Method for recording and erasing a visible image on a card

Abstract: A method for recording and erasing a visible image on a card having a recording area with a smooth surface of a synthetic resin, which comprises a step of subjecting the smooth surface in the recording area to frosting treatment at a temperature within a range of from the glass transition temperature to the melting point of the synthetic resin, to form a frosted surface having a strain, and a step of defrosting the frosted surface by heating it at a temperature higher than the temperature for the frosting treatment, to return it to a smooth surface, whereby a visible image is formed in the recording area by the contrast between the frosted surface and the smooth surface.

Description: The present invention relates to a method for recording and erasing visible images on cards for repeated use, such as commutation passes, admission cards or pre-paid cards. Commutation passes for transportion systems or admission cards for convention halls or buildings are repeatedly used every day. However, there is no effective means to check abuse thereof for illegal rides or unauthorized entrance. In recent years, a checking method by magnetic cards has been employed in some fields. However, the magnetic checking is not visible, and default in checking is likely to occur due to a trouble of the apparatus. Therefore, such magnetic cards have been inconvenient to both users and administrators. GB-A-2 176 746 discloses a magnetic card with a magnetic recording layer on a base sheet. The card comprises a display sheet having a transparent display area with a display cell formed between the display sheet and the magnetic recording sheet. Patent Abstracts of Japan., Vol. 12, No. 259 (P-733), July 21, 1988 and JP-A-63 047 733 teaches that an erasable frasted image may be produced on a thermoplastic sheet coated with a thermoplastic resin. DE-B-2 701 176 teaches that in order to check the validity of an information storage medium, the medium can be provided with a visible image by the application of heat to form a surface under strain in the thermoplastic material of the information storage medium. Magnetic cards and IC cards are used also as various pre-paid papers. Again, the recorded information is not visible, and the amounts used or the remaining amounts can not easily be checked. Therefore, there has been a problem in respect of the guarantee in the content to the users. It is an object of the present invention to provide a method for recording and erasing a visible image on a card to be repeatedly used such as a commutation card, an admission card or a pre-paid card of various types. The present invention provides a method for recording and erasing a visible image as specified in claim 1. In the accompanying drawings: Figure 1 is a perspective view of an example of the card used for the method of the present invention. Figure 2 is a partial plan view of a card on which a frost image was formed. Figure 3 is a perspective view of an example of the card used for the method of the present invention. Figure 4 is a cross sectional view along line V-V in Figure 3. Figures 5 and 6 are cross sectional views of different types of cards. Figures 7 to 10 illustrate a second embodiment of the method of the present invention. Figure 11 illustrates another example of the card used for the method of the present invention in which a metallic specular layer is provided. Now, the present invention will be described in detail with reference to the drawings. An admission card C has a smooth surface 1 of a synthetic resin on at least a part of its surface. A predetermined frosted image 2 of e.g. a letter or a symbol is formed on this smooth surface 1. This frosted image 2 is formed at a temperature within a range of from the glass transition temperature to the melting point of the resin of the smooth surface 1, whereby it has an internal strain. Accordingly, it has such a nature that when heated, the frosted surface disappears and returns to the initial smooth surface. Now, the present invention will be described in further detail step by step. With the card C to be used the surface layer 1 made of a synthetic resin having a smooth surface is exposed on the card surface to constitute a recording area 13, as shown in Figure 1. On the card surface other than the recording area 13, a necessary description or a decorative design is printed as shown by printing 12. On the rear side of the smooth surface layer 1, a base material 3 having a high strength, such as a polyethyleneterephthalate sheet or a paper, is laminated. Further, on its surface, a magnetic recording layer 4 is provided so that various information can be recorded. As the synthetic resin constituting the smooth surface layer 1, various thermoplastic resins inducing polyethylene, polypropylene, polyvinyl chloride, polystyrene, polymethyl (meth)acrylate, polyethyleneterephthalate, polyamide, polycarbonate, polyacetal, ABS resin and copolymer resins thereof, may be employed alone or in combination as a mixture. Among them, non-crystalline resins such as polyvinyl chloride, polystyrene, polymethyl (meth)acrylate, and polycarbonate, are preferred since they are easy to treat. Further, it is possible to employ a resin obtained by cross linking a cross linkable acrylate resin, a cross linkable urethane resin or one of the above-mentioned various resins by a cross linking agent, an electron beam, a γ-ray and