WO2010076807A1

WO2010076807A1 - Film labels for rotational moulding and the process for manufacturing the same.

Info

Publication number: WO2010076807A1
Application number: PCT/IN2009/000231
Authority: WO
Inventors: Pradip Hiralal Shroff; Inderpal Singh Khandpur; Somnath Bhattacharya; Dinesh Mathradas Anam
Original assignee: Prs Solutions Private Limited
Priority date: 2009-01-01
Filing date: 2009-04-09
Publication date: 2010-07-08
Also published as: WO2010076807A4; WO2010076807A9

Abstract

A method is disclosed for imparting designs, logos, words, graphics, etc. on the surface of rotationally moulded products during their manufacture. The film label manufactured by the present invention is a pressure sensitive label which becomes an integral part of the moulded product when applied to the inner surface of the mould cavity by slight pressure, the mould is charged with pulverizes polyethylene or polypropylene powder, heated and rotate on at least two axes. The said film label comprises of an opaque white micro porous plastic film, with or without printing an adhesive layer and an application tape. The film label is easy to apply on the mould cavity by simple 'peel and stick' technique and does not require application of adhesive spray or burnishing for transfer.

Description

FILM LABELS FOR ROTATIONAL MOULDING AND THE PROCESS FOR MANUFACTURING THE SAME.

PRS Solutions Private Limited, a Company incorporated under the Companies Act, 1956 and having its office at 63, Bombay Samachar Marg, Mumbai - 400 001 Maharashtra State, India.

The following specification particularly describes the nature of this invention and the manner in which it is to be performed. FIELD OF THE INVENTION:

This invention relates to Tilm labels for rotational movilding' and the process of manufacturing the same.

DESCRIPTION OF THE PRIOR-ART:

Rotational moulding process is the cheapest and most convenient process for fabricating / manufacturing hollow plastic objects, irrespective of size and shape, such as water storage tanks, traffic barricades etc. For rotational moulding process the moulds used are made in two parts and are normally made out of cheap sheet metals or cast aluminium, which may or may not be polished. In rotational molding, products are formed within a mould cavity for which pulverized polymeric resin is filled in one half of the mould and the same is closed by clamping the other half. The said mould is then simultaneously heated over an open flame or inside a heating chamber and rotated over its major and minor axis in a slow speed for a sufficient time to disperse the resin particles into a molten polymer which coats the interior walls of the cavity with a coating of uniform thickness. Thereafter the mould is cooled, opened and the rotationally moulded product is removed.

Conventionally polyolefin resins such as low, medium or high density polyethylene, polypropylene, ethylene vinyl acetate copolymers are used for manufacturing rotational moulde.^" objects. Polyolefin resins, particularly polyethylene are n:'; receptive to paints, inks, adhesives and the like. This makes application of graphics, indicia, labels etc. difficult to apply on such moulded objects. Traditionally such objects are printed using inks after treating the surface by flame treatment. Such printings is done on the moulded object as a post operation and are costly, time consuming and even the best coating cannot resist abrasion and scratches. The simpler and faster method would be incorporating the graphic at the time of moulding the object so that the graphic transfers to the object and becomes an integral part of it.

In US patent no. 4352762 a process for applying a decorative or printed pattern in the surface of roto moulded products has been disclosed in which a printed pattern is first created on the surface of the mould cavity by stenciling or ccrecri printing of pigments suspended in viscous hydrocarbon oil. This process has its own drawbacks as it takes long time to print the matter on the mould cavity; requires a high degree of skill particularly for multicolour printed patterns and is not suitable for transferring a decorative pattern to a surface having a complex or compound curvatures as silk ccreen and/ or stenciling are only suitable for flat surfaces. Further improvement in the above process was disclosed in US patent no. 4519972 where the decorative patterns are first formed on a sheet film having silicone release coating by screen printing pigments dispersed in microcrystalline petroleum wax. The decorative wax pattern is transferred from the carrier filπi by burnishing the pattern on to the interior wall of the preheated mould cavity. This process is expensive as it requires screen printing of patterns to be carried out using screens made out of stainless steel wire and maintaining high temperatures on the screen by electrical heating during printing process.

