WO2001094121A2

WO2001094121A2 - Printing apparatus for linerless printing sheet

Info

Publication number: WO2001094121A2
Application number: PCT/JP2001/004707
Authority: WO
Inventors: Mitsuyoshi Shirai; Hidetoshi Itou; Yoshikazu Soeda; Shinji Mutou; Wataru Kakimoto
Original assignee: Nitto Denko Corporation
Priority date: 2000-06-07
Filing date: 2001-06-04
Publication date: 2001-12-13
Also published as: WO2001094121A3; TW490399B

Abstract

A printing apparatus for a linerless printing sheet comprising: a printing device (2) for forming ink information on an upper surface of the linerless printing sheet (1) including a print backing material (11) having a back surface provided with an adhesive layer (12); and a transporting means for unwinding and transporting the sheet from a roll (13) of the sheet; the printing device forming the ink information while the transportation is transporting the sheet; wherein the transporting means transports the sheet while keeping contact with the adhesive layer, and at least has its outer surface formed of a silicone rubber containing a silicone oil.

Description

PRINTING APPARATUS FOR LINERLESS PRINTING SHEET

TECHNICAL FIELD The present invention relates to a printing apparatus for linerless printing sheet, comprising: a printing device for forming ink information on an upper surface of the linerless printing sheet made of a print backing material having a back surface providedwith an adhesive layer; and transporting means forunwindingandtransporting the sheet froma roll of the sheet; wherein the printing device forms the ink information while the sheet is being transported by the transporting means.

BACKGROUND ART There is already known a printing apparatus that uses a linerless printing sheet (hereinafter may also be called the sheet for simplicity) made of a print backing material having a back surface provided with an adhesive layer for sticking onto an intended object. The sheet is provided as a compact roll and is incorporated in the apparatus, and while unwinding the sheet out of the roll, a sheet of printed matter such as a label is produced continuously. Further, there has been a long time since a demandwas expressed for the sheetnothaving aprotective cover such as a separator which covers the adhesive layer. The reason behind the demand is that the protective cover such as the separator eventually has to be peeled off the adhesive layer and then discarded, which requires extra operation for the peeling as well as producing unwanted byproduct such as trash.

On the other hand, in order to transport the linerless printing sheet which does not have the protective cover, a transporting roller (corresponding to the transporting means) thatmakes contactwith the adhesive layermust satisfy a special requirement. Specifically, in order to transport the sheet smoothly, the roller must have a surface made of a material not easily adhere to the adhesive layer of the sheet. In order to achievethis, conventionally, the transportingrollerthatmakes contact with the sheet adhesive layer is a metal roller having a surface coated with baked silicone or fluororesin, or a roller made of a silicone.

These rollers according to the prior art can transport the sheet stably when the printing is being performed continuously. However, there is aproblemoflowpracticability. Specifically, once theprinting is haltedandthe transportation is stopped for some time, then, increased adhesion causes the print backing material to be entangled around the transporting roller, making impossible to continue the printing operation for example.

Further, according to the metal roller having the surface coatedwith baked fluororesin and so on in the prior artprinting apparatus , once the separability of the fluororesin decreases , adhesion between the baked layer of coating and the adhesive layer increases . In other words, if the baked layer of coating wears quickly, it becomes impossible to transport the sheet, and transportation life is short. Another problem is that the metal roller having the surface ofbaked coating requires a large number of steps to manufacture, and therefore manufacturing efficiency is low (manufacturing cost is high) .

DISCLOSURE OF THE INVENTION

The present invention was made under the circumstances described above, and it is therefore an object of the present invention toprovide aprinting apparatus incorporating a roller enabling to print while the linerless printing sheet is stably and continuously unwound from the roll of the sheet, enabling to continue the printing stably even if the printing is resumed after a long period of halt, with just as smooth unwinding and transportation as before the halt, enabling to provide the above-described favorable printing characteristic for a long period of time, having a long service life, and easy to manufacture.

In order to solve the above problems, a printing apparatus for alinerlessprintingsheet accordingto thepresent invention comprises : a printing device for forming ink information on an upper surface of the linerless printing sheet including a print backingmaterial having a back surface providedwith an adhesive layer; and a transporting means for unwinding and transporting the sheet from a roll of the sheet; the printing device forming the ink information during the transportation of the sheet by the transporting means; wherein the transportingmeans transports the sheet while keeping contact with the adhesive layer, and at least has its outer surface formed of a silicone rubber containing a silicone oil.

According to this arrangement, the surface of the transportingmeans such as a roller is formedof a silicone rubber containing a silicone oil . Because of lubrication provided by the silicone oil, even if the adhesive layer of the linerless printing sheet makes contact with the transporting means for a long period of time, adhesion does not increase. The transporting means may entirely be made of the silicone rubber, or only the surface of the transporting means may be formed of the silicone rubber. In any case, it is only necessary that the surface of the transporting means that makes contact with the adhesive layer is made as described above.

As described, according to the arrangement provided by the present invention, it becomes possible to print while the linerless printing sheet is stably andcontinuously unwound from the roll of the sheet, and to continue the printing stably even if the printing is resumed after a long period of halt, with just as smooth unwinding and transportation as before the halt. Therefore, the above-described favorable printing characteristic can be maintained for a long period of time, and the service life is extended. Further, since the only requirement is to impregnate the silicone rubberwith the silicon oil, manufacture of the transportingmeans is easier as compared with the roller having the surface coatedwithbaked fluororesin and so on, being superior also in terms of manufacturing efficiency.

Anotherprintingapparatus fora linerlessprintingsheet, according to the present invention comprises: a printing device for orming ink information on an upper surface ofthe linerlessprinting sheet includingaprintbacking material having a back surface provided with an adhesive layer; and a transporting means for unwinding and transporting the sheet from a roll of the sheet; the printing device forming the ink information while the transporting means is transporting the sheet; wherein: the transporting means includes a transporting roller transporting the sheet while keeping contact with the adhesive layer, the transporting roller including a roller portion having at least its outer surface formed of a silicone rubber andprovidedaroundan outer circumference of a supporting shaft; the supporting shaft being provided with a plurality of communicatingholes communicatingbetween an inside of the shaft andan outer surface of the shaft; the inside of the shaftholding a silicone oil; the oil being supplied from the inside of the supporting shaft to the outer surface of the shaft via the communicating holes.

If the supporting shaft of the transporting roller holds the silicone oil, the oil can be supplied and replenished to the silicone rubber layer, thereby preventing loss of oil for a long period of time and therefore maintaining the above-described favorable printing characteristic for a longer period of time.

Further, the surface of the transporting roller can be formed of a silicone rubber containing a silicone oil. Because of lubricationprovidedby the silicone oil , even if the adhesive layer of the linerless printing sheet makes contact with the transporting means for a long period of time, adhesion does not increase.

Still another printing apparatus for the linerless printing sheet, according to the present invention comprises: a printing device for forming ink information on an upper surface of the linerlessprintingsheet includingaprintbacking material having a back surface provided with an adhesive layer; and a transporting means for unwinding and transporting the sheet from a roll of the sheet; the printing device forming the ink information while the transporting means is transporting the sheet; wherein: the transporting means includes a transporting roller transporting the sheet while keeping contact with the adhesive layer, the transporting roller including a roller portion having at least its outer surface formed of a silicone rubber andprovidedaroundan outer circumference of a supporting shaft; the supporting shaft being symmetric, with two end portions having a smaller diameter and an intermediate portion having a greater diameter.

With the prior art, for example, if a pressure between a thermal head and the platen roller is not constant over the entire width of the sheet, or if the thickness of the linerless printing sheet is not constant over the entire width of the sheet, then there is occasionally such a problem as that linerless printing sheet is transported in a snaky pattern at the platen roller (the transportingroller) , or that the ink ribbonwrinkles on the platen roller, resulting in poor-quality printing. By making greater the diameter of the intermediate portion of the supporting shaft of the transporting roller than that of the end portion as described above, the snaky transportation can be eliminated, and a favorable printing quality canbe achieved.

Still another printing apparatus for the linerless printing sheet, according to the present invention comprises: a printing device for forming ink information on an upper surface of the linerlessprintingsheet includingaprintbacking material having a back surface provided with an adhesive layer; and a transporting means for unwinding and transporting the sheet from a roll of the sheet; the printing device forming the ink information while the transporting means is transporting the sheet; wherein the transporting means includes a transporting roller transporting the sheet while keeping contact with the adhesive layer, the transporting roller including a roller portion having atleastits outersurface formedofa silicone rubberandprovided around an outer circumference of a supporting shaft, the roller having at least its surface impregnated with a silicone oil and at least the surface of the roller being made rugged.

