Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/40—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used characterised by the base backcoat, intermediate, or covering layers, e.g. for thermal transfer dye-donor or dye-receiver sheets; Heat, radiation filtering or absorbing means or layers; combined with other image registration layers or compositions; Special originals for reproduction by thermography
  • B41M5/41—Base layers supports or substrates

Definitions

• the present invention relates to an image-receiving sheet for heat sensitive transfer recording. More specifically, it relates to an excellent image-receiving sheet for use in heat sensitive transfer recording, capable of obtaining clear images with no printing unevenness, excellent dimensional stability, with less heat shrinkage and with no deformations such as curling, by using a polyester film containing minute closed-cells at the surface and the inside thereof.
• the heat sensitive transfer recording comprises overlaying, with each other, a transfer sheet having a transfer layer containing a subliming or volatile dye or a dye fusible under moderate heating and an image receiving sheet; heating the transfer sheet thereby sublimating, volatiling or melting the dye contained in the transfer layer; dyeing or transferring the dye onto the image receiving sheet and forming dye images on the image receiving sheet.
• the function of the recording method in this type has also been made more versatile and improved, for example, increase in the printing speed, improvement in the resolution power, improvement in the printing quality, etc.
• the image-receiving sheet used in such heat sensitive transfer recording can include, for example, conventional printing paper such as cellulose paper, calen­dered gravure paper, coated paper such as art paper or coat paper prepared by coating the surface unevenness or pores of paper with a pigment comprising fine particles thereby obtaining paper surface of excellent smoothness and gloss.
• synthetic paper excellent in the strength, dimensional stability, dust-freeness, etc. is also used.
• image-receiving sheets improved with overall characteristics such as mechanical strength, satisfactory dimensional stability and, moreover, excellent heat resistance and whitening power, and free from printing unevenness upon heat sensitive transfer. Therefore, cellulose paper, synthetic paper or plastic film conventionally employed can not satisfy all of these requirements.
• conventional printing paper such as cellulose paper has drawbacks in that the thickness can not be reduced since the strength is lowered to cause easy tearing, the dust-free property is poor and, in addition, the water resistance is low. Further, since the unevenness on the paper surfaces is marked, printing unevenness is liable to be caused and it is difficult to obtain clear images.
• polyester films have been utilized generally in various industrial fields owing to their excellent heat resistance, mechanical property, chemical resistance, weather resistance, etc.
• biaxially oriented poly(ethylene terephthalate) films being particularly excellent in the dimensional stability, strength, flatness, etc., are used as image-receiving sheets for heat sensitive transfer recording, original pictures for overhead projectors, etc.
• biaxially oriented poly­(ethylene terephthalate) films as the image receiving sheet for use in heat sensitive transfer recording.
• the biaxially oriented poly(ethylene terephthalate) films are tough and rigid material and lack in flexibility, they involve a drawback that the close contact between the transfer sheet and the image-receiving sheet at the thermal head is not sufficient, which causes printing uneveness, leading to a defect that no clear images can be obtained.
• whiteness and opacifying power are necessary for preventing images from seeing-through the film when used as a substitute for the conventional paper.
• a white pigment is added for providing such performance.
• the film is made more rigid to impair the flexibility, failing to obtain clear images.
• the present inventors have made an earnest study for overcoming such problems and, as a result, have found that the foregoing problems can be overcome and an image-receiving sheet for use in heat sensitive transfer recording, which is excellent over conventional paper or synthetic paper can be obtained by using a polyester film containing minute closed-­cells and satisfying specific properties.
• the present invention has accomplished based on this finding.
• an image-receiving sheet for heat sensitive transfer recording which comprises a monoaxially or biaxially oriented minute-cellular polyester film having an apparent specific gravity of 0.4 to 1.3, an opacifying power of not less than 0.2 and an air leakage index of 50 to 10,000 sec.
• the present invention relates to an image-receiving sheet for heat sensitive transfer recording, which comprises a monoaxially or biaxially oriented minute-cellular polyester film having an apparent specific gravity of 0.4 to 1.3, an opacifying power of not less than 0.2 and an air leakage index of 50 to 10,000 sec.
• the polyester referred to in the present invention includes those polyesters prepared by polycondensating an aromatic dicarboxylic acid such as terephthalic acid, isoph­thalic acid or naphthalene dicarboxylic acid or the ester thereof, and a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol or 1,4-cyclohexane dimethanol.