Subsequently other developments took place for graphic transfers for rotational moulded objects during moulding;. Such graphics are in the form of screen printed matter on a silicone release coated papers or films which require spraying the interior surfaces of the mold with an adhesive to enhance bonding, and hence transfer, of the graphics to the mould surface from the release coated film. Although a pattern is formed as part of the moulded product, this process has itc shortcomings: pattern sizes are limited as handling cπ:! transferring of bigger graphics is troublesome; the transfer- patterns are very thin and fragile; cracking due to brittleneεs of the pattern is common; shipping damage is common; fractures of the pattern during application are common; burnishing is required to transfer the pattern from the car.-lor film to the mould; this burnishing is not only troublesome cvλ also may injure the mould surface, requiring frequent mo\:id refinishing; a transfer pattern cannot be moved in its location on the mould wall, once burnishing is started; the transfer of the pattern from the carrier onto the inner mould surface is difficult, costly, and time consuming; and their adherence to the carrier film is, by design, precarious since they must release easily from the transfer carrier when transferred to the mould; if an error in location is noted, the entire burnished area must be removed, the transfer pattern discarded, and a new one located properly and burnished into position; the adhesives are often not applied uniformly and frequently are used in excess, causing product discoloration and adhesive buildup on the mould surfaces. The adhesives sprays also use volatile solvents which present environmental concerns during use, shipment and storage. If not completely expelled prior to application of the transfer, any residual solvent will damage the graphic of the transfer. The application of an adhesive to the mould surface prior to application of the transfer also adds a further step to the moulding operation, prolonging the mouding cycle time.

Rotomoulding industry is today looking for a printed label which can be simply adhered on the mould cavity without application of adhesive and /or need for burnishing. Hence the objective of the present invention is to provide a printed film label which is cost effective, easy to apply and does not require application of adhesive spray for transfer.

SUMMARY OF INVENTION:

The film label manufactured by the present invention is a pressure sensitive adhesive label which becomes an integral part of the moulded product when applied to the inner surface of the mould cavity by slight pressure, the mould is charged with pulverized polyethylene or polypropylene powder, heated and rotated on at least two axes. The method of manufacturing the said label for rotational moulded product comprises of following steps: 1. sheeting a thick opaque micro porous plastic film to the desired size;

2. printing on one surface of the said film which may be comprising of one or more colours by using solvent based and /or radiation curable inks where one colour is printed at a time and is followed by drying in air / oven or curing under ultra violet radiation;

3. Printing of a clear, glossy, transparent layer if ink on the printed side of the said film;

4. applying a layer of pressure sensitive adhesive on the printed side of the film by laminating a transfer adhesive tape and siliconised paper or film;

5. cutting the printed film to the desired pattern from the non printed side of the label and stripping the unwanted portions;

6. applying a low tack application tape on the non printed side of the label; and

7. cutting each film labels from the sheet.

Finally, these labels are supplied to customer for moulding into their product by rotational moulding technique. During the rotational moulding process the said label is separated from the said release liner or film with the help of said application tape; applied on the inner surface of the rotational mould cavity so that the pressure sensitive layer is in contact with the surface of the mould; sticking the said label to the mould surface by applying pressure using rubber roller or squeeze; removing the application tape from the applied label; filling the mould cavity with pulverized polyethylene or polypropylene powder; closing the mould and heating the mould to the moulding temperature along with rotating the mould on its major and minor axis at a slow speed for specified time. After the moulding process is over the mould is allowed to cool and the moulded object is removed. The residues of adhesive on the film label in the moulded object can be easily removed by lightly wiping the. film label with a cloth soaked with a cleaning solvent.

