WO2017138930A1 - Inflation molding equipment for producing cylindrical film - Google Patents

Abstract

Inflation molding equipment and a process for producing a cylindrical film are disclosed. The inflation molding equipment comprises an extruder for melt extruding a stock material, a single-layer or multi-layer cylindrical die attached to a discharge port of the extruder, and an air ring device for cooling a cylindrical film extruded from the cylindrical die, wherein the cylindrical die has an annular discharge port having an outer diameter of D1, the air ring de-vice is attached on the cylindrical die, and the air ring device has at least one cooling gas outlet port, the cooling gas outlet port having a cooling gas channel defined by an outer circumferential wall having a height of H and an inner circumferential wall having a height; lower than the outer circumferential wall, and D1 and H satisfy a relationship of Q. 5xD1≤H≤1. 5xD1.

Description

DESCRIPTION

Title of Invention: Inflation Molding Equipment for Producing Cylindrical Film

Technical Field

[ 0001 ] The present invention relates to an inflation molding equipment and a process for producing a

cylindrical film. More specifically, the present invention relates to an inflation molding (blown film extrusion molding) equipment capable of producing a cylindrical film having excellent quality with a high dimensional precision, a process for producing a cylindrical film using the inflation molding equipment, and a process for producing a pneumatic tire using the cylindrical film.

Background Art

[ 0002 ] It is known to extrude a melt of a

thermoplastic resin composition or a thermoplastic elastomer composition comprising as a continuous phase

(sea phase) a thermoplastic resin and as a disperse phase (island phase) an elastomer dispersed in the

thermoplastic resin by an extrusion molding equipment into a molded article in the form of film, etc. (see PLT 1) . When a cylindrical film is produced from such a composition by the inflation molding method, in the process in which a cylindrical film (hereinafter referred to also as a "bubble") in a softened state melt-extruded from a cylindrical die is drawn in the vertical direction to thereby expanding the bubble while cooling it, the bubble is stretched in the vertical direction (machine direction or conveyance direction) and transverse direction (circumferential direction) perpendicular to the vertical direction. When a cylindrical film is produced from a thermoplastic elastomer composition, if the elastomer particles present as a disperse phase in the thermoplastic elastomer composition are drawn and stretched in the vertical and transverse directions of the bubble in the process of expanding the bubble melt- extruded from a cylindrical die, and accordingly, when the drawing force applied to the cylindrical film is released after inflation molding, the cylindrical film easily shrinks, and consequently the resulting

cylindrical film has low dimensional precision, i.e., low precision to a target dimension value. Further, the resulting film has a problem that the film has wrinkles or waviness due to shrinkage. Therefore, when a cooling gas is blown from an air ring device to the bubble to cool down the bubble, it is desirable to expand the bubble to a target maximum diameter while gradually cooling the bubble. In order to improve productivity and yield, it is desirable to expand the bubble to a target maximum diameter while gradually cooling the bubble without impairing the stability of the bubble.

Citations List

Patent Literature

[0003] PLT 1: Japanese Unexamined Patent Publication

(JP-A) No. 2015-143317

Summary of Invention

Technical Problem

[0004] In view of the above conventional problems, the present invention is directed to provide an inflation molding equipment capable of improving the stability of a bubble and capable of reducing shrinkage of the

cylindrical film, and as a result capable of producing a cylindrical film with a high dimensional precision. [ 0005 ] The inventors have carried out experiments to achieve the above object, and as a result found that, in an inflation molding equipment for producing a

cylindrical film, when an outer diameter Dl of an annular discharge port of a cylindrical die and a height H of an outer circumferential wall of a cooling gas outlet port of an air ring device for cooling a bubble extruded from the annular discharge port satisfy a specific

relationship, it is possible to improve the stability of the bubble and to reduce shrinkage of the cylindrical film, and as a result it is possible to produce a cylindrical film having a high dimensional precision, and consequently completed the present invention.

Solution to Problem

[ 0006 ] The present invention includes the following

[Embodiment 1] to [Embodiment 7] .

[Embodiment 1] An inflation molding equipment

comprising :

an extruder for melt extruding a stock material, a single-layer or multi-layer cylindrical die attached to a discharge port of the extruder, and

an air ring device for cooling a cylindrical film extruded from the cylindrical die, wherein

the cylindrical die has an annular discharge port having an outer diameter of Dl,

the air ring device is attached on the cylindrical die, and

the air ring device has at least one cooling gas outlet port, the cooling gas outlet port having a cooling gas channel defined by an outer circumferential wall having a height of H and an inner circumferential wall having a height lower than the outer circumferential wall, and Dl and H satisfy a relationship of the following formula ( 1 ) :

0.5xDl<H<l .5xDl ( 1) .

[0007] [Embodiment 2] The inflation molding equipment according to Embodiment 1, wherein the stock material is a thermoplastic elastomer composition having an island- in-sea structure comprised of a continuous phase comprising a thermoplastic resin and a disperse phase comprising an elastomer.

[0008] [Embodiment 3] The inflation molding equipment according to Embodiment 1, wherein Dl and H satisfy a relationship of the following formula (2) :

0.8xDl<H<l .2xDl (2) .

