Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-05-31
2001-07-10
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C528S272000, C528S295300, C528S296000, C528S298000, C528S300000, C528S302000, C528S307000, C528S308000, C525S445000
Reexamination Certificate
active
06258897
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to polyester polyols of low molar mass, their preparation and use in coating compositions.
2. Description of Related Art
Presently used two-component polyurethane coating materials are based on anhydroxy-functional polyesters or polyacrylates, on acrylic-modified polyesters or polyester-modified polyacrylates, or mixtures of these resins, and are more environmentally compatible than their prior art counterparts. This is because presently used two component polyurethane coating materials generally require less solvent for dilution, thus enabling them to be formulated to give a ready-to-spray transparent or pigmented coating material or surfacer. These low-solvent or high-solids coating materials can only be prepared because the hydroxy-functional polymers employed (also referred to as binders), still exhibit sufficiently good physical initial drying despite their low degree of polymerization.
In order to have sufficient initial drying (i.e. short time span until the applied coating is no longer tacky) properties, these low molar mass polyols must comprise rigid chain units, which initially reduces the solution viscosity and at the same time leads to glass transition temperatures (T
g
) of at least 20° C. It is precisely at very low degrees of polymerization that the dependence of the glass transition temperature on the degree of polymerization is critical, and predictions made on the basis of additivity equations which link the mass fraction or weighted molar proportions of the units with the T
g
are generally not valid. One is forced to look for suitable units on a purely empircal basis which will then, it is hoped, lead to a low molar mass polymer having the desired properties described above.
Examples of acrylate polyols which, in pure form or as mixtures, generally meet these requirements are described for example in EP-A 0 638 591 and EP-A 0 741 149. Coating compositions based on these branched polymers are notable for good weathering stability, high solids contents, rapid drying, a long pot life (at least 8 hours) and, in particular, the possibility of universal application in intermediate coats and in pigmented and unpigmented systems.
Examples of polyester polyols that have aliphatic branched and monocyclic units are also described in EP-A 0 705 858. They are notable for good weathering stability, high solids contents, good elasticity, and rapid drying. However, they have disadvantages in terms of their adhesion to various substrates, such as base coat in automotive refinish, and various metallic substrates (cold-rolled sheet iron).
Surprisingly it has now been found that two-component polyurethane coating materials which comprise, as a hydroxy-functional component, low molar mass polyester polyols of the present invention, which are based on selected starting materials and are described in more detail below, possess one or more of certain favorable properties including those referred to above and, moreover, exhibit good adhesion to base coat in automotive refinshes and to various metallic substrates.
SUMMARY OF THE INVENTION
In accordance with these and other objects, there is provided a low molar mass polyester polyol having a weight-average molar mass M
w
of not more than 2000 g/mol, with a hydroxyl number of from 80 to 300 mg/g and an acid number of from 5 to 35 mg/g, comprising mole fractions [in %=mol/(100 mol)] of structural units derived from:
a) from 1 to 45% of an aliphatic polycyclic polyhydroxy compound having at least two hydroxyl groups per molecule;
b) from 5 to 50% of a branched aliphatic acyclic dihydroxy compound;
c) from 30 to 50% of an aliphatic cyclic polycarboxylic acid;
d) from 0 to 30% of an aliphatic acyclic or monocyclic polyhydroxy compound having three or more hydroxyl groups per molecule;
e) from 0 to 10% of a polyfunctional compound selected from the group consisting of aliphatic linear and monocyclic dihydroxy compounds, aliphatic linear and branched dicarboxylic acids, aromatic dicarboxylic acids and polycarboxylic acids having three or more carboxyl groups per molecule; and
f) from 0 to 10% of a monofunctional unit selected from the group consisting of monocarboxylic acids and monoalcohols,
the mole fractions indicated in each case under a), b), c), d), e) and f) adding up to 100%.
The present invention also includes mixtures and coating materials comprising a low molar mass polyester polyol.
Additional objects, features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects, features and advantages of the invention may be realized and obtained in whole or in part by means of the instrumentalities and combinations particularly pointed out in the appended claims.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The low molar mass polyester polyols of the invention preferably comprise aliphatic polycyclic structural units. These units are typically at least bicyclic and each preferably contain at least two functional groups, most preferably hydroxyl groups. At least two of the hydroxyl groups of these units are preferably attached to nonequivalent carbon atoms of the cyclic structures. The term equivalent as it relates to carbon atoms of the cyclic structures described above, refers to those carbon atoms which can be interchanged by an operation of symmetry on the corresponding unsubstituted parent hydrocarbon.
The particular suitability of the low molar mass polyesterpolyols of the invention, inter alia, can be attributed to the nature and proportions of the starting materials on which the low molar mass polyester polyols are based. In this context polycyclic compounds which have been found particularly suitable include those which carry two hydroxyl groups as functional groups.
Good adhesion can be obtained, for example, in particular based on the presence in the low molar mass polyester polyols that include units of 3(4),8(9)-bishydroxymethyltricyclo[5.2.1.0
2,6
]decane (“TCD diol” isomer mixture), a tricyclic dialcohol. TCD diol is, therefore, one of the preferred units according to the invention.
The invention provides low molar mass polyester polyols generally having a weight-average molar mass M
w
of not more than 2000 g/mol, with a hydroxyl number of from 80 to 300 mg/g and a acid number of from 5 to 35 mg/g, comprising the stated mole fractions (in %=mol/100 mol) of structural units derived from:
a) from 1 to 45% of aliphatic polycyclic polyhydroxy compounds having at least two hydroxyl groups per molecule,
b) from 5 to 50% of branched aliphatic acyclic dihydroxy compounds,
c) from 30 to 50% of aliphatic cyclic polycarboxylic acids,
d) from 0 to 30% of aliphatic acyclic or monocyclic polyhydroxy compounds having three or more hydroxyl groups per molecule, and
e) from 0 to 10% of polyfunctional compounds selected from aliphatic linear and monocyclic dihydroxy compounds, aliphatic linear and branched dicarboxylic acids, aromatic dicarboxylic acids, aromatic hydroxycarboxylic acids, and polycarboxylic acids having three or more carboxyl groups per molecule, and also
f) from 0 to 10% of monofunctional units selected from monocarboxylic acids and monoalcohols,
the mole fractions indicated in each case under a), b), c), d), e) and f) adding up to 100%.
Preferably, the compounds of groups a) and c) each have 2 functional groups (hydroxyl and/or carboxyl groups).
The molar masses of the polyester polyols can be determined by any known suitable method such as by gel permeation chromatography using polystyrene gel in accordance with known customary methods. The calibration substance used is conventional polystyrene.
The acid number is defined by DIN 53 402 (incorporated herein by reference) as the quotient of the mass m
KOH
of potassium hydroxide that is required to neutralize a sample for analysis and the mass m
B
of this sample (mass of the solid in the sample in the case of solution
Epple Ulrich
Kuttler Ulrike
Pietsch Claudia
Acquah Samuel A.
Foley & Lardner
Vianova Resins AG
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