DD156874A3 - METHOD FOR IMPROVING THE CONTENT OF PLASTDISPERSIONS - Google Patents

Abstract

The invention relates to a process for improving the whitening of plastic dispersions which are used for the surface coating of various carrier substances. The aim is to prevent the rapid fluorescence quenching of the white-colored plastic dispersion and thus to increase the long-term effect of the whitening. The objective is achieved by combining the whitening with the incorporation of sulfites in amounts of 0.03 to 10 wt.%. This method offers particular advantages in the inventive whitening of chlorine-containing plastic dispersions.

Description

The invention relates to a method for improving the whitening of plastic dispersions, which can be used for surface coating or as binders for substrates. Pulp dispersions are used in a wide variety of industrial sectors as binders for substrates. As a rule, plastic films are formed which adhere to the surface of the substrate or penetrate the substrate. All of these films are more or less subject to aging. Under the influence of light and oxygen, the films change their appearance and mechanical properties. Especially when using chlorine-containing plastic dispersions, the process of yellowing of the film proceeds rapidly.

Characteristic of the known technical solution

It is known that to improve the light stability ^: Of plastic dispersions and the recoverable from them films many different UV stabilizers and / or antioxidants are introduced into the plastic dispersion. However, no sufficient improvement in the whiteness of the plastic dispersions and the films made from them has been achieved. This fact significantly curtailed the use of lower cost plastic dispersions in many applications, such as the packaging industry. It is also known to achieve the whitening of plastic dispersions by the incorporation of whiteners to increase the whiteness of plastic dispersions and the films which can be produced therefrom. Also well known is water-soluble stilbene derivatives of the general formula

R ₁ - ΈΕ - "^} - CH

-3 ·

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where R 1 is to be substituted in 3 and 5-substituted triazine rings and R 8-> 8CUH groups or salts thereof for the purpose of lightening solid polymers based on monoolefins, for example polypropylene fibers, polyethylene plates and polypropylene powder. The optical brighteners are able to generate incident UV rays. Transforming light into visible light and show even in this area only a small self-absorption. The amount of optical brightener used to brighten up the plastic dispersion and the films made therefrom can vary widely, but clear whitening effects are already achieved by very small amounts. The whitening of plastic dispersions, according to the known methods, however, a very significant deficiency adheres to, which consists in the fact that the white-tinted plastic dispersion already decreases in their white content after storage for a short time on the original value of the untreated raw dispersion "The whitened plastic dispersions must therefore very soon after of their whitening effect, if no loss of whiteness of the polymer films obtainable from the stored whitened plastic dispersions is to be tolerated. "This leads to considerable difficulties in transport, storage and processing of the whitened plastic dispersions."

Object of the invention

The object of the invention is to prevent the yellowing of whitened plastic dispersions and the films or coatings which can be produced therefrom and to improve the storability of whitened plastic dispersions in such a way that long-term use of these plastic dispersions with good yellowing stability of the films is possible.

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- The technical task

The invention has for its object to develop a method for improving the Weißtönimg of plastic dispersions with optical brighteners, in which the whitewashed plastic dispersions and the films produced therefrom, even after a long time have no yellowing.

, ; ^; · - The features of the invention

It has surprisingly been found that improved white-tinted plastic dispersions are obtained by adding water-soluble optical brighteners, preferably water-soluble stilbene derivatives, in dissolved form in combination with reducing sulfite compounds to the plastic dispersion in order to reduce fluorescence quenching. "Alkali hydrogen sulfite solutions or those suitable for reducing sulfite compounds are suitable aqueous solution sulfite forming alkali metal sulfites, Älkalipyrosulfite or the same effective Rongalit. The treatment according to the invention with the effective sulphite solution can be carried out before, during or even after the whitening of the plastic dispersion to be carried out in a known manner. It has proved particularly advantageous to combine the whitening and the stabilization of the whitening according to the invention by the said active substances , as whiteners and sulfite, are incorporated together in aqueous solution in the plastic dispersion, substance amounts of O ₅ OT Gev /,% to 10 Gevi.% _t preferably 0.03 Gevi,% to 1.5 Gevi.% Of the solid sulfite based on the total weight of the plastic dispersion,

