KR101538053B1 - Strengthening method of borosilicate glass, and borosilicate glass strengthened by the same - Google Patents

Abstract

The present invention relates to a method of strengthening borosilicate glass and a borosilicate glass reinforced thereby, comprising applying alkali ions to at least one side of a borosilicate glass, and applying the applied alkaline ion to the borosilicate glass by heat treating the alkali- Thereby allowing ions to penetrate into the borosilicate glass, and a borosilicate glass produced thereby.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method for strengthening borosilicate glass and a borosilicate glass reinforced by the borosilicate glass,

The present invention relates to a method for strengthening borosilicate glass and a borosilicate glass reinforced thereby, and more particularly to a method for strengthening borosilicate glass by applying a potassium salt to a borosilicate glass followed by heat treatment.

Bulletproof glass, an important material in the defense industry, is tempered glass designed to protect people and equipment from external threats. The ballistic performance standard of the bulletproof material conforms to the American specification MIL-G-5485D standard, and the detailed standard of the bulletproof material for the performance evaluation is the area of 40 × 57 × 60mm ² , and the bullet which collides with the bullet speed of 851m / And the light transmittance according to the thickness should be satisfied.

In producing bulletproof glass, at least one polymer film selected from PVB (polyvinyl butyral), PU (polyurethane), main defense (200MD) and safety film is bonded to soda-lime silicate (SLS) Has been developed. The bulletproof glass manufactured by bonding the SLS and the polymer film could be thinned from 40 mm to 29 mm in the thickness of the full protective bulletproof material only by adjusting the lamination arrangement of the materials. The thinning of the bulletproof material thickness is highly desirable from the viewpoints of lightening the bulletproof material and facilitating handling when the bulletproof material is realized within a range that does not compromise its mechanical properties.

However, since the amount of impact applied to the bulletproof glass gradually increases according to the type of the gun and the development of the technology applied to the firearm, the development of a bulletproof glass material and a mechanical property reinforcing method, Is required.

Such bulletproof glass is widely used in various facilities and vehicles to safeguard human lives and property. In particular, bulletproof bullets mounted on firearms having strong impact force, M19 antitank land mines, M16 civilian mines, M14 civilian mines, grenades, It is aimed to prevent warheads, fragments, etc. of bombs, such as cremona, from permeating them.

In order to comply with this function, the bulletproof glass must have a thickness of at least 34 mm. In particular, in order to have the bulletproof ability to prevent the warhead of the M60 lightning strike gun, Of the total thickness of the film.

Currently, in Korea, bulletproof glass using bulletproof glass or bulletproof processed polyester film having bulletproof ability and bulletproof glass using Lexan material are being imported.

In particular, in order to manufacture a bulletproof glass having a thickness of 34 mm or more or 45 mm or more, it is necessary to laminate a plurality of general glass or a bulletproof film having a plurality of layers to a glass, which is heavy, The process is complicated.

In addition, when such bullet-proof glass is applied to a facility, there is a complexity in that various designing complementary measures have to be taken to support the heavy load.

In addition, when such a bulletproof glass is applied to a vehicle, a vessel, or a military equipment, there is a problem in that mobility is reduced due to a high load, and excessive fuel is consumed.

It is an object of the present invention to provide a method for strengthening borosilicate glass wherein Vickers hardness, fracture toughness, strength are evaluated to be relatively high relative to other glasses.

Another object of the present invention is to improve the thickness and weight of the bulletproof glass, simplify the bulletproof glass manufacturing process, and improve the functionality of the bulletproof glass by applying the reinforced borosilicate glass to the use of the bulletproof glass.

It is also an object of the present invention to provide a reinforced borosilicate glass having almost the same weight feeling as that of the ordinary glass when applied to vehicles, traps, and military equipment.

It is another object of the present invention to provide a method for strengthening borosilicate glass that can attain a relatively light transmittance enhancing effect because it can be made thinner than conventional SLS glass.

