Apparatus for forming blown films

Claim 2

Apparatus for forming a blown film comprising: (a) an inflation forming die having a circular slit, (b) an air ring surrounding the circular slit of said die and provided with an air flow passage leading to an air ejecting slit, (c) said air ring being mounted on said die without any appreciable gap, (d) said air ejecting slit being defined by an outer lip having a tapered surface, the inner diameter thereof increasing in a direction of withdrawal of a cylindrical film extruded through said circular slit, and an inner lip disposed closer to said die than said outer lip, and (e) means for reducing air pressure in a space between said inner lip and said cylindrical film inwardly of said air ejecting slit, said air pressure reducing means including: (i) an air suction passage one end of which opens in said space and the other end of which opens in said air flow passage in said air ring and (ii) Venturi tube effect creating means for reducing air pressure in said space through said air suction passage.

Claim 3

The apparatus according to claim 1 wherein said air suction passage extends through said inner lip.

Claim 4

The apparatus according to claim 1 wherein said air suction passage is opened in a direction of withdrawal of said cylindrical film.

Claim 5

The apparatus according to claim 1 wherein said Venturi tube effect creating means is located in said air flow passage.

Claim 6

The apparatus according to claim 4 wherein said Venturi tube effect creating means comprises a cover plate overlying one end of said air suction passage opposite to the end opening in said space.

Claim 7

The apparatus according to claim 1 which further comprises baffle plates provided in an air flow passage leading to said air ejecting slit.

Claim 8

The apparatus according to claim 1 which further comprises an annular air flow rectifying member disposed above said outer lip to surround said blown film.

Claim 9

The apparatus according to claim 1 wherein said air suction passage extends through said inner lip, one end of said air suction passage being opened into said space while the other end is opened into an air passage disposed between said outer and inner lips and leading to said air ejection slit, and wherein said outer lip is provided with a projection on a bottom surface thereof at a position above said other end of said air suction passage.

Claim 10

The apparatus according to claim 1 wherein said air suction passage is defined by an inner flange of said inner lip and an annular ring surrounding said inner flange.

Claim 11

The apparatus according to claim 1 wherein said die is adapted to extrude a resin selected from the group consisting of a high density polyethylene and a linear low density polyethylene.

Claim 12

The apparatus according to claim 1 wherein an upward projection is provided for a central portion of said die for supporting said air ring at a lower level, whereby an opening of said air suction passage opens in the direction of withdrawal of said blown film.

Claim 13

Apparatus for forming a blown film, said apparatus comprising: (a) an inflation forming die having a circular slit; (b) an air ring surrounding the circular slit of said die downstream of said die and being mounted on said die without any appreciable gap between said die and said air ring, said air ring being provided with an air flow passage leading to an annular air ejecting slit, said annular air ejecting slit being defined by: (i) an inner lip disposed downstream of said die, whereby a first annular empty chamber is formed during the extrusion of a blown film, said first annular empty chamber being bounded at least in part by said die, said inner lip, and the exterior of said film being blown, and (ii) an outer lip disposed downstream of said inner lip and radially outwardly of said inner lip; and (c) means for reducing air pressure in said first annular empty chamber, said means including: (i) an air suction passage one end of which opens in said first annular empty chamber and the other end of which opens in said air flow passage in said air ring and (ii) means for creating an under-pressure in said air suction passage, said means comprising means for creating a Venturi tube effect in said air flow passage, thereby creating an under-pressure region in said air flow passage, said air suction passage communicating with the under-pressure region in said air flow passage, thereby communicating the under-pressure in said air flow passage to said first annular empty chamber, the under-pressure in said first annular empty chamber serving to attract the exterior of said film being blown radially outwardly, whereby said film being blown is moved downstream with its diameter increased to some extent.

