JP2005125522A - Porous sheet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous sheet usable as a recording sheet of a thermal transfer recording system, an ink jet recording system or the like, and its manufacturing method. <P>SOLUTION: This porous sheet has a sheetlike support and the porous coating layer comprising a resin-containing film formed at least on one side of the sheetlike support. The average void diameter of the surface of the porous coating layer is 0.5-50 μm and the opening area ratio thereof is 20-70% while the 75° blank paper glossiness of the surfcace of the porous coating layer, after the surface of the porous coating layer is bonded at 150°C under heating and pressure, is set to 60% or above. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention has a large number of voids on the surface and inside of the coating layer, and is excellent in transferability of the thermal transfer ink, cushioning properties, heat insulating properties, and white paper gloss when heat-pressed, thermal transfer recording method, inkjet recording method, etc. The present invention relates to a porous sheet that can be used as a recording sheet and a method for producing the same.

  In recent years, printers and copiers using thermal transfer recording methods such as the fusion thermal transfer method and the sublimation type thermal transfer method, or the ink jet method have become full-color and high-quality images, and the amount of image receiving sheets used has increased. At the same time, the use is expanding.

  Various improvements have been made to recording sheets in order to obtain good prints with thermal transfer printers, color copiers and color printers. For example, a recording sheet is used in which a recording layer containing an ink receiving resin as a main component is formed on a sheet-like support such as paper or a biaxially stretched polyethylene terephthalate film. Since such a recording sheet has a uniform thickness and flexibility, a uniform transfer image can be obtained.

  Patent Document 1 discloses a thermal transfer recording sheet having a dye receiving layer composed of silicon-containing modified polyvinyl alcohol, and Patent Document 2 discloses a dye receiving layer composed of polymer particles having a crosslinked structure. A thermal transfer recording sheet is disclosed, and Patent Document 3 discloses a thermal transfer recording sheet having a dye-receiving layer composed of a urethane resin and a copolymer of a silicone macromonomer and a vinyl monomer. Is disclosed. Patent Document 4 discloses an image transfer sheet having an image receiving layer made of a crosslinked resin.

However, in these recording sheets, a thermosetting or crosslinkable resin or a resin containing an inorganic compound is used as the recording layer, and the structure thereof is also non-porous, so that the thermal followability of the recording layer is inferior. Therefore, when thermal transfer recording or the like is performed on a recording sheet using a stretched film or a paper substrate as a sheet-like support, the recording is caused by a difference in shrinkage or expansion characteristics between the sheet-like support and the recording layer due to heating. Curling and wrinkling occur in the sheet for printing, and the running performance in the printer is reduced, and in the paper base material, image unevenness occurs due to surface nonuniformity. In addition, these recording sheets have low heat insulating properties, the heat of the thermal head is dissipated, and the transfer of the image from the ink ribbon to the recording sheet is not effectively performed. May occur. In addition, in a method of obtaining an image by printing with ink used such as an ink jet method, ink is not sufficiently absorbed, and uneven gloss may occur.
Japanese Patent Laid-Open No. 10-337965 JP-A-10-338813 JP-A-12-86862 Japanese Patent Laid-Open No. 5-127413

  The present invention solves the above problems, is excellent in transferability of the thermal transfer ink, cushioning properties, heat insulation and gloss of blank paper when heat-pressed, and is suitable as a recording sheet for thermal transfer recording methods, ink jet recording methods, and the like. A porous sheet and a method for producing the same are provided.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have determined that the average pore diameter, the area ratio of the pores on the surface of the porous coating layer comprising a resin-containing film formed on the sheet-like support, and the thermocompression bonding The present inventors have found that the above-mentioned problems can be solved by optimizing the glossiness of the blank paper at the time, and have completed the present invention.

