocking article is designed to be lightweight but effective to block most incident actinic radiation and can be designed into fabrics, curtains, and other materials. Such an article has an opacifying layer that is capable of blocking predetermined electromagnetic radiation. The article contains (a) porous particles comprising a continuous polymeric binder and pores within the continuous polymeric binder, the porous particles having a glass transition temperature of at least 25° C. and a mode particle size of at least 2 μm and up to and including 50 μm. The article also contains an opacifying colorant that absorbs the predetermined electromagnetic radiation (such as within 400 nm to 700 nm), in an amount of at least 0.001 weight % based on the total dry weight of the opacifying layer, and a matrix polymer in which the porous particles and opacifying colorant are dispersed.
1. An article comprising a dry opacifying layer that comprises:
(a) porous particles comprising a continuous polymeric binder and pores within the continuous polymeric binder, the (a) porous particles having a glass transition temperature of at least 25° C., a porosity of at least 10% and up to and including 70%, and a mode particle size of at least 3 μm and up to and including 40 μm, the (a) porous particles being present in an amount of at least 40 weight % based on the total dry weight of the dry opacifying layer,
(b) an opacifying colorant that absorbs predetermined electromagnetic radiation within at least 380 nm and up to and including 780 nm, the (b) opacifying colorant being present in an amount of at least 0.001 weight % and up to and including 0.3 weight %, based on the total dry weight of the dry opacifying layer, and
(c) a matrix polymer in which the (a) porous particles and all (b) opacifying colorant are dispersed, the (c) matrix polymer being water-soluble or water-dispersible and having a glass transition temperature that is less than 25° C., and is present in an amount of at least 10 weight % and up to and including 60 weight %, based on the total weight of the dry opacifying layer,
wherein:
the (b) opacifying colorant is present within the (c) matrix polymer of the dry opacifying layer and in no other location within the dry opacifying layer;
the weight ratio of the (c) matrix polymer to the (b) opacifying colorant in the dry opacifying layer is from 33.3:1 to 60,000:1; and
the dry opacifying layer has an interstitial void volume of at least 5 volume % and less than 30 volume %;
provided that:
the article is capable of blocking at least 85% of the predetermined electromagnetic radiation compared to a control article from which the (a) porous particles have been omitted, and the article has a CIELAB L* greater than 70.
2. The article of claim 1 , further comprising a substrate on which the dry opacifying layer is disposed.
3. The article of claim 2 , further comprising an underlying layer that has a glass transition temperature below 25° C. and that is disposed between the substrate and the dry opacifying layer.
4. The article of claim 1 , wherein the (b) opacifying colorant is a neutral or black pigment.
5. The article of claim 1 , wherein the (b) opacifying colorant is a carbon black.
6. The article of claim 1 , wherein the (b) opacifying colorant comprises a combination of two or more component colorants.
7. The article of claim 1 , wherein the dry opacifying layer is disposed on a substrate that comprises a woven or non-woven textile fabric, polymer, cellulosic material, glass, or ceramic.
8. The article of claim 1 , wherein all of the (b) opacifying colorant is present within the (c) matrix polymer of the dry opacifying layer in an amount of at least 0.003 weight % and up to and including 0.1 weight %, based on the total dry weight of the dry opacifying layer.
9. The article of claim 1 , wherein the (a) porous particles comprise a plurality of discrete pores having an average pore size of at least 100 nm and up to and including 4,000 nm.
10. The article of claim 1 , wherein the (a) porous particles have porosity of at least 10% and up to and including 50%.
11. The article of claim 1 , wherein the dry opacifying layer has an average dry thickness of at least 50 μm.
12. The article of claim 1 further comprising a tinting colorant other than the (b) opacifying colorant in the dry opacifying layer in an amount of at least 0.001 weight %, based on the total dry weight of the dry opacifying layer.
13. The article of claim 1 , selected from one of the following embodiments (i) through (vi):
(i) the article further comprises one or more tinting colorants in either or both of the pores and continuous polymeric binder of the same (a) porous particles;
(ii) the article further comprises a second set of (a) porous particles and one or more tinting colorants in either or both of the pores and continuous polymeric binder of the second set of (a) porous particles;
(iii) the article further comprises one or more tinting colorants in the (c) matrix polymer;
(iv) the article further comprises one or more tinting colorants only in the (c) matrix polymer;
(v) the article further comprises non-porous particles and one or more tinting colorants within these nonporous particles; and
(vi) the article further comprises one or more tinting colorants in either or both of the pores and continuous polymeric binder of the (a) porous particles.
14. The article of claim 1 having a CIELAB L* value that is greater than 80.
15. The article of claim 1 , wherein the dry opacifying layer has an interstitial void volume of at least 20 volume % and less than 30 volume %.
16. The article of claim 1 , wherein the (a) porous particles are present in the dry opacifying layer in an amount of at least 50 weight % and up to and including 80 weight %, based on the total dry weight of the dry opacifying layer.