JP2020045439A - Polyester film for receiving paper - Google Patents

Abstract

To provide a polyester film for receiving paper that can satisfy both print misalignment and image clarity.SOLUTION: Provided is a polyester film for receiving paper, in which the apparent density of the film is 0.60 g/cmor more and less than 0.90 g/cm, and the Pickers hardness of at least one surface of the film is 0.5 gf/μmor more and 2.0 gf/μmor less.SELECTED DRAWING: None

Description

  TECHNICAL FIELD The present invention relates to a polyester film for receiving paper, which is free from printing deviation and has excellent image clarity.

Conventionally, a polyester film has been used as a base material of a receiving paper such as a heat-sensitive recording sheet, and generally has a structure of a receiving sheet of natural paper / adhesive layer / polyester film / (easy adhesive layer) / coat layer for forming a receiving layer. Some are used. The ink ribbon is heated while being pressed by the thermal head on the receiving layer forming coat layer, and the ink is transferred to the surface side of the polyester film through the receiving layer forming coat layer and printed.
Since the polyester film is used as the base material of the receiving paper, it has both surface smoothness and moderate cushioning property, so that the thermal head and ink ribbon during transfer can make uniform contact with the base material surface, This is because good printability that cannot be obtained with natural paper can be obtained.
The polyester film has a two-layer structure of an outer layer having gloss and a cavity layer having cushioning properties, or an outer layer having gloss is laminated on both sides of the cavity layer having cushioning properties. A three-layer film is known. For example, as described in Patent Documents 1 to 3, a nucleus material for forming a cavity is added to a polyester film to provide cushioning with a layer containing the cavity, and a cavity is formed on the surface of the layer containing the cavity. Layers that are not formed as much as possible are laminated to improve printability.

JP-A-11-240972 JP 2000-355166 A JP 2005-238622 A

  Normally, an ink ribbon in which C (cyan), M (magenta), Y (yellow) and a surface protection coating are arranged on a receiving sheet is heated and transferred by a thermal head, and C (cyan) is applied to the surface of the receiving sheet. , M (magenta) and Y (yellow) are sequentially transferred to the same position, and the density of those colors is adjusted to form color images of various colors on the surface of the receiving sheet. In order to obtain sharpness of the image, it is necessary to impart cushioning properties to the base material so that the ink ribbon is firmly in contact with the base material. Also, in the natural paper provided at the lowermost position of the receiving sheet, the surface roughness of the natural paper in contact with the polyester film is coarser than the polyester film. Therefore, unless sufficient cushioning properties are imparted to the polyester film, the roughness of the natural paper affects the printing surface of the receiving sheet, causing the imprint to appear, resulting in a lack of apparent clarity.

  The methods described in Patent Literatures 1 to 3 have excellent cushioning properties in order to obtain the clarity of the print, but the thermal head is incorporated in the receiving sheet, and the running properties of the ink ribbon are deteriorated. Are stacked at different positions, and the contour and color of the design of the object included in the image tend to shift.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a polyester film for receiving paper, which can achieve both print misregistration and image clarity in view of the above-mentioned problems of the related art.

The present inventors have made in view of the above problems, and found that a film having a specific configuration can solve the above problems, and have completed the present invention.
That is, the present invention can be obtained as follows.
(1) Receiving paper having an apparent density of the film of 0.60 g / cm ³ or more and less than 0.90 g / cm ³ and a Pickers hardness of the film surface of 0.5 gf / μm ² or more and 2.0 gf / μm ² or less. For polyester film.
(2) The polyester film for receiving paper according to (1), which has at least one layer containing a cavity (layer B).
(3) The film has a total thickness of 70 μm or more and 150 μm or less, and has a polyester layer (A layer and / or C layer) on at least one side of the layer containing the cavity (B layer). The polyester film for receiving paper according to (2), wherein the thickness of the polyester film is 4 μm or more and 15 μm or less.

  ADVANTAGE OF THE INVENTION According to this invention, the polyester film for receiving papers which can make printing gap and the sharpness of an image parallel can be provided.

