Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-08-24
2002-10-29
Jagannathan, Vasu (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C106S403000
Reexamination Certificate
active
06472455
ABSTRACT:
This invention relates to a printing ink composition comprising first and second multi-layered thin-film interference pigments showing a colour shift which depends on the viewing angle.
Pigments consisting of thin multi-layered film interference structures which show a viewing-angle dependent shift of colour have been described in various publications as, for example, L. Schmid, M. Mronga, V. Radtke, O. Seeger “Luster pigments with optically variable properties”, European Coatings Journal, 7-8/1997, and patents, e.g. U.S. Pat. No. 4,434,010, U.S. Pat. No. 5,059,245, U.S. Pat. No. 5,084,351, U.S. Pat. No. 5,281,480.
The general principle of these types of interference pigments is basically a sequence of alternate thin layers parallel to each other consisting of partially and/or totally reflecting materials and low refractive index material. The hue, the colour-shift and chroma of these multi-layered interference pigments, which will be abbreviated hereinafter as OVP (Optically Variable Pigments), depend on the material of the layers, the sequence of the layers, the number of layers and the layer thicknesses but also on the production process. OVP may be produced by two different categories of processes:
1. Physical vapour deposition (PVD) technologies:
Summarized, the method consists in forming a multi-layered, thin film coating by advanced PVD techniques such as roll coaters, sputtering techniques, etc. on a flexible web of a material, which is preferably soluble in a predetermined solvent. The web is typically a polymer material, such as polyvinyl alcohol or polyethyleneterephthalate. After separating the web from the multi-layered, thin film coating, flakes are produced therefrom by shredding or grinding them down to the desired flake size. The separation can be accomplished by stripping the multi-layered coating from the web. For this, preferably a stripping layer is deposited onto the web prior to the other layers. Heat and/or solvent may be used to facilitate the stripping process. Alternatively, instead of stripping, the web may be dissolved in a suitable solvent to accomplish the separation. The coated web may optionally be cut or shredded prior to the dissolution step. As the multi-layered thin film coating is separated from the web, it typically breaks into pieces of irregular shapes and sizes. These pieces usually require further processing to achieve the desired flake size which is suitable for use as pigment flakes in coating compositions and particularly ink compositions. The flakes can be ground down to a size ranging from 2-5 microns without destroying their colour characteristics. Preferably the average particle size is between 5 and 40 microns, but not greater than 120 microns. The flakes are produced to have an aspect ratio of at least 2:1. The aspect ratio is ascertained by taking the ratio of the largest dimension of a surface of the flake parallel to the planes of the layers to the thickness dimension to the flake (perpendicular to the plane). The flakes can be achieved by all major categories of processing known in the art such as milling, grinding or ultrasonic agitation, optionally in the presence of solvents and/or further auxiliary materials.
OVP produced by this production process are characterized in that the pigment flakes consist of a stack of plane layers lying parallel to each other with outer pigment flake surfaces parallel to each plane layer. Due to the shredding and grinding process, the surfaces of the pigment flake perpendicular to the plane of the layers are irregularly formed with the inner layers not covered by the outer layers. OVP having these characteristics will be referred to hereinafter as OVP A.
2. By wet chemical type reactions or Chemical Vapour Deposition (CVD)—U.S. Pat. No. 4,328,042:
The principle of the chemical synthesis of OVP is to coat commercially available plate-like reflecting pigments with a predetermined number of weakly refracting and semi-opaque thin films. A typical process of this kind may be described more exactly by means of a specific production process run:
In a first step the plate-like pigments are suspended in an alcohol with dispersion aids. Tetraethoxysilane and an aqueous solution of ammonia is continuously added to this solution. Under these conditions, tetraethoxysilane is hydrolysed and the resulting hydrolysis product, the hypothetical silicic acid Si(OH)
4
, condenses and forms SiO
2
as a smooth film on the surfaces of the plate-like pigments. The SiO
2
-coating can also be carried out in a fluidized-bed reactor. In this case, vapours of tetraethoxysilane must react with water vapour. However, at the preferred temperatures of the gas-phase deposition (100-300° C.), tetraethoxysilane does not react in satisfactory yields. Special precursors, which are more reactive have to be used. Suitable precursors are of Si(OR)
2
(OOCR)
2
-type. They vaporize at 150° C. and decompose easily with water at 200° C.
Subsequently in a chemical vapour deposition process, the silicon oxide-coated pigments are coated with metal oxides or metal films. The coating takes place in a fluidized-bed reactor. The SiO
2
coated pigments are fluidized with inert gases, which are charged with gaseous metal carbonyls. At 200° C. the carbonyls decompose. If iron carbonyl is used, it can be oxidized to Fe
2
O
3
, which forms smooth thin films on the pigment surfaces. As an alternative method, the iron oxide coating can be carried out in a sol-gel technique known from conventional micas.
When the carbonyls of chromium, molybdenum or tungsten are decomposed under inert conditions, metallic films can be obtain. Since Mo films are not stable against water attack, they are therefore converted to molybdenum sulphide.
OVP produced by this process possess just one coherent surface. The outer coatings surround and encompass inner coatings and/or the reflective core flake. Because of this, the outer layers are not planes, but are substantially parallel to each other. The outer pigment surface is not continuously parallel to the first and second surface of the plate-like reflecting pigment. OVP showing these shape characteristics will be referred to hereinafter as OVP B.
Irrespective of whether type OVP A or OVP B, OVP includes a totally reflecting layer of a material which in the majority of cases is a metal such as aluminum, gold, copper or silver or a metal-oxide or even non-metallic materials. The first reflecting layer has a suitable thickness in the range of
50-150 nm but can be up to 300 nm. Deposited onto the totally reflecting material is a material with a low-refractive index; such material is often called dielectric material. This layer of a dielectric material must be transparent, with a refraction index not higher than 1.65. SiO
2
or MgF
2
are the preferred dielectric materials. The subsequent semi-opaque layer or layers are of a metal, metal oxides or sulphids as, for example, aluminum, chromium, MoS
2
or Fe
2
O
3
. Opaqueness of metal is a function of the layer thickness. Aluminum, for example, becomes opaque at approximately 35 to 40 nanometers. Typically the thickness of the semi-opaque layer is between 5 to 10 nanometers. The thickness of the dielectric layer depends on the colour desired. It is thicker if longer wave-lengths are required. OVPA can be of a symmetrical or asymmetrical multi-layered structure with regard to the totally reflecting layer.
A quantification of calorimetric properties is possible through the CIELAB color space diagram. In the CIELAB color space, L* indicates lightness, and a* and b* are the chromaticity coordinates. In the diagram, +a* is the red direction, −a* is green, +b* is yellow, and −b* is blue. Chroma C*=sqrt(a*
2
+b*
2
) increases from the center of the circle outward. Hue angle h=arctg(a*/b*) is 0° along the +a*-axis, 90° along the +b*-axis, 180° along the −a*-axis, 270° along the −b*-axis and 360° (same as 0°) along the +a*-axis(see Römpp Chemie Lexikon, “Lacke und Druckfarben”, Ed. U. Zorll, Georg Thieme Verlag Stu
Bleikolm Anton
Müller Edgar
Rozumek Olivier
Jagannathan Vasu
Shoemaker and Mattare
Shosho Callie E.
SICPA Holding S.A.
LandOfFree
Ink composition comprising first and second optically... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ink composition comprising first and second optically..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ink composition comprising first and second optically... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2939553