GB2329870A

GB2329870A - Thermal transfer printer having an ink carrier elastic film with pore(s) expandable on heating

Info

Publication number: GB2329870A
Application number: GB9821194A
Authority: GB
Inventors: Minoru Suzuki
Original assignee: Asahi Kogaku Kogyo Co Ltd
Current assignee: Pentax Corp
Priority date: 1997-09-30
Filing date: 1998-09-30
Publication date: 1999-04-07
Anticipated expiration: 2018-09-30
Also published as: CA2248434A1; FR2768963B1; FR2768963A1; DE19844973B4; GB2329870B; GB9821194D0; DE19844973A1

Abstract

The printer comprises an elastic film 602 adhered to a thermal line head 603 (Fig.1) via a spacer 608 which together define a space 601 containing ink supplied from a reservoir 606 (Fig.1). The film has pore(s) 25 (Fig.4A), which under usual temperature and pressure conditions do not allow the passage of ink therethrough, but widen when the film is heated. The thermal head has heating elements 635 in spaced relation from the film to face one or more of the pore(s). When a heating element is heated according to print data, the ink thereat is heated and expanded to produce a local pressure enabling the ink to pass through the widened pore(s) to print onto a recording sheet P. Additional, the reservoir may be supplied with a one-way resilient valve (210,Fig.9) and a chamber portion (200,Fig.9) which collects air in the reservoir. A partition (210,Fig.16) may also be provided in the reservoir to define the air chamber. A conductive support plate (28,Fig.17), placed over a heating element (35,Fig.17), may be used instead of the spacer 608.

Description

2329870 1 INK TRANSFER TYPE PRINTER The present invention relates to an

ink transfer type printer which transfers ink to a recording sheet (such as plain paper) to form an image thereon.

Among printers which transfer ink onto a recording sheet such as plain paper, the following printers are known: an ink jet printer that jets ink onto a recording sheet as liquid droplets from nozzles; a thermal transfer printer that heats an ink ribbon (which can be melted by heat) using a thermal head thereby to transfer the ink onto a recording sheet; and a wire impact dot matrix printer that uses a steel wire for striking ink ribbons against a recording sheet. However, these known printers have the following problems: the ink jet printer may encounter clogging of ink in the nozzle; the thermal transfer printer may increase running costs due to the consumption of ink ribbons; and the wire dot printer is inferior in processing speed. Thus, a printer in which ink clogging is prevented, which has a low running cost and a high processing speed has been desired.

It is therefoy an object of the present invention to provide an improved printer wherein ink clogging is prevented, the running cost is small and the processing speed is fast.

According to one aspect of the present invention there is provided an ink transfer printer comprising a thermal line head comprising a plurality of heating elements disposed in a predetermined direction, a film with predetermined through-holes which is faced to the thermal line head, an urging means for adhering recording sheet to the surface of the film which is faced to the thermal line head, a space formed between the thermal line head and the film to hold the ink therein; and a feeding means for sequentially feeding recording sheet, wherein the heating elements on the thermal line head selectively heat the ink in the space and the film so that the ink can permeate through the through-holes in the film and transferred to the recording sheet.

With this arrangement, since the film contacts with the - 11 i- 3 recording sheet, the reduction of the resolution caused by the splashing of the ink (as in an ink jet printer that require a gap between the nozzles and the recording sheet) is prevented. Thus, a higher resolution can be obtained. in addition, since the through-holes of the film are used instead of nozzles as in the ink jet printer, the structure becomes simple, which significantly reduces manufacturing costs. In addition, the use of the through-holes in the film enables the use of the line head in a simple manner, which increases the printing speed.

The printer may be so constituted that a pressure generated in the ink during heating forces the ink to permeate through the through-holes. With this, the ink does not enter the through-holes when not required, thereby preventing the clogging of the ink. Furthermore, it is possible to use a film with an elastic modulus decreasing when heated. With this, the synergistic effect of the pressure in the ink and the decrease in the elastic modulus of the film allows the ink to permeate through the through- holes. with this arrangement, it is possible to set the pressure relatively small.

Alternatively, if the film includes a material that reversibly converts its polarity between hydrophilicity and hydrophobicity according to the temperature, it is possible that the change in the polarity of the film caused by heating allows the ink to permeate through the throughholes. Furthermore, the printer may be configured so that the decrease in surface tension (that is the effect of the change between hydrophilicity and hydrophobicity and the decrease in the viscosity of the ink caused by heating) allows the ink to permeate through the through-holes.

The film is adhered to the thermal line head via a spacer comprising a material that does not normally transfer the ink. The space is a region surrounded by the film, the thermal line head and the spacer (the spacer may be an adhesive). With this arrangement, the structure for holding the ink becomes simple. An ink reservoir may be provided for refilling the ink in the space. The ink reservoir may be long in the direction in which the heating elements are arranged. This arrangement can reduce the size of the ink reservoir as seen in side view. In addition, by disposing the heating elements in the space, the heat from the heating elements can be more effectively transmitted to the ink.