[0009] [Embodiment 4] The inflation molding equipment according to any one of Embodiments 1 to 3 wherein a ratio of an effective length L of a screw to a screw diameter D of the extruder, L/D, is 32 or more.

[0010] [Embodiment 5] The inflation molding equipment according to any one of Embodiments 1 to 4, wherein the air ring device does not have a rectifying cylinder spaced apart from the outer circumferential wall of the cooling gas outlet port at the outer circumferential side of the outer circumferential wall.

[0011] [Embodiment 6] A process for producing a cylindrical film, comprising:

providing the inflation molding equipment according to any one of Embodiments 1 to 5;

melt extruding a molten thermoplastic elastomer composition from the extruder to the cylindrical die, the molten thermoplastic elastomer composition comprising a thermoplastic resin selected from the group consisting of a polyamide-based resin, a polyvinyl-based resin, a polyester-based resin, and a blend of two or more of these resins as a continuous phase, and a modified elastomer as a disperse phase; and

extruding the molten thermoplastic elastomer composition as a cylindrical film from the cylindrical die .

[0012] [Embodiment 7] A process for producing a pneumatic tire comprising:

producing a cylindrical film by the process according to Embodiment 6;

cutting the resulting film in accordance with a size of the pneumatic tire to form an inner liner;

forming a green tire comprising the inner liner; and vulcanizing the green tire to form a pneumatic tire.

[0013] Advantageous Effects of Invention

According to the inflation molding equipment of the present invention, it is possible to improve the stability of a bubble and to reduce shrinkage of the cylindrical film, and as a result, it is possible to produce a cylindrical film with a high dimensional precision. The cylindrical film produced using the inflation molding equipment of the present invention has excellent features of a high dimensional precision and few wrinkles or waviness on the surface thereof. Further, since the inflation molding equipment of the present invention can produce a cylindrical film having a high dimensional precision without arranging a rectifying cylinder spaced apart from the outer circumferential wall of the cooling gas outlet port of the air ring device as described in Embodiment 1 at the outer circumferential side of the outer circumferential wall, and therefore it is possible to eliminate a preliminary adjustment of the inflation molding equipment accompanying use of a conventional rectifying cylinder and to reduce the costs or work involved in the rectifying cylinder.

Brief Description of Drawings

[0014] [FIG. 1] FIG. 1 is a schematic view showing one embodiment of a process for producing a cylindrical film using an inflation molding equipment according to the present invention.

[FIG. 2] FIG. 2 is a schematic view showing another embodiment of a process for producing a cylindrical film using an inflation molding equipment according to the present invention.

[FIG. 3] FIG. 3 is a schematic view showing a mechanism of cooling a cylindrical film by an air ring device when producing a cylindrical film using an inflation molding equipment according to the present invention.

Description of Embodiments

[0015] Embodiments of the present invention will be explained below in detail along referring to the attached drawings. FIG. 1 shows one embodiment of an inflation molding equipment according to the present invention. This inflation molding equipment 1 comprises extruder 10 comprising stock material feeder 11, cylinder 12 and discharge port 13, and cylindrical die 20 connected to discharge port 13 of extruder 10. A melt-extrudable stock material is introduced into cylinder 12 set to a melt extrusion temperature from stock material feeder 11 of extruder 10, and the stock material is allowed to melt in cylinder 12 while extruding it by a rotating screw (not shown) to the discharge port side, and then the resulting molten stock material is extruded from discharge port 13 to cylindrical die 20. Cylindrical die 20 has an annular discharge port 21 having an outer diameter Dl . The molten stock material introduced into cylindrical die 20 is extruded from annular discharge port 21 as a cylindrical film (bubble) Fl in a softened state, and cylindrical film Fl gradually expands until the diameter thereof reaches the maximum diameter D2 while being cooled along with being conveyed upward. The term "the diameter of the cylindrical film" refers herein to the outer diameter of the cylindrical film. The target value of D2 is

determined in accordance with the desired size of the cylindrical film. Hereinafter, the ratio of D2 to Dl , D2/D1, will be referred to as a "blow ratio". In FIG. 1, a pair of stabilizing plates 40A, 40B facing each other are provided above air ring device 30. Cylindrical film Fl is cooled along with being conveyed upward and is deformed into flat while being conveyed by the pair of stabilizing plates 40A, 40B facing each other. In place of the pair of stabilizing plates 40A, 40B, for example, a plurality of guide rollers arranged in parallel with each other in a direction perpendicular to the conveyance direction of bubble B may be used. Above stabilizing plates 40A, 40B, a pair of pinch rolls 50A, 50B are arranged for folding cylindrical film Fl deformed into flat by stabilizing plates 40A, 40B, into a sheet.

Cylindrical film (lay-flat film) F2 which is obtained by folding the cylindrical film by the pair of pinch rolls 50A, 50B is wound up by windup roll 60 through guide rolls 51, 52A, 52B, 53. Before cylindrical film F2 is wound up by the windup roll or after it is wound up, one end of cylindrical film F2 may be cut open to obtain a wide film, or both ends of cylindrical film F2 may be slit to obtain two films, as necessary.

