115)
`United States Patent
`4,963,412
`Oct. 16, 1990
`Kokeguchi
`[45] Date of Patent:
`
`[11] Patent Number:
`
`[54] SHEET MATERIAL FOR VEHICLE SAFETY
`AIR BAGS
`
`[75]
`
`Inventor: Akira Kokeguchi, Shiga, Japan
`
`[73] Assignee: Takata Corporation, Tokyo, Japan
`
`....scsecssesssens 428/140 X
`2,264,190 11/1941 Sherts et ab.
`.
`3,842,583 10/1974. Gage.........
`3,892,425
`7/1975 Sakairi et al.
`.
`280/743
`
`8/1979 Alban «0... .esesecseneeeeeeeees 428/140
`4,165,403
`
`- 428/140 X
`4,229,473 10/1980 Elber.....
`5/1986 AKa0 ...cssscessereererrerereeees 428/134 X
`4,587,175
`
`(21) Appl. No.: 365,689
`
`{22] Filed:
`
`Jun. 14, 1989
`
`Foreign Application Priority Data
`[30]
`Jun. 17, 1988 {JP]
`Japan vcscsscssscssssssssesusssssene 63-148072
`
`[51] Unt. C15 oa ccccsssscesssssseseee B32B 3/10; B6OR 21/16
`[52] U.S. Che cessesssssesesectsssssssssssssssenee 428/137; 428/138;
`428/139; 428/140; 428/423.7; 428/198:
`280/743
`[58] Field of Search .......0+...... 428/137, 138, 139, 140,
`428/423.7, 198; 280/743
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`Primary Examiner—Ellis P. Robinson
`Assistant Examiner—William P. Watkins, III
`Attorney, Agent, or Firm—Brumbaugh, Graves,
`Donohue & Raymond
`
`ABSTRACT
`[57]
`Sheet material for use in vehicle safety air bags com-
`prises a multiplicity of perforated films of polymeric
`material having holes, the perforated films being super-
`posed on each othersuchthatthe holesin adjacentfilms
`do not overlap to any great extent, and adhesivefilling
`the holes of all of the perforated films. other than the
`outermost ones and uniting them into a laminate.
`
`—
`
`665,931
`
`1/1901 Pratt 0... cteecssceecsseecesneees 428/140
`
`9 Claims, 13 Drawing Sheets
`
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`Page 1 of 19
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`US. Patent
`
`Oct. 16, 1990
`
`Sheet 1of13
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`4,963,412
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`Page 2 of 19
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`US. Patent
`
`Oct. 16, 1990
`
`Sheet20f13
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`4,963,412
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`Page 3 of 19
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`US. Patent
`
`Oct. 16, 1990
`
`Sheet 3 of 13
`
`4,963,412
`
`FIG. 6B
`
`FIG. 6C
`
`FIG. 6D
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`US. Patent
`
`Oct. 16, 1990
`
`Sheet4 of 13
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`4,963,412
`
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`Page 5 of 19
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`
`
`US. Patent—Oct.16, 1990 Sheet 50f13
`
`4,963,412
`
`Page6 of 19
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`
`US. Patent—Oct. 16, 1990 Sheet 60f13 4,963,412
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`Page 7 of 19
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`US.Patent
`
`Oct. 16, 1990
`
`Sheet 70f13
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`4,963,412
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`4,963,412
`US.Patent—Oct. 16, 1990
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`US. Patent
`
`Oct. 16, 1990
`
`Sheet 90f13
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`4,963,412
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`US. Patent
`
`— Oct. 16, 1990
`
`Sheet 100f13
`
`4,963,412
`
`FIG. 11E
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`
`US. Patent—Oct. 16, 1990 Sheet 11 0f 13 4,963,412
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`US. Patent
`
`Oct. 16, 1990
`
`Sheet 12 of 13
`
`4,963,412
`
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`US. Patent
`
`Oct. 16, 1990
`
`Sheet 13 0f 13.
`
`4,963,412
`
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`1
`
`4,963,412
`
`SHEET MATERIAL FOR VEHICLE SAFETY AIR
`BAGS
`
`FIELD OF THE INVENTION
`
`The present invention relates to sheet material for
`vehicle safety air bags and, in particular, to sheet mate-
`rial composed of several perforated polymeric films
`joined by an adhesive to form a laminate.