If a plurality of through holes in the film correspond to a single heating element, it is not necessary to precisely align the through-holes in the film with respect to the heating elements. Alternatively, if a plurality of heating elements correspond to a single through-hole in the direction in-which the elements are - 5 arranged, it is possible to perform tone control by changing the number of heating elements to be heated.

The through-holes can be punched through the film using a needle. Since the punching of the film is much easier than the processing of nozzles as in an ink jet printer, manufacturing costs can be significantly reduced. In addition, if the through-holes are inclined at a predetermined angle from the direction of the thickness of the film so that the film is constantly pressurized between the thermal head and for example, the platen rollerto squeeze the through- holes, the ink does not leak from the through-holes even if the printer suffers unintended vibration while the printer is not used. In addition, by forming the film from a porous material, the through holes need not be punched, thereby further reducing manufacturing costs.

The film may include a shape memory resin, that is, a material that reversibly changes between the glassy state and the rubber state according to the temperature. In this case, if the through holes are punched through the film while the film is in the rubber state (above the glass transition temperature and below the shape fixing temperature) so that at the room temperature, the film can change to the glassy state with the through holes closed.

Thus, the ink does not leak from the through holes even if I- 6 the printer suffers unintended vibration while the printer is not used, because the through holes are closed.

According to yet other aspect of the present invention there is provided an ink transfer attachment used to dispose a supporting plate and a film with predetermined through holes in such a manner that they face each other and to hold ink in a space between the supporting pl ate and the film. By installing the attachment in a thermal line printer in such a manner that the supporting- plate faces the thermal line head and that the film faces a recording sheet feeding path, the ink in the attachment heated by the thermal line head is transm-itted through the film and transferred to the recording sheet. In addition, when the attachment is removed from the printer, the printer can be used as a thermal line printer.

with this arrangement, a conventional thermal line printer can be used as an ink transfer printer simply by installing the attachment in the printer. By allowing the attachment to be inserted from an inlet opening of the thermal line printer, not only the installation of the attachment but also maintenance operations can be performed easily.

According to another aspect of the invention an inktransfertype printer comprises a film member which allows the permeation of ink when the film is heated to a - 7 predetermined temperature or higher while normally preventing the permeation of ink.a heating member that partially heats the film member based on printing information, one surface of the film member being arranged to contact a recording sheet while the other surface faces the heating member 2 an ink-space formed between the film member and the heating member to hold ink therein an ink reservoir connected to the inkspace; and an air chamber portion formed on the top part of the ink reservoir for collecting air in the ink.

optionally, a partition member is provided on the top part of the ink reservoir to define the air chamber portion, the partition member comprising a pair of opposing wings, between which a top slit being formed, both of the wings being upwardly inclined toward said top slit.

Preferably, the roof surface of the ink reservoir is formed to become higher as it is more away from the ink space to lead bubbles in the ink toward the air chamber portion.

The air chamber portion is preferable to be provided with a top opening for connecting the interior of the ink reservoir with the exterior, the top opening being covered by a one-way valve member which uncovers the opening when the atmospheric pressure in the air chamber becomes less than a predetermined one to allow the external air to be introduced into the air chamber portion.

The valve member may be adhered to the inner peripheral portion of the top opening of the ink reservoir with leaving a section unadhered, the unadhered section of the valve member being deformable to be away from the inner peripheral portion of the opening of the ink reservoir.

The top opening and the valve member may be both roundshaped, the diameter of the valve member being larger than that of the opening.

It is desirable that the valve member is made of such a resilient material as to be deformed to increase the volume of the air chamber portion so as to absorb the pressure increase in the air chamber portion when the atmospheric pressure in the air chamber portion becomes higher than a predetermined one.

Examples of the present invention will now be described with reference to the accompanying drawings, in which:

2 Fig. 1 is a side sectional view showing a basic 0 arrangement of an ink transfer printer embodying the invention; Fig. 2 is an exploded perspective view showing the ink transfer printer of Fig. 1 without a platen roller; Fig. 3 shows heating elements in a thermal line head and pores in a film for the printer of Fig. 1; Figs. 4A and 4B are schematic views showing the principle of the permeation of ink through a film with the printer of Fig. 1; Fig. 5 shows heating elements in a thermal line head and pores in a film for an alternative ink transfer printer embodying the invention; Fig. 6 shows a thermal line head and an ink space for another alternative ink transfer printer embodying the invention; Fig. 7 is a sectional view showing pores in a film for another ink transfer printer embodying the invention; Fig. 8 is a side sectional view showing an ink transfer printer embodying the invention in which a porous body is provided in the ink space; Fig. 9 is a sectional view showing a principal construction of another ink transfer type printer embodying the invention; Fig. 10 is a perspective view showing major parts of the printer of Fig. 9; Figs. 11A and 11B are schematic views showing the principle of image formation with the ink transfer type printer of Fig. 9; Fig. 12 is a perspective view showing how to attach a valve member to a top opening of an ink reservoir; Figs. 13A and 13B are schematic views for explaining actuation of the valve member of Fig. 12; Fig. 14 is a sectional view illustrating the case that bubbles enter into an ink space; Fig. 15 is a schematic sectional view illustrating 2 - 10 actuation of the valve member of Fig. 12 when the pressure in an ink reservoir increases; Fig. 16 is a sectional view showing a modification of the ink transfer type printer shown in Fig. 9; Fig. 17 is a sectional view showing a principal construction of another embodiment of an ink transfer type printer; Fig. 18 is a perspective view showing major parts of the printer of Fig. 17; Figs. 19A and 19B are sectional views showing the principle of image formation with the ink transfer type printer of Fig. 17; and Fig. 20 is a graph showing the relationship between the temperature and Young's modulus of a shape memory resin.

