Patent Application
20060051540
The present invention relates to a shape-memory polybutylene terephthalate laminate film useful for package sheets and its production method and use, and a method for producing a polybutylene terephthalate film excellent in the uniformity of a film thickness and a thermal shrinkage resistance, and a functional polybutylene terephthalate film having excellent ease-to-tear and twist retention characteristics useful for package sheets, etc.
Conventionally known lid sheets for sealing the openings of instant food containers are laminates comprising an easily peelable sealant film, an aluminum foil and paper in this order, for instance, in the case of containers for instant noodles.
The lid sheet having an aluminum foil layer is excellent in barrier to steam, etc., dimensional stability to heat, etc., filling adaptability (no curling occurs in the lid sheet when filling the container with a content and sealing it), light screening, etc. The lid sheet having an aluminum foil layer has properties of keeping a lift-up state when it is peeled from the container substantially to its center position and lifted up (dead-folding characteristics). Because of the dead-folding characteristics, hot water can easily be poured into a container for instant Chinese noodle, etc., for instance, with the peeled lid kept in a half-open state. Thereafter, the lid is closed until the instant noodle becomes eatable, and then reopened to eat.
However, the aluminum-foil-containing lid sheets are disadvantages in that when incinerated after use, aluminum foils are fused like ingots in an incinerator, damaging the incinerator and lowering its burning efficiency. From the aspect of environmental protection, it is desirable to use as few aluminum-foil-containing lid sheets as possible. In the case of instant foods like cupped Chinese noodles, it is necessary from the aspect of food safety to inspect whether or not foreign metallic materials are present in containers. However, the inspection with a metal detector cannot be conducted after the heat-sealing of aluminum-foil-containing lids. Accordingly, the inspection is presently conducted before heat-sealing the lids. Also, the aluminum-foil-containing lids are disadvantageously heavy.
As a lid sheet containing no aluminum foil, for instance, a laminate film having a paper layer, an adhesion resin layer, a polyethylene terephthalate film layer and an easy-to-peel resin layer in this order is proposed. The polyethylene terephthalate (PET) film has such properties as steam barrier, dimensional stability to heat, filling adaptability (no curling), etc. However, because the PET film has large toughness, it fails to be kept in an open state, (poor in dead-folding characteristics). Accordingly, the lid is easily closed after opening, making it difficult to pour hot water into the container.
It is required that a laminate film constituting a lid sheet used for containers of instant noodle, etc. is not curled when sealed to the container, and that it keeps a curled state when peeled from the container (having dead-folding characteristics). Because the lid sheet is usually heat-sealed to the container, it would be extremely useful, if it had a shape memory that it is not curled before heat sealing and returns to a curled shape by heat sealing.
However, no package sheets formed by shape-memory laminate films have been known so far. Shape-memory resins are generally subjected to large modulus change before and after their glass transition temperatures. A shape memory mechanism comprises, for instance, (1) forming a shape memory article having an arbitrary shape M, heating it in a state of the shape M for crystallization (entanglement of crystal portions) or intermolecular cross-linking to generate fixing points for shape memory; (2) applying an external force thereto at a temperature equal to or higher than a glass transition temperature and lower than the above heating temperature to cause deformation to a shape N, and making its temperature lower than the glass transition temperature without changing the shape, thereby fixing it to the shape N; and (3) heating it to the glass transition temperature or higher, thereby recovering the shape M without applying an external force. Though the PET has shape-memory characteristics, it has too high a shape recovery temperature because of the glass transition temperature of about 70 to 80° C.
Because polybutylene terephthalate (PBT) has a glass transition temperature of about 20 to 45° C., its shape-memory characteristics at practical temperatures would be utilized if possible to use as package sheets. For instance, JP 2-123129 A discloses a shape-memory resin composed of a block copolymer of PBT and aliphatic polylactone. JP 2-269735 A discloses shape-memory copolyester moldings composed of polyethylene terephthalate copolymerized with a third component to have a crystal-melting entropy of 3 cal/g or less. JP 2-240135 A discloses a shape-memory resin composed of a block copolymer of PBT and polyethylene glycol. However, any of these references fails to teach films of shape-memory PBT resins.
JP 7-33048 B proposes a method for forming a PBT resin having an intrinsic viscosity of 1.0 or more into a film by an inflation method under the condition that the resin extrusion temperature meets the formula of melting point (° C.)<resin extrusion temperature (° C.)<melting point −26+53×intrinsic viscosity (° C.). However, in this method, a combination of a blow-up ratio, a resin extrusion temperature and a resin-extruding pressure are not optimized, and the resultant PBT film has a relatively large thermal shrinkage ratio.
With respect to functions as package sheets, because the PBT film has excellent gas barrier and odor retention, it is preferable to provide the PBT film with functions such as easy tearing, twist retention, etc. An ease-to-tear polyester film, JP 2002-80705 A discloses a biaxially stretched polyester film comprising 80 to 95% by mass of polyethylene terephthalate (PET) and 20 to 5% by mass of modified PBT (modified PBT). However, this biaxially stretched polyester film has insufficient ease to tear.
JP 5-104618 A discloses a method for producing a polyester film having good twist retention comprising the steps of laminating a resin (B) having a higher melting point than the melting point of a polyester resin layer (A) by 10° C. or higher to at least one surface of the polyester resin layer (A), such that the thickness of the resin (B) is 5 to 60% of the total film thickness; and heat-treating the resultant laminate at a temperature equal to or higher than (the melting point of (A) −10° C.) and lower than the melting point of (B), after monoaxial elongation. However, this production method of a polyester film having twist retention has complicated steps and thus high cost.
Accordingly, an object of the present invention is to provide a polybutylene terephthalate laminate film having excellent shape memory and high-temperature dimensional stability, and its production method and use.
Another object of the present invention is to provide a method for producing a polybutylene terephthalate film, which is thin and excellent in the uniformity of a film thickness and thermal shrinkage resistance.
A further object of the present invention is to provide a polybutylene terephthalate film with excellent ease to tear.
A still further object of the present invention is to provide a polybutylene terephthalate film having excellent twist retention, which can be produced at a low cost.
As a result of intensive research in view of the above objects, the inventor has found as follows:
The present invention has been completed based on these findings.
Thus, the shape-memory polybutylene terephthalate laminate film of the present invention comprises (1) a polybutylene terephthalate film, and (2) at least one selected from the group consisting of a paper sheet, another resin film and a metal foil, or a laminate comprising it, having a first shape memorized in a predetermined temperature range.
The shape-memory polybutylene terephthalate laminate film of the present invention substantially recovers the first shape when exposed to a temperature equal to or higher than the temperature at which the first shape is memorized, after deformed to the second shape in a different temperature range from the predetermined temperature range.
In a preferred example of the shape-memory polybutylene terephthalate laminate film, the temperature at which the first shape is recovered is equal to or lower than the Tg of the polybutylene terephthalate. The temperature at which the first shape is recovered is more preferably 35° C. or lower.
The temperature at which the shape-memory polybutylene terephthalate laminate film recovers the first shape is higher than the Tg and lower than the melting point of the polybutylene terephthalate. The temperature at which the first shape is recovered is more preferably 75 to 100° C.
The first shape is preferably a curled shape, and the second shape is preferably a substantially flat shape or an oppositely curled shape.
A lot of substantially parallel linear scratches are preferably formed on at least one of on its entire surface the polybutylene terephthalate film, so that the shape-memory polybutylene terephthalate laminate film can be torn substantially straight along the linear scratches. The depth of the linear scratches is preferably 1 to 40% of the thickness of the polybutylene terephthalate film layer. Specifically, it is preferable that the depth of the linear scratches is 0.1 to 10 μm, that the width of the linear scratches is 0.1 to 10 μm, and that the intervals of the linear scratches are 10 to 200 μm. At least one surface of the polybutylene terephthalate film may be vapor-deposited with ceramics or metals.
A preferred example of the layer structure of the shape-memory polybutylene terephthalate laminate film of the present invention comprises the polybutylene terephthalate film, the paper sheet, and a sealant film in this order. Another example of the layer structure of the shape-memory polybutylene terephthalate laminate film of the present invention comprises the polybutylene terephthalate film, the paper sheet, a rigid film, and a sealant film in this order. A further example of the layer structure of the shape-memory polybutylene terephthalate laminate film of the present invention comprises the polybutylene terephthalate film, a rigid film, and a sealant film in this order. A light-screening ink layer may be formed on the polybutylene terephthalate film on the side of the paper sheet, or on the rigid film on the side of the sealant film.
The shape-memory polybutylene terephthalate laminate film of the present invention is useful as package sheets, particularly useful as package sheets for container lids.
The first method of the present invention for producing a shape-memory polybutylene terephthalate laminate film comprising (a) a polybutylene terephthalate film, and (b) at least one selected from the group consisting of a paper sheet, another resin film and a metal foil, or a laminate comprising it, comprises the steps of (1) subjecting a laminate film comprising the polybutylene terephthalate film and another film or film laminate to a shaping treatment at a temperature T1 equal to or lower than the glass transition temperature of the polybutylene terephthalate while maintaining a first shape; (2) deforming the shaped laminate film to a second shape at a temperature T2 higher than the glass transition temperature; and (3) cooling the laminate film to a temperature T3 equal to or lower than the glass transition temperature so that the laminate film is fixed to the second shape.
