FR2755059A1 - Transfer support for heat sensitive image - Google Patents

Abstract

Transfer support for heat sensitive image comprises substrate layer for acceleration of transfer to the substrate, which contains wax; and layer of ink applied to accelerating layer, which contains colourant and thermoplastic resin. The ink has viscosity of 1\*10<3> - 1\*10<5>Pa.s at 90 deg C. Also claimed is the use of the support.

Description

The present invention relates to a thermosensitive image transfer medium and a recording method which uses this medium.

A heat-sensitive image transfer recording medium is adapted to imageally transfer molten ink from one of its surfaces to a recording sheet, such as paper, when heated according to an image. by a thermal head while the recording sheet is disposed between the thermal head and a cylinder. Such a recording medium may be in the form of a ribbon for use in a line type printer.

With a conventional in-line type printer, the heated recording medium is generally separated from the recording sheet after being cooled to room temperature. Thus, the recording medium heated by the thermal head is separated from the recording sheet after being moved away from the thermal head by a distance of 3 to 15 mm. In order to increase the printing speed, the use of a thermal head with close edges has been proposed. During printing with such a thermal head, the heated recording medium is separated from the recording sheet at a temperature of 70 "C or more, that is, the heated recording medium by the thermal head is separated from the recording sheet after being moved away from the thermal head by a distance of only about 80 to 300 µm.

However, known heat-sensitive image transfer media cannot be suitably used with a printer having such a close-edged thermal head. In particular, the resulting printed image tends to form "streaks", so that it is not possible to obtain sharp images. Further, the known heat-sensitive image transfer media have a problem because it is not possible to obtain high quality images on a printing sheet with a rough surface. For this reason, it is necessary that the printing sheet be treated, for example by calendering, so as to have a smooth surface.

It is therefore an object of the present invention to provide a heat-sensitive image transfer medium which can give a printed image of high quality not only on a smooth surface such as that of a polymer film, but also on a rough surface such as that of a polymer film. of a fibrous paper.

Another object of the present invention is to provide a heat-sensitive image transfer medium which exhibits good ink transferability and which can give a printed image devoid of streaks.

Another object of the present invention is to provide a thermosensitive image transfer medium which is suitable for a printing system using a thermal head with close edges.

Another object of the present invention is to provide a recording method which uses the above thermosensitive image transfer medium.

To achieve the above-mentioned objects, the present invention provides a heat-sensitive image transfer recording medium comprising a substrate, a transfer accelerating layer disposed on a surface of said substrate and containing a wax, and an ink layer. disposed on said transfer accelerating layer and containing a coloring agent and thermoplastic resin, said ink layer having a viscosity of 103 to 105 Pa.s (106 to 108 cP) at 90 C.

The present invention also provides a recording method comprising image-heating of the above heat-sensitive image transfer recording medium by means of a thermal head while said ink layer is in contact with a sheet. image receiving sheet, whereby said ink is melted and transferred to said image receiving sheet.

Other characteristics and advantages of the invention will appear better in the detailed description which follows and refers to the appended drawing, given solely by way of example, and in which:
- the single figure is a front view schematically showing a printer of the line type, that is to say in which the paper moves in the same direction as the ink ribbon.

The heat-sensitive image transfer medium according to the present invention comprises a substrate, a transfer accelerating layer and an ink layer superposed on each other in this order.

The substrate can be a synthetic resin film, paper or any other sheet used in conventional image transfer media. It is preferable that the substrate has relatively good heat resistance. It can be a polyester film, for example a polyethyleneterephthalate film, a polycarbonate film, a triacetylcellulose film, a nylon film, a polyimide film, cellophane or parchment paper.

The medium is coated with the transfer accelerating layer which contains a wax and which serves to improve the transferability of heated ink from the heat-sensitive image transfer medium to an image receiving sheet such as paper. Preferably, the wax has a softening or melting point such that, when heated by a thermal head, the transfer accelerating layer is melted and has a low viscosity. Generally, the wax has a softening or melting point of 70 to 1200C.

Suitable waxes include, for example, natural waxes such as beeswax, mineral wax, whale white wax, waxeswax.
Japan, candelilla wax, carnauba wax and rice wax, synthetic waxes such as oxidized paraffin wax, microcrystalline wax, ozocerite, ceresin, ester wax or polyethylene wax, a higher saturated fatty acid such as margaric acid, lauric acid, myristic acid, palmitic acid, furoic acid, stearic acid or behenic acid, a higher saturated alcohol such as stearyl alcohol or behenyl alcohol, a higher ester such as a sorbitan fatty acid ester, or a higher fatty acid amide such as stearamide or oleamide.