According to an embodiment of the present invention, there is provided a method of forming a borosilicate glass comprising the steps of: applying alkali ions to at least one side of a borosilicate glass; and heat treating the alkali silicate coated borosilicate glass to cause the applied alkali ions to penetrate into the borosilicate glass A method of strengthening the borosilicate glass can be provided.

The alkali ion may be at least one selected from the group consisting of K ⁺ , Cs ⁺ , Li ⁺ and Rb ⁺ , and may be, for example, K ⁺ contained in the potassium salt.

The heat treatment is performed at a temperature of 540 to 560 캜 for 8 to 15 minutes.

In this case, the borosilicate glass includes SiO ₂ , Na ₂ O, Al ₂ O ₃ and B ₂ O ₃ .

Further, according to an embodiment of the present invention, a borosilicate glass produced by any one of the above strengthening methods can be provided.

According to the embodiment of the present invention as described above, the borosilicate glass which is evaluated as relatively high in Vickers hardness, fracture toughness and three-point bending strength as compared with glass of other compositions is reinforced and applied as a bulletproof glass, It is possible to reduce the thickness and weight of the bulletproof glass, to simplify the bulletproof glass manufacturing process, and to improve the functionality of the bulletproof glass.

Further, when the borosilicate glass is applied to vehicles, traps, and military equipments as a bulletproof glass, since it has almost the same weight feeling as in the case of attaching ordinary glass, its maneuverability can be prevented from deteriorating.

Further, the borosilicate glass exhibits higher strength, hardness and fracture toughness than conventional SLS bulletproof glass, and thus can be made thinner, so that a relatively higher light transmittance can be realized more easily.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the penetration depth change of K ⁺ ions according to the strengthening temperature (a) and the strengthening holding time (b) in the method for strengthening borosilicate glass according to an embodiment of the present invention.
2 is a graph showing the (a) Vickers hardness, (b) the fracture toughness, and (c) the three-point bending strength according to the tempering temperature in the method for strengthening borosilicate glass according to an embodiment of the present invention.
FIG. 3 is a graph showing (a) Vickers hardness, (b) fracture toughness, and (c) three-point bending strength according to the reinforcing holding time in the method of reinforcing borosilicate glass according to an embodiment of the present invention.
FIG. 4 is a graph illustrating light transmittance measured in a visible light region according to an enhancement condition in a method for strengthening borosilicate glass according to an embodiment of the present invention. FIG.

Hereinafter, a method of strengthening a borosilicate glass according to the present invention will be described in detail with reference to the drawings.

In the present specification, the same or similar reference numerals are given to different embodiments in the same or similar configurations. As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to preferred embodiments and accompanying drawings.

In one embodiment of the present invention, the use of a borosilicate glass as a bulletproof material which has not been applied so far has been clarified and applied, and borosilicate glass is reinforced by an ion exchange method to provide a bulletproof material having excellent performance.

In the ion exchange method, a solid phase or liquid phase coating method or a molten salt immersion method can be used. In one embodiment of the present invention, experimental examples and results obtained by applying a solid phase or liquid phase coating method are shown as the best examples.

Table 1 below shows mechanical properties of SLS glass and borosilicate glass which have been conventionally applied as bulletproof glass materials.

As will be found from the table below, the Vickers hardness, fracture toughness, and 3-point bending strength of the glass SLS are each ^{569kg / mm 2, 0.7190MPam 1/} 2, 150MPa, if the borosilicate glass is 610kg / mm ^2, 0.7657MPam ^1/2 , and 219 MPa, respectively. The Vickers hardness, fracture toughness, and three-point bending strength of borosilicate glass were 7%, 6%, and 46% superior to those of SLS glass.

