Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-04-25
2002-07-02
Seldleck, James J. (Department: 1755)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S052000, C524S053000
Reexamination Certificate
active
06414055
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to processes for making aqueous paper size compositions.
BACKGROUND OF THE INVENTION
Current applications for fine paper require particular attention to sizing before conversion or end-use, such as high speed photocopies, envelopes, forms bond, including computer paper, and adding machine paper. Paper is conventionally sized by addition of sizing agents to the “wet end” of the paper process (internal addition), i.e., to the pulp before sheet formation, or by addition of sizing agents to the surface of already formed paper sheet that has been at least partially dried (surface sizing).
Alkyl ketene dimers (AKD's) and alkenylsuccinic anhydrides are widely used paper sizing agents. Although they are described in the literature as being useful for both internal and surface sizing, they are generally not used for surface sizing commercially. Cellulose reactive sizes, such as ketene dimers and alkenylsuccinic anhydrides display high sizing efficiency, but may cause problems in size reversion, toner adhesion and high speed paper converting. Variable coefficient of friction is at least one factor leading to the problems in high speed converting operations.
Recently alkenyl ketene dimers and ketene multimers have been described that are useful for internal and surface sizing and that overcome the deficiencies in high speed converting. These materials are disclosed in U.S. Pat. Nos. 5,846,663 and 5,685,815, both of which are incorporated herein by reference in their entireties. Precis®2000 and Precis®3000 sizing agents (available from Hercules Incorporated, Wilmington, Del.) are examples of such sizes. They are widely used commercially for internal sizing, but not for surface sizing because they do not contribute to good toner adhesion and other surface properties.
Cellulose non-reactive sizes have been used for some time as surface sizes. Examples of such materials are starch and other polymeric sizes such as copolymers of styrene with vinyl monomers such as maleic anhydride, acrylic acid and its alkyl esters, acrylamide, etc. In particular, styrene/maleic anhydride resins are widely used for surface sizing. Cellulose non-reactive sizes generally exhibit improved toner adhesion, little or no effect on coefficient of friction, no effect, or an improved effect on high speed converting, and no size reversion when compared to reactive sizes; however, they are less efficient at sizing than the reactive sizes.
As a result of all of the above, most papers at the present time are internally sized with alkenylsuccinic anhydride, alkyl ketene dimers, alkenyl ketene dimers or rosin sizes.
Co-pending patent application Ser. No. 08/940,514, filed Sep. 30, 1997, which is incorporated herein by reference in its entirety, discloses that treatment of paper with a combination of reactive and non-reactive sizes can produce paper with a unique balance of final properties that cannot be achieved by using either of the size types alone. The combination of cellulose reactive and cellulose non-reactive sizes provides paper that exhibits better water holdout than paper that is the same except that the sizing composition contains only cellulose non-reactive size. The combination size also provides paper that performs better in ink jet printing than does paper that is the same except that the size composition contains only cellulose reactive or only cellulose non-reactive size. Furthermore, the paper exhibits better toner adhesion, higher coefficient of friction and a lower coefficient of friction bandwidth than does paper that is the same except that the size composition contains only cellulose reactive size. The paper is also capable of performing effectively in tests that measure its convertibility on state-of-the-art converting equipment and its performance on high speed end-use machinery.
U.S. Pat. No. 5,498,648 discloses paper size mixtures which are prepared by mixing an aqueous suspension of a digested cationic starch with a finely divided, aqueous polymer dispersion which is a paper size and emulsifying C
14
-C
22
-alkyldiketene in this mixture at not less than 70° C.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a novel process for preparing an aqueous size composition comprising at least one cellulose reactive size that is not solid at 25° C., and at least one polymer.
In one embodiment the invention relates to a process for preparing an aqueous size composition comprising: a) providing a cellulose reactive size not solid at 25° C., and a starch stabilized aqueous polymer dispersion; and b) emulsifying the cellulose reactive size into the aqueous polymer dispersion.
In another embodiment the invention relates to a process for preparing an aqueous size composition comprising: a) providing a cellulose reactive size comprising ketene dimer or multimer not solid at 25° C. that is a mixture of compounds having the structure:
wherein n is an integer of 0 to about 20, R and R″, which may be the same or different, are saturated or unsaturated straight chain or branched alkyl groups having 6 to 24 carbon atoms; and R′ is a saturated or unsaturated straight chain or branched alkyl group having from about 2 to about 40 carbon atoms, and wherein at least 25% of the R and R″ groups is unsaturated; b) providing a starch stabilized aqueous dispersion of a polymer having a weight average molecular weight greater than about 10,000, comprising a water-insoluble copolymer made from monomers comprising styrene or substituted styrene, alkyl acrylate or methacrylate and ethylenically unsaturated carboxylic acid, wherein the styrene or substituted styrene is selected from the group consisting of styrene, &agr;-methylstyrene, vinyl toluene and mixtures thereof, wherein the alkyl group of the alkyl acrylate or methacrylate contains from 1 to about 12 carbon atoms and wherein the ethylenically unsaturated carboxylic acid is selected from the group consisting of acrylic acid, methacrylic acid, maleic acid or anhydride, fumaric acid, itaconic acid and mixtures thereof; and c) emulsifying the cellulose reactive size into the aqueous dispersion of polymer at a temperature of from about 20° C. to about 60° C.
DETAILED DESCRIPTION OF THE INVENTION
Cellulose reactive sizes are defined as those sizes believed to be capable of forming covalent chemical bonds by reaction with the hydroxyl groups of cellulose, and cellulose non-reactive sizes are defined as those that do not form these covalent bonds with cellulose.
Cellulose reactive sizes for use in the invention include ketene dimers and multimers, alkenylsuccinic anhydrides, organic epoxides, acyl halides, fatty acid anhydrides, and organic isocyanates, all of which that are not solid at 25° C.
A preferred group of cellulose reactive sizes for use in the invention includes ketene dimers and multimers that are not solid at 25° C. (not substantially crystalline, semi-crystalline or waxy solid; i.e., they flow on heating without heat of fusion). More preferably they are not solid at 20° C. Even more preferably they are liquid at 25° C., and most preferably liquid at 20° C. These liquid dimers and multimers are mixtures of compounds of formula I in which n is preferably 0 to 6, more preferably 0 to 3, and most preferably 0; R and R″, which can be the same or different, are saturated or unsaturated, straight chain or branched alkyl groups having 6 to 24 carbon atoms; R′ is a saturated or unsaturated, straight chain or branched alkyl group having 2 to 40 carbon atoms, preferably 4 to 32 carbon atoms; and wherein at least 25% of the R and R″ groups in the mixture of compounds is unsaturated.
Ketene dimers for use in the process of this invention are mixtures of compounds having the structure of formula 1 where n=0 and the R and R″ groups, which can be the same or different, are hydrocarbon radicals and where at least 25% of the R and R″ groups in the mixture of compounds is unsaturated.
The ketene dimers and multimers not solid at 25° C. may comprise a mixture o
Hercules Incorporated
Rajguru U. K.
Seldleck James J.
Sloan Martin F.
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