  An embodiment for implementing the polyester film of the present invention will be described below.

  The polyester film of the present invention is a film made of a polyester resin containing polyester as a main component. Polyester resin is a general term for polymers having an ester bond as a main bonding chain, and includes ethylene terephthalate, ethylene-2,6-naphthalate, butylene terephthalate, and ethylene-α, β-bis (2-chlorophenoxy). At least one component selected from ethane-4,4'-dicarboxylate and the like is used as a main component, and these components may be used alone or in combination of two or more. It is preferable to use polyethylene terephthalate as a main component in consideration of overall economy and the like. Further, in these polyester resins, other dicarboxylic acid components and diol components may be partially copolymerized, preferably 20 mol% or less.

The apparent density of the film of the present invention needs to be 0.60 g / cm ³ or more and less than 0.90 g / cm ³ . When the apparent density is less than 0.60 g / cm ³ , the cushioning property of the film is improved, the surface roughness of natural paper is absorbed, and the thermal head is more easily brought into contact with the surface of the receiving sheet. Although the sharpness is improved, the cushioning property becomes too high, so that the friction with the thermal head is increased and printing misregistration occurs. When the apparent density exceeds 0.90 g / cm ³ , the cushioning property is reduced, so that the friction with the thermal head is reduced and printing misregistration is difficult to occur. Since the contact property of the head is deteriorated due to the surface of the receiving sheet and the heat insulation property is reduced, the sharpness of the image tends to be reduced. As will be described in detail later, this cushioning property can be easily achieved by including a cavity in the film. More preferably, it is 0.65 g / cm ³ or more and less than 0.85 g / cm ³ .

In the film of the present invention, the Pickers hardness of at least one surface needs to be 0.5 gf / μm ² or more and 2.0 gf / μm ² or less. If the Pickers hardness is less than 0.5 gf / μm ² , the friction between the receiving sheet and the thermal head is increased, and printing misalignment is likely to occur. If the Pickers hardness exceeds 2.0 gf / μm ² , friction between the receiving sheet and the thermal head is small, and printing misalignment is less likely to occur. However, the thermal head is less likely to contact the receiving sheet surface via the ink ribbon, The heat from the head cannot be insulated at a portion close to the surface layer of the receiving sheet, and the sharpness of the image tends to decrease. Further, the Pickers hardness is easily affected by the apparent density, and if the hardness is less than 0.5 gf / μm ² , when the receiving sheet is formed, the sheet may be easily broken and wrinkles may be generated on the surface of the receiving layer. In order to set the Pickers hardness within the above range, the total thickness of the polyester film, the total apparent density, the thickness of the polyester layer (A layer), and the particle content of the polyester layer (A layer) are 1.0% by mass or less. And the like.

  The film of the present invention preferably has at least one layer containing a cavity (layer B). This is because having a layer containing a cavity (layer B) in the film makes it easy to impart cushioning properties to the film. The layer containing the voids (layer B) can be made to contain the voids by (1) adding a foaming agent to the polyester and foaming it by heating during extrusion or film formation, or foaming it by chemical decomposition to form bubbles. (2) a method of adding a gas or a vaporizable substance at the time of extrusion of the polyester, (3) adding a thermoplastic resin (incompatible resin) incompatible with the polyester to the polyester and uniaxially or A method of generating fine bubbles by biaxial stretching, (4) a method of adding a large amount of bubble-forming inorganic particles instead of the incompatible resin, and the like are preferably used. Any method may be used as long as it is within the range of the object of the present invention.However, film forming properties, ease of adjusting the amount of bubbles to be contained therein, formation of bubbles of finer and uniform size are formed. The method using the immiscible resin of the above (3) is particularly preferably used in terms of comprehensiveness such as easiness and light weight. The immiscible resin referred to herein is a thermoplastic resin other than the polyester, and a thermoplastic resin exhibiting incompatibility with the polyester. It is preferable to use a resin having a large effect of forming bubbles in the resin. More specifically, the incompatible resin refers to a system obtained by melting a polyester and the incompatible resin by a known method, preferably by a differential scanning calorimeter (DSC), dynamic viscoelasticity measurement, or the like. When measured, Tg corresponding to the incompatible resin is observed in addition to the glass transition temperature (hereinafter abbreviated as Tg) corresponding to the polyester.

