Use of polymer dispersions as binding agents for sealing...

Details Use of polymer dispersions as binding agents for sealing... Use of polymer dispersions as binding agents for sealing...

1999-07-26

2001-06-05

Cain, Edward J. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C427S393500, C428S393000, C524S191000, C524S543000, C524S601000, C524S602000

Reexamination Certificate

active

06242515

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the use of polymer dispersions as binder for sealing or coating compositions comprising at least one aqueous polymer dispersion, in which the polymerisate has functional groups, and at least one compound having two or more NH
2
groups per molecule as binder for sealing or coating compositions for hydrophobic substrates. The present invention also relates to sealing or coating compositions comprising such a formulation, which are suitable for the coating of substrates, especially hydrophobic substrates such as polyurethane foams or EPDM components.
2. Description of the Background
Construction materials are often sealed with coating compositions in order to protect against environmental effects, including the processes of weathering. Examples of such environmental effects, especially outdoors, are sunlight, fluctuating temperatures, moisture, the chemical effects of increasing pollution, and mechanical effects as well. To be suitable, coating compositions must be stable toward the environmental conditions mentioned, i. e. they should have little water uptake tendency, high photostability, and high resistance to oxidizing conditions as may occur, in particular, when intense solar irradiation and polluted air act in combination. The compositions must also be of high mechanical stability, especially high tensile strength, so that the dimensional changes in the components, induced by fluctuating temperatures, do not lead to cracks being formed. Moreover, this is a property which they must not lose at low temperatures. Conversely, at high temperatures they must not become tacky, which would lead to unwanted soiling. A further quality desirable in the coating compositions is the ability to reflect light and heat, so as to avoid extreme temperature fluctuations in the construction materials. Good adhesion of the coating compositions to the substrate to be sealed is of particular importance, especially in the case of hydrophobic construction materials, such as polyurethane foams, or components made of EPDM plastics, to which the adherence of conventional coating compositions is poor.
The properties required of the coating compositions depend largely on the particular binder used. Thus W. A. Zissmann (Advances in Chemistry, Series 43, Gould edition, ACS Washington 1964) showed that good adhesion to substrates with low surface tension and low polarity (hydrophobic substrates) is achieved if the binder polymers are in turn of Low surface tension and low polarity. In general, the surface of polymer particles in polymer dispersions is populated by polar groups as a result, for example, of the adsorption of ionic surface active substances. This restricts the choice of possible polymers and of surface active substances. Moreover, the polymers used as binders should, as films, possess high tear strength and good extensibility. Further still, the binder polymers must possess a high pigment binding capacity in order to ensure the stability of the coating compositions.
There have been various reports of binder polymers which meet some of the properties desired. For instance, EP A 187 505 describes a binder polymer which couples heightened tear strength with comparatively high flexibility. This polymer is obtained by reacting a primary latex in the swollen state with a monomer having at least two ethylenically unsaturated bonds. However, this two stage process is highly complex and increases the cost involved in preparing such binderxpolymers.
U.S. Pat. No. 3,345,336 describes polymers having carbonyl groups which can be crosslinked with hydrazides of the polybasic carboxylic acids. In the crosslinked state these polymers are of high solvent resistance; they are used for treating leather, textiles and paper.
EP-B 258 988 describes a coating composition for polyurethane foams that includes a binder polymer having acetoacetyl or cyanoacetyl groups. A distinctive feature of the coating composition is its high degree of adhesion to the polyurethane foam. While the incorporated functional groups increase the tear strength of such binder polymers, there is at the same time a marked reduction in the extensibility of these coatings. This loss of extensibility is probably a consequence of crosslinking reactions by the reactive methylene and carbonyl groups of the abovementioned functional units present in the polymer.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a polymer based binder which goes a long way toward meeting the desired set of properties.
We have found that this object is achieved, surprisingly, by formulations comprising aqueous polymer dispersions a) whose polymers include functional groups which are able to react with NH
2
groups to form stable bonds and are selected from keto groups and oxirane rings, and compounds b) which have two or more NH
2
groups, and that these formulations can be used as binders for coating compositions having the desired set of properties.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention accordingly relates to the use of compositions, in which a coating composition whose binder is a formulation comprising as component a) at least one aqueous dispersion of a polymer having functional groups —X—Y—R
1
, where R
1
is hydrogen, alkyl, aryl or aralkyl, Y is C═O or an oxirane ring, —X— is a single bond, alkylene, arylene, —R
2
—O—R
3
—, —R
2
—Z—O—R
3
—, —R
2
—Z—CH
2
—R
3
—, —R
2
—Z—N(R
4
)—R
3
—, —R
2
—O—Z—O—R
3
, —R
2
—O—Z—CH
2
—R
3
—, —R
2
—O—Z—N(R
4
)—R
3
—, —R
2
—N(R
5
)—Z—O—R
3
—, —R
2
—N(R
5
)—Z—CH
2
—R
3
—, —R
2
—N(R
5
)—Z—N(R
4
)—R
3
—, where —R
2
— is a single bond, alkylene, oxyalkylene, polyoxyalkylene or arylene and is attached to the polymer, —R
3
— is alkylene or arylene and is attached to Y, Z is SO
2
or C═O, and R
4
and R
5
independently are hydrogen, alkyl, aryl, aralkyl or a group —R
3
—Y—R
1
, where Y, R
1
and R
3
are as defined above,
and as component b) at least one compound having at least two NH
2
groups per molecule, is applied to the substrate which is to be coated.
The novel compositions are preferably used as binders in sealing or coating compositions for hydrophobic substrates. Hydrophobic substrates are understood to be surfaces having a surface tension <50 mN/m, preferably <40 mN/m and in particular <30 mN/m, and which are of low polarity, for example surfaces of polyurethane foams or polyurethane compositions, asphalt and bitumen compositions, components or structural compositions of polyolefins, such as polyethylene, polypropylene, EPM-EPDM polymers (EPM=ethylene propylene rubber; EPDM=ethylene propylene diene rubber) or of polymer blends whose principal constituent comprises polyolefins.
Alkyl below is preferably linear or branched C
1
-C
12
-alkyl, especially C
l
-C
8
-alkyl, for example methyl, ethyl, n-propyl, isopropyl, 1-butyl, 2-butyl, isobutyl, t-butyl, 1-pentyl, 2-pentyl, 3-pentyl, 1-hexyl or 2-ethylhexyl. Aryl is preferably phenyl or naphthyl each of which is unsubstituted or substituted by 1-4 groups selected independently from C
1
-C
4
-alkyl, especially methyl or ethyl, C
1
-C
4
-alkoxy, for example methoxy or ethoxy, hydroxyl (which may also be ethoxylated) and halogen. Alkylene is a divalent alkyl, preferably C
1
-C
12
-alkyl, for example methylene, 1,1- or 1,2-ethylene, 1,1- , 1,2- , 1,3- or 2,2-propylene. Arylene is a divalent aryl, preferably 1,2- or 1,4-phenylene. Aralkyl is aryl attached to the respective center via an alkylene. Oxyalkylene is alkylene attached to the polymer via an oxygen, and, correspondingly, polyoxyalkylene comprises alkylene units each linked to one another by bxygens.
The polymers present in the novel binder formulations have reactive centers Y which are able, without themselves reacting with one another, to undergo reaction with NH
2
groups to form a bond. Suitable reactive centers are carbonyls (CO) and oxirane rings. The reactive center Y is attached to the polymer either directly or via a bridge X. The reacti

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