Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Aqueous continuous liquid phase and discontinuous phase...
Reexamination Certificate
2000-04-07
2002-04-09
Lovering, Richard D. (Department: 1712)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Aqueous continuous liquid phase and discontinuous phase...
C106S208400, C106S214200, C106S219000, C516S066000, C516S067000, C516S925000
Reexamination Certificate
active
06369119
ABSTRACT:
The present invention relates to rosin emulsions for use in the sizing of paper, board and like materials and also relates to a method of sizing using the rosin emulsion.
It is well established practice to effect paper sizing by use of a rosin emulsion and a soluble aluminium salt such as aluminium sulphate (e.g. in the form of paper-makers alum [Al
2
(SO
4
)
3
.16-18H
2
O], aluminium chloride, poly-aluminium chloride or aluminium chlorohydrate. (Although the term “emulsion” is conventionally used to describe the rosin product it should more properly be called a dispersion since although made as an emulsion, the particles are effectively solid at ambient temperature). The rosin emulsion and aluminium salt are generally used as separate additions to the paper making process although it is also known to formulate so-called “one-shot” compositions which are formed by pre-mixing a rosin emulsion and an aluminium salt.
One method of producing a rosin emulsion is by the well established Bewoid process as disclosed in U.K. Patent No. 335 902. In this process, sizes with about 90% free rosin are produced using a protective colloid (casein) as the stabilizer and a small amount of rosin soap as the dispersant. In this process, approx. 1-2% of sodium hydroxide or potassium hydroxide on the weight of rosin is used to form a rosin soap dispersant by adding it to the molten rosin (usually at a temperature of about 130° C.) so as partially to saponify the rosin, followed by the casein dissolved in approx. 10% of its weight of sodium hydroxide (although potassium hydroxide or borax are occasionally used instead). Finally, water at ambient temperature is added to produce a dispersion at a much lower temperature, usually containing between 30 and 50% solids. During the cooling back process, emulsion inversion occurs in that the initially formed water-in-rosin emulsion inverts as more water is added to give a rosin-in-water emulsion. As the temperature of the emulsion falls, the rosin emulsion droplets solidify to give a dispersion of rosin in an aqueous medium (i.e, the so-called rosin emulsion).
The rosin emulsion so formed is anionic by virtue of the presence of the anionic dispersant (rosin soap) and the casein stabilizer. Such anionic dispersions are conventional and are extensively used for sizing paper, board and like materials.
There are also disclosures in which casein has been replaced by anionic surfactants. Thus, U.S. Pat. No. 4,199,369 describes the use of a specific dispersant that is of the type alkylethyleneoxide sulphites without the use of an additional stabiliser in an inversion process leading to the production of an anionic emulsion.
Cationic sizing emulsions are also known and are preferred for various applications in that they arc considered to provide improved sizing efficiency as compared to anionic dispersions. Generally, commercial cationic rosin emulsions are produced by homogenization of rosin at high temperature and high pressure (usually approx. 160° C. and 15 bar respectively) using a dispersant and a polymeric cationic stabilizer. Instead of lowering the viscosity by raising the temperature to greater than 160° C., an alternative is to dissolve the rosin in a solvent (e.g. dichloromethane—see EP 0 719 892 and EP 0 719 893) to give a solution of low viscosity which can then be homogenized at a temperature below 100° C. The stabilizer is usually a synthetic cationic polymer or it can be a cationic starch. In this respect, it should be noted that attempts to prepare cationic rosin emulsions by a “Bewoid-type” inversion process but using a cationic stabilizer instead of the anionic casein have generally been unsuccessful although U.S. Pat. No. 4,983,257 discloses an inversion process for producing a rosin emulsion by an inversion process in which pan of the casein is replaced by a cationic starch.
A development relating to cationic emulsions is disclosed in WO-A-9824972 (Roe Lee Paper Chemicals Co. Ltd.) in which a “one-shot” sizing composition is produced from an admixture of an anionic rosin emulsion, a soluble aluminium salt and a cationic starch derivative which has been produced by a process in which the starch structure was split prior to the cationizing step (e.g. as available under the trade mark RAIFIX). The requirement for the initial production of an anionic emulsion is clearly a disadvantage in that it increases the number of steps required to produce the cationic emulsion. There is also the disadvantage of the need to store the anionic emulsion before conversion to the cationic product. Because casein and a cationic stabilizer are used, the total raw material cost can be greater than producing a cationic rosin emulsion by direct homogenization of rosin, a dispersant and a cationic stabilizer.
It is therefore an object of the present invention to obviate or mitigate the abovementioned disadvantages.
According to a first aspect of the present invention there is provided a cationic rosin-in-water emulsion which has been prepared without intermediate isolation of an anionic rosin-in-water emulsion and in which the dispersed rosin phase is stabilised by a cationic polymer derived from a degraded starch, said polymer having a degree of substitution of at least 0.15 quatenary groups per glucose unit.
According to a second aspect of the present invention there is provided a method of producing a cationic rosin-in-water emulsion comprising effecting emulsification of rosin in water in the presence of a cationic polymer derived from a degraded starch, said polymer having a degree of substitution of at least 0.15 quatemary groups per glucose unit.
The invention has been based on our discovery that cationic polymers derived from degraded starch (as defined in the previous paragraph) may be used for directly producing cationic rosin size emulsions from rosin without the need for preliminary isolation of an anionic rosin emulsion, avoiding the disadvantages of the prior art as discussed above.
The rosin emulsion of the invention may be produced in various ways which are described more fully below. Briefly, however, the emulsions may be prepared by an inversion process in which an emulsion of water in molten rosin is “inverted” in the presence of the cationic polymer derived from degraded starch to produce a rosin-in-water emulsion. A further possibility is for the rosin emulsion to be produced by homogenization of a rosin and the cationic polymer.
The important feature of the invention is the use of a cationic polymer derived from a degraded starch and having a degree of substitution of at least 0.15 quaternary nitrogen groups per glucose unit. Such polymers may be produced, from starch, by splitting the starch structure and then effecting cationization producing a polymer which has a very high level of cationicity. Such starch derivatives may be produced with a range of relative molar masses and degree of cationization.
Preferably the cationic polymer used in the present invention has 0.15 to 1.30 quaternary groups per glucose unit. More preferably, this degree of substitution is from 0.20 to 1.10, even more preferably from 0.20 to 0.80 and most preferably from 0.50 to 0.80 quaternary groups per glucose unit.
The degree of substitution (i.e. at least 0.15 quaternary groups per glucose unit) in the cationic polymers employed in the present invention is considerably higher than that found in the cationic starches conventionally used for producing cationic emulsions for use in paper sizing. Thus, the cationic polymers have a higher charge density than the conventional starches. For example, conventional cationic starches are generally considered to have a charge density expressed in milli-equivalents per gramme (i.e. the average number of milli-equivalents of quaternised nitrogen per gramme of the polymer) in the range of 0.1-0.3. Typically the cationic polymers employed in the present invention have a charged density of 1.0 to 3.5 milli-equivalents per gramme. Whilst we do not wish to be bound by theory, we believe that the success of the present invention i
Phillipson Martin
Roberts John C.
Lovering Richard D.
Rasio Chemcials UK Ltd
Woodard Emhardt Naughton Moriarty & McNett
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