Common components in the drawings bear common numbers.

reference An ink transfer type printer embodying the invention will be described hereafter by referring to the accompanying drawings.

Fig. 1 is a side sectional view showing a basic arrangement of an ink transfer printer embodying the invention. The ink transfer printer includes a thermal line head 603 with a plurality of heating elements 635 arranged in the direction perpendicular to the sheet of the drawing; and a film 602 adhered to the thermal line head 11 603 via a spacer 608. There is a gap of about 0.1 mm between the thermal line head 603 and the film 602.

A case 603a of the thermal line head 603 and the spacer 608 are formed of a material that prevents the permeation of the ink. The space defined by the spacer 608, the case 603a of the thermal line head 603 and the film 602.forms an ink space 601 in which ink is held. The film 602 is located at a small distance from the heating elements 635 on the thermal line head 603 or is in contact with the thermal line head 603.

A platen roller 604 is provided above the film 602 to push a recording sheet P onto the top surface of the film 602. The platen roller 604 is a rubber roller and is disposed in such a manner that its axial direction is aligned with the direction in which the heating elements 635 of the thermal head 603 are arranged. The rotation of the platen roller 604 produces traction between the platen roller and the recording sheet P, which feeds the paper P in the direction shown by the arrow in the figure.

Fig. 2 is an exploded perspective view showing the ink transfer printer without the platen roller 604. The spacer 608 is a thin plate that surrounds the heating elements 635 arranged in a line so that all the heating elements 635 are housed in the ink space 601. An ink 25reservoir 606 for supplying the ink in the ink space 601 is provided behind the spacer 608 (shown in the left of the figure) and the ink in the ink reservoir 606 is drawn to the ink space 601 through a supply hole 685 in the spacer 608 due to capillary action. The spacer 608 may be an 5 adhesive.

A number of pores or through holes 625 are formed in a part of the film 602 so that the pores 625 are positioned above the heating elements 635. Under usual temperature and Dressure conditions, the size of the pore is such that the pore does not allow the permeation of ink (liquid) and solvent vapor therethrough. Fig. 3 shows the spatial relationship between the pores 625 and the heating elements 635. In the direction in which the heating elements 635 are disposed (the main scanning direction: direction X), a plurality of pores 625 are located to correspond to a single heating element 635. In addition, the pores 625. are staggered in the direction perpendicular to the above main scanning direction (i.e. in the subscanning direction:

direction Y).

It is preferable that the material of the film 602 has a certain elasticity, high abrasion and heat resistance, and transferability. In this embodiment, polytetrafluoroethylene (Teflon trademark)) is used. The film 602 preferably has a thickness of 0.03 to 0.08 mm.

Figs. 4A and 4B show the principle of printing by the ink transfer printer of Fig. 1. In Fig.

4A, when the heating element 635 is heated, the ink near the heating element 635 and also the film 602 generally in contact with the heating element 635 are heated. AS shown in Fig. 4B, the heated ink is vaporized and expands.

This vapor pressure causes a local pressure on the ink whilst at the same time. the elasticity of the heated part ofthe film 602 is decreased. Thus, this pressure pushes the ink into the pores 625 of the film 602 as the pores 625 in the film 602 are widened. Therefore, the ink permeates through the pore 625 of the film 602 and is transferred onto the recording sheet P (omitted in Figs. 4A and 4B) at the top surface of the film 602. After the ink is transferred onto the paper P, the ink and the heated part of the film 602 are cooled by the surrounding ink so that the pore 625 in the film 602 returns to its original size and prevents the permeation of the ink.

Thus, as shown in Fig. 1, a two-dimensional ink image can be formed on the recording sheet P by controlling the heating of the thermal line head 603 according to desired print information and also by controlling the rotation of the platen roller 604 so as to feed the recording sheet P by 20 one line.

In this manner, since the ink transfer printer is arranged to transfer the ink with the film 602 and the recording sheet P in contact with each other, splashing of the ink (as in an ink jet printer with gaps between the nozzles and the recording sheet) is prevented. This 14 - prevents a decrease in the resolution associated with splashing of the ink thereby improving the resolution accordingly. In addition, it is easier to form pores 625 in the film 602 than to manufacture a nozzle of an ink jet 5 printer. Thus, manufacturing costs can be reduced.

