GB2269236A - Thermal transfer recording process - Google Patents

Abstract

A thermal transfer recording process comprises heating an ink ribbon having a dye-containing ink layer on a substrate in an imagewise pattern to thermally transfer the ink of the imagewise pattern to a dye-receiving layer of a printing sheet made of a cellulose ester, and subjecting the transferred image to thermal treatment preferably between 60 DEG and 200 DEG C. By the thermal treatment, the image is improved in light fastness and resistance to grease and plasticizers. The cellulose ester may be mixed with up to 50% of another polymer such as polyester or vinyl chloride - vinyl acetate copolymer.

Description

THERMAL TRANSFER RECORDING PROCESS This invention relates to a thermal transfer recording process wherein a dye is thermally transferred in an imagewise pattern to a printing or transfer sheet.

The printing sheet may be paper or a plastic film coated on the surface with an image-receiving layer made of cellulose ester resins.

In recent years, personal computers and word processors have been in wide use. In addition, video printers are now being developed extensively. Under these circumstances, thermal transfer recording processes have been adopted as a procedure of making hard copies of letter and image information.

As a thermal transfer recording medium which is employed in the thermal transfer recording process, there is used an ink ribbon which comprises, on one side of a substrate such as a polyester film, an ink layer made of a mixture of dyes such as, for example, sublimable dyes, thermally fusible, transferable dyes and the like, and binder resins for retaining the dyes and, on the other side, a heat-resistant lubricating layer. The heat-resistant lubricating layer serves to prevent the thermal transfer recording medium from being bonded to a thermal head by application of heat from the thermal head and also to smoothly transmit the thermal transfer recording medium.

On the other hand, the printing paper or sheet which has been heretofore used is one which has a dyereceiving layer on a substrate. The dye-receiving layer makes use of polyesters, vinyl chloride copolymers, polycarbonates and the like.

In thermal transfer recording processes using known printing sheet, the resultant image is not satisfactory with respect to the light fastness and the weatherability, with the attendant problem that the image may be lowered in clarity or may be discolored.

To cope with the above problem, Japanese Patent Application No. 3-62013 proposes the use of cellulose esters in the dye-receiving layer of the printing sheet so as to improve the light fastness, fade resistance in the dark and writing properties. When the thermal transfer is effected using this type of printing sheet, the resultant image becomes better in the light fastness than previous printing sheets using polyesters in the dye receiving layer. However, a problem is involved in that such an image is not beyond photograph and that a sebum resistance is low. In addition, the printing sheet has a low plasticizer resistance. When the print is placed in a paste-in album as covered with a vinyl chloride resin sheet, the image may migrate on the vinyl chloride resin sheet of the album.

In order to improve the light fastness and the sebum resistance, it may occur to use a process in which after the thermal transfer on a printing sheet, a thermoplastic transparent film is further laminated.

However, this leads to the disadvantage that the print becomes thick with an increase of costs.

In accordance with the present invention, there is provided a thermal transfer recording process which comprises heating an ink ribbon having a dye-containing ink layer on a substrate in an imagewise pattern to thermally transfer the ink of the imagewise pattern to a dye-receiving layer of a printing sheet comprising a cellulose ester, and subjecting the transferred image to thermal treatment whereby the image is improved in characteristic properties. The thermal treatment temperature is preferably in the range of from 60 to 200"C.

The invention is based on the discovery that when printing sheets having a cellulose ester dye-receiving layer are subjected to thermal transfer printing and subsequently to thermal treatment at a predetermined temperature, the image is significantly improved in the light fastness and sebum and plasticizer resistances.

Embodiments of the invention provide a thermal transfer recording process which overcomes the drawbacks of the previously proposed processes mentioned above.

Embodiments of the invention provide a thermal transfer recording process wherein when printing sheets having a cellulose ester dye-receiving layer are used, the resultant image can be improved with respect to the light fastness. sebum resistance and plasticizer resistance.

