OPTIMISED PROCEDURE AND DEVICE FOR PRINTING ON VULCANISED RUBBER

Abstract

 This invention describes a process for printing on a removable film base that can be added to the rubber surface of an item which will undergo the vulcanisation process, to enable the transfer of graphics onto the vulcanised rubber. The process to construct the graphical element on the film base guarantees high-definition graphics thanks to a specific blend of pigments used according to the digital printing technique.

Description

Field of application of the Invention

[0001] This invention is categorised as a technique for printing graphics on surfaces, in particular rubber surfaces that have undergone the process known as 'vulcanisation', which is a chemical and thermal process that changes the rubber's characteristics, making it more stable, elastic and stronger. This process also eliminates unwanted aspects of rubber, such as adhesiveness, spalling and a tendency to react with oxygen in the air.

Background to the Invention

[0002] At an industrial level rubber is a material that is well-known and used in various processes to make goods, thanks to intrinsic physical characteristics that are very desirable, and its versatility.

[0003] There are two types of rubber available on the market - natural rubber obtained from latex and synthetic rubber obtained from hydrocarbons.

[0004] In industry, rubber undergoes treatments designed to enhance or eliminate some of its physical qualities, depending on the final application required.

[0005] One of the optional rubber treatments is vulcanisation, which changes the structure of the aforementioned polymer by means of a high-temperature process and the use of additives. This is possible thanks to crosslinking of the rubber polymer, resulting in a finished product that is elastic yet strong, without adhesiveness or spalling, and which is not very reactive to oxygen in the air compared with non-vulcanised rubber. The patent GB791095A1, for example, describes a vulcanisation process integrated with the use of specific additives.

[0006] The resulting mechanical and physical characteristics obtained enable a wide range of uses, such as the construction of pipes and sheaths, mechanical transmission belts, any type of protective coating, vehicle tyres, seals, flexible joints etc.

[0007] For each type of predominant feature of an item, the vulcanisation process is accompanied by additional procedures that change the characteristics of the rubber, in order to obtain particular benefits. For example, fire-resistant silicone rubbers, which are extremely elastic at low and very high temperatures, are obtained by mixing specific chemical components and performing a vulcanisation process with radiated energy using a beam of electrons.

[0008] The rubber items may subsequently contain additional reinforcement structures within, which thereby combine various characteristics not obtainable from the rubber alone and the processes it undergoes.

[0009] Tyres, for example, have an inner metal casing that provides the basic rigidity and strength required to handle impact forces when rolling on asphalt. The compound with rubber and other additives, in a formulation that varies depending on the tyre, enables adherence to the road surface and contributes to the non-traumatic absorption of roughness.

[0010] Considering the vast range of vulcanised rubber applications, printing processes on this material should be deemed of major importance, as they enable items to be characterised and permanently marked with standard information for their correct use.

[0011] By way of example, a transmission belt for mechanical equipment may need to enter the respective pulleys in a specific direction. This type of technical information must be detailed on the body of the belt to minimise the risk of incorrect assembly.

[0012] Another important example comes from electromedical devices used in medicine, such as probes for medical investigations on organs in the human body.

[0013] The characteristics of these probes are impressed on their rubber coatings so that one can be distinguished from another. Naturally these printed graphics contribute significantly to safety when using the electromedical equipment.

[0014] There are generally two types of printing on vulcanised rubber - the first is not actually printing but embossing, whereby graphical elements and/or other alphanumerical characters stand out in relief on items.

[0015] The second is a technique based on screen printing, and more specifically by screen printing a graphical element onto a film base in polypropylene or similar material.

[0016] The ink used for screen printing onto the film base is made of elements that are chemically compatible with rubber i.e. an ink made with synthetic rubber with a pigment added.

[0017] The use of a synthetic rubber-based ink is of major importance for the aforementioned application of printing on rubber.

[0018] The printed polypropylene film obtained is then cut and attached to the rubber surface of the item, which will undergo the vulcanisation process, for example a steam heating process in an autoclave at a temperature of 130° centigrade.

[0019] The vulcanisation process will bond the screen printing onto the rubber surface of the item permanently, as the printing ink has a precursor chemical derived from the same rubber, whereas the polypropylene film base will be removed appropriately.

