Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2001-03-16
2002-12-31
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...
C522S093000, C522S096000, C522S097000, C522S098000, C522S174000, C528S059000, C528S060000, C528S065000, C528S066000
Reexamination Certificate
active
06500876
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a coating composition containing a mixture of ultraviolet(UV)-curable urethane (meth)acrylates containing isocyanate groups and UV-curable urethane (meth)acrylates containing hydroxyl groups, and to the preparation of coatings from these compositions.
2. Description of the Prior Art
EP-A 928 800 (believed to correspond to copending U.S. Ser. No. 09/225,977) describes coating compositions containing:
a) a urethane (meth)acrylate that contains (meth)acryloyl groups and free isocyanate groups,
b) optionally, a further polyisocyanate,
c) a UV initiator that initiates the radical polymerization and
d) one or more compounds that react with isocyanates.
Furthermore, EP-A 928 800 teaches a process in which surfaces are prepared by UV-initiated radical polymerization and the final properties are produced by subsequent NCO reaction. In this process curing of the coating at unexposed or poorly exposed points by NCO reaction ensures a “minimum necessary resistance level”. The examples show, however, that the NCO reaction proceeds to completion only as a result of brief heating (30 min, 130° C.) or by standing (7 d) at room temperature for several days.
For some applications, in particular for the coating of heat-sensitive articles or articles that cannot be economically heated to temperatures of approximately 130° C. because of their size and geometry, a curing of the lacquer even without heating and, optionally, without UV exposure is required within a few hours.
It was found that coating compositions that contain urethane (meth)acrylates also containing hydroxyl groups in addition to urethane (meth)acrylates containing isocyanate groups have a substantially improved curing, than compared to coating compositions according to the prior art, especially in unexposed areas.
SUMMARY OF THE INVENTION
The invention relates to a coating composition comprising:
a) urethane (meth)acrylates that contain (meth)acryloyl groups and free isocyanate groups,
b) urethane (meth)acrylates that contain (meth)acryloyl groups and free hydroxyl groups,
c) a UV initiator that initiates radical polymerization and
d) optionally, one or more compounds that react with isocyanates.
DETAILED DESCRIPTION OF THE INVENTION
Preferably, the present coating composition is prepared in two components, wherein component I preferably contains constituent a) and component II contains constituents b), c) and d).
To achieve or improve weathering resistance, the following may optionally be added preferably to component II:
e) a UV absorber having an absorption range up to a maximum of 390 nm,
f) a HALS (hindered amine light stabilizer);
g) lacquer additives, such as flow control agents or deaerating agents and
h) catalysts for accelerating the NCO reaction.
For the purpose of dilution, components I and II may each contain a solvent that is inert with respect to isocyanate groups and C═C double bonds, such as esters, ketones, ethers, ether esters, alkanes or aromatic solvents, such as xylene or toluene.
Component I and component II are combined to provide an equivalent ratio of the NCO groups and the NCO-reactive groups of 2:1 to 0.8:1, preferably of 1.2:1 to 0.8:1.
Compounds a) are prepared from alcohols containing (meth)acryloyl groups and polyisocyanates. Processes for preparing urethane (meth)acrylates are known and are described, for example, in DE-A 1 644 798, DE-A 2 115 373 or DE-A 2 737 406. A review can be found in Chemistry & Technology of UV and EB Formulations for Coatings, Inks & Paints, by P. K. T. Oldring (ed.), vol. 2, 1991, SITA Technology, London, pages 73-123. For the urethane (meth)acrylates containing free isocyanate groups, the molar ratio of NCO groups of the polyisocyanates to the OH groups of the alcohols containing (meth)acryloyl groups is from 1:0.2 to 1:0.8, preferably from 1:0.3 to 1:0.6, particularly preferably 1:0.4 to 1:0.5.
