Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-09-15
2001-06-12
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S053000, C524S457000, C524S458000, C524S459000, C524S460000, C524S560000, C524S561000, C524S832000, C524S833000, C428S407000
Reexamination Certificate
active
06245838
ABSTRACT:
The present invention relates to a novel method for aqueous bead-type suspension polymerization of (meth)acrylic monomers to prepare non-agglomerating, storage stable (meth)acrylic polymer beads which are extrudable at low temperatures. The invention also relates to the polymer beads which are obtainable by said method and to their use as adhesive and further to adhesive compositions comprising the polymer beads.
Known polymerization processes in heterogeneous aqueous dispersions comprise emulsion polymerization, dispersion polymerization, and bead-type suspension polymerization (see C. E. Schildknecht, Ed.,
Polymerization Processes
, John Wiley & Sons, 1977, p. 106 and 107).
The polymers obtained via emulsion polymerization comprise fine particles of polymer stabilized by an emulsifier or surfactant and dispersed uniformly in the aqueous phase. The polymer product obtained is often referred to as a “latex”, and the particle size is generally in the range of 0.05 to 0.2 &mgr;m. No beads are obtained during emulsion polymerization. The use of dextrin in emulsion polymerization methods in order to form adhesive compositions is known.
U.S. Pat. No. 5,004,768 discloses an adhesive composition comprising dextrin, a surfactant, and a polymer at least some of the repeating units of which are derived from an acrylate of at least one saturated aliphatic alcohol having from 4 to 12 carbon atoms. The manufacture of the composition may be carried out in any manner suitable for preparing acrylic polymers in the presence of a surfactant, emulsion polymerization being preferred.
EP-A-0 351 193 discloses a composition comprising dextrin, a surfactant, a polymer a major proportion of the repeating units of which are derivable from an acrylate of at least one saturated aliphatic alcohol having from two to twelve carbon atoms, and, optionally, a tackifier. If a tackifier is present, the dextrin level may be up to 7%, based on the total weight of dextrin, surfactant, and acrylate polymer. In the absence of tackifier, the maximum dextrin level is 3.5%. Preparation of the composition by emulsion polymerization is preferred.
Polymers obtained via dispersion polymerization are in the form of viscous, latex-like dispersions having a particle size in the range of 0.5 to 10 &mgr;m. The use of dextrin as a “protective colloid” in this type of polymerization is also known.
U.S. Pat. No. 5,004,767 teaches an aqueous acrylate polymer dispersion having a total solids content of 30 to 60% by weight, which has been made by polymerizing one or more acrylate monomers optionally together with other olefinically unsaturated monomer(s) in the presence of a dextrin, at least 70% of the dextrin having a molecular weight in the range of 1000 to 25000 and not more than 10% of the dextrin having a molecular weight above 25000.
U.S. Pat. No. 4,560,724 discloses a process for the preparation of aqueous polymer dispersions comprising polymerizing compounds with unsaturated ethylenic bonds at a temperature of 10 to 100° C. in the presence of an at least partially water-soluble free-radical initiator and at least one starch and/or starch derivative.
Bead-type suspension polymerization in general is a well known method of polymerization in which the polymer formed is obtained as spherical beads or pearls. Various different methods of avoiding agglomeration of the beads have been disclosed.
U.S. Pat. No. 4,833,179 and U.S. Pat. No. 4,952,650 teach a method for suspension polymerization of pressure-sensitive acrylate copolymer beads having a glass transition temperature of 0° C. or less. The copolymer beads are prepared by an aqueous suspension polymerization technique utilizing a modifier moiety selected from polystyryl macromers, reactive zinc salts, and hydrophobic silica. The modifier moiety is used in an amount sufficient to render the copolymer beads non-agglomerating at room temperature for handling and transportation purposes. According to U.S. Pat. No. 5,292,844, although the beads disclosed in U.S. Pat. No. 4,833,179 and U.S. Pat. No. 4,952,650 are easily transportable, they are not easily extrudable at low temperatures and must be extruded at 171° C. to 194° C., which is disadvantageous because polymers are more susceptible to decomposition at such high temperatures. In order to overcome the extrusion problem, U.S. Pat. No. 5,292,844 teaches the use of vinyl acetate as a comonomer in the suspension polymerization of pressure-sensitive adhesives (PSAs), in combination with a modifier moiety. The non-agglomerating, storage stable acrylate copolymer PSA beads thus obtained can be extruded below 170° C.
