Curable coatings with improved adhesion to glass

Details Curable coatings with improved adhesion to glass Curable coatings with improved adhesion to glass

1996-12-31

2002-03-12

Moore, Margaret G. (Department: 1712)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

Reexamination Certificate

active

06355751

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to curable materials which are derived from (meth)acrylates and alkoxy-substituted organosilanes. A compound containing an alkoxy-substituted organosilane group is covalently attached to a relatively long molecule that has (meth)acrylate functionality. As part of a photo-curable formulation, this long chain provides improved adhesion to glass substrates by covalently tying the polymeric network to the glass substrate.
BACKGROUND OF THE INVENTION
Photo-curing formulations used as coatings for glass optical fibers typically contain adhesion promoters to improve the adhesion between the polymer layer and the glass substrate. The most common kind of adhesion promoters (also known as coupling agents) consists of alkoxy-substituted organosilanes that have another reactive group capable of reacting with the polymerizable coating (Plueddemann, “Silane Coupling Agents”, Plenum, 1982). The alkoxysilane group can react with Si—OH groups present on the glass surface. Thus, the coupling agent provides a covalent linkage between the glass surface and the polymeric coating. U.S. Pat. No. 5,146,531 discloses several suitable organofunctional silanes for use in optical fiber coatings, such as amino-functional silanes, mercapto-functional silanes, methacrylate-functional silanes, acrylamido-functional silanes, allyl-functional silanes, vinyl-functional silanes and acrylate-functional silanes. These silanes are preferably methoxy- or ethoxy-substituted. Some preferred organofunctional silanes include 3 aminopropyltriethoxysilane, 3-methacryloxypropyltrimetoxysilane, 3-mercaptopropyl trimethoxysilane, and 3-mercaptopropyltriehtoxysilane. WO 91/03503 and U.S. Pat. No. 4,849,462 disclose the use of mercaptan-functional alkoxysilanes as preferred adhesion promoters (e.g. 3-mercaptopropyl trimethoxysilane, also known as &ggr;-mercaptopropyl trimethoxysilane).
The adhesion promoter is typically added to the photo-curable formulation (usually a mixture of acrylate monomers and oligomers) in amounts from about 0.1% by weight to about 5% by weight. During radiation exposure, the adhesion promoter reacts with the polymerizing mixture, getting incorporated into the polymer network. After radiation exposure the adhesion promoter molecules are tied to the polymer network. Only a small percent of these tied adhesion promoter molecules are close enough to the glass surface to react with it. Thus, the vast majority of adhesion promoter molecules are ineffective because they cannot reach the glass since they are constrained by being attached to the polymer network.
It is an object of the present invention to provide a method to improve the adhesion of photo-curable coatings to glass.
SUMMARY OF THE INVENTION
The present invention comprises covalently attaching an alkoxysilane molecule to a relatively long molecule that is part of a photo-curable formulation and that can copolymerize with this formulation upon photo-irradiation. After the long molecule reacts through radiation exposure, the alkoxysilane functionalities are tied to the network through the relatively long backbone. The long length of this backbone gives the alkoxysilane groups a higher probability to reach and react with the glass surface as compared to traditional adhesion promoters that are randomly linked to the polymer network.
DETAILED DESCRIPTION OF THE INVENTION
The present invention more specifically relates to a method to improve the adhesion of photo-curable polymeric coatings to glass substrates such as glass optical fibers by using a more effective adhesion promoter. It should be noted that the present compositions are used as coatings for glass substrates such as fibers and the term coating where appropriate encompasses but does not exclusively include cladding of glass fibers. In the case of a cladding, the coating has a lower refractive index than the (glass) fiber and can therefore be used as a cladding in the optical sense to guide electromagnetic wave energy within the fiber.