`BACKGROUND OF THE INVENTION
`
`Air bags are increasingly being installed in motor
`vehicles and have proven to reduce greatly the risk of
`injury and death to the protected vehicle occupants.
`The technology of air bags has been the subject of ex-
`tensive research over many years. One aspect of that
`research has involved the material of the air bag.
`The air bags in current use are usually made of a
`coated woven fabric. The fabric provides the strength
`required to endure the large forces exerted on the mate-
`rial uponinflation and upon impact by the vehicle occu-
`pant. The coating is present to seal the fabric against gas
`leakage. The manufacture of the air bag involves sew-
`ing two pieces of the fabric material together and also
`sewing reinforcement and inflation control elements
`onto the basic bag or envelope.
`Coated fabric air bags have three disadvantages. One
`is that the coated fabricis relatively thick, usually about
`400 micrometers. Accordingly,
`the enclosure in the
`vehicle into which the air bag is folded in readiness for
`deploymentis of a relatively large size. A second disad-
`vantage is the complexity of the manufacturing process,
`which makes the air bag expensive to make. A third
`disadvantageis that the air bag is opaque, so the driver
`cannot see ahead when. the bag is deployed.
`An obvious candidate for the bag material, of course,
`is a polymeric film. Thermoplastic polymeric films can
`be vacuum-formed to give the air bag a desired shape
`and can be fusion-bonded, which is a more economical
`manufacturing technique than sewing. Many suitable
`polymeric films are transparent, so the driver’s view
`ahead would be preserved. Thus, a polymeric film air
`bag would overcome the above-mentioned disadvan-
`tages.
`Many polymeric films, especially uniaxially and biaxi-
`ally stretched films, have sufficient tensile and rupture
`strengths for air bags, but they do not have adequate
`notchtear strength (resistance to tearing at a notch). On
`the other hand, polymeric films, especially stretched
`polymeric films, have good edge tear strength (resis-
`tance to tearing at an edge with no notch). Because of
`an insufficient notch tear strength, ordinary polymeric
`films (unstretched or stretched) are not satisfactory for
`air bags.
`
`SUMMARY OF THE INVENTION
`
`An objectof the present invention is to provide an air
`bag material that can be producedefficiently and eco-
`nomically, has excellent mechanical properties, is thin
`and occupies less volume when folded and is transpar-
`ent.
`There is provided, according to the present inven-
`tion, sheet material for use in vehicle safety air bags
`comprising a multiplicity of perforated films of poly-
`meric material having holes, the perforated films being
`superposed on each other such that the holes in adjacent
`films do not substantially overlap, and adhesive filling
`
`10
`
`—_ 5
`
`35
`
`40
`
`45
`
`50
`
`35
`
`60
`
`2
`the holes of all of the perforated films other than the
`outermost ones and uniting them into a laminate.
`In preferred embodiments, sheet material according
`to the invention may include a non-perforated film ad-
`hered to an outermost perforated film and an adhesive
`filling the perforations of the outermost film to unite it
`to the laminate. The perforated films have curved edges
`throughoutfree of corners. The maximum dimension of
`the holes in any direction is preferably about 20 mm,
`and the minimum dimension of the holes in any direc-
`tion is about 5 mm. Thetotal area of the holes in each
`perforated film should not exceed about 50% of the
`total area ofthe film andis desirably from about 25% to
`about 45% ofthe total area of the film. The sheet mate-
`rial may havea total thickness of up to about 300 mi-
`crometers, say in the range of from about 250 microme-
`ters to about 300 micrometers.
`Fora better understanding of the invention, reference
`may be madeto the following description of exemplary
`embodiments, taken in conjunction with the accompa-
`nying drawings.
`
`DESCRIPTION OF THE DRAWINGS
`
`.
