U.S. patent application number 09/962750 was filed with the patent office on 2002-05-23 for intrusion resistant glass laminates.
This patent application is currently assigned to Solutia, Inc.. Invention is credited to Lu, Jun, Moran, James R..
Application Number | 20020061395 09/962750 |
Document ID | / |
Family ID | 22888066 |
Filed Date | 2002-05-23 |
United States Patent
Application |
20020061395 |
Kind Code |
A1 |
Moran, James R. ; et
al. |
May 23, 2002 |
Intrusion resistant glass laminates
Abstract
Composite laminate interlayers for adhering a glass laminate
comprising two sheets of polyethylene terephthalate (PET) between
layers of plasticized polyvinyl butyral (PVB) adhesive layers,
wherein the two PET layers provide increased stiffness for the
laminate without sacrificing the optical clarity of the
laminate.
Inventors: |
Moran, James R.;
(Longmeadow, MA) ; Lu, Jun; (East Longmeadow,
MA) |
Correspondence
Address: |
Patricia A. Kammerer
HOWREY SIMON ARNOLD & WHITE, LLP
750 Bering Drive
Houston
TX
77057
US
|
Assignee: |
Solutia, Inc.
|
Family ID: |
22888066 |
Appl. No.: |
09/962750 |
Filed: |
September 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60236082 |
Sep 28, 2000 |
|
|
|
Current U.S.
Class: |
428/215 ;
428/437; 428/480; 428/483 |
Current CPC
Class: |
Y10T 428/266 20150115;
Y10T 428/31786 20150401; Y10T 428/269 20150115; Y10T 428/24942
20150115; Y10T 428/3163 20150401; Y10S 428/91 20130101; Y10T
428/24967 20150115; Y10T 428/26 20150115; B32B 17/10761 20130101;
Y10T 428/2495 20150115; Y10T 428/31797 20150401; B32B 17/10743
20130101; B32B 27/36 20130101; Y10T 428/31616 20150401; B32B
17/10036 20130101; B32B 17/10005 20210101; B32B 2367/00
20130101 |
Class at
Publication: |
428/215 ;
428/437; 428/480; 428/483 |
International
Class: |
B32B 007/02; B32B
017/10; B32B 027/36 |
Claims
I claim:
1. A composite laminate interlayer for a glass laminate comprising:
two or more sheets of bonded optical-grade polyethylene
terephthalate between two layers of plasticized polyvinyl
butyral.
2. The interlayer of claim 1 wherein the thickness of each
polyethylene terephthalate layer is between about 0.025 mm (1 mil)
and about 0.175 mm (7 mil) and the thickness of each plasticized
polyvinyl butyral layer is between about 0.125 mm (5 mil) and about
2 mm (80 mil).
3. The interlayer of claim 2 wherein each polyethylene
terephthalate layer has a different thickness.
4. The interlayer of claim 2 wherein each polyethylene
terephthalate layer has about the same thickness.
5. The interlayer of claim 2 wherein the thickness of each
polyethylene terephthalate layer is about 0.175 mm (7 mil).
6. The interlayer of claim 2 wherein the thickness of each
plasticized polyvinyl butyral layer is between about 0.375 mm (15
mil) and about 1.5 mm (60 mil).
7. The interlayer of claim 6 wherein the thickness of each
plasticized polyvinyl butyral layer is about 0.76 mm (30.4
mil).
8. The interlayer of claim 1 wherein the each layer of polyethylene
terephthalate has a haze of less than about 1%.
9. The interlayer of claim 2 further comprising an additional
functional layer.
10. The interlayer of claim 9 wherein the functional layer is a
sound attenuating elastomer layer or a radiation blocking
layer.
11. The interlayer of claim 1, wherein the two or more sheets of
bonded optical-grade polyethylene terephthalate are bonded with a
pressure sensitive acrylic resin.
12. The interlayer of claim 1, wherein the two or more sheets of
bonded optical-grade polyethylene terephthalate are bonded with a
layer of plasticized polyvinyl butyral.
13. The interlayer of claim 1, wherein at least one layer of
plasticized polyvinyl butyral has a Tg of at least 35.degree.
C.
14. A composite laminate interlayer for a glass laminate consisting
essentially of two sheets of bonded optical-grade polyethylene
terephthalate between layers of plasticized polyvinyl butyral.
15. The interlayer of claim 14 wherein the thickness of each
polyethylene terephthalate layer is between about 0.025 mm (1 mil)
and about 0.175 mm (7 mil) and the thickness of each plasticized
polyvinyl butyral layer is between about 0.125 mm (4 mil) and about
2 mm (80 mil).
16. The interlayer of claim 14, wherein the two sheets of bonded
optical-grade polyethylene terephthalate are bonded with a pressure
sensitive acrylic resin.
17. The interlayer of claim 14, wherein the two sheets of bonded
optical-grade polyethylene terephthalate are bonded with a layer of
plasticized polyvinyl butyral.
18. The interlayer of claim 14, wherein at least one layer of
plasticized polyvinyl butyral has a Tg of at least 35.degree.
C.