[ 0016 ] FIG. 2 shows another embodiment of an inflation molding equipment according to the present invention. This inflation molding equipment comprises a first extruder 10A for extruding the molten first stock material and a second extruder 10B for extruding the molten second stock material. The first extruder 10A and the second extruder 10B respectively comprise stock material feeder 11A, 11B, cylinder 12A, 12B, and discharge port 13A, 13B. A multilayer cylindrical spiral die is attached to each of discharge port 13A of the first extruder 10A and discharge port 13B of the second extruder 10B. The stock material melt extruded from the first extruder and the stock material melt extruded from the second extruder may be the same or different. A multilayer film can be produced using an extrusion molding equipment having a configuration as shown in FIG. 2.

[0017] FIG. 3 is a view schematically showing a mechanism for cooling a cylindrical film by the air ring device when using an inflation molding equipment according to the present invention to produce a

cylindrical film. In FIG. 3, one embodiment of the cylindrical die and the air ring device is shown by a schematic vertical cross-sectional view. The air ring device schematically shown in FIG. 3 is a "dual lip" type air ring device and has two annular cooling gas outlet ports. Air ring device 30 is mounted on cylindrical die 20. Air ring device 30 has annular plenum chamber 31. A cooling gas is fed from an external supply source (not shown) to annular plenum chamber 31. The cooling gas fed to annular plenum chamber 31 passes through annular channel 32 to lower annular outlet port 33 and upper annular outlet port 34. The cooling gas is blown from lower annular outlet port 33 and upper annular outlet port 34 to the cylindrical film. Upper annular outlet port 34 has cooling gas channel 35 defined by outer circumferential wall 34A and inner circumferential wall 34B having a height H Lower than that of the outer circumferential wall. Lower annular outlet port 33 and upper annular outlet port 34 are arranged concentrically and have a common center axis. The direction of this common center axis coincides with the direction of the center axis of the cylindrical die or the direction at which the bubble extruded from the cylindrical die is drawn. When the air ring device has two or more annular cooling gas outlet ports, the outer circumferential walls of the cooling gas outlet ports are preferably higher in height from the common center axis toward the outer circumferential sides. That is, it is preferable that a plurality of cooling gas outlet ports are arranged concentrically so that the line connecting the topmost parts of the outer circumferential walls of the plurality of cooling gas outlet ports forms a U-shape or recessed shape with respect to the direction at which the molten stock material extruded from the cylindrical die is drawn. The "height H of the outer circumferential wall" refers herein to the distance from the top surface of the cylindrical die at which the air ring device is mounted to the topmost part of the outer circumferential wall. When the air ring device has a plurality of cooling gas outlet ports, the "height H of the outer circumferential wall" means the highest height of the outer

circumferential wall at the outermost side. The topmost part of the outer circumferential wall having the height H is preferably arranged at a position spaced apart from the inside wall of the outer lip of the cylindrical die by a distance of from 12.5 to 88 mm in a direction perpendicular to the direction of the center axis of the cylindrical die. The outer circumferential wall of the cooling gas outlet port may be configured to enable adjustment of the height H. For example, the outer circumferential wall of a cooling gas outlet port may be comprised of an annular base part and an annular component part connected to the annular base part. For example, when the annular base part and the annular component part have mutually engaging threaded parts, the height H can be adjusted by rotating the annular component part while engaging the annular base part with the annular component part. Air ring device 30 has a gas inlet port (not shown) for taking in a cooling gas from an external supply source to the inside of the air ring device. The cooling gas can be selected from air and an inert gas (for example, nitrogen and argon), etc.

Although the mechanism for cooling the cylindrical film by the air ring device is schematically illustrated along referring to FIG. 3, the configuration of the air ring device is not limited to the embodiment shown in FIG. 3. In the inflation molding equipment of the present invention, it is possible to produce a cylindrical film having a high dimensional precision without arranging a rectifying cylinder at the outer circumferential side of the outer circumferential wall of the cooling gas outlet port of the air ring device while spacing apart from the outer circumferential wall, as described above. When a rectifying cylinder is arranged spaced apart from the outer circumferential wall at the outer circumferential side of the outer circumferential wall of the cooling gas outlet port, the bubble is stabilized due to the venturi effect, but resulting in an easily shrinkable cylindrical film. For this reason, in the inflation molding equipment of the present invention, the air ring device preferably does not have a rectifying cylinder spaced apart from the outer circumferential wall of the cooling gas outlet port at the outer circumferential side of the outer

circumferential wall.

[0018] In the inflation molding equipment of the present invention, the outer diameter Dl of the annular discharge port of the cylindrical die and the height H of the outer circumferential wall of the air ring device satisfy the relationship of the following formula (1) :

0.5xDl≤H≤l .5xDl ( 1) .

Preferably, Dl and H satisfy the relationship of the following formula (2) :

0.8xDl<H<l .2xDl (2) .