As still another embodiment of the present invention, kinematicviscosityofthe silicone oil ispreferably30 to 100000 mmVs (25°C) .

By selecting the silicone oil havinga kinematic viscosity in this range, an appropriate blooming can be performed, and agoodunwindingandtransporting of the linerlessprinting sheet can be maintained.

In order to solve the problems described above, still another printing apparatus for a linerless printing sheet, according to the present invention comprises : a printing device for forming ink information on an upper surface of the linerless printing sheet made of a print backing material having a back surface provided with an adhesive layer; and transporting means forunwindingandtransportingthe sheet froma roll of the sheet; the printing device forming the ink information while the sheet is being transported by the transporting means; wherein the transportingmeans transports the sheet while keeping contact with the adhesive layer, and has at least its outer surface formed of a silicone rubber and made rugged.

According to this arrangement, the outer surface of the transportingmeans such as a roller is formedof a silicone rubber and made rugged, and therefore does not increase adhesion even if there is a prolonged contact between the adhesive layer of the linerless printing sheet and the transporting means as compared to the transporting means having a non-rugged, smooth outer surface. The transporting means may entirely be made of the silicone rubber, or only the surface portion. of the transporting means may be formed of the silicone rubber. In anycase, itis onlynecessarythatthe surfaceofthetransporting means that makes contact with the adhesive layer is made as described above.

As described, according to the arrangement provided by the present invention, it becomes possible to print while the linerless printing sheet is stably andcontinuouslyunwound from the roll of the sheet; and to continue the printing stably even if the printing is resumed after a long period of halt, with just as smooth unwinding and transportation as before the halt. Therefore, the favorable printing characteristic as described above canbe maintained for a longperiod of time, and the service life is extended. Further, since the only requirement is to form a rugged pattern on the outer surface of the transporting means , manufacture of the transporting means becomes easier as compared with the roller having the surface coated with baked fluororesin and so on, being superior also in terms of manufacturing efficiency.

As an embodiment of the present invention, the rugged pattern is preferably one as expressed by the following two expressions (1) and (2) : 100a > b > 0.5a ... (1) c > b > 0.5c ... (2) (where "a" represents a depth of a groove, ^wb" represents a width of the groove and c" represents a pitch of the groove.)

By selecting the values specified as above for the rugged pattern, a good transporting by the transporting means can be maintained. More preferable values are 10 to 1000 μ for ^wa", 500 to 3000 μm for ^wb", and ^Bb" = "c".

As still another preferred embodiment of the present invention, a printing method used in the printing device is selectedfromagroup consistingof thermo fusion transfermethod, thermo sublimation transfer method, inkjet method and thermo sensitive method. By using these printing methods having a wide range of applicability, a printed sheet such as a label can be formed continuously and stably.

Further, the linerless printing sheet, particularly the print backing material , can be varied depending on ink fixing characteristic in the selected printing method, intended use oftheprintedmaterial andso on. Specifically, heatresistance, water resistance, resistance to solvent, resistance to weathering and so on canbe selectedas appropriate in accordance with the intended use, and a wide range of adaptation can be made. Therefore, the printed sheet can be continuously formed efficiently by means of these printing methods having a wide applicability, and in addition, a printed sheet can be issued on demand in situ by using a commercially available thermo transfer printer.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a partially enlarged diagram illustrating a printing apparatus according to a preferred embodiment;

Fig.2 is a sectional view of a linerless printing sheet;

Fig.3 is a sideviewshowingaprintingapparatus according to another embodiment;

Fig. 4 is a diagram illustrating a supporting shaft of a transporting roller;

Fig. 5 a diagram illustrating a supporting shaft of a transporting roller;

Fig. 6 is a sectional view of a silicone rubber roller having a rugged outer surface; and

Fig. 7 includes diagrams showing a forming direction of the rugged pattern on the outer surface of the silicone rubber roller.

BEST MODE FOR CARRYING OUT THE INVENTION Now, preferred embodiments of the present invention will be described in detail, with reference to the drawings.

A printing apparatus according to the present invention is a printing apparatus for linerless printing sheet, comprising: a printing device for forming ink information on an upper surface of the linerless printing sheet made of a print backingmaterial having a back surface providedwith an adhesive layer; and transporting means for unwinding and transporting the sheet from a roll of the sheet; wherein the printing device forms the ink information while the sheet is being transported by the transporting means . The transporting means includes a roller that transports the sheet while keeping contact with the adhesive layer of the sheet. The roller has at least its outer surface formed of a silicone rubber containing a silicone oil. The linerless printing sheethas aprintbackingmaterial, to which ink information is to be provided, whereby a printed label sheet is obtained. In this linerless printing sheet, the print backing material has a back surface provided with an adhesive layer. However, no protective layer, such as a separator, for protection of the adhesive layer is provided. Use of the linerless printing sheet enables to eliminate an operation to peel and remove the protective layer such as the separator, as well as production of unwanted byproduct, namely the removed protective cover to be discarded. Further, use of the sheet in the form of a roll allows the sheet to be handled in a compact form. Still further, smooth on-site production of the label sheet becomes possible. Since there is no needtopeel theprotective sheet off, operation of sticking thelabel sheetontoan intendedobjectcanbeperformedsmoothly.

[Configuration of the Printing Apparatus According to the Present Embodiment]

Fig. 1 shows a preferred embodiment of the printing apparatus according to the present invention.

The linerless printing sheet 1 includes a long ribbon-like continuous print backing material 11 having a back surface provided with an adhesive layer 12. The adhesive layer 12 is not provided with a protective cover. The linerless printing sheet 1 has its adhesive layer.12 wound around a core 13a and is made into a form of roll as a roll 13. While the sheet 1 is being unwound from the roll 13 and being transported in a direction indicated by the arrow, information 26 by means of an ink is provided in an upper surface of the print backing material 11 by a printing device 2. After a predetermined printingismade ontheuppersurfaceoftheprintbackingmaterial 11, cutting device 4 which is provided on the downstream side ofthetransportationcourse cuts the sheet1 into apredetermined dimension. The configuration described above enables continuous formation of a printed sheet 14 (label sheet) such as a label.

The printing device 2 shown in Fig.1 is a thermo transfer printing device 2 including a platen roller 21, a thermal head 22 disposed above the platen roller 21, an ink ribbon 23, an unwindingroller 24 andawindingroller 25 for the ribbon. Thus , the platen roller 21 functions as the transporting means that makes contact with the adhesive layer 12 provided in the back surface of the print backing material. The platen roller 21 has atleast its outer surfaceportion formed of a silicone rubber containing a silicone oil.

According to the present invention, when printing is performed to the linerless printing sheet 1, the sheet 1 is successively unwound from the roll 13 as shown in Fig.2, which is a roll of the sheet 1 made of the print backing material 11 having its back surface provided with the adhesive layer 12. Further, theplatenroller21 , whichhas atleastits outersurface portion formed of a silicone rubber containing a silicone oil is used as transporting means on the side that makes contact with the adhesive layer 12 of the sheet 1. While being unwound and transported, the print backing material 11 allows its upper surface to receive the inkinformation26providedbytheprinting device 2.

The platen roller 21 may entirely be made of the silicone rubber, or only the surfaceportionmaybe formed of the silicone rubber. In any case, it is important that the surface portion is formed of a silicone rubber containing a silicone oil.

According to the present invention, as shown in Fig. 1, the cutting device 4 that cuts the linerless printing sheet 1 as after the printing into a predetermined dimension may be disposedas necessary. For example, accordingto the embodiment in Fig. 1, a successive transporting mechanism 3 provided by apair of embossedpinchrollers 31, 32 is providedon theupstream side of the cutting device 4.

In the above case, the successive transporting mechanism 3 can also include a roller functioning as the transportingmeans that makes contact with the adhesive layer 12 of the linerless printing sheet 1. In this case, such a roller thatmakes contact with the adhesive layer 12 has at least its outer surface formed of the silicone rubber impregnated with the silicone oil. For example, in the successive transporting mechanism 3 shown in Fig. 1, the roller 32 (the lower roller in Fig. 1) that makes contact with the adhesive layer 12 has at least its outer surface formed of the silicone rubber impregnated with the silicone rubber.

