EP0992360A2

EP0992360A2 - Thermal dye transfer ribbon

Info

Publication number: EP0992360A2
Application number: EP99119687A
Authority: EP
Inventors: Jun c/o Techn. Cent. of Fujicopian Co. Sogabe; Fumio c/o Techn. Cent. of Fujicopian Co. Uetsuji; Yoshiyuki Alps Electric Co. Ltd. Asabe; Isao c/o Alps Electric Co. Ltd. Ohwada; Osamu c/o Alps Electric Co. Ltd. Ogiyama; Noriko c/o Alps Electric Co. Ltd. Takikawa
Original assignee: Alps Electric Co Ltd; Fuji Kagakushi Kogyo Co Ltd; Fujicopian Co Ltd
Current assignee: Fujicopian Co Ltd; Alps Alpine Co Ltd
Priority date: 1998-10-06
Filing date: 1999-10-05
Publication date: 2000-04-12
Also published as: EP0992360A3; JP2000108532A

Abstract

A thermal transfer ribbon for thermally transferring a preprinting layer onto a receptor with a poor surface smoothness in advance of formation of a printed image on the receptor is provided which comprises a foundation and at least a preprinting layer provided on the foundation, the preprinting layer comprising a release layer, an intermediate layer and an adhesive layer stacked in this order from the foundation side, the intermediate layer having a melt viscosity of not less than 10⁶ cps/160°C, and the adhesive layer having a melt viscosity of 10⁴ to 10⁶ cps/160°C.

