WO1991019606A1 - Method for enhancing the strength of a glass container and strength enhanced glass container - Google Patents

Abstract

A method for enhancing the strength of glass containers is presented wherein the containers are preheated to 500 °C and coated with the strength enhancement coating within six (6) hours after the heat treatment. In one embodiment, a coating station (26) for the strength enhancing coating is located between the exit from a lehr (18) and a cold end spray station (20). In a second embodiment, the strength enhancing coating station (26) is positioned downstream of the cold end station (20).

Description

METHOD FOR ENHANCING THE STRENGTH OF A GLASS CONTAINER AND STRENGTH ENHANCED GLASS CONTAINER

Background of the Invention;

This invention relates to the field of glass containers. More particularly, this invention relates to the field of strength enhancement for glass containers. The present invention will be described with reference to bottles, but it will be understood that as used herein, the term "glass container" is intended to include all types of glass articles used for the storage and/or containment of various substances, including, for example, bottles, jars, tumblers, glasses, etc.

It is well known in the glass container industry that flaws on the surface of a bottle (e.g., chips, nicks, scratches and similar blemishes) result in significant reduction in the strength of the bottle.

Such blemishes may occur at any time during the life of the bottle, such as in the manufacturing process when the bottles are brought into contact with each other at various stages of manufacture, in the filling stage where contents are introduced into the bottle, in handling, inspection, packaging, or shipping, or in consumer use of the bottle. These blemishes reduce both the burst strength of the bottle, i.e., the resistance to internal pressure loading and the impact strength of the bottle, i.e., the resistance to external impact loading.

The flaw sites on the surface of a bottle are stress concentration sites, and breakage tends to occur at such stress concentration sites. It is also known that water on the surface of a bottle contributes to strength degradation and bottle failure. Chemically absorbed water forms hydroxyl bonds with silica, and this tends to further weaken the bottle at the site of any flaw. Thus, the strength of a bottle degrades over time.

The problems with flaws and degradation of bottle strength are particularly acute with bottles that contain carbonated liquids or other pressurized contents, such as soda, beer, champagne, etc. Bottles with such contents are under substantial internal pressure, and surface flaws can lead to bursting of the bottle (either spontaneously or as the result of a small impact load that would not affect an unflawed, or less flawed, bottle) . As well as resulting in loss of the contents of the bottle, such bursting poses a threat of injury to anyone in the vicinity from glass fragments, and it also results in a substantial mess that has to be cleaned up.

Within the glass container industry attempts have been made to address the problem of bottle flaws by applying "hot end" and/or "cold end" coatings to the bottles during the manufacturing process to serve as damage prevention coatings. That is, the purpose of such coatings is to serve as a protective layer to prevent or reduce the occurrence of scratches, nicks and similar flaws during the manufacturing process to thereby prevent degradation of bottle strength.

Another approach has been to apply to bottles a coating that acts to retain glass fragments when a bottle is fractured. While some of these coatings referred to above purport to enhance the impact resistance of glass containers, these coatings do not enhance the burst strength of the bottles to which the coating is applied.

Summary of the Invention:

In accordance with a first embodiment of this invention, a coating is applied to glass container to enhance the burst and impact strength of the containers. The coating can be applied to new bottles during the manufacturing process, or the coating can be applied to used bottles in the course of bottle recycling. While use of the process of the first embodiment during the manufacture of new bottles should be of special interest to bottle manufacturers, the use of the process for treating recycled bottles should also be of considerable interest and importance in view of increased environmental concerns and the expansion of recycling practices, whether voluntary or mandatory. The material used for the coating in both the first and second embodiments of the present invention is a film forming acrylate monomer, a crosslinking acrylate monomer, a silane adhesion promoting agent reactive with glass and with additional functionality capable of reacting with acrylates, a curing agent, and additives (such as surface active agents, cure speed enhancers, flow agents) . Important aspects of the process of the first embodiment are that (1) the bottles be heated prior to application of the strength enhancing coating, with new bottles being heated to the annealing temperature of 550°C and recycled bottles being heated to at least 500°C and (2) that the strength enhancement coating be applied within six (6) hours after the bottles have been returned to room temperature (RT) . With newly manufactured bottles, best results are obtained if the coating is applied immediately after the bottles exit from the annealing lehr (where the bottle temperature may be anywhere between 50 C and 200 C) or within one hour after the bottles leave the annealing lehr. In the manufacture of new bottles the strength enhancing coating of the first embodiment is applied before the cold and coating to bottles that have been heated to the annealing temperature of 550°C and cooled in a lehr; or the coating can be applied in lieu of the cold end coating if a sufficiently lubricious hot end coating is used whereby the cold end coating can be eliminated. Alternatively, if the manufacturing process eliminates the hot end coating, the coating of the first embodiment is still to be applied prior to or in lieu of the cold end coating. For application of the coating to recycled bottles, the bottles must be heated to the range of 500°C - 520°C, preferably, to at least 510°C before the strength enhancing coating is applied. It is important to note that this temperature is below the annealing temperature of glass, thereby eliminating the need for a long controlled cool-down required when the annealing temperature is reached. In accordance with a second embodiment of this invention, the strength enhancement coating is applied after and over the conventional cold end coating in the manufacture of new bottles. The second embodiment involves the discovery that the strength enhancement coating can be applied over a cold end coating and still produce an effective strength enhancement. This is unexpected and surprising, and it is of particular interest in the manufacture of new bottles, but is also useful in bottle recycling.

It should be understood that either embodiment of the present invention can be used either to increase the strength of newly formed bottles or to make thinner and lighter bottles having the strength of thicker and heavier bottles.

As indicated above, the material used for the coating in both the first and second embodiments is a film forming acrylate monomer, a crosslinking acrylate monomer, a silane adhesion promoting agent with additional functionality capable of reacting with acrylates, a curing agent and additives.

The class of film forming monomers suitable for use in the invention includes the following examples: ethylene glycol dimethacrylate, 1,6 hexanediol di(meth)acrylate, neopentyl glycol diacrylate, ethoxylated bisphenol A di(meth)acrylate, 2-ethoxyethyl (meth) acrylate, isobornyl acrylate, tetrahydrofurfuryl (meth)acrylate and many others known from the literature and commercial suppliers. The class of crosslinking agents suitable for use in the invention including the following representative examples: trimethylolpropane trimethacrylate, ditrimethylolpropane tetraacrylate, triacrylate of tris (2-hydroxyethyl) isocyanurate, pentaerythritol triacrylate. The class of silane adhesion promoters suitable for use in the invention includes the following representative examples: methacryloxypropyltrichlorosilane, methacryloxypropyl- methyldiethoxysilane, mercaptopropylmethyl dimethoxysilane, mercaptopropyltrimethoxysilane, mercaptomethylmethyldiethoxy- silane, acryloxypropylmethyl dichlorosilane, aminophenyl- trimethoxysilane, 3-aminopropyltrimethoxysilane, 4-aminobutyl- triethoxysilane.

