Patent Publication Number: US-6656546-B2

Title: Transfer sheet, method of manufacturing the same and transfer printing method

Description:
This is a divisional of application Ser. No. 09/310,581, filed May 12, 1999, now U.S. Pat. No. 6,333,295. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a transfer sheet suitable for making ink ribbons for transfer printers, a method of manufacturing the same, and a transfer printing method. 
     2. Description of the Related Art 
     FIG. 2 is a typical view of assistance in explaining a conventional transfer sheet and a method of manufacturing the same. 
     A conventional transfer sheet  20  in the form of an ink ribbon (JP-B No. 6-96307) by way of example comprises a ribbon (base sheet)  21 , a plurality of ink regions each of a plurality of color ink regions (yellow, magenta and cyan ink regions), (thermal transfer layers)  22  ( 22 Y,  22 M,  22 C), and color lines (identification marks)  23  of colors of the color ink regions  22 , extending perpendicularly to the length of the ink ribbon. 
     The transfer sheet  20  is manufactured by a suitable method, such as a gravure printing method, using printing cylinders  201 ,  202 ,  203  and  204  each having a circumference three times the length of the ink regions. First, a Y transfer region  22 Y is printed by using the yellow (Y) printing cylinder  201 , an M transfer region  22 M is printed by using the magenta (M) printing cylinder  202 , and a C transfer region  22 C is printed by using the cyan (C) printing cylinder  203 , Finally, the mark printing cylinder  204  prints the identification marks  23 . 
     This method of manufacturing the conventional transfer sheet is not efficient because the transfer layers are printed one by one by using the Y, the M and the C printing cylinder. The efficiency of this method may be improved by using a printing cylinder provided with a plurality of transfer layer printing plates, i.e., multiple plate printing cylinder. 
     Transfer layers of an ink ribbon printed by using a printing cylinder provided with a plurality of transfer layer printing plates differ subtly in thickness from each other because of dimensional errors in the transfer layer printing plates. When such an ink ribbon is used for printing (transfer printing), colors appear in hues different from expected hues. When a sublimation transfer method capable of full-color image transfer is used, different pictures differ from each other in the gray hue of highlights and middle tone areas. 
     In general, transfer printers use a plurality of ink ribbons, such as a three-color type of ribbon (Y, M, C), a four-color type of ribbon (Y, M, C, Bk), a ribbon with a protective layer (Y, M, C, OP) or a ribbon with high density. 
     In a conventional transfer printer, a cassette which contains an ink ribbon, has a detection hole corresponding the ink ribbon for determining the type of the ink ribbon (JP-A No. 64-27981). When the cassette is inserted into the transfer printer, the detection hole is detected by a suitable mechanical measure. Another cassette may have a reflection mark representing the type of a contained ink ribbon, and the reflection mark is detected by a sensor for determining the type of the ink ribbon (JM-A No. 3-29367). 
     The third method is that a ribbon on which an ink ribbon is wound has a bar-code representing the type of the ink ribbon, and the bar-code is detected by the transfer printer. 
     However, the above three methods cause the increase of manufacturing costs of printers, because the printers need to be provided with particular mechanisms for detecting the hole, the reflection mark or the bar-code. In addition, the detection hole and the reflection mark should be changed in accordance with the corresponding ink ribbon, which leads cost increase. 
     Identification marks including information about the type of ink ribbon have been developed to solve the above problems. For example, identification marks representing colors whose number and width are changed in accordance with the type of media for determining the type of media (JP-B No. 6-96307) (JM-B No. 7-12004) (JP-A No. 9-10956). 
     In this case, however, the area of identification marks and the length of ink ribbon have been increased because of the increase of the number of the identification marks, and therefore the effective recording length and width of the ink ribbon have been shortened. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a transfer sheet capable of being manufactured at a high production efficiency and of forming a transfer-printed image of a satisfactory picture quality, a method of manufacturing the transfer sheet, and a transfer printing method. 
     According to a first aspect of the present invention, a transfer sheet comprises a base sheet, a thermal transfer layer having a plurality of transfer region sets, each transfer region set having a plurality of transfer regions with functions different from each other, and identification marks formed in the transfer region sets, in which the identification marks formed in the YMC transfer region sets consist of at least two different types. 
     The identification marks of one transfer region set may be formed by using different printing plates formed on a printing cylinder and may have different forms, respectively. 
     The identification marks of one transfer region set may be formed in the transfer regions, respectively, the identification marks of the transfer region set may be formed in the same form, and the identification mark formed in one of the transfer regions of the transfer region set may have a characteristic different from those of the identification marks formed in the other transfer regions of the same transfer region set. 
     The identification marks of one transfer region set may have the same form, and the identification marks of different transfer region sets may have different characteristics, respectively. 
     According to a second aspect of the present invention, a transfer sheet comprises a base sheet, a thermal transfer layer having a plurality of transfer region sets, each transfer region set having a plurality of transfer regions with functions different from each other, and identification marks formed in the transfer region sets, in which the identification marks comprises an identification mark having a plurality of parts, one part having a characteristic different from those of the other parts. 
     The identification marks of one transfer region set may be formed in the transfer regions, respectively, and the identification mark formed in one of the transfer regions of the transfer region set may have a characteristic different from those of the identification marks formed in the other transfer regions of the same transfer region set. 
     According to a third aspect of the present invention, a method of manufacturing a transfer sheet comprising a base sheet, a thermal transfer layer having a plurality of transfer region sets, each transfer region set having a plurality of transfer regions with functions different from each other, and identification marks formed in the transfer region sets comprises the steps of forming the thermal transfer layer having the plurality of transfer region sets on the base sheet by using a plurality of transfer region printing cylinders each provided with a plurality of printing plates for printing the transfer regions of different functions, and forming the different identification marks in the transfer region sets. 
     The identification marks of one transfer region set may be formed by the different printing plates mounted on the same printing cylinder and may have different forms, respectively. 
     The identification marks of one transfer region set may be, for each transfer region, formed by the different printing plates mounted on the same printing cylinder in the transfer regions, respectively, the identification marks of the transfer region set may have the same form, and the identification mark of one of the transfer regions of the transfer region set has a characteristic different from those for the identification marks of the other transfer regions of the same transfer region set. 
