DOUBLE-GLAZING UNIT

Abstract: This invention relates to double glazing having two glass sheets with numerous spacers arranged therebetween, a void therebetween being sealed in a decompressed condition. Conventionally, the glass sheets have edges thereof spaced from each other by a seal. Under the influence of the binding force of the seal, atmospheric pressure tends to act less on outermost spacers than on the other spacers. Consequently, the outermost spacers tend to move between the glass sheets. According to this invention, an outer interval (L1) between each outermost row of spacers (2) and a seal (4) is set at least equal to a basic interval (L0) between the outermost row and a second row adjacent thereto. Consequently, the spacers in the outermost rows bear a larger share of atmospheric pressure acting on the sheet surfaces than the spacers in the other rows. A sufficient force is secured to hold the spacers in the outermost rows in place, thereby preventing the spacers in the outermost rows from moving between the two glass sheets.

Description: TECHNICAL FIELD This invention relates to double glazing in which two sheets of glass having numerous first void sustaining elements arranged in rows at predetermined intervals along and between sheet surfaces, and a second void sustaining element disposed between entire outer edges of the glass sheets for sealing a void between said glass sheets in a decompressed state. BACKGROUND ART Generally, heat insulation may be provided for partitions (walls and roofs) of structures by using an insulating material. However, partitions with openings such as doors and windows must be opened and closed with facility and have transparency. It is therefore difficult to apply an insulating material to such partitions over entire areas thereof. The openings having no insulating material applied hereto tend to be defective in terms of heat insulation. Double glazing has been conceived for use in these openings, which includes two sheets of glass joined together with a layer of air formed therebetween to act as an insulating layer. Such double glazing has a disadvantage that the glass sheets per se are thick and, in combination with the sash, tend to present an unsightly appearance. Thus, a thin and highly insulating double glazing has been conceived, in which two sheets of glass having numerous spacers (corresponding to the above-mentioned first void sustaining elements and in the form of small columns not to be obstructive to transparency) distributed therebetween, and the second void sustaining element disposed between entire edges of the two glass sheets, to provide a decompressed void between the glass sheets. WO-A-95 01 493 discloses a spacer interval and radius for reducing a tensile force acting between the sheet glasses and reducing the heat transmitted through the void sustaining elements. With the first void sustaining elements and the second void sustaining element provided, a predetermined void is secured between the glass sheets even if the void is decompressed. This type of double glazing will be described with reference to Fig. 4. Spacers 10 are arranged at basic spacer intervals (hereinafter called basic intervals) 11 which are set based on the strength of glass sheets 1. The intervals between outermost spacers 10a and second void sustaining element 12 (hereinafter called outer intervals) are often determined by calculating down to a fraction, to be within a range not exceeding the basic intervals 11, and by taking the width (or length) of the glass sheets into account. This is because the size of glass sheets usually is not an integral multiple of the above basic interval. The edges of the two glass sheets are bound by the second void sustaining element. However, where, in the above double glazing the outer intervals 13 are smaller than the basic intervals 11, atmospheric pressure tends to act less on the outermost spacers 10a than on the other spacers under the influence of the binding force of the second void sustaining element 12. In other words, in case e.g. the outer intervals 13 are smaller than the basic intervals 11, the second void sustaining element 12 binds the outer edges of the sheet glasses, whereby the share of atmospheric pressure acting on the sheet surfaces to be supported by the outermost spacers 10a is decreased. As a result these outermost spacers 10a may be easily moved. Consequently, the glass sheets impart an insufficient holding force to the spacers, whereby the spacers could easily move between the glass sheets. If the spacers move between the glass sheets, the spacer arrangement becomes unbalanced to impair appearance. In addition, increased variations occur in the stress condition of the glass sheets to reduce their strength. The object of this invention, therefore, is to provide a double glazing which overcomes the above disadvantage and restrains movement of the first void sustaining elements. DISCLOSURE OF THE INVENTION The above object is fulfilled by the invention as defined in claim 1. This invention provides double glazing comprising two sheets of glass having numerous first void sustaining elements arranged in rows at a predetermined basic interval along sheet surfaces between glass sheets, and a second void sustaining element disposed between entire outer edges of the glass sheets for sealing a void between said glass sheets in a decompressed state, the first void sustaining elements being free to move between the sheet glass until the void therebetween is sufficiently decompressed, the first void sustaining elements being subsequently held in place by frictional forces exerted upon the sheet glasses as a result of external atmospheric pressure acting thereon, an outer interval between each outermost row of the first void sustaining elements and the second void sustaining element being set at least equal to the basic interval between each outermost row and a second row adjacent thereto. According to this construction, since the outer interval is set at least equal to the basic interval, the first void