The class of photoinitiators suitable for use in the invention includes the following representative examples: benzil, benzophenone, camphorquinone, benzoin n-butyl ether, thioxanthone, isopropyl thioxanthone, 2,2-dimethoxy-2-phenyl- acetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-benzyl-2-N-Dimethylamino 1- (4-morpholinoρhenyl-l-butanone)

For both embodiments of the invention, the coating is cured by UV irradiation. It should also be obvious to those skilled in the art that thermally activated free-radical initiators may also be used either in conjunction with photoinitiators or by themselves for curing. Examples of these compounds include: azobisisobutyronitrile, paramethane hydroperoxide, benzoyl hydroperoxide, pinane hydroperoxide, azobiscyanovaleric acid and dicumyl peroxide.

Description of the Drawings:

FIGURE 1 shows a schematic of a glass container manufacturing line in accordance with the first embodiment.

FIGURE 2 shows a schematic of a glass container manufacturing line in accordance with the second embodiment. Description of the Preferred Embodiment:

FIGURE 1 shows a schematic of a glass container manufacturing line. The line shown in FIGURE 1 is conventional except for the addition of the strength enhancement coating station between the exit from the lehr and the cold end spray station. In the conventional manufacturing process, molten glass is delivered from a furnace 10 to molds in a forming machine 12 where the bottles are formed. The bottles then move in a single line on to a hot end coating hood 14 where a thin (typically a few Angstroms thick) coating of tin oxide (or titanium oxide) is formed on the bottle. The bottles are then formed into a multi-bottle row and are moved by a push bar 16 onto a conveyer belt which carries the rows of bottles through annealing lehr 18 where the bottles are heated to the annealing temperature of about 550 C and then cooled to a lehr exit temperature of from 50 C to 200°C (typically, about 100-120°C) . After exiting the lehr, the bottles, in conventional manufacture, pass through a cold end coating station 20 where a thin (typically 0.5 Angstroms thick) cold end coating is applied. The cold end coating is a lubricious coating to permit the bottles to slip or slide by each other to minimize impact damage between contacting bottles in subsequent manufacturing steps. The bottles then return to single line formation and are then delivered to an inspection line 22 and then to a palletizer 24 for packaging. In accordance with the first embodiment of this invention, a strength enhancement coating station 26 is added to the conventional manufacturing line at a location between the exit from lehr 18 and the cold end spray station 20. At strength enhancement coating station 26, the bottles are coated with the strength enhancement coating to achieve a significant enhancement of strength. The coating delivered at station 26 is a thin film of a film forming acrylate monomer, a crosslinking acrylate monomer, a silane adhesion promoting agent (to promote binding of the film to the bottle) with additional functionality capable of reacting with acrylates, a UV curing agent, and additives (such as, for example, surface active agents, cure speed enhancers, flow agents). The ingredients can be mixed together to form a neat formation to be applied to the bottles in a single application step, or the ingredients can be diluted with suitable solvents (such as, e.g., methyl ethyl ketone) . Alternatively, a two step process can be employed, with the silane adhesion promoting agent being applied first to the outer surface of the bottles, and the rest of the ingredients then being applied as a separate mixture in a second step. The coating is cured at station 26 by exposure to UV radiation until it is tack free (usually requiring about 1-5 seconds of UV exposure) . Any suitable bottle handling apparatus can be used at station 26 to dip or spray coat the bottles so that preferably the full exterior surface (including the bottom) of each bottle will be coated. Alternatively, the coating could be applied to only those portions of the bottles most susceptible to breakage.

For examples 1-10 discussed in more detail hereinafter relative to the first embodiment, the following neat mixtures were prepared and used: MIXTURE 1

For examples 1-6, 8, 10 and 11 the following neat mixture was prepared and applied by dip coating slides or bottles followed by an approximate hang time of 10 minutes. The film thicknesses after UV curing ranged from 0.75 micron up to 10 microns on some areas of the bottles.

71 gm 1,3 butylene diacrylate (Sartomer 297) 23 gm trimethylolpropane triacrylate

(Sartomer 351)

1.5 gm methacryloxypropane trimethoxy silane (Petrarch Chemical Co.)

5.0 gm 2-hydroxy-2 methyl-1 phenylpropan-1-one E. Merck

(Darocure 1173)

MIXTURE 2

For example 7 the neat mixture below was used to dip coat slides which were then hung for 10 minutes. The final thickness after UV curing of the film was approximately 1 micron.

50 gm 1H, 1H, 5H octafluoropentyl acrylate (PCR Chemical Co.)

10 gm trimethlolpropane triacrylate 20 gm 1,3 butylene glycol diacrylate

14 gm methacryloxypropane trimethoxysilane

6 gm 2-hydroxy-2 methyl-1 phenylpropan-1-one (D1173) MIXTURE 3

Example 9 was performed using the mixture listed here which produced an approximately 1 micron thick coating after dip coating, hanging for 10 minutes and UV curing.

70 gm 1,3 butylene glycol diacrylate

10 gm trimethlolpropane triacrylate

14 gm methacryloxypropane trimethoxysilane

6 gm 2-hydroxy-2 methyl-1 phenylpropan-1-one (D1173)

In some of the examples discussed below, bottles were treated in accordance with the present invention and then burst tested; and the results were compared to similar untreated bottles. In other of the examples, glass slides were treated in accordance with the present invention, and then broken on a tensile tester; and the results were compared to similar untreated glass slides (such testing of glass slides being an accepted test method for determining strength and other properties of glass) .

The standard procedure used for treating glass slides (Standard Procedure 1) was as follows:

1. Microscope slides (1" x 3" x 0.25") were visually selected to be free of gross defects, especially at the edges.

2. The slides were purposely flawed, either by a Vickers indentation, or by grit blast abrasion.

3. The flawed slides were then heat treated, some without water aging and others after water aging as indicated in the examples. 4. After the heat treatment, the slides were dip coated at room temperature (about 25°C) with the strength enhancing coating, and the slides were hung to dry for about 10 minutes. (Reference or control slides were not coated.)