The film labels for rotational moulding produced as per this invention are printed pressure sensitive labels which when applied during the moulding process becomes an integral part of the rotational moulded product. The said label for rotational moulding in supplied condition comprises of the following layers:

1. a low tack application tape;

2. an opaque white micro porous plastic film layer;

3. an optional printed graphic layer (as shown in Fig. 1 of 2); printing may not be required (as shown in Figure 2 of 2) when the natural opaque white colour of the film is required; 4. a protective transparent layer to protect the label from abrasions and ultra violet radiations;

5. a pressure sensitive adhesive layer; and

6. a silicone coated release paper or film to protect the adhesive layer.

Use of the labels for rotational moulding as described in this invention provides many benefits to the processor of the rotational moulded products. The most beneficial part is that such pre-printed labels eliminate the need for subsequent flame treatment and printing operation. This also helps in reducing the component cost as the labels can be applied both on cold or hot surface and without application of adhesive spray and /or burnishing thereby reducing the cycle time. The moulding process using labels for rotational moulding as described in this invention is environment friendly as the said film labels can be applied on the mould surface by simple 'peel and stick technique' and there is no release of volatile organic compounds (VOC) associated with adhesive spray. The tooling costs and processing cycle time for rotational moulding process using labels for rotational moulding as described in this invention is much lower than the processes described in the prior art. The process of rotational moulding of hollow objects using labels for rotational moulding further provides the liberty of producing different designs, logos, words, graphics at the same setting by simply changing the graphics even while using the same moulding tool. Various types of printed materials such as names of products, their manufacturer, various designs, instructions etc. can be applied on the surface of the moulded objects, particularly plastic objects, at the time of moulding process to produce moulded parts having a permanently bonded label which can not be peeled off and are weather and abrasion resistant.

The film labels of the present invention comprise a micro porous plastic film. The micro porous plastic film is constructed by processing methods that cause the material to consist of a matrix of interconnected micro size pores that allow gases and vapours to flow freely there through. A number of processes can be used to create such a film including, but not limited to, stretching the film, radiation treatment of the film, and addition of film additives such as fillers that may or may not be removed from the film during processing.

The label is printed on one of the surfaces of the said opaque white micro porous plastic film by screen printing technique and/ or other printing techniques. In one of the preferred embodiment the said label for rotational moulding does not have the printed layer. For screen printing screens made of polyester fabric using dimensionally exact filaments are coated uniformly on both surfaces with photosensitive emulsions and then developed against respective positives to get desired stencil. Fabric thread diameter, emulsion deposition, squeeze angle etc. are selected to have the desired ink deposition of each layer. Inks used for manufacture of labels for rotational moulding in present invention are the conventional pigmented screen printable inks that are either solvent based and/ or radiation curable inks. Labels for rotational moulding of this invention can be single or multicolour labels. After each colour printing the sheets are dried in an air circulating oven when solvent based inks are used or passed through a conveyor under medium pressure mercury vapour lamp(s) when printing is done using radiation curable inks. Oven temperature and duration of drying is controlled to avoid distortion of the film.

A clear, transparent and glossy protective layer is printed on the top of the ink layers to provide desired abrasion resistance and weather resistance to the moulded label. The said protective layer is an ink layer printed by screen printing technique and using radiation curable clear and transparent ink. After printing the said clear ink the sheets are subjected to radiation curing by passing through conveyor under medium pressure mercury vapour lamps.

The pressure sensitive adhesive layer is applied on the ink printed side and over the ink layer by laminating a transfer adhesive tape. The manufacturing of said transfer adhesive tape consists of suitably coating 5 to 50 grams per square meter of a pressure sensitive adhesive on one side of a both sides release coated liner having sufficient differential release in order to retain the adhesive on the side to which it was originally coated, followed by drying. The said pressure sensitive adhesive may be a solvent based acrylic adhesive or a pressure sensitive rubber adhesive. The process of applying the adhesive is done by conventional method of coating equipment followed by using known drying methods. The said tape is then slit in desired length and width.

