Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
1996-01-04
2002-07-23
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S303000, C528S306000, C528S307000, C560S146000, C252S182280
Reexamination Certificate
active
06423816
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to new polyester polyols and their use as a binder component in two-component polyurethane coating compositions (2K PUR coating compositions), preferably for automotive refinish and for coating heavy vehicles.
2. Description of the Prior Art
It is known to coat relatively inflexible substrates, such as metal or wood, with two-component polyurethane coating compositions based on organic polyisocyanates and hydroxy-functional polyacrylates, polyethers and polyesters. The resulting coatings are distinguished in particular by excellent hardness, very good adhesion and high weather resistance. The chemical principles behind these compositions and coatings are described, inter alia, in “Lackkunstharze” (Synthetic resins for lacquers) by Hans Wagner and Hans Friedrich Sarx, Carl Hanser Verlag publishers, Munich, pp. 153 to 173, 1971.
Because the two-component polyurethane coating compositions of the prior art, especially those based on aromatic polyester polyols, often result in coatings having a tendency to yellow, particularly when exposed to short-wave UV light, they frequently fail to meet the requirements in this respect for coatings which are resistant to weathering, chalking and yellowing in automotive refinish and heavy vehicle lacquering.
A typical example of coating compositions that are susceptible to yellowing are the binders according to DE-AS 1,271,867. Although coatings prepared from these binders (aromatic polyester polyols and polyisocyanates based on hexamethylene diisocyanate) show neither loss of gloss, chalking or shade alteration after 2000 Weather-o-meter hours, they yellow distinctly after 1000 hours of exposure to short-wave UV light.
A substantial improvement in the susceptibility to yellowing of 2K PUR coatings when exposed to short-wave UV light can be achieved with the polyester polyols described in EP-A 0,318,800 and EP-A 0,571,829. However, these polyester polyols are not suitable for manufacturing 2K PUR coatings for automotive refinish and heavy vehicle lacquering because the dry time (partial drying and through drying) is too long and because the resulting coatings are highly elastic and, thus, do not have the required surface hardness.
EP-A 0,494,442 describes thermosetting one-component coating compositions which also provide UV-resistant coatings. The polyester polyols used in these coating compositions are not suitable for use as the polyol component in 2K PUR coatings for automotive refinish and heavy vehicle lacquering because the degree of branching, hardness and OH-content of the polyesters are too low to achieve quick-drying, hard coatings that are resistant to solvents and chemicals.
An object of the present invention is to provide new two-component polyurethane coating compositions which meet industry requirements and are optimally suitable in particular for automotive refinish and heavy vehicle lacquering. The new coating compositions should meet the following requirements:
1. Yellowing-free film surfaces when exposed to short-wave UV light: the coating must withstand exposure to short-wave UV light (wavelength <400 nm) for a period of at least 1000 hours without essential yellowing.
2. Good resistance to light and weather: The coating may show neither loss of gloss, chalking nor shade alteration after 2000 Weather-o-meter hours and weathering in the industrial atmosphere.
3. Quick drying at room temperature: The coating should be “sand” dry after approx. 3 hours and thoroughly dry after approx. 8 hours (DIN 53150).
4. Very good resistance to solvents and chemicals: The coating must withstand effects of common lacquer solvents, such as xylene, butyl acetate, acetone, methyl ethyl ketone and super grade gasoline and chemicals such as caustic soda solution, sulphuric acid, tree resin, pancreatin and tar, without damage.
5. High film hardness and mechanical strength: The coating should have a hardness (pendulum damping>120 s) after as few days as possible (3 to 7) and thus be scratch and abrasion resistant.
6. Adequate processing time: As a minimum, freshly prepared coating compositions must have a processing time of 6 hours, i.e., the viscosity measured as flow time out of a DIN 4 mm cup should not double within 6 hours.
These objects may be achieved in accordance with the present invention by using the polyester polyols described hereinafter as at least a portion of the polyhydroxyl component in two-component polyurethane coating compositions. The resulting coatings possess good resistance properties and are especially resistant to yellowing, quick-drying and hard.
SUMMARY OF THE INVENTION
The present invention relates to polyester polyols having a hydroxyl number of 60 to 400, which are esterification products of
a) an alcohol component containing
a1) one or more aliphatic or cycloaliphatic alcohols having at least 3 hydroxyl groups and 3 to 8 carbon atoms,
a2) optionally one or more aliphatic or cycloaliphatic alcohols having 2 hydroxyl groups and 2 to 18 carbon atoms and
a3) optionally one or more aliphatic or cycloaliphatic, optionally unsaturated alcohols having one hydroxyl group and 1 to 18 carbon atoms,
with
b) a carboxylic acid component containing
b1) itaconic acid, maleic acid, their anhydrides and/or fumaric acid,
b2) optionally one or more aliphatic or cycloaliphatic, saturated or unsaturated dicarboxylic acids having at least 2 carbon atoms and/or their anhydrides other than those set forth under b1) and
b3) optionally one or more aliphatic or cycloaliphatic, saturated or unsaturated monocarboxylic acids having 1 to 18 carbon atoms and/or their anhydrides,
provided that component a3) is used in an amount of at least 10 mole %, based on the total moles of component a), or component b3) is used in an amount of at least 10 mole %, based on the total moles of component b).
The present invention also relates to two-component polyurethane coating compositions containing these polyester polyols and lacquer polyisocyanates as the binder.
Finally, the present invention relates to coated substrates, in particular automotive substrates, coated with these two-component polyurethane coating compositions.
DETAILED DESCRIPTION OF THE INVENTION
The polyester polyols according to the invention differ quite substantially in their composition from the polyester polyols according to EP-A 0,318,800, EP-A 0,494,442 and EP-A 0,571,829 and German Offenlegungsschrift 43 43 452. In addition, the polyester polyols according to the invention are intended in particular for an application that is not disclosed in the above European patent applications.
The particularly good suitability of the polyester polyols according to the invention for use in the previously described coating applications is attributable to the selection of the starting materials and their amounts for preparing the polyester polyols. The polyester polyols have hydroxyl numbers of 60 to 400, preferably 80 to 350 and more preferably 100 to 300; acid numbers of 0.5 to 80, preferably 0.5 to 60 and more preferably 0.5 to 50; and a number average molecular weight, which can be calculated from the stoichiometry of the starting materials, of 500 to 10,000, preferably 600 to 5,000. The polyester polyols according to the invention are highly viscous, virtually colorless, clear resins which dissolve to give a clear solution in lacquer solvents, e.g., hydrocarbons such as toluene, xylene and higher alkylbenzenes; esters such as ethyl acetate, propyl acetate, butyl acetate, methylglycol acetate, ethylglycol acetate and methoxypropyl acetate, ketones such as acetone, methyl ethyl ketone and methylisobutyl ketone; and mixtures of these solvents.
Alcohol component a) is composed of the individual components a1) and optionally a2) and/or a3).
Component a1) is selected from aliphatic alcohols having at least 3 hydroxyl groups and 3 to 8, preferably 3 to 6, carbon atoms, such as glycerol, trimethylolpropane, pentaerythritol, sorbitol and mixtures of these alcohols.
Component a2) is selected from aliphatic or cyclo
Sonntag Michael
Wamprecht Christian
Bayer Aktiengesellscahft
Gil Joseph C.
Gorr Rachel
Roy Thomas W.
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