Thermoplastic interlayer film

High clarity optical and safety glass laminate interlayer films and optical laminates are described. The films and their laminates comprise very low density polyethylene and/or its copolymers, preferably polymerized with metallocene catalysts, and modified with additives, such as coupling agents, clarifying or nucleation agents, UV-light absorbers, pigment or color concentrate, and IR-light blockers.

FIELD OF THE INVENTION 
The invention relates to films of thermoplastic blends. The films are used 
to make safety glass interlayers for optical laminates. 
BACKGROUND 
Safety glass has existed for more than 80 years, and is widely used for 
windows in trains, planes, ships, etc. and in the automotive industry, for 
example, in windshields for cars, trucks and other forms of 
transportation. It is characterized by high impact and penetration 
resistance and it does not scatter glass shards and debris when shattered. 
Safety glass is also used in the construction industry and in the design 
of modern buildings. It is used, for example, as windows for stores and 
offices. 
Safety glass usually consists of a sandwich of two glass sheets or panels 
bonded together by means of an interlayer of a polymer film placed between 
the two glass sheets. One or both of the glass sheets may be replaced by 
optically clear rigid polymer sheets, such as sheets of a polycarbonate 
polymer. 
The interlayer is made of a relatively thick polymer film exhibiting a 
toughness and bondability as will cause the glass to adhere to the 
interlayer in the event of its being cracked or crashed. A number of 
polymers and polymer compositions have been used to produce transparent 
interlayer films for bilayer and multiple layer mineral or polymer glass 
sheets. 
Polymer interlayers for mineral and plastic glass must possess a 
combination of characteristics including very high clarity (low haze), 
high impact and penetration resistance, excellent UV-light stability, good 
bondability to glass, low UV-light transmittance, low moisture absorption, 
high moisture resistance, and extremely high weatherability. Widely used 
interlayers in safety glass production today are made of complex 
multicomponent formulations based on polyvinyl butyral (PVB), polyurethane 
(PU), polyvinylchloride (PVC), ethylene copolymers such as 
ethylenevinylacetate (EVA), polymeric fatty acid polyamide (PAM), 
polyester resins such as polyethyleneterephthalate (PET), silicone 
elastomers (SEL), epoxy resins (ER) or polycarbonates (PC) such as 
elastomeric polycarbonates (EPC). 
Many major glass laminate manufacturers are of the opinion that PVB 
compositions provide the best overall performance taking costs into 
consideration. These PVB compositions, therefore, have become the 
interlayer of choice for many laminated glass applications. Although 
conventional PVB interlayers perform well, they do, nevertheless, suffer 
from several drawbacks. 
One major drawback of PVB is its moisture sensitivity. Increased moisture 
in interlayer films results in increased haze and may cause bubble 
formation in the final laminated flat glass product. This is a problem 
particularly around the edges of laminates and the extent of the problem 
increases markedly over time. This is unacceptable to both the 
manufacturers and their customers. Therefore, special precautions have to 
be taken to keep the moisture content of the PVB film, and ultimately the 
haze of the laminated flat glass product, to a minimum. These special 
precautions may include reducing storage time of the PVB film; 
refrigeration of the PVB film prior to lamination; pre-drying of the PVB 
film; and/or using dehumidifiers in the clean rooms where the laminates 
are prepared. These requisite precautions increase the cost and the 
difficulty of manufacturing laminates made with a polyvinyl butyral 
interlayer. Furthermore, despite these precautions and added manufacturing 
costs, when the edges of the laminated glass are exposed to moisture, a 
haze will still develop. This becomes a serious problem with the modern 
flush-mounted windshield favored by modern car designers. These designs 
call for far less overlap of the rubber mounting holding the laminate in 
the window aperture. To conceal any haze formation that may develop over 
time, manufacturers have taken to printing a pattern of black dots, the 
density of which decreases with distance from the edge of the laminate, 
around all of the edges. 
Another drawback of PVB is the need for a plasticizer in the film 
formulation for improving the impact, tear and penetration resistance and 
for improving the bonding of the PVB to the glass. Over time, the 
plasticizer tends to migrate, leading to changes in the properties of the 
laminate. One particular concern is that delamination will begin to occur 
at the edges of the laminated glass and the interlayer will become brittle 
and lose its safety features. 
A very significant drawback of PVB film and optical laminates made using 
PVB film is the low impact resistance at low temperatures due to the very 
high glass transition temperature (Tg) of PVB which is close to room 
temperature 21.degree. C. (70.degree. F.). The Tg of plasticized 
formulations is in the range from 0.degree. C. to minus 10.degree. C. At 
temperatures below zero the safety glass made using PVB can be relatively 
easily destroyed by impacting, and may lose its safety properties. 
