LIQUID-REPELLENT PLASTIC MOLDED BODY AND METHOD FOR PRODUCING THE SAME

A liquid-repellent plastic molded body 1 according to the present invention has a liquid-repellent surface. The liquid-repellent surface has a re-entrant structure surface formed by an array of pillars 20 each having a head portion 20a with an enlarged diameter. At least a part of the re-entrant structure surface has a fluorine-containing surface in which fluorine atoms are distributed.

TECHNICAL FIELD

The present invention relates to a plastic molded body having a surface excellent in liquid repellency and a method for producing the same.

BACKGROUND ART

Plastics, which are usually easier to mold than glass, metals and the like, can be molded easily into various shapes, and thus they are used in various applications. Among them, the field of packaging containers such as a pouched container and a bottle is a typical field of plastics applications.

Meanwhile, in a case where a container as mentioned above contains a viscous fluid, it is required to have dischargeability. More specifically, the container to contain a viscous fluid needs to allow the contents to be discharged rapidly and completely with nothing adhering and remaining inside the container.

In order to enhance dischargeability with respect to a viscous fluid, a plastic surface forming an inner surface of the container is imparted with higher liquid repellency to the contents so as to improve lubricity to the contents.

For this purpose, it is known to form ruggedness on the surface.

Forming ruggedness on the surface is a way to physically impart liquid repellency by means of the surface shape. More specifically, when a liquid flows on the rugged surface, air pockets are formed in recessed portions, allowing solid-liquid contact and gas-liquid contact to be made between the rugged surface and the liquid. Since gas (air) is the most hydrophobic substance, remarkably high liquid repellency is achieved by appropriately setting the density of the ruggedness. With this technique, however, as the liquid flows repeatedly on the rugged surface, the liquid gradually accumulates in the recessed portions, so that the air pockets are gradually lost. As a result, liquid repellency is gradually decreased.

The applicant of the present application proposes in Patent document 1 a plastic molded body that suppresses time degradation of liquid repellency when achieving liquid repellency by means of a rugged surface. In this document, the plastic molded body has a fractal hierarchical rugged surface structure in which primary ruggedness is formed on the surface, and fine secondary ruggedness is formed in at least a part of the primary ruggedness.

In this molded body, since the additional fine secondary ruggedness is formed in a region of the primary ruggedness, the entrance of liquid into the primary ruggedness is effectively suppressed, and thus liquid repellency by means of the primary ruggedness is stably maintained.

However, even with this technique, there is a limit in suppressing a decrease in liquid draining property and liquid falling property. In other words, it is impossible to completely prevent the entrance of liquid into the secondary ruggedness, and there is a gradual decrease in liquid repellency by means of the air pockets formed in the secondary ruggedness, which gradually causes the liquid to enter the primary ruggedness. As a result, time degradation of liquid repellency is inevitable.

The present applicant also proposes in Patent document 2 a technique in which, in a molded body with a fractal rugged surface structure (rough surface) as described above, the rough surface is subjected to a fluorine plasma treatment, thereby incorporating fluorine atoms into a resin forming the surface.

This technique is a way to chemically improve liquid repellency of the rugged surface by distributing fluorine atoms on the surface. This considerably improves a decrease in liquid repellency after a liquid flows repeatedly on the rugged surface. Moreover, since fluorine atoms are distributed on the surface by a fluorine plasma treatment, there is no possibility that a film of the fluorine atoms peels off from the surface to cause a decrease in liquid repellency of the surface.

However, although this technique is favorable, for example, to impart liquid repellency to an opening of a container to prevent liquid dripping, sufficient liquid repellency may not be obtained when a viscous fluid is in constant contact with the liquid-repellent surface. Thus, further improvement is required.

Further, Patent document 3, which discloses a nozzle plate for an ink jet head having a re-entrant structure, describes that the nozzle plate having this structure exhibits excellent liquid repellency and effectively prevents ink contamination of the nozzle head.

However, this re-entrant structure is produced through an extremely complicated process as follows: forming a mask material on a predetermined surface portion of the nozzle plate by photolithography; forming, by etching with a dry etching device, recessed portions that form the re-entrant structure; and removing the mask material. Though this technique is applicable to a nozzle plate for an ink jet head made of silicone or the like, it is totally inapplicable to the field of packaging materials in terms of cost, productivity and the like. Moreover, Patent document 3 gives no consideration to, for example, the life of liquid repellency in a state where a viscous liquid is in constant contact.

