TRANSPARENT RECORDING SHEET AND METHOD FOR PREPARING SUCH SHEETS

Abstract: By having a surface coat formed on a transparent recording sheet, which coat dissolves or swells upon contact with a high-boiling solvent contained in the ink, it is possible to print characters or figures as well on transparent sheets, such as those for an overhead projector, by the means of printing, such as a word processor, which use inks containing high-boiling solvents. In this method of direct recording, the property of characters, figures, or the like to take on a transparent film is the most important factor which governs its commercial feasibility.

Description: BACKGROUND OF THE INVENTION The present invention relates to ink-receptive recording materials which become a basis for the preparation of transparent originals, and especially to sheets which are used in the preparation of transparent originals which, when applied to an overhead projector, enable excellent images to be shown on a screen, and to a method for making such recording materials. Transparent recording sheets are generally prepared by the application, on a transparent film base, of various recording processes, such as handwriting with a pen, reproducing by electronic photography, heat transfer by flashlight (thermographic practice), or printing by a printer (hereinafter referred to as the means of printing). While various recording processes such as described above are adopted, recourse is had, however, to handwriting or to the above mentioned means of printing in order to record characters, figures, or the like directly on transparent base material, generally on transparent film, without having to prepare an original copy or drawing. The fixing ability, as mentioned in the present invention, refers to a combination of the apparent speed of drying of the ink in printing with its ability to fix, i.e. that level of drying at which the ink ceases coming off when rubbed lightly with the finger. Generally, the fixing ability depends for its quality on the multiplying effect of the drying ability of the ink used and the ink-absorbing ability of the recording material surface. The film surface is therefor treated to raise the ink-absorbing ability, for which purpose the surface is, for example, provided with a coat having fine holes. Application of this method, however, involves the problem of causing the film to be less transparent. Apart from this, in the case of handwriting, if recording is done on a transparent film surface with an oil-base felt tip pen containing an ink whose composition includes a low-boiling solvent, then the fixing ability does not involve so much of a problem due to the quick-drying property of the ink itself. The representative forms of printers in the means of printing include the ink jet type or the impact type which latter includes wire dot printers or type printers. In all of them the printing function is greatly affected by the physical properties of inks. Of particular note, inks composed largely of low-boiling solvents cannot be used for ink ribbons of the impact application type because the inks need to be retained in an undried state almost permanently. Therefore, the solvents which are included in the composition of inks used for the means of printing must be high-boiling. Consequently, the inks themselves are extremely poor in drying ability. Generally, whatever the means of printing used, any recording effected on the surface of a conventional transparent film with such inks proves extremely poor in taking capacity and hardly usable for commercial applications. The remarkably increased use of CAD systems, word processors, etc., however, has given rise to strong wishes for transparent recording media by the means of printing and to corresponding requirements for transparent materials capable of recording with these means of printing. SUMMARY OF THE INVENTION The present invention offers transparent recording sheets which, by the means of printing such as word processors, employing inks whose composition includes high-boiling solvents, are capable of printing characters, figures, etc., with a good fixing ability while retaining an excellent transparency. Of excellent performance, in particular, is the color transparent recording sheet multicolor-printed with an ink ribbon whose ink composition includes a colori ng agent; the sheet, for example, becomes a projection original of highly excellent performance when lit with an overhead projector. Firstly, in the present invention, for achievement of the objectives noted above, solvents indicated by HO(C n H₂ n O) m H (m being an integer of 2 to 7, n of 2 or 3) or HO(C₂H₄O) a (C₃H₆O) b H (7 ≧ a + b ≧ 2, a and b being integers ≧ 1) have been selected as high-boiling solvents to be contained in the inks, and surface coats formed on the transparent recording sheets which coats dissolve or swell upon contact with said solvents. This enables printing to be conducted on those transparent sheets which so far have failed to fix the inks of word processors or the same. Secondly, in the present invention, the solubility, in high-boiling solvents, of resins contained in the inks has been made lower than that of resins contained in the surface coats of transparent recording sheets. As long as this relation exists, the object of the present invention can be accomplished without qualifying or limiting the high-boiling-solvent and surface-coat materials as done in the first invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has developed good ink-fixing transparent recording sheets by forming on ink-nonfixing transparent synthetic resin films coats which dissolve or swell by high-boiling solvents included in the ink composition. If coats are provided on transparent base materials of compounds whose composition includes resins dissolving to the ink