The first shape is preferably a curled shape, and the second shape is preferably a substantially flat shape or an oppositely curled shape. The laminate film comprising the polybutylene terephthalate film adhered to another film or film laminate is preferably conveyed by a roll, and treated at the temperature T1 along a peripheral surface of the roll to provide a curled laminate film. Deformation at the temperature T2 is preferably conducted for 30 to 60 seconds. It is preferable that the temperature T1 is 35° C. or lower, that the temperature T2 is higher than 45° C. and 65° C. or lower, and that the temperature T3 is 15 to 25° C. The temperature T1 is more preferably 15 to 25° C. The curled laminate film is cooled to the temperature T3, and then wound in an uncurling direction. A tension of 4 kgf/m (width) or more is applied to the polybutylene terephthalate film, so that the polybutylene terephthalate film is adhered to another film or film laminate. The tension is more preferably 10 to 20 kgf/m (width).
The second method of the present invention for producing a shape-memory polybutylene terephthalate laminate film comprising (a) polybutylene terephthalate film, and (b) at least one selected from the group consisting of a paper sheet, another resin film and a metal foil, or a laminate comprising it, comprises the steps of (1) (i) producing a laminate film of the polybutylene terephthalate film and another film or film laminate in advance, and subjecting it to a shaping treatment at the temperature T4 while maintaining it in the first shape to produce the shaped laminate film having the first shape, or (ii) producing a laminate film having the first shape by subjecting the polybutylene terephthalate film to a shape treatment at a temperature T4 higher than the glass transition temperature and lower than the melting point of the polybutylene terephthalate while maintaining it in the first shape and then laminating it with another film or film laminate; (2) cooling the shaped laminate film to a temperature T5 equal to or lower than the glass transition temperature to fix it to the first shape; (3) deforming the shaped laminate film to a second shape at a temperature T6 higher than the glass transition temperature and lower than the temperature T4; and then (4) cooling the deformed laminate film to a temperature T7 equal to or lower than the glass transition temperature to fix it to the second shape.
The first shape is preferably a curled shape, and the second shape is preferably a substantially flat shape or an oppositely curled shape. It is preferable that the temperature T4 is 75 to 100° C., that the temperature T5 is 40° C. or lower, that the temperature T6 is 45 to 65° C., and that the temperature T7 is 40° C. or lower.
When the shaped polybutylene terephthalate film is adhered to another film or film laminate to produce the shaped laminate film, the polybutylene terephthalate film is preferably conveyed while keeping it in contact with a peripheral surface of one of a pair of heat rolls, and heated at the temperature T4 along the peripheral surface of the heat roll to impart a curled shape to the polybutylene terephthalate film, and the resultant curled polybutylene terephthalate film and another film or film laminate are caused to pass through a pair of the heat rolls for continuous adhesion.
When the polybutylene terephthalate laminate film comprising the polybutylene terephthalate film adhered to another film or film laminate is subjected to a shaping treatment, the polybutylene terephthalate laminate film is preferably conveyed by a heat roll, and treated at the temperature T4 along the peripheral surface of the heat roll to impart a curled shape.
A tension of 4 kgf/m (width) or more is preferably applied to the polybutylene terephthalate film, so that the polybutylene terephthalate film is adhered to another film or film laminate. The tension is preferably 10 to 20 kgf/m (width). The curled laminate film is preferably cooled to the temperature T5, and then treated at the temperature T6 or lower and the temperature T7 in an uncurling direction winding.
The method of the present invention for producing a container having a lid heat-sealed to a container body, the lid being composed of a shape-memory polybutylene terephthalate laminate film, comprises the steps of annealing the shape-memory polybutylene terephthalate laminate film at a temperature T8 higher than the glass transition temperature of the polybutylene terephthalate while keeping it flat; and punching and heat-sealing the resultant substantially flat shape-memory polybutylene terephthalate laminate film to the container body by a lid-sealing means, thereby adhering the lid composed of the shape-memory polybutylene terephthalate laminate film to the container.
The annealing is preferably conducted for 30 to 60 seconds. The temperature T8 is preferably 80 to 120° C.
The method of the present invention for producing a polybutylene terephthalate film from a polybutylene terephthalate resin by an air-cooled inflation method, comprises the steps of ejecting a humid air through a first cooling ring disposed near an annular die to cool a neck portion of a bubble at a blow-up ratio of 1.5 to 2.8, a resin extrusion temperature of 210 to 250° C., and a resin-extruding pressure of 9.8 to 13.7 NPa.
The bubble is preferably further cooled by a cooling air ejecting from the second cooling ring disposed slightly above a frost line of the bubble; and wherein the temperature around a cylindrical net disposed between the first cooling ring and the second cooling ring is kept constant, thereby stabilizing the temperature of the bubble cooled by the first cooling ring and the second cooling ring.
A humid air ejected from a cooling-air-ejecting means disposed in a lower portion of the net is preferably blown up along an outer surface of the cylindrical net, to cool the surrounding of the net. The bubble is preferably further cooled by a third cooling ring disposed slightly above the second cooling ring. Further, the cooling air ejected from the second cooling ring and the third cooling ring is preferably a humid air. The temperature of the humid air is preferably 15 to 25° C.
The easy-to-straight-tear polybutylene terephthalate film of the present invention comprises a polybutylene terephthalate film having a lot of substantially parallel linear scratches at least one entire surface, so that it can be torn substantially straight along the linear scratches from any point.
The depth of the linear scratches is preferably 1 to 40% of the film thickness. The depth of the linear scratches is preferably 0.1 to 10 μm, the width of the linear scratches is preferably 0.1 to 10 μm, and the intervals of the linear scratches are preferably 10 to 200 μm.
The easy-to-straight-tear polybutylene terephthalate film may be either one of a single-layer film or a laminate film. In the case of the laminate film, the laminate film preferably comprises at least one layer composed of a film having the linear scratches, and a sealant film layer. A ceramic or a metal is preferably vapor-deposited on the easy-to-straight-tear polybutylene terephthalate film of the present invention to improve gas barrier. Package sheets and wrapping bags constituted by the easy-to-straight-tear polybutylene terephthalate film of the present invention are suitable for applications needing easy tearing.
The porous polybutylene terephthalate film of the present invention comprises a polybutylene terephthalate film having a lot of fine penetrating pores and/or non-penetrating pores formed uniformly, thereby having good twist retention.
The fine pores preferably have an average opening diameter of 0.5 to 100 μm, and their density is preferably about 500/cm2 or more. Package sheets constituted by the porous polybutylene terephthalate film of the present invention are suitable for applications needing twist retention.
[1] Layer Structure of Shape-Memory Polybutylene Terephthalate Laminate Film
The shape-memory polybutylene terephthalate (PBT) laminate film of the present invention comprises (a) a PBT film layer, and (b) at least one selected from the group consisting of a paper sheet, another resin film and a metal foil, or a laminate comprising it (hereinafter referred to simply as “another film or film laminate”).
(1) Polybutylene Terephthalate Film
The PBT film is essentially a film of a saturation polyester composed of 1,4-butanediol and terephthalic acid. Within ranges not deteriorating properties such as a thermal shrinkage resistance, etc., other diols than 1,4-butanediol and other carboxylic acids than terephthalic acid may be included as comonomers. Such diols may be, for instance, ethylene glycol, diethylene glycol, neopentyl glycol, 1,4-cyclohexanemethanol, etc. The dicarboxylic acids may be, for instance, isophthalic acid, sebacic acid, adipic acid, azelaic acid, succinic acid, etc. A specific example of PBT resins forming the PBT film may be, for instance, a homo-PBT resin commercially available from Toray Industries, Inc. under the tradename of “Toraycon.”
The PBT resin is not restricted to PBT only, but may contain other thermoplastic resins within ranges not hindering the effects of the present invention depending on its applications. The other resins may be polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); polyphenylene sulfide (PPS); polyamides (PA); polyimides (PI); polyamideimides (PAI); polyethersulfone (PES); poltetheretherketone (PEEK); polycarbonates; polyurethanes; fluororesins; polyolefins such as polyethylene and polypropylene; polyvinyl chlorides; elastomers, etc. When the other resins are contained, their proportions are preferably 5 to 20% by mass, more preferably 5 to 15% by mass, particularly 5 to 10% by mass, based on the entire PBT resin (100% by mass). Accordingly, unless otherwise particularly mentioned, it should be noted that the term “PBT resin” used herein includes both PBT only, and a composition comprising PBT and other resins.
The PBT film may properly contain plasticizers, stabilizers such as antioxidants, UV absorbents, etc., antistatics, surfactants, coloring agents such as dyes and pigments, lubricants for improving flowability, nucleating agents, inorganic fillers, etc., depending on the use of the shape-memory PBT laminate film.
Though not particularly restrictive, the thickness of the PBT film is preferably about 5 to 50 μm for practical applications. It is technically difficult to make the PBT film as thin as less than about 5 μm, resulting in a higher cost. On the other hand, when the PBT film is as thick as more than about 50 μm, the film is expensive, resulting in limited use for the resultant shape-memory PBT laminate films.
The production method of the PBT film is not particularly restricted, but may be an inflation method or a casting method. The PBT film is preferably produced by the inflation method or the casting method described below.
