JP3133862B2 - Measurement method of moisture content of recording paper - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the water content of recording paper.
It relates Law, measured in particular water content of a suitable recording paper for the measurement of the measurement as well as the distribution in the depth direction of the water content of the water content of the thermal recording paper surface
Related to the setting method .

[0002]

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

[0003] Incidentally, it is known that the sensitivity characteristics of the thermosensitive recording paper vary depending on the moisture content of the thermosensitive coloring layer in addition to the type of the thermosensitive material constituting the thermosensitive coloring layer. Since the moisture content of the thermosensitive coloring layer also changes depending on the moisture permeating from the support, the sensitivity characteristics of the thermosensitive recording paper also change depending on the moisture content of the support. Further, if the moisture content in the thickness direction of the heat-sensitive coloring layer or the support is non-uniform, the heat-sensitive recording paper is deformed such as curving or waving, causing paper jam in the paper transport path.

As described above, there is a close relationship between the heat-sensitive recording paper and the water content, and the heat-sensitive coloring layer (the surface of the heat-sensitive recording paper) contains water to improve the image quality of the formed image and to stably convey the paper. It is necessary to accurately determine the water content or the moisture content distribution in the thickness direction including the support. Conventionally, various methods have been proposed for measuring the moisture content on the surface of a thermosensitive recording paper. For example, there is a method of obtaining the water content by using the fact that the electrical resistivity changes depending on the amount of water. In this method, a main electrode and a counter electrode are brought into contact with the surface of a thermosensitive recording paper and a guard electrode is brought into contact with the other surface by using three concentric electrodes, and a DC voltage is applied to these electrodes to flow at that time. In this method, the current value is measured to determine the surface resistivity, and the 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 has been determined in advance.

[0005] Further, water has a large relative dielectric constant.
A change in the amount of water can be treated as a change in capacitance. The method for measuring the capacitance is such that the thermosensitive recording paper is sandwiched between two opposing flat plate electrodes, or the thermosensitive recording paper is inserted between two flat plate electrodes arranged to face each other at a predetermined interval. The capacitance is determined from the potential difference generated by applying an AC voltage to the electrode, and the moisture content on the surface of the thermosensitive recording paper corresponding to the measured capacitance is determined from a calibration curve in which the relationship between the water content and the capacitance is determined in advance. It is a method of calculating the rate.

In addition to the above-described electrical measurement method, there is a method of measuring the water content using an infrared sensor. This method irradiates infrared recording paper and measures the amount of reflected light to determine the infrared absorptance of the thermal recording paper. This is to obtain the water content of the surface. In addition,
Assuming that the thermal recording paper and the surrounding humidity are in equilibrium,
The method of estimating the water content from the humidity near the thermosensitive recording paper, the method of calculating the water content from the amount of warpage of the thermosensitive recording paper, and the method of obtaining the water content by measuring the friction coefficient, etc. Is measured.

[0007]

As described above, the moisture content of the heat-sensitive coloring layer and the support affects the sensitivity characteristics and shape of the heat-sensitive recording paper and is a factor that causes deterioration of image quality and paper jam. ing. Therefore, it is desired that the moisture content on the surface of the thermosensitive recording paper and the moisture content distribution in the thickness direction thereof are obtained as accurately as possible, and the values are fed back to the image forming conditions as correction parameters.

However, of the above methods for measuring the moisture content, the method of measuring the humidity near the thermosensitive recording paper, the amount of warpage of the thermosensitive recording paper, and the coefficient of friction to determine the moisture content is not preferable because of poor reproducibility and accuracy. . Further, in the method using the infrared sensor, the entire device in which the sensor components are expensive is expensive. The method of obtaining the moisture content from the surface electrical resistivity and capacitance is an electrical measurement, which has the advantage of being excellent in reproducibility and measurement accuracy, and of being simple in the structure of the measurement device and easy in the measurement method. However, when measuring the surface electrical resistivity, a high applied voltage is required.When measuring the electrostatic capacitance, the thermosensitive recording paper is sandwiched between the electrodes or inserted between the electrodes. Therefore, the moisture content of the entire thermosensitive recording paper including the support as well as the intended thermosensitive coloring layer is measured.

