Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-07-14
2002-11-12
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
active
06479577
ABSTRACT:
The present invention relates to aqueous dispersions which contain polyurethanes containing hydrophilic groups and radiation-curable (meth)acrylate prepolymers having limited water-dilutability, and to processes for their preparation and their use for coating substrates.
It is known that aqueous dispersions of radiation-curable resins can be used for coating or impregnating substrates. Thus, DE-C 4413619 discloses the use of mixtures of acrylate dispersions and melamine and/or urea resins for coating substrates in the production of finish films by coating impregnated or laminated substrates (referred to as paper having good internal bond strength). DE-C 4413619 proposes using, for the coating of such substrates, electron beam curable water-dilutable or water-soluble acrylates in the form of a dispersion, emulsion or solution, with which melamine and/or urea resins have preferably been mixed. DE-C 4413619 does not give any more detailed information about the acrylates or about embodiments. Substrates mentioned are those comprising paper, polyethylene terephthalate, polyolefins and polyvinyl chloride. After evaporation of the water and subsequent coating, the treated substrate is cured by means of electron beams. In DE-C 4413619, the object is to ensure that less water has to be treated in the production process and to reduce the drying capacity.
Aqueous dispersions of mixtures of polyurethanes having hydrophilic groups and radiation-curable acrylate resins, i.e. acrylate prepolymers for coating substrates, are known. Reference may be made in particular to DE-A 19716020 of the applicant. DE-A 19716020 describes aqueous dispersions which contain, in dispersed form, (a) a polyurethane which has hydrophilic groups or potentially hydrophilic groups for achieving water dispersibility but contains no C—C double bonds, and (b) a non-self-dispersible radiation-curable prepolymer containing from 0.1 to 1 mol of polymerizable double bonds per 100 g of prepolymer. The aqueous dispersions described in DE-A 19716020 and comprising mixtures of polyurethanes and (meth)acrylate prepolymers have a long shelf life and, on coating wood, exhibit sufficient hardness, adhesion and resistance to chemicals after UV curing, but, owing to their penetration behavior, are not particularly suitable for coating or impregnating paper substrates.
It is an object of the present invention to provide radiation-curable dispersions which, in addition to sufficient blocking resistance of the dried uncured film and good flexibility of the film after radiation curing, exhibit improved penetration behavior and higher polymer absorption into the paper during the coating of paper.
We have found that this object is achieved when radiation-curable (meth)acrylate prepolymers which have limited water dilutability are used or are concomitantly used in aqueous dispersions of mixtures of hydrophilic polyurethanes (A) and prepolymers (B). Preferably, the (meth)acrylate prepolymers having limited water dilutability should be dissolved both in the polyurethane phase and in the aqueous phase in the aqueous polyurethane dispersions.
The present invention thus relates to aqueous dispersions which are essentially free of protective colloids and emulsifiers and contain:
a) at least one polyurethane (A) having hydrophilic groups which result in water dispersibility of the polyurethane, the polyurethane (A) being essentially free of C—C double bonds capable of free radical polymerization, and
b) at least one prepolymer (B) containing from 0.1 to 1 mol of C—C double bonds capable of free radical polymerization per 100 g of prepolymer,
wherein the radiation-curable (meth)acrylate prepolymer (B) has a water dilutability of at least 5% by weight, based on the solids content of the (meth)acrylate prepolymer (B), of water.
The defining feature of the present invention is thus to use, in the aqueous dispersions of mixtures of polyurethanes (A) with prepolymers (B), radiation-curable (meth)acrylate prepolymers (B) having limited water dilutability, in particular those having hydrophilic groups and preferably hydroxyl groups. Preferred (meth)acrylate prepolymers (B) having limited water dilutability are dissolved both in the phases of the polyurethanes (A) and in the aqueous phase of the dispersions. For the prepolymers (B) used according to the invention, improved penetration behavior of the aqueous dispersions into the paper substrates as well as higher internal bond strength of the impregnated paper is achieved.
The (meth)acrylate prepolymers (B) should have limited water dilutability, the water dilutability being determined by adding small portions of defined amounts of water successively to the (meth)acrylate prepolymers (B) and mixing them in until the occurrence of permanent turbidity indicates that the water dilutability limit has been reached. Thus, the maximum amount of water which can be added and at which there is still no permanent turbidity is defined as the limit of water dilutability. In the case of the suitable (meth)acrylate prepolymers (B) according to the invention, at least 0.05 part of water per part of (meth)acrylate prepolymer (B) should still give homogeneous water mixtures, i.e. the (meth)acrylate prepolymer should be capable of being diluted with at least 5, in particular from 5 to 100, preferably from 10 to 100, particularly preferably from 20 to 50, % by weight, based on the solids content of the (meth)acrylate prepolymer (B), of water. This can be achieved by using one or more (meth)acrylate prepolymers which has or have the abovementioned water dilutability per se. Alternatively, it is possible to use a mixture which has the abovementioned water dilutability but contains one or more (meth)acrylate prepolymers which do not have this water dilutability per se. For example, such a mixture may contain one (or more) (meth)acrylate prepolymer(s) having said water dilutability and one (or more) (meth)acrylate prepolymer(s) whose water dilutability does not correspond to the abovementioned value. Alternatively, the mixture may also be formed from two or more (meth)acrylate prepolymers which have the above water dilutability only when mixed but not by themselves.
Among the commercial (meth)acrylate prepolymers used in the examples, the product Laromer® LR 8982 has a water dilutability limit of 20.4% by weight of water and the product Laromer® LR 8765 has a water dilutability limit of 38.7% by weight of water, based in each case on the solids content of the (meth)acrylate prepolymers. The product Laromer® PO 43F has a water dilutability limit of less than 3% by weight of water and is the only (meth)acrylate prepolymer not suitable for the preparation of the novel aqueous dispersions. However, it can be used as a mixture with another (meth)acrylate prepolymer (B) which has a water dilutability of at least 5% by weight. The preferably used (meth)acrylate prepolymers (B) ensure that the (meth)acrylates (B) are dissolved both in the polyurethane phase and in the aqueous phase of the aqueous dispersions, which is to be noted in particular at a water dilutability above 100% by weight of water.
Radiation-curable (meth)acrylate prepolymers (B) include reaction products known as radiation-curable acrylate resins and obtained from the reaction of (i) methacrylic and/or acrylic acid with (ii) polyesters, polyethers, polyurethanes containing at least 2 hydroxyl groups and epoxy resins having at least 2 functional groups reacting with (meth)acrylic acid, and reaction products of (i) hydroxyalkyl (meth)acrylates with (ii) isocyanate-containing compounds. Such radiation-curable acrylate resins are commercially available and are described, for example, in P.K.T. Oldring, Chemistry & Technology of UV & EB formulations for coatings, inks and paints, Vol. II: Prepolymers & Reactive Diluents, J. Wiley and Sons, New York and Sita Technology Ltd., London 1997, Depending on preparation and repeating structural units in the molecular chain, the (meth)acrylate prepolymers or acrylate resins are subdivided into polyester acrylates, polyether acrylate
Jaworek Thomas
Lokai Matthias
Paulus Wolfgang
Reich Wolfgang
BASF - Aktiengesellschaft
Michl Paul R.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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