  It is particularly preferable that the melting point of such an incompatible resin is lower than the melting point of the polyester and higher than the temperature (heat treatment temperature) when the film is heat-set and oriented during film formation. From this point, among the incompatible resins, polyethylene, polypropylene, polybutene, polyolefin resins such as polymethylpentene, polystyrene resins, polyacrylate resins, polycarbonate resins, polyacrylonitrile resins, polyphenylene sulfide resins, fluorine resins and the like are preferably used. Can be These incompatible resins may be a homopolymer or a copolymer, and two or more incompatible resins may be used in combination. Among these, polyolefin resins such as polypropylene and polymethylpentene having a small critical surface tension are preferable, and polymethylpentene is most preferable. Since polymethylpentene has a relatively large difference in surface tension from polyester and a high melting point, it has a feature that the effect of forming bubbles per addition amount is large, and is particularly preferable as an incompatible resin.

The fine cavities in the present invention are those that can contribute to imparting heat insulating properties and cushioning properties to the film itself for the purpose of improving sensitivity, and are generated using the incompatible resin contained in polyester as a core. Most preferably. Furthermore, when the cross section (thickness direction) of the layer (B) containing a cavity is observed by a scanning electron microscope (SEM) or a transmission electron microscope (TEM), the cross-sectional area of the bubble portion (however, the nucleus of bubble generation) preferably has an average value of the incompatible resin portion is excluded) is 1 to 25 m ² for a, more preferably 1.5～20Myuemu ^2, more preferably from 2 to 15 [mu] m ^2.

  The content of the incompatible resin in the cavity-containing layer (B layer) is preferably from 1 to 35% by weight, more preferably from 5 to 30% by weight, and even more preferably from 10 to 25% by weight, based on the entire B layer. Is most preferable. The film of the present invention used for receiving paper applications is required to have whiteness similar to paper, but if the content is less than the above range, it is difficult to improve the whiteness and concealability of the film, and conversely. When the content is more than the above range, the film may be easily broken at the time of stretching, and the productivity may be reduced.

  Further, in the layer containing cavities (layer B), the dispersion diameter of the incompatible resin is reduced, so that the bubbles generated by stretching can be made finer, and as a result, the whiteness and film forming properties of the film are improved. Therefore, it is more preferable to add a dispersant in addition to the polyester and the incompatible resin described above. Examples of the dispersant having the above-mentioned effects include olefin polymers or copolymers having a polar group such as a carboxyl group or an epoxy group or a functional group reactive with polyester, diethylene glycol, polyalkylene glycol, and a surfactant. And a heat-adhesive resin. Of course, these may be used alone or in combination of two or more. Such a dispersant may be used as a polyester obtained by previously copolymerizing the dispersant in a polymerization reaction, or may be used directly as it is.

  The total thickness of the film of the present invention is not particularly limited, but is preferably from 70 to 150 μm from the viewpoint of balance between workability such as fold wrinkle resistance, whiteness, heat insulation, and printing characteristics.

  The film of the present invention preferably has a polyester layer (A layer and / or C layer) on at least one surface of a layer containing cavities (B layer). By having the polyester layer (A layer or C layer) on at least one side of the layer containing the cavity (B layer), it is possible to easily obtain a film satisfying the apparent density and Pickers hardness of the present invention. Has a polyester layer (A layer, C layer) on both sides of a layer containing (B), it is possible to prevent contamination of the layer B caused by falling off of particles in the film production process. Further, by providing polyester layers on both sides of a layer containing cavities such as A layer / B layer / A layer (two types and three layers) and A layer / B layer / C layer (three types and three layers), the appearance of the film is improved. Although it depends on the density and the thickness of the polyester layer, folding wrinkles are likely to be generated when the receiving sheet is used.