By satisfying the relationship of the above formula (1), the stability of the bubble can be improved while the shrinkage of the cylindrical film can be reduced, and as a result a cylindrical film can be produced having high dimensional precision. When the relationship of the above formula (1) is satisfied, it is believed that the gradual cooling of the cylindrical film (bubble) in a softened state which is melt-extruded from the cylindrical die can be carried out effectively until the film expands to the diameter D2. If H is less than 0.5xDl, it is difficult to form a bubble steadily, and therefore, it is difficult to produce a cylindrical film having high precision. If H is more than 1.5xDl, the dimensional precision is decreased and wrinkling or waviness occurs in the film. The value of Dl is determined in accordance with the desired size of the cylindrical film. The size of Dl is not

particularly limited, but in the case that the

cylindrical film produced by the inflation molding equipment of the present invention is used, for example, as an inner liner for the pneumatic tire of a passenger car, Dl is typically from 400 mm to 800 mm. In the inflation molding equipment of the present invention, so long as Dl and H satisfy the relationship of the above formula (1), the values of Dl and H are not particularly limited, but for example in the case of an 8 inch die, Dl is 203 mm, and in that case, H is from 102 mm to 304 mm, preferably from 142 mm to 264 mm, and more preferably from 162 nun to 244 mm.

[0019] The film produced using the inflation molding equipment of the present invention preferably has a thickness of 0.01 to 0.2 mm. The film produced using the inflation molding equipment of the present invention can achieve a sufficient air pressure retention rate sufficient, when it is used, for example, as an inner liner of a pneumatic tire at such a thickness.

[0020] A thermoplastic resin composition or a thermoplastic elastomer composition comprising a thermoplastic resin as a continuous phase (sea phase) and an elastomer as a disperse phase (island phase), in which the elastomer is dispersed in the thermoplastic resin, can be used as the stock material for producing a film by the inflation molding equipment of the present invention. Examples of the thermoplastic resin which can form the thermoplastic resin composition or thermoplastic elastomer composition include polyamide-based resins, polyvinyl-based resins, polyester-based resins,

polynitrile-based resins, polymethacrylate-based resins, cellulosic resins, fluororesins, imide-based resins, polystyrenic resins, polyolefinic resins, etc. The thermoplastic resin composition or thermoplastic elastomer composition may include at least one

thermoplastic resin. The film produced from the

thermoplastic elastomer composition is lighter in weight compared with an inner liner based on conventional butyl rubber and, further, has an air pressure retention rate which is equal to or higher than that of an inner liner based on conventional butyl rubber, and therefore it is preferable to produce a pneumatic tire inner liner from a thermoplastic elastomer composition. When a thermoplastic elastomer composition is used as the stock material, the thermoplastic elastomer composition preferably comprises a combination of a thermoplastic resin having high barrier properties and a modified elastomer having a high affinity to the thermoplastic resin.

[0021] Examples of polyamide-based resins include, Nylon 6 (N6) , Nylon 66 (N66) , Nylon 46 (N46), Nylon 11

(Nil), Nylon 12 (N12), Nylon 69 (N69) , Nylon 610 (N610) , Nylon 612 (N612), Nylon 6/66 copolymer (N6/66), Nylon 6/610 copolymer (N6/610), Nylon 6/66/610 copolymer

(N6/ 66/ 610 ) ; semi-aromatic and all-aromatic nylons such as Nylon MXD6 (MXD6), Nylon 6T, Nylon 9T, Nylon 6/6T copolymer; Nylon 66/PP copolymer, Nylon 66/PPS copolymer, a copolymer of a polyamide and polyether (for example, a copolymer of at least one type of the above Nylon and a polyether) , and A7-alkoxyalkylates thereof, for example methoxymethylate of Nylon 6, methoxymethylate of Nylon 6/610, methoxymethylate of Nylon 612, etc. Examples of polyvinyl-based resins include ethylene-vinyl acetate copolymer (EVA), polyfvinyl alcohol) (PVA) , vinyl alcohol-ethylene copolymer (EVOH) , pol (vinylidene chloride) (PVDC) , polyvinyl chloride) (PVC) , vinyl chloride/vinylidene chloride copolymer, vinylidene chloride/methylacrylate copolymer, vinylidene

chloride/acrylonitrile copolymer, etc. Examples of polyester-based resins include polybutylene terephthalate

(PBT) , polyethylene terephthalate (PET), polyethylene isophthalate (PEI), PET/PEI copolymer, polyarylate (PAR), polybutylene naphthalate (PBN) , liquid crystal polyesters, polyoxyalkylenediimidic acid/polybutylate terephthalate copolymers, or other aromatic polyesters, a copolymer of a polyester and polyether, a copolymer of a polyester and an aliphatic polycarbonate, etc. Examples of polynitrile-based resins include polyacrylonitrile

(PAN) , polymethacrylonitrile, acrylonitrile/styrene copolymer (AS), methacrylonitrile/ styrene copolymer, methacrylonitrile/styrene/butadiene copolymer, etc.

Examples of polymethacrylate-based resins include poly(methyl methacrylate ) ( PMMA) , poly(ethyl

methacrylate ) , etc. Examples of cellulosic resins include cellulose acetate, cellulose acetate butyrate, etc.

