Self supporting piastic bottle with textured thin walls

A plastic bottle, made of polyethylene (PE), polypropylene (PP), or poly(ethylene terephthalate) (PET), blown with a very thin overall wall thickness within the range 0.1 to 0.3 mm, includes a triangular or polygonal cross-section, the bottle being preferably surrounded by a supporting jacket. The bottle can be blown with a uniform wall thickness and adequate strength without the need for reinforcing ribs via walls formed by pressing them against the surface of a blow mold which has been worked at least in some areas by etching, form-cutting or eroding, having features with heights of 0.05 to 0.15 mm.

BACKGROUND 
1. Field of the Invention 
This invention relates to a generally thin-walled, blow-molded plastic 
bottles, and more particularly to such bottles typically surrounded by a 
bottomless and topless supporting jacket of either polyethylene (PE), 
polypropylene (PP) or polyethylene terephthalate (PET) with a very thin 
overall wall thickness of 0.1 to 0.3 mm 
2. Discussion of Related Art 
Known processes for the production of plastic bottles in blow molds, 
so-called bottle blowing processes, are also suitable for the production 
of extremely thin-walled plastic bottles. Plastic bottles of polyethylene 
terephthalate (PET) are produced, for example, by initially 
injection-molding a parison and then blow-molding the parison under the 
effect of heat into the required bottle shape. Plastic bottles of 
polyethylene (PE) are produced, for example, by feeding a PE tube to the 
blow molds of bottle blowing machines and blow-molding the tube in the 
blow molds to form bottles. It is known that very thin-walled plastic 
bottles can be produced by these bottle blowing processes. These plastic 
bottles have a smooth surface texture. To increase the strength and 
stability of the bottles and to prevent them from bulging, particularly 
during and after filling with liquid, it is known (cf. EP-A-0 198 587) 
that the bottles can be provided with pronounced stabilizing and 
stiffening ribs and recesses. This requires particularly expensive and 
relatively complicated blow molds. The need for a uniform and constant 
wall thickness over the entire extent of the bottle wall is a problem 
which has not been satisfactorily solved in these known bottles. 
Very thin-walled blow-molded plastic bottles of polyethylene (PE) with a 
wall thickness of 0.1 to 0.3 mm and a rectangular cross-section surrounded 
by a bottomless and topless supporting jacket of cardboard are known from 
DE-A-39 21 258 and have been on the market for some time. The need for a 
uniform and constant wall thickness over the entire extent of the bottle 
wall is again a problem which has not been satisfactorily solved in these 
bottles either. During blow molding in the blow molds, extremely thin 
zones well below the required wall thickness are formed in the 0.1 to 0.3 
mm thick bottle wall; in some cases, holes are even formed in the bottle 
wall. Another disadvantage of these thin-walled plastic bottles is that 
the side walls show signs of buckling on removal from the blow mold and 
bulge out when filled with liquid or free-flowing product. 
In addition, it is generally known that plastic bottles with standard wall 
thicknesses of 0.35 to 0.8 mm can be produced in blow molds toughened, for 
example, by etching or sandblasting if parts of the outer surface of the 
bottle are to have a matt or rough texture for reasons of optical design. 
However, this does not affect the stability or rigidity of the bottles on 
account of the relatively thick walls of the bottles to which this process 
has hitherto been applied. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a very thin-walled plastic bottle 
free from stiffening ribs which can be produced by blow molding, has a 
uniform wall thickness, and has sufficient strength to resist bulging. 
In a plastic bottle of the invention, are at least the side bottle walls 
are formed by application to a blow molding surface at least locally 
prepared by etching, profile milling or erosion for texturing the wall to 
depths of 0.05 to 0.15 mm. 
Blow-molded plastic bottles with a total wall thickness of 0.1 to 0.3 mm 
textured to depths of 0.05 to 0.15 mm in their walls are improved in their 
overall stability and, in particular, in their resistance to bulging by 
comparison with smooth-surface plastic bottles having the same wall 
thickness. It is sufficient in regard to improved resistance to bulging if 
only the side walls of the plastic bottle are textured in accordance with 
the invention. The texturing is achieved by preparing the corresponding 
surfaces of the blow mold, to which those parts of the plastic material to 
be textured are applied during blow molding of the plastic bottle, by 
etching, profile milling or erosion in such a way that the bottle is 
textured to depths of 0.05 to 0.15 mm in the applied parts of the bottle 
wall. It has been found in this regard that it is sufficient to prepare 
the blow molds in such a way that the prepared surfaces are textured to 
depths of 0.01 to 0.03 mm. In view of the very thin overall wall 
thicknesses of 0.1 to 0.3 mm, the texture is reproduced both on the outer 
surface and on the inner surface of the corresponding parts of the plastic 
bottle. In this way, the distance between the outer surface and the inner 
surface (overall wall thickness) in the textured parts of the bottle wall 
is increased by comparison with smooth-walled plastic bottles having the 
same wall thickness of 0.1 to 0.3 mm, without the actual wall thickness 
being increased or an increased amount of plastic material being used. 
Those parts of the bottle wall textured to depths of 0.05 to 0.15 mm show 
improved and increased stiffness in flexure. The thin-walled plastic 
bottles according to the invention with overall wall thicknesses of 0.1 to 
0.3 mm locally textured to depths of 0.05 to 0.15 mm on their walls can be 
produced in bottle blowing machines designed for standard thick-walled 
plastic bottles. To produce the thin-walled plastic bottles, the blow 
molds used in the bottle blowing process have to be prepared by etching, 
profile milling or erosion, etching being understood to include 
photoetching, graining, structuring or texturing. The plastic bottles 
blow-molded in such blow molds have a constant and uniform wall thickness 
over the extent of their walls and high stability and strength despite 
their extremely low wall thickness and overall wall thickness values. 
Compared with the smooth thin-walled plastic bottles known from DE-A-39 21 
258, they are distinctly improved in their stability and strength and are 
distinguished by uniform wall thickness over their walls. In corners in 
particular, there are no longer any thin zones with undesirably low wall 
thickness values. The plastic bottles thus produced show very high 
dimensional accuracy whereas untextured thin-walled bottles have a marked 
tendency to bulge, particularly over flat surfaces, such as the side 
walls. They undergo negligible, i.e. unproblematical, bulging during and 
after filling with liquid or free-flowing product. There is no longer any 
need for stiffening ribs and/or recesses. The production of thin-walled 
plastic bottles in correspondingly prepared blow molds also affords 
advantages for the bottle blowing process. It has been found that textured 
blow molds provide for better mold venting at the faces and mold parting 
lines, for better cooling and for a shorter cycle time in the actual 
bottle blowing process. In addition, it has been found that plastic 
bottles textured to depths of 0.05 to 0.15 mm in parts of their walls can 
be transported particularly effectively on the conveyor belts of filling 
machines when the bottom wall is also correspondingly textured. Compared 
with smooth-walled plastic bottles with the same wall thickness and hence 
equally light weight, the plastic bottle according to the invention is 
distinguished by distinctly better slip and transport behavior on conveyor 
belts of filling machines. 
It is sufficient, particularly in the case of plastic bottles surrounded by 
a bottomless and topless supporting jacket, to texture only the side walls 
in order to achieve the above-mentioned advantages and improvements over 
smooth-surface or smooth-walled light-weight plastic bottles. It is of 
advantage in the absence of a cardboard jacket to texture to depths of 
0.05 to 0.15 mm those parts of the bottle wall which are formed by 
application to a blow molding surface prepared in its entirety by etching, 
profile milling or erosion. 
It is also possible to produce various surface textures, which enable 
various parts of the bottle wall to be differently textured, by etching 
certain portions of the molding surfaces of the bottle blowing molds and 
sand-blasting other portions thereof. Basically, portions of the molding 
surfaces of the bottle blowing molds may be prepared by different 
texturing methods. The entire molding surface of a bottle blowing mold may 
thus be locally textured by application of one of the methods mentioned 
above. In other words, the roughness is produced by a combination of two 
or more of the methods mentioned above. The combination of various 
texturing methods also influences the strength of the plastic bottle 
produced. Thus, those parts of the bottle blowing mold which form the 
shoulder of the bottle may be sandblasted while those parts which form the 
body and base of the bottle may be etched. 
Known bottle blowing machines and blow molds may be used for the production 
of the thin-walled blow-molded plastic bottles with an overall wall 
thickness of 0.1 to 0.3 mm, of which the walls are locally textured to 
depths of 0.05 to 0.15 mm. The molding surfaces of the bottle blowing 
molds are prepared by etching, profile milling, sand blasting and erosion. 
The bottles are then blown as in standard bottle blowing processes. For 
the plastic bottles according to the invention, the bottle blowing 
compound is used in a quantity of, for example, 24.+-.1 g or less for a 
1-liter PE bottle. Those parts of the bottle blowing molds to which the 
bottle compound is applied during blow molding to form the wall zones of 
the plastic bottle textured in accordance with the invention are prepared 
by etching, profile milling or erosion in such a way that, after the 
bottle compound has been blow-molded to form thin-walled plastic bottles 
with overall wall thicknesses of 0.1 to 0.3 mm, these zones of the plastic 
bottle have depths of 0.05 to 0.15 mm. The texture is so deep that it also 
appears on the inside of the bottle. The plastic bottles with walls 
textured in accordance with the invention may have any of the 
cross-sectional forms typical of standard blow-molded plastic bottles, 
i.e. they may have round, polygonal or similar cross-sections. It is 
preferred that the walls have a triangular or polygonal or trapezoidal 
cross-section where they are surrounded by a bottomless and topless 
supporting jacket.

