JPH0768679B2 - Recording sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a recording sheet, and particularly, it can be suitably used as a recording sheet by printing and an image receiving recording sheet by thermal transfer.

[Prior Art] In recent years, the demand for color printers has been expanding. Above all, thermal transfer recording, which is a kind of non-impact recording method,
In particular, fusion type thermal transfer recording is highly reliable with a simple device.
It has been highly praised for its ability to obtain relatively high-resolution images, color recording, and its extremely quiet operation compared to impact printers such as dot printers, making it easy to use in the office. With the widespread use of color recording in recent years, recording uniformity in color thermal transfer recording,
There is an increasing demand for further quality improvement regarding resolution, printing speed, and the like.

Conventionally, a plain paper having a high smoothness has been generally used as an image receiving paper for thermal transfer recording. Further, recently, the corresponding ink ribbon has been improved, and it is in a state of being able to print sufficiently on plain paper having low smoothness. However, in order to meet the demand for further quality improvement in color recording, it is difficult to transfer ink evenly on conventional plain paper with a rough surface, and print faintness, dot dropouts, print unevenness, etc. occur, resulting in halftone. Including the full-color record including.

For the purpose of improving these, some proposals of a coated paper type thermal transfer image receiving paper have been made. For example, Japanese Patent Publication Sho 59-
Japanese Patent No. 16950 proposes an image receiving paper provided with a coating layer composed of a water-soluble binder and a pigment. In addition, JP-A-59-1827
No. 87 discloses an image-receiving paper having a coating layer mainly composed of a non-plate-like inorganic pigment and having a glossiness of 20% or more, and JP-A No. 60-192690 discloses an aragonite-based light calcium carbonate and a synthetic polymer latex. An image receiving paper as a binder has been proposed. The basic idea of these conventional coated paper type image-receiving papers for thermal transfer recording is to obtain a uniform surface by smoothing the image-receiving paper surface and increasing gloss to achieve uniform transfer of the heat-meltable ink. It was

Compared to conventional plain paper, these technologies enable faster printing speeds, overlapping transfer of hot-melt ink for color development, and
Although some improvements have been made in terms of resolution improvement, etc., dot reproducibility is good, there are no fine line breaks, and there is no uneven recording, etc. It was enough. Further, a high smoothness image receiving paper according to the prior art generally has a high glossiness, and although such an image receiving paper has a good appearance, the gloss is an obstacle when trying to read a recorded image, especially a printed record. It has also been pointed out that the printing is difficult to read.

[Problems to be Solved by the Invention] The present invention is excellent in dot reproducibility in single dots of single color or overlapping colors, improves fine line breaks and uneven recording, and is suitable for printing, line drawing and full-color recording. A sheet, particularly an image-receiving sheet for thermal transfer recording is provided.

[Means for Solving the Problems] In the recording sheet, the conditions required for the image receiving sheet for transferring the ink to the sheet to be recorded (referred to as the image receiving sheet) in a satisfactory state are as follows.

First, in order for the ink to be transferred uniformly and at a high speed, the surface of the image receiving sheet must be generally macroscopically smooth and highly smooth.

Secondly, in order to transfer uniformly and reliably, it is necessary that Pa> Pb, where Pa is the binding force between the ink and the image receiving sheet and Pb is the binding force between the ink and its support. . In the case of further color recording, multi-color dots are transferred at the same point, so between each color, the coupling force between the first transferred ink and the image receiving paper is Pa, and the second transferred ink is the first. Let Pc be the binding force with the ink and Pd be the binding force between the third transferred ink and the second transferred ink, and Pa> Pc
The condition of ≧ Pd> Pb is necessary. The ink support is an ink ribbon base for thermal transfer recording.

Pb is determined by the ink and the ink support, Pa is determined by the ink and the image receiving sheet, and Pc and Pd are binding forces that are affected not only by the binding force between the inks but also by the state of the image receiving sheet.

With the increase in recording speed, the recording ink is required to be transferred and fixed to the image receiving sheet in a very short time.In thermal transfer recording, the viscosity is relatively high and the cohesive force is high for the purpose of improving the ink shortage. Strong inks are being used. This corresponds to the fact that Pc or Pd is increasing, and it is necessary to further increase Pa accordingly. Therefore, the condition on the image receiving sheet side that realizes the large coupling force Pa between the ink and the image receiving paper is Required.