  The porous sheet according to the present invention has a sheet-like support and a porous coating layer formed on at least one surface thereof and made of a resin-containing coating, and the average pores on the surface of the porous coating layer After the diameter of 0.5 to 50 μm and the area ratio of open pores of 20 to 70% and the surface of the porous coating layer is heat-pressed at 150 ° C., the 75 ° white paper glossiness of the surface is 60% or more. It is characterized by being.

  The porous coating layer preferably has a large number of fine pores formed by mechanically stirring the resin-containing liquid, and the resin-containing film has a melting peak temperature of 50 by DSC. It is preferable that the main component is a thermoplastic resin having a temperature of ˜130 ° C.

  Furthermore, the manufacturing method of the porous sheet which concerns on this invention gives mechanical stirring to the resin containing liquid containing the thermoplastic resin whose melting peak temperature by DSC is 50-130 degreeC, and contains many fine pores. The porous resin liquid is applied to at least one surface of the sheet-like support, dried, and the surface has an average pore diameter of 0.5 to 50 μm and a pore area ratio of 20 to 70%. A coating layer is formed.

  The present invention is a porous sheet that is excellent in transferability, cushioning properties, heat insulating properties and glossiness of white paper when heat-pressed, and suitable as a recording sheet for thermal transfer recording methods, ink jet recording methods, etc. It is extremely useful.

  The porous coating layer formed on the sheet-like support of the present invention contains a resin or a resin and a pigment as main components. Such a porous coating layer is obtained by subjecting a liquid material containing a resin or a mixture of a resin and a pigment to mechanical stirring and the like to disperse and contain a large number of fine bubbles therein. Can be formed on a sheet-like support.

  Examples of resins that can be used to form a porous coating layer in the present invention include polyvinyl alcohols and derivatives thereof having various molecular weights and saponification degrees, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose; Acid soda, polyvinylpyrrolidone, acrylic acid amide-acrylic acid ester copolymer, acrylic acid amide-acrylic acid ester-methacrylic acid ester copolymer, alkali salt of styrene-maleic anhydride copolymer, polyacrylamide and its derivatives, Water-soluble polymers such as polyethylene glycol, polyolefins such as polyethylene, ionomers such as ethylene-methacrylic acid copolymer, polyvinyl acetate, polyurethane, styrene-butadiene copolymer, Acrylonitrile-butadiene copolymer, methyl methacrylate-butadiene copolymer, polyacrylate, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer, styrene-butadiene-acrylic copolymer Examples include coalesced water-dispersible resins such as polyvinylidene chloride, but are not limited thereto. These resins can be used alone or in combination of two or more as required. Moreover, it is preferable to use the thermoplastic resin whose melting peak temperature by DSC is 50-130 degreeC among these resin.

   The resin used for the porous coating layer is preferably substantially made of a thermoplastic resin because the 75 degree white paper gloss after thermocompression bonding at 150 ° C. is 60% or more, and further has a melting peak by DSC. It is preferable that temperature is 50-130 degreeC.

  In the present invention, examples of the pigment that can be contained in the porous coating layer include zinc oxide, titanium oxide, calcium carbonate, silicic acid, silicate, clay, talc, mica, calcined clay, aluminum hydroxide, and sulfuric acid. Inorganic pigments such as barium, lithopone, silica, colloidal silica, etc., processed into spherical, hollow, solid, through-hole or various shapes such as polystyrene, polyethylene, polypropylene, epoxy resin, styrene-acrylic copolymer Organic pigments referred to as plastic pigments of the type, starch powder, cellulose powder and the like can be used, but are not limited thereto. Moreover, these pigments can be used individually or in mixture of 2 or more types as needed.

  In the resin before foaming, or a mixture of resin and pigment, a known foam stabilizer, a surfactant called a foaming agent, a viscosity modifier (so-called thickener, etc.), a dispersant, A dyeing agent (dye), a waterproofing agent, a lubricant, a crosslinking agent, a plasticizer, a conductive agent, and the like can be added.