19. A glass laminate comprising in order: a) a first glass sheet,
b) a first layer of plasticized polyvinyl butyral, c) a first layer
of optical grade polyethylene terephthalate, d) a second layer of
optical grade polyethylene terephthalate, e) a second layer of
plasticized polyvinyl butyral, and f) a second glass sheet.
20. The glass laminate of claim 19 wherein the thickness of the
first and second glass sheets is between about 1 mm and about 10
mm, the thickness of each polyethylene terephthalate layer is
between about 0.025 mm (1 mil) and about 0.175 mm (7 mil), and the
thickness of each plasticized polyvinyl butyral layer is between
about 0.1 mm (4 mil) and about 2 mm (80 mil).
21. The glass laminate of claim 20 wherein the thickness of the
first and second glass sheets is between about 1 mm and about 10
mm, the thickness of each polyethylene terephthalate layer is about
0.175 mm (7 mil), and the thickness of each plasticized polyvinyl
butyral layer is between about 0.375 mm (15 mil) and about 1.5 mm
(60 mil).
22. The glass laminate of claim 19 wherein each layer of
polyethylene terephthalate has a haze of less than 1%.
23. The glass laminate of claim 19 further comprising an additional
functional layer.
24. The glass laminate of claim 23 wherein the functional layer is
a sound attenuating elastomer layer or a radiation blocking
layer.
25. The glass laminate of claim 19, wherein the first layer of
optical grade polyethylene terephthalate is bonded to the second
layer of optical grade polyethylene terephthalate.
26. The glass laminate of claim 25, wherein the first layer of
optical grade polyethylene terephthalate is bonded to the second
layer of optical grade polyethylene terephthalate with a pressure
sensitive acrylic resin.
27. The glass laminate of claim 25, wherein the first layer of
optical grade polyethylene terephthalate is bonded to the second
layer of optical grade polyethylene terephthalate with a layer of
plasticized polyvinyl butyral.
28. The glass laminate of claim 19, wherein at least one layer of
plasticized polyvinyl butyral has a Tg of at least 35.degree.
C.
29. A glass laminate consisting essentially of in order: a) a first
glass sheet, b) a first layer of plasticized polyvinyl butyral, c)
a first layer of optical grade polyethylene terephthalate bonded to
a second layer of optical grade polyethylene terephthalate, d) a
second layer of plasticized polyvinyl butyral, and e) a second
glass sheet, wherein at least one layer of plasticized polyvinyl
butyral has a Tg of at least 35.degree. C.
30. The glass laminate of claim 29 wherein the thickness of the
first and second glass sheets is between about 1 mm and about 20
mm, the thickness of each polyethylene terephthalate layer is
between about 0.025 mm (1 mil) and about 0.175 mm (7 mil), and the
thickness of each plasticized polyvinyl butyral layer is between
about 0.1 mm (4 mil) and about 2 mm (80 mil).
31. The glass laminate of claim 30 wherein the thickness of the
first and second glass sheets is between about 1 mm and about 10
mm, the thickness of each polyethylene terephthalate layer is about
0.175 mm (7 mil), and the thickness of each plasticized polyvinyl
butyral layer is between about 0.375 mm (16 mil) and about 1.5 mm
(60 mil).
32. The glass laminate of claim 29 wherein each layer of
polyethylene terephthalate has a haze of less than 1%.
33. The glass laminate of claim 29, wherein the first layer of
optical grade polyethylene terephthalate is bonded to the second
layer of optical grade polyethylene terephthalate with a pressure
sensitive acrylic resin.
34. The glass laminate of claim 29, wherein the first layer of
optical grade polyethylene terephthalate is bonded to the second
layer of optical grade polyethylene terephthalate with a layer of
plasticized polyvinyl butyral.
Description
BACKGROUND
[0001] It is known to use an energy absorbing interlayer of
plasticized polyvinyl butyral (PVB) with one or more rigid layers
such as glass in a safety glazing. Such a glazing is usually
prepared by interposing the PVB layer between glass sheets while
eliminating air from between the engaging surfaces and then
subjecting the assembly to elevated temperature and pressure in an
autoclave to fusion bond the PVB and glass and form an optically
clear structure. These glazings are used in windows such as the
front, side and rear windows in motor vehicles, particularly
windshields, where the interlayer can absorb a blow from the head
of an occupant without penetration of the windshield.
[0002] Automobile and homeowners, especially those who have
experienced a vehicle break-in, theft or hurricane damage, are
increasingly interested in intrusion resistant glazings. Glass has
been identified as the weak link in the overall intrusion
resistance of vehicles and buildings. For instance, some police
reports estimate that broken glass is the entry route for at least
60% of unauthorized entry into passenger vehicles. There is also a
belief that a 30-second delay in entry is sufficient to discourage
many spontaneous thieves because the increased break-in time and
additional noise call attention to the thief. In response,
carmakers, at least, are replacing traditional tempered glass with
laminated glass for enhanced security. Common automotive laminated
glass, though, can be defeated by determined thieves who use more
sophisticated tools to puncture by impact and pull laminated glass
out from its frame.
[0003] Many attempts to improve the performance of glass laminates
have been made, including modifying the stiffness and/or impact
resistance of the PVB interlayer. For example, U.S. Pat. No.
