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
2000-06-20
2003-05-20
Reddick, Judy M. (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...
C523S201000, C524S296000, C524S297000, C524S458000, C524S523000, C524S561000, C524S562000
Reexamination Certificate
active
06566441
ABSTRACT:
DESCRIPTION
This invention relates to poly(meth)acrylate plastisols and to a process for the production thereof. The invention in particular relates to plastisols which contain binders based on poly(meth)acrylates, which in turn exhibit a bimodal primary particle size distribution. The invention furthermore relates to a process for the production of such poly(meth)acrylates having a bimodal primary particle size distribution as are used in the plastisols of the invention.
Plastisols comprise colloidal suspensions of a polymer component (binder) in plasticiser. Plastisols thus generally comprise two-phase systems, one component of which is a polymer and the other a suitable plasticiser. Plastisols are conventionally converted into the finished product form by spreading, casting, dipping, spraying and the like. “Gelation” then proceeds by heating; the plasticisers dissolve the polymer particles. In this manner, a homogeneous product with a greater or lesser degree of flexibility which may be compact or foamed is obtained after cooling. In principle, it is conceivable to use binders based on the most varied polymers. However, only very few polymers are used industrially. By far the most significant class of polymers used for this purpose is derived from polyvinyl chloride (PVC). However, from an environmental standpoint, it would be highly expedient to replace PVC plastisols with more environmentally friendly plastisols. Plastisols based on poly(meth)acrylates have, for example, been available for this purpose for some time. The following publications are cited as close prior art relating to poly(meth)acrylate plastisols:
D1=DE-PS 934 498;
D2=FR-A 2,291,248;
D3=EP 0 774 483 A2;
D4=JP published patent application Hei 10-298391 (10.11.1998).
To some extent depending upon the desired application, plastisols must meet a complex range of requirements. The rheological properties of the plastisol, in particular the viscosity thereof, plastisol storage stability, plasticiser compatibility and the mechanical properties of the products produced from the plastisol are inter alia of vital significance in this connection. The ratio of resin (binder or polymer) to plasticiser is also important for many applications.
The most important characteristic of a plastisol is for it to be processable at a low temperature, i.e. to exhibit a relatively low viscosity and only to gel to yield a solid film on heating and subsequent cooling. Another industrial requirement is for the plastisol to have the lowest possible viscosity in order to permit processing by a wide range of methods. For example, when spreading plastisols, no dilatancy may occur on exposure to the shear rate under the coating knife. Dilatancy may result in coating defects such as non-uniform thickness. Moreover, dilatancy results in the application of large forces onto the knife coater. When applying adhesion layers onto fabrics, the viscosity at low shear rates must be sufficiently high to prevent the plastisol from striking through the fabric. A yield point may additionally be of benefit in this case. Pseudoplasticity is consequently desired for fabric coating. In contrast, a low viscosity at low shear rates is required for impregnation coatings, for example for coating tarpaulins, so that the plastisol completely penetrates the fabric. When dipping gloves which have support fabrics, the viscosity must be sufficiently high for the plastisol not to penetrate too deeply into the fabric during the dipping and draining operation. Although the rheological properties of the plastisol may be modified with additives, it is essentially the resin or binder which exerts the main influence in all the stated cases. While the use of prior art spray-dried emulsion polymers based on poly(meth)acrylates in combination with selected plasticisers does indeed give rise to good gelation characteristics, it also results in low storage stability and relatively high processing viscosities.
Another significant problem of poly(meth)acrylate plastisols is still their inadequate storage stability, i.e. an excessive change in viscosity over extended periods of storage, in comparison with conventional plastisols. D3 attempts to solve the problem of storage stability inter alia by adding ground suspension polymers to emulsion polymers. The addition of such extender polymers firstly results in a considerable reduction in costs. Suspension polymers are distinctly lower in cost than emulsion polymers or dispersions. Moreover, the viscosity of the plastisols is generally reduced and the average particle size is increased. The disadvantage of this process is the fact that a larger particle size makes gelation of the plastisol more difficult, as, under certain circumstances, the larger suspension polymers no longer completely gel within the short time required for industrial use.
It is considered advantageous for many purposes to be able to use plastisols having the highest possible resin content and lowest possible plasticiser content. An elevated plasticiser content in the plastisol may moreover give rise to environmental problems. Pastes (plastisols) having a very high plasticiser content of certain types of plasticiser may accordingly give rise to gelled films from which the plasticiser has a tendency to evaporate or even exude. In such cases, a proportion of the plasticiser is deposited as a liquid film onto the surface of the gelled product. In PMMA plastisols, this occurs especially with dialkyl phthalates which, due to their low cost, otherwise seem to be a very attractive option. According to the prior art, it is possible to process PMMA plastisols having a maximum binder content of 40 to 45%. An increase in the resin content of the plastisol with a concomitant reduction in the plasticiser content would be welcome.
D4 discloses acrylic resin plastisols which are obtained by mixing pulverulent acrylic resins with a small quantity of larger polymer particles of another acrylic resin. Two peaks thus occur in the particle size distribution curve of these resins. In this case, the pulverulent acrylic resin consists to an extent of 90 to 60 wt. % of a fraction having an average particle size of below 10 &mgr;m and to an extent of 10 to 40 wt. % of a fraction having an average particle size of between 10 and 500 &mgr;m. Benzoic acid esters, such as for example tripropylene glycol dibenzoate, are in particular used as the plasticiser for the acrylic resin plastisols stated in D4. The plastisol systems of D4 thus comprise per se known extender systems, i.e. a monomodal emulsion polymer is extended with a finely ground bead polymer (suspension polymer). Although the systems disclosed by D4 exhibit very good compatibility values and the binder content may be greater than 50 wt. % (relative to the total weight of resin and plasticiser), the viscosity and viscosity stability values still appear to require further improvement.
In the light of the prior art cited and discussed above, the object of the present invention was to provide a plastisol based on poly(meth)acrylates and plasticiser which exhibits excellent rheological properties suiting it to numerous different processing methods. The plastisol should here exhibit the lowest possible viscosity which should also remain as stable as possible over an extended period.
Another object of the invention is to provide plastisols having good or improved plasticiser compatibility, i.e. the widest possible range of plasticisers should be usable without substantially degrading the properties of the plastisol or of the films producible therefrom. In particular, compatibility should also be ensured with inexpensive, low cost plasticisers.
Another object of the invention was to provide a plastisol which combines good film characteristics and good gelling capacity with acceptable storage stability.
A further object of the invention was to improve the mechanical properties of gelled plastisol films.
Another object of the invention was to provide poly(meth)acrylate plastisols which permit an elevated binder con
Lohden Gerd
Trabing Mauren
Reddick Judy M.
Roehm GmbH & Co KG
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