(2) Other Films or Film Laminates
(a) Paper Sheet
When the shape-memory PBT laminate film is used for lids for instant food containers, it preferably has a layer composed of a paper sheet as a layer for providing dead-folding characteristics. The types of papers for the paper sheet are not restricted, but may include synthetic papers. The thickness of the paper sheet is preferably about 60 to 110 g/m2, more preferably about 75 to 90 g/m2. When the thickness of the paper sheet is less than about 60 g/m2, the paper sheet is easily foldable, failing to provide sufficient dead-folding characteristics. On the other hand, even when the thickness of the paper sheet is made more than about 110 g/m2, there is no further improvement in dead-folding characteristics, resulting in only cost increase.
(b) Sealant Film
When the shape-memory PBT laminate film is used for lids for instant food containers, it has a sealant film heat-sealed to an upper flange of a container body. The sealant film may be formed by a polyethylene film, an unstretched polypropylene film, an ionomer film, a polystyrene film, etc. In order that a lid is easily peeled from the container body, the sealant film is preferably easy-to-peel. For this purpose, the sealant film preferably has relatively weak heat adhesiveness. Materials for the heat seal may be known hot melts.
Usable as the sealant films are, for instance, a polyethylene base film on the side of the paper sheet, and a laminate film with a low-molecular-weight polyethylene film on the side of the upper flange of the container body. The thickness of this polyethylene base film is preferably about 10 to 40 μm, more preferably about 20 to 30 μm. The thickness of the low-molecular-weight polyethylene film is preferably about 5 to 20 μm, more preferably about 7 to 15 μm. Such laminating polyethylene film is, for instance, 760FD commercially available from Toray Plastic Films Co., Ltd. Also usable as the sealant film is a film made of a mixture comprising an ethylene-vinyl acetate copolymer (EVA) and polyethylene. In the film made of this mixture, the polyethylene is preferably linear low-density polyethylene (LLDPE). The thickness of the film made of this mixture is also preferably about 10 to 40 μm, more preferably about 20 to 30 μm. The thickness of the hot-melt layer is preferably 10 to 50 μm, more preferably 20 to 40 μm.
A usable sealant film is also disclosed in Japanese Patent Application 2002-183197. The sealant film disclosed in Japanese Patent Application 2002-183197 is made of a resin composition comprising a linear ethylene-α-olefin copolymer of ethylene and an a-olefin having 3 to 18 carbon atoms, which has a density (JIS K6922) of 0.870 to 0.910 g/cm3, and MFR of 1 to 100 g/10 minutes (JIS K6921, at 190° C. and under a load of 2.16 kg), and polystyrene. Whichever polyethylene or polystyrene is used for the seal surface of the container body, the lid of the present invention comprising this sealant film can form a multi-sealant layer having both sealability and easy-to-open characteristic when heat-sealed to the seal surface of the container body.
(c) Rigid Film
To increase the rigidity of the shape-memory PBT laminate film, it may have a rigid film. The rigid film may be a PET film, a biaxially stretched polypropylene film (OPP film), a nylon film, etc. The use of a monoaxially orientated PET film or a PET film biaxially orientated to different degrees as the PET film is advantageous when the shape-memory PBT laminate film should be easy-to-tear. The monoaxially orientated PET film or the PET film biaxially orientated to different degrees may be, for instance, “Emblet PC” commercially available from Unitika Ltd.
(d) Light-Screening Ink Layer
When light screening is needed, the shape-memory PBT laminate film is provided with a light-screening ink layer or a metal foil layer. The light-screening ink is not particularly restrictive, as long as it is an ink containing a black or dark-color pigment or dye such as carbon black. The use of the light-screening ink layer makes it possible to avoid adverse effect on environment at the time of incineration. It also makes it possible to detect foreign metallic materials by a metal detector after sealing when the shape-memory PBT laminate film is used for a lid for an instant food container. This further improves the safety of instant food, and extremely decreases an examination cost because the metal detector can be utilized. When the shape-memory PBT laminate film having a metal foil layer is used for a lid for an instant food container, the metal foil is preferably an aluminum foil. The formation of an aluminum foil layer can provide excellent light screening, gas barrier, odor retention, etc.
Though depending on the concentration of black pigment or dye in the ink, the light-screening ink layer may generally have such thickness as sufficiently cutting ultraviolet rays and visible rays. The thickness of the aluminum foil is preferably 3 to 15 μm, more preferably 7 to 12 μm.
(3) Examples of Layer Structure
Because the lid for a container for semisolid food is not required to have resealability after pouring hot water, unlike lids for instant food containers, it sometimes does not have a paper sheet or an aluminum foil having strong dead-folding characteristics. However, if only two layers of the PBT film and the polyethylene film were adhered to each other, the resultant laminate film would be likely to have insufficient shape recoverability, because deformation is easily absorbed by the polyethylene film when the PBT film is caused to recover the first shape. Accordingly, in the case of producing a shape-memory PBT laminate film having a PBT film layer and a polyethylene film layer, it is preferable to insert the above rigid film between the PBT film layer and the polyethylene film layer.
[2] Production Method of Shape-Memory Polybutylene Terephthalate Laminate Film
The production method of the shape-memory PBT laminate film will be explained in detail below referring to the drawings.
(1) First Production Method
The first production method of the shape-memory PBT laminate film comprises the steps of (a) subjecting a laminate film of the above PBT film and another film or film laminate to a shaping treatment (cold working) at a temperature T1 equal to or lower than the Tg of the PBT, while maintaining the first shape; (c) deforming the shaped laminate film to a second shape at a temperature T2 higher than the glass transition temperature Tg; and (c) cooling it to a temperature T3 equal to or lower than the glass transition temperature, so that it is fixed to the second shape.
Explanation will be made below taking for example a case where the first shape is a curled shape, and the second shape is a flat shape.
The cold-working temperature T1, which should be Tg of PBT or lower, is preferably 35° C. or lower, more preferably 15 to 25° C. The temperature T3, at which the curlable laminate film 10 is cooled after annealing, should be the above Tg or lower, and is preferably 15 to 25° C. The PBT film generally has Tg of about 20 to 45° C. Tg can be measured by JIS K7121.
The annealing treatment for deforming the curlable laminate film flat at a temperature T2 higher than Tg should be carried out to such an extent that the curlability provided by the cold working does not disappear. Accordingly, the temperature T2 is preferably higher than 45° C. and 65° C. or lower, to which the laminate film is rapidly heated, deformed and then annealed for 30 to 60 seconds. A tension of 5 to 10 kgf/m (width) is applied to the laminate film to keep it flat between two nip rolls 107, 107′. After the annealing treatment at a temperature T2, the laminate film is preferably rapidly cooled to a temperature T3. In
In the embodiment shown in
When the shape-memory PBT laminate film is used for lids for instant food containers and semisolid food containers, another film or film laminate laminated to the PBT film is constituted in advance such that the resultant shape-memory PBT laminate film has the layer structure described in [1] (3) above. Another film or film laminate 13 may be formed by an extrusion lamination method or a dry lamination method, though the extrusion lamination method is more preferable.
As shown in
When the PBT film 2 and the another film or film laminate 13 are caused to pass between the cooling roll 105 and the rubber roll 105′ for adhesion, a tension of 4 kgf/m (width) or more is usually applied to the PBT film 2 by the pressure-controlling roll 103. Particularly when a tension of 10 to 20 kgf/m (width) is applied to the PBT film 2, the PBT film 2 can be stretched to an elastically shrinkable degree in a longitudinal direction while being adhered to another film or film laminate 13. This makes it possible to adhere the PBT film 2 to another film or film laminate 13 in a state where the elongated PBT film 2 keeps an elastic recovery force. The passage “in a state where the elongated PBT film 2 keeps an elastic recovery force” means a state where the PBT film 2 keeps a force to shrink to the original shape when a force to fix the elongation is removed. This state further improves the curlability of the shape-memory PBT laminate film 1. The passage “stretched to an elastically shrinkable degree” generally means that the PBT film is stretched by about 1 to 3% to such an extent that no wrinkle appears on the PBT film.
Though another film or film laminate 13 is adhered to only one surface of the PBT film 2 in the embodiment shown in
Next, explanation will be made, taking for example a case where the shape-memory PBT laminate film is in a tray shape as the first shape and in a flat shape as the second shape.
(2) Second Production Method
The second production method of the shape-memory PBT laminate film comprises the steps of (a) (i) producing a laminate film of the above PBT film and another film or film laminate in advance, and subjecting it to a shaping treatment while maintaining it in a first shape at a temperature T4 higher than Tg and lower than the melting point, or (ii) producing a laminate film having the first shape by subjecting the above PBT film to a shaping treatment at the temperature T4 while maintaining it in the first shape and then laminating it with another film or film laminate; (b) cooling the resultant shaped laminate film to a temperature T5 equal to or lower than Tg to fix it to the first shape; (c) deforming the shaped laminate film to the second shape at a temperature T6 higher than Tg and lower than the temperature T4; and then (d) cooling the shaped laminate film to a temperature T7 equal to or lower than Tg to fix it to the second shape.
Because the PBT resin has Tg of 22 to 45° C., close to room temperature, it is easily heated to Tg or higher and cooled to lower than Tg. In addition, because the PBT resin has a melting point as high as about 230° C., there is a wide temperature range between Tg and the melting point, resulting in a large difference between the temperature T4 and the temperature T5. Accordingly, the above operations (A) to (D) can be easily conducted.