  The thickness of one layer of the polyester layer (A layer and / or C layer) of 4 μm or more and 15 μm or less is less susceptible to natural paper, and the film of the present invention can be printed with higher sensitivity. It is preferable to increase sharpness. If the thickness of one layer of the polyester layer (layer A and / or layer C) is thin and less than 4 μm, the sensitivity becomes high and the sharpness of the image is improved, but the surface roughness of natural paper is roughened, so The sharpness is reduced and the layer containing the voids (layer B) is susceptible to the cushioning property, and the printing misalignment is likely to occur. When the thickness of one layer of the polyester layer (A layer and / or C layer) exceeds 15 μm, the printing deviation is hardly affected by the surface roughness of natural paper and the cushioning property of the layer (B layer) containing voids. Although it hardly occurs, the sharpness of an image is impaired due to a decrease in sensitivity. The thickness per layer of the polyester layer (A layer and / or C layer) is more preferably 7 μm or more and 14 μ or less.

  The polyester layer (A layer and / or C layer) may contain inorganic particles in an amount of 1 to 35% by weight based on the whole layer. Examples of the inorganic particles include wet and dry silica, colloidal silica, calcium carbonate, aluminum silicate, calcium phosphate, alumina, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide (zinc white), antimony oxide, cerium oxide, zirconium oxide, and oxide. Tin, lanthanum oxide, magnesium oxide, barium carbonate, zinc carbonate, basic lead carbonate (white lead), barium sulfate, calcium sulfate, lead sulfate, zinc sulfide, mica, titanium mica, talc, clay, kaolin, lithium fluoride and Calcium fluoride or the like can be used, and by containing particles, the film can be provided with lubricity. In addition, from the viewpoint of glossiness, two or more types of inorganic particles are combined in the polyester layer (A layer and / or C layer), and a part of the content of one type of inorganic particles is reduced. It is also possible to make the gloss larger while making the lubricity larger by increasing the lubricity. From the viewpoint of improving whiteness, titanium oxide and calcium carbonate or barium sulfate are more preferably selected.

  The inorganic particles preferably have an average particle size in the polyester of preferably 0.05 to 10 μm, more preferably 0.1 to 3 μm. If the average particle size is outside the above range, the uniform dispersibility of the inorganic particles may be poor due to aggregation or the like, or the gloss or smoothness of the film surface may be reduced by the particles themselves, which is not preferable.

  Organic particles can also be used as particles contained in the layer (A layer and / or C layer). Examples include crosslinked polymer particles, calcium oxalate, acrylic particles, imide particles, and the like.

