Description:FIELD OF INVENTION

The present invention relates to the dual-cure hemming adhesive which includes anaerobic-curing and heat-curing. Anaerobic-curing will occur on the minimum overlap areas of hemming joints and heat-curing will occur at the remaining flanges where sufficient overlap area is available.

BACKGROUND OF THE INVENTION

The hemming involves bending the edge of a metal sheet which provides a neat and a compact sheet metal joint. The hemming process is an important joining method during the manufacture of BIWs. It is used to produce highly effective bonding of automotive doors, hoods and tailgates in combination with a hemming adhesive which also protects the hemmed joints from corrosion and increases the rigidity thereof.

Currently, panel deformation issues are being faced at the BIW hood corners during Partial Treatment Cathode Electro Deposition (PTCED) process involving multiple 3600 rotations of the BIW. This deformation occurs due to the hemming adhesive being present on the hood inner and outer panel joinery at the corners/edges, which are not in a cured state and uniform particles of glass bubbles present in the hemming adhesive provide a temporary tack and help to retain the BIW panels in position before the curing operation takes place. There is no sufficient bond strength to withstand the forces generated during the rotation of the BIW during the PTCED process.

During the aforesaid hemming process in automotive body shop, the dual-cure hemming adhesive spreads evenly between outer and inner panels 10, 20. For example, a rubber and epoxy glass-bead hemming adhesive is used in this process, to protect the hemmed-flange from corrosion and to impart sufficient stiffness to the panel assembly. After completion of the hemming process, the hemmed car body (BIW) is dispatched to the paint shop for further processing thereon. In the paint shop, after pre-treatment cleaning (for cleaning all dust, dirt, grease particles etc. from the sheet metal), the car body is transferred to a PTCED (cathodic electro-deposition) bath. At this stage, an anti-corrosive coating is applied by using an electro-chemical process like electroplating (in which the body parts function as the cathode and the coating bath functions as the anode). Here, the car body is given a negative charge and immersed in a dip tank of a positively charged anti-corrosive coating. After immersion in PTCED bath, the car body is rinsed properly and transferred to an oven to complete this PTCED process by curing therein. During this oven-curing, the dual-care hemming adhesive is cured by cross-linking at 180°C.

However, a major disadvantage with the above process is that during this PTCED process BIW will rotate 3600 several times at various stages dipped in liquids such as DI water and in PTCED bath. This rotation creates forces on the hemmed car body or the like, which leads to panel deformation at the corner/edges of the inner and outer hem joint thereof. This mainly occurs due to poor strength as the hemming adhesive is present at a minimum overlap area of the corner/edges and thus does not provide sufficient bond strength.

To overcome this concern, dual cure hemming adhesive to be used, wherein the adhesive at corners with less overlap will get cured in room temperature and the adhesive at remaining closed overlap section, will get cured in oven.

US patent US 8382929 B2 concerns an adhesive composition comprising as principal components, a polymerizable component, an ambient temperature radical polymerization catalyst system and a photo-initiator. The adhesive may optionally comprise an adhesion promoter, a toughener, an epoxy, and a filler material. Further, a two-part reactive adhesive comprising, a first part comprising, (i) at least one free radical-polymerizable monomer, (ii) at least one reducing agent, and (iii) a photo-initiator, and a second part comprising an oxidizing agent that is reactive at ambient temperature with the reducing agent to produce free radicals that are capable of initiating and propagating free radical polymerization. It deals with an adhesive with an ambient-temperature cure system and a photo initiator. The adhesive is cured by the activation of the ambient temperature cure system and the photo-initiator to cure the surface portions of the adhesive. However, this invention does not relate to the adhesive used for the hemming application.

US patent publication US 20170081571 A1 relates to an adhesive composition having an added component of the rubber-epoxy like XNBR-epoxy adducts. It was found that this new adhesive composition significantly reduces meander formation during the manufacture of the automotive parts. This document relates to a crash-stable adhesive to be used in hem flanges to prevent the meander formation by addition of component of the rubber-epoxy like XNBR-epoxy adducts. However, this invention particularly relates to the crash performance and only involves a heat-curing capability.