Explanation will be made below taking for example a case where the first shape is a curled shape, and the second shape is a flat shape.
The heating temperature T4 at the heat roll 115 should be a temperature higher than the Tg of PBT and lower than the melting point of PBT, and it is preferably 75 to 100° C., more preferably 90 to 100° C. The cooling temperature T5 at the cooling roll 109 should be a temperature equal to or lower than the above Tg, and it is preferably 40° C. or lower. The cooling of the curlable laminate film 10 may be conducted by using a cooling air instead of the cooling roll 109. The heating temperature T6 of the wound film 11 should be higher than the above Tg and lower than the temperature T4, and it is preferably 45 to 65° C., and more preferably 45 to 50° C. The heating treatment at the temperature T6 is preferably conducted for about 24 hours. The cooling temperature T7 of the wound film 11 after the heating treatment should be the above Tg or lower, and it is preferably 40° C. or lower. In the embodiment shown in
The winding of the PBT film 2 around the heat roll 115 is preferably such that an angle ° 2 between the winding direction of the PBT film 112 shown in
As described in (1) above with respect to the first production method, when the PBT film 2 and another film or film laminate 13 are caused to pass between the heat roll 115 and the abutting roll 115′ for adhesion, a tension of 4 kgf/m (width) or more is usually applied to the PBT film 2 by a pair of pressure-controlling rolls 103, 103. Like the first production method, a tension of 10 to 20 kgf/m (width) is preferably applied to the PBT film 2.
In the embodiment shown in
By the second production method, too, a shape-memory PBT laminate film that has a tray shape as the first shape and a flat shape as the second shape can be produced. Because a production apparatus therefor may be the same as shown in
[3] Shape-Memory Polybutylene Terephthalate Laminate Film
The shape-memory PBT laminate film obtained by the above first method substantially recovers the first shape because of the shape recoverability at a temperature equal to or higher than T1. It is not necessarily clear why the PBT film recovers the first shape at a temperature equal to or higher than T1 even though it is fixed to the second shape by the above annealing and cooling steps. However, it may be considered that strain is kept in the entanglement of polymer chains, for instance, by cold working at the temperature T1, and that most of this strain is not relaxed by annealing at the temperature T2 for a short period of time, so that the first shape is recovered at a temperature equal to or higher than T1.
The shape-memory PBT laminate film obtained by the above second method substantially recovers the first shape because of the shape recoverability at a temperature equal to or higher than T4. It is not necessarily clear why the PBT film recovers the first shape at a temperature equal to or higher than T4, even though it is fixed to the second shape by the above thermal deformation and cooling steps. However, It may be considered that the PBT film is easily thermally shaped, for instance, at the temperature T4 or higher because of a rubbery state, with its deformation fixed at the temperature T5 because of a glassy state, and that though the deformation at the temperature T4 is partially relaxed by the thermal deformation at the temperature T6 so that PBT film is turned to have the second shape, it recovers the first shape at the temperature T4 or higher because the orientation of most molecular chains does not change.
The shape-memory PBT laminate films having shape recoverability to the first shape is useful as various package sheets. Particularly because the PBT laminate films having a curled shape memory produced by the method described in [2] above can be sufficiently curled when used for lids containing no metal foils such as an aluminum foil, etc. such lids are suitable as package sheets for instant food containers. In the production of an instant food container, the shape-memory PBT laminate film is punched out by a lid-sealing means, and the resultant lid is immediately heat-sealed to the container. At the heat-sealing step, a seal portion of the lid is usually heated to 120 to 160° C. by a seal head of the lid-sealing means, and because heat is also transmitted to other portions than the seal portion of the lid, the lid is treated at a temperature equal to or higher than T1 or T4. Accordingly, the lid recovers a curled shape, so that it is flat when sealed to the container, but curled when peeled from the container. Particularly when the PBT film is adhered to a paper sheet in an elongated state where the PBT film has an elastic recovery force as described above, the laminate film has further improved curlability.
[4] Production Method of Container Having Lid Composed of Shape-Memory Polybutylene Terephthalate Laminate Film
The production method of a container having a lid composed of a shape-memory PBT laminate film will be explained below. Because the shape-memory PBT laminate film 1 obtained by the method described in [2] above is made substantially flat on appearance in its production step and stored as a wound film 11, it is substantially flat on appearance when unwound. However, when the shape-recovering temperature is relatively low, when it is stored for a long period of time, or when it is exposed to room temperature in the hot summer time, etc., it sometimes gradually recovers a curled shape during storing, or deflects toward the opposite direction to the memorized curled shape due to winding during storing.
The container with a lid composed of a shape-memory PBT laminate film is produced by punching out the shape-memory PBT laminate film having a memorized curled shape, and heat-sealing it to the container. However, unless the shape-memory PBT laminate film is substantially flat when unwound, it cannot be heat-sealed to the container, or even if possible, defective products with deflected lids are produced. Accordingly, in the production of the container with a lid, the shape-memory PBT laminate film, which is not flat when unwound, is made substantially flat immediately before heat-sealing.
The annealing at the temperature T8 is conducted to such an extent that the shape-memory PBT laminate film does not lose memorized curlability. Thus, the temperature T8 is preferably 80 to 120° C., more preferably 90 to 100° C. The shape-memory PBT laminate film is rapidly heated to the temperature T8 and kept flat for 30 to 60 seconds for annealing. A tension of 5 to 10 kgf/m (width) is applied to make the laminate film flat between the two nip rolls 116, 116′. The moving speed of the shape-memory PBT laminate film 1 is usually 30 to 100 m/minute. Though both surfaces of the shape-memory PBT laminate film 1 are heated by the heaters 117, 117 in
Because the punching of the lid and its heat sealing to the container 140 are conducted intermittently, a deflection-preventing roll 118 movable up and down is preferably disposed as shown in
During the heat sealing, in which a seal portion of the lid is usually heated to 120 to 160° C. by the seal head of the lid-sealing means 121, heat is also added to other portions of the lid than the seal portion, so that the lid is treated at a temperature equal to or higher than T1 or T4. Accordingly, the lid recovers the curled shape, so that it is curled when peeled form the container though it is flat while being sealed.
[5] Container for Food
The lid for a container obtained by the production method described in [4] above exhibits a curled shape due to shape memory when peeled from the container. For instance, when the shape-memory PBT laminate film is used for the lid for an instant food container, as shown in
When the shape-memory PBT laminate film having a PBT film layer having linear scratches described below is used for a lid for an instant food container, as shown in
When the flap 134 is returned to the original position after pouring hot water, jagged rupture portions 134a, 134a of the paper one or both sides of the flap 134 engage jagged rupture portions 133a, 133a of the paper at the opening 133, so that the flap 134 does not lift up. In this case, the opening 133 has a smaller area than that of the opening of a conventional full-open lid, and the flap 134 is kept engaging the opening 133. Accordingly, even if the container 140 erroneously falls, only a small amount of the hot water leaks. In
The container body 140 may be formed, for instance, by paper, synthetic resins such as foamed polystyrene, etc. The paper container body is advantageous in easy incineration and the generation of no gas exerting adverse effects on the environment by incineration. The foamed polystyrene container body is advantageous in excellent temperature-keeping properties. The shape of the container body 140 is not restricted to that depicted, but may be variously modified depending on the types of contents.
When the shape-memory PBT laminate film memorizing a tray shape described in [2] above is cut to a unit length of each tray shape while being flat, it can be used as a food tray as it is. As shown in
The wrapping film 125 of the food tray 123 is preferably provided with a lot of substantially parallel linear scratches on at least one surface by the method described below. The substantially parallel linear scratches provide the wrapping film 125 with easy-to-straight-tear characteristics in one direction regardless of its orientation, so that the wrapping film 125 can be torn straight along the linear scratches from any point. Thus, the wrapping film 125 can be easily partially open when to eat. Because such linear scratches do not penetrate the film, the wrapping film 125 has an excellent gas barrier after provided with the linear scratches.
[6] Production Method of Polybutylene Terephthalate Film
The PBT film used for the shape-memory PBT laminate film of the present invention is preferably produced by an inflation method or a monoaxial orientating method described below. The shape-memory PBT laminate film obtained by using the PBT film obtained by these methods can stably recover the given shape.
(1) Polybutylene Terephthalate Resin Material
Because the PBT resin material per se may be the same as described in [1] (1) above, its explanation will be omitted.
(2) Inflation Method
To produce the PBT film, the PBT resin and desired additives, etc. are blended at a resin temperature of 240 to 260° C. When the blending temperature is higher than 260° C., the thermal degradation of the resin is likely to proceed. Thus, when the blending is carried out in an extruder such as a double-screw extruder, the extruder should have a screw structure causing no heat generation, or should be provided with a proper cooling means. Incidentally, when the lower limit of the blending temperature becomes lower than 240°, the extrusion rate becomes unpreferably unstable.
The temperature of the resin extruded from the annular inflation die 201 is 210 to 250° C. When the temperature of the resin extruded from the annular die 201 exceeds 250° C., the bubble 207 cannot sufficiently be cooled by the first cooling ring 202. The temperature of the resin extruded from the annular die 201 is preferably 220 to 230° C. The pressure of the resin extruded from the annular inflation die 201 is 9.8 to 13.7 MPa (100 to 140 kgf/cm2). The resin-extruding pressure is preferably 9.8 to 11.8 MPa (100 to 120 kgf cm2). The diameter of the annular inflation die 201 is preferably 120 to 300 mm.