[0020] The adhesion obtained between the item and the graphical element applied via vulcanisation is perfect, as the two materials are completely similar and homogeneous, and the vulcanisation process bonds both permanently.

[0021] The prior art regarding the printing process, where reported, has a limitation in its characteristics, as while the level of definition obtainable with graphics applied through vulcanisation is of good quality, it does not permit migration to the photographic quality now required by recent printing applications. Publication US2007231514A1 describes a transfer printing process in which the graphical element adheres to a vulcanised surface, however no particular characteristic is highlighted to be able to apply high-definition printing. Publication US5707472A describes a support element onto which a graphical element is applied and held during a process to cool vulcanised rubber, however even in this application details are not provided on how it is possible to achieve high-definition printing on vulcanised bases. Publication JPH0232821A describes a method for printing on a vulcanised material whereby the graphical element is in relief but without high-definition characteristics.

[0022] Basically the printing process in the prior art on rubber to be vulcanised does not enable sufficient definition for those graphical elements that need to have an extremely high level of detail, therefore managing very small graphics is complicated.

[0023] To date this limitation has represented a significant drawback. The widespread use of QR codes for example, or other techniques for identifying/endorsing similar items, is based on graphical complexity that guarantees a certain density of information in the space available which is intelligible to reading systems - first and foremost surveillance cameras - only if these codes continue to have a high level of graphical detail.

[0024] The process to apply complex graphics to rubber is therefore more complicated on smaller items, where print definition which is not high does not enable the correct density of information.

[0025] Another limitation with the printing process in the prior art is the fact that a specific printing frame has to be created for every graphics variation. By way of example, applying 50 different barcodes would require the creation of 50 printing frames. This limitation is intrinsic to screen printing and is difficult to circumvent if the aforementioned technique is also used in printing processes on vulcanised rubber.

[0026] Considering the details outlined in the previous sections, the main aim of this invention is to devise a printing process on rubber that will undergo the vulcanisation process, to guarantee high-definition graphics while maintaining backward compatibility with the graphics definition standards in the prior art.

[0027] The aim of this invention is also to devise the aforementioned innovative printing process on vulcanised rubber characterised by a processing speed which is faster than the printing processes in the prior art.

[0028] An additional aim of this invention is to implement a variation of the process to print graphics on vulcanised rubber, which guarantees typical physical features with 3D-type effects.

Summary of the Invention

[0029] This invention describes a process for printing one or more graphical elements onto a base with a removable film using a transfer technique that enables the transfer element to be added to the rubber surface of an item. This item will undergo the vulcanisation process to enable the transfer of these graphical elements onto the vulcanised rubber.

[0030] The process to construct the graphical element on the film base guarantees high-definition graphics thanks to a specific blend of pigments used according to the digital printing technique. The vulcanisation process required to retain these graphical elements does not alter their quality. Moreover, in the transfer technique the film base is separated from the graphical elements once they have been permanently attached to the surface in vulcanised rubber.

Benefits of the Invention

[0031] This invention features the following benefits: a) the graphical elements applied to the vulcanised rubber have a high level of definition, to photographic standard, making them highly faithful to the original design; b) the high definition of the graphical elements enables printing on small surfaces; c) the high definition of the graphical elements in this invention enables the use of graphics codes such as QR codes or similar; d) the process to construct the graphical element on the base, as per the idea of the invention, eliminates the need to use the screen printing techniques in the prior art which entail a significant increase in the cost of industrial printing processes.

Description of Diagrams

[0032] The table of diagrams is included in the documentation for this application to illustrate the characteristics of the invention, with application variants highlighted where described. In particular, the sections and dimensions of features mentioned in the table are not to scale, in order to make the main characteristics of this invention visible. The following are included:

Fig.1
[fig. 1] illustrating a BOPP layer as per the idea of the invention,

Fig.2
[fig. 2] illustrating the application of the transparent resin layer as per the idea of the invention,

Fig.3
[fig. 3] illustrating the digital printing of the graphics as per the idea of the invention,

Fig.4
[fig. 4] illustrating an additional transparent resin layer as per the idea of the invention,

Fig.5
[fig. 5] illustrating the application of the transparent resin layer as per the idea of the invention,

Fig.6
[fig. 6] illustrating a section, which is not to scale, of the new feature resulting from the idea of the invention,

Fig.7
[fig. 7] illustrating an item with the new feature resulting from the idea of the invention, applied via a vulcanisation process,

Fig.8
[fig. 8] illustrating a sheath in vulcanised rubber applied to a rubber pipe in food production equipment, with the new feature resulting from the idea of the invention applied.