Embodiments of the present invention are characterized in that the printing sheet used has a dye-receiving layer which is made of cellulose esters and that after the thermal transfer, the resultant image is further heated for better fixing. Accordingly, the thermal transfer recording process is feasible in the same manner as in currently employed procedures or apparatus provided that the above requirements are satisfied.

The printing sheets used in embodiments of the invention are, for example, video printing sheets as is set out in the afore-indicated Japanese Patent Application No. 362013. More particularly, the dye-receiving layer may be made of cellulose esters such as cellulose acetate butyrate (CAB), cellulose acetate propionate (CAP), cellulose acetate (CA) and the like. For the formation of the dye-receiving layer, commercially available cellulose esters can be used.

Aside from the cellulose esters, resins which are compatible with cellulose esters may be formulated.

Examples of the resins include polyester resins, polyacrylic ester resins, polycarbonates resins, polyvinyl acetate resin, styrene-acrylate resins, vinyltoluene acrylate resin, polyurethane resins, polyamide resins, urea resins, polycaprolactone resins, polystyrene resins, polyvinyl chloride resins, polyacrylonitrile resin, and the like in amounts not impeding the characteristic properties of the cellulose esters. The amount is in the range of from 0 to 50 wt% based on the total of both resins.

Other various additives may also be added to the dye-receiving layer. Examples of the additives include plasticizers such as dimethyl phthalate, diethyl phthalate, dioctyl phthalate and the like, parting agents such as silicone oils, solid waxes, fluorine and phosphate surface active agents and the like, crosslinking agents such as isocyanates, fluorescent brighteners, white pigments, antistatic agents and the like.

The substrate on which the dye-receiving layer is formed may be sheets such as of polyethylene terephthalate, synthetic paper and the like.

In the practice, the printing sheet having a cellulose ester dye-receiving layer may be thermally transferred with a dye of an imagewise pattern from an ink ribbon by a usual manner using a thermal head or a laser beam. Subsequently, the thermally transferred image is subjected to thermal treatment.

The thermal treatment conditions preferably include a temperature ranging from 60 to 2000C. If the. treating temperature is lower than 600C, the effect of the thermal treatment does not appear significantly. On the contrary, when the temperature exceeds 2000C, the dyereceiving layer is undesirably more liable to physically or chemically change. The thermal treatment time may be appropriately determined depending on the temperature used.

For the thermal treatment, the manner of heating is not critical and various types of heating means may be used, if necessary. For instance, where a plurality of the print sheets on which images have been already formed are thermally treated at one time, it is preferred to use a hot oven. When the thermal treatment is effected whenever an image is formed by means of a video printer, it is preferred to subject the transferred image to so-called blind printing by use of the heating head of the video printer. In general, use of a heat roller is preferred.

Tn embodiments of the invention, the resultant image can be improved in the light fastness and resistances to sebum and plasticizers.

A preferred embodiment of the invention will now be describe by way of illustrative and non-liting example.

(a) Fabrication of Printing Sheets Resin Nos. 1 to 5 indicated in Table 1 were, respectively, mixed with the following ingredients to prepare dye-receiving layer compositions. Each composition was applied onto a 150 Fm thick synthetic paper (FPG-150, available from Ohji Yuka Co., Ltd.) in a dry thickness of 10 ym, followed by curing at 50 C for 48 hours to obtain a printing sheet.