4,814,529, to Cartier et al., discloses lightly cross-linking PVB
resin to selectively increase molecular weight of the PVB and the
modulus of a plasticized sheet formed therefrom for use in
laminated safety glass assemblies. U.S. Pat. No. 5,246,764, to
LaPorte et al., discloses laminated glazing with improved impact
strength where mean break height for a dropped mass of a glass
laminate increased by dispersing adhesion resistant means on the
surface of PVB sheet. U.S. Pat. No. 5,482,767, to Karagiannis et
al., discloses glass laminates of improved impact resistance
comprising a PVB interlayer having discrete particles of
crosslinked polyvinyl butyral integrally randomly dispersed
throughout a matrix of PVB.
[0004] In recent years additional sophisticated features are
appearing in such windows to enhance performance. These include
special, layered metal/dielectric stacks for solar radiation
control which may also be electrically conductive for defrosting,
defogging, etc; holographic layers as solar reflecting mirrors and
in head-up displays to facilitate viewing instruments on the
vehicle dashboard while looking straight ahead; photochromic and
electrochromic layers which controllably change color and/or
visible transmission upon exposure to solar radiation or
application of a voltage; layered protective antilacerative
structures on the inboard side of a conventional three layer
glass/PVB sheet/glass laminate to minimize lacerations from sharp
edges of broken glass; special plastic layers in bilayer structures
replacing one glass layer of such a three layer glass laminate, and
similar, functional performance-enhancing layers and coatings.
These performance layers are usually deposited on or adhered to a
carrier layer which is different from the low modulus, elastomeric
PVB which is unsuitable as a carrier. For use in safety glazings a
carrier layer should have good clarity, be relatively uniform in
thickness and strong having high modulus to facilitate ease of
handling and processing during association with the performance
layer(s). Frequently biaxially oriented polyethylene terephthalate
is used as noted, for example, in U.S. Pat. No. 4,465,736.
[0005] Using PET in glass laminates offers many advantages. As U.S.
Pat. No. 5,024,895, to Kavanagh et al., and U.S. Pat. No.
5,091,258, to Moran, disclose, PET can be biaxially stretched to
improve strength and can be heat stabilized to provide low
shrinkage characteristics when subjected to elevated temperatures.
The tensile modulus, a desired property of glass laminate
interlayers and an indication of the stiffness of the interlayer,
at 21.degree. C.-25.degree. C. of PET is about 10.sup.10 Pa as
compared with about 10.sup.7 Pa for PVB of the type used in safety
glazings. This increased stiffness of PET is a desirable property
for use in glass laminates.
[0006] Many applications of PET involve a layer of PET being used
as a carrier for the aforementioned functional layers, such as
solar radiation blockers, antennas or heat strips. U.S. Pat. No.
5,979,932, to Jourdaine et al., U.S. Pat. No. 5,091,258, to Moran,
and U.S. Pat. No. 5,932,329, to Frost et al., disclose a PET layer
between two PVB layers wherein the PET layer is provided with an
infrared-reflective coating. U.S. Pat. No. 4,017,661, to Gillery,
discloses a composite interlayer wherein a PET sheet is coated with
an optically clear, electrically conductive, transparent coating
used as a carrier for metal layers which can be electrically heated
for defrosting the glass laminate. U.S. Pat. No. 5,024,895, to
Kavanagh et al., discloses a PET layer between two PVB layers that
includes an integrated infrared-reflective and an electrically
conductive coating.
[0007] Although most prior art laminates generally provide
acceptable resistance to shattering when struck with a blunt
object, there is often unacceptable resistance to penetration and
pullout. For example, in the case of automobile break-ins, prior
art glass laminates often will not shatter, but will break. After
being broken, though, the prior art glass laminates usually are
significantly weakened and are thus susceptible to being pulled out
of their frames. This lack of stiffness in prior art glass
laminates can effectively offset the otherwise acceptable
shatter-resistant nature of the glass laminates, particularly in
automotive break-in situations. Many prior art glass laminates do
not exhibit acceptable strength properties after being broken.
[0008] Furthermore, although simply increasing the PVB thickness
can improve resistance to penetration, this solution does not
alleviate the poor resistance to pullout problem. Increased
thickness laminates can also be limited by optical clarity. It is
of utmost importance that glass laminates used for automotive
safety glazings exhibit a high degree of optical clarity; that is,
exhibit high level of visible transmission and low levels of
optical haze or light scattering. Prior art laminates do not
provide a means to achieve a significant increase in laminate
stiffness without compromising optical clarity.
[0009] It would thus be desirable to develop a glass laminate that
exhibited superior penetration resistant qualities, as well as an
increased stiffness so as to improve the glass laminate's resistant
to pullout after the glass is broken, for example, for use in
security glazing applications such as architectural and automotive
glazing. Furthermore, it would be desirable to improve the
stiffness of a laminate without sacrificing its optical
clarity.
SUMMARY OF THE INVENTION
[0010] This invention provides a composite laminate interlayer for
use in manufacturing intrusion resistant glass laminates having a
higher laminate stiffness. Such laminates of the present invention
comprise an interlayer having two outside layers of PVB, and two
inside layers of bonded optical grade PET. To increase the
stiffness in the laminate, it has been found that using two pieces
of optical grade PET improves the stiffness of the laminate but
does not significantly reduce the optical clarity of the laminate.