sustaining elements in the outermost rows bear a larger share of atmospheric pressure acting on the sheet surfaces than the first void sustaining elements in the other rows. The increased share of atmospheric pressure can compensate for the shortage of the holding force for the first void sustaining elements in the outermost rows due to the binding force of the second void sustaining element applied to the glass sheets as encountered in the prior art. As a result, substantially the same holding force acts on all of the first void sustaining elements, thereby preventing the first void sustaining elements in the outermost rows from moving between the two glass sheets. With the double glazing, according to this invention, it is now possible to avoid the arrangement of the first void sustaining elements becoming unbalanced to impair appearance and reduce strength as a result of movement of the first void sustaining elements between the glass sheets. Moreover, the second void sustaining element applies an increased binding force to the glass sheets, thereby providing an improved sealing performance. Preferably, the outer interval is set equal to twice the basic interval. It is still more desirable to set the outer interval 1.25 times to twice the basic interval. With this construction, besides avoiding the first void sustaining elements becoming unstable and easily movable as noted above, the glass sheets are protected against breakage. If the outer interval were larger to excess than the-basic interval, increased surface tensile stress would occur with the glass sheets bound by the second void sustaining element increases, to break the glass sheets. That is, movement of the first void sustaining elements may be prevented since the multiplying factor of the outer interval with respect to the basic interval has minimum value 1. When the multiplying factor has maximum value 2, the surface tensile stress in edge regions of the glass sheets bound by the second void sustaining element may be restrained within a permissible level of stress of the glass sheets to avoid breaking of the glass sheets. Advantageous features of this invention are set forth in the other dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view showing a double glazing; Fig. 2 is a front view showing the double glazing; Fig. 3 is a view showing surface tensile stress at edges of glass sheets; and Fig. 4 is a sectional view of a conventional double glazing for comparison with the double glazing according to this invention. BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of this invention will be described in detail hereinafter with reference to the drawings. Figs. 1 and 2 show an example of double glazing according to this invention. The double glazing P intrudes a pair of glass sheets 1, with numerous spacers (which are one example of the first void sustaining elements) 2 arranged at intervals along and between sheet surfaces, to provide a decompressed void V between the glass sheets 1A and 1B. Each of the glass sheets 1 is 3mm thick and formed of transparent float glass sheet. The void V is sealed with a seal (which is one example of the second void sustaining element) 4 formed of low melting point glass (e.g. solder glass) between outer edges of the two glass sheets 1. The void V is decompressed (1.0 X 10 -3 Torr or less), for example, by manufacturing the double glazing in a vacuum environment or by applying suction after the double glazing is manufactured. The outer edges of the glass sheets 1 are formed such that one of the glass sheets 1A projects in directions parallel to the plate surfaces. Peripheries of the void V are sealed efficiently and reliably by depositing a sealing material on projecting portions 5 when forming the seal 5. Preferably, the first void sustaining elements 2 are formed of a material having a compressive strength of at least 491 Nmm -2 (5t/cm 2 ). In this embodiment, the first void sustaining elements 2 are formed of stainless steel (e.g. JIS SUS304). Where the first void sustaining elements 2 have low strength, the first void sustaining elements 2 will be broken under atmospheric pressure acting on the glass sheets 1. Then, it is impossible to secure the void V, thereby lowering insulating performance. The first void sustaining elements 2 are in the form of cylindrical columns. Their diameter is set to about 0.5mm and the height to about 0.2mm (±0.01mm). With the shape of cylindrical column, portions contacting the glass sheets 1 include no corners where stress would tend to concentrate. Thus, the spacers 2 provide reliable support for the glass sheets 1. Further, the cylindrical columns may advantageously have rounded peripheries (instead of defining sharp edges). Regarding the arrangement of numerous first void sustaining elements 2, outer interval L1 between each outermost row of first void sustaining elements 2 and the seal 5 is set equal to or larger than basic interval L1 between each outermost row and each second row of first void sustaining elements 2 adjacent the outermost row. In this embodiment, basic interval L0 is about 20mm, and outer interval L1 is in the range of about 20 to 40mm which is equal to to twice basic interval L0. Where outer interval L1 is set equal to basic interval L0, ie. L1 = 20mm, substantially the same compressive stress (holding stress) acts on first void sustaining elements 2a in the outermost rows and the second void sustaining element 2b in the second rows. This avoids a situation where the first void sustaining elements 2a in the outermost rows in particular may move easily. It has been confirmed that the smaller the outer interval L1 is than the basic interval L0, the smaller share of atmospheric pressure acting on the sheet surfaces is borne by the first void sustaining elements 2a in the outermost rows, and the less compressive stress (holding stress) acts on the first void sustaining elements 2a in the outermost rows because of the binding force of the seal 5 applied to the edges of the double glazing, whereby the first void sustaining elements 2a