Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2000-10-27
2003-02-18
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S175000, C162S177000, C162S178000, C106S207100, C106S215100, C427S395000
Reexamination Certificate
active
06521088
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to degraded, particulate starches that are hydrophobically modified and especially effective in reducing the porosity of paper, improving the resistance to penetration by liquids and improving the surface strength when applied as a paper surface size. Blends of a degraded, particulate starch and a film former are also effective as a paper surface size to provide these properties.
The use of surface sizing in paper is known to provide several beneficial attributes to the paper and processing thereof including paper strength, retarding liquid penetration into the sheet and the quality and ease of printing on the paper. Starches are one of the most used raw materials in the paper industry and are often added in the wet end of the papermaking machine or as a surface size or coating.
Various paper grades require a low level of porosity to air in order to feed properly in copiers and sorting machines for example. Other paper grades require a highly continuous film on their surface that will resist penetration by non-aqueous fluids.
Surprisingly, it has been found that use as a paper surface size of a degraded, particulate starch which is hydrophobically modified, is especially effective in reducing paper porosity, resisting the penetration of liquids and improving surface strength as well as being cost effective.
SUMMARY OF THE INVENTION
Now, in accordance with this invention, it has been found that selected degraded, particulate starches that are hydrophobically modified are particularly useful as paper surface sizes to provide improved properties, particularly reduced porosity of paper, resistance to liquid penetration and increased surface strength.
More particularly, this invention relates to a method of providing paper with improved surface sizing properties comprising applying to the surface of a paper substrate an effective amount of a surface sizing composition which comprises a degraded, particulate, hydrophobic starch wherein the starch is modified with a hydrophobic hydrocarbon group of 5 to 23 carbon atoms at about 1 to 20% substitution level by weight of bound hydrophobe based on the weight of dry starch, the volume average size of the hydrated starch particles is at least about 20 microns and the volume fraction of the hydrated starch particles at 1% weight concentration in water is at least about 5%. Typically, the starch base is degraded to a water fluidity (WF) of from about 10 to 80 or the hydrophobically modified and/or particulate starch is degraded using an equivalent amount of degradation agent and substantially the same reaction conditions.
It has also been found that blends of a degraded, particulate starch and a film forming material are effective at improving surface sizing properties such as porosity reduction, resistance to liquid penetration and surface strength when used as a surface size on paper. More particularly, the level of degradation, the volume average size and the volume fraction of hydrated starch particles at 1% solids that are useful for the degraded, particulate starch are the same as that described above for the hydrophobically modified, degraded, particulate starch. A film former (film forming material) is intended to mean a polymer which helps to provide improved surface sizing properties such as porosity reduction, resistance to liquid penetration and surface strength, when added to the degraded particulate starch. The film former may be a hydrophobically modified starch, wherein the starch is modified with a hydrophobic hydrocarbon group of 5 to 23 carbon atoms at about 1 to 20% substitution level by weight of bound hydrophobe based on the weight of dry starch. Other illustrative film formers that may be used are modified starch, alginate, pectin, carboxymethylcellulose, polyvinyl alcohol, xanthan gum, rhamsan gum and welan gum. Typical modified starches include hydroxyalkylated starch with the alkyl group possessing 1 to 4 carbon atoms, oxidized, enzyme converted, thermally converted, acetylated and cationized starches. The degraded, particulate starch:film former blends may be used in amounts of from about 1:99 to 99:1 parts by weight of starch per part by weight of film former.
DETAILED DESCRIPTION OF THE INVENTION
The selected starches provided by this invention and useful in surface sizing paper are degraded, hydrophobically modified particulate starches. The terms “surface sizing”, “surface application” and “paper coating” as used herein refer to the use or application of the starch composition of this invention on paper to provide properties including reduced porosity, resistance to penetration by liquids (e.g. water and aqueous solutions, inks, oils, solvents, greases, and silicone fluids) and improved surface strength.
All starches and flours (hereinafter “starch”) may be suitable for use as a base material herein and may be derived from any native source. A native starch as used herein, is one as it is found in nature. Also suitable are starches derived from a plant obtained by breeding techniques including crossbreeding, translocation, inversion, transformation or any other method of gene or chromosome engineering to include variations thereof. In addition, starch derived from a plant grown from artificial mutations and variations of the above generic composition which may be produced by known standard methods of mutation breeding are also suitable herein.
Typical sources for the starch are cereals, tubers, roots, legumes and fruits. The native source can be corn, pea, potato, sweet potato, banana, barley, wheat, rice, sago, amaranth, tapioca, arrowroot, canna, sorghum, and waxy or high amylose varieties thereof. As used herein, the term “waxy” is intended to include a starch containing at least about 95% by weight amylopectin and the term “high amylose” is intended to include a starch containing at least about 40% by weight amylose. Also included are derivatized or modified starches such as cationic and anionic starches.
The starches of this invention generally are converted or degraded starches, particularly those in which the base or native, unmodified and non-particulate starch has a water fluidity (WF) of from about 10 to 80, particularly about 30 to 70, or the modified and/or particulate starch is degraded using an equivalent amount of degradation agent and substantially the same reaction conditions. The measurement for water fluidity as described herein is made using a Thomas Rotational Shear type Viscometer in accordance with standard procedures such as disclosed in Zwiercan, et al., U.S. Pat. No. 4,499,116 issued Feb. 12, 1985, which patent is incorporated by reference herein. The starch may be converted or degraded to the selected water fluidity using known procedures such as oxidative hydrolysis, acid hydrolysis or enzyme hydrolysis. A particularly useful method of converting starch involves the use of hydrogen peroxide with a manganese catalyst such as potassium permanganate as disclosed in U.S. Pat. No. 4,838,944 issued Jun. 13, 1989 to L. Kruger. Another useful starch conversion process involves the use of a metal-based coordination complex catalyst, such as a manganese complex, as disclosed in U.S. Pat. No. 5,833,755 issued Nov. 10, 1998 to P. Schlom, et al. The starch conversion processes as disclosed in both the '944 and '755 patents are incorporated herein by reference.
Degradation of the starch can be performed before or after treatment that will create a particulate starch upon hydration (i.e. by cooking) and/or hydrophobic substitution. The degree of degradation or hydrolytic treatment of the modified and/or particulate starch is the same as used to achieve a 10 to 80 WF for a native, unmodified and non-particulate starch base.
The starches of this invention are formed into particulate starches. By particulate starch it is meant that the starch, after hydration, retains some granular structure such that there remains discrete particles. The starches of this invention have a volume average size of hydrated particles of at least about 20 micron
Richardson Paul H.
Trksak Ralph M.
Tsai John J.
Weisser Eric M.
Chin Peter
Dec, Esq. Ellen T.
National Starch and Chemical Investment Holding Corporation
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