`FIG. 1 is a plan view of a first embodiment;
`FIG.2 is a cross-sectional view of the first embodi-
`ment, taken along the lines II—II of FIG. 1,
`FIG. 3 is a fragmentary cross-sectional view of the
`first embodiment on enlarged scale, as indicated by the
`circle [II of FIG.2;
`FIG. 4 is a diagrammatic plan view of one form. of
`hole in a perforated film for the sheet material;
`FIG. 5 is a diagrammatic plan view of another form
`of hole in a film of the sheet material;
`Each of FIGS. 6 to 11 comprises a plan view (A) and
`a cross-sectional view (B) of the laminated miaterial-and
`two or more plan views (C, D,etc.) of the individual
`films of further embodiments of the invention;
`FIG.12 is a cross-sectional view of an embodimentin
`which the outermostfilms of the laminated sheet mate-
`rial are non-perforated film;
`FIGS.13 to 15 are cross-sectional views in represen-
`tational form illustrating the effect of including an im-
`perforate film as the innermost element of the air bag
`sheet material;
`FIG. 16 is a schematic view of apparatus for making
`the sheet material; and
`FIG.17 is a projected diagrammatic view of an adhe-
`sive applicator roller of the apparatus of FIG. 16.
`DESCRIPTION OF THE EMBODIMENT
`The embodiment of FIGS. 1 to 3, which is intended
`to be representative of all embodiments of the inven-
`tion,
`is a sheet material 1 composed of several perfo-
`rated polymeric films 3. Each film 3 (e.g., each of the
`four films 3a, 3b, 3c and 3d, FIGS. 2 and 3) has holes 2.
`Thefilms 3 are placed one over the other andare joined
`by an adhesive to form a laminate. The holes 2 in each
`film 3 are arranged relative to each other, and the films
`3 are positioned relative to each other, such that the
`holes in adjacent films do not overlap to any great ex-
`tent. The adhesive 4 that joins the films 3 fills the holes
`2 ofall the films other than the outermost ones. If de-
`sired, the adhesive 4 mayalso fill the holesof the outer-
`mostfilms of the sheet1. In particular, as shown in FIG.
`3, adhesive 45 filis the holes 2b in the sheet 3b, and
`adhesive 4¢ fills the holes 2c in the sheet 3c. The adhe-
`sive 4b bonds the films 3a and 3c to each other, thus
`capturing the film 35 in a sub-laminate of films 3a, 3b
`
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`3
`and 3c. Similarly, the adhesive 4c in the holes 2c bonds
`the films 3b and 3d and formsa sub-laminate of films 3d,
`3e'and3d.
`The material of the films used in the invention is not
`especially limited, and transparent films such as Poly-
`ethylene Terephthalate (PET), Polyethylene (PE),
`Polypropylene (PP), Polystyrene (PS), and Polypropyl-
`ene Sulfide (PPS) may be used. Of these materials, PET
`is the most desirable from the standpoint ofits mechani-
`cal properties. The materials of the films of the sheet
`material also do not haveto be the same;films of differ-
`ent materials may be laminated to makethe air bag sheet
`material.
`The films may be non-stretched, uniaxially stretched
`or biaxially stretched. It is, however, desirable to use
`stretched films, because they have higher tensile and
`rupture strengths and edge tear resistance. Also, when
`uniaxially and biaxially stretched films are compared to
`each other, it is desirable to use the biaxially stretched
`films in the invention, because they have better mechan-
`ical properties, other than edge tear resistance. It is
`advantageous
`to combine uniaxially and biaxially
`stretched films inasmuch as the former has a higher
`resistance to edge-tearing (a high edge tear strength).
`With a combination, the biaxially stretched film pro-
`vides high tensile strength and the uniaxially stretched
`film provides edge tear resistance.
`In the following paragraphs, the shape of the holes in
`the porousfilm, the open area ratio, the numberoffilms
`and other characteristics for the sheet material of the
`invention are described.
`
`SHAPE OF HOLE
`
`4
`larger. If the hole diameter is excessively large, how-
`ever, the tensile strength and the resistance to tearing of
`the film as a whole becomes smaller. It is, therefore,
`desirable to have a hole diameter D of about 10 to 20
`mm.In the case of the oblong hole 2B shownin FIG.5,
`a longer dimension D1 of about 10 to 20 mm and a
`shorter dimension D2 of about 5 to 10 mm aredesirable.
`Theholes in each film, and the holesin the several films
`of the sheet material, need not be of the samesize, and
`large and small holes may be combined in each film or
`in the several films.