It should be noted that the embodiment in Fig. 1 shows the printing device 2 that uses a thermo transfer method. This thermo transfermethodmaybe whichever of thermo fusion transfer methodor thermo sublimation transfermethod, or canbe otherwise. For example, an inkjet printing method that uses a thermo fixing inkor a dryinginkmaybeutilizedappropriately. Still further, a printing device of a thermo sensitive method may also be utilized.

As the successive transportingmechanism3, alternatively to a pinch roller method, any mechanism may be adopted as appropriate.

According to the present invention, the platen roller 21 as the transporting means that makes contact with the adhesive layer 12 of the linerless printing sheet 1 has at least its outer surface formed of a silicone rubber impregnated with a silicone oil. Preferably however, other transporting rollers and guiding members (such as a guide) other than the platen roller 21 should also have relevant outer surfaces be formed of the silicone rubber impregnated with the silicone oil.

In this case, in consideration of roller service life and other issues relatedwith abrasion of the silicone rubber layer, it is preferable that the silicone rubber layer should have a thickness not smaller than 0.1 mm, ormorepreferably not smaller than 0.5 mm, and most preferably not smaller than 1 mm. Alternatively, this portion may entirelybe made of the silicone rubber for example.

[Silicone Oil]

The silicone oil used in the present invention should preferablyhave a kinematic viscosity of 30 to 100000 mm²/s (25°C) . If the value is lower than 30 mm²/s, blooming of the silicone oil in the silicon rubber surface is too quick and too much, making difficult to maintain a good state of unwinding and transportation. On the other hand, if the kinematic viscosity exceeds 100000 m²/s, then blooming of the oil in the silicon rubber surfacebecomes insufficient, resultinginno improvement in the state of unwinding and transportation. An amount of the silicone oil to be added should preferably be 2 to 50 weight percent.

It should be noted here that bonding strength between the surface of the adhesive layer 12 and the silicone rubber impregnated with the silicone oil can be determined as appropriate, in accordance with such a factor of consideration as balance between bonding strength to the transporting means (theroller) andbondingstrengthtoanobjecttowhichtheprinted labeled is to stick. In general, in consideration of such a factor as automatic transportability of the linerless printing sheet 1 in a thermo transfer printer for example, a preferable bonding strength is not greater than 98 mN/50 mm, more preferably not greater than 9.8 mN/50 mm, and most preferably not greater than 0.98 mN/50mm, based on a 180-degree peeling adhesion (at 300 mm/min peeling speed) to the silicone rubber impregnated with the silicone oil.

Formationof the silicone rubber layer onthe outer surf ce of the transportingmeans (such as a roller) can be accomplished as appropriatebyamethodsuch as injectionmolding, application of a polymer liquid, and lamination with a sheet. Therefore, if one of these methods is to be used, an existing conventional printing apparatus can be converted into the printing apparatus according to the present invention by providing the silicone rubber layer to a roll thatmakes contact with the adhesive layer of the linerless printing sheet and to other members of the transporting means as necessary.

The silicone rubber may be provided for example by polydimethylsiloxane, polymethylphenylsiloxane, polydialkylsiloxane, and other polymers having an appropriate polymer structure. For such a purpose as improved durability to abrasion, the siliconrubbermaybe subjectedto a crosslinking process as appropriate, provided by such a method as electron beam radiation. Further, for such a purpose as reduced bonding strength, the silicon rubber may be mixed with 1 to 10 weight percent of a releasing polymer of a suitable kind such as a silicone, long chain alkyl or fluorine polymer.

The silicone oil used in the present invention may be one or a combination of two or more of suitable polysiloxane such as polydimethylsiloxane, polymethylphenylsiloxane, and polydialkylsiloxane. Further, the silicone oil may be a reactive silicon oil such as modified amino, modified epoxy, modified carboxyl, modified carbinol, modified methacrylic, modifiedmercapto, andmodifiedphenol, or maybe a non-reactive silicone oil such as modifiedpolyether, modifiedmethylstyryl, modified alkyl, modified higher fatty acid, andmodified higher alkoxy, may have a functional group or may be modified one.

A method of impregnating the silicon rubber with the silicone oil may be selected from adding and mixing the silicone oil with the silicone rubber as before crosslinking, soaking the silicone rubber as after crosslinking into the silicone oil and allowing the rubber to absorb the oil, and so on.

On the other hand, portions of the transporting means (transporting guide for example) of the printing apparatus that may be contacted by the adhesive layer of the linerless printing sheetmaybeprovidedwithmeans for suchpurposes as facilitating the transportation by preventing the adhesive layer from adhering to these portions.

The printing apparatus according to the present invention may be provided with the cutting device 4 as shown in Fig. 1 as necessary. The cutting device 4 may be anything that can cutthe linerlessprinting sheet 1 into apredetermineddimension. For example, a cutting blade may be intermittently driven by a cam thereby performing the cutting into a desired dimension, or any other mechanism may be used as appropriate. Further, the cutting may be made over the entire width of the linerless printing sheet, or may be partial , leaving an uncut portion that allows easy separation by hand for example.

[Print Backing Material]

Appropriate methods of printing include a thermo fusion transfer method by means of a thermal head and an ink ribbon, a thermo sublimation transfer method, an Inkjet method by means of an Inkjet head and ink, and a thermo sensitive method. By using any of these widely applicableprintingmethods , favorably fixed printing can be achieved. Therefore, the print backing material 11 can be formed by using a sheet material made of an appropriate raw material such as paper, polymer and so on.

The linerless printing sheet 1 can be selected as appropriate, from those made of a variety of print backing material 11 having a back surface providedwith an adhesive layer 12 but without a protective cover, as shown in Fig.2. The print backing material 11 and the adhesive layer 12 may have a single-layer, double-layer or multi-layer structure.

Therefore, the print backing material can be formed as appropriate depending on an intended use of the linerless printing sheet, from a rawmaterial selected from: various kinds of paper; film or sheet or foam sheet made of a polymer; fiber, woven or unwoven fabric made of a polymer. Other appropriate rawmaterial includes a laminatedmaterial made of a combination of two or more of the materials such as paper and film, foam sheet and a fabric, and a composite sheet made from a material combination as described above reinforced by another material such as a metal foil.

Therefore, the print backing material for the linerless printing sheetaccordingto thepresent invention canbeprovided by any print backing material known to be used in conventional thermo fusion transfer method, thermo sublimation transfer method, thermo sensitive method, and Inkjet method, as well as other printing methods such as screen printing, photogravure printing, relief printing, offset printing and so on.

Required characteristics of a preferable print backing material include: that the print backing material can firmly support the adhesive layer; that the adhesion between the adhesive layer andanupper surface of theprintbackingmaterial when the sheet is wound into the roll is weak enough not to require a large amount of force to unwind; and that the print backing material allows good fixing of ink. Examples of the print backing material that satisfies these requirements include: a print backing material entirely formed by a layer of mixture of an ink-accepting polymer and a low-adhering polymer; one having a reinforcing layer on which said layer of mixture is provided; one including an ink-accepting layer formed of paper orpolymer, onwhich a thin, porous ormesh layer of a low-adhering polymer is provided; and one including a reinforcing layer and so on, onwhich said ink-accepting layer andlow-adheringpolymer layer are provided.

Other kinds of the print backing material that can be preferably used include: one in which the print backingmaterial is made of a polymer having a weak adhesion to a specific adhesive layer and accepting a specific kind of printing ink; and one that includes a reinforcing layer provided with said polymer layer. In this case, the linerless printing sheet made from theseprintbackingmaterials is providedwith the adhesive layer having the weak adhesion to said specific polymer layer, and the printing is made by using said specific ink accepted by said specific polymer layer, so that a desired label sheet can be produced.

In the above, the ink-accepting polymer used for such a purpose as fixingthe inkina durablemanner includes : polyolefin such as polyethylene and polypropylene; polyamide, polyester, poly vinyl acetate, ethylene-vinyl acetate copolymer, urethane polymer, acrylicpolymer such as poly (metha) acrylic alkyl ester, poly vinyl chloride, styrene polymer, silicone polymer, natural rubber, plastic polymers or rubber polymers such as polyisobutylene, polyisoprene chloroprene rubber, isoprene isobutylene rubber, nitryl butyl rubber, styrene-butadiene rubber, styrene-butadiene styrene rubber, styrene isoprene-styrene rubber, styrene ethylene butadiene rubber, styrene ethylene-butylene-styrene rubber, styrene-isoprene-propylene styrene rubber, ethylene propylene polymer, and a blended material thereof.

