JP2728537B2 - Liquid crystal mask type laser marker - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal mask type laser marker using a liquid crystal element as a pattern mask.

[Conventional technology]

A laser marker using a liquid crystal element as a pattern mask for marking is disclosed in JP-A-56-38888 and JP-A-60-177461.
Nos. 6,127,710 and 64-11088 describe the configuration. As for the specifications of the liquid crystal element for display, Japanese Patent Application Laid-Open Nos. 60-107020 and 61-210324 describe the liquid crystal twist angle and the product of the liquid crystal layer thickness d and the refractive index anisotropy Δn of the liquid crystal. I have.

[Problems to be solved by the invention]

These prior arts relate to a configuration in which a liquid crystal element is used as a pattern mask for laser marking,
No consideration is given to what type of liquid crystal element is required. Therefore, in the case of a combination of a YAG laser widely used as an oscillator for a laser marker and a liquid crystal element for a general display, there were concerns about the sharpness of marking and the efficiency of laser use.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal mask type laser marker having high laser use efficiency and capable of performing clear marking.

[Means for solving the problem]

To achieve this object, the product Δn · d of the thickness d (μm) of the liquid crystal layer of the liquid crystal element used for the laser marker and the refractive index anisotropy Δn of the liquid crystal is 1.4 μm to 2.3 μm which is larger than Δnd of the general display. And the liquid crystal twist angle is 18
The polarization axis of the polarization element is shifted from the polarization direction of the pulse laser by a certain angle with respect to the polarization direction of the pulse laser.

Further, the liquid crystal element is arranged such that the liquid crystal molecule arrangement direction on the laser incident side of the liquid crystal element is shifted by a certain angle with respect to the pulse laser polarization direction.

[Action]

By specifying the range of the liquid crystal element Δn and the twist angle of the liquid crystal and shifting the polarization axis of the polarization element by a fixed angle with respect to the pulse laser polarization direction, excellent laser polarization direction rotation performance related to laser power and optical performance can be obtained. A liquid crystal element having a high contrast ratio and applicable as a liquid crystal mask for a laser marker can be manufactured.

In addition, by arranging the liquid crystal element so that the polarization direction of the pulse laser and the liquid crystal molecule arrangement direction of the liquid crystal element on the laser incident side are deviated by a certain angle, the laser pattern light used for marking can be transmitted efficiently. A highly efficient liquid crystal mask type laser marker with a small laser loss can be provided.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1, 2, and 3. FIG.

As shown in FIG. 1, a linearly polarized laser beam 2 emitted from a pulse laser 1 is applied to a liquid crystal element 4 via a beam expander / shaper 3. A power supply 5 is connected to the pulse laser 1, and is operated by a central control unit 8 together with a liquid crystal element drive circuit 6 and a liquid crystal element control circuit 7. The laser beam 9 transmitted through the liquid crystal element 4 is separated by a polarizing element 10 into a non-marking pattern light 12 and a marking pattern light 13 directed to an absorber 11, and the marking pattern light 13 is combined by a folding mirror 14. It is guided to the image optical system 15 and forms an image on the surface of the workpiece 16, and printing is performed by evaporating the material, for example, the resin in this portion.

In this configuration, consider the case of printing the character AH shown in FIG. In a liquid crystal mask type laser marker, if the liquid crystal element manufacturing specification is not properly selected, the laser energy reaching the background portion 30 increases, and the laser energy ratio between the printing portion 31 and the background portion 30, that is, the contrast ratio becomes poor. This passed from the experiment. Various liquid crystal elements 4 were manufactured, and a printing experiment was carried out. As a result, it was found that clear marking can be realized even on a semiconductor mold resin or ink paper if the contrast ratio of the laser marker is 4 or more. The above-mentioned contrast ratio refers to the ratio of the laser energy density of the printing portion / laser energy density of the background portion. The higher the contrast ratio, the higher the sharpness of the marking. However, similar to the general display, it can be confirmed by experiments that the twist angle θ _LC in the liquid crystal layer thickness direction of the liquid crystal element 4 shown in FIG. 4 should be increased. It has been found that a liquid crystal twist angle of at least 180 degrees is required to make the contrast ratio 4 or more.

On the other hand, in order to avoid excessive heat input to the workpiece 16 and minimize the thermal effect of the laser marking, the laser energy density P reaching the background portion 30 shown in FIG. desirable. This is because a liquid crystal element capable of obtaining such characteristics can naturally increase the contrast ratio. The conditions for manufacturing the liquid crystal element will be described with reference to FIG.