In other words, such a measurement result is a meaningful result for predicting the possibility of borosilicate glass as a bulletproof material, the possibility of substituting for SLS glass, and the actual application superiority.

division Vickers hardness (kg / mm ² ) Fracture Toughness (MPam ^1/2) 3 point bending strength (MPa) SLS glass 569 0.7190 150 Borosilicate glass 610 0.7657 219 Reinforced borosilicate glass 775 1.91 764

Borosilicate glass having a composition of 80.4SiO ₂ -4.2Na ₂ O-2.4Al ₂ O ₃ -13B ₂ O ₃ (mol%) is excellent in chemical durability and mechanical properties and is widely used as a chemical product. The material is made of ordinary SLS glass. Hardness, fracture toughness, and 3-point bending strength of normal glass SLS is ^{569kg / mm 2, 0.7190MPam 1/} 2, borosilicate glass enhanced by 150MPa, and the ion exchange method is ^{775kg / mm 2, 1.91MPam 1/} 2, 764MPa, which is 36%, 166% and 409% higher than that of SLS glass. Therefore, by substituting reinforced borosilicate glass for general SLS glass, which is currently used for bulletproof materials, it is possible to produce a new bulletproof material with reduced thickness and weight.

Table 2 below shows bulletproof glass laminated materials produced by laminating general SLS glass and polymers currently in use, and Table 3 below shows bulletproof glass laminated materials prepared by laminating borosilicate and polymers reinforced by ion exchange Lt; / RTI >

Configuration
G PVB G PU PC PU G Safety Film Total thickness (mm) weight
(kg) thickness
(mm) 10 1.52 5 1.25 5 1.25 5 0.35 29.37 18.50

Here, G denotes glass, and PVB (polyvinyl butyral), PU (polyurethane), and PC (polycarbonate), which are applied to enhance mechanical properties and prevent glass scattering, Respectively. Table 3 below is also the same. In Table 2, G is a general SLS glass, and in Table 3 is a borosilicate glass reinforced by ion exchange.

Configuration
G PVB G PU PC PU G Safety Film Total thickness (mm) weight
(kg) thickness
(mm) 4 1.52 3 1.25 5 1.25 3 0.35 19.37 13.30

Here, the density of the borosilicate glass is 2.23 g / cm ³ , and the weight is calculated by using the thickness of the bulletproof glass laminated material (19.37 mm) and the density of the bulletproof glass laminated material (405 mm × 760 mm) , It is thinner than 10mm than the conventional bulletproof material in which general SLS glass is laminated with 13.3kg, and it can be lightened more than 5kg.

In other words, as can be seen from the above table, since the thickness of the borosilicate glass can be made thinner than that of the ordinary SLS glass, it is advantageous in terms of light transmittance as well as light weight, Reinforced borosilicate glass can be a good alternative to general SLS glass to expand its applicability as a bulletproof material.

In order to manufacture such a new bulletproof material, a technique of processing the borosilicate glass so as to faithfully use the bulletproof material should be developed. In one embodiment of the present invention, the borosilicate glass is reinforced using the ion exchange method, Possibility. If the possibility of using the borosilicate glass as a bulletproof material is proved, it will be more advantageous from the viewpoint of thinning and weight saving compared with a fully protective bulletproof material (29 mm) in which SLS glass is laminated.

Hereinafter, a method of strengthening borosilicate glass according to an embodiment of the present invention will be described.

First, the reinforcing process by the ion exchange method of borosilicate glass will be described.

To further enhance the mechanical properties of the borosilicate glass with high strength, the borosilicate glass was ion-exchanged using K ⁺ ions in one embodiment of the present invention. Various kinds of elements such as K ⁺ , Cs ⁺ , Li ⁺ , and Rb ⁺ having a large atomic radius can be used for strengthening the glass by ion exchange. However, in an embodiment of the present invention, K ⁺ ions that can provide a high strengthening effect in the melting point, ion radius, etc., except for expensive rare metals, can be most suitably used.

The reaction equation through ion exchange can be generally expressed as the following equation (1).

XA ₊ + B ⁺ - &^gt; XB ⁺ + A ⁺ ----------------------- (1)

Here, X represents a glass base, A ⁺ represents an alkali ion in a glass base, and B ⁺ represents an alkali ion having a large atomic radius in a molten salt in the case of a molten salt ion exchange system. When temperature and holding time are maintained, they are interchanged by diffusion.

