AU2014101510A4 - Masking System for Painting - Google Patents

Abstract

Abstract A method of masking portion of a surface which is desired to be masked preparatory 5 to a painting operation. The method comprises: - unrolling and separating a panel of plastic film from a spool having a longitudinal axis, said film having a crosswise direction parallel to said spool axis and a lengthwise direction perpendicular to said crosswise direction; and 10 - adhering said panel of film to an edge of said surface. The plastic film is readily tearable by hand to substantially the same extent along both the lengthwise direction and the crosswise direction without significant stretching of the plastic film. 26_ _32

Description

1 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION INNOVATION PATENT "Masking System for Painting" The following statement is a full description of this invention, including the best method of performing it known to me: 2 MASKING SYSTEM FOR PAINTING. 5 Field of the Invention This invention concerns the use of sheet materials to mask areas when painting. It is particularly applicable to use when spray painting automotive body panels. 10 Background to the Invention The automotive body repair industry makes wide use of spray painting systems to apply paint to body panels of vehicles being repaired. A wide range of paint types is used for this purpose. In many situations it is desired for some areas to be masked 15 from paint deposition during the spraying operation. Many systems have been developed for masking, but the system most commonly used at the present time is to use sheets of cheaply available kraft paper and adhere them to the bodywork of the vehicle by adhesive paper-based tape. A mobile 20 masking machine may be used to apply the tape to the edge of the paper. The tape is applied so that it overlaps the edge of the paper. The paper is then adhered, by the tape, to the surface to be masked. However many of the paints used in the auto body repair industry have particularly 25 aggressive solvent based systems and these have a marked tendency to bleed through paper sheets. This is particularly so with the increasing tendency to use cheaper and lighter grade papers as a cost saving measure. Another difficulty with the use of paper as a masking medium in this industry is that 30 when a painter wants to create a curved edge for the area being painted, and the adhesive tape is therefore stuck to the surface with its free edge curved on the surface, the paper has a tendency to crease and crinkle abruptly which makes the creation of a 3 smooth curve difficult and can cause the edge of the tape adhering to the auto body to lift slightly and thus cause a jagged edge to the paint. There have been attempts in the past to substitute thin plastic film for paper in auto 5 body masking applications, but these attempts have suffered disadvantages. In particular, the thin plastic films have been difficult to work with as they have had a poor ability to drape against the surface being covered so making their positioning difficult. In addition, overspray which hits and adheres to the plastic sheet has not adhered very tightly so that when the sheet is removed, the dried particles of paint 10 easily fall away from the film so contaminating the area with the paint particles. A disadvantage shared by paper and most previously used plastic films is that they slip off the surface of any prepainted body metal on which they are placed. 15 Plastic film has been used which has a greater resistance to tearing along one direction than along the transverse direction. Although providing an improvement over the previous systems, this suffers the disadvantage that the film is not readily tearable by hand in all directions and any attempt to do so results in stretching and distortion of the film at its edge which makes accurate masking difficult. 20 An aim of the present invention is to provide a method of masking which overcomes or at least reduces the difficulties described above. Summary of the Invention 25 Accordingly, in one aspect the invention provides a method of masking portion of a surface which is desired to be masked preparatory to a spray painting operation, said method comprising: - unrolling and separating a panel of plastic film from a spool having a 30 longitudinal axis, said film having a crosswise direction parallel to said spool axis and a lengthwise direction perpendicular to said crosswise direction; 4 - adhering said panel of film to an edge of said surface; wherein said plastic film is readily tearable by hand to substantially the same extent along both said lengthwise direction and said crosswise direction without significant stretching of the plastic film. 5 Preferably said panel is separated from said spool by tearing said film. Adhesive tape may be applied to an edge of said panel such that it overlaps an edge of said panel; and said panel adhered to said edge of said surface by said tape. The 10 adhesive tape may be applied to said panel during the process of unrolling the panel from the spool. Preferably said painting operation is a spray painting operation and said surface is portion of the body of an automotive vehicle. 15 The plastic film preferably has a weight in the range of 40 to 75 g/m2, more preferably in the range of 40 to 60 g/m 2 . Preferably the film carries an electrostatic charge during said step of adhering the tape 20 with the attached film to a surface. Preferably the film is at least predominantly polyethylene. Preferably the film is at least predominantly polyethylene and preferably the outer 25 surface of the film when it is on the spool has been treated by a corona discharge to improve the adhesion of paint thereto. Description of the Preferred Embodiment and Other Examples of the Invention 30 In order that the invention may be more fully understood there will now be described, by way of example only, a preferred embodiment and other elements of the invention with reference to the accompanying drawing, labelled Figure 1, which shows an apparatus as used in performing said preferred embodiment of the invention.