• aromatic dicarboxylic acid such as terephthalic acid, isoph­thalic acid or naphthalene dicarboxylic acid or the ester thereof
• a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol or 1,4-cyclohexane dimethanol.
• any of customarily employed methods can be used. For instance, there may be used a method which comprises forming a bisglycol ester of the aromatic dicarboxylic acid or the polymer thereof of a low polymeri­zation degree by an ester-exchange reaction between a lower alkyl ester of an aromatic dicarboxylic acid and a glycol, or by a direct esterification of an aromatic dicarboxylic acid with a glycol, then polycondensating them under a reduced pressure and at a temperature of not lower than 240°C.
• usual catalyst, stabilizer, various additives, etc. can be used optionally.
• polyesters there can be mentioned poly(ethylene terephthalate), poly(ethylene naphthalate) or poly(butylene terephthalate), etc.
• the polyester may be a homopolyester or copolyester. Further, it may be a mixture of two or more of polyesters.
• a preferred polyester is one in which not less than 70 mol%, preferably, not less than 80 mol% and, more preferably, not less than 90 mol% of the constitutional repeating units is ethylene terephthalates units, ethylene naphthalate units, butylene terephthalate units or a mixture thereof.
• the polymeriza­tion degree of such a polyester is excessively low, it is not preferred since the mechanical strength is lowered.
• the intrinsic viscosity of the polyester is, therefore, not less than 0.4, preferably, from 0.5 to 1.2 and, more preferably, from 0.55 to 0.85.
• a film is prepared by using such a polyester.
• the film used in the present invention contains minute closed-cells at the surface and the inside thereof and it is necessary that the film has an apparent specific gravity from 0.4 to 1.3 and, preferably, from 0.6 to 1.3. If the apparent specific gravity is in excess of 1.3, it is not preferred since the amount of cells contained in the film is reduced, which deteriorates the flexibility and causes uneven printing. On the other hand, if the apparent specific gravity is less than 0.4, it is neither preferred since the mechanical strength of the film becomes insufficient to cause tearing upon heat sensitive transfer.
• the opacifying power of the polyester film is not less than 0.2 and, preferably, not less than 0.3. If the opacifying power is less than 0.2, it is not preferred since remarkable see-through of transferred images at the back of the film occurs to worsen the contrast and the images are difficult to be seen, as well as they are difficult to be read.
• the polyester film that the air leakage index is from 50 to 10,000 sec., more preferably, 100 to 5,000 sec. If it is less than 50 sec, it is not preferred since the close contact between the transfer sheet and the image receiving sheet in the heat sensitive transfer head comes to insufficient, the transfer efficiency is reduced and the printing unevenness is increased. On the other hand, if it exceeds 10,000 sec, it is neither preferred since the slipperiness of the film is extremely worsened to deteriorate the film feeding property, and causing running troubles such as paper jamming upon heat sensitive transfer recording.
• the polyester film is oriented at least monoaxially by stretching.
• the stretch ratio is preferably not less than 4 times and, pre­ferably, from 9 to 20 times in the areal ratio, because a non-stretched polyester film is remarkably poor in the mechanical strength failing to obtain required sufficient strength and dimensional stability when used as an image receiving sheet for use in heat sensitive transfer according to the present invention.
• the individual strech ratio for the longitudinal direction or the transverse direction can be properly selected under the limitation for the areal stretch ratio defined above.
• the polyester film As has been described above, it is necessary for the polyester film as a substrate of the image receiving sheet for use in heat sensitive transfer recording according to the present invention that it posesses characteristics as described above. So long as the film contains minute cells and can satisfy such properties and requirements as described above, there is no particular restriction for the method of manufacturing the film.
• the method of manufacturing a film containing such fine cells there can be used any of the methods, i.e., a method of adding gas or gasifiable substance as described in, for example, Japanese Patent Application Laid-Open (KOKAI) No. 50-38765 or Japanese Patent Publication (KOKOKU) No.
• this method comprises blending a specific polypropylene with a polyester, extrusion molding them into a form of sheet and then stretching the sheet at least monoaxially to produce a film.