The amount of wax in the transfer accelerating layer is generally 50 to 100% by mass, preferably 80 to 100% by mass.

A rubber such as isoprene rubber, butadiene rubber, ethylene propylene rubber, butyl rubber or nitrile rubber can be incorporated into the transfer accelerating layer to impart elasticity to it and thereby improve the quality. Closeness of the contact between the thermosensitive recording medium and an image receiving sheet. The transfer accelerating layer may also contain a binder resin to improve its adhesion to the substrate. The binder resin can be, for example, an ethylene-vinyl acetate copolymer or an ethylene-ethyl acrylate copolymer. The transfer accelerating layer generally has a thickness of 0.3 to 2 µm, preferably 0.5 to 1.5 µm.

The ink layer disposed on the transfer accelerating layer contains a coloring agent and a thermoplastic resin. It is important that the ink layer, when heated to 90 "C, melt and have a viscosity of 103 to 105 Pa.s (106 to 108 cP) at 90" C.

The coloring agent can be, for example, carbon black, an organic pigment, an inorganic pigment or a dye and is generally used in an amount of 10 to 50% by mass, preferably 10 to 30% by mass, per relative to the mass of the ink layer.

Within the scope of the invention, it is possible to use any thermoplastic resin provided that it can adhere to an image receiving sheet and that the ink layer has the above specific viscosity when melted. Such a thermoplastic resin can be, for example, an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, a polyamide, a polyester, a polyurethane, a poly (vinyl chloride) resin, a cellulose derivative, a polystyrene resin. , a polybutyral resin, a phenolic resin or an epoxy resin. It is particularly preferred to use a polyester resin having a weight average molecular weight (Mw) of 5000 to 30,000 as the thermoplastic resin for reasons of good ink transferability and absence of streaks. It is also preferred to use a polyester resin having a glass transition temperature (Tg) of 20 to 60 "C for reasons of good ink transferability and absence of streaking. The polyester resin can be prepared by any known process, for example by polycondensation of a polyol such as a glycol with a polyacid such as a diacid, or by ring-opening polymerization of a cyclic ester such as a lactone.

The thermoplastic resin is generally used in an amount of 20 to 80% by mass, preferably 30 to 70% by mass, based on the mass of the ink layer.

It is possible to incorporate one or more additives in the ink layer in order to improve transferability and resolution. To reduce the viscosity in the molten state, it is possible to use as an additive a fatty acid amide, a solvent, a synthetic wax such as a paraffin wax, a natural wax such as candelilla wax or carnauba wax, or an oil such as silicone oil or perfluoroalkyl ether. Phosphoric acid esters, silicone resins, tetrafluoroethylene resins, fluoroalkyl ether resins and inorganic lubricants such as silicon carbide and silica can also be used as additives.

The thickness of the ink layer is generally 0.5 to 6 µm, preferably 1 to 4 µm.

If desired, an intermediate layer is provided between the substrate and the transfer accelerating layer in order to increase the adhesion between the substrate and the transfer accelerating layer. The presence of such an intermediate layer can prevent the transfer accelerating layer from separating from the substrate even when the image transfer medium is stressed from the thermal head. Such a constraint is likely to appear in the case of a thermal head printer with close edges.

The intermediate layer contains an adhesive material which can firmly bond the wax-containing transfer accelerating layer and the substrate outside of printing operations. Such an adhesive material can be, for example, an unvulcanized rubber such as isoprene rubber, butadiene rubber, ethylene-propylene rubber, butyl rubber or nitrile rubber, a polyolefin such as an ethylene acetate copolymer. vinyl or an ethylene-acrylate copolymer, a polyurethane resin, a polyacrylate resin, a cellulose resin, a phenolic resin or a petroleum resin. These materials can be crosslinked to prevent the formation of a mixture with the components of the transfer accelerating layer.

It is preferable that the surface of the intermediate layer is roughened in order to increase the contact surface with the transfer accelerating layer. This can be achieved by incorporating an inorganic filler such as carbon black, graphite, calcium carbonate or titanium oxide or an organic filler such as poly (vinyl chloride) powder in the intermediate layer. . The thickness of the intermediate layer is generally 0.05 to 2 cm, preferably 0.1 to 0.5 m.

If desired, it is possible to provide a protective layer on the surface of the substrate which is opposite to the ink layer, in order to protect the substrate during thermal printing with a thermal head. The protective layer contains a heat resistant thermoplastic or thermosetting resin, a UV curable resin or an electron beam curable resin.

Such a resin can be, for example, a fluorine resin, a silicone resin, a polyimide resin, a phenolic resin or a melamine resin.