As described above, a method for accurately measuring the moisture content of the thermosensitive coloring layer or the moisture content distribution of the thermosensitive recording paper including the support has not yet been established, and no apparatus for this purpose has been developed. The present invention has been made in view of the above circumstances, it is possible to accurately measure the moisture content distribution in the thickness direction of the thermosensitive recording paper including the support and the moisture content of the thermosensitive coloring layer of the thermosensitive recording paper, In addition, it is an object of the present invention to provide a method for measuring the water content of recording paper capable of preventing deterioration of an image and paper jam by feeding a measurement result back to a printing condition of an image forming apparatus such as a printer. .

[0010]

Means for Solving the Problems In order to achieve the above object, the present invention provides a method in which a parallel electrode is brought into contact with the same surface of a recording paper to be measured by applying a pressing force of 10 g / cm ² or more. the electrostatic parameters of the recording paper surface is measured by supplying an alternating current to the parallel electrodes was the electrostatic parameters to be fed back to the printing conditions of the image forming apparatus using the recording paper.

Further, in order to achieve the same object, the present invention provides an alternating current supplied to the parallel electrodes while changing the interval between the parallel electrodes (hereinafter, referred to as a gap width), thereby providing a recording medium in the depth direction of the recording paper. Like measuring electrostatic parameters
I made it. According to the method 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 in the depth direction of the recording paper can be measured with a small voltage. Can be.

Further, by feeding back the measured electrostatic parameters to the printing conditions of an image forming apparatus such as a printer, a change in sensitivity and a change in shape due to the water content of the thermal recording paper can be suppressed, and appropriate correction can be performed. As a result, it is possible to perform stable image formation while preventing deterioration in image quality and paper jam. Furthermore, since the gap width corresponds to the measurement depth, by supplying an alternating current while changing the gap width, it is possible to continuously measure the electrostatic parameters in the thickness direction of the thermosensitive recording paper including the support. And the water content distribution can be determined.

The method for measuring the water content of the recording paper according to the present invention is described below.
The moisture content sensor used in the method will be described with reference to the accompanying drawings. As shown in FIG. 1, the moisture content sensor 1
Is composed of 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 (recording paper) 50 is placed on the table 60 such that the thermosensitive coloring layer faces the parallel electrodes 10. At this time, the thermal recording paper 5
0 and the parallel electrode 10 may be in contact with each other, or may be in a state where they are opposed to each other with a certain distance therebetween.
When the thermal 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 entire parallel electrode 10 so that the two are uniformly pressed. By bringing them into close contact, a larger value of the electrostatic parameter can be obtained, which is preferable in terms of measurement accuracy and reproducibility. The pressing force at this time was determined by the load-dependent data shown in FIG. 2 (Yellow-colored thermal paper was placed in an environment of 23 ° C. and 65% humidity, 1 MHz alternating current was applied to a parallel electrode having an effective electrode length of 6.3 m and a distance between electrodes of 150 μm). As is clear from the measurement of the capacitance by supplying a current and changing the pressing force), even if it is too large, the effect does not change.
There is no practical problem if the contact is performed by applying a pressing force of g / cm ² or more.

The parallel electrode 10 may be formed by arranging linear electrodes in parallel at a predetermined interval. However, the longer the electrode length, the larger the value of the electrostatic parameter can be obtained. It is preferable to make the electrode length as long as possible. For example, in an environment of 23 ° C. and 65% humidity, Yellow
w Place the color-sensitive thermal paper and change the electrode length.
When an alternating current of 1 MHz was supplied to the μm parallel electrode and the capacitance was measured, as shown in FIG. 3, when the electrode length was 1 cm, the measurement value was about several pF, but the electrode length was 10pF at 30cm, 15pF at 100cm,
At 700 cm, it increased to 45 pF, and the parallel electrode 10
It was recognized that the capacitance value increased as the electrode length increased.

However, as the electrode length increases, the area of the electrode also increases, which makes it difficult to install the device in a layer forming apparatus such as a printer or the like in order to feed back measured values as printing conditions. 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. For example, as shown in FIG. 4, the parallel electrode 10 has a shape in which a pair of comb-shaped electrodes are opposed to each other (FIG. 4A), or a pair of rectangular wave-shaped electrodes are shifted and superimposed in the amplitude axis direction. By arranging and arranging them in a simple shape (FIG. 2B), the electrode length can be increased with a small occupied area. However, in this case, adjacent electrodes must be formed so as to be at the same interval.

