FR2552770A1 - Process for curing unsaturated polyester resins. - Google Patents

Abstract

This process is characterised in that the three-dimensional crosslinking is carried out in the presence of 0.005 to 0.5 % and preferably 0.01 to 0.1 %, on the weight of the polyester resin, of a compound of general formula: in which R<1>, R<2>, R<3> and R<4> denote H, -OH, -NO2, -SO3H or -SO3Na, provided that at least one of the other symbols R denotes something other than a hydrogen atom and that the progress of the three- dimensional crosslinking is monitored using the change in the colour of the mixture. Application to the process for controlled crosslinking of unsaturated polyester resins.

Description

Process for curing unsaturated polyester resins
The invention relates to a process for curing unsaturated polyester resins using accelerators containing metal ions and initiators of the organic peroxide type.

It is known that all unsaturated polyester resins undergo three-dimensional crosslinking or final curing under the action of initiators of the organic peroxide type, most often called catalysts. Most often, to speed up the process, compounds containing metal ions are used. The initiators and accelerators mixed with the resin do not cause a coloring effect, that is, neither their presence and the homogeneity of their distribution nor the curing process can be observed visually.

For the curing of the polyester resin, the prescribed amount of initiator and accelerator according to the existing technological conditions is absolutely necessary: if something is missing, a scrap is obtained. If the initiator and the accelerator are mixed with the resin in a non-uniform way, the finished article presents defective places: places insufficiently polymerized or polymerized too quickly, or there reigns great internal stresses. In the case of conventional colorless initiator-accelerator systems, it can only be determined whether a polymer object is sufficiently hardened by palpation or by complicated methods.

A process is known in which different colored indicators are used during the three-dimensional crosslinking of unsaturated polyester resins. From US Pat. No. 3,382,296, it is known that certain p-phenylenediamines, mixed with the unsaturated polyester resin, are known to be cause a discoloration of the peroxide-type initiator, initially colorless, and thus make its presence detectable.

A more modern and better process is that of US Pat. No. 4,232,136 which allows indicators (thiazines, indamines, oxazines, azines) to be incorporated into the organic peroxide type initiator. The purpose of the two processes is to make controllable, by a coloring effect, an important step of the process for converting polyester resins, namely the incorporation of the indicator.

However, no process is known which makes it possible to follow, by means of colored indicators, all the technological steps necessary in the three-dimensional crosslinking of polyester resins.

As already indicated, during the three-dimensional crosslinking of unsaturated polyesters, in addition to the initiator of the organic peroxide type, an accelerator is also introduced because thanks to this, on the one hand, the treatment temperature can be lowered, on the other hand, the amount of initiator required is less. Since the accelerator does not cause three-dimensional crosslinking in the resin but only promotes initiator decomposition and radical formation, it can be added to the resin at any stage of the processing. In many cases, the manufacturing plant is already mixing the necessary amount of accelerator with the resin. The accelerator, which is usually an organic metal compound, is in itself colorless, its presence in the resin is not detectable, so it often happens that the transformer does not know whether the resin contains or not. the accelerator. A lot of rejects, a lot of defects are already caused by the fact that one mixes only with organic peroxide a resin which does not contain an accelerator. This resin hardens only very slowly and incompletely, the object which is made of it is unusable. In the case of automatic resin processing, for example in the continuous manufacture of rollable plates or sheets, the resin, accelerator and initiator are metered by separate pumps. If the accelerator metering pump is damaged, the absence of the accelerator is not visible in the resin. In the continuous manufacture of plates, such a defect means about 100 m2 of scrap.

In accordance with the peculiarities of the processing of polyesters, it would be advantageous to obtain a coloring effect by mixing a suitable compound either with the polyester resin or with the accelerator itself; the coloring effect occurs when the accelerator comes into contact with the resin. The coloring should preferably disappear during the three-dimensional crosslinking so that the product exhibits the original natural color of the resin. No such process was known until now.

The aim of the invention was to develop a process for manufacturing polyester resins in which the presence of the accelerator is indicated by a coloring effect and in which this coloring effect disappears during the three-dimensional crosslinking, c that is, does not influence the color of the product.

