Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2001-01-12
2004-06-29
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C528S048000, C528S052000, C528S053000, C528S054000, C528S056000, C528S058000, C528S067000, C528S070000, C528S073000, C528S076000
Reexamination Certificate
active
06756468
ABSTRACT:
The present invention relates to high dry content polyurethane compositions based on perfluoropolyether oligomers. Said compositions are used for application to various substrata, such as for example metals, ceramic and stony materials, plastic and glass surfaces and they are able to completely crosslink also at temperatures lower than 20° C., also of about 10° C., forming thin films having good mechanical and surface properties.
Coatings obtained from polyurethane formulations based on perfluoropolyethers (PFPE) are known in the prior art. According to EP 665,253 it is possible to prepare high dry content polyurethane resins, by crosslinking PFPEs having hydroxyl terminations and functionality comprised between 2 and 4, or mixtures thereof, with polyisocyanic adducts obtained by reaction of polyols with diisocyanates, of the type for example TMP-IPDI (trimethylolpropane-isophorondiisocyanate) having a ratio by moles 1/3). Said formulations have the drawback not to completely crosslink at a temperature of 25° C. or lower. Therefore the properties of the obtained coating are unsatisfactory as regards the chemical resistance, permeability and duration in the time.
From EP 812,891 bicomponent “no dirt pick up” formulations are known in which the PFPE resin diol is crosslinkable with prepolymers obtained by prepolymerization of a PFPE diol with polyisocyanates obtained by cyclotrimerization of HDI, IPDI or other monomeric diisocyanates, alone or in admixture therewith. The examples of this application describe formulations having a dry content higher than 70% by weight but not higher than 85% by weight. The “no dirt pick up” properties are good but it is desirable to further improve them. In conclusion, the protective coatings obtainable by crosslinking the prior art formulations, containing PFPEs having hydroxyl terminations, with polyisocyanates, have a lower crosslinking temperature limit, generally from +25° C., which compromises the possibility of application and complete crosslinking in the field and they do not show an optimal combination of properties as indicated hereinafter.
The need was therefore felt to have available PFPE-based polyurethane compositions combining the following properties:
applicability to dry contents>80% by weight, preferably in the range 85-90% by weight,
filming capability and complete crosslinkability also at temperatures in the range 5° C.-20° C.,
as regards the properties of the coatings obtainable by said formulations:
improved chemical resistance and stability to UV ageing photooxidation,
improved “no dirt pick us” surface properties,
good mechanical properties and in particular good surface hardness (pencil hardness≧B) and abrasion resistance.
Compositions based on polyisocyanates and perfluoropolyethers meeting the combination of the above mentioned properties have now been surprisingly and unexpectedly found by the Applicant.
An object of the present invention are compositions for coatings having a dry content higher than 80%, preferably of about 85-90% by weight, based on polyisocyanates and PFPE, completely crosslinkable also in a range of temperatures between 5° C. and 20° C., said compositions comprising the following components:
Component 1): mixture comprising:
1.a) Partially fluorinated prepolymers, having free NCO groups, obtained by reaction of (per)fluoropolyethers (PFPEs) diols having number average molecular weight Mn in the range 800-1,500, preferably 1,000-1,200, with the cyclic trimer of the isophorondiisocyanate (IPDI), in said reaction the ratio in equivalents between the OH/NCO groups being in the range 0.20-0.25,
1.b) non cyclic isocyanic trimer of hexamethylendiisocyanate (biuret of HDI) having an absolute viscosity at 20° C. lower than 5,000 mPa.s, in component 1) the ratio referred to the dry product between the compound 1.b) and the compound 1.a) being in the range 10-90, preferably 30-60 parts of compound 1.b)/100 parts of compound 1.a);
Component 2): (per) fluoropolyether (PFPE) diol having Mn in the range 350-700, preferably 500-0650, the amount of PFPE diol component 2) being such that the ratio in equivalents between the OH and NCO groups in the composition is in the range 0.9-1.1;
Component 3): inert organic solvent under the crosslinking conditions, complement to 100% by weight of the composition.