While many of the other polymers and formulations do not have a moisture 
absorption problem as significant as PVB or Surlyn.TM. resin (a Dupont 
ionomeric resin), they lack the overall performance of the PVB films at 
comparable costs. Furthermore, some of these polymers and formulations 
require enhanced processing such as irradiation or the use of additional 
chemical components such as plasticizers which affect the cost and 
properties of the film and the optical laminates, e.g., flat glass 
products, made using the film. Plasticizers tend to migrate over time. 
This adversely affects the properties of both the film and the products 
made using the film. 
Recently developed metallocene catalyzed, linear low density polyethylene 
(LLDPE) having very low heat seal temperature, low extractables and 
improved clarity (compared to LLDPE polymerized using conventional and 
modified Ziegler-Natta catalysts) has been designed for packaging 
applications. For example, a metallocene LLDPE film which exhibits a 
density of at least 0.900 g/ccm, low heat seal temperature, low 
extractables, and a haze value of less than 20%, is disclosed in U.S. Pat. 
No. 5,420,220. Packaging film according to this disclosure has less haze 
when compared to a film extruded of a conventional Ziegler-Natta LLDPE 
(exhibiting typical haze values greater than 10%). However, haze was 
measured by ASTM method D-1003 for very thin film samples (0.8-1.0 mil, or 
approx. 20-25 mcm). Films of much higher thickness (7-14 mil) are used for 
optical laminates, and the disclosed packaging film is not able to provide 
the required optical properties. For example safety glass products have to 
exhibit a haze lower than 4%, some of them lower than 2 or 1%, and in the 
most demanding car windshields applications 0.3-0.5%, for thicknesses in 
the range from 5 mil to 40 mil. 
It has now been discovered that an economical, easily processed optical 
laminate with improved properties may be fabricated from polymer glass 
and/or mineral safety glass containing an interlayer film made of a 
formulation based on a substantially linear very low or ultra-low density 
polyethylenic polymer, copolymer, or terpolymer, their blends and alloys. 
In modern industry the term linear low density polyethylene (LLDPE) 
relates to an ethylenic polymer or copolymer having a density from 0.925 
g/ccm to 0.910 g/ccm; the term linear very low density polyethylene 
(LVLDPE)--from 0.910 g/ccm to 0.880 g/ccm; and the term linear ultra-low 
density polyethylene (LULDPE)--from 0.880 g/ccm to 0.850 g/ccm. 
Very low and ultra-low density polyethylene and their copolymers with 
butene, octene, hexene, propylene, pentene, and other comonomers are 
produced using various metallocene catalyst systems. The substantially 
linear, very low and ultra-low density ethylenic polymers and copolymers 
provide an interlayer film and a glass "sandwich" having high clarity, 
very high moisture resistance, extremely low moisture absorption during 
storage, handling and use, very high UV-light stability, and good heat 
resistance. Low density, high yield (a higher number of square meters of 
film produced from one weight unit of resin) and higher impact and 
penetration resistance of these polymers enables one to use a thinner 
interlayer film and provides significant economical advantages compared to 
PVB and EVA films and their optical laminates. The costs of suggested 
interlayer can be 30-300% less than conventional PVB interlayer. The cost 
of an interlayer is usually about 30% of the cost of the final optical 
laminate. Therefore the significant cost reduction of the interlayer 
translates into substantial cost reduction of the laminated glass product. 
SUMMARY OF THE INVENTION 
This invention provides an economical, easily processed, safety glass 
interlayer film made of a formulation based on at least one linear low 
density polyolefin having a polydispersity index of less than 3.5, a 
density from about 0.850 to about 0.905 g/ccm and having less than 20% 
crystallinity, which has improved properties such as high clarity, 
extremely low moisture absorption, low moisture sensitivity during storage 
and handling, very high UV-light stability, good heat resistance, and high 
yield, and which provides high impact and penetration resistance of 
laminates made using the proposed interlayer. 
This invention also provides optical laminates containing the interlayer 
film and a process for manufacturing these products comprising the steps 
of selecting a metallocene catalyzed substantially linear, very low 
density polyethylene (LVLDPE) having a density lower than about 0.905 
g/ccm or ultra-low density polyethelyne (LULDPE) having a density lower 
than about 0.880 g/ccm, as an interlayer material and incorporating this 
interlayer between at least two sheets of mineral or polymer glass. It is 
understood that the terms "LVLDPE" and "LULDPE" as used herein embrace not 
only homopolyethylene but also copolymers of ethylene with other 
comonomers known in the art, such as alpha olefins (e.g., butene, octene, 
propylene, pentene and hexene). 
