JP2023045523A - Refractive index measurement device - Google Patents

Abstract

A technique for measuring the refractive index of a paint applied to a two-dimensionally spreading area including during curing and drying is provided. SOLUTION: For a sample coated with a mixed paint in which a powder having a known refractive index is mixed with the paint to be evaluated, digital holography (measurement unit 10) is used to measure a predetermined area of the sample Ob at predetermined time intervals. A reproduced image creating unit 21 for creating a reproduced image of transmitted light, an intensity determining unit 23 for determining the transmitted light intensity of the region for each time interval based on the created reproduced image, and the determined transmitted light intensity and an output unit 25 for outputting the derived time and the known refractive index as a set. Refractive index measuring device 1 to. [Selection drawing] Fig. 1

Description

There is an application for exception to loss of novelty

TECHNICAL FIELD The present invention relates to a technology for evaluating the refractive index of a coating applied to a wide area surface using digital holography.

Conventionally, paints have been used in various industries for the purpose of protecting products and improving aesthetic appearance. In recent years, there has been a further increase in diversity, such as adding functionality (heat resistance, scratch resistance, insulation, antifouling, deodorizing, etc.) and environmentally friendly formulations.
This diversity can be realized by changing the compounding ratio of the basic composition, adding or reducing multiple admixtures and many additives, etc., so it can be said that the combinations are infinite. Appearance and texture, which are considered important in many paints, are greatly related to the refractive index that changes the film thickness direction of the paint film.
Here, although the time required for drying and curing of the paint varies depending on the presence or absence of volatile components, the refractive index generally changes during the period from application to drying and curing. Therefore, it is extremely important as basic information for the development of paint to grasp the refractive index before coating and the refractive index after drying and curing.

However, the conventional technique has the following problems.
As described above, new admixtures and additives resulting from the recent diversity of paints make it difficult to predict changes in the refractive index, and there have been cases where the refractive index during drying and curing has also changed significantly.
In addition, there are cases where the properties of the coating film during drying and curing exactly match the required specifications. There is a desire to know the
On the other hand, if a refractometer is used, it is possible to sequentially determine the refractive index. However, the relevant information as described above is still not available.
In addition, with a refractometer, information on the refractive index of only one measurement point can be obtained. However, there is a problem that sufficient refractive index information cannot be obtained for an object whose refractive index needs to be measured or evaluated.

JP 2014-211395 A JP 2017-044611 JP 2019-194526 A

S.G. Croll : Journal of Coatings Technology., 58, 41-58 (1986) R. E. IMHOF, C. J. WHITTERS and D. J. S. BIRCH: Materials Science and Engineering, B5 113-117 (1990) T. Yasui, T. Yasuda, K. Sawada, and T. Araki : Appl. Opt., 44, 6849-6856 (2005) T. Yasuda, T. Iwata, T. Araki, and T. Yasui : Appl. Opt., 46, 7518-7526 (2007) Iwao Takarasako and Kaori Fukunaga : Proceedings of the 25th Paint and Coating Research Conference, pp.32-33 (2010) J. I. Amalvy, C. Lasquibar, R. Arizaga, H. Rabal, and M. Trivi: Progress in Organic Coatings, 42, 89-99 (2001) R. Arizaga, E. Grumel, N. Cap, and M. Trivi: JCT Research, 3, 295-299 (2006) I. Yamaguchi, M. Yokota, T. Ida, M. Sunaga, and K. Kobayashi: Opt. Rev., 14, 362-364 (2007) G. G. Romero, E. E. Alanis and H. J. Rabal: Opt. Eng. 39[6] 1652-1658 (2000) R. Arizaga, N. Cap, H. Rabal and M. Trivi: Opt. Eng. 41[2] 287-294 (2002) Yoshiki Kimoto, Ichiro Yamaguchi, Masayuki Yokota, “Observation and Analysis of Painted Surfaces in the Early Drying Stage Using Digital Holography,” Journal of Paint Engineering, 45, 448-456 (2010) Masayuki Yokota, Koichi Kobayashi, “Evaluation of paint drying by phase shift digital holography and gravimetric method and estimation of evaporation solvent by calculation of reduced volume for clear paint”, Coating Engineering, 48, 556-569 (2013)

The present invention has been made in view of the above, and an object of the present invention is to provide a technique for measuring the refractive index of a coating applied to a two-dimensionally spreading area, including during curing and drying. do.