In measuring electrostatic parameters,
The gap width of the parallel electrode 10 is also a large parameter,
It is preferable to measure by setting the optimum gap width. For this purpose, first, the thermosensitive recording paper whose humidity has been adjusted in the high humidity and the low humidity is taken out to the measurement environment, and the electrostatic parameters after a lapse of a predetermined time have been measured using various parallel electrodes having different gap widths. The ratio of the measured values of the humidity and low humidity thermosensitive recording paper is plotted against the gap width to create a gap width to electrostatic parameter ratio curve. On the other hand, the actual printing was performed on the high- and low-humidity thermosensitive recording paper, the sensitivity of the thermosensitive recording paper was measured from the print density, and the sensitivity ratio of the two thermosensitive recording papers was calculated. The corresponding gap width is obtained by substituting into the electrostatic parameter ratio of the electric parameter ratio curve, and is determined as the optimum gap width.

For example, FIG. 5 shows a state in a high humidity (23 ° C., humidity 8
0%) and a yellow-colored thermal paper wet-adjusted in low humidity (23 ° C., 15% humidity) were taken out to a measurement environment of 23 ° C. and 60% humidity, and the gap width was 40 μm and 70 μm.
m, 150 μm and 300 μm parallel electrodes
It is a gap width-capacitance ratio curve obtained by measuring the capacitance after 0 minutes and plotting the capacitance ratio against the gap width. The capacitance ratio of the gap width-capacitance ratio curve is shown. Is substituted for the sensitivity ratio (1.1) obtained by measuring the print density of the similar high- and low-humidity Yellow-colored thermal paper, to obtain a gap width of 150 μm corresponding to that value.
Is obtained.

The parallel electrode 10 as described above is formed by forming a known conductive material, for example, copper, tin, or silver alloy on a substrate such as glass epoxy into a thin film by a method such as vapor deposition, plating, or coating. Is obtained by patterning by etching such that the distance between the electrodes becomes the above. The alternating current is supplied from the alternating current generating means 20 to the parallel electrodes 10.
As the alternating current, an alternating current is convenient in terms of handleability, but a pulse current may be used. 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 of the thermosensitive recording paper 50 is measured by the electrostatic parameter measuring means 30. This electrostatic parameter measuring means 30 is composed of a known LCR circuit,
In addition to the capacitance, various electrostatic parameters such as dielectric loss, Q value, L (reactance), R (resistance), and Z (impedance) can be measured.

The setting of the gap width, the supply of the alternating current, the recording of the measured values of the electrostatic parameters, the data processing, and the like are performed by the controller 40. It is generally known that the higher the moisture content of thermosensitive recording paper, the higher the density of printed characters and images. Therefore, the electrostatic parameters and the print density of the thermal recording paper placed under various humidity are measured to prepare a curve of the electrostatic parameters versus the print density (sensitivity), and the thermal recording paper used immediately before printing is started. By measuring the electrostatic parameters of the corresponding curve and determining the corresponding sensitivity from the same curve, the printing is performed by adjusting the supply voltage to the print head, the printing speed, and the like based on the sensitivity, thereby forming a high-quality image. it can.

In this case, since the print density varies depending on the type of the thermal recording paper, similar electrostatic parameter versus print density curves are prepared for various thermal recording papers, and the same curve corresponding to the used thermal recording paper is created. Must choose. In addition, since the optimum gap width changes depending on the type of thermal recording paper, it is necessary to perform a series of operations for setting the gap width and set the optimum gap width before measurement.

As described above, a high quality image can be obtained by measuring the electrostatic parameter and feeding it back to the printing conditions of an image forming apparatus such as a printer. By the way, the electric field strength formed by the parallel electrodes is
The electric field distribution generally decreases in proportion to the square of the distance from the electrode, and its electric field distribution shows a cylindrical shape whose diameter is the distance between adjacent electrodes. Therefore, when measuring the electrostatic parameter using the parallel electrodes, the actual measured value is the integrated value of the electrostatic parameter from the surface of the measurement object to a depth substantially equal to the gap width.