The interlayer film may also comprise an additive package consisting of: 
coupling agents (0.1 to 2.0%, by weight) to improve adhesion to glass 
and/or plastic panels; clarifying (nucleation) agents (0.02 to 2.0%, by 
weight) to increase the light transmittance (reduce the haze) of the 
interlayer; and UV-light absorbers to decrease the UV-light transmittance. 
Other additives also can be incorporated to achieve special properties in 
the safety glass and/or plastic laminates. A crosslinking agent may be 
added in the amount of from about 0.05% to about 2% by weight of the total 
formulation. Examples of other additives include pigments, colorizing 
agents or concentrates and IR-light blockers. 
The films of the present invention also may be used as an interlayer in 
other multilayer products manufactured using mineral glass or plastic 
sheets or panels. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Film made of substantially linear LVLDPE and LULDPE used herein should have 
a clarity higher than 70%, preferably higher than 75%, and most preferably 
higher than 80%, and a haze value lower than 4% preferably lower than 2% 
and most preferably lower than 1% (both optical parameters measured in 
accordance to ASTM D-1003) to be suitable for production of an interlayer 
film in optical laminates. It is preferable to use substantially linear 
ethylenic polymers/copolymers polymerized using metallocene catalyst 
systems because this type of catalyst provides thermoplastic polymers with 
a low density and very narrow molecular weight distribution (MWD). The MWD 
of polymers is commonly characterized by the polydispersity index (PI), 
i.e. the ratio between the weight average molecular weight and the number 
average molecular weight (Mw/Mn), each of which is calculated from 
molecular weight distribution measured by gel permeation chromatography 
(GPC). The PI values for metallocene catalyzed PE are very small, i.e. the 
MWDs are very narrow. The PI values of metallocene PE are usually lower 
than 3.5, and there are available industrial grades of substantially LLDPE 
typically having PI in a narrow range 2.0-2.5. Narrow MWD, i.e. very 
uniform length of the macromolecular chains, along with extremely narrow 
and uniform comonomer and branches distribution leads to low crystallinity 
(less than 20%), high clarity and low film haze. 
High optical quality film and mineral safety glass (haze less than 3%) is 
produced by using ethylenic resin with polydispersity less than 3.5, 
preferably less than 2.5, most preferably less than 2.3; density 
preferably less than 0.905 g/ccm, most preferably less than 0.885 g/ccm; 
and crystallinity of less than 20%, by weight, preferably less than 15%, 
most preferably less than 10%. Additional requirements include a comonomer 
content of no more than 10 mole % and, for most products, a film additive 
package. 
The choice of the most preferable resin depends on the type of laminate to 
be produced and optical properties requirements for different 
applications. For example, if the required haze of interlayer film and 
glass laminate (good quality mineral glass up to 5-6 mm thick does not 
increase the haze of the laminae) is less than 3%, a LVLDPE with PI=3.5, 
density 0.910 g/ccm, and crystallinity less than 20% can be used as a 
basic resin to produce the interlayer. Such an interlayer can be used in 
manufacturing of sound shields, screens, etc. For more demanding 
applications such as special glass screens, windshields and some types of 
architectural glass, the industry standards require a higher transparency 
of the final product, i.e. haze on a level of 2% and lower. In this case 
only LULDPE with a PI lower than 2.5, density lower than 0.880 g/ccm, and 
crystallinity lower than 15% is appropriate. For many important 
applications such as large public building windows and other types of 
special architectural glass and glazing of cars and windows for trains and 
ships, the haze of an optical laminate should not exceed 1%, and for these 
applications LULDPE grades with PI less than 2.5, density less than 0.880 
g/ccm, and crystallinity less than 10% should be used. For automobile 
windshields (the most demanding type of safety glass in terms of haze 
values) polymers with PI less than 2.3, density lower than 0.880 g/ccm, 
and crystallinity lower than 10% are preferred. 
Light transparency and haze of film and glass laminate depends on the 
thickness of the interlayer. The minimum thickness of the interlayer film 
is determined by the safety requirements (impact and penetration 
resistance and ability to hold glass debris while crashing). The very high 
impact, notch and tear resistance of the films allows a reduction of the 
thickness of the interlayer needed to meet the safety standards for the 
glass "sandwich". For example, 0.35 mm (14 mil) thick PVB-based film 
commonly used in manufacturing of architectural safety glass can be 
replaced by the glass made using a 0.25 mm (10 mil) thick interlayer 
according to the invention. For some optical products even a 0.175 mm (7 
mil) interlayer can be used. Significant reduction of the interlayer 
thickness helps further to increase the yield of film, reduce the haze, 
and make the interlayer and the laminated product more economical. 