composition and indicated by the general formulae HO(C n H₂ n O) m H (m being an integer of 2 to 7, n of 2 or 3) or HO(C₂H₄O)₂(C₃H₆O) b H (7 ≧ a + b ≧ 2; a, b, each being integers≧1, then the high-boiling solvents cause said coats to dissolve or swell immediately after printing, resulting in transparent recording sheets of excellent commercial utility which offer an extremely high fixing ability of printed characters, figures, etc. The high-boiling solvents indicated by the general formulas HO(C n H₂ n O) m H or HO(C₂H₄O) a (C₃H₆O) b H (7≧a + b≧2; a, b each being integers≧ 1) are highly excellent solvents to supersede nondrying oils, including mineral oils, oleic acid, etc.; the inks composed by using these solvents claim excellent physical properties as special inks (e.g. inks for ink ribbons) in the means of printing, including the ink jet process or the impact process. The coating materials can be supplemented with suitable additives for imparting adhesion to transparent base material surfaces or lending abrasion resistance, damage resistance, antiskid and antistatic properties, etc., to the surface of coats formed by said compounds, and they also can be made colored compounds by the addition of coloring agents. Furthermore, penetrant surface-active agents can be added in order to make the invention more effective. These additions must, of course, not be permitted to interfere with transparency. Again, the deposition of said compounds on transparent base materials can safely be made in several layers, say two or three. Alternatively, an anchor coat may be provided between the surface coat and transparent base material in order to improve the adherence. As the coating materials in the present invention, it is possible to use natural resins, such as shellac, resins which swell or dissolve in the high-boiling solvents mentioned before, such as cellulose acetate, cellulose nitrate, polyvinyl alcohol, and ployacrylamide, high polymer derivatives denatured through partial introduction of polar radicals, such as -COO⁻NH₄⁺, -COO⁻M⁺, -NH₄·HCl, and -OH, so that they may be caused to swell or d issolve in the high-boiling solvents mentioned before, or copolymer resins whose compositions include at least the monomers which constitute resins swelling or dissolving in the above-mentioned high-boiling solvents, and derivatives of such resins. The resins noted here do not limit the present invention; any resins which swell or dissolve in the high-boiling solvents given by the structural formulae HO(C n H₂ n O) m H or HO(C₂H₄O) a (C₃H₆O) b H and which have good transparency can be used for the coats in the present invention. Apart from the foregoing descriptions of transparent recording sheets obtained through the treatment of transparent base material surfaces by said resin-base compounds, the object of the present invention which is to obtain transparent recording sheets can be achieved also by converting these resin-base compounds into a film form. It does not particularly matter how to deposit the compounds on transparent base material surfaces, yet in this case the coats preferably should have a thickness of 1 µm to 20 µm in order to exhibit an excellent transparency and an excellent fixing ability for characters, figures, etc., by the means of printing. Among the transparent base materials used in the present invention, mention may be made of transparent synthetic resin film, transparent paper, etc.; the higher their transparency, the better, and they should preferably have a total luminous transmittance of over 90%. To be concrete, suitable materials belonging to the structural formula HO(C n H₂ n O) m H include polyester film, polypropylene film, polyvinyl chloride film, and acetate film, while those of the structural formula HO(C₂H₄O) a (C₃H₆O) b H include polypropylene glycol polyethylene glycol ether and diethylene glycol propylene glycol ether. Again, these transparent base materials have a thickness selected according to their intended uses; as a rule they preferably should be 25 µm to 180µm thick for recording characters or figures by the means of printing. Next, a second embodiment of the invention is explained. While the fixing ability of an ink on recording sheets in printing depends on the apparent ink drying speed of printed areas provided on the recording sheet surface, multiplied by the sticking property (adhesion to the recording sheet surface) of the ink, the second embodiment represents an improvement on the fixing ability of inks as well as an increased ink drying speed on printed areas. The transparent recording sheets of the second embodiment, intended for printing with inks composed of high-boiling solvents, resin ingredients, coloring agents, and if necessary, other additives, are coated at least on one side with a composition led by a resin ingredient (hereinafter referred to as resin ingredient B) of higher solubility in high-boiling solvents contained in the composition of an ink used in printing than a resin ingredient (hereinafter referred to as resin ingredient A) contained in the same ink. If the transparent recording sheets of the second embodiment are printed with an ink composed of high-boiling solvent, resin ingredient A, colorant, and other additives, the high-boiling solvent in the ink of the printed area will penetrate into the coat of the transparent recording sheet, leading to a change in the balance between the solvent and resin ingredients in the ink composition of the printed area, so that the apparent drying speed of printing is increased substantially. This is explained by the difference (A < B) in solubility in the high-boiling solvent in the ink composition between the resin ingredient A of the ink and the resin ingredient B of the coat, that is, the fact that the resin ingredient B in the coat of the transparent recording sheet