Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Patent
1996-02-06
1998-10-20
Michl, Paul R.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
347139, 522 16, 522 26, 522103, C08F 246
Patent
active
058247157
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a marking composition for forming a clear-cut mark on the surface of a molded article by laser beam irradiation, and a laser marking method using such a composition.
BACKGROUND ART
Recently, as means for marking letters and signs such as marker's name, product name, date of production, lot number, etc., on the surfaces of various commercial products, for example, electronic parts such as IC's, resistors, condensors, inductors, etc., electrical parts such as relays, switches, connectors, printed circuit boards, etc., housings of the electrical devices, automobile parts, machine parts, cables, sheets, packaging sheets, cards, labels, various containers of foods and medicines, caps of containers, etc., the printing method using a marking ink has been employed popularly. This method, however, has involved the problems such as requiring a long time for completing the process from printing to drying of the ink, difficulty in marking on a small part, complexity for maintenance and management of print quality, high cost, etc., and improvements on these matters have been required.
For more rational and efficient marking, there has been deviced and practically used a laser marking method in which laser beams are directly applied to the surface of an object to be marked, such as a machine part, so as to etch a part of the object surface by means of thermal decomposition or vaporization to thereby accomplish desired marking. However, this marking method still has the problems such as inability to form a clear-cut mark on an object made of a certain type of material and difficulty in giving a vivid mark on a tinted object. Thus, this conventional marking technique can not adapt itself to all types of material that may be used for the commercial products.
As a solution to the above problems, a method has been proposed in which an ultraviolet curing resin, which is capable of laser marking, is coated on the surface of an object to be marked, such as an electronic or electric part, housing, package, etc., and after the resin coating has been cured, laser beams are applied thereto to thereby effect desired marking by etching the resin. This method has the advantage that the whole process can be completed in a short time, that it allows marking on a small article, and that the marks formed are of high quality. However, this method also has the disadvantage in that in case a commercial ultraviolet curing resin is used, the formed mark may be effaced due to, for instance, adhesion of an oil when the object to be marked is of a specific type. Further, in case the ink used was of the type which develops a color, especially a black color on laser irradiation, a compound containing a heavy metal such as lead has been employed as color former, but use of such compound involves the problem of environmental pollution by the heavy metal contained in the compound and the problem of unclear marking. As a compound capable of forming a black color without using a heavy metal that may cause environmental pollution, a system comprising a leuco dye, which is known as a useful material for thermal recording, and a color developer appears useful, but when a system comprising such leuco dye and color developer is applied to an ultraviolet curing resin, there arises the problem that the color is developed gradually even with no laser beams being applied (this phenomenon is hereinafter referred to as discoloration of the ground).
DISCLOSURE OF INVENTION
The present inventors have made researches on a laser marking composition containing an ultraviolet curing resin, which composition is capable of suppressing or minimizing discoloration of the ground even when incorporated with a system comprising a leuco dye and a color developer, and can develop a vivid black color and form a mark with excellent color fastness. As a result, it was found that a marking composition which meets said requirements can be obtained by using a leuco dye with low solubility in toluene, particularly a solubility bel
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Hayashihara Shoiti
Kudo Masaru
Shinmoto Masaki
Michl Paul R.
Nippon Kayaku Kabushiki Kaisha
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