Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2001-04-27
2003-05-27
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C525S474000, C525S477000, C525S478000, C528S012000, C528S015000, C528S033000, C428S447000
Reexamination Certificate
active
06569914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to silicone release coatings.
2. Background Art
Silicone release coatings are used in large quantities in diverse commercial fields. For example, in the structural composites field, curable resin-impregnated carbon or glass fiber prepregs are manufactured on release-coated substrates from which the tacky prepregs are separated prior to assembling into laminates and curing. Similar release substrates, generally release coated paper, are used with film adhesives, and as protective, pre-use coverings for a variety of adhesive-coated articles. Pressure sensitive labels, for example, are generally supplied on release coated substrates. It is safe to say that virtually all curable or pressure-sensitive film adhesives and articles coated with them are supplied on a release-coated substrate or backing.
Silicones have become the predominant release coating due to their superior surface qualities and favorable economics. However, because of the diverse applications in which the release coatings are used, and the varying tack of the wide variety of adhesives with which they are used, it is necessary to have the ability to tailor characteristics such as peel strength, and, in particular, the coating coefficient of friction (COF). In the past, changes in COF were rather difficult to make, often requiring the synthesis of new friction-modifying components or even wholly new release formulations. Coatings with low COF have been the most difficult in this regard.
The coatings must be capable of application to the substrate by conventional processes, such as spraying, doctor coating, printing techniques, etc. These application methods require a coating of relatively low viscosity, preferably with some degree of self-leveling characteristics. Following application to the substrate, the coating must be cured. Among the curable compositions and their associated curing mechanisms which have been used are moisture curable compositions, condensation curable compositions, addition curable compositions, and photocurable compositions. Thermocurable and photocurable addition curing systems dominate the market.
In many applications, very low levels of extractables are required. However, some silicone release coatings actually rely on the exudation of liquid organopolysiloxanes from a cured and crosslinked organopolysiloxane matrix for their release properties. Such compositions are described in European published application EP-013703. The exudation is significant enough that the latter published application is directed to employing a special substrate backcoating containing absorbent particles to absorb excess silicone oil when the release film is wound up on a roll. However, such special backcoatings do not prevent later extraction of silicon fluid upon use of the release film.
Other conventional silicone release coatings are disclosed by U.S. Pat. No. 4,184,006, incorporated herein by reference, comprising a vinyl-terminated diorganopolysiloxane, a diorganopolysiloxane having minimally three Si—H bonded reactive hydrogens, a platinum hydrosilylation catalyst, and a hydrosilylation inhibitor. The compositions may be applied by conventional coating and printing techniques. However, low COF coatings are difficult to obtain. For low COF coatings, solvent-based tin catalyzed condensation-curable coatings have traditionally been used. However, tin-catalyzed coatings not only contain appreciable tin residues, they have high levels of extractables as well. Moreover, most solvent based systems do not meet volatile organic compound (VOC) emission standards due to the relatively large amounts of solvents used.
It would be desirable to provide silicone coating compositions, suitable for use as release coatings, with COF values which can be adjusted over a wide range without drastic alteration of the coating composition. It would be further desirable to provide coating composition components which allow for adjustment of COF by the coating applicator rather than only the coating manufacturer. Finally, it would be desirable to provide low VOC content or VOC-free coatings which have a low level of extractables after curing. It would be yet further desirable to provide low COF coatings which do not require the use of tin catalysts.
SUMMARY OF THE INVENTION
It has now been surprisingly discovered that silicone release coatings with adjustable COF, in particular low values of COF, may be formulated as neat, solventless compositions, or as compositions containing minimal organic solvent. These release coatings may be applied by conventional coating techniques, and cure to provide release coatings having very low levels of extractables.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The present invention compositions are addition-curable or photocurable organopolysiloxane release coating compositions which contain, as a COF modifier, a very high molecular weight, and hence high viscosity (>500,000 mm
2
/s) organopolysiloxane which does not react substantially with the remaining ingredients of the curable organopolysiloxane composition. The release coating compositions may be defined and described in several ways, for example by weight percent composition. However, it is advantageous to consider the compositions as comprising a curable organopolysiloxane base composition, and a COF modifier, preferably supplied as a COF modifier master batch composition. By varying the amount of the latter, the COF of the cured coating composition may be varied over wide limits without necessitating fundamental changes in the base composition. Thus, release coatings with varied COF may be formulated by the applicator from a limited number of standard components.
The base composition is an addition crosslinkable system which may be thermally crosslinkable or photochemically crosslinkable. Hybrid systems are useful as well. The base compositions are conventional, and well known to those skilled in the art.
Addition crosslinkable systems contain a “crosslinkable component” which is preferably an organopolysiloxane containing hydrocarbon groups which have carbon—carbon unsaturation. Both ethylenically unsaturated and ethylynically unsaturated groups may be present. Preferably, the unsaturated hydrocarbon radicals are vinyl, vinylether, or &ohgr;-terminal alkenyl or alkenylether groups. Allyl groups and allylether groups are also highly useful, as are also acrylates and methacrylates, maleates, fumarates, etc.
The unsaturated hydrocarbon groups may be pendant or terminal, or both pendant and terminal, and the polysiloxanes which bear these groups may be linear or branched, preferably lightly branched such that they contain less than about 5 mol percent total RSiO
3/2
and SiO
4/2
groups based on total mol of siloxy groups, where R is an optionally substituted hydrocarbon group. Linear, &agr;,&ohgr;-divinylpolydiorganosiloxanes are preferred, more preferably &agr;,&ohgr;-divinylpolydimethylsiloxanes. Thus, more generally, the unsaturated group-containing organopolysiloxanes preferably contain the following groups:
R
1
a
R
b
SiO
1/2
(I),
R
1
e
R
d
SiO
2/2
(II),
R
1
e
R
f
SiO
3/2
(III), and
SiO
4/2
(IV),
where
a and b are individually 0, 1, 2, or 3 and the sum of a+b is 3;
where c and d are individually 0, 1, or 2 and the sum of c+d is 2;
where e and f are individually 0 or 1 and the sum of e+f is 1;
where R
1
is an unsaturated, optionally substituted hydrocarbon, preferably a C
2-18
ethylenically unsaturated hydrocarbon, and more preferably, an &ohgr;-unsaturated C
2-18
hydrocarbon, optionally substituted by substituents which are non-reactive with other coating composition components. Examples of such substituents, in a non-limiting sense include, halo, especially fluoro and chloro; cyano; hydroxyl; sulfhydryl; primary, secondary, and tertiary amino, or salts thereof; alkoxy; and polyoxyalkylenyl. In the above formulae, R is an optionally substituted hydrocarbon group free of ethylenic unsaturation, or a hydroxyl or alkoxy group, pre
Beekel Kathleen D.
Conti Andrew J.
Zoellner Oliver H.
Berman Susan W.
Brooks & Kushman P.C.
Wacker Silicones Corporation
LandOfFree
Additive for modifying the coefficient of friction of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Additive for modifying the coefficient of friction of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Additive for modifying the coefficient of friction of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3024424