JPS61132387A - Thermal transfer recording sheet - Google Patents

Abstract

PURPOSE:To obtain developed color images having continuous gradation, high density and high transparency and free of decoloration for a long period of time, by using a cross-linked product of a polyurethane polyol and a polyisocyanate as a main constituent of a receiving layer of a thermal transfer recording sheet. CONSTITUTION:The thermal transfer recording sheet 1 to be used in combination with a thermal transfer sheet may comprise a receiving layer 3 provided on a base 2, or may be constituted solely of the receiving layer 3. Where the receiving layer 3 is provided on the base 2, the thickness of the layer 3 is preferably 5-15mum. Where the receiving layer 3 is solely used, the thickness thereof is preferably 90-150mum. The receiving layer 3 comprises a cross-linked product of a polyurethane polyol and a polyisocyanate as a main constituent. The mixing ratio of the polyurethane polyol to the polyisocyanate is determined in terms of the ratio (NCO/OH) of the NCO content of the polyisocyanate to the OH content of the polyurethan polyol, the ratio being 0.3-3.5, preferably, 1-3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal transfer sheet, and more specifically, thermal printing is performed according to image information using a thermal head, laser, or the like. The present invention relates to a thermal transfer medium used in combination with a thermal transfer medium.

2. Description of the Related Art Conventionally, thermosensitive coloring paper has been mainly used to obtain images according to image information using a thermal head or a laser. In this heat-sensitive coloring paper, a colorless or light-colored leuco dye provided on a base abrasive at room temperature and a color developer are brought into contact with each other by heating to obtain a colored image. As such color developers, phenolic compounds, salutyl powder zinc derivatives, ctzin, etc. are generally used. However, the above-mentioned thermal coloring paper has the fatal drawback that the color image will fade if stored for a long period of time.
Furthermore, color printing is limited to two colors or less, making it impossible to obtain color images with continuous gradations.

On the other hand, thermal transfer paper in which a heat-melting wax layer in which an M material is dispersed is provided on a base paper has recently begun to be used. When the thermal transfer paper and the transfer paper are placed one on top of the other and thermal printing is performed from the back side of the thermal transfer paper, the wax layer containing the pigment is transferred onto the transfer paper to obtain an image. According to this better printing method.

Durable images can be obtained, and multicolor images can be obtained by printing one or more times using thermal transfer paper containing pigments of the three primary colors;
You can't get a better picture of the photos you have.

Incidentally, in recent years, there has been a growing demand for obtaining photograph-like images directly from electrical signals, and 91 various attempts have been made.

One such attempt is to project an image on a CRT and photograph it using gold-silver-salt film, but if silver-salt film is used as an instant film, running costs tend to increase, which is a drawback. ), when the silver halide film is a 35mm film, there is a drawback that it is not instantaneous because development processing is required after photographing. As another method, an impact ribbon method or an inkjet method has been proposed, but the former has the disadvantage of poor image quality, and the latter requires image processing, making it difficult to easily obtain photographic images. There are some drawbacks.

In order to resolve these shortcomings, we combined a thermal transfer sheet with a sublimable disperse dye layer that completely blinds the transfer of color when heated with a thermal transfer target, and used a thermal transfer sheet to transfer the thermal transfer while controlling the sublimable disperse dye. A method has been proposed in which the image is transferred onto a sheet to obtain a photograph-like image with uneven gradation. This method is attracting attention because an image having continuous gradation can be obtained from a television signal through simple processing, and the equipment used therein is not complicated.

One of the conventional techniques similar to this method is the dry transfer printing method for polyester fibers, which involves dispersing or dissolving dyes such as sublimable disperse dyes in a synthetic resin solution. M material, apply this paint in a pattern on thin paper etc. and make a frame line to make a thermal transfer sheet,
This thermal transfer sheet is overlapped with polyester fibers to be thermally transferred, heated in close contact with each other, and a disperse dye is dyed onto the polyester fibers to obtain an image.

However, when a thermal transfer sheet like the one above and a thermal transfer sheet made of polyester fiber are layered together.

Even if this is heated and printed using a thermal head or the like, a high-density colored image cannot be obtained. One of the reasons for this is that the surface smoothness of the polyester fiber cloth is not good, but it is believed that this is mainly due to the following reasons. In other words, 1. In the normal dry transfer printing method or wet transfer printing method.