Next, an example of the method for producing a polyester film for an image receiving paper of the present invention will be described, but the present invention is not limited to only such an example.
In a composite film forming apparatus having an extruder (A), an extruder (B) and an extruder (C), in order to form a polyester layer (B), it is incompatible with vacuum-dried polyester chips and vacuum-dried polyester. The resin-containing chip is mixed with the immiscible resin and the inorganic particles in an amount of 1 to 35% by weight, and the mixture is supplied to an extruder (B) heated to 260 to 300 ° C. Thereafter, the mixture is filtered through a filter having a cut of 10 to 50 μm, and then introduced into a T-die composite mouthpiece. If necessary, a dispersant may be added to this raw material in an amount of 0.05 to 10% by weight. The addition of the immiscible resin may be performed by vacuum-drying a master chip which has been used in advance. On the other hand, in order to laminate a polyester layer (A layer and / or C layer), a polyester chip and a master chip of inorganic particles are mixed so that the inorganic particles become 1 to 35% by weight, and sufficiently dried in vacuum. If necessary, a fluorescent whitening agent may be added to this raw material in an amount of 0.01 to 1.5% by weight. Next, this dried raw material is supplied to an extruder (A) and an extruder (C) heated to 260 to 300 ° C., melted and filtered in the same manner as in the case of the polyester (B) layer, and subjected to a T-die composite die. Introduce within.
In the T-die composite die, the polymer of the extruder (B) is in the center, the polymer of the extruder (A) is on one side of the extruder (B), and the polymer of the extruder (C) is the extruder (A). And then co-extruded into a sheet to obtain a melt-laminated sheet.
This molten laminated sheet is closely cooled and solidified by static electricity on a drum cooled to a surface temperature of 10 to 60 ° C. to produce an unstretched laminated film. The unstretched laminated film is guided to a group of rolls heated to 70 to 120 ° C., stretched 2 to 5 times in a longitudinal direction (longitudinal direction, that is, a direction in which the film advances), and cooled by a group of rolls of 20 to 30 ° C.
Subsequently, after applying a corona discharge treatment to the polyester layer (layer A) side of the film stretched in the longitudinal direction, if necessary, a coating liquid for forming a coating layer is applied to the treated surface. Thereafter, the film is guided to a tenter while holding both ends of the film with clips, and stretched 2 to 5 times in a direction perpendicular to the longitudinal direction (lateral direction) in an atmosphere heated to 90 to 150 ° C.
The stretching ratio is 2 to 5 times each in the vertical and horizontal directions, and the area ratio (longitudinal stretching ratio × lateral stretching ratio) is preferably 6 to 20 times. When the area magnification is less than 6 times, the whiteness and film strength of the obtained film become insufficient, and when the area magnification exceeds 20 times, the film tends to be easily broken during stretching.
In order to complete the crystal orientation of the biaxially stretched film thus obtained and to impart flatness and dimensional stability, a heat treatment is continuously performed in a tenter at 150 to 240 ° C. for 1 to 30 seconds to obtain a uniform film. After cooling slowly to room temperature, the polyester film of the present invention can be obtained by winding it up. During the heat treatment step, a 3 to 12% relaxation treatment may be performed in the horizontal or vertical direction as necessary. Further, the biaxial stretching may be either sequential stretching or simultaneous biaxial stretching, and may be re-stretched in either the longitudinal or transverse direction after the biaxial stretching.

[Method of measuring and evaluating characteristics]
The characteristic values of the present invention are determined by the following evaluation methods and evaluation criteria.

(1) Film, thickness of each layer (μm)
The thickness of the film is measured using a micrometer according to JIS C2151 (1990). The measurement was performed at arbitrary five points, and the average value was defined as the overall thickness of the film.
After the sample was frozen, a cross section was cut out, and the cross section was observed at a magnification of 500 to 5,000 times using a scanning electron microscope S-2100A (manufactured by Hitachi, Ltd.). The presence or absence of the presence of any air bubbles was examined. The presence or absence of bubbles is determined as an average value when the average cross-sectional area of the bubble portion in the cross-sectional photograph is converted to a perfect circle. If the average value is 1 μm ² or more, the layer is determined to be a bubble-containing layer, and bubbles are continuously contained. The layer was distinguished from a layer containing air bubbles (layer B) and a layer not containing air bubbles into a polyester layer (layer A and / or layer C).
In addition, the length in the thickness direction of each polyester layer was measured from a cross-sectional photograph, and the thickness of each layer was determined by back calculation from the magnification. In determining the cross-sectional area of the air bubble portion and the thickness of each polyester layer, a cross-sectional photograph of a total of five locations arbitrarily selected from different measurement fields of view was used, the average was calculated, and measured with a micrometer. The thickness of each layer was calculated by multiplying the total thickness by the ratio of each layer calculated from the layer ratio.

(2) The apparent density film is cut into a 100 × 100 mm square, and the thickness at 10 points is measured with a dial gauge attached, and the average value d (μm) of the thickness is calculated. In addition, the weight is weighed by a balance, and the weight w (g) is read to the unit of 10-4 g. At this time, the apparent density was determined by the following equation.