In addition, as shown in Fig. 5, a plurality of heating elements 635 correspond to a single pore 625 in the main scanning direction (direction X) and the pores 625 are staggered in the sub-scanning direction (direction Y).

Thus, each heating element 635 can correspond to any of the pores 625 even if the film 602 is not accurately aligned with the thermal line head 603. Thus, the film 602 can be relatively roughly aligned with the thermal line head 603. Furthermore, as the recording sheet P is fed, the shape of the pore 625 is deformed in such a manner that it becomes longer in the direction in which the recording sheet P is fed (the sub-scanning direction: direction Y) and the ink transferred from the film 602 to the recording sheet P trails in direction Y. As a result, the shape of ink dots on the recording sheet P tends to be longer in the direction Y. Thus, by forming the pores in the film 602 in such a manner that the pores are longer in the main scanning direction (direction X) as shown in Fig. 3, the deformation of ink dots caused by the deformation of the pores 625 and the trailing of the ink can be compensated.

As shown in Fig. 5, a plurality of heating elements 636 may also correspond to a single pore 625 in the main scanning direction (direction X). With this arrangement, the size of dots transferred to the recording sheet P can be varied. That is, it is possible to perform tone control by changing the number of heating elements 636 (corresponding to a single pore 625)which are to be heated. If the heating elements 635 in Fig. 3 are used, it is possible to perform tone control (energy tone control) by varying the heating energy (voltage or application time) to be applied to the individual heating elements 635.

In addition, although in Fig. 2 all the heating elements 635 are disposed in a single ink space 601, the heating elements 635 may be accommodated in separate ink spaces 611 as shown in Fig. 6. With this arrangement, the heat of the heating elements 635 or the pressure associated therewith can be efficiently converted to the pressure facilitating the permeation of the ink. Further, the pore 625 in the film 602 can be formed in such a manner that the pores 25 are inclined at a predetermined angle with respect to the direction of the thickness (t) of the film 602 as shown in Fig. 7. Thus, under the usual condition, the film 602 closely contacts the platen roller 604 and the thermal head 603 so that the inclined pores 625 of the film 602 are contracted and the ink does not 16 permeate through the pore 625. When the film 602 is heated, the film 602 becomes more resilient or elastic so that a gap in the pores can be created between the roller 604 and the head 635, through which ink is transferred to the recording sheet P.

The film 602 may be formed of a material such as the shape memory resin which polarity (hydrophilicity /hydrophobicity) changes according to the temperature.

For example, the film 602 can be made of a resin consisting of polynorbornene, trans-1,4-polyisoprene, polyurethane or the like. In this embodiment, a polyurethane resin (which is low cost and has excellent moldability) is used.

Fig. 20 shows the relationship between temperature and Young's modulus of the shape memory resin. The shape memory resin exhibits rubber elasticity above the glass transition temperature Tg due to the active micro-Brownian motion of molecular chains (region (b)), whereas it exhibits the glassy state below the glass transition temperature Tg due to the freezing of micro-Brownian motion (region (a)). That is, the shape memory resin can be arbitrarily deformed by heating it above the glass transition temperature Tg and its shape can be fixed by cooling it below Tg. The shape memory resin can then recover its original shape by again heating it to higher than Tg, k - 17 In this embodiment, the range of the glass transition temperature Tg is between 600C and 800C.

According to the.change between the rubber state and the glassy state, the polarity (hydrophilicity /hydrophobicity) of the shape memory resin also changes. That is, the shape memory resin is hydrophilic in the rubber state (region (b)), whereas it is hydrophobic in the glassy state (region (a)). In addition, the film is reversibly converted between hydrophilicity and hydrophobicity.

The surface tension of the ink with respect to the film 602 decreases as the temperature increases, due to the effect of the change in viscosity of the ink and in the polarity of the film. It is possible to utilize such a decrease in surface tension to allow the permeation of the ink through the film.

In order to smoothly supply the ink from the ink reservoir 606 to the ink space 601, a porous body 661 may be disposed between the heating elements 635 on the thermal head 603 and the film 602, as shown in Fig. 8. This arrangement allows the ink contained in the porous body 661 to be supplied to each pore 625 in the film 602. Thus, the entry of the ink into the pore 625 is not prevented by bubbles remaining in the ink. In addition, instead of forming the pores 625 in the film 602 using a needle, the 1 18 film 602 may include a porous body. Thus, the pores of the porous body can be used as the pores 625.

Fig. 9 is a side sectional view showing a principal constitution of another ink transfer type printer embodying the invention. The printer comprises a thermal line head 3 having a plurality of heating members 35 arranged in the direction perpendicular to the sheet of the drawing, and a film member 2 secured to the thermal line head 3 via a spacer 8 to leave a clearance of 0.1 mm therebetween. The film member 2 is arranged to be slightly spaced from or in contact with the heating members 35 of the thermal line head 3.

The spacer 8 and a casing 3a of the thermal line head 3 are made of materials which do not allow ink to pass therethrough. The'space defined by the film member 2, the spacer 8 and the casing 3a of the thermal line head 3 constitutes an ink-space 1 for holding ink therein.