5 Figure 1 shows a mobile masking machine 10 of a type often used in automotive body repair shops. The machine has a frame 12 formed primarily from 25 mm2 hollow section steel. 5 The frame 12 comprises a U-shaped base 16 and an upright spine member 14 which extends upwardly from one corner of the base 16 to the top of the frame 12 where it curves over to form a generally horizontal handle 20 onto which is slipped a rubber hand grip 22. A pair of wheels 18 are attached to the base 16 so the machine 10 may 10 be readily moved from job to job by using the handle 20 to manually tilt and move the machine. The spine 14 supports a cantilevered spindle 32 which extends in a generally horizontal direction back over the base 16. Mounted onto the spindle is a spool 30 of 15 plastic film 31. The spool 30 has a longitudinal axis 44 in common with the longitudinal axis of the spindle 32, and this is parallel to that direction on the sheet of film which is crosswise of the spool. 20 The spine 14 carries below the spindle a short axle 36 having a hub 38 onto which is mounted a roll 40 of paper-based adhesive tape 42. The tape 42 is arranged such that it is caused to be applied to the inwards edge 34 of 25 the spool 30 of plastic film 31 at the same time as the film is drawn from the spool 30. Affixed to the spine 14 and extending generally horizontally above the spool 30, is a flat blade member 24 which is used to tear the film. The blade 24 has a lower edge 30 26 incorporating a continuous array of sharp serrations 28. The serrations are pointed downwards towards the spool 30.

6 To dispense the film, the film is manually pulled down from the spool and as the film unrolls, the tape 42 is applied to its inwards edge 34. When the desired length of film has been unrolled, it is raised upwards to bring it into contact with the serrations in order to tear off the desired length of film. 5 Mobile masking machines of this type, and arrangements for dispensing tape onto paper rolls in this manner, are well known in the art and do not need to be further described here. 10 Most plastic films which have been tried for the purpose have been difficult to tear in this manner. Fixed sharp blades and sliding blades have been tried but these have been clumsy to use and/or have not provided a satisfactory means for cutting or tearing the film. It has been found that a major cause of this difficulty is that during the production of conventional plastic films, the extrusion and subsequent cooling 15 processes produce a plastic film which has a significantly greater resistance to tearing across the roll than lengthways down the roll. This means that it is relatively easy to tear the film in a long strip running around and around the spool, but it is substantially more difficult to tear the film across the spool parallel to the direction of the spindle. 20 An alternative system successfully implemented for some years uses a film which has a greater resistance to tearing along the lengthwise direction than along the crosswise direction. However it has now been found that significant advantages can be achieved by using a film which is readily tearable by hand in any direction. While the overall tear strength of the film may be reduced from previously used films, the 25 advantages deriving from being able to easily trim the size and shape of a panel of film to fit around an opening are substantial. After the preferred plastic film is extruded and cooled during its manufacture, it is subjected to a corona treatment to that entire surface which is oriented towards the 30 outside of the spool. This corona treatment provides a surface to which paint adheres more strongly than to the untreated surface on the opposite face. The adherence of paint so achieved is such that conventional automotive paints adhere strongly to the treated surface whereas they would flake off from an untreated surface.

7 The most preferred film 31 has been found to be sold under the trade mark "True White" by GPI Automotive Products of Mulgrave, Victoria. It has a weight of about 50 g/m 2 . It has been found that this provides a satisfactory drape for the film to allow 5 its satisfactory manipulation on the surface. The film 31 is formulated from a mixture of LDPE, LLD and HDPE such that the film has the characteristic of retaining an electrostatic charge for up to 8 hours after it is drawn from the spool. This electrostatic charge means that the film tends to cling to an already painted surface of a motor vehicle which is being masked and this provides for easy manipulation of the 10 film into position. The plastic film provides a greater level of "give" than does paper when the tape is being applied to form a curved masked edge. Thus improved sharpness of curved edges is achieved when compared to paper. 15 Whilst the above description includes the preferred embodiments of the invention, it is to be understood that many variations, alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the essential features or the spirit or ambit of the 20 invention. For example, the invention in its broadest aspect is not limited to its application in the repair of motor vehicles. The painting operation may use air-powered spraying or airless spraying or may even be a non-spray operation such as brush or roller 25 application of the paint. It will be also understood that where the word "comprise", and variations such as "comprises" and "comprising", are used in this specification, unless the context requires otherwise such use is intended to imply the inclusion of a stated feature or 30 features but is not to be taken as excluding the presence of other feature or features.

8 The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge in Australia.

Claims (8)

1. A method of masking portion of a surface which is desired to be masked 5 preparatory to a painting operation, said method comprising: - unrolling and separating a panel of plastic film from a spool having a longitudinal axis, said film having a crosswise direction parallel to said spool axis and a lengthwise direction perpendicular to said crosswise direction; 10 - adhering said panel of film to an edge of said surface; wherein said plastic film is readily tearable by hand to substantially the same extent along both said lengthwise direction and said crosswise direction without significant stretching of the plastic film. 15

2. A method as defined in claim 1 wherein said panel is separated from said spool by tearing said film.

3. A method as defined in claim 1 or 2 wherein: - adhesive tape is applied to an edge of said panel such that it overlaps an 20 edge of said panel; and - said panel is adhered to said edge of said surface by said tape.

4. A method as defined in claim 3 wherein said adhesive tape is applied to said panel during the process of unrolling the panel from the spool. 25

5. A method as defined in any one of the previous claims wherein said painting operation is a spray painting operation and said surface is portion of the body of an automotive vehicle. 30

6. A method as defined in any one of the previous claims wherein said plastic film has a weight in the range 40 to 75 g/m 2 and carries an electrostatic charge during said step of adhering the tape with the attached film to a surface. 10

7. A method as defined in any one of the previous claims wherein the film is at least predominantly polyethylene. 5

8. A method as defined in any one of the previous claims wherein the outer surface of the film when it is on the spool has been treated by a corona discharge to improve the adhesion of paint thereto. 10