This contrasts common practice which recognizes that as the
thickness of a single layer of PET increases, its optical clarity
is reduced. Optical grade PET with haze levels less than
.about.1.0% is limited to about 0.175 mm (7 mil) or less. Combining
two pieces of optical grade PET, for example two 7-mil pieces,
improves the laminate's resistance to breaking and pullout/push-in
as a single layer of PET of the same combined thickness would,
without significantly sacrificing the optical clarity of the
laminate.
[0011] Another aspect of this invention provides a composite
laminate interlayer comprising two layers of PET between layers of
plasticized PVB adhesive where at least one of the PVB layers
exhibits enhanced stiffness. In one aspect of the invention, high
stiffness in plasticized PVB is provided by reducing the level of
plasticizer in the PVB. This is indicated by a rise in glass
transition temperature (Tg) of the plasticized PVB, e.g. about 2 to
3.degree. C. above typical values for a commercial application. For
instance, for automotive applications, where plasticized PVB sheet
typically has a Tg of about 30-33.degree. C., high stiffness PVB of
this invention will have a Tg of at least 35.degree. C.
[0012] Another aspect of this invention provides interlayer
composites with other functional layers, e.g. sound dampening
elastomer layers or radiation blocking layers.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0013] As used herein glass transition temperature (Tg) of
plasticized PVB is determined by rheometric dynamic analysis using
the following procedure. Plasticized PVB sheet is molded into a
sample disc of 25 millimeters (mm) in diameter. The PVB sample disc
is placed between two 25-mm diameter parallel plate test fixtures
of a Rheometrics Dynamic Spectrometer II. The PVB sample disc is
tested in shear mode at an oscillation frequency of 1 Hertz as the
temperature of the PVB sample is increased from -20 to 70.degree.
C. at a rate of 2.degree. C./minute. Experience indicates that the
method is reproducible to within +/-1.degree. C. Commercially used
PVB typically has a Tg in the range of 30-33.degree. C.
[0014] Visual haze for both the PET film components and the glass
laminate are measured according to ASTM D1003 using Illuminant C
and an observer angle of 2.degree..
[0015] As used herein, the units of "mils, "mm" and "inch" will be
used in describing the thickness of a glass laminate interlayer.
The relationship of these units is illustrated as such: 0.25 mm is
roughly equivalent to 10 mils and 0.01 inch.
[0016] The preferred embodiment of the present invention is a glass
laminate in which two bonded PET sheets are placed between two
standard sheets of PVB. It has been found that increasing the
thickness of the PET layer greatly enhances the stiffness of the
glass laminate, thus improving the strength of the glass laminate
after breaking. Optical quality of PET film, particularly visual
haze, though, is a problem above thicknesses of about 7 mil,
whereas PET of about 7 mil or less exhibits acceptable haze of 1%
or less. For example, typical haze levels for 10 mil Mylar film
produced by E. I. du Pont de Nemours is 2% and above that thickness
the haze levels are much higher. The high haze of the PET layers
greater than about 7 mil prohibits the use of these thick layers in
combination with PVB for use as automotive glazings, where optical
clarity is essential.
[0017] A key advantage of the present invention involves the
inherent nature of layers of PET over 10 mils having unacceptable
haze characteristics. It has been found that using two layers of
PET with acceptable haze characteristics (less than about 1% haze)
in combination have the desired and required optical clarity for
use in glass laminates. Thus, for instance, providing two 7 mil
layers of PET for a total PET layer thickness of 14 mil gives the
laminate improved stiffness qualities, without significantly
diminishing the optical clarity of the laminate. Providing two
layers of PET with acceptable optical clarity between two layers of
PVB provides many advantages, including a laminate with increased
stiffness (when compared to a conventional laminate) without
sacrificing the optical clarity of the laminate.
[0018] In the preferred embodiment, two optical grade PET sheets
are used in place of a thicker PET sheet. The most preferred
embodiment employs two PET sheets of about 7-mil thickness each
bonded together between two PVB layers. The application of the PET
in this manner significantly reduces the haze problem otherwise
associated when a single, 14 mil thick PET layer is used.
[0019] Preferably, the two PET layers are bonded with an adhesive.
A layer of plasticized PVB, polyurethane 2-component reactive cure,
pressure sensitive acrylic resins, and other known adhesives can
all be used so long as the chosen adhesive does not substantially
increase the haze of glass laminate of this invention. The chosen
adhesive used with the composite interlayer of the present
invention preferably should not substantially differ in sound
attenuating performance from that of a laminated glass made with
standard PVB. Laminated glass having high sound attenuation will
most likely have decreased intrusion resistance, which is not a
desired property of the present invention.
[0020] One preferred adhesive is a pressure sensitive acrylic
resin. This class of adhesives exhibits the preferred clarity that
is a desired component of this invention. The acrylic resin
preferably comprises polyacrylate esters of varying molecular
weights and ester functionalities. The acrylic resin may also
contain functional monomers which are used to provide a means for
crosslinking of polymer molecules to increase the creep resistance
or shear strength. The most preferred adhesive is commercially
available from Solutia, Inc. as Gelva multi-polymer solution
adhesive (GMS 263).