According to U.S. Pat. No. 5,292,844, the concept of inherent viscosity is important to the understanding of both extrudability and storage stability of suspension polymer beads. A low viscosity polymer is easier to coat due to its low internal resistance. However, a bead comprising a low viscosity polymer is more likely to clump during storage, due to its softness. This can cause problems during transportation and subsequent use since the beads will not easily pour when clumped together. Suspension beads comprising high viscosity polymers are less likely to be sticky and clump together. Thus, they have better storability. However, high viscosity polymers, due to their high internal resistance and lack of flow, are difficult to pass through an extrusion coater unless high temperatures are employed. Beads formed without vinyl acetate which are storage stable must have an inherent viscosity that is so high (e.g., 1.1) that they can only be extruded at high temperatures. Suspension beads which do not contain vinyl acetate can be prepared which are extrudable at low temperatures but which are not storage stable (IV 0.7 dl/g) (see U.S. Pat. No. 5,292,844, column 11, lines 26-35).
The adhesives formed from the beads comprising vinyl acetate as taught in U.S. Pat. No. 5,292,844 typically have inherent viscosities of about 0.6 to about 1.5 dl/g in ethyl acetate, preferably about 0.65 to about 0.8 dl/g in order to facilitate extrusion at low temperatures (below about 170° C.).
Using vinyl acetate as comonomer results in more easily extrudable beads but will also modify the adhesive properties, as is known in the art of solution and emulsion polymerization (see, e.g., Donatas Satas,
Handbook of Pressure Sensitive Adhesive Technology
, 2nd Ed., p. 402, Van Nostrand Reinhold, 1989). Furthermore, the adhesives are limited in inherent viscosity.
It is an object of the present invention to provide a method of suspension polymerization of (meth)acrylic monomers for making storage stable, low temperature extrudable suspension polymer beads that does not require the presence of a modifier moiety. It is a further object of the present invention to provide a method as defined above that does not require the presence of a specific monomer such as vinyl acetate. It is a further object of the present invention to provide storage stable, low temperature extrudable suspension polymer beads of a (meth)acrylic polymer having a broad range of inherent viscosities.
It has been discovered that these objects can surprisingly be achieved through the use of a dextrin or of a derivate thereof as a stabilizer in the suspension polymerization of (meth)acrylic monomers.
Briefly, in one aspect, this invention provides a method of suspension polymerization of (meth)acrylic monomers wherein a monomer premix comprising
(i) at least one (meth)acrylic acid ester of at least one nontertiary alkyl alcohol, the alcohol having from 1 to 18 carbon atoms; and
(ii) at least one free-radical initiator
is polymerized in an aqueous medium in the presence of at least one stabilizer selected from dextrins and dextrin derivatives and said monomer premix further comprising at least one polar monomer or polar macromer copolymerizable with the (meth)acrylic acid ester and/or said aqueous medium further comprising a water soluble or water dispersible polymeric costabiliser.
In addition, the monomer premix may further comprise other monomers and/or additives such as chain transf
Bogaert Yvan A.
D'Haese Francois C.
Moonen Eric B. T.
Smolders Robert R. L.
3M Innovative Properties Company
Egwim Kelechi
Wu David W.
LandOfFree
Method of suspension polymerization of (meth)acrylic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of suspension polymerization of (meth)acrylic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of suspension polymerization of (meth)acrylic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2449467