Description of the Invention

[0033] A description of the various ways of implementing this invention is discussed here for illustration and is not intended to be exhaustive or limited to the form of implementation described.

[0034] All potential obvious modifications to the invention and its field of application implemented by industry experts do not limit the actual patent protection conditions.

[0035] As per the invention implementation method, a temporary or removable, transparent or coloured film base is created, onto which printed graphical elements will subsequently be implemented then applied to a surface in rubber to be vulcanised. On completion of the vulcanisation process the film base will be removed, as in the phases in transfer printing processes.

[0036] The aforementioned graphical elements to be applied to a surface in rubber to be vulcanised can vary in type, for example they may be text characters, ID codes, QR codes, designs, barcodes, logos etc.

[0037] As per the invention implementation method, the temporary or removable film base must have two particular physical characteristics i.e. flexibility and resistance. The former guarantees the option of applying it to any type of rubber surface, and the latter ensures it does not lose its characteristics during the printing and vulcanising processes.

[0038] As per the invention implementation method, a film base made of biaxially-oriented polypropylene (BOPP) is chosen for this purpose (10). This material guarantees more flexibility and resistance than a simple polypropylene film.

[0039] As per the invention implementation method, an effective thickness and good compromise for constructing the BOPP film base for this application could be 72um i.e. 72×10^-6 metres. Different thicknesses of this material are possible however, preferably between 30um and 180 um.

[0040] As per another invention implementation method, the BOPP base sheet could be replaced with a base that is completely synthetic rubber and could also be pigmented, especially when the level of resistance and flexibility of this material in the base format, as per the idea of the invention, enables certain printing applications on rubber to be vulcanised.

[0041] As per the invention implementation method, one of the BOPP film surfaces is treated with a transparent resin (21), made of an acrylic base + a polyurethane base + a synthetic base with an average distribution of between 0.4 grammes/dm² and 1.8 grammes/dm², preferably between 0.8 grammes/dm² and 1.2 grammes/dm².

[0042] The application of this resin enables an increase in the general resistance of the new feature and is made with a roller coater or embosser (20), or other application technique that produces the same results.

[0043] As per the invention implementation method, the graphical elements are actually printed onto the resin-coated BOPP film, then on the aforementioned resin. This process is implemented preferably using digital transfer printing method with a dry toner (30) i.e. a printing process in mirror mode, such that once the transfer is applied to the item to be decorated the logo will be legible, with this process able to replace the screen printing process in the prior art. Digital transfer printing can be implemented advantageously with a very high resolution such as 1200 dpi or 2400 dpi.

[0044] As per the invention implementation method, the dry toner for the digital transfer printing is made up in the following substance proportions:

a. a part greater than/equal to 70% in polyester polymers;

b. the remainder in ink and additives for printing.

[0045] The aforementioned digital printing process can of course be backward compatible with lower print resolution i.e. levels already known in the prior art. Moreover, the resin printed on the BOPP base, as per the idea of the invention, is applicable with printing techniques already known in the prior art, such as inkjet printing or similar techniques, obviously with different resolution results. Obviously these printing processes can be repeated several times on the resin-coated BOPP base surface.

[0046] As per another invention implementation method, the digital printing process on the BOPP base could also be carried out using a digital UV ink, already known in the prior art, characterised by considerable adhesion capability and resistance to ambient light exposure. The polymerisation of this ink occurs via exposure to UV rays generated by the same printing equipment.

[0047] As per another invention implementation method, the digital printing process on the BOPP base could also be carried out using a polypropylene or polyethylene-based ink, already known in the prior art, in which pigmented elements are added which determine the print colour.

[0048] Once the phase to print the graphical elements is complete, as per another invention implementation method there is the option to add a layer of polyurethane and acrylic-based binder to the digital print, preferably with an average distribution of 1g/m² to consolidate the aforementioned print.