is more soluble tha he resin ingredient A. Particularly those high-boiling solvents in the ink composition whose vapor pressure at 20°C is below 1 mmHg proved capable of affording favorable physical ink properties. Concretely, mention may be made of aromatic hydrocarbons, including triethyl benzene, ditepene, and aromatic petroleum naphtha, low-molecular-weight polyethylene glycols, including n-octyl alcohol, n-decyl alcohol, and diethylene glycols, polypropylene glycols, including dipropylene glycol, and ester-base solvents, including ethylene glycol monophenyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, ethylene glycol monohexyl ethers, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether acetate. In the preparation of a composition to form a coat at least on one side of the transparent recording sheets in the second embodiment the resin ingredient B is selected as the composition's principal component such that its solubility in high-boiling solvents such as mentioned above, used in the composition of an ink, is greater than that of the resin ingredient A, also a component of the same ink. It may be selected from dissimilar resins which are different in said solubility, or advantage may be taken of the fact that said solubility varies according to different molecular weights in the same resin. Another alternative is to replace the resin ingredient B with a resin of the same system which has been transformed through the copolymerization of other monomers or through the introduction of substituents or the like. Not both of the resign ingredients A and B, of course, need to be a simplex component; they may be a mixture of two or more resin ingredients, or other surface-active agents, such as penetrants, or plasticizers, may be added. To be more concrete about the selection of the resin ingredients A and B, when, for example, aromatic hydrocarbons, including triethyl benzene and aromatic naphtha, are used for high-boiling solvents, styrene resins and chlorinated paraffins are desirable choices since they are highly soluble. On the other hand, in the case of so-called cellosolve solvents, such as ethylene glycol monoethyl ethers, or their ester acetate base solvents, cellulose base resins, including cellulose acetate, cellulose butyrate, cellulose acetate butyrate, and nitrocellulose are desirable for the resin ingredient B. In particular, the resin ingredients A and B can be selected by taking separate advantage of the fact that the solubility of these cellulose-base resins in cellosolve-base or ester-acetate-base solvents varies with differences in molecular weight or in the degree of esterification. When nitrocellulose resins are to be used, for example, their difference in solubility due to molecular weight is utilized to select nitrocellulose resins of 1/2- to 1/4-second viscosity for the resin ingredient A and those of 1/8- to 1/64-second viscosity for the resin ingredient B. Also, when polyethylene glycol base high-boiling solvents are to be used, then poly vinyl alcohol, polyacrylamide, and other comparable resins, or acrylic resins, can be used for the resin ingredient B by transforming them into more soluble resins with the introduction of polar radicals, such as -COO⁻NH₄⁺, -COO⁻M⁺, -NH₄·HC1, and -OH. Examples of the invention are given below. Example 1. As an ink composition I-1 for ink ribbons, the following substances were mixed, and using a red ink dispersed with a 3-roll mill, an ink ribbon with a controlled ink deposition rate of 15 g/m² was prepared: On the other hand, an organic-solvent-base paint composed of the following was prepared as a surface coating composition S-1 for a biaxially-extended polyester film of 100µm thickness, applied to one side of the film, and dried, thereby producing a transparent recording sheet with a coating thickness of 3µm and a total lumin ous transmittance of 93%: This recording sheet was printed with a wire dot printer, using the ink ribbon prepared before; the ink completely took in about 5 seconds after printing, and prints were obtained which gave no ink erasure even when rubbed with the finger or something. The printed sheet was lit with an overhead projector, and a distinct red image projection obtained. For the purpose of comparison, sheets of untreated 100 µm biaxially-extended polyester film were equally printed with the ink ribbon used in the invention and conventional ink ribbon; the sheets proved quite unserviceable as the ink readily came off the printed surface when rubbed with the finger or something, at the end of 5 minutes when the former ribbon was used and even at the end of a week when the latter ribbon was used. Example 2. The following ink composition I-2 was used to prepare an ink ribbon corresponding to Example 1: Next, an organic solvent base paint of the following surface coating composition S-2 was applied with a wire bar to one side of a 100 µm biaxially-extended polyester resin film preprimed for increased adherence, and dried, thus preparing a transparent recording sheet with a coating thickness of 4 µm and a total luminous transmittance of 92%: This recording sheet was printed with a wire dot printer, using said ink ribbon; the ink completely took in about 10 seconds after printing, and prints were obtained which gave no ink erasure even when rubbed with the finger or something. The printed sheet was lit with an overhead projector, and a distinct blue image projection obtained. For the purpose of comparison, sheets of untreated 100 µm biaxially-extended polyester film were equally printed with the ink ribbon used in the invention and a conventional ink ribbon; the sheets proved quite unserviceable as the ink readily came off the printed surface in both cases when rubbed with the finger or something,even at the end of an hour. Example 3. One side of a 100 µm thick biaxially-extended polyester film preprimed for proper adherence was coated by a wire bar process with the following composition S-3 and dried to obtain a transparent recording sheet with a controlled coating thickness of 6 µm: Example 4. One side of a 100 µm thick triacetate film was coated with the following composition S-4 corresponding to Example 3 so as to provide a coating thickness of 8 µm: The transparent recording sheets obtained in the above Examples 3 and 4 were printed with a wire dot printer, using an ink ribbon charged with an ink of the following composition I-3 so as to provide a deposition rate of 15 g/m²; both sheets showed a highly excellent fixing ability of characters or figures, and when lit with an overhead projector, gave distinct blue images: Comparison Example 1: The untreated 100 µm thick biaxially-extended polyester film, used in Example 3, was printed with a wire dot printer, using the same ink ribbon that was used in Examples 3 and 4; the printed ink was found to be taken in poorly,coming off readily when rubbed lightly with the finger at the end of an hour after printing. As the physical properties found in the above examples are summarily compared in the following table, the transparent recording sheets of the invention have proved to offer an unimpaired transparency and also an excellent fixing ability of printed ink. Example 5. A transparent recording sheet was obtained by depositing a coat (formed by a wire bar process so as to be 7 µm thick) of the following composition S-5 on a preprimed side of a 100 µm thick biaxially-extended polyester film. The coat of the transparent recording sheet thus obtained was printed with a wire dot printer, using an ink ribbon whose foundation cloth was charged with an ink of the following composition I-4; the apparent drying time of the printed area proved extremely short, 5 seconds, while the taking power of printing and the obtained transparency of the recording sheet were both found excellent. Comparison Example 2: A transparent recording sheet was obtained by depositing a coat of the following composition S-6 on the same polyester film and in the same manner as used in Example 5: The coat of the transparent recording sheet obtained was printed with the ink ribbon used in Example 5; the apparent drying time of the printed area was found to be 60 seconds. The above Example 5 and Example 2 may be compared in terms of apparent drying time as shown in the table below, which tells how quick is the drying speed of printing on the transparent recording sheets specified in the invention.

Claims: 1. A transparent recording sheet possessing at least on one side a surface coat which dissolves or swells with a high-boiling solvent contained in ink. 2. The recording sheet in accordance with claim 1,characterized in thatthe high-boiling solvent is a solvent indicated by the formula HO(C nH₂ nO) mH, wherein m is an integer of 2 to 7 and n an integer of 2 or 3. 3. The recording sheet in accordance with claim 1 or 2characterized in thatthe high-boiling solvent is polyethylene glycol or polypropylene glycol. 4. The recording sheet in accordance with any of claims 1 to 3,characterized in thatthe resin ingredient of surface coat is more soluble in high-boiling solvent than the resin ingredient of ink. 5. The recording sheet in accordance with claim 1,characterized in thatthe high-boiling solvent is a solvent indicated by HO(C₂H₄O) a(C₃H₆O) bHwherein 7 ≧ a + b ≧ 2; and a and b each being integers ≧ 1. 6. The recording sheet in accordance with claim 5,characterized in thatthe high-boiling solvent is polypropylene glycol polyethylene glycol ether or diethylene glycol propylene glycol ether. 7. The recording sheet in accordance with any of claims 1 to 6, characterized in thatthe total luminous transmittance is over 80 %. 8. The recording sheet in accordance with any of claims 1 to 7, characterized in thatthe surface coat additionally contains a coloring agent. 9. The recording sheet in accordance with any of claims 1 to 8, characterized in thatthe surface coat additionally contains a surface-active agent. 10. The recording sheet in accordance with any of claims 1 to 9, characterized in thatthe surface coat consists of multiple layers. 11. The recording sheet in accordance with any of claims 1 to 10, characterized in thatan anchor layer is provided between transparent recording sheet proper and surface coat. 12. The recording sheet in accordance with any of claims 1 to 11, characterized in thatthe surface coat consists of natural resin derivatives, high polymer derivatives or copolymer resins. 13. The recording sheet in accordance with any of claims 1 to 12, characterized in thatthe surface coat has a thickness of 1 to 20 µm. 14. The recording sheet i n accordance with any of claims 1 to 13, characterized in thatthe own thickness is 20 to 180 µm. 15. The recording sheet in accordance with any of claims 1 to 14, characterized in thatthe own material is the same as that of its surface coat. 16. The recording sheet in accordance with any of claims 1 to 15, characterized in thatthe own material is specified to be either polyester film, polypropylene film, polyvinyl chloride film, or acetate film. 17. Method for preparing an ink receptive transparent recording sheet to be used as printing films, overhead films and the like, characterized by providing at least one side of a transparent base sheet material with a transparent surface coat which consists of natural resin derivatives, high polymer derivatives or copolymer resins, and which dissolves or swells with a high-boiling solvent contained in an ink when applied to the recording sheet.

Inventors: HANEDA, AKIRA DYNIC CORPORATION TOKYO PLANT, YOKOZAWA, SHIGERU DYNIC CORPORATION TOKYO PLANT
Applicants: DYNIC CORPORATION
Application year: 1986
Main classification: B41M1
IPC codes: B41M5