Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1999-10-29
2002-05-14
Zirker, Daniel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C522S170000, C522S172000, C522S181000, C522S182000
Reexamination Certificate
active
06387486
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
The present invention is directed to a pressure sensitive adhesive tape and a novel silicone-free release coating used therewith.
Release coatings are used to control or diminish the adhesion between an adhesive and a backing or substrate to which the adhesive is applied. Release coatings may be employed in conjunction with release films, release liners, non-stick carrier webs, and coatings for paper and polymer substrates. A release coating may also comprise a component of a multi-layer or laminated construction. For example, a typical multi-layer or laminated construction may comprise a pressure sensitive adhesive attached to a foamed or non-foamed sheet or film, with one or more release layers being employed on one or more of the backing or adhesive layers. The release layer in such a construction may serve as a protective layer during handling or storage, especially when the adhesive layer is wound upon itself such as in the form of an adhesive tape.
Adhesives find wide applicability in the electronics industry. Commonly, silicone-based, release coatings are employed in conjunction with such adhesives. See, for example, U.S. Pat. Nos. 4,576,999; 4,994,299; 5,010,118; 5,082,686; and 5,658,965. However, it has been found that a small fraction of silicone compounds in the release coating frequently migrate to the adjacent adhesive layer. Silicone contamination has been linked to premature failure of electronic devices. This is a significant disadvantage when such adhesives are used in the production of sensitive electronic or computer devices. Also, the silicone dust produced during the normal handling of the liners in the clean room is unacceptable. It has been proposed to use fluorine-based release coatings as a substitute for silicone-based release coatings to reduce such contamination. However, fluorine-based release coatings are significantly more expensive than the silicone-based release coatings and their use is frequently limited to very specialized applications such as those requiring high temperature tolerance. The fluorine-based release liners also exhibit a static cling resulting in handling problems and the possibility of static discharge in electronic components.
OBJECTS AND SUMMARY OF THE PRESENT INVENTION
It is therefore an object of the present invention to provide a silicone-free release coating for use in a release film.
It is also an object of the present invention to provide a silicone-free release coating for use in conjunction with pressure sensitive adhesives.
It is also an object of the present invention to provide an improved pressure senstive adhesive tape which includes a silicone-free release coating.
In accordance with the present invention, there is thus provided a release film comprising:
(1) a backing layer; and
(2) at least one silicone-free release layer, said release layer comprising a crosslinked poly(alkylene oxide), said poly(alkylene oxide) being defined by the formula X
1
—(O—R)
n
—OX
2
where X
1
and X
2
are terminal groups at least one of which permits crosslinking of said poly(alkylene oxide) between said X
1
and X
2
groups and/or with a crosslinking agent, n ranges from 1 to 200,000, R is a straight or branched alkylene group having the formula (CR
1
R
2
)
m
where m is an integer from 1 to 10 and R
1
and R
2
may independently be hydrogen and C
1-3
alkyl.
In accordance with another embodiment of the present invention, there is provided a pressure sensitive adhesive tape comprising:
(1) at least one backing layer;
(2) at least one pressure sensitive adhesive layer; and
(3) at least one silicone-free release layer, said release layer comprising a crosslinked poly(alkylene oxide), said poly(alkylene oxide) being defined by the formula X
1
—(O—R)
n
—OX
2
where X
1
and X
2
are terminal groups at least one of which permits crosslinking of said poly(alkylene oxide) between said X
1
and X
2
groups and/or with a crosslinking agent, n ranges from 1 to 200,000, R is a straight or branched alkylene group having the formula (CR
1
R
2
)
m
where m is an integer from 1 to 10 and R
1
and R
2
may independently be hydrogen and C
1-3
alkyl.
