WO2019008470A1

WO2019008470A1 - Method laminating thin glass with pressing plate

Info

Publication number: WO2019008470A1
Application number: PCT/IB2018/054722
Authority: WO
Inventors: Mario Arturo MANNHEIM ASTETE; Mauricio Fernando CORNEJO POL; Charles Stephan VOELTZEL; Juan Pablo Suarez
Original assignee: Agp America S.A.
Priority date: 2017-07-02
Filing date: 2018-06-26
Publication date: 2019-01-10
Also published as: DE112018003395T5; CO2017009265A1

Abstract

Thin glass is finding increasing application in laminates. However, conventional processing methods have short coming when applied to very thin glass. This invention provides for an improved method of laminating thin glass. A male full surface pressing plate, comprising a bent sheet of glass, is used in the lamination process to prevent wrinkles and other defects. The pressing plate is formed by conventional glass bending methods.

Description

METHOD LAMINATING THIN GLASS WITH PRESSING PLATE

Field of Invention

This invention relates to the field of the lamination process for glazings comprising thin glass layers.

Background

In response to the regulatory requirements for increased automotive fuel efficiency as well as the growing public awareness and demand for environmentally friendly products, automotive original equipment manufacturers, around the world, have been working to improve the efficiency of their vehicles.

One of the key elements of the strategy to improve efficiency has been the concept of light weighting. Often times, more traditional, less expensive, conventional materials and processes are being replaced by innovative new materials and processes which while sometime being more expensive, still have higher utility than the materials and processes being replaced due to their lower weight and the corresponding increase in fuel efficiency. Vehicle glazing has been no exception. For many years, the standard automotive windshield had a thickness of 5.4 mm. In more recent years, we have seen the typical thickness decrease to 4.75 mm. Today, windshields with a 2.1 mm outer ply, a 1.6 mm inner ply and a 0.76 mm plastic interlay er, totaling just under 4.5 mm in total thickness, are becoming common. This is at or very near the limits of how thin an annealed soda- lime glass windshield can be while still retaining safety and durability.

Annealed glass is glass that has been slowly cooled from the bending temperature through the glass transition range to relieve any stress in the glass. In a laminate, two sheets of annealed glass are bonded together using a sheet of thermo plastic. If the laminated glass should break, the plastic layer holds the shards of glass together, helping to maintain the structural integrity of the glass. The shards of broken glass are held together much like the pieces of a jigsaw puzzle. A vehicle with a broken windshield can still be operated. On impact, the plastic layer also helps to prevent penetration by the occupant or by objects striking the laminate from the exterior.

Heat strengthened glass, with a compressive strength in the range of 70 Mpa, can be used in all vehicle positions other than the windshield. Heat strengthened (tempered) glass has a layer of high compression on the outside surfaces of the glass, balanced by tension on the inside of the glass. When tempered glass breaks, the tension and compression are no longer in balance and the glass breaks into small beads with dull edges. Tempered glass is much stronger than annealed laminated glass. The minimum thickness limits of the typical automotive heat strengthening process are in the 3.2mm to 3.6 mm range. This is due to the rapid heat transfer that is required. It is not possible to achieve the high surface compression needed for a full temper with thinner glass using the typical low-pressure air quenching systems.

Glass can also be chemically tempered. In this process, ions in and near the outside surface of the glass are exchanged with ions that are larger. This places the outer layer of glass in compression. The maximum strength of chemically tempered soda lime glass is limited. However, with some other glass compositions, compressive strengths in excess of 700 Mpa are possible. The practice of chemically tempering glass is well known to those of ordinary skill in the art and shall not be detailed here.

Unlike heat tempered glass, chemically tempered glass breaks into shards rather than beads. This property allows for its use in windshields. However, in standard windshield thicknesses chemically strengthened glass would actually be too strong. In the event of a crash and a head impact, the windshield must break, absorbing the energy of the impact rather than the head of the occupant. Therefore, depending upon the tempered strength, thicknesses of 1.6 mm or less must typically be used.

Lamination of thin glass layers presents some problems that are unique in thin glass. Due to the high strength of the chemically tempered thin glass sheets, it can be difficult to get the glass to conform to and bond to the other glass layers in the laminate if there is even a small mismatch between the surfaces. This is even more of a problem when it has the cold bending process of the flat or partially bent thin glass layers as a previous step.

Cold bending is a relatively new technology. As the name suggest, the glass is bent, while cold to its final shape, without the use of heat. On parts with minimal curvature a flat sheet of glass can be bent cold to the contour of the part. This is possible because as the thickness of glass decreases, the sheets become increasingly more flexible and can be bent without inducing stress levels high enough to significantly increase the long-term probability of breakage. Thin sheets of annealed soda-lime glass, in thicknesses of about 1 mm, can be bent to large radii cylindrical shapes (greater than 6 m). When the glass is chemically or heat strengthened the glass is able to endure much higher levels of stress and can be bent along both major axis. The process is primarily used to bend chemically tempered thin glass sheets (<=1 mm) to shape.