Above the film member 2, a platen roller 4 is disposed to press a recording sheet P against the upper surface of the film member 2. The platen roller 4 is a so-called rubber roller, and is disposed such that the axis of the roller 4 is coincident with the direction of arrangement of the heating members 35 of the thermal line head 3. When the platen roller 4 is rotated, traction force is applied to the recording sheet P which is fed in the direction of 18 the arrow in Fig. 9.

Fig. 10 is an exploded perspective view of the printer of Fig. 9 excluding the platen roller 4 with the spacer partially cut away. The spacer 8 comprises a thin frame plate having a square opening for receiving a plurality of heating members 35 which are arranged to form a line. Adjacent the ink space 1, an ink reservoir 100 is provided. Ink in the ink reservoir 100 is led into the ink space 1, through a connecting slit 85 formed in the spacer 8, due to capillary action.

The film member 2 is provided with a plurality of pores 25 arranged to form two parallel lines in the direction corresponding to that of the arrangement of the heating members 35 of the thermal line head 3, and the film member 2 is placed above the heating members 35 when it is adhered onto the spacer 8.

Figs. 11A and 11B are schematic views for explaining the principles to form an image with the ink transfer type printer of Fig. 9. In these figures, the ink reservoir 100 and the platen roller 4 are omitted.

As illustrated in Fig. 11A, the pores 25 of the film member 2 are formed to have inner diameters such as not to allow ink to pass therethrough under normal conditions. When the heating members 35 generate heat, the ink around the heating members 35, as well as the portions of the film member 2 near the heating members 35, - are heated. The ink heated by the heating members 35 is evaporated and/or expanded to increase the pressure locally, and the heated portions of the film member 2 become easy to be deformed as the elastic modulus 5 decreases.

Thus, as illustrated in Fig. 11B, the ink is pressed against the pores 25 of the film member 2 due to the above pressure increase, and the pores 25 are deformed to increase the size of the openings to allow the ink to pass therethrough. Thereby, the ink is transferred onto the recording sheet P (see Fig. 1) which is contacted with the other side of the film member 2.

Thereafter, upon ceasing of heat generation by the selected heating members 35, the heated ink and the heated portions of the film member 2 are cooled down by the surrounding ink, and the opening size of the deformed pores 25 are restored to normal i.e., sizes which do not allow ink to pass therethrough.

As above, by controlling the heat generation of the heating members 35 of the thermal line head 3 in accordance with printing data while transferring the recording If sheet P by rotating the platen roller 4, an ink image is formed on the recording sheet P.

more particularly, in accordance with the printing data, the heating members 35 to be heated are selected, - 21 whereby the pares 25 corresponding to the selected heating members 35 are deformed to allow the ink to pass therethrough so that the ink is transferred onto the portions on the recording sheet P contacting the deformed pores 25 of the film member 2. Thus, the ink image corresponding to the printing data is formed on the recording sheet P.

Next, the ink reservoir 100 will be described in detail.

As shown in Fig. 9, the bottom surface 101 of the ink reservoir 100 extends along the upper surface of the thermal line head casing 3a, while an upper surface 102 of the ink reservoir 100 is formed to incline so as to increase in height the further away it is from the ink-space 1. Thus, any bubbles generated in the ink space 1 are led away and move along the roof surface 102 of the ink reservoir 102 in the direction away from the ink space 1.

Further, the upper most part of the ink reservoir 100 is formed as an air chamber portion 200 for collecting air contained in the ink reservoir 100. At the top of the air chamber portion 200 of the ink reservoir 100, an opening is formed, and a one-way valve member 210 made of a resilient materialis provided to cover the opening 105 therewith.

As illustrated in Fig. 12 in detail, both the opening - 22 and the valve member 210 are circular, and the outer diameter of the valve member 210 is' set"to be larger than that of the opening 105. The valve member 210 is adhered to the inner top surface of the ink reservoir 100 at its peripheral portion leaving a section 212a unadhered.

The valve member 210 is provided for preventing air entering into the ink-space 1 through the pores 25 of the film member 2, as well as for preventing an increase of - the inner atmospheric pressure of the ink reservoir 100.

That is, in the case that the ink transfer type printer is located in a relatively low temperature, or in th e case that the remaining amount of the ink in the ink reservoir 100 becomes low due to consumption of ink, then the atmo3pheric pressure in the air chamber portion 200 will decrease, which may cause a corresponding reduction of the liquid pressure of the ink in the ink reservoir 100. If the liquid pressure of the inkreduces, as illustrated in Fig. 14, external air may be introduced into the ink space 1 through the pores 25 of the film member 2.

On the other hand, in the case that the printer is located in a relatively high temperature, the internal atmospheric pressure of the ink reservoir 100 will increase due to evaporation of ink and so on, which may cause a corresponding increase of the liquid pressure of the ink in the ink reservoir 100.

