JP5911086B2 - Method for producing thermal recording material - Google Patents

Description

  The present invention relates to a method for producing a heat-sensitive recording material, and more particularly to a method for producing a heat-sensitive recording material in which at least two layers of a heat-sensitive recording layer and an upper protective layer are formed on a substrate. In detail, it is related with the manufacturing method of the thermosensitive recording body using curtain coating.

  A thermal recording medium generally comprises a thermal recording layer that develops color when heated on a substrate, and a protective layer for protecting the thermal recording layer thereon, a thermal head, a hot stamp, a laser beam, etc. The heat-sensitive recording layer can be colored and recorded by heating, such as a printer, a medical measurement recorder, a facsimile, an automatic ticket vending machine, a thermal copying machine, a handy terminal, etc. In the field, it is widely used as thermal recording paper or the like (see, for example, Patent Document 1).

  In the production of such a heat-sensitive recording material, there are a gravure coating method, a rod method, a roll coating method and the like as a conventional coating method for applying a heat-sensitive recording layer, a protective layer or the like on a substrate. However, since these coatings are performed in contact with the substrate, there is a drawback that so-called streaks are likely to occur on the surface of the thermal recording material.

JP 2009-067017 A

  Unlike the above gravure coating, etc., curtain coating is a non-contact coating on the base material, so the above disadvantages are unlikely to occur. Can be increased.

  In this multi-layer simultaneous coating, paints corresponding to each layer are laminated on a slide inclined surface, and in the laminated state, a curtain is formed and dropped onto a moving base material, so that multi-layer simultaneous coating is performed.

  However, with this multilayer simultaneous coating, the print storability of the resulting thermal recording material may be reduced. Therefore, as a result of earnest research on this cause, when laminating the paint of each layer and flowing down, the component having a specific gravity greater than that of the base resin as the main component in the paint of the upper protective layer reaches the lower thermal recording layer. The knowledge that it was settled and print storage stability was reduced was obtained.

  The present invention has been made on the basis of the above-described knowledge, and an object of the present invention is to provide a method for producing a thermal recording body by curtain coating, which can prevent a decrease in print storage stability of the thermal recording body. .

The method for producing a thermal recording material according to the present invention forms a plurality of layers of paint flow on an inclined slide surface, naturally drops from the slide surface, and forms a plurality of coating films on a moving substrate. A method for producing a heat-sensitive recording material by curtain coating to be laminated,
The coating film of the plurality of layers includes a thermosensitive recording layer and a protective layer above the thermosensitive recording layer, and the low shear viscosity of the coating material of the protective layer is the low shear viscosity of the coating material immediately below the protective layer. 5 times or more and 8 times or less.

The low shear viscosity is preferably a shear viscosity at a shear rate of 10 s ⁻¹ .

  The protective layer preferably contains a base resin and at least one of a pigment and a wax.

  The protective layer preferably contains a base resin and at least one of a pigment and a wax.

The layer immediately below the protective layer may be a barrier layer.
The coating for the protective layer preferably does not contain zinc stearate, and preferably contains urethane-modified polyether.

In the present invention, since the low shear viscosity of the protective layer paint is 5 to 8 times the low shear viscosity of the paint immediately below the protective layer, the protective layer paint contains a component having a large specific gravity. However, the component does not settle down to the coating material of the lower thermal recording layer, and it is possible to prevent a decrease in print storage stability of the thermal recording material obtained by curtain coating.

FIG. 1 is a schematic configuration diagram of a curtain coater. FIG. 2 is a cross-sectional view of the thermal recording material. FIG. 3 is a diagram illustrating a state in which the edge guide and the curtain coating film are viewed from the front. 4 is a cross-sectional view taken along line AA in FIG.

  Hereinafter, a method for producing a thermal recording material according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. As will be described later, the manufacturing method of the embodiment is a method for curtain coating of a three-layer structure having a thermosensitive recording layer, a barrier layer, and a top layer as a protective layer on a substrate. Manufactured by.

  FIG. 1 is a schematic configuration diagram of a curtain coater used for the simultaneous multilayer coating. The curtain coater includes a slide die 1, and the slide die 1 has a slide inclined surface 3 that is inclined downward on its upper surface. The slide inclined surface 3 is provided with slots 5a to 5c for discharging paints Sa to Sc for forming the respective layers of the thermal recording body.

  Paint reservoirs 7a to 7c are provided on the upstream side of the slots 5a to 5c. The paint supply pipes 9a to 9c are connected to the lower ends of the slots 5a to 5c, and the paints Sa to Sc are supplied to the paint reservoirs 7a to 7c through the pumps 10a to 10c provided in the paint supply pipes 9a to 9c. Is done.

