Cured fluorine-containing material

Details Cured fluorine-containing material Cured fluorine-containing material

2001-06-21

2004-01-06

Dawson, Robert (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

C528S031000, C528S042000, C528S401000

Reexamination Certificate

active

06673887

ABSTRACT:

This invention relates to cured fluorine-containing materials having a refractive index of up to 1.335 at 25° C. and best suited as optical materials such as antireflection films as well as rubber materials, tent film materials, sealants, coating materials, and parting agents where solvent resistance is required.
BACKGROUND OF THE INVENTION
Heretofore, curable fluorine-containing compositions primarily comprising a polymer of fluorine-containing organic compound and a crosslinking agent have been used in a variety of applications.
With the rapid development of the information society, large size displays of the liquid crystal, CRT, plasma and other systems are on widespread use. Those displays, especially of the portable type, used outdoor or in an illuminated space are required to improve their recognition capability. One common means for improving the recognition capability is to provide the substrate of a display device with an antireflection film of low refractive index materials, typically fluorine compounds. Such antireflection films are formed by vacuum evaporating inorganic materials or by depositing alternating films of high and low refractive index materials, which techniques lack productivity.
Known low refractive index materials which can be coated have a refractive index of 1.34 at the lowest. There is a need for a material having a lower refractive index.
SUMMARY OF THE INVENTION
An object of the invention is to provide a cured fluorine-containing material having a sufficiently low refractive index to be used as an antireflection film or the like.
It has been found that a curable composition comprising (A) a linear fluoropolyether compound having at least two alkenyl groups per molecule and a perfluoroalkyl ether structure in the backbone, (B) a fluorine-containing organohydrogensiloxane, and (C) a platinum group catalyst can be coated in solution form and converted, by holding at room temperature or heating, into a cured thin film comprising a perfluoropolyether backbone and having a refractive index of up to 1.335 at 25° C., especially when the fluorine content in the cured film is at least 61.0% by weight.
Briefly stated, the invention provides a cured fluorine-containing material having a refractive index of up to 1.335 at 25° C. comprising as the backbone a perfluoropolyether of the following general formula (1):
—(Rf—O)
q
—  (1)
wherein Rf is a perfluoroalkylene group of 1 to 6 carbon atoms and q is a number of 1 to 500.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The cured fluorine-containing material of the invention is obtained by curing a curable composition comprising (A) a linear fluoropolyether compound having at least two alkenyl groups per molecule and a perfluoroalkyl ether structure of the formula (1) in the backbone, (B) a fluorine-containing organohydrogensiloxane, and (C) a platinum group catalyst.
The linear fluoropolyether compound (A) should have at least two alkenyl groups per molecule and a perfluoroalkyl ether structure in the backbone. It is used as a base polymer in the composition.
The alkenyl groups in the linear fluoropolyether compound are, for example, groups having a CH
2
═CH— structure at the terminus such as vinyl, allyl, propenyl, isopropenyl, butenyl and hexenyl, and preferably vinyl and allyl. The alkenyl groups may be attached to the backbone of linear fluoropolyether compound at opposite ends directly or through divalent linking groups such as —CH
2
—, —CH
2
O— or —Y— NR—CO—. Herein Y is —CH
2
— or:
(wherein the free valence bond may be at an o-, m- or p-position), and R is hydrogen, methyl, phenyl or allyl.
The perfluoroalkyl ether structure in the linear fluoropolyether compound is of the general formula (1) as mentioned above.
—(Rf—O)
q
—  (1)
Rf is a straight or branched perfluoroalkylene group of 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, and q is an integer of 1 to 500, preferably 2 to 400, and more 3 preferably 10 to 200.