- 23 If the liquid pressure of the ink increases, ink may unintentionally permeate the pores 25 of the film member 2. In the case that the inner atmospheric pressure of the ink reservoir 100 is reduced, as illustrated in Fig. 13A, the unadhered peripheral section 212a is inwardly (downwardly in figure) deformed due to the external atmospheric pressure, and a gap is formed between the inner top surface of the ink reservoir 100 and the unadhered peripheral section 212a to allow the external air to enter into the ink reservoir 100. Thereby, the atmospheric pressure in the ink reservoir 100 becomes equal to the external atmospheric pressure.

As the liquid pressure of the ink and the inner atmospheric pressure of the ink reservoir 100 are associated with each other, the former is also returned to its normal pressure.

Thus, even if the atmospheric pressure in the air chamber portion 200 decreases, it is immediately restored to the external atmospheric pressure level. This prevents bubbles being. introduced into the ink- space 1 through the pores 25 of the film member 2.

Further, as the opening 105 is normally closed by the valve member 210, it is possible to prevent the ink being unnecessarily vaporized therethrough.

Further, if the atmospheric pressure in the air chamber 24 - portion 200 increases due to an increase of the surrounding temperature, the valve member 210 is deformed at a pressure which is less than the minimum pressure for the ink to pass through the pores 25, as illustrated in Fig. 15 (Fig. 13B) so as to absorb the pressure increase. In this respect, the diameter of the value member 210 is set to be sufficiently larger than that of the opening 105 so as to'be able to keep closure of the opening 105 even when the atmospheric pressure in the air chamber portion 200 increases and the valve member 210 is forced to expand outwardly.

As described above, with the ink.transfer type printer embodying the invention, as the bubbles generated in the ink space are led to the air chamber through the ink reservoir, it is possible to prevent the ink containing the bubbles being transferred onto the recording sheet.

Fig. 16 shows a modified embodiment of the printer shown in Fig. 9. In this modified embodiment, a partition is provided towards the top portion of the ink reservoir 100 to define the air chamber portion 200.

The partition 120 comprises a pair of opposing wings 120a and 120 b, both of which are upwardly inclined to form a top slit 122 therebetween which extends in the direction perpendicular to the sheet of the drawing.

Further, the wing 120b is formed to be a continuous - extension from the roof surface 102 of the ink reservoir 100.

The ink reservoir 100 is to be fully filled with ink to such an extent that the surface level of the ink reaches above the top slit 122.

Thus, the air bubbles contained in the ink reservoir are all led to the air chamber portion 200 through the top slit 122,guided by the roof surface 102 of the ink reservoir 100 and the wings 120a and 120b of the partition 120. Some of the gaseous substance vaporized from the solvents in the ink, that reached the air chamber 200, may cool down and liquefy again there.

Further, as the top slit 122 is formed between the wings 120a and 120b, both of which are upwardly inclined toward the top slit 122, even if the printer is placed upside-down, the air or bubbles in the air chamber 200 are led by the inclined wings 120a and 120b toward the bottom corners of the air chamber 200 and are hardly reintroduced into the ink reservoir 100.

Fig. 17 through 19 show another embodiment of an ink transfer printer of the present invention. It should be noted that the parts common to those in the embodiment of Figs. 9 and/or 16 carry the same reference numerals and the explanation therefor is omitted.

In this embodiment, as shown in Figs. 17 and 18, - 26 instead of the square-frame spacer 8 in the embodiment of Fig. 9 or Fig. 16, a supporting plate 28 is employed, and a film member 22 is placed over the supporting plate 28,to leave a very narrow space therebetween,,and extends to cover one end of the supporting plate 28 so as to def ine an ink space 21 which is a continuation of the ink reservoir 100.

The supporting plate 28 comprises a thin plate made of a material having a good heat conductivity such as a metal- and so on, and the thickness thereof is about 0.01 mm. Further, the supporting plate 28 overlaps with a bottom surface 101 of the ink reservoir 100 at their adjacent edges to form a continuous surface. At the bottom surface 101 of the ink reservoir 100, a pair of leg bars 150 are provided, which are secured on the casing 3a of the thermal head 3, and the supporting plate 28 is placed over the heating members 35 of the thermal head 3.

The film member 22 comprises a thin plate member made of a substance having a good heat conductivity. Further, the film member 22 overlaps with the roof surface 102 of the ink reservoir 100 at their adjacent edges to form a continuous surface.

Thus, the ink reservoir 100 and the ink-space 21 are formed to be connected to each other. In order to surely lead the ink in the ink reservoir 100 to the ink-space 21, - 27 a member (not shown) having a good ink absorbing character such as a wick employed in an alcohol lamp may be placed around the border between the ink-space 21 and the ink reservoir 100.

Figs. 19A and 19B are schematic views for explaining the principles to form an image with the ink transfer type printer shown in Fig. 17. In these figures, the ink reservoir 100 and the platen roller 4 are omitted.