The coating amount of the porous coating layer is preferably in the range of ² to 40 g / m ² on one surface of the sheet-like support. When the coating amount is less than 2 g / m ² , it becomes difficult to sufficiently cover the roughness of the surface of the sheet-like support, and the roughness of the image quality increases. On the other hand, when it exceeds 40 g / m ² , the thickness of the porous coating layer becomes excessive, and the coating layer is easily peeled off or damaged. Accordingly, it is natural that sufficient attention should be paid to optimizing the coating amount of the porous coating layer in the same manner as optimizing the resin-containing liquid composition.

The method for forming the porous coating layer is not particularly limited, but the resin-containing mixed solution is applied to one surface of the sheet-like support and contains a large number of fine bubbles formed in the resin mixed solution. It can obtain preferably by drying in a state. There are no particular limitations on the method and equipment for forming and containing bubbles, and the coating method.
Specifically, examples of the method for forming the porous coating layer on the sheet-like support include the following methods. (1) A method in which a resin mixed liquid containing foam is applied onto a sheet-like support and gas is generated during or after application to form pores. (2) Two types in which gas is generated by contact with each other A method in which at least one of the above components is coated on a sheet-like support in advance, and a resin mixed solution containing other components is coated on the coated surface to form a foam film; (3) 1 atm A method in which a resin mixed solution in which a gas is dissolved at a higher pressure is applied to a sheet-like support under normal pressure and foamed to form pores. (4) A number of mechanically agitated resin mixtures are added to this. There is a method such as a method of applying a bubble-containing resin mixed liquid in which bubbles are formed and dispersed to a sheet-like support and drying the mixture. Any of these methods (1) to (4) may be used, but in the present invention, the method (4) is most preferable.
Therefore, the method for producing a porous sheet according to the present invention includes the following steps.
(1) a step in which bubbles are contained in the resin mixture by mechanical stirring, and
(2) A step of forming a porous resin layer on one surface of the sheet-like support by applying the resin mixture containing the bubbles.

  There is no particular limitation on the bubble-containing state of the mixed resin liquid containing bubbles, but when used as a recording sheet for a thermal transfer method, an inkjet method, etc., the volume ratio of the bubble-containing resin liquid to the stock solution (hereinafter referred to as the expansion ratio). .) Is preferably more than 1 and not more than 10 times, more preferably 1.5 to 3 times. That is, the expansion ratio is a scale indicating the bubble content in the bubble-containing resin mixed solution, and when the expansion ratio increases, it means that the thickness of the resin film (wall) constituting the bubbles is reduced. Moreover, when it is the same expansion ratio, it means that a resin film becomes thin, so that solid content concentration of the resin containing liquid mixture before foaming is low. Thus, when the resin film becomes thin, it may be difficult to maintain the strength of the resulting porous coating layer at a sufficient level. In this respect, the expansion ratio and the composition of the resin-containing mixture liquid Careful attention should be paid to balance.

  When the porous sheet of the present invention is used as an information recording sheet for a transfer recording method, an ink jet recording method, etc., it exhibits excellent recording performance. The reason is considered that the physical characteristics (structural characteristics and surface smoothness) of the porous sheet are involved. In other words, from the viewpoint of structural characteristics, since there are many fine pores on the surface of the porous coating layer of the porous sheet, excellent ink absorption effect and anchoring effect due to capillary action are manifested. In addition, the penetration of the ink into the porous sheet is improved, and it is considered that the ink has a high acceptability.