Chinese patent publication CN 102115654 A relates to an automobile hemming adhesive and a method of preparation thereof. It concerns the technical field of single-component epoxy adhesives. The automobile hemming adhesive is mainly used for bonding an automobile hemming part and is mainly characterized by comprising (A) epoxy resin, (B) modified epoxy resin, (C) toughener, (D) epoxy diluter, (E) thermoplastic resin, (F) plasticizer, (G) thermal stabilizer, (H) latent curing agent, (I) coupling agent, (J) filler and (K) pigment. The method of preparation comprises the following steps: (1) evenly stirring (E) and (F) at 5-35 DEG C; (2) adding the mixed liquid composition in the step (1), and (A), (B), (C), (D), (G), (H), (I), (J) and (K) into a movable mixer, and stirring the mixture evenly at 5-350C; (3) passing the mixture in the step (2) through a three-roller machine once or twice; and (4) vacuumizing the movable mixer, stirring, defoaming, and discharging for later use. This invention mainly solves the problems of low environmental-protection index, poor technical properties of sizing, short storage period, low modulus, poor moisture and heat resistance and the like in the existing hemming adhesive and relates to a hemming adhesive and a method of preparation thereof. It concerns the technical field of single-component epoxy adhesives. It does not deal with any sort of dual-curing nature of the adhesive.

In all above cases, different type of adhesives are used for either a dual-cure purpose or as a hemming adhesive with heat-curing ability. None of the prior art talks about an anaerobic plus heat curing hemming adhesive.

DESCRIPTION OF THE INVENTION

Currently, due to an excess clearance provided at the corners of the BIW hood, the mechanical clamping of the hem flange is unable to hold the inner and outer panel of the joinery during the PTCED process when the BIW is rotated at 3600 several times during various stages. Therefore, a panel deformation is observed at these corner locations.

In accordance with the present invention, a dual-cure hemming adhesive is developed to overcome above problem, wherein such panel deformation is avoided by an anaerobic curing at the zones with the minimum overlap to impart the handling strength to the hood assembly.

Here, the corner areas have a cured adhesive to provide a sufficient bond strength to the joinery. The remaining portion of the hem flange having a sufficient overlap area available thereon, is heat-cured in the oven after the PTCED process.

This provides a sufficient strength during the PTCED process and thus, helps in achieving the final strength after the heat-curing thereof.

As a result, before the BIW or parts thereof are transported to the CED station, the handling strength is improved substantially in comparison to the conventional hemming-adhesive application discussed above. This prevents the aforesaid panel deformation at the edges. When this BIW or parts thereof are subsequently passed through the oven for curing, the final strength is substantially improved further because of this heat-curing.

The introduction of the dual-cure hemming adhesive provides partial strength to the BIW or part thereof before conducting the heat-curing process in paint shop due to its anaerobic curing at the locations of minimum overlap area during the clinching process.

During the rotation of BIW in the PTCED process, many forces act on the hemmed joineries, leading to the panel deformation, which are also prevented by this dual-cure hemming adhesive, at the areas with minimum overlap.

Currently, the hemmed part (e.g., hood, doors, tail door) needs to be baked before assembling it to the BIW to avoid any panel deformation. The dual-cure hemming adhesive gives a good partial strength due to anaerobic curing thereof and prevents the panel deformation at the minimum overlap areas.

Thus, the dual-cure hemming adhesive gives a dual advantage of anaerobic curing (at minimum overlap areas) and heat curing (at the rest of the panel overlap during oven curing).

OBJECTS OF THE INVENTION

Some of the objects of the present invention - satisfied by at least one embodiment of the present invention - are as follows:

An object of the present invention is to provide a dual-cure hemming adhesive for hemming applications in BIW or parts thereof.

Another object of the present invention is to provide a dual-cure hemming adhesive for avoiding panel deformation in hemming applications during BIW or parts thereof.

Still another object of the present invention is to provide a dual-cure hemming adhesive for hemming applications imparting good partial strength for handling after the assembly of BIW or parts thereof.

Yet another object of the present invention is to provide a method of applying a dual-cure hemming adhesive for hemming of BIW or parts thereof.

A further object of the present invention is to provide a method of applying a dual-cure hemming adhesive to avoid panel deformation during hemming of BIW or parts thereof.

Still further object of the present invention is to provide a method of applying a dual-cure hemming adhesive to impart good partial strength for handling after the assembly of BIW or parts thereof.

These and other objects and advantages of the present invention will become more apparent from the following description, when read with the accompanying figures of drawing, which are however not intended to limit the scope of the present invention in any way.