  Among the coating materials Sa to Sc, the coating material Sa is a coating material used for forming the top layer of the heat-sensitive recording material, except for the zinc stearate described later, and the like in the base resin, which is the main component, as in the past. The various components are contained. The paint Sb is a paint used for forming the barrier layer, and is mainly made of a resin as in the conventional case. The coating material Sc is a coating material used for forming the heat-sensitive recording layer, and includes the color former, the developer, the binder, and the like, and is the same as the conventional coating material for forming the heat-sensitive recording layer except for the binder content described later.

  The lip 13 at the tip of the slide inclined surface 3 is a place where each layer coating film 17a to 17c becomes a curtain coating film 19 from the slide inclined surface 3 and starts free fall. The edge guides 15 that guide both ends of the curtain coating film 19 are arranged so as to extend vertically downward on both sides in the width direction of the lip 13. The curtain coating film 19 becomes narrower during free fall from the lip 13, and a so-called neck-in phenomenon occurs. The edge guide 15 guides both ends of the curtain coating film 19 in the width direction so as to prevent such neck-in phenomenon and stabilize the width of the curtain coating film 19. Further, below the edge guide 15, the base material 21 continuously travels in the horizontal direction of the arrow, and three layers of coating films are laminated on the base material 21.

  The curtain coating film 19 is guided from the lip 13 by the edge guide 15, falls onto the continuously running base material 21, moves in the direction of the arrow, and is subjected to a necessary process such as drying.

  The coating materials Sa to Sc are discharged onto the sliding inclined surface 3 from the upper end openings of the slots 5 a to 5 c of the sliding inclined surface 3 and are laminated on the three-layer coating films 17 a to 17 c in the process of flowing down the sliding inclined surface 3. The

  In this case, in order to prevent the laminated state of the respective layer paint films 17a to 17c on the slide inclined surface 3, the viscosity and surface tension of each layer paint film 17a to 17c, the discharge amount onto the slide inclined surface 3, Others are set so as to satisfy the conditions described later.

  FIG. 2 shows a cross section of a heat-sensitive recording material according to this embodiment produced using the curtain coater. A heat-sensitive recording material 23 shown in FIG. 2 is obtained by forming a three-layer coating film 25 on a base material 21. In this embodiment, the multilayer coating film 25 is composed of a total of three layers including an upper layer 25a, an intermediate barrier layer 25b, and a lower thermal recording layer 25c. The thermal recording layer 25c is laminated thereon. In addition, a heat-sensitive recording body having a two-layer structure with a protective layer protecting the heat-sensitive recording layer 25c may be manufactured, or a heat-sensitive recording body having three or more layers may be manufactured as necessary. In the case of producing a heat-sensitive recording material having three or more layers, the number of layers for simultaneous multilayer coating by a curtain coater may be increased, or separately from the simultaneous multilayer coating by a curtain coater. A layer such as an undercoat layer may be formed.

  In this embodiment, the thermal recording material 23 shown in FIG. 2 is coated with the coatings Sa to Sc used for forming the top layer 25a, the barrier layer 25b, and the thermal recording layer 25c as described above with the sliding inclined surface 3 and the coating films 17a to 17c. It is manufactured by stacking 17c.

  Among these layer paint films 17a to 17c, the paint Sa used for forming the top layer paint film 17a is used for the purpose of improving the matching with the thermal head during thermal recording, improving the water resistance of the protective layer, and the like. A pigment, wax, etc. are added to the base resin as the main component, and a surfactant for uniformly forming the top layer on the heat-sensitive recording layer or barrier layer, a thickener for adjusting the viscosity, etc. Is added.

  In the case of the top layer coating film 17a formed of the coating material Sa, if the pigment, wax, or the like contains a component having a specific gravity greater than that of the base resin, such as zinc stearate described later, each layer coating film 17a. In the process in which .about.17c are laminated on the slide inclined surface 3, a component having a large specific gravity in the top layer coating film 17a may settle on the thermosensitive recording layer coating film 17c. When a component having a large specific gravity such as wax enters the heat-sensitive recording layer coating film 17c as described above, the print storability of the obtained heat-sensitive recording material is lowered.

In order to prevent such deterioration in print storage stability, the top layer paint film 17a on the slide inclined surface 3 is prevented from sinking a component having a large specific gravity in the paint Sa of the top layer paint film 17a to the lower layer side. The viscosity of the paint Sa, that is, the low shear viscosity at a low shear rate of 10S ⁻¹ is preferably higher than the low shear viscosity of the paint Sb of the paint film 17b immediately below it. This low shear viscosity is a shear viscosity at a shear rate of 10 s ⁻¹ .

Specifically, Roshea viscosity of the paint Sa of the top layer coating film 17a is more than five times the Roshea viscosity of the paint Sb paint film 17b is a layer immediately below, to set a range of 8 times or less.