Therefore, by measuring the gap width of the parallel electrode continuously, it is possible to obtain the electrostatic parameter distribution in the thickness direction of the thermal recording paper. The means and method for measuring the electrostatic parameter distribution will be described again with reference to FIG. The basic configuration is a configuration in which an electrode moving unit is added to the surface electrostatic parameter measuring unit.

As a mechanism for continuously changing the gap width of the parallel electrode 10, a pair of electrodes constituting the parallel electrode 10 are formed on different substrates, respectively, and these electrode substrates are mounted on a moving stage (not shown). Thereby, it can be made movable. This moving stage is driven using various motors. The motor to be used is not particularly limited, but is preferably a motor that can easily control the position and can drive the electrode substrate at a fine pitch.
A C motor, a piezo actuator, or the like can be used. In addition, by moving the electrodes in the vertical direction in addition to the parallel movement, the electrostatic parameters of the thermosensitive recording paper 50 can be measured three-dimensionally.

Further, by measuring the change amount of the gap width more minutely, a precise electrostatic parameter distribution can be obtained. For example, when the electrodes are moved using a pulse motor, a more precise distribution of electrostatic parameters can be obtained by rotating the motor for each pulse and measuring the electrostatic parameters each time. The gap width can be continuously changed from a state in which 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 paper surface of the thermal recording paper 50 to be measured. However, in the measurement of the electrostatic parameter distribution in the thickness direction of the thermal recording paper 50, the upper limit is about the thickness (about several hundred μm). It is sufficient to increase the gap width.

At the time of measurement, the thermosensitive recording paper 50 and the parallel electrode 10 may be in contact with each other, or may be in a state where they face each other at a predetermined distance. In addition, the thermal recording paper 50
When the measurement is carried out by contacting with the parallel electrode 10, it is preferable that a weight of about 10 g / cm ² is placed on the parallel electrode 10 and the two are evenly adhered to each other for the above-mentioned reason. Although the shape of the parallel electrode 10 is not limited, it is preferable that the measurement is performed by making a point contact with the surface of the thermosensitive recording paper 50 using a needle-shaped electrode or by separating the surface by a predetermined distance.

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

First, the thermosensitive recording paper 50 was placed on the table 6
In a state where the blank is not set to 0, the data of the blank is measured in the same manner as the procedure described later. The blank value is for removing a disturbance factor (noise) from the actually obtained measured value, and the measured value is processed by subtracting the blank value. Next, the thermal recording paper 50 is placed on the table 6.
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 electrode 10 is brought into contact with the thermal recording paper 50 (or separated 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 integral 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. Can be Also, since the electric field intensity 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 greater than the thickness of the thermal recording paper 50, an electrostatic parameter distribution in the thickness direction of the thermal recording paper 50 can be obtained.

[0031]

[Example 1]

Prior to the actual measurement, the capacitance and sensitivity of the thermosensitive paper whose humidity was adjusted at high humidity (23 ° C., humidity 80%) and low humidity (23 ° C., humidity 15%) were measured, and the capacitance ratio and sensitivity were measured. The optimum gap width of 150 μm was obtained from the ratio. Then, a pair of comb-shaped electrodes composed of 40 copper electrodes with a total length of 80 mm on a glass epoxy substrate were arranged in the same shape as in FIG. 2A so as to have a gap width of 150 μm to form parallel electrodes.

Next, the thermosensitive paper whose humidity was adjusted in the same manner as described above was taken out in a measurement environment (temperature: 23 ° C., humidity: 65%), and the parallel electrode was placed thereon, and 10 g / cm was further placed thereon.
^In the state where the flat weight is placed so as to have a pressing force of ² , an AC waveform having a frequency of 1 MHz is supplied, and the capacitance and the capacitance immediately after the placement of the electrode using a 4284A type LCR meter manufactured by Hewlett-Packard Co. The change with time of the dielectric loss was measured.

In parallel with the measurement of capacitance and dielectric loss,
Printing was performed on the same thermal paper under the conditions of a head temperature of 30 ° C. and a voltage of 27 V, and an X-rite measuring device (Grandville) was used.
Print density). FIG. 6 shows the obtained capacitance versus print density curve, and FIG. 7 shows the dielectric loss versus print density curve. As is apparent from these figures, a correlation is recognized between the printing density, that is, the sensitivity of the thermal recording paper and the electrostatic parameter.