     The identification marks of one transfer region set may be formed in the same form by the different printing plates mounted on the same printing cylinder, and the transfer region sets may differ from each other in the characteristics of the identification marks. 
     A transfer printing method using a transfer sheet comprising a base sheet, a thermal transfer layer having a plurality of transfer region sets, each transfer region set having a plurality of transfer regions with functions different from each other, and identification marks formed in the transfer region sets comprises the steps of recording information in the identification marks of the transfer region sets, reading the identification marks of the transfer region sets, correcting transfer conditions on the basis of the information represented by the identification marks, and transferring the transfer regions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a typical view of a transfer sheet in example 1-1 of a first embodiment according to the present invention of assistance in explaining a method of manufacturing the same transfer sheet; 
     FIG. 2 is a typical view of a conventional transfer sheet of assistance in explaining a method of manufacturing the same transfer sheet; 
     FIGS.  3 (A)(B)(C)(D) are plan views of transfer sheets in comparative examples; 
     FIGS.  4 (A)(B) are plan views of transfer sheets in examples 1-2 and 1-3 of the first embodiment according to the present invention; 
     FIGS.  5 (A)(B)(C)(D)(E) are plan views of transfer sheets in examples 1-4, 1-5, 1-6 and 1-7 of the first embodiment according to the present invention; 
     FIGS.  6 (A)(B)(C) are plan views of transfer sheets in examples 1-8, 1-9 and 1-10 of the first embodiment according to the present invention; 
     FIGS.  7 (A),  7 (B) and  7 ( c ) are views of an identification mark formed on a transfer sheet and modifications thereof; 
     FIGS.  8 (A) and  8 (B) are typical views of a transfer sheet in an example 2-1 of a second embodiment according to the present invention; 
     FIGS.  9 (A),  9 (B),  9 (C) and  9 (D) are plan views of transfer sheets in examples 2-2, 2-3, 2-4 and 2-5 of the second embodiment according to the present invention; 
     FIGS.  10 (A),  10 (B) and  10 (C) are enlarged views of identification marks formed in transfer sheets in examples 2-6, 2-7 and 2-8 of the second embodiment according to the present invention; 
     FIGS.  11 (A),  11 (B) and  11 (C) are plan views of transfer sheets in examples 2-9, 2-10 and 2-11 of the second embodiment according to the present invention; 
     FIGS.  12 (A),  12 (B) and  12 (C) are plan views of transfer sheets in examples 2-12, 2-13 and 2-14 of the second embodiment according to the present invention; 
     FIGS.  13 (A) and  13 (B) are plan views of transfer sheets in examples 2-15 and 2-16 in the second embodiment according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     EXAMPLE 1-1 
     Referring to FIG. 1 showing a transfer sheet  10  in an example 1-1 of the first embodiment according to the present invention, the transfer sheet  10  comprises a base sheet  11 , a thermal transfer layer  12  formed on the base sheet  11 , and identification marks  13  ( 13   a  and  13   b ). The thermal transfer layer  12  has a plurality of YMC transfer region sets a and b, each transfer region set a, b having a plurality of thermal transfer regions  12 Y,  12 M and  12 C respectively. The thermal transfer regions  12 Y,  12 M and  12 C have different functions to each other. The identification marks  13  are formed in each of the YMC transfer region sets a and b. 
     The base sheet  11  serves as a carrier member of the transfer sheet  10  and may be a sheet having sufficient heat resistance and strength. The base sheet may be a paper sheet, a plastic sheet, such as a PET sheet, or a metal foil of a thickness in the range of 0.5 to 50 μm, preferably, in the range of 3 to 10 μm. 
     The thermal transfer layer  12  is formed on the base sheet  11 , and has the plurality of YMC transfer region sets a and b. Each of the sets has an yellow transfer region  12 Y, a magenta transfer region  12 M and a cyan transfer region  12 C longitudinally arranged in that order. 
     The transfer layer  12  is formed of a resin containing dyes that are melted or sublimated when heated. Preferably, the dyes are hot-sublimable disperse dyes, oil colors or basic dyes, and have a molecular weight in the range of 150 to 800, preferably, in the range of 310 to 700. The dyes are selected from those dyes and colors, taking into consideration the temperature of sublimation, hue, weathering resistance and solubility in an ink base or a binder. 
     The thermal transfer layer  12  is formed in a thickness in the range of 0.3 to 2 μm by a suitable printing process, such as a gravure printing process, using composite printing inks each prepared by dissolving a selected dye and a selected resin in a solvent. 
     The identification marks  13  indicate information about the thermal transfer sheet  10 . The identification marks  13  may be formed of any suitable material, provided that the identification marks  13  can be detected by an optical, electrical or magnetic detector. 
     The information about the thermal transfer sheet  10  indicates the attributes of the thermal transfer sheet  10  including means for discriminating between the front and the back side, means for discriminating between the head and the tail (direction), type, grade, the number of available frames, advanced notification of end, boundaries between the thermal transfer regions, maker, applicable printers and means for indicating genuineness. 
     The quality of the identification marks  13  is dependent on the detector to be used for detecting the identification marks  13 . For example, the identification marks  13  are formed of an optically detectable material prepared by mixing an optically identifiable pigment or dye into a resin, an electrically detectable material, such as a conductive resin prepared by mixing powder of a metal or carbon into a resin, or a metal foil, a magnetically detectable material, such as a magnetic resin prepared by mixing a magnetic metal or a magnetic compound in a resin, or a magnetic metal film formed by evaporation. 
     Although the detector may be of an optical type, an electrical type or a magnetic type, the use of an optical detector is the simplest in configuration. 
     When each identification mark  13  is formed in the corresponding transfer region of the thermal transfer layer  12  and the dye or the pigment contained in the material forming the identification mark  13  is of an ordinary hue, a suitable color filter is necessary to detect the identification mark  13 . When the transfer region of the thermal transfer layer  12  is formed of a material containing an infrared ray transmitting dye and the identification mark  13  is formed of an infrared ray cutting material, the identification mark  13  can be detected by using an infrared detector regardless of the hue of the corresponding transfer region of the thermal transfer layer  12 . 
     The infrared ray cutting identification mark  13  can be formed of a composite material prepared by mixing an infrared ray cutting substance into a resin. An optimum infrared ray cutting substance is carbon black which absorbs infrared rays very effectively. 