PRIOR ART DOCUMENTS

Patent Documents

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

Therefore, an object of the present invention is to provide a liquid-repellent plastic molded body that maintains excellent liquid repellency for a long period even in a case where a liquid, especially a viscous fluid, is kept in constant contact, and that can be produced by a method applicable also to the field of packaging materials, and a method for producing the same.

Means for Solving the Problems

The present invention provides a liquid-repellent plastic molded body having a liquid-repellent surface. The liquid-repellent surface has a re-entrant structure surface formed by an array of pillars each having a head portion with an enlarged diameter, and at least a part of the re-entrant structure surface has a fluorine-containing surface in which fluorine atoms are distributed.

According to the liquid-repellent plastic molded body of the present invention, it is preferable that:(1) the fluorine-containing surfaces is a fluorine plasma-treated surface; and(2) the liquid-repellent plastic molded body has a film form.

In particular, the liquid-repellent plastic molded body in a film form is formed into a pouched container.

Further, the present invention provides a method (a transfer method 1 or a reflow method) for producing a liquid-repellent plastic molded body. The method includes the steps of:preparing a plastic molded body molded into a predetermined shape and a transfer mold having, as a transfer surface, a rugged surface formed by an array of straight body-shaped protruded columnar portions;transferring the rugged transfer surface of the transfer mold, which is made to face a surface of the plastic molded body, to the surface of the plastic molded body so as to form a precursor of a re-entrant structure surface;deforming the precursor into a re-entrant structure surface by heating and/or pressurizing pillars distributed on the precursor formed by transfer so as to enlarge a diameter of a top portion of each of the pillars; anddistributing fluorine atoms to at least a part of the re-entrant structure surface.

The present invention also provides a method (a transfer method 2) for producing a liquid-repellent plastic molded body. The method includes the steps of:preparing a plastic molded body molded into a predetermined shape and a transfer mold having a rugged transfer surface for forming a rugged re-entrant structure surface by transfer;transferring the rugged transfer surface of the transfer mold, which is made to face a surface of the plastic molded body, to the surface of the plastic molded body so as to form a re-entrant structure surface on the surface of the plastic molded body; anddistributing fluorine atoms to at least a part of the re-entrant structure surface.

According to the above-described two methods, which are referred to as a transfer method, it is preferable that:(1) in the step of distributing fluorine atoms, the surface of the plastic molded body is formed of a resin that contains a fluorine-containing compound, and when the fluorine-containing compound bleeds out, the fluorine atoms are distributed on the surface; or(2) in the step of distributing fluorine atoms, at least a part of the re-entrant structure surface is subjected to a fluorine plasma treatment, so that the fluorine atoms are distributed on the surface.

Furthermore, the present invention provides a method for producing a liquid-repellent plastic molded body. The method includes the steps of:preparing a plastic molded body molded into a predetermined shape and a plastic columnar body having an end surface with an enlarged diameter;forming a re-entrant structure surface by joining a plurality of the plastic columnar bodies to a surface of the plastic molded body; anddistributing fluorine atoms to at least a part of the re-entrant structure surface.

This method is referred to as a joining method, in which the columnar bodies of a predetermined shape are joined to the surface of the plastic molded body, thereby forming the re-entrant structure. According to the joining method,(1) in the step of forming a re-entrant structure surface, the plastic columnar bodies are joined to the surface of the plastic molded body by electrostatic flocking (which is referred to as an electrostatic flocking method), or(2) in the step of forming a re-entrant structure surface, the plastic columnar bodies are joined to the surface of the plastic molded body by thermally spraying the plastic columnar bodies on the surface of the plastic molded body (which is referred to as a thermal spraying method).

According to the electrostatic flocking method or the thermal spraying method, it is preferable that:(a) in the step of distributing fluorine atoms, at least a part of the re-entrant structure surface is formed of a resin that contains a fluorine-containing compound, and when the fluorine-containing compound bleeds out, the fluorine atoms are distributed on the surface; or(b) in the step of distributing fluorine atoms, at least a part of the re-entrant structure surface is subjected to a fluorine plasma treatment, so that the fluorine atoms are distributed on the surface.