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Λ Π rt "η j η ir. Ί» '' - '>' - · ->

- / -. "1 7 8 6 7

are "* reaching" for the intended stabilization effect

The incorporation of the solution mixture or the separate addition of the active substance solutions of the whitener and the sulfite is preferably carried out at normal temperature. But it can also be done at elevated temperature without loss of effect «

It proved expedient to avoid coagulations in the plastic dispersion to mix thoroughly the crude dispersion during incorporation and not to add the aqueous solutions of the active substances to be added with pesticide contents above 20% by weight. If appropriate, the active substance solutions or their mixtures may still be added Carrier and / or dispersing aids such as soaps, polyglycol ethers, fatty amines U ₆ a <. Auxiliaries are added. The mixture can be worked in the alkaline, neutral or weakly acidic range. The whitened plastic dispersions obtained by the process according to the invention can be processed in the usual manner. The physiological safety of the substances mentioned according to the invention also makes it possible to use the stabilized whitened plastic dispersion in the food packaging sector «

By the method according to the invention surprisingly stable, whitened plastic dispersions are obtained, which enable the production of yellowing-resistant films even after prolonged storage. The stability of the whitening in the plastic dispersion can be measured expediently on the white content of the plastic films to be obtained from the temporally stored plastic dispersions on thermal paper. The paper is coated on one side with the stabilized, white-tinted plastic dispersion and after drying the film in the air by means of a leukometer.

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The invention will be explained in more detail below play two Ausführungsbei.

Example 1 . '.

An aqueous Polyvinylidenchloriddispersion with 50 wt. ^ Peststoffanteile is prepared by slowly stirring of "20 ml of a 10.% 1gen aqueous solution of a stilbene derivative commonly 'used for the white tint white tinted, ο The incorporation is carried out at a temperature of 20 ⁰ C and a constant pH ~ 77ert of 8 After application of the tinted polyvinylidene chloride dispersion to thermal paper, after complete drying in air, a white content of 80.2 % (compared to annealed magnesium oxide) is measured by means of a leukometer followed over several weeks by the white content of the tinted crude dispersion during conventional storage of the dispersion ,, so can a rapid degradation of the whiteness follow such that one pulls from the whitened polyvinylidene chloride dispersion at intervals of one week in each case a film on the same paper and this is missing after drying:

Film after one week storage of the dispersion

two-week " ^tr "

three-week " ⁿ "

four weeks ".." "

five-week "" "

six weeks

79.5 78.2 77.0 76.4 75.1 74.0

of

/O

Example 2

When a sample of the same folyvinylidene chloride dispersion is mixed with 2.5% by weight of a 20% by weight fig.

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solution and the whitening is then carried out as explained in Example 1, so you can measure the following whiteness of the film with the same handling of the sample:

Initial sample *

Film after one-week storage of the dispersion "' ^T two-week ^{! L tr} """ three-week """

. ":" four-week ^tr """'" five-week. """""" Six - week "" V

82.0 rf /O 81, 8 % 81.5 % 81.3 , rf /O 81.2 % 81.1 % 81.0 at / ο

Claims (1)

He f induri gs Process for improving the whitening of plant dispersions with water-soluble optical brighteners, preferably water-soluble stilbene derivatives, characterized in that the plastic dispersions contain from 0.01 to 10% by weight, preferably from 0.03 to 1.5% by weight, of a sulphite compound to the total weight of the plastic dispersion, preferably sodium sulfite, sodium hydrogen sulfite, sodium pyrosulfite and / or Rongalit, in dissolved form, before, during or after the addition of optical brighteners.