Antislip, heat sealable plastic flexible packaging bag and method and apparatus for its production

A method for providing an antislip, heat sealable plastic packaging bag, the method including:

• providing particles of a first substance and of a suitable size and shape, the first substance being a thermoplastic polymer,
• providing a film blowing machine having an annular die gap and an external bubble-cooling unit above the die gap and a haul-off unit above the external bubble-cooling unit,
• providing a blown film bubble consisting of a plastic wall emerging from the die gap and proceeding toward the haul-off unit,
• the plastic wall having an outer surface of a second substance, the second substance different in some property from the first substance and suitable to fuse with the first substance,
• providing a neck of the bubble, in which the wall is suitably hot and plastic-state, between the die gap and a freezing line of the bubble, the freezing line being a part of the bubble where the wall is made to reach a final thickness of the wall,
• selecting an area, the landing area, of the neck between the die gap and the external bubble-cooling unit, where the outer surface is tacky,
• in the landing area bringing and sticking, with a random distribution, the particles to the outer surface of at least a part, the roughened part, of the wall,
• using a heat content of the suitably hot wall for starting a fusing process in the proceeding wall for fusing the stuck particles to the outer surface,
• ending the fusing process, by cooling, at a desired extent of the fusing for forming a suitably strong fixation between the outer surface and the particles fused to it,
• freezing the wall by cooling, for providing a heat sealable, plastic, flexible frozen wall,
• providing in the frozen wall an average surface weight of at most 500 g/m2,
• thereby forming, from the particles fused to the wall, a multiplicity of separate antislip protrusions of the first substance randomly distributed on the outer surface of the frozen wall and projecting from the outer surface to a protrusion height of between 50 micrometres and 10000 micrometres with an average of top-plan-view aspect ratios of the multiplicity of the antislip protrusions being at least 1.0 and at most 5.0,
• providing at least some of the antislip protrusions with a hidden surface portion being a portion of a free surface of the antislip protrusion which the antislip protrusion covers from a viewer in a top plan view of the wall taken from above the antislip protrusions,
• the frozen wall together with the antislip protrusions projecting from its outer surface constituting an antislip flexible packaging material,
• forming from the antislip flexible packaging material a packaging bag with the multiplicity of the antislip protrusions looking toward an outside of the packaging bag, and
• selecting the first substance to have a melt mass flow rate of at least 0.6 g/10 min. determined at 190° C. under a load of 2.16 kg in accordance with ISO 1133-1.

An apparatus for roughening a blown film, the apparatus having a sub-unit for a film blowing machine, the film blowing machine for producing a blown film plastic wall for a packaging material, the apparatus including:

• a film blowing die head with an annular die gap, and an external cooling air ring above the die head, the die gap having an outer diameter, and the air ring having a bottom,
• the die gap and the air ring together suitable to define a path of an outer surface of the plastic wall, the path having a shape of a bubble extending from the die gap up through the air ring, and
• at least above the air ring bottom the bubble having one or more expanding areas in which the wall is exposed to a horizontal expansion and planes tangent to the path close angles, the angles of expansion, of at least 2.5 degrees with the vertical,
• the sub-unit further including a particle dispersing unit defining a landing area of the path by being suitable for dispersing in the landing area, with a random distribution, thermoplastic polymer particles on the outer surface between the die gap and the air ring, and
• at least one of:
• a.) a second vertical distance, in a side view of the apparatus, between the landing area and the air ring bottom being either zero or at most 2.0 times the die gap outer diameter, and
• b.) at least one of the one or more expanding areas including at least a part of the landing area.