Ethylenic copolymer resin used to produce an interlayer film according to 
the present disclosure should be chosen from ethylenic copolymers with a 
limited content of comonomers relative to ethylene monomer. The increase 
of the content of comonomer higher than 10 mole % leads to a decrease in 
the melting and softening points of the resin. This is undesirable because 
the mineral safety glass has to pass the "boiling test" (boiling the 
laminate in water for an hour should not increase the haze of the product 
and should not lead to creation of bubbles in the interlayer). 
Use of linear ethylenic copolymers or terpolymers with a content of more 
than 10% mole of comonomers is not advisable due to their low melting 
(softening) temperatures of about 50.degree. C. to 75.degree. C. To be 
useful herein, these polymers may be crosslinked to increase their melting 
temperature to the necessary level (100.degree.-140.degree. C.). The 
crosslinking requires a treatment with, for example, peroxides or 
radiation. However, increased content of peroxides increases the melt 
viscosity, and energy consumption, and can lead to the loss of optical 
quality of film due to creation of gels. High radiation intensity (for 
example, higher than 10 MRad for E-Beam treatment) creates similar 
problems and economic disadvantages. 
Unlike PVB film, the interlayer film made according to the present 
invention does not need plasticizers due to the high impact, notch and 
tear resistance characteristics of substantially linear ethylenic 
polymers/copolymers. 
Because polyolefins have poor adhesion to substrates including other 
polymers and mineral glass due to the non-polarity of polyolefin 
molecules, interlayer film according to the present invention preferably 
contains a coupling agent to provide a good bond to glass and other 
substrates. The interlayer film also preferably contains an efficient 
UV-light absorber. Other additives also can be incorporated to achieve 
special properties in the optical laminates. Examples of other additives 
include pigments, colorizing agents or concentrates and IR-blockers. The 
films of the present invention can be used as an interlayer in safety 
glass and for other bilayer and multilayer products manufactured using 
mineral glass or plastic sheets or panels. 
The recrystallization which occurs during hot lamination of the interlayer 
to the polymer or mineral substrate is controlled to avoid haze formation. 
The process of lamination of optical laminates is carried out under 
pressure at elevated temperatures. For example, modern safety glass is 
produced commercially using PVB interlayer film in an autoclave under 
pressure at temperatures in the range of about 110.degree.-185.degree. C. 
The film is exposed to these conditions for a relatively long time, up to 
several hours. Crystallization ("recrystallisation") of the polymer in the 
interlayer under these conditions can lead to haze increase and loss of 
optical quality. Crosslinking of the resin may be used to minimize 
recrystallisation during the heat-lamination process. In addition, a low 
or medium grade of crosslinking provides an increase of the softening 
temperature of substantially linear polyethylenic resin up to the use 
temperature 80.degree.-130.degree. C. typical for PVB or even higher. 
Various crosslinking methods can be used, for example, peroxide, 
peroxide-silanol and radiation (E-beam) treatment. Peroxide technology is 
preferred. 
Additional stabilization of the morphological structure of the polymer to 
maintain the crystallinity and haze on a very low level during lamination 
and thermal exposure of the final laminate (to heat and sun) can be 
achieved by incorporation of a nucleation (clarifying) agent into the 
interlayer formulation. 
The laminated products according to the present invention are optical 
laminates made using interlayer films of 0.125-1.0 mm (5-40 mil) thickness 
made of formulations based on substantially linear VLDPE and ULDPE 
polymers and their copolymers, blends and alloys having densities 
respectively in the range from about 0.905 g/ccm to about 0.880 g/ccm 
(LVLDPE), and from about 0.880 g/ccm to 0.850 g/ccm (LULDPE). These may be 
polymerized using a metallocene catalyst system which provides a 
substantially linear structure of macromolecular chains and a very narrow 
MWD, i.e. Polydispersity Index lower than 3.5, preferably lower than 2.5 
and most preferably lower than 2.3, and a very low initial crystallinity 
of the resin, i.e., lower than 20% by weight, preferably lower than 15%, 
and most preferably lower than 10%. Substantially linear polyethylenic 
polymers or copolymers with density lower than 0.850 g/ccm have a 
crystallinity less than 10% by weight, and a very low initial haze 
(0.3-3%). However, the very low melting temperature (55.degree.-60.degree. 