in the outermost rows move easily (see Table 1). Table 1 shows results of experiment carried out by the arranging the first void sustaining elements at intervals L0 set to 20mm and intervals L1 set every 5mm in the 10 to 40mm range, and counting the number of first void sustaining elements 2a in the outermost rows having moved. The experiment has shown that, where L1 was set to 10mm and 15mm, 51 and 12, respectively, out of a total of 60 first void sustaining elements in the outermost rows moved, which would be problematic in practical use. Where L1 was set to 20 to 40mm movement of the first void sustaining elements in the outermost rows was substantially prevented It is particularly desirable to set L1 in the range of 25 to 40mm. That is, L1 should be set to 1.25 times to twice L0. With such setting, movement of the first void sustaining elements in the outermost rows is prevented reliably, appearance is not impaired, and variations in the stress condition of the glass sheets are minimized to produce no defect in terms of strength. L0 (mm) L1 (mm) spacer movement number moved total in outermost rows 20 10 51 60 15 12 60 20 1 56 25 0 56 30 0 52 35 0 52 40 0 48 It has also been confirmed that, where outer interval L1 is set to twice basic interval L0, i.e. L1 = 40mm, surface tensile stress in edge regions of the glass sheets bound by the seal 5 reaches approximately the same value as permissible long-term tensile stress of the glass sheets. Thus, by setting the outer interval L1 within twice the basic interval L0, the internal stress of the glass sheets is restained within the permissible tensile stress, thereby to avoid the glass sheets breaking due to the sealed decompression of the void V. Fig. 3 shows results of experiment carried out on the above double glazing P to determine the relationship between outer interval L1 and the surface tensile stress in the edge regions of the glass sheets bound by the seal 5. In this experiment, the surface tensile stress in the edge regions 6 of the glass sheets bound by the seal 5 was measured for six cases in which the outer intervals L1 were increased every 5mm from 28mm to 53mm. The results show that the surface tensile stress tends to increase with outer interval L1. Where L1 = 40mm (corresponding to twice the value of L0), the surface tensile stress reaches 100kg/cm 2 which is the permissible long-term tensile stress of 3mm thick float glass sheets. Other Embodiments Other embodiments will be described hereunder. (1) The first void sustaining elements are not limited to the stainless steel spacers described in the foregoing embodiment, but may be formed of inconel 718 alloy, a metal having a compressive strength of at least 491 Nmm -2 (5t/m 2 ), quartz glass, ceramics or a compound of these materials. In short, the first void sustaining elements may be formed of any material having a compressive strength of at least 491 Nmm -2 (5t/m 2 ), which is not easily deformable under external force to maintain the two glass sheets out of contact with each other. The first void sustaining elements may also have varied dimensions and shapes. (2) The basic intervals are not limited to the 20mm noted in the foregoing embodiment, but may be set appropriately based on the thickness and strength of the glass sheets. The outer intervals are set based on the basic intervals. In short, the outer intervals serve the purpose if set equal to or larger than the basic interval. Preferably, the outer intervals are set equal to twice the basic interval, and particularly 1.25 times to twice the basic interval. (3) The glass sheets are not limited to the 3mm thickness noted in the foregoing embodiment, but may have a different thickness. The type of glass may be selected as desired, such as from figured glass, frosted glass (glass given surface treatment to diffuse light), wire glass or other reinforced glass, heat absorbing glass, ultraviolet absorbing glass and heat reflecting glass.

Claims: Double glazing comprising two sheets of glass having numerous first void sustaining elements arranged in rows at a predetermined basic interval (L0) along and between sheet surfaces, and a second void sustaining element disposed between entire outer edges of the glass sheets for sealing a void between said glass sheets in a decompressed state, characterized in that the first void sustaining elements are free to move between the glass sheets until the void therebetween is sufficiently decompressed, the first void sustaining elements being subsequently held in place by frictional forces exerted upon the glass sheets as a result of external atmospheric pressure acting thereon; an outer interval (L1) between each outermost row of said first void sustaining elements (2) and said second void sustaining element (4) being set at least equal to the basic interval (L0) between said outermost row and a second row adjacent thereto. Double glazing as defined in claim 1, wherein said outer interval (L1) is set equal to twice said basic interval (L0). Double glazing as defined in clam 2, wherein said outer interval (L1) is set 1.25 times to twice said basic interval (L0). Double glazing as defined in claim 3, wherein one of said glass sheets has outer edges projecting along said plate surfaces. Double glazing as defined in claim 3, wherein said first void sustaining elements (2) are formed of a stainless steel material having a compressive strength of at least 491 Nmm -2 (5t/cm 2 ). Double glazing as defined in claim 3, wherein said first void sustaining elements (2) in form of cylindrical columns about 0.5mm in diameter and about 0.2mm (±0.01mm) in height. Double glazing a defined in claim 3, wherein said basic interval (L0) is about 20mm and said outer interval (L1) is in a range of about 25 to 40mm.

Inventors: KATO HIDEMI, MINAAI TETSUO, KATO, HIDEMI, MINAAI, TETSUO, KATO, Hidemi Nippon Sheet Glass Co., Ltd., MINAAI, Tetsuo Nippon Sheet Glass Co., Ltd.
Applicants: NIPPON SHEET GLASS CO LTD, NIPPON SHEET GLASS CO., LTD.
Application year: 1997
Main classification: C03C27
IPC codes: C03C27, E06B3