Marking process for plastics.

0001The invention relates to a method for labeling plastics, in that a dye by means of a heat transfer medium. ^Git is transferred to a plastic.

0002In the case of measuring, control, switching and operating devices, legible, easily readable inscriptions are often to be attached, which differ from case to case in the composition and size of the characters. This applies in particular to the keys of input units such as typewriters.

0003Transfer printing is known, in which a carrier made of paper and provided with a dye is pressed against the plastic by means of a hot pressure stamp with slight pressure, the dye being transferred to the surface.

0004The disadvantage of this method is that special stamps are required for each character, so that the method is inflexible with regard to fonts and is expensive for smaller quantities. With such a stamp, it is also difficult to maintain the temperature, and these fluctuations can lead to a loss of quality with regard to the addition of dye and surface of the plastic.

0005It is also known to label a plastic part with a laser beam, which is guided in accordance with the lettering.

0006The disadvantage of this method is that the action of the energy of the laser beam leads to irreversible reactions in the plastic, which are usually associated with significant color changes. The color change can only be set to a limited extent: this means that only a light font on a dark background or a dark font on a light background is possible.

0007The invention has for its object to find an economical, flexible method for inscribing plastics with which sharp, abrasion-resistant characters in any desired color and size to any^Gem background can only be created by drawing or electronic specification, whereby destruction of the plastic must not occur.

0008The object is achieved in that the subtimation dye is diffused via the gaseous phase into the respectively heated surface of the plastic by means of at least one laser beam which can be controlled in accordance with the characters.

0009It has surprisingly been found that despite a short-wave radiation, in particular a laser beam, the sublimation dye _Pchange of hare without significant change of color in accordance with the ^Ge-desired characters one after the other heated surface of the plastic can be diffused so deeply as a result of the partial pressure drop that a sharply contoured, abrasion-resistant, easy-to-read, colored character is produced, the color being able to be chosen as desired depending on the meaning (eg signal red) and background. Due to the short, targeted, uniform irradiation and the contactless energy transfer, no material damage occurs.^Gon. A further advantage of the method according to the invention is flexibility, since the laser beam can be controlled via guidelines (drawings) or computer programs.

0010Laser beams with a wavelength λ of 100-1500 nm, in particular of 1000-1500 nm, have proven successful for colored printing. The power density should be 114 - 220 J / cm², in particular 124-150 J / cm², with an exposure time of 0.2 - 0.8 s / mm², in particular 0.5 - 0.7 s / mm², amount. Advantageous results are with an Nd-YAG solid-state laser (λ = 1.06 µm) with a focal spot diameter between 0.05 - 0.1 mm in diameter at a repetition frequency of 0.5 - 15 KHz under a current of 10-25 A and one To achieve speeds of 5 - 50 mm / s, especially 5-15 mm / s. The amount of diffusion depends on the current multiplied by the number of modes through speed. The softening temperature of the plastic should be at least 30 ° C above the sublimation temperature of the dye.

0011In a special implementation of the method, the sublimation dye applied directly to the surface is diffused.

0012By applying a dye across the board by pouring, spraying, brushing or printing, it is possible to scan each character with the laser beam in accordance with the specified course. The undiffused dye residues are then removed.

0013In another implementation of the method, the sublimation dye is guided past the surface of the plastic on a carrier material.

0014With the help of carrier material, which can consist of paper, tissue or foil, the sublimation dye is brought to the place where the laser beam hits. A device with a step-wise continuous tape is advantageous for this, which is wound up from one spool before use and rewound on the next spool after signing.

0015In an advantageous implementation of the method, the path opposite to the direction of propagation of the laser beam is blocked for the gaseous dye.

0016Due to a gas-impermeable layer, which can also serve as a carrier material, the gaseous phase of the sublimation dye can only migrate in the direction of the plastic to be labeled.

0017In a useful implementation of the method, the sublimation dye is pressed directly onto the plastic over the carrier material.

0018By means of a mechanical tensioning device or by applying a vacuum to the gas-tight carrier material, very short paths for the diffusion of the dye are created.

0019In a preferred implementation of the method, the carrier material is pressed against the plastic by means of a transparent device which allows the laser beam to pass through almost unhindered.

0020Since, for example, a transparent PU body at wavelengths in the range of 1000 - 1500 nm, in which, for example, the Nd-YAG solid-state laser emits, has practically no change when irradiating with a laser beam during the usual exposure time, it is possible to do this using fluid cushions Press the carrier material cleanly, the fluid being able to serve as an energy carrier, for example for preheating the dye and thus for faster entry into the gaseous phase.

0021In a further implementation of the method, the sublimation dye is passed in the gaseous phase to the area where the laser beam strikes at high speed with simultaneous compression.

0022An intensive effect can be achieved by adding dye in the gaseous phase at high speed and compression by funnel-shaped formation of the gas channel, the excess dye being sucked off again and again in order to be added to the cycle again.

0023In one implementation of the method, the sublimation dye is diffused into thermoplastically processable, pourable or pressable plastics.

0024Among other things, the process can be advantageous for materials such as acrylonitrile butadiene styrene (Novodur <img file="EP0201627A2_D0001.tif" />) Cellulose acetate (Cellidor <img file="EP0201627A2_D0002.tif" />) - polyamides (Durethan <img file="EP0201627A2_D0003.tif" />) Polycarbonate (Makrolon <img file="EP0201627A2_D0004.tif" />), Polyester and polybutylene terephthalate (Pocan <img file="EP0201627A2_D0005.tif" />) or a mixture of the polymers mentioned and preferably (PC / ABS blend (Bayblend <img file="EP0201627A2_D0006.tif" />) PC / PBTP blend (macro blend <img file="EP0201627A2_D0007.tif" />) and polyurethane as well as silicone rubbers can be used. In particular, thermoplastic materials can be processed.

0025Thermal diffusion dyes and sublimation dyes (RESIREN T®) are suitable as dyes.

example 1

0026A transfer printing paper printed with Resiren T, blue area, is positioned on a typewriter key made of Novodur PH-AT (ABS) and arranged under the laser optics of a Nd-YAG solid-state laser. A focused laser beam is generated (λ = 1.06 µm and (in a circle) over the paper. After removing the paper, the dye in the irradiated zone has penetrated the plastic.

Example 2

0027A polyester film (Hostaphan RE 0.050 mm) printed with a red surface with Resiren T, is placed on a switch cover made of Pocan B 1505 (PBTP) and arranged under the laser optics of a Nd-YAG solid-state laser. A focused laser beam is generated (λ = 1.06 µm) and (in a circular shape) guided over the film. After removing the film, the dye in the irradiated zone has penetrated the plastic.

Example 3

0028A polyester film (Hostaphan RE 0.050 n) printed with black Resiren T, is positioned on a plastic housing made of Durethan BKV 30 and arranged under the laser optics of a Nd-YAG solid-state laser. A focused laser beam is generated (λ = 1.06µm) and (in a circular shape) guided over the film. After removing the film, the dye in the irradiated zone has penetrated the plastic.