The glass to be cold bent is placed with a bent glass layer and with a plastic bonding layer placed between the glass to be cold bent and the bent glass layer. The assembly is placed in what is known as a vacuum bag. The vacuum bag is an airtight set of plastic sheets, enclosing the assembly and bonded together it the edges, which allows for the air to be evacuated from the assembly and which also applies pressure on the assembly forcing the layers into contact. The assembly, in the evacuated vacuum bag, is then heated to seal the assembly. The assembly is next placed into an autoclave which heats the assembly and applies high pressure. This completes the cold bending process as the flat glass at this point has conformed to the shape of the bent layer and is permanently affixed. The cold bending process is very similar to a standard vacuum bag/autoclave process, well known in the art, with the exception of having an unbent glass layer added to the stack of glass.

The problem to have a cold bending process as a pre-lamination is that this process, further due to the thin glass layer, causes waves in the edges of the bent assembly resulting in distortion and also modifying the esthetic. Similarly, in the standard lamination process occurs some mismatch problems that can lead to delamination, trapped air, distortion and wrinkles.

As can be appreciated, a better process would be beneficial. Brief Description of the invention.

It is object of the invention to provide a method of laminating thin glass using a pressing plate. Likewise, is an object of the invention to provide a laminate fabricated by the method previously mentioned.

The pressing plate comprise a sheet of glass formed by means of conventional glass bending tooling and processes. Any convenient suitable process, that can achieve the correct shape can be used. These include but are not limited to gravity bending using a ring type or full surface mold, partial or full surface pressing. Depending upon the process, the same tooling and process used to produce the final laminated glazing may be used to also produce the pressing plate. The pressing plate may be thermally or chemically tempered or annealed. Any glass composition may be used. The method for laminating a glazing having at least two glass layers, being one of them a thin glass inner layer, and at least one plastic bonding interlayer, comprises the step of providing a pressing plate. The pressing plate comprises a bent sheet of glass. One of the major faces of the pressing plate is placed in contact with the corresponding major face of the thin glass inner layer. Then, the assembled laminate is enclosed, and the air is evacuated from the enclosure. Heat and pressure are applied to the assembly in a standard lamination process. In case of having a cold bending as a previous step of lamination, the method using the pressing plate would help to force the contact between the layers preventing the appearance of wrinkles or waves in the edges. In the lamination process, the method using a pressing plate provides an improvement of quality and yields in the lamination.

This method of this invention has a number of advantages.

• Prevents thin glass wrinkles during lamination.

• Provides an efficient means of laminating thin glass.

• Improves lamination quality and yields. Brief Description of the Several Views of the Drawings

Figure 1 shows the typical laminate cross section.

Figure 2A shows the exploded view: Laminate with cold bent thin glass layer.

Figure 2B shows the exploded view: Laminate with thermally bent thin glass layer.

Reference Numerals of Drawings

2 Glass

4 Thin glass

6 Plastic interlayer

10 Pressing Plate

101 Surface one

102 Surface two

103 Surface three

104 Surface four

201 Vehicle exterior layer

202 Vehicle interior layer

Detailed Description of the Invention

In the drawings and discussion, the following terminology is used to describe the configuration of a laminated glazing. A typical automotive laminate, shown in Figure 1, is comprised of two layers of glass, the exterior or outer 201 and interior or inner 202 that are permanently bonded together by a plastic layer 6 (interlayer). The glass surface that is on the exterior of the vehicle is referred to as surface one 101 or the number one surface. The opposite face of the exterior glass layer 201 is surface two 102 or the number two surface. The glass 2 surface that is on the interior of the vehicle is referred to as surface four 104 or the number four surface. The opposite face of the interior layer of glass 202 is surface three 103 or the number three surface. Surfaces two 102 and three 103 are bonded together by the plastic layer 6. While a vacuum bag process is used in the discussion and the preferred embodiments, other methods such as a vacuum ring and other means may be used and are considered as equivalent and do not deviate from the intend of the invention. In the same manner, the pressing plate may be formed by press bending, ring type mold gravity bending or by any other means that had the capability to produce the desired shape.