Further, from the viewpoint of the solidity of the recording after recording and the legibility, especially the readability, it is preferable that the surface of the recording sheet has a low gloss, and it is necessary that the surface of the image receiving paper has unevenness.

There are three problems that arise when such conditions are not met: reproducibility of individual dots, continuity of fine lines when dots are continuously struck, and color reproducibility when multiple colors are overlaid on the entire surface. Further study will be made in two cases.

In the case of a thermal transfer printer called high resolution or full color recording, the size of the transferred dots is about 60 to 130μ.
In such a printer, the quality of dot reproducibility is an important issue. For poor dot reproducibility,
When Pa <Pb or when the unevenness of the image receiving sheet is large, dots are not transferred at all, or when Pc or Pd of the overlaid dots is larger than Pa, the image receiving sheet is temporarily transferred when the second or third color is transferred. Reverse transfer that causes all or part of the dots transferred to the ink supply side to peel off on the ink supply side, missing dots that cause part of the transferred dots to drop when Pa = Pb, and lack of smoothness around the dots. May be transcribed.

The poor continuity of fine lines when dots are continuously shot is also called thin line breakage, and there are cases where a single dot that constitutes a thin line is missing in some places, or multiple dots are continuously missing. This is caused not only by the relationship between the ink and the image receiving sheet, the ink and its support in a single dot, but also by the relationship with the binding force between adjacent inks, because the thin line is a series of dots. The thin line breaks cause faint prints in printing and deteriorate the image quality in pictorial images, which is a particularly serious drawback in plotter applications such as CAD and CAM.

Poor color reproducibility when multiple colors are overprinted on the entire surface appears as color unevenness, and in many cases defective dot reproducibility and fine line breaks occur in combination. In particular, reverse transfer and transfer defect are major problems.

As described above, the conditions required on the surface of the image receiving sheet to solve the problems include conditions that are contradictory to each other, and thus it is difficult to satisfy these conditions at the same time.

As a result of intensive studies on specific methods for realizing these conditions, the present inventors have found that the shape of the calcium carbonate in a recording sheet provided with a coating layer containing calcium carbonate on a support is The present invention was completed by solving the above-mentioned problems and satisfying the above-mentioned conditions of the surface of the image receiving layer by using the one characterized in that the granular calcium carbonate which is in the form of rice is secondarily aggregated in an irregular shape.

The coating layer of the recording sheet of the present invention is prepared by coating the above-mentioned agglomerated calcium carbonate on a support as a coating material together with an adhesive and optionally added additives.

Colloidal calcium carbonate, which is the primary particle of calcium carbonate used in the present invention, is produced by growing and accumulating crystals around fine cubic calcium carbonate of 0.1 μm or less as a nucleus. Therefore, in addition to rice grains, various shapes are seen, mainly rice grains,
In addition, spindle-shaped, columnar, needle-shaped, and bale-shaped ones are also mixed and included. The terms such as needle-shaped, spindle-shaped, rice-grained, bales-shaped, and column-shaped used as the shape of primary particles are a graphic representation of the ratio of the minor axis to the major axis of a spheroid becoming smaller in this order. The expression "rice grain" is also intuitively determined as the range corresponding to this expression is naturally decided, and it is natural that the range includes deviations from a perfect spheroid such as irregularities of the outer shape of particles. Is.

The average particle size of the primary particles of these rice granular colloidal calcium carbonate is 0.1 to 1.0 μm. The agglomerated calcium carbonate of the present invention is obtained by agglomerating these primary particles in an irregular shape with an average particle diameter of 1.0 μm or more, preferably about 3.5 μm to 10 μm. Further, the cohesive hardness of the agglomerated calcium carbonate is such that even the primary particles are not dispersed in the dispersion by a stirrer which is carried out by adding a dispersant which is usually used for dispersing the filler.

