Low molar mass aliphatic polyester polyols, their...

Details Low molar mass aliphatic polyester polyols, their... Low molar mass aliphatic polyester polyols, their...

2001-06-15

2003-07-22

Hampton-Hightower, P. (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...

C525S124000, C525S170000, C525S437000, C525S439000, C525S440030, C525S443000, C525S444000, C523S402000, C523S412000, C523S415000, C523S416000, C523S417000, C427S385500, C427S386000, C427S393500

Reexamination Certificate

active

06596817

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to low molar mass aliphatic polyester polyols, to their preparation and to their use in coating compositions.
BACKGROUND OF THE INVENTION
Present-day ready-to-spray clearcoat materials and pigmented topcoat materials, and also primer-surfacer materials, are relatively low in solvents, i.e., they contain fewer volatile organic compounds (VOCs) which are emitted into the atmosphere in the course of the application and drying of said coating materials. These more environmentally friendly coating compositions comprise low molar mass binders and a curing agent. In the case of a two-component (2K) coating composition curing agents are used which react even at low temperature with the functional groups of the binder to form a crosslinked film (usually polyfunctional isocyanates); in the case of one-component (1K) coating compositions, curing agents are used which react only at increased temperature (usually, for example, melamine resins).
In many cases, such binders are hydroxy-functional polyesters or polyacrylates, and also acrylic-modified polyesters or polyester-modified polyacrylates, or mixtures of these resins with one another, or resins of this kind to which reacted diluents have been added.
Reactive diluents are organic chemicals which, in the form of a mixture with the binder, reduce its viscosity, but which are able to react with the respective curing agent. In the case of 2K curing they are, for example, sterically bulky amine compounds (e.g., aspartic esters), blocked amine compounds (e.g., ketimines, aldimines) or blocked &bgr;-hydroxyamine compounds (e.g., oxazolidines). Disadvantages of all of these compounds are their intrinsic yellow to brown color, the high yellowing propensity of coating materials comprising them, after application, the short pot life (about 1.5 h, whereas the requirement is for about 8 h, i.e., one working day), and the absence of application reliability under different weathering conditions in practice (e.g., unmasking of the amine compounds by exposure to atmospheric moisture). The pot life (paint processing time) is defined as the time within which the initial viscosity of the ready-to-apply coating material doubles. Accordingly, such compounds are unsuitable as additives for the abovementioned high performance coating systems.
It is also known that the drying rate of the so-called high solids coating materials (with a high mass fraction of solids) may be accelerated by means of external catalysis (for example, with dibutyltin dilaurate, zinc octoate, triethylenediamine, diethylethanolamine, volatile acids, etc.), although this also leads to a severe curtailment of the pot life or paint processing time. Moreover, attempts are made to improve the reactivity with isocyanate curing agents by modifying the binder, by altering the polarity of the polymer framework in the case of acrylate resins (e.g., by introducing carboxyl groups) (cf. EP-A 0 680 977).
Low molar mass polyester resins known to date, with rapid initial drying, contain special, expensive, sterically hindered units and have an acid number of from 5 to 35 mg/g (DE-A 198 09 461) but nevertheless have longer drying times until a dust-dry or tack-free state is achieved than the known systems containing the customary binders of relatively high molar mass. Moreover, coating materials containing these low molar mass polyesters have only a short pot life (about 3 h) and a surface quality (leveling) which is in need of improvement. There is therefore a desire for inexpensive low molar mass polyester resins without these special units and with more rapid drying, a long pot life, and a good surface without a propensity to yellow after application.
SUMMARY OF THE INVENTION
It has surprisingly been found that by using electron-rich heterocyclic functional units containing hydroxyl and/or epoxide groups, and using trifunctional hydroxy compounds additionally to difunctional hydroxy compounds, it is possible for the first time to obtain new low molar mass aliphatic OH-functional polyester resins which exhibit accelerated drying on isocyanate curing while nevertheless showing a sufficiently long pot life (from 6 to 8 h) and good leveling of the paint film and little propensity to yellow after application.
The electron-rich heterocyclic OH-functional and/or epoxy-functional units suitable for the invention are at least difunctional compounds which possess at least one cyclic structure and contain at least, in addition to carbon, hydrogen and oxygen, a heteroatom such as nitrogen, sulfur or phosphorus. This heteroatom is preferably in the vicinity of, and in particular positioned alpha to, a carbonyl function. A particularly suitable heteroatom is nitrogen. Examples of OH-functional monomer units of this kind are 4,5-dihydroxy-N,N′-dimethylolethyleneurea or trishydroxyethyl isocyanurate (1,3,5-tris (2-hydroxyethyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione). An example of an epoxy-functional unit is triglycidyl isocyanurate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention accordingly provides low molar mass polyester polyols having a weight-average molar mass M
m
of up to 3500 g/mol, having hydroxyl numbers of from 80 to 280 mg/g and acid numbers of from 5 to 40 mg/g, containing the following mole fractions (in %=mol/100 mol) of structural units derived from
a) from 1 to 18%, preferably from 3 to 15%, with particular preference from 5 to 12%, of aliphatic monocyclic or polycyclic polyhydroxy or polyepoxy compounds A containing at least two hydroxyl and/or epoxy groups and at least one heteroatom, preferably a nitrogen atom, which is preferably positioned alpha to a carbonyl group,
b) from 1 to 30%, preferably from 3 to 25%, with particular preference from 5 to 20%, of aliphatic acyclic or cyclic polyhydroxy compounds B containing three or more hydroxyl groups per molecule,
c) from 15 to 50%, preferably from 20 to 45%, with particular preference form 25 to 40%, of linear or branched aliphatic dihydroxy compounds C,
d) from 25 to 60%, preferably from 30 to 55%, with particular preference from 35 to 50%, of aliphatic cyclic polycarboxylic acids D
and
e) from 0 to 20%, preferably from 1 to 15%, with particular preference from 2 to 10%, of polyfunctional compounds E selected from aliphatic linear and branched dicarboxylic acids, aromatic dicarboxylic acids and polycarboxylic acids containing three or more carboxyl groups per molecule, and also
f) from 0 to 15%, preferably from 1 to 12%, with particular preference from 2 to 10%, of monofunctional units F selected from monocarboxylic acids, monoalcohols and monoepoxides,
the ratio of the sum of the amounts of substance of hydroxyl groups and epoxide groups of the components A and B and the amount of substance of hydroxyl groups of the component C being at least 1 or greater than 1, and the mole fractions indicated respectively under a), b), c), d), e) and f) adding up to 100%.
The acid number is defined in accordance with DIN EN ISO 3682 as the ratio of that mass M
KOH
of potassium hydroxide which is required to neutralize a sample for analysis to the mass m
B
of the sample (mass of the solids in the sample in the case of solutions or dispersions); its customary unit is mg/g. The hydroxyl number is defined in accordance with DIN EN ISO 4629 as the ratio of that mass m
KOH
of potassium hydroxide which has exactly the same number of hydroxyl groups as a sample for analysis to the mass m
B
of said sample (mass of the solids in the sample in the case of solutions or dispersions); its customary unit is mg/g.
The aliphatic monocyclic or polycyclic polyhydroxy or polyepoxy compounds A have preferably 5- or 6-membered rings in which at least one atom is other than carbon and is preferably a nitrogen atom. The carbonyl group preferably adjacent to the nitrogen atom is likewise preferably part of the ring. Particular preference is given to those compounds A having two or three nitrogen atoms in one ring. The hydroxyl groups are preferably present in methylol, hydroxyethyl or 2-hydroxypropyl g

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