Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1998-12-22
2002-08-06
Fiorilla, Christopher A. (Department: 1731)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C162S164100, C162S164600, C528S489000
Reexamination Certificate
active
06429267
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the process of reducing the absorbable organic halogen (AOX) level in wet-strength resins while maintaining or improving their wet-strength effectiveness and more particularly it relates to treating such resins with base.
2. Description of the Prior Art
Commercial polyaminopolyamide-epichlorohydrin resins typically contain 1-10% (dry basis) of the epichlorohydrin (epi) by-products, 1,3-dichloropropanol (1,3-DCP), 2,3-dichloropropanol (2,3-DCP) and 3-chloropropanediol (3-CPD). Production of wet-strength resins with reduced levels of epi by-products has been the subject of much investigation. Environmental pressures to produce wet-strength resins with lower levels of absorbable organic halogen (AOX) species have been increasing. “AOX” refers to the absorbable organic halogen content of the wet strength resin which can be determined by means of adsorption unto carbon. Accordingly, AOX includes epichlorohydrin (epi) and epi by-products (1,3-dichloropropanol, 2,3-dichloropropanol and 3-chloropropanediol) as well as organic halogen bound to the polymer backbone.
Azetidinium-containing, polyaminopolyamide-epi resins have been treated with a basic ion exchange column to give a low AOX and low total chloride resin (WO/92/22601, assigned to Akzo NV). After this treatment, the resin was acidified. A disadvantage of this process is the ion exchange column has limited capacity and needs to be regenerated once the basicity is consumed. An additional disadvantage is the resin has reduced effectiveness when treated with the basic ion exchange column.
Other technologies remove epi by-products but do not remove polymer-bound AOX (i.e., polymeric aminochlorohydrin). Polyaminopolyamide-epi resins have been treated with microorganisms to reduce epi by-products to less than 10 ppm (EP 510987, assigned to Hercules Incorporated). This treatment, however, does not remove organic halogen bound to the polymer backbone. Another process to remove epi by-products uses a column of carbon adsorbent (WO 93/21384, assigned to E. I. duPont de Nemours). Such columns have limited capacity and to need to be regenerated once the adsorbent no longer efficiently removes the epi by-products.
SUMMARY OF THE INVENTION
According to the present invention there is provided a process for reducing the AOX content of a starting water-soluble wet-strength resin comprising azetidinium ions and tertiary aminohalohydrin, comprising treating said resin in aqueous solution with base to form treated resin, wherein at least about 20% of the tertiary aminohalohydrin present in the starting resin is converted into epoxide and the level of azetidinium ion is substantially unchanged, and the effectiveness of the treated resin in imparting wet strength is at least about as great as that of said starting wet-strength resin.
Further provided is the water-soluble wet-strength resin prepared by the process of the present invention.
Still further provided is the process for preparing paper using the wet-strength resin prepared by the present invention and the paper so made.
DETAILED DESCRIPTION OF INVENTION
It surprisingly has been discovered that the AOX content of azetidinium and aminochlorohydrin containing wet strength resins can be greatly reduced while maintaining or even improving their wet strength characteristics. The starting water-soluble wet-strength resins of the present invention can be polyaminopolyamide-epi resins or polyalkylene polyamine-epi resins and mixtures thereof.
The conversion of the tertiary aminochlorohydrin (ACH) of the wet-strength resins of the present invention to tertiary epoxide by base treatment can be illustrated by the following formula:
Polyaminopolyamide-epichlorohydrin resins comprise the water-soluble polymeric reaction product of epichlorohydrin and polyamide derived from polyalkylene polyamine and saturated aliphatic dibasic carboxylic acid containing from about 3 to about 10 carbon atoms. It has been found that resins of this type impart wet-strength to paper whether made under acidic, alkaline or neutral conditions. Moreover, such resins are substantive to cellulosic fibers so that they may be economically applied thereto while the fibers are in dilute aqueous suspensions of the consistency used in paper mills.
In the preparation of the cationic resins contemplated for use herein, the dibasic carboxylic acid is first reacted with the polyalkylene polyamine, under conditions such as to produce a water-soluble polyamide containing the recurring groups
—NH(C
n
H
2n
NH)
x
—CORCO—
where n and x are each 2 or more and R is the divalent hydrocarbon radical of the dibasic carboxylic acid. This water soluble polyamide is then reacted with epi to form the water-soluble cationic thermosetting resins.
The dicarboxylic acids contemplated for use in preparing the resins of the invention are the saturated aliphatic dibasic carboxylic acids containing from 3 to 10 carbon atoms such as succinic, glutaric, adipic, azelaic and the like. The saturated dibasic acids having from 4 to 8 carbon atoms in the molecule, such as adipic and glutaric acids are preferred. Blends of two or more of the saturated dibasic carboxylic acids may also be used.
A variety of polyalkylene polyamines including polyethylene polyamines, polypropylene polyamines, polybutylene polyamines, polypentylene polyamines, polyhexylene polyamines and so on and their mixtures may be employed of which the polyethylene polyamines represent an economically preferred class. More specifically, the polyalkylene polyamines contemplated for use may be represented as polyamines in which the nitrogen atoms are linked together by groups of the formula —C
n
H
2n
—where n is a small integer greater than unity and the number of such groups in the molecule ranges from two up to about eight. The nitrogen atoms may be attached to adjacent carbon atoms in the group —C
n
H
2n
—or to carbon atoms further apart, but not to the same carbon atom. This invention contemplates not only the use of such polyamines as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and dipropylenetriamine, which can be obtained in reasonably pure form, but also mixtures and various crude polyamine materials. For example, the mixture of polyethylene polyamines obtained by the reaction of ammonia and ethylene dichloride, refined only to the extent of removal of chlorides, water, excess ammonia, and ethylenediamine, is a satisfactory starting material. The term “polyalkylene polyamine” employed in the claims, therefore, refers to and includes any of the polyalkylene polyamines referred to above or to a mixture of such polyalkylene polyamines and derivatives thereof.
It is desirable, in some cases, to increase the spacing of secondary amino groups on the polyamide molecule in order to change the reactivity of the polyamide-epichlorohydrin complex. This can be accomplished by substituting a diamine such as ethylenediamine, propylenediamine, hexamethylenediamine and the like for a portion of the polyalkylene polyamine. For this purpose, up to about 80% of the polyalkylene polyamine may be replaced by molecularly equivalent amount of the diamine. Usually, a replacement of about 50% or less will serve the purpose.
In converting the polyamide, formed as above described, to a cationic thermosetting resin, it is reacted with epichlorohydrin at a temperature from about 25° C., to about 100° C. and preferably between about 35° C. to about 70° C. until the viscosity of a 20% solids solution at 25° C. has reached about C or higher on the Gardner Holdt scale. This reaction is preferably carried out in aqueous solution to moderate the reaction. Although not necessary, pH adjustment can be done to increase or decrease the rate of crosslinking.
When the desired viscosity is reached, sufficient water is then added to adjust the solids content of the resin solution to the desired amount, i.e., about 15% more or less, the product cooled to about 25° C. and then stabilized by adding sufficient acid to reduce the pH
Fiorilla Christopher A.
Hercules Incorporated
Morrell Dennis G.
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