Examples of the recurring units represented by —(Rf—O)— include —CF
2
—, —CF
2
CF
2
O—, —CF
2
CF
2
CF
2
O—, —CF(CF
3
)CF
2
O—, —CF
2
CF
2
CF
2
CF
2
O—, —CF
2
CF
2
CF
2
CF
2
CF
2
CF
2
O—, and —C(CF
3
)
2
O—, Preferred among these are —CF
2
—, —CF
2
CF
2
O—, —CF
2
CF
2
CF
2
O—, and —CF(CF
3
)CF
2
O—. Especially preferred are perfluoropolyethers comprising recurring units of hexafluoropropenoxide. The perfluoroalkyl ether structure may consist of one or more types of recurring units represented by —(Rf—O)—.
Examples of the linear fluoropolyether compound (A) are linear fluoropolyether compounds of the following general formula (2):
wherein X is independently —CH
2
—, —CH
2
O—, or —Y—NR—CO—, Y is —CH
2
— or:
(wherein the free valence bond may be at an o-, m- or p-position), R is hydrogen, methyl, phenyl or allyl, p is independently 0 or 1, k is an integer of 2 to 6, m and n each are an integer of 0 to 200, preferably 5 to 150, and having a weight average molecular weight of about 400 to 100,000, preferably about 2,000 to 50,000.
Illustrative, non-limiting examples of the linear fluoropolyether compound (A) are shown below:
In the above formulas, m and n are as defined in formula (1), Me is methyl and Ph is phenyl.
These linear fluoropolyether compounds may be used alone or in admixture of two or more.
The linear fluoropolyether compound (A) used herein may range from a low viscosity polymer having a viscosity of several ten centistokes at 25° C. to a solid gum-like polymer. From the ease of handling standpoint, polymers having a viscosity of about 1,000 to 100,000 centistokes at 25° C. are advantageously used for coating purposes. Polymers having a too low viscosity may result in cured films having reduced film strength and/or adhesion, failing to provide a good profile of physical properties.
The fluorine-containing organohydrogensiloxane (B) serves as a crosslinking agent or chain extender for the linear fluoropolyether compound (A). The fluorine-containing organohydrogensiloxane is not critical as long as it has at least one monovalent perfluoroalkyl group, monovalent perfluorooxyalkyl group, divalent perfluoroalkylene or divalent perfluorooxyalkylene group and at least two, preferably at least three hydrosilyl groups, i.e., Si—H groups in a molecule. The perfluoroalkyl, perfluorooxyalkyl, perfluoroalkylene and perfluorooxyalkylene groups are exemplified by the groups of the following general formulae.
monovalent perfluoroalkyl groups:
C
p
F
2p+1
—
Letter p is an integer of 1 to 20, preferably 2 to 10. divalent perfluoroalkylene groups:
—C
p
F
2p
—
Letter p is an integer of 1 to 20, preferably 2 to 10. monovalent perfluorooxyalkyl groups:
Letter q is an integer of 1 to 5.
divalent perfluorooxyalkylene groups:
The sum of r+s is an integer of 2 to 100 on average.
The divalent linking group which links the perfluoroalkyl, perfluorooxyalkyl, perfluoroalkylene or perfluorooxyalkylene group to the silicon atom is an alkylene group, arylene group or a mixture thereof, which may further have an ether bond oxygen atom, amide bond or carbonyl bond. Such divalent linking groups of 2 to 12 carbon atoms are preferred. Illustrative examples thereof include
—CH
2
CH
2
—, —CH
2
CH
2
CH
2
—, —CH
2
CH
2
CH
2
OCH
2
—,
—CH
2
CH
2
CH
2
—NH—CO—, —CH
2
CH
2
CH
2
—N(Ph)—CO—,
—CH
2
CH
2
CH
2
—N(CH
3
)—CO—, and —CH
2
CH
2
CH
2
—O—CO—
wherein Ph is phenyl.
In addition to the monovalent organic group containing a monovalent or divalent fluorinated substituent, that is, a perfluoroalkyl, perfluorooxyalkyl, perfluoroalkylene or perfluorooxyalkylene group, the fluorine-containing organohydrogensiloxane (B) may have a monovalent substituent attached to a silicon atom. Exemplary monovalent substituents are substituted or unsubstituted hydrocarbon groups of 1 to 20 carbon atoms including alkyl groups such as methyl, ethyl, propyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, octyl and decyl; cycloalkyl groups such as cyclopentyl, cyclohexyl and cycloheptyl; alkenyl groups such as vinyl, allyl, propenyl, isopropenyl, butenyl and hexenyl; aryl groups such as phenyl, tolyl, xylyl and nap

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