Effects of the Invention

According to the liquid-repellent plastic molded body of the present invention, the pillars each having a top portion with an enlarged diameter are arrayed on its surface. The array of the pillars forms the re-entrant structure. Namely, each recessed portion formed between the pillars is narrowed at its top. In the present invention, this re-entrant structure makes it difficult for a liquid flowing on its surface to enter the recessed portion, maintaining the so-called stability of the Cassie mode, thereby achieving stable liquid repellency. Especially importantly, since fluorine atoms are distributed on the surface, liquid repellency is maintained stably for a remarkably long period even in a case where the liquid is kept in constant contact.

Further, since this liquid-repellent plastic molded body can be produced continuously without, for example, directly etching the surface of the molded body, there is an advantage in that it is cheap to produce and has high productivity.

Accordingly, the liquid-repellent plastic molded body of the present invention is applied preferably to the field of packaging (especially, containers) in which a liquid is to be kept in constant contact. For example, in a case where the present invention is used as a pouched container to contain a viscous fluid (e.g., having a viscosity of 250 mPa·s or more at 25° C.) such as a curry, the contents can be discharged rapidly with nothing adhering and remaining inside even after a lapse of as long as six months to one year after production.

MODE FOR CARRYING OUT THE INVENTION

A description will be given of the principle of liquid repellency by means of a rough surface (rugged surface) with reference toFIG. 1. In the Cassie mode in which a liquid droplet is placed on a rough surface100, recessed portions in the rough surface100serve as air pockets, allowing the liquid droplet to be in composite contact with a solid and a gas (air). It is known that the composite contact achieves high liquid repellency because the liquid droplet has a small radius R on a contact interface, and the liquid is in contact with air as the most hydrophobic substance. Specifically, an apparent contract angle θ* is close to 180°.

On the other hand, in a case where the liquid droplet enters the recessed portions in the rough surface100, which is shown as the Wenzel mode, the liquid droplet is not in composite contact but in contact only with the solid. In the Wenzel mode, the liquid droplet has a large contact radius R on the contact interface, and the apparent contract angle θ* is similarly close to 180°. It is known that liquid repellency is exhibited also in this case.

As described above, it is known that liquid repellency is improved in either state of the Wenzel mode and the Cassie mode. However, in order to enhance liquid repellency, it is considered to be necessary that the Cassie mode, instead of the

Wenzel mode, be maintained stably (the air pockets in the recessed portions be maintained stably). More specifically, in the Wenzel mode, since the interface between a liquid phase and a solid phase is larger, and thus a stronger adsorption power is applied physically to the interface, the liquid droplet does not fall easily while the contact angle is large enough to show liquid repellency. In the Cassie mode, since the interface is smaller, the liquid droplet only needs to overcome a low energy barrier to fall. Thus, it is considered that the liquid droplet falls easily and repeatedly.

In the present invention, in order to effectively maintain the contact of the liquid droplet in the Cassie mode, a re-entrant structure is formed on the surface100of a plastic molded body1.

The re-entrant structure has a configuration in which the top of the recessed portion in the rugged surface is narrower than the bottom thereof, so that the liquid droplet is prevented from easily entering the recessed portion. As a result, the Cassie mode is maintained stably for a long period.

A more specific description will be given with reference toFIGS. 2 and 3each showing a form of the rugged surface. Each of these figures is a schematic diagram showing the rugged surface (rough surface)100formed by an array of pillars (columnar bodies)10or20on a surface of the plastic molded body1.

InFIG. 2, straight body-shaped pillars (hereinafter, referred to as normal pillars)10are arrayed. The rugged surface100formed from this pattern, which is known conventionally, may be hereinafter referred to as a pillar structure.

On the other hand,FIGS. 3(a) and 3(b)shows the rugged surface100formed from a pattern of the re-entrant structure adopted in the present invention. According to this pattern, pillars (hereinafter, referred to as pinning pillars)20each having a head portion with an enlarged diameter are arrayed. Thus, a recessed portion100ahas a larger bottom and a narrower top. Namely, the re-entrant structure is formed.