SUMMARY OF INVENTION

In accordance with the present invention, there is provided a dual-cure hemming adhesive formulation for hemming applications in BIW manufacture, the hemming adhesive formulation comprises:

• 30-50 parts by weight (PBW) of Urethane acrylate;

• 5-25 parts by weight (PBW) of Glycidyl Methacrylate (GMA);

• 0.1-1.5 parts by weight (PBW) of Cumene Hydroperoxide;

• 0.1-2.0 parts by weight (PBW) of Saccharin;

• 0.005-0.1 parts by weight (PBW) N- Acetyl N- Phenyl Hydrazine;

• 0.001-0.1 parts by weight (PBW) of Ethylenediaminetetraacetic acid (EDTA) Tetrasodium salt;
• 0.001-0.01 parts by weight (PBW) of 2,5 Di-Tert Butyl Hydroquinone; and

• 30-70 parts by weight (PBW) of Silicon dioxide;

wherein at room temperature, the initial anaerobic curing of the hemmed joint formed between an outer panel and inner panel of the BIW or parts thereof after applying the formulation therebetween increases the shear strength of the hemmed joint in a range of 2.5 to 3 times to impart the handling strength at the zones with the minimum overlap, and the subsequent heat-curing in an oven further increases the shear strength of the initially cured hemmed joint in a range of 3 to 3.25 times to impart sufficient bond strength thereto.

In accordance with the present invention, there is provided a method of application of a dual-cure hemming adhesive formulation comprising the steps of:

(i) applying a hemming adhesive formulation between an inner panel and outer panel for forming a metal sheet hemmed-joint;

(ii) using a first stage of robotic clinching process conducted by rollers; and

(iii) using a second stage of robotic clinching process conducted by rollers;

wherein the dual-care hemming adhesive prevents any panel deformation on joining together the inner and outer sheet metal panels without any externally visible joint.

Typically, the method comprises the steps of:

- initial anaerobic curing at room temperature at the zones with the minimum overlap of the hemmed joints of the BIW or parts thereof, to impart the handling strength thereto during the subsequent Partial Treatment Cathode Electro Deposition (PTCED) process of the BIW or parts thereof;

- conducting Partial Treatment Cathode Electro Deposition (PTCED) process on the BIW or parts thereof to provide sufficient bond strength thereto; and

- final heat-curing at substantially elevated temperature, of the BIW or parts thereof.

Typically, the anaerobic curing of the BIW or parts thereof is carried out at a room temperature in the range of 23±20C for about 4 hours.

Typically, the final heat-curing of the BIW or parts thereof is done in an oven at 1600C for about 20 minutes after completion of the Partial Treatment Cathode Electro Deposition (PTCED) process conducted thereon.

Typically, the corner areas of the hemmed joint are anaerobically cured by the dual-cure hemming formulation.

Typically, the final heat-curing of the remaining portions of the hemmed flanges is done by the dual-cure hemming formulation to achieve the final strength of the BIW or parts thereof.

Typically, the anaerobically cured hemmed joint has a shear strength increased over the initially cured hemmed joint in a range of 2.5 to 3 times.

Typically, the final heat-cured hemmed joint has a shear strength increased over the initially cured hemmed joint, in a range of 3 to 3.25 times to impart sufficient bond strength thereto.

Typically, the method of application of the dual-cure hemming adhesive formulation is conducted on automotive components such as doors, hoods and tailgates or the like.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will be briefly described in the following with reference to the accompanying drawings.

Figure 1 shows a hemming adhesive formulation applied between the inner and outer panel of a metal sheet hemmed-joint.

Figure 2 shows the first stage of a clinching process using the rollers in a robotic process.

Figure 3 shows the second of a clinching process using the rollers in a robotic process.

Figure 4 shows a location of the BIW using a hemmed joint, such as an automobile hood, doors, and tail gate.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

In the following, a quick-grip hemming-adhesive dual-care adhesive formulation for hemming applications and configured in accordance with the present invention will be described in more details with reference to the accompanying drawings without limiting the scope and ambit of the present invention.

Figure 1 shows a hemming adhesive formulation applied between the inner and outer panel for making a hemmed-joint for an automotive sheet-metal panel. It includes an inner panel having an edge 12 and an outer panel 20 having an edge 22. The inner panel 10 is placed over the outer panel 20 with its edge 12 to be folded over the edge 22 of the outer panel 20 and applying a dual-care hemming adhesive between the inner and outer panels 10, 20 as shown.

Figure 2 shows the first stage of a clinching process using the rollers in a robotic process. Here, the edge 22 of the outer panel 20 is rotated/turned R be as edge 24 bent over the edge 12 of inner panel 10, by which the dual-care adhesive 32 is spread over a larger area between outer and inner panels 10, 20, as shown.