The bubble 207 extruded from the annular die 201 is oriented in both MD and TD while being cooled by the cooling means. This is schematically shown in
In
In the apparatus having the above structure, because the arrangement of each cooling ring is determined by the temperature control to of the bubble 207 formed by an air-cooled inflation method, the shape and temperature distribution of the bubble 207 will be described below.
A molten PBT resin or a molten PBT resin composition is extruded from the annular orifice 211 of the die 201 to form the bubble 207. However, the bubble 207 immediately after extrusion has a small-diameter portion, the so-called neck portion 271, because of a low melt tension. The bubble 207 is oriented mainly in MD in the neck portion 271. The bubble 207 is then rapidly expanded to a predetermined bubble diameter. In this expanding portion 272, the bubble 207 is oriented not only in MD but also in TD. The PBT resin composition is solidified at a frost line 274 slightly above the expanding portion 272. The bubble 207 is further cooled by the second and third cooling rings 203, 204 disposed in the bubble region 273 above the frost line 274.
To obtain the PBT film by such air-cooled inflation method, the temperature of each portion of the bubble 207 is controlled as follows:
The condition (a) is as described above. With respect to the condition (b), unless the bubble is cooled to 130° C. or lower in the neck portion 271, sufficient orientation in TD cannot be achieved in the next expanding portion 272. In other words, the bubble does not have a sufficient melt tension in the expanding portion 272 unless it is cooled to 130° C. or lower in the neck portion 271, resulting in the orientation predominantly in MD.
To meet such temperature condition, the blow-up ratio is 1.5 to 2.8, preferably 2.0 to 2.8.
With respect to the condition (c), the cold orientation of the bubble 207 can be achieved by lowering the bubble temperature to 100° C. or lower at the frost line 274. If the bubble temperature is higher than 100° C. at the frost line 274, the orientation of the bubble 207 is insufficient in both MD and TD in the expanding portion 272.
With respect to the condition (d), the formation of a uniform, thin bubble 207 can be stabilized by cooling the bubble 207 to 80° C. or lower above the frost line 274. If the temperature of the bubble 207 is kept higher than 80° C. above the frost line 274 without the second cooling ring 203, non-uniform orientation is likely to occur, making the entire bubble 207 unstable.
As the condition (e), the bubble is preferably cooled to 50° C. or lower by the third cooling ring 204 after cooling by the second cooling ring. If the bubble 207 were completely cooled only by the second cooling ring 203, non-uniform cooling would be likely to occur. The bubble 207 is preferably cooled to 30 to 40° C. by the third cooling ring 204. These second and third cooling rings 203, 204 do not cause orientation in the bubble 207 thereabove.
To conduct the above temperature control to of the bubble 207, arrangement of the first cooling ring 202, the second cooling ring 203, the third cooling ring 204, the net 205 and the cooling-air-ejecting means 206 is as follows:
(A) First Cooling Ring 202
It is disposed just near the annular die 201 to eject a cooling air to cool the neck portion 271 to 130° C. Thus, the temperature of the bubble 207 becomes 100° C. or lower at the frost line 274 downstream of the expanding portion 272.
(B) Second Cooling Ring 203
It is disposed above the annular die 201 by the distance H1 5 to 10 times the opening diameter of the annular die 201, to eject a cooling air to make the temperature of the bubble 207 80° C. or lower.
(C) Third Cooling Ring 204
It is disposed above the second cooling ring 203 by the distance H2 0.5 to 5.0 times the opening diameter of the annular die 201, to eject a cooling air to make the temperature of the bubble 207 50° C. or lower.
(D) Net 205
The net 205 having a cylindrical shape is positioned between the first cooling ring 202 and the second cooling ring 203, such that it surrounds the bubble 207. The net 205 is cooled by a cooling-air-ejecting means 206 described below, and the cooling of the net 205 by the first and second cooling rings 202, 203 is carried out always under the same conditions without being influenced by the ambient environment (air temperature, etc.), whereby the temperature around the bubble 207 is kept uniform such that the temperature of the bubble 207 meets the above-described conditions (b) to (d).
(E) Cooling-Air-Blowing Apparatus 206
It is disposed outside and below the net 205, and has a circular cooling-air-blowing orifice along the lower end of the net 205, to eject a cooling air slantingly upward such that the temperature around the net 205 is stable in a range of 30 to 40° C., preferably 30 to 35° C. The cooling air blown slantingly upward goes upward along the net 205 to cool the entire net (shown by the arrow in
In the above method, the cooling air ejected from the first cooling ring 202 onto the bubble 207 is preferably a humid air. The humid air, which is humidified and cooled by cold water, contains moisture substantially in a saturated state, having larger cooling effects than a simple cooling air by about 5° C. As the cooling air ejected from the second and third cooling rings 203, 204 onto the bubble 207, it is also preferable to use the humid air from the aspect of cooling efficiency. Because the bubble 207 would be unstable without stable cooling effects, the temperature and humidity of the cooling air are controlled as constant as possible.
The cooling air ejected from the cooling-air-ejecting means 206 onto the net 205 may be a humid air, or usually an air in the room adjusted to the desired temperature, as in the case of cooling by the first to third cooling rings 202-204.
The net 205 may be made of plastics such as nylon, polypropylene, polyesters, etc., or metals such as stainless steel, copper, brass, nickel, etc., preferably with 5 to 20 mesh, particularly 8 to 10 mesh.
As shown in
Though not particularly restrictive, the materials of the partition 220 are preferably acrylic resins such that the bubble region 273 surrounded by the partition 220 can be inspected. As long as it surrounds the bubble region 273, the shape of the partition 220 is not particularly restricted. For instance, it may have a cylindrical or rectangular structure, and preferably a cylindrical structure.
If necessary, a heating means 230 may be disposed inside the partition 220. The heating means 230 may be, for instance, an electric heater in a rod or ribbon shape. Pluralities of rod-shaped electric heaters are preferably disposed. An aluminum foil may be attached to the inner surface of the partition 220 to shut heat radiation. If necessary, a means for blowing up a cold air at about room temperature may be disposed under the partition 220 (immediately above the cooling-air-ejecting means 206). This makes it easy to control the temperature and the flow rate of the air inside the partition 220.
As shown in
As shown in
The production of a PBT resin film by an inflation method can meet the above requirements, and other conditions may be those generally used in the inflation method. Namely, a molten tubular PBT resin is continuously extruded from a crosshead die upward or downward with its thickness prevented from being uneven by rotating the die in one or other direction, inflated with the air introduced thereinto to a predetermined size with its end pinched by rolls, and taken off by winding.
The thermal shrinkage ratio of the PBT film thus produced is substantially 0% at temperatures up to 200° C., with substantially no thermal shrinkage at temperatures up to 200° C. Accordingly, the film size does not change at any secondary working steps such as heat sealing, printing, etc. The orientation of the film can be conducted with or without heating. For instance, it can be easily orientated to about 3.2 times at about 130° C. to obtain a milky-white to translucent orientated film. The film orientated without heating is transparent. The above-described production method provides the PBT film having a thickness of 10 μm or more and a width of 400 to 1200 mm.
Because each portion of the bubble, such as a portion immediately after extrusion, a neck portion, an inflated portion, a frost line, etc. is always kept at the desired temperature by the above-described production method, the resultant film always has a uniform quality. In addition, because the cooling speed can be increased, the film can be formed at a high speed.
(3) Monoaxial Orientating Method
(a) Step of Forming Crystallized Sheet
The PBT resin is melt-blended with additives, other resins, etc. described in [1] (1) above, to produce a molten resin 305. Though not particularly restrictive, the melt blending method is usually carried out by uniformly blending in a double-screw extruder. The blending temperature is preferably 230 to 260° C. When the blending temperature is higher than 260° C., the thermal deterioration of the resin is likely to occur. Thus, when the blending is carried out in an extruder such as a double-screw extruder, the extruder having a screw structure generating no heat, or that having a proper cooling means is used. Incidentally, when the lower limit of the blending temperature is lower than 230° C., the extrusion rate is undesirably unstable.
The melt-blended resin 305 is extruded from the sheet-forming die 307 directly or via another extruder, or via an extruder after pelletized by cooling. The sheet-forming die 307 usually has a gap of 5 mm or less. The temperature of the resin extruded from the sheet-forming die 307 is preferably 210 to 250° C., more preferably 220 to 230° C.
Thus, the molten resin 305 extruded from the sheet-forming die 307 is slowly cooled on the thermal casting roll 301 to form a crystallized sheet 306. The crystallized sheet 306 is easily stretched to a thin, high-orientation film. In order that the extruded resin 305 is not cooled to 200° C. or lower before contact with the thermal casting roll 301, the distance between the sheet-forming die 307 and the thermal casting roll 301 is preferably 20 cm or less. The temperature of the thermal casting roll 301 is preferably controlled to 150 to 200° C. When the temperature of the thermal casting roll 301 is higher than 200° C., the extruded resin 305 has a low melt tension, resulting in difficulty in the formation of the crystallized sheet 306. On the other hand, when the temperature of the thermal casting roll 301 is lower than 150° C., the resultant crystallized sheet 306 has low crystallinity, it is not easily stretched in subsequent steps.