`
`OPEN AREA RATIO
`
`A higher openarea ratio will result in reduced tensile
`and rupture strength. Such strength may be regained to
`some extent by laminating and adheringfilms in various
`ways, but it will be difficult to compensate by so doing
`if the open.area ratio is extremely large. Less than 50%
`of open area, normally 25% to 45% of open area, is
`desirable. (The percentages are expressed as the per-
`centage ofthetotal area of the film that the holes take
`up,i.e., the area of the holes divided by the total area of
`the film times 100).
`
`HOLE PITCH
`
`The hole pitch is a function of the hole size and shape
`and the desired open area. Normally, a hole pitch of 10
`to 30 mm is desirable.
`
`HOLE ARRANGEMENT
`
`There are no special limitations on hole arrangement.
`Various arrangements, including irregular and regular,
`may be adopted.
`
`FILM THICKNESS
`
`Film thickness is determined with a view to the ease
`of folding the material whenit is made into an air bag.
`It is, therefore, dependent as a rule on the bending
`strength (or bendingelasticity) of the film. A film of
`higher bending strength may be made thinner
`to
`achieve higherflexibility and foldability. On the other
`hand, a film of low bending strength may be made
`thicker, but the film thickness should be less than 50
`micrometers normally. When using PET as the film
`material, the film should be less than 25 micrometers
`thick, as PET has a very high bendingstrength.Ifit is
`madethicker than that, it will have a high resistance to
`being folded. In case of PET film,a thickness of 12 to 25
`micrometeris desirable.
`:
`
`NUMBEROF FILMS IN THE SHEET MATERIAL
`
`The numberoffilms in the sheet material is deter-
`mined according to hole arrangement, open area, and
`film thickness. It is, however, desirable to limit the
`thickness of the laminated sheet to less than 300 mi-
`crometers, because the advantages of making the air bag
`thinner may not be obtained if the sheet is too thick. A
`sufficient strength may not be obtained if the numberof
`films is small and the sheet is not thick enough. There-
`fore, the number of films should be determined so that
`the sheet will be about 250 to 300 micrometers thick.
`In FIGS. 6 to 11, the films are designated by the
`numeral 3 followed by a letter and a numberthat relate
`the particular film, as shownin oneof the plan views of
`the films (Figs. C, D, E, etc.),
`to the cross-sectional
`view. Films identified by the same letter are the same,
`and the numeral in that case designates a different posi-
`tion of the film in the laminated sheet — i.e., the regis-
`
`= 0
`
`20
`
`25
`
`30
`
`35
`
`40
`
`There are no special limitations on the shapes of the
`holes, except that it is important that the holes have
`entirely curved edges, suchas circles, ovals, orellipses,
`and have no corners or angles. In order to provide
`uniformity or balancing of resistance to edge tearing, a
`circular hole 2A is desirable, as the stress will be uni-
`formly distributed, as shown in FIG. 4. But even with
`holes of oval shape or oblong holes 2B with straight
`parallel side edges and semi-circular end edges, as
`shownin FIG.5, good results may be obtained in some
`cases. To be specific, with the holes 2B of FIG.5, the
`resistance to edge tearing at the edge of the holes from
`the crack 5 is almost equal to the edge tear strength on
`the straight line 2), and the resistance to edge tearingis
`extremely high. By orienting the stretch axis X of the
`film parallel to the straight edges 2b ofthe holes 2B, the
`against tearing can be improved. An overall balance of 50
`strength against edge tearing at the edges of the holes
`can be attained by using films in which half the holes are
`oriented with their longer axes perpendicular to the
`axes of the remaining holes. Also, films with all of their
`holes oriented in the samedirection can be laminated so
`that half the films have their holes oriented perpendicu-
`lar to the holes of the other half of the films.
`It is not necessary for all of the holes in a film of the
`sheet material to be of the same shape, noris it neces-
`sary forall films of the sheet to have holes of the same
`shape. The shapesofthe holes can vary within each film
`or amongthefilms of the sheet material.