The refractive index measuring device according to claim 1 uses digital holography for a sample coated with a mixed paint in which a powder having a known refractive index is mixed with the paint to be evaluated, and measures a predetermined area of the sample at a predetermined time interval. reproduction image creating means for creating a reproduced image of transmitted light for each time interval; intensity determining means for determining the transmitted light intensity of the region at each time interval based on the reproduced image created by the reproduced image creating means; Based on the transmitted light intensity determined by the determination means, a time derivation means for deriving the time at which the transmitted light intensity reaches a maximum, the time derived by the time derivation means, and the known refractive index are output as a set. and output means.

That is, the invention according to claim 1 uses the fact that the intensity of transmitted light in an area is maximized when the refractive index of the paint matches or approaches the refractive index of the powder dispersed in the paint. It is possible to measure the refractive index of the paint in the middle of drying or curing in the area with the spread.
In other words, it is possible to provide a basic technique for evaluating the dynamic refractive index of paint in a situation close to actual coating.

Paint shall include adhesives. The adhesive is not limited to one that solidifies and hardens naturally, and may be a UV-curable adhesive. In addition to colorless paints containing no coloring material, colored transparent paints may be used. Colored paints may be evaluated by appropriately thinning the sample thickness and increasing the intensity of the irradiation light. .
The powder used has a refractive index between the refractive index before application of the paint and the refractive index after drying and curing, and its size and mixing amount are such that it does not affect the evaluation of the paint. Examples include 1 μm to 50 μm and 1 vol % to 5 vol %. Needless to say, it should not dissolve, degrade, or react with the paint. It should be noted that good dispersibility is preferable, but in principle, the intensity of transmitted light is maximized when the refractive indices are the same.
The size of the sample (evaluation area) depends on the optical system of digital holography, but can be 1 mm×1 mm to 100 mm×100 mm. The intensity distribution of the reproduced image in the region can be considered as the refractive index distribution.
The transmitted light intensity may be determined based on the result of simply calculating the average value, calculating the median value, or performing a leveling process or a smoothing process.
Although the predetermined time interval is not limited, it may be every 5 seconds or every 30 seconds. However, it is preferable to set the time interval at which phase jump does not occur or phase connection is possible.
The maximum time may be calculated as the time at which the maximum value is given, but in most cases, the value is given approximately the same value for a certain period of time while fluctuating in small increments, so it may be the middle time (time) of the staying time.
The term "output" is used in a broad sense, and includes output to a monitor as well as output to storage means, and is not particularly limited.

The refractive index measuring device according to claim 2 is the refractive index measuring device according to claim 1, wherein powders with different refractive indices are used, the output means is controlled, and the time derived by the time deriving means is calculated. It is characterized by comprising output control means for plotting the refractive index of the powder over a determined period of time and outputting a graph of changes in the refractive index of the paint over time.

That is, the invention according to claim 2 makes it possible to know the temporal change of the refractive index of the widened region.

As for how to use powders with different refractive indices, in addition to the method of collecting data separately as a mixed paint mixed with powder 1, a mixed paint mixed with powder 2, etc., powders in paint If it can be distinguished, it may be measured as a mixed powder mixed with paint (if the paint is simple, the intensity of transmitted light with multiple peaks is measured over time). In addition, since holograms are suitable for capturing an area, the intensity may be measured by partitioning and coloring the area.
A refractive index curve can also be plotted by interpolating the obtained points. Plot or graph output is preferably on a PC monitor.