5. The slides were then exposed to ultraviolet irradiation from Fusion Co. mercury lamps to cure the coating until tack free.

6. The slides were then broken by a four point bend test on an Instron tensile tester. The breaking load is referred to as inert strength.

7. The breaking stresses of the treated slides were compared with the breaking stress of untreated slides (which were broken as in step 6) to generate strength enhancement data and ratios.

Reference or control slides were treated as above, except that they were not exposed to steps 4 and 5.

The standard procedure used for treating new glass bottles (Standard Procedure 2) was as follows: (1) Freshly formed containers (pressure ware; beer or soda bottles) on a production line were carefully picked off the line just after the molding operation using gloved personnel. The bottles selected were all formed in the same mold. These bottles were marked for identification, and placed back on the line upstream of the hot end coating (tin oxide) for application of the hot end coating before entering the lehr.

(2) The bottles were passed through the lehr for heat treatment (where the bottles were heated to or above the annealing temperatures of 550 C) and control cooled to at or near room temperature. (3) These same bottles were then taken off the line after the lehr but before the cold end application section. All bottles were then scribed with a glazier's wheel (silicon carbide) on the center sidewall creating a scratch about one inch in length.

All bottles were packed carefully into cases where they were individually protected These cases were transported to an off-line station.

(4) The bottles were dip coated with the strength enhancing coating. Coating was performed by dipping the bottles individually in the formulation in a stainless steel container kept at 50 C. The bottles were allowed to sit for 10 minutes to drain. Reference or control bottles were not coated. (5) The bottles were then cured by exposure to UV irradiation. Curing was done by inverting the bottles on a turn-table pedestal and irradiated with three Fusion Co. mercury lamps until the coating surface was tack free. (6) Strength values were determined by bursting the containers on an American Glass Research (AGR) Co. pressure tester. Water was pumped into the containers until they burst and the pressure recorded. The bursting load is referred to as inert strength. (7) The bursting loads of the treated bottles were compared with the bursting loads of untreated bottles (which were broken as in step (6) to generate strength enhancement data and ratios.

Reference or control bottles were treated as above, except that they were not exposed to steps 4 and 5. For both the slides and the bottles tested, fracture origin was at the sites of the induced flaws. For the data obtained in the test, strength enhancement ratio (SE) is defined as the ratio of the mean of the fracture loading value for the coated population

(bottles or slides) to the mean of the fracture loading value for the untreated population.

Heat treatment prior to application of the strength enhancing coating is an important feature of the present invention; and application of the strength enhancing coating upon exiting of the bottles from the lehr or within six (6) hours after reaching room temperature is also an important feature of the invention. Preferably, bottles should be heated above the annealing temperature of 550 C. That is easily accomplished as part of the manufacturing process for new bottles which are heated to or above the annealing temperature and control cooled in the lehr. However, for used bottles being recycled it may not be practicable to heat the bottles to the annealing temperature and then go through the required controlled cool down. For recycled bottles, the bottles should be heated to a temperature of from about 500°C to about 520°C, preferably, from about 510°C to 520°C, which will be sufficient to relieve stresses in the glass but which should not be so high as to require annealing controlled cool-down.

The following examples 1-10 illustrate the first embodiment and it's features and advantages. EXAMPLE 1

Groups of twelve newly formed commercial pressure ware bottles were selected and treated in accordance with Standard Procedure 2 set forth above, so as to be intentionally flawed and have a UV cured coating of strength enhancing Mixture 1 thereon. Groups of twelve bottles, newly formed at about the same time from the same mold but without the strength enhancing coating, were also selected for reference purposes. All of the bottles were heated to at least the annealing temperature of 550 C and subjected to controlled cool down in a lehr. Both the test and reference bottles were intentionally flawed by forming a one inch scratch on the center sidewall with a (silicon carbide) glazier's wheel. Water was then pumped into each of the bottles to load the bottles to bursting on an AGR pressure tester, and the burst pressure was recorded. This test was performed for four groups of coated bottles. In Group 1, the bottles were coated with Mixture 1 immediately after the bottles reached room temperature (RT) after exiting from the lehr. In Group 2, the bottles were coated one hour after reaching room temperature, i.e. RT + 1 HR. In Group 3 the bottles were coated six hours after reaching room temperature. In Group 4, the bottles were coated after a 16 hour water immersion. Except for coating and UV cure, the strength enhancement (SE) ratio for these bottles as compared to the similarly treated but uncoated bottles was as follows: CONDITION SE RATIO

AT COATING COATED/UNCOATED

Group 1 RT 2.2

Group 2 RT+1 HR 1.80

Group 3 RT+6 HRs 1.93

Group 4 RT+16 HRs 1.50 water immersion

Separate groups of 12 uncoated bottles each were used as control or reference groups for the coated bottles of Groups 1 - 4. Except for coating and UV cure, each of the control groups was treated the same as the coated bottles for which it was used as a reference.

Example 1 shows a significant strength enhancement for the coated bottles. It also shows that strength enhancement was greatest for those bottles coated immediately after RT was reached; that substantial strength enhancement was achieved when the bottles were coated 6 hours after reaching RT (the ratios of 1.80 and 1.93 being considered essentially the same); and that strength enhancement dropped off for the Group 4 bottles, which represent an extended aged condition of the bottles before coating. EXAMPLE 2

In this example, several groups of ten (10) slides each were selected and treated in accordance with Standard Procedure 1 set forth above. Groups of 10 slides were designated as the control or reference groups, and these groups were heat treated but not coated with a strength enhancing coating. Five groups of 10 slides each were heat treated by heating to 600°C for 1 hour and then cooled to room temperature of 32°C in a chamber of 55% relative humidity. All of the slides, heat treated and control, were purposely flawed by Vickers indentation at 3 kg loading. Groups of 10 slides each were then coated with Mixture 1, and UVcured at RT, Rt + 1 HR, RT + 6 HRs, and RT + immersion in boiling water for 30 minutes (to simulate aging) . The breaking stresses in thousands of pounds per square inch (ksi) for all groups (coated and control) and strength enhancement data were as follows:

The results of Example 2 confirm the results of Example 1 for recycled glass which is heated above the annealing temperature. Table 1 shows the SE ratio results for the various groups of bottles and slides of Examples 1 and 2 normalized to room temperature. This shows that the level of strength enhancement falls of with increased passage of time between reaching room temperature and the application of the strength enhancing coating (the water immersion and water boil being aging procedures) .

