JP4701032B2 - Print paper back-through evaluation method and evaluation apparatus - Google Patents

Description

  The present invention relates to a through-through evaluation method and an evaluation apparatus for quantitatively evaluating through-through of a printing paper, and relates to a through-through evaluation method and an evaluation apparatus having a high correlation with visual evaluation.

In recent years, printing paper has become thinner in the printing field. For example, in newsprint, but referred to as ultra-lightweight conventional 43 g / m ² product is in circulation, it is referred to as ultra lightweight basis weight 40 g / m ^2, it has replaced those thinner ing. On the other hand, in the field of commercial printed matter, lightweight, thin-type coated paper such as finely coated printing paper is mainly used for flyers. In most cases, printing is performed on both sides of the printing paper. However, since the printing paper is thin, the problem that the printing on the surface can be seen from the back side (back-through, print-through) is likely to occur.

  In general, the phenomenon of `` back-through '' refers to `` a phenomenon where the printing on the front side is visible from the back side '', and the causes are `` show-through '' and `` strike-through '' of the printing paper It is divided into. “Through-through” is a phenomenon in which printing on the front side of the printing paper can be seen through from the back side, and is mainly caused by insufficient opacity of the printing paper. Further, “penetration” is a phenomenon that occurs when the ink vehicle on the printing surface or the ink itself penetrates into the printing paper and reaches the back surface opposite to the printing surface.

Conventionally, opacity and printing opacity have been measured for the opacity of printing paper. Opacity (JIS P 8138) is an index indicating the degree to which light rays do not pass through the paper. The reflectance of the paper surface when a black plate is applied to the back of the same sheet of paper and when a white plate is applied. The ratio is calculated by the following formula (1) as a percentage.
Opacity (%) = 100 × R ₀ / R _∞ (1)
Here, R _{0 is} the reflectance of the sample when the backing black plate is used, and R _{∞ is} the reflectance of the sample when the backing white plate is used.

  The printing opacity (TAPPI T 425) is a value indicating the ratio of the reflectance when a black plate is applied to the back side of the test paper and when a large number of test papers are applied, expressed as a percentage.

On the other hand, as a conventional evaluation method for showthrough in printing paper, a simple printing machine such as an actual printing machine or an RI printing machine is used to actually print on printing paper and leave the printed matter for about one day. After fully drying, the part of the back side corresponding to the blank paper part of the printed surface that has not been printed (hereinafter, this part is referred to as "white part back side"), and the same printed The Y value of each tristimulus value XYZ is measured for a wide area of a part of the back side corresponding to the part (hereinafter, this part is referred to as “printed part back side” ), and is defined by the following formula (2). Evaluation has been carried out by calculating the strike-through value. The smaller the strikethrough value, the greater the strikethrough. Specifically, for example, using a color difference colorimeter (X-RITE918, manufactured by X-Rite Co., Ltd.) for a sample of 50 mm × 50 mm, Y value is measured about 10 points in a field of view with a diameter of 3.4 mm, and the average value is calculated. I was calculating.
Back-through value (%) = 100 × (Y value on the back side of the printed part) / (Y value on the back side of the blank page part) (2)

As another method, there is a method (Carlson's method) in which the reflectance of each of the back side of the blank paper portion and the back side of the print portion is measured and the strikethrough value defined by the following formula (3) is calculated and evaluated. However, this is essentially the same as the case of evaluating with the Y value.
Back-through value = log (reflectance of the back side of the blank page) −log (reflectance of the back side of the printing part) (3)

  Furthermore, as a technique for quantitatively evaluating printing unevenness, for example, a minute color difference photometer is installed on the XY stage so that it can be seen directly from above the paper surface, and the beam can be adjusted to a range of millimeters or less and the irradiation angle can be varied. The light source device can be installed obliquely above the XY stage, and the XY stage is configured to be movable at a plurality of pitches by a stepping motor, and the paper is continuously placed on the XY stage. The CIE color system tristimulus value XYZ, Hunter color system Lab value, and whiteness by blue reflectance are measured by a computer having software that performs statistical analysis on the output of the minute color difference photometer. The WB value is calculated for each continuous multipoint, and from the standard deviation, average, and coefficient of variation obtained from the WB value and the fluctuation range between the spectral curves of each continuous multipoint, white unevenness and printing unevenness are obtained. That blank, characterized in that the surface feeling was to measure, there is a quantitative measurement method of printing paper sensitive (see Patent Document 1).

