Patterned paper

Details Patterned paper Patterned paper

1997-11-21

2002-10-22

Fortuna, Jose (Department: 1731)

Paper making and fiber liberation

Processes and products

With printing and/or variegated coloring

C162S183000, C162S169000, C162S140000, C428S211100

Reexamination Certificate

active

06468393

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to the production, on the paper machine, of paper which is patterned in contrasting colours without the use of printing techniques. Papers of this general kind are commercially available from Arjo Wiggins Limited under the trademark COUNTRYSIDE and are typically used when it is desired to impart distinctive aesthetic appeal to products such as brochures, folders, menus, invitations, and stationery. Although the paper is patterned during its production on the paper machine, it can be overprinted if desired to give additional decorative effects.
The pattern is introduced into the paper by the incorporation in the papermaking furnish of inclusions which contrast in appearance with the papermaking fibres which make up the bulk of the finished paper. The contrast in appearance arises as a result of the papermaking fibres being of a contrasting colour, shade or hue from that of the inclusions. For example, the papermaking fibres can be coloured and the inclusions white or vice versa. Alternatively both the papermaking fibres and the inclusions can be coloured, provided that the contrast between their colours is adequate.
Suitable inclusions are long contrasting-colour fibres of the kind known in the paper industry as “Silurian fibres”, which impart a mineral or rock-like appearance to the paper; planchettes of contrasting appearance to the paper itself; or dark coloured particulate or fibrous material, which imparts a dark-speckled effect.
Just as dark-coloured inclusions give a dark-speckled effect, a white- or colour-speckled effect can be achieved by the addition to the papermaking furnish of small pieces of partially wet-disintegrated white or coloured paper (or, in principle, other material). The wet-disintegration can be carried out in a hydropulper or other apparatus of the kind used to disintegrate pulp bales at the start of the papermaking process (the starting paper must be a wet-strengthened or water-resistant coated paper, or else it will disintegrate to such an extent that it will not produce suitable speckles). Whilst a speckled paper produced in this way is fairly distinctive, the speckles lack sharpness, and hence the aesthetic appeal is not as great as desirable.
It is an object of the present invention to provide a method of making patterned paper with a white- or colour-speckled effect in which the speckles are of generally random size and shape and are sharp and well-defined, and which consequently has an attractive appearance.
SUMMARY OF THE INVENTION
We have now found that the key to achievement of this objective lies in the manner in which the speckle-forming material is produced. Specifically, we have found that suitable speckle-forming material can be formed by pre-agglomerating a mixture of papermaking fibre, particulate pigment and a binder, or by dry comminution of cellulose fibre aggregates. These starting aggregates can be in the form of paper, or of clumps of entangled fibres such as are obtained on breaking up bales of papermaking or other fibre pulp, and need not consist entirely of cellulose fibre. Dry comminution as just referred to is to be contrasted with wet disintegration as described above.
Accordingly, the present invention provides a process for the production of speckle- or similarly-patterned paper, said process comprising the steps of:
(1) preparing speckle-forming material by either
(A) agglomerating a mixture of papermaking fibre, particulate pigment and, preferably, a latex or other binder, by the addition to the mixture of one or more flocculants, coagulants or other agglomerating agents (“Process Variant A”); or
(B) dry comminution of cellulose fibre aggregates (“Process Variant B”)
(2) introducing the resulting speckle-forming material into a papermaking furnish of which the fibres are of a contrasting colour to that of the speckle-forming material and on which dye, if present, has been fully fixed; and
(3) draining the speckle-containing furnish to produce a patterned paper web.
The invention also extends to the patterned paper so produced and to the production of speckle-forming material for use in the process.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The term “paper” in this specification includes heavyweight papers of the kind often referred to as “boards”.
Of the two process variants set out above, we have so far found Process Variant A to be preferred.
The speckles in the final paper product are of varying dimensions, being of generally random size and shape (in contrast to conventional planchettes). They are generally elongate or fibrous in appearance (particularly when produced by Process Variant A), and appear sharp and well-defined, the whole giving an attractive decorative effect. The speckle-forming material can be white or coloured. If the latter, the colour can be the result of the use of coloured starting materials. Alternatively, the speckle-forming material can be dyed during or after its production. When dye is used, it should desirably be fully-fixed before the speckle-forming material is mixed with the papermaking furnish.
The presence of fibres in the speckles is thought to assist in anchoring the speckles in the paper, since the speckle fibres can bond chemically and mechanically with the other fibres in the normal way.
The speckle-forming material is introduced to the furnish at a point close to the headbox of the papermaking machine, in order that the agglomerated or comminuted material is not re-dispersed or otherwise adversely affected by conditions of heavy shear and is not removed from the furnish altogether (as might happen, for example, if the agglomerated or comminuted material were introduced prior to a stock cleaning operation). It is important that any dye present should be fully fixed before addition of the speckle-forming material, as otherwise the speckle-forming material might itself become dyed to a colour similar to that of the background paper.
In Process Variant A, the agglomerating agent is typically a material of the kind used in the paper industry for increasing retention of fibre fines and/or fillers on the papermaking wire, i.e. a so-called retention aid, or a flocculant of the kind used to promote sedimentation in waste water treatment in the paper or other industries. The agglomerating agent can be termed either a flocculant or a coagulant (usage of these expressions in the paper industry tends to be imprecise).
Preferably, a combination of oppositely-charged agglomerating agents is used to generate an enhanced agglomerating action and thereby agglomerate said mixture.
In a preferred embodiment of Process Variant A, the fibre and pigment to be agglomerated are mixed in aqueous suspension, together with a suitable latex, for example a styrene-acrylic or styrene-butadiene latex, and an anionic flocculant is added (typically this has a relatively high molecular weight and a relatively low charge density). A cationic flocculant (typically having a relatively high molecular weight and a relatively low charge density) or a cationic coagulant (typically having a relatively low molecular weight and relatively high charge density) is then added to enhance the stability of the initial agglomerate. This enhancement probably results from reaction or interaction between the cationic flocculant or coagulant on the one hand and the anionic flocculant and the latex (also anionic) on the other. However, we do not wish to be bound by any particular theory as to the processes involved. The papermaking fibre content of the aqueous suspension prior to the anionic flocculant addition is typically from 1.5% to 3% by weight.
Although the mixing sequence and order of addition just described is currently considered to be preferred, it will be appreciated that the key point is the formation of adequately stable fibre/pigment agglomerates, and that the precise sequence of mixing and addition of raw materials which achieves this is secondary. However, we have found that although satisfactory agglomerates can be formed when cationic flocculant or coagula

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