Here, when ions having a large ionic radius penetrate into a glass base, the glass is strengthened by forming a surface compressive stress according to the penetration depth of the ions.

In one embodiment of the present invention, after ion-exchange strengthening the borosilicate glass, the ion exchange optimum condition is secured by measuring the mechanical properties and the light transmittance according to the depth of ion penetration of K ⁺ ions, and the thickness and weight of the reinforced borosilicate glass And evaluated the possibility of using it as a transparent bulletproof material.

First, a borosilicate glass having a composition of 80.4SiO ₂ -4.2Na ₂ O-2.4Al ₂ O ₃ -13B ₂ O ₃ (Product, 3mm, Germany) was laminated in a thickness (t) × width (w) × length 3 × 4 × 36 mm 3, and the sides and edges of the cut borosilicate glass were polished step by step using SiC paper having a roughness of # 400, # 1,000 and # 2,000. This is a standard commonly applied to SLS glass and borosilicate glass shown in Table 1 above.

KNO ₃ powder (Ducsan, Korea) was used for the ion exchange, and the powder was of high purity (Extra Pure grade, 3N, 99.9%).

The KNO ₃ powder was applied to an alumina square tray, the cut borosilicate glass was placed thereon, and KNO ₃ Powder was applied and heat treatment was performed to perform ion exchange. At this time, the ion exchange method used has advantages such as uniformity of ion exchange and simplicity of the process as compared with the conventional molten salt method.

At this time, heat treatment temperature and holding time were maintained at 530 ~ 570 ℃ for 0 ~ 20 minutes to ensure the optimum penetration depth of K ⁺ ion after ion exchange.

The physical properties of the borosilicate glass reinforced by the ion exchange method were evaluated as described above.

First, the penetration depth of K ⁺ ions according to ion exchange temperature and holding time was measured by line profile using SEM / EDS (S-4200, Hitachi, Japan).

The 3-point bending strength of the reinforced borosilicate glass was also measured using UTM (H10K-C, Hounsfield, U.K.). The three-point bending strength was calculated from the following equation (2).

---------------------(2)

---------------------(2)

Where σ is the 3-point bending strength, P is the load of the specimen, L is the specimen length, w is the width of the specimen, and t is the specimen thickness.

The Vickers hardness (HV) of the reinforced borosilicate glass was calculated from equation (3) using Vickers micro hardness tester (MXD-CX3E, Matsuzawa, Japan). The indentation load (P) was maintained at 1,000 gf for 30 seconds and the average value was calculated by measuring 10 times per specimen.

--------------------(3)

-------------------- (3)

Here, HV is the Vickers hardness, P is the load at the time of indentation, and a is the indentation radius.

In addition, the fracture toughness (KIC) of the reinforced borosilicate glass was calculated by substituting the following equation (4) based on the Vickers hardness value.

---------------------(4)

---------------------(4)

Where K is the fracture toughness, Φ is the suppression constant, P is the load at the press-in (1,000 gf), K is a constant, c is the crack length after indentation, a is the indentation radius, and Hv is Vickers hardness. At this time, the inhibition constant is 3 and K is 3.2.

The light transmittance of the reinforced borosilicate glass was measured using a UV / VIS spectrophotometer (Jasco, V-570, Japan). The light transmittance was measured at 200 ~ 800nm wavelength and 400nm / min scan speed.

Hereinafter, the measurement results will be described.

First, the K ⁺ ion penetration rate will be examined.

The penetration depth of the K ⁺ ion into the glass during the ion exchange for a period of from 0 to 20 minutes at a temperature in the range of 530 to 570 ° C is shown in FIG.

FIG. 1A shows the depth of ion penetration by temperature, and FIG. 1B shows the depth of ion penetration by the holding time.

