CA1047705A

CA1047705A - Release coating for glass manufacture

Info

Publication number: CA1047705A
Application number: CA238,151A
Authority: CA
Inventors: Archie L. Bickling (Jr.); Kent G. Roller; Richard E. Brown; Virgil R. Friebel
Original assignee: Ball Brothers Research Corp
Current assignee: Ball Aerospace and Technologies Corp
Priority date: 1974-10-23
Filing date: 1975-10-22
Publication date: 1979-02-06
Also published as: DE2547363A1; IT1048325B; JPS5184786A; GB1525395A; FR2289456A1

Abstract

A B S T R A C T
A composition and method of preparation are herein described for molten release and parting com-positions adaptable for use in glass-forming operations.
The novel composition comprises an aqueous dispersion of a mixture of a solid lubricant, a water-soluble silicate binder, a setting agent, and a water-soluble phosphate. A preferred composition comprises a mixture of flake graphite, boron nitride, sodium silicate, zinc oxide and potassium phosphate tribasic.

Description

:~047705 The present invention relates to compositions of matter and methods of using said compositions. More partic-ularly, it relateq to compositions of matters useful as mold release and parting agents, for protecting and lub-ricating the surfaces of molds and other article-forming parts, especially such as are useful in the manufacture, forming and handling of glass articles or the like at high temperatures.
In glass manufacturing, a glob of molten glass is formed by a blank mold into a parison having a finished portion corresponding to the neck portion of the desired glass article. It is a requirement that the molding sur-face of the blank mold not become abraded or pitted so that the molten glass will readily flow over the molding surface of the mold, take the shape thereof, add then separate therefrom. Protection and lubrication are therefore re-quired. It is known that the glob of molten glass delivered to a glass forming machine has an average surface tempera-ture of about 1600 to 1700F. Thereafter, during the final process of shaping and forming, the molten glass has cooled to a temperature between about 1250 and 1350F. As can be appreciated, this cooling process renders the glass less plastic and often creates a dragging effect upon the mold-ing surface of the equipment. -Several practices have been followed in the past for the protection and lubrication of such molds used in forming glass articles. Typically, it has been the practice to apply to such molds various compositions or dopes con-taining a graphite compound or the like suspended in a carrier. Often hydrocarbons of some type, such as kerosene ~ .

have been used. Generally these compositions are applied by spraying, painting or swabbing during the forming opera-tions so as to provide lubrication of the interacting mold sections and to prevent sticking of the molten glass to the mold surfaces. It will be appreciated that there are some ~ -drawbacks in such compositions containing hydrocarbons as well as their method of application. Since the glass molds are at an elevated temperature, the hydrocarbon materials are quickly driven off into the atmosphere. Aside from the obnoxious odors, the vaporized materials create considerable volumes of smoke which reduce visibility, and produce upon condensation serious fire hazards which often times become progressively worse as the accumulation increases. Further, the application of the composition to various moving parts of the machine in actual production must be regularly re-peated a number of times on a regular basis which could re-sult in injury to the operators. Needless to say, these disadvantages have required that the industry employ other solutions to circumvent these undesirable conditions.
A number of aqueous systems have been employed with various degrees of success. Various mixtures and com-positions employing inorganic binders have been used for coating molds for their protection in which water is used as a carrier. Illustrative of these aqueous formulations containing an inorganic binder is one which consists of an inert refractory material such as clay, lampblack and a soluble silicate.
After investigation, it has been found composi-tions of matter which are thought advantageous in several respects over prior art compositions, particularly in their ,~ .

~047705 capacity to hold up and serve as a lubricant and parting agent under a wide range of rigorous commercial operations.
Accordingly, one aspect of the present invention provides effective compositions of matter suitable for coating molds used in casting or forming materials at high temperatures without emitting organic pollutants to the atmosphere.
A further aspect of the subject invention provides a parting and lubrication system which significantly m;nim;zes periodic swabbing or treat-ment of surfaces which come into contact with hot glass bodies.
From another aspect the present invention provides an improved parting and lubrication system which minimize the necessity of using conven-tional swabbing of surfaces which come in contact with hot glass articles.
Still another aspect of the present invention is to provide a part-ing and lubricating system for glassware molds which may be conveniently ap-plied away from and prior to the production process. -Yet still another aspect of the present invention is to provide a ~
lubrication system for glassware molds which produces a glass article of ex- --cellent quality. -~
Accordinglr, the present invention provides a release and lubricat-ing composition capable of rendering release and lubricating characteristics `
in excess of twenty hours d~ring glassware manufacture at temperatures in excess of 1600 F., said composition consisting essentially of an aqueous dis-persion of a mixture of boron nitride and graphite as solid lubricants, said solid lubricants being present in an amount between about 5 and 70 weight ~
percent of the aqueous dispersion, the weight ratio of said graphite to boron ~ -nitride being between a range of about 1:2 to about 5:1, a water-soluble silicate binder, said binder being present in an amount between about 10 and 40 weight percent, a setting agent for said silicate binder, said setting agent being present in an amount bet~e;en about 0.05 and about 15 weight per-.: -..

