JPH06308072A - Water content rate sensor - Google Patents

Abstract

PURPOSE:To provide a water content rate sensor which is suitable for measurement of a water content rate of the surface of a specimen of a heat sensitive record paper and the like or measurement of water content rate distribution of the direction of its depth and with which feedback of obtained data is conducted for a printing condition of a printer and the like, sensitive change caused by the water content rate is corrected and good printing is performed. CONSTITUTION:A parallel electrode 10 is mounted on the same surface of a specimen of a heat sensitive record paper 50 and the like or arranged in a distance-separated state, alternating current is supplied to the parallel electrode 10 from an alternating current generation means 20 and electrostatic parameters of an electrostatic capacity and the like of a specimen surface are measured. Printing concentration is measured in parallel with the measurement of the electrostatic parameters, a correlation between the electrostatic parameters and the sensitivity of the heat sensitive record paper is found and feedback of its data is performed for a printing condition of a printer. In the case of measurement of water content rate distribution, because an electrode interval corresponds to measuring depth, similar measurement is conducted as the electrode interval of the parallel electrode 10 is changed and electrostatic parameter distribution is obtained in the direction of depth.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moisture content sensor,
In particular, the present invention relates to a water content sensor suitable for measuring the water content on the surface of thermosensitive recording paper and the distribution of the water content in the depth direction.

[0002]

2. Description of the Related Art Conventionally, there has been known a method of forming an image by coloring a thermosensitive coloring material by heat energy or light energy using a thermosensitive recording paper having a thermosensitive coloring layer provided on a support. Various thermal image forming apparatuses such as printers and laser printers have been put into practical use.

By the way, it is known that the sensitivity characteristic of the heat-sensitive recording paper changes depending on the water content of the heat-sensitive color forming layer in addition to the type of heat-sensitive material constituting the heat-sensitive color forming layer. Since the water content of the thermosensitive color developing layer also changes depending on the water content permeating from the support, the sensitivity characteristic of the thermosensitive recording paper also changes depending on the water content of the support. In addition, if the moisture content in the thickness direction of the thermosensitive coloring layer or the support is not uniform, the thermosensitive recording paper may be deformed such as curved or corrugated, which may cause a paper jam in the paper conveyance path.

As described above, there is a close relationship between the thermosensitive recording paper and the water content, and in order to improve the image quality of the formed image and to stably convey the paper, the water content of the thermosensitive coloring layer (surface of the thermosensitive recording paper). It is necessary to accurately determine the water content distribution in the thickness direction including the rate or the support. Various methods have heretofore been proposed as a method for measuring the water content on the surface of a thermosensitive recording paper. For example, there is a method of obtaining the water content by utilizing the fact that the electrical resistivity changes depending on the water content. This method uses three concentric electrodes, a main electrode and a counter electrode are brought into contact with the surface of the thermosensitive recording paper, and a guard electrode is brought into contact with the other surface, and a DC voltage is applied to these electrodes, which flow at that time. This is a method in which a current value is measured to obtain a surface resistivity, and a moisture content on the surface of the thermosensitive recording paper corresponding to the measured electrical resistivity is determined from a calibration curve in which the relationship between the moisture content and the electrical resistivity is previously determined.

Further, since water has a large relative dielectric constant,
A change in water content can be treated as a change in capacitance. This method of measuring the capacitance is performed in a state where the thermal recording paper is sandwiched between two opposing flat plate electrodes, or a thermal recording paper is inserted between two flat plate electrodes that are opposed to each other at a predetermined interval. , The capacitance is calculated from the potential difference generated by applying an AC voltage to the electrodes, and the relationship between the moisture content and the capacitance is determined in advance from the calibration curve. It is a method of obtaining the rate.