Alcohols containing (meth)acryloyl groups include the esters of acrylic acid or (meth)acrylic acid with dihydric alcohols. Examples include 2-hydroxyethyl, 2- or 3-hydroxypropyl or 2-, 3- or 4-hydroxybutyl (meth)acrylate and any mixture of such compounds. In addition, monohydric alcohols containing (meth)acryloyl groups or reaction products substantially composed of such alcohols that are obtained by esterification of n-hydric alcohols with (meth)acrylic acid are suitable. Mixtures of various alcohols can be used, such that n stands for an integer or a statistical average of greater than 2 to 4, preferably 3. Per mole of the alcohols mentioned, from (n−0.6) to (n−2.2), preferably from (n−0.8) to (n−1.2), and particularly preferably (n−1) moles of (meth)acrylic acid are used. These compounds or product mixtures include the reaction products of (i) trihydric alcohols such as glycerol, trimethylol propane and/or pentaerythritol; low-molecular-weight alkoxylation products of such alcohols (such as ethoxylated or propoxylated trimethylolpropane more specifically the addition product of ethylene oxide to trimethylolpropane having an OH number of 550); or mixtures of at least trihydric alcohols with dihydric alcohols (such as, ethylene glycol or propylene glycol) with
(ii) (meth)acrylic acid in the stated molar ratio. Said compounds have a molecular weight of 116 to 1000, preferably 116 to 750 and more preferably 116 to 158.
Furthermore, the reaction products of said monohydric alcohols containing (meth)acryloyl groups with, for example, &egr;-caprolactone can also be used. Such products can be obtained, for example, as Tone Monomer 100 supplied by Union Carbide. These compounds have a molecular weight of 230 to 3000, preferably 230 to 1206 and more preferably 344 to 572.
Suitable polyisocyanates include aliphatic, araliphatic and aromatic compounds. Aliphatic compounds are preferred. Examples include butylene diisocyanate, hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), trimethylhexamethylene diisocyanate (=2,2,4- and/or 2,4,4-trimethylhexamethylene diisocyanate), di(isocyanatocyclohexyl)methane, isocyanatomethyl-1,8-octane diisocyanate or their derivatives having a urethane, isocyanurate, allophanate, biuret, uretdione and/or iminooxadiazinedione groups and mixtures of the same. Particularly preferred are the derivatives of HDI and/or IPDI with isocyanurate groups.
The reaction to form urethane (meth)acrylate in accordance with a) can be accelerated in a known manner by means of suitable catalysts, such as tin octoate, dibutyltin dilaurate (DBTL) or tertiary amines.
The resultant urethane (meth)acrylate containing free NCO groups is preferably stabilized against premature polymerization, for example by adding suitable inhibitors and antioxidants including phenols, cresols, hydroquinone and, optionally, also quinones, such as, 2,5-di-tert-butylquinone. Suitable additives of this type are described, for example, in “Methoden der organischen Chemie” (“Methods of organic chemistry”) (Houben-Weyl), 4
th
edition, vol. XIV/1, page 433 ff, Georg Thieme Verlag, Stuttgart 1961.
Said inhibitors are added in amounts of 0.001 to 0.3 wt. % in each case during or following the preparation.
The coating compositions according to the invention can be prepared in solvents that are inert with respect to isocyanate groups and C═C double bonds, such as esters, ketones, ethers, ether esters, alkanes or aromatic solvents, such as xylene or toluene. Urethane (meth)acrylates that contain (meth)acryloyl groups and free hydroxyl groups (component b)) include reaction products of urethane (meth)acrylates with diols, optionally mixed with polyols.
Aliphatic, cycloaliphatic or, less preferably, aromatic diols can be used as diols, for example ethylene glycol, the isomeric propanediols, butanediols, pentanediols, hexanediols, heptanediols, octanediols, and nonanediols and cyclohexanedimethanol, hydrogenated bisphenol-A and derivatives of the above mentioned diols substituted with one or more C
1
-C
6
-alkyl groups . Also suitable are diols containing ester groups, ether gro
Mundstock Holger
Sonntag Michael
Weikard Jan
Bayer Aktiengesellschaft
Berman Susan W.
Gil Joseph C.
Roy Thomas W.
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