The thickness of the crystallized sheet 306 is preferably 50 to 100 μm to easily stretch the sheet 306 in subsequent steps. To suppress a neck-in phenomenon, by which a sheet extruded from the die and cast becomes narrower than the effective width of the die, from occurring during the formation of the crystallized sheet 306 having a thickness of 50 to 100 μm as much as possible, the peripheral speed of the thermal casting roll 301 is determined as 5 to 15 m/minute. The outer diameter of the thermal casting roll 1 is preferably 35 to 70 cm.
(b) Orientation Step
(i) Primary Orientation (Stretching)
As shown in
The orientation is preferably 1.5 times or more, more preferably 2 to 4 times, though variable depending on the thickness of the crystallized sheet 306. The larger the orientation, the higher the transparency of the stretched film. With a proper peripheral speed ratio of the thermal casting roll 301 to the second roll 302, crystallized sheet 306 can be stretched to the desired extent. Though not particularly restrictive, the outer diameter of the second roll 302 may be 35 to 70 cm, like the thermal casting roll 301.
When reorientation (secondary stretching) is conducted after the primary stretching as described below, the temperature of the second roll 302 is preferably controlled to 100 to 150° C. On the other hand, when the orientation step consists of the primary stretching only, a cooling-fixing treatment can be conducted on the primarily stretched film by controlling the temperature of the second roll 302 to 40° C. or lower. The cooling-fixing treatment herein means a treatment of the film at a temperature equal to or lower than the Tg of PBT (20 to 45° C.). The cooling-fixing treatment stabilizes the stretched state of the film. What is necessary to make the cooling-fixing treatment longer is to bring the primarily stretched film into contact with a third roll 303 disposed in parallel with the second roll 302 as shown in
When the cooling-fixing treatment is conducted by the third roll 303, the temperature of the second roll 302 may be controlled between a temperature higher than the Tg of PBT and a temperature of (the melting point of PBT −50° C.), to further reduce the thermal shrinkage ratio of the film.
(ii) Secondary Stretching
The primarily orientated film is preferably further stretched in a machine direction (secondary stretching). The secondary stretching further provides the film with improved transparency and a smaller thickness. The secondary stretching is conducted in a machine direction by a peripheral speed difference between the second roll 302 and the third roll 303 shown in
When orientation (tertiary stretching) described below is conducted again after the secondary stretching, the temperature of the third roll 303 is preferably controlled to 40 to 100° C. On the other hand, when no tertiary stretching is conducted, the secondarily stretched film can be subjected to a cooling-fixing treatment by controlling the temperature of the third roll 303 to 40° C. or lower. When the cooling-fixing treatment is conducted for a longer period of time, the secondarily stretched film is brought into contact with a fourth roll 304 disposed in parallel with the third roll 303 as shown in
When the cooling-fixing treatment is conducted by the fourth roll 304, the temperature of the third roll 303 may be controlled to a temperature higher than the Tg of PBT and the melting point of PBT −50° C. or lower, to further decrease the thermal shrinkage ratio of the film.
(iii) Tertiary Stretching
The secondarily stretched film may be further oriented in a machine direction (tertiary stretching). When the tertiary stretching is conducted, the secondarily stretched film is stretched in a machine direction by a peripheral speed difference between the third roll 303 and the fourth roll 304 shown in
(iv) Lateral Orientation
The PBT film produced by any one of the above methods (i) to (iii) may subsequently be subjected to lateral orientation in TD (width direction). The lateral orientation may be conducted by known methods such as a tentering method, etc.
(v) Heat Treatment
Though the PBT film thus produced has excellent dimensional stability, it may further be subjected to a heat treatment to improve its thermal shrinkage ratio. The heat treatment may be conducted by a heat-fixing treatment method or a heat shrinkage treatment method. These heat treatments are preferably conducted at a temperature higher than the Tg of PBT and the melting point of PBT −50° C. or lower.
The heat-fixing treatment is conducted by a tentering method, a rolling method or a compression method. The heat shrinkage treatment may be conducted by a tentering method, a rolling method or a compression method, using a belt conveyor or floating. The heat-fixing treatment and the heat shrinkage treatment may be combined.
The PBT film thus produced is translucent or transparent, with higher uniformity of thickness and a lower thermal shrinkage ratio than those of the conventional monoaxially orientated film. Specifically, the film having an average thickness of 8 to 20 μm has a thickness difference of 1 to 2 μm, and a thermal shrinkage ratio of 0.1% or less in MD (machine direction) and 0.2% or less in TD (width direction). The thickness difference is a difference between the maximum thickness and the minimum thickness among those measured on the PBT film at six points in total in a width direction in a center portion and both end portions (two points each). The smaller difference means good results. The thermal shrinkage ratio was measured on the PBT film exposed to 150° C. for 10 minutes in both MD and TD. Because of such uniformity, it is possible to form a print layer and a vapor-deposited metal layer with little unevenness, with little variation in a film size in the secondary working such as heat sealing, printing, etc.
Because the thermal casting roll and the first to fourth rolls are always kept at the desired temperatures in the production method described above, the resultant film always has uniform quality. In addition, because a cooling step is not inserted into the production of the unoriented film, high-speed film formation can be achieved.
[7] Formation of Linear Scratches on Film
To impart the easy-to-straight-tear characteristics to the shape-memory PBT laminate film, at least one of the PBT film, the rigid film and the sealant film is preferably provided with a lot of substantially parallel linear scratches formed by the method described below on the entire surface. Such linear scratches make it possible to easily tear the shape-memory PBT laminate film straight. Accordingly, when the shape-memory PBT laminate film is used as package sheets for lids for instant food containers, for instance, the lids can be partially opened. Such linear scratches are preferably formed particularly on the PBT film. The linear scratches can be formed by bringing a continuously running film into contact with a means having a lot of fine projections for forming linear-scratches. The method for forming linear scratches will be explained below in detail referring to the drawings.
(1) Formation of Linear Scratches on Film in Progressing Direction
As shown in
The nip rolls 412 and 413 disposed upstream and downstream of the pattern roll 402 as the tension-controlling rolls give a tension to the film 401 moving over the pattern roll 402. Further as shown in
Because the pattern roll 402 has a lower peripheral speed than the progressing speed of the film 401, it is preferable to rotate the pattern roll 402 in an opposite direction to the progressing direction of the film 401. This can prevent wrinkles from being generated on the film and dust generated by the formation of linear scratches from remaining on the surface of the pattern roll 402, thereby forming linear scratches of proper length and depth. In the present invention, the progressing speed of the film 401 is preferably 10 to 500 m/minute. The peripheral speed of the pattern roll 402 (rotation speed in an opposite direction to the progressing direction of the film 401) is preferably 1 to 50 m/minute.
Usable as the pattern roll 402 is, for instance, that described in JP 2002-59487 A. This has a structure having a lot of fine particles having Mohs' hardness of 5 or more attached to the surface of a metal roll by an electrodeposition method or by an organic or inorganic binder. The metal roll is made of iron, iron alloys, etc. The metal roll preferably has a plating layer of nickel or chromium. The fine particles having Mohs' hardness of 5 or more are, for instance, cemented carbide particles such as tungsten carbide, silicon carbide particles, boron carbide particles, sapphire particles, cubic boron nitride (CBN) particles, natural or fine synthetic diamond particles, etc. Fine synthetic diamond particles having large hardness and strength are particularly desirable. The particle size of the fine particles is properly determined depending on the depth and width of linear scratches formed. In the present invention, the fine particles desirably have a particle size of 10 to 100 μm with unevenness of 5% or less. How many fine particles are attached to the roll surface is properly selected such that the formed linear scratches have desired intervals. To form uniform linear scratches, the fine particles are preferably attached to 50% or more of the roll surface. A specific example of the pattern roll 402 may be a pattern roll having a lot of fine synthetic diamond particles fixed with a nickel electrodeposition layer to the surface of an iron roll at an area ratio of 50% or more. The outer diameter of the pattern roll 402 is preferably 2 to 20 cm, more preferably 3 to 10 cm.
The pattern roll 402 may also be a needle roll having metal needles embedded in the surface of a metal roll regularly in a lattice pattern with extremely small intervals. In addition to the pattern roll 402, the means for forming linear scratches may be a pattern plate having many fine particles having Mohs' hardness of 5 or more as described above on the surface of a plate body.