Further, the low-adhering polymers used for the purpose of reduced bonding strength and so on include: polymers for release coating known the field of silicone adhesive sheet, long chain alkyl adhesive sheet and fluorine adhesive sheet, polyethylene of a low molecular weight, phosphoric ester surfactant, polypropylene, and rubber polymer. Preferably usable among others are the release coating polymers, and particularly preferable are the silicone polymers .

If the mixture layer described above is to be formed, a preferable mixing ratio between the ink-accepting polymer and the low-adhering polymer as derived from considerations on reduced in adhesion and prevention of ink fixing ability is 100 weight part ink-accepting polymer to 0.01 to 10 weight part of low-adhering polymer. More preferably, the ratio of the low-adheringpolymer is 0.1 to 8 weightpart, andmost preferably 1 to 5 weight part.

On the other hand, in the method in which a thin layer of a low-adhering polymer is provided on an ink-accepting layer made ofpaper orpolymer, a goal of the method is to reduce bonding strength of the low-adhering polymer to the adhesive layer while maintaining good ink fixing. The thickness of the low-adhering polymer layer in such a case as this is, in consideration of the above goal, 0.01 to 10 μm preferably. More preferably, the thickness is 0.05 to 5 μm, and most preferably 0.1 to 2 μ .

Further, in the method in which a porous or mesh layer of a low-adheringpolymer is providedonthe ink-accepting layer , a goal of the method is to reduce bonding strength of the low-adhering polymer to the adhesive layer while enabling ink fixing via gaps in the low-adhering polymer. In consideration of this goal, a percentage of the porous or mesh, low-adhering polymer on the ink-accepting layer is preferably 1 to 90% . More preferably, thepercentage shouldbe 2 to 70% , andmostpreferably 5 to 50%. Further, the thickness of the low-adhering polymer layer in this case is, in consideration of the above goal, 0.01 to lOOμm. More preferably, the thickness shouldbe 0.05 to 50 μm, and most preferably, 0.1 to 20 μm.

The porous or mesh, low-adhering polymer layer may be formed by as appropriate, but preferably with the gap in the low-adhering polymer distributed as uniformly as possible. Examples ofthe formingmethodof theporous ormesh, low-adhering polymer layer include photogravure printing method, screen printing method, pattern formation by means of photo resist, known dry and wet methods of porous film formation, melt blow method, curtain spraymethod, lamination ofporous ormesh films , and so on.

Examples of thepolymerhavingaweakadhesionto a specific adhesive layer and accepting a specific kind of printing ink include polyolefin polymers such as polyethylene and polypropylene, silicone polymer, rubber polymer, long chain alkyl polymer and so on. The molecular weight of the polymer can be selected as appropriate in consideration of matching with ink and other characteristics. As an example, if a polyolefin polymer is used, 500 to 6,000,000 ispreferablebasedonviscosity averagemolecularweight, in consideration of solvent resistance, ink fixing and so on.

Inthe above, theprintbackingmaterial or its back surface, or the ink-accepting layer that supports the thin, porous or otherwise low-adheringpolymer layer canbemade as appropriate, by using such a method as forming or applying, thereby making one or more kinds of polymers into a thin film or a porous film. During the film making process, an additive may be used as appropriate, including: reinforcing material such as fiber, pigment or coloring agent such as silica, titania, alumina, zinc white, zirconia, calcium oxide and mica, and antioxidant. An amount of the additives to be mixed is preferably not greater than 30 weight percent in consideration of maintaining a good printability.

It should be noted here that the linerless printing sheet shouldonlyhave its one surfacehavingtheprintbackingmaterial exposed and the other surface having the adhesive layer exposed. Therefore, a layer such as a reinforcing layer can be placed as appropriate between the print backing material and the adhesive layer. The reinforcing layer is used as necessary in order to reinforce the print backing material for example, depending on an intendeduse of the label sheet and other factors . Thus , the reinforcing layer can be provided by a polymer-coated layer or a polymer film, fiber or woven fabric, paper or unwoven fabric, metal foil or net, wire and so on as appropriate. Material characteristic of the linerless printing sheet or the label sheet can be controlled easily by selection of the reinforcingmaterial . Further, amodification as required from time to time, such as improvement in contrast between the formed ink informationandthebackground, canbemade to the reinforcing layer.

Formation of the linerless printing sheet having the reinforcing layer can be achieved suitably by one of the methods selected from: providing the ink-accepting layer made of the print backing material on the reinforcing layer by using thermal laminate method or extrusion coating method; impregnating the reinforcing layer with a solution or a molten of a formation material of the print backing layer; placing the reinforcing layer in theprintbackingmaterial , and so on. Theprintbacking material should preferably have a high elasticity in consideration of easiness in winding into the roll or good adhesion onto a curved surface.

For example, a linerless printing sheet including paper as the print backing material and a low-adhering adhesive layer provided thereon, can serve for a variety of printing methods due to a good ink acceptance provided by the paper. Likewise, a linerless printing sheet may include a layer of mixture of the low-adhering polymer such as a silicon polymer and the ink-accepting polymer such as polyester polymer as the print backing material , or include an ink-accepting polymer provided thereon with a thin layer of the low-adhering polymer as the print backing material, or include said layer provided on a reinforcing layer made of polypropylene paper. To these print backing material, a rubber or other general-purpose adhesive layer is provided. Each of these linerless printing sheets can serve very well for printing in a thermo sublimation transfer printer.

Further, a print backing material may be made of the ink-accepting polymer layer provided by a hydrophilic polymer and a porous layer provided by the low-adhering polymer such as a silicone polymer, or the print backing material may be made of said layer provided on a reinforcing layer made of paper for example. To these print backing material, a general-purpose adhesive layer of an acrylic material for example is provided. Each of such linerless printing sheets can serve very well for printing in an Inkjet printer.

An example of the printing method for a specific combination of the above print backing material, an adhesive layer having a low adhesion to the back surface thereof and a printing ink is a thermo fusion transfer printing method. In this particular method, the print backing material is made of a layer of a polyolefin polymer mixed as necessary with a low-adheringpolymer such as a silicone polymer. The layer may be supported by a reinforcing layer provided by paper. The low-adhering adhesive layer is providedby a polyester adhesive, acrylic adhesive and so on. The ink is made from a polyolefin polymer and a coloring agent.

On the other hand, the print backing material may be a thermo sensitive paper, i.e. one on which ink information can be printed by means of heat. A preferably usable thermo sensitive print backing material is a heat insulating sheet having a surface formedwith a thermo sensitive color-developing layer. The use of the heat insulating sheet enables to prevent unwanted color development in the thermo sensitive color-developing layer due to temperature rise in the printing apparatus as a result of continuous thermo sensitive printing, and a vivid thermo-sensitive coloringpattern superb in contrast between the thermally developed color and the background can be formed. Therefore, the heat insulating sheet enables continuous, high-volume formation of the thermo-sensitive coloring pattern by means of the thermal printing.

The heat insulating sheet can be selected as appropriate, depending on an intended use of the linerless printing sheet, from such materials as a polymer sheet, a composite sheet made of the polymer sheet and a reinforcing material such as fiber or woven fabric, unwoven fabric or metal foil and so on, or a laminated sheet of two or more of a foam sheet, paper, polymer film and so on. Another example of the heat insulating sheet is a sheet of apolyethylene having a crystal melting temperature not higher than 120°C.

The thermo sensitive color development layer canbe formed appropriately by using a leuco dye and developer thereby giving a layer a thermo sensitive coloring characteristic. Further, a commonly marketed thermo sensitive paper may be provided with the adhesive layer. The thermo sensitive color development layer shouldhave a thickness not greater than 500 μm, preferably not greater than 200 μm, andmostpreferably 5 to 100 μm, although these values are not limiting.

It shouldbe notedthat a release coat layermaybeprovided as necessary on an upper surface of the thermo sensitive color development layer for a purpose of decreased adhesion to the adhesive layer. The release coat layer can be formed by using the release agents as listed earlier. However, formation of the release coat layer can cause the thermo sensitive color development, which must be prevented. In consideration of this and other factors , it is preferable to use a release agent made from a silicone polymer containing two or more acryloyl groups or methacryloyl groups. From this material, a hardened film can be formedby means of ionized radiation. Thus , the hardened film can be formed at a low temperature, and unwanted color development of the thermo sensitive color development layer can be prevented.