  In this way, by setting the low shear viscosity of the paint Sa of the top layer paint film 17a as described above, a component having a large specific gravity contained in the paint Sa of the top layer paint film 17a settles down to the lower layer side and is recorded in heat. It is possible to prevent entry into the layer paint film 17c.

  In this embodiment, as shown in Table 1, the low shear viscosity of the paint Sb of the barrier layer paint film 17b that is a layer immediately below the top layer paint film 17a is constant, and the low shear viscosity of the paint Sa of the top layer paint film 17a is The value of the ratio of the low shear viscosity of the paint Sa of the top layer paint film 17a to the low shear viscosity of the paint Sb of the barrier layer paint film 17b (= top layer paint film viscosity / lower layer side viscosity) is 1 is 0.16, no. 2 is 1.00, no. 3 is 5.00, no. 4 is 8.33, no. In No. 5, the print storability and coating suitability as a heat-sensitive recording material when changed to 10.00 were evaluated.

この印字保存性の確認は、マクベス濃度計（ビジュアルフィルタ）で１．３０以上の発色サンプルを用意して行った。厚み１５μｍの塩化ビニル製のラップを、３枚重ねで、発色サンプル表裏面を挟み込む。ついで、３００ｇ／ｃｍ²の荷重をかけて、４０℃１５時間の環境下に放置する。そして、塩化ビニル製のラップを剥がした後の印字濃度が、試験前の７５％以上に残存していれば、印字保存性良好とした。

This print storability was confirmed by preparing a color sample of 1.30 or more with a Macbeth densitometer (visual filter). Three layers of vinyl chloride wrap with a thickness of 15 μm are stacked, and the color sample front and back surfaces are sandwiched. Next, it is left under an environment of 40 ° C. for 15 hours under a load of 300 g / cm ² . If the print density after peeling the vinyl chloride wrap remained at 75% or more before the test, the print storage stability was considered good.

  The coating suitability was determined by visual observation of the front shape of the curtain coating film. In Table 5, “x” indicates a defect, “Δ” indicates a slight defect, “◯” indicates good, and “◎” indicates very good.

  As shown in Table 1, when the ratio value is 0.16, the printing storability is poor, and the ratio value is 1.00 to 10.00, and the printing storability is good or very good. Therefore, the low shear viscosity of the paint Sa of the top layer paint film 17a is set to be in the range of 1 to 10 times the low shear viscosity of the paint Sb of the barrier layer paint film 17b immediately below it. It is preferable for improving the property.

  As for coating suitability, as shown in Table 1, the value of the ratio was 5.00 or less, that is, good at 5 times or less, but was slightly poor at 8.33 that was 8 times or more, It was not good at 10.00 which is 10 times.

As described above, in the manufacturing method of this embodiment, the low shear viscosity of the paint Sa of the top layer paint film 17a is set to 5 times or more and 8 times or less than the low shear viscosity of the paint Sb of the barrier layer paint film 17b. Even if the paint Sa of the top layer paint film 17a contains a component having a specific gravity greater than that of the base resin in the pigment or wax, the component can be prevented from settling in the lower thermal recording layer, It is possible to prevent a decrease in print storability of the resulting thermal recording material.

  In the embodiment, the heat-sensitive recording body has a three-layer structure, but the present invention can also be applied to a heat-sensitive recording body composed of two layers, a heat-sensitive recording layer and a top layer. In the above, it is preferable that the low shear viscosity of the paint Sa of the top layer paint film 17a is 1 to 10 times that of the paint Sc of the thermosensitive recording layer paint film 17C.

  Next, in the curtain coater of FIG. 1, various conditions for producing the thermosensitive recording body 23, for example, the binder content of the thermosensitive recording layer, the dynamic surface tension of each paint Sa to Sc, and other conditions are as follows. Explained.

(1) Binder content of heat-sensitive recording layer The heat-sensitive recording layer generally contains a binder to increase the strength of the heat-sensitive recording layer. Since this binder deteriorates the color development performance of the thermosensitive recording layer, it is preferable to reduce this binder. Generally, the strength of the layer when the thermosensitive recording medium is used as a product such as thermosensitive recording paper is required to be 70 g / 25 mm or more.
The reason is that if the layer strength is 70 g / 25 mm or more, the coating layer is unlikely to drop off during normal printing.

  In the heat-sensitive recording material by gravure coating, which is mainly employed as a conventional coating method, the binder content is about 10.0% by weight or more when the strength of the layer is to be 70 g / 25 mm or more required as a product. is necessary.

