Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-09-13
2001-09-18
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S205000, C523S171000, C523S217000, C524S387000, C524S449000, C524S486000, C430S270100, C430S338000, C430S945000
Reexamination Certificate
active
06291551
ABSTRACT:
The present invention relates to laser-markable plastics comprising as a dopant anthracene- and/or pentaerythritol-coated effect pigments or a mixture comprising one or more effect pigments and anthracene and/or pentaerythritol.
BACKGROUND OF THE INVENTION
The identity marking of production goods is becoming increasingly important across almost all sectors of industry. For example, it is frequently necessary to apply production dates, expiry dates, bar codes, company logos, serial numbers, etc., to plastics or polymer films. At the present time, these marks are made predominantly using conventional techniques such as printing, embossing, stamping and labelling. Growing importance is being acquired, however, by contactless, high-speed and flexible marking using lasers, especially in the case of plastics. This technique makes it possible to apply graphic inscriptions, for example bar codes, at high speed even to a non-planar surface. Since the inscription is within the plastics article itself, it is durably abrasion-resistant.
Many plastics, such as polyolefins and polystyrenes, for example, have hitherto proved to be very difficult or even impossible to mark by means of the laser. A CO
2
laser which emits light in the infrared region at 10.6 m produces only a faint, barely legible mark on polyolefins and polystyrenes even at very high output levels. In the case of the elastomers polyurethane and polyether esters, there is no interaction with Nd-YAG lasers whereas with CO
2
lasers engraving occurs. The plastic must not completely reflect or transmit the laser light, since if it did so there would be no interaction. However, there must also not be strong absorption, since in that case the plastic would evaporate to leave only an engraving. The absorption of the laser beams, and hence the interaction with the material, is dependent on the chemical structure of the plastic and on the laser wavelength employed. In many cases it is necessary to add appropriate additives, such as absorbers, in order to render plastics laser-inscribable.
For the laser identity marking of plastics, use is increasingly being made, besides CO
2
lasers, of Nd:YAG lasers. The YAG lasers commonly used emit a pulsed energy beam having a characteristic wavelength of 1064 nm or 532 nm. The absorber material must exhibit pronounced absorption within this specific NIR range in order to show a sufficient reaction in the rapid inscription processes.
The laser marking of plastics with pearl luster pigments was first described in Speciality Chemicals, Pearl Lustre Pigments—Characteristics and Functional Effects—May 1982.
The use of organic additives as dopants in laser marking is known, for example, from WO 95/30716, DE 195 360 47 A1, US 5,576,377 and DE 197 26 136 A1.
The prior art dopants all, however, possess the disadvantage that they persistently color the plastic that is to be inscribed, as a consequence of which the laser inscription, which is normally a dark script on a light background, lacks a sufficient contrast. Moreover, they have to be added in comparatively high concentrations, and in many cases are toxicologically objectionable.
SUMMARY OF THE INVENTION
An object of the present invention, therefore, was to provide laser-markable plastics which permit high-contrast marking under the action of laser light. The filler, or the successful absorption agent, should therefore possess a very light intrinsic color or should need to be used only in very small amounts.
It has surprisingly been found that the laser markability of plastics, and in particular the contrast of the marking, may be improved by coating effect pigments with anthracene and/or pentaerythritol or using a mixture of effect pigments and these organic additives.
Effect pigments are pigments which show in formulations like lacquers, printing inks, plastics and cosmetic formulations an optical effect based on light reflection phenonema. Effect pigments are for example metal effect pigments and pearlescent pigments, platelet-shaped iron oxide and platelet-shaped graphite. See, e.g., Römpp Chemie Lexikon, George Thieme Verlag, 1998, pp. 176, 378 and 438.
Through the addition of the coated effect pigments in concentrations of preferably about 0.5 to 10% by weight based on the plastics system, more preferably 1 to 5% by weight, and in particular 1.5 to 3% by weight, a high contrast is achieved in the laser marking of thermoplastics.
If a mixture of effect pigments and anthracene or effect pigments and pentaerythritol is used, then the overall concentration of the dopant in the plastic is preferably not more than 10% by weight. More preferably it is 1 to 5% by weight, in particular 1.5 to 3% by weight. (″Dopant refers to a mixture of pigment and anthracene or pentaerythritol or a pearlescent pigment coated with anthracene or pentaerythritol.
The mixing ratio of effect pigment to anthracene or effect pigment to pentaerythritol is preferably about 1:4 to 10:1, more preferably 1:3 to 5:1, in particular 1:2 to 2:1.
The concentration of the dopant in the plastic is, however, dependent on the plastics system used. The small fraction of effect pigment and anthracene and/or pentaerythritol does not substantially alter the plastics system and does not affect its ability to be processed.
Transparent thermoplastics comprising the aforementioned dopants in straight coloring exhibit a slightly metallic glimmer but retain their transparency. This metallic gleam, especially in the case of polyolefins, can be completely masked if required by the addition of preferably about 0.2 to 10% by weight, more preferably 0.5 to 3% by weight, of hiding pigments, such as titanium dioxide, for example. Furthermore, colorants may be added to the plastics, permitting color variations of any kind and at the same time ensuring retention of the laser marking. Appropriate colorants include, in particular, colored metal oxide pigments and also organic pigments and dyes.
The effect pigments suitable for marking are based preferably on platelet-shaped substrates, preferably transparent or semitransparent substrates comprising, for example phyllosilicates, such as synthetic or natural mica, talc, kaolin, glass flakes, Sio
2
platelets or synthetic unsupported platelets. Also suitable are platelet-shaped metal oxides such as platelet-shaped iron oxide, aluminium oxide, titanium dioxide, silicon dioxide, LCPs (liquid crystal polymers), holographic pigments, coated graphite platelets, or bismuth oxychloride.
As platelet-shaped pigments it is also possible to use metal flakes, which may be uncoated or else covered with one or more metal oxide layers; preference is given, for example, to Al, Cr, Fe, Au, Ag and steel flakes. If corrosion-susceptible metal flakes such as Al, Fe or steel flakes are to be used uncoated, they are preferably covered with a protective polymer layer.
Particularly preferred substrates are mica flakes coated with one or more metal oxides. Metal oxides used in this case include both colorless metal oxides of high refractive index, such as especially titanium dioxide, zinc oxide, tin oxide and/or zirconium dioxide, and colored metal oxides such as chromium oxide, nickel oxide, copper oxide, cobalt oxide and especially iron oxide (Fe
2
O
3
, Fe
3
O
4
), for example.
These platelet-shaped pigments are known and to a very large extent are available commercially, for example under the brand name Iriodin® from Merck KGaA, and/or may be prepared by standard methods known to the person skilled in the art. Pearl luster pigments based on transparent or semitransparent platelet-shaped substrates, for example, are described in the German Patents and Patent Applications 14 67 468, 19 59 998, 20 09 566, 22 14 454, 22 15 191, 22 44 298, 23 13 331, 25 22 572, 31 37 808, 31 37 809, 31 51 343, 31 51 354, 31 51 355, 32 11 602, 32 35 017 and 38 42 330.
Coated SiO
2
platelets are known, for example, from WO 93/08237 (wet-chemical coating) and DE-A 196 14 637 (CVD technique).
Particularly suitable are pearl luster pigments in combination with pentaerythritol and/or anthracene. The p
Delp Reiner
Heinz Dieter
Kniess Helge
Kuntz Matthias
Pfaff Gerhard
Merck Patent Gesellschaft mit beschrankter Haftung
Millen, White, Zelando & Branigan, P.C.
Yoon Tae H.
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