Formation of the above-described release coat layer can be achieved for example, by first applying the release agent containing said silicone polymer on the thermo sensitive color development layer by using appropriate equipment such as a squeeze coater, and then exposing the applied coat to the ionized radiation thereby hardening the coat. In this case, an amount of application of the silicone polymer is preferably 0.05 to 5 g/m² , and particularly 0.1 to 3 g/m². If the mount is smaller than 0.05 g/m², the film thickness is too small, resulting in a largepeeling force, and the peeling force can be inconsistent. The amount exceeding 5 g/m² is not practical in that a long time must be used for the radiation.

Athickness of theprintbackingmaterial maybe determined as appropriate, depending on an intended use of the linerless printing sheet and other factors. In general, the thickness should be not greater than 1 mm in consideration of ink fixing and strength. More preferably, the thickness should be 1 to 500 μm, and most preferably 5 to 200 μm. If the reinforcing layer is provided, the ink accepting layer of the print backing material should have a thickness preferably not smaller than 0.1 μm, more preferably not smaller than 0.5 μm, and most preferably not smaller than 1 μm.

The print backing material should preferably have a, high elasticity in consideration of easiness in winding into the roll or good adhesion onto a curved surface. Further, an additive such as silica, titania, alumina, zinc white, zirconia, calcium oxide and mica may be mixed in the print backing material to appropriately color the material in white for example.

The adhesive layer provided in the back surface of the printbackingmaterial is to allow the label sheet to stick easily onto an intended object. According to the present invention, theadhesive layeradheres tothebacksurface oftheprintbacking material when the print backing material is wound into a roll without a protective cover such as a separator, and allows easy unwinding from the roll and smooth transportation within the printing apparatus by the transporting means.

In consideration of the easy unwinding from the roll, a preferable bonding strength to the surface of the print backing material is notgreaterthan4900mN/50mm, basedonthe 180-degree peelingadhesion (at 300 mm/minpeeling speed) . Morepreferable value, taking into consideration a balance between automatic unwinding via the printer for example and the adhesion to the intended object, is 9.8 to 2940 mN/50 mm, and most preferably 49 to 1470 mN/50mm.

The adhesive layer can be formed by using one or more of adhesive materials as appropriate, and there is no specific limitation to the kinds of the materials . Examples are : rubber, acrylic, silicone, vinyl alkyl ether, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, cellulose, urethane, polyester, and polyamide.

Further, alternatively, the adhesive layer may be formed as a thermo active layer. The thermo active adhesive layer does not show tack before being heated. When heated, the tack develops to show characteristic as the adhesive layer (pressure sensitive adhesive layer) . Formation of the thermo active adhesive layer can be made for example, by mixing a crystalline plasticizer with an adhesive selected from those listed earlier.

The crystalline plasticizer can be selected from a number of plasticizers which stay solid under room temperatures . In particular, phthalic acid plasticizers such as dicyclohexylphthalate (meltingpoint: 64°C) , dimethylphthalate (melting point: 67°C) , and diphenylphthalate (melting point: 69°C) , and reactive plasticizers such as dibutyl itaconate (meltingpoint: 38°C) , monobutyl itaconate (meltingpoint: 40°C) , and monomethyl itaconate (meltingpoint: 67°C) can be used more preferably in consideration of good tack development by heating and pressure-sensitive adhesion characteristic.

If no release coat is to be formed in the upper surface of the print backing material, a preferable adhesive layer is selected in consideration of low adhesion to the print backing material, retention of initial adhesion; in other words, easiness and stability when unwinding from the roll , and stable adhesion to an intended object to stick to. Examples of the preferred adhesive layer are those formed by using one or more of: urethane adhesive, polyester adhesive, polyamide adhesive and acrylic adhesive.

Formation of the adhesive layer canbe achieved for example by first providing an adhesive layer on a separator with an appropriate method of application including a rolling method such as calendar roll method or an application method such as doctor blade method and photogravure roll coater method. The layer thus formed is then transferred onto a desired surface of the print backing material . Likewise, an adhesive layer may be directly provided in the back surface of the print backing material .

A thickness of the adhesive layer can be determined as appropriate. In general however, a preferable thickness is 1 to 500 μm in consideration of the bonding strength and adaptability to a common printer. If further consideration is made into stable formation of the adhesive layer having a uniform thickness, then the preferred thickness is 5 to 100 μm, more preferably 10 to 60 μm, and most preferably 15 to 40 μm.

In the embodiment shown in Fig. 1, the thermo fusion transfer printing device 2 that uses a thermal head and a fusion ink ribbon is described. According to the present invention however, the printing apparatus can incorporate a different printing device of a different printing method as appropriate, for example from inkjet method by means of an Ink et head and ink, thermo sensitive method using a thermal printhead such as a thermal head or laser beammethod, thermo sublimation transfer method by means of a thermal head and a sublimation ink ribbon, and so on. It should also be noted here that if the thermo sensitive method is used, a thermal printing component such as aheatingpenorheatingstampmaybe employed, withanappropriate thermal printing method, to allow on-site issuance of a label sheet.

Further, in the above, if the printing device is of the thermo sublimation transfer method, it is preferable in consideration of printing operability and so on, that the ink layer of the ink ribbon should be one treated by a release agent for example. It is particularly preferable that the ink ribbon incorporates a hardened film of a silicone polymer for clean release of the ink. If the printing device is of the inkjet method, it is preferable in consideration of printing operability and so on, that use is made of a thermo fusion ink that contains a polymer serving as a binder component. This polymer may be one selected from those listed earlier as the adhesive material which is adherent at room temperatures. As for loading of the roll of linerless printing sheet onto the printing apparatus , a cassette method can be used, in which the roll is encased in a cassette. On the other hand, if the adhesive layer is provided by the thermo active material, heating must be provided in order to develop the tack. This can be achieved as appropriate in manyways . Forexample, a thermal head, heatingroller, infrared radiator , drier or other hot-air blower may be incorporated in the apparatus, or the heating may be provided from outside of the apparatus.

A specific example of the above-described printing apparatus is shown in Fig. 3. This is a thermo fusion transfer printing apparatus (printer) . According to this apparatus, a linerless printing sheet 5 is unwound from a roll 51 and continuously transportedby a transporting roller 62 coatedwith a silicone rubber, in the printer. During the transportation, a guide 61 made of polyolefin and located upstream performs widthwise positioning. A tip of the linerless printing sheet 1 is detected by a sensor 63 , and is guided to a printing device 6 which includes an ink ribbon 64, a thermal head 65, a platen roller 66 coated with a silicone rubber.

In the printing device 6 , ink in the ink ribbon 64 is melted by heat from the thermal head 65 which is driven based onprinting data. Themolten ink is then thermally transferredby apressure via the platen roller 66 onto a surface of the print backing material of the linerless printing sheet 1, thereby fixing intended ink information. The ink layer of the ink ribbon adhering to the print backing material is then separated via a release plate 67, completing the printing,, and then the ink ribbon 64 is wound around a collection reel 68.

Next, the linerless printing sheet 1 as afterbeingprinted receives inspection via a verification device 7 on the quality of print, and then reaches a cutting device 8 operating cooperatively with the verification device 7. The linerless printing sheet 1 is cut widthwise into a predetermined size, yielding a label sheet 52 provided by the cut piece. If the print fails in the verification, then the cutting system 8 makes a symbolic cut as a loss mark.

The ink information provided to the linerless printing sheet 1 via theprintingapparatus can, for example , be a character pattern, a picture pattern, a barcode pattern, or any others formed arbitrary by using letters, figures, symbols and so on. Therefore, a label sheet such as an ID label carrying appropriate information can be formed. The ink information can be continually printed for continuous formation of the intended labels , or single piece or a given number of pieces of the label sheets can be produced.

Therefore, on-demand production of a label sheet such as performed on site becomes possible. The label sheet thus obtained is cut into a predetermined size, and then stuck and fixedvia its adhesive layeronto adesiredobj ect as appropriate.

[Embodiments] [Example 1]

A low-density polyethylene of a viscosity average molecular weight of 300,000 was mixed with 0.4 weight percent of antioxidant, and extrusion-laminated on an upper surface of a wood-free paper having a basis weight of 80 g/m² to form a printing layer having a thickness of 18 μm. An emulsion adhesive made of butyl acrylate acrylic acid copolymer was applied uniformly to form an adhesive layer having a thickness of 25 μm, which was transferred onto the other surface of the paper, and a linerless printing sheet was obtained. This sheet was wound into a roll , allowing the adhesive layer to adhere to the upper surface of the print backing material.