dans lesquels R1, R2, R3 et R4 représentent H, -OH, -N02, - S03H ou -S03Na, sous cette réserve qu'au moins un des quatre symboles R représente autre chose qu'un atome d'hydrogène, colorent la résine de polyester lorsqu'on ajoute l'accélérateur contenant des ions métalliques, mais que cet effet de coloration disparaît à nouveau au cours de la réticulation tridimensionnelle. L'invention repose en outre sur cette idée que les composés de formule générale (1) donnent aussi, avec les accélérateurs contenant des ions métalliques, un effet de coloration. Par suite, on peut aussi ajouter les composés à l'accélérateur. Toutefois, on peut aussi les ajouter à la résine.Enfin, on a reconnu que les composés utilisables selon l'invention peuvent etre appliqués avec tous les peroxydes organiques, donc aussi avec des peroxydes colorés.The invention is based on the idea that the compounds of the general formula:

in which R1, R2, R3 and R4 represent H, -OH, -N02, -S03H or -S03Na, with the proviso that at least one of the four symbols R represents other than a hydrogen atom, color the resin of polyester when the accelerator containing metal ions is added, but this coloring effect disappears again during the three-dimensional crosslinking. The invention is further based on the idea that the compounds of general formula (1) also give, with the accelerators containing metal ions, a coloring effect. Therefore, the compounds can also be added to the accelerator. However, they can also be added to the resin. Finally, it has been recognized that the compounds which can be used according to the invention can be applied with all organic peroxides, and therefore also with colored peroxides.

This is why the subject of the invention is a process for the controlled crosslinking of unsaturated polyester resins by means of accelerators containing metal ions and of initiators of the organic peroxide type, optionally with the use of adjuvants. A characteristic of the process according to the invention is that the three-dimensional crosslinking is carried out in the presence of 0.005 to 0.5% and preferably from 0.01 to 0.1% of a compound of general formula (1) - according to above definition - relative to the weight of the polyester resin, and that the progress of the three-dimensional crosslinking is followed from the variation in color of the mixture.

In the method of processing the polyester resins according to the invention, it is possible, on the one hand, to control the homogeneity of distribution of the constituents incorporated mechanically or manually. On the other hand, both in the discontinuous process (manufacture of molded parts of polyester reinforced with glass fibers) and in the continuous manufacturing process (profiling, manufacture of flat and corrugated sheets), it can always be said with certainty whether the The resin may or may not contain the accelerator since the resin, when it contains a compound of general formula (1), becomes strongly colored in the presence of the accelerator.

The process according to the invention is explained more precisely below. It is suitable for all technologies in which the three-dimensional crosslinking of the polyester resin is accelerated by means of accelerators containing metal ions, which is practically the case for 90% of the volume to be transformed.

According to a preferred embodiment of the process according to the invention, the compound of general formula (I), for example a Na alizarinesulphonate, is incorporated into the usual accelerator solution containing cobalt naphthenate. The accelerator thus takes on a very intense dark red-lilac color. When the colored accelerator is incorporated into the resin, the latter takes on a transparent red color. During the three-dimensional crosslinking, this color gradually disappears. If the colored initiator according to the cited US patent is used for the three-dimensional crosslinking, the resin, initially red, becomes lilac after the addition of the blue initiator, but this color also disappears during the three-dimensional crosslinking.

According to another preferred embodiment of the process according to the invention, the compound of general formula (I), for example sodium alizarinesulphonate mentioned above, is added to the polyester resin. The change in color thus caused is in itself barely detectable. But if subsequently, at any stage of the transformation, the accelerator containing metal ions is added, for example a solution of cobalt naphthenate (generally 0.2 to 3 8 by mass), the strong red coloration appears. immediately in the resin and does not disappear until the end of the three-dimensional crosslinking. Also in this process, a colored initiator can be introduced.

From the point of view of the process according to the invention, it is irrelevant whether the organic peroxides belong to one type or another and whether they are colored or not.

By the invention, it was possible for the first time to indicate the presence of the accelerator. This means that - if a colored initiator is used - all technological steps of the three-dimensional crosslinking process can be visually controlled.

Preparing the fully homogeneous mixture of resin, accelerator and initiators is an essential step in any polyester processing technology. In the process according to the invention, the pronounced coloring effect of the compound of general formula (I) not only indicates the presence of the accelerator but also indicates whether the distribution has been carried out with the homogeneity absolutely necessary for the quality of the product; the intensity of color also indicates to a certain extent the concentration. This has advantages for processors which have not hitherto existed in this form. However, the process according to the invention is also advantageous for the manufacturer because he can manufacture and market resins which contain the one of the compounds which can be used according to the invention and which, during their transformation, indicates the addition of the accelerator. It is also possible - in accordance with the prior practice - to place on the market types of resin which already contain the accelerator. This can easily be recognized, even after years, by their red color.

Finally, the application of the invention is also of importance in the accelerator manufacturing industry because, by the addition of the compound of general formula (I), the accelerator strongly changes color, which is advantageous for the user for the reasons already explained.

To recap, the invention therefore has the following advantages a) if the compounds of general formula (I) are contained
in the polyester resin, they indicate by an effect
coloring the incorporation of the accelerator; b) if the compounds of general formula (I) are contained
in the accelerator they also indicate the incorpo
ration of the resin accelerator by an effect of
coloring; c) the coloring effect caused by the process according to in
vention disappears - regardless of the nature of the
morceur of the type of organic peroxides used - after
the end of the three-dimensional crosslinking; d) the compounds of general formula (I) can also, in
in the case of using colored initiators, be in
bodied with resin or accelerator, because by mixing
of the two colors it appears a third color fa
cile to distinguish and which disappears after the end of the
three-dimensional crosslinking; in this way, we
can control the two important constituents.