  In this respect, the pore size on the surface of the porous coating layer formed on the sheet-like support is important. That is, when the ink at the time of information recording is transferred, in order to form a good image on the porous sheet of the present invention, the average diameter of pores distributed on the surface of the porous coating layer is 0.5 to It is necessary to be 50 μm, preferably 0.5 to 20 μm. When the average pore diameter is less than 0.5 μm, the ink hardly penetrates into the porous coating layer and a sufficient absorption capacity cannot be obtained. On the other hand, if it is larger than 50 μm, the ink is buried in the pores, and transfer unevenness is likely to occur, resulting in poor dot reproducibility and failing to form a good image. However, when the porous sheet of the present invention is used as an image-receiving sheet for the melt thermal transfer recording system, the above-mentioned transfer unevenness and burial are likely to occur due to the mechanism of the melt thermal transfer recording system, so the average pores on the surface of the porous coating layer The diameter is preferably 0.5 to 30 μm. The pore diameter on the surface of the porous coating layer can be measured using an optical microscope or a scanning electron micrograph and an image analyzer.

  In addition, the pore size is the composition of the resin-containing mixed solution before the bubble formation / dispersion treatment, that is, the type of material, the mixing ratio, the solid content concentration, that is, in the porous coating layer after foaming, coating, and drying. It is often affected by various factors such as the amount remaining as a component directly related to the film thickness, the foaming ratio, the coating method, etc. Therefore, it is necessary to set appropriate conditions. Furthermore, the pores on the surface of the porous coating layer in the present invention are also related to the size of the bubbles of the bubble-containing resin liquid. Generally, the smaller the bubbles in the resin-containing liquid, the coating layer after coating and drying. Since the pores on the surface are also small, there is no particular restriction on the bubble-containing state of the resin-containing mixture, but the same size as the surface of the porous coating layer, that is, the average diameter is in the range of 0.5 to 50 μm. Some days are preferred.

  In the present invention, the aperture area ratio of the porous coating layer needs to be 20 to 70%. The larger the aperture area ratio, the better the ink penetration into the coating layer, but if it exceeds 70%, the ink penetration will be excessive and the surface recording density will be insufficient. It becomes. Moreover, there exists a possibility that the intensity | strength of coating layer itself may fall. On the other hand, if the aperture area ratio is less than 20%, the penetration of the molten ink into the coating layer becomes insufficient, a good image cannot be obtained, and unevenness may occur on the surface, resulting in uneven gloss. . Preferably, the pore area ratio is in the range of 30 to 60%, and the porous coating layer can maintain sufficient strength. Here, the pore area ratio means the ratio of the total area of the pores occupied by the pores to the total surface area of the porous coating layer surface.

Further, as another structural feature, when the cross section of the porous coating layer of the present invention is observed with a scanning electron microscope or the like, the pores of the coating layer have a large number of holes in the resin-containing film surrounding the pores. Open and adjacent pores are in communication with each other (ie, forming continuous pores). Therefore, since the porous coating layer of the present invention has the internal structure as described above, the transferred ink penetrates into the pores on the surface of the coating layer at the time of image fixing, and the inside of the coating layer. Since it is captured, it exhibits a high ink receiving ability. Furthermore, the density of the porous coating layer needs to be 0.1 to 0.8 g / cm ³ , and preferably 0.2 to 0.7 g / cm ³ . When the density is less than 0.1 g / cm ³ , the strength of the porous coating layer is insufficient, and when it exceeds 0.8 g / cm ³ , the ink does not penetrate sufficiently due to insufficient voids in the coating layer, Moreover, sufficient cushioning properties and heat insulation properties cannot be obtained.

