Paper making and fiber liberation – Processes and products – With coating after drying
Reexamination Certificate
2001-07-23
2004-10-12
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
With coating after drying
C162S168500, C162S168200, C162S168300, C162S164500, C524S714000, C524S742000, C524S750000, C524S796000
Reexamination Certificate
active
06802939
ABSTRACT:
The present invention relates to novel compositions comprising an aqueous dispersion of water insoluble polymer particles, wherein the polymer particles further comprise at their surface an oligomeric compound. The invention also encompasses a method of sizing paper and a method for improving the printability of paper.
It is known to produce dispersions of water insoluble polymer particles by emulsion polymerisation or by suspension polymerisation. In such processes it would be usual to disperse a water insoluble monomer or monomer blend into an aqueous continuous phase to form droplets of monomer. In aqueous emulsion polymerisation or aqueous suspension polymerisation it is standard practice to use surface active ingredients such as emulsifiers, surfactants or polymerisation stabilisers. Typically such compounds would have a high Hydrophilic Lipophilic Balance (HLB) so that the compound would partition preferentially in the aqueous continuous phase.
It is known to use oligomeric compounds as emulsifiers or polymerisation stabilisers in the emulsion polymerisation of water insoluble monomers such as styrene, acrylonitrile, ethyl acrylate and butyl acrylate and the like. Such compositions have been produced as rubber or plastic latexes from which the solid polymer could be obtained. Generally such compositions were produced in order to provide products that exhibited low viscosity and reduced foaming characteristics and yet were able to form suitable solid rubber or plastic materials.
It is standard practice in the field of paper and board manufacture to both internally and externally size paper. The sizing agent imparts hydrophobicity to the paper or paper board and improves the resistance to penetration by liquids, especially water. Internal sizing is normally achieved by incorporating a sizing agent into the paper making stock prior to draining on the machine wire. The sizing agent may be a non-reactive size such as rosin, but more usually is a reactive size such as alkenyl succinic anhydride (ASA). ASA would easily be dispersed throughout the cellulosic suspension and chemically reacts with the cellulose and is therefore generally regarded as a very efficient sizing agent. However, due to the reactivity of ASA size, and the ease with which it easily hydrolyses the aqueous sizing emulsions are normally made up in situ. If hydrolysis of the ASA anhydride groups take place to any significant degree before application, this could result in gummy deposits which would damage paper formation and in severe cases stop paper production. Therefore care has to be taken when applying reactive size.
It is known to use various hydrophobic materials such as waxes and water insoluble polymers and reactive sizes, such as ASA as paper surface sizing compositions. Generally such compositions are prepared as aqueous dispersions or emulsions and are blended with other materials such as starch prior to being applied to the paper sheet at the size press. It is important to impart the right degree of hydrophobicity and thus water resistance without impairing the brightness of the paper. It is often the case that a product that imparts optimum hydrophobicity significantly reduces brightness. Often it is necessary to strike a compromise between hydrophobicity and brightness and the product that is chosen does not impair brightness too significantly and yet provides adequate water resistance. Where products provide maximum water resistance to the paper, the resolution of images during printing would normally be improved. However, any significant reduction in paper brightness would mean that there would also be a poor contrast between the paper and image.
It would therefore be desirable to provide a paper sizing composition which imparts significantly improved hydrophobicity and printability characteristics and yet does not significantly reduce the brightness of the paper or board.
Thus a method of sizing paper or paper board is provided wherein a composition (A) is applied to at least one of,
i) the surface of a formed paper or paper board sheet,
ii) a paper or paper board making cellulosic suspension prior to draining, wherein the composition (A) comprisies an aqueous dispersion of polymeric particles of particle size up to 1 micron, wherein the polymeric particles comprise a water insoluble polymer matrix, comprising characterised in that an oligomer formed from a monomer blend comprised of ethylenically unsaturated monomer or ethylenically unsaturated monomer blend,
(a) (meth)acrylamide and
(b) an organic mercaptan or organic sulphone,
is located at the surface of the polymer particles.
It has been found that the application of composition (A) to a paper making stock prior to draining on the machine wire produces effective internally sized paper. The composition (A) may be applied as the neat polymer dispersion as a single addition to the paper making stock or may be combined with for instance the retention, drainage aids or strength aids. Often it is preferred to apply the composition as a formulation in pre cooked starch. Typically the formulation would comprise 90-99.5 weight % starch and 0.5-10 weight % polymer particles, preferably 92.5-97.5 weight % starch and 2.5-7.5 weight % polymer particles, more preferably 95-97.5 weight % starch and 2.5-5 weight % polymer particles, based on total dry weight of starch and polymer particles. It has surprisingly been found that the composition can be used to form internally sized paper with superior properties.
Composition (A) is particularly suited for surface sizing of paper and provides unique properties to the paper. Incorporated in the method of sizing paper or board composition (A) is applied to the surface of a formed sheet of paper or paper board. Often it is preferred to apply the composition as a formulation in pre cooked starch. Typically the formulation would comprise 90-99.5 weight % starch and 0.5-10 weight % polymer particles, preferably 92.5-97.5 weight % starch and 2.5-7.5 weight % polymer particles, more preferably 95-97.5 weight % starch and 2.5-5 weight % polymer particles, based on total dry weight of starch and polymer particles. Although the composition (A) would be desirably applied as a blend with starch it may also be applied as a neat aqueous dispersion of polymer particles. In addition to combining composition (A) with starch it may also be desirable to combine other ingredients normally applied during surface sizing, for instance Optical Brightening Agents (OBA). Normally the neat composition is applied at the size press in order to achieve maximum benefits of the sizing method disclosed herein.
Preferably in the method of sizing paper and paper board the composition comprises an aqueous dispersion of polymeric particles of particle size up to 1 micron, wherein the polymeric particles comprise a water insoluble polymer matrix and at the surface an oligomer formed from a monomer blend comprising,
(a) (meth)acrylamide,
(b) an organic mercaptan or organic sulphone,
(c) an ethylenically unsaturated monomer comprising either a tertiary amine group or a quaternary ammonium group and
(d) optionally other monomers.
The oligomer comprised in the composition used in the method of sizing paper may incorporate any organic mercaptan or organic sulphone but is preferably C
1-20
optionally substituted alkyl mercaptans, C
1-20
optionally substituted alkyl sulphones, optionally substituted C
5-7
cycloalkyl mercaptans, optionally substituted aromatic mercaptans, optionally substituted C
5-7
cycloalkyl sulphones or optionally substituted aromatic sulphones are preferred. More preferred are C
8-20
alkyl mercaptans, C
5-7
cycloalkyl mercaptans, aromatic mercaptans, C
8-20
alkyl sulphones, C
5-7
cycloalkyl sulphones or aromatic sulphones. Particularly preferred is either dodecyl mercaptan or dodecyl sulphone. Suitable substituted alkyl mercaptans include 3-mercaptopropanoic acid, 2-mercaptoethanol whilst 2-sulphonylethanol and 3sulphonylpropanoic acid are suitable substituted alkylsulphones. The amount of organic mercaptan or organic sulph
Donnelly Simon
Plonka John
Stockwell John Robert
Chin Peter
Ciba Specialty Chemicals Water Treatments Limited
Crichton David R.
Mansfield Kevin T.
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