Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1987-11-19
1990-05-08
Schofer, Joseph L.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525 62, 526319, C08F 1606
Patent
active
049239228
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an ethyl alcohol process for polyvinyl acetate production
It is well-known that the actual production of polyvinylchloride in suspension is principally based on the use of secondary suspending agents which are obtained from the partial hydrolysis of polyvinylacetate polymerized in methanol solution (methyl alcohol), or by partial hydrolysis of methanolic solutions of polyvinylacetate obtained by means of bulk polymerization.
It is well-known that the plastic material which can be obtained utilizing said suspending agents is a PVC containing toxic residue due to the presence of methyl alcohol and methylacetate.
The scope of this invention is to find a solution to allow production of PVC for foodstuffs and for pharmaceutical use, which is less toxic than traditional PVC materials.
It is important to point out that the production process of the polyvinylchloride in aqueous suspension leads to problems of toxicity due to the presence of methyl alcohol.
Different methods to produce polyvinylacetate with polymerization in ethyl alcohol are well-known in the prior art to avoid said drawbacks.
These well known methods have, however, demostrated that they are not sufficiently suitable, whether for the difficulties encountered in reaction or for the respective product quality.
Experts are aware that when, as an auxiliary suspending agent in the polymerization of vinylchloride monomer, a polyvinylacetate with a molecular weight expressed in K values (relative viscosity) between 20 and 30, and hydrolysis values equal to 45% mole OH, is used, a finished PVC-S (polyvinylchloride suspension) with excellent morphological characteristics, high internal porosity, low level of "fish-eyes" (colloidability), minimal residual gas of VCM (vinylchloride monomer) occluded in its particles, is obtained (see patent IT-020246; US-PS-4,324,878; European Patent 0002861).
At present, partially hydrolysed polyvinylacetate is supplied in solutions with methyl alcohol and ethyl methyl acetate which are highly toxic, and which contain all the fractions of molecular weights which form during polymerization in solution or in block of the polyvinyl acetate.
After long industrial experience, it has been noted that, together with the well-known advantages previously described, the use of these particular auxiliary suspending agents shows, apart from the problems of toxicity, precise phenomena of the formation of unwanted foaming during polymerization, and this happens if a reflux condenser is used, said drawback appearing in more effective incidence during degassing of the non-reacted VCM, when the reaction is interrupted, as is commonly done, at the conversion of 90-92% of the material into PVC-S. There are, besides, noted grave problems of colour of the PVS-S with a tendency towards a very pale yellow.
The inventor has discovered that all these damaging phenomena can be attributed to the fraction of low molecular weight materials present in partially hydrolyzed polyvinyl acetate which are used in PVC-S polymerization, without previous fractioning of the molecular weight materials themselves.
In order to avoid said drawbacks a particular object of this invention is consequently to supply a fractioning process of molecular weight materials of solutions of polyvinyl acetates at different levels of concentration in ethyl alcohol.
Ethyl alcohol has been shown to be the most suitable for this type of practical and economic fractioning, presenting further advantages becasuse it does not generate dangerous situations of toxicity in the industrial PVC-S production process and in the respective products to be utilized in pharmaceutical and foodstuffs fields.
A further object of this invention is to inexpensively improve the vinylchloride monomer polymerization in a suspension process, utilizing polyvinylacetate fractioned and hydrolyzed in ethyl alcohol.
The invention is intended to provide a remedy to the above-mentioned disadvantages. It solves the problem providing a method of polymerization of vinyl acetate monomer (
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Reddick J. M.
Schofer Joseph L.
Tecnoassistance S.R.L.
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