[0021] PVB resin is produced by known aqueous or solvent
acetalization processes reacting PVOH with butyraldehyde in the
presence of acid catalyst, followed by neutralization of the
catalyst, separation, stabilization and drying of the resin. It is
commercially available from Solutia, Inc. as Butvar.RTM. resin. PVB
resin typically has a weight average molecular weight greater than
70,000, preferably about 100,000 to 250,000, as measured by size
exclusion chromatography using low angle laser light scattering. On
a weight basis PVB typically comprises less than 22%, preferably
about 17 to 19% hydroxyl groups calculated as polyvinyl alcohol
(PVOH); up to 10%, preferably 0 to 3% residual ester groups,
calculated as polyvinyl ester, e.g. acetate, with the balance being
acetal, preferably butyraldehyde acetal, but optionally including a
minor amount of acetal groups other than butyral, for example
2-ethyl hexanal as disclosed in U.S. Pat. No. 5,137,954.
[0022] The PVB resin of the sheet is typically plasticized with
about 20 to 80 and more commonly 25 to 45 parts plasticizer per
hundred parts of resin. Plasticizers commonly employed are esters
of a polybasic acid or a polyhydric alcohol. Suitable plasticizers
are triethylene glycol di-(2-ethylbutyrate), triethyleneglycol
di-(2-ethylhexanoate), tetraethyleneglycol diheptanoate, dihexyl
adipate, dioctyl adipate, mixtures of heptyl and nonyl adipates,
dibutyl sebacate, polymeric plasticizers such as the oil-modified
sebacic alkyds, and mixtures of phosphates and adipates such as
disclosed in U.S. Pat. No. 3,841,890 and adipates and alkyl benzyl
phthalates as disclosed in U.S. Pat. No. 4,144,217. Also mixed
adipates made from C.sub.4 to C.sub.9 alkyl alcohols and cyclo
C.sub.4 to C.sub.10 alcohols as disclosed in U.S. Pat. No.
5,013,779. C.sub.6 to C.sub.8 adipate esters such as hexyl adipate
are preferred plasticizers. A more preferred plasticizer is
triethylene glycol di-(2-ethylhexanoate).
[0023] In an alternative embodiment, the amount of plasticizer used
is a convenient means to modifying and controlling the stiffness of
the PVB. A useful surrogate property for stiffness is Tg which is
directly related to the level of plasticizer. The plasticized PVB
sheet used in the laminates of the preferred embodiment, though,
have normal Tg values of about 33.degree. C. or less. Some
embodiments of this invention can have a Tg of at least 35.degree.
C. or higher by modifying the plasticizer content of the PVB.
[0024] As disclosed in U.S. Pat. No. 5,618,863 it is also often
useful or desirable to incorporate a UV absorber in PVB. In
addition to plasticizer, optional UV absorber and adhesion control
agent, PVB sheet may contain other performance-enhancing additives
such as pigments or dyes for coloring all or part of the sheet,
antioxidants and the like. PVB sheet is prepared by mixing combined
plasticizer and other additives (e.g. UV-absorber, adhesion control
agent and the like) with PVB resin and forcing the mixture under
pressure through a die opening to form a sheet. Thickness of the
PVB sheet can range from about 0.1 to 2 mm (about 4-80 mil) thick,
typically about 0.375 to about 1.5 mm (about 15-60 mils) thick to
provide the desired performance in the glass laminate.
[0025] The PET sheets for use in the composite interlayer of this
invention are preferably biaxially stretched to improve strength
and been heat stabilized to provide low shrinkage characteristics
when subjected to elevated temperatures (i.e. less than 2%
shrinkage in both directions after 30 min. exposure at 150.degree.
C.). The tensile modulus (at 21-25.degree. C.) of polyethylene
terephthalate is about 10.sup.10 Pa as compared with about 10.sup.7
Pa for a plasticized polyvinyl butyral of the type used in safety
glazings. To facilitate bonding of PVB to PET, any known coating
and/or surface treatment may be applied to the PET. Preferably,
plasma treatment of biaxially stretched polyester to improve
adhesion as disclosed in European Patent 157030 B1, and U.S. Pat.
No. 4,732,814, incorporated herein by reference, is used. Another
method for treating the surface of PET film includes deposition of
a thin layer of carbon by vacuum sputtering as disclosed by Kittler
in U.S. Pat. No. 4,865,711 (incorporated herein by reference).
[0026] Composite interlayers according to this invention are
prepared by known procedures. See for instance, U.S. Pat. Nos.
4,973,511, 5,024,895 and 5,091,258 (incorporated herein by
reference) for methods for laminating plasticized PVB to
surface-treated PET sheet. Because final bonding conditions will be
experienced when the interlayer is bonded to glass, the degree of
bonding of PVB to PET in the composite interlayer is not critical.
If a layer of plasticized PVB in the composite interlayers of this
invention has a Tg higher than convention, a person of ordinary
skill in the art will appreciate a need to raise the processing
temperature of the PVB sheet by an amount corresponding to the
elevation in Tg. Suitable temperatures for bonding PVB to PET will
typically be in the range of 50 to 120.degree. C. The PET/PVB
composites can be pressed, e.g. in a nip roller, to improve
adhesion.