Examples of fluororesins include poly (vinylidene fluoride) (PYDF) , poly(vinyl fluoride) (PVF) ,

polychloro fluoroethylene (PCTFE) , tetrafluoroethylene/ ethylene copolymer (ETFE), etc. Examples of imide-based resins include aromatic polyimides (PI), etc. Examples of polystyrenic resins include polystyrene (PS), etc.

Examples of polyolefinic resins include polyethylene

(PE) , polypropylene (PP) , etc. Among these thermoplastic resins, Nylon 6, Nylon 66, Nylon 46, Nylon 11, Nylon 12, Nylon 69, Nylon 610, Nylon 612, Nylon 6/66, Nylon

6/66/12, and Nylon 6/66/610 and semi-aromatic and all- aromatic nylons such as Nylon MXD6, Nylon 6T, Nylon 9T, and Nylon 6/6T are preferred, in view of gas barrier properties .

[0022] Common ingredients for common thermoplastic resin compositions, such as fillers, reinforcing agents, processing aids, stabilizers, antioxidants, etc., may optionally be added at a common amount to the

thermoplastic resin which constitutes the thermoplastic resin composition or thermoplastic elastomer composition which is extruded using the inflation molding equipment according to the present invention. In view of the gas barrier properties and heat resistance of the film obtained by extrusion molding of the thermoplastic resin composition or thermoplastic elastomer composition, it is preferred to not add a plasticizer to the thermoplastic resin composition or thermoplastic elastomer composition. A film having a reduced shrinkage after extrusion molding can be produced even if a plasticizer such as, for example, higher alcohol-based plasticizers, aromatic sulfoneamide-based plasticizers, phenolic plasticizers, etc., conventionally used in the extrusion molding of a thermoplastic resin composition or thermoplastic elastomer composition, is not incorporated into the thermoplastic resin composition or thermoplastic elastomer composition, and therefore it is possible to prevent the decrease in the gas barrier properties and heat resistance which may be caused when a plasticizer is added to a thermoplastic resin composition or

thermoplastic elastomer composition.

[0023] The thermoplastic elastomer composition comprises at least one rubber dispersed in at least one thermoplastic resin, wherein the at least one

thermoplastic resin constitutes a matrix phase (or a continuous phase) and the rubber constitutes a disperse phase (or a discontinuous phase) . The rubber is dispersed in the form of particles in the thermoplastic resin.

Examples of the rubber which can constitute the

thermoplastic elastomer composition include diene-based rubbers, olefin-based rubbers, and their hydrogenates, epoxy-modi fied products, carboxylic acid-modified products, halogenates, etc., for example, natural rubber, polyisoprene, polybutadiene, styrene-butadiene copolymer, butadiene rubber, acrylonitrile-butadiene copolymer, epoxydized natural rubber, hydrogenated NBR, hydrogenated SBR, ethylene-propylene rubber, ethylene-propylene-diene rubber, ethylene-glycidyl methacrylate copolymer, ethylene-alkylacrylate copolymer, ethylene-methacrylate copolymer, polybutene, polyisobutylene , maleic anhydride- modified ethylene-propylene rubber, maleic anhydride- modified ethylene-a-olefin copolymer, succinic anhydride- modified polyisobutylene, maleic anhydride-modified ethylene-ethylacrylate copolymer, butyl rubber, a copolymer of isobutylene and aromatic vinyl or diene- based monomer (for example, isobutylene-p-alkylstyrene copolymer, styrene-isobutylene-styrene terpolymer and hydrogenates thereof, acid anhydride-modified styrene- isobutylene-styrene block copolymer, etc.), brominated butyl rubber (Br-IIR) , chlorinated butyl rubber (Cl-IIR) , brominated isobutylene-p-methylstyrene copolymer (Br- IPMS), halogenated isobutylene-isoprene copolymer rubber, etc. Among these rubbers, brominated isobutylene-p- methylstyrene copolymer, maleic anhydride-modified ethylene-«-olefin copolymer, and succinic anhydride- modified polyisobutylene are

are preferred in view of gas barrier properties, durability and processability .

[0024] Examples of the combination of the

thermoplastic resin and rubber, capable of forming the thermoplastic elastomer composition which can be used in the present invention include a combination of (a) a polyamide-based resin, (b) an ethylene-vinyl alcohol copolymer, or (c) a blend of a polyamide-based resin and ethylene-vinyl alcohol copolymer, as a thermoplastic resin, and (i) butyl rubber, (ii) a maleic anhydride- modified ethylene-«-olefin copolymer, or (iii) a blend of brominated isobutylene-p-methylstyrene copolymer rubber and maleic anhydride-modified ethylene- -olefin

copolymer, as a rubber, i.e., a combination of a thermoplastic resin selected from (a) to (c) and a rubber selected from (i) to (iii) . The combination of butyl rubber having excellent gas barrier properties and a polyamide-based resin is preferred. Among these, a combination of a brominated isobutylene-p-methylstyrene copolymer rubber, which is a modified butyl rubber, and one or more polyamide-based resins (for example Nylon 6, Nylon 6/66, Nylon 612, etc.) is specifically preferred in view of achieving both fatigue resistance and gas barrier properties .