cent, and a water-soluble phosphate, said phosphate being present in an amount between about 1 and about 25 weight percent.
In a preferred form the invention provides a release and lubricating composition for forming molten glass at temperatures above about 1600 ~., said composition capable of rendering release and lubricating characteristics in excess of twenty hours, said composition consisting essentially of an aqueous dispersion of a mixture of about 5 to 70 weight percent of solid lubricants comprising graphite and boron nitride, the particle size of said boron ni-tride being between about 0.5 and 2 microns and the particle size of said graphite being between about 10 and 200 microns, the weight ratio of said graphite to boron nitride being between a range of about 1:2 to about 5:1, about 10 to 40 weight percent of sodium silicate binder, about 0.5 to 15 weight percent of a setting agent selected from the group consisting of zinc oxide, calcium chloride, magnesium sulfate, aluminum sulfate, sodium borate, sodium metaborate, sod~um fluorosilicate~ kaolinitic clays and mixtures thereof, 1 to 25 weight percent of potassium phosphate and about 0.01 to 3 weight per-cent of a wetting agent.
According to the present invention, surfaces which come in con-tact with hot plastic fluids such as molten glass may be properly lubri-cated by a composition comprising an aqueous dispersion of a mixture of a -solid lubricant, a water-soluble silicate binder~ a setting agent, ; ~ - 4a -and a water-soluble phosphate. Also, this invention re-lates to a method of forming a lubricating and release coàting on a surface which comes in contact with hot glass bodies in the manufacture of glass articles, comprising applying an aqueous dispersion of a mixture of a solid lubricant, a water-soluble silicate binder, a setting agent, and a water-soluble phosphate to said surface to be coated and removing the water from said dispersion to affix the coating thereon. As used herein, "dispersion" is used gen-erically to include sùspensions, solutions and mixtures.
The solid lubricant may be any of a large familyof inorganic components which have high temperature resis-tance characteristics. Illustrative of such solid lubri-cants are graphite, boron nitride, silicon nitride and tungsten disulfide. The graphite may be any of the various particulate forms, such as flake, electrolytic and colloidal graphite or conventional gràphite known to the trade. Fur- -ther it is understood that either natural or synthetic forms of graphite can be satisfactorily employed in accordance with the present invention. While particle size of the graphite is not critical, particles ranging from 10 to 200 microns are useful, and preferably particle sizes less than 75 microns should be employed. The nitrides of boron and silicon are very suitable solid lubricants. Further, com-binations of boron nitride and graphite are preferred solidlubricants. Generally, the particle size for such nitrides is between about 0.5 to 2 microns. The tungsten disulfide may also be employed, especially in a finely divided state, and generally, a particle size smaller than 2.0 microns is very suitable for the compositions herein described. The - .
." ' .' ', . - ,,, : .