The thermo fusion transfer printer shown in Fig. 3 was loaded with a commonly available thermo fusion ink sheet. The roll obtained in the above was also loaded into the printer, and printing was made by thermally transferring the ink onto the upper surface of the print backing material . A label sheet was obtained. The thermo fusion transfer printer was provided with a platen roller 66 made of a silicon rubber containing 10 weight percent of dimethylsiloxane (kinematic viscosity: 1000 mm²/s) .

[Example 2]

A label sheet was obtained from the same procedure as used in Example 1, except that the adhesive layer (thickness: 25 μm) was formed with a natural rubber adhesive.

[Example 3]

A label sheet was obtained from the same procedure as used in Example 1 , except that the platen roller made of the silicone rubber did not contain silicone oil.

[Example 4]

A label sheet was obtained from the same procedure as used in Example 2 , except that the platen roller made of the silicone rubber did not contain silicone oil.

[Evaluation Test]

When the label sheets of Examples 1 - 4 were produced, the following characteristics were checked.

(1) Unwinding and transportation

Unwinding and transportation of the linerless printing sheets were checked in a continuous printing operation and a resumed printing operation after halting for five hours.

(2) Durability

A continuous printing for four hours was performed twice in a day. This operation cycle was repeated for 30 days to check durability.

Results of the above tests are summarized in the following table.

[Another Embodiment of the Transporting Means (part 1) ]

Next, another embodiment of the transporting roller serving as the transportingmeans will be described. Aprinting apparatus has a configuration essentially the same as shown in Fig. 1 and Fig.3. The transporting roller includes, as shown in Fig.1, a supporting shaft 20, around which a roller portion 21 is provided.

The transporting roller can be of any rolling mechanism as appropriate. For example, the roller portion may be fixed around the supporting shaft, to rotate together with the supporting shaft, or the roller portion may be supported around the supporting shaft via bearings for example, to rotate relatively to the supporting shaft. Further, the supporting shaft canbe a reservoir of a silicone oil, to supply or replenish the oil to the silicone rubber layer. In this case, the supply of the silicone oil via the supporting shaft can prolong the effect of reduced adhesion. If the supporting shaft allows replenishing of the silicone oil, then the effect of reduced adhesion can be maintained even for much longer period of time.Because the replenishing of the silicone oil can be repeated.

The above-described, silicone-oil replenishable shaft can have such a structure that the supporting shaft has an inner space capable of holding the silicone oil, and the shaft is provided with a large number of communicating holes communicating between the inner space of the shaft and an outer surface of the shaft. The silicone oil is supplied from the inside of the supporting shaft to the outer surface of the shaft via the communicating holes. In this case, the roller portion should preferably be of the above-described construction, i.e. the roller portion should be fixed around the supporting shaft so as to rotate together with the supporting shaft, considering smooth supply of the silicone oil to the silicone rubber layer or the roller portion.

Therefore, the supporting shaft of the silicone-oil replenishable type can be made as appropriate, from a material that can provide the space as the reservoir of oil. Examples are sponge-like porous material and a pipe formed with a large number of through holes. In the present embodiment, the transporting roller (platen roller) 21 has its supporting shaft 20 , which is hollow like a pipe as shown Fig.3 , and the silicone oil can be stored in this hollow space.

Further, the outer surface of the supporting shaft is formed with a large number of communicating holes 20a communicating with the hollow space, enabling the silicone oil stored in the space to be supplied to the outer surface of the shaft via these holes. With this arrangement, the silicone oil supplied on the outer surface of the shaft permeates and dissipates into the roller portion which is provided around the outer circumference of the shaft and made of a silicone rubber, and then is supplied to the outer surface of the roller portion. Further, the supporting shaft 20 has a threaded open end 21b, to which a threadedplug canbe attached. Theplug canbe removed to replenish the silicone oil, and then be reattached to close the reservoir.

In the above, size of the holes and density at which the communicationholes are formedto communicatebetween the inside and the outer surface of the supporting shaft can be determined as appropriate in accordance with a supply speed as a function of kinematic viscosity of the silicone oil. In general however, a circular hole having a diameter of 0.2 to 5 mm is preferable in consideration of smooth supply of the oil.

Further, in the case of the silicone-oil replenishable shaft, the silicone rubber that forms at least the roller outer surface will eventually receive and contain the silicone oil as a result of oil supply from the supporting shaft even if the rubber does not contain the oil initially. However, when considering smooth supply of the oil to the outer surface of the roller, it is preferable that the roller portion is formed initially of the silicone rubber containing a silicone oil . The oil impregnatedinthe silicone rubber andthe silicone oil filled in the supporting shaft may be the same oil, or these oils may be different in molecular structure, kinematic viscosity, and so on.

Further, other portions such as a guide for the linerless printing sheet and other portions of the transporting means, orthe entire transportingmeansmayalsobe formedof the silicone rubber impregnated with the silicone oil or otherwise so as to provide appropriate reduction of the bonding strength. In this case, like the silicone-oil replenishable supporting shaft in the transporting roller, means for replenishing the silicone oil to the silicone rubber layer may be incorporated as appropriate.

In the apparatus shown in Fig. 4 described earlier, the platen roller 66 has a construction similar to that of the transporting roller 21. Specifically, the supporting shaft 60 is the silicone-oil replenishable type, to which a rollerportion made of a silicone rubber is provided. Auxiliary rollers 62 disposed upstream of the platen roller facilitate unwinding of the roli. For this purpose, the roller that makes contact with the adhesive layer of the linerless printing sheet has an outer surface provided with a silicone rubber layer.

The silicone rubber impregnated with the silicone oil as described above may eventually lose enough amount of silicone oil, to make printing operation instable. In such a case, the silicone oil may be applied to the rubber, or the rubber may be soaked into a bath of silicone oil, thereby allowing the silicone oil re-impregnated into the silicone rubber appropriately. If the transporting roller is the silicone-oil replenishable type, then the recovery may also be accomplished by replenishing the supporting shaft with the silicone oil. Therefore, according to the present invention, the bonding strength reducing function of the silicone-oil containing silicon rubber can be made permanent by using an appropriate maintenance method.

[Embodiments] [Example 1]

A low-density polyethylene of a viscosity average molecular weight of 300,000 was mixed with 0.4 weight percent of antioxidant, and extrusion-laminated on an upper surface of a wood-free paper having a basis weight of 80 g/m² to form a printing layer having a thickness of 18 μm. An emulsion adhesive made of butyl acrylate acrylic acid copolymer was applied uniformly to the back surface of the paper to form an acrylic adhesive layer having a thickness of 25 μm, and a linerless printing sheet was obtained. This sheet was wound into a roll, allowing the adhesive layer to adhere to the upper surface of the print backing material. The thermo fusion transfer printer shown in Fig. 4 was loaded with a commonly available thermo fusion ink ribbon. The roll obtained in the above was also loaded into the printer, and printing was made by thermally transferring the ink onto the upper surface of the print backing material. A label sheet was obtained. The thermo fusion transfer printer was provided with the platen roller 66 including the supporting shaft formed with communicating holes of 1 mm diameter at a density of 200 holesper 100 cm² surface area. To this shaft, there was provided a roller portion made of a silicone rubber containing 10 weight percent of polydimethylsiloxane (a silicone oil) having a kinematic viscosity at 25°C of 1000 mm²/s. The inside hollow space of the supporting shaft was filled with the same silicone oil and the plug was attached to seal.

[Example 2]

A label sheet was obtained from the same procedure as used in Example 1, except that the adhesive layer of the linerless printing sheet used was formed with a natural rubber adhesive.

[Example 3]

A label sheet was obtained from the same procedure as used in Example 1, except that the supporting shaft of the platen roller was not loaded with silicone oil. [Example 4]

A label sheet was obtained from the same procedure as used in Example 2 , except that the supporting shaft of the platen roller was not loaded with silicone oil.

[Example 5]

A label sheet was obtained from the same procedure as used in Example 1, except that of the platen roller had its roller portion made of the silicone rubber not containing the silicone oil and the supporting shaft was not loaded with silicone oil .

[Example 6]

A label sheet was obtained from the same procedure as used in Example 2, except that of the platen roller had its roller portion made of the silicone rubber not containing the silicone oil and the supporting shaft was not loaded with silicone oil.

[Evaluation Test]

When the label sheets of Examples 1 to 6 were produced, the following characteristics were checked.