Although the coating layer of the present invention is mainly composed of the above-mentioned agglomerated calcium carbonate, it is possible to add fillers other than those mentioned above within the range suitable for the purpose of the present invention in order to meet various needs. Examples thereof include colloidal calcium carbonate other than the present invention, slight calcium carbonate, heavy calcium carbonate, clay, kaolin, calcined kaolin, acid clay,
Talc, synthetic silica (especially wet precipitation and gel method silica), alumina, aluminum hydroxide, zinc oxide, calcium silicate, synthetic silicate, titanium oxide, diatomaceous earth, barium sulfate, satin white, organic resin pigment, etc. is there.

The adhesive used in the coating layer of the present invention is not particularly limited, and may be a synthetic polymer latex or a water-soluble polymer adhesive.

As the synthetic polymer latex, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, methylmethacrylate-butadiene copolymer, chloroprene latex, a polymer or copolymer of acrylic acid ester and methacrylic acid ester, ethylene Vinyl acetate copolymer, vinyl acetate-maleic acid ester copolymer,
Examples thereof include acrylic-vinyl acetate copolymers and vinyl acetate polymers.

Examples of the water-soluble polymer include starch, cation-modified starch, polyvinyl alcohol, cellulose derivatives such as hydroxyethyl cellulose and carboxymethyl cellulose, polyacrylamides, polyvinyl pyridine, polyethylene oxide, polyvinyl pyrrolidone, casein, gelatin, sodium alginate, polystyrene sulfone. Examples thereof include acid soda, sodium polyacrylate, starch-acrylonitrile graft polymer hydrolyzate, sulfonated chitin, carboxylated chitin, chitosan and their derivatives.

In particular, examples of the water-soluble polymer that forms a coating layer suitable for a thermal transfer recording sheet include polyvinyl alcohol, oxidized starch, and polyvinylpyrrolidone.

As the adhesive for the agglomerated calcium carbonate of the present invention, one or more of these synthetic polymer latexes or water-soluble polymer adhesives can be selected and used. For the thermal transfer recording sheet, the synthetic polymer latex is used. By using at least one of the above and at least one of the water-soluble polymers in combination, it becomes a preferable coating layer particularly suitable for the purpose of the present invention.

The composition of the aggregate calcium carbonate and the adhesive constituting the coating layer is 50% of the aggregate calcium carbonate in the solid content of the entire coating layer.
˜85 parts, 10˜40 parts of synthetic polymer latex, and 2˜15 parts of water-soluble polymer are desirable. If the amount of agglomerated calcium carbonate is too large, the ink penetration is insufficient and the ink bite is poor. If the amount of latex is too large, the ink penetration is not sufficient, and transfer defects and reverse transfer are increased. On the other hand, if the amount of the water-soluble polymer is too large, the smoothness of the surface cannot be obtained, and dot dropout easily occurs.

On the other hand, if the amount of agglomerated calcium carbonate is too small, dot dropouts and fine line breaks increase, and if the amount of latex is small, the surface strength decreases and reverse transfer is facilitated. If the amount of water-soluble polymer is small, uniform transfer cannot be obtained.

The coating material of the coating layer of the present invention may optionally contain additives for the purpose of improving the coating material. They include, for example, dispersants, thickeners, release agents, surfactants,
It is a viscosity modifier, a flocculant, a leveling agent, a water resistant agent, and the like.

Examples of the support of the present invention include plant pulp fibers centering on wood fibers, sheets composed of synthetic pulp fibers, synthetic fibers, inorganic fibers, etc., sheets of organic / inorganic polymer resins, and metal sheets. Etc. can be mentioned.

The coating method of the present invention, a size press,
Examples thereof include an air knife coater, a roll coater, a blade coater, a bar coater, a curtain coater and a spray method.

The coating layer of the recording sheet of the present invention is prepared by mixing agglomerated calcium carbonate and an adhesive, and stirring and dispersing the mixture with the time of addition, which is added as necessary, to a coating material, and 1 to 20 g / m ² on the support, preferably After coating and drying about ² to 15 g / m ² , it is usually smoothed to finish. The smoothing treatment is usually a calendar treatment, which is a gloss calendar or a super calendar and a combination thereof.