  In the heat-sensitive recording material of the embodiment having a three-layer structure, 70 g / 25 mm or more, which requires the strength of the formed layer, is secured by curtain coating, and the binder content in the heat-sensitive recording layer is less than 8.0% by weight. Has been reduced. Table 2 shows the relationship between the layer strength of the heat-sensitive recording material 23 and the binder content.

表２のバインダ含有量は、乾燥処理後の感熱記録層のバインダ含有量、いわゆるドライ状態のバインダ含有量であり、感熱記録層の形成に用いる塗料の配合時に、異なるバインダ含有量となるように調合したものである。この表１では、比較例として、従来のグラビア塗工方式の感熱記録体についても同様に、バインダ含有量を変化させた場合の層強度を示している。

The binder content in Table 2 is the binder content of the heat-sensitive recording layer after the drying treatment, that is, the binder content in a so-called dry state, so that the binder content differs when blending the paint used for forming the heat-sensitive recording layer. It is a blended one. In Table 1, as a comparative example, the layer strength when the binder content is changed is also shown for the heat-sensitive recording material of the conventional gravure coating method.

  The test for obtaining the measurement data of the layer strength shown in Table 2 was performed as follows using a high-speed peel tester manufactured by Tester Sangyo Co., Ltd.

In this testing machine, a part (25 mm width, 200 mm length) of the thermal recording material was used as a test piece. The test piece has a heat-sensitive recording layer thickness of about 4.5 μm (a dry coating amount of about 4.5 g / m ² ), a barrier layer thickness of about 1.5 μm (a dry coating amount of about 1.5 g / m ² ), top A heat-sensitive recording material having a layer thickness of about 1.5 μm (a dry coating amount of about 1.52 g / m ² ) was obtained. A fine paper was used as the substrate. A PET tape was attached to the test piece by reciprocating once with a 2 kg roller at a pressure of 2 kg / 25 mm, a part of the PET tape was peeled off, and the tip was attached to a fixture. Then, the test piece was peeled at a peeling angle of 180 degrees and a peeling speed of 80 m / min with the PET tape tip fixed, and the peel strength in this case was measured as the layer strength.

  As shown in Table 2, in the thermal recording material of the curtain coating method, when the binder content of the thermal recording layer is 12.0% by weight, 8.0% by weight, the layer strength is such that the base material is destroyed. Obtained.

  Furthermore, when the binder content was 6.0% by weight, 4.5% by weight, and 3.0% by weight, the layer strengths were 100 g / 25 mm, 75 g / 25 mm, and 63 g / 25 mm, respectively.

  Therefore, in the case of the thermal recording material by the curtain coating method, if the binder content is 4.0% by weight or more, it is estimated that a layer strength of 70 g / 25 mm or more necessary for use as a product can be obtained. .

  In the thermosensitive recording material of the gravure coating method, when the binder content of the thermosensitive recording layer is 12.0% by weight or 8.0% by weight, the layer strength enough to break the substrate cannot be obtained, and the layer strength is 75 g. / 25 mm and 40 g / 25 mm. Furthermore, when binder content became low, layer strength fell too much and it was not able to measure.

  Therefore, in the case of a thermosensitive recording material by a gravure coating method, it is estimated that a layer strength of 70 g / 25 mm or more necessary for use as a product can be obtained if the binder content is 10.0% by weight or more. .

  As a result, in the heat-sensitive recording material of the curtain coating method, the binder content of the heat-sensitive recording layer for obtaining the layer strength generally required as a product can be significantly reduced as compared with the heat-sensitive recording material of gravure coating. Further, the color development performance of the thermosensitive recording layer can be improved by reducing the binder content.

(2) Viscosity of each paint In the coating method using a curtain coater, it is necessary to stack the paints Sa to Sc discharged onto the slide inclined surface 3 as paint films 17a to 17c and to be stacked vertically while flowing down. The viscosities of the coating films 17a to 17c on the slide inclined surface 3 are the above-described low shear viscosity, that is, the shear viscosity at a shear rate of 10 s- ¹ .

  In each of the layer paint films 17a to 17c on the slide inclined surface 3, for example, if the viscosity of the paint on the upper layer side paint film is lower than the viscosity of the paint on the lower layer side paint film, the upper layer side paint film on the slide inclined surface 3 This paint overtakes the paint of the lower layer side paint film and mixes with the lower layer side paint film, and as a result, the laminated form is destroyed.

  In order to prevent such collapse of the laminated form, in each of the coating films 17a to 17c, the viscosity of the coating material of the upper-layer side coating film is relatively more than 1 times the viscosity of the coating material of the lower-layer side coating film. , 15 times or less is preferable.

  In this embodiment, since it has a three-layer structure, the viscosity of each of the coating films 17a to 17c is set to a ratio shown in Table 3.

なお、この表３には、後述する動的表面張力のデータも併せて示している。

Table 3 also shows dynamic surface tension data, which will be described later.