TABLE 1

CONDITION SE RATIO NORMALIZED TO RT AT COATING BOTTLES SLIDES

RT 1.00 1.00

RT+1 Hr. 0.82 0.92

RT+6 Hrs. 0.88 0.79

RT+24 Hrs. 0.73

RT+16 Hrs. 0.68 0.56 water immersion

RT+0.5 Hr. 0.45 boil

EXAMPLE 3

In this example, groups of 10 slides each, coated and uncoated, were tested for the effects of different flaw sizes. The slides were treated as per Standard Procedure 1 (the coating step being omitted for the uncoated slides). For one test, groups of 10 slides each were flawed by 3 kg Vickers loading and then heated to 600°C for 1 hour. Two groups were then coated with Mixture 1, and two other groups were left uncoated. The slides were then loaded to the breaking point on the Instron tester. This test was repeated for three groups of 10 slides each with the only difference being that the flaw was effected by 750g Vickers loading. The results were as follows:

INSERT SE COATED/

CONDITION STRENGTH.ksi UNCOATED

Group 3 kg Vickers; 23.1; 21.3 3.3; 2.56 1 and 2 600°C/1 Hr.; RT COATED

Group 3 kg Vickers; 7.0; 8.3 3 and 4 600°C/1 Hr.; UNCOATED

Group 750 g Vickers; 25.3; 23.6; 2.02; 1.98; 5 thru 7 600°C/1 Hr.; 24.4 2.26 RT COATED

Group 750 g Vickers; 12.5; 11.9; ) 8 thru 600°C/1 Hr. ; 10.8 10 UNCOATED

The results of Example 3 indicate that significant strength enhancement is achieved for both smaller and larger flaws, and that greater strength enhancement is achieved for more serious flaws.

This is particularly important in that it means that more severely damaged bottles (i.e., those closer to failure limits) are strengthened proportionally more than less seriously flawed bottles. The practical effect of this is that those bottles most in need of strength enhancement are, in fact, those that experience the needed enhancement. For a bottle manufacturer, this means that design limits, which are predicted on the weakest bottles in a normal production population, can be raised because this invention has strengthened what would otherwise be the weakest part of the bottle population. EXAMPLE 4

The procedure of Example 3 was repeated for three groups of 10 slides each. The slides were all subjected to 3 kg Vickers loading and all slides were coated with Mixture 1. The variable in this test was the temperature at which the slides were coated after heat treatment to 600 C for 1 hour. One group was coated at RT, a second group was coated at 200°C, before reaching RT and a third group was coated at

440000°°CC,, bbefore reaching RT. The results were as follows:

INERT

CONDITION STRENGTH.ksi

Group 1 3 kg Vickers;600°C/ 23.1 1 HR; RT COATED

Group 2 3 kg Vickers;600°C/ 24.0 1 HR;200°C COATED

Group 3 3 kg Vickers;600°C/ 27.5 1 HR;400°C COATED

These inert strengths are viewed as essentially the same. The results of this example indicate that the temperature at which application of the strength enhancing coating takes place does not matter as long as the glass is properly heat treated prior to coating.

EXAMPLE 5

The procedure of Example 4 was repeated for two groups of 10 slides, each group being coated at 400°C. The variable was that one group was cooled to RT and then heated to 400°C for coating; the other group was coated at 400 C before reaching RT. The results were as follows:

INERT

CONDITION STRENGTH.ksi

Group 1 3 kg Vickers;600°C/ 24.8 1 HR; COOLED TO RT: HEAT TO 400°C COATED

Group 2 3 kg Vickers;600°C/ 27.5 1 HR;400°C COATED

These inert strengths are viewed as essentially the same. The results of this example also indicate that the strength enhancing coating can be effectively applied prior to or after the glass has been cooled to RT, as long as the glass is properly heat treated prior to coating.

EXAMPLE 6

The procedure of Example 3 was repeated for three groups of 10 slides each, with the variables being water immersion (to simulate aging) and heat treatment. All of the slides were heated to 600°F for 1 hour. One group was coated at RT. A second group was cooled to RT, aged in water for 24 hours, and then coated at RT. A third group was cooled to RT, aged 24 hours (without water immersion), and then heated to 400°C and coated. The results were as follows:

INERT

CONDITION STRENGTH.ksi

Group 1 3 kg Vickers;600°C/ 23.1

1 HR; RT Coated;

Group 2 3 kg Vickers;600°C/ 13.3

1 HR; Cool to RT; age in H2O 24 Hours; RT Coated;

Group 3 3 kg Vickers; 600°C/ 22.3

1 HR; Cool to RT; age 24 Hours; 400°C coated

The results of this example indicate that:

(1) the beneficial effects of the strength enhancement coating are significantly reduced or lost by long delay in coating (the water immersions of the Group 2 slides simulating extended aging before the coating was applied) , and

(2) the beneficial effects of the coating can be obtained even after 24 hours of RT aging if the glass is heated to 400 C for coating.

EXAMPLE 7

In this example, Standard Procedure 1 was followed for a plurality of groups of 10 slides each, some coated and some uncoated, except that the heat treatment was varied. The variations in heat treatment are indicated in the "Pretreatment" column below. An entry "NONE" means there was no heat treatment for either the coated or uncoated slides. The entries of 100°C, 300°C, etc. mean that the slides were heated to the indicated temperature, allowed to cool to RT, and then coated with the strength enhancing coating at the indicated times after the temperature was reached (e.g., RT + IM (immediate); RT + 1 Hr., RT + ID (day) etc.). The other header columns listed below are Group No. (self explanatory); T/B Hrs. = hours between time of coating and placing the slides on the machine to be cooled to breaking; % H @ B = relative humidity at break; SE % = mean increase in inert strength (at break), i.e., % strength enhancement expressed as a percentage increase relative to uncoated slides rather than as a ratio as in previous examples; X = mean load at break for 10 slides; = 1 standard deviation; X - 3 = 3 standard deviations; RE = relative error. The coating in this example was Mixture 2. The tests of this example took place over about two weeks. Group members in this data refer to the dates on which the various tests were conducted (i.e., all group 1 tests were on the same day, etc.). The results of this example are as follows:

EET The results of this example show that while varying degrees of strength enhancements are obtained for all coated slides, consistently significant increases in inert strength, and consistently significant strength enhancement was realized when the slides were heated to at least 500°C and the strength enhancement coating was applied within six (6) hours of the completion of the heat treatment. Maximum strength enhancement occurred when the slides were heated to 500-575°C. These results also show that the "window" of time within which to apply the coating after heat treatment and still obtain significant strength enhancement increases to a day or more as the heat treatment temperature increases above 500 , at least at the relatively low relative humidities at which these tests were performed. These results are of particular interest in regard to the recycling of used containers.