`SIZE OF HOLE
`
`45
`
`55
`
`60
`
`In the case of a circular hole 2A, as shown in FIG.4,
`the arc approximates a straight line and the edge tear
`strength approaches the edge tear strength at the point
`2a opposite a tear or crack 5 as the hole diameter D gets
`
`65
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`30
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`35
`’
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`45
`
`6
`5
`selected taking into consideration such factors as the
`tration of the film. A capital roman numeral and an
`arabic numeral designate edges ofthefilms that register
`adhesion properties in relation to the polymeric film to
`be used. For PET film, for instance, synthetic resins of
`in the laminated sheet material. For clarity, the adhesive
`nitrile rubber, polyester, cyanoacrylate, acrylate, ep-
`in the holes of the films is not shown, butit is apparent
`oxy, polyolefin, urethane rubber and neoprenephenolic
`that the unshaded areas in Figs. B contain adhesive. As
`are desirable. Of these, adhesives of urethan rubber,
`mentioned above, the holes of the outermost filmsof the
`laminated sheets need not befilled with adhesive.
`epoxy, polyester and nitrile rubber are especially desir-
`In the embodiment shown in FIG. 6, the films 3C
`able. In addition, adhesives of silicon rubber are desir-
`able, as they are excellent in flexibility and heat-resist-
`havethe relatively small circular holes 2C (for instance,
`ance properties, though their adhesion strength is lim-
`diameter: 10 to 12 mm,open area: 39.3%) arranged in a
`ited.
`zig-zag or staggered fashion and are laminated so that
`The adhesivefills the holes in the films, and the films
`the holes in adjacent layers do not overlap. In other
`are adhered to each other so that the holes are posi-
`words,the film 3C; of the hole arrangementas shownin
`FIG. 6C and the films 3C2 as shown in-FIG. 6D are
`tioned without overlapping of the holes in adjacent
`laminated in the order of 3C), 3C2, 3C1, 3C2, 3C1, 3C2,
`films to any great extent. For example, in FIGS.1, 2,
`and 3,the film 3d is adheredto the films 3¢ and 3c with
`3C}... (ten films in this embodiment) so that the edge Ii
`the adhesive 46 thatfills the holes 25 in the film 3b.
`registers with the edge Iz and the edge IT registers with
`Tn
`Also, the film 3c is adhered to the films 3b and-3d with
`the adhesive 4c that fills the holes 2c in the film 3c.It is,
`In the embodiment shownin FIG.7, films 3D with
`relatively large circular holes 2D (for instance, diame-
`therefore, not necessary to fill the holes on the outer-
`most films of the laminated sheet (the films 3¢ and 3d in
`ter: 18 to 20 mm, open area: 39.3%) arranged in stag-
`gered relation are laminated so that the holesin thefifth
`the example shown in FIG. 3) with an adhesive,butit is
`possible, on the other hand,to fill the adhesive in the
`film will be on the same position as those on the first
`holes on the outermost films. In this way, byfilling the
`film. In other words, the films 3D, through 3D4, as
`adhesive in the holes on the porousplastic films and
`shown in FIGS. 7C through 7F, are laminated in the
`thus by not forming adhesive layers between the films,
`order of 3D1, 3D2, 3D3, 3D4, 3D), 3D2, 3D3, 3D4. .
`. (12
`almost no thickness of adhesive is added to the lami-
`films in this embodiment) and so that the edges [I;,
`nated sheet, making the thickness of the laminated sheet
`TIIz, IIK3, and ITI, register and the edges IV), IV2, [V3,
`approximately the sameas thetotal of the thicknesses of
`and IV4 register.
`In the embodiment shown in FIG.8, films 3E with
`the films. This results in the air bag sheet material being
`thin and strong. Byfilling the holes: with the adhesive,
`oblong holes 2E arranged in staggered relation (with an
`the flexibility of the sheet material is also improved.
`open area of 44.6%,for instance) are laminated with the
`The holesin the polymeric films may be positioned in
`holes oriented in alternate directions so that the long
`the air bag material in partially overlapped relation, but
`dimensions. of the holes in adjacent films are perpendic-
`the holes in the films haveto be positioned, of course, so
`ular to each other. Thus, eight films 3E; through 3E3
`that there will be no holes completely through the sheet
`with the hole arrangements as shown in FIGS. 8C
`material.
