Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-09-21
2003-05-06
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S222000, C525S263000, C525S273000, C525S309000, C525S221000, C525S227000, C428S441000, C428S442000, C428S483000
Reexamination Certificate
active
06559230
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to thermosetting ethylene/&agr;-olefin compositions. In one aspect, this invention relates to such compositions comprising an ethylene/&agr;-olefin copolymer in combination with a compound containing multiple vinyl groups while in another aspect, this invention relates to a film made from the composition. In yet another aspect, this invention relates to safety glass in which the film made from the composition is used as an interlayer in a laminated safety glass.
BACKGROUND OF THE INVENTION
Laminated safety glass has been used in the windshields of automobiles and the windows of buildings since the late 1930's. Safety glass typically consists of two sheets of glass bonded together by an interlayer of polymer film. When this laminated structure or sandwich is impacted by a rock or other object, the interlayer acts to absorb some of the impact energy. If the energy is sufficient to break the first sheet of glass, the interlayer reduces the total energy transmitted to the second sheet and spreads the energy from the crack across a wider area. If the energy is sufficient to also crack the second sheet of glass, the interlayer becomes the only structural element left to resist penetration of the rock. Accordingly, the tear resistance of the polymer film from which the interlayer is made is a critical performance parameter. In addition, of course, the interlayer must have excellent transparency (i.e., low haze).
Plasticized polyvinyl butyral (PVB) has historically been the material of choice for the interlayer because of its combination of excellent clarity and tear resistance. At a thickness of 0.76 mm (30 mil), PVB yields a glass laminate with a haze of 0.3%, well below the 1% value typically required for architectural applications and even the 0.5% value required for automotive windshields. When tested by ASTM D-624, Method B, plasticized PVB yields a value of 50 kN/m. The denominator in this calculation is the thickness of the test specimen.
As excellent as plasticized PVB is for forming the interlayer of laminated safety glass, it is not without disadvantages. Plasticized PVB is moisture sensitive which requires the exercise of special precautions during manufacturing and use. Plasticized PVB also has an inherent tackiness which requires that it be shipped and stored refrigerated. Moreover, plasticized PVB becomes brittle at just below its glass transition temperature of 21 C. and this, in turn, decreases the penetration resistance of safety glass with a plasticized PVB interlayer at subambient temperatures.
One response to these disadvantages of plasticized PVB is an interlayer film based on a substantially linear, very-low or ultra-low density polyethylenic interpolymer and its blends and alloys as taught by Friedman, et al. in U.S. Pat. No. 5,792,560 which is incorporated herein by reference. Friedman, et al. teach that interlayer films made from these polyethylenic materials do not need a plasticizer because of the high impact, notch and tear resistance characteristics of the substantially linear ethylenic interpolymer. However, Friedman, et al. also teach that these interpolymers have relatively poor adhesion to substrates such as mineral glass and as such, are blended with a coupling agent such as vinyl triethoxysilane or amino propyl triethoxysilane. While the Friedman, et al. interlayer overcomes some of the disadvantages of plasticized PVB, e.g., films made from the Friedman, et al. compositions are less moisture sensitive and provide better tear resistance at subambient temperatures, the thickness of the film required to achieve commercial standards of tear resistance is such that the haze value does not meet commercial standards. In other words, in order to achieve an acceptable tear resistance, the thickness of the interlayer film must be increased to a point that the haze value of the film is unacceptable.
Accordingly, the industry still has an interest in the development of an interlayer film for safety glass that has the plasticized PVB combination of high tear strength and low haze properties without the plasticized PVB disadvantages of moisture sensitivity, tackiness and relatively poor tear resistance at subambient temperatures. In this regard, an interlayer film with a Tear Haze Index (THI) of 50 or more is desirable. For purposes of this invention, THI is defined as the tear strength measured according to ASTM D-624, Method B, reported in kN/m divided by the percent haze measured at 0.76 mm (30 mil) thickness. Plasticized PVB, with a tear strength of 50 kN/m and haze of 0.3 scores a THI of 167 (which is excellent). The minimum requirement for architectural safety glass is a tear strength of 50 kN/m and haze of 1%. This equates to a THI of 50. Automotive windshields with a haze requirement of less than 0.5% require a THI of at least 100.
SUMMARY OF THE INVENTION
According to this invention, films useful as an interlayer for safety glass are prepared from a thermosetting composition comprising, in weight percent based upon the total weight of the composition:
A. about 90 to about 98 percent of a homogeneously linear or substantially linear ethylene/&agr;-olefin interpolymer with a crystallinity of about 10 percent or more;
B. about 2 to about 10 percent of a coagent containing at least two vinyl groups; and
C. at least an initiating amount of an organic peroxide.
Films made from these compositions have an improved THI relative to films made (i) from compositions substantially similar in all respects except for the co-agent (which is absent), and (ii) under similar conditions. The ethylene/&agr;-olefin interpolymer is typically an ethylene/&agr;-olefin copolymer or terpolymer of ethylene and at least one C
3
-C
10
&agr;-olefin. The co-agent can be any compound containing at least two vinyl groups, but preferably is an (meth)acrylate with at least two vinyl groups, e.g., trimethyol propane tri(meth)acrylate. The thermosetting compositions of this invention can include other materials, such as silane functional coupling agents, ultraviolet (UV) light absorbers, infrared (IR) light-blockers, tints and dyes.
DETAILED DESCRIPTION OF THE INVENTION
The homogeneously linear and substantially linear ethylene/&agr;-olefin interpolymers of this invention comprise ethylene and at least one C
3
-C
20
&agr;-olefin (preferably an aliphatic &agr;-olefin) comonomer. Examples of the C
3
-C
20
&agr;-olefins include propene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicosene. The &agr;-olefin can also contain a cyclic structure such as cyclohexane or cyclopentane, resulting in an &agr;-olefin such as 3-cyclohexyl-1-propene (allyl-cyclohexane) and vinyl-cyclohexane. Although not &agr;-olefins in the classical sense of the term, for purposes of this invention vinyl acetate, acrylic acid and the class of alkyl acrylates and methacrylates are &agr;-olefins and can be used in place of some or all of the &agr;-olefins described above. Similarly, styrene and its related olefins (e.g., &agr;-methylstyrene, etc.) are &agr;-olefins for purposes of this invention.
By way of definition, as used herein, “interpolymer” means a polymer of two or more comonomers, e.g. a copolymer, terpolymer, etc.
The homogeneous linear or substantially linear polymer is an ethylene polymer prepared using a single site catalyst. By the term homogenous, it is meant that any comonomer is randomly distributed within a given interpolymer molecule and substantially all of the interpolymer molecules have the same ethylene/comonomer ratio within that interpolymer. The DSC melting peak of homogeneous linear and substantially linear ethylene polymers will broaden as the density decreases and/or as the number average molecular weight decreases. However, unlike heterogeneous polymers, when a homogeneous polymer has a melting peak greater than 115° C. (such as is the case of polymers having a density greater than 0.940 g/cm
3
), such polymers do not additionally have a distinct lower temperature
Heck Henry G.
Waszeciak Douglas P.
Asinovsky Olga
DuPont Dow Elastomers L.L.C.
Seidleck James J.
Whyte Hirschboeck Dudek SC
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