Japanese Patent No. 2780657

  However, in the evaluation based on the opacity based on the above formula (1) and the evaluation of the printing opacity, it is possible to evaluate the “through” of the printing paper to some extent, but the “through” and the “immersion” It was impossible to accurately evaluate the “behind-the-shoulder” that occurs when “through” is combined. In addition, the method for calculating and evaluating the strike-through value by the above formulas (2) and (3) actually has a big problem that the correlation between the strike-through value and the visual evaluation of the strike-through is low. . Therefore, when verifying the case where the see-through value and the see-through evaluation do not match, the visual evaluation shows not only the brightness contrast represented by the above-described see-through value but also the back side of the printed surface. It was revealed that the evaluation was performed in consideration of the non-uniformity of the printed portion. In other words, the conventional evaluation method for the show-through is an evaluation using only the show-through value, and the variation in the show-through value is not taken into account, and therefore, it may not always coincide with the visual evaluation.

  In addition, in the quantitative measurement method of white paper and printing paper surface texture disclosed in Patent Document 1, white unevenness and printing unevenness are measured, and measurement is performed by reflected light from the surface of the printing surface. Cannot be done.

  As described above, under the present situation where printing paper is becoming thinner, the evaluation of the strikethrough is important for the suitability of the product, and the consumer evaluates the actual printed surface sensuously. The evaluation of omission also correlates well with visual evaluation, and establishment of a method capable of quantitative evaluation has been strongly desired.

In order to respond to such a request, the present inventor examined various optical characteristics such as opacity and whiteness when evaluating the back-through, and as a result, the tristimulus value of the color on the back side not printed. It has been found that measuring the Y value of XYZ is most correlated with visual evaluation. Therefore, the present inventor has studied to quantify the non-uniformity of the printed portion of the printed surface that can be seen through from the back side based on the above idea, and has completed the present invention.

  That is, the present invention can quantitatively evaluate the printing paper strike-through, and has a high correlation with the visual evaluation, and can reliably evaluate the strike-through. It is intended to provide a device.

As a technical means for achieving the above object, the printing paper back-through evaluation method according to the present invention quantifies the through-through phenomenon in which the printing applied to the printing surface of the printing paper affects the back surface corresponding to the printing portion. In the print paper back-through evaluation method for evaluation, a part of the back corresponding to the printing part on which the printing of the print surface is applied is applied to the back of the print paper that is used for the back-through evaluation. A measurement area is set on each of the printing part back surface and the white part back surface that is a part of the back surface corresponding to the blank paper part on which the printing surface is not printed , and the measurement area is divided into minute areas, The measurement light is irradiated into the minute area by a pair of light projecting means that are at an angle of about 45 ° with respect to the minute area and whose optical axes are located in substantially the same plane and whose optical path lengths are substantially equal. , Almost the midpoint of the measurement light irradiation position The reflected and scattered light of the measurement light is photographed by the photographing means having an optical axis in a direction substantially perpendicular to the minute region, and the tristimulus values XYZ of the color of the measurement image photographed by the photographing means are obtained. Then, the Y value of the tristimulus values XYZ is obtained, and the Y value obtained for all of the minute regions is evaluated using the strikethrough evaluation index calculated by applying the following formula (I). It is a feature.
Back-through evaluation index = 100 × (Y value average value on the back side of the printed part) / {(Average Y value on the back side of the blank paper part) × (Standard deviation of the Y value on the back side of the printed part)} (I)

  With respect to the back surface that has not been printed, the measurement light is irradiated to each of the minute areas on the back surface of the printing section and the back surface of the blank paper section, and an image of the reflected scattered light is captured by the imaging means. Using this captured image as a measurement image, tristimulus values XYZ of colors are obtained, and further, a Y value is obtained. A value obtained by substituting the average value of the obtained Y values and the standard deviation of the Y values on the back surface of the printed part into the formula (I) is used as a back-through evaluation index. Then, the strike-through evaluation is performed from the value of the strike-through evaluation index. The measurement light is incident on a certain range including the measurement point from the pair of light projecting means, and the optical axes of these light projecting means are located in substantially the same plane so that the measurement light is almost in the same plane. Incident light is incident from 45 °. That is, the pair of light projecting means are arranged at positions facing each other at 180 °, and irradiate the measurement light with an approximately equal illuminance at an incident angle of 45 °. In addition, the imaging unit captures an image of the reflected scattered light from directly above the midpoint of the measurement light irradiation position.