EXAMPLE 8

In this Example, Standard Procedure 1 was followed for groups of 10 glass slides flawed at 3 kg Vickers and heat treated to 600 C for 1 Hr. and then cooled to RT. The slides were then water aged either by water immersion for 16 hours or 0.5 Hr. boil, and then groups of the slides were coated, either with or without reheating. The results of this example are as follows:

SE RATIO

CONDITION COATED/UNCOATED

Group 1 3 kg Vickers; 600°C/ 1.71 1 HR; Cool to RT: age in H2O 16 Hrs.; RT coated

Group 2 3 kg Vickers; 600°C/ 1.37

1 HR; Cool to RT: H₂0 boil 0.5 HR; RT coated

Group 3 3 kg Vickers; 600°C/ 2.93

1 HR; Cool to RT: age in H₂0 16 HR; heat to 400°C; RT coated

Group 4 3 kg Vickers; 600°C/ 2.44

1 HR; Cool to RT; age in H₂0 16 HR; heat to 200°C; 200°C coated

Group 5 3 kg Vickers; 600°C/ 2.05

1 HR; Cool to RT; age in H₂0 16 HR; heat to 200°C; RT coated

The results of this example indicate that the effects of aging on heat treated glass (as simulated by water immersion and/or boiling) can be somewhat offset by reheating to about 400°C before coating with the strength enhancing coating. That result may be due to the fact that heating to 400°C will drive off all physically adsorbed water.

-27-

EXAM LE 9

In this Example Standard Procedure 1 was followed for four groups of 10 slides, coated and uncoated, which were flawed by grit blast abrasion. The four groups of slides were coated at RT after no heat treatment, heating to 520°C for 1 Hr., hating to 520°C for 8 Hrs., and heating to 600°C for 1 Hr. The coated slides were compared to similarly treated uncoated slides. Mixture 3 was used for the coating of this example. The results are as follows:

The results of this example indicate that consistently significant strength enhancement is achieved by heat treating to 520°C and coating with the strength enhancement coating. Additional increases inert strength are noted when the heat treatment is increased to 600°C. However, that additional increase in inert strength is apparently attributable to stress relief occurring as the result of heating the glass to or beyond the annealing temperature, since no additional strength enhancement was noted.

EXAMPLE 10

Groups of twelve newly formed commercial pressure ware bottles were selected and treated in accordance with Standard Procedure 2 set forth above, so as to be intentionally flawed and have a UV cured coating of strength enhancing Mixture 1 thereon. Groups of twelve bottles, newly formed at about the same time and from the same mold but without the strength enhancing coating, were also selected for reference purposes. All of the bottles were heated to at least the annealing temperature of 550 C and subjected to controlled cool down in a lehr. The reference bottles were also intentionally flawed by forming a scratch on the center sidewall with a (silicon carbide) glaziers wheel. Water was then pumped into each of the bottles to load the bottles to bursting on an AGR pressure tester, and the burst pressure was recorded. This test was performed for several groups of coated bottles and similarly treated uncoated bottles. The results are as follows:

SE

CONDITION RATIO

AT INERT STRENGTH (MEAN) (1)COATED/ COATING COATED UNCOATED UNCOATED

Group 1 AM mfg; 420 135 3.11

20 min. coated

Group 2 PM mfg; 419 165 2.54

20 min. coated Group 3 Day2 mfg; 423 148 2.86

20 min.coated (1) psi of the water at burst

The bottles in Group 1 were manufactured in the morning of a given day; the bottles in group 2 were made in the afternoon of that same day; the bottles in Group 3 were made the next day.

The results of this example indicate that significant increases in inert strength and SE ratio are achieved by this invention for newly formed bottles having a range of surface flaws over a range of normally varying production conditions.

The data of the examples 1-10 indicate some surprising and unexpected results. It is known that water is physically absorbed on the surface of glass, and that water is a negative for strength enhancements because it interferes with the bonding of strength enhancing coatings to the glass. It is also known that this physically absorbed water begins to be driven off if the glass is heated to about 100°C, and substantially all of this physically absorbed water is driven off at about 400°C. It has also heretofore been thought that the efficacy of strength enhancement coatings could be improved by heating the glass to 400 C to drive off the physically absorbed water to thereby promote bonding of strength enhancing coatings to the glass. If that were the case, the data should have shown a marked improvement at 400 C; but that was not the case with this invention. In accordance with the second embodiment, the strength enhancing coating is applied downstream of and after the application of a conventional cold end coating, or perhaps a modified version thereof. FIGURE 2 illustrates the second embodiment where the strength enhancing station 26 is located downstream of the cold end spray station 20. Station 26 is shown at a location where the bottles are in multi-bottle rows. However, the strength enhancing station could be located downstream of the point where the rows of bottles converge to form a single line, because the lubricating effects of the cold end coating are available for the transition to the single line arrangement of bottles.

For the examples of the second embodiment, the following mixture was used:

MIXTURE 4

56 gm 1,3 butylene glycol diacrylate

23 gm trimethlolpropane triacrylate

1.5 gm methacryloxypropane trimethoxysilane

20 gm 2-hydroxy-2 methyl-1 phenylproρan-1-One

In the following examples 11 and 12 Standard Procedure 3 for new glass bottles was used as follows: (1) Freshly formed containers (pressure ware; beer or soda bottles) on a production line were carefully picked off the line just after the molding operation used gloved personnel. The bottles selected were all formed in the same mold. These bottles were marked for identification. Some bottles were placed back on the line upstream of the hot end coating (tin oxide) for application of the hot end coating before entering the lehr. Some bottles were placed back on the line downstream of the hot end coating but before the lehr, so they did not receive a hot end coating.

(2) The bottles were passed through the lehr for heat treatment (where the bottles were heated to or above the annealing temperatures of 550 C) and control cooled to at or near room temperature.

(3) After exiting the lehr, the bottles were taken off the line and were then scribed with a glazier's wheel (silicon carbide) on the center sidewall creating a scratch about one inch in length. (4) A cold end coating was then applied to the bottles by hand spraying. Except for oleic acid, the cold end coating was applied by hand spraying rather than at station 20 because the experiment required application of several different cold end coatings. The oleic acid was applied by a commercial vapor hood. All bottles were packed carefully into cases where they were individually protected. These cases were transported to an off-line dipping station station.