Dye-receiving Layer Composition: Resin indicated in Table 1 20 parts by weight Silicone 0.2 parts by weight (SF8427, available from Toray-Dow Coning Co., Ltd.) Isocyanate 1.0 part by weight (Takenate D-11ON, available from Takeda Pharm. Co., Ltd.) Methyl ethyl ketone 40 parts by weight Toluene 40 parts by weight Dioctyl phthalate (Wako Junyaku K.K.) 2 parts by weight (used only in combination with Resin 1) Table 1 Resin 1 Cellulose acetate butyrate 20 parts by weight (CAB500-5, available from Eastman Kodak) Resin 2 Cellulose acetate butyrate 10 parts by weight (CAB500-5, available from Eastman Kodak) Cellulose acetate butyrate 10 parts by weight (CAB551-0.01 available from Eastman Kodak) Resin 3 Cellulose acetate butyrate 15 parts by weight (CAB500-5, available from Eastman Kodak) Polyester resin 5 parts by weight (Biron 600, Toyobo Ltd.) Resin 4 Cellulose acetate butyrate 10 parts by weight (CAB500-5, available from Eastman Kodak) Vinyl chloride-vinyl 10 parts by weight acetate copolymer (Denki Chem. Ind. Co., Ltd.) Resin 5 Cellulose acetate butyrate 20 parts by weight (CAB500-5, available from Eastman Kodak) (b) Thermal Transfer Recording Process An ink ribbon (VPM-30STA of Sony Co., Ltd.) was used on the respective printing sheets obtained in (a) so that each sheet was subjected to twelve gradation stair-stepped printing by use of a video printer (CVP G500 of Sony Co., Ltd.), followed by thermal treatment.

The thermal treatment was effected according to six thermal treating procedures A to F indicated in Table 2 for the respective printing sheets.

Table 2 Heating Means Heating Temperature Heating Time A temperature controlled 400C 24 hours chamber B temperature controlled 600C 24 hours chamber C temperature & humidity 600C (85% R.H.) 24 hours controlled chamber D temperature & humidity 1200C (85% R.H.) 10 minutes controlled chamber E solid print on the printing surface by application of a heat energy at the 10th gradation of the twelve gradation stair-stepped printing of the video printer (CVP-GfOO of Sony Co., Ltd.) F heat roller 1200C 0.5 m/minute (c) Evaluation The printed matters obtained after the thermal treatment of (b) were evaluated with respect to light fastness and sebum and plasticizer resistances. For comparison, printed matters which were not thermally treated were similarly evaluated.

i) Light fastness A print sample was irradiated with light from a Xenon arc fade meter (Suga Testing Machine Co., Ltd.) under conditions of a temperature of 300C, a humidity of 65% and 90,000 Kj/m2. The densities near 1.0 prior to and after the irradiation were measured for the respective colors (Y, M, C, B), from which a residual density rate was calculated according to the following equation.

Residual density rate (%) = (density after irradiation/density prior to irradiation) x 100.

The results are shown in Table 3.

Table 3 Example Comp.Ex.

Resin Dye (Manner of Heating) (non-heated) A B C D E F 1 Y 70.2 86.2 87.1 93.4 82.1 93.1 56.3 M 91.9 94.2 96.9 98.6 94.1 97.4 86.9 C 60.1 78.1 80.2 90.1 72.7 85.2 52.1 B 70.3 86.7 89.7 94.4 81.7 92.8 64.6 2 Y 71.8 88.9 89.7 94.7 85.6 91.1 60.3 M 92.4 92.7 92.6 96.2 94.0 97.0 88.4 C 64.7 78.7 80.2 90.3 72.2 84.5 55.2 B 74.5 87.3 92.0 93.9 85.6 92.2 69.5 3 Y 79.1 88.8 90.5 95.9 87.5 94.4 69.1 M 89.3 95.8 95.6 97.4 94.6 95.4 85.3 C 63.6 76.0 79.0 87.5 73.1 83.4 53.0 B 77.0 85.6 87.0 94.1 83.8 93.4 71.4 4 Y 79.8 87.4 90.5 93.7 83.8 90.7 76.2 M 93.4 94.4 95.6 96.5 95.0 99.1 86.6 C 61.7 73.9 77.6 85.4 69.1 82.2 50.0 B 73.5 86.4 87.1 91.0 80.8 93.1 69.2 5 Y 78.0 90.5 92.1 97.0 88.0 93.4 77.4 M 94.8 93.8 95.9 98.8 93.1 98.2 88.1 C 66.6 79.7 82.8 93.9 74.7 85.9 57.0 B 78.0 89.4 93.6 94.6 87.5 93.8 73.4 ii) Sebum Resistance In general, when artificial sebum (fatty acid ester) is applied onto the surface of print and wiped off, the dye on the print is migrated to the artificial sebum, causing the decrease of the density. The densities were measured in the vicinity of a black density of 1.0 for Black B, Yellow component BY of black, Magenta component BM of black, and Cyan component BC of black component, and the residual density rate was calculated according to the following equation.