Apparent density (g / cm ³ ) = w / d × 100
(3) Pickers hardness test by nano indenter According to Pickers hardness test (JIS Z 2244),
An indentation test was performed using a Nano Indenter G200 (manufactured by Agilent Technologies, Inc.) at a maximum load of 0.2 gf using a Berkovich indenter. From the obtained results, the hardness HIT was calculated.
Note that the slope S used for the calculation was calculated from the range from the maximum load to the 30% load of the maximum load among the unloading curves of the load displacement curve obtained by the test. The measurement was performed three times, and the average was obtained, which was defined as hardness HIT. The hardness HIT is multiplied by a coefficient 0.9269 × 10 ³ to obtain Hv1 (kg / mm ² ), and the Hv1 is multiplied by a coefficient 9.8 × 10 ⁻⁶ to obtain Hv2 (gf / μm ² ). This was calculated and used as Pickers hardness. The table shows the Pickers hardness of the layer A or the layer C. When the A layer and the C layer have different thicknesses, it indicates the Pickers hardness of the surface of the thinner layer.

(4) Evaluation of print misregistration On the surface of the polyester film of the present invention (in the case of the A layer or the C layer, when the A layer and the C layer have different thicknesses, the surface of the thinner layer) is coated with the receiving layer forming coating liquid. Apply.
[Receptive layer forming coating liquid]
Polyester resin (manufactured by Toyobo Co., Ltd., Byron 200) 20 parts Silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd., X-22-3000T) 2 parts Toluene 39 parts Methyl ethyl ketone 39 parts Next, a paper weighing 125 g / m ² is used. Lamination is performed so that the receiving layer is on the outside on both sides, and a card photo printer "CP-300" (manufactured by Canon) and a special ink ribbon (color ink, attached to the paper set KL-36IP) are attached. A test print was made on the surface of the receiving sheet on which the receiving layer was formed. ◎ and 〇 are acceptable.
：: No misalignment of the print was observed, and the image was clean and good.
〇: Although the print is slightly misaligned, it is generally beautiful and good.
×: Displacement of the print can be clearly confirmed.

(5) Evaluation of image clarity In the same manner as in (4), a solid gray print is formed on the receiving layer. The obtained prints were evaluated as follows. ◎ and 〇 are acceptable.
A: Printing was performed without unevenness.
〇: Slight unevenness and linear pattern are observed.
×: Clear unevenness and linear pattern are observed.

(6) Comprehensive evaluation of printability Both the print deviation and the sharpness of prints evaluated in (4) and (5) were evaluated as a comprehensive evaluation as described below.
◎: All evaluations of ◎.
〇: Any one of the evaluations of 〇 and no evaluation of ×.
X: A substance having at least one evaluation of x.

(Example 1)
In a composite film forming apparatus having an extruder (a) and an extruder (b), polyethylene terephthalate (melting point: 256 ° C .: hereinafter) obtained by a conventional method to form a polyester layer (A layer) and (C layer) Polyethylene terephthalate in which agglomerated silica particles (average particle diameter 2.6 μm) are contained in a ratio of 0.26% by weight with respect to the polyester layer (A layer) and (C layer), respectively. (Melting point: 256 ° C.) was vacuum-dried at 180 ° C. for 3 hours, fed to the extruder (a), melt-extruded at 280 ° C., and subjected to foreign matter filtration by a 35 μm cut filter. Introduced.

  To form a layer containing cavities (B layer), polymethylpentene (manufactured by Mitsui Chemicals, Inc., TPX, DX820: hereinafter referred to as PMP) is dispersed in PET-1 by 19% by weight in PET-1. A copolymer PET containing 10% by weight of polyethylene glycol having a molecular weight of 4,000 (hereinafter abbreviated as PEG) as an agent is 1% by weight based on the whole resin constituting the layer (B layer) in which PEG has cavities. And then added with 0.05% by weight of a hindered phenol-based antioxidant, vacuum-dried at 180 ° C. for 3 hours, fed to the extruder (b) side, and melted at 280 ° C. After extruding, foreign matter was filtered with a 35 μm cut filter, and then introduced into a T-die composite die.

