Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1995-11-06
2002-04-23
Page, Thurman K. (Department: 1615)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C162S164300, C528S482000
Reexamination Certificate
active
06376578
ABSTRACT:
The invention pertains to a process for the preparation of a water-soluble, nitrogen-containing, epihalohydrin-based resin comprising the step of subjecting the resin to an organic halogen reducing after-treatment.
Resins of the above type, mainly polyaminoamide-epihalohydrin resins, are well-known and find wide usage as wet-strength agents for paper. Epihalohydrin is known to impart wet-strength efficacy to polyaminoamides, but also causes the eventual resins to contain large amounts of organic halogen. A significant number of efforts to overcome this problem while retaining the product's wet-strength imparting effect has been reported.
Thus, a process of the type mentioned in the opening paragraph, which can be based on conventional previous reaction steps, e.g. comprising the reaction of polyaminoamide and epihalohydrin, is known from published European Patent Application No. 0 349 935. Said step consists of contacting the prepared resin with a base to convert it into a product having a pH >8, after which neutralization can take place. In this manner the organic chlorine content can be reduced to as little as 1% by weight. However, it is disclosed that, irrespective of the extent of the reduction of the organic chlorine content, the total chlorine content will remain unchanged. This is a serious limitation of the effect of the after-treatment, the remaining inorganic chlorine being a potential source of newly formed organic chlorine since it is the aqueous resin solution in which a new equilibrium will be established.
The invention has for one of its objects to obviate this drawback by providing a method for reducing the total chlorine content. Also, the invention meets the objective of further reducing the content of organic halogen without the resin's favourable properties being adversely affected.
In order to meet these and other objectives, the invention consists in that in a process of the above-described known type the after-treatment comprises contacting the resin with a basic ion-exchanger.
Unexpectedly, the after-treatment according to the present invention results in the resin subjected to it having a surprisingly low total halogen content of 1% by weight or lower, calculated on solid resin. It should be noted that in EP 369 935 the total halogen content remains at a level of 13,52% by weight, calculated on solid resin. So, clearly, the process according to the invention results in an unobvious improvement, further evidenced by the fact that the total halogen content in the novel resins prepared in accordance with the invention is even lower than the organic halogen content of the known resins.
Evidently, the total halogen content of the resins prepared in accordance with the present invention being considerably lower than in known resins, the resulting organic halogen content is lower also, viz. below 0,1% by weight, calculated on solid resin. In this respect it should be noted that the following art-recognized definitions of halogen contents apply to the description of subject invention:
Total halogen content obviously indicates all halogen present and this is the sum of all organic and inorganic halogen present.
Organic halogen content indicates all halogen linked to organic molecules, i.e. total halogen minus inorganic halide ions.
Adsorbable organic halogen, hereinafter referred to as AOX, is a term widely used in the art of wet-strength agents for paper. It indicates all organic halogen that can be determined by means of adsorption onto activated carbon using the method according to DIN 38409, part 14.
By-products content refers to 1,3-dihalo-2-propanol (DXP) and 1-halo-2,3-propane diol (MXP), which are the most important undesired by-products formed when a resin is prepared from a reaction mixture containing epihalohydrin. Since the most common epihalohydrin in the art is epichlorohydrin, by-products content frequently indicates DCP (dichloro propanol) and MCP (mono chloro propane diol).
A different approach towards low halogen contents is followed in EP 335 158, which discloses substitution of epihalohydrin by halogen-free crosslinkers. The crosslinker being allowed to contain a maximum of 15 mole % epihalohydrin, the resin is not an epihalohydrin-based resin in accordance with the present invention. Particularly low halogen values are disclosed if no epihalohydrin is present at all.
Several other processes for the preparation of water-soluble, nitrogen-containing, epihalohydrin-based resins with reduced halogen contents have been reported, but the halogen contents of the resins prepared by the disclosed processes by no means approximate the low level of the novel resins prepared in accordance with the present invention.
EP 282 862, which discloses a process of the type mentioned in the opening paragraph in which the after-treatment consists of reacting the epihalohydrin-based reaction products with a base followed by conversion with halogen-free acids, presents an organic halogen content of 2,73% by weight, calculated on solid resin. EP 332 967, which discloses a process similar to the EP 282 862 process but in which essentially a mixture of polyamines is applied, presents an organic halogen content of 0,74%, calculated on solid resin. Another disclosure, EP 374 938, only demonstrates a reduced by-product content when referring to organic halogen. The products prepared in accordance with the present invention not only display unexpectedly low total and organic halogen contents, but also unexpectedly low AOX and by-products contents.
It is noted that basic ion-exchangers are known to remove inorganic halide ions. It should be stressed that this does not at all suggest their aiding in the removal of organic halogen, let alone the present finding which provides a significant reduction of total halogen, organic halogen, AOX, and by-products contents and thus presents a solution to a serious problem in the art. The nature of the frequently complicated processes disclosed, which typically includes the alteration of several process parameters, does not at all suggest that a relatively simple after-treatment as applied in accordance with the present invention would have such an impact on the total halogen content, let alone the organic halogen, AOX, and by-products contents. The after-treatment, which in itself can be carried out in a simple manner, generally results in novel products having a total halogen content of below 1% by weight, an organic halogen content of below 0,1% by weight, an AOX content of below 0,002% by weight and by-product contents of below 0,025% by weight of DXP and 0,005% by weight of MXP, calculated on solid resin.
In order to perform the process of the present invention it is a requirement to use a basic, preferably strongly basic ion-exchanger. Ion-exchangers are known in the art and can generally be described as solid substances which upon contact with an electrolyte solution are capable of taking up ions (either positive or negative) and exchange these for an equivalent amount of different ions bearing the same sign. Though the invention process is not limited with respect to the specific type of ion-exchanger used, the most important class of materials is formed by ion-exchanger resins, more specifically synthetic resins. Ion-exchangers of this kind generally comprise a high polymer network of hydrocarbon chains that acts as a matrix for charge-carrying groups linked to it. Basic ion-exchangers generally carry cationic groups such as —NH
3
+
, ═NH
2
+
, ═N
+
, —S
+
. Ion-exchanger resins can be regarded as polyelectrolytes that, due to their crosslinked matrix structure, swell in water rather than dissolve. Since ion-exchangers belong to the common knowledge of the skilled artisan, a detailed explanation need not be given here. Reference is made to Ullmann,
Encyclopadie der Technischen Chemie
, which has a chapter on ion-exchangers (in the 1957 edition this is Volume 8, pages 787 ff.). Good examples of basic ion-exchangers that can be used in the process of the present invention include th
Gorzynski Marek
Pingel Andreas
Akzo Nobel NV
Joynes R.
Mancini Ralph J.
Parker Lainie E.
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