  Further, since the through-through evaluation by the through-through evaluation method of the printing paper needs to be relatively performed for each sample, it is necessary to perform the printing conditions at the time of offset printing at a constant. This printing condition is not particularly limited as long as it is a solid printing condition performed in normal printing. Further, one-color printing or multi-color overprinting may be used, but multi-color overprinting is preferable because variations in back-through are emphasized and comparison between samples is easy. As an example of the printing conditions in the present invention, a printing speed of 8000 sheets / hour, a printing pressure of 15/100 mm (thickness of the paper and blanket being crushed), and a solid ink with a blue ink stamping surface density of 1.2, red ink There are two-color offset printing, in which a solid printing with a printing surface density of 1.1 is overprinted. A sample printed under such a constant condition is used for evaluation of show-through. Furthermore, it is possible to print with a standardized pattern such as a test pattern.

Also, strike-through evaluation method of the printing paper according to the invention of claim 2, the range the measuring area of 1600 mm ² ～10000Mm ² as a measurement region, and the length of one side of the small area as 0.20mm~2.50mm It is characterized by being almost square.

The quality, including the optical properties of the paper, varies in the paper flow direction (MD direction) and in the direction orthogonal to the flow direction (CD direction) in the paper machine, and the paper texture that affects the back-through varies. Therefore, in order to accurately and quantitatively evaluate the strikethrough, take the widest possible measurement area on the back side of the printed surface, divide this into small areas, and set all the Y values in the small area. It is necessary to measure However, if the measurement region is excessively wide, it takes too much time to measure the Y value described later in the present invention, resulting in a problem of lack of simplicity and speed. These balance, measurement area is preferably 1600～10000Mm ^2, more preferably 1600~6400mm ^2, 1600~4900mm ² is more preferable. The shape of the measurement region is preferably a square or a rectangle. In the case of a rectangle, the length of the short side is required to be at least 40 mm.

  Further, the measurement area is divided into small areas each having a smaller square as a unit. The Y value is measured for all of the divided minute regions, and the average value of the Y values (hereinafter referred to as “Y value average value”) is calculated and used for the strikethrough evaluation. If the small area of the square is small, the number of Y-value data increases and the evaluation can be performed more accurately. However, the accuracy of the incidence of light from the light projecting means is required to be higher, and There is a risk that inconveniences such as an increase in data processing time may occur. For this reason, the length of one side of the minute region is preferably 0.20 to 2.5 mm, more preferably 0.20 to 2.0 mm, and still more preferably 0.20 to 1.0 mm. In the present invention, all the Y values of the divided minute regions are measured for the back surface of the printing part and the back surface of the blank paper part, and the Y value average value is calculated.

Also, strike-through evaluation method of the printing paper according to the invention of claim 3, said light projecting means, is characterized by using the light source by color for standard illuminant D ₆₅ measured.

A variety of light sources can be used as the light projecting means, but the correlativity with the visual evaluation is good in performing the back-through evaluation, and the tristimulus values XYZ can be reliably obtained from the photographed image. The color measurement standard illuminant D ₆₅ defined in JIS Z 8720 is used.