The refractive index measurement apparatus according to claim 3 is the refractive index measurement apparatus according to claim 2, wherein digital holography is used to create a phase image and/or a phase difference image for each of the time intervals for the region. The image forming means is provided, and the output control means performs control to output the reproduced image and the phase image and/or the phase difference image as a moving image.

That is, the invention according to claim 3 can dynamically grasp the state of the coating film during drying and curing (for example, fluidity, surface properties, etc.) from various angles, and can contribute to the development of coating materials.

For moving image output, the reproduced image and the phase image and/or the phase difference image are synchronized and continuously output at equal time intervals. The time interval at this time does not need to match the time interval of the reproduced image. For example, a reproduced image is created as an image every 5 seconds, and a moving image output is changed every 0.1 seconds.

The refractive index measuring device according to claim 4 uses digital holography for a sample coated with a mixed paint in which a powder having a known refractive index is mixed with the paint to be evaluated, and measures a predetermined area of the sample at predetermined time intervals. a reproduced image creating means for creating a reproduced image of the reflected light for each time interval; an intensity determining means for determining the reflected light intensity of the region at each time interval based on the reproduced image created by the reproduced image creating means; Based on the reflected light intensity determined by the determination means, a time determination means for determining the time at which the reflected light intensity becomes minimum, the time determined by the time determination means, and the known refractive index are output as a set. and output means.

That is, the invention according to claim 4 utilizes the fact that the intensity of reflected light in an area is minimized when the refractive index of the paint matches or approaches the refractive index of the powder dispersed in the paint, and the two-dimensional It is possible to measure the refractive index of the paint in the middle of drying or curing in the area with the spread.
In other words, the refractive index in the middle stage of drying and curing can be measured based on the reflectance that has a strong correlation with the refractive index.

In addition, using powders with different refractive indexes, controlling the output means, plotting the refractive index of the powder over the determined time with respect to the time derived by the time deriving means, and changing the refractive index of the paint over time You may comprise the output control means which outputs the graph of.
Similarly, digital holography is used to provide phase image creation means for creating a phase image and/or a phase difference image for each of the time intervals for the region, and the output control means comprises a reproduced image, a phase image and/or A phase difference image may be controlled to be output as a moving image.

ADVANTAGE OF THE INVENTION According to this invention, the technique of measuring the refractive index of the coating material apply|coated to the area|region with a two-dimensional spread including the middle of hardening drying can be provided.
In addition, the state of the coating film during drying and curing can be dynamically grasped from various angles, which can contribute to the development of coating materials.

1 is a schematic diagram showing an optical system (measuring system) and a processing system, which are basic configurations of a refractive index measuring apparatus; FIG. FIG. 4 is an explanatory view showing a petri dish on which a sample is applied and a state of a mask; FIG. 4 is an explanatory conceptual diagram showing a drawing example of graphs and moving images on a monitor; 4 is a graph showing changes over time in the refractive index of a mixed paint.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, digital holography is combined with an immersion method to measure the refractive index of a surface in the middle stage of drying and curing of a paint. Also, the paint mainly described in the present embodiment is a transparent paint.

FIG. 1 is a schematic diagram showing an optical system (measurement system) and a processing system, which are basic configurations of a refractive index measurement apparatus.
The refractive index measuring apparatus 1 is roughly divided into a measuring section 10 that constitutes an optical system and a processing section 20 that performs data processing.

The measurement unit 10 is functionally a digital holography, and includes a laser emission unit 11, a lens-filter unit 12, beam splitters 13 (13a, 13b), mirrors 14 (14a, 14b), and a CMOS camera 15. , and a biconvex lens 16 . A sample Ob is inserted in the optical path of the emitted light reflected by the beam splitter 13a.