(1) Unwinding and transportation

Unwinding and transportation of the linerless printing sheets were checked in a continuous printing operation and a resumed printing operation after halting for five hours. .

(2) Durability A continuous printing for four hours was performed twice in a day. This operation cycle was repeated for 30 days, 60 days or 100 days to check durability.

Results of the above tests are summarized in the following table.

[Another Embodiment of the Transporting Means (part 2) ]

The supportingrollerhas at least its outer surface formed ofa silicone rubbercontaininga silicone oil, andthe supporting shaft is symmetric, with two end portions having a smaller diameter and an intermediate portion having a greater diameter. According to the apparatus disclosed in Fig. 1, a platen roller 21 serves as the transporting means that makes contact with an adhesive layer 12 provided on a back surface of a print backing material 11. Therefore, the platen roller 21 has at least its outer surface formed of a silicone rubber containing a silicone oil, and further, a supporting shaft 20 is symmetric, with two end portions having a smaller diameter and an intermediate portion having a greater diameter. This prevents suchproblems as that the platen roller 21 adheres to the adhesive layer too strongly to become unable to transport, and that the transportation is made in a snaky pattern.

As described above, the supporting shaft of the transporting roller is symmetric, with two end portions having a smaller diameter and an intermediate portion having a greater diameter. This arrangement prevents the snaky transportation even if the thickness of the linerless printing sheet is not constant over the entire width of the sheet. Further, the snaky transportation is also prevented even if a pressure between a thermal head andtheplaten roller is not constant over the entire width of the sheet. In addition, this also prevents the problem that the ink ribbon wrinkles on the platen roller resulting in poor-quality printing.

Figs . 5 (a) to (g) show examples of the symmetric pattern of the supporting shaft, in which two endportions have a smaller diameter and an intermediate portion having a greater diameter. As exemplified in the figure, the symmetric pattern of the supporting shaft 20 can be varied as appropriate. For example, in patterns (a) and (b) , the diameter increases linearly from each end or intermediate point toward the center. In patterns (c) and (d) , the diameter at a center portion is constant over a predetermined width. In pattern (e) , the diameter of the center portion only is enlarged but to a constant value over a predetermined width. In patterns (f) and (g) , the diameter increases in a curved pattern from each end toward the center. The pattern (c) is more preferable in preventing the snaky transportation and poor printing.

In the apparatus shown in Fig. 1, auxiliary rollers 32, 33 in the successive transportation mechanism can also make contact with the adhesive layer 12 of the linerless printing sheet. In such a case , atleastthe outer surface of the auxiliary rollerthatcontacts the adhesive layermaybe formedofa silicone rubber containing a silicon oil . Further, the supporting shaft of the auxiliary roller may be made symmetric, with two end portions having a smaller diameter and an intermediate portion having a greater diameter, in order to prevent the snaky transportation. According to the successive transportation mechanism 3 illustrated in Fig. 1, the auxiliary roller 32 on the side to contact the adhesive layer 12 is made similarly to the transportingroller 21. Inotherwords , the supportingshaft is symmetric, with two end portions having a smaller diameter and an intermediate portion having a greater diameter, and the rollerportion is made of a silicone rubber containing a silicone oil.

In the apparatus shown in Fig. 3 described earlier, the platen roller 66 is formed similarly to the above-described transporting roller 21. Specifically, the supporting shaft 60 is symmetric, with two end portions having a smaller diameter and an intermediate portion having a greater diameter, and the roller portion is made of a silicone rubber containing a silicon oil.

[Embodiments] [Example 1]

A low-density polyethylene of a viscosity average molecular weight of 300,000 was mixed with 0.4 weight percent of antioxidant, and extrusion-laminated on an upper surface of a wood-free paper having a basis weight of 80 g/m² to form a printing layer having a thickness of 18 μm. An emulsion adhesive made of butyl acrylate acrylic acid copolymer was applied uniformly to the back surface of the paper to form an acrylic adhesive layer having a thickness of 25 μm, and a linerless printing sheet was obtained. This sheet was wound into a roll, allowing the adhesive layer to adhere to the upper surface of the print backing material.

The thermo fusion transfer printer shown in Fig. 3 was loaded with a commonly available thermo fusion ink ribbon. The roll obtained in the above was also loaded into the printer, and printing was made by thermally transferring the ink onto the upper surface of the print backing material . A label sheet was obtained. The thermo fusion transfer printer was provided with the platen roller 66 including a symmetric supporting shaft similar to that shown in Fig.5 (c) , with two end portions having a smaller diameter and an intermediate portion having a greater diameter. To this shaft, there was provided a roller portion made of a silicone rubber containing 10 weight percent of polydimethylsiloxane (a silicone oil) having a kinematic viscosity at 25°C of 1000 mm/s.

[Example 2]

A label sheet was obtained from the same procedure as used in Example 1, except that the adhesive layer of the linerless printing sheet used was formed with a natural rubber adhesive in place of acrylic adhesive, and the platen roller supporting shaft was similar to that shown in Fig. 5(f).

[Comparative Example 1]

A label sheet was obtained from the same procedure as used in Example 1 , except that the supporting shaft of the platen roller was a straight bar of a constant diameter.

[Comparative Example 2]

A label sheet was obtained from the same procedure as used in Example 2, except that the supporting shaft of the platen roller was a straight bar of a constant diameter.

[Evaluation Test]

When the label sheets of the examples and the comparative examples were produced, transportation stability was checked. Evaluation test procedure was as follows : A continuous printing for four hours was performed twice in a day, first in the morning andsecondin the afternoo , each at a ixed time. This operation cycle was repeated for 30 days , and observation was made if there is snaky transportation or ink ribbon entanglement resulting in poor quality printing.

Results of the above tests are summarized in the following table.

In the above, none of the Examples showed poor printing quality due to other causes, e.g. resumed printing operation.

[Another Embodiment of the Transporting Means (part 3) ]

Next, another embodiment of the transporting roller serving as the transportingmeans will be described. Aprinting apparatus has a configuration essentially the same as shown in Fig. 1 and Fig. 3. The transporting roller includes, as shown in Fig. 1, a supporting shaft 20, around which a roller portion 21 is provided.

In the apparatus shown in Fig. 1, the platen roller has at least its outer surface formed of a silicone rubber and made rugged. This platen roller 21 serves as the transporting means that makes contact with an adhesive layer 12. While being unwound and transported, the print backing material 11 has its upper surface receive ink information 26 providedby theprinting device 2.

The platen roller 21 may entirely be made of the silicone rubber, or only the surface portion may be formed of the silicone rubber. In any case, it is important that the surface portion is formed with a rugged pattern.

Further, the successive transportation mechanism 3 can also include a roller that makes contact with the adhesive layer 12 of the linerless printing sheet 1. In such a case, at least the outer surface of the roller that makes contact with the adhesive layer 12 is formed of a silicone rubber andmade rugged. According to the successive transportation mechanism 3 illustrated in Fig. 1, the roller 32 (the lower roller in Fig. 1) on the side to contact the adhesive layer 12 at least has its outer surface formed of a silicone rubber and made rugged.

According to the present invention, the platen roller 21 as the transporting means that makes contact with the adhesive layer 12 of the linerless printing sheet 1 has at least its outer surface formed of a silicone rubber andmade rugged. Preferably however, other transporting rollers and guiding members (such as a guide) other than the platen roller 21 should also be formed of the silicone rubber and made rugged. In this case, in consideration of roller service life and other issues related with abrasion of the silicone rubber layer, it is preferable that the silicone rubber layer should have a thickness not smaller than 0.1 mm, ormore preferably not smaller than 0.5 mm, and most preferably not smaller than 1 mm. Alternatively, this portion may entirely be made of the silicone rubber for example.

[Rugged Pattern]

Fig.6 shows sections of the silicone rubber rollers that have the outer surface made rugged. As shown in Fig. 6, the rugged pattern is preferably one as expressed by the following two expressions (1) and (2) : 100a > b > 0.5a ... (1) c > b > 0.5c ... (2) (where a represents "a" depth of a groove, ^wb^w represents a width of the groove and ^Λc" represents a pitch of the groove.)

In the expression (1) , if b" is greater than 100a, the adhesive layer 12 adheres to the trough portion of the groove, interfering with unwinding and transporting operation. On the other hand, if ^wb" is smaller than 0.5a, the adhesive fills and clogs the trough portion of the groove, again interfering with unwinding and transporting operation.