C.) of these polyethylenic resins creates a need for heavy cross-linking 
to increase their use temperature, and avoid processing problems. The 
industry requirements for safety glass, cannot be met using LULDPE resin 
with density lower than 0.850 g/ccm because the amount of crosslinking 
needed to thermally stabilize the resin creates an increase in laminate 
haze. 
The formulations may be blended with an additive package in a high speed 
dry mixer and compounded using a melt compounding extruder. Twin screw 
co-rotating extruder Model ZSK-30 with 30 mm screws and Model ZDS-53 with 
53 mm screws made by Werner Pfleiderer Corporation was utilized in the 
present invention but any other suitable compounding extruder can be used. 
The compounding machine should provide a uniform mixing of the basic 
thermoplastic resin with relatively small quantities of required 
additives. 
In a preferred method of producing the films useful in the invention, a 
melt exiting the extruder may be formed into strings using a die plate 
with a number of holes, e.g., 6 holes. The strings may be cooled in a 
water bath; cut into pellets of standard size (1-4 mm in diameter and 
2.5-5 mm in length); and dried. The pelletized formulation may be stored 
and extruded into a film as needed. Both melt casting extrusion technology 
and melt blown extrusion technologies can be used for film manufacturing. 
In a suitable process film extrusion lines may be equipped with flat 
extrusion dies and casting rolls or drums used to calibrate the thickness 
and to cool the film web. After cooling, the film may be wound into rolls. 
The thickness and the width of the product selected depend on the 
particular application (e.g., architectural glass, automotive glass, 
special plastic laminates), and can vary in the range from about 125 mcm 
(5 mil) to 1,000 mcm (40 mil). 
The polymer can be crosslinked if necessary before or after film formation 
to increase the softening point and the use temperature of the interlayer. 
Methods of polyolefin crosslinking are known in the industry and include 
peroxide, peroxide-silanol, and radiation technologies. 
In all films and laminates herein, the basic preferred resin is a VLDPE 
thermoplastic material (plastomer or elastomer) chosen from the PE 
polymers and copolymers polymerized using metallocenes catalyst systems 
and having densities lower than about 0.905 g/ccm. The conventional low 
density polyethylenes (LDPE), typically have densities in the range of 
from about 0.915-0.925 g/cc, and the so-called medium density 
polyethylenes (MDPE) have densities in the range of from about 0.926-0.940 
g/ccm. 
The VLDPE group of resins is usually further subdivided into PE plastomers 
which are resins with low crystallinity, ranging from about 10-20%, having 
densities in the range of from about 0.914-0.900 g/ccm; and PE elastomers 
which are completely amorphous resins having densities in the range of 
from about 0.899 to 0.860 g/cc which contain a comonomer which when 
polymerized yields a rubber such as a diene rubber. 
Many grades of linear ethylene polymer (plastomers and elastomers), such as 
Exxon "EXACT" family of metallocenes PE plastomers and elastomers, Dow 
"AFFINITY" family of PE plastomers, and Dow "ENGAGE" family of PE 
elastomers, are suitable for extrusion of the interlayer according to the 
present invention. Examples of some of the basic resin grades suitable for 
the interlayer film are given below in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Properties of some LVLDPE and LULDPE Polymers 
Tensile 
Elongation 
strength 
at break 
Impact 
Polymer 
Density 
DSC MD/TD 
MD/TD resistance.sup.b 
Haze.sup.a 
grade 
Comonomer 
g/ccm 
.degree.C. 
Psi % g/mil 
% 
__________________________________________________________________________ 
Exxon EXACT Resin: 
3027 Butene 
0.900 
92 8160/5210 
450/700 
408 0.4 
3033 Terpolymer 
0.900 
94 9800/9020 
470/580 
1125 2.9 
3034 Terpolymer 
0.900 
95 10420/8280 
350/610 
1450 0.3 
4011 Butene 
0.885 
66 3260/3260 
800/800 
350 0.4 
3028 Butene 
0.900 
92 8670/7250 
590/680 
177 3.1 
4015 Butene 
0.896 
83 7409/6372 
480/587 
1368 0.8 
4049 Butene 
0.875 
82 4670/4450 
690/780 
345 0.3 
SLP Terpolymer 
0.900 
96 8150/8200 
460/550 
1125 0.8 
9042 
SLP Terpolymer 
0.900 
99 7390/5100 
400/700 
2062 0.3 
9045 
Dow "AFFINITY" Resin: 
PL 1880 
a-olefin 
0.902 
100 7170/3800 
570/560 
500 1.1 
PL 1845 
a-olefin 
0.910 
103 6580/4870 
527/660 
362 0.7 
SM 1250 
a-olefin 
0.885 
51 3700/3950 
1000/900 
500 1.3 
Dow "ENGAGE" Resin: 
KC 8852 
a-olefin 
0.875 
79 4600/4900 
890/850 
150 0.5 
EG 8150 
a-olefin 
0.868 
62 1600/1750 
880/790 
450 0.4 
__________________________________________________________________________ 
.sup.a Haze is measured using ASTM D1003 method for 0.8-1.0 mil cast film 
samples. 