heat cross linking to such an extent that sufficient heat flowability remains. The thickness of the smooth surface layer 1 is at least 3 µm to form a frosted image and is usually within a range of from 10 µm to 3 mm. The overall thickness of the card C is not particularly limited, but is usually from 0.1 to 3 mm. This smooth surface layer 1 may be a film or sheet formed by extrusion molding, or may be formed by coating. The background is constituted by the frosted surface, and the image of a letter or the like is constituted by a smooth surface. This frosting treatment is conducted at a temperature within a range of from the glass transition temperature (Tg) to the melting point (Tm) of the synthetic resin constituting the smooth surface layer 1, to provice a strain. At a temperature lower than Tg, no strain will be formed by frosting treatment, or a formed strain will immediately be released even without heating. At a temperature higher than Tm, frosting can be conducted, but the formed frost will not retain a strain, and the frost can not be erased even by reheating, whereby the object of the present invention can not be attained. Non-crystalline resins do not show distinct Tm in many cases. In such cases, the flow temperature may be taken as the melting point. Likewise, in the case of a cross linked resin which usually does not show Tm, frosting treatment may be conducted at a temperature of not higher than the flow temperature (or the decomposition-initiation temperature). Further, in the case of a resin mixture or a copolymer resin showing two or more Tg, the higher Tg may be used as the glass transition temperature for the purpose of the present invention. The frosted image 2 thus formed, disappears when heated at a temperature higher than the frosting treatment. Therefore, the frosting treatment is preferably conducted at a temperature of at least 60°C within the above-mentioned range from the viewpoint of the stability of the image. As an example for a method of frosting treatment, a method may be mentioned in which a stamp with a frosted surface is pressed against the smooth surface layer 1. In this case, the stamp may be heated, or the smooth surface layer 1 may be heated. With respect to the frosted condition, the surface roughness of the frosted surface 21 of the frosted image 2 is within a range of from 1 to 10 µm as a 10 point average roughness (Rz) in accordance with Japanese Industrial Standard (JIS) B-0601. If the surface roughness is less than 1 µm, the difference between the frosted image and the smooth surface is small, and it tends to be difficult to determine the presence or absence of the image. On the other hand, if the surface roughness exceeds 10 µm, it tends to be difficult to completely erase the frost at the time of erasing the visible image, such being troublesome for reuse. In the case of an admission card or a commutation card, the image 2 may be not only the indication of the entrance, but also the location, the day and the time of the entrance, etc. In the case of a pre-paid card, the amount used and the amount remaining may be recorded. For example, in the case of a card to be used for the entrance and exit, such as the commutation card, an image may be formed at one of the entrance and the exit and erased at the other. In the case of a pre-paid card to be used for shopping, the amount used and the amount remaining may be recorded at the time of using the card, and erasing and fresh recording may be conducted at the next time of its use. The card in Figure 1 is provided with a magnetic recording layer 4 on its rear side. A magnetic card or an IC card is capable of recording various information such as a specification for its use and permits easy calculation by an apparatus. Therefore, by applying the method of the present invention to such a card, it is possible to utilize such functions and to display the main items of the recorded information in a visually observable form. For example, the amount used and the amount remaining may be displayed in the form of a visual image each time when a pre-paid card is used. A magnetic recording layer 4 may be provided at an appropriate position, e.g. inside of the card as an inner layer, depending upon the apparatus to be used. Now, referring to Figures 3 to 6, the structures of cards to be used for the method of the present invention will be described. The card shown in Figures 3 and 4 comprises a smooth surface layer 1 and a base material 3 provided with an window 31 bonded on each side the smooth surface layer 1, wherein the smooth surface layer 1 is partially exposed to constitute a recording area. The smooth surface layer 1 is transparent when it is not frosted. Necessary explanations or decorative designs may be printed on one or both of the base materials. With this card, when a frosted image is formed at the portion which is transparent from the front side to the rear side of the card, not only the difference in the light reflection between the frosted surface and the smooth surface, but also the difference in the transparency can be utilized to observe the frosted image clearly. To enable the frosted image of the card to be seen more readily, it is advisable to color the smooth surface layer 1 with a dark color. Namely, the frosted image 2 may be made more readily observable when the smooth surface layer is colored to have a lightness (V) of at most 5 as stipulated by JIS Z-8721. As another method for making the image readily observable, a background layer 5 may be formed beneath the smooth surface layer 1 as in the card shown in Figure 6. As the background layer 5, the following two are effective. 