As for the specification of the liquid crystal device, the product Δn · d of the thickness d (μm) of the liquid crystal layer and the refractive index anisotropy Δn of the liquid crystal, and the above-mentioned liquid crystal twist angle are important. Widely known. With respect to the liquid crystal twist angle, if the angle is 180 degrees or less than the above-described contrast ratio point, the contrast ratio is low, and it is difficult to obtain sharpness. If it is higher than this, sharpness can be obtained, but practically, the upper limit of stable production is 270 degrees, so that Δnd
Is described below.

Considering a typical pulse laser such as an Nd: YAG laser (wavelength 1064 nm) as a laser for a laser marker, the liquid crystal element 4 and the polarizing element 10 can completely laser light the liquid crystal element 4 and the polarizing element 10 when the liquid crystal element driving circuit 6 is not operating. The theoretical conditions are shown in FIG. Since the theoretical characteristics themselves have different target wavelengths, the region relating to general displays (Δnd <1.
Located in a different area from 3). In this case, Δn uses a value at a wavelength of 1064 nm. In general, a value at a wavelength of 589 nm (visible light) is often used as a constant of a liquid crystal material, and a value at a wavelength of 633 nm is partially used instead. Therefore, it is important to recognize how the physical property values of the YAG laser light change with respect to these constant wavelengths.

The experiment using the liquid crystal mask showed that the wavelength was 589nm.
For Δn at The result was obtained. Considering the coefficient of 0.8 which attenuates to the maximum, the characteristic B is obtained by correcting the characteristic A in FIG. Therefore, from Δn · d, 1.4 μm in the region between the two characteristics
If a liquid crystal element is manufactured in the range of 2.3 μm, it will almost satisfy theoretical conditions and light conditions under the YAG laser beam. Therefore, when a liquid crystal element within the above range is used, pattern information can be clearly marked.

Another embodiment of the present invention will be described with reference to FIGS. In the liquid crystal element 4, the liquid crystal twist angle θ _LC shown in FIG. 2 is determined by the laser incident side liquid crystal molecule arrangement direction 17 and the laser emission side liquid crystal molecule arrangement direction 18. Pulsed laser polarization direction 19
Is not practical unless the angle is set to a certain angle θ _P. This will be described below with reference to FIGS. 5 and 6.

FIG. 5 shows an electro-optical characteristic of how the laser energy density of the printing unit 31 and the background unit 30 changes with respect to the liquid crystal element driving voltage V _OP transmitted from the central control unit 8 to the liquid crystal element control circuit 7. It was shown to. Here, when the drive voltage V _OP of the liquid crystal element 4 is increased and the ratio of the laser light passing through the polarizing element 10 to the laser light applied to the liquid crystal element 4, that is, the maximum value of the transmittance is T _ON , It is changing as I connexion FIG. 6 to θ _P. θ _P refers to the angle between the laser polarization direction 19 irradiating the liquid crystal mask 4 and the liquid crystal molecular axis 17 on the laser incident side.

As shown in the figure, in the experimental results in which the liquid crystal twist angle θ _LC was 240 degrees, the maximum transmittance was obtained when θ _P was 60 degrees. Considering from the viewpoint of laser usage, but preferably is of course higher transmittance T _ON is higher, from the viewpoint of the contrast ratio during laser marking, theta _P good range of at least 40 degrees of 80 degrees, the liquid crystal twist angle If θ _LC is about 240 degrees, it has been found that θ _P should preferably be set in the range of 45 degrees to 65 degrees. FIG. 6 shows the characteristics of the liquid crystal twist angle θ.
Although it depends on the _LC , θ _P may be at least in the range described above, that is, in the range of 40 to 80 degrees.

According to this embodiment, the transmittance when the driving voltage _{VOP is} applied to the liquid crystal element 4 can be increased, so that the linearly polarized laser light 2 obtained from the pulse laser 1 can be used effectively.

Another embodiment of the present invention will be described with reference to FIG. In the first embodiment of the present invention, the specifications of the liquid crystal element 4 are described. In the second embodiment, the positional relationship between the pulse laser polarization direction 19 and the liquid crystal molecule arrangement direction 17 of the liquid crystal element 4 on the laser incident side is described. Here, the setting direction of the polarization axis 20 of the polarizing element 10 provided after the liquid crystal element 4 will be described.

As described with reference to FIG. 1, the polarizing element 10 separates the laser light transmitted through the liquid crystal element 4 into the non-marking pattern light 12 and the marking pattern light 13. It is important how many times the polarization axis 20 of the polarization element 10 is rotated and set with respect to the direction 19.