• this method comprises blending from 3 to 50 wt% of a crystalline polypropylene homopolymer with a melt flow index (hereinafter simply referred to as M.F.I.) of 0.2 to 120 with a polyester, melt-extruding them into a substantially amorphous sheet and at least monoaxially stretching the sheet by an areal stretch ratio of 4 times or greater, thereby forming a polyester film containing a great amount of minute cells in the surface and the inside of the film.
• M.F.I. melt flow index
• the crystalline polypropylene homopolymer means such a polymer as comprising propylene units by at least 95 mol%, preferably, 98 mol% of the constitutional repeating units. If the polypropylene to be used is amorphous, polypropylene would breed out at the surface of the sheet when preparing the amorphous sheet, and contaminate the surface of the cooling roll or stretching roll, etc. Meanwhile, if a polypropylene having, for example, 10 mol% or more of ethylene unit, the amount of minute cells contained in the film becomes insuffi­cient.
• the M.F.I. of the crystalline polypropylene homo­polymer is 0.2 to 120, preferably 0.5 to 50. If the M.F.I. is less than 0.2, the size of the generated cells becomes excessively large, causing frequent bursts at the time of stretching. On the other hand, if the M.F.I. exceeds 120, the sheet slips off from clips during the stretching by using a tenter. The above-described cases are not preferable because the productivity is deteriorated.
• the amount of the crystalline polypropylene homo­polymer to be mixed with polyester is 3 to 50 wt%, preferably 3 to 30 wt% based on the amount of the polyester. If the amount is less than 3 wt%, the amount of generated minute cells is too small, therefore, it becomes difficult to obtain a polyester film having an apparent specific gravity of not higher than 1.3. On the other hand, if it exceeds 50 wt%, it is not preferable because burst occurs at the time of stretching.
• the amorphous sheet is stretched at least in monoaxial direction.
• the reason for this lies in that, in addition to the above-­described object of giving a mechanical strength, the minute and closed cells cannot be obtained by merely mixing the polyester and the crystalline polypropylene homopolymer, but it can be obtained by employing the stretching process.
• the method of stretching does not need any special condition. It can employ the conditions similar to those employed in a usual method for producing polyester film.
• a mixture of polyester and the crystalline polypropylene homopolymer is melted at 250 to 320°C in an extrusion machine and is extruded into a form of a sheet through a die. Next, it is cooled down below about 70°C to be made a substantially amorphous sheet. Then, this sheet is stretched in the machine and/or transverse direction by 4 times or more, preferably 9 to 20 times in the areal stretch ratio.
• a polyester film having a thickness of 10 to 500 ⁇ m, preferably 10 to 250 ⁇ m, an apparent specific gravity of 0.4 to 1.3, an opacifying power of 0.2 or more, an air leakage index of 50 to 10,000 and minute cells of a diameter of 1 to 300 ⁇ m, preferably 2 to 100 ⁇ m.
• the biaxial stretching may be conducted in either way of simultaneously biaxial stretching or successively biaxial stretching.
• the stretch ratio in the machine direction is 2 to 7 times, preferably 3 to 5 times, and the stretch ratio in transverse direction is 1.5 to 7 times, preferably 2 to 5 times.
• the film used in the present invention can be produced as a white polyester with a low apparent specific gravity and a high opacifying power, to which various kinds of additives may be blended with no troubles so long as they do not impair the basic properties.
• additives there can be mentioned, for example, anti-oxidants, UV-absorbers, lubricants, antistatic agents, dyes, pigments, fluorescent whiteners, matting agents, surface active agents, etc. and they are blended each in an appropriate amount by an adequate method at an optional time as required.
• the film of the present invention may be subjected to various surface treatments in order to improve the dyeability, bondability, etc. with dyes, or preventing blocking or electrostatic charging in a heat sensitive transfer apparatus.
• the surface treatment there can be mentioned, for example, coating treatment, flaming treatment, solvent treatment, plasma treatment, corona discharging treatment, UV-ray treatment, ion plating treatment and sand blasting treatment, which may be applied in an appropriate time.
• the coating treatment is employed particularly preferably in the present invention.
• the material for the coating and the coating thickness can freely be selected depending on other requirements and purposes so long as they do not impair the film properties as the substrate required in the present invention.
• a thermoplastic resin, a cross-linkable resin or a mixture of such a resin and various additives, etc. can be used as required.