The said acrylic pressure sensitive adhesive used in this invention is the conventional acrylic adhesive available in the market. The said rubber based adhesive is manufactured by blending one of the synthetic rubbers such as, but not limited to, Styrene-Isoprene-Styrene (SIS); Styrene-Butadiene- Styrene (SBS); Styrene-Butadiene Rubber (SBR) with one or more of tackifiers which can be formed of hydrocarbon resins, rosin derivatives, polyterpenes, coumarone-indene resins, any compatible conventional tackifiers or mixtures thereof and hydrocarbon resins, rosin derivatives, polyterpenes, coumarone- indene resins, any compatible conventional tackifiers or mixtures thereof and hydrocarbon/ aromatic solvents to form a compound of coatable consistency and texture commensurate to the coating equipment.

Film labels are given the desired shape and size by conventional punching technique or by cutting the sheets on a plotter. The film labels of this invention are punched or cut from the non printed side of the plastic film using a design which is exact mirror image of the desired final design so that when the label gets embedded on the product the contents of the label are readable. After punching or cutting the label unwanted portions are stripped off and a low tack application tape is applied on the non printed side of the plastic film. In case of multiple ups are printed on one ' sheet individual labels are separated by cutting the release paper or film.

This invention describes the steps involved in the production of film labels suitable for transferring designs, logos, words, graphics, etc. on rotational moulded products. The said labels can be used by those skilled in the art of rotational moulding to make hollow plastic products. Further, the various parameters discussed herein may be adjusted by those of skill in the art in order to maximize results.

The Figures 1 and 2 are the schematic representations of the construction of Film labels for rotational moulding.

Claims

WB CLAIM:

1. Film label for rotational moulding and the process for manufacturing the same comprises of the following steps: -

a. sheeting a thick opaque micro porous plastic film to the desired size;

b. printing on one surface of the said film which may be comprising of one or more colours by using solvent based and/ or radiation curable inks where one colour is printed at a time and is followed by drying in air / oven or curing under ultra violet radiation;

c. Printing of a clear, glossy, transparent layer if ink on the printed side of the said film;

d. applying a layer of pressure sensitive adhesive on the printed side of the film by laminating a transfer adhesive tape and siliconised paper or film;

e. cutting the printed film to the desired pattern from the non printed side of the label and stripping the unwanted portions;

f. applying a low tack application tape on the non printed side of the label; and

g. cutting each film label from the sheet.

2. Film label for rotational moulding and the process for manufacturing the same as claimed in claim 1 wherein the said plastic film is a opaque white micro porous polyolefin film having thickness of 0.150 mm to 0.250 mm.

3. Film label for rotational moulding and the process for manufacturing the same as claimed in Claim 1 wherein label is printed by screen printing and /or other printing techniques.

4. Film label for rotational moulding and the process for manufacturing the same as claimed in Claim 1 wherein the inks used are solvent based and/ or radiation curable screen printable inks.

5. Film label for rotational moulding and the process for manufacturing the same as claimed in Claim 1 wherein the inks used are having excellent out door weather resistance and high temperature withstanding^' properties.

6. Film label for rotational moulding and the process for manufacturing the same as claimed in Claim 1 wherein the said pressure sensitive adhesive is an acrylic adhesive.

7. Film label for rotational moulding and the process for manufacturing the same as claimed in Claims 1 and 6, wherein the said pressure sensitive adhesive is a blend of synthetic rubber such as Styrene-Isoprene-Styrene (SIS); Styrene-Butadieήe-Styrene (SBS); Styrene-Butadiene Rubber (SBR) and the tackifϊer is formed of hydrocarbon resins, rosin derivatives, polyterpenes, coumarone-indene resins, any compatible conventional tackifiers or mixtures thereof.

8. Film label for rotational moulding and the process for manufacturing the same as claimed in claims 1 wherein the labels are cut from the non printed side and is in the mirror image of the actual label.

9. Film label for rotational moulding and the process for manufacturing the same as claimed in Claim 1 wherein the said application tape is a film based low tack adhesive tape having peel strength of 35 g/2.5cm to 300 g/2.5cm and supports application of the said label on the mould cavity by simple 'peel and stick' technique.

10. Film label for rotational moulding manufactured by the method as claimed in claims 1 to 9 above.