[0025] The rubber particles included in the

thermoplastic elastomer composition may contain carbon black, silica, or other reinforcing agents (fillers), cross-linking agent, antioxidant, processing aid, or other compounding agents that are commonly blended into a rubber composition to the extent that the effects of the present invention are not impaired.

[0026] Before the thermoplastic elastomer composition is introduced into extruder 10, the thermoplastic elastomer composition can be prepared in advance by melt- kneading at least one thermoplastic resin, at least one rubber, and optionally additives by, for example, a single-screw or twin-screw kneading extruder, to disperse the rubber particles as a disperse phase in the

thermoplastic resin which forms a matrix phase. The weight ratio of the thermoplastic resin to the rubber is preferably from 10/90 to 90/10, and more preferably from 15/85 to 90/10, but is not limited thereto. In order to fix the dispersed state of the rubber in the

thermoplastic resin, the rubber is preferably dynamically cross-linked while melt- kneading the thermoplastic resin and rubber. The term "dynamic cross-Linking" refers herein to cross-linking simultaneous with melt-kneading. The melt-kneading temperature may be equal to or higher than the melting point of the thermoplastic resin, and is preferably a temperature which is higher than the melting point of the thermoplastic resin by 20 °C, for example, is from 200 to 250°C. The total time of the kneading operation is not particularly limited, but is usually from 1 minute to 10 minutes. The thermoplastic elastomer composition which is obtained after melt-kneading the thermoplastic resin and the rubber can be extruded into, for example, a strand form, and then pelletized with a resin pelletizer.

[0027] The cross-linking agent can be suitably selected depending on the type of rubber and is not particularly limited. Examples of the cross-linking agent include zinc oxide, stearic acid, zinc stearate, magnesium oxide, m-phenylene bismaleimide, alkylphenol resin, and halogenates thereof, a polymerized 2,2,4- trimethyl-l, 2-dihydroquinoline, etc. Among these cross- linking agents, zinc oxide, stearic acid, and calcium stearate are preferable. The amount of the cross-linking agent is preferably 0.1 to 12 parts by weight, and more preferably 1 to 9 parts by weight, with respect to 100 parts by weight of the rubber.

[0028] The thermoplastic elastomer composition which can be extrusion molded using the inflation molding equipment of the present invention can be formed in-situ by introducing the thermoplastic resin, rubber, and optionally additives from stock material feeder 11 of extruder 10 which is a single-screw or twin-screw kneading extruder, to the inside of cylinder 12, and melt-kneading them by means of rotating single or double screws. In this case, the resulting thermoplastic elastomer composition can be extruded as a cylindrical film without being pelletized, from the cylindrical die attached to the discharge port of the extruder.

[ 0029 ] The film produced using the inflation molding equipment of the present invention is useful as an inner liner of a pneumatic tire due to excellent gas barrier properties thereof. Any conventional process may be used as the process for producing a pneumatic tire. For example, when the film produced using the inflation molding equipment of the present invention is used as an inner liner in the production of a pneumatic tire, a pneumatic tire can be produced by laminating the film produced using the inflation molding equipment of the present invention onto a tire molding drum in cylindrical form; sequentially laminating thereon tire members such as a carcass layer, a belt layer, a tread layer, etc., to form a green tire; removing the resulting green tire from the tire molding drum, and subsequently vulcanizing the green tire according to a conventional method. The film produced using the inflation molding equipment of the present invention has a reduced shrinkage as described above, and accordingly has fewer wrinkles and is excellent in dimensional stability. Therefore, the film produced using the inflation molding equipment of the present invention can suppress defects due to the wrinkles and delamination of the film, thereby reducing the failure rate of the tire after vulcanization.

Examples

[ 0030 ] The present invention will be further explained with reference to the following examples, and it should be understood that the scope of the present invention is not limited by these examples. [0031] [Preparation of Thermoplastic Elastomer

Composition]

Among the stock materials shown in Table 1 below, a brominated isobutylene p-methylstyrene copolymer (Br- IPMS) was processed into pellets in advance by a rubber pelletizer (manufactured by Moriyama Works) . The

resulting pellets of Br-IPMS and the other elastomers, thermoplastic resins, and additives (that is,

plasticizer, antioxidant, and cross-linking agent) were charged into a twin-screw extruder (manufactured by Japan Steel Works) at the compounding ratio (unit: "phr", parts by weight with respect to 100 parts by weight of total elastomers) shown in Table 1 and were kneaded at 250°C for 3 minutes. The resulting kneaded mass was continuously extruded into a strand form from the extruder, cooled with water, and subsequently cut by a cutter to obtain a thermoplastic elastomer composition in the form of pellets .