In the present invention, a method for containing and dispersing bubbles in a resin-containing liquid (hereinafter referred to as a foaming method) is, for example, a so-called confectionery foaming machine having a stirring blade that rotates while performing planetary motion, and is generally emulsified and dispersed. Stirring mechanically while continuously feeding a mixture of air and resin-containing liquid into a stirrer such as a homomixer or cowless dissolver used in a closed system or a closed system, and dispersing the air into fine bubbles A continuous foaming machine such as a product manufactured by Gaston County of the United States or a product of Stoke of the Netherlands can be used.
In addition, the resin-containing liquid includes a foam stabilizer, a foaming agent and the like for the purpose of supplementing the performance of mechanical stirring equipment to obtain a higher bubble-containing state, or for improving the stability of bubbles in the bubbles. It is possible to appropriately select and add additives referred to from materials having a wide range of surface activity. Such a surfactant may be appropriately selected in consideration of the flow of the resin-containing liquid and the coating workability, but in particular, the effect of increasing the foamability of the resin-containing liquid, the dispersion, and the stability of the contained bubbles Therefore, higher fatty acids, higher fatty acid modified products, higher fatty acid alkali salts, and the like can be preferably used. For example, in the case of a water-dispersed resin-containing liquid, the blending amount (solid content) of the surfactant added as a foam stabilizer or a foaming agent is preferably 0 to 30 parts by mass with respect to 100 parts by mass of the solid content. Preferably it is 1-20 mass parts. Even if it exceeds 30 parts by mass, the effect is saturated, and it is often disadvantageous economically.

  For the purpose of adjusting the surface electrical resistance value of the porous coating layer to a desired range, a conductive agent can also be blended in the resin-containing liquid. As the conductive agent, for example, sodium chloride, potassium chloride, sodium sulfate, styrene-maleic acid copolymer, quaternary ammonium salt and the like are preferably used, but are not limited thereto.

Coating methods for forming a porous coating layer on a sheet-like support include Mayer bar method, gravure roll method, roll method, reverse roll method, blade method, knife method, air knife method, extrusion method, cast It can be arbitrarily selected from known methods such as a method, a lip coating method, and a die coating method.
Thus, after apply | coating a resin containing liquid uniformly to one side of a sheet-like support body, it can be made to dry and a porous coating layer can be obtained.

  The sheet having the porous coating layer of the present invention can be obtained by coating a bubble-containing resin mixed solution and obtaining a good image even after being dried, and high white paper gloss after thermocompression bonding. And using a super calender composed of a combination of resin rolls or metal rolls and cotton rolls as appropriate, the porous coating layer can be finished to further improve the surface smoothness. it can. Further, after coating, a semi-dried or dried sheet may be brought into contact with a mirror-finished heated or non-heated cast drum or the like to form a porous coating layer imparted with surface smoothness. . However, if the above smooth finish treatment is performed under excessive pressure, the resin wall surrounding the air bubbles in the porous coating layer is destroyed, resulting in densification of the coating layer, resulting in a decrease in heat insulation and cushioning properties, or porosity. Since the pores and destruction occur on the surface of the porous coating layer, the excellent transfer performance of the porous coating layer may not be obtained.

  In addition, as the sheet-like support used in the present invention, paper such as paper mainly composed of cellulose, coated paper, and laminated paper as well as cloth such as woven fabric and non-woven fabric can be used. Further, plastic films such as polyolefin, cellulose acetate, and polyethylene terephthalate, synthetic paper made of polyolefin and pigment, and porous synthetic resin films such as foamed polyethylene terephthalate film and foamed polypropylene film can be used.

  Further, when the porous sheet of the present invention is produced by applying a bubble-containing resin liquid on the sheet-like support, in the steps of coating, drying and winding, the sheet itself is placed inside the coated surface. Or it may curl outward. In this case, if the sheet is used after being processed into an image forming sheet having a predetermined size by cutting, the feeding to various printers may not be performed normally, or the running performance inside the apparatus may deteriorate. Trouble may occur. In particular, the thermal transfer recording method is a method in which a heat source is brought into contact with an ink ribbon to transfer a dye component in the ribbon onto a recording sheet. Therefore, a resin layer that forms an image forming surface and a sheet-like support layer Due to the difference in shrinkage due to heating or the difference in expansion characteristics, the image receiving sheet is curled inside the apparatus, and the above-described trouble occurs. Due to the occurrence of such curling, the image is formed obliquely with respect to the normal paper surface direction, or the sheet tends to wrinkle inside the apparatus, and therefore the contact between the ink ribbon and the image receiving sheet is not normally performed, Ink transfer failure may occur and as a result image quality may deteriorate.