In addition to the above-mentioned electrical measuring method, there is also a method of measuring the water content using an infrared sensor. This method radiates infrared rays to a thermosensitive recording paper and measures the amount of reflected light to obtain the infrared absorption rate of the thermosensitive recording paper, and the thermosensitive recording paper is measured from the ratio to the infrared absorption rate measured by the same method at standard humidity. The water content of the surface is obtained. Besides,
Assuming that the thermal recording paper and the surrounding humidity are in equilibrium,
The surface of the thermosensitive recording paper can be estimated by various methods, such as the method of estimating the water content from the humidity in the vicinity of the thermosensitive recording paper, the method of determining the water content from the amount of warp of the thermosensitive recording paper, or the method of determining the water content by measuring the friction coefficient. The water content of is measured.

[0007]

As described above, the water content of the thermosensitive coloring layer and the support affects the sensitivity characteristics and shape of the thermosensitive recording paper, which causes deterioration of image quality and paper jam. ing. Therefore, it is desired to obtain the water content on the surface of the thermal recording paper and the water content distribution in the thickness direction as accurately as possible, and feed back these values to the image forming conditions as correction parameters.

However, among the above-mentioned methods for measuring the water content, the method of determining the water content by measuring the humidity in the vicinity of the heat-sensitive recording paper, the warp amount of the heat-sensitive recording paper, and the friction coefficient is not preferable because the reproducibility and accuracy are poor. . Further, in the method using the infrared sensor, the cost of the entire device, which is expensive for the sensor parts, becomes high. The method of obtaining the water content from the surface electrical resistivity or capacitance is excellent in reproducibility and measurement accuracy because it is an electrical measurement, and the structure of the measuring device is simple and the measuring method is easy. However, when measuring the surface electrical resistivity, a high applied voltage is required, and when measuring the capacitance, the thermal recording paper is sandwiched between electrodes or inserted between the electrodes for measurement. Therefore, not only the desired thermosensitive coloring layer but also the water content of the entire thermosensitive recording paper including the support is measured.

As described above, a method for accurately measuring the water content of the thermosensitive color developing layer or the water content distribution of the thermosensitive recording paper including the support has not been established yet, and an apparatus therefor has not been developed. The present invention has been made in view of the above circumstances, and it is possible to accurately measure the water content distribution in the thickness direction of the thermosensitive recording paper including the support and the water content of the thermosensitive coloring layer of the thermosensitive recording paper, Moreover, it is an object of the present invention to provide a water content sensor capable of feeding back the measurement result to the printing conditions of an image forming apparatus such as a printer to prevent image deterioration and paper jam.

[0010]

In order to achieve the above object, the present invention provides a water content sensor with an alternating current applied to parallel electrodes in a state where the parallel electrodes are in contact with or separated from the same surface of an object to be measured. It is configured to measure the electrostatic parameter of the surface of the measurement object by supplying it. Further, in order to achieve the same object, the present invention has a configuration in which the moisture content sensor feeds back the measured electrostatic parameter to the printing condition of the image forming apparatus.

Further, in order to achieve the same object, the present invention provides a water content sensor, in which the parallel electrodes are in contact with or separated from the same surface of the object to be measured, or the interval between the parallel electrodes (hereinafter referred to as the gap width). The electrostatic parameter in the depth direction of the object to be measured is measured by supplying an alternating current while changing (). According to the above means of the present invention, since the parallel electrodes are on the same surface side of the object to be measured and the supplied current is an alternating current, the electrostatic parameter of the surface can be measured with a small voltage.

Further, by feeding back the measured electrostatic parameter to the printing condition of the image forming apparatus such as a printer, it is possible to suppress the change of the sensitivity and the change of the shape due to the water content of the thermal recording paper and to make an appropriate correction. By doing so, stable image formation can be performed by preventing deterioration of image quality and paper jam. Further, since the gap width corresponds to the measurement depth, the electrostatic parameter in the thickness direction of the thermal recording paper including the support can be continuously measured by supplying the alternating current while changing the gap width. It is possible to obtain the water content distribution.