Description

The present invention relates to a thermal transfer ribbon which is used for the purpose of thermally transferring a transparent or white ink (preprinting ink) onto a receptor with an uneven surface such as paper sheet to fill in depressed portions of the receptor, thereby smoothing the surface thereof, before formation of a printed image on the receptor by selectively thermally transferring a colored ink from a thermal transfer ink ribbon.
Heretofore, a preprinting thermal transfer ribbon wherein a preprinting ink comprising a wax as a main component is applied in a large thickness on a foundation was used to effectively fill in depressed portions of a paper sheet.
However, when a resin-based colored ink comes into use to form a printed image with high-definition and high durability, the problem arises that the transferability (superimposing performance) of a colored ink on the preprinting ink comprising a wax as a main component is inferior and, hence, a printed image with high-definition and high durability cannot be obtained. If a preprinting ink composed of a resin material having a high melt viscosity is used to solve this problem, the problem that the release of the preprinting ink from the foundation when thermally transferring the preprinting ink cannot be ensured arises.
Further, since the filling treatment using the preprinting ink is accompanied by superimposing transfer of a colored ink onto the transferred preprinting ink, the preprinting ink is required to withstand the pressure and heat when thermally transferring the colored ink so that the surface smoothness of the transferred preprinting ink is maintained. However, there are no conventional preprinting thermal transfer ribbons which satisfy these requirements sufficiently.
For example, JP, A, 7-257058 discloses a preprinting thermal transfer ribbon having a structure wherein a release layer, an intermediate layer and an adhesive layer are stacked on a foundation. However, the intermediate layer of this thermal transfer ribbon does not have a high melt viscosity and the adhesive layer has a small thickness. Consequently, the smoothness of the intermediate layer transferred cannot be maintained when superimposing transfer of a colored ink, resulting in failure to obtain a printed image with high quality.
In view of the foregoing, an object of the present invention is to provide a preprinting thermal transfer ribbon which exerts a satisfactory filling effect against the uneven surface of a receptor with a poor surface smoothness and provides a smooth preprinting layer on the receptor on which a colored ink is satisfactorily superimposed, thereby giving a printed image with high quality.
This and other objects of the present invention will become apparent from the description hereinafter.
The present invention provides a thermal transfer ribbon comprising a foundation and at least a preprinting layer provided on the foundation, the preprinting layer being thermally transferred onto a receptor in advance of formation of a printed image thereon,
the preprinting layer comprising a release layer, an intermediate layer and an adhesive layer stacked in this order from the foundation side, the intermediate layer comprising a main component having a melt viscosity of not less than 10⁶ cps/ 160°C, and the adhesive layer comprising a main component having a melt viscosity of 10⁴ to 10⁶ cps/160°C.
In a preferred embodiment of the present invention, the release layer has a thickness of 0.05 to 0.5 µm, the intermediate layer has a thickness of 0.1 to 1.0 µm, and the adhesive layer has a thickness of not less than 3.5 µm.
The preprinting thermal transfer ribbon of the present invention has a preprinting layer which contains an intermediate layer comprising a material having a melt viscosity of not less than 10⁶ cps/160°C as a main component and an adhesive layer comprising a material having a melt viscosity of 10⁴ to 10⁶ cps/160°C as a main component. The intermediate layer exerts such an effect that it is transferred as bridging over depressed portions of a receptor to smooth the surface of the receptor (so-called "bridging effect") due to its high melt viscosity, and the adhesive layer having a lower melt viscosity than that of the intermediate layer is transferred so as to fill in depressed portions of the receptor, so that the surface of the receptor on which the preprinting layer has been transferred is smoothed. Further, by virtue of the combination of the bridging effect of the intermediate layer and the filling effect of the adhesive layer, the smoothness of the surface of the preprinting layer transferred is maintained even if the preprinting layer undergoes the pressure and heat when a colored ink is thermally transferred. Consequently, a printed image with high quality can be formed in the portion of the receptor on which the preprinting ink has been transferred. Furthermore, since a release layer is provided between the foundation and the intermediate layer, the thermal transfer sensitivity is excellent in spite of the high melt viscosity of the intermediate layer.
The present invention will be explained in detail.
The thermal transfer ribbon of the present invention has at least a preprinting layer provided on a foundation and the preprinting layer has a three-layer structure wherein a release layer, an intermediate layer and an adhesive layer are stacked in this order from the foundation side.
As the foundation in the present invention, various materials conventionally used as foundations for thermal transfer ribbons can be used. In view of durability, heat conduction and cost, polyethylene terephthalate film having a thickness of 2 to 6 µm is preferably used. A stick-preventive layer is preferably provided on the back side of the foundation.
The release layer used in the present invention is a layer comprising a heat meltable material composed of a wax as a main component. As required, the release layer may be incorporated with a heat meltable resin.
Examples of waxes include natural waxes such as haze wax, bees wax, carnauba wax, candelilla wax, montan wax and ceresine wax, petroleum waxes such as paraffin wax and microcrystalline wax, synthetic waxes such as oxidized wax and ester wax, and higher fatty acids. Examples of heat meltable resins (inclusive of elastomers) include olefin copolymers such as ethylene-vinyl acetate copolymer and ethylene-acrylic ester copolymers, polyamides, polyesters and natural rubber.