.sup.b Impact resistance is Dart Drop Impact, F50 values measured using 
ASTM D1709 method. 
The resin grades in Table 1 are given as an illustration only. A number of 
other metallocenes LVLDPE and LULDPE plastomers and elastomers with a 
density of less than about 0.905 g/ccm also can be used to produce an 
interlayer for glass and plastic laminates. 
The additive package may include various functional components. The type 
and content depend on the type and application of the safety glass and/or 
plastic laminate to be produced. Examples of some additives are described 
herein. These, as well as conventional additives, may be incorporated into 
the interlayer formulation. 
Coupling agents may be added to improve the adhesion of the plastic 
interlayer to glass and other substrates without primer coating of the 
substrate. Preferred coupling agents include vinyl-triethoxy-silane, and 
amino-propyl-triethoxysilane but other coupling agents can also be 
incorporated into the formulations. The concentration of the coupling 
agent should be in the range from about 0.2% to about 2.0%. Silanes do not 
improve the adhesion of the interlayer to glass when they are used in 
concentrations lower than about 0.2%. In concentrations higher than about 
2.0% they increase the haze of the interlayer. The preferable range of the 
coupling agent is from about 0.5% to about 2.0%, and the most preferable 
is from about 0.7% to about 1.5%. 
A UV-light absorber may be added to block the UV-light and to provide 
protection from the negative influence of the transmission of UV-light. A 
number of UV-light absorbers known in the industry can be used. Preferred 
are CHIMASORB TINUVIN 944 UV-light absorber, supplied by CIBA-Geigy 
Corporation (Switzerland/Germany); CYASORB UV-9 absorber, available from 
American Cyanamid Corporation, and polymerizable benzotriazole 
(NORBLOCK.TM.) absorber, supplied by Noramco Corporation (USA). Absorbers 
should be used in concentrations in the range from about 0.1% to about 
1.5%, preferable in the range from about 0.25% to about 1.5%, and most 
preferable in the range from about 1.0% to about 1.5%. 
Nucleation agent may be added to improve optical properties and clarity; to 
reduce the haze of the film, and to stabilize the morphological structure 
of the material. Incorporation of a nucleation agent helps to reduce the 
dimensions of crystallinic units and provides stability after reheating of 
the film during lamination or after exposure to sun or other sources of 
heat. Various nucleation agents are commercially available. Most of them 
are based on adipic acid compounds. One suitable type of nucleating agent 
is available from Milliken Corporation under the MILLAD trade name. 
Several grades of Milliken products are available and the more preferred 
include: MILLAD 3905, 3940 and 3988 grades. 
The concentration of the nucleation agent may be in the range of from about 
0.05% to about 2.0%. The content of the nucleating agent depends on the 
initial haze of the polymeric matrix, the thickness of film to be 
clarified and the density and crystallinity of the resin. The preferable 
concentration of MILLAD 3905, 3940 and 3988 nucleating agent in the 
metallocenes LVLDPE and LULDPE polymers according to the present invention 
is in the range of from about 0.2% to about 2.0% by weight of the 
formulation and the most preferable being from about 0.5% to about 1.0%. 
Very small particles of minerals can also be used as nucleation agents. For 
example, submicronized powders of calcium sulfate or calcium carbonate 
(with equivalent particle size in the range from about 0.1% cm to about 3 
mcm) of high purity have practically the same efficiency as adipic acid 
type nucleation agents. 
Pigments, dyes, and/or color concentrates may be added when special color 
effects are needed in the safety glass or plastic laminate for 
architectural, decorative and other applications. They are used in such 
concentrations as are determined by coloration technology. 
Other additives can also be incorporated to achieve special properties of 
the interlayer and resultant interlayer film product such as, for example, 
to achieve reduced IR-light transmittance; to increase reflection, and to 
decrease the blocking and to improve the slipping of film. 