     The resin as the component of the infrared ray cutting composite material may be a polyurethane resin, a polyamide resin, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-polyacrylate copolymer, a cellulose acetate butyrate or a mixture of some of those resins. A resin produced by crosslinking some of those resins with a polyisocyanate compound may be used as the component of the infrared ray cutting composite material. 
     The weight ratio of the infrared ray cutting substance to the resin is in the range of 1/10 to 10/1. The identification marks  13  are formed in a thickness in the range of about 0.5 to about 5 μm. 
     The detector for detecting the infrared ray cutting identification marks  13  comprises, for example, an infrared projector  1   a,  such as an infrared emitting diode, disposed on one side of the traveling thermal transfer sheet  10 , an infrared photoelectric sensor  1  capable of sensing infrared rays projected by the infrared ray projector  1   a,  a reflector disposed on the other side of the thermal transfer sheet  10 , and a controller  2  connected to the infrared photoelectric sensor  1 . The controller  1  gives control signals to a printer  3  on the basis of signals given thereto by the infrared photoelectric sensor  1 . 
     When the infrared projector projects infrared rays of a wavelength in the range of 900 to 2500 nm, more preferably, in the range of 900 to 1000 nm, and the infrared sensor is capable of sensing the infrared rays projected by the infrared projector, infrared rays projected by the infrared projector penetrate the thermal transfer layer  12  regardless of the hues of the dyes contained in the thermal transfer layer  12  because those dyes do not absorb infrared rays, and hence the infrared ray cutting identification marks  13  can efficiently be detected. 
     Accordingly, it is preferable to use substantially infrared ray transmitting dyes for forming the thermal transfer layer  12 . 
     The composition of the components of such a thermal transfer sheet is described in detail in an invention proposed by the applicant of the present patent application in JP-A No. 1-202491, and hence the further description of the composition will be omitted. 
     The identification marks  13  include at least two different type of identification marks  13   a  and  13   b  respectively having different printed forms for the YMC transfer region sets a and b as shown in a right-hand region of FIG.  1 . The identification marks  13   a  and  13   b  are formed so as to correspond to the transfer regions  12 Y,  12 M and  12 C of the YMC transfer region sets a and b, respectively. 
     A method of manufacturing the transfer sheet  10  will be described. 
     A Y printing cylinder  101  (Y transfer region printing cylinder), an M printing cylinder (M transfer region printing cylinder)  102  and a C printing cylinder  103  (C transfer region printing cylinder) has a circumference six times the length of the transfer regions  12 Y,  12 M and  12 C. The Y printing cylinder  101  is provided with printing plates  101   a  and  101   b  for printing the Y transfer regions  12 Y, the M printing cylinder  102  is provided with printing plates  102   a  and  102   b  for printing the M transfer regions  12 M, and the C printing cylinder  103  is provided with printing plates  103   a  and  103   b  for printing the C transfer regions  12 C. A mark printing cylinder (identification mark printing cylinder)  104  has a circumference equal to those of the printing cylinders  101 ,  102  and  103 . The mark printing cylinder  104  is provided with a first set of printing plates  104   a  for printing first marks  13   a,  and a second set of printing plates  104   b  for printing second marks  13   b.  The first marks  13   a  are printed in the transfer regions  12 Y,  12 M and  12 C of the first YMC transfer region set a, and the second marks  13   b  are printed in the transfer regions  12 Y,  12 M and  12 C of the second YMC transfer region set b. 
     The Y printing cylinder  101  prints two Y transfer regions  12 Y successively, the M printing cylinder  102  prints two M transfer regions  12 M successively, and then the C printing cylinder prints two C transfer regions  12 C successively. 
     Subsequently, the mark printing cylinder  104  prints the first identification marks  13   a  and the second identification marks  13   b  successively. 
     The identification marks  13   a  and  13   b  indicate, in addition to information about the colors of the corresponding transfer regions  12 Y,  12 M and  12 C, information about the positional relation between the YMC transfer region sets a and b. The characteristics of the transfer regions  12 Y,  12 M and  12 C of the thermal transfer layer  12  of the transfer sheet  10  are measured beforehand by the controller  2  by reading the identification marks  13   a  and  13   b  by the infrared photoelectric sensor  1 , and the controller  2  gives correction signals to the printer  3  to correct transfer conditions so that the tones of colors are adjusted properly when the printer operates for printing by using the transfer sheet  10 . 
     The printing cylinders  101 ,  102  and  103 , each provided with the two printing plates enable the efficient manufacture of the transfer sheet  10 . 
     Since the positional relation between the YMC transfer region sets a and b can be known from the identification marks  13   a  and  13   b,  the printer  3  is able to operate so as to correct transfer conditions according to the characteristics of the transfer regions  12 Y,  12 M and  12 C to print a satisfactory image. 
     In this embodiment, the different identification marks  13   a  and  13   b  are printed in the respective transfer regions  12 Y,  12 M and  12 C of the YMC transfer region sets a and b by the different printing plates  104   a  and  104   b  mounted on the mark printing cylinder  104 , respectively. In the following embodiments, the identification marks formed in each YMC transfer region set have the same form and at least one of the identification marks  13   a  and  13   b  formed in the transfer regions  12 Y,  12 M and  12 C of each YMC transfer region set has a characteristic different from those of the other identification marks  13   a  and  13   b  of the same YMC transfer region set, or the identification marks of each YMC transfer region set have the same form and the identification marks  13   a  and  13   b  of at least one YMC transfer region set have a characteristics different from those of the identification marks  13   a  and  13   b  of the other YMC transfer region sets. 
     A method of forming the identification marks  13   a  and  13   b  in a comparative example will be described and the difference between transfer sheets in comparative examples and the embodiments of the present invention will be elucidated. 
     FIGS.  3 (A)(B)(C) are plan views of transfer sheets in comparative examples. In those comparative examples, the identification marks have the same characteristic. 
     In a transfer sheet  40 A, an identification mark  43 Y is formed only in a head transfer region  42 Y of each of YMC transfer region sets. Only one photoelectric sensor is necessary to detect the identification marks  43 Y. However, the determination of the starting positions of transfer regions  42 M and  42 C includes large errors because only the identification mark  43 Y formed in the head transfer region  42 Y is detected and the starting positions of the transfer regions  42 M and  42 C are estimated on a time basis by counting pulses indicating an angle through which the output shaft of a motor has rotated. Consequently, the starting position of the last transfer region  42 C must be formed in a sufficient length longer than that of an actual image area to avoid the extension of the image outside the image area, which increases material costs. 
