Zinc phosphate glass compositions

Details Zinc phosphate glass compositions Zinc phosphate glass compositions

2002-01-04

2003-12-23

Sample, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S032000, C501S045000, C524S494000

Reexamination Certificate

active

06667258

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to low glass transition temperature zinc phosphate glass compositions and glass/polymer blends containing the same. More particularly, the present invention relates to tin-free zinc phosphate glass compositions with a low and reproducible melt-to-melt glass transition temperature and glass/polymer blends containing the same.
BACKGROUND OF THE INVENTION
In recent years, composite bodies consisting of inorganic glasses exhibiting low glass transition temperature (T
g
) and organic polymers that exhibit the combined properties of inorganic glasses and polymers have been disclosed. For example, U.S. Pat. No. 3,732,181 describes several general methods by which glass in the form of fibers, films, flakes, powder, or sheets is combined with a polymer to form a composite mixture which can be formed into a desired configuration through a variety of shaping means. As disclosed therein, the ratio of polymer-to-glass may range from 0.1:99.9 to 99.9:0.1 on a volume basis, but more typically, about 5-66% by volume. This reference also discloses three broad glass compositions exhibiting properties which render the glasses suitable for use in glass-plastic composite articles, namely:
PbO+P
2
O
5
≧95 mol %, wherein PbO constitutes 20-80 mol %;
PbO+R
2
O (alkali metal oxides)≧95 mol %, wherein PbO comprises 5-60 mol %, R
2
O constitutes 5-35 mol %, and P
2
O
5
is present up to 85 mol %; and
PbO+R
2
O+B
2
O
3
+P
2
O
5
≧95 mol %, wherein PbO comprises 5-30 mol %, R
2
O constitutes 5-30 mol %, B
2
O
3
comprises 5-20 mol %, and P
2
O
5
makes up 15-85 mol %.
U.S. Pat. Nos. 3,885,973, 3,935,018, 3,964,919 and 3,926,649 disclose glasses which may be suitable for co-pressing with organic polymers to form composite articles of the type discussed in detail in U.S. Pat. No. 3,732,181, supra.
Recently, U.S. Pat. No. 5,043,369, herein incorporated by reference in its entirety, has disclosed a glass/polymer blend wherein the glass phase and the polymer phase being simultaneously enclosed within larger regions of another phase (i.e., localized phase inversion/reversal.) In this patent, the glass and polymer demonstrate at least partial miscibility and/or a reaction therebetween such that the two components are intimately blended together. The blend results in the formation of a compatibilizing component in-situ to yield an alloy. Also, the glass/polymer blend of this reference exhibits an essentially uniform, fine-grained microstructure wherein the glass and polymer elements comprising the microstructure are of relatively uniform dimensions. The reference patent discloses a phosphate-based glass within two general narrow composition regions which are essentially non-hygroscopic and exhibit good resistance to chemical and moisture attack, and which can interact with a variety of polymers to produce alloy articles.
Most recently, U.S. Pat. No. 6,103,810, herein incorporated by reference, has disclosed a glass/polymer blend comprised of low-temperature softening glasses and a plurality of high temperature aromatic thermoplastic or thermosetting polymers that can be used to produce durable, dimensionally stable and injection moldable articles. Also disclosed therein are glass/polymer blends that exhibit essentially uniform, fine-grained microstructure in which preferably, the glass and polymer elements comprising the microstructure are of relatively of uniform dimensions, and in which the glass interacts with the polymers to form alloys exhibiting a combination of the desirable properties of the glass and the polymers. In one particular aspect, the patent discloses a glass/polymer blend containing at least two high-temperature polymers, preferably using a mixed-alkali-zinc-pyrophosphate glass, resulting in a blend that exhibits excellent mechanical properties and flame retardance.
With regard to low-temperature glasses particularly suitable for compounding with high-temperature polymers, U.S. Pat. No. 4,940,677 discloses zinc-containing phosphate glass compositions exhibiting a glass transition temperature below 450° C., a working temperature below 500° C., and excellent resistance to attack by water and mild aqueous alkaline solutions. The glasses consist essentially, in mole percent, of at least 65% total of 23-55% ZnO, 28-40% P
2
O
5
, and 10-35% R
2
O, wherein R
2
O consists of at least two a metal oxides in the indicated proportions selected from the group consisting of 0-25% Li
2
O, 1-25% Na
2
O, and 0-25% K
2
O, and up to 35% total of optional ingredients. Method of producing the glasses is also provided in this patent.
In search for the ideal low-temperature glasses and glass/polymer blends containing the same, the present inventor has found that matching of the viscosity of the glass and polymers at the processing temperature are of great importance for an intimate blending of the glass and the polymer. Glass transition temperature is customarily defined as the temperature at which increases in specific heat and coefficient of thermal expansion take place with an accompanying sharp drop of viscosity. This temperature is frequently deemed to lie in the vicinity of the glass annealing point. Working temperature of a glass is customarily defined as the temperature at which the glass demonstrates a viscosity of about 10
4
-10
7
poises. Glass transition temperature is a useful parameter for measuring the complete viscosity versus temperature curve of a glass and, in turn, indicates the temperature at which the glass may be compounded with a polymer. For a glass to have a stable viscosity to achieve a successful compounding with polymers, it is desired that the glasses produced from successive melts of the same batch composition have substantially the same glass transition temperature.
The present inventor has discovered that generally the tin-containing zinc phosphate glasses do not have a substantially stable T
g
. As a result, glasses produced from the same batch composition in different melts cannot always be used for compounding with the same polymer. Without intending to be bound by a theory, the present inventor believed that this is the result of tin oxide used in the starting materials, which is in +2 valence status, being oxidized to +4 valence in different proportions in different melts during the glass melting process. It is known that oxidation of tin from +2 valence to +4 valence increases the T
g
of the glass. As such, glasses from different melts were subject to difficulty in compounding with polymers, or lead to inconsistent properties of glass/polymer blends containing them.
One way to solve this T
g
fluctuation problem of tin-containing zinc phosphate low-temperature glasses is to add reducing agents into the batch materials to prevent or inhibit oxidation of tin oxide. Such reducing agents commonly used include ammonium phosphate, charcoal, sugar, starch, or any mixture thereof. However, use of such reducing agents, though helpful, could not eliminate completely oxidation of tin oxide, and hence, the T
g
fluctuation problem. Moreover, effective amount of reducing agents was difficult to control in practical production. For example, exceeding amount of reducing agent, such as charcoal, reduces the quality of the final glass product, and renders it undesirable to be compounded with polymers. Charcoal also tends to float on the top of the batch materials during the melting, adding to the difficulty of processing. As for ammonium phosphate, it is known to be particularly hazardous for platinum melting and delivery system because of the corrosive effect of its decomposition product during the melting process, thereby rendering it undesirable for industrial application.
As such there remains a need for tin-free low-temperature zinc phosphate glasses suitable for forming blends with polymers, that exhibit reproducible stable T
g
from melt to melt from the same batch composition, and a high water durability.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a glas

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