  In order to prevent various troubles caused by such curling, it is necessary to reduce the difference in shrinkage characteristics or the difference in expansion characteristics due to heating between the porous coating layer and the sheet-like support layer as much as possible. desirable. Therefore, an anti-curl layer may be coated or laminated on the back surface of the sheet, that is, the surface opposite to the porous coating layer. There are no restrictions on the material, formation method, coating amount, lamination amount, etc. of this anti-curl layer, and the type, thickness, or properties of the porous coating layer, that is, the material composition, expansion ratio, coating amount, etc. It can be optimized by considering various factors such as the amount of work.

  In addition, depending on the material selected for the sheet-like support, the resulting porous sheet is subject to various frictional forces on the mechanism of the device when it runs in the printer, and the influence of heating such as a decrease in humidity inside the device is independent. Alternatively, the porous sheet may be electrostatically charged in combination. When a large number of images are continuously formed in such a state, the image forming surface of the porous sheet and the back surface of the next porous sheet are electrostatically in close contact and are difficult to peel off. In particular, since various plastic sheets or synthetic papers are inherently easily charged, when they are used as a sheet-like support, static electricity is generated during sheeting by cutting or during storage after processing. Occurrence makes it difficult to peel the front and back of the sheet. As a matter of course, the above-described trouble can occur even when paper is used as a sheet-like support. In order to prevent troubles associated with such charging, it is extremely effective to form a so-called antistatic layer on the back surface of the transfer sheet. It can also be achieved by using an antistatic material or by reducing the coefficient of friction between the sheet back surface and the porous coating layer. Accordingly, the antistatic layer can be formed by appropriately selecting from a wide range of materials and methods as in the case of forming the anticurl layer.

  In addition, after the production of the porous sheet, on the surface of the sheet-like support opposite to the porous coating layer, for identification of the porous coating layer surface, and for printing of the company name, product name or logo mark Therefore, various types of printing may be performed for detection marks for control necessary for image formation in the printer. Therefore, it is possible to impart ink setting properties by forming a layer having printability on the back surface of the porous sheet. The anti-curl layer, the antistatic layer and the printability imparting layer can be individually formed on the back surface of the sheet-like support to obtain the desired performance, but the production process is simplified and the production cost is reduced. The material can be formed in a single layer and the object can be achieved by appropriately selecting a material and a forming method as necessary, such as a reduction or an intended functional level. That is, it is possible to provide functions such as curling prevention, antistatic and printability with a single layer. Therefore, there is no limitation on the number of layers formed on the back surface of the sheet-like support.

  When the same porous coating layer is provided on both sides of the sheet-like support, the porous coating layers on both sides have the same shrinkage or expansion characteristics. There is an advantage that curling due to heating is difficult to occur.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the following examples and comparative examples, “parts” and “%” represent “parts by mass” and “% by mass” unless otherwise specified.

Example 1
(Resin mixture 1, paint solid content 25%, paint viscosity 2000 mPa · s)
Resin: 100 parts of ethylene-methacrylic acid copolymer resin (Chemical S75N, manufactured by Mitsui Chemicals) Foam stabilizer: Higher fatty acid (SN foam 200, manufactured by San Nopco) 10 parts Thickener: Polyether (SN thickener 612, 2 parts of the above-mentioned resin mixed solution 1 is mixed and stirred with air at a stirring speed of 1200 rpm using a continuous foaming machine (trade name: Turbo Whip TW-70, manufactured by Aikosha Seisakusho Co., Ltd.) and foamed. Foaming was performed so that the magnification was 2.5 times. Immediately after the foaming treatment, use the applicator bar on the surface of the high-quality paper having a basis weight of 104 g / m ^{2 so} that the obtained foam-containing resin mixture is 10 g / m ² after drying. The porous sheet was produced by coating and drying. The physical properties of the obtained porous sheet are summarized in Table 1.