FIG. 3(a)shows a typical re-entrant structure (hereinafter, may be referred to as a single re-entrant structure). In the pattern shown inFIG. 3(b), the circumferential rim of a head portion20aof each of the pinning pillars20is folded, so that a void20bis formed within the head portion20a. This pattern can be referred to as a double re-entrant structure.

In the pillar structure inFIG. 2, in a state where a liquid droplet is placed on the rugged surface100, a pressure Δp is applied due to the self-weight of the liquid droplet, disturbance, and the like. In a liquid-repellent state in which the liquid droplet forms a contact angle θE of more than 90° with a material of the rugged surface (inFIG. 2, θE=130°), a downwardly convex meniscus is formed by the surface tension of the liquid droplet (pinning effect), and thus the liquid droplet does not enter the recessed portion100a. However, in a lyophilic state in which the liquid droplet forms a contact angle θE of 90° or less, an upwardly convex meniscus is formed, and thus the liquid droplet enters the recessed portion100a.

On the other hand, in the re-entrant structure shown inFIGS. 3(a) and 3(b), even in the lyophilic state in which the liquid droplet forms a contact angle θE of 90° or less (inFIG. 3, θE=20°), a downwardly convex meniscus formed by the surface tension (pinning effect), allowing a capillary phenomenon to occur in an upward direction, and thus the liquid droplet does not enter the recessed portion100a.

In particular, in the double re-entrant structure inFIG. 3(b), the meniscus has a smaller curvature, allowing a stronger capillary phenomenon to occur in an upward direction. Even if a large pressure AP (>Op) is applied, the structure can support it, whereby excellent liquid repellency is maintained for a long time.

In the re-entrant structure inFIGS. 3(a) and 3(b)adopted in the present invention, in order to maintain liquid repellency for a long period by making sufficient use of the pinning effect, as well as to obtain initial liquid repellency, it is preferable that the pinning pillar20has a pitch p of about 100 nm to 500 μm, the recessed portion100ahas a depth d in a range of about 100 nm to 500 μm, and the head portion20aof the pinning pillar20has a flange width f1, a flange thickness e1, a second flange width f2, and a second flange thickness e2of about 10 nm to 10 μm.

Further, it is preferable that the rate φ of area per unit projected area occupied by the head portions20aof the pinning pillars20in the rugged surface100is in a range of 0.05 to 0.8.

As described above, the re-entrant structure shown inFIG. 3(a)or3(b) serves to maintain excellent liquid repellency for a long period even if a liquid is kept in constant contact with the rugged surface100. In the present invention, fluorine atoms are distributed on the rugged surface100, so that the effect of maintaining liquid repellency is enhanced further. The amount of fluorine atoms to be distributed depends on how to distribute them on the surface. In particular, when, at a top surface of the head portion20aof the pinning pillar20and a bottom surface of the recessed portion100a, the element ratio between fluorine atoms and carbon (F/C) is 40% or more, particularly in a range of 50% to 300%, it is possible to obtain super liquid repellency stably as described above without impairing surface strength. The element ratio can be calculated by analyzing the surface elemental composition with an X-ray photoelectron spectroscope device.

By distributing fluorine atoms, in a case, for example, where a viscous fluid such as a curry is in constant contact, liquid repellency as high as that in the initial state is maintained for about six months or more in the single re-entrant structure inFIG. 3(a), and for about almost one year in the double re-entrant structure inFIG. 3(b).

In the present invention, the plastic molded body1having the re-entrant structure as described above on its surface and the pinning pillar20may be formed of any plastics as long as they can be formed into a predetermined shape, such as a thermoplastic resin, a thermosetting resin and a photocurable resin. Depending on the intended use of the molded body1, a suitable resin may be selected, and a multilayerd structure may also be applicable.

In general, in the field of packaging materials, typical examples of a resin for the surface formation include olefin-based resins such as polyethylene, polypropylene and a copolymer of ethylene or propylene and another olefin, and polyesters such as polyethylene terephthalate (PET), polyethylene isophthalate and polyethylene naphthalate.

