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
2000-04-18
2002-08-27
Mulcahy, Peter D. (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...
C523S223000
Reexamination Certificate
active
06441085
ABSTRACT:
This is a 371 application of PCT/NO98/00206 filed Jul. 8, 1998.
Paste PVC is a type of polyvinyl chloride which is processed in liquid form as plastisols or pastes. This segment accounts for approximately 10% of total PVC consumption, which is more than 5 million tonnes per annum in Western Europe. Plastisols are processed by coating (reverse roll-coating, knife coating, screen coating), gravure printing and screen printing, rotational casting and dipping. Common products are flooring, wallpaper, tarpaulins, roofing materials, rainwear, panelling and gloves. Both compact and foamed articles can be produced.
Various production processes for paste PVC are known. Both continuous and discontinuous methods can be used. All the methods are based on techniques known from emulsion polymerisation technology. Norwegian patent application no. 844819 (Chemische Werke Hüls AG) discusses the advantages and disadvantages of the various techniques and references to current patent specifications are given.
As Norwegian patent application no. 844819 states, the advantage of discontinuous polymerisation is that relatively low emulsifier quantities can be used. However, a disadvantage is that the plastisols which can be produced from these polymers have a higher viscosity and they are also usually dilatant pastes, which restricts their area of application.
An attempt is made to solve the problem with dilatant pastes in the Norwegian patent by dosing part of the emulsifier solution at a later stage during the polymerisation instead of using the entire quantity of emulsifier from the start. Another technique used commercially is so-called seed polymerisation for the production of bimodal latexes. This is discussed in detail by M. J. Bunten in the Encyclopedia of Polymer Science and Engineering; Vinyl Chloride Polymers, Polymerization, 2
nd
ed., Vol. 17, page 329-376, 1989.
To achieve low viscosities in PVC plastisols, it is an advantage to have large particles. This gives reduced particle surface area for the plasticiser to cover in addition to fewer particles and thus less effect from particle-particle interaction occurs. However, another effect, the effective volume fraction, is the most important factor which determines viscosity. By preparing a particle size distribution which gives maximum packing of the particles, the effective volume fraction of the particles can be minimized. Optimal packing of the particles can also be retained even if the shear rate is increased, making it possible to produce plastisols with Newtonian flow.
The traditional emulsion polymerisation process contains a major restriction regarding the preparation of large particles and the particle size is usually limited to approximately 1 micrometer. Using the so-called microsuspension technique, in which the monomer is finely distributed by mechanical homogenisation, it is possible to produce particles up to 3 to 5 micrometers. However, this process usually produces a majority of particles which are not spherical and have different shapes. Together with an unfavourable particle distribution, this leads to the known dilatant flow behaviour of plastisols from such products. An attempt is made to solve this problem by producing plastisols as a mixture of paste PVC powder and extender PVC. Extender PVC consists of particles produced by suspension polymerisation and often has particles between 35 and 60 micrometers. However, it also often contains larger particles, which limits the film thickness which the products can have. Extender PVC particles produced from suspension polymerisation will have a non-spherical form, which again produces an increase in particle surface area.
The present invention provides a method for producing paste PVC products and a PVC mixture with a very special particle size distribution. Plastisols produced from these products are distinguished by particularly low viscosity in connection with both low and high shear rates. The products also have a reduced quantity of emulsifier from the emulsion polymerisation, thus reducing the disadvantages caused by the emulsifier in the finished products. It is also unnecessary to use extender, which means that the products are also suitable for thinner films and the plastisols can be produced from only one PVC product. Particularly suitable areas of application are for roofing materials and wallpapers.
The procedure for producing paste PVC products suitable for the stated plastisol processes involves polymerisation of vinyl chloride or mixtures of vinyl chloride with up to 30 per cent weight copolymerisable monomers by discontinuous polymerisation in the presence of water-soluble or monomer-soluble polymerisation initiators and a predispersion produced either from a mixture of emulsifier and a fatty alcohol with 12-20 carbon atoms, emulsifier can be an alkali salt or ammonium salt of a branched or straight-chained fatty acid with 12 to 18 carbon atoms, or an alkyl sulphonic acid, or an alkyl aryl sulphonic acid or a sulphosuccinate ester, characterised in that this mixture is heated to over the melting point of the fatty alcohol before it enters the presence of the monomer, or a finely distributed emulsion of a totally water-insoluble compound produced by mechanical homogenisation of a mixture of water, emulsifier and water-insoluble compound, in such a way that a polymer latex is produced which consists of particles with a relatively narrow size distribution, with mean diameter around 1 micrometer, and that this latex is mixed, in a subsequent stage, with a polymer dispersion of spherical PVC particles with a very narrow size distribution, mostly between 10 and 50 micrometers, produced, for example, according to the method described in Norwegian patent application no. 961625, and that this mixture, which can have any quantity ratio between the two polymer types, is processed into a dry powder which can be used in PVC mixtures for plastisols for use according to conventional processing techniques for paste PVC. It is particularly advantageous for the polymer dispersion which is mixed with the latex to consist of spherical particles which have a very narrow size distribution, but this is not absolutely necessary.
Surprisingly enough, it turned out that the mixture of the two polymer dispersions was mechanically stable so that it could be agitated, transported by pumping and spray-dried without coagulation problems. Spray-drying by means of rotary disc or nozzle atomisation is a common method of drying paste PVC. It was also surprising that the resulting powder product (PVC-resin) could be dispersed in the plasticiser to form a plastisol without large aggregates of particles, which would have limited the applicability of the plastisol.
PVC latexes with a particle size in the region of 1 micrometer can also be produced by other known techniques such as emulsion polymerisation, seed polymerisation and microsuspension polymerisation. In the examples which follow later, it is possible to see the enormous improvement achieved when the particle distribution is changed from monomodal, mostly around 1 micrometer, to bidisperse, mostly 0.2 and 1 micrometer, to bidisperse with 1 micrometer and 20 micrometers. Examples of tridisperse particle distributions are also shown.
The procedure shown avoids many of the disadvantages of the existing paste PVC products. The paste viscosity is one of the most important properties and is essential for the use of the plastisol in the various processing processes. It is known that the viscosity drops as the particle size increases and that it is advantageous to have a mixture of large and small particles. Together, this produces the maximum packing of the particles in the plastisol and smallest total particle surface possible so that as much of the plasticiser as possible can contribute to producing flow. By using a considerable proportion of particles with a size between 10 and 30 micrometers, a much larger average diameter is produced than can be achieved by only using particles produced by emulsion polymerisation. A very powerful effect i
Pedersen Steinar
Sæthre Bård
Mulcahy Peter D.
Norsk Hydro ASA
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
PVC mixture and method for its production does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with PVC mixture and method for its production, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and PVC mixture and method for its production will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2895814