Also, strike-through evaluation device of the printing paper according to the invention of claim 4 relates to a rating system for implementing an evaluation method according to the invention of claim 1, for printing printing unit which has been subjected to the printing surface of the printing paper In a print paper back-through evaluation apparatus for quantitatively evaluating the back-through phenomenon affecting the corresponding back surface, a pair of light projecting means for irradiating measurement light at approximately 45 ° to the measurement surface of the sample paper. In addition, the optical axes of the pair of light projecting means are positioned in substantially the same plane, and the optical path lengths are arranged to be substantially equal to each other, and the reflected scattered light on the measurement surface irradiated by the light projecting means is photographed. An imaging means is disposed as an optical axis of the imaging means passing through a substantially midpoint of the measurement light irradiation position and substantially perpendicular to the measurement surface, and the color of the image taken by the imaging means is tristimulated A Y value among the tristimulus values XYZ is calculated while calculating the value XYZ Printing that is a part of the back surface corresponding to the printing portion on which the printing surface has been printed, with the back surface of the printing paper used for back-through evaluation being not printed as the measurement surface A measurement area is set on each of the back surface and the white part back surface that is a part of the back surface corresponding to the blank paper portion on which the printing surface is not printed , and the measurement region is divided into micro regions, and the micro regions A calculation means for obtaining a strike-through evaluation index is provided by applying the Y value obtained for all of the above to the following formula (I), and the strike-through evaluation is performed based on the strike-through evaluation index.
Back-through evaluation index = 100 × (Y value average value on the back side of the printed part) / {(Average Y value on the back side of the blank paper part) × (Standard deviation of the Y value on the back side of the printed part)} (I)

Also, strike-through evaluation device of the printing paper according to the invention of claim 5, the range the measuring area of 1600mm ² ~10000mm ² as a measurement region, and the length of one side of the small area as 0.20mm~2.50mm It is characterized by being almost square.

Also, strike-through evaluation device of the printing paper according to the invention of claim 6, said light projecting means, is characterized by using the light source by color for standard illuminant D ₆₅ measured.

According to the printing paper show-through evaluation method or evaluation apparatus according to the present invention, when evaluating the print paper show-through, a high correlation with the visual evaluation can be obtained. In addition, quantitative evaluation can be performed quickly, and the quality of the printed material can be determined quickly, simply and with good reproducibility. Furthermore , since the strikethrough can be evaluated quantitatively with good reproducibility, it is possible to accurately adjust the formation of the printing paper that is the cause of the strikethrough.

  Further, according to the print paper back-through evaluation method according to the invention of claim 2 or the print paper back-through evaluation apparatus according to the invention of claim 5, the correlation between the visual evaluation and the correlation is performed while the data is processed quickly. High strikethrough evaluation can be obtained.

  Further, according to the print paper back-through evaluation method according to the invention of claim 3 or the print paper back-through evaluation apparatus according to the invention of claim 6, the reflected scattered light can be reliably photographed. The tristimulus value XYZ of the color of the photographed image can be reliably acquired. Therefore, the arithmetic processing for acquiring the Y value can be performed simply, and desired data can be acquired with certainty.

  Hereinafter, based on the illustrated preferred embodiment, a print paper back-through evaluation method and an evaluation apparatus according to the present invention will be described in detail.

  FIG. 1 shows a schematic configuration of a print paper back-through evaluation apparatus according to the present invention. This evaluation apparatus includes a sample table 1 on which a sample S of a printing paper to be evaluated is stretched and placed, and a pair of light projecting means for irradiating the sample S placed on the sample table 1 with measurement light. 2. A photographing unit 3 for photographing reflected light from the sample S of the measuring light emitted from the light projecting unit 2 as a color image, and a predetermined process for a measurement image photographed in response to an output signal of the photographing unit 3 And an image analysis arithmetic device 4 that performs the above.

  The sample table 1 is movable in an XY direction orthogonal to the plane and a Z direction orthogonal to the plane, and is fixed at an arbitrary position. In the light projecting means 2, the respective optical axes 2a are located in substantially the same plane, the optical axis 2a is at an angle of approximately 45 ° with respect to the sample S, and the measurement emitted from the light projecting means 2 is further performed. The optical path lengths of light are provided to be substantially equal. In addition, the irradiation position of the measurement light of these light projecting means 2 is set to be in a minute region to be described later. The optical path lengths are made substantially equal because the light projecting means 2 allows the measurement light to enter the sample S with substantially the same illuminance. The optical path lengths may be different as long as the same illuminance can be secured. .

  The photographing means 3 is for photographing a color image of this minute region, and the optical axis 3a of the photographing optical system passes through substantially the midpoint of each irradiation position of the light projecting means 2 and is substantially orthogonal to the sample S. As the direction to do. That is, each optical axis 2a of the light projecting means 2 and the optical axis 3a of the photographing means 3 are located in substantially the same plane, and the light projecting means 2 is substantially symmetrical about the optical axis 3a. It is arranged.