A water content sensor according to the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, the water content sensor 1 includes a parallel electrode 10, an alternating current generating means 20 for supplying an alternating current to the parallel electrode 10, an electrostatic parameter measuring means 30 and a controller 40.
The thermosensitive recording paper 50 is placed on the table 60 so that the thermosensitive coloring layer faces the parallel electrodes 10. At this time, the thermal recording paper 50 and the parallel electrode 10 may be in contact with each other,
Alternatively, they may face each other with a certain distance therebetween.
When the thermosensitive recording paper 50 and the parallel electrode 10 are brought into contact with each other for measurement, a weight (not shown) is placed on the parallel electrode 10 to press the parallel electrode 10 as a whole so that both are evenly distributed. By bringing them into close contact, a larger value of the electrostatic parameter can be obtained, which is preferable from the viewpoint of measurement accuracy or reproducibility. The pressing force at this time is the load-dependent data shown in FIG. As is clear from measuring the electrostatic capacity by supplying a current and changing the pressing force), the effect does not change even if it is too large, and it is about 10
If it is g / cm ² or more, there is no practical problem.

The parallel electrode 10 may be formed by arranging linear electrodes in parallel at a predetermined interval. However, since a larger value of the electrostatic parameter can be obtained as the electrode length becomes longer, measurement accuracy is improved. It is preferable to make the electrode length as long as possible. For example, in an environment of 23 ° C and humidity of 65%, Yellow
w Distance between electrodes 150 with color thermosensitive paper and different electrode length
When the capacitance was measured by supplying an alternating current of 1 MHz to the parallel electrodes of μm, as shown in FIG. 3, when the electrode length was 1 cm, the measured value was about several pF, but the electrode length was 10pF at 30cm, 15pF at 100cm,
It increased to 45 pF at 700 cm, and the parallel electrode 10
It was confirmed that the capacitance value increases with the increase of the electrode length.

However, if the electrode length becomes long, the area of the electrode also becomes large, and the measurement value is fed back as a printing condition, so that it becomes difficult to install it in an image forming apparatus such as a printer, or it becomes difficult to install it. Considering measurement performance and the like, there is no practical problem if the electrode length is 1 cm or more, preferably 10 cm or more. As shown in FIG. 4, for example, the parallel electrode 10 has a shape in which a pair of comb-shaped electrodes are opposed to each other ((a) in FIG. 4), or a pair of rectangular-wave electrodes are offset in the amplitude axis direction and overlapped. By arranging and arranging in such a shape ((b) in the figure), the electrode length can be increased with a small occupied area. However, in this case, adjacent electrodes must be formed with the same interval.

In measuring electrostatic parameters,
The gap width of the parallel electrode 10 is also a large parameter,
It is preferable to set and measure the optimum gap width. To do so, first take out the thermosensitive recording paper whose humidity is adjusted in high humidity and low humidity into the measurement environment, measure the electrostatic parameters after a lapse of a predetermined time using various parallel electrodes with different gap widths, and The ratio of the measured values of humidity and low humidity thermal recording paper is plotted against the gap width to create a gap width vs. electrostatic parameter ratio curve. On the other hand, actual printing is performed on high- and low-humidity thermal recording papers, the sensitivity of the thermal recording papers is measured from the print density, and the sensitivity ratio of both thermal recording papers is calculated. The optimum gap width is obtained by substituting it into the electrostatic parameter ratio of the electric parameter ratio curve to find the corresponding gap width.

For example, FIG. 5 shows high humidity (23 ° C., humidity 8).
(0%) and low humidity (23 ° C, humidity 15%) wet-adjusted Yellow color thermosensitive paper was taken out to a measurement environment of 23 ° C, humidity 60%, and the gap width was 40 μm, 70 μm.
m, 150 μm and 300 μm using parallel electrodes
It is a gap width-capacitance ratio curve in which the capacitance after 0 minutes is measured and the capacitance ratio is plotted against the gap width. By substituting the sensitivity ratio (1.1) obtained by measuring the print density of the yellow color thermal paper having the same high humidity and low humidity, the gap width corresponding to the value is 150 μm.
Is obtained.

The parallel electrode 10 as described above is formed into a thin film by forming a known conductive material such as copper, tin or silver alloy on a substrate such as glass epoxy by a method such as vapor deposition, plating or coating and then predetermined. It is obtained by patterning by etching so as to have a distance between electrodes. An alternating current is supplied from the alternating current generating means 20 to the parallel electrodes 10.
The alternating current is convenient because an alternating current is convenient in terms of handleability, but may be a pulse current. Further, the frequency of the supply current is not particularly limited, and a high frequency alternating current of about tens of thousands Hz to several MHz can be used.

