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
2000-08-28
2004-05-04
Egwim, Kelechi C. (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...
C524S416000, C525S326200, C525S330700, C525S331400, C525S331500, C525S332500, C525S333400, C525S334100, C525S340000
Reexamination Certificate
active
06730726
ABSTRACT:
The invention relates to a process for the preparation of an aqueous dispersion of halogenated vinyl polymers, to the aqueous dispersion obtained and to its use in the coating of substrates.
Aqueous dispersions of halogenated vinyl polymers, such as vinylidene chloride and/or vinyl chloride polymers, are characterized after polymerization by a pH which is generally less than approximately 2. Unfortunately, these aqueous dispersions exhibit both poor compatibility with waxes, which is revealed by poor mechanical stability, and poor thermal stability, from which result problems of sealability and problems of corrosion of the thermoforming equipment during the production of pharmaceutical blister packs.
It is known to add a certain amount of specific basic agents to these aqueous dispersions of halogenated vinyl polymers, which have a pH of less than approximately 2, so that the dispersions have a pH of greater than approximately 5.
Thus, Patent Application DE-A-2,246,499 discloses the addition of a certain amount of aqueous ammonia to aqueous dispersions of vinyl chloride and/or vinylidene chloride copolymers, so that the latter have a pH of greater than or equal to 5. It is nevertheless necessary to add, to the aqueous dispersions obtained, in addition to aqueous ammonia, an epoxide compound in order to prevent the dispersions from becoming coloured over time. This process exhibits the disadvantage of requiring the addition of an epoxide compound to the aqueous dispersions. This is because this further addition results in an increase in the costs and complicates the preparation of the aqueous dispersions of halogenated polymers.
Patent Application EP-A-0,469,405 discloses the addition, to aqueous dispersions of polymers obtained by polymerization of a mixture of monomers comprising 10 to 100% by weight of halogen-comprising monomers, of a basic agent in an amount such that the pH is regulated at a value of between 5 and 10. The process presented by Patent Application EP-A-0,469,405 makes it possible to avoid the use of an epoxide compound in addition to the basic agent. It has nevertheless been found that the aqueous dispersions disclosed in this patent application are not entirely satisfactory with regard to the stability of their colouring over time.
Patent Application EP-A-0,524,497 teaches the addition of an active substance, in addition to the basic agent, in order to overcome the disadvantages presented by the process of Patent Application EP-A-0,469,405. This process nevertheless exhibits the disadvantage of requiring the addition of an active substance to the aqueous dispersions. This further addition necessarily results in an increase in the costs and complicates the preparation of the aqueous dispersions of halogenated polymers.
In order to overcome the disadvantages presented by the processes of the prior art, a subject-matter of the present invention is a process which is particularly suited to the preparation of an aqueous dispersion of halogenated vinyl polymers which exhibits compatibility with waxes, a thermal stability and a colouring stability over time which are improved with respect to those of the aqueous dispersions of halogenated vinyl polymers of the prior art and which avoids the necessity of adding an epoxide compound, an active substance and/or another substance which would increase the costs and/or would complicate the preparation of the aqueous dispersions of halogenated polymers.
Another subject-matter of the invention is such an aqueous dispersion of halogenated vinyl polymers which does not exhibit the disadvantages of the aqueous dispersions of halogenated vinyl polymers of the prior art.
Another subject-matter of the invention is the use of the said aqueous dispersion of halogenated vinyl polymers for the coating of substrates.
To this end, the invention relates to a process for the preparation of an aqueous dispersion of halogenated vinyl polymers by polymerization, according to which, after polymerization, a basic agent is added in an amount such that the pH of the aqueous dispersion is less than approximately 5.
The invention also relates to an aqueous dispersion of halogenated vinyl polymers, according to which the aqueous dispersion comprises a basic agent in an amount such that the pH is less than approximately 5.
The present invention also relates to the use of the aqueous dispersion of halogenated vinyl polymers obtained for the coating of substrates made of polymers, of paper or of regenerated cellulose.
The term “basic agent” is understood to denote, for the purposes of the present invention, any material which, when it is added to an aqueous dispersion of halogenated vinyl polymers, renders the aqueous dispersion more basic than it was beforehand. More specifically, the term “basic agent” is understood to denote any material which, placed in an aqueous solution, provides it with a pH of greater than approximately 2.
In a preferred embodiment, the basic agent is chosen from alkali metal phosphates or the mixtures of these with one another or with another basic agent. The particularly preferred basic agent is chosen from phosphates not having more than one phosphorus atom or the mixtures of these with one another or with another basic agent. Mention may be made, among the phosphates not having more than one phosphorus atom, in a non-limiting way, of trisodium and tripotassium phosphates, disodium and dipotassium phosphates, and monosodium and monopotassium phosphates. A very particularly preferred basic agent is trisodium phosphate (Na
3
PO
4
).
In another preferred embodiment, the basic agent is chosen from sodium hydroxides and the mixtures of the latter with another basic agent. A very particularly preferred basic agent is sodium hydroxide.
In another preferred embodiment, the basic agent is chosen from alkaline earth metal hydroxides or the mixtures of these with one another or with another basic agent. Mention may be made, among alkaline earth metal hydroxides, in a non-limiting way, of calcium hydroxide.
In another preferred embodiment, the basic agent is chosen from alkali metal phosphites or the mixtures of these with one another or with another basic agent. Mention may be made, among alkali metal phosphites, in a non-limiting way, of trisodium and tripotassium phosphites, disodium and dipotassium phosphites, and monosodium and monopotassium phosphites.
In another preferred embodiment, the basic agent is chosen from alkali metal carbonates or the mixtures of these with one another or with another basic agent. Mention may be made, among alkali metal carbonates, in a non-limiting way, of sodium carbonate, potassium carbonate and potassium bicarbonate.
In another preferred embodiment, the basic agent is chosen from alkali metal citrates or the mixtures of these with one another or with another basic agent. Mention may be made, among alkali metal citrates, in a non-limiting way, of sodium citrate and potassium citrate.
In another preferred embodiment, the basic agent is chosen from alkali metal acetates or the mixtures of these with one another or with another basic agent. Mention may be made, among alkali metal acetates, in a non-limiting way, of sodium acetate and potassium acetate.
In another preferred embodiment, the basic agent is chosen from alkali metal formates or the mixtures of these with one another or with another basic agent. Mention may be made, among alkali metal formates, in a non-limiting way, of sodium formate and potassium formate.
In a preferred embodiment, the basic agent is chosen from alkali metal oxides or the mixtures of these with one another or with another basic agent.
The amount of basic agent to be added to the aqueous dispersion will be such that the pH of the aqueous dispersion is less than approximately 5.
The pH of the aqueous dispersion is generally adjusted to a value of less than approximately 5, preferably to a value of less than or equal to 4.5, in a particularly preferred way to a value of less than or equal to 4 and in a very particularly preferred way to a value of less than or equal to 3.
Bacque Xavier
Guenaire Bernard
Vanderveken Yves
Egwim Kelechi C.
Solvay ( Societe Anonyme)
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