[0027] Glass laminates using sheets of the invention are prepared
by known procedures, e.g. as disclosed in U.S. Pat. Nos. 5,024,895;
5,091,258; 5,145,744; 5,189,551; 5,264,058 and 5,529,654 (all of
which are incorporated herein by reference). In one conventional
method, the composite interlayer is placed between two sheets of
glass and heated under vacuum to a temperature in the range of
about 85 to 120.degree. C. for about 10 to 30 minutes, depending on
temperature, to remove air from between the layers of the laminate
and to seal the laminate edge prior to autoclave lamination. After
de-airing and edge sealing are completed, the laminate is
preferably heated in an autoclave at elevated temperature (about 90
to 165.degree. C.) and pressure (about 1000 to 2000 kPa) for
sufficient time to firmly bond the layers of the laminate.
Non-autoclave methods as disclosed in U.S. Pat. No. 5,536,347 may
are also useful, e.g. for plasticized PVB having only moderate
increases in Tg.
[0028] A typical glass laminate of the current invention contains
glass sheets that are usually float glass, heat strengthened glass
or tempered glass typically in the range of 1 to 10 millimeters
(mm) thick, preferably in the range of 1-5 mm thick. Between and
bonded to the glass sheets is a composite interlayer comprising two
PET sheets between layers of plasticized PVB adhesive. Each PVB
sheet is preferably about 0.76 mm thick, and each PET sheet is
biaxially-oriented and can be in the range of about 0.025 to 0.25
mm thick (1 to 10 mils), preferably about 0.175 mm thick (7 mils)
thick, for a total preferred PET thickness of 0.350 mm (14 mils).
The optical clarity of each PET layer must exhibit acceptable
optical clarity characteristics, preferably below 1% haze. The PET
layers are bonded together, preferably with a pressure sensitive
acrylic resin.
[0029] For desired adhesion to the PVB, the surface of the PET is
preferably modified, such as by roughening of the surface or by
chemical modification of the material at the surface. Such
modification can be effected by flame treatment, chemical
oxidation, corona discharge, carbon sputtering, plasma treatment in
vacuum or in air or other treatments well known to those of
ordinary skill in the art.
[0030] The PVB is plasticized, most preferably with triethylene
glycol di-(2-ethylhexanoate). The plasticizer can be added,
alternatively, in an amount to provide a Tg of at least 35.degree.
C. In the laminates of this invention, the PVB layers can be
similar, e.g. both PVB layers having a Tg of at least 35.degree. C.
or, having a conventional Tg value, with the preferred embodiment
encompassing similar layers of conventional PVB. Alternatively, the
two layers can be different, e.g. one plasticized PVB layer having
a conventional Tg of about 30 to 33.degree. C. and the other PVB
layer being stiffened by having a Tg of at least 35.degree. C.
[0031] A further embodiment of the present invention is a glass
laminate containing an additional functional layer. This layer can
be, e.g., a sound attenuating elastomer layer as disclosed in U.S.
Pat. No. 5,796,055 (incorporated herein by reference) or a
radiation blocking layer, e.g. comprising a composite of one or
more layers of metal or metal oxide deposited onto either PET layer
as disclosed in any of U.S. Pat. Nos. 5,024,895, 5,091,258 or
5,932,329 (the disclosures of all four patents being incorporated
herein by reference). If a sound attenuating layer is used, it
should be added to the glass laminate of the present invention by
replacing one of the two PVB layers.
[0032] An alternative embodiment to the present invention is the
use of multiple layers of optical grade PET, limited only by the
haze characteristics of the final glass laminate. For instance,
using two 5-mil sheets and one 2-mil sheet of optical grade PET
could be used to improve the stiffness of the glass laminate
without reducing its optical clarity. It is within the scope of
this invention to use multiple thinner, optical grade PET sheets in
place of an equivalent thicker sheet of PET, the total number of
sheets used being limited only to having an acceptable optical
clarity.
[0033] The following Examples illustrate and do not limit or
restrict the invention and are illustrated using the following
materials.
EXAMPLE 1
[0034] Haze Measurements
[0035] A series of glass laminates were made to assess the effects
of the inclusion of various PET films on the optical haze. These
glass laminate structures were prepared using conventional PVB
laminating techniques in combination with two pieces of 2.3-mm
thickness clear annealed float glass and various combinations of
PET and PVB as described in the table below. The 14 mil (0.35 mm)
PET component was a composite of two layers of 7 mil (0.18 mm)
films bonded together with the Gelva 263 acrylic pressure sensitive
adhesive. Haze measurements were made in accordance with ASTM D1003
using Illuminant C (2.degree. observer angle), the results of which
are disclosed in TABLE 1.
1TABLE 1 Haze Measurements of Glass Laminates of Varying PET
Thicknesses Laminate Description Haze (%) #1 0.76 mm PVB (standard
laminate) 0.50 #2 0.76 mm PVB/0.18 mm PET/0.76 mm PVB 1.0 #3 0.76
mm PVB/0.35 mm PET/0.76 mm PVB 1.3
[0036] While an increased haze level was observed for laminate #3
as compared to the standard laminate, the observed haze for
laminate #3 is significantly less than what would be observed for a
laminate containing a single layer of PET of comparable
thickness.