The release layer preferably has a thickness of 0.05 to 0.5 µm. When the thickness of the release layer is smaller than 0.05 µm, the thermal transfer sensitivity is lowered. When the thickness of the release layer is more than 0.5 µm, a wax layer in a large thickness exists on the transferred intermediate layer, which makes it difficult to ensure the superimposing transfer of a colored ink onto the preprinting layer. The thickness of the release layer is more preferably from 0.05 to 0.25 µm.
Examples of materials having a melt viscosity of not less than 10⁶ cps/160°C used as a main component in the intermediate layer include homopolymers and coploymers of methacrylic esters such as methyl methacrylate, ethyl methacrylate and butyl methacylate, homopolymers and coploymers of acrylic esters such as methyl acrylate and ethyl acrylate, homopolymers and copolymers of styrene and styrene derivatives such as vinyltoluene, polyvinyl butyral, polyvinyl alcohol and polyesters. Since a material having a high melt viscosity is used in the intermediate layer, the bridging effect of the intermediate layer transferred on a receptor with a poor surface smoothness is not reduced even when a colored ink is transferred onto the preprinting layer, and, hence, a satisfactory superimposing transfer of the colored ink becomes possible, resulting in a printed image with high quality. The total amount of materials having a melt viscosity of not less than 10⁶ cps/160°C as a main component is preferably not less than 50 % by weight, more preferably not less than 70 % by weight, of the intermediate layer. When the content of the main component is less than the above range, it is difficult to achieve the desired object.
The thickness of the intermediate layer is preferably 0.1 to 1.0 µm in order that the desired object is favorably achieved and the thermal transfer sensitivity is not degraded. When the thickness of the intermediate layer is less than 0.1 µm, the bridging effect of the intermediate layer is hardly exhibited. When the thickness of the intermediate layer is more than 1.0 µm, the transferability of the preprinting layer is prone to be degraded.
Examples of materials having a melt viscosity of 10⁴ to 10⁶ cps/160°C used as a main component in the adhesive layer include olefin copolymers such as ethylene-vinyl acetate copolymer and ethylene-acrylic ester copolymers, polyamides, natural rubber, isoprene rubber and nitrile rubber. When the melt viscosity of the main component is less than 10⁴ cps/160°C, the adhesive layer shows a insufficient adhesive strength against a receptor. When the melt viscosity of the main component is more than 10⁶ cps/160 °C, the adhesive layer cannot follow up the uneven surface of the receptor so that the uneven surface is not satisfactorily filled in with the adhesive. From these points of view, the melt viscosity of the main component is preferably from 5 × 10⁴ to 2 × 10⁵ cps/160°C. The total amount of main components having a melt viscosity of 10⁴ to 10⁶ cps/160°C is preferably not less than 50 % by weight, more preferably 70 % by weight, of the adhesive layer. When the content of the main component is less than the above range, it is difficult to achieve the desired object.
The thickness of the adhesive layer is preferably not less than 3.5 µm. When the thickness of the adhesive layer is less than this range, the filling effect against the uneven surface of the receptor is degraded. From the viewpoint of thermal transfer sensitivity, the thickness of the adhesive layer is more preferably from 3.5 to 10 µm.
In the present invention, it is preferable that the color of portions of a receptor where the preprinting layer has been transferred is substantially the same as the color of the receptor because a printed image is formed on the preprinting layer transferred on the receptor. For this reason, it is preferable that the preprinting layer is colorlessly transparent or has the same color as that of the receptor. The colorlessly transparent preprinting layer can be obtained by incorporating substantially no coloring agent into any one of the release layer, the intermediate layer and the adhesive layer. The preprinting layer having the same color as that of a receptor can be usually obtained by incorporating a coloring agent into the intermediate layer. Since paper sheets as the receptor are usually white, a white pigment or a body pigment is usually incorporated into the intermediate layer in the case of incorporating the coloring agent thereinto. Of course, in the case that a colored receptor is used, the preprinting layer may be colored in the same color as that of the receptor by incorporating thereinto carbon black, or other inorganic or organic pigments, and if necessary, dyes. However, it is not always necessary that the preprinting layer has the same color as that of the receptor, and the preprinting layer may be colored in a color different from that of the receptor.
Examples of the aforesaid white pigments or body pigments include titanium oxide, silica powder, calcium carbonate, precipitated barium sulfate, magnesium carbonate and alumina. These pigments can be used either alone or in combination.
The adhesive layer may be incorporated with a body pigment to improve selective transferability. The term "selective transferability" means that portions of a transfer layer that are heated are separated from adjacent unheated portions of the transfer layer and only the heated portions are transferred with no unwanted portions being transferred.
The thermal transfer ribbon of the present invention may have either a structure wherein only the preprinting layer is provided on a foundation or a structure wherein a region of the preprinting layer and a region of colored ink layer (e.g. including yellow ink layer, magenta ink layer, cyan ink layer, and optionally black ink layer) are alternately repeatedly arranged on the same foundation in a side-by-side relation in the longitudinal direction of the foundation.
The present invention will be more fully described by way of Examples. It is to be understood that the present invention is not limited to the Examples, and various change and modifications may be made in the invention without departing from the spirit and scope thereof.