The invention is explained more precisely with respect to the following examples
Example 1
To make a polyester plate reinforced with glass fibers, a solution of 40 g of cobalt naphthenate in toluene (1% by mass of Co) is mixed with 0.4 g of sodium alizarinesulphonate. The dark red-lilac accelerator is mixed with 2 kg of n-phthalic acid polyester resin containing 600 g of styrene. The resin takes on a red color. 20 g of 50% solution by mass of methyl ethyl ketone peroxide are then incorporated into the resin as initiator and the mixture is homogenized. One third of the resin is then applied, with a brush, on a glass plate previously treated with a mold release agent and it is distributed uniformly over a surface of 1 m2. On this film of resin, a fleece of fibers of glass with a surface area of 1 m2 and a mass per unit area of 450 g / m2 and it is impregnated with half of the resin still present. On the impregnated fleece, we put a second fleece of the same quality and the same size and on this one, we apply with a brush the rest of the resin. After impregnation, the semi-finished product has an intense red-lilac color. After 30 minutes, the resin begins to gel and the color fades. After 2-3 hours at 20-250C, the resin has become completely colorless, that is, the hardening process is complete.

Example 2
To manufacture coiled tubes formed of polyester resin reinforced with glass fibers, is introduced into the impregnation trough, with the metering pump, a polyester solution of isophthalic acid containing 40% by mass of styrene. Using a pulling device, skeins of glass fibers are pulled through the polyester resin. The skeins of. Glass fibers are completely soaked with resin in the impregnation trough and then, pulled by a gauge, they arrive on the winding core where the glass fibers are wound into a tube. At 1 kg of resin used for the impregnation, is added by means of a metering pump the accelerator mixture comprising 5 g of solution of cobalt naphthenate in toluene (containing 0.05 g of Co ++) and 0.05 of quinizarin, another metering pump supplies, per kg of resin, 10 g of acetylacetone peroxide solution at 40% by mass as initiator.

The accelerator containing quinizarin colors the polyester resin bright red. As a result, the resin impregnated glass fiber skeins are also red. About 30 minutes after mixing the components, the color begins to fade and (assuming the temperature is 20-25oC), after 2-3 hours altogether, the cured resin has become completely colorless.

Example 3
To manufacture corrugated sheets reinforced with glass fibers, on the cellophane sheet continuously drawn by the sheet pulling machine, a metering pump is applied by means of a metering pump of a polyester resin of n-phthalic acid containing 30%. by mass of styrene and 10% by mass of methyl methacrylate, in an amount sufficient to soak the fleece with glass fibers also continuously transported by the machine. To 1 kg of resin, 12 g of 50% by mass solution of methyl ethyl ketone peroxide are added as initiator as well as a mixture of 10 g of a solution of cobalt naphthenate prepared with toluene (containing 0.1 g of Co ++) and 0.1 g of 3-nitroalizarin.

The accelerator colors the polyester resin a bright red-brown. Then, the resin and the fiberglass fleece pass through the impregnation section of the machine.

The impregnated fleece also has a bright red-brown color.

The impregnated fleece is then transported between sheets of cellophane and arrives in the curing section of the machine, which it traverses at 800C within 5 minutes. Then the resin is hardened as indicated by its complete discoloration.

Example 4
To 200 kg of unsaturated isophthalic acid polyester resin containing 40% by mass of styrene, 20 g of sodium alizarinesulphonate are added (first a thick paste is prepared with a small amount of resin, then it is distributed in the totality of the resin). Once everything has dissolved, the resin turns a light yellow color.

2 kg of cobalt naphthenate solution prepared with toluene and containing 1% by mass of cobalt are added to the resin. The mixture turns pink in a short time. Approximately 24 hours after the incorporation of the accelerator, the color variation is complete, the resin now exhibits a red-lilac color which indicates to the manufacturer and the user that the polyester resin contains accelerator.

Claims (2)

1. Controlled crosslinking process of unsaturated polyester resins by means of accelerators containing metal ions and initiators of the organic peroxide type, characterized in that the three-dimensional crosslinking is carried out in the presence of 0.005 to 0.5 %, and preferably 0.01 to 0.1%, by weight of the polyester resin, of a compound of general formula

R1 R2 R3 and R4 in which R1, R2, R3 and R4 represent H, -OH, -NO2 -S03H or -S03Na, with the proviso that at least one of the four symbols R represents other than a hydrogen atom , and that the progress of the three-dimensional crosslinking is followed from the change in color of the mixture. 2. Method according to claim 1, characterized in that as compound of general formula (I), alizarin, sodium alizarinesulphonate, 3-nitroalizarin or purpurine is used.