AS illustrated in Fig. 19A, the pores 25 of the film member 22 are formed to have inner diameters such as not to allow the ink to pass therethrough under normal conditions. When the heating members 35 generate heat, the heat is transferred to the ink via the supporting plate 28. As the supporting plate 28 is very thin (about 0.01 mm) and the ink-space 21 is very narrow, the ink as well as the film member 22 in the area just above the heating members 35 are heated. The ink heated by the heating members 35 is evaporated and/or expanded to increase the pressure locally, and the heated portions of the film member 22 become easy to be deformed as the elastic modulus decreases.

Thus, as illustrated in Fig. 19B, the ink is pressed against the pores 25 of the film member 22 due to the above pressure increase, and the pores 25 are deformed to increase the size of the openings to allow the ink to pass therethrough. Thereby, the ink is transferred onto the recording sheet P (see Fig. 17) which is contacted with the other side of the film member 22.

Thereafter, upon ceasing of heat' generation by the selected heating members 35, the heated ink and the heated portions of the film member 22 are cooled down by the surrounding ink, and the opening size of the deformed pores 25 are restored to normal i.e., sizes which do not allow the ink to Dass therethrough.

As above, by controlling the heat generation with the heating members 35 of the thermal line head 3 in accordance with the printing data while transferring the recording sheet P by rotating the platen roller 4, the ink image is formed on the recording sheet P.

it will be understood that the present invention is capable of modification and can be applied to many different configurations, the detailed embodiments being straightforward for those skilled in the art to implement.

- 29

Claims

CLAIMS:

1. An ink transfer printer comprising:a thermal line head comprising a plurality of heating elements arranged in a predetermined direction; a film for contacting a recording sheet, the film having predetermined through holes located to face the thermal line head; and a space formed between said thermal line head and said film to hold the ink therein; and wherein said heating elements on said thermal line head selectively heat said ink in said space and said film so that the ink can permeate through said through-holes in the film and be transferred to said recording sheet.

2. An ink transfer printer according to claim 1 wherein a pressure generated in said ink during heating allows said ink to permeate through said through-holes.

An, ink transfer printer according to claim 2. wherein 29 - 30 the elastic modulus of said film decreases due to the heating of said heating element, and wherein the pressure generated in said ink during heating and the decrease in the elastic modulus of the film associated with the heating of said film allows said ink to permeate through said through-holes.

4. An ink transfer printer according to claim 1 wherein said film comprises a material taking a polarity which can be changed between hydrophilicity and hydrophobicity according to the temperature; and wherein the change in the polarity of said film caused by heating allows said ink to permeate through said through.holes.

5. An ink transfer printer according to claim 4 wherein said change in the polarity of said film and the decrease in the viscosity of said ink caused by heating reduce the surface tension of said ink on said film;and wherein the decrease in the surface tension allows the permeation of said ink through said through-holes.

6. An ink transfer printer according to claim 4 or 5 wherein except during heating, the diameter of said through hole is smaller than the minimum diameter such that the permeation 31 - of said ink is allowed.

7. An ink transfer printer according to claim 6 wherein except during heating, the diameter of said through-hole is small enough to prevent the permeation of a vapor of said ink.

8._ An ink transfer printer according to any preceding claim wherein said film is attached to said thermal line head via a spacer; and wherein said space comprises the region surrounded by said film, said thermal line head and said spacer.

9. An ink transfer printer according to claim 8 wherein said spacer comprises an adhesive.

10. An ink transfer printer according to claim 8 or 9 wherein said heating elements are located within said space.

11. An ink transfer printer according to any preceding claim further including an ink reservoir for supplying ink in said space which is long in the direction in which said heating elements are arranged.

12. An ink transfer printer according to any preceding claim wherein a plurality of through holes in said film correspond to a single heating element.

13. An ink transfer printer according to any one of claims 1 to 11 wherein a plurality of heating elements correspond to a said single through hole in the direction in which said heating elements are arranged.

14. An ink transfer printer according to any preceding claim wherein said through holes in said film are formed so as to be long in the direction in which said heating elements are arranged.

15. An ink transfer printer according to any preceding claim wherein said through holes are inclined at a predetermined angle from the direction of the thickness of said film.

16. An ink transfer printer according to any preceding claim wherein said film comprises polytetrafluoroethylene or other compounds.

17. An ink transfer printer according to any one of claims 25 1 to 15 wherein said film comprises a shape memory resin which state is varied according to the temperature.

18. An ink transfer printer according to any preceding claim further comprising a platen roller for contacting the recording sheet, the platen roller having a shaft which is parallel to the direction in which said heating elements on said thermal line head are arranged.

19. An ink transfer printer according to claim 18 wherein said platen roller is also used as a feeding means for sequentially feeding said recording sheet.

20. An ink transfer type printer comprising:a film member which allows the permeation of ink when the film is heated to a predetermined temperature or higher while normally preventing the permeation of ink; a heating member that partially heats the film member based on printing information, one surface of the film member being arranged to contact a recording sheet while other surface to face the heating member; an ink- space formed between said film member and said heating member to hold ink therein; an ink reservoir connected to said ink-space; and an air chamber portion formed on the top part of said ink reservoir for collecting air in the ink.