     In a transfer sheet  40 B, an identification mark  43 YY of two lines is formed only in a head transfer region  42 Y of each of YMC transfer region sets, and identification marks  43 M and  43 C each having a single line are formed in other transfer regions  42 M and  42 C, respectively. Only a single photoelectric sensor is necessary. Each of the identification marks  43 YY has two lines, and hence the length of the transfer sheet  40 B increases accordingly, which increases the cost of the transfer sheet  40 B. 
     In a transfer sheet  40 C, an identification mark  43 Y formed in the head transfer region  42 Y of each of YMC transfer region sets is a long line of a length equal to the width of the transfer sheet  40 C, and identification marks  43   m  and  43   c  formed in the other regions  42 M and  42 C are a short line of a length shorter than the width of the transfer sheet  40 C. Although two photoelectric sensors must be arranged along the width of the transfer sheet  40 C to detect the long identification marks  43 Y and the short identification marks  43   m  and  43   c,  the length of the transfer sheet  40 C need not be increased and time necessary for detection can be reduced. 
     In a transfer sheet  40 D, an identification mark  43 Y 1  of a thick line is formed in the head transfer region  42 Y of each of YMC transfer region sets, and identification marks  43 M and  43 C of a thin line are formed in the other regions  42 M and  42 C, respectively. Only a single photoelectric sensor is necessary. The head of each YMC transfer region set can be identified by a long duration of detecting the identification mark  43 Y 1  of a thick line, and the head of each of the transfer regions  43 M and  43 C can be identified by a short duration of detecting the identification marks  43 M and  43 C of a thin line. The length of the transfer sheet  40 D increases by a length corresponding to the difference between the thick line forming the identification mark  43 Y 1  and the thin line forming the identification marks  43 M and  43 C. 
     EXAMPLES 1-2 and 1-3 
     FIGS.  4 (A) and  4 (B) are plan views of transfer sheets in examples 1-2 and 1-3 of the first embodiment according to the present invention, respectively. 
     Referring to FIG.  4 (A), a transfer sheet  50 A in the example 1-2 has an alternate arrangement of two YMC transfer region sets a and b, each having three transfer regions  52 Y,  52 M and  52 C respectively of different colors (yellow, magenta and cyan). Identification marks  53 Ya and  53 Y′b are formed in the head transfer regions  52 Y of the YMC transfer region sets a and b, respectively. 
     The identification marks  53 Ya and  53 Y′b are the same in form but differ from each other in transmissivity (or reflectivity). 
     In the following description, an identification mark designated by a reference character without a dash (′) has a small transmissivity (high optical density), and an identification mark designated by a reference character with a dash (′) has a large transmissivity (low optical density). A photoelectric sensor provides a high-level signal upon the detection of the identification mark designated by a reference character without a dash and provides a low-level signal upon the detection of the identification mark designated by a reference character with a dash. 
     The transfer sheet  50 A can be manufactured by the same method as that of manufacturing the transfer sheet shown in FIG. 1 using printing cylinders each provided with two printing plates. 
     When the infrared photoelectric sensor  1  is sensitive to infrared rays of a wavelength in the range of 800 to 950 nm, it is preferable in view of avoiding faulty detection that the largest difference in transmissivity (or reflectivity) between the identification marks  53 Ya and  53 Y′b is 10% or below of the larger one. 
     The sensitivity of the infrared photoelectric sensor  1  may be adjusted to a level high enough to detect either of the identification marks  53 Ya or  53 Y′b, having a lower transmissivity. 
     The positional relation between the two YMC transfer region sets a and b of the transfer sheet  50 A can be known because the identification marks  53 Ya and  53 Y′b have different transmissivities (or reflectivities), respectively. Therefore a satisfactory image can be formed by printing the image after correcting transfer conditions according to the characteristics of the YMC transfer region sets a and b. 
     As shown in FIG.  4 (B), a transfer sheet  50 B in an example 1-3 has transfer regions  52 Y,  52 M and  52 C arranged in an arrangement similar to that of the transfer regions  52 Y,  52 M and  52 C of the transfer sheet  50 A in the example 1-2. In the transfer sheet  50 B, identification marks  53 Y′a,  53 Ma,  53 Ca are formed in the transfer regions  52 Ya,  52 Ma and  52 Ca of a YMC transfer region set a, respectively, and identification marks  53 Y′b,  53 M′b and  53 Cb are formed in the transfer regions  52 Yb,  52 Mb and  52 Cb of a YMC transfer region set b, respectively. The respective identification marks  53 a ( 53 Y′a,  53 Ma and  53 Ca) and  53   b  ( 53 Y′b,  53 M′b and  53 Cb) of the YMC transfer region sets a and b have the same form. 
     In the YMC transfer region set a, the identification mark  53 Y′a have a transmissivity (reflectivity) different from those of the identification marks  53 Ma and  53 Ca. In the YMC transfer region set b, the identification mark  53 Cb has a transmissivity (reflectivity) different from those of the identification marks  53 Y′b and  53 M′b. 
     The identification mark  53 Ma of the YMC transfer region set a and the identification mark  53 M′b of the YMC transfer region set b differ from each other in transmissivity (reflectivity). 
     The identification marks  53 Y′a and  53 Y′b may be of the same form, and the identification marks  53 Ca and  53 Cb may be of the same form. 
     An increased number of pieces of information about the thermal transfer sheet  50 B can be recorded. 
     The width and the number of lines of the identification marks differing from each other in property, such as transmissivity, may properly be determined, and information expressed by the identification mark can be identified by the width or the number of pulses generated upon the detection of the identification mark. For example, since the transmissivity cannot visually be determined, the genuineness can easily be known from an identification mark having a complicated form. 
     For example, when the thermal transfer sheet is loaded into an inappropriate printer other than specified printers or when a nongenuine thermal transfer sheet is loaded into a printer, an error signal is generated to stop using the inappropriate printer or the nongenuine thermal transfer sheet. 
     A detecting method to be carried out by a printer is described in Japanese Patent No. 2-21951. 