The thickness of the protective layer is generally 0.01 to 3 µm, preferably 0.01 to 1 µm.

The formation of the intermediate layer, the transfer accelerating layer and the ink layer can be accomplished in any known manner, for example by a melt coating process, an aqueous liquid coating process or a liquid coating process. coating process in a liquid medium in an organic solvent. The total thickness of the layers formed on the substrate is generally 0.5 to 10 fa.

During printing, the heat-sensitive image transfer medium according to the present invention is heated imagewise by means of a thermal head while the ink layer is kept in contact with the image receiving sheet, whereby the ink is melted and transferred to the image receiving sheet. The image receiving sheet whose surface smoothness extends over a wide range, i.e., 100 to 20,000 seconds, can be suitably printed by means of the image transfer medium according to the present invention. invention.

The single figure shows a printing system for which it is possible to suitably adopt the image transfer medium 1 according to the present invention. The carrier 1 and an image receiving sheet 2 which move in the same direction are pressurized into contact with each other at a gap P formed between a cylinder 4 and a thermal head 3.

At the gap, the transfer medium 1 is image-wise heated by the thermal head 5, so that the ink is melted and transferred to the receiver sheet 2 during the contact of the transfer medium 1 with the receiver sheet. 2.

The receiver sheet 2 is separated from the transfer medium 1 at point Q. The heat-sensitive image transfer medium according to the present invention is particularly suitable for the above printing system in which the distance from P to
Q is around 80 to 300ym. Such a printing system, referred to as a near edge thermal head type printing system, differs from the generally employed in-line type printing system, in which the distance from P to
Q is about 3 to 15mm.

The following examples illustrate the present invention more precisely. In these examples, the parts are en masse.

Example 1
An intermediate layer with a thickness of 0.2 µm, a transfer accelerating layer with a thickness of 1.0 µm and an ink layer with a thickness of 1.0 µm were successively formed in this order. on one side of a 4.5 µm thick polyethylene terephthalate film (substrate) by applying the coating compositions shown below and drying the coating. A protective layer with a thickness of 0.4 m was formed on the other side of the substrate to obtain a heat-sensitive image transfer medium according to the present invention.

Composition of the intermediate layer.

1 part ethylene vinyl acetate copolymer
6-part carbon black
Toluene 93 parts
Composition of the transfer accelerating layer:
Carnauba wax 35 parts
5-part styrene-butadiene rubber
28 parts water
Methanol 32 parts
Composition of the ink layer:
4-part carbon black
Polyester resin (Tg: 60 "C, Mp: 25,000) 12 parts
4-part dibenzyl oxalate
Methyl ethyl ketone 80 parts
Composition of the protective layer
7-part silicone resin
Methyl ethyl ketone 93 parts
Example2
Example 1 was repeated as described, except that the following composition was used as the ink layer composition, to obtain a heat-sensitive image transfer medium.

Composition of the ink layer:
6-part carbon black
Polyester resin (Tg: 22 "C, Mp: 22,000) 7 parts
7-part acrylic resin
Methyl ethyl ketone 80 parts
Example3
Example 1 was repeated as described, except that the following composition was used as the ink layer composition, to obtain a heat-sensitive image transfer medium.

Composition of the ink layer:
4-part carbon black
Candelilla wax 14 parts
2 part ethylene vinyl acetate copolymer
Methyl ethyl ketone 80 parts
Example4
Example 1 was repeated as described, except that the following transfer accelerating layer composition and ink layer composition were used, to obtain a heat-sensitive image transfer medium.

Composition of the transfer accelerating layer:
16 parts carnauba wax
1 part ethylene vinyl acetate copolymer
2-part acrylonitrile-butadiene copolymer
Butadiene 1 part
Toluene 80 parts
Composition of the ink layer.

Nitrocellulose 13 parts
Paratoluenesulfonamide 2 parts
Methanol 80 parts
Carbon black 5 parts
Comparative example 1
A commercial heat-sensitive image transfer ribbon was used. The tape is composed of a 6.5 ssm thick polyethylene terephthalate film (substrate), a transfer accelerating layer containing carnauba wax and modified polyethylene, and an ink layer containing black of carbon, polyester resin and carnauba wax. The total thickness of the ink layer and the transfer accelerating layer is 1.5-2.0 µm.

Comparative example 2
Example 1 was repeated as described, except that the following composition was used as the ink layer composition, to obtain a heat-sensitive image transfer medium.