  In Table 3, the lower value of the viscosity (mPa · s) of the paint Sc of the heat-sensitive recording layer paint film 17c is shown as a reference “1”, and the paint Sc of the heat-sensitive recording layer paint film 17c. The viscosity ratio of the coating layer Sb of the barrier layer coating film 17b is 2 to 6, the viscosity ratio of the coating layer Sa of the top layer coating film 17a is 6 to 30.

  Since the ratio of the viscosity of the paint Sa in the top layer paint film 17a is 6 to 30 and the ratio of the viscosity of the paint Sb in the barrier layer paint film 17b is 2 to 6, the top layer paint film 17a of the upper layer side The viscosity of the paint Sa is 1 to 15 times the viscosity of the paint Sb of the lower barrier layer paint film 17b.

  Since the ratio of the viscosity of the coating material Sb of the barrier layer coating film 17b is 2 to 6 and the ratio of the viscosity of the coating material Sc of the thermal recording layer coating film 17c is 1 to 2, the barrier layer coating film 17b on the upper layer side. The viscosity of the coating material Sb is 1 to 6 times the viscosity of the coating material Sc of the lower thermal recording layer coating film 17c. In any case, the viscosity of the paint of the upper-layer-side paint film is 1 to 15 times less than the viscosity of the paint of the lower-layer-side paint film between the respective layer paint films 17a to 17c.

(3) About the dynamic surface tension of each paint Dynamic surface tension acts on the mutual contact surface on the slide inclined surface 3 of each layer paint film 17a-17c in the process of flowing down.

  Regarding the dynamic surface tension, if the difference between the dynamic surface tension of the upper-layer-side paint film and the dynamic surface tension of the lower-layer-side paint film is too large, the film thickness or the film shape of each of the layer-coating films 17a to 17c Since the laminated form tends to collapse, it is important to balance the dynamic surface tension between the respective coating materials 17a to 17c in order to improve the laminated state.

  In order to make this lamination state good, the dynamic surface tension of the coating material of the lower layer coating film is 0.8 times or more and 1.1 times or less of the dynamic surface tension of the coating material of the upper layer coating film. Preferably there is.

  In this embodiment, since it has a three-layer structure, the dynamic surface tension between the paints Sa to Sc of the respective layer paint films 17a to 17c is adjusted to the ratio shown in Table 3 above.

  In Table 3, the lower value of the dynamic surface tension (mN / m) of the paint Sa of the top layer paint film 17a is shown as a reference “1”, and the paint Sa of the top layer paint film 17a is shown. The ratio of the dynamic surface tension of 1-1.13, the ratio of the dynamic surface tension of the paint Sb of the barrier layer paint film 17b is 1.07-1.13, and the dynamic of the paint Sc of the thermosensitive recording layer paint film 17c. The ratio of the surface tension is 1.10 to 1.16. This ratio of dynamic surface tension is the ratio of dynamic surface tension when the interface life is 50 ms.

  Between the top layer paint film 17a and the barrier layer paint film 17b, the ratio of the dynamic surface tension of the paint Sb of the lower layer barrier layer paint film 17b is 1.07 to 1.13. Since the ratio of the dynamic surface tension of the paint Sa in the layer paint film 17a is 1-1.13, the dynamic surface tension of the paint Sb in the barrier layer paint film 17b on the lower layer side is the top layer paint film on the upper layer side. It is 0.88 times or more and 1.06 times or less of the dynamic surface tension of the paint Sa of 17a.

  Between the barrier layer coating film 17b and the thermal recording layer coating film 17c, the ratio of the dynamic surface tension of the coating Sc of the lower thermal recording layer coating film 17c is 1.10 to 1.16. Since the ratio of the dynamic surface tension of the coating Sb of the barrier layer coating film 17b is 1.07 to 1.13, the dynamic surface tension of the coating Sc of the lower thermal recording layer coating film 17c is the upper layer side. The dynamic surface tension of the coating material Sb of the barrier layer coating film 17b is 0.92 times or more and 1.03 times or less.

  In any case, the dynamic surface tension of the paint film on the lower layer side is relatively 0.8 times or more than the dynamic surface tension of the paint film on the upper layer side between the respective layer paint films 17a to 17c. The range is 1.1 times or less.

(4) Discharge amount of each paint When the paints Sa to Sc of the respective layer paint films 17a to 17c are discharged onto the slide inclined surface 3, the discharge amount of the upper layer side paint is relatively larger than the lower layer side paint. Then, the upper-layer-side paint film overtakes the lower-layer paint film on the slide inclined surface 3, and the paint films of these layers are mixed, so that the respective layer paint films 17a to 17c cannot be laminated in a required laminated state. On the contrary, if the discharge amount of the upper layer side paint is too small compared to the lower layer side paint, the upper layer side paint film cannot be laminated on the lower layer side paint film.