1) A colored layer having a lightness (V) of at most 5 as stipulated by JIS Japanese Industrial Standard Z-8721. The material may be paper or a synthetic resin, and is not particularly limited. 2) Metallic specular i.e. reflective layer The metallic specular layer having a 60° specular glossiness of at least 100% as stipulated by JIS Z-8741 is particularly preferred. As the metal, aluminum, nickel, chromium, tin or copper may be employed. When a background layer 5 is provided, the smooth surface layer 1 is made of a material which is transparent in a non-frosted state. By the provision of such a background layer 5, the frosted image 2 becomes distinctive against the dark background or against the metallic reflective layer, whereby the visual observation of the image will be easy. Particularly effective is the use of a metallic specular layer. Figure 6 shows an example of the card having a metallic specular layer formed as a background layer 5 on one side of a base material 3 by vapor deposition of a metal. In this case, it is preferred to apply a printing 12 on the upper surface of surface layer 1 to present a necessary information and to prevent the vapor deposited metallic layer from being seen through from above. Figure 7 is a cross sectional view of the card shown in Figure 1, wherein a recording area 13 is formed with a smooth surface layer 1 exposed. Now, the recording method to the card will be described. Firstly, as shown in Figure 8, the entire surface of the recording area 13 of the card is subjected to frosting treatment to form a frosted surface 21. This frosting treatment is conducted at a temperature between the glass transition temperature (Tg) and the melting point (Tm) of the resin constituting the smooth surface layer 11 to provide a strain. For this frosting treatment, a usual method may be employed in which a frosting plate or a frosting roll is employed. As mentioned above, the frosted state is preferably such that the surface roughness of the frosted surface 21 is within a range of from 1 to 10 µm by a 10 point average roughness in accordance with JIS B-0601. When this card is used as an admission card, the recording area 13 of the frosted card 1 is partially heated to a temperature higher than the temperature for the frosting treatment to defrost the portion and to form a smooth surface image 2′ as shown in Figures 9 and 10. The frosted surface 21 has a strain as mentioned above, and when heated to a temperature higher than the temperature for imparting the strain, the strain will be released, and the heated portion of the frosted surface 21 returns to a smooth surface, whereby the image 2′ of e.g. a letter, a symbol or a design appears due to the difference in the reflectance between the frosted surface and the smooth surface. The heating may be conducted by pressing or approaching a heated stamp to the frosted surface 21. However, it is usually preferred to employ a thermal head which is commonly employed for a thermal printer. Here, the thermal head is a head where fine heating elements are gathered together in the form of a matrix so that only necessary points will be heated by signals from outside. By means of a such a thermal head, an image is formed by gathering a number of dots, whereby the boundary will be distinct, the image will be sharp, and the resolving power will be large. Further, by means of such a thermal head, it is possible to record not only a predetermined image, but also an image of an optional letter or size, as the case requires. Furthermore, recording can be conducted after displaying an image on e.g. a CRT display and confirming it. The size of the fine dots constituting an image may suitably be selected depending upon the size of the image. However, from the viewpoint of the sharpness of letters, the size is preferably within a range of from 35 to 2,304 dots/mm². The recorded image 2′ may include in addition to the indication of entrance, also the location, the day and the time of the entrance. At the exit, the entire surface of the recording area 13 is subjected to frosting treatment to erase the image 2′. This frosting treatment may be the same as the first frosting treatment and conducted at a temperature within a range of from Tg to Tm of the synthetic resin to provide a strain in the synthetic resin. Thus, the card is returned to the condition prior to the formation of the image (Figure 8) and can thereafter be repeatedly used. This erasing of a recorded image can be conducted at a suitable time depending upon the particular purpose of the card. For example, the erasing may be conducted immediately prior to conducting a new recording for the use of the card for the next time. Figure 11 shows an example of the card, in which a metallic specular layer (reflective layer) 5 is provided. The reflective layer 5 may not necessarily be immediately beneath the smooth surface layer 1 and may be provided beneath a base material 3 if the base material 3 is transparent (i.e. smooth surface layer 1/base material 3/reflective layer 5). Further, a magnetic recording layer 4 may be provided at an appropriate position, e.g. inside the card as an inner layer, so long as it does not impair the functions of the reflective layer 5. According to the method of the