Migration of sublimable dyes onto polyester fiber fabrics.

Whereas the heating time is sufficient.

Heating using a thermal head etc. is usually extremely short.

For this reason, the dye does not transfer sufficiently onto the fiber cloth. By the way, in the dry transfer printing method, dye transfer is achieved by heating at 200°C for about 1 minute, whereas heating with a thermal head takes several m56cm at 400°C.
It is rather short.

The inventors of the present invention have conducted research to solve the above-mentioned drawbacks by improving heat transfer sheets, and have discovered the following facts.

Binding clay coated paper or synthetic paper to thermal transfer sheet 1
When used, there is a drawback that the dyes transferred from the thermal transfer sheet cannot be sufficiently received, and therefore, high-density colored images cannot be obtained.

On the other hand, if a thermal transfer sheet having a low melting point synthetic resin as a receptor layer is used, the heat and pressure applied to the thermal transfer sheet will cause the synthetic resin layer itself to become thermally adhesive. has the disadvantage that it tends to be transferred onto the thermal transfer sheet, impairing the clarity and resolution of the resulting image.

In addition, when using a thermal transfer sheet having a synthetic resin with a low glass transition temperature as the entire receiving layer, the dye thermally transferred onto the thermal transfer sheet is sufficiently fixed and a high-density colored image can be temporarily obtained, but it takes about 1 hour. It was also found that the dye was thermally diffused and the processed image was distorted. On the other hand, it was found that if the receiving layer of the transfer target was made of a synthetic resin with a high glass transition temperature, the above-mentioned thermal diffusion could be prevented, but the fixability of the dye transferred from the thermal transfer tot would be poor. . As an extreme example, if a flexible polyvinyl chloride resin containing an ester group-containing compound, such as dioctyl phthalate, is used as the receiving layer of a thermal transfer sheet, an excellent colored image with high density can be obtained immediately after thermal transfer. is obtained once, but since the dye dissolves in the plasticizer and diffuses into the 7-t, normally if it is left at room temperature for about a week, the colored image obtained becomes extremely unclear and storage of the colored image becomes difficult. turned out to be virtually impossible.

The present invention attempts to solve the drawbacks associated with the prior art by using a thermal transfer sheet having a specific structure. It aims to achieve the following objectives.

&) Obtaining a colored image with continuous gradation like a photograph directly from an electrical signal.

b) To obtain a colored image with high density and high transparency, and also to obtain a clear, high-resolution image that does not fade even if stored for a long period of time.

C) To provide a thermal transfer sheet in which the thermal transfer layer does not peel off and transfer to the thermal transfer layer and the thermal transfer sheet and the thermal transfer sheet do not fuse together during thermal transfer.

d) To obtain high-quality images with excellent dot shape reproducibility of the thermal head.

In order to achieve the above object, the present inventors conducted extensive research and found that a thermal transfer target/printer having a specific structure could achieve the above object, leading to the present invention.

That is, the present invention provides a thermally transferred odor coating having a receptor layer in which dyes transferred from the thermal transfer sheet are received when heated; The gist of this paper is a thermal transfer target characterized by the fact that it is a component.

Preferred specific examples of the present invention shown in the drawings will be explained below. The present invention (the thermal transfer sheet 1 is constructed by providing a receiving layer 3t on a base material 2, as shown in FIG. 1). As shown in FIG. 2, the receiving layer 3 alone has a thermal transfer target of
may be configured. When the receptive layer 3 is provided on the base material 2, the thickness of the receptive layer 3 is 3 to 50 μm, preferably 5 to 1 μm.
It is about 5 μm. On the other hand, the receiving layer 3 alone is thermally transferred/-
In the case of human 1t-configuration, the thickness of the receptive layer 3 is 60 to 20
It is about 0 μm, preferably about 90 to 150 μm.

The material for the base material 2 is art paper or coated paper.

Examples include papers such as high-quality paper and gearst coated paper 3 synthetic paper, and plastic films such as polyethylene terephthalate and polyglobylene.

The receptor layer 3 in the present invention is formed mainly of a crosslinked product of polyurethane polyol and polyincyanate.

In the present invention, the crosslinked product of polyurethane polyol and polyisocyanate forming the receptor layer 3 has a -10
It has a glass transition temperature of 0-20°C.