  Therefore, it is necessary to discharge the paints Sa to Sc in an appropriate discharge amount on the slide inclined surface 3 corresponding to the respective layer paint films 17a to 17c.

  Therefore, regarding the discharge amount of each of the paints Sa to Sc, the discharge amount of the lower layer side paint is set to be 1 to 5 times, preferably 1 to 4 times the discharge amount of the upper layer side paint. It is preferable to set it in order to keep the laminated state of the respective layer coating films 17a to 17c on the slide inclined surface 3.

In this embodiment, since it has a three-layer configuration, the ratio of the discharge amount of each of the paints Sa to Sc is set to the ratio shown in Application Example 1 in Table 4 and Application Example 2 in Table 5. In each of the coating examples in Tables 4 and 5, the discharge amount is indicated by a ratio in which the discharge amount (L / min) of the paint Sa used for forming the top layer paint film 17a is set to “1” as a reference. Yes. Further, the coating amount is a coating amount in a dry state after the drying process, and the coating amount (g / m ² ) of the coating material Sa used for forming the top layer coating film 17a is a ratio of “1” as a reference. Show.

表４に示す塗工例１では、トップ層塗料膜１７ａ、バリア層塗料膜１７ｂ、感熱記録層塗料膜１７ｃそれぞれの形成に用いる各塗料Ｓａ〜Ｓｃの吐出量の割合は、それぞれ、１．０、１．１８、１．８７であった。

In the coating example 1 shown in Table 4, the ratio of the discharge amount of each of the coating materials Sa to Sc used for forming the top layer coating film 17a, the barrier layer coating film 17b, and the thermal recording layer coating film 17c is 1.0. 1.18, 1.87.

  In this case, between the top layer paint film 17a and the barrier layer paint film 17b, the ratio of the discharge amount of the paint Sb of the lower layer barrier layer paint film 17b is 1.18, and the upper layer top layer paint film The ratio of the discharge amount of the paint Sa of 17a is 1.0. Therefore, the discharge amount of the paint Sb of the lower barrier layer paint film 17b is equal to the discharge amount of the paint Sa of the upper layer paint film 17a of the upper layer. It is about 1.2 times.

  Further, between the barrier layer coating film 17b and the thermal recording layer coating film 17c, the ratio of the discharge amount of the coating Sc of the lower thermal recording layer coating film 17c is 1.87, and the upper barrier layer coating is applied. The ratio of the discharge amount of the paint Sb on the film 17b is 1.18. Therefore, the discharge amount of the paint Sc on the lower thermal recording layer paint film 17c is the discharge of the paint Sb on the upper barrier layer paint film 17b. About 1.6 times the amount. In any case, between the respective layer coating films 17a to 17c, the discharging amount of the coating film on the lower layer side is 1 to 4 times the discharging amount of the coating film on the upper layer side.

  In the coating example 2 shown in Table 5, the ratios of the discharge amounts of the top layer coating film 17a, the barrier layer coating film 17b, and the thermal recording layer coating film 17c were 1.0, 1.68, and 3.75, respectively. .

  In this case, between the top layer paint film 17a and the barrier layer paint film 17b, the ratio of the discharge amount of the paint Sb of the lower layer barrier layer paint film 17b is 1.68, and the upper layer top layer paint film The ratio of the discharge amount of the paint Sa of 17a is 1.0. Therefore, the discharge amount of the paint Sb of the lower barrier layer paint film 17b is equal to the discharge amount of the paint Sa of the upper layer paint film 17a of the upper layer. It is about 1.7 times.

  Further, between the barrier layer coating film 17b and the thermal recording layer coating film 17c, the ratio of the discharge amount of the coating Sc of the lower thermal recording layer coating film 17c is 3.75, and the upper barrier layer coating is applied. The ratio of the discharge amount of the paint Sb on the film 17b is 1.68. Therefore, the discharge amount of the paint Sc on the lower thermal recording layer paint film 17c is the discharge of the paint Sb on the upper barrier layer paint film 17b. About 2.2 times the amount.

  In any of the coating examples, the discharge amount of the lower layer-side paint is 1 to 4 times the discharge amount of the upper-layer side paint.

(5) About the blending of the coating material for forming the top layer (5-1) About zinc stearate Each coating material Sa to Sc is discharged on the slide inclined surface 5 of the slide die 1 of the curtain coater, and each coating material film 17a to 17c flows down. In this case, the thermal recording layer paint film 17c is laminated on the lower layer side, and the top layer paint film 17a is laminated on the upper layer side. In that case, as described above, the coating material Sa used for forming the top layer coating film 17a is added with a pigment, wax, or the like in the base resin which is the main component, and the top layer on the thermal recording layer or the barrier layer. A surfactant for uniformly forming a layer, a thickener for viscosity adjustment, and the like are included, and the wax conventionally contains zinc stearate, which is a component having a specific gravity greater than that of the base resin.