Embodiments

1.) In first embodiment, as shown in Figure 2A, thin glass 4 is chemically tempered. 2.1 mm soda-lime glass 2 is press bent to shape separately. A laminate is prepared comprising the

2.1 mm bent soda-lime glass 2 outer layer and with an 0.7 mm thin aluminosilicate glass inner layer. A layer of 0.76 mm transparent polyvinyl butyl (PVB) thermo plastic 6 is placed between the two glass layers. The bent pressing plate 10, covered with a layer of fine mesh fiberglass cloth to prevent scratching, is placed in contact with the surface four of the 0.7 thin glass 4 inner layer. The assembled laminate and pressing plate 10 are placed in a plastic "bag", the bag is sealed and a vacuum is drawn. This bag is then processed through a standard autoclave process where heat and pressure are applied. Upon completion of the lamination processed, the pressing plate 10 can be reused. 2.) In a second embodiment, as shown in Figure 2 A, thin glass 4 is chemically tempered. 2.1 mm soda-lime glass 2 is press bent to shape separately. A laminate is prepared comprising the 2.1 mm bent soda-lime glass 2 outer layer and with the 0.4 mm aluminosilicate inner layer. A layer of 0.76 mm transparent polyvinyl butyl (PVB) thermo plastic is placed between the two glass layers. The pressing plate 10, covered with a layer of fine mesh fiberglass cloth to prevent scratching, is placed in contact with the surface four of the thin glass 4 inner layer. The assembled laminate and pressing plate 10 are placed in a plastic "bag", the bag is sealed and a vacuum is drawn. This bag is then processed through a standard autoclave process where heat and pressure are applied. Upon completion of the lamination process, the pressing plate 10 can be reused. 3. ) In a third embodiment, as shown in Figure 2A, thin glass 4 is chemically tempered. 2.1 mm soda-lime glass 2 is press bent to shape separately. A laminate is prepared comprising the 2.1 mm bent soda-lime glass 2 outer layer and with the 1.2 mm aluminosilicate inner layer. A layer of 0.76 mm transparent polyvinyl butyl (PVB) thermo plastic is placed between the two glass layers. The pressing plate 10, covered with a layer of fine mesh fiberglass cloth to prevent scratching, is placed in contact with the surface four of the 0.7 thin glass 4 inner layer. The assembled laminate and pressing plate 10 are placed in a plastic "bag", the bag is sealed and a vacuum is drawn. This bag is then processed through a standard autoclave process where heat and pressure are applied. Upon completion of the lamination process, the pressing plate 10 can be reused.

4. ) In a forth embodiment, as shown in Figure 2B, a sheet of 0.4 mm aluminosilicate glass is cut to size and then chemically tempered while flat. A laminate is prepared comprising a 1.2 mm bent aluminosilicate 2 outer layer with an 0.4 mm aluminosilicate inner layer. A layer of 0.76 mm transparent polyvinyl butyl (PVB) thermo plastic is placed between the two glass layers. The bent pressing plate 10, covered with a layer of fine mesh fiberglass cloth to prevent scratching, is placed in contact with the surface four of the 0.4 thin glass 4 inner layer. The assembled laminate and pressing plate 10 are placed in a plastic "bag", the bag is sealed and a vacuum is drawn. This bag is then processed through a standard autoclave process where heat and pressure are applied. The pressure and vacuum bend the flat glass to the desired bent shape. Upon completion of the lamination process, the pressing plate 10 can be reused.

The forms of the invention shown and described in this specification represent illustrative preferred embodiments and it is understood that various changes may be made without departing from the spirit of the invention as defined in the following claimed subject matter.

Claims

1. A method for laminating a glazing having at least two glass layers, being one of them a thin glass inner layer, and at least one plastic bonding interlayer between said at least two glass layers, the method comprising the step of:

providing a pressing plate comprising a bent sheet of glass;

assembling said at least two glass layers and said at least one plastic bonding interlayers to conform the final laminate;

placing the pressing plate such that one of the pressing plate major faces is in contact with the corresponding major face of the thin glass inner layer;

enclosing assembled laminate and evacuating the air from the enclosure;

applying heat and pressure to the assembly in a standard lamination process.

2. The method of claim 1, wherein the pressing plate is produced by thermal bending of the glass.

3. The method of claim 1 , wherein the size of the pressing plate is slightly larger than the glass to be laminated.

4. The method of claim 1 , wherein the pressing plate is chemically strengthened.

5. The pressing plate of claim 1, wherein the pressing plate is thermally strengthened.

6. The pressing plate of claim 1, wherein the pressing plate is not part of the final laminate.

7. The method of claim 1 , wherein the thin glass inner layer is flat.

8. The method of claim 1, wherein the thin glass inner layer is partially bent.

9. The method of claim 1 , wherein the thin glass inner layer is cold bent to the desired shape.

10. A laminated glazing produced by the method of claim 1.

11. A vehicle comprising the laminated glazing of claim 10.