Further, the aforementioned resin may contain a bleeding-type fluorine-containing compound or the like so that fluorine atoms are distributed on the surface as will be described later.

Furthermore, depending on the intended use, a metallic foil such as an aluminum foil may be adhesion-fixed on a back face of the plastic molded body1, and only the pinning pillar20may be formed of another resin depending on the production method to be described later.

The liquid-repellent plastic molded body having the above-described re-entrant structure surface according to the present invention is produced mainly by a transfer method or a joining method.

1. Transfer method

The following transfer method can be referred to as a reflow method (transfer method 1). This method is performed through the processes shown inFIG. 4, and a process of preparing a transfer mold and a transfer process may be performed using the following known art or the like (see, for example, Keisuke Nagato et al.; J. Mat. Proc. Tech., 214, 2444-2449 (2014)).

First, the plastic molded body1molded into a predetermined shape and a transfer mold3for forming a surface of a precursor of the re-entrant structure are prepared.

The transfer mold3includes a laser light-transmissive transparent substrate5such as quartz glass and a transfer portion7formed on one surface of the substrate5. The transfer portion7is formed by evaporating a material with high laser absorption. For example, the transfer portion7is formed of an evaporated film of diamond-like carbon or the like. In the transfer portion7, holes7afor transferring straight body-shaped protruded columnar portions are arranged by the known technique of photography and dry etching, thereby forming a transfer surface for forming the precursor of the re-entrant structure.

If the surface itself of the transparent substrate5is used as a transfer surface, a laser is transmitted through the transparent plate. Accordingly, the material for the plastic molded body1is limited to a material with high laser absorption.

As shown inFIG. 4(a), the surface of the plastic molded body1is made to face the transfer surface of the transfer mold3as described above.

Next, as shown inFIG. 4(b), the plastic molded body1is subjected to a pressure P so as to be pressure-welded to the transfer surface, while a laser light is irradiated from the side of the transparent substrate5so as to locally heat the holes7aformed in the transfer surface, and the holes7aare pushed into the surface of the plastic molded body1. The laser light to be used may be any laser as long as it can heat the holes7ato a level that allows the pushing of the holes7a.

While the plastic molded body1is pressure-welded to the transfer surface as described above, the laser light irradiation position is scanned, so that spot heating and cooling is performed repeatedly. As a result, as shown inFIG. 4(c), the holes7aare pushed into the predetermined whole surface of the plastic molded body1.

By the spot heating, only the surface of the molded body1is subjected to heating and pushing. Thus, the entire molded body1is free from thermal deformation. In particular, even if the molded body1is a film-shaped non-rigid product, no wrinkle is produced due to thermal deformation.

Subsequently, the plastic molded body1is cooled in the state ofFIG. 4(c), and then detached from the transfer surface, whereby the precursor of the re-entrant structure surface having ruggedness reversed from that on the transfer surface is formed over the predetermined whole surface of the plastic molded body1.

On the thus-obtained precursor of the re-entrant structure surface, pencil-type pillars30each having a tapered tip as shown inFIG. 4(d)are arrayed.

In the reflow method, the top of the pillar30on the thus-obtained precursor of the re-entrant structure surface is heated and pressurized or heated under pressure, so that the top portion of the pillar30has an enlarged diameter. As a result, as shown inFIG. 4(e), the pinning pillar20having the head portion20awith an enlarged diameter is formed. An array of the thus-shaped pinning pillars20forms, for example, the above-described single re-entrant structure surface shown inFIG. 3(a).

Alternatively, the re-entrant structure surface may also be formed by using another transfer mold having a different form from the transfer mold3used in the reflow method.

This method is a normal transfer method (transfer method 2), in which the transfer mold3as described above allows the re-entrant structure surface to be formed directly on the surface of the plastic molded body1by transfer.

For example, as shown inFIG. 5, the transfer mold3to be used here includes the transparent substrate5and a transfer substrate9, which are connected to each other by a screw or the like. In the transfer substrate9, through holes9a,each having an enlarged-diameter width portion9bat its top, are arranged. In view of demolding property, the enlarged-diameter width portion9bhas a tapered surface such that the diameter becomes larger toward the top.