Usable in place of a nozzle having a strip-shaped blowing orifice 431 (the same as shown in FIGS. 25 to 26) shown in
The winding of the film 401 around the fixed pattern roll 402 is preferably conducted such that an angle θ between the winding direction of the film 401 and the unwinding direction of the film 401 is in a range of 60° to 170° as shown in
In place of the air-blowing means, a brush may be brought into sliding contact with the opposite side of the roll-sliding surface, to give a uniform contact force to the roll-sliding surface. The brush hairs are preferably movable on a sliding surface of the brush on the film 401 (hereinafter referred to as “brush-sliding surface” unless otherwise described), at a lower speed than the progressing speed of the film 401 in an opposite direction to the progressing direction of the film 401. Thus, as shown in
The outer diameter of the rotatable roll brush 405 is preferably 5 to 10 cm. The hairs 451 of the rotatable roll brush 405 preferably has a bending recovery ratio of 70% or more, a diameter of 0.1 to 1.8 mm, and a length of 1 to 5 cm. The hairs 451 of the rotatable roll brush 405 have a density of 100 to 500/cm2 on the brush-sliding surface. The bending recovery ratio is determined as follows: First, two looped hair fibers having a length of about 26 cm are crossed like a chain with an upper loop fixed to a hook, and a load (g) as heavy as half of the denier of the hair fiber is applied to a lower loop for 3 minutes, and a sample having a length of about 3 cm is cut out of a pair of loops bent like pine leaves, and left to stand for 60 minutes. An open angle (θ4) of the sample is measured to calculate the bending recovery ratio by the equation of (θ4/180)×100 (%). Though not particularly restrictive, the tip end of the hairs 451 is preferably substantially in a U-shape or in a tapered shape. The materials of the hairs 451 are preferably synthetic resins such as polypropylene, nylon, acrylic resins, polyethylene, etc., though not particularly restrictive.
The rotatable roll brush 405 is preferably in sliding contact with the film 401 at a pressure of 1 to 490 kPa (0.01 to 5 kgf/cm2) on the brush-sliding surface. The peripheral speed of the rotatable roll brush 405 (rotation speed in an opposite direction to the progressing direction of the film 401) is preferably 1 to 50 m/minute.
The length and depth of linear scratches are adjusted to obtain the desired level of the easy-to-straight-tear characteristics, by properly changing the moving speed of the film 401, the peripheral speed of the pattern roll 402, the size of the fine diamond particles 404, the outer diameter of the pattern roll, the gas pressure from the nozzle 403, the pressure of the rotatable roll brush 405, a tension given to the nip rolls 412 and 413, etc.
(2) Formation of Slanting Linear Scratches on Film
The endless pattern belt 406 is rotated in the width direction of the film 401 as shown in FIGS. 31(a) and 31(b), such that small pattern rolls 421 are in sliding contact with the continuous film 401 to form linear scratches on the film 401 slantingly to the progressing direction of the film 401. The endless pattern belt 406 is preferably constituted by a larger number of the pattern rolls 421 at a high density. The longitudinal length and outer diameter of each small pattern rolls 421 are both preferably 5 to 10 cm.
The angle of the slanting linear scratches to the progressing direction of the film can be changed by properly adjusting the peripheral speed of the endless pattern belt 406 and the speed of the film 401. The peripheral speed of the endless pattern belt 406 is usually 1 to 100 m/minute. Small pattern rolls 421 are rotated in an opposite direction to the progressing direction of the endless pattern belt 406 on the roll-sliding surface at a peripheral speed of 1 to 50 m/minute as in the case of the pattern roll 402 described in (1) above.
The endless brush 407 is preferably rotated, such that the direction of the hairs 471 moving in sliding contact with the film 401 is opposite to the direction of the endless pattern belt 406 moving in sliding contact with the film 401. Thus, the endless brush 407 and the endless pattern belt 406 are rotated in the same direction. The hairs 471 of the endless brush 407 are preferably as long as 4 to 8 cm. The preferred requirements of the hairs 471 of the endless brush 407 concerning a bending recovery ratio, a diameter, a density on the brush-sliding surface, a tip shape and a material are the same as those of the rotatable roll brush 405 described in (1) above. The pressure of the endless brush 407 on the brush-sliding surface may be 1 to 490 kPa (0.01 to 5 kgf/cm2), the same as that of the rotatable roll brush 405 described in (1) above. The pressure for forcing the endless brush 407 to come into sliding contact with the film 401 may be controlled by properly adjusting the vertical position of the endless brush 407 by rotating a height-controlling knob 473. The peripheral speed of the endless brush 407 is preferably 1 to 50 m/minute. The peripheral speed of the endless brush 407 may be controlled by properly adjusting the rotation speed of a motor 474.
The endless pattern belt 406 and the endless brush 407 are preferably longer than the width of the film 401 in their progressing directions, such that the entire film 401 in the width direction are in sliding contact with the endless pattern belt 406 and the endless brush 407.
Support shafts 491a and 491b supporting the pattern rolls 422a and 422b are movable up and down, and the roll trains 408a and 408b are movable straight along the guide rails 481a and 481b, respectively, in the width direction of the film 401. The guide means comprising the support shafts 491a and 491b movable up and down and the guide rails 481a and 481b can independently move the roll trains 408a and 408b in the width direction of the film 401. Accordingly, the roll trains 408a and 408b move from one end of the film 401 to the other end thereof in sliding contact with the film 401, and then separate from the film 401 and return to the original position, and this cycle is repeated. During this cycle, the movement of the roll trains 408a and 408b is controlled such that any of the roll trains is always in sliding contact with the entire width of the film 401, thereby forming linear scratches on the film slantingly to its progressing direction. As the guide means, instead of making the support shafts 491a and 491b not movable up and down relative to the guide rails 481a and 481b, the guide rails 481a and 481b may move up and down.
The longitudinal length and outer diameter of each pattern roll 422a, 422b may be about 5 to 10 cm. Intervals between the adjacent pattern rolls 422a, 422b are preferably narrower than at least the width of the pattern roll, such that the pattern rolls are disposed at a high density. Each roll train 408a, 408b is longer than the width of the film 401.
The apparatus shown in
The endless brushes 407a and 407b are preferably rotated such that the moving direction of their hairs in sliding contact with the film 401 is opposite to the moving direction of the roll trains 408a and 408b in sliding contact with the film 401. The preferred requirements of the hairs of the endless brushes 407a and 407b concerning a bending recovery ratio, a diameter, a length, a density on the brush-sliding surface, a tip shape and a material, and the preferred requirements of the endless brushes 407a and 407b concerning a pressure on the brush-sliding surface, and a peripheral speed may be the same as those of the endless brush 407 in the apparatus shown in
The angle of the slanting linear scratches to the progressing direction of the film may be changed by properly adjusting the speed of the roll trains 408a and 408b in sliding contact with the film 401 and the moving speed of the film 401. The pattern rolls 422a and 422b are rotated in an opposite direction to the moving direction of the roll trains 408a and 408b on the roll-sliding surface. Their peripheral speed may be the same as that of the pattern rolls 402 described in (1) above.
FIGS. 34(a) and 34(b) show another example of an apparatus for forming linear scratches slanting relative to the progressing direction of the film 401. In this embodiment, two pattern rolls 423a and 423b each having a larger longitudinal length than the width of the film 401 are disposed in parallel in two rows in the progressing direction of the film 401. The longitudinal length of the pattern rolls 423a and 423b is preferably 2 times the width of the film 401 or more.
Support shafts 492a and 492b supporting the pattern rolls 423a and 423b are movable up and down, and the pattern rolls 423a and 423b are movable straight along guide rails 482a and 482b in the width direction of the film 401. The pattern rolls 423a and 423b can move independently in the width direction of the film 401 by a guide means comprising the 492a and 492b movable up and down and the guide rails 482a and 482b. Accordingly, the pattern rolls 423a and 423b are moved from one end of the film 401 to the other end thereof in sliding contact with the film 401, and then separate from the film 401 and return to the original position, and this cycle is repeated. During the cycle, the movement of the pattern rolls 423a and 423b can be controlled such that any of the pattern rolls are always in sliding contact with the entire width of the film 401, thereby forming linear scratches slanting to the progressing direction of the film. The angle of the slanting linear scratches to the progressing direction of the film can be changed by properly adjusting the sliding speed of the pattern rolls 423a and 423b and the moving speed of the film 401.
The apparatus shown in
Though the apparatuses shown in FIGS. 30 to 34 comprise the endless brushes as film-pressing means, they may comprise the air-blowing means described in (1) above.
(3) Formation of Linear Scratches on Film in Width Direction
Using the apparatus having the structure shown in
FIGS. 38(a) and 38(b) show another example of an apparatus for forming linear scratches on the film 401 in a width direction.
Support shafts 493a and 493b supporting the pattern rolls 424a and 424b are movable up and down, and the pattern rolls 424a and 424b are movable straight along guide rails 483a and 483b at a predetermined angle relative to the center line 417 of the film 401. The pattern rolls 424a and 424b can move independently at a predetermined angle relative to the center line 417 of the film 401, by a guide means comprising 493a and 493b movable up and down and the guide rails 483a and 483b. Because the pattern roll 424b is longer than the pattern roll 424a in a longitudinal direction, the pattern rolls 424a and 424b can cross each other during moving in opposite directions. The pattern rolls 424a and 424b thus move from one end of the film 401 to the other end thereof in sliding contact with the film 401, and separate from the film 401 and return to the original position, and this cycle is repeated. Linear scratches can be formed on the film in a width direction thereof, by controlling the movement of the pattern rolls 424a and 424b such that any of the pattern rolls is always in sliding contact with the entire width of the film 401.
As shown in
In the apparatuses shown in FIGS. 35 to 38, linear scratches can be formed on the film 401 slantingly to a progressing direction thereof, by properly adjusting operation conditions, etc. Though the apparatuses shown in FIGS. 35 to 38 comprise the endless brushes as film-pressing means, they may comprise the air-blowing means described in (1) above.