     EXAMPLES 1-4 to 1-7 
     FIGS.  5 (A) to  5 (E) are plan views of transfer sheets in examples 1-4 to 1-7 of the first embodiment according to the present invention. 
     In each of the transfer sheets shown in FIGS.  5 (A) to  5 (E), an identification mark formed in the head transfer region of each YMC transfer region set is two lines, and identification marks formed in the other transfer regions of the same YMC transfer region set are a single line. 
     In a transfer sheet  60 A in the example 1-4 shown in FIG.  5 (A), identification marks  63 YYa and  63 Y′Y′b formed respectively in the respective head transfer regions of YMC transfer region sets a and b are different from each other in transmissivity. 
     Each of the Y printing cylinder  101 , the M printing cylinder, the C printing cylinder  103  and the mark printing cylinder  104  is provided with three printing plates when forming the transfer regions and the identification marks of a transfer sheet  60 B in the example 1-5 shown in FIG.  5 (B). An arrangement of three successive YMC transfer region sets a, b and c is formed repeatedly. Identification marks  63 YYa,  63 YY′b and  63 Y′Y′c formed respectively in the respective head transfer regions of YMC transfer region sets a, b and c are different from each other in transmissivity. 
     A transfer sheet  60 C in the example 1-6 shown in FIG.  5 (C) is the same in construction as the transfer sheet  60 B in the example 1-5, except that each of the YMC transfer region sets a, b and c has a protective region OP in addition to the Y, M and C transfer regions. 
     A transfer sheet  60 D in the example 1-6 shown in FIG.  5 (D) is similar to the transfer sheet  60 A in the example 1-4. The transfer sheet  60 D differs from the transfer sheet  60 A in that, in the transfer sheet  60 D, the same identification marks  63 Y are formed respectively in the respective head transfer regions of YMC transfer region sets a and b, and identification marks  63 Ma and  63 M′b formed respectively in the magenta transfer regions of the YMC transfer region sets a and b are different from each other in transmissivity. 
     Each of the Y printing cylinder  101 , the M printing cylinder, the C printing cylinder  103  and the mark printing cylinder  104  is provided with three printing plates when forming the transfer regions and the identification marks of a transfer sheet  60 E in the example 1-7 shown in FIG.  5 (E). An arrangement of three successive YMC transfer region sets a, b and c is formed repeatedly. An identification mark  63 Ma formed in the magenta transfer region of the YMC transfer region set a differs in transmissivity from an identification mark  63 M′b formed in the magenta transfer region of the YMC transfer region set b, and an identification mark  63 Ca formed in the cyan transfer region of the YMC transfer region set a differs in transmissivity from an identification mark  63 C′c formed in the cyan transfer region of the YMC transfer region set c. 
     EXAMPLES 1-8 to 1-10 
     FIGS.  6 (A),  6 (B) and  6 (C) are plan views of transfer sheets  70 A,  70 B and  70 C in examples 1-8 to 1-10, respectively, of the first embodiment according to the present invention. 
     In each of the transfer sheets  70 A,  70 B and  70 C, an identification mark formed in the head transfer region of each YMC transfer region set is a single long line of a length equal to the width of the transfer sheet, and identification marks formed in the other transfer regions are a single short line of a length equal to about half the width of the transfer sheet. Two photoelectric sensors must be arranged along the width of each of the transfer sheets  70 A,  70 B and  70 C to detect the long identification marks and the short identification marks of each of the transfer sheets  70 A,  70 B and  70 C. 
     In the transfer sheet  70 A in the example 1-8 shown in FIG.  6 (A), identification marks  73 Ya and  73 Y′b formed in the respective head transfer regions of YMC transfer regions a and b differ from each other in transmissivity. 
     Each of the Y printing cylinder  101 , the M printing cylinder, the C printing cylinder  103  and the mark printing cylinder  104  is provided with three printing plates when forming the transfer regions and the identification marks of the transfer sheet  70 B in the example 1-9 shown in FIG.  6 (B). An arrangement of three successive YMC transfer region sets a, b and c is formed repeatedly. Identification marks  73 Ya,  73   yy′b′  and  73 Y′c formed respectively in the respective head transfer regions of the YMC transfer region sets a, b and c differ from each other in transmissivity. The identification mark  73   yy′b  is a single line having one half part having a small transmissivity and the other half part having a large transmissivity. 
     The transfer regions and the identification marks of the transfer sheet  70 C in the example 1-10 shown in FIG.  6 (C), similarly to those of the transfer sheet  70 B, are formed by using the Y printing cylinder  101 , the M printing cylinder, the C printing cylinder  103  and the mark printing cylinder  104  each provided with three printing plates. The transfer sheet  70 C, similarly to the transfer sheet  60 C in the example 1-6, is provided with protective regions OP. An identification mark  73 Ya formed in the head transfer region of a YMC transfer region set a have a transmissivity different from those of identification marks  73   y′yb  and  73   yy′c  formed respectively in the head transfer regions of YMC transfer region sets b and c. Each of the identification marks  73   y′yb  and  73   yy′c  is a single line having one half part having a small transmissivity and the other half part having a large transmissivity. As viewed in FIG.  6 (C), the upper half part of the identification mark  73   y′yb  has a large transmissivity and the lower half part of the same has a small transmissivity, while the upper half part of the identification mark  73   yy′c  has a small transmissivity and the lower half part of the same has a large transmissivity. 
     According to this example, one photoelectric sensor  1  can securely detect the identification marks in the head transfer region and the other transfer regions of each YMC transfer region set, and the transfer sheets can have a reasonable length, not an unnecessarily longer one, and the time for detecting the identification marks can be reduced. 
     FIGS.  7 (A) to  7 (C) are enlarged views of the identification marks formed in the transfer sheet  70 C in the example 1-10 and modifications of the same. 
     As shown in FIG.  7 (A), the identification mark  73   y′yb  has one half part  73   y ′ having a small transmissivity, and the other half part  73   y  having a large transmissivity. An identification mark in a modification shown in FIG.  7 (B) has three parallel parts  73   y,    73   y ′ and  73   y  arranged longitudinally in that order and having different transmissivities, respectively. This identification mark is capable of carrying an increased number of pieces of information. An identification mark in a further modification may consists of two, four or more than four parallel parts having different transmissivities, respectively. 