Figure 3 shows the second stage of a clinching process using the rollers in a robotic process. Here, the rotated/turned edge 24 of outer panel 20 (Figure 2) is bent further as in U shaped edge 26 folded over the edge 12 of the inner panel 10, by which the dual-care adhesive 32 is spread further as a thin layer 34 bonded over the complete area between the edges 12, 26 of the outer and inner panels 10, 20, as shown.

Figure 4 shows an exemplary automobile A and the door panel D thereof, in which the dual-care hemming adhesive 34 is used for preventing panel deformation. The location of the hemmed joint used in Figure 3 is also visible. By applying the dual-care hemming adhesive 34 here, both inner and outer sheet metal panels 10, 20 are joined together without any externally visible joint. This hemming process can be used in other automotive body shop to join similar parts like hoods, tail gates etc., to have a higher loading capacity.

Accordingly, the disadvantage with the hemming process discussed in the background section above is that when the BIW is rotated by 3600 several times at various stages, while dipped in liquids like DI water and in CED bath during PTCED process, it produces forces on the hemmed car body or the like, leading to panel deformation at the corner/edges of the inner and outer hem joints thereof, which results in an insufficient bond strength due to the presence of the hemming adhesive at a minimum overlap area of the corner/edges thereof.

This disadvantage is overcome by using a dual-cure hemming-adhesive, wherein this hemming adhesive present at the corners with less overlap gets cured at room temperature and the hemming adhesive at the remaining closed overlap section, gets cured in the oven. Therefore, the BIW or parts thereof, e.g. a hood assembly starts developing strength as soon as it is assembled by the hemming process.

The specification of the dual-cure hemming-adhesive formulation given below:

Raw Material (RM) CAS Number PBW (Parts by weight)
Urethane Acrylate 68987-79-1 30- 50
GMA (Glycidyl Methacrylate) 106-91-2 5-25
Cumene Hydroperoxide 80-15-9 0.1-1.5
Saccharin 81-07-2 0.1-2
N- Acetyl N- Phenyl Hydrazine 114-83-0 0.005- 0.1
EDTA Tetrasodium Salt 13235-36-4 0.001-0.1
2,5 Di – Tert Butyl Hydroquinone 88-58-4 0.001-0.01
Silicon dioxide 14808-60-7 30-70

Following are the test results of the dual-cure hemming adhesive:

S. No. TEST ITEM RESULTS
Trial 01 Trial 02 Trial 03
1. Shear strength (MPa)
1.1. Initial strength (23±2 °C after 30 mins) 1.23 1.15 1.29
1.2. Strength after 4 h (23±2 °C after 4 h) 3.12 3.24 3.45
1.3. Room temperature + After heat-curing (At 160 °C for 20 mins) 10.14 10.25 10.32

TECHNICAL ADVANTAGES AND ECONOMIC SIGNIFICANCE

The dual-cure hemming adhesive for hemming applications in BIW manufacture and configured in accordance with the present invention offers the following advantages:

• Provides partial strength to the BIW or part thereof before the heat-curing process in paint shop.

• Prevent the panel deformation at the areas with minimum overlap.

• Gives a good partial strength due to anaerobic curing thereof.

• Offers the dual advantage of anaerobic curing and heat curing.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments.

It is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation. The exemplary embodiments described in this specification are intended merely to provide an understanding of various manners in which this embodiment may be used and to further enable the skilled person in the relevant art to practice this invention.

Although, the embodiments presented in this disclosure have been described in terms of its preferred embodiments, the skilled person in the art would readily recognize that these embodiments can be applied with modifications possible within the spirit and scope of the present invention as described in this specification by making innumerable changes, variations, modifications, alterations and/or integrations in terms of materials and method used to configure, manufacture and assemble various constituents, components, subassemblies and assemblies, in terms of their size, shapes, orientations and interrelationships without departing from the scope and spirit of the present invention.

The numerical values given of various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher or lower than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the disclosure unless there is a statement in the specification to the contrary.

Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising”, shall be understood to imply including a described element, integer or method step, or group of elements, integers or method steps, however, does not imply excluding any other element, integer or step, or group of elements, integers or method steps.

The use of the expression “a”, “at least” or “at least one” shall imply using one or more elements or ingredients or quantities, as used in the embodiment of the disclosure in order to achieve one or more of the intended objects or results of the present invention.