The transfer mold3is formed of the transfer substrate9and the transparent substrate5connected to each other such that the side of the enlarged-diameter width portion9bof the transfer substrate9faces the transparent substrate5. By arranging the through holes9a,each having the enlarged-diameter width portion9bat its top, the re-entrant structure surface can be formed directly on the surface of the plastic molded body1by transfer. Namely, as with the method described above, the plastic molded body1is put on the transfer mold3(transfer substrate9), subjected to pressure under laser light irradiation, and then detached, resulting in the plastic molded body1with the re-entrant structure surface transferred to its surface.

Alternatively, a heat sink substrate5may be prepared instead of the transparent substrate5. A coating material (such as a black coating material) that absorbs a heat beam source such as a halogen lamp and a laser is applied to the surface of the heat sink substrate5that does not face the transfer substrate9, or alternatively this surface is roughened, for example, so that a heat beam is highly absorbed. The transfer mold3is irradiated with a halogen lamp or a laser from the side of the heat sink substrate5so as to be heated. Thereafter, the plastic molded body1is put thereon, subjected to pressure, and then detached, resulting in the plastic molded body1with the re-entrant structure surface transferred to its surface.

The transfer substrate9having the through holes9acan be manufactured as follows. That is, each of the through holes9ais punched by a laser treatment or the like through a plate-like body made of a metal, a thermosetting resin, or the like, and the top of the through hole9ais chamfered with a cutter or the like.

The above-described transfer method (transfer method2) has an advantage in that the re-entrant structure surface can be formed directly without involving the precursor of the re-entrant structure surface. However, in view of demolding property, there is a limit on the size of the enlarged-diameter width portion9b.

In the above-described method, fluorine atoms are distributed on the surface of the re-entrant structure formed as described above.

As a means for distributing fluorine atoms, it is most preferable that a bleeding-type fluorine-containing compound is contained in the aforementioned resin for use in molding the plastic molded body1. That is, in the plastic molded body1molded using a resin that contains a fluorine-containing compound, the fluorine-containing compound bleeds out on the surface with time, so that fluorine atoms are distributed on the surface.

The amount of the fluorine-containing compound to be contained may be set so that the above-mentioned amount of fluorine atoms is distributed on the surface.

Examples of the fluorine-containing compound include a modified olefin-based resin having a fluorine-containing alkyl group, a silane coupling agent having a fluorine-containing alkyl group, a fluorine-containing surfactant, and the like. In particular, if an olefin-based resin is used as a resin for molding the plastic molded body1, the modified olefin-based resin is preferable.

As an example of the fluorine-containing modified olefin-based resin, a double-chain polymer having a fluoroalkyl group which is represented by the following formula is known (see, for example, Technology for Super Water and Oil Repellency by Tokuzo Kawase, Journal of the Japan Research Association for Textile End-uses, 55(6), 2014).

where n is an integer that represents the number of repeating units, and

Rf is a perfluorohexyl group (C6F13).

Other examples of the fluorine-containing compound include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene difluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesin (PFA), a tetrafluoroethylene-hexafluoropropylene copolymer (FEP), an ethylen-tetrafluoroethylen copolymer (ETFE), an ethylene-chlorotrifluoroethylene copolymer (ECTFE), and the like. In the present invention, in order to enable injection molding and achieve high liquid repellency, a fluorine-containing acrylic resin, a fluorine-containing silicone resin, and the like are preferable. An example of the fluorine-containing acrylic resin is represented by the following formula:

where Rf is a fluorine-containing alkyl group such as a perfluoroalkyl group, and

X is a hydrogen atom or an alkyl group such as a methyl group.

A polymer obtained by polymerizing this fluorine-containing acrylic resin is preferable.

Further, an example of the fluorine-containing silicone resin is polyorgano siloxane represented by the following formula:

where R is a hydrogen atom or an alkyl group such as a methyl group,

Rf is a fluorine-containing group such as a fluoroalkyl group, and

n is a number representing the degree of polymerization.

In the present invention, from a safety point of view, it is usually considered preferable that the fluorine-containing compound has a fluorine-containing group with a molecular weight less than that of a C8 telomer.

Further, fluorine atoms can also be distributed on the surface by subjecting the re-entrant structure surface to a fluorine plasma treatment.