• additives there can be mentioned dyes, pigments, lubricants, antioxidants, UV-absorbers, antistatic agents, inorganic fine particles, surface active agents, etc., which may be blended each in an appropriate amount as required.
• the method of forming the coating layer there is no particular restriction for the method of forming the coating layer and it may be coated on a film already formed or coated during a film-production.
• a method which comprises coating a coating agent to a film mono­axially stretched in the longitudinal direction, stretching in the transverse direction before or after the coating agent is dried, and then directly applying heat treatment is employed particularly preferably because it can provide a great merit also in view of the production cost since the film formation, coating and drying can be conducted simultaneously.
• the coating layer may be formed either on one side or both sides. In the case of forming the coating layer on both sides, the coating agent may be identical or different with each other.
• the image-receiving sheet for use in heat sensitive transfer according to the present invention which is produced from a polyester film containing minute closed-cells at the surface and the inside thereof, is of higher strength, excellent in dimensional stability and heat resistance, free from shrinkage or curling due to the heat upon image receiving and also satisfactory in dust-free property, as compared with conventional image receiving sheets made of cellulose paper, synthetic paper, etc.
• a 10 x 10 cm square was cut as a sample from a desired part of a given film.
• the volume of this sample was calculated using the average thickness obtained by measuring thicknesses thereof at nine arbitrarily chosen points of the sample with a micrometer and averaging the values of measurement.
• the sample was weighed and the weight thereof per unit cm3 was reported as an apparent specific gravity of the given film. This determination was conducted on five samples and the average of five values was employed as the result of the determination.
• Macbeth TD-904 model By the use of a densitometer, Macbeth TD-904 model, the density of transmitted light through a given film was measured under Filter G to find the opacifying power. The numerical value thus found increases with increasing opaci­fying power. The measurement was conducted for three points and the average value therefor was determined as a measured value.
• Air leakage index was measured by using a Bekk flatness meter according to JIS P 8119-1976. As the value was greater, the flatness was greater at the surface. Measurement was conducted at 5 points and the average value therefor was determined as a measured value.
• the film was cut into A-4 size and applied with heat sensitive transfer recording by using CX-5000 colour printer manufactured by Sharp Corp.
• the resultant hard copy was observed with naked eyes for the degr ee of the printed density, printing unevenness and the contrast by the following five ratings respectively.
• the film was cut into 20 sheets each of A-4 size and they were stacked and set to a image-receiving paper feeding cassette in the heat sensitive transfer recording apparatus used for the printing quality test.
• Heat sensitive transfer recording was conducted for successive 20 sheets to observe paper jamming at the image receiving paper feed section and the state of occurrence for operation troubles such as running failure in the apparatus. Evaluation was made as " ⁇ " for the case with no occurrence of troubles at all and as "X" with once or more times of occurrence of troubles for the test of 20 sheets.
• Starting material prepared by blending a poly(ethylene terephthalate) chips of an intrinsic viscosity of 0.648 containing 5 wt% of white pigment comprising 0.3 ⁇ m of titanium oxide with 10 wt% of a crystalline polypropylene homopolymer chips having M.F.I of 5 was melted at 290°C in an extruder, and then extruded into a shape of sheet on a cooling drum at 40°C to obtain an amorphous sheet of 0.7 mm thickness. Then, the sheet was stretched longitudinally by three times at 85°C and transversely by 3.2 times at 95°C, and then subjected to heat treatment at 240°C for 5 sec to obtain a white biaxially stretched polyester film of 100 ⁇ m thickness.
• the film had an apparent specific gravity of 0.98, an opacifying power of 0.5, an air leakage index of 4,000 sec, a heat shrinkage of 1.1% in the longitudinal direction and 1.6% in the transverse direction, and flexibility ⁇ of 40 deg.
• Example 2 In the same procedures as in Example 1 except for using poly(ethylene terephthalate) with an intrinsic viscosity of 0.650 and not containing a pigment instead of the poly(ethylene telephthalate ) containing the white pigment used in Example 1 and increasing the blending amount of poly­propylene to 20 wt%, a biaxially stretched white polyester film with 100 ⁇ m thickness was obtained. In this case, the amount of the polymer extruded from the extruder was controlled to make the thickness of the amorphous sheet to 0.5 mm in order to attain 100 ⁇ m thickness for the finally obtained biaxially stretched film.