An alternating current is supplied to the parallel electrodes 10 to generate an electric field between the electrodes, and the electrostatic parameter measuring means 30 measures the electrostatic parameters of the thermal recording paper 50. The electrostatic parameter measuring means 30 comprises a known LCR circuit,
In addition to the electrostatic capacitance, various electrostatic parameters such as dielectric loss, Q value, L (reactance), R (resistance) and Z (impedance) can be measured.

The controller 40 is used to set the gap width, supply the alternating current, record the measured value of the electrostatic parameter, and process the data. Further, it is generally known that the higher the water content of the thermal recording paper, the higher the density of the characters or images printed. Therefore, the electrostatic parameters and the print density of the thermosensitive recording paper placed under various humidities are measured to create a curve of the electrostatic parameter vs. the print density (sensitivity), and the thermosensitive recording paper used immediately before the printing is started. It is possible to form a high-quality image by measuring the electrostatic parameters of the above and obtaining the corresponding sensitivity from the same curve, and adjusting the supply voltage to the print head and the printing speed based on this sensitivity before printing. it can.

In this case, since the printing density differs depending on the type of the thermal recording paper, similar electrostatic parameter-printing density curves are prepared for various thermal recording papers, and the same curve corresponding to the thermal recording paper used is prepared. You have to choose. Further, since the optimum gap width changes depending on the type of thermal recording paper, it is necessary to perform the series of operations for setting the above-mentioned gap width and set the optimum gap width before performing the measurement.

By thus measuring the electrostatic parameter and feeding it back to the printing conditions of the image forming apparatus such as a printer, a high quality image can be obtained. By the way, the electric field strength formed by the parallel electrodes is
The electric field distribution decreases in proportion to the square of the distance from the electrodes, and the electric field distribution thereof exhibits a cylindrical shape having a diameter between adjacent electrodes. Therefore, when the electrostatic parameter is measured using the parallel electrodes, the actual measured value is the integrated value of the electrostatic parameter from the surface of the measuring object to a depth approximately equal to the gap width.

Therefore, the electrostatic parameter distribution in the thickness direction of the thermosensitive recording paper can be obtained by continuously changing and measuring the gap width of the parallel electrodes. The electrostatic parameter distribution measuring means and measuring method will be described with reference to FIG. 1 again. The basic configuration is a configuration in which an electrode moving means is added to the surface electrostatic parameter measuring means.

As a mechanism for continuously changing the gap width of the parallel electrodes 10, a pair of electrodes forming the parallel electrodes 10 are formed on different substrates, and these electrode substrates are attached to a moving stage (not shown). As a result, it can be made movable. This moving stage is driven by using various motors. The motor used is not particularly limited, but it is preferable that the position control is easy and the electrode substrate can be driven at a fine pitch, such as a pulse motor or a D motor.
A C motor, a piezo actuator, etc. can be used. Further, the electrostatic parameters of the thermal recording paper 50 can be three-dimensionally measured by moving the electrodes in the vertical direction in addition to the parallel movement.

Further, a fine electrostatic parameter distribution can be obtained by making the change amount of the gap width smaller and measuring it. For example, when the electrodes are moved using a pulse motor, the motor is rotated every pulse and the electrostatic parameter is measured each time, so that a more precise electrostatic parameter distribution can be obtained. The gap width can be continuously changed from a state where the pair of electrodes are in contact with each other, that is, the gap width is zero. The upper limit can be up to the size of the surface of the thermal recording paper 50 to be measured, but in the measurement of the electrostatic parameter distribution in the thickness direction of the thermal recording paper 50, up to the thickness (about several hundreds of μm). It is enough to widen the gap width.