The fluorine plasma treatment can be performed in a publicly known manner. For example, with the use of CF4gas, SiF4gas, or the like, the plastic molded body1with the re-entrant structure surface, which is placed between a pair of electrodes, is subjected to a high-frequency electric field, so that a plasma of fluorine atoms (atomic fluorine) is generated, and the plasma is allowed to collide with the re-entrant structure surface, whereby the fluorine atoms can be incorporated into molecular chains of a resin forming the re-entrant structure surface. Namely, the surface resin is vaporized or decomposed, while the fluorine atoms are incorporated at the same time.

The above-described transfer method is applied particularly preferably to the production of the liquid-repellent plastic molded body with the re-entrant structure surface shown inFIG. 3(a).

2. Joining Method

The above-described transfer method is to form the re-entrant structure surface by processing the surface of the plastic molded body1. On the other hand, the joining method is to externally join the pinning pillars20that form the re-entrant structure surface.

In order to perform this method, columnar bodies for forming the pinning pillars, as well as the above-described plastic molded body1, are prepared.

The columnar body to be used has a form as shown inFIG. 6. InFIG. 6, reference numeral40denotes the columnar body.

For example, a columnar body40shown inFIG. 6(a)is obtained by cutting plastic staple fiber. By cutting plastic staple fiber, both ends40ahave enlarged diameters, and one of the enlarged-diameter portions corresponds to the head portion20aof the pinning pillar20.

Similarly, the columnar body40having a form shown inFIG. 6(b)is obtained by cutting a twisted yarn made of plastic fiber. Also in this columnar body40, the ends40ahave enlarged diameters by the cutting, and the end40acorresponds to the head portion20aof the pinning pillar20. Since the columnar body40shown inFIG. 6(b)is obtained by cutting a twisted yarn, the end40ais folded. Thus, this columnar body40is used preferably particularly for forming the double re-entrant structure inFIG. 3(b).

The plastic fiber for forming the above-described columnar body40is of a resin material that is easily fusion-joined to the surface of the plastic molded body1. While a nylon material is usually used preferably in terms of cost and availability, the same resin material as that used for the surface of the plastic molded body1may be spun.

Further, the staple fiber and the twisted yarn to be used for forming the columnar body40may have any thickness and length as long as they correspond to the aforementioned pinning pillar20.

The above-described columnar body40can be joined externally to the surface of the plastic molded body1by electrostatic flocking or thermal spraying.FIGS. 7 and 8show respective joining methods.

InFIGS. 7 and 8, the plastic molded body1has a film shape.

Joining by Electrostatic Flocking:

In the method shown inFIG. 7, the plastic molded body1as a film is wound around a master roller51. When the film1passes through a conveyance path to be wound by a winding roller53, joining by electrostatic flocking is performed.

More specifically, a coating roller55, which is placed to face the master roller51, applies a heat seal lacquer to one surface (on which the re-entrant structure is to be formed) of the film1.

Further, between the master roller51and the winding roller53, a pair of electrodes57(an anode57aand a cathode57b) and an oven59are placed. The film1to which the heat seal lacquer has been applied passes between the pair of electrodes57, is heated by the oven59, and then is would by the winding roller53.

In the configuration as described above, the columnar bodies40for forming the aforementioned pinning pillars20are held on the cathode57b,and the film1moves along the anode57asuch that the surface on which the heat seal lacquer has been applied faces the cathode side. When the film1passes between the electrodes57in this manner, a DC voltage (usually, about 40 kV) is applied by a power source61, so that the columnar bodies40on the cathode57bfly along the electric field, and adhere vertically to the surface of the film1on which the heat seal lacquer has been applied. The film1on the surface of which the columnar bodies40adhere in this manner is heated in the oven59, so that the columnar bodies40are fixed firmly to the surface of the film1. As a result, the pinning pillars20are joined to the surface of the film1, thereby forming the re-entrant structure. Then, the film1is wound by the winding roller53to complete the external joining operation.

Joining by Thermal Spraying:

In the method shown inFIG. 8, the plastic molded body1as a film is wound around the master roller51. When the film1passes through a conveyance path to be wound by the winding roller53, the aforementioned columnar bodies40are thermally sprayed.