The description of the exemplary embodiments is intended to be read in conjunction with the accompanying drawings, which are to be considered part of the entire written description. In the description, relative terms such as “lower”, “upper”, “horizontal”, “vertical”, “above”, “below”, “up”, “down”, “top”, and “bottom” as well as derivatives thereof (e.g. “horizontally”, “inwardly”, “outwardly”; “downwardly”, “upwardly” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the corresponding apparatus or device be constructed or operated in a particular orientation.

Terms concerning attachments, coupling and the like, such as “connected” and “interconnected”, refer to a relationship, wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. , Claims:We claim:

1. A dual-cure hemming adhesive formulation for hemming applications in BIW manufacture, said hemming adhesive formulation comprises:

• 30-50 parts by weight (PBW) of Urethane acrylate;

• 5-25 parts by weight (PBW) of Glycidyl Methacrylate (GMA);

• 0.1-1.5 parts by weight (PBW) of Cumene Hydroperoxide;

• 0.1-2.0 parts by weight (PBW) of Saccharin;

• 0.005-0.1 parts by weight (PBW) N- Acetyl N- Phenyl Hydrazine;

• 0.001-0.1 parts by weight (PBW) of Ethylenediaminetetraacetic acid (EDTA) Tetrasodium salt;

• 0.001-0.01 parts by weight (PBW) of 2,5 Di-Tert Butyl Hydroquinone; and

• 30-70 parts by weight (PBW) of Silicon dioxide;

wherein at room temperature, the initial anaerobic curing of the hemmed joint formed between an outer panel and inner panel of the BIW or parts thereof after applying said formulation therebetween increases the shear strength of said hemmed joint in a range of 2.5 to 3 times to impart the handling strength at the zones with the minimum overlap, and the subsequent heat-curing in an oven further increases the shear strength of said initially cured hemmed joint in a range of 3 to 3.25 times to impart sufficient bond strength thereto.

2. A method of application of a dual-cure hemming adhesive formulation as claimed in claim 1, said method comprising the steps of:

(iv) applying a hemming adhesive formulation (34) between an inner panel (10) and outer panel (20) for forming a metal sheet hemmed-joint;
(v) using a first stage of robotic clinching process conducted by rollers; and

(vi) using a second stage of robotic clinching process conducted by rollers;

wherein said dual-care hemming adhesive (34) prevents any panel deformation on joining together said inner and outer sheet metal panels (10, 20) without any externally visible joint.

3. The method as claimed in claim 2, wherein said method is conducted on the BIW or parts thereof and comprises the steps of:

(a) initial anaerobic curing at room temperature at the zones with the minimum overlap of the hemmed joints of said BIW or parts thereof, to impart the handling strength thereto during the subsequent Partial Treatment Cathode Electro Deposition (PTCED) process of said BIW or parts thereof;

(b) conducting Partial Treatment Cathode Electro Deposition (PTCED) process on said BIW or parts thereof to provide sufficient bond strength thereto; and

(c) final heat-curing at substantially elevated temperature, of said BIW or parts thereof.

4. The method as claimed in claim 3, wherein said anaerobic curing of said BIW or parts thereof is carried out at a room temperature in the range of 23±20C for about 4 hours.

5. The method as claimed in claim 3, wherein said final heat-curing of said BIW or parts thereof is done in an oven at 1600C for about 20 minutes after completion of the Partial Treatment Cathode Electro Deposition (PTCED) process conducted thereon.
6. The method as claimed in claim 3, wherein the corner areas of said hemmed joint are anaerobically cured by said dual-cure hemming formulation (34).

7. The method as claimed in claim 5, wherein said final heat-curing of the remaining portions of the hemmed flanges is done by said dual-cure hemming formulation (34) to achieve the final strength of said BIW or parts thereof.

8. The method as claimed in claim 6, wherein said anaerobically cured hemmed joint has a shear strength increased over said initially cured hemmed joint in a range of 2.5 to 3 times.

9. The method as claimed in claim 7, wherein said final heat-cured hemmed joint has a shear strength increased over said initially cured hemmed joint, in a range of 3 to 3.25 times to impart sufficient bond strength thereto.

10. The method as claimed in claim 3, wherein said method of application of the dual-cure hemming adhesive formulation (34) is conducted on automotive components such as doors, hoods and tailgates or the like.

Dated this 24th day of March 2023.

Digitally / e-Signed by:

(SANJAY KESHARWANI)
APPLICANT’S PATENT AGENT
REGN. NO. IN/PA-2043.