The smoothing process is usually performed when the smoothness is 100 seconds to 2000 seconds. If the smoothness is too high at 2000 seconds or more, the voids on the surface will be crushed, and the initial permeation of the ink will be delayed, and reverse transfer or the like will be more likely to occur and uniform transfer will not be achieved. Further, if the smoothness is too low, dot defects and the like are observed, and the image becomes non-uniform as a whole, which is not preferable.

The preferable smoothness depends on the type of printing machine, thermal transfer printer, etc., and the recording sheet of the present invention can be set to a desired value without greatly changing other properties.

The gloss of the recording sheet thus obtained shows only a small change for the change in smoothness, and is mainly determined by the composition of the coating layer, the type of calender, and the use of the calender.

In any case, a paper with a smoothness of 2000 seconds and a glossiness of about 20% has never been seen in the past, and perfect transfer can be obtained in thermal transfer recording, and the transferred image is very easy to see.

[Operation] By providing a coating layer containing agglomerated calcium carbonate obtained by secondarily agglomerating colloidal calcium carbonate, which has a primary particle shape of rice grain, on a support, a mono-colored or superposed color can be obtained. A recording sheet, especially a thermal transfer recording sheet, which is excellent in dot reproducibility in a single dot and is suitable for color recording in which fine line breaks and recording unevenness are extremely small, can be obtained, and it is considered that the reason is as follows.

When the surface of the recording sheet of the present invention is observed, it can be seen that pores of 20 μm to 30 μm, particularly 20 to 30 μm, are distributed substantially uniformly. It is considered that these pores appear as gaps between the agglomerated particles by using calcium carbonate agglomerated to have an appropriate size and hardness. And
Aggregated particles having such properties will be described below. From the fact that the effect of the present invention cannot be obtained with calcium carbonate obtained by aggregating primary particles having other forms, it is considered that this is a peculiar property due to aggregating colloidal calcium carbonate having a rice grain shape.

If such pores are present, even recording dots having a relatively high viscosity of about 60 to 130 μm can be partially captured in the pores. This corresponds to an increase in the binding force Pa between the ink and the surface of the coating layer, and therefore dot reproducibility is improved and fine line breaks are less likely to occur. Furthermore, even in color recording, these pores do not disappear even with the dot ink that was initially transferred.
There are many areas where the anchoring effect is maintained even for the third color ink or the third color ink, so the coupling force between the inks Pc, Pd
It is considered that the value becomes larger than the binding force Pb between the ink and its support, and reverse transfer hardly occurs, and as a result, excellent color recording without color unevenness can be obtained.

In addition, since aggregated particles of appropriate size and hardness are used, the entire coating layer has appropriate elasticity, and when supercalendering is applied, the surface is smoothed but pores are not crushed too much. Therefore, it is considered that a recording sheet with high smoothness and low gloss can be obtained.

[Examples] Hereinafter, the present invention will be specifically described with reference to Examples. still,
In the following examples, parts and% indicate parts by weight of solid content and% by weight of solid content, unless otherwise specified.

The amorphous granular agglomerated calcium carbonate of the present invention was obtained by the following method.

Synthesis Example 1 500 parts of a fine cubic calcium carbonate suspension having an average particle size of less than 0.1 μm and a concentration of 4% was mixed with 60 parts of a 10% calcium hydroxide suspension to obtain a 4.64% mixed suspension. Obtained. After the liquid temperature of the suspension was adjusted to 20 ° C., the suspension was put into a carbonation reactor and carbon dioxide gas having a volume concentration of 30% was introduced to carry out a carbonation reaction. Further, the obtained calcium carbonate suspension was dehydrated by a filter press, dried and pulverized to obtain an aggregated calcium carbonate powder having an aggregate diameter of 4.4 μm. This agglomerated calcium carbonate is an agglomerate of rice grain-like colloidal calcium carbonate having a primary particle diameter of about 0.5 μm, which is irregularly aggregated.

