Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2003-05-05
2004-06-29
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S114000, C524S141000, C524S143000, C524S296000, C524S297000, C524S306000, C524S581000, C524S582000, C524S583000, C525S240000, C525S329500, C525S329700, C525S330300
Reexamination Certificate
active
06756450
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to chlorine-free polyolefin-based plastisol or organosol and method for producing the same
2. Description of the Prior Art
The terms plastisols or organosols generally refer to dispersions of fine-particle plastic powders in softeners that harden or gelate when heated to higher temperatures. Organosols or plastisols currently in use are typically composed of fine-particle
polyvinyl chloride (PVC),
polyvinyl chloride-vinyl acetate copolymers (PVC/PVAc),
polymethyl methacrylate (PMMA), and
polyalkyl methacrylate (PAMA) such as polymethyl methacrylate copolymers,
that is dispersed in a liquid softener and forms a paste.
These pastes can be mixed with multifunctional monomers, oligomers and prepolymers capable of polymerization or copolymerization and the respective initiator systems to influence processing and application characteristics as desired.
The plastisols or organosols thus obtained can be used for various purposes, especially as a sealing and soundproofing compound, car undersealant, corrosion-protective coatings for metals, coil coatings, for impregnating and coating of textile and paper substrates, as a final finish of PVC floor coatings, cable insulating materials, etc.
PMMA- and PAMA-based plastisols or organosols however, despite their environmental compatibility, could not assert themselves against PVC-containing plastisols or organosols in all these applications for all sorts of reasons. For example, PMMA- or PAMA-based plastisols or organosols form a stable coating after gelating at approx. 150° C. When the coating has cooled down, however, softeners contained in the material start bleeding. This phenomenon is particularly pronounced for phthalic acid ester softeners that are most commonly used.
Improving the compatibility of the polymers or copolymers with phthalic ester softeners can produce a stable coating. This is achieved by increasing the portion of acrylic or methacrylic esters of higher alcohols in the copolymers using methyl methacrylate.
But here the problem occurs that spray coating is no longer an option because the viscosity of the plastisol produced in this way increases in a short time so that a solidified product is formed.
The use of polymer particles with greater diameters was proposed to improve storage life. But this measure has natural limits because polymer particles with a diameter of more than 10 microns cause problems when the coating is applied (spray nozzle clogging, sprinkling width limitation). In addition to their limited storage life, it was mainly poor cost efficiency and industrial health issues of the production and processing of PMMA- or PAMA-based plastisols or organosols that placed them at a disadvantage as compared to PVC-containing plastisols or organosols.
PVC/containing plastisols or organosols are currently the most commonly used materials for the applications listed above.
However, a number of severe problems occur when producing and using PVC-containing plastisols or organosols. Monomer residues in the PVC can endanger people during processing. It is a disadvantage when using PVC-containing plastisols or organosols that PVC is sensitive to both heat and light and that it tends to split off hydrogen chloride. Splitting off hydrogen chloride is a serious application problem because any hydrogen chloride that may be released at the prevailing gelating temperatures is corrosive and attacks metal substrates.
Heat stabilizers are used to remove this disadvantage but these are often toxic and a source of danger when applying the coat or using the product.
A particularly severe problem is waste disposal and the disposal of used coatings of PVC-containing plastisols or organosols. Hydrochloric acid gas (HCl) and polychlorinated dibenzofuranes and dioxins are formed during thermal disposal, which causes considerable environmental problems. Accordingly, waste and used coatings made of PVC-containing plastisols or organosols can only be disposed of in landfills for hazardous waste and at considerable cost. This also causes a considerably worse cost efficiency of PVC plastisols or organosols.
Efforts are being made to reduce the quantity of hydrochloric acid gas released when incinerating PVC. It is known that compounds such as oxides, carbonates, hydroxides, or organic acid salts of alkaline or alkaline earth metals that bind or neutralize any hydrochloric acid gas that may be released can be embedded into the plastisols or organosols. But then the problem arises that the plastisols or organosols show an increase in viscosity that renders them unsuitable for spray coating and that the specific weight of the coatings is also considerably increased.
Polyolefins, particularly polyethylene, are widely used as a chlorine-free coating material. Polyethylene coatings are characterized by excellent resistance to chemicals and moisture, high elasticity and corrosion resistance. They are applied as a molten film by rolling or extruding, or as powders by flame spraying, electrostatic spraying, or fluidized bed coating. Attempts were made to process these compounds, especially polyethylene, as a dispersion as this considerably extends the scope of application of polyethylene coatings. Dispersion coatings are not limited to all-over application, are excellently suited for surfaces that have an irregular shape and for special application processes (such as egoutteur blade coating).
Several proposals have been made to produce aqueous polyethylene dispersions. EP 0246729 describes the production of an aqueous dispersion from a hydrophobic polymer, i.e. from a polyolefin or copolymers derived from the same and a water soluble thermoplastic olefin copolymer that contains carboxylate groups (0.1 to 5 mg COO per g). Solid polyolefin dispersions are obtained in conjunction with anionic or non-ionic surface-active agents, organic solvents and water; these can be converted into flowable dispersions by adding more water. The publication mentions the suitability of these products as coating materials but does not give any specifications as to thicknesses of layer, drying conditions, and coating quality.
It is also known that aqueous PE dispersions can be produced by suspending fine-particle PE powder in water using surface-active agents and mixing in viscosity-lowering, thixotropy-imparting and coagulating additives [Kunststoffe 59 (1969) 9 pp. 545/549]. As fine-particle PE powders are very expensive, such dispersions have a poor cost efficiency [Kunststoffe 84 (1994) 11 pp. 1611/1613].
Aqueous dispersions of polyethylene with medium viscosity that can be used for coating paper are obtained using a suspending agent from a reaction product of fatty alcohols with ethylene oxide in combination with water-soluble, non-ionogenic polymers that have a thickening effect (DE-PS 3740155).
A disadvantage of such dispersions is their relatively low solids content (typically 10 to 40%) which makes them suitable for thin varnish-like coatings (50 to 500 microns) only. When used as a sealing compound and for thicker coatings, the high content of volatile ingredients may result in the formation of bubbles, tension cracks, etc. It is further known that the adhesive capacity of the polyethylene films mainly depends on the hot melt temperature. Coatings with excellent adhesion can only be obtained at temperatures in the range from 200° C. to 230° C., which means that the process is characterized by a high demand for energy.
The volume contraction as a consequence of crystallization further results in deformation and wear of PE coatings, especially when coating film-like substrates, textiles, or paper, which render the composite unusable.
As PE is non-polar, there can be no printing or applying varnish onto such coatings.
DE-OS 4331667 describes the production of a polyolefin-based coating material by functionalizing polyolefin powder while putting through a plasma gas such as argon, oxygen, nitrogen, vinyl acetate, acryl nitrile using high frequency or microwave stimulation. D
Szekely Peter
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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