[0032] Table 1

Amount (phr)

Elastomer Brominated isobutylene p-methylstyrene 70

Copolymer

Maleic anhydride-modified ethylene-a- 20 olefin copolymer

Succinic anhydride-modif ed 10 Polyisobutylene

Thermoplastic Nylon 6 40 resin Nylon 6/66 6

Nylon 6/12 12

Ethylene-vinyl alcohol copolymer 3

Ingredients Antioxidant (p-phenylenediamine ) 1.0

Zinc oxide 0.7

Stearic acid 10

Calcium stearate 1.0 [0033] Footnote of Table 1:

Brominated isobutylene-p-methylstyrene copolymer (Br- IPMS) : Exxpro® MDX89-4 from ExxonMobil Chemical Company) Maleic anhydride-modified ethylene-a-olefin copolymer: Tafmer® MH7010 from Mitsui Chemicals

Succinic anhydride-modified polyisobutylene : DOVERMULSE H1000 fromDover Chemical Corporation

Nylon 6: UBE Nylon® 1013FB from Ube Industries, Ltd. Nylon 6/66 copolymer: UBE Nylon® 5023B from Ube

Industries, Ltd.

Nylon 6/12 copolymer: UBE Nylon® 7024B from Ube

Industries, Ltd.

Ethylene-vinyl alcohol copolymer: H4815B from Nippon Synthetic Chemical Industry

Antioxidant: N- ( 1 , 3-dimethylbutyl ) -W'-phenyl-p- phenylenediamine (Santoflex 6PPD from Solutia)

Zinc oxide: Zinc White No. 3 from Seido Chemical Industry Co., Ltd.

Stearic acid: Beads Stearic Acid from NOF Corporation Calcium stearate: Calcium stearate from NOF Corporation

[0034] [Configuration of Inflation Molding Equipment]

An inflation molding equipment comprising a φ90 mm single-screw extruder, a cylindrical die, and an air ring device (manufactured by Macro Engineering & Technology Inc.) was used to produce a cylindrical film. The cylindrical die had an annular discharge port with an outer diameter of 20.32 cm (8 inches) . The annular discharge port of the cylindrical die was directed upward in the vertical direction (that is, the direction opposite to direction of gravity) . A pair of guides and pair of pinch rolls were arranged above the annular discharge port in the vertical direction. A plurality of guide rolls and a windup roll were arranged so that the cylindrical film extruded from the annular discharge port is folded by the pair of pinch rolls, then the folded cylindrical film is wound up by the windup roll through the plurality of guide rolls. D10S dual lip air ring manufactured by Macro Engineering & Technology Inc. with an inside diameter of 9 inch was used as an air ring device .

[0035] [Molding Conditions]

The cylinder temperature of the extruder was 230°C, and the cylinder temperature of the cylindrical die was 240°C. The molten thermoplastic elastomer composition was shaped at a drawing speed of about 10 m/min so as to give a cylindrical film having a thickness of 0.1 mm and a diameter of 400 mm by a discharge rate of 80 kg/h from the cylindrical die. Cooling of the bubble was carried out by an air-cooling method in which air is blown as a cooling gas to the bubble from the air ring device. The cooling gas flow rate was 1487 m³/h, and the temperature of the cooling gas was 5°C.

[0036] [Production of Cylindrical Film]

An inflation molding eguipment having the above construction was used to form a thermoplastic elastomer composition into a cylindrical film under the above molding conditions. The bubble stability and dimensional precision when producing a cylindrical film and the shrinkage of the produced film were evaluated by the evaluation criteria described below. The results of evaluation are shown in Table 2 below.

[0037] [Bubble Stability]

At a position 50 cm above the die, a pair of infrared sensors were arranged at opposing positions across the bubble. The distances from the bubble were measured and the standard deviation σ of the variation thereof was used to evaluate the bubble stability of Examples 1 to 6 and Comparative Examples 1 to 5.

σ of 20% or more was rated at "1".

σ of 10% or more and less than 20% was rated as "2". σ of 5% or more and less than 10% was rated as "3". σ of 1% or more and less than 5% was rated as "4". σ of less than 1% was rated as "5".

[0038] The ratings "3", "4", and "5" are levels where a member for inner liner could be obtained, but the rating "2" is a level where there was severe wrinkling at the time of winding of the cylindrical film and according the cylindrical film was unsuitable for inner liner applications, or it was difficult to carry out molding over a long period of time. The rating "1" is a level where the bubble was unstable and accordingly it is difficult to continue molding.

[0039] [Dimensional Precision]

Each of the cylindrical films of Examples 1 to 6 and Comparative Examples 1 to 5 was cut into five pieces in compliance with the width of the desired tire inner liner immediately after being formed. Each piece was measured for circumferential direction length LI of the

cylindrical film at three locations of both cut ends and center part. The rating of the dimensional precision was carried out as follows.

The case where there was a cylindrical film having a variation in LI of three locations of more than 10 mm was rated as " 1 " .

The case where there was a cylindrical film having a variation in LI of three locations of more than 5 mm and 10 mm or less was rated as "2". The case where there was a cylindrical film having a variation in LI of three locations of more than 3 mm and 5 mm or less was rated as "3".

The case where there was a cylindrical film having a variation in LI of three locations of more than 2 mm and 3 mm or less was rated as "4".

The case where there was a cylindrical film having a variation in the LI of three locations of 2 mm or less was rated as " 5 " .