More specifically, thermal spraying equipment71and an anode73are placed so as to face each other with the conveyance path therebetween. The film1moves between the thermal spraying equipment71and the anode73such that one surface thereof is along the anode73.

The thermal spraying equipment71includes a metallic nozzle75having a straight cylindrical space inside, a spraying medium supply pipe77for supplying a spraying medium into the straight cylindrical space, and hot air supply pipes79for heating the spraying medium.

In the thermal spraying method, the aforementioned columnar bodies40are used as the spraying medium. The heated columnar bodies40are sprayed on the surface of the film1that passes on the cathode73, so that the columnar bodies40are joined to the surface of the film1. As a result, the re-entrant structure surface on which the pinning pillars20are arrayed is formed.

For example, the spraying medium supply pipe77of the thermal spraying equipment71is supplied with the aforementioned columnar bodies40. The hot air supply pipes79supply hot air for heating the columnar bodies40as the spraying medium. The temperature of the hot air is set so that the columnar bodies40sprayed on the surface of the film1are heated to be fusion-joined on the surface of the film1with their forms maintained. The temperature differs depending on the material of the columnar bodies40. Specifically, in case of the columnar bodies40made of polyethylene, the temperature is set so that it is about 400° C. to 500° C. just above the surface of the film1.

As shown inFIG. 8, the spraying medium supply pipe77extends straight to the center of the nozzle75so that the columnar bodies40are sprayed on the surface of the film1assuming a certain direction. A plurality of the hot air supply pipes79are provided inclined so as to surround the spraying medium supply pipe77, thereby heating the columnar bodies40uniformly.

When the columnar bodies40heated by hot air are sprayed in the above-described manner, a voltage (usually, about 40 kV) is applied between the anode73and the nozzle75by a power source81. This allows the heated columnar bodies40to be sprayed along the electric field vertically to the surface of the film1on the anode73.

The heated columnar bodies40are sprayed to be joined on the surface of the film1in this manner, thereby forming the re-entrant structure surface on which the pinning pillars20are fixed and arrayed. Then, the film1is wound by the winding roller53in this state to complete the joining operation.

In the above-described examples shown inFIGS. 7 and 8, the molded body1has a film form. However, as is obvious for a person skilled in the art, even if the molded body1does not have a film form, it is similarly possible to join the columnar bodies40to form the re-entrant structure surface on which the pinning pillars20are arrayed, unless the molded body1is to be conveyed by the roller.

The molded body1on the surface of which the re-entrant structure is formed by electrostatic flocking or thermal spraying in the above-described manner is subjected to the aforementioned fluorine plasma treatment, so that fluorine atoms are distributed on the re-entrant structure surface, thereby providing the liquid-repellent plastic molded body of the present invention. Alternatively, a bleeding-type fluorine-containing compound is contained in the plastic molded body1and the columnar bodies40, so that fluorine atoms are distributed by migration, thereby providing the liquid-repellent plastic molded body of the present invention.

The thus-obtained liquid-repellent plastic molded body of the present invention is excellent in liquid repellency or lubricity to various fluids, and thus it is used in various applications. In particular, the liquid-repellent plastic molded body of the present invention achieves excellent liquid repellency, which is as high as that in the initial state, for a long period even in a case where a liquid is kept in constant contact. Further, the above-described re-entrant structure is not damaged by a heat treatment such as retort sterilization, and thus the present invention is applied preferably to the field of packaging.

For example, one having a film form, which is subjected to post-processing for bag forming or the like, is used most preferably as a pouched container or a tube container in which contents are to be preserved for a long period. In particular, even in a case where viscous paste-like contents having a viscosity (25° C.) of 250 mPa·s or more are contained, excellent liquid repellency is achieved, so that the contents can be discharged rapidly and completely with nothing adhering and remaining inside the container.

Typical examples of the paste-like contents include a curry, various kinds of thickened food, a gel-like substance such as pudding and yogurt, jam, shampoo, conditioner, a liquid detergent, toothpaste, and the like.

The present invention is not limited to a pouched container or a tube container, and it is also applicable to a cup-shaped container or a tray-type container.

EXPLANATIONS OF LETTERS OR NUMERALS

100: rough surface