[0049] As per the invention implementation method, once the optional phase to apply a binder is complete, a transparent resin coating can be applied (40). This coating is completely identical to the first applied to the BOPP film before the digital printing process described in sections 0051, 0052, 0053, 0054 and 0055, therefore the same formulation described in section 0049.

[0050] As per the invention implementation method, at this point an element must be added to enable the perfect bonding of the graphical elements created via digital printing, suitably protected by the transparent resin, to the rubber surface to undergo the vulcanisation process.

[0051] For this purpose a process is devised to apply a coloured synthetic rubber base (50) over the previous graphics layer (the digital printing) with protection (the transparent resin) already implemented on the BOPP film and described in the previous sections.

[0052] As per the invention implementation method, the application of this coloured synthetic rubber-based layer provides the following characteristics: a) a contrasting element with a coloured base to highlight the graphics created with the digital printing; b) a layer of rubber material which will adhere perfectly to the rubber on the item to which it is to be attached during the vulcanisation process.

[0053] The rubber-based layer can conveniently be applied using a printing/depositing technique already known in the prior art.

[0054] As per the invention implementation method, the thickness of the synthetic rubber layer will be between 15 cm³ and 40 cm³ per square metre, preferably between 24 cm³ and 30 cm³ per square metre.

[0055] Fig. 6 illustrates an enlarged side section of the constituent parts of the new feature in this invention. In this diagram the individual parts are not shown to scale in order to emphasise the informative nature of the design. The BOPP film (60) is covered by the layer of transparent resin (61) onto which the required graphics are applied (62), via digital transfer printing for example, with the characteristic dry toner blend, which are in turn covered with a binder and another layer of transparent resin (63), then incorporated within the synthetic rubber layer (64).

[0056] As per the invention implementation method, at this point the new feature is ready to be applied to the surface of a rubber item before the vulcanisation process. Obviously the coloured synthetic rubber layer on the new feature is the part which must face onto and remain in contact with the rubber on the item, so that during vulcanisation the two substances can interact and bond permanently due to that process.

[0057] As per the invention implementation method, vulcanisation will not compromise or change the resin layers containing the digitally printed graphics when implemented according to the technical principles described in this invention.

[0058] Once the vulcanisation process is complete, the BOPP film base (70) can be removed from the vulcanised rubber surface on the item (71), as the printed graphics will have adhered to the item through the fusion of the coloured synthetic rubber layer.

[0059] The graphics and protective elements forming the new feature in this invention can conveniently be implemented in sequence on a continuous strip of BOPP film base. This strip can then be punched and/or cut and/or shaped for the various printing applications required in industry.

[0060] As per another invention implementation method, the BOPP film base containing the print, as per the idea of the invention, can also be wound onto reels to feed transfer printing equipment.

[0061] As per another invention implementation method, the BOPP film base can be replaced with another material depending on the required industrial applications. A material that can be used in place of the BOPP is polyurethane.

[0062] Example of the invention: figure 8 illustrates an example of the new feature resulting from this invention, in the form of a rubber pipe (80) used for the extraction of a liquid food (81) treated via ultrasound (82) with a pipe with a QR code (83) which refers to a technical data sheet for the same pipe published on a specific web page.

Industrial Applications of the Invention

[0063] This invention is applicable to all fields that process rubber and use the vulcanisation process, and which require graphics and/or text to be placed on the surface of these rubber items. More specifically, those applications in which graphics definition and the resolution of the graphics must be very high, even of a photographic nature, for example: a) sheathing to cover electric cables b) coatings on sensors c) small hoses for fluids d) seals e) O-rings f) mechanical transmission belts g) controls for electronic applications etc.

[0064] This invention is however a printing technique applicable to any item, provided it contains rubber to undergo the vulcanisation process.

References in the Invention

[0065] No references.

Patent Literature

[0066] 

PLT1: GB791095A1

PTL2: US2007231514A1

PLT3: US5707472A

PLT4: JPH0232821A

Non-Patent Literature

[0067] NPL1: none.

