Special polyether-based polyurethane formulations for the production of holographic media
The present invention relates to novel polyurethane compositions which are advantageous for the production of holographic media, inter alia for data storage, but also for optical applications of different types.
1. A polyurethane composition comprising
A) a polyisocyanate component;
B) an isocyanate-reactive component comprising a hydroxy-functional multiblock copolymer B1) of the type Y(X i —H) n having a number average molecular weight of greater than 1000 g/mol; wherein
X i is an oxyalkylene units of formula (I):
—CH 2 —CH(R)—O— (I);
i is an integer from 1 to 10;
n is an integer from 2 to 8;
R is a hydrogen, alkyl, or aryl radical, wherein said alkyl or aryl radical is optionally substituted or interrupted by a heteroatom; and
Y is the fundamental initiator and the proportion of the segments X i , based on the total amount of the segments X i and Y, accounts for at least 50% by weight;
C) free-radically polymerizable compound free of NCO groups;
D) free radical stabilizers;
E) photoinitiators;
F) optionally catalysts; and
G) optionally auxiliaries and additives.
2. The polyurethane composition of claim 1 , wherein A) comprises a polyisocyanate and/or a prepolymer based on HDI, TMDI, and/or TIN.
3. The polyurethane composition of claim 1 , wherein A) comprises a polyisocyanate based on HDI with isocyanurate and/or iminooxadiazinedione structures or prepolymers having an NCO functionality of from 2 to 5 and exclusively primary NCO groups.
4. The polyurethane composition of claim 1 , wherein A) has a residual content of free monomeric isocyanate of less than 0.5% by weight.
5. The polyurethane composition of claim 1 , wherein at least one segment X i is a propylene oxide-based homopolymer or random or block copolymer comprising oxyethylene, oxypropylene and/or oxybutylene units, wherein the proportion of said oxypropylene units, based on the total amount of all oxyethylene, oxypropylene, and oxybutylene units, accounts for at least 20% by weight.
6. The polyurethane composition of claim 1 , wherein said starter segment Y is based on a difunctional, aliphatic polycarbonate polyol, poly(ε-caprolactone), or polymer of tetrahydrofuran having a number average molar mass greater than 250 g/mol and less than 2100 g/mol.
7. The polyurethane composition of claim 1 , wherein said multiblock copolymers B1) has a number average molecular weight of from 1200 to 12 000 g/mol.
8. The polyurethane composition of claim 1 , wherein said compound of C) has a refractive index n D 20 of greater than 1.55.
9. The polyurethane composition of claim 1 , wherein C) comprises a urethane acrylate and/or a urethane methacrylate based on an aromatic isocyanate and 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, polyethylene oxide mono(meth)acrylate, polypropylene oxide mono(meth)acrylate, polyalkylene oxide mono(meth)acrylate, and/or a poly(ε-caprolactone) mono(meth)acrylate.
10. A process for producing media for recording visual holograms comprising (1) applying the polyurethane composition of claim 1 to a substrate or in a mould and (2) curing said polyurethane composition.
11. A medium for recording visual holograms produced by the process of claim 10 .
12. An optical element or image comprising the medium of claim 11 .
13. A method for recording a hologram comprising exposing the medium of claim 12 .