The glass transition temperature of the crosslinked product forming the receiving layer 3 is -
If the temperature is less than 100°C, the disadvantage is that the image tends to fade over time.69. Moreover, when the temperature exceeds 20° C., there is a drawback that the recording density tends to decrease.

The blending ratio of polyurethane polyol and polyisocyanate in the cross-linked product applied to the present invention and the receptor layer 3t to be formed is the ratio of the NCO content in the polyyne/anate to the OH content in the polyurethane polyol (NGOloH
), and in the present invention, the ratio is 0.5 to
3.5 and 9, preferably 1 to 3.

When the NC010H ratio is less than 0.5, a problem arises in that storage stability is lacking. 9. If one storage acceleration test is performed while the sheet is open at 60° C., there will be a problem that the dye transferred from the thermal transfer sheet will blur the image in the receiving layer 3.

Furthermore, if the above NC010H ratio exceeds 3.5t-, it is necessary to increase the heating temperature or increase the heating time in order to maintain a constant temperature for the dye transferred from the thermal transfer sheet to the receptor layer 3. A malfunctioning sound occurs.

In forming the thermal transfer sheet 1t of the present invention.

For example, a polyurethane polyol, a polyinsyanate, and an additive are dissolved in a solvent, a crosslinked polyurethane polyol and a polyisocyanate are applied onto the substrate 2, and then heated to evaporate the solvent, resulting in a thermal transfer target of 1 ton. - get.

Examples of the polyurethane polyol used in forming the crosslinked product of the present invention include 1, for example, Takerank'F
J-550, Takerac XE-916゜Takerac Xg
-8, Takerak XE-12, Takerak T-4000
(manufactured by Takeda Pharmaceutical Co., Ltd.), Desmophen D80. Examples include Desmofeno D81 (Sumitomo vinyl urethane ■!).

Also, polyino/anate, tolylene diinocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthylene diiso7anate.

1.6-hexamethylene diisocyanate, inphorone diisocyanate, quinlene diisocyanate, lysine isocyanate, triisocyanate, etc.
Anate e-conductors can be used, such as Takenate D11. ON, Takenate E-40, Takenate D
]03H (manufactured by Takeda Pharmaceutical Co., Ltd.), Sumitul L, Sumir z-le IL, Desmodur N3200. Desmosier E3260 (manufactured by Sumitomo Bayer Urethane ■),
Coronet) HL.

Coronate N, Coronate L (Japan Polyurethane.

■fi) etc.

In addition, the above-mentioned additives should be selected from those that do not interfere with the fixation of dyes that migrate from the thermal transfer sheet during heating, and such additives should be Examples of the enhancer include cured products of silicone compounds, such as cured products of ebony/modified/licon oil and amine-modified silicone oil.

It can also be used as an ultraviolet absorber t-additive to prevent color fading of single color images due to light.

Furthermore, an amino-based or tin-based catalyst may be added to promote the crosslinking reaction between the polyurethane polyol and the polyinsyanate.

The thermal transfer target 1 as described above is used in combination with a thermal transfer sheet. A typical thermal transfer sheet 4 has a structure in which a thermal transfer layer 6 is provided on one side of a support 5, as shown in FIG.

When this thermal transfer layer 6 is heated, the dye or pigment contained therein is transferred onto the thermal transfer sheet 1.

The support 5 has the role of holding the thermal transfer layer 6, and since heat is applied during thermal transfer, it is desirable that the support 5 has a mechanical strength that does not cause any trouble in handling even when heated. Furthermore, in many cases, thermal energy for thermal transfer is applied from the side of the support 5 where the thermal transfer layer 60 is not provided, so it is desirable that the support 5 also has the property of easily transmitting thermal energy.

Specific examples of such a support 5 include a flexible thin-layer sheet such as Condenser Vapor 1 glassine paper, parchment paper, or high Xi Xi paper, or IA a plastic film. These paperboards, conte/surpafer, and polyethylene terephthalate film are often used, and when heat resistance is important, condenser paper is mainly used.1 When all emphasis is placed on preventing breakage during handling with a mechanical device, Polyethylene terephthalate film is used as a cover. The thickness of this support 5 is 2
It is usually about 3 to 50 μm, preferably about 5 to 15 μm.