An interlayer film product according to the present invention may be smooth 
surfaced or it may also have embossed patterns on its surface which assist 
the evacuation of air between the glass plates (sheets) and the interlayer 
during lamination. The product may have embossed patterns on one or both 
sides of the film which are made with an embossing roll. Patterns also may 
be created using an extrusion die with a specific design profile. 
Crosslinking of the polymer according to the present invention can be 
achieved by different techniques. The peroxide technology using organic 
peroxides (for example dicumyl peroxide) incorporated into the formulation 
is very efficient. It increases the use temperature up to at least 
20.degree.-70.degree. C. However, this technology requires very precise 
feeding equipment and must be used very carefully since it can lead to an 
increase of the haze and gel content in the film. 
Peroxide-silanol technology requires a much lower quantity of peroxide and 
is a convenient process. Peroxide-silanol crosslinking provides a slightly 
lower grade of crosslinking compared to organic peroxides, but it does not 
require special feeding equipment, and does not create difficulties in 
achieving required optical properties of the product. The silanol 
technology may be implemented using a concentrate of the 
peroxide-silanol-catalyst mixture in a polyolefin matrix. This type of 
concentrate is available, for example, from OSI Corporation (USA) under 
the SILCAT R trademark. The concentrate is mixed with the basic resin and 
other additives in a dry blender, compounded in a twin-screw extruder, 
pelletized, and extruded into film. The silanol is grafted to the polymer 
chains during compounding and film extrusion. The crosslinking of the 
polymer occurs only after water treatment of the film. The crosslinking 
can be accelerated by treatment in hot water by boiling or by steam 
treatment. The final product should be dried before lamination to glass or 
plastic substrates. 
Peroxide-silanol-catalyst SILCAT R concentrate should be used in 
concentrations in the range from about 0.2% to about 5%, more preferable 
from about 0.5% to about 3%, and most preferable from about 0.5% to about 
1.7%. The concentration of the crosslinking agent should be higher for 
basic plastomer/elastomer resins with lower densities and lower softening 
points. 
Another method of crosslinking of the polymer material according to the 
present disclosure is radiation, for example, E-beam treatment of the 
extruded film. E-beam radiation with an intensity in the range from about 
2 MRd to about 20 MRd provides an increase of the softening point by 
20.degree.-50.degree. C. The most preferable range of the radiation 
intensity is in the range from about 5 MRd to about 15 MRd for film made 
of formulations based on metallocenes PE elastomers with an initial 
softening point of 55.degree.-90.degree. C., and in the range from about 
2.5 MRd to about 10 MRd for film made of formulations based on 
metallocenes PE plastomers with an initial softening point of 
90.degree.-105.degree. C. E-beam treatment of the above intensities 
provides the softening temperature (Vicat Softening Point) in the range 
from 110.degree.-145.degree. C. required for safety glass applications, 
and which is comparable to the PVB interlayer being currently used in the 
industry. 
Different additive packages using the above compounds may be used for 
manufacturing of interlayer film for different applications. 
The properties of the resultant products depend on the basic resin, 
additive package, and thickness of film. A number of properties of the 
product according to the present invention such as moisture absorption, 
UV-light stability, impact resistance, low temperature brittleness, 
processability and costs are superior to the PVB interlayer currently 
being used for lamination of glass and other substrates. Some properties 
such as reduced haze, UV-light blockage, penetration resistance of the 
present product are comparable to PVB. The products according to the 
present invention do not contain plasticizers which may cause yellowness 
of the interlayer with time, and provide a higher yield (more sq. ft. of 
film per pound of resin) due to the lower density of the basic material 
(0.850-0.905 g/ccm compared to 1.10-1.15 g/ccm for PVB). 
The interlayer according to the present invention can be laminated to 
mineral glass and polymer substrates using the same technology and 
conditions being used for the PVB interlayer. Good quality mineral glass 
laminates can be manufactured in autoclaves at temperature in the range 
from 140.degree. C. to 170.degree. C. and pressure in the range from 12 
bar to 23 bar. Frequently used autoclave lamination conditions are: 
temperature in the range from 135.degree. C. to 165.degree. C. and 
pressure in the range from 13 bar to 17 bar. 
The following examples of embodiments of the invention can be used for 
specific illustration of the above. These examples and comparative 
examples are given to illustrate the invention in more detail and are not 
intended to be limiting. 