  If the top layer coating film 17a contains zinc stearate having a specific gravity greater than that of the base resin as in the prior art, the zinc stearate may settle on the heat-sensitive recording layer coating film 17c. As described above, when zinc stearate settles and enters the lower thermal recording layer coating film 17c, the print storability of the thermal recording medium decreases.

  In order to prevent the printing storability from deteriorating, it is preferable to remove zinc stearate from the paint Sa used for forming the top layer among the paints Sa to Sc. In this embodiment, the top layer paint film 17a The paint Sa used for formation does not contain zinc stearate.

Table 6 shows the print storability when each component contained in the top layer is individually removed when the coating of the top layer of the thermosensitive recording material is not contained. This print storability was evaluated in the same manner as in Table 1 above. In the paint, a base resin for the top layer , a pigment, zinc stearate as a wax, a surfactant, and a thickener are blended.

表６に示すように、塗料にステアリン酸亜鉛を配合し、顔料、界面活性剤、増粘剤を除去すると、いずれも印字保存性は不良であったが、ステアリン酸亜鉛のみを除去すると、印字保存性は良好となった。

As shown in Table 6, when zinc stearate was added to the paint and the pigment, surfactant, and thickener were removed, the print storability was poor, but when only zinc stearate was removed, printing The storage stability was good.

  In addition, although the zinc stearate was demonstrated above, when components with larger specific gravity than a base resin, for example, a carnauba wax, a montanic acid ester wax, a stearic acid amide, etc. are contained, they may be removed in the same manner as described above. Good.

(5-2) Urethane-modified polyether Generally, zinc stearate is blended as a wax in the top layer coating film 17a to improve matching properties such as sliding with a thermal head. Therefore, if zinc stearate is not blended in the top layer coating film 17a, matching with the thermal head is lowered.

  For this reason, it is preferable to mix | blend the additive for preventing the fall of the matching property with a thermal head with a coating material.

  In this embodiment, urethane-modified polyether is blended in the paint Sa used for forming the top layer paint film 17a as the additive. As this urethane-modified polyether, for example, trade name “SN Sixner 621” manufactured by San Nopco Co., Ltd. can be used.

  Further, the urethane-modified polyether has a specific gravity smaller than that of the base resin, which is the main component of the paint, so unlike the zinc stearate, it settles from the top layer paint film 17a to the thermosensitive recording layer paint film 17c on the slide inclined surface 3. Therefore, it is possible to maintain good print storability of the thermal recording material.

表７に、トップ層塗料膜１７ａの形成に用いる塗料Ｓａに、ステアリン酸亜鉛を８．０重量％、４．０重量％配合したときの印字適正と、ステアリン酸亜鉛とウレタン変性ポリエーテルを共に配合していないときの印字適正と、ウレタン変性ポリエーテルを４．０重量％配合したときの印字適正を示す。この表７に示すように、ウレタン変性ポリエーテルは、トップ層塗料膜１７ａに添加したとき、ステアリン酸亜鉛と同様に印字適正を良好にすることが判る。

Table 7 shows both printing suitability when zinc stearate is mixed in the coating material Sa used for forming the top layer coating film 17a at 8.0% by weight and 4.0% by weight, and zinc stearate and urethane-modified polyether. The printability when not blended and the printability when 4.0% by weight of urethane-modified polyether is blended are shown. As shown in Table 7, when the urethane-modified polyether is added to the top layer coating film 17a, it can be seen that printing suitability is improved as in the case of zinc stearate.

  Further, when a polyethylene wax or the like is further added, it becomes possible to make the printing suitability better.

(6) Surface tension difference between edge guide water and curtain coating film As described above, the edge guide 15 regulates the width of the curtain coating film 19 and at the same time guides and stabilizes both ends of the curtain coating film 19. The edge guide 15 is supplied with lubricating edge guide water on the surface thereof.

  If the difference between the surface tension of the edge guide water and the surface tension of the end portion of the curtain coating film 19 is large and unbalanced, the end portion of the curtain coating film 19 enters the edge guide water side and its end thickness Is deformed thinly, or conversely, the edge guide water enters the end.

  Therefore, it is preferable that the difference between the surface tension of the edge guide water and the surface tension at the end of the curtain coating film 19 is approximately 4 mN / m or less in terms of absolute value. Thus, when the difference between the two surface tensions is 4 mN / m or less in absolute value, the two surface tensions are almost balanced, and the curtain coating film 19 has a substantially uniform film thickness in the entire width direction. It falls to the top and this makes the coating suitability good.