Composition of the ink layer:
4-part carbon black
Polyester resin (Tg: 60 "C, Mp: 25,000) 10 parts
6-part acrylic resin
Methyl ethyl ketone 80 parts
Comparative example 3
A 1.0 µm thick transfer accelerating layer and 1.0 µm thick ink layer were successively formed in this order on one side of a 4.5 ssm thick polyethylene terephthalate film (substrate). by applying the coating compositions given below and drying the coating to obtain a heat sensitive image transfer medium.

Composition of the transfer accelerating layer:
Carnauba wax 14 parts
6-part silicone resin
Toluene 80 parts
Composition of the ink layer:
4-part carbon black
Polyester resin (Tg: 720 C, Mp: 25,000) 10 parts
6-part acrylic resin
Methyl ethyl ketone 80 parts
The image transfer media thus obtained were tested for the ability to transfer the images and the smear formation on the images, according to the following methods.

Printing conditions:
Thermal head: partial gloss thin film type (8 points / mm)
Cylinder pressure: 150 g / cm2
Direction in which the image transfer medium is pulled for separation from the receiver sheet: 300 from the receiver sheet
Pulling torque: 200 g
Printing speed: 10 cm / s
Receiver sheet: polyethylene terephthalate film containing white filler (Bekk smoothness (smoothness measured by a Bekk tester according to Japanese Industrial Standard JIS P8119): 25,000 s) and synthetic paper (Bekk smoothness 2000 s).

Ability to transfer images.

A printed image obtained for an applied energy of 20 mJ / mm2 was evaluated according to the following criteria:
A: absence of gaps and spots
B: noticeably no gaps or stains
C: slight appearance of gaps and spots
D: No image is transferred to the receiving sheet.

Formation of streaks on the images:
Streaking on images is a phenomenon that an unexcited part of the ink layer of the image transfer medium is transferred to the receiver sheet at the same time as the energized part, so that streaks appear in the image transfer medium. edge of the image. A bar code of 2 dots wide and 6 dots long is printed on the white PET receiver sheet at an applied energy of 20 mJ / mm2 and the printing is evaluated according to the following criteria:
A: no streaks. The image has sharp edges.

B: noticeably no streaks.

C: slight appearance of streaks.

D: The bar code is not readable because of the streaks.

The results are summarized in Table 1 below. In Table 1, the viscosity of the ink layer of each of the image transfer media at 90 ° C is also shown. To measure the viscosity, an ink layer with a thickness of 1.2. This ink layer was held at 90 ° C for over 1 hour, then subjected to a shear rate of 1.1 x 102 rad / s. Viscosity was measured from the stress due to this shear rate.

TABLE 1
Ability to transfer
pictures
Example Viscosity White PET Paper Streak formation
10 ~ 3Pa.s (cP) synthetic on images 1 9.21 x 107 AAA 2 1.03x106 AAA 3 4.96x106 AAA 4 5.26 x 107 AAA
Ex. Comp. 1 3.25 x 105 BAC
Ex.comp.2 2.22x108 BCB
Ex. Comp. 3 6.96 x 108 BCB
From the results of Table 1, it is understood that the image transfer media according to the present invention can give high quality images free of streaks on smooth receiver sheets and on non-smooth receiver sheets.

Claims (8)

1. Heat-sensitive image transfer recording medium, characterized in that it comprises a substrate, a transfer accelerating layer disposed on a surface of said substrate and containing a wax, and an ink layer disposed on said accelerating layer the transfer and containing a coloring agent and a thermoplastic resin, said ink layer having a viscosity of 103 to 105 Pa.s (106 to 108 cP) at 90 "C. 2. Heat-sensitive image transfer recording medium according to claim 1, characterized in that it further comprises an intermediate layer disposed between said substrate and said transfer accelerating layer. A heat-sensitive image transfer recording medium according to claim 1 or claim 2, characterized in that said thermoplastic resin is a polyester resin having a weight average molecular weight of 5,000 to 30,000. A heat-sensitive image transfer recording medium according to any one of the preceding claims, characterized in that said thermoplastic resin is a polyester resin having a glass transition temperature of 20 to 60 "C. 5. Recording method, characterized in that it comprises the heating according to an image of a recording medium by heat-sensitive image transfer (1) according to any one of claims 1 to 4 by means of a thermal head (3), while said ink layer is in contact with an image receiving sheet 2, so that said ink is melted and transferred to said image receiving sheet. 6. Method according to claim 5, characterized in that said recording medium comprises an intermediate layer disposed between said substrate and said transfer accelerating layer, and said thermal head is a thermal head with close edges. 7. A method according to any one of claims 5 and 6, characterized in that said image receiving sheet has a surface smoothness of 100 to 20,000 s. 8. Method according to any one of claims 5 to 7, characterized in that said image receiving sheet is a polyethylene terephthalate film containing one or more fillers.