DETAILED DESCRIPTION OF THE INVENTION
The novel release coating of the present invention is comprised of a crosslinked silicone-free poly(alkylene oxide). The poly(alkylene oxide) is defined by the formula X
1
—(O—R)
n
—OX
2
where X
1
and X
2
are terminal groups at least one of which permits crosslinking of said poly(alkylene oxide) between said X
1
and X
2
groups and/or with a crosslinking agent, n ranges from 1 to 200,000, R is a straight or branched alkylene group having the formula (CR
1
R
2
)
m
where m is an integer from 1 to 10 and R
1
and R
2
may independently be hydrogen and C
1-3
alkyl.
By way of example, the alkylene group R may be selected from the group consisting of —CH
2
CH
2
—, CH(CH
3
)—CH
2
, —CH(CH
2
CH
3
)CH
2
—, —CH
2
CH
2
CH
2
CH
2
—, —CH(CH
3
)CH(CH
3
)—, —C(CH
3
CH
3
)CH(CH
3
)—, and —CH
2
C(CH
3
)
2
—.
The poly (alkylene oxide) can be crosslinked by mean of groups X
1
and X
2
reacting by condensation, addition or ring opening reactions. These are called self-crosslinking systems. If required, an external crosslinking agent capable of reacting with X
1
and X
2
may be added.
The requisite crosslinking reaction can occur by means of condensation (either thermal or photoinitiated), cationic (either thermal or photoinitiated) reaction and/or free radical (either thermal or photo initiated) reaction.
The choice of X
1
and X
2
permits the requisite crosslinking to occur. For instance, isocyanate terminal groups will crosslink with hydroxyl and amine groups. Acid terminal groups will crosslink with hydroxyl, epoxy and amine groups. Epoxy terminal groups will crosslink with hydroxyl groups. By way of example, a hydroxyl-terminated poly (alkylene oxide) will crosslink with an epoxy compound.
Exemplary X
1
and X
2
terminal groups for use with a self-crosslinking poly (alkylene oxide) include acrylate, methacrylate, epoxy, vinyl ether, propenyl ether and alkoxy silane.
Self-crosslinking poly (alkylene oxides) generally have, on average, at least one polymerizable functional group per molecule and preferably 2-4 groups per molecule. Epoxy, vinyl ether and propenyl ether terminated poly (alkylene oxides) can be crosslinked in the presence of cationic photoinitiators and radiation. One skilled in the art can readily determine suitable radiation/photoinitiator conditions. Acrylate and methacrylate terminated poly (alkylene oxide) can be crosslinked in the presence of free radical initiators. Depending upon the initiator, either thermal or radiation curing may be used to initiate the reaction. Alkoxy silane terminated poly (alkylene oxides) can be crosslinked by thermal means in the presence of a suitable catalyst.
Crosslinking can also occur between the poly (alkylene oxide) and a crosslinking agent each having functionally compatible terminal groups. Exemplary X
1
and X
2
terminal groups for use in connection with reaction with a crosslinking agent include epoxy, hydroxyl, amine, acid and isocyanate groups. Complementary functional terminal groups on the crosslinking agent include alcohol, acid, epoxy, isocyanate and amine funtionalities. Exemplary crosslinking agents may be di- or multi functional.
The identity of the crosslinking compound is not critical to practice of the claimed invention, as a variety of crosslinking compounds may be employed.
The crosslinking compound may be defined by the formula
wherein Z is a functional group such as an alcohol, acid, epoxy, isocyanate or amine capable of reacting with terminal groups X
1
and X
2
on the poly (alkylene oxide), and R
3
, R
4
, R
5
, R
6
, R
7
, R
8
and R
9
are spacer groups the identity of which is not critical. For instance, the spacer groups may be alkylene groups defined by the formula (CR
10
R
11
)
p
where R
10
and R
11
may be independently hydrogen and C
1-3
alkyl and p is an integer from 1 to 10.
Crosslinking compounds useful in the present invention include organ
Clonan Julie
Malik Ranjit
Adhesives Research Inc.
Birch & Stewart Kolasch & Birch, LLP
Zirker Daniel
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