EXAMPLE 2
[0037] Standard Laminate
[0038] A standard glass laminate was prepared for use as a control
during the experiments. This control was a sandwich of two pieces
of heat-strengthened float glass with a homogeneous interlayer of
conventional PVB having a Tg of about 33.degree. C. Each layer of
glass typically measured 2.1 mm thick, while the PVB layer was 0.76
mm. The standard laminate performed acceptably in blunt-pendulum
impact testing, with tests indicating that the standard laminate
required 20-30 sec to penetrate, as opposed to less than 2 sec for
tempered glass.
[0039] Formal blunt-pendulum tests were conducted according to the
British Standards Institute (BS) AU 209, part 4a, which is a
pendulum test that uses a 9.5 kg blunt pendulum to inflict 65
joules (J) of impact energy on the target glass laminate.
Furthermore, pendulum impact and headform pullout/push in tests
were performed, in which a pendulum test was first performed
followed by the pullout/push in tests.
[0040] The target of these tests was a front side door, with glass
edge engagement of at least 14 mm. At the 65 J impact level, the
standard laminate showed a considerable deformation (.about.3 cm),
suggesting that the standard laminate was on the edge of its
ability to pass this test.
[0041] With there being increasing awareness for the need for
tougher, stronger glass laminates, a modification of the BS AU 209,
part 4a test was done in which a 19.5 kg pendulum replaced the 9.5
kg pendulum, delivering 134 J of impact energy onto the glass
laminate. This resulted in failure, i.e. penetration by the
pendulum or separation between the metal frame and the glazing, for
all standard laminate test samples. Thus, it is desirable to
develop an improved stiffness glass laminate, resulting in a
product that can withstand the increased forces that are common to
criminal attacks.
EXAMPLE 3
[0042] Improved Laminates Used in Testing
[0043] Based on the results of the modified, heavy-pendulum testing
described in Example 2, modifications were made to the laminates to
improve both penetration resistance and stiffness. In light of
this, the following laminates were used for further testing:
2TABLE 2 Test Laminates for Intrusion Resistant Trials PVB-A PVB-A
Laminate PVB (mm) (mm) PET (mm) (mm) PVB (mm) A 0.76 -- 0.18 --
0.76 B -- 0.76 0.18 0.76 -- C 0.76 -- 0.35 -- 0.76 D 1.52 -- -- --
-- (Standard)
[0044] The PVB used in laminates A, C and D was industry standard
automotive grade Saflex.RTM. PVB made by Solutia Inc. containing
normal plasticizer levels. The PVB used in laminate B (PVB-A) was
an experimental material with increased stiffness, wherein the
plasticizer level was adjusted so as to give a PVB layer with a Tg
greater than 35.degree. C. The PET layers used in laminates A and B
comprised a single sheet of optical grade 7 mil (0.18 mm) thickness
PET film. The PET layer used in laminate C comprised two sheets of
optical grade 7 mil (0.18 mm) thickness PET film bonded together
with acrylic adhesive. Testing of these trial laminates followed
the parameters of BS AU 209, part 4a. Flat annealed glass 2.3 mm
thick was used for fabrication of the laminates. A generic door was
fitted with a 45.times.60-cm opening, with the laminate fully
secured in the testing frame having a glass-edge engagement of at
least 10-mm. The following testing protocols shown in Table 3 were
used to examine the major weaknesses of the laminates in real-world
type attacks of various tools, and employed the energy levels of
the same order of magnitude as is known in criminal attacks.
3TABLE 3 Test Types and Data Recorded Test Test Element Description
1 Pendulum impact testing Std. (65 J) + modified (134 J) BS AU 209
4a test procedure was used. Deformation was recorded. number of
impacts until penetration was recorded. 2 Axehead impact testing
Modified BS AU 209 4a test procedure using axehead strike tool.
Deformation was recorded; number of impacts until penetration was
recorded. 3 Headform pull-out/push-in Performed after pendulum
impact; resistance load vs. deformation were recorded. 4 Blunt head
impact then Multiple strike/same location blunt headform pull
out/push in head impact. Load vs. deformation were recorded after
penetration. 5 Axehead impact then Multiple strike/same location
axehead headform pull out/push in impact. Load vs. deformation
performed after axehead penetrated laminate; load vs. deformation
were recorded.
EXAMPLE 4
[0045] Pendulum Impact Test (Test #1)
[0046] The pendulum mass used was either 9.5 kg, delivering an
impact energy of 65 J, or at 19.5 kg, delivering an impact energy
of 134 J. All impacts were made at the center of the laminates
instead of toward the top center as specified by BS AU 209, part
4a, and were in a diamond shaped pattern, as in the standard
method.
[0047] Results of the pendulum impact test are summarized in TABLE
4. Because the laminate was fully secured in the testing frame, the
standard laminate passed the pendulum impact test at the higher
impact energy (134 J). However, the severe deformation of the
laminate indicates that in real-world situations, it would most
likely result in window failure, either through collapse (folding),
or pullout. Laminates A-C all showed substantial improvements in
resistance to the blunt-head impact, with significantly less
severity of laminate deformation. As shown in TABLE 4, laminates B
and C, the preferred embodiment of the present invention, exhibited
the best resistance to the blunt-head impact.
