Associations for stabilizing vinyl resins

The invention relates to a combination of derivatives of dihydropyridine and .beta.-aminocrotonic acid derivatives intended for the stabilization of vinyl resins. The combination of a dihydropyridine derivative and a .beta.-aminocrotonic derivative gives rise to synergism of the stabilizing powers of each of those products.

This invention concerns the stabilization of vinyl resins vis-a-vis agents 
which induce physical and physicochemical deterioration. 
The term "vinyl resin" is understood here to include both the homopolymers 
of vinyl chloride, vinyl acetate, vinylidene chloride type derivatives and 
the copolymers of these various monomers, in any relative proportions and 
in any and all applications. 
It is known that vinyl resins have a tendency to deteriorate under the 
influence of heat and that it is essential to add stabilizing agents to 
these masses of synthetic material with a view to delaying thermic 
deterioration, and hence coloration. 
It is also known that vinyl resins may deterioriate under the influence of 
sunlight, which may result in an alteration of the original coloration of 
the resin. This problem is particularly crucial in food packaging, as it 
is conceivable that it would be impossible to market foodstuffs in 
packages whose color shifts over time. 
Finally, it is likewise known that vinyl resins undergo deterioration under 
the impact of whatever oxidizing conditions may prevail at their location, 
notably the presence of oxygen in the atmosphere. 
This explains why much time has been spent in the search for agents which 
can effectively resist these various deterioriations, and preferably are 
effective against all of them at once. 
Among these agents, reference may be made first to the phenols, generally 
used as anti-oxidants in these resins and including, for example, 
2,6-di-t-butyl-4-methylphenol. 
More recently, derivatives of dihydropyridines have been proposed for the 
same use. They may be represented by general formula I below: 
##STR1## 
in which R represents a linear alkyl radical containing from 1 to 22 
carbon atoms, a linear alkenyl radical containing 3 to 18 carbon atoms, a 
linear alkynyl radical containing 3 to 11 carbon atoms, or an aralkyl 
radical, optionally substituted in the ortho or para position by a halogen 
atom or by a methyl or methoxy radical, or R represents a phenyl radical, 
optionally substituted in the para position by a methoxy radical or R 
represents a radical R.sub.1 --O--(CH.sub.2).sub.n -- in which n has the 
value 2, 3 or 4, and R.sub.1 represents a linear alkyl radical containing 
1 to 4 carbon atoms or a phenyl radical. 
Compounds with Formula I have been described in French Pat. Nos. 2,239,496, 
2,405,937, 2,405,974, 2,407,236 and 2,439,215, and may be prepared in 
accordance with the methods described in said patents. They are used as 
thermostabilizers for vinyl resins in proportions which, according to 
French Pat. No. 2,239,496, range from 0.2 to 1.5 percent by weight with 
respect to the resin. 
Also known for the same application are the .beta.-aminocrotonates with 
general formulas II and III. 
##STR2## 
in which: R.sub.2 represents a linear alkyl radical with 1 to 8 carbon 
atoms or a mixture of linear alkyl radicals containing 16 to 18 carbon 
atoms, and 
X represents a sulfur or oxygen atom or a single bond. 
R.sub.2 may represent, in particular, a methyl, ethyl or octyl radical. 
The .beta.-aminocrotonates II and III are well-known organic 
thermostabilizers for vinyl resins. 
These agents are hence described in the said application in the work by 
Rene LEFAUX entitled "Les matieres plastiques dans l'industrie 
alimentaire" (Plastic materials in the food industry, CFE, 1972, pp. 
230-232 and 527). They are usually added to masses to be stabilized in a 
proportion of 0.5 to 1.5 percent by weight. 
Among these aminocrotonates, especially used as thermostabilizers are: 
.beta.-aminocrotonate of butanediol; 
.beta.-aminocrotonate of thiodiglycol; 
.beta.-aminocrotonate of a mixture of C.sub.16 -C.sub.18 alcohols; 
methyl .beta.-aminocrotonate. 
It is also widely known that these various stabilizing agents, in 
particular as used in the food industry, have the drawback of giving rise 
to several disturbing phenomena such as migration toward the food, 
sublimation, and phosphorescense, which are all the more pronounced as the 
proportion of the agents is higher. This problem has been referred to in 
French Pat. No. 2,405,974. 
Likewise, in the case of the application of the stabilizers to vinyl 
copolymers, used for example in the manufacture of phonograph records, 
reduction of their proportions is desired insofar as that would improve 
sound quality. 
It is evident that reducing the proportion of stabilizer is also sought in 
all its applications, as it would make it possible to reduce the cost of 
stabilization. 
The invention is based on the discovery that the association or combination 
of a dihydropyridine of Type I with a .beta.-aminocrotonic derivative of 
Type II or III has a synergistic effect on the stabilizing powers of each 
of these products, thereby making it possible to use, while achieving an 
equivalent stabilizing power, much smaller quantities of the two products, 
or to obtain a much higher stabilizing power with the customary quantities 
of these products. 
