Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-07-26
2003-12-23
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S503000, C524S522000, C524S523000, C524S524000
Reexamination Certificate
active
06667352
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to protective colloid-stabilized copolymerizate latex particles with heterogeneous morphology based on a vinyl acetate-ethylene copolymerizate, processes for the production thereof and the use thereof.
BACKGROUND OF THE INVENTION
For some time now copolymerizates in the form of stabilized, aqueous polymerizate dispersions (latices) or preferably as redispersible powders have been increasingly used for modifying mineral building materials. As a result of such additives the characteristics profiles of mineral building materials, such as mortar, concrete, etc. can be controlled in a planned manner and the copolymerizates can be based on the most varied monomers. The modifying action is based less on the chemical characteristics of the copolymerizate used than on its physical characteristics. In particular, copolymerizates based on the monomers vinyl acetate and ethylene have particular advantages as modifying additives in the building sector,for hydraulically setting systems.
The production of so-called heterogeneous latex morphologies is of interest in this connection. Due to their molecular structure such latex particles have special characteristics, which not only permit their universal use, but also a more planned setting of the desired characteristics. In this heterogeneous structure of the latex particles, a distinction is in each case made between a relatively hydrophobic and a relatively hydrophilic area. For thermodynamic equilibrium reasons, under normal conditions there is frequently a hydrophilic shell (outer phase) and a hydrophobic core (inner phase), because this structure can generally be more easily produced by a conventional emulsion polymerization. However, it is much more difficult to produce systems having a so-called inverse core-shell structure, in which firstly the shell and then the core are produced. This is more particularly the case when performing so-called pressure polymerizations, if e.g. ethylene is used.
Please note that the core-shell morphology as described herein, is not a stabilized latex particle known in the art, wherein a protective colloid or surfactant is arranged on the surface of the polymer particle to stabilize it in an additional phase. In contrary, the polymer particle itself should be structured in the present invention, i.e. should have a heterogeneous morphology.
Apart from aqueous polymer dispersions, a further very appropriate application form of the polymer additive acting in a modifying manner is a redispersible powder available from such dispersions by drying. These powders are, due to their easy handling, easier, space-saving transportation, easier dosability and less expensive storage, very advantageous. Due to the readily available dispersing medium “water”, the powder form is also desired in this respect.
The prior art provides numerous publications dealing with vinyl acetate-ethylene copolymers and which in part would result in redispersible powders. For example, EP 444 827 A1 describes copolymer particles with a core-shell structure, in which the Tg-value is in the range 0 to −30° C. and the core, apart from 10 to 30 wt. % alkylene and 1 to 10 wt. % alkylacrylate, also contains 10 to 60 wt. % vinyl alkanoate, 10 to 40 wt. % vinyl esters having a specific chemical formula and 0.1 to 5 wt. % vinyl silane. The particles are used in the form of copolymer emulsions for pigmented surface coatings.
However, a dispersible powder is not described.
The 1969 DE-OS 2 055 978 relates to the preparation of a water-based gloss paint, which contains a vinyl acetate-ethylene copolymerizate as the binder. The copolymerizate is produced by (1) preparing an aqueous polymerization starting medium with water, catalyst and a small amount of vinyl acetate, (2) polymerizing the vinyl acetate, (3) introducing ethylene into the reaction mixture in order to obtain a pressure in the range 3.5 to 105 atü, as well as the gradual addition of vinyl acetate and an acrylamide and polymerizing both monomers in the presence of the previously formed polyvinyl acetate at a temperature of 40 to 90° C., (4) releasing the overpressure, (5) adding a water-soluble emulsifier and a small amount of an alkyl acrylate and (6) polymerizing the alkyl acrylate in the presence of the polymer dispersion obtained. A surfactant can optionally be present in the first polymerization stage. However, this cannot produce a heterogeneous morphology. In addition, only dispersions, but not redispersible powders are described.
According to the disclosure of EP 757 065 A3 a protective colloid-stabilized copolymerizate is prepared, which has a glass transition temperature of −40° C. to 10° C., as well as an ethylene content of at least 30 wt. %, based on the total quantity of the monomers, the heterogeneous structure of the copolymer particles containing a first copolymerizate phase with vinyl acetate and >40 wt. % ethylene, based on the total monomer quantity in this phase and a final copolymerizate phase with vinyl acetate and 5 to 40 wt. % ethylene, based on the total monomer quantity in this phase.
The process for the production of this copolymerizate is based on the polymerization of vinyl acetate and ethylene and optionally further comonomers, part of the monomers undergoes radical copolymerization at an ethylene pressure of 55 to 150 bar in the presence of a protective colloid, optionally further monomers are polymerized and then, under an ethylene pressure between 1 and 55 bar, further radical copolymerization takes place. The copolymerizates described are used in the form of dispersions or redispersible powders as binders in building materials or sealing sludges.
The problem of the invention is to further develop the previously described vinyl acetate-ethylene copolymerizate latex particles or the aqueous dispersions obtained in such a way that, whilst retaining advantageous characteristics, or in individual cases even better characteristics, a heterogeneous morphology is obtained in the latex particles. In addition, the copolymerizate latex particles are to be improved in that in their final applications, such as e.g. in plastics-containing, cement-bonded systems, due to the desirable successive reactions, they lead to improved use products. Apart from the aqueous dispersions, redispersible powders are to be accessible, which substantially maintain their advantageous characteristics following redispersion in the aqueous medium. In addition, a process is to be provided, which permits the planned setting and modification of the heterogeneous morphology of latex particles, also when performing a pressure emulsion polymerization.
SUMMARY OF THE INVENTION
According to the invention, this problem is solved by protective colloid-stabilized copolymerizate latex particles with a heterogeneous morphology based on a vinyl acetate-ethylene copolymerizate and optionally further monomers, the latex particles having an ethylene content of less than 30 wt. %, based on the total monomer quantity, comprising an outer phase with a polymer of vinyl acetate and approximately 0 to 40 wt. % ethylene, based on the monomers of the outer phase, and an inner phase with a polymer of vinyl acetate and approximately 0 to 40 wt. % ethylene, based on the monomers of the inner phase and in which at least one of the two phases contains ethylene.
DESCRIPTION OF THE INVENTION
Copolymer latex particles with heterogeneous morphology and a total ethylene content of less than 30 wt. %, based on the total monomer quantity are made available, the ethylene content in the individual phases being in the range approximately 0 to 40 wt. %, based on the monomers of the particular phase. A polymer with ethylene content need not simultaneously be present in both phases and instead, for bringing about the characteristics according to the invention, it is sufficient if one of the two phases only contains a vinyl acetate homopolymer, optionally a vinyl acetate copolymer without ethylene.
It is important for solving the aforementioned set problem for the indicated we
Cook Wendy J.
Koelliker Robert
Kusters Jos M. H.
Vlad Florin I.
Almer Charles W.
Lipman Bernard
National Starch and Chemical Investment Holding Corporation
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