Next, the polyester layers (A layer) and (C layer) were merged so as to be laminated on both surface layers of the cavity-containing layer (B layer) in the die, and then co-extruded into a sheet to form a molten laminated sheet. . Then, the molten laminated sheet was tightly cooled and solidified by an electrostatic charge method on a drum maintained at a surface temperature of 25 ° C. to obtain an unstretched laminated film. Subsequently, the unstretched laminated film was preheated by a group of rolls heated to 85 ° C according to a conventional method, and then slightly stretched 1.1 times in the longitudinal direction (longitudinal direction) using a 90 ° C heating roll. The film was stretched by one time and cooled by a roll group at 25 ° C. to obtain a uniaxially stretched film. The uniaxially stretched film was guided to a preheating zone at 130 ° C. in a tenter while holding both ends of the film with clips, and continuously stretched 3.3 times in a direction perpendicular to the longitudinal direction (transverse direction) in a heating zone at 110 ° C. . Subsequently, a heat treatment at 220 ° C. is performed in a heat treatment zone in the tenter, a further 4% relaxation treatment at 180 ° C. is performed, then a 1% relaxation treatment is further performed at 140 ° C., and then a uniform slow cooling is performed. After winding, a polyester film having a thickness of 135 μm was obtained, in which the polyester layer (layer A) and the polyester layer (layer C) were 10.0 μm on one side, and the layer containing voids (layer B) was 115 μm.
The properties of the polyester film thus obtained are shown in Table 1, and it can be seen that the polyester film is excellent as a receiving paper sheet substrate for thermal transfer recording.

(Example 2)
A polyester film was obtained in the same manner as in Example 1 except that a polyester layer of layer C was not formed, and a two-layer configuration of layer A / layer B was used.

(Example 3)
A polyester film was obtained in the same manner as in Example 1 except that the thickness configuration of Example 1 was as shown in Table 1.

(Example 4)
A polyester film was obtained in the same manner as in Example 3 except that the content of PMP in the layer B was adjusted to the density of Table 1 in the polyester film of Example 1, and the thickness configuration was changed to Table 1.

(Comparative Example 1)
The polyester layer A and the layer C were not formed, and a film of the layer B alone was produced. To the B layer, the aggregated silica particles and the PMP for forming the voids were not added, and titanium particles were added to the polyester resin so as to be 14% by weight for whitening. Similarly, a polyester film was obtained.
The receiving sheet using the film of Comparative Example 1 had poor print clarity. This is probably because the surface roughness of the natural paper was deposited on the surface of the receiving sheet and the surface was roughened, and there was no layer performing the heat insulating function, so that the calorific value of the thermal head was diffused in the thickness direction.

(Comparative Example 2)
A polyester film was obtained in the same manner as in Example 3 except that the content of PMP in the layer B was adjusted so as to obtain the density shown in Table 1, and the thickness configuration was changed to Table 1.
The receiving sheet using the film of Comparative Example 2 had a low apparent density, the outer layer was thinner than the thickness of the cushion layer, the Pickers hardness was reduced, and printing deviation occurred.

(Comparative Example 3)
A polyester film was obtained in the same manner as in Comparative Example 2 except that the two-layer structure of Comparative Example 2 was adopted. As in Comparative Example 2, the receiving sheet using the film of Comparative Example 3 had a low apparent density, the outer layer was thinner than the thickness of the cushion layer, the Pickers hardness was reduced, and printing deviation occurred.
Further, the film was wrinkled.

(Comparative Example 4)
A polyester film was obtained in the same manner as in Example 1 except that the content of PMP in the layer B was adjusted so as to obtain the density shown in Table 1, and the thickness configuration was changed to Table 1.

  The receiving sheet using Comparative Example 4 had a higher Pickers hardness and a reduced print sharpness.

Claims (3)

Receiving paper having an apparent density of the film of 0.60 g / cm ³ or more and less than 0.90 g / cm ³ , and a Pickers hardness of at least one surface of the film of 0.5 gf / μm ² or more and 2.0 gf / μm ² or less. For polyester film. The polyester film for a receiving paper according to claim 1, wherein the polyester film has at least one layer containing a cavity (layer B). The film has a total thickness of 70 μm or more and 150 μm or less, has a polyester layer (A layer and / or C layer) on at least one surface of the layer containing the cavity (B layer), and has a thickness per one polyester layer. 3. The polyester film for receiving paper according to claim 2, wherein the thickness is more than 4 μm and 15 μm or less.