Residual density rate (8) = (density prior to coating of artificial sebum/density after removal of artificial sebum) x 100 The results are shown in Table 4 below.

Table 4 Example Comp.Ex.

Resin Dye (Manner of Heating) (non-heated) A B C D E F 1 B 68.0 82.3 83.3 96.3 79.2 93.5 42.0 BY 80.7 84.9 83.9 96.5 82.2 92.7 56.5 BM 73.3 84.8 83.0 95.7 82.0 93.4 48.8 BC 53.9 75.3 78.2 95.0 70.0 91.0 28.6 2 B 64.4 82.1 84.6 96.3 79.0 93.6 45.0 BY 75.6 84.6 91.0 97.7 82.4 92.7 57.0 BM 69.1 87.3 88.9 91.7 82.0 93.4 50.0 BC 51.9 75.1 79.1 96.4 70.9 91.3 33.0 3 B 63.8 82.4 83.8 93.4 78.0 90.9 43.7 BY 76.4 85.8 84.7 95.2 85.1 93.2 60.9 BM 68.9 83.3 83.7 93.5 81.8 93.0 50.8 BC 50.6 74.2 78.4 91.5 69.2 90.3 31.7 4 B 65.3 81.1 82.5 92.0 75.4 90.7 50.0 BY 77.0 82.3 82.3 93.8 81.6 92.5 62.4 BM 70.0 81.7 82.3 94.1 78.5 90.8 55.4 BC 52.5 73.8 77.3 89.5 . 68.8 87.2 38.6 5 B 71.2 84.1 88.0 96.2 80.0 91.2 47.6 BY 83.3 84.3 91.7 96.4 83.2 89.1 61.5 BM 75.8 83.9 89.9 96.4 83.3 90.3 56.0 BC 57.8 77.4 82.4 95.9 72.4 90.0 33.7 iii) Plasticizer Resistance A vinyl chloride resin sheet containing 50% of DOP as a plasticizer was placed on a print a portion having a black density of approximately 2.0 and loaded with a weight of 250 kg, followed by standing at normal temperatures of 10 minutes to determined a black density of the dye migrated on the vinyl chloride resin sheet.

The migration density was evaluated according to the following standards.

Migration Density O - 0.1; Co 0.1 - 0.5: 0 0.5 - 1.0: A over 1.0: X The results are shown in Table 5.

Table 5 Example Comp.Ex.

Resin (Manner of Heating) (non-heated)

A B C D E F 1 A O 0 O O Co X 2 A O 0 Co O Q X 3 A O O Co o Co X 4 A O O Co O Co X 5 A O 0 O Q Co X From the results of Tables 3 to 5, it will be seen that the thermally treated printed matters obtained have good light fastness and good resistances to sebum and plasticizer.

Claims (6)

1. A thermal transfer recording process which comprises heating an ink ribbon having a dye-containing ink layer on a substrate in an imagewise pattern to thermally transfer the ink of the imagewise pattern to a dye-receiving layer of a printing sheet which comprises a cellulose ester, and subjecting the transferred image to thermal treatment whereby the image is improved in characteristic properties.

2. The process according to Claim 1, wherein the thermal treatment is effected at a temperature ranging from 60 to 2000C.

3. The process according to Claim 1, wherein the thermal treatment is effected by contacting the transferred image with a heat roll.

4. The process according to Claim 1, wherein said dye-receiving layer consists essentially of a cellulose ester.

5. The process according to Claim 1, wherein said dye-receiving layer comprises a mixture of a cellulose ester and at least one resin compatible with said cellulose ester, at least one resin being present in an amount of from 0 to 50 wt% of the mixture.

6. A thermal transfer recording process substantially as hereinbefore described with reference to the examples.