At the time of measurement, the thermal recording paper 50 and the parallel electrode 10 may be in contact with each other, or may be in a state of facing each other with a certain distance therebetween. The thermal recording paper 50
When the measurement is performed by contacting the parallel electrode 10 with the parallel electrode 10, it is preferable to place a weight of about 10 g / cm ² on the parallel electrode 10 for the above-mentioned reason so as to bring them into close contact with each other uniformly. Further, the shape of the parallel electrode 10 is not limited, but it is preferable to use a needle-shaped electrode to make a point contact with the surface of the thermal recording paper 50 or to separate it by a predetermined distance.

As the controller 40, the alternating current generating means 20, and the electrostatic parameter measuring means 30, those used for the surface electrostatic parameter measurement can be used as they are. Therefore, the measured electrostatic parameters are also the same, and various electrostatic parameters such as electrostatic capacitance, dielectric loss, Q value, L (reactance), R (resistance), and Z (impedance) are measured.

In the measurement, first, the thermosensitive recording paper 50 is placed on the table 6
Blank data is measured in the same manner as the procedure described later in a state where the blank data is not placed. This blank value is for removing the disturbance factor (noise) from the actually obtained measured value, and the measured value is processed by subtracting this blank value. Next, the thermal recording paper 50 is placed on the table 6
Then, the parallel electrode 10 is moved by a minute distance, for example, one pulse of the motor by driving the moving stage. After the movement, the parallel electrodes 10 are brought into contact with the thermal recording paper 50 (or separated from each other by a certain distance), and an alternating current is supplied from the alternating current generating means 20 to measure the electrostatic parameter.

Since the measured electrostatic parameter is an integrated value from the surface to the depth corresponding to the gap width, the measured value at each depth is obtained by taking the difference from the measured value at a narrower gap width. To be Further, since the electric field strength decreases in proportion to the square of the gap width, the measured value decreases as the depth increases. Therefore, the value of the gap width is multiplied by the measured value at that time and weighted for processing.

By repeating such electrode movement and measurement until the gap width becomes equal to or larger than the thickness of the thermosensitive recording paper 50, the electrostatic parameter distribution in the thickness direction of the thermosensitive recording paper 50 can be obtained.

[0031]

EXAMPLES A water content sensor according to the present invention will be described in more detail based on examples. However, this embodiment is an example,
It is not limited to this. [Example 1] Prior to the actual measurement, the capacitance and sensitivity of the thermal paper whose humidity was adjusted at high humidity (23 ° C, 80% humidity) and low humidity (23 ° C, 15% humidity) were measured, and the static value was measured. The optimum gap width of 150 μm was obtained from the capacitance ratio and the sensitivity ratio.
Therefore, 40 pieces with a total length of 80 m are mounted on the glass epoxy substrate.
A pair of comb-shaped electrodes made of copper electrodes with a gap width of 150
The electrodes were arranged in the same shape as in FIG.

Then, the thermal paper whose humidity was adjusted in the same manner as above was taken out to a measurement environment (temperature 23 ° C., humidity 65%), the parallel electrodes were placed thereon, and further 10 g / cm 2 was placed thereon.
^{With a} flat weight placed so that a pressing force of ² is applied, an AC waveform with a frequency of 1 MHz is supplied, and a capacitance and a capacitance immediately after the electrode placement is performed by using a Hewlett Packard 4284A type LCR meter. The change with time of the dielectric loss was measured.

In parallel with the measurement of capacitance and dielectric loss,
Print on the same thermal paper under the conditions of head temperature of 30 ° C. and voltage of 27 V, and use an X-rite measuring device (Grandville).
The print density was measured by using a product manufactured by K.K. The obtained capacitance vs. print density curve is shown in FIG. 6, and the dielectric loss vs. print density curve is shown in FIG. 7, respectively. As is clear from these figures, there is a correlation between the print density, that is, the sensitivity of the thermal recording paper and the electrostatic parameter.

Thermal printer (Fuji Photo Film Co., Ltd .: FT
I210) and fed back to a high water content thermal recording paper with a water content of 10% and a low water content thermal recording paper with a water content of 3%, both thermal recording papers have good gradation and high quality images are obtained. Was given. [Comparative Example] The same humidity-sensitive thermal paper as in Example 1 was used.
The plate was sandwiched by a pair of flat plate copper electrodes, an AC waveform of 1 V was applied, and the change in capacitance with time was measured.