DETAILED DESCRIPTION OF THE INVENTION 
The plastic bottle is preferably surrounded by a bottomless and topless 
supporting jacket (not shown). The plastic bottle, including the wall 
detail shown in the drawing, has an overall wall thickness 1 of 0.1 to 0.3 
mm. The wall is textured both on its outer surface 2 and on its inner 
surface 3. The texture formed on the outer surface 2 and on the inner 
surface 3 has depths 4, 5 of 0.05 to 0.15 mm. The texture is produced by 
application of the outer surface 2 to blow mold surfaces prepared by 
etching, profile milling or erosion during the blow molding of the plastic 
bottle. In this production process, the texture produced on the outer 
surface 2 of the wall by the prepared blow mold surfaces is also 
reproduced on the inner surface 3 of the wall, i.e. on the inside of the 
plastic bottle. Although this does not increase the actual wall thickness 
6 of the plastic bottle, it does increase the wall thickness 1 relative to 
the actual wall thickness 6 because the distance between the outer surface 
2 and the inner surface 3 is greater because of the texture. 
Although various embodiments of the present invention have been shown and 
described herein, they are not meant to be limiting. Those of skill in the 
art may recognize certain modifications to these embodiments, which 
modifications are meant to be covered by the spirit and scope of the 
appended claims.