`through 8J are laminated in the order of 3E), 3E2, 3E3,
`Atleast one of the two outermostfilms of the sheet
`3Eq4, 3Es, 3E6, 3E7, and 3Eg so that the edges Vi, V2,
`material may be non-perforated. In FIG. 12, a sheet
`V3, Va, V5, Ve, V7, and V3 register and the edges VI},
`material 1A is made by laminating non-perforted films
`Vh, VIs, Vi, VIs, VIe, VI7, and VIs register. *
`In the embodiment shown in FIG.9,films 3F with
`6a and 6b on eachside of the perforated plastic films 3a,
`3b, 3c and 3d. The non-perforated films 6a and 65 im-
`small circular holes. 2G andfilms 3G with large circular
`holes 2G are combined in the order of 3F1, 3G2, 3G3,
`prove the tensile and rupture strength of sheet material.
`Asshownin FIG.13, for example, if an air bag is made
`3G4, 3Gs, 3Ge6, 3G7 and 3Fg so that the edges VII,
`of an air bag sheet material 1B which is made by lami-
`VIT2, VII3, VII4, VIIs, VITs, VII7, and VIIg register and
`nating and adhering with the adhesive 4 perforated
`the edges VIII;, VIII2, VIII3,. VITI4, VIIIs, VIIIe,
`films 3a, 3b and 3c, the part W on the film 30 located
`VIII; and VIIIs register.
`between the holes 2a and 25 of the films 3a and 3c will
`In the embodiment shownin FIG. 10, films 3C with
`small circular holes 2C, the same films as used in the
`support theinternal pressureof the air bag only with the
`embodiment shownin FIG.6, and the films 3E with the
`strength of a single film, and in some extremecases, the
`part. W may distend and be ruptured (FIG. 14). In case
`oblong holes 2E used in the embodiment shownin FIG.
`of the sheet material 1C in which the internal surface of
`8 are laminated in the order of 3C, 3E;, 3E2, 3E3, 3E4,
`the air bag material is covered with a non-perforated
`3Es, 3E¢6, 3E7, 3Eg, and 3C2 (ten films) so that the eges
`film 6 (FIG. 15), no internal pressure will be directly
`ty, Vi, V2, V3,-V4, Vs, Ve, V7, Va, and I; register and
`applied onto the part W onthe film 3d, and the pressure
`the edges Ij, -Vlu, VIn, VI3, V4, VIs, Vic, V17, VIs,
`will be distributed over the entire surface of the non-
`and IIregister.
`In the embodimentof FIG. 11, films 3H with small
`perforated film 6, thus preventing local rupture.
`It.is, therefore, desirable to provide a non-perforated
`circular holes 2H arranged at relatively large pitch
`film at least on the internal surface of the air bag. If a
`distances and with a low open area percentage (about
`non-perforated film is also provided on the external
`26.2%, for instance) are laminated in the order of 3H,
`surface of the air bag, in addition to distributing the
`3H, 3H3, 3Hi, 3H2, 3H3...
`. (nine films) so that the
`internal pressure, contact of the adhesive with the air
`edges IX1, [X2, and [X3 register and the edges Xj, X2,
`(oxygen) and deterioration of the adhesive over time
`and X3register.
`The adhesive used to adhere the perforated poly-
`will be prevented, thus to improve the durability of the
`meric films.is required to be flexible and transparent and
`air bag.
`There are no special limitations on the thickness of
`to have a high strength, especially against peeling and
`delamination, and to have a high heat resistance charac-
`the non-perforated film, and the thickness will be deter-
`teristic (over 125° C.). Therefore, an adhesive will be
`mined within the parameterssuitable to the air bag sheet
`
`55
`
`65
`
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`

`

`4,963,412
`7
`material stated above, with attention to such factors as
`strength. Generally,
`the thickness of non-perforated
`films may be 12 to 25 micrometers. The non-perforated
`film may be of the same material as the porous perfo-
`rated polymeric films of the sheet.
`In accordance with the invention, a laminated sheet
`of eight to ten PET films of 12 to 25 micrometers thick-
`ness with an open area of about 25% to 45% and the
`holes arranged as shown in FIGS.6, 8 and 10, and of a
`PET non-porous film of 12 to 25 micrometers thick on
`at least the inner side is most desirable for an air bag.