A thermal printer (manufactured by Fuji Photo Film Co., Ltd .: FT)
I210) was fed back and printed on a high-moisture thermal recording paper with a water content of 10% and a low-moisture thermal recording paper with a water content of 3%. As a result, high-quality images with good gradation were obtained for both thermosensitive recording papers. Was done. [Comparative Example] The same thermosensitive paper as in Example 1 was subjected to humidity
An AC waveform of 1 V was applied while being sandwiched between two flat copper electrodes, and the change over time in the capacitance was measured.

When the measured values were plotted against the print density data of Example 1 to create a capacitance vs. print density curve, no correlation was observed. [Example 2] 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 was applied as a first layer on a glass plate, and a second layer was formed thereon. A solution (small dielectric constant) prepared by dissolving 0.125 g of Sumilizer (manufactured by Sumitomo Chemical Co., Ltd.) in 5 cc of 1-methoxy-2-propanol was applied, and the same solution as the first layer was applied as a third layer to obtain a dielectric. Samples having a three-layer structure with different rates were prepared. This sample is placed on a pulse stage (Chuo Seiki PS-30).
E) Placed on the controller, CPC-3 (Chuo Seiki Co., Ltd.)
While increasing the interval between the strip-shaped parallel electrodes by 2 μm by DN), an AC waveform having a frequency of 100 kHz was supplied to measure the capacitance. FIG. 8 shows the measurement results. Since the value of the capacitance (C) decreases as the gap width (W) increases, data processing was performed by multiplying the rate of change of the 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 at a position between about 30 μm from the surface of the sample and at a distance of about 60 μm from the surface. It can be seen that these layers exist in the range from about to 80 μm. Further, it can be seen that a region having a larger gap width is a support.

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

[0037]

The recording paper according to the present invention as described above
According to the water content measurement method described above, 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 be measured. In addition, since the method only requires setting the gap width or continuously changing the gap width, the measurement can be performed extremely easily.

Further, in order to measure using the alternating current,
Measurement can be performed without affecting the material of the measurement object. Furthermore, since moisture content data of only the surface portion, which cannot be obtained with the conventional sensor, can be obtained, by feeding back this data as printing conditions of an image forming apparatus such as a printer, more appropriate printing adjustment can be performed. it can.

[Brief description of the drawings]

FIG. 1 is used in the method for measuring the water content of recording paper according to the present invention.
FIG. 2 is a diagram showing a configuration of a moisture content sensor according to the first embodiment.

FIG. 2 is used in the method for measuring the water content of recording paper according to the present invention.
FIG. 6 is a diagram for explaining the effect of electrode pressing force when using a moisture content sensor.

FIG. 3 is used in the method for measuring the water content of recording paper according to the present invention.
FIG. 4 is a diagram for explaining the influence of the electrode length when using the moisture content sensor.

FIG. 4 is used in the method for measuring the water content of recording paper according to the present invention.
FIG. 4 is a diagram showing an example of an electrode shape of a moisture content sensor.

FIG. 5 is used in the method for measuring the water content of recording paper according to the present invention.
FIG. 5 is a diagram for explaining an optimum gap width when the moisture content sensor is used.

FIG. 6 is a plot of capacitance versus print density obtained in Example 1.

FIG. 7 is a plot of a dielectric loss versus a print density obtained in Example 1.

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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 27/00-27/24 G03G 15/00-15/36

Claims (2)

(57) [Claims] 1. An alternating current is supplied to a parallel electrode in a state where a parallel electrode is brought into contact with the same surface of a recording paper to be measured by applying a pressing force of 10 g / cm ² or more, thereby supplying the recording paper. electrostatic parameters of the surface was measured, measuring the moisture content of the recording paper, characterized by feeding back the electrostatic parameters to the printing conditions of the image forming apparatus using the recording paper
Fixed method . 2. The electrostatic parameter distribution in a depth direction of the recording paper is measured by supplying the alternating current to the parallel electrodes while changing the interval between the parallel electrodes. Measurement of water content of recording paper described
How .