When the measured values were plotted against the print density data of Example 1 to prepare a capacitance vs. print density curve, no correlation was observed. Example 2 A glass plate was coated with a solution (large dielectric constant) in which 0.25 g of CR-C (manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in 5 cc of fluoroalcohol as a first layer, and a second layer was formed thereon. A solution (small dielectric constant) of 0.125 g of Sumilizer (Sumitomo Chemical Co., Ltd.) dissolved in 5 cc of 1-methoxy-2-propanol was applied, and the same solution as the first layer was applied as the third layer to induce dielectric. Three-layer structure samples with different rates were prepared. A pulse stage (PS-30 of Chuo Seiki Co., Ltd.
E) Place it on the controller (CPC-3, Chuo Seiki Co., Ltd.)
The capacitance was measured by supplying an AC waveform with a frequency of 100 kHz while widening the interval between the strip parallel electrodes by 2 μm by DN). The measurement result is shown in FIG. Since the value of the electrostatic capacitance (C) becomes smaller as the gap width (W) becomes larger, data processing was performed by multiplying the rate of change of the electrostatic capacitance by the gap width at the time of measurement. In the figure, peaks (a) and (b) correspond to the first and third layers having a large dielectric constant, and are located between the surface of the sample and about 30 μm and at a position where the distance from the surface is about 60 μm. It can be seen that these layers are present in the range from 1 to 80 μm. Further, it can be seen that the region having a larger gap width than that is the support.

In the above embodiment, the capacitance and the dielectric loss were measured as the electrostatic parameters, but not limited to these, other electrostatic parameters such as Q value, L (reactance), R (resistance) and Z. (Impedance) and the like can be measured, and similar processing can be performed based on these values. Further, the measurement object is not limited to the thermal recording paper, and the water content of various materials can be measured.

[0037]

As described above, according to the water content sensor of the present invention, the water content of only the surface of the object to be measured can be measured, and the water content distribution in the thickness direction can also be measured. Moreover, in that method, the gap width may be simply set or the gap width may be continuously changed, so that the measurement can be performed extremely easily.

Further, in order to perform measurement using an alternating current,
It is possible to perform the measurement without affecting the material of the measurement object. Further, since water content data only for the surface portion, which cannot be obtained by the conventional sensor, can be obtained, by feeding back this data as the printing condition of the image forming apparatus such as a printer, more proper printing adjustment can be performed. it can.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a water content sensor according to the present invention.

FIG. 2 is a diagram for explaining the influence of electrode pressing force when the water content sensor according to the present invention is used.

FIG. 3 is a diagram for explaining the influence of the electrode length when the water content sensor according to the present invention is used.

FIG. 4 is a diagram showing an example of an electrode shape of a water content sensor according to the present invention.

FIG. 5 is a diagram for explaining an optimum gap width when the water content sensor according to the present invention is used.

6 is a capacitance vs. print density curve obtained in Example 1. FIG.

7 is a dielectric loss vs. print density curve obtained in Example 1. FIG.

8 is a water content distribution obtained in Example 2. FIG.

[Explanation of symbols]

 1 Water Content Sensor 10 Parallel Electrode 20 Alternating Current Generating Means 30 Electrostatic Parameter Measuring Means 40 Controller 50 Thermosensitive Recording Paper 60 Table

Claims (3)

[Claims] 1. An electrostatic parameter of a surface of a measurement object is measured by supplying an alternating current to the parallel electrode in a state where the parallel electrode is in contact with or separated from the same surface of the measurement object. Moisture content sensor. 2. The measured electrostatic parameter is fed back to the printing condition of the image forming apparatus.
The water content sensor described in 1. 3. An electrostatic parameter in the depth direction of a measurement object by supplying an alternating current while changing the distance between the parallel electrodes in a state where the parallel electrodes are in contact with or separated from the same surface of the measurement object. A water content sensor characterized by measuring.