The thermal transfer layer 6 contains a coloring material that can be extracted from the thermal transfer layer 6 and transferred to the receiver Mj3 of the thermal transfer target sort 1 when heated.

Examples of such coloring materials include disperse dyes, oil dyes, certain basic dyes, and intermediates that can be converted into these dyes, which have a relatively small molecular weight of about 150 to 400. One is selected from among these and used in consideration of thermal transfer temperature, thermal transfer efficiency, two hues, color rendering properties, weather resistance, etc.

The above coloring material is dispersed in a suitable synthetic resin binder forming the thermal transfer layer 6.1. It is provided on the support body 5.

As such a synthetic resin binder, it is usually preferable to select one that has high heat resistance but does not hinder the migration of the coloring material when heated; for example, the following are used.

(1) Cellulose resins ethyl cellulose, hydroquine ethyl cellulose, ethyl hydroxy cellulose, hydroquine globil cellulose, methyl cellulose, vinegar cellulose, vinegar-butylated cellulose, etc.

(11) Vinyl resins polyvinyl alcohol, polyvinyl acetate, polyvinylgutyral, polyvinylpyrrolidone.

polyester, polyacrylamide, etc.

Among the above synthetic resin binders, polyvinylgtyral resin or cellulose resin is preferred from the viewpoint of heat resistance.

A thermal transfer layer 6 is provided on the support 5 (1) by mixing a coloring material and a synthetic resin binder together with a solvent or diluent.
A coating composition for a thermal transfer layer may be provided on the support 5 by an appropriate printing method or coating method. In addition,
As necessary 1. Any additives may be added to the coating composition for the thermal transfer layer.

The basic structure of the thermal transfer plate 4 is as described above, but when the surface of the support is directly heated by a heating means of a contact plate such as a thermal head, the thermal transfer layer of the support 5 is provided. By providing a slippery layer containing a lubricant such as wax or a mold release agent on the side that is not coated, it is possible to prevent the heating means such as a thermal head from adhering to the support and to improve the sliding properties. .

The thermal transfer sheet 4 may be in the form of a single sheet cut into required dimensions, or may be continuous or wound, or may be in the form of a narrow tape.

When providing the thermal transfer layer 6t on the support 5, the support 5
A coating composition for a thermal transfer layer containing the same coloring material may be applied over the entire surface of the optical surface of 1. However, in some cases, a coating composition for a thermal transfer layer containing a plurality of coating compositions for a thermal transfer layer, each containing a different coloring material, may be applied. may be formed in different areas on the surface of the support 50, respectively. For example, a thermal transfer sheet in which a black thermal transfer layer and a red thermal transfer layer are laminated in parallel on a support 5, or a yellow thermal transfer layer.

A thermal transfer sorting method may be used in which a red thermal transfer layer, a blue thermal transfer layer, and a black thermal transfer layer are provided on a support KM repeatedly. By using a thermal transfer sheet provided with a plurality of thermal transfer layers having different hues, an advantage arises in that a multicolor image can be obtained from a single thermal transfer notebook.

Note that it is also possible to improve convenience in use by forming perforations on the thermal transfer sheet or providing register marks for detecting the positions of areas with different hues.

The thermal transfer sheet 4 and the thermal transfer target 1 prepared as described above are placed facing each other so that the thermal transfer layer 6 of the thermal transfer sheet 4 and the receiving layer 3 of the thermal transfer sheet 1 are in contact with each other, as shown in FIG. The coloring material in the thermal transfer layer 6 is transferred to the receptor layer 3 by applying thermal energy according to image information to the interface between the thermal transfer layer 6 and the receptor layer 3 .

In addition to thermal heads, laser sources and infrared flashes can be used as heat sources that provide thermal energy.

A known device such as a thermal pen can be used. Thermal energy can be applied from the thermal transfer sheet 4 side, from the thermal transfer recipient/person 1, or from both sides, but from the viewpoint of effective use of thermal energy, from the thermal transfer sheet 4 side. It's good to do it. However, it is better to apply thermal energy from the thermal transfer sheet 1@ to control the applied thermal energy and express the gradation of light and shade of the image.

Alternatively, it is preferable in the sense that it promotes the diffusion of the coloring material on the thermally transferred notebook 1 to further ensure the continuous tone expression of the image, and in the method of applying thermal energy from both sides 4, there are advantages of both of the above methods. can be enjoyed at the same time.