     An identification mark in a modification shown in FIG.  7 (C) has one part  73   y ′ and the other part  73   y  surrounded by the part  73   y ′. In a further modification, two or more than two parts  73   y  may be formed in a part  73   y′.    
     The first embodiment according to the present invention is not limited in its practical application to the examples 1-1 to 1-10, and various changes and variations are possible therein without departing from the scope of the present invention. 
     For example, printing cylinders each provided with four or more than four printing plates may be used for printing the transfer regions and the identification marks. 
     The transfer sheets may be provided, in addition to the protective regions OP, with receiving regions. 
     As is apparent from the foregoing description, according to the present invention, the transfer sheet can efficiently be manufactured by using printing cylinders each provided with a plurality of printing plates. 
     Since the YMC transfer region sets formed by using printing cylinders each provided with a plurality of printing plates can be identified by the identification marks, images of a satisfactory picture quality can be formed by printing the image after correcting transfer conditions according to the characteristics of the YMC transfer region sets. 
     Second Embodiment 
     EXAMPLE 2-1 
     FIGS.  8 (A) and  8 (B) are typical plan views of a transfer sheet  110  in an example 2-1 of a second embodiment according to the present invention and an enlarged view of a part of the transfer sheet, respectively. 
     The transfer sheet  110  comprises a base sheet  111 , a thermal transfer layer  112  formed on the base sheet  111 , and identification marks  113 . The thermal transfer layer  112  has a plurality of YMC transfer region sets a and b, each transfer region set having transfer regions  112 Y,  112 M and  112 C respectively having different functions. 
     The base sheet  111  serves as a carrier member of the transfer sheet  110  and may be a sheet having sufficient heat resistance and strength. The base sheet may be a paper sheet, a plastic sheet, such as a PET sheet, or a metal foil of a thickness in the range of 0.5 to 50 μm, preferably, in the range of 3 to 10 μm. 
     The thermal transfer layer  112  is formed on the base sheet  111 , and has the plurality of YMC transfer region sets a and b each of an yellow transfer region  112 Y, a magenta transfer region  112 M and a cyan transfer region  112 C longitudinally arranged in that order. 
     The transfer layer  112  is formed of a resin containing dyes that are melted or sublimated when heated. Preferably, the dyes are hot-sublimable disperse dyes, oil colors or basic dyes, and have a molecular weight in the range of 150 to 800, preferably, in the range of 310 to 700. The dyes are selected from those dyes and colors, taking into consideration the temperature of sublimation, hue, weathering resistance and solubility in an ink base or a binder. 
     The thermal transfer layer  112  is formed in a thickness in the range of 0.3 to 2 μm by a suitable printing process, such as a gravure printing process, using composite printing inks each prepared by dissolving a selected dye and a selected resin in a solvent. 
     The identification marks  113  indicate information about the thermal transfer sheet  110 . The identification marks  113  may be formed of any suitable material, provided that the identification marks  113  can be detected by an optical, electrical or magnetic detector. 
     The information about the thermal transfer sheet  110  indicates the attributes of the thermal transfer sheet  110  including means for discriminating between the front and the back side, a recording starting position, means for discriminating between the head and the tail (direction), type, grade, the number of available frames, advanced notification of end, boundaries between the thermal transfer regions, maker, applicable printers and means for indicating genuineness. 
     The quality of the identification marks  113  is dependent on the detector to be used for detecting the identification marks  113 . For example, the identification marks  113  are formed of an optically detectable material prepared by mixing an optically identifiable pigment or dye into a resin, an electrically detectable material, such as a conductive resin prepared by mixing powder of a metal or carbon into a resin, or a metal foil, a magnetically detectable material, such as a magnetic resin prepared by mixing a magnetic metal or a magnetic compound in a resin, or a magnetic metal film formed by evaporation. 
     Although the detector may be of an optical type, an electrical type or a magnetic type, the use of an optical detector is the simplest in configuration. 
     When each identification mark  113  is formed in the corresponding transfer region of the thermal transfer layer  112  and the dye or the pigment contained in the material forming the identification mark  113  is of an ordinary hue, a suitable color filter is necessary to detect the identification mark  113 . When the transfer region of the thermal transfer layer  112  is formed of a material containing an infrared ray transmitting dye and the identification mark  113  is formed of an infrared ray cutting material, the identification mark  113  can be detected by using an infrared detector regardless of the hue of the corresponding transfer region of the thermal transfer layer  112 . 
     The infrared ray cutting identification mark  113  can be formed of a composite material prepared by mixing an infrared ray cutting substance into a resin. An optimum infrared ray cutting substance is carbon black which absorbs infrared rays very effectively. 
     The resin as the component of the infrared ray cutting composite material may be a polyurethane resin, a polyamide resin, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-polyacrylate copolymer, a cellulose acetate butyrate or a mixture of some of those resins. A resin produced by crosslinking some of those resins with a polyisocyanate compound may be used as the component of the infrared ray cutting composite material. 
     The weight ratio of the infrared ray cutting substance to the resin is in the range of 1/10 to 10/1. The identification marks  113  are formed in a thickness in the range of about 0.5 to about 5 μm. 
     The detector for detecting the infrared ray cutting identification marks  113  comprises, for example, an infrared projector  1   a,  such as an infrared emitting diode, disposed on one side of the traveling thermal transfer sheet  110 , an infrared photoelectric sensor  1  capable of sensing infrared rays projected by the infrared ray projector  1   a,  a reflector disposed on the other side of the thermal transfer sheet  110 , and a controller  2  connected to the infrared photoelectric sensor  1 . The controller  1  gives control signals to a printer  3  on the basis of signals given thereto by the infrared photoelectric sensor  1 . 
     When the infrared projector projects infrared rays of a wavelength in the range of 900 to 2500 nm, more preferably, in the range of 900 to 1000 nm, and the infrared sensor is capable of sensing the infrared rays projected by the infrared projector, infrared rays projected by the infrared projector penetrate the thermal transfer layer  112  regardless of the hues of the dyes contained in the thermal transfer layer  112  because those dyes do not absorb infrared rays, and hence the infrared ray cutting identification marks  113  can efficiently be detected. 
     Accordingly, it is preferable to use substantially infrared ray transmitting dyes for forming the thermal transfer layer  112 . 