(5) The bottles were dip coated with the strength enhancing coating. Coating was performed by dipping the bottles individually in the formulation in a stainless steel container kept at 50°C. The bottles were allowed to sit for 10 minutes to drain. Reference or control bottles were not coated. (6) The bottles were then cured by exposure to UV irradiation. Curing was done by inverting the bottles on a turn-table pedestal and irradiated with three Fusion Co. mercury lamps until the coating surface was tack free.

(7) Strength values were determined by bursting the containers on an American Glass Research (AGR) Co. pressure tester. Water was pumped into the containers until they burst and the pressure of the water at burst was recorded. The bursting load is referred to as inert strength.

(8) The bursting loads of the treated bottles were compared with the bursting loads of untreated bottles (which were broken as in step 6) to generate strength enhancement data and ratios.

Reference or control bottles were treated as above, except that they were not exposed to steps 5 and 6. The following examples 11 and 12 illustrate the second embodiment:

EXAMPLE 11

In this example, groups of 12 bottles each were treated as per Standard Procedure 3 and coated with strength enhancing Mixture 4. Some groups of bottles were given a hot end (HE) coating, and some were not hot end coated. Different groups of bottles were given the following cold end coatings: P110 Polyethylene AP5 Oleic Acid GL1000 Beeswax Stearate

AP5 Oleic Acid and P110 Polyethylene (two successive groups) Control or reference groups of 12 bottles each were also established by treating as above, but omitting the strength enhancement coating. Master control groups were formed by omitting the cold end coating. The results were as follows:

SE

COLD HOT RATIO

END END INERT STRENGTH (MEAN) COATED/

COATING COATING COATED UNCOATED UNCOATED

Group 1 No Yes 430 196 2.19 Group 2 No No 465 132 3.52

Group Yes 192 134 1.43

3 Polyethylene

Group No 272 140 1.94

4 Polyethylene

Group Yes 202 116 1.74

5 Beeswax

Group No 315 147 2.14

6 Beeswax

Group Yes 125 137 0.91

7 Stearate

Group No 171 135 1.27

8 Stearate

Group Yes 368 137 2.69

9 Oleic Acid

Group No 310 143 2.17

10 Oleic Acid

Group Yes 183 147 1.24

11 Oleic Acid/ Polyethylene

Group No 184 152 1.21

12 Oleic Acid/ Polyethylene These results show that significant strength enhancement is achieved for bottles which are coated with the strength enhancement coating applied over a cold end coating, with an SE Ratio of 1.4 or above being considered significant. The results also show that some cold end coatings may be less suitable or undesirable for use with this invention. The results generally show a higher SE ratio when there is not hot end coating, but Groups 9 and 11 showed a higher SE ratio when a hot end coating was present. That may have been due to lack of proper control in applying the strength enhancing coating, i.e., a heavier coating may have been applied. If so, it shows an advantage for this invention in that good results can be obtained without precise control over the thickness of the strength enhancing coating.

EXAMPLE 12

In this example, groups of 12 bottles each were treated as per Standard Procedure 3 and coated with strength enhancing Mixture 4. Some groups of bottles were given a hot end (HE) coating, and some were not hot end coated. Different groups of bottles were given the following cold end coatings: P110 Polyethylene AP5 Oleic Acid

GL1000 Beeswax Stearate

AP5 Oleic Acid and P110 Polyethylene Water Spray Control or reference groups of 12 bottles each were also established by treating as above, but omitting the strength enhancement coating. Master control groups were formed by omitting the cold end coating. The results were as follows:

Groups No 2.45 3.16 1 & 2

Groups No 2.09 2.51 3 & 4

Groups P110 Polyethylene 5 & 6 0.08 Wt% (2/rev/3sec)<¹) 1.41 1.95

Groups 0.25 Wt% (2/rev/3sec) 1.20 1.90 7 & 8

Groups AP5 Oleic Acid (²> 9 & 10 400°F 2.51 2.14

Groups 200°F 1.55 2.24 11 & 12

Groups GL1000 Beeswax 1.44 2.04 13 & 14

Groups Stearate 0.96 1.26 15 & 16

Groups Water Spray 2.19 2.19 17 & 18

(1) Wt% = weight % of polyethylene; rev/sec = rate of rotation of bottle during coating

(2) temperature is temperature of glass at time of coating. These results confirm the results of Example 11 that (1) significant strength enhancement can be achieved with the strength enhancement coating applied over a cold end coating, and (2) some cold end coatings may be less suitable or undesirable. The results for Oleic Acid also show that better SE results are obtained with a thinner cold end coating (when a hot end coating is also present) , because a higher glass Oemperature results in a thinner cold end coating. Therefore, it is desirable to use a thinner cold end coating, which will be consistent with obtaining desired lubricity, but which will not inhibit the beneficial effects of the strength enhancing coating. These results generally point out the desirability of using a thin coating for the cold end coating. Water is an effective thin coating, and the results show that its use yields a significant strength enhancement.

In any population of manufactured bottles, there will be a bell curve shaped distribution of weak and strong bottles. An important and unexpected result of this invention is that the greatest improvement in strength occurs for the weakest bottles (see e.g., Example 3, the results of which are relevant t both embodiments) . This means that the distribution spread both narrows and moves to a higher mean strength value. This is unexpected and of special benefit in the manufacture of bottles.

While we do not want or intend to be bound by any specific theory, it may be that the unexpected results of this invention occur because of the individual and/or combined effects of (1) the heat treatment actually changing the surface of the glass by driving off hydroxyl groups that are chemically bonded to the silica (which hydroxyl groups, in the prior art were desired to be present as bonding sites for adhesion of coatings, but which by being driven off in this invention may increase the strength enhancing properties of the coating to the glass far beyond previous practice), and/or (2) the glass is fully or almost fully stress relieved by being brought to or near the annealing temperature, and/or (3) the coating composition has superior strength enhancing capabilities.

Another theory that may explain the unexpected results of this invention is that the coating may be acting as a "getter" to prevent water from reaching the sites of flaws on the glass surface. It is known that water is involved in degradation and failure of glass. A theory of the present invention, but by which we do not wish or intend to be bound, may be that the coating is passivating the stress sites (i.e., the flaws) by absorbing water until the coating gets saturated and then no more water gets absorbed; and this prevents or reduces water getting to the flaw sites.

As to the second embodiment where the strength enhancing coating is applied after and over the cold end coating, the mechanism which is at work is not fully understood. There are several theories; but we do not want or intend to be bound by any of these theories. One theory is that the strength enhancing coating penetrates through the cold end coating and bonds to the glass to passivate the flaw sites to prevent degradation even if water gets to the flaw sites. Another theory is that the strength enhancing coating may be acting as a "getter" to absorb water until it becomes saturated, and then no more water gets absorbed. Still another, but believed to be less likely, theory is that the strength enhancing coating may be sitting on top of the cold end coating and contributing to the strength enhancement to some degree by acting as a stress dissipation or stress transfer laminate.