Claims

1. Transfer type printing procedure on a rubber surface, before starting its vulcanization process, by means of Digital Glass Decal Printing technique on a Bi-Oriented Polypropylene film (BOPP) in which:

a. the thickness of BOPP is between 30um, that is 30×10^-6 meters and 180um, that is 180×10^-6 meters, preferably 72um, that is 72×10^-6 meters,

b. by means of engraved roller technique or embossed roller or spreading machine, a transparent resin is applied on a side of the BOPP film consists of a mixture of acrylic resin, polyurethane resin and synthetic resin, with an average distribution on the BOPP film between 0,4 grams/dm² and 1,8 grams/dm², preferably between 0,8 grams/dm² and 1,2 grams/dm²,

c. a Digital Glass Decal Printing is performed on the transparent resin surface using a Dry Toner consisting, on a total of 100% of the mixture of its components, of:

i. a fraction greater than/equal to 70% in polyester polymers,

ii. the remaining part in ink and additives for printing.

d. by means of engraved roller technique or embossed roller or spreading machine, a transparent resin, consisting of a mixture of acrylic resin and polyurethane resin and synthetic resin, is applied on the binder layer with an average distribution between 0,4 grams/dm² and 1,8 grams/dm², preferably between 0,8 grams/dm² and 1,2 grams/dm²,

e. upon the transparent resin a layer of synthetic rubber is applied in an amount between 15cm³ and 40cm³ per square meter, preferably between 24cm³ and 30cm³ per square meter,

f. the film in BOPP is applied to a rubber article before the vulcanization process, by adhering the synthetic rubber surface on the film in BOPP to that of the article,

g. at the end of the vulcanization process the film in BOPP is separated from the surface of the rubber article.

2. Transfer type printing procedure of the Claim1 wherein the Digital Printing is made by Ultraviolet digital inch or polypropylene and/or polyethylene inch based with the addition of pigments.

3. Transfer type printing procedure of the Claim1 and 2 wherein on the Digital Glass Decal Printing a layer of binder made of acrylic based resin and polyurethane based resin is applied by means of a spreader, preferably with an average distribution of 1gr/m²,

4. Device for Transfer printing of Claim 1 consisting of:

a. a Bi-Oriented Polypropylene film (BOPP) of a thickness between 30um, that is 30×10^-6 meters and 180um, that is 180×10^-6 meters, preferably 72um, that is 72×10^-6 meters,

b. a layer in transparent resin consisting of a mixture of acrylic resin and a polyurethane resin and a synthetic resin with an average distribution between 0,4 grams/dm² and 1,8 grams/dm², preferably between 0,8 grams/dm² and 1,2 grams/dm²,

c. a layer in Digital Glass Decal Printing using Dry Toner obtained by a mixture of pigments, on a total of 100% of its components, from:

i. a fraction greater than/equal to 70% in polyester polymers,

ii. the remaining part in ink and additives for printing,

d. a transparent resin layer consisting of a mixture of an acrylic resin, a polyurethane resin and an synthetic resin with an average distribution between 0,4 grams/dm² and 1,8 grams/dm², preferably between 0,8 grams/dm² and 1,2 grams/dm²,

e. a synthetic rubber layer in an amount between 15cm³ and 40cm³ per square meter, preferably between 24cm³ and 30cm³ per square meter.

5. Device for Transfer printing of the Claims 4 wherein the Digital Printing is made by Ultraviolet digital inch or polypropylene and/or polyethylene inch based with the addition of pigments.

6. Device for Transfer printing of the Claims 4 and 5 wherein on the Digital Printing is added a layer of binder made of acrylic based resin and polyurethane based resin, preferably with an average distribution of 1gr/m2,

7. Device for Transfer printing of Claims 4, 5 and 6 in which the film in BOPP is die-cut or cut.

8. Device for Transfer printing of Claims 4, 5 and 6 in which the film in BOPP is replaced by a Polyurethane (PU) film.

9. Device for Transfer printing of Claims 4, 5 and 6 in which the film in BOPP is pigmented.

10. Device for Transfer printing of Claim 4, 5 and 6 in which the film in BOPP is replaced by a synthetic rubber film, also characterized by various pigmentations.

11. Device for Transfer printing of Claims 4, 5 and 6 in which the resin spread on the film in BOPP is printed by means of an inkjet technique.

12. Device for Transfer printing of Claims 4, 5 and 6 in which multiple Digital printing processes are applied on the film in BOPP, also by means of an ink jet technique or other similar technique.

13. Device for Transfer printing of Claims 4, 5 and 6 in which, once printed, the film in BOPP is rolled up into reels.

Drawing