This possibility of using lower proportions of stabilizer is of particular 
value in the case of resins intended for the manufacture of food 
packaging. Indeed, it is a desirable objective to reduce the proportions 
of stabilizers in polyvinyl chloride for food usage in order to reduce 
migration into the food, and hence the toxicity problem, to the greatest 
possible extent. 
Another advantage stemming from the associations according to the invention 
is applicable to the stabilization of the vinyl copolymers used in the 
manufacture of records, the sound reproduction quality of which is 
improved when small quantities of stabilizers are used, while at the same 
time the cost of stabilization is reduced. 
A further advantage which the associations according to this invention can 
provide in the formulations for vinyl copolymers is the observation that 
these associations do not modify the sticking-time when used in such 
copolymers. This property is important as it makes it possible to use the 
PVC compound on industrial machines for the extrusion-blowing phase. 
Moreover, it also sometimes makes it possible to reduce the levels of 
internal and external lubricants used in the corresponding formulas. 
As regards food applications of the stabilized vinyl resin compounds 
according to this invention, the French patents referred to above indicate 
that the Formula I compounds have slight acute toxicity, with the 
LD.sub.50 exceeding 2 g/kg orally in mice. Likewise, the 
.beta.-aminocrotonates are compounds which have no toxicity at all; they 
have the desired characteristics of stabilizers for packaging food and 
drink. By way of example, LD.sub.50 in rats for .beta.-aminocrotonate of 
butanediol is in excess of 4 g/kg, and that of the .beta.-aminocrotonate 
of thiodiglycol is in excess of 7.24 g/kg. 
It hence appears that the associations according to this invention will 
present no toxicity problem and that their use for food wrapping 
stabilization may be envisaged, as migration is all the lower when the 
quantities of stabilizers to be used are lower, one of the major 
advantages of this invention. 
It will be recalled, moreover, that the .beta.-aminocrotonates are 
insoluble in water and have been approved in France and throughout the 
E.E.C. for several years as stabilizers for packaging food and drink. 
Experimental study of the associations according to the invention has made 
it possible to show that: 
1. the components of these associations are mutually compatible and 
compatible with vinyl resins (homopolymers and copolymers); 
2. The associations thermostabilize polyvinyl chloride and its copolymers, 
making it possible to reduce the quantity of .beta.-aminocrotonic 
stabilizer. 
It is very advantageous to be able to reduce the quantity of 
.beta.-aminocrotonic stabilizer in formulas designed for food packaging by 
using the associations according to this invention, as this type of 
stabilizer often imparts an ammonia-like taste to the food when it is used 
in quantities needed for stabilization. 
3. The associations photostabilize polyvinyl chloride and its copolymers. 
4. When associated, Formula I compounds and .beta.-aminocrotonic compounds 
demonstrate synergism of their thermostabilizing properties. 
The objects of this invention are thus: 
First, a new stabilizing association for vinyl resins made up of vinyl 
polymers or copolymers for purposes of stabilizing them with respect to 
the destructive effects of heat, light, and chemical oxidizing agents, 
said association consisting of a Formula I dihydropyridine derivative and 
a Formula II or III .beta.-aminocrotonate. 
Second, a vinyl resin stabilized by the addition to said resin of a Formula 
I dihydropyridine derivative in the proportion of 0.01 to 0.5, preferably 
0.01 to 0.3, part by weight per 100 parts of resin and a Formula II or III 
.beta.-aminocrotonic derivative in the proportion of 0.1 to 1.0, and 
preferably 0.1 to 0.5, part by weight per 100 parts of resin. 
Third, a procedure for the stabilization of vinyl resins against the 
deteriorating effects of heat, light and chemical oxidizing agents, said 
procedure consisting in adding an association such as that described above 
to said resin. 
Four, the application of said stabilized vinyl resins to the manufacture of 
commercial and industrial articles, especially, but not exclusively, 
intended for the food industry. 
The synergy phenomenon resulting from the use of the stabilizing 
associations according to the invention may, as indicated above, present 
several different aspects. 
Accordingly, notably in the food industry, it may be advantageous to 
decrease the proportions of stabilizing agents so as to obtain the 
necessary and sufficient stabilizing effects which are already known, but 
to do so without the drawbacks which previously resulted from the higher 
proportions of said agents. 
Likewise, it may be desirable to decrease the proportion of only one of the 
agents used, taking advantage of the synergy effect resulting from the 
presence of a small proportion of the other agent. 
A different stabilizing effect may also be achieved, for example, one which 
sets in more rapidly or which is longer lasting and/or one which is more 
effective against conditions which cause deterioration, as for example, 
higher temperature or a more corrosive atmosphere. 
It is hence possible to modify the application of the invention depending 
on the objectives sought by varying not only the nature of each of the 
components of the association, but also its relative proportions, said 
factors themselves depending also on the nature of the resin mass treated. 
The following experimental studies show the broad range of possibilities. 
It goes without saying that known means are used to add the stabilizing 
compositions of this invention to the resin mass.