• the amount of the polymer extruded was varied to control the thickness of the amorphous sheet for controlling the thickness of the finally obtained stretched film.
• the thus obtained biaxially stretched film had an apparent specific gravity of 0.71, an opacifying power of 0.6 an air leakage index of 1,100 seconds.
• the film also had a heat shrinkage of 1.2 % in the longitudinal direction, 1.9 % in the transverse direction and a flexibility ⁇ of 35 deg.
• the resultant film had an apparent specific gravity of 0.72, an opacifying power of 0.6, an air leakage index on the side of the coated layer of 5,000 sec and on the opposite side of 1,100 sec.
• the values for the heat shrinkage and the flexi­bility ⁇ were the same as those in Example 2.
• the film was set to a heat sensitive transfer apparatus such that images were received on the side of the coating layer of the film and excellent copied images were obtained, with the printing density of 5, the printing unevenness of 5 and the contact of 5.
• the film was excellent in the practical applicability with neither paper jamming nor running failure in the apparatus.
• the resultant film was a transparent and smooth film having an apparent specific gravity of 1.4, an opacifying power of 0.1 and an air leakage index of 12,000 sec.
• the film also had a heat shrinkage of 1.2% in the longitudinal direction and 1.4% in the transverse direction and flexibility ⁇ of 44 deg.
• a biaxially stretched polyester film with 100 ⁇ m thickness was obtained in the same procedures as in Comparative Example 1 except for using poly(ethylene terephthalate) having intrinsic viscosity of 0.653 containing 15 wt% of titanium oxide of 0.3 ⁇ m particle size instead of the starting material used in Comparative Example 1.
• the resultant film had an excellent opacifying power and flat surface, with an opacifying power of 1.2 and an air leakage index of 7,000 sec, the value for the apparent specific gravity was as high as 1.5.
• the heat shrinkage was 1.0% in the longi­tudinal direction and 1.1% in the transverse direction, and the flexibility was 46 deg.
• Example 2 Film preparation was tried in the same procedures as in Example 1 except for increasing the blending amount of polypropylene in Example 1 to 50 wt%, but it was found that the productivity was extremely poor since breakage occurred frequently during stretching. By the way, a small sheet-like specimens were sampled and measured for the apparent specific gravity for a portion having 100 ⁇ m thickness. It was found to be 0.4. However, since the mechanical strength was so poor that evaluation for the film physical property and printing quality was impossible.
• Table 1 shows the blending composition for the starting material, and physical properties, printing quality and practical applicability of the films obtained in Examples 1 - 3 and Comparative Examples 1 - 4. All of the results for the evaluation of the printing quality and the practical applica­bility for the films of Examples 1 - 3 obtained by the present invention were satisfactory.
• the films had a sufficient opacifying power, therefore, printing images were not seen through from the rear face thereof. Since the heat shrinkage was not greater than 2% in any of the cases of Examples 1 to 3 and the dimensional stability was also excellent, neither waving nor curling was recognized in the film after the printing. In addition, since the flexibility was also satisfactory, the handling property was also improved in addition to the satisfactory printing quality and the practical applicability.
• the film according to the present invention is excellent as an image-receiving sheet for use in heat sensitive transfer.
• Example 1 no no 1.4 0.1 12,000 3 3 1 x x Comp.
• Example 2 no 2.5 ⁇ m Titanium oxide (10wt%) 1.2 0.8 30 2 1 3 o o Comp.
• Example 3 no 0.3 ⁇ m Titanium oxide (15wt%) 1.5 1.2 7,000 3 2 5 o x Comp.
• Example 4 50 0.3 ⁇ m Titanium oxide (5 wt%) 0.4 - - - - - - - - - - - - - - - - -

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
• Shaping By String And By Release Of Stress In Plastics And The Like (AREA)
• Thermal Transfer Or Thermal Recording In General (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Manufacture Of Macromolecular Shaped Articles (AREA)
• Laminated Bodies (AREA)

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Cited By (13)

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• 1987
  • 1987-12-25 JP JP62329253A patent/JPH01168493A/ja active Granted
• 1988
  • 1988-12-22 EP EP19880121526 patent/EP0322771A3/fr not_active Withdrawn
  • 1988-12-24 KR KR1019880017470A patent/KR960016057B1/ko not_active Expired - Fee Related

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