4TABLE 4 Results of Pendulum Testing Laminate Impact Pass/Fail Type
Energy (J) BS AU 209 Laminate Integrity Standard 65 Pass 3-cm
deformation Standard 134 Pass 4-cm deformation A 65 Pass <1.0-cm
deformation A 134 Pass <1.5-cm deformation B 65 Pass <0.5-cm
deformation B 134 Pass <1.0-cm deformation C 65 Pass <0.5-cm
deformation C 134 Pass <1.0-cm deformation
EXAMPLE 5
[0048] Axehead Impact Testing (Test #2)
[0049] An axehead impact was performed on a BS AU 209 apparatus at
an impact energy level of 65 J. The laminate was continuously
impacted with the axehead at the same strike position until
penetration occurred. A 9-cm long slit was created on the laminate
after the axehead penetration.
[0050] Test results are summarized in TABLE 5. While standard
laminate delivers reasonably good resistance to axehead impact, the
PVB composite laminates, particularly the preferred embodiment of
the present invention laminate C, revealed exceptionally high
resistance to the attack of the cutting tool. The stiffness data
from TABLE 5 is discussed in Example 8 below.
5TABLE 5 Results of Axehead Impact Laminate Number of Apparent
Laminate Maximum Laminate Type Impacts to Fail Stiffness Stiffness
Standard 3 70 120 A 4 315 545 B 7 680 900 C 16 450 760
EXAMPLE 6
[0051] Headform Pullout/Push-in Resistance (Test #3)
[0052] Prior to headform pullout/push-in testing, each laminate was
impacted per the modified BS AU 209, part 4a test at an energy
level of 65 J (using the 9.5 kg pendulum). Headform pullout/push-in
resistance was done with a ram having an 18-cm diameter,
hemispherical metal head. Pullout/push-in speed was 10 cm/min
perpendicular to the impacted side of the laminate. Force (load)
applied to the laminate vs. the displacement (distance the laminate
was pushed in) was recorded. The apparent laminate modulus was
obtained by dividing the maximum load by the maximum displacement.
Maximum laminate modulus was the highest average of the slopes from
the pullout force vs. displacement curve over a range of 2-cm
displacement. Results are summarized in TABLE 6.
[0053] As shown, laminates B and C showed much improved modulus
properties over the standard laminate and laminate A. This
increased resistance to headform pullout/push-in testing represents
improved strength of the laminates after being broken with a blunt
object. This increased laminate modulus or stiffness after glass
breakage is a very desirable property in automotive laminates as a
deterrent to break-ins.
6TABLE 6 Results of Headform Pullout/Push-In Resistance Testing
Apparent Laminate Maximum Laminate Modulus Modulus Interlayer Type
(N/cm displacement) (N/cm displacement) Standard 150 230 A 440 690
B 800 1100 C 695 1000
EXAMPLE 7
[0054] Blunt-Head Impact & Headform Pullout/Push-in Sequence
(Test #4)
[0055] In real world attacks, the thief could smash a 3 to 4 cm
diameter hole through the laminate, insert a hook through the hole,
and pull outward. A blunt-head impact headform pullout/push-in
testing sequence was first used to examine how well the laminates
resist such attacks. All laminates were subjected to continuous
impacts at 134 J of impact energy (using the 19.5 kg pendulum) at
the same position until blunt head penetration occurred. After the
penetration, the laminates were tested for pullout/push-in
resistance. The results are summarized in TABLE 7.
7TABLE 7 Results of Blunt-Head Impact & Headform
Pullout/Push-in Sequence Interlayer Number of Apparent Laminate
Maximum Laminate Type Impacts to Fail Stiffness Stiffness Standard
3 70 110 A 7 295 510 B 12 600 875 C 9 395 770
[0056] The standard laminate loses half of the stiffness after the
penetration and is, thus, vulnerable to this type of testing
sequence. The laminates B and C showed greater resistance to the
blunt-head impact at higher energy level, and they had the highest
measured stiffness after the penetration. It would take tremendous
effort to pull these laminates out of the window frame, even though
a 3 to 4 cm diameter hole has been made in each laminate.
EXAMPLE 8
[0057] Axehead Impact & Headform Pullout/Push-in Sequence (Test
#5)
[0058] The axehead impact--headform pullout/push-in test sequence
was carried out in a matter similar to that of Example 7, except
that 65 J of impact energy was used (using the 9.5 kg pendulum).
Similar results were obtained as in Example 7, and the results are
summarized in TABLE 5. Laminates B and C showed the greatest
resistance to the axehead impact, and they had the highest measured
stiffness after the penetration. It would take tremendous effort to
pull these laminates out of the window frame, even though a 9 cm
slit has been made in each laminate.
[0059] The preceding description is set forth for purposes of
illustration only and is not to be taken in a limited sense.
Various modifications and alterations will be readily apparent to
persons skilled in the art. It is intended, therefore, that the
foregoing be considered as exemplary only and that the scope of the
invention be ascertained from the following claims.
* * * * *