[0040] In the case of the ratings "3", "4", and "5", the resulting film can be laminated with the adjacent rubber members to form a tire, but in the case of the rating "3", wrinkles were easily formed in the

circumferential direction of the film, and in the case of the rating "4", wrinkles were occasionally formed. In the case of the rating "5", wrinkles were not formed. In the case of the rating "2", wrinkling was severe and many air pockets were formed between the film and adjacent rubber members, or wrinkles became folded parts, resulting portions not contacting with the adjacent rubber members, and consequently tire molding is difficult. The rating "1" is the level where almost all wrinkles became folded parts and it is difficult to produce a tire.

[0041] [Shrinkage Factor]

Each of the cylindrical films of Examples 1 to 6 and Comparative Examples 1 to 5 was cut to in compliance with the width of the desired tire inner liner immediately after being formed and was measured for circumferential direction length LI. After measurement, the film was hung in a room and allowed to stand at normal temperature for one week, and then was again measured for circumferential direction length L2 at the same position. The shrinkage factor (%) was determined in accordance with the formula ΙΟΟ (L1-L2 ) /LI .

The case where shrinkage factor (%) was 2.0% or more was rated as " 1 " .

The case where the shrinkage factor (%) was more than 1.5% and less than 2.0% was rated as "2".

The case where the shrinkage factor ( ) was more than 1.0% and less than 1.5% was rated as "3".

The case where the shrinkage factor (%) was more than 0.5% and less than 1.0% was rated as "4".

The case where the shrinkage factor (%) was 0.5% or less was rated as "5".

[ 0042 ] The higher the shrinkage factor, the lower the dimensional precision. The lower the original dimensional precision and the higher the shrinkage factor, the more failures of wrinkling or folding of the film when laminating it with the adjacent rubber members.

[ 0043 ] Table 2

[ 0044 ] Table 2 shows that the inflation molding eguipment of the present invention leads to excellent bubble stability, enables production of a cylindrical film with a high dimensional precision and enables reduction in shrinkage of the resulting cylindrical fi Industrial Applicability

[ 0045 ] The inflation molding equipment of the present invention can be suitably used for the production of a cylindrical film. Further, the cylindrical film produced using the inflation molding equipment of the present invention can be suitably used as an inner liner of a pneumatic tire for the production of a pneumatic tire. Reference Signs List

[ 0046 ] 1. Inflation molding equipment

10. Extruder

20. Cylindrical die

21. Annular discharge port

30. Air ring device

33. Lower annular outlet port

34. Upper annular outlet port

34A. Outer circumferential wall

40A, 40B. Stabilizing plates

50A, 50B. Pinch rolls

60. Windup roll

Dl . Outer diameter of annular discharge port

D2. Diameter of cylindrical film

Fl . Cylindrical film

F2. Folded cylindrical film

Claims

Claim 1. Inflation molding equipment comprising: an extruder for melt extruding a stock material, a single-layer or multi-layer cylindrical die attached to a discharge port of the extruder, and

an air ring device for cooling a cylindrical film extruded from the cylindrical die, wherein

the cylindrical die has an annular discharge port having an outer diameter of Dl,

the air ring device is attached on the cylindrical die, and

the air ring device has at least one cooling gas outlet port, the cooling gas outlet port having a cooling gas channel defined by an outer circumferential wall having a height of H and an inner circumferential wall having a height lower than the outer circumferential wall, and

Dl and H satisfy a relationship of the following formula ( 1 ) :

0.5xDl<H<l .5xDl (1) .

Claim 2. The inflation molding equipment according to claim 1, wherein said stock material is a

thermoplastic elastomer composition having an island-in- sea structure comprised of a continuous phase comprising a thermoplastic resin and a disperse phase comprising an elastome .

Claim 3. The inflation molding equipment according to claim 1, wherein Dl and H satisfy a relationship of the following formula (2) :

0.8xDl<H<l .2xDl (2)

Claim 4. The inflation molding equipment according to any one of claims 1 to 3 wherein a ratio of an effective length L of a screw to a screw diameter D of the extruder, L/D, is 32 or more.

Claim 5. The inflation molding equipment according to any one of claims 1 to 4, wherein the air ring device does not have a rectifying cylinder spaced apart from the outer circumferential wall of the cooling gas outlet port at the outer circumferential side of the outer

circumferential wall.

Claim 6. A process for producing a cylindrical film, comprising:

providing the inflation molding equipment according to any one of claims 1 to 5;

melt extruding a molten thermoplastic elastomer composition from the extruder to the cylindrical die, the molten thermoplastic elastomer composition comprising a thermoplastic resin selected from the group consisting of a polyamide-based resin, a polyvinyl-based resin, a polyester-based resin, and a blend of two or more of these resins as a continuous phase, and a modified elastomer as a disperse phase; and

extruding the molten thermoplastic elastomer composition as a cylindrical film from the cylindrical die .

Claim . A process for producing a pneumatic tire comprising :

producing a cylindrical film by the process according to claim 6;

cutting the resulting film in accordance with a size of the pneumatic tire to form an inner liner;

forming a green tire comprising the inner liner; and vulcanizing the green tire to form a pneumatic tire.