`Next, the manner of producing the air bag sheet mate-
`rial of the invention is described.
`,
`Whenproducing the air bag sheet material shown in
`FIGS. 1 through 3, for instance, two perforated poly-
`meric films 3¢ and 3d are positioned in proper register
`with each other, as shown in FIG. 16. Adhesive 4 is
`transferred into the holes 2c on the film 3c by applying
`the adhesive onto projections 11 of a roller 10 from an
`adhesive container 12. The roller 10 is provided with
`circular projections 11 arranged in the same pattern as
`the holes 26 in the film 3c, as shown in FIG. 17. The
`laminated sheet of the films 3b and 3a, to which the
`adhesive 4 is transferred in the same manner, is placed
`on the films 3¢ and 3d, and pressure is applied using the
`rollers 13 and 14. By placing the four films thus ob-
`tained on top of another four films combined in the
`same manner, a laminated sheet of eight films will be
`obtained. A non-perforated film can be combined with
`several perforated films by depositing adhesive in the
`holes of the outermost perforated film and feeding the
`perforated films and the non-perforated films through
`rollers.
`An air bag can be produced extremely easily from the
`air bag sheet material by vacuum-forming two members
`of the sheet material to provide two generally. hemi-
`spherical parts of the air bag and joining them together
`along their perimeters by fusion-welding, such as by
`ultraviolet light irradiation fusion-welding. An air bag
`need not be madeentirely of the sheet material of the
`present invention, but can have its base portion (the
`portion adjacent the gas generator, to which theair bag
`is attached) made of conventional coated cloth.
`Theholes in the polymeric films impart a high resis-
`tance to rupture of the material by tearing. The films
`have high tensile, rupture and edge tearing strengths.
`By laminating the perforated films so that the holes do
`not substantially overlap and by adhering the films with
`the adhesive filling in the holes, the strength of the
`laminated sheet can be considerably improved without
`excessively increasing its thickness. A non-perforated
`film on one or both surfaces of the laminated sheet
`further enhances the mechanical strength and durability
`of the sheet material. It is, therefore, possible to make an
`air bag that is thinner, and the volume and weightof the
`air bag in folded condition will be significantly less than
`those of conventional air bags. Moreover, as polymeric
`films can be easily shaped by vacuum-forming and
`joined by fusion-welding, the production process for
`making the air bag can be considerably simplified. Also,
`the air bag can be made transparent to expandthefield
`of vision of the driver.
`Set forth below in Table 1 are the results of measure-
`ments and evaluations of the characteristics of several
`examples of polymeric films, a laminated sheet material
`of the invention, a conventional air bag sheet material,
`and a laminate not according to the invention, as fol-
`lows:
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`65
`
`8
`
`Examples of Reference 1 and 2, Example of
`Embodiment 1, and Examples of Comparison 1 through
`5.
`
`Reference Example 1: Perforated Film
`Material: PET biaxially stretched film
`Thickness: 25 micrometer
`Hole Shape: Circular
`Hole Diameter: 10 mm
`Open Area Ratio: 39.3%
`Hole Arrangement: FIGS. 6A and 6B
`Reference Example 2: Perforated Film
`Material: PET biaxially stretched film
`Thickness: 25 micrometer
`Hole Shape: Circular
`Hole Diameter: 10 mm
`Open Area Ratio: 39.3%
`Hole Arrangement: FIGS. 6A and 6B
`EMBODIMENT EXAMPLE 1L
`
`Perforated Film Laminated Sheet Material
`
`Perforated Film: That of Reference Example 1
`Numberof Films Laminated: 12 films
`Total Thickness: 320 micrometer
`Adhesive: Epoxy
`Comparison Example 1: Conventional Air Bag Fab-
`ric
`
`Material: 840d-Cr. coated cloth (Cr-coated nylon 66)
`Thickness: 400 micrometer
`Comparison Example 2: Non-perforated film
`Material: Polyethylene non-stretched film
`Thickness: 25 micrometer
`Comparison Example 3: Non-perforated film
`Material: PET non-stretched film
`Thickness: 25 micrometer
`Comparison Example 4: Non-perforated film
`Material: PET biaxially stretched film
`Thickness: 25 micrometer
`Comparison Example 5: Non-perforated film lami-
`nated Sheet
`Two polyethylene uniaxially stretched films lami-
`nated so that the stretch axes are mutually perpen-
`dicular Thickness: 37 micrometer
`The measurement techniques were as follows:
`a. Tensile Strength (kgf/cm)
`Using a constant speed tensile testing machine and
`with the testing machine holder distance being about
`100 mm,the test sample wasattached to the holders and
`pulled at a rate of about 200 mm per minute. Thetensile
`load at rupture was measured. In Comparison Example
`1 only, a holding distance of 76.2 mm and a pulling rate
`of 300+20 mm/min were used.