Synthesis Example 2 62.5 parts of a 10% calcium hydroxide suspension was mixed with 500 parts of a 5.0% fine cubic calcium carbonate suspension having an average particle size of less than 0.1 μm to prepare a 5.56% mixed suspension. Obtained. After adjusting the liquid temperature to 30 ° C., the solution was put into a carbonation reactor, and carbon dioxide gas having a volume concentration of 30% was introduced to carry out the carbonation reaction. After completion of the reaction, the obtained calcium carbonate suspension was dehydrated by a filter press, dried and then pulverized to obtain an aggregated calcium carbonate powder having an aggregate diameter of 5.0 μm. The agglomerated calcium carbonate is an agglomerate of agglomerate calcium carbonate having a primary particle diameter of 0.7 μm and having an irregular shape.

Example 1 350 ml of freeness (CSF) as a raw material pulp for a support
Using 100 parts of LBKP, kaolin (kaolinite genus, spherical aggregate, average primary particle size 0.1μ, specific gravity 2.2) as filler
In addition to 10 parts, 0.15 parts of a reinforced rosin sizing agent (Coropearl CS, manufactured by Seikou Kagaku Kogyo Co., Ltd.) as a sizing agent and 1 part of a sulfuric acid band were added, and a paper machine was used to make a paper having a basis weight of 62 g / m ² . Got the sheet.

Next, 3 parts of 40% concentration of sodium acrylate (Aron T-40, manufactured by Toagosei Co., Ltd.) as a dispersant was added to about 127 ml of water, and agglomerated calcium carbonate (average agglomerated particle size) of Synthesis Example 1 was added. 100 parts of 4.4 μm and BET specific surface area of 7.0 m ² / g) were dispersed. Next, 46 parts of 50% styrene-butadiene copolymer emulsion (Tg-12 ° C) as a binder and polyvinyl alcohol (saponification degree about 99%, average degree of polymerization 1800)
100 parts of 10% aqueous solution of was added to prepare a coating solution of 35% solid content aqueous solution as a whole. This coating solution was coated on the above-mentioned support sheet with a Meyer bar at 12 g / m ² (solid content) on one side and dried. Further, this image-receiving sheet was subjected to a smoothing treatment on the surface of the coating layer at a linear pressure of 200 kg / cm using a test super calendar to obtain a recording sheet of Example 1.

Example 2 A recording sheet of Example 2 was obtained in the same manner as in Example 1 except that the coating layer surface was smoothed with a test supercalender at a linear pressure of 80 kg / cm.

Examples 3 to 4 Recording sheets of Examples 3 and 4 were obtained in the same manner as in Example 1 except that the coating amount of Example 1 was changed to 3 g / m ² and 6 g / m ² .

Example 5 Aggregated calcium carbonate of Example 1 was synthesized Aggregated calcium carbonate of Example 2 (average agglomerated particle diameter 5.0 μm, BET specific surface area 6.5 m ² /
A recording sheet of Example 4 was obtained in the same manner as in Example 1 except that g) was changed.

Example 6 Next, 3 parts of 40% concentration of sodium acrylate (Aron T-40, manufactured by Toagosei Co., Ltd.) as a dispersant was added to about 172 ml of water, and the aggregated calcium carbonate of Synthesis Example 1 (average) was added. Aggregated particle size 4.4μm, BET specific surface area 7.0m ² / g) 100 parts was dispersed, and then as a binder, vinyl acetate-maleic acid dibutyric acid copolymer emulsion with a concentration of 48% (Tg-10 ° C) 58
Parts and 140 parts of a 10% aqueous solution of polyvinyl alcohol (saponification degree: about 99%, average polymerization degree: 1100) were added to prepare a coating solution of a 30% solid content aqueous solution as a whole. This coating solution
An image receiving sheet was prepared by applying 12 g / m ² (solid content) on one side onto a support sheet similar to that used in Example 1 with a Meyer bar and drying. Further, this image-receiving sheet was subjected to a smoothing treatment on the surface of the image-receiving sheet with a test super calendar to obtain a recording sheet of Example 6.

Comparative Examples 1 to 7 Recording sheets of Comparative Examples 1 to 7 were obtained in the same manner as in Example 1 except that the aggregated calcium carbonate of Example 1 was changed to the calcium carbonates 1 to 6 shown in Table 1.

In Comparative Example 2, the conditions of the calendar are 200 kg / cm and 80 kg / cm.
Both were tested.