21. A printer according to claim 20 wherein said heating member comprises a thermal line head and wherein said film member is provided with a plurality of pores corresponding 34 to said thermal line head.

22. A printer according to claim 20 or 21 wherein a partition member is provided on said top part of the ink reservoir to define said air chamber portion, said partition member comprising a pair of opposing wings, between which a top slit is formed, both of said wings being upwardly inclined toward said top slit.

23. A printer according to claim 22 wherein the upper surface of said ink reservoir is formed to increase in height the further away from said ink space so as to lead bubbles in the ink toward said air chamber portion.

24. A printer according to any one of claims 20 to 23 wherein said thermal line head comprises a plurality of heating members arranged in a row, and wherein said air chamber portion is formed to extend along said row of heating members.

25. A printer according to any one of claims 20 to 24 wherein said air chamber portion is formed with a top opening for connecting the interior of the ink reservoir with the exterior, said top opening being covered by a oneway valve member which uncovers the opening when the atmospheric pressure in the air chamber becomes less than a - predetermined one to allow the external air to be introduced into the air chamber portion.

26. A printer according to claim 25 wherein said valve member is adhered to the inner peripheral portion of said top opening of the ink reservoir with leaving a section unadhered, said unadhered section of the valve member being deformable to be away of the inner peripheral portion of said opening of the ink reservoir.

27. A printer according to claim 25or 26 wherein said top opening and said valve member are both round-shaped, the diameter of said valve member being larger than that of said opening.

28. A printer according to any one of claims 25 to 27 wherein said valve member is made of such a resilient material as to be deformed to increase the volume of the air chamber portion so as to absorb the pressure increase in the air chamber portion when the atmospheric pressure in the air chamber portion becomes higher than a predetermined one.

29. An ink transfer type printer comprising:a film member which allows the permeation of ink when the film is heated to a predetermined temperature or higher 1 36 while normally preventing the permeation of ink; a heating member that partially heats the film member based on printing information, one surface of the film member being arranged to contact a recording sheet while other surface to face the heating member; an ink-space formed between said film member and said heating member to hold ink therein; an ink reservoir connected to said ink-space; a top opening for connecting the interior of the ink reservoir with the exterior; and a one-way valve member provided to said top opening.

30. A printer according to claim 29 wherein said valve member comprises a resilient member and is at least partly deformed inwardly of the ink reservoir to allow the external air to be introduced into the ink reservoir.

31. A printer according to claim 29 or 30 wherein said valve member is deformed outwardly of the ink reservoir to avoid the increase of the atmospheric pressure in the ink reservoir.

32. A printer according to any of claims 29 to 31 wherein said valve member is adhered to the inner peripheral portion of said top opening of the ink reservoir with leaving a section unadhered. said unadhered section of the valve member being deformable to be away from the inner peripheral portion of said opening of the ink reservoir.

33. A printer according to any one of claims 29 to 32 wherein said top opening and said valve member are both circular, the diameter of said valve member being slightly larger than that of said opening.

34. A printer according to any one of claims 29 to 33 wherein said valve member is made of such a resilient material as to be deformed to increase the volume of the air chamber portion so as to absorb the pressure increase in the air chamber portion when the atmospheric pressure in the air chamber portion becomes higher than a predetermined one.

35. An ink transfer type printer comprising:a film member which allows the permeation of ink when the film is heated to a predeterm-lned temperature or higher while normally preventing the permeation of ink; a heating member that partially heats the film member based on printing information, one surface of the film member being arranged to contact a recording sheet while other surface to face the heating member; an ink- space formed between said film member and said - 38 heating member to hold ink therein; an ink reservoir connected to said ink-space; a top opening formed on said ink reservoir for connecting the interior of the ink reservoir with the exterior; and a resilient valve member provided to said top opening, said valve member being deformable outwardly of said ink reservoir to avoid the increase of the atmospheric pressure in the ink reservoir.

36. The printer according to claim 35, wherein said valve member is adhered to the inner peripheral portion of said top opening of the ink reservoir with leaving a section unadhered.

37. The printer according to claim 36, wherein said top opening and said valve member are both round-shaped, the diameter of said valve member being larger than that of said opening.

38. An ink transfer printer substantially as herein described with reference to the accompanying drawings.

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39 A method of printing comprising:providing a film with a plurality of through holes dimensioned to prevent passage of ink therethrough in an unheated condition; locating a plurality of heating elements at or in spaced relation from the film to face one or more associated through holes; providing ink at locations of the heating elements; and selective heating a said heating element according to printing data to produce localised heating whereby ink thereat becomes passable through said through holes.

40. An ink transfer printer comprising:a film with a plurality of through holes dimensioned to prevent passage of ink therethrough in an unheated condition; a plurality of heating elements located at or in spaced relation form the film to face one or more associated through holes; an ink supply for providing ink at locations of the heating elements; and control means for selectively heating a said heating element according to printing data to produce localised heating whereby ink thereat becomes passable through said through holes.