Method and apparatus for coating plastics bottles

A method of coating a container (1) including a structure defining an aperture comprises the steps of supporting the container (1) by the said structure, causing the container (1) to rotate about an axis thereof, causing the rotating container (1) to translate across the surface of a liquid coating composition (7) a portion of the container being immersed in the composition, and causing the composition to solidify upon the surface of the container. The method is particularly applicable to coating plastics bottles.

This invention relates to a method for coating plastics bottles, and to an 
apparatus for use in carrying out the method. 
Plastic bottles are commonly used for storage of carbonated beverages. The 
gaseous pressure developed within such bottles has restricted use of small 
plastics bottles, for example having a capacity of 250 cm.sup.3. The 
relatively high surface area of such small bottles results in leakage of 
gas upon storage for prolonged periods. Leakage is also a problem with 
larger bottles. 
According to a first aspect of the present invention a method of coating a 
container including a structure defining an aperture comprises the steps 
of supporting the container by the said structure, causing the container 
to rotate about an axis thereof, causing the rotating container to 
translate across the surface of a liquid coating composition a portion of 
the container being immersed in the composition, and causing the 
composition to solidify upon the surface of the container. 
The method is particularly applicable to coating plastics bottles which are 
preferably secured by the necks thereof. Containers not including a neck 
may be supported by a member inserted into the aperture. 
Rotation of the container serves to provide a coating of uniform thickness. 
Preferably the container is caused to rotate about a generally horizontal 
axis. 
More preferably the container is caused to rotate about a horizontally 
disposed axis of symmetry. The container may be cylindrical although a 
container having many sides may be coated by this method. 
The container may be caused to skim across the surface of the composition, 
the depth of immersion in the composition determining the thickness of the 
resultant coating. 
Rotation of the container preferably continues as the composition 
solidifies. 
The container may be arranged after translation across the liquid 
composition, to rotate with the axis thereof inclined to the horizontal, 
for example at 45.degree.. Excess liquid coating composition may thereby 
drain from the container. 
Solidification of the coating upon the container may be caused to occur 
after the excess composition has been removed by passage through an oven. 
When the container comprises a shoulder leading to a neck or other 
constriction, the shoulder may be coated by passage over a platform 
extending above the body of the liquid composition, liquid composition 
being caused to flow over the platform and to contact the container as it 
passes. 
When the container is a bottle, the coating composition is preferably 
prevented from contacting the neck thereof so that the screw thread or 
other means of closure is not coated. The means of supporting the 
container is also kept clear of the composition. 
The composition preferably comprises a latex or any other convenient liquid 
which serves to seal the container and prevent escape of the contents 
thereof. 
According to a second aspect of the present invention apparatus for coating 
a container including a structure defining an aperture comprises means for 
engaging said structure and supporting the container, means for rotating 
the container about an axis thereof and means for translating the rotating 
container across the surface of a liquid coating composition with a 
portion of the container being immersed in the composition. 
The apparatus may comprise part of an endless conveyor of a larger 
apparatus used to manufacture the containers. The container is preferably 
a plastics bottle and the said structure may comprise the neck thereof. 
The means for engaging the structure preferably facilitates rotation 
thereof, the container either being loosely engaged so that it is free to 
rotate or the means including an articulated linkage adapted for 
rotational movement. 
Means for engaging the neck of a bottle may comprise a U-shaped member, an 
aperture within which a collar on the neck may be engaged or any other 
convenient arrangement. 
The means for rotating the container preferably comprises a surface having 
a high coefficient of friction adapted to engage the structure as it 
passes along the conveyor. Alternatively, a surface may be adapted to 
cooperate with the means for engaging the neck of the bottle and cause the 
latter to rotate as it translates across the coating composition. 
The coating composition may be disposed in a bath containing a weir to 
maintain the liquid level at a constant location. There may be a platform, 
plate or other member located above the liquid level and provided over the 
surface with a constant flow of coating composition. The shape of the 
plate is preferably arranged to cooperate with the neck or other contour 
of the container to provide even coating thereof. 
The apparatus may also comprise means adapted to rotate the container after 
it has been removed from the bath, the container being preferably inclined 
to the horizontal, for example at an angle of 45.degree.. 
The apparatus may further comprise an oven adapted to cause solidification 
of the coating.

FIG. 1 shows a partial view of an apparatus in accordance with the 
invention with a bottle supported in three different attitudes. 
The apparatus is adapted to receive an endless supply of bottles from a 
moulding station (not shown), the bottle 1 being received in a vertical 
orientation. The apparatus comprises a neck support member 2, hinged at 3 
to a drive mechanism comprising a roller 4. The roller 4 is constrained to 
movement within a track 5. The bottle 1 is supported by the neck in a slot 
in the member 2. The end of the member 2 remote from the hinge 3 rests on 
a guide rail 6. The vertical location of the guide rail 6 alters during 
passage of the member 2 along the track 5, passing through an intermediate 
position 6a in which the bottle 1a is inclined at 45.degree., to a 
position 6b in which the bottle 1b is disposed horizontally. The bottle 1b 
may then translate across the surface of a liquid coating composition 7 
contained in a bath 8. The bottle 1b is caused to spin axially as it 
translates across the composition 7, causing the sides thereof to be 
coated with the composition. Coating is applied to the shoulder of the 
bottle 10 by means of a platform 9 arranged so that the bottle passes 
adjacent to it within the bath 8. A stream of the composition passes over 
the platform to coat the shoulder 10 as the bottle rotates. 
The mechanism which causes the bottle to rotate is illustrated in FIG. 2. 
The neck of the bottle 1b loosely located in the slot in the member 2 is 
urged by a roller 11 into engagement with a pad 12 which extends 
continuously over the length of the bath and subsequent drying stations. 
Friction between the pad 12 and bottle 1b causes the latter to rotate. 
FIG. 3 illustrates a plan view of the layout of the apparatus, which forms 
part of a conveyor for manufacture of plastics bottles. The bottle 
moulding station is indicated generally at 13. 
The bottles supported by respective members 2 (not shown) are caused to 
adopt a horizontal attitude by the guide rail 6 moving upwardly and 
laterally relative to the track 5. The position of the rail 6b in which 
the bottle passes across the bath 8 of coating composition is shown. The 
platform 10 which serves to coat the necks of the bottles is located at 
the downstream end of the bath. After passage through the bath the bottles 
move to a location where the guide rail 6a causes them to be inclined at 
45.degree.. Excess coating composition drains from the spinning bottles 
and is collected in a tray 14. The guide rail then moves to a dispostion 
relative to the members 2 in which the bottles pass vertically through a 
drying oven. The bottles may remain in the oven at a temperature of 
60.degree. C. for a period of 90 seconds.