Examples 1 to 6 and Comparative Examples 1 to 7 thus obtained
The recording sheet of No. 2 was evaluated for recording density, dot reproducibility, fine line breaks, recording unevenness, glossiness, and smoothness, and the results are shown in Tables 2 and 3.

The evaluation of each item was performed by the following method.

(1) Recording density: Solid black (cyan, magenta, and yellow 3 layers of ribbons) using a color hard copy device COMTEC HB1552 (printing speed: A4 40 seconds) manufactured by Daikin Industries, Ltd. Recording was performed, and the recorded density was measured with a Macbeth densitometer. A value of 1.3 or higher was considered good.

(2) Dot reproducibility: An enlarged photograph of a single dot was taken, 50 dots were randomly selected, and the shape of each dot and transfer defects or missing dots were visually observed. A was accepted.

A: There are 2 or less missing dots, and almost no transfer defects are seen.

B: The number of missing dots is 10 or less, and transfer defects are slightly visible.

C: There are many missing dots and transfer defects, and some dots have deformed shapes.

(3) Fine line break: A grid pattern was recorded on the entire surface of the A4 recording paper with one dot by the above printer, and visually judged in the state of fine line break or dot dropout.

A: Almost no thin or fine lines are seen in both vertical and horizontal lines.

B: Some thin lines are broken.

C: There are quite a few broken thin lines.

(4) Uneven recording: Cyan, magenta,
Each solid recording including 10 monotones of each yellow single color, each two color superposition, and three color superposition is performed in a size of 10 cm square, and the unevenness of recording and dot omission state of the recording portion are visually observed. evaluated.

A: The image quality is good with almost no missing dots or uneven color.

B: Some missing dots and uneven color are seen, and the image quality is slightly degraded.

C: There are many missing dots and uneven color, and the image quality is poor.

(5) Smoothness: According to JIS P8119 Beck tester smoothness test method.

(6) Gloss: According to JIS P8142, 75 ° specular gloss test method.

Comparing Table 2 showing the evaluation of the example and Table 3 showing the evaluation of the comparative example, it can be seen that the recording sheet using the aggregated calcium carbonate of the present invention has extremely excellent results in all the evaluation items. On the other hand, the recording sheet of the comparative example using calcium carbonate other than the present invention has a sufficient recording density,
The dot reproducibility was poor, there were many fine line breaks, and there were many recording irregularities.

Further, the recording sheet of the present invention has a smoothness of about 17 even at 1500 seconds as compared with the recording sheet of the comparative example, and is a sheet having a characteristic of high smoothness and low gloss. Comparative Example 2 shows that when calcium carbonate other than the present invention is used, the ink transfer becomes worse as the smoothness becomes smaller.
It is shown that the recording sheet of the present invention retains excellent ink transferability regardless of smoothness or glossiness.

[Effects of the Invention] As described above, by providing a coating layer containing calcium carbonate in which primary particles agglomerate colloidal calcium carbonate in the form of rice are irregularly aggregated on the support, the recording density is high, It was possible to obtain an unprecedented recording sheet which is excellent in dot reproducibility, is free from fine line breaks and recording irregularities, and is particularly suitable for high-resolution thermal transfer full-color recording. Further, as a matter of course, even if a recording sheet for conventional monochrome thermal transfer is used, an image quality higher than that of the conventional image can be obtained. Further, the recording sheet of the present invention is a sheet having high smoothness and low gloss as compared with the conventional general coated paper for printing, and the obtained record is clear and heavy, and the record which is very easy to see is obtained.

Claims (3)

[Claims] 1. A recording sheet having a coating layer containing calcium carbonate formed on a support, wherein the calcium carbonate secondary aggregates the colloidal calcium carbonate whose primary particles are rice grains in an irregular shape. A recording sheet characterized by being a thing. 2. The recording sheet according to claim 1, wherein the glossiness of the surface of the coating layer measured according to JIS P8142 is 20% or less. 3. The recording sheet according to claim 1, wherein the Bekk smoothness of the coating layer surface measured according to JIS P8119 is 100 seconds to 2000 seconds.