Claim 14

Apparatus for forming a blown film, said apparatus comprising: (a) an inflation forming die having a circular slit; (b) an air ring surrounding the circular slit of said die downstream of said die and being mounted on said die without any appreciable gap between said die and said air ring, said air ring being provided with an air flow passage leading to an annular air ejecting slit, said annular air ejecting slit being defined by: (i) an inner lip disposed downstream of said die, whereby a first annular empty chamber is formed during the extrusion of a blown film, said first annular empty chamber being bounded at least in part by said die, said inner lip, and the exterior of said film being blown, and (ii) an outer lip disposed downstream of said inner lip and radially outwardly of said inner lip; and (c) means for reducing air pressure in said first annular empty chamber, said means including: (i) an air suction passage one end of which opens in said first annular empty chamber and the other end of which opens in said air flow passage in said air ring and (ii) means for creating an under-pressure in said air suction passage, said means comprising means for creating a Venturi tube effect in said air flow passage, thereby creating an under-pressure region in said air flow passage, said air suction passage communicating with the under-pressure region in said air flow passage, thereby communicating the under-pressure in said air flow passage to said first annular empty chamber, the under-pressure in said first annular empty chamber serving to attract the exterior of said film being blown radially outwardly, whereby said film being blown is moved downstream with its diameter increased to some extent.

Claim 15

Apparatus as recited in claim 12 wherein: (a) said inner lip is at least generally in the form of a cone diverging outwardly in the downstream direction by an angle of up to 15° and (b) said outer lip is at least generally in the form of a cone diverging outwardly in the downstream direction by an angle of between 5° and 30°.

Claim 16

Apparatus as recited in claim 13 wherein said outer lip diverges outwardly in the downstream direction by an angle which is greater than the angle by which said inner lip diverges outwardly in the downstream direction.

Claim 17

Apparatus as recited in claim 12 wherein said first annular empty chamber is further bounded by an annular spacer disposed between said die and said air ring.

Claim 18

Apparatus as recited in claim 12 wherein said outer lip is mounted in said air ring for axial movement, whereby the width of said annular air ejecting slit can be adjusted.

Claim 19

Apparatus as recited in claim 12 wherein said air suction passage opens perpendicularly to the direction of motion of the blown film.

Claim 20

Apparatus as recited in claim 12 wherein said air suction passage has an annular opening facing in the downstream direction.

Claim 21

Apparatus as recited in claim 12 and further comprising an annular air flow rectifying member disposed downstream of said outer lip and radially outwardly of said outer lip, whereby a second annular empty chamber is formed during the extrusion of a blown film, said second annular empty chamber being bounded at least in part by said outer lip, said annular air flow rectifying member, and the exterior of the blown film.

Claim 22

Apparatus as recited in claim 19 wherein: (a) said inner lip is at least generally in the form of a cone diverging outwardly in the downstream direction by an angle of up to 15°; (b) said outer lip is at least generally in the form of a cone diverging outwardly in the downstream direction by an angle of between 5° and 30°; and (c) said annular air flow rectifying member is at least generally in the form of a cone diverging outwardly in the downstream direction by an angle of between 10° and 45°.

Claim 23

Apparatus as recited in claim 20 wherein: (a) said outer lip diverges outwardly in the downstream direction by an angle which is greater than the angle at which said inner lip diverges outwardly in the downstream direction and (b) said annular air flow rectifying member diverges outwardly in the downstream direction by an angle which is greater than the angle by which said outer lip diverges outwardly in the downstream direction.

Claim 24

Apparatus as recited in claim 19 and further comprising a vent hole extending between said second annular empty chamber and ambient air, said vent hole providing a source of replacement air for air removed from said second annular empty chamber by the motion of the blown film.

Claim 25

Apparatus as recited in claim 19 wherein said annular air flow rectifying member is mounted for axial movement, whereby the width of said second annular empty chamber can be adjusted.

Claim 26

Apparatus as recited in claim 12 wherein: (a) an upward projection is provided on the portion of said die containing the central slit; (b) said air ring is supported on said die downstream of the portion of said die containing the central slit; (c) said first annular empty chamber extends upstream of the portion of said die containing the central slit; and (d) said air suction passage opens in said first annular empty chamber upstream of the portion of said die containing the central slit.