     As shown in FIG.  8 (B), each of the identification marks  113  consists of parts  113   a  and  113   b  differing from each other in transmissivity (or reflectivity). Each of the YMC transfer region sets a and b may be provided with only one identification mark  113  as shown in FIG.  8 (A). 
     When the infrared photoelectric sensor  1  is sensitive to infrared rays of a wavelength in the range of 400 to 700 nm (range of visibility), it is preferable in view of avoiding faulty detection that the largest difference in transmissivity (reflectivity) between the identification marks  113   a  and  113   b  is 10% or below of the larger one. 
     In addition, when the infrared photoelectric sensor  1  is sensitive to infrared rays of a wavelength in the range of 800 to 950 nm, it is also preferable that the largest transmissivity or reflectivity is 1 to 10% and the smallest transmissivity or reflectivity is below 1%. 
     In general, the identification marks consist of black marks including carbon black. When a general-purpose  1 R sensor detects the identification marks whose transmissivity is more than 10%, the detection of the identification marks can not be stable. It is also preferable in view of avoiding faulty detection that the transmissivity of the identification marks has 10% or below for any wavelength. 
     The parts  113   a  and  113   b  of the identification mark  113  differing from each other in transmissivity (or reflectivity) can be formed by a gravure printing process using a gravure printing plate having depressed areas of different thicknesses for the parts  113   a  and  113   b,  respectively. The identification mark  113  may consists of any suitable number of parts of any suitable width. Information represented by the identification mark  113  can be known from the width or the number of pulses generated upon the detection of the identification mark  113 . 
     The sensitivity of the photoelectric sensor is adjusted so as to be able to detect either the parts  113   a  or the part  113   b  having a smaller transmissivity. For example, since the transmissivity cannot visually be determined, the genuineness can easily be known from an identification mark having a complicated form. 
     The identification mark  113  having the parts  113   a  and  113   b  differing from each other in transmissivity (or reflectivity) is able to express an increased number of pieces of information. 
     For example, when the thermal transfer sheet is loaded into an inappropriate printer other than specified printers or when a nongenuine thermal transfer sheet is loaded into a printer, an error signal is generated to stop using the inappropriate printer or the nongenuine thermal transfer sheet. 
     EXAMPLES 2-2 to 2-5 
     FIGS.  9 (A) to  9 (D) are plan views of transfer sheets  110 A,  110 B,  110 C and  110 D in examples 2-2 to 2-5 of the second embodiment according to the present invention. 
     Each of identification marks  113  formed in the transfer sheets  110 A,  110 B,  110 C and  110 D, similarly to those formed in the transfer sheet  110  in the example 2-1, consists of two parts  113   a  and  113   b  differing from each other in transmissivity (or reflectivity). 
     In the transfer sheet  110 A in the example 2-2 shown in FIG.  9 (A), identification marks  113 Y,  113 M and  113 C are formed in Y transfer regions  112 Y, M transfer regions  112 M and C transfer regions  112 C, respectively. Each of the identification marks  113 Y,  113 M and  113 C is a single line of a length equal to the width of the transfer sheet  110 A. Each of the identification marks  113 Y,  113 M and  113 C indicates information about the starting edge and the color of the corresponding transfer region. Therefore, it is possible to avoid the faulty detection of the transfer regions  112 Y,  112 M and  112 C due to an accidental skip of the identification marks in detecting the identification marks  113 Y,  113 M and  113 C. 
     The transfer sheet  110 B in the example 2-3 has a protective layer having protective regions  1120 P in addition to a thermal transfer layer  112  having Y transfer regions  112 Y, M transfer regions  112 M and C transfer regions  112 C as shown in FIG.  9 (B). Identification marks  113 YY,  113   m,    113   c  and  113   op  are formed in the Y transfer regions  112 Y, the M transfer regions  112 M, the C transfer regions  112 C and the protective regions  112 OP, respectively. The identification mark  113 YY consists of two lines of a length equal to the width of the transfer sheet  110 B, and each of the identification marks  113   m,    113   c  and  113   op  is a line of a length shorter than the width of the transfer sheet  110 B. 
     The transfer sheet  110 C in the example 2-4 has a thermal transfer layer  112  having black transfer regions  112 Bk and protective regions  112 OP as shown in FIG.  9 (C). Identification marks  113 Bk and  113   op  are formed in the black transfer regions  112 Bk and protective regions  112 OP, respectively. Each of the identification marks  113 Bk is a line of a length equal to the width of the transfer sheet  110 C, and each of the identification marks  113   op  is a line of a length shorter than the width of the transfer sheet  110 C. 
     The transfer sheet  110 D in the example 2-5 has a thermal transfer layer  112  having transfer regions  112 Y,  112 M and  112 C as shown in FIG.  9 (D). Identification marks  113   y,    113   mm  and  113   ccc  are formed in the transfer regions  112 Y,  112 M and  112 C, respectively. The identification marks  113   y,    113   mm  and  113   ccc  are a single rectangle, two rectangles and three rectangles formed on one side edge of the corresponding transfer regions  112 Y,  112 M and  112 C, respectively. 
     EXAMPLES 2-6 to 2-8 
     FIGS.  10 (A) to  10 (C) are enlarged fragmentary plan views of identification marks  113 A,  113 B and  113 C employed in transfer sheets in examples 2-6 to 2-8. 
     As shown in FIG.  10 (A), the identification mark  113 A employed in the example 2-6 has one half part  113   c  having a small transmissivity, and the other half part  113   d  having a large transmissivity. 
     As shown in FIG.  10 (B), the identification mark  113 B employed in the example 2-7 has three parallel parts  113   e,    113   f  and  113   g  arranged longitudinally in that order and having different transmissivities, respectively. This identification mark is capable of carrying an increased number of pieces of information. In a modification, an identification mark may consists of four or more than four parallel parts having different transmissivities, respectively. 
     The identification mark  113 C shown in FIG.  10 (C) has one part  113   h  and the other part  113   i  surrounding the part  113   h.  In a modification, two or more than two parts  113   h  may be formed in a part  113   i.    
     Each of the identification marks employed in those examples consists of the two parts differing from each other in characteristic. In the following examples, identification marks of different characteristics are formed in different transfer regions, respectively. 
     EXAMPLES 2-9 to 2-11 
     FIGS.  11 (A) to  11 (C) are plan views of transfer sheets  150 A,  150 B and  150 C in examples 2-9 to 2-11, respectively. 