In the easy-to-straight-tear film produced by the above-described method, the above linear scratches are preferably as deep as 1 to 40% of the film thickness, to meet both requirements of high film strength and good easy-to-straight-tear characteristics. The linear scratches are preferably as deep as 0.1 to 10 μm and as wide as 0.1 to 10 μm, and the intervals of the linear scratches are preferably 10 to 200 μm.
[8] Formation of Fine Pores on Film
To provide the shape-memory PBT laminate film with easy-to-straight-tear characteristics, at least one of the PBT film, the rigid film and the sealant film may be entirely provided with fine penetrating pores. The fine penetrating pores are particularly preferably formed in the sealant film. The fine pores have an average opening diameter of 0.5 to 100 μm, and a distribution density of about 500/cm2 or more. When the distribution density of the fine pores is less than about 500/cm2, easy tearing is insufficient. Incidentally, the upper limit of the density of the fine pores is not particularly restricted as long as technically possible.
To form the fine pores on the film, the methods disclosed in Japanese patent 2,071,842 and JP 2002-059487 A, for instance, may be used. Using the method disclosed in Japanese patent 2,071,842, for instance, a film is caused to pass between a first roll having a lot of particles with sharp edges and a Mohs' hardness of 5 or more on the surface (the same as the pattern roll 402 described in [7] above), and a second roll having a smooth surface, with pressure applied to the film passing between the rolls adjusted uniform over the entire surface of the film in contact with the roll, to form a lot of fine pores described above on the film with sharp edges of a lot of particles on the first roll surface. The second roll may be, for instance, an iron roll, an iron roll plated with Ni, Cr, etc., a stainless steel roll, a specialty steel roll, etc.
[9] Vapor Deposition of Ceramics or Metals
To improve the gas barrier of the shape-memory PBT laminate film, the PBT film may be vapor-deposited with metals, ceramics, etc., or coated with resins. Specific examples of the ceramics for vapor deposition include silica, alumina, etc. The vapor deposition of metals, ceramics, etc. may be carried out by known methods.
[10] Functional Polybutylene Terephthalate Film
(1) Easy-to-Straight-Tear Polybutylene Terephthalate Film
The easy-to-straight-tear PBT film of the present invention has a lot of substantially parallel linear scratches formed on at least one surface thereof by the method described in the above [7]. It can be easily torn straight from any point along the linear scratches, because of the characteristics of easily tearing straight in one direction regardless of the orientation of the original film. A wrapping bag formed from the easy-to-straight-tear PBT film of the present invention can be opened in a strip shape without tapering while keeping a constant width. In addition, the easy-to-straight-tear PBT film of the present invention has excellent gas barrier, because the linear scratches do not penetrate the film.
Though not particularly restrictive, the PBT film used for the production of the easy-to-straight-tear PBT film is preferably obtained by the method described in [6] above. Because the PBT film obtained by the method described in [6] above has a small thermal shrinkage ratio, a stable vapor deposition layer can be formed thereon.
The depth of the linear scratches of the easy-to-straight-tear PBT film is preferably 1 to 40% of the film thickness, to meet both requirements of high film strength and good easy-to-straight-tear characteristics. The linear scratches are preferably as deep as 0.1 to 10 μm and as wide as 0.1 to 10 μm, and the intervals of the linear scratches are preferably 10 to 200 μm.
The thickness of the easy-to-straight-tear PBT film is preferably about 5 to 50 μm, more preferably about 10 to 20 μm, for instance, about 12 μm. With the thickness of about 5 to 50 μm, sufficient odor retention and gas barrier as well as good gloss and printability are obtained.
The easy-to-straight-tear PBT film may be vapor-deposited with metals, ceramics, etc., or coated with resins. Specific examples of the ceramics for vapor deposition include silica, alumina, etc. The vapor deposition of such ceramics provides the easy-to-straight-tear PBT film with improved gas barrier. The vapor deposition of metals, ceramics, etc. may be carried out by known methods. The metals, ceramics, etc. may be vapor-deposited on the film with or without linear scratches.
The easy-to-straight-tear PBT film may be a laminate film having a layer of common polyolefins and special polyolefins. Specifically, they are low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), cast polypropylene (CPP), linear-low-density polyethylene (LLDPE), very-low-density polyethylene (VLDPE), ethylene-vinyl acetate copolymers (EVA), ethylene-acrylic acid copolymers (EAA), ethylene methacrylic acid copolymers (EMAA), ethylene ethyl acrylate copolymers (EEA), ethylene-methylmethacrylate copolymers (EMMA), ethylene-methyl acrylate copolymers (EMA), ionomers (IO), etc. To further improve moisture resistance and gas barrier, the laminate film preferably comprises an intermediate layer formed by an aluminum foil, a silica-deposited polyethylene terephthalate film, an alumina-deposited polyethylene terephthalate film, etc.
In the production of the laminate film, the PBT film may be formed with linear scratches and then laminated with another film or film laminate layer with or without the above intermediate layer, as described below. The lamination is carried out by extrusion with an adhesive layer between the layers. The adhesive layer is preferably made of polyethylene.
The easy-to-straight-tear PBT film having linear scratches formed in a progressing direction thereof (longitudinal direction) may be used for wrapping bags for stick cookies. The wrapping bags formed by the easy-to-straight-tear PBT film of the present invention having linear scratches in a longitudinal direction can be opened in a strip shape without tapering while keeping a constant width, the cookies are not damaged. Though wrappings formed by OPP films for rice balls, etc. are provided with cutting tapes (tear tapes) in alignment with the opening width, the easy-to-straight-tear PBT film of the present invention having linear scratches in a longitudinal direction does not need a tear tape, because it can be opened while keeping the opening width.
The easy-to-straight-tear PBT film having linear scratches slanting to a progressing direction thereof may be used for wrapping bags of powdery medicine, seasonings for lunch boxes, etc. A wrapping bag formed by the easy-to-straight-tear PBT film of the present invention having slanting linear scratches can be easily torn slantingly in a corner thereof.
The easy-to-straight-tear PBT film having linear scratches in a width direction (transverse direction) may be used for stick-shaped wrapping bags of powdery instant food, etc. Using the easy-to-straight-tear PBT film of the present invention having linear scratches in a transverse direction, stick-shaped wrapping bags having increasing demand can be produced at a low cost.
The easy-to-straight-tear PBT film can be uniformly formed with a lot of fine penetrating pores and/or a lot of fine non-penetrating pores by the method described in [8] above, to further improve its easy-to-straight-tear characteristics, and to impart easy tearing characteristics in other directions than the direction of the linear scratches.
(2) Porous Polybutylene Terephthalate Film
The porous PBT film of the present invention has a lot of fine penetrating pores and/or a lot of fine non-penetrating pores uniformly formed by the method described in [8] above. Accordingly, the porous PBT film of the present invention has good twistability and twist retention, without suffering from tearing when twisted. The fine pores preferably have an average opening diameter of 0.5 to 100 μm and a density of about 500/cm2 or more. When the density of the fine pores is less than about 500/cm2, the twist retention is insufficient.
Though not particularly restrictive, the PBT film used for the production of the porous PBT film is preferably obtained by the method described in [6] above.
The porous PBT films of the present invention are useful as package sheets provided with good tearability and twist retention as well as practical properties without losing heat resistance, odor retention, water resistance, etc., excellent properties of the PBT film. When gas barrier is required for package sheets formed by the porous PBT film of the present invention, those having non-penetrating fine pores should be used.
Though the present invention has been explained above referring to the drawings, the present invention is not restricted thereto, and various modifications may be added to the present invention unless changing the spirit thereof.
The present invention will be explained in more detail referring to Examples below without intention of restricting the present invention thereto.
Using two types of PBT resins (“Toraycon 1209X01” and “Toraycon 1200S” (tradenames) both commercially available from Toray Industries, Inc.), a tubular film was extruded from a die having a die lip of 150 mm in outer diameter at a resin extrusion temperature of 230° C., a resin-extruding pressure of 11.8 MPa (120 kgf/cm2) and a blow-up ratio of 1.5 to 2.5, and taken up to obtain a film while cooling by first to third cooling rings and a humid air ejected from a cooling-air-ejecting means. The properties of the resultant film were measured by the following methods. The results are shown in Table 1.
Average thickness: Measured by a dial gauge.
Average bulk density: The weight of a rectangular test piece of 10 cm×10 cm was measured by a precise weighing machine.
Tensile rupture strength: The tensile rupture strength of a 10-mm-wide rectangular test piece was measured according to ASTM D882.
Tensile rupture elongation: The tensile rupture elongation of a 10-mm-wide rectangular test piece was measured according to ASTM D882.
Thermal shrinkage ratio: The shrinkage ratio of a film was measured in both machine direction (MD) and transverse direction (TD) when exposed to 100° C., 130° C., 160° C., 175° C. and 200° C., respectively, for 10 minutes.
Note: (1)“Toraycon” (trade name) commercially available from Toray Industries, Inc.
As shown in Table 1, the PBT films produced by the method of the present invention have a thermal shrinkage ratio of substantially zero even when heated to 200° C., indicating excellent thermal shrinkage resistance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002-275939 | Sep 2002 | JP | national |
| 2003-1533 | Jan 2003 | JP | national |
| 2003-1534 | Jan 2003 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP03/12102 | 9/22/2003 | WO | 3/18/2005 |