`b. Rupture Strength (kg/cm?)
`Using a Mullen rupture testing machine, and applying
`a pressure up to 80 kgf/cm?in 3 to 5 seconds,the pres-
`sure at rupture was recorded in kgf/cm2
`c. Tear Resistance (kgf)
`With thetensile rate of 100 mm/min., the load when
`tearing. occurred was
`recorded on the chart
`(50
`mm/min.), and the average value of peak loadsat tear-
`ing was taken as the tear resistance.
`d. Edge Tear Strength (kgf/20 mm)
`Using a V-grooved steel sheet, the film was folded so
`that its surface was in contact with the V-groove, the
`sheet was pulled at the rate of about 200 mm/min. The
`average and lowest values of the force when tearing
`occurred were measured.
`
`Page 18 of 19
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`

`9
`
`TABLE1
`
`4,963,412
`
`10
`
`3.5-4.0
`
`3.5-4.0 60
`
`58.3
`
`42
`
`42
`
`22
`
`22
`
`74.7
`
`
`
`16
`
`
`
`-
`
`63-
`70
`
`60
`
`6.0
`
`40
`
`22
`
`6.6
`
`270
`
`=170
`
`Reference
`
`—ExampleEmbodiment, ___-__ComparisonExample
`4
`5
`Example
`1
`2
`1
`1
`2
`3
`25
`100
`Sample
`25
`25
`320
`400
`25
`25
`Thickness
`(micrometers)
`Tensile
`strength
`(kgf/cm)
`0.5-
`Rupture |
`0.635
`strength
`(kg/cm?)
`4.5
`0.02
`
`Tear 0.02—-=0.005-1.2~ 3.67 28 30-33.
`
`
`Resistance*
`2.0
`8.67
`0.75
`0.013
`(kgf)
`Edge Tear
`strength
`(kgi/20 mm)
`Melting
`Temperature
`CC.) (Approx.)
`*Reference Example 2 was by the Travezoid Method, Comparison Examples 2, 3 and 4, the Elemen-
`dorf Method and the others the Tong Method.
`In the Table, “—-”indicates not tested.
`
`0.75-
`1.13
`
`1.5-
`2.5
`
`-
`
`-_
`
`_
`
`—
`
`270
`
`270
`
`270
`
`260
`
`170
`
`270
`
`meric material having holes, the holes in the films being
`free of corners and the perforated films being super-
`posed directly on each other and aligned such that the
`holes in adjacent films do not entirely overlap, and
`adhesive filling the holes of all of the perforated films
`other than the outermost one and uniting them into.a
`laminate.
`2.. Sheet material according to claim 1 and further
`comprising a non-perforated film adhered to an outer-
`most perforated film and an adhesivefilling the holes of
`said outermost film to unite the non-perforated film to
`the laminate.
`3. Sheet material according to claim 1 wherein the
`holes in the perforated films have curved edges
`throughout.
`4. Sheet material according to claim 1 wherein the
`maximum dimension of the holes in any direction is
`about 20 mm.
`5. Sheet material according to claim 1 wherein the
`minimum dimension of the holes in any direction is
`about 5 mm.
`6. Sheet material according to claim 1 wherein the
`total area of the holes in each perforated film does not
`exceed about 50% of the total area of the film.
`7. Sheet material according to claim 6 wherein the
`total area of the holes in each perforated film is from
`about 25% to about 45% ofthe total area of thefilm.
`8. Sheet material according to claim 1 wherein the
`total thickness of the sheet material does not exceed
`about 300 micrometers.
`9, Sheet material according to claim 8 wherein the
`total th