Photo-curable coatings for optical fibers generally comprise a (meth)acrylated oligomer, one or more (meth)acrylate monomers, optionally other monomers that can copolymerize with (meth)acrylates, a photoinitiator, and other additives. The present invention comprises the use of an adhesion promoter with the following formula:
(X)
m
—R—[—(Y)
s
—Si(OR
1
)
n
(R
2
)
3-n
]
p
where X contains a functional group capable of reacting with a (meth)acrylate group; R is a relatively long chain radical whose molecular weight is at least 500; Y is an atom or group of atoms whose structure depends on the chemistry used to attach Si to R; R
1
and R
2
are independently Alkyl groups; m≧1, n≧1, p≧1, and s can be 0 or 1.
The preferred structure of X contains a (meth)acrylate group:
[—C
q
(R
3
)(R
4
)—O—]
r
C(O)—C(R
5
)═CH
2
wherein R
3
, R
4
, and R
5
are independently hydrogen, methyl, ethyl or propyl, q is an integer from 1 to 10, r is either zero or an integer from 1 to 10. A specific example of a preferred X is
—CH
2
—CH
2
—O—C(O)—CH═CH
2
Other examples of adequate structures for X include, for example, ethylenically unsaturated groups, such as vinyl and allyl functionalities.
R
1
is preferably a methyl or an ethyl group, R
2
is preferably a methyl or an ethyl group, and n is preferably 3. The preferred values for m and p are 1.
There is no special requirement as to the chemical nature of R, as long it is compatible with the photo-curing formulation and it does not interfere with the curing reaction. Its preferred molecular weight is at least 1,500. A preferred structure of R is
—O—C(O)—NH—R
6
—NH—C—(O)—R
7
—C(O)—NH—R
8
—NH—C(O)
wherein R
6
and R
8
are independently linear, branched or cyclic alkylene of from six to twenty carbon atoms that may or may not contain aromatic rings. Some exemplary structures of R
7
include perfluoropolyethers such as
O(CH
2
CH
2
O)
n
1
(CF
2
CF
2
O)
p
1
(CF
2
O)
q
1
(CH
2
CH
2
O)
n
1
O(CH
2
CH
2
O)
n
1
CH
2
CF
2
O(CF
2
CF
2
O)
p
1
(CF
2
O)
q
1
CF
2
CH
2
O(CH
2
CH
2
O)
n
1
O CH
2
CF
2
O(CF
2
CF
2
O)
p
1
(CF
2
O)
q
1
CF
2
CH
2
O
{OCH
2
CF(CF
3
)O[CF(CF
3
)CF
2
O]
2
C
2
F
4
}
2
O CH
2
CH(OH)CH
2
OCH
2
CF
2
O(CF
2
CF
2
O)
p
1
(CF
2
O)
q
1
CF
2
CH
2
CH(OH)CH
2
O
wherein
0≦n
1
≦5, 0.2≦p
1
/c
1
≦5
and the actual values of p
1
and q
1
are such that the molecular weight of the fluorinated diol is between 500 and 10,000 and wherein the repeating fluorinated ether groups maybe random or block repeating units polyethers, such as
—O—(CH
2
—CH
2
—O)
r
11
—
—O—[CH(CH
3
)—CH
2
—O]
r
11
—
—O—(CH
2
—CH
2
—CH
2
—CH
2
—O)
r
11
—;
polyesters, such as
—O—[R
9
O—C(O)—R
10
—C(O)—O]
p
11
—R
9
—O—;
polycarbonates such as
—O—[R
11
—O—C(O)—O]
r
11
;
or end-capped hydrocarbon chains, such as
—O—R
12
—O—
In the preceding structures, R
9
, R
10
and R
11
are independently linear, branched or cyclic alkylene of from six to twenty carbon atoms that may or may not contain aromatic rings. R
12
is a linear or branched hydrocarbon chain that may or may not contain unsaturated bonds, and whose molecular weight is at least 500, and preferably at least 1,500. The value of r
11
in the preceding structures is such that the molecular weight of R
7
is at least 500, preferably at least 1,500.
The structure of Y depends on the structure of the silane starting material and the chemical reaction used to attach it to the pre-polymer R. A general structure of Y that can be used with the R structure shown previously is
—NH—R
13
—
where R
13
is an alkylene chain. A preferred structure for R
13
is —[CH
2
]
3
—.
Alternately, the structure of Y could be chosen to be
—C(O)—NH—R
13
—
in which case—the structure of R mentioned earlier would be replaced by the following structure
—O—C (O)—NH—R
6
—NH—C(O)—R
7
—
Yet another possibility is for the value of s in the adhesion promoter molecule to be zero. In this case, the structure of R would be either
R
7
[—C
q
(R
3
)(R
4
)—O]
r
—C(O)—C(H)(R
5
)CH
2
—
or
—O—C(O)—NH—R
6

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