As can be seen from FIGS. 1A and 1B, the depth of K ⁺ ions penetrating into the glass during ion exchange increased in proportion to the temperature and the holding time. The penetration depth of K ⁺ ion was maintained at 530 ℃ for 10 min. The penetration depth of K ⁺ ion increased to 88.6 ㎛ when the ion exchange temperature was maintained at 570 ℃ for 10 min. The penetration depths of K ⁺ ions after 50min, 0min (very fast), 10min, and 20min were increased to 50.2μm, 59.8μm and 65.5μm, respectively. The diffusion coefficients of K ⁺ ions are proportional to temperature and time as shown in the following equations (5) and (6).

-----------------------(5)

----------------------- (5)

Where d is the depth of ion penetration, Deff is the effective diffusion coefficient, and τ is the retention time.

The dependence of effective diffusion coefficient on temperature can be confirmed from the following equation (6).

-----------------(6)

----------------- (6)

Where D is the effective diffusion coefficient, D0 is the pre-exponential term, Q is the activation energy of the effective diffusion, and R is the molar gas constant.

Therefore, the mechanical properties (Vickers hardness, fracture toughness, 3-point bending strength) of the borosilicate glass were evaluated on the basis of the penetration rate (㎛ / min) of K ⁺ ion depending on the ion exchange temperature and the holding time, Can be obtained.

Hereinafter, the mechanical properties of glass reinforced by the ion exchange method will be described.

FIG. 2 is a graph showing Vickers hardness, fracture toughness, and three-point bending strength according to temperature (530 to 570 ° C) while maintaining the ion exchange time at 10 minutes. As the ion exchange temperature and the retention time increased, the penetration rate of K ⁺ ion increased proportionally. However, the mechanical properties of FIG. 2 were confirmed, and the mechanical properties increased until 550 ° C., and then decreased. This phenomenon shows that as the ion exchange temperature and time increase, the penetration amount of K ⁺ ions increases in the glass, but when the amount exceeds the critical ion exchange capacity, the K ⁺ ion destroys Si-O, which is a network former structure of glass , Rather, a phenomenon that relaxes the stress occurs, thereby reducing the mechanical properties. This phenomenon is called stress relaxation phenomenon and it is necessary to secure the optimum K ⁺ ion infiltration amount depending on the ion exchange temperature and the holding time of the borosilicate glass.

FIG. 3 is a graph showing the mechanical properties of a borosilicate glass according to an embodiment of the present invention, measured at an ion exchange temperature of 550.degree. After the ion exchange temperature was fixed at 550 ° C, the ion exchange time was increased from 0 minutes to 20 minutes at intervals of 5 minutes. As a result, the mechanical properties were increased up to 10 minutes, but then the stress relaxation phenomenon rapidly decreased.

2 and 3, it was confirmed that the stress relaxation phenomenon was observed, and at the same time, the optimum conditions for ion exchange of borosilicate glass having a thickness of 3 mm were maintained at 550 ° C for 10 minutes. The Vickers hardness, fracture toughness , three-point bending strength was increased by 27% to 150%, 249% from borosilicate glass which have, not strengthen each ^{775kg / mm 2, 1.91MPam 1/} 2, 764MPa.

On the other hand, when laminated bulletproof materials, various thicknesses of borosilicate glass are required, and the glass is classified into thicknesses (3 mm, 4 mm, 6 mm) and the three point bending strength measurement The results are shown in Table 4 below.

Ion exchange time (min) 3 point bending strength (MPa) Thickness (mm) 3mm 4mm 6mm 8mm Parent (no ion exchange) 219 221 230 245 10 764 772 764 - 12 - 783 791 - 15 650 767 810 792 17 - - - 815 18 - - - 835 19 - - - 802 20 643 750 801 -

Optimum ion exchange conditions of borosilicate glass by thickness was 3mm In case the exchange 10 minutes 550 ℃, ions, K ⁺ ions penetration depth 59㎛, the bending strength was about 764MPa. The 4 mm borosilicate glass had a K ⁺ ion penetration depth of 72 μm when ion exchanged at 550 ° C. for 12 minutes, wherein the bending strength was 783 MPa. When ion exchanged at 550 ℃ for 15 min, the K ⁺ ion penetration depth was 90 ㎛ and the bending strength was increased to 810 MPa. Finally, when ion exchanged at 550 ℃ for 18 minutes, the K ⁺ ion penetration depth was 110 ㎛ and the bending strength increased to 810 MPa.