It is also to be noted that bottles which are coated as per the present invention during initial manufacture can be recycled and recoated as taught herein without the need for any special steps to remove the original coating. The original coating will be dissipated by the heat treatment for recoating. We Claim:

Claims

CLAIM 1. A method of enhancing the strength of a glass container, including the steps of: heat treating the glass container to a temperature of at least 500°C; applying to the glass container after heat treating a coating comprising an acrylate monomer, a crosslinking acrylate monomer, a silane adhesion promoting agent with additional functionality capable of reacting with acrylates, and a curing agent; and curing the coating.

CLAIM 2. The method of CLAIM 1 wherein the step of applying a coating to the glass container includes: applying the coating within six hours after heat treating the glass container.

CLAIM 3. The method of CLAIM 1 wherein the step of applying a coating to the glass container includes: applying the coating within one hour after heating the glass container.

CLAIM 4. The method of CLAIM 1 wherein the step of applying a coating to the glass container includes: applying the coating essentially upon completion of the heat treatment.

CLAIM 5. The method of CLAIM 1 wherein: the step of heat treating includes heating the glass container to at least the annealing temperature in a lehr; and the step of applying a coating includes applying a coating to the glass container within six hours after the glass container exits the lehr.

CLAIM 6. The method of CLAIM 5 wherein: the coating is applied to the glass container within one hour after the glass container exits the lehr.

CLAIM 7. The method of CLAIM 5 wherein: the coating is applied to the glass container essentially immediately upon exiting the lehr.

CLAIM 8. The method of CLAIM 5 wherein: the coating is applied to the glass container at substantially the time the glass container reaches room temperature.

CLAIM 9. The method of CLAIM 1 wherein: the step of heat treating includes heating the glass container to a temperature of at least 510°C; and the step of applying a coating includes applying a coating within six hours after heating the glass container.

CLAIM 10. The method of CLAIM 9 wherein: the coating is applied to the glass container within one hour after heating the glass container.

CLAIM 11. The method of CLAIM 9 wherein: the coating is applied to the glass container essentially upon completion of the heat treatment.

CLAIM 12. The method of CLAIM 1 wherein: the step of heat treating includes heating the glass container to a temperature of at least 520 C; and the step of applying a coating includes applying a coating within six hours after heating the glass container.

CLAIM 13. The method of CLAIM 12 wherein: the coating is applied to the glass container within one hour after heating the glass container.

CLAIM 14. The method of CLAIM 12 wherein: the coating is applied to the glass container essentially upon completion of the heat treatment.

CLAIM 15. The method of CLAIM 1 wherein the coating includes: a film forming monomer selected from the group comprising: ethylene glycol dimethacrylate, 1,6 hexanediol di(meth)acrylate, neopentyl glycol diacrylate, ethoxylated bisphenol A di(meth)acrylate, 2-ethoxyethyl (meth)acrylate, isobornyl acrylate, tetrahydrofurfuryl (meth)acrylate.

CLAIM 16. The method of CLAIM 1 wherein the coating includes: a crosslinking acrylate monomer selected from the group comprising: trimethylolpropane trimethacrylate, ditrimethylolpropane tetraacrylate, triacrylate of tris (2-hydroxyethyl) isocyanurate, pentaerythritol triacrylate.

CLAIM 17. The method of CLAIM 1 wherein the coating includes: a silane adhesion promoting agent selected from the group comprising: methacryloxypropyltrichlorosilane, methacryloxypropyl- methyldiethoxysilane, mercaptopropylmethyl dimethoxysilane, mercaptopropyltrimethoxysilane, mercaptomethylmethyldiethoxy- silane, acryloxypropylmethyl dichlorosilane, aminophenyl- trimethoxysilane, 3-aminopropyltrimethoxysilane, 4-aminobutyl- triethoxysilane.

CLAIM 18. The method of CLAIM 1 wherein the coating includes: a curing agent selected from the group comprising: benzil, benzophenone, camphorquinone, benzoin n-butyl ether, thioxanthone, isopropyl thioxanthone, 2,2-dimethoxy-2- pheny1-acetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-benzyl-2-N-Dimethylamino 1- (4-morρholinophenyl-l-butanone)

CLAIM 19. The method of CLAIM 1 wherein: the step of curing is effected by UV irradiation.

CLAIM 20. A strength enhanced glass container, the glass container having: a strength enhancing coating comprised of an acrylate monomer, a crosslinking acrylate monomer, a silane adhesion promoting agent with additional functionality capable of reacting with acrylates, and a curing agent; the container having been heated to a temperature of at least 500°C before application of the coating.

CLAIM 21. The glass container of CLAIM 20 wherein: the glass container is heated to at least the annealing temperature prior to application of the coating.

CLAIM 22. The glass container of CLAIM 21 wherein: the coating is applied to the glass container within six hours after heating of the glass container to the annealing temperature and cooling the glass container to lehr exiting temperature.

CLAIM 23. The glass container of CLAIM 20 wherein: the coating is applied to the glass container within six hours after heating of the glass container to at least 500°C.

CLAIM 24. The glass container of CLAIM 20 wherein the coating includes: a film forming monomer selected from the group comprising: ethylene glycol dimethacrylate, 1,6 hexanediol di(meth)acrylate, neopentyl glycol diacrylate, ethoxylated bisphenol A di(meth)acrylate, 2-ethoxyethyl (meth)acrylate, isobornyl acrylate, tetrahydrofurfuryll (meth)acrylate.

CLAIM 25. The glass container of CLAIM 20 wherein the coating includes: a crosslinking acrylate monomer selected from the group comprising: trimethylolpropane trimethacrylate, ditrimethylolpropane tetraacrylate, triacrylate of tris (2-hydroxyethyl) isocyanurate, pentaerythritol triacrylate.

CLAIM 26. The glass container of CLAIM 20 wherein the coating includes: a silane adhesion promoting agent selected from the group comprising: methacryloxypropyltrichlorosilane, methacryloxypropyl- methyldiethoxysilane, mercaptopropylmethyl dimethoxysilane, mercaptopropyltrimethoxysilane, mercaptomethylmethyldiethoxy- silane, acryloxypropylmethyl dichlorosilane, aminophenyl- trimethoxysilane, 3-aminopropyltrimethoxysilane, 4-aminobutyl- triethoxysilane.

