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
2001-09-25
2003-11-11
Lipman, Bernard (Department: 1713)
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
06646041
ABSTRACT:
This invention relates to an aqueous dispersion of particles of an addition polymer of ethylenically unsaturated monomers, to a process for making the dispersion and to compositions containing the dispersions, especially a coating composition and an adhesive composition.
The continuing drive to reduce solvent emissions in many products, such as coating compositions and adhesives formulated at least in part using dispersions of polymer particles, has focussed attention on waterborne polymer particles, that is to say polymers which can be carried in water or mixtures of water and water miscible organic solvent where the water is the predominant carrier liquid. In this way potentially harmful solvents can be totally or substantially replaced by water. A particular class of such polymers is the so called emulsion (also known as latex) polymers made by emulsion polymerisation. Typically such a process involves the addition polymerisation of substantially water immiscible ethylenically unsaturated monomers using a water soluble polymerisation initiator in water. On raising the temperature, polymerisation takes place in the water phase producing substantially water insoluble polymer which, as polymerisation proceeds, increases in molecular weight until it becomes completely insoluble in the water and consequently precipitates to form a particle. In order to make such polymers as stable dispersions it is well known that water soluble surfactants are required to emulsify the monomers to be polymerised and subsequently to stabilise the resulting polymer particles as they are formed, otherwise the polymer particles will form coarse agglomerates, which cannot be formulated into useful products. Typical water soluble surfactants used are low molecular weight ionic or non ionic molecules having a hydrophobic and hydrophilic portion. Unfortunately, when the dispersion is converted to dried formulated products, for example as in the case of coatings and adhesives such water soluble surfactants remain in the composition resulting in poor resistance to water and humidity and contributing to flash rusting when applied directly to ferreous metals.
An attempt to overcome the poor water resistance was disclosed by United States patent specification U.S. Pat. No. 5,889,101 issued in 1999. U.S. Pat. No. 5,889,101 discloses a method whereby as a first stage a polymeric protective colloid of weight average molecular weight of at least 20,000 is made by free radical polymerisation in solvent, followed by a second stage polymerisation of monomers in the presence of the protective colloid to form a stable polymer dispersion which is free of low molecular weight surfactant. U.S. Pat. No. 5,889,101 cautions against the use of large amounts of crosslinking species, in this case particular types of multi-unsaturated monomers, when making the protective colloid and in particular teaches the use of no more than 0.2 wt % of them presumably to avoid the known risk of gelling. This results in only modest water resistance. This level of water resistance remains inadequate in some critical applications such as adhesives and coatings, especially paint compositions for painting motor vehicles (especially cars).
It has now been discovered that highly water resistant, stable aqueous dispersions of addition polymer particles can be made without using surfactants. This is achieved by using stabilizing solution copolymers containing amounts of crosslinking species which are significantly higher than previously proposed. Such dispersions when formulated into coatings result in substantially improved water resistance and improved flash rusting on bare steel.
Accordingly, this invention provides an aqueous dispersion of particles of an addition polymer of ethylenically unsaturated monomers which dispersion also contains a stabilizing solution copolymer comprising
a) weak acid containing species
b) crosslinking species and optionally
c) ethylenically singly unsaturated comonomers
wherein the stabilizing solution copolymer contains at least 0.3% by weight of crosslinking species.
It is believed that the presence of the crosslinking species results in a degree of copolymer chain branching and/or crosslinking during copolymerisation and reaction to form a branched stabilizing solution copolymer. A measure of this branching is the alpha parameter. This is determined in tetrahydrofuran (THF) at 23° C. using the technique described in detail later in the specification. The alpha parameter is indicative of the molecular structure of the stabilizing solution copolymer and under specified conditions of solvent and temperature alpha indicates the degree of branching. It is thought that too low a value of the alpha parameter means that the stabilizing solution copolymer is so highly branched that it behaves as a hard sphere, rendering it insufficiently dispersible in water and consequently inadequate as a stabiliser in an emulsion polymerisation, whilst too high a value of alpha means that the stabilizing solution copolymer is easily extractable by water and hence the water resistance of the dried formulations is poor.
Preferably the stabilizing solution copolymer has an alpha parameter derived from the Mark-Houwink equation of from 0.3-0.6 and more preferably from 0.3 to 0.5.
The invention also provides a stabilizing solution copolymer for use in the aqueous dispersions which is a copolymer of;
a) weak acid containing species
b) crosslinking species and optionally
c) ethylenically singly unsaturated comonomers
wherein the stabilizing solution copolymer contains at least 0.3% by weight of crosslinking species.
Preferably, the stabilizing solution copolymer is selected so as to have an alpha parameter derived from the Mark-Houwink equation of from 0.3-0.6 and more preferably from 0.3 to 0.5.
The crosslinking species referred to in b) is any species capable of reacting with the monomer of a) and c) to produce crosslinks and/or branches in the stabilizing solution copolymer.
Suitable examples of such crosslinking species include ethylenically multi-unsaturated monomers; that is to say, monomers that have more than one ethylenic unsaturation which can copolymerise with the other ethylenically unsaturated comonomers so as to form the crosslinks and/or branches described above. Such monomers are known as crosslinking comonomers. Examples of suitable such crosslinking comonomers include allyl methacrylate, vinyl acrylate, divinyl benzene, ethylene glycol dimethacrylate, di-allyl phthalate, hexane diol diacrylate, trimethylol propane triacrylate, penta erythritol triallyl ether, dicyclopentenyl oxyethyl methacrylate and glycerol triacryl ate.
Preferably the crosslinking comonomer contains two ethylenically unsaturated bonds.
The crosslinking species can also be a mixture of two ethylenically singly-unsaturated monomers each having a co-reactive functional group, sometimes referred to as a co-reactive monomer pair. It is thought that when such monomers copolymerise with the other ethylenically unsaturated monomers and the co-reactive functional groups on one polymer chain react with those of another polymer chain, crossliriks and/or branches are formed. When such a reaction takes place, the functional groups are substantially consumed. Suitable examples of such co-reactive functional groups include epoxy and carboxyl, anhydride and hydroxyl, isocyanate and hydroxyl, epoxy and hydroxyl, isocyanate and amine, acetoacetate and amine and alkoxysilane and hydroxyl. Examples of suitable monomers having an epoxy group are glycidyl methacrylate and glycidyl acrylate. Suitable examples of monomers having carboxyl groups include (meth)acrylic acid and beta-carboxyethyl acrylate. An example of a suitable monomer having an anhydride group is maleic anhydride. Suitable examples of monomers having hydroxyl groups include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate and hydroxybutyl (meth)acrylate. An example of a monomer having an isocyanate group is 1-1 (isocyanato 1-methylethyl)-3-(1-methyl ethenyl) benzene. A suitable example of monomer contai
Downing Stephen Barry
St. John Williams Neal
Imperial Chemical Industries PLC
Lipman Bernard
Stachel Kenneth J.
LandOfFree
Aqueous dispersion of addition polymer particles does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Aqueous dispersion of addition polymer particles, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aqueous dispersion of addition polymer particles will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3169152