amount of solid lubricant useful in the compositions herein described may range from about 5 to 70 weight percent of the aqueous dispersion.
The water-soluble silicates used in the process and compositions of this invention are those silicates of inorganic bases. Exemplary of such silicates are sodium silicate, potassium silicate and lithium silicate. Also, the organic silicates may be satisfactorily employed and include guanidine silicate, tetramethylammonium and tetra-ethanolammonium silicate. The preferred silicate is sodiumsi~icate. This silicate is readily available from commercial sources and includes aqueous solutions of sodium silicate having molar ratios of SiO2 to Na20 from 1:1, in the~case of sodium metasilicate, to as high as 3.9:1. Although the amount of silicate incorporated in the instant formulation may vary over a wide range, a preferred range is between about 10 to 40 weight percent of the aqueous dispersion.
It has been found essential to incorporate with the water-soluble silicate herein described a setting agent.
In general the term setting agent as employed herein denotes certain compositions that greatly enhance the usefulness of the coating compositions. Although the setting agents seemingly function as curing agents for the silicate, they also apparently function as buffers to allow any water in-corporated in the silicates or any water of crystallizationto leave the coating surface upon drying. Seemingly, the setting agents serve to tie up any water momentarily so that there is no burst of steam or bubbling on the surface. In this regard, it is understood that the setting agents herein described enhance the silicate of this invention, although 1~)477Q5 it is only hypothesized as to their specific functional characteristics. The se`tting agents used in the subject invention include zinc oxide, calcium chloride, magnesium sulfate, aluminum sulfate, sodium borate, sodium metaborate and sodium fluorosilicate, kaolinitic clays and minerals and mixtures thereof.
In the composition herein described it has been found a requirement to add phosphate component compound, said phosphate being water-soluble and neutral or alkaline when dissolved in water. Upon drying the phosphate component -;~
seemingly enhances the cohesive and retention properties of the silicate binder to a given surface. A most preferred phosphate is potassium phosphate tribasic.
In carrying out the process of this invention, it is generally desirable to clean the surface of the glass-forming equipment beforehand to remove all contamination such as metal oxides, loose particles, oil, dirt and the like to assure a better adhesion and longer life of the coatings. ~ -In treating molds and mold parts including blank molds, rings and the like with the compositions herein, the application and subsequent drying of these compositions may be carried out in a straightforward manner. Simply, the treatment of such molds and mold parts consists in applying the aqueous dispersion described herein and allowing the water to be evaporated or removed by heating. It is under-stood that the water in the aqueous dispersion may be re-moved by any number of convention means. Subjecting the - compositions herein to temperatures between about 300 and 400F. generally for a period of 30 minutes to one hour serves to adequately remove the water. The dispersions of the subject invention may be applied to the surface which contacts the hot plastic glass body by any of the normal or conventional means such as brushing, spraying, dipping, or blowing onto the surface. Spraying is preferred.
After removing the water from the mixture the release and lubricating compositions form a coating which adheres tenaciously to the surface in a thin, uniform coat-ing. The coating thickne~s may vary considerably depending upon, of course, the amount applied and may range between 0.5 and 5 mils. The coating itself is thermally stable, offers good oxidation resistance and allows for good heat transfer. Further, the compositions herein discussed are very effective in producing g~ass articles of excellent quality.
While the heating operation serves to drive off any water or other volatile constituents, it also sets the silicate and stabilizes the solid lubricant in the form of disseminated particles upon the surface with the result that a firmly adherent coating is produced. Because of the firm adherence and durability of the coating obtained in the foregoing manner, it is integrally bonded to such surfaces as compared to many superficial mold coatings and composi-tions of the prior art.
It is often found that wetting agents may be used in conjunction with the foregoing compositions. Wetting agents may be readily employed to facilitate dispersion of the solid lubricants and to stabilize the resulting disper-sion. A wide range of wetting agents are available and any of the conventional wetting agents can be utilized in conjunction with the subject invention.
In addition, thixotropic agents and the like may also be employed to achieve a desired fluidity. The pre-ferred thixotropic agent is sodium bentonite. Further, a ` 5 filler such as diatomaceous earth may be included.
The results obtained through use of the afore-described compositions demonstrate that the ordinary opera-tional life on conventional machines is many times greater than the operational life of other coatings. Further, by ~
the composition herein disclosed and claimed, there is -produced great savings in time and cost since it is now possible to operate glass-forming and handling equipment for considerably longer periods of operational time, as well -as to appreciably minimize the necessity of hand swabbing ~ -the lding equipment and other portions thereof that come in contact with hot glass bodies.
Although the present formulation and methods are ; addressed particularly to glass-forming machines and associ- -ated parts, it will be appreciated that such compositions and methods are also very useful for molds and the like -when parting and lubricating are necessary. Thus, the herein described composition may be useful in the metal forming industries such as for zinc, aluminum, and alloys thereof.
The following EXAMPLES are offered to illustrate the invention in detail:
EXAMPLE I
An aqueous dispersion comprising 31.8 weight percent sodium silicate, 25.4 weight percent graphite, 1.4 ~-weight percent sodium bentonite, 5.6 weight percent ~, .

. .

potassium phosphate tribasic, 5.1 weight percent zinc oxide 0.43 weight percent sodium alkyl sulfate and 30.1 weight percent water was made by adding 7.3 lb. sodium silicate (52 Baume), 5.9 lb. flake graphite, .33 lb. sodium bento-nite, 1.3 lb. potassium phosphate tribasic, 1.2 lb. zinc oxide, 0.1 lbs. sodium alkyl sulfate with constant mixing --with 6.9 lb. of water in a conventional ball mill for about 30 hours.
The aqueous dispersion was lightly sprayed by a spray gun over a cleanly prepared metal surface of a blank mold. The coated mold was placed in an oven for 30 minutes at 350F. The treated mold had a coating comprising 29.7 weight percent sodium silicate, 47.6 weight percent graphite, - -

2.68 weight percent sodium bentonite, 10.56 weight percent potassium phosphate and 9.50 weight percent zinc oxide. The m-thickness of the dried coating was about 2 mils.
The treated blank mold was used to product glass bottles without any swabbing. The coated mold performed satisfactorily and was used continuously for about 20 hours.
EXAMPLE II
An aqueous dispersion comprising 27.4 weight per- -cent sodium silicate, 21.9 weight percent boron nitride, 1.2 weight percent sodium bentonite, 4.8 weight percent potassium phosphate tribasic, 4.3 weight percent zinc oxide, 0.20 weight percent sodium alkyl sulfate and 40.3 weight percent water was made by adding 4.8 lb. sodium silicate (52 Baume), 3.8 boron nitride, 0.21 lb. sodium bentonite, 0.83 lb. potassium phosphate tribasic, 0.7 lb. zinc oxide, 0.03 lbs. sodium alkyl sulfate with constant mixing with 7.0 lb. of water in a conventional ball mill for about 30 1~4770.5 .