CLAIM 27. The glass container of CLAIM 20 wherein the coating includes: a curing agent selected from the group comprising: benzil, benzophenone, camphorquinone, benzoin n-butyl ether, thioxanthone, isopropyl thioxanthone, 2,2-dimethoxy-2- phenyl-acetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-benzyl-2-N-Dimethylamino 1- (4-morpholinophenyl-l-butanone)

CLAIM 28. The glass container of CLAIM 1 wherein: the coating is cured by UV irradiation.

CLAIM 29. A method of enhancing the strength of a glass container, including the steps of: delivering the glass container to an annealing lehr; heat treating the glass container in the lehr to a temperature of at least the annealing temperature of the glass; applying a cold end coating to the glass container after exiting from the lehr; applying to the glass container over the cold end coating a strength enhancing coating comprising an acrylate monomer, a crosslinking acrylate monomer, a silane adhesion promoting agent with additional functionality capable of reacting with acrylates, and a curing agent; and curing the strength enhancing coating.

CLAIM 30. The method of CLAIM 29 wherein the step of applying a strength enhancing coating to the glass container includes: applying the strength enhancing coating within six hours after heat treating the glass container.

CLAIM 31. The method of CLAIM 29 wherein the step of applying a strength enhancing coating to the glass container includes: applying the strength enhancing coating within one hour after heating the glass container.

CLAIM 32. The method of CLAIM 29 wherein the step of applying a strength enhancing coating to the glass container includes: applying the strength enhancing coating essentially upon completion of the heat treatment.

CLAIM 33. The method of CLAIM 29 wherein: the step of heat treating includes heating the glass container to a temperature of at about 550°C; and the step of applying a strength enhancing coating includes applying a strength enhancing coating within six hours after heating the glass container.

CLAIM 34. The method of CLAIM 33 wherein: the strength enhancing coating is applied to the glass container within one hour after heating the glass container.

CLAIM 35. The method of CLAIM 33 wherein: the strength enhancing coating is applied to the glass container essentially upon completion of the heat treatment.

CLAIM 36. The glass container of CLAIM 29 wherein the coating includes: a film forming monomer selected from the group comprising: ethylene glycol dimethacrylate, 1,6 hexanediol di(meth)acrylate, neopentyl glycol diacrylate, ethoxylated bisphenol A di(meth)acrylate, 2-ethoxyethyl (meth)acrylate, isobornyl acrylate, tetrahydrofurfuryll (meth)acrylate.

CLAIM 37. The glass container of CLAIM 29 wherein the coating includes: a crosslinking acrylate monomer selected from the group comprising: trimethylolpropane trimethacrylate, ditrimethylolpropane tetraacrylate, triacrylate of tris (2-hydroxyethyl) isocyanurate, pentaerythritol triacrylate.

CLAIM 38. The glass container of CLAIM 29 wherein the coating includes: a silane adhesion promoting agent selected from the group comprising: methacryloxypropyltrichlorosilane, methacryloxypropyl- methyldiethoxysilane, mercaptopropylmethyl dimethoxysilane, mercaptopropyltrimethoxysilane, mercaptomethylmethyldiethoxy- silane, acryloxypropylmethyl dichlorosilane, aminophenyl- trimethoxysilane, 3-aminopropyltrimethoxysilane, 4-aminobutyl- triethoxysilane.

CLAIM 39. The glass container of CLAIM 29 wherein the strength enhancing coating includes: a curing agent selected from the group comprising: benzil, benzophenone, camphorquinone, benzoin n-butyl ether, thioxanthone, isopropyl thioxanthone, 2,2-dimethoxy-2- phenyl-acetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-benzyl-2-N-Dimethylamino 1- (4-morpholinophenyl-l-butanone)

CLAIM 40. The method of CLAIM 29 wherein: the curing agent is a UV curable material, and the curing is effected by UV irradiation.

CLAIM 41. A strength enhanced glass container, the glass container having: a strength enhancing coating comprised of an acrylate monomer, a crosslinking acrylate monomer, a silane adhesion promoting agent with additional functionality capable of reacting with acrylates, and a curing agent; the strength enhancing coating having been applied over a cold end coating during the manufacture of glass, and the container having been heated to a temperature of at least the annealing temperature of the glass in an annealing lehr before application of the strength enhancing coating.

CLAIM 42. The glass container of CLAIM 41 wherein: the strength enhancing coating is applied to the glass container within six hours after heating of the glass container to the annealing temperature and cooling the glass container to lehr exiting temperature.

CLAIM 43. The glass container of CLAIM 41 wherein: the coating is applied to the glass container within six hours after heating of the glass container to at least the annealing temperature.

CLAIM 44. The glass container of CLAIM 41 wherein the strength enhancing coating includes: a film forming monomer selected from the group comprising: ethylene glycol dimethacrylate, 1,6 hexanediol di(meth)acrylate, neopentyl glycol diacrylate, ethoxylated bisphenol A di(meth)acrylate, 2-ethoxyethyl (meth)acrylate, isobornyl acrylate, tetrahydrofurfuryl (meth)acrylate.

CLAIM 45. The glass container of CLAIM 41 wherein the strength enhancing coating includes: a crosslinking acrylate monomer selected from the group comprising: trimethylolpropane trimethacrylate, ditrimethylolpropane tetraacrylate, triacrylate of tris (2-hydroxyethyl) isocyanurate, pentaerythritol triacrylate.

CLAIM 46. The glass container of CLAIM 41 wherein the strength enhancing coating includes: a silane adhesion promoting agent selected from the group comprising: methacryloxypropyltrichlorosilane, methacryloxypropyl- methyldiethoxysilane, mercaptopropylmethyl dimethoxysilane, mercaptopropyltrimethoxysilane, mercaptomethylmethyldiethoxy- silane, aer loxypropylmethyl dichlorosilane, aminophenyl- trimethoxysilane, 3-aminoproρyltrimethoxysilane, 4-aminobutyl- triethoxysilane.

CLAIM 47. The glass container of CLAIM 41 wherein the strength enhancing coating includes: a curing agent selected from the group comprising: benzil, benzophenone, camphorquinone, benzoin n-butyl ether, thioxanthone, isopropyl thioxanthone, 2,2-dimethoxy-2- pheny1-acetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-benzyl-2-N-Dimethylamino 1- (4-morpholinophenyl-l-butanone)

CLAIM 48. The glass container of CLAIM 41 wherein: the curing agent is a UV curable material, and the curing is effected by UV irradiation.