According to the experiment, when the angle between the laser polarization direction 19 and the polarization axis 20 of the polarization element 10 is 60 degrees or more, the smooth electro-optical characteristics as shown in FIG. may result in characteristic having a convex portion, Matsuda and limited setting range of the drive voltage V _OP. Therefore, the angle between the laser polarization direction 19 and the polarization axis 20 of the polarization element 10 is 0 to 60 degrees.
If the range of degrees is good and the liquid crystal twist angle θ _LC is about 240 degrees,
More preferably, by setting the angle between 25 degrees and 35 degrees, the liquid crystal element 4 can have a smooth electro-optical characteristic as shown in FIG.

According to the present embodiment, the electro-optical characteristics such that the transmitted laser energy density increases smoothly with the application of the drive voltage can be obtained without losing the laser or the optical properties when the drive voltage is not applied to the liquid crystal element 4. Thus, drive voltage control is facilitated.

〔The invention's effect〕

According to the present invention, a liquid crystal element that can be used as a laser marker pattern forming mask can be manufactured.

Further, since the YAG laser beam can be emitted, there is an effect of improving the contrast ratio at the time of marking.

Furthermore, when the driving voltage is applied to the liquid crystal element, the energy reaching the workpiece can be increased, so that the laser utilization rate can be improved and the pulse laser can be downsized.

By satisfying the setting conditions for the polarization direction of the pulse laser and the polarization axes of the liquid crystal element and the polarization element, a liquid crystal mask laser marker can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a liquid crystal mask type laser marker of the present invention, FIG. 2 is an explanatory diagram showing an allowable range of a relationship between a liquid crystal twist angle and Δn · d in the liquid crystal mask of FIG. 1, and FIG. FIG. 4 is an explanatory diagram of a contrast ratio of an object, FIG. 4 is an explanatory diagram of an angle θ _P formed by a liquid crystal molecule alignment direction on a laser incident side with respect to a laser polarization direction of the present invention, FIG.
FIG. 4 is an explanatory diagram of θ _P dependence of laser light transmitted through the polarizing element when a driving voltage is applied to the liquid crystal element, and FIG. 7 is an explanatory view of a polarization axis setting rotation angle of the polarizing element with respect to the laser polarization direction in FIG. FIG. 8 is an explanatory diagram of electro-optical characteristics. 4 ... Liquid crystal element, 10 ... Polarization element, 17 ... Laser incident side liquid crystal molecular alignment direction, 19 ... Laser polarization direction, 20 ... Polarization element polarization axis, θ _LC ... Liquid crystal twist angle, Δn · d… Liquid crystal refractive index difference Anisotropy × liquid crystal layer thickness, θ _P ... An angle formed by the liquid crystal molecule arrangement direction on the laser incident side with respect to the laser polarization direction.

Claims (6)

(57) [Claims] 1. A liquid crystal mask type laser marker comprising a pulse laser, a liquid crystal element, a polarizing element and an imaging optical system, wherein a product of a thickness d (μm) of a liquid crystal layer of the liquid crystal element and a refractive index anisotropy Δn of the liquid crystal. A liquid crystal mask type laser marker using a liquid crystal element having Δn · d in a range of 1.4 μm to 2.3 μm. 2. The liquid crystal mask type laser marker according to claim 1, wherein a liquid crystal element having a liquid crystal twist angle in a liquid crystal layer thickness direction of the liquid crystal element of between 180 degrees and 270 degrees is used. 3. The liquid crystal device according to claim 1, wherein the liquid crystal molecules are arranged such that the liquid crystal molecule alignment direction on the laser incident side of the liquid crystal device is between 40 degrees and 80 degrees with respect to the pulse laser polarization direction.
Or a liquid crystal mask type laser marker according to 2. 4. The liquid crystal device according to claim 1, wherein one side of the outer periphery of the liquid crystal device is disposed vertically or horizontally so that a polarization direction of the pulse laser is between 40 degrees and 80 degrees with respect to a liquid crystal molecule alignment direction on a pulse laser incidence side of the liquid crystal device. The liquid crystal mask type laser marker according to any one of claims 1 to 3, wherein a rotation direction of a polarization direction of the pulse laser is controlled. 5. A liquid crystal device comprising: a liquid crystal element having a twist angle of about 240 degrees in a thickness direction of a liquid crystal layer; an angle between a pulse laser polarization direction and a liquid crystal molecule arrangement direction on a laser incident side in a range of 45 degrees to 65 degrees; 2. The liquid crystal mask type laser marker according to claim 1, wherein the angle between the laser polarization direction and the polarization axis of the polarization element is between 25 degrees and 35 degrees. 6. The liquid crystal mask type laser marker according to claim 1, wherein the angle between the polarization direction of the pulse laser and the polarization axis of the polarization element is shifted within a range of 0 to 60 degrees. .