Paper making and fiber liberation – Processes and products – Non-uniform – irregular or configured web or sheet
Patent
1998-06-29
2000-05-16
Chin, Peter
Paper making and fiber liberation
Processes and products
Non-uniform, irregular or configured web or sheet
162116, 162140, 162146, 1621572, 1621573, 162109, D21F 144, D21F 1100, D21H 1100
Patent
active
060632399
DESCRIPTION:
BRIEF SUMMARY
The invention relates to security paper and in particular to a method for the manufacture of security paper which are provided with high-quality watermarks.
It is well-known to those skilled in the art of papermaking that the tear strength of paper can be increased by the use of relatively long synthetic fibres. Cotton fibres used in the manufacture of security paper such as banknote paper are typically 1 mm long. Tear-enhancing synthetic fibres are however typically in the region of 3 to 5 mm long. It is further well-known in the papermaking art that the doublefold and tensile strength properties are generally also improved by the addition of synthetic fibres, but only if such fibres can be effectively bonded into the surrounding matrix of cotton fibres. Bonding of the appropriate type has been achieved in the past by three techniques: such as viscose or polyvinyl alcohol. This technique is of limited value because the surface area of synthetic fibres is generally rather low compared to that of natural fibres with the consequence that the hydrogen bonding forces with individual synthetic fibres are proportionately less than for a cellulosic fibre. This reduction in bonding forces is only partially compensated by using fibres of greater length than cellulosic or other natural fibres. such as polyvinyl alcohol or gelatin. In practice it is rather difficult to make this method work effectively without resorting to either solvent-based systems and/or hot calendaring, neither of which are desirable due to their high cost. In the case of solvent-based systems, environmental considerations also mitigate against this approach. reinforcing fibre. The binding fibre must be capable of either melting or dissolving during the drying process thereby serving to bond the synthetic and natural components of the fibre substrate.
Dutch Patent publication No.9301835 discloses a procedure for manufacturing paper for security applications and in addition to cellulose fibres, uses insoluble polyvinyl alcohol fibres, or a quantity of soluble and insoluble polyvinyl alcohol fibres. The use of the insoluble polyvinyl alcohol fibres improves the strength and stiffness of the paper compared with paper containing only cellulose fibres. In comparison with paper using other synthetic fibres such as polyamide or polyethylene fibres, the paper in accordance with this patent publication exhibits better stiffness and definition of a watermark. The soluble polyvinyl alcohol fibres which may be used in accordance with the disclosure are those which dissolve in water at a temperature 60.degree. C. or higher and during the dissolving the soluble fibres disappear. The molecules of polyvinyl alcohol act as a binding agent and may provide a surface effect such that no normal surface treatment is required in order to provide a good print performance. The specification as a whole makes it clear that reasonable watermark quality is achieved even though a synthetic fibre is used, namely the insoluble polyvinyl alcohol fibres. In contrast to the invention disclosed in Dutch patent publication No.9301835 this present invention is concerned with obtaining improved strength relative to security paper made from cellulosic fibres alone and also improved watermark quality relative to other types of insoluble PVOH fibre by the use of a certain amount of polyvinyl alcohol fibres which have the ability to dissolve at temperatures of 95.degree. C. to 100.degree. C.
The mould made panel watermark is one of the most critical and important security features used in bank notes to deter forgery. This is clearly illustrated by the almost universal use of such watermarks throughout the world's currencies. It is critical to the counterfeit deterrent value of a watermark that it be of the highest quality.
Judging the quality of a watermark is essentially a subjective issue. However those skilled in the art of producing mould made panel watermarks, referred to as shadow watermarks in Dutch patent application 9310835, are familiar with several distinct quality criteria. A
REFERENCES:
patent: 1616222 (1927-02-01), Harrigan
patent: 3114670 (1963-12-01), Iwasaki
patent: 4267016 (1981-05-01), Okazaki et al.
patent: 4534398 (1985-08-01), Crane
O. A. Battista, "Synthetic Fibers in Papermaking", Interscience Publishers, pp. 69-70, 1964.
Foulkes Jonathan Paul
Howland Paul
Chin Peter
Portals Limited
Walls Dionne A.
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