A semiconductor laser beam having a wavelength λ of 657.8 nm is emitted from the laser emitting portion 11 .
The lens-filter unit 12 is composed of a biconvex lens, an optical isolator, a wavelength plate, a polarizer, a spatial filter, a biconvex lens, a diaphragm (pinhole), a planoconvex lens, and the like. The emitted light is collimated by a biconvex lens, and the transmitted light is linearly polarized while preventing return light with an optical isolator. The light is transmitted through a λ/2 wavelength plate and a polarizer, and is passed through a pinhole with an aperture of 5 μm at the focal position by a biconvex lens to cut off diffraction images due to dust and the like. The transmitted light is collimated through a plano-convex lens with a focal length of 100 mm.
Subsequently, this light is split into two by the beam splitter 13a, and the reflected light passes through the sample Ob, is collected by the biconvex lens 16, and passes through the beam splitter 13b as object light. The light transmitted through the beam splitter 13a is reflected by the mirrors 14a and 14b, and is reflected by the beam splitter 13b as reference light. Incidentally, the mirror 14b is slightly tilted and set at an off-axis angle. By off-axis, it is possible to suppress the image deterioration that occurs when the 0-order light, the real image, and the conjugate image are superimposed on each other in the reproduced image.
The object light and the reference light are combined through the beam splitter 13b, and the obtained image (hologram) is recorded by the CMOS camera 15. FIG. A CMOS sensor with 1024×1024 pixels (pixel pitch, which is the size of one pixel, is 5.5 μm×5.5 μm) was used. Note that the recording time interval was every 5.0 seconds. The recording data is sent to the processing unit 20 in sequence.

Next, the sample Ob will be described.
The sample Ob is a paint containing powder (mixed paint), which is applied to a petri dish.

As for the paint, a water-soluble clear paint H30 (GSI Creos) is used here in order to evaluate the refractive index and the like during drying and curing based on changes in the intensity of transmitted light. Raw materials are mainly composed of acrylic synthetic resin, pigment, organic solvent, and water.
1 to 5 vol % of CaF ₂ powder (particle size: several μm to 10 μm: refractive index n=1.4338) is added to this and dispersed to obtain a mixed paint. This mixed paint is applied to a Petri dish to a thickness of 1 mm.

The petri dish was made by bonding a 1 mm thick acrylic plate with a 12 x 12 mm window to a glass substrate, and a mask with an outer diameter of 3.0 mm x 3.0 mm and an opening of 2.0 mm x 1.5 mm was placed on the opposite side of the acrylic plate. It is formed by bonding to the side glass substrate. In other words, the petri dish is constructed as a container from which the drying and curing information of the paint in the opening can be obtained (Fig. 2).

The evaluation principle will be explained.
The refractive index of the paint part in the mixed paint gradually changes due to drying and curing. By utilizing the fact that the transmitted light intensity of the mixed paint is the strongest when it matches the refractive index of the CaF ₂ powder, the refractive index of the paint in the middle of drying and curing can be known (immersion method). Assuming that the refractive indices of the paint and the powder are nl and np, respectively, the light transmittance Tr of the mixed paint is given by Tr=4nl·np/(nl+np) ² .
The refractive index measurement device 1 measures changes in transmittance (changes in intensity of transmitted light), and measures and evaluates temporal changes in the refractive index of the paint during drying and curing.

Next, the processing section 20 will be described. The processing unit 20 is a personal computer as hardware, and includes a CPU, RAM, HDD, video card, monitor, NIC, etc., and has an OS and processing applications installed. The illustration of the OS and processing applications installed in the hardware and HDD is omitted.

The processing unit 20 has a reproduced image creating unit 21, a phase image creating unit 22, an intensity determining unit 23, a time deriving unit 24, an output unit 25, and an output control unit 26 as functional configurations.

The reconstructed image creating unit 21 sequentially receives the information of each pixel from the measuring unit 10, particularly the CMOS camera 15, and performs predetermined processing to create a reconstructed image. Specifically, for the transmitted light (refracted light) that has passed through the rectangular window inside the mask of the sample Ob, a reproduced image is created based on the transmitted light intensity at each pixel on the CMOS. Naturally, this image is a rectangular image reflecting the transparent portion. Here, a reproduced image is created every 5 seconds.
The reproduced image creating unit 21 can realize its function by a processing application, HDD, RAM, and the like.

