Wet-strength agent with low DCP content

Details Wet-strength agent with low DCP content Wet-strength agent with low DCP content

2001-07-02

2003-06-10

Moore, Margaret G. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S800000, C524S845000, C525S430000, C528S341000, C528S408000, C528S422000

Reexamination Certificate

active

06576687

ABSTRACT:

The present invention relates to a novel process for the preparation of polycondensate solutions based on polyamidoamine/epichlorohydrin resins having a 1,3-dichloro-2-propanol content of <0.1%.
Reaction products of polyamidoamines and/or polyamines with epichlorohydrin have long been used for imparting wet strength to paper.
The products contain organic chlorine compounds, some of which are polymer-bound while the others consist of low molecular weight secondary components which are formed by undesired secondary reactions of the epichlorohydrin with water and chloride ions, preferably in the acidic range, e.g. 1,3-dichloro-2-propanol (DCP) and 1-chloro-2,3-propanediol (CPD).
These low molecular weight components, some of which are adsorbed only slightly by the cellulose fibers in the production of papers having wet strength, finally enter the wastewater of the paper mill, where they are detected as AOX (adsorbable organic halogen content) (DIN 38409). In recent years, the authorities have imposed taxes according to the AOX emissions and have also set limits for the AOX pollution of the wastewater which are to be complied with, so that a reduction of the AOX pollution was required for epichlorohydrin resins as a source of the AOX pollution.
A large number of proposed solutions for reducing the organic chlorine content of the polycondensates are already known.
Thus, for example, an aftertreatment of the polycondensate with a base is carried out in the European Patent Applications EP-A 282 862 and EP-A 332 967 and with an inorganic base and an organic mono- or polyamine or with ammonia in EP-A 512 423.
EP-A 0 349 935 describes polycondensates which contain polyamines and alkanolamines as amine component and which are likewise subjected to a base aftertreatment for reducing the organic chlorine content.
In these processes, it is true that the organic chlorine content is substantially reduced. However, they are all very complicated since a repeated change in the pH is required and in all cases the final addition of acid is required, which is intended to stabilize the polycondensate in the acidic pH range. The result is a relatively high electrolyte content of the commercial product, which adversely affects the shelf-life and can cause corrosion problems during use. If it is necessary to impart sufficiently high wet strength to paper, it is moreover necessary in this process to use relatively large amounts of ≧1.0 mole of epichlorohydrin per base nitrogen. Although it is possible also to employ smaller amounts of epichlorohydrin, a substantial loss of the wet strength activity must then be accepted.
Since products having a high DCP content may constitute a health risk, labeling of commercial products based on epichlorohydrin resins was demanded in Germany when the DCP content exceeds a value of 0.1%. For this reason, the manufacturers of wet strength agents based on epichlorohydrin had to make considerable additional effort to fall below these limits, to avoid the levies and to formulate the product to be toxicologically safe.
EP 469 891 describes, for example, a process for the reaction of polyamidoamine with epichlorohydrin at temperatures of not more than 60° C. to a conversion of 70-100%, addition of an acid and further reaction, a reduction of the organically bound chlorine by at least 10% being achieved. Here, the acid is added during the condensation itself and has the function of reducing the rate of the condensation in the final stage.
Furthermore, processes are known (cf. for example EP-A 488 767, EP-A 717 146, EP-A 374 938, U.S. Pat. No. 5 239 047 and U.S. Pat. No. 5 364 927) which aim at reducing the content of organic chlorine and DCP in the polycondensate by a special reaction procedure and a reduction in the molar amount of epichlorohydrin used per mole of base nitrogen.
EP-A 540 943 describes a process for the preparation of polycondensates by reacting polyamidoamine and/or polyamine with epichlorohydrin, an inert gas being passed through the reaction mixture before and optionally also during the partial crosslinking.
EP-A 320 121 describes a process for the stabilization of aqueous, at least 15% strength solutions of a polyamide/epichlorohydrin resin to gelling and viscosity reduction, an aqueous mixture of a weak and a strong acid being added to said resin solution in amounts of from 0.6 to 1.2 mmol of protons per g of solid resin. The molar ratio of the weak acid to the strong acid is from 0.5 to 10, preferably from 2.0 to 4.0 and particularly preferably from 3.0 to 3.1 (relative to protons). In this process the pH is generally brought to from 3 to 4.2, preferably to from 3.2 to 3.4. This process is preferably applied to resins which are prepared by an addition reaction of from 1.0 to 1.7 mol of epichlorohydrin per secondary amino-N of the polyamide at temperatures of from 45 to 70° C. In the case of smaller amounts of epichlorohydrin, a loss of activity is to be expected; in the case of a larger amount of epichlorohydrin, stability problems are envisaged. No information is given about the content of DCP.
As shown by the large number of citations mentioned as prior art, various experiments were carried out in the past to formulate optimum polyamidoamine/epichlorohydrin resins. The desired parameters of satisfactory ecological behavior through a low content of organic chlorine compounds (AOX, DCP, CPD), high wet strength and good shelf-life in combination with an economically advantageous preparation process without complicated additional steps could not be simultaneously achieved since some of them require contradictory measures in the preparation process.
In many cases, in particular an adequate shelf-life also remained a problem which usually manifested itself after a short storage time, depending on the preparation process and on the formulation as well as on the storage conditions, in an undesirable change in the physical data, for example in an increase in the pH, an increase or decrease in the viscosity, increasing discoloration and a loss of activity.
Thus, it was furthermore the object to provide an improved simple process for the preparation of polycondensate solutions having a very low content of organic chlorine compounds, in particular of 1,3-dichloro-2-propanol, high wet strength activity and a good shelf-life.
The process according to the invention achieves this object by permitting the preparation of polycondensate solutions based on polyamidoamine/epichlorohydrin resins having a very low content of organic chlorine compounds, in particular of 1,3-dichloro-2-propanol, in particular a content of 1,3-dichloro-2-propanol of <0.1%, high activity and a good shelf-life. The present process for the preparation of polycondensate solutions is characterized by
a) reaction of a1) at least one basic polyamidoamine and/or at least one polyamine in the form of a 10-50% strength solution with a2) epichlorohydrin at 10-25° C., the molar ratio of epichlorohydrin to base-N in al) being from 0.5 to 0.85;
b) subsequent further reaction at 10-25° C. to an epichlorohydrin conversion of not more than 90-99%;
c) subsequent reaction of the product from b) with further solution al) for completion of the epichlorohydrin conversion in a molar ratio of the base-N contained in solution a1) to epichlorohydrin of from 1:1 to 1.2:1, the pH being kept above 6;
d) heating to 30-70° C. until the viscosity of a 15% strength solution is 30-100 mPas at 25° C., and
e) reaction of the product from d) with formic acid and/or sulfuric acid, the pH being brought to from 2.0 to 3.0.
The process according to the invention is distinguished by technically simple conditions and requires no complicated additional steps, like many of the processes described above. Surprisingly, the polycondensates prepared by this process nevertheless have both a very low DCP content of <0.1% and a wet strength activity improved compared with known processes, as well as an improved shelf-life.
The polyamidoamine stated under a1) is prepared by reacting an aliphatic dicarboxylic acid with a polyalkylene

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