Processing of LVLDPE and LULDPE-based Formulations into Films 
Formulations based on LVLDPE and LULDPE polymers were produced by mixing 
their melts with an additive packages using the twin-screw extruder ZSK-30 
made by Werner Pfleiderer Co. of Ramsey, N.J., equipped with two 
co-rotating screws with a diameter of 30 mm. All formulations were 
premixed in a dry high speed (turbo) mixer at 300 rpm for 20 min and then 
fed into the twin-screw extruder. Extruder ZSK-30 was equipped with a die 
plate having six holes. All formulations were extruded into strings. The 
strings were cooled in a water bath and then cut into pellets of a 
standard size (2.5-3 mm in diameter and 3-4 mm in length). The twin-screw 
extruder had the following temperatures at the barrel: feeding zone 
#1--115.degree.-125.degree. C., barrel zone #2--180.degree.-195.degree. 
C., barrel zone #3--205.degree.-225.degree. C., barrel zone 
#4--215.degree.-230.degree. C., die plate--220.degree.-245.degree. C. The 
speed of the screws was 150 rpm. The pellets were dried using a room 
temperature air stream. 
The extruded pellets were processed into films using a cast film line 
consisting of a 30 mm single screw extruder made by Davis 
Standard-Killion, New Jersey. The screw of the Killion extruder had a 
diameter of 30 mm and a relative screw length of 24 diameters. The 
extruder was equipped with a flat extrusion die having an orifice which 
was approximately 28 cm (11 inches) wide. Films of two thicknesses (0.18 
and 0.36 mm) were produced from each formulation. Table 2 describes the 
formulations produced. The barrel of the single screw film extruder was 
divided into four heating zones progressively increasing the temperature 
of the polymer material up to the adapter, filter, and the flat die. The 
barrel temperature was maintained in each of zones 1-6 in the range 
150.degree.-160.degree., 190.degree.-200.degree. C., 
180.degree.-220.degree. C., 230.degree.-245.degree. C., 
240.degree.-260.degree. C. and 240.degree.-260.degree. C., respectively. 
The temperature of the adapter was maintained at approximately 
230.degree.-260.degree. C. The temperature of the die was maintained 
approximately at 245.degree.-255.degree. C. in the middle sections, at 
255.degree.-265.degree. C. at the both edges of the die, and at 
260.degree.-270.degree. C. at the lips of the die. 
The temperatures were varied in each zone in a relatively narrow range 
according to the melt flow rate of the resin used. The speed of the screw 
was maintained at between 14-17 rpm for 0.18 mm thick films and 19-22 rpm 
for 0.36 mm thick films. 
Each film was extruded and cooled using a three roll casting roll stock and 
was wound onto 7.6 cm cores. Fifteen samples were cut for testing from 
each film produced. At each of five sampling locations which were 10 
linear feet apart, samples were obtained at three points across the film 
web (from each of the edges and from the middle). 
Film Testing Procedures 
The transmission and the haze were measured after laminating 0.36 mm film 
between two layers of 3 mm thick sheets of clear, soda-lime-silicate 
glass. The transmission was measured using ANSI Standard Z26.1T2. The haze 
was measured using German Standard DIN R43-A.3/4. 
Glass Laminate Preparation 
Samples of safety glass laminates were prepared as described below for use 
in these examples. All samples were produced using clear 
soda-lime-silicate glass sheets of 3 mm thickness and dimensions of 
10.times.10 cm which were cleaned using acetone to remove dust, grease and 
other contaminates from the glass surface. Prior to this step PVB film for 
the control samples was dried for several hours to reduce the moisture 
content to 0.5% by weight or lower, and was used for lamination 
immediately after drying. The other films did not require a drying step 
before lamination. 
For laminating, a piece of film was cut to obtain a sample which was 
10.times.10 cm. This sample was put onto the surface of the bottom glass 
sheet and pressed onto the glass sheet using a rubber roll. Another glass 
sheet was placed on top of the film obtaining a sandwich structure which 
was then clamped. This sandwich was placed in a laboratory press, Model 
3891, manufactured by Carver, Inc., Wabash, Ind., equipped with a 
temperature-pressure-time control system monitored by a microprocessor. 
The following cycle was used to laminate the glass: heating from room 
temperature to 135.degree. C. in 1 hour, holding at 135.degree. C. and 
pressure 13.5 Bar for 30 minutes, slow release to normal pressure, and 
cooling to room temperature in 2 hours. Heating melts the film surfaces 
during the lamination process. 
The glass-film-glass laminates were tested and results were compared with 
those obtained for PVB film sold under the Saflex SR 41 trademark by 
Monsanto, St. Louis, Mo., and ethylene-vinyl-acetate (EVA) film sold under 
the EVA Poly BD 300 trademark by Elf Atochem, Philadelphia, Pa., which are 
used commercially as interlayers in safety glass manufacturing.