Similarly, the phase image creating unit 22 sequentially inputs information of each pixel from the CMOS camera 15 and performs predetermined processing to create a phase image. Specifically, similarly to the reconstructed image, a phase image is created for transmitted light (refracted light) that has passed through the rectangular window based on the phase of each pixel on the CMOS. Naturally, this image is a rectangular image reflecting the transparent portion. Moreover, since a phase image is created every 5 seconds, a phase contrast image is also created based on the difference from the phase 10 seconds before (a multiple of 5 seconds will suffice).
The phase image generator 22 can realize its function by a processing application, HDD, RAM, and the like.

Note that the method of constructing the reconstructed image and the phase image is disclosed in Patent Documents 1 to 3 by the inventors of the present application, and the description thereof will be omitted.

Based on the reproduced image reproduced by the reproduced image creating unit 21, the intensity determination unit 23 determines the transmitted light intensity of the reproduction region (determines the intensity of each image, that is, every 5 seconds). Refracted light (transmitted light in this case), which greatly affects the texture of the paint, should not be evaluated with pinpoint accuracy. Reflecting this, the intensity determining unit 23 determines the transmitted light intensity (in the present embodiment, the intensity is calculated as an average value (total intensity of each point/total number of points)).
The intensity determination unit 23 can realize its function by a processing application, a CPU, a RAM, and the like.

The time derivation unit 24 derives the time at which the transmitted light intensity reaches its maximum based on the transmitted light intensity determined by the intensity determination unit 23 . The base point of this time may be the application start time or the measurement start time. As described above, when the area average value is used, the maximum time itself may be used. The time may be calculated and applied.
The function of the time derivation unit 24 can be realized by a processing application, OS, RAM, and the like.

The output unit 25 pairs the time derived by the time deriving unit 24 and the refractive index of the CaF ₂ powder, records them in the HDD, and outputs them for monitor drawing as necessary.
The function of the output unit 25 can be realized by an OS, HDD, monitor, and the like.

The output control unit 26 controls the output unit 25 to plot the refractive index with respect to time derived by the time deriving unit 24 on the monitor, and outputs (renders) a graph of the temporal change of the refractive index of the paint.
In addition, since only one point can be drawn with CaF ₂ shown in the above explanation, CaF ₂ powder whose particle size is changed as appropriate and whose refractive index is changed by containing impurities, or A plurality of sets of data are obtained by using powders of different compositions or types, and these data are plotted and graphed.

The output control unit 26 also performs control to output the reproduced image, the phase image, and the phase difference image as moving images. FIG. 3 is an explanatory conceptual diagram showing an example of drawing graphs and moving images on a monitor. In the figure, a graph 31 shows the temporal change of the refractive index, a graph 32 shows the reproduced image, a graph 33 shows the phase image, and a graph 34 shows the phase difference image.

The graph 31 is drawn so that the vertical line 31a slides along the horizontal axis, making it easy to recognize the elapsed time. In conjunction with this, the graphs 32 to 34 are designed to draw images at the relevant times. In each graph, elapsed time is also displayed.
A moving image is reproduced by updating each image every 5 seconds in a short period of time. For example, if recording is taken every 5 seconds from application up to 10000 seconds, each image will be 2000 sheets. If this is played back 40 times per second, it becomes a moving image of 50 seconds. At the time of reproduction, conversion into an image format suitable for reproduction is appropriately performed. It should be noted that the number of images to be reproduced or the length of the moving image can be changed as appropriate, and an interactive operation such as pinching the vertical line 31a and sliding it left or right on the screen may be performed.
The output control unit 26 can realize its function by a video card, monitor, CPU, OS, and processing application.

