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
2001-07-16
2003-10-14
Wu, David W. (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...
C524S503000, C524S458000, C524S461000, C524S765000, C524S800000, C524S803000, C526S202000, C526S203000, C526S219500, C525S056000, C525S057000
Reexamination Certificate
active
06632869
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for preparing aqueous polymer dispersions based on vinyl esters, ethylene and optionally further comonomers, the polymer dispersions having a solids content of greater than 65% and a viscosity less than 10,000 mPa·s, and to the use thereof.
2. Background Art
Protective-colloid-stabilized polymers are employed, particularly in the form of their aqueous dispersions or in the form of water-redispersible polymer powders, in a variety of applications. Examples include coating compositions and adhesives for a very wide variety of substrates, for example as cementitious tile adhesives, as wood glue, or as flooring adhesives. Many varieties of polyvinyl alcohols are used as protective colloids. Polyvinyl alcohols are desirable as protective colloids, because they contribute to the strength of the end product, for example improved tensile bonding strength in tile adhesives as compared to systems stabilized by low molecular weight compounds (emulsifiers). Furthermore, it is desirable from an environmental standpoint to forego the use of low molecular weight surfactants, especially alkylphenol ethoxylates, and to carry out stabilization using protective colloids exclusively.
A high solids content in such polymer dispersions is desirable for a number of reasons. High solids content affords logistical advantages, since less water has to be transported, as well as technical advantages, such as more rapid drying of the adhesives. Numerous patents disclose the preparation of high solids dispersions. The standard approach involves producing a bimodal or polymodal particle size distribution using specific polymerization techniques. The products are stabilized predominantly by emulsifiers, or by both emulsifier and polyvinyl alcohol. Emulsifier-free dispersions with a high solids content have not been available to date.
U.S. Pat. No. 5,426,146 provides a process for preparing high solids dispersions by initiating polymerization in the presence of a seed latex consisting of a mixture of two or more dispersions containing relatively small particles having a size of from 20 to 100 nm. This process yields dispersions with a specific particle size distribution, which creates better flow properties. The process in question is relatively complex, with specific conditions to be observed with regard to the bulk density, the specific volume, and the particle diameter.
EP-A 614922 (U.S. Pat. No. 5,430,092) describes a process for preparing aqueous polymer dispersions with high solids content and good flow properties in the presence of a seed latex having a particle size of from 90 nm to 500 nm. The seed latex which must be included in its entirety in the initial charge. The polymerization takes place in a multistage feed process in which a defined portion of the monomers is polymerized initially and then a specific polymer conversion must be attained. Again, the highly complex procedure is disadvantageous.
DE-A 4213968 (U.S. Pat. No. 5,340,859) describes a procedure for preparing high solids dispersions in the presence of two seed latices, of which one contains both large (greater than 300 nm) and relatively small (less than 50 nm) particles and is metered in gradually, whereas the second seed latex is included in its entirety in the initial charge. Additionally, there are certain parameters which must be observed with regard to conversion and molar number of the seed latex particles. Here again, the highly complex procedure is disadvantageous.
EP-A 814103 (U.S. Pat. No. 6,028,135) relates to a procedure for preparing aqueous polymer dispersions of high solids content that is intended to avoid the formation of gel specks, in particular those produced during polymerization. This improvement is realized by preemulsifying the majority of the polymerizable monomers into a seed latex, which is then metered into the polymerization.
DE-A 19642762 relates to a process for preparing polymer dispersions of high solids content, where, to avoid the formation of gel specks, functional comonomers are copolymerized, and during the polymerization, the pH is altered. Polymerization first takes place at pH conditions under which the functional groups are in neutralized form, the pH then being changed such that the functional groups are converted into charged groups.
DE-A 19645427 also relates to a process for preparing polymer dispersions with high solids content where polymerization is conducted in the presence of functional comonomers, but utilizes a two-stage feed technique in which, in the first stage, the feed rate is continuously increased, and in the second stage polymerization is carried out at constant feed rate. No seed latex is used in the process.
EP-A 889068 describes a process for preparing vinyl acetate-ethylene dispersions of high solids content, where some of the vinyl acetate is included in the initial charge and some is metered in, the polymerization being conducted in the presence of a mixture of polyvinyl alcohol and nonionic emulsifier.
EP-A 814096 (U.S. Pat. No. 6,028,135) describes a process for preparing dispersions having a solids content of at least 70%. In order to avoid microcoagulum, a water-miscible organic solvent is used during the emulsion polymerization. Stabilization is carried out using an emulsifier.
EP-A 785970 describes dispersions having a solids content of at least 77%. The particle size distribution is at least bimodal. Polymerization takes place in the presence of a seed latex which is introduced in the initial charge. Stabilization is again carried out with emulsifier and, if desired, also with polyvinyl alcohol.
U.S. Pat. No. 6,001,916 describes a process for preparing vinyl acetate-ethylene dispersions having a solids content of at least 65%. The polymerization is preferably carried out with the use of polyvinyl alcohol in combination with a nonionic emulsifier as dispersant. In the procedure described therein, all of the seed latex is included in the initial charge.
In U.S. Pat. No. 5,936,020 a process is described for preparing vinyl acetate-ethylene copolymer dispersions having a solids content of at least 65%. The polymerization takes place in the presence of a dispersant combination comprising polyvinyl alcohol, nonionic emulsifier, and the salt of a polyacid.
EP-A 928798 relates to the preparation of aqueous dispersions of vinyl acetate-ethylene copolymers having a solids content of at least 65%. The dispersions are stabilized by means of a specific emulsifier system comprising polyvinyl alcohol and nonionic emulsifier.
SUMMARY OF THE INVENTION
It was an object of the invention to provide a stable polymer dispersion based on vinyl esters, ethylene and, if desired, further comonomers the dispersion having a solids content of greater than 65% and a Brookfield viscosity less than 10000 mPa·s, stabilized by means of polyvinyl alcohol.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The invention provides a process for preparing copolymers based on vinyl ester and ethylene, and optionally further comonomers, in the form of aqueous dispersions having a solids content greater than 65% and a Brookfield (20 s
−1
) viscosity of less than 10,000 mPa·s by means of free-radical initiated polymerization of one or more vinyl ester monomers and ethylene, and optionally further copolymerizable monomers, in the presence of one or more protective colloids, polymerization being conducted in the presence of from 2 to 15% by weight of seed latex, based on the amount of vinyl ester, by:
a) polymerizing the comonomers, without adding emulsifier, and in the presence of one or more polyvinyl alcohol protective colloids, the polyvinyl alcohols having a degree of hydrolysis of from 80 to 95 mol % and a Höppler viscosity in 4% by weight aqueous solution of from 3 to 30 mPa·s, and
b) introducing the seed latex in a fraction of from 30 to 75% by weight before beginning the polymerization and metering in the remainder during the polymerization, the seed latex having an average particle size (weight averag
Brooks & Kushman P.C.
Sastri Satya
Wacker Polymer Systems GmbH & Co. KG
Wu David W.
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