  The surface tension relationship between the edge guide water and the end portion of the curtain coating film 19 will be described with reference to FIGS. FIG. 3 is a front view of the edge guide 15 and the curtain coating film 19, and FIGS. 4A, 4B, and 4C are cross-sectional views taken along line AA in FIG. The state of the boundary part of edge guide water and curtain coating-film edge part at the time of changing the surface tension of water is shown.

  In these drawings, the edge guide 15 has a structure in which a porous glass 15b is sandwiched between a pair of metal plates 15a, and edge guide water 15c containing a surfactant for adjusting the surface tension is provided on the porous glass 15b. Water is supplied. As this surfactant, for example, an acetylene glycol surfactant can be used.

  Table 8 shows the difference in surface tension between the curtain coating film 19 and the edge guide water 15c as an absolute value. In addition, the surface tension of each coating material Sa to Sc constituting the curtain coating film 19 was adjusted to be the same surface tension.

この表８では、カーテン塗膜１９の表面張力を一定とし、エッジガイド水１５ｃの表面張力を変化させて、これら両表面張力の差を絶対値で３５ｍＮ／ｍ、１１ｍＮ／ｍ、２ｍＮ／ｍ、５ｍＮ／ｍと変化させたときのカーテン塗膜の状態を記載している。ただし、３５ｍＮ／ｍ、１１ｍＮ／ｍは、エッジガイド水１５ｃの表面張力がカーテン塗膜１９の表面張力よりも大きい場合の表面張力差であり、２ｍＮ／ｍ、５ｍＮ／ｍは、エッジガイド水１３ｄの表面張力がカーテン塗膜１９の表面張力よりも小さい場合の表面張力差である。

In Table 8, the surface tension of the curtain coating film 19 is made constant, the surface tension of the edge guide water 15c is changed, and the difference between these two surface tensions in absolute values is 35 mN / m, 11 mN / m, 2 mN / m, The state of the curtain coating film when it is changed to 5 mN / m is described. However, 35 mN / m and 11 mN / m are surface tension differences when the surface tension of the edge guide water 15c is larger than the surface tension of the curtain coating film 19, and 2 mN / m and 5 mN / m are the edge guide water 13d. Is the surface tension difference when the surface tension is smaller than the surface tension of the curtain coating film 19.

  As shown in Table 8, when both surface tension differences are 35 mN / m and 11 mN / m in absolute value, the edge 19a of the curtain coating film 19 is an edge guide as shown in FIG. It spreads wet on the surface of the water 15c and becomes partially thin. Therefore, it can be seen that the two surface tensions are not balanced by the difference.

  When the surface tension difference is 2 mN / m in absolute value, the end 19a of the curtain coating film 19 does not wet and spread on the surface of the edge guide water 15c as shown in FIG. 4B, and the edge guide water 15c. The end 19a of the curtain coating film 19 was balanced, and the film thickness of the curtain coating film 19 became uniform over the entire width direction. It can be seen that the two surface tensions are balanced by the difference.

  If the surface tension difference is 5 mN / m in absolute value, the edge guide water 15c enters the end 19a of the curtain coating film 19 as shown in FIG. Then you can see that there is no balance.

  Therefore, the edge guide water 15c and the end portion 19a of the curtain coating film 19 are balanced and the coating suitability is improved when both surface tension differences are 4 mN / m or less in absolute value.

DESCRIPTION OF SYMBOLS 1 Slide die 3 Sloping inclined surface 5a-5c Slot 13 Lip 15 Edge guide 17a-17c Each layer coating film 19 Curtain coating film 21 Base material 23 Thermal recording body 25 Coating film 25a Top layer 25b Barrier layer 25c Thermal recording layer Sa-Sc Coating material

Claims (4)

Production of thermal recording material by curtain coating, in which a flow of multiple layers of paint is formed on an inclined slide surface, and is naturally dropped from the slide surface, and a plurality of layers of coating film is laminated on a moving substrate. A method,
The plurality of coating films include a heat-sensitive recording layer and a protective layer above the heat-sensitive recording layer,
A method for producing a thermal recording material, wherein the low shear viscosity of the coating material of the protective layer is 5 to 8 times the low shear viscosity of the coating material immediately below the protective layer. The low shear viscosity is a shear viscosity at a shear rate of 10 s ⁻¹ .
The method for producing a heat-sensitive recording material according to claim 1. The method for producing a thermal recording material according to claim 1, wherein the protective layer contains a base resin and at least one of a pigment and a wax. The layer immediately below the protective layer is a barrier layer,
The method for producing a heat-sensitive recording material according to any one of claims 1 to 3.

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