<Specific example>
Next, a specific example of measuring the refractive index of the water-soluble clear paint H30 using _CaF2 will be described. FIG. 4 is a graph showing changes in the refractive index of the mixed paint over time. The figure also shows the result of measuring the change in the refractive index from the application of the clear paint H30 alone with a separate refractometer.
The refractive index of the mixed paint gradually increased immediately after application, reached a maximum value 105 minutes (6300 seconds) after application, and then gradually decreased. The refractive index of the clear paint H30 alone after 105 minutes from application is about 1.43. That is, as expected, it was confirmed that the refractive index of the paint alone coincides with the refractive index of CaF ₂ where the refractive index of the mixed paint is maximized.
Based on the above, digital holography was used for a sample coated with a mixed paint mixed with powder with a known refractive index for the paint (single paint) to be evaluated. At the maximum, the refractive index of the paint alone matches the refractive index of the powder. Become. By varying the powder (that is, the refractive index), it is possible to obtain the relationship (graph) between the elapsed time from application and the refractive index of the paint (single paint) at that time. A time-refractive index change curve can be obtained by appropriately performing interpolation processing between points.

As described above, according to the refractive index measuring device 1, the refractive index of a coating applied to a two-dimensionally spreading area can be measured including during curing and drying. The state of change and the state of drying and curing (reproduced image, phase image, phase contrast image) can be linked and grasped, which can contribute to the development of paints including adhesives. In particular, since the impression of the texture of the coating film is not pinpointed, but rather depends on the refractive index distribution on a broad two-dimensional surface, it is possible to measure or evaluate it in a practical manner.

Incidentally, colored transparent paints can be evaluated in the same manner, and even colored opaque paints can be evaluated based on transmitted light by, for example, thinning the coating film.
It is also possible to evaluate the refractive index of paint using reflected light, which has a strong correlation with transmitted light. In this case, the elapsed time from application minus the maximum value of the refractive index of the paint can be evaluated from the time that gives the minimum value of the reflected light.

Since the present invention can also obtain a phase image and a phase contrast image, it is also possible to obtain basic information or basic technology regarding the relationship between the refractive index and uneven coating.

1 refractive index measuring device 10 measurement unit 11 laser emission unit 12 lens-filter unit 13 beam splitter 14 mirror 15 CMOS camera 16 biconvex lens 20 processing unit 21 reproduced image creation unit 22 phase image creation unit 23 intensity determination unit 24 time derivation unit 25 Output unit 26 Output control unit 31 Temporal change graph 31a of refractive index Vertical line 32 Reconstructed image 33 Phase image 34 Phase contrast image Ob Sample

Claims (4)

Regarding a sample applied with a mixed paint in which powder with a known refractive index is mixed with the paint to be evaluated,
a reproduced image creating means for creating a reproduced image of transmitted light at predetermined time intervals for a predetermined region of a sample using digital holography;
intensity determining means for determining the transmitted light intensity of the region at each time interval based on the reproduced image created by the reproduced image creating means;
a time derivation means for deriving a time at which the transmitted light intensity reaches a maximum based on the transmitted light intensity determined by the intensity determination means;
output means for outputting the time derived by the time derivation means and the known refractive index as a set;
A refractive index measuring device comprising: Using powders with different refractive indices,
Output control means for controlling the output means to plot the refractive index of the powder over the determined time against the time derived by the time deriving means, and outputting a graph of the change in the refractive index of the paint over time. 2. The refractive index measuring device according to claim 1, wherein the refractive index measuring device is characterized by: Using digital holography, phase image creating means for creating a phase image and/or a phase difference image for each of the time intervals for the region,
3. The refractive index measurement apparatus according to claim 2, wherein the output control means performs control to output the reproduced image and the phase image and/or the phase contrast image as a moving image. Regarding a sample applied with a mixed paint in which powder with a known refractive index is mixed with the paint to be evaluated,
a reproduced image creating means for creating a reproduced image of reflected light at predetermined time intervals for a predetermined region of a sample using digital holography;
intensity determining means for determining the reflected light intensity of the region at each time interval based on the reproduced image created by the reproduced image creating means;
a time derivation means for deriving a time at which the reflected light intensity is minimized based on the reflected light intensity determined by the intensity determination means;
output means for outputting the time derived by the time derivation means and the known refractive index as a set;
A refractive index measuring device comprising:

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