EXAMPLES 1 to 2 and COMPARATIVE EXAMPLE 1

A 2.5 µm thick polyethylene terephthalate film having a 0.2 µm thick stick-preventive layer composed of a silicone resin on one side thereof was used as the foundation. Onto the opposite side of the film were successively applied the below-mentioned coating liquids by means of Mayer bar, followed by drying at 60°C. Thus, a thermal transfer ribbon having stacked three layers each having the thickness shown in Table 1 was obtained.

Coating liquid for release layer

Aqueous emulsion of carnauba wax (melting point: 85°C)

Coating liquid for intermediate layer

Component	Part by weight
Acrylic resin (glass transition point: 105°C, melt viscosity: 10⁶ cps/160°C)	10
Methyl ethyl ketone	90

Coating liquid for adhesive layer

Component	Part by weight
Ethylene-vinyl acetate copolymer (vinyl acetate content: 19 % by weight, melt flow rate: 150 ml/190°C, melt viscosity: 10⁵ cps/160°C)	8
Silica powder (average particle size: 1.0 µm)	2
Toluene	90

Using each of the thus obtained thermal transfer ribbons, preprinting was performed under the below-mentioned conditions to transfer a preprinting layer on a receptor and then color-printing was performed on the preprinting layer under the below-mentioned conditions. The quality of the obtained color images was evaluated according to the below-mentioned criterion. The results are shown in Table 1.

Preprinting

Printer:: thermal transfer printer MD 1300 made by Alps Electric Co., Ltd.
Print mode:: white ink ribbon
Pattern:: solid printing
Receptor:: Xerox #4024 (Bekk smoothness: 29 seconds)

Color printing

Printer:: MD 1300
Ink ribbon:: color ink ribbons for standard paper sheet for the above printer
Pattern:: full-color image

Evaluation criterion

○ :: A clear image is obtained.
▵:: A fairly clear image is obtained.
X: An unclear image is obtained.

	Ex. 1	Ex. 2	Com. Ex. 1
Thickness (µm)
Release layer	0.1	1.0	1.0
Intermediate layer	0.5	0.5	-
Adhesive layer	4.0	4.0	4.0
Image quality	○	▵	X

The preprinting thermal transfer ribbon of the present invention exerts a satisfactory filling effect against the uneven surface of a receptor with a poor surface smoothness and provides a smooth preprinting layer on the receptor on which a colored ink is satisfactorily superimposed, thereby giving a printed image with high quality.
A thermal transfer ribbon for thermally transferring a preprinting layer onto a receptor with a poor surface smoothness in advance of formation of a printed image on the receptor is provided which comprises a foundation and at least a preprinting layer provided on the foundation, the preprinting layer comprising a release layer, an intermediate layer and an adhesive layer stacked in this order from the foundation side, the intermediate layer having a melt viscosity of not less than 10⁶ cps/160°C, and the adhesive layer having a melt viscosity of 10⁴ to 10⁶ cps/160°C.

Claims

A thermal transfer ribbon comprising a foundation and at least a preprinting layer provided on the foundation, the preprinting layer being thermally transferred onto a receptor in advance of formation of a printed image thereon,

the preprinting layer comprising a release layer, an intermediate layer and an adhesive layer stacked in this order from the foundation side, the intermediate layer comprising a main component having a melt viscosity of not less than 10⁶ cps/160°C, and the adhesive layer comprising a main component having a melt viscosity of 10⁴ to 10⁶ cps/160°C.
The thermal transfer ribbon of Claim 1, wherein the release layer has a thickness of 0.05 to 0.5 µm, the intermediate layer has a thickness of 0.1 to 1.0 µm, and the adhesive layer has a thickness of not less than 3.5 µm.