The component 1.a) is obtainable by hot dissolving (for example 40°-80° C.) the trimer of IPDI and the (per)fluoropolyether diol in a solvent as those indicated in component 3), maintaining the stoichiometric ratio in equivalents OH/NCO within the indicated limits and a dry content in the range 65%-85% by weight. Then the polymerization catalyst is added, see later on, preferably dibutyltin-bis-isooctylthioacetate and the reaction is hot maintained until the theoretic NCO content is obtained, determined by titration according to ASTM D 2572.
As component 2 also (2a) mixtures of PFPE oligomer diols having Mn in the range 800-1,500, preferably 1,000-1,200, with PFPE oligomer diols having Mn in the range 350-700, preferably 500-650, can be used, in said mixtures of oligomers the weight ratio between, respectively, the high and low molecular weight oligomers being in the range 1/2-1/10, or alternatively the number average molecular weight of the mixtures of PFPE oligomer diols being lower than or equal to 700.
The inert solvent component 3) under crosslinking conditions is a solvent which does not react with the OH and NCO groups present in the composition of the invention.
As component 3) an aprotic dipolar solvent such as ethyl or butyl acetate is preferably used.
As cyclic trimer of isophorondiisocyanate (IPDI) of component 1.a, the commercial product Vestanat® T1890, Huels can for example be used.
As component 1.b) non cyclic isocyanic trimer of hexamethylendiisocyanate (biuret of HDI), the commercial products Tolonate® HDB-LV, Rhodia® or Desmodur® 3200, Bayer, can be used.
The (per)fluoropolyether diol compounds comprise one or more of the following (per)fluorooxyalkylene units —(C
3
F
6
O)—, —(CFYO)—, —(C
2
F
4
O)—, —CR
4
R
5
CF
2
CF
2
O—,—(CF
2
)
a′
O—, wherein Y is F or CF
3
, R
4
and R
5
are equal to or different from each other and selected from H, Cl, a′ is an integer equal to 3 or 4.
The preferred PFPE diol compounds for the compositions of the present invention are the following, wherein the (per) fluoropolyoxyalkylene units are statistically distributed along the chain:
aI) —(C
3
F
6
O)m′ (CFYO)n′— wherein the (C
3
F
6
O) and (CFYO) units are perfluorooxyalkylene units statistically distributed along the chain; m′ and n′ are integers such as to give the above mentioned molecular weights, and m′
′ are comprised between 5 and 40, n′ being different from 0; Y is F or CF
3
;
when the unit (CFYO) is absent in this case n′ can also be equal to 0;
bI) —(C
2
F
4
O)p′(CYFO) q′—(C
3
F
6
O)t′— wherein p′ and q′ are integers such that p′/q′ ranges between 5 and 0.3, preferably between 2.7 and 0.5 and such that the molecular weight is within the above indicated limits; t′ is an integer with the meaning of m′, Y=F or CF
3
; t′ can be 0 and q′/(q′+p′+t′) is equal to 1/10or lower and the t′/p′ ratio ranges from 0.2 to 6;
cI) —CR
4
R
5
CF
2
CF
2
O— wherein R
4
and R
5
are equal to or different from each other and selected from H, Cl, the molecular weight such as to be comprised in the above mentioned limits, a fluorine atom of the perfluoromethylene unit can be substituted with H, Cl, or perfluoroalkyl group, having for example from 1 to 4 carbon atoms;
dI) —(CF
2
)
a′
O— wherein a′ is an integer equal to 3 or 4. The (per) fluoropolyethers are obtainable by known processes. See U.S. Pat. Nos. 3,665,041, 3,242,218, 3,715,378 and EP 239,123.
The two end groups, equal to or different from each other, of the bifunctional (per)fluoropolyethers are of the type
HO (CH
2
CH
2
O)
x0
CH
2
—CF
2
—
wherein x0 is an integer from 0 to 4, pr
Pogliani Carlo
Turri Stefano
Arent Fox PLLC.
Ausimont S.p.A.
Sergent Rabon
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