present invention, the checking or non-checking of the entrance or the exit, or the amount used or the amount remaining of a pre-paid card, can easily be visually confirmed by forming a heat-erasable visible frosted image on the card, whereby an omission of recording due to a trouble of an apparatus, or an error in recording can immediately be detected. Therefore, the method is convenient not only to the administrators, but also to the users of the cards and gives the users a feeling of assuredness. Further, the card can be used repeatedly with the same performance for recording-erasing-rerecording and has high reliability. Now, the present invention will be further described with reference to Examples. However, it should be understood that the present invention is by no means restricted by such specific Examples. EXAMPLE 1 (A) Referring to the card C having the structure shown in Figure 1, a card was prepared by using a black colored polyvinyl chloride resin sheet (thickness: 30 µm, Tg: 70°C, Tm: 202°C) as the smooth surface layer 1 and a polyethyleneterephthalate sheet (thickness: 150 µm) as the base material 3 and applying a white printing 12 on the black sheet except for the recording area 13. (B) Then, frosting treatment was conducted by pressing the recording area 13 by a frosting hot plate under the following conditions: Rz i.e. ten point means roughness of the frosted surface of the hot plate: 15 µm Temperature of the hot plate: 80°C Pressing condition: 20 kg/cm², 0.5 second By the above operation, a frosted surface 21 having a Rz of 8 µm was formed in the recording area 13. (C) Then, an indication of "entrance" was displayed on a CRT display, and it was printed on the recording area by permitting a thermal head printer (120°C) with 24 dots (size of each letter: 5 mm in each side) to run on the recording area, to obtain a clear smooth surface image. (D) Then, the recording area 13 was subjected to frosting treatment under the same condition as in step (B), whereby the image disappeared completely. Further, the treatment of the above steps (C) to (D) was repeated 1,000 times, whereby the same performance was obtained. EXAMPLE 2 A card having the structure shown in Figure 11 was prepared. By using a white polyethyleneterephthalate sheet (thickness: 150 µm) as the base material 3, a magnetic layer 4 was formed on one side and on the other side, a reflective layer 5 (vapor deposited aluminum layer having a thickness of 0.05 µm) and a smooth surface layer 1 (a colorless transparent polyvinyl chloride resin layer having a thickness of 10 µm, Tg: 70°C, Tm: 202°C) were sequentially laminated, and a white printing 12 was applied except for the recording area, to obtain a card. The specular glossiness of the reflective layer 5 was 180%. The recording and erasing were conducted in the following manner. (A) Firstly, a frosting plate having Rz of 15 µm heated to 80°C, was pressed against the recording area under a pressure of 20 kg/cm² for 0.5 second to form a frosted surface having Rz of 8 µm. (B) Then, an indication of "entrance" was printed in the recording area by permitting a thermal head (heated to 120°C) with 24 dots (size of each letter: 5 mm in each side) to run on the recording area, based on the signals for "entrance" preliminarily recorded on the magnetic layer 4. (C) Then, the recording area was subjected to frosting treatment in the same manner as in step (A), whereby the image disappeared. The above cycle of image forming-erasing was repeated 1,000 times, whereby the same performance was obtained. Further, the sharpness of the image on the card was very high as compared with the case where the reflective layer 5 was not provided.

Claims: A method for recording and erasing a visible image on a data carrier card (C) having a recording area with a smooth surface (1) of a synthetic resin having a glass transition temperature and a melting point at a higher temperature, which comprises preliminarily pressing the entire recording area with a frosting surface pressure plate or roll at a temperature within the range from the glass transition temperature to the melting point of the synthetic resin to form a frosted surface (2) having a strain over the entire recording area; for recording, heating a localized part of the surface frosted recording area at a temperature higher than the temperature employed for the frosting surface pressure treatment to form a defrosted image; and, for erasing the image, pressing the entire recording area with a frosting pressure plate or roll having a temperature within the range from the glass transition temperature to the melting point of said synthetic resin to refrost the entire recording area. The method according to Claim 1, wherein a metallic specular i.e. reflective layer is disposed beneath the synthetic resin to enhance the contrast between the defrosted image and the frosted surface. The method according to Claim 2, wherein the metallic specular layer has a 60° specular glossiness of at least 100 % as stipulated by Japanese Industrial Standard JIS Z-8741. The method according to Claim 1, wherein the synthetic resin is polyvinyl chloride. The method according to Claim 1, wherein the synthetic resin is polystyrene.

Inventors: KITAMURA MASAMI MITSUBISHI PLA, KITAMURA, MASAMI MITSUBISHI PLASTICS IND. LTD.
Applicants: MITSUBISHI PLASTICS IND, MITSUBISHI PLASTICS INDUSTRIES LIMITED
Application year: 1989
Main classification: G06K19
IPC codes: B42D15, B44F1