     The transfer sheets  150 A,  150 B and  150 C are the same in morphology as the transfer sheet  40 B shown in FIG.  3 (B) and differ from each other in type. 
     In the transfer sheet  150 A in the example 2-9, an identification mark  153 Y′Y′ consisting of two lines having a large transmissivity (or reflectivity) is formed in the head transfer region  152 Y of each of YMC transfer region sets a and b, and identification marks  153 M and  153 C each of a single line having a small transmissivity (or reflectivity) are formed in the other transfer regions  152 M and  152 C of the same YMC transfer region set, respectively. 
     The identification mark  153 Y′Y′ differs from the identification marks  153 M and  153 C in transmissivity (or reflectivity) to a light beam used by the infrared photoelectric sensor  1 . 
     When the infrared photoelectric sensor  1  is sensitive to infrared rays of a wavelength in the range of 800 to 950 nm, it is preferable in view of avoiding faulty detection that the largest difference in transmissivity (reflectivity) between the identification marks  153 Y′Y′, and the identification marks  153 M and  153 C is 10% or below of the larger one. The relation in transmissivity (or reflectivity) between the identification marks  153 Y′Y′,  153 M and  153 C is the same as that between the identification marks in the example 2-1, and hence the further description thereof will be omitted. In the following description, it is assumed that the identification marks differ from each other in transmissivity. 
     In the transfer sheet  150 B in the example 2-10, an identification mark  153 YY consisting of two lines having a small transmissivity is formed in the head transfer region  152 Y of each of YMC transfer region sets a and b, an identification mark  153 M of a single line having a small transmissivity is formed in transfer regions  152 M, and an identification mark  153 C′ of a single line having a large transmissivity is formed in transfer regions  152 C as shown in FIG  11 (B). 
     In the transfer sheet  150 C in the example 2-11, an identification mark  153 YY′ consisting of two lines, one line having a small transmissivity and the other line having a large transmissivity, is formed in the head transfer region  152 Y of each of YMC transfer region sets a and b, and identification marks  153 M,  153 C and  153 OP, each having a single line having a small transmissivity are formed in transfer regions  152 M,  152 C and  152 OP, respectively, as shown in FIG.  11 (C). 
     EXAMPLES 2-12 to 2-14 
     FIGS.  12 (A) to  12 (C) are plan views of transfer sheets  160 A,  160 B and  160 C in examples 2-12 to 2-14, respectively. 
     The transfer sheets  160 A,  160 B and  160 C are the same in morphology as the transfer sheet  40 C shown in FIG.  3 (C) and differ from each other in type. 
     In the transfer sheet  160 A in the example 2-12, an identification mark  163 Y′ of a single line having a length equal to the width of the transfer sheet  160 A and a large transmissivity, is formed in the head transfer region  162 Y of each of YMC transfer region sets a and b, and identification marks  163   m  and  163   c,  each having a single line having a length shorter than the width of the transfer sheet  160 A and a large transmissivity are formed in the other transfer regions  162 M and  162 C of the same YMC transfer region set, respectively. 
     In the transfer sheet  160 B in the example 2-13, an identification mark  163 Y of a single line having a length equal to the width of the transfer sheet  160 B and a small transmissivity is formed in the head transfer region  162 Y of each of YMC transfer region sets a and b, an identification mark  163   m  of a single line having a length shorter than the width of the transfer sheet  160 B and a large transmissivity is formed in transfer regions  162 M, and an identification mark  163   c ′ of a single line having a length shorter than the width of the transfer sheet  160 B and a small transmissivity is formed in transfer regions  162 C as shown in FIG.  12 (B). 
     In the transfer sheet  160 C in the example 2-14, an identification mark  163   yy ′ of a single line having a length equal to the width of the transfer sheet  160 C is formed in the head transfer region  162 Y of each of YMC transfer region sets a and b, and identification marks  163   m,    163   c  and  163   op,  each having a single line having a length shorter than the width of the transfer sheet  160 C and a large transmissivity are formed in transfer regions  162 M and  162 C and protective regions  162 OP, respectively, as shown in FIG.  12 (C). The identification mark  163   yy ′ has one part having a small transmissivity and the other part having a large transmissivity. 
     The transfer regions of the transfer sheets  160 A,  160 B and  160 C in these examples can be identified by using a single photoelectric sensor  1 . An increased number of pieces of information are available if two photoelectric sensors  1  are used. The identification marks do not increase the lengths of the transfer sheets  160 A,  160 B and  160 C and can be detected in a short time. 
     EXAMPLES 2-15 and 2-16 
     FIGS.  13 (A) and  13 (B) are plan views of a transfer sheet  170 A in an example 2-15 and a transfer sheet  170 B in an example 2-16. 
     In the transfer sheet  170 A in the example 2-15, an identification mark  173 Y′ of a single line having a large transmissivity is formed in the head transfer region  172 Y of each of two YMC transfer region sets a and b, and identification marks  173 M and  173 C each of a single line having a small transmissivity are formed in the other transfer regions  172 M and  172 C of the same YMC transfer region set as shown in FIG.  13 (A). 
     In the transfer sheet  170 B in the example 2-16, an identification mark  173 Y′ of a single line having a large transmissivity is formed in the head transfer region  172 Y of each of two YMC transfer region sets a and b, and identification marks  173 M,  173 C and  173 OP each of a single line having a small transmissivity are formed in the other transfer regions  172 M,  172 C and  172 OP of the same YMC transfer region set as shown in FIG.  13 (B). 
     The transfer sheets  170 A and  170 B are subject to various changes and variations without departing from the scope of the present invention. 
     For example, different parts of an identification mark and different identification marks may differ from each other in electrical characteristics or magnetic characteristics. 
     The transfer sheet may additionally be provided with receiving regions. 
     Bar codes capable of representing a large number of pieces of information may be used as the identification mark. 
     The different identification marks (examples 2-9 to 2-16) may have a part of a characteristic different from that of the other part (examples 2-11 to 2-8). 
     As is apparent from the foregoing description, according to the present invention, the identification marks of the same form and each having a part of a characteristic different from that of the other part enable the detection of the transfer regions and are capable of representing an increased number of pieces of information. The YMC transfer region sets and the transfer regions can exactly be identified by the identification marks of different characteristics.