Example 2
(Resin mixture 2, paint solid content 30%, paint viscosity 2000 mPa · s)
Resin: Olefin-acrylic resin (ET-1000, manufactured by Chuo Rika Co., Ltd.) 100 parts Foam stabilizer: Higher fatty acid type (SN foam 200, manufactured by San Nopco) 10 parts Thickener: Polyether type (SN thickener 612, San Nopco) (Product made) 2 parts Using the resin mixed solution 2, in the same manner as in Example 1, it was mixed and stirred with air at a stirring speed of 1000 rpm, and subjected to foaming treatment so that the foaming ratio would be 3 times. Thereafter, a porous sheet was produced in the same manner as in Example 1.

Example 3
(Resin mixture 3, paint solid content 30%, paint viscosity 2000 mPa · s)
Resin: Polyurethane resin (HUX-380A, manufactured by Asahi Denka Co., Ltd.) 100 parts Foam stabilizer: Higher fatty acid type (SN foam 200, manufactured by San Nopco) 10 parts Thickener: Polyether type (SN thickener 612, manufactured by San Nopco) 2 parts Using the resin mixed solution 3, in the same manner as in Example 1, it was mixed and stirred with air at a stirring speed of 1000 rpm, and subjected to foaming treatment so that the foaming ratio was 3 times. Thereafter, coating and drying were performed in the same manner as in Example 1, followed by smoothing using a super calender to produce a porous sheet.

Example 4
(Resin mixture 4, paint solid content 25%, paint viscosity 3500 mPa · s)
Resin: Polyethylene resin (PEM-17, manufactured by San Nopco) 90 parts Polyvinyl alcohol (PVA-205, manufactured by Kuraray Co., Ltd.) 10 parts Foam stabilizer: Higher fatty acid type (SN foam 200, manufactured by San Nopco) 10 parts The resin mixture 4 and the mixture was stirred and mixed with air at a stirring speed of 1200 rpm in the same manner as in Example 1, and the foaming treatment was performed so that the expansion ratio was 2.5 times. Thereafter, a porous sheet was produced in the same manner as in Example 1.

Comparative Example 1
(Resin mixture 5, paint solid content 25%, paint viscosity 2500 mPa · s)
Resin: Polyvinyl alcohol (PVA-205, manufactured by Kuraray Co., Ltd.) 100 parts Foam stabilizer: Higher fatty acid type (SN foam 200, manufactured by San Nopco) 10 parts Using the resin mixture 5, stirring is performed in the same manner as in Example 1. The foaming was performed by mixing with air at a speed of 600 rpm and stirring, so that the foaming ratio was 2.5 times. Thereafter, a porous sheet was produced in the same manner as in Example 1.

Comparative Example 2
(Resin mixture 6, paint solid content 25%, paint viscosity 2500 mPa · s)
Resin: Acetoacetylated starch (Petrocoat C8, manufactured by Dainippon Ink & Chemicals, Inc.) 100 parts Foam stabilizer: Higher fatty acid type (SN foam 200, manufactured by San Nopco) 10 parts Example 1 using the resin mixture 6 In the same manner as above, the mixture was mixed and stirred with air at a stirring speed of 600 rpm, and the foaming treatment was performed so that the expansion ratio was 2.5 times. Thereafter, a porous sheet was produced in the same manner as in Example 1.

Comparative Example 3
(Resin mixture 7, paint solids 25%, paint viscosity 2500 mPa · s)
Resin: Ethylene-methacrylic acid copolymer resin (Chemical S75N, Mitsui Chemicals) 50 parts Polyvinyl alcohol (PVA-205, Kuraray Co.) 50 parts Foam stabilizer: Higher fatty acid type (SN foam 200, San Nopco) 10 Part Using the resin mixed solution 7, in the same manner as in Example 1, it was mixed and stirred with air at a stirring speed of 1000 rpm, and subjected to foaming treatment so that the foaming ratio was 3 times. Thereafter, a porous sheet was produced in the same manner as in Example 1.