When a length-wise head is used as a heat source for applying thermal energy, the applied thermal energy can be varied continuously or in multiple steps by modulating the voltage or pulse width applied to the thermal head.

When a laser beam is used as a heat source for providing thermal energy, the thermal energy provided can be changed by changing the amount of laser light or the irradiation area. If a dot generator with a built-in acousto-optic element is used, thermal energy can be applied depending on the size of the halftone dot. When using a laser beam, it is preferable that the thermal transfer sheet 4 and the thermal transfer sheet 1 be brought into close contact with each other.

The surface to be irradiated with laser light may be colored, for example, black to improve the absorption of laser light.

When using an infrared flash lamp as a heat source for providing thermal energy, it is best to use a single line through a colored layer such as black, similar to when using laser light, or a pattern that continuously expresses the light and shade of one image such as black. Alternatively, you can use halftone turf to create one line through these patterns.

Alternatively, a colored layer such as black on the negative side and a negative pattern corresponding to the negative of the pattern described above may be used in combination.

When thermal energy is applied to the interface between the thermal transfer layer S 1 and the receptor layer 3 as described above, the coloring material in the thermal transfer layer 6 is vaporized or melted in an amount corresponding to the applied thermal energy, and the coloring material in the thermal transfer layer 6 is vaporized or melted. The heat is transferred to and accepted.

With the above thermal transfer recording, nine color materials are thermally transferred to the receiving layer according to the thermal energy, and it is possible to record a one-color image, but there are two or more methods. By sequentially replacing yellow, red, indigo, and, if necessary, black thermal transfer sheets, and performing thermal transfer according to each color, it is also possible to obtain a color photo-like color image consisting of a combination of υ11 colors. . In addition, in this way, in order to use the thermal transfer sheet 7-4 of each color, a thermal transfer sheet 4 gold having a pre-formed area for each color was used, and the yellow colored image was first thermally transferred using the yellow area. 9
Next, the red area of the thermal transfer sheet 4 is used to thermally transfer the separated color images of yellow, red, indigo, and if necessary, black by repeating the process sequentially. This has the advantage that it is no longer necessary.

The size of the heat source used to provide thermal energy,
The quality of the image obtained can be improved by appropriately adjusting the adhesion between the thermal transfer sheet 4 and the thermal transfer sheet 1 and the thermal energy.

The thermal transfer sheet 1 according to the present invention can be used in combination with the thermal transfer sheet 4 to print using each of the eight thermal printing printers, facsimile, TJ, or photo printing using a magnetic recording method.

It can be used to create prints from the television screen.

For example, a received television screen can be stored on a storage medium such as a magnetic tape or magnetic disk.

The signal of each color separation pattern of yellow, red, indigo, and black if necessary is stored at intervals of τ, the signal of each stored color separation pattern is output, and the thermal energy corresponding to this signal is transmitted to the theme head, etc. is applied to the stacked body of the heat transfer sheet 4 and the heat transfer target 1 by the above-mentioned heat source,
By sequentially performing thermal transfer for each color, it can be reproduced as a print similar to that of a television screen. When the combination of the thermal transfer sheet 1 and the thermal transfer sheet 40 according to the present invention is used for printing out such a television screen, the thermal transfer sheet /-F is usually the white receptor layer 3 alone, or Or base material 2 such as colorless and transparent receptive N3 gold paper.
It is convenient to obtain a reflective image by using a material lined with a substrate 2 such as a white receptive layer or a substrate 2 such as 3-karat gold paper.

The same thing as above can be done by computer operation.
This can also be done when using a graphic butter/character formed on a screen as an original image.

In addition, when the original image is a fixed image such as a painting, photograph, or printed matter, or an actual object such as a person, still life, or landscape, it can be prepared by using an appropriate means such as a video camera as a medium.
This can be done in the same way as above. Furthermore, when creating signals for each color separation pattern from the original image, an electronic plate making machine (color scanner) used for photolithography for printing may be used.

As explained above, the heat-transferable 7-t spreading receptor layer of the present invention is mainly composed of a crosslinked product of polyurethane polyol and polyisocyanate. A colored image with continuous gradations like a photograph can be directly obtained using the optical signal.