In the expression (2) , it is physically impossible that "b" is greater than V. On the other hand, if b" is smaller than 0.5c, the flat area provided by the ridge portion of the groove becomes dominant (See Fig. 6(B)) , (i.e. similar to the state where there is no trough provided) , causing interference with unwinding and transporting operation.

The rugged pattern can be many. In Fig. 6 (A) , the trough portion has a circular (or oval,egg-shape) section, whereas in Fig. 6(B) , the section is triangular. However, the pattern of the section is not limited to any specific pattern.

Fig. 7 shows a development as obtained by developing the silicon rubber, showing the surface pattern. The x axis denotes the roller longitudinal direction, whereas the y axis denotes the roller circumferential direction. Fig. 7(A) shows a direction (in which the rugged groove pattern is formed) , that is slanted from the x axis by an angle θ. The section shown in Fig. 6 is a section taken along a line perpendicular to the above-described direction. A preferable range of the angle θ is θ=45° to 135°. If θ is 135°, the direction of rugged groove pattern formation is symmetric of the direction shown in Fig. 6 (A) with respect to the y axis .

The rugged groove pattern may be formed not only in one direction but also in two directions as shown in Fig. 6(B) or in more directions.

A preferable diameter of the silicone rubber roller is not smaller than 8 mmφ and not greater than 50 mmφ.

It should be noted here that bonding strength between the surface of the adhesive layer 12 and the rugged surface of the silicone rubber can be determined as appropriate , in accordance with such a factor of consideration as balance between bonding strength to the transporting means (the roller) and bonding strength to an intended object to which the printed labeled is to stick. In general, in consideration of such a factor as automatic transportability of the linerless printing sheet 1 in a thermal transfer printer for example, a preferable bonding strength is not greater than 98 mN/50 mm, more preferably not greater than 9.8 mN/50 mm, and most preferably 0.98 mN/50mm, based on a 180-degree peeling adhesion (at 300 mm/min. peeling speed) to the rugged surface of silicone rubber.

[Embodiment] [Example 1]

The thermo fusion transfer printer shown in Fig. 3 was loaded with a commonly available thermo fusion ink sheet. The roll obtained in the above was also loaded into the printer, and printing was made by thermally transferring the ink onto the upper surface of the print backing material. A label sheet was obtained. The thermo fusion transfer printer was provided with a platen roller 66 made of a silicon rubber having a rugged outer surface, with a = 40 μm, b = 1500 μm and c = 1500 μm.

[Example 2]

[Example 3]

A label sheet was obtained from the same procedure as used in Example 1 , except that the platen roller made of the silicone rubber had no rugged pattern on the outer surface.

[Example 4]

A label sheet was obtained from the same procedure as used in Example 2 , except that the platen roller made of the silicone rubber had no rugged pattern on the outer surface. [Evaluation Test]

(1) Unwinding and transportation

(2) Durability

Results of the above tests are summarized in the following table.

[Another Embodiment of the Transporting Means]

According to the present embodiment, rollers (platen roller and so on) are used as the transporting means. This is not limiting however. The present invention is also applicable to other transporting means such as a belt.

Any of the configurations disclosed in each of the claims of the present invention can be arbitrary combined, for implementation, with any of the configurations disclosed in the embodiments of the present invention, within a reasonable range of scope.

Claims

CLAIMS We claim:

1. A printing apparatus for a linerless printing sheet comprising: a printing device for forming ink information on an upper surface of the linerlessprinting sheet includingaprintbacking material having a back surface provided with an adhesive layer; and a transporting means for unwinding and transporting said sheet from a roll of the sheet; said printing device forming said ink information while said transporting means is transporting said sheet; wherein said transporting means transports said sheet while keeping contact with said adhesive layer, and has at least its outer surface formed of a silicone rubber containing a silicone oil.

2. The printing apparatus for a linerless printing sheet according to Claim 1, wherein said silicon oil has a kinematic viscosity of 30 to 100000 mm²/s (25°C) .

3. A printing apparatus for a linerless printing sheet, comprising: a printing device for forming ink information on an upper surface of the linerlessprinting sheet includingaprintbacking material having a back surface provided with an adhesive layer; and a transporting means for unwinding and transporting said sheet from a roll of the sheet; said printing device forming said ink information while said transporting means is transporting said sheet; wherein: said transporting means includes a transporting roller transporting said sheet while keeping contact with said adhesive layer, said transporting roller including a roller portion having at least its outer surface formed of a silicone rubberandprovidedaroundan outer circumference of a supporting shaft; said supporting shaft being provided with a plurality of communicating holes communicating between an inside of the shaft and an outer surface of the shaft; the inside of said shaft holding a silicone oil; the oil being supplied from the inside of said supporting shaft to the outer surface of said shaft via said communicating holes .

4. The printing apparatus for a linerless printing sheet according to Claim 3, wherein said silicon oil has a kinematic viscosity of 30 to 100000 mm²/s (25°C) .

5. The printing apparatus for a linerless printing sheet according to Claim 3, wherein said supporting shaft is symmetric, with two end portions having a smaller diameter and an intermediate portion having a greater diameter.

6. A printing apparatus for a linerless printing sheet, comprising: a printing device for forming ink information on an upper surface of the linerless printing sheet including aprintbacking material having a back surface provided with an adhesive layer; and a transporting means for unwinding and transporting said sheet from a roll of the sheet; said printing device forming said ink information while said transporting means is transporting said sheet; wherein: said transporting means includes a transporting roller transporting said sheet while keeping contact with said adhesive layer, said transporting roller including a roller portion having at least its outer surface formed of a silicone rubber andprovidedaroundan outer circumference of a supporting shaft; said supporting shaft being symmetric, with two end portions having a smaller diameter and an intermediate portion having a greater diameter.

7. A printing apparatus for a linerless printing sheet, comprising: a printing device for forming ink information on an upper surface of the linerless printing sheet includingaprintbacking material having a back surface provided with an adhesive layer; and a transporting means for unwinding and transporting said sheet from a roll of the sheet; said printing device forming said ink information while said transporting means is transporting said sheet; wherein said transporting means includes a transporting roller transporting said sheet while keeping contact with said adhesive layer, saidtransportingroller includinga rollerportionhaving atleast its outer surface formedofa silicone rubberandprovided around an outer circumference of a supporting shaft, said roller having at least its surface impregnated with a silicone oil and at least said surface of said roller being made rugged.

8. The printing apparatus for a linerless printing sheet according to Claim 1, wherein said printing device uses a printing method selectedfroma group consisting of thermo fusion transfermethod, thermo sublimation transfer method, inkjet method and thermo sensitive method.

9. A printing apparatus for a linerless printing sheet comprising: a printing device for forming ink information on an upper surface of a linerless printing sheet made of a print backing material having a back surface provided with an adhesive layer; and transporting means for unwinding and transporting said sheet from a roll of the sheet; said printing device forming said ink information while said transporting means is transporting said sheet; wherein said transporting means transports said sheet while keeping contact with said adhesive layer, and has at least its surface formed of a silicone rubber and made rugged.

10. Theprinting apparatus for a linerless printing sheet according to Claim 9, wherein said rugged pattern is expressed by the following two expressions (1) and (2) : 100a > b > 0.5a ... (1) c > b ≥ 0.5c ... (2) (where ^wa" represents a depth of a groove, ^wb" represents a width of the groove and ^wc^w represents a pitch of the groove.)

11. Theprintingapparatus for a linerless printing sheet according to Claim 10, wherein a" has a value 10 to 1000 μm, "b" having a value 500 to 3000 μm, and "b" = ^wc^w.

12. Theprintingapparatus for a linerless printing sheet according to Claim 9, wherein said printing device uses a printing method selectedfroma group consistingof thermo fusion transfermethod, thermo sublimation transfer method, inkjet method and thermo sensitive method.

13. A method for printing on a linerless printing sheet comprising: a printing step for forming ink information on an upper surface of the linerlessprinting sheet includingaprintbacking material having a back surface provided with an adhesive layer; and a transporting step of unwinding and transporting said sheet from a roll of the sheet; saidprinting step for forming said ink information during said transportation of said sheet by said transporting means; whereinthe transportingmeans transports saidsheetwhile keeping contact with said adhesive layer in said transporting step, and at least has its outer surface formed of a silicone rubber containing a silicone oil.

14. Themethod forprinting on a linerless printing sheet according to Claim 13, wherein the silicon oil has a kinematic viscosity of 30 to 100000 mm²/s at 25°C.