Comparative Example 4
The resin mixed solution 1 was not foamed and coated and dried in the same manner as in Example 1 to produce a sheet.

In addition, the measurement and evaluation described in the Example and the comparative example were performed by the following method. Each physical property was measured after conditioning the sample to be measured in an ISO standard environment (23 ° C., relative humidity 50%) for 24 hours.
<Evaluation method>
(1) Average pore diameter and open area ratio on the surface of the porous coating layer After photographing the surface of the porous coating layer using a scanning electron microscope (SEM) or an optical microscope, the outline of the pores on the surface Was accurately drawn on a transparent film with a black pen or the like and measured using an image analyzer (Image Analyzer V10, manufactured by Toyobo Co., Ltd.). Since the pore shape on the surface of the porous resin film of each master was not necessarily a perfect circle, the average pore diameter was converted to an equivalent circle diameter based on the area in the outline of the pores obtained by image analysis, and the average pore diameter was obtained. Moreover, the ratio (hole area ratio) which a hole part occupies is a ratio of the area which the opening part by a pore occupies with respect to the total area of each master surface, and it computed by following Formula.
(Percentage of the hole portion) = (Area occupied by the opening portion due to the pores) / (Total area of the master surface for stencil printing) × 100

(2) DSC measurement (measurement of melting peak temperature)
10 mg of the thermoplastic resin used in Examples and Comparative Examples was set in a thermal analysis system manufactured by SII, DSC6200, and heated at a rate of temperature increase of 10 ° C./min in a N ₂ gas stream, and the endothermic behavior accompanying melting of the resin. Was analyzed by the first and second derivatives, the temperature showing the peak or shoulder was determined, and this was taken as the melting peak temperature.

(3) Thermocompression bonding Using a heat seal tester (manufactured by Tester Sangyo Co., Ltd.), the surface of the porous coating layer was thermocompression bonded to melt the surface. Thermocompression bonding conditions: temperature 150 ° C., pressure 9.8 N, pressurization time 0.5 seconds

(3) Measurement of glossiness of blank paper Based on the method described in JIS Z 8741, the glossiness of the blank paper surface after thermocompression bonding was measured under the condition of an incident image and a light receiving angle of 75 °. The glossiness was measured using a gloss meter (GM-26D type, manufactured by Murakami Color Research Laboratory).

The porous sheet according to the present invention has a large number of voids on the surface and inside, and is excellent in white paper gloss when absorbed by ink or toner, cushioning properties, heat insulation and thermocompression bonding, thermal transfer recording method, ink jet recording method It can be suitably used for recording sheets such as and is extremely useful in practice.

Claims (4)

In a porous sheet having a sheet-like support and a porous coating layer formed on at least one surface thereof and made of a resin-containing film, the average pore diameter of the surface of the porous coating layer is 0.5 to The surface area of the porous coating layer is 50 μm, the area ratio of the open area is 20 to 70%, and the surface of the porous coating layer is heat-pressed at 150 ° C., and then the 75 ° white paper glossiness of the surface is 60% or more. Porous sheet. The porous sheet according to claim 1, wherein the porous coating layer has a large number of fine pores formed by mechanically stirring the resin-containing liquid. The porous sheet according to claim 1 or 2, wherein the resin-containing film is mainly composed of a thermoplastic resin having a melting peak temperature by DSC of 50 to 130 ° C. At least one surface of the sheet-like support is obtained by subjecting a resin-containing liquid containing a thermoplastic resin having a melting peak temperature by DSC of 50 to 130 ° C. to mechanical stirring and containing a large number of fine pores. The porous sheet is characterized by forming a porous coating layer having an average surface pore diameter of 0.5 to 50 μm and an open area ratio of 20 to 70%, which is coated on the substrate and dried. Manufacturing method.