hours.
The aqueo~s dispersion was lightly sprayed by a ~ spray gun over a cleanly prepared metal surface of a blank Y~ mold. The coated mold was placed in an oven for 30 minutes at 350F. The treated mold had a coating comprising 29.8 weight percent sodium silicate, 47.8 weight percent graphite, 2.6 weight percent sodium bentonite, 10.4 weight percent potassium phosphate and 9.3 weight percent zinc oxide. The thickness of the dried coating was about 2 mils.
The treated blank mold was used to produce glass ; bottles without any swabbing. The coated mold performed satisfactorily and was used continuously for about 20 hours.
EXAMPLE III
An aqueous dispersion comprising 23.5 weight per-cent sodium silicate, 4.5 weight percent boron nitride, 13.6 weight percent graphite, 1.0 weight percent sodium bentonite, 4.2 weight percent potassium phosphate tribasic, 3.5 weight percent zinc oxide, 0.4 weight percent sodium alkyl sulfate and 48.5 weight percent water was made by adding 45 lb.
sodium silicate (52 Baume), 8.7 lb. boron nitride and 26.0 lb. graphite, 1.9 lb. sodium bentonite, 8.1 lb. potassium phosphate tribasic, 6.8 lb. zinc oxide, 0.7 lb. sodium alkyl sulfate with constant mixing with 9.3 lb. water in a conven-tional ball mill for about 30 hours.
The aqueous dispersion was lightly sprayed by a spray gun over a cleanly prepared metal surface of a blank mold. The coated mold was placed in an oven for 30 minutes at 350 F. The treated mold had a coating comprising 30.4 weight percent sodium silicate, 11.8 weight percent boron nitride and 35.1 weight percent graphite, 2.6 weight percent sodium bentonite, 10.9 weight percent potassium phosphate and 9.2 weight percent zinc oxide. The thickness of the dried coating was about 2 mils.
The treated blank mold was used to produce glass bottles without any swabbing. The coated mold performed satisfactorily and was used continuously for about 35 hours.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A release and lubricating composition capable of rendering release and lubricating characteristics in excess of twenty hours during glassware manufacture at temperatures in excess of 1600°F., said composition consisting essentially of an aqueous dispersion of a mixture of boron nitride and graphite as solid lubricants, said solid lubricants being present in an amount between about 5 and 70 weight percent of the aqueous dispersion, the weight ratio of said graphite to boron nitride being between a range of about 1:2 to about 5:1, a water-soluble silicate binder, said binder being present in an amount between about 10 and 40 weight percent, a setting agent for said silicate binder, said setting agent being present in an amount between about 0.05 and about 15 weight percent, and a water-soluble phosphate, said phos-phate being present in an amount between about 1 and about 25 weight percent.

2. A release and lubricating composition as recited in claim 1 wherein the boron nitride has a particle size of between about 0.5 and about 2 microns and graphite has a particle size of between about 10 and about 200 microns.

3. A release and lubricating composition as recited in claim 1 wherein the said water-soluble binder is an alkali metal silicate.

4. A release and lubricating composition as recited in claim 1, wherein the setting agent is a member selected from the group consisting of zinc oxide, calcium chlorate, magnesium sulphate, aluminum sulphate, sodium borate, sodium metaborate, sodium fluorosilicate, kaolinitic clays and mix-tures thereof.

5. A release and lubricating composition as recited in claim 1 wherein the water-soluble phosphate is potassium phosphate.

6. A release and lubricating composition for forming molten glass at temperatures above about 1600°F., said composition capable of rendering re-lease and lubricating characteristics in excess of twenty hours, said composi-tion consisting essentially of an aqueous dispersion of a mixture of about 5 to 70 weight percent of solid lubricants comprising graphite and boron nitride, the particle size of said boron nitride being between about 0.5 and 2 microns and the particle size of said graphite being between about 10 and 200 microns, the weight ratio of said graphite to boron nitride being between a range of about 1:2 to about 5:1, about 10 to 40 weight percent of sodium silicate binder, about 0.5 to 15 weight percent of a setting agent selected from the group consisting of zinc oxide, calcium chloride, magnesium sulfate, aluminum sulfate, sodium borate, sodium metaborate, sodium fluorosilicate, kaolinitic clays and mixtures thereof, 1 to 25 weight percent of potassium phosphate and about 0.01 to 3 weight percent of a wetting agent.