Further, it is possible to obtain a colored image with high density and high transparency, and it is also possible to obtain a clear image with high sharpness, which can be stored for a long period of time without any color fading of the colored image.

Furthermore, during thermal transfer, there is no peeling transfer of the thermal transfer layer to the thermal transfer layer, there is no fusion between the thermal transfer sheet and the thermal transfer sheet, and a high-quality image with excellent reproducibility of the dot shape of the thermal layer is obtained. It has various effects such as being able to.

Hereinafter, the present invention will be described in more detail with specific examples, but the present invention is not limited to these examples.

Example 1 A 9 μm thick PET film (5PET manufactured by Toyobo Co., Ltd.) with corona treatment on one side was used as a support, and a heat transfer 4 required coating composition having the following composition was applied to the corona treated film surface using a wire. Apply bar coating to a thickness of 1 μm when dry and apply 1 or 2 drops of silicone oil (X-41-4003A, manufactured by Shin-Etsu Silicone) on the back surface using a dropper, then spread it over the entire surface. A back side treatment coat was applied to prepare a thermal transfer sheet.

Coating composition for thermal transfer layer (manufactured by Herkieless) Toluene 40 parts by weight Methyl ethyl ketone 4 parts by weight Dioxane
10 parts by weight A 150 μm synthetic paper (YUPO-FPG-150 manufactured by Tamago Yuka Co., Ltd.) was used as a base material, and a receiving layer coating composition having the following composition was coated with a wire bar on the surface to a dry thickness of 5 μm. After coating and drying with hot air, heat curing treatment was performed in an oven at 100° C. for 30 minutes (to thoroughly blow off the solvent).

Coating Composition for Receptive Layer Furthermore, a discrete coating composition having the following composition is coated on the surface of the receptor layer with a wire bar so that the thickness when dried is 0.
It was applied to a thickness of 3 μm to form a thermal transfer sheet.

Drying was performed for 30 minutes in a 100° C. oven after temporary drying using a Dokiya.

Coating composition for base release layer Thermal transfer sheet obtained as above and thermally transferred target/-
The output IW/dot of the thermal head, pulse width 0.3-4.
As a result of recording under the conditions of 5 m5 et and a dot density of 3 dots/mark, the optical reflection density of the high color density recording area was measured using a Macbeth RD918 reflection densitometer.
．． A value of 5 was obtained. Note that the color tone obtained at this time has the same transparent BAm as when the color is produced by dispersing each dye as a single molecule, and furthermore, high-quality images with extremely excellent dot shape reproducibility of the thermal head are obtained. It was done.

When the recorded sheet was left in an oven at 60°C for 7 days and a thermal diffusion acceleration test was performed, it was found that i.
n! ii. No disturbance of the image was observed, and no decrease in the density of the recorded area occurred.

In addition, a light emission test was conducted on the recorded sheet using a sunshine weather meter.

An excellent value of JIS grade 3 or higher was obtained.

Example 2 Recording was carried out in exactly the same manner as in Example 1, except that the receiving layer coating composition in Example 1 was replaced with the following composition.

Similar to Example 1, the image obtained from the coating composition for the receptor layer was of high quality with excellent color development, storage stability, dot reproducibility, and light resistance.

Example 3 In Example I, recording was carried out in exactly the same manner as in Example 1, except that the receiving layer coating composition was replaced with the following composition.

Coating composition for receptor layer The obtained image had 1 color development as in Example 1.

The image quality was high with excellent storage stability, dot reproducibility, and light resistance.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and FIG. 1 is a longitudinal sectional view showing an embodiment of the thermal transfer sheet of the present invention. FIG. 2 is a vertical cross-sectional view showing another embodiment of the thermal transfer sheet of the present invention, FIG. 3 is a vertical cross-sectional view showing an example of the thermal transfer sheet, and FIG. FIG. 1---1 Heat transfer notebook 3---111 Receptive layer 4---1 Heat transfer sheet Patent applicant Dai Nippon Printing Co., Ltd. Figure 1 Figure 2 Figure N3

Claims (1)

[Claims] A thermal transfer sheet having a receptor layer that receives dye transferred from the thermal transfer sheet when heated, characterized in that the receptor layer is mainly composed of a crosslinked product of polyurethane polyol and polyisocyanate. Heat transfer sheet.