These reinforced borosilicate glasses have increased mechanical properties by 36%, 166% and 409% compared to ordinary SLS glass, which is currently used as a bulletproof material, so that when bulletproof materials are replaced by reinforced borosilicate glass from SLS glass, , And weight reduction.

Ion exchange time (min) 3 point bending strength (MPa) thickness 3mm 4mm 6mm Parent (no ion exchange) 145 154 160 10 630 640 653 12 618 700 712 15 610 691 761 17 607 688 750 20 595 683 727

In Table 5, the general SLS glass was fixed at a temperature of 480 캜 and the three-point bending strength was measured by changing the ion exchange time. The optimal conditions for ion exchange of SLS glass by thickness were 3 μm and 480 ° C for 10 min ion exchange, K ⁺ ion penetration depth was 15 μm and bending strength was about 630 MPa. The SLS glass with a thickness of 4 mm had a K ⁺ ion penetration depth of 21 μm when subjected to ion exchange at 480 ° C. for 12 minutes, wherein the bending strength was 700 MPa. In the 6mm thick SLS glass, the K ⁺ ion penetration depth was 34μm and the bending strength was increased to 761MPa when ion exchanged at 480 ℃ for 15 minutes.

However, the bending strength of the reinforced SLS glass was somewhat lower than the bending strength of the reinforced borosilicate glass according to the present invention, so that borosilicate glass could be evaluated as an alternative to SLS glass.

Hereinafter, the optical properties of the borosilicate glass reinforced according to one embodiment of the present invention will be described.

As a physical property to be considered for use as a bulletproof material, there is a mechanical property and a light transmittance which is an optical property required for each thickness in a visible light region.

Table 6 below shows the minimum light transmittance (%) required for the thickness of the bulletproof glass manufactured according to the MIL-G-5485D standard, which is a product standard of the bulletproof material.

Thickness (mm) Minimum Transmittance (%) 12.7 81 19.0 78 25.4 76 31.8 73 38.1 70 44.5 68 50.8 66

The minimum optical transmittance according to the thickness as shown in Table 6 above is used to measure the optical properties as well as the mechanical properties obtained under the optimum conditions at the time of ion exchange.

In one embodiment of the present invention, the ion exchange temperature and time-dependent light transmittance of the ion-exchanged borosilicate glass are shown in the graph of FIG.

In FIG. 4, as the ion exchange temperature and time were increased, the light transmittance measured in the visible region was 91.2%, which was slightly lower than the light transmittance of unreinforced borosilicate glass of 91.6% The light transmittance of the borosilicate glass subjected to the minute ion exchange was measured to be 91.4%, and it was confirmed that it can be used as a transparent bulletproof material.

Although not shown in the table, SLS glass of the same strength should naturally be made thicker than borosilicate glass, so that a loss of light transmittance is expected to be expected. Therefore, the borosilicate glass according to one embodiment of the present invention is superior to the SLS glass of the same strength in light transmittance.

The above-described reinforcing method of borosilicate glass is not limited to the configuration and method of the above-described embodiments, but the embodiments may be modified such that all or some of the embodiments are selectively combined .

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (7)

Applying KNO ₃ powder having at least 99% purity on at least one side of the borosilicate glass; And
Heat treating the borosilicate glass coated with KNO ₃ to cause the applied alkali ions to penetrate into the borosilicate glass,
The alkali ion is K ⁺ contained in KNO ₃ ,
Wherein the heat treatment is performed at a temperature of 540 to 560 캜 for 8 to 18 minutes so that the depth of the penetration of the K ⁺ ions into the borosilicate glass is 38 to 90 탆. delete delete delete delete The method according to claim 1,
Wherein the borosilicate glass comprises SiO ₂ , Na ₂ O, Al ₂ O ₃ and B ₂ O ₃ . A borosilicate glass reinforced by any one of claims 1 to 6.

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