  Data of the measurement image photographed by the photographing means 3 is sent to the image analysis calculation means 4, and the colors contained in the measurement image are XYZ defined by JIS Z 8701 (Publication CIE No. 15.2). The tristimulus value XYZ of the color system is obtained. Further, the Y value of the obtained tristimulus values XYZ is obtained, and arithmetic processing described later is performed.

  A description will be given of the back-through evaluation performed on the sample S by the printing paper back-through evaluation apparatus according to the present invention configured as described above.

As mentioned above, the optical characteristics of paper are affected by the orientation of the fiber, etc., and there are variations in the MD direction and CD direction of the paper machine, and the paper formation that affects the back-through varies. Then, it is preferable to divide the sample S into minute regions and evaluate the strike-through for each minute region. In addition, it is preferable to evaluate the entire paper area. However, excessively widening the region to be evaluated only increases the processing time in the image analysis calculation means 4 and increases the accuracy of data for evaluation. For this reason, it is necessary to ensure sufficient accuracy in performing the behind-the-scenes evaluation and not to increase the processing time. Therefore, results of investigation in consideration of the evaluation accuracy and processing time, as the measurement region to be acquired measurement image for the sample S, the area is preferably 1600～10000Mm ^2, more preferably 1600~6400mm ^2, 1600~ 4900 mm ² is more preferable. That is, the minimum area may be 1600 mm ² or more. The shape of the measurement region is preferably a square or a rectangle. In the case of a rectangle, the length of the short side is required to be at least 40 mm.

  The measurement area is further divided into minute areas. It is preferable that the minute area has such a size that, when irradiated with the measurement light from the light projecting means 2, it can be incident on the minute area and can take an image of reflected scattered light that can be sufficiently evaluated for see-through. For this reason, it is preferable that the minute region is substantially square and the length of one side is 0.20 to 2.5 mm, more preferably 0.20 to 2.0 mm, and further preferably 0.20 to 1.0 mm. That is, the minute region is a substantially square with one side having a minimum length of 0.20 mm.

  Then, the sample S is placed on the sample table 1 while maintaining the flat state with the unprinted back surface facing upward. The sample stage 1 is moved in the Z direction as necessary, and the measurement light from the light projecting means 2 is irradiated to an appropriate position, and the focus of the photographing means 3 photographs the reflected scattered light from the sample S. Adjust so that it is suitable for Note that not only the sample stage 1 but also the light projecting means 2 and the photographing means 3 can be moved in the respective optical axis directions, and the light projecting means 2 and the photographing means 3 are moved so that the positional relationship with the sample S is changed. It can also be a mechanism to adjust.

  The sample light placed on the sample stage 1 is irradiated with measurement light from the light projecting means 2. On the other hand, an image of the reflected scattered light reflected by the sample S by the photographing means 3 is photographed as a measurement image. This measurement image is acquired for all the minute regions. At this time, by moving the sample stage 1 in the X and Y directions, the micro regions are sequentially moved, and measurement images are acquired for the micro regions.

The measurement image acquired by the photographing unit 3 is sent to the image analysis calculation unit 4. The image analysis calculation means 4 obtains tristimulus values XYZ of the color of the measurement image for each minute region. Further, the Y value of the obtained tristimulus values XYZ is obtained for each minute region. By substituting the obtained Y value into the following equation (4), the strike-through value is calculated.
Strike through value (%)
= 100 × (Y value average value on the back side of the printed part) / (Y value average value on the back side of the blank paper part) (4)
Here, the Y value average value on the back surface of the printing part is a value obtained by averaging the measured values of all the Y values on the back surface of the printing part of the divided minute region, and the Y value average value on the back surface of the blank paper part is divided. It is an average value for all the Y values obtained for the back surface of the white paper portion of the minute region.

The inventors of the present invention diligently studied to establish a quantitative evaluation method capable of obtaining a high correlation with the visual evaluation of the strikethrough. As a result, when the value obtained by dividing the strikethrough value obtained by the above equation (4) by the standard deviation of the Y value measured for the minute area on the back surface of the printed portion is used as an index, it is extremely highly correlated with the strikethrough of visual evaluation. I found out. That is, the print paper show-through evaluation method of the present invention evaluates the show-through using the show-through evaluation index represented by the following formula (5).
Back-through evaluation index = (back-through value) / (standard deviation of Y value on the back side of the printed part) (5)
Here, the see-through value is a value calculated by the above formula (4), and the standard deviation of the Y value on the back surface of the printing unit is the standard deviation of the Y value measured for a minute region on the back surface of the printing unit.

From formula (4) and formula (5), the strikethrough evaluation index used in the present invention is expressed by the following formula.
Back-through evaluation index = 100 × (Y value average value on the back side of the printed part) / {(Average Y value on the back side of the blank paper part) × (Standard deviation of the Y value on the back side of the printed part)} (6)
The larger the value of this strike-through evaluation index, the less the breakthrough, and the smaller the value, the greater the breakthrough.

  In the above formula for calculating the strikethrough evaluation index, the standard deviation of the Y value is used. However, since the same result can be obtained as long as it represents the degree of dispersion with respect to the average value, instead of the standard deviation, for example, the average Other indicators such as deviation may be used. However, since the standard deviation is the most common, it is preferable to use the standard deviation.

  As described above, in the printing paper back-through evaluation method and evaluation apparatus according to the present invention, the back-through evaluation is quantitatively performed. Therefore, in order to perform comparison between samples, printing that is an evaluation target sample is performed. The printing performed on the paper needs to be performed under certain conditions. The printing conditions are not particularly limited as long as they are normal solid printing conditions. Further, either single color printing or multicolor overprinting may be used, but multicolor overprinting is preferable because variations in back-through are emphasized and comparison between samples is easy. Furthermore, as a print for performing the strike-through evaluation, it is also possible to print a pattern or the like by a test pattern.

Next, a description will be given of an embodiment in which the print paper back-through evaluation is performed by the print paper back-through evaluation apparatus. At this time, the colorimetric standard illuminant D ₆₅ was used as the light source of the light projecting means 2 and the image color difference meter finder TA (manufactured by Kurashiki Textile Co., Ltd.) was used as the photographing means 3.

  In addition, the offset printing conditions of the printing paper used as a sample were a two-color sheet-fed printing machine (Roland 202 Mann Roland), and the ink was Hi-Echo Indigo, Red L (Toyo Ink Co., Ltd.), Dampening Water As a 5% aqueous solution of isopropyl alcohol, the blanket is S7400 (manufactured by Kinyo), printing speed is 8000 sheets / hour (90m / min), printing pressure is 15 / 100mm, and the indigo ink printing surface density is 1.2. A solid printing with a printing surface density of 1.1 was overprinted.

  Eight types of high-quality printing papers were subjected to offset printing according to the above conditions and tested. The table | surface about the specification of these fine papers AH and the value of the conventional see-through evaluation by visual observation is shown in FIG. The print-through visual evaluation of the printed matter is shown by a five-step evaluation of 1 (inferior) to 5 (excellent). As shown in the figure, the high-quality printing paper D has the highest evaluation value, and the high-quality printing paper H is considered to cause the phenomenon of see-through.

The eight types of high-quality printing papers were evaluated for back-through by the back-through evaluation device for printing paper according to the present invention. For these high-quality printing papers A to H, the measurement area on the back side of the printing part and the back side of the white paper part is a square of 50 mm x 50 mm, and this is divided into square micro areas of 0.24 mm x 0.24 mm. The Y value was measured, and the average Y value on the back side of the printed part and the average Y value on the back side of the blank paper part were calculated. Based on the average value of both Y values, the strike-through value was obtained according to the above equation (4), and the standard deviation of the Y value on the back surface of the printed part was calculated. From these, the strike-through evaluation index was determined according to equation (5). Examples 2 to 4 and Comparative Examples to be described later are the results of the average Y value on the back surface of the printing unit, the average Y value on the back surface of the blank paper portion, the back-through value, the standard deviation of the Y value on the back surface of the printing portion, and the back-through evaluation index. This is shown in FIG. Furthermore, as shown in the correlation between the visual evaluation of the strike-through evaluation index and strike through, a list of the coefficient of determination R ² is a so-called contribution in FIG. In addition, a measurement example (high-quality printing paper H) in which the variation in the Y value on the back surface of the printing part was the largest among the tested printing papers is shown in FIG. 5, and a measurement example in which the variation in the Y value on the back surface of the printing part is the smallest ( A high-quality printing paper D) is shown in FIG.

The same measurement area as in Example 1 was performed in the same manner as in Example 1 except that the minute area was a square of 0.48 mm × 0.48 mm. The results of the average Y value on the back surface of the printed portion, the average Y value on the back surface of the blank paper portion, the back-through value, the standard deviation of the Y value on the back surface of the printed portion, and the back-through evaluation index are shown in the list of FIG. FIG. 4 shows the coefficient of determination R ² between the see-through evaluation index and the visual evaluation of the see-through.

The same measurement region as in Example 1 was performed in the same manner as in Example 1 except that the minute region was a 0.96 mm × 0.96 mm square. Fig. 3 shows the results of the Y value average value on the back side of the printed portion, the Y value average value on the back side of the blank paper portion, the back-through value, the standard deviation of the Y value on the back side of the printed portion, and the back-through evaluation index. the coefficient of determination R ² of the visual evaluation of spots in FIG. 4, shown respectively.

The same measurement area as in Example 1 was performed in the same manner as in Example 1 except that the minute area was a square of 1.92 mm × 1.92 mm. Fig. 3 shows the results of the Y value average value on the back side of the printed portion, the Y value average value on the back side of the blank paper portion, the back-through value, the standard deviation of the Y value on the back side of the printed portion, and the back-through evaluation index. the coefficient of determination R ² of the visual evaluation of spots in FIG. 4, shown respectively.
[Comparative Example 1]

For the same measurement region as in Example 1, the Y value was measured by a conventional method, and the strike-through value was calculated according to the above equation (2). As a measuring instrument, a color difference colorimeter (X-RITE918, manufactured by X-Rite Co., Ltd.) was used. FIG. 3 shows the obtained strikethrough value, and FIG. 4 shows the determination coefficient R ² between the strikethrough value and the visual evaluation of the strikethrough.
[Comparative Example 2]

The same measurement area as in Example 1 was performed in the same manner as in Example 1 except that the minute area was a 3.84 mm × 3.84 mm square. FIG. 3 shows the results of the Y value average value on the back surface of the printed portion, the Y value average value on the back surface of the blank paper portion, the back-through value, the standard deviation of the Y value on the back surface of the printed portion, and the back-through evaluation index. FIG. 4 shows the coefficient of determination R ² between the see-through evaluation index and the visual evaluation of the see-through.

The coefficient of determination R ² of the visual evaluation of strike-through evaluation index and strike through is 0.85 in Example 1, Example 2 0.90, 0.86 in Example 3, was significantly high correlation. In Example 4 in which the minute area was widened to 1.92 mm × 1.92 mm, the determination coefficient R ² was somewhat low, 0.56, but it is still at a level where it can be practically used. However, in Comparative Example 2 in which the minute region is further widened to 3.84 mm × 3.84 mm, the determination coefficient R ² is reduced to 0.20, the correlation becomes too low, and cannot be put to practical use. On the other hand, the coefficient of determination R ² of the visual evaluation of the spots strike through value and back of Comparative Example 1 as measured by conventional methods was 0.10, it can be seen that at all uncorrelated.

  According to the printing paper back-through evaluation method and evaluation apparatus according to the present invention, the degree of back-through considering the non-uniformity of the printed portion seen through the back surface of the printing surface is quantitatively determined between various printing papers. Since they can be compared and grasped, the printability of the printed paper can be easily grasped, and the improvement of the paper quality to be made can be quickly dealt with.

1 is a diagram illustrating a schematic configuration of a print paper back-through evaluation apparatus according to the present invention. FIG. It is a table | surface which shows the specification regarding each sample about the eight types of printing paper as a sample, and the evaluation value of the see-through by visual observation. It is a table | surface which shows the predetermined value calculated by the evaluation method using the show-through evaluation apparatus based on this invention about said 8 types of printing paper. FIG. 4 is a table of determination coefficients for the strike-through evaluation index and the see-through visual evaluation in FIG. 3. It is a figure which shows the example of a measurement with the largest variation of the Y value of the printing part back surface in the test printing paper. It is a figure which shows the example of a measurement with the smallest variation of Y value of the printing part back surface in the test paper tested.

Explanation of symbols

S Sample (printing paper)
DESCRIPTION OF SYMBOLS 1 Sample stand 2 Light projection means 3 Imaging | photography means 4 Image analysis calculation means

Claims (6)

In the printing paper back-through evaluation method for quantitatively evaluating the back-through phenomenon in which the printing applied to the printing surface of the printing paper affects the back surface corresponding to the printing portion,
For the back side of the printing paper that has not been printed,
On the back side of the printing part, which is a part of the back side corresponding to the printing part on which the printing of the printing side has been performed, and on the back side of the white part, which is a part of the back side corresponding to the blank part on which the printing of the printing surface has not been performed , Set each measurement area,
Dividing the measurement area into small areas;
Measuring light is radiated into the minute area by a pair of light projecting means which are substantially 45 ° to the minute area and whose optical axes are substantially in the same plane and whose optical path lengths are substantially equal. And
The reflected and scattered light of the measurement light is photographed by photographing means having an optical axis in a direction substantially perpendicular to the minute region, passing through substantially the midpoint of the measurement light irradiation position,
Obtaining tristimulus values XYZ of colors of the measurement image photographed by the photographing means;
Obtaining a Y value of the tristimulus values XYZ;
A print-through evaluation method for printing paper, characterized in that a through-through evaluation is performed by using the Y-value obtained for all of the minute areas by applying the following expression (I) to a through-through evaluation index.
Back-through evaluation index = 100 × (Y value average value on the back side of the printed part) / {(Average Y value on the back side of the blank paper part) × (Standard deviation of the Y value on the back side of the printed part)} (I) The measurement region and the measurement region in the range of 1600mm ² ~10000mm ^2,
2. The method for evaluating the see-through of printing paper according to claim 1, wherein the minute region is formed in a substantially square shape having a side length of 0.20 mm to 2.50 mm. Wherein the light emitting means, strike-through evaluation method of the printing paper according to claim 1 or claim 2 characterized by using the light source by color for standard illuminant D ₆₅ measured. In the printing paper back-through evaluation device for quantitatively evaluating the back-through phenomenon in which the printing applied to the printing surface of the printing paper affects the back surface corresponding to the printing unit,
A pair of light projecting means for irradiating measurement light at approximately 45 ° with respect to the measurement surface of the sample paper, wherein the optical axes of the pair of light projecting means are positioned in substantially the same plane and the optical path lengths are substantially equal Arranged,
The imaging means for imaging the reflected and scattered light on the measurement surface irradiated by the light projecting means, the optical axis of the imaging means is set in a direction substantially passing through the middle point of the measurement light irradiation position and substantially perpendicular to the measurement surface. Arranged as
An image analysis device that calculates the color of an image photographed by the photographing means to a tristimulus value XYZ and obtains a Y value of the tristimulus value XYZ,
The back side of the printing paper that is used for the back-through evaluation is not measured, and the measurement side is the measurement side.
On the back side of the printing part, which is a part of the back side corresponding to the printing part on which the printing of the printing side has been performed, and on the back side of the white part, which is a part of the back side corresponding to the blank part on which the printing of the printing surface has not been performed , Set each measurement area,
Dividing the measurement area into small areas;
A calculation means for obtaining a strikethrough evaluation index by applying the Y value obtained for all of the minute regions to the following formula (I):
A print-through evaluation apparatus for printing paper, wherein a through-through evaluation is performed based on the show-through evaluation index.
Back-through evaluation index = 100 × (Y value average value on the back side of the printed part) / {(Average Y value on the back side of the blank paper part) × (Standard deviation of the Y value on the back side of the printed part)} (I) Range the measurement area 1600mm ² ~10000mm ² as a measurement region,
5. The print paper back-through evaluation apparatus according to claim 4, wherein the minute region has a substantially square shape with a side length of 0.20 mm to 2.50 mm. Wherein